Encyclopedia of Food Grains - 2nd Edition (4 Volume Set) (2016)

ENCYCLOPEDIA OF FOOD GRAINS Second Edition

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ENCYCLOPEDIA OF FOOD GRAINS Second Edition VOLUME 1

THE WORLD OF FOOD GRAINS EDITORS

COLIN WRIGLEY University of Queensland, Brisbane, Australia

HAROLD CORKE University of Hong Kong, Hong Kong, People’s Republic of China

KOUSHIK SEETHARAMAN{ JON FAUBION Kansas State University, Manhattan KS, USA

{

deceased

AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Academic Press is an imprint of Elsevier

Academic Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB 225 Wyman Street, Waltham MA 02451 First edition 2004 (as Encyclopedia of Grain Science) Copyright © 2016 Elsevier Ltd. All rights reserved The following articles are US government works in the public domain and are not subject to copyright: Grain Crops, Overview; Maize Overview. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers may always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library SET ISBN 978-0-12-394437-5 VOLUME 1 ISBN 978-0-12-803537-5 VOLUME 2 ISBN 978-0-12-803536-8 VOLUME 3 ISBN 978-0-12-803535-1 VOLUME 4 ISBN 978-0-12-803538-2 For information on all publications visit our website at http://store.elsevier.com Printed and bound in the UK.

Publisher: Lisa Tickner Acquisition Editor: Rachel Gerlis Content Project Manager: Mark Harper Production Project Manager: Paul Prasad Chandramohan Designer: Victoria Pearson Esser

CONTENTS Preface

xvii

Tributes to Former Co-Editors

xix

Editors‘ Biography Editorial Advisory Board Contributors

xxiii xxv xxvii

VOLUME 1 THE WORLD OF FOOD GRAINS

1

The Basics

1

The Grains that Feed the World

1

CW Wrigley, H Corke, and J Faubion

Course Structures: Based on EFG Articles

13

H Corke

The Grain Crops: An Overview

16

RA Graybosch

The Grain Chain: The Route from Genes to Grain-Based Products

22

CW Wrigley

Taxonomic Classification of Grain Species

31

LA Morrison and CW Wrigley

Grain: Morphology of Internal Structure

41

H Corke

Grain and Plant Morphology of Cereals and how characters can be used to identify varieties

51

J Wyatt

The Cereal Grains

73

An Overview of the Family of Cereal Grains Prominent in World Agriculture

73

CW Wrigley

Cereals: Domestication of the Cereal Grains

86

LA Morrison

Maize: Overview

99

MP Scott and M Emery

Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’

105

CW Wrigley

v

vi

Contents

Durum Wheat: Overview

117

GP Kadkol and M Sissons

Rice: Overview

125

BO Juliano

Wildrice, Zizania: Overview

130

EA Oelke and RA Porter

African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts

140

JT Manful and S Graham-Acquaah

Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses

147

AM Stanca, A Gianinetti, F Rizza, and V Terzi

Sorghum Grain, Its Production and Uses: Overview

153

A Cruickshank

Rye Grain: Its Genetics, Production, and Utilization

159

HD Sapirstein and W Bushuk

Triticale: Overview

168

BJ Furman

Oats: Overview

173

PK Zwer

Coix: Overview

184

H Corke, Y Huang, and JS Li

Millet Pearl: Overview

190

JRN Taylor

Millet Minor: Overview

199

GK Chandi and GA Annor

Teff: Overview

209

G Bultosa

The Oilseeds

221

Oilseeds: Overview

221

RJ Mailer

Soybean: Overview

228

K Liu

Canola: Overview

237

VJ Barthet

Cottonseed: Overview

242

E Hernandez

Sunflower: Overview

247

GJ Seiler and TJ Gulya

Overview of the Oilseed Safflower (Carthamus tinctorius L.)

254

C Hall III

Linseed: Overview

259

S Cloutier

The Legumes and Pseudocereals

265

Grain Legumes and Their Dietary Impact: Overview

265

TE Michaels

Contents

Pseudocereals: Overview

vii

274

RJ Fletcher

Lupin: Overview

280

DS Petterson

Amaranth: Overview

287

H Corke, YZ Cai, and HX Wu

Beans: Overview

297

SK Sathe

Buckwheat: Overview

307

YZ Cai, H Corke, D Wang, and WD Li

Chickpea: Overview

316

EJ Knights and KB Hobson

Pea: Overview

324

TN Khan, A Meldrum, and JS Croser

Peanuts: Overview

334

RCN Rachaputi and G Wright

Quinoa: Overview

341

SA Valencia-Chamorro

Grains Around the World

349

Grain Production and Consumption: Overview

349

T Beta and C Isaak

Grain Production and Consumption: Africa

359

JRN Taylor

Production and Consumption of Grains: India

367

BS Khatkar, N Chaudhary, and P Dangi

Grain Production and Consumption: China and South-East Asia

374

H Corke and YZ Cai

Grain Production and Consumption: Europe

383

MG Lindhauer

Grain Production and Consumption: Cereal Grains in North America

391

JA Fox and LL Ward

Grain Production and Consumption: Oilseeds in North America

401

PBE McVetty, OM Lukow, LM Hall, I Rajcan, and H Rahman

Grain Production and Consumption in Oceania: Australia and Pacific Countries

409

CW Wrigley and RJ French

Grain Production and Consumption: South America

420

OR Larroque and JC Catullo

Scientific Organizations Related to Grains

429

Research Organizations of the World: CGIAR

429

JH Skerritt

Research Organizations of the World: Europe and North America

436

JH Skerritt

Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East JH Skerritt

444

viii

Contents

Research Organizations of the World: Global Trends and the Commercial Sector

451

JH Skerritt

Scientific Societies Associated with Grain Science

457

SC Nelson and CW Wrigley

VOLUME 2 NUTRITION AND FOOD GRAINS

1

Food Grains and Well-Being

1

Functional Foods: Overview

1

G Bultosa

Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics

11

G Bultosa

Nutrition: Soy-Based Foods

17

AM Fehily

Food Grains and the Consumer

23

Grains and Health: Misinformation and Misconceptions

23

DB Sheats and JM Jones

Consumer Trends in Grain Consumption

29

JM Jones and DB Sheats

Cultural Differences in Processing and Consumption

35

AMR Hayes and JM Jones

Fortification of Grain-Based Foods

43

CM Rosell

Genetically Modified Grains and the Consumer

50

A Mathiowetz and JM Jones

Labelling of Grain-Based Foods

57

JM Jones

Grains and Health

63

R Korczak, D Hauge, B Maschoff, L Marquart, P Jacques, R Lindberg, and R Menon

Food Grains: Intolerance, Allergy and Diseases

72

Cereal Allergens

72

AS Tatham

Nutrition: Beriberi, A Deficiency Related to Grains

77

KJ Carpenter

Celiac Disease

83

P Koehler, H Wieser, and KA Scherf

The Gluten-Free Diet

91

V Zevallos and I Herencia

Proteins

98

The Protein Chemistry of Cereal Grains

98

F Be´ke´s and CW Wrigley

The Protein Chemistry of Dicotyledonous Grains PR Shewry

109

Contents

Protein Synthesis and Deposition

ix

115

PR Shewry and P Tosi

Nitrogen Metabolism

123

CA Atkins

Nitrogen in Grain Production Systems

129

XM Zhou, BL Ma, and DL Smith

The Enzymes Associated with Food Grains and Their Functions in Processing

138

DJ Mares, K Mrva, and GB Fincher

Proteomic Analysis Relevant to Cereal Grains

146

A Juha´sz, R Haraszi, F Be´ke´s, DJ Skylas, and CW Wrigley

Thiolomics of the Gluten Protein Network of Wheat Dough

154

F Bonomi and S Iametti

Carbohydrates

161

Carbohydrate Metabolism

161

RN Chibbar, S Jaiswal, M Gangola, and M Ba˚ga

Starch: Chemistry

174

FL Stoddard

Starch: Synthesis

181

A Regina, S Rahman, Z Li, and MK Morell

Starch: Starch Architecture and Structure

190

V Vamadevan and Q Liu

Starch: Analysis of Quality

198

A Gunaratne and H Corke

Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides

208

GB Fincher

Grains other than Cereals: Non-starch Polysaccharides

224

L Ramsden

Resistant Starch and Health

230

A Evans

Health Effects of b-Glucans Found in Cereals

236

SM Tosh and S Shea Miller

Glycemic Index, Glycemic Load, and Their Health Benefits

241

D Dan Ramdath

Fats

248

Lipid Chemistry

248

L Day

Healthy Fats and Oils

257

SM Ghazani and AG Marangoni

Bioactives and Toxins

268

Bioactive Compounds in Wheat Bran

268

HD Sapirstein

Bioactives: Antioxidants T Beta and KG Duodu

277

x

Contents

The Antinutritional Components of Grains

283

CK Madsen and H Brinch-Pedersen

Mycotoxins

290

MT Fletcher and BJ Blaney

Grain Composition and Analysis

297

The Composition of Food Grains and Grain-Based Products

297

CW Wrigley

Standardized Test Methods for Grains and Grain-Based Products

300

AR Bridges and CW Wrigley

Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units

308

W Huang and CW Wrigley

VOLUME 3 GRAIN-BASED PRODUCTS AND THEIR PROCESSING

1

Wheat-Based Foods

1

Cereals: Overview of Uses: Accent on Wheat Grain

1

CF Morris

Breads

8

TR Moore

Flatbreads of the World

19

KJ Quail

Sour Dough Technology

25

SP Cauvain

Cakes, Muffins and Bagels

30

DE Ortiz

Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics

37

SP Cauvain

Cookies: A Diverse Family of Baked Goods

44

S Zydenbos, V Humphrey-Taylor, and CW Wrigley

Wafers: Methods of Manufacture

51

K Tiefenbacher and CW Wrigley

Cookies and Crackers: Commercial Production

59

LC Paulson and CW Wrigley

Noodles: Starch

64

LS Collado and H Corke

Noodles: Asian Wheat Flour Noodles

72

GB Crosbie and AS Ross

Pasta

79

M Sissons

Tortillas

90

LW Rooney and SO Serna-Saldivar

Non-wheat Foods

97

Maize: Foods from Maize

97

SO Serna-Saldivar

Contents

Rice: Chinese Food Uses

xi

110

S Lu

Sorghum: Utilization

116

RD Waniska, LW Rooney, and CM McDonough

Soybean: Soy-Based Fermented Foods

124

DK O’Toole

Soybean: Soymilk, Tofu, and Okara

134

DK O’Toole

Food-quality Testing

144

The Application of Sensory Science to the Evaluation of Grain-Based Foods

144

LM Duizer and SB Walker

Noodles: Testing for Quality

154

VA Solah and GB Crosbie

Pasta: Quality Testing Methods

161

A Marti, MG D’Egidio, and MA Pagani

Rice: Eating Quality

166

JS Bao

Beverages from Grains

176

Fermentation: Origins and Applications

176

BJB Wood

Fermentation: Foods and Nonalcoholic Beverages

183

JRN Taylor

Beverages: Distilled

193

GH Palmer

Beverages: Asian Alcoholic Beverages

206

DK O’Toole

Non-food Products from Grains

215

Cereal Grains as Animal Feed

215

JL Black

Pet Foods

223

RCE Guy

Utilization of the Whole Cereal Plant to Maximize its Value

228

L Munck

Fuel Alcohol Production

235

YN Guragain, KV Probst, and PV Vadlani

Biodiesel

245

Y Yan

Processing of Grains

251

Evaluation of Wheat-Grain Quality Attributes

251

CF Morris

Grain Quality Attributes for Cereals Other than Wheat CF Morris

257

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Contents

Cereals: Breakfast Cereals

262

EF Caldwell, JD McKeehen, and RS Kadan

Extrusion Technologies

268

RCE Guy

Starch: Uses of Native Starch

274

JW Lawton

Starch: Modification

282

JN BeMiller

b-Glucans: Measurement and Processing

287

MS Izydorczyk

Wheat Processing

299

Milling and Baking: History

299

CE Walker and WD Eustace

Wheat: Dry Milling

307

AK Sarkar and JE Dexter

Wet Milling of Wheat

320

R Velicogna and S Shea Miller

Oven Technologies

325

CE Walker

Bakeries: The Source of Our Unique Wheat-Based Food, Bread

335

JE Bock, CW Wrigley, and CE Walker

Analysis of Dough Rheology in Breadmaking

343

B Dobraszczyk

Frozen Dough

354

D Domingues and C Dowd

Refrigerated Dough

359

D Domingues, C Dowd, and W Atwell

Chemistry of Cake Manufacturing

367

TS Palav

The Gluten Proteins of the Wheat Grain in Relation to Flour Quality

375

F Be´ke´s, MC Gianibelli, and CW Wrigley

Ultrastructure of the Wheat Grain, Flour, and Dough

384

S Grundas and CW Wrigley

Cereal Food Production with Low Salt

396

L Day

Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies

403

A Goldstein and K Seetharaman

Gluten and Modified Gluten

408

IL Batey and W Huang

Snack Foods: Processing

414

MN Riaz

Barley, Rice and Maize Processing

423

Barley: Malting

423

L MacLeod and E Evans

Barley: Milling and Processing MS Izydorczyk and JE Dexter

434

Contents

Rice Processing: Beyond the Farm Gate

xiii

446

L Pallas

Oil from Rice and Maize

453

JS Godber

Maize: Dry Milling

458

KD Rausch and SR Eckhoff

Maize: Wet Milling

467


Oilseed and Legume Processing

482

Soybean: Soy Concentrates and Isolates

482

C-Y Ma

Soybean: Processing

489

T Wang

Canola: Processing

497

JK Daun and EH Unger

VOLUME 4 THE PRODUCTION AND GENETICS OF FOOD GRAINS

1

Grain Marketing and Grading

1

Wheat: Grading and Segregation

1

RL Cracknell and RM Williams

Wheat: Marketing

9


Barley: Grading and Marketing

16

A MacLeod, M Edney, and MS Izydorczyk

Soybean: Grading and Marketing

25

EG Hammond, LA Johnson, and PA Murphy

Identification of Varieties of Food Grains

29

DM Miskelly and CW Wrigley

Grain Harvest, Storage and Transport

42

Wheat: Harvesting, Transport, and Storage

42


Barley: Harvesting, Storage, and Transport

50

RJ Henry

Sorghum: Harvest, Storage, and Transport

54

T Beta, M Chisi, and ES Monyo

Canola: Harvest, Transport, and Storage

62

JJ Mayko

Cereals: Grain Defects

68

SA Barton

The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species

74

RA McIntosh, PM Williamson, and CW Wrigley

Contaminants of Grain J McLean and CW Wrigley

83

xiv

Contents

Chemicals for Grain Production and Protection

99

PC Annis

Handling from Farm to Storage Terminal

105

D Richard-Molard and CW Wrigley

Stored Grain: Invertebrate Pests

110

PC Annis

Postharvest Operations for Quality Preservation of Stored Grain

117

F Fleurat-Lessard

Stored-Grain Pest Management

126

F Fleurat-Lessard

Agronomy of Grain Growing

140

Implication of Climate Changes

140

S Ceccarelli

Sustainable Grain Production and Utilization

144

L Munck

Organic Grain Production and Food Processing

154

P Ge´linas and C David

Precision Agriculture

162

EC Leonard

Plants: Diseases and Pests

168

SA Barton

Wheat: Agronomy

176

GM Paulsen, JP Shroyer, and KJ Shroyer

Barley: Agronomy

186

RD Horsley and M Hochhalter

Maize: Agronomy

194

ED Nafziger

Sorghum: Production and Improvement Practices

201

WL Rooney

Canola: Agronomy

207

NJ Mendham and MJ Robertson

Chickpea: Agronomy

216

KHM Siddique and L Krishnamurthy

Lentil: Agronomy

223

T Nleya, A Vandenberg, FL Walley, and D Deneke

Lupin: Agronomy

231

RJ French

Field Pea: Agronomy

240

RJ French

Soybean: Agronomy

251

ED Nafziger

Natural Disease Control in Cereal Grains

257

WK Mousa and MN Raizada

Wheat: Biotrophic Pathogen Resistance RF Park

264

Contents

Necrotrophic Pathogens of Wheat

xv

273

RP Oliver, K-C Tan, and CS Moffat

Breeding of Grains

279

Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation

279

R DePauw and L O’Brien

Barley: Genetics and Breeding

287

A Cuesta-Marcos, JG Kling, AR Belcher, T Filichkin, SP Fisk, R Graebner, L Helgerson, D Herb, B Meints, AS Ross, PM Hayes, and SE Ulrich

Maize: Breeding

296

EA Lee and LW Kannenberg

Rice: Breeding

304

Qingyao Shu and Dianxing Wu

Canola/Rapeseed: Genetics and Breeding

311

PBE McVetty and RW Duncan

Lentil: Breeding

317

W Erskine, A Sarker, and S Kumar

Lupin: Breeding

325

LC Trugo, E von Baer, and D von Baer

Soybean: Germplasm, Breeding, and Genetics

333

RG Palmer and T Hymowitz

Genetics of Grains

343

Development of Genetically Modified Grains

343

L Privalle

Detection of Genetically Modified Grains

350

RD Shillito

Genomics of Food Grains

360

RJ Henry

Genome Mapping

365

VK Tiwari, JD Faris, B Friebe, and BS Gill

Wheat Genetics

376

RA McIntosh

Wheat Genetics and Genomics

382

E Akhunov

Biotic Stress Resistance Genes in Wheat

388

J Singla and SG Krattinger

Abiotic Stress Genes and Mechanisms in Wheat

393

SJ Roy, NC Collins, and R Munns

Rice: Genetics

398

JS Bao and H Corke

Maize: Genetics

407

EA Lee

Maize: Quality Protein Maize

420

JS Li and SK Vasal

Maize: Other Maize Mutants MH Blanco, H Yangcheng, and J Jane

425

xvi

Contents

Appendix 1. Nutrient-Composition Tables for Grains and for Grain-Based Products

433

SF Schakel, N Van Heel, and J Harnack

Appendix 2. Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods

450


Appendix 3. Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease

460

JM Jones, V Zevallos, and CW Wrigley

Glossary

467

Index

491

PREFACE The grain-producing plants are essential to life on earth. They are the primary means by which sunlight, the primary source of the earth’s energy, is captured via photosynthesis to turn carbon dioxide and water into carbohydrates and thus into the wider range of the biochemicals needed by all life forms. The summary is simple: The sun’s energy þ CO2 þ H2O # Grain-bearing plants which provide: Food, Fats, Fuel and Fiber for ourselves Feed, Forage, Fodder for our animals Food for Fish Farms Directly, grains supply over half of humanity’s energy and protein. Indirectly, grains contribute to our food supply via the feeding of grains and grain by-products to animals, birds and fish. Grains are increasingly a renewable source of fuels (ethanol and oils). Grain species, such as cottonseed, contribute fiber for our clothing.

Grains to Feed and Fuel our World As its title indicates, the Encyclopedia of Food Grains concentrates on the food uses of grains, but details are also provided about the wider roles of grains. Greater detail about the use of grains for animal feeding is already available via the on-line Feedipedia encyclopedia (http://www.feedipedia.org/). Worldwide, however, it is our food that is our obsession – first and foremost. We see our health (or otherwise) to be intimately related to our diet. Therefore nutrition is a major accent of this second edition, occupying the whole of the second volume, following the first volume’s description of the basic aspects of the world of grains. The third and fourth volumes work their ways back up the value-added grain chain to describe grain processing and production, thence to breeding and genetics. The sequence of articles in the first edition (the Encyclopedia of Grain Science, 2004) followed an alphabetical order. In contrast, the distinct ordering of articles in the second edition assembles fundamental concepts in Volume 1 – The World of Food Grains. Moving into the later volumes, greater complexity and erudition are evident. Thus, unusual terms such as “Transcriptomics”, “Aeciospore” and “Allelopathy” are more likely to be found in later volumes than in the first. In any case, reference to the glossary and the index should help in elucidating such terms.

The First and Second Editions - Editors This second edition is a considerable expansion on the content of the first edition, with its three print volumes and 168 articles. Now, some twelve years later, the four print volumes of the Encyclopedia of Food Grains provide

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Preface

216 articles, many newly written for the new edition. Those articles that have been reprinted from the first edition have been updated. In all cases, authors and reviewers are world renowned experts in their respective fields. This second edition has been more than three years in its development. In the early stages, the editors were Harold Corke, Chuck Walker and Colin Wrigley (the three editors of the first edition). Sadly in 2012, Chuck Walker passed away, leaving a gap that was difficult to fill. Chuck was replaced by Koushik Seetharaman, who worked avidly in developing the concepts for this second edition, including his contributions to a meeting of the editors and Elsevier staff in Sydney, January, 2013. Sadly, Koushik suffered a heart attack in June, 2014. However, his contributions to the second edition during this critical development stage were such that Elsevier decided that his name should remain as a co-editor. Tributes to Professors Walker and Seetharaman are provided below. In July, 2014, Professor Jon Faubion was appointed as a co-editor. Dr Faubion is the Charles Singleton Professor of Baking and Cereal Science in the Department of Grain Science, Kansas State University. He is a more than worthy replacement under such tragic circumstances. Acknowledgement to All Involved The production of an encyclopedia involves a wide range of experts with expertise in a diversity of areas of knowledge. We acknowledge with grateful thanks the groups of contributors:

• Members of the Editorial Advisory Board; • Authors who have shared their special knowledge and experience; • Elsevier staff who have provided extensive advice and administrative services, especially Donna de Weerd-Wilson, Simon Holt and Rachel Gerlis (successive Supervisory Staff) and Gemma Tomalin, Gemma Taft, Joanne Williams and Mark Harper (successive Content Project Managers).

The Editors Harold Corke, Jon Faubion, Koushik Seetharaman, and Colin Wrigley

TRIBUTES TO FORMER CO-EDITORS

Professor Emeritus Charles (‘Chuck’) E. Walker

Chuck Walker was one of the three editors of the first edition of Elsevier’s Grains Encyclopedia (the Encyclopedia of Grain Science, 2004). He was again appointed as an editor of this second edition. He participated in the planning stages for the second edition until his untimely death on 26 April 2012. At the time of his death, Chuck was a Professor Emeritus at the Department of Grain Science and Industry at Kansas State University, Manhattan, KS, USA. Charles Eugene Walker was born on 17 December 1936, in Winterset, Madison county, IA, USA, during the great depression. He was the eldest child of Albert Cecil and Bessie Irene Headley Walker, poor farmers in Winterset, Madison county, IA, USA. He walked more than a mile to attend rural one-room grammar schools in Warren county and graduated from high school in New Virginia, IA, USA. Better known as ‘Chuck’ in later life, Dr Walker received a BS degree in Chemical Engineering from Iowa State University, Ames, IA, USA, in May 1959. At a ‘mixer’ party in the fall of 1957, he met Shannon Rose Philp, a pretty freshman student from Loup city, NE, USA. This was just after a summer spent working alone on a fire-lookout tower for the US Forest Service, in the wilds of Clearwater National Forest, in Northern Idaho. They were married on 1 June 1958 and she became his wife of 54 years. She later rewarded him with two sons, Alan Eugene and Tomas Charles, and they adopted a daughter, Bekianne. Upon graduation, Chuck worked in flour milling research at the General Mills Central Research Laboratories in the Minneapolis area from 1959 to 1962. He then accepted a fellowship to graduate school at North Dakota State University in Fargo from 1962 to 1965, majoring in Cereal Chemistry. Chuck received his PhD in Chemistry in the summer of 1966. For his PhD dissertation, he developed a micro brewery and studied barley proteins and their influence on beer quality – a rather ironic choice of topics, considering he remained a strict teetotaler all his life. While finishing his thesis, he joined the faculty of the North Dakota State College, Valley city, ND, USA (1965–1974), teaching various physical science and chemistry courses to undergraduate students. Feeling the pull of industry, he moved south to work for the Fairmont Foods Central Research Laboratory in Omaha, NE, USA (1974–1980), where he did research, product development, and technical assistance on baking, pizza, snack, and dairy products, eventually reaching the position of Associate Director of Research. Dismemberment and sale of this Fortune-500 company provided him an opportunity to return to academia at the University of Nebraska, Lincoln, NE, USA (1980–1987), where he developed a Cereal Technology Program within the Department of Food Technology. He developed and taught various food science and technology courses to both undergraduate and graduate students, and developed a vigorous research program. He became Interim Department Head and Food Processing Center Director. In December 1987, Chuck joined the Department of Grain Science and Industry at Kansas State University as the Bakers National Educational Foundation’s Baking Science Professor. There he maintained a busy program

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in research, teaching, graduate student advising, publishing, traveling and consulting, specializing in baking technology. During his career, Chuck published more than 100 technical papers, and advised about 50 MS and PhD graduate students. He was heavily involved in applied rheology (mixing and flow characteristics) of flour products. In recognition of his commitment to international graduate students, Mr Roland Temme, TMCO, Lincoln, NE, USA, established an international graduate student fellowship in his honor. Chuck entered 50% phased-in retirement at age 65 þ in 2002 and retired in 2005, only to be hired back 1/ 10-time afterward to assist with seminars and the department’s centennial recognition in 2010. He continued to support the department’s activities on a volunteer basis. Chuck’s research and consulting travels took him to more than a dozen countries, including many extended trips to Australia, eventually earning permanent resident status in Australia – a country which had fascinated him since childhood. Most of his time in Australia was spent with the Bread Research Institute in Sydney. He also made several extended trips to China, serving as guest lecturer at ShanDong Agricultural University, Tai’An, and at Henan University of Technology, Zhengzhou. Chuck always commented that “the best legacy a person could leave is the knowledge he has shared.” A significant way in which his knowledge has been shared is represented by his contributions to the first and second editions of Elsevier’s Encyclopedia of Food Grains. Colin Wrigley on behalf of the Editors.

Professor Koushik Seetharaman

In August 2012, Koushik Seetharaman was appointed as the third editor of this second edition of Elsevier’s Grains Encyclopedia, replacing Professor Walker. Tragically, Koushik’s many contributions to the Encyclopedia of Food Grains were cut short by his untimely death at 48 years in June 2014. Koushik received his BS at the Gujarat Agricultural University, Anand, Gujarat, India. His MS training was at Cornell University, Ithaca, NY, USA, and his PhD research was carried out at Texas A&M University, College Station, TX, USA. At the time of Koushik’s appointment as encyclopedia editor (August 2012), he was Associate Professor and Cereals Chair in the Department of Food Science at the University of Guelph, Canada. Research in his laboratory spanned the cereal-grain value chain, focusing on grain quality, processing and ingredient interactions, and on consumer acceptability and health. His research on grain quality at Guelph involved collaboration with cereal-breeding companies, grain farmers of Ontario and local processors, by analyzing Ontario wheats for functionality and nutritional attributes. Special accents were on antioxidant activity, and on fiber and phenolics contents. Interactions with breeders and processor related to the chemistry, sensory properties and consumer acceptance of whole grain products, with specific focus on red versus white wheats in different product matrices. Koushik had a special interest in the behavior of starch in water-poor systems, such as dough and baked products. His research group had demonstrated that the constituent polymers of wheat starch are a series of biopolymers ranging from linear to branched, depending on several factors including genetics and growth environment. Moreover, the proportion of these polymers further defines their functional properties. Research funding had been provided by the Canadian Agricultural Adaptation Council with contributions from the Ontario Cereal Industry Research Council, Kellogg, Kraft, Kraft Canada Mill, Dow AgroSciences, C&M Seeds, Grain Farmers of Ontario and Brabender GmbH. Several months before his death, Koushik had been appointed as an Associate Professor to the Department of Food Science and Nutrition at the University of Minnesota, St Paul, MN, USA, there taking the position of General Mills Cereal Chair. In that capacity, Koushik had again initiated collaborations with breeders and geneticists, millers and processors, with a focus on what product quality means for the consumer. His research focused on interactions of grain biopolymers – starch and gluten in particular – and the impact on processing, product attributes and consumer health.


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His group included three postdoctoral research associates, five doctoral students and one MS student. They were collaborating extensively with research groups around the world including University of Milan, Italy; University of Copenhagen, Denmark; Lille University, France; ONIRIS, France; Tamilnadu Agricultural University, India; Iowa State University, USA; African Rice Research Institute, Benin; University of Guelph, Canada; and Memorial University, Newfoundland, Canada. Koushik’s research background and his collaborations placed him well to contribute to the preparation of the grains encyclopedia, both by his our writing and via his contacts to engage world-authority contributors. The grain-science community world-wide was shocked by Koushik’s sudden passing. Koushik left a wife Debra Freedman and an eight-year-old son, Samuel. Koushik’s contribution to the encyclopedia was such that Elsevier decided that his name should remain as a co-editor even though he did not live to see the end result of his contributions. Colin Wrigley on behalf of the Editors.


EDITORS’ BIOGRAPHY Colin W. Wrigley’s 55 years in grain-science research have earned him international recognition in the form of several international and Australian research awards. His work is described in about 600 research publications, including several patents, a series of eight books on Australian cereal varieties, and many edited books. He was Editor-in-Chief of the first edition of the Encyclopedia of Grain Science (2004). His research interests have centered on the characterization of cereal-grain proteins in relation to processing quality. This has involved developing new methods of protein fractionation, including gel isoelectric focusing and its 2D combination with gel electrophoresis, leading into proteomic mapping. Other diagnostic methods developed relate to the evaluation of grain quality in wheat and barley, such as better methods for variety identification and for characterizing quality in starch and sprouted grain (as co-patentee of the Rapid ViscoAnalyser). Research involvement has also included elucidation of grain-quality variation due to environmental factors (heat stress, fertilizer use, CO2 levels and storage conditions). In 2009, Wrigley was appointed a Member of the Order of Australia (AM) ‘for service to primary industry, particularly to grain science as a researcher, and to the development of methods for improving wheat quality.’ He is currently an Honorary Professor at the University of Queensland, Brisbane, Australia. Harold Corke is a professor in the Food and Nutritional Sciences program at The University of Hong Kong, and a Chutian Scholar Distinguished Foreign Professor in the Glyn O. Phillips Hydrocolloid Research Center at HUT, Hubei University of Technology, Wuhan, China. In more than 22 years in Hong Kong, he has had responsibility for teaching a diverse array of food science courses, including the major courses Grain Production and Utilization, Food Safety and Quality Management, Food Product Development, and general education courses Feeding the World, and Food: Technology, Trade and Culture. He is author or co-author of 180 refereed journal articles, and his 22 PhD graduates have gone on to successful careers in academia and industry around the world. He is on the editorial boards of Journal of Food Composition and Analysis, LWT Food Science and Technology and Journal of Cereal Science, and with Colin Wrigley and Chuck Walker was one of the editors of the first edition of Encyclopedia of Grain Science, published in 2004. Corke is active in consulting in grain processing and food safety in Asia and Eastern Europe.

Jon Faubion is the Charles Singleton Professor of Baking and Cereal Science in the Department of Grain Science, Kansas State University. Over his 35þ year career, he has had the sole or shared responsibility for teaching nine different cereal or food science courses at Texas A&M University, The University of Minnesota and Kansas State. In 2011, he received the Excellence in Teaching Award from the American Association of Cereal Chemists International. He is a senior editor of Cereal Chemistry, and a member of the Board of Directors of the American Association of Cereal Chemists International and an executive editor of Journal of the Science of Food and Agriculture. Prior to rejoining the department faculty in 2005, he directed the Applied Technology and Sensory Science Groups for the research and development arm of The Schwan Food Company.

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EDITORIAL ADVISORY BOARD Jinsong Bao Zhejiang University, Hangzhou, PR China Frank Bekes Director R&D FBFD Pty Ltd, Beecroft, NSW, Australia Trust Beta University of Manitoba, Winnipeg, MB, Canada Stanley Cauvain BakeTran, Witney, United Kingdom; Curtin University, Perth, WA, Australia

Bob French Department of Agriculture and Food, Western Australia, Merredin, WA, Australia Robert Graybosch Agricultural Research Service, USDA, Lincoln, NE, USA Robert Henry University of Queensland, Brisbane, QLD, Australia Barry V. McCleary Megazyme International Ireland, Bray, Wicklow, Ireland

Robert Cracknell Crackers Consulting, Mount Eliza, VIC, Australia

Lindsay O’Brien University of Sydney, Narrabri, NSW, Australia

Yapeng Fang Hubei University of Technology, Wuhan, PR China

Paul Scott USDA-ARS Corn Insects and Crop Genetics Research Unit, Ames, IA, USA

Jon Faubion Kansas State University, Manhattan, KS, USA

John Reginald Nuttall Taylor University of Pretoria, Pretoria, South Africa

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CONTRIBUTORS E Akhunov Kansas State University, Manhattan, KS, USA

BJ Blaney The University of Queensland, St Lucia, Australia

PC Annis CSIRO Entomology, Canberra, ACT, Australia

JE Bock University of Guelph, Guelph, ON, Canada

GA Annor University of Ghana, Accra, Ghana

F Bonomi University of Milan, Milan, Italy

CA Atkins The University of Western Australia, Crawley, WA, Australia

AR Bridges AACC International, St Paul, MN, USA

W Atwell Bill Atwell Consulting, Champlin, MN, USA

H Brinch-Pedersen Aarhus University, Slagelse, Denmark

M Ba˚ga University of Saskatchewan, Saskatoon, SK, Canada

G Bultosa Haramaya University, Dire Dawa, Ethiopia; Botswana College of Agriculture, Gaborone, Botswana

JS Bao Zhejiang University, Hangzhou, PR China

W Bushuk University of Manitoba, Winnipeg, MB, Canada

VJ Barthet Canadian Grain Commission, Winnipeg, MB, Canada

YZ Cai China National Seed Group, Beijing, PR China; Huazhong Agricultural University, Wuhan, PR China; The University of Hong Kong, Hong Kong, PR China; Hubei University of Technology, Wuhan, PR China

SA Barton Oxford Agricultural Trials Ltd, Oxford, UK IL Batey Sunset Cereal Services, Meadowbank, NSW, Australia F Be´ke´s FBFD PTY LTD, Beecroft, NSW, Australia AR Belcher Oregon State University, Corvallis, OR, USA JN BeMiller Purdue University, West Lafayette, IN, USA T Beta University of Manitoba, Winnipeg, Manitoba, Canada JL Black John L Black Consulting, Warrimoo, NSW, Australia MH Blanco (Retired) Plant Breeder and Geneticist, Encinitas, CA, USA

EF Caldwell AACC International, Roseville, MN, USA KJ Carpenter University of California, Berkeley, CA, USA JC Catullo INTA, Buenos Aires, Argentina SP Cauvain BakeTran, Witney, OX, UK S Ceccarelli Via delle Begonie 2, Ascoli Piceno, Italy GK Chandi University of Guelph, Guelph, ON, Canada N Chaudhary G. J. University of Science and Technology, Hisar, India

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Contributors

RN Chibbar University of Saskatchewan, Saskatoon, SK, Canada

JE Dexter Canadian Grain Commission, Winnipeg, MB, Canada

M Chisi Golden Valley Research Station, Chisamba, Zambia

B Dobraszczyk Reading Science Centre, Reading, UK

S Cloutier Agriculture and Agri-Food Canada, Ottawa, ON, Canada

D Domingues General Mills Inc., Minneapolis, MN, USA

LS Collado The University of the Philippines Los Banos, Laguna, Philippines NC Collins School of Agriculture Food and Wine, The University of Adelaide, Glen Osmond, SA, Australia H Corke The University of Hong Kong, Hong Kong, Pokfulam, PR China; Hubei University of Technology, Wuhan, PR China

C Dowd General Mills Inc., Minneapolis, MN, USA LM Duizer University of Guelph, Guelph, ON, Canada RW Duncan University of Manitoba, Winnipeg, MB, Canada KG Duodu University of Pretoria, Pretoria, South Africa SR Eckhoff (Retired) University of Illinois, Urbana, IL, USA

RL Cracknell Crackers Consulting, Mount Eliza, VIC, Australia

M Edney Canadian Grain Commission, Winnipeg, MB, Canada

GB Crosbie Crosbie Grain Quality Consulting, East Fremantle, WA, Australia

M Emery Iowa State University, Ames, IA, USA

JS Croser University of Western Australia, Crawley, WA, Australia A Cruickshank DAFF Queensland, Warwick, QLD, Australia A Cuesta-Marcos Oregon State University, Corvallis, OR, USA MG D’Egidio Unita` di ricerca per la Valorizzazione Qualitativa dei Cereali, Rome, Italy D Dan Ramdath Agriculture and Agri-Food Canada, Guelph, ON, Canada P Dangi G. J. University of Science and Technology, Hisar, India JK Daun (Deceased) C David ISARA Lyon, Lyon, France L Day AgResearch Ltd., Palmerston North, New Zealand D Deneke South Dakota State University, Brookings, SD, USA R DePauw Agriculture and AgriFood Canada, Swift Current, SK, Canada

W Erskine University of Western Australia, Crawley, WA, Australia WD Eustace (Retired) Kansas State University, Manhattan, KS, USA A Evans Tate and Lyle, Hoffman Estates, IL, USA E Evans The Tassie Beer Dr, Lindisfarne, TAS, Australia JD Faris USDA-ARS Cereal Crops Research Unit, Fargo, ND, USA J Faubion Kansas State University, Manhattan, KS, USA AM Fehily Tinuviel Software, Warrington, UK T Filichkin Oregon State University, Corvallis, OR, USA GB Fincher Australian Research Council Centre of Excellence in Plant Cell Walls, University of Adelaide, Glen Osmond, SA, Australia SP Fisk Oregon State University, Corvallis, OR, USA MT Fletcher The University of Queensland, St Lucia, Australia

Contributors

RJ Fletcher University of Queensland, Gatton, QLD, Australia

A Gunaratne The University of Hong Kong, Hong Kong, PR China

F Fleurat-Lessard INRA, Mycology and Food Safety Research Unit, Villenave d’Ornon, France

YN Guragain Kansas State University, Manhattan, KS, USA

JA Fox Kansas State University, Manhattan, KS, USA RJ French The University of Western Australia, Crawley, WA, Australia B Friebe Kansas State University, Manhattan, KS, USA BJ Furman San Jose State University, San Jose, CA, USA M Gangola University of Saskatchewan, Saskatoon, SK, Canada P Ge´linas Food Research and Development Centre, Agriculture and Agri-Food Canada, Saint-Hyacinthe, QC, Canada SM Ghazani University of Guelph, Guelph, ON, Canada MC Gianibelli (Retired) A Gianinetti Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria, CRA-GPG, Fiorenzuola d’Arda, Italy BS Gill Kansas State University, Manhattan, KS, USA JS Godber LSU Agricultural Center, Baton Rouge, LA, USA A Goldstein University of Minnesota, St. Paul, MN, USA R Graebner Oregon State University, Corvallis, OR, USA S Graham-Acquaah Africa Rice Center, Cotonou, Republic of Benin RA Graybosch USDA-ARS, University of Nebraska Lincoln, Lincoln, NE, USA S Grundas Bohdan Dobrzanski Institute of Agrophysics of the Polish Academy of Sciences, Lublin, Poland TJ Gulya USDA-ARS, Northern Crop Science Laboratory, Fargo, ND, USA

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RCE Guy Campden and Chorleywood Food Research Association, Chipping Campden, UK C Hall III North Dakota State University, Fargo, ND, USA LM Hall University of Alberta, Edmonton, AB, Canada EG Hammond Iowa State University, Ames, IA, USA R Haraszi Campden BRI, Gloucestershire, UK J Harnack University of Minnesota, Minneapolis, MN, USA D Hauge Grains for Health Foundation, St. Louis Park, MN, USA AMR Hayes St. Catherine University, Lafayette, MN, USA PM Hayes Oregon State University, Corvallis, OR, USA L Helgerson Oregon State University, Corvallis, OR, USA RJ Henry University of Queensland, Brisbane, QLD, Australia D Herb Oregon State University, Corvallis, OR, USA I Herencia Universidad Politecnica de Madrid, Madrid, Spain E Hernandez Texas A&M University, College Station, TX, USA KB Hobson New South Wales Department of Primary Industries, Tamworth, NSW, Australia M Hochhalter North Dakota State University, Fargo, ND, USA RD Horsley North Dakota State University, Fargo, ND, USA W Huang Jiangsu Academy of Agricultural Sciences, Nanjing, PR China; Jiangnan University, Wuxi, Jiangsu, PR China Y Huang China Agricultural University, Beijing, PR China

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Contributors

V Humphrey-Taylor (Retired) New Zealand Institute for Crop Food Research Limited, Christchurch, New Zealand

P Koehler Deutsche Forschungsanstalt fu¨r Lebensmittelchemie, Leibniz Institut, Freising, Germany

T Hymowitz University of Illinois at Champaign-Urbana, Urbana, IL, USA

R Korczak University of Minnesota, St. Paul, MN, USA

S Iametti University of Milan, Milan, Italy C Isaak University of Manitoba, Winnipeg, MB, Canada MS Izydorczyk Canadian Grain Commission, Winnipeg, MB, Canada P Jacques Tufts University, Boston, MA, USA S Jaiswal University of Saskatchewan, Saskatoon, SK, Canada J Jane Iowa State University, Ames, IA, USA LA Johnson Iowa State University, Ames, IA, USA JM Jones St. Catherine University, Arden Hills, MN, USA A Juha´sz Centre for Agricultural Research of the Hungarian Academy of Sciences, Martonva´sa´r, Hungary BO Juliano Philippine Rice Research Institute Los Banõs, Laguna, Philippines RS Kadan (Deceased) GP Kadkol NSW Department of Primary Industries, Calala, NSW, Australia LW Kannenberg University of Guelph, Guelph, ON, Canada

SG Krattinger University of Zurich, Zurich, Switzerland L Krishnamurthy International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India S Kumar International Center for Agricultural Research in the Dry Areas (ICARDA), Rabat, Morocco OR Larroque CSIRO Agriculture Flagship, Canberra, Australia JW Lawton (Retired) ARS-USDA EA Lee University of Guelph, Guelph, ON, Canada EC Leonard AgriKnowHow, Maitland, SA, Australia JS Li China Agricultural University, Beijing, PR China WD Li Shanxi University, Taiyuan, PR China Z Li CSIRO Food Futures National Research Flagship, Canberra, ACT, Australia; CSIRO Plant Industry, Canberra, ACT, Australia R Lindberg Minneapolis Heart Institute Foundation, Minneapolis, MN, USA MG Lindhauer Max Rubner-Institut (MRI), Detmold, Germany

TN Khan University of Western Australia, Crawley, WA, Australia

K Liu Agricultural Research Service, US Department of Agriculture, Aberdeen, ID, USA

BS Khatkar G. J. University of Science and Technology, Hisar, India

Q Liu Agriculture and Agri-Food Canada, Guelph, ON, Canada

JG Kling Oregon State University, Corvallis, OR, USA

S Lu National Chung Hsing University, Taichung, Taiwan

EJ Knights New South Wales Department of Primary Industries, Tamworth, NSW, Australia

OM Lukow Agriculture and Agri-Food Canada, Winnipeg, MB, Canada

Contributors

BL Ma Agriculture and Agri-Food Canada, Ottawa, ON, Canada

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NJ Mendham University of Tasmania, Hobart, TAS, Australia

C-Y Ma The University of Hong Kong, Hong Kong, PR China

R Menon The General Mills Bell Institute of Health and Nutrition, Minneapolis, MN, USA

A MacLeod Canadian Grain Commission, Winnipeg, MB, Canada

TE Michaels University of Minnesota, St. Paul, MN, USA

L MacLeod Dairy Innovation Australia, Werribee, VIC, Australia

DM Miskelly Westcott Consultants P/L, Goulburn, NSW, Australia

CK Madsen Aarhus University, Slagelse, Denmark RJ Mailer Australian Oils Research, Lambton, NSW, Australia JT Manful Africa Rice Center, Cotonou, Republic of Benin AG Marangoni University of Guelph, Guelph, ON, Canada DJ Mares University of Adelaide, Glen Osmond, SA, Australia L Marquart University of Minnesota, St. Paul, MN, USA; Grains for Health Foundation, St. Louis Park, MN, USA A Marti Universita` degli Studi di Milano, Milan, Italy B Maschoff Grains for Health Foundation, St. Louis Park, MN, USA A Mathiowetz University of Minnesota, St. Paul, MN, USA; Rochester, MN, USA

CS Moffat Curtin University, Bentley, WA, Australia ES Monyo ICRISAT, Nairobi, Kenya TR Moore AIB International, Manhattan, KS, USA MK Morell International Rice Research Institute, Los Banõs, Philippines CF Morris USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA LA Morrison Oregon State University, Corvallis, OR, USA WK Mousa University of Guelph, Guelph, ON, Canada; Mansoura University, Mansoura, Egypt K Mrva University of Adelaide, Glen Osmond, SA, Australia

JJ Mayko Canola Council of Canada, Mundare, AB, Canada

L Munck University of Copenhagen, Frederiksberg C, Denmark

CM McDonough Texas A&M University, College Station, TX, USA

R Munns CSIRO Agriculture, Canberra, ACT, Australia; The University of Western Australia, Crawley, WA, Australia

RA McIntosh The University of Sydney, Cobbitty, NSW, Australia JD McKeehen Cereal Partners Worldwide, Minneapolis, MN, USA J McLean The University of Newcastle, Callaghan, NSW, Australia PBE McVetty University of Manitoba, Winnipeg, MB, Canada B Meints Oregon State University, Corvallis, OR, USA A Meldrum Pulse Australia, Perth, WA, Australia

PA Murphy Iowa State University, Ames, IA, USA ED Nafziger University of Illinois, Urbana, IL, USA SC Nelson AACC International (AACCI), St. Paul, MN, USA T Nleya South Dakota State University, Brookings, SD, USA L O’Brien The University of Sydney, Narrabri, NSW, Australia; Solheimar Pty Ltd, Narrabri, NSW, Australia

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Contributors

DK O’Toole City University of Hong Kong, Hong Kong, PR China

I Rajcan University of Guelph, Guelph, ON, Canada

EA Oelke University of Minnesota, St. Paul, MN, USA

L Ramsden University of Hong Kong, Hong Kong, PR China

RP Oliver Curtin University, Bentley, WA, Australia

KD Rausch University of Illinois at Urbana–Champaign, Urbana, IL, USA

DE Ortiz W. K. Kellogg Institute, Battle Creek, MI, USA MA Pagani Universita` degli Studi di Milano, Milan, Italy TS Palav Rich Products Corporation, Buffalo, NY, USA L Pallas Yanco Agricultural Institute, Yanco, NSW, Australia GH Palmer Heriot-Watt University, Edinburgh, UK RG Palmer Iowa State University, Ames, IA, USA RF Park The University of Sydney, Narellan, NSW, Australia GM Paulsen Kansas State University, Manhattan, KS, USA LC Paulson The Bama Companies, Tulsa, OK, USA DS Petterson Department of Agriculture, Nedlands, WA, Australia RA Porter University of Minnesota-NCROC, Grand Rapids, MN, USA L Privalle Bayer CropScience, Research Triangle Park, Durham, NC, USA KV Probst Kansas State University, Manhattan, KS, USA; Grain Processing Corporation, Muscatine, IA, USA KJ Quail Grain Growers Limited, North Ryde, NSW, Australia RCN Rachaputi University of Queensland, Kingaroy, QLD, Australia

A Regina CSIRO Food Futures National Research Flagship, Canberra, ACT, Australia; CSIRO Plant Industry, Canberra, ACT, Australia MN Riaz Texas A&M University, College Station, TX, USA D Richard-Molard (Retired) INRA, Nantes, France F Rizza Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria, CRA-GPG, Fiorenzuola d’Arda, Italy MJ Robertson CSIRO Sustainable Ecosystems, St. Lucia, QLD, Australia LW Rooney Texas A&M University, College Station, TX, USA WL Rooney Texas A&M University, College Station, TX, USA CM Rosell Institute of Agrochemistry and Food Technology (IATACSIC), Paterna, Valencia, Spain AS Ross Oregon State University, Corvallis, OR, USA SJ Roy School of Agriculture Food and Wine, The University of Adelaide, Glen Osmond, SA, Australia HD Sapirstein University of Manitoba, Winnipeg, MB, Canada AK Sarkar Canadian International Grains Institute, Winnipeg, MB, Canada

H Rahman University of Alberta, Edmonton, AB, Canada

A Sarker International Center for Agricultural Research in the Dry Areas (ICARDA), New Delhi, India

S Rahman Monash University Malaysia, Bandar Sunway, Malaysia

SK Sathe Florida State University, Tallahassee, FL, USA

MN Raizada University of Guelph, Guelph, ON, Canada

SF Schakel University of Minnesota, Minneapolis, MN, USA

Contributors

KA Scherf Deutsche Forschungsanstalt fu¨r Lebensmittelchemie, Leibniz Institut, Freising, Germany

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VA Solah Curtin University, Perth, WA, Australia

MP Scott Iowa State University, Ames, IA, USA

AM Stanca University of Modena and Reggio Emilia, Reggio Emilia, Italy

K Seetharaman (Deceased)

FL Stoddard University of Helsinki, Helsinki, Finland

GJ Seiler USDA-ARS, Northern Crop Science Laboratory, Fargo, ND, USA

K-C Tan Curtin University, Bentley, WA, Australia

SO Serna-Saldivar Centro de Biotecnologıá FEMSA, Escuela de Ingenierıá y Ciencias, Monterrey, Mexico S Shea Miller Eastern Cereals and Oilseeds Research Centre, Agriculture and Agri-Food Canada, Ottawa, ON, Canada DB Sheats St. Catherine University, St. Paul, MN, USA PR Shewry Rothamsted Research, Harpenden, UK; University of Reading, Reading, UK RD Shillito Bayer CropScience, Durham, NC, USA JP Shroyer Kansas State University, Manhattan, KS, USA KJ Shroyer Kansas State University, Manhattan, KS, USA Qingyao Shu Zhejiang University, Hangzhou, PR China KHM Siddique University of Western Australia, Crawley, WA, Australia J Singla University of Zurich, Zurich, Switzerland M Sissons NSW Department of Primary Industries, Calala, NSW, Australia; Tamworth Agricultural Institute, Tamworth, NSW, Australia JH Skerritt University of Queensland, St Lucia, QLD, Australia DJ Skylas Grain Growers Limited, North Ryde, NSW, Australia DL Smith McGill University, Ste-Anne-de-Bellevue, QC, Canada

AS Tatham Cardiff Metropolitan University, Cardiff, UK JRN Taylor University of Pretoria, Hatfield, South Africa V Terzi Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria, CRA-GPG, Fiorenzuola d’Arda, Italy K Tiefenbacher (Retired) VK Tiwari Kansas State University, Manhattan, KS, USA SM Tosh Agriculture and Agri-Food Canada, Guelph, ON, Canada P Tosi University of Reading, Reading, UK LC Trugo Federal University of Rio de Janeiro, Rio de Janeiro, Brazil SE Ulrich Washington State University, Pullman, WA, USA EH Unger Eagle Rock Solutions, Inc., Idaho Falls, ID, USA PV Vadlani Kansas State University, Manhattan, KS, USA SA Valencia-Chamorro Escuela Politećnica Nacional, Quito, Ecuador V Vamadevan University of Minnesota, St. Paul, MN, USA; Agriculture and Agri-Food Canada, Guelph, ON, Canada N Van Heel University of Minnesota, Minneapolis, MN, USA A Vandenberg University of Saskatchewan, Saskatoon, SK, Canada SK Vasal BISA, Punjab, India

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Contributors

R Velicogna Archer Daniels Midland, Montreal, QC, Canada

BJB Wood Strathclyde University, Glasgow, UK

D von Baer Seeds Baer, Temuco, Chile

G Wright Peanut Company of Australia, Kingaroy, QLD, Australia

E von Baer CAMPEX Semillas Baer, Temuco, Chile

CW Wrigley Honorary Professor, QAAFI; The University of Queensland, Brisbane, QLD, Australia

CE Walker (Deceased) SB Walker University of Guelph, Guelph, ON, Canada FL Walley University of Saskatchewan, Saskatoon, SK, Canada D Wang Huazhong Agricultural University, Wuhan, PR China T Wang Iowa State University, Ames, IA, USA RD Waniska Texas A&M University, College Station, TX, USA

Dianxing Wu Zhejiang University, Hangzhou, PR China HX Wu Wuhan Chortle Biotechnology Company Limited, Wuhan, PR China J Wyatt NIAB, Cambridge, UK Y Yan Huazhong University of Science and Technology, Wuhan, PR China H Yangcheng Iowa State University, Ames, IA, USA

LL Ward Kansas State University, Manhattan, KS, USA

V Zevallos Johannes Gutenberg Mainz, Mainz, Germany; University Medical Center, Mainz, Germany

H Wieser Deutsche Forschungsanstalt fu¨r Lebensmittelchemie, Leibniz Institut, Freising, Germany

XM Zhou McGill University, Ste-Anne-de-Bellevue, QC, Canada

RM Williams CBH Group, West Perth, WA, Australia

PK Zwer South Australian Research and Development Institute (SARDI), Urrbrae, SA, Australia

PM Williamson (Retired) Leslie Research Centre, Toowoomba, QLD, Australia; CBH Group, West Perth, WA, Australia

S Zydenbos (Retired) New Zealand Institute for Crop Food Research Limited, Christchurch, New Zealand

THE WORLD OF FOOD GRAINS The Basics

Contents The Grains that Feed the World Course Structures: Based on EFG Articles The Grain Crops: An Overview The Grain Chain: The Route from Genes to Grain-Based Products Taxonomic Classification of Grain Species Grain: Morphology of Internal Structure Grain and Plant Morphology of Cereals and how characters can be used to identify varieties

The Grains that Feed the World CW Wrigley, University of Queensland, Brisbane, QLD, Australia H Corke, University of Hong Kong, Hong Kong, Pokfulam, China J Faubion, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

•

Grains are responsible directly or indirectly for most of the food we eat. The big three cereal grains (rice, wheat, and maize) have roles as staple foods (major daily sources of carbohydrate-based energy) and for processing into animal feeds and other diverse uses such as fuel bioethanol. There has been an explosive growth in meat consumption globally, as more and more people come out of poverty and enter into a growing middle class. This is most apparent in China, where demand for meat and other animal products (eggs and milk) drives the production of maize domestically and production of soy beans in major exporting countries (the United States, Argentina, and Brazil). A billion people worldwide are obese; a third of the food produced in industrialized countries is thrown away uneaten. In this exuberant excess of food production lie many serious problems – a billion people worldwide are chronically malnourished, food production competes with industry and domestic usage for scarce resources of energy and water, human populations continue to increase, and food production impacts on the environment in ways that may not be sustainable. People care about what they eat, about their health, about longevity, and about fitness. In the news media, nutrition sells; there is thus a constant output of information on topics such as gluten-free diets,

• • • • •

Grains are the source of half of our food and protein consumption. Current world production for all grains equals 1 kg per person per day. Grains also contribute to the wider range of foods via animals. Major media claims about grains and health are presented in this article. Some myths about grain-based foods are busted. Some claims are supported, at least in part.

Learning Objectives

• • •

To understand the significance of grains in feeding the growing human population To adopt a critical attitude to production and nutritional information about grains presented in the media and to know how to seek and research authentic information To be motivated to pursue further topics in depth, starting with investigating relevant articles in the Encyclopedia of Food Grains and going back where necessary to primary scientific research articles.

Encyclopedia of Food Grains, Second Edition

http://dx.doi.org/10.1016/B978-0-12-394437-5.00003-6

1

2

THE BASICS | The Grains that Feed the World

obesity, genetically modified organisms (GMOs), and organic agriculture. Unfortunately, much of the popular media reporting on grains and health is wrong, sometimes the result of journalistic carelessness or ignorance, sometimes from demand for an ideological spin on knowledge, and sometimes out of a crass calculation that hysteria sells better than truth. This encyclopedia sets out to redress the balance and rectify these popular misconceptions. What do you expect from an encyclopedia? Obviously, everything you want to know about the general topic. Just as importantly, you expect correct information, provided by world-recognized authorities, knowing that all facts have been checked. These expectations are fulfilled in this encyclopedia, in its four print volumes, in its hundreds of articles, in its broad-ranging website, and in its extension as part of Elsevier’s Food Science Reference Module, as a general source of advice to the food industry worldwide. Often, the expectation of an encyclopedia is to check whether what-I-have-heard is actually so. This introductory article explores some of those what-I-have-heard sayings, listed in groups of dot points, with commentary, plus referral to relevant encyclopedia articles. The authors of the encyclopedia articles are recognized as world authorities in their respective fields. The articles have all undergone peer review by members of the editorial advisory board and the editors, thereby ensuring that the information is correct and free from the many myths, misconceptions, and misinformation that have been spread by nefarious advertising and unbridled websites.

Grains and Our Future

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Climate change will lead to less grain production. Not necessarily! We have become so dependent upon eating cereal grains (grass seeds) that it has prompted at least one author to say that we have become ‘canaries.’ Yes, we are dependent on grains, but ‘canaries,’ no! ‘Cereal grains literally stand between humankind and starvation.’ Maybe. Humankind will run out of food in the foreseeable future. Probably not. – What ultimately is the source of our food? How vulnerable are we?

Our Dependence on Grains as Food The 1960s were a time of great pessimism about the future of humanity and the possibility of massive famines due to population increases, especially in Asia and Africa, and the failure of national agricultural to produce enough to feed these growing populations. The Green Revolution was spearheaded by the research of Dr. Norman Borlaug (Figure 1) on dwarf wheat at CIMMYT in Mexico and was complemented by similar work on dwarf rice at International Rice Research Institute in the Philippines. These advances led to rapid increases in grain production. India went from being a chronic major importer of wheat to avert famine to being a significant exporter of grain. The relative abundance in grain production today, the power of biotechnology, and the excesses in consumption we often see around us (wastage of food and increasing meat consumption) may make us forget how tenuous is our ability to produce the grains we need year after year. Humankind has certainly become dependent upon eating cereal grains.

Figure 1 Norman Borlaug was awarded the Nobel Peace Prize in 1970 for his work to end world hunger by creating new strains of drought-resistant wheat. This statue was placed in the US Capitol Building’s National Statuary Hall in 2014 to celebrate the 100th anniversary of Borlaug’s birth.

This dependence is inevitable, given our vast population and the contribution of grains to food and feed production. Grains provide over half our protein and energy needs. But it is hardly justified to claim that, as a result, we have become ‘canaries.’ A recurring theme of this encyclopedia is the great diversity of ways in which we prepare grains in our diet – not only as ‘our daily bread’ (Bible, Matthew 4:4) and not only as the staple food of boiled rice. A complete volume is devoted to the great diversity of grain-based products and their processing.

What Ultimately Is the Source of Our Food on Earth? This question was addressed in 1648 by a Belgian scientist, Jan Baptist van Helmont, with respect to plants in general. He planted a tree in a pot of soil. He first weighed the soil (after drying it) and also the small tree. For 5 years, he added water only to the pot. He then weighed the remaining soil and the tree, which had grown considerably. There was negligible weight loss from the soil, so he concluded that all the weight gain of the tree had come from the water that he added: thus, wood is made from water! (Figure 2).

THE BASICS | The Grains that Feed the World Today, we know that Jan did not control two important factors: the sun and the air (CO2), which together produce all plant life via photosynthesis according to the following reactions: CO2 þ H2 O þ light ! O2 þ glucose ða simple sugarÞ Glucose ! carbohydrates, lignin, and cellulose ðplant componentsÞ Jan Baptist lived in an age of the Aristotelian belief in four elements: water, earth, air, and fire. Even considering these elements, he took into account the first two, but neglected air (CO2) and fire (sunlight). Thus, all our food comes from these sources – sunlight, CO2, and water – either directly in the cases of grains, vegetables, and fruit or indirectly in the cases of animals who eat the grain and plants. In addition, the soil does contribute

In 1648, a scientist provided water only to a small tree ... for 5 years

Thus, he concluded that trees are made from water! He neglected the roles of light and CO2

Figure 2 The experiment of Belgian scientist, Jan Baptist van Helmont, seeking to determine what plants are made from.

the wide range of elements described later in this article, especially nitrogen for protein synthesis. When grain is harvested, these elements are removed from the field, and they must ultimately be replaced by some form of fertilizer. However, the other essentials – sunlight, CO2, and water – are readily available for free on an ongoing basis. Of course, that might not be claimed for water in many dry climates. The free claim can certainly be made for CO2 given the rising levels of this component of our atmosphere. In fact, the sequestration of CO2 by plants is one of the many solutions for mitigating the rising levels of CO2. There needs to be a realization of the essential nature of CO2 as the source of all plant life and thus of all our food, thereby to reverse the bad press attributed to CO2.

Will We Run Out of Food in the Foreseeable Future? Our reliance on the grains of cereal plants (especially wheat, rice, and corn) is so great that they supply nearly 60% of our food energy and 50% of the protein consumed on Earth. Thus, grains really do ‘stand between us and starvation.’ Grains offer the great advantages that they can be stored safely for long periods and thus transported far from their growth sites. Grains are adaptable with respect to the wide range of foods made from them. Grains are also important as animal food and for various forms of industrial processing. But will we run out of food in the foreseeable future? Efforts continue to improve methods of breeding, agronomy, harvesting, and processing, showing good signs that grain production and quality will continue to increase, providing for a world of hungry people. The production and yield of wheat have tripled in the past 40 years, as explained in the Wheat Overview article (The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’). Furthermore, Figure 3 shows how there is an ongoing increase in the

Cereal production, utilization and stocks Million tonnes

Million tonnes 2600

800

2400

600

2200

400

2000

200

1800 2004/05

2006/07

2008/09

Production (left axis)

3

2010/11

2012/13

0 2014/15 f’cast

Utilization (left axis)

Stocks (right axis) Figure 3 The past decade of production and utilization of cereal grains. Source: FAOSTAT.

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Earth’s atmospheric CO2 concentration and temperature 14.5 390 14.3

370 350

14.1 ppm 330 CO2 310

°C CO2

°C

13.9

290 13.7 270 250 13.5 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Year Figure 4 Increasing temperatures and levels of carbon dioxide promise increasing grain yields due to the carbon-fertilizer effect.

worldwide production of cereal grains, also including maize, rice, barley, and other grass-related grains. The future therefore looks hopeful. However, we still have great inequalities in food supply in terms of grains. Although current world production for all grains is equivalent to 1 kg per person per day, there is still hunger because some of this great volume of grain serves alternative important nonfood purposes, such as animal feed and industrial uses. The greatest problem, however, is that the major sites of production are distant from the major sites of need, and those in need lack the resources to access the excess grain. Increasing levels of carbon dioxide (Figure 4) offer the promise of increasing grain yields, but with growth conditions changing, breeders and agronomists need to focus research on adapting to a changing world scene.

stresses of over 35 C during grain filling. However, there are indications that some wheat genotypes are available that provide stable grain quality despite such heat-stress conditions, thereby opening up promising research directions. So, considerable research effort is concentrated on breeding for changed growth conditions (see articles Agronomy of Grain Growing: Implication of Climate Changes; Sustainable Grain Production and Utilization; Wheat: Biotrophic Pathogen Resistance; Genetics of Grains: Abiotic Stress Genes and Mechanisms in Wheat; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture).

Climate Change and the Future of Grain Production

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Predictions of global climate change include increased levels of carbon dioxide in the atmosphere, causing warmer temperatures (especially the daily minima), changed patterns of rainfall, and increased frequency and severity of heat-stress episodes, together with decreased frost frequency and rising sea levels. These trends imply a future of fluctuations in grain yield and quality, but overall increases in grain yield are predicted. Rising sea levels have serious implications for many low-lying rice-growing areas in Asia. Irrespective of arguments about causes, increases in atmospheric levels in carbon dioxide have been clearly demonstrated, rising from ancient levels of 150–280 to 400 ppm and beyond, with a predicted doubling in a century or so. One consequence is the provision of carbon fertilizer, leading in the future to more efficient biomass production and greater yields for many grain species. However, the yield increases may be largely in carbohydrate, potentially leaving reduced grainprotein levels. The fertilizing effects of carbon dioxide are more significant at higher temperatures, the other major effect predicted to accompany the global climate challenge. For wheat, the increases in temperature are also expected to affect potential dough-forming properties. Temperatures in the range 15–30 C during grain filling have been shown to provide optimal dough strength, but grain with weaker dough quality is produced when plants are subjected to a few days of heat

Growing Our Grains

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Organic-grown grain is superior nutritionally to other grain. Wrong! GMO grain is hazardous to your health. Wrong!

Organic Growing Organic is an adjective used with the whole range of foods and even fibers. The term is associated with a higher price and presumed higher value. It should also indicate products of such quality and composition as are expected from growing these products in the absence of chemicals, instead using natural means of farm management. Are organically grown grains, for example, any different nutritionally from other sources of grain? The answer is generally no. Organic grain will look the same as conventionally grown grain and will not likely to have more favorable nutritional content. Organic grain is likely to have a protein content similar to that of other grains grown under similar conditions. With respect to chemicals, the levels of pesticides and herbicides of organic grain may be less than those for conventionally grown grain, but the latter are still required to have such compounds at levels below the minimum residue levels. A report by the UK Crop Protection Association found “lower levels of pesticide residues in organic produce when compared to conventional” but “these differences are relatively small, for example, a typical residue of 0.1 mg/kg is equivalent to a fly on a ten-ton truck.” The encyclopedia’s article on organic grain points out that the great advantage of organic farming is the benefit to land

THE BASICS | The Grains that Feed the World use and the environment (see articles Agronomy of Grain Growing: Organic Grain Production and Food Processing; Sustainable Grain Production and Utilization; Food Grains and the Consumer: Labelling of Grain-Based Foods).

Genetically Modified Organisms It is well over a century since grain scientists commenced the now usual practice of cross pollination to combine the benefits of one parental line with those of another. Previously, plant improvements had involved the selection of promising plants (by appearance) from the common mix of plants in the field. Cross pollination greatly extended the genetic variability of populations from which to select promising new genotypes for use in developing new improved varieties. However, this approach to plant breeding is limited because cross pollination is generally restricted to plants of the same genus, perhaps even the same species. Thus, for example, it is not possible to source genetic resistance to a disease from beyond the target grain species. In recent decades, this limitation has been removed by the introduction of genetic engineering techniques, permitting not only very precise inter-genus transfer of genes but also the targeting of single genes or groups of genes for transfer from unrelated genera (which could, e.g., be as distant as a fish and a different plant). The improved plant or animal that carries functional genes from an unrelated genus (a gene transfer that could not happen in nature) is termed genetically modified (GM). Many improved grain genotypes have been introduced into agricultural production on a very large scale. Such improvements may include not only agronomic and disease benefits but also improvements in nutritional value. The major crops involved for large-scale production are maize, soybean, canola, and cotton. In the case of GMO cotton especially, there has been great environmental benefit of reduced use of insecticides. There are GMO variations of many other grain crops, such as golden rice, GM to contain beta-carotene, a source of vitamin A. There has been political/philosophical/activist and consumer resistance to the benefits offered by GMO technology, such that the range of GMO grains has been restricted and the potential benefits have not yet become available. For example, there is thus no widespread cultivation of GMO wheat, barley, or rice. Much of the scientific evidence presented on the potential harm of GM foods is simply spurious, generated with disregard to normal experimental practices, and with results predetermined by a bias on the part of the authors. In consequence of consumer resistance, the spread of GMO grains has been restricted to some countries and regions – mainly to the Americas. In Argentina, for example, many farmers grow two crops a year – wheat and GMO soy. As the soy is herbicideresistant, weeds are eliminated during the soy-growth phase, and the subsequent wheat crop is harvested free of weed seeds. Much of Europe and Africa has been far more circumspect about permitting introduction of GM grains. There is a valid and essential ongoing public debate to be made about the ownership or intellectual property basis of genetic resources that underpin GMO production. There is valid unease about the potentially excess control that a few biotechnology companies may exert on world agriculture. There are also arguments to be made about the environmental impacts – both positive and negative – of all forms of agriculture, including that involving GM plants and animals. But these arguments should be made on the basis of accurate and apolitical information

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on the actual composition of GM food and the actual effects of GM plant and animal agricultural practices (see articles Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Detection of Genetically Modified Grains; Development of Genetically Modified Grains; The Cereal Grains: Maize: Overview; The Oilseeds: Cottonseed: Overview; Canola: Overview; Soybean: Overview).

Grains, Our Health, and the Media What can we believe? We all know that the French queen Marie Antoinette (Figure 5) famously declared “Let them eat cake” when she was told that her starving subjects were clamoring for bread. Wrong! The saying is stuck in historical tradition because it has been a convenient prećis of the aristocratic arrogance of the times preceding the French revolution (1789–99). However, the line about eating cake was actually written in the mid-1760s when Marie Antoinette was a young girl living in Austria. It appears in a work entitled Confessions written by Jean-Jacques Rousseau. Furthermore, much has been lost in translation. The word ‘cake’ is a mistranslation of the French brioche that is a pastry with tender crumb made with generous inclusion of egg and butter, hardly like our general concept of ‘cake.’ The linkage to Marie Antoinette has been attributed to Jean-Baptiste Alphonse Karr (1808–90), who wrote it 50 years after her death. How does it happen that society accepts the authenticity of a phrase or story even though it is just plain wrong? The ‘Let them eat cake’ story may be no more than a trivial error of history. More important are the multitude of other errors and misconceptions in the public mind. To the extent that this misinformation affects our way of life and our personal well

Figure 5 The peasants of France were starving for lack of bread. Marie Antoinette responded: “No bread? Then let them eat cake.” Did she?

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being, there is a serious need for authentic information to be offered and adopted. There may be no combination of issues where this need is more apparent than in the matter of nutrition, our diet being closely allied to our health, quality of life, and our death, thus prompting sayings such as the following:

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What we eat today walks and talks tomorrow. Digging our graves with our teeth. We are what we eat. Mens sana in corpore sano (a healthy mind in a healthy body).

The Encyclopedia of Food Grains: A Source of Authentic Information This encyclopedia offers authentic information about all aspects of food grains as they relate to us – and about all sorts of grains: chickpeas, rice, maize, barley, quinoa, soya, plus buckwheat, and the real wheat (the last two grains are unrelated!). The encyclopedia’s coverage takes us through the various stages of the breeding of grains, their growth, production, processing, and the retailing of the wide range of grainbased foods. All these issues impact us as consumers, situated as we are at the culmination of the ‘grain chain’ (see article The Basics: The Grain Chain: The Route from Genes to Grain-Based Products). Veracity for the articles is assured due to authorship by world authorities, followed by peer review by members of the editorial advisory board, the editors, and external experts.

Some Popular Mythconceptions About Food Grains In this opening article, we examine and correct some of the myths and misconceptions (mythconceptions) about grainrelated nutrition and grain production. These errors appear in popular books and on questionable websites and inferred in advertising, in general gossip, and in popular concepts. Beyond this article, more mythconceptions are addressed in detail throughout the encyclopedia. How about the following ideas?

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Bread makes you fat. Wrong! The fat you eat goes straight to your hips. Wrong! Eat fat-free products and you won’t get fat. Wrong! Trans fats, produced in fats from oilseeds, are bad for you. Maybe! Food additives are all badditives! Wrong! New types of oilseeds have fats that are nutritionally beneficial. True! Only children get celiac disease and they can grow out of it anyway. No and no! A gluten-free diet will make you feel better. Wrong or not necessarily. A gluten-free diet is damaging to your health. Wrong! A gluten-free diet will cause you to miss essential nutrients. Maybe. A gluten-free diet means that I cannot eat buckwheat. Wrong!

Figure 6 This type of corn dolly is not made from corn (maize); they are usually made from the stalks and heads of wheat, rye, triticale, and barley. This apparent misnomer arises from the use of corn to signify any grain species; this connotation is still prevalent in parts of Britain, whereas corn is used in North America to signify maize.

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At least we know that milk and coffee are gluten-free. Not necessarily. Corn dollies are made from corn (maize). No, not usually! (See Figure 6.) There are dietary imbalances in the cereal grains. Partly true! Spinach is the best source of iron in our diet; we know that because we grew up with Popeye the Sailor Man who ate all his spinach. Wrong! Wild flax growing in New Zealand differs from cultivated flax. Correct! (See Figure 7.) Organic-grown grain is superior nutritionally to other grain. Wrong! GMO grain is hazardous to your health. Wrong!

Authentic information is needed on the aforementioned topics and on many more. Ask a question about grains and seek an authentic answer via the hypertext features or the conventional index of this encyclopedia. The assurance of authenticity of this encyclopedia is that world authorities have been sought to write every chapter, and subsequently, all articles have been peer-reviewed. None of those involved have any commercial interest in the topic about which they have written. Those assurances cannot be made for the authors of many popular books, magazine articles, or websites.

What Do Our Bodies Need and How Much? Let’s get to the facts of our nutrition. Our bodies are composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), calcium (Ca), phosphorus (P), and the wide range of other chemical elements illustrated in Figure 8. These then are the elements that are essential in our diet. Their distribution varies across the various foods we eat, as illustrated for breakfast time in Figure 9. The importance of the grain-based foods is evident as a source of an important combination of these elements. In addition to the trace elements, there are the compounds that we cannot make ourselves, including vitamins, essential amino acids (forming proteins), and essential fatty acids. This information is thus the starting point for good nutrition. Beyond these essential components is the matter of how


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Finally, there is the important factor of how much food we should consume. While an excess of food consumption is a critical health factor in many countries, elsewhere, hunger is still present. How can this contrast exist when grain production is so great?

Correcting Misinformation Overlaying the elementary recommendations coming from Figures 8 and 9, there are many, many points of discussion, various arguments, and gross issues of misinformation about our nutrition. The points listed in the preceding text are covered in the succeeding text.

Grains, Fats, and Weight Loss

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The fat you eat goes straight to your hips. Wrong! Eat fat-free products and you won’t get fat. Wrong! Bread makes you fat. Wrong! Food additives are all badditives! Wrong! Trans fats, produced in fats from oilseeds, are bad for you. Maybe! New types of oilseeds have fats that are nutritionally extra beneficial. True!

The Fat We Eat: Where Does It Go?

Figure 7 (a) This is flax. It is wild flax growing in New Zealand, a form of lily (Phormium tenax and Phormium colensoi). It is used by the Maoris to make fabrics. (b) This is flax. It is seed from cultivated flax (Linum usitatissimum). This flax or linseed is valuable for its oil content. In addition, the leaves are used to produce linen. The genus name was adapted for the floor covering linoleum (informally abbreviated to lino), which is made from solidified linseed oil (linoxyn). Flax seed is reputed to assist in lowering serum cholesterol levels.

much of them and in what proportions. This topic has been addressed in many countries by the provision of nutritional guidelines, such as those in Figures 10 and 11. They emphasize the quantitative importance of the grain-based foods in our diets, either as the base of the pyramid or as the largest sector of the dinner plate. In fact, the major cereal grains (wheat, maize, rice, barley, sorghum, oats, rye, and millet) provide about half the protein needs of mankind and over half of our food energy consumption. Additional contributions are made by the noncereal grains, including soy, canola, sunflower, and legumes. Worldwide, annual grain production exceeds 2.5 billion tonnes. This equates to about 1 kg of grain person per day for the whole world’s population! Why is there hunger anywhere?

All the food we eat is broken down to simpler components in our stomach and intestine before it is absorbed. Starch is hydrolyzed and absorbed as glucose. Fats are absorbed as the fatty acids. These simpler compounds are metabolized to acetyl coenzyme A, which in turn is digested via the Krebs cycle (Figure 12) to carbon dioxide and compounds that store the resulting energy. Subsequently, these metabolites provide energy to our muscles and replace almost all of the material in our bodies in regular turnover activities. Some excess will be laid down as fat deposits (maybe in the hips), but these fat deposits come indirectly from any of the components in our diet, not only from fats. Thus, eating fat-free foods does not necessarily relate to weight loss or gain any more than any other food source (see article Food Grains and the Consumer: Grains and Health: Misinformation and Misconceptions).

Bread as a Food Bread provides good proportions of protein, starch, fiber, and fat. But watch what goes onto the bread as a spread or as sandwich filling! Flour and ground grain are obviously the main ingredients in bread and baked goods generally. In addition, there are various ingredients (some sugar, salt, and fat, plus rising agents such as yeast and baking powder), including some ingredients that may be classed as ‘additives.’ The added ingredients have the functions of enhancing the quality and nutritional value of the baked foods. But they certainly cannot be labeled as

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OTHERS

ABUNDANT ELEMENTS 1.5% PHOSPHORUS

RARE SULFUR

1.0%

POTASSIUM SODIUM CHLORINE

CALCIUM

MAGNESIUM

1.5%

VERY RARE IRON FLUORINE SILICON

NITROGEN

3.0%

ZINC STRONTIUM RUBIDIUM LEAD

HYDROGEN MANGANESE

10%

COPPER ULTRA RARE ALUMINUM CADMIUM

CARBON

TIN

18%

BARIUM MERCURY SELENIUM IODINE

OXYGEN

MOLYBDENUM

65%

NICKEL BORON CHROMIUM ARSENIC COBALT VANADIUM

= MINERALS

Figure 8 The proportions of the chemical elements that make up our bodies. Reproduced from Bunpei Y (2012) Wonderful Life with the Elements. San Francisco, CA: No Starch Press.

badditives. All such ingredients must be approved by the respective government agencies (see articles Food Grains and the Consumer: Fortification of Grain-Based Foods; WheatBased Foods: Breads; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Flatbreads of the World; Sour Dough Technology).

Different Types of Fats The various species of oilseeds provide edible oils for many of our food sources. An example is margarine. In its processing, some trans fats may be produced; being unnatural, trans fats are suspect and thus discouraged. Polyunsaturated fatty acids in our diet are considered superior to fully saturated fats, which come mainly from animal sources. Grains are major sources of polyunsaturated fatty acids, such as oleic acid, linoleic acid, and linolenic acid. Some of these are essential in our diet. Especially desirable in our diet are the long-chain omega-3 oils (eicosapentaenoic acid and docosahexaenoic acid), mainly

sourced from fish; they are now becoming available in grains via new genotypes of oilseeds such as canola (Figure 13) (see articles Breeding of Grains: Canola/Rapeseed: Genetics and Breeding; Fats: Healthy Fats and Oils; Lipid Chemistry; The Oilseeds: Canola: Overview).

Celiac Disease: Going Gluten-Free or Not

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Only children get celiac disease and they can grow out of it anyway. No and no! A gluten-free diet will make you feel better. Wrong or not necessarily. A gluten-free diet is damaging to your health. Wrong! A gluten-free diet will cause you to miss essential nutrients. Maybe. A gluten-free diet means that I cannot eat buckwheat. Wrong! At least we know that coffee and milk are gluten-free. Not necessarily.

SALAD

BREAD

K

P Na

K

Fe

YOGURT

Zn

Mg

Mn

Ca

Mo

K

Mg

P

I

Co

Na

Mg

Cu

Zn

P

Fe

CI

FRUIT YOGURT

Ca

FRUITS

Ca

K Mn P

BUTTER

BACON AND EGGS BACON

P

Cl

Mg

Na

K

S

BLACK PEPPER

Cr

K

Ca

Mg

Na

K

Co

P

Se

Cu

Ca

Fe

K

Na

P

Zn

Cu EGGS

Se

Fe

Ca

P

S

Zn

Co

K

Cr

COFFEE

K

EUROPEAN AND AMERICAN BREAKFAST

Figure 9 Sources of the chemical elements in breakfast. The elements carbon, oxygen, hydrogen, and nitrogen are not included because they are in all these foods. Reproduced from Bunpei Y (2012) Wonderful Life with the Elements. San Francisco, CA: No Starch Press.

Fats, Oils & Sweets USE SPARINGLY

KEY Fat (naturally occurring and added) Sugars (added) These symbols show fats and added sugars in foods.

Milk, Yogurt & Cheese Group 2-3 SERVINGS

Vegetable Group 3-5 SERVINGS

Meat, Poultry, Fish, Dry Beans, Eggs & Nuts Group 2-3 SERVINGS

Fruit Group 2-4 SERVINGS

Bread, Cereal, Rice & Pasta Group 6-11 SERVINGS

Figure 10 Nutritional guide pyramid provided by the US Department of Agriculture.

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Why the Gluten-Free Diet? People who are diagnosed with celiac disease must adhere to a gluten-free diet. Celiac disease is a disease affecting all ages; the only treatment, a gluten-free diet, is a lifelong commitment. There are other conditions, less well characterized, for which benefit has been obtained by the omission of gluten from the diet. In these cases, perhaps, a gluten-free diet will make you

Figure 11 Nutritional guidelines as a dinner plate provided by the Australian government.

feel better. However, beyond these cases, gluten-free diet has become a dietary fad with many adherents. The inferior quality of much of the gluten-free bread available is a testament to the value of gluten in bread making. Nevertheless, there are many substitutes for the function of gluten in the production of gluten-free foods (Figure 14). Strict adherence to a gluten-free is difficult given the use of wheat, rye, triticale, and barley in many processed foods. In the process of avoiding gluten, it may be possible that some normal nutrient sources are also avoided with the consequent risk of missing out on some essential nutrients. But overall, it is unlikely that eating gluten-free diets will be damaging to your health (see articles Appendix 3: Grains, Foods, and Ingredients Suiting

Figure 13 Canola in flower in Scotland.

sugars, fats

Acetyl-CoA

oxaloacetate

more oxidized

malate

fumarate

citrate

more reduced [cis-aconitate]

isocitrate

succinate

[oxalosuccinate]

succinyl-coA

α–ketoglutarate

Figure 12 The Krebs cycle via which fats and sugars are broken down to CO2 releasing energy that is stored in compounds such as adenosine triphosphate.


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In practice, these imbalances are a problem only for some populations where there is scarce supply of complementary food sources and also in the case of animal feeds. In contrast to the cereal grains, the oilseed and legume grains more than compensate for the cereals with respect to these essential amino acids.

Spinach?

Figure 14 The gluten-free symbol used to indicate foods with <20 ppm of gluten protein from wheat, rye, triticale, and barley. Buckwheat, however, is a misnomer; it is unrelated to wheat and it is satisfactory for people who must have a gluten-free diet (see article The Legumes and Pseudocereals: Buckwheat: Overview).

Gluten-Free Diets for Celiac Disease; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Cereal Allergens; The Gluten-Free Diet, the Appendix on eating gluten-free). Even milk and coffee may not be gluten-free. Various substitutes for dairy milk involve the use of grains. The most obvious is soy milk, which is intrinsically gluten-free as the soya bean is unrelated to wheat. In addition, rice, oats, and other cereals have been used to make milk substitutes, having the dietary advantage of being lactose-free. Rice milk is glutenfree. Oats is a satisfactory grain for most people with celiac disease, but intake of this borderline cereal should be limited; the equivalent of ‘less than one cup per day’ is recommended in this encyclopedia’s appendix (see articles Appendix 3: Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease) on gluten-free diets for celiac disease. There are various roasted-grain beverages marketed as a caffeine-free alternatives to coffee. These coffee substitutes may also be known as grain coffee or ersatz coffee. During World War II, roasted wheat and barley were used as a basis for coffee. Commercial products provide a powder form to be reconstituted with hot water, for example, Nestle´ Caro.

In his comic strip, Popeye’s superhuman strength was attributed to the iron of his spinach diet, consumed by the canful. There is a statue of Popeye in Crystal City, Texas, commemorating his contribution to increasing the consumption of spinach by 33% at about the time he was invented. In the meat-scarce years of World War II, this was an encouraging propaganda, but it was fraudulent. (According to Mould RF (1984) Mould’s Medical Anecdotes. Bristopl, UK: Adam Hilger Ltd, p. 33.) The original researchers displaced the decimal point, giving a tenfold overestimate of the iron content for spinach. In fact, spinach has about 30 mg of iron per kilogram. The population would have done better to concentrate on a grain-based diet, such as wheat germ with an iron content of about 100 mg kg1 (see articles Appendix 1: Nutrient-Composition Tables for Grains and for Grain-Based Products; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products, the Appendix of Grain Composition).

In Summary Given that grains comprise such a major part of our diet, it would be good to be able to assert that no food grains are poisonous. However, that is not completely true, because there is the very unusual exception of the Calabar bean; see Figure 15. With that possible exception, it is certainly true that the wide family of food grains is responsible directly or indirectly for most of the food we eat. Given that current world production for all grains equals about a kilogram of grain per person per day, how can the world’s nations work toward the elimination of malnutrition?

Exercises for Revision

Grains and General Nutrition

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There are dietary imbalances in the cereal grains. Partly true! Spinach is the best source of iron in our diet, because we grew up with Popeye the Sailor Man who ate up all his spinach. Wrong!

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Dietary Imbalances? The proteins of the major cereal grains can be criticized for having a balance of essential amino acids that does not fully conform to our dietary requirements. That is so. On the other hand, the cereal grains provide an excellent balance of proteins, carbohydrates, and fats. Some cereals are partly deficient in some of the essential amino acids, particularly lysine, methionine, isoleucine, and tryptophan.

• •

How is it possible to adopt a critical attitude to assessing nutritional information about grains presented in the media? What procedures should be followed to seek and research authentic information? Select topics, covered in this article, that are relevant to you personally. Describe what benefit (or otherwise) that you have obtained from information provided in this article and from relevant articles in the Encyclopedia of Food Grains. Describe how grain-based foods provide the major categories of nutrients needed in our nutrition. In which cases might certain grain products be nutritionally deficient? Describe the categories of people who really need glutenfree foods. Who else can be expected to benefit from glutenfree foods?

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Exercises for Readers to Explore the Topic Further

•

•

• •

Select a few of the topics presented in this article; for these, contrast some popular misconceptions with the authentic concepts presented in the cross-referenced articles in the encyclopedia and in other reliable sources, including primary scientific research articles. Investigate some less well-known grains (e.g., chia, guar bean, quinoa, freekeh, and macha wheat) and compare their potential benefits (in production, utilization, and nutrition) with those of the more popular species (e.g., wheat, rice, maize, and soy). Investigate the routes of the major food nutrients (e.g., proteins, carbohydrates, fats, and vitamins) in human digestion. How do these compounds differ in the ways our bodies use them? Investigate the world production of GMO grains. What differences are there in the regions of their production, processing, and consumption?

Further Reading Harlan JR (1992) Crops and Man. Madison, WI: American Society of Agronomy. Mangelsdorf PC (1966) Genetic potentials for increasing yields of food crops and animals. Proceedings of the National Academy of Sciences 56: 370–375. Stoskopf NC (1985) Cereal Grain Crops. Reston, VA: Reston Publishing Company.

Figure 15 The Calabar bean is poisonous because it contains physostigmine, a reversible cholinesterase inhibitor alkaloid. It was the likely cause of death for a Nigerian boy in London; the death has been attributed to Nigerian witchcraft.

Course Structures: Based on EFG Articles H Corke, The University of Hong Kong, Hong Kong, Pokfulam, China; Hubei University of Technology, Wuhan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• •

Suggested guidelines are presented for the use of the Encyclopedia of Food Grains as a resource for teaching undergraduate courses in food, nutrition, and agriculture. The Encyclopedia of Food Grains is a good starting source for authoritative material for students preparing for further indepth research on a topic, essays, presentations, and other project work.

Learning Objectives

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To view Encyclopedia of Food Grains as a resource for undergraduate and graduate coursework. To understand how Encyclopedia of Food Grains chapters can fit additional diverse teaching and learning needs, such as for student research project-based work and for industryfocussed training.

Introduction One of the special features of this new Encyclopedia of Food Grains is the effort made to maximize its usefulness as a teaching resource, particularly at the undergraduate level but also for graduate-level training and industry-specific technology courses. Education in hands-on technology-based fields such as food science and nutrition is not all about providing suitable material for the instructor to use in preparing lectures or for the student to read in preparation for examinations. Modern education is less concerned about the acquisition of specific knowledge and more about the process of learning and inquiry, such that the student will be prepared for lifelong learning and innovation. The knowledge content of a subject – for example, the nutritional potential of a grain – may change, but a well-prepared student will always be able to seek out new information and new ways to integrate and use the information, if they have a sound understanding of basic concepts.

A Core Technology Course: Cereal Science/Grain Science/Grain Processing

students in big city Hong Kong are surprisingly ignorant about the basics of cereal and other grain production and usage, even though they live facing the giant agricultural expanses of mainland China. Many will be unclear on the basic formulation of baked bread (guessing rice instead of wheat), and most will not know about yeast or other leavening agents, why their favorite rice has the texture it does, or why bioethanol is not going to replace petroleum-based fuels. In addition, most students will not become professional food technologists and will hence not be interested in an engineering unit operations approach to cereal processing. I use the theme ‘Food sufficiency and the global future’ to try to convince the students that food grains are at the heart of human economic life, from bread and rice to sweeteners, meat (via animal feeding), soy proteins, and many more. The emphasis in this course is on the interactions among technology and markets in producing, processing, and distributing grain products. The basic principles are interesting for such students as they come to realize at first how little they know about the products they eat every day – rice, bread, steamed bread, noodles, etc. I tell them that I am worried that after taking a course like this, their relatives (usually a know-it-all uncle) may ask them something like “So you learned about grains at university, are instant noodles as bad as everyone says? Everybody listen now! The expert is going to speak.” The student needs a core of factual knowledge to be able to answer questions like that. Another major part of the course concerns the global-scale (with an emphasis on Asia) patterns of economic growth and land utilization that determine the production, import, and export of food. The student should be able to think about issues such as “If oil costs $40 a barrel, or $200 a barrel, who will eat and who will starve?” Can agriculture (bioethanol and biodiesel) provide meaningful contributions to fuel production? Where will the grains for meat production for China come from? These types of question are addressed on a regular basis in the media, at least in the business context. For students who will go on to become bankers, or personal investors, or just consumers, the ability to read such media reports with a higher level of insight can prove very useful. An essential part of the course is the requirement for a hands-on lab-based group project. The theme will vary from year to year, but a typical instruction would be

Global grain production and consumption. International grain trade. Wheat: flour milling, dough rheology, the baking process and baking quality, quality of Asian products including steamed bread and noodles, gluten. Rice: nutritional quality and consumer preferences. Maize: products of wet-milling, animal feed development. Biofuels.

Conduct a laboratory investigation into any aspect of grain quality measurement or the effect of ingredients on a process. The preferred focus this year is WHEAT QUALITY – BAKING or STEAMED BREAD or NOODLES – NUTRITIONAL IMPROVEMENT. For example, the effect of protein or fiber or other additive on quality as measured by objective means (e.g., color, texture) and by sensory evaluation. Some attempt at OPTIMIZATION and some attempt at SENSORY TESTING should be made. Multiple small-scale baking machines or noodle machines can be used to design an experimental with multiple treatment comparisons.

Having taught this course for 20 years, I can explain in more depth the underlying concepts and ideas. In my experience,

Clearly, the students can use a resource such as Encyclopedia of Food Grains to determine how to make their product of

I teach an upper-level undergraduate course at the University of Hong Kong called Grain Production and Utilization, which covers


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THE BASICS | Course Structures: Based on EFG Articles

interest, to understand the likely effect of varying formulations, and to seek out interesting nutritional problems – and feasible additives – to make an interesting project. The use of small-scale processing equipment has the advantage of allowing students to make multiple samples of a product – bread, steamed bread, or noodles – and with the repetition, they can remember better the basics and develop the ‘intuition’ to make intelligent adjustments to the process. By observing the work of their fellow groups in the class, and by listening to the final project presentations of all groups (in a formal half-day final symposium), they become well acquainted with a diversity of topics. Minimum expectations at the end of such a course would be the ability to discuss freely, with good technical knowledge and comparative insight, such issues as the following:

• • • • • • • • • •

What are the differences among rice, wheat, maize, and barley? What climatic factors influence production of the major cereal grains? What are the major food uses for each? How many fermented and distilled products are made from grains? To what extent are grains used for industrial products? What limits substitution of one for the other? What are the roles of cereal starch, oil, and protein? What is the nutritional contribution of cereals to the human diet? How does meat production depend critically on grain production? Who will feed China?

Suitable Encyclopedia of Food Grains coverage that would support the teaching elements of this course could include the following:

• • • • •

• • •

Any overview articles such as those focussing on wheat, maize, rice, and soy. Material on grain production and consumption at the global and regional levels. For selected health topics, individual topics such as Functional Foods: Dietary Fiber, Prebiotics, Probiotics, and Synbiotics. Elements of starch structure and functionality and analysis of quality would help in later study of starch quality-based products such as noodles. Protein chemistry of cereal grains is central to any study of cereal science. For processing wheat, an overview on wheat could be supplemented with selected topics according to the instructor’s and student’s interest, such as, on breads and on noodles. Understanding would be strengthened by concept material such as on sensory testing and noodle quality. Similarly for rice, basic ideas on processing could be supported according to student need along, for example, more in-depth genetic material or perhaps additional material on eating quality or on the diverse uses of rice. For maize, it is important for students to understand at least wet-milling uses and to have a general view on animal feed. Traditionally, soy bean has not been considered part of ‘grain’ in English language materials emphasizing cereal grains. However, soy bean is classified with grain in Chinese, and it is key agricultural product for worldwide trade, animal feed production, and processing into food ingredients. A student must know about soy processing, and about the use of soy concentrates and isolates.

Kansas State University has a graduate-level course Cereal Science, with the simple course description ‘The characteristics of

cereals, legumes, their components, and their processing to foods.’ Clearly, the subject area coverage overlaps considerably with my course, described in detail earlier, and it would be up to the individual instructor for any such course to set out the precise learning objectives and to select and recommend particular sections of Encyclopedia of Food Grains that would be most helpful for the student. At graduate level, even in-depth study of particular areas of emphasis, such as genetics and breeding for quality, or international uses of grains, or fractionation of grain, or health uses of grains, could easily be supported by Encyclopedia of Food Grains.

Science Requirement or Reading-Intensive Introductory Courses: Feeding the World Most undergraduate degrees have a requirement for crossdisciplinary knowledge, which can be developed by, for example, requiring nonscience students to take science-based courses (Rocks for Jocks being the famous parody of an easy geology course designed for athletes). Another typical requirement is for a first year seminar-style course that imparts a university-level way of thinking, of using sources, and of intensive research and reporting. In many cases, this may be the student’s first experience of small-group discussion and of academic standards for writing and citation. In any case, such courses should be accessible to students with little science background yet challenging for those students who do have strong science training. Food and nutrition provide in many ways ideal material for such courses. The material is intrinsically interesting and accessible to students, and valuable insights can be added from almost any perspective, from chemistry to economics, history, or anthropology. I run a freshman-level course as part of the breadth requirement for our degree programs called Feeding the World. In a sense, this is a ‘world agriculture’ course, where students learn about the key inputs in agriculture (e.g., energy, water, chemicals, and knowledge) and examine the scale of world production and its sustainability in face of constraints such as excessive waste. The course description reads Continuing human population increases, competition for water supplies, and concern about energy prices have led to profound pessimism about long-term food supplies. Already a billion people go hungry every day. This course will offer an in-depth look at key issues in global food sufficiency, food production, food distribution, prospects and constraints. It is accessible to students from all fields of study and academic backgrounds. You will develop an integrated technical, economic and political understanding of the global food supply crisis. You will be equipped to understand and appreciate media reports related to this issue in your lives as informed and influential citizens. We consider the technological, political, economic and ethical dimensions of the global food supply enterprise. The capacity of modern agriculture to produce food, and the capacity of the political system to distribute food globally will be examined. The idea is to give an academically rigorous course that will cross disciplinary boundaries and help develop your analytical skills and general understanding of an important topic. The course is open to students of all backgrounds, and hopefully this diversity can enhance the classroom environment. The level of science required is quite low, and none of the assessments (for example class test) will particularly favor students with greater science background.

The week-by-week topic coverage includes Global Production, Focus on China, The Green Revolution, Energy, Water, Chemical Inputs, Genetic Modification, Biofuels, Waste, and Sustainability. Clearly, these topics can be aided

THE BASICS | Course Structures: Based on EFG Articles by reference to selected chapters from Encyclopedia of Food Grains. However, a major part of the course is the student project, for which typical guidelines might be Identify an important topic within the general theme of “Who Will Feed Africa?” [other themes could be Who Will Feed China?, or Who Can Produce Rice?, or Can Chinese Money Feed the World?]. The topic should be one that can be investigated using statistical data (such as production, import and export data for crops, livestock, or chemicals; and/or data on human health and nutrition indicators). Collect and analyze the data (preferably drawing as far as possible on FAOStat and OECD.Stat databases). Further research the topic using any other appropriate sources of information and prepare a written report in Powerpoint form. Be prepared to lead a 20 min presentation

The student is then guided to pick a very narrow and specific topic for in-depth research, for example, the potential for Chinese investment in rice production in Mozambique. In order to make any sense of this, they need to develop a base of agronomic knowledge, a sense of how transferable the breeding or agronomic technologies may be, and an understanding of rice import/export balances, quality requirements, and utilization in different regions. The typical Internet search may provide a lot of fragmented and often technically superficial information. However, Internet sources for up-to-date information, and articles from magazines such as the Economist on the investment climate for agriculture, seem to fit well with the solid agricultural, production, and processing information provided by Encyclopedia of Food Grains.

Table 1 Core courses for the food science and industry major, Kansas State University FDSCI 101 – Foundations in Food Science & Industry Credits: (1) GENAG 200 – Topics in Agriculture (0–3) College Careers (0) FDSCI 302 – Introduction to Food Science (3) FDSCI 305 – Fundamentals of Food Processing (3) FDSCI 500 – Food Science Seminar (1) FDSCI 501 – Food Chemistry (3) FDSCI 600 – Food Microbiology (2) FDSCI 601 – Food Microbiology Lab (2) FDSCI 690 – Principles of HACCP (2) FDSCI 727 – Chemical Methods of Food Analysis (2) FDSCI 728 – Physical Methods of Food Analysis (2) GRSC 540 – Engineering Applications to Grain/Food Products (3) GRSC 541 – Engineering Applications to Grain/Food Products Laboratory (1) Select one ASI 318 – Fundamentals of Nutrition (3) HN 132 – Basic Nutrition (3) Select one FDSCI 695 – Quality Assurance of Food Products (3) FDSCI 740 – Research and Development of Food Products (4)

•

The Diversity of Courses in a Major I have described just two typical types of undergraduate course, rooted in knowledge of grains and grain products. We can examine the diversity of courses spanning a typical food science major (Table 1), albeit one with a stronger-thanaverage focus on grains. Literally, all of these courses could potentially be drawing on Encyclopedia of Food Grains for course material, whether in agriculture, processing, chemistry, microbiology, analysis, engineering, or nutrition. A similar listing of courses for a major in agriculture/agronomy or nutrition would also reveal substantial overlap of course coverage with material that could be taken from Encyclopedia of Food Grains.

Industry Training Typical training for industry includes 2–3-day short courses on fairly general topics, such as starch quality, Asian foods, breakfast cereals, frozen doughs, and functional foods. These are often aimed at technical or sales staff from related areas moving into work on a new topic for the first time. There are also in-house training courses run by big companies to keep their staff up-to-date with developments in, for example, grain processing for healthy ingredients, quality testing, or new product development. The flexibility and diversity of materials in Encyclopedia of Food Grains provide a good starting point for instructors building course materials for most such training.


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Choose a relevant undergraduate course and prepare a study plan drawing on the resources of Encyclopedia of Food Grains.

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Develop the outline for a course in Food Product Development, and suggest a health-based theme for the students to follow in developing a team-based new product development project. Show how the use of Encyclopedia of Food Grains could help in providing a starting point for project planning.


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Use Encyclopedia of Food Grains to develop teaching materials for your favorite course, and share the materials online with our website!

See also: Barley, Rice and Maize Processing: Maize: Wet Milling; Rice Processing: Beyond the Farm Gate; Carbohydrates: Resistant Starch and Health; Starch: Analysis of Quality; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Food-quality Testing: Noodles: Testing for Quality; The Application of Sensory Science to the Evaluation of Grain-Based Foods; Grains Around the World: Grain Production and Consumption: Overview; Non-food Products from Grains: Cereal Grains as Animal Feed; Oilseed and Legume Processing: Soybean: Processing; Soybean: Soy Concentrates and Isolates; Proteins: The Protein Chemistry of Cereal Grains; The Cereal Grains: Maize: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Oilseeds: Soybean: Overview; Wheat-Based Foods: Breads; Cereals: Overview of Uses: Accent on Wheat Grain; Noodles: Asian Wheat Flour Noodles.

Relevant Websites http://www.grains.k-state.edu/undergraduate-programs/ – Website of the Department of Grain Science and Industry of Kansas State University, with listing and descriptions of all undergraduate courses.

The Grain Crops: An Overview RA Graybosch, USDA-ARS, University of Nebraska Lincoln, Lincoln, NE, USA Published by Elsevier Ltd.

Topic Highlights

• • • • • •

Definition of a grain Botanical classification of grain crops Utilization of grain crops Definition and classification of a pseudocereal Systematic listing of grain crop species and their botanical families Classification of primitive grain crops

Learning Objectives

• • • • •

To understand the definition of ‘grain’ To appreciate the evolutionary diversity of grains and structures utilized as grains To comprehend the difference between common and scientific names and understand the need for precision and the need for scientific names in technical literature To have knowledge of the difference between cereals and pseudocereals To appreciate the diversity of grain crops and their utilization

Introduction Plants considered ‘grain crops’ are those producing small, hard, dry seed or fruit consumed by man or his domesticated animals as a foodstuff or processed for food or industrial purposes. ‘Grain crops,’ as a grouping, is, however, largely artificial. Plants producing useful grains have evolved in a number of plant families, and these families are not always closely related. Botanically speaking, grains themselves are heterogeneous. The term was derived from the Latin granum meaning ‘seed.’ Cereal grains, however, actually are formed of an entire fruit (caryopsis), while those of other grain crops are the dry seeds of various types of fruits including legumes (pulses), achenes (sunflowers and buckwheats), siliques (canola), and capsules (cotton). Grains, therefore, are the result of convergent evolution or the development of similar structures (grains) in diverse organisms. The actual genes involved in the formation of these structures might be different in each family of grain crops.

The Grain Crops Grain crops of significance are listed in Table 1 according to their common English names and the equivalent botanical names (as genus and species). When such lists are formulated, it is valuable to arrange species in a systematic or taxonomic fashion. This has been accomplished in Table 1 by grouping

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included species in orders, families, and, for the two most important families, the Poaceae and the Fabaceae, into tribes. Listed crops may have relatives cultivated locally (see ars-grin. gov http://www.ars-grin.gov for additional information). Common names are the local, regional, or national names for plants. With the multitude of spoken languages in existence, common names for many crop species often are numerous. In scientific literature, common names for plants should be used only when the scientific name is presented at first mention of a plant species. The use of common rather than scientific names can lead to needless confusion. Some plant species are known, even within a single language, by a multitude of common names. For example, the grain crop proso millet (Panicum miliaceum L.) is also known by the English common names common millet, French millet, hog millet, broomcorn, and broomcorn millet. Also, some common names have been applied to totally different species. In the Americas, ‘corn’ refers to Zea mays L., while in Europe, the term has been applied to barley (Hordeum vulgare L.) or to spelt wheat (Triticum aestivum L. subsp. spelta (L.) Thell.). The use of the scientific name would avoid the obvious confusion that might result from use of common names. Due to extensive morphological variation, numerous subspecific names have been assigned to some grain crops and their relatives. Subspecies names are useful as a means of differentiating various forms of cultivated crops, especially when distinct market classes exist for each type. For example, common or bread wheat is classified as T. aestivum subsp. aestivum. Two morphologically distinct forms of T. aestivum L., club wheat (T. aestivum L. subsp. compactum (Host) Mackey) and spelt (T. aestivum L. subsp. spelta (L.) Thell.) are grown and marketed for different end uses. The use of the subspecies names, in such cases, is useful as it differentiates the various cultivated forms. Subspecies names also are useful to differentiate cultivated forms of plant species from wild ones. For example, durum wheat (T. turgidum L. subsp. durum) has several wild, semiwild, and formerly cultivated relatives including T. turgidum subsp. dicoccoides and T. turgidum subsp. dicoccon. In both examples, the use of the subspecies names serves to differentiate the morphologically different forms while retaining an indication of the close genetic relationships between the various types. Such information is useful as an indication of the existence of close relatives of grain crops for use as gene donors in crop improvement programs. It also is useful as an indicator to people with dietary restrictions (e.g., those afflicted with celiac disease) of the true genetic relationship between grain crops. Plants classified as grain crops are found in both classes of the division Anthophyta (Table 1) and include representatives of 10 orders and 11 families. The families with the largest number of members are the Poaceae (Gramineae), also known as the grass or cereal family, and the Fabaceae (Leguminosae), the legume or bean family. These two families


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THE BASICS | The Grain Crops: An Overview Table 1

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The grain crops, their family groupings, and botanical names (genus and species), plus common names

Taxonomic grouping

Genus

Species (accepted namea)

English common names

Class: Liliopsida Order: Cyperales Family: Poaceae (Gramineae) Subfamily: Pooideae Tribe Poeae

Avena

Avena abyssinica Hochst. in Schimper Avena brevis Roth Avena nuda L. Avena sativa L. Avena strigosa Schreb. Phalaris canariensis L. Hordeum vulgare L. Secale cereale L. Secale derzhavinii Tzvelev Triticosecale Wittm. Triticum aestivum L. subsp. aestivum Triticum aestivum L. subsp. compactum (Host) Mackey Triticum aestivum L. subsp. spelta (L.) Thell. Triticum monococcum L. subsp. monococcum Triticum timopheevii (Zhuk.) Zhuk. subsp. timopheevii Triticum turgidum L. subsp. durum (Desf.) Husn. Triticum turgidum L. subsp. carthlicum (Nevski) A. & D. Lo¨ve Triticum turgidum L. subsp. dicoccon (Schrank) Thell. Triticum turgidum L. subsp. polonicum (L.) Thell. Triticum turgidum L. subsp. turanicum (Jakubc.) A. & D. Lo¨ve Triticum turgidum L. subsp. turgidum Achnatherum hymenoides (Roem. & Schult.) Barkworth

Abyssinian oat Short oat Naked oat Oats, common oat Black oat, small oat Canary grass Barley Rye Perennial rye Triticale Common wheat, bread wheat Club wheat

Coix lacryma-jobi L. Zea mays L. Sorghum bicolor (L.) Moench Pennisetum glaucum (L.) R. Br. Panicum miliaceum L.

Urochloa

Panicum hiritcaule J. Presl Panicum sumatrense Roth Setaria italica (L.) P. Beauv. Echinochloa esculenta (A. Braun) H. Scholz Echinochloa frumentacea Link Paspalum scrobiculatum L. Digitaria exilis (Kipp.) Stapf Digitaria iburua Stapf Urochloa deflexa (Schumach.) H. Scholz

Coix, Job’s tears Maize, Indian corn, corn Sorghum Pearl millet Proso millet, common millet, French millet, hog millet, broomcorn millet Sowi millet, sauwi Little millet, blue panic Foxtail millet, Hungarian millet, Italian millet Japanese millet, Japanese barnyard millet Sawa millet, sawa, billion dollar grass Kodo millet Fonio, white fonio, white fonio millet Black fonio Guinea millet, animal fonio

Eleusine Eragrostis

Eleusine coracana (L.) Gaertn. Eragrostis tef (Zuccagni) Trotter

Finger millet, birdsfoot Teff

Oryza

Oryza sativa L. Oryza glaberrima Steud. Zizania palustris L. Zizania aquatica L.

Rice African rice Northern wild rice Wild rice, zizania

Arachis hypogaea L. subsp. hypogaea Arachis hypogaea L. subsp. fastigiata Waldr. Cicer arietinum L.

Virginia peanut Peanut, Spanish or Valencia types Chickpea

Tribe Triticeae

Phalaris Hordeum Secale X Triticosecale Triticum

Tribe Stipeae

Achnatherum

Spelt, farro Small spelt, einkorn, farro Zanduri wheat, Georgian wheat Durum, durum wheat Persian wheat Emmer Polish wheat Khorasan wheat Cone wheat, pollard wheat, rivet wheat Indian ricegrass

Subfamily: Panicoideae

Tribe Andropogoneae Tribe Paniceae

Coix Zea Sorghum Pennisetum Panicum

Setaria Echinochloa Paspalum Digitaria

Subfamily: Chloridoideae Tribe Chlorideae Tribe Eragrosteae Subfamily: Bambusoideae Tribe Oryzeae

Zizania Class: Magnoliopsida Order: Fabales Family: Fabaceae (Leguminosae) Tribe Dalbergieae Arachis Tribe Cicereae

Cicer

(Continued)

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THE BASICS | The Grain Crops: An Overview

Table 1

(Continued)

Taxonomic grouping

Genus

Species (accepted namea)

English common names

Tribe Genisteae

Lupinus

Tribe Indigofereae

Cyamopsis

Yellow lupin Blue lupin White lupin Guar

Tribe Phaseoleae

Cajanus Canavalia

Lupinus luteus L. Lupinus angustifolius L. Lupinus albus L. Cyamopsis tetragonoloba (L.) Taub. (L.) Taub. in Engl. & Prantl Cajanus cajan (L.) Huth Canavalia ensiformis (L.) DC. Canavalia gladiata (Jacq.) DC. Glycine max (L.) Merr. Lablab purpureus (L.) Sweet Macrotyloma geocarpum (Harms) Marechal & Baudet Mucuna pruriens (L.) DC. Phaseolus acutifolius A. Gray Phaseolus coccineus L. Phaseolus lunatus L. Phaseolus vulgaris L.

Glycine Lablab Macrotyloma Mucuna Phaseolus

Psophocarpus tetragonolobus (Stickm.) DC. Vigna aconitifolia (Jacq.) Marechal Vigna angularis (Willd.) Ohwi & Ohashi Vigna radiata (L.) R. Wilczek Vigna mungo (L.) Hepper Vigna subterranea (L.) Verdc. Vigna umbellata (Thumb.) Ohwi & Ohashi Vigna unguiculata (L.) Walp. Lathyrus sativus L. Lens culinaris Medik. Pisum abyssinicum A. Braun Pisum sativum L. subsp. sativum

Velvet bean Tepary bean Runner bean, scarlet runner bean Butter bean, lima bean Dry edible beans, kidney bean, navy bean, wax bean, green bean, field bean, etc. Winged bean Moth bean Adzuki bean Mung bean Black gram Bambara groundnut Rice bean Black-eyed pea, cowpea Chickling pea, chickling vetch Lentil Abyssinian pea Pea, field pea, sugar pea

Carthamus Guizotia

Pisum sativum L. subsp. asiaticum Govor. Pisum sativum L. subsp. transcaucasicum Govor. Vicia ervilia (L.) Willd. Vicia faba L. Amaranthus hypochondriacus L. Amaranthus caudatus L. Amaranthus cruentus L. Chenopodium quinoa Willd. Chenopodium pallidicaule Aellen Carthamus tinctorius L. Guizotia abyssinica (L.f.) Cass.

Asiatic pea Caucasus Mountain pea Bitter vetch Broad bean; fava, fava bean Grain amaranth; prince’s feather Amaranth, Inca wheat Purple amaranth, red amaranth, amaranth Quinoa Canihua Safflower Niger thistle, niger

Helianthus Salvia Ricinus

Helianthus annuus L. Salvia potus Epling Ricinus communis L.

Sunflower Chia Castor bean

Linum

Linum usitatissimum L.

Linseed, flax, linola

Sesamum

Sesamum indicum L.

Sesame

Fagopyrum

Fagopyrum esculentum Moench

Buckwheat, Japanese buckwheat

Fagopyrum tataricum (L.) Gaertn. Brassica napus L. Brassica nigra (L.) Koch Brassica juncea (L.) Czern Crambe hispanica L. subsp. abyssinica (Hochst. ex R. E. Fr.) Prina

Tartary buckwheat Canola, rape, oilseed rape Black mustard Brown mustard, sarson Crambe

Gossypium arboreum L. Gossypium barbadense L. Gossypium herbaceum L. Gossypium hirsutum L.

Tree cotton American Pima cotton, Sea Island cotton Arabian, Levant or Maltese cotton American cotton, upland cotton

Psophocarpus Vigna

Tribe Fabeae

Lathyrus Lens Pisum

Vicia Order: Caryophyllales Family: Amaranthaceae Family: Chenopodiaceae Family: Chenopodiaceae Order: Asterales Family: Compositae (Asteraceae) Order: Lamiales Order: Euphorbiales Euphorbiaceae Order: Linales Family: Linaceae Order: Scrophulariales Family: Pedaliaceae Order: Polygonales Family: Polygonaceae Order: Capparales Family: Brassicaceae (Cruciferae)

Order: Malvales Family: Malvaceae

a

Pigeon pea Jack bean, horse bean Sword bean Soybean, soya Hyacinth bean Kersting’s groundnut

Amaranthus

Chenopodium

Brassica

Gossypium

From USDA-ARS grin taxonomy for plants (http://www.ars-grin.gov/cgi-bin/npgs/html/index.pl?language¼en).

THE BASICS | The Grain Crops: An Overview contain over about 70% of the species considered grain crops. Five species alone, including four grasses, wheat (T. aestivum and T. turgidum subsp. durum), maize (Z. mays L.), rice (Oryza sativa L.), and barley (H. vulgare L.), and the legume soybean (Glycine max (L.) Merr.) also provide over 70% of the world’s metric tonnage of food from annual plants.

The Grasses The grass family (Poaceae) contains the largest and, in terms of annual production, most important grain crops, the cereals. The Poaceae is one of the largest plant families, commonly divided into subfamilies, each, in turn, containing one or more tribes. Cereal grains (Table 1) are found in the subfamilies Pooideae, Bambusoideae, Chloridoideae, and Panicoideae, with the Pooideae and Panicoideae containing the largest numbers of grain crop species. Early systems of grass taxonomy relied heavily on morphological features, especially spikelet and inflorescence morphology. However, beginning in the 1950s, information regarding chromosome numbers, embryo structure, leaf anatomy, interspecific hybridizations, and types of photosynthetic systems began to accumulate, and it became clear that the early arrangement of grass genera into subfamilies and tribes was largely artificial. In the 1960s, grass taxonomy was completely revised. Many earlier volumes still in wide use (e.g., Hitchcock and Chase’s ‘Manual of the Grasses of the United States’) reflect the original groupings of grass genera. More recent references (e.g., Watson and Dallwitz’s ‘Grass Genera of the World’ http://delta-intkey.com/grass/), followed herein, should be consulted for proper tribal affiliation of grass genera. Wheat and other members of the tribe Triticeae (subfamily Pooideae) are among the most important grain crops. Common or bread wheat, T. aestivum L. subsp. aestivum, and durum wheat, T. turgidum (L.) subsp. durum (Desf.) Husn., are the two most widely cultivated. Two additional subspecies of T. aestivum, T. aestivum L. subsp. compactum (Host) Mackey (club wheat) and T. aestivum L. subsp. spelta (L.) Thell. (spelt or farro), also are cultivated. Club wheats are used to produce pastry and other low protein flours, and spelt is grown largely as an heirloom crop, often in organic production systems. Some authors consider these to be separate species, but they both differ from typical bread wheat only in some aspects of spike morphology controlled by one or a few genes, and the forms will all freely hybridize, so recognition as separate species is unwarranted. T. monococcum L. subsp. monococcum (small spelt, einkorn, or farro) was once grown as a grain crop in most states bordering the Mediterranean Sea and throughout Europe. T. timopheevii (Zhuk.) Zhuk. (Georgian or zanduri wheat) was cultivated in what is now the nation of Georgia. Both T. monococcum and T. timopheevii have all but disappeared from modern cultivation. Several additional subspecies of T. turgidum have been cultivated in historical times, but either their importance has diminished, or they are cultivated in local, isolated areas as relic crops. These include T. turgidum L. subsp. carthlicum (Nevski) A. & D. Lo¨ve (Persian wheat), T. turgidum L. subsp. dicoccon (Schrank) Thell. (emmer), T. turgidum L. subsp. polonicum (L.) Thell. (Polish wheat), T. turgidum L. subsp. turanicum (Jakubc.) A. & D. Lo¨ve

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(Khorasan wheat), and T. turgidum L. subsp. turgidum (cone, pollard, or rivet wheat). Other important members of the tribe Triticeae include barley (H. vulgare L.) and rye (Secale cereale L.). Triticale (X Triticosecale Wittm.) is a man-made crop, grown primarily not only as forage but also as a grain in some parts of the world. Triticales were developed via hybridizations between common or durum wheats and rye. Octoploid triticales contain all the genes of hexaploid wheat and rye, while hexaploid triticales contain the genes of tetraploid durum wheat and rye. Secale derzhavinii Tzvelev, another man-made crop, has been developed as a perennial grain crop. Its cultivation is limited. The oats, Avena, are more distantly related, being placed along with the wheats in the subfamily Pooideae, but in a different tribe, the Poeae. Common oat, Avena sativa L., is the most commonly cultivated species. Its importance has diminished in historical times with the change from animal-driven to mechanized agriculture, but oats are still an important grain crop for human consumption, especially in the northern hemisphere. Other species of Avena have been grown as grain crops, but they either are no longer cultivated or have been reduced to the status of relic crops. These included A. abyssinica Hochst. in Schimper (Abyssinian oat), A. brevis Roth (short oat), A. nuda L. (naked oat), and A. strigosa Schreb. (black or small oat). Phalaris canariensis L., another member of the tribe Poeae, primarily is grown as a source of feed for caged birds.

Maize, sorghum, and Job’s tears Maize (Z. mays L.) and sorghum (S. bicolor (L.) Moench.) are both members of the subfamily Andropogoneae. Job’s tears (Coix lacryma-jobi L.), rarely cultivated as a grain, but more frequent now as an ornamental crop, also is a member of this tribe. Many morphological types of both maize and sorghum exist; in both cases, however, only a single species and subspecies are recognized.

The millets and teff The millets are a taxonomically confusing group. The term ‘millet’ evidently has been applied to any grass with a small round seed. Thus, the term is used to describe a number of, at times, only distantly related species. Most of the millets are placed in the subfamily Panicoideae, tribe Paniceae. The most important millet in terms of annual production is pearl millet (Pennisetum glaucum (L.) R.Br.), most commonly grown in subSaharan Africa and in India. The remaining millets often are termed ‘minor millets.’ Of these, proso millet (P. miliaceum L.) is the most widespread, grown as a grain crop throughout Asia and into Eastern Europe. In North America, it is largely grown as a feed for caged and domestic birds. Several additional millets are grown, primarily in Asia. The following also are members of the tribe Paniceae: Setaria italica (L.) P. Beauv. (foxtail millet), Echinochloa esculenta (A. Braun) H. Scholz (Japanese millet), E. frumentacea Link. (sawa millet), Paspalum scrobiculatum L. (kodo millet), Digitaria exilis (Kipp.) Stapf (fonio or white fonio), D. iburua Stapf (black fonio), and Urochloa deflexa (Schumach.) H. Scholz (Guinea millet). Eleusine coracana (L.) Gaertn, known as finger millet or birdsfoot, actually is a member of the subfamily Chloridoideae, tribe Chlorideae, indicating that it is more closely related to teff than it is to the rest of the millets. Teff (Eragrostis tef (Zuccagni) Trotter), subfamily Chloridoideae, tribe Eragrosteae, is

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THE BASICS | The Grain Crops: An Overview

cultivated as a grain crop in Ethiopia and as a forage grass elsewhere. It is the only cultivated grain species from a fairly large genus of grasses.

Rice and its relatives Rice (O. sativa L., tribe Oryzeae) is the major food of nearly 50% of the world’s population. Two forms or races of rice are recognized, ‘indica’ types (race indica), grown in the tropics, and ‘japonica’ types (races japonica and javonica), the temperate forms. These types are not recognized as subspecies. African rice (O. glaberrima Steud.) long has been cultivated in Western and Central Africa, but it has largely been replaced by O. sativa. Zizania palustris L., northern wild rice, and Z. aquatica L. also members of the tribe Oryzeae, are cultivated and gathered from wild populations in North America. Oryza and Zizania are the only grain crops assigned to the subfamily Bambusoideae. Indian ricegrass (Achnatherum hymenoides (Roem. & Schult.) Barkworth), formerly was gathered as a grain crop by Native Americans, and there have been some recent attempts to cultivate and market it. Indian ricegrass is so named for its superficial morphological resemblance to rice, but it actually is a member of the subfamily Pooideae.

The Legumes The Fabaceae (legume or bean family) is second only to the Poaceae in terms of economic importance to man. This large family is divided into three subfamilies, the Papilionoideae, Caesalpinioideae, and Mimosoideae. Some authors treat these as separate families. All of the grain legumes are members of the Papilionoideae. Most grain legumes are members of the tribes Phaseoleae and Vicieae, although some also are assigned to the tribes Dalbergieae, Cicereae, Genisteae, and Indigofereae (Table 1). Soybean, or soya (Glycine max L.), is the most important, in terms of annual metric tonnage of production. G. soja Siebold & Zucc., the wild progenitor of soybean, is a close relative, and the two are, at times, treated as one species. Intermediate types exist and formerly were designated G. gracilis Skvortzov, but they now are recognized as representatives of the subspecies G. max subsp. gracilis (Skvortzov) Enken. Edible dry beans are assigned to the species Phaseolus vulgaris L. A large number of morphological variants exist for this species, some being consumed as pulses, others for the edible pods. Common names include dry edible beans, kidney bean, navy bean, wax bean, green bean, and field bean. All are considered members of the same species. Other species of Phaseolus are cultivated, including the tepary bean, P. acutifolius A. Gray, P. coccineus L. (scarlet runner bean), and P. lunatus L. (butter bean or lima bean). Arachis hypogaea L. (peanut) is widely cultivated in both the Old and New Worlds. Two subspecies are grown, A. hypogaea L. subsp. hypogaea (Virginia peanut) and A. hypogaea L. subsp. fastigiata Waldr. (Spanish or Valencia peanut). Other important grain legumes include Vicia faba L. (broad bean or fava), Cajanus cajan (L.) Millsp. (pigeon pea), Cicer arietinum L. (chickpea), Lens culinaris Medik. (lentil), and Pisum sativum L. (field or sweet pea). Several subspecies of P. sativum are cultivated, with P. sativum L. subsp. sativum, the common garden pea, being the predominant form. Other less common forms

include P. sativum L. subsp. asiaticum Govor. (Asiatic pea), cultivated in Asia, and P. sativum L. subsp. transcaucasicum Govor., cultivated in the Caucasus mountain region. Legumes of lesser importance include Cyamopsis tetragonoloba (L.) Taub. (L.) Taub. in Engl. & Prantl (guar), cultivated at times as a grain but now more important as a source of guar gum. Other less common grain legumes are three species of the genus Lupinus, L. luteus L. (yellow lupin), L. angustifolius (blue lupin), and L. albus (white lupin). The lupins also are grown as ornamental plants. Widely cultivated, though of only local importance as grain crops, are two species of the genus Canavalia (jack bean and sword bean), Lablab purpureus (L.) Sweet (hyacinth bean), Lathyrus sativus L. (chickling pea), Macrotyloma geocarpum (Harms) Marechal & Baudet (Kersting’s groundnut), Psophocarpus tetragonolobus (Stickm.) DC. (winged bean), Vicia ervilia (L.) Willd. (bitter vetch), Mucuna pruriens (L.) DC. (velvet bean), and several species of the genus Vigna, V. angularis (Willd.) Ohwi & Ohashi (adzuki bean), V. aconitifolia (Jacq.) Marechal (moth bean), V. radiata (L.) R. Wilczek (mung bean), V. mungo (L.) Hepper (black gram), V. subterranea (L.) Verdc. (Bambara groundnut), V. umbellata (Thunb.) Ohwi & Ohashi (rice bean), and V. unguiculata (L.) Walp. (black-eyed pea or cowpea).

Oilseed Crops and Pseudocereals Several crops of various families produce grains from which edible or industrial oils are processed. The mustard family (Brassicaceae or Cruciferae) contains several oilseed species, most important of which is Brassica napus L. (rapeseed or canola). B. nigra (L.) Koch in Ro¨hling (black mustard) and B. juncea (L.) Czern. (brown mustard) occasionally are cultivated for oil and to produce mustard. Crambe hispanica L. subsp. abyssinica (Hochst. ex R. E. Fr.) Prina (crambe) is another member of the mustard family used as a source of oil for various industrial purposes. One member of the family Pedaliaceae, Sesamum indicum L. (sesame), is cultivated as both a spice and a source of sesame oil. Ricinus communis L. (castor bean), of the family Euphorbiaceae, is the source of castor oil, used in industrial applications. It is also infamous as the source of the toxin ricin, a seed protein. Linseed oil is derived from Linum usitatissimum L., a member of the Linaceae. L. usitatissimum also is the source of flax. Chia (Salvia potus Epling) a member of the mint family (Lamiaceae) is used as a source of edible oil and consumed directly in various ways including a topping for yogurt and as an ingredient for breakfast cereals. Chia seed also is used to produce ‘chia pets.’ The Compositae (Asteraceae), or sunflower family, probably is the world’s largest family, in terms of number of species. However, it contains only three members cultivated as grain crops, Helianthus annuus L. (sunflower), Guizotia abyssinica (L. f.) Cass. (Niger thistle), and Carthamus tinctorius L. (safflower). Sunflower and safflower primarily are grown as oilseed crops, but sunflower also is used as a grain for human and avian consumers. Niger thistle also is grown for birdseed. Cotton species (family Malvaceae, genus Gossypium) independently were domesticated in both the Old and New Worlds. G. herbaceum L. (Arabian or Egyptian cotton) was of Old World origin, while G. hirsutum L. (American upland cotton) and G. barbadense L. (American Pima cotton) and

THE BASICS | The Grain Crops: An Overview G. arboreum L. (tree cotton) were domesticated in the New World. Over 90% of the world’s cotton production now is from G. hirsutum L. While primarily grown as a fiber crop, both oil and protein are processed from cotton seeds. Pseudocereals are nonmembers of the grass family often milled to flour and used to produce flat breads and other products similar to those derived from true cereals. This is another artificial grouping, containing members of several plant families. Two members of the Chenopodiaceae are cultivated, Chenopodium quinoa Willd. (quinoa) and C. pallidicaule Aellen (canihua). The grain amaranths, Amaranthus hypochondriacus L., A. caudatus L., and A. cruentus L., are assigned to the Amaranthaceae. These five species all were components of the ancestral cultivated flora of Mesoamerica and South America. Additional pseudocereals include Fagopyrum esculentum Moench. (buckwheat) and F. tataricum (L.) Gaertn. (Tartary buckwheat), both members of the Polygonaceae. Buckwheats probably were first cultivated in Western China.


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What is the difference between a cereal and a pseudocereal? Explain the difference between a scientific and a common name? When should scientific names be used? What is the point of using names that are difficult to spell and remember? What is the difference between a species and a subspecies? What is a millet? Are all millets derived from the same species? Which are more closely related – wheat and oats or wheat and rice? Why? Why do you suppose the majority of our grain crops derive from only two plant families?


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Has the world’s biodiversity of grain crops been fully explored? Are there under- or nonutilized species that could be produced and consumed for nutritional, environmental, or cultural enrichment? Can pseudocereals be more effectively used in modern food manufacturing? Will their increased use slow or diminish the rate of incidence of celiac disease? Can wild or semiwild relatives of grain crops be more effectively exploited? Can useful genes in these species be accessed without genetic engineering? Could ancient crops no longer cultivated be resurrected, and would more widespread culture and utilization improve nutritional composition of modern diets and lead to less environmentally damaging agricultural systems?

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Breeding of Grains: Barley: Genetics and Breeding; Canola/Rapeseed: Genetics and Breeding; Lentil: Breeding;

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Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Maize: Genetics; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains; Rice: Overview; The Legumes and Pseudocereals: Amaranth: Overview; Beans: Overview; Buckwheat: Overview; Chickpea: Overview; Grain Legumes and Their Dietary Impact: Overview; Lupin: Overview; Pea: Overview; Pseudocereals: Overview; The Oilseeds: Oilseeds: Overview.

Further Reading Belton PS and Taylor JRN (2002) Pseudocereals and Less Common Cereals: Grain Properties and Utilization Potential. Berlin: Springer. Brummitt RK and Powell CE (eds.) (1992) Authors of Plant Names. Kew, UK: Royal Botanical Gardens. Cronquist A (1981) An Integrated System of Classification of Flowering Plants. New York: Columbia University Press. Cronquist A (1988) Evolution and Classification of Flowering Plants. New York: New York Botanical Gardens. Duke JA (1981) Handbook of Legumes of World Economic Importance. New York: Plenum Press. Gould FW (1968) Grass Systematics. New York: McGraw Hill. Hanelt P (ed.) (2001) Mansfeld’s Encyclopedia of Agricultural and Horticultural Crops. Heidelberg: Springer. Harlan JR (1992) Crops and Man, 2nd edn. Madison, WI: American Society of Agronomy. Hitchcock AS (1971) Manual of the Grasses of the United States, 2nd edn. New York: Dover, revised by A. Chase. Lawrence GHM (1951) Taxonomy of Vascular Plants. New York: Macmillan. Mabberley DJ (1997) The Plant-Book. Cambridge: Cambridge University Press. Pohlhill RM and Raven PH (1981) Advances in Legume Systematics. Kew, UK: Royal Botanic Gardens. Smartt J (1990) Grain Legumes. Evolution and Genetic Resources. Cambridge: Cambridge University Press. Vavilov NI (1960) World Resources of Cereals, Leguminous Seed Crops and Flax and Their Utilization in Plant Breeding. Jerusalem: Israel Program for Scientific Translations. Wiersema JH and Blanca L (1999) World Economic Plants: A Standard. Boca Raton, FL: CRC Press.

Relevant Websites http://www.ars-grin.gov – On-line searchable version of “World Economic Plants: A Standard Reference”. This version includes all plant species listed in the reference and maintained in the United States Department Agriculture’s National Plant Germplasm Collection. Searches can be performed on scientific names and plant uses or other attributes of economic importance. Also includes complete lists of common names and synonyms. The grass genera of the world L. Watson and M. J. Dallwitz, http://delta-intkey.com/ grass/ – This website provides a complete taxonomic description of the world’s grass genera, including information on assignment to tribes, descriptions. http://www.iapt-taxon.org/nomen/main.php – International Code of Botanical Nomenclature – accepted rules for naming plant species. http://www.ildis.org/LegumeWeb k – LegumeWeb from the International Legume Data and Information Service World Database of Legumes, a searchable database providing complete information on legume taxonomy, including accepted names, assignment to tribes, references, etc. mansfeld.ipk-gatersleben.de http://mansfeld.ipk-gatersleben.de/pls/htmldb_pgrc/f? p ¼ 185:3:0 – On-line version of “Mansfeld’s Encyclopedia of Agricultural and Horticultural Crops”. Searchable, includes scientific names, synonyms, common names, discussion, and references for what seems to include every plant species ever cultivated by man.

The Grain Chain: The Route from Genes to Grain-Based Products CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The value-addition chain for grain starts with the breeder, who builds suitable genes into a specific variety so that it will provide a good yield of quality grain. Farm management is designed to optimize yield and grain quality, although some aspects of the growth environment may be beyond the grower’s control. After harvest, grain may be tested and segregated according to its suitability for processing. The next stage of processing covers a wide range of possibilities, given the many grain species and the great variety of possible processes. Some examples are given. The emphasis is on the consumer as the ultimate person to determine product quality by deciding what products to buy. Thus, there is feedback up the grain chain according to the quality of the product or intermediate provided by the previous person in the chain.

On the other hand, the whole sequence may occur in one village for a family on subsistence farming, with some grains being cooked and consumed ‘as is’ by the family and other grains being processed in a village-owned mill. In place of the marketing stage of the chain in Figure 1, there may be the interchange of various types of food or labor. Nevertheless, even in this case, there will be the aspect of consumer reaction affecting decisions about what species and type of grain to sow in the subsequent season. A circle format (Figure 2) is an alternative representation of the value-addition sequence because it emphasizes the feedback function, primarily the communication from the consumer back to the breeder, who must produce varieties with quality traits that suit the specific consumer products. But in addition, many other feedback functions are needed:

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Learning Objectives

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To achieve an understanding of all the stages leading to the eventual consumer product, via breeding, grain production, processing, and marketing To gain an appreciation of the need for those involved at each stage to satisfy the requirements of those further down the chain, most importantly the consumer

Introduction When you bite into a delicious pastry, do you consider where its ingredients came from? The main component is wheat flour, which came through the sequence of stages shown in Figure 1. This chain of events relates to the development, production, and processing of all grain species through their utilization. The sequence has been called ‘field to fork’ and ‘paddock to plate’ for grain-based foods, but it applies similarly for industrial products such as adhesives, starch for paper manufacture, animal feeds, and bioethanol as a vehicle fuel. In some cases, the processing ends at the stage of the whole grain, such as rice, couscous, and sweet corn. This grain chain is a value-adding sequence. In the case of the pastry, which may have cost you about US$3, the major component (flour) came from the processing of about US $0.03 worth of grain (based on the per tonne price of wheat). The value addition from the farm gate to the pastry shop or patisserie was a 100-fold. In the case of a pastry bought in some countries, this sequence may occur over long distances involving rail and sea transport from farm production to the sites of processing and retail sale.

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From the grower to the breeder (‘I need disease-resistant, high-yielding varieties’) From the rice-mill operator to the grower (‘I need rice grain that mills well with a minimum of broken grains’) From the maltster to the grower (‘I need barley that germinates uniformly’) From the hummus maker to the grower or grain trader (‘I need good chickpea grain for making my hummus’) From the miller to the grower (‘I need clean grain that gives a high flour yield’) From the baker to the miller (‘I need flour that forms a strong extensible dough that makes good bread’) From the retailer to the food processer (‘I need products that look attractive, that taste good, and that sell well’)

The Grain-Supply Sequence Reflected in This Encyclopedia The arrangement of articles in this four-volume encyclopedia reflects the grain-supply chain, but in reverse. Volume 4 covers grain production and genetics. Volume 3 describes grain-based products and their processing methods. The consumer and nutritional topics are featured prominently in Volume 2, these being issues of special public interest. Volume 1 provides a general overview of grains under the title ‘The World of Grains.’ Issues of grain processing and products were considered to warrant a full volume (3). Volume 4 features most of the reverse grain chain of marketing and grading, transport, agronomy, breeding, and genetics.

Breed: The Production of Improved Varieties Is a Critical Contribution of Grain Science Plant breeding has developed during the past century as the means of producing suitable genotypes, selecting them on the basis of the required attributes, after the use of crossbreeding to expand the genetic diversity available from which to make the


http://dx.doi.org/10.1016/B978-0-12-394437-5.00004-8

THE BASICS | The Grain Chain: The Route from Genes to Grain-Based Products

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Figure 1 The grain-supply chain extends from the breeding of a variety to the product that reaches the consumer.

THE GRAIN CIRCLE The Consumer Breed

Retail

Sow

Process

Store and Transport

Grow Harvest and Segregate

Figure 2 The grain-supply chain can be visualized as a circle of interactions and communications between the many functions.

selections. Over a century ago, entrepreneurial farmers selected good-looking plants to keep as seed in hopes of plant improvement. The late nineteenth century brought the innovation of crossbreeding and selection from the resulting progeny, with the aim of combining the better attributes of each parent into one variety. One of these early breeders was William Farrer, represented in the drawings of Figure 3. Farrer’s vocation as a surveyor in southeastern Australia led him to see that the wheat varieties brought from England were unsuited to the new country, so he set about importing seed from more suitable

countries, corresponding with breeders overseas and crossbreeding. Today, conventional crossbreeding involves the same basic method as a century ago, namely, to take pollen from the anthers of the male parent during anthesis and to dust the pollen onto the stigma of the proposed female parent. The anthers of the female have previously been removed to prevent self-pollination, which is the usual form of reproduction for wheat and its close relatives. By contrast, the crossbreeding of maize involves interfering with its normal reproduction by which pollen, produced from the tassels on top of the stalk, falls onto the silks protruding from the end of the immature cob. The tedious part of breeding is the subsequent task of growing on the progeny and selecting desirable individuals resulting from the cross. When ‘elite lines’ have been selected, they are grown on in field trials at various sites to see how they perform in a range of conditions (Figure 4). After selecting the most promising lines, they must be registered for plant breeders’ rights, depending on the system operating in the specific country, so that royalty payments may be returned to the breeding organization. The breeder’s involvement is primarily limited to introducing desirable genetic traits, but these benefits may subsequently be modified by environmental factors during growth, such as climate and farm management practices. Nevertheless, it has proved possible for breeders to ‘build in’ genetic tolerance to some environmental risk factors, such as disease attack and

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Figure 3 Depiction of a breeder at work in the 1890s when crossbreeding was in its infancy. (a) Cross-pollinating. (b) Examining progeny from a cross. Note the great height of mature wheat plants of that time.

Figure 5 Equipment for sowing seed, together with fertilizer. In this case, it is designed for sowing narrow plots for breeder use. Figure 4 Breeders’ advanced lines, sown in relatively small plots for further evaluation.

tolerance to premature sprouting in the case of a wet harvest. Recent decades have seen the introduction of novel methods of genetic manipulation, permitting breeders to employ a wider range of options for genotype improvement.

Sow: Seed Must Be Clean and Genetically Pure A critical decision for the grain grower is the choice of variety for sowing, plus when to sow and in what situations on the farm (Figure 5). The variety must suit the expected growth

conditions and the risks of disease and of environmental fluctuations. Ideally, the grower attempts to target desired grain qualities that would achieve premium prices upon delivery to the mill or grain elevator. In addition, the grower must ensure that the seed for sowing is free of weed seeds that would stifle the desired crop, as well as causing the harvested grain to be downgraded upon delivery due to the presence of contaminating seeds. The source of seed may be saved-seed from a previous harvest, or it may be obtained from a neighbor. However, growers would ideally obtain pure seed (annually or every few years) from a licensed pure-seed grower. Seed growers

THE BASICS | The Grain Chain: The Route from Genes to Grain-Based Products interact with breeders to obtain authentic seed of specific varieties for growing under controlled conditions to ensure that the resulting grain conforms to the requirements for ‘foundation’ or ‘registered’ seed.

Grow: Farm Management Must Optimize Grain Yield and Quality In addition to decisions relating to seed for sowing, the grain grower has decisions about soil preparation, fertilizer use at sowing and during growth, sowing rate, and the possible use of irrigation and of herbicides and pesticides. The task of maximizing financial returns involves on-farm management of grain quality as well as grain yield, paying attention to the combination of grain volume harvested, and market value upon delivery. Even before harvest, the grower may have negotiated marketing of the crop, based on expectations of yield and quality attributes.

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When grain is delivered to the mill, storage silo, or grain elevator, it must be assessed for its quality and variety. This assessment determines both the price to be paid to the grower and the manner of segregation of the grain delivered. At any delivery site, there may be several different grades or types of grain. It is obviously critical that a new delivery of grain should be combined with grain of similar quality type in a distinct storage cell.

Harvest, Deliver, and Segregate: Grain Production Goes Beyond the Farm Gate Harvest is a busy time, with a sense of urgency to get the grain into storage or delivered before rain comes. A wet harvest brings the risk of the grain starting to sprout in the head, thus being downgraded in price. Furthermore, most regions have an upper limit on grain moisture, so the grain grower must ensure that the grain is fully dried before harvesting the crop. Many large farms have storage facilities (Figure 6) so that the harvested grain can be stored immediately and the grower can then take some time about negotiating a good price for the grain and appropriate conditions of transport. Alternatively, as soon as the grain comes out of the header, the harvested grain is trucked to a storage facility (‘elevator’ or ‘silo’) or directly to a flour mill or feed mill (Figures 7 and 8). Whereas bulk transport and storage are the general modes today in most grain-growing areas, many years ago, grain was packed in bags (Figure 9), which were ‘man-handled’ and stored in stacks. Regional centers for grain delivery and storage are traditionally sited on rail lines because of the efficiency of rail to transport large amounts of bulk grain (Figure 10(a) and 10(b)).

Figure 6 A healthy field of awned wheat. After harvest, much of the grain will be stored on farm in these bins, providing the grower with flexibility to seek the best prices.

Figure 7 A truck full of grain is being sampled from the elevated platform of the testing room, where the sample is evaluated to determine its quality and thus where the load will be tipped.

Figure 8 Grain being tipped from the farmer’s truck for delivery at the country storage facility.

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Storage and Transport: Identity Preservation Is Needed for Grain Type and Quality

Process: Production of the Many Grain-Based Foods and Nonfood Items

Further grain transport may involve delivery, probably by rail, to the export terminal for loading into the hold of a ship (Figure 11). In any case, some grain is likely to be stored onfarm for seed use in the next season and for animal feed. In situations of subsistence farming, the family will be directly dependent on the stored grain for food throughout the coming year. Beyond the initial stage of storage, the value of the segregated grain must be preserved throughout transport and on through further storage so that it still conforms to the original quality type when the grain is delivered for ultimate processing. Throughout these stages, the grain is at risk of deterioration especially due to insect attack. Also, throughout these stages, commencing even before the farm gate, there is the marketing of the grain – at the level of the grain grower, by grain merchants, and internationally often at intergovernmental levels.

It is at the stage of processing that the effectiveness of qualitybased segregation is evident and its cost-effectiveness can be evaluated; for any situation, the advantages of better processing outcomes must justify the significant costs involved in the activities of testing and identity preservation. Due to these commitments, grain-quality assessment is again a priority when the grain arrives at the flour mill, malt house, feed mill, or other forms of processing factory. This type of assessment determines how a specific grain shipment will be stored, utilized, and managed in the sequence of events leading to the product that is offered for final sale to the consumer. This sequence may be short: for example, the milling and boiling of rice grown by a subsistence farmer, with the family commenting on the eating quality. Even in a commercial situation, processing may be minimal involving whole-grain foods such as rice, couscous, sweet corn, and beans (Figure 12). Minimal processing may involve sprouting to provide salad foods (Figure 13). It may involve the stages of flour milling, leading to bread and cake baking for sale in a hot-bread shop (Figure 14). Further processes include the manufacture of breakfast cereals, the use of cooked rice for sushi (Figure 15), the recovery of oils

Figure 9 storage.

Bags of grain, as used for storage and transport prior to bulk

Figure 11 Loading grain into the hold of a ship for international trade.

Figure 10 Grain storage facilities are generally situated beside rail connections to facilitate transport to the mill or export terminal.


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Figure 14 Bread rolls require the further stages of flour milling and baking.

Figure 12 Beans of various types, ready for sale without further processing.

Figure 15 Sushi represents further value addition, compared to boiled rice.

Figure 13 Sprouted beans. One more step of processing than in Figure 12.

and their further processing, the separation of gluten from wheat starch for paper manufacture, and the production of sweeteners. Alternatively, there may be the much longer route of animal feeding to produce meat, milk, cheese, or eggs via grain-based pellets for animals or poultry (Figure 16).

Retail: The Stage When We Are All Involved in Expressing Our Preferences When the great diversity of grain-based products reaches the retail stage, the ultimate in value addition is reached, with only

the extension of restaurant service taking value addition any further. At this stage, the consumer (all of us) casts the votes that determine the future success of the many variations of products – votes that may ultimately determine the future of one baker against another or of one brand of breakfast cereal versus others.

The Consumer The consumer is thus the ultimate arbiter of quality for grainbased products by voting with buying power. The identity of the consumer ranges from the family members of the subsistence farmer to the household expressing preferences for foods from either the local baker or the supermarket. Thence, preferences by the respective bakers for flour quality pass up the feedback loop back to the miller and so on to have repercussions further back up the grain-supply chain (Figures 1 and 2).

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↓

GENOME Genes (DNA) PROTEOME Polypeptides ↓ FUNCTIONAL PROTEINS ↓ GRAIN COMPOSITION ↓ PROCESSING ↓ PRODUCTS Consumer acceptance

↓

↓

TRANSCRIPTOME mRNA of expressed genes ENVIRONMENT Climate, nutrients CO2

Figure 17 The sequence of biochemical events that occur in the grain, leading to the grain-based products that reach the consumer.

Human Figure 16 Feed pellets, made from partly ground mixed grains, are destined for animal feed – a further stage of food production beyond the stages in Figure 1.

This feedback loop from the consumer to others up the chain may be short (a subsistence farming community) or long (involving great distances and long time periods). The latter case relates to the extent of worldwide grain trade as the source of the grain involved. The ultimate feedback is to the grain breeder, for whom a change in breeding direction involves the many years from an initial cross to the selection of an elite line ready for registration and sale to growers. Coming back around the grain circle (clockwise in Figure 2), there is the further lag factor of the many months that grain may be in storage and transport before it is processed. In addition, feedback may involve long distances, such as a flour miller in the Middle East or a legume trader in India reporting grain defects to grain traders or breeders in grain-producing countries such as the Americas, Australia, or Europe. Consumer preferences also relate to their perception of nutritional quality. Government agencies publicize nutritional guidelines that generally recommend the consumption of grain-based foods as a major part of food intake. This emphasis on grains in the diet provides a major boost for the graingrowing and grain-processing industries of the world. More specific recommendations, such as for greater levels of soluble fiber, may well target the breeder as the ultimate source of significant changes in grain nutrition. Consumer feedback may also target the processor with demands relating to the incorporation of specific additives in foods as well as targeting government agencies about legislation and food labeling.

The Biochemical Grain Chain In contrast to the supply-chain concepts of Figures 1 and 2, there is the biochemical concept of Figure 17 that sets out the events in the context of genome, proteome, and grain composition, for the events in the developing grain, and the many changes that occur during processing prior to the product

Arabidopsis Rice

Wheat

Cotton

Barley

Figure 18 Comparative sizes of the genomes of several plant species. Illustration kindly supplied by Dr. Colin Cavanagh, CSIRO, Canberra, Australia.

reaching its ultimate destination – the consumer. The general sequence in Figure 17 is true for all grains with respect to their production and end-use quality. Central to the sequence is the genome – the full DNA complement of genes. The relative sizes of several genomes are depicted in Figure 18. Outstandingly large is the genome of wheat, partly because common (bread) wheat is a hexaploid, having three subgenomes, giving it a complex genotype (the genetic makeup of the plant). The first opportunity to examine the effects of growth conditions, according to the scheme in Figure 17, comes by the analysis of the transcriptome (mRNA) – the transcripts from those genes that are active under the environmental conditions at the specific stage of grain development. This is the first indication of what genes are being expressed in the endosperm and also of how much of each gene product will be produced. The next biological step is the resulting synthesis of the many polypeptides corresponding to the mRNA transcripts – the proteome. The growth, yield, and suitability of grain for processing of a grain are determined by the interaction of its genotype (variety) with the environment (G E). Genes being expressed in the transcriptome (mRNA) are the focus of research attention as candidates for use as markers for specific attributes, thus being candidates for ‘marker-assisted selection’ in breeding. The corresponding polypeptides in the proteome may also serve this purpose if the proteome is used as the target

THE BASICS | The Grain Chain: The Route from Genes to Grain-Based Products for marker selection. In either of these cases, the breeder has the satisfaction of knowing that expressed genes are being targeted, rather than genes in the genome that may not even be expressed. The transcriptome and the proteome also offer the advantage of reflecting the effects of the growth environment. In recent decades, we have learned much more about genotype relationships than about the effects of environmental factors, the latter being more difficult to study. With respect to wheatdough quality, research has concentrated on the genes coding for the polypeptides that cross-link by disulfide bonds to form the polymers of glutenin protein, the critical part of dough. These polypeptides (subunits) are classed as the high- and low-molecular-weight subunits, HMW-GS and LMW-GS, whose many alleles are coded at the Glu-1 and Glu-3 loci, respectively, on the Group-1 chromosomes of wheat. Information about these gluten genes is available for many wheat varieties from around the world. This allele information can be used to predict dough properties as dough strength (Rmax) and extensibility (Ext) (both parameters from the Brabender Extensigraph), based on the alleles for both HMW-GS and LMW-GS, assuming normal grain-filling conditions and average protein content. Although we realize that wheat quality is also governed by some other protein factors, this information is valuable to breeders and further down the grain chain for quality-based segregation at harvest. However, there are still serious gaps in our knowledge surrounding the effects of fluctuations in growth conditions. More important, but more poorly understood, is the manner by which these glutenin polypeptides are disulfide crosslinked into functional glutenin (Figure 17). The glutenin polymers are so large that conventional methods of protein analysis are inadequate. Field-flow fractionation (FFF) has been used to examine the upper size ranges, which are critical to dough strength. FFF has shown, for example, that the doughweakening effects of high temperatures during grain filling are accompanied by a reduction in the proportion of very large glutenin polymers. However, we are yet to form a valid understanding of the factors that determine the formation of disulfide bonds between glutenin subunits and the extent of the ongoing polymerizations. Models have been suggested for the interactions between the HMW-GS and LMW-GS and for polymeric glutenin with gliadin proteins, but we do not understand the G E aspects of this very significant stage of grain-quality determination. We are aware that the formation of disulfide bonds within the gluten complex can continue during storage, especially at temperatures over about 30 C. In addition, disulfide bonds are a target for manipulation during processing (P) – the third factor that determines end-product quality (G E P). Past the farm gate, there is a marketing opportunity that we cannot presently grasp fully – the possibility of segregating grain deliveries based on their suitability for end-product manufacture, considering the effects of both G and E. At this stage, knowledge of variety is of less importance than of quality type, which might be better specified by quantitative analysis of glutenin alleles. Some promise is offered for this purpose by on-the-spot equipment for the analysis of glutenin-subunit

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composition to permit segregation prior to dumping (comingling), after which distinct identity is lost. More specific knowledge of the grain quality of specific storage cells offers valuable market intelligence for use in maximizing return on grain and in providing the processor (next in the grain chain) with grain of the required quality specifications.

Future Prospects The general sequence of grain production and processing in Figures 1 and 2 must continue into the future, but there will be changes within each of the stages. The breeding of new and improved genotypes (varieties) is ongoing, so too are developments in agronomy and farm management. However, these strategies will need to change and develop in view of the ongoing climate challenges. The rising levels of carbon dioxide in the atmosphere constitute an effective ‘carbon fertilizer.’ Field experiments with ambient and elevated carbon dioxide have clearly shown that the carbon fertilizer effect produces greater yields of biomass and of grain. However, the protein content of the grain is lower, thus affecting grain quality and utilization. Grain production will also be affected by predictions of rising temperatures, shifting rainfall patterns, and more frequent stress situations such as heat shock, storms, and violent winds. Furthermore, rising sea levels present the risk that some agricultural regions will become unsuitable for cropping. The grain-production industry worldwide needs to able to adapt to a changing climate while also ensuring that the necessary changes are consistent with sustainable production. In line with these production challenges, markets will require greater uniformity and certainty of grain-quality specifications, although these discerning markets must be prepared to pay premiums in contrast to commodity-level grain. Processors and retailers will meet more customer-based pressure to supply specific nutritional requirements, while large supermarket companies will exert downward pressure on suppliers.


• • • •

What features distinguish the added-value route of one grain species from another? Compare the stages for two or three contrasting grain species. Describe some grain-based products that have shorter and longer chains. What are some critical feedback messages that are indicated by the grain chains in Figures 1 and 2? The shorthand expression ‘G E P’ is used in relation to Figure 17. To what extent does it explain the grain chain?


•

Select some grain-based products and outline the grain chain that has led to the production of each of these. Some examples are – high-fructose syrups used as sweetening agents,

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• • • •

THE BASICS | The Grain Chain: The Route from Genes to Grain-Based Products – margarine from canola or any other oilseed, – cornflakes or another breakfast cereal, – ethanol-based biofuels, – oilseed-based diesel fuel. In your region, identify the main grains that are grown and/ or processed. What forms of quality-based segregation, storage, and transport are used? Investigate the biochemical sequence in Figure 17 for some grain species other than wheat. Protein isolates are produced from several grains. Investigate the production and uses of some, such as wheat gluten, soy-protein isolate, and corn protein (sometimes called corn gluten). Examine some current consumer issues related to grainbased foods. In which of the upstream parts of the grain chain is there the need for more diligent attention to quality?

See also: Barley, Rice and Maize Processing: Rice Processing: Beyond the Farm Gate; Breeding of Grains: Maize: Breeding; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Genomics of Food Grains; Grain Harvest, Storage and Transport: Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Barley: Grading and

Marketing; Wheat: Grading and Segregation; Non-wheat Foods: Maize: Foods from Maize; Rice: Chinese Food Uses; Processing of Grains: Grain Quality Attributes for Cereals Other than Wheat; Evaluation of Wheat-Grain Quality Attributes; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview; The Oilseeds: Oilseeds: Overview; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Abdel-Aal E and Peter Wood P (eds.) (2005) Specialty Grains for Food and Feed. St Paul, MN: AACC International Press. Arendt EK and Zannini E (eds.) (2013) Cereal Grains for the Food and Beverage Industries. Oxford: Woodhead Publishing Ltd. Faridi H and Faubion J (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. Henry RJ and Kettlewell PS (eds.) (1996) Cereal Grain Quality. London: Chapman and Hall. Kent NL and Evers AD (eds.) (1994) Technology of Cereals. An Introduction for Students of Food Science and Agriculture, 4th edn. Oxford: Pergamon Press. Wrigley CW and Batey IL (eds.) (2010) Cereal Grains: Assessing and Managing Quality. Oxford: Woodhead Publishing Ltd.

Taxonomic Classification of Grain Species LA Morrison, Oregon State University, Corvallis, OR, USA CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Taxonomy: A System of Names to Avoid Confusion

•

Common names can often have multiple or misleading associations. If not qualified, pigweed can collectively refer to members of the genus Amaranthus without distinguishing between the weedy and grain amaranth forms. The ‘wheat’ in buckwheat (Fagopyrum esculentum; Figure 1) and Inca wheat (Amaranthus caudatus; Figure 2) creates the false impression of a relationship with wheat (Triticum species; Figure 3), when in fact wheat and these two pseudocereal species are far apart from each other in evolutionary relationships, in biology, and in grain attributes. A more reliable means of communicating is provided by scientific names, which are assigned by a system known as taxonomy. A scientific or taxonomic name consists of a genus and a species name that, when combined as a binomial, provide a unique identifier for the grain in question. This name is universally recognized in all scientific circles and removes the confusion created by common names, as the following example illustrates. Amaranthus caudatus, A. creuntas, and A. hypochondriacus form the group known as grain amaranths, major food staples in the pre-Columbian Americas, which have now regained importance and promise as pseudocereal grains in international agriculture. Their taxonomic names distinguish these grain amaranths from other weedy Amaranthus species variously known as pigweed, amaranth, or water hemp. Although some common names have been accepted into international usage, they can still create problems within a scientific context. For example, in large species groups such as the wheats, scientific names make distinctions where common names cannot. The term wheat does not differentiate between the wild and domesticated species of Triticum nor between the species of Triticum and its sister genus Aegilops, whose members are all wild species. The common name farro can collectively refer to any one of three domesticated wheat species, all hulled (non-free-threshing) – T. monococcum, a diploid wheat that is a minor crop species; T. dicoccum, a primitive tetraploid wheat also known as emmer; and T. spelta (T. aestivum ssp. spelta), a hexaploid wheat known as spelt that is still grown in Europe and Asia and now a specialty wheat in the United States and Canada. Common wheat and bread wheat are equivalent names that can encompass a complex of domesticated hexaploid wheats when they are classified under one species name, Triticum aestivum, thereby including forms that are neither common nor necessarily amenable to bread-making (Figure 3).

• • • • • • • •

Modern taxonomy is a uniform system for assigning scientific names to plant species, thereby aiding communication among scientists. Classification is structured as a hierarchical system that follows a concise set of rules for both wild and domesticated plant species. Species names often convey information about a grain’s function or traits or the activities associated with its use. Grains can be divided into two large groups, each with different evolutionary histories: cereals (grass species) and pseudocereals and pulses (nongrass species categories). Taxonomic groupings reflect evolutionary relationships with interpretations often varying among traditional versus phylogenetic classifications. For domesticated plants, the terms ‘cultivar’ and ‘landrace’ are not interchangeable. Taxonomic classification enables informed decisions for accurately identifying and selecting research material of grain species. Evolutionary relationships are useful for identifying potential allergic cross-reactions to grain species. Using classification to display phylogenetic relationships is at the center of current controversies over the future direction of Linnaean taxonomy.

Learning Objective

•

To achieve understanding of the role of taxonomy as a scientific system for both classifying domesticated grain species and facilitating communication about them among scientists

Introduction The common names of grain species often derive from localized, figurative terms. They can lead to considerable confusion due to variations in region and language. In English, the problem is exacerbated by the adoption of common names from several languages, either as Anglicized words or direct translations. The grain legume Cicer arietinum offers a very good example of multiple common names. In languages of Europe and Asia, it is known as ‘cece’ (Italian), ‘channa dhal’ (Hindi), ‘garbanzo’ (Spanish), ‘graõ-de-bico’ (Portuguese: beaked grain), ‘hummus’ (Arabic), ‘Kichererbse’ (German: ‘giggle peas’), and ‘pois chiche’ (French: chickpea). In English, it is variously known as chickpea, gram, Bengal gram, chana, Egyptian pea, and garbanzo bean. Another problem is the changed usage of a common name from one region to another. In Europe, corn refers to cereal grains generally, whereas in the Americas, it specifically refers to maize (Zea mays).


Taxonomy: A System of Relationships Inherent in taxonomic groupings is an indication of evolutionary relationships. Thus, the taxonomy of grain species has some bearing on shared traits of plant morphology, grain

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THE BASICS | Taxonomic Classification of Grain Species

Figure 1 Buckwheat (Fagopyrum esculentum). Its dried, triangularshaped fruit, a nut, resembles the beechnut produced by beech trees (Fagus spp.). This similarity is the source for the genus name Fagopyrum, which translates to ‘beechwheat.’ It also explains the derivation of the English common name buckwheat. ‘Buck’ is the Anglicized version of the German word for beech, ‘Buche.’ Adapted from Williams JT (ed.) (1995) Cereals and Pseudocereals. London: Chapman and Hall.

composition and function, and many other attributes important to grain science. As a tool for categorizing biological organisms, taxonomy is not an exact science and thus is subject to conceptual disagreements and opposing interpretations. Current debates primarily center on its ability to accurately represent phylogeny – the branching ancestor/descendant relationships that connect all plant species. On one side are molecular systematists, who argue that classifications must reflect evolutionary relationships. On the other side are traditionalists, who counter that the reliable order and structure of taxonomy is more important than an exact representation of modern phylogenetic concepts that are often changing in response to new research evidence. Problematic for phylogenetic classifications are (1) their continuous state of flux based

Figure 2 A mature specimen of Amaranthus caudatus, the most important of the Andean grain amaranths. It is still known by the ancient Incan name ‘kiwicha.’ Seeds (left) are about 1 mm in diameter and have a curved embryo. Reproduced from Vietmeyer ND (ed.) (1989) Lost Crops of the Incas. Washington, DC: National Academy Press, with permission.

on the availability of new genetic evidence supporting revisions of accepted and unresolved groups and (2) their inability to accommodate interspecific hybridization and introgression, two plant speciation mechanisms that violate the monophyletic rule that all descendants in a phylogenetic tree derive from a single common ancestor species. Another key element in taxonomic debates is how to construct uniformly accepted treatments, particularly for domesticated species. Grain researchers often encounter conflicting views in differing names and classification schemes for the same grain species or species groups. In the midst of such debates, the taxonomic system developed in the eighteenth century by the Swedish scientist Carl Linnaeus is still intact. While providing a relatively flexible structure for building modern classifications, the Linnaean traditional approach faces challenges when robust genetic evidence reveals classification inconsistencies with a group’s actual evolutionary relationships. For additional detail on the practice of taxonomy and classification issues related to evolutionary relationships.


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Figure 3 Variations in the appearance of heads of wheat species, one of many morphological characteristics used for their taxonomic classification. From left to right, the wheat species are (including their genome assignments and common names): T. boeoticum (2x: wild einkorn), T. monococcum (2x: einkorn), T. dicoccoides (4x: wild emmer), T. dicoccum (4x: emmer), T. durum (4x: macaroni wheat), T. carthlicum (4x: Persian wheat), T. turgidum (4x: rivet wheat, cone wheat), T. polonicum (4x: Polish wheat), T. timopheevii (4x: Timopheev’s wheat), T. aestivum (6x: bread wheat), T. sphaerococcum (6x: shot wheat, Indian dwarf wheat), T. compactum (6x: club wheat), T. spelta (6x: spelt), and T. macha (6x: macha wheat). The diploid A-genome species, T. urartu, is not shown here. 2x ¼ diploid; 4x ¼ tetraploid; 6x ¼ hexaploid. Adapted from Mangelsdorf PC (1953) Wheat. Scientific American 189: 50–59, ã 1953 by Scientific American Inc.

Taxonomy: What It Is and How It Started Taxonomy provides a system by which plants are classified, named, and identified. Classification consists of the circumscription, grouping, and hierarchical ranking of a plant entity

(taxon) or entities (taxa). Naming, or nomenclature, is governed by a set of rules laid out in the International Code of Botanical Nomenclature (ICBN) and by the specialized rules for domesticated plants found in the International Code of Nomenclature for Cultivated Plants (ICNCP). Identification,

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which usually goes hand in hand with nomenclature, is a determination based on similarity of a taxon’s membership in an existing group or a new group. Linnaeus initiated modern taxonomy with the publication of Species Plantarum in 1753, which classified every plant then known to him. The Linnaean system was not an isolated endeavor. It was built on a long history of scientific attempts, beginning with the Greek Theophrastus (third century BC) and the Roman Pliny the Elder (first century AD), to construct universal naming and classification systems. The Linnaean binomial system, consisting of genus and species names, resolved the problem of concisely and uniquely naming a plant. Continuing with the scientific heritage that preceded him, Linnaeus used Latin as the language of taxonomic names and descriptions. In his time, Latin was the universal language by which European scholars could communicate. Linnaeus took classical Latin and created a new botanical form with its own terminology for plant structures and the flexibility for adopting Latinized words taken from other languages. Modern attempts to replace botanical Latin with English for taxonomic descriptions have so far been unsuccessful, leaving this particular Linnaean heritage intact.

Origins of Taxonomic Names Many Linnaean scientific names for agricultural plants have their roots in the vernacular of the ancient Greeks and Romans. For example, the genus names for grains were derived from terms that often related to a particular function, activity, or trait or to an association with a person. Thus, Triticum comes from the Latin ‘tero’ meaning ‘I thresh’; Cicer, which translates to chickpea, likely has its origin in the Greek ‘kikus’ meaning strength and power, a feature of chickpeas embodied in their high nutritional value and a reputation as an aphrodisiac. For Cicer, the story is also tied up in family names. In time, the early Greek name for chickpea evolved to ‘kiros,’ which became ‘cicer’ in Latin. Early Roman families would take surnames that related to their prosperity. Given the importance of legumes, it is not surprising that Cicero was the family name taken from ‘cicer’; likewise three other famous Roman families carried ‘legume’ names: Fabius (faba: fava bean), Lentulus (lens: lentil), and Piso (pisum: pea). In the original Linnaean system, species names usually conveyed information about a trait. For example, cereale traces to ‘Ceres’ the Roman goddess of agriculture and more specifically to ‘Cerealis’ (of or relating to Ceres) from which the term ‘cereals’ was derived for collectively naming the edible grains of grass species. The genus and species names together produce an identifying designation for taxa as these examples illustrate: Amaranthus caudatus translates as the ‘amaranth ending with a taillike appendage,’ a reference to this species’ long, taillike inflorescence (Figure 2); Cicer arietinum as ‘chickpea shaped like a ram’s head,’ a reference to its seed shape; Fagopyrum esculentum as ‘edible buckwheat’ (Figure 1); Triticum monococcum as ‘one-grained wheat’ (Figure 3); and Secale cereale as ‘cereal rye.’ For species named by Linnaeus, the intertwining of scientific names with the original vernacular helps to explain their respective derivations. The origin of the term common wheat

hails back to an older, no longer accepted, species name T. vulgare, which translates as ‘common wheat.’ The use and derivation of corn and the genus name, Zea, provide another example. The English word corn has its roots in the German word for grain, ‘korn.’ The Greek word ‘zea,’ like corn, referred to grain in a general sense. Linnaeus selected Zea as a genus name for the new cereal grain species that had arrived in Europe following the discovery of America and for which there was no European vernacular name upon which to draw. As a consequence, the English common name corn was adopted into the American English vernacular to refer to the only major New World cereal grain known in the eighteenth century.

The Use of Genus and Species Names Tables 1 and 2 list common and scientific names for grain species. The convention is to write both genus and species names in italics, with the genus name having a capital as the first letter, followed by the species name (known as the specific epithet) all in lower case. When a grain consists of a group of species, the plural abbreviation ‘spp.’ is used. In text, the genus name component of the binomial is spelled out the first time and abbreviated to its first letter, except when beginning a sentence, for each following use as was done earlier in the text with the species examples of Amaranthus and Triticum. In cases where two genera with the same first letter are discussed together, then the second letter of the species name is included in the abbreviation, for example, in discussions of the millets, Pa. for Panicum and Pe. for Pennisetum. Following the species and subspecies epithets is the name (usually abbreviated and not in italics) of the botanist or researcher who named the species, for example, ‘L.’ for Linnaeus in T. monococcum L. and ‘Desf.’ for R. L. Desfontaines in T. durum Desf. Known as the ‘authority,’ this part of the scientific name is important for synonymy, the component of taxonomy that deals with the historical naming of a species. When the name and classification of a grain species are in question due to competing treatments, synonymy provides a way to trace its taxonomic handling and to determine which is the correct and legitimate name according to the ICBN. Authority names are not included in Tables 1 and 2 as they are not essential for the completeness of the binomial in text discussions such as this. However, it is useful in research articles and literature reports to include the authority citation at the first mention of the species to clarify which taxonomic concept is being followed.

Taxonomy: Rank and Hierarchy In classification, taxonomy provides a system for grouping species into ranked hierarchies. All grain species are flowering plants and thus are classified together as angiosperms. Members of this group reproduce sexually with the male and female organs located in the flowers, which can be showy (pseudocereals, pulses, and oilseeds) or inconspicuous (cereals). Their seeds are protected by a fruit, which can be fleshy or dried. In the case of cereals, the fruit is reduced to a thin outer tissue that

THE BASICS | Taxonomic Classification of Grain Species Table 1

Classification of the grass family, Poaceae (Gramineae), all monocotyledonous plants: cereal grain species and their common namesa

Subfamily Ehrhartoideae

b

Tribe

Genus and species

Common name

Oryzeae

Oryza glaberrima Oryza sativa Zizania aquatica Zizania palustris Eleusine coracana Eragrostis tef Sorghum bicolor Zea mays Coix lacryma-jobi Digitaria exilis Echinochloa esculenta Panicum miliaceum Panicum sumatrense Paspalum scrobiculatum Pennisetum glaucum Setaria italica Avena sativa Avena abyssinica Phalaris aquatica Hordeum vulgare Secale cereale Triticosecalec Triticum aestivum Triticum dicoccum Triticum durum Triticum monococcum Triticum spelta Triticum turgidum

African rice Rice Wild rice Northern wild rice Finger millet, African millet, Indian millet Tef, teff, teff grass Sorghum, grain sorghum, great millet, Kaffir corn, durra, milo Corn, maize Coix, Job’s tears, Adlay millet Fonio, fonio millet, hungry rice Japanese barnyard millet, Japanese millet, Siberian, or marsh millet Common millet, broom millet, broomcorn millet, proso millet Blue panic, little millet, sama Kodo millet Pearl millet, cattail millet Foxtail millet, Italian millet Oat, side oat Abyssinian oat Bulbous canary grass, Harding grass, Toowoomba canary grass Barley Rye, cereal rye Triticale Wheat, common wheat, bread wheat Emmer, farro Durum wheat, hard wheat, macaroni wheat Einkorn, small spelt, farro Spelt, spelt wheat, hulled wheat, dinkel wheat, farro Rivet wheat, cone wheat

Chloridoideae

Eragrostideae

Panicoideae

Andropogoneae

Paniceae

Pooïdeae

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Poeaeb

Triticeae

a

Following the classification system outlined in Heywood VH, Brummitt RK, Culham A, and Seberg O (2007) Flowering Plants of the World. Ontario, Canada: Firefly Books, and updated by the Angiosperm Phylogeny Group. b Subfamily and tribal classification assignment according to the Grass Phylogeny Working Group (GPWG). c Triticale (Triticosecale) is an intergeneric hybrid that was created by crosses between wheat and cereal rye. The preceding Triticosecale, which combines Triticum and Secale, indicates its hybrid origin. Given the multiple hybrid combinations by which Triticale forms have been derived, only cultivar names are assigned.

is adherent to the seed. In botanical terminology, the cereal grain is called a caryopsis. Traditional Linnaean classifications have followed the hierarchical structure of Kingdom–Class–Order–Family–Tribe– Genus–Species with subdivisions in each of these ranks, for example, subclass. Largely morphological in concept, these classifications do not always track well with current evidence on evolutionary relationships. On the other hand, phylogenetic classifications are structured around monophyletic groups that each consist of all descendants of a common ancestor, which share the group’s identifying characteristics. Given that ongoing molecular genetic research leads to changing evolutionary concepts, phylogenetic classifications are in flux and have unresolved groupings. While some of the lower Linnaean hierarchical rankings have been retained in these classifications, groupings above ‘Order,’ as well as unresolved groups at lower ranks, are designated as ‘clades.’ As a general term denoting a group consisting of an ancestor and all its descendants, ‘clade’ is used in this latter context to indicate a group whose phylogenetic status is still open to question. Differences distinguishing traditional versus phylogenetic classifications come into play for the monocot and dicot evolutionary lines of grain species. In older classifications, flowering plants belong to the Class Angiospermae, which is divided into

monocots (subclass Monocotyledoneae) and dicots (subclass Dicotyledoneae). From a more current phylogenetic perspective, angiosperms are classified as a clade with three subgroupings: dicots, monocots, and eudicots. Monocots and eudicots (true dicots) are each designated as a clade (Table 3). Dicots are not treated as a clade because they are a nonmonophyletic group of primitive angiosperms with various members ancestral to both monocots and eudicots, respectively. Grain species covered in this article fall within the monocot and eudicot clades. Therefore, the biological features associated with monocots and dicots are useful for distinguishing among cereal (monocot) and noncereal (dicot) species. The terms monocot and dicot refer to the presence of one or two embryonic leaves (cotyledons) in the seed and young seedling. Other easily identifiable morphological traits differentiate between them. Monocots have flower parts in threes, parallel-veined leaves, scattered vascular bundles, and fibrous adventitious root system. Dicots have flower parts in fours or fives, net-veined leaves, vascular bundles located in a ring, and a primary tap root. Tables 1–3 present current taxonomic treatments for cereal and noncereal grain and oilseed species. For additional detail on traditional and phylogenetic classification approaches. Family is the most useful of the higher taxonomic ranks. Family names end in ‘-aceae’ except for several older names

36 Table 2

THE BASICS | Taxonomic Classification of Grain Species Dicotyledonous grain and oilseed species and their common namesa

Family

Tribe

Genus and species

Common name

Amaranthaceae

Amaranthoideae

Asteraceae (Compositae)b

Atripliceae Cynareae Heliantheae

Brassicaceae (Cruciferae)b

Brassiceae

Fabaceae (Leguminosae)b

Dalbergieae Cicereae Genisteae

Amaranthus caudatus Amaranthus cruentas Amaranthus hypochondriacus Chenopodium quinoa Carthamus tinctorius Guizotia abyssinica Helianthus annuus Brassica napus Brassica spp. Crambe abyssinica Arachis hypogaea Cicer arietinum Lupinus albus Lupinus angustifolius Cajanus cajan Glycine max Phaseolus lunatus Phaseolus vulgaris Vigna angularis Vigna mungo Vigna radiata Vigna unguiculata Lathyrus sativus Lens esculentus Pisum sativa Vicia faba Salvia hispanica Linum usitatissimum Gossypium spp. Sesamum indicum Fagopyrum esculentum

Amaranth, grain amaranth, Inca wheat, kiwicha Purple amaranth, red amaranth Prince’s feather Quinoa Safflower Niger, niger seed, ramtil Sunflower Canola, oilseed rape, rape Mustard Crambe Peanut, groundnut, goober Chickpea, garbanzo bean, gram White lupin Blue lupin Pigeon pea, Congo pea, red gram Soybean Lima bean, butter bean Bean, kidney bean, pinto bean, navy bean, cannellini bean Adzuki bean, azuki bean, aduki bean Black gram, urad bean Mung bean, golden gram, green gram Black-eyed pea, cowpea Chickling pea, chickling vetch Lentil Garden pea, field pea Faba bean, broad bean Chia, salba Linseed, flax, Linola™ Cottonseed Sesame, sesame seed, benne, benne seed Buckwheat, Japanese buckwheat, silverhull buckwheat

Phaseoleae

Fabeae

Lamiaceae (Labiatae)b Linaceae Malvaceae Pedaliaceae Polygonaceae

Mentheae Gossypieae

a Following the classification system to family rank outlined in Heywood VH, Brummitt RK, Culham A, and Seberg O (2007) Flowering Plants of the World. Ontario, Canada: Firefly Books and updated by the Angiosperm Phylogeny Group. b Original family name predating ICBN standardization.

that were in use before the ICBN standardized the suffix spelling. Thus, in grain taxonomy, two family names are occasionally encountered – Gramineae (old) and Poaceae (new), Leguminosae (old) and Fabaceae (new), Cruciferae (old) and Brassicaceae (new), and Compositae (old) and Asteraceae (new). The other useful higher taxonomic ranking is tribe, a subdivision of family, that is identified by an ‘-eae’ ending. All the cereal grains (e.g., maize, rice, sorghum, and wheat) are monocots and belong to the grass family Poaceae. Dicot grains and oilseeds comprise a diverse mixture of families. The pulses or grain legumes (e.g., beans, peas, and soybeans), which are the largest group of dicot grains, are classified in Fabaceae. Other families include one or just a few species, for example, Amaranthaceae (grain amaranths and quinoa), Polygonaceae (buckwheat), Asteraceae (niger, safflower, and sunflower), Malvaceae (cottonseed), and Brassicaceae (canola, mustard, and crambe). Subdivisions into subfamilies and/or tribes reflect the size and diversity of the family. Grain species can be subdivided into infraspecific categories known as subspecies (ssp.), variety (var.), and forma (f.). Because there is no clear agreement on use of subspecies versus variety, the two are often used interchangeably, although it is possible to treat variety as a subrank to subspecies. When the subspecies (or variety) is the taxonomic type that defines a

particular species, then the ICBN requires that this subspecies (or variety) repeats the species name – for example, T. aestivum ssp. aestivum. In general discussions, it is not necessary to include the repetitious infraspecific form. Thus, in this example, it is sufficient to cite only the species name T. aestivum when referring to bread wheat. Forma is the smallest category and is infrequently encountered. The infraspecific ranks are intended to describe variants that form distinct groups defined by genetics, morphology, ecology, and distribution. How a particular taxonomist chooses to classify infraspecific taxa can appear arbitrary. For example, a current taxonomic treatment of the wheats uses variety for the wild wheat genus Aegilops (e.g., A. speltoides var. ligustica) but subspecies for the domesticated genus Triticum (e.g., T. turgidum ssp. durum). Here, the infraspecific ranks should be viewed as approximately equivalent. This example also illustrates the difficulty in reflecting evolutionary relationships within the framework of taxonomic classification. The infraspecific variation in domesticated Triticum species is the product of human selection pressure, which is arguably on a different evolutionary scale than the variation in the wild species of Aegilops. Thus, in this example, the taxonomist’s choice of variety for Aegilops and subspecies for Triticum should not be construed as a definitive reflection on evolutionary status.

THE BASICS | Taxonomic Classification of Grain Species Table 3

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Hierarchical classificationa for grain and oilseed speciesb with their use-category assignments

Cladec

Order

Family

Subfamily

Tribe

Genus

Use category

Monocots Commelinids

Poales

Poaceae

Ehrhartoideaed

Oryzeae

Chloridoideae

Eragrostideae

Panicoideae

Andropogoneae

Oryza Zizania Eleusine Eragrostis Coix Sorghum Zea Digitaria Echinochloa Panicum Paspalum Pennisetum Setaria Avena Phalaris Hordeum Secale Triticosecale Triticum

Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal Cereal

Amaranthus Chenopodium Fagopyrum Carthamus Guizotia Helianthus Salvia Sesamum Arachis Cicer Lupinus Cajanus Glycine Phaseolus Vigna Lathyrus Lens Pisum Vicia Brassica Crambe Linum Gossypium

Pseudocereal Pseudocereal Pseudocereal Oilseed Oilseed Oilseed Oilseed Oilseed Pulse, oilseed Pulse Pulse Pulse Pulse, oilseed Pulse Pulse Pulse Pulse Pulse Pulse Oilseed Oilseed Oilseed Oilseed

Paniceae

Poeaed

Pooïdeae

Triticeae

Eudicots Core eudicots

Asterids

Caryophyllales

Asterales

Lamiales Rosids

Fabales

Amaranthaceae Polygonaceae Asteraceae

Lamiaceae Pedaliaceae Fabaceae

Amaranthoideae Chenopodioideae

Atripliceae

Lactucoideae Asteroideae

Cardueae Heliantheae

Nepetoideae

Mentheae

Papilionoideae

Aeschynomeneae Cicereae Genisteae Phaseoleae

Vicieae

Geraniales

Brassicaceae

Malpighiales Malvales

Linaceae Malvaceae

Brassiceae Linoideae Malvoideae

Gossypieae

a Following the classification system to family rank outlined in Heywood VH, Brummitt RK, Culham A, and Seberg O (2007) Flowering Plants of the World. Ontario, Canada: Firefly Books as updated by the Angiosperm Phylogeny Group. b For additional information on individual taxa. c To view the associated phylogenetic trees and clade subdivisions, see http://www.mobot.org/MOBOT/research/APweb/welcome.html. d Alternative subfamily and tribal classification assignment following the Grass Phylogeny Working Group (GPWG) revision.

Taxonomic Disagreements With taxonomic classification, there is not necessarily a right or a wrong treatment. Taxonomists and the researchers working with a particular group can often disagree with each other. As a consequence, different names for the same species can be found in use. For those who are not schooled in the ICBN or unfamiliar with the underlying details of a taxonomic controversy, conflicting classifications are confusing and can be

difficult to sort out. In the case of domesticated species, debates usually deal with both the taxonomic status of taxa (usually species versus an infraspecific rank) and the relative importance of genetic evidence in defining species concepts and evolutionary relationships. There is no clear separation of these two points, partly due to the historical tradition on which taxonomy has been built and the inconsistencies in how domesticated plants are viewed within an evolutionary context.

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The opposing species concepts at play in wheat taxonomy offer an example of the different directions that a taxonomic debate can take. Morphological diversity in the domesticated tetraploid and hexaploid wheats illustrates the potential for variation that developed with humans acting as evolutionary selection agents. This variation originally correlated with ecogeographic distributions and, if allowed to continue in isolation over geologic time, would have possibly led to new species. Wheat geneticists stress the need to portray accurate genetic relationships, circumscribing wheat species on the basis of their close genetic similarities. Thus, in the AB- and ABDgenome groups, geneticists accept only two species, each with several infraspecific forms – T. turgidum and T. aestivum. On the other side of the fence are those who stress the importance of recognizing the distinct variation among domesticated forms by naming multiple tetraploid and hexaploid wheat species (Figure 3 and Table 1). Provided that the rules of nomenclature are followed, differing treatment concepts are acceptable. On this basis, T. spelta and T. aestivum ssp. spelta are both correct as are T. durum and T. turgidum ssp. durum, respectively, describing the same wheats, albeit from different taxonomic perspectives.

Cultivated Plant Taxonomy Grain and oilseed species are classified as botanical entities under the ICBN. Their man-made forms derived through artificial selection, known by the general term cultigens, are classified under the ICNCP in two possible categories: cultivar (deliberately selected plants, either domesticated or wild) and group (an assemblage of cultivars). The term cultivar was developed from ‘cultivated variety’ by combining the first five and three letters of these two terms, respectively. According to the ICNCP, a cultivar is designated by one or more distinct, uniform, and stable characters that persist through propagation. Although often used interchangeably, the terms ‘cultivar’ and ‘variety’ are not equivalent, that is, ‘variety’ is not a nomenclatural term under the ICNCP. However, in the context of cultivar registration, the term variety is often used to refer to a cultivar. Of note, ‘variety’ is a legal term under the International Union for the Protection of New Varieties of Plants convention, which oversees the recognition of plant breeders’ rights for a particular domesticated cultivar. Regarding terminology differences between the ICBN and the ICNCP, the botanical term ‘variety’ (also as varietas) applies only as a name for one of the infraspecific ranks under the ICBN. A domesticated cultivar has a non-Latin name (cultigen epithet) that is not italicized and enclosed by single quotation marks. Several examples should help to clarify this usage – Zea mays ‘Bronze Beauty’ or maize cultivar ‘Bronze Beauty’, Lens culinaris ‘Laird’, Avena sativa ‘Wallaroo’, Arachis hypogaea ssp. fastigiata ‘Georgia Red’, Amaranthus cruentus ‘K343’, and Cicer arietinum ‘Kranthi’. Following a cultivar’s first mention, the single quotation marks can be dropped. The term landrace is often encountered in discussions of crop germplasm. It refers to an indigenous grain species within a local farming system. Landraces predate modern agriculture and often are ancient infraspecific forms that may have been in cultivation for hundreds or thousands of years. Landraces are usually composed of a mixed population whose members vary

by agronomic traits such as disease resistance, maturity, yield, and cold tolerance. The mixture also may include different species. For example, wheat landraces collected during the late 1940s in southeastern Turkey can be composed of ten or more different forms of the two species T. aestivum (T. aestivum ssp. aestivum) and T. durum (T. turgidum ssp. durum). The advantage of landraces in subsistence farming systems is the guarantee of a crop under all types of growing conditions. For example, if the farmer faces a particularly bad disease year, the resistant types of the landrace will survive and yield a harvestable grain. Unfortunately, a clear-cut distinction between landrace and cultivar is not always maintained. It is not uncommon for a landrace to be cataloged as a cultivar by one gene bank and as a landrace by another. While vernacular names are useful for identifying landraces, they do not have taxonomic standing.

Taxonomy: In Use As a standardized system for classification of plants, taxonomy provides a useful way for tracing the origins of grain species. By knowing the names of wild progenitors and related domesticated species, researchers can make informed decisions when selecting material for study or for breeding programs. Likewise, knowing the taxonomic traits by which species are classified enables researchers to verify the identity of research material. This is particularly important given the possibility that gene bank and research collections may hold and distribute mislabeled or misidentified wild and domesticated germplasm. The wheats offer a practical example of the importance of taxonomy in the selection and use of research material. Because there are several conflicting taxonomic concepts for the wild and domesticated wheats, a seed request may not be filled with the taxon actually requested. A general, unspecified request for accessions of the diploid A-genome progenitor of tetraploid and hexaploid wheat species may be incorrectly filled with either T. boeoticum or T. monococcum. While the wild T. boeoticum and domesticated T. monococcum both have a form of the A-genome, neither was involved in the evolution of T. durum (AB genomes) and T. aestivum (ABD genomes) (Figure 3). The correct species for this request would be T. urartu. Since T. urartu and T. boeoticum are morphologically very similar to each other, a researcher, who is unfamiliar with the taxonomic characters that differentiate them, may erroneously mistake T. boeoticum for T. urartu.

Taxonomy and Allergies Taxonomic relationships have a practical application for identifying potential allergic cross-reactions. For example, a person with a proven allergic reaction to wheat grain would be more likely to have similar problems with rye but less with the more distantly related cereal grain species such as rice or maize (Table 1). This consideration is particularly relevant to celiac disease, for which the prime cause is the gluten proteins found in wheat. Celiacs are also warned to avoid eating the grain of barley, rye, and triticale, closely related species in the tribe Triticeae. Although oats, which are classified in tribe Poeae, are considered to be less harmful for celiacs, some such

THE BASICS | Taxonomic Classification of Grain Species individuals find that they must avoid them. On the other hand, celiacs may eat foods based on other cereal grains, which are classified in more distantly related tribes (e.g., maize, millet, rice, and sorghum) and any of the dicot species. Within the context of taxonomy, the possible cross-reaction with oats but not with maize, millet, rice, and sorghum is understandable. The tribes Triticeae and Poeae are located in the same subfamily, the Pooïdeae. On the other hand, maize, millet, and sorghum are classified in the subfamily Panicoideae and rice in the subfamily Ehrhartoideae. Attempts at prediction of allergic cross-reaction may not be valid if making comparisons with respect to different vegetative or reproductive parts of the plant and different routes into the body – for example, the inhalation of pollen versus the ingestion of grain. It may thus be possible for a person, who is allergic to wheat pollen, to suffer no adverse reactions to the wheat grain. However, there is at least anecdotal evidence that individuals, who experience mild ingestion intolerance to cereal grains, may have these symptoms exacerbated in pollen season. Also, allergic cross-reactions are observed between pollens of different species, implying that sensitization by one species can confer allergy to others. Thus, a positive test reaction to pollen from one species does not necessarily mean that it is the one causing clinical symptoms, nor need it have been the one responsible for the original sensitization. The real culprit may be another cross-reacting pollen. Here, taxonomy offers a practical tool for elucidating such situations. For the monocot grains, only the grass family Poaceae is necessary to consider. Within the very diverse dicot group of pulses, pseudocereals, and oilseeds, the higher taxonomic rankings above Family are of practical use for evaluating allergic crossreactions. In providing only a brief introduction into the taxonomy of grain species, Table 3 illustrates the hierarchical relationships that should be considered in dealing with potential cross-reactions.

Future Trends in Taxonomy As is evident in the previously mentioned discussion, taxonomy is subject to conflicting, and often changing, interpretations. When taxonomic disagreements prevail, the focus shifts away from taxonomy’s real value in aiding communication among scientists. For example, a long-running debate among wheat researchers dating from the 1950s over how to classify wild and domesticated taxa by evolutionary relationships has created a confusing situation with many different classifications and no consensus for names or species concepts. This controversy illustrates the possible problems that lie ahead should the current trend continue among molecular systematists and research geneticists to restructure traditional taxonomy of lower-ranking groups into a ‘natural’ system that displays phylogenetic relationships even when they are not fully resolved and/or open to widely varying interpretations. Because concepts of plant phylogeny are changing rapidly with the sophisticated tools of molecular biology, an attempt to structure taxonomy on molecular evidence may lead to a situation of constant taxonomic flux. Traditionalists argue that taxonomy should continue as it now stands guided by the ICBN. The current approach of the Angiosperm Phylogeny

39

Group and its followers offers a viable example of combining the two systems: structuring higher-order relationships in an ordinal phylogenetic system while drawing on the stability of the Linnaean system for treating the lower ranks (Family– Genus–Species) and revising their classifications as robust phylogenetic evidence becomes available.


• • • • • •

• • •

What is the function of scientific names for the grains and why are they preferred over common names in research, germplasm conservation, and communication among scientists? How do common names convey cultural and historical information about the societies that cultivated domesticated grains? What role have common names played in the taxonomic naming system? What are the distinct differences among these taxonomic ranks: family, genus, species, subspecies, variety, and cultivar? In what case is ‘variety’ and ‘cultivar’ used interchangeably and why is this practice not advisable? Why is the ICNCP important as a separate set of rules for naming and classifying domesticated grains? For grain species, what types of issues is the ICNCP able to better address than possible with the ICBN? How does taxonomic classification help in distinguishing between cereal and dicot grains and the species classified within each of these two major grain groups? With the much-enhanced ability to elucidate phylogenetic relationships with data from molecular genetic studies, what types of challenges does the traditional Linnaean system face when incorporating this information into taxonomic classification? How do competing taxonomic classifications create difficulties for grain researchers? What types of solutions can be developed to address the controversies associated with traditional versus natural phylogenetic classifications? How do evolutionary groupings of grain species in taxonomic classifications aid in assessments of potential allergic cross-reactions? Since landraces are often mixtures of multiple species, what are the challenges faced in cataloging and classifying landrace diversity? Why is it important to differentiate among individual types within a single landrace collection?


• • •

Explore the advantages and conflicts posed by the application of molecular technologies to taxonomy. For example, examine and expand on the statement in ‘Future Trends’: “molecular systematists (may) suggest other naming systems and other ways of classifying, which could lead to a re-invention of taxonomy.” Refer to the article on variety identification, which describes the use of protein composition and DNA analysis to differentiate cultivars in agriculture. Consider how these methods might be expanded to compare a wider range of taxonomic relationships.

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See also: Breeding of Grains: Barley: Genetics and Breeding; Canola/Rapeseed: Genetics and Breeding; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Genetics of Grains: Maize: Genetics; Rice: Genetics; Wheat Genetics; The Cereal Grains: Cereals: Domestication of the Cereal Grains; The Legumes and Pseudocereals: Amaranth: Overview; Buckwheat: Overview; Pseudocereals: Overview; The Oilseeds: Oilseeds: Overview.

Further Reading Angiosperm Phylogeny Group (1998) An ordinal classification for the families of flowering plants. Annals of Missouri Botanical Garden 85: 531–553. Angiosperm Phylogeny Group II (2003) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: 399–436. Angiosperm Phylogeny Group III (2009) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society 161: 105–121. Brickell CD, Alexander C, and David JC, et al. (eds.) (2009) International Code of Nomenclature for Cultivated Plants, 8th edn. In: Regnum Vegetabile, 8th edn., 151: Belgium: Drukkerji Geers Scripta Horticulturae 10. Hanelt P and Institute of Plant Genetics and Crop Plant Research (eds.) (2001) Mansfeld’s Encyclopedia of Agricultural and Horticultural Crops (Except Ornamentals) Germany: Springer-Verlag, English edition. Heywood VH, Brummitt RK, Culham A, and Seberg O (2007) Flowering Plants of the World. Ontario, Canada: Firefly Books. Judd WS, Campbell CS, Kellogg EA, Stevens PF, and Donoghue MJ (2007) Plant Systematics: A Phylogenetic Approach, 3rd edn. Sunderland, MA: Sinauer Associates. Linnaeus C (1753) Species Plantarum. Sweden: Laurentius Salvius. Mangelsdorf PC (1953) Wheat. Scientific American 189: 50–59. McNeill J, Buck WR, and Burdet HM, et al. (eds.) (2012) International Code of Botanical Nomenclature (Melbourne Code). In: Regnum Vegetabile154: Ko¨nigstein, Germany: Koeltz Scientific Books. Stuessy TF (2009) Plant Taxonomy: The Systematic Evaluation of Comparative Data, 2nd edn. New York: Columbia University Press. Vietmeyer ND (ed.) (1989) Lost Crops of the Incas Washington, DC: National Academy Press. Watson L and Wrigley CW (1984) Relationships between plants relevant to allergy. Medical Journal of Australia 141(5 Suppl.): S18.

Wiersema JH and Leoń B (2013) World Economic Plants: A Standard Reference, 2nd edn. Boca Raton, FL: CRC Press. Williams JT (ed.) (1995) Cereals and Pseudocereals London: Chapman and Hall.

Relevant Websites http://www.ars-grin.gov – The United States Department of Agriculture website for GRIN (Germplasm Resources Information Network) is set up for taxonomic queries on holdings of economic plants and with links to other relevant websites for the taxonomy of economic plants. Economic plant listings include vernacular names and economic uses. Information on this website is drawn from “World Economic Plants: A Standard Reference.” http://www.eti.uva.nl – The Expert Center for Taxonomic Identification (ETI) is an online taxonomic database service supported by an international consortium. The site hosts a searchable taxonomic database for taxonomic hierarchies, species names, synonyms, and descriptions. http://www.iapt-taxon.org/nomen/main.php – The online version for the most recent edition of the ICBN (2012), which is known as the Melbourne Code, is in English. http://www.ildis.org – Location for the International Legume Database and Information Service (ILDIS), this website has a searchable database for species information about the grain pulses. http://www.ipni.org – The International Plant Names Index (IPNI) is a comprehensive online database of plant names and bibliographic information. https://www.ksu.edu.wgrc.Taxonomy.taxintro.html – This website has comprehensive listings of historical and current taxonomic treatments of the wheats. http://www.mobot.org/MOBOT/research/APweb/welcome.html – The Angiosperm Phylogeny Group website has up-to-date revisions to the Angiosperm phylogenetic trees, extensive reviews of current evidence, and references. http://www.plantnames.unimelb.edu.au – The Multilingual Multiscript Plant Name Database has a searchable database for locating scientific and vernacular names in all applicable languages for a particular grain species. http://tolweb.org.tree.phylogeny.html – The Tree of Life Web Project is a searchable internet source for information on biodiversity, phylogeny, and characteristics of biological groups. http://www.umsl.edu.services.kellogg.gpwg.default.htm – As a collaborative group of systematic botanists, the Grass Phylogeny Working Group (GPWG) produced a phylogeny of the grass family by combining existing data sets. Although GPWG is no longer active, this website provides access to its results. http://upov.int/about/en/benefits_upov_system.html – The International Union for the Protection of New Varieties of Plants is an intergovernmental organization that oversees the convention for protecting intellectual property rights to new plant cultivars introduced into commerce.

Grain: Morphology of Internal Structure H Corke, University of Hong Kong, Hong Kong, Pokfulam, China; Hubei University of Technology, Wuhan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Grain structure determines the necessity for dehulling and the consequences of wet and dry milling. The major cereal grains (wheat, rice, and maize), although botanically similar, have significant differences in organization of starch and protein reserves. Wet milling results in separation of major grain components; dry milling is generally a size reduction process.

Learning Objectives

• • •

To be able to visualize and explain the major anatomical features of cereal grains. To understand the distribution of major nutritional components in the grains. To understand how the specific structure of different cereal grains drives the choice and consequence of wet and dry milling.

Introduction This is a wide topic because virtually every aspect of grain technology is related to grain structure. Handling, processing, and utilization of grains depend on specific details of their structure. For example, in dry milling of rice and wheat, removal of the bran layers is necessary. The wheat grain is not covered with a tightly attached hull, so unlike in rice, initial dehulling is not required. Bran removal in wheat is part of the process of producing fine particulate flour by crushing the endosperm. Bran removal in rice should leave an unbroken polished rice grain. In both wheat and rice, endosperm should be at a specific hardness to achieve the desired outcome. Wet milling is a fractionation process. In maize, starch, oil, and protein components are separated. Again, the physical structure of the grain is exploited in the design of the milling process. Issues such as these will be covered in detail in this article. More specifically, the following aspects will be covered: wheat grain morphology and its effect on dry and wet milling, rice grain morphology and its effect on dry milling and nutrition, maize grain morphology and its effect on handling and wet milling, barley structure and its effect on brewing, and a comparative summary of general effects of grain structure.

Wheat Grain Morphology and Its Effect on Dry and Wet Milling The relationship of the grain to overall spike structure is important in milling (Figure 1). Historically, the wheat ancestors (e.g., the diploid Triticum monococcum) had a brittle rachis trait. This means that after ripening of the grain and drying of


the plant, the rachis (where the spikelet is attached to the axis) breaks naturally and the seed (still surrounded by a tightly bound palea, lemma, and awn) falls from the plant. This is an essential survival feature for a plant whose seeds are dispersed in nature through the action of wind, insects, etc. In a farmer’s field, a brittle rachis would not be viable, as harvesting would be extremely difficult. The genetic step from brittle to nonbrittle rachis is the key to domestication of small-grain cereals (e.g., wheat, rice, and barley). However, wheat has a further useful adaptation to domestication, which differs from rice. In wheat, the palea and lemma naturally separate from the grain – this is called a ‘naked’ grain characteristic. In rice, the grain is ‘covered,’ that is, the hull is attached to the grain and requires a separate processing stage (dehulling) to remove it.

Bran The wheat grain has been described as ‘a single-seeded fruit called a caryopsis, in which the ripened ovary wall is fused to the seed.’ The classical diagram for hexaploid common (bread) wheat (Triticum aestivum) grain structure was produced by the Wheat Flour Institute, Washington, DC (Figure 2). The objective of flour milling is to remove the embryo (germ) outer layers (epidermis, hypodermis, cross cells, tube cells, seed coat, and nucellar tissue), which collectively are termed the bran. The aleurone layer, part of the endosperm, is also removed with the bran and from a miller’s point of view may be included as a bran layer. Much of the vitamin and mineral content of the grain is contained in the bran. In many countries, wheat flour is enriched or fortified to replace some of the nutrients lost in milling. Removal of the bran (which, including the aleurone layer, comprises 15% of the grain by weight) permits production of white flour. Apart from appearance, white flour has different technological properties to whole-wheat meal (that produced by grinding the whole grain without bran separation). The presence of large amounts of bran dilutes the proportion of gluten in the product and results in a denser, more fiber-rich product. The presence of small amounts of bran (as bran specks) results in off-white color in flour and in many final products (e.g., steamed bread). In fresh white noodles, discoloration to gray is associated with polyphenol oxidase (PPO) content of flour, and most PPO is present in bran. In Chinese steamed bread, formation of brown spots on the surface may also be associated with PPO effects from bran contamination (and the use of NaCl in the formulation). Because of the high mineral content of bran relative to endosperm, bran content in flour can be estimated by ashing (furnace heating) a flour sample and weighing the residue. For the same flour yield, a variety that gives lower ash content (less bran) is of course preferable. In wheat flour milling, grain is tempered to a uniform moisture content (usually 15.5%). The effect of this is to make the bran layers flexible so that under the crushing action

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THE BASICS | Grain: Morphology of Internal Structure

Awn (not always present)

Spikelet Rachis

Palea Pales Lemma Floret Grain Rachilla Glume

(a)

(b)

Figure 1 The structure of the wheat spike (ear). Cultivated wheat requires a nonbrittle rachis so that mechanical harvesting is possible and a loosely attached palea and lemma so that a dehulling step is not required. Reproduced from Evers AD and Bechtel DB (1988) Microscopic structure of the wheat grain. In: Pomeranz Y (ed.) Wheat: Chemistry and Technology, 3rd edn., vol. 1, pp. 47–95. St. Paul, MN: American Association of Cereal Chemists.

of roller milling, bran will break into large flakes, not be crushed into powder. This formation of flakes of bran results in pieces that are of different sizes, shapes, and densities to the endosperm particles, which on size reduction become flour particles. Without this physical flexibility in bran, milling would not be possible. However, with crushing, some endosperm is likely to be attached to some of the bran flakes. Continuing milling to remove the last particles of endosperm (i.e., aiming for a high flour yield or percentage yield of flour relative to starting weight of grain) will increase contamination of flour with bran. The flour yield also depends on several other properties of bran: 1. The thickness of the bran layers, which is under genetic control 2. The size of the grain (bran will be a relatively lower fraction of a larger grain; also, a plump well-filled grain will be preferable) 3. The characteristics of the crease The crease in a wheat grain is the lateral fold (Figures 2 and 3) ending with the pigment strand. A deep crease results in more problems with bran removal in milling – more bran particles attached to endosperm chunks usually result from a deep crease. Also, the crease can trap contaminants, for example, dust and fungal spores, which can cause problems in storage and in cleaning the grain before milling. Grain color in wheat, usually due to red pigmentation in the bran (seed coat), is usually classified as red (the presence of pigmentation) or white (absence). White wheat flour, if contaminated with bran, will show less discoloration than red wheat flour. This is why hard white-type wheat is becoming more widely accepted as suitable for Asian noodles. Other colors are possible but rare in commercial trade – for example, blue, purple, or even ‘black’ wheat, with a dark purple pigment in the seed coat, which is used in some specialty products in China.

Endosperm The product of wheat dry milling is flour, the result of crushing endosperm. The endosperm consists of cells surrounded by a pentosan-rich cell wall (mostly arabinoxylans) and contains starch granules embedded in a protein matrix. The size of the cell and the thickness of the cell wall affect the proportion of cell wall material relative to starch and protein in the endosperm. The cell wall absorbs water during dough mixing, so it is significant in determining optimum water absorption of flour. The dimensions of the cell wall are genetically variable. The starch granules consist of two types, larger A granules and smaller B granules. Starch composition (proportion of amylose to amylopectin in starch) determines physical properties of any gelatinized starch product resulting from cooking the flour. This is most important in Japanese white-salted noodles (‘udon’) where a low-amylose (partial waxy), high-swelling starch gives favorable texture. In many other products, such as baked bread, the starch composition, within normal limits for wheat flour, does not have much impact on product quality. Starch granules are subject to shear or breakage, termed ‘starch damage’ in milling, if the endosperm is too hard (e.g., genetically hard texture or too low moisture content in milling) or if milling equipment is not adjusted correctly. A broken granule, exposing the interior, is much more readily subject to hydrolysis by amylases during the bread-making process (during fermentation and early stages of baking before the enzyme is inactivated). Some starch damage may be desirable to provide a substrate for yeast growth, but excessive damage adversely impacts on quality and may result in a sticky texture in the final loaf. Endosperm hardness is largely due to the structure of two puroindolines (components of friabilin), which are amyloplast membrane proteins present in the endosperm. There is a widespread confusion about grain hardness (protein-influenced) and noodle texture (starchinfluenced). A high-swelling starch, but not necessarily a soft


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Hairs of brush

Endosperm Cell filled with starch granules in protein matrix Cellulose walls of cells Aleurone cell layer (part of endosperm but separated with bran) Nucellar tissue Seedcoat (testa) Tube cells Cross cells Hypodermis Epidermis Scutellum Sheath of shoot Rudimentary shoot Rudimentary primary root Root sheath Root cap Longitudinal section of grain of wheat (enlarged ~35 times)

Crease Endosperm Pigment strand Bran Germ Cross-sectional view Figure 2 The structure of the wheat grain – longitudinal and cross-sectional views. Reproduced from Pomeranz Y (1987) Modern Cereal Science and Technology, pp. 25–39. Weinheim, Germany: VCH Publishers.

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Outer kernel layers

Central starchy endosperm

Crease region

Wheat

100 µm

100 µm

100 µm

Barley

100 µm

100 µm

100 µm

Oat

100 µm

100 µm

100 µm

Rye

100 µm

100 µm

100 µm

Figure 3 Outer kernel layers, central starchy endosperm, and crease region of kernel cross sections of wheat, barley, oat, and rye stained with acid fuchsin – calcofluor. Reproduced from Dornez E, Holopainen U, Cuyvers S, et al. (2011) Study of grain cell wall structures by microscopic analysis with four different staining techniques. Journal of Cereal Science 54: 363–373.

endosperm, is required to make a soft-textured noodle (such as Japanese udon).

Embryo (Germ) The embryo consists of the rudimentary structures (shoot and root) of the plant, which can grow from the grain, plus the root and shoot sheathes, the root cap, and the scutellar tissue. The embryo, 3% of the grain weight, contains 8% of the grain protein, but it is mostly in the form of enzymes related to subsequent growth of the seedling, not storage protein (gluten)

as in the endosperm. Thus, the wheat germ protein is of higher quality (more favorable amino acid balance, such as higher lysine content) for human nutrition. The lysine level in protein in the embryo is 8%; in endosperm protein 2%, and in bran protein 4.5%. In addition, 20% of the lipids of the grain are in the embryo (oil-containing spherosomes are present in the aleurone layer and in scutellar cells), but there are also high levels of lipase and lipoxygenase enzymes, which hydrolyze and oxidize oil, causing rancidity. Wheat germ hence has uses as a food material or supplement for human nutrition and is valuable as an additive to animal feed (particularly for

THE BASICS | Grain: Morphology of Internal Structure monogastric animals such as pigs and poultry). On the other hand, wheat germ, unless treated, has a short shelf life. Wholewheat meal also has a shorter shelf life than white flour. Removal of germ to produce flour results in a product that is stable for long periods of time.

Other Features Dry milling of durum (Triticum durum) wheat (a tetraploid species) to make semolina (larger particle size than flour from common wheat) has a few special features related to the durum endosperm texture. The physical hardness (vitreousness) of durum endosperm makes the grain liable to break during combine harvesting. These broken grains should be separated and recovered during cleaning of grain before milling, or a high level of wastage may occur. Optimum tempering of durum grain before milling is also essential and varies with the vitreousness of the endosperm. Careful milling (e.g., more break rolls than for bread wheat) is needed to achieve suitably fine semolina for high-quality pasta. In wheat wet milling (to produce wheat starch, gluten, and wheat germ oil), separation is by soaking the grain, crushing, and sedimenting off the starch component. B-type starch granules are too small to easily sediment, and their complete removal would require expensive centrifugation steps. Hence,

a genetically low proportion of B-type compared to A-type granules would be a strong advantage for increased starch yield in wet milling. Considerable effort is being expended to identify more suitable wheat varieties for this use. A significant recent development has been the application of Raman microscopy (in combination with further development of selective staining for optical microscopy) to image and localize the presence of, for example, b-glucans, protein, starch, and ferulic acid in wheat and barley grain. The advantage of Raman microscopy, applied alone, is the absence of required pretreatment or staining. An example of the capability of highquality selective staining can be seen in Figure 3; such information as the cell wall size and thickness, the size and packing of starch granules, the nature of the bran layers, and the geometry of the crease can be invaluable for genetic improvement of wheat.

Rice Grain Morphology and Its Effect on Dry Milling and Nutrition Grain Structure The anatomical structure of rice (Figure 4) is of course very similar to that of wheat. However, grain shape is of more significance. Short-, medium-, and long-grain rice are common

Awn

Lemma Palea

Pericarp Seedcoat Nucellus Aleurone layer Subaleurone layer Starchy endosperm

Hull

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Endosperm

Scutellum Plumule Embryo Radicle Epiblast Sterile lemmae Rachilla Figure 4 The structure of the rice grain. Reproduced from Juliano JB and Aldama MJ (1937) Morphology of Oryza sativa L. Philippines Agriculturalist 26: 1–134; Juliano BO (1993).

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classifications. In the United States, texture can be recognized from grain length – short grain is low amylose (sticky) and long grain is intermediate amylose (20–25%) (harder cooked texture such that grains are separate after boiling). This is a marketing phenomenon, not a genetic relationship, and in other countries, long grain may well be waxy or sticky types, sometimes a source of confusion to traveling Americans. Grain shape (expressed as ratio of length to width) affects milling. A rounded grain with a low length/width ratio will be more resistant to breakage than a slender type of grain. Rice lacks the crease found in wheat grains. This enables abrasive milling to remove the bran and leave only the endosperm, greatly simplifying the milling process. The hull, which covers the rough (also known as paddy) rice, comprises 17–24% of the weight of the paddy rice. It consists of lemma and palea, awn, the rachilla, and lemmas. Varietal differences in percentage of hull affect yield of brown rice, and this in turn affects milled rice recovery (yield of white polished rice). The hull (husk) is silica-rich and indigestible for human nutrition, even after heat treatment, even though it is rich in minerals.

Cracking In producing polished white rice, the control of cracking is essential. Cracks caused by poor drying conditions after harvest, for example, will result in grain that breaks easily in milling (dehulling or polishing) producing a lower yield of head rice and consequently much lower value product. In the production of parboiled rice, rice with the hull still attached is

steamed, driving nutrients from the hull and the bran into the endosperm, inactivating enzymes that would cause rancidity, and reducing microbial load. However, after steaming, the parboiled rice must be dried slowly before it is dehulled and polished, or cracks will form with the same effect as before. Parboiled rice, despite the steaming treatment, does not require less time to cook by the consumer than ordinary white rice, because water penetration to the center of the grain is slow. Instant rice is prepared by steaming polished white rice. It is dried rapidly, forming numerous internal cracks. These cracks, not the starch gelatinization induced by steaming, allow the product to be cooked by the consumer in a few minutes because they aid water penetration. Instant rice is more physically liable to breakage in transportation than raw polished white rice, and the softer texture resulting from the cracks is unattractive to traditional rice consumers in many parts of the world.

Rice Bran Layers The bran layers (pericarp, seed coat, nucellus, and aleurone layer) contain most of the minerals (represented as ash), vitamins, fiber, fat, and much of the protein present in the rice grain (Figure 5). Considerable debate over the years has taken place over the suitability of white polished rice, compared to brown rice, in nutritionally deficient diets in some developing nations. In fact, bran also contains phytate (phytic acid), which binds to available minerals provided by brown rice, and may also bind and remove additional minerals from the gastrointestinal tract. Brown rice consumption may therefore cause a

100 Starch 80

(%)

60

40 Fiber Ash 20

Fat Protein

20

40

60

Outer layer

80

100 Center

Proportion of the kernel Figure 5 The effect of progressive surface abrasion of brown rice on content of major constituents. Reproduced from Barber S (1972) Milled rice and changes during aging. In: Houston DF (ed.) Rice: Chemistry and Technology, pp. 215–263. St. Paul, MN: American Association of Cereal Chemists; Juliano BO (1993).


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Large spherical

Crystalline Compound starch granule

Protein bodies

Small spherical

1 µm Figure 6 The rice endosperm indicating structure of spherical and crystalline protein bodies. Reproduced from Coffman WR and Juliano BO (1987) Rice. In: Olson RA (ed.) Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement. Madison, WI: Agronomy Society of America; Juliano BO (1993).

net loss of minerals to the body and in addition is susceptible to rancidity in storage (lipids and lipases still present) and more susceptible than polished rice to storage pest attack.

Rice Endosperm Rice starch granules are small (2–4 mm), polygonal, and compound, that is, many small granules are compacted together. Compositionally, rice starch varies from 0% (waxy, sticky, and glutinous) amylose to over 35%. This range is much wider than found naturally in hexaploid wheat starch. Expression of naturally occurring waxy mutants is more likely in a diploid cereal (e.g., rice, maize, and sorghum) than in a hexaploid where the effect is buffered by the other two sets of chromosomes present. Rice differs from wheat and maize in having crystalline protein bodies rich in glutelin, in addition to the prolamin-rich protein bodies common to all cereal endosperms (Figure 6). The aleurone layer (considered here as the botanical part of the endosperm, although it is processed as part of the bran) differs in thickness (usually one to seven cell layers) depending on variety. The aleurone cells contain protein bodies and lipid bodies.

Rice Embryo The rice embryo is smaller relative to the whole grain than in wheat. It contains several types of parenchymatous cells, containing protein bodies and/or lipid bodies. The main parts of the embryo are the cotyledon and the embryonic axis. The plumule and radicle are similar to other cereal grains. The high lipid content of the embryo contributes to susceptibility to rancidity in storage of brown rice.

Maize Grain Morphology and Its Effect on Handling and Wet Milling Maize is monoecious, having separate male and female flowering parts on the same plant. The female seed-bearing part of the plant (called the ear) develops off the lower-middle side of the

plant and consists of a central cob with 800 seeds attached in rows by the pedicel and covered by a husk. The pedicel acts as a conduit for photosynthetic products supplying the developing grain. The male part of the flower – the tassel – produces pollen and is at the top of the plant. The maize grain (Figure 7) is 10 times larger than small-grain cereals, an average dent maize grain weighing 300 mg. The flattened sides of the mature grain are due to pressure from the tight packing in rows on the cob. After removal of the husk, the maize grain is exposed (‘naked’ characteristic) and easily separated from the cob.

Handling Shelled maize grain (grain separated from the cob and packed in bulk) is more likely than other grains to enter export markets. A high proportion of the US maize harvest is exported, often to highly quality-conscious markets such as Japan. A typical export grain may enter the transportation system by traveling by barge down the Mississippi, entering the Gulf of Mexico for the long voyage to Asian markets. This is physically stressful on the grain, and a poorly dried grain with internal cracks is liable to breakage. This contributes to quality loss and increased susceptibility to insect or fungal attack and moisture damage. The primary criteria for successful shipment of maize are suitable endosperm texture (hard enough) and suitably controlled harvesting and drying to avoid cracking.

Wet Milling Most maize that is not fed to animals is processed by wet milling to produce starch (with many diverse applications, such as further processing high fructose corn syrup, bioethanol, or modified starch for food and nonfood industries), oil (a high-quality cooking oil), and protein or fiber-rich fractions that are used in livestock feed. The composition of these components in the grain is of course of the utmost importance. As the maize seed is much larger than wheat or rice, the relative proportion by weight taken up by the bran layers (including aleurone layer) (5%) is less than in these other cereals.

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Hull

Epidermis Mesocarp Cross cells Tube cells Seedcoat (testa) Aleurone layer (part of endosperm but separated with bran) Horny endosperm Floury endosperm Cells filled with starch granules in protein matrix Walls of cells Scutellum Plumule or rudimentary shoot and leaves

Longitudinal section of a grain of corn (enlarged -30 times)

Radicle or primary root Tip cap

Scutellum

Embryonic axis

Pericarp

Horny endosperm

Floury endosperm

Cross-sectional view

Figure 7 The structure of the maize grain – longitudinal and cross-sectional views. Reproduced from Pomeranz Y (1987) Modern Cereal Science and Technology, pp. 25–39. Weinheim, Germany: VCH Publishers.

The embryo of maize is a much higher proportion of the grain (11%, containing 33% of the oil) than in other cereals; hence, the overall oil content of the grain is quite high (typically 5%). Also, a higher proportion of the total protein is nonstorage in nature (e.g., enzymes of the embryo), so overall, the protein of maize is higher quality for human nutrition than that of wheat flour. However, maize protein, like other cereals, is deficient in lysine. High-lysine mutants (opaque-2) give more favorable amino acid balance suitable for feeding people or monogastric animals even without

additional protein sources. In practice, spread of opaque-2 varieties has been limited because in most cases, production of normal endosperm maize, and supplementation with soy protein, is easier for animal feed production. Similarly, a classic long-term selection experiment at the University of Illinois showed that the oil content of maize could be increased to extremes of over 40%. This was basically a result of increased embryo size relative to endosperm. The maize endosperm, the source of starch and most of the protein, has several interesting features. Maize types are

THE BASICS | Grain: Morphology of Internal Structure classified by endosperm hardness. ‘Floury’ is a soft endosperm that can be easily crushed to a friable powder. It is physically susceptible to storage pest (mainly insect) and fungal attack. An example of floury maize is the opaque-2 mutant. ‘Dent’ has a high proportion of floury endosperm, but some horny or hard endosperm (Figure 7) and is the most widely produced commercial maize. The ‘dent’ refers to the indentation at the top of the grain on drying when it contracts due to the floury endosperm component. ‘Flint’ maize (of which popcorn is one special type) has only horny and no floury endosperm. The top of the seed is rounded, not indented, and it is physically very hard, even after cooking meal prepared from it. The outer layers of maize (the seed coat in particular) contribute the color, which is white or yellow in nearly all commercial maize production. Mass production of maize for feed and industrial use, for example, in the United States, is predominantly yellow dent. Some white dent is produced for breakfast cereal (e.g., corn flake) production (which follows maize dry milling). The carotenoids (xanthophylls) of yellow maize are nutritionally important and also, in poultry feed, contribute yellow color to egg yolks and to skin and fat of meat poultry. People in regions where maize is a daily food staple may have strong color preferences; for example, in southern Africa, white (dent) maize is strongly preferred because yellow maize is historically associated with flintiness (although there is no genetic relationship).

Maize Dry Milling This also requires a physically sound clean sample with appropriate hardness. Dry milling in the United States usually implies use of white maize (a minor proportion of total US production) to make endosperm chunks, which may be steamed and flaked to make corn flakes. Larger dry milling industries exist to serve the needs of maize tortilla production (Mexico) and maize porridge production (a staple diet in much of sub-Saharan Africa) requiring maize meal.

Barley Grain Structure and Effect on Malting The barley grain is similar in structure to the wheat grain. For a diagram and further information on this topic, see elsewhere in this encyclopedia.

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binding needs to be loosened by soaking in a solution, such as in alkaline wet milling, where the physical properties of the starch may be affected. Care should be taken that the fractions separated still achieve proper functionality in the intended use. For a useful further overview of the developmental aspects of cereal grain structure, the reader may refer to Evers and Millar.


• •

Draw a ‘typical’ cereal grain representing the major anatomical features common to all cereal species. Explain how starch, protein, and oil are stored in different cereal grain species.


• • •

Investigate the concept of domestication for a selected cereal grain crop, showing the necessary and desirable changes from wild relatives to modern cultivated plants. Design an ideal maize grain for different processing applications (e.g., bioethanol and high oil), and indicate what genetic approaches have been and could be taken to produce it. The bran is often discarded after processing. What unusual and interesting variants in bran compositional features exist (e.g., in pigmentation), and how could these be better exploited for value-added uses?

See also: Barley, Rice and Maize Processing: Barley: Malting; Maize: Wet Milling; Beverages from Grains: Beverages: Distilled; Breeding of Grains: Maize: Breeding; Food Grains and the Consumer: Fortification of Grain-Based Foods; Genetics of Grains: Maize: Genetics; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Cereal Grains: Rice: Overview.

Overview

Further Reading

The same principles apply when considering the structure and utilization of other grains, such as sorghum, millets, oats, or even the pseudocereals buckwheat and Amaranthus. First, consideration should be the required product, flour, separation of starch/protein/oil, or malt, which drives the choice of process – wet or dry milling or malting. The size and shape of the grain, particularly the dimensions of the outer layers will mostly affect dry milling. In some cases, the seed is extremely small (e.g., with Amaranthus) and dry milling flour yield will be low. For such crops, selection for larger grain size can greatly increase flour yield. For wet milling, the fraction of most value (usually starch) will drive the design of the separation process. Usually, the starch–protein

Barber S (1972) Milled rice and changes during aging. In: Houston DF (ed.) Rice: Chemistry and Technology, pp. 215–263. St. Paul, MN: American Association of Cereal Chemists. Coffman WR and Juliano BO (1987) Rice. In: Olson RA (ed.) Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement. Madison, WI: Agronomy Society of America. Dornez E, Holopainen U, Cuyvers S, et al. (2011) Study of grain cell wall structures by microscopic analysis with four different staining techniques. Journal of Cereal Science 54: 363–373. Evers AD and Bechtel DB (1988) Microscopic structure of the wheat grain. In: Pomeranz Y (ed.) Wheat: Chemistry and Technology, vol. 1, pp. 47–95. St. Paul, MN: American Association of Cereal Chemists 3rd edn. Evers T and Millar S (2002) Cereal grain structure and development: Some implications for quality. Journal of Cereal Science 36: 261–284. Hoseney RC (1994) Cereal Science and Technology, pp. 1–28. St. Paul, MN: American Association of Cereal Chemists 2nd edn.

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Jaä¨skelaïnen AS, Holopainen-Mantila U, Tamminen T, and Vuorinen T (2013) Endosperm and aleurone cell structure in barley and wheat as studied by optical and Raman microscopy. Journal of Cereal Science 57: 543–550. Juliano JB and Aldama MJ (1937) Morphology of Oryza sativa L. Philippines Agriculturalist 26: 1–134. Juliano BO and Bechtel DB (1985) The rice grain and its gross composition. In: Juliano BO (ed.) Rice: Chemistry and Technology, pp. 17–57. St. Paul, MN: American Association of Cereal Chemists 2nd edn. Pomeranz Y (1987) Modern Cereal Science and Technology, pp. 25–39. Weinheim, Germany: VCH Publishers. Watson SA (2003) Structure and composition. In: Watson SA and Ramstad PE (eds.) Corn: Chemistry and Technology, pp. 53–82. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.cerealsdb.uk.net/cerealgenomics/WheatBP/Documents/DOC_Milling.php – Website from School of Biological Sciences, Bristol University, with interesting images information related to wheat processing. http://www.namamillers.org/education/ – Website of the North American Millers’ Association has useful information on the relationship between grain structure and milling for various cereal grains. http://www.qaafi.uq.edu.au/rice-grain-storage-protein-composition – A presentation by Dr. Daniel Waters of Southern Cross University on aspects of rice grain and protein structure and composition.

Grain and Plant Morphology of Cereals and how characters can be used to identify varieties J Wyatt, NIAB, Cambridge, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

An introduction summarizing the definition of plant morphology, how it has evolved, and how it can be used to identify cereal varieties A table giving a list, in order of importance, of the species covered in the manuscript A general section outlining the characters that are shared by the different cereal species Specific sections for each species on general growth habit and inflorescence How specific parts of a mature grain can be used to identify many characters Drawings and photographs to illustrate the text Identifies some of the differences between the Triticum species

General Cereal Morphology

Learning Objectives

•

The article can only give a brief introduction to cereal plant and grain morphology and how the major characters can be used in the varietal identification of cereals. It is hoped that this article will lay a foundation for encouraging the student to partake in further studying cereal plant and grain morphology and how that knowledge gained can be used to research the many other factors that influence the growing of cereals across the world.

Introduction The definition of plant morphology is the physical appearance of a plant. It can be applied to any species and involves a detailed study of vegetative and reproductive characters in order to form a profile of a plant, which can be used to make general comparisons of plant species displaying a similar structure or detailed comparisons within a species to identify varieties (cultivars). Identifying varieties and species of plants or grains by morphological means is still the main method used in cereal breeding and varietal identification and provides the basis for the definitive description of a variety. Plants within a species share a similar genetic base, and thus, it is possible to group them into a taxonomic family. ‘Cereals’ is a generic term used to encompass the major grain-producing species whose products are some of the world’s most important staple foods and have been since man started growing them for food some 12 000 years ago. A cereal variety is a population of plants that can be identified as being clearly distinguishable from another population by stable inherited morphological characters. Wheat (Triticum aestivum), rice (Oryza sativa), and maize (Zea mays) account for over half of the cereals consumed worldwide. Cereals sit in the family Poaceae (synonymous with Gramineae). While cereals differ in detail in the way the Encyclopedia of Food Grains, Second Edition

characters of each species are expressed, they share a general commonality in growth habit and flowering parts. By understanding the morphology of each species, it is possible to use it to identify the varieties (cultivars) that exist in each classification. Recognition of the importance attached to identifying varieties is highlighted by the existence of UPOV (The International Union for the Protection of New Plant Varieties). The test guidelines put together by the 71 members of UPOV provide useful information of the major characters used in establishing the morphological identification of the different varieties of cereal species. The following section begins with a description of the main morphological characters common to all the cereal species and is followed by further sections specific to each species. Illustrations and photographs are used to help in the identification of the characters described.

Cereals are annuals within the family Poaceae (synonymous with Gramineae). The method of production of the cereal species is dependent on the climatic/soil conditions, whether the crops are planted as seeds or as small plants, and whether the variety requires a cold period for initiation of the flowering process (vernalization) and subsequent development of the grain. Cereals are classified as monocotyledons (one embryo leaf per seed) and share the following characters: an adventitious root system where numerous roots develop below the surface from the stem, the early development of stems from the lower leaf sheaths, and a series of alternating leaves on the stem that are linear in shape and display parallel veins within the leaf blade. The flower structure is arranged in threes or multiples of three (trimerous). The distribution variation, that is, length, width, curvature, and the frequency of different morphological characters, is used to distinguish between different varieties. The morphology of rice and maize shows some variation from other cereals, having evolved over the centuries by adapting to suit the climate and locality in which they grow. Examples of this are the hollow stems of rice that can store air and the brace roots of maize that act as additional anchorage. The typical growth habit of (a) maize and (b) other cereals is shown in Figure 1. Once the grain has germinated below ground, the sheath (coleoptile) protecting the first leaf emerges above the soil surface. As the plant grows, the leaves develop from a growing point, which remains below the soil surface, with new leaves emerging from each subsequent leaf sheath. By the fifth to sixth leaf stage, side shoots (tillers) will start to emerge from the base of the first leaf (axil). These tillers will go on to form new leaves in the same manner as those of the first leaf (Figure 2). The leaves on the primary and secondary tillers grow in a tubelike structure and break out as a leaf blade at the node. It is at this juncture that the auricles are found (Figure 3). If

http://dx.doi.org/10.1016/B978-0-12-394437-5.00009-7

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THE BASICS | Grain and Plant Morphology of Cereals and how characters can be used to identify varieties

(n) (a) adventitious root system (b) basal leaf sheath if present (c) leaf sheath (d i) early leaf formation (d ii) twisted leaf of barley (e) tiller emerging from leaf sheath (f) node (g) auricles if present (h) ligules if present (i) leaf blade (j) stem (k) flag leaf (l) neck (m) ear or panicle

(j) (a) adventitious roots (b) additional brace roots (c) soil surface (d) secondary tiller (e) leaf blade margins either straight or lobed (f) flag leaf (g) leaf node auricles absent (h) silk (i) leaves which cover emerging cob (j) tassle

(f) (i)

(e)

(m)

(l) (k)

(j)

(i) (h) (g)

(g)

(h) (f)

(e)

(e)

(e) (d)

(d i) (d ii)

(c)

(b) (c)

(b) (a)

(b)

(a)

Figure 1 (a) Typical growth habit of maize. (b) Typical growth habit of a cereal.

(a) auricle if present (b) ligule if present (c) node (d) stem/tiller

(d) (c)

(b) (d) (a) (d)

(d)

Figure 2 Early stem (tiller) formation.

(a)


hairs present rice (numerous) wheat (sparse) triticale (occasional)

hairs absent, e.g., barley

(b)

no auricles oats maize triticum turgidum secale x secale

(a)

(c)

Figure 3 Auricles and the difference between cereal species.

Weak (a)

Weak (b)

Strong

Strong

Photo 1 (a) Flag leaf glaucosity in winter wheat. (b) Ear glaucosity in winter wheat.

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present, they encircle the stem and are thought to provide a barrier within the node to prevent moisture and fungal pathogens from entering. Generally, the stems develop as a hollow stem and continue elongating until the uppermost leaf appears (flag leaf), from which the inflorescence emerges. The number of leaves on the stem is dependent on the eventual height of the plant with the ultimate leaf (flag leaf) usually smaller than the other leaves. The exterior surface of a leaf is covered by the cuticle, a structure that helps prevent moisture loss and the penetration of the external surface by dirt and harmful microorganisms. Those plants that display a

(a)

Pigment absent (c)

high level of gray coloration have an extra layer of a waxlike material (epicuticular wax) on the surface, giving the plant an additional defense mechanism against moisture loss. Color differences due to a difference in glaucosity can be observed in different species and in different parts of the plant, ranging from green to blue gray in the leaves and stem (Photo 1(a) and 1(b)). It is also possible to observe different levels of glaucosity on the glumes and grain. Anthocyanin coloration (pigment), if present, is found in different levels of intensity and at different locations within the plant, depending on species (Photo 2(a)–2(c)).

(b)

Pigment present

Photo 2 (a) Pigment on grain of barley. (b) Pigment on anthers of maize. (c) Basal leaf sheath barley.


55

(h)

(g)

(f)

(b)

(d) (a)

(a) glumes (b) lemma (c) rachis (d) ovary (e) lodicule (f) stigmas (g) filament (h) anther

(e)

(c)

Figure 4 Inflorescence of a cereal floret.

Each species shares common ground in having an inflorescence made up of a series of florets attached to a central stem, which contain (in all species) the male and female reproductive organs (Figure 4). Wheat, rye, triticale, durum wheat, and barley have a central stem (rachis) with a series of spikelets attached to it. Each spikelet is made up of several florets, and once fertilization has taken place, these florets develop into individual grains arranged alternately on the stem (Figure 5). The first rachis segment attaches the ear to the stem. Rice, maize, and oats share a similar inflorescence with a series of branches forming from the uppermost node (panicle). Panicles can be one-sided (unilateral), spreading, or triangular (equilateral) in appearance (Figure 6) with a series of florets lying along the branches. Maize has a separate male and female inflorescence, where numerous male florets (tassel) are to be found at the apex of the plant and the female florets (silk) located within the stem node(s) (Photo 3). All cereal species are able to self-pollinate with male and female flower parts on the same plant (monoecious), although pollen is accepted from other sources if their own pollen supply is scarce. Once fertilization has taken place, the front (ventral view) of the developing caryopsis is protected by the palea, the back (dorsal view) by the lemma, which overlaps the palea at the side. In wheat and oats, the whole structure is protected further by the glumes. In order to assist pollination, two swollen structures (lodicules), on either side of the ovary, prise open the lemma and palea. Once fertilization has taken place, the lodicules shrivel but remain attached to the lemma base. For species other than maize, the developing grain may have a bristle of varying lengths extending from the lemma.

The structures are known as awns (barley) or beards (wheat, durum, rye, and triticale) if they are present on each spikelet. Where they appear in a reduced form on the apex or upper part of a wheat ear, they are referred to as scurs. Once fertilization has taken place and providing that no outside influence affects the structure, the grains will go on to produce viable seeds. Each caryopsis (grain) is made up of (i) the embryo that contains all the structures essential for development and (ii) the endosperm that provides nutrients essential for the germinating seed, mostly in the form of starch. The whole is held in a covering (pericarp) and remains dormant until the right conditions for germination are present, normally moisture and the optimum temperature.

Species Specific Plant and Grain Morphology Rice (Oryza sativa) (Table 1(a)) In terms of human consumption, rice is the most important cereal grown. There are two subspecies: O. japonica that produces a short-grained sticky rice and is more tolerant of temperate climates and O. indica that produces a longer-grained, nonsticky type of rice that has a high moisture and temperature requirement and is more suited to tropical conditions. There are two main types: rice that grows on flooded land (paddy) and deepwater rice that requires more than 50 cm of rain for at least 1 month (Photo 4). Deepwater rice varieties are capable of floating in depths from 80 to 100 cm and, by having longer leaves than the traditional tall paddy varieties, ensure that a supply of oxygen is available to sustain the whole plant. As the stems elongate, they are capable of producing their own roots (nodal roots) and becoming independent from the primary

56


(c) (a) first rachis segment (b) rachis segment varies in length and curvature (c) sterile spikelet (d) glumes (e) collar

(d)

(b)

(a)

(b) Note: rachis segment of wheat, durum, triticale, and rye follow similar format

Single line of rachis segments of maize “cob,” showing truncation of the rachis

(e)

(a)

Figure 5 (a) Rachis segments of barley. (b) Single line of rachis segments of maize ‘cob,’ showing truncation of the rachis.

ear e.g., wheat barley

Figure 6 Different forms of inflorescence.

one-sided panicle (unilateral) e.g., oat many-branched spreading panicle e.g., rice


57

stem. The stems are especially adapted to contain a large number of air cells that allow oxygen to pass through to the root system. A typical rice plant has a hollow stem and will attain an average height of 1–1.8 m. Depending on environmental conditions, the fertility of the soil, and the variety, it can grow to 5 m in length. Rice is the only cereal species that is germinated before planting and set out once the seedling has a minimum of

three leaves. The adventitious roots develop from underground stem nodes and form the basis of the root system. Whether the root or the shoot emerges first is determined on whether germination takes place in aerobic conditions (when the root will appear first) or in flooded conditions (anaerobic) when the shoot will appear first. As the main (primary) tiller develops and if growing conditions are favorable, a secondary tiller will grow from the primary tiller, followed by a third (tertiary) tiller. The earlier a variety matures, the shorter the plant and the distance between internodes. A typical flag leaf encloses the emerging panicle. The flower (floret) structure differs from other cereals in having six well-developed stamens with short filaments but follows other cereals in having a pistil with a feathery stigma and lodicules (Figure 7). Depending on the variety, the color of the inflorescence and the subsequent grain can be gold, brown, light to dark red, purple, or black. Virtually, all varieties show basal leaf sheath coloration and colored auricles, which can extend into the lemma tip and keel.

Photo 3 Maize plant.

Photo 4 Rice crop.

Table 1 List of the cereal species covered by this article in order of their importance worldwide. The common name is given first, followed by the Latin declination and a further column, which highlights additional information on the usage of the species. It will be noted that in terms of human consumption, rice is the most important cereal but that maize is the most important in terms of worldwide production Species (common name)

Latin name

Usage Most important cereal in terms of human consumption

(1(b)) Maize

Oryza sativa (subsp. O. indica and O. japonica) Zea mays

(1(c)) Wheat (1(d)) Durum (1(e)) Triticale

Triticum aestivum Triticum durum Triticale (X Triticosecale)

(1(f)) Rye (1(g)) Barley

Secale X cereale Hordeum vulgare

(1(h)) Oats

Avena sativa

(1(a)) Rice

Most important in terms of worldwide production but not all the grain produced goes for human consumption Second to rice in terms of human consumption. Both winter and spring types exist Second most important Triticum species after wheat Hybrid of wheat (♀) and rye (♂) has the yield of wheat with the additional advantage of tolerance to diseases and environmental changes Suited to much poorer soils than wheat and durum Ranks fourth in importance and used primarily as a food source and as a raw material in the brewing/distilling industry A higher tolerance to cool conditions and rainfall

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(f)

(g)

(d i) (e) (c)

(d)

(a) pedicel (b) glumes (c) palea (d) lemma (d i) lemma nerves (e) feathery stigma (f) six anthers

(b)

(a)

Figure 7 Typical floret of rice.

Maize (Zea mays) (Table 1(b)) In terms of the volume grown, maize is the most important cereal species, but much is used for purposes other than food, which places it second to rice in terms of worldwide staple food consumption. It displays major differences when compared with the other species covered in this article. The main stem grows to 1.2–3 m in height. In the early stages of development, a mass of underground adventitious roots are produced just below the soil surface, and as the plant grows, a series of additional ‘brace roots’ (Photo 5) emerge above the surface from the two lowermost leaf nodes. Although the brace roots have the facility to grow quickly and provide stability for the plant, maize is still very susceptible to wind damage. Depending on the eventual plant height, an average of twenty alternate leaves will develop up the stem. Maize is classified as a hermaphrodite plant in having the male and female reproductive organs sited in different locations on the same plant. The staminate (male) inflorescence (tassel) develops at the apex of the plant, normally after the emergence of the 14th or 15th leaf, as a panicle producing a series of spikelets in which fertile and sterile florets sit. The pistillate (female) inflorescence (silk) lies normally in the leaf axils of the 11th–13th leaves (Photo 6(a) and 6(b)) with pairs of spikelets sitting on a much truncated rachis. From each silk, a series of tubelike structures emerge with small leaves, which will form the covering of the cob at maturity (husk leaves). At one end is the undeveloped grain and at the other a feathery

Photo 5 Brace roots of maize.

style. Pollen is released from the male anthers in the tassel and dispersed by the wind (anemophilous dispersal). As a result of the relative heaviness of the pollen, it drops the short distance to the silk below or onto a neighboring plant. Once fertilization has taken place, each individual maize grain develops on the shortened rachis, the whole structure forming the cob (Photo 7). The color of the cob is related to the variety and can vary from white, to yellow, to orange, to red, to purple, to brown, to black, to variations of the color range within the cob.

Wheat (Triticum aestivum) (Table 1(c)) Wheat is grown in all the temperate climates of the world and is second to rice in terms of human consumption. True winter wheat varieties require a period of cold to initiate the reproductive stage of development (vernalization). Spring wheat varieties do not need a cold period for ear formation although they can respond to cold by flowering earlier. Wheat has a higher protein content than any other major cereal, and a further distinction is made in the type of flour produced. Hard milling varieties produce flour suitable for bread production. Soft milling varieties are used in the production of commodities such as animal feed or biscuits. Because winter wheat has a longer growing season, they are usually denser in ear formation than spring wheat (Photo 8). The average height of wheat is 75–150 cm, and unlike other cereal species, the stems can be solid and hollow (Photo 9). The wheat ear is made up of a series of spikelets arranged alternately on the central rachis and each one is made up of a cluster of six florets (Figure 8). Close study will identify the different structures that form the spikelet, the most important being the lower glume, which lies opposite the lemma with the


Tassle

59

Silk

Photo 6 Tassel and silk of maize.

Lax

Medium (profile view)

Dense

Photo 8 Ear density wheat.

Photo 7 Maize: structure of a ‘corn cob.’

longer beak. In order to ensure consistency when assessing their morphological characters, only the lower glumes from spikelets in the mid third of the ear are examined in detail (Figure 9). On studying the exterior surface of the glume (dorsal view), distinct differences can be observed between varieties. These include the length and curvature of the lower glume beak and the width and shape of the lower glume shoulder.

60


The wheat grain can be separated by shape into those that are round, elliptical, or ovate. At the opposite end to the embryo, ‘brush hair’ may be identified. If present, a distinction can be made as to whether the hair is short or long in length (Figure 10).

Durum Wheat T. turgidum (syn T. durum) (Table 1(d)) Commonly known as durum wheat and developed through artificial selection many thousands of years ago, it is the hardest milling variety of all the wheat species and used extensively in the production of pasta. It grows well in countries bordering the Mediterranean where precipitation is low and temperatures high. Similar in height (1.2–1.5 m) and appearance to bearded wheat, but usually with a shorter denser ear (Photo 10), durum wheat is characterized by having well-developed, firm glumes and a pronounced keel along the glume length (Figure 11(a)). The lemmas have a rounded appearance due to the absence of a keel. The yellowish, brown-colored caryopsis is often ridged. Brush hairs are either absent or very short (Figure 11(b)).

Triticale (Table 1(e))

Sections through stems of wheat straw. (cut midway between ear and first node) Photo 9 Straw wall thickness.

Triticale X secale was developed as a species in the nineteenth century by crossing rye with wheat. It can grow to an average height of 75–150 cm, but does not tiller as much as wheat and is used mainly as a fodder product. However, it has the potential to produce a yield similar to that of some wheat and can be grown in poorer conditions more suitable for rye production. Similar in height and density to wheat, the apical spikelet is sterile (Photo 11). At the top of the stem just below

(e) Floret 6 Floret 5 Floret 4

(d ii)

(d i)

Floret 1 Floret 2

(c ii)

(a i) lower glume: always opposite the lemma with the longer lemma beak (a ii) upper glume (b i) lower lemma (b ii) upper lemma (c i) palea (c ii) palea (d i) lemma - wheat caryopsis between lemma and palea (d ii) lemma (e) apical spike (f) rachis

(c i)

(b i) (b ii)

(a ii) (a i)

(f)

Figure 8 Structure of a wheat spikelet.


(a)

Extent of glume beak

Extent of shoulder (b)

(d)

(e)

(f) (c)

(a) lower glume beak (b) shoulder (c) keel (d) papery membrane not used in shoulder width assessment (e) narrow wing (f) broad wing (g) basal hairs

(g)

Figure 9 Structure of the lower glume.

brush hair long brush hair short

Round Figure 10 Wheat grain, shape, and brush hair.

Ovate

Elliptical

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THE BASICS | Grain and Plant Morphology of Cereals and how characters can be used to identify varieties Barley (Hordeum vulgare) (Table 1(g))

Photo 10 Triticum turgidum (syn T. durum).

the first rachis, it is possible in some varieties to observe neck hairs. Glumes are of a thin papery structure and long and narrow in shape. They may have hairs or weak ‘toothlike’ structures along the lemma margins (Figure 12(a)). In common with durum and rye, the glumes are strongly keeled and have a much reduced shoulder. The elliptical caryopsis is gray-brown in color and often ridged with a prominent embryo. Brush hairs are present and short in length (Figure 12(b)).

Rye (Secale X Secale) (Table 1(f)) Rye is a species that has been in cultivation for many centuries and is the main cereal for bread production in parts of North and Eastern Europe as it can withstand the cold better than wheat and tolerate poorer growing conditions. It is also an important forage crop. Depending on whether it is grown as a fodder crop or for human consumption, rye will reach an average height of 1.2–1.8 m. Until the caryopsis develops, the ear has a narrow flattened appearance, and then, as the ear fills, the caryopsis becomes highly visible between the lemma and palea (Photo 12). The lemmas are strongly keeled and have a series of ‘toothlike’ structures along the margins and keel (Figure 13(a)). The papery glumes are very narrow and have no broad wing. The elliptical caryopsis is greenish brown and strongly ridged and has a prominent embryo. Brush hairs are present and of medium length (Figure 13(b)).

Barley was one of the first cereal species to be cultivated, and the grain has a wide variety of uses, from providing staple food for humans and livestock to the production of certain forms of alcohol. It is grown widely across the more temperate zones of the world and ranks fourth in terms of food production. As a species, barley has more morphological characters that are useful in determining varietal identity than any other cereal. Depending on their tolerance to winter conditions and whether they need a period of vernalization, barley varieties are also classified as either winter or spring types. Winter barley in particular has small straight hairs at right angles to the stem (basal leaf sheath hairs) on the lowermost leaves (Figure 14). It is important to observe the character at the optimum growth stage (five to nine tillers) as assessment is more difficult once the lower leaves wither and die. In common with other cereals, the presence of pigment is a major character in barley variety identification. Levels of pigment vary in intensity and can be subject to environmental factors such as sunlight and drought (Photo 13). An ear of barley is classified as being a 6-row/4-row or 2-row, depending on whether each potential grain site has developed and whether the developed grain has the characteristic awn present (Photo 14). The size and shape of a barley grain are determined by variety and environmental influences, although six-row barleys have small asymmetrical lateral grains caused by their proximity to the median grain. A conventional two-row barley has two rows of undeveloped grain running up through the center of the ear (sterile spikelets), either parallel to each other or diverging out from the center. Where sterile spikelets are so reduced in size to be barely visible, they are classified as being ‘deficiens’ (Photo 15). The grains sit on a rachis with the first rachis segment located in a collar-like structure at the top of the stem neck (Photo 16); the width, length, and curvature of the collar provide further identifying characters. The uppermost part of the stem immediately below the collar is the neck. Once the grain has been fertilized, the ventral surface of the developing grain is protected by the palea, while the lemma protects the dorsal surface and overlaps the palea on either side. Sometimes, the lemma and palea do not meet properly at the sides (gape), and it is possible to see the kernel within (Figure 15). Barley grains have two distinct views: the ventral view that can be distinguished by the ventral furrow running the length of the grain and the dorsal view that presents a number of ridges (lemma nerves) on its surface (Figures 15 and 16, respectively). Located on the dorsal side are the two-side (lateral) lemma nerves, which extend down and form the margins of the awn and the median (central) nerve. If pigment is present, it will be evident in these nerves. On some varieties, small thornlike structures (spicules) will be present. Spicules occur frequently on the margins of the awns and sometimes on the inner lateral nerves. They can be sparse, one or two per nerve, or numerous and can extend out from the lateral nerves onto the surface of the lemma on the lateral nerves at the awn end (Photo 17).


(a) glumes (narrow shoulder) (b) lemma (not keeled) apical floret present Note: short ear, long awns

(b) (b)

(a)

(a)

(a)

Glume long and narrow firm, strongly keeled throughout

Caryopsis elliptical, often ridged, brush hairs short or absent, yellow/brown in color

(b)

Figure 11 (a) Triticum turgidum (syn T. durum) spikelet. (b) Triticum turgidum, glume and caryopsis.

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64


Note hairs on stem neck Photo 12 Secale X secale (rye).

Photo 11 Triticale X secale.

(a) glumes; long and narrow, thin and papery, strongly keeled throughout, glume shoulder much reduced (b) lemma; slightly keeled, may have hairs and weak teeth along lemma margin and keel

(a) (b) Glume Note: strongy keel, may have weak hairs (b) (a)

(a)

Figure 12 (a) Spikelet of Triticale X Triticosecale. (b) Triticale X Triticosecale.

Caryopsis Elliptical, often ridged, brush hairs present. (a) prominent embryo greyish brown in color


(a) glume; very narrow and papery, no broad wing (b) lemma, strongy keeled, strong teeth along margins and keel

(b)

(a)

(a)

Caryopsis Glumes very narrow papery, no broad wing

elliptical, strongly ridged, brush hairs present, greenish brown color (a) prominent embryo

(b)

Figure 13 (a) Spikelet of rye (Secale X secale). (b) Rye (Secale X secale).

(a)

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66


(b)

(a) basal leaf sheath hair (b) hairs on base of leaf blade

(a)

Figure 14 Barley plant showing basal leaf sheath hairs, and base of leaf blade.

THE BASICS | Grain and Plant Morphology of Cereals and how characters can be used to identify varieties At the base of the grain and lying within the ventral furrow is a small rodlike structure covered in hairs (rachilla) and used extensively in the identity of varieties. In some varieties, there are an additional three distinct linked characters to observe in barley grain. It is rare for these characters to be separated, so if one is present, then the other two will also be present. They are fence hairs (ventral view) that lie in a vertical position at the base of the grain and ventral furrow hairs that are extremely small white hairs lying along the edge of the ventral furrow and often extending beyond the rachilla. The third linked character

is observed on the dorsal side at the awn end, where it is possible to identify very small protrusions that create a rough surface on the areas between the lateral and median nerves (sharkskin). It should be noted that this area may also be associated with many rows of spicules.

6 row

2 row

Photo 13 Range of pigmentation in different varieties of barley.

Deficiens Photo 15 Barley sterile spikelet attitude in two-row varieties.

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Photo 14 Ears of barley showing different structures between a tworow barley and a six-row barley.

Divergent

Parallel

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Platform collar

Cup collar

Photo 16 Barley first rachis segment and collar.

(e) (a) lemma (b) palea (c) ventral furrow (d) lemma base (attachment point to rachis) (e) broken off awn (f) rachilla (g) gape may not always be present (h) inter glume hair

(c)

(a)

(b)

(g)

(f)

(h) (d) Figure 15 Ventral view of grain of barley.


(a)

(b)

(g)

(c)

(d)

(a) original attachment to rachis (b) embryo (c) median nerve (d) lateral nerves (e) outer lateral nerves (note spicules) (f) broken off awn (g) lemma (h) area where sharskin is observed (if present) Figure 16 Structure of a barley grain dorsal view.

(d)

(h)

(e) (f)

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THE BASICS | Grain and Plant Morphology of Cereals and how characters can be used to identify varieties The uppermost node (upper culm node) from which the flag leaf emerges is a swollen thickening of the stem and shrinks on maturity. Fine hairs above and below the node are present in some varieties. The branches of the panicle emerge from swollen nodes on the flowering stem with single spikelets interspersed along the main branches (Photo 18). A single spikelet will develop into one (primary) that is always the largest grain and can develop into second (secondary) and third (tertiary) grains, each attached to the other by a rachilla. Each caryopsis is protected by a lemma and a palea, the whole protected by papery glumes (Figure 17). Awns if present emerge from the median nerve of the lemma of the primary grain. At the base of each grain, grain basal callus hair may be present at either side. The rachilla can vary in length from short to long and vary from plain to strongly grooved.

Conclusion Photo 17 Barley: dorsal view showing spicules on inner lateral nerves.

From the earliest times, man recognized the different cereals as an important food source. The crops they produced were subject to continual change and selection over the decades resulting in the gradual improvement of yield and quality. At the same time, others were recognizing similarities between plants and evolving a system that placed them into taxonomic groups. The more detailed and precise the study of plants and their morphology became, the more demand it placed on using a greater range of identifying morphological characters. It was this assessment of morphological characters that gave the discriminatory evidence essential for laying the foundation for varietal identification, which could in turn be used for establishing variety ownership through the introduction of plant variety rights. Modern techniques such as the use of DNA fingerprinting are already being used to determine varietal identity, but for the purposes of UPOV and plant breeders’ rights, they can only be used as an addition to the use of morphological characters.

Equilateral Unilateral (spreading) (one sided)

Photo 18 Oat panicles.


• Oats (Avena sativa) (Table 1(h)) Oats are an important crop providing food for human consumption and livestock and are particularly useful in NW Europe where they tolerate the cooler and often moister conditions during the growing season. On average, an oat plant reaches a height of 1.2–1.8 m, but oat characters such as height and the frequency of awns are liable to be affected by environmental factors. Hairs on the basal leaf sheaths are present in some varieties (Figure 14) and on the margins of the leaf blade. They are best seen at leaf emergence when they vary from a few at the base to half the leaf length.

• •

•

Using the UPOV technical guidelines for a cereal species of major importance within your country, identify the characters that could be used to generate a description for the most widely grown variety. Select a species of lesser importance and write a description for a variety based on the UPOV guidelines for the species. Using the UPOV guidelines, select one of the species grown widely within your country and study in detail those characteristics not covered in this chapter. Write a summary as to how these additional characters could be used to produce a detailed description of a variety, illustrating with photos or drawings where necessary. A characteristic of cereal species is the presence of glumes. Write a paper on the importance and evolution of the glume to each.


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Spikelet structure

(a) glumes (b) primary grain (c) secondary grain (d) awn (e) basal callus hair present, 1-2 per side of in tufts (f) lemma (g) palea (h i) rachilla (note length) (h ii) rachilla medium long in length (i) basal callus

(a) (b)

(d)

(c)

(i) (i)

(e)

Primary grain characters (h i)

(g)

(f)

(f)

(h ii) (g)

Figure 17 Oat spikelet and grains showing spikelet structure.


•

•

Currently, variety descriptions are produced using methods that have remained largely unchanged since their introduction. Some biotechnological methods have now been incorporated into existing systems. Using a species with which you are familiar, identify any available biotechnology methods and undertake research to assess the advantages that could be gained by their inclusion. Could varietal identification be carried out partly or wholly by biotechnology?

See also: Grain Marketing and Grading: Identification of Varieties of Food Grains; The Basics: Grain: Morphology of Internal Structure; Taxonomic Classification of Grain Species; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Detailed descriptions of characters for varietal identification can be found in the UPOV Guidelines under the following headings: (upov.int/test guidelines/choice of language). The guidelines are available worldwide and provide a standardized format for the characters used in varietal identification.

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Barley (Hordeum vulgare) UPOV TG/19/10. Durum wheat (Tritium turgidum syn T. durum) UPOV TG/120/3. Hervey-Murray CG (1980) The Identification of Cereal Varieties. Cambridge: Cambridge University Press. HGCA: Milling wheat: quality control criteria and tests. Ikisan: morphology of rice. Ikisan: morphology of maize. Institute of rice research – www.irri.org. Maize (Zea mays) UPOV TG2/7.

NIAB: Botanical descriptions of varieties – [email protected]. Oat (Avena sativa) UPOV TG 20/10. Rice (Oryza sativa) UPOV TG16/8. Rye (Secale x secale) UPOV TG58/6. The biology of maize – www.ogtr.gov.au. The biology of Triticum turgidum – www.inspection.gc.ca/triticum turgidum. Triticale (triticale) X triticosecale UPOV TG/3/11. Wheat (Triticum aestivum) UPOV TG/3/11.

The Cereal Grains

Contents An Overview of the Family of Cereal Grains Prominent in World Agriculture Cereals: Domestication of the Cereal Grains Maize: Overview Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’ Durum Wheat: Overview Rice: Overview Wildrice, Zizania: Overview African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses Sorghum Grain, Its Production and Uses: Overview Rye Grain: Its Genetics, Production, and Utilization Triticale: Overview Oats: Overview Coix: Overview Millet Pearl: Overview Millet Minor: Overview Teff: Overview

An Overview of the Family of Cereal Grains Prominent in World Agriculture CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

•

Colloquially, we often use the word ‘cereal’ to mean a breakfast cereal, such as cornflakes. The manufacture of ‘cereal’ in this narrow sense is described in this encyclopedia, but more broadly, the term ‘cereal’ applies to the many grain genera that are ‘flowering plants of the grass family (Poaceae or Gramineae), whose seeds are used as food.’ It may be difficult to imagine wheat, for example, as a flowering plant, but wheat flowers are illustrated in Figure 1. (And do not get confused between this flower and the flour of similar-sounding name, meaning crushed grain.)

• • • • • •

Cereal grains are produced by flowering plants of the grass family. Wheat, rice, and maize (corn) are the major cereals, each produced in quantities of about 600 million tonnes annually. Other cereals are barley, rye, triticale, oats, sorghum, and the millets. Cereal grains have a high proportion of starch, present as distinct granules in the floury endosperm. Cereals are a valuable source of protein; their low fat content is mainly in the germ (embryo), from which the new plant emerges during germination. Processed foods from cereals include a wide range of bread types, pasta, noodles, breakfast cereals, beer, and porridge. Cereals are major sources of animal feed (grain and plant) and fuel for transport.

Learning Objective

•

To achieve understanding of the agriculturally significant species and uses of cereal-grain family.


‘Seed’ or ‘Grain’? The name ‘cereal’ derives from Ceres, the Roman goddess of grain. The words ‘seed,’ ‘kernel,’ and ‘caryopsis’ are also used to denote cereal grain. In addition, the term ‘corn’ is sometimes used for the grains of cereal species in general, but more often (especially in the United States), the word ‘corn’ denotes the cereal species maize, also known as ‘Indian corn.’ Wheat and barley seeds are shown in Figures 2 and 3, as they appear by scanning electron microscopy.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00006-1

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THE CEREAL GRAINS | An Overview of the Family of Cereal Grains Prominent in World Agriculture

Figure 1 A flower of wheat. The outer glumes have opened wide. Anthers are seen above the feathery style, which will receive pollen grains shed by the anthers.

Cereal grain serves two contrasting functions: 1. For the plant, the mature grain is solely of significance as a seed, that is, the means by which the species is perpetuated. When the plant has died, the ongoing life of a cereal seed is in its embryo or germ. Most of the grain’s mass is taken up by the endosperm (Figure 4), which is the storage organ of the grain. It contains the starch and protein for the ‘rainy day’ when moisture will trigger the dormant seed to start swelling and producing roots and a shoot. In that situation, the endosperm provides the essential nutrients for germination before the emergence of the green leaf, allowing photosynthesis to take over as the source of energy and nutrients. 2. For mankind, the mature grain is mainly of significance as an important source of nutrients, that is, an item of food for humans and a source of feed for man’s animals. Examples of these many processed foods are shown in Figure 5. The major cereal grains of economic importance (Figure 6) are the cool-season crops (wheat, barley, oats, and rye) and the warm-season cereals (rice (paddy), maize (corn), sorghum, and the millets). Table 1 lists their botanical names and major uses. Cereals are monocotyledonous plants, as distinct from the dicotyledonous members of the wider family of

Figure 2 The wheat grain (a) in dorsal view and (b) in ventral view, showing the ‘brush’ (top left) at the end opposite from the point of attachment (the ‘hilum’) of the grain to the rachis of the wheat head. The ‘crease’ extends along the ventral side of the grain. The germ can be seen as a rough area in the dorsal view (a) at the hilum end. These images were provided by scanning electron microscopy, with the grain resting on the stage of the microscope. Reproduced from Wrigley CW (2004) Cereal sprouting. In: Goodman RM (ed.) Encyclopedia of Plant and Crop Science. New York: Marcel Dekker, with permission.

grains. The dicot grain species include the oilseeds and the pulses (grain legumes). Cereal plants are also divided according to their photosynthetic systems, namely, either C3 or C4. The C4 photosynthetic carbon cycle offers metabolic advantages over C3 photosynthesis in dry situations with high light intensity and high temperature. The approximately half of grass species that are C4 include maize, sorghum, and millet.


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Figure 3 Scanning electron micrographs of (a) a barley grain, covered by the integrated glumes (lemma and palea); (b) the rachilla lying in the groove of the crease; (c) the base of the rachilla with many of the long hairs broken off as a result of grain handling; (d) dust from the movement of barley grain showing the spear-like rachilla hairs. Note the different degrees of magnifications: the black bar at the bottom right represents a length of (a) 1 mm, (b) 400 mm, (c) 40 mm, and (d) 100 mm.

Historical Perspective Cereal grains have the great distinction of being the catalyst that transformed humans, as the hunter-gatherers into agriculturalists no longer living as nomads. The origins of civilization involved the enormous step of primitive mankind discovering that it was possible to remain in one place where cereal seed, sown intentionally, would yield a reasonably reliable source of food, which could be stored indefinitely. As a result, people found that a fixed dwelling place could be established near cereal crops. Further consequences were the development of permanent forms of housing, the domestication of animals (fed with cereal grain), and the spare time to develop the many other characteristics of civilization. Early consumption of cereals involved merely chewing the raw grain. Primitive forms of processing were developed, such as grinding the grain between stones and soaking the grain in water to make it easier to chew. Next, heat was discovered as a further means of easing mastication and digestion, producing a porridge or gruel. Placing a stiff porridge in the hot stones or ashes of a fire would have made it more palatable, resulting in baked foods.

A porridge left overnight would gain wild yeasts, leading to the discovery of leavening as a means of making the baked product lighter. Further refinements would have been the sieving step, to remove husks and bran particles after grinding, and the identification of wheat as the ideal grain for the baking of leavened bread due to its dough-forming properties. There is archaeological evidence that primitive baked products were being made in the late stages of the Stone Age. Purpose-built ovens were used in ancient Egypt as far back as 2700 BC, with reasonably sophisticated milling and baking a millennium later. As a result of this long history of cereal-grain use, diverse uses have been developed worldwide for their processing, taking advantage of the specific characteristics of the individual cereal species (see Table 1 and Figures 5 and 7).

World Production of Cereals Cereal grains are grown extensively in all continents, with the obvious exception of Antarctica. They are the major sources of food for mankind, especially in developing countries. In

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Brush

Aleurone cells Storage protein

Cuticle Epidermis Hypodermis

Cell nucleus Cell wall

Thin-walled cells Cross cells Testa

Endosperm Starch granules

Nucellar epidermis

Figure 5 Some of the many foods made from cereals (mainly wheat).

Pericarp

Aleurone grains

Scutellum Plumule Embryo (a)

Root Sheath and cap

(b)

Figure 4 (a) Diagram of the many parts of a wheat grain, cut in half to show its subcellular structure. (b) Scanning electron microscope image of the cut surface of a wheat grain. The bran layer, visible at the top left, covers the layer of square-shaped aleurone cells, which in turn enclose the endosperm (the lower right half of the photo). Starch granules can be seen as flattened spheres embedded in the protein matrix, surrounded by endosperm cell walls.

addition to their use as a major source of feed for animals, cereal grains are extensively processed industrially for food and nonfood products. Table 2 provides grain-production statistics for the world’s cereal-growing countries. The statistician’s term ‘coarse grains’

includes maize, barley, rye, triticale, and oats. In this case, the production statistics for rice appear much less than in some comparable tables because they show volumes for milled rice, with the outer coverings removed. The provision of such data for one harvest year permits direct comparison between cereals and countries, but it should be regarded as a ‘snapshot’ of production and trade, because of the fluctuations that occur from 1 year to another. Figure 8, on the other hand, shows how statistics vary from year to year for all cereals, for their production and utilization, with the added indications of carryover stocks from year to year. The statistics in Table 2 also illustrate the regional distribution of centers of production for the prominent cereals, namely, tropical countries for rice (and maize) and cooler regions for wheat and other coarse grains. The annual world production of all cereal grains is now about 2.5 billion tonnes (Table 2, Figure 8). Assuming a world population of about seven billion people, this amount of grain represents about 360 kg of cereal grain per person per year or 1 kg per person per day for the whole world’s population. It thus appears that world hunger could readily be alleviated, assuming that all cereal grains might be used for food and assuming that it could be transported to all the regions where it is needed. Of course, this is neither practicable nor possible, since many of the regions of production are distant from the places of need. In addition, the world’s animal agriculture and industrial operations are reliant on significant amounts of cereal grain. World production of wheat has ranged between 690 and 710 million tonnes (Mt) annually in recent years. This production has come from an area of about 220 Mha, with a world average yield of 3.2 tonnes ha 1. Two-thirds of world production of wheat goes to food; the remainder goes to a combination of seed use, animal feed, and industrial processing. World trade in wheat is about 20% of total production. Production of wheat’s close relative, rye, is minor by comparison with wheat; world rye production is about 20 million tonnes annually, the main production regions being in eastern parts of Europe, especially Poland, Germany, and Russia. World production of rice is similar to that of wheat, if the production of unmilled paddy rice is considered. On the basis


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Figure 6 Grains of major cereal species: (a) bread wheat; (b) durum wheat; (c) triticale; (d) rye; (e) barley; (f) oats; (g) sorghum; (h) corn; (i) Japanese millet. Adapted from Fitzsimmons RW and Wrigley CW (1984) Australian Barleys: Identification of Varieties, Grain Defects and Foreign Seeds, 2nd edn., pp. A11–A13. Melbourne: CSIRO.

of milled rice, annual world production averages over 500 million tonnes. International trade in rice is much less than for wheat and maize. Rice, together with maize, provides the major energy and protein source for many cultures. Annual production of maize (950 million tonnes in 2013/ 14) is greater than that of wheat. Statistically, maize is included in ‘coarse grains,’ production of which totals 1.2 billion tonnes annually (Table 2). World trade in coarse grains is about 100 million tonnes. In addition to maize, coarse grains include barley

(production averaging about 150 million tonnes annually), sorghum (50 million tonnes), and oats (30 million tonnes).

Morphology of Cereals: What They Look Like Cereal grasses have narrow leaves, hollow jointed stems, and spikes or clusters of membranous flowers (Figure 1). Figure 9 shows how the mature grain of wheat is held within glumes on

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Table 1 Common names Pooids Common wheat Durum wheat Rye Triticale Barley Oats Oryzoids Rice Wild rice Chloridoids Teff, Indian millet Finger millet Panicoids Corn (maize) Sorghum Pearl millet Common millet Japanese millet Foxtail millet

Cereal-grain species (in taxonomic groups) and their uses Genus and species

Uses

Triticum aestivum

Breads (leavened and unleavened), noodles, breakfast cereals (processed porridge), cakes, cookies, chapatis, snack foods, bulgur, ingredients for a wide range of foods, animal feed, industrial uses Pasta (e.g., spaghetti and macaroni)

Triticum turgidum subsp. durum Secale cereale Triticosecale Hordeum vulgare Avena sativa

Bread (often together with wheat), crispbread, spirits Bread (often together with wheat), animal feed Malt, beer, spirits, porridge, cooked grains (e.g., soup ingredient) Porridge (as rolled oats, oatmeal), muesli, oatcakes, animal feed

Oryza sativa Zizania aquatica

Cooked and fried grain, sake, extruded snack foods Cooked grain

Eragrostis tef

Cooked grain, porridge

Eleusine coracana


Zea mays Sorghum bicolor Pennisetum glaucum Panicum miliaceum

Polenta, breakfast cereals, tortilla, cornbread, porridge, snack foods, a wide range of industrial uses (e.g., corn syrup and food ingredients) Animal feed, cooked grain, porridge, beer, flat cakes Cooked grain, porridge Cooked grain, porridge

Echinochloa species


Setaria italica


The flowers of oats and rice, on the other hand, are arranged in an inflorescence called a panicle (Figure 11). The grains of oats and rice do not thresh as the free seed. The term ‘groat’ applies to the oat seed with the glumes removed. The term ‘paddy rice,’ or just ‘paddy,’ refers to the rice grain with its husks in place, the form in which it is harvested. The familiar cob (ear) of corn (maize) is distinct from the seed-bearing structures of the other cereals described earlier (Figure 12).

The Diversity of Cereal Grains Wheat

Figure 7 Chinese steamed bread.

the single stem of the head (ear) (Figure 10). The threshing process at harvest separates the wheat grain (as in Figures 2 and 6) from the glumes, rachis, and other parts of the plant. The structure of the barley head (Figure 10) is similar to that of wheat, but on threshing, the glumes of barley remain with the grain (Figures 3 and 6), whereas the wheat grain threshes free from the glumes. The rye grain also threshes free of the glumes (Figure 6).

Wheat is prominent among cereals, because of its unique dough-forming properties. These viscoelastic characteristics are due to the gluten–protein complex, formed from the major storage protein of its endosperm. This is the basis of man’s attraction to wheat – the reason for the annual cultivation of over 1014 wheat plants – because wheat gluten alone can sustain man’s desire for leavened bread products. There is a great diversity of uses of common or bread wheat (Table 1), such as pan breads, pocket (Arabic) breads, noodles, and steamed breads (Figures 5 and 7). In addition, there is a diversity of processing methods, especially for the range of leavened breads. There is thus the need to breed a range of wheat varieties to suit the various processing specifications. In addition, there is the need for the appropriate variety to be grown in a suitable climate and region, with the right management, aimed at achieving target attributes of bulk density, lack

THE CEREAL GRAINS | An Overview of the Family of Cereal Grains Prominent in World Agriculture Table 2

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World production in the year 2013/14 of cereal grains by countries/regions, in millions of tonnes (metric tons)

Region

Wheat

Coarse grainsa

Riceb

All cereal grains

Argentina Australia Brazil Canada China EU India Indonesia Mexico Pakistan Russia South Africa Thailand Turkey Ukraine The United States World

11 26 5 33 121 143 93 – 3 24 52 2 – 18 22 58 706

35 11 73 26 218 159 42 9 29 4 36 14 5 13 38 372 1252

1 1 8 – 142 2 105 38 – 6 1 – 21 1 – 6 473

47 37 86 59 480 304 240 47 33 34 88 15 26 32 60 436 2432

a

The category ‘coarse grains’ includes maize, barley, rye, triticale, and oats. Calculated as milled rice (not paddy). Source: Data from United States Department of Agriculture. b

Cereal production, utilization and stocks Million tonnes 2500

Million tonnes 800

2300

600

2100

400 Awn Palea

200

1900

Grain

0 1700 2003/04 2005/06 2007/08 2009/10 2011/12 2013/14 f’cast Production (left axis)

Utilization (left axis)

Stocks (right axis)

Lemma Outer glume Rachis

Figure 8 Production, utilization, and stocks of cereal grains during recent years. Reproduced with permission from FAO.

of defects and contaminants, grain hardness, protein content, milling quality, and dough-forming properties. It is usual to segregate wheat after harvest into specific grades, each being suited to appropriate uses and prices. These grades carry through into world trade, forming a basis for buyers to select based on the combination of quality and price. Durum, a distinct species of wheat (Table 1, Figure 6), has a harder, larger grain, with a yellowish hue (‘amber’ according to the title of the international durum grade). Because its endosperm is so hard, it fragments on milling into particles that are larger than the particles from common wheat (especially soft

Figure 9 A spikelet of wheat. The mature grain is held within glumes, and all are attached to the rachis (the central stem of the head). Other spikelets have been removed from the rachis for clarity. Reproduced from Fitzsimmons RW, Martin RH, and Wrigley CW (1983) Australian Wheat Varieties: Identification According to Growth, Head and Grain Characteristics, 2nd edn., p. 13. Melbourne: CSIRO, with permission.

wheats). This coarse flour from durum wheat (‘semolina’) is suited for pasta manufacture (extruded from a relatively dry dough) and also for couscous, frike, and bulgar (also known as ‘bulghur’ or ‘burghul’). Some of these foods are also made from common wheat in some regions.

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(a)

(b)

(c)

Figure 10 (a) Heads of wheat. (b) Heads of two-row barley. (c) Heads of six-row barley.

Spikelets

Branch

Rachis Figure 12 The cob of corn.

First node of rachis – with whorl of branches Neck Flagleaf

Flagleaf sheath

Top ligule

Uppermost stem node

Figure 11 The head (panicle) of oats. Reproduced from Fitzsimmons RW, Roberts GL, and Wrigley CW (1983) Australian Oat Varieties: Identification of Plants, Panicles and Grains, p. 11. Melbourne: CSIRO, with permission.

Rice Like wheat, rice is another cereal with a special place in man’s diet, providing a dietary staple for over half of the world’s population, thus constituting their major source of energy and protein. Unlike other cereals, rice is usually consumed as the whole grain, after removal of the bran layers. Rice can be grown under a wide range of climates, either in flooded irrigation or under dryland conditions. Some 90% of the world’s rice production is in Asia, especially in developing countries. International trade in rice accounts for only about 4% of world production. Prices vary greatly depending on the type of rice. For example, Basmati scented rice from Pakistan and northwest India might command four times the domestic price of ‘ordinary’ rice. Quality grades of rice are partly based on dimensions – long-, medium-, and short-grain rice. Quality attributes relate


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Figure 14 Plants of maize (corn). The pollen-dispersing ‘tassels’ are at the top of the plants. Developing cobs, sheathed in leaf material, appear halfway up the stalk of the plant on the right. Figure 13 Rice-based ‘fast food’ sold by the road side in Thailand, demonstrated by Professor Siriamornpun of Mahasarakham University, Thailand. Rice has been cooked inside a length of bamboo. Stripping off the outside of the bamboo reveals the cooked rice inside.

to the milled grain: shape, color, translucency, and uniformity and also the absence of broken grains. For human consumption, paddy rice is dehulled and milled to remove the bran layers, leaving the familiar lustrous, white grain. Brown rice, much less popular for eating, retains the bran layers, together with added nutrients. Short-grain waxy (having low amylose content) varieties (japonica types) usually become sticky on cooking, a characteristic that is preferred in many parts of north Asia. There is a preference in many Western countries for the drier, flaky quality usually provided by the long-grain nonwaxy varieties (indica types), more often grown in tropical regions. A novel example of rice for food is illustrated by the Thai ‘fast food’ in Figure 13. Rice, water, and flavoring have been cooked inside the stem of a length of bamboo. The result is sold by the roadside. To eat the cooked rice, the outside of the bamboo is stripped back; the cooked rice is retained by the membrane inside the bamboo. Whereas milled rice is mainly consumed as the cooked grain, there are also many food products made from rice, namely, parboiled rice, rice crackers and noodles, rice cakes and snack foods, rice flour, and fermented drinks (sake and rice wine).

Maize (Corn) Maize, indigenous to the Americas, is produced worldwide – mainly in tropical and warm regions. It is an annual plant with

an erect, leafy stalk. The ear consists of a central pithy section (the cob, Figure 12), via which nutrients are transported from the leaves and stalk to the grains (some hundreds or up to one thousand grains per cob). The tassels (Figure 14) of the immature cob constitute the inflorescence bearing the male flowers. There is a wide range of types of grain. Variations in grain types include size, color, and hardness. Colors range from white, to yellow, to red, to almost black. Endosperm types include soft and floury to hard and flinty. Popcorn is a special type of endosperm that expands suddenly on heating, due to vapor expansion inside the grain. Sweet corn, with an unusually high sugar content, is generally harvested immature, retaining a high water content to provide the familiar juicy mouthfeel. There is extensive industrial processing of maize, especially in the United States and Europe. An important group of products is the wide range of breakfast cereals and snack foods. Industrial processing also involves fractionation of the maize grain by wet milling into its major biochemical components. The main product of processing is cornstarch, which is the largest component of the corn endosperm. By-products are maize oil, from the germ and the protein fraction, which is traded under the inappropriate term ‘corn gluten.’ These direct products may be further processed, especially the starch, much of which is hydrolyzed to simple sugars as a sweetening agent, as well as being used to make syrups and spirits.

Barley The main uses of barley (Figures 3 and 6) are for animal feed and for the production of pearled barley, malt, and beer (Table 1). These two uses (feed and food) form the basis of

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the two main grades for trade in barley (known as feed barley vs. malting barley). Another major distinction is based on head morphology, namely, ‘two row’ or ‘six row’ depending on whether there are grains in the full set of florets in the head (six row) or if there is only one set of grains on either side of the head, with the other florets sterile (Figure 10). In some barleygrowing countries (Europe and Australia), six-row barley varieties are often of feed quality, but six-row varieties are also of malting quality in North America. Barley is the grain used for Scotch and Irish whiskies. In addition, a proportion of the barley crop is used directly for human consumption; after pearling (abrasion) to remove the adhering lemma and palea, the barley grain is boiled in soup as the whole pearled grain, or it is coarsely ground and cooked as gruel. Barley flour is also used for a range of baked products, but barley is not suitable for the production of leavened bread, lacking the gluten proteins of dough-forming quality. Nevertheless, barley appears to have been used for bread making by ancient civilizations. Barley, for example, appeared on Greek coins several centuries BC, and it was the staple diet of Roman gladiators, who were thus known as hordearii (reflecting the origins of the genus name, Hordeum).

Oats The oat grain and plant and grain are illustrated in Figures 6 and 11. Oat plants thrive in temperate climates, with cooler moister conditions, compared to other cereals. Oats are often used as fodder for stock, grazing off the growing plants. In such cases, it may also be possible for the farmer to harvest a crop of grain, which in turn may also be stored on-farm for stock feed. In addition, oats may be grown primarily as a grain crop, generally using varieties that have been bred specifically for use as grain. A large proportion of harvested oats is used for animal feed, especially for horses. Compared to the other cereal grains, the oat grain tends to have higher contents of protein, lipid, and soluble fiber (b-glucan). Oats are reported to have beneficial hypocholesterolemic properties and are useful in the management of the insulin response in diabetics. For human consumption, the adhering glumes are abraded from the oat grain. The resulting groat is cut, rolled, or ground to yield products such as oatmeal, rolled (flaked) oats, and oat flour, for processing into ‘instant oats’ for porridge, oat cakes, breakfast cereal, and infant foods. The groat has a higher content of lipid (fats) than wheat, plus significant lipase activity (fat-splitting enzyme), and these factors must be taken into account in oat processing. There is the consequent risk that after milling, fat rancidity, bitterness, and a soapy taste will be produced by the actions of various endogenous enzymes, namely, lipase, lipoxygenase, and peroxidase. To prevent this, it is usual for milled oats to undergo some form of heat treatment to inactivate the lipase activity. This is often done by steam treatment, together with kiln drying.

Rye and Triticale Rye is the only cereal grain that approaches wheat with respect to bread-making properties, although the achievement of bread quality in rye breads usually requires the incorporation of a considerable proportion of wheat flour (Table 1, Figure 6).

Rye is a popular human diet in Europe. The production of rye in Germany exceeded that of wheat from about 1940 to 1960, but more recently, the production of wheat has increased considerably, and a higher proportion of the rye crop has been used for animal feed. Rye is particularly susceptible to contamination with ergot, a toxic fungus that replaces the grain in the rye head during development, so that a long black ergot body protrudes from the mature head. Ideally, the production of ergot in the crop is avoided, but there are techniques for the removal of intact ergot bodies prior to milling. In addition to the manufacture of rye breads, rye-based crispbread is an important use of rye, generally with rye wholemeal or from flaked rye. Other baked products include Ryvita and pumpernickel. In human nutrition, the rye grain offers an unusually high level of pentosans. This source of soluble fiber offers advantages of giving a feeling of satisfaction, thus helping in slimming diets, as well as reducing the rate of rise in the blood sugar level after ingestion. Triticale is a man-made crop that combines the genomes of wheat and rye (Table 1). Most cultivated triticales are hexaploid types, containing the genomes of durum wheat and rye. It thus tends to be intermediate between rye and wheat in its grain composition and characteristics. The expectations for the grain have been that it would contribute the disease resistance and growth hardiness of rye to wheat while also combining the baking quality of wheat with the unique flavor of rye bread. Triticale has thus been used for baking; nevertheless, its main use is for animal feed.

Sorghum and the Millets The grains of sorghum and of various millet species (Table 1, Figure 6) constitute a major source of protein and energy for many people in Africa and Asia, where these grains are used as porridge, boiled in water after grinding. In such situations, these cereals offer the advantage for subsistence farming of tolerance to drought and suitability for tropical growth environments. Pearl millet is the most widely grown of the millet family, with an estimated area worldwide of about 30 Mha. Second in importance are common millet and finger millet (Table 1). Many millets, due to small grain size, are used as feed for wild and domesticated birds. In addition to the use of sorghum in cooking, it is also drymilled and fermented for various forms of beer. On the other hand, the main use of sorghum in developed countries is for animal feed and, to a lesser extent, for industrial processing. There are various mutant forms of sorghum with distinct characteristics that include high lysine content, waxy starch, high sugar content (stalks), and even scented endosperm. The grain of many sorghum varieties is pigmented, largely due to tannins located in the outer layers (testa) of the grain. The high-tannin varieties are also somewhat less nutritious, because the tannins interfere with protein digestibility. Some sorghum varieties have bitter flavors, which confer resistance to attack by birds.

Composition Starch, a polymer of glucose, is the major component of the endosperm of cereal grains (Table 3). It is the stored form of

THE CEREAL GRAINS | An Overview of the Family of Cereal Grains Prominent in World Agriculture Table 3

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Approximate composition of the major cereal grains, as percentages of dry weight of whole grain, except for rice

Component

Wheat

Rice (milled)

Maize

Barley

Oats (groats)

Rye

Starch Protein Fat Crude fiber Minerals

75–80 9–16 2–3 2–3 1–2

85–90 8–11 0.5–1.0 0.2–0.6 0.4–0.6

75–80 10–12 4–10 2–3 1–2

75–80 9–12 1–2 5–6 2–3

70–80 12–15 6–8 1–2 2–3

75–80 12–15 1–2 2–3 2–3

In addition, grains (‘as is’) would contain moisture at a level of 9–15%.

energy that is released on germination when amylase enzymes are produced to break the starch down to glucose units for the developing embryo, roots, and shoots. For feed and food, starch also provides the major source of energy, providing it in a ‘slow-release’ form that is well suited to our digestive systems. Although cereal-grain proteins do not have the ideal combination of essential amino acids, being slightly deficient in lysine especially, they are generally ingested together with other sources of protein whose amino acid composition complements that of cereal grains. The relatively low fat content of cereal grains is a dietary advantage, especially when coupled with the levels of nonstarch polysaccharides, which act as important sources of fiber in the human diet.

Cereal Grains and Our Health For some individuals, cereal-based foods may cause dietary problems. One of the best characterized of these intolerances is celiac disease, a condition caused by the ingestion of wheat gluten–protein and of related grain proteins, namely, rye, triticale, barley, and (for some individuals) oats. Despite its misleading name, buckwheat is not a grain that is toxic to celiacs. On the other hand, cereal grains (milled or not) provide good sources of protein, fiber, and complex carbohydrates, earning for cereal grains a major place in dietary guidelines (Figure 15). Additional health benefits may be provided by the inclusion of the outer layers of cereal grains, in whole-grainfoods. This is because these parts of the grain (Figure 4(a)) provide an additional source of vitamins and minerals and because they contribute increased amounts of fiber to the diet. During their growth, cereals also produce pollen that may cause allergy problems on inhalation. The pollen grains of the various cereal flowers have distinctive shapes (Figure 16). The germination of the pollen grain commences on exposure to moisture, normally when it alights on the stylus of a flower of the same species (Figure 1), but the same reaction may occur if the pollen comes in contact with the mucosa of the respiratory tract. The proteins so released may cause swelling of the mucosa, resulting in rhinitis and asthma. The cultivated cereals may be the cause of this scenario, but it is more common for inhalant allergy to be caused by a wider range of plants species, not necessarily propagated for their grain. Dust from cereal grains also causes irritation in the respiratory tract. Dust produced during the movement of barley grain (Figure 3(d)) consists partly of hairs broken off the rachilla (Figure 3(b) and 3(c)), which lies in the crease of the barley grain. Barley varieties differ in the length of the rachilla hairs,

Figure 15 An example of the nutrition pyramid recommending that foods containing grains (base of pyramid) should make a greater contribution to our diet than other foods, such as fruits, dairy, meat, and fats.

this characteristic being useful in visual variety identification. Irritation of the skin and respiratory tract is worse for dust from varieties with long rachilla hairs.

Future Prospects Although world production of cereal grains is equivalent to 1 kg per person per day for the world’s population, many parts of the world still experience hunger. How can we share the cereal-grain harvest more equally? This problem is epitomized in the inscription on the old plate in Figure 17; the translation reads: “Old bread is not hard – no bread, that is hard.” With this old problem in mind, new research methods are being directed toward improving the yield and quality of the grain produced, especially by breeding. Despite the success of cereal grains as the major food source for mankind, there are many stresses that reduce grain yield. These stresses include a range of pathogens and predators, as well as many abiotic factors (heat, cold, frost, drought, waterlogging, and heavymetal toxicity). Traditional breeding has provided great improvements and it will continue to do so. These advances are being assisted by the identification and characterization of specific remedial genes. Some of these genetic opportunities lie in plants of

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Figure 16 Pollen grains from the flowers of cereal species, revealed by scanning electron microscopy.

species distantly related to the species of interest. Novel genetic technologies (genetic modification (GM)) facilitate these cross species transfers, thus augmenting conventional breeding, leading to new varieties that are better at surviving stresses, plus providing novel grain qualities. GM technologies have been more successful in commercial practice for noncereal species, especially soybean, cotton, and canola. Nevertheless, GM corn is grown widely, especially in the United States, accounting for about one-third of the area worldwide for GM crops. For other cereal species, GM and conventional breeding offer useful traits, such as abiotic stress tolerance, pathogen

resistance, drought tolerance, and insect resistance. The various aspects of improved grain composition include increased levels of specific vitamins (e.g., vitamin A) and minerals (e.g., iron) and a reduced level of gluten-type protein in barley, permitting the production of ‘gluten-free’ beer. The composition and functional properties of the edible grains offer a wide diversity of possibilities for new and varied end uses. Given this genetic diversity, and the consequent access to the genes responsible, combined with the capabilities of novel methods of genetic manipulation, we have many possibilities for extending the compositional diversity of any grain to provide it with new functional properties.


• •

Figure 17 The inscription on this old plate portrays the ongoing problem of finding enough grain to provide food for everyone in the world. The words “Altes Brot ist nicht hart – kein Brot, das ist hart!” translate as “Old bread is not hard – no bread, that is hard.” Reproduced from Ng PKW and Wrigley CW (eds.) (2002) Wheat Quality Elucidation, p. 24. St. Paul, MN: American Association of Cereal Chemists, with permission.


• • • • • • • •

What features distinguish cereal grains from other food grains, for example, from the oilseeds and legumes? What are the distinct meanings of the terms ‘seed,’ ‘kernel,’ ‘corn,’ and ‘caryopsis’? Which three cereal grains are grown to the greatest extent worldwide? Which cereal genus and species is best suited to (a) bread making and (b) pasta making? Which cereal grain is favored for making beer; or are several cereal grains used for this purpose? How do we come to use the term ‘cereal’ in common speech for breakfast foods such as cornflakes and rice bubbles? What protein part of wheat flour makes it uniquely suitable for bread making? Cereals are members of the flowering plant family. What is the important function of the cereal flower for our intervention in producing new varieties? Cross-reference to breeding articles.


• •

The gluten–protein complex of wheat dough is made up of many proteins. What are the names and functions of some of the component proteins? Cross-reference to cereal proteins. Select several countries and identify their national foods derived from cereals, especially the species most grown in each country or region.

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How are cereal species most similar and most divergent with respect to the morphology (shape) of the plants, the grain-bearing head (panicle), and the grain/seed? Investigate the specific advantages offered by GM cereals. Which of these are at the research or commercial stages? In which regions or countries are these permitted?

See also: Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Food Grains and the Consumer: Grains and Health; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Non-wheat Foods: Maize: Foods from Maize; Rice: Chinese Food Uses; Sorghum: Utilization; Processing of Grains: Cereals: Breakfast Cereals; Extrusion Technologies; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Grain Crops: An Overview; Grain: Morphology of Internal Structure; The Grain Chain: The Route from Genes to Grain-Based Products; The Cereal Grains: African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Durum Wheat: Overview; Maize: Overview; Millet Minor: Overview; Millet Pearl: Overview; Oats: Overview; Rice: Overview; Rye Grain: Its Genetics, Production, and Utilization; Sorghum Grain, Its Production and Uses: Overview; Teff: Overview; Triticale: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wildrice, Zizania: Overview; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; WheatBased Foods: Breads; Cakes, Muffins and Bagels; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Flatbreads of the World; Noodles: Asian Wheat Flour Noodles; Noodles: Starch; Pasta; Sour Dough Technology; Tortillas; Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Abdel-Aal E and Peter Wood P (eds.) (2005) Specialty Grains for Food and Feed. St Paul, MN: AACC International Press. Arendt EK and Zannini E (eds.) (2013) Cereal Grains for the Food and Beverage Industries. Oxford: Woodhead Publishing. Bhattacharya KR (2011) Rice Quality. Cambridge: Woodhead Publishing. Champagne ET (ed.) (2004) Rice: Chemistry and Technology, 3rd edn. St Paul, MN: AACC International Press. Dendy DAV (ed.) (1994) Sorghum and Millets: Chemistry and Technology. St Paul, MN: AACC International Press. Henry RJ and Kettlewell PS (eds.) (1996) Cereal Grain Quality. London, UK: Chapman and Hall. Kent NL and Evers AD (eds.) (1994) Technology of Cereals. An Introduction for Students of Food Science and Agriculture, 4th edn. Oxford, UK: Pergamon Press. Khan K and Shewry PR (eds.) (2009) Wheat: Chemistry and Technology, 4th edn. St Paul, MN: AACC International Press. Shewry PR and Ullrich SE (eds.) (2014) Barley: Chemistry and Technology, 2nd edn. St Paul, MN: AACC International Press. Sissons MJ, Abecassis J, Marchylo B, and Carcea M (eds.) (2012) Durum Wheat: Chemistry and Technology, 2nd edn. St Paul, MN: AACC International Press. Webster FH and Wood PJ (eds.) (2011) Oats: Chemistry and Technology, 2nd edn. St Paul, MN: AACC International Press. White PJ and Johnson LA (eds.) (2003) Corn: Chemistry and Technology, 2nd edn. St Paul, MN: AACC International Press. Wrigley CW and Batey IL (eds.) (2010) Cereal Grains: Assessing and Managing Quality. Oxford: Woodhead Publishing.

Cereals: Domestication of the Cereal Grains LA Morrison, Oregon State University, Corvallis, OR, USA ã 2016 Elsevier Ltd. All rights reserved.

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Topic Highlights

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As members of the grass family, cereals have inconspicuous flowers located on a complex inflorescence structure that can be one of three types: spike, raceme, or panicle. The florets of cross-pollinating cereals open up at anthesis to allow the stamens to shed their pollen out into the wind and air currents, which move the pollen to the stigma of another floret for fertilization. Opening of the bracts on grass florets and spikelets during pollination to both spread and receive pollen fosters the hybrid speciation that characterizes cereal evolution. Dispersal strategies in wild progenitors of cereals shed the mature grain off of the mother plant in a protective dispersal unit known as a diaspore, which is formed by the adherent sterile bracts (glumes, lemmas, and paleas) whose shape, awns, and bristles aid in its movement to a suitable habitat for seedling establishment. Domestication altered the wild dispersal systems of cereal progenitors by developing forms that retain the grain on the mother plant while easily releasing the grain during threshing, the two significant changes that led cereal evolution. As Old World cereals originating in the Fertile Crescent, wheat and barley are primary domesticates whereas oats and rye are secondary forms given their initial status as weedy wild species infesting early wheat and barley fields. Maize is the only New World cereal and unusual for its highly compressed raceme that developed from a pistillate inflorescence. Pearl millet and sorghum are drought-tolerant cereals domesticated in Africa, which spread into South Asia where they underwent secondary domestication. Rice is a semiaquatic cereal initially domesticated in southern China, whose phylogeny is characterized by extensive introgressive hybridization between wild and domesticated forms and between the two domesticated races indica and japonica. Wheat offers the unusual evolutionary example of a multilevel phylogenetic mosaic built on multiple rounds of homoploid and polyploid hybrid speciation events. Weedy cereal relatives have been ‘domesticated’ as a consequence of human agricultural practices and in some cases such as pearl millet, have increased their diversity and adaptability through introgressive hybridization with the crop to form crop–weed races. While the major cereals represent a large component of agricultural economies, the minor grains are greater in number and represent a more diverse distribution, particularly in subsistence farming systems where they are major food staples. Plant breeding applications of the Brachypodium and Setaria functional grass model systems promise major advancements in improving agronomic and physiological traits of cereals.

Realizing the full potential of well-defined phylogenetic relationships that can guide plant breeders in efforts to tap the diversity of cereal crop gene pools requires a global commitment to germplasm conservation.

Learning Objective

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To achieve understanding of the mechanisms of domestication from the standpoint of grass reproductive biology, the associated natural evolutionary processes such as hybrid speciation, and the human activities that led the development of cereal species

Introduction Cereals comprise a diverse collection of species, all belonging to the grass family (Poaceae). Collectively, these species cluster in only four of the 12 grass subfamilies: Chloridoideae, Ehrhartoideae, Panicoideae, and Pooïdeae. As a group, they are named for the Roman goddess Ceres who was worshipped as the mother of agriculture and goddess of grain. The cult surrounding Ceres built on her earlier Greek (Demeter) and Egyptian (Isis) counterparts. In the case of Ceres and Demeter, their symbols included heads or sheaves of grain, usually wheat for Ceres and barley for Demeter. Cereal evolution is a complex subject given the vast array of grass species adopted into agriculture. Most researchers and consumers think in terms of the relatively narrow selection of species that dominate international commerce as dietary staples and constituents in processed food products. In this select group are barley, maize, pearl millet, oats, rice, rye, sorghum, and wheat. Cereals actually comprise a much larger group with many lesser-known species cultivated and utilized on a local basis, particularly in subsistence farming cultures.

Inflorescence Structure Members of the grass family all have inconspicuous flowers that have been reduced to the essential reproductive structures. There are no showy bracts, nectaries, and other features to attract animal pollinators. Unless self-pollinated, cereal species rely on the wind to spread their pollen. Although grass flowers all have the same basic design (Figure 1), they can vary in terms of presence and functionality of the female and male reproductive structures. Each flower is borne singly in a floral unit (floret) enclosed by two outer leaf-like bracts (lemma and palea) (Figure 1). Florets can be bisexual, pistillate (female), or staminate (male). Fertile florets contain three stamens (filament and anther) and one pistil (stigma, style, and ovary) with two tiny, scale-like appendages (lodicules) positioned at its base.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00007-3

THE CEREAL GRAINS | Cereals: Domestication of the Cereal Grains

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Anther Stigma Stamen Pistil

Style Filament

Ovary Lodicule Rachilla

Palea Lemma

Upper (second) glume Lower (first) glume Palea Lemma

Rachilla joint

Callus

Figure 1 Stylized drawings of a grass flower (upper left), floret with adjacent rachilla internode (lower left), and spikelet with subtending rachis internode (right). Reproduced with permission from Clark LG and Pohl RW (1996) Agnes Chase’s First Book of Grasses. Smithsonian Press.

The floret is attached to a secondary stem axis, the rachilla. Subtending the rachilla are two empty bracts, the glumes. One or more florets, packaged within the glumes, form a spikelet (Figure 1). Spikelets are alternately positioned at attachment points (nodes) located along the main inflorescence axis (rachis) or on branches extending off the rachis. The interval between two nodes on the rachis is the internode. Within the spikelets, florets are similarly arranged, alternately along the rachilla. Although grass inflorescence morphology is complex, a simplistic classification designates three basic types (Figure 2), each differing in rachis branch development and spikelet attachment: (1) panicle with long, open branches or dense branches, each bearing a pediceled spikelet; (2) raceme with spikelets borne on short pedicels along the rachis; and (3) spike with spikelets sessile along the rachis.

Pollination, Fertilization, and Grain Development Cereal species can be either self- or cross-pollinating. In the latter species, the lodicules swell at anthesis, forcing the florets open to expose the stigmatic surfaces of the pistil to incoming pollen. While the florets are open, the stem-like filaments on the stamens elongate to push the anthers upward and out of the floret where they dehisce and shed pollen into the wind and air currents. The glumes can bend outward at their bases, enabling a wider opening of the florets. For self-pollinating cereal species whose florets do not stay tightly closed at anthesis, cross-pollination can occur at low levels. This functional morphology of the floret and spikelet at play during pollination sets the stage for the hybrid speciation that characterizes cereal evolution.

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(a)

(b)

(c)

Figure 2 Illustrations of the three general inflorescence types found in grasses: (a) panicle, (b) raceme, and (c) spike. Reproduced with permission from Clark LG and Pohl RW (1996) Agnes Chase’s First Book of Grasses. Smithsonian Press.

The stigma, a collection of sticky feather-like branches, acts as the pollen trap (Figure 1). Upon pollination, a pollen tube grows downward through the stigma and style into the ovary, which holds a single ovule (egg). Fertilization occurs when the two pollen sperm nuclei unite, respectively, with the egg and two female polar nuclei. From this event, a grain develops with a 2n embryo and 3n endosperm. When fully developed, the cereal grain is the fruit and seed combined, that is, a specialized fruit known as a caryopsis, whose outermost layer is formed by the dried remains of the ovary (pericarp), now adherent to the seed it surrounds.

Dispersal Wild relatives of cereal species depend on dispersal strategies to move the propagule unit enclosing the mature caryopses off and beyond the mother plant. Propagule units (diaspores) consist of one or more grains surrounded by the dried inflorescence structures. They are shed from the mother plant by spontaneous shattering (disarticulation) at abscission zones located at the nodes along the rachis or rachilla (Figure 3). Disarticulation is typically described as above (rachilla disarticulates into floret units) or below the glumes (rachis disarticulates into spikelet, branch, or inflorescence units). The rachilla or rachis internodal pieces that remain attached may either subtend or lie adjacent to the diaspore (Figures 1 and 3). Sterile reproductive units or nonfloral vegetative structures may also form part of the diaspore. Examples include the two sterile awn-like lateral spikelets on the wild barley diaspore and the reduced inflorescence

(a)

(b)

(c)

Figure 3 Disarticulation points along the rachis of a spike inflorescence type illustrating the location of the break and the internode piece attached to the diaspore: (a) arrow-shaped diaspore with subtending rachis piece, (b) cylindrical diaspore with adjacent rachis piece, and (c) tough rachis with no disarticulation. Disarticulation points along the rachis for racemes and panicles, as well as along the rachilla for floret units, are analogous to the patterns illustrated here. Reproduced with permission from Peterson RF (1965) Wheat: Botany, cultivation, and utilization. In: Polunin N (ed.) World Crop Books. New York: Interscience.

branches that form a bristly fascicle (involucre) surrounding the spikelet on the wild pearl millet diaspore. Wild species also have developed strategies both to move diaspores to a favorable habitat and to protect the seed from predation and environmental damage until seedling establishment. For example, hardened glumes (wild wheat) or a rachis cupule and glume together (wild maize) can completely enclose the mature spikelet in a protective package; the lemma and palea can adhere to the grain (wild barley) or form a hard shell around it (pearl millet). Diaspore shape and awns, barbs, and bristly hairs or branches determine the mode of movement once the diaspore separates from the mother plant. Cylindricalshaped (wild wheat: Aegilops tauschii) or angular-shaped (wild maize) diaspores move by rolling or tumbling across the ground, floating on water, or getting caught in mud that sticks to the hides or in the hooves of animals. Arrow-shaped units fall or are moved point downward into soil cracks (wild rye). Awns, panicle branches, and bristles subtending spikelets can aid in the movement of the diaspore to an ideal site for establishment.

THE CEREAL GRAINS | Cereals: Domestication of the Cereal Grains Diaspores generally move only a short distance from the mother plant unless aided by animals, humans, or water. Awns, which are extensions of the vascular nerves of glumes and lemmas, can move the dispersal units in a variety of ways. Natural humidity–drying cycles can cause awns to spread open and close, thereby moving the diaspore by passive mechanical force with the seed end pointing forward for short unidirectional distances or down into the soil (wild wheat: Triticum urartu). Other hygroscopic awns will coil and uncoil in response to moisture changes, thereby drilling the diaspore into the ground (wild oat). Tiny barbs on awns or bristles can ratchet the movement of diaspores across the ground for short distances, lock the diaspore in place in the soil, or catch the diaspore on the fur of animals or clothing of humans. Awns can also vibrate in the wind to push the diaspore downward into the soil or soil crack. Lightweight, feathery bristles of a fascicle can move a diaspore in the wind (wild pearl millet). In contrast to their wild relatives, domesticated cereal species retain the mature caryopsis on the plant and have more easily extractable grains due to reduced or absent lemmas, paleas, and glumes. Thus, humans must remove the mature grains from the mother plant by hand or mechanical harvesting, thresh the harvested heads to free the grain from their enclosing bracts, protect the grain from predation and environmental threats, and plant it for a new crop. Some of the more primitive cereal species still retain wild-type features. For example, semibrittle forms of emmer and spelt wheat (T. dicoccum and T. spelta) can naturally disarticulate or break under relatively little mechanical pressure into spikelet diaspores enclosed by tough glumes.

Evolution and Domestication Domestication constitutes an evolutionary change and speciation mediated by humans acting as selection agents. For the cereal grains, early humans channeled the inherent genetic variation of wild grasses in the direction of agricultural traits that eased work to cultivate, harvest, and extricate grain. Then, through their ancient migrations and trade routes, they spread domesticated cereals and associated weed species beyond the original sites of domestication. With the expansion of early agriculture, opportunities opened for hybrid speciation events between otherwise allopatric species or between weedy wild forms and crop species. These expanded associations led to new domesticated forms (for example, T. aestivum) or introgressed forms with more complex phylogenies (maize, rice, and sorghum). Ancient farmers further exploited the domestication process by developing unique land races adapted to the growing conditions and food needs of their locales. As a result of these factors, discerning phylogenetic relationships can be challenging. Thus, taxonomic classifications constructed to reflect phylogenetic evidence can be dynamic, changing as the evidence changes. The practice of classifying the wild and domesticated cereal forms as one biological species, usually named with the domesticated species name, can lead to confusion if the wild versus domesticated forms at the infraspecific levels of subspecies or variety are not specified (for example, T. turgidum and Sorghum bicolor can refer broadly to both wild and domesticated taxa).

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Domestication Syndrome Under domestication, features of dispersal, reproduction, plant growth, and survival of wild grasses were transformed into desirable agricultural traits designated as the domestication syndrome. The two leading transitions were: (1) the retention of the mature grain on the mother plant due to the development of a nonshattering, tough rachis and (2) the easy release of the grain from the bracts due to morphological changes reducing or eliminating glume tenacity and adherence of the lemma and palea to the mature grain. Following these initial changes, humans manipulated a suite of desirable physiological and agronomic traits to further advance early forms into fully agricultural species: (1) Reduction of seed dormancy either by loss of physiological dormancy or by loss or reduction of enclosing bracts that contained germination inhibitors (2) Increase in seed production by development of reproductively functional florets from sterile or vestigial ones (3) Increase in seed size (4) Synchronous development of tillers and ripening of the grain (5) Changes in photoperiod sensitivity (6) Greater agricultural fitness for soil and climatic conditions and pest resistance. The speed and spread of the transition to agriculture is still debated with differing interpretations of domestication as rapid versus gradual and spread of initial domesticates as an outward diffusion from a primary place of origin versus a series of relatively concurrent events in different locales. Reduction or full loss of the rachis nodal abscission zones is responsible for the tough rachis trait. Semishattering forms naturally break into diaspores in the upper portion of the inflorescence or break when pressure is applied in partially formed abscission zones. Changes in bract morphology led to free-threshing cereals. The tough tenacious glumes softened or became more brittle, losing their clasping feature that enclosed the spikelet at maturity. Lemmas and paleas lost their tendency to adhere to the mature grain. Size reduction, anatomical thinning, and increased brittleness of the bracts allowed them to easily fall away with mechanical threshing to release a naked grain. The term hulled cereal refers to different protective features of the bracts that have not completely lost wild-type features: Hulled grains either are encased within the lemma and palea, which either form a hard shell around the grain (pearl millet) or adhere to the grain surface (barley); hulled spikelets have hardened, tough glumes that tightly enclose one or more grains in a spikelet package (spelt wheat, that is, T. spelta).

Domestication Parallels: Crop and Weed Races Domestication followed different routes for each cereal species and did not necessarily involve a straightforward, one-time transition from wild to domesticated species. Introgressive hybridization has played a significant role and followed a variety of pathways. Domesticated races intercrossed with each other (rice), with weedy wild relatives (barley), or with wild species related to the original wild progenitor (sorghum, pearl millet, and maize). Polyploid speciation in the wheats

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and oats illustrates how new genome material introduced through interspecific hybridization formed new species. These types of events increased the narrowed diversity arising from the domestication bottleneck, thereby expanding the adaptability of domesticated forms and their distribution ranges. The common element among wild cereal progenitors is their amenability to cultivation in human-modified habitats. Along with domesticated forms came weeds, the unwanted species that also thrive in these habitats. The development of weed races parallels crop evolution from the standpoint of unintended human selection of weedy forms through agricultural practices and introgressive hybridization between the crop species and its weedy wild relatives. Weed races in crop– weed complexes can be serious pests of agricultural fields as is the case for sorghum and rice. Or, weeds can develop into crop species as happened to the weedy races of oats and rye that infested early wheat fields. As wheat and barley agriculture spread outward from Southwest Asia, wild oat and rye traveled along as grain contaminants into regions where they developed into domesticated forms suited to growing conditions that were less favorable to wheat or barley.

Major Cereal Species Major cereal species (Table 1) are those that are in international commerce and serve as dietary staples beyond a localized region. Wheat and barley are temperate cereal crops of the Fertile Crescent, and along with oats and rye, formed the major grain complex for Western Asia, North Africa, and Europe. Maize and rice are the tropical cereals upon which civilizations in the New World and Eastern Asia developed. Although sorghum, pearl millet, and African rice, all tropical African species, have historically been given a lesser role, they are equally important in the establishment of early human civilizations in Africa and South Asia.

Barley Domesticated barley (Hordeum vulgare) is an annual diploid species derived from the wild progenitor species H. spontaneum. In preagricultural archaeological finds, barley is a universal companion of wheat. While considered inferior as Table 1

Maize Among the domesticated cereals, maize (Zea mays subsp. mays) has an unusual reproductive biology. It is a diploid, crosspollinating monoecious species (staminate and pistillate inflorescences on the same plant) whose pistillate inflorescence is a highly compressed raceme that develops into a cob bearing naked grains. Maize originated from a single domestication

Major cereals and their wild progenitors

Common name Barley Common oat Maize Pearl millet Rice Cereal rye Sorghum Durum wheat Bread wheat a

a staple, barley’s greater adaptability to poor soils and tolerance of soil salinity increased its culture in areas and climatic conditions unfavorable to wheat. The barley spike (or spike-like raceme) has three spikelets at each rachis node. Spikelets contain one floret. Their row-like appearance along both sides of the spike and floret fertility is the basis for dividing domesticated barley into two groups: (1) two-rowed barley with a central fertile spikelet and two adjacent sterile spikelets, each containing a male floret (primitive form; ¼subsp. distichum) and (2) six-rowed barley with all three spikelets fertile (advanced form; ¼subsp. hexastichum). Most domesticated barley has a hulled grain (adherent lemma and palea), although there are naked six-rowed cultivars with the botanical ranking of var. coeleste (¼var. nudum). The domestication of barley has been traditionally treated as a single event occurring in the Fertile Crescent. Although current genetic evidence has supported one independent origin, recent studies show a second primary center of origin located in the region east of the Zagros Mountains. Thus, the barleys of Europe and North Africa developed from the Fertile Crescent line whereas those of Central and East Asia developed from the Zagros Mountains line. The H. spontaneum wild weedy complex spread from its primary habitats in the Fertile Crescent to secondary habitats westward in the Mediterranean– Aegean regions and eastward across Central Asia to Tibet. The weedy forms (¼H. spontaneum) have played a role in building diversity through introgressive hybridization with domesticated barley. For example, the fragile-rachis, sixrowed domesticated barley discovered in Tibet, and originally proposed as a distinct wild progenitor species (H. agriocrithon), is an introgressed form. Although barley has a lengthy agricultural history and development of an extensive number of cultivars and land races, its morphological diversity is relatively limited.

Domesticated species

Wild progenitor species

Hordeum vulgare Avena sativa Zea mays Pennisetum glaucum Oryza sativa Secale cereale Sorghum bicolor Triticum durum Triticum aestivum

Hordeum spontaneum Avena sterilis Zea mays subsp. parviglumis Pennisetum violaceum (¼P. mollissimum) Oryza rufipogon Secale vavilovii Sorghum arundinaceum Triticum dicoccoides unknown

Region of primary domestication

Date of primary domesticationa

Southwest Asia Europe Mesoamerica West and Central Africa

10 200–9550 BP 7600–7400 BP 8700 BP 4800 BP

Southeast Asia Southwest Asia Northeast Africa Southwest Asia West Asia

8000–13500 BP 9450–8450 BP 8000 bp 10 200–9550 BP 8000–7000 BP

Approximate dates of first appearance of domesticated cereals based on current reports of archeological and genetic evidence.

THE CEREAL GRAINS | Cereals: Domestication of the Cereal Grains event in the lowland regions of southwestern Mexico where its wild annual progenitor, Balsas teosinte (Z. mays subsp. parviglumis) is still endemic. Interestingly, maize ancestry has proved to be more complex than a straight wild to crop species development. Genetically, all maize cultivars in the Americas can be traced to highland maize, which also is the maize most closely related to the wild progenitor parviglumis. This ancestral relationship sets up a geographic contradiction due to a lowland origin but a highland ancestral line. With parviglumis distribution restricted to mid- and lowland regions, a highland ancestral form is difficult to explain. Recent genetic research, which tracks with ecological and archaeological findings, has helped resolve the conflicting evidence by identifying a secondary teosinte progenitor, Z. mays subsp. mexicana. Highland teosinte grows sympatrically with highland maize and is interfertile with maize and parviglumis. While mexicana is not the direct progenitor of maize, evidence now points to gene flow from this wild relative as the explanation for highland maize holding the ancestral genetic position. In this respect, maize offers an informative example of the complexities of discerning crop origins when geography and introgressive hybridization between the domesticated form and secondary wild relatives play a role.

Pearl Millet Millet in a broad sense comprises a loose grouping of smallseeded, drought-tolerant species that can be cultivated on poor soils (Figure 4). Collectively, the millets belong to nine genera in the grass subfamilies Paniceae (eight genera) and Chloridoideae (one genus) (Table 2). Due to their small size and a hardened lemma and palea, millet grains are insect-resistant, a feature that adds to their value for the African and Asian cultures that cultivate them. Only pearl millet (Pennisetum glaucum) is a major cereal grain on an international scale. It is a largely cross-pollinating plant due to the unsynchronized maturity of the respective female and male florets. A diploid

Figure 4 Diversity and form in the millets. From left to right: panicles of pearl millet, broomcorn millet, foxtail millet, and Japanese millet. Reproduced with permission from Hancock JF (2004) Plant Evolution and the Origin of Crop Species 2nd edn., Portland, OR: Book News Inc.

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annual, pearl millet was domesticated in the arid regions of West Africa approximately 5500 BP, moving to East Africa and then India 3000 BP and to Southern Africa 2000 BP. In West Africa, pearl millet still forms an integral component of dećrue (flood stage to dryland) agriculture in the Central African river deltas where it is cultivated along with African rice (Oryza glaberrima) and sorghum (Sorghum bicolor). Pearl millet is more drought-tolerant than sorghum and maize. Low genetic variation suggests a relatively limited region of origin, although there are a diversity of morphological forms varying in seed shape, seed color ranging from red to gray to black, and a spike-like compressed panicle that can measure up to 2 m. Pearl millets are grouped into four ecogeographic races with characteristic morphological traits: typhoides (Africa and India), nigritarum (eastern Sahel), globosum (western Sahel), and leonis (West African coast). Active introgression makes it difficult to draw clear phylogenetic lines between pearl millet, its wild progenitor P. violaceum, and the weedy species P. sieberanum, which evolved from crosses between P. violaceum and domesticated millet. Crop mimicry is a problem in African fields of pearl millet where weed races of P. sieberanum, known as shibras, are almost indistinguishable from the domesticated species.

Oats Oats form a polyploid series (2, 4, and 6) of selfpollinating species following different evolutionary lines. Four genomes characterize this group: A and C evolved independently of one another; B and D are derivatives of A. The dominant domesticated species is the common oat, Avena sativa (ACD), which developed from a Southwest Asian ecogeographic race of the wild progenitor species A. sterilis. The less important but closely related red oat, A. byzantina (¼ A. sativa subsp. byzantina) was likely derived from a different disjunct regional A. sterilis race. The diploid sand oat, A. strigosa (As, a variant of A), evolved in Spain from the wild form of this species. The semidomesticated, weedy tetraploid Ethiopian oat, A. abyssinica (AB), evolved in Ethiopia from the wild species A. vaviloviana. A. strigosa and A. abyssinica did not play a role in the evolution of the hexaploids. More water-tolerant than the other major temperate cereals, common oat is suited to cultivation in temperate regions with wet, cool summers. It has an open, nonshattering panicle with hulled (adherent lemma and palea) seeds except for two naked forms: the hexaploid A. sativa subsp. nuda with origins in Mongolia and northwest China and the diploid A. strigosa subsp. nudibrevis, which developed in England. With its center of origin located in the western Mediterranean, A. sterilis has a distribution extending from the Atlantic coast to the Zagros Mountains. A species of primary habitats often growing alongside wild wheat and barley, wild oat also populates abandoned and actively cultivated agricultural land and sites associated with human disturbance. Its initial domestication began as a weed in the newly opened habitats of cultivated wheat and barley fields. As A. sterilis spread eastward and westward with wheat and barley agriculture, a complex of weed races evolved alongside the domesticated common oat, which began to appear c. 4000–3000 BP in Europe. In addition to these domesticated and weedy A. sativa forms, the A. sterilis

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Table 2

Minor cereal grains either cultivated or harvested as cultivated or uncultivated wild species

Cereal

Species

Region where cultivated or collected

Domestication statusa

Adlay millet Fonio Raishan White Fonio Black fonio Polish millet Wild fonio

Coix lacryma-jobi Digitaria D. cruciata D. exilis D. iburua D. sanguinalis D. fuscescens D. longiflora

South Asia, East Asia

Domesticated

South Asia, East Asia West Africa West Africa Europe, Asia West Africa

Domesticated Domesticated Domesticated Domesticated Wild

Brachiaria deflexa Brachiaria ramosa Echinochloa frumentacea Echinochloa colona Echinochloa esculenta Eleusine coracanab Panicum laetum Panicum miliaceum Panicum hirticaule Panicum sumatrense Paspalum scrobiculatum Paspalum scrobiculatum Setaria italica Avena A. abyssinica A. byzantina A. strigosa

West Africa South Asia Asia Africa East Asia Africa, Asia Africa Asia North America Asia South Asia Africa Southeast Asia

Domesticated Domesticated Domesticated Wild Domesticated Domesticated Wild Domesticated Domesticated Domesticated Domesticated Semidomesticated Domesticated

East Africa Mediterranean Basin, West Asia Southern Europe

Semidomesticated Domesticated Domesticated

Oryza barthii Oryza punctata Oryza glaberrima Zizania aquatica Zizania palustris Secale segetale Cenchrus biflorus Eragrostis tef Triticosecale Triticum T. monococcum Triticum T. dicoccum T. ispahanicum T. paleocolchicum T. aethiopicum T. turanicum T. carthlicum T. polonicum T. turgidum T. timopheevii Triticum T. spelta T. macha T. vavilovii T. sphaerococcum T. zhukovskyi

West Africa East Africa West Africa North America North America West Asia Africa, Asia East Africa Worldwide

Wild Wild Domesticated Wild Wild, domesticated Semidomesticated Wild Domesticated Domesticated

Eurasia

Domesticated

Eurasia South Asia Western Asia East Africa South Asia Southwest Asia Southwest Asia, Mediterranean Basin Eurasia West Asia

Domesticated Domesticated Domesticated Domesticated Domesticated Domesticated Domesticated Domesticated Domesticated

Eurasia West Asia West Asia South Asia West Asia

Domesticated Domesticated Domesticated Domesticated Domesticated

Millets Guinea millet Browntop millet Sawa millet Shama millet Japanese millet Finger millet Desert panic Broomcorn millet Mexican panicgrass Little millet Kodo millet Kodo millet Foxtail millet Oats Abyssinian oat Red oat Sand oat Rice Wild rice Wild rice African rice Southern wild rice Northern wild rice Rye Sand Bur Tef Triticale Wheat (2) Small spelt Wheat (4) Emmer Isfahan wheat Georgian emmer Ethiopian wheat Khorasan wheat Persian wheat (4, 6) Polish wheat Rivet wheat Timopheev’s wheat Wheat (6) Spelt wheat Macha wheat Vavilov’s wheat Shot wheat Zhukovsky’s wheat a

For additional information, see Luven P (1988) Traditional Food Plants. FAO Food and Nutrition Paper 42. FAO; Vietmeyer (Director) ND (1996) Lost Crops of Africa: Grains, vol. 1. Washington, DC: Board on Science and Technology for International Development, National Research Council, National Academy Press; Wiersema JH and Leon B (2013) World Economic Plants: A Standard Reference, 2nd edn. New York: CRC Press, Taylor & Francis Group. Williams JT (ed.) (1995) Cereals and Pseudocereals. London: Chapman and Hall, and website sources listed at the end of this article. b Member of the subfamily Chloridoideae. All other millet species belong to the subfamily Paniceae.

THE CEREAL GRAINS | Cereals: Domestication of the Cereal Grains line gave rise to other interfertile weedy wild hexaploid species: A. ludoviciana, A. occidentalis, and A. fatua. Of these, A. fatua is an aggressive agricultural weed whose extensive distribution is aided by its spring type habit, that is, it does not require vernalization. Similarly, the wild tetraploid A. barbata (AB) is a noxious weed worldwide wherever it has been introduced into Mediterranean-like habitats.

Rice Although there are two species of rice, only one of these, Oryza sativa, which was domesticated in Asia, has become a major cereal staple in international agriculture. In contrast, O. glaberrima is a minor cereal whose cultivation is confined to a small area in the equatorial belt of its native West Africa. Both domesticated species and their wild relatives are diploid, semiaquatic plants whose premodern cultivation was tied to seasonal flooding and rains. Of the two, O. sativa has a greater climatic and latitudinal diversity with a range of forms found from tropical to temperate zones and cultivated in different habitats defined by water availability: semiaquatic, either rainfed or irrigated (lowland); deep water (floating); coastal wetland; and dryland (upland). It is a highly diverse species with two major races, sometimes treated as subspecies – indica and japonica. Based on current archeological and genetic evidence, the japonica form was first domesticated from its wild relative O. rufipogon in the middle area of the Pearl River in southern China c. 13 500–8000 BP. Indica subsequently developed from hybridization events between O. rufipogon and the initial japonica cultivars as they spread into Southeast and South Asia. Diversity within the two races and distinctive differences between them are attributable to introgression between the wild and domesticated forms as well as introgression of indica into japonica forms. This variation is grouped into five subpopulations whose boundaries are not always well defined: temperate japonica, tropical japonica (¼javanica), basmati-type (¼aromatic), aus–boro, and indica. Domestication of the considerably less diverse O. glaberrima is dated to 3500 BP in the upper Niger River Delta. Its direct wild progenitor is the wild annual species, O. barthii, which populates savanna water holes and has weedy forms that infest rice fields located in the high rainfall belt of the African savanna. Oryza sativa was introduced into West Africa from Europe in the fifteenth century CE and now predominates. Hybrid cultivars known as NERICA (NEw RICe for Africa) developed from crosses combining the stress and disease tolerance of O. glaberrima with the yield potential of O. sativa show promise for improving food security in the rice-growing areas of Africa.

Rye Cereal rye (Secale cereale) belongs to a small Old World genus of mostly annual diploid species whose phylogenetic relationships are complicated by nondomesticated taxa with an obligate cross-pollinating reproductive biology and perennial habit. Its spikes are nonshattering, producing free-threshing grains at maturity. Cultivation extends into areas requiring winter hardiness, drought-resistance, and tolerance of sandy and acid soils. Preagricultural forms of wild-type rye found in

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Neolithic archaeological sites suggest its status as a tolerated weed of wheat fields. Domesticated rye began to appear circa 9500–8500 BP and likely originated in eastern Turkey and western Armenia. From there, it spread across the Mediterranean Basin, into Europe, and eastward into Central Asia. An interfertile crop complex of wild, weedy, and domesticated races, cereal rye is classified into four groups according to spike fragility or shattering: (1) nonshattering domesticated varieties (S. cereale subsp. cereale); (2) weedy forms (¼segetale) that mimic wheat in spike and grain morphology and are harvested and threshed as part of the wheat crop; (3) semishattering weeds (¼afghanicum) whose upper spike shatters, spreading seed in the field while the lower, intact portion is harvested with the wheat; (4) shattering wild-types (ancestrale) found in secondary habitats whose spikes fully disarticulate into spikelet dispersal units enclosed by brittle glumes. Included in the wild type group is the wild species S. vavilovii (¼S. cereale subsp. vavilovii) that grows in primary basaltic bedrock habitats in Turkey. Evidence points to S. vavilovii as rye’s wild progenitor. The wild annual relatives S. iranicum and S. sylvestre, both self-pollinating species, are reproductively isolated from cereal rye. All the wild perennial rye forms belong to S. montanum (¼S. strictum), a diverse species with intergrading and interfertile ecogeographic races, among them dalmaticum (Mediterranean Basin), anatolicum and ciliatoglume (Anatolia), and kupriyanowii (Iran and Transcaucasia). On the Anatolian plateau of Turkey where weedy cereal rye and S. montanum come into contact, the two species hybridize to produce intermediate, introgressed forms.

Sorghum Sorghum (S. bicolor) is a drought-tolerant, self-pollinating C4 cereal grown throughout the arid and semiarid tropics and particularly important in subsistence farming cultures. In cultivation, sorghum is treated as an annual although most forms are perennial. Domestication took place in the northeastern savanna/steppe region of Africa in an area stretching from present-day Sudan to Ethiopia around 8000 BP. From there, sorghum spread to West Africa, down into southern Africa, and eastward to India, Pakistan, and China. The early extensive range of sorghum has led to a diverse mix of regional forms. The wild progenitor S. arundinaceum; (¼S. bicolor subsp. verticilliflorum), is still found in primary grassland habitats in East Africa. Secondary introgression from hybridization events between domesticated sorghum and S. arundinaceum may be responsible for expanding sorghum’s ecological range from arid savanna habitats into areas with higher rainfall and humidity where it can tolerate up to 5000 mm of rain during the growing season. The crop–weed complexes of sorghum’s native Africa also characterize its cultivation in Asia, Australia, and the Americas due to the introduction of contaminated seed stocks. Thus, the bidirectional gene flow between the crop and weed essentially occurs worldwide. Through domestication, the shattering, open panicles of S. arundinaceum evolved toward nonshattering, compact panicles with larger grains. Traditionally, sorghum is classified into five races – bicolor, guinea, caudatum, kafir, and durra – and ten two-by-two race combinations, all 15 with a distinctive

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S.R. Guinea

Bicolor

S.R.

Caudatum

Kaffir

Durra

Figure 5 Panicles and mature grains still enclosed by their glumes for each of the five sorghum races. Reproduced with permission from Luven P (1988) Traditional Food Plants. FAO Food and Nutrition Paper 42. FAO.

ecogeographic range and place in indigenous African and Asian agriculture as well as morphological and use differences (Figure 5). Bicolor, the most primitive and similar in appearance to wild sorghum with its loose, open panicle, was the first domesticated race from which the other three races were derived. Caudatum, which is found from Lake Chad to Ethiopia in bicolor’s primary domestication zone, is unique for its grain shape – flat on one side, convex on the other. Kafir is associated with the Bantu-speaking peoples of East and Southeastern Africa who migrated there from West Africa. Durra, which has dense, compact head-like panicles, was developed in India, where it is now largely grown. African durra likely arrived from India during Islamic migrations into Africa. Recent research confirms that the fifth race (¼guinea), now designated the guinea margaritiferum group, is the product of a second domestication event in West Africa. Divergent from the four other sorghum races, the guinea margaritiferum group is intermediate between sorghum and its wild progenitor and suited to the poor soils and erratic rainfall conditions of West Africa. Guinea margaritiferum sorghum and the wild Southeast Asian

species S. propinquum, which is interfertile with domesticated sorghum, both offer ‘new,’ untapped genetic resources for breeding programs.

Wheat The wheats comprise a large allopolyploid complex of wild and domesticated species taxonomically classified in the genera Triticum (wild and domesticated) and Aegilops (wild). They are annual, self-pollinating species. Together, hexaploid bread wheat (T. aestivum) and durum wheat (T. durum; ¼ T. turgidum subsp. durum) are the two major wheats cultivated worldwide, ranking third in cereal production after corn and rice. The evolution and domestication of wheat traces an interesting path in diploid genome development and polyploid speciation. Bread wheat’s three ancestral genomes A, B, and D are closely related. A and B diverged approximately 7 million years ago (mya), giving rise to the D genome 5–6 mya through homoploid speciation. The wild diploid species that carry the respective genomes are T. urartu (A), Ae. speltoides, the putative

THE CEREAL GRAINS | Cereals: Domestication of the Cereal Grains B donor species whose subgenome within the Aegilops genus is traditionally distinguished as S: and Ae. tauschii (D). The evolutionary lines leading from ancient ancestral diploid wheats to tetraploid and hexaploid wheats constitute a multilevel phylogenetic mosaic built on multiple rounds of homoploid and polyploid hybrid speciation events. The diploid progenitor T. urartu has no domesticated form. T. dicoccoides (¼T. turgidum subsp. dicocccoides), the wild tetraploid wheat (BA), originated from an Ae. speltoides x T. urartu cross. Emmer wheat (T. dicoccum; ¼T. turgidum subsp. dicoccum) (Figure 6) was domesticated from T. dicoccoides circa 10 000 BP in the Fertile Crescent. A primitive form, emmer has a semifragile spike and hulled grains (clasping glumes). Its spread eastward brought it into contact with Ae. tauschii, which populated primary habitats in the Caspian Sea Belt. The hexaploid hybrid speciation event that formed T. aestivum (BAD) (Figure 6) likely took place along the edges of cultivated fields where emmer and weedy Ae. tauschii subsp. strangulata came into contact. Bread wheat has no known wild hexaploid progenitor. Evidence suggests that the preliminary hexaploid form was a primitive hulled T. spelta type. Naked T. aestivum forms likely developed within a short period afterwards c.8000–7000 BP. European forms of T. spelta may have arisen independently from T. aestivum T. dicoccum crosses. The diploid and tetraploid wheats of the bread wheat line are suited to the Mediterranean-type habitats of Southwest Asia with mild winters and dry summers. The addition of the D genome to hexaploid forms extended the ecogeographic range

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to continental temperate regions with colder winters and humid summers. As wheat cultivation of the respective tetraploid and hexaploid forms diffused across Asia, Europe, and North Africa, humans developed more advanced, specialized naked grain forms (for example, tetraploid durum and rivet wheats) (Figure 6; Table 2) as well as a diverse array of landraces unique for their regional distribution and morphological and agronomic features. Of note, the transition from wild-type shattering spikes and hulled grain to tough rachis, freethreshing domesticated forms follows two paths in the bread wheat line. The spikelet dispersal units for T. urartu and T. dicocccoides are wedge-shaped, with the rachis internode piece subtending the spikelet. In the case of the semishattering T. spelta, its hulled spikelet units are cylindrical (barrelshaped), with the rachis internode adjacent to the spikelet (Figure 3). Aegilops tauschii also exhibits the cylindrical mode of spikelet dispersal. All other Triticum (sensu stricto) wild wheats shatter into the wedge units. Two other evolutionary lines characterize the wheats. A different hybrid speciation event between T. urartu and Ae. speltoides produced the wild tetraploid species T. araraticum (GA). While T. araraticum is almost identical in morphology to T. dicoccoides and shares the same distribution ranges in Turkey, Iraq, and Iran, the two species are reproductively isolated from each other. Thus, the B and G assignments for the Ae. speltoides genome contribution recognize the respective origins for the two tetraploid species. Two domesticated forms complete this evolutionary line: T. timopheevii (GA) and T. zhukovskyi (GAAm). Triticum zhukovskyi has no known wild hexaploid progenitor. The third evolutionary wheat line has two diploid species: the wild T. boeoticum and its domesticated offshoot, T. monococcum (Figure 6). Their A genome is different from that found in the bread wheat line and variously noted at Ab or Am. Triticum monococcum (einkorn) is an important player in the early archaeological record but today is considered a relic domesticated species.

Minor Cereals

Figure 6 Diversity within the wheats. From left to right: T. monococcum, T. dicoccum, and T. spelta (all hulled wheats), T. polonicum (Polish wheat), T. turgidum (rivet wheat: branched form), T. aestivum (compactum form), T. durum, T. aestivum (awned*: ‘Turkey’), and T. aestivum (awnless: ‘Wilhelmina’). (Adapted from The Field Museum, negative B79676.) *Awns on ‘Turkey’ are barely visible due to photographic quality and their smaller diameter and weaker anatomy relative to the awns on the T. durum specimen to its left.

The major cereals discussed earlier in the text represent a small sampling of the diverse collection of grass species that have been domesticated. Table 2 provides a partial listing of lesserknown cereals that are currently, or at one time were, important crops or are still harvested from wild stands. Some of the domesticated cereals are cultivated on an extensive scale or across large regions (foxtail millet). Others are locally restricted: white fonio in West Africa (Figure 7) and raishan in India. Their importance is measured by their role as dietary staples for the peoples who cultivate them. Many of these species have been supplanted by the major cereals. For example, broomcorn millet (Panicum miliaceum), once cultivated widely in Europe and the United States, has declined in acreage and use for human consumption. As discussed in the preceding text, African rice (O. glaberrima), an indigenous species of dećrue agriculture on the river deltas of Central Africa, is being replaced by O. sativa and NERICA hybrids. On the other hand, some minor grains are popular in Western specialty markets, for example, tef and the hulled wheats farro (T. dicoccum) and spelt (T. spelta).

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Figure 7 Vegetative and reproductive structures of white fonio (D. exilis). The inflorescence is a digitate raceme with a winged rachis. Reproduced with permission from Haq N (1995) A neglected cereal and two promising ones. In: Willams JT (ed.) Cereals and Pseudocereals. Chapman and Hall.

Wild grasses and partially domesticated grasses still play an important role in the diet for subsistence cultures. West Africans gather the wild fonio species D. fuscescens and D. longiflora in famine times and benefit from harvestable semidomesticated kodo millet infesting their fields if they lose the rice crop. The weedy oat species, A. abyssinica, forms an integral component of the grain harvested from wheat and barley fields in Ethiopia. Subsistence farmers on the Anatolian plateau of Turkey allow weedy forms of S. cereale, which are more cold- and drought-tolerant than the wheat crop that they infest. In bad years, this harvestable weed rye crop provides the ‘wheat of Allah’ for this traditional culture.

Research Trends Fully characterizing the genetic diversity of cereal species and that of their wild and weedy relatives is a primary focus of current cereal research. Along with genome sequencing projects that are underway or completed, the development of the annual diploid Brachypodium distachyon as a model grass system will open avenues for discerning genetic pathways and gene functions for crop traits such as plant–pathogen interactions, yield, and stress tolerance. Where the Brachypodium model will serve for photosynthetic studies of C3 cereals (rice,

barley, wheat, rye, and oats), the C4 model species Setaria viridis will do the same for maize, millet, and sorghum. Both grass models will provide the functional framework for moving the more efficient C4 system into wheat, rice, and barley and in developing the promising C4 energy crops such as switchgrass (Panicum virgatum) and giant miscanthus (Miscanthus giganteus). Phylogenetic research is at various stages of progress dependent on the complexity of the cereal genomes. Availability of research funding is also a factor governed by position in international cereal markets. For example, pearl millet is lower on the funding scale than corn, rice, and wheat. With robust phylogenetic trees tracing a well-defined picture of relationships, cereal breeders will have a more reliable roadmap for efficiently exploiting genetic diversity to improve crop traits and create new cereal crops. The combined potential of the Brachypodium–Setaria grass model systems and phylogenetic studies promises a future of expanded efforts in high-tech cereal breeding, which will become increasingly more important for addressing the food security issues of growing populations, changing climatic conditions, eroding aquifers, and loss of arable land. An underlying factor in meeting these challenges will be the availability of germplasm resources. Successfully advancing the possibilities of modern ‘domestication’ requires an active effort to preserve the existing crop wild species diversity. Historically, germplasm conservation has suffered from a lack of consistent funding and a coordinated global commitment. Realizing the full potential of twentyfirst century cereal breeding will require a top priority status for germplasm conservation programs equal to today’s international research collaborations driving genome mapping initiatives and grass model systems development.


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How does the functional morphology of grass flowers influence the natural speciation events that shaped the phylogeny of wild and domesticated grain species? Using the example of maize, sorghum, and wheat, explain the morphological changes under domestication that altered their respective inflorescences from the wild-type raceme, panicle, and spike to the advanced domesticated forms. What is the significance of the development of grain retention and easily threshed grains in the early development of agriculture and why did these domestication syndrome traits predate changes in dormancy, seed size, etc.? Take one of the positions in the debate over the speed and spread of domestication and explain why it is the likely scenario in the development of agriculture. What is a weed race and what kinds of roles do weeds play in domestication and the development of agriculture? How has introgressive hybridization played a role in cereal evolution and what are examples of the different mechanisms by which introgression has influenced the phylogenetic relationships in wild and domesticated crop complexes? How did their respective evolutionary pathways differ for the Old World Founder crops barley and wheat? Explain the features of maize domestication that distinguish it from the other major cereals and clarify the


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differences between the human-mediated changes and those that would have happened by natural biological processes. How did phenotypic diversity in pearl millet and sorghum become extensive and what features of their domestication pathways have encouraged these trends? How did habitat and the geographic spread of early domesticated forms affect rice diversity and its phylogenetic relationships? Although African rice is a minor grain, why is it important and what are the negative effects of its reduction in acreage in Africa? Why are minor grains greater in number and what is their importance to the regions where they are cultivated? How will genetic evidence of phylogenetic relationships advance development of cereal cultivars that will improve food security under changing climatic conditions and loss of arable land? Why is preservation of germplasm diversity, particularly wild cereal relatives and land race cultivars, of critical importance for plant breeding and what role can molecular genetics play in building a more complete picture of cereal diversity? How will a functional grass model guide future cereal research to improve agronomic and physiological traits and what benefits will be gained from moving a C4 photosynthetic system into rice and wheat?


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Examine the advantages of multidisciplinary archaeological–genetic studies in discerning the timing of domestication and the location of primary and secondary centers of cereal domestication and discuss how this work will inform germplasm conservation strategies and plant breeding programs. NERICA hybrids combine the yield benefits of Asian rice with the drought tolerance and weed and pest resistance of African rice. Consider the advantages and disadvantages of NERICA introductions relative to a balance between diversity conservation and food security in Africa. Explore the role of mapping initiatives and other comprehensive genetic studies of cereal species in advancing modern agriculture. What is the importance of educating the public in their importance to global food security both from the perspective of public funding and collaborative international projects?

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Breeding of Grains: Barley: Genetics and Breeding; Genetics of Grains: Rice: Genetics; Wheat Genetics and Genomics; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Maize: Overview; Millet Minor: Overview; Millet Pearl: Overview; Oats:

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Overview; Rye Grain: Its Genetics, Production, and Utilization; Triticale: Overview.

Further Reading Clark LG and Pohl RW (1996) Agnes Chase’s First Book of Grasses. Washington, DC: Smithsonian Press. Elbaum R, Zaltzman L, Burgert I, and Fratzl P (2007) The role of wheat awns in the seed dispersal unit. Science 316: 884–886. Doebley JF, Gaut BS, and Smith BD (2006) The molecular genetics of crop domestication. Cell 127: 1309–1321. Abbo S, Gopher A, Peleg Z, et al. (2006) The ripples of “The Big (agricultural) Bang”: The spread of early wheat cultivation. Genome 49: 861–863. Allaby RG, Fuller DQ, and Brown TA (2008) The genetic expectations of a protracted model for the origins of domesticated crops. PNAS 105: 13982–13986. Diamond J (2002) Evolution, consequences and future of plant and animal domestication. Nature 418: 700–707. Tanno K-I and Willcox G (2006) How fast was wild wheat domesticated? Science 311: 1886. Harlan JR (1992) Crops and Man, 2nd edn. Madison, WI: American Society of Agronomy. Zohary D, Hopf M, and Weiss H (2014) Domestication of Plants in the Old World: The Origin and Spread of Cultivated Plants in South-West Asia, Europe and the Mediterranean Basin, 4th edn. New York: Oxford University Press. Badr A, Mu¨ller K, Scha¨fer-Pregl R, et al. (2000) On the origin and domestication history of barley (Hordeum vulgare). Molecular Biology and Evolution 17: 499–510. Morrell PL and Clegg MT (2007) Genetic evidence for a second domestication of barley (Hordeum vulgare) east of the Fertile Crescent. PNAS 104: 3289–3294. Van Heerwaarden J, Doebley J, Briggs WH, et al. (2011) Genetic signals of origin, spread, and introgression in a large sample of maize landraces. PNAS 108: 1088–1092. Mathur PN (2012) Global Strategy for the Ex Situ Conservation of Pearl Millet and Its Wild Relatives. Rome, Italy: Global Crop Diversity Trust. Harlan JR (1996) The tropical African cereals. In: Harris DR and Hillman GG (eds.) Foraging and Farming: The Evolution of Plant Exploitation. London: Unwin Hyman Ltd. Loskutov IG (2008) On evolutionary pathways of Avena species. Genetic Resources and Crop Evolution 55: 211–220. Yuan X, Xu Q, Dong G, et al. (2012) A map of rice genome variation reveals the origin of cultivated rice. Nature 490: 497–501. Sackville-Hamilton R (2010) Global Strategy for the Ex Situ Conservation of Rice Genetic Resources. Manila, Philippines: International Rice Research Institute. Linares OF (2002) African rice (Oryza glaberrima): History and future potential. PNAS 99: 16360–16365. Shang H-Y, Wei Y-M, Wang X-R, and Zheng Y-L (2006) Genetic diversity and phylogenetic relationships in the rye genus Secale L. (rye) based on Secale cereale microsatellite markers. Genetics and Molecular Biology 29: 685–691. Mace ES, Tai S, Gilding EK, et al. (2013) Whole-genome sequencing reveals untapped genetic potential in Africa’s indigenous cereal crop sorghum. Nature Communications 4: 2320. http://dx.doi.org/10.1038/ncomms3320. Marcussen T, Sandve SR, Heier L, et al. (2014) Ancient hybridizations among the ancestral genomes of bread wheat. Science 345: 287-12–287-15. http://dx.doi.org/ 10.1126/science.1250092. Kilian B, O¨zkan H, Deusch O, et al. (2007) Independent wheat B and G genome origins in outcrossing Aegilops progenitor haplotypes. Molecular Biology and Evolution 24: 217–227. Luven P (1988) Traditional Food Plants. FAO Food and Nutrition Paper 42. FAO. Vietmeyer ND (1996) Lost Crops of Africa: Grains. vol. 1. Washington, DC: Board on Science and Technology for International Development, National Research Council, National Academy Press. Wiersema JH and Leon B (2013) World Economic Plants: A Standard Reference, 2nd edn. New York: CRC Press, Taylor & Francis Group. Williams JT (ed.) (1995) Cereals and Pseudocereals London: Chapman and Hall. Brkljacic J, Grotewold E, Scholl R, et al. (2011) Brachypodium as a model for the grasses: Today and the future. Plant Physiology 157: 3–13. Brutnell TP, Wang L, Swartwood K, et al. (2010) Setaria viridis: A model for C4 photosynthesis. Plant Cell 22: 2537–2544.

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Relevant Websites http://www.ars-grin.gov – A searchable United States Department of Agriculture crop germplasm database providing information on scientific and common names, distribution, economic importance, and references. http://www.ceg.icrisat.org/ipgsc.html – International Pearl Millet Genome Sequencing Consortium (global reference genotype Tift 23D2B1). http://www.cgiar.org/cgiar-consortium/ – Consultative Group on International Agricultural Research (CGIAR) with five independent international centers conducting basic and applied research on barley, maize, millet, rice, sorghum, and wheat. http://www.croptrust.org/ – A CGIAR partner with crop diversity programs targeting conservation of the major cereal grains. http://mansfeld.ipk-gatersleben.de – An internet-searchable, version of Mansfeld’s World Database of Agricultural and Horticultural Crops, which is set up for queries

on the taxonomy, common names, distribution, and other miscellaneous information about crop plants. http://www.public.iastate.edu/imagefpc/IBSC%20Webpage/IBSC%20Templatehome. html – International Barley Sequencing Consortium. http://rgp.dna.affrc.go.jp/IRGSP/ – International Rice Gene Sequencing Project (Oryza sativa ssp. japonica cv. ‘Nipponbare’). http://www.theplantlist.org/ – Searchable database offering current listings of accepted plant names and direct links to checklist data held by collaborating institutions. http://wheat.pw.usda.gov – The United States Department of Agriculture searchable database for a variety of topics dealing with the genomics, mapping, germplasm, pathology, and taxonomy of barley, rye, triticale, wheat, and oats. http://www.wheatgenome.org/ – International Wheat Genome Sequencing Consortium (Triticum aestivum).

Maize: Overview MP Scott and M Emery, Iowa State University, Ames, IA, USA Published by Elsevier Ltd.

Topic Highlights

Maize Reproduction

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Maize is a monoecious plant, meaning it has both male and female reproductive organs on the same plant. Flowers mature after 60–70 days of vegetative plant growth. Male staminate flowers develop into tassels and are found on the uppermost tip of the main stem. Female pistillate flowers are found in one or more ears located at nodes along of the stem. Typical maize varieties are diploid, containing two sets of ten chromosomes. Copious amounts of pollen (up to 1 billion grains per plant) are shed from anthers and dispersed by air currents. While the majority of the pollen falls close to the plant, a small portion of the pollen can be carried over great distances via the wind. Industry standards typically consider plants separated by a distance of 200 m to be reproductively isolated. Fertilization occurs by the process of ‘double fertilization’ common to angiosperm species. A pollen grain carrying two nuclei lands on a silk and germinates to produce a pollen tube. The pollen tube grows down the length of the silk until it reaches the embryo sac where it ruptures releasing the two sperm nuclei. The first sperm cell fuses with the egg cell to produce the embryo, the organ that ultimately develops into the next-generation plant. The second sperm cell fuses with the central cell of the embryo sac giving rise to the endosperm, the storage tissue that nourishes the developing seedling until it is capable of living independently. Grain fill to maturity takes about 40 days.

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Maize is a member of the grass family Poaceae and the closest known relative is the grassy weed teosinte. Maize is a major crop, accounting for 32% of the total cereal production worldwide in 2013. Maize kernels provide nutrition in the form of starch, oil, and protein. Culinary dishes incorporating maize as an ingredient are consumed worldwide. Maize is processed via dry milling and wet milling and nixtamalization. Maize is a model organism in research. Maize cultivars include inbred lines, single-cross hybrids, double-cross hybrids, and open-pollinated varieties. Biotechnology has allowed for reduced inputs and higher outputs in maize production; however, some societies have concerns regarding the use of genetically modified maize.

Learning Objective

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To acquire a greater understanding of the role maize plays in the world and how technology seeks to enhance maize quality and profitability.

Introduction

Maize Kernel Composition

Zea mays, more commonly referred to as maize, is a member of the grass family Poaceae, or true grasses. Maize is thought to have originated 55–70 million years ago in what is now Central or South America and has since diversified into nearly 10 000 nondomestic relatives. Figure 1 shows a phylogenetic tree of grass species related to maize. There exists no direct ancestor for maize; however, to date, the closest relative to maize are the teosintes. Prehistoric selection has resulted in ears lacking seed cases called glumes and seeds that adhere to the cob until manual removal. These alterations limit the ability of maize to survive without human intervention. Maize is an annual plant with C4 metabolism, making it very efficient at carbon fixation. It has the greatest global production of any crop species around 800 million tonnes was produced worldwide in 2013, accounting for 32% of the total cereal production. The top three producers include the United States, China, and Brazil. Maize is grown on more areas of the planet than any other crop and is grown on every continent except Antarctica. The grain of maize is used for food, feed, and industrial products including biodegradable foams, plastics, and adhesives. Additionally, maize stover, the leaves and stalk of the maize plant, is used for forage, biofuel production, and chemical production.

The mature maize kernel is referred to as a caryopsis and is not a true seed but rather a one-seeded fruit. Kernels are composed of four organs: the pericarp, embryo, endosperm, and pedicel. Physical properties, such as hardness, shape, size, color, and composition, vary among maize varieties. The main organs of a maize kernel are shown in Figure 2. The outer layer of the kernel is the pericarp and encloses the kernel for protection. The endosperm comprises the majority of the kernel’s inner contents. The endosperm itself is composed of four tissue types: the aleurone (outer) layer, the starchy endosperm, the basal endosperm transfer layer, and the embryosurrounding region. The endosperm provides nutrients in the form of sugars and amino acids to the growing embryo. The embryo is composed of the following: the scutellum (the monocotyledon that absorbs nutrients during germination), the coleoptile (protective sheath of the emerging shoot), the plumule (young plant), the radicle (primary root), and the coleorhizae (protective sheath of emerging root). The tip cap serves to attach the kernel to the cob and protect the kernel. In terms of nutritive composition, the kernel can be further classified into five main components. The typical number 2 yellow dent maize kernel contains 72% starch, 9.5% protein, 4.3% oil, 1.4% ash, and 2.6% sugar.


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Starch Starch is the most abundant component in maize kernels and serves as an efficient storage molecule for glucose. Starch accumulates in the form of dense-insoluble granules. It is composed of two main components: amylose and amylopectin. Amylose is predominantly a linear polymer composed of 1,4linked a-D-glucan chains. In contrast, amylopectin is highly branched by a-1,6-glycosidic bonds. Starch biosynthesis requires the coordinated activities of a myriad of enzymes, including starch synthases and starch branching enzymes and starch debranching enzymes. Enzymatic activity within the kernel alters starch content and properties. The degree of branching and branch chain length are starch properties that can vary considerably among maize varieties. Maturity also affects starch quality. Traits sought in a commercial setting include gel strength, viscosity, and thermal properties such as gelatinization. Maize starch provides 4 cal g1. Genetic mutations can confer altered starch phenotypes. Mutant alleles of waxy1 (wxy1) produce 100% amylopectin starch, which is useful as a thickening agent in foods. Mutation of the amylose-extender (ae) gene leads to high-amylose starch (HAS) with a range of amylose values from 25% to 80%. HAS A phylogeny of diploid grass species Barley Goat Grass Einkorn Wheat Tall Fescue Asian Rice Teosinte

is known for its slow digestion in vivo. The sugary-1 (su1) and shrunken-2 (sh2) lead to kernel phenotypes that are sweeter than field corn and are used to produce sweet corn varieties for canning and fresh consumption.

Oil Oil from a kernel of typical Corn Belt maize, number 2 yellow dent, contains 62% linoleic acid, 25% oleic acid, 10% palmitic acid, 2% stearic acid, and 1% linolenic acid; saturated fatty acids equate to 12% of the total lipid content. The oil within the maize kernel provides 9 cal g1. Linoleic, linolenic, eicosapentaenoic, and docosahexaenoic fatty acids are shown to have a positive correlation with cardiovascular health. A ratio of 6:1, linoleic to linolenic, is recommended. Similar to starch content and quality, studies demonstrate that exotic germplasm possesses extensive ranges of fatty acid composition. Exotic lines are crossed to yield varieties with increased oil content. Oil content varies across inbred maize lines and across varied environments. Total fatty acid composition varies throughout kernel development and ultimately increases as the kernel matures. Oil content is believed to be affected by a large number of loci and is a highly heritable trait. Certain breeding schemes aim solely at increasing lipid content and/or quality. Duvick (2003) altered fatty acid content by introducing Tripsacum genes, a wild relative of maize, into various maize lines. Fatty acid stability is directly correlated to saturation level. Linolenic is the least stable fatty acid, containing three points of unsaturation. Oleic fatty acids are much more stable and less prone to oxidation. Oleic fatty acids are monounsaturated. Once oxidation begins, it cannot be stopped or reversed and ultimately leads to rancidity.

Maize Eastern Gammagrass Sorghum Fountain Grass Figure 1 A phylogeny of diploid grass species. Adapted from Gaut BS, Le Thierry D’Ennequin M, Peek AS, and Sawkins MC (2000) Maize as a model for the evolution of plant nuclear genomes. PNAS 97: 7008–7015. http://dx.doi.org/10.1073/pnas.97.13.7008.

Figure 2 The mature maize kernel, showing component parts. Reproduced from Encyclopedia of Grain Science.

Protein Protein is another vital component in the maize kernel. Seed proteins are divided into four classes: albumin, globulin, prolamin, and glutelins. The major storage proteins in maize are prolamins, also referred to as zeins. Eighty percent of the stored protein in maize is found in the endosperm. Because of the amino acid balance of zeins and their abundance in the endosperm, lysine, tryptophan, and methionine are typically at low levels in maize. Maize is therefore not a complete protein source and must be eaten with complementary protein sources to ensure requirements for the essential amino acids are met. Many countries rely on maize as their main food source; in turn, essential amino acid deficiencies such as kwashiorkor and pellagra frequently occur. Maize protein provides 4 cal g1. Research aims to increase the quality of protein in maize. First observed in 1920, the Opaque-2 (o2) mutation causes a decrease in the amount of zein content and thus a higher ratio of nonzein proteins with increased levels of essential amino acids. Unfortunately, this mutation results in reduced kernel hardness, yield, and fungal and pest resistance. To overcome this deficiency, modifier genes have been introduced into o2 varieties that increase kernel hardness. The resulting maize is called quality protein maize and grown in many parts of the world where it has contributed to improved nutrition. In addition to o2 mutants, Floury2 (fl2) mutants have shown to have

THE CEREAL GRAINS | Maize: Overview improved amino acid balance. Less abundant components of the maize kernel include fiber, minerals, vitamins, anthocyanins, and antinutrients.

Maize in Food Maize is a food ingredient that brings commonality to culinary cultures across the world. Cultural traditions and corn varieties dictate how maize is incorporated into a wide variety of foods. The main kernel components can be separated and processed into products such as corn starch for thickening and binding agents and corn oil for frying and baking; whole grain kernels are used in popped popcorn or ground into corn meal and used in breads, biscuits, and cereals. From enchiladas, tamales, totopos, tostaditas, and tortillas, virtually every Mexican dish uses maize. Maize porridges are seen across the world: referred to as puliszka and malderash in Hungary, posho in Africa, polenta in Europe, grits in the United States, and kpekple in Ghana. Maize meal can be ground and fermented into sora, a maize beer in Peru, or used to make hard alcohols such as whiskey and bourbon. Maize is truly a cross-cultural food.

Maize Processing Maize kernel quality and physical attributes determine its end use. The United States recognizes five grades of maize and three classes: yellow, white, and mixed maizes. Food maize typically specifies number 1 grade yellow or white dent corn (Figure 3). Additionally, the manner in which maize is processed is a vital component in its incorporation into foods (Figure 4). Harder kernels are desirable for storage, shipping, and handling; dry milling calls for a kernel with a harder endosperm void of cracks. Dry milling is often used to produce baked goods, breakfast cereals, and ethanol. In the dry-milling process, tempering the grain is a vital first step. A hammer mill is

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then used to coarsely grind the maize kernels. Several steps of size and weight separation, in addition to regrinding, yield maize grits, flour, and fiber. The quality, content, and end use of the maize must be considered before entering the wet- or dry-milling process. Maize kernels with a softer endosperm perform better in the wet-milling process. The wet-milling process entails steeping maize in a dilute sulfur dioxide solution to soften the kernel and separate it into its smaller components. The germ can be first removed and later processed for oil. The remaining components are ground and separated further into grits, flour, and fiber. Further processing yields corn gluten meal, and starch. Maize starch and high-fructose corn syrup are a main end product of the wet-milling process in the United States.

Maize Kernels

Dry milling

Wet milling

Nixtamalization

Flaking frits Brewing grits Other grits Corn meal/flour Germ Bran

Starch Germ Gluten Bran Steep water liquor

Masa Dry masa flour

Food industries Breakfast cereals, snacks, baking, brewing, distilled spirits, oil, sweeteners, corn and tortilla chips

Figure 4 Maize food processing determines maize as food ingredient. Adapted from Encyclopedia of Grain Science.

U.S. Grades and Grade Requirements for Maize

Grade U.S. 1 U.S. 2 U.S. 3 U.S. 4 U.S. 5

Minimum Test, Weight/Bushel (Ib) 56.0 54.0 52.0 49.0 46.0

Maximum Percent Allowed Damaged Kernels Broken Kernels and Heat-Damaged Total Foreign Material 2.0 0.1 3.0 3.0 0.2 5.0 4.0 0.5 7.0 5.0 1.0 10.0 7.0 3.0 15.0

U.S. Sample Grade: (a) Does not meet the requirements for grades U.S. No. 1,2,3,4, or 5: or (b) Contains stones which have an aggregate weight in excess of 0.1 percent of the sample weight, 2 or more pieces of glass, 3 or more crotalaria seeds (Crotalaria spp.), 2 or more caster beans (Ricinus communis L.), 4 or more particles of an unknown foreign substance(s) or a commonly recognized harmful or toxic substance(s), 8 or more cockleburs (Xanthium spp.) or similar seeds singly or in combination, or animal filth in excess of 0.20 percent in 1,000 grams; or (c) Has a musty, sour, or commercially objectionable foreign odor; or (d) Is heating or otherwise of distinctly low quality.

Figure 3 The US maize grading scale. Reproduced from USDA (2013) Grain Inspection Handbook. Pamphlet. USDA Federal Gain Inspection Service, Washington, DC.

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Nixtamalization, dating back from 1200 to 1500 BC, is an ancient type of maize processing that includes rendering kernels into a paste to increase the bioavailable nutrients such as calcium and digestible iron. Kernels are steeped in a water/lime solution over heat and ground into masa, also known as maize dough, that is used to produce tortillas, corn chips, and other food products.

Maize in Science Maize is an important model organism in genetic research. It has several attributes that make it attractive for this purpose. It is a large plant and phenotypic analyses are easily done. Each plant produces an ear typically containing 100–400 kernels. It is broadly adapted and has tremendous genetic diversity. Maize has a moderately sized genome of 2.5 gigabase pairs. A vast collection of mutant stocks have also been developed that assist in research; this has allowed for many genes to first be characterized molecularly in maize. Being a diploid species, genetic manipulation and analysis is less complex than in species with a higher ploidy level. Additionally, the large physical size of the maize chromosomes is a great benefit to cytogenetic researchers. Research on maize has led to several key discoveries. Perhaps most notable is the discovery of transposons by Barbara McClintock, for which she was awarded the Nobel Prize in Physiology or Medicine in 1983. Cytogenetic studies in maize resulted in an understanding of genetic recombination and enabled genetic mapping. The role of telomeres was determined in maize. Through collaborative efforts, it was one of the first crops to have its genome completely sequenced.

Maize Breeding, Genetics, and Biotechnology Maize Cultivar Types A cultivar is a plant variety that has been developed for a specific use. Several types of maize cultivars are grown including inbred lines, single-cross hybrids, double-cross hybrids, and open-pollinated varieties (Figure 5). Inbred lines are created by successive generations of self-pollination. The resulting plants are genetically homozygous and phenotypically

Single cross

Inbred line Inbred line A B

Modified single cross

Inbred line Inbred line Inbred line A1 A2 B

Three-way cross

Inbred line Inbred line Inbred line A B C

Double cross Inbred line Inbred line Inbred line Inbred line A B C D Figure 5 Types of hybrids grown commercially in North America. Reproduced from Encyclopedia of Grain Science.

homogeneous. Due to inbreeding depression, inbred lines have low yield and are not used for grain production. Their main purpose is in the production of hybrid seed. When two inbreds are cross-pollinated, a single-cross hybrid results. Single-cross hybrids are genetically heterozygous and phenotypically uniform. Because of the difficulties of producing seed on inbred lines, several types of hybrids have been developed. An open-pollinated variety is a population of plants that is genetically heterozygous and phenotypically nonuniform. As the name implies, the seed of open-pollinated varieties is produced by allowing natural pollination to occur in the population. Synthetic populations are derived from intermating several varieties that are frequently used in breeding programs to produce inbred lines. Mechanized agriculture has led to a preference for hybrids because of their uniformity and high yields. The process of hybrid improvement and seed production has become highly industrialized. Industrial maize breeding has led to greatly increased yields. Open-pollinated varieties require much less infrastructure for seed production and genetic improvement and are often grown in developing countries.

Hybrid Maize Breeding Hybrid maize breeding allows breeders to capture and fix extremely productive genotypes by taking advantage of hybrid vigor. Productivity and vigor in maize plants are generally proportional to the degree of heterozygosity. Thus, inbred lines, although uniform and reproducible, are usually poor agronomic purposes. Heterozygosity and performance can be restored by crossing unrelated inbred lines to make hybrids. Inbred lines are classified into heterotic groups according to their ability to form productive hybrids in combination with other groups and their suitability as a male or female parent. For example, nearly all inbreds used as females in North American hybrids are in the Stiff Stalk heterotic group. Development and maintenance of inbred lines and testing hybrid combinations require a great deal of infrastructure and expertise that are not available to most farmers or even small seed companies and are therefore largely done by large seed companies. Uniformity is essential in efficient and profitable production of maize. Superior technology and machinery has assisted with such uniformity. Improved accuracy in the evaluation of cultivars has allowed for large genetic gains and the overall creation and advancement of superior maize inbreds. Superior farm equipment equipped with GPS and computer monitoring systems has led to optimal planting depth, density, and spacing and precise measurements of grain yield during harvest. In the future, precision agriculture will continue to increase productivity by optimizing inputs, such as maize variety and fertilizer amount, on a per land area basis.

Maize Biotechnology Biotechnology gives the ability to introduce genes from any source into the maize genome. Two types of traits derived from genetic engineering methods are currently in commercial production: insect resistance and herbicide tolerance.

THE CEREAL GRAINS | Maize: Overview Insect-resistant maize decreases the need of pesticide applications directly to the plant. The use of pesticides in the United States has been reduced to 6% since 1996, a total of 172 million kilograms per year. Fewer tonnes of chemical are applied, benefiting the health of the environment and proving economically beneficial for the farmer. From 1996 to 2010, the income of US farmers increased to a total of $21.7 billion dollars, 23% of that profit was derived from 2010 alone. The percentage of genetically engineered (GE) maize has increased almost fourfold in 12 years (Figure 6.). The US Department of Agriculture (USDA) Economic Research Service reports that Bacillus thuringiensis (Bt)-resistant maize decreased the amount of insecticides per planted acres of Bt maize by 8% in the United States. Herbicide-tolerant maize is amenable to low to no-till agriculture. Minimal to no tillage results in decreased fuel usage and reduction of greenhouse gas emissions, as well as less soil compaction and erosion. Additionally, crop residue left on top of the soil increases the levels of organic carbon sequestration. Soil and water quality are increased due to decreasing soil erosion and nutrient loss (Committee on the Impact of Biotechnology on Farm-Level Economic and Sustainability and National Research Council, 2010; National Research Council, 2010). Of the 159 million hectares of maize grown globally in 2012, 55.1 million hectares (35%) was genetically modified (GM) maize. Legislation regulating such crops varies among countries. The United States regulates genetically modified organisms based on the end product. Three groups with differing perspectives and expertise regulate GM crops in the United States: the US Environmental Protection Agency, the Food and Drug Administration (FDA), and USDA. GM crops must be verified free from environmental and human toxins and foreign proteins deemed allergenic. The FDA policy established in 1992 considers the currently approved GM crops to be ‘substantially equivalent’ to non-GM crops and deemed ‘generally

recognized as safe’ under the Federal Food, Drug, and Cosmetic Act; therefore, foods made with approved GM varieties do not require premarket approval. Acceptance of GM maize by the consumer varies by country. The European Union (EU) regulates GM crops based on the process in which they are produced. The EU tends to be cautious of GM crop consumption. The British Press often refers to such crops as ‘Frankenstein Foods.’ Protester of third-world countries have been known to destroy entire fields of GM crop despite starvation in the country. The major concerns over the production of GM maize are pollination of weedy species or non-GM maize by GM pollen resulting in undesirable transfer of the transgene and the impact of transgenes on nontarget species, particularly beneficial insects, and the development of insects resistant to the mode of action of the insecticidal transgenes in use. Researchers and regulatory agencies continue to develop new deployment strategies in an effort to minimize these risks.


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How has human selection led to the evolution of maize? What countries are the top three producers of maize in the world? What kernel characteristics must be taken into consideration when processing? Why? What characteristics make maize a good model organism? Imagine a scenario where a GM maize line is created that corrects a serious nutritional deficiency; however, the pollen of the maize line is known to be compatible with weeds grown in the area where the nutritional deficiency is found. Should this maize line be released in this area? Explain your reasoning. Does GM maize support or hinder progression toward a sustainable agriculture?


GE Maize in the Unites States 100

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Figure 6 Percentage of all maize grown in the United States that is genetically engineered (GE). Reproduced from USDA (2014) Adoption of genetically engineered crops in the U.S.

Research continually strives to produce maize that requires fewer inputs and produces higher outputs while maintaining kernel quality, yield, and nutritive composition. The creation of new maize lines with novel traits will continue to be seen. What novel traits do you think should be introduced? Continued improvements in breeding and biotechnology will allow the development of maize varieties with improved yield and agronomic traits. What do you think are the practical limits to yield improvement. Educating consumers about the food they consume and advocating individuals to take an active interest in the production of their food will be helpful in ensuring sustainable food production. Design educational material for maize-based food in your community.

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; Oil from Rice and Maize; Carbohydrates: Resistant Starch and Health; Starch: Starch Architecture and Structure; Starch: Synthesis; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Maize:

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Genetics; Maize: Other Maize Mutants; Non-wheat Foods: Maize: Foods from Maize.

Further Reading Brookes G and Barfoot P (2005) GM crops: The global economic and environmental impact-the first nine years 1996–2004. AgBioforum 8: 187–196. Campbell MR, White PJ, and Pollak LM (1994) Dosage effect at the sugary-2 locus on maize starch structure and function. Cereal Chemistry 71: 464–468. Corn Breeding: Types of Cultivars (2014) from http://passel.unl.edu/pages/ informationmodule.php?idinformationmodule¼1099683867&topicorder¼8& maxto¼9&minto¼1. Crawley MJ, Brown SL, Hails RS, Kohn DD, and Rees M (2001) Transgenic crops in natural habitats. Nature 409: 682–683. Dudley JW and Lambert RJ (1992) Ninety generations of selection for oil and protein in maize. Maydica 37: 1–7. Duvick D (1996) Plant breeding, an evolutionary concept. Crop Science 36: 539–548. Eckhoff SR (2004) Wet milling. In: Wrigley C (ed.) Encyclopedia of Food Grains, 1st ed., pp. 225–241. Oxford: Academic Press. Flint-Garcia SA, Bodnar AL, and Scott MP (2009) Wide variability in kernel composition, seed characteristics, and zein profiles among diverse maize inbreds, landraces, and teosinte. Theoretical and Applied Genetics 119: 1129–1142. Gaut BS, Le Thierry D’Ennequin M, Peek AS, and Sawkins MC (2000) Maize as a model for the evolution of plant nuclear genomes. PNAS 97: 7008–7015. http://dx.doi.org/ 10.1073/pnas.97.13.7008. Hallauer AR (2004) Specialty corns. In: Corn: Origin, History, Technology, and Production, pp. 897–933. Hoboken, NJ: Wiley. Hannah LC (2005) Starch synthesis in the maize endosperm. Maydica 50: 497–506. Jellum MD (1970) Plant introductions of maize as a sourced of oil with unusual fatty acid composition. Journal of Agricultural and Food Chemistry 18: 365–370. Jennings S, Myers D, Johnson L, and Pollak LM (2002) Effects of maturity on corn starch properties. Cereal Chemistry 79: 703–706. Jeon J, Ryoo N, Hahn T, Walia H, and Nakamura Y (2010) Starch biosynthesis in cereal endosperm. Plant Physiology and Biochemistry 48: 383–392. Kiesselbach TA (1949) The structure and reproduction of corn. Lincoln, NE: University of Nebraska. Lorenz A, Scott P, and Lamkey K (2008) Genetic variation and breeding potential of phytate and inorganic phosphorus in a maize population. Crop Science Society of America 48: 79–84. McClintock B (1950) The origin and behavior of mutable loci in maize. Genetics 36: 344–355. Mertz ET, Bates LS, and Nelson OE (1964) Mutant gene that changes protein composition and increases lysine content of maize endosperm. Science 145: 279–280.

Nelson OE, Mertz ET, and Bates LS (1965) Second mutant gene affecting the amino acid pattern of maize endosperm proteins. Science 150: 1469–1470. Orthoefer FT and Eastman J (2004) Corn processing and products. In: Corn: Origin, History, Technology, and Production, pp. 867–896. Hoboken, NJ: Wiley. Pollak LM and Scott MP (2005) Breeding for grain quality traits. Maydica 50: 247–257. Poneleit CG and Davis DL (1972) Fatty acid composition of oil during maize kernel development. Phytochemistry 11: 3421–3426. Prasanna BM, Vasal SK, Kassahun B, and Singh NN (2001) Quality protein maize. Current Science 81: 1308–1319. Rooney LW, McDonough CM, and Waniska RD (2004) The corn kernel. In: Smith CW, Betran J, and Runge ECA (eds.) Corn: Origin, History, Technology, and Production, pp. 273–303. Hoboken, NJ: Wiley. Scanlon MJ and Takacs EM (2009) Kernel biology. In: Bennetzen JL and Hake SC (eds.) Handbook of Maize. New York, NY: Springer ScienceþBusiness Media. Sema-Saldivar SO (2004) Foods from maize. In: Wrigley C (ed.) Encyclopedia of Food Grains, 1st ed., pp. 242–253. Oxford: Academic Press. Snow AA (2002) Transgenic crops: Why gene flow matters. Nature Biotechnology 20: 542. Strable J and Scanion M (2013) Maize (Zea mays): A model organism for basic and applied research in plant biology. In: Cold Spring Harbor Protocols, pp. 1–9. New York: Cold Spring Harbor Laboratory Press. Tucker J (2011) U.S. Regulation of Genetically Modified Crops. Case Studies in Agricultural Biosecurity. 2014, from http://www.fas.org/biosecurity/education/ dualuse-agriculture/2-agricultural-biotechnology/us-regulation-of-geneticallyengineered-crops.html USDA (2013) Grain Inspection Handbook. Pamphlet. USDA Federal Gain Inspection Service, Washington, DC. USDA (2014) Adoption of genetically engineered crops in the U.S., 2014. Vasal SK (2000) High quality protein corn. In: Hallauer AR (ed.) Specialty Corns, 2nd edn. Boca Raton, FL: CRC Press. Velu V, Nagender A, Prabhakara Rao PG, and Rao DG (2006) Dry milling characteristics of microwave dried maize grains. Journal of Food Engineering 74: 30–36. Vineyard ML and Bear RP (1952) Amylose content. Maize Genetics Cooperation Newsletter 26: 5. Vogel K and Burson B (2004) Breeding and Genetics. Madison, WI: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, Chapter 3. Wijendran V and Hayes KC (2004) Dietary n-6 and n-3 fatty acid balance and cardiovascular health. Annual Review of Nutrition 24: 597–615. http://dx.doi.org/ 10.1146/annurev.nutr.24.012003.132106. Wilkes G (2004) Corn, strange and marvelous: But is a definitive origin known? In: Smith WC, Betran J, and Runge ECA (eds.) Corn: Origin, History, Technology, and Production, pp. 3–64. Hoboken, NJ: Wiley. Wu R, Lou X-Y, Ma C-X, Wang X, Larkins BA, and Casella G (2002) An improved genetic model generates high-resolution mapping of QTL for protein quality in maize endosperm. Proceedings of the National Academy of Sciences of the United States of America 99: 11281–11286.

Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’ CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Wheat is unique in its suitability for bread production because of its gluten protein. Bread has a major place in world language and culture because of its importance in our diet. Wheat, a member of the cereal family, is a monocotyledonous grass of the genus Triticum. There are two species – common (bread) wheat and durum (suited to pasta). Wheat is grown in a wide range of environments, including tropical and very cold regions. Worldwide wheat production is equivalent to about 300 g of wheat per day for each person on Earth. Wheat-based breads include leavened loaves, Arabic and Middle Eastern flatbreads, and Chinese steamed breads. Wheat has many other food uses, including noodles, pasta, pastry, donuts, cakes, and cookies. Nonfood uses include animal and fish feeds, starch–gluten manufacture, sweeteners, adhesives, and biofuels. The main component of wheat flour is starch, followed by protein, which is largely the gluten-forming gliadins and glutenins. The fat content is low. Wheat is a major source of energy, fiber, vitamins, and minerals in our diet. Some individuals are intolerant to wheat in the diet. The best characterized intolerance is celiac disease.

Learning Objective

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To achieve understanding of wheat as a grain species, including its origins, genetics, production, utilization, and its value in our diet.

Introduction Wheat is unique among the food grains. Only the wheat grain contains storage proteins that form into a cohesive dough after milling, adding water, and mixing. Only the dough from wheat flour has the extensibility and elasticity to allow the growth of gas bubbles (generally air and carbon dioxide) and to allow the retention of the bubble structure throughout the bread baking process. Wheat protein’s dough-forming ability also accounts for its value for making the wider range of foods, including noodles, pasta, pastry and pizza crust, cakes, cookies, and even candies. These are the reasons for the success of wheat not only as one of the three most popular grains, together with rice and maize, but also as the grain with the most stringent quality specifications.

Wheat, Bread, and the Human Race Despite the wide range of uses of wheat, it is the word ‘bread’ that epitomizes the use of wheat. Bread and wheat are central


in the symbol of the FAO (Food and Agriculture Organization of the United Nations); a wheat ear is the logo and the motto in Latin Fiat panis, which means ‘Let there be bread’ (Figure 1). Likewise, the word ‘bread’ has entered our everyday languages as a symbol of food more generally. Bread is international, but in its variations, there are national characteristics, as illustrated in Figure 2. In the lives of Polish and Russian people, bread (‘chleb’) is a sacred item. In such cultures, an honored guest is welcomed by the presentation of a loaf of bread, covered with a lace cloth on a platter. In Iran, sweet bread (Persian ‘naan’) may be taken as a gift when visiting friends. In the Jewish Passover celebration, the bread must be unleavened, as a reminder of the Israelites’ hurried departure from slavery in Egypt, when there was no time to leave the bread to rise overnight. From Jewish and Christian cultures, various bread-related expressions have entered everyday English: ‘Cast your bread upon the waters,’ ‘Give us this day our daily bread,’ and ‘Man shall not live by bread alone.’ Similar expressions are found in other languages, cultures, and religions. Wheat is even more than bread, because its dough-forming properties suit its use for the further range of foods in Figure 3 – crackers, cookies, pastries, and noodles of many types (Figure 4). Pasta types (such as spaghetti, macaroni, and tagliatelle), distinct from noodles, are correctly made from durum wheat (Figure 5). In addition, wheat is an important feed source for animals, birds, and fish. Industrial uses include the separation of starch from gluten protein. The starch fraction is used for paper, adhesives, and even to produce ethanol as a fuel. Gluten is used to augment dough quality in baked goods and as an additive to a wide range of foods. The Greek goddess Demeter (depicted in Figure 6 with awned wheat heads and stalks) was probably adopted and renamed Ceres by the Romans, thus providing the origin of our word ‘cereal,’ which now includes all the grasslike grains, for example, barley, rye, rice, and maize.

Wheat Species The ancestors of modern wheats still grow in the regions where they had their origins in the ‘Fertile Crescent’ (Egypt through Syria to the Tigris–Euphrates valley) and further eastward. They include the diploid einkorn wheats (Triticum boeoticum and T. monococcum) and the tetraploid emmer wheats (T. dicoccoides and T. dicoccum). Hexaploid bread wheat arose from natural hybridizations between these tetraploid wheats and the diploid species T. tauschii. There are two modern wheat species: bread (or common) wheat, T. aestivum, and durum wheat, T. durum (also designated T. turgidum ssp. durum), which is less common and is mainly used for pasta and whole-grain uses such as couscous. Figure 7 shows stands of common wheat almost ready to

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THE CEREAL GRAINS | Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’

Figure 1 The logo of the Food and Agriculture Organization uses bread (‘panis’) as a symbol of food in general. Reproduced with FAO permission.

Figure 4 The many types of wheat-based noodles. Reproduced with the permission of AWB Ltd.

Figure 2 Bread types from various nations and cultures. Reproduced with the permission of Perten Instruments.

Figure 5 Pasta types, such as spaghetti, are made from durum wheat, a distinct species from bread wheat.

Figure 3 The wider range of foods made from wheat flour. Reproduced with the permission of Perten Instruments.

harvest. The most obvious distinction between these crops is that one is an awned (bearded) variety and the other is not. Not evident in the photos, however, are important distinctions that indicate the suitability of the mature grain for the various uses of wheat grain, such as protein content, grain hardness, and potential for dough quality needed for specific food types. Common wheat has 21 pairs of chromosomes, arranged in three genomes (A, B, and D), reflecting the three original diploid progenitors (seven pairs each) of hexaploid wheat. The chromosomes are numbered 1A to 7A, 1B to 7B, and 1D to 7D. Durum wheat, in contrast, has only 14 pairs of chromosomes, numbered 1A to 7A and 1B to 7B, reflecting in turn its origins. The genomes, and the chromosomes of corresponding number (e.g., 1A vs. 1B vs. 1D), are said to be homoeologous – that is, they are similar but not homologous (identical). So, for example, chromosomes 3A, 3B, and 3D have homoeologous genes for red grain color.


Figure 6 The Greek god of wheat, Demeter, drawn originally from a painting found in Pompeii. Reproduced from Buller AHR (1919) Essays on Wheat, p. 281. New York: McMillan Company.

Wheat Production and Utilization Worldwide On average, world production of wheat totals about 700 million tonnes (Mt) annually, grown on some 220 million hectares (Mha), with a world average yield of 3.2 tonnes ha 1. Table 1 lists the countries with an annual production of over 3 million tonnes. The European Union appears at the top as the largest wheat producer; the contributing EU countries are listed individually. The total cereal grain production is also listed for some countries, indicating the relative importance of wheat compared with other grains, especially rice and maize. Countries such as Indonesia, Thailand, Mexico, and South Africa are significant grain producers, but wheat is not their main crop. The single-season data in Table 1 fail to show the fluctuations in yield that occur from season to season. These year-toyear changes are evident in the 5-year data in Table 2, but even in this case, fluctuations are less obvious due to the averaging effects of summing the production of many countries. The ideal wheat-growing climates are subtropical, with mean summer temperatures of about 15 C and an annual rainfall of 300–700 mm falling more in spring (during grain filling) than in summer (providing opportunity for a dry harvest). Nevertheless, the climates in which wheat can be grown vary greatly, as is exemplified by wheat growing in the far north of America versus Mexico. In northern parts of Europe and the United States, winter wheats are sown in autumn, to lie under a snow cover throughout winter, ready for the warmth of spring to bring them back into growth and grain production. This vernalization process is

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essential to the ongoing development of the plants into heading, pollination, and grain development. Distinct varieties (winter genotypes) of wheat are needed to suit these climatic conditions. On the Canadian prairies and the northern US plains (North Dakota and Montana), the winters are too harsh to permit the growing of the higher yielding winter-habit wheats. In these very cold regions, spring wheats are sown after the snow has melted, as soon as it is possible to access the fields in spring. Thereafter, there is very rapid growth, permitting the grain to mature for harvest just before the snows of autumn. Harvesting can thus be difficult sometimes as the grain does not finish its maturity and drying out in the head. In this case, the crop is swathed – cut down and left to dry prior to harvesting (Figure 7(c)). By contrast, wheat growing in Kansas, the United States, and down into Mexico may involve heat stress in the late stages of grain filling, coming into summer. Wheat growing in parts of Mexico and the Indian subcontinent involves regions of high altitude. Average wheat yields vary considerably between the countries in Table 1. Some of the highest yields are in European countries where their intensive agricultural practices combine with adequate rainfall. In some regions, where high inputs are possible, there are ‘ten-ton clubs,’ involving groups of growers who regularly achieve yields of over 10 tonnes ha 1. By contrast, regions of dryland farming may reckon on little more than 1 tonnes ha 1 (Table 1). Drought and disease may reduce yields in either of these extreme cases. Today’s world average yield of about 3 tonnes ha 1 (Table 2) contrasts with historical yields, which was only 1 tonnes ha 1 at the end of the 1950s (Figure 8). This threefold increase has been partly due to improved agricultural practices and especially because of the introduction of wheat varieties with improved yield traits. Figure 8 also shows that there have been only minor increases in recent decades in the area sown to wheat worldwide. In temperate regions, ‘dual-purpose’ wheats may be sown. These are usually late-maturing varieties sown early so that stock may graze the early leaves but allow the grazed plants to recover and produce grain. The times of year for sowing and harvesting vary around the world (Table 3). Harvest generally coincides with summer, thus reflecting whether the particular country is in the northern or southern hemisphere. Other factors include sowing date and the maturity of the particular variety sown, plus constraints such as avoidance of extremes of climate – both very cold and very hot. The choices of sowing date and the maturity of the variety sown are often challenging decisions. Rough calculations may be made about the critical time of flowering. Very early flowering brings the risk that a late frost will prevent proper flowering with the consequence that many florets may be sterile. Late flowering risks heat stress during grain filling with the consequences of reduced grain yield and weakening of the dough quality of the mature grain. Much of wheat production is used in the countries in which it is grown, but world trade accounts for about 20% of total production, a higher proportion than for cereal grains more broadly (Table 2). World wheat production is equivalent to about 300 g of wheat per day for each person on Earth. This

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Figure 7 Wheat in the field: (a) unawned wheat, (b) awned wheat, and (c) wheat that has been swathed to hasten the drying of the grain ready for harvesting.

statistic suggests that there should be no problem with hunger. However, about one-third of world wheat production is used for a combination of seed use, animal feed (about 20%), and industrial processing (about 10%). Furthermore, the places of excess production are far from the places of human need. Many countries produce more wheat than their domestic requirements, resulting in world trade of about 140 million tonnes annually. The main wheat-exporting nations are the United States, Canada, Europe, Australia, and Argentina. Recipient countries that import grain include Brazil, Egypt, Japan, South Korea, Indonesia, Iran, and Iraq. Such international trade and transport over thousands of kilometers contrast with the subsistence farming of wheat in some regions, where farmgrown grain is milled locally for the farm family.

The Grain That Becomes Our Food The wheat grain is the result of internal fertilization of the wheat flower. The glumes that enclosed the flower can be seen in Figure 9 in which other florets have been removed from the rachis (the backbone of the wheat head) to show how the mature grain is held within the protecting outer glumes, lemma, and palea (the husks of the mature wheat head). At the time of fertilization, anthers released pollen to fertilize the

ovum, resulting in a grain, which grows through the series of anatomical stages shown in Figure 10. The diagram in Figure 10(c) corresponds to the transmission electron micrograph in Figure 11. The lowest third of Figure 11 is the outer part of the endosperm, showing cell walls that enclose starch granules (both large (A-type) and small (B-type)). These outer endosperm cells have a larger proportion of storage protein (forming the matrix between the starch granules) than the inner endosperm. Enclosing the endosperm is a layer of aleurone cells; beyond that are the bran layers, which are shriveled in the mature grain, having served their functions for the developing grain (as seen in Figure 10). It is the aim of the flour miller to remove these outer layers and the germ, to produce white flour made up of the endosperm, and then to reduce the endosperm to a fine powder. Moisture is used to render the bran layers ‘leathery’ so that they leave the grain during milling as large flakes that are readily sieved from the endosperm particles. Flour milling involves repeated passes between rolls, first fluted and later smooth, with sieving steps between the rolling. From one stage to another, the flour stocks are conveyed pneumatically through the complex system of pipes shown in Figure 12. Grain hardness is a significant factor to the miller. The endosperm of a soft wheat has air pockets that render the intact

THE CEREAL GRAINS | Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’ Table 1

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Wheat production by countries

Country/region

Wheat production (Mt)

Wheat yields (tonnes ha 1)

Production of all cereal grains (Mt)

The European Union China India The United States Russia France Canada Australia Germany Pakistan Ukraine Turkey Kazakhstan Iran The United Kingdom Argentina Egypt Poland Spain Italy Morocco Romania Uzbekistan Bulgaria Denmark Hungary Afghanistan Syria World

143 121 93 58 52 39 33 26 25 24 22 18 16 15 12 11 9 9 8 7 7 7 7 5 5 5 4 4 706

5.5 5.0 3.1 3.2 2.2 7.2 3.2 1.9 8.0 2.8 3.4 2.3 1.2 2.1 7.5 3.0 6.3 4.4 3.6 3.9 2.1 3.6 4.9 4.1 6.8 4.7 1.6 2.7 3.2

304 480 240 436 88 59 37 34 60 32

47

2432

Data from the United States Department of Agriculture.

Table 2

Production and trade involving wheat (and all cereals) over five recent years

Wheat

2009/10

2010/11

2011/12

2012/13

2013/14a

Production Utilization Trade Yield (tonnes ha 1)

686 656 131 –

654 658 120 –

702 699 147 3.15

660 684 140 3.03

711 695 142 3.21

All cereals

2009/10

2010/11

2011/12

2012/13

2013/14a

Production Utilization Trade

2266 2234 278

2257 2271 289

2353 2326 319

2305 2323 309

2500 2413 318

a

Estimate.

endosperm opaque and whitish. On crushing, the endosperm of a soft wheat readily disintegrates into a fine powder, with little damage to the starch granules. In contrast, the intact endosperm of a hard wheat or durum grain is translucent and vitreous. The starch granules are held firmly in the matrix of storage protein. More energy must be put into milling a hard grain, with the initial mill pass producing a coarse powder (‘semolina’ for durum), which must be further reduced with repeated milling.

Starch damage results; some granules may be split into pieces. In any case, some of the protein matrix will remain on the surface of the granules, as is shown by the rough surface of the large A granule in Figure 13. A small B granule was caught on top of the A granule in the process of sample preparation. The scanning electron micrograph thus shows the contrast in size of the two types of granule. A granule from a soft flour would have a smooth surface. Starch damage is desirable for most bread making as it facilitates access by starch-degrading enzymes (amylases) to

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700 600

Area (Mha) Production (Mt)

500 400 300 200 100 0 61 964 967 970 973 976 979 982 985 988 991 994 997 000 1 1 1 2 1 1 1 1 19 1 1 1 1 1 Figure 8 Worldwide wheat production compared to area sown. Reproduced with permission from Marshall DR, Langridge P, and Appels R (2001) Wheat breeding in the new century – Preface. Australian Journal of Agricultural Research 52: i–iv.

Table 3

Wheat harvesting dates

Country

Hemisphere

Harvest dates

Argentina Australia Canada China England France India Italy Russia The United States

South South North North North North North North North North

November–January October–January July–September May–September August–September June–July February–May June–July July–September May–September

the starch substrate and increases water absorption. The lower absorption of water for soft wheats is desirable for cookie and cake manufacture on the other hand. Figure 14 illustrates the result of amylase action on a starch granule, which may have had its surface damaged during milling to provide ready access by the enzyme. The layered crystalline structure inside the granule can be seen.

Dough Formation and Baking The formation of suitable gluten structure in dough requires both the addition of water and mixing action. The course of dough development can be followed by equipment used to analyze dough quality, such as the mixograph (Figure 15). The broad trace of mixing action reflects the movement of the bowl containing the dough. From little initial resistance to mixing, the progressive dough formation is shown by the rise of the curve until it reaches a maximum. Beyond the peak, resistance becomes less. Usually, a dough mixed to peak development is most desirable for bread baking.

Figure 9 A spikelet of wheat with other spikelets removed from the rachis (backbone) of the head. The lowest floret (at right) has been opened to reveal a grain lying between the glumes (husks – lemma and palea). The lemma bears a short awn. There are further florets to the left and above.

During the mixing process, the grain’s storage protein hydrates and coalesces to form gluten strands that bind together forming an elastic matrix holding the starch granules and the gas cells. The strands of gluten are clearly seen in the scanning electron micrograph of mixed dough in Figure 16. Also visible are the gaps of gas cells and the larger (A-type) starch granules. The smaller B-type granules are covered by the gluten strands. Bread making can involve a simple combination of flour, water, salt, and yeast, with the mixed dough left for yeast action to produce bubbles of carbon dioxide prior to baking. A series

STYLE PERICARP

OUTER INTEGUMENT

EMBRYO

NUCELLAR EPIDERMIS

INNER INTEGUMENT VASCULAR BUNDLE

CREASE

FUNICULUS (a)

0.8 mm EMBRYO SAC DEGENERATING NUCELLUS

0.5 mm (b)

ALEURONE CELLS PERIPHERAL ENDOSPERM

PERICARP ALEURONE CELLS

PRISMATIC ENDOSPERM

PERIPHERAL ENDOSPERM

CENTRAL ENDOSPERM

PRISMATIC ENDOSPERM

VASCULAR BUNDLE

CREASE

Figure 10 Diagrams of the wheat grain through stages of development. (a) The wheat ovule prior to fertilization. (b) The developing grain. (c) The mature grain.

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(c)


PERICARP OUTER INTEGUMENT INNER INTEGUMENT ANTIPODAL EMBRYO SAC ENDOSPERM NUCELLUS

112


Figure 13 Scanning electron micrograph of wheat starch granules (A-type [large granule] and B-type).

Figure 11 Transmission electron micrograph of the almost mature grain, showing endosperm cells with starch granules.

Figure 12 The many pipes of the pilot flour mill at Kansas State University carry the various flour stocks pneumatically from one stage of the milling process to another.

of loaves resulting from this simplest procedure (Figure 17) shows that different flour samples can produce a variety of loaf sizes from the same starting amount of dough, the loaf with the largest volume (height) being considered the best. In practice, the baking of leavened breads (Figure 2) is more complex, as is described in relevant articles in this encyclopedia. In addition, ‘bread’ comes in many different forms. There is a wide family of flatbreads made in the Middle East and through the Indian subcontinent. Indian chapati bread is illustrated in Figure 18. The baking of both chapatis and Arabic

Figure 14 Scanning electron micrograph of a wheat starch granule that has been eroded by amylase enzymic action, revealing the crystalline layers of internal structure.

flatbreads (classed as hearth breads, Figure 19) takes place rapidly on a very hot surface such as a flat hearth or the side of an oven. It is desirable for the two crusts of an Arabic bread to separate during baking so that fillings may be inserted before eating. These breads thus come from the oven looking like an inflated balloon (Figure 19). Yeast-leavened breads may be heated by means other than an oven. Chinese steamed breads have steam as the means of heating. For bagels, the initial form of heat is boiling water; a ring of yeasted dough is briefly boiled and then baked, producing a chewy texture. On the other hand, boiling oil is the means of heating for a doughnut (Figure 20), which may be


113

400

Resistance

Breakdown Bandwidth at peak 200 Peak resistance Mixing time

0 0 (c)

400 200 Time (seconds)

600

Figure 15 (a) The mixograph (original mechanical design) used for measuring dough properties. (b) The mixing bowl is connected to a swinging arm, which creates (c) the trace of dough properties.

Figure 17 Loaves made in testing flour quality differ in volume, height, and crust color.

Figure 16 Scanning electron micrograph of a wheat-flour dough, showing the strands of gluten surrounding discreet starch granules.

formed from a yeasted dough or from a cake batter with a chemical raising agent. Cookies and crackers (Figure 3) may or may not be leavened, but oven baking is usual. Leavening is not needed for the wide range of pasta (extruded from a dough of durum semolina) or noodles (generally cut into strips from a sheet of dough made from common wheat flour). These products (Figures 4 and 5) are typically air-dried, permitting them to be stored for subsequent boiling or deep-frying (noodles) before being ready to eat. The range of wheat-based foods also includes the great variety of ready-to-eat breakfast cereals, pizzas, pretzels, and snack bars, many of which involve oven baking. Others are formed and steam-heated by the process of extrusion.

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Figure 18 Chapati bread.

Figure 19 Arabic flatbreads just taken from the oven resemble balloons because the process is designed to separate the two outside crusts.

Figure 20 The doughnut. Heating is provided by boiling oil.

Grain Composition Starch is the main component (up to 85%) of the mature wheat grain. The white granules of starch are visible in the micrograph of endosperm (Figure 11) as larger A-type and

smaller B-type granules (Figures 13 and 14). When starch is heated in the presence of excess water, its crystalline structure is lost in the process of gelatinization. The resulting amylose and amylopectin macromolecules serve to bind together the other flour components. The major industrial uses of wheat flour involve preparing starch by forming a dough and washing out the intact starch granules. These are then used for a wide range of food and nonfood purposes, the latter including the manufacture of paper, adhesives, the sizing for textiles, hydrolysis for sweeteners, and fermentation for biofuels. Fats (lipids) make up only 3–4% of the whole grain (mainly in the germ) and 1–2% of straight-run white flour. Despite being a minor constituent, lipid plays a significant role in dough formation and the baking process. The grain is a significant source of micronutrients, especially minerals and B and E vitamins (but not vitamin C). Carotenoids provide color to wheat-based products, especially pasta from durum wheat. Much of the micronutrient content resides in the bran and aleurone layers (Figures 10 and 11), forming the basis for recommending the consumption of whole-grain foods. Nevertheless, a significant amount of aleurone cell contents is included in straight-run flour. Another reason for the recommendation of whole-grain foods is the contribution of dietary fiber, especially in the form of nonstarch polysaccharides. Again, a useful proportion of this material is present in white flour. Protein is a very important part of the wheat grain. Protein content typically ranges from 8% to 15%. Its importance is indicated by the relevance of premium payments provided for this component and the indications of utilization procedures being based on protein content. Conventional baking use is associated with the upper range of protein content, whereas cake and cookie uses relate to lower protein levels. The gluten-forming protein of white flour represents about 80% of the protein; the remaining proteins are the albumin and globulin fractions, largely made up of proteins involved with the synthetic functions of the grain. Gluten is a very complex mixture of proteins – about half classed as gliadins (with a molecular weight range below 100 000 Da) and the remainder as glutenins (with a molecular weight ranging up into the millions of Daltons). These glutenin proteins are large polymers of polypeptides (subunits) joined together by disulfide bonds. The glutenin polymers, especially the very large ones, contribute to the elasticity of dough. To demonstrate the importance of their large size, dough properties are lost if disulfide bonds are broken. The industrial process of starch preparation involves the production of gluten, which is generally dried under conditions that preserve its dough-forming properties. Vital dry gluten is used extensively as a bakery ingredient to increase dough strength. It also has wide uses in many foods as a protein extender, for example, in cheese and processed meats. In some applications that do not call for its elastic properties, gluten is devitalized by excess heat during drying.

Wheat and Health Issues The many and various wheat-based foods provide a major source of nutrition for the world. They are an important source

THE CEREAL GRAINS | Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’ of energy, protein, essential amino acids (even if slightly deficient in lysine), essential fatty acids, vitamins (with the exception of vitamin C), minerals, and fiber. For these reasons, wheat and the wider range of cereals are generally placed at the base of nutrition pyramids as the category of ‘eat most.’ Glycemic index and response vary between the many wheat-based foods. Research attention has recently indicated new genotypes and processing methods that will increase glycemic index in breads and related foods. However, certain individuals have difficulty in tolerating wheat in their diet. These wheat intolerances take various forms; the best categorized is celiac disease. If celiac disease is diagnosed, the remedy is lifelong avoidance of wheat, together with the related species rye, triticale, barley, and possibly oats. The storage protein of all these cereals is sufficiently similar to that of wheat gluten in amino acid composition as to cause celiac symptoms, though not sufficiently similar as to provide the dough-forming properties of wheat gluten. Despite the unique requirement of wheat gluten for dough formation, various substitutes are available for the manufacture of gluten-free breads, but it has proved difficult to produce these products to the same quality as normal bread. However, these gluten-free foods mean that celiacs need not avoid breadlike products completely. The use of the word ‘gluten’ to indicate both dietary intolerances and dough-forming properties shows it to be a misused term, having different meanings depending on the context. Even more confusing is the term ‘corn gluten,’ meaning the protein from maize grain, although that protein has neither dough-forming properties nor toxicity for celiacs. The term ‘glutinous rice’ (different spelling for this ‘glutin’) refers primarily to starch properties. The possible presence of contaminants is a general risk with wheat and other grains. These include mycotoxins and ergot. However, effective screening measures at grain receival mean that there is a very low risk that such grain will enter the human food chain or even animal feed. Wheat flour is also an occupational health risk for bakers and millers who are inevitably exposed to flour on a regular basis. Symptoms may include rhinitis and asthma. This occupational problem has been recognized for centuries, as indicated by the cartoon in Figure 21. The female baker is identified in the conversation as Mrs. Caquet (meaning Mrs. Gossip). She is illustrated with nasal discharge, indicating rhinitis presumably due to flour allergy. However, the main point of the cartoon relates to the lack of hygiene in the baking trade at that time and the consequent health risks. The old French translates: So you have sacked Catherine? What else could I do Mrs Caquet, in my trade cleanliness is essential. I couldn’t keep a girl who bathed every fifteen days. She must have been naturally very dirty as I’ve never bathed in my life.

Bakers’ asthma is an occupational hazard that can suddenly affect bakers who have been in the trade for many years. For them, the only alternative is usually to leave baking and find a different employment. The rhinitis and asthma are a consequence of immediate hypersensitivity to flour protein via immunoglobulin E of the nasal and bronchial tracts. In some cases, the development of asthmatic symptoms is not immediate but delayed, occurring during the night following exposure.

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Figure 21 The dripping nose of the woman at the left in this very old cartoon indicates that bakery workers have long had flour-related allergies. Reproduced with permission from Rohlich M (1978) Korn und Brot im Spiegel der graphischen Ku¨nste. 7 Teil. Getreide, Mehl und Brot 32: 337–341.

Future Prospects Wheat breeders have made enormous contributions to the improvement of wheat for more than a century. The increases in production shown in Figure 8 are largely attributed to the contributions of breeders. Breeders will continue to provide improvements to yield, via better tolerance to pests, better adaptation to specific environments and better processing quality as they make informed crosses, growing out the progeny (Figure 22) and selecting for desirable traits. Marker-assisted selection will continue to make wheat improvement more efficient as geneticists identify better markers and more efficient screening procedures. Improvements will still come from conventional breeding methods, but novel approaches to genetic modification are already permitting breakthroughs that are not otherwise possible. Wheat growers have lessons to learn from organic growers, without necessarily going ‘all the way organic.’ As a result, agronomic strategies will improve to ensure better sustainability and more efficient uses of agricultural inputs. The adoption of precision agriculture is set to increase, plus its extension to targeted harvesting so as to maximize the quality specifications of the harvested grain. Advances in screening methods used in breeding have the potential for adaptation post-farm gate at harvest. Depending on the economy of grain segregation, such screening methods can distinguish load deliveries according to suitability for utilization and provide a basis for identity preservation of these

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• • • •

Figure 22 Breeders’ lines of wheat being tested in small plots for their agronomic traits.

premium grades during storage and transport to the respective destinations. In these respects, wheat growers are increasingly working on the strategy of considering the dollar value return per hectare, rather than grain yield, by targeting premium payments for their grain. A further step along this approach involves a paddock-to-plate strategy by some farming entrepreneurs, who have milled their own grain, grown to suit quality specifications, for local manufacture of food products ready to go straight onto supermarket shelves, for example, pasta, noodles, bread mix, and instant noodles.

In your local region, find out the origins of wheat used for the many food and nonfood products available. Is there wheat growing nearby? Are there local milling and manufacturing facilities? What are the meanings of ‘bread’ in your home, district, and country? Compare the advantages and problems of using wholegrain flour versus white flour for wheat-based foods. Investigate the origins and progenitors of modern wheats.

See also: Agronomy of Grain Growing: Wheat: Agronomy; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains: Intolerance, Allergy and Diseases: Cereal Allergens; Celiac Disease; The GlutenFree Diet; Genetics of Grains: Wheat Genetics and Genomics; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Grading and Segregation; Wheat: Marketing; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains; Wheat Processing: Gluten and Modified Gluten; Analysis of Dough Rheology in Breadmaking; Wheat: Dry Milling; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Ultrastructure of the Wheat Grain, Flour, and Dough; Wet Milling of Wheat; Wheat-Based Foods: Breads.

Further Reading Exercises for Revision

• • • • •

What features distinguish wheat from other cereal grains? Review the range of growth conditions under which wheat is grown around the world. What problems and adaptations are needed to accommodate these extremes? How do wheat and bread impact our lives and culture? In your local region, what are the most popular uses of wheat? Consider both food and nonfood uses. What are the factors that affect the yield and quality of wheat grain?


•

The gluten protein of wheat can readily be separated from the starch of flour by making a dough and kneading it under a gentle stream of water. Attempt to perform this separation to gain a better understanding of the nature of a bread-making dough.

Anderson RP and Wieser H (2006) Medical applications of gluten-composition knowledge. In: Wrigley CW, Be´ke´s F, and Bushuk W (eds.) Gliadin and Glutenin. The Unique Balance of Wheat Quality, pp. 387–409. St Paul, MN: AACCI Press. Arendt EK and Zannini E (eds.) (2013) Cereal Grains for the Food and Beverage Industries. Oxford: Woodhead Publishing Ltd. Baldo BA and Wrigley CW (1984) Allergies to cereals. Advances in Cereal Science and Technology 6: 289–356. Carver B (ed.) (2009) Wheat: Science and Trade. Ames, IA: Wiley-Blackwell. Cauvain SP (ed.) (2003) Bread Making: Improving Quality. Oxford: Woodhead Publishing Ltd. Cauvain SP (ed.) (2012) Bread Making: Improving Quality, 2nd edn. Oxford: Woodhead Publishing Ltd. Day L, Batey IL, Wrigley CW, and Augustin MA (2006) Gluten uses and food industry needs. Trends in Food Science and Technology 17: 82–90. Faridi H and Faubion J (1995) Wheat End Uses Around the World. St Paul, MN: AACCI. Hammed AM and Simsek S (2014) Hulled Wheats: A Review of Nutritional Properties and Processing Methods. Cereal Chemistry 91: 97–104. Henry RJ (2014) Wheat genomics for grain quality improvement. Cereal Foods World 59: 22–24. Khan K and Shewry PR (eds.) (2009) Wheat: Chemistry and Technology, 4th edn. St Paul, MN: AACC International. Wrigley CW (2012) Proteins – The basis of life. Teaching Science 58: 56–59. Wrigley CW and Batey IL (2010) Cereal Grains: Assessing and Managing Quality. Cambridge: Woodhead Publishing.

Durum Wheat: Overview GP Kadkol and M Sissons, NSW Department of Primary Industries, Calala, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

• • • •

Durum wheat is a related but separate species of wheat. It is a cereal and it belongs to the same genus as bread wheat. Its origin is similar to bread wheat. Durum is a tetraploid with A and B genomes represented, which are also found in bread wheat. Durum is adapted to more diverse environments than bread wheat, and it performs very well in semiarid regions. World production of durum wheat is 5–8% of bread wheat production. Durum grain is typically very hard with high protein content, amber-colored, and vitreous. Durum has a special niche as a food crop being the main grain used for making pasta, couscous, burghul, and several other traditional foods. Durum breeding objectives include higher yield, disease resistance, higher grain protein content, increased grain weight, low screenings, higher grain vitreosity, higher semolina yield, semolina color, stronger dough characteristics, and improved pasta-making characteristics. Durum, similar to bread wheat, is self-pollinated, and therefore, pedigree breeding is a common method of breeding used in durum. The main diseases of durum are Fusarium head blight, crown rot, stem, leaf, and stripe rusts. Management of nitrogen nutrition to the crop is an important aspect of durum agronomy because grain protein content together with physical grain quality determines the delivery grade and price for the farmer. Future prospects for durum appear to be good as pasta production has increased substantially over the previous decade.

Learning Objectives

• •

To learn about durum wheat as a related but separate species of wheat and as a world food crop To learn about the science behind the durum crop including breeding, quality evaluation, and agronomy

Introduction Durum wheat (Triticum durum) is a separate tetraploid species of wheat. Durum has 28 chromosomes representing A and B genomes compared with 42 in the hexaploid (bread) wheat with A, B, and D genomes. The typical durum grain is very hard, vitreous, and amber-colored with high protein content. Durum wheat is used to produce a range of food products, such as semolina, pasta, burghul wheat, couscous, and desserts (Figure 1). The main durum-growing regions are the Middle


East, southern Europe, North Africa, the former Soviet Union, North America (including Mexico), and India. Worldwide, durum is grown approximately over 13 m ha with an approximate annual production of 30 mt (Figure 2). Although durum constitutes only 5–8% of the world wheat production, it is an economically important crop because of its unique characteristics and its use in making important food products such as pasta.

Origin and Spread of Durum Wheat It is thought that modern durum evolved from the wild tetraploid, T. dicoccoides. This tetraploid, in turn, originated in the Near East through hybridization of diploid Triticum urartu (Au genome) and another diploid species, possibly Aegilops speltoides. T. dicoccoides possesses a brittle rachis and is hulled making it difficult to harvest and hard to thresh the grain out of the spikelets. Gradually, during domestication, these types evolved into a tough rachis but hulled grain form, T. dicoccum, commonly known as cultivated emmer, which is considered to be the first cultivated tetraploid. Emmer is still hard to thresh but can be gathered more easily compared with T. dicoccoides because the spikes stay intact. Emmer spread from the Near East to various European, African, and Asian regions. Archaeological evidence has shown the arrival of emmer into regions far away from the Near East (its center of origin) into Britain, to the West, around 3500 BCE and in the Indian subcontinent, to the East, around 5000 BCE. Emmer is still cultivated on a small scale in Ethiopia, India, Iran, Italy, Spain, eastern Turkey, and the Balkans. The process of domestication of emmer influenced by its wide distribution and local cultural practices gradually resulted in selection of mutations that resulted in the loss of the tight covering of the kernel by the glumes giving rise to ‘naked’ free threshing forms. This change is thought to have occurred approximately around 7000–5000 BCE. Domestication also influenced other traits such as seed size. The first archaeological occurrence of modern durum was recorded in Egypt during the Greco-Roman period (332 BCE–395 CE). Durum evolved in the eastern Mediterranean region and it had established as a major crop by 2300 BCE. Gradually, durum replaced emmer in cultivation and spread to other parts of the world and became a food crop of antiquity in Mediterranean Europe, several North African and Middle Eastern countries, and the Indian subcontinent and is an important ingredient of traditional foods in these regions.

Adaptation of Durum As a species, durum is adapted to a wide range of conditions from temperate colder climates to warm tropical and semiarid

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Figure 1 Images from left to right: Durum wheat plants, field plots of durum wheat, durum grain, semolina (http://shop.icnussa.com.au/p/8670107/ semolina–durum-wheat-1kg-.html), pasta shapes (https://thewindroseblog.wordpress.com/2014/10/24/happy-world-pasta-day/), and couscous (http://adashofflavour.blogspot.com.au/2010/10/moroccan-couscous-salad.html).

Figure 2 Worldwide area (brown), production (blue), and yield (blue line) statistics for durum wheat. USDA Foreign Agricultural Service – http://www. pecad.fas.usda.gov/highlights/2010/11/global%20durum/images/GlobalDurumChart.jpg.

conditions and is thus able to be grown in regions where bread wheat may not be profitable. The majority of the world production of durum occurs under rainfed conditions in semiarid regions with relatively dry climate, warm days, and cool nights during crop growth. Drought stress occurs frequently in these regions. Most durum varieties are spring types. In the warmer regions of southern Europe, North Africa, and Australia, spring durum is planted in late autumn or early winter and is

harvested in summer. In North America, spring varieties are planted in spring and harvested in late summer. In the colder parts of Turkey and certain other Middle Eastern countries, winter durum varieties are planted in autumn and harvested in summer. Winter durum is shown to be well adapted to some areas of North America and Germany, and there is interest to develop winter durum cropping in these regions. Generally, durum yields are competitive with bread wheat under favorable soil conditions. However, under low pH and

THE CEREAL GRAINS | Durum Wheat: Overview in the presence of mineral toxicities in the soil, durum yields are typically lower than bread wheat.

Durum Breeding Improving productivity of durum by enhancing the inherent ability of durum varieties to produce higher yields combined with high quality is essential for the continued viability of the durum industry. Good varieties combining high yields and high quality to meet the market demand have been the basis of strong durum industries. In durum breeding, as with many other cereals, the breeder must try to satisfy the requirements of the entire production chain consisting of farmers, grain handlers, millers, pasta makers, and consumers and is usually assisted by experts from other fields like cereal chemistry, agronomy, pathology, molecular biology, and biometry. Durum breeding, historically, has been mainly conducted by public institutions such as government departments of agriculture and universities, while in the United States and EU, private breeding companies are common. Durum breeding commenced in EU in the early decades of the twentieth century. Italy was a pioneer in durum breeding with the first variety released in 1915. Breeding in the early years involved the use of European, Near Eastern, and North African landraces. However, these early varieties were tall, responded poorly to nitrogen fertilizers, were prone to lodging, and were relatively low yielding. In the 1960s, semidwarf durum germplasm became available from International Maize and Wheat Improvement Centre, Mexico (CIMMYT). Use of this germplasm in durum breeding has delivered large improvements in yield in most countries. The modern durum varieties are shorter, more resistant to lodging, responsive to nitrogen application, and better adapted to their target environments.

Durum Breeding Methods Durum wheat is a self-pollinated crop and therefore a pure-line breeding approach is used, that is, the final product is a uniform true-breeding variety. This is achieved by several generations of selection in the segregating material from crosses, ensuring selfpollination at each stage. Crosses are made between carefully chosen parent lines that have performed well in evaluation trials or lines that carry particular traits. Many programs use not only simple two-way crosses but also three-way crosses and backcrosses. Most durum breeding programs use variations of the standard pedigree breeding method (which involves making selections under self-pollination while maintaining lineage and identity information on the selections in each segregating generation until the breeding material reaches homozygosity), and lines are generally bulked at F4 or F5 stage. Some programs conduct early generation yield testing and then reselect from high yielding bulks. The North American programs make use of off-season nurseries in the southern hemisphere (New Zealand or Chile) to speed up breeding. Quality testing in early stages is limited to visual inspection of grain quality and evaluation of protein and yellow pigment using near-infrared spectroscopy (NIR). For further information on breeding methods, please refer to the chapter on wheat breeding.

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In addition to the methods mentioned earlier, some programs also use doubled haploids (DHs) to accelerate progress to homozygosity. DHs are completely homozygous lines generated by artificially doubling the haploid set of chromosomes in pollen mother cells. DHs are more expensive to produce in durum, compared with bread wheat, because of a lower success rate. Single seed descent is a cheaper acceleration strategy and it could typically achieve progression from F1 seed to F4 seed in a year compared with 4 years required in the field-based conventional approach. All the previously mentioned strategies could be combined with molecular marker-assisted selection to achieve more rapid breeding progress. Molecular markers are available in durum to screen for several quality traits (e.g., grain yellow pigment content, favorable lipoxygenase alleles, grain cadmium content, and grain protein concentration), disease resistance (mainly rust resistance genes), and genes involved in determining phenology such as vernalization and photoperiod response. Advanced evaluation of experimental lines is conducted in replicated yield trials in several key locations in the target regions. Detailed testing of grain, semolina, and pasta-making quality is conducted at this stage of breeding. Testing for disease resistance is normally conducted at all stages of breeding, but in advanced stages, the tests would include seedling resistance evaluation. In some countries, varieties selected through this process are progressed to independent variety tests where they are evaluated against check varieties and the best new varieties/breeding lines from other breeders.

Breeding for Yield and Agronomic Traits Substantial improvement in the yield potential of durum has been achieved through reducing crop stature, improving lodging resistance, and manipulating phenology to suit local growing conditions. Reduction of plant height was achieved by incorporating the reduced height gene, Rht1, from CIMMYT, which makes plants insensitive to the plant growth hormone, gibberellin. The height reduction from Rht1 also resulted in resistance to lodging and in turn made it possible to apply higher rates of fertilizers, use irrigation (if available), and practice better agronomy to obtain higher yields. Reducing plant height also improved the harvest index with more of the plant’s resources going into grain formation. Further improvements in productivity have come from other improvements in plant type such as erect leaves and fine tuning of crop development and maturity. Some breeders have preferred medium height varieties in an effort to obtain higher yields through the ‘tall dwarf’ plant type, which produces a higher biomass. Breeding has also produced changes in reproductive development phases of modern durums leading to increases in the duration of the period between initiation of the terminal spikelet and ear emergence resulting in improved floret fertility and grains per spikelet. A disadvantage of Rht1 is the reduced coleoptile length in varieties containing this gene that makes the varieties unsuitable for deep sowing. It is considered that gibberellin-sensitive reduced height genes, such as Rht18, would result in longer coleoptile length and provide better adaptation to deep

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sowing, which would allow seed placement in moist soil, deeper down, under dry sowing conditions.

Breeding for Tolerance to Abiotic Stresses Tolerance to moisture stress is very important considering the majority of the durum crop is rainfed and the durum-growing regions of the world are semiarid. In general, breeding durum wheat for tolerance to moisture stress is currently conducted by evaluating yield potential of the experimental lines over several years and locations. Such evaluation will expose the experimental lines to moisture stress conditions and provide opportunities to select for higher but stable yields combined with maintenance of grain quality under drought conditions. Tolerance to salinity has been recently researched in Australia. Two genes, Nax-1 and Nax-2, have been incorporated into durum wheat from conventional crosses with a salttolerant Triticum monococcum line. Nax-2 has been found to be more useful for breeding because, unlike Nax-1, there was no evidence of yield loss associated with the presence of Nax-2. Molecular markers have been developed for these genes to increase efficiency of selection. Lack of tolerance to acid soils in durum germplasm has limited the growth of durum in low-pH regions. The impact of acid soils is through increased concentration of aluminum in the soil solution, which is toxic to durum and limits root growth. Recent research in Australia has achieved transfer of a gene from bread wheat, TaALMT1, conferring tolerance to aluminum toxicity to a popular durum cultivar, Jandaroi, using conventional breeding methods. There is scope also for using variation within durum germplasm as there are reports of variation for Al tolerance comparable to bread wheat.

Breeding for Quality Traits Durum wheat is mostly used to prepare pasta, either dried or fresh. Other products made from durum wheat include bread (flat and leavened), bulgur, freekeh, couscous, pastry, pancakes, and some traditional Indian savory dishes and desserts. The following discussion will focus on the selection methods and objectives in breeding for technological quality to meet customer requirements for pasta products. In addition, there is new interest in breeding for nutritional quality but this will be covered elsewhere in this book. The choice of testing procedures to select for technological quality used in breeding programs around the world will vary depending on the program objectives, but many breeding targets are common across the world and will be described here.

breeding process that determines the amount of seed available for testing. Generally, the earlier the generation cycle, where seed availability is limited, the more the requirement for tests that use only small amounts of grain/semolina with preference for nondestructive testing. It is at these stages where there may be several thousand lines to evaluate that the test should allow effective screening and reduction of the population to more manageable quantities for replicated field testing. At the later stages of breeding, more grain is available allowing more detailed testing.

Grain Size and Test Weight Test weight (TW), which is affected by the size and shape of the grain, is a widely used specification in wheat grading because it is internationally recognized as an index of wheat soundness and wheat milling potential. TW is lowered by grain weathering, caused by rain at harvest, and grain shriveling due to terminal drought. Shriveled, high-protein grain produces a reduced semolina milling performance. This is because small kernels contain a lesser percentage of endosperm, the main economically valuable part of the grain. Generally, a high thousand grain weight (TGW >40 g) and TW (>76 kg/hl) are desirable and further improvements of grain size are sought.

Percentage of Hard Vitreous Kernels Durum wheat kernels should have a translucent, vitreous appearance to ensure good semolina yield and to avoid pasta issues such as weak strands, poor cooking quality, and white specks, which occur when grain vitreousness is very low (<50%). Nonvitreous or starchy or piebald kernels tend to produce more flour than semolina upon milling because they are softer and the flour can give undesirable white specks in pasta (Figure 3). Where the grain protein content is high, hard vitreous kernels (HVK) is not usually an issue and has become less important where millers use finer granulations. Genotypes that produce low HVK grain compared with control varieties having similar protein achievement across multiple environments should be selected against, but the influence of environment on protein content makes selection for HVK difficult to achieve in practice.

% Hard vitreous kernels (HVK) Vitreous Piebald Starchy

Key Technological Requirements The process of selecting the many genotypes produced in breeding programs for quality typically compares the performance of the test line(s) with commercial (control) varieties from the same field trial. A new test line generally needs to match or exceed the quality characteristics of the controls. The methods used to assess quality depend on the stage of the

Bleached Nonvitreous

Figure 3 Classification of grain vitreosity.

THE CEREAL GRAINS | Durum Wheat: Overview Screenings These are undersized grains that fall through a 2 mm screen. Grain with high percentage of such grain is undesirable for milling because it reduces semolina yield and creates a less uniform particle size, and this causes white spots in pasta due to uneven hydration. Therefore, lines with a tendency to high screenings are avoided by breeders.

Grain Protein A key quality parameter in durum is grain protein content that should be above 13% (11%moisture basis) to ensure about 12% protein in the semolina and pasta that is important to obtain a good texture of cooked pasta. Dry pasta made from high-protein semolina (12%) is physically stronger and more elastic than pasta from lower protein semolina. Generally, as protein content increases, cooked pasta becomes firmer and less sticky and resists overcooking better. Negative aspects of high protein content are lower TW and semolina yield, which produces duller pasta. With very low levels of protein, fragile spaghetti is produced with low firmness. High-protein durum wheat allows spaghetti to swell when cooked, reduces cooking loss, and allows retention of firmness with overcooking, which is also associated with less stickiness. Typically, farmers use nitrogen fertilizers to achieve these protein levels, but due to the increasing cost and environmental concerns about the use of too much fertilizer, breeders select for inherently high protein content. Significant advances have been made by breeders with new varieties from Canada (Strongfield and CDC Verona) and Australia (EGA Bellaroi and Jandaroi) that are inherently high-protein achievers. Grain protein content is easily measured using NIR allowing large numbers of experimental lines to be assessed in breeding programs.

Yellow Pigment This is important in the market place as it contributes to the desirable yellow color typical of pasta products that consumers desire and provides valuable antioxidants. The yellow pigment content in the grain is strongly inherited, which has allowed large improvements in this trait worldwide over the last decade from breeding. Yellow pigment can be measured using NIR or extraction of the yellow pigment from wholemeal using solvents or measurement of the semolina color with a camera to measure the color space parameters, brightness (L*), redness (a*), and yellowness (b*). These methods allow measurement on small amounts of grain/semolina at very early stages in the breeding program allowing rapid genetic gain.

Gluten Quality Gluten strength is important in pasta manufacture and influences cooking quality (loss of solids into the cooking water) and texture (bite, stickiness, and adhesiveness) of the cooked product. Gluten strength is a property of the dough that has become sought after in many markets where a higher price can be commanded. This is because semolina from extra strong durum varieties is thought to produce firmer pasta. The heritability of gluten strength is moderate and genetic gain has

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been obtained over the years leading to stronger gluten types. Gluten strength can be measured by several methods (mixograph, extensograph, farinograph, glutograph, alveograph, and gluten index) that use from 10 to 300 g of semolina that can rank cultivars with diverse strength equally well.

Semolina Yield A miller is mainly concerned with the milling yield or percentage of the grain converted to semolina of acceptable purity with minimal flour production because semolina commands a higher price. TW appears to be a better predictor of durum wheat milling performance than kernel weight. Purity is assessed as ash content (mineral content remaining when all the organic content has been removed by combustion at very high temperatures) and the number of brown specks per unit area in the semolina. High mill extraction rates produce semolina with higher ash (0.9–1.1% dry weight basis) due to contamination by the bran and this reduces semolina’s brightness and yellowness. Ash content is affected by the genotype and environment. It is desirable to avoid genotypes with a tendency to higher ash contents. There are currently no satisfactory small-scale predictive measures of milling performance, and typically, a minimum of 100 g of grain has to be milled but larger quantities (3 kg) are desirable when using a Buhler mill, for example. The higher grain quantities required and the cost of such milling have meant that these tests are conducted on small elite sets of lines toward the end of the selection process, and this necessity has made improvements in this trait difficult. Nevertheless, a small improvement in semolina yield has been achieved in Australia.

Pasta Quality Evaluation of the quality of the final pasta product is the ultimate test of acceptability of a new variety. In traditional pasta-consuming countries, the consumer is concerned about the aroma, color, appearance, texture, flavor, and nutritional value of the pasta. The color of the pasta is very important and selection of lines giving high brightness and yellowness in uncooked and cooked pasta is desirable. This can be achieved easily using a Minolta chroma meter or spectrophotometer. A high level of yellow pigment in the semolina does not guarantee a high color in the pasta because it depends on the activity the enzyme lipoxygenase (LOX) in the semolina during pasta processing. LOX levels in durum wheat are affected by genotype and environment, and assays for the enzyme or molecular markers exist to screen genotypes for low LOX levels. The pasta after cooking should maintain its texture and not become a thick, sticky mass. Mechanical texture is typically described by a range of terms (firmness, elasticity, stickiness, chewiness, and bulkiness) and can be measured by a sensory panel or by objective tests with the latter typically used. Also, cooking tests are employed to measure water absorption, degree of swelling, and solid loss to the cooking water to assess pasta quality. Selection for end use quality as discussed earlier has led to release of several varieties in many durum-growing countries that combine high yield and high quality. Some examples are

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Svevo and Normanno in Italy; Strongfield, Eurostar, and Brigade in Canada; and EGA Bellaroi, Caparoi, and Jandaroi in Australia.

Durum Diseases and Breeding for Disease Resistance The most important disease of durum, worldwide, is Fusarium head blight (FHB) caused by several fungi including Fusarium graminearum, F. culmorum, F. avenaceum, and F. sporotrichioides. While the first two are more common causes of FHB, often, there are more than one species present in infected crops. FHB development is generally favored by wet conditions during flowering and grain filling. Durum is considered more susceptible to FHB than bread wheat. Infected heads are often sterile and any seed formed is shriveled and may have a pinkish color. FHB produces mycotoxins that make the infected grain unsuitable for human and animal consumption. The most common mycotoxin is deoxynivalenol for which there are legislated maximum acceptable levels for grain trade. While there are sources of resistance available in bread wheat and closely related tetraploid species, resistance to FHB has been difficult to characterize and incorporate into durum due to the influence of the environment in expression of the disease. Control measures include adding nongrass crops in rotations and avoiding corn that is highly susceptible to Fusarium and fungicide sprays. Fusarium spp. are also involved in causing crown rot (CR) in durum. F. pseudograminearum and F. culmorum are the main species involved. CR-infected plants have a honey-brown discoloration on lower leaf sheaths and stem bases. There could also be plant death at all growth stages. Affected heads ripen prematurely and produce none or shriveled grain and are known as ‘whiteheads.’ Moisture stress from the flowering stage onward promotes the disease expression and can produce heavy yield losses. CR expression is also higher under higher rates of nitrogen application that promotes vegetative growth and leads to higher levels of moisture stress upon postanthesis drought. Durum varieties are considered more susceptible to CR than bread wheat. There is some variation for susceptibility to CR in durum germplasm, and some progress has been achieved in developing varieties tolerant to CR, but it is difficult to characterize the genetic effects due to large environmental effects on expression. Currently, rotation with broad-leaved crops is the best control measure for CR. Yellow leaf spot (tan spot) caused by Pyrenophora triticirepentis and Septoria leaf blotch (Mycosphaerella graminicola) are important leaf diseases in several countries. These diseases, being stubble-borne, are increasing in their importance as a consequence of the increased popularity of minimum tillage. A single recessive gene, tsn1, on chromosome 5BL controls resistance to races 1 and 2 of tan spot. A marker is available to screen for this gene. Resistance to races 3 and 5 is controlled by another recessive gene, tsn2, on 3BL. The Australian varieties, Caparoi, Jandaroi, and EGA Bellaroi, are resistant to tan spot. While currently there are minimal yield losses in Australia and North America from rust diseases due to good genetic resistance, in EU countries, resistant varieties are not widely available, and as a consequence, there is substantial reliance on fungicides. All three rusts (stem, leaf, and stripe rust) are the

most important diseases of durum as they can produce substantial and widespread yield losses as they are airborne diseases. Ensuring an adequate level of genetic resistance to all current rust races is a major breeding objective in most breeding programs. There have been significant changes of race from time to time, and it is a significant challenge to durum breeders and pathologists to maintain resistance in the current varieties. For example, a new stem rust race, UG99, also known as TTKS, has evolved in Africa overcoming two previously effective resistance genes, Sr24 and Sr31. Most Australian durum varieties carry three stem rust resistance genes, Sr8b, Sr9e, and Sr13. This combination is expected to be effective against UG99 due to Sr13, but it would be important to pyramid additional genes into new varieties to improve the durability of resistance. Resistance to leaf and stripe rust is based on adult plant resistance (APR) genes. Leaf rust is normally not observed because it develops later in the season when the weather is warm and APR genes are effective. Kernel discoloration (black point and red smudge) is associated with the same fungi that cause leaf spots but are not associated with mycotoxins. Their economic impact on durum is from the loss of clean, vitreous appearance of the grain that reduces the value of the grain. Durums are more susceptible to black point than bread wheat, but there is some genetic variation in susceptibility. The main control measures are to practice good rotations to reduce fungal diseases and in irrigated crops reduce watering after flowering.

Agronomy of Durum Production For successful durum crop production, it is important to start with selecting a suitable variety for the quality type targeted. Varieties differ in their adaptation, maturity, lodging and disease resistance, and their ability to achieve the required grain protein content and quality. It is also important to choose a suitable paddock that does not have a high disease inoculum load to reduce the incidence of diseases such as crown rot. Rotation with broad-leaved crops, such as grain legumes and canola, is very important to reduce buildup of disease inoculum, provide opportunities for weed control, and, in the case of grain legumes, build up soil fertility. A good diversified crop rotation would be beneficial economically and environmentally. It is also important to avoid low-pH soils because of likely aluminum toxicity. Minimum tillage or no tillage systems are gaining popularity in cropping as chemical weed control is widely available. These systems conserve moisture, improve soil structure and soil organic matter, and reduce the cost of production. In many regions, no tillage produces higher yields than the conventional tillage systems. A disadvantage of no tillage systems is the likelihood of disease inoculum buildup leading to higher incidence of leaf spot diseases and crown rot. However, this disadvantage can be overcome by adopting suitable rotations. The timing of sowing for achieving optimum yield depends upon location of the crop and should be determined to avoid periods of stress including frost and terminal drought. In most durum areas, early sowing is desirable to avoid loss of yield potential and drought during grain development. Early sowing allows the crop to establish and flower under favorable

THE CEREAL GRAINS | Durum Wheat: Overview conditions, and this helps reduce the impact of crown rot. However, these benefits should be balanced against the risk of flowering during the frost-risk period. Sowing rates are lower for rainfed crops to conserve moisture, but in high-rainfall and irrigated conditions, higher plant populations are targeted. Irrigation, whether protective (strategic application of water during spells of drought or at key growth stages) or for intensive crop production, increases the yield potential of durum crops. The modern durum varieties with short, stiff straw withstand irrigation and higher rates of fertilizers and produce high yields compared with older varieties. It is important to avoid irrigation after ear emergence to achieve high grain protein content, HVK; to maintain good yellow pigment content; and to reduce the incidence of kernel discoloration. Higher rates of nitrogen nutrition are required, especially under irrigation, to achieve the required grain protein levels. It is possible to manage nitrogen requirements by conducting soil tests and calculating the extra nitrogen required to achieve the grain protein content required for the expected level of yield. Split applications of nitrogen are more efficient at raising grain protein content than applying all fertilizer at sowing. With the availability of yield mapping, it is possible to apply fertilizers more judiciously according to the observed variation in fertility in the paddocks. Depending upon the nutrient status of the soil, it may be necessary to apply other nutrients such as phosphorus, sulfur, and zinc. There are reports of both boron deficiency (Turkey) and toxicity (Australia) in durum. Chloride deficiency and consequent need to use chloride containing fertilizers have been reported in the United States and it is expressed occasionally in Australian crops.

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East/Africa regions with great potential for pasta consumption in India and China. Pasta is a low-glycemic-index food and it contains high levels of lutein, which is an antioxidant and a vitamin A precursor. Regular intake of lutein could help prevent macular degeneration. There are significant opportunities for continued improvements in productivity and quality of durum crops through breeding and better agronomic management by developing specific management practices to suit particular varieties. World durum production has a potential to expand despite the challenges from the changing climate, loss of arable land to other uses, and competition from other crops. There is considerable scope to improve the nutritional quality and functional food properties of durum wheat to expand consumer demand. Some examples of functional food properties in durum under development are high amylose content (to increase resistant starch) and soft durum (possible applications in noodles and biscuits). Development of such durum lines could provide scope for an expanded durum industry.


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How is durum wheat different from bread wheat? Why do we need ongoing breeding work? Why is grain quality important in durum wheat? Which is the most dangerous disease of durum from a human consumption point of view? What is the importance of plant height in durum breeding?

Future


The future for durum as a world crop appears bright as pasta production in the EU has increased since 2010 (Figure 4) although global growth is coming from Asia Pacific and Middle

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Check the various dry and fresh pasta products in the local supermarket and note any differences in their appearance and origin of the product.

4.600 4.500 4.400 4.300 4.200 4.100 4.000 3.900 3.800 3.700 3.600 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 (000 tons) Figure 4 Pasta production in the EU countries from 2003 to 2012. http://www.pasta-unafpa.org/ingstatistics2.htm.

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Check for the less popular durum foods in the local supermarket. Try finding semolina, couscous, burghul, freekeh, and durum bread. Note whether the semolina is white or yellow and work out the reason. Check whether durum wheat is part of any traditional preparations in your family. Discuss whether you can cross durum wheat with bread wheat. Compare the glycemic index of pasta with other foods including bread. Investigate the chemical nature of yellow pigment in durum grain and its importance for human nutrition.

Acknowledgments The authors acknowledge assistance from various colleagues who were very generous with information.

See also: Grain Harvest, Storage and Transport: Contaminants of Grain; Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Marketing; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Grain Crops: An Overview; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Pasta.

Further Reading Abecassis J, Cuq B, Boggini G, and Namoune H (2012) Other traditional durum derived products. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 177–200. Eagan, MN: American Association of Cereal Chemists International. Bariana HS, Brown GN, Bansal UK, Miah H, Standen GE, and Lu M (2007) Breeding triple rust resistant wheat cultivars for Australia using conventional and marker-assisted selection technologies. Australian Journal of Agricultural Research 2007(58): 576–587. Blanco A, De Pace C, Porceddu E, and Mugnozza GTS (1988) Genetics and breeding of durum wheat in Europe. In: Fabriani G and Lintas C (eds.) Durum Wheat Chemistry and Technology, 1st edn., pp. 17–46. American Association of Cereal Chemists: MN, USA. Bozzini A, David J, and Natoli V (2012) Origin and distribution of durum wheat genetic diversity in the world. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 1–14. Eagan, MN: American Association of Cereal Chemists International. Clarke JM, DeAmbrogio E, Hare RA, and Roumet P (2012) Genetics and breeding of durum wheat. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 15–36. Eagan, MN: American Association of Cereal Chemists International. http://www.ipmcenters.org/cropprofiles/docs/NDwheat.pdf – “Crop profile for hard red spring and durum wheats in North Dakota”.

Engel RE, Bruebaker L, and Emborg TJ (2001) A chloride deficient leaf spot of durum wheat. Soil Science Society of America Journal 65: 1448–1454. Grant CA, Di Fonzo N, and Pisante M (2012) Agronomy of durum wheat production. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 37–55. Eagan, MN: American Association of Cereal Chemists International. Isidro J, Alvaro F, Royo C, Villegas D, Miralles DJ, and Garcıá del Moral LF (2011) Changes in duration of developmental phases of durum wheat caused by breeding in Spain and Italy during the 20th century and its impact on yield. Annals of Botany 107: 1355–1366. Joppa LR and Williams ND (1988) Genetics and breeding of durum wheat in the United States. In: Fabriani G and Lintas C (eds.) Durum Wheat Chemistry and Technology, 1st edn., pp. 47–68. Eagan, MN: American Association of Cereal Chemists. Kimber G and Sears ER (1987) Evolution in the genus Triticum and the origin of cultivated wheat. In: Heyne EG (ed.) Wheat and Wheat Improvement, pp. 154–164. Madison, WI: American Society of Agronomy. http://en.magazinebbm.com/?p¼235 – “The future of pasta is in less developed countries.” Martia J and Slafer GA (2014) Bread and durum wheat yields under a wide range of environmental conditions. Field Crops Research 156: 258–271. Matthews P, McCaffery D, and Jenkins L (2014) Winter crop variety sowing guide 2014. NSW Department of Primary Industries. http://www.dpi.nsw.gov.au/agriculture/ broadacre/guides/winter-crop-variety-sowing-guide. Morris CE and Sands DC (2006) The breeder’s dilemma – Yield or nutrition? Nature Biotechnology 24(9): 1078–1080. DePauw R and O’Brien L (2014) Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn, vol. 4, pp. 279–286. Elsevier Ltd. Park RF (2014) Wheat: Biotrophic Pathogen Resistance. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn, vol. 4, pp. 264–272. Elsevier Ltd. Periyannan SK, Qamar ZU, Bansal UK, and Bariana HS (2014) Development and validation of molecular markers linked with stem rust resistance gene Sr13 in durum wheat. Crop & Pasture Science 65: 74–79. Royo C, Nachit M, Di Fonzo N, Araus JL, Pfeiffer M, and Slafer JA (2005) Durum Wheat Breeding – Current Approaches and Future Strategies. volume 1, New York, NY: Food Products Press. Sissons MJ (2004) Pasta. In: Wrigley C, Corke H, and Walker C (eds.) Encyclopedia of Grain Science, pp. 409–418. Australia: Elsevier. Sissons MJ (2014) Pasta. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn, vol. 3, pp. 79–90. Elsevier Ltd. Sissons M, Abecassis J, Marchylo B, and Cubadda R (2012) Methods used to assess and predict quality of durum wheat, semolina and pasta. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edition, pp. 213–234. Eagan, MN: American Association of Cereal Chemists International. Torrey G Lutein May Decrease Your Risk of Macular Degeneration. American Macular Degeneration Foundation, https://www.macular.org/lutein. Troccoli A, Borrelli GM, De Vita P, Fares C, and Di Fonzo N (2000) Durum wheat quality: A multidisciplinary concept. Journal of Cereal Science 32: 99–113. Wallwork H (2000) Cereal Leaf and Stem Diseases, GRDC and SARDI, ISBN 1 875477 86 1. Wallwork H (2000) Cereal Root and Crown Diseases, GRDC and SARDI, ISBN 1 875477 74 8. http://herbarium.usu.edu/webmanual/info2.asp? name¼Triticum_durumþ&type¼treatment – Wheat taxonomy. Wrigley C (2016) Wheat - An Overview of the Grain that provides “Our Daily Bread”. In: Wrigley C, Corke H, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn, vol. 1, pp. 105–116. Oxford, UK: Elsevier.

Rice: Overview BO Juliano, Philippine Rice Research Institute Los Banõs, Laguna, Philippines ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Rice is the most important crop in the world in terms of total developing world production and the number of consumers dependent on it as their staple. Semidwarf and hybrid rice, together with tolerance/ resistance to abiotic and biotic stresses, have increased rice production. Rice is hypoallergenic with protein of good quality, and its net protein utilization (NPU) is not affected by cooking. Its wide range of apparent amylose content (AC) has contributed to wide differences in eating quality preferences for table rice and for rice products within the various regions of Asia. Differences in starch gelatinization temperature and gel and Rapid Visco Analyser consistency are due to differences in amylopectin properties, where amylose content is similar. Glycemic index decreases with increase in AC. g-Oryzanols and tocols in unsaponifiable matter of undefatted brown rice and bran have hypocholesterolemic properties.

9% flood-prone wetland, corresponding to a total rough rice production of 76% from irrigated, 16% from rainfed lowland, 4% from upland, and 4% from flood-prone wetland. Since the rice-growing area is shrinking, rice production must keep up with the annual increase in population in tropical Asia through increased yield. Rice is mainly the species Oryza sativa L., plus Oryza glaberrima L., grown in West Africa. There are estimated to be about 100 000 rice varieties; only a small proportion is actually widely cultivated. They vary in grain weight, size and shape, degree of dormancy, longevity, and seedling vigor, and some have red to purple-black pigments. About 75% of Asia’s rice area is planted with varieties of improved semidwarf plant type with erect leaves. The newer, improved varieties have a similar yield potential to the first variety (IR8) but have a better resistance or tolerance to biotic and abiotic stresses. Although essentially self-pollinated, three-line cytoplasmic male sterile hybrids and two-line thermogenic male sterile hybrids have been successfully produced and grown first in China with increased yields. Complete sequencing of the rice genome in 2002 has accelerated the use of molecular markers in breeding for yield, stress tolerance, and, lately, grain quality.

Learning Objectives

• • •

To appreciate the wide adaptability of the rice plant and the unique properties of the rice grain To be able to relate structure and composition of rice to its nutritional properties To understand the diversity in rice texture and the causes of textural differences

Commercial Importance, Global Distribution, and Varieties Rice is the most important crop in the world in terms of total developing world production (480 106 tonnes of rough rice in 2012) and the number of consumers (3.5 billion) dependent on it as their staple food. It is widely grown in over 100 countries in every continent (except Antarctica), from 53 N to 40 S and from sea level to an altitude of 3 km. The total production in 2012 was 697 106 tonnes of rough rice. Asia accounts for 149 106 of the 158 106 ha world area that is used for rice cultivation. The mean rough rice yield was 4.40 tonnes ha1 in 2012. About 90% of the world’s rice is grown and consumed in Asia, in 200 million rice farms most of which are smaller than 1 ha. The major rice producers in 2012 were China, India, Indonesia, Bangladesh, Vietnam, and Thailand. Rice can grow in both flooded (anaerobic soil) and upland (aerobic) conditions. The plant has air channels that connect to its roots. In terms of water regime, 54% of the total rice area was irrigated in 1991, 25% rainfed lowland, 13% upland, and


Structure of the Rice Grain The rice grain (rough rice or paddy) consists of an outer protective covering, the hull (husk), and the edible rice caryopsis or fruit (brown, cargo, dehulled, or dehusked rice) (Figure 1). Brown rice consists of the outer layers of pericarp, seed coat, nucellus, and germ or embryo, which are the maternal tissues, and the endosperm. The endosperm consists of the aleurone layer and the starchy or inner endosperm. Pigment is confined to the pericarp, but there is a varietal difference in the extent of retention of pigment with the degree of milling. The aleurone layer encloses the embryo. The inedible hull constitutes 16–28% (mean 20%) of rough rice weight. Brown rice consists of 1–2% pericarp, 4–6% aleurone plus nucellus and seed coat, 1% embryo, 2% scutellum, and 90–91% endosperm. The aleurone and embryo cells are rich in lipid bodies (spherosomes, 0.2–1.5 mm) and in protein bodies (aleurone grains containing inclusions of phytic acid bodies or globoids (1–3 mm)). The endosperm cells are thin-walled and packed with amyloplasts containing polyhedral compound starch granules about 3–9 mm in size. Protein occurs mainly in the form of large (1–2 mm) and small (0.5–0.8 mm) spherical protein bodies and crystalline protein bodies (2–4 mm). Spherical protein bodies (PB I) are rich in prolamin (alcohol-soluble protein), and crystalline protein bodies (PB II) are rich in glutelin (alkalisoluble protein). High night ripening temperature increases PB II/PB I ratio. Spherosomes are present in the subaleurone or the two outermost cell layers of rice endosperm.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00015-2

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Awn

Hull

Starchy endosperm

Lemma Palea

Inner endosperm

Pericarp Seedcoat Nucellus Aleurone layer VENTRAL

Subaleurone layer DORSAL

Scutellum Epiblast Plumule

Embryo

Radicle Rachilla Sterile lemmae

Figure 1 Longitudinal section of the rice grain. Reproduced with permission from Juliano BO (1984) Rice starch: Production, properties and uses. In: Whistler RL, BeMiller JN, and Paschall EF (eds.). Starch Chemistry and Technology, 2nd edn., p. 509. Orlando, FL: Academic Press.

Grading, Handling, and Storage There is no international standard for milled rice size and shape. The International Rice Research Institute (IRRI) uses the following scale for size: extra long, >7.50 mm; long, 6.61–7.50 mm; medium, 5.51–6.60 mm; and short, <5.50 mm. For grain shape based on the length/width ratio, the following scale is used: slender, > 3.0; medium, 2.1–3.0; bold, 1.1–2.0; and round, 1.0. Grades are based on grain size and shape, degree of milling, percentage of head or wholegrain milled rice, immature grains, damages (discolored) and heat-damaged grains (chalky grains, red grains, and redstreaked grains), aroma, and organic extraneous matter and inorganic extraneous matter. An important property of harvested grain is its moisture content: 14% on a wet-weight basis is considered a safe storage value; grains become susceptible to fissuring from moisture adsorption stress below critical moisture contents of 12–16%, depending on the variety. Aging of sun-/oven-dried rough rice for up to 2 months after harvest at ambient temperature >15 C improves milling yields and makes milled rice expand more during cooking, with less dissolve solids, and become more flaky. Heating during grain drying accelerates aging. About 20% of rice is consumed as parboiled rice. Parboiling consists of boiling or steaming steeped aged rough rice until the hull starts to open and then cooling and drying the gelatinized grain. Diffusion of bran B vitamins into the endosperm occurs during parboiling but with some heat decomposition. Mycotoxins are a potential problem in parboiled rice. Milling involves dehulling, followed by removal of the outer 7–10% of the brown rice, either by friction or by abrasion, removing most of the pericarp, seed coat, nucellus,

aleurone layer, and the germ. In the Engelberg mills, hull and bran are removed together in one step with high grain breakage. Milling is done in several steps in modern cone mills with tempering in between to minimize breakage. Many modern mills have shifted to milling at >14% moisture to minimize breakage and to moisture mist treatment (through hollow shaft) during milling to soften the bran and improve surface gloss. Only about 4–5% of the world’s rice production enters the international trade. The major exporters in 2012 were Thailand, India, Vietnam, the United States, and Pakistan. The major importers in 2012 were Nigeria, China, Iran, the Philippines, Iraq, Saudi Arabia, Ivory Coast, and Malaysia.

Chemical and Nutritional Composition Rice has one of the lowest protein contents (7%) among the cereals. The bran layers and embryo are richer in nonstarch constituents than the milled (white) rice (Table 1). The major nutritional advantage of brown rice over milled rice is its higher content of B vitamins. Although higher in minerals, bran phytic acid forms complexes with minerals and proteins, reducing their bioavailability. Thus, the available iron (mg per meal) is similar in brown and milled rice meals, but probably higher in brown rice for zinc (mg per meal) than for milled rice. The energy content of brown rice and bran is higher than that in milled rice, owing to the higher fat content. Rice has no vitamin A, C, or D. Although cereal proteins are deficient in lysine, rice protein has one of the highest lysine contents among them, corresponding to an amino acid score of 67% in milled rice based

THE CEREAL GRAINS | Rice: Overview Table 1

127

Comparison of nutrient composition of brown rice, milled rice, and rice bran Amounts (per 100 g)

Property

Brown rice

Milled rice

Rice bran

Moisture (g) Energy content (kJ) Energy content (kcal) Crude protein (g) Crude fat (g) Crude fiber (g) Crude ash (g) Available carbohydrates (g) Total dietary fiber (g) Water-insoluble fiber (g) Sugars (g) Thiamin (mg) Riboflavin (mg) Niacin (mg) Pantothenic acid (mg) Vitamin B6 (mg) Folate (mg) Vitamin E, a-tocopherol (mg) Calcium (mg) Phosphorus (mg) Phytic acid P (mg) Iron (mg) Zinc (mg)

14.0 1480–1610 355–385 7.1–8.3 1.6–2.8 0.6–1.0 1.0–1.5 73–87 2.9–4.4 2.0 0.8–1.9 0.4–0.6 0.04–0.14 3.5–6.2 1.4–1.6 0.5–0.7 16–20 0.8–2.5 10–50 0.17–0.43 0.13–0.27 1.4–5.2 1.9–2.8

14.0 1460–1560 349–373 6.3–7.1 0.3–0.6 0.2–0.5 0.3–0.8 77–89 0.7–2.7 0.5 0.1–0.5 0.07–0.17 0.02–0.06 1.3–2.5 0.8–1.3 0.1–0.4 4–9 0.1–0.3 10–30 0.08–0.15 0.02–0.07 0.3–0.8 0.8–2.3

14.0 1670–1990 399–476 11.3–14.9 15.0–19.7 7.0–11.4 6.6–9.9 34–62 24–29 15–27 5.5–6.9 1.2–2.5 0.18–0.43 27–50 20–60 3.7 40–140 3–15 30–120 1.1–2.5 0.9–2.2 8.6–43 4.3–26

Juliano BO (2007) Rice Chemistry and Quality. Munõz, Nueva Ecija: Philippines Rice Research Institute; Champagne ET, Wood DF, Juliano BO, and Bechtel DB (2004) The rice grain and its gross composition. In: Champagne ET (ed.). Rice Chemistry and Technology, 3rd edn., pp 77–108. St. Paul, MN: American Association of Cereal Chemists; United States Department of Agriculture (2012) National Nutrient Database for Standard Reference, Release 25. http://www.ars.usda.gov/ba/bhnrc/ndl.

Table 2

Amino acid profile and energy and nitrogen balance in five growing rats of raw brown rice, milled rice, and rice bran

Property

Brown rice

Milled rice

Rice bran

Arginine (gram per 16 g N) Histidine (gram per 16 g N) Isoleucine (gram per 16 g N) Leucine (gram per 16 g N) Lysine (gram per 16 g N) Methionine (gram per 16 g N) Methionine þ cystine (gram per 16 g N) Phenylalanine (gram per 16 g N) Phenylalanine þ tyrosine (gram per 16 g N) Threonine (gram per 16 g N) Tryptophan (gram per 16 g N) Valine (gram per 16 g N) Digestible energy (% of total) True digestibility (TD, % of diet N) Biological value (% of digested N) Net protein utilization (% of diet N) Amino acid score (%) Amino acid score TD (%)

7.2 2.4 4.0 7.9 3.6 2.1 3.3 4.9 8.5 3.5 1.2 5.6 94.3b 96.9b 68.9b 66.7b 71lys 68lys

7.9 2.2 4.1 7.8 3.4 2.2 4.2 5.1 8.3 3.4 1.1 5.8 96.6a 98.4a 67.5b 66.4b 67lys 66lys

7.5 2.5 4.0 7.3 4.6 2.2 4.4 4.5 7.5 4.0 0.8 6.3 67.4c 78.8c 86.6a 68.3a 90lys 71lys

Means in the same line followed by a common letter are not significantly different at the 5% level by Duncan’s (1955) multiple range test. lys ¼ lysine is the first-limiting amino acid. United States Department of Agriculture (2012) National Nutrient Database for Standard. Reference, Release 25. http://www.ars.usda.gov.ba/bhnrc/ndl; Eggum BO, Juliano BO, and Manin˜gat CC (1982) Protein and energy utilization of rice milling fractions by rats. Qualitas Plantarum-Plant Foods for Human Nutrition 31: 371–376.

on the US Food and Nutrition Board amino acid requirement pattern for the 1–3-year-old child of 5.1% lysine as 100% (Table 2). The solubility fractions of protein are about 15% of albumin–globulin (water- and salt-soluble), 20% prolamin (PB I, alcohol-soluble), and 65% glutelin (PB II, alkali-soluble)

in milled rice. Bran proteins are 66–98% albumins. Prolamin is poor in lysine but rich in sulfur amino acids. The high lysine content of rice protein is due to the low prolamin content. The energy digestibility is higher in milled rice than in brown rice owing to the lower dietary fiber and phytic acid

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levels, as verified by the poor energy digestibility of rice bran (Table 2). The true digestibility (TD) of milled rice protein is also higher than that of brown rice, but the biological value (BV) is lower, resulting in a similar NPU. Bran protein has a lower TD but a higher BV than brown and milled rice proteins. The amino acid score corrected for TD in rats proposed by the Food and Agriculture Organization as a protein quality index shows similar values to NPU for the rice proteins. Black or purple rice has a lower brown rice NPU (72%) and higher phenolics level (0.6%, anthocyanin) than red rice (NPU; 83% and 0.2% phenolics, proanthocyanidins) and nonpigmented rice (NPU 97% and 0.02% phenolics), but their milled rice have identical NPUs. Rice complements legumes (deficient in sulfur amino acids) in amino acid composition for human diets. Cooking and parboiling reduces the TD in growing rats by 5–15%, with a corresponding increase in BV but little change in NPU. However, lysine digestibility remains close to 100%, and cystine digestibility drops to about 82%. The fraction that remains in the feces as fecal protein particles represents the lipid-rich core of large PB I, with < 1% lysine in the protein but rich in cystine. PB II is readily digested. Starch varies in apparent AC (as determined by iodine colorimetry in acetate buffer): waxy, 0–2%; very low, 2–10%; low, 10–20%, intermediate, 20–25%; and high, >25%, all on a milled rice dry-weight basis since the 1950s. Actual AC values by differential scanning calorimetry (by melting or crystallization enthalpy of amylose–lysolecithin complex) are slightly lower and closer to AC values with iodine colorimetry in ammonium buffer pH 9 of low, 10–17%; intermediate, 17–22%; and high, >22%. The glycemic index of cooked brown rice tends to be lower than that of cooked milled rice owing to the higher amounts of phytic acid and fiber in brown rice. However, the lowering in glycemic index from milled rice to brown rice is highest in waxy and low-AC rice. Among cooked milled rice, the glycemic index decreases with increasing AC regardless of the cooking method. Processing, including parboiling, tends to reduce the glycemic index. In vivo resistant starch in an ileostomate (large intestine surgically removed) is 5% and may be not as discriminating as the glycemic index in humans. Short-term satiety may also be influenced by AC. The use of rice bran and brown rice in cereal products has increased in recent years owing to the US Food and Drug Administration’s recent approval of brown rice as a whole grain and the hypocholesterolemic effect, in humans, of the factors in the high (up to 4.4%) unsaponifiable fraction of its oil, such as g-oryzanol, (cycloartenol, 24-methylenecycloartanol and campestrol esters of ferulic acid), tocopherols, and tocotrienols, an analog of tocopherol (vitamin E). Defatted bran has no hypocholesterolemic activity, unlike in oats, where the active principle is soluble b-glucan. Inactivation of antinutritional factors – trypsin inhibitor, oryzacystatin, and hemagglutinin–lectin – and lipase and lipoxygenase that are concentrated in the rice bran by heat treatment and extrusion cooking improves the shelf life of the bran and its nutritional value to poultry. By contrast, the antinutritional factor phytic acid is heat-stable. Phytic acid in rice bran and brown rice has been reported to have some medicinal activity in preventing some types of cancer. Phytic acid content of rice bran is highest among cereal brans (3–8% phytic acid).

Essential fatty acid content of rice oil is 33.4% linoleic acid and 1.6% linolenic acid. Levels of oryzanol, tocopherols, tocotrienols, and unsaponifiable matter differ among crude oils, and oryzanol, tocopherols, and tocotrienols may be reduced by up to 90% by conventional refining and deodorizing. Contents of these antioxidants are also lower in Philippine rice than in US rice. Breeding efforts to improve the nutritional value of rice grain include a higher micronutrient density (higher iron, zinc, and vitamin A), low phytic acid (high inorganic phosphate) content, low prolamin content, the absence of lipoxygenase-3 activity and allergenic globulin, and transgenic rice endosperm with vitamin A, with the soybean glycinin gene and with the soybean ferritin gene.

Processing and Food Uses The mean worldwide per capita consumption of milled rice was 53 kg per year in 2009. It was 77 kg in Asia, 31 kg in South America, 21 kg in Africa, 14 kg in Oceania, and <10 kg in Europe and North America. Per capita, rice consumption was highest in Southeast Asia at 129 kg per year, followed by South Asia at 71 kg per year. More than 3.5 billion people depended on rice for more than 20% of their daily energy in 2009. Rice provides more than 50% of energy supply for about 520 million people in Asia, most of them poor to very poor. There are various ways of cooking milled rice. In tropical Asia, they are prewashed to remove dirt, which results in losses of B vitamins and fat. Presoaking for 30 min reduces cooking time (particularly of parboiled and brown rice). Grain cracking during soaking is minimized by adjusting milled rice moisture content to 15% by high-pressure hydration to minimize cracking. Rice may be cooked in the amount of water that it will absorb or boiled in excess water and the cooking water discarded. A steaming step is used in Indonesia and also for waxy rice. Oil or ghee may be added in the Middle East, and this reduces surface stickiness. Enriched rice premixes containing iron and B vitamins resistant to washing have been developed for rice, but have not been popular because of additional expense; the enriched rice premix can be readily distinguished from ordinary rice. Rice is hypoallergenic. Its AC correlates positively with water absorption and volume expansion during cooking and with hardness of boiled rice. South Asian consumers prefer high-AC intermediate-high gelatinization temperature (GT >70 C) rice; Southeast Asians prefer intermediate-AC, intermediate-GT rice. Japonica (temperate) short-grain rice preferred in Japan, Korea, Taiwan, and northern China have mainly low AC and low GT (70 C), with some having an intermediate AC in Europe. Only in Laos and north and northeast Thailand is steamed waxy (glutinous) rice consumed as a staple. The low GT and intermediate–high GT result from the differences in proportion of debranched amylopectin with chain lengths below 24 glucose units: Low GT has more of the shorter chains. The higher longer chains increase not only GT but also the staling of cooked starch. Among waxy and lowAC rice, low-GT rice is a softer cooked rice than high-GT rice (intermediate GT is rare at low AC), but among intermediateand high-AC rice, intermediate-GT rice is a softer freshly

THE CEREAL GRAINS | Rice: Overview cooked rice than low-GT rice. High-AC rice with high content of long-chain amylopectin (blue staining with iodine) have hard gel consistency, as long-chain amylopectin behaves like amylose. Native long-chain amylopectin crystallizes from water-saturated 1-butanol only after debranching with isoamylase. Various rice products are prepared for which specific AC types are preferred. Freshly and well-milled rice is preferred for rice products to prolong shelf life by minimizing fat rancidity in the stored products. Parboiled rice are preferably aged high- and intermediate-AC, whereas extruded and flat noodles use mainly aged, high-AC, low-GT rice. Rice with a low GT of starch is preferred in rice puddings, breads and cakes, and beer adjuncts. Waxy and low-AC rice are preferred for rice wines (for a higher ethanol yield) and in frozen sauces, desserts, snacks, and sweets, because of their slow staling rate. Rice crackers are prepared from waxy and nonwaxy rice. Parboiled rice is preferred over raw rice for idli (pudding) and dosai (cake) with rice-black gram usually fermented at a 3:1 weight ratio. The thermophysical properties of starch such as glass transition temperature, GT, enthalpy of raw starch, staled amylopectin melting (45–60 C), amylose–lipid complex I (<100 C) and II (>100 C) melting, and staled amylose melting (>130 C) of gelatinized starch affect the properties of rice products in addition to the amylose–amylopectin ratio and protein content. Specialty rice include Italian Arborio rice for making risotto, waxy rice (sweet rice with an opaque grain), Thai Jasmine rice (aromatic low-AC long-grain), and Punjab Basmati (aromatic intermediate-AC long-grain that elongates when presoaked rice is cooked). 2-Acetyl-1-pyrroline is the first major aroma principle identified in raw and cooked aromatic rice, and others are being characterized. Endosperm 2-acetyl-1-pyrroline bound to starch requires a higher extraction temperature than the free form.


• • • • •

While total maize production exceeds that of rice, why is rice a more important food crop than maize? Does waxy or glutinous rice contain gluten? Why was the approval by the US Food and Drug Administration of brown rice as a whole grain delayed as compared with the other cereal grains? The N content of rice glutelin is 16.8%. What Kjeldahl N factor would one use for rice glutelin? Note: The factor 6.25 is used for most proteins containing 16.0% N. Why is it harder to manipulate the composition of a whole grain such as rice than that of a flour such as wheat?


• • •

What factors would influence satiety index of cooked milled and brown rice? How would a low-phytic acid mutant affect iron absorption from brown rice? Speculate on how global warming would affect rice grain properties.

• • •

129

How may mutants low in lipoxygenase and lipase improve shelf life of rice? How does amylose differ from long-chain amylopectin in properties? Speculate on the binding of 2-acetyl-1-pyrroline with starch.

See also: Barley, Rice and Maize Processing: Oil from Rice and Maize; Rice Processing: Beyond the Farm Gate; Beverages from Grains: Beverages: Asian Alcoholic Beverages; Breeding of Grains: Rice: Breeding; Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Resistant Starch and Health; Starch: Analysis of Quality; Starch: Starch Architecture and Structure; Food Grains: Intolerance, Allergy and Diseases: Nutrition: Beriberi, A Deficiency Related to Grains; Food-quality Testing: Rice: Eating Quality; Genetics of Grains: Rice: Genetics; Non-wheat Foods: Rice: Chinese Food Uses; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Cereal Grains: African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts; An Overview of the Family of Cereal Grains Prominent in World Agriculture.

Further Reading Atkinson FS, Foster-Powell K, and Brand-Miller JC (2008) International tables of glycemic index and glycemic load values. Diabetes Care 31: 2281–2283. Biliaderis CG, Tonogai JR, Perez CM, and Juliano BO (1993) Thermophysical properties of milled rice starch as influenced by variety and parboiling method. Cereal Chemistry 79: 512–516. Champagne ET, Wood DF, Juliano BO, and Bechtel DB (2004) The rice grain and its gross composition. In: Champagne ET (ed.) Rice: Chemistry and Technology, 3rd edn., pp. 77–108. St Paul, MN: American Association of Cereal Chemists. Eggum BO, Juliano BO, and Manin˜gat CC (1982) Protein and energy utilization of rice milling fractions by rats. Qualitas Plantarum-Plant Foods for Human Nutrition 31: 371–376. Food and Nutrition Board Institute of Medicine (2002) Dietary References Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (Macronutrients). Washington, DC: National Academy Press.http://www.nap. edu/opcabook/html/. Hanashiro I, Matsugasako J, Egashira T, and Takeda Y (2005) Structural characterization of long unit-chains of amylopectin. Journal of Applied Glycoscience 52: 233–237. International Rice Research Institute, 2013. World Rice Statistics. irri.org/world-ricestatistics. Juliano BO (1985) Rice starch: Production, properties and uses. In: Whistler RL, BeMiller JN, and Paschall EF (eds.) Starch Chemistry and Technology, 2nd edn., p. 509. Orlando, FL: Academic Press. Juliano BO (2004) Rice/overview. In: Wrigley C, Corke H, and Walker CE (eds.). Encyclopedia of Grain Science, vol. 3, pp. 41–48. Oxford, UK: Academic Press/ Elsevier. Juliano BO (2007) Rice Chemistry and Quality. Munõz, Nueva Ecija: Philippine Rice Research Institute. Juliano BO, Tuanõ APP, Monteroso DN, et al. (2012) Replacement of acetate by ammonium buffer to determine apparent amylose content of milled rice. Cereal Foods World 57: 14–19. Tuanõ APP, Xu Z, Castillo MB, et al. (2011) Content of tocols, g-oryzanol and total phenolics and grain quality of brown rice and milled rice applied with pesticides and organic and inorganic nitrogen fertilizer. Philippine Agricultural Scientist 94: 211–216. United States Department of Agriculture, 2012. National Nutrient Database for Standard Reference, Release 25.http://www.ars.usda.gov/ba/bhnrc/ndl. Yoshihashi T, Huong NTT, Surojanametakul V, Tungtrakul P, and Varanyanond W (2005) Effect of storage conditions on 2-acetyl-1-pyrroline content in aromatic rice variety, KhaoDawk Mali 105. Journal of Food Science 70: S34–S37.

Wildrice, Zizania: Overview EA Oelke, University of Minnesota, St. Paul, MN, USA RA Porter, University of Minnesota-NCROC, Grand Rapids, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • • •

Wildrice (wild rice), Zizania, belongs to the grass family, is a cereal grain, and has four species, three naturally occurring in North America and one in Asia. The grain from wildrice growing in lakes and rivers in North America has been hand harvested, using a canoe, and processed by Native Americans for thousands of years as a carbohydrate food. Most cereal grains have been under cultivation and domestication for centuries, but for wildrice, this first began in the early 1950s in Minnesota. Improved cultivars have been developed for better yields than natural plants and adapted for harvesting with large combines. Wildrice cultivation is similar to rice, Oryza, in diked fields (paddies) to allow flooding and draining. Today, most of the cultivation is done in Minnesota and California, the United States. Yields per hectare of cultivated wildrice are about ten times that from hand harvested natural stands, but still well below that of rice. Processing of the cultivated grain follows similar steps used by Native Americans of parching (roasting and drying) and hulling, however using modern equipment in inspected processing facilities. Processed wildrice is a unique, specialty cereal grain with a distinct flavor and has a good amount of protein, similar to wheat, and twice the dietary fiber of brown rice. The processed grain (kernel) without hulls is very versatile and is often featured in soups, salads, breads, side dishes, entrees, and even desserts. In Minnesota, any packaged processed wildrice sold in the state must be labeled as to where and how it is grown.

Wildrice Species

Learning Objective

•

To learn about this native North American naturally growing aquatic grass plant, wildrice (Zizania), which is in the very early stage of cultivation/domestication as a cereal grain.

Introduction Wildrice (Zizania sp.) is in its infancy in cultivation and domestication compared to other cereals such as rice (Oryza sativa L.). Rice has been under this process for thousands of years. In the North American continent, the Native Americans did some expansion of natural stands by hand seeding new lakes and areas of lakes with sparse stands. But it was not until 1950 that a 0.5 ha paddy in Minnesota was specifically constructed to grow wildrice. Subsequently, more hectares were developed,

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and some breeding efforts were initiated in the early 1960s with a full-scale breeding program started in 1972 by the University of Minnesota. Today, wildrice is cultivated mainly in Minnesota and California in the United States and outside of the United States on a few hectares in Hungary. The Canadians have expanded lake production by seeding new lakes in several provinces. In Canada, the natural stands as well as newly seeded lakes are harvested by airboats with catchers attached to the front. There are three species of wildrice that grow naturally in the North American continent: Zizania aquatica L., Zizania palustris L., and Zizania texana A.S. Hitchc. Z. aquatica grows along the eastern seacoast and has thin kernels. Z. palustris grows around the Great Lakes region and has large seeds. It was gathered by Native Americans for thousands of years as a food source. Both of these species are annual aquatic grasses. Z. texana is a perennial with small seeds and grows only in a very small area in Texas. Z. latifolia Turcz. grows in Asia, and the fungal infected base of the stem is harvested as a vegetable, ‘Makomo-taki.’ Wildrice is a recently cultivated and partially domesticated cereal grain; thus, the purpose of this article is to acquaint the reader with this new crop. Wildrice is cultivated using similar practices as is used for lowland rice, in that it only grows in flooded soils. Harvesting the newly developed cultivars is done with combines similar to ones used for rice in the United States. Processing is different, however, giving wildrice its unique roasted flavor. The nutritional value of wildrice is considerably better than rice having nearly twice as much protein and an amino acid complex similar to oat groats (hulls removed). Wildrice is often mixed with rice and served as a blend. The pure product serves as a side dish similar to potatoes or rice. Continued improvement in yield/ha should make wildrice more available in stores and restaurants not only in the United States but also in other countries.

Wildrice was first classified by C. Linnaeus, in England in 1753. He used the description sent to him by J. F. Gronovius, Leiden, Holland. Gronovius described a plant sent to him by John Clayton that he collected in Virginia in 1739. C. Linnaeus gave the plant the binomial Zizania aquatica L. Zizania is a small genus of aquatic grasses in the tribe Zizanieae. Rice, Oryza sativa L., belongs to the tribe Oryzeae, which precedes the tribe Zizanieae. Both wildrice and rice belong to the grass family, Gramineae, and the subfamily, Poacoideae. The earlier hierarchical classification is presented in Gray’s Manual of Botany, eighth edition, by Fernald (1950). However, in more recent publications Grass Systematics by Gould and Shaw in 1983, second edition, and Flowering Plants of the World by Heywood (1993), both wildrice and rice are classed in the family, Poaceae, subfamily Bambusoideae, and tribe, Oryzeae. Subsequently, wildrice growing naturally in lakes and rivers


http://dx.doi.org/10.1016/B978-0-12-394437-5.00014-0

THE CEREAL GRAINS | Wildrice, Zizania: Overview

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Zizania palustris varieties palustris and interior Zizania aquatica variety aquatica

Zizania aquatica variety brevis

Zizania texana

Figure 1 The natural distribution in shallow lakes and rivers in North America of the three species of Zizania. Reproduced from Oelke EA, Porter RA, Grombacher AW, and Addis PB (1997) Wild rice – New interest in an old crop. Cereal Foods World 42: 234–247. American Association of Cereal Chemists, Minneapolis, MN, with permission.

was classed into three different species by Linnaeus and others. They are two annual species Z. aquatica L. and Z. palustris L. and one perennial species, Z. texana Hitchc. The distribution of the three species in North America is shown in Figure 1. There are two varieties of annual Z. aquatica that grow along the eastern Atlantic seacoast. Their seed is long and thin and generally not harvested for food. Z. aquatica can also be found in the Z. palustris area but to a limited extent. The two varieties of annual Z. palustris have relatively large grains and have been and are harvested as food by Native Americans. Today, the most extensive natural stands occur in the states of Minnesota and Wisconsin in the United States and in the provinces of Manitoba and Ontario, Canada. Z. texana is a perennial and only grows in a small stream in Texas; it has small grains and is not harvested. Z. latifolia Turcz. is also a perennial and can be found in Asia. There are accounts that the grain has been used by the elite as a special food. However, today in Asia, the base of the plant, which is infected with a fungus, is used as a vegetable, ‘Makomo-taki.’ A brief description of each species is given in Table 1.

Historical Use of Species Zizania palustris L.

The large seed from this species, ranging from 8 to 16 mm long and 1.2–2.5 mm in diameter, has been harvested from lakes and rivers in the Great Lakes region by the Chippewa (Ojibwa) and Menominee Native American tribes for

hundreds of years. After harvest, it was processed and stored and used as a carbohydrate source for the long, cold winters. Many battles were fought for control of the prized wildrice stands. In most cases, the Chippewa ended up controlling the wildrice stands. The Ojibwa name for wildrice is ‘Manoomin’ meaning good berry or good seed, but the exact meaning is not agreed upon. The early explorers, both English and French, who often traded with the Ojibwa, gave various names to this plant; some were Indian rice, wild rice, Canadian rice, squaw rice, water oats, march oats, and water rice. The French explorers called the plant folle avoine, fools oats, or wild oats. The name that was most commonly used was wild rice and is used in the trade today. To avoid confusion with the wild species of Oryza genus, writers often use the hyphenated, wild-rice, or the single word, wildrice. In this article, we are using the single word wildrice. Today, stands of wildrice on reservations in Minnesota and Wisconsin are controlled by Native Americans, but in lakes and rivers outside of the reservations, the stands are controlled by the Departments of Natural Resources of each state. In Minnesota and Wisconsin, a license is required by everyone to harvest from lakes and rivers that are not on Native American reservations. Today, natural stands in Minnesota are harvested, by law, in the traditional method using a flat bottom boat or canoe. The canoe is pushed through the stand by one individual using a long pole, while the other individual uses two flails (knockers) to knock the grain into the canoe. Since the grain ripens at different times on the same panicle and easily falls (shatters) from the plant when

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THE CEREAL GRAINS | Wildrice, Zizania: Overview Description of Zizania species

Species name

Description

Zizania aquatica var. aquatica L. southern wildrice

Annual, tall, large panicles, many branched florets. Grows in muddy shores of streams in southern Ontario and Quebec, southward to Florida and Louisiana. Average seed size: 14.3 mm long and 0.9 mm diameter Annual, short, small panicle with few branched florets. Grows in tidal areas of St. Lawrence River estuary. Average seed size: 6.7 mm long and 1.0 mm diameter Annual, height ranges from short to tall, slender few-flowered panicle. Grows in water up to 120 cm deep in southern Canada from New Brunswick to Manitoba and northern US states. Average seed size: 16.7 mm long and 1.4 mm diameter Annual, medium tall, medium to large panicle with numerous florets. Grows in water 30–60 cm deep along rivers in southeastern Manitoba and adjoining Ontario and in the North Central States. The germplasm of this species and variety has been used to develop cultivars for cultivation. Average seed size: 10.7 mm long and 1.8 mm diameter Perennial, decumbent with many long stems, panicles short, short seeds. Grows only in a localized area in San Marcos River in Texas. Average seed size: 6 mm long and 1.2 mm diameter Perennial, spreads by subterranean runners, tall, medium panicles, seeds short to medium in length. Native grass of Manchuria, Korea, Japan, Burma, and northeastern India. Base of plant often becomes infected with a fungus that is used as a ‘vegetable’ delicacy. This species is commercially grown in Japan, Korea, and China for its vegetable. Average seed size of collections from Japan: 7 mm long and 1.3 mm diameter

Zizania aquatica var. brevis, Fassett, estuarine wildrice Zizania palustris var. palustris L. northern wildrice Zizania palustris var. interior (Fassett), Dore, interior wild rice

Zizania texana A.S. Hitchc., Texas wildrice Zizania latifolia Turcz. Manchurian water rice

Figure 2 The traditional way (canoe and flail) of harvesting natural stands of wildrice. One individual (standing) propels the canoe through the stand, while the other uses two flails (knockers) to remove the grain from the stalks. Photographs by Oelke EA, left photograph appeared in Oelke EA (2007) Saga of the Grain – A Tribute to Minnesota Cultivated Wild Rice Growers. Lakeville, MN: Hobar Publications.

mature, stands are harvested by this method every other day for a period of 2 weeks. Enough grain falls back into the water before and during harvest to reseed the lake or river for the next year. Figure 2 depicts the traditional harvest method. In Canada, natural stands are generally harvested by airboats fitted with a grain catcher onto the front. The traditional method of processing the harvested wildrice was to lay it on the ground for drying since the grain has 40% moisture when harvested. Later, the Native Americans used an iron kettle over a fire to parch (roast and dry) the grain (Figures 3 and 4). The hulls (lemma and palea) were removed from the warm grain by placing it into a round-bottom container or leather-lined hole and then walking in place (jigging) in the container. The chaff was removed by tossing the grain into the air (winnowing) and allowing the wind to blow it away. The heavier grain was caught in the container. Today, very little of the grain harvested from natural stands is

processed in this manner. Most of it is processed with mechanical equipment as described later.

Zizania aquatica L. and Zizania texana Hitchc.

The seed from these species is either too thin or small to make it worthwhile to harvest as a food source. Z. texana is on the endangered species list.

Zizania latifolia Turcz.

This species is a perennial and is a native grass of Manchuria, Korea, Japan, Burma, and northeastern India. The plant generally is not used for grain production but grown commercially for its vegetable delicacy, especially in Japan, Korea, and China. The base of the plant becomes infected with a fungus. The infected base of the plant is harvested and eaten as a vegetable. In Japan, they call the vegetable ‘Makomo-taki.’ The infected part is also dried and allowed to develop spores. The spores are


Figure 3 The traditional method of drying wildrice grain in a kettle above a fire. The grain is stirred while drying. Photograph by Oelke EA, appeared in Oelke EA, Grava J, Noetzel D, et al. (1982) Wild Rice Production in Minnesota. St. Paul, MN: University of Minnesota. Agricultural Extension Service, Bulletin 464.

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Figure 4 The traditional way (jigging) to remove the outer hull of the wildrice grains. The individual walks in place to rub the grain against each other and also the kettle. Photograph by Oelke EA, appeared in Oelke EA, Grava J, Noetzel D, et al. (1982) Wild Rice Production in Minnesota, St. Paul: University of Minnesota. Agricultural Extension Service, Bulletin 464.

then used by artists to develop lacquered, antique-looking woodwork, such as plates and small boxes (Figure 5).

Cultivation of Zizania palustris L. Domestication Versus Cultivation The expansion of this species of wildrice represents one of the largest modern efforts to domesticate a cereal grain. Peperno describes cultivation as “a routine cycle of sowing and harvesting.” Native Americans did some form of cultivation but under natural conditions. They annually harvested natural stands relying on self-seeding of the lakes but sometimes added seeds to lakes with poor stands. Most crops are now truly domesticated, which means they depend mostly on human care for their perpetuation such as annual seeding. Wildrice is not far removed from the early cultivation phase of relying on self-seeding. Cultivars are being developed that shatter less than the plants growing in the lakes and rivers. They also produce more grain per hectare but still only 10–15% of that produced by rice.

History of Cultivation/Domestication Rice has been under the cultivation/domestication process for some thousands of years. Interest in cultivating this plant has been expressed for well over 100 years by businessmen and botanists. Early explorers collected seed for planting in Europe,

Figure 5 The base of the stem of Zizania latifolia, which is infected with a fungus, left. This base is harvested especially in Japan and used as a vegetable ‘Makomo-taki’ delicacy, slices in frying pan. Photograph by Oelke EA.

but they failed. In 1828, Timothy Flint in Geography and History wondered why no attention was paid to this plant. In 1852 and in 1853, Joseph Bowron and Oliver Kelly, respectively, also thought about why this plant is not cultivated. Charles Chambliss, USDA, ARS, in the early 1900s researched wildrice as a potential crop. In 1917, H. B. Williams and Z. Durand started mechanically harvesting private land in Canada. The first individuals to construct a field specifically to commercially produce this aquatic grain were James and Gerald Godward. They grew wildrice in 0.5 ha diked field (paddy) at Bass Lake near Merrifield, Minnesota. During the first 3 years, the Godwards had good crops, but disease destroyed the crop in the

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fourth year. They continued their pioneering efforts and by 1958 had a 50 ha diked field for growing wildrice. During the mid-1950s and early 1960s, others started growing wildrice. In 1965, Uncle Ben’s, Inc. started contracting for production, which was a big impetus to produce wildrice. Today, there are 5000 ha in Minnesota and in California. A few ha are now also being grown in Hungary, Europe.

Genetics and Breeding Domestication of a wild species requires that plants are selected from wild populations that maintain their grains on the plant even after maturity (nonshattering). The grain also needs to mature uniformly and has more grain production in relation to vegetative production. One of the important factors in the domestication process was the 1963 discovery, in a grower’s field, of a nonshattering plant by the grower and two University of Minnesota scientists (Figure 6). All wildrice species are mostly cross-pollinated with the male and female flowers separated on the same stem. Male flower retention and seed shattering are almost always associated, facilitating selection for nonshattering. Subsequently improved cultivars were developed from this germplasm by individuals, companies, and the University of Minnesota. Up until that time, fields

were planted with seed collected from lakes. These fields were harvested with picker/harvesters on tracks. The fields had to be harvested several times during a 2-week period, due to seed shattering, without cutting off the plants. Yields with this method were 68–90 kg ha1 of processed grain. Fields planted to the newer nonshattering cultivars could be harvested once with a regular grain combine and yielded over 700 kg ha1 (Figure 7). The development of the nonshattering cultivars resulted in a tremendous expansion of cultivated hectares in Minnesota and later in California. Figure 8 shows the cultivated wildrice production after processing for Minnesota and California since 1968. Individual wildrice growers began their own selection programs to select better plant types in the 1960s, and some are continuing today. The wildrice breeding program at the University of Minnesota began in 1972. It continues till today and is

Female flowers (grain) Male flowers Panicle

Stem

Leaves

Tillers

Internode section

Parchment-like cross-partitions Adventitious root Figure 6 The panicle on the left is a nonshattering type, while the one on the right is a shattering type. The nonshattering type can be recognized by loss of male flowers soon after pollen shed on the branched (lower) portion of the panicle. Photograph by Oelke EA, appeared in Oelke EA, Grava J, Noetzel D, et al. (1982) Wild Rice Production in Minnesota. St. Paul, MN: University of Minnesota. Agricultural Extension Service, Bulletin 464.

Figure 7 A drawing of a Zizania palustris plant. This type is a typical nonshattering plant cultivated in fields. Reproduced from Oelke, EA, Elliott WA, Kernkamp MF, and Noetzel DM (1973) Commercial Production of Wild Rice. St. Paul, MN: University of Minnesota. Agricultural Extension Service, Folder 284.


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14000

MN+CA

12000

CA

Annual production (x1000 kg)

MN 10000

Lakes

8000

6000

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2000

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10

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08

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06

20

04

20

02

20

00

20

98

20

96

19

94

19

92

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90

19

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82

19

80

19

78

19

76

19

74

19

72

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70

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19

19

68

0

Figure 8 The amount of processed wildrice in 1000 kg from 1968 to 2013 from lakes and rivers in Minnesota (30%) and Canada (bottom red line), Minnesota cultivated fields (yellow line), California cultivated fields (purple line), and the total from cultivated fields in Minnesota plus California (top blue line). Graph by Porter RA (2014) Data provided by the Minnesota Cultivated Wild Rice Council, California Wild Rice Board, various wildrice industry sources and Minnesota Department of Natural Resources.

the only public wildrice breeding program in the United States. To date, nine cultivars have been released all with some desirable characteristics needed to further the domestication of wildrice. Improved shattering resistance is the primary goal, but disease resistance is a close secondary goal. Another goal is shorter plants with higher yields. Yields have nearly doubled from the original ‘Johnson’ nonshattering (some resistance to shattering) cultivar developed from the nonshattering plants found in 1963. A private breeding program exists today in California, which has developed cultivars for their warmer and longer growing season. The genetic material for that program basically came from Minnesota. Thus far, all of the breeding is done by conventional selection and not genetic engineering. A program at Lakehead University, Thunder Bay, Canada, selected types of plants that did well in specific lakes, but that program has been reduced. Cultivated wildrice (Zizania palustris var. interior and palustris L.) of North America is an annual diploid with a chromosome number of 2n ¼ 2x ¼ 30; thus, it has 15 chromosome pairs. Compared with rice (Oryza sativa), wildrice has three more pairs of chromosomes and twice as much DNA content as rice. This research also indicated that when total wildrice DNA was used as a probe in southern hybridization to different Poaceae genera such as rice, oat, barley, wheat, and maize, there was a strong hybridization signal with rice but relatively little with oat, barley, wheat, or maize. The close relationship of wildrice to rice will benefit the mapping of genes in wildrice. Similar probes used for mapping genes in rice have been used in wildrice and some of the same genetic markers have been found to be located in the same area in wildrice as in rice. Locating markers for important genes such as seed shattering has facilitated the wildrice breeding efforts for domestication.

Cultivation Practices Wildrice is well adapted to northern latitudes with its cooler climate. In southern latitudes of the United States, such as Arkansas, shorter day lengths and higher temperatures speed

up development resulting in a short, unproductive plant. The high humidity also results in severe leaf disease problems. Cultivars have been developed that grow well in the warm day but cooler night temperatures of Northern California. The cultivation practices for wildrice are similar to rice. Fields need to be kept flooded until several weeks before harvest. Wildrice will grow well on organic or inorganic soils if nutrients are supplied. Wildrice requires less nitrogen than rice since it can get too tall and lodge (fall down) if overfertilized. It will grow in deeper and cooler water than rice; thus, water depth can be used as a means of weed control in wildrice. Handling wildrice seed is critical in establishing fields. Wildrice seed must be stored wet and in cold (3 C) water for 3 months to release seed dormancy. In Minnesota, new fields are seeded in the fall and the fields flooded either in the fall or in the spring to a depth of 30 cm. In Minnesota, fields can be kept in production for 2–3 years and then rotated with other crops. After the first year, the fields seed themselves from shattered seed even when initially seeded to the newer more shatter, resistant cultivars. In the Sacramento Valley of California, the fields are seeded in the spring of each year due to loss of viability of the shattered seed in the dry soil between seasons. Seed has to be stored in cool wet conditions over the winter and then seeded the next spring. In the northern higher elevations in the valleys between Mount Lassen and Mount Shasta, the production practices are similar to Minnesota (Figures 9 and 10). Fungal brown spot (Bipolaris sp.) is a severe disease in Minnesota, but not a problem in California. The wildrice worm (Apamea apamiformis Guenee), which is the larval stage of noctuid moth, is the most serious insect pest in the Upper Midwest but not a problem in California. In Minnesota and California, fields are drained 3 weeks before harvest. Grain combines are adapted, with larger reels and often full tracks, for harvesting wildrice. The grain has to be harvested at 20–35% moisture since seed shattering will occur if harvested at lower moisture content. The grain is immediately transported to processing plants (Figure 11).

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Processing

Nutritional Properties

Processing consists of curing, parching (roasting and drying), hulling, cleaning, scarification, and grading. When the grain arrives at the processing plant, it is put into piles or containers and kept for 1 or 2 days to allow for more uniform color. Then, the grain is put into rotating, heated drums (parchers) that will hold 225–370 kg and heated for 1 h (Figure 12). The grain is dried to 7% moisture and to 135 C. After parching, the hot grain is passed through a huller consisting of two rubber rollers going at different speeds. The light chaff and other foreign material are evacuated from the kernels, and the hulled kernels are graded with graders and gravity tables for size (Figure 13). Sometimes before grading, the kernels are scarified by passing through a tube with rubber paddles. This removes some of the darker, impermeable outer layer of the kernel to allow a faster cooking time (Figure 14). The parched, graded kernels can then be stored for future packaging (Figure 13).

The wildrice kernel with the hulls removed is similar to other cereals and consists of a pericarp, aleurone layer, endosperm, and embryo. The pericarp and embryo each represent 5% of the kernel weight. The rest, 90%, is largely endosperm and a smaller amount of the aleurone layer. The nutritional quality is very good for a cereal grain. It is equal to or better than other cereals such as wheat, barley, or rice. The protein content is about that of hard red spring wheat 13–15%, while brown rice has 8%. The sum of lysine, threonine, and methionine content is similar to hulled oats, which is considered one of the better cereals for humans. The mineral content of the wildrice kernel varies but can be similar to oats. Processed wildrice contains no vitamin A but is an excellent source of B vitamins. Wildrice is nutritious, since it is not refined but consumed as a whole grain (Tables 2–4). Wildrice has good antioxidant properties. There is considerable interest in antioxidants, which can slow diseases such as coronary heart disease and certain types of cancer. Hydrated wildrice mixed with ground beef has significant antioxidant activity.

Markets and Uses

Figure 9 Aerial view of northern Minnesota wildrice fields after flooding in the spring. The main source of water is the river in the foreground. Photograph by Oelke EA.

The cultivation and domestication of wildrice provided a large, consistent supply of wildrice compared to the inconsistency of that from natural stands. Today, 95% of the wildrice in the marketplace comes from cultivated fields. The wildrice market expanded rapidly during the 1960s through the 1980s primarily in the blend market. Sales increased an average of 15% per year when Uncle Ben’s, Inc., introduced the first packaged blend of wildrice, long grain rice, and herbs. Many other blends are now available including soups, vegetable-based side dishes, and convenience foods such as dehydrated mixes and frozen entrees. Increased use of wildrice as a pure product as well as in blends should continue. There are many recipes available for preparation and use of wildrice. Numerous

Figure 10 In Minnesota, wildrice fields in production for two or more years, plant populations are reduced by airboats. V-shaped blades mounted on the rear are dropped into the water to the soil line to remove excess plants, which leaves rows of plants for production. Excessive amounts of seeds, even from the more shatter resistant cultivars, fall onto the soil before and during harvest often producing too many plants the following year. Photographs by Oelke EA.


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wildrice cookbooks are available. In Minnesota, by law, the pure product has to be labeled ‘cultivated’ if it is produced in cultivated fields and sold in Minnesota. Wildrice is a nutritious food, and even though it is considered a gourmet food, it is not very expensive on a per serving basis. Production of wildrice should increase as new, better yielding cultivars and production practices are developed.


• • Figure 11 Cultivated wildrice, nonshattering cultivars, being harvested in Minnesota with a combine with full tracks needed for the soft wet peat or mineral soils. Photograph by Hansen DL (2012) Agricultural Experiment Station, University of Minnesota, St. Paul.

• • • • • • •

Why is the name wildrice used in scientific literature instead of wild rice? What morphological features of wildrice make it different from rice? Why is only one species of wildrice used for harvesting the grain and which one is it? In North America, why did Native Americans revere wildrice? Describe the cultivation and domestication of plants. Is there a difference between the two? Do production practices differ from other cereal grains and in what way? How do the yields on a hectare basis of wildrice compare to rice and why? How would you compare the wildrice nutritional value for humans to other cereal grains? Is wildrice available in large enough quantity to remove it from the specialty cereal grain category?


• Figure 12 Rotating drums heated on the bottom to dry (parch) the wildrice grain. The drums are covered after the grain is put in to allow some steaming of the grain. Temperature of the grain can be checked with a laser thermometer. Modern processing is based on the principle of traditional methods. In California, some of the wildrice grain is parboiled. Photograph by Oelke EA.

Wildrice seeds need to be held in wet, cool conditions to release dormancy; thus, better seed handling and storage techniques are needed to facilitate growing and plant breeding. See Further Reading references: Cardwell VB, Oelke EA, Elliott WA (1978) Seed dormancy mechanisms in wild rice (Zizania aquatica). Agronomy Journal 70: 481; Oelke EA (2007) Saga of the Grain – A Tribute to Minnesota Cultivated Wild Rice Growers. Lakeville, MN: Hobar Publications.

Figure 13 Processing is done with modern grain handling equipment in clean processing plants. Storage is done in clean warehouses before sale or packaging. Photographs by Oelke EA.

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Figure 14 Processed kernels from cultivated fields that were slightly scarified for faster cooking (left). Kernels without and with hulls on the right. Hulls are removed during processing. Hand-processed kernels, from lakes and rivers, most often are lighter in color than the ones in the left photograph. Photographs Oelke EA. Table 2

Composition of wildrice, medium grain brown rice, hard red spring wheat, and oats in 100 g

Nutrient

Unit

Wildrice

Brown rice, medium grain

Wheat, hard red spring

Oats

Water Protein Total lipid (fat) Fiber, total dietary Carbohydrates Sugars Calcium Iron Magnesium Phosphorus Potassium Sodium Zinc Copper Manganese

g g g g (by difference) g mg mg mg mg mg mg mg mg mg

7.76 14.73 1.08 6.2 74.9 2.5 21 1.96 177 433 427 7 5.96 0.524 1.329

12.37 7.5 2.68 3.4 76.17 – 33 1.8 143 264 268 4 2.02 0.277 3.74

12.76 15.4 1.92 12.2 8.03 0.41 25 3.6 124 332 340 2 2.78 0.41 4.055

12.82 16.89 6.9 10.6 66.27 – 54 4.72 177 523 429 2 3.97 0.626 4.916

Data from US Department of Agriculture, Agricultural Research Service (2013) USDA National Nutrient Database for Standard Reference, Release 26.

•

To facilitate the selection of better cultivars, better and new genetic markers are needed. See Further Reading references: Hass BL, Pires JC, Porter R, Phillips RL (2003) Comparative genetics at the gene and chromosome levels between Oryza sativa and wildrice Zizania palustris. Theoretical and Applied Genetics 107: 773–782; Kennard WC, Phillips RL, Porter RL (2002). Genetic dissection of shattering, agronomic, and color traits in American wildrice (Zizania palustris var. interior L.) with a comparative map. Theoretical and Applied Genetics 105: 1075–1086; Kennard WC, Phillips RL, Porter RA, Grombacher AW (2000) A comparative map of wild rice (Zizania palustris L. 2n ¼ 2X ¼ 30). Theoretical and Applied Genetics 101: 677–684.

•

•

Processing of wildrice is still a batch system that slows processing; thus, there is a need to develop storage techniques for the high moisture grain before processing. See Further Reading references: Marcum DB (2007) Wild Rice Production in California. Davis, CA: University of California. Extension Publication, No.21622; Oelke EA, Boedicker JJ (2000) Wild rice: Processing and utilization. In: Kulp K, Ponte JG (eds.) Handbook of Cereal Science and Technology, pp. 275–306. New York: Marcel Dekker; Oelke EA (2007) Saga of the Grain – A Tribute to Minnesota Cultivated Wild Rice Growers. Lakeville, MN: Hobar Publications. Additional research needs to be conducted to verify the low presence or absence of gluten in processed wildrice.

THE CEREAL GRAINS | Wildrice, Zizania: Overview Table 3 Amino acids in wildrice, oats, medium grain brown rice, and hard red spring wheat in 100 g Amino acid

Unit

Wildrice

Oats

Brown rice

Wheat

Tryptophan Threonine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Tyrosine Valine Arginine Histidine Alanine Aspartic acid Glutamic acid Glycine Proline Serine

g g g g g g g g g g g g g g g g g g

0.179 0.469 0.618 1.018 0.629 0.438 0.174 0.721 0.622 0.858 1.136 0.384 0.825 1.419 2.565 0.672 0.519 0.778

0.234 0.575 0.694 1.284 0.701 0.312 0.408 0.895 0.573 0.937 1.192 0.405 0.881 1.448 3.712 0.841 0.934 0.750

0.096 0.275 0.318 0.620 0.286 0.169 0.091 0.387 0.281 0.440 0.569 0.190 0.437 0.702 1.528 0.369 0.352 0.388

0.195 0.433 0.541 1.038 0.404 0.230 0.404 0.724 0.441 0.679 0.702 0.330 0.555 0.808 4.946 0.621 1.680 0.663

Data from US Department of Agriculture, Agricultural Research Service (2013) National Nutrient Database for Standard Reference, Release 26.

Table 4 The amounts of nutrients based on 1/2 cup serving of cooked product Nutrients (based on 1/2 cup serving (cooked)) Calories Protein (g) Fat (g) Dietary fiber (g) Total carbohydrates (g) Minerals Phosphorus (mg) Iron (mg) Potassium (mg) Zinc (mg) Vitamins Riboflavin (mg) Niacin (mg) Vitamin E (mg)

Wildrice

Enriched white rice (long grain)

Brown rice (long grain)

83 3.27 0.28 1.5 17.5

103 2.13 0.22 0.3 22.25

108 2.52 0.88 1.8 22.39

67 0.49 83 1.1

34 0.95 28 0.39

81 0.41 42 0.61

0.07 1.05 0.2

0.01 1.16 0.03

0.02 1.49 0.03

Reproduced with permission from the Minnesota Cultivated Wild Rice Council, St. Paul. Data from the U. S. Department of Agriculture, Agricultural Research Service (2013) USDA National Database for Standard References, Release 26.

See also: Breeding of Grains: Rice: Breeding; Genetics of Grains: Rice: Genetics; Non-wheat Foods: Rice: Chinese Food Uses; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Oats: Overview.

Further Reading Aiken SG, Lee PF, Punter D, and Stewart JM (1988) Wild Rice in Canada. Winnipeg: Agriculture Canada.

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Archibold OW (1994) Wild Rice in Saskatchewan – Agricultural Development in Harmony with Nature. Saskatoon: Saskatchewan Agriculture and Food. Cardwell VB, Oelke EA, and Elliott WA (1978) Seed dormancy mechanisms in wild rice (Zizania aquatica). Agronomy Journal 70: 481. Chang TT (1989) Domestication and spread of the cultivated rices. In: Hillman GC and Harris DR (eds.) Foraging and Farming: The Evolution of Plant Exploitation, pp. 408–417. UK: Routledge. Fassett NC (1924) A study of the genus Zizania. Rhodora 26: 153. Hass BL, Pires JC, Porter R, and Phillips RL (2003) Comparative genetics at the gene and chromosome levels between Oryza sativa and wildrice Zizania palustris. Theoretical and Applied Genetics 107: 773–782. Jenks AE (1900) The wild rice gatherers of the Upper Lakes: A study in American primitive economics. In: 19th Annual Report of the Bureau of American Ethnology, 1897–98, Part 2, pp. 1013–1137. Washington, DC: US Department of Interior. Kennard WC, Phillips RL, Porter RA, and Grombacher AW (2000) A comparative map of wild rice (Zizania palustris L. 2n ¼ 2X ¼ 30). Theoretical and Applied Genetics 101: 677–684. Kennard WC, Phillips RL, and Porter RL (2002) Genetic dissection of shattering, agronomic, and color traits in American wildrice (Zizania palustris var. interior L.) with a comparative map. Theoretical and Applied Genetics 105: 1075–1086. Kosbau H (2005) The Taming of Wild Rice. Grand Rapids, MN: Treasure Bay Printing. Marcum DB (2007) Wild Rice Production in California. Extension Publication, Davis, CA: University of California, No.21622. Nelson RN and Dahl RP (1985) Wild Rice Market Shows Vigorous Growth. St. Paul, MN: University of Minnesota, Minnesota Agriculture Economics, No.649. Oelke EA (2007) Saga of the Grain – A Tribute to Minnesota Cultivated Wild Rice Growers. Lakeville, MN: Hobar Publications. Oelke EA and Boedicker JJ (2000) Wild rice: Processing and utilization. In: Kulp K and Ponte JG (eds.) Handbook of Cereal Science and Technology, pp. 275–306. New York: Marcel Dekker. Oelke EA, Elliott WA, Kernkamp MF, and Noetzel DM (1973) Commercial Production of Wild Rice. St. Paul, MN: University of Minnesota, Agricultural Extension, Service Extension Folder 284. Oelke EA, Grava J, Noetzel D, et al. (1982) Wild Rice Production in Minnesota. Agricultural Extension Service, St. Paul, MN: University of Minnesota, Extension Bulletin 464. Oelke EA, Porter RA, Grombacher AW, and Addis PB (1997) Wild rice – New interest in an old crop. Cereal Foods World 42: 234–247, American Association of Cereal Chemists, Minneapolis, MN. Piperno DR (2012) Archaeobotanical information on early cultivation and plant domestication involving microplant (phytolyth and starch grain) rements. In: Gepts P, Famula TR, Bettinger RI, Brush SB, Damania AB, McGuire PE, and Qualset CO (eds.) Biodiversity in Agriculture: Domestication, Evolution, and Sustainability, p. 203. Cambridge: Cambridge University Press. Steeves TA (1952) Wild rice Indian food and a modern delicacy. Economic Botany 26: 107–142. Vennum T (1988) Wild Rice and the Ojibway People. St. Paul, MN: Minnesota Historical Society. Wu K, Zhang W, Addis PB, Epley RJ, Salih A, and Lehrfeld J (1994) Antioxidant properties of wild rice. Journal of Agricultural and Food Chemistry 42: 34.

Relevant Websites http://www.ars.usda.gov/ba/bhnrc/ndl – This website is an excellent source for nutrient content of many grains and foods including wildrice. http://www.cawildrice.com/ – This is the website of the California Wild Research and Advisory Board of the California cultivated wild rice growers. Information on California wildrice cultivation, food preparation and recipes can be found on this website. http://www.mnwildrice.org – This is the website of the Minnesota Cultivated Wild Rice Council whose members consist of Minnesota cultivated wildrice growers. Information on wildrice history, Minnesota cultivation, research, processing, nutrition, gluten content, cooking, and recipes can be found on this website. http://www.wildrice.org – This website is the one for the International Wild Rice Association (IWRA). IWRA consists of wildrice growers, processors and marketers. Members include individuals from the US and Canada. Information on wildrice history and links to other wildrice websites can be found on this website.

African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts JT Manful and S Graham-Acquaah, Africa Rice Center, Cotonou, Republic of Benin ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

•

The two cultivated species of rice are Oryza sativa (Asian rice) and Oryza glaberrima (African rice). O. glaberrima have tolerance to several biotic and abiotic stresses and are particularly suited for low-input subsistence farming as practiced in many African communities. African rice has yield potential comparable to O. sativa as evidenced by yield-related morphoagronomic traits. Their tendency to easily shatter is a responsible factor for the lower yields observed. NERICA (New Rice for Africa) – a product of interspecific breeding between O. glaberrima and O. sativa developed by the Africa Rice Center – combines the stress tolerance of African rice with the high yield potential of Asian rice. The recent release of O. glaberrima genome and the development of African rice-specific single-nucleotide polymorphisms will enhance the identification and exploitation of adaptive traits in African rice in rice improvement programs. Very little work has been done on the physicochemical properties of O. glaberrima. Ongoing studies by the Africa Rice Center show that a high level of genetic diversity exists in the accessions of O. glaberrima from the West Africa subregion as evidenced by variations in both apparent amylose content and pasting properties.

Learning Objectives At the end of this article, it is expected that readers would

• • • •

have knowledge of the origin, domestication history, and diversity in African rice; understand the traits that set O. glaberrima apart from O. sativa; know how O. glaberrima is used in classical breeding; have an appreciation of ongoing research work on the physicochemical properties of African rice.

Introduction Rice is a major staple in the world and belongs to the genus Oryza. Out of over 20 species in the genus Oryza, only two species are cultivated: Oryza glaberrima (African rice) and Oryza sativa (Asian rice). O. glaberrima is native to sub-Saharan Africa (SSA) thought to have been domesticated from the wild ancestor Oryza barthii (formerly known as Oryza breviligulata). O. glaberrima is presently being replaced everywhere in Africa by O. sativa and is rapidly diminishing in importance. Recent advances now allow for gene transfer between the two

140

species, thus creating crosses that are better adapted, and higher yielding under adverse conditions, than either parent. This article discusses the history of glaberrima, its genetic and morphoagronomic diversity, its use in conventional breeding, and some of its physicochemical characteristics.

Origin and History of O. glaberrima O. glaberrima is unique to Africa. It is believed to have been domesticated from the wild ancestor O. barthii over 3000 years ago. The many indigenous words for rice in several West African language groups predate the Portuguese-derived words associated with Asian rice and offer linguistic evidence to the fact that rice was cultivated prior to the arrival of Europeans in Africa. Two distinct theories have been advanced as to the exact origin and domestication of the African species. The first theory propounded by Porteres suggests that O. glaberrima was first domesticated in the Inland Delta of the Niger River in presentday Mali and then subsequently spread to other centers of diversification, some being the coast of Gambia, the Casamance region of Senegal, and Guinea Bissau along the Niger River and then in the Guinea forest between Sierra Leone and the western Ivory Coast. Others claim that ancient hunting and gathering human populations living in different localities within the vast forest and savanna areas where O. barthii grew may have selected for O. glaberrima. Recent studies into the population structure and genomics of O. glaberrima accessions tend to support a single domestication origin of African rice in areas of the upper Niger and Senegal Rivers. African rice, as has been asserted, was introduced into the new world via the trans-Atlantic slave trade. Botanical evidence and historical records suggest that African rice was grown in El Salvador, French Guiana, Brazil, Jamaica, South Carolina, and Suriname and is to this day grown, eaten, and exported by the Maroons. Although it has diminished in terms of cultivated area as a result of the introduction of O. sativa, O. glaberrima remains an important crop for certain communities in West Africa who still grow them for use in rituals and as food due to its unique taste and texture. Their hardiness in the field also makes them ideal for subsistence farming.

What Makes O. glaberrima Different? Differentiating between the two cultivated species of rice in the field can be cumbersome for the untrained as they differ marginally in their morphology. In general, O. glaberrima has short round ligules, while the panicles are erect and simply branched with small spikelets. The grains are small and pear-shaped with a reddish-brown to purple bran color and olive to black seed coats. As a result of this bran color, O. glaberrima are often


http://dx.doi.org/10.1016/B978-0-12-394437-5.00016-4

THE CEREAL GRAINS | African Rice (Oryza glaberrima): History and Its Growing Importance in Rice Breeding Efforts

Plate 1

141

Panicles of O. sativa (a) and (b) and O. glaberrima (c) and (d).

referred to as red rice. Compared with Asian varieties, African rice usually gives lower grain yields, readily shatters, and is difficult to mill because of the brittle nature of the grains (Plate 1). These notwithstanding, O. glaberrima possess distinct characteristics, perhaps due to the fact that they have survived with little interference from humans, which make them ideal for the low-input subsistence farming still practiced in many African communities. The plants have wider leaves that shade out weeds and are more tolerant than O. sativa to biotic and abiotic stresses such as diseases, pests, fluctuations in water depth, iron toxicity, infertile soils, severe climatic conditions, and neglect.

Diversity in African Rice O. glaberrima is largely being replaced by O. sativa because of the higher yields obtained from the latter. In spite of this, it is still being grown in many areas because of their preference for the preparation of certain traditional foods and also for their tolerance to biotic and abiotic stresses. This stress tolerance prompted efforts at its conservation and use as a gene pool for improving Asian rice varieties. The Africa Rice Center (www.africarice.org) is leading efforts at conservation and exploitation of O. glaberrima in breeding. The gene bank of the center contains about 3000 accessions of O. glaberrima that are being systematically screened. O. glaberrima has long been perceived to possess less genetic diversity in comparison with O. sativa. In fact, African rice is reported to have only one-sixth of the nucleotide diversity found in Asian rice. Indica rice (O. sativa ssp. indica) alone has higher diversity (ysil ¼ 0.0028–0.0029) than either African rice (ysil ¼ 0.0007) or its wild ancestor O. barthii (ysil ¼ 0.0024) (Watterson’s estimator of y per base pair calculated based on

silent sites). African rice is reported to have more than 70% less diversity compared to its wild progenitor resulting from a severe genetic bottleneck during its domestication from the initial population of O. barthii. An earlier characterization of 198 accessions using SSR (simple sequence repeat) markers showed a range of 2–27 alleles per locus with an average of 9.4 alleles per locus. Based on this characterization, O. glaberrima were grouped into five genetic groups with two of these segregating with O. sativa indicating intermediaries and thus gene flow between the two species. A morphoagronomic and molecular characterization of African rice varieties collected from the inland delta of the Niger River (Mopti and Tombouctou), Sikasso, and Gao Region in Mali believed to be centers of domestication for O. glaberrima revealed a higher average heterozygosity (0.18) in O. glaberrima than previously reported. The population collected from Mopti and Gao Region had higher diversity than other populations. Although there was no clear clustering of individuals based on location or growing condition because of the probable higher gene flow that occurs between different growing conditions within a location, a higher differentiation was observed between populations from different locations than from different ecologies, while within locations, similarities were observed between populations from similar growing conditions. The accessions RAM116, RAM100, and RAM122 outperformed the best check varieties under drought conditions. Recently, single-nucleotide polymorphisms (SNPs) specific to African rice have been developed and used to genotype some 279 O. glaberrima accessions, selected based on their impact in current breeding programs and their geographic distribution, and 101 O. barthii accessions, selected based on their geographic origins. A structuring of accessions into three populations of O. barthii associated with geography and two

142


populations of O. glaberrima that are yet to be linked with any phenotyped traits was reported. Also, an apparent misclassification in both O. glaberrima and O. barthii was identified in addition to a new form of O. sativa within the African rice varieties. The complete genomic sequence of O. glaberrima has been deciphered through immense global research effort. The release of O. glaberrima genome and the development of African rice-specific SNPs bring in their wake hitherto nonexisting opportunity for the identification and exploitation of adaptive traits in African rice in rice improvement programs. Little variation has been reported in the morphoagronomic traits of O. glaberrima compared with O. sativa. With respect to their vegetative growth, more than 90% of O. glaberrima screened by the Africa Rice Center exhibited high seedling vigor. A very rapid vegetative growth culminating in large number of tillers and droopy lower leaves was observed. These vegetative growth characteristics (vigorous initial growth) typified by their high tillering ability, large leaf area, and droopy leaves provided rapid ground cover, thus suppressing weeds and making them weed-competitive (Plate 2). O. glaberrima also vary greatly in their growth durations with as much as 89 days between some varieties. Whereas traditional O. sativa and improved varieties have maturity days ranging between 120–140 days and 80–120 days, respectively, some O. glaberrima can mature within 75 days. Such

early-maturing varieties ensure that they escape drought in drier areas and late-season fungal disease in wet ecologies. Rice plant height and stem strength are related to lodging. Generally taller varieties with weaker stems are more prone to lodging especially in high soil fertility conditions. Most O. glaberrima varieties are deemed intermediate in stature (80–100 cm) but possess fragile culms that render them susceptible to lodging during their vegetative stage. A number of O. glaberrima have, however, been observed to have thick leaf sheaths making them resistant to lodging. Such varieties may be useful in breeding. The greatest limitation to the cultivation of O. glaberrima is their lower yields. Yield-related characteristics have been studied, and results point to the fact that O. glaberrima have the same yield potential as O. sativa. Yield-related morphoagronomic traits such as average panicle number in O. glaberrima are comparable to O. sativa. Shattering could also be a contributory factor to the inferior yields as spikelet number in O. glaberrima prior to shattering is no less than in O. sativa. O. glaberrima possess higher dry matter production and greater leaf area than O. sativa at least until heading. They have lower photosynthetic rate per leaf area but a higher rate against the same leaf nitrogen content in a low content range. Their response to dry matter, leaf area, and leaf photosynthesis to increases in nitrogen inputs is higher than in O. sativa.

AG: Vigor of selected O. glaberrima and O. sativa after 14 days of seeding – dry season

AG: Vigor of selected O. glaberrima and O. sativa after 21 days of seeding – wet season Plate 2

Seedling vigor in O. sativa and O. glaberrima. Photo courtesy of Venuprasad Ramaiah; Africa Rice Center.

THE CEREAL GRAINS | African Rice (Oryza glaberrima): History and Its Growing Importance in Rice Breeding Efforts Additionally, water use efficiency on dry matter accumulation and gas exchange bases is lower compared with that of O. sativa, while both leaf senescence during maturity and grain filling are faster in O. glaberrima than O. sativa. The greatest attribute of O. glaberrima is their resilience. Accessions of O. glaberrima have been found to be highly resistant to pests and diseases such as African rice gall midge, the rice yellow mottle virus, and blast. O. glaberrima can limit water loss through stomata closure and leaf curling. This trait in addition to the well-developed root system makes them well adapted to drought conditions. The ability for strong leaf elongation underwater that leads to enhanced expansion of leaf area and photosynthesis, requirements for escaping complete submergence underwater over a prolonged period (up to 37 days), has also been observed in O. glaberrima, making them a promising reservoir of genes for selecting and breeding rice genotypes for different flood-prone environments in Africa. Tolerance to iron toxicity and saline environments has also been documented in O. glaberrima. Although some O. sativa varieties are better at tolerating some specific stresses, a unique trait in O. glaberrima is that some can possess multiple tolerances to various stresses. CG 14 is one such O. glaberrima variety that has weed competiveness and iron toxicity and drought tolerance. These make them ideally suited for cultivation in SSA where rice farming is predominantly carried out by resource-poor farmers.

O. glaberrima in Classical Plant Breeding At the Africa Rice Center (AfricaRice), attempts have been made to develop new interspecific rice varieties from crosses between O. sativa and O. glaberrima. Initially, this proved difficult as the progenies were sterile. This problem was, however, successfully overcome, and the first large-scale hybridization of the two cultivated species of rice occurred. The resulting varieties were collectively named NERICA (New Rice for Africa). These varieties, developed for both upland and lowland ecologies, combine the high yield of O. sativa with the stress tolerance and adaptability to local growing conditions of O. glaberrima. The NERICA development process began with an initial screening of 1721 accessions comprising 1130 O. glaberrima and 591 O. sativa based on their morphoagronomic performance. O. glaberrima (CG 14) and three O. sativa ssp. japonica (WAB56-104, WAB5650, and WAB181-18) are the parental lines for the first set of NERICAs (NERICA 1–18). These varieties were crossed to obtain interspecific lines that were backcrossed and the progenies subjected to pedigree selection to obtain the first NERICAs (NERICA 1–18) for upland ecology. Further research and improved methodology led to the release of 60 varieties (NERICA L1–L60) for lowlands. The NERICA-S lines have also been bred for the Sahelian zones of West Africa. These NERICA varieties developed and disseminated have affected farmers’ livelihoods and contributed to poverty reduction in SSA.

Physicochemical Properties of O. glaberrima The physicochemical properties of rice such as milling recoveries, physical appearance (grain dimensions and chalkiness), aroma, cooking and pasting properties are important as they

143

determine the market value and reputation of rice varieties. Hitherto, studies on the physicochemical properties of O. glaberrima have not received as much attention as work on their agronomic traits. The few studies conducted suggest that generally, O. glaberrima tend to break easily during milling; thus, head rice recovery is lower compared with O. sativa. The red pericarps of African rice make them less attractive when polished. O. glaberrima is preferred by certain groups of consumers, particularly in regions where they are still cultivated, because of their distinct taste and flavor. Some aroma compounds such as 4-ethylphenol (‘musty’) and (E, E)-2,4heptadienal (‘fruity’) have been found to be unique to O. glaberrima. On cooking, O. glaberrima have firmer texture, perhaps due to their higher apparent amylose content (AAC) and unique pasting properties (low peak, low breakdown, and higher setback viscosities) compared with O. sativa. Asian rice however has greater diversity in AAC than African rice. While waxy varieties exist among Asian rice, waxy varieties are yet to be encountered among O. glaberrima. With the broad objective of contributing to better understanding the physicochemical properties of O. glaberrima, AfricaRice and its partners characterized over 1000 O. glaberrima accessions from its gene bank based on data of their Rapid Visco Analyser (RVA) pasting characteristics and AAC. Based on the AAC and RVA pasting parameters of the rice flours, the accessions were hierarchically clustered into five groups – C I, C II, C III, C IV, and C V (Figure 1). The distribution pattern indicated that the maximum number of accessions (282) was included in C I, followed by C IV (242), C V (231), C III (161), and C II (104), with all five clusters showing a large diversity of AAC and pasting properties. Cluster I had 282 accessions and constituted 27.6% of the entire population. These accessions were further grouped into five subclusters – SC IA, SC IB, SC IC, SC ID, and SC IE – with a population of 44 (15.6%), 84 (29.8%), 107 (37.9), 26 (9.2%), and 21 (7.4%), respectively. All the subclusters under cluster I had similar ranges of AAC – all of them fell under high-amylose rice category. However, their pasting characteristics differed greatly as shown in Table 1. Wide variations were observed for peak and trough viscosities in all the five subclusters. With respect to breakdown viscosity, while SC IB, SC IC, SC ID, and SC IE were close, that of SC IA was relatively very distinct. SC IA, SC IC, and SC IE were likewise similar with respect to final and setback viscosities, but SC IB and SC ID showed diversity. Cluster II with 104 accessions composed the lowest proportion (10.2%) of the entire population. The broadest ranges of peak, trough, setback, and final viscosities were observed in this cluster. However, it had the second broadest AAC range and the narrowest pasting temperature range. The range of AAC for accessions in C II conferred them to intermediate and highamylose types of rice. Three subclusters SC IIA, SC IIB, and SC IIC were formed under cluster II with populations of 26 (25%), 54 (52%), and 24 (23%) accessions, respectively. SC IIA and SC IIB had similar ranges of AAC, with SC IIC having the broadest range (Table 1). SC IIC also had the broadest range of peak, final, setback, and trough viscosities, while SC IIB had the narrowest range as regards peak, final, and trough viscosities. With 161 accessions, cluster III constituted 15.8% of the entire population of the O. glaberrima analyzed (Table 1) and had five subclusters, namely, SC IIIA, SC IIIB, SC IIIC, SC IIID,

144


O. glaberrima accessions

∗C I (N = 282)

C II (N = 104)

#SC

SC IC IA SC IB (N = 44) (N = 84) (N = 107) SC ID SC IE (N = 26) (N = 21)

C VI (N = 242)

C III (N = 161)

CV (N = 231

SC IIIA SC IIIB SC IIIC (N = 37) (N = 39) (N = 43)

SC VA SC VB SC VC (N -59) (N -35) (N = 76)

SC IIID SC IIIE (N = 18) (N = 24)

SC VD SC VE (N = 21) (N = 40) SC IVA SC VIB (N = 80) (N = 94)

SC IIA SC IIB SC IIC (N = 26) (N = 54) (N = 24)

SC VIC (N = 42)

SC IVD SC IVE (N = 13) (N = 13) Figure 1 Graphical representation of distribution of 1020 African rice accessions into 5 clusters and 23 subclusters.

and SC IIIE, making up 23%, 24.2%, 26.7%, 11.2%, and 14.9% of the accessions, respectively. Cluster III had the narrowest ranges of peak, trough, setback, and final viscosities. The accessions in this cluster belonged to the category of intermediate- to high-amylose rice based on their AAC range. SC IIIA had the broadest apparent amylose range, SC IIID had the narrowest range, and that of SC IIIB and SC IIIE was similar. SC IIIA also had the broadest ranges with respect to peak, trough, breakdown, and final viscosities (Table 1). Despite having the narrowest final viscosity range, SC IIIC had the second broadest ranges of apparent amylose, peak viscosity, and breakdown viscosity (Figure 2). Accessions in cluster IV had the broadest range of apparent amylose, the second broadest peak viscosity range, and the fourth broadest ranges of both final and setback viscosities but the narrowest range of breakdown viscosity. Low-, intermediate-, and high-amylose rice types were all included in the accessions within this cluster. Cluster IV formed 23.7% of the entire population analyzed (242 accessions) and contained five subclusters, namely, SC IVA, SC IVB, SC IVC, SC IVD, and SC IVE, which constituted 33.1%, 38.8%, 17.4%, 5.4%, and 5.4% of the accessions, respectively (Table 1). Whereas SC IVA, SC IVB, and SC IVC shared some similarities in AAC and peak time, very diverse peak, trough, breakdown, final, and setback viscosities were observed in all the five subclusters except in SC IVE, which, though distinct with respect to breakdown viscosity, showed very close similarity to SC IVB with regard to peak, breakdown, final, and setback viscosities. The 231 accessions in cluster were intermediate to highamylose rice types and formed 22.6% of the total number of accessions analyzed. This cluster also contained five subclusters, namely, SC VA, SC VB, SC VC, SC VD, and SC VE, which constituted 25.5%, 15.2%, 32.9%, 9.1%, and 17.3% of accessions, respectively (Table 1). Very similar AAC ranges were observed in the subclusters except for SC VE. The accessions in cluster V also had the broadest range of final viscosity,

second broadest range of setback and breakdown viscosities, and the third broadest AAC range.

Conclusions The tremendous amount of work on O. glaberrima at AfricaRice notwithstanding the full potential of the species is yet to be exploited. There remains the need to consider intraspecific breeding within O. glaberrima and ways in which the multiple resistance traits of O. glaberrima could be transferred into new varieties. The studies of the physicochemical properties supported the idea that there is a high level of genetic diversity in the O. glaberrima accessions as evidenced by the variation in both AAC and pasting properties in and within the clusters and subclusters. This suggests that there may be a valuable resource of potentially very important gene pool that may be of benefit to interested rice breeding programs. Additionally, a detailed molecular analysis of a representative sample of these accessions from the clusters such as those with a high tendency to retrograde (high setback and potentially slower rate of digestion due to retrogradation) or form viscous paste/gel after cooking and cooling (high final viscosities) will ensure the use of the diversity in O. glaberrima in the future development of acceptable commercial cultivated rice varieties that have the desired amylose content and pasting characteristics to meet consumer preferences in Africa and elsewhere.


• •

Outline the theories of domestication of African rice. How do the two cultivated species of rice differ from each other?

Table 1

Distribution of 1020 O. glaberrima rice accessions obtained through cluster analysis using SPSS Range

I

II

III

IV

V

Cluster distribution (N)

AAC (%)

PV (RVU)

TV (RVU)

BDV (RVU)

FV (RVU)

SBV (RVU)

PT (s)

PTemp ( C)

C I (282) SC IA (44) SC IB (84) SC IC (107) SC ID (26) SC IE (21) C II (104) SC IIA (26) SC IIB (54) SC IIC (24) C III (161)

24.7–29.4 25.3–29.4 24.8–27.9 24.7–28.5 26.0–29.0 25.4–27.7 20.6–29.6 23.0–29.2 23.9–29.6 20.6–28.5 21.7–26.8

67.3–123.8 76.8–115.6 67.3–87.4 76.3–101.6 92.9–123.8 89.4–107.9 152.2–230.7 137.8–182.7 135.5–165.8 152.2–230.7 80.9–125.5

66.7–124.2 73.3–113.4 66.7–87.3 76.6–101.8 93.0–124.2 89.7–105.8 113.0–183.5 125.3–160.9 115.9–143.0 113.0–183.5 80.4–122.2

149.6–296.8 160.1–225.4 149.6–188.3 170.4–234.9 217.7–296.8 176.3–217.1 246.5–421.5 308.1–394.8 246.5–327.3 247.0–421.5 159.9–258.8

71.7–173.0 71.7–124.5 75.0–104.3 75.8–139.5 118.0–173.0 86.8–116.8 94.9–224.8 54.8–224.8 95.3–170.7 94.9–190.8 68.3–149.8

5.9–7.0 5.9–6.5 6.1–7.0 6.3–7.0 6.3–7.0 6.4–7.0 5.7–5.9 5.7–6.2 5.7–5.9 5.7–5.9 5.9–7.0

89.6–94.5 90.7–93.6 91.9–94.0 91.9–94.5 91.5–93.6 89.6–92.8 86.4–91.9 88.3–91.9 87.2–91.0 86.4–89.2 89.6–94.0

SC IIIA (37)

21.7–26.8

89.2–125.5

88.2–122.3

228.3–258.8

120.8–149.8

5.9–7.0

90.7–93.6

SC IIIB (39) SC IIIC (43)

23.2–26.6 22.6–26.5

89.8–110.8 80.9–110.0

89.8–103.1 80.4–104.1

212.1–232.8 194.3–211.5

107.8–132.2 92.1–119.1

5.9–7.0 5.9–7.0

90.7–93.6 89.9–94.0

SC IIID (18) SC IIIE (24) C IV (242) SC IVA (80) SC IVB (94) SC IVC (42) SC IVD (13) SC IVE (13) C V (231) SC VA (59) SC VB (35) SC VC (76) SC VD (21) SC VE (40)

24.6–26.4 23.4–26.4 15.1–28.6 22.4–27.8 15.1–28.6 23.0–27.6 21.3–27.4 21.7–25.6 21.0–28.8 25.3–28.8 25.7–28.8 25.5–28.5 25.6–28.1 21.0–27.5

108.2–121.3 82.9–107.9 36.4–93.1 53.6–73.4 63.6–83.9 36.4–63.3 74.5–93.1 50.8–83.3 96.3–152.3 117.3–152.3 114.3–151.1 100.8–131.6 96.3–117.2 108.3–141.5

100.7–115.5 81.0–105.0 36.5–93.0 54.0–73.8 63.7–84.0 36.5–63.4 74.3–93.0 50.4–82.9 87.1–141.4 104.9–139.3 108.5–141.4 198.3–124.8 87.1–104.2 95.9–127.5

0.4to 6.6 1.0–6.6 0.4 to 2.2 0.4 to 0.8 0.3 to 2.2 0.2 to 2.2 6.0–49.5 6.0–32.4 6.9–34.2 21.9–49.5 0.2 to 12.8 0.2 to 12.8 0.2 to 9.2 0.2 to 11.8 2.4–10.1 0.1–6.5 0.5 to 1.2 0.5 to 0.0 0.4 to 0.2 0.4 to 0.1 0.2 to 0.4 0.4 to 1.2 0.8–22.2 6.3–22.2 1.6–14.8 0.8–10.1 3.1–22.0 5.7–17.0

213.6–236.1 159.9–196.6 70.8–205.8 119.8–158.4 135.8–180.4 70.8–118.7 171.0–205.8 123.4–176.0 194.2–343.5 212.4–275.3 255.7–343.5 209.7–268.1 194.2–229.4 237.5–306.7

103.3–117.2 68.3–101.2 33.0–122.0 57.9–89.8 62.3–105.0 33.0–67.8 81.2–122.0 60.4–98.0 84.8–197.7 84.8–137.7 135.2–197.7 91.3–153.2 90.5–117.3 111.4–167.7

5.9–6.2 6.0–7.0 6.3–7.0 7.0–7.0 6.8–7.0 7.0–7.0 6.6–7.0 6.3–6.7 5.7–6.4 5.7–6.0 5.8–6.3 5.9–6.4 5.7–6.0 5.7–6.2

89.6–92.0 90.3–92.4 91.5–95.6 92.8–95.2 91.5–94.7 92.4–95.6 92.0–94.4 91.9–94.0 87.1–92.4 87.1–91.1 89.9–92.4 89.1–92.4 89.3–91.5 88.7–92.0

C, cluster; SC, subcluster; PV, peak viscosity; TV, trough viscosity; BDV, breakdown viscosity; FV, final viscosity; SBV, setback viscosity; PT, peak time; PTemp, peak temperature; AAC, apparent amylose content.

4000

TOG 14365 (glaberrima) TOG 12440 (glaberrima) Basmati Wita 4

RAM 123 (glaberrima) IRGC 86741 (glaberrima) Koshihikari Temperature (°C)

95 3500 85

65

2000

55

1500 1000

45

500

35

0

25 0 36 68 100 132 164 196 228 260 292 324 356 388 420 452 484 516 548 580 612 644 676 708 740

Viscosity (cP)

75 2500

Time (s) Figure 2 RVA profile of selected O. glaberrima and O. sativa varieties.

Temperature (°C)

3000

146

• • • •


Discuss why O. glaberrima is particularly suited to low-input subsistence farming. Provide reasons to support the assertion that O. glaberrima could have the same yield potential as Asian rice. Why is O. glaberrima an important food security crop in Africa? Briefly describe the variations in the physicochemical properties of O. glaberrima.


• •

What are the prospects for intraspecific breeding within O. glaberrima and how can the multiple trait resistance of O. glaberrima be transferred into new varieties. Does the nutritional profile of O. glaberrima differ from O. sativa and can we derive functional foods from African rice?

See also: Barley, Rice and Maize Processing: Rice Processing: Beyond the Farm Gate; Breeding of Grains: Rice: Breeding; Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Food Grains and Well-being: Functional Foods: Overview; Genetics of Grains: Rice: Genetics; Processing of Grains: Grain Quality Attributes for Cereals Other than Wheat; The Cereal Grains: Cereals: Domestication of the Cereal Grains; Rice: Overview; Wildrice, Zizania: Overview.

Further Reading Agnoun YB, Samadori SH, Sie´ M, Vodouhe` RS, and Ahanche´de´ A (2012) The African rice Oryza glaberrima Steud: Knowledge distribution and prospects. International Journal of Biology 4(3). http://dx.doi.org/10.5539/ijb.v4n3p158. Chang TT, Marciano AP, and Loresto GC (1977) Morpho-agronomic variousness and economic potentials of Oryza glaberrima and wild species in the genus Oryza. Paper presented at the Meeting on African Rice Species. Futakuchi K, Fofana M, and Sie M (2008) Varietal differences in lodging resistance of African rice (Oryza glaberrima Steud.). Asian Journal of Plant Sciences 7(6): 569–573. Futakuchi K and Sie M (2009) Better exploitation of African rice (Oryza glaberrima Steud.) in varietal development for resource-poor farmers in West and Central Africa. Agricultural Journal 4(2): 96–102.

Futakuchi K, Sie´ M, and Saito K (2012) Yield potential and physiological and morphological characteristics related to yield performance in Oryza glaberrima Steud. Plant Production Science 15(3): 151–163. Gayin J, Chandi GK, Manful J, and Seetharaman K (2015) Classification of rice based on statistical analysis of pasting properties and apparent amylose content: The case of Oryza glaberrima accessions from Africa. Cereal Chemistry 92(1): 22–28. Jones MP, Mande S, and Aluko K (1997) Diversity and potential of Oryza glaberrima Steud in upland breeding. Breeding Science 47: 395–398. Li ZM, Zheng XM, and Ge S (2011) Genetic diversity and domestication history of African rice (Oryza glaberrima) as inferred from multiple gene sequences. Theoretical and Applied Genetics 123(1): 21–31. Linares OF (2002) African rice (Oryza glaberrima): History and future potential. Proceedings of the National Academy of Sciences of the United States of America 99(25): 16360–16365. http://dx.doi.org/10.1073/pnas.252604599. Manners G (2001) NERICA: The new rice transforming agriculture for West Africa. Science in Africa http://www.scienceinafrica.com/old/index.php?q¼nerica.htm. Ndjiondjop MN, Cisse F, Girma G, et al. (2010) Morpho-agronomic and molecular characterisation of Oryza glaberrima germplasm from Mali. African Journal of Biotechnology 9(44): 7409–7417. Orjuela J, Sabot F, Che´ron S, et al. (2014) An extensive analysis of the African rice genetic diversity through a global genotyping. Theoretical and Applied Genetics 127: 2211–2223. http://dx.doi.org/10.1007/s00122-014-2374-z. Sahrawat KL and Sika M (2002) Comparative tolerance of Oryza sativa and O. glaberrima rice cultivars for iron toxicity in West Africa. International Rice Research Notes 27(2): 30–31. Sakagami JI, Joho Y, and Ito O (2009) Contrasting physiological responses by cultivars of Oryza sativa and O. glaberrima to prolonged submergence. Annals of Botany 103: 171–180. http://dx.doi.org/10.1093/aob/mcn201. Semon M, Nielsen R, Jones MP, and McCouch SR (2005) The population structure of African cultivated rice Oryza glaberrima (Steud.) evidence for elevated levels of linkage disequilibrium caused by admixture with O. sativa and ecological adaptation. Genetics 169(3): 1639–1647. Sie´ M, Sanni K, Futakuchi K, et al. (2012) Towards a rational use of African rice (Oryza glaberrima Steud.) for breeding in Sub-Saharan Africa. Genes, Genomes and Genomics 6(Special Issue 1): 1–7. Van Andel T (2010) African rice (Oryza glaberrima Steud.): Lost crop of the enslaved Africans discovered in Suriname. Economic Botany 64(1): 1–10. Wang M, Yu Y, Habere G, et al. (2014) The genome sequence of African rice (Oryza glaberrima) and evidence for independent domestication. Nature Genetics 46: 982–988. http://dx.doi.org/10.1038/ng.3044. Watanabe H, Futakuchi K, Jones MP, and Sobambo BA (2006) Grain protein content of interspecific progenies derived from the cross of African rice (Oryza glaberrima Steud.) and Asian rice (Oryza sativa L.). Plant Production Science 9(3): 287–293. Watanabe H, Futakuchi K, Teslim I, and Sobambo BA (2002) Milling characteristics and grain quality traits of interspecific progenies of Asian rice (Oryza sativa) with African rice (Oryza glaberrima). Japanese Journal of Tropical Agriculture 46: 47–55.

Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses AM Stanca, University of Modena and Reggio Emilia, Reggio Emilia, Italy A Gianinetti, F Rizza, and V Terzi, Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria, CRA-GPG, Fiorenzuola d’Arda, Italy ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Barley was domesticated from its wild relative Hordeum vulgare subsp. spontaneum in the Fertile Crescent about 10 000 years ago. Barley is a model organism for genetic and genomic studies in small grain cereals because it is a true diploid (2n ¼ 2x ¼ 14). Barley is the fourth most important cereal crop in the world. Today, barley is used as grain for livestock feed (80–90%) and as malt for beer and other alcoholic beverages (10%), and a small fraction is used as human food. Specific characteristics of barley grain composition allow barley flour to be used for the production of functional food due to the high content of beta-glucan (4–8%). Barley, in comparison with the other cereals, shows high genetic variability for positive adaptation to environmental stresses and growth in extreme climatic conditions.

Learning Objective

•

To achieve an overview of the botany, physiology, genetics, and agronomy of barley and of the main uses of this small grain cereal.

Barley Domestication and Spread Barley, one of the earliest domesticated plants, has been crucial to the development of mankind, providing both a regular staple and a source of compounds essential for life – carbohydrates, proteins, fat, and secondary metabolites. Its history as a crop begins in the ‘Fertile Crescent,’ a cradle area that today includes part of Iran, Turkey, Syria, and Jordan. The domestication of its wild ancestor, with a two-row brittle rachis allowing shattering of the seeds, Hordeum spontaneum (Figure 1), which is still to be found in the Middle East, dates to the Neolithic (10 000 years BC). It is from here that the species set out first to colonize the Mediterranean Basin and then, following the great river and sea migration routes of the time, fanned out to Central and Northern Europe, the Himalayas, and the Far East. Human intervention has been a decisive factor in the breeding of this species down through the millennia, the cultivars currently available manifesting completely different traits from those found in either its original parent or those populations that have evolved in the wild. During the process of domestication, barley has gradually accumulated traits that facilitated agricultural production. The perfecting of crop management techniques during the period of Roman dominion contributed to the spread of barley in the fertile as well as in the poorer soils of the empire.


The Mediterranean lands featured two barley types with very precise traits. The first was the six-row type because it grew rapidly in the mild Mediterranean climate, characterized by low and erratic rainfall. The second, called two-row barley, features high-quality grain and was sown in spring for direct human consumption. Gladiators, whose diet consisted almost entirely of food made from barley flour, were even called ‘hordearii,’ meaning ‘barley men.’ Genotypes that had a naked kernel were often resorted to as foodstuffs because of their superior nutritional value. It was during the Roman era too (Figure 2) that all the criteria for a rational use of grain and straw were defined and refined to perfection, Columella providing a detailed description in his Res rustica. The yield per hectare in the fertile lands was about tenfold the number of seeds employed. Barley further expanded its horizons in conjunction with Columbus’s second voyage, when it was introduced to the New World. Later, Dutch, English, French, and Danish colonists promoted its spread throughout North America, as did their Spanish and Portuguese counterparts in Central and South America. On the Altiplano of the Andean nations of Peru and Bolivia, barley is grown for grain at higher elevations – over 4550 m – than oat, wheat, and maize.

Morphology and Botany Since the turn of the twentieth century, our insights into plant growth, reproduction, and trait inheritance have been of indispensable support to barley field management and the improvement of cultivars. Several morphological forms have evolved, including winter, spring, two-row, six-row, awned, awnless, hooded, naked and covered, malting, feed (grain and forage), and food type. The high diversity of barley phenotypes, true diploid nature (2n ¼ 2x ¼ 14), and ease of hybridization and cultivation have made barley a model genetic organism since the rediscovery of Mendel’s laws. Barley belongs to Triticeae and has seven pairs of distinct chromosomes, five of them being without satellites (1H, 2H, 3H, 4H, and 7H) and two with satellites (5H and 7H). Cultivated barley is an inbreeder and it has more or less cleistogamous flowers, but under stress conditions, it can be more open flowering. The normal outcrossing rate has been determined to a maximum of 1.7–1.8%. Despite a very high inbreeding rate, a high degree of diversity is maintained, which is a sufficient basis for rapid adaptation to varying environmental conditions.

Barley as Model for Triticeae Genetics and Genomics Barley is a model organism for genetic and genomic studies in small grain cereals because of several reasons, ranging from its high degree of natural variation and wide adaptability to the diploid

http://dx.doi.org/10.1016/B978-0-12-394437-5.00021-8

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THE CEREAL GRAINS | Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses

Figure 1 Fragile spike of Hordeum spontaneum.

Figure 2 Corona obsidionalis made with six-row barley spike as virtus exercitus Romanorum.

genome structure and the strongly inbreeding-based mating system, as well as the wide array of genomic resources. Its seven chromosomes represent the basic genome of all Triticeae, and the first complete release of genome sequence has been publicly available from October 2012, overcoming the difficulties linked to the size (about 5500 Mb) and the presence of repetitive DNA regions. The springboard for the sequencing of the barley genome has been offered by key molecular tools developed in the near past, like barley ESTs (expressed sequence tags), BACs (bacterial artificial chromosomes), and the physical maps. Historically, barley genetic studies have their foundations in Mendelian mutants, characterized by altered physiology and/or morphology and still preserved as Barley Genetic Stocks (Figure 3). In this regard, there are examples of morphological mutations described in the past for which the gene/genes responsible have been recently cloned and characterized. An example is the Nud gene that controls lipid biosynthesis in the pericarp, which glues the husks to the kernels and results in either covered or naked barley seeds. Genetics knowledge has been applied to barley breeding, a dynamic process that has its pillars, on one hand, from short-, medium- and long-term objectives and, on the other hand, on perfecting selection criteria. Figure 4 traces the progress of barley production obtained in the course of history thanks to successful breeding activities. Structural and functional genomics, which merged in the integrative genomics, is supporting a knowledge-oriented breeding to design the ‘barley for the future’ in which good alleles will be operating all together in a superior genotype. Barley structural genomics has developed EST sequences databases and

Figure 3 Developmental mutants of barley spike.

Neolithic* 500 seeds/m2 0.1–0.15 t/ha

PostMendel 8000 seeds/m2 2.5 t/ha

Roman period 2000 seeds/m2 0.4–0.5 t/ha

1970 14 000 seeds/m2 5 t/ha

Renaissance Pre-Mendel 3000 seeds/m2 0.6–0.8 t/ha

Today 20 000 seeds/m2 9–10 t/ha

Figure 4 Estimated ‘yield potential’ of barley from domestication (10 000 BC) to the beginning of twenty-first century. *Hordeum spontaneum in situ conservation.

genotyping platforms based on different types of molecular markers. The new genomic platforms based on NGS technologies are providing opportunities to advance radically in the discovery of beneficial genes and alleles for barley breeding. Functional genomics use transcriptome analysis – that is, comprehensive and high-throughput analysis of gene expression for screening candidate genes, predicting gene function, discovering cis-regulatory motifs, and characterizing transcriptional

THE CEREAL GRAINS | Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses regulatory networks – models and reverse genetics. Genome-wide reverse genetics have been developed in barley to understand the gene–function relationships, including both transgenic strategies, like insertional mutagenesis or activation tagging, and nontransgenic ones, like TILLING (targeting induced local lesions in genomes). Even metabolomics – that is, the characterization of metabolites present in a tissue in a specific environment condition – can be very informative. Integrative genomics deals with combining the different data from these multiple-omics technologies to study biological systems multilaterally. In particular, the combined analysis of a relevant amount of genotyping and phenotyping data can give information useful for genetic mapping and advanced breeding programs of barley. Barley genetic resources remain the basis for this flowchart. For this reason, barley collections representative of existing natural genetic diversity are maintained worldwide in situ and ex situ, in the gene banks. New barley genetic resources are now developed for more efficient phenotyping–genotyping, like nested association mapping (NAM) populations obtained by crossing diverse genotypes to a reference parent or multiparent advanced generation inter-cross (MAGIC) based on the cross of several parentals. Talking about genetics, it is required to talk even of epigenetics: epigenetic effects have been shown to be strongly involved in developmental and physiological processes in model plants. Although barley has been poorly investigated from this point of view, some evidence exists on the impact of epigenetic factors on seed development and response to hormones. Finally, from a practical point of view, what we need is not new: efficient and inexpensive tools to select for agronomic and quality traits. Molecular markers developed in the last decades have been demonstrated to be of great help, in particular for pyramiding resistance genes in a marker-assisted selection (MAS) scheme of breeding. What is around the corner is genomic assisted selection (GAS) that means to build breeding schemes based on the selection of large portions of the genome. This strategy has been applied successfully in barley prebreeding/breeding for selecting barley genotypes improved for disease resistance and other agronomic traits.

feeding: improving grain protein quality, reducing grain phytic acid content, reducing beta-glucan content in feed for monogastric animals, reducing rumen grain fermentation rate, and increasing grain starch content. Barley’s economic importance also extends to the whole plant, which can be used for both livestock feed and industrial purposes. The use of the whole plant harvested at the end of the milk-ripe stage for silage is a practice that is becoming increasingly common in a number of barley-producing areas. This approach makes it possible to develop the double-cropping system in irrigated fields by growing in the same soil and same year barley silage followed by a crop of summer maize, sorghum, or soybean. Silage quality can be improved only when varieties exhibit an overall grain/ biomass ratio (harvest index) greater than 50%. As food, the human health benefit of consuming barley grain in food formulations is well known. The kernel of barley has a level of beta-glucans that is much higher than that found in other grains. Beta-glucans are a kind of soluble dietary fiber having hypoglycemic and hypocholesterolemic effects, as it swells in the presence of water to form highly viscous solutions that can trap glucose and cholesterol and slow down their absorption. The reduction of the rate at which glucose is released to the intestine and to the blood is particularly interesting when barley flour is included in the preparation of bread, a high glycemic food. Thus, incorporation of betaglucans derived from barley into this widely consumed food can reduce the glycemic response to its consumption. The use of beta-glucan-enriched barley flour is recommended to produce bread dough made of wheat/barley flour blends with a not-too-high proportion of barley flour. The majority of the Waxy barley genotypes (which have a very low to null amylose content) also have high beta-glucan content and can therefore be used to improve the hypocholesterolemic effects of foods. Barley flour can be easily incorporated into many wheatbased baked or not baked products such as cookies, bread, flatbread, tortillas, puffed sacks, and pasta for producing the so-called functional foods (Figure 5). In addition, tocols and phenolic compounds of barley are also considered bioactive components.

Barley Use Today, 80–90% of barley grain yield throughout the world is earmarked for livestock feed, about 10% is slated as malt production for beer, whisky, and other alcoholic beverages, and only a very small fraction is still directly consumed by man. Barley is still used today, albeit on a much reduced scale, as a surrogate for coffee, under the guise of peeled barley in the preparation of soups, and as an important staple in the diet of populations in North Africa and Asia. Barley grain is utilized in the diets of ruminants and nonruminant livestock, poultry, and fish. Attempts to improve the kernel for livestock feed have been focused on upgrading the nutritional value of proteins, the digestible energy of meals, and gum content (beta-glucan). A great deal of work has been done on proteins, in that barley prolamins (hordein) are lacking in essential amino acids, particularly lysine. However, five paths have been identified to improve barley grain quality for animal

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Figure 5 Functional pasta type made with durum wheat semolina (75%) and barley flour (25%).

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Malting Quality Barley is, and has been since the dawn of civilization, the cereal par excellence in the production of malt for beer, whisky, and other alcoholic beverages. Indeed, ever since the development of the most essential techniques by the ancient Egyptians and Babylonians, the art of brewing has continued to be perfected down through the ages and its secrets jealously guarded by the master brewers, despite the fact that fermentation technology had remained entirely shrouded in the dark until the nineteenth century. The transformation of barley into malt and of the latter into beer is a biotechnological process that is markedly dependent on the initial raw material, that is, on the barley grain that gives rise to the malt. To this aim, barley has first to be converted into malt, to increase its content of enzymes. Among them, amylases are needed to convert polymeric starch into soluble sugars, which can be used by yeasts for alcoholic fermentation. Malting is a controlled process of germination. As the first step of malting, barley is steeped to imbibe the grains and start germination. After 1–3 days of germination, depending on the malting conditions, the aleurone layer responds to gibberellin hormone from the embryo and releases hydrolytic enzymes that disaggregate and solubilize the endosperm. They can break down starch and storage proteins into simple molecules that nourish the growing embryo. Since starch and storage proteins are enclosed in the walls of the dead endosperm cells, these cell walls have to be dismantled to allow access of the hydrolytic enzymes to the internal reserves. Breakdown of endosperm cell walls mainly involves degradation of beta-glucans, which are the major constituent of the walls (>70%). This initial step is performed by endo-(1!3),(1!4)-beta-D-glucanase (shortly, beta-glucanase), which is the chief enzyme responsible for beta-glucan degradation and is therefore the enzyme leading endosperm modification. ‘Modification’ is a term used to mean all the chemical and physical changes that occur when barley is converted into malt, particularly the weakening in the consistence of the endosperm consequent to the degradation of the cell walls. Prior to milling, malt appearance resembles the original barley grain but is friable when crushed, revealing the physical–chemical changes that have occurred during malting. Secretion of beta-glucanase and other hydrolytic enzymes starts from the embryo’s scutellum and proceeds in the aleurone layer from near the embryo to the distal end of the grain. Much research has focused on the role of endosperm components in determining these aspects, and beta-glucans are considered to play a negative role. On the other hand, beta-glucans have also received much interest recently with regard to potential health benefits. Thus, whereas high beta-glucans are required for food functionality, low beta-glucans are usually desirable for the best malting quality. The endosperm of unmalted grains is compact and inaccessible to hydrolytic enzymes because large proteins cannot permeate cell walls. Thus, in the germinating barley grain, thorough breakdown of endosperm cell walls and partial digestion of the protein matrix inside the endosperm cells are necessary steps to render starch granules accessible to amylolytic enzymes. These two processes are the chief causes of the physical–chemical modification of the endosperm that occurs during malting and make the starch susceptible to degradation

during mashing. During the malting process, high production and/or activation of hydrolytic enzymes is required for cellwall degradation and protein solubilization, but starch breakdown should be minimal, to avoid unwanted consumption of utilizable dry matter by the embryo. To this aim, malting should both accelerate modification and retard embryo growth, which are partially conflicting purposes. It is well known that the higher the level of protein in the barley grain, the lower the percentage of carbohydrate and, then, the extract yield of the malt. In addition to this negative relationship with starch level, storage proteins have been suggested to play a significant part in determining the rate at which the whole endosperm is broken down during malting. More specifically, malting barley must have soft and mealy rather than hard and flinty endosperm and include such other characteristics as high germinative energy, a certain degree of dormancy to prevent pregermination in case of rain at harvest, adequate enzyme activity (amylase, beta-glucanase, and protease), low beta-glucan content, low protein content, high starch content, reduced glumeal hulls, and high extract percentage. The percentage of extract is directly linked to starch content and seed size and inversely correlated to protein content. A high nitrogen content adversely affects malt production by reducing the amount of extract and lowering quality. This is because a longer period is required for the modification process, which results in a greater development of rootlets and coleoptiles and consequent respiratory losses, and because of an abundance of soluble proteins that enter the extract and form suspensions in the beer. It is, however, important that the extract contain a permanent fraction of soluble nitrogen (0.5%) to feed the yeasts during fermentation. Malting begins with the soaking of the kernel in water to raise its moisture content to 42–45%, followed by the period (4 days) of modification. The changeover from barley to malt commences when the embryo secretes gibberellic acid, which immediately stimulates the production of enzymes (glucanase and pentosanase) that alter the endosperm’s structure by dissolving the walls of its cells and freeing starch grains. Other enzymes as phosphatase, phytase, glucanases, pentosanases, and protease also become active in the early stages of modification, while the amylases are triggered later. All of this activity, which serves as a vehicle to move substances from the endosperm to the embryo for the formation of new tissues and organs (rootlet and coleoptile), is accompanied by a marked increase in respiration: the resulting losses can range from 5% to 9% unless restricted by a rapid and uniform germination. From what we have mentioned thus far, it is not difficult to see that malting quality depends on a host of organic factors. The analytic data of a single character are insufficient to judge either the grain quality initially or the malt quality thereafter. Genetically speaking, breeding for malt varieties is a complex issue because many traits at grain, malt, and wort level have to be taken into account.

Biotic and Abiotic Stress Resistance Barley, despite its proven adaptability to a range of ecological situations throughout its evolution, is nonetheless susceptible to extreme environmental situations and a number of


Diseases

Heat shock

Lodging

Cold

Soil of low fertility Salt Heavy metals

Anoxia and drought Ions - acid and alkaline

Figure 6 Traits to cope with biotic and abiotic stresses in barley.

pathogens (Figure 6). These adversities can determine crop stress, ensuing yield losses of varying magnitude. Such field management practices as irrigation, fertilization, and pest control provide a certain measure of crop protection, although they increase the energy input required for successful harvests. Studies of genetic resistance have focused intensely on the selection of those plant genotypes less subject than others to the insults of a biotic and abiotic nature so as to increase yields and yield stability.

Abiotic Stress Response The optimum development of barley over its life cycle depends on a number of environmental stress factors that can prevent the plant’s expressing its maximum genetic potential. Severe grain losses are often caused by high or low temperatures, drought, anaerobiosis, and such soil anomalies as excess salt or heavy metals. The responses elicited from the plant by these stresses, when not lethal, include alterations in its processes of photosynthesis, respiration, and hormonal regulation through the development of specific, adaptive defense systems and mechanisms that are molecularly controlled. The duration of the stress and the plant’s growth stage at the former’s onset in turn affect yield. One can also find differing reactions as to plant susceptibility to adverse conditions. Thus, genetic variability plays a primary role in determining positive adaptation to environmental stresses and, hence, in supporting the spread of various barley genotypes to extreme climatic conditions. The integration of molecular genetics with physiology is leading to the identification of the most relevant genes controlling abiotic stress tolerance with the final aim to develop high yielding cultivars able to improve performance in both high- and lowyielding environments.

Biotic Stresses The Compendium of Barley Diseases lists 37 viral, 36 fungal, and 4 bacterial diseases, including 6 nematodes as well as a

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substantial number of insect species, which regularly or casually cause damage during the entire life cycle. The level of crop losses in barley at global scale, due to diseases and pests, has been estimated to be 10.5% and 8.5%, respectively. The fight between barley and its parasites is a dynamic process in which two different strategies of resistance are activated. The first type is resistance to infection synonymous of hypersensitivity, racespecific, vertical, or major gene resistance. This type works as gene-to-gene interaction between barley genes for resistance and pathogen genes for avirulence. The second type is defined as quantitative or partial resistance, field resistance, durable resistance, non-race-specific resistance, horizontal resistance, or minor gene resistance. The diseases and insects inflicting severe crop losses on a worldwide scale are described here (Table 1). With the development of molecular marker technology, marker-assisted selection (MAS) has been routinely used as tool for detecting genetic loci underlying the traits for resistance and for incorporating them in elite genotypes. Although chemical treatments and agronomic techniques are effective in controlling pests and diseases of barley, the availability of resistant cultivars is the most economic and environmentally sound strategy for reducing losses.

Conclusions and Future Prospects Barley today ranks fourth behind wheat, rice, and maize among the world’s cereals for the importance of its contribution, whether direct or indirect, to the production of food. The global production is estimated in 2013 as 135 millions of metric tons (Mt) in a harvested area of 50 million hectares (Mha) with an average of 2.7 metric tons (t ha1) of grain per hectare. Grown in almost every country throughout the globe, it is generally found as a crop in areas that are less conducive to the survival of other cereals. It is very widespread in the drought-prone lands of the Near East, Northern Africa, and the highlands of India; in the saline soils of Australia; in Nordic countries; and in areas that, while fertile, are marked by a very short growing season (<100 days). This flexibility is doubtlessly due to barley’s range of genetic variants. The plant appears capable of producing yields that are competitive with yet require less energy input than other cereals. Barley as a winter crop can register yields as high as 10 t ha1 of grain at lower costs than the other cereals due mainly to high tillering capacity and its high nitrogen use efficiency (NUE) and water use efficiency (WUE). Barley’s capacity to produce biomass even under restrictive conditions implies that in all likelihood, it will continue to play a strategic role in food production for the foreseeable future in many areas of the world where drought and other adverse climatic phenomena are inimical to the plant growth and development. Due to phenotypic plasticity, further improvements in ‘yield potential and stability ’ can be expected in the near future in the modern barley farming system.


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Are specific barley varieties used for malting? Explain the difference between naked and hulled grains.

152 Table 1

THE CEREAL GRAINS | Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses Major diseases and pests of barley

Disease common name Fungal disease Barley stripe Powdery mildew Net blotch Fusarium Head Blight Snow rot Spot blotch Leaf blotch or scald Loose smut Ramularia leaf spot Yellow rust Brown rust Black stem rust (including Ug99) Septoria leaf blotch Rhizoctonia root rot Root rot Ergot Covered smut Loose smut Take-all Eye-spot Leaf non parasitic spots Bacterial disease Black chaff Bacterial blight Viral disease Barley yellow mosaic virusBAYMV, BAMMV Barley yellow dwarf virus – BYDV Pests and nematodes Cereal cyst nematode Root lesion nematode Green bug Aphids Hessian fly Cereal leaf beetle Cereal ground beetle Frit fly Cutworms

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Causal agent Pyrenophora graminea Blumeria graminis Pyrenophora teres Fusaria Typhula incarnata Cochliobolus sativum Rynchosporium secalis Ustilago nuda Ramularia collo-cygni Puccinia striiformis Puccinia hordei Puccinia graminis Septoria passerini Pythium Rhizoctonia solani Claviceps purpurea Ustilago hordei Ustilago nuda Gaeumannomyces graminis Pseudocercosporella herpotrichoides Unknown

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Are the barley mutants useful to increase secondary metabolites for food? Which strategy is still active for disease resistance in barley: monogenic or quantitative resistance?

See also: Agronomy of Grain Growing: Barley: Agronomy; Barley, Rice and Maize Processing: Barley: Malting; Barley: Milling and Processing; Beverages from Grains: Beverages: Distilled; Fermentation: Foods and Nonalcoholic Beverages; Fermentation: Origins and Applications; Bioactives and Toxins: Bioactives: Antioxidants; Mycotoxins; Breeding of Grains: Barley: Genetics and Breeding; Carbohydrates: Health Effects of b-Glucans Found in Cereals; Cereals: Chemistry and Physicochemistry of Nonstarchy Polysaccharides; Glycemic Index, Glycemic Load, and Their Health Benefits; Resistant Starch and Health; Food Grains and Wellbeing: Functional Foods: Overview; Genetics of Grains: Genomics of Food Grains; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Grain Marketing and Grading: Barley: Grading and Marketing; Non-food Products from Grains: Cereal Grains as Animal Feed; Processing of Grains: b-Glucans: Measurement and Processing; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains.

Xanthomonas translucens Xanthomonas campestris Potyviridae (soil borne disease transmitted by Polymixa graminis) Luteoviridae (transmitted by aphids)

Heterodera avenae Pratylenchus spp. Elymus canadensis Mayetiola destructor Oulema melanopus Zabrus tenebroides Oscinella frit Agrotis

Is the whole barley plant used for forage? Explain the difference between winter, alternative, and spring barley varieties. Are there in barley grain secondary metabolites for human health other than beta-glucans? Why is the barley plant considered more economically and environmentally suitable than other cereal crops? What is the barley genome size?


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WUE (water use efficiency) and NUE (nitrogen use efficiency) are considered two strategic traits to develop plants to cope with environments. Is barley a more efficient species within cereals? How do the agronomic practices improve yield and quality of the barley grain?

Further Reading Bulgarelli D, Biselli C, Collins NC, et al. (2010) The CC-NB-LRR-type Rdg2a resistance gene confers immunity to the seed-borne barley leaf stripe pathogen in the absence of hypersensitive cell death. PLoS One 5(9): e12599. Demetriou K, Kapazoglou A, Tondelli A, et al. (2009) Epigenetic chromatin modifiers in barley: I. Cloning, mapping and expression analysis of the plant specific HD2 family of histone deacetylases from barley, during seed development and after hormonal treatment. Physiologia Plantarum 136: 358–368. Fincher GB (2011) Biochemistry, physiology, and genetics of endosperm mobilization in germinated barley. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 449–477. Chichester, UK: Wiley-Blackwell. Finocchiaro F, Ferrari B, Gianinetti A, et al. (2012) Effects of barley beta-glucanenriched flour fractions on the glycaemic index of bread. International Journal of Food Sciences and Nutrition 63(1): 23–29. Francia E, Tondelli A, Rizza F, et al. (2011) Determinants of barley grain yield in a wide range of Mediterranean environments. Field Crops Research 120: 169–178. Graner A, Kilian A, and Kleinhofs A (2011) Barley genome organization, mapping and synteny. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 63–84. Chichester, UK: Wiley-Blackwell. Mathre DE (1997) Compendium of Barley Diseases. St. Paul, MN: American Phytopathological Society. Paulitz TC and Steffenson BJ (2011) Biotic stress in barley: Disease problems and solutions. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 307–354. Chichester, UK: Wiley-Blackwell. Rizza F, Pagani D, Gut M, et al. (2011) Diversity in the response to low temperature in representative barley genotypes cultivated in Europe. Crop Science 51: 2759–2779. Stanca AM, Tumino G, Pagani D, et al. (2013) The “Italian” barley genetics mutant collection: conservation, development of new mutants and use. Advance in Barley Sciences 30–35. Thomas WTB, Hayes P, and Dahleen L (2011) Application of molecular genetics and transformation to barley improvement. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 122–143. Chichester, UK: Wiley-Blackwell. Ullrich S (2011) Significance, adaptation, production and trade of barley. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 3–13. Chichester, UK: Wiley-Blackwell. von Bothmer R and Komatsuda T (2011) Barley origin and related species. In: Ullrich S (ed.) Barley: Production, Improvement and Uses, pp. 14–62. Chichester, UK: Wiley-Blackwell.

Sorghum Grain, Its Production and Uses: Overview A Cruickshank, DAFF Queensland, Warwick, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

The Origins of Domesticated Sorghum

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Botanically sorghum belongs to the grass family and the tribe Andropogoneae. This is a tropical and subtropical group of grasses, which also includes sugarcane (Saccharum spp.) and maize (Zea mays). Like all the grasses in this tribe, sorghum has a C4 photosynthetic pathway. The genus Sorghum has at least 20 species extending from Africa through Asia and including 12 species endemic to Oceania. Sorghum bicolor, a native of Africa that has spread throughout the world, has three subspecies: S. bicolor bicolor, S. bicolor verticilliflorum, and S. bicolor drummondii, with distinct morphology for the respective heads (Figure 1).

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The sorghum grain is a high-energy cereal grain that is a staple to many poorer farmers in Africa and parts of Asia. Sorghum is a genetically diverse and robust plant, possessing resistances to many biotic and abiotic stresses. Sorghum is a (sub)tropical grass (like sugarcane and maize) with a C4 photosynthetic pathway. Sorghum bicolor is classified into five races: bicolor, kafir, caudatum, durra, and guinea. Major sorghum producers are Nigeria, the United States, India, Argentina, Ethiopia, and Australia. Sorghum can grow in temperatures from 15 to over 40 C Flowering and seed set require temperatures between 20 and 39 C. Significant diseases are downy mildew, ergot, and grain mold. Significant insect pests include sorghum midge and greenbugs (aphids). Sorghum grain can be white, yellow, red, or purple. Sorghum is consumed as a thin porridge or gruel, as a thick porridge or dough, as various flatbreads, as popped or puffed sorghum grain, or as alcoholic beverages.

To achieve an overall understanding of sorghum as a grain worldwide: its origins, breeding, agronomy, production, processing, and utilization

Introduction All grain sorghum is the product of cultivated types of Sorghum bicolor (L.) Moench. Sorghum bicolor is an African species and the crop was first domesticated in East Africa. In traditional agriculture, tall varieties of sorghum are grown for multiple purposes including various uses of grain, fodder, and extract of sweet syrup (by crushing stems in the same manner as with sugar cane) and use of the panicles for broom heads. Today, sorghum is a staple for approximately half a billion people. In developed agriculture, particularly in the Americas and Australia, sorghum has been selected and bred for specific end uses – grain sorghums as short plants suited to mechanized agriculture and taller types for forage, fodder, and silage production. Grain sorghum is a crop with great genetic diversity and adaptation to drier and hotter environments. It has traditionally been used in many different ways in Africa and Asia. It is now an important world crop and the most important crop locally in some hot and dry regions.


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Learning Objective

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S. bicolor subsp. verticilliflorum is the wild progenitor species. These sorghums have small seed, < 1 mm thick. These seeds are shed soon after they ripen. This process is called shattering, and selection of nonshattering off-types is one of the first steps in domesticating a wild plant to develop a crop. S. bicolor subsp. bicolor incorporates all the cultivated types. The cultivated types have been further classified on the basis of the shape of heads and grain into five races: bicolor, kafir, caudatum, durra, and guinea. The range of head types is illustrated in Figure 2. S. bicolor nothosubsp. drummondii incorporates all material derived from natural crossing between S. bicolor subsp. bicolor and S. bicolor subsp. verticilliflorum types. In some production systems, weedy S. bicolor nothosubsp. drummondii types (known as shattercanes) are problem weeds.

Analysis of DNA sequence data has led scientists to believe there have been at least two, possibly more, domestications of sorghum. There is little doubt that the original domestication occurred in East Africa – somewhere in Ethiopia or possibly Sudan. Evidence from DNA sequence analysis suggests that there has been at least one other more recent domestication in West Africa, giving rise to the group that has been distinguished by the name margaritiferum. These plants have a lot of wild plant features and are grown separately from other sorghums, named as a different crop and prepared in different foods.

Sorghum Production Sorghum is produced in the tropics and in subtropical or temperate regions throughout Africa, Asia, and the Americas (only a small amount of grain sorghum is produced in Europe). Prior to the colonial era, maize was the dominant grain crop in the Americas and sorghum the most important summer cereal in Africa. Since both crops have been available worldwide, there has been a general trend for maize to be more popular in higher rainfall areas and sorghum to be cultivated

http://dx.doi.org/10.1016/B978-0-12-394437-5.00023-1

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THE CEREAL GRAINS | Sorghum Grain, Its Production and Uses: Overview

Figure 1 Heads of the three subspecies of Sorghum bicolor: left – S. bicolor subsp. verticilliflorum, middle – S. bicolor nothosubsp. drummondii, and right – S. bicolor subsp. bicolor.

from 2004 to 2013 of 1.8 t ha 1 compared to an Africa-wide average of <1 t ha 1. Sudan, Burkina Faso, Niger, Mali, and Cameroon have all steadily increased their sorghum production and currently average 1–1.5 mt pa. Sudan has the highest ratio of sorghum to maize in the world, this being an indicator of the importance of sorghum to a particular country. India is still a major sorghum producer, but there has been a decline of production since 1995, due to a number of changing factors including the increased capacity to irrigate higher value crops such as rice, and the cost and availability of labor for sorghum production. In the 1960s, China produced over 8 mt of sorghum pa, but this has declined to around 2 mt pa. Over this time, sorghum yields in China have improved to an average of just under 4 t ha 1. Total production appears to have declined in China, apparently for similar reasons to the changes in India, particularly involving the greater availability of rice. Consumption of sorghum as food in China has declined but the use in distilled spirits has increased. Mexican sorghum production has increased over the past 50 years but appears to have stabilized at just over 6 mt from 2007 to 2013, with impressive average yields of 3.7 t ha 1. Mexico consumes all the sorghum it can produce plus significant imports from the United States. In the early 1980s, Argentina produced approximately 8 mt pa but this has since fallen dramatically. Despite sorghum being displaced by herbicideresistant maize and soybean, the average yield of sorghum in Argentina is over 4.5 t ha 1. Brazil produced 1.8 mt pa at a yield of 2.4 t ha 1 over 2004–13, the result of steady increase over the past 50 years. Australia is the only non-African country where sorghum production significantly exceeds that of maize. A study using simulation to compare climate-adjusted yield improvement found sorghum yield improvement was substantially better than that of wheat in subtropical Australia. This has contributed to sorghum production rising to average 2.1 mt pa and yields of 3.1 t ha 1 over 2004–13.

Figure 2 Variation in head type for Sorghum bicolor.

in more marginal environments. Some exceptions to this occur where either sorghum or maize is more suited to preparation of an important food. Africa produced 40% of the world’s sorghum in the 10 years from 2004 to 2013, and West Africa produced just over half of that. Over the same period, 37% of world sorghum production was in the Americas and 20% in Asia and Oceania (Figure 3). Sorghum is produced in over 100 countries, but of these, only 14 produce about a million tonnes or more annually (mt pa) (Table 1). During the decade 2004–13, the United States produced the most sorghum (averaging just under 10 mpa) at an average yield of 4 t ha 1. However, there has been a downward production trend in the United States over the past 50 years. Other major sorghum producers are Nigeria, India, and Mexico, each producing 6–8 mt pa in the decade 2004–13. Nigeria experienced dramatic growth in sorghum production from 1964 to 2006 with a slight decline since then. Ethiopia is also a major producer of sorghum in Africa with a marked increase in sorghum production since 2000. The Ethiopian increase has been characterized by average yields

Adaptation of the Sorghum Crop Although it is essentially a tropical and subtropical species, the cultivated form of sorghum is also grown to 40 latitude as a warm season crop. Generally, sorghum needs soil temperatures over 15 C for crop establishment. Crop growth can occur from these temperatures to just over 40 C. Flowering and seed set require temperatures between 20 and 39 C, the most sensitive process being pollen production with higher and lower temperatures leading to sterility. Recent research has found genetic variation in the extreme temperature tolerances of both germination and flowering. This means there is the capacity to improve grain sorghum’s tolerance of extreme weather events that are projected to increase in the future. Sorghum as a species also possesses many characteristics that enable growth and development in water-limited environments including ‘staygreen’ drought resistance during grain-filling and transpiration efficiency. Many traditional landrace varieties are sensitive to photoperiod, requiring days shorter than a certain maximum before they will flower and produce grain. Such varieties may fail to flower and produce grain when grown at different


South-Eastern Asia

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Western Central Oceania Asia Asia Middle Africa

Eastern Africa Middle Africa

Eastern Africa

Northern Africa Western Africa

Southern Asia Eastern Asia

Northern Africa

Southern Africa Europe Northern America South America

Central America

Caribbean Western Africa

Central America Eastern Asia Southern Asia

Caribbean

South America South-Eastern Asia Western Asia Northern America

Southern Africa Europe

Central Asia Oceania

Figure 3 Sorghum production worldwide by region, averaged for the decade 2004–13. Source: FAOSTAT. Table 1 Production of sorghum by major countries, averaged for the decade 2004–13 Country

Tonnes

%

World The United States Nigeria India Mexico Sudan (former) Argentina Ethiopia Australia China, mainland Brazil Burkina Faso Niger Mali Cameroon

59 850 648 9 327 805 7 891 520 6 883 880 6 361 639 3 873 500 3 056 573 2 943 216 2 171 743 2 141 650 1 813 631 1 673 123 1 018 760 993 038 961 818

100 15.6 13.2 11.5 10.6 6.5 5.1 4.9 3.6 3.6 3.0 2.8 1.7 1.7 1.6

Source: FAOSTAT.

latitudes or even similar latitudes with different temperature regimes. Sorghum is adapted to a wide range of soil conditions. Some of the genetic characteristics that confer this adaptation are being discovered: a general tolerance of salinity, greater tolerance to acidic aluminum ions, more efficient uptake of essential phosphorus, and different angles of nodal root growth. As with other cereal grains, in most circumstances, nitrogen will be the limiting nutrient in grain production. Sorghum will form mycorrhizal associations with fungi that improve the nutrient efficiencies of elements that are present in

the soil, but fertilization with phosphorus, potassium, and other minor nutrients will often still be necessary to remove limitations to yield. The agronomy of sorghum production in mechanized agriculture is quite different to that in traditional production systems. In developed agriculture, sorghum is grown as a row crop at plant densities suited to the available moisture. Nitrogen fertilizer may be applied entirely preplanting or split between a ‘starter’ application and a later targeted ‘top-up’ when the likely yield is more predictable. Herbicide application may be used to desiccate the sorghum plant and grain in preparation for harvest.

Sorghum Breeding Traditional farmers have been responsible for the selection and maintenance of the great diversity that exists in the landraces of sorghum. When some of these landraces were introduced to the Americas, any off-types that had dwarfing genes or different maturities were selected and (just as important) were studied. An understanding of the differences in height and maturity developed that allowed selection of types that were more suited to mechanized agriculture. Subsequently in the United States, there was a great plant breeding initiative called the sorghum conversion program in which landraces were ‘converted’ by crossing them to short, photoperiod-insensitive types and the progeny back-crossed to the landrace while selecting for short photoperiod-insensitive plant type. This provided a resource to sorghum breeders from which many improved traits could be bred into other genetic backgrounds including high yield, drought resistance traits, and midge resistance.

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Sorghum now has a published genome sequence that allows breeders to develop understanding of the genetics of traits of which their predecessors could only dream. Given the great diversity available within the species, this understanding should allow development of grain sorghum with robust adaptation to extreme environments and grain qualities that provide a range of products fit for many purposes.

Sorghum Diseases and Pests Like all crops, sorghum productivity is affected by a range of pests and diseases. Some pests or diseases have a specific interaction with sorghum; others are more widely adapted and are a threat to other crops also. Some directly affect yield of usable grain through killing plants or reducing the amount of grain produced per plant. Diseases also indirectly influence productivity through damaging and devaluing grain or by causing farmers to sacrifice potential yield with management decisions that are part of a strategy to avoid disease. To show the diversity of pest and disease biology, three diseases, downy mildew, ergot, and grain mold, and two important insect pests, sorghum midge and greenbugs (aphids), will be considered. Downy mildew is caused by the pseudofungus Peronosclerospora sorghi. This pathogen can infect other species including maize. It can survive for years in the soil as a resistant oospore and can do most damage when oospores infect a young crop in moist soils. This is called systemic infection and the pathogen can then grow throughout the plant. Symptoms include initially leaf yellowing but eventually leaves are completely dead and visibly shredded. When warm humid conditions favor growth of the pathogen, it can produce short-lived spores called conidia that can infect the aerial plant parts. Conidial infection may cause minimal damage in mature plant or lead to systemic infection in a very young plant. Control is achieved by host plant resistance, seed treatment with fungicides, and cultural measures such as crop rotation (to reduce oospore infection) and early sowing (to reduce conidial infection from plants infected earlier). Sorghum ergot is caused by the fungus Claviceps africana (in the Indian subcontinent by C. sorghi). It is host-specific to plants of the genus Sorghum and has one very specialized mode of infection: conidia of sorghum ergot can only infect nonfertilized stigmas of flowering sorghum heads. Genetic and environmental factors can contribute to nonfertilized stigmas being exposed to infection. Male-sterile lines used in the production of hybrid seed are particularly vulnerable; and seed production is done in lower risk environments and protected with fungicides if needed. The environmental factors that lead to ergot disease are factors that prevent successful pollination: rainfall and high humidity at flowering and cool temperatures prior to and at flowering. The sensitivity of the flowering period influences farmer decisions on when to sow sorghum, often choosing not to sow sorghum after a certain date to avoid a high risk of ergot infection. Sorghum grains are exposed to the weather, and moisture on the grain can lead to infection by a number of species of fungi particularly Fusarium and Curvularia. Collectively, these infections are referred to as grain mold. Some cause nothing

more than discoloration of the grain, but other species in some circumstances produce toxins that make the grain unsuitable for consumption. Many traditional varieties, particularly in West Africa, flower in response to changes in day length so that most if not all of their grain-filling period occurs after the end of the rainy season. The sorghum midge (Stenodiplosis sorghicola) is an insect that is totally dependent on sorghum plants for its survival and reproduction. The female midge seeks out flowering sorghum to lay its eggs at the base of florets. The larvae of the midge then feed on the ovary and prevent the development of grain. In susceptible sorghum types, if the environment is warm and humid, losses can be substantial. The level of damage is also dependent on the number of flying female midge present when a crop is flowering. Most commonly, these females come from wild or volunteer sorghum (particularly Sorghum halepense) or an earlier crop of cultivated sorghum. Pupae can overwinter in plant trash in a diapause state. There are sorghum lines that resist the oviposition or the larval feeding. With resistant cultivars and cultural practices, such as early sowing, good control of midge damage can be achieved without the use of insecticide. In Australia, the widespread use of midge-resistant sorghum has allowed the survival of many more beneficial arthropods (predatory insects, spiders, etc.), and this has aided integrated pest management in other summer crops also. A range of aphid species will feed on sorghum but the most common pest is the greenbug (Schizaphis spp.). They are grass feeders and are also pests of other cereals in farming systems. In sorghum, they cause damage by degrading tissue with their saliva, by depletion of nutrients and energy, by contaminating harvested grain with honeydew, and by being a vector for plant pathogenic viruses notably maize dwarf mosaic. Greenbugs are capable of both sexual reproduction and parthenogenesis. They also have a short generation time and a capacity for rapid population increase. This has led to rapid emergence of new ‘biotypes’ with different preferences in feeding or resistances to pesticide, when control measures provided selection pressure on the greenbug population. Resistant varieties and natural enemies, together with careful use of pesticide, can provide adequate control.

Sorghum Grain Composition and Utilization The sorghum grain is a typical grass seed but it has been selected over time for larger seed size and other particular characteristics. Each grain is a caryopsis – the botanical name for a fruit containing a single seed with the fruit wall (pericarp) and seed coat (testa) fused. The color of the grain is mostly determined by the pericarp that can be white, yellow, red, or purple (almost black), but the presence of condensed tannins in the testa causes a strong brown subcoat. Tannin-rich sorghums offer the advantage of being ‘bird-proof’ to a degree, but they also offer greater difficulty in most forms of processing. Variations in head shape and grain color are illustrated in Figure 4. The embryo of a cultivated sorghum grain is larger than the embryo of wild sorghum, but the increase is not proportional to the increase in grain size with domestication. Most of the


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Figure 4 A range of sorghum grain colors, including some white grains stained by grain mold.

Figure 5 Injera, a fermented flatbread popular in Ethiopia, made from teff or sorghum. Source: Illustration from Wikipedia.

volume of the grain is made up of endosperm, but different sorghum seed lines have very different endosperm structures and textures, which determine their value for different uses of the grain. When the grain is mature, its endosperm is composed of starch granules, spherical bodies composed of kafirin proteins, and a protein matrix of glutelin. These three components can be loosely packed in what is called floury endosperm or tightly packed in what is called corneous endosperm. Kafirins can form disulfide bonds, with one another and with glutelin, which are very resistant to digestion. The resistance of these bonds to hydrolysis is believed to reduce the digestibility of both protein and starch, particularly in tightly packed corneous endosperm. There are other factors present in whole grain that can cause resistance to digestion – condensed tannins in the testa and phytate in both the embryo and the pericarp. The tannins, when present, can interfere with protein digestion. Phytate can interfere with the digestibility of protein, phosphorus, and iron. The end uses of sorghum can be divided for convenience into traditional uses associated with cultivation of landraces in traditional African and Asian societies and uses in the developed economies of the Americas, Australia, and Europe. Throughout Africa, sorghum grain is prepared as a wide range of foods. Traditionally, the milling of sorghum grain has been a laborious manual task with tools that are variations on the theme of a mortar and pestle. The milled grain can then be used in a variety of ways; broadly, most foods can be classed as a thin porridge or gruel, as a thick porridge or dough, as various flatbreads, as popped or puffed sorghum grain, or as alcoholic beverages. In West Africa, the margaritifera types are cultivated separately and often used in a manner similar to rice. The variety in the foods produced is influenced by the choice of sorghum, that is, use of the whole grain meal or some fraction or use of a white-, red-, or brown-seeded sorghum containing condensed tannins. Variation within these foods is also

produced by the absence or the presence (and nature) of fermentation. When sorghum is prepared as a heavy porridge, it is usually eaten by hand with a savory sauce. In Ethiopia, sorghum is made into injera (Figure 5), a fermented flatbread that looks to western eyes like a pancake. The preparation of injera includes a lactic acid fermentation leading to a marked sour taste. The most valued grain for injera is the Ethiopian grain teff, but sorghum is produced in much greater quantities than teff and is preferred over wheat or barley for making injera. Consequently, Ethiopia is one of the few places in the world where sorghum attracts a higher price than wheat. Injera is usually made with little or no bran. In Sudan, a similar bread called kisra is made with whole grain meal. In India, sorghum is used in roti-style flatbreads or as a boiled grain substituting for rice. Rotis are often made with a mixture with wheat flour. As in many other uses, the elastic nature of the gluten in wheat flour helps maintain the structure of a roti for longer than if made with sorghum flour only. In East Asia, particularly China, sorghum grain is used (either on its own or in combination with other grains) in the production of highly alcoholic distilled spirits. These spirits are produced for both high-value exclusive markets and more traditional local consumption. Because the sorghum production in China has declined and there is a demand for sorghumderived spirits in the growing middle class, China may be developing as a market for sorghum-exporting countries like the United States and Australia. Sorghum grain produced in the Americas, Australia, and Europe is used primarily as animal feed. It is most commonly used in intensive production of poultry, pigs, and feedlot cattle. (The use of sorghum grain as supplementary feed for dairy cattle is comparatively rare.) Smaller volumes are used in pet food. The grain is prepared in various ways for use in different animal production systems. The simplest preparation is to break the grain in a hammer mill or similar device and offer as meal to animals. Due to the potential antinutritive factors present in sorghum, this is not the most efficient use

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of the grain. More commonly sorghum is offered to poultry and pigs in prepared complete-ration pellets and to cattle as steam-flaked grain. When sorghum is used in pelleted rations, it is frequently as a cheaper substitute or complement for wheat. Due to different gelatinization temperatures, a greater degree of heat energy may be required to successfully bind a pellet-containing sorghum. Many feed producers will add artificially produced digestive enzymes to improve the digestibility of both the protein and starch of the sorghum. Enzymes used in this way include phytase, xylanase, and proteases thought to help break down kafirins more efficiently.

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Future Prospects for Sorghum

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Over decades, there has been the trend in many sorghumproducing countries for eating habits to move away from sorghum-based foods as living standards have improved. On the other hand, these changes may be progressively complemented by increased use of sorghum for livestock feed and alcoholic beverages (mainly sorghum beers in the same regions) and also the likely use of sorghum as a basis for fuel ethanol production. In addition, the specific properties of sorghum starch may increase its use as an industrial source of starch. The environment favorable for sorghum production can be expected to become greater with trends of climate change toward warmer growth temperatures and elevated levels of carbon dioxide in the atmosphere. Like plant breeders in general, sorghum breeders are planning to change breeding strategies. However, the expected increases in grain yield for cereals, such as wheat (a C3 plant), are not expected to be so great for C4 plants such as sorghum. Regarding climate change, the greatest concern of sorghum breeders is the probable more frequent occurrence of extreme heat events that have the capacity to reduce seed set dramatically.


• • •

List the major regions of sorghum production worldwide. How do they differ in their utilization? What climatic and soil conditions suit these places to sorghum production? Discuss rainfall, temperatures, day length, and latitude with respect to stages of plant growth. How have plant breeding and selection changed the original growth conditions for sorghum?

• • •

What climate conditions encourage or deter the diseases and pests of sorghum? What agronomic management can be used to reduce the risks of damage by diseases and pests? Describe the range of foods for which sorghum is used. How can sorghum’s resistance to digestion be mitigated for humans and animals?


•

•

The protein complex of the sorghum grain is made up of many proteins. What are their names and possible functions? Sorghum varieties differ in grain color. Find out the chemical reasons and the possible advantages and disadvantages of these differences. Sorghum, like sugarcane and maize, has a C4 photosynthetic pathway. It is thus distinct from C3 cereals such as wheat and barley. What is the significance of this distinction for sorghum production now and into the future?

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Grain Harvest, Storage and Transport: Sorghum: Harvest, Storage, and Transport; Non-wheat Foods: Sorghum: Utilization; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains.

Further Reading Anonymous (2012) The U.S. Sorghum Industry. Washington, DC: US Department of Agriculture. Dendy DAD (ed.) (1994) Sorghum and Millets: Chemistry and Technology St Paul, MN: AACC International. Doggett H (1988) Sorghum, 2nd edn. London: Longman Scientific & Technical. Pereira TD (2012) Sorghum: Cultivation, Varieties & Uses. New York: Nova Science Publishers Inc. Ramirez JA and Manuel Vazquez M (2012) Sorghum: Food & Energy Source. New York: Nova Science Publishers Inc. Smith CW and Frederiksen RA (2000) Sorghum: Origin, History, Technology, and Production. New York: Wiley.

Relevant Websites faostat.fao.org – FAOSTAT. www.icrisat.org – ICRISAT.

Rye Grain: Its Genetics, Production, and Utilization HD Sapirstein and W Bushuk, University of Manitoba, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by W. Bushuk, volume 3, pp. 85–91, ã 2004, Elsevier Ltd.

Topic Highlights

Center of Origin and History

•

The primary center of origin of the rye plant is considered to be in the Anatolian Plateau of the Middle East (Asia Minor), encompassing the eastern region of Turkey and neighboring portions of what is now Georgia, Armenia, Azerbaijan, Iran, Iraq, and Syria. This northern region of the Fertile Crescent is also the center of origin of wheat, barley, oats, and lentils. There is no evidence of rye cultivation in ancient Egypt. Cereal rye is believed to have diverged genetically from related Secale species about 10 000 years ago. Rye grain is mentioned in early writings of northern Europe suggesting this region as an important area of historic cultivation. Cultivation of rye migrated from its center of origin in the Middle East to northern Europe in the first millennium BC. One possible route of migration was from Asia Minor to western Russia and, from there, westward to Poland and Germany where it is highly adaptable and popular with farmers. Another possible route of rye plant migration was from Turkey by way of the Balkan Peninsula to north-central Europe. Rye was brought to North America and South America by European settlers during the sixteenth and seventeenth centuries. At about the same time, its cultivation spread eastward in Europe to Siberia. During the nineteenth and twentieth centuries, its cultivation began in Argentina, southern Brazil, Uruguay, Australia, and South Africa. Today, rye cultivation like that of wheat is worldwide, but the largest production is in central and eastern Europe (Table 1).

• • • • • • • • •

The origins and history of rye production and uses are discussed. Rye production worldwide is falling. International trade in rye is about 13% of world production. Starch (stored in discreet granules) is the major component of rye endosperm. Secalin is the major protein of the rye grain, but rye is not as suitable for bread making as wheat. The rye grain contains more fiber than wheat and other cereal grains. Rye contains some compounds with antinutritional properties for monogastric animals. Rye endosperm has a soft texture, releasing flour readily in milling. Breads may be made from 100% rye flour but up to 90% wheat flour may be added. Baked goods include rye bread, rye rolls, crisp bread, and pumpernickel.

Learning Objectives

•

To recognize the place of rye within the range of cereal grains and to understand rye’s genetics, morphology, composition, and utilization.

Botanical Classification

Introduction Cereal rye (Secale cereale L.) is an annual grass plant that is typically fall-sown and cultivated worldwide. Historically, rye was a major food crop in eastern European countries in the Middle Ages due to its ample winter hardiness and lower soil moisture requirements compared to wheat. Rye grain is used mainly for feed and food and also for ethanol production. Cereal rye is also used as a winter cover crop because it grows quickly in the fall to produce ground cover that protects soil from erosion. Cultivated area and production worldwide have declined considerably in the past half century and currently stand at about 6 Mha and 15 Mt, respectively (2008–12 average). Rye is second after wheat for production of bread, and the grain contains the highest levels of fiber among all cereal crops. Rye is also used as a grazing or forage crop and for silage. The grain is also important in the production of mixed feeds for livestock and as feedstock for the distillation of rye whisky. Unprocessed straw is used in livestock feeds as low-digestibility roughage and as bedding in animal husbandry. Rye straw can also be used as a building material, for example, roof thatch and particle board, and for other applications.


Rye belongs to the grass family Poaceae (also called Gramineae) and the genus Secale. The most common cultivated species is S. cereale, which is presumed to have evolved from the wild perennial grass of the species S. montanum. Rye, along with evolutionarily related cereal grains barley and wheat, is botanically classified in the same tribe of Poaceae, that is, the Triticeae. Rye and wheat are placed in a separate botanical subtribe, called Triticinae, on the basis of the morphology of their inflorescences or spikes in which the grain forms after flowering. DNA studies have indicated that barley originated from a common ancestor before the divergence of wheat and rye. Cereal rye should not be confused with ryegrass that belongs to a different genus (Lolium) of the Poaceae family and is typically used for forage and production of turf.

Worldwide Production and Trade Worldwide production of rye grain has declined significantly over the past decade (Table 2), a trend that has continued for the past half century reflecting a declining area of harvested

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159

160 Table 1

THE CEREAL GRAINS | Rye Grain: Its Genetics, Production, and Utilization Rye production worldwide (in thousands of tonnes)

Country

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

Germany Poland Russian Federation Belarus Ukraine China Denmark Turkey Canada World total

2277 3172 4152 1151 624 709 169 240 327 14 610

3830 4281 2872 1397 1593 600 146 270 398 17 695

2794 3404 3628 1155 1054 554 132 270 330 15 165

2644 2622 2959 1072 584 350 130 271 383 12 650

2698 3126 3909 1305 563 700 135 241 252 15 174

3744 3449 4505 1492 1051 645 152 247 316 18 127

4329 3713 4333 1227 954 630 238 343 281 18 294

2903 2852 1636 735 465 570 255 366 232 11 963

2521 2601 2971 801 579 680 294 366 195 13 029

3893 2875 2132 1082 677 659 384 370 340 14 562

FAOSTAT data, 2014. Food and Agricultural Organization of the United Nations. Accessed via the web site www.fao.org.

Table 2

Worldwide grain production (in millions of tonnes)

Grain

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

Maize Rice Wheat Soybeans Barley Canola Sorghum Millet Rye

615.5 597.5 589.8 178.2 144.0 35.9 59.8 29.0 23.3

604.9 569.1 574.7 181.7 136.7 34.4 53.5 23.9 20.9

645.2 585.1 560.1 190.7 142.6 36.8 59.0 34.8 14.6

729.0 605.8 632.1 205.5 153.9 46.5 58.1 29.6 17.7

713.7 632.2 626.7 214.6 138.7 50.0 59.6 31.0 15.2

706.8 639.1 602.3 222.0 139.5 48.0 57.7 31.9 12.7

789.9 654.8 612.9 219.7 134.2 51.4 62.7 33.7 15.2

830.3 686.2 683.0 231.3 154.8 57.9 66.5 34.4 18.1

820.0 687.0 687.5 223.4 151.8 62.6 56.8 26.1 18.3

851.2 703.2 649.5 265.2 123.7 60.1 60.0 32.6 12.0

888.0 725.0 699.5 262.4 133.0 62.7 58.4 27.2 13.0

872.1 719.7 670.9 241.8 132.9 65.1 57.0 29.9 14.6


grain over this period. Rye production is significant in absolute terms but ranks last of eight grain species, including canola, grown for human food and/or animal feed (Table 2), the position it has occupied over the past five decades. The decline in harvested area and production of rye is mainly due to a decrease in demand for both food and feed and, undoubtedly, economic returns to farmers compared with those for other grains. Rye is grown in over 30 countries worldwide, and 9 of these (Germany, Poland, Russian Federation, Belarus, Ukraine, China, Denmark, Turkey, and Canada) are the main producers that together represent over 85% of world rye grain production (Table 1). The four leading countries, Germany, Poland, Russian Federation and Belarus, combined to produce close to 70% of world rye production in 2012 (Table 1). Most of the rye grain produced is used domestically. This is reflected in the low proportion of worldwide production that is traded internationally; that figure is approximately 13%. The majority of rye commerce (85%), considering both exports and imports, is handled by 12 countries (Table 3). Based on most recent international statistics, between 2009 and 2011, Poland, Germany, and Canada were the leading rye exporters that, when combined, supply 66% of the world market on average. In the same years, the major importers of rye were Germany, Netherlands, and the United States, which together accounted for 52% of total imports.

Plant and Grain Morphology The mature rye plant has a slender, tough, fibrous stem (straw), and elongated leaves. Plant heights vary widely from about 30 cm to over 2 m. The inflorescence (spike) is long and slender with stiff long awns (beards). The appearance of rye spikes at different stages of maturity is shown in Figure 1. The protruding anthers during flowering as shown in the figure tend to be a feature of cereal grain plants, like rye, which typically propagate by outcrossing. Rye grain (caryopsis) is arranged in pairs alternately on a zigzag-shaped rachis (Figure 2). The grain is covered with a lemma, a palea, and a glume (chaff), which is normally awned. At maturity, individual grains can be easily seen by bending the inflorescence (Figure 3). Like wheat, rye grain is free-threshing; the mature grain separates easily from the glume during threshing. Rye grains or kernels tend to be more slender and longer than wheat (Figure 4) ranging in length from 4.5 to 10 mm and in width from 1.5 to 3.5 mm. The grains are normally of grayishyellow color but the color can vary widely (Figure 4) depending on rye cultivar, region of cultivation, and harvesting conditions. As in wheat, a crease extends the full length of the ventral side of the grain. The surface of the grain is usually shriveled and has a rough texture. A single grain weighs about 20 mg. Rye grains comprise three distinct morphological parts (Figure 5). They are the starchy endosperm, bran (pericarp

THE CEREAL GRAINS | Rye Grain: Its Genetics, Production, and Utilization Table 3

161

Rye grain exports and imports by leading countries (in thousands of tonnes)

Exports

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Germany Canada Denmark Poland Russian Federation Sweden Imports Germany The United States The Netherlands Japan Poland Lithuania Finland

1001 85 136 0 0 83 2001 14 132 107 339 332 3 37

1003 58 140 2 49 44 2002 17 129 173 355 13 45 57

954 50 44 10 400 16 2003 79 94 147 406 84 47 21

1344 213 4 74 1 2 2004 20 162 246 288 16 13 53

1196 108 4 347 0 7 2005 145 124 249 282 3 23 80

1392 158 2 64 3 5 2006 101 142 121 272 18 18 89

584 246 3 59 129 26 2007 167 139 104 215 167 18 50

367 97 7 79 23 13 2008 198 144 153 59 54 3 69

465 100 16 592 8 16 2009 354 120 380 65 6 5 60

355 160 48 403 9 54 2010 322 120 211 121 5 24 44

225 200 105 103 85 42 2011 268 171 109 88 45 41 38


(a)

(b)

(c)

(d)

Figure 1 Rye inflorescence (spikes) at different stages of maturity. (a) Before flowering; (b) early-stage flowering; (c) late-stage flowering; (d) soft dough stage close to physiological maturity. Spikes (b) and (c) show anthers, which contain pollen, clearly protruding from the florets in which rye kernels will develop. Photo courtesy of Dr. Jamie Larsen, Agriculture and Agri-Food Canada, Lethbridge Research Station.

and testa or seed coat), and germ (embryo and scutellum). By weight proportions, these three parts of the kernel comprise 86.5%, 10%, and 3.5%, respectively. When rye grains are processed by milling, the bran and germ are typically separated from the endosperm, which is ground into flour.

Composition and Nutritional Properties of Rye Grain The composition of rye grain (Table 4) for the most part is typical of all cereal grains, with carbohydrate being the main

Figure 2 Rye inflorescence with two florets removed from zigzagshaped rachis, which is enlarged in the inset. Photo courtesy of Dr. Jamie Larsen, Agriculture and Agri-Food Canada, Lethbridge Research Station.

proximate constituent of the grain, which includes starch and nonstarch polysaccharides. Similar to all cereal grains, starch is the major carbohydrate component of rye. Like wheat and barley (but unlike other cereal grains), rye starch is stored in the endosperm in mainly two types of granules, large lenticular

THE CEREAL GRAINS | Rye Grain: Its Genetics, Production, and Utilization

162

Figure 3 Rye inflorescence approaching maturity with developing grains. Photo courtesy of Dr. Jamie Larsen, Agriculture and Agri-Food Canada, Lethbridge Research Station.

(a)

(b)

(c)

(d)

Figure 4 Kernels of wheat (a), blue rye (b), red rye (c), and white rye (d). Photo courtesy of Dr. Jamie Larsen, Agriculture and Agri-Food Canada, Lethbridge Research Station.

granules measuring about 35 mm and small spherical granules about 10 mm in diameter. In terms of thermal properties, that is, when starch suspensions in water are heated close to the boiling point and then cooled, rye starch has similar properties of gelatinization and retrogradation compared with those of wheat and barley starch. Interestingly, cereal chemistry research has shown that the starch fractions of rye, wheat, and barley are essentially interchangeable; that is, they have similar functionality in bread making. Rye grain contains more fiber than wheat and other cereal grains, and that fiber resides in tissue cell walls as both watersoluble and water-insoluble polymers. That fiber component along with its composition and related functional properties for health or processing properties for, for example, bread making are the principal distinguishing features of rye compared with other cereal grains. The main chemical component of rye fiber is a polysaccharide fraction that is often referred to as arabinoxylans and sometimes pentosans owing to its makeup of the five-carbon sugars, arabinose and xylose. Traditionally, this fraction was called hemicellulose, a term that is now infrequently used. Pentosans are the main distinguishing chemical component of rye compared with other cereal grains. On average, the pentosan content of whole grain rye is about 30% greater compared with that of wheat, while for the endosperm portion of the grain from which

refined flour derives, rye contains about twice the concentration of pentosans compared with wheat (Table 4). Pentosans contribute significantly to the functional properties of rye flour in bread making because of their high water-binding capacity and interaction with storage proteins, which prevents their aggregation into gluten required for the viscoelastic properties of bread doughs. The mineral and vitamin content and composition of rye are similar to those of other cereals (Table 4). Rye is considered a good source of B vitamins thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, and folate and an excellent source of a-tocopherol, the vitamin E isomer with the highest biological activity. These micronutrients are mostly removed during milling of flour, as the B vitamins are stored mainly in the aleurone layer of bran, while the vitamin E isomers are found in the germ. Rye has some advantages over wheat and other cereal grains in properties related to human nutrition and health. The higher dietary fiber content of rye in whole grain products is beneficial for laxation and has been shown in studies to be more effective than whole grain wheat in overall improvement of biomarkers of bowel health. Rye is also higher in lysine content to the extent that this amino acid is not the first limiting amino acid in rye as it is in other cereals. Tryptophan is considered the first limiting amino acid in rye. The stronger flavor and gummier texture of rye-baked products are well liked by many consumers. Rye grain also contains compounds that have antinutritional properties especially for monogastric animals where whole grain is used in feed in high proportion. The problematic constituents include soluble pentosans and b-glucans, which increase the viscosity of gastrointestinal contents that interferes with feed digestion, conversion efficiency, and growth rate and also causes sticky fecal droppings especially in poultry. These problems can be largely eliminated with the use of appropriate enzymes (e.g., b-glucanases and xylanases), which hydrolyze the fiber components. For swine and cattle, it is generally recommended that rye grain comprises no more than about 50% of the diet. Another issue with rye is that during flowering, florets are often infected by a parasitic fungus (Claviceps purpurea), which replaces the developing grain with elongated dark purple to black dense masses of mycelia, termed sclerotia, that protrude from the spikelets at maturity. Other cereal grains and grasses can also be infected with this fungus, but rye is most susceptible due to its open-pollination character that facilitates access of the fungus into the flowering head. This plant disease is called ergot, and the resulting ergot bodies contain many toxic alkaloid compounds, most notably ergotamine and ergonovine, which can cause serious health problems in livestock depending on amount consumed and continuity of feeding. Symptoms of acute ergot poisoning can include lameness and gangrene due to impaired blood circulation, abortions in pregnant animals, seizures, and death. Contaminated feeds with sublethal doses may still lead to problems of reduced feed intake, poor growth and performance, and loss of milk production in lactating animals. While sporadic cases of ergotism can occur in cattle, swine, and sheep, particularly in foraging animals, commercially prepared feed grain rations rarely contain ergot. Ergot is of little to no significance in human consumption of rye products due to the low tolerance of ergot


163

Crease Brush

Vascular bundle Central endosperm Prismatic endosperm Peripheral endosperm Aleurone cells 0.5 mm Scutellum Coleoptile

Cuticle

Plumule

Epidermis Hypodermis Thin walled cells Cross cells Testa Nucellar epidermis Aleurone cells

Rcot Sheath and cap Cell nucleus Starch granules

0.5 mm

Tube cells Peripheral endosperm

Storage protein

Prismatic endosperm

Cell wall

(a)

100 µm

(b)

Pericarp

Figure 5 Diagrammatic view of rye grain in (a) longitudinal section and (b) transverse midsection. Reproduced with permission from Simmonds, D.H., Campbell, W.P., 1976. Morphology and chemistry of the rye grain. In: Bushuk, W. (Ed.), Rye: Production, Chemistry, and Technology, first ed. American Association of Cereal Chemists, St. Paul, MN, pp. 63–110.

sclerotia in commercial handling and grading of rye, removal of ergot bodies along with other foreign material by modern cleaning equipment prior to milling of rye grain, and the substantial inactivation of alkaloids that occurs during baking.

Genetics, Plant Breeding, and Agronomy Essentially, all of the commercial cereal rye grown is the diploid S. cereale type. Cultivated rye contains seven pairs of chromosomes belonging to a single genome designated by the letter ‘R.’ Accordingly, diploid rye has the genome makeup ‘RR.’ This basic genomic composition of rye is similar to that that exists in the genetically related cereal grains, wheat, and barley, which are all botanically classified in the same tribe of the Poaceae family, that is, the Triticeae. Like rye, barley is also

a diploid and has seven pairs of chromosomes in its genome. Wheat is more complex as it has a polyploidy makeup comprising either two or three basic sets of seven pairs of chromosomes, which provide a much larger genetic framework for plant breeding aimed at improving adaptation and agronomic performance, protein content, and other grain composition components and end-use properties. With this goal in mind, there have been attempts to develop tetraploid rye by doubling the number of chromosomes with the chemical colchicine, which inhibits cell division. While tetraploidy has been achieved in rye, results have been mixed in terms of practical outcomes, and little progress has been made beyond the experimental stage. Rye, unlike most other cereal grains, is considered to be an allogamous breeding plant; that is, it cross pollinates naturally and extensively with other rye plants. Therefore, it is difficult to

164 Table 4

THE CEREAL GRAINS | Rye Grain: Its Genetics, Production, and Utilization Chemical and nutrient composition of rye compared with other cereal grainsa,b

Kernel weight, mg Protein, % Lysine, % of total protein Ash, % Lipid, % Carbohydrate, % Starch Fiber Pentosan (whole grain) Pentosan (endosperm) b-Glucan (whole grain) b-Glucan (endosperm) Free or reducing sugars Minerals, mg per 100 g Phosphorus Potassium Calcium Magnesium Iron Copper Manganese Zinc Vitamins, mg per 100 g Thiamin Riboflavin Niacin Pantothenic acid Pyridoxine Folate a-Tocopherol

Rye

Wheat

Pearled or hulless barley

Oat groats or oatmeal

Brown rice

Corn

15–33 10–15 3.5–4.5 1.6–2.1 2–3

25–45 9–16 2.7–2.9 1.8 2–3

40 10.6–16 2.6 1.2–1.8 1.6–2.4

20–27 15.3 3.7 2.0 8.7

25–29 8.2–9.6 3.7 1.6 3.2

250–500 9–13 2–6 1.4–2.1 4.3–8.4

58–64 15–17 6.6–9.6 3.6–4.2 2.0–2.6 1.5–2.0 1.3

63–72 10–13 4.3–6.6 1.4–2.5 0.6–0.8 0.2–0.4 2.0

50–64 8.0 1.2–4.7 n/a 3.6–5.9 n/ac n/a

54.9–55.8 11–13 2.0 n/a 4.4–6.3 n/a n/a

77 3.5 1.4–2.4 n/a 0.11 n/a 0.8–1.5

61–78 9.5 5.8–6.7 n/a 0.3 n/a 1–3

359–422 387–520 31–70 92–130 2.7–10 0.5–0.9 2.0–7.5 3.4–3.9

150–540 290–620 5–122 90–290 2.8–4.2 0.4–2.4 0.5–26 1.9–10

270 319 27 89 3.0 0.43 1.3 2.3

502 425 59 158 4.7 0.48 4.5 3.7

344 281 25. 145 1.8 0.64 3.4 2.2

290 370 30 140 3.0 0.4 0.5 1.4

0.46 0.18–0.29 1.5 1.0 0.34 0.052 1.12–1.20

0.5–1.0 0.13–0.31 4.8–6.4 0.77–0.91 0.33–0.47 0.056 0.50–1.18

0.26 0.09 5.0 0.35 0.32 0.019 0.34

0.80 0.14 0.96 1.34 0.24 0.06 0.94–1.81

0.54 0.08 5.58 1.54 0.68 0.34 0.13–0.80

0.38 0.14 2.8 0.66 0.53 0.03 0.98–2.11

Dry basis, single value ¼ typical value. Various sources in the cereal chemistry literature were used to compile the data in this table. c Value not available. a

b

maintain genetic purity in conventional rye populations. Owing to the close botanical and, in essence, genetic relationship between wheat and rye, their cross fertilization can be achieved relatively easily. This is the basis for the man-made development of the rye–wheat hybrid grain called triticale. Like rye, triticale sees modest production levels worldwide but is a significant grain for food and feed uses. Most of cultivated rye is a fall-sown annual crop called ‘winter rye’ although spring rye is grown in some countries, such as Canada. Rye has excellent winter hardiness and therefore can be grown in areas where the climate is too severe for winter wheat. Another distinct feature of rye that contributes to its robust agronomic performance is its drought tolerance, which is considered to be the best among all cereal grains and is explained by its ability to produce an extensive root system. Rye has been used extensively as a source of disease resistance in wheat breeding programs. The disease-resistant genes are incorporated through a translocation of 1R chromosome into 1A or 1B chromosome of wheat. Many commercial wheat varieties contain one of these two translocations. Rye breeding efforts, whether for conventional or hybrid rye, are typically focused on improving grain yield as the most important objective. Other yield-related objectives include improving resistance to drought and nutrient stress, shortness

of straw and lodging resistance, and disease resistance (snow mold, mildew, leaf rust, Fusarium head blight, and ergot). Improving end-use quality of rye grain for baking is another goal of breeding efforts. The main quality characteristic that continues to be a detriment in rye processing is its tendency to sprout in the head under wet harvest conditions. In contrast to wheat, rye grain developing to maturity on the plant has relatively low dormancy, which leads to preharvest sprouting. The latter results in substantially increasing levels of the starchhydrolyzing enzyme, a-amylase, which transfers into flour causing very sticky doughs that are difficult to handle in commercial bread making. The most significant aspect of rye breeding to date has been the development of commercial hybrid rye varieties with considerably enhanced grain yields, up to 15–20% higher on average, compared with the best conventional open-pollinated counterparts. Indeed, impressive grain yields of hybrid rye of over 11 tonnes per hectare have been reported. In Germany, where hybrid rye research originated in the 1970s, hybrid rye varieties today comprise 70% or more of total acreage. Hybrid breeding that is much more complex than conventional population breeding exploits the heterosis effect, that is, enhanced vigor, when two carefully selected genetically uniform but divergent inbred parents are crossed by controlled pollination

THE CEREAL GRAINS | Rye Grain: Its Genetics, Production, and Utilization to obtain fertile hybrid seed. Apart from the grain yield advantage to producers growing hybrid rye, the breeder benefits by being the exclusive commercial source of that seed and through royalties.

Primary Processing of Rye Grain Agricultural products, including grains, vary in composition and processing quality caused by fluctuations in abiotic (e.g., weather) and biotic (pests) factors during the growing season. To facilitate marketing and processing, the grain is graded, separated, or combined into parcels of relatively uniform properties. In countries where rye grades exist, they are based on physical characteristics of the grain and on the presence of foreign contaminants. Test weight, a measure of bulk density related to milling quality, is the only grading factor that is measured objectively. All other factors are assessed subjectively by visual inspection. Normal or straight grades usually have a prescribed maximum moisture content, for example, 14% in Canada and the United States. The number of grades of milling rye varies among countries. Germany has one grade, whereas Canada has three, and the United States has four grades. In transforming rye grain into food for human consumption, the primary processing step is milling the grain into flour, which basically involves two multistep processing operations, that is, a break and reduction systems. The break system breaks open the grain using corrugated rolls to separate bran from endosperm and involves some additional grinding of endosperm into flour, while the reduction system basically involves reducing to flour, the so-called middling particles of more or less pure endosperm. Despite some significant differences between the physical structure of rye and that of wheat, the milling processes for the two grains are similar. The first step is the removal of all undesirable contaminants. This is achieved by a series of special cleaning machines functioning consecutively. Differences in shape, size, and density are all used to improve the efficiency of the cleaning. The final step of the cleaning section is tempering that involves addition of water to toughen the bran and mellow the endosperm to facilitate their separation. Moisture levels for tempering rye are usually in the range 14.5–15.5% depending on kernel texture, and this range is about 1% lower than that used for hard spring wheat, as rye Table 5

grain is softer. For the same reason, the tempering time for rye is shorter, typically 6–15 h compared with 16–24 h for hard spring wheat. Because of its softer texture, rye endosperm releases a high proportion of its weight as flour during the break operations. Reduction is achieved by corrugated rolls instead of the smooth rolls used in wheat milling, as smooth reduction rolls tend to flake rye flour, which minimizes proper flour generation. Rye milling requires a larger sifting area than that for hard wheat types because rye flour particles tend to clump together because of its finer particle size distribution arising from the softer endosperm texture. Rye mills produce a number of different grades of flour by systematic blending of product streams to produce flours containing different proportions of endosperm and bran. In North America, usually three flour grades are distinguished based on degree of refinement (Table 5), which can be evaluated based on ash or mineral content, fiber content, or flour color. A relatively refined flour such as white or light rye will contain mostly endosperm, and as the ash (and fiber along with protein) content of endosperm is lower than that for bran, this explains why light rye flour has lower ash (and protein) compared with medium and dark rye flour (Table 5). There is no standard of identity of North American flours compared with the situation that exists in Europe and Germany in particular where rye milling and baking considerations are more precise. A modern German rye mill will produce as many as seven different flours designated by ash content and several types of meals processed by crushing and cutting over a range of particle size (Table 6). Regardless of where rye is milled, the main quality parameter for flour is ash content, which has a close relationship to flour extraction, that is, the proportion of the whole grain that is blended into flour. Ash content in turn has a close correspondence with flour color; that is, the higher the ash content, the darker the flour (Table 5).

Rye for Bread Making Bread and other baked products are the main foods produced from rye. Many types of baked products are made including bread from 100% rye flour or whole meal; rye–wheat bread containing at least 50% rye; wheat–rye bread containing at least 50% wheat and at least 10% rye, rye bread, rye rolls,

Rye flour grades in North America

Flour grade The United States White rye Medium rye Dark rye Rye meal (various granulations) Canada Light rye Medium rye Dark rye a

Extractiona

Ash (%)

Protein (%)b

80% of straight grade rye flour, 65% extraction Straight grade (SG), for example, 83% Clears (flour removed from SG to produce white rye flour) 100%, that is, whole grain product

0.6–0.7 1.0–1.5 2.5–3.0 1.8

7–9 10–13 14–16 10–15

75–80% 83–85% 92–95%

0.7–0.9 1.0–1.2 1.3–1.8

– – –

Extraction refers to weight percentage of whole grain milled to flour. Typical values. Adapted from Bushuk, W. (Ed.), 2001. Rye: Production, Chemistry and Technology, second ed. AACC International, St. Paul, MN, 144 pp. b

165

166


Table 6

General Uses of Rye

Rye flour grades in Germany a

Flour grade

Extraction (%)

Ash content (%, dry basis)

815 997 1150 1370 1740 1800 (meal) Whole-kernel flour

78–82 82–86 85 90

0.90 0.91–1.10 1.11–1.30 1.31–1.60 1.61–1.80 >1.80

95–100 100

a

The grade number is based on the ash content. 815 indicates a flour with an ash content of 0.815%. Adapted from Bushuk, W. (Ed.), 2001. Rye: Production, Chemistry and Technology, second ed. AACC International, St. Paul, MN, 144 pp.

crisp bread, and pumpernickel; and other dark rye breads made by a sourdough process that involves the use of acidforming bacteria and sourdough yeasts. Accordingly, rye breads vary in color, flavor, and texture in keeping with rye flour grade and the blended proportion of wheat flour and other ingredients that may be used in the dough formula besides the obligatory water, yeast, and salt. Those other ingredients include shortening, sugar, molasses, caramel color, buttermilk, lactic and acetic acid sours, and caraway seeds. The distinct taste and aroma of rye breads, particularly of the darker and heavier types, derive from Lactobacillus fermentation of rye flour dough, which produces lactic and acetic acids, among other organic acids. The proportions of rye and wheat flour used in the bread making formula depend on the density of the bread and intensity of flavor desired by the baker. A higher proportion of rye flour will produce bread of lower volume and more intense flavor. The reason for this is mainly attributable to the different composition and balance of rye endosperm proteins compared with those found in wheat, particularly in the polymeric protein fraction, which is called glutelin in rye. Unlike wheat proteins, rye proteins cannot form viscoelastic gluten when the flour is mixed with water to produce dough. It may also be the case that the high pentosan content of rye flour, and the propensity of pentosans to bind water, could be interfering with the normal gluten-forming process as occurs in wheat flour doughs. Regardless of the cause, rye flour doughs are completely inelastic, tend to be sticky, and cannot be stretched and formed like wheat flour doughs. This makes the machinability and processing of rye doughs more challenging compared with those of wheat. Also, rye doughs are capable of very little carbon dioxide gas retention due to the leavening action of yeast and bacterial fermentation in the case of sour doughs, resulting in low-volume bread with a coarse crumb. Where gluten proteins in wheat are primarily responsible for gas retention and loaf volume, in rye doughs, it is the pentosan component and the viscosity this fraction contributes when hydrated that is likely the principal mechanism of gas retention. For all these reasons, unlike the situation in wheat where protein content is valued as one of the most important quality factors, the protein content of rye flour is largely irrelevant for bread making. Hence, when rye breads of lighter texture and color are sought by consumers, there is a need to include an appropriate measure of wheat flour and therefore glutenforming proteins in the formulation.

Worldwide, over 50% of rye grain is used for incorporation into livestock feed. The key factors for this application are price relative to other feed grains such as corn and barley, energy per unit weight, and absence of toxicants. As noted in the preceding text, the principal potential toxicant stems from ergot infection. Ergot bodies must be removed or minimized by cleaning. For rye to be used successfully as a feed grain, consideration needs to be given to its relatively high level of pentosan content. Monogastrics and younger animals in general tolerate this fiber component less so than ruminant animals, and generally, no more than about 30% of the feed should contain rye for this reason. Technology has been developed in the use of enzymes and other additives to mitigate the effects of the antinutrients such as the soluble pentosans. Rye grain imports by some countries, for example, Japan and South Korea, are based almost entirely on the livestockfeed industry. For some other countries, such as Finland, rye grain is mainly used for bread making. Worldwide, small quantity of rye is used in nonfeed and nonfood industries. Traditionally, rye straw is used on the farm as livestock bedding. In Canada and the United States, rye is fermented and distilled to give alcohol that is used as a rye whiskey beverage. Rye flour is used as an adhesive in the production of wallpaper, corrugated packaging materials, and plywood. The capacity of the rye plant to produce a large quantity of biomass on lowfertility soil has not been exploited by the biomass energy industry. The pentosan component of rye is used to make furfural, as starting material for many industrial chemicals. Rye plant has been reported as a significant component of a sustainable system of agriculture, for example, as a cover crop, but its use in this way remains to be exploited. For additional information on rye, the reader is referred to the monographs ‘Rye: Production, Chemistry and Technology (2001)’ and the recently published ‘Rye: Genetics, Breeding and Cultivation (2014).’ Other suggestions for further reading on rye and relevant websites are provided in the succeeding text.


• • • • •

Trace the origins and history of rye as a crop and as a food. What reasons may be given for the gradual decline of rye production worldwide? How might hybrid rye reverse that decline? Contrast the positive and negative aspects of using rye grain for – human food, – animal feed. Describe the taxonomic and genetic relationships of rye to other cereal species. Why is it difficult to retain genetic purity in rye?


•

How does rye differ from other grain species with respect to its genetics, disease risks, grain composition, and utilization? List the advantages offered by rye. What disadvantages


• •

would need to be altered to promote rye? How might breeding assist? Investigate the advantages offered by F1 hybrid vigor for other grain species (e.g., maize). What advantages could be expected for hybrid rye? Taking pumpernickel (or another rye-based food) as an example, devise a marketing strategy to increase the food use of rye, based on nutritional advantages, product appearance, fashion, trendiness, international culture, or any other perceived advantages.

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Contaminants of Grain; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Grains Around the World: Grain Production and Consumption: Europe; Grain Production and Consumption: Africa; The Basics: Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Triticale: Overview; Wheat-Based Foods: Breads.

167

Further Reading Bushuk W (ed.) (2001) Rye: Production, Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Gorton, L.A. (2009). Formulating. In: (Editors: Pyler, E.J. and Gorton, L.A.) 4th edition. Baking Science and Technology Volume II. Sosland Publishing, Kansas City, MO, pp. 212–220. Schlegel Rolf HJ (2014) Rye: Genetics, Breeding and Cultivation. Boca Raton, FL: CRC Press. Simmonds DH and Campbell WP (1976) Morphology and chemistry of the rye grain. In: Bushuk W (ed.) Rye: Production, Chemistry, and Technology, first ed., pp. 63–110. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW (2010) Rye and triticale: characteristics and quality requirements. In: Wrigley CW and Batey IL (eds.) Cereal Grains: Assessing and Managing Qualitypp. 112–140. Boca Raton, FL: CRC Press.

Relevant Websites http://www.gipsa.usda.gov/publications/pub_fgis.html – Grain Inspection Handbook. Book II. Rye (2013). http://www.grainscanada.gc.ca/oggg-gocg/ggg-gcg-eng.htm – Canadian Grain Commission Official Grain Grading Guide. Chapter 5. Rye (2014). http://faostat3.fao.org – FAOSTAT Data Base, Food and Agricultural Organization of the United Nations (2014).

Triticale: Overview BJ Furman, San Jose State University, San Jose, CA, USA ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp 298–303, ã 2004, Elsevier Ltd.

Topic Highlights

• • •

Triticale is a man-made crop derived from hybridization of wheat and rye. Triticale has desirable agronomic traits including high yield, and resistance to biotic and abiotic stresses. Most triticale is used for animal, use of triticale flour has been limited by quality issues, although there are opportunities in new product development.

Learning Objectives

• • •

To understand the origin and development of triticale and the underlying genetics behind this new crop development. To understand where and why triticale is produced, and its agronomic advantages and limitations. To understand the basics of triticale processing and utilization, especially in relation to protein quality.

Introduction Triticale is the first man-made cereal grain crop species resulting from the hybridization of wheat (Triticum) with rye (Secale), the name of which combines the scientific names of the two genera involved. This synthetic amphiploid is obtained by chromosomal doubling after artificial crossing to produce fertile hybrids. It is a small-seeded cereal grain that is used for both human consumption and livestock feed. As a hybrid species, it combines many of the better qualities of both of its parents. Triticale possesses wheat’s properties for food production and rye’s adaptive properties, and under certain conditions can out-yield both parents. This promising crop species is grown on more than 3 million hectares (Mha) worldwide. Furthermore, triticale is an important germplasm source for wheat improvement, providing a vehicle to transfer desirable rye characteristics to wheat.

Origin and Types The Scottish scientist Alexander Stephen Wilson produced the first triticale in 1876. Triticale was initially developed to combine the positive traits of both parent types: the vigor and winter hardiness as well as the higher protein content of rye combined with the higher-quality gluten and baking properties of wheat. However, initial progress was limited by the fact that resulting hybrid progeny was sterile. In the 1930s, the discovery and use of the chemical colchicine, a natural chemical

168

extracted from the autumn crocus plant to create chromosome “doubling,” overcame this sterility problem. In 1938, Arne Mu¨ntzing from Sweden applied colchicine to wheat/rye hybrids, obtaining fertile plants. Once a fertile hybrid was established, it became possible to utilize modern plantbreeding methodologies. Early varieties were primitive and had numerous agronomic disadvantages such as low grain yield, poor seed set, shriveled grain, excessive height, low germination, and late maturity. Triticale improvement commenced in the 1960s to create new and better combinations between wheat and rye, triticale and triticale, and triticale and wheat. Most notable were breeding programs at the International Center for Maize and Wheat Improvement (CIMMYT) in Mexico and the University of California at Davis (UCD) for spring triticales and programs in Poland and the University of Manitoba, Canada for winter varieties. There are two main types of cultivated triticales: octoploid types produced from the hybridization of bread wheat, Triticum aestivum L., with rye, Secale cereale L., and hexaploid types using durum wheat, T. turgidum L., followed by chromosome doubling of the hybrid plant (Figure 1). Octoploid triticales (2n ¼ 56) contain the A, B, and D genomes of bread wheat and the R genome of rye, while the hexaploid triticales (2n ¼ 42) contain the A and B genomes of durum wheat and the R genome of rye. However, most triticale cultivars are hexaploids. There is a third type of triticale (2n ¼ 28) produced from the hybridization of diploid wheat, T. monococcum (2n ¼ 14) with rye, but is not considered to be important economically. Although triticale is a cross between wheat and rye, it is selfpollinating (similar to wheat) rather than cross-pollinating (like rye). Most agronomically desirable triticales that breed true have resulted from several cycles of improvement, and are primarily from the durum–rye crosses with some common wheat parentage occasionally involved. In general, triticales can be divided into three groups (Table 1): 1. “Primary triticales” are the initial product of the wheat rye hybridization followed by doubling of chromosome numbers to produce the hexaploid or octoploid types. 2. “Secondary triticales” are produced by intercrossing primary triticales or by crossing a primary triticale with wheat. 3. “Substituted secondary triticales” are hexaploid with A, B, or D genomes of wheat substituted for one or more R genome chromosomes of rye. Primary triticales are often found to be fragile, poor producers, and genetically unstable. They are used as breeding stock to produce the more stable and agronomically favorable secondary and substituted secondary triticales. Secondary triticales can be either hexaploid or octoploid and often contain complete genomes of wheat and rye, whereas substituted triticales


http://dx.doi.org/10.1016/B978-0-12-394437-5.00019-X

THE CEREAL GRAINS | Triticale: Overview

Bread wheat Rye (Triticum aestivum) × (Secale cereale ) 2n = 42, AABBDD 2n = 14, RR (female) (male)

Table 1 Development and examples of primary, secondary, and substituted triticales Primary triticalea Common wheat X Triticum aestivum L. AABBDD (2n ¼ 42)

Rye Secale cereale L. RR (2n ¼ 14)

Octoploid triticale !

AABBDDRR (2n ¼ 56) Hexaploid triticale

!

AABBRR (2n ¼ 42) Tetraploid triticale AARR (2n ¼ 28)

n = 28, ABDR Embryo culture Seedling treated with colchicines to double chromosome number Figure 1 Flow diagram for octoploid triticale development showing chromosome number and genome identifications. The hexaploid type (2n ¼ 42) is produced similarly, though using durum wheat (T. turgidum, 2n¼ 28, AABB) as the female parent. (Adapted with permission from Qualset CO (2002). Triticale. In: McGraw Hill Encyclopedia of Science and Technology, 9th edn. The McGraw-Hill Companies, Inc.)

never have complete rye genomes (Table 1). One advantage of the secondary hexaploid triticale is increased genomic diversity, resulting from the insertion of portions of the D genome from the hexaploid wheats. Spike type is often used as a visual morphological marker to distinguish types. Octoploid triticale spikes appear similar to wheat spikes, whereas hexaploid triticales have more distinctive spike types (Figure 2), and are classified as Beagle (for complete triticales) and Armadillo (for substituted triticales).

169

Durum wheatX T. turgidum L. AABB (2n ¼ 28) Einkorn wheatX T. monococcum L. Secondary triticaleb Triticale X AABBDDRR AABBDDRR AABBRR Triticale X AABBDDRR or AABBRR AABBDDRR or AABBRR AABBDDRR or AABBRR Substituted triticalec A7A7B7B7D2D2R3R3 A6A6B6B6D6D6R3R3 A7A7B6B6D7D7R1R1

Rye Secale cereale L. RR (2n ¼ 14) Rye Secale cereale L. Triticale AABBDD AABBRR AABBRR Wheat AABBDD

!

! ! !

AABBDDRR AABBDDRR or AABBRR AABBRR

AABB AA

a

Colchicine treatment is given to hybrid plants to double chromosome number. Products of these hybrids have variable chromosome constitutions. c Examples with 2n ¼ 42. Subscripts indicate the number of chromosomes present from each genome. Adapted from Qualset CO, EA Rupert, and JD Prato (1973) Triticale in California: Review of current research and appraisal as a new cereal crop. In: Yang SP (ed.) Proceedings of the International Triticale Symposium. Lubbock, TX: International Center for Arid and Semi-Arid Land Studies. b

Adaptation and Production Triticale is grown using cultural practices similar to wheat and rye. However under some conditions, earlier planting can result in better yields. It works well planted alone, as a companion crop for establishing alfalfa and for interseeding into established alfalfa, and as a double crop with corn and other summer annuals. There are both spring and winter growth habits depending on the parents used in the cross, with environmental requirements similar to other winter and spring sown cereal grains. Drought tolerance is the primary advantage that spring triticales have over other spring cereal crops. Winter triticale provides a high-yielding early maturing alternative to spring triticale for short-season areas. The University of Manitoba began the first intensive program in North America in 1953, working mostly with durum wheat–rye crosses. Since then, triticale has been the subject of modern plant breeding efforts for and has resulted in excellent gains in yield and quality. Triticale most closely resembles its wheat parent but exhibits more vigorous growth characteristics. As a hybrid species, it contains many of the better traits from each parent (Table 2). Triticale can combine the bread-making qualities of wheat with much of rye’s adaptive properties such as disease resistances, drought tolerance, and adaptability to harsh soil conditions. As a result, varieties have been produced with a wide adaptive range as well as site-specific adaptation. Triticale

Figure 2 Spike types representing substituted (left, Armadillo) and complete (right, Beagle) forms of triticale.

170 Table 2

THE CEREAL GRAINS | Triticale: Overview Desirable characteristics of wheat, rye, and triticalea

Table 3

World triticale production, 2002

Wheat

Rye

Triticale

Country

Growth typea

Area (ha)

% World

High-yield potential Large, filled grain High harvest index Tillering efficiency Short straw Sprouting resistance High-energy grain

Many grains per ear High biomass Low-temperature growth Winter hardiness Drought tolerance Disease resistance Grain high in lysine

High yield High-quality straw High feed value Disease resistant Stress tolerant Winter hardiness High lysine content

China Poland Germany France Australia Hungary Belarus Czech Republic Canada Denmark Austria Sweden Spain Portugal Lithuania Slovakia Latvia United Kingdom Switzerland Belgium United States Estonia Netherlands Luxembourg Norway Tunisia Mexico Algeria World

SþW W W SþW S W W W SþW W W W S S W W W W W W SþW W W W W S S S

500 000 920 523 560 466 269 000 264 000 132 000 94 200 53 093 47 282 37 657 37 621 30 740 29 900 25 000 20 000 18 372 15 500 14 000 13 500 12 000 8979 6847 4618 4000 1000 1000 850 3 3 122 151

16.1 29.7 18.1 8.7 8.5 4.3 3.0 1.7 1.5 1.2 1.2 1.0 1.0 0.8 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.2 0.1 0.1 0.03 0.03 0.03 0.0001 100

a

Modified from Semundo Limited (1994) Triticale The Hybrid Evolution. Cambridge: Semundo Limited.

does well in regions where wheat performs poorly, such as cold and infertile soils, extremely sandy soils, soils with high levels of boron, salty soils, acidic soils, manganese-deficient soils, and dry soils. One particular concern, however, is the presence of ergot infection (caused by the fungus Claviceps purpurea) in some areas. The first commercial triticale cultivars were released in 1969. Today triticale is becoming a crop in its own right and is grown on over 3 Mha worldwide and in at least 27 countries (Table 3). This crop contributes more than 10 Mt year1 to global cereal production. Since its introduction, the area harvested has increased over 7 times and amount harvested has increased over 18 times (Figure 3). Although it is grown throughout the globe, the countries that produce the most triticale are China, Poland, and Germany. There is also significant production in Canada and United States.

Usage Use of triticale for human consumption has not yet become widespread. Although triticale flour and products are available commercially (namely in specialty markets such as health food stores), this availability is limited. It comes in several forms including whole berry, flakes, and flour. Whole triticale can be cooked and used in a variety of dishes. Quality evaluations have shown triticale grain inferior to wheat for milling and baking, making large-scale commercial baking not feasible. Triticale flour is low in gluten, and bread made from it alone is heavy. For that reason, it is usually combined half-and-half with wheat flour. If mixed with wheat or rye flour, triticale flour can be used to make a number of breads and pastries. In developing countries, triticale flour is often mixed with wheat flour during wheat shortages. It is of course important that the crop is not infected with ergot, as this is highly toxic to humans. Most triticale production is used for animal feed. It offers better amino acid balance, lysine content, and higher protein, particularly important for swine and poultry. However, triticale has lower energy content than other grains, and feeding of triticale must be supplemented with other grains. It can also be used as forage, silage, or hay for ruminants, offering high digestibility and out-yielding traditional crops in dry soils.

a

S: spring type; W: winter type. Sources: United Nations FAOSTATS, Statistics Canada, and United States Census of Agriculture.

Care should also be taken to insure that the crop is not infected with ergot. Alternative uses of triticale include use as a cover crop to prevent soil erosion and land reclamation. Triticale has also been used in limited amounts as raw material in bioethanol production. Ethanol plants pay a premium for triticale over barley, since it has more starch and no hull, making alcohol production more efficient.

Genetic Resources As a synthesized species, triticale has no wild ancestors and there are no existing landrace varieties. In addition, the actual wheat and rye parents used in triticale synthesis are often either unknown or no longer available. It is therefore often not possible to resynthesize unique triticale genotypes through hybridization. Genetic resources for the development and enhancement of triticale include existing triticales, wheat and rye, and the ancestral species of both wheat and rye. Itself, triticale exists as a genetic resource for the improvement of wheat, providing a vehicle to transfer desirable characteristics from rye.


171

20 000 000 production (Mt) area (ha)

10 000 000

8 000 000

6 000 000

4 000 000

2 000 000

76 19 78 19 80 19 82 19 84 19 86 19 88 19 90 19 92 19 94 19 96 19 98 20 00 20 02

74

19

19

19

72

0

Figure 3 World production (Mt) and area (ha) trends since the 1970s. (Source: United Nations FAOSTAT.)

In order to insure continued improvement in triticale, it is important to maintain a comprehensive genetic resource collection. CIMMYT has established a world gene bank for triticale and has over 15 000 accessions. The North American triticale genetic resource collection was evaluated at the UCD and showed a great deal of variation in both qualitative and quantitative traits. The collection is now maintained at the USDA Small Grains Collection in Aberdeen, ID, and at CIMMYT in Mexico.

Future Prospects Triticale production has increased tremendously since the 1970s and genetic improvements have been vast. It can only be expected that improvements will continue, especially with the tools provided by biotechnology. In vitro regeneration of plants will allow for successful genetic transformation. Genomic maps for wheat and rye have been completed and will provide invaluable assistance for marker-aided selection. Although used primarily for animal culture, it holds promise on a number of additional levels. Perhaps one of triticale’s greatest potential is as a vehicle for gene exchange for wheat improvement, extending wheat’s gene pool. It, however, still holds promise to be a leading food crop in some areas of the world. Continual improvements are being made to increase triticale’s grain quality for commercial production. There is a great deal of potential for triticale products in the specialty markets, especially in the west where a healthier and more varied diet is becoming increasingly popular and commercialized. Triticale also has potential for increasing global food production in developing countries. It grows in many areas unsuitable for wheat production and can out-yield wheat in certain areas. Already used in many of these countries to some degree, increased production for food would likely find a market, especially in areas where wheat shortages are prevalent. Triticale may also play an ecological role in the future, both for soil reclamation and biogas usage.


• •

Draw up a comparative table on the genetics, production, and utilization of wheat, rye, triticale, and barley. For any selected wheat flour based product, investigate the likely effects of full or partial substitution with triticale flour.


• •

What contributions are being made to triticale improvement through modern genomic information resources? What are current markets and demand for triticale? What are likely future trends?

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Genetics of Grains: Wheat Genetics; Non-food Products from Grains: Cereal Grains as Animal Feed; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: Rye Grain: Its Genetics, Production, and Utilization.

Further Reading Darvey NL, Naeem H, and Gustafson JP (1991) Triticale: Production and utilization. In: Kulp K and Ponte JG Jr. (eds.) Handbook of Cereal Science and Technology New York: Marcel Dekker. Forsberg RA (ed.) (1985) Triticale CSSA Special Publication Number 9. Madison, WI: Crop Science Society of America. Furman BJ, Qualset CO, Skovmand B, Heaton JH, Corke H, and Wesenberg DM (1997) Characterization and analysis of North American triticale genetic resources. Crop Science 37: 1951–1959. Guedes-Pinto H, Darvey N, and Carnde VP (eds.) (1996) Triticale: Today and Tomorrow Boston, MA: Kluwer Academic. Gupta PK and Priyadarshan PM (1982) Triticale: Present status and future prospects. Advances in Genetics 21: 255–345.

172


International Board for Plant Genetic Resources (1985) Descriptors for rye and triticale. Rome: IBPGR Secretariat. Limited Semundo (1994) Triticale The Hybrid Evolution. Cambridge: Semundo Limited. Lorenz K (1974) The history, development, and utilization of Triticale. Critical Reviews in Food Technology 5(2): 175–280. MacIntyre R and Campbell M (eds.) (1973) Triticale Proceedings of an International Symposium Ottawa, Canada: International Development Research Center. Muntzing A (1979) Triticale Results and Problems. Berlin, Germany: Verlag Parl Parey. National Research Council (1989) Triticale: A Promising Addition to the World’s Cereal Grains. Washington, DC: National Academy Press.

Qualset CO (2002) Triticale, McGraw Hill Encyclopedia of Science and Technology, 9th edn. The McGraw-Hill Companies, Inc. Qualset CO, Rupert EA, and Prato JD (1973) Triticale in California: Review of current research and appraisal as a new cereal crop. In: Yang SP (ed.) Proceedings of the International Triticale Symposium Lubbock, Texas: International Center for Arid and Semi-Arid Land Studies. Tsen CC (ed.) (1974) Triticale: First Man-Made Cereal. St. Paul, MN: American Association of Cereal Chemists. Yang SP (ed.) (1973) Proceedings of the International Triticale Symposium Lubbock, TX: International Center for Arid and Semi-Arid Land Studies.

Oats: Overview PK Zwer, South Australian Research and Development Institute (SARDI), Urrbrae, SA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

The history of oat including speciation, domestication, and early cultivation Oat plant growth and morphology Growing oat including agronomy, soil factors, and climate Growing oat – diseases and pests Processing oat Using oat for feed, human consumption, industrial, nonfood, and fodder end uses Breeding improved oat varieties

Learning Objectives

• • • • • •

To become familiar with the development of oat as a cultivated crop To gain general knowledge of the morphological parts of an oat plant and developmental stages To learn production constraints such as agronomy, diseases, and pests To understand basic processing of oat for human consumption To become familiar with the many uses of oat grain and fodder To know the basic knowledge of oat variety improvement, breeding systems, and new breeding technology

Introduction Oat has played a significant role in farming systems from domestication to the present due to the versatile uses of the grain and plant (Figure 1). Oat currently ranks seventh in world production of cereals after maize, rice, wheat, barley, sorghum, and millet. World oat production exceeded rye and triticale. Oat is primarily grown in cool temperate climates with 67% of world production occurring in the northern hemisphere. The Russian Federation, Canada, Poland, Finland, Australia, and Finland were ranked as the top six countries for world oat production. Oat is also grown in the southern hemisphere with Australia ranked first in production while Argentina, Chile, and Brazil are also significant producers. There are two types of oats – husked oat, with hulls surrounding the kernel or groat after harvest, and naked oat, where the hull is removed when the crop is harvested. Naked oat has the free threshing character similar to wheat. Husked oats represent the majority of global oat production except in China where naked oat is the most common type. Naked oat is gaining prominence for specialist markets as improved varieties are being developed.


Oat is used for animal feed, human consumption, and nonfood uses. Figure 2 shows the uses of oat relative to the proportions utilized. Oat was a traditional feed on farms for centuries and powered workhorses until the introduction of machinery powered by fossil fuels. Between 50% and 90% of the world oat production is used as animal feed for horses, cattle, and sheep. Naked oat is particularly suited for poultry, pigs, racehorses, and birds. Oat as an animal fodder is also important for domestic and export markets. Oat can be grazed as a green feed, made into silage, utilized as straw, or baled for hay. Oat for human consumption is used to produce traditional, functional, and medicinal products. Oat is differentiated from other cereal grains by using the entire kernel after the hull is removed for many food products. Porridge or oatmeal, hot cereals, bread, biscuits, infant food, and muesli or granola bars are a few examples of food products produced from oat. Nondairy food uses have been developed resulting in oat milk, yogurt, and ice cream. Oat has been shown to have health benefits for lowering blood cholesterol, normalizing blood glucose levels, and reducing the risk of colorectal cancer. Pharmacological properties are reported in the literature and products are being developed for commercialization. Nonfood and industrial oat products vary from cosmetics, to the production of cardboard products, to the manufacture of furfural and furan compounds used for solvents, adhesives, filtering aids, and the construction of board material and cellulose pulp. Although oat production is declining globally, specialization for animal feed, hay, food, industrial, and pharmaceutical products is growing and provides opportunities for adding value to the oat crop. This article will briefly outline the significance of oat as a cereal crop including origin, domestication, plant morphology, production, end uses, and variety improvement.

Classification The genus of oat is Avena L. (Poaceae) and belongs to the tribe Aveneae of the family Gramineae. The primary species cultivated is Avena sativa. However, Avena byzantina and Avena strigosa are also grown in some regions for animal feed and fodder. The species described in Avena form a polyploid series varying from 1 to 3 chromosome sets with the basic chromosome number (n) 7. Each chromosome set has genome designations A, B, C, and D donated by a different oat species in the evolution of the genus. The different species with varying ploidy levels evolved over time and will be discussed in the next section. The diploid species have one set of chromosomes and are designated as 2n ¼ 2x ¼ 14. This designation indicates the diploid is composed of one genome with 14 chromosomes. The tetraploid

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THE CEREAL GRAINS | Oats: Overview species have two sets of chromosomes and are designated 2n ¼ 4x ¼ 28. This designation indicates the tetraploid has two different genomes each with 14 chromosomes, totaling 28 chromosomes. The hexaploid species include cultivated oats and have three sets of chromosomes designated 2n ¼ 6x ¼ 42. This designation shows that the hexaploid species are composed of three genomes each with 14 chromosomes, totaling 42 chromosomes.

The History of Oat Speciation Three distinct diploid genomes A, C, and D hybridized in the development of cultivated oat. Each genome was composed of 14 chromosomes. The specific species that hybridized to form cultivated oat has been difficult to ascertain. Several species have been described with the A and C genomes, but no species have been identified with the D genome. Nonetheless, domesticated oat evolved from a hexaploid wild oat species composed of A, C, and D genomes with Avena sterilis, Avena fatua, or Avena hybrida all hypothesized as the progenitors of domesticated oat.

Domestication and Early Cultivation

Figure 1 Oat plants pictured at heading.

Figure 2 The main end uses of oats are shown with the largest proportion used for animal feed, the second major use for human consumption, and minor uses for industrial, cosmetic, and pharmaceuticals.

Although it is not certain where the center of origin for oat is located, the greatest genetic diversity encompasses the Canary Islands, the Mediterranean, the Middle East, and the Himalayan region. Avena species were identified at several sites in the Near East dating from 10 500 to 5750 BC. The Neolithic Revolution spread from the Near East to the European continent, Great Britain, and east to Asia. By 2000 BC, farming and trading prospered in Europe. Wheat and barley seed moved into these regions bringing oat and rye as weed contaminants. Although the historical record is limited, cultivated oat was identified in the northern regions of western Europe between 4500 and 400 BC when the region experienced cool and wet climatic changes. Oat and rye were favored in these conditions compared to wheat and barley. There are references about oat for fodder, animal feed, human food, and medicinal properties by Greek and Roman authors AD 23–AD 79. Oat cultivation continued during the Dark Ages, and by the Renaissance, oat was ranked fourth in importance after wheat, barley, and rye. Oat was the dominant crop in Scotland by the thirteenth century. Oat could flourish in areas where wheat and barley produced marginal yield and became known as a crop that could be produced on less productive land. Although the primary use of oat was for animal feed, by 1500–1700, it was the principal grain crop for human consumption in Scotland, Wales, Ireland, and Britain. Oat also continued to be an important feed for horses, cattle, and sheep. During the potato crop failure in Ireland during 1740–41, oat was used in soup to sustain the hungry. Immigrants and explorers from Great Britain and Spain introduced oat into North America. The English introduced oat into Canada, New England, and eastern United States in 1500–1600 as an animal feed. Scottish immigrants to North America continued to use oat for porridge and other foods. The

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Spanish brought oat to the Pacific coast and the southwestern and southeastern United States in the early 1800s to feed their horses. The general public continued to use oat for the sick, purchasing the product at chemists. Oat production moved west to the Upper Mississippi River Valley and into Canada by the 1880s. Oatmeal as a breakfast food began to flourish by 1900 in United States because local mills began milling oat for breakfast cereal, and subsequently, the product was sold in grocery stores instead of pharmacies or drugstores. Governor Phillip introduced oat into New South Wales, Australia, in 1791. The primary use of oat was green fodder and hay for horses, dairy cattle, and pigs. Oat varieties, introduced from Europe, were late-maturing in Australia, so successful production was primarily in Tasmania and the elevated regions of mainland Australia until the early-maturing variety Algerian was introduced for lower rainfall regions. Human consumption of rolled oat was associated with immigrants from Great Britain. Leonard and George Parsons emigrated from England to Australia in 1861 and, by the late 1880s, began manufacturing the John Bull brand of rolled oat. In 1854, Harry Clifford Love emigrated from Dublin to Australia. After several businesses, Harry and his son Joseph formed the Imperial Manufacturing Company, Ltd., which began producing Uncle Tobys, a brand of rolled oat in 1893.

Plant Growth and Morphology Oat is an annual crop with tall and short stature depending on the presence of dwarfing alleles. Each plant produces about five stems depending on the growing season, and each stem produces about five to six leaves on dwarf stature plants and eight to ten leaves on tall plants (Figure 3). Each stem or culm produces a terminal panicle where the seeds develop. Plant height will vary with growing season and the presence or absence of dwarfing alleles. Varieties with dwarfing alleles will vary in height between 45 and 70 cm in Australia. Tall varieties without dwarfing alleles will vary in height between 70 and 135 cm in Australia. Root development is fibrous and will vary according to aboveground growth and maturity but is 1 m deep. Temperature and day length influence the length of the growing period for producing oat grain. Winter and spring oat differ by vernalization requirements. Winter oat requires cold temperatures to produce grain, whereas spring oat will produce grain without the vernalization period. Due to mild winter temperatures in the Mediterranean climates of the southern and northern hemispheres, spring oat can be sown in the winter season. The major developmental stages of plant growth are germination, leaf production, tiller production, stem elongation, panicle development and emergence, anthesis, grain filling, and ripening. When the seed germinates, starch reserves in the seed provide energy for root and leaf development until the plant begins to photosynthesize. Leaves develop at regular intervals until panicle emergence. Tiller production begins when the seedling has three to four leaves. The number of tillers that live to produce grain is dependent on environmental conditions and the age of the tiller. Internodes of the plant begin to elongate when about four to seven leaves are present,

Figure 3 The main morphological parts of an oat plant.

resulting in increased height of the plant. Preanthesis panicle development occurs when the growing point is <1 mm. As the internodes elongate, the developing panicle grows upward. Unlike wheat, barley, and rye, oat forms a panicle composed of branches with the seed produced at the tip. Flowering or anthesis occurs when pollen is shed on the feathery stigmas enclosed by the lemma and palea with outer tissues called glumes (Figure 4). This stage occurs when the panicle has fully emerged from the flag leaf in tall varieties but may occur while the head is still contained in the flag leaf for dwarf varieties. Fertilization occurs within 24 h. Grain size and weight increase as sugars are converted to starch. As the seed matures, the plant begins to lose moisture and senesces. The mature oat grain consists of a groat or caryopsis tightly covered by a hull or husk, previously the lemma and palea (Figure 5). The hull represents 30–40% of the total grain

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Figure 4 The plant parts that comprise an oat floret. (Reproduced with permission from Marshall HG and Sorrells ME (eds.) (1992) Oat Science and Technology, Agronomy number 33, p. 72. Madison, Wisconsin: American Society of Agronomy.)

weight. It is composed of cellulose, hemicellulose, and lignin. Compared with other cereals, the oat groat is slender and covered with hairs or trichomes under the hull. There is a groove on the inner surface of the groat. The groat is composed of three major fractions, bran, endosperm, and germ or embryo. Several layers of compressed tissue and aleurone cells constitute the bran located in the outer layers of the groat (Figure 5). The aleurone cells represent the largest component of the bran and play a role in seed germination. The endosperm represents from 55% to 80% of the groat. It is composed of starch, protein, lipids, and the major concentration of b-glucans. The endosperm provides nutrients for the growing embryo. The embryo has three structures, the scutellum, plumule, and radicle. The scutellum is located between the embryo and endosperm and is involved in germination and food transfer. The plumule has two to three leaf primordia and the radicle has two to three root primordia.

Growing Oat: Agronomy Good management practices are necessary to realize the genetic potential of oat varieties. Sowing reliable seed, using optimum

Figure 5 Composition of an oat kernel. (Reproduced with permission from Youngs VL (1986) Oat lipids and lipid-related enzymes. In: Webster FH (ed.) Oats: Chemistry and Technology. St. Paul, MN: The American Association of Cereal Chemists.)

sowing and fertilizer rates, and timely disease and pest control constitute good management practices.

Soil Factors Oat tolerates a wide range of soil types. The crop will tolerate acid soils to a pH of 4.5 and alkaline soils to a pH of 8.5, but optimum productivity occurs with pH range from 5 to 6. Acid soils can be associated with aluminum toxicity in oat. Oat is not as tolerant of salt as wheat, barley, and rye, but is more tolerant than sorghum. Australian oat varieties are more tolerant than barley to boron, but slightly less tolerant than wheat. Oat is generally tolerant of high manganese levels in the soil.

Climate The most significant climatic factors affecting oat productivity are temperature and moisture. Oat flourishes in cool moist environments and requires more moisture to produce a unit of dry matter than other cereals. Oat-producing regions in North America, Europe, and Asia are primarily located between 40 N and 60 N latitudes. Maritime climates in northern Europe are also oat-producing regions. The length of the growing season in the northern hemisphere varies from 90 to 110 days with decreasing day length as the growing season progresses. The prime oat-growing regions in the southern hemisphere occur within the latitudes 20 S and 45 S. Oat is grown

THE CEREAL GRAINS | Oats: Overview between 30 S and 40 S latitudes in Australia, between 25 S and 45 S latitudes in New Zealand, and between 20 S and 30 S latitude in South America. The growing season in Australia and South America can vary from 150 to 180 days with increasing day length as the growing season progresses. Although oat tolerates cold in seedling and tillering stages, yield loss can result once the panicle emerges. However, oat tolerates frost better than wheat and barley. Hot dry weather can also reduce grain yield and quality especially from anthesis to grain filling.

Agronomy Spring varieties are primarily sown in the southern hemisphere during the winter months. Both spring and winter varieties are grown in the northern hemisphere and the time of sowing will vary with latitude. Sowing rates are dependent on a combination of climate, soil conditions, and use of the crop. Sowing rates are higher for fodder production when compared to grain production. Seed size also varies extensively in oat. Hence, sowing rates need to be calculated as the number of seeds m2 rather than the weight of seeds m2 to achieve optimum plant density. Adequate nutrition of oat is essential to achieve maximum yields. Inputs such as nitrogen, phosphorus, potassium, and sulfur are applied based on soil tests. Micronutrient deficiencies for copper, zinc, manganese, molybdenum, and iron occur in some soils. Micronutrient toxicity for boron, aluminum, and manganese also occurs in some soils. Oat generally tends to be more sensitive to herbicides than wheat or barley. Sensitivity is also variety-dependent. A harvester is used to cut standing plants and threshes the grain from the plant. Wind rowing is another option for harvest and requires that plants are cut and put into rows for grain threshing at a later date.

Figure 6 Oat stem rust.

Growing Oat: Diseases and Pests A wide range of pests and diseases caused by fungi, bacteria, viruses, nematodes, and insects affect all stages of plant growth, resulting in reduced grain yield, dry-matter production, and decreased grain quality. Control measures include genetic resistance, chemical control, and management practices. This brief overview summarizes the major diseases and pests in oats.

Diseases Caused by Fungi Powdery mildew caused by Erysiphe graminis D.C. ex Marat f. sp. avenae Marshal is an important disease in cool humid climates such as northwest Europe. Stem rust caused by Puccinia graminis Pers. f. sp. avenae Erikss. & Henn. (Figure 6) and crown or leaf rust caused by Puccinia coronata Cda f. sp. avenae Erikss. (Figure 7) are the two most devastating foliar diseases in oat. Significant grain yield and quality losses result from infection. It occurs in both the northern and southern hemispheres where oat is sown. Genetic resistance is the preferred means of control for these diseases. Although septoria leaf blotch (caused by Stagonospora avenae) is considered a minor disease compared to stem and leaf

Figure 7 Oat leaf rust.

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Figure 8 Septoria on oat plants.

Figure 9 Septoria on oat leaves.

Nematodes rust, the disease causes significant yield losses when it occurs. The disease is reported in eastern Canada, the United States, Australia, Europe, Great Britain, and Israel. Septoria is a major production constraint in Western Australia (Figures 8 and 9). Pyrenophora leaf blotch caused by Pyrenophora avenae Ito & Kuribayashi apud Ito occurs worldwide with varying economic significance (Figure 10). Pyrenophora was the third most important disease in Germany, significant in Brazil, and common in Scandinavia. Red leather leaf caused by Spermospora avenae Sprague & A.G. Johnson is a minor disease identified in northwestern United States, Turkey, and Australia (Figure 11).

Diseases Caused by Bacteria Halo (Pseudomonas syringae pv. coronafaciens) and stripe blight (P. syringae pv. striafaciens) are collectively called bacterial blight (Figure 12). The disease is common while cool, moist conditions persist. Severe foliar symptoms develop on susceptible varieties. Dry conditions limit the spread of bacterial blight.

Diseases Caused by Viruses Barley yellow dwarf virus is the most yield-limiting viral disease of oat and is an economic threat worldwide (Figures 13 and 14). The virus is transmitted by a number of aphid species.

Cereal cyst nematode (CCN), Heterodera avenae Wollenweber, causes a serious economic threat to oat production worldwide (Figure 15). In regions where CCN is abundant, genetic resistance reduces CCN population sizes and oat varieties with genetic tolerance ensure maximum productivity. Genetic resistance and tolerance are independently inherited. Stem nematode, Ditylenchus dipsaci (Kuhn) Filipjev, limits oat production in cool moist climatic conditions (Figure 16). Winter oat sown where mild winters occur and spring oat sown in the winter (Mediterranean climates) are affected by the nematode. Resistance and tolerance appear to be more closely associated for stem nematode than CCN. Root lesion nematode, Pratylenchus neglectus, affects oat crops in Europe, Iran, the United States, and Australia. Yield losses up to 37% were recently demonstrated in South Australian trials where the nematode population was high. Resistance and tolerance mechanisms are inherited similar to CCN.

Insect Pests Russian wheat aphid (Diuraphis noxia), greenbug (Schizaphis graminum), bird cherry-oat aphid (Rhopalosiphum padi), grain aphid (Macrosiphum avenae), and rose grain aphid (Metopolophium dirhodum) can attack oat with varying effects on productivity. Army worm (Phalaenidae spp.), fruit fly (Oscinella frit (L.)), and wireworms (Agriotes spp.) are insect pests that affect oat production in varying capacities worldwide.

Figure 12 Bacterial blight in oat.

Figure 10 Pyrenophora leaf blotch of oat.

Figure 11 Red leather leaf in oat.

Figure 13 Barley yellow dwarf virus causing blasted florets and leaf discoloration.

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Figure 14 Barley yellow dwarf virus causing leaf discoloration, seed blast, and dwarfing. Figure 16 Symptoms of stem nematode in the left and middle plant compared with a tolerant plant on the right.

Figure 15 Cereal cyst nematode-affected plants are yellow and poorly developed (six rows in left plot are intolerant compared with six tolerant rows in plot behind).

Processing Oat In order for oat to be processed, the hull must be removed from the groat, contaminants removed, and a product produced with quality appearance and taste. There are specifications for milling oat that include hull to groat ratio, color, and flavor. Milling and processing operations consist of cleaning, grading, hulling, hull and fine separation, groat separation, and

kilning (Figure 17). Grading occurs when groats are separated into two or three streams based on groat length or thickness. The hulling process is the next step when groats are separated from the hull using either impact- or stone-hulling systems. Impact hulling is more common than stone hulling. Hulls and fines are separated from whole groats, broken groats, and unhulled oats. Further refinement occurs when groats are separated based on physical characters, such as groat size and weight. Because oat groats have a high oil content, a heat treatment is required to inactivate enzymes that cause rancidity and bitterness in the final product. Kilning is a process that heats the groat at a certain temperature and moisture content to inactivate the enzymes. Kilning can occur before grading or after groat separation (Figure 17). Commercial processors generally can produce 100 kg of product from 175 kg of oats. Milling efficiency varies according to the variety and the mill-operating efficiency. Products produced include steel-cut groats, rolled oat, quick oat, baby oat, instant oat flakes, oat flour, and oat bran.

Using Oat Oat is a versatile crop used as grain and fodder for animal feed, human foods, industrial products, cosmetics, and pharmaceuticals. Figure 2 shows the diversity of oat products relative to


Oats Stone milling Impact milling

Cleaning

Impact milling

Kilning Grading

Grading

Hulling

Hulling

Hull and fines seperation

Hull and fines seperation

Groat separation

Groat separation Kilning

Cut groats

Broken or small groats

Large groats

Cutting

Flaking

Grinding

Premium oat flakes

Oat flour

Milling

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corn, wheat, and barley. Lignin is the primary fiber fraction of the hull and reduces grain digestibility in animals. Lignin content also varies in different varieties. Although hulls with high lignin reduce digestibility, varieties with lower-hull lignin content can have a beneficial effect for horses, cattle, and sheep. The hull reduces digestive problems in these animals. The hull is a major constraint as a feed grain for poultry and pigs. It reduces digestibility resulting in low protein and poor energy. Because naked oat does not have a hull, the grain provides a good source of energy for grower and weaner pigs, broilers, and laying hens. Overall, oat is a favorable feed for ruminants such as cattle and sheep. Oat is also the preferred feed for horses due to the palatability, digestibility, and nutritive value of the grain. Naked oat is also used for racehorses, due to the limited requirement of grain intake and the need for a good source of energy.

Oat Grain for Human Consumption

Oat bran Oat flour Fast cooking oats Figure 17 The milling process of an oat kernel.

the proportion used. Animal feed is the largest use of oat; cereal products and other human food the second most common use. Although pharmaceuticals represent the smallest group of products, they have the greatest potential for future growth and value.

Oat for Feed Grain Oat has been a traditional feed grain for centuries. Recent advances in corn, wheat, barley, soybean, and canola as feed grains have resulted in a worldwide decline of oat production for feed. Despite the decline, the primary use of oats remains as a feed grain. Prior to mechanization, oat was the primary feed for horses that powered farm equipment. Oat is a suitable feed for dairy and beef cattle, sheep, and horses. Although not as prevalent, oat can also be used for poultry, pigs, cats, dogs, birds, rabbits, bison, deer, and fish. In recent years, naked oat is being developed as a feed grain with improved nutritional value for markets such as weaner and grower pigs, poultry, racehorses, and birds. The following discussion centers on the traditional oat grain possessing a hull. The nutrient value for animal feed is based on the proportion of groat to hull. The ratio varies with variety and environment. Oat groats have a higher oil or lipid content than other cereals, varying between 3% and 11%. The oil is composed primarily of unsaturated fatty acids, which can alter the fatty acid composition of the animal fat. Protein content in oat groats varies from 9% to 15% with higher lysine content than

Products produced from oat are generally made with the whole grain after the hull is removed, whereas other cereal products are produced from grain with the germ and bran removed. Whole oat has the highest protein and a favorable ratio of unsaturated to saturated fatty acids compared with other cereals. Whole oat also provides vitamins, minerals, and antioxidants. The heat treatment used to stop rancidity also enhances the unique sensory characters of oat. The unique composition of whole oat results in healthy products. b-Glucan content in the groat varies between 1.8% and 7.5% on a dry-matter basis. The high level of water-soluble dietary fiber of which b-glucans are the main component helps to reduce high blood cholesterol and normalize blood glucose levels. The fiber also reduces the risk of colorectal cancer. The groat also contains vitamins and antioxidants. Lactoseintolerant individuals can now purchase nondairy oat products. The main product produced from oat is porridge or oatmeal. Other food products processed from oat are cold cereals, infant foods, muesli or granola bars, breads, biscuits or cookies, thickeners, and specialty flour. New processes were developed recently to manufacture nondairy products such as milk, ice cream, and yogurt using oat. Antioxidants in oat flour can be used to stabilize some milk and meat products sensitive to fat oxidation during storage. Oat gum primarily composed of b-glucans is used to stabilize ice cream. Oat proteins have been used in many food products including heat-resistant chocolate, because of viscosity and emulsification properties.

Oat Grain for Industrial and Nonfood Uses There are many potential uses of oat grain fractions and hulls in products such as adhesives, cosmetic products, pharmaceuticals, and oil-spill cleanup. Some of the uses are proposed, whereas the technology for other uses has been developed and implemented. The unique chemical composition of the oat groat is responsible for oat starch gels having more elastic, adhesive, and translucent properties than wheat or maize starches. Oat starch could replace products produced from wheat or maize

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with the waxy starches the exception. Products currently produced from starch include brown paper and cardboard products and coating agents for tablets in the pharmaceutical industry. Oat has been used in cosmetic products for some time. The starch characteristics make oat a useful ingredient in bath products to relieve itching and nappy rash. Other products produced from oat include cleansers to replace soap in facial masks, soap for cleansing dry and oily skin, shampoo, lotions, bath additives, and skin care. Pharmaceutical products have great potential, but are not currently tapped. The health benefits of oat fractions were discussed in the preceding section. The hull can also be used to produce industrial products. Oat hulls are used to produce furfural and furan compounds. These compounds are used in the manufacturing process of crude petroleum; nylons; formaldehyde furfural resins; solvents for dyes, resins, lacquers, paints, and varnish; elastomers and thermoplastics; phenolic resin glues and plywood adhesives; construction board material; and cellulose pulp. A very different aspect of hull utilization is the cariostatic properties of tooth protection.

Oat for Fodder Fodder production is also an important component of animal feed shown in Figure 2. Several types of oat fodder, such as hay, silage, grazing, and straw, are produced as an essential component of animal production systems worldwide. Oat hay is produced for dairy and beef cattle, horses, and sheep. Hay not only is an important commodity domestically but also is traded internationally. A significant market is the Asian dairy and beef cattle industry. The oat hay crop is cut at the watery-ripe growth stage (Zadoks 71) for optimum hay quality. Hay quality characters that may be associated with palatability are digestibility, water-soluble carbohydrates, acid detergent fiber, neutral detergent fiber, and stem diameter. Sensory quality characters are also important and include hay color and aroma. Cattle and sheep graze oat during the vegetative stage when the plant height is from 20 to 40 cm. Animals are removed from the oat crop before the growing point of the plants is damaged, so the crop produces grain. Grazing is important in countries worldwide including New Zealand, Australia, South America, northern Africa, Nepal, and the United States. Silage production using oat is used in the dairy and beef cattle industry worldwide. Oat is cut in the early heading stage, chopped, and ensiled.

Breeding-Improved Oat Varieties History Early oat improvement occurred when farmers selected the best-performing plants in their paddocks. The first attempt to introduce genetic variation by crossing different oat genotypes was reported in England and accomplished by Shirreff in the 1860s. The first variety developed from hybridizing oat, Abundance, was released from Garton’s Ltd., Warrington, England.

Breeding Priorities Breeding priorities determine selection criteria that eventually result with the release of oat varieties with improved traits. Understanding production and processing constraints of oat is the initial step in identifying breeding priorities for improving varieties. These priorities will differ or change in emphasis depending on the growing environment and end use of the oat plant or grain. Breeding priorities are based on gross margin for growers and processors, resulting in a superior product for the consumer and processor. Breeding priorities set to achieve long-term goals are based on developing varieties that offer new products or increased value for both growers and industry. The long-term breeding priorities are particularly important for oat due to the global decline of production. Although there are many different growing environments and end uses globally, the primary breeding priorities deal with productivity, disease resistance, agronomy, and quality. Increased grain and hay yields are the primary aims of increased productivity. Improved disease resistance increases yield and enhances quality. The significance of oat diseases varies with region and continent and is prioritized by breeding programs. Diseases such as stem and leaf or crown rust are two global diseases that cause significant losses to the oat industry. Barley yellow dwarf virus, smut, and septoria also reduce yield and quality in certain production areas of the world. Cereal cyst, stem, and root lesion nematodes when present in the production environment are equally as devastating, but more regionally localized in the world. Important agronomic characters are standing ability, maturity of the plant, and the ability of the plant to resist shattering or loss of seed at maturity. Winter hardiness is also an important agronomic trait of the varieties that require a cold period to produce seed. Grain quality characters that are essential for the industry are high groat to hull ratio and groat color. Weather and disease can cause groat discoloration. Other grain quality characters of importance for variety development are protein, oil, b-glucan content, hectoliter weight, and screening percentage. The most important aspect of fodder quality is palatability. The traits that comprise palatability are being researched but are most likely a combination of digestibility, water-soluble carbohydrates, neutral detergent, and acid detergent fibers, color, and smell.

Breeding Methods Breeding systems should be flexible and easily modified for changes in breeding priorities. A combination of breeding methods is combined in a program to produce improved oat varieties. Classical breeding methods used for decades are pedigree, bulk, recurrent selection, backcross, and single-seed descent. More detailed information about the breeding methods is available in Plant Breeding Methodologies by Neal Jensen. Doubled haploids (DH) are true breeding homozygous lines produced in one generation. An economically viable method for DH production in oat is currently not available, but new developments using isolated microspore culture hold promise for

THE CEREAL GRAINS | Oats: Overview future implementation. DH technology is used commercially for wheat, barley, and canola breeding. Molecular marker technologies for oat have only recently started compared with those for wheat and barley. Molecular markers are a selection tool using DNA to identify lines with desirable combinations of traits. It provides fast and accurate trait selection compared to traditional data collection in field trials where the environment influences the phenotype. However, it is necessary to have an accurate phenotypic analysis to establish the closest linkage between the trait and molecular markers for marker development.

Germplasm Collections Oat germplasm collections are maintained in many countries and are a source of new genetic variation for improving oat. Without these collections and the exchange of advanced germplasm from oat-breeding programs, oat variety improvement would not advance. Several collections of notable importance are located in the United Kingdom, Canada, the United States, Israel, the Russian Federation, and China.


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Describe the main end uses of oat and what proportion of the crop is used for each. Describe the history of oat utilization from the first documentation until the 1700s. Name the morphological parts of an oat plant and oat floret. Discuss the composition of an oat kernel. Name three fungal diseases of oat and their causal pathogens. Name virus and nematode diseases and their pathogens. Discuss breeding methods including new technologies.


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What are the healthy components of the oat grain? What is the current research status for molecular markers and doubled haploids in oat? What is the current research on the healthy aspects of oat for animal feed? What is happening with drought tolerance research in oat?

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Grain Harvest, Storage and Transport: Cereals: Grain Defects; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Non-food Products from Grains: Cereal Grains as Animal Feed; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

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Further Reading Baum BR (1977) Oats: Wild and Cultivated. A Monograph of the Genus Avena L. (Poaceae). Ottawa, ON: Department of Agricultural Supply and Services Canada. Bonnett OT (1961) Morphology and development. In: Coffman FA (ed.) Oats and Oat Improvement. Madison, WI: American Society of Agronomy. Bowden CW (1987) Oats. In: Lazenby A and Matheson EM (eds.) Australian Field Crops: Wheat and Other Temperate Cereals. North Ryde, NSW: Angus and Robertson. Clifford BC (1995) Diseases, pests, and disorders of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Cuddeford D (1995) Oats for animal feed. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Ferrie AMR, Irmen KI, Beattie AD, and Rossnagel BG (2013) Isolated microspore culture of oat (Avena sativa L.) for the production of doubled haploids: Effect of pre-culture conditions. Plant Cell, Tissue and Organ Culture 116: 89–96. Forsberg RA and Reeves DL (1995) Agronomy of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Ganssmann W and Vorwerk K (1995) Oat milling, processing, and storage. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Hoffman LA (1995) World production and use of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Jensen NF (1988) Plant Breeding Methodology. New York, USA: John Wiley and Sons. Leggett JM (1992) Classification and speciation in Avena. In: Marshall HG and Sorrells ME (eds.) Oat Science and Technology. Madison, WI: American Society of Agronomy. Moore-Coyler RJ (1995) Oats and oat production in history and prehistory. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Murphy JP and Hoffman LA (1992) Origin, history, and production of oat. In: Marshall HG and Sorrells ME (eds.) Oat Science and Technology. Madison, WI: American Society of Agronomy. Pomeranz Y (1995) Industrial uses of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Ranhotra GS and Gelroth JA (1995) Food uses of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Schrickel DJ, Burrows VD, and Ingemansen JA (1992) Oat harvesting, storing, and feeding. In: Marshall HG and Sorrells ME (eds.) Oat Science and Technology. Madison, WI: American Society of Agronomy. Sidhu PK and Davies PA (2009) Regeneration of fertile green plants from oat isolated microspore culture. Plant Cell Reports 28: 571–577. Webster FH (1986) Oat utilization: Past, present, and future. In: Webster FH (ed.) Oats Chemistry and Technology. St. Paul, MN: American Society of Cereal Chemists. White EM (1995) Structure and development of oats. In: Welch RW (ed.) The Oat Crop: Production and Utilization. London, UK: Chapman and Hall. Youngs VL (1986) Oat lipids and lipid-related enzymes. In: Webster FH (ed.) Oats Chemistry and Technology. St. Paul, MN: American Society of Cereal Chemists. Zadoks JC, Chang TT, and Konzak CF (1974) A decimal code for the growth stages of cereals. Weed Research 14: 415–421.

Relevant Websites www.eatmoreoats.com – This website gives information about health, recipes, and products. www.grdc.com.au – This website gives research information in Australia and Worldwide. www.quakeroats.com.au – This website gives information about oat products. www.rirdc.com.au – This website gives information about fodder research for oat hay varieties. www.taste.com.au – This website gives information about oat recipes. www.uncletobys.com.au – This website gives information about oat product, health and nutrition, and oat recipes. www.whfoods.com – This website gives information about oat nutrients, health benefits, history, and cooking.

Coix: Overview H Corke, University of Hong Kong, Hong Kong, Pokfulam, China; Hubei University of Technology, Wuhan, China Y Huang and JS Li, China Agricultural University, Beijing, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Native to Asia, coix is a close relative of maize and produces a grain widely used in Chinese medicine. The storage protein of coix largely comprises a prolamin fraction termed coixin. Various components of the coix grain, particularly coixol, coixin, and coixenolide, are of medicinal and nutritional importance.

Vegetative Organization

Learning Objectives

• • •

To understand the origin and taxonomy of coix and its relationship to maize. To understand the uses of coix, both as food and in traditional medicine. To understand the basics of the chemical composition of coix that contribute to its medicinal properties.

Introduction

The coix plant is 70–400 cm high. Its stems are erect or straggling with branches and prop roots from the lower nodes. The internodes of the culms are solid. Leaves are not basally aggregated and nonauriculate, the leaf blades are lanceolate and broad and 30–70 mm wide, the shape is cordate or not cordate but not sagittate, they are flat and persistent without cross venation, they are rolled in bud with a ligule present, and there is an unfringed to a fringed membrane.

Reproductive Organization

Coix lacryma-jobi L., commonly called Adlay, Job’s tears, adley, adley millet, or coix millet, is an annual crop. Botanically, coix belongs to the tribe Maydeae (Tripsaceae) of the family Poaceae, and it is classified as a close relative to maize. This annual grass is native to India, Burma, China, and Malaysia and has been grown extensively in Southeast Asia for several thousand years. The plant is typically 1 m high with knobbly bamboolike stems, and the new ‘tillers’ arise from the base of stems. The glossy deep green leaves are up to 5 cm wide with slightly wavy edges. The flowering and fruiting spikelets are insignificant; the grain is pear-shaped and 5 mm in diameter and has a hard, shiny dark brown to gray–black hull. The grain is used in soups and beverages and is popular in traditional Chinese medicine. It is well known to have pharmacological properties. The ancient Chinese medical book ‘Pen-tsao kang mu’ described it as an effective remedy for a number of maladies and particularly beneficial to the digestive system. Coix has been considered as a good potential germplasm resource for maize improvement because it is tolerant to lateritic soils and low pH, less prone to attacks by viruses, and less susceptible to waterlogging and has a low variation in photoperiod. Accurate world production figures are impossible to ascertain, but coix has a value beyond that of a typical commodity grain for food use.

Botany Habit Coix is a light-sensitive and short-day-length plant and prefers wet soils and cool weather. Although it is an annual crop, the

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plant is perennial in essentially frost-free areas. It is reported to tolerate annual precipitation of 6.1–42.9 dm, annual temperature of 9.6–27.8 C, and soil of pH 4.5–8. It can be grown in a variety of environments – from cool-temperate moist to wet to tropical very dry to wet forest life zones, forest margins, and swamps. Although this annual grass is native to Southeast Asia, it is now distributed throughout the tropical, subtropical, and temperate zones.

The coix plant is monoecious with all the fertile spikelets being unisexual but without hermaphrodite florets (Figure 1). The spikelets of sexually distinct forms (female-only or male-only) are on the same plant, the glumes of the fertile spikelet are several-nerved, and all are enclosed finally in a bony beadlike involucre containing a minute fertile female flower and two sterile flowers. Pollen-bearing male flowers are produced on a slender stalk that extends out of the bead through a tiny pore. Two feathery stigmata from the fertile female flower also protrude from the pore – ready to receive pollen from the male flowers: 1. Female-sterile spikelets: Male spikelets grow in pairs or triads, several per disarticulating raceme. Rachilla of male spikelets is terminated by a male floret. The male spikelets have glumes and proximal incomplete florets or not (the lower floret sterile or male). 2. Female-fertile spikelets: Spikelets fall with the glumes. Rachilla is terminated by a female-fertile floret. Usually, it is pollinated by the wind.

Seed The shiny gray to black beads are dispersed and planted like seeds, but they are like little shells containing flowers and grains. The seeds are usually oval-shaped or egg-shaped, with a milky white outer surface and a slightly sweet taste (Figure 2). Fruit is medium sized with globular form and 6–12 mm long. Close-up view of flowering coix shows the hollow, beadlike involucres, which have a natural hole in them.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00008-5

THE CEREAL GRAINS | Coix: Overview

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Thrumb Female spikelet Flower stalk Male spikelet

Figure 3 The karyotype of Coix. Reproduced from Zhang F and Yi Z (1994) Natural Science Journal of Changsha Normal University of Water Resources and Electric Power 9(2): 187–191.

lacryma-jobi var. monilifer); 2n ¼ 20 ¼ 14m þ 6sm (þ1 2B) (Coix lacryma-jobi var. formosana); and 2n ¼ 20 ¼ 18m (2 sats) þ 2sm (Coix lacryma-jobi var. ma-yuen (Roman) Stapf). In another research, the chromosome complement of 2n ¼ 10 and 2n ¼ 20 was also found in different populations of coix of Indian origin (Figure 3).

Biochemistry

Figure 1 Inflorescence of Coix. Adapted from the images from http:// www.desert-tropicals.com/plants/Poaceae/coix_lacryma-jobi.html.

Figure 2 Photograph of flower and seed of Coix. http://www.biherb. com/CoixSeedExtract.html.

Cytology The standard karyotype formula is 2n ¼ 20 ¼ 20m (Coix puellarum). But there are other karyotype formulas outside of the standard types, such as 2n ¼ 20 ¼ 18m þ 2sm (C. stenocarpa); 2n ¼ 20 ¼ 18m þ 2sm and 2n ¼ 20 ¼ 16m þ 4sm (Coix lacrymajobi var. lacryma-jobi); 2n ¼ 20 ¼ 12m þ 2m (sat) þ 6sm (Coix

Like other members of the grass family, coix has seeds containing prolamin as the major storage protein. The coix prolamin is known as coixin and represents more than 70% of the endosperm protein. Based on differential solubility, coixins can be separated into two factions: a-coixins and g-coixins. a-Coixins are constituted by four size classes, while g-coixins comprise only one molecular weight class. a-Coixins are synthesized at earlier developmental stages than g-coixins. The deduced amino acid sequence of a full-length cDNA clone encoding a sulfur-rich coix prolamin predicted a polypeptide of 194 residues, which shared 64% homology with the 17 kDa b-zein. The mature protein contains the familiar composition of prolamins and an unusually high content of the sulfur-containing amino acids methionine (11.6%) and cysteine (5.2%). Hydropathy analysis showed that a-coixin is slightly more hydrophobic than b-zein. The anticomplementary polysaccharides CA-1 and CA-2 purified from the seed of Coix lacryma-jobi L. var. ma-yuen both consist of rhamnose, arabinose, xylose, galactose, galacturonic acid, and glucuronic acid but in different ratios. CA-2 contains more mannose and glucose. CA-2 showed more potent anticomplementary activity than CA-1 in low dose. The seeds of C. lacryma-jobi L. var. ma-yuen Stapf are used as a traditional Chinese medicine reputably possessing antitumor activity, attributed to an acidic fraction. Infrared spectroscopy and gas–liquid chromatography showed that this acidic fraction was composed of four free fatty acids: palmitic, stearic, oleic, and linoleic acids. A protein inhibitor of locust gut a-amylase that was purified from coix seeds consists of two major isomers, each dimer of two closely similar or identical subunits of Mr 26 400 Da and associated by interchain disulfide bonds. These isomers also have closely similar amino acid compositions. The major isomer shows no inhibitory activity against amylases from other sources (human saliva, porcine pancreas, Bacillus subtilis, Aspergillus oryzae, and barley malt). This highly specific function may be relevant to protection of the grain from insect feeding and fungal infection. The complete amino acid sequence of the polypeptide of the major trypsin inhibitor from coix seeds showed 64 amino acids with a high content of cysteine. The sequence exhibits strong homology with a

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number of Bowman–Birk inhibitors from legume seeds and similar proteins recently isolated from wheat and rice. The amylose contents of normal coix ranged from 15.9% to 25.8%, and those of waxy coix were 0.7–1.1%. Swelling power of waxy coix starches varied between 28.6 and 41.0 g per g, generally higher than waxy maize. Normal coix starches had significantly higher gelatinization peak temperature (71.1–71.4 C) than normal maize (71.9–75.5 C), similar to waxy maize. Rapid Visco Analyser pasting profiles of normal coix show some variation but closely match the normal maize starch profile. Pasting profiles of waxy coix have more variation and lower peak viscosities than waxy maize starch. Waxy coix starches form very weak gels, while the gel hardness of normal coix starches was 11.4–31.1 g. The gelatinization temperature of waxy coix starches varies between 63.4 and 76.4 C, and water-binding capacity ranges from 103% to 108%. The starch yield from coix grains averages 45%, the birefringence loss of starch granules begins at 65 C and finishes at 75 C, and breakdown during pasting in a Brabender Visco-Amylo-Graph is substantial. The properties of waxy coix starch are similar to those of waxy maize starch. Amylose content is the main factor controlling differences in starch properties of coix starches. Oil yields ranged from 3.03 to 4.83 wt%, ferulate phytosterol esters in oils ranged from 0.109 to 0.119 wt%, free phytosterol varied from 0.54 to 0.61 wt%, phytosterol fatty acyl esters in the oil ranged from 0.79 to 0.98 wt%, total phytosterols were from 1.43 to 1.69 wt%, and g-tocopherol varied between 0.030 and 0.045 wt%. Whole kernel oil yields of coix are generally higher than Zea mays ssp. mays and teosinte accessions. Whole kernel oil yields and levels of four phytonutrients (free phytosterols, fatty acyl phytosterol esters, ferulate phytosterol esters, and g-tocopherol) in oils were measured from three coix accessions (C. lacryma-jobi L.).

Molecular Biology The seed storage proteins of coix, sorghum, and maize are coded by homologous genes, which are coordinately expressed in the endosperm in a temporal-specific fashion. Opaque-2 (O-2), a bZIP protein originally isolated from maize, has been described as a transcription activator of a-prolamin and b-prolamin genes. The coding region of the coix O-2 gene is interrupted by five introns and codes a polypeptide of 408 amino acids. Comparison of the deduced amino acid sequence with two different sequences of maize O-2 protein showed that the coix O-2 protein is similar to the maize O-2 isolated from a maize inbred line, W22. The coix O-2 protein has the same binding specificity and expression pattern of the maize O-2. Dihydrodipicolinate synthase (DHPS) is the main enzyme of a specific branch of the aspartate pathway leading to lysine biosynthesis in higher plants. The open reading frame of the DHPS-encoding DapA gene from C. lacryma-jobi is interrupted by two introns and encodes the 326-amino acid-long coix DHPS protein, which is 95% identical to the maize DHPS protein. DHPS transcripts are present in coleoptiles, embryos, endosperms, and roots but are almost undetectable in blades of young leaves of both coix and maize. The 50 -flanking region of DapA gene contains a TGACTC GCN4-like element located 372 bp upstream from the putative translation start codon.

Steady-state levels of DHPS mRNA are slightly reduced in the endosperms and embryos of the maize lysine-rich O-2 mutants when compared with those in normal kernels. Also, the DHPS gene is not under the control of O-2. Using random amplified polymorphic DNA (RAPD) markers, 21 coix accessions were characterized for genetic variations and relationships. The results indicated considerable variation at the DNA level among the coix germplasm, and the classification by RAPD data reflected the differences in geographic origins and evolution of coix. Recently, a coix genetic linkage map with restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphism (AFLP) markers was constructed. The map consisted of ten linkage groups, consistent with the chromosome numbers observed cytogenetically.

Utilization Coix may be a source of ornamental beads, a staple sustenance, and a productive fodder grass increasingly viewed as a potential energy source. It has long been consumed both as a nourishing food and as an herbal medicine.

Food Before maize became popular in South Asia, coix was rather widely cultivated as a cereal in India and still occurs as a minor cereal. Coix was used as food, particularly by peasants in the Far East, very early in agricultural history. In wild varieties, the fruit has a hard, shiny coat. After domestication, this coat became less hard and easier to cook, for example, into porridge. Coix ranks along with wheat and barley in the Near East; beans, maize, squash, and pepper in the Americas; and rice in Asia as one of the earliest domesticated plants. As with other cereals, there are many coix genotypes, including soft-shelled, easily threshed types with a sweet kernel. Though the hard seed coat, removed by decortication, makes extraction of the flour rather difficult, this is a potentially very useful grain because it has a higher protein to carbohydrate ratio than any other cereal (Table 1). Reported data differ somewhat. According to List and Horhammer, 100 g of seed contains 358 cal, 11.2 g H2O, 15.4 g protein, 6.2 g fat, Table 1 Typical composition of Coix seed compared with other grains (on a 14% moisture basis)

Energy (cal) Protein (%) Fat Starch (%) P (mg) Mg (mg) Ca (mg) Fe (mg) Zn (mg) Mn (mg)

Coix

Rice

Wheat

Maize

1500 14.2 3.6 67.2 299 126 49.0 2.90 1.89 1.89

1460 7.8 1.3 76.6 203

1480 9.9 1.8 74.6 268

1510 8.4 4.3 70.2

9

38 4.2

34

Per 100 g for fat and mineral contents. Source: www.fao.org, www.chinafeedbank.com.cn, and www.cmymy.51.net.

THE CEREAL GRAINS | Coix: Overview Table 2 aa

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Amino acid (aa) composition as % of crude protein Arg

Cys

Gly

Hys

Ile

Leu

Lys

Met

Phe

Thr

Try

Tyr

Val

4.4

1.7

2.8

2.3

4.0

14.4

1.9

3.0

4.8

3.1

nd

4.2

5.6

nd, not detected. Source: www.fao.org.

65.3 g total carbohydrate, 0.8 g fiber, 1.9 g ash, 25 mg Ca, 435 mg P, 5.0 mg Fe, 0 mg b-carotene equivalent, 0.28 mg thiamine, 0.19 mg riboflavin, 4.3 mg niacin, and 0 mg ascorbic acid. There is 50–60% starch, 18.7% protein (mainly glutamine, leucine, tyrosine, arginine, histidine, and lysine), and 5–10% oil with glycerides of myristic and palmitic acids. The partial amino acid composition of crude protein in coix seeds is shown in Table 2. It should be noted that despite the level of lysine noted, it is still deficient relative to human dietary needs. Coix seeds can be used for baking, mixed with wheat flour, and for making porridge and beer. They are usually pounded, threshed, and winnowed. The pounded flour is sometimes mixed with water, similar to use of barley for the beverage barley water. The pounded kernel is also made into a sweet dish by frying and coating with sugar. The grains are also utilized in soups, broths, porridge, drinks, and pastries. In India, the Nagas, a group of tribes near the Myanmar border, use the grain for brewing a beer called ‘zhu’ or ‘dzu.’ A Japanese variety called ‘Ma-Yuen’ is brewed into a tea and an alcoholic beverage, and roasted seeds are made into a coffee-like drink. In some cases, the hulled grain is adapted for parching or boiling like rice; it is also dehusked and eaten like a peanut. Beers and wines are made from the fermented grain. Continuing recent interest in new product development from coix is apparent, and coix bran may be particularly notable as a highpotential food ingredient.

warts. It is also used in the treatment of lung abscess, lobar pneumonia, appendicitis, rheumatoid arthritis, beriberi, diarrhea, edema, and difficult urination. The action of coix seeds against many kinds of disease can be attributed to various components with pharmacologically different activities. Coix roots can be also used in the treatment of menstrual disorders. A major development in the utilization of coix has been the advance of Kanglaite®, which is coix seed oil injected intravenously as a treatment for many forms of cancer. Coixenolide and coixol (regarded as anticancer and anti-inflammatory, respectively) are two major active fractions of coix oil (see Figure 3). It has become a widely used cancer therapy, and a much-hyped treatment in the West. Clinical evidence is positive to some degree, and many studies have recently been conducted, for example, on gastric cancer, on pancreatic cancer xenografts, and on stimulation of anticancer-related immune responses. In fact, numerous recent studies indicate possible anticancer and other medicinal roles of polysaccharide, protein (antidiabetic), polyphenols, bran, and oil of coix. Some of these uses may come to lack support from future rigorous clinical trials. Some uses may depend on complex interactions of coix components with other aspects of a long-term healthful diet. But certainly, there is abundant evidence that coix may have vast future potential as a nutraceutical source.

Fodder Medicine and the Rise of KanglaiteW According to traditional Chinese medicine, coix seeds serve several functions. They stimulate function of the spleen and lung, remove heat, help in the drainage of pus, and induce diuresis. Coix seeds have been widely employed as a diuretic, stomachic, analgesic, and antispasmodic agent from ancient times. They are also used to treat the symptoms of diarrhea and arthritis. The fruits are anodyne, anti-inflammatory, antipyretic, antiseptic, antispasmodic, hypoglycemic, hypotensive, sedative, and vermifugal. According to Hartwell, the fruits are used in folk remedies for abdominal tumors; esophageal, gastrointestinal, and lung cancers; various tumors; and excrescences, warts, and whitlows. This folk reputation is all the more interesting when reading that coixenolide (Figure 4) has antitumor activity. It is also a folk remedy for abscess, helminthiasis, anthrax, appendicitis, arthritis, beriberi, bronchitis, cancer, catarrh, diabetes, dysentery, dysuria, edema, fever, headache, phthisis, pleurisy, pneumonia, rheumatism, small pox, splenitis, etc., is an anodyne and tonic, and can be used during puerperium. Coix seeds are reportedly effective in treating verrucas caused by the human papillomavirus. A tea from the boiled seeds is drunk as part of a treatment to cure

The leaves and stems provide a useful fodder for cattle and buffalo. The grass is very suitable for growing in waterlogged areas. Its average yield is 29 tonnes ha1. The grass can also be turned into silage.

Genetic Resources Coix is reported to tolerate lateritic soils, low pH, slope, viruses, and waterlogging and to be photoperiod-insensitive. It is a potential gene resource for improvement of other cereal crops. It is a perennial plant, which forms several stalks, and its pollen can be collected throughout the year when the plant is maintained in a controlled environment. It can be used as the pollen parent for wheat crosses for haploid production without requiring synchronization of flowering dates.

Cultivation Generally, coix is propagated by seeds. The plant prefers light (sandy), medium (loamy), and heavy (clay) soils. It prefers neutral and basic soils but can grow in very acidic soil, and it

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Name Synonyms

Coixol 6-Methoxy-3H-benzoxazol-2-one H N

Molecular Structure

O O

Molecular Formula Molecular Weight

Name Synonyms

O

C8H7NO3 165.15

Coixenolide [(2S,3R )-3-[(Z)-hexadec-9-enoyl]oxybutan-2-yl] (E)-octadec-11-enoate O H3C

Molecular Structure

O O

H3C

CH3

CH3 O C17566

Molecular Formula

C38H70O4

Molecular Weight

590.96

Figure 4 Molecular data and structure of coixol (from www.Chemblink.com) and coixenolide (from Kegg Brite via www.genome.jp).

requires moist soil. It is sown at rate of 6–10 kg ha1. Seed is planted 2.5 cm deep, at a spacing of 60 60 cm. One intercultivation, before the plants tiller and cast shade on the ground, may be necessary. The largest plants result when the plant is given partial shade although it will tolerate full sun. It adapts to wet soils and so may be used near water. Sufficient rains in the early stage of growth and a dry period when grain is setting are necessary for good yields. Plants respond well to liberal applications of organic manure. The grain is usually harvested in the fall when the plant matures and is dried in the sun. Plants are cut off at base and grain is separated by threshing. Coix yields depend on varieties cultivated in different countries. Usually, unhusked grain yields vary from 2.1 to 3.5 tonnes ha1. Leaf blight, caused by Bipolaris coicis, is one of the most destructive and major yield-limiting diseases in coix. Plant response to leaf blight is quantitative rather than qualitative, varying greatly among cultivars or lines tested. Yield reductions are primarily associated with decrease in kernel numbers per plant, thousand kernel weight, and percent kernel ripeness. Other diseases common in coix are rusts and smuts. Rusts are caused by Puccinia, while smuts are caused by Tilletia and Ustilago. Leaf-gall virus and the nematode Meloidogyne incognita acrita also attack this plant.


• •

Compare and contrast the composition and reported medicinal claims for coix and other minor grain crops, such as Amaranthus, buckwheat, and quinoa. Prepare a map illustrating global production and uses of coix.


• • •

Write a proposal for the development of a line of nutraceutical ingredients based on coix. Suggest how traditional food uses of coix could be modernized and marketed as new products. Investigate the potential for transfer of medicinally important components of coix grain to the high-yielding and related crop species, maize.

See also: Breeding of Grains: Maize: Breeding; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Functional Foods: Overview; Genetics of Grains: Maize: Genetics; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Maize: Overview; The Legumes and Pseudocereals: Amaranth: Overview; Buckwheat: Overview; Pseudocereals: Overview; Quinoa: Overview.

Further Reading Ary MB, Richardson M, and Shewry PR (1989) Purification and characterization of an insect alpha-amylase inhibitor/endochitinase from seeds of Job’s tears (Coix lachryma-jobi). Biochimica et Biophysica Acta 999: 260–266. Ary MB, Shewry PR, and Richardson M (1988) The amino acid sequence of a cereal Bowman-Birk type trypsin inhibitor from seeds of Jobs’ tears (Coix lachryma-jobi L.). FEBS Letters 229: 111–118. Dante RA, Neto GC, Leite A, Yunes JA, and Arruda P (1999) The DapA gene encoding the lysine biosynthetic enzyme dihydrodipicolinate synthase from Coix lacrymajobi: Cloning, characterization, and expression analysis. Plant Molecular Biology 41: 551–561.

THE CEREAL GRAINS | Coix: Overview Duke JA and Ayensu ES (1985) Medicinal Plants of China. Algonac, MI: Reference Publications. Hartwell JL (1971) Plants used against cancer, a survey. Lloydia 34: 386–425. Huang X, Qin J, and Lu S (2014) Kanglaite stimulates anticancer immune responses and inhibits HepG2 cell transplantation-induced tumor growth. Molecular Medicine Reports 10: 2153–2159. Jain SK and Banerjee DK (1974) Preliminary observations on the ethnobotany of the genus coix. Economic Botany 28: 38–42. Leite A, Yunes JA, Turcinelli SR, and Arruda P (1992) Cloning and characterization of a cDNA encoding a sulfur-rich coixin. Plant Molecular Biology 18: 171–174. Li SC (1596) Pen-tsao kang mu (Systematic Pharmacopoeia), China. Li J and Corke H (1999) Physicochemical properties of normal and waxy Job’s tears (Coix lachryma-jobi L.) starch. Cereal Chemistry 76: 413–416. Li XH, Huang YQ, Li JS, and Corke H (2001) Characterization of genetic variation and relationships among Coix germplasm accessions using RAPD markers. Genetic Resources and Crop Evolution 48: 189–194. List PH and Horhammer L (1979) Hager’s Handbuch der Pharmazeutischen Praxis. Berlin: Springer, vols. 2–6. Liu Y, Zhang W, Wang X-J, and Liu S (2014) Antitumor effect of KanglaiteW injection in human pancreatic cancer xenografts. BMC Complementary and Alternative Medicine 14: 6, Article Number 228. Moreau RA, Singh V, and Hicks KB (2001) Comparison of oil and phytosterol levels in germplasm accessions of corn, teosinte, and Job’s tears. Journal of Agricultural and Food Chemistry 49: 3793–3795. Numata M, Yamamoto A, Moribayashi A, and Yamada H (1994) Antitumor components isolated from the Chinese herbal medicine Coix lachryma-jobi. Planta Medica 60: 356–359. Schaaffhausen RV (1952) Adlay or Job’s tears: A cereal of potentially greater economic importance. Economic Botany 6: 216–227.

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Vettore AL, Yunes JA, Neto GC, da Silva MJ, Arruda P, and Leite A (1998) The molecular and functional characterization of an Opaque2 homologue gene from Coix and a new classification of plant bZIP proteins. Plant Molecular Biology 36: 249–263. Yamada H, Yanahira S, Kiyohara H, Cyong J-C, and Otsuka Y (1987) Characterization of anti complementary acidic heteroglycans from the seed of Coix lacryma jobi var ma yuen. Phytochemistry 26: 3269–3276. Yeung HC (1985) Handbook of Chinese Herbs and Formulas. Los Angeles: Institute of Chinese Medicine. Zhan YP, Huang XE, Cao J, et al. (2012) Clinical safety and efficacy of KanglaiteW (Coix Seed Oil) injection combined with chemotherapy in treating patients with gastric cancer. Asian Pacific Journal of Cancer Prevention 13: 5319–5321. Zhang F and Yi Z (1994) Cytological studies of the genus Coix. Natural Science Journal of Changsha Normal University of Water Resources and Electric Power 9(2): 187–191.

Relevant Websites http://www.fao.org – The website of Food and Agriculture Organization of the United Nations. Search for coix information within the site, such as: http://www.fao.org/ag/ agp/AGPC/doc/Gbase/data/pf000205.htm. http://www.hort.purdue.edu – The website of the center for new crop and plant products at Purdue University. Search for coix information within the site, such as: https:// www.hort.purdue.edu/newcrop/duke_energy/Coix_lacryma-jobi.html. http://www.itmonline.org/articles/coix/coix.htm – A useful article by Dr. Subhuti Dharmananda on Coix: Food and Medicine.

Millet Pearl: Overview JRN Taylor, University of Pretoria, Hatfield, South Africa ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Production and Agronomic Issues

•

Pearl millet’s great advantage over other cereals is the fact that it can be and is cultivated in areas of very low rainfall (300–500 mm per year). However, it requires evenly distributed rainfall during the growing season, and too much rain at flowering can cause a crop failure. Pearl millet can be cultivated in areas with very high temperatures (daytime temperatures above 30 C), and it germinates well at soil temperatures of 23–30 C. Its importance in food security in dry, marginal agricultural areas is immense. It is estimated that more than 90 million people in the semiarid tropics depend on pearl millet food and income. The major areas of pearl millet cultivation are India and Western and Central Africa. It is also cultivated in Eastern and Southern Africa. In Western and Central Africa, there is a broad band of cultivation from Senegal in the west, across the Sahel region. It is also cultivated in Sudan, South Sudan, Eastern Africa, and Southern Africa where there is a band of cultivation from Angola and northern Namibia, to Zimbabwe and northern Southern Africa, to Mozambique. There is also some production in Brazil and the United States. Figures for pearl millet production are only approximate as indicated by the wide reported ranges. FAOSTAT data do not distinguish between the different types of millets. Pearl millet is generally a subsistence grain crop and hence not commercially traded in quantity. Thus, precise figures are not always available. Pearl millet accounts for about half of the world millet crop, which is at least 29 Mt per year. The major pearl millet grain-producing countries are India, 8.3 Mt per year; Western and Central Africa, 14.1 Mt, with Niger being the major producer, followed by Mali, Burkina Faso, Nigeria, and Senegal; and Eastern and Southern Africa, 1.8 Mt. It is also increasingly grown as a forage crop and as an ornamental grass. Relative to other major cereal grains, yields are in general very low, on average <1 t ha1. This is because pearl millet is grown in areas of low rainfall and high temperature, often on light, welldrained soils. Generally, traditional farming practices are used with very low inputs, that is, no biocides or inorganic fertilizers and little application of organic fertilizer, and use of traditional landraces. Pearl millet has, however, much greater potential. In areas, especially India, where new varieties and hybrids are being widely cultivated, with some irrigation and using higher-input agriculture, yields can be well in excess of 2 t ha1. Postharvest practices also remain backward in many areas, for example, manual threshing and winnowing of the grain (Figure 1). Pearl millet can also suffer severe storage losses, particularly as a result of insects such as the rice moth (Corcyra cephalonica). The larvae contaminate the grain by producing webbing (silk) and consume the protein- and fat-rich grain germs. Control is traditionally affected by putting wood ash in the storage bin. Today, application of the fumigant phostoxin (active ingredient phosphine gas) is becoming more widespread.

• • • • •

Pearl millet is quantitatively the most important millet species. Pearl millet is uniquely hardy and can be cultivated in hot and dry conditions. Pearl millet grain has better nutritional value than most other cereals. Many traditional foods and beverages and specialty products are produced from pearl millet. Pearl millet is becoming widely used in commercial smallscale food manufacture. Iron- and zinc-biofortified pearl millet has been developed for improved nutrition.

Learning Objectives

• • • •

To provide an introduction to the importance of pearl millet as a staple food crop. To provide brief and accurate information about pearl grain structure, nutritional composition, and traditional food and beverage uses. To provide brief and interesting information on the technologies used to produce traditional foods and beverages from pearl millet. To sensitize the reader to the potential of pearl millet as a global staple food crop in the age of climate change.

Introduction Pearl millet, commonly known as bulrush millet (Pennisetum glaucum (L.) R. Br.), also classified as P. typhoides, P. americanum, or P. spicatum, is a cultivated, small-grain, C4 tropical cereal grass. Vernacular names include ‘bajra’ (India), ‘gero’ (Nigeria, Hausa language), ‘hegni’ (Niger, Djerma language), ‘sanyo’ (Mali), ‘dukhon’ (Sudan, Arabic), and ‘mahangu’ (Namibia). It is diploid (2n ¼ 2x ¼ 14) with a large genome (2450 Mbp). Pearl millet is quantitatively the most important millet, with a world annual production of some 15–25 million tonnes (Mt). It is cultivated mainly in the semiarid tropics, almost exclusively by subsistence and small-scale commercial farmers. This article will examine pearl millet production and agronomic issues, grain structure, chemistry and nutritional aspects, primary processing technologies, important foods and beverages produced from pearl millet, pearl millet’s future prospects, and research and development challenges.

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http://dx.doi.org/10.1016/B978-0-12-394437-5.00011-5

THE CEREAL GRAINS | Millet Pearl: Overview

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Style Pericarp Seed coat Aleurone layer Corneous endosperm Peripheral endosperm Floury endosperm Scutellar Epithelium Scutellum Embryonic axis

Figure 1 Winnowing of pearl millet in northern Namibia.

Hilum Figure 3 Diagrammatic longitudinal section through a pearl millet grain. Courtesy of Mr S C Barrion.

Figure 2 Pearl millet grain. Courtesy of Dr L A M Pelembe.

Grain Structure, Chemical Composition, and Nutritional Value Grain Structure Pearl millet grains are tear-shaped to ovoid (Figure 2). They are up to 2 mm in length, and the 1000-kernel weight is in the range 3–15 g (typically 8 g), about one-quarter that of a wheat grain. The overall grain color varies from pearly white (hence the name) to yellow, slate gray, brown, or purple. Individual grains are often not uniformly colored. The anthocyanin pigments responsible for grain color are concentrated in the pericarp. The general grain structure is essentially the same as other major tropical cereals, maize and sorghum (Figure 3). The kernel is naked, that is, it generally threshes free of the hull. A feature characterizing pearl millet grain structure is the proportionally very large germ and hence relatively smaller endosperm. This impacts the chemical composition of the grain.

The endosperm comprises two major components: the outer corneous (also referred to as vitreous or hard) endosperm and the inner floury (also referred to a soft) endosperm. The cells of the corneous endosperm are filled with an airspace-free continuous matrix of proteins comprising protein bodies and matrix protein. It contains few starch granules. In contrast, the cells of the floury endosperm have airspaces in them and contain many more starch granules and less protein. The pericarp is variable in thickness, dependent on variety, and composed of three layers: the epicarp, mesocarp, and endocarp. The mesocarp may contain starch granules such as in sorghum grain. Beneath the pericarp is a seed coat, which may be pigmented, and beneath this is the aleurone layer, part of the endosperm, which is one cell thick. The kernel is enveloped in a waxy cutin layer, which protects the grain against weathering.

Chemical Composition and Nutritional Value The general chemical composition and major nutrient contents of pearl millet grain are given in Table 1. It should be noted that these values refer to the whole, unprocessed grain. Processing by milling and malting will affect both the content and availability of many nutrients.

Energy Whole pearl millet grain has higher energy content (1720 kJ 100 g1 (db)) than all other cereal grains except maize.

192 Table 1

THE CEREAL GRAINS | Millet Pearl: Overview Proximate chemical and nutrient composition of pearl millet grain

Proximate composition (db) (g 100 g1)a

Minerals (db) (mg 100 g1)a

Essential amino acids (g 100 g protein1)b

Food energy (kJ) 1670–1800 (1720) Protein 8.6–19.4 (14.5) Starch 63.1–78.5 (71.6) Fat 1.5–6.8 (5.1) Dietary fiber 8.0–9.0 (8.5) Ash 1.6–3.6 (2.0) Vitamins (db) (mg 100 g1)a 24 Vitamin A (RE)d Thiamin 0.3 Riboflavin 0.2 Niacin 2.9 Vitamin E 1.9

Ca Cl Cu Fe Mg Mn P K Na Zn

Isoleucine Leucine Lysine Phenylalanine þ tyrosine Threonine Tryptophan Valine Cystine þ methionine

41 47 0.5 10.8 125 0.8 373 460 17 2.4

3.9–4.6 (2.3)c 9.5–12.4 (4.4) 2.8–3.2 (3.5) 7.1–9.3 (3.0) 3.3–4.1 (1.8) 1.4–1.5 (0.5) 4.9–6.0 (2.9) 3.4–4.4 (1.8)

a

Range and typical values. Typical range. c Ideal pattern for 3–10-year-olds. d Retinol equivalents. Data from Serna-Saldivar S and Rooney LW (1995) Structure and chemistry of sorghum and millets. In: Dendy DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 69–124. St Paul, MN: American Association of Cereal Chemists; Klopfenstein CF and Hoseney RC (1995) Nutritional properties of sorghum and the millets. In: Dendy, DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 124–168. St Paul, MN: American Association of Cereal Chemists; National Research Council (1996) Lost Crops of Africa, vol. 1. Washington, DC: National Academies Press; Abdalla AA, El Tinay AH, Mohamed BE, and Abdalla AH (1998) Proximate composition, starch, phytate and mineral contents of 10 pearl millet genotypes. Food Chemistry 63: 243–246. b

This is due to its high fat content, a consequence of the relatively large germ.

Carbohydrates

As with all other cereals, the predominant carbohydrate in pearl millet is starch. The starch content, typically 71–72 g 100 g1 (db), is perhaps slightly lower than most other cereals, due to the fact that the endosperm is proportionally smaller than other cereals. The percentage amylose in pearl millet starch is in the range 17.0–21.5%, which is relatively low for normal (nonwaxy) starches. Waxy (essentially 100% amylopectin) pearl millet has not been reported. The starch gelatinization temperature is in the range 61–69 C, typical of tropical cereal starches. Soluble sugars in pearl millet grain, as in all sound cereal grains, are low, in the range 1.4–2.8 100 g1, with the major sugars being sucrose and raffinose. The dietary fiber content of pearl millet grain is 8–9 100 g1 (db). The dietary fiber of pearl millet, as with sorghum, is mainly of the insoluble (water-inextractable) type.

Proteins and amino acids

Pearl millet grain protein content, typically 14.5 g 100 g1 (db), is high for cereal grains. This is because the grain has a large germ. This, in turn, also affects the balance of Osborne protein solubility groups and the overall amino acid composition of the pearl millet protein. Considering the protein fractions, the prolamin (aqueous alcohol-soluble) proteins, 31–41% of total protein, are, as in most other cereals, the major fraction in pearl millet. However, this level is lower than most other cereals as prolamins are endosperm-specific proteins. In contrast, the amount of albumin and globulin (saline-soluble) proteins, 25–26% of total proteins, is probably somewhat higher than in most other cereals. The prolamin proteins of pearl millet are called pennisetins and are similar to the prolamins of maize and sorghum, with high

contents of glutamine (23–24 g 100 g protein1), alanine (8–9 g 100 g protein1), and leucine ( 10–12 g 100 g protein1), but relatively low in proline ( 8 g 100 g1 protein1) and cystine and methionine ( 1 g 100 g protein1 each). Sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions shows a major band of Mr 22 kDa and minor bands of Mr 20 and 10 kDa. Research indicates that, unlike the situation with sorghum, wet cooking, as occurs in porridge making, does not substantially reduce the digestibility of pearl millet protein. This is probably a consequence of the somewhat lower percentage of prolamin proteins and the low content of cystine. However, like the other tropical cereals, the prolamins of pearl millet differ so much from those of wheat that it is considered as being ‘gluten-free.’ The amino acid composition of pearl millet protein (Table 1) is characterized by a relatively high content (compared with most cereal grains) of the essential amino acid lysine, in the range 2.8–3.2 g 100 g protein1. This is a consequence of the relatively high proportion of lysine-rich albumin and globulins, due to pearl millet’s large germ. However, the lysine content of pearl millet does not meet the requirements of infants, but it is close to that of young school age children. This emphasizes the importance of supplementation of cereals in the diet with meat, dairy, or legumes, as sources of lysine. Pearl millet protein is, as shown, a satisfactory source of the other indispensible amino acids.

Fats

The fat content of pearl millet grain, typically 5.1 g 100 g1 (db), is high compared with all other cereal grains, except maize. In the case of both pearl millet and maize, the high fat content is due to the large germ. As with all other cereals, the major fatty acids are linoleic acid (C18:2), typically 43–45% of the total; oleic acid (C18:1), 26–27% of the total; and palmitic acid (C16:0), 20–21% of the total. The high content of fat and

THE CEREAL GRAINS | Millet Pearl: Overview in particular of polyunsaturated fatty acids means that wholegrain pearl millet, when milled, is highly subject to deterioration through oxidative rancidity.

Vitamins

Pearl millet, like other cereal grains, is an important source of B vitamins (Table 1). These are concentrated in the aleurone layer and germ. Hence, their content can be adversely affected by milling. Niacin occurs partially bound to carbohydrate. To make it fully available, the flour has to be treated with alkali. This is done by treatment with wood ash in the preparation of the Western African porridge called ‘toˆ.’ Because of its high fat content, pearl millet is a good source of tocopherols (vitamin E), located mainly in the germ.

Minerals

Pearl millet grain, like other grains, is a good source of most dietary minerals (Table 1), with the exception of calcium. Quantitatively, the highest contents are of phosphorus and potassium. However, the availability of the former and of the multivalent metal ions is negatively affected by the presence of phytate (see the succeeding text). The minerals are concentrated in the pericarp, aleurone layer, and germ. Hence, their content can be adversely affected by milling.

Phytochemicals With regard to phenolic phytochemicals, when compared with other millets, pearl millet seems to be very low in soluble and insoluble forms of hydroxybenzoic acids and flavonoids but contains reasonable levels of both soluble and bound hydroxycinnamic acids. However, the available data are very limited, and it is probable that levels vary greatly with genotype and cultivation environment.

Antinutrients There is evidence that pearl millet contains goitrogens. It appears that the goitrogens are primarily phenolic flavonoidtype compounds, the C-glycosyl flavones: vitexin, glucosyl vitexin, and glucosyl orientin. Other phenolic compounds, such as phloroglucinol, resorcinol, and p-hydroxybenzoic acid, could also be involved. These compounds apparently inhibit the deiodination of the hormone thyroxine to its more active form triiodothyronine. They are concentrated in the outer layers of the grain and are considerably reduced when the grain is ‘dehulled’ during milling. The nutritional significance of the goitrogens in pearl millet should not be overstated. Although some rural people, for example, in Sudan/ South Sudan and areas of India, who consume pearl millet as a staple have been found to suffer from goiter, it is probable that this is because their diet is very restricted and hence deficient in iodine. The C-glycosyl flavones contribute to the brown/gray color of pearl millet and also appear to be responsible for the characteristic musty flavor of damp pearl millet flour, which is probably of greater significance. Some people describe the flavor as being ‘mousy’ or ‘mouse-dropping’ like. In pearl millet foods, such as porridges, it can be rather disagreeable to those not familiar with the food.

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Pearl millet, like all grains, contains the phosphoruscontaining compound phytate, myo-inositol hexaphosphate. Phytate acts as the main phosphorus store in seeds. In grain foods, it has the undesirable property of binding multivalent metal cations such as iron, zinc, and calcium and rendering them biologically unavailable. The level of phytate in pearl millet grain, in the range 350–800 mg 100 g1, is typical of cereal grains (Table 1). Phytate in pearl millet, as in other cereal grains, is located in the aleurone layer and germ. Hence, ‘dehulling’ the grain during milling substantially reduces the level of phytate (but also the minerals) in flour. Malting and fermentation specifically reduce the level of phytate by enzymatically degrading it, freeing the minerals. It should be noted that contrary to what is written in some texts, pearl millet, unlike some varieties of sorghum and finger millet, does not contain condensed tannins (proanthocyanidins).

Primary Processing Milling Pearl millet is milled into flour for porridge and bread making and into semolina (coarse grits) for couscous making. The milling process used in northern Namibia is shown in Figure 4 and will be described in detail as it has some unique features.

Dehulling To improve the palatability and storage quality of the flour, the bran (pericarp and germ) is generally removed from the grain first. This process of bran removal is referred to as dehulling. Cleaned pearl millet grain Decorticate (PRL dehuller)

Lactic acid ferment (soak overnight)

Partially dry (solar drying)

Mill (hammer mill) Fine flour Fully dry (solar dry)

Pack flour (paper or woven sacks) Figure 4 Pearl millet milling process used in northern Namibia.

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Figure 6 Pearl millet malt before drying. Courtesy of Dr L A M Pelembe. Figure 5 Small-scale commercial pearl millet mill in northern Namibia. Foreground – hammer mill; background – PRL dehuller.

Strictly speaking, decortication is the correct term since the pearl millet grain does not have a hull. Figure 5 shows the equipment used in a small-scale commercial pearl millet mill in Namibia. In the background is a Prairie Research Laboratory (PRL) abrasive-type dehuller. Today, abrasive-type hullers are manufactured in a number of countries in Southern and Western Africa. The PRL dehuller comprises an axle with 12 Carborundum disks mounted on it, within a cylindrical box. The axle revolves at high speed and the disks abrade off the bran from the grain. A suction fan removes the bran. Alternatively, pearl millet dehullers in Western Africa incorporate revolving brushes and screens to remove and separate the loose bran from the ‘dehulled’ grain. The amount of dehulling is determined by the duration of the dehulling process. Anything between 10% and 30% of the grain is removed, depending on the desired final color and fat content of the flour. Dehulling has the effect of reducing the fiber, fat, and protein contents of the grain due to the removal of pericarp and germ material. The quality of the protein will also be adversely affected as the quantity of the lysine-rich germ proteins is reduced. The starch content is increased slightly.

Steeping In the Namibian process, the dehulled grain is steeped in ambient temperature water overnight. This steeping process is actually a lactic acid fermentation. A lactic acid bacterial ‘culture,’ maintained by the process of ‘back slopping,’ is used to inoculate the steep water. The culture comprises a portion of the previous steep, with a high load of suitable lactic acid bacteria. The purpose of the lactic acid steep seems to be severalfold. It lightens and brightens the flour. The low pH of the steep water is responsible for lightening the color and partially leaching out the brown/gray polyphenolic pigments of the grain. Goitrogens may also be leached out of the grain. However, it is probable that water-soluble proteins, vitamins, and minerals are lost in the steeping process. The steep softens the grain, facilitating its reduction into a fine flour. The resulting flour has an acidic flavor, which consumers prefer.

Solar drying The dehulled, steeped grain is partially dried before milling, and after milling, the flour must be fully dried to a shelf-stable moisture content of 10%. Solar drying is used for both steps. The grain or flour is dried on polythene sheets, either directly on a concrete floor or on long tables made of wooden slats.

Milling The partially dried, dehulled steeped grain is milled into a fine flour using a powerful hammer mill. The high moisture content (30–40%) of the grain necessitates relatively powerful milling. Thus, the process is actually semiwet milling. This apparently rather inefficient process seems to be necessary in order to mill the grain into fine flour. In Western Africa, disk mills are generally used to produce semolina for couscous making.

Malting In sub-Saharan Africa, pearl millet is malted to produce malt for brewing traditional opaque beer and nonalcoholic beverages. Pearl millet malting is almost exclusively done in the home, although one large-scale commercial malting operation in Zimbabwe malts pearl millet together with sorghum. Figure 6 shows pearl millet malt prior to drying. It can be seen that there is extensive root and shoot growth. The optimum temperature conditions of pearl millet malting are in the range 24–28 C, identical to that for sorghum. The malting process involves three steps: steeping, germination, and drying. The steeping time for pearl millet is short, up to 8 h, as the grain germinates rapidly. Germination is allowed to progress for 4–5 days. Like sorghum, pearl millet must be watered during germination. Drying is at ambient temperature or up to 50 C in order to conserve malt enzyme activity. Pearl millet malt quality seems to be somewhat higher than that of sorghum malt. Diastatic power (total amylase activity) is similar, 30–50 sorghum diastatic units g1. However, the activity of the b-amylase component is higher. b-Amylase is the enzyme that produces the fermentable sugar maltose. The higher b-amylase activity indicates that pearl millet malt could have potential as partial substitute for barley malt for brewing lager beer. Free amino nitrogen and extract are also higher in pearl millet malt than sorghum malt. Of particular significance

THE CEREAL GRAINS | Millet Pearl: Overview is the fact that malting almost completely eliminates the mousy flavor associated with pearl millet flour. Some nutritional improvements also occur, in particular improvement in carbohydrate and protein availability. However, against this, there is a substantial overall loss in mass of grain, 10–15%, due to respiration during germination.

Food and Beverage Production Worldwide, pearl millet is processed into many different traditional foods and beverages. Foods include ‘rice’ and flatbreads (‘roti’) in India, ‘couscous’ in Mali and Senegal, doughs such as ‘fura’ in Ghana, thick porridges such as ‘toˆ’ in Western Africa and ‘bogobe’ in Southern Africa, thin fermented porridges such as ‘uji’ in Eastern Africa, and gruels like ‘ogi’ in Nigeria. Beverages can be nonalcoholic like ‘oshikundu’ in Namibia or alcoholic like the opaque beer of Southern Africa.

Foods

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Western African countries such as Mali and Burkina Faso is often produced from highly refined flour giving it a gel-like consistency. It may be cooked with tamarind or lemon or with wood ash or potash, giving it acidic or alkaline taste, respectively. These porridge products are traditionally eaten cool or cold with the hand and served with a vegetable relish. Doughs and gruels made from pearl millet are invariably lactic acid bacteria-fermented. The fermentation used in fura dough making has been reported to produce bacteriocins with inhibitory activity against a wide range of pathogens.

Couscous

In the Sahel region of Western Africa, couscous made from pearl millet and sorghum is a very popular food (Figure 7). Couscous making involves processing coarse endosperm particles (semolina) in repeated steps of agglomerating, steaming, and sifting to ultimately produce cooked granular particles of uniform size (Figure 8). The steaming gelatinizes the starch on the surface of the particles so that they stick together. The couscous is often served with yogurt, the product being called ‘thiakri.’

Porridges, doughs, and gruels In sub-Saharan Africa, pearl millet is most frequently consumed as a porridge. A traditional Pedi (Limpopo Province, South Africa) recipe to make ‘bogobe bia bupi bja leotsa’ (literally porridge of pearl millet) involves cooking 1 kg of whole-grain pearl millet meal in 1.9 l water. The porridge has greenish-brown color and a thick, smooth viscous consistency. Because of the high ratio of starch to water, the porridge gels on cooling. The flavor is musty, sweet, and bitter. The meal ration size is 1 kg, which provides some 2205 kJ, 20–25% of an adult’s recommended dietary allowance. ‘Toˆ’ porridge from

Figure 7 Pearl millet couscous from Senegal.

Flatbreads In India, pearl millet is generally consumed as a crisp flatbread, called roti or ‘chapatti.’ Figure 9 shows a flowchart for making roti. A problem in making breads from non-gluten-containing grains such as pearl millet is that the product tends to break into pieces. It is notable that in the milling process, the flour is ground to fine particle size, 43% having a particle size <75 mm. This increases the surface area of the flour particles and damages the starch granules, increasing their water absorption. Both factors increase the cohesiveness of the dough.

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Pearl millet grain Mill (disk or plate mill) Whole grain flour Sieve (850 mm screen) Flour (50 g) + Warm water (45 ml) Knead by hand into dough

Flatten and work into circular sheet (120 − 250 mm diameter, 1.3 − 3.0 mm thick)

Bake (iron or earthenware pan 300–325 ⬚C) top side moistened Figure 8 Sieving agglomerated pearl millet and sorghum couscous in Senegal.

Puff (unmoistened side exposed to dry heat) Roti

Variations on the roti-making process, which also alleviate the problem, can involve cooking part of the flour in water and mixing it together with the uncooked flour. Cooking gelatinizes the starch making it into a binder, as with couscous, which improves the cohesiveness and elasticity of the dough. Alternatively, pearl millet flour can be composited with flours such as gram (mung bean) or other legume flours that give better cohesiveness or wheat flour that gives elasticity. Because of the absence of gluten in pearl millet, breads made from pearl millet flour are unleavened. However, in the roti-making process, as shown in Figure 9, the flatbread is exposed on one side to high heat, which puffs it giving the bread some ‘leavened’ texture. Puffing takes place as result of the fact that the moistening water added during baking is very rapidly turned into steam. The resulting increase in volume creates an air sac as the steam escapes. Roti is served with a small amount of hot pickle, ‘dhal,’ or vegetable sauce.

Beverages Throughout Africa, sorghum, maize, and millets are used to produce both nonalcoholic and alcoholic beverages. Invariably, these beverages have undergone a lactic acid fermentation, giving them a refreshing sour taste. The low pH of the beverages renders them free from foodborne pathogenic bacteria and helps protect them against microbial spoilage.

Figure 9 Roti-making process.

Nonalcoholic A very popular nonalcoholic fermented beverage in Namibia is ‘oshikundu’ made from pearl millet and sorghum malt flour. Some 200 g of pearl millet flour are thoroughly mixed into 500 ml of boiling water. Then, 100 g of sorghum malt flour is added. Sorghum malt provides amylase enzymes and lactic acid bacteria. a-Amylase thins the porridge into gruel by hydrolyzing the starch into dextrins, and b-amylase further hydrolyzes the dextrins into maltose. The thinning and hydrolysis actions of the amylases improve food palatability and carbohydrate availability. The lactic acid bacteria use the fermentable sugars for respiration, producing lactic acid and other flavor compounds. After the mixture has cooled to room temperature, 1–1.5 l of cold water is mixed in. The container is closed and the mixture is allowed to ferment overnight before consumption. Oshikundu is greenish brown in color and has the consistency of drinking yogurt. It is slightly effervescent with a buttery sour taste. A lactic acid content of 0.6% has been measured.

Opaque beer In several southern African countries, pearl millet malt is used to brew traditional, opaque-type beer. Figure 10 shows a


Pearl millet malt (3.7 kg)

Ferment in clay pot (24 h warm temp)

Luke warm water (3.4 l)

Decant off supematant Supematant (8.6 l)

Residue

Bring supematent to boil Stir in residue and boil (1 h)

Hold to gel (24 h room temp)

Mash and ferment (24 h warm temp)

Pearl millet malt (1.8 kg)

Strain by wringing through grass bag

Strainings (spent grain) (4.7 kg)

Beer (12.3 l) Figure 10 Pearl millet opaque beer-making process.

flowchart for a Pedi recipe for making ‘bjalwa bja leotsa’ (literally beer of pearl millet). The process has some interesting features. It is noteworthy that only malt is used in the recipe. In contrast to brewing traditional opaque sorghum beer, no unmalted grain adjunct is used. In fact, part of the malt is used as adjunct by cooking it after the first fermentation process. The first fermentation process is probably primarily a lactic acid fermentation, but some fermentable sugar production will also take place. As there is no unmalted adjunct in the recipe, it means that there is a proportionally higher ratio of amylase enzymes to starch, producing more fermentable sugars. Coupled with the fact that pearl millet malt intrinsically contains a higher ratio of b-amylase, this probably accounts for the fact the pearl millet beer is claimed to be more intoxicating than sorghum beer. Typical of traditional recipes, more than one process takes place during a particular step. This is unlike modern food and beverage manufacturing processes where there is a system of unit operations. In the mashing and fermentation stage, gelatinized starch is hydrolyzed by the malt amylase enzymes into fermentable sugars, which are fermented by both yeast and lactic acid bacteria to produce ethanol, carbon dioxide, and lactic acid as the main products. The beer is described as turbid, greenish brown in color, with a milk like consistency. The flavor is musty and bitter sour, with a lactic acid content of 1.8%. Pearl millet beer seems to be much thinner and more acidic than sorghum beer.

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Future Prospects and Challenges With the world beginning to experience climatic change, pearl millet with its unique ability to produce a crop under hot and dry conditions should become a far more globally important food grain. In the developing world, the need for food and nutrition security demands that pearl millet increasingly becomes a commercially cultivated, traded grain and processed into food products, instead of just being a subsistence crop. The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is leading a project to develop pearl millet with substantially increased levels of the iron and zinc using varietal selection and conventional breeding. Varieties of this biofortified pearl millet were released for cultivation in India and Africa in 2013. Further, as a result of rapid urbanization and rising incomes across much of Africa, small-scale commercial enterprises based on making convenience versions of traditional pearl millet food and beverage products are becoming widespread. Related to both nutritional value and commercial value, the high-energy, fat, and protein content, coupled with its relatively high level of lysine, is leading to increasing cultivation of pearl millet for poultry feeding, particularly in Western Africa. Numerous scientific and technological problems still require further research and development for pearl millet to achieve its global potential. These include improving its resistance to a range of plant diseases, creating sustainable seed production and supply systems, more efficient milling of grain to reduce losses, eliminating the ‘mousy aroma’ in pearl millet foods, and determining the significance of the reported goitrogen problem.


• • • • • •

Draw the structure of the pearl millet grain, naming the grain tissues. Explain the major nutritional advantages of pearl millet compared with other cereals. Name the antinutrients present in pearl millet and explain their nutritional significance. Draw a flow diagram showing the steps in producing a traditional pearl millet food of your own choice. Draw a flow diagram showing the steps in producing a traditional pearl millet beverage of your own choice. Explain the science of how textured dry food products can be produced from pearl millet, despite the fact that it does not contain gluten.


• • •

There is value in biofortification of pearl millet with other essential micronutrients than iron and zinc, for example, provitamin A. How can the yields of pearl millet in Africa be substantially improved to help eliminate food insecurity? The phenolic phytochemicals in a pearl millet need to be far better characterized across a wide range of genotypes and

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• •


individual functional and antinutrient properties determined. A more efficient way to mill the pearl millet grain is required in order to reduce losses and eliminate the ‘mousy aroma’ in pearl millet foods. The real extent of the goitrogen problem in pearl millet must be established.

See also: Beverages from Grains: Fermentation: Foods and Nonalcoholic Beverages; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure; Taxonomic Classification of Grain Species; The Cereal Grains: Millet Minor: Overview; Teff: Overview.

Further Reading Abdalla AA, El Tinay AH, Mohamed BE, and Abdalla AH (1998) Proximate composition, starch, phytate and mineral contents of 10 pearl millet genotypes. Food Chemistry 63: 243–246. Chandkara A and Shahidi F (2011) Determination of antioxidant activity in free and hydrolysed fractions of millet grains and characterization of their phenolic profiles by HPLC-ESI-MSn. Journal of Functional Foods 3: 144–158. Emmambux MN and Taylor JRN (2013) Morphology, physical, chemical and functional properties of starches from cereals, legumes and tubers cultivated in Africa: A review. Starch/Sta¨rke 65: 715–729. FAOSTAT. Production: Crops. http://faostat.fao.org/ (access 14.02.01).

Germplasm Resources Information Network (GRIN). GRIN Taxonomy for Plants. http:// www.ars-grin.gov/ (assessed 14.02.01). ICRISAT EXPLOREit. Pearl millet. http://exploreit.icrisat.org/ (accessed 14.01.08). ICRISAT and FAO (1996) The World Sorghum and Millet Economies. Patancheru, India/ Rome: International Crops Research Institute for the Semi-Arid Tropics/Food and Agriculture Organization of the United Nations. Klopfenstein CF and Hoseney RC (1995) Nutritional properties of sorghum and the millets. In: Dendy DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 124–168. St Paul, MN: American Association of Cereal Chemists. Murty DS and Kumar KA (1995) Traditional uses of sorghum and millets. In: Dendy DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 185–222. St Paul, MN: American Association of Cereal Chemists. National Research Council (1996) Lost Crops of Africa, vol. 1. Washington, DC: National Academies Press. Obilana AB and Manyasa E (2002) Millets. In: Belton PS and Taylor JRN (eds.) Pseudocereals and Less Common Cereals, pp. 177–217. Berlin: Springer. Quin PJ (1959) Food and Feeding Habits of the Pedi. Johannesburg: Witwatersrand University Press. Rai KN, Govindaraj M, and Rao AS (2012) Genetic enhancement of grain iron and zinc content in pearl millet. Quality Assurance & Safety of Crops and Food 4: 119–125. Serna-Saldivar S and Rooney LW (1995) Structure and chemistry of sorghum and millets. In: Dendy DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 69–124. St Paul, MN: American Association of Cereal Chemists. Taylor JRN and Emmambux MN (2008a) Millets. In: Arendt E and Dal Bello F (eds.) Gluten Free Cereal Products and Beverages, pp. 119–148. London: Elsevier. Taylor JRN and Emmambux MN (2008b) Products containing other speciality grains: Sorghum, the millets and pseudocereals. In: Hamaker BR (ed.) Technology of Functional Cereal Products, pp. 281–335. Abington, UK: Woodhead Publishing. Taylor JRN, Barrion SC, and Rooney LW (2010) Pearl millet – New developments in an ancient food grain. Cereal Foods World 55: 16–19. World Health Organization (2002) Joint FAO/WHO/UNU expert consultation on protein and amino acid requirements in human nutrition, WHO Technical Report Series; No. 935. Geneva: WHO.

Millet Minor: Overview GK Chandi, University of Guelph, Guelph, ON, Canada GA Annor, University of Ghana, Accra, Ghana ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Minor millets are domesticated and used as food across different parts of the world. Millets are generally used for pancakes, flatbreads, porridge, fermented beverages, boiled grains, gruel, etc. Minor millets are decorticated before grinding them into coarse or fine flours or grits of various particle sizes. Hypoglycemic properties of millets may be attributed to various factors such as phenolic compounds, soluble fibers, and starch–lipid–protein interactions. Owing to their potential therapeutic properties and resistance to severe weather conditions, minor millets have a great potential to address the health and food security issues.

Learning Objectives

• •

Understand the processing and utilization of minor millets. Identify the key attributes responsible for nutritional benefits of minor millets.

Introduction Minor millets are a heterogeneous group of small-grain cereal species, grown around the world for food and fodder. Millets comprise a diverse range of species belonging to different genera, which originated in different parts of the world. Some of these millets are cultivated by small farmers in Africa and Asia, while others grow as wild grasses or weeds (Figure 1, Table 1). Minor millets are highly adapted to drought and low-fertility soils. The color and structural features of minor millet grains vary among different genera (Figure 2, Table 2). Minor millets fall in one of following genera: Eleusine, Setaria, Paspalum, Panicum, Brachiaria, Echinochloa, and Digitaria, with some examples including the following: 1. Finger millet (Eleusine coracana): This millet species is cultivated in more than 25 countries in Africa. It has been grown in India in the last 4000 years. It is highly adaptable to higher elevations and hence grown in the Himalayas up to an altitude of 2300 m. It however has a higher water requirement than most of other millets. 2. Common or proso millet (Panicum miliaceum): This millet species was domesticated in China by about 5000 BP and between 5000 and 4000 BP in Europe. Proso millet is considered a self-pollinated crop, but natural crosspollination may exceed 10%. Proso millet is found high in mountains up to 3500 m in India. It grows in temperate climates and is tolerant to wide range of temperatures. It matures in 60–90 days.


3. Foxtail or Italian millet (Setaria italica): This millet species is a native of China and ranks first in its global production. Its cultivation in Europe dates to about 2000 BP. Although found in the tropics, it is adapted to temperate regions. It has a broad range of days of maturity (70–120 days). Green foxtail millet (Setaria viridis) is the wild antecedent of foxtail millet and has very limited food usage. 4. Kodo millet (Paspalum scrobiculatum): This millet species is commonly harvested as a wild cereal in tropical Africa and the Deccan region of India. It was introduced in India almost 3000 years ago. It is self-pollinating, and its florets generally remain closed during the flowering period. It matures late compared to other cereals. Sometimes, due to fungal infections after the rain, kodo millet grains become poisonous. 5. Little millet (Panicum sumatrense): This millet species grows up to an altitude of 2100 m in India. It is commonly grown in India and cooked like rice. It is primarily a selfpollinating crop with about 3.5% cross-pollination. It matures between 2.5 and 5 months. Besides the aforementioned millets, there are other minor millets that are cultivated in restricted geographic regions and have no importance in world agriculture trade. Some of these millets include the following: Barnyard or sawa millet (Echinochloa utilis): This millet species is grown on a small scale in Japan, China, India, Pakistan, Nepal, and Korea. Barnyard grasses grow as weeds and become a nuisance when not managed. It is usually harvested within 6 weeks and is grown as a substitute for rice when paddy crop fails. Browntop millet (Brachiaria ramosa): This millet species is a warm-season annual grass and reaches about 10–70 cm height. It can tolerate drought and is known to be cultivated and/or utilized from wild harvests today, although in very restricted regions of Kenya, Tanzania, South Africa, and tropical Asia. White fonio (Digitaria exilis) and black fonio (Digitaria iburua): These millet species are commonly eaten by inhabitants of semiarid regions of West Africa. Their cultivation seems to have started around 7000 years ago. White fonio is cultivated throughout much of this region, except Liberia. It is a very important crop in Southern Mali, Northeastern Nigeria, extreme Southern Niger, Western Burkina Faso, Eastern Senegal, and Northern Guinea. Black fonio is found in isolated pockets in the Jos Bauchi Plateau of Nigeria and the northern parts of Togo and Benin. Fonios are staple crop of many poor rural communities of these regions and are characterized by a short production time of 10 weeks. Guinea millet (Brachiaria deflexa): This millet species is also among minor cereals of Western Africa. However, its cultivation is confined to the Fouta Djallon Plateau of Guinea and Sierra Leone. Some cultivars are very early maturing and thus

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THE CEREAL GRAINS | Millet Minor: Overview

Figure 1 Minor millet crops and grain. (a) Foxtail millet, (b) little millet, (c) kodo millet, (d) common millet, (e) barnyard millet, and (f) finger millet. Reproduced from Balasubramanian S (2013) Processing of millets. In: National Seminar on Recent Advances in Processing, Utilization and Nutritional Impact of Small Millets. Madurai Symposium, Thamukkam Grounds, Madurai, 13 September 2013. Table 1

Common name, origin, and occurrence of minor millets

Common name

Origin

Where found/cultivated

Finger millet (Eleusine coracana)

Uganda or neighboring region Central and Eastern Asia

Eastern Africa and in Asia (India and Nepal)

Proso (common) millet (Panicum miliaceum) Foxtail millet (Setaria italica) Barnyard millet (Echinochloa utilis) Little millet (Panicum sumatrense) Kodo millet (Paspalum scrobiculatum)

Eastern Asia (China) Japan Southeast Asia India

Ukraine, Kazakhstan, the United States, Argentina, and Australia China, India, Indonesia, the Korean Peninsula, and some parts of southern Europe Tropics and subtropics of India India, Nepal, Pakistan, Sri Lanka, eastern Indonesia, and western Myanmar Wild cereal in Western Africa and India

Source: FAO.org.

suited for intercropping cultivation practices with other grain crops in dry lands under unreliable rainfall.

Nutritional Importance of Millets Minor millets are good sources of macronutrients and some micronutrients, as shown in Table 3. The gluten-free nature of these millets makes them a reasonable alternative for people suffering from celiac disease and allergies that result from the

consumption of wheat-based products. With total carbohydrate and protein contents of about 70% and 12%, respectively, there is no doubt that minor millets contribute significantly to the energy and protein needs of populations in regions where they are principal source of food.

Minerals and Vitamins Minor millets especially finger millets are important sources of minerals especially calcium relative to other cereals. With


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Figure 2 Minor millet grains. Reproduced from Balasubramanian S (2013) Processing of millets. In: National Seminar on Recent Advances in Processing, Utilization and Nutritional Impact of Small Millets. Madurai Symposium, Thamukkam Grounds, Madurai, 13 September 2013.

Table 2

Structural comparison of some minor millets

Millet

Plant height (cm)

Finger millet Proso millet

40–100 30–100

Foxtail millet Barnyard millet Little millet Kodo millet

Seed color

Seed shape

Seed size (mm)

Thousand kernel weight (g, 12% mb)

Globose Oval

1–2 32

2.6 4.7–7.2

0.5–200 50–100

Yellow, white, red, brown, violet White cream, yellow, orange, red, black, to brown Yellow, pale yellow Yellow, red, brown

Elliptical Globose

2–3 1.3

1.86 4.17

30–90 55

White, yellow, red, brown Light red to dark gray

Elliptical –

2.3 1.6 –

– –

Source: Upadhyaya HD, Dwivedi SL, Singh SK, Singh S, Vetriventhan M, and Sharma S (2014) Forming core collections in Barnyard, Kodo, and Little Millets using morph agronomic descriptors. Crop Science 54: 2673–2682 and FAO.org.

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Table 3 Parameter

Nutrient profile of minor millets (per 100 g edible portion) Finger millet

Moisture (g) 13.1 Protein (N ¼ 6.25) (g) 7.3 Fat (g) 1.3 Minerals (g) 2.7 Dietary fiber (g) 11.5 Carbohydrates (g) 72.0 Energy (kJ) 1372 Vitamins Beta-carotene (mg) 42 Thiamine (mg) 0.42 Riboflavin (mg) 0.19 Niacin (mg) 1.1 Total B6 (mg) – Folic acid (mg) Free 5.2 Total 18.3 Vitamin C (mg) 0 Choline (mg) – Minerals and trace elements Calcium (mg) 344 Phosphorus (mg) 283 Iron (mg) 3.9 Magnesium (mg) 137 Sodium (mg) 11 Potassium (mg) 408 Copper (mg) 0.47 Manganese (mg) 5.49 Molybdenum (mg) 0.102 Zinc (mg) 2.3 Chromium (mg) 0.028 Sulfur (mg) 160 Chlorine (mg) 44 Essential amino acids (mg/16 g N protein) Arginine 300 Histidine 130 Lysine 220 Tryptophan 100 Phenylalanine 310 Tyrosine 220 Methionine 210 Cystine 140 Threonine 240 Leucine 690 Isoleucine 400 Valine 480

Proso millet

Foxtail millet

Little millet

Kodo millet

Barnyard millet

11.9 12.5 1.1 1.9 – 70.4 1426

11.2 12.3 4.3 3.3 2.4 60.9 1384

11.5 7.7 4.7 1.5 2.5 67 1426

12.8 8.3 1.4 2.6 25 65.9 1284

11.9 6.2 2.2 4.4 2.08 65.5 1284

0 0.20 0.18 2.3 –

32 0.59 0.11 3.2 –

0 0.30 0.09 3.2 –

0 0.303 0.09 2.0 –

0 0.33 0.10 4.2 –

– – 0 748

4.2 15.0 0 –

2.2 9.0 0 –

7.4 23.1 0 –

– – 0 –

14 206 0.8 153 8.2 113 1.60 0.60 – 1.4 0.020 157 19

31 290 2.8 81 4.6 250 1.40 0.60 0.70 2.4 0.030 171 37

17 220 9.3 133 8.1 129 1.00 0.68 0.016 3.7 0.180 149 13

27 188 0.5 147 4.6 144 1.60 1.10 – 0.7 0.020 136 11

20 280 5.0 82 – – 0.60 0.96 – 3.0 0.090 – –

290 110 190 050 310 – 160 – 150 760 410 410

220 130 140 060 420 – 180 100 190 1040 480 430

250 120 110 060 330 – 180 090 190 760 370 350

270 120 150 050 430 – 180 110 200 650 360 410

– – – – – – – – – – – –

Source: Shobana S, Krishnaswamy K, Sudha V, et al. (2012) Finger millet (ragi, Eleusine coracana L.): A review of its nutritional properties, processing, and plausible health benefits. Advances in Food and Nutrition Research 69: 1–39; Gopalan C, Rama Sastri BV, and Balasubramanian SC (2009) Nutritive Value of Indian Foods. Hyderabad, India: National Institute of Nutrition, Indian Council of Medical Research. Geervani P and Eggum BO (1989) Nutrient composition and protein quality of minor millets. Plant Foods for Human Nutrition 39(2): 201–208.

calcium levels of about 344 mg/100 g, finger millet arguably has the highest calcium content when compared with other cereals. Using proton-induced x-ray emission spectrometry, Kruger et al. confirmed the high calcium content of finger millet and also showed that calcium was distributed throughout the endosperm where phytate levels were low. Phosphorus, iron, magnesium, potassium, sulfur, and zinc, for example, are all found in considerable amounts in minor millets. In terms of vitamins, some minor millets have been found to have low amounts of carotenoids thiamine, riboflavin, niacin, and

choline. Finger and foxtail millets have been reported to contain 42 mg/100 g and 32 mg/100 g carotenoid, respectively (Table 3).

Fat Fat in minor millets, as in other cereals, is mainly composed of unsaturated fatty acids. Oleic and linoleic acids are the main unsaturated fatty acids in minor millets, with palmitic acid as the main saturated fatty acid. Depending on the species of

THE CEREAL GRAINS | Millet Minor: Overview millet palmitic, oleic and linoleic acids can range from 6% to 23%, 20% to 66%, and 22% to 65%, respectively, of the total lipid content of the millet flours. Though these unsaturated fatty acids may have health benefits, they are also responsible for the rancidity that is normally observed in stored millet flours with relatively high fat contents.

Fiber The dietary fiber contents of minor millets also confer some health benefits when they are consumed. Total dietary fiber values of about 27%, 20%, and 30% of grain weight have been reported for barnyard, kodo, and little millets, respectively, out of which 0.59%, 1.94%, and 1.33% are soluble fiber, respectively.

Amino Acids Just like most of the cereals, the minor millets are deficient in lysine, which is usually complemented when mixed with legumes.

Phytochemicals The pericarp of minor millets is rich in several phenolic phytochemicals, which are associated with various health benefits. The inhibitory effects of finger millet phenolic compounds on a-glucosidase and pancreatic a-amylase have been mentioned. It is thought that these millet phenolic compounds noncompetitively inhibit carbohydrate-hydrolyzing enzymes. Millet phenolic compounds have also been suggested to delay or interfere with the absorption of dietary carbohydrates in the small intestine resulting in the suppression of postprandial glucose spikes. A comprehensive review of phytochemicals in minor millets and their health benefits has been reported by Taylor et al. and Taylor and Duodu.

Hypoglycemic Properties The hypoglycemic property of millets and its importance in the management of type II diabetes were reported as far back as 1957. Since then, several other scientists have also reported on the lowering effects the regular consumption of minor millets has on postprandial blood glucose levels. It will also be of interest to understand the factors that contribute to the hypoglycemic property of millets to help maintain this property during processing and also to develop hypoglycemic food products. Some attempts have been made in this regard.

Role of Fiber Dietary fiber in millets has been mentioned as one of the reasons for its hypoglycemic property. With millets containing about 2% soluble and 30% insoluble fiber contents, their role in hypoglycemic property of millets cannot be overlooked. Fiber reduces the glycemic response of foods by increasing their viscosity, especially the soluble fiber. A considerable increase in soluble fiber content of finger millet is observed after decortication, though total dietary fiber decreases. This

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increase in the soluble fiber content has special nutritional significance due to its physiological advantages in terms of hypoglycemic and hypocholesterolemic characteristics.

Starch–Protein Interactions Some researchers have attributed the hypoglycemic property of finger millet to their rigid starch granule architecture. This rigidity slows down the rate at which the millet starch granules are hydrolyzed by starch digestive enzymes. The effects of protein-encapsulated granule matrix have been suggested as part of the reason for the hypoglycemic property of kodo millet. Some protein fractions glue protein bodies into a matrix surrounding starch granules, which then acts as a barrier to amylases. The removal of protein from kodo millet flour clearly results in a significant increase in its starch hydrolysis.

Starch–Lipid Interactions The presence of starch–lipid complexes, particularly lipid complexes with millet amylose, also influences the susceptibility of millet starch to enzymatic degradation. Annor et al. reported significant effects of starch–lipid complexes on the starch hydrolysis rates of millets. Foxtail, little, barnyard, kodo, and proso millets still contain a considerable amount of lipids even after decortication. The residual lipids in the endosperm are still sufficient to result in significant reductions in starch hydrolysis rates of the decorticated millet flour.

Fatty Acid Profile In addition to starch–lipid complexes influencing the glycemic properties of millets, the type of lipid and their amounts present in millets also significantly contribute to their hypoglycemic property. The main fatty acids present in millets in no particular order are palmitic, oleic, and linoleic acids. These three fatty acids form more than 80% of the total fatty acids present in millets. These fatty acids form complexes with millet starches and thereby reduce the rate at which the resulting starch–lipid complexes are hydrolyzed by digestive enzymes. The unsaturated fatty acids form more complexes than the saturated fatty acids. With regard to their effects on starch hydrolysis rates, all the fatty acids significantly reduce the millet starch hydrolysis rates and their expected glycemic index. Starch–oleic acid complex are the most stable against amylolysis. The amounts of these fatty acids present in the respective millet flour samples also significantly influence the expected glycemic index of millet flours. The greater the quantity of a particular fatty acid that is present in the millet flour, the more it reduces the starch hydrolysis rates and their resulting expected glycemic index. It is therefore important to retain the fatty acids present in millet flours when they are being processed to utilize their beneficial hypoglycemic property. Apart from hypoglycemic benefits, the regular consumption of minor millets has been associated to a myriad of health benefits. Germinated finger millet flour has been reported to improve hemoglobin status of school children in Tanzania and also have antimicrobial, antifungal, antioxidant free radicalscavenging, antiulcerative, cholesterol-lowering, and woundhealing properties.

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THE CEREAL GRAINS | Millet Minor: Overview faster cooking of the grain. For food purposes, postharvest processing of millets depends on the cultural preferences and traditions.

Storage of Grains Minor millets are important food crops of a large group of people living in rural, tribal, and hilly areas across the globe. About 90% of millets produced are used as food, and the rest of it is used as fodder or for medicinal purposes. The millet grains are stored either as unthreshed along with their ear heads or as threshed and clean grains. The unthreshed grains are normally heaped on the ground and covered with straw. The threshed and clean grains are packed in jute sacks and stacked in piles on the floor or wooden platforms. Some farmers also utilize silos or bins to store grains when needed. The larger storage structures are built with metal, wood, stone, or bamboo. In the absence of silos, the grains are stored in pits lined with straw. Once the pit is full, the grains are covered with straw and soil or dung. Clay pots are also sometimes used to store the millet grains. Occasionally, grains are exposed to sunshine to dry and also to prevent them from insect infestation.

Traditional Processing For the small-headed grains, husk (hull) is usually removed by hand pounding and less often by mechanical dehusking or polishing units. Grain is sometimes moistened before pounding. This is done by adding about 10% water to loosen the fibrous bran and also to separate the germ and the endosperm, if desired. The traditional processing of minor millets involves, in no particular order, dehulling, winnowing, washing, drying, milling, and sieving. Local small-scale mills are usually based on crude stone mortar and pestle or one horizontal hand millstone rotating on another. Both types of mills deliver whole meal. A wooden pestle and mortar (Figure. 4) is also commonly used in which by dampening, pounding, winnowing, and pounding again, millet is separated into fine and coarse semolina, flour, and bran.

Postharvest Processing Figure 3 depicts the major steps involved in processing of the millets. The millet kernels are smaller as compared with the size of majority of the cereal grains. The color of the millets is confined to the pericarp, which is strongly adhered to the endosperm. Millet milling is done to remove the hulls and bran (pericarp) of the grain. It lightens the color, improves the overall acceptability and nutritional quality, and leads to

Mechanical Processing Treatments such as parboiling, steaming, and drying are occasionally applied prior to mechanical milling of millets to facilitate complete removal of the husk. Parboiling is reported to help in dehusking kodo millet and to eliminate the stickiness in cooked finger millet porridge. Parboiling is basically the

HARVESTING Stems/Panicles/long straws/weeds/leaves

THRESHING AND WINNOWING

Husk/stems/chaffs/weeds

Spikelets/long straws/chaffs

STORAGE Spikelets/same sized weeds

SOURING POPPING

MALTING

MILLING AND POUNDING Grain/chaff/small weeds

(Lactic acid fermentation)

Husk/chaff/weeds

Tempering

Steep Cooking

Conditioning Heating

Germinate

Mashing

Kiln

Straining

Dehusking/Debranning Popped grains

Roller Milling

Grinding and Sieving Grinding Polished grains

Fully refined flour

Alcoholic fermentation Adjuncts for brewing

Flour Opaque Beer

Figure 3 Postharvest processing of minor millets.


Figure 4 Women husking fonio millet. Reproduced from Gari JA (2001) Review of African millet diversity. IPGRI/IFAD, Bamako, Mali, 19–22 November 2001, www.FAO.org.

process of partial cooking the grain along with its husk or bran. The resulting product is dried and decorticated.

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Figure 5 Tangential abrasive dehulling device. Reproduced from Balasubramanian S (2013) Processing of millets. In: National Seminar on Recent Advances in Processing, Utilization and Nutritional impact of small millets. Madurai Symposium, Thamukkam Grounds, Madurai, 13 September 2013.

corners or surface irregularities being knocked off. These techniques are used only to a limited extent at commercial scale.

Decortication Decortication improves the biological availability of nutrients and consumer acceptability of minor millets. It reduces total protein and lysine, but it also improves the utilization of the remaining protein. Decortication is sometimes accomplished by using rice dehullers or other abrasive dehullers. Technically, there are three types of decortication techniques that can be employed to minor millets: 1. Abrasive decorticators: Abrasive decorticators abrade away the fibrous pericarp (Figure 5). If all parts of the grains could be abraded away at the same rate, abrasive decortication would be an efficient way of removing the pericarp. However, different parts of individual grains are abraded away at different rates, and there is some loss of endosperm (particularly from damaged grains) even when the grain is only lightly abraded. 2. Rubbing technique: For this technique, decortication is achieved by a steel rotor, rotating the grain mass within a generally cylindrical chamber. When the grain is properly tempered, the pericarp is rubbed off by the movement of one seed against another. However, when the grain is too dry, abrasion of the internal components of the mill becomes severe. The hulls and the endosperm fragments are separated in a cyclone, and the endosperm particles are milled in a proprietary mill. 3. Metal friction machines: This is when attrition mills are used. Attrition usually means particles getting smaller due to their

Milling After dehulling, the material separated from the endosperm by aspiration comprises the hull, bran, germ, and also a portion of the endosperm in the form of broken grains and powder, which is used as poultry feed. The types of mills used for pulverizing minor millets are hammer mills, burr mills, and plate or disk mills. Wet milling is not performed for the minor millets. Most of the minor millet processing involves semiwet or dry milling techniques. Hammer mills are probably the cheapest and simplest mills used for reducing the particle size of the decorticated grains. These mills are available in different sizes depending on the size of operations. They consist of hammers installed on the rotor rotating rapidly in an enclosed casing. The outlet is covered by a screen that determines the particle size of the flour. Overheating and moisture built up during the hammer milling result in caking of the flour and cause reduction in the throughput of the process. Roller flour milling is rarely used for minor millets as it is designed for wheat milling. If roller mills are used for separating the endosperm from the offal, the particle size is usually reduced in roller mills with smooth rollers. In cereals, the functional properties of flours are defined by the particle size distribution and damaged starch contents. However, there is not much research to evaluate the differences in the functionality of the millet flours owing to different milling procedures. Also, there

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appears to be a difference between the flour produced by the wooden pestle and mortar and that produced by mechanical methods. The former seems to have better nutritional qualities. The biggest challenge is to develop a dehulling and milling technology according to specific physical characteristics of millet grains that can yield flour with uniform quality. It is important to note that some efforts have been made in this regard. The growth of this industry will depend upon constant demand of millet-based products and regular feeding of the mills with millet grains, which have been properly harvested and stored in good conditions.

(2011), a thresher-cum-pearler for finger millet and barnyard millet has been designed and developed. It works on the principle of impact and shear on the grains. The threshing drum is provided with six leather flats, which provide gentle impact and shear and a mild rubbing action for threshing, dehusking, pearling, and polishing of the grains. A sieve assembly is also attached with different operations. The design is simple and easily adaptable in rural areas for efficient postharvest processing of these crops.

Utilization of Minor Millets Recent Advancements A new eco-friendly and energy-efficient continuous-type CIAEMillet mill (models I and II) (Figure 6) has been designed and developed for all kinds of minor millets. It has provisions to adjust the clearance between the dehusking surfaces to suit the different sizes of minor millets. The dehusking efficiency of the machine is about 95%. The separation of the husk is simultaneous with the suction arrangement and cyclone separator. Another compression-based and shear-based machine has been patented in India to dehull the preconditioned grains. The hulls are removed using aspirator. The dehulled grains are separated using conventional grader and hot air-dried to 10% moisture content (dry basis). Dried dehulled grains are then polished in abrasive-type polishers where bran and germ are removed from the grain. The germ and bran are separated by screen. Then, the polished endosperm is ground in a burr mill to obtain refined flour of the required particle size. In another patent filed by the Indian Agriculture Research Institute

In some regions, minor millets remain cultivated only on a small scale but are culturally important for particular food stuffs, such as ritual breads made from browntop millet in India. Some varieties of proso and foxtail millets were historically used to prepare noodles in Northwestern China 4000 years ago. In Europe and Asia, green foxtail grains are eaten as boiled, roasted, or ground into flour. The Chinese call this simply gao wei cao (dog tail grass) to distinguish it from cultivated foxtail millet. Yellow bristle grass (S. pallidifusca) grains are used as fodder in Nepal. Plains bristle grass (S. macrostachya) is a pre-Columbian and historic Mexican cereal. The grains are toasted, ground, and eaten as gruel. Yellow foxtail millet (S. glauca) has been observed to be parboiled in South India. In general, foods prepared with minor millets can be classified into two broad categories – whole-grain millet foods and flour foods prepared after grinding of millets. Some of the popular millet foods of each category (Figure 7) are described in the succeeding text.

Figure 6 CIAE-Millet mill (models I and II). Reproduced from Balasubramanian S (2013) Processing of millets. In: National Seminar on Recent Advances in Processing, Utilization and Nutritional Impact of Small Millets. Madurai Symposium, Thamukkam Grounds, Madurai, 13 September 2013.


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The Millet Flour Foods These are mostly prepared by baking or frying with vegetable oil:

Figure 7 Foods prepared with minor millets in India. Source: Millet Network of India – Deccan Development Society – FIAN, India.

The Whole-Grain Millet Foods These are prepared with millet grains with or without milling and need little preparation before cooking. Most of the millet grain foods are prepared by boiling with water: 1. Pudding: Millet pudding is prepared by boiling proso millet grains with water or milk until they become soft and then mixed with sugar or jaggery and garnished with nuts and raisins. It is usually prepared on festivals or special occasions. 2. Boiled grains: The preparation is similar to rice. The polished barnyard millet grains are washed and boiled in hot water over a strong fire for about 6 min. and stirred occasionally. After draining the excess water, the grains are steamed over a weak fire for 3 min. The cooked grain complements vegetable stew or yogurt. 3. Porridge: Millet porridge is prepared with whole or broken grains of kodo, foxtail, or finger millets. Sometimes, the grains are sprouted before boiling with water. Sprouting greatly improves the carbohydrate digestibility and palatability. This is of particular importance in weaning foods. 4. Millet gruel: This is prepared by boiling broken kodo, foxtail, or finger millet grains with excess water, salt, and pepper until the grains are tender and fully cooked. 5. Popped grains: Proso or finger millet grains are sprayed with water and tempered to equilibrate the moisture. The tempered grains are popped at high temperature for short time. They are used as snacks or adjuncts in brewing. The popped grains may be ground into flour and blended with legume flours. These flours are used in weaning and supplementary foods. 6. Dumpling: It is prepared by using a composite mix of the broken proso millet grains and flour. Grains and flour are mixed in a 1:4 proportion and cooked in boiling water for 3 min. The cooked batter is well kneaded with a wooden stick and hand-shaped into balls. 7. Stir fried millets: This seems to be a new variation of millet foods that has appeared recently. The broken grains of barnyard millet grains are washed in water and added to the stir-fried vegetables with spices and boiled together.

1. Unleavened bread (roti): In some regions of south India, browntop millet is particularly preferred for making traditional breads. The flour is kneaded with water and mixed with chopped onion. Chopped green chilies, broken groundnut, and salt are added to taste. Dough is shaped into a flat round pancake by hand or rolling pin and then baked with a spoonful of oil in a frying pan on both sides. Finger millet is also used for making rotis. 2. Leavened thin pancake: It is common in south India by the name of dosai. Finger millet flour is mixed with water to form a thin batter, which is spread on a frying pan and baked with a spoonful of vegetable oil for about 4 min. Dosai is normally served with a vegetable stew. Another kind of pancake is injera, which is a staple food of Ethiopia. It is commonly prepared with teff and to some extent with millets. It is 50 cm diameter leavened pancake with a honeycomb-like texture. Dough is partly cooked to gelatinize the starch; the carbon dioxide produced by the lactic acid fermentation leavens the injera on baking as it escapes. Additionally, the low pH protects these foods against the growth of pathogenic bacteria. 3. Snack foods: The common millet snack foods in India are nippattu, chakkulli, haralu, kodubale, and kadubu. These are deep-fried snack foods prepared by mixing flour of browntop millet or finger millet with black gram flour or wheat flour in various proportions. Fried Bengal gram and groundnut are mixed while preparing the dough for nippattu. 4. Millet sweet dish: Flour of browntop millet is mixed with water to make dough. A small quantity of this dough is taken and flattened using a rolling pin and then stuffed with sweet ingredients and deep-fried in groundnut oil until golden brown. Traditionally, it is known as kadubu in India. Apart from the food uses, minor millets also have been used for therapeutic reasons. For example, bitter seeds of Liebmann’s bristle grass (S. liebmannii) are used to treat toothache in Mexico. Palm grass (S. palmifolia) is a part of a religious festival of new rice harvest in the Philippines. Shoots are cooked as green vegetable in New Guinea. Sections of the stem of the young plant are steamed in a bamboo tube and then eaten. The Topnaar people of Namibia use seeds of bristly foxtail (S. verticillata) in porridge and also to brew beer. It has been used as fodder in Okinawa and the Ryukyu Islands (Japan), while in India, the grains are eaten. Besides the traditional foods, there are lots of novel foods being developed and researched worldwide, for example, convenience mixes, composite flours, weaning foods, fermented and germinated foods and gruels, and alcoholic and nonalcoholic beverages. Millets are largely consumed in rural areas and are commonly known as poor man’s grains. However, in recent years, local crop patterns have completely changed due to the popularity of other crops like wheat and rice, which brings better monetary returns to the farmers. The global availability of

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inexpensive foods prepared with other cereals like wheat breads and biscuits has made minor crops like millets lose their significance even in the local regions where they are produced. Marketing millets as nutraceutical grains, while highlighting their key health benefits to create awareness among consumers, could trigger demand of the millet-based products. Support from the local governments at financial and policy framework levels and involvement of cooperatives may help establish millet processing industry as a model in selected sites, which can be replicated in other parts of the world. Minor millets are early maturing and can be cultivated under severe drought conditions. Thus, there exists a great potential of exploiting these underutilized genetic germplasms to address the current and future issues of health and global food security.


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Give a few examples of minor millets and their genera. What is the nutritional significance of polyphenols in minor millets? What are the factors responsible for the hypoglycemic property of minor millets? List a few food products prepared from minor millet flour.


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Find out the production and consumption trends of millets in the last three decades. Investigate the recent advances in processing of minor millet grains. Explore how minor millets could be a solution to global food security issues. Determine how the molecular structure of minor millet starches influences their hypoglycemic properties.

Acknowledgments We gratefully acknowledge the late Dr. Koushik Seetharaman for the inspiration to write this article. We also appreciate the support from Canadian International Food Security Research Fund – International Development Research Center and the Department of Foreign Affairs, Trade and Development, Government of Canada.

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grain Harvest, Storage and Transport: The Nature, Causes, and Control of Grain

Diseases in the Major Cereal Species; Grains Around the World: Grain Production and Consumption: Africa; Non-wheat Foods: Sorghum: Utilization; Proteins: Protein Synthesis and Deposition; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Basics: Grain: Morphology of Internal Structure; Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains; Millet Pearl: Overview; Teff: Overview; The Legumes and Pseudocereals: Amaranth: Overview; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Annor GA (2013) Millet Starches: Structural Characteristics and Glycemic Attributes. Doctoral dissertation, Canada: University of Guelph. Annor GA, Marcone M, Bertoft E, and Seetharaman K (2013) In vitro starch digestibility and expected glycemic index of kodo millet (Paspalum scrobiculatum) as affected by starch–protein–lipid interactions. Cereal Chemistry 90(3): 211–217. Balasubramanian S (2013) Processing of millets. National Seminar on Recent Advances in Processing, Utilization and Nutritional Impact of Small Millets. Madurai Symposium, Thamukkam Grounds, Madurai, 13 September 2013. Bora P (2014) Nutritional Properties of Different Millet Types and Their Selected Products. Masters dissertation, Canada: University of Guelph. Devi PB, Vijayabharathi R, Sathyabama S, Malleshi NG, and Priyadarisini VB (2011) Health benefits of finger millet (Eleusine coracana L.) polyphenols and dietary fiber: A review. Journal of Food Science and Technology 51(6): 1021–1040. http://dx.doi. org/10.1007/s13197-011-0584-9. Geervani P and Eggum BO (1989) Nutrient composition and protein quality of minor millets. Plant Foods for Human Nutrition 39(2): 201–208. Kruger J, Pina-Vardas C, Vinis-Ndimba R, and Taylor JRN (2014) Visualisation of the distribution of minerals in red non-tannin finger millet using PIXE microanalysis. Journal of Cereal Science 60: 1–3. Rajasekaran NS, Nithya M, Rose C, and Chandra TS (2004) The effect of finger millet feeding on the early responses during the process of wound healing in diabetic rats. Biochimica et Biophysica Acta 1689: 190–201. Ramanathan MK and Gopalan C (1957) Effect of different cereals on blood sugar levels. Indian Journal of Medical Research 45: 255–262. Shobana S, Krishnaswamy K, Sudha V, et al. (2012) Finger millet (ragi, Eleusine coracana L.): A review of its nutritional properties, processing, and plausible health benefits. Advances in Food and Nutrition Research 69: 1–39. Sripriya G, Chandrasekharan K, Murthy VS, and Chandra TS (1996) ESR spectroscopic studies on free radical quenching action of finger millet (Eleusine coracana). Food Chemistry 57(4): 537–540. Taylor JRN, Belton PS, Beta T, and Duodu KG (2014) Increasing the utilisation of sorghum, millets and pseudocereals: Developments in the science of their phenolic phytochemicals, biofortification and protein functionality. Journal of Cereal Science 59(3): 257–275. Taylor JRN and Duodu KG (2014) Effects of processing sorghum and millets on their phenolic phytochemicals and the implications of this to the health-enhancing properties of sorghum and millet food and beverage products. Journal of the Science of Food and Agriculture 95(2): 225–237. http://dx.doi.org/10.1002/ jsfa.6713. Tovey FI, Jayaraj AP, and Clark CG (1975) The possibility of dietary protective factors in duodenal ulcer. Postgraduate Medical Journal 51: 366–372. Upadhyaya HD, Dwivedi SL, Singh SK, Singh S, Vetriventhan M, and Sharma S (2014) Forming core collections in Barnyard, Kodo, and Little Millets using morph agronomic descriptors. Crop Science 54: 2673–2682.

Teff: Overview G Bultosa, Haramaya University, Dire Dawa, Ethiopia; Botswana College of Agriculture, Gaborone, Botswana ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Teff crop description, origin, cultivation, and production. Teff grain production constraints and progress of improvement. Teff grain morphology, anatomical structure, composition, and physicochemical and functional properties of the major constituents of teff grain. Teff grain nutrient merits, always consumed as whole-grain, gluten-free alternative food for celiac patients, high in mineral nutrients particularly in iron with well-balanced amino acids. Processing of teff grain flour to injera (lactic acid bacteria and yeast-fermented, soft, spongy, sour, circular flatbread, staple food for majority of Ethiopians). Prospect for future teff productivity improvement and utilization and diversification of teff products.

and recommendations for further research to improve the teff crop and grain utilization are suggested.

Teff Crop Description and Cultivation Description Teff is a C4 self-pollinated tetraploid cereal plant with a chromosome number of 2n ¼ 4x ¼ 40. Teff is also an allotetraploid plant. The teff plant and panicles of some varieties are shown in Figure 1. Teff’s root system is fibrous and most stems are erect, while others are bending or elbowing types. It has a panicle type of inflorescence showing different forms, from loose to compact. Its spikelets have 2–12 florets. Each floret has a lemma, a palea, three stamens, mostly two ovaries (in some exceptional cases three), and feathery stigmas. In most varieties, the plant height is 50–120 cm. A single teff plant is known to produce from 9000 to 90 000 grains depending upon the variety and production conditions.

Learning Objectives

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Achieve understanding on teff origin, description, grain production, and constraints associated to grain production systems. Understand and apply the knowledge of teff grain morphology, anatomical structures, nutrient compositions, and grain component functionalities for processing into various food products such as for gluten-free and wholegrain foods. Achieve understanding on teff injera processing stages, nature of fermentation involved, characteristic of injera for global consumers, and highlights on other traditional teff grain food products. See teff as a traditional Ethiopian grain, strongly linked to national dietary culture, but with nutritional and sensory benefits that could lead to product development in new markets.

Introduction Teff (Eragrostis tef (Zucc.) Trotter), today generally written as ‘tef,’ is a tropical cereal. Teff cultivation and usage as human food are mostly confined to Ethiopia. This article highlights the origin, cultivation of the teff plant, and production and storage of the teff grain. Teff grain structure, anatomy, chemical composition, and physicochemical properties of the major chemical components are assessed and described. Teff milling, processing of injera (the staple food of the majority of Ethiopians, a fermented, pancake-like, soft, spongy, sour, circular flatbread), and other food products made from teff are described. Lastly, teff potential, grain production limitations,


Name and Origin Teff (Eragrostis tef (Zucc.) Trotter) belongs to the family of Poaceae, subfamily Eragrostoideae, tribe Eragrosteae, and genus Eragrostis. About 350 species are known in the genus Eragrostis of which teff is the only cultivated species. Chloridoideae is used synonymously for Eragrostoideae of teff. Vernacular names in different parts of the world are as follows:

• • • • •

Tahf: Arabic Tef, teff, and Williams love grass: English Xaafi/tafi/taafi: Oromo (O)/Afar/Sodo; tafe-e: Had; and t’ef, teff, and taff: Amarinya (A) and Tigrinya (T) (Ethiopian languages) Mil e`thiopien: French Chimanganga, ndzungula (Ch), and chidzanjala (Lo): Malawi

Teff is indigenous to Ethiopia. Ethiopia is also considered the leading world center for teff genetic diversity. As of 2013, the Ethiopian Institute of Biodiversity had conserved a total of 5169 accessions and 10 000 teff genotypes for varietal improvement study and to reduce loss of genetic diversity. The exact details on teff domestication are unclear. However, teff is believed to have been first domesticated by the pre-Semitic inhabitants of Ethiopia between 4000 and 1000 BCE and is assumed to have originated in northeastern Africa. Even though teff is an allotetraploid plant, to date, its diploid putative ancestors are not exactly established. But, based on the morphological data and cytological evidence, the following species have been suggested as the ancestors and contributors to teff origin:

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Eragrostis aethiopica, E. atrovirens, E. longifolia, E. macilenta, E. pilosa, and E. pseudo tef as ancestor species of teff

http://dx.doi.org/10.1016/B978-0-12-394437-5.00018-8

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(a)

(b)

(c)

(d)

Figure 1 Typical teff field plant and panicles of some teff varieties: (a) teff field of DZ-01-196, (b) panicles of DZ-01-196 (compact), (c) panicles of DZ-Cr-37 (less compact), and (d) panicles of DZ-01-99 (loose). Reproduced with permission from Tefera, H., Ayele, M., Assefa, K., 1995. Improved varieties of tef [Eragrostis tef (Zucc.) Trotter] release of 1970–1995. Research Bulletin 1. Debre Zeit Agricultural Research Center, Ethiopia.

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E. aethiopica, E. bicolor, E. cilianensis, E. curvula, E. pilosa, and E. mexicana as contributor species to the origin of teff E. aethiopica, E. barrelieri, E. bicolor, E. cilianensis, E. heteromera, E. mexicana, E. minor, E. papposa, and E. pilosa as very closely related species to teff E. aethiopica 2; E. barrelieri 6 ; E. cilianensis 2 , 4 , and 6; E. mexicana 6 ; E. minor 2 and 4 ; and E. pilosa 2 based on cytological evidence as closely related species to teff

An attempted interspecific cross between teff and some wild Eragrostis species (E. curvula, E. cilianensis (4 ), E. pilosa (4),

and E. minor) was not successful. However, it was recently reported that E. tef and E. pilosa can be crossed with fertile offspring, suggesting that E. pilosa or an ancestor closely related to E. pilosa is the most probable putative ancestor of teff.

Cultivation and Production Teff is one of the major cereals in Ethiopia with annual grain production estimated to be ca. 3.5 106 t (ca. 21% of the cereal grain production). In Idaho, the United States, some teff grain is produced for the health-food market and for injera

THE CEREAL GRAINS | Teff: Overview making. In South Africa, teff is widely grown as a fodder crop during the summer-rainfall season. However, the production of a combination of grain and fodder varieties has been introduced only recently. In Australia, India, Kenya, and the United States, it is cultivated as a forage crop. Teff has been started to be cultivated in the Netherlands. Teff can adapt to a wide range of environments, that is, moisture stress, high rainfall, different soil types, and a wide range of altitudes from near sea level to over 3000 m. However, the best conditions are 1800–2100 m above sea level, a temperature range of 10–27 C during the cultivation period, an annual rainfall of 750–850 mm, and rainfall of 450–550 mm during the growing season. Teff is known to have fewer disease and pest problems in the field as compared with maize, sorghum, wheat, and barley. However, the productivity is low. Lack of high-yielding cultivars, lodging, weeds, waterlogging, low moisture, low-fertility conditions, loss of grains on harvesting, threshing, and cleaning are major factors that contribute to the low grain yield. The yields of improved varieties under improved technologies (fertilizer, weed control, appropriate harvesting, and grain threshing) on farms are in the range of 1.4–2.7 t ha1, and for some under research-managed farms, the yield is as high as 3.6 t ha1. Reduction of seeding rate from traditionally recommended 25–30 kg ha1 to 2.5 kg ha1 had recently demonstrated a substantial grain yield increase as compared with previous grain yield recorded. Because of adaption of some of the improved technologies by teff farmers, the average national yield in Ethiopia has increased annually from about 0.84 t ha1 in 2003 to about 1.26 t ha1 in 2011.

Harvesting and Storage Teff grain is harvested when the vegetative and reproductive parts (pedicel, lemma, palea, and glumes) turn yellow or straw color (45–60 days for very early maturing, 60–120 days for early maturing, and 120–160 days for late maturing). If harvested late, the grain loss will be significant due to shattering and the natural grain color can also fade. However, if the grain is harvested early, it may become vitreous or translucent. In Ethiopia, traditional harvesting is done manually using a sickle (Figure 2(a)). The harvested panicles are gathered in batches, either on the day harvested or after 1–3 days, and temporarily stacked (in a conical shape, with the panicles toward the center) (Figure 2(b)) outdoors, under the shade, till it is ready for threshing. Such storage duration will help the teff grain to undergo the ripening process and dormancy breaking stages. At present, teff grain pre- and postharvest losses are high (25–30%), largely incurred by lodging, shattering on harvest and harvest handling, threshing, and cleaning by traditional practices. Threshing is usually done by oxen feet trampling or manually by beating with sticks after spreading the dried panicles on a dry circular threshing floor. The threshing floor is prepared by smearing with cow dung, cement, or other suitable materials. The grain is traditionally winnowed by wafting in the open air with the help of a rectangular flat piece of dried leather called an afarsa or hafarsaa (O) (ca. 0.4 m width 0.8 m length). Threshers or combine harvesters can be also used. However, grain loss is large because teff grain is very

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small and of light mass and can be easily blown away with the chaff. Use of mechanical threshers has recently shown an improvement in grain yield and quality. Teff productivity may be improved in the future by adaption of this technology. In Ethiopia, the grain is traditionally stored in gotera (A, T) or gotaara (O) (small hut-like stores) or pots or sacks. In comparison with other common cereals, teff grain is less prone to attacks by weevils and other storage pests. Thus, it can be safely stored under traditional storage conditions.

Teff Grain Marketing In local markets of Ethiopia, several small-scale grain traders distribute teff grain from major growing areas to the urban consumers and to regions of shortage in teff grain production. At Addis Ababa, teff grain is marketed in a place called Ehil berenda (Markato). Even though teff grain fetches premium price in the global cereal grain markets, at present, international teff grain export from Ethiopia is not practiced because of limited production. But when permitted, wherever the market is, companies (government-owned, joint ventures, farmers union associations, and private firms), such as Ethiopian Grain Trading Enterprise and Oromo Development Association, which export oil and pulses, have the potential to export teff grain as well.

Physicochemical Properties of Teff Grain Morphology Teff grain is hull-less (naked) and comes in a range of colors – from milky white to almost dark brown. The most common colors are white, creamy white, light brown, and dark brown (Figure 3). The grain is oval-shaped with size 0.9–1.7 mm (length) and 0.7–1.0 mm (diameter). The individual grain mass is generally 2 mg, 0.6–0.8% of the wheat grain mass. The thousand kernel weights and hectoliter weight of teff grain are in the range 0.19–0.42 g and 85–87 kg hl1, respectively.

Anatomy Pericarp The outer pericarp is thin and membranous and is equivalent to the beeswing bran of wheat. In the pericarp, beneath the cuticle toward the nucellar epidermis, teff grain is known to bear slime layer rich in pectins, which form uniform layers on the inner surface of the cell wall. The ability of this slime layer to absorb and maintain moisture around the grain is implicated as a contributor to teff adaptive features to moisture stress. In the inner surface of the pericarp, the mesocarp and endocarp are fused and appear as a single layer. In this fused layer, some starch granules are observed, as in the pericarp of sorghum grain.

Seed coat (testa) Next to the endocarp is the testa, which is adjacent to the aleurone layer. In some teff varieties, the testa is reported to contain tannins and is thus presumed to be thick. However, in

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THE CEREAL GRAINS | Teff: Overview the varieties that the author analyzed, including brown varieties, there is no significant tannin content found.

Aleurone layer The aleurone layer is one cell thick and is rich in protein and lipid bodies.

Germ (embryo) Like in other small-grain cereals, the germ occupies a relatively large proportion of the grain and is rich in protein and lipids.

Endosperm The endosperm is the largest component of the grain and consists of outer and inner layers. The outer layer is vitreous and contains most of the protein reserves of the endosperm and a few starch granules. The inner layer is mealy consisting mainly of thin-walled cells containing mostly starch granules with a few protein bodies. Teff has compound-type starch granules (Figure 4(a)), representing the contents of one amyloplastlike rice, oats, Amaranthus, and quinoa starches. On milling, individual starch granules are released along with small groups of protein bodies. The protein bodies are individual entities in nature and spherical in shape (Figure 4(a)), and unlike those of wheat, they do not coalesce to form a matrix.

Teff Grain Chemical Composition The proximate chemical composition of teff grain is shown in Table 1.

Carbohydrate

Figure 2 (a) Harvesting of teff plant by the traditional method, (b) stacked teff panicles after harvest, and (c) teff grain after cleaning by winnowing and wafting, where TF ¼ threshing floor top layer smeared with cow dung and dried, GS ¼ grass straw made of traditional bucket, and IM ¼ impurities.

Carbohydrate content of teff grain is 73%, of which virtually all is starch. The teff starch properties are given in Table 2. Individual starch granules are very small (2–6 mm in diameter) (Figures 4(b)–4(f)), similar in size to rice starch granules, but larger than Amaranthus and quinoa starch granules. The shape is polygonal, smooth with no surface pores (Figure 4(f)). A few granules are essentially cubic, and at high magnification, some appear tortoise shell-shaped (Figure 4(e)). The composition of teff starch granules is similar to other normal native cereal starches, with 25–30% amylose. Gelatinization temperature is high, similar to other tropical cereal starches. The x-ray diffraction pattern of teff starch granule is A-type with crystallinity of 37% similar to rice starch granule. Pasting temperature is similar to that of maize starch, but cooking time for peak viscosity is longer. Peak, breakdown, and setback viscosities are lower than those of maize starch. The paste clarity of teff starch is opaque. The gel texture is short and smooth. a-Amylase degradation of teff starch granules is by surface erosion and endocorrosion in nature. Because teff starch granules are very small, smooth, and of uniform size, they offer good functionality as a fat substitute and a flavor and aroma carrier, similar to other small-granule starches. Teff starch has good resistance to shear breakdown, and thus, it may find good application in high-shear processed foods. Also, because of its slow retrogradation tendency, it


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Figure 3 Grains of different teff varieties: (a) DZ-01-196 (white), (b) DZ-Cr-37 (creamy white), (c) DZ-01-99 (light brown), and (d) South African brown (dark brown).

Table 1

The proximate composition (db) of teff grain, Osborne protein fractions, and food energy

Biochemical class Protein (%) (N 6.25) Carbohydrate (%) Crude fiber (%) Fat (%) Ash (%) Osborne protein fractions (% protein recov.)

Food energy (kJ per 100 g) a

Compound

Albumins Globulins Prolamins Glutelins

Range (%)

Typical value (%)

9.4–13.3 73.0 2.0–3.5 2.0–3.1 2.7–3.0 24–39 7–34 3–15a, 38–43b 28–42 1406

11.0 73.0 3.0 2.5 2.8 36 18 – 40 1406

Extracted with 60% ethanol. Extracted with tert-butanol containing 0.05% 1,4 dithiothreitol. Source: Bultosa, G., Taylor, J.R.N., 2004. Teff. In: Wrigley, C., Corke, H., Walker, C.E. (Eds.), Encyclopedia of Grain Science, vol. 3. Elsevier, Oxford, UK, pp. 281–290; Ketema, S., 1997. Tef Eragrostis tef (Zucc.) Trotter. Promoting the Conservation and Use of Underutilized and Neglected Crops, Institute of Plant Genetics and Crop Plant Research, Gatersleben/ International Plant Genetic Resources Institute, Rome, Italy, Booklet 12; Assefa, K., Chanyalew, S., Tadele, Z. (Eds.), 2013. Achievements and Prospects of Tef Improvement: Proceedings of the Second International Workshop, 7–9 November, 2011, Debre Zeit, Ethiopia. Ethiopian Institute of Agricultural Research/Institute of Plant Sciences, University of Bern, Addis Ababa, Ethiopia/Bern, Switzerland; NRC (National Research Council of the USA). 1996. Tef. In: Lost Crops of Africa, vol. 1, Grains, pp. 214–338. Washington, DC: National Academy Press.; Hundera, F., 1998. Variations of morpho–agronomic characters and grain chemical composition of released varieties of tef [Eragrostis tef (Zucc.) Trotter]. J. Genet. Breed. 52, 307–311. b


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cw

sg

pg

sg sg

pb

pb

pb

cb

(a)

(d)

pg tr cb

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f

cb

nsp

pg

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Figure 4 Compound (a) and individual (b–f) starch granules from different teff varieties: (a, b) South African brown, (c) DZ-01-1681, and (d–f) DZ-01-196 (sg ¼ starch granules, pg ¼ polygonal, cb ¼ cubic, Tr ¼ tortoise-shell, pb ¼ protein, f ¼ fiber, and nsp ¼ no surface pores). Reproduced from Bultosa, G., 2003. Physico–Chemical and Functional Properties of Grain tef [Eragrostis tef (Zucc.) Trotter] Starch. PhD thesis, University of Pretoria, Pretoria, South Africa.

could have attractive applications where starch staling is preferred to be reduced (i.e., in baked and in refrigerated foods).

Fiber The fiber content of teff grain (Table 1) is apparently higher than most other common cereals, because the grain is very small and the bran is proportionally large.

Protein and amino acids Typical teff grain protein content (N 6.25) is 11%, with a normal range of 9–13%. Thus, the protein content of teff grain is similar to other common cereals. The major amino acids are glutamic acid, alanine, proline, aspartic acid, leucine, and valine (Table 3). Methionine, phenylalanine, and histidine are slightly higher than in most other cereals, but

THE CEREAL GRAINS | Teff: Overview Table 2

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Physicochemical properties of teff grain starch

Property Individual granule diameter (mm) and shape

Mean and standard deviation for five teff varieties

Amylose weight-average molar mass, g mol1 Amylopectin weight-average molar mass, g mol1 Ash (%) (db) Protein (%) (N 6.25) (db) Lipids (db): total (mg g1)

2–6 (majority are 3–5), polygonal shape, smooth surface 28.4 2.8 28.2 0.8 (1.5–3.0) 106 (10.1–16.5) 107 0.16 0.04 0.19 0.03 8.9 0.7

Internal lipids (mg g1) Phosphorus (db) (mg g1) Kofler gelatinization temp. range ( C): To–Tp–Tc

7.8 0.4 0.65 0.08 68.0–74.0–80.0

DSC gelatinization endotherms range: To, Tp, and Tc in C and DH in J g1, respectively Pasting properties: Ti ( C), PV (RVU), BV (RVU), Rst (RVU min1), SBV (RVU)

63.8–65.4, 70.2–71.3, and 81.3–81.5 and 2.28–7.22 74.0 1.1, 269 13, 79 17, 8.4 1.8, 101 11

Peak viscosity Resistance to shear Retrogradation tendency Crystallinity (%) x-Ray diffraction: d-value (A˚) and intensity (%)

Medium–low Medium–high Medium–low 37 5.85 (83.8), 5.16 (97.0), 4.89 (99.4), 4.41 (36.4), and 3.84 (80.2) Opaque Short Surface erosion and endocorrosion type Gradual surface degradation (etching)

Amylose (%) (db)

Paste clarity Gel texture In vitro digestibility with porcine pancreatic a-amylase Acid hydrolysis

Remark Individuals are from compound granules Concanavalin A method Iodine-binding method

24% HCl hydrolysis followed n-hexane and in situ generated ethyl formate extract Hot (90 C) water-saturated butanol extract To is onset, Tp is peak, and Tc is conclusion gelatinization temperatures DH is gelatinization enthalpy Where Ti, PV, BV, Rst, and SBV are pasting temperature, peak viscosity, breakdown viscosity, rate of shear thinning, and setback viscosity, respectively

A-type starch crystalline polymorph

Source: Bultosa, G., 2003. Physico–Chemical and Functional Properties of Grain tef [Eragrostis tef (Zucc.) Trotter] Starch. PhD thesis, University of Pretoria, Pretoria, South Africa; Bultosa, G., Hamaker, B.R., BeMiller, J.N., 2008. An SEC-MALLS study of molecular features of water-soluble amylopectin and amylose of tef [Eragrostis tef (Zucc.) Trotter] starches. Starch/Sta¨rke 60, 8–22.

serine and glycine are lower. Lysine and arginine are essentially higher in teff than in most other cereals, except rice and oats. The balance among essential amino acids is similar to the whole edible portion of egg protein, except for its lower lysine content. The overall amino acid profile of teff can be regarded as well balanced. Osborne protein fractions of teff grain are shown in Table 1. Glutelins, albumins, and globulins are major fractions. The teff prolamin fractions are reported variable (low and high) depending on solvent type used in the extraction. The major prolamins of teff are somewhat similar to the a-prolamins of maize, sorghum, and Coix. Teff is different from other cereals in having higher albumins and globulins. Teff protein is essentially free of the type of gluten found in wheat. Because of this, teff grain foods are today increasingly became important for consumers allergic to wheat gluten (e.g., for celiac patients). As the main protein fractions (albumins and globulins) are the most digestible types, teff protein digestibility is also presumed high. Amino acid compositions of the various Osborne protein fractions are shown in Table 3.

Ash and minerals The ash content in teff grain (Table 1) is apparently higher than in wheat, rye, maize, barley, oats, rice, and millets, in part

because teff grain bran is proportionally large. In particular, calcium, copper, iron, and zinc (Table 4) contents are higher compared with those in barley, wheat, and sorghum. The iron content of traditionally harvested teff grain is especially high ( 15.7 mg per 100 g and in some reports as high as 27 mg per 100 g), in part because of grain contamination with the soil during harvest. However, when cleaned (with water and/or dilute acid), the level ( 5.7 mg per 100 g) is similar to other cereals. Most teff foods such as injera are fermented. Fermentation for injera processing is known to destroy phytic acid to the extent of 90%, and such destruction is known to contribute to high iron bioavailability in diets where fermented teff foods are the staples. Because of these two factors, irondeficiency disease anemia is rare among regular teff injera consumers in Ethiopia.

Fat and fatty acids Teff grain fat (Table 1) is lower than, for example, in maize and oats. Thus, teff is different from other small-grain cereals in having low fat even though the germ is large. As in most other cereal grains, palmitic, oleic, and linoleic acids are the major fatty acids (Table 5). Linolenic acid in teff is higher than in maize, sorghum, and wheat.

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Table 3

Amino acid composition of the whole teff grain protein and of the Osborne protein fractions (g per 100 g protein)

Asx is Asp þ Asn and Glx is Glu þ Gln Amino acid Asx Thr Ser Glx Pro Gly Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg Trp

Whole grain Range 5.8–7.2 2.4–4.4 2.8–5.6 18.7–24.9 5.1–11.4 1.7–4.1 5.5–14.7 0.5–2.5 4.1–9.9 2.0–4.6 3.2–5.4 6.0–9.7 1.7–4.0 2.7–5.9 2.1–3.7 1.4–4.0 2.9–6.2 1.3

Mean 6.4 3.6 4.1 21.8 8.2 3.1 10.1 1.8 5.9 3.3 4.0 8.1 3.0 5.0 2.8 3.0 4.5 1.3

Albumin Range 10.7–14.4 3.3–4.5 3.1–3.9 3.9–10.5 6.7–11.7 4.1–8.4 13.1–21.7 0.4–0.8 8.0–9.6 0.5–0.8 3.4–4.7 6.1–6.5 0.9–2.5 2.3–3.5 2.8–4.2 3.7–6.6 5.8–7.3

Mean 12.7 4.2 3.6 9.0 8.3 7.2 15.4 0.6 8.6 0.7 4.2 6.3 1.3 2.9 3.4 5.6 6.4

Globulin Range 10.3–14.1 0.0–4.2 0.1–2.4 1.5–9.8 8.0–16.6 1.8–5.3 13.3–23.7 0.4–2.1 9.2–11.4 0.4–1.2 3.4–5.1 5.4–7.4 0.9–1.6 2.1–3.9 3.6–5.6 1.4–4.2 8.4–13.7

Mean 12.9 2.6 1.3 6.9 10.6 3.9 17.2 0.9 10.5 0.6 4.5 6.5 1.3 3.0 4.6 3.0 10.3

Glutelin Range 12.7–14.4 2.0–4.2 0.8–2.2 6.5–9.5 8.0–11.0 3.5–5.4 13.5–17.9 0.4–1.3 9.2–10.9 0.4–0.7 3.9–5.1 6.6–7.4 0.8–1.7 2.6–3.9 4.5–5.1 2.5–3.9 8.9–10.7

Mean 13.7 3.3 1.6 8.7 8.8 4.5 14.6 0.8 10.0 0.6 4.5 7.0 1.3 3.2 4.8 3.2 9.5

Prolamin Range 3.6–20.7 2.8–4.1 3.4–4.3 4.8–26.3 6.8–13.5 4.3–6.0 10.5–19.3 0.0–1.3 7.3–9.2 0.7–2.8 2.5–4.6 5.1–7.3 1.3–4.8 2.5–6.6 0.7–3.7 0.3–2.7 1.2–5.3

Mean 9.8 3.5 3.8 20.6 10.0 4.9 12.7 1.3 7.8 1.8 4.0 6.5 3.4 5.1 1.9 1.3 2.8

Source: Bultosa, G., Taylor, J.R.N., 2004. Teff. In: Wrigley, C., Corke, H., Walker, C.E. (Eds.), Encyclopedia of Grain Science, vol. 3. Elsevier, Oxford, UK, pp. 281–290; Ketema, S., 1997. Tef Eragrostis tef (Zucc.) Trotter. Promoting the Conservation and Use of Underutilized and Neglected Crops, Institute of Plant Genetics and Crop Plant Research, Gatersleben/ International Plant Genetic Resources Institute, Rome, Italy, Booklet 12; Assefa, K., Chanyalew, S., Tadele, Z. (Eds.), 2013. Achievements and Prospects of Tef Improvement: Proceedings of the Second International Workshop, 7–9 November, 2011, Debre Zeit, Ethiopia. Ethiopian Institute of Agricultural Research/Institute of Plant Sciences, University of Bern, Addis Ababa, Ethiopia/Bern, Switzerland; Hundera, F., 1998. Variations of morpho–agronomic characters and grain chemical composition of released varieties of tef [Eragrostis tef (Zucc.) Trotter]. J. Genet. Breed. 52, 307–311; Bekele, E., 1995. Essential and non-essential amino acids in a free state and in the major protein fractions of teff seeds. SINET: Ethiop. J. Sci. 18, 79–99.

Table 4

Vitamins

Microelement composition of teff grain (db)

Microelements (mg per 100 g or mg per 100 g)

Range

Typical value

Calcium (mg) Chloride (mg) Chromium (mg) Copper (mg) Iron (mg) Magnesium (mg) Manganese (mg) Phosphorus (mg) Potassium (mg) Sodium (mg) Zinc (mg)

104–223 13 250 0.7–5.3 4.7–19.6 138–190 1.6–6.4 378–480 330–570 11.8–47.0 2.0–6.7

165.2 13.0 250.0 2.6 5.7a, 15.7b 169.8 3.8 425.4 380.0 15.9 4.8

a

Mean of iron from cleaned, acid- and/or water-washed samples. Mean of iron from uncleaned samples. Source: Ketema, S., 1997. Tef Eragrostis tef (Zucc.) Trotter. Promoting the Conservation and Use of Underutilized and Neglected Crops, Institute of Plant Genetics and Crop Plant Research, Gatersleben/International Plant Genetic Resources Institute, Rome, Italy, Booklet 12; Assefa, K., Chanyalew, S., Tadele, Z. (Eds.), 2013. Achievements and Prospects of Tef Improvement: Proceedings of the Second International Workshop, 7–9 November, 2011, Debre Zeit, Ethiopia. Ethiopian Institute of Agricultural Research/ Institute of Plant Sciences, University of Bern, Addis Ababa, Ethiopia/Bern, Switzerland; Bultosa, G., 2003. Physico–Chemical and Functional Properties of Grain tef [Eragrostis tef (Zucc.) Trotter] Starch. PhD thesis, University of Pretoria, Pretoria, South Africa; NRC (National Research Council of the USA). 1996. Tef. In: Lost Crops of Africa, vol. 1, Grains, pp. 214–338. Washington, DC: National Academy Press.; Umeta, M., West, C.E., Fufa, H., 2005. Content of zinc, iron, calcium and their absorption inhibitors in foods commonly consumed in Ethiopia. J. Food Comp. Anal. 18, 803–817. b

In teff (Table 6), thiamin content is typically lower, when compared with that in wheat, rye, barley, oats, rice, maize, millet, and sorghum. Though riboflavin content is considered to be high, it is nevertheless lower than in rye, barley, and oats. Niacin levels are similar to those in maize.

Processing and Usage of Teff Grain Cleaning Normally, the grain is cleaned by manual sifting and sieving.

Milling The cleaned grain is usually dry-milled to obtain whole flour. Traditionally in Ethiopia, this was done by wafcho (A) (T) or wafcoo (O) (top and bottom hard stones). Today, milling by hand, using hard stone, has been replaced by grist mills run by electric power and, where electric power is not available, by diesel engine or water power. The grist mill is made up of two abrasive hard-disk stones. During operation, one stone is stationary, while the other is rotating. The grain, fed into the center (eye) of the upper stone, is fragmented and ground between the two stones, and flour is issued at the periphery. At present, wet milling of teff grain for chemical component extraction like starch is not carried out.

THE CEREAL GRAINS | Teff: Overview Table 5

Fatty acid composition of teff grain fat

Fatty acids (%)

Range

Mean

Palmitic (C16:0) Palmitoleic (C16:1) Stearic (C18:0) Oleic (C18:1) Linoleic (C18:2) Linolenic (C18:3) Arachidic (C20:0) Arachidonic (C20:1) Behenic (C22:0) Erucic (C22:1)

14.0–16.4 0.1–0.6 3.0–3.7 23.3–24.9 41.3–46.5 6.9–9.9 0.6–0.9 0.5–1.2 0.3–1.1 0.0–0.9

15.9 0.3 3.3 24.0 44.2 7.9 0.7 0.8 0.5 0.4

Source: Hundera, F., 1998. Variations of morpho–agronomic characters and grain chemical composition of released varieties of tef [Eragrostis tef (Zucc.) Trotter]. J. Genet. Breed. 52, 307–311.

Table 6

Vitamin and antinutrient composition of teff grain (db)

Component Vitamins Vitamin A (mg per 100 g as RE) Thiamine (mg per 100 g) Riboflavin (mg per 100 g) Niacin (mg per 100 g) Vitamin C (mg per 100 g) Antinutrients Phytate (mg per 100 g) Trypsin inhibitor activity (TIU per gram)

Typical value 8 0.3 0.2 2.5 88 707 5584

RE is retinol equivalent; TIU is trypsin inhibitor unit. Source: Assefa, K., Chanyalew, S., Tadele, Z. (Eds.), 2013. Achievements and Prospects of Tef Improvement: Proceedings of the Second International Workshop, 7–9 November, 2011, Debre Zeit, Ethiopia. Ethiopian Institute of Agricultural Research/ Institute of Plant Sciences, University of Bern, Addis Ababa, Ethiopia/Bern, Switzerland; Bultosa, G., 2003. Physico–Chemical and Functional Properties of Grain tef [Eragrostis tef (Zucc.) Trotter] Starch. PhD thesis, University of Pretoria, Pretoria, South Africa; NRC (National Research Council of the USA). 1996. Tef. In: Lost Crops of Africa, vol. 1, Grains, pp. 214–338. Washington, DC: National Academy Press.

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plasticity losses after a day. The rice flour injera-making ability is similar to teff probably because of somewhat similar starches in both grains. The hydrophobic and less polymerized nature of teff grain protein prolamins is in part implicated as contributor to the making of superior semileavened flatbread injera when compared with sorghum injera. Teff grain flour is also used to make sweet unleavened bread called kitta (A), bixxille (O), and daguwalo (T). Kitta can be consumed as bread, or it can be used as an adjunct in traditional opaque beer (tella (A) or farsoo (O)) or local spirit (katikalla (A) or araqii (O)). Porridge (genefo (A) or marqaa (O)) can also be made from teff flour. Thin, fermented teff flour batter is used to prepare soup (muk, (A)). Unfermented teff flour dough is also used in the preparation of traditional snacks (dabo kolo (A) or hunkuroo (O)), where the dough is rolled into small balls and then roasted on a hot griddle. In the United States, teff has been promoted as a thickener for soups, stews, and gravies probably because teff flour paste gives the product a short and stiff texture. Teff grain flour imparts a slight molasses-like sweetness to food products, making its inclusion in porridges, pancakes, biscuits, cookies, cakes, stir-fry dishes, casseroles, soups, stews, and puddings desirable. Processing of teff grain in Ethiopia has been limited to the household level. To date, technologies for large-scale commercial processing of teff grain, for the preparation of foods like injera, are not well advanced. However, apart from traditional usage, recent reports indicate that teff grains, along with soybean, chickpea, and other grains, are being used in the baby food industry. Teff grain flours are used to improve dietary fiber, starch, protein, and mineral content supply in gluten-free food products and in wheat bread to improve the iron and antioxidant contents of the bread.

Teff Grain Injera Making In Ethiopia, injera is regarded as the national staple food. Flowcharts of the injera-making process and injera-baking process are shown in Figures 5 and 6, respectively. The process involves fermentation and then baking of the batter.

Fermentation Usage Food made from teff grain is a staple diet for many Ethiopians. Teff is considered to have a better food value than major grains, namely, wheat, barley, sorghum, and maize, as it is normally used as a whole grain, that is, the germ and bran are consumed along with the endosperm. Teff flour is used primarily for making of injera (A), caabitaa or budeena (O), and tayeta (T). Teff injera is regarded to have pre- and probiotic potentials due to dietary fiber from whole grain and fermentation, respectively. Although the lactic acid bacteria (LAB) and yeast involved in the fermentation of injera are killed during baking, their dead cells and metabolic products are consumed as part of the diet, and these were implicated as promoters of gut health. In injera-making features, teff grain flours are superior to any other cereal grain flours used. The Ethiopian diaspora is using injera from rice or blend of rice and wheat flour, although the injera suffers from staling, resilience, and

Flour is mixed with water and the dough is kneaded, usually by hand. Fermentation for injera making involves two phases that can last a total of 24–72 h. The first phase starts spontaneously when the flour is wetted, due to contaminating microorganisms. Or it can be initiated by addition of irsho (A) (T) or raacitii (O) (yellowish liquid saved from the previous batch fermentation). The initial 18–24 h is notable for vigorous gas evolution and maximum dough expansion. At about 30–33 h, an acidic yellowish liquid appears on the dough surface. This phase is characterized by a decrease in gas evolution up to 31 h, an increase in liquid volume up to 48 h, and a decrease in pH to below 5.8. The first phase of fermentation results in a liquid/solid separation after 24 h. The layer of liquid is then removed. About 10% of the fermenting dough is mixed with water (1:3 ratio) and boiled (2–5 min), and as a result of starch gelatinization, a dough binder, called absit, is formed. The absit is cooled and added to the fermentation vat signaling the second phase of fermentation. The second phase (0.5–2 h) is

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Teff grain

Cleaning

Millings

Water (ca 6 L)

Irsho (starter, yellowish liquid saved from previous fermentation) (ca. 480 g)

Teff flour (ca. 3 kg)

Fermented paste separation (ca. 30–33 h)

First phase fermentation (24–72 h)

Sediment (90%)

Supernatant (irsho)

Mixing of 10% sediment with water (1:3) and cooking for 2–5 min

Air cooling to not less than 46°C

Absit (a dough binder) Second phase fermentation (0.5–2 h)

Thinning of fermented batter

Water

Pouring of the batter on hot griddle and covering with griddle lid

Heat and steam baking (2–3 min)

Injera (18 total each weigh ca. 450 g) Figure 5 Flowchart of teff injera-making process.

characterized by a short duration of dough expansion and gas formation. During the first phase of fermentation, the yellowish liquid that is removed contains water-soluble nutrients (amino acids, sugars, and minerals) and a large number of microorganisms involved in the fermentation. This has negative nutritional consequences. Thus, injera baked from a batter at 31 h of fermentation without discarding the liquid is recommended as being more nutritious. A complex group of microorganisms is known to be involved in teff fermentation. A total of 107 LAB (some heterofermentative and some homofermentative) and 68 yeast strains are reported in the teff fermentation. Bacteria belonging

to the Enterobacteriaceae family are thought to initiate the fermentation. During the first 18 h of fermentation, the activities of these bacteria reduce the dough pH to 5.8. A group of LAB of which major ones are Leuconostoc mesenteroides, Streptococcus faecalis, Pediococcus cerevisiae, P. pentosaceus, Lactobacillus brevis, L. plantarum, and L. fermentum are involved at the later phase of fermentation (18–72 h) in reducing the dough pH from 5.8 to 3.8. During the later phase of fermentation (22– 24 h), yeasts of two genera Saccharomyces and Torulopsis are reported to be involved. In the later phase ( 48 h), yeasts belonging to the genera Candida and Pichia are the dominant types isolated from the yellowish liquid removed from the dough. In addition to amylases present in the grain, the


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DZ-01-196

DZ-01-787

DZ-01-99

Figure 6 Teff injera baking from fermented batter on electrically heated baking griddle (a). Portion of baked injera from white (b and c) and brown (d) teff grains.

bacteria species Bacillus sp. A-001 involved in the fermentation has been characterized as one of the amylase-producing bacteria involved in partially attacking the starch granules. In the traditional teff fermentation for injera making, commercial yeast is not added externally. The source of the yeast is either from irsho or from the endogenous microflora of teff grain and its flour that grows in the batter after the flour is wetted with water. Therefore, the yeast in the fermentation of teff for injera making can be regarded as symbiotic yeast.

nutritious. The thick batter used for aflegna injera is also used to prepare a slightly concave, thick flatbread called cumboo (O). Cumboo is traditionally baked on the preheated surface of a small-size concave griddle called bedde, which is placed upside down on a flat larger griddle called elle chumbo. After pouring the 12–24 h fermented thick batter onto the upside down concave bedde surface and covering with the lid, gentle heat is applied underneath of the larger griddle, and depending on the batter size and heat intensity applied, the baking time for cumboo is between 1 and 3 h.

Baking Injera is usually baked after 24 h of fermentation. After the fermentation, the batter is diluted slightly with water and then poured using circular motion from the outer perimeter toward the center onto a hot, round, smooth griddle called a metad (A) or eelee caabitaa (O). It is then covered with a metad lid called akambalo (A), qadaada eelee caabitaa (O) to prevent steam from escaping. The griddle is traditionally made from clay. Before pouring the batter, the metad surface is swabbed with ground oilseeds, commonly rapeseed or with animal fat in a piece of cloth. This prevents the injera from sticking to the metad surface. Depending on the batter thickness, heat intensity applied, and steaming, with the current electrically heated baking griddle, injera can be baked in 2–3 min. Based on the duration and nature of the fermentation involved, three common types of injera are prepared:(1) injera made from dough that does not contain absit, characterized by a soft, thin, fine appearance and a sour taste without the ‘eyes’ of injera (surface air cells); (2) injera made from partially fermented paste (12–24 h fermentation) called aflegna (A) (O) or bekuo (T), characterized by a sweet flavor, a pleasant odor, and a rusty red underside; and (3) injera made from overfermented paste called komtata injera (A) (T) or qomxoxaa caabitaa (O) that tastes very sour and is regarded as less

Prospects, Problems, and Recommendations Teff can be cultivated under harsh environmental conditions where most other cereals are less viable. It has relatively few pest and disease problems in the field. The grain is less attacked by weevils. The nutrient composition of teff grain indicates that it has good potential to be used in various diets and as functional foods in health-food markets worldwide. However, the grain yield of teff is low. The mechanized farming technologies that are used for the production of other cereal grains can be problematic for teff because the plant stems are very thin and short and the grain is very small. Manipulation of teff plant genes through research on germplasm genetic diversity, improvement of yield using molecular breeding approach, and a continuous teff production technology improvement for maximum grain production are required. At present, the milling of teff grain is limited to cottage-type millers. Processing of teff for different foods is usually by traditional ways and mostly limited to the household level. Over the last decade, utilization of teff grain as whole grain supplements and for gluten-free markets is increased. More research on teff large-scale milling and processing of teff grain

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for different commercial foods is required to promote worldwide teff product utilization.

Overview of the Family of Cereal Grains Prominent in World Agriculture; Millet Minor: Overview; Oats: Overview; Rice: Overview; The Legumes and Pseudocereals: Amaranth: Overview.


• • • •

What major features distinguish teff grain (particularly its starch and protein) from other common tropical cereals like sorghum, rice, and maize? Why is the productivity of the teff plants so low compared with that of maize and rice? Could teff be grown near where you live? Why are teff grain products nutritionally and functionally attractive for health-food markets (e.g., for celiac patients)? Can you design and develop a novel food product utilizing teff grain? How is injera made? Is teff grain essential for injera manufacture? Does teff injera have prebiotic and probiotic effects?


•

• • •

Value chain efficiency for teff productivity improvement such as high-yielding and lodge-resistant variety developments coupled with mechanized or semiautomated production technologies that suit very thin, short teff plant stems and very small grain size of light mass that would boost teff grain production and minimizes grain postharvest losses. Development of teff grain-based composite flours for injera and other teff products. Efficiency of teff injera processing stages and cottage and large-scale injera processing and preservation. Teff grain-based ready to eat foods for health-food markets such as gluten-free foods for celiac patients.

See also: Beverages from Grains: Fermentation: Foods and Nonalcoholic Beverages; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grains and Health; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Functional Foods: Overview; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; The Gluten-Free Diet; Appendix 1: Nutrient-Composition Tables for Grains and for Grain-Based Products; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grains Around the World: Grain Production and Consumption: Africa; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Grain Crops: An Overview; Grain: Morphology of Internal Structure; Taxonomic Classification of Grain Species; The Cereal Grains: An

Further Reading Adebowale AA, Emmambux MN, Beukes M, and Taylor JRN (2011) Fractionation and characterization of tef proteins. J. Cereal Sci. 30: 1–7. Assefa K, Chanyalew S, and Tadele Z (eds.) (2013) Achievements and Prospects of Tef Improvement: Proceedings of the Second International Workshop, November 7–9, 2011, Debre Zeit, Ethiopia, Addis Ababa, Ethiopia/Bern, Switzerland: Ethiopian Institute of Agricultural Research/Institute of Plant Sciences, University of Bern. Bekele E (1995) Essential and non-essential amino acids in a free state and in the major protein fractions of teff seeds. SINET: Ethiop. J. Sci. 18: 79–99. Bergamo P, Maurano F, Mazzarella G, Iaquinto G, Vocca I, Rivelli AR, et al. (2011) Immunological evaluation of the alcohol-soluble protein fraction from gluten-free grains in relation to celiac disease. Mol. Nutr. Food Res. 55: 1266–1270. Bultosa, G., 2003. Physico–Chemical and Functional Properties of Grain tef [Eragrostis tef (Zucc.) Trotter] Starch. PhD thesis, University of Pretoria, Pretoria, South Africa. Bultosa G and Taylor JRN (2004) Teff. In: Wrigley C, Corke H, and Walker CE (eds.) Encyclopedia of Grain Science, vol. 3, pp. 281–290. Oxford, UK: Elsevier Ltd. Bultosa G, Hamaker BR, and BeMiller JN (2008) An SEC-MALLS study of molecular features of water-soluble amylopectin and amylose of tef [Eragrostis tef (Zucc.) Trotter] starches. Starch/Sta¨rke 60: 8–22. Desiye A and Abegaz K (2013) Isolation, characterization and identification of lactic acid bacteria and yeast involved in fermentation of teff (Eragrostis tef) batter. Adv. Res. Biol. Sci. 1(3): 36–44. Ebba T (1969) Tef (Eragrostis tef): the cultivation, usage and some of the known diseases and insect pests. Part I. Debre Zeit Agricultural Experiment Station. Dire Dawa, Ethiopia: Addis Ababa University, College of Agriculture. Hundera F (1998) Variations of morpho-agronomic characters and grain chemical composition of released varieties of tef [Eragrostis tef (Zucc.) Trotter]. J. Genet. Breed. 52: 307–311. Ketema S (1997) Tef Eragrostis tef (Zucc.) Trotter. Promoting the Conservation and Use of Underutilized and Neglected Crops. Gatersleben/Rome: Institute of Plant Genetics and Crop Plant Research/International Plant Genetic Resources Institute Booklet 12. Kreitschitz A, Tadele Z, and Gola EM (2009) Slime cells on the surface of Eragrostis seeds maintain a level of moisture around the grain to enhance germination. Seed Sci. Res. 19: 27–35. NRC (National Research Council of the USA) (1996) Tef. In: Lost Crops of Africa, vol. 1. Grains, pp. 214–338. Washington, DC: National Academy Press. Tefera H, Ayele M., Assefa, K., 1995. Improved varieties of tef [Eragrostis tef (Zucc.) Trotter] release of 1970–1995. Research Bulletin 1. Debre Zeit Agricultural Research Center, Ethiopia. Umeta M and Parker ML (1996) Microscopic studies of the major macro-components of seeds, dough and injera from tef (Eragrostis tef). SINET: Ethiop. J. Sci. 19: 141–148. Umeta M, West CE, and Fufa H (2005) Content of zinc, iron, calcium and their absorption inhibitors in foods commonly consumed in Ethiopia. J. Food Comp. Anal. 18: 803–817.

Relevant Websites http://www.ars-grin.gov – USDA’s GRIN database. http://mansfeld.ipk-gatersleben.de – Mansfeld’s world database of agricultural and horticultural crops. http://www.tef-research.org/-Tef – Research project.

The Oilseeds

Contents Oilseeds: Overview Soybean: Overview Canola: Overview Cottonseed: Overview Sunflower: Overview Overview of the Oilseed Safflower (Carthamus tinctorius L.) Linseed: Overview

Oilseeds: Overview RJ Mailer, Australian Oils Research, Lambton, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

•

Oilseed crops are generally grown for the oil in their seeds and vary considerably in oil content, quality, and composition – factors that rely heavily on the crop species or cultivar and upon the environmental conditions in which the crop is grown. The seed meal left after the oil has been extracted can provide a high-protein product for use in either animal or human food. In some crops, the seed meal or some other factors are more important than the oil, and the oil is a byproduct. For example, soybean is primarily grown for its highprotein meal and cotton for its fiber. Consequently, in oil-producing crops, plant-breeding programs are aimed at increasing both oil production and quality with the additional aim of increasing meal quality. In some oil crops, antinutritional components are present (such as gossypol in cottonseed and glucosinolates in rapeseed); they also need to be considered and may limit the use of the meal.

• • • • • • • •

The major oilseed crops of the world include soybean, cottonseed, rapeseed, sunflower, groundnut, sesame seed, linseed, safflower, and mustard seed. The global oilseed market is dominated by soybean with a total of 242 Mt produced in 2012. Rapeseed is now rated in second position in world production of oilseeds with 65 Mt produced in 2012. Plant-breeding programs are aimed at increasing oil production and quality. World oilseed production is forecast to expand by 20% for the period 2012–21. The use of edible oil for biodiesel is forecast to increase by 76% or 30 Mt by 2021. Meal is utilized as stock feed, in particular pork and poultry and, more recently, aquaculture. Palm oil fruit production in 2012 exceeded 50 Mt, second only to soybean. The biggest changes will come in the future from genetic modification.

Learning Objectives

• • •

This article is designed to provide the reader with some basic information about the major oilseed crops of the world. The reader should have a basic understanding of the importance of each crop and its uses. Information on production and export are provided to show which countries are the major producers and exporters.


Oilseeds and Their Uses The major component of oilseed crops is the oil, which, in many cases, accounts for up to 80% of the crop value. The oilfree meal provides additional value along with various byproducts, such as lecithin, and a range of extracts from both meal and oil. Vegetable oils contain 95–98% triacylglycerols (or triglycerides). The remaining fraction consists of phospholipids, monoacylglycerols and diacylglycerols, and unsaponifiable components including sterols and tocopherols. The oils consist of long-chain fatty acids from C14 to C24 in length, and the proportion of these fatty acids in the oil has a significant contribution to its nutritional value. In recent years, there has

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THE OILSEEDS | Oilseeds: Overview

been a trend in human diets toward reduction of saturated fats such as palmitic acid (C16:0) and an increase in polyunsaturated (C18:2 and C18:3) and monounsaturated (C18:1) fats. Plant breeders have successfully developed more nutritionally favorable products from traditional oilseed crops by altering their fatty acid profiles and other constituents. There is strong demand for food, feed, and biofuel. According to the OECD-FAO Agricultural Outlook 2012–21, world oilseed production is forecast to expand by 20% for the period, exceeding 529 Mt by 2021. This is a marked slowdown compared with that of the last decade and is as a result of reduced area expansion, environmental constraints, and competing crops. Vegetable oil production, however, will increase by about 28% due to the contribution of palm and coconut oil. By 2021, palm oil is expected to make up one-third of world vegetable oil production. World consumption of oils is forecast by FAO to grow by only 2% per year, half the growth rate of the last decade. China and the European Union are the dominant importers of oilseeds and their products. Although demand for food use is slowing down in developed countries as they reach saturation levels, consumption in developing countries is steadily increasing. There has been and continues to be a significant increase in biodiesel use in developed and developing countries. The use of edible oil for biodiesel is forecast to increase by 76% or 30 Mt by 2021, raising the share of vegetable oil for biodiesel from 12% to 16%. Nonfood uses of vegetable oils in developed countries are estimated to continue to increase due to developments in the oleochemical industries with a shift away from petroleum-based products to environmentally friendly oleochemicals. In addition, there is an increase in technological developments, particularly with the genetic modification of oilseeds to create a new range of products. For cooking oils and salad dressings, plant breeders have selected cultivars with lower levels of polyunsaturated and saturated fats and an increase in monounsaturates for increased oxidative stability. New developments include oils with increased stearic acid to provide margarine type fats without the need for hydrogenation and the subsequent production of trans-fatty acids. The uses of vegetable oils in paints, lubricants, cosmetics, and pharmaceuticals have been well documented. Meal production globally will increase by 23% or about 315 Mt by 2021, much of this as a result of expansion of rapeseed for biodiesel in the European Union. World consumption of oilseed meal is also expected to increase by 23%, which compared with the past decade reflects a slowing down with livestock industries growing at a slower pace. Soybean meal dominates the market although it is expected that future meal production from sunflower and rapeseed will increase relative to soybean. Much of the meal is utilized as stock feed and in the production of livestock products, in particular pork and poultry and, more recently, aquaculture. Meal products, such as protein extracts, are used for edible purposes, and consumption of whole seed, including roasted soybeans, peanuts, and sesame seed, is common. The meal also has industrial applications in cosmetics, paints, and adhesives.

Oil Analysis The traditional methods of oilseed analysis made plant breeding and selection a slow and tedious process. The Goldfisch or Soxhlet methods of oil extraction required several hours to

Table 1 Approximate oil content of seed and protein content of oil-free meal and the main uses of selected oilseed crops Oilseed

Oil (%)

Protein (%)

Main use

Soybeans Cottonseed Peanut Rapeseed Sunflower seed Sesame seed Linseed Safflower seed Mustard seed

20 16 41 41 40 40–60 40 34 20–50

46 37 46 34 28 42 32–34 23 35

Food Fiber Food Oil Oil Food Oil Oil Condiment/oil

Source: Adapted from Australian Oilseed Federation Technical and Quality Standards – 2014 and other literature values.

complete and involved the use of hazardous flammable solvents. In addition, only a few samples could be processed at a time reducing the capacity of the laboratories to service the needs of plant-breeding programs. Kjeldahl nitrogen analysis to determine the nitrogen content of the meal also required the use of dangerous chemicals and strong acids. More recent advances in oil content determination include nondestructive seed analysis, such as the use of nuclear magnetic resonance spectroscopy. The rapid and accurate nondestructive testing of seed for oil content allows the breeder to retain the seed of potentially suitable lines. The introduction of near-infrared reflectance spectroscopy has further enhanced the ability of laboratories to determine a wider range of seed components including oil, protein, moisture, fiber, and numerous others on relatively small samples in a short time. Consequently, hundreds of seed samples can now be analyzed each day and the intact seed returned to the breeder for further growth and evaluation.

New Variations on Old Crops The major oilseed crops of the world include soybean, cottonseed, rapeseed, sunflower, groundnut (or peanut), sesame seed, linseed (from which the name linolenic acid is derived), safflower, and mustard seed. Many other crops can be used for oilseed production including castor beans, grape seed, tobacco seed, flax, corn oil, tung beans, and okra. The oil and protein content of the major oilseed crops is shown in Table 1. From these crops, plant breeders have developed specialty oil types within the different species. Sunflower oil, for example, is traditionally high in linoleic (polyunsaturated) acid and is promoted as such for its health benefits. With further plant breeding, there are now several grades of sunflower oil, from high-linoleic acid, to high-oleic acid (monounsaturated), to intermediate types. Oleic acid, being monounsaturated, has higher oxidative stability. In addition, the reduction in linoleic acid means that the need for hydrogenation to reduce polyunsaturated oils and the formation of trans-fatty acids is reduced. Trans-fatty acids are nutritionally undesirable and similar to saturated fats in their effects. Examples of plant species, which have been bred with increased oleic acid, include sunflowers (high oleic acid and NuSun™), linseed (solin, Linola™), cottonseed, soybean, rapeseed (canola, Monola™), safflower, and mustard.

THE OILSEEDS | Oilseeds: Overview Table 2

223

The fatty acid components and quantities in the major oilseed crops (amounts in rounded percentages)

Fatty acid

Name

Palmitic

Palmitoleic

Stearic

Oleic

Linoleic

Linolenic

Arachidic

Gadoleic

Behenic

Erucic

Symbol

C16:0

C16:1

C18:0

C18:1

C18:2

C18:3

C20:0

C20:1

C22:0

C22:1

8–14 6 21–26 8.3 2–7 1.5–6

<0.2

2–6 3 2–3 3.1 1–3 0.5–3

17–30 84 15–22 56 51–70 8–60

48–59 2 47–58 26 15–30 11–23

4–11 4 <0.5

<0.6

<0.5

<0.7

<0.3

<0.1

<0.6

<0.3

5–14 5–13

0.2–0.5 2 0.2–1.5 <3

0.1–5 3–15

<0.6 <2

<2.0 2–60

2–3 2–7 3–4 3–7 5–6

63–76 14–40 50–75 75–91 36–42

13–25 48–74 20–30 2–17 42–48

2–3 <0.3 <1 <0.3 0.3–0.4

0.1–0.5

1–2 <0.3

<0.6 0.3–1.5

<0.2 <0.3

0.2–0.5 0.3–0.6

0.1–0.5 <0.3

0.5–1.5 <0.3

<0.3

<1.0 <0.4

<1.8 <0.3 20–50 33–45 <40

Oilseed

Type

Soybean Soybean Cottonseed Peanuts Rapeseed

Normal High oleic acid Normal Normal Low erucic acid High erucic acid High oleic acid Linoleic acid Mid-oleic acid Oleic acid Normal

Sunflower

Sesame seed Linseed

Safflower Mustard seed

Normal Low linolenic acid Linoleic acid Oleic acid B. carinata B. nigra B. juncea

3–4 5–8 4–5 2–5 8–12

<1.2 <0.6 <3 <0.3 <0.1 <0.2

5–7 6

<0.3

3–4 3–4

19–20 15

14–17 73

52–61 2–3

<0.5

<0.6

5–8 3–6 4–10 2–7 3–10

<0.2 <0.2

2–3 1–3 <2 <2 1–3

8–22 70–84 8–23 10–27 15–64

68–83 9–20 15–22 15–22 14–28

<0.1 <1 18–27 11–27 9–24

0.2–0.4 0.3–0.6

<0.3 <0.5 <2 1–3

Source: Adapted from Codex Alimentarius Commission, Codex Stan 210-1999, Amend. 2013 and other literature values.

Other changes of significance to oilseed crops have been the development of genetically modified plants with specific applications other than for edible oils. The most obvious example of these is soybean in which large numbers of products are in development including those containing antibodies, altered amino acid profiles, and zero lipoxygenase. Rapeseed is also in the process of undergoing numerous transformations to produce products for polymers and detergents, inks, cosmetics, pharmaceuticals, lubricants, plasticizers, and resins.

The Crops Soybean Seed The seeds are rich in protein, mainly globulins, which make up 90% of the total proteins and 36% of the seed weight. Ten percent of the seed weight is carbohydrate, mainly sugars, and 3% is starch. The seed is relatively low in oil compared with other oilseed crops at 20%. Following oil extraction, heat treatment is used to inactivate enzymes in the high-protein meal that otherwise reduce the digestibility of the stock feed. Traditional soybean oil is polyunsaturated with 48–59% linoleic acid (C18:2) and 4–11% linolenic acid (C18:3) (Table 2). Breeding has produced cultivars with various fatty acid profiles; in particular, high-oleic acid soybean oil, which contains up to 84% oleic, has less saturated (palmitic) acid and is more stable for cooking purposes. The meal may also be used for industrial purposes such as cosmetics, paints, and adhesives and various edible purposes.

Cottonseed Cotton is basically grown for its fiber, but the seed has several important components consisting of oil (16%), protein (37%), hull (37%), and linters (10%). Also, within the kernel is a phenolic compound called gossypol, 1% of the seed weight: toxic to humans and monogastric animals. Cottonseed oil, prior to refining, is red due to the residual gossypol and associated products. Increased seed oil content has been a secondary objective to fiber production although the value of the oil is significant. Cottonseed oil contains 47–58% linoleic acid. To make the oil more stable for cooking and to reduce the need for hydrogenation, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia have developed an alternative cottonseed oil. By ‘switching off’ genes that convert oleic acid to linoleic acid, they have been able to produce high-oleic acid (73%), low-linoleic acid (5%) oil with increased oxidative stability. Additionally, they have found that it is possible to alter the proportions of saturated fatty acids, palmitic and stearic, which provide the solid properties necessary for making margarine.

Groundnut or Peanut Peanuts are a valuable source of oil and also produce a highprotein meal for stock feed. Increased yields are an important breeding priority, particularly in developing countries where yield is poor. Increased oil content is also desirable as peanuts have a wide range from 40% to >60% in wild types. Reduction in linoleic acid produces oil with a better oxidative stability.

224


Meal protein is high at 46%, but the amino acid profile is lacking in sulfur-containing amino acids particularly methionine. The components of whole peanuts are protein (26%), oil (41%), and carbohydrates (24%). The main product is the oil that has 80% unsaturated fatty acids making it a nutritionally favorable oil. Additionally, the level of oleic acid and palmitic acid makes it stable with good keeping qualities for cooking and in food mixtures. Plant selection has seen the development of new cultivars with high oleic acid levels of up to 60% and a subsequent reduction in linoleic acid content. Fatty acid profiles are influenced significantly by environmental conditions with high temperatures favoring high oleic acid contents.

Rapeseed Traditional rapeseed oil characteristically contains high levels of erucic acid, found to have detrimental effects on the myocardial muscle of rats fed the oil. The value of the meal was also low due to the presence of sulfur-containing compounds called glucosinolates, found to have deleterious effects on the thyroid gland of monogastric animals. Through plant breeding, major changes have been achieved to traditional rapeseed by increasing yield and oil while simultaneously increasing meal protein content. The development of cultivars with very low levels of glucosinolate in the meal has also been achieved. With the dramatic change in rapeseed from traditional types to those grown today, new terms have been used to discriminate between the types. Canola is recognized under ISO 5725, Codex Alimentarius, and ISTA as cultivars of rapeseed with <2% erucic acid in the oil and < 30 mmol of aliphatic glucosinolates in the meal. European nomenclature to describe cultivars of rapeseed includes low-erucic acid rapeseed and Colza, which is the French name for B. napus rapeseed in general. The seed oil is the main value of the crop yielding 42% oil, while the meal contains 35% protein. Current canola cultivars have very low erucic acid and saturated fatty acid levels and a good proportion of oleic (C18:1), linoleic (C18:2), and o-3 linolenic (C18:3) fatty acids. The balanced fatty acid profile makes rapeseed ideal for mayonnaise and salad dressings and a wide range of applications in the bakery and confectionary industries. New high-oleic acid/lowlinolenic acid types have improved oxidative stability for cooking and longer shelf life. Alternatively, high-erucic acid oil is utilized for industrial purposes such as cutting oils. Erucic acid is extracted from high-erucic acid rapeseed and converted to erucamide for plastic manufacture.

Sunflower Sunflower is grown for the seed oil, which is 80% of the seed value. The dehulled meal has 28–42% protein. The oil is highly considered due to its low linolenic acid value and therefore oxidative stability for cooking, salad oil, and margarines. Heritability of high oil is reliable, and it has been possible to increase oil contents from 30% in early types to over 50% in recent years. Sunflower cultivars with a range of fatty acid profiles have been developed including high oleic acid (75–91%) with reduced levels of linoleic acid (2–17%) and high levels of alpha-tocopherol (vitamin E), providing the market with very stable monounsaturated oil for cooking purposes. Mid-oleic

acid cultivars are also available, such as NuSun™, with saturated fatty acid levels of 8% and only 20–30% linoleic acid. The meal has high protein content and is used in animal feed for livestock and poultry. A small percentage of the crop is used for nonoilseed production for confectionary purposes.

Sesame Seed Sesame seeds are used intact or as oil and meal. The seeds generally have high oil content of 50% and 25% protein, although the oil content can vary between 40% and 60%. The fatty acid composition also shows a large range (Table 2). A high oleic acid (40%) and linoleic acid (45%) content makes the oil nutritionally beneficial. The unsaponifiable fraction of the oil contains sesamin and sesamolin that during the refining process form sesamol and sesaminol. These are strong antioxidants that give the oil exceptional resistance to oxidation and rancidity. The oil-free meal is high in protein (34–50%), depending on the variety, and has a favorable amino acid profile with high methionine and low lysine content. Today, the seed is used for human consumption on bread rolls, health food, and confectionary.

Linseed Due to its high iodine value, linseed oil has been used primarily for industrial purposes, such as linoleum floor covering, with a high level of unsaturated fatty acids making the oil very reactive and resulting in a short shelf life. Low linolenic acid cultivars have introduced linseed to the edible food market. In 1994, the Flax Council of Canada developed the term ‘solin’ to describe linseed with < 5% linolenic acid. The original hybridization work was carried out by the CSIRO in Australia with the release of two Linola cultivars in 1992 under the Plant Variety Rights scheme. Linola 947 was the first solin cultivar registered in Canada. Solin cv. Linola™ 989 has been reported as 46% oil (dry basis) and 34% protein. Linseed meal has a high crude protein value but low lysine levels. It also has a high level of soluble fiber, called mucilage, that is indigestible to nonruminants and reduces the energy value of the meal. Linseed is traded at 40% oil although the oil can range significantly depending on growing conditions.

Safflower Safflower was originally domesticated for its flowers: red carthamin dye was extracted for coloring food and cloth. Early cultivars were unsuitable for commercial development due to low oil content of 30%. Breeding programs have since increased oil contents and altered the fatty acid profiles to take it from an industrial product to the edible oil market with modern cultivars containing 34% or more oil. Traditional high-linoleic acid types contain 68–83% linoleic acid and 8–22% oleic acid (Table 2). Through plant breeding, high oleic acid levels (70–84%) have been achieved. Due to the wide range of environmental conditions from countries as diverse as Australia, India, and China, fatty acids may vary considerably. The meal from safflower seed is also valued as a stock feed. The protein content of the meal remains relatively low in relation to other oilseeds at only 23%.


Cottonseed

Peanuts

Linseed

Mustard seed

Rapeseed

Safflower seed

Sesame seed

Soybeans

Sunflower seed

225

1000

Production (Mt)

100

10

1

12 20

11 20

10 20

09 20

20

08

07 20

06 20

20

05

0

Year Figure 1 Global production of major oilseed crops (log10) from 2005 to 2012 in million tonnes (Mt). Adapted from Food and Agricultural Organization of the United Nations Statistics.

Mustard Seed Typically, mustard oil is high in erucic acid (20–50%) and the meal is high in glucosinolate compounds (50–150 mM g 1), providing pungency to mustard for condiments but reducing the palatability of the meal for stock feed. With plant breeding, very low levels of erucic acid have been achieved, and current aims are to develop cultivars that are more closely related to LEAR cultivars, with increased oleic acid content.

Production and Trade For the purpose of this article, fruit oils will not be discussed although production is significant. Palm oil fruit (from which palmitic acid derives its name) production in 2012 exceeded 50 Mt, second only to soybean. Oilseed production from 2005 to 2012 is shown in Figure 1 and the area grown and yields of the various crops in 2011 and 2012 in Table 3.

Table 3 2012

World production of the major oilseed crops for 2011 and Area harvested (Mha)

Soybeans Rapeseed Cottonseed Groundnuts Sunflower seed Sesame seed Linseed Safflower seed Mustard seed

Production (Mt)

2011

2012

2011

2012

104 34 NA 25 26 9 2 0.8 0.7

107 34 NA 25 25 8 3 1.0 0.6

262 63 49 40 41 5 2 0.7 0.6

253 65 47 41 38 4 2 0.8 0.5

NA, not available. Source: Adapted from FAOSTAT | ã FAO Statistics Division 2014 | 03 February 2014.

226


Soybean The global oilseed market is dominated by soybean with a total of 242 Mt produced in 2012, making up almost 50% of the total oilseed production (Table 3). The United States of America, in 2012, produced 29% of world soybean production, with Brazil (24%), Argentina (16%), India (10%), and China (6%) also producing significant amounts. Not unexpectedly, the United States is the largest exporter followed by Brazil and Argentina.

Rapeseed Rapeseed is now rated in second position in world production of oilseeds with 65 Mt produced in 2012. There has been a continual increase from 2005 to 2012 (Figure 1) in part due to increased production in Canada. Canada is now the largest producer of rapeseed with 15.4 Mt per annum or 24% of the world production. China is second with 14 Mt with India, France, Germany, and Australia also being major producers. Canada is also the major exporter of rapeseed (canola) with exports of nearly 8 Mt in 2011, while France and Australia exported around 1.6 Mt each. Germany is the biggest importer of rapeseed (canola) importing 3.2 Mt in 2011, with Japan (2.3), the Netherlands (2.3), Belgium (2.2), Mexico (1.6), and China (1.3) also being major importers.

Cottonseed The major purpose of cotton is for textile use. Production of cottonseed for oil has continued to increase in the last 20 years (Figure 1) although it has recently slipped back from the second largest oilseed crop to third place after rapeseed. Global production is 47 Mt with China being the largest producer at 14 Mt per annum. Other major producers include India (10.8 Mt), United States (5.1 Mt), Pakistan (3.2 Mt), Brazil (3.3 Mt), Uzbekistan (2.0 Mt), Australia (1.7 Mt), and Turkey (1.3 Mt). Australia is the leading exporter of cottonseed while Mexico, Spain, Japan, Italy, Korea, and the United States are large importers.

Groundnuts or Peanuts A global groundnut production of 41 Mt is led by China (17 Mt or 41%) with India (14%), Nigeria (8%), the United States (7%), and Myanmar (3%) also being significant producers. The major exporters of groundnuts include India (0.8 Mt), Argentina (0.2 Mt), and the United States of America (0.1 Mt). Importers are the Netherlands (0.3 Mt), Indonesia (0.1 Mt), Mexico (0.1 Mt), and Russian Federation (0.1 Mt).

Sunflower Sunflower production has continued to increase in recent years, in the period between 2005 and 2012, from 31 to 38 Mt (Figure 1). Ukraine is now the biggest producer with 8.4 Mt in 2012, which is 22% of world production. The Russian Federation also produced 8 Mt in 2012. Argentina, China, and France are other major producers. Romania (1.2 Mt) and Bulgaria (1.0 Mt) were the major exporters in

2012. Other exporters included Ukraine, Hungary, and France. Major importers include Turkey (0.9 Mt), the Netherlands (0.6 Mt), France (0.4 Mt), Germany (0.4 Mt), and Spain (0.3 Mt).

Sesame World production of sesame seed has increased from 3.17 Mt in 2001 to over 4 Mt in 2012. All but a small part of total world production is from developing countries including Myanmar (0.6 Mt), India (0.6 Mt), China (0.6 Mt), and the United Republic of Tanzania (0.5 Mt). India (0.4 Mt), Ethiopia (0.3 Mt), Nigeria (0.1 Mt), and Sudan (0.1 Mt) are the largest exporters of sesame. Major importers were China (0.4 Mt), Japan (0.2 Mt), Turkey (0.1 Mt), Vietnam (0.1 Mt), and Republic of Korea (0.1 Mt).

Linseed World production of linseed has shown a gradual decline since the 1980s despite a peak in 1999 of almost 3 Mt. The production has continued to fall between 2005 (2.8 Mt) and 2012 (2.1 Mt) (Figure 1). The total production of 1.7 Mt in 2007 was the lowest level of production in the previous 46 years. Canada, the largest producer, decreased production from 1.0 Mt in 2005 to 0.5 Mt in 2012. The major producers of linseed are Canada, Russia, China, Kazakhstan, the United States, and India. Canada is the major exporter with 359 000 T exported in 2011. Russia, Belgium, and Kazakhstan are also major exporters. Belgium, the United States, Germany, and China are major importers.

Safflower Production of safflower has also been relatively stable over many years, falling from 900 kt in 1985 to 600 kt in 2002 but rising again in 2012 back to 800 kt. This failure to increase may reflect the increased demand for monounsaturated oil in place of polyunsaturated oils. The major safflower-producing countries in 2012 are Mexico (258 kt), India (152 kt), Kazakhstan (127 kt), Argentina (108 kt), and the United States (81 kt). The United States and Australia are major exporters of safflower, but the United States is also a net importer of safflower oil. Japan is a major importer.

Mustard There has been no increase in world production of mustard in recent years (Figure 1) from 565 kt in 2005 to 494 kt in 2012. Major producers in 2012 include Nepal (145 kt), Canada (118 kt), Myanmar (68 kt), and Russia (41 kt). In 2011, Canada exported 130 kt of mustard, while Ukraine (39 kt), Russia (34 kt), Germany (21 kt), and Czech Republic (12 kt) were also significant exporters. The United States (68 kt), Germany (50 kt), Nepal (32 kt), France (25 kt), and Bangladesh were the major importers in 2011.


Future Developments Oilseeds play an increasingly important role in society, both as an edible food product and for industrial uses. The benefits include the valuable oil component and the secondary but also useful meal that provides high-energy and nutritionally important food. Breeders have been able to optimize the characteristics of many of these crops to achieve higher levels of production and to alter the products to suit specific requirements. These changes include improvements in nutritional value, particularly with changes in fatty acid profiles and the reduction in antinutritional components. Undoubtedly the biggest changes will come in the future from genetic modification in which long-term breeding programs can be dramatically reduced to relatively short periods of time. Traditional, breeding techniques rely on natural variability in plant populations to achieve change. Genetic engineering can create new products previously out of the reach of established breeding techniques. Engineering plants for specific aims or more suitable to environmental conditions can increase production. Nutritionally, fatty acid profiles can be dramatically altered to reduce saturated and trans-fatty acids and simultaneously improve oxidative stability. Vegetable oils are already being substituted, in many instances, for less environmentally friendly petroleum products. The major competition to oilseed crops in the future will only be from the ever-growing range of additional oilseed types.


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Discuss the major oilseed crops of the world and their uses. Which are the major producing and importing countries for each species of oilseed? Consider and discuss what changes have been made to make oilseed crops more useful? Evaluate the importance of fruit oils and how do they rate against oilseed crops? Compare oilseeds that are used for oil with the ones that are grown for their high-protein meal and consider why?


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Consider the changes in oilseed production over years and the ability of breeders and producers to keep pace with the demand of an increasing population.

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Are the same countries always the largest producers or is this changing? Why are some countries reducing production, while others are increasing? How are the uses of oil, meal, and oilseeds changing? Look at the new applications for these products, which differ from the original use for food. What will be the impact of industrial uses, particularly biodiesel to the food supply in the future?

See also: Agronomy of Grain Growing: Canola: Agronomy; Soybean: Agronomy; The Legumes and Pseudocereals: Peanuts: Overview; The Oilseeds: Cottonseed: Overview; Sunflower: Overview.

Further Reading Appelqvist L-A and Ohlson R (eds.) (1972) Rapeseed: Cultivation, Composition Processing and Utilization Amsterdam: Elsevier. Benedict JH, Treacy MF, and Kinard DH (eds.) (1994) Vegetable Oils and Agrichemicals Memphis, TN: Cotton Foundation and National Cottonseed Products Association. Bennett M (1998) Sesame seed. In: A Handbook for Farmers and Investors Australia: Rural Industries Research and Development Corporation. FAO (2003) FAO Statistical Database. Rome: Food and Agriculture Organization of the United Nations. Hui YH (ed.) (1996) Baileys Industrial Oil and Fat Products, 5th edn., Series 3. New York: Wiley ISBN: 047159427X. Karleskind A (1996) Oil and Fats Manual. France: Lavoisier Publishing. KeShun L (1997) Soybeans: Chemistry, Technology and Utilization. New York: Chapman and Hall, ISBN: 0-8342-1299-4. Kimber DS and McGregor DI (eds.) (1995) Brassica Oilseeds, Production and Utilisation Wallingford: CAB International. Ro¨bbelen G, Downey RK, and Ashri A (1989) Oil Crops of the World. New York: McGraw-Hill. Weiss E (2000) Oilseed Crops, 2nd edn. Malden, MA: Iowa State Press. Woodroof JG (1983) Peanut Production, Processing, Products, 3rd edn. Westport, CT: AVI.

Relevant Websites http://www.amsoy.org – American Soybean Association. http://www.aocs.org – American Oil Chemists’ Society. http://www.apps.fao.org – Food and Agriculture Organization. http://www.australianoilseeds.com – Australian Oilseed Federation. http://www.australianoilseeds.com – 7th International Safflower Conference. http://www.canola-council.org – Canola Council of Canada. http://www.codexalimentarius.net – Codex Alimentarius Commission. http://www.cottonseed.com – National Cottonseed Products Association. http://www.flaxcouncil.ca – Flax Council of Canada. http://www.grainscanada.gc.ca – Canadian Grain Commission. www.sunflowernsa.com – National Sunflower Association. www.regional.org.au – 10th International Rapeseed Congress. http://www.rirdc.gov.au – Australian Rural Industries and Research Foundation.

Soybean: Overview K Liu, Agricultural Research Service, US Department of Agriculture, Aberdeen, ID, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Soybean is an ancient Chinese grain and now a top oilseed crop, with world annual production reaching more than 300 million tonnes. Soybean is also a legume, having the ability to fix nitrogen from air through its roots. Soybean has the highest protein content (40%) and the second highest oil content (20%) among food legumes. It also contains an array of phytochemicals. Soybean has a versatile use as food, feed, and industrial material. Soyfoods come in various types: traditional, modern (Westernized), fermented, and nonfermented. Soyfoods are not only nutritious but also healthy since regular consumption of soyfoods can help prevent certain chronic diseases. The majority of soybean produced annually is currently crushed into oil for edible consumption and defatted meal mostly for animal feed. Only a small portion of annual production is used for whole soy food or soybean protein ingredients.

Learning Objective

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To have a basic understanding of soybeans with respect to its history, current production, agronomic traits, chemistry, nutrition, processing, and various end uses

Introduction From one of the five sacred grains in ancient China to one of top cash crops, the soybean (Figure 1) has played a very important role in nourishing humans and animals. For the past several decades, progress has been made on many fronts of soybean research, from production management to variety development, from genome mapping to compositional modification, from processing to new product development, from health benefits to identification of key responsible components, and from animal nutrition to new industrial uses. Since there are so many topics to be covered on soybeans, it is impossible to give a detailed account in this article. Readers are advised to refer to several specific, topical chapters on soybeans as well as further reading under each article.

Production For the past six decades, the soybean has emerged as one of the most important agricultural crops in the world, with a steady increase in annual production. In 1955, the world soybean production was only about 20 million tonnes (MT). In 2014, global production increased to about 311 MMT (Figure 2).

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During the same period, soybean production in the United States increased from about 9 to 106 MMT and in Brazil and Argentina from virtually negligible amounts to 94 and 55 MMT, respectively, while soybean production in China went up and down within a small range of 10–15 MMT. These differential changes have made the United States, Brazil, and Argentina the top three soybean producers and China from the world’s number 1 prior to the 1950s to the world’s number 4 soybean producer at the present time. There are several reasons for the rapid and sustainable worldwide growth in soybean production. First, soybeans have many possible end uses, including as human food, animal feed, and industrial materials. Second, advances in plant breeding and production management have led to a steady increase in production yields in the field and improvements in the seed quality. This is particularly true in recent years when application of crop biotechnology has resulted in the development of new soybean varieties that are resistant to certain diseases and pests, tolerant to herbicides, and/or improved in seed composition. Third, the soybean is capable of producing a higher amount of edible protein than any other crops per hectare of land while producing a significant amount of edible oil. Fourth, like other members of the legume family, soybeans have an ability to fix nitrogen due to its characteristic symbiosis with root bacteroids. This feature makes the soybean a good rotational crop. Fifth, recent medical discoveries have linked the consumption of soyfoods to the prevention and treatment of chronic diseases such as heart diseases, cancer, and bone diseases. This new development helps promote soybean utilization as food. Finally, growth and globalization of world economy and trades have been another important driving force. We are seeing a rapid interchanging trend with respect to soybean utilization between China and the rest of the world. In China, where soybeans originated and traditional soyfoods are popular, rapid economic development in recent years has led to increased demand for soybeans as refined oil and animal feed. In the rest of world, particularly in North America and Europe, where historically soybeans are crushed for edible oil and animal feed, interest in soyfoods and soy-enriched food has experienced a phenomenal rise over the past 2 decades.

Origins Historical and geographic evidence indicates that soybeans originated in northern China and that its cultivation in the region started approximately 5000 years ago. The soybean was considered one of the five sacred grains, along with rice, wheat, barley, and millets. It was repeatedly mentioned in later records. The Chinese gradually developed many nutritious foods out of soybeans, including soy milk, tofu, soy sprouts, fermented soy paste, and soy sauce (Figure 3). Soybean cultivation and soyfood preparation methods were gradually introduced into Japan, Korea, and other neighboring countries about 1100 years ago. People in these countries not only


http://dx.doi.org/10.1016/B978-0-12-394437-5.00028-0

THE OILSEEDS | Soybean: Overview accepted the Chinese way of preparing soyfoods but also created new soyfoods. Japanese natto¯ and Indonesian tempeh are two good examples. All these foods are now known as traditional soyfoods. The soybean and soybean products were introduced into Europe during the Age of Discovery (sixteenth to seventeenth centuries) and into the North America during the mideighteenth century. Yet, large-scale official introduction into the United States did not occur until late nineteenth century and early twentieth century, during which the US Department of Agriculture developed a national soybean germplasm collection, and thousands of new varieties were collected, mostly from China. Currently, the collection contains over 20 000 strains, serving as a primary genetic source for soybean research and variety development.

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Agronomic Characteristics The soybean belongs to the family Leguminosae. The cultivated form, Glycine max (L.) Merrill, grows annually. Its plant is bushy, with a height between 0.2 and 2.0 m, and produces a fruit having three to five hairy pods in a cluster (Figure 4). Each pod, 3–8 cm long, contains two to four seeds that are sphericalto oval-shaped. Most seeds are yellow, but they can also be green, dark brown, purplish black, or black. Most mature plant seeds are made of three basic parts: the seed coat, embryo, and one or more food storage structures (such as the endosperm). The soybean seed, however, like other legume seeds, is essentially devoid of endosperm and consists of only a seed coat and a large, well-developed

Figure 3 Traditional soyfoods: soy milk, soy sauce, soy milk film, soy sprouts, tofu, and okara (soy fiber).

Figure 1 Soybean seeds.

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Figure 2 Soybean production around the world. Data extracted from oil crops outlook, Economic Research Service, US Department of Agriculture, Washington, DC.

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THE OILSEEDS | Soybean: Overview

Figure 4 Harvesting soybeans in the field. Courtesy of the United Soybean Board.

embryo. The seed coat is marked with a hilum (also known as seed scar) that varies in color. The embryo contains two equal cotyledons and three other structural parts: radical, hypocotyl, and epicotyls. The radicle and hypocotyl, together known as embryonic axis or germ, are located under the seed coat at one end of the hilum, just below the micropyle, which is a tiny hole formed by the integuments during seed development. The epicotyl is tucked between the pair of cotyledons. During germination, the radicle becomes the primary root, whereas the hypocotyl lifts the cotyledons above the soil surface. The epicotyl is the main stem and growing point. Cotyledons function as a nutrient reservoir. In general, cultivated soybeans constitute approximately 8% hull, 90% cotyledons, and 2% germ. The soybean plant has two major growth stages: the vegetative stage and the reproductive stage. The period between the emergence and the appearance of the first flower is the vegetative stage. This usually takes 6–8 weeks. The soybean plant is photoperiod-sensitive and makes the transition from vegetative to flowering stages in direct response to day length. Most soybean varieties begin flowering soon after the day length begins to shorten. Because of this feature, latitude plays a major role in the adoption of soybeans to various geographic regions. Following the period of vegetative growth, the soybean plant enters the reproductive stage in which maxillary buds develop into flower clusters of 2–35 flowers each. This is followed by pod development, seed development, and maturation. The whole stage lasts from 7 to 12 weeks. Like other farm crops, soybean plants are vulnerable to a wide range of bacterial, fungal, and viral diseases and parasites (such as cyst nematodes). They are also exposed to weeds and other environmental stresses, such as saline or alkaline soils, drought, and chilling temperatures. Rotating crops, spraying chemicals, and choosing resistant cultivars have been the primary tools used by farmers to control diseases, pests, and weeds and manage other stresses. However, the wide use of pesticides, herbicides, and other chemicals has caused environmental concerns. Fortunately, advances in plant breeding and genetic engineering have made the biological control quite possible. New soybean varieties with herbicide tolerance, insect resistance, and disease resistance have been developed and successfully commercialized. Among them, glyphosate-

Figure 5 General composition of soybean seeds. Courtesy of the United Soybean Board.

tolerant soybeans and Bt soybeans, both transgenic in nature (also known as genetically modified organism), have been widely adapted in the field.

Chemistry and Nutrition General Composition Soybeans are known as ‘yellow jewel’ or ‘miracle beans,’ because of their unique chemical composition (Figure 5). By average, on a dry matter basis, mature soybeans contain about 20% oil, 40% protein, and 5% ash and the remaining 35% is total carbohydrate. With this composition, the soybean has the highest protein content among cereal and other legume species. Protein content in other legumes ranges between 20% and 30%, whereas those in cereals range between 8% and 15%. The soybean also has the second highest oil content among all food legumes (after the peanut). Because of this, the soybean is considered an oilseed as well. Other minor components found in soybeans include minerals, vitamins, and various biologically active substances. The majority of soybean protein is storage protein. Based on solubility patterns, soybean seed proteins are divided into albumins and globulins. Albumins are soluble in water, whereas globulins are soluble in a salt solution. Soybean globulins are the primary portion of total seed proteins and can be further divided into glycinin and conglycinin. Due to differences in composition and structure, the two exhibit differences in nutritional quality (amino acid composition) and functional properties (such as gelation and thermal stability). During seed development, soybeans store their lipids in an organelle known as oil bodies, mainly in the form of triglycerides. During processing, components extracted from soybeans by hexane are classified as crude oil. Triglycerides are the major component of crude oil, while minor components include phospholipids, unsaponifiable material, free fatty acids, and trace metals. Soybean oil typically contains about 11% palmitic, 4% stearic, 23% oleic, 53% linoleic, and 8% linolenic acids. With this fatty acid composition, soybean oil remains liquid over a wide range of temperatures. Soybean carbohydrates can be grouped into insoluble and soluble ones. The insoluble carbohydrates include cellulose, hemicellulose, pectin, and a trace amount of starch. They are

THE OILSEEDS | Soybean: Overview structural components found mainly in cell walls. Soluble carbohydrates include measurable amounts of di- and oligosaccharides, with sucrose in the range of 2.5–8.2%; raffinose, 0.1–0.9%; and stachyose, 1.4–4.1%, and trace amounts of monosaccharides, such as glucose and arabinose. The oligosaccharides are nonreducing sugars, containing fructose, glucose, and galactose as three or four units, linked by beta-fructosidic and alpha-galactosidic linkages. The content of major minerals in soybeans ranges from 0.2% to 2.1%. Among them, potassium is in the highest concentration, followed by phosphorus, magnesium, sulfur, calcium, chloride, and sodium. The minor minerals present in soybeans are silicon, iron, zinc, manganese, copper, molybdenum, fluorine, chromium, selenium, cobalt, cadmium, lead, arsenic, mercury, and iodine. Their content ranges from 0.01 to 140 ppm. Soybeans also contain both water-soluble and oil-soluble vitamins. The water-soluble vitamins present in soybeans include thiamin, riboflavin, niacin, pantothenic acid, and folic acid. The oil-soluble vitamins present in soybeans are vitamins A and E with essentially no measurable vitamins D and K.

Biological Active Components There are an unusually large number of heat-stable and heatlabile substances that are naturally found in soybeans. These compounds, although present in a trace amount, are capable of eliciting diverse nutritional, biological, and physiological responses in humans and animals. These biological and physiological responses can be adverse or beneficial to human and animals, and as such, some substances are known as antinutritional factors, while others are referred to as phytochemicals or nutraceuticals. Sometimes, the same substances may exert both adverse and beneficial effects, depending on the dosage and specific application. Due to page limitations, only a few key compounds are briefly described in the succeeding text. Proteinase inhibitors present in soybeans fall into two types: Kunitz trypsin inhibitor and Bowman–Birk inhibitor. The significance of soybean trypsin inhibitors lies in their nutritional implications toward both humans and animals. Unless inactivated by heat, these inhibitors can cause growth depression by reducing the digestibility of proteins. Lectin, also known as hemagglutinin, is another antinutritional factor that is of protein nature found in soybeans. It possesses a remarkable ability to agglutinate erythrocytes and other types of cells. As demonstrated by animal studies, soybean lectin is linked to an enlargement of the pancreas, a lowering of blood insulin levels, an inhibition of disaccharidase and proteases in the intestines, and degenerative changes in the liver and kidneys, in addition to growth inhibition. Phytate is the calcium–magnesium–potassium salt of inositol hexaphosphoric acid, which is commonly known as phytic acid or phytin in the literature. As in most seeds, phytate is the principal source of phosphorus in soybeans. Its content ranges from 1.00% to 1.47% on a dry matter basis. This value represents a little more than 50% of the total phosphorus in soybean seeds and 60–70% of total phosphorus in defatted soybean meal. Phytate P is nutritionally unavailable to monogastric animals. Supplementation with inorganic P into

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soy-based feed has been a practical way to address the problem. Excess P due to unavailability or oversupplementation in animal feed is excreted in feces, raising environmental concerns. Among soybean carbohydrates, raffinose and stachyose garner the most attention, mainly because human and monogastric animals cannot digest these sugars well due to the lack of a specific, endogenous alpha-galactosidase. As a result, their presence has been linked to flatulence and abdominal discomfort associated with soybean consumption. Phospholipids are polar lipids, constituting 0.5–1.5% of the soybean seed and 1–3% of crude soybean oil. The commercial product of phospholipids is known as lecithin, a major by-product of the soybean oil refining process. Phospholipids are good emulsifying agents, soluble in alcohol and insoluble in acetone. In living tissues, they are the major components of cell membranes. Isoflavones belong to a group of compounds that share a basic structure consisting of two benzyl rings joined by a threecarbon bridge that may or may not be closed in a pyran ring. The soybean is unique in that it contains the highest amount of isoflavones, being up to 3 mg g 1 dry weight. Among all the health-promoting components, isoflavones are thought to be most responsible for many of the hypothesized health benefits of soyfoods and thus have gained the most attention in the scientific community. Soybeans contain 0.1–0.3% saponins, which are composed of sugars bound to alkaloid, steroid, or triterpene compounds and have detergent surfactant properties. Saponins have blood cholesterol-lowering properties rendered by their binding of cholesterol. The bound cholesterol is then passed to the colon and excreted. Phytosterols are lipid-like compounds found in plants. Soybeans, rapeseeds, and coniferous trees are the three major commercial sources of phytosterols. The total phytosterol content of soybeans is estimated at 0.3–0.6 mg g 1. Soybean sterols are obtained during oil processing as by-products of vitamin E manufacturing. Although phytosterols are structurally related to cholesterol, they have been clinically proven to reduce blood cholesterol in our bodies.

Nutritional Values In addition to their high content in soybeans, soybean oil and protein are both of high quality. Like other edible oils, aside from culinary roles, soybean oil provides us with calories, essential fatty acids, and fat-soluble vitamins. Since soybean oil contains very high percentages of unsaturated fatty acids, it is an excellent source of essential fatty acids. Soybean protein contains all the identified essential amino acids for animals: isoleucine, leucine, lysine, methionine, cysteine, phenylalanine and tyrosine, threonine, tryptophan, valine, and histidine. Most of these amino acids are present in amounts that closely match those required for humans and other animals. The only potentially limiting amino acids are sulfur-containing ones, primarily methionine and cysteine. Yet, such deficiency is increasingly considered less problematic, with respect to human nutrition. Protein quality depends on the amino acid composition of the protein, amino acid requirements for humans or animals fed with the protein, the active amounts of antinutritional factors, digestibility of the

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protein, and the method for assaying protein quality. In the earlier days, protein quality was assayed by the protein efficiency ratio, which was measured by feeding the protein of interest to rats. Since rats have a much higher need for sulfurcontaining amino acids than humans, soybean protein quality was underestimated. Today, the protein digestibility-corrected amino acid score (PDCAAS), a newer method, has been adopted. Since it compares the pattern of essential amino acids in a protein with the requirements that humans have for essential amino acids and then adjusts for how well that protein is digested, PDCAAS measures how limiting each individual amino acid is in a protein. Under this new assay method, soybean protein has a score very close to 1, the highest rating possible, which is the same rating for animal proteins, such as egg white and casein. The deficiency in sulfur-containing amino acids associated with soybean proteins can readily be corrected by a simple change in the dietary patterns in humans. For example, since cereal grains are normally rich in sulfur-containing amino acids (but poor in lysine), one easy solution has been to combine soyfoods with cereals. This dietary pattern has in fact been practiced in the Orient throughout the history of soyfood consumption even without much understanding of food chemistry and human nutrition. For monogastric animals, suboptimal concentrations of cystine and methionine in soy-based feed are effectively addressed by methionine supplementation.

Health Benefits Historically, the soybean has been primarily identified with its high protein quantity and quality. Yet, for the past several decades, medical research has linked consumption of soy to the prevention and treatment of several chronic diseases and implicated soybean proteins, isoflavones, and other phytochemicals as contributing factors. For example, a mega study conducted in 1995 showed that soybean protein can lower total cholesterol (9.3%), low-density lipoprotein (LDL) cholesterol (12.9%), and triacylglycerols (10.5%), with a small increase in high-density lipoprotein (HDL) cholesterol. Formal recognition of the cholesterol-lowering properties of soybean protein came in 1999 when the US Food and Drug Administration approved a health claim for the cholesterol-lowering effects of soybean protein. This ruling has set off a rush by many US mainstream food companies to enter the soyfood market, helped increase the awareness of soyfood products, and created an incentive for food processors to incorporate soybean protein ingredients into many types of existing food. As a result, the soyfood industry in the United States and around the world has experienced phenomenal growth and opportunity.

Soybean Processing Simply boiling whole soybeans for direct use is mostly limited to immature soybeans. For any effective use, soybeans have to be processed into food, dietary ingredients, or coproducts. Narrowly defined, soybean processing includes traditional processing, modern processing, and alternative processing, all

Figure 6 Soybean oil and defatted meal. Courtesy of the United Soybean Board.

starting with whole beans. Broadly defined, soybean processing also includes secondary processing, which starts with soy ingredients or intermediate products, such as crude oil refining, soybean oil processing, soybean protein processing, and coproduct recovering.

Modern Processing Modern processing is basically a solvent extraction to produce crude oil and defatted meal (Figure 6). The process consists of preparation, extraction, and desolventization. Soybean preparation includes cleaning, drying, cracking, conditioning, and flaking, with dehulling (before conditioning) as an optional step. During solvent extraction, oil is extracted from the soy flakes by an organic solvent (most often hexane). Two intermediate products come out of the extractors: an oil–solvent mixture and defatted soy flakes. Both need to be desolventized to remove solvent. The oil–solvent mixture has about 25–40% hexane, which can be removed and recycled by an evaporator. Defatted flakes contain about 30% hexane, and the choice of desolventing equipment depends on the end use of desolventized flakes (also known as defatted meal). For the majority of meal used as animal feed, flakes are processed through a desolventizer–toaster, which uses hot steam to remove solvent and inactivate heat-labile antinutritional factors, such as trypsin inhibitors and lectins. This is to ensure optimal nutritional value of meals. For food aimed at human consumption, it is necessary to minimize heat denaturation during desolventization of flakes to main high water solubility of soybean proteins. This is carried out in a vapor desolventizing system or a flash desolventizing system. Crude oil contains variable amounts of nontriglyceride compounds. In order to remove these impurities to produce high-quality edible oil, crude oil needs to be subjected to a series of refining operations. This includes degumming, neutralization, bleaching, and deodorization. Degumming removes phospholipids (also known as gums). The recovered gums are the source of commercial lecithin. Neutralization removes free fatty acids. Bleaching removes most colorants and some residues from previous refining steps. Deodorization is a steam stripping process to vaporize undesirable volatile

THE OILSEEDS | Soybean: Overview components. It is the final step after general processing. The final product is refined, bleached, and deodorized (RBD) oil, commonly known as RBD oil. Yet, due to its high concentrations of polyunsaturated fatty acids, RBD oil is prone to oxidation and off-flavor formation. It also lacks certain physical and functional properties. To overcome these limitations, additional processes (collectively known as soybean oil modification), such as hydrogenation, interesterification, winterization, and/or fractionation, may also be used.

Alternative Processes There has been increased concern over the past several decades with the safety and environmental impact of hexane solventbased extraction. Several alternative oilseed milling processes have been available or under development. Screw pressing or expelling is an old way of processing soybeans and other oilseeds, which existed long before solvent extraction was developed. The method, also known as mechanical extraction, has relatively low oil removal efficiency (leaving 4–8% residual oil in the meal) and low production efficiency. The advantages are low initial cost and no solvent requirements. Dry extrusion is another alternative processing method for soybeans. It was developed in the 1960s to enable Midwestern US soybean growers to cook soybeans for use as livestock feed right on the farm where soybeans were produced. The process generates friction as the sole source of heat to deactivate antinutrients in soybeans. It does not remove any oil, though. Yet, when dry extrusion is combined with expelling, the throughput of the mechanical extraction is greatly improved. The process, known as extruding–expelling, was developed in the 1980s and has become the primary choice for alternative processing of soybeans. Another alternative method for processing soybeans is aqueous extraction process. The method differs radically from standard oil milling processes in that an aqueous system is used to extract oil. Although the concept and general features of the aqueous method appear attractive compared to the conventional hexane-based method, the comparatively low oil yield and relatively high content of oil in the remaining fractions have discouraged its commercial application.

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Traditional Soyfoods Over the course of several thousand years, long before the modern processing emerged in the twentieth century, soybeans had been processed into various soyfoods, known as traditional soyfoods. Since these foods were created in China and neighboring countries, they are also known as Oriental soyfoods. In general, traditional soyfoods are classified as nonfermented and fermented. Nonfermented soyfoods include soy milk, tofu, soy sprouts, yuba (soy milk film), okara (soy pulp), immature soybeans, soynuts, and toasted soy flour (Figure 3). Traditionally, soy milk is made in China by soaking, rinsing, and grinding soybeans into slurry. This is followed by filtering the slurry to separate the residue (okara) and cooking the extract to become edible. As shown in Figure 7, the processes for making tofu, soy milk film, and okara are directly linked to soy milk production; tofu and soy milk film all start with soy milk making while okara is a by-product of soy milk making. To make tofu, soy milk is boiled for about 10 min, and a coagulant suspension is added to form curds, which is then shaped and pressed into tofu. There are four major fermented soyfoods – fermented soy paste (miso), soy sauce, tempeh, and natto¯ – and two minor fermented soyfoods: sufu (fermented tofu) and soy nuggets (fermented whole soybeans). They vary greatly in the methods of preparation, microorganisms involved, and utilization. While it takes less than a week to prepare tempeh and natto¯, the preparation of the remaining types of fermented soyfoods generally requires several months to complete. Except for natto¯, which results from bacterial (Bacillus natto¯) fermentation, all others are fermented mainly by fungi: soy paste, soy sauce, and soy nuggets are all fermented by Aspergillus oryzae; tempeh by Rhizopus oligosporus; and sufu by Mucor sp., Actinomucor sp., and others. Almost all nonfermented soyfoods are consumed primarily for nourishment. In contrast, the majority of fermented

Whole soybeans Soaking Water

Rinsing Grinding

Soybean Utilization The soybean is the most versatile grain in terms of its end use. Broadly speaking, it can be used as human food, animal feed, and industrial materials. At the present, the majority of the annual soybean production is crushed, and its oil is solventextracted with hexane for edible use. The defatted soybean meal is generally toasted and serves as feed for various farm animals and fish. A very small proportion of annual soybean production is processed into many types of traditional and modern soyfoods. In addition, both the oil and protein meal have been explored for a broad range of industrial uses, including paints, plastics, and adhesives. Most notably, soybean oil has been used as a feedstock for producing biodiesel to replace petroleum-based transportation fuels.

Filtrating

Okara

Cooking Soymilk Coagulant

Coagulating Pressing (optional)

Whey

Tofu Figure 7 Outline of soy milk and tofu making. Adapted from Liu K (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman & Hall, Figure 4.2, with kind permission of Springer Science & Business Media.

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soyfoods contain salt and/or by-products (such as lactic acid) from a desirable fermentation. Both inhibit, delay, or slow down spoilage of these products and allow them to have a relatively long shelf lives. They are generally served as seasonings or condiments in cooking or making soups and contribute more in flavor than in nutrition to the diet. Tempeh and natto¯ are two exceptions, which have short shelf lives, are often consumed as a part of the main meal, and contribute protein and oil to the diet in addition to their characteristic flavor. In commercial processing, most traditional ways of making soyfoods are now modernized. For example, in making modern soy milk, several key steps are modified or added to reduce beany flavor, increase production yield, and improve overall product quality and consumer acceptance, even though the basic principle is very similar to the traditional Chinese method. The new steps include dehulling, blanching, fine milling, centrifuging, formulation, fortification, homogenization, thermal processing, and aseptic packaging.

Soybean Oil Nearly all soybeans are processed for their oil and defatted meal. With rare exceptions, crude soybean oil will have been refined, bleached, and deodorized to produce a high-quality RBD oil. About 85% of soybean oil is used for human consumption. The rest is sold for biodiesel production or industrial uses. Soybean oil is the leading edible oil and widely used in various food products. Among them are salad and cooking oil, shortening, margarine, mayonnaise, and salad dressing. Other applications include uses in canned foods, confectionery coatings, pudding mixes, pancake and waffle mixes, macaroni and cheese mixes, spaghetti sauces, dry breakfast cereals, frozenfried seafood, meat patties, pizza mixes, and others. Since soybean oil contains relatively high proportions of unsaturated linoleic and linolenic acids, it is susceptible to offflavor development. It also lacks some physical properties for certain applications, such as shortening and margarine. To increase oxidative stability and the melting point of soybean oil, hydrogenation was commonly used until a few years ago. The process chemically adds two hydrogen atoms to a double bond of an unsaturated fatty acid in the oil. As a result, lower unsaturated fatty acids are converted to saturated acids and higher unsaturated fatty acid to lower unsaturated acids in the oil. However, hydrogenation causes the formation of trans-fatty acids. In recent years, the adverse health effects of trans fat has been well established, causing US regulatory agencies to call for reducing or even totally eliminating trans fat from foods commercially prepared for human consumption. This has created a great challenge for the food industry to find alternatives for meeting different application needs. One effective way to solve the trans fat issue, while keeping the stability and functional properties of soybean oil required for many edible applications, is through plant breeding and genetic engineering. Already, several genotypes possessing large variation in fatty acid composition have been successfully developed or released as commercial varieties with yields comparative to other soybean varieties in the United States. Among them are soybeans with linolenic acid as low as 3%, stearic as high as 20%, and oleic as high as 80%. Oils from these lines are

targeted for specific applications for their functional advantages over common soybean oil. Such effort will provide benefits to food and industrial users and could increase the value of soybeans as an oilseed.

Soybean Protein Products The largest nutritionally valuable component present in soybeans is protein. Unlike soybean oil, which is used mainly for human consumption, soybean protein is used largely as feedstuff. Only a small portion is for direct human consumption as either traditional soyfoods or protein ingredients. Therefore, soybean protein has been severely underutilized in terms of human consumption. Soybean protein products are mostly made from defatted soy flakes, the main coproduct of modern soybean processing. They are not consumed directly as food, but as versatile ingredients used in virtually every type of food system, including bakery, dairy, meat, breakfast cereal, beverages, infant formulas, and dairy and meat analogs. In these food systems, they not only boost protein content but also provide many functional properties, including gelling, emulsifying, water-holding, and fat-absorbing properties. There are four major types of soybean protein products: flour, concentrates, isolates, and textured soybean protein. Soy flour is one of the least-processed soybean protein products. Many types are available in the market, including defatted, full-fat, and low-fat, as well as enzyme-active, toasted, and textured. Defatted soy flour has been the most common type. It is produced by simply grinding defatted soy flakes after modern soybean processing, containing about 50% protein. Full-fat soy flour is made by grinding dehulled whole soybeans. Low-fat soy flour can be made by extruding–expelling soybeans, followed by milling the cake. In general, soy flour is primarily used as an ingredient in the bakery industry. Soybean protein concentrate is traditionally made by aqueous alcohol extraction of defatted soy flakes. The resulting product has about 70% protein with the remaining portion being mainly insoluble carbohydrates. The product may be further processed by thermal processing and homogenization for better functionality. Soybean protein concentrate is widely used in the meat industry to bind water and emulsify fat and as a key ingredient for many meat alternatives. It is also used for protein fortification of various types of food. Soybean protein isolate is produced by alkaline extraction followed by precipitation at an acid pH. The process removes both soluble and insoluble carbohydrates. The resulting product has a protein content of 90% and is light in color and bland in flavor. It has many functional properties, including gelation and emulsification. As the most refined soybean protein product, soybean protein isolate is used in processed meat, meat analogs, soup and sauce bases, nutritional beverages, infant formulas, and dairy replacement. Textured soybean proteins are made by a process that imparts a structure, such as fiber, to a proteinaceous material. The process is known as protein texturization. It is a unique way to make vegetable proteins palatable. Among several processes, thermoplastic extrusion has been the most popular one for soybean protein texturization. In a typical thermoplastic extrusion process, dry proteinaceous materials, predominantly

THE OILSEEDS | Soybean: Overview defatted soy flour or soybean protein concentrate, are mixed with water, salts, flavorings, and/or colorants and then fed into an extruder. Under high temperature and low moisture (<30%) conditions, the extrudate expands rapidly upon emerging from the die. The final product, having porous texture, comes in a variety of shapes, sizes, and colors. Its use ranges from meat extenders to meat analogs. It must be rehydrated with water before use.

Western Soyfoods Traditional soyfoods, along with soybeans, were officially introduced to the West during the nineteenth and twentieth centuries. Since then, some of them, such as soy sauce, have been accepted by Westerners, whereas many others have been modified to suite local food culture and tastes. Furthermore, many new soyfoods have been developed. The modified and new soyfoods are known collectively as second-generation or modern soyfoods. They can also be called Western or Westernized soyfoods, simply because they were developed in the West and may look or taste like Western foods (Figure 8). Examples include soy ice cream, soy yogurts, soy cheese, soy butter, soy puddings, tofu spreads, soy burgers, meatless meatballs, imitation bacon bits, and imitation chicken strips.

Soybean as Animal Feed The majority of soybeans are used as animal feed mainly in the form of soybean meal, which is the coproduct of modern soybean processing. On a historical note, soybean meal has been an accepted part of livestock and poultry diets in the United States since the mid-1930s. Soybean feed production expanded rapidly in the mid-1970s and further accelerated in the early 1990s due to a growing demand for animal feed from developing countries. Prohibiting the use of slaughterhouse by-products in animal feeds and expanding aquaculture industry have also fueled the demand for this high-quality protein source. Soybean meal is characterized by high protein content, low crude fiber, and high palatability. It contains high amounts of lysine, tryptophan, threonine, and isoleucine that are often lacking in cereal grains. Because of these features, soybean meal is the most important protein source used to feed

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livestock, representing two-thirds of the total world output of protein feedstuffs, which include all other major oilseed meals and fish meal. Over half of soybean meal processed for livestock feed is fed to poultry, about one-quarter is fed to swine, and the rest is used for beef cattle, dairy cattle, and pet food. Soybean protein is increasingly found in fish food, for both home aquariums and commercial aquaculture. Furthermore, limited availability and increasing cost of fish meal have led to the use of soybean meal as a dietary protein source for a variety of cultured marine species as well.

Soybean as Industrial Materials: The New Use While the soybean has been traditionally used as food for human consumption and is primarily used as animal feed at present, its versatility and chemical composition make it an attractive material for industrial uses as well. In recent years, the desire for biodegradable and less toxic polymers from renewable resources instead of fossil-based chemicals has been intensified. This has stimulated research on using soybean as an industrial material. About 15% of soybean oil is now used as feedstock for biodiesel, emulsifiers, lubricants, plasticizers, surfactants, plastics, solvents, resins, and more. Soybean and other vegetable oils have desirable environmental qualities, such as being inherently biodegradable and renewable, having low ecotoxicity and low toxicity toward humans, and contributing no volatile organic chemicals. For example, soy-based engine oil emits fewer harmful emissions than petrochemical-based oil for increased worker safety. Soy ink is superior to petroleum-based inks, because it is not toxic, renewable, and environmentally friendly. When soybean oil is converted into fatty acid methyl ester through transesterification with methanol, the product is biodiesel. Soy biodiesel is nontoxic, renewable, and environmentally friendly. Soybean protein products, particularly defatted soybean meal, also have industrial applications, mostly as adhesives and paper coatings. These applications are essentially based on such functional properties of soybean protein products, including adhesive strength, texture modification, film forming, heat resistance, water retention, emulsification, and protective colloid properties. For example, biocomposites are building materials made from recycled newspaper and soy flour. They replace other products traditionally made from wood, such as furniture, flooring, and countertops. Particleboard, laminated plywood, and finger-jointed lumber are made with soy-based wood adhesives. Soy-based foams are currently being developed for use in coolers, refrigerators, automotive interiors, and even footwear. Soybean products are also found in many popular brands of home and commercial carpet and in auto upholstery applications.

Conclusion and Outlook

Figure 8 Imitation chicken strips made with soybean and other vegetable proteins. Courtesy of Beyond Meat (www.beyondmeat.com).

Soybeans have a unique composition and an array of old and new uses. The past four decades have provided many breakthroughs in soybean production, processing, and end use. As research progresses and technology advances on many fronts, soybeans are poised to become the most important source of

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protein for humans and animals and an important renewable source of industrial materials in the twenty-first century.


• • • • • • • •

Why is soybean considered an oilseed? What differentiates it from other oilseeds? What features make soybean a legume? Why has soybean become a top cash crop in the world since the middle of the last century? If the typical soybean oil is healthy, why do we need to modify it through processing and/or genetic manipulation? Why are the majority of traditional soyfoods not favored in the West, and why do soyfoods have to be Westernized or localized? Why is soybean prized for its use as animal feed at the present time? Do you think that genetically engineered soybeans are the future for improving soybean production and quality? Which type of soybean uses do you think will increase in the future: food, feed, or industrial material?


• •

•

Currently, the food industry is making an effort to ban or eliminate trans fats from food. What are the best solutions for the soybean industry to meet this challenge? Soyfood consumption in the West has been increasing significantly for the past 2–3 decades. However, compared with other foods, the room for growth is still huge. What efforts need to be undertaken to further increase soyfood consumption? Industrial use of soybeans has been considered new. What research needs to be carried out to further increase this type of use?

See also: Agronomy of Grain Growing: Soybean: Agronomy; Breeding of Grains: Soybean: Germplasm, Breeding, and Genetics;

Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Food Grains and Well-being: Nutrition: Soy-Based Foods; Grain Marketing and Grading: Soybean: Grading and Marketing; Grains Around the World: Grain Production and Consumption: Oilseeds in North America;Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara; Oilseed and Legume Processing: Soybean: Processing; Soybean: Soy Concentrates and Isolates; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Basics: Taxonomic Classification of Grain Species; The Grain Chain: The Route from Genes to Grain-Based Products; The Grains that Feed the World; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview; The Oilseeds: Oilseeds: Overview; The Basics: The Grain Crops: An Overview.

Further Reading Anderson JW, Johnstone BM, and Cook-Newell ML (1995) Meta-analysis of the effects of soy protein intake on serum lipids. New England Journal of Medicine 333: 276. Campbell KA, Glatz CE, Johnson LA, et al. (2011) Advances in aqueous extraction processing of soybeans. Journal of the American Oil Chemists’ Society 88: 449–465. Chen KI, Erh MH, Su NW, Liu WH, Chou CC, and Cheng KC (2012) Soyfoods and soybean products: From traditional use to modern applications. Applied Microbiology and Biotechnology 96: 9–22. Erickson DR (ed.) (1995) Practical Handbook of Soybean Processing and Utilization. Champaign, IL: AOCS Press. Isanga J and Zhang GN (2008) Soybean bioactive components and their implications to health – A review. Food Reviews International 24: 252–276. Johnson LA, White PJ, and Galloway R (eds.) (2008) Soybeans Chemistry, Production, Processing and Utilization. Champaign, IL: AOCS Press. Liu K (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman & Hall. Liu K (ed.) (2005) Soybeans as Functional Foods and Ingredients. Champaign, IL: AOCS Press. Messina M and Lane B (2007) Soy protein, soybean isoflavones and coronary heart disease risk: Where do we stand? Future Lipidology 2: 55–74. Sikora S, Blazinkov M, Babic K, Sudaric A, and Redzepovic S (2008) Symbiotic nitrogen fixation and sustainable soybean production. Cereal Research Communications 36: 1483–1486. Stupar RM and Specht JE (2013) Insights from the soybean (Glycine max and Glycine soja) genome: Past, present, and future. Advances in Agronomy 118: 177–204. Wang X, Cai X, and Zhang J, et al. (eds.) (1997) Zhong Guo Da Dou Zhi Ping (Chinese Soybean Food Products) (in Chinese). Beijing: China Light Industry Publisher.

Canola: Overview VJ Barthet, Canadian Grain Commission, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Development of rapeseed into Canola Canola production in Canada since 1943 Canola, countries exporting and importing low-erucic-acid (LEA) rapeseed Canola major compound contents – oil, protein, and glucosinolate Main fatty acid present in Canola and LEA rapeseeds Canola processing and health effects

Learning Objective

•

In the following article, the reader will learn about canola, its production, composition, and processing.

Introduction Canola is a Canadian crop and the name canola is a trademark; it came from the contraction of ‘Canada’ and ‘ola’ for oil. Canola plants belong to the Brassicaceae (Cruciferae) family that comprises about 350 genera and 3000 species including Brassica rapa (syn. B. campestris subsp. oleifera (turnip rape)), B. napus (rutabagas), B. oleracea (cabbage and cauliflower), and B. juncea (mustard). B. campestris originated in the foothills of the Himalayan mountains; B. napus most likely originated in the Mediterranean region and was the result of natural crosses between B. campestris and B. oleracea plants.

Development of Low-Glucosinolate Low-Erucic-Acid Rapeseed Rapeseed culture was introduced in western Canada during World War II (WWII). The seeds were crushed and the oil was used principally as a lubricant. At the time, two types of rapeseeds were grown: B. napus, also called Argentine canola, and B. campestris (rapa), referred to as Polish seed. To make lubricants, the iodine value of the oil should be in the 103–105 range; it was found that B. napus was ideal, with an iodine value close to 105, whereas Polish seeds (B. campestris) were not as suitable since the iodine value of the oil was close to 115. A breeding program was begun to develop rapeseed varieties with improved agronomy such as uniformity and lodging and an increased oil content while lowering the iodine value of the oil. Later on, rapeseed almost disappeared from the prairies because the oil demands changed and other oilseed crops were available. However, rapeseed had shown that its culture was quite favorable for western Canada since it needed fewer heat units to grow than the other oilseeds (soybean or


sunflower). Oil uses became easier since work on rapeseed oil processing, refining, bleaching, and deodorizing showed that rapeseed oil could be used as an edible oil, as soybean oil was. This led to the use of rapeseed oil as an edible oil in Canada. However, work done in the early 1950’s by Caroll on rats showed that rapeseed oil, and erucic acid in particular, had a negative effect on the heath of the rats. This led, in 1956, the Food and Drug Directorate of the Department of National Health and Welfare (now Health Canada) to prohibit rapeseed oil in human food. Even though this directive was canceled within months, it gave a very strong push to the Canadian rapeseed breeding programs to develop a low-erucic-acid (LEA) rapeseed. These breeding programs were located in the prairies, Winnipeg with Dr. Stefansson (University of Manitoba) and Saskatoon with Dr. Downey (Dominion Forage Crop Laboratory, now Agriculture and Agri-Food Canada). In 1958, a first variety trial was conducted with six varieties (Argentine, Arlo, Golden, Gute, Polish, and Regina II) of rapeseed (B. napus and B. campestris) grown in 22 locations throughout the western provinces. This led in 1961 to the first paper showing an effect of variety and environment on the fatty acid composition of the oil for all fatty acids except linolenic acid. The paper also showed an inverse relationship between oleic acid content and erucic acid content for both B. napus and B. campestris. The author concluded by saying “singles plant selection and crosses should yield valuable information of individual fatty acid and the development of gas liquid chromatography (GC) makes it possible to do such studies.” Truly, the development of LEA rapeseed became linked to the development of GC, since precise and short-time analysis was a requirement to analyze accurately a large number of samples. To look for LEA rapeseed (and high), single-plant analyses of Liho (a variety of B. napus from Germany), known for its LEA content compared to other varieties, were conducted and large variations in erucic acid content were observed (6–50%). This led to the first LEA rapeseed plants; progeny of selected LEA plants, grown in both Winnipeg and Saskatoon, gave plants with seeds containing 0% erucic acid in their oil in both locations. In 1963, Downey and Harvey developed a technique where only half of the seed was analyzed for the fatty acid composition while the other half, formed by half of the cotyledon attached to the radicle, was germinated and planted. This innovative technique allowed growing plants with a better knowledge and control of the oil composition. Subsequent work showed that the fatty acid composition was controlled by the genotype of the developing seeds and not by the maternal plant, and several genes were involved and their actions were additive. Later on, it was shown that five genes (e, Ea, Eb, Ec, and Ed) controlled the level of erucic in B. napus in an additive manner. Work was also conducted with B. campestris (rapa) to get LEA B. campestris varieties. In 1964, Downey reported on the selection of inbred seed from a Polish LEA variety of

http://dx.doi.org/10.1016/B978-0-12-394437-5.00029-2

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THE OILSEEDS | Canola: Overview

B. campestris having no erucic acid in its oil. Then, Dorrel and Downey showed that fatty acid composition (erucic acid content) of B. campestris was as in B. napus, controlled by the genotype of the developing seed; however, they could not confirm their hypothesis that a single gene controls the erucic level. Instead, they showed that the fatty acid composition was affected by the stage of the seed development. Simultaneously, work was started to reduce the glucosinolate content of the seeds since several studies had shown that glucosinolates had a negative effect on animal health. All these nutritional studies were summarized in 1965 by Bowland et al. in a report. In 1959, the first Canadian report showing significant variations of isothiocyanate contents between varieties but not locations was published. Important differences were reported between Argentine-type (B. napus L.) rapeseed and Polish-type (B. campestris (rapa) L.) rapeseed. In 1970, Kondra and Downey reported that, opposite to erucic acid, gluconapin, glucobrassicanapin, and progoitrin (the main glucosinolates) contents were determined by the genotype of the maternal plant. The work was done using Bronowski, a variety from Poland containing low levels of the three glucosinolates, and Target, a Canadian variety with high levels of glucosinolates. Work was also done in Europe with winter rape to develop low-glucosinolate rapeseeds also using the Bronowski variety. This led in 1974 to the registration of Tower, the first summer rape (B. napus) with LEA content in the oil and lowglucosinolate content of the meal. In 1977, the first B. campestris low in erucic acid and in total glucosinolates, called Candle, was registered in Canada by the Agriculture and Agri-Food Canada Saskatoon Research Centre. In 1978, the Rapeseed Association of Canada decided to name this new crop (low-glucosinolate LEA or double-low rapeseed) canola, a name made from the condensation of ‘can’ from Canada to represent the Canadian origin of the new crop and ‘ola’ to follow some famous brand name examples (cola, Mazola, etc.). Canola is now defined as a rapeseed that produces an oil that must contain less than 2% erucic acid, and the solid component of the seed must contain less than 30 mmol of any one or any mixture of 3-butenyl glucosinolate, 4-pentenyl glucosinolate, 2-hydroxy-3-butenyl glucosinolate, and 2-hydroxy-4-pentenyl glucosinolate per gram of air-dry, oil-free solid (http://www.canolacouncil.org/oil-and-meal/ what-is-canola/). Canola varieties can belong to any of the following three species: B. napus L., B. rapa (campestris) L. (with the three subspecies B. rapa subsp. oleifera, B. rapa subsp. trilocularis, and B. rapa subsp. dichotoma), and B. juncea L. Czern. However, in Canada, most canola varieties grown belong to the B. napus L. species. In Europe, canola is referred as low-glucosinolate LEA rapeseed. The work to produce LEA varieties showed how high-erucicacid rapeseed (HEAR) varieties could also be produced. This led to the development of rapeseed with very high levels of erucic acid so the oil had applications in the lubricant industry and with very low levels of glucosinolates so the meal could be used by the feed industry. One of the first varieties with very high level of erucic acid and low glucosinolate in the meal was Hero – 50.2% erucic acid in the oil and 15 mmol g1 of total glucosinolate in the meal. Due to their high levels of erucic

acid, these varieties are not canola varieties; they are lowglucosinolate HEAR. An important breeding program to develop varieties with very high erucic acid and low glucosinolates is still present at the University of Manitoba. In order to increase variation and create new potential for breeding, ethyl methanesulfonate was tested on B. napus to promote mutations. As a result, in 1987, Stellar was registered. It was the first low-linolenic (3.3%), high-linoleic (28.9%) canola (0.1% erucic acid in the oil and 8 mmol g1 glucosinolate in the meal) variety registered in Canada.

Production Rapeseed has been an important source of edible vegetable oil in Asia for almost 4000 years, used as a lighting oil and edible oil in Europe since at least the middle ages. However, in Canada, rapeseed production started during WWII as a source of high-quality lubricant for marine engines. It was a very small production about 1000 metric tonnes in 1943 (Figure 1). The development of the first canola variety in 1974 led to an increase in production and a switch from rapeseed to canola. By 1977, almost 2 million tonnes of canola was produced in western Canada. Canola production increased steadily up to 1995; then, the introduction of the first herbicide-resistant varieties led to another jump in production (Figure 1). This was followed by the development of new varieties, mostly hybrid, with better agronomic traits allowing a rapid production increase since 2000. Starting in 2004, the demand in canola increased due to a sharp increase in the world biodiesel production. This demand was matched by an increase in production due to varieties with better yields. In 2013, western Canadian canola production reached 17.96 million tonnes (Figure 1). Canola is considered as the Cinderella crop in Canada, from a forgotten crop to a major cash crop for Canadian farmers. Today, almost all canola varieties grown in Canada are herbicide-tolerant. Three types are found, two were obtained by insertion of a gene and are GMO (Roundup

18,000 Production (metric tonnes × 1000)

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16,000 14,000 12,000 10,000 8000 6000 4000 2000 0 1940

1950

1960

1970

1980 Year

1990

2000

2010

Figure 1 Canadian production of rapeseed and canola in metric tonnes (1000) from 1943 to 2013.

THE OILSEEDS | Canola: Overview Ready® and LibertyLink®), and one was obtained by mutation and is a non-GMO (Clearfield®). The world canola and LEA rapeseed production is concentrated in the European Community, Canada, and Australia (Table 1). China and India are important rapeseed producers; however, most of the rapeseed crops grown in these countries are not low in erucic acid and low in glucosinolate (Table 3). Canola/LEA rapeseed trade data are presented in Table 2. The European Community, China, Japan, and Mexico are the main importing countries, whereas Canada, Australia, and Ukraine are the main, if not the only, exporting countries. Canada is the main canola exporter; since 2004, Canada has been responsible of 70% of the world total canola exports. The United States is the main canola customer for Canada, importing an equivalent of 5 million tonnes of seeds; however, less than 0.5 million tonnes of seeds is exported to the United States from Canada. Canadian canola export to the United States is in the form of oil, about 1.5 million tonnes of canola oil. There is also an important export in the form of canola meal – well over 2.5 million tonnes – mainly used by the US dairy industry.

seeded in August and harvested the next year from early July to August. Australia also grows canola, but opposite to Canada, Australian canola is a winter crop seeded at the end of summer–early autumn and harvested the following year end of spring–early summer.

Composition Canola is marketed for its oil. Therefore, canola quality can be defined by its oil content and the fatty acid composition of the oil. Canola meal (what is left of the seed after crushing) is used for animal feed so the glucosinolate content is also an important parameter in determining canola seed quality for feed. Table 3 presents the proximate analysis and the relative fatty acid composition of canola and rapeseed grown in various part of the world.

Processing and Uses Canola seeds (LEA rapeseed and rapeseed) are processed by crushing plant to produce oil and meal. When the seed is delivered to the crushing plant, they are stored in bins to be processed. Processing steps might depend on the crushing plan and the country. In Canada, the weather is usually dry and cold, so the first step of the processing is to pass the seed through a conditioner with heat and moisture allowing better flaking and to heat the seed, making the oil more fluid and

Growing Conditions Canola, in Canada, is a summer crop. It is seeded in spring (May) and harvested from August to October. In Europe and China, LEA rapeseed and rapeseed are winter crops; they are Table 1

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Top five canola/rapeseed producing countries and world production for the last 10 years (1000 tonnes) Country

Year

European Union

Canada

China

India

Australia

World total

2003–04 2004–05 2005–06 2006–07 2007–08 2008–09 2009–10 2010–11 2011–12 2012–13

11 214 15 458 15 564 16 112 18 397 19 062 21 633 20 300 18 954 19 300

6771 7673 9483 9000 9611 12 644 12 898 12 789 14 608 13 310

11 420 13 182 13 052 10 966 10 573 12 100 13 500 12 900 13 000 12 900

6800 6500 7000 5800 5450 6700 6400 7100 6200 6900

1703 1542 1419 573 1214 1844 1907 2359 3427 3898

39 464 46 144 48 589 45 155 48 560 57 971 60 905 59 891 60 840 61 626

Table 2

Rapeseed (canola) trade from 2004 to 2012 (1000 tonnes) Importing country

Exporting country

Year

European Community

China

Japan

Mexico

Pakistan

World total

Canada

Australia

Ukraine

World total

2004–05 2005–06 2006–07 2007–08 2008–09 2009–10 2010–11 2011–12

224 712 433 1388 2897 2284 2829 3485

362 713 954 855 3085 2059 1100 2487

2277 2333 2170 2210 2061 2287 2337 2391

1196 1259 1065 1317 1077 1403 1492 1653

672 820 806 535 596 940 811 932

5507 7521 7106 8648 11 584 11 146 10 484 13 071

3756 5846 5426 5916 7660 7315 7249 8680

927 827 230 508 1111 1172 1507 2486

160 357 755 1496 2157 1910 1116 1341

5507 7521 7106 8648 11 584 11 146 10 484 13 071

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Table 3 Oil, protein, and total glucosinolate content ranges (dry basis) and relative fatty acid composition of canola/LEA rapeseed and rapeseed grown in various parts of the world Canadaa (2004–13) Proximate composition (dry basis) Oil content (%) 48.4 Protein (%) 22.5 Meal protein 43.6 Glucosinolate (mmol g1) 12.2 Fatty acid composition (% in the oil) Oleic acid 61.8 Linoleic acid 19.1 a-Linolenic acid 9.9 Erucic acid 0.03

Australiab (2000–12)

Francec (2004–13)

Chinad (2000–10)

44.5–46.8 23.6–25.3 40.2–46.4 4.3–10.6

43.6c

39.7–42.6

38.8c 14.5

27.6–38.0

59.0–63.0 18.2–20.4 9.0–11.0 <0.1

62.9d 19.6d 9.3c 3.14–16.3

a

Canadian Grain Commission data. Australian Oilseeds Federation data. c Centre Technique Interprofessionnel des Oleágineux et du Chanvre data. d Li et al. (2011). b

easier to extract. The second step is flaking where the seeds are placed into big rollers in order to break the seed structure to allow an easier crush and facilitate the oil extraction. A cooking step follows to ease the oil extraction and to inactivate endogenous enzymes of the seeds. Canola contains low levels of glucosinolates; however, it is important to ensure that they are not hydrolyzed during the processing to guarantee good quality for the meal. The myrosinase responsible for the glucosinolate hydrolysis should be inactivated. Enzymes (lipases) able to degrade the triglycerides must also be inactivated to ensure no oil degradation occurs during the processing. Then, the seeds are submitted to a screw press (expeller press) that squeezes the oil out of the seeds. Not all oil is recovered at this step. A solvent extraction, usually with hexane, is performed on the expeller press cake. After solvent extraction, depending on the crushing plan, up to 99% of the oil could be recovered from the seeds. The last step of canola processing is a refining process during which undesirable substances are removed from the crude oil to give the yellowish oil found in supermarkets. Chlorophyll is present in canola seeds when the seeds are harvested before reaching full maturity. Canadian canola seeds usually contain higher levels of chlorophyll because the growing season is very short – May to September – compared to canola grown in Europe, Australia, or China, September to June. Chlorophyll is an undesirable substance in canola oil and has to be removed. Chlorophyll with its heme structure and the magnesium ion in the center is highly reactive and can oxidize unsaturated fatty acids in the oil. Canola oil contains about 20% linoleic acid (C18:2) and 10% a-linolenic acid (ALA) (C18:3); these fatty acids can oxidize 10 (linoleic acid) and 50 times (ALA) faster than oleic acid (C18:1). To protect the canola oil from oxidation and to allow further processing of the oil, chlorophylls have to be removed during refining. Refined canola oil can be further processed to give other food products such as margarines and shortenings or industrial products such as biodiesel. Canola meal, the leftover from the seed once the oil is removed, can also be further processed. It is then used by the feed industry as pellet or mash product. Canola meal is considered a premium ingredient in dairy diets where it has been

shown to increase milk production when compared to diets containing cottonseed or soybean. It is also used in poultry and swine feeds.

Food Uses and Health Effects Canola oil is considered a very healthy oil due to its fatty acid composition. It averages about 60% oleic acid (C18:1), 20% linoleic acid (C18:2), and 10% ALA (C18:3) (Table 1). This makes canola oil a good source of ALA with the ideal ratio (2:1) of omega-6 (o-6) to omega-3 (o-3). When compared to the other vegetable oils, it has the lowest amount of saturated fatty acid (7% or less) compared to sunflower (12%). Studies with diets containing canola oil suggested that canola could reduce blood cholesterol levels and reduce the risk of cardiovascular disease. Canola oil can be used by food manufactures to produce various kinds of salad dressing. It is also found at local food stores as a salad oil, which can also be used as cooking oil. Margarines with canola can also be found at food markets and used by processors for baking. In response to the mandatory labeling of trans-fatty acids in food products, canola varieties with high-stability oils (ALA < 3%) were grown. These new oils have higher levels of oleic acid (65–74% vs. 60%) and lower levels of ALA (1–3% vs. 10%) than the conventional canola oil. These high-stability oils are used by the food industry for frying, allowing the reduction/elimination of trans-fatty acids from fried foods (e.g., potato chips) making these products a healthier choice. In North America, some chip brands and other fried snacks are processed using high-stability canola oil.


• • • •

What are the three Brassica species that can be called canola? What are the major producing and importing countries for canola seeds? What is the main fatty acid in canola oil? What were the two compounds reduced from rapeseed to give canola?


• •

What is the ratio of omega-6/omega-3 for conventional canola? Why must chlorophyll be removed from canola crude oil?


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What are the advantages of modifying the fatty acid composition of canola seeds? Why can changes in weather patterns affect the quality parameters (chlorophyll, oil, and fatty acid composition) of Canadian canola seeds?

See also: Breeding of Grains: Canola/Rapeseed: Genetics and Breeding; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Grain Harvest, Storage and Transport: Canola: Harvest, Transport, and Storage; Grains Around the World: Grain Production and Consumption: Oilseeds in North America; Oilseed and Legume Processing: Canola: Processing; The Basics: The Grain Crops: An Overview.

Further Reading Abraham V and de Man JM (1986) Hydrogenation of canola oil as affected by chlorophyll. Journal of the American Oil Chemists Society 63(9): 1185–1188. Anand IJ and Downey RK (1981) A study of erucic acid alleles in digenomic rapeseeds (Brassica napus L.). Canadian Journal of Plant Science 61: 199–203. Aukema H and Campbell L (2011) Oil nutrition and utilization. In: Daun JK, Eskin NAM, and Hickling D (eds.) Canola, Chemistry, Production, Processing and Utilization, pp. 245–280. Urbana, IL: AOCS Press, Chapter 9. Bowland JP, Clandinin DR, and Wetter LR (1965) Oil and Meal from Canadian Rapeseed. Ottawa, Canada: Department of Agriculture, Publication # 1257. https:// archive.org/details/oilmealfromcanad00bell. Busch H and Ro¨bbelen G (1981) Neidriger glucosinolatgehalt als zuchtzeil fu˝ winterraps. Agew. Botanik 55: 361–371. Craig BM (1961) Varietal and environmental effects on rapeseed III. Fatty acid composition of 1958 varietal test. Canadian Journal of Plant Science 41: 204–210. Downey RK and Harvey BL (1963) Methods of breeding for oil quality in rape. Canadian Journal of Plant Science 43: 271–275. Fowler DB and Stefansson BR (1972) Effects of the mutagenic agent ethyl methanesulfonate on the M1 generation of rape (Brassica napus). Canadian Journal of Plant Science 52(1): 53–62. Fowler DB and Stefansson BR (1975) Ethyl methanesulfonate-induced mutations in rape (Brassica napus). Canadian Journal of Plant Science 55(3): 817–821. Harvey BL and Downey RK (1964) The inheritance of erucic acid content in rapeseed (Brassica napus). Canadian Journal of Plant Science 44: 104–111.

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Jahries G and Scha¨fer U (2011) Rapeseed (Brassica napus) oil and its benefits for human health. In: Preedy V, Watson R, and Patel V (eds.) Nuts and Seeds in Health and Disease Prevention, 1st ed., Chapter 114, pp. 967–974. ISBN 9780123756893. Krzymanski J and Downey RK (1969) Inheritance of fatty acid composition in winter forms of rapeseed Brassica napus. Canadian Journal of Plant Science 49: 313–319. Le MHA, Landero JL, Beltranena E, and Zijlstra RT (2014) The effect of feeding increasing inclusion of extruded Brassica juncea canola expeller on growth performance and nutrient digestibility in weaned pigs. Animal Feed Science and Technology 192: 73–80. http://dx.doi.org/10.1016/j.anifeedsci.2014.02.006. Li P, Ding X, and Zhou H (2011) Rapeseed quality improvement and monitoring plan in China from 2000 to 2010. In: Proceeding of the 13th International Rapeseed Congress, Prague, Czech Republic, 5–9 June 2011. Mag TK (1983) Canola oil processing in Canada. Journal of the American Oil Chemists Society 60(2): 380–384. Martineau R, Ouellet DR, and Lapierre H (2013) Feeding canola meal to dairy cows: A meta-analysis on lactational responses. Journal of Dairy Science 96(3): 1701–1714. Mulrooney CN, Schingoethe DJ, Kalscheur KF, and Hippen AR (2009) Canola meal replacing distillers grains with solubles for lactating dairy cows. Journal of Dairy Science 92(11): 5669–5676. Scarth R, McVetty PBE, Rimmer SR, and Stefansson BR (1988) Stellar low linolenichigh linoleic acid summer rape. Canadian Journal of Plant Science 68: 509–511. Scarth R, McVetty PBE, Rimmer SR, and Stefansson BR (1991) Hero summer rape. Canadian Journal of Plant Science 71: 865–866. Slominski BA, Simbaya J, Campbell LD, Rakow G, and Guenter W (1999) Nutritive value for broilers of meals derived from newly developed varieties of yellow-seeded canola. Animal Feed Science and Technology 78(3–4): 249–262. Stefansson BR and Hougen FW (1964) Selection of rape plants (Brassica napus) with seed oil practically free of erucic acid. Canadian Journal of Plant Science 44(4): 359–364. Stefansson BR, Hougen FW, and Downey RK (1961) Note on the isolation of rape plants with seed oil free from erucic acid. Canadian Journal of Plant Science 41(1): 218–219. Stefansson RR and Kondra ZP (1975) Tower summer rape. Canadian Journal of Plant Science 55: 343–344. Stricker H, Duchini F, Facchini M, and Mombelli G (2008) Canola oil decreases cholesterol and improves endothelial function in patients with peripheral arterial occlusive disease – A pilot study. Artery Research 2(2): 67–73. Tautorus CL and Low NH (1993) Chemical aspects of chlorophyll breakdown products and their relevance to canola oil stability. Journal of the American Oil Chemists Society 70(9): 843–847.

Relevant Websites http://www.australianoilseeds.com/oilseeds_industry/quality_of_australian_canola – Australian Oilseeds Federation. http://www.cetiom.fr/index.php?id¼15446 – Centre Technique Interprofessionnel des Oleágineux et du Chanvre. http://grainscanada.gc.ca/canola/hqcm-mqrc-eng.htm – Canadian Grain Commission. http://www5.statcan.gc.ca/cansim/a26?lang¼eng&retrLang¼eng&id¼0010010& paSer¼&pattern¼&stByVal¼1&p1¼1&p2¼31&tabMode¼dataTable&csid¼ – Statistics Canada.

Cottonseed: Overview E Hernandez, Texas A&M University, College Station, TX, USA ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp 343–348, ã 2004, Elsevier Ltd.

Topic Highlights

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Traditional varieties of cottonseed contain gossypol (0.6–2.0% in raw cottonseed kernels). Gossypol is a polyphenolic compound that is toxic to man and monogastric animals, presumably functioning as a natural insecticide for the plant. Gossypol is located in “glands”, appearing as black specks in the stems, leaves, and seed. The breeding of “glandless” cotton varieties (since the 1960s) means that cottonseed is available without gossypol. Meal and oil from glandless cottonseed are similar in composition to these products from the traditional glanded seeds. Glandless cottonseed offers the advantages for processing of reduced energy costs, elimination of prepress operations, and the absence of color in the resulting oil. Food products from glandless cottonseed include whole roasted seeds, flour, protein concentrates, and isolates. Glandless cottonseed is suitable to feed monogastric animals, not only due to the absence of gossypol but also because of higher available energy.

Learning Objectives

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Understand the important differences between glandless and the traditional glanded cotton varieties. Become familiar with the processing involved in producing the various products from cottonseed for food and feed uses.

Introduction Most varieties of cotton (Gossypium hirsutum L., G. aboreum L., G. barbadense L., or G. herbaceum L.) are grown mainly in warm climates around the world. Over 98.5 million tonnes (Mt) of cotton were produced worldwide in 2001–02 and over 33.6 Mt of cottonseed. Cotton is grown for its fiber (over 80% of its value) and the seed is used mostly for oil recovery and feed. Whole cottonseed can be fed to dairy cattle, and the meal resulting from oil extraction is fed primarily to ruminants and, in limited amounts, to poultry and swine. Traditional varieties of cottonseed contain gossypol, a yellow-green polyphenolic compound considered toxic to man and monogastric animals (Figure 1), reportedly affecting the heart, liver, and reproductive organs. It has been used in China as a male contraceptive but the practice was abandoned because of permanent side effects. Gossypol is dispersed in the plant as deposited structures or “glands,” which can be seen as black specks in the stems, leaves, and seed (Figure 2).

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The glands in the seed are ovoid structures containing 35–50% gossypol and are 0.025–0.178 mm in diameter. These gossypol glands are difficult to break by mechanical means, but heat generated in extraction of oil by pressing, binds gossypol to protein, turning it nontoxic. Switching to solvent extraction with hexane, where no appreciable heat is generated, increases the free gossypol content in the meal over ten times. Raw cottonseed kernels may contain 0.6–2.0% free gossypol. The Food and Drug Administration in the US (FDA) limits free gossypol in human food products and ingredients at 450 ppm, and the Protein Advisory Group of the United Nations Food and Agriculture Organization (FAO) and World Health Organization (WHO) has set maximum guidelines of 600 ppm for free gossypol and 12 000 ppm total gossypol. The feed industry in the US set limits for free gossypol levels in poultry diets at 100 ppm maximum for broilers and 40 ppm for laying hens. Removal by mechanical separation of the gossypol-containing glands has also been reported. Also addition of iron salts, such as ferrous sulfate, which bind the gossypol in feeds and render it biologically inactive, is practiced in some countries. Solvent extraction with hexane of cottonseed oil, commonly used commercially, removes only small amounts of gossypol with the oil. However, extraction with more polar solvents is effective in removing gossypol. Examples of polar solvents used include aqueous acetone, a mixture of acetone and hexane, and sequential extraction with hexane, aqueous acetone, and anhydrous acetone. Blends of methylene chloride and hexane-acetic acid have also been used. These solvents are not widely used commercially. Techniques have also been reported that mill cottonseed in the presence of hexane and then remove the intact, heavier gossypol glands by the liquid cyclone process. Also, an air classification process has been developed to separate intact gossypol glands from solvent-extracted ground flour.

Glandless Cottonseed Some of the first studies on the development of glandless cottonseed in the US were done in the early 1950s. These studies described that selection of plants from the “Hopi Moencopi” variety could result in almost complete elimination of pigment glands from leaves and bolls. When crossing Moencopi with upland cotton varieties (G. hirsutum), it was found that glandless seed appeared in later segregating generations. Production of glandless cotton was first conducted in Iguala, Mexico in 1960. Basically two genes, gl-2 and gl-3, in the plant are found to control the production of gossypol pigments in the seed. When present in the homozygous recessive condition (gl2gl2–gl3gl3),


http://dx.doi.org/10.1016/B978-0-12-394437-5.00025-5

THE OILSEEDS | Cottonseed: Overview

Figure 1 Gossypol.

Figure 2 Cross-section of glanded cottonseed (left) and glandless seed (right). (Data from Miravalle RJ (1972) J. Am. Oil Chem. Soc. 49: 24–26.)

all parts of the plant aboveground, including the seed, have no pigment glands. The presence of pigmented glands can be easily seen as black specks by cross-sectioning a seed (Figure 2). Recently, the value of the whole seed as cattle feed has increased making it less profitable to extract the oil and sell the meal. In some cases cottonseed is left at the gin in exchange for ginning and baling services. Sometimes glandless cottonseed is considered to produce fiber of lower yield and quality than traditional “glanded” varieties. Some studies have shown that the glandless factor in itself does not decrease fiber yield or quality as long as care is taken to prevent weed and insect infestation. Gossypol is regarded also to be a natural insecticide. Reports show that glandless cotton attracts more insects than glanded varieties. Entomology studies have shown that cotton bollworm (Heliothis zea Boddie), tobacco budworm (H. virescens F.), pink bollworm (Pectinophua gossyprella Saunders), and lygus insects prefer glandless cotton. It is generally recognized that glandless varieties require closer supervision to intercept and control insect infestations. Processing and utilization of glandless cottonseed was reported in the early 1960s in the US. Glandless cottonseed oil and meal were evaluated in poultry broiler and layer rations. Glandless cottonseed meal was found nearly as effective as soybean meal in achieving broiler gains and did not

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produce the green yolk discoloration in eggs commonly experienced with feeding glanded cottonseed meal. The first commercial glandless cotton variety was a stormproof, boll-type cotton. It was evaluated in farm-scale trials and made available for commercial planting in the late 1960s in the US. Commercial sale of glandless cottonseed began in the early 1970s, with FDA approval. In 1976, under title 21 (Food and Drugs) of the Code of Federal Regulations, sale of glandless cottonseed kernels and cottonseed flour as food additives was allowed. It included restrictions on gossypol (450 ppm). In 1978 the National Cottonseed Products Association (NCPA) in the US established grades of glandless cottonseed products: class A, to contain not more than 400 ppm of total gossypol; class AA, to contain not more than 100 ppm total gossypol; and class AAA, to contain not more than 10 ppm total gossypol. Glandless cottonseed kernels started to be sold for use as snack foods, in baked goods and in soft candy. Research and production of glandless cotton for food and feed is also reported in Europe, Africa, and Asia. Some US cotton varieties were adapted to African crops. Development and study of some Egyptian varieties of glandless cotton have also been reported. From studies done in the Ivory Coast, it has been suggested that glandless cottonseed cultivation and oil mill processing is more economically viable in that part of Africa. Conditions there may be better for glandless cotton considering that in larger industrialized countries other competitive oil seed proteins are more readily available. An additional advantage is that large, isolated land areas can be dedicated to this crop and less problems of cross-pollination would be encountered.

Processing and Products Other than gossypol content very few differences are found in glandless compared with glanded cottonseeds. Evaluations of eight varieties each of glanded and glandless cottonseed were reported (Table 1). Amino acid profiles were similar for glanded and glandless seed. The storage and processing characteristics of glandless and glanded cottonseed are also reported to be essentially identical with regard to development of free fatty acids, moisture levels, and refining losses in the crude oils. No major differences were encountered either in solvent extraction of glanded versus glandless cottonseed. Extraction rates of oil from glandless cottonseed flakes are about the same as from glanded flakes, using commercial hexane. It has also been suggested that glandless cottonseed can also be a source of a new type of lecithin. Cottonseed has the highest content of phospholipids after soybeans, present at about 2.2% in the oil, but due to gossypol presence it was not commercially viable. Currently, the major commercial source of lecithin is soybean oil. Composition of cottonseed phospholipids consists of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositiol (33%, 22%, and 37%, respectively) and is considered more oxidatively stable than soybean phospholipids due to lower content of unsaturated fatty acids. One of the main advantages of milling glandless cottonseed is that it simplifies direct solvent extraction. Current commercial practice of refining glanded cottonseed oil requires that the oil

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Table 1 Comparative analysis means of eight varieties each of glanded and glandless cottonseed and their productsa Product and assay Whole cottonseed Oil (%) Iodine no. Protein (N 6.25; %) Wt. 100 fumed kernels (g) No. fumed seed/100 ml % Kernels in lint-free seed Cottonseed kernels Oil (%) Protein (N 6.25; %) Crude fiber (%) Total phosphorus (%) Total sugars (%) Total gossypol (%) Wt. 100 kernels (g) No. kernels/100 ml Hexane-extracted flour (meal) Oil (%) Protein (N 6.25; %) Crude fiber (%) Ash (%) Total phosphorus (%) Total sugars (%) Total gossypol (%) Color, Hunter “L” values Dry Wet (5 water:1 flour) Crude oil Cyclopropenoid fatty acids (%) Fatty acids (%) Myristic Palmitic Stearic Oleic Linoleic Unknown Refined oil Refined oil color, red Bleached oil color, red

Glanded cottonseed

Glandless cottonseed

21.0 108.9 23.1 10.0 542 61.7

21.1 109.9 22.5 10.6 510 59.6

37.8 39.3 1.6 0.8 7.4 1.2 6.5 912

39.7 38.9 1.7 0.9 6.8 0.02 7.0 844

0.8 63.2 2.7 8.0 1.3 13.4 1.6

0.8 62.6 2.8 7.8 1.4 13.7 0.02

84.3 48.1

89.8 71.3

0.23

0.23

0.9 23.0 2.2 17.7 55.8 0.4

0.7 22.6 2.1 17.7 56.5 0.4

6.9 2.9

3.7 2.2

a

Dry weight basis. (Source: Lawhon JT, Cater CM, and Mattil KF (1977) Journal of the American Oil Chemists’ Society 54: 75.)

be refined in its miscella state (oil–hexane solution) right after extraction. This is necessary because if the solvent is removed from the oil prior to refining, the color fixes into the oil and is very difficult to remove in subsequent bleaching operations. This means the equipment in refining of miscella has to be explosion-proof, which is more expensive and more difficult to maintain. This is no longer the case with glandless seed processing, where binding of gossypol (by cooking and hard press or prepress) or miscella refining become unnecessary. The oil from glandless seed is in lighter colored oil and the meal has greater amounts of soluble protein. Protein solubility of processed glandless cottonseed flakes or press cake has been reported to be higher than that of glanded seed (89.6%) compared with 84.8% for extracted flakes, and 59.3% for press cake.

Advantages of processing glandless cottonseed over glanded seed include: 1. reduction in electrical energy used for flaking; 2. elimination of prepress operations with larger solvent extractors with lower maintenance costs, and reduction in processing energy; 3. since there is no color setting problem, crude cottonseed oil can be held longer in storage; 4. elimination of more dangerous miscella (oil-solvent solution) processing or on-site conventional refineries; 5. lower refining loss of glandless seed oil due to reduced use of alkali to eliminate color; 6. reduction of bleaching earth needs; and 7. marketing of a light-colored, gossypol-free oil. Some emulsification problems have been reported in refining desolventized crude due to higher concentration of lecithin. There are some drawbacks when switching to glandless crops; varying levels of gossypol can exist among individual seeds from the same plant. It is also difficult growing large acreages of glandless cottonseed, without cross-fertilization by windblown or insect-carried pollen of glanded varieties. In order to preserve the variety and seed lot purity in the production of glandless cottonseed products, it is important to monitor both, cross-fertilization from cotton plants in nearby fields and reversion to the glanded condition during successive plantings due to fertilization between heterozygous plants. Furthermore, segregated handling of glandless cottonseed in gins and oil mills can also be costlier. As a result large cottonseed processors may be hesitant to handle glandless cottonseed and dedicate separate processing facilities.

Foods Uses Several food uses of glandless cottonseed kernels have been reported as well as applications on the use of glandless cottonseed blended with other foods. Even though glanded cottonseed is not considered suitable for human consumption, there have been cases where cottonseed flour with bound gossypol has been used in nutrition intervention feeding products, such as Incaparina in South America. Food products from glandless cottonseed include whole roasted seeds, flour, protein concentrates, and isolates. From these products many foods were reported to be prepared. The technologies for the production of high-protein products have been well established and apply similarly to all vegetable proteins. Specific technologies were developed for the production of cottonseed protein products that were later applied for processing of other vegetable proteins like soybean. The preliminary steps in preparing glandless cottonseed products are similar to the process used with glanded cottonseed, i.e., ginned cottonseed is first cleaned to remove dirt and other impurities, conditioned, de-hulled, and separated to produce kernels. The kernels may be size-sorted and the larger particles roasted and color-sorted. The whole kernels are separated for roasting or conditioning. The smaller or broken kernels may then be further conditioned, flaked, and solventextracted for production of flours, concentrates, and isolates.

THE OILSEEDS | Cottonseed: Overview Whole glandless cottonseed kernels are prepared either for direct use as whole nut substitutes or for food ingredients. These are also used in the production of high-quality flours and food protein concentrates or isolates. The use of glandless cottonseed kernels for the production of nutlike products by means of various roasting methods has been reported, including dry roasting at several temperatures, roasting under vacuum followed by steam injection, pressure steaming followed by oven roasting, and deep fat frying in various oils (including corn, cottonseed, peanut, safflower, soybean, and sunflower oils). When the main product is to produce high-protein flours, less care needs to be taken to minimize breakage during de-hulling. Glandless cottonseed flour can be prepared by extracting dehulled glandless seed flakes with hexane. The extracted flakes are then desolventized and ground to a desired mesh size. In the production of cottonseed concentrates, the defatted flakes are reextracted with acidified water or ethanol to remove the soluble sugars and flavor compounds, and dried to produce protein concentrate. A spray dryer can also be used in preparing concentrates where the defatted flakes are ground prior to extraction. Concentrates have been prepared from flour by a dry air classification method and by acidic water extraction. Figure 3 shows a simplified diagram of the process to be used to generate protein concentrate from glandless cottonseed. Three major techniques have been reported for making glandless cottonseed isolates. These isolates can be conventional protein isolates, storage proteins (SP) (soluble at high and low pH), and nonstorage proteins (NSP) (soluble at near neutrality): 1. Ground flour is first extracted with dilute alkali (at pH 10) and the insoluble residue removed by continuous centrifuging or decanting. The clarified liquor is then precipitated at one pH (5.0). The resulting solids are concentrated by centrifugation and then dried to produce a mixture of storage protein and nonstorage protein. 2. In the “selective precipitation” procedure the protein is precipitated with alkali at a pH 10, the solids are then

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separated by centrifugation. The solids in the liquor are also precipitated at pH 7, and the storage protein curd removed by centrifugation and then dried. The liquor is further acidified to pH 4 to precipitate the NSP, also removed by centrifugation and then dried. The soluble matter remaining in the whey is then removed by either the selective extraction or selective precipitation method. A relatively pure storage protein fraction, containing over 90% protein (dry weight basis), can be prepared. 3. The “selective extraction” procedure consists basically of leaching the proteins soluble with water at neutral pH, where the solids are then centrifuged out. The liquor is then acidified to pH 4; this results in a precipitated protein curd. The curd is dried to produce an NSP isolate. The solids from the original water leaching are then solubilized in alkali at pH 10 and centrifuged to remove insolubles. The liquor is then precipitated at pH 7 and the resulting curd is concentrated and dried to produce an SP isolate. A patented process for the preparation of glandless cottonseed protein concentrate from solvent-extracted flour using industrial membranes has also been used. Defatted flour is sieved through an 80-mesh screen to break up any agglomerates and remove hull particles, and suspended in acidified water at pH 4.0–4.5. This solution is passed through an ultrafiltration membrane (100 000 MW cutoff) and the solids retained are either dried directly or neutralized before drying. The liquid fraction permeate may then be passed through a reverse osmosis membrane to concentrate the soluble solids and to recover water which may be reused in the process.

Feed Uses Glandless cottonseed has been reported to be suitable for monogastric animal feed not just for its lack of gossypol but also for higher available energy. The lower heat treatment required for glandless cottonseed during milling is reported to degrade less protein than the prepress method normally

Figure 3 Protein concentrate production from glandless cottonseed. (Data from Lusas EW and Jividen GM (1987) J. Am. Oil Chem. Soc. 64(6): 839–854.)

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used with glanded cottonseed. Commercial glanded cottonseed meal intended for poultry feeding usually receives considerable heat during processing to intentionally bind the gossypol. Also in order to increase the amount of glanded meal gossypol, addition of iron to the meal is used to inactivate gossypol. In the cases of glandless cotton meal, it would be expected that lower heat treatment needed for glandless cotton would have beneficial effects in the protein availability and quality of the meal. Some heat pretreatment of the meal is still recommended, however, before hexane extraction, to improve protein efficiency. Heating glandless cottonseed with 12% added water for 10 min at 82 C, followed by 105 C for 20 min before hexane extraction, was reported to appreciably increase broiler weight gains when compared with glanded cottonseed feed. It has also been shown that meal from glandless cottonseed had an equal protein availability to soybean meal in supporting chick growth. Feed trials with glanded cottonseed meal with swine, catfish, fish, and shrimp have also been described.


• •

• • •

What is the meaning of “Glandless” in relation to cottonseed? What is gossypol? ○ What natural advantage does gossypol offer to the cotton plant? ○ Where is gossypol located in the cotton plant? ○ What is the toxicity of gossypol to humans, to animals and to insects? Describe the ramifications of breeding glandless cotton for the cotton-production industry, for the cotton-oil industry and for the food and feed industries. Explain the relative advantages (and disadvantages) of glandless cotton (versus glanded cotton) to all parts of the cotton industry. List the food uses of cottonseed and compare these with the food uses of the soybean.


•

• • •

Find out about the differences between the three major species of cotton (Gossypium hirsutum L., G. aboreum L., G. barbadense L., G. herbaceum L.). What potential advantages might accrue from the transfer of genes from one of these to the more common cotton species? Consider the possibility of extracting gossypol from glanded cottonseed for use as an insecticide for growing glandless cotton. Research the uses and value of lecithin, and examine the possibility of producing lecithin from glandless cottonseed. Find out about genetically modified (GM) cotton, the nature of its consequent tolerance to insect attack, its suitability for producing cotton, oil and meal, and the possible public resistance to cotton as a genetically modified organism (“GMO”).

See also: Agronomy of Grain Growing: Soybean: Agronomy; Barley, Rice and Maize Processing: Oil from Rice and Maize; Fats: Healthy Fats and Oils; Lipid Chemistry; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Grains Around the World: Grain Production and Consumption: Oilseeds in North America; Non-food Products from Grains: Biodiesel; Cereal Grains as Animal Feed; Oilseed and Legume Processing: Soybean: Processing; Soybean: Soy Concentrates and Isolates; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Oilseeds: Oilseeds: Overview; Soybean: Overview.

Further Reading Berot S, Chenu M, Coutret J, and Gueguen J (1995) Cottonseed protein-rich products from glandless African varieties: 1. Pilot-plant scale production of protein concentrates, Sciences-des-Aliments 15(3): 203–215. Camire ME, King CC, and Bittner DR (1991) Characteristics of extruded mixtures of cornmeal and glandless cottonseed flour. Cereal Chemistry 68(4): 419–424. Cater CM (1968) Processing glandless cottonseed. Oil Mill Gazeteer 72(7): 8–15. Cherry JP, Gray MS, and Jones LA (1981) A review of lecithin chemistry and glandless cottonseed as a potential commercial source. Seed-oil content of glanded and glandless, cottons. Journal of the American Oil Chemists’ Society 58(10): 903–913. Glandless cotton: Its significance, status, and prospects: Proceedings of a conference, December 13–14, 1977, Dallas, Texas/sponsored by Agricultural Research Service, United States Department of Agriculture and National Cottonseed Products Association, Inc., Agricultural Research Service – Southern Region, US Dept. of Agriculture, 1978. Kohel RJ and Lee JA (1984) Genetic analysis of Egyptian glandless cotton. Crop Science 24(6): 1119–1121. Lawhon JT, Cater CM, and Mattil KF (1977) Journal of the American Oil Chemists’ Society 54: 75. La-Rue DC, Knabe DA, Izard RS, and Tanksley TD (1986) Glandless cottonseed kernels for starter, grower and finisher swine. Journal of Animal Science 64(4): 1051–1059. Lusas EW and Jividen GM (1987) Glandless cottonseed: A review of the first 25 years of processing and utilization research. Journal of the American Oil Chemists’ Society 64(6): 839–854. Miravalle RJ (1972) The plant geneticist’s contribution toward changing the lipid and amino acid composition of cottonseed. Journal of the American Oil Chemists’ Society 49: 24–26. Percival AE, Wendel JF, and Stewart JM (1999) Taxonomy and Germ plasm resources. In: Smith CW and Cothren JT (eds.) Cotton. New York: Wiley. Robinson EH, Rawles SD, Oldenburg PW, and Stickney RR (1984) Effects of feeding glandless or glanded cottonseed products and gossypol to Tilapia aurea. Aquaculture 38(2): 145–154. Ryan JR, Kratzer FH, Grau CR, and Vohra P (1986) Glandless cottonseed meal for laying and breeding hens and broiler chicks. Poultary Science 65(5): 949–955. Simmons RG and Golightly NH (1981) Cottonseed Cookery. College Station, TX: Food Protein R&D Center, Texas A&M University. Silva-Ramos LC and Kohel RJ (1987) Seed-oil content of glanded and glandless cottons. Journal of the American Oil Chemists’ Society 64(9): 1337–1340.

Relevant Website cottonseed.com http://www.cottonseed.com – National Cottonseed Products Association (NCPA) is a trade association for the cottonseed processing industry. Besides commercial information, it has further links to technical information on cottonseed products.

Sunflower: Overview GJ Seiler and TJ Gulya, USDA-ARS, Northern Crop Science Laboratory, Fargo, ND, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Sunflower history – origin and crop development Sunflower botany Sunflower production practices in North America Sunflower agronomic problems: insect, disease, and predators (birds) Sunflower processing and uses

Learning Objectives

• • •

To understand the basics of the origin of sunflower and its agronomy, production, processing, and uses To understand the diversity of sunflower types and where sunflower is produced To understand the variation in fatty acid composition and its significance in sunflower utilization

Overview Sunflower (Helianthus annuus) is grown as an oilseed crop worldwide in temperate and subtropical climates in 72 countries. Among oilseeds, sunflower generally ranks fifth behind soybean, rapeseed, cottonseed, and peanut, with an average annual world production of 32–44 million tonnes (Table 1). Unlike soybean, sunflower is primarily an oil crop, with high-protein meal being a by-product. Sunflower is grown on every continent, except Antarctica, with Ukraine being the largest producer, followed by the Russian Federation, Argentina, China, France, Romania, Bulgaria, Turkey, Hungary, and the United States in 2011–12 (Table 2). US production accounts for 3–5% of the world output. Nutritionally, sunflower oil is somewhat superior to other vegetable oils due to the greater proportion of the unsaturated fatty acids (oleic, linoleic, and linolenic) and lower saturated fatty acids (palmitic and stearic), especially in the recently developed midoleic content NuSun™ hybrids (Table 3). Sunflower oil contains zero trans fats, which have been implicated in elevated cholesterol levels and increased risk of coronary heart disease.

Midwest and as far as northern Mexico. The Native Americans also used sunflower hulls as a source of dye, leaves for herbal medicines, and pollen in religious ceremonies. Historical records indicate that the Spanish were the first to introduce sunflower to Europe in the early 1500s. Sunflower was initially grown as an ornamental plant. Early English and French explorers also introduced it to their respective countries. From Western Europe, sunflower spread along the trade routes to Egypt, Afghanistan, India, China, and Russia. By the early 1700s, sunflower seeds were eaten as a snack, and in 1716, the first patent for the use of sunflower oil (for industrial purposes) was filed in England. The most significant boost for sunflower as a crop, however, came from the Russian Orthodox Church. Lenten regulations prohibited the consumption of many oily foods, but since sunflower was not specifically listed, the seed and oil became a staple diet item in Russia. Efforts by Russian scientists led to significant crop improvements with oil contents soon exceeding 40%. While sunflower was grown throughout Western and Eastern Europe, Russia historically was the largest producer with in excess of 3 million hectares in the early twentieth century, compared to one-half million hectares for the rest of Europe. Russian immigrants are credited with introducing sunflower to North America. In fact, the open-pollinated variety ‘Russian Mammoth’ still sold by garden seed firms traces its lineage back to the same-named variety initially introduced in the 1880s. Early cultivation of sunflower in North America was primarily for livestock silage and seed for poultry. By the second half of the twentieth century, improved Russian varieties with oil levels of 45–55% were available. Increased US production of these high-oil sunflower varieties spurred interest by oil crushers, which led to expanded US production, especially in the Northern Great Plains (North Dakota and Minnesota). The discovery of cytoplasmic male sterility (CMS) by French scientists laid the foundation for the development of sunflower hybrids in the early 1970s. Hybrid sunflower, with higher yields and oil content, more uniformity, and disease resistance, in comparison with open-pollinated varieties, provided the last great impetus in establishing sunflower as a worldwide crop (Figure 1).

Botany History Sunflower was domesticated by Native Americans in the Eastern United States in about 3000 BC. They used the seeds directly as food and crudely extracted the oil. Native Americans had selected a tall, single-headed variety by the time European explorers reached North America in the sixteenth century. While sunflower was not the staple that the ‘three sisters’ (maize, beans, and squash) were, it nonetheless was cultivated by many tribes from eastern North America through the


Domesticated sunflower, Helianthus annuus L., is the same species as the wild, multiheaded common annual sunflower found throughout the contiguous United States, northern Mexico, and southern Canada (Figure 2). The genus Helianthus comprises 52 species within the tribe Heliantheae of the family Asteraceae. The only other Helianthus species grown commercially is the perennial H. tuberosus, commonly known as Jerusalem artichoke. There are 14 annual Helianthus species, all with 2n ¼ 34 chromosomes, and 38 perennial species, which may be diploid, tetraploid, or hexaploid. Many species

http://dx.doi.org/10.1016/B978-0-12-394437-5.00027-9

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THE OILSEEDS | Sunflower: Overview

Table 1

World production (million tonnes) of major oilseed crops over the last 5 years

Commodity

2007/08

2008/09

2009/10

2010/11

2011/12

Soybean Rapeseed Cottonseed Peanut Sunflower Palm kernel Coconut Total

260 61 39 36 32 12 6 446

264 61 44 39 34 13 6 461

239 61 48 38 41 14 6 447

268 63 46 39 36 14 6 472

287 70 44 39 44 15 6 505

Source: http://apps.fas.usda.gov/psdonline/circulars/oilseeds.pdf.

Table 2

World sunflower seed production (in 1000 tonnes) over the last 5 years

Country

2007/08

2008/09

2009/10

2010/11

2011/12

Ukraine Russian Federation Argentina China France Romania Bulgaria Turkey Hungary The United States Others Total

6526 7350 4650 1791 1598 1170 1300 992 1468 1552 7852 36 249

6364 6454 2483 1955 1716 1098 1317 1057 1265 1377 7793 32 878

6771 5345 2220 2298 1635 1263 1536 1320 970 1240 6891 31 489

8670 9697 3672 2313 1880 1789 1439 1335 1374 924 7620 40 713

8387 7993 3340 2369 1573 1398 1387 1370 1316 1263 7053 37 449

Source: http://faostat.fao.org/.

Table 3

Fatty acid composition of traditional, high oleic and NuSun™ sunflower oil in comparison with other vegetable oils

Crop

Sunflower, traditional Sunflower, high oleic Sunflower, NuSun™ Olive Rapeseed Soybean Corn

Unsaturated fatty acids

Saturated fatty acids Palmitic and stearic

Oleic

Linoleic

Linolenic

12.5 9 9 17 6 15 13

20 82 65 72 62 24 25

69 9 26 11 22 61 61

0.1 0.1 0.1 1 10 7 1

Source: http://www.sunflowernsa.com.

freely hybridize with each other in nature, giving rise to intermediate forms, which has led to confusion in taxonomy. While H. annuus is a geographically diverse species occupying a wide range of habitats, other Helianthus species are very habitatspecific and thus are endemic in a limited number of locations. For example, H. niveus ssp. tephrodes is only found in active sand dunes in southern California and in northern Sonora, Mexico. H. paradoxus is only found in saline, marshy sites in western Texas and New Mexico, and H. exilis is only found in serpentine sites in Northern California whose soils are nearly toxic to many nonadapted plants. Wild Helianthus species, both annual and perennial, have contributed many useful traits to domesticated sunflower, including disease resistance, drought and salt tolerance, herbicide resistance, CMS, and

improved oil quality. All annual species, except H. agrestis, can be crossed with cultivated H. annuus. There has been more success in crossing tetraploid and hexaploid perennial species with cultivated H. annuus than with the diploid perennial species.

Production Practices in North America Sunflower production in the United States is concentrated in the Northern Great Plains (North Dakota, South Dakota, and Minnesota) with a secondary production area in the Central Great Plains (western Kansas, Nebraska, and eastern Colorado) (Table 4), but there is some amount of sunflower grown in


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Table 4 Sunflower production (hectares planted) and yield by state in the United States over the last 3 years Production ( 1000 ha)

Yield (kg ha1)

US state

2010

2011

2012

2010

2011

2012

North Dakota South Dakota Kansas Minnesota Colorado Nebraska Texas Other Total

272 162 43 21 37 10 11 15 571

202 163 43 11 39 14 9 18 499

305 227 26 15 25 12 13 21 644

1702 2016 1769 1568 1478 1343 1007 1343 1750

1530 1863 1372 1395 1231 1574 998 1140 1566

1663 1451 1372 1941 876 1022 1242 1341 1516

Source: http://www.sunflowernsa.com/.

Figure 1 Sunflower field in bloom. Courtesy of Dr. Brady Vick (Retired), USDA-ARS Sunflower and Plant Biology Unit, Fargo, ND, USA.

Figure 2 Common annual sunflower, Helianthus annuus, the progenitor of cultivated sunflower, with multiple flowers on a branched stem. Courtesy of Dr. Brady Vick (retired), USDA-ARS Sunflower and Plant Biology Unit, Fargo, ND, USA.

each of the 48 contiguous states (especially for birdseed). Most of the production recommendations have come from research conducted in North Dakota, but as interest in sunflower increases in other areas, new research generated from other states addresses these different environments. Sunflower is traditionally planted between May 1 and the middle of June in the Northern Great Plains, with hybrid maturities of 100–120 days to fit the short, 120-day average frost-free growing season of this region. Longer maturing hybrids are used where short growing seasons are not a restriction. Similarly, there are early maturing hybrids that would be suitable for a double-crop situation. Double-crop sunflowers are typically planted in July, either following the failure of an initial crop or after harvest of a small grain crop. Yields of 2200–3500 kg ha1 are attainable under optimal, irrigated conditions, while the average dryland yield of sunflower in the United States ranges from 1516 to 1750 kg ha1. The phenology of sunflower hybrid maturation is depicted in Table 5.

Sunflower is typically planted when soil temperatures reach 10 C. Below 10 C, germination is very slow. Sunflower is generally planted in row widths of 50–75 cm to match the available equipment, although solid seeding (widths < 30 cm) is also practiced. Sunflower is planted from 4 to 7 cm deep at rates of 37–62 000 seeds ha1 for oilseed and 35–50 000 seeds ha1 for confection. Lower plant populations for confectionery sunflower produce larger-sized heads and a greater proportion of large seed, which is desirable. Conversely, high plant populations will result in smaller heads, which not only dry down faster but also have thinner stalks that are more prone to lodging. Sunflower has a root system characterized by both a deep taproot and an extensive fibrous root system, which makes it efficient at both water uptake and nutrient uptake. While its water requirements are similar to that of corn, sunflower’s greater efficiency can result in higher returns under moisture-limiting conditions. Sunflower responds well to nitrogen fertilization, with a general rule of 5 kg ha1 nitrogen required for 100 kg seed ha1. Thus, for a yield target of 2000 kg seed ha1, the soil nitrogen content plus added nitrogen would be 100 kg ha1. Early weed control is important in sunflower with several preplant, preemergence herbicides available for grass control and now postemergent ones for broadleaf weed control. Hybrids have been developed through conventional breeding with tolerance to both imidazolinone and sulfonylurea herbicides, allowing for postemergent applications. There are no glyphosate-resistant hybrids in any country, nor are there currently any other commercially available traits introduced into sunflower from other organisms beyond the genus Helianthus (i.e., sunflower is currently still a non-GMO crop). Sunflower in the Northern Great Plains typically flowers in August, about 60–70 days after planting. Four to five weeks post-pollination is required for seed maturation, at which point seed moisture is 30–40%. If the crop is killed by frost, seeds may be harvested without use of a chemical desiccant. Any conventional grain combine can be used to harvest sunflower, with a variety of attachments to facilitate harvesting of the sunflower heads. Chemical desiccants can be used to reduce seed moisture, minimizing losses due to birds, lodging, and severe disease attack of the heads. Seed moisture must be at 10% or less to retard fungal deterioration in storage, with 8% moisture preferable for long-term storage.

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Table 5

Sunflower growth stages and approximate time and growing degree days (GDD) to reach each stage

Sunflower growth stage

Description

GDD

Days to reach stage

VE V4 V8 V12 V16 V20 R1 R2 R3 R4 R5.1 R5.5 R6 R7 R8 R9

Emergence 4 True leaves 8 True leaves 12 True leaves 16 True leaves 20 True leaves Miniature terminal bud Bud <2 cm from last leaf Bud >2 cm from last leaf Bud open, ray flowers visible Early flower 50% flowered Flowering complete Back of head pale yellow Bracts green, head back yellow Bracts yellow, head back brown

93 194 303 383 429 484 511 695 774 829 859 902 989 1140 1228 1372

10 20 28 34 38 44 46 61 67 71 73 77 84 86 104 119

(GDD ¼ ((Max. temp. in C) (Min. temp. in C)/2) 10 C). Source: NDSU Extension Bulletin 25 (revised). Sunflower Production.

Pest Problems Cultivated sunflower has a number of pest problems, including diseases, insects, and birds. Since the genus Helianthus is indigenous to North America and coevolved with the pests, there are a great diversity of insects and pathogens adapted to sunflower, plus a natural reservoir of these pests on the wild progenitors. On other continents, the diversity of sunflower pests and pathogens is generally less, although international seed movement has dispersed most sunflower pathogens around the globe.

Diseases Sunflower is subject to a number of fungal, bacterial, and viral diseases, with fungi the most numerous and economically serious. Diseases causing the most losses worldwide are Sclerotinia head rot and stalk rot, Phomopsis stem canker, rust, and downy mildew. Some diseases are serious in only a few countries, such as Verticillium wilt in Argentina or white rust (Albugo) in South Africa. Most sunflower diseases are caused by pathogens specific to sunflower, such as Phomopsis helianthi, Alternaria helianthi, and Plasmopara halstedii. Some of the most serious diseases, however, are caused by pathogens with wide host ranges, such as Sclerotinia sclerotiorum that occurs on 137 different genera of plants. Disease organisms may be grouped based on plant parts affected. The only significant seedling disease is downy mildew (Plasmopara halstedii). Foliar diseases on sunflower include rust (Puccinia helianthi), blights caused by Alternaria (five species) and Septoria helianthi, powdery mildew (Erysiphe cichoracearum), bacterial blight (Pseudomonas syringae pv. helianthi), apical chlorosis (Pseudomonas syringae pv. tagetis), sunflower mosaic virus, and sunflower chlorotic mottle virus. The main stem diseases of sunflower are Sclerotinia stalk rot (S. sclerotiorum), stalk rots caused by S. minor and Sclerotium rolfsii, Phomopsis stem canker (P. helianthi), charcoal rot (Macrophomina phaseolina), and bacterial stalk rot (Erwinia carotovora). Head rots are probably the most devastating because of their direct impact upon seed yield.

The main head rot pathogens are Sclerotinia sclerotiorum, Rhizopus (three species), Botrytis cinerea, and Erwinia carotovora. Control of most diseases is accomplished primarily with resistant hybrids and, to a lesser extent, with cultural practices. Single dominant genes are used to confer resistance to rust, Verticillium wilt, and downy mildew. At least two dominant genes are required for resistance to Phomopsis stem canker, while resistance to Sclerotinia head rot and stalk rot is controlled polygenically, making it the most difficult disease to select for resistance. Very few diseases are managed with fungicides, primarily because of economics. Seed treatments for control of downy mildew had been very effective until the pathogen developed resistance to the fungicide metalaxyl. In some countries, foliar fungicides are used to manage Phomopsis disease and rust. The use of foliar fungicides is more practical with confection sunflower where the profit margin is greater than with oilseeds.

Insects In the United States, there is a wide variety of sunflowerspecific, native insects that preferentially feed on stems, leaves, roots, or seeds. Stem-feeding insects on sunflower include at least three different cutworms (Euxoa species and Feltia jaculifera), the sunflower stem weevil (Cylindrocopturus adspersus), the black sunflower stem weevil (Apion occidentale), the sunflower maggot (Strauzia longipennis), and the long-horned sunflower stem girdler (Dectes texanus). Root-feeding insects include the carrot beetle (Ligyrus gibbosus), the sunflower root weevil (Baris strenua), and occasionally wireworms. Leaf-feeding insects include grasshoppers (four Melanoplus species and Camnula pellucida), aphids (primarily Aphis helianthi and Masonaphis masoni), the painted lady caterpillar (Vanessa cardui), the sunflower beetle (Zygogramma exclamationis), and the palestriped flea beetle (Systena blanda). Seed- and head-feeding insects include the sunflower moth (Homoeosoma electellum), the sunflower midge (Contarinia schulzi), the red sunflower seed weevil (Smicronyx fulvus), the gray seed weevil (Smicronyx sordidus), the

THE OILSEEDS | Sunflower: Overview banded sunflower moth (Cochylis hospes), the sunflower head moth (Gymnocarena diffusa), the sunflower seed maggot (Neotephritis finalis), the sunflower headclipping weevil (Haplorhynchites aeneus), and the tarnished plant bug (Lygus lineolaris). In other continents, insects are generally considered minimal or infrequent problems, and when they occur, they are generally caused by omnivorous insects such as aphids, plant bugs (Lygus spp.), and other non-sunflower-specific insects. Management of sunflower insect pests usually concentrates on cultural and chemical strategies. To date, selection for effective insect resistance has been limited in cultivated sunflower.

Birds Sunflower is vulnerable to damage by birds due to its easy accessibility and high nutritional value of the seed. Ranging from tiny sparrows (Passeridae) to large parrots (Psittacidae), birds are a constant problem to sunflower on all continents. In commercial birdseed mixtures, sunflower is the preferred seed, so it is not surprising that the crop is beset by depredation by a wide variety of birds. In the United States, the migratory redwinged blackbird (Agelaius phoeniceus) causes the most damage. In Europe, many different sparrows (Passer species) and doves (Streptopelia spp.) are the major problems, while in South America, parakeets (Psittacidae) and doves (Columbidae) predominate. Seed losses due to bird feeding can easily exceed 10% in fields planted close to nesting areas, and losses of 100% are not unheard of. In the United States, yield loss due to birds is significant enough that many different management strategies have been investigated. There has been limited success in breeding for sunflower varieties that have physical barriers (long necks, tight bracts, and seed coloration) to bird feeding. Most research efforts have explored cultural methods, habitat management, and mechanical frightening devices (noise makers). Various registered avicides have been tested, but none have been successful in reducing bird depredation. However, one novel approach under investigation is a commercial product, which contains the FDA-approved grape flavor component, which ironically many birds find repellent.

Sunflower Oil, Processing, and Uses Sunflower is grown worldwide, primarily as an edible oil crop. Traditional sunflower oil (high linoleic) is used mainly as salad oil and frying oil, although it can be hydrogenated for use in margarines. In terms of world production, sunflower usually ranks fifth among oilseed crops behind soybean, rapeseed or canola, cottonseed, and peanut. The oil content of oilseed sunflower varies from 40% to 50% by weight. There are currently three categories of sunflower oil: traditional, NuSun™, and high oleic. Traditional sunflower oil is characterized by a high concentration of linoleic acid (70%) and a moderate amount of oleic acid (20%). Plant breeders, using conventional methods, have selected lines in which oleic acid is the major fatty acid component (65%), and this oil has been given the trade name of NuSun™. High oleic oil has an oleic acid content of 85–90%. Oleic acid, a monounsaturated fatty acid, is considered by health and dietary experts to be better

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nutritionally than polyunsaturated fatty acids, like linoleic acid, and far superior to saturated fatty acids. While oleic acid levels of 80–90% are attainable, the frying industry prefers an oleic acid content of 55–60%, primarily because of the taste associated with the remnant linoleic acid. High and mid-oleic sunflower oil also has a very high oxidative stability, almost 10 that of traditional sunflower oil, extending product shelf life and longevity of the frying oil. For a complete comparison of the fatty acid composition of various vegetable oils (see Table 3). Oil extraction from sunflower seed is a relatively straightforward process. Seed is first thoroughly dried, dehulled, and then flaked or rolled and heated to 85–90 C. The crushed seed is then subjected to one of three extraction methods: (1) a mechanical screw press, (2) extraction with an organic solvent, usually hexane, followed by distillation to remove the solvent, and (3) a combination of the screw press and solvent extraction. In the United States, the latter is the preferred method and generally recovers about 99% of the total seed oil. The crude oil is further processed to remove gums, waxes, free fatty acids, and odors. The refined oil is now suitable as a vegetable oil or can be hydrogenated and blended with soybean or canola oil for margarines. Sunflower oil can be used as an alternative or additive to diesel fuel to create biodiesel, a clean burning alternative fuel produced from a renewable resource. This could help farmers decrease their dependence upon petroleum fuels by substituting ‘farm-grown’ fuel. For diesel engine use, sunflower oil requires more extensive purification including removal of waxes and gums. Minor engine modifications, including improved fuel filters, are also necessary to burn any vegetable oil. Since the energy content of sunflower oil is less than that of diesel, fuel consumption would be greater and power output less. As the price of diesel increases and the world supply diminishes, the feasibility of vegetable oil use in diesel engines becomes more of a reality.

Sunflower By-products Sunflower Meal After sunflower seeds are crushed, the remaining meal is a highprotein product commonly used in livestock and poultry feeds. The meal contains 260–500 g kg1 protein, 120–350 g kg1 fiber (from remnant hulls), and 10–90 g kg1 fat. Sunflower meal is lower in lysine content and higher in methionine than soybean meal and thus is usually combined with soybean meal in livestock feeds. Feeding trials with both dairy and beef cattle have adequately demonstrated the utility of sunflower meal since the meal is more ruminally degradable than either soybean or canola meal.

Hulls Sunflower hulls comprise 21–30% of the total seed weight and are often a waste by-product. In oil extraction factories, the hulls are often burned as a source of heat, both for the plant and for the distillation process to remove the hexane solvent. Hulls, mixed with appropriate binders and glue, have also been molded into cylinders and sold as ersatz fireplace logs. Public

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buildings in the vicinity of processing plants have also used sunflower hulls for heating, with only minor modifications of their boilers. A red dye, suitable as an FDA-approved food colorant, can be extracted from the hulls of purple-seeded sunflower. With the trend away from the use of synthetic dyes, many foods high in anthocyanin content have been viewed as dye sources. The anthocyanin content of purple-hulled seed ranges from 6 to 16 g kg1 of hulls, which compares favorably with that of other sources (grape skins and beet pulp). Natural red dyes lack the chemical stability of synthetic dyes and thus may only be usable in certain applications. Pectin, used in jellies and as a general food thickener, can be extracted from sunflower heads. The pectin content, after seed removal, is from 150 to 250 g kg1, and thus, a hectare of sunflower could yield 200–350 kg pectin. Sunflower pectin is chemically a low-methoxyl pectin, as contrasted to highmethoxyl pectins in apples and citrus. Low-methoxyl pectins are used in making jellies low in sugar and thus would be used primarily in the diet food market. Sunflower butter, a relatively new product marketed as SunButter®, is a delicious and healthy alternative to peanut butter. Packed with nutrition, it is an excellent choice for people with peanut allergies. Made from specially roasted sunflower seeds, it is completely peanut-free, tree nut-free, and gluten-free. A single serving of SunButter® Natural Omega-3 provides 461 mg of omega-3, with 1/3 less saturated fat than peanut butter.

Confection Sunflower Sunflower hybrids grown for human consumption are termed confectionery sunflower. The seeds are generally roasted, salted, and eaten as a snack food, either ‘in-shell’ or dehulled to produce ‘nutmeats.’ The nutmeats are also used in breakfast cereals, ‘trail mixes,’ and baked goods. Sunflower kernels have been chocolate- or candy-coated as a snack. In shell, they have also been coated with various flavorings, such as bacon, barbeque, salt, and pepper to name a few. Confectionery sunflower comprises 18–22% of US total sunflower production, with the United States the largest producer in the world market, followed by Argentina. Confectionery sunflower is characterized by its larger seed size and by having white or gray stripes on a black or brown background, as compared to uniform black color of oilseed sunflower. Confectionery seed is graded on the basis of size. The largest seeds, referred to as ‘in-shell,’ are those passing over a 7.9 mm round-hole screen and generally make up 15–25% of the harvested seed. The medium-sized seed, destined for dehulling for use as nutmeats, comprises 30–50% of the crop and is that fraction recovered between a 7.9 and 7.1 mm round-hole screen. The smallest seeds, passing through the 7.1 mm round-hole screen, are used primarily as birdseed and comprise 15–20% of the crop. Confectionery sunflower is genetically unique from oilseed sunflower, primarily because seed size and hull coloration are more important than oil content. As a group, they are much more susceptible to diseases and insects. Since the profit to the grower

may be 25–100% greater than with oilseeds, extra management practices to control insects and diseases are more feasible.

Future Trends Sunflower production in the United States is in direct competition with soybean and rapeseed, which currently have the advantage of glyphosate resistance for weed management. Sunflower is also confronted by disease and insect problems that are lesser concerns in soybeans and rapeseed. The challenge to the sunflower industry is to make the crop as easy and profitable to grow as its competitors. The development of imidazolinone- and sulfonylurea-resistant hybrids gives growers new tools to control postemergent weeds, similar to the glyphosate resistance technology. Finding management schemes to control insects and diseases in sunflower is a continuing challenge. Worldwide, Sclerotinia and Phomopsis diseases are the two most devastating diseases. Both diseases can be managed to some degree with fungicides, but genetic resistance would be more economical and safer for the environment. The many native Helianthus species offer untapped resources for resistance genes for Sclerotinia and other diseases. Another option to make sunflower more competitive is to change its fatty acid composition to make the oil nutritionally better than other oils, the so-called designer-specialty oils. Moves in this direction include the NuSun™ hybrids, with oil nearly comparable to olive oil. The global sunflower market is trending toward high oleic (85–90%) oil, which has zero trans fats, low saturated fats, and high monounsaturated fatty acid with high oxidative stability. The transformation is already under way but will probably take 10 years to totally convert the industry. As the world public becomes more health-conscious and with the trend to increase label information, consumers are demanding to know what in a product makes it a healthy choice. Healthy sunflower oil will benefit from these demands and in turn generate more interest among growers. Commitments by large snack food processors and fast-food chain restaurants in the use of NuSun™ have been the first step in increasing domestic usage of sunflower oil.


• • • • • • • •

From which continent did the sunflower originate? Who introduced the sunflower to Europe? Which are the main sunflower-producing countries? Who were the first to increase sunflower oil content? How many days are needed for sunflower to reach maturity in North America? What are the various uses of sunflower? What are NuSun sunflowers? Which birds are the main problems in North and South Americas?


•

Propose novel technological or plant breeding solutions to the problem of bird damage in sunflower production.


• •

Compare the productivity of sunflower with that of other oilseed crops in a region of interest to you. What scope is there for further value-added development of specialty oils from sunflower?

Further Reading Berglund DR (2007) Sunflower Production. Fargo, ND: North Dakota State University Extension Service Bulletin 25 (revised), 119 pp. Fick GN (1989) Sunflower. In: Robbelen G, Downey RK, and Shri A (eds.) Oil Crops of the World. New York: McGraw-Hill, 553 pp. Heiser Jr. CB (1976) The Sunflower. Norman, OK: University Oklahoma Press, 198 pp. Heiser Jr. CB, Smith DM, Clevenger SB, and Martin Jr. WC (1969) The North American sunflowers (Helianthus). Memoirs of the Torrey Botanical Club 22(3): 1–218. Jan CC and Seiler GJ (2007) Sunflower. In: Singh RJ (ed.) Genetics Resources, Chromosome Engineering, and Crop Improvement. Oilseed Crops, vol. 4. New York: CRC Press, Taylor and Francis Group Chapter 5, 304 pp. Maiti RK, Singh VP, Purohit SS, and Vidyasagar P (eds.) (2007) Research Advances in Sunflower. Jodhpur, India: Agrobios International, 512 pp. Miller JF (1987) Sunflower. In: Fehr WR (ed.) Principles of Cultivar Development, vol. 2. New York: Macmillan Publication, 761 pp. Pappalardo J (2008) Sunflower, the Secret History. Woodstock, NY: The Overlook Press, 256 pp. Rogers CE, Thompson TE, and Seiler GJ (1982) Sunflower Species of the United States. Bismarck, ND: National Sunflower Association, 75 pp.

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Salunkhe DK, Chavan JK, Adsule RN, and Kadam SS (1992) Sunflower. In: World Oilseeds: Chemistry, Technology, and Utilization. New York: Van Nostrand Reinhold, 554 pp. Schneiter AA (1997) Sunflower Technology and Production. Madison WI: American Society of Agronomy Monograph #35. Seiler GJ (ed.) (1992) Sunflower: Special Issue. Field Crops Research 30(3–4): 191–448. Seiler GJ and Jan CC (2010) Basic sunflower information. In: Hu J, Seiler G, and Kole C (eds.) Genetics, Genomics, and Breeding of Sunflower, pp. 1–50. Enfield, NH: Science Publishers Chapter 1, 335 pp. Skoric D, Seiler GJ, Zhao L, Jan CC, Miller JF, and Charlet L (eds.) (2012) Sunflower Genetics and Breeding. Novi Sad, Serbia: Serbian Academy of Science and Arts, 520 pp. Weiss EA (ed.) (2000) Sunflower. In: Oilseed Crops, 364 pp. Malden, MA: Blackwell Science.

Relevant Websites www.ars.usda.gov/main/site_main.htm?modecode¼54-42-05-20 – U.S. Department of Agriculture – Agricultural Research Service, “Sunflower and Plant Biology Research Unit”. http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/eb25w-12.htm – North Dakota State University Extension Service, with individual bulletins on many aspects of sunflower production. www.isasunflower.org – International Sunflower Association. www.sunflowernsa.com – National Sunflower Association.

Overview of the Oilseed Safflower (Carthamus tinctorius L.) C Hall III, North Dakota State University, Fargo, ND, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

Carthamus is part of the Compositae or Asteraceae family. Carthamus tinctorius L. is the cultivated species of safflower. Flowers of safflower are used as a food colorant and clothing dye and in traditional Chinese medicine. The oil from safflower is 90% oleic and linoleic acids and is relatively stable to oxidation. Safflower contains high levels of flavonoids and tocopherols. Oil composition can be manipulated to create healthpromoting oils or biofuel feedstock. Safflower is an oilseed used in commercial bird foods. Defatted safflower meal can be used as a cattle feed.

Learning Objective

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To gain knowledge in the fundamental aspects of safflower production, composition, and uses.

Introduction The Food and Agriculture Organization considers safflower (Carthamus tinctorius L.) as a minor oilseed crop since only about 647 000 MT, on 783 000 Ha, is produced annually. Safflower can be produced on arid and semiarid land, including moderate salinity, and is therefore produced across the world where water is scarce or high salinity water is used for irrigation. Carthamus tinctorius L. is the cultivated species of safflower. The word tinctorius essentially means ‘for dyeing’ in English. The flowers of safflower have been used historically as a colorant in food and as dye in the clothing industry and as a traditional Chinese medicine. However, the primary purpose today is as an oilseed crop. The oil is typically used for cooking and frying, but interest as a feedstock for biodiesel is growing. Safflower oil composition varies widely, but 90% of the oil is made up of oleic and linoleic acids. However, the genes of Carthamus species can be easily manipulated to produce oils with unique fatty acids, which can then be used for specific purposes. In North America, much of the safflower is used as wild bird feed. This article provides the most recent information on safflower, and readers are encouraged to review materials found in the referenced materials, as sources for historical and early agronomic information.

Taxonomy, Morphology, and Agronomics A number of locations have been proposed as the center of origin for safflower. These include Central Asia and the Middle East. Weiss provided an excellent historical perspective of

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safflower, which dates to 2000 BC in Egypt. The height of safflower production occurred shortly after World War II and has since been replaced with other oilseed crops. Safflower production ranks eighth among oilseeds. The evolutionary history of safflower has been documented to approximately 1753. Although C. tinctorius L. is the only cultivated species, there were as many as 25 species linked to the genus Carthamus. However, clarification over the last two decades supports the presence of approximately 15 species in the genus Carthamus. Much of the confusion around this genus was due to limited morphological observation such as spiny leaves or cypselas. The advent of molecular biology allowed for the differentiation of Carthamus species. Carthamus species are grouped into sections based on chromosome pairs. Species with 12 chromosomal pairs include C. tinctorius, C. palaestinus, and C. oxyacantha, while other species contain 10, 11, 22, and 32 chromosomal pairs. C. tinctorius, C. persicus Desf. Ex Willd, C. palaestinus, and C. oxyacantha have 12 chromosomal pairs and can readily cross-pollinate. Only C. tinctorius is commercially produced, while the other three species are wild. However, these species can cross-pollinate resulting in altered seed characteristics. C. tinctorius also can cross with wild species having 10 and 22 chromosomal pairs but not 32. The crossing of C. tinctorius with weedy Carthamus species (e.g., C. lanatus) has been documented. However, the propensity for weediness in the resulting F1 hybrid was less than the parent wild species and no F2 hybrid (i.e., result of crossing of two F1 hybrids) was produced. A number of factors contribute to the growth characteristics of Carthamus species. However, much of the plant breeding efforts have focused on C. tinctorius L. Therefore, only this commercially relevant species will be presented in the remaining part of this article. Safflower is a thistle-like (Figure 1) plant with yellow, orange, red, or white flowers. Leaves of the mature plants are spiny in nature and thus compared to a thistle, while the seeds resemble a small sunflower (Figure 2). Germination of seeds occurs readily (i.e., 3–4 days) above 60 F, but growth slows during the rosette (i.e., a circular pattern of growth) stage that lasts up to 3 weeks. The development of a tap root, which can reach lengths of 305 cm, occurs during the rosette stage. This stage of growth is followed by a profuse branching stage of growth. Overall growth behavior is dictated by the plant population, where bush-type plants result from greater spacing, while closer spacing results in an upright plant form. Typical C. tinctorius L. plant heights range from 42 to 113 cm. However, plants can reach heights of 251 cm in Asia. The plant growth behavior also impacts seed yield. Bush-type plants yield greater numbers of flowers as each branch typically has five flowers with up to 50 flower heads per plant. Harvesting of seeds usually begins 30 days after maturing and seed moisture should not exceed 8% moisture. Much of the current breeding focus has been directed at improving oil composition.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00030-9

THE OILSEEDS | Overview of the Oilseed Safflower (Carthamus tinctorius L.)

Figure 1 Safflower (Carthamus tinctorius L.) in bloom. Photo courtesy of Dr. Hans Kandel, Extension Agronomist Broadleaf Crops, North Dakota State University.

Figure 2 Safflower (Carthamus tinctorius L.) seed.

Both cultivated safflower and wild species grow in temperate zones under arid and semiarid conditions. Safflower can be grown under diverse conditions, such as drought and salinity, due to the long taproot accessing deep soil moisture. Continued research in area further supports the resilience of this plant. Although safflower can grow under water-restricted environments, Kizil et al. reported that higher amounts of rain significantly increased a number of agronomic characteristics of safflower grown over a 2-year period.

Composition Protein, Fiber, Oil, and Fatty Acids Safflower is composed of approximately 33–45% hull and the remaining fraction being the kernel. Oil content is variable, ranging from 27% to 60% in thick- and thin-hulled cultivars, respectively. The oil is located primarily in the kernel, where

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greater than 95% of the oil is found. The kernel typically contains approximately 60% oil and 26% protein. However, the protein content of whole seed ranges from 14% to 23%. Fiber content ranges from approximately 11% in thin-hulled cultivars to as high as 34% in thick-walled cultivars. Most commercial safflower oil consists of 72–78% linoleic acid and represents cultivar and environmental effects on oil composition. Oleic acid is the second most common fatty acid and accounts for 15–20% of the fatty acids in safflower oil. Other fatty acids include palmitic and stearic at levels ranging from 1.5% to 6%. Only a small (<0.2%) amount of linolenic acid exists in safflower oil. Cultivar (i.e., genotype) is one of the drivers for the diverse oil content and oil fatty acid composition of safflower. Environment also contributes to alteration in oil content and composition. In recent years, modification of genes through molecular approaches has also been used to change oil and fatty acid contents. Crossing of different C. tinctorius genotypes produces plants with varying oil and fatty acid compositions. Oil contents of 25–33% for eight experimental safflower genotypes have been reported. Linoleic acid represents between 56% and 75% of the fatty acids in the oil. The genotype with the lowest linoleic acid content had both the highest oil content and oleic acid content (i.e., 35% of oil). Attempts to improve oil yields by crossing C. tinctorius genotypes with wild species have had little success, one reason being that the wild species have lower oil contents, that is, 32%, 25%, and 17% for C. tinctorius, C. oxyacantha, and C. lanatus, respectively, compared to greater than 40% for cultivated safflower. However, the two wild species did have slightly higher oleic acid contents compared to C. tinctorius. Recently, C. tinctorius L. cv. Centennial genotype was genetically altered using a cloned delta-6-desaturase gene from Saprolegnia diclina inserted into the safflower genome by Agrobacterium tumefaciens. This genome manipulation resulted in a safflower with approximately 67% gamma-linolenic acid (GLA), which is not normally present in safflower oil. The health benefit of GLA has been documented and is the primary reason for the development of high-GLA safflower. In contrast, by happenstance, a high-oleic acid safflower was identified in 1957 from seeds grown in India. The seed composition was 77–81% oleic acid and 10–15% linoleic, the opposite of traditional safflower. High-oleic acid safflower is available today due to commercial production of this cultivar. Although a few reports indicate that temperature can impact linoleic acid content in safflower oil, temperature during growing appears to have less influence on linoleic acid content of safflower compared to other oilseeds. Oleoyl phosphatidylcholine D12-desaturase is an enzyme that regulates linoleic acid conversion from oleic acid. Esteban et al. reported that this enzyme was more thermally stable and less oxygendependent in safflower compared to the same enzyme in sunflower. The high-(i.e., 72–78%)linoleic acid content observed in safflower grown under high temperatures is contrary to other oilseeds. Other agronomic practices have significant bearing on agronomic traits. Linoleic acid content was higher in mature seed from the parent seed having later planting dates, while all other agronomic traits such as oil content decreased. Several authors observed that early planting of safflower leads to higher oil

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content. Seed planting density is another agronomic practice used to enhance yield of many crops. However, safflower tends to branch when sown in wide seed spacing (i.e., less seed density) and thus compensates for the lower plant numbers by producing more seeds per plant compared to greater seed densities. As a result, oil yield per hectare and oil content per seed are not significantly different among plants grown from low- and high-density seeding rates. Harvesting of safflower usually begins 35–40 days after flowering. These harvesting dates also coincide with maximum oil content. Thus, harvesting date can influence oil yield. The maturity of seed also contributes to the final composition of the seeds. Over the course of 100 days, palmitic and oleic acids increased, while stearic acid decreased. In contrast, linoleic acid reached a maximum at day 75 and then decreased when measured at day 100. Safflower can grow on marginal cropland, including soils of moderate salinity. Under hydroponic conditions, 50 mM sodium chloride was found to inhibit safflower growth and increase the oxygenated essential oils. In general, 7% and 29% reductions in oil content and oil yield, respectively, in safflower subjected to saline stress have been reported. Also, oleic acid tended to increase under saline conditions, while linoleic decreased.

Nonsaponifiable Components Tocopherols, carotenoids, and phytosterols make up the nonsaponifiable lipid components of safflower oil. Traditional and high-oleic acid safflower oils are composed of approximately 250 mg tocopherol per gram of oil or 50–100 mg tocopherol per gram of seed. However, tocopherol contents as high as 684 and 941 mg g 1 of oil have been reported for traditional safflower and high-oleic acid safflower oil, respectively. Mean tocopherol concentrations from seven geographic regions in the range of 676–827 mg g 1 of oil have been reported. No differentiation of safflower oil type was provided, but the lowest and highest tocopherol contents were from East Africa and Southwest Asia geographic locations, respectively. In traditional safflower, a-tocopherol accounts for 93–98% of the total tocopherols, while b-, g-, and d-tocopherols account for the remaining in varying concentrations. a-Tocopherol accounted for 83–98% of the tocopherols in high-oleic acid safflower oil; however, no b analog was found. In addition to tocopherols, 5 and 12 mg of a- and g-tocotrienols per gram oil, respectively, were reported in cultivated safflower. In contrast to cultivated species, g-tocopherol contents as high as 36% were reported in oil obtained from wild safflower. A mutant safflower obtained through breeding contained a unique tocopherol profile where g-tocopherol accounted for 96% of the total tocopherols. Approximately 29% of the tocopherols are removed during refining, with the greatest removal occurring during the bleaching and deodorization steps of the process. Thus, adjustments to the aforementioned numbers should be considered when refining safflower oil. Roasting of the safflower at temperatures between 140 and 180 C did not negatively impact tocopherols or tocotrienols. The safflower carotenoids are present in trace amounts in the oil. Total carotenoid levels of less than 2.5 mg g 1 oil are

common. Lutein and zeaxanthin levels are approximately 0.8 and 1.5 mg g 1 oil, respectively, as determined by HPLC. However, photometric (445 nm) analysis indicated levels as high as 7 mg g 1 seed. The underestimations of carotenoids could occur for oils that contain predominantly carotenes. In the case of safflower, trans- and cis-b-carotene levels were only 0.14–0.16 mg ml 1 oil, while a-carotene accounted for less than 0.04 mg ml 1 oil. Therefore, the total carotenoid level close to 2.5 mg g 1 oil is realistic. Contrary to expectations, the yellow pigments in the flowers of safflower are not carotenoids. Although carotenoid levels as high as 650 mg g 1 dried flower petals have been reported, hydroxyl safflower yellow A, safflower yellow B, and anhydrosafflor yellow B are the predominant yellow pigments. These pigments are glycosylated flavonoids and thus have high water solubility in contrast to carotenoids. A significant variation in literature among total, free, and esterified sterol exists. The phytosterol content in safflowers is approximately 2000–4500 mg g 1 seed. The highest sterol content was obtained in seeds at 24 days after anthesis (i.e., flowering) and stabilized at 2400 mg g 1 seed at day 47 (i.e., end of maturity). Therefore, the variation in phytosterol data may be due to seed maturity. Phytosterol contents of 1520–5745 mg g 1 of oil have been reported. In general, the free (48%) sterol form accounts for the majority of the phytosterol content followed by esterified (39%) form. Steryl glycosides and acyl steryl glycosides collectively make up about 13% of the total sterols. Regardless of the sterol form, b-sitosterol accounts for the largest percentage (50–70%) of the phytosterols. Campesterol, D7-stigmastenol, D5avenasterol, and stigmasterol each make up 6–12% of the total phytosterol content. Reductions in total sterols due to maturity and refining have been documented; however, the percentage of each phytosterol remains relatively consistent, for example, b-sitosterol accounting for the greatest percentage.

Phenolic Components The majority of the phenolic compounds of safflower are located in the flower petals and meal component of the seed. The meals contain 3800–5700 mg g 1 of phenolic glycosides. Although humans find these compounds bitter, animals appear to be less impacted by the bitterness, and thus, safflower is often used as a protein source in animal rations. Total phenolic contents of water extracts were 40 and 126.0 mg gallic acid equivalence (GAE) per gram flowers and seed, respectively. In contrast, only 26 mg GAE per gram was observed in the oil. Flavonoid contents of safflower water extract obtained from the seed were 62.2 1.9 mg quercetin equivalence per gram, while an extract from dried flowers contained approximately 10 catechin equivalences per gram extract. Further characterization of the water extract of the seed indicated that the main phenolic compound was ( )-epigallocatechin (109.6 mg g 1). Other phenolics including 4-hydroxy-benzhydrazide derivative (18.2 mg g 1), 2amino-3,4-dimethylbenzoic acid (16.8 mg g 1), and gallocatechin (17.0 mg g 1) account for the majority of the remaining phenolic compounds. The phenolic acids trans-ferulic,

THE OILSEEDS | Overview of the Oilseed Safflower (Carthamus tinctorius L.) chlorogenic, p-coumaric, and syringic acids are present at 3.0, 2.4, 0.5, and 0.2 mg g 1 extract, respectively. Additional flavonoids included naringin, rutin hydrate, quercetin dehydrate, luteolin, and kaempferol at concentrations of 6.0, 3.7, 2.2, 1.6, and 0.8 mg g 1, respectively. Chlorogenic acid, quercetin-3galactoside, and gallic acid are present at concentrations of 37–42, 15–16, and 10–12.1 mg g 1 dried flower petals, respectively. Other phenolic compounds were present at concentrations less than 9 mg g 1. Although differences in concentrations of phenolics were observed, the general trend in individual phenolics remained consistent regardless of growing location and cultivar.

Uses Although considered a modern use, safflower as a vegetable oil dates to around 260 BC. The use of safflower as a vegetable oil is limited due to the availability of inexpensive commodity oils. However, high-oleic acid safflower has promise as frying oil due to the low level of polyunsaturated fatty acids. Many oxidative stability index evaluations indicate that high-oleic acid safflower oil has comparable oxidative stability to that of high-oleic acid sunflower oil. The oxidative stability of higholeic acid safflower was further enhanced in a safflower line that contained high g-tocopherol content. The nonsaponifiable fraction of safflower was found to inhibit frying oil polymerization. In countries such as Korea, safflower oil is used as condiment oil and is therefore roasted prior to oil extraction. Mild roasting of the safflower seed does not affect fatty acid composition, but increases in tocopherols and oxidative stability have been documented by several researchers. However, excessive heat treatments such as boiling and microwaving decrease tocopherol concentration and oxidative stability. In addition to tocopherol and Maillard browning compounds, formed during roasting, phytosterols and phenolic compounds are thought to stabilize the safflower oil. Extracts of safflower have been shown to exhibit antioxidant activity and thus could potentially serve as a source of natural antioxidants. Water extracts of safflower seeds showed dose-dependent activity in several radical scavenging assays. The ORAC value of 63 mM Trolox equivalence per gram of seed extract was comparable to that of tomatoes. Radical scavenging properties were also found for extracts of the flower petals. Roasting increased slightly the Trolox equivalent antioxidant capacity (TEAC), while microwaving of the seed significantly increased TEAC compared to the control or raw seed. The list of studies supporting the antioxidant activity of safflower continues to grow. The diverse phenolic composition, yellow pigments, and tocopherol are just a few examples of compounds that likely contribute to the antioxidant activity. In addition to their antioxidant activity, the pigments of the flowers have been used extensively as a food, cosmetic, and textile dye. Hydroxyl safflower yellow A, safflower yellow B, and anhydrosafflor yellow B are the yellow pigments of safflower, while carthamin is the red color. Unlike the yellow pigments, carthamin has limited water solubility and is therefore used in lipid-based products such as chocolate. The yellow pigments have been used to color cheese and sausage, juice,

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and candy. The stability of the pigments can be problematic under the presence of light. Carthamin in particular has poor stability when added to aqueous-based food systems. The stability improves in a 75% sucrose–choline solution compared to water. A 90% glucose–choline chloride solution had the greatest stabilizing effect on carthamin. Although degradation occurred, carthamin had greater stability in a xylitol–choline solution than in water under thermal degradation conditions. In contrast to carthamin, the yellow pigments tend to be more stable but tend to degrade slightly under acid conditions. Solution containing lactic acid and ethanol facilitated the rapid degradation of carthamin and to a lesser extent the yellow pigments. Multiple studies have demonstrated the stability issues of safflower pigment. The importance of the food matrix in stabilizing/destabilizing the colorants must be considered if safflower pigments are to be used in foods. Traditional Chinese medicine has used safflower as a cure for many ailments. However, until relatively recently, evidence supporting the use of safflower as a treatment for many ailments has been lacking. A summary of the pharmacological and medicinal benefits can be found in the literature. However, a few examples include the antiatherogenic effect of N-(p-coumaroyl)serotonin and antiadipogenic effects of N-feruloylserotonin of safflower seed extract. The serotonin derivatives are believed to inhibit the activation of the vascular smooth muscle cells, thereby preventing atherosclerosis. Alcohol extracts of the flowers had matrix metalloproteases-2 (MMP-2) inhibitory activity. MMP-2 are important for many biological functions but if not properly controlled can contribute to the development of diseases such as cancer and atherosclerosis. Therefore, the MMP-2 inhibitory activity of hydroxyl safflower yellow A and safflower yellow B could be important treatments for disease affected by MMP-2. The use as a clothing dye and a coloring for food has been documented. Safflower as a potential source of healthpromoting oil (i.e., high g-linolenic acid) and as a biodiesel feed stock has attracted attention from commercial entities. Safflower is also a common bird food. Recently, pharmacological and medicinal benefits of safflower have attracted the attention of health researchers. Therefore, the author invites readers to review these source materials.

Future Prospects A significant body of knowledge exists regarding the production and composition of safflower. However, additional production research related to stressed environments such as high salinity and low moisture conditions are needed, specifically improving yield under stress conditions. Furthermore, the use of molecular techniques to alter or enhance composition is needed. The genetic manipulation of safflower to produce high g-linolenic acid safflower oil represents an opportunity to produce safflower oil with eicosapentaenoic acid and docosahexaenoic acid, that is, long chain omega-3 fatty acids are important for health and are normally found in fish and algae. Safflower is unique among many oilseeds in that temperature during growing and seed filling does not significantly affect unsaturated fatty acid content. Therefore, greater production

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area could be achieved in contrast to oilseeds that have temperature-dependent regulation of unsaturated fatty acids. Expanding the understanding of the functional characteristics of safflower seed and flower is needed. Several studies have documented the color stability of flower extracts in various model systems. However, additional investigation is needed in food-based systems. The bitterness associated the meal, while not a deterrent in animal feed, is not well suited for human consumption. Identifying ways to reduce or eliminate the bitterness at a commercial level is needed. Alternatively, methods to extract and purify the bitter compounds could be justified if sufficient bioactives could be isolated. Some of the bitter compounds have biological activity in model systems. Traditional Chinese medicine has used safflower for treatment of a number of aliments; however, the active components are not fully characterized. Although a number of studies have been completed, there is still a need to assess the bioactivity of safflower.


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What parts of the safflower can be used for food, feed, biofuel, coloring, and bioactive compounds? Why is safflower grown worldwide? What factors influence the growth of safflower? Why is the taproot of safflower important? How does growing environment affect safflower seed composition? Why is safflower unique among oilseeds in terms of fatty acid composition? What bioactive compounds are present in safflower and what part of the plant can these compounds be found? What type of safflower oil can be used as frying oil? What makes this oil well suited for frying applications? Why is safflower a potential source of omega-3 lipid? Why is the yellow pigment not commonly used in food systems?


• • •

How does safflower differ from other oilseeds in terms of production and oil content and fatty acid composition? Cross-reference to oilseed articles. Identify several countries that produce safflower and compare production practices and oilseed qualities among the produced seeds? Do any countries use wild safflower? Why is defatted safflower meal used only for livestock feed and not human food? How does this compare to other oilseed meals? Cross-reference to oilseed articles.

See also: Bioactives and Toxins: Bioactives: Antioxidants; Fats: Healthy Fats and Oils; Lipid Chemistry; Food Grains and Wellbeing: Functional Foods: Overview; Genetics of Grains: Development of Genetically Modified Grains; The Oilseeds: Canola: Overview; Linseed: Overview; Oilseeds: Overview; Soybean: Overview; Sunflower: Overview; Cottonseed: Overview.

Further Reading Asgarpanah J and Kazemivash N (2013) Phytochemistry, pharmacology and medicinal properties of Carthamus tinctorius L. Chinese Journal of Integrative Medicine 19(2): 153–159. Esteban A, Sicardo M, Mancha M, and Martıńez-Rivas J (2004) Growth temperature control of the linoleic acid content in safflower (Carthamus tinctorius) seed oil. Journal of Agricultural and Food Chemistry 52: 332–336. Hamrouni-Sellami I, Salah H, Kchouk M, and Marzouk B (2007) Variations in phytosterol composition during the ripening of Tunisian safflower Carthamus tinctorius L. seeds. Pakistan Journal of Biological Sciences 10(21): 3829–3834. Kisha T and Johnson R (2012) Safflower. In: Gupta SK (ed.) Technological Innovations in Major World Oil Crops. Breeding, Vol. 1, pp. 147–164. Berlin: Springer. Kizil S, Çakmak O¨, Kirici S, and ˙Inan M (2008) A comprehensive study on safflower (Carthamus tinctorius L.) in semi-arid conditions. Biotechnology and Biotechnological Equipment 22(4): 947–953. Li B, Zong X, Zhang H, et al. (2014) Screening and structural characterization of mmp-2 inhibitor from Carthamus tinctorius L. using ultrafiltration liquid chromatography–mass spectrometry. Journal of Liquid Chromatography and Related Technologies 37: 2327–2336. Luterottia S, Franko M, Sˇikovec M, and Bicanic D (2002) Ultrasensitive assays of transand cis-b-carotenes in vegetable oils by high-performance liquid chromatography–thermal lens detection. Analytica Chimica Acta 460: 193–200. Mariod A, Ahmed S, Abdelwahab S, et al. (2012) Effects of roasting and boiling on the chemical composition, amino acids and oil stability of safflower seeds. International Journal of Food Science and Technology 47: 1737–1743. Mayerhofer M, Mayerhofer R, Topinka D, Christianson J, and Good A (2011) Introgression potential between safflower (Carthamus tinctorius) and wild relatives of genus Carthamus. BMC Plant Biology 11: 47. http://dx.doi.org/10.1186/14712229-11-47. Nykiforuk C, Shewmaker C, Harry I, et al. (2012) High level accumulation of gamma linolenic acid (C18:3D6.9,12 cis) in transgenic safflower (Carthamus tinctorius) seeds. Transgenic Research 21: 367–381. Ortega-Garcıá J, Ga´mez-Meza N, Noriega-Rodriguez J, et al. (2006) Refining of high oleic safflower oil: Effect on the sterols and tocopherols content. European Food Research and Technology 223: 775–779. Singh V and Nimbkar N (2006) Safflower (Carthamus tinctorius L.). In: Singh RJ (ed.) Genetic Resources, Chromosome Engineering, and Crop Improvement, Vol. 4. Oilseed Crops, pp. 167–194. Boca Raton, FL: CRC Press, Taylor & Francis Group. Smith J (1996) Safflower. Champaign, IL: AOCS Press. Vilatersana R, Garnatje T, Susanna A, and Garcia-Jacas N (2005) Taxonomic problems in Carthamus (Asteraceae): RAPD markers and sectional classification. Botanical Journal of the Linnean Society 147: 375–383. Weiss EA (2000) Safflower. In: Weiss EA (ed.) Oilseed Crops, pp. 93–129. Oxford: Blackwell Science.

Linseed: Overview S Cloutier, Agriculture and Agri-Food Canada, Ottawa, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Linseed is an ancient crop that has been useful and versatile through the ages. Linseed is a minor oilseed crop with a unique fatty acid profile. Linseed oil is rich in alpha-linolenic acid (ALA) that gives the oil unique drying properties. Many health benefits have been attributed to the consumption of linseed. Low yield relative to other major oilseeds limits the expansion of the crop.

Learning Objectives

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In the following article, the reader is expected to understand the uniqueness of linseed compared to other oilseed crops. An overview of the agronomic practices and production limitations is presented to illustrate the challenges associated with the development of improved cultivars and of cultivating this crop. Emphases have been placed on not only the composition of linseed as it relates to its multiple end uses but also the multiple health benefits associated with the consumption of linseed.

Introduction The species epithet of the Latin name of flax, Linum usitatissimum L., means ‘most useful,’ an appropriate name because this crop has been highly versatile and esteemed through the ages. Flax has two morphotypes: fiber and oilseed. Tall and branched only in the top quarter of the plant, fiber flax is grown for its stem fibers that are extracted and processed into linen, nonwoven mats, paper, and various other products. Oilseed flax plants, also called linseed or flaxseed, are shorter and more branched and have larger seeds than the fiber type. Flax is one of the world’s oldest cultivated crops, praised by ancient civilizations for its fiber and seed uses. Today, varieties are grown for either stem fiber or seed, although value can be extracted from the seeds of fiber flax and, conversely, the stem fiber of linseed. Over the last 50 years, the world’s production of linseed fluctuated between 2 and 4 million tonnes (Mt), but in the last decade, it has stabilized at a little more than 2 Mt with the largest producers being Canada, the Russian Federation, and China. In 2012, world oil production from the top 12 major oilseed crops amounted to 157 Mt, of which linseed oil production at 544 t accounted for a mere 0.35%. As such, linseed is a minor oilseed crop worldwide, but the unique characteristics of its oil combined with its high content of seed dietary fibers and lignans respond to specific markets not addressed by the major oilseeds.


The term linseed often refers to the seed destined for oil extraction with industrial end uses while the term flaxseed is more commonly associated with nonprocessed seed used directly in human food or animal feed. In reality, the two terms represent flaxseed with the same oilseed quality and they can be used interchangeably. Currently cultivated linseed varieties contain 40–50% oil, of which 55–57% is ALA, an essential fatty acid. LinolaTM is a trademark name of the solin (generic term) type of flax that contains < 5% linolenic acid, resulting in oil similar in composition to sunflower. In Canada, LinolaTM or solin varieties were required to have a yellow seed coat to make them visually distinguishable from brown seeded linseed varieties, although there are also yellow linseed varieties. High linolenic acid content varieties characterized by more than 60% ALA are generically referred to as ‘high-lin’ such as the European variety ‘Omega’ or under the registered name Nulin®.

End Uses An overview of the end use versatility of fiber flax and linseed is illustrated (Figure 1). For the purpose of this article, the focus will be strictly on the seeds. Linseed is used as human food in baked goods and other products, either whole or ground. Whole seeds can also be fed to poultry because they can grind the seeds with their gizzard. The processing of linseed to extract oil produces a by-product called meal. Rich in protein and energy, the meal is a high-value feed for livestock. The extracted oil can be utilized as human food, mostly as a supplement, but its main application is as industrial oil in, for example, stains, paints and linoleum flooring.

Composition Expressed on a dry basis, typical linseed contains 41–43% oil, 28% dietary fiber, 21–23% protein, 6% carbohydrate, and 4% ash but these can vary substantially among genotypes, particularly oil content. In genebanks, oil contents ranging from 31.4% to 45.7% were reported while levels up to 52.3% were recorded in field plot trials. Most modern linseed cultivars field-grown in temperate climates contain 45–49% oil. The fatty acid composition of linseed oil is unique among plants because it is particularly high in ALA, the parent fatty acid of the omega-3 family. The major oilseeds of the world contain much less ALA than linseed (Figure 2). Rapeseed (canola) and soybean oils have 10% and 8% ALA, respectively, while sunflower, cottonseed, corn, and peanut oils only have traces (<1%). Conventional linseed varieties typically contain 57% ALA, 16% linoleic acid (LA), 18% oleic acid, 4% stearic acid, and 5% palmitic acid. With 73% polyunsaturated fatty acid content, linseed oil has unique drying properties.

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THE OILSEEDS | Linseed: Overview

0%

20%

40%

60%

80%

100%

Linseed Rapeseed Soybean Solin Sunflower Cottonseed Corn Extraction

Peanut

Oil

Food

Industrial

Meal

Processing

Animal feed

Linoleum coatings, paints, stains, lubricants, etc.

Linen, paper, nonwoven mats, insulation, fire logs, etc.

Figure 1 The versatility of flax (Linum usitatissimum L.). Stem fibers extracted from the fiber morphotype can be processed into high-quality linen. Lower-quality fibers or other straw components such as the shives can be used to produce a wide variety of products. Whole seeds from the oilseed morphotype (linseed or flaxseed) can be used in the food industry or as animal feed. Linseed oil extraction generates a by-product called meal, which is an excellent animal high-protein feed source. The highly unsaturated oil has some food usage in salad dressing or as a functional food, but its tendency to quickly become rancid makes special handling a requirement. The uniqueness of the fatty acid composition of linseed oil gives it distinctive drying properties desirable for many industrial applications.

LinolaTM or solin varieties, developed through mutation breeding and selected for their inactive fatty acid desaturases 3A and 3B, have < 5% ALA, often only 2–3%, but contain 65–75% LA. The fatty acid composition of LinolaTM or solin varieties is similar to conventional sunflower (Figure 2). These varieties were developed to meet the market need of the margarine industry. Unfortunately for LinolaTM, the margarine sector developed different formulations using mostly nonhydrogenated soybean and canola oils and the demand for LinolaTM oil was not sustained. Today, these types of linseed varieties are no longer commercially grown. Linseed varieties with very high ALA content (high-lin) ranging from 60% to 75% have been developed and marketed. Similar to chia seeds (52–69%) in terms of ALA content, both conventional linseed and high-lin varieties constitute a richer source of ALA because their oil content of 40–50% exceeds that of chia (Salvia hispanica L.) seeds, which ranges from 26% to 38%. High-lin varieties were developed for human food markets including the nutraceutical and functional food sectors, but they can also be used as a high ALA source for blending of industrial linseed oil to ensure the desired oil properties.

Saturated fat

Monounsaturated fat

Linoleic acid

Alpha linolenic acid

Figure 2 Fatty acid composition of linseed and solin (LinolaTM) oil compared to six of the major oilseed crops of the world. With 57% alpha-linolenic acid (ALA) content, linseed oil is unique because none of the other major oilseed crops exceed 10% ALA. Solin (LinolaTM) are varieties selected through mutation breeding that have <5% ALA content, and as such, their overall fatty acid composition is similar to sunflower oil. Data obtained from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Boca Raton, FL: CRC Press, Taylor & Francis Group.

Linseed contains 21–23% protein on a dry-weight basis but the meal obtained after oil extraction has an enriched protein fraction of 31–33%. The amino acid composition is considered to be generally good because it contains all of the essential amino acids. On a dry-weight basis, linseed has 28% dietary fiber with a soluble to insoluble fiber ratio ranging from 20:80 to 40:60. These dietary fibers (not to be confused with the stem fibers) are for the most part present in the seed coat. In a small subset of varieties, mucilage (main soluble fiber of linseed) content was shown to vary from 3% to 8% of the dry seed weight indicating that the variation for this trait would possibly be more substantial in a diverse panel of accessions. Mucilage dissolved in water is viscous and this viscosity can be a quantitative measurement of its quality. In a study of Canadian varieties, the mean mucilage indicator values ranged from 90 to 246 cSt ml g1. Hence, two varieties with the same mucilage content may have very different functional properties.

Health Benefits Both ALA and LA are essential fatty acids because humans do not have the ability to synthesize them from their precursors. We must incorporate them into our diet because they play important physiological roles. In the human body, they can be further elongated and desaturated to produce docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA), and other very long polyunsaturated fatty acids with proven functionalities. ALA, DHA, and EPA are omega-3 fatty acids whose health benefits include roles in reduction of blood pressure, blood triglycerides, inflammation, and the

THE OILSEEDS | Linseed: Overview incidence of cardiovascular diseases. Recently, Health Canada has granted a health claim regarding the effectiveness of ground flaxseed on lowering cholesterol allowing health claims such as the following to be made on flaxseed labels: 16 g or 2 tablespoons of ground flaxseed supplies 40% of the daily amount shown to help lower cholesterol. On the other hand, LA can be converted into omega-6 AA, which has been shown to be detrimental by promoting inflammatory reactions. The enzymes delta-6, delta-5, and delta-4 desaturases are shared between the omega-3 and omega-6 pathways. Fortunately, the high omega-3 to omega-6 ratio of linseed favors the omega-3 pathway over the omega-6 pathway. The Western diet is generally considered to have an omega-6 to omega-3 ratio that is too high (20:1) due to the types of fats and oils consumed (e.g., soybean; Figure 2) and hence favoring the omega-6 pathway. The replacement of some of these fats and oils with whole and ground linseed or linseed oil would represent a healthy alternative to meet the recommended 2:1 to 6:1 ratio. Linseed contains both soluble and insoluble dietary fibers. The predominant fraction of the soluble fiber is the mucilage, which has been associated with lowering of blood cholesterol and glucose. Lignans are phytoestrogens that are also part of the dietary fiber component. Linseed is one of the best sources of these diphenolic compounds. Secoisolariciresinol diglucoside, the major linseed lignan, has been associated with reduced risks of hormone-sensitive cancers such as prostate, colon, and breast cancers. Lignans also have antioxidant properties leading to their positive role in reducing the activity of free radicals.

Antinutritional Factors There are two main well-documented antinutritional components in linseed: cyanogenic glucosides and linatine. The two main cyanogenic glucosides contained in mature seeds are linustatin and neolinustatin. Following ingestion, hydrolysis can lead to the release of hydrogen cyanide that can impede the essential process of cell respiration. Fortunately, the amount of cyanogenic glucosides in linseed is low, and because the acute lethal dose of hydrogen cyanide in human is 0.5–3.5 mg Kg1 of body weight, an average adult would have to consume 1000 g of linseed in a day to receive a fatal dose. The recommended daily intake of linseed of 30–40 grams contains well below the toxic dosage. Moreover, the acidic environment of the human stomach is not conducive to cyanogenic glucoside hydrolysis. As a consequence, these toxic degradation products are more of a concern in ruminants. Linatine is an antagonist of vitamin B6. Symptoms associated with B6 deficiencies were observed in young poultry; hence, their ration should be limited to <10% linseed meal. As mentioned earlier, the mucilage comprises soluble dietary fibers well known for their positive role in laxation. In animal feed, the outcome of rapid passage in the intestinal tract is poor nutrient absorption and its consequent performance reduction, particularly in poultry, a consequence that also limits the linseed meal proportion of the ration.

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Animal Feed and Omega-3-Enriched Products Linseed meal, ground or whole flaxseed, can be used as feed for poultry, swine, and cattle because it is a good source of protein, oil, and energy although whole flaxseed can only be used with poultry. There are several reports on the health benefits associated with feeding linseed-derived products to livestock. However, as outlined in the earlier-mentioned section, livestock producers must follow recommended guidelines to avoid the side effects associated with deficiencies, antinutritional effects, or ability to process the ration. A main driver for using linseed as feed is for the production of omega-3-enriched eggs and meat. The feeding of 10% linseed ration to laying hens increased the omega-3 content in eggs by a factor of 4. In Canada, a minimum of 300 mg of omega-3 fatty acid per serving is required to allow the labeling of a product as a source of omega-3. Such labeling commands a premium that health-conscious consumers are willing to pay. Omega-3-enriched chicken and pork products are also available to consumers.

Agronomy In temperate climates, linseed is grown as a summer annual crop that matures in 90–150 days including a vegetative, a flowering, and a seed maturation period. In some areas of the world, winter-type linseed is grown. These varieties do not require vernalization per se to flower but they have the ability to endure some cold temperatures in the early developmental stages. While each boll may contain a maximum of ten seeds, linseed and fiber flax accessions in western Canadian field trials produced only 3.5–8.1 seeds per boll. The flat, oval, and pointed seeds are small with thousand-seed weight ranging from 2.7 to 8.4 g, but the majority of Canadian and US linseed varieties have thousand-seed weight of 5–5.5 g. Ideally, linseed is sown in firm, moist soil 1.5–3.0 cm deep in rows 15–20 cm apart at a seeding rate of 30–45 kg ha1. Early seeding is recommended to avoid some diseases (see succeeding text) and drought and heat during flowering and seed filling, which translates into higher yield, oil content, and quality. Heat and drought stresses at flowering time and during seed filling result in significant yield losses and lower oil content. Seeding practices for linseed differ greatly from those of fiber flax where a high plant density is critical to fiber production and quality. In general, the utilization of agronomic best management practices such as early seeding, crop rotation, and weed and disease control has a major effect on linseed yield.

Genetics Linum usitatissimum L. is a diploid species with 15 pairs of chromosomes (2n ¼ 30). Its genome is composed of an estimated 373 Mbp of nucleotides for which an assembled sequence is available (www.phytozome.net). There are 48 000 accessions of cultivated flax preserved in genebanks around the world but only 10 000 are estimated to be unique because of the redundancy between collections. Nevertheless, these

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collections represent a tremendous amount of diversity for genetic enhancement (Figure 3). Other important genetic resources include a large collection of expressed sequences (genes), a consensus genetic map, and a physical map that were used to order and annotate the genome sequence.

A core collection of flax including more than 300 linseed types and 92 fiber types was extensively characterized in the field at two locations during four consecutive years. Agronomic traits such as yield and its components (thousand-seed weight, seeds per boll, and bolls per area), lodging, maturity, flowering

Figure 3 Genetic diversity in cultivated flax, Linum usitatissimum. (a) Flower color varies from white to shades of pink or blue and petals’ overlap, margin, and folding are also indicative of the breadth of the genetic diversity. (b) At maturity, some accessions have completely closed bolls (or capsules) while others are slightly or completely dehiscent. The latter is a useful trait to disseminate the seeds in the wild but is undesirable and selected against by breeders for usage as a crop. (c) The seed coat color of linseed can vary from bright yellow to olive to dark brown and even include variegated. Photos, reproduced with permission, are courtesy of Dr. Axel Diederichsen, Plant Gene Resources of Canada, Saskatoon, SK, Canada.

THE OILSEEDS | Linseed: Overview time, height, and plant branching were measured. Seed quality traits such as fatty acid composition, iodine value, oil content, and protein content were also evaluated. Finally, disease ratings for rust, pasmo, and powdery mildew were recorded. The collection was genotyped with molecular markers and a genome-wide association study revealed several marker-trait associations. These important studies provided background information on the flax genome and the genetics of important traits that, combined together, will assist and accelerate improvement of linseed by plant breeders.

Yield In western Canadian field plots, yield of linseed accessions as high as 2.5 tonnes per hectare (t ha1) was reported, but higher yields have been measured (Paul Dribnenki, personal communication, January 2014). However, this yield potential is not achieved for the crop at large and the yields of linseed worldwide remain at < 1 t ha1. Even in the main producing countries, it is still only 1.4 t ha1 and the rate of yield increase remains below 1.5% per year, far less than its oilseed competitors canola (1.6–2 t ha1) and soybean (1.6–2.6 t ha1). Yield improvement is therefore the main objective of linseed breeding programs because it is the single most important trait to ensure competitiveness. In recent years, plant breeders have realized that the narrow genetic base of the germplasm has limited yield improvement. To overcome this limitation, linseed breeders are now incorporating exotic material, using modified breeding schemes, and applying molecular markers into breeding programs. For example, backcrosses of molecular markers associated with thousand-seed weight to introgress the trait into adapted elite germplasm are being implemented. Genomic selection could also prove useful toward yield improvement, although there are no reports yet on its usage in linseed improvement. Many oilseed crops such as corn, canola, and soybean have well-established hybrid systems that can take advantage of heterosis, also known as hybrid vigor. As mentioned earlier, linseed is highly self-pollinated, and to date, a single hybrid has been released in China. Although hybrid production of linseed bears promise and is theoretically possible, the development of an economically viable and stable system poses major challenges.

Diseases Several diseases can affect the crop during its growing season. The most important are fungal diseases that are prevalent in most growing areas of the world: fusarium wilt caused by Fusarium oxysporum, rust caused by Melampsora lini, pasmo caused by Septoria linicola, and powdery mildew caused by Oidium lini. The crop can also be affected by other fungal, phytoplasma, and viral diseases but these tend to either be localized or have a negligible impact on yield or quality. Fusarium wilt, a soil-borne pathogen, can wreak havoc on a crop because heavy infection of susceptible varieties results in complete wilting of the plants and major yield reduction. The combination of moderate resistant varieties and crop rotation

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to keep the soil inoculum low are effective ways of controlling the disease. The host disease resistance mechanism seems to be controlled by a few major genes meaning that the development of resistant varieties should be highly feasible in a reasonable time frame. However, the large environmental component involved in the expression of wilt tolerance challenges plant breeders and continues to impede breeding progress. Rust spores are airborne and can infect flax plants when temperature and moisture conditions are conducive. Visual symptoms are the presence of pustules with or without chlorosis or necrosis on the aerial parts of the plants. Interestingly, it was while studying flax rust in the 1950s that Harold Henry Flor came up with the gene-for-gene concept, stating that for each gene conditioning rust reaction in the host, there is a gene counterpart in the fungus conditioning pathogenicity. This concept has since been found to be applicable to many plant diseases. In flax, several rust resistance genes (R genes) have been cloned in the last two decades assisting in their introgression in breeding lines, an important asset to breeders because rust-resistant varieties are the best way to counter this disease. Powdery mildew infection appears as a white mass of mycelium and spores on the leaves. Heavy infection can occur under high humidity conditions. Similarly to fusarium wilt, resistance seems to be controlled by a few major genes. As with the other two previous fungal diseases, genetic resistance exists and planting resistant cultivars is the best practice to control the disease in areas where it is prevalent. Pasmo is the most prevalent disease on the Canadian Prairies. Early infection of pasmo has a major detrimental impact on yield and quality. The early brown spots can evolve into complete leaf desiccation. The disease girdles the stems and increases the prevalence of lodging, which has also been shown to cause significant yield reduction in flax and negatively affect seed quality. Early seeding of clean seeds, crop rotation, and fungicide application are the best control methods because commercial cultivars released to date seem to lack resistance to this disease.

Transgenic In 1996, CDC Triffid was the first and only genetically modified (GM) linseed variety to be registered in Canada. CDC Triffid was the result of the transformation of NorLin with a modified Arabidopsis acetolactate synthase gene that conferred resistance to residual soil activity of sulfonylurea herbicides. Breeder seed of the variety was distributed to seed growers for pedigreed seed production. In 1997–98, in light of the European Union (EU) moratorium on GM crops and foods, the seed company owning the right to CDC Triffid voluntarily halted its seed multiplication and coordinated its retrieval and destruction with the Flax Council of Canada to prevent potential harm to the industry. CDC Triffid pedigreed seed production was recalled and destroyed. In 2009, a shipment of linseed from Canada to the EU tested positive for a wellknown GM marker. Further testing confirmed the low-level presence of CDC Triffid. While this variety had received approval for feed and industrial uses in Canada and the United States, it constituted a nonapproved event in the EU and there is zero tolerance for such. Canada and the EU entered into

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discussions to mitigate the crisis that led to the establishment of a stewardship program and testing protocols. In 2013, one can conclude that the monitoring has been a success because the low-level presence of the CDC Triffid gene construct in Canadian linseed has been substantially reduced. Unfortunately, exports to the EU are only half what they were prior to 2009 indicating that market confidence remains to be fully regained.

sequencing, is proving viable in many major crops such as wheat, corn, barley, and rice and bears promise for other crops such as linseed that has the advantage of a small genome. Genetic transformation has the potential to bring about novel products because linseed is readily amenable to this type of technologies. As a health food, the antinutritional compounds of linseed remain and will continue to be an important research target and the topic of various research activities.

Conclusion Linseed is a unique oilseed crop that combines high oil content with high content of ALA giving the oil distinctive drying properties sought in the manufacturing of biodegradable industrial products. ALA, lignans, and high fiber content of linseed are also contributing to making linseed highly suitable for the food and feed markets because these seed components have been linked to several health attributes in human and animals. While linseed remains a minor oilseed crop worldwide, its versatility and uniqueness continue to be unmatched by the main oilseed crops.


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What components of linseed are associated with health attributes? What is the main fatty acid of linseed and how does its composition compare to other major oilseed crops? What makes ALA an essential fatty acid? Why is Linum usitatissimum L. considered a dual purpose or total utilization crop? What morphological features distinguish fiber flax from oilseed flax (linseed)? What is the main characteristic distinguishing the solin-type (LinolaTM) from the conventional linseed? How is linseed used to create omega-3-enriched chicken and pork meats? What are some of the main production challenges currently limiting the expansion of linseed as a crop?


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Molecular genetics is making great strides in gene discovery for discrete and quantitative traits but the translation of this research into breeding is generally slower in minor crops such as linseed because of limited investments. Phenotyping is expensive but necessary to identify and validate functional genetic variants. To survive and thrive as a crop, linseed yield must be improved and further research toward that goal will certainly encompass the genomics– translation–phenotyping continuum including also agronomy and disease research activities. Genomic selection, a method of predicting breeding values using genomic

Acknowledgments The author sincerely thanks Drs. Helen Booker, Axel Diederichsen, Paul Dribnenki, and Gordon Rowland and Mr. Andrzej Walichnowski for their comments and edits made to this article. The author also thanks Ms. Michelle Beaith and Drs. Allan Green and Paul Dribnenki for the information on the status of LinolaTM around the world and Ms. Kelley Fitzpatrick for the information on the regulatory affairs of flax health claims.

Further Reading Anonymous (2008) Flax feed industry guide. Winnipeg: Flax Canada 2015. Diederichsen A (2007) Ex situ collections of cultivated flax (Linum usitatissimum L.) and other species of the genus Linum L. Genetic Resources and Crop Evolution 54: 661–678. Diederichsen A, Kusters PM, Kessler D, Bainas Z, and Gugel RK (2013) Assembling a core collection from the flax world collection maintained by Plant Gene Resources of Canada. Genetic Resources and Crops Evolution 60: 1479–1485. Dribnenki JCP and Green AG (1995) Linola ‘947’ low linolenic acid flax. Canadian Journal of Plant Science 75: 201–202. FAOSTAT (2013) Production: Crops. Available at http://faostat3.fao.org/home/index. html (accessed December 2013). Fofana B, Ragupathy R, and Cloutier S (2010) Flax lipids: Classes, biosynthesis, genetics and the promise of applied genomics for understanding and altering of fatty acids. In: Gilmore PL (ed.) Lipids: Categories, Biological Functions and Metabolism, Nutrition and Health, pp. 71–98. New York: Nova Science Publishers Inc. McHughen A, Rowland GG, Holm FA, Bhatty RS, and Kenaschuk EO (1997) CDC Triffid transgenic flax. Canadian Journal of Plant Science 77: 641–643. Muir AD and Westcott ND (2003) Flax: The genus linum. Boca Raton, FL: CRC Press. Rashid KY (2003) Diseases of flax. In: Bailey KL, Gossen BD, Gugel RK, and Morrall RAA (eds.) Diseases of Field Crops in Canada, 3rd edn., pp. 147–154. Saskatoon: University Extension Press. Ryan CD and Smyth SJ (2012) Economic implications of low-level presence in a zero-tolerance European import market: The case of Canadian Triffid flax. AgBioforum 15: 21–30. Soto-Cerda BJ, Duguid S, Booker H, Rowland G, Diederichsen A, and Cloutier S (2014a) Association mapping of seed quality traits using the Canadian flax (Linum usitatissimum L.) core collection. Theoretical and Applied Genetics 127: 881–896. Soto-Cerda BJ, Duguid S, Booker H, Rowland G, Diederichsen A, and Cloutier S (2014b) Genomic regions underlying agronomic traits in linseed (Linum usitatissimum L.) as revealed by association mapping. Journal of Integrative Plant Biology 56: 75–87. Souci SW, Fachmann W, and Kraut H (2008) Food composition and nutrition tables, 7th edn. Boca Raton, FL: CRC Press, Taylor & Francis Group. Wang Z, Hobson N, Galindo L, et al. (2012) The genome of flax (Linum usitatissimum) assembled de novo from short shotgun sequence reads. Plant Journal 72: 461–473.


Contents Grain Legumes and Their Dietary Impact: Overview Pseudocereals: Overview Lupin: Overview Amaranth: Overview Beans: Overview Buckwheat: Overview Chickpea: Overview Pea: Overview Peanuts: Overview Quinoa: Overview

Grain Legumes and Their Dietary Impact: Overview TE Michaels, University of Minnesota, St. Paul, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Introduction

Grain legumes have seeds that are prepared for use as human food. Pulse seeds are a rich source of protein in diets around the world. Legumes support Rhizobium bacteria that fix atmospheric nitrogen for use by the plant and so are indispensible in sustainable cropping systems. Pulse consumption is constrained by low digestibility, antinutritional factors, flatulence, and stigmatization as a food for the poor. Combining cereal and legume grains at meals provides inexpensive plant-based diets with balanced amino acid composition. Seed yield can be hampered by the plants’ sensitivities to environmental stress. Grain legumes can relieve malnutrition in food-deficit regions and protect against diet-related diseases such as obesity, diabetes, and heart disease in food surplus regions.

Learning Objective

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To obtain a comprehensive understanding of the agronomy, consumption, composition, antinutritional factors, and protein complementation of grain legumes


As the field is now prepared, we shall proceed to speak of the nature of the various kinds of grain; we must premise, however, that there are two principal classes of grain, the cereals, comprising wheat and barley, and the legumina, such as the bean and the chick-pea, for instance. The difference between these two classes is too well known to require any further description. The Natural History. Pliny the Elder. John Bostock, M.D., F.R.S. H.T. Riley, Esq., B.A. London. Taylor and Francis, Red Lion Court, Fleet Street. 1855. Book 18 Chapter 9

Despite Pliny the Elder’s assertion that the difference between classes of grain is too well known to warrant further description, let us do so anyway. In this overview, we will consider grain legumes to be plants with two major characteristics: they belong to the legume family (Fabaceae or Leguminosae) and preparations based on their dry seeds are consumed by humans for food (although they may have other uses as well). In contrast to cereal grains, humans particularly value legume grains as a concentrated source of protein for our diets. Grain legumes are commonly subdivided into partially overlapping groups according to their dominant use and seed composition. Pulses, such as the common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata), are classic grain legumes in that their dry seed composition includes high protein (>19%), high carbohydrate (>60%), and low lipid (<6%) and where the primary culinary interest focuses on the dry seeds

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266 Table 1

THE LEGUMES AND PSEUDOCEREALS | Grain Legumes and Their Dietary Impact: Overview Names and regions of greatest genetic diversity for major grain legume species

Botanical name

Common and vernacular names

Center of domestication

Arachis hypogaea Cajanus cajan Cicer arietinum Glycine max Lathyrus sativus Lens culinaris

Peanut, groundnut Pigeon pea, Angola pea, Congo pea, dhal, no-eye pea, red gram Chickpea, garbanzo bean, gram Soybean, soyabean, sojabean Grass pea, chickling vetch Lentil, split pea, red dhal, masur, lenteja, lentille, manssor, burssum

Lupinus albus; L. angustifolius; L. mutabilis Macrotyloma uniflorum Phaseolus vulgaris

Mediterranean white lupin, narrow-leafed lupin, Australian sweet lupin, Andean pearl lupin, tarwi Horse gram Common bean, dry bean, kidney bean, frijol, caraota, poroto, habichuela, haricot bean, snap bean Lima bean Field pea, garden pea, guisante, muttar, pois, arveja, Alaska pea

Southern Bolivia, northwest Argentina India Southeast Turkey China Southern Europe, Southwest Asia Eastern Mediterranean, the Fertile Crescent (Iraq and Iran) Greece, western Turkey, Eastern Mediterranean, Peru (L. mutabilis) Southern India Mexico and Peru

Phaseolus lunatus Pisum sativum Vicia faba Vigna radiata Vigna mungo Vigna unguiculata

Broad bean, faba bean, horse bean, Windsor bean, haba, feve Green gram, golden gram, mung bean, Oregon pea, chickasano pea Mung bean, black gram, urd, kambulu, uride Cowpea, catjang, Hindu cowpea, kaffir bean, black-eyed pea, frijol, caupi

Peru, Central America, the Caribbean The Fertile Crescent (Iraq and Iran), Turkey, Greece Eastern Mediterranean, West Asia India, Southeast Asia India Sub-Saharan Africa

Adapted from Sinha SK (1977) Food Legumes: Distribution, Adaptability and Biology of Yield. Rome, Italy: Food and Agriculture Organization of the United Nations. Based on Sinha (FAO) and Adams MW and Pipoly JJ III (1980) Biological structure, classification and distribution of economic legumes. In: Summerfield RJ and Bunting AH (eds.) Advances in Legume Science, pp. 1–16. Kew, UK: Royal Botanic Gardens; Zohary D, Hopf M, and Weiss E (2012) Domestication of Plants in the Old World, pp. 98–100. Oxford, UK: Oxford University Press; Grabiele M, Chalup L, Robledo G, and Seijo G (2012) Genetic and geographic origin of domesticated peanut as evidenced by 5S rDNA and chloroplast; DNA sequences. Plant Systematics and Evolution 298: 1151–1165.

Table 2 Protein and other nutritional constituents of grain legumes and other reference foods (g constituent 100 g food1) Food Pulses Common bean Lima bean Chickpea Green gram Cowpea Lupin Oilseeds Soybean Peanut Cereals Wheat, hard white Brown rice, raw Animal products Beef, lean ground Pork, ground Fish, cod Milk, cow’s 3.25% fat Egg, hen’s

Protein

Lipid

Carbohydrate

Water

22.2 21.5 19.3 23.9 23.8 36.7

1.1 0.7 6.0 1.1 2.1 11.5

61.5 63.4 60.7 62.6 59.6 45.4

11.5 10.7 11.5 9.0 11.1 –

36.5 25.8

19.9 49.2

30.2 16.1

8.5 6.5

11.3 7.5

1.7 2.7

75.9 76.2

9.6 12.4

20.0 16.9 17.8 3.3 12.5

10.0 21.2 0.7 3.3 10.0

0.0 0.0 0.0 4.7 1.2

69.5 61.0 81.2 88.0 75.3

Based on data from FAOSTAT Database – http://www.fao.org/ag/; Mohamed AA and Rayas-Duarte P (1995) Composition of Lupinus albus. Cereal Chemistry 72: 643–647; Kohajdova´ Z, Karovicˇova´ J, and Schmidt Sˇ (2011) Lupin composition and possible use in bakery – A review. Czech Journal of Food Sciences 29: 203–211.

(Tables 1 and 2). Pulses also contain high levels of dietary fiber (20 g fiber per 100 g compared with 12 g fiber per 100 g for wheat, 9 g fiber per 100 g for soybean, and 3 g fiber per 100 g for

rice). Oilseed legumes, including soybean (Glycine max) and peanut (groundnut, Arachis hypogaea), in contrast to pulses, accumulate higher protein, lower carbohydrate, and higher lipid. Because of the high lipid content, they are often utilized as a source of vegetable oil for culinary and industrial uses, but they are also important as pulse-like ingredients in prepared foods. For example, soybean is the base of many nonfermented and fermented foods such as tofu and tempeh, while peanut is the main ingredient in some snacks and sandwich spreads. Lupin (Lupinus L.) seed’s protein, lipid, and carbohydrate composition is intermediate to that of pulses and oilseeds, and its dominant use in many areas of the world is as an animal feed. However, in Europe and South America, it has a long, pulse-like history of human consumption and now enjoys increasing popularity as a food crop in North America and Australia. Grain legumes are ancient foods that help fulfill the ageless need for human sustenance. The word ‘pulse’ arrived in modern English from the Greek ‘poltos’ meaning ‘porridge of meal,’ by way of Latin (‘puls’ and ‘pultis’), Old French (‘pols’), and Middle English (‘puls’). Gathering plant parts for food is a reliable way (in comparison with episodic hunts for animal prey) of feeding oneself in a hunting and gathering society. Gathering pulse seeds is particularly convenient compared with parts of other plants. Pods from grain legume plants are handy and easily grabbed compared with subterranean roots and tubers. No tools other than fingers and palms are needed to grab and hang on to the large seeds. Keeping both feet firmly on the ground is less daunting than climbing trees for aerial fruits and nuts. The dense seeds are more filling than leaves and will satisfy hunger in the absence of meat if hunting is unsuccessful. As a bonus to

THE LEGUMES AND PSEUDOCEREALS | Grain Legumes and Their Dietary Impact: Overview those concerned about times of scarcity, the seeds can be dried and stored for a period of months or more without loss of food value when eaten or viability when planted. Pulse seeds are large relative to cereals, so they are convenient to handle for food preparation and planting. Because of their convenience, availability, and composition, wild pulses were an accessible, nutritional contributor to early hunting and gathering societies across the world. The wild progenitors from which pulses were domesticated have been identified, with the exception of Vicia faba. The archeological record for some pulses, particularly Phaseolus species and Lens culinaris, is more complete than for others such as Vigna unguiculata and Cajanus cajan. In whatever manner they were developed, the domesticates quickly spread across regions and continents, particularly to regions lacking a wide range of highly desirable, locally domesticated food crops such as Europe and North America. Over time, domestication, selection, and trade resulted in a wide variety of pulses grown, contributing protein to human diets across the globe. Pulse and cereal grain domestication appear to have taken place at roughly the same time in human history, which suggests that these two foods may be ancient partners in providing human nutrition. While cereals provided most of the energy and much of the protein requirements of humans, pulses played a strong supporting role as a contributor of concentrated dietary protein. Concurrent pulse and cereal production and their dietary consumption resulted in more sustainable farming systems, as well as better nutritional balance, than would have been derived from production and consumption of cereals alone.

Consumption Current grain legume consumption in many parts of the Old World and New World appears to be affected by cultural inertia; past consumption patterns in those regions are echoed in the present. While pulses are common components of diets around the world, the extent to which they contribute to the diet correlates closely with the historic availability and acceptance of animal protein. Ancient civilizations that consumed more pulses were those where animal protein was less available or acceptable. They included those that maintained high human population densities and overwhelmed local supplies of wild and domestic animal protein (East Asian Old World civilizations), those where few animals were domesticated Table 3

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(Aztec and Mayan New World civilizations), and those where predominant religious practices excluded animal protein consumption (Hindu veneration of the cow in South Central Asia). Even today, those regions of the world consume more pulses than elsewhere. Besides influencing the amount of pulse contribution to the diet, cultural inertia expresses a parallel effect on the pulse species consumed within a region. Those pulses with long records of use in a particular country or region of the world continue as dietary preferences today (Table 3). The common bean, Phaseolus vulgaris, appears to be the most universally consumed pulse species. Early in the Common Era, the 40-day fast of Jesus in the desert became the standard reference for monks belonging to the Roman Church for the custom of mortification of the body. The fasting monks were required to remain engaged in conducting the monastery’s daily functions; thus, the elders of the monastic community began, in the fourth century, to standardize the fast diet in order to ensure that their workforce received at least the nutrition required to keep the body and soul intact but without arousing earthly sensuality in monks eating flavorful food. A satisfyingly dull puree of pulses, accompanied perhaps by a vegetable soup, became typical of the single meal allowed during fasts. Monks certainly had their fill of pulses as they contemplated eternity; the fifth-century monasteries scheduled 230 fast days per year. Before widespread adoption in seventeenth-century Europe of cuisine innovations such as leavened bread, people of medieval societies typically ate warm servings of porridge twice daily. These plates or bowls of boiled gruel incorporated readily available and affordable cereal grains such as barley and wheat and also pulses such as the wild-growing or domesticated lentils first found in the Eastern Mediterranean and West Asia. Meat consumption declined with increasing population, decline of wild game stocks, and movement of people into towns and cities. World trade, natural sciences, and the influence of aristocratic culture began to influence diets in the late 1600s. Three-a-day meals became common across socioeconomic groups, and cookbooks spread food culture throughout the urban and rural societies. New foods – including spices, potatoes, and a thickener made by browning flour in fat known as roux – made their appearance and elbowed the cereal-andpulse-based porridge out of popularity. The Protestant Reformation deemphasized fasting, which further reduced the consumption of sturdy but unglamorous pulse porridges. Two vastly different problems influence contemporary grain legume consumption: malnutrition in food-deficit

Pulses consumed in various world regions

Country or region

Pulse species commonly consumed

Mexico North America Brazil The Caribbean islands India Africa The Mediterranean and Europe

Phaseolus vulgaris, P. coccineus, P. lunatus, P. acutifolius, Vicia faba Phaseolus vulgaris, P. lunatus Phaseolus vulgaris, P. lunatus, Cicer arietinum, Vigna unguiculata Phaseolus vulgaris, P. lunatus, Vigna unguiculata, Cajanus cajan Vigna radiate, V. mungo, Cajanus arietinum, Cajanus cajan, Pisum sativum, Lens culinaris, Lathyrus sativus Vigna unguiculata, Phaseolus vulgaris, P. lunatus, Vicia faba Vicia faba, Pisum sativum, Phaseolus vulgaris

Adapted from Smart J (1990) Grain Legumes: Evolution and Genetic Resources. Cambridge: Cambridge University Press.

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THE LEGUMES AND PSEUDOCEREALS | Grain Legumes and Their Dietary Impact: Overview

regions and diet-related diseases such as obesity, diabetes, and heart disease in food surplus regions. In food-deficit regions, increased consumption of pulse crops could provide a concentrated source of protein, vitamins, and micronutrients that complement traditional low-protein, high-carbohydrate grain and root-based diets. Additionally, because of the legume’s ability to support biological nitrogen fixation and its contribution to increased crop diversity, local farms could benefit from agricultural systems that integrate pulse crops adapted to the regional environment. In food surplus regions, substitution of plant-based diets for excessive meat consumption and consumption of foods rich in dietary fiber such as pulses are among the strategies promoted to combat the dramatic increase in diet-related diseases.

Composition Pulses, with roughly double the protein content of cereals, are damned with faint praise as the protein of the poor. They contribute excellent nutrition to all, but because they are inexpensive relative to meat, they are particularly beneficial to subsistence farmers and those with low disposable income in food-deficient countries. In such circumstances, pulses can account for 11% of daily protein intake and 6% of the daily energy in the human diet (Tables 4 and 5). The praise, however, is faint and damning because this association with poverty, a connection perhaps firmly established with the porridges of the Middle Ages, stigmatizes pulse foods among those with or aspiring to have higher income who increasingly favor meat protein. In developed nations, protein consumption has increased from the 1960s to now and is associated with increased consumption of animal products. Scarcely, 2% of dietary protein in developed nations, and 1% of energy, comes from pulses. In more affluent settings, pulses remain an underused alternative to high-priced animal protein. Interestingly, as noted in the preceding text, at least one segment of affluent society, lifestyle- or health-conscious eaters such as vegetarians or those seeking the nutritional benefits of high dietary fiber, still values these plants. Even so, the consumption Table 4 Protein per capita consumption in two decades by country groupings (g protein per person per day) Least developed nations Protein sources Total plant Pulses Cereals Starchy roots Oilseeds Total animal Meat Eggs Milk Fish Grand total

1962–71 a

40.3 (80) 5.2 (10) 29.1 (58) 1.8 (4) 1.6 (3) 9.9 (20) 4.1 (8) 0.3 (1) 2.8 (6) 2.1 (4) 50.2

Developed nations

2002–11

1962–71

2002–11

45.0 (78) 6.1 (11) 31.2 (54) 2.5 (4) 2.2 (4) 12.6 (22) 4.7 (8) 0.4 (1) 3.8 (7) 3.0 (5) 57.6

43.9 (48) 2.2 (2) 31.2 (34) 3.5 (4) 0.9 (1) 48.1 (52) 19.6 (21) 3.4 (4) 17.5 (19) 5.4 (6) 92.0

42.5 (42) 1.9 (2) 27.8 (28) 3.1 (3) 1.3 (1) 58.0 (58) 25.8 (26) 3.5 (3) 19.5 (19) 6.9 (7) 100.5

g capita1 day1 (% of grand total). Based on data from FAOSTAT Database – http://www.fao.org.

a

trend in developed countries between the 1960s and now is, if anything, to include slightly less pulse in diets. In contrast, the increased protein and energy consumption between the 1960s and now reported in the least developed countries (as defined by the Food and Agriculture Organization of the United Nations) results from inclusion of both more animal protein and more plant protein in the diets, including a small increase in pulse consumption. One aggravating reason for low pulse consumption is flatulence resulting from intestinal fermentation of complex sugars and dietary fiber. If gassiness causes the consumer discomfort or embarrassment, pulse foods will be avoided when other choices are available. As one might expect, food use of pulses is higher in least developed countries when compared with developed countries (Table 6). However, the percentage of total domestic pulse supply used for food in the least developed countries declined substantially over the past 40 years, while in developed countries, it increased slightly. Feed use and food use are mutually exclusive, so in the least developed countries, there is a relatively low percentage of supply used for feed, while in developed countries, there is a high percentage used for feed. Table 6 indicates that on average both the least developed and the developed countries exported more pulse seed than they imported, with the exception of developed countries in the 1960s. Trade Table 5 Energy per capita consumption in two decades by country groupings (kcal per person per day) Least developed countries

Developed countries

Protein sources

1962–71

2002–11

1962–71

2002–11

Total plant Pulses Cereals Starchy roots Oilseeds Total animal Meat Eggs Milk Fish Grand total

1818 (93)a 79 (4) 1248 (64) 171 (9) 43 (2) 142 (7) 54 (3) 3 (0) 53 (3) 13 (1) 1961

2055 (92) 94 (4) 1324 (59) 202 (9) 50 (2) 180 (8) 67 (3) 5 (0) 70 (3) 19 (1) 2236

2176 (71) 34 (1) 1030 (34) 146 (5) 19 (1) 886 (29) 277 (9) 42 (1) 296 (10) 35 (1) 3061

2339 (71) 28 (1) 954 (29) 132 (4) 30 (1) 935 (29) 352 (11) 44 (1) 313 (10) 48 (1) 3274

a kcal capita1 day1 (% of grand total). Based on data from FAOSTAT Database – http://www.fao.org.

Table 6 Pulse domestic production and utilization in two decades by country groupings (% of total domestic supply) Least developed countries

Developed countries

Source

1962–71

2002–11

1962–71

2002–11

Domestic production Food use Feed use Imports Exports

109 81 1 1 10

108 66 16 8 15

101 31 57 9 7

137 34 54 24 60

Based on data from FAOSTAT Database – http://www.fao.org.

THE LEGUMES AND PSEUDOCEREALS | Grain Legumes and Their Dietary Impact: Overview movement of pulses, however, is much more complex than can be summarized using these aggregates of countries grouped by economic development. The reader is encouraged to examine trade data at the regional and country levels in order to discern how pulses are moving around the globe.

Protein Complementation Understanding amino acid balance is key to recognizing the special contribution made by grain legumes to protein complementation in cereal-based diets. Different sources of plant protein are made up of characteristic concentrations of indispensable (essential) amino acids and therefore contribute upon digestion a different balance of amino acids for human nutrition. Amino acid balance in a particular protein source can be scored against that of a reference protein, typically hen’s egg (regarded as well balanced in relation to adult human metabolic needs) or milk (Table 7). No plant-based protein mimics the indispensable amino acid balance present in eggs, so it follows that each type of plant protein must exhibit a characteristic set of limiting amino acids. For example, whole wheat flour and whiteseeded common beans generally have lower proportions of the indispensable amino acids than eggs or milk does. In particular, the amino acid lysine limits efficient utilization of wheat protein in human metabolism, while the indispensable sulfurcontaining amino acid methionine limits bean protein. The indispensable amino acid balance of wheat and bean is characteristic of other cereal grains and pulses. Cereal grains are typically deficient in lysine but high in methionine, while the opposite is the case for pulses: high in lysine and low in methionine. Cysteine, a dispensable sulfur-containing amino acid synthesized from methionine and serine, is in many references listed along with methionine as a limiting amino acid of pulses. Plant protein complementation, accomplished by consuming protein from more than one plant source, can provide humans with a balanced diet of amino acids approximating that found in hen’s egg. Grain legumes, with their high concentration of lysine relative to lysine-deficient cereals, and cereals, with their high concentration of methionine and cysteine relative to that found in pulses, combine as ideal dietary partners, because the amino acids making up their proteins are very good complements. For example, at 0.7 g kg1 body mass per day, an 85 kg adult would require 60 g of protein per day containing Table 7

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at least 2820 mg lysine. This requirement could be satisfied by consumption of 288 g of wheat (Triticum aestivum) and 124 g of bean (Phaseolus vulgaris) (Tables 2 and 7). To meet the lysine requirement through consumption of wheat alone, the same adult would need to eat 960 g wheat containing 108 g total protein. The intentional combination of cereals and pulses at meals offers inexpensive (in comparison with meat) plant-based diets with balanced amino acid composition. While the central theme of this overview is the enormous contribution made by dry grain legume seeds, and in particular pulse seeds, to the human diet, these crops have other food uses. Some species are used as vegetables, as either green mature or immature seeds or pods, as sprouted seeds, or even as stocks for fermentation. As noted earlier, soybean is the base of many nonfermented and fermented foods such as tofu and tempeh. Fermented pulse seeds – primarily involving black gram (Vigna mungo), Bengal gram (Cicer arietinum), and green gram (Vigna radiata) – are components of diets particularly in India as ‘idli,’ ‘dhokla,’ and ‘khaman.’ Fermentation, sometimes in combination with cereal grains, causes desirable reduction in beany flavor, aroma, and consistency and improves digestibility. Nonfood uses include dry seeds used as animal feed and forage from pulse vegetation, in aquaculture feeds, and even as ornamentals. In a Southeast Asian setting, well-established shrubs of pigeon pea, a short-term perennial grown on field banks or as an intercrop, as well as dry season-grown horse gram and cowpea, can be intermittently grazed or cut for hay. N concentration of the hay varies between 2.5% and 4.5%, but livestock may need a few days to be accustomed to the feed. Dairy cattle are reported to similarly consume and utilize faba bean silage and grass–legume silage. From a cool season perspective, the seeds of soybean, pea, lentil, faba bean, and chickpea can be used as a protein source in livestock feed. Oil and fiber contents of the seeds affect the metabolizable energy (MEn) values of pulses when fed to various types of livestock. For example, the relatively lowoil, high-fiber pea has a low (2570 kcal kg1) MEn when fed to poultry, while for swine, the pea MEn is much higher (3740 kcal kg1). The pulse seed amino acid profile for monogastric feeds, while good, is inferior to soybean. Pea and faba bean protein is highly digested, but some livestock feeding studies have shown an increased excretion of endogenous protein, which may be due to seed antinutrients. Dry roasting the whole seeds has been shown to improve

Indispensable amino acid requirements in dietary protein and the amino acid composition of selected foods (mg amino acid per g protein)

Amino acid

Infant requirement

Adult requirement

Hen’s egg

Cow’s milk

Whole wheat flour

White bean flour

Histidine Isoleucine Leucine Lysine Methionine þ cysteine Phenylalanine þ tyrosine Threonine Tryptophan Valine

23 57 101 69 38 87 47 18 56

17 23 52 47 23 41 24 6 29

24 63 88 70 56 98 49 16 72

28 60 98 79 34 96 45 14 67

22 40 63 26 35 81 27 11 43

28 42 76 72 19 77 39 10 46

Based on data from Anonymous (2002) Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Protein and Amino Acids (Macronutrients), Chapter 10, p. 71. Washington, DC: National Academies Press (online version available on p. 535 at the URL http://www.nap.edu/books/0309085373/html/).

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digestibility and protein utilization. Pulses have great potential for use in aquaculture diets, but in this application, they are hampered by their carbohydrates. However, field peas (Pisum sativum), faba beans (Vicia faba), chickpeas (Cicer arietinum), and vetch (Vicia sativa) seeds can be used in aquaculture feeds for juvenile silver perch following dehulling, which removes much of the undesirable carbohydrate fraction.

Antinutritional Factors Low digestibility hampers full utilization of grain legume protein. In part, the problem may result from the more rapid discharge, relative to other foods, of digesting pulses from the intestinal tract and reduced protein hydrolysis by gut enzymes. However, antinutritional factors, compounds in pulses that interfere with their digestion and metabolism, also play a major role in restricting dietary utilization in some pulse species. These compounds generally include proteinaceous molecules such as protease inhibitors (particularly trypsin inhibitors) and lectins and also nonproteinaceous compounds such as tannins. Most of the wild relatives of pulses contain toxins and antimetabolites. One of the key features of pulse domestication from wild forms is human selection for lower levels of these compounds. Traditional food preparation techniques used for pulse seeds result in reduction or elimination of these metabolic impediments. Some modern food pulses today, in particular the Phaseolus species, can still contain sufficiently high levels of antinutritional factors in their dry seeds to cause digestive difficulties if eaten without proper processing. For this reason, pulse seeds are not eaten raw, but processed in a way (moist heat >100 C, sprouting, and fermentation) that inactivates the antinutritional factors. Protease inhibitors, a major class of antinutritional factors in pulses, often inhibit the digestive enzyme trypsin but may act more broadly by inhibiting chymotrypsin and other serine proteases. The role of these inhibitors in the plants that produce them is uncertain but may involve defense against disease and insects. An alternative explanation is that these compounds might simply serve as protein reserves high in sulfurcontaining amino acids such as cysteine and coincidentally inhibit human digestion. The primary concern regarding raw pulse consumption is with very young humans and other young animals that are more susceptible to the effects of protease inhibitors than adults. In vitro studies suggest that protease inhibitors can impair nutrient utilization and reduce growth rates in these groups. In vivo animal studies indicate that interference with growth occurs primarily when the level of dietary protein itself is limiting. Pancreas activity can be affected when dietary protein digestion is inhibited and high levels of undigested protein interfere with appropriate pancreatic regulatory control. Since pulses are used in some human infant diets, cooking must be done with particular care to ensure that protease inhibitors are inactivated. Lectins, another major class of antinutritional factors in pulses, are proteins that bind to carbohydrates or to molecules containing carbohydrates. This binding capacity allows them to agglutinate red blood cells (lectins are sometimes called

phytohemagglutinins) of different animal species depending on the specific receptors on the cell membrane surface. This agglutination specificity provides a method of rapid detection and classification. Lectins differ in the severity of their impact. Some (mainly found in Phaseolus vulgaris) are classified as toxic, others are considered only growth inhibitory (Phaseolus lunatus), and still others essentially nontoxic (Pisum sativum, Lens culinaris, and Vicia faba). The role of lectins in the plant is not well established, although they appear to help the plant defend itself against specific bacteria, fungi, and insects. They may also aid processing and movements of glycosylated storage materials during seed maturation, assist in the establishment of the symbiotic relationship of legumes and rhizobia, and promote cell growth and division. Or, like protease inhibitors, lectins may simply serve as storage proteins. The effect of ingested lectins on human and other animal metabolisms varies according to the lectin type, the species ingesting the protein, and the age, nutritional, and health status of that human or animal. To affect human metabolism, plant lectins first must bind to epithelial cells in the gut. This binding requires the presence of particular carbohydrate groups on the lumen of the gut epithelial cells. Dietary lectins strongly resist proteolytic degradation in the gut. Toxic dietary lectins can modify hormone balance and lipid and muscle metabolism. These modifications deplete stores of lipid, glycogen, and protein and lead to weight loss. Some nontoxic lectins bind to the gut epithelium but have no deleterious effect on metabolism, while others exhibit only limited binding capacity. Deleterious lectin effects appear to be reversible. Tannins can form strong cross-linked complexes with dietary proteins and enzymes. The antinutritional impact of tannins on digestion and metabolism is not fully understood. Protease inhibitors and lectins are heat labile and rendered innocuous by usual methods of cooking. Moist heat treatment – such as the traditional soaking of beans, followed by cooking in boiling water – is generally considered to be sufficient to inactivate protease inhibitors. Soaking may help leach out some tannins, but heat treatment will not reduce the impact of that remaining in the seeds. Particular grain legume species accumulate additional classes of antinutrients. For example, Lupinus albus seeds may contain quinolizidine alkaloids that give the seeds a bitter flavor and, if not successfully removed prior to ingestion, can result in poisoning. A. hypogaea cotyledons contain lowmolecular-weight glycoproteins to which some individuals exhibit allergic reaction upon contact and ingestion. Neuroand osteolathyrism, the former a reversible paralysis and the latter a skeletal abnormality, have been linked to excessive consumption of grass pea (Lathyrus sativus) seeds. Broad bean (Vicia faba) antinutrient levels are low and do not require moist heating or fermentation to inactivate but can induce favism, a hemolytic anemia, in individuals with congenital deficiency of glucose-6-phosphate dehydrogenase. Pulses of Mediterranean origin – such as peas (Pisum sativum), chickpeas (Cicer arietinum), and lentils (Lens culinaris) – generally have low toxic and antinutrient levels. While protease inhibitors have been found in cowpeas (Vigna unguiculata), they are apparently not present in serious levels, nor have harmful quantities of cowpea lectins been reported. Vigna mungo and Vigna radiata seeds likewise contain little in the way of antinutritional factors.


Agronomy The Leguminosae family is enormous, with an estimated 16 000–19 000 species in 750 genera. If the raw number of species were to determine the greatness of a family, Leguminosae would be eclipsed only by Orchidaceae and Compositae. If instead the economic value of a family were considered, legumes would be second only to Gramineae. Taxonomists place pulses in the legume subfamily Papilionoideae, mostly in tribe Phaseoleae, but a few in the tribes Vicieae, Cicereae, and Genisteae. Cropping systems develop in response to the demand for particular crops, soil nutrient status, soil physical structure, and biotic competition and are constrained by available resources (including climate) and knowledge. Pulses in temperate cropping systems are commonly planted in monocultures as part of a rotational sequence with maize (Zea mays), small grain cereals, or occasionally forages or periods of fallow in dryland areas. Since in these cropping systems pulses are typically cash crops and occasionally feed crops, their inclusion in the rotation and total acreage from year to year depends on the status of cash markets and economic benefits of growing that pulse crop relative to other crops, rather than with maintaining a set crop rotation, maintaining particular soil characteristics, or addressing biotic competition. Higher-value crop alternatives may be readily substituted for pulses in the rotation in some climates. National farm strategies with strong economic impact, such as government subsidies or deficiency payments, can affect pulse production by inclusion or exclusion of particular pulse crops from the programs. For example, in the United States, the Agricultural Act of 2014 identifies specialty crops, including pulse crops, for indirect support such as assistance with marketing, promotion and trade, crop insurance, and research and research-based information extended to growers. While not a big producer of any of these pulse crops, the United States is an exporter, and additional production stimulated by the Agricultural Act could affect prices in other pulseexporting or pulse-importing countries. Leguminosae will collaborate with genus Rhizobium bacteria in an ecologically unique symbiotic relationship. This symbiosis supports biological nitrogen fixation and frees legumes from the need to access soil sources of fixed nitrogen. Rhizobia invade the legume root hairs and reside in cortical root swellings (nodules) where nitrogen from the atmosphere is fixed for eventual transport within the plant and assimilation into protein. Even though a legume can support the symbiotic relationship, it will not occur unless the rhizosphere contains compatible rhizobia. Strains of rhizobia differ according to the particular legume hosts that they will inoculate and are classified according to this host range. Cropping systems in developing countries typically rely on intercropping where pulses are planted along with other species, commonly cereals and vegetables. The intercropping strategy can provide subsistence farmers with several essential foods from one plot of land, produce higher protein yield per hectare, combine complementary canopy structures (lowstature pulses with high-stature sorghum (Sorghum bicolor) and maize (Z. mays)), balance utilization of soil moisture following rainy periods, or reduce crop competition by weeds and insects. It is unlikely that a nonlegume companion crop of

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similar growth period will benefit directly from the pulse crop’s nitrogen fixation, but perennials, crops with longer growth periods, or subsequent crops may benefit from the nutrients released through the decomposition of pulse crop litter. The agronomic impact of a legume crop on the intercrop will depend on the crop species (and even the cultivar) in the intercrop, the extent of its inclusion in the plot, tillage, and soil type. Pulses can assist in soil improvement, particularly when used as green manure crops when the whole plant is plowed down into the soil. Fixed nitrogen and in some cases phosphorus are made available to subsequent crops, and the added organic matter contributes to improved soil structure. Also, the deep tap roots of some crops such as pigeon pea reduce soil erosion and mine deep soil for nutrients that are returned to the surface through leaf drop. In sustainable shifting cultivation systems of intercropping, a few years of crop production are followed by a decade or more of bush fallow where cropping is suspended and native vegetation regrows. Cultivated pulses grown during the cropping years provide concentrated protein for human diets using nitrogen fixed from the atmosphere and help maintain the soil nitrogen status by not depleting fixed soil nitrogen. During the bush fallow stage, indigenous legumes, including trees, contribute to the restoration of soil nitrogen. When the human population density is low, relative to available land, and bush fallow periods are sufficiently long to restore soil nutrients, shifting cultivation can be sustained. With increased population or decreased land base, the cropping period must be extended, bush fallow period reduced, and as a result, soil nutrient status and crop productivity decline. Since in most cases pulse crops are not alternate hosts for cereal crop diseases, their use in crop rotations will help reduce cereal disease inocula. However, pulses are certainly not immune to pests; they are attacked by many fungal, bacterial, and viral diseases and a range of sucking, boring, and chewing insects. Also, pulses are typically poor competitors against weeds, except perhaps under stress conditions such as drought conditions where annual weeds are also checked. At harvest time, pulses often disappoint and frustrate growers by failing to meet yield potential. Pulses are often considered to be extremely sensitive to environmental stress, relative to the more robust cereals, a sensitivity which may in part be associated with maintaining the symbiotic relationship with Rhizobium. The Rhizobium–Leguminosae symbiosis requires energy supplied by the host plant to support the metabolic needs of the bacterial colonies in return for assimilated nitrogen. In the case of the pulses, which are typically grown as annual crops, the symbiotic relationship must be reestablished with every new crop. Farmers watching the color of the growing annual pulse crops in their fields can clearly see the lag time between planting and the establishment of functioning nodules. For example, a temperate common bean crop planted in a soil with compatible rhizobia will tend to have a deeper shade of green about a month after planting, as fixed nitrogen becomes available to the plant. During the early portion of the growing season, the host plant pays the costs of establishment and only later receives the benefits. Plantgenerated energy used to support the symbiotic relationship is not available to the plant for dry matter production, so some

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amount of yield penalty should be anticipated. Effective nodulation and nitrogen fixation depend on favorable interactions between the host and appropriate Rhizobium genotypes and the environment. If these interactions falter and nitrogen fixation lags behind demand, dry matter production will suffer.

Final Words Declining per capita pulse consumption, particularly given the nutritional value of pulses and their affordability, is a cause for concern. Although some regions in developed countries now benefit from new pulse export opportunities and are increasing production, this expansion reflects changing markets and increased population, not increased dietary utilization. Much more global impact could be accomplished by addressing constraints to consumption, including the social stigma associated with eating poor pulses compared with rich meat, flatulence, yield variation, and agronomic constraints to product quality and stable high yield. Further increasing pulse consumption in developing and low-income countries may be impossible given the strength of the human drive toward diets associated with affluence. Perhaps, the greatest initial gains could occur among consumers in developed countries currently with very low pulse consumption. The keys to higher consumption in those countries may involve increasing the availability of value-added pulses such as those produced by certified organic methods or food quality assurance programs and highlighting their inclusion in national and regional cuisine initiatives. In tandem, these efforts to add value and visibility could impart some cache to pulses and improve their appeal. Then said Daniel to Melzar, whom the prince of the eunuchs had set over Daniel, Hananiah, Mishael, and Azariah, prove thy servants, I beseech thee, ten days; and let them give us pulse to eat, and water to drink. Then let our countenances be looked upon before thee, and the countenance of the children that eat of the portion of the king’s meat: and as thou seest, deal with thy servants. So he consented to them in this matter, and proved them ten days. And at the end of ten days their countenances appeared fairer and fatter in flesh than all the children which did eat the portion of the king’s meat. Thus Melzar took away the portion of their meat, and the wine that they should drink; and gave them pulse. Daniel 1:11–16 (RSV)

• • • • • • • •


• • • • • •


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What seed constituents are similar between pulses and oilseed legumes? What seed constituents differ? Which grain legume’s seed constituents are roughly intermediate between pulses and oilseed legumes? How do seed constituents of grain legumes compare with those of cereal grains? Did domestication of grain legumes generally occur in the same region of the world or in vastly different regions? Provide examples that support your answer. Identify at least two reasons why pulse consumption tends to be high in regions of the world where meat consumption is low.

Which pulse crop is the most universally consumed? A porridge made of grain legumes and cereal grains was a common food in medieval societies. What events and cultural shifts resulted in the decline of porridge in diets? When did this transition take place? Review the change in protein consumption from pulses and from meat in the 1960s compared with recent years. How do the trends differ between developed and developing nations? Identify examples of protein complementation in your diet. Do any of your examples involve combinations of cereal grains and grain legumes? What are examples of nonfood uses of grain legumes? Identify a reason for and a reason against using grain legumes for animal feed. Why are pulse seeds not eaten raw? What types of processing are necessary and how do they change the grain? How would you integrate grain legumes into a cropping system? What benefit would they provide to the system? Describe the symbiosis that is key to the role of grain legumes in the cropping system. What constraints to consumption must be addressed before grain legumes can play a larger role in global nutrition?

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Can you outline a climate change scenario that would influence the production and consumption of grain legumes? Genetic transformation is not a common strategy for the improvement of pulse crop cultivars. Why is this? What factors might encourage or discourage the development of GMO pulse cultivars? What are the key challenges in producing pulse crops in organic production systems? What are the benefits? Few ‘fast-food’ outlets include pulse-based foods on their menus. Why is this? What types of meals made from pulses might have promise as a fast and nutritious food? What types of research have been conducted on the impact of pulse-based foods on cancer and obesity? What have been the outcomes of those research projects? How can the social stigmas associated with pulse-based foods (poverty and flatulence) be overcome? How could the legume–Rhizobium symbiosis be improved?

See also: The Basics: Taxonomic Classification of Grain Species; The Oilseeds: Oilseeds: Overview; Soybean: Overview; Grains Around the World: Grain Production and Consumption: Overview.

Further Reading Adams MW and Pipoly III JJ (1980) Biological structure, classification and distribution of economic legumes. In: Summerfield RJ and Bunting AH (eds.) Advances in Legume Science, pp. 1–16. Kew, UK: Royal Botanic Gardens. Allen ON and Allen EK (1981) The Leguminosae: A Source Book of Characteristics, Uses and Nodulation. Madison, WI: University of Wisconsin Press.

THE LEGUMES AND PSEUDOCEREALS | Grain Legumes and Their Dietary Impact: Overview Booth MA, Allan GL, Frances J, and Parkinson S (2001) Replacement of fish meal in diets for Australian silver perch, Bidyanus bidyanus: IV. Effects of dehulling and protein concentration on digestibility of grain legumes. Aquaculture 196: 67–85. Dembin´ska M (1986) Fasting and working monks: Regulations of the fifth to eleventh centuries. In: Fenton A and Kisbań E (eds.) Food in Change, pp. 152–160. Edinburgh: John Donald Publishers. Duke JA (1981) Handbook of Legumes of World Economic Importance. New York: Plenum Press. FAO (2002) Agriculture 21. Agriculture Department, Food and Agriculture Organization of the United Nations. Rome, Italy: FAO Publishing and Multimedia Service (http:// www.fao.org/ag/). Huisman J and van der Poel AFB (1994) Aspects of the nutritional quality and use of cool season food legumes in animal feed. In: Muehlbauer FJ and Kaiser WJ (eds.) Expanding the Production and Use of Cool Season Food Legumes, pp. 53–76. Dordrecht, The Netherlands: Kluwer Academic. Jansman AJM, Hill GD, Huisman J, and van der Poel AFB (eds.) (1998) Recent Advances of Research in Antinutritional Factors in Legume Seeds and Rapeseed. Wageningen, The Netherlands: Wageningen Pers. Labuza TP and Erdman Jr. JW (1984) Food Science and Nutritional Health: An Introduction. St. Paul, MN: West Publishing. Marquardt RR and Bell JM (1988) Future potential of pulses of use in animal feeds. In: Summerfield RJ (ed.) World Crops: Cool Season Food Legumes, pp. 421–444. Dordrecht, The Netherlands: Kluwer Academic. Reddy NR, Pierson MD, and Salunkhe DK (eds.) (1986) Legume-Based Fermented Foods. Boca Raton, FL: CRC Press.

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Reeds PJ and Beckett PR (1996) Protein and amino acids. In: Ziegler EE and Filer Jr. LJ (eds.) Present Knowledge in Nutrition, 7th edn., pp. 67–86. Washington, DC: ILSI Press. Sinha SK (1977) Food Legumes: Distribution, Adaptability and Biology of Yield. Rome, Italy: Food and Agriculture Organization of the United Nations. Smart J (1990) Grain Legumes: Evolution and Genetic Resources. Cambridge: Cambridge University Press. Summerfield RJ and Roberts EH (eds.) (1985) Grain Legume Crops. London: Collins Professional and Technical Books. ’t Mannetje L and Jones RM (eds.) (1992) Plant Resources of Southeast Asia. No 4. Forages. Wageningen, The Netherlands: Pudoc Scientific Publishers. Toussaint-Samat M (1992) History of Food. Cambridge, MA: Blackwell Publishers (translated from the French by Bell A).

Relevant Websites http://www.fao.org – FAOSTAT Database, a comprehensive resource for agricultural production data, including than on pulse crops. http://www.icarda.org – The website of the International Center for Agricultural Research in the Dry Areas, based in Syria, has useful information on pulse agronomy and utilization.

Pseudocereals: Overview RJ Fletcher, University of Queensland, Gatton, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 488–493, ã 2004, Elsevier Ltd.

Topic Highlights

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A pseudocereal is a plant grown to produce starchy grain suitable for human food, excluding the cereals, legumes, oilseeds and nuts. The term “pseudocereal” combines “cereal”, referring to grains of grass species, with the prefix “pseudo-” meaning “false” or “resembling”. The major pseudocereals are grain amaranth, quinoa and buckwheat. o Amaranth (“Inca wheat”); the seeds are used sprouted, toasted, ground into flour, baked, cooked as porridge and popped. o Quinoa is rich in protein, fat and fiber, with a good balance of essential amino acids. o Buckwheat (unrelated to wheat) is milled into grits for breakfast food or roasted to be boiled, steamed or baked. Most pseudocereals have smaller seeds than the major cereal grains. Many pseudocereals can grow in poor soils and situations not suitable for other grain species. A large number of species are described that have the potential to be useful as pseudocereals.

The proportion of embryo, endosperm, or perisperm within any grain is primarily determined by a plant’s genetic make-up. The eventual composition of the grain can be influenced by the natural growing conditions and the manner in which the crop and its product have been managed. Important environmental factors not only include the growing conditions but also the method of harvesting, the manner in which the grain was stored, the nature of any processing carried out, including the extraction method used, and the presence of any antinutritional factors. Grains used in the human diet come from surprisingly few crops. Such crops are collectively referred to as the cereals (including crops such as wheat, rice, maize, barley, oats, rye, etc.), pulses (including bean, chickpea, cowpea, pigeonpea, lentil, lupin, etc.), oilseeds (including canola, sunflower, safflower, sesame, coconut, cottonseed, flaxseed, mustard, etc., as well as some pulse crops, such as soybean and peanut) or pseudocereals. There can be some confusion with the use of such crop groupings, since each grouping is not mutually exclusive; for example, some pulse crops are used as oilseed crops and the term pseudocereal is sometimes used to refer to crops more commonly identified as oilseeds or legumes.

Learning Objectives

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Understand the range of grains in the category of pseudocereals, and the potential advantages they offer with respect to growth situations, utilization and nutritional attributes.

Introduction Most human foods come from plants. Roots, underground storage or propagation organs, stems, petioles, shoots, flowers, or fruits are eaten. Fruits in the form of grains or seeds are the major form of human food. Almost all of the grains eaten by humans are cereals. A cereal grain contains an embryo and usually a quantity of endosperm, enclosed within a seedcoat. Cereals are one type of monocotyledonous plant (all of which present a single shoot on germination); pseudocereals are noncereals, comprising noncereal monocotyledonous plants as well as dicotyledonous plants; the latter have grains containing no endosperm but an embryo enclosing perisperm. The usefulness of any grain as human food (its functionality) depends on the quantity and quality of protein, starch, and lipid (fats and oils) present in the tissues of the grain (embryo, endosperm and/or seedcoat). Grain functionality depends principally on the genetic and environmental influences on protein, starch, and lipid.

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Definition The American Heritage Dictionary of the English language defines a pseudocereal as “any of several plants, such as quinoa, that do not belong to the grass family but produce fruits and seeds used as flour for bread and other staples.” The Oxford English Dictionary defines the term cereal as “a name given to those plants of the family Graminaceae [now Poaceae] or grasses which are cultivated for their seed as human food . . . sometimes extended to cultivated leguminous plants.” The term pseudo is defined as “false, pretended, counterfeit, spurious, sham, falsely so called or represented.” When combined with another element, such as the term cereal, pseudo is defined as “indicating close or deceptive resemblance to the thing denoted by the second element, without real identity or affinity with it.” The term pseudocereal is best used to refer to a plant which is grown as a crop to produce starchy grain suitable for human food, excluding plants already classified in a grouping such as the cereals (those species from the grass family Gramineae), legumes (those species from the legume families Leguminosae-Caesalpinioideae, Leguminosae-Mimosoideae, and Leguminosae-Papilionoideae), oilseeds (those species described in terms of the commercially useful lipid or tricylglycerol content), or nuts.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00039-5

THE LEGUMES AND PSEUDOCEREALS | Pseudocereals: Overview

Current Role of Pseudocereals The pseudocereals are relatively unimportant on a global scale today. However, they have been significant contributors to the human diet in certain defined regions in the past and could be developed again as important new crops. For example, pseudocereals may play a role in human nutrition for those who have allergies to traditional cereals; for the primary producer, pseudocereals can play a role in cereal rotations, reducing the buildup of grass weeds, pests, or diseases. The three best-known pseudocereal crops are grain amaranth (Amaranthus caudatus; A. cruentus; A. hypochondriacus; family: Amaranthceae), quinoa (Chenopodium quinoa subsp. quinoa; Chenopodiaceae), and buckwheat (Fagopyrum esculentum; Polygonaceae). Each is briefly described below, from the viewpoint of functionality. A range of potential pseudocereals from other plant families is then presented, with dicotyledonous families followed by monocotyledonous families.

Weeds Many of the species listed as potential pseudocereals below are currently regarded, in some areas, as weeds; one of them, Amaranthus retroflexus, could be regarded as the world’s most cosmopolitan weed. A weed is defined as a plant which is growing in the wrong place. If some of the potential pseudocereals listed below can be commercialized, they would no longer be regarded as weeds.

with sugar to make confectionery items, rolled into balls, cooked as porridge or popped. Grain amaranth has enjoyed a resurgence in recent years, especially through the health food market, since its crude protein is high (14–19%), with a high lysine (up to perhaps 6% of the protein) and tryptophan content. It appeals to the modern consumer since these essential amino acids are low in cereals. Grain amaranth is being developed as an energy food to be combined with traditional cereal grains in breakfast food, bread, multigrain crackers, pastes, pancake mixes, or popped as a snack food product. Popping can, however, affect its nutritional quality. The grain is easy to digest and heat processing improves its digestibility. Amaranth starch (up to 69% of the grain) is principally amylopectin; granules are relatively small (1–3 mm) compared with cereals (3–30 mm) and have a higher solubility and gelatinization temperature, rendering a distinctive gel. The seed can comprise as much as 10% oil; this oil contains squalene, which is used in cosmetics manufacturing. Antinutritional trypsin inhibitors occur in concentrations up to twice that observed in wheat.

Potential pseudocereals in the Amaranthaceae family

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Warning The historic use of any obscure plant by a culture for medicinal or similar personal use does not mean that the plant is safe for use as a human food. Poisonous or antinutritional factors exist in many plants and their historic use was often complemented by elaborate preparation to reduce the effect of any poison. As an example, Australian aborigines were able to consume cycad seeds and yams but only after extensive preparation, which reduced the toxicity of the material. Regular use of a plant over a lifetime by a group of people may also render a plant relatively safe for that group of people, whereas a newcomer who has never eaten the food can suffer serious effects on eating it for the first time.

Amaranthaceae Amaranthus caudatus, A. cruentus, A. hypochondriacus (grain amaranth) Amaranthus caudatus (Inca wheat, love-lies-bleeding) is native to the northern higher-altitude regions of Bolivia, Peru, and Ecuador, whereas Amaranthus cruentus (Purple amaranth) and Amaranthus hypochondriacus (Prince’s feather) are native to Guatemala and Mexico. The species were grown by preColombian civilizations, Aztecs, and indigenous US tribes but have mostly been replaced by cereal crops. Depending on the species, grain amaranth seeds are sprouted, parched, toasted, ground into flour, baked, mixed

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Amaranthus dubius (spleen amaranth, khada sag), Amaranthus frumentaceous (poong keeray, tola kura), Amaranthus tricolor (tampala), Amaranthus graecizans (spreading pigweed), Amaranthus blitum (livid amaranth), Amaranthus quitensis (yuyo colorado, sangorache), Amaranthus retroflexus (redroot, pigweed), Amaranthus spinosus (spiny amaranth): the seeds are eaten raw in India and other places or mixed with other grains or processed into flour or other products. Achyranthes aspera (devil’s horsewhip, prickly chaff-flower): the seeds have been used in desert areas in India as a famine food. Celosia argentea var. argentea (red-fox), Celosia argentea var. cristata (cockscomb): the seeds of these species have been used as famine foods.

Chenopodiaceae Chenopodium quinoa subsp. quinoa (quinoa)

Chenopodium quinoa subsp. quinoa is native to the border areas between Peru and Bolivia. It held a special position in the agricultural and ceremonial life of the Inca people and was grown in Colombia, Peru, the southern areas of Bolivia, the northern areas of Argentina, and the central areas of Chile. Quinoa grain has a protein content ranging as high as 22.8%, a carbohydrate content up to 77.4%, a fat content up to 9.5% (and relatively stable), and a fiber content up to 5.8%. The grain is higher in protein, fat and fiber, and lower in carbohydrate content than most comparable cereals, due principally to the proportional size of the embryo within the grain (up to 30% of the grain’s gross weight, compared with 1% for most cereals). The proteins in quinoa are principally albumins and globulins, which are at higher concentrations than is normally

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found in the major cereals (wheat, rice, or maize). The amino acid balance (higher in histidine, lysine, isoleucine, methionine, and cysteine content) and mineral content (calcium, magnesium, phosphorus, potassium, and iron) of quinoa grain is superior to most cereals. However, there are saponins in the seedcoat which have antinutritional properties.

Potential pseudocereals in the Chenopodiaceae family

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Chenopodium album (fat hen, lamb’s quarters). The seed is sprouted or ground into flour for breads, pancakes, muffins, and biscuits in Russia and China; the grain is reported to have 16.1% protein, 6.9% fat, 48.9% carbohydrate, and 5.8% ash. Chenopodium ambrosioides (wormseed, Mexican tea). In the Himalayas, the seed is ground into flour and mixed with warm water or roasted or added to alcoholic beverages; care needs to be taken with its preparation and use. Chenopodium berlandieri subsp. nuttalliae (southern huauzontle). The seed is ground to a meal and used for bread or gruel (a light form of porridge produced by boiling meal in water or milk). Chenopodium murale (nettle-leaf goosefoot, sowbane). The seed is popped or parched and ground to make gruel. Chenopodium pallidicaule (canihua). The seed is toasted and ground into a flour and eaten as a breakfast food, mixed with wheat flour in baked products or drunk as a beverage. Chenopodium sp. (California Yokuts lamb’s quarters). This selection was used as a semi-domesticated grain crop by Yokuts Indian villages, in the Central Valley, California. Atriplex canescens (fourwing saltbush). The seed is ground into meal and used as flour, or as a beverage. Atriplex confertifolia (shadscale). The seed is ground into meal and used for bread or mush (a heavier form of porridge than gruel, produced by boiling meal in water or milk). Atriplex hortensis (orache). Flour is prepared from the seeds and used in soup and muffins; the seed is reportedly rich in vitamin A. Atriplex lentiformis (quail bush) and Atriplex polycarpa (all scale).The seeds are eaten by the Native American Pima group, located in Arizona. Atriplex patula (halberd-leaved saltbush). The seed is ground and mixed with corn and steamed as meat balls by the Zuni Indians. Atriplex prostrata (hastate saltplant). The seed is ground into flour for use in baked products. Haloxylon sadicornicum.The seeds are mixed with other grains for bread making in India. Suaeda corniculata and Suaeda heteroptera. The seeds are eaten raw in Manchuria. Tecticornia verrucosa. The seeds are ground to flour by Australian aborigines and baked.

Polygonaceae Fagopyrum esculentum (buckwheat)

Buckwheat originated from south central China. This crop is harvested with its green pericarp intact; once the pericarp (hull) has been removed, the groat can be coarsely milled into grits for breakfast food or roasted and sold in whole

or a granulated form to be boiled, steamed, or baked. Buckwheat flour itself is used in soba-style Japanese noodles, polenta (a form of porridge), desserts, ice cream cones, dietetic foods, and canned meat or vegetable products and as a component (30–40%) of the flour used in pancakes, breads, pasta products, cakes and dumplings, often combined with wheat flour. It is expected that buckwheat flour could be used more readily in specialty breads, pasta, extruded snack food, and ready-to-eat cereals. The proteins in buckwheat grain are principally globulins with a small proportion of prolamins; buckwheat protein has twice the lysine content of wheat or white rice. The grains are relatively high in potassium, magnesium, phosphate, iron, and vitamins B1 and B2.

Potential pseudocereals in the Polygonaceae family

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Fagopyrum cymosum (perennial buckwheat) or Fagopyrum tataricum (Tartary buckwheat). In the Himalayas, the seeds are eaten or ground into flour. Calligonum polygonoides (phog, phogalli).The seeds are eaten raw in India. Polygonum aviculare (knotgrass, gooseweed). The seeds are eaten or ground into flour for use in cookies or pancakes; they are sometimes mixed with wheat; care needs to be taken with their preparation and eating. Polygonum glabrum (sauri arak, jioti, aatlaria). The seeds are parched and made into a kind of Indian “sattu” (a traditional weaning food mix often eaten by adults, usually based upon roasted Bengal gram, wheat, and sugar with spices added and served in a number of ways, including as a porridge). Polygonum orientale (Prince’s feather).The seeds are eaten in China. Polygonum plebeium (chimtee sag, raniphul, machichi). The seeds are crushed on stones, cooked, and eaten in the form of a damper; the dry seed contains 17.4% protein, 50.4% carbohydrate, 3% fat, and 16.2% fiber. Rumex acetosa (sorrel dock). The seeds are used as a base for bread in Scandinavian countries; care needs to be taken with their preparation and eating. Rumex acetosella subsp. acetosella (sheep sorrel). The seeds are ground into flour to make a flat bread called sygrasbrod. Rumex crispus (curled dock). The seeds are ground into meal or flour and used in pancakes; care needs to be taken with preparation and eating.

Potential Pseudocereals in Other Dicot Families Other dicotyledonous families with potential pseudocereal species producing starchy grains include: Bixaceae, Cactaceae, Cannabidaceae, Caryophyllaceae, Chloranthaceae, Cistaceae, Portulacaceae, and Trapaceae. Species of potential interest are named in the following. There are many other minor dicotyledonous families with plants producing starchy grains which will not be referred to again; these include: Ancistrocladaceae, Basellaceae, Buddlejaceae, Desfontainiaceae, Dioncophyllaceae, Droseraceae, Erythroxylaceae, Frankeniaceae, Gelsemiaceae, Leitneriaceae,

THE LEGUMES AND PSEUDOCEREALS | Pseudocereals: Overview Lennoaceae, Molluginaceae, Nepenthaceae, Nyctaginaceae, Orobanchaeae, Pentaphragmataceae, Phytolaccaceae, Retziaceae, Sarcolaenaceae, Sargentodoxaceae, Saururaceae, Schisandraceae, Stegnospermataceae, and Tamaricaceae. Most of these families have very limited numbers of species.

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Portulacaceae Portulaca oleracea (purslane).The seeds are sprouted or ground for use in gruel, cake, bread, or pancakes; the content of glycine and tyrosine in the seeds is reportedly high; care needs to be taken with their preparation and eating.

Bixaceae Bixa orellana (annatto). The seeds are used as coloring and flavoring for meat, poultry, or fish; the seedcoat contains the carotenoid, bixin, which is used as a tasteless coloring for cheese, butter, margarine and chocolate and for color in soap and skin products.

Trapaceae

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Trapa natans (water caltrop, water truffle).The seeds are eaten raw, roasted, boiled, fried, or ground into flour for bread and sweet puddings. Trapa bispinosa. The seeds are cooked and eaten in India.

Cactaceae

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Carnegiea gigantea (giant cactus). The seeds are ground into flour and used to make soup, paste, and other products by the Native American Papago group. Ferocactus wislizeni (fishhook cactus). The seeds are ground, parched, and used for bread and gruel. Opuntia clavata (ishikana). The seeds are roasted by Native Americans of the Acoma and Laguna groups; however, the mucilage in the fruit can render the food objectionable. Opuntia phaeacantha (bastard fig). The seeds are dried, parched, and ground into meal for gruel and cakes. Opuntia soehrensii (ayrampo). A violet dye is extracted from the seeds and used as a food coloring. Pachycereus pecten-aboriginum (cardon hecho hecho). In Mexico, the seeds are ground and made into cakes. Pachycereus pringlei (cardon). The seeds are toasted, ground, and fashioned into balls. Stenocereus stellatus (xoconochtli, joconostle). The seeds have been eaten.

Potential Pseudocereals in Monocot Families Monocotyledonous families with potential pseudocereal species include: Araceae, Cannaceae, Commelinaceae, Cyperaceae, Marantaceae, Musaceae, Palmae, Pandanaceae, Pontederiaceae, Typhaceae, and Zingiberaceae. Species of potential interest are named in the following. There are also many minor monocotyledonous families with plants that produce starchy grains which will not be referred to again; these include: Alismataceae, Anarthriaceae, Aponogetonaceae, Bromeliaceae, Burmanniaceae, Butomaceae, Centrolepidaceae, Costaceae, Cyanastraceae, Cyclanthaceae, Eriocaulaceae, Flagellariaceae, Haemodoraceae, Hydatellaceae, Hydrocharitaceae, Joinvilleaceae, Juncaceae, Juncaginaceae, Lemnaceae, Mayacaceae, Melanthiaceae, Najadaceae, Philydraceae, Potamogetonaceae, Rapateaceae, Rhipogonaceae, Scheuchzeriaceae, Sparganiaceae, Triuridaceae, and Velloziaceae.

Cannabidaceae Cannabis sativa (hemp). The seeds are parched, fried as cakes, used in asanomi (in Japan), in the spice mix shichimi, in ale or are eaten as sprouts.

Araceae Peltandra virginica (arrow arum, tuckahoe). The seed produces a bread similar to corn bread, with a cocoa flavor.

Caryophyllaceae

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Lychnia segetum. The seeds have been eaten as a famine food in France. Spergularia arvensis (corn spurrey). The seeds are used for bread flour in Norway and Sweden. Stellaria media (chickweed). The seeds are used as bread or as a soup thickening in India.

Chloranthaceae Sarcandra glabra (tea scent). The seeds are roasted and used as a sesame substitute.

Cistaceae Cistus ladanifer (labdanum). The seeds are ground and used for cakes and breads.

Cannaceae Canna edulis (Queensland arrowroot). Immature seeds are cooked in tortillas or cakes; the plant is used as a source of arrowroot in Colombia.

Commelinaceae

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Commelina benghalensis (keng, bokna, mu-Kengeria), Commelina forskailii (kansura, kanshura). The seeds are ground into flour for bread. Commelina communis (spider wort, day flower), Commelina obliqua (kena, keni, kana, kanjura). The seeds are eaten. Cyanotis axilaris (vichaka, narido, damro, soltra). The seeds are ground into flour for bread or bhadku, a mixture of flour and salt.

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Cyperaceae

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Cyperus bulbosus (theg, motha, mothabasa). The seed is ground into flour and made into bread or “ghes” or “rab” in India; Australian aborigines ate the seed raw or roasted. Mariscus sieberianus (tall sedge). The seeds are made into flour in China. Scirpus lacustris (great bulrush).The seeds are ground and mixed with meal for bread, mush, or pancakes. Scirpus maritimus (chid, dila). The seeds are eaten raw or pounded, made into flour and mixed with millet in India. Scirpus validus (tall bulrush).The seeds are eaten.

Marantaceae Thaumatococcus danielli (miracle berry). The seeds are used as a sweetener but the extract does not withstand heat.

Musaceae

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Elettaria cardamomum (cardamom). The seeds are used as flavoring. Etlingera elatior (Phillipine wax-flower, ondje). The seeds are eaten raw in Malaysia.

Conclusion In the past, the pseudocereals have represented an important component of the diet of many people in a wide range of cultures. The representative list of potential pseudocereals included above demonstrates the opportunities for future development of functional foods that exist amongst the pseudocereals, based on the usefulness of these foods in the past. In addition, the reputation of so many of the species as weeds indicates that they will probably have growth characteristics which should assist with their development into modern commercial production systems.

Ensete ventricosum (Abyssinian banana). The endosperm of the seed is eaten in Africa.

Palmae/Arecaceae Hyphaene thebaica (gingerbread palm). The kernels are crushed and mixed with porridge; the edible portion of the kernel has 2.8% protein, 74.7% carbohydrate, 0.4% fat, and 11% crude fiber.

Pandanaceae


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Pandanus tectorius (Nicobar breadfruit, screwpine). The seeds are edible but only after careful preparation.

Pontederiaceae Pontederia cordata var. cordata (lance-leaf pickerel weed). The seeds are eaten raw, boiled or parched, and ground into flour for bread.

Typhaceae Typha angustifolia (narrow-leaf cattail). The seeds are roasted and eaten.

Zingiberaceae

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Aframomum angustifolium (Madagascar cardamom). The dried seeds are used like pepper or added to coffee. Aframomum melegueta (Melegueta pepper). The seeds are used as flavoring for beverages, meats, ice cream, candy, and bread. Amomum compactum (round cardamom). The seeds are used in cakes in Malaysia. Amomum subulatum (Indian cardamom). The seeds are used for flavoring in char masala, in Afghanistan. Amomum xanthioides (bastard cardamom). The seeds are used as flavoring in liqueurs in China.

Pseudocereals constitute a diverse group. How is this group defined? What are the most valuable attributes of the pseudocereals? Contrast and compare the characteristics (grain yield and utilization value) of the three main pseudocereals: amaranth, quinoa and buckwheat. Consider a further six potential pseudocereal species (e.g., chia) and indicate what beneficial attributes they offer.


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Find out the potential situations in which some of the less common pseudocereals might become useful, considering growth vigor and seed usefulness (including antinutritional properties, such as saponins). Amaranthus retroflexus is considered a weed in some situations, but it appears to have some potential for animal feed, possibly even for human food. Investigate the situations in which its potential value might be harnessed for good.

See also: Food Grains and the Consumer: Grains and Health; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Food Grains: Intolerance, Allergy and Diseases: The Gluten-Free Diet; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Non-food Products from Grains: Cereal Grains as Animal Feed; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Legumes and Pseudocereals: Amaranth: Overview; Buckwheat: Overview; Quinoa: Overview.


Further Reading Belton PS and Taylor JRN (2002) Pseudocereals and Less Common Cereals. Berlin: Springer. Crawford M (2000) Edible Plants for Temperate Climates. Totnes, Devon: Agroforestry Research Trust. Facciola S (1998) Cornucopia II. A Source Book of Edible Plants. Vistas, CA: Kampong Publications. Hegarty MP, Hegarty EE, and Wills RBH (2001) Food Safety of Australian Plant Bushfoods. Canberra, ACT: Rural Industries Research and Development Corporation. Mabberley DJ (1997) The Plant-Book. A Portable Dictionary of the Vascular Plants, 2nd edn Cambridge: Cambridge University Press.

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Wiersema JH and Leon B (1999) World Economic Plants. Boca Raton, Florida: CRC Press. Williams JT (1995) Cereals and Pseudocereals. London: Chapman and Hall.

Relevant Websites Biodiversity Research Collection, University of Connecticut - The families of flowering plants: descriptions. http://www.biodiversity.uconn.edu. http://www.pfaf.org/ – Plants for a future. hort.purdue.edu http://www.hort.purdue.edu – Center for new crops and plant products, Purdue University and Famine Foods database.

Lupin: Overview DS Petterson, Department of Agriculture, Nedlands, WA, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp 166–174, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • •

springtime and early summer. The (bluebonnet) flower of L. texensis is the floral emblem of Texas. It is widely accepted that Lupinus evolved from the tropical and subtropical Sophoreae, a primitive tribe of the subfamily Papilionoideae (pea-flowering plants), 40 Ma. Nowadays, wild lupin species cover almost all climatic zones: sub-Arctic Alaska and Iceland, Mediterranean and semidesert regions, the highlands of East Africa, Mexico and the Andes, and the subtropical lowlands of the eastern Americas.

Origin of lupins Grain morphology and composition Lupin processing Food uses of lupins Allergenicity Feed uses

Learning Objectives

• • • •

To understand the structural and compositional aspects of lupins To understand the origin and uses of various types of lupins To appreciate the requirements for and types of lupin processing To understand the various antinutritional factors present in some lupins

Definition and Origins of Lupins The seed or grains of domesticated Lupinus species are generically called lupins. The same term is used widely in the community in referring to wild and domesticated plants and the seed/grain of all Lupinus species. The genus Lupinus belongs to the Fabaceae, a family of legumes. There are 12 lupin species, all large-seeded, native to Europe and the Mediterranean regions. Three of these are now fully domesticated. Lupinus albus, the European white lupin or albus lupin has a white flower. Wild types of L. angustifolius, the narrow-leafed lupin, have a blue flower: however, modern cultivars bred for low alkaloid content in Australia have a white flower and are known widely as the Australian sweet lupin (ASL). L. luteus, the yellow lupin (YL), has a yellow flower. Their grain is widely used in the animal feeds industry and to a lesser extent as a food (or food ingredient). There are 100 lupin species native to the Americas. They are mostly small-seeded, and only L. mutabilis, the pearl or Andean lupin, has been used as a food source. Worldwide, several species are being domesticated for possible use in agriculture. The main value of lupin crops to farmers is their replenishment of soil nitrogen, providing a disease break for cereals in crop rotation systems and a marketable grain. Lupins tend to grow relatively better on poorer soils than most other crop species. Lupins are also well known for their spectacular flowers. The Russell lupin, a hybrid derived from L. polyphyllus, is widely used as an ornamental flower, particularly in Europe. Parts of the southern highlands in New Zealand are a blaze of color from the alpine lupin, a variant of the Russell lupin, in

280

Grain Morphology and Composition Lupins have a typical dicotyledon structure. Their thick seed coat (hull or testa) composes 30% of the seed weight for L. luteus, 25% for L. angustifolius, 15% for L. albus, and 12% for L. mutabilis. This is considerably higher than for most domesticated grain species. Within the cotyledons (kernels), energy is mostly stored in the form of thickened cell wall material ( 25% of the cotyledons) and oil bodies ( 6–14%). There is virtually no starch in any of the lupin species. This is in marked contrast to crops such as field peas and chickpeas, which can have 50–70% of the cotyledon weight as starch and have low protein and oil content, and the soybean with 15–20% oil, some starch, and a high protein content. Their crude protein content ranges from 28% to 42%. Proximate analyses for the whole grain of the major domesticated species, and the Andean lupin, are shown in Table 1. There are some wild and partly domesticated Lupinus lines containing up to 45% crude protein and up to 21% oil; others have as little as 20% crude protein and 3% oil. The thick seed coat, which is mostly cellulose and hemicellulose, of Lupinus species means that it is important to also consider the composition and nutritional value of their cotyledons: these data are in Table 2. The major lupin proteins are a group of globulins, called conglutins. The three major ones are conglutin a (which sediments at 11–12S and is analogous to the legumin of peas and glycinin of soybeans), conglutin b (which sediments at 7S and is analogous to the vicilin of peas and conglycinins a and b of soybeans), and conglutin g (a sulfur-rich protein that sediments at 2S and is analogous to the conglycinin of soybeans). They compose 85% of the total protein and have similar sizes and physical properties to the storage proteins of other grain legume species. The remaining 15% of proteins are albumins, which are soluble at pH 5 and vary in size from 6000 to 117 000 Da. There is evidence for the 2S globulin actually being an albumin: depending on the species, this fraction consists of four (L. luteus), five (L. albus), or six (L. angustifolius) proteins. For more details on lupin and other legume proteins, see CEREALS | Protein Chemistry.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00036-X

THE LEGUMES AND PSEUDOCEREALS | Lupin: Overview Table 1 received)a

Chemical composition of the major lupin species (g kg1 as

Moisture Protein (N 6.25) Ash Crude fat Crude fiber ADF NDF TDF Lignin Starchb Gross energy (MJ)

L. angustifolius (Australian sweet L. albus lupin, L. luteus (albus lupin, narrow-leafed (yellow white lupin) lupin) lupin)

L. mutabilis (pearl lupin, Andean lupin)

86 361

85 322

94 414

71 460

33 91 104 152 171 390 15 <10 19.0

28 58 150 197 227 284 7 <10 18.6

37 57 127 195 230 320 5 <10 18.6

40 110 110

Table 3 Essential amino acid profile for major lupin species (% in grain)a Amino acid

L. albus

L. angustifolius

L. luteus

L. mutabilis

Arginine Cystine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Tyrosine Valine

4.7 0.5 0.6 1.4 2.3 1.6 0.2 1.2 1.2 0.4 1.7 1.4

3.6 0.5 0.8 1.2 2.1 1.4 0.2 1.1 1.0 0.3 1.1 1.2

4.4 0.7 1.4 1.5 2.8 2.1 0.4 1.8 1.5 0.8 1.2 1.3

4.6 0.7 1.3 2.0 2.9 2.5 0.3 1.7 1.8 0.3 1.4 1.7

a

Data are averaged from values obtained worldwide.

ADF, acid detergent fiber; NDF, neutral detergent fiber; TDF, total dietary fiber. a Average of worldwide data. b Most analysts report no starch present.

Table 2 Chemical composition of the kernels of major lupin species (g kg1 as received)a

Moisture Protein (N 6.25) Ash Crude fat Crude fiber ADF NDF TDF Lignin Gross energy (MJ)

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L. albus

L. angustifolius

L. luteus

75 401 36 114 150 62 140 440 30 20.4

100 400 27 66 88 71 77 380 7 18.9

85 530 45 73 195 220 300 420

Table 4 Nonstarch polysaccharide components for major lupin species (g kg1 in grain)a

Rhamnose Arabinose Xylose Mannose Galactose Glucose Uronic acids NSP (total)

L. albus (albus lupin, white lupin)

L. angustifolius (Australian sweet lupin, narrow-leafed lupin)

L. luteus (yellow lupin)

13 67 22 1 202 23 50

10 50 10 1 170 13 29

10 70 21 1 133 42 43

390

284

320

a

Data are averaged from values obtained worldwide.

19.7

ADF, acid detergent fiber; NDF, neutral detergent fiber; TDF, total dietary fiber. a Average of worldwide data.

Typical amino acid profiles for the domesticated lupin species, compared with the FAO standards for infants and others, are shown in Table 3. The deficiencies in lysine and methionine are common to most grain legumes. The seed hulls and cotyledons contain different types of carbohydrate. Lupin hulls are predominantly composed of structural polysaccharides: cellulose, hemicelluloses, and pectins. The main carbohydrate reserves of the cotyledons are the nonstructural polysaccharides of the cell walls, with the main components being galactose, arabinose, and uronic acid. These complex compounds are referred to as nonstarch polysaccharides (NSPs). Their structure, based on a rhamnogalacturonans backbone, is not yet fully defined. The water-soluble portion, 5% of the seed, is considered to have an antinutritional effect due to its viscous nature and effect on intestinal transit time. The insoluble NSP, 30% of the seed, has a minimal effect on nutrient utilization by monogastric species. An important attribute of insoluble NSP is their ability to hold large quantities of

water, about eightfold by weight for lupins, and maintain normal gut motility. The profiles for various species are shown in Table 4. The oil content of lupins varies from 15% in the pearl lupin down to 4% in the YL. There are differences in individual fatty acid profiles; they are typically high in oleic and/or linoleic acids and contain a total of 75% unsaturated fatty acids (cf. 85% in olive oil). The oil is heatstable and has a high antioxidant capacity. Variation in the content of major essential minerals in lupins, up to 30% of the mean, is typical of legume species, probably reflecting both genotype and environmental factors (Table 5). The essential trace mineral content of lupin species not only is influenced by genotype but also tends to reflect the soil types on which they are grown. For example, the selenium content of lupin seeds grown in Western Australia varies according to species and rainfall zone. Where the species were grown together, the selenium content of L. albus > L. luteus > L. angustifolius. In all cases, the higher the rainfall, the lower the selenium content. Similar variations apply to the content of copper, cobalt, and zinc in lupins. The accumulation of manganese by L. albus is well documented with most of

282 Table 5

THE LEGUMES AND PSEUDOCEREALS | Lupin: Overview Mineral content of major lupin species (range of data sets) L. albus

L. angustifolius

L. luteus

1

Mineral content (g kg ) Calcium 1.2–3.3 Magnesium 0.9–1.6 Phosphorus 2.5–9.0 Potassium 2.8–11.1 Sulfur 2.1–2.7 Sodium <0.1–1.1 Mineral content (mg kg1) Copper 3.1–8.1 Iron 21–44 Manganese 23–3772 Molybdenum 0.8–3.1 Zinc 22–38 Mineral content (mg kg1) Cobalt 10–430 Selenium 20–360

Table 6

Antinutritional factors in the major lupin speciesa

Botanical name 1

1.5–3.1 1.1–2.0 2.1–4.3 6.6–109.1 1.5–2.9 0.3–1.1

1.8–3.0 2.2–3.2 3.4–7.3 8.8–11.6 4.0–4.9 <0.1

2.5–6.8 31–150 6.7–76 0.7–2.9 24–45

5.9–12.0 52–87 25–59

10–260 18–240

n.a. n.a.

39–82

n.a., not available.

the low values coming from crops grown on sandy soils and high values coming from crops grown on heavy red clays. In contrast, the manganese content of L. angustifolius is low, from 9% to 30% the amount in L. albus grown at the same site (Table 5). A survey of the cadmium and lead contents of L. angustifolius (178 samples) and L. albus (12 samples) grown in Australia found that no samples exceeded the Codex Alimentarius limits of 0.1 and 2.0 mg kg1, respectively. There can be some accumulation of cadmium by L. luteus, which may be a consequence of the different root architecture in this species and the soils in which it is grown. Legume grains contain a range of compounds, traditionally known as antinutritional factors (ANFs) or antinutrients, with apparent untoward effects on species ingesting them. These are also known as bioactive compounds. These compounds had a protective role in evolution by protecting against predators and may have other important functional roles. Plant breeders have mostly reduced their content to a point of balance between lowering the content of ANFs, to enhance the nutritional value of the grain, and retaining the defensive or, otherwise, functional role. While some ANFs have a negative effect on feed utilization by farmed livestock, they can also have beneficial effects in humans, such as preventing the development of some forms of cancer and of osteoporosis. A summary of data for the ANF content of lupins is shown in Table 6. The content of proteinaceous ANF in domesticated lupin species is very low. Typically, trypsin inhibitor activity is < 0.3 mg kg1, and chymotrypsin inhibitor activity, <0.6 mgkg1. Lectin activity is virtually nonexistent in all lupin species. So, unlike most legume grains, lupins do not need to be heated to denature the proteinaceous ANF and make them safe for consumption by humans or animals. Phytate (inositol hexaphosphate and lower substituted homologues and their salts) contributes about one-half of the total phosphorus content in lupins. This is rapidly mobilized upon germination. Phytate can form insoluble complexes with divalent cations, particularly Ca2þ and Zn2þ, thus making them less available for absorption and utilization. The net

Total alkaloids (mg kg ) Oligosaccharides (%) Saponins (mg kg1) Condensed tannins (%) Lectins (activityb) Trypsin inhibitors (mg g1) Phytate (%)

L. albus

L. angustifolius

L. luteus

<200 7.5 <1 0.01 Trace 0.13 0.79

<200 5.2 570 <0.01 Trace 0.14 0.58

200–500 12.3 55 0.02 Trace 0.29 0.96

a

Data are averaged across worldwide figures. Lectin activity is usually measured as units of agglutinating activity against red cell preparations from the blood of various mammalian species. Several authors argue that there is no significant activity in Lupinus species; some have detected activity against specially sensitized cells or against species not considered significant for human concern. b

effect of phytate in the diet depends on the overall composition of the food particularly the amount and types of protein content and the total mineral content. Human studies have shown similar rates of absorption of phosphorus from lupinbased foods and comparable soy products. Germination lowers the phytate content by 60% and fermentation by 80%. Tannins are compounds of plant origin with molecular weights ranging from 500 to 2000 Da and with one to two phenolic hydroxyl groups per 100 Da. This enables them to form cross-linkages between proteins and other macromolecules. There are two subgroups of tannins. Hydrolyzable tannins typically have a central glucose core with the hydroxyl groups being wholly or partly esterified with gallic acid or hexahydrodiphenic acid. Condensed, nonhydrolyzable tannins are higher oligomers of flavan-3-ols with varying degrees of substitution. Their astringent taste and ability to precipitate proteins, resulting especially in the inactivation of gut enzymes, give the tannins their antinutritional role. In lupins, as with other grain legumes, the tannins are concentrated in the seed coats (hulls), and the simple act of dehulling will minimize any adverse effects. The concentration of condensed tannins, those most responsible for protein binding, is so low in lupins that it is unlikely to affect human or animal nutrition. Saponins are plant glycosides in which the nonsugar moiety is a steroid or a triterpenoid compound. Their bitter taste acts as a feed deterrent, and they have a secondary antinutritional effect by increasing the permeability of small intestinal mucosal cells. This causes a loss of essential electrochemical concentration gradients, facilitating the uptake of materials to which the gut would not normally be permeable. Only traces of saponins are present in L. albus, while concentrations in L. angustifolius and L. luteus range from 55 to 730 mgkg1. Saponins are generally harmless to humans: some are claimed to be beneficial in lowering blood cholesterol levels and protecting against coronary heart disease. The concentrations in lupins are lower than in many other legume species. Lupin oligosaccharides are higher a-galactosides of sucrose. Raffinose has one galactose moiety linked to sucrose through an a-1,4 bond, while stachyose has two, verbascose three, and ajugose four. These compounds cannot be metabolized by humans and other nonruminant species, and they undergo

THE LEGUMES AND PSEUDOCEREALS | Lupin: Overview bacterial fermentation in the colon to produce carbon dioxide, methane, and hydrogen. This causes abdominal discomfort and cramps and leads to flatulence, which seems to be a major reason for the low interest in consuming grain legumes in many societies. The oligosaccharides are a rich source of nutrients for bifidobacteria in the colon. This can have a beneficial effect, as the bifidobacteria counter the activity of putrefying bacteria and reduce their production of harmful, and possibly carcinogenic, fermentation products. One further source of confusion about the significance of oligosaccharides is the inclusion by some authors of sucrose in their total for oligosaccharides. This is nutritionally confusing as sucrose can be absorbed from the stomach and upper digestive tract of humans and nonruminant animals. Isoflavones have generally been regarded as ANFs because of their negative effects on fertility in ruminants grazing pasture medics and subterranean clovers. However, they are now recognized as preventative agents against some forms of cancer and osteoporosis in women. Isoflavones are present in greenleaf material and in the hypocotyls of germinating seeds (sprouts). There is conflicting evidence as to their presence in mature grain. The lupin alkaloids are usually bicyclic, tricyclic, or tetracyclic derivatives of quinolizidine (Figure 1). The individual alkaloids and their concentrations vary widely between, and sometimes within, species (Table 7). Grain of modern domesticated lupin cultivars typically contains less than 200 mg kg1 alkaloids. In contrast, grain from ‘bitter’ wild types that still exist in many countries may contain from 5000 to 40 000 mg kg1 alkaloids. There have been human deaths associated with the consumption of grain from bitter wild types of lupin. One would need to eat 10 kg of the modern varieties of lupin grain in a very short time to absorb sufficient alkaloids to be at risk. The quinolizidine alkaloids have a short half-life in humans and are excreted largely unchanged in the urine of >90% of humans. Traces of

N Quinolizidine

283

gramine, an indole alkaloid, occur in some lines of L. luteus, but the significance of these levels is not known. The only mycotoxin associated with lupins to date is the family of phomopsins, a group of linear hexapeptides with an antimicrotubule effect, which is most pronounced in the liver and kidneys. They are capable of disrupting mitosis and of reducing the activity of motile cells and organisms, rendering their host prone to secondary infections. There is no relationship between lupinosis and lupin alkaloid poisoning that can occur when sheep graze bitter lupins and their stubble or graze the perennial lupins of North America. Grains that contain phomopsins are smaller and less dense than normal-colored, nontoxin-containing grain and can be easily removed from the rest of the harvested grain by grading, using screens, gravity tables, and aspirators. A rapid enzyme-linked immunosorbent assay for the phomopsins is readily available to the food industry. The most recent cultivars of L. angustifolius are resistant to invasion by the responsible fungus (Diaporthe toxica), so that the risk of phomopsin ingestion is now extremely low and likely to be even less in the future.

Grain Processing Dehulling The simplest processing of lupin grain is repetitive abrasion of the testa in a ripple flow mill, tangentially abrasive dehulling device, or similar device. (The thickness and hardness of the testa make it harder to dehull lupins than most grains.) Alternatively, the grain may be conditioned by the addition of water, to swell the grain, followed by a mild heat treatment to help break the bonding between the testa and cotyledons. It is then possible to dehull using the same roller mills as used for milling wheat and other cereals. The major components are separated by air aspiration and grading across gravity tables. The germ fraction usually separates with the hulls and is mostly lost. The main reason for dehulling is that the cotyledons are much more nutritious than whole grain for nonruminant animals such as pigs, poultry, and fish. It is then possible to mill the cotyledons to make flour or to separate it into protein-rich and fiber-rich fractions for the feed, human food, and cosmetic industries.

Figure 1 Structure of quinolizidine.

Milling Table 7 Quinolizidine alkaloids in the major lupin species (% in alkaloid fraction)a L. albus L. angustifolius L. luteus L. mutabilis Albine Lupanine Multiflorine 13-Hydroxylupanine 4-Hydroxylupanine Angustifoline Lupinine Sparteine a

15 70 3 8 1

70

70

12

2 7 <1

10 60 30

20

Data are for modern cultivars or developing lines of these species. Up to 10% gramine, an indole alkaloid, is present in L. luteus.

Hammer milling of whole grain to make a coarse meal is common in the animal feed industry, simply to make the constituents more available to ruminant animals by increasing the surface area of material for digestion, and in some cases, it may be uneconomic to dehull for nonruminant feeds. Hammer cutting and roller milling of the splits are used to make a meal or fine flour for nonruminant feeds. The particle size range can be from 10 to 800 mm, which is far greater than for cereal, pea, and soy flours.

Fractionation Several reports in the scientific literature and patents describe the separation of protein, fiber, and oil fractions from cotyledons.

284

THE LEGUMES AND PSEUDOCEREALS | Lupin: Overview

Some processes cater for the recovery of alkaloids, for use as biological agents against insect pests and some microorganisms, and low-molecular-weight carbohydrates for use in the chemical industry. These mostly involve wet grinding of the cotyledons and separation of fractions according to solubility at different pH or in different solvents. There may be an initial dry milling and separation of particles by air classification.

Extrusion Extrusion can improve the quality of lupin-based formulated feeds. There is no expansion of the pellets as with starchenriched feeds, but there are improvements in feed digestibility, which makes the process cost-effective.

Food Uses Traditional Uses Lupins have been used as a food for as much as 6000 years in the Andean highlands and over 3000 years around the Mediterranean. The pearl lupin of the Andean highlands of South America, known locally as ‘tarwi’ or ‘chocho,’ was extensively cultivated, and consumers would soak the seed in running water to remove most of the bitter alkaloids before toasting or boiling and drying to make ‘kirku.’ Andean people have long recognized the benefits of consuming lupins, associating their use with religious festivals. In South America, the traditional use of tarwi as staple food continues in many Andean communities. Around the Mediterranean, lupini beans, largeseeded bitter grains of L. albus, have been extensively used as a snack food and as a bean substitute in times of drought. They are still commonly used as a snack bar. The beans (grains) are substantially debittered before being pickled and bottled or canned for use as a snack food. In the Middle East, the grain of L. albus is used to make snack foods, most commonly at the time of Ramadan (several thousand tonnes are imported from Australia each year for this). They are usually boiled whole and spiced, with the testa being removed before eating. Another use is to make a paste similar to the traditional ‘falafel’ from faba beans.

Bean/Sprout Immature seeds do not yet contain any alkaloids and have a similar taste and nutritional value to immature (green) peas. They can be used as an alternative to soybeans to make ‘edamame.’ Lupins can be germinated to make a sprout suitable for vegetable or salad use. Germination lowers not only the content of alkaloids, phytate, and oligosaccharides on a dry weight basis but also the overall content of the protein fraction. The lupin sprout compares favorably with soy and mung sprouts for taste and texture, although it has a slight beany and bitter aftertaste. Unlike most species, there is no vitamin C production on germination. There is, however, considerable production of the isoflavones, genistein and daidzein. Whole seeds may be deep-fried or made into spreads similar in nature to ‘hummus’ (traditionally made from chickpeas) and falafel (traditionally made from faba beans) and used with salads or breads.

Fermented Foods ‘Tempeh’ is a traditional Indonesian food, made by two successive fermentations using soybeans as substrate. A bacterial fermentation during the soaking of cooked dehulled soybeans is followed by a solid-state fermentation of the bean mass by the mold Rhizopus oligosporus. Tempeh has been successfully made from L. albus, L. angustifolius, and blends of both with soybeans. Indonesian consumers like the taste of lupin-based tempeh but frequently comment that the texture is too firm. The production of second-generation products, such as burgers and patties, from lupin-based tempeh seems to overcome this objection. ‘Miso’ is a fermented paste made from soybeans, usually mixed with rice. A traditional process involves preparing a rice ‘koji’ by fermenting cooked rice with a culture of Aspergillus oryzae (‘tane-koji’) and then adding cooked soybeans and salt to the koji. Lupins have been used experimentally to make miso of comparable quality with soy miso. ‘Natto¯,’ another Japanese fermented food, can also be made from lupin grain. ‘Sho¯yu’ is the traditional soy sauce of Japan. Some Japanese people now use lupin sho¯yu as an alternative. Lupins can be used to make sauces similar in flavor and texture to the traditional soy sauces of China, Korea, and Indonesia. Several thousand tonnes of ASLs have been used commercially in Indonesia for tempeh production, and small commercial batches of lupin-based miso have been sold in Japan.

Flour Additive Lupin kernel flour can be mixed in with wheat or wholemeal flours to make bread more nutritious, by giving a better balance of essential amino acids. Legume grains contain relatively more lysine and less methionine than cereal grains; so, adding 10% lupin flour to wheat flours will give a product with similar properties to the full wheat product but with an improvement in amino acid score from under 40% to over 70% relative to egg albumin. Loaf volume is compromised with increasing lupin content but fortifying with gluten or using harder wheat in the blend can overcome this. In practice, the limit of inclusion is 10%. There is an increase in waterholding capacity. The texture, flavor, and golden color of the lupin–wheat flour are appealing to many consumers. In Australia, some bread manufacturers use lupin hull flour to provide ‘bulk’ in high-fiber breads. Ultrafine kernel flour has an attractive yellow color, good dispersion in aqueous systems, and good emulsifying properties. Albus lupin flour can be added into wheat flour to make the traditional Chilean breads ‘hallulla’ and ‘marraqueta.’ Up to 10% micronized flour from L. albus cotyledons could be included in breads, biscuits, and cakes, enhancing protein quality, color, and taste. The added lupin flour retards staling, probably by increased water retention and better emulsification properties. Studies have shown a high acceptability of pasta enriched with L. angustifolius kernel flour, and up to 15% substitution of L. albus flour for semolina or durum flours enhanced the protein quality and appearance of spaghetti noodles without affecting sensory qualities. Flour from L. albus has been blended with noodle wheat flour to make unsalted white noodles with improved protein and

THE LEGUMES AND PSEUDOCEREALS | Lupin: Overview dietary fiber contents and color and texture. Up to 50% lupin flour can be incorporated into a range of cakes and biscuits. There are several suppliers of lupin flour and other products in Europe, but there are no available data on sales.

Lupin Kernel Fiber The purified cell wall fraction from lupin kernels is virtually colorless, odorless, and tasteless and can hold up to eight times its own weight of water. The fiber has cholesterol-lowering properties and acts as a fecal bulking agent, thus reducing stool transit time and benefiting bowel health. It also enhances satiety, probably due to its high water-holding capacity, and has potential as an antiobesity agent. The soluble fiber fraction can function as a fat replacer. The fiber can be used to supplement breads, pastas, biscuits, mousses, and jellies.

Protein Fractions Lupin kernel proteins have some valuable functional properties, combining good emulsifying, foaming, and water- and oil-holding properties but with less thermal stability than soy proteins. Nevertheless, lupin protein concentrates and isolates are used as meat extenders and refined fractions used to enhance the foaming properties of dairy desserts and other foods.

285

Feed Uses Ruminants Almost all of the testa can be fermented in the rumen, so there is no need to dehull lupins for ruminant feeds. The whole grain is highly fermentable with a minimal risk of acidosis. It is best to crack the grain open as a minimum action, to increase access for the rumen flora, but any grinding should not be too fine because there can be a loss of material to the hindgut where it is used less efficiently. A significant amount of protein degradation occurs in the rumen, but some protection from this is possible by treating the grain with formaldehyde before feeding. Other methods include flame roasting the grain, steaming and rolling the grain into flakes, and coarsely grinding the grain and then extruding the meal. Lupins are a valuable component of diets of feedlot cattle (up to 40% of the diet), and milking cows can readily consume large amounts of (cracked) grain while in the milking sheds. Rangeland farmers often supplement their grazing sheep with 50–250 g grain per head per day in dry periods when pastures are low. There is ample evidence for an enhancement of the reproductive performance of both rams and ewes when their diets are supplemented with lupin grain prior to mating. No specific factor has been attributed to this. Several hundred thousand tonnes of grain are retained onfarm in Australia each year for grazing supplements for sheep. The greatest consumption of traded lupin grain is by cattle, either in feedlots or under intensive housing, when fed with formulated diets containing lupin grain.

Vegetable Milk Products A lupin-based milk was used in the Chilean program for children’s nutrition for several years and is still used by households in some parts of the country. In making ‘tofu,’ it is possible to incorporate up to 30% lupin (L. angustifolius) milk with soy milk before the coagulation stage and produce an acceptable product, with the advantage of a lower unit cost of production. Higher levels of incorporation are not possible because the lupin proteins lack the necessary tertiary structures to produce a good curd. Sensory evaluations showed that tofu from a 30/70 lupin/soy blend was equally acceptable as a tofu made from soy milk. Fermentation of lupin milk produces a yogurt-like product of stable texture and with no beany flavor. It is comparable with the yogurts made from soy milk. Malted lupins could be used as a health drink base. The presence of the beneficial isoflavones – genistein and daidzein – in the hypocotyls of developing lupin sprouts is well reported. Lupin tea, made in the same way as pearl barley tea, has been developed in Japan.

Allergenicity of Lupins There are some reports of lupin allergenicity in the medical and scientific literature. Nearly all of the affected subjects had a history of reactions to other protein foods (e.g., peanuts, soybeans, and shellfish). The evidence to date suggests that lupin proteins have a lower allergenicity than most other protein foods.

Nonruminant Animals The testa is virtually worthless to all nonruminant species. It is removed whenever economical to do so. Otherwise, it simply supplies some bulk nonfermentable fiber. Processed lupin kernel meal is frequently used in commercial feeds for pigs, poultry, and aquatic species. The actual inclusion levels will depend on price and availability of the meal and alternative ingredients and any constraints imposed by any individual ingredient. The meal is low in lysine and methionine relative to most animal needs, but this is not a significant problem. Firstly, this deficiency is reflected in the price of the ingredient; secondly, deficiencies of one ingredient in the formulation will be at least partly offset by other ingredients; thirdly, crystalline amino acids are readily available to the feeds industry.

Pigs The digestible energy (DE) value of whole lupin grain for pigs is 14–15 MJ kg1; however, there is a lot of hindgut fermentation and the net energy value is 10.5 MJ kg1. Nevertheless, lupins are widely used in the pig industry. Recommended inclusion levels of ASL vary from 100 to 350 g kg1 depending on the age and physiological status of the animal. YLs have a similar energy value and are also widely used. Albus lupins are not used because they contain an inappetence factor for pigs. This reduces feed intake, slows growth, and makes it uneconomic to use such a diet. The addition of industrial carbohydrase enzymes to lupinbased pig diets can improve their net energy value.

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Pigs rank second to cattle in the overall consumption of lupin grain, almost entirely as a component of formulated feeds.

Poultry The apparent metabolizable energy content of both ASL and YL grains is 8.6 MJ kg1. It is not practical to use more than 100 g kg1 feed because of the high water-holding capacity of the undigested carbohydrates, which can cause wet droppings. For layer birds, it is possible to include up to 300 g kg1 in the diets, as the wet droppings are less of a problem. Albus lupins can be readily included in poultry diets. There is some benefit from adding carbohydrase enzymes to poultry diets. The oligosaccharides in lupin meals seem to have a beneficial effect on the osmotic stability of the gut enhancing nutrient absorption. Poultry ranks third as a consumer of lupins in formulated feeds.

Finfish and crustaceans Lupins can be used in both high nutrient density (HND; high protein and oil content) and low nutrient density (low protein and oil content) diets for finfish. When included in HND diets fed to rainbow trout (Oncorhynchus mykiss), the DE value of lupin kernel meals ranges from 12.8 MJ kg1 for L. angustifolius to 14.8 MJ kg1 for L. albus. Protein digestibility of all lupin varieties when fed to fish is high, typically greater than 95%. The low essential amino acid content is less of a problem for finfish fed with HND diets than for pigs and poultry because of the high level of protein required in the diets restricting the practical inclusion levels of the meal and also that so much of the dietary protein is metabolized as an energy source. Good acceptance and palatability of HND diets containing L. angustifolius, L. albus, and L. luteus have been reported, with acceptable inclusion levels up to 500 g kg1. Lupin meals are used commercially in diets for freshwater, estuarine, and marine finfish and crustaceans. This is a small but emerging market, as the relative value of the splits seems high for finfish.


• • •

How can lupins be used in fermented foods? What antinutrients can be present in lupins? Characterize the major lupin proteins.


• •

Increase the applications of lupin flours in foods Increase the industrial-scale production of traditional lupin-containing foods

See also: Agronomy of Grain Growing: Lupin: Agronomy; Breeding of Grains: Lupin: Breeding; Food Grains and the Consumer: Grains and Health; Non-food Products from Grains: Cereal Grains as Animal Feed; Processing of Grains: Extrusion Technologies; Proteins: The Protein Chemistry of Dicotyledonous Grains; The Basics: Grain: Morphology of Internal Structure; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview.

Further Reading Gladstones JS, Atkins C, and Hamblin J (eds.) (1998) Lupin as Crop Plants: Biology, Production and Utilization. Oxon, UK: CAB International. This book is the definitive work on all aspects of the Genus Lupinus, and was drawn on for this article. Nahrung 45(6) (2002) A special edition covering the processing of lupins and other grain legumes. Petterson DS (2000) The use of lupins in feeding systems: Review. Asian-Australasian Journal of Animal Sciences 13(6): 861–882. Van Barneveld RJ (1999) Understanding the nutritional chemistry of lupin (Lupinus sp.) seed to improve livestock production efficiency. Nutrition Research Reviews 12: 1–30. Wink M, Meissner C, and Witte L (1995) Patterns of quinolizidine alkaloids in 56 species of the genus Lupinus. Phytochemistry 38(1): 139–153.

Relevant Websites http://www.agric.wa.gov.au – Department of Agriculture, Western Australia. http://www.rala.is – The International Lupin Association.

Amaranth: Overview H Corke and YZ Cai, Hubei University of Technology, Wuhan, China; University of Hong Kong, Hong Kong, China HX Wu, Wuhan Chortle Biotechnology Company Limited, Wuhan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The distribution and importance of different agricultural crops can change fast: 80 years ago, soy bean was not important in the United States; now, it is perhaps the most valuable crop. Can grain amaranth rise from niche status to major crop? Grain Amaranthus, a small-seeded pseudocereal long cultivated in Central and South America, is fast-growing, adaptable, and generally pest- and disease-resistant. Amaranthus produces a starchy seed with a nutritious nonallergenic and gluten-free protein. The oil is high quality and contains significant squalene. The plant can be used a source of red pigments and as a leafy biomass for animal feed. Research effort on Amaranthus lags far behind the countless thousands of scientist-years devoted to major crops such as maize, wheat, or rice. Hence, it is agronomically underdeveloped and has modest grain yields. The market lacks a critical mass of stable, uniform supply. Modern biotechnology may aid the transfer of useful traits from Amaranthus to other more established crop plants.

Learning Objectives

• • •

To understand the history and future potential of Amaranthus species as agricultural crops, for grain production, for biomass, and for fractionation into value-added components To understand the properties and uses of Amaranthus starch, protein, oil, pigments, and other fractions and how these properties relate to new product development for food and other applications To understand the current state of Amaranthus production and that in the major producer, China, its major use for livestock feed

Amaranth Production and Development Although amaranth has long been cultivated as a minor crop in Central and South America and some areas of Asia and Africa, its production seemed to rapidly expand from the early 1980s, particularly in developing countries. However, growth seems to have stagnated in recent years and no clear commercial markets have developed. In many countries, especially in Asia and Africa (e.g., China, India, Nepal, Ethiopia, and Kenya), introduction, cultivation, and development of amaranth have been undertaken. Since 1982, the Chinese Academy of Agricultural Sciences has introduced hundreds of amaranth lines/ varieties from the United States and other countries to China. Some selected superior varieties (e.g., R104 and K112) have


been successfully grown in over 20 provinces. Amaranth has attained some popularity in China not only mainly for use in feed but also for food and for other purposes. Although amaranth is cultivated as a minor crop in China, it has been widely used for animal feed because of its high biomass and good feed value. At one time, amaranth production in China was claimed to have reached 300 000 ha annually, ranking as the top amaranth producer in the world. In the last 10 years, amaranth production in China has not been changed greatly. It still ranks on the top amaranth producer in the world. Some significant production in Russia, India, and Mexico continues as well. Despite the fact that in China and Russia there is larger-scale cultivation of amaranth mainly for feed use, there is still appreciable commercial cultivation of amaranth for human nutrition in Mexico, South American countries, China, the United States, Poland, Austria, etc. Current (2014) production in the United States is estimated at 1200 ha, primarily to supply four major corporate buyers (Arrowhead Mills, Health Valley, Amaranth Resources, and Nu-World Amaranth). There is considerable variation in amaranth yield per hectare in different countries. In China, depending on environmental conditions and cultivation systems, field production may yield 2200–5500 kg ha1 of amaranth grain (Figure 1) and 90 000–180 000 kg ha1 of fresh plants (silage). During cultivation trials, 3000 kg ha1 is achieved with good agronomic practice and good seed sources, and even a maximum yield of 4000 kg ha1 has been obtained in Montana, the United States, and 6000 kg ha1 in Peru. There was an average yield of 2250 kg ha1 in the northwest hills of India and 2000 kg ha1 in Austria. In the United States, extensive research work on amaranth has been conducted, especially under an amaranth research program at the Rodale Research Center, which started in 1976 and lasted for 14 years. The richest genetic resources of Amaranthus from many countries and regions in the world were collected and introduced. Special breeding varieties and different products have been developed, which are sometimes sold in health food shops or supermarkets. Although amaranth cultivation in the United States ranges from the Great Plains to the Rocky Mountains in Colorado, production is very limited, with perhaps only a few hundred acres planted. Notably, through collaboration of scientists from all over the world, initiated by this center, amaranth development has been stimulated worldwide. Research and development of grain amaranth in China; amaranth biology, chemistry, and processing; and other technologies have been summarized and reviewed. A series of studies on Amaranthus were carried out at the University of Hong Kong demonstrating the unusual properties of Amaranthus starch, protein, oil, and pigments and reveal their potential for use as food, being helpful to enhance future development and utilization of amaranth. More recent notable research is coming out of Argentina (e.g., papers by Anõń et al.).

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THE LEGUMES AND PSEUDOCEREALS | Amaranth: Overview Amaranth seed morphology is unlike common true cereal grains. Seed coat color ranges from black, brown, yellow, to white. Seed embryo is campylotropous, that is, circular, with the ends nearly touching and enclosing the perisperm (Figure 2). The seeds are extremely small, with 0.5–1.2 g per 1000 seeds or 850–1700 seeds per gram (30–70 times smaller than a typical wheat grain). A single plant can produce more than 500 g of grain. However, in actual field production, seed yield of amaranth varies greatly (15–50 g per plant), depending on the varieties used and soil fertility conditions.

Composition of Amaranth Grains and Vegetative Tissues Grains

Figure 1 Field production of grain amaranth in northern China, illustrating the generally well-developed agronomic level leading to grain production in the range of 4 tonne ha1.

Biological and Agronomic Characteristics of Amaranth Amaranth, a pseudocereal crop, is a dicotyledonous C4 plant belonging to the genus Amaranthus (which consists of some 75 species) of the family Amaranthaceae. There are two major types of amaranth: grain amaranth (e.g., A. cruentus L., A. caudatus L., A. hybridus L., and A. hypochondriacus L.) and vegetable amaranth (e.g., A. tricolor L., A. dubius L., and A. lividus L.). Grain amaranth is believed to originate from Central and South America, whereas the main vegetable types are believed to originate from Southeast Asia. Amaranthus plants usually prefer hot, bright sunlight and are distributed from the tropics to the semiarid regions. Cultivated species can grow in the tropics, subtropics, and temperate zones and grow well even in some cold areas such as Nepal and Chinese Tibet. Amaranth possesses high yield potential and high stress tolerance to drought, salinity, alkalinity, or acidic soil conditions. It typically gives a grain yield of 2250–4500 kg ha1 and a fresh leaf and stem weight of 30 000–60 000 kg ha1. The amaranth plant varies from branched to unbranched, prostrate to erect, and dwarf to over 4 m in height. The leaves are normally elliptical, with an acute tip and a cuneate base; leaf size varies significantly between and within species. The flowers are indefinite inflorescences.

Amaranth is one of the few multipurpose plants that can supply grains and leafy vegetables of high nutritional quality for use as food and feed. Amaranth grain is characterized by a relatively higher content of protein, higher lipid content, and lower starch content than those of the major cereals. A comparison of the average chemical compositions between amaranth (A. hypochondriacus) and main cereals (maize, rice, and wheat) is shown in Table 1. Table 2 shows the proximate chemical compositions of the grains of several Amaranthus species, indicating that there is some variation within an overall pattern among and within species. Total dietary fiber content (soluble and insoluble) in amaranth grains from A. caudatus, A. cruentus, and A. hypochondriacus ranges between 7.1% and 16.4%. The nonstarch polysaccharides make up 6–7% in the light-colored or dark grains. The content of various mineral elements and vitamins in amaranth grains from major species was analyzed. The levels of P, Ca, K, and Mg are usually higher than those found in common cereal grains. The P/Ca ratio varies from 1.9 to 2.6. It is of nutritional interest to find that amaranth grains contain relatively higher level of iron than that in cereal grains. Amaranth grains are relatively high in tocopherol (546 ppm), riboflavin, etc.

Leaves Amaranth leaves contain 27.8–48.6% dry matter as crude protein and, on average, have somewhat more protein than spinach, as shown in Table 3. The fat content ranges from 2.9% to 7.1% and contains linoleic acid as the major concentration of unsaturated fatty acid (40–55%) and palmitic acid as saturated fatty acid (18–25%). Amaranth leaves and stems are a very good source of fiber (11.1–22.9%). Minerals such as P, Fe, Mg, and Ca also exist in high concentrations, giving a total of 33.1–40.7% of ash content. Vitamins C and A are in concentrations of nutritionally significant levels, averaging 420 and 250 ppm, respectively. Seedlings, leaves, and stems of amaranth extensively save as tasty vegetables and animal feeds in the numerous places of the world, especially in China, India, and Southeast Asia. The protein isolated from leaves of Amaranthus species is rich in lysine (6.2–6.8%), higher than that of alfalfa, cabbage, and maize. It also has relatively good amounts of other amino acids. The edible and nutritional quality of vegetable amaranth is almost equal to spinach. In addition, it has been found that red-colored vegetative tissues (seedlings, leaves, inflorescences, etc.) of Amaranthus species contain high level of betalain pigments as natural colorants.

THE LEGUMES AND PSEUDOCEREALS | Amaranth: Overview

289

Cotyledons Procambium Starchy perisperm

Cotyledons Seed coat

Vascular bundles Endosperm

Shoot apex Procambium

Perisperm Root

Procambium (a)

Cross-section

Radicle (Root) Longitudinal section

(b)

Figure 2 (a) Illustration of A. cruentus seed in cross and longitudinal sections; (b) scanning electron micrograph of A. cruentus seed. Adapted from Irving DW, Betschart AA, and Saunders RM (1981) Morphological studies on Amaranthus cruentus. Journal of Food Science 46(4): 1170; Becker R (1994) Amaranth oil: Composition, processing, and nutritional qualities. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, p. 135. Boca Raton, FL: CRC Press.

There has also been much information on other compounds in amaranth (tannin, phytic acid, oxalate, saponins, nitrates, trypsin inhibitor, etc.) with antiphysiological activity in animal performance. Tannins are of importance from the nutritional point of view, since they may influence protein digestibility and reduce mineral bioavailability. Tannins in different amaranth species range between 0.1% and 0.25% and seem to be low enough not to have nutritional impact. The phytate content (0.34–0.61%) in amaranth is higher than that found in rice (0.1–0.14%), but lower than that detected in maize and wheat.

Amaranth Starch Starch is the main component of amaranth grain, composing 48–69% of its total dry weight. Starch generally consists of straight-chain and branched-chain molecules, that is, amylose

and amylopectin. Table 4 shows that amylose makes up from 0% (waxy) to 34.3% of total starch in amaranth grain with the balance being the amylopectin, showing that there is considerable variation in amylose/amylopectin ratio among and within the Amaranthus species. Light-colored grains normally contain more starch (mean 69%) than dark-colored grains. Starches isolated from A. hypochondriacus genotypes contain the lowest amount of amylose (7.8%), whereas A. retroflexus genotypes have the highest amylose (34.3%). The average amylose content of 124 genotypes is 19.2%. Amaranth starch granules come in polygonal, lenticular, circular, and elliptical shapes. Amaranth starch granules are extremely small, ranging from 0.8 to 2.5 mm in diameter. Comparatively, diameters of the granules in commercial starch range from 3 to 8 mm for rice starch to 15–100 mm for potato starch. Amaranth starch granule size and its size distribution are characteristics that influence the functional properties of starch.

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Table 1 Comparison of proximate composition between amaranth grains and some cerealsa Composition

Amaranthb

Wheat

Corn

Rice

Carbohydrate Crude protein Fat Crude fiber Ash Moisture

59.2 16.6c 7.2 4.1 3.3 9.6

66.9 14.0d 2.1 2.6 1.9 12.5

67.7 10.3e 4.5 2.3 1.4 13.8

75.4 8.5e 2.1 0.9 1.4 11.7

a

Percentage on dry weight basis. Mean values of four Amaranthus species (A. cruentus, A. caudatus, A. hypochondriacus, and A. hybridus). c N 5.85. d N 5.7. e N 6.25. Data from Saunders RM and Becker R (1984) Amaranthus: A potential food and feed resource. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 6, pp. 357–396. St. Paul, MN: American Association of Cereal Chemists; Singhal RS and Kulkarni PR (1988) Composition of the seeds of some Amaranthus species. Journal of the Science of Food and Agriculture 42(4): 325–331; Yue SX, Sun HL, and Tang DF (1993) The Research and Development of Grain and Amaranth in China (in Chinese). Beijing: Chinese Agricultural Science and Technology Press; Segura-Nieto M, Barba de la Rosa AP, and Paredes-Lo´pez O (1994) Biochemistry of amaranth proteins. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 75–106. Boca Raton, FL: CRC Press. b

Table 2

Since the 1970s, some interesting findings on physicochemical and functional properties of amaranth starch have been reported, for example, stable paste properties and a wide range of viscosity, resistance to shear thinning, and gelatinization temperatures. The focus of such research was restricted to very few Amaranthus species or genotypes and sometimes gave contradictory results due to the genetic variation of the properties of amaranth starch. A. hypochondriacus starch had a higher amylograph viscosity, a higher gelatinization temperature, a lower swelling power, and a higher solubility than wheat starch. A. paniculatus (synonym: A. cruentus) starch had moderate swelling power, higher solubility, and lower pasting viscosity than foxtail millet starch. Compared to maize starch, A. paniculatus starch had a higher paste viscosity, lower paste clarity, and higher freeze/thaw stability. A large number of Amaranthus germplasm (26 species) accessions were introduced into China for the evaluation of amaranth starch properties. Compared to the reference maize, rice, potato, and wheat starches, Amaranthus starch tended to have more stable paste, that is, lower pasting viscosities (lower shear thinning and lower retrogradation), higher gelatinization temperature, and higher energy of enthalpy for gelatinization. Also, Amaranthus starch paste was more resistant to cold storage and had softer gel texture and lower changes of hardness, cohesiveness, modulus, and adhesiveness. Figure 3

Chemical composition of amaranth grains from various speciesa

Component

A. caudatus

A. cruentus

A. hybridus

A. hypochondriacus

Carbohydrate Crude proteinb Fat Crude fiber Ash Moisture

59.6–62.8 17.6–18.4 6.9–8.1 3.2–5.8 3.1–4.4 9.5–11.6

60.7–62.6 13.2–18.2 6.3–8.1 3.6–4.4 2.8–3.9 6.2–8.8

58.6 14.0 6.7 6.6 3.6 10.5

57.0 17.9 7.7 2.2 4.1 11.1

a

Percentage on dry weight basis. N 5.85. Data from Singhal RS and Kulkarni PR (1988) Composition of the seeds of some Amaranthus species. Journal of the Science of Food and Agriculture 42(4): 325–331; Yue SX, Sun HL, and Tang DF (1993) The Research and Development of Grain Amaranth in China (in Chinese). Beijing: Chinese Agricultural Science and Technology Press; Segura-Nieto M, Barba de la Rosa AP, and Paredes-Lo´pez O (1994) Biochemistry of amaranth proteins. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 75–106. Boca Raton, FL: CRC Press. b

Table 3

Proximate composition of leaves from several Amaranthus speciesa Amaranthus speciesb

Component

1

2

3

4

5

6

Spinach

Crude proteinc Fat Crude fiber Ash

48.6 3.3 12.8 35.2

46.5 6.8 11.1 35.4

33.3 2.9 22.9 40.7

27.8 3.9 17.5

44.5 4.6 14.1 33.1

32.7 7.1

34.4 3.2 46.2 16.1

a

Percentage on dry weight basis. (1) A. caudatus, (2) A. cruentus, (3) A. edulis, (4) A. hybridus, (5) A. spinosus, (6) A. tricolor. c N 6.25. Adapted from Saunders RM and Becker R (1984) Amaranthus: A potential food and feed resource. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 6, pp. 357–396. St. Paul, MN: American Association of Cereal Chemists; Teutonico RA and Knorr D (1985) Amaranth: Composition, properties, and applications of a rediscovered food crop. Food Technology 39(4):49–54; Segura-Nieto M, Barba de la Rosa AP, and Paredes-Lo´pez O (1994) Biochemistry of amaranth proteins. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 75–106. Boca Raton, FL: CRC Press. b

THE LEGUMES AND PSEUDOCEREALS | Amaranth: Overview displays the Rapid Visco Analyzer (RVA) pasting profiles of Amaranthus starch compared with maize starch. A wide range of variation was found in the several tested properties of starch among the Amaranthus species and among genotypes within the same species, suggesting that the wide genetic diversity necessitates specific choices for specific uses. Interestingly, it was observed that there were significant effects of environment on the tested properties of Amaranthus starch, indicating that starch of the same genotype might have different starch properties if grown in different locations. Additionally, obvious effects on pasting and rheological properties from genotypic, pH, and salt factors were found. Recently, amaranth starch has attracted increasing attention because of its unusual properties. Possible product uses of amaranth starch, capitalizing on its small granule size, could include food thickeners, dusting powders for cosmetic as well as food uses, laundry starch, and even possible biodegradable Table 4

Starch and amylose content of amaranth grains (%)a

Species

Starch

Amylose

A. cruentus A. hybridus A. hypochondriacus A. retroflexus A. spinosus A. tricolor A. viridis 124 genotypes Light-colored seeds

48–63 55 52–62

22.1 (n ¼ 48) 21.1 (n ¼ 14) 7.8 (n ¼ 6) 34.3 (n ¼ 3) 18.1 (n ¼ 4) 29.0 (n ¼ 8) 12.9 (n ¼ 3) 19.2 13.9

51 69 3 (n ¼ 9)

a

n, numbers of genotypes. Data from Saunders RM and Becker R (1984) Amaranthus: A potential food and feed resource. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 6, pp. 357–396. St. Paul, MN: American Association of Cereal Chemists; Yue SX, Sun HL, and Tang DF (1993) The Research and Development of Grain Amaranth in China (in Chinese). Beijing: Chinese Agricultural Science and Technology Press; Wu HX and Corke H (1999) Genetic diversity in physical properties of starch from a world collection of Amaranthus. Cereal Chemistry 76: 877–883.

100

200

80

Viscosity (RVU)

160 K112 120

60

Corn

80

40

R104

20

40 0 0

Temperature (°C)

Profile

2

4

6 8 Time (min)

10

12

0 14

Figure 3 RVA pasting profiles of two Amaranthus genotypes (K112 and R104) compared with corn. Adapted from Wu HX, Yue SX, Sun HL, and Corke H (1995) Physical properties of starch from two genotypes of Amaranthus cruentus of agricultural significance in China. Starch/ Sta¨rke 47: 295–297; Corke H, Wu HX, Yue SX, and Sun HL (1997) Developing specialty starches from new crops: A case study using grain amaranth. In: Campbell GM, Webb C, and McKee SL (eds.) Cereals: Novel Uses and Processes, pp. 91–102. New York: Plenum Press.

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plastics. The unique properties of A. caudatus starch, namely, its pasting properties and high susceptibility to amylase, might represent potential uses as food, feed, and fuel. A. hypochondriacus starch had relatively low gelatinization temperature and food freeze/thaw stability, indicating its use in gravies, sauces, and soups. A. paniculatus starch could be used in salad dressings and custard preparations. There were also reports on chemical modification (e.g., succinylation and hydroxypropylation) of amaranth starches and their properties. Many studies demonstrated that starches isolated from many Amaranthus species could be used as good thickeners and stabilizers in salad dressing, canned food, sauce, frozen food, etc., because of their stable paste, low retrogradation, freeze/thaw resistance, and heating and cooling resistance. Also, there has been a report that describes amaranth starch as behaving very poorly in breads and cakes from the standpoint of color and appearance, texture, and volume, probably because of its low amylose content. During starch application, it is worth paying attention to a fairly wide variation of amaranth starch properties among different species and genotypes.

Amaranth Protein The second most abundant component of amaranth grains is protein. Based on the amino acid composition, amaranth seed protein is known to be of higher quality than most of the major cereal grains. The essential amino acid composition of amaranth grains from different Amaranthus species is summarized in Table 5. The lysine content is two to three times higher than that of the most common cereals, and sulfur amino acid content is also relatively high as compared with that of the most important legumes (pea, bean, soybeans, etc.). Table 5 also shows clear variation in amino acid composition among different species. Because amaranth protein has a better balance of the essential amino acids than in cereals and legumes, it Table 5 Essential amino acid composition of grains from three major Amaranthus species (g per 100 g protein) Amino acid

A. caudatus

A. cruentus

A. hypochondriacus

Cystine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Tyrosine Valine MetCys PhetTyr

2.3 3.6–4.1 5.9–6.3 5.7–6.4 2.4–3.3 3.4–4.0 3.8 1.1 2.8 4.1–4.7 4.7 6.2

2.0–3.8 3.4–3.7 4.8–5.9 4.8–5.8 1.8–2.6 3.2–4.5 3.2–4.2 n.d. 2.4–4.0 3.9–4.3 3.8–5.4 5.6–8.5

2.0–3.9 2.8–3.8 5.0–5.8 3.2–6.0 0.6–1.6 3.8–4.5 2.6–4.3 1.1–4.0 3.1–4.0 3.2–4.2 2.6–5.5 6.9–8.5

n.d., not determined. Data from Saunders RM and Becker R (1984) Amaranthus: a potential food and feed resource. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 6, pp. 357–396. St. Paul, MN: American Association of Cereal Chemists; Segura-Nieto M, Barba de la Rosa AP, and Paredes-Lo´pez O (1994) Biochemistry of amaranth proteins. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 75–106. Boca Raton, FL: CRC Press.

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scores higher than other seeds (e.g., wheat, barley, soybean, and maize) in the FAO/WHO Nutritionist’s Protein Value Chart: a score of 100 is the ideal, whereas amaranth protein received the highest score of 75, compared to cow milk (score 72), soybeans (68), and peanuts (52), indicating that its balance was closer to the optimum required in the human diet (FAO/WHO). Seed proteins are generally classified into four types based on solubility: albumin, globulin, prolamin, and glutelin. Most studies on amaranth proteins suggested that albumin was the major fraction (49–65%), followed by glutelin (22–42%), globulin (14–18%), and prolamin (1.0–3.2%). However, there was variation in amaranth protein fractions because of protein extraction and fractionation procedures and due to genetic variation. For instance, it was reported that the fractionated proteins from five different Amaranthus species averaged albumin (65%), globulin (17%), prolamin (11%), and glutelin (7%). Also, it was reported that the isolated proteins from A. hypochondriacus consisted of 46–49% albumin plus globulin, 3% prolamin, and 30–33% glutelin, and in another study of same species, similar percentages of albumin, globulin, prolamin, and glutelin were 51.0, 15.9, 2.0, and 31.1, respectively. In the 1980s and 1990s, many researchers isolated major fractions (albumin, globulin, and glutelin) of proteins from main Amaranthus species and examined their biochemical and physicochemical properties and molecular weights. Based on their measurements of its emulsion activity, foaming stability, and surface hydroscopicity, along with its relatively high heat stability, it was concluded that amaranth proteins could be useful as effective emulsifying and foaming agents. On the other hand, there were reports that A. cruentus and A. hypochondriacus protein fractions had poor emulsifying and foaming properties, limited water absorption, and good gel-foaming properties. It was found that protein concentrates made from amaranth grains of five genotypes exhibited better solubility, emulsification, and foaming properties than the commercially available soy proteins (Table 6). The effect of proteins on starch gelatinization and retrogradation was investigated using the hydrolyzed and native protein concentrates of amaranth. The results suggested that native proteins tend to be attracted toward the starch granule and contribute to the regulation of swelling and amylase leaching during gelatinization, therefore resulting in a weaker starch gel. However, hydrolyzed Table 6

proteins showed similar effect, but to a much lesser extent. Furthermore, amaranth protein concentrates were examined for direct application in certain food systems (wheat dough and noodle). It was found that the mixing properties of wheat flour were improved by the addition of the protein concentrates. Addition of protein concentrates to a noodle formulation also showed some positive influence on final product quality. A few amaranth protein concentrates were also evaluated as fillers for an emulsion-type meat product. Only one of the amaranth protein concentrates (genotype K112) gave some favorable results.

Amaranth Oil Oil is another chemical component of much interest in amaranth grain, because it contains relatively higher levels of oil (5–8%) than cereal grains; moreover, there is a considerable amount of squalene in amaranth oil (5%) compared with that in oils of cereals and other oil crops (0.01–0.4%) (Table 7). Palmitic, oleic, and linoleic acids are the major fatty acids in amaranth oil, with the saturated/unsaturated fatty acid (S/U) ratios ranging from 0.12 to 0.50. Published data showed that the fatty acid profiles in amaranth oil from different species were as follows: palmitic (12–25%), oleic (19–35%), linoleic (25–62%), stearic (2–8.6%), and linolenic (0.3–2.2%) acids. The squalene levels range from 5% to 8% in A. cruentus oil. Lower amounts of squalene (2–5%) are tested in some Table 7

Oil and squalene content of amaranth grains and other seeds

Species

Oil (%)

Squalene (%)

A. cruentus (1) A. cruentus (2)a A. hybridus A. hypochondriacus A. tricolor Maize Cottonseed Rice Olive Peanut

5.57–7.72

4.52–5.44 5.0–8.0 5.23 3.62–5.01 6.14 0.03 0.01 0.3 0.4 0.03

6.40 5.35–7.05 5.08 4.0 7.0 1.0–3.0 36.0 47.0

a

Data from Lyon and Becker (1987), other data in the table from Becker R (1994) and He HP, Cai YZ, Sun M, and Corke H (2002). Extraction and purification of squalene from Amaranthus grain. Journal of Agricultural and Food Chemistry 50: 368–372.

Functional properties of amaranth protein concentrations, compared to soy protein isolates

Species

Genotypes

Emulsifying activity (%)

Solubility (%)

Foam expansion (ml)

Foam stability (ml)

A. cruentus A. cruentus A. cruentus A. cruentus A. hybridus Soybean Soybean LSD0.05a

K112 K350 K459 R104 No.3 Soy A Soy B

55.6 73.3 61.9 56.0 62.2 50.6 45.7 3.1

19.9 56.5 42.1 47.2 60.5 33.3 21.3 4.5

49 91 52 35 68 23 28 20

34 56 26 18 26 20 22 9

Least significant difference (p < 0.05) for comparison of means in the same column. Data from Bejosano FP and Corke H (1999) Protein quality evaluation of Amaranthus wholemeal flours and protein concentrates. Industrial Crops and Products 76: 100–106.

a

THE LEGUMES AND PSEUDOCEREALS | Amaranth: Overview Amaranthus species of West Africa. Other lipids in amaranth, such as triglycerides, sterols, methyl sterols, terpenic and aliphatic alcohols, tocopherols, and hydrocarbons, have also been identified. Recent results indicated that the major fatty acids in amaranth oil from 11 Amaranthus genotypes included palmitic acid (19.1–23.4%), oleic acid (18.7–38.9%), and linoleic acid (36.7–55.9%), with S/U ratios of 0.26–0.32. The squalene content in amaranth oils from 11 genotypes of four species ranges from 3.6% to 6.1% (Table 7). These reports reveal the significant variation in oil composition content among various species and genotypes. Squalene is a biosynthetic precursor to all steroids. It is an important functional ingredient in skin cosmetics and also as an excellent computer-disk lubricant. It has been reported that the decreased risk for some cancers might be associated with squalene consumption, and the use of squalene alone is effective in decreasing serum cholesterol levels. The traditional source of squalene is from shark and whale liver oil. Estimates in 2015 place the world market at 2600 tonne year1, with a growth in demand of perhaps 10% per year. It is very expensive ($43 000 per tonne). Amaranth oil will attract more attention as an alternative plant source of squalene because of its abundant squalene content, although efforts to further increase the level are necessary. Squalene can be easily extracted from amaranth grain by simple vacuum distillation. Recently, work to screen genotypes containing a higher content of squalene in a wide range of Amaranthus species and to develop efficient large-scale separation technique has been conducted; a method was established to separate and purify squalene from amaranth oils. After saponification, squalene content increased from 4.2% to 43.3% in the unsaponifiables by the removal of the saponifiables. The unsaponifiables were fractionated by a chromatographic method to obtain highly purified squalene. The final purity of squalene reached 94–98%. However, amaranth oil occurs in very low levels and at higher cost than oils of peanut, olive, rapeseed, etc. Unless a specialty starch or protein could also be produced from the defatted meal, a substantial decrease in raw product cost will probably be required before amaranth oil goes commercial.

Amaranth Pigments There has been an increasing trend toward replacement of synthetic colorants with natural pigments since the 1980s Table 8

293

because of safety and health concerns. Red-colored vegetative tissues of Amaranthus plants contain a high concentration of betalain pigments and are often produced in high biomass (Table 8). They have attracted considerable interest as potential substitutes for the well-known betalains from beetroot (Beta vulgaris), which are extensively used in the food industry worldwide. A comprehensive systematic study on amaranth pigments has covered field evaluation and selection of betalainproducing genotypes/species; extraction, identification, and quantification of betalain components; determination and evaluation of properties and antioxidant activity; and pigment production and utilization in certain food systems. Betalains are divided into two major structural groups, that is, red-violet betacyanins and yellow betaxanthins. Amaranth pigments belong to betacyanins. They could be easily extracted with water or methanol. Sixteen kinds of betacyanins were isolated and characterized from plants in the Amaranthaceae. Figure 4 shows HPLC profile of amaranthine-type betacyanins and their molecular structures, which are predominant pigments in all Amaranthus species. Quantitative analysis data showed that the screened amaranth species/varieties yield higher betacyanin pigments than feasible in beetroot production. Colorant properties and stability of the betacyanins are the key factors of pigment quality that directly influence their application in food systems. Assessment of color characteristics and stability of betacyanins from Amaranthus species showed that Amaranthus betacyanins exhibited bright red-violet color and favorable stability under selected conditions (pH 5–7 and temperature <14 C), as compared to red radish anthocyanins. Dried Amaranthus pigments had good storage stability (t1/ 2 ¼ 23.3 months) at room temperature. The presented data support the potential development and utilization of Amaranthus betacyanins as new natural colorants for use in the food industry, particularly for low-temperature uses. Aqueous extracts of natural pigments are commonly unstable and sensitive to storage environmental factors. Spray drying can significantly improve storage stability. Amaranthus betacyanin extracts were spray-dried using a range of 10–25 DE maltodextrins as carrier and coating agents at different inlet/outlet air temperatures and various feed solid contents. The best dried pigment powder made was superior to commercial red beet powder in terms of physical properties (Table 9). The results demonstrated the feasibility of the production of spray-dried Amaranthus betacyanin extracts as a food-grade colorant.

Pigment content and fresh weight of 12 genotypes from seven Amaranthus species

Species

Genotypes

Fresh weight of colored parts (kg ha1)a

Total betalain content (mg per 100 g FW)

A. cruentus A. caudatus A. tricolor A. hypochondriacus A. hybridus A. lividus A. paniculatus

12 2 3 1 1 1 1

56 390 7225 (Lv, In) 42 520 (In) 20 520 (Lv) 29 160 (In) 39 285 (In) 17 370 (Sl) 44 550 (In)

42–199 82–144 51–143 47 82 46 127

FW, fresh weight. a Sl, seedlings; Lv, leaves; In, inflorescences. Estimated as Sl, Lv, or In weight per plant planting density. Data from Cai YZ, Sun M, Wu HX, Huang RH, and Corke H (1998) Characterization and quantification of betacyanin pigments from diverse Amaranthus species. Journal of Agricultural and Food Chemistry 46(6): 2063–2070.

294


mAU

1 1: amaranthine 1′: isoamaranthine (C15 epimer)

2500 2000

HO

HO

O

6’

H

1’ O 5

HO HOOC

O 2”

HO

1500

HOCH2

O HO

7

COO–

N

1”

OH

1′

1000

2 +

H

15

N HOOC

COOH

H

500 0 0

2.5

5

7.5

10

12.5

15

17.5

20 min

Figure 4 Structure and HPLC elution profile of amaranthine-type betacyanins from A. tricolor. The isomeric form (10) is the C-15 epimer of corresponding betacyanin (not drawn).

Table 9

Comparison of amaranth pigment powder and commercial beet powder (No. 3600 or E162)a Color parameters

Spray-dried powder

Betacyanin content (%)b

Hygroscopic moisture (g/100 g)

L*

a*

b*

H0

Amaranth powder

0.74

48.5

49.35

32.60

2.47

Beet powder

0.31

58.8

51.54

19.64

0.71

355.7 (4.3) 2.0

Pigment retention (%)c 87.9 1.8 84.3 1.4

a

Amaranth pigment powder made by spray drying at 180ºC inlet temperature using 19.8% solids in feed mixture (15 DE maltodextrin). Calculated as % amaranthine and % betanin. c Determined at 25 C and 32% RH after 16 week storage. Data from Cai YZ and Corke H (2000) Production and properties of spray-dried Amaranthus betacyanin pigments. Journal of Food Science 65: 1248–1252. b

Application of Amaranthus betacyanins in jelly, ice cream, and a model beverage was evaluated by comparison to commercial colorants (red radish anthocyanins and synthetic colorant FD&C Red#3). The results revealed the feasibility and potential of Amaranthus betacyanins for use in the model food systems at low temperature. Amaranthus betacyanins in the foods examined exhibited better color characteristics than red radish anthocyanins at the same levels, but were not as bright as FD&C Red#3. The betacyanins had color stability comparable to red radish and FD&C Red#3 at lower temperature (<14 C) and also similar color stability at 25 C, but not as stable as the two commercial colorants at higher temperature (37 C). Additionally, all betalains isolated from plants in the Amaranthaceae exhibited strong antioxidant activity. To date, there has been evidence suggesting that certain natural colorants as nutritional antioxidants in the diet may reduce the risk of some diseases. This gives the possibility of these betalains being used both as natural colorants and as potential natural antioxidants.

Food and Feed Utilization of Amaranth Traditional foods are made from amaranth grains in many countries, for example, ‘alegria’ and ‘atole’ in Mexico, ‘alboroto’ in Guatemala, ‘bollos’ in Peru, ‘Chapati’ in

Himalayas, ‘laddoos’ in India, and ‘sattoo’ in Nepal. These amaranth-based foods are still consumed today in various areas of the world. Modern food applications of amaranth grains include breakfast foods, infant/weaning food formulations, breads, pastas, flakes, drinks, and beverages. Currently available consumer food products include popped foods, baking mixes, malted flours, breakfast cereals, snacks, baked goods, and whole amaranth products. In China, a wide range of amaranth food products has been developed for retail sale. These include instant flour for beverages or porridge, packaged dried noodles, cakes, biscuits, and soy sauce made from brown/black amaranth and other grains (wheat and soybean). China has a wide diversity of traditional food products made from specialty grains, such as buckwheat, millets, sorghum, and legumes. By adapting products made from these, additional amaranth-based foods have been developed, such as composite flour instant noodles, distilled spirits, and vinegar. Based on the properties of diverse fractions of amaranth grain, and depending on the physical, nutritional, and sensory requirements of specific products, there is continuing potential for new product development based on amaranth. Examples of recent studies include that of Martinez et al. who investigated the effect of A. mantegazzianus flour on the technological and sensory quality of bread wheat pasta. Also, Diaz et al. drew attention to the significance of amaranth as source of glutenfree ingredients. They added 20% amaranth to a maize base

THE LEGUMES AND PSEUDOCEREALS | Amaranth: Overview used in twin screw extrusion. Addition of amaranth conferred increased sectional expansion index. Also, in recent years, amaranth grains have been developed and processed for many innovative new food products in China, such as amaranthflavored cake, amaranth yogurt, and amaranth Taosu (a type of traditional Chinese sweet cake). Furthermore, vegetable amaranth has been used as a traditional vegetable for several centuries in China. In sub-Saharan Africa and Central and South America, vegetable amaranth is also an important leafy vegetable, consumed as a cooked green vegetable or used in soup. Amaranth is a fast-growing, high-nitrogen, and highbiomass plant that can be used fresh or as silage for animal feed. Amaranth grain flour or powdered leaf meal can be used to make commercial pelleted or other compound feeds. Currently, feed application of amaranth has been successful and popular in China and has played a role in developing Chinese animal husbandry. Amaranth feeds made from leaves, stems, panicles, and grains include green fodder, silage, leaf and seedmeal feed, pellet feed, etc. The evaluation of feed use has shown that amaranth feeds efficiently raise pigs, chickens, cattle, sheep, and fish to improve the quality and productivity of animal production. Chinese peasant households are accustomed to raise livestock and poultry, and nowadays, in many areas, amaranth is the main source of silage for household pig production. However, it is not widely used as feed in other countries.

Other Uses Considerable further research has been conducted over the past 10 years on potentially healthful or functional components of amaranth grain. Amaranth grain was 11% dietary fiber, of which 78% was insoluble and 22% was soluble. These levels were similar to quinoa, but the soluble fraction was greater than in maize. Quiroga et al. tested lectins from the amaranth protein hydrophobic fraction of A. mantegazzianus and A. caudatus and found high activity as cell-proliferation inhibitors, the effect being attributed to a cytotoxic effect, followed by apoptosis, and inhibition of cell adhesion. Similarly, Sabbione et al. produced fractions and hydrolysates of amaranth seed protein fractions and showed that antithrombotic activity was particularly high in the glutelin fraction. In a general review of amaranth nutritional components, Venskutonis and Kraujalis summarized the potentially valuable fractions of the plant, classifying into macrocomponents (lipids, proteins, and carbohydrates including dietary fiber and starch) and other important constituents, such as squalene, tocopherols, phenolic compounds, phytates, and vitamins.

Conclusions In summary, amaranth possesses high yield potential and high stress tolerance to drought, salinity, alkalinity, or acidic soil conditions. Its grains have attractive chemical composition, superior nutritive value, and some special functional properties. Its vegetative parts with high biomass can be used for

295

animal feed. Its red-colored vegetative tissue with high level of betacyanins is a potential alternative source of well-known beetroot pigments (betalains). Amaranth has been attracting worldwide attention and will be a high-potential new crop with multiple uses. Since the first edition of this article 12 years ago, more than 250 research papers in international scientific journals have been published on food science aspects of amaranth, most regarding novel applications of nutritional fractions of the grain. This developing corps of technical knowledge may help to increase demand to a level that will justify investment in major production and processing systems. However, intense and continuous efforts are necessary in several aspects, such as amaranth breeding and field cultivation (for yield, shattering, and lodging), relevant food/feed processing and development, product industrialization, and marketing.


• •

What makes Amaranthus most suited for food or for feed production? What are the general properties of Amaranthus starch and protein?


•

•

•

For your production conditions and regulatory environment, is Amaranthus betacyanin a viable competitor for red beet pigments? Consider potential yield, production cost, coproducts, and range of pigment colors that can be produced. Squalene is a high-value lipid, with critical applications in the computer industry. Animal sources are limited and unsustainable, and plant sources such as Amaranthus yield low amounts relative to total biomass. What is the potential for genetic engineering of microbes or other high-yield crops with Amaranthus genes for enhanced squalene production?. Speculate or brainstorm on what it would take to turn Amaranthus into a breakthrough crop leading to production at the level of maize or soy bean within 50 years.

See also: The Cereal Grains: Coix: Overview; The Legumes and Pseudocereals: Buckwheat: Overview; Pseudocereals: Overview; Quinoa: Overview.

Further Reading AgMRC (2015) http://www.agmrc.org/commodities__products/specialty_crops/ amaranth/ Agricultural Marketing Resource Center, Iowa State University. Becker R (1994) Amaranth oil: Composition, processing, and nutritional qualities. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 133–141. Boca Raton, FL: CRC Press. Bejosano FP and Corke H (1999) Protein quality evaluation of Amaranthus wholemeal flours and protein concentrates. Industrial Crops and Products 76: 100–106. Berghofer E and Schoenlechner R (2002) Grain amaranth. In: Belton PS and Taylor JRN (eds.) Pseudocereals and Less Common Cereals – Grain Properties and Utilization Potential, pp. 219–260. Berlin: Springer.

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Cai YZ and Corke H (2000) Production and properties of spray-dried Amaranthus betacyanin pigments. Journal of Food Science 65: 1248–1252. Cai Y, Sun M, and Corke H (2005) Development and application of betalains from the Amaranthaceae. Trends in Food Science and Technology 16: 370–376. Cai YZ, Sun M, Wu HX, Huang RH, and Corke H (1998) Characterization and quantification of betacyanin pigments from diverse Amaranthus species. Journal of Agricultural and Food Chemistry 46(6): 2063–2070. Chen JZ (2011) Development and preparation of amaranth yogurt. Food Research and Development (in Chinese) 12: 72–73. Corke H, Wu HX, Yue SX, and Sun HL (1997) Developing specialty starches from new crops: A case study using grain amaranth. In: Campbell GM, Webb C, and McKee SL (eds.) Cereals: Novel Uses and Processes, pp. 91–102. New York: Plenum. Diaz JMR, Kirjoranta S, Tenitz S, et al. (2013) Use of amaranth, quinoa and kaniwa in extruded corn-based snacks. Journal of Cereal Science 58: 59–67. He HP, Cai YZ, Sun M, and Corke H (2002) Extraction and purification of squalene from Amaranthus grain. Journal of Agricultural and Food Chemistry 50: 368–372. Irving DW, Betschart AA, and Saunders RM (1981) Morphological studies on Amaranthus cruentus. Journal of Food Science 46(4): 1170–1174. Lamothe LM, Srichuwong S, Reuhs BL, and Hamaker BR (2015) Quinoa (Chenopodium quinoa W.) and amaranth (Amaranthus caudatus L.) provide dietary fibres high in pectic substances and xyloglucans. Food Chemistry 167: 490–496. Leon-Camacho M, Garcia-Gonzalez DL, and Aparicio R (2001) A detailed and comprehensive study of amaranth (Amaranthus cruentus L.) oil fatty profile. European Food Research and Technology 213: 349–355. Lyon CK and Becker R (1987) Extraction and refining of oil from amaranth seed. Journal of the American Oil Chemists’ Society 64: 233–236. Martinez CS, Ribotta PD, Anon MC, and Leon AE (2014) Effect of amaranth flour (Amaranthus mantegazzianus) on the technological and sensory quality of bread wheat pasta. Food Science and Technology International 20: 127–135. Paredes-Lo´pez O (1994) Amaranth: Biology, Chemistry, and Technology. Boca Raton, FL: CRC Press. Quiroga AV, Barrio DA, and Anõń MC (2015) Amaranth lectin presents potential antitumor properties. LWT – Food Science and Technology 60: 478–485. Sabbione AC, Scilingo A, and Anõń MC (2015) Potential antithrombotic activity detected in amaranth proteins and its hydrolysates. LWT – Food Science and Technology 60: 171–177.

Saunders RM and Becker R (1984) Amaranthus: A potential food and feed resource. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 6, pp. 357–396. St. Paul, MN: American Association of Cereal Chemists. Segura-Nieto M, Barba de la Rosa AP, and Paredes-Lo´pez O (1994) Biochemistry of amaranth proteins. In: Paredes-Lo´pez O (ed.) Amaranth: Biology, Chemistry, and Technology, pp. 75–106. Boca Raton, FL: CRC Press. Singhal RS and Kulkarni PR (1988) Composition of the seeds of some Amaranthus species. Journal of the Science of Food and Agriculture 42(4): 325–331. Sleugh BB, Moore KJ, Brummer EC, Knapp AD, Russell J, and Gibson L (2001) Forage nutritive value of various amaranth species at different harvest dates. Crop Science 41: 466–472. Teutonico RA and Knorr D (1985) Amaranth: Composition, properties, and applications of a rediscovered food crop. Food Technology 39(4): 49–54. Venskutonis PR and Kraujalis P (2013) Nutritional components of amaranth seeds and vegetables: A review on composition, properties, and uses. Comprehensive Reviews in Food Science and Food Safety 12: 381–412. Wang YY, Wang HS, Zhang HT, and Cui YH (2011) Research advances of amaranth as a high-quality feed plant. Feed Research (in Chinese) 1: 19–20. Williams JT and Brenner D (1995) Grain amaranth (Amaranthus species). In: Williams JT (ed.) Cereals and Pseudocereals, pp. 129–186. London: Chapman and Hall. Wu HX and Corke H (1999) Genetic diversity in physical properties of starch from a world collection of Amaranthus. Cereal Chemistry 76: 877–883. Wu HX, Yue SX, Sun HL, and Corke H (1995) Physical properties of starch from two genotypes of Amaranthus cruentus of agricultural significance in China. Starch/ Sta¨rke 47: 295–297. Yue SX, Sun HL, and Tang DF (1993) The Research and Development of Grain Amaranth in China (in Chinese). Beijing: Chinese Agricultural Science and Technology Press. Zhang FF, Jiang YP, Cao YJ, and Sun HN (2014) Feed value of amaranth and its utilization in poultry. Poultry Science (in Chinese) 3: 6–8.

Relevant Websites http://www.agmrc.org/commodities__products/specialty_crops/amaranth/ – Website of the Agricultural Marketing Resource Center, Iowa State University.

Beans: Overview SK Sathe, Florida State University, Tallahassee, FL, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

On a caloric basis, dry beans are more nutrient-dense than cereals. Among dry beans, the common bean Phaseolus vulgaris is globally consumed in the largest quantity. Dry beans contain two to three times more protein than cereals. Dry beans are low in lipids and contain no cholesterol. Dry beans are a good source of complex carbohydrates including fiber. Dry beans contain several different types of proteins that include storage proteins (e.g., 7S and 11S). Dry beans contain antinutritional factors. Dry beans are consumed in a variety of forms including split cotyledons (dal), sprouts, bean flour, porridge, fermented beans, gruel, fried beans, and others. Dry beans are often used with cereals and/or animal foods (e.g., meats).

Learning Objective

•

To achieve understanding of the global importance of legume plants, particularly the dry beans, in human food and animal feed supply

Introduction Globally, of the 50 000 edible plant species, 15 crop plants provide 90% of the world’s food energy intake. Of these 15 crops, three cereals – rice, maize, and wheat – make up twothirds of this 90% of the world’s food energy intake as they serve as the staples for over 4000 million people. Comparatively, contribution of legumes is less. However, because legumes contain almost two to three times more protein than cereals, their dietary importance as protein source is well appreciated. Of more than 1300 species of legumes, only 20 are most commonly consumed by humans. Among these, the common dry bean, Phaseolus vulgaris, is consumed in the largest quantity on a worldwide basis. Dry beans (excluding oilseeds) are low in lipids, are low in sodium, and contain no cholesterol. They are a rich source of proteins, complex carbohydrates including fiber, vitamins, and certain minerals. On a caloric basis, dry beans are more nutrient-dense than cereals. Dry beans are less expensive than animal food products and, when stored properly, have considerably longer shelf life than several animal, fruit, and vegetable products. Since legumes have the ability to fix atmospheric nitrogen and therefore add nitrogen to the crop–soil ecosystem, they are important in soil conservation and maintenance of soil quality.


Global Distribution, Varieties, and Commercial Importance The word ‘legume’ is derived from the Latin word ‘legumen,’ which means seeds harvested in pods. The term ‘pulse’ (from Latin word ‘puls’ meaning pottage) is used for legume seeds that contain small amounts of fat, while for those containing large amounts of fat (such as soybeans and peanuts), the term ‘leguminous oilseed’ is used. According to the Food and Agriculture Organization (FAO), the word ‘legume’ is used for all leguminous plants. The most commonly used legumes as human food are listed in Table 1. Although legumes have been cultivated for several thousand years, the chronology and origins of domestication of food legumes are almost impossible to reconstruct. Some legumes (e.g., lentils) have been dated back to 7000–6000 BC. Leguminosae (or Fabaceae) is the third largest family of flowering plants (after Compositae and Orchidaceae) in size and economic importance and is second only to the grasses (Gramineae). Current estimates indicate that Leguminosae has 16 000–19 000 species in 750 genera. The subclassification is somewhat controversial. Almost all of the domesticated legumes used as food are members of Papilionoideae. All of the common beans belong to the tribe Phaseolae. Global production of dry beans and pulses (Table 2) remains important for human and animal nutrition. On a worldwide basis, the common beans (Phaseolus spp.) are the number one crop among dry beans (excluding oilseeds) in both production and consumption and are therefore economically an important crop. In 2009, the global dry bean supply was 2.4 kg per capita per year. Asia produces the largest quantity (46.11% of the total world production) of dry beans followed by the Americas (31.08%), Africa (20.48%), Europe (2.11%), and Oceania (0.22%). In 2011, Brazil (12.19%), India (15.69%), China (6.32%), Myanmar (16.08%), Mexico (4.67%), and the United States (6.26%) accounted for 61.21% of the global dry bean production. Europe (21.41%), the Americas (16.08%), and Africa (10.28%) lead world imports of dry beans in terms of dollar value (Table 2). India, Japan, the United States, Brazil, the United Kingdom, Italy, Mexico, and China, respectively, accounted for 17.58%, 6.70%, 6.13%, 4.60%, 4.35%, 4.22%, 3.18%, and 2.07% of the total dollar value (42.76%) of worldwide imports ($3 227 563 000) of dry beans. Asia (49.55%) and the Americas (34.99%) account for 84.54% of the global export of dry beans (Table 2). In 2011, the leading exporting countries of dry beans were China, Myanmar, Argentina, the United States, and Canada, respectively, accounting for 29.17%, 15.88%, 10.67%, 9.74%, and 6.96% of the total dollar value (72.42%) of worldwide dry bean exports.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00033-4

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298 Table 1

THE LEGUMES AND PSEUDOCEREALS | Beans: Overview Grain legume species commonly used for food purposes

Botanical name

Common name

Arachis hypogaea Cajanus cajan Ca. indicus Canavalia ensiformis C. gladiata Cicer arietinum Ci. minotinum Cyamopsis tetragonoloba Dolichos biflorus D. lablab Ervum vulgaris Faba vulgaris Glycine max G. hispida G. soja Lablab niger La. purpureus Lathyrus sativus Lens esculenta Le. culinaris Lupinus spp. Macrotyloma uniflorum Mucuna pruriens Phaseolus aconitifolius Ph. acutifolius Ph. angularis Ph. aureus Ph. calcaratus Ph. lunatus Ph. mungo Ph. radiatus Ph. vulgaris

Groundnut, peanut, monkey nut, goober pea, nguba Pigeon pea, arhar, red gram, tur, toovar Angola pea, gandal, ambre vade, alverja Pigeon pea, Congo pea, yellow dal Jack bean, horsebean, gotani bean, haba de burro, Chickasaw lima Sword bean, maxima Chickpea, Bengal gram, chana, desi chana, kabuli, chiche Chana, garbanzo Cluster bean, guar, aconite, cyamopse Horse gram Hyacinth bean, bonavist, field bean, caballeros, Indian butter bean, val bean, Egyptian kidney bean Lentils, masoor dal Windsor bean Soybean, soja

Pisum sativum Pi. angularis Pi. arvense Psophocarpus tetragonolobus Sphenostylis stenocarpa Stizolobium spp. Tetragonolobus purpureus Trigonella foenumgraecum Tylosema esculentum Vicia faba Vic. sativa Vigna aconitifolia Vig. aureus Vig. radiata Vig. mungo Vig. sinensis Vig. umbellata Vig. unguiculata Voandzeia subterranea

Lablab bean Kidney bean, hyacinth bean, Indian bean, lubia bean Grass pea, kesari dal, vetch, chickling vetch, chicaro Lentils, masoor dal, red dal, lentil, split pea, lentija Lupins, tarwi, tarin, pearl lupin, wolf bean, tremoco Horse gram, Madras gram, kallu, kulthi bean Velvet bean, cowage, Mauritius bean, stizolobia Moth bean Tepary bean, pavi, Yorimuni, dinawa Adzuki bean, feijao Mung bean, green gram, golden gram, chiroko, chicka sano pea Rice bean, frijol arroz Lima bean, sieva bean, Madagascar bean, sugar bean, Burmabean, towe bean, pole bean, caraota, panguita Mung bean, mungo bean, urd dal, black gram, urad, woolly pyrol, kambulu Mung bean, golden graham, green gram Dry bean, haricot, common bean, kidney bean, navy bean, pinto or snap bean, feijao, opoca, rajma, French bean, chumbinho Dry pea, green pea, garden pea, field pea

Winged bean (humid tropics), goa bean, asparagus bean, Colombo, four-angled bean, princess bean Yam bean Velvet bean Winged bean (Europe) Methi, fenugreek Marama bean Broad bean, horsebean, faba bean, field bean, Windsor bean Vetch Moth bean, matki, mouth bean, mat, math Mung bean Black gram, urd, urad, kambulu, pyrol Dry cowpea Rice bean, red bean, mambi bean Black-eyed cowpea, black-eye pea, cowpea, kaffir bean, Hindu pea, asparagus pea Bambara groundnut, Madagascar groundnut, earthpea, Congo goober, kaffir pea, jugo bean, haricot pistache

Data from Deshpande SS and Srinivasan D (1990) Food legumes: Chemistry and technology. Advances in Cereal Sciences and Technology 10: 147–241; Doughty J and Walker A (1982) Legumes in Human Nutrition. Food and Nutrition Paper 20, 152 pp. Rome, Italy: Food and Agriculture Organization of the United Nations.

Morphology of the Pods/Seeds Regardless of the fat content, most legume seeds have similar structure. Mature legume seeds have three major components:

the seed coat, the cotyledons, and the embryo axis. In most dry seeds, they account for 8–20%, 80–90%, and 1–2% of the seed weight, respectively. The majority of the nutrients are present in cotyledons. Typical seed structure and various anatomical

THE LEGUMES AND PSEUDOCEREALS | Beans: Overview Table 2

World Africa Asia Caribbean Europe Central America North America South America Oceania

299

Acreage, production, yield, and import/export data for pulses and dry beans Area harvested (Ha)

Yield (Hg/Ha)

Production (tons)

Import

Export

P

D

P

D

P

D

Tons D

$ D

Tons D

$ D

5 903 158 1 890 425 2 617 155 2156 688 286 8750

28 780 377 7 198 019 14 499 325 257 317 263 487 2 278 678

8554 6357 6404 13 919 17 230 31 657

8040 6585 7359 9195 18 536 7240

5 049 539 1 201 768 1 675 921 3001 1 185 919 27 700

23 140 276 4 740 016 10 670 688 236 602 488 408 1 649 772

3 321 726 408 551 1 397 795 100 273 609 885 230 600

3 227 563 000 331 881 000 1 343 293 89 401 000 690 887 000 220 369 000

3 393 895 311 174 1 681 843 897 139 648 104 363

3 074 549 000 212 970 000 1 523 401 000 1 019 000 167 956 000 117 170 000

NA

804 482

NA

21 392

NA

1 720 950

225 709

258 776 000

603 769

513 547 000

1790

3 419 069

14 441

10 482

2585

3 583 840

332 041

272 811 000

455 509

444 047

694 596

60 000

13 715

8333

952 645

50 000

15 872

20 145 000

96 692

94 439 000

P, pulses; D, dry beans. The import export data are for 2011 and the rest for 2012. Data from FAO (2012 and 2011) Statistical Databases. Rome, Italy: Food and Agricultural Organization of the United Nations (http://faostat.org/site339/default.aspx and http://faostat. fao.org/site/535/default.aspx#ancor; accessed on 01.05.2014).

Seedcoat (testa) Cotyledon Raphe Plumule Hypocotyl Radicle

Hilum Micropyle (a)

(b)

Micropyle (c) Hilum

Outer integument Seedcoat Inner integument

Epidermis Cotyledon Storage parenchyma cells (d)

Figure 1 Dry bean (Phaseolus vulgaris) seed: (a) external side view, (b) external face or edge view (viewing at hilum side), (c) cross section (one cotyledon removed), and (d) detailed cross section across seed coat and cotyledon. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 407, Elsevier Ltd.

parts of legume seeds are shown in Figure 1. The outermost layer of the seed is the seed coat or testa. The external seed structure includes the hilum, micropyle, and raphe. The hilum is a scar-like structure (usually oval shaped) near the middle edge where the seed breaks away from the stalk. The micropyle

is the small opening in the seed coat where originally the pollen tube enters the valve. The raphe is the ridge at the side of hilum opposite to the micropyle and represents the base of the stalk that fuses with the seed coat upon seed maturation. In most legumes, the endosperm is short-lived and shrinks to a

300

THE LEGUMES AND PSEUDOCEREALS | Beans: Overview

thin layer surrounding the cotyledons (or embryo). On soaking the seeds, the endosperm is easily removed along with the seed coat. The remainder (embryo) of the seed consists of shoot (which contains two cotyledons) and a short axis above and below the cotyledons and terminates in the shoot tip. The plumule or embryonic stem is well developed in the resting seed and lies between two cotyledons. The outermost layer of seed coat is the cuticle, which has papillae or papillae-like growth in some legumes (e.g., green gram), but in most legumes, it is a smooth structure. The thickness of the seed coat is quite variable depending upon the type of bean. Generally, seeds containing thick seed coats tend to have high fat content. Both the hilum and micropyle are important in water imbibition by the testa. Palisade cells derived from the outer epidermis of the outer integument, which are next to the cuticle, are either loosely packed or densely packed, depending upon the seed maturity, and may affect seed hydration. Next to palisade cells are the hourglass cells. The shape of hourglass cells can vary from bottle-shaped (guar) to dumbbell-shaped (broad beans) to hourglassshaped (soybeans). Only a few legume species (such as Dolichos, Cajanus, and Vigna) have more than one layer of hourglass cells. The remainder of the testa contains primarily mesophyll cells. Legume cotyledons are primarily composed of parenchyma cells, which have variable size (70–100 mM) and act as storage sites for most nutrients. Each cell of the cotyledon is bound by the cell wall and the middle lamella. Vascular bundles in cotyledons generally are devoid of any filling material. Vascular bundles Table 3

are often used as key structures in the identification of different plant types.

Chemical and Nutritional Composition The majority of nutrients in dry beans are primarily located in the cotyledons and account for up to 90% of the total nutritive value. Typically, dry beans provide 1255–1464 kilojoules (kJ) per 100 g of dry seeds. The main constituents of cotyledons are proteins and carbohydrates and, respectively, account for 15–25% and 50–75% of the total seed weight. The remaining components consist of lipids, minerals, fiber, and vitamins. With the exception of oilseeds, dry beans generally contain low amounts (1–3% of seed weight) of lipids. Although most minerals are present in cotyledons, some (such as calcium and iron) may be present in the seed coat in significant proportion. Typical nutrient composition of several Phaseolus beans is shown in Table 3. Dry beans contain not only significant amounts of nutrients but also several undesirable components and attributes: inhibitors of enzymes such as trypsin, chymotrypsin, subtilisin, amylases, and elastase; lectins; phenolic compounds including tannins; phytates; toxic amino acids mimosine and djenkolic acid; cyanogenic glycosides, which produce HCN; flatulence-causing oligosaccharides raffinose, stachyose, and verbascose; lipoxygenases, which catalyze the development of rancidity; and off odors often described as beany, grassy, painty, cardboard-like, and chalky.

Proximate composition of Phaseolus beans

Bean

Moisture (%)

Protein (%)

Carbohydrates (%)

Fat (%)

Ash (%)

Crude fiber (%)

Adzuki Black beauty Black gram California small white Cranberry Great Northern Lima Baby Large Mung Green Black Navy Pinto Red kidney Light Dark Rice bean Roshina G2 Roshina pink Sanilac Tepary Small red Small white Viva pink

11.00 10.41 10.2–10.9 9.65 12.71 8.5–13.3 13.30–20.40 8.90

20.20 22.87 19.7–24.0 25.90 23.43 21.0–24.37 20.40 22.30

49.80 70.79 56.6–63.4 58.00 71.26 61.2–71.07 62.10 63.80

1.90 4.48 1.3–1.6 0.25 1.09 1.0–3.48 0.80 0.80

4.39 1.86 3.2–3.4

4.90 4.4–6.4

4.22 3.5–4.86 3.40 4.20

6.70 6.00 7.40

17.92 13.64 9.4–18.2 9.05–14.70

27.12 25.68 23.13–24.65 18.8–24.97

62.85 64.20 61.2–66.19 61.8–69.47

1.53 0.45 1.5–4.3 1.2–3.6

4.01 4.32 2.90–4.27 3.07–4.10

4.50 5.30 3.4–6.6 3.9–6.3

10.52 13.22

20.89 20.32 18.0–25.0 25.77–26.30 19.40 18.98 21.0–25.0 22.45 19.73 21.30

73.20 73.68 60.0–77.0 63.33–64.02 68.80 75.09 70.0–73.0 71.97 74.34 73.23

1.52 1.58 1.0–1.6 1.85–2.00 3.50 1.65 0.8–0.9 1.43 1.99 1.06

4.39 4.42 3.8–4.3 3.19–3.79 3.40 4.28 4.1–4.8 4.15 3.94 4.41

9.89–11.11 4.90 11.61 13.12 13.03 12.69

3.3–4.8 4.6–5.1 4.60

Data expressed on dry weight basis. Data compiled from Sathe SK, Deshpande SS, and Salunkhe DK (1984) Dry beans of Phaseolus: A review. Part 1. Chemical composition: Proteins. CRC Critical Reviews in Food Science and Nutrition 20: 1–46; Salunkhe DK and Kadam SS (1989) Handbook of World Food Legumes: Nutritional Chemistry, Processing Technology, and Utilization, Vols. I (310 pp.), II (294 pp.), and III (323 pp.). Boca Raton, FL: CRC Press.

THE LEGUMES AND PSEUDOCEREALS | Beans: Overview Proteins Phaseolus beans not only are important for their caloric contribution to human diet but also are especially valued for their protein content since they are a major protein contributor to the human diet on a global basis. In certain parts of the world, they are the sole source of dietary protein. Dry bean proteins can be classified as storage and metabolic proteins. The original protein classification proposed by Osborne was based on solubility of proteins in a series of solvents. In this scheme, the water- and dilute salt-soluble proteins were termed as albumins and globulins, respectively. Dry beans contain 40–60% globulins and 20–40% albumins based on Osborne’s protein classification. Globulins are exclusively storage proteins, while albumin fraction contains both storage and metabolic proteins. The protein content of dry beans is usually calculated by multiplying Kjeldahl nitrogen content by a factor of 6.25. Because dry beans contain 10–15% of total nitrogen as nonprotein nitrogen, most dry bean protein values are typically overestimated by 1–2%. The major storage proteins in dry beans have been identified by several names and therefore their nomenclature is somewhat unclear. Based on the nomenclature using ultracentrifugation sedimentation coefficient (S), dry beans contain both 7S (vicilin-like) and 11S (legumin-like) storage proteins. Depending on the bean variety, the relative proportion of these two types of proteins varies considerably. The 11S-type proteins typically are nonglycosylated proteins with estimated molecular weight (MW) in the range 300 000–400 000. They are usually composed of six subunits (MW 60 000), each consisting one acidic (MW 40 000) and one basic (MW 20 000) polypeptide linked by disulfide bond(s). Usually, 11S proteins are present in minor amounts in Phaseolus beans. The 7S globulin in Phaseolus beans has also been referred to as glycoprotein II, globulin 1, euphaseolin, globulin, and phaseolin. Depending on the type of bean, the 7S globulin type and quantity vary considerably. In Phaseolus beans, the 7S globulins are, however, the major storage proteins and account for 40–60% of the total proteins. The three major types of 7S proteins that have been identified, biochemically purified, and characterized are (1) phaseolin, (2) lectin (also called glycoprotein II, phytoagglutinins or phytohemagglutinins, and protein II), and (3) arcelin in wild bean accessions from Mexico (named after town Arcelia in Mexico, where some of the accessions were collected). All the 7S globulins are glycosylated and contain D-mannose and D-glucosamine as the major sugar constituents.

Phaseolin Phaseolin is the major globulin in domesticated Phaseolus beans. It is a trimeric, vicilin-like 7S globulin known to exhibit polymorphism. The polypeptide polymorphism is believed to be not only due to the differential glycosylation but also because phaseolin polypeptides are encoded by a small multigene family. Phaseolin is soluble in 0.5 M NaCl at all pH values. It undergoes reversible pH-dependent dissociation–association with sedimentation coefficients of 3.0S (pH 12.0), 7.1S (pH 7.0), and 18.2S (pH 3.6) known as peptides (MW 44 000), protomers (MW 163 000), and tetramers of protomers (MW 653 000). Phaseolin consists of a group of subunit polypeptides with MWs 43 000–54 000 and isoelectric points

301

from pH 5.6 to 5.8, depending on phaseolin type. Among Phaseolus beans, three distinct types of phaseolins – named after cultivars Tendergreen (T), Sanilac (S), and Contender (C) – have been identified. Screening of 107 cultivars has revealed that S-, T-, and C-type phaseolins accounted for 69%, 25%, and 6%, respectively, of the total cultivars. These types can be easily distinguished by one-dimensional or twodimensional gel electrophoresis using sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) for onedimensional or isoelectric focussing in first dimension followed by SDS-PAGE in the second dimension for twodimensional gel electrophoresis. The C-type phaseolin is believed to have originated from T and S types. Regardless of the type of phaseolin, phaseolin contains 3–5% carbohydrates and its amino acid composition is dominated by acidic amino acids (30–40% of total). Typically, the N-glycosylation sites in phaseolin polypeptides occur at amino acid residue numbers 252 and 341. Sulfur-containing amino acids (notably methionine) are the limiting amino acids in phaseolin as well as other major storage proteins in Phaseolus beans. The secondary structure of phaseolin in 0.5 M NaCl typically has a low a-helix content (10%) and b-turns (9.0%) and large amount of b-sheet (48.0%) and random coils (33.0%). Native phaseolin is quite resistant to digestive proteases such as pepsin, trypsin, and chymotrypsin and is degraded to polypeptides with MWs 24 000–28 000. However, heat-denatured phaseolin is easily digested by these proteases.

Lectin Bean lectins agglutinate erythrocytes due their ability to bind with cell surface glycoproteins and glycolipids. Although the precise function of lectins in beans is not known, they are thought to offer protection to the plant. Since lectins are toxic, they are of nutritional concern. Lectins occur in both albumin and globulin fractions. Certain bean cultivars lack lectins. When present, lectins represent 6–12% of total protein. In addition to agglutinating activity, many bean lectins have mitogenic activity. Most lectins of Phaseolus beans have subunits of MWs 29 000–36 500 with isoelectric pH in the range 4.9–7.9 (most are in the pH range 5–6). The majority of the native lectins have tetrameric nature (MWs 100 000–150 000) although some (e.g., lima beans) have dimeric nature. The majority of Phaseolus lectins have 4–6% carbohydrate, low sulfur-containing amino acids, and sugar specificity toward D-acetylgalactosamine. Lectins are very resistant to common digestive proteases and are slowly hydrolyzed in vitro even after extensive heat denaturation. Proper moist-heat denaturation can completely inactivate the biological activity of lectins and therefore can render them nontoxic.

Arcelin Arcelin was first discovered in wild accessions of Mexican Phaseolus beans. It also occurs in lines that contain phaseolin as well as lectin. Because it is present in equal or greater levels than phaseolin in certain lines, it is one of the major storage proteins in Phaseolus beans. The MWs of arcelin subunit polypeptides range from 35 000 to 42 000 depending on the variant and are more basic than both lectin and phaseolin. The native arcelin has an MW of 89 000 and is therefore a dimeric protein. Arcelin has many similarities with lectin

302


(including agglutinating activity) with respect to chemical composition.

shown to be 50 000. Appropriate moist-heat treatment (such as cooking or autoclaving) can inactivate both the protease and amylase inhibitors.

Other proteins Phaseolus beans contain trypsin inhibitors (many of them also inhibit chymotrypsin), amylase inhibitors, lipoxygenases, and several other minor protein components. Most of these proteins are a part of albumins. Trypsin and chymotrypsin inhibitors in Phaseolus beans typically account for up to 10% of the total proteins and are generally rich in sulfur amino acids. The MWs of these inhibitors range from 2000 to 23 000. Most Phaseolus beans lack Kunitz-type (inhibitors with 170–200 amino acids with MW of 20 000) trypsin inhibitors. Amylase inhibitors in dry beans have been characterized from only a few cultivars and therefore not yet extensively studied. The MW of kidney bean amylase inhibitor (a glycoprotein) has been Table 4

Dry beans Chickpea Cicer arietinum Cowpea Vigna sinensis Grass pea Lathyrus sativus Green pea Pisum sativum French (green) bean Lentil Lens culinaris

Mung bean Vigna radiata

MW (kDa) SDS-PAGE

Identity

Allergen designation

Seq.a

Accession number

10–106

41, 55

20, 20–30, 33, 50 1.8 8.8–9

Albumins

12546052

11295670

Vicilin-like proteins

12589366

Glycoprotein Nonspecific lipid transfer protein type 1 (ns-LTP-1) Nonspecific lipid transfer protein 1b precursor

991447 C

GQ434007.1

C

GQ434008.1

12–84

48 66 16

11080720, 10604559, 9893199 Vicilin-like protein Seed-specific biotinylated protein Pathogenesis-related protein, PR-10 Bet v 1 family member 8S globulin (vicilin) Albumin Cytokinin-specific binding protein (CSBP), Bet v 1 family member

Len c 1 Len c 2

11.2

2S albumin

12

2S albumin 11S crystalloid protein Protein doublet

47/51 30–175

PubMed index

11527247, 10705224

21, 28, 46

53 30 18

Lupin Lupinus albus Peanut

With heightened concerns about food allergies and the increased frequency of food recalls due to actual or suspected presence of allergen in food, food-induced allergens are of increased interest to consumers and regulatory agencies alike. Since any food protein could be a potential allergen, it is important to recognize that dry bean proteins may be allergenic. Compared to aeroallergens, such as pollen, perhaps with the exception of peanut and soybean proteins, very little is known about dry bean protein allergens. A few dry bean proteins have been identified to be allergens (Table 4) and even

Recognized legume allergens

Legume

Oil seeds Castor bean Ricinus communis

Allergenic Proteins

C P C

AY792956.1

C C C

Q198W3, B1NPN8 Q43680 AB012218

Ric c 1

C

P01089

Ric c 3 Ric c 2

P

11080720

9430499 9430499 3392372 3392372 10359910

THE LEGUMES AND PSEUDOCEREALS | Beans: Overview Table 4 Legume Arachis hypogaea

Soybean Glycine max

303

(Continued) MW (kDa) SDS-PAGE

Identity

Allergen designation

Seq.a

Accession number

PubMed index

63.5

Vicilin-like protein

Ara h 1

C

7560062

17

Conglutin

Ara h 2

C

60

Glycinin

Ara h 3

C

37

Glycinin

Ara h 4

C

15 15 15 17 30, 50, 68 12

Profilin Hom: conglutin Hom: conglutin Pathogenesis-related protein (PR-10) Oleosin oligomers Oleosin monomer

Ara h 5 Ara h 6 Ara h 7 Ara h 8

C C C C

L34402, L38853, AF432231 L77197, AY158467, AY117434 AF093541, AF510854 AF086821, AF510854 AF059616 AF092846 AF091737 AY328088

7

Hydrophobic seed protein (HPS)

Gly m 1A/1B

P

8 14

Hull protein Profilin 1, Profilin 2

Gly m 2 Gly m 3

P C

17 21 26

(SAM 22) PR-10 prot. Trypsin inhibitor Vicilin-like glycoprotein

Gly m 4

C

AAB34755, AAB34756 A57106 AJ223981, AJ223982 X60043

C

AB046874

34

Oil body associated glycoprotein

Gly m Bd 28k Gly m Bd 30k Gly m Bd 60k

12417891 8836337, 11799388 11267676

C

AB013289

11227798

Alpha-subunit of beta-conglycinin 22 15 7, 12, 20, 39, 57 12 20

14538941, 11295663 10021462 10474031 10474031 10474031 10474031 12144563 12144563 7603155

10589015

7787297

G2 glycinin Glycinin G1 acidic chain Soy lecithins

11112856 11146387 11752879

Methionine-rich protein (MRP), 2S albumin Soybean Kunitz-type trypsin inhibitor (SKTI)

P

11752879

P

11752879

a

Sequence source: P, protein; C, cDNA. Compiled in part from the International Union of Immunological Societies, Allergen Nomenclature Sub-committee http://www.allergen.org/list.htm.

fewer have been characterized at molecular level. Phaseolin, the major storage globulin in dry beans, has not yet been reported to be an allergen. Among the legume proteins identified to be allergens, majority appear to be storage proteins such as 2S albumins (e.g., Ric c 1, Ric c 3, and soybean MRP), 7S or vicilin-like proteins (e.g., Ara h 1, b-conglycinin, and Len c 1), and 11S or legumin-like proteins (e.g., soybean glycinin, Ara h 3, and Ara h 4), some of which are glycosylated (Ara h 1 and Gly m Bd 28 k), while others are not (soybean glycinin). Since typical thermal food processing does not significantly hydrolyze food proteins, linear stretches of amino acids responsible for IgE binding, the linear epitopes, are expected to survive normal food processing operations. For these reasons, food processing is often unable to completely inactivate food allergens. It is therefore also not surprising that some investigators find many legume allergens to be acid- and heat-resistant.

Carbohydrates Total carbohydrates in Phaseolus beans contribute 50–70% of the seed weight and include mono-, di-, and oligosaccharides; starch; and other polysaccharides. Starch is the most abundant nutrient in Phaseolus beans accounting for up to 70–80% of total carbohydrates. Among the simple sugars, oligosaccharides (raffinose, stachyose, verbascose, and ajugose) are the major constituents (up to 10% of seed weight) and are at least partially responsible for flatulence production. Crude fiber is primarily composed of cellulose, hemicellulose, lignins (not a carbohydrate), and other nonstarchy polysaccharides such as arabinogalactans, arabinoxylans, glucomannans, galactomannans, and pectins. The hypocholesterolemic effect of dry beans is partially attributed to the presence of nonstarchy polysaccharides. Phaseolus bean starch granules are quite variable in

304


shape (round, oval, oblong, elliptical, spherical, kidney-shaped, and irregular) and size (5–60 mm) and typically contain 10–45% (of total starch) amylose. The average degree of polymerization for amyloses and chain lengths for amylopectins of Phaseolus bean starches ranges from 1600 to 1900 and 22 to 26, respectively. Based on x-ray diffraction spectra, Phaseolus dry bean starches are mostly C type (mixture of A (typical of cereal starches) and B (typical of root and tuber and high-amylose cereal starches) types). These starches have restricted swelling, gelatinization temperature range of 60–89 C, high solution viscosities, and good thermal stabilities. Upon gelatinization, they produce opaque gels. Dry bean starches (especially if cooked) are well digested (digestibility is comparable to those of many cereal and tuber starches) by humans. However, as dry bean starches are digested slowly, they are hypoglycemic and therefore useful in the diets of diabetics. The nonstarchy polysaccharides are not digestible in many mammals due to the lack of required enzymes in their digestive tracts and therefore contribute to the total dietary fiber. These nonstarchy polysaccharides help increase viscosity and may thereby lower digestion rate of starch (i.e., lower glycemic index). Further, they may assist removal of dietary lipids (i.e., hypocholesterolemic effect).

Vitamins and Minerals Phaseolus beans are a good source of B vitamins, especially thiamin, riboflavin, niacin, and folacin. Typically, thiamine, riboflavin, niacin, and folacin contents (on a dry weight basis) of Phaseolus beans are, respectively, 0.5–1.14, 0.1–0.25, 0.4–3.14, and 0.037–0.676 mg per 100 g. Vitamin E content ranges from 0.72 to 1.97 mg per 100 g and B6 content ranges from 0.2 to 0.659 mg per 100 g. Phaseolus beans are not good sources of vitamin A and C. Phaseolus beans are excellent sources of several minerals including Ca, Fe, Cu, Zn, P, K, and Mg. Typically, raw beans contain 70–260, 0.5–1.40, 3.34–13.5, 160–320, 1.0–2.1, 380–570, 1320–1780, 4.0–21.0, and 1.9–6.5 (all expressed as mg per 100 g, dry weight basis) of Ca, Cu, Fe, Mg, Mn, P, K, Na, and Zn, respectively. The low sodium and high potassium content of raw beans makes them a desirable constituent of human food (especially for people with hypertension).

Antinutritional Factors In addition to protease inhibitors and amylase inhibitors, Phaseolus beans contain several other antinutritional and antiphysiological factors such as phytic acid, tannins, cyanogenic glycosides, saponins, and allergens. Because these components are usually present in small quantities (less than 5% of the total seed weight), they do not pose a serious health hazard under normal conditions (i.e., when beans are a part of total diet and are properly processed prior to consumption). Of these antinutritional factors, phytates and tannins are of particular concern because both of them are heat-stable and cannot be easily removed from beans during normal home processing. Phytate is a general term used for mono- to dodeca anions of phytate along with esters lower than hexaphosphate. Ca–Mg salts of phytic acid (myoinositol 1, 2, 3, 4, 5, 6-hexakis (dihydrogen phosphate)) are referred to as phytin. In most dry

beans, phytate phosphorus accounts for up to 80% of the total phosphorus. The amount of phytate in Phaseolus beans ranges from 0.6% to 2.1% (by weight) of the total seed weight. Because phytates are chelating agents, they may interfere in mineral utilization. Germination, fermentation, and soaking followed by cooking (if both soak and cook waters are discarded) are effective methods of removing phytates (50–80% reduction). Tannins (especially condensed tannins) are heatstable compounds and are present in Phaseolus seeds (especially in colored varieties) up to 2% of total seed weight. Because of their ionic character, they may interact with other constituents (notably proteins) and adversely affect the nutritional bioavailability of that constituent. Tannins are thought to offer protection to the plant from insects and pests.

Lipids Phaseolus beans contain 1–3% lipids (by weight) depending upon the species. Neutral lipids (30–50% of total) and phospholipids (25–35% of total) are the major constituents, and glycolipids may account for up to 10% of the total lipids. Regardless of the variety, Phaseolus bean lipids primarily contain palmitic, oleic, linoleic, and linolenic acids. Polyunsaturated fatty acids and saturated fatty acids typically account for 55–87% and 12–28% of total lipids.

Beneficial Bioactive Compounds Continuing research on raffinose oligosaccharides, phytates, tannins, simple phenolic compounds, sterols, protease inhibitors, and several other major and minor constituents of dry beans suggests that some of these compounds, under appropriate conditions, may offer beneficial effects for human health. Numerous reports suggesting the beneficial effects of one or more components (either alone or in combination) have appeared. These investigations have used in vitro and in vivo model studies to decipher possible beneficial effect(s). The primary goals of these investigations are to (a) derive nutritionally beneficial effect for long-term good physical and mental health and (b) treat/cure disease. Experimental demonstration of cause–effect relationship can be tenuous and difficult to prove/disprove and may depend on the experimental design. With the simultaneous presence of several compounds in the same food source, establishing unequivocal relationship between the compound(s) and their physiological effect(s) is, at best, very difficult. In recent years, attempts to investigate the underlying molecular and mechanistic basis for the reported beneficial effect(s) of tested compound(s)/component(s) have therefore often resulted in outcomes with very limited success. Long-term detailed and fundamental research is needed to fully realize the potential health benefits of dry bean consumption.

Grading, Handling, and Storage Dry beans are usually harvested at maturity. The seeds are removed from the pods either manually or mechanically and cleaned to remove dirt, stalks, leaves, blemished, wrinkled, and broken seeds and packaged prior to storage. The grading of


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seeds is usually based on external characteristics such as color, gloss, seed size, seed soundness, seed firmness, and presence of contaminating substances. The seeds are stored at farmer, trader, or government levels. Typically, farmers hold up to 8% of harvested seeds until next season so that they can be used as planting seeds if crop failures occur. In developed and developing nations, a majority of the seeds are stored by traders and/or governments to protect against subsequent crop failures (or low yields), price fluctuations, and fluctuations in supply (change in demand, shortages, and famines). Losses in seeds occur both pre- and postharvest. The normal preharvest losses are mainly due to birds and mammals feeding on bean plant seeds. Drought/floods, insects, and rodents can also contribute to preharvest losses. In developed nations, preharvest losses are usually small (as low as 1% of the crop). A majority of the losses occur during postharvest handling and storage and can range from 8% to as high as 50% of total crop. It is estimated that as much as 48% of food produced in the world is lost (due to pre- and postharvest losses). Factors that influence postharvest losses of legumes include moisture, temperature, respiration rate, insect damage, microbial spoilage, and damage caused by mites and rodents. Properly packaged dry beans should be stored at low relative humidity and temperature conditions. High relative humidity and temperature favor the ‘hard-to-cook’ beans. These conditions also favor the growth of molds and insects. Three major insect genera that cause much of the damage to stored legumes are Bruchus, Acanthoscelides, and Callosobruchus. Dehusked, split stored pulses are also damaged by Rhyzopertha, Trogoderma, and Tribolium species. Usually, pests seem to have preference for the type of bean they infest although the basis for such preference (or the lack of it) has not been elucidated yet. The major microbial problem during bean storage is contamination by aflatoxin-producing molds (Aspergillus flavus and Aspergillus parasiticus). Mites can consume food up to their own weight (6–8 mg) and because of their large numbers can cause serious losses. Rodents cause twofold damage to stored legumes by not only consuming but also contaminating (up to 20 times the amount they would eat). Because rodents are carriers of many communicable diseases, they pose serious damage to stored beans. The species that most commonly cause damage include Rattus rattus, R. norvegicus, Bandicota indica, B. bengalensis, and Mus musculus.

preparation of ‘idli,’ a breakfast food popular in India and Sri Lanka, after fermenting it with rice. Industrial processing includes freezing for such beans as green French beans and snap beans, milling (production of flours and high-protein flours), baking (baked beans), cooking and frying (refried beans), and canning (alone in saltwater or tomato juice or in combination with meats such as beef and pork). In developing countries, dehusking and splitting to produce ‘dal’ is also done at industrial scale. In developing and underdeveloped countries, Phaseolus beans are used in numerous ways depending on the type of bean and regional preference. They may be eaten as raw, immature seeds; cooked as green vegetables (such as French beans); consumed as part of salads; used in making curry; used as a soup ingredient; cooked, mashed, and mixed with condiments and spices and used as gruels and porridges; prepared as pastes to be extruded to prepare fried snack products; sprouted; puffed or roasted and eaten as snack foods; and fermented to prepare numerous fermented products. In developed countries, Phaseolus beans are consumed as salad and soup ingredient, sprouts, canned, frozen, and refried beans. They are also extensively used in the preparation of Mexican-style preparations, such as burrito, chimichanga, taco, bean dips, and tamale, and often canned with meats such as beef and pork. In many South American countries, cooked black beans are a preferred part of breakfast. With increased ethnic populations in the Western world, increased emphasis on vegetarian foods, and recommended reduction of meats and animal foods in the human diet, opportunities need to be explored to incorporate dry beans in food products for improved and nutritious food products. Although there is a good potential for the preparation of protein concentrates and isolates and the development of food starches, Phaseolus beans have not been used on large scale for such purposes. In many countries, especially the developed ones, Phaseolus beans have been extensively used as animal feed. In developing and underdeveloped countries, the green foliage, deseeded pods, and roots and shoots of bean plants are used as natural fertilizers especially after composting. Because the legume roots fix nitrogen, they help conserve soil quality. For this reason, in many developing countries, they are extensively used for soil quality conservation.

Processing and Food Uses


Phaseolus beans are processed and used in a variety of ways. The processing of beans is mostly at the household level in developing and underdeveloped countries, while in most developed countries, the majority of the processing is done at the industrial level. Home processing methods include milling, soaking, cooking, frying, germination, fermentation (either alone or in combination with cereals), roasting, puffing, parching, extrusion and frying, and toasting. The method(s) used for home processing depends on regional preference for bean variety and the desired end product. For example, mung beans in sprouted form are popular on global scale and therefore germination is one of the preferred household processing methods used. Black gram, on the other hand, is extensively used for the

• • • • • • •

What distinguishes cereals from legumes? What is the difference between the terms legume and oilseed? Which type of beans are the most widely consumed in the world? Which compound(s) account for 80% phosphorus in dry beans? What is the advantage of using dry beans with cereals in foods? What is the advantage of the nonstarchy polysaccharides present in dry beans in human nutrition? What is the difference between the terms ‘pulse’ and ‘legume’?

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• • • •

What are the possible beneficial actions of bioactive components of dry bean? What are the factors that result in pre- and postharvest losses? How does the ionic character of phytic acid influence its interaction with dietary minerals and proteins? In what ways can the dry bean utilization be improved?

See also: Agronomy of Grain Growing: Lentil: Agronomy; Breeding of Grains: Lentil: Breeding; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Proteins: The Protein Chemistry of Dicotyledonous Grains; The Basics: Taxonomic Classification of Grain Species; The Legumes and Pseudocereals: Chickpea: Overview; Grain Legumes and Their Dietary Impact: Overview; Pea: Overview.

Further Reading Broughton WJ, Hernandez G, Blair M, Beebe S, Gepts P, and Vanderleyden J (2003) Beans (Phaseolus spp.) – Model food legumes. Plant and Soil 252: 55–128. Derbyshire E, Wright DJ, and Boulter D (1976) Legumin and vicilin, storage proteins of legume seeds. Photochemistry 15: 3–24. Deshpande SS (1992) Food legumes in human nutrition: A personal perspective. CRC Critical Reviews in Food Science and Nutrition 32: 333–363.

Doughty J and Walker A (1982) Legumes in Human Nutrition, p. 152. Rome, Italy: Food and Agriculture Organization of the United Nations Food and Nutrition Paper 20. FAO (2013) http://faostat.fao.org/site/567/DesktopDefault.aspx?PageID¼567#ancor (accessed 22.02.2014). FAO (2013) Dimensions of Need – Staple Food: What Do People Eat? http://www.fao. org/docrep/u8480e/u8480e07.htm (accessed 22.02.2014). Geil PB and Anderson JW (1994) Nutrition and health implications of dry beans: A review. Journal of the American College of Nutrition 13: 549–558. Guillon F and Champ MM (2002) Carbohydrate fractions of legumes: Uses in human nutrition and potential for health. British Journal of Nutrition 88: S293–S306. Kami JA, Velasquez VB, Debouck DG, and Gepts P (1995) Identification of presumed ancestral DNA sequences of phaseolin in Phaseolus vulgaris. Proceedings of the National Academy of Sciences of the United States of America 92: 1101–1104. Muntz K (1998) Deposition of storage proteins. Plant Molecular Biology 38: 77–99. Osborn TC (1988) Genetic control of bean seed proteins. Critical Reviews in Plant Sciences 7: 93–116. Patwardhan VN (1962) Pulses and beans in human nutrition. American Journal of Clinical Nutrition 11: 12–30. Reddy NR, Pierson MD, Sathe SK, and Salunkhe DK (1984) Chemical, nutritional and physiological aspects of dry bean carbohydrates: A review. Food Chemistry 13: 25–68. Reddy NR, Pierson MD, and Salunkhe DK (1986) Legume-Based Fermented Foods, p. 254. Boca Raton, FL: CRC Press. Salunkhe DK and Kadam SS (1989) Handbook of World Food Legumes: Nutritional Chemistry, Processing Technology, and Utilization. Boca Raton, FL: CRC Press vols. I (310 pp.), II (294 pp.), and III (323 pp.). Sathe SK (2002) Dry bean protein functionality. Critical Reviews in Biotechnology 22: 175–223. Sathe SK, Deshpande SS, and Salunkhe DK (1984) Dry beans of Phaseolus: A review. Part 1. Chemical composition: Proteins. CRC Critical Reviews in Food Science and Nutrition 20: 1–46. Siddiq M and Uebersax MA (eds.) (2013) Dry Beans and Pulses: Production, Processing and Nutrition, pp. 398. Ames, IA: Wiley.

Buckwheat: Overview YZ Cai, China National Seed Group, Beijing, China; Huazhong Agricultural University, Wuhan, China H Corke, The University of Hong Kong, Hong Kong, Pokfulam, China; Hubei University of Technology, Wuhan, China D Wang, Huazhong Agricultural University, Wuhan, China WD Li, Shanxi University, Taiyuan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Cultivated buckwheat comprises two species of the genus Fagopyrum, namely, F. esculentum Moench (common buckwheat) and F. tataricum L. (Tartary or bitter buckwheat). Originating in China and widely produced, mostly in Asia and in eastern Europe, buckwheat produces a pseudocereal grain that can be dehulled and milled to flour, for use in a wide range of food products. The composition and properties of buckwheat flour, derived from its components of starch, protein, and various therapeutic components such as flavonoids and phytosterols, give a wide scope for development of healthful grain-based products.

Learning Objectives

• • •

To understand the origin, geographic distribution, production, and potential of buckwheat as a traditional grain with emerging uses in healthful products To understand the composition and properties of the major components of buckwheat flour (starch and protein) and how these contribute to the nutritional and physical characteristics of products To understand the diverse array of therapeutic components present in buckwheat seed and how these can be manipulated for maximum benefit

Introduction Buckwheat originated in China and is widely cultivated as a minor crop in many places of the world. It is a pseudocereal crop, belonging to the genus Fagopyrum of the family Polygonaceae. There are two cultivated species, namely, common buckwheat (Fagopyrum esculentum) and Tartary buckwheat (Fagopyrum tataricum). Common buckwheat is most widely cultivated and utilized, while Tartary buckwheat is mainly grown and consumed in China. The major buckwheat-producing and buckwheat-consuming countries include China, Japan, Korea, Nepal, India, Russia, Ukraine, Poland, Hungary, Slovenia, Italy, Canada, Brazil, and the United States. Buckwheat is mostly consumed in the form of groats and flour, which are used as material for porridge, noodles, bread, pancakes, spaghetti, and other food items. Many traditional buckwheat foods are still popular in some countries, such as Japanese ‘soba’ and ‘wantuo’ and ‘helao’ in China. Buckwheat is rich in protein of excellent quality and starch with special properties that are different from other


cereals. In addition, it also contains high levels of fiber, minerals, and vitamins and other bioactive compounds (e.g., flavonoids, phytosterols, D-chiro-inositol, myo-inositol, free and bound phenolic acids, and phenylpropanoid glycosides) with positive therapeutic effects on the human body. Buckwheat with both edible and pharmaceutical values has increasingly attracted attention because of its positive effects on some chronic disease conditions, such as hypertension, hypercholesterolemia, diabetes, and other cardiovascular diseases. Buckwheat has further potential for use as an important functional food source.

General Aspects of Buckwheat Production Buckwheat grows mainly in the northern hemisphere, notably in Russia, China, Japan, India, Poland, Ukraine, Canada, and the United States. Buckwheat is also planted in the southern hemisphere, for example, in Brazil, Australia, and South Africa. In 1993, Russia was the biggest producer of buckwheat in the world, with a planting area of more than 4 million hectares (Mha), mainly in the eastern and northeastern parts of the country. It is reported that in 1990, buckwheat yield per hectare reached 3400 kg in Russia. China has the longest history (since the AD seventh century) of buckwheat cultivation and now ranks second in world production with an average annual cultivation area of 1.33 Mha and production fluctuating in the range of 0.5–0.9 million tonnes (Mt). Average yield per hectare is 527 kg for common buckwheat and 1294 kg for Tartary buckwheat in 1986. Major production areas of buckwheat in China include four production regions, distributed in Inner Mongolia, Shanxi, Gansu, Shaanxi, Sichuan, Yunnan, and Guizhou. From 2006 to 2010, the harvested area and total production of buckwheat in China and the world decreased by year (Table 1). However, in recent years, the planting area and total production of buckwheat in China have increased, close to 1 Mha and around 0.9 Mt per year. The total production of buckwheat in China has accounted for about 40% in the world. Moreover, China is the biggest producer of Tartary buckwheat in the world, with over 90% production.

Biological Aspects of Buckwheat Buckwheat, a dicotyledonous plant, belongs to the genus Fagopyrum of the family Polygonaceae. Fagopyrum has 15 species, including two groups: (1) annual species such as F. esculentum Moench (common buckwheat), F. tataricum L. (Tartary or bitter buckwheat), and Fagopyrum giganteum Krotov and (2)

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THE LEGUMES AND PSEUDOCEREALS | Buckwheat: Overview

perennial species such as Fagopyrum cymosum Meissn and Fagopyrum suffruticosum Fr. Schmidt. Among these species, only F. esculentum and F. tataricum are cultivated species while others are wild species. Buckwheat has broad ecological adaptability and can grow well in adverse soil and climatic conditions; in particular, Tartary buckwheat can grow in poor soils even at low temperature and low precipitation, such as in highaltitude mountainous regions. Common buckwheat is characterized by petiolate leaves, with terminal and axillary flowers, and corymbose or paniculate cyme. Tartary buckwheat has narrow-shaped leaves, more branches, and smaller flowers than common buckwheat, with inconspicuous greenish-white sepals. Buckwheat flowers are indefinite inflorescences that are white, pink, or yellow. Because of its flourishing flowers, buckwheat is cultivated in China to support the production of honey, considering one of the highestyielding honey plants. Buckwheat grain is actually a fruit (achene) whose color ranges from a glossy or dull gray to brown or black. Buckwheat grain (achene) consists of hull (pericarp) and kernel or seed (testa, aleurone layer, embryo, and endosperm). Such achenes are mostly triangular, 4–9 mm long with 1000 grain weight ranging from 15 to 35 g. Common buckwheat grain is generally bigger and huskier than Tartary buckwheat grain. Common buckwheat has a softer hull than Tartary buckwheat. Common buckwheat grain tastes harsh, and Tartary buckwheat tastes slightly bitter.

Chemical Composition of Buckwheat Chemical components of buckwheat include protein/amino acids, starch, lipids, fiber, minerals, vitamins, and other functional components (e.g., flavonoids, phytosterols, fagopyrins, D-chiro-inositol, myo-inositol, and phenylpropanoid Table 1 The harvested area and total production of buckwheat in China and the world (2006–10) 2006 The harvested area (Mha) China 0.868 World 2.740 Total production (Mt) China 0.500 World 1.993

2007

2008

2009

2010

0.750 2.727

0.725 2.422

0.724 2.016

0.700 1.882

0.650 2.369

0.600 2.181

0.570 1.794

0.590 1.518

Source: Data from FAOSTAT database.

Table 2

glycosides). These are distributed in different parts of the buckwheat grain, for example, protein mainly occurs in the aleurone layer and embryo, starch in the endosperm, and fiber, ash, and flavonoids are normally in the testa and pericarp. Milling procedures, fineness, and flour yield influence chemical composition in the final products of buckwheat milling (Table 2). Different buckwheat varieties (genotypes) and plant conditions (soil and climate) also cause compositional differences.

Protein and Amino Acids Buckwheat grain contains not only a high level of protein but also a good quality or nutritional balance of protein. Protein content of buckwheat grain and flour is similar to or slightly higher than that in wheat grain and flour (Table 2) but significantly higher than those in many other cereals (e.g., rice, maize, and sorghum). Amino acid composition of buckwheat protein is nutritionally well balanced and is rich in essential types (e.g., lysine and arginine), compared with most cereals. Table 3 shows that all amino acids are higher in buckwheat grain than in wheat grain, except for glutamic acid and proline.

Carbohydrate Carbohydrate (mainly starch) is the major component (59–74%) of buckwheat grain (Table 2). Amylose content in starch generally ranges from 20% to 26%. Starch granules are 2–15 mm in diameter, round, oval, or polygonal in shape with a few holes and pits on the surface. Buckwheat starch exhibits a typical A-type x-ray diffraction pattern and the crystallinity varies from 38.3% to 51.3%. Buckwheat grains also contain 0.65–0.76% reducing sugars, 0.79–1.16% oligosaccharides, and 0.1–0.2% nonstarchy polysaccharides.

Lipids Buckwheat grain contains 2.0–2.6% oil (Table 2). Major fatty acids are palmitic (16:0), oleic (18:1), and linoleic (18:2) acids, with average values of 14.8%, 36.5%, and 35.5%, respectively. Unsaturated fatty acids constitute 75–80% of total fatty acids.

Fiber Buckwheat grain contains 9.3–10.9% crude fiber (Table 2), 20–30% of which is soluble dietary fiber. Common

Proximate composition of buckwheat compared with wheata

Composition

Buckwheat seeds

Buckwheat groats

Buckwheat crude flour

Buckwheat fine flour

Wheat grain

Bread wheat flour

Carbohydrate Protein Fat Fiber Ash Moisture

58.5–73.5 10–14.5 2.0–2.6 9.3–10.9 2.0–2.5 12–14.0

70.9 9.7 1.8 3.7 1.7 12.3

67.4 12.0 2.3 7.2 2.1 10.3

70.7 10.9 1.7

66.9 14.0 2.1 2.6 1.9 12.5

74.7 11.8 1.1 0.3 0.4 11.7

a

1.6 13.1

Percentage on dry weight basis: data from Lin RF (1994) Buckwheat in China (in Chinese). Beijing: Chinese Agriculture Publishing House; Li SQ and Zhang QH (2001) Advances in the development of functional foods from buckwheat. Critical Reviews in Food Science and Nutrition 41: 451–464.

THE LEGUMES AND PSEUDOCEREALS | Buckwheat: Overview buckwheat grain generally has higher crude fiber than Tartary buckwheat. Content of crude fiber in buckwheat flour commonly depends on the milling process because fiber is mainly distributed in the testa and pericarp. Crude flour contains more fiber (3.4–6.9%) than fine flour (0.1–1.6%).

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Vitamins Buckwheat grain contains higher levels of vitamin B1 (thiamine), B2 (riboflavin), E (tocopherol), and PP (nicotinic acid/amide) than most cereals (Table 4). Generally, Tartary buckwheat has more vitamin B1, B2, and PP, but less vitamin E than common buckwheat.

Minerals Buckwheat grain is rich in minerals including Mg, Se, Fe, K, Ca, Cu, Mn, and Zn. Some studies show that buckwheat flour contains more Mg (11–13 times), Sr (5–36 times), Li (5–7 times), Fe (3–4 times), and K (2.9–3.6 times) than wheat flour. Additionally, a high level of Se is detected in Tartary buckwheat flour (0.43 mg kg1). Table 3 Amino acid contents of grains from 1505 buckwheat genotypes compared to wheat grainsa Tartary buckwheat

Amino acid

Range

Mean

Range

Mean

Wheat

Ala Argb Asp Cys Glu Gly Hisb Ileb Leub Lysb Metb Pheb Pro Ser Thrb Trpb Tyr Valb

0.28–0.75 0.69–1.72 0.10–2.34 0.03–0.33 0.67–3.49 0.44–0.95 0.17–0.40 0.04–1.65 0.49–1.83 0.06–1.96 0.02–0.33 0.31–1.79 0.20–1.06 0.35–0.91 0.16–0.67 0.06–0.18 0.09–0.55 0.38–1.24

0.51 1.11 1.09 0.17 2.21 0.65 0.26 0.46 0.77 0.66 0.17 0.57 0.44 0.57 0.44 0.12 0.32 0.58

0.26–0.79 0.11–1.61 0.60–1.84 0.03–0.44 0.60–3.12 0.07–2.54 0.03–0.50 0.05–0.71 0.08–1.07 0.12–1.86 0.03–0.34 0.05–0.99 0.11–1.22 0.05–0.90 0.24–0.62 0.06–0.18 0.07–0.55 0.26–1.18

0.50 1.09 1.06 0.16 2.05 0.64 0.27 0.46 0.75 0.64 0.17 0.55 0.41 0.58 0.43 0.13 0.33 0.58

0.33 0.51 0.43 0.11 2.44 0.33 0.20 0.27 0.50 0.29 0.16 0.36 0.92 0.36 0.21 0.23 0.36

Percentage on dry weight basis: data from Lin RF, Zhou MD, Tao YR, Li JY, and Zhang ZW (eds.) (1992) Proceedings of the 5th International Symposium on Buckwheat, 20–26 August, Taiyuan, China. Beijing: Agricultural Publishing House; Wei YM (1995) Quality and Processing of Buckwheat Grain (in Chinese). Xi’an, China: World Publishing Corporation. b Essential amino acids.

Table 4

Buckwheat is also rich in components with therapeutic effects, including flavonoids, phytosterols, fagopyrins, D-chiroinositol, myo-inositol, phenylpropanoid glycosides, free and bound phenolic acids, and proanthocyanidins.

Flavonoids

Common buckwheat

a

Therapeutic Components

Several flavonoids have been identified in Tartary and common buckwheat, that is, rutin, quercetin, kaempferol, orientin/ isoorientin, and vitexin/isovitexin. Rutin is the major and most important flavonoid component in buckwheat, which is not found in cereals. All parts of the buckwheat plant (seeds, hulls, leaves, stems, flowers, and even roots) contain flavonoids. The flavonoid components and content in buckwheat differ among growth periods and among species and genotypes. Generally, the flavonoids in Tartary buckwheat are significantly higher than those in common buckwheat. It is reported that common buckwheat grain contains 4–13 mg g1 flavonoids, whereas Tartary buckwheat grain has 40 mg g1. In Tartary buckwheat flowers, leaves, and stems, total flavonoid content reaches over 100 mg g1.

Phytosterols Buckwheat contains several kinds of phytosterols, for example, b-sitosterol, campesterol, stigmasterol, and isofucosterol. b-Sitosterol is the major sterol component, accounting for 70% of total sterol content. Some studies report that dehulled buckwheat groats after lipid extraction have 667–753 mg kg1 b-sitosterol, 89–97 mg kg1 campesterol, and a trace of stigmasterol. Phytosterols also occur in buckwheat pollen.

Comparison of vitamin contents between buckwheat flour and some cereal flour

Vitamina

Buckwheat

Wheat

Rice

Maize

Oat

Sorghum

Vitamin B1 Vitamin B2 Vitamin PP Vitamin E Vitamin E

0.38 0.22 4.1 1.4 0.79b 0.92 0.45c

0.19 0.06 1.6

0.21 0.06 2.2

0.09 1.6

0.29 0.17 0.8

0.27 0.09 2.8

a

mg per 100 g dwb (dry weight basis). Mean of 565 common buckwheat genotypes. c Mean of 491 Tartary buckwheat genotypes. Source: Data from Wang LM, Zhong SH, and Cai SL (1991) Contents of vitamin PP and vitamin E in Chinese (common and tartary) buckwheat. Crop Genetic Resources 2: 23–25; Wei YM (1995) Quality and Processing of Buckwheat Grain (in Chinese). Xi’an, China: World Publishing Corporation. b

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Fagopyritols Two digalactosyl D-chiro-inositols and two trigalactosyl D-chiro-inositols, members of the fagopyritol A series and fagopyritol B series, were isolated from buckwheat (F. esculentum Moench) seeds.

Fagopyrins Fagopyrins are naturally occurring substances in the buckwheat plant. Its chemical structure contains a naphthodianthrone skeleton similar that of to hypericin. Fagopyrins occur in buckwheat grain in low quantity and are difficult to separate.

Other Phenolic Compounds Many other phenolic compounds (e.g., free and bound phenolic acids, phenylpropanoid glycosides, anthocyanins, and procyanidin) have been identified in buckwheat, particularly in Tartary buckwheat. Some phenolic compounds have been recently isolated and identified for the first time in Tartary buckwheat, for example, 1, 3, 6, 60 -tetra-feruloyl sucrose, 3, 6-di-p-coumaroyl-1, 60 -di-feruloyl sucrose, 1, 6, 60 -tri-feruloyl-3-p-coumaroyl sucrose, N-trans-feruloyl tyramine, quercetin-3-O-[b-D-xyloxyl-(1!2)-a-L-rhamnoside], and proanthocyanidins (procyanidin A).

Antinutritional Inhibitors Antinutritional factors have been found in buckwheat grain, such as trypsin inhibitors (I, II, and III) and tannin. They may influence digestibility of buckwheat protein. Also, a high level of fiber in buckwheat may be considered as an antinutritional factor.

Nutritional Value and Properties of Major Components Protein Buckwheat is one of the best sources of high biological value (BV) protein in the plant kingdom. The BV of buckwheat protein is 93, compared to egg albumin (100), soybean protein (68), and wheat protein (63). The high BV of buckwheat protein results in much higher utilizable protein value (20–30%) compared to other cereals, although its digestibility is relatively lower. Buckwheat protein complements other food proteins to improve the dietary amino acid balance. In buckwheat protein, threonine and methionine are the first and the second limiting amino acids, respectively, but they are quite abundant in other plant proteins. Compared with cereal Table 5

proteins, buckwheat protein is particularly rich in lysine and contains more arginine and aspartic acid. Buckwheat protein also shows different bioactive effects, for example, cholesterollowering effect, antihypertensive effect, antitumor activity, and improvement in the constipation and obesity conditions by acting in a similar way as dietary fiber and interrupting in vivo metabolisms. In buckwheat grain, protein albumin is the major fraction (28–42%), and glutelin (11–21%) and globulin (14–20%) are next, whereas prolamin is the minor fraction (1.7–2.3%). Comparatively, wheat grain is high in prolamin and glutelin (70–75%). These differences between buckwheat and wheat lead to differences in food functional properties and processing quality. Because of the very low level of prolamin in buckwheat (i.e., free from gluten) and based on chemical and immunologic studies, buckwheat protein is a valuable source of dietary protein for gluten-sensitive individuals and can be used for patients with gluten sensitivity (celiac disease). Studies at the University of Hong Kong found that buckwheat protein exhibited much higher solubility, better emulsifying activity, and slightly lower foaming ability, compared to soy protein, and poorer foaming ability than amaranth protein (Table 5). Japanese studies indicated that the physicochemical properties of buckwheat protein were obviously different from those of soy protein and casein. Buckwheat protein affected the rheological properties of maize starch. An increase in the peak viscosity due to the addition of buckwheat protein concentrate was observed, but a lesser increase from the addition of buckwheat protein hydrolysates. From the established relationship between pasting viscosity and granule swelling during gelatinization, it was concluded that the observations were due to the protein exerting a stabilizing factor on starch granule integrity. It was also observed that buckwheat protein addition weakened starch gel structure. This phenomenon was most likely due to the preferential interactions between starch granules and proteins during gelatinization and retrogradation. Furthermore, buckwheat protein concentrate was examined for direct utilization in an emulsion-type meat product comprising lean beef, pork fat, salt, and water. It was found that the use of buckwheat protein concentrate considerably affected both the emulsion and the cooked meat gel properties. Buckwheat protein showed favorable effects to be suitable as a meat extender, as good as soy protein. Also, buckwheat protein concentrate was tested for direct application in other food systems (wheat dough and noodles). The addition of the buckwheat protein concentrate could improve the mixing properties of wheat flour and produce a positive influence on noodle formulation and final product quality. However, some reports pointed out a problem of the low digestibility of buckwheat protein, which might result from

Functional properties of common buckwheat protein concentrates, compared to other protein isolates

Protein concentrate

Emulsifying activity at pH 7.0 (%)

Solubility (%)

Foam stability (ml)

Buckwheat Soybean Amarantha

63.8 50.6 73.3

64.2 33.3 56.5

14 20 56

a

From A. cruentus genotype (K350). Source: Data from Bejosano FP and Corke H (1998) Amaranthus and buckwheat protein concentrate effects on an emulsion-type meat product. Meat Science 50: 343–353.

THE LEGUMES AND PSEUDOCEREALS | Buckwheat: Overview antinutritional factors: trypsin inhibitors, tannin, and a high content of dietary fiber. Buckwheat trypsin inhibitors are relatively thermostable, acid-resistant, and partially susceptible to pepsin action. In addition, allergens in buckwheat proteins have attracted attention. During buckwheat grain milling and food processing, some workers have allergic reactions, such as nose itching, sneezing, rhinorrhea, dyspnea, asthma, and even more serious symptoms. It is necessary to know more about the behavior and processing properties of specific buckwheat allergenic proteins.

Starch Buckwheat starch normally has higher peak viscosity, higher gelatinization temperature, greater swelling power, and higher susceptibility to acid and enzymatic degradation when compared with cereal starches (maize and wheat). Buckwheat starch retrogradation is generally slower than that of maize and wheat starch. Buckwheat starch has lower syneresis when stored at 4 C for 3–10 days and has better stability to syneresis after freeze–thaw cycles at 12 to 25 C. The starch properties of common and Tartary buckwheat compared to wheat starch. Clear differences were found in physicochemical properties between buckwheat and wheat, but less variation was observed between three common and three Tartary buckwheat genotypes. Buckwheat starch had higher peak gelatinization temperature (average Tp ¼ 68.7 C) than standard wheat starch (Tp ¼ 63.7 C). The important pasting properties of buckwheat starch were higher hot paste viscosity and cool paste viscosity, better resistance to shear thinning, and less effect of NaCl on peak viscosity than for wheat starch. Starch swelling volume is 27.4–28.0 ml for common buckwheat and 26.5–30.8 ml for Tartary buckwheat, compared to the reference (20.1 ml) for wheat starch. Investigations on the nutritional properties of buckwheat starch showed that it has potential use in the design of foods with lower glycemic index properties. The in vitro rate of starch hydrolysis and resistant-starch formation in boiled buckwheat groats and in a series of buckwheat/wheat breads and noodles (30–70% buckwheat flour) were evaluated. The highest level of resistant starch (6% total starch basis) and the lowest starch hydrolysis index were found in boiled buckwheat groats. The rate of in vitro amylolysis was much lower in all buckwheat products compared to the reference whole wheat bread or noodles. Consumption of boiled buckwheat groats or bread Table 6

and noodles containing more buckwheat induced significantly lower postprandial blood glucose and insulin responses than with whole wheat bread. Additionally, there are effects of processing treatments (including steaming or autoclaving and extruding) on buckwheat starch properties. The results showed that hydrothermal treatment increases gelatinization temperature, swelling power, and solubility of buckwheat starch. Autoclaving/cooling treatment of buckwheat groats resulted in improved availability of buckwheat starch and led to more apparent amylose and true amylose in the buckwheat starch and more resistantstarch formation in comparison to the untreated samples. It was also reported that extrusion influenced the physicochemical properties of starch and formation of starch–protein and starch–lipid complexes in extruded mixtures containing buckwheat flour and starch. Starch–protein complexes formed during extrusion played an important role in the stability of the porous structure in the extruded products containing buckwheat starch.

Therapeutic Effects of Buckwheat Buckwheat, especially Tartary buckwheat, has been regarded as an effective medicinal herb in Chinese medicine for more than 1000 years. Over 80 prescriptions utilizing buckwheat in the treatment of many diseases have been described in Chinese traditional medicine books. In modern times, buckwheat products are popular as functional or therapeutic foods in China and some other countries. Regular consumption of buckwheat foods may reduce the occurrence of hyperlipidemia, obesity, and diabetes. A clinical trial in Beijing Tongren Hospital showed that Tartary buckwheat flour had hypolipidemic and hypoglycemic effects in treating hyperlipidemia and diabetes (Table 6). Table 7 shows that health foods made from Tartary buckwheat have positive effects in reducing cholesterol, blood lipid, blood sugar, urinary sugar, and other indices. These therapeutic effects should be attributed to unique proteins, resistant starch, and dietary fiber as well as vitamins, minerals, flavonoids, and phytosterols in buckwheat. Protein and indigestible carbohydrates (fiber and resistant starch) of buckwheat (particularly Tartary buckwheat) can be used as potential functional food additives to treat conditions such as hypertension, obesity, and constipation. Buckwheat protein extract could lower blood cholesterol level more

Clinical effects of tartary buckwheat flour on hyperlipidemia and diabetes (hyperglycemia) after 1-month dietary treatment

Testing indexa Hypolipidemic effect Serum triglyceride (mg dl1) (n ¼ 18) Serum cholesterol (mg dl1) (n ¼ 13) Hypoglycemic effect Blood sugar (mg dl1) (n ¼ 23) Urinary sugar (g 24 h1) (n ¼ 27) a

311

Before treatment

After treatment

310 241 247 57

233 173 197 43

202 46 44 43

157 40 20 22

n is number of subjects. Source: Data from Lin RF, Zhou MD, Tao YR, Li JY, and Zhang ZW (eds.) (1992) Proceedings of the 5th International Symposium on Buckwheat, 20–26 August, Taiyuan, China. Beijing: Agricultural Publishing House; Corke H and Lin RF (eds.) (1998) Proceedings of the 1st International Conference on Asian Food Product Development – Focus on Specialty Grains and Grain Products, 6–10 September, Taiyuan, China. Beijing and New York: Science Press.

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Table 7

Therapeutic effects of health foods made from Tartary buckwheata

Treatment

Triglyceride (mg dl1)

Cholesterol (mg dl1)

Lipoprotein (mg dl1)

Blood sugar (mg dl1)

Urinary sugar (nmol 24 h1)

Buckwheat Control

207.8 286.9

148.1 202.6

503.2 616.0

178.5 255.6

284 363

a

Statistical data from 187 samples of clinical observations by Beijing Grain Science Research Institute, Beijing. Lin RF, Zhou MD, Tao YR, Li JY, and Zhang ZW (eds.) (1992) Proceedings of the 5th International Symposium on Buckwheat, 20–26 August, Taiyuan, China. Beijing: Agricultural Publishing House; Corke H and Lin RF (eds.) (1998) Proceedings of the 1st International Conference on Asian Food Product Development – Focus on Specialty Grains and Grain Products, 6–10 September, Taiyuan, China. Beijing and New York: Science Press.

efficiently, compared with soy protein and casein. Sulfurcontaining amino acids and glycine and arginine and lysine are also considered to have important influence on this cholesterol-lowering effect. These amino acids can conduct downregulation of hepatic LDL receptors and improve the removal of cholesterol and its esters in outlying tissues and thus reduce the serum cholesterol level. Many studies have further indicated that consumption of buckwheat protein can cause suppression in body fat, constipation, mammary carcinogenesis, and colon carcinogenesis in rats and in the formation of cholesterol gallstones in hamsters. Some researchers explain that the cholesterol-lowering, obesity-treating, and diabetes-controlling effects are also possibly associated with other components (dietary fiber and resistant starch) in buckwheat. The metabolites, formed during fermentation of resistant starch and other indigestible carbohydrates in the large intestine, contribute to the maintenance of colon health and also have beneficial effects on glucose metabolism. Moreover, a novel protein isolated from Tartary buckwheat water-soluble extracts exhibited antiproliferative effect and antitumor activity. The flavonoids from buckwheat (especially Tartary buckwheat) have been found to be effective in reducing blood cholesterol levels, keeping capillaries and arteries strong and flexible, improving blood microcirculation, and protecting blood vessels from rupturing and forming clots. These flavonoids also demonstrate antioxidant, antimicrobial, and antiinflammatory activities. Because Tartary buckwheat leaves and stems contain high concentrations of rutin and other flavonoids at flowering, extracts of buckwheat plants are helpful for treating keratitis, while dried powdered buckwheat plants are sometimes used for curing external wounds and ulcers. The vitamins and minerals (including Mg, Fe, and Se) in buckwheat can also play a crucial complementary role in the previously mentioned therapeutic effects. Phytosterols found in buckwheat grain, although at a low level, also showed positive effects on blood cholesterol level. Other functions of buckwheat sterols are waiting for further investigation, because some phytosterols from other plant sources were found to have strong pharmaceutical effects, for example, antivirus and antitumor activities. Also, there is a report that the fagopyrins isolated in buckwheat grain are an effective component for the treatment of type 2 diabetes. However, there is still some dispute on this issue.

Buckwheat Food Products Buckwheat products are recognized as functional food in some Asian countries. Buckwheat, as a nutritional staple crop and

medicinal herb for Chinese consumption, has been widely grown for a long time. A rich array of traditional buckwheat foods are found in various places of China, such as buckwheat wantuo and helao (or hele), buckwheat cat’s-ear noodles, buckwheat noodles (vermicelli), pancake, griddle cakes, jelly noodles, and porridge. These foods are famous and popular in China, particularly for their long history, rich nutritional profile, special flavor, various processing methods, and ‘functional food’ role in maintaining human health. For example, buckwheat helao (hele), wantuo, and cat’s-ear noodles are wellknown local foods in the northern region of China (Sha¯nxı¯ and Shaanxi provinces). In Japan, buckwheat noodles called soba and buckwheat roasted groats have long been very popular, while in Korea, a favorite jelly-type food called ‘mook’ is also made from buckwheat. In India, buckwheat flour is used for making ‘chillare,’ an unleavened bread fried with ghee, and also for a crisp food called ‘pakora.’ Honey produced from common buckwheat is prized in both China and India. In eastern Europe, buckwheat grain forms an important part of the traditional diet. Buckwheat groat porridge and meals and soup made from flour are still favorite traditional foods in Poland, Russia, and some other eastern European countries. In the United States, although buckwheat is mainly used for animal feed, buckwheat cake was once a special breakfast item and buckwheat flour is also an ingredient of some pancake mixes. Modern buckwheat food products include buckwheat dried noodles or vermicelli, instant noodles, spaghetti or macaroni, biscuits, breads, cakes, pastry, breakfast cereals and snacks, vinegar, drinks, and beverages (Tartary buckwheat tea, buckwheat beer, and liquor). Most of these products, particularly made from Tartary buckwheat, are popular healthy foods in China. It is estimated that commercial food products made from buckwheat have produced over 10 billion RMB of value in China. In addition, tender buckwheat shoots are used as fresh vegetables and are also processed into canned vegetables.

Buckwheat Processing and Development Buckwheat grains are dehulled and milled into flour for food processing. Buckwheat flour milling is similar to wheat dry milling. Buckwheat flour yield ranges from 58% to 75%, mainly depending on variety and milling techniques. Buckwheat flour contains similar levels of starch and protein to wheat flour. However, the behavior of buckwheat flour is different from wheat flour, and it is difficult to make wheat flour-like foods because there is no gluten. Therefore,

THE LEGUMES AND PSEUDOCEREALS | Buckwheat: Overview buckwheat flour is usually mixed with wheat flour and other flours before use. Chinese researchers and food factories have mixed buckwheat and wheat flour along with other flours to successfully make buckwheat pastry, sandwich cake, dried noodles, instant noodles, and spaghetti (Tables 8 and 9). The processing steps for dried noodles are shown in Figure 1. Suitable levels of buckwheat flour are 10% for crisp pastry and cakes, 20–40% for noodles, and 30–50% for palatable spaghetti. The cooking quality of spaghettis mixed from different ratios of buckwheat and wheat flours is shown in Table 9. Buckwheat/wheat spaghettis generally have higher water absorption, higher cooking loss, and higher protein loss rate than pure wheat spaghetti, because buckwheat flour contains much more albumins (water-soluble) and globulins (soluble in salt water) than wheat flour. These commercial foods are produced by modern food-processing equipment. However, most traditional buckwheat foods are still handmade in the countryside and even cities in China. An example of the basic handpreparation method for buckwheat helao is shown in Figure 2. In Japan, there are many noodle-making factories producing soba noodles. Buckwheat flour used for making soba is commonly mixed with 10–50% wheat flour. These noodles are sold in precooked, boiled, dried, or instant stages, as well as being made for direct sale to buckwheat noodle restaurants, small shops, and stands. In Europe and the United States, buckwheat flour is mixed with other cereal flours to

Table 8

313

make pancakes, flakes, biscuits, bread, noodles, spaghetti or macaroni, and ready-to-eat breakfast cereals. The processing of these foods can be conducted using ordinary baking, extruding, or expansion methods. The amount of buckwheat flour added to other cereal flours is generally < 50%. For instance, acceptable bread contained 25% buckwheat flour with a formulation that included vital gluten, whey, or sour milk. A recipe for bread with 10% Tartary buckwheat flour is shown in Table 8. It was also reported that the buckwheat corn flakes were produced by extrusion processing. The formulations with an addition of 18%, 22%, and 33% buckwheat flour were used. The addition of 30% buckwheat flour gave the best organoleptic properties. Although buckwheat is still cultivated as a minor crop in the world, buckwheat product development has quickened since the 1990s, particularly in China. To date, there has been an emerging trend in the research and development of high valueadded buckwheat products, especially Tartary buckwheat products. Tartary buckwheat has high potential in the health food market. Since Tartary buckwheat contains a high level of flavonoids and other therapeutic components, some cosmetics and medicine products have successfully been developed and marketed using buckwheat materials in China, such as cream, shampoo, lotion, toothpaste, and flavonoid capsules. However, many such new products have not been accepted well in the marketplace, because of their high cost and erratic quality control.

Recipes for three selected buckwheat baked foodsa

Materials (g)

Chinese crisp pastry

Sandwich cake

Mixing bread

Buckwheat flour Wheat flour Soybean flour Egg Shortening oil Salt Sugar Refined maltose Skimmed milk Dried yeast Flavor (prickly ash) Jam Buckwheat flour paste

1.0 8.5 0.5

1.0 8.5 0.5 10

25b 225

3 0.01

10 3.75 10

8.0 1.6

1.0

5 3 0.1–0.15 3 0.5

a

In these selected foods, buckwheat flour accounts for 10% of total composite flour in the baking foods: data from Lin RF, Zhou MD, Tao YR, Li JY, and Zhang ZW (eds.) (1992) Proceedings of the 5th International Symposium on Buckwheat, 20–26 August, Taiyuan, China. Beijing: Agricultural Publishing House. b Tartary buckwheat flour.

Table 9

Cooking quality of spaghetti made from common buckwheat and wheat flour at different ratios Loss of protein (%)

Buckwheat/wheat flour ratio

Water absorption (%)

Cooking loss of dry materials (%)

Cooking in water

Cooking in salt water

0:100 25:75 50:50 75:25

218 235 251 278

6.4 6.6 8.2 8.5

1.4 2.0 3.7 2.7

6.6 7.5 13.9 9.4

Source: Data from Wei YM (1995) Quality and Processing of Buckwheat Grain (in Chinese). Xi’an, China: World Publishing Corporation.

314


Buckwheat and wheat flour (3 : 7)

Buckwheat grains

Mix flour

De-hull and stone-mill into flour

Add ~40 °C water (1% NaCl) (H2O : flour » 3.5 : 6.5)

Add water (water : flour » 4 : 6) and a little limewash

Knead dough for 20 min and ripe for 20 min

Mix and knead well into soft and smooth dough (light green)

Roll (1.2–1.4 mm thickness) and slice (1.5–1.8 mm width) Press dough into rough noodle shape by helao instrument Dry at <40 °C for 7–8 h Fresh noodle strands are directly dropped into boiling water Cut (20 cm length)

Cook at ~ 100 °C for 10–15 min Final product of dried noodles Figure 1 Processing procedure for dried noodles of common or Tartary buckwheat.

Nowadays, buckwheat functional foods and related products have attracted widespread interest and have become more popular. Much more attention should be paid to the biological functions, palatability, and acceptability of buckwheat products. It is necessary to enhance development and commercialization of traditional buckwheat foods and to improve modern buckwheat food-processing techniques.

Buckwheat helao Figure 2 Traditional method of buckwheat helao preparation.

•

into added-value components that would be attractive to the health food industry. Compare Chinese and Japanese buckwheat noodles in depth, showing how different traditional products achieve their required quality outcomes. Suggest new product ideas for buckwheat-based noodles.


• • •

Describe the composition of buckwheat seed in relation to physical properties of the food product (e.g., the effect of starch on noodle texture). Outline the health claims made for the various fractions and components of the buckwheat seed. Try to make buckwheat noodles, experimenting with the effect of varying the proportion of wheat flour to buckwheat flour.

See also: Carbohydrates: Starch: Chemistry; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Legumes and Pseudocereals: Amaranth: Overview; Pseudocereals: Overview.

Further Reading Exercises for Readers to Explore the Topic Further

•

Design a breeding program for the development of nutritionally improved buckwheat, suitable for fractionation

Bejosano FP and Corke H (1998) Amaranthus and buckwheat protein concentrate effects on an emulsion-type meat product. Meat Science 50: 343–353. Corke H and Lin RF (eds.) (1998) Proceedings of the 1st International Conference on Asian Food Product Development – Focus on Specialty Grains and Grain Products, Taiyuan, China, 6–10 September. Beijing and New York: Science Press.

THE LEGUMES AND PSEUDOCEREALS | Buckwheat: Overview Guo XN, Zhu KX, Zhang H, and Yao HY (2010) Anti-tumor activity of a novel protein obtained from tartary buckwheat. International Journal of Molecular Sciences 11: 5202–5212. Joshi BD and Rana RS (1995) Buckwheat (Fagopyrum esculentum). In: Williams JT (ed.) Cereals and Pseudocereals, pp. 85–127. London: Chapman and Hall. Li WD, Lin RF, and Corke H (1997) Physicochemical properties of common and tartary buckwheat starch. Cereal Chemistry 74: 79–82. Li SQ and Zhang QH (2001) Advances in the development of functional foods from buckwheat. Critical Reviews in Food Science and Nutrition 41: 451–464. Lin RF (1994) Buckwheat in China. (in Chinese). Beijing: Chinese Agriculture Publishing House. Lin R, Li W, and Corke H (1998) Spotlight on Shanxi province China: Its minor crops and specialty foods. Cereal Foods World 43: 189–192. Lin RF, Zhou MD, Tao YR, Li JY, and Zhang ZW (eds.) (1992) Proceedings of the 5th International Symposium on Buckwheat. Taiyuan, China, 20–26 August. Beijing: Chinese Agricultural Publishing House. Ren Q, Wu CS, Ren Y, and Zhang JL (2013) Characterization and identification of the chemical constituents from tartary buckwheat (Fagopyrum tataricum Gaertn) by high performance liquid chromatography/photodiode array detector/linear ion trap FTICR hybrid mass spectrometry. Food Chemistry 136: 1377–1389.

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Tao CJ, Yuan P, Wang X, and Liao B (2014) Advances in the development of buckwheat products. Cereal and Food Industry 21: 52–54. Wang LM, Zhong SH, and Cai SL (1991) Contents of vitamin PP and vitamin E in Chinese (common and tartary) buckwheat. Crop Genetic Resources 2: 23–25. Wei YM (1995) Quality and Processing of Buckwheat Grain (in Chinese). Xi’an, China: World Publishing Corporation. Zhang ZL, Zhou ML, Tang Y, et al. (2012) Bioactive compounds in functional buckwheat food. Food Research International 49: 389–395. Zhao G and Shan F (2009) Tartary Buckwheat (Fagopyrum tataricum) in China. (in Chinese). Beijing: Chinese Science Press.

Relevant Websites http://www.buckwheatgrowers.com – Information on buckwheat growers, products and services. https://www.hort.purdue.edu/newcrop/afcm/buckwheat.html – Center for New Crops and Plant Products at Purdue University. New CROP provides windows to new and specialty crop profiles, including buckwheat.

Chickpea: Overview EJ Knights and KB Hobson, New South Wales Department of Primary Industries, Tamworth, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by E.J. Knights, volume 1, pp 280–287, ã 2004, Elsevier Ltd.

Topic Highlights

Origin and Spread

• •

The genus Cicer contains 43 species, 34 perennial and 9 annual. All annual species are diploids and have 16 chromosomes (2N ¼ 16). Among these, C. reticulatum is the most closely related to the cultivated chickpea and the presumed progenitor. Domestication occurred about 10 000 years ago in the region of southeastern Turkey, part of the ‘Fertile Crescent.’ Recent evidence suggests this occurred as a single event due to the limited geographic distribution of the wild species populations and the very low genetic variation of the cultigen. About 4000–5000 years ago, the domesticated forms, initially desi types, commenced a westward movement along established trade routes toward the Mediterranean. Subsequent spread to southern Europe and North Africa, including Ethiopia, occurred by land and/or sea routes. Differentiation of the kabuli type is thought to have occurred in the Mediterranean region in comparatively recent times. The eastward movement of desi types to India commenced about 4000 years ago, whereas kabuli types did not arrive there until about 300 years ago. (The prominence of Kabul on the ‘Silk Road’ suggests both an overland introduction and the origin of the word ‘kabuli.’) In the sixteenth century, Spanish and Portuguese travelers carried kabuli types to South and Central America where they came to be known by their Spanish name ‘garbanzo.’ Chickpea industries have comparatively recent histories in the United States (1950s), Australia (1970s), and Canada (1990s).

• • • •

Chickpea is an annual legume belonging to the Cicer genus. Seed shape separates the species into three main groups: desi, kabuli, and pea. Chickpea is a key dietary component in many countries where vegetarian diets dominate or animal protein is too expensive. Chickpea is grown mainly as a sole crop in a range of rotations. World production averages 10 Mha annually. India produces more than 67% of the world’s annual production.

Learning Objective

•

To achieve understanding of the agriculturally important species in both farming systems and its end uses

Introduction Chickpea (Cicer arietinum L.) is a herbaceous, annual legume. Plants are typically short (20–50 cm) with a semierect to erect growth habit and a variable number of primary and secondary branches. An imparipinnate leaf type, producing 11–18 small leaflets, gives the foliage its distinct fernlike appearance (Figure 1). Chickpea is a long day plant; however, time to flowering is accelerated by increasing temperature. Flowering is indeterminate with single (rarely double), small purple or white flowers produced on racemes arising from the leaf axil. Pods have a characteristic oval to rhomboid shape and inflate rapidly after (self-) fertilization (Figure 1). All aerial plant parts excepting flowers have a dense covering of fine hairs, which secrete a mixture of organic acids. Roots are colonized by Mesorhizobium ciceri, a nitrogen-fixing bacterium specific to the genus Cicer. Nodules formed by these bacteria vary in size, the largest approaching 3 cm in diameter. The seed is highly variable in appearance but invariably possesses the characteristic chickpea ‘beak’ protruding over the embryo. Seed shape, color, and, to a lesser extent, size separate the species into three main groups: ‘desi,’ ‘kabuli,’ and ‘pea’ (Figure 2). Desi (derived from the Hindi and Urdu word for ‘native’ or ‘local’) seeds have an angular shape and thick, colored (mostly brown) seed coat. In contrast, kabuli seeds have a more rounded shape and thin, white to cream-beige seed coat. There is considerable overlap between these two seed types in seed size; however, desi seeds are generally smaller (weighing 80–350 mg) than kabuli seeds (100–750 mg). The pea-type seed has little commercial significance.

316

Production During the 1990s, world chickpea production has averaged 8 million tonnes (Mt) from 10.5 million hectares (Mha). In the 2000s, this increased to 8.5 Mt from a similar area, with the increased production coming from increased yield. Crop area for the past 3 years (2011–2013) has averaged 13 Mha, which is the highest 3-year average production (Figure 3). Historically, Asia has been the major chickpea producer. For years 2009–2013, it accounted for 85.1% of all production, followed by Australia (5.3%), Africa (5.0%), Americas (3.8%), and Europe (0.9%). Desi types contribute 70% of production worldwide. Chickpea is cropped in approximately 80 countries. India produces two-thirds of the world crop (Table 1), and after a steady decline in the 1990s, production has been increasing in recent years. A similar trend has occurred in Pakistan, the world’s second largest producer. In European countries, chickpea production has fallen dramatically, by 60–97% since the 1960s. On the other hand, production has risen significantly in some countries. In Australia, the world’s fourth largest producer, chickpea area increased rapidly during the 2000s as the demand increased for cereal break crops and alternatives were sought for nitrogen fertilizer. Expanded chickpea


http://dx.doi.org/10.1016/B978-0-12-394437-5.00035-8

THE LEGUMES AND PSEUDOCEREALS | Chickpea: Overview

Figure 1 Chickpea branch showing typical leaf and pod shape. (Chickpea normally produces single, axillary flowers; the ‘double-podded’ variant shown here may confer some yield advantage in low-productivity environments.)

317

such as India (5.1 kg pc) and Pakistan (4.4 kg pc), than in developed, nonproducing countries such as the United Kingdom (0.2 kg pc). Consumption is also comparatively high in some wealthier, producing countries such as Turkey (6.3 kg pc) and Spain (2.3 kg pc). Historically, most chickpeas were consumed in their country of origin. Until the late 1970s, international trade accounted for only 2% of world production. This percentage rose to 9% in the following three decades as demand exceeded supply in major producing countries, especially in east Asia. During the period 2008–2011, India was the largest importer (183 000 tonnes) followed by Pakistan (177 000 tonnes) and Bangladesh (129 000 tonnes). For the same period, Australia was the largest exporter (414 000 tonnes), followed by India (154 000 tonnes) and Mexico (104 000 tonnes). India’s position as the second largest exporter of chickpea is driven by a rapid increase in the production of large kabuli types. Globally, the volumes of desi and kabuli types now traded are similar. Prices fluctuate according to supply and demand; however, there is generally a premium for kabuli types and particularly for those with large seed (diameter 9–11 mm).

Role in Farming Systems Chickpea is grown in a range of environments encompassing extensive variation in latitude (53 N to 39 S), altitude, soil type, photoperiod, temperature, and rainfall. Seven broadly different regions can be distinguished.

Indian Subcontinent (India, Pakistan, Nepal, Bangladesh, and Myanmar)

Figure 2 Seed type in chickpea showing, clockwise from top of picture: kabuli, desi, and pea (intermediate) forms.

areas in African countries such as Ethiopia, Malawi, and Tanzania have also helped stabilize or even increase world production in recent years. Average world yield over the period 2009–2013 was 925 kg ha1. Central and North America had the highest yields (1772 kg ha1) followed by Europe (1529 kg ha1), Australia (1222 kg ha1), Africa (1076 kg ha1), and Asia (883 kg ha1). Yields were generally highest in countries where all or most of the crop was irrigated, such as Israel (4723 kg ha1), Lebanon (2592 kg ha1), and Egypt (2071 kg ha1).

Consumption and Trade Chickpea is an important part of the diet in most producing countries and is gaining in popularity elsewhere. Per capita consumption is generally much higher in producing countries,

Desi types predominate in this region; however, the production of kabuli has expanded rapidly in recent years. Chickpea is typically grown as a ‘winter’ crop with sowing from October to December and harvest from February to April. The crop is mostly rainfed, relying essentially on soil moisture conserved from monsoon rains; there is little effective growing season rainfall. Soil types vary from the heavy, black ‘cotton’ soils of central and southern India to the alluvial soils of the IndoGangetic Plain and the much lighter textured sands of Rajasthan in India and the Thal area of Pakistan. There has been a large shift in chickpea area from north to south over the past four decades. Chickpea is grown mainly as a sole crop in a range of rotations. Where sufficient rainfall or irrigation allows, for example, in northwestern India or in the rice-based systems of northeastern India, Bangladesh, and Myanmar, chickpea follows rainy season crops such as rice, millet, sorghum, maize, sugarcane, cotton, guar, and sesame. However, in lower rainfall zones where only one crop per year is possible, chickpea is grown as a fallow crop. Less frequently, it is intercropped in varying proportions with Brassica spp., linseed, safflower, or sorghum or sown as a mixed crop with wheat, barley, linseed, or sorghum. Fertilizer and pesticide use is generally low and there is minimal mechanization of sowing, harvest, or weed, insect, and disease control. Traditionally, these operations are performed by hand or with the assistance of animal drawn

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16000

1000

area production yield

900

700 600 500

8000

400

Yield (kg ha-1)

Area (x1000 ha)/production (x1000 t)

800 12000

300 4000

200 100 0 2013

2010

2007

2004

2001

1998

1995

1992

1989

1986

1983

1980

1977

1974

1971

1968

1965

1962

0

Figure 3 World area, production and yield of chickpea, 1961–2013. Each datum is the mean for a 3-year period. Source: FAO.

Table 1

Mean area, production, and yield of chickpea in major chickpea-producing countries (2009–2013)

Country

Area (ha)

Production (tonne)a

Yield (kg ha1)

India Pakistan Iran (Islamic Republic of) Australia Turkey Myanmar Ethiopia Malawi Mexico United Republic of Tanzania Syrian Arab Republic

8 634 000 1 049 660 549 175 509 162 437 471 326 106 202 927 115 545 92 938 77 083 76 944

7 858 400 (67.8) 568 000 (4.9) 275 385 (2.4) 609 402 (5.3) 520 935 (4.5) 461 708 (4.0) 333 377 (2.9) 61 075 (0.5) 163 674 (1.4) 74 425 (0.6) 52 749 (0.5)

910 543 502 1222 1191 1414 1673 526 1705 938 685

a

Percentage of world production in brackets. Data from FAO.

implements, although some regions are introducing mechanized processes.

West Asia, North Africa, and Southern Europe Production in this region is almost exclusively of kabuli types. The crop is grown at high altitudes in west Asia (Afghanistan, Iran, and Turkey) but at comparatively lower altitudes in the Middle East (Syria, Yemen, Jordan, Israel, and Iraq), North Africa (Egypt, Sudan, Algeria, Tunisia, and Morocco), and southern Europe (Greece, Italy, Spain, and Portugal). It is grown as a ‘spring’ crop in this Mediterranean-type environment, relying

mainly on growing season rainfall. Winter sowing occurs in Egypt and Sudan. Sowing is usually delayed until late February to May to minimize losses from cold and/or ascochyta blight. Rapidly increasing temperatures and moisture stress in summer hasten maturity and limit crop duration to 90–120 days. Chickpea is generally confined to areas having an annual rainfall above 400 mm. It is grown as a sole crop in rotation with wheat (bread or durum) or barley; a fallow phase or summer or forage crop may be included in drier areas. There is some mechanization of production, particularly sowing and weeding, but harvest is still largely manual. High labor costs have contributed to the decline in chickpea production in parts of the region, especially in Europe.


East Africa (Ethiopia, Eritrea, Kenya, Tanzania, Malawi, and Uganda) Mostly desi and some kabuli chickpeas are grown in this region, usually at high altitudes (up to 2400 m). The area of kabuli is increasing in some countries with the introduction of improved varieties and is up to one-third of the crop in Ethiopia. Crops are mainly sown as pure stands in rotation with wheat, barley, and teff, but to a lesser extent as mixtures with sorghum, safflower, and maize. Crop growth relies mainly on residual soil moisture. Sowing follows the wet season, from July to early September in Ethiopia and from February to April further south. Inputs of fertilizers and pesticides are minimal, and although there is some use of tractors in sowing, harvest and threshing remain manual operations.

Central and Southern America (Mexico and Argentina) In Mexico, desi chickpeas are produced under rainfed conditions in the west-central parts of the country and kabuli types under irrigation in the drier northwest. Chickpea is grown as a ‘winter’ crop following maize in the west-central region and following soybean or sesame in the northwest. Sowing is from October to December and harvest from March to May. There has been some recent transition to mechanized production, particularly for kabuli types. Production in Argentina has recently increased to 40 000 ha of kabuli type. It is sown from April to July.

North America (Canada and the United States) The North American chickpea industry began in coastal districts of California where spring-sown kabuli crops were grown on residual soil moisture. Later, winter crops were grown under irrigation in the drier San Joaquin Valley. During the 1980s, both desi and kabuli chickpeas were introduced to the Palouse region of northwestern United States and, in the following decade, to the brown and dark brown soil zones of Saskatchewan and Alberta in Canada. Current production areas are the Pacific Northwest in the United States and the province of Saskatchewan in Canada. The threat of cold and ascochyta blight forces chickpeas to be grown as a ‘spring crop’ in both these regions. Sowing commences in May and harvest, particularly in Canada, needs to be completed by September to avoid freezing injury to immature seeds. In the United States and Canada, all stages of chickpea production, including seed inoculation; sowing; weed, disease, and insect control; harvest; and seed drying, are highly mechanized. In most cases, the machinery and processes have been modified from those used in cereal production.

Australia National production (90%) is mainly desi type and this predominantly occurs in the summer rainfall-dominant regions in the northeast of Australia. In the winter rainfall-dominant Mediterranean-type environments in the

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southeast and southwest, production in the southeast region is mainly kabuli type. Chickpea is grown as a ‘winter’ crop, sown from May to July and harvested from October to January. Most crops are produced under rainfed conditions; incrop rainfall is a major yield determinant in most regions, especially in the southeast and southwest. As in North America, production is highly mechanized. Control of ascochyta blight, the major industry problem in most regions, relies heavily on ground rig application of foliar fungicides. In northeast Australia, Phytophthora root rot is a common biotic constraint, particularly in seasons conducive to the disease.

Production Constraints There is a large discrepancy between the yield in farmers’ fields and that commonly obtained under experimental conditions. The low yields generally obtained by farmers reflect a plethora of problems that beset the crop. The major production constraints and their impacts are described below.

Physical Constraints Drought and Heat Chickpea is mostly grown in low rainfall environments. Inadequate soil moisture is therefore a critical production constraint and may occur throughout the growth cycle. Winter/ spring rains in west Asia, or soil moisture remaining from the wet season in the Indian subcontinent and East Africa, may not be sufficient for farmers to sow; for many regions, variability in main season rainfall explains much of the year-to-year variation in chickpea area. Receding soil moisture, particularly in low rainfall areas in India and Pakistan, may also be inadequate to sustain seedlings. Intermittent moisture stress of established crops can result from breaks in winter and early spring rainfall, but a more serious problem is terminal moisture stress suffered by spring-sown crops (and winter crops in the Indian subcontinent) as podding coincides with rapidly declining soil moisture. Terminal drought is a major constraint in an estimated 80% of the global chickpea area. Heat stress (temperature >35 C) during the reproductive phase has become a serious constraint as chickpea moves from cooler long-season environments to warmer short-season environments, an increased area under later sowing, and expected increases in temperatures due to increased climate variability.

Cold Low temperatures affect the plant in two main ways: tissue damage through disruption of cell membranes and abortion of flowers. Sensitivity to low temperatures (<5 C) is one reason for spring sowing in higher elevation areas of west Asia. However, genotypes have now been identified that can survive temperatures as low as 25 C. Winter sowing of these cold-tolerant genotypes can increase yield potential by 70% through increased biomass production and improved water-use efficiency. Where the crop is sown in autumn/winter, such as in northern India, Pakistan, and Australia, chilling damage in the early flowering phase narrows the ‘window’ for pod setting. Sowing is normally delayed so that commencement of

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flowering coincides with mean daily temperatures favorable for podding (15 C).

Hostile Soils A range of soil chemical and physical problems limit chickpea growth. The most important of these is salinity, since chickpea is comparatively intolerant of the ionic imbalances characteristic of ‘saline’ soils. ‘Sodic’ soils, in which high levels of exchangeable sodium are associated with increased bulk density, low water infiltration, and poor aeration, are also common in northern India and in other regions where soil pH is very high. Retarded root growth and poor nodulation inhibit chickpea growth and productivity under such conditions. Other locally important soil factors are acidity (poor nodulation), deficiencies of iron and zinc, and either a deficiency or toxicity of boron.

Diseases Ascochyta Blight Ascochyta blight is the most important disease of chickpea worldwide and has been recorded in nearly all producing countries. Recent epidemics in the United States (1980s) and Australia (1990s) caused major industry disruptions, reflected by a sharp decline in the area sown. Elsewhere, for example, in west Asia and the Mediterranean region, the threat of ascochyta blight causes sowing to be delayed, thereby significantly reducing yield potential. The causal agent of ascochyta blight is Ascochyta rabiei (Passerini) Labrousse (syn. Phoma rabiei and teleomorph Didymella rabiei (Kovachevski)), a fungus spread by infected seed and crop residues, long-range dispersal of sexually produced ascospores, or, within the crop, short-range dispersal of asexually produced pycnidiospores. Lesions are formed on leaves, stems, pods (Figure 4), and seeds. The disease progresses quickly under favorable wet conditions and can cause total crop failure. Ascochyta can be controlled by an integrated disease management approach based on host resistance and, depending on location, removal of infected plant debris, delayed sowing, seed dressing, and foliar fungicides.

Other Foliar Diseases Botrytis gray mold (Botrytis cinerea Pres.) is the most important of the foliar diseases after ascochyta. The pathogen has a very broad host range; therefore, the disease is widely distributed. Most damage occurs under high humidity and generally at temperatures higher than optimum for ascochyta. Botrytis has contributed to the decline of the Bangladesh chickpea industry and has also caused significant or total crop losses in the higher rainfall zones of northeastern India and in Australia. The following diseases are also regarded as locally significant: sclerotinia stem rot (Sclerotinia sclerotiorum (Lib.) de Bary), phoma blight (Phoma medicaginis Malbr. and Roumegue`re), alternaria blight (Alternaria alternata (Fries: Fries) Keissler), stemphylium blight (Stemphylium sarciniforme (Cavara) Wiltshire), and rust (Uromyces ciceris-arietini Jaczewski in Boyer & Jaczewski).

Figure 4 Ascochyta blight on pods. The concentric rings of darkcolored pycnidia (fruiting bodies) are a useful diagnostic feature for this disease in chickpea.

Fusarium Wilt Fusarium wilt is the other major disease of chickpea and, like ascochyta blight, causes economic damage in a large number of producing countries. It is a soil- and seed-borne disease caused by different races of the fungus Fusarium oxysporum f.sp.ciceris Matuo and K. Sato. The races are differentiated on their ability to incite specific reactions causing two types of symptoms: yellowing syndrome and wilting syndrome. The wilting syndrome is more destructive and economically more important than yellowing syndrome. Fusarium wilt is more frequently expressed under warm, dry growing conditions and is therefore a greater problem in the Indian subcontinent and in regions where the crop is spring-sown. Fungicidal seed dressings provide protection against seed-borne infection, but the longevity of the pathogen in soil makes host resistance the most successful way of combating the disease.

Root and Collar Rots A number of fungal root or collar diseases have the potential to inflict significant yield losses. Dry root rot (Rhizoctonia bataticola (Taubenhaus) Butler) is the most important of these, especially on the Indian subcontinent. The disease generally presents as a sudden drying of scattered plants at the podding stage and is favored by hot, dry conditions. Other diseases include wet root rot (Rhizoctonia solani Ku¨hn), black root rot (Fusarium solani (Martius) Saccardo), collar rot (Sclerotium rolfsii Saccardo), and phytophthora root rot (Phytophthora medicaginis Hansen and Maxwell). The latter has been recorded in a number of countries, but economically significant damage has only been observed in northeastern Australia where it is the major production problem.

Viruses Considerable crop losses have been attributed to virus disease, especially in India, Pakistan, Iran, the United States, and Australia. In most cases, a complex of viruses has been


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implicated. Aphids, particularly Aphis craccivora Koch, are almost always the vector responsible for disease transmission. In India, chickpea stunt is the name given to a syndrome characterized by foliage discoloration (red in desi and yellow in kabuli), stunting, phloem browning, and plant death. The disease has been ascribed to the leafhopper-transmitted chickpea chlorotic dwarf virus and some aphid-transmitted luteoviruses, including bean leafroll luteovirus. Other viruses known to cause disease are alfalfa mosaic virus, cucumber mosaic virus, beet western yellows virus, and subterranean clover red leaf virus.

cultivation. Options for pre- and postemergent control of both grass and broadleaf weeds are now available and used extensively in Australia, the United States, and Canada. Grass herbicides are very effective, have no toxicity to chickpea, and contribute to the productivity of ensuing cereal crops by eliminating graminaceous diseases that can otherwise survive on grass weeds. The development of herbicide-tolerant varieties will also provide further weed control options.

Nematodes

Nutritional Status

Nematodes reduce yield by colonizing and damaging roots, reducing the efficiency of nitrogen fixation and in some cases acting synergistically with fungal diseases such as fusarium wilt. Many nematode species are known to infect chickpea although only three are considered economically important. Root-knot nematodes (Meloidogyne spp.) cause abundant formation of galls, whereas both cyst nematode (Heterodera ciceri Vovlas, Greco & di Vito) and root-lesion nematodes (mainly Pratylenchus thornei Sher and Allenand and P. neglectus (Rensch) Chitwood and Oteifa) damage root cellular tissue causing necrotic regions. Root-knot nematodes and root-lesion nematodes have an extensive host range and are widely distributed; cyst nematode has a very limited host range and its distribution is confined to the Middle East.

Desi chickpea seeds are composed of the embryo (1.5%), seed coat (15.5%), and cotyledons (83%); the seed coat fraction of kabuli seeds is much lower (6.5%), resulting in a higher cotyledon fraction (92%). Protein averages 23% and is deficient in the sulfur-containing amino acids methionine and cystine. Carbohydrate, the main constituent, averages 63.5% of total seed and is mainly starch. Soluble sugars comprise 10% of the starch and include oligosaccharides such as stachyose and raffinose that cannot be broken down by human digestive enzymes. Gases produced by bacterial degradation of these oligosaccharides cause flatulence and intestinal discomfit. Oils comprise 5% of the seed but are well below commercially extractable levels. Chickpea is generally low in antinutritional factors such as protease and amylase inhibitors, whose activities are further reduced by cooking, and protein-binding phenolics, which are largely removed with processing.

Insects The small number of insect pests causing economic damage to chickpea is attributed to the antibiotic effect of the plant’s acidic (mainly malic acid) exudate. The most widespread and damaging pest is the pod borer (Helicoverpa spp.). Various larval instars feed on leaves, flowers, and pods. Most yield loss is caused when late instar larvae enter the pod and partly or fully consume the developing seed. There is little effective host resistance within chickpea so control is reliant on a combination of chemical and biopesticides (such as nuclear polyhedrosis virus). Genetic transformation has been used to develop chickpea containing the toxins from the bacterium Bt and it is currently undergoing field testing. The other major field pest is leaf miner (Liriomyza cicerina (Rondani)) whose distribution is confined to the Mediterranean region. Larvae tunnel through the leaf parenchyma causing loss of photosynthetic tissue and premature leaf drop. Infestation of stored seed is mainly by small bruchid beetles (Callosobruchus spp.). Larvae emerge from eggs laid on the (stored) seed surface and tunnel beneath the seed coat where they feed and pupate. Adults emerge from the seed, ready for the next life cycle and leaving a substantial cavity.

Weeds Chickpea’s slow early growth and low total biomass predispose the crop to severe weed competition. In most countries, weed control is done by manual weeding or cultivation by animalor tractor-drawn implements. These practices are feasible where crop area is small, although yield potential is often compromised where wide rows are employed to facilitate

Utilization

Uses and Processing Chickpea is a key dietary component in many countries where animal protein is too expensive or in other countries where the crop has a long history of cultivation and consumption. The complementarity of pulse and cereal proteins has given rise to many traditional dishes in which chickpea is combined with wheat, rice, or some locally important cereal, such as teff, to provide the bulk of dietary protein and calories. The use of chickpea as human food is hugely varied, reflecting both the crop’s antiquity and its broad cultural base (Table 2). The mature seed, either whole or processed, accounts for nearly all consumption. However, there are specialty uses for the green, immature plant. Fully podded plants are commonly sold in street markets in India and the Middle East. The seeds are either roasted in the pod, consumed raw as a snack, or boiled; fresh leaves are also used as a vegetable. Ripe seeds (desi and kabuli) are presoaked and boiled, with or without the addition of vegetables or meat, to produce a range of traditional dishes. Kabuli seeds are also canned after cooking, but a more important use is as hommos bitihneh (pureed and mixed with oil). Both desi and kabuli seeds are also roasted. This process generally requires a quick soaking followed by hightemperature treatment (e.g., at 250 C) for 2–3 min in preheated sand or an oven. Variations to the soaking, roasting, and final processing (e.g., decortication, polishing, or sugar coating) give this snack food its regional characteristics. Most desi seeds are milled to produce dhal, a process that involves removal of the seed coat and cleaving of the cotyledons (Figure 5). Milling of chickpeas is a major industry in the

322 Table 2

THE LEGUMES AND PSEUDOCEREALS | Chickpea: Overview Main uses of chickpea for human consumption

Plant/seed part used

Process/product

Country/region

Green leaves Immature plant Unripened pods Whole seed – kabuli

Boiled as vegetable Roasted, pods shelled Pods shelled, seeds raw or boiled Soaked, boiled alone or with vegetables, rice, meat, spices Soaked, boiled, canned Soaked (briefly), roasted Soaked, boiled, pureed (hommos) Soaked, boiled with vegetables, rice, spices Soaked (briefly), roasted Germinated Soaked, boiled with spices Batter for fried vegetables Batter with rice, fermented Thickener for gravies Fried extrusion products Mixed with wheat flour, bread

Indian subcontinent (ISC) ISC, Middle East, Ethiopia ISC, Ethiopia, Turkey Most countries North America, Europe, Australia, Middle East Middle East, North Africa Middle East, North Africa ISC ISC ISC ISC ISC ISC ISC ISC ISC, Middle East

Whole seed – desi

Dhal Flour (besan)

Figure 5 Dhal produced from desi seeds following removal of the seed coat and separation of the cotyledons.

Indian subcontinent and the newer high-throughput mills achieve a dhal yield close to the theoretical maximum of 83–85%. Dhal is the main form of consumption in the Indian subcontinent; the prepared dish, also called ‘dhal,’ is almost always part of the main meal. The third main use of chickpea is as ‘besan,’ the flour milled from dhal. (Small kabuli seeds have recently been substituted to produce a cheaper, but inferior product.) Besan is used for a range of purposes, most commonly as a batter or to produce fried, extrusion products. Chickpea also plays an important, if secondary, role in animal nutrition. In Mexico, desi types are grown specifically for inclusion in pig rations. Elsewhere, residues from processing (seed coat and kibble from milling and damaged or undersized seeds from grading) are routinely used in intensive livestock production. Residues from harvest (stems, leaves, pods, and seeds) are also a valuable feed source for ruminant animals.

countries despite the new varieties being released by national programs and the major international centers ICRISAT and ICARDA. Major breakthroughs have been achieved in developing resistance to the major diseases ascochyta blight and fusarium wilt. Cold tolerance, coupled with ascochyta resistance, has been deployed in new varieties that enable winter sowing in traditional spring-sowing areas, and early maturing varieties, providing some escape from drought, have facilitated the wider adoption of chickpeas in central and southern India. Mechanization of harvest has been facilitated by the development of erect plant types, which grow up to 1 m tall and have stronger, more lodging-resistant branches than the traditional semierect forms. There is a paucity of genes for many economically important traits in C. arietinum, presumably as a consequence of the genetic ‘bottleneck’ caused by domestication. However, genes conferring improved resistance to many biotic stresses, such as bruchids, cyst nematode, and phytophthora root rot, can be found in either or both the closely related ‘wild’ species C. reticulatum and C. echinospermum. Breeding programs are regularly using backcross programs to incorporate a range of attributes from these species into adapted backgrounds. Introgression of genes from unrelated taxa has also been achieved by Agrobacterium-mediated transformation. ‘Transformed’ plants containing genes with the potential to confer improved protein quality and insect and disease resistance have been developed to undergo field evaluation. In recent years, there have been major advances in chickpea genomic resources; saturated genetic maps and the publication of genome sequences of kabuli and desi chickpea types are key steps that will allow researchers and breeders to develop a full understanding of the variations found in each genotype.

Exercises for Revision Genetic Improvement Worldwide, there has only been a limited breeding effort in chickpea compared to the major cereals and oilseeds. Primitive landraces still account for much of the crop area in developing

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Why are chickpeas and other grain legumes important for sustainable farming systems? What are the three main groups of the species and how do their end uses differ?


• • • •

What is the most important disease of chickpea worldwide? What are the main abiotic constraints of chickpea? What is the average protein content of the grain? Which two wild relatives of chickpea are being exploited by breeding programs?


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The Cicer genus contains nine annual species. How diverse are they and what is their potential for use in chickpea improvement programs? What are the products made from besan (chickpea flour) in the subcontinent?

See also: Agronomy of Grain Growing: Chickpea: Agronomy; Appendix 1: Nutrient-Composition Tables for Grains and for GrainBased Products; Appendix 2: Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Fortification of GrainBased Foods; Genetically Modified Grains and the Consumer; Grains and Health; Food Grains and Well-being: Functional Foods: Overview; Food-quality Testing: The Application of Sensory Science to the Evaluation of Grain-Based Foods; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; The Composition of Food Grains and Grain-Based Products; Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units; Grains Around the World: Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; Production and Consumption of Grains: India; Non-food Products from Grains: Cereal Grains as Animal Feed; Proteins: Nitrogen in Grain Production Systems; Nitrogen Metabolism; Protein Synthesis and Deposition; The Protein Chemistry of Dicotyledonous Grains; Scientific Organizations Related to Grains: Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East; Research Organizations of the World: CGIAR; The

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Basics: Taxonomic Classification of Grain Species; The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview.

Further Reading Gaur PM, Jukanti AK, and Varshney RK (2012) Impact of genomic technologies on chickpea breeding strategies. Agron 2: 199–221. Knight R (ed.) (2000) Linking Research and Marketing Opportunities for Pulses in the 21st Century. Dordrecht: Kluwer Academic. Loss S, Brandon N, and Siddique KHM (eds.) (1998) The Chickpea Book: A Technical Guide to Chickpea Production. Western Australia: Department of Agriculture and Food. Maiti R and Wesche-Ebeling P (eds.) (2001) Advances in Chickpea Science. Enfield: Science Publishers. Saxena MC and Singh KB (eds.) (1987) The Chickpea. Wallingford: CAB International. Saxena NP (1984) Chickpea. In: Goldsworthy PR and Fisher NM (eds.) The Physiology of Tropical Field Crops, pp. 419–452. Chichester: Wiley. Sharma RN, Shrivastava GK, Rathore AL, Sharma ML, and Khan MA (eds.) (2003) Chickpea Research for the Millennium. Raipur: Indira Gandhi Agricultural University. Singh KB and Saxena MC (eds.) (1999) The Tropical Agriculturalist: Chickpeas. London: MacMillan. Smithson JB, Thompson JA, and Summerfield RJ (1985) Chickpea (Cicer arietinum L.). In: Summerfield RJ and Roberts EH (eds.) Grain Legume Crops, pp. 312–390. London: Collins. van der Maesen LJG (1972) Cicer L, A Monograph of the Genus, with Special Reference to the Chickpea (Cicer arietinum L.), Its Ecology and Cultivation. Wageningen: H Veenman and Zonen NV. Van Rheenen HA and Saxena MC (eds.) (1990) Chickpea in the Nineties. Patancheru: ICRISAT. Varshney RK, Song C, Saxena RK, et al. (2013) Draft genome sequence of chickpea (Cicer arietinum) provides a resource for trait improvement. Nature Biotechnology 31: 240–246. Yadav SS, Redden R, Chen W, and Sharma B (eds.) (2007) Chickpea Breeding and Management. Wallingford: CAB International.

Relevant Websites http://www.ars.usda.gov – R&D undertaken on chickpea in the USA. http://www.cgiar.org – Consultative Group on International Agricultural Research. http://www.icarda.org – Information on kabuli chickpeas, mainly in Mediterranean-type environments. http://www.icrisat.org – Information on chickpeas (mainly desi) in semiarid areas.

Pea: Overview TN Khan, University of Western Australia, Crawley, WA, Australia A Meldrum, Pulse Australia, Perth, WA, Australia JS Croser, University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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• • •

Pea is the second most important grain legume crop in the world and is widely adapted to cooler climates. The major pea producers are Canada, parts of Europe, the United States, and Australia. Pea is used as human food, both as a grain crop and as a popular vegetable. It is also used for animal feed. Pea seed is high in protein and a good source of vitamins such as riboflavin and niacin. Pea is a climbing plant with a weak stem where tendrils allow it to trail if support is available. Over the last few decades, the afila gene that modifies leaflets into tendrils has been exploited to develop pea varieties with improved standing ability. The genetics of the pea plant have been studied in great detail and dense linkage maps are now available. Biotechnology techniques including genetic transformation, embryogenesis, and fast-track technologies are well established for peas. Pea production and consumption are likely to remain stable with increases likely to be proportional to human population increases.

Learning Objective

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To understand pea as a grain legume crop in human food and animal feed and its significance as a legume in crop rotations.

Introduction This overview is focussed on the production of the grain legume crop Pisum sativum (L.), referred to as dry pea or field pea. Pea is one of the most ancient crop plants domesticated at around the same time as the major cereals. It is a cool-season plant requiring moderate mean temperatures in the range of 12–18 C with a relatively humid climate for optimum growth. Hot, dry weather is detrimental to seed set. However, it is also one of the most adaptable cool-season legumes and can give economic yields in areas that may not conform to the optimum requirement. A symbiotic relationship with Rhizobium enables pea to fix atmospheric nitrogen and make it available for the following crop. Thus, peas are of considerable significance in cropping rotations and overall economic value in the cropping system. The field pea plant has many uses. Green peas are one of the most popular vegetable items throughout the world. Some variants with edible pods are also used as a whole-pod vegetable, for example, sugar-podded peas and snow peas. It is also a forage plant that makes excellent hay and silage and can

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be used as a green manure crop. Dry peas are used whole in confectionery and snacks or milled to produce split peas for making soups, ‘dal’ (a curried soup-like preparation widely used in the Indian subcontinent), flour, and canned products such as mushy peas. Dry peas are also used in the feed industry, particularly in the diet of pigs and poultry due to their amino acid balance. World pea production has declined by 34% since 1993 to just under 100 million tonnes (Figure 1). Competition for land from cereals and oilseed crops, which usually deliver higher profits, is the main reason. There are over 6 million hectares (Mha) of field pea grown in the world today (Table 1). This figure has been stable for the last 10 years. As of early 2010s, Canada has the largest area under pea cultivation, followed in order by the Russian Federation, China, India, and France (Table 1). Canada has maintained its pea cultivation area at over 1.0 Mha since the 1990s, reaching a high of 1.58 Mha in 2008. Canada leads total production with more than 3.5 million tonnes produced in 2008 and 3.3 million tonnes (Mt) of crop produced in 2012, followed by the Russian Federation with a production of 1.6 Mt. Sixty-nine percent of the total world production comes from the five highest field pea-producing nations (Table 1). The yield per hectare varies widely between growing regions (Table 1). Among the largest producers, France has the highest yields per hectare of over 4 t against the world average of 1.62 t, while the leading producer Canada’s average yield is 2 t. Yields generally reflect the degree of industrialization of field pea production and the inherent variability in the climate. Average yields in India are below 1 t ha1. In most countries where it is produced, pea seed is retained for domestic consumption, as are other pulse crops. The United States and Australia are the other major exporters of field pea.

The Plant Field pea belongs to the family Fabaceae and although a number of Pisum species were designated for various cultivated pea types, they have all been assigned to P. sativum L. Some taxonomists, however, still insist on subdividing field pea, garden pea, and vegetable pea into separate subspecies, although differences are often based on a few genes, rather than broad genomic differences. All subspecies cross and recombine freely. Despite archaeological evidence indicating its cultivation as early as 6000 BC in Near Eastern and Greek settlements, there is no clear consensus on its exact place of origin. The Near East, Central Asia including Afghanistan, the Mediterranean, and Ethiopia abound with primitive forms and are sources of immense genetic diversity. A distinct species Pisum fulvum Sibth. and Sm., partially cross-fertile with P. sativum, has been


http://dx.doi.org/10.1016/B978-0-12-394437-5.00037-1

THE LEGUMES AND PSEUDOCEREALS | Pea: Overview

325

Global dry pea production (1993 to 2013)

16

Production (´106 tonnes)

14 12 10 8 6 4 2 0 1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

2014

Source: FAO Stats

Figure 1 Global dry pea area, production, and yield from 2003 to 2012. Source: FAO Statistic.

Table 1

Area, production, and yield figures for the five highest producers as compared with the world total Canada

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Russian Federation

China

India

France

World

Aa

Pb

Yc

A

P

Y

A

P

Y

A

P

Y

A

P

Y

A

P

Y

0.98 1.15 1.24 1.27 1.23 1.44 1.58 1.49 1.39 0.91 1.31

1.28 1.93 3.10 2.99 2.52 2.93 3.57 3.38 3.02 2.12 3.34

1.31 1.68 2.49 2.36 2.05 2.03 2.26 2.27 2.17 2.31 2.14

0.76 0.72 0.72 0.71 0.71 0.62 0.64 0.77 0.82 1.11 1.16

1.27 1.05 1.24 1.13 1.15 0.86 1.26 1.35 1.19 2.02 1.66

1.67 1.47 1.72 1.58 1.62 1.39 1.98 1.75 1.45 1.82 1.43

0.95 0.94 0.88 1.00 0.90 0.98 0.93 0.88 0.87 0.87 0.93

1.50 1.40 1.06 1.16 1.01 1.08 1.10 0.96 0.91 1.19 1.11

1.58 1.49 1.21 1.16 1.13 1.10 1.19 1.10 1.05 1.36 1.20

0.67 0.66 0.71 0.79 0.78 0.81 0.68 0.72 0.76 0.73 0.74

0.61 0.59 0.73 0.79 0.71 0.85 0.75 0.66 0.67 0.59 0.63

0.91 0.89 1.02 0.99 0.91 1.05 1.10 0.92 0.88 0.82 0.85

0.34 0.37 0.36 0.32 0.24 0.16 0.10 0.12 0.24 0.19 0.14

1.66 1.62 1.68 1.33 1.02 0.59 0.45 0.55 1.07 0.67 0.57

4.92 4.41 4.71 4.21 4.21 3.61 4.50 4.72 4.44 3.58 4.05

6.02 6.15 6.34 6.57 6.39 6.32 6.11 6.38 6.58 6.14 6.33

9.63 9.89 11.74 11.29 9.82 9.37 10.07 10.46 10.31 9.73 9.86

1.60 1.61 1.85 1.72 1.54 1.48 1.65 1.64 1.57 1.58 1.56

Area: ha 106. Production: t 106. c Yield: t ha1. http://apps.fao.org (February 2015). a

b

identified as a source of useful variation for disease and insect pest resistance and drought tolerance. The plant, a spreading or tendril-climbing herb, is typically 30–150 cm tall (Figure 2). Papilionaceous flowers may be white or purple or various shades of purple including pink. It is predominantly self-pollinated with cross-pollination rarely exceeding 1%. The stem is typically weak, leading to lodging as the plant gains biomass. The compound leaves generally have one or more leaflets modified into tendrils, although variants are known that have no tendrils. Of significance are the forms where an entire leaf modifies to form tendrils (Figure 3) as this may help the crop to stand better by intertwining with plants. Greater attention to this character will be given while discussing genetic improvement. White-flowered plants give rise to white/cream or translucent testae, whereas colored flowers produce variously colored testae. Cotyledon color ranges from various shades of yellow to green, although genotypes

with red cotyledon color are also known. The testa color largely determines the seed appearance, which is of commercial significance. Traders recognize five field pea seed types (Figure 4). The round white (also known as yellow), as the name suggests, is round with white to cream testae and yellow cotyledons. The dun type is variously dimpled with greenish brown (dun) testae and yellow cotyledons. The maple type is round with a brown testa that is mottled with light-colored spots giving it a marbling effect and yellow cotyledons. The blue type (also known as green) has a translucent testa with green cotyledons giving the seed a bluish hue. The marrowfat is typically a large seed (>280 mg), slightly dimpled and flattened, with blue/ green testae and green cotyledons. The diploid chromosome number is 14. Chromosomal interchanges can be common. Considerable attention has been given to the genetics of pea following the pioneering experiments of Mendel in the nineteenth century. Several

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thousand mutants have been identified and those conforming to Mendelian genetics were placed on a linkage map as early as the middle of the last century. A book assembling a comprehensive account of pea genome was published toward the end of the last century. Since then, rapid advances have been made and are covered in the section ‘Biotechnology and In vitro Culture Techniques for Field Pea Improvement.’ Updated maps, now including biochemical and molecular markers, have regularly appeared in Pisum Genetics.

Figure 2 P. sativum normal leaf, white-flowered type showing pod and seed development.

Nutritional Value, Processing, and Utilization The field pea seed is a rich source of protein, carbohydrate, and some minerals, although the nutritional content of the seed varies with the environment and genetic factors. By far, the highest proportion of nutrient value in field pea is in the cotyledons, with the embryo and seed coat contributing less than 10% to nutritional value. The protein content is typically about 22% but ranges widely, depending on the genotype and growing conditions (Tables 2 and 3). Although sulfur-containing amino acid is low, it compares favorably with other grain legumes. About 60% of the carbohydrate content of the seed is made up of sucrose and oligosaccharides, starch, and crude fiber. The fat content is low and the seeds are a good source of vitamins such as thiamine, riboflavin, and niacin, although considerable loss of vitamins may occur in processing. Antinutritional factors are present in quantities lower than in other grain legumes; the field pea has the lowest trypsin inhibitor activity among grain legumes commonly used as food in India. The flatulence activity resulting from oligosaccharides of the raffinose family is also relatively low, as are phytic acid and saponins. Lipoxygenase activity that causes deteriorative changes during the processing and storage of field peas is high, but these enzymes can be inactivated via heat treatment. The dry pea seed is processed via soaking, germination, milling, cooking, roasting, or fermentation. In Western diets, the seed is mainly used in soups or in mushy pea preparations. In South Asian diets, it has varied uses: as dal (spicy soup-like preparation in the Indian subcontinent), whole pea boiled as a snack food, as sweet and savory snacks made from pea flour, or as a supplement to wheat flour to make nutritious breads. In addition, peas can be processed into protein, starch, and fiber fractions. These products can then be used in baked goods,

Figure 3 P. sativum types: (a) semileafless, colored flowered type, and (b) normal leaf, white-flowered type.


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Figure 4 The five seed types of P. sativum: top left, yellow; top right, marrowfat; center, dun; bottom left, green; and bottom right, maple. Table 2 Nutritional content of field pea seed measured from a representative number of samples Nutritional factor Dry matter Protein Ash Fat Fiber Acid detergent fiber Neutral detergent fiber Lignin Calcium Magnesium Phosphorus Potassium Sodium Sulfur

Content (g kg1) 889.0–918.0 193.4–273.0 21.0–33.1 7.3–23.6 45.3–79.0 76.0–176.0 71.0–245.0 0.5–10.0 0.5–1.1 1.0–1.5 2.6–8.5 2.0–11.0 <0.1–0.10 1.6–2.2

Data from Petterson DS, Sipsas S, and Mackintosh JB (1997) The Chemical Composition and Nutritive Value of Australian Pulses. Canberra, Australia: Grains Research and Development Corporation.

baking mixes, soup mixes, processed meats, health foods, pastas, and purees. There are also several industrial starch uses. Field peas also serve as excellent animal feed. In an amino acid-balanced diet, there is no limit on the inclusion rate of field peas in rations for sows, weaners, and porkers. For poultry, up to 25% can be included in rations. It may also be fed in high doses to ruminants as a palatable energy and protein-rich feed.

Genetic Improvement Field pea yield is predominantly determined by the additive gene action, but nonadditive factors may also play a significant role. The heritability of yield may vary depending on

Table 3 Amino acid content of field pea seed measured from a representative number of samples Amino acid

Content (% in seed)

Alanine Arginine Aspartic acid Cystine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine Cys þ Met Tyr þ Phe

0.97 2.35 2.46 0.34 3.85 0.97 0.59 0.93 1.56 1.61 0.19 0.99 0.97 1.03 0.79 0.18 0.73 1.02 0.57 1.70

Data from Petterson DS, Sipsas S, and Mackintosh JB (1997) The Chemical Composition and Nutritive Value of Australian Pulses. Canberra, Australia: Grains Research and Development Corporation.

environmental conditions leading to variable yield stability. The logical yield components are pods per plant, seed number, and seed weight. Among these, pods per plant appear to be the best correlated with yield. However, selection for yield based on any one of these components is often ineffective. Further, yield selection in early generations is not very effective, and these generations are used for culling the population against easily recognized undesirable traits based on flower color, seed type, disease susceptibility, and plant type. Various breeding

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methods are in use, and their application depends on the type and amount of genetic variation in crosses, objectives of breeding, and available resources. In Europe, the pedigree method is commonly used. Single-seed descent (SSD) is becoming popular to hasten breeding and is sometimes used in conjunction with recurrent selection to increase the frequency of desirable alleles in the population. Bulk pedigree method has been successfully applied in the Western Australian short-season environment where biomass appears to be an important asset in combating terminal drought. Here, bulking early generations allows for natural selection to favor vigorous and tall plants. There is considerable interest in restructuring the field pea plant since the discovery of a recessive mutant designated as afila (af) where leaflets are modified into tendrils. Plants with the afila characteristics are popularly known as semileafless, although strictly speaking, they should be termed leafless. An increased number of tendrils in the semileafless crop help the plant to stand upright through intertwining with adjacent plants. When combined with dwarf plant stature and stiff stem characteristics, semileaflessness has considerably improved the standing ability of the crop. Improved standing ability has important implications in allowing for efficient machine harvestability and enhanced aeration through the canopy that may help to reduce disease epidemics. Semileafless field pea varieties have become popular in Europe, North America, New Zealand, and Australia and more recently in countries such as India. However, in limiting environments, conventional leaf types still outperform semileafless types. In such environments, high biomass appears to be an important factor in determining yield, and semileafless types tend to have a lower biomass even at a high plant density. As a result, semileafless cultivars adapted in Australia are much taller and more vigorous than those in Europe and North America. There is interest in Australia in conventional leaf type forage field pea varieties, such as PBA Hayman, that have high biomass production and are targeted for the dairy industry. Breeding against yield limitations such as diseases, insect pests, and abiotic factors has played a significant role in improving field pea yields. The impact of these factors varies with agroecology and crop management practices. Among the diseases, root rot diseases caused by Pythium spp. and Aphanomyces euteiches f. sp. pisi Pfender and Hagedorn and wilt caused by Fusarium solani (Mart.) Sacc. f. sp. pisi (Jones) Snyd. and Hans. are significant. The significant aboveground diseases are (1) wilt caused by the bacterium Pseudomonas syringae pv. pisi Sackett, powdery mildew (Erysiphe pisi Syd.), downy mildew (Peronospora pisi Syd.), and black spot disease complex caused by Ascochyta pisi Lib., Phoma medicaginis var. pinodella (Jones) Boerema, and Didymella pinodes (Berk. and Blox.) (formerly known as Mycosphaerella pinodes) Petrak (Figure 5). A number of viruses attack field peas with the most devastating being pea seed-borne mosaic virus (PSbMV) and pea enation mosaic virus (PEMV). Of these, PSbMV is widely distributed throughout the world, whereas the distribution of PEMV is more restricted. Resistance is available against some root rots and wilt, powdery mildew, downy mildew, and black spots caused by A. pisi and P. medicaginis var. pinodella, as well as the two important viruses – PSbMV and PEMV. However, it is resistance against black spot caused by D. pinodes, the single most

Figure 5 Black spot on P. sativum caused by Didymella pinodes, the most widespread pea disease in the temperate and Mediterranean climates.

important disease of field pea throughout the temperate growing zones, that has been difficult to control through breeding. Only low to moderate resistance has been identified in several screening attempts of large germplasm collections in North America, Europe, and Australasia. More recently, over 3000 accessions from the Vavilov Institute, St. Petersburg, collection were screened offshore in Ethiopia by a Western Australiabased project. The more pronounced expression of partial resistance has been identified in primitive accessions originating from Afghanistan, Ethiopia, and China. However, such accessions generally carry a number of wild characteristics including extraordinarily delayed flowering. Delayed flowering is recognized to help the field pea plant to resist D. pinodes, and hence, it is not always clear whether the resistance shown has a true genetic basis or is an artifact of late flowering habit. There is some variation in reaction to D. pinodes infection within the improved germplasm and that a small degree of resistance scattered in a wide variety of sources can be recombined. Both wild and improved sources have been used in recurrent selection programs across Australia and New Zealand, and some new improved lines show resistance levels that are equal to or better than the wild germplasm. Availability of such moderately resistant improved varieties may allow integration of disease management packages for more effective disease control. The major field pea crop pests worldwide are pea and bean weevil (Sitona lineatus L.), pea moth (Cydia nigricana F.), pea aphid (Acyrthosiphon pisum Harris), pod borers (Helicoverpa armigera Hub. and H. punctigera (Wallengren)), and pea seed weevil (Bruchus pisorum L.). The red-legged earth mite (Halotydeus destructor Tucker) is more destructive in the Southern Hemisphere, for example, Australia, where pasture legumes are widely grown. There has been some work on studying variation in resistance levels, but the most promising work so far has been on pea weevil (B. pisorum) in Australia. Resistance has been identified in a wild species P. fulvum that is partially cross-fertile with P. sativum. Resistance has been backcrossed to field pea lines, and such lines will have application as parents in crossing. Waterlogging, freezing temperatures particularly during flowering and podding, and moisture stress are the most

THE LEGUMES AND PSEUDOCEREALS | Pea: Overview serious abiotic constraints to field pea productivity. No true resistance to waterlogging or frost has been reported so far. There are reports regarding cold tolerance, but whether it relates to avoiding damage during frost is not known. There are two aspects of freezing tolerance. In higher latitudes, such as Europe, freezing tolerance is important during the vegetative phase in the winter-sown crop, whereas in subtropical and Mediterranean climates, frost tolerance during the reproductive stage is more important. A deeper root system has been reported to increase tolerance to moisture stress. However, osmoregulation/osmotic adjustment is a more measurable character, and it has shown good correlation with yield under water stress in studies done in Spain and Western Australia. Studies in Western Australia have shown that the most adapted field pea variety showed one of the highest levels of osmotic adjustment.

Biotechnology and In Vitro Culture Techniques for Field Pea Improvement

329

Genetic relationships among Pisum accessions have also been assessed using genomic techniques. Molecular analysis of pea collections has shown that although substantial variation is present within the cultivated Pisum gene pool, wild Pisum species offer the possibility to incorporate novel traits that may have been inadvertently eliminated from the cultivated gene pool via selection. Association mapping analysis of diverse pea germplasm will result in the identification of genetic variation related to desirable agronomic traits. The availability of high-throughput ‘omics’ methodologies will translate in the future into the development of novel, highly accurate selective breeding tools. Interspecific hybridization to transfer useful traits from P. fulvum and wild-type P. sativum accessions such as ssp. P. elatius to cultivated P. sativum would also benefit from techniques such as MAS and following QTLs. Targeted application of existing molecular techniques and the advent of new techniques such as the analysis of gene function through functional genomics will yield rapid gains in the understanding of field pea genetics.

Molecular Markers and Linkage Mapping

In Vitro Mediated Interspecific and Intergeneric Hybridization

Pea was the model species used by Austrian monk Gregor Mendel in 1866 to determine the laws of inheritance in plant genetics. Unfortunately, the large size of the pea genome, coupled with its repetitive nature, has constrained the achievement of a complete genomic sequence. However, comprehensive genomic and postgenomic resources have been developed for peas including BAC libraries, transcriptome and proteome data sets, and several types of molecular marker sets. Molecular markers offer the potential to advance plant breeding by analysis of genetic variation, unequivocal identification of genotypes and true hybrids, purity testing of breeding lines, genome mapping, and marker-assisted selection (MAS). In field peas, classical physiological, biochemical, and hybridization-based markers have been joined by polymerase chain reaction-generated markers. The polymorphic markers identified using these techniques have been used to construct dense linkage maps of the field pea genome, indicating the position and relative genetic distances between markers along chromosomes. The recent availability of full genome sequences for three other legume species has provided opportunities for genomewide comparison. This approach has led to the identification of genes underlying agronomically important traits, some of which have been applied to MAS programs to improve Pisum germplasm. When markers that are closely linked to desirable genes have been identified and validated in specific environments, plant breeders can use them to select plants on the basis of genotype, rather than phenotype. The application of MAS can reduce unreliable phenotypic screening and cultivar development time as markers enable the selection of genotypes at the seedling stage. Molecular linkage maps and trait mapping are valuable tools for characterizing the genetics of disease resistance, localizing resistance loci on linkage maps, and identifying linked polymorphic DNA sequences that might be used for MAS. This is particularly true for traits that are inherited in a quantitative manner, for which quantitative trait loci (QTLs) may be identified. Despite progress in the area of marker discovery, complete translation to pea breeding is yet to be achieved.

Targeted utilization of wild relatives for adaptation to climate change will almost certainly be an urgent priority this century. Legume crops and pastures are estimated to use 35–60% less fossil energy than N-fertilized cereal or grasslands. The reduced energy use was primarily attributed to reduced N fertilizer use in the legume and subsequent nonlegume crops. Interspecific hybridization is the crossing of two species from the same genus. This allows the exploitation of useful genes from wild, unimproved species for the benefit of the cultivated species. The Pisum species are diploid self-pollinators sharing a similar karyotype. P. fulvum is the only separate wild species and a useful source of disease and insect resistance. Fertile hybrids of P. sativum P. fulvum have been produced via conventional unidirectional crossing with P. fulvum as the pollen donor. Intergeneric crossing is another technique for improving genetic diversity within species. It is possible to regenerate plants from protoplasts in field pea via organogenesis and somatic embryogenesis. Somatic protoplast fusion, whereby genomes from different genera are combined without pollination through protoplast fusion, has been attempted for intergeneric hybridization between field pea and grass pea. A low frequency (5%) of protoplast fusion has been achieved; however, these hybrids have not been regenerated to whole plants.

Transformation Plant genetic engineering provides an opportunity to introduce traits such as pest and disease resistance, improved protein quality, and herbicide tolerance from previously unavailable sources. Since the first production of diploid transgenic field pea plants in the early 1990s, Agrobacterium-mediated genetic transformation has become a routine procedure in a number of laboratories worldwide. The embryonic axis of immature seeds or the lateral cotyledonary meristems from germinating seeds are the most responsive target explants, and regeneration is generally via organogenesis. In addition to Agrobacterium-mediated transformation, several other approaches have been developed to produce

330


transgenic field pea plants: transgenic callus has been obtained by electroporation of protoplasts, as has transient expression following particle bombardment of meristems. Microinjection, particle gun, agroinfection, and the pollen tube pathway are at present less efficient or require expensive and sophisticated equipment. As in other species, transformation efficiency is dependent on the genotype, explant type, and other physical parameters. Despite transformation being a well-established technique in peas, there are currently no commercially available pea cultivars developed using this technology.

Double Haploid Production Doubled haploids (DHs) are plants derived from a single immature pollen grain and doubled artificially to form homozygous diploids. A DH individual has two identical homologues so that the amount of recombination information is equivalent to a backcross. The advantage of using a DH population in molecular mapping is that all individuals are homozygous. Therefore, DHs may be transferred between different laboratories and environments for assessing the effect of the environment on gene expression. Pea, along with many of the large-seeded leguminous species, has traditionally been considered recalcitrant to this technique. In 2009, the first production of confirmed haploid plantlets of pea from the culture of immature pollen was reported. Research is ongoing to develop a robust protocol that will be applicable across a range of genotypes. The mechanisms for switching the immature pollen from normal gametic development have also been recently elucidated for peas. Successful production of DHs on a routine basis would reduce cultivar development time and provide excellent recombinant inbred lines for molecular mapping applications.

In vitro Generation Acceleration In the absence of a robust, widely applicable, DH protocol, an in vitro modified SSD system has been developed to accelerate the achievement of homozygosity in peas. Conventional SSD consists of randomly selecting one seed per plant from an F2 population following a cross and advancing it through the early segregating generations, thus permitting rapid fixation of genes in breeding lines. As only one seed is needed to produce the next generation, plants can be grown under conditions that accelerate flowering and seed set, but do not encourage high yield. Current SSD methodologies enable a maximum of three generations per year. The in vitro SSD technique involves further shortening of the generation time by culturing immature seeds developed after forced in vitro flowering under conditions for accelerated flowering and seed set. This leads to rapid generation turnover by reducing the length of the generation cycle, enabling up to eight generations per year.

Grain Quality and Marketing Market requirements for grain quality relate predominantly to shape, size, and color (testa and cotyledon). For all seed types, large size is desired, and in marrowfat, there may be a limit for the minimum seed size from the buyer.

With blue peas, resistance to bleaching is an important criterion. Round white types must have a smooth round surface with white to creamy color and bright yellow cotyledons. The dun types should ideally have a mix of greenish to brownish testae and fewer and shallower dimples with bright yellow cotyledons. Maple type, mainly used for pigeon and bird feed, must have white markings on a brown testa and yellow cotyledon. Both round white and dun types are milled, as are blue types. However, currently, there are no standards for milling recovery. Seed moisture content at sale is normally between 10% and 15%. All types of field peas are generally accepted by the feed industry, but a preference is made for the noncolored type as they tend to have less antinutritional factors. The Southeast Asian market for sprouting field pea prefers dun types with large seed size and fewer hard seeds. Irrespective of the type, the following qualities are important for visual assessment in the trade:

• • • • • •

Levels of admixture Levels of insect damage and presence of live or dead insects Product color Product size Product cleanliness Product uniformity

Today, almost 50% of the field pea production is traded throughout the world compared with just 20% 15 years ago and double that traded in 2002 (Figures 3 and 4), which compares with temperate cereals where 5% is traded. The world field pea production has been mostly stable in the last decade, but trading across the board is showing a strong increasing trend. The prices have been generally steady since the early 2000s, but wide variations occur depending upon the season, time of the year, and proximity to the market. Canada and the Russian Federation are currently the world’s leading exporters with Canada having dominated the export market for many years. The quantity exported from France has halved since 1999 (Figures 6 and 7). India and China are now the largest importer of field pea with Bangladesh and Pakistan importing dry pea as demand requires. Germany, Spain, and Belgium continue to be consistent importers among European countries (Figures 8 and 9). In general, the market for field pea is rather unsophisticated in terms of both product definition and terminology used. For instance, in dun-type field peas that are normally milled, traders often use slight variation in testa color in an attempt to discount price that is irrelevant to the product utilization. There are various terminologies used to describe the same product as in the case of white round type that is traded as yellow pea from North America. Work continues at an international level to improve the marketing of pulses through development of standardized nomenclature and methods of testing quality parameters in order to meet consumer needs. The International Pulse Trade and Industries Confederation (CICILS/IPTIC) and various major importing organizations are collaborating to develop standardized nomenclature and methods for quality evaluation that will facilitate improvement of quality assurance in the international pulse trade including field peas. Progress is available on the CICILS website (http:// www.cicilsiptic.org/).


331

Dry Pea Exports by Country 2002 (tonnes)

391,022 Canada 672,731

835,857

Russian Federation United States of America France Australia

94,622 130,867

Source: FAO Stats

Global total (top 20)= 2,703,233

Figure 6 Dry pea exports by the top six exporting countries in 2002.

Dry Pea exports by Country 2011 (tonnes)

324,883

243,791

335,570

Canada

460,797

Russian Federation

2,854,580

United States of America France Australia Global total (top 20)= 4,761,297

Source: FAO Stats

Figure 7 Dry pea exports by the top six exporting countries in 2011.

Dry Pea Imports by Country 2002 (tonnes)

India 37,755

99,634

China

91,203 Bangladesh Spain

215,494 869,803 214,545

Belgium Pakistan

277,199

Germany Italy

110,857


Figure 8 Dry pea imports by the top eight importing countries in 2002.

Future Prospects The pea crop is likely to retain its importance as human food and animal feed. While yield improvement per se will continue, seed quality will become critical as market sophistication develops. While pea breeding will continue to make improvements in

yield and quality, some serious challenges need to be addressed, which include both biotic and abiotic stresses. Among biotic stresses, the black spot diseases and major insect pests continue to be major limitations to achieving high yields. Abiotic stresses such as tolerance to drought, frost, and waterlogging also need attention. Advances in new

332


Dry Pea Imports by Country 2011 (tonnes)

India

97,345 104,431

China

102,533 82,527

Bangladesh

123,113

Spain

211,784 730,434

Belgium

1,866,735

Pakistan Germany Italy

Source: FAO Stats


Figure 9 Dry pea imports by the top eight importing countries in 2011.

technologies such as those that accelerate generation turnover, DH, and molecular markers will greatly assist in addressing future pea breeding objectives. Genetic modification will play a more dramatic role in addressing some key challenges where natural variation in pea germplasm is deficient.


• • • • • • • • • • •

What is the status of pea as a crop on the world scene? What are the climatic conditions most suitable for pea growing? What are the uses of pea and how do they relate to seed characteristics? What are the major nutritional benefits of pea seeds? What other advantage does pea crop offer to a cropping system? What are the major diseases and insect pests of pea crop? What is semileafless character in pea plant? Describe the significance of this characteristic for improving pea varieties. How does molecular marker technology help in pea breeding? Is there a protocol for reliable production of transgenic peas? Can interbreeding with wild relatives improve pea? What improvement would you like to see in trading pea seeds?


• •

•

Greater improvement in standing ability of mature pea crop through combining afila characteristic and greater stem strength characteristics. What features contribute to stem strength and their inheritance? Availability of suitable broad fungal resistance genes for improving resistance to Didymella pinodes through genetic modification. Would they be more effective if transferred to the moderately resistant varieties that have become available in recent years? Search for more effective fungicides for D. pinodes control. Can current fungicides be more effective if used on moderately resistant varieties available now?

• • • •

Continuous improvement of doubled haploid production to enable reliable and cost-effective techniques for accelerating breeding. More targeted studies in the available gene pool of P. fulvum to find traits of interest for transfer to P. sativum. Frost resistance/tolerance at pod development. Challenges of possible climate change: heat and drought resistance/tolerance.

See also: Agronomy of Grain Growing: Field Pea: Agronomy; Plants: Diseases and Pests; Bioactives and Toxins: The Antinutritional Components of Grains; Food Grains and the Consumer: Grains and Health; Genetics of Grains: Development of Genetically Modified Grains; Genome Mapping; Genomics of Food Grains; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grains Around the World: Grain Production and Consumption: China and South-East Asia; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; Production and Consumption of Grains: India; Proteins: Nitrogen in Grain Production Systems; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Basics: Taxonomic Classification of Grain Species; The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview.

Further Reading Byrne OM, Hardie DC, Khan TN, Speijers J, and Yan G (2008) Genetic analysis of pod and seed resistance to pea weevil in a Pisum sativum P. fulvum interspecific cross. Australian Journal of Agricultural Research 59: 854–862. Casey R and Davies DR (eds.) (1993) Peas: Genetics, Molecular Biology and Biotechnology. Oxon, UK: CAB International. FAOSTAT database. Area, yield and production data. http://faostat.fao.org/site/339/ default.aspx; Export and import data. http://faostat.fao.org/site/342/default.aspx (both accessed 13.12.13). Hebblethwaite PD, Heath MC, and Dawkins TCK (eds.) (1986) The Pea Crop: A Basis for Improvement. London: Butterworths.

THE LEGUMES AND PSEUDOCEREALS | Pea: Overview Khan TN, Timmerman-Vaughn GM, Rubiales D, et al. (2013) Didymella pinodes and its management in field pea: Challenges and opportunities. Field Crops Research 148: 61–77. Kraft JM and Pfleger FL (eds.) (2001) Compendium of Pea Diseases and Pests, 2nd edn. St Paul, MN: The American Phytopathological Association. Makasheva RK (1986) The Pea. Rotterdam: A.A. Balkema. Ochatt S, Pech C, Grewal R, Conreux C, Lulsdorf M, and Jacas L (2009) Abiotic stress enhances androgenesis from isolated microspores of some legume species (Fabaceae). Journal of Plant Physiology 166: 1314–1328. Ribalta FM, Croser JS, Erskine W, Finnegan PM, Lulsdorf MM, and Ochatt SJ (2013) Antigibberellin-induced reduction of internode length favors in vitro flowering and seed-set in different pea genotypes. Biologia Plantarum 58(1): 39–46. http://dx.doi. org/10.1007/s10535-013-0379-0. Ribalta FM, Croser JS, and Ochatt SJ (2012) Flow cytometry enables identification of sporophytic eliciting stress treatments in gametic cells. Journal of Plant Physiology 169: 104–110. Schroeder HE, Schotz AH, Wardley-Richardson T, Spencer D, and Higgins TJV (1993) Transformation and regeneration of two cultivars of pea (Pisum sativum L.). Plant Physiology 101: 751–757. Siddique KHM, Erskine W, Hobson K, et al. (2013) Cool-season grain legume improvement in Australia: Use of genetic resources. Crop and Pasture Science 64: 347–360.

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Smy´kal P, Aubert G, Burstin J, et al. (2012) Pea (Pisum sativum L.) in the genomic era. Agronomy 2: 74–115.

Relevant Websites http://www.cicilsiptic.org/ – CICILS/IPTIC– world trade association for pulses. http://www.grdc.com.au/ – Australian Grains Research and Development Corporation (GRDC) field pea growing guidelines including disease information. http://hermes.bionet.nsc.ru/pg/ – Pisum Genetics, published periodically by Pisum Genetics Association, Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, MT 59717, USA. http://www.pea-lentil.com/ – USA dry pea and lentil council site with USDA policy positions and research updates. http://www.pgro.org/ – Processors and Growers Research Organisation (PGRO), United Kingdom. http://www.pulseaus.com.au/ – Pulse Australia is the peak industry body representing all sectors of the Australia Pulse Industry. http://www.pulsecanada.com/ – Pulse Canada is the national industry association that represents growers, processors and traders of pulse crops in Canada. http://www.saskpulse.com/ – Saskatchewan Pulse Growers Group with agronomic advice, markets and food uses.

Peanuts: Overview RCN Rachaputi, University of Queensland, Kingaroy, QLD, Australia G Wright, Peanut Company of Australia, Kingaroy, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

Background, distribution, utilization, and trade. An overview of morphology, growth, and development. Yield and quality constraints. Peanut as a source of oil and quality snack food. Food safety issues. Advances in breeding. Innovations in biotechnology. Future prospects for increased yield and quality.

Brazil in South America. The Spaniards are believed to have taken the crop to the western Pacific, Indonesia, and China early in the sixteenth century. Arachis hypogaea is an annual member of the family Papilionaceae, which shows a unique feature of maturing their fruits underground (Figure 1). The plant comprises a number of subspecies – Arachis fastigiata var. fastigiata (Valencia) and var. vulgaris (Spanish), both bunch forms, and subspecies Arachis hypogaea var. hypogaea (Virginia bunch and runner). Large variations in growth habit (erect vs. spreading), branching type (alternate or sequential), maturity (90–160 days), and traditional market types (Virginia, Spanish, or Valencia) exist.

Learning Objective

•

To achieve understanding of the significant issues related to production, utilization, genetic improvement, and food safety issues of peanut or groundnut.

Introduction Peanut or groundnut (Arachis hypogaea L.) is a tropical legume grown as an oilseed or food crop in more than 100 countries between 40 N and 40 S, with the main commercial production occurring in the northern hemisphere. Peanut area has increased from 21 million hectares in 2009 to 23 million hectares in 2013, with an annual production increasing from 33 to 37 million tonnes in the same period. Peanut kernel is the most economically important component with an oil content of 50% and protein content of 25%. The vegetative parts of groundnut are used as hay for livestock in developing countries, while the by-products of oil extraction, that is, shells, peanut meal, and residues, are used either as livestock feed or as fertilizer in crop husbandry. Peanut being a leguminous plant, can fix atmospheric N (up to 300 kg N ha1), and crop residues incorporated into soil can potentially contribute up to 120 kg N ha1. This article provides information on distribution, utilization, and quality issues, especially, on the unique features of peanut, which lead to its reputation as a high-value crop. The article also provides an overview of morphology and recent innovations in biotechnology. Further detail on other topics not covered in the article can be found in the list of suggested further reading and related web links.

Historical Background Peanut is known by many other local names such as earthnut, groundnut, goober, monkey-nut, pygmy nut, and pignut. Despite its name and appearance, the peanut is not a nut, but rather a legume. Peanut genus Arachis, originated in central

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World Peanut Production and Utilization Production and Yields The global nut-in-shell production has averaged around 36 million tonnes during the period 2009–12, which represents a 24% increase over 1996–2002 production figures. Most of the production occurs in Asia followed by Africa and America (Table 1). This increase in production has been due to the combination of increased area planted (nearly fourfold) and increased yields. Although the average yields have more than doubled during 1990–2005, further yield increases have been modest in most countries during 2009–12.

Utilization About 48% of the world production is used as food and 52% is crushed for oil, although large country variations exist. For example, India crushes nearly 90% and China 52% of the production for oil compared with countries such as Indonesia, Mexico, and Ghana that directly consume over 95% of the crop for food purposes. In developed countries, about half the production is used for peanut butter, with the remainder used for peanut snacks. Peanut is also an important source of vegetable protein in addition to 30 essential nutrients. The use of peanut kernels and their value-added products such as fresh, dry, boiled, or roasted peanut butter and snack food is on the rise due to growing vegetarianism and demand for healthy foods. More recently, peanut has been identified as a source of resveratrol, an antioxidant linked with reduced cardiovascular disease and reduced cancer risk. The peanut haulms are also of very high nutritional value as livestock feed in developing countries and attract high market price, particularly in dry years. The shells of the mature pods can also be used as fuel, fiber filler in animal feeds, garden mulch, and more recently a possible source for deactivated carbon (biochar).


http://dx.doi.org/10.1016/B978-0-12-394437-5.00038-3

THE LEGUMES AND PSEUDOCEREALS | Peanuts: Overview

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Leaf

Flower

Pod Kernel in pod

Peg

Embryo Roots

Figure 1 Diagram of a peanut plant showing its unique underground fruiting habit. Source: http://upload.wikimedia.org/wikipedia/commons/a/a4/ Arachis_hypogaea_-_K%C3%B6hler%E2%80%93s_Medizinal-Pflanzen-163.jpg. Table 1

Country China India Nigeria The United States Myanmar Indonesia Argentina Sudan Senegal Vietnam World production

Annual peanut production and yields for the ten major world-producing countries during the periods Production (million Mt) 2008–09a

Production (million Mt) 2011–12b

% Change since 2008–09

Average yield (dry pods) (kg ha1) 2008–09

Average yield (dry pods) (kg ha1) 2011–12

%Change since 2009

14.30 6.25 1.55 2.34

16.05 5.50 2.96 1.66

þ12.2 12.0 þ91.0 29.1

3.36 0.92 1.24 3.83

3.5 1.04 1.26 3.8

þ4.2 þ13 þ1.6 0.8

1.00 1.25 0.58 0.85 0.71 0.50 34.43

1.39 1.17 0.98 0.85 0.53 0.47 37.87

þ39.0 6.4 þ69.0 0.0 25.4 6.0 þ10

1.49 1.67 3.80 0.85 0.97 2.11 1.64

1.58 1.66 3.19 0.85 0.61 2.13 1.64

þ6.0 0.6 16.1 0 37.1 þ0.9 0

a

2009 (adapted from www.en.wikipedia.org/wiki/peanut). 2011–12 (adapted from USDA).

b

Trade Peanut is generally traded in two product qualities, that is, as food quality (snack food) and crush quality (cooking oil). The crush-quality trade is generally mostly domestic to meet demand for cooking oil. Food-quality peanut in general is international and receive a quality premium relative to crushquality groundnuts. The world trade market for peanuts can be considered as a residual market, as only < 6% of the world production is traded internationally owing to most of the production being utilized domestically. The major producers–exporters of peanuts are the United States, Argentina, Sudan, Senegal, and

Brazil, which in total account for 71% of total world exports. The peanut trade has steadily shifted from a crush for oil to a snack food market, which meant rising demand for higherquality peanuts, especially with low aflatoxin contamination (see section ‘Aflatoxin’). More than 48 peanut-growing countries have established limits for total aflatoxins in food, but standards varied widely, ranging from 0 to 50 parts per billion. Very strict aflatoxin regulatory limits in European markets (e.g., <4 ppb total aflatoxins) have impeded a number of Asian (China, Vietnam, and India) and African (Nigeria and Sudan) countries in competing in the edible peanut market.

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Morphology and Growth Physiology Peanut varieties grown in the world can be grouped into four major botanical types, Spanish, Virginia bunch, Virginia runner, and Valencia, distinguishable by their branching, flowering, and fruiting habit. Being an indeterminate in growth, peanut supports simultaneous growth of vegetative and reproductive structures that compete for nutrients and assimilates throughout most of the crop life cycle. Flowers appear about 25–35 days after planting, depending on the botanical type of the variety and ambient temperature during the crop growth, and continue to be produced until final maturity. The rate of flower initiation increases to a maximum and then declines as the pod load increases and the crop approaches maturity. Bursts of flowering are common when crop recovers from dry spells after rain during the vegetative phase and can lead to more synchronous pod set and higher yields and quality given favorable growing conditions during the pod-filling period. Peanut has a selffertilized flower that fades and withers soon after fertilization. Rates of natural outcrossing are low and have been estimated between 0.7% and 2.5%. After 5–7 days of fertilization, the base of the fertilized ovary (gynophore or peg) begins to elongate toward the soil, penetrating the soil up to a depth of 4–5 cm. The ovary then begins to swell and turns horizontally away from the plant (Figure 1), which takes between 15 and 20 days from the initial flowering event. There may be 1–4 kernels per pod depending on the botanical type. The pod volume expands as the kernels inside the pod inside fill, reaching full dimensions characteristic of the variety over the next few weeks. Because of the slow rate of pod addition, many pods must be added and seeds initiated to form a full pod load on the plant. Pod growth rates vary depending on temperature, water status, and varietal maturity and partitioning ability.

Farming Systems Peanuts are grown as a rotation crop in a range of irrigated or rainfed cropping systems around the world. In most developed countries, peanut is grown as a sole crop in rotation with cereal or sugarcane crops under rainfed or irrigated conditions, using fully mechanized cultural practices from sowing to harvest. In countries such as the United States and Australia, it is not uncommon for one farming family to farm 500 or more hectares per annum. Peanuts are generally grown in a rotation of one peanut crop in two or three summer cereal crops in order to minimize soilborne diseases and use of nitrogen fertilizers and allow more effective weed control. In developing countries throughout Asia and Africa, smaller-scale peanut production on 1–2 ha plots is more common, under a variety of cropping systems. In most regions in Asia, peanut is often grown as a cash crop with both kernels (as food) and haulms (as fodder) are sold in markets. Peanuts are important component in rice-based cropping systems throughout Southeast Asia. The crop is either planted with irrigation before a rice crop or grown on residual soil moisture after the rice harvest. In Asia, peanut is also

grown as an intercrop with longer season annual and perennial crops, including castor, cassava, maize, and sugarcane. Peanut can also be grown underneath perennial tree canopies such as coconut, cocoa, oil palm, and rubber, owing to its effective shade tolerance. Under these systems, peanut can provide cash income until the plantation trees are old enough to produce their end products.

Biotic and Abiotic Constraints to Yield Biotic Constraints Insect pests Around 360 species of arthropod pests are known to attack in different regions of the world. In general, the foliage pests are of lesser importance than the soil-inhabiting pests, which can cause direct economic damage to pods. A large number of thrips species that attack peanut and have become vectors of some of the debilitating peanut viruses such as tomato spotted wilt virus (TSWV). The most important soilborne pests in the developed world are the lesser cornstalk borer, Elasmopalpus lignosellus, and white grubs, the larvae of which attack pegs and pods and cause substantial economic damage. Etiella behrii is endemic to Australia and is known to be only Etiella species that affects peanuts. The pod damage caused by the soil insects can lead to aflatoxin contamination in kernels following infection via the fungus Aspergillus flavus.

Fungal pests The most important fungi causing economic damage to peanut crops around the world are the leaf spots (early and late) and leaf rust. These diseases cause leaf necrosis and can lead to severe yield losses if not effectively controlled by fungicides. A number of highly efficient chemical formulations have been developed over recent years to control both diseases. Genetic resistance is also available; however, there is a known negative association between foliar disease resistance and yield potential. A number of soilborne diseases can cause significant economic losses in peanuts, via seedling and plant death, as well as via direct pod damage due to pod rots. The most important diseases include white mold (Sclerotium rolfsii), Cylindrocladium black rot, and Sclerotinia blight. More detailed coverage of this topic can be found in the references suggested in the bibliography.

Viruses Many viruses infect peanut, and historically, they have not caused widespread economic losses. This situation has changed over the past decade, with the arrival of the potyvirus peanut stripe virus (PStV) in Asia and the United States and TSWV in the United States. A system of cultural practices have been implemented to control these diseases, including planting date and plant and row spacing to control thrips vectors such as the western flower thrips. Some genetic tolerance has been identified for TSWV in the United States, but there is no known genetic resistance to PStV, although a recent collaborative project involving Australian, Indonesian, and Chinese scientists has developed resistant breeding lines using molecular

THE LEGUMES AND PSEUDOCEREALS | Peanuts: Overview approaches. More information on virus-impacting peanut can be found in the website listed under bibliography.

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reproductive efficiency increasing at higher temperatures (e.g., mean daily temperatures exceeding 26 C).

Soil nutrition

Abiotic Constraints About 80% of the world’s groundnut production comes from dryland regions of the semiarid tropics, which are characterized by poor soil fertility and drought coupled with elevated seasonal temperatures.

Drought The major effect of soil and crop water deficits on peanut yield relates to reduction in canopy development and pod growth ultimately affecting pod yield. Peanut has a reputation of being a drought-tolerant crop, which is associated with a number of important plant traits. Significant genetic variation in these traits exists and breeding programs are exploiting these traits to further enhance peanut drought resistance. Readers are referred to detailed reviews on this subject by Boote and Ketring, Wright and Nageswara Rao, and Nageswara Rao et al.

Temperature Peanut is known to grow well under a wide range of temperatures, with daily optima for the rate of development, growth processes, and yield being around 25–30 C. High temperatures in excess of 35 C can reduce leaf area development, reduce the number of pods, and result in lowered harvest indices and yields. The interactions of water deficits with temperature cannot be ignored as high temperatures can accentuate negative impacts of water deficit. In fact, the subterranean fruiting habit of groundnut renders it more sensitive when soil surface temperature exceeds 40 C even under well-watered conditions. The threshold temperature for growth and developmental processes in peanut is listed in Table 2.

Photoperiod While growth and yield of peanut are known to be linearly related to total solar radiation receipt, reproductive development and quality can be strongly related to photoperiod (day length) in sensitive cultivars. Peanuts were previously thought to be day-neutral, with phenology mainly driven by temperature. Controlled environment and field experiments have since determined that reproductive efficiency can be modified considerably by varying photoperiod. Studies have found that longer photoperiods reduced shelling percentage in sensitive cultivars. More recent data have shown that significant photothermal interactions exist in peanut, with the sensitivity of Table 2 Temperature limits of various growth and developmental processes in groundnut Process

Tbase ( C)

Topt ( C)

Tmax ( C)

Germination Leaf appearance Leaf photosynthesis Onset of anthesis Pollen viability and seed setting Pod size and pod growth rate Harvest index

8–11.6 10

29–36.5 30 29–36 29–33 27–32 24–28 27–32

41–47

11

38 37–43 37–44

The specific nutritional issues of most importance for peanut production include calcium (Ca) and biologically fixed nitrogen (BNF). Peanut pods absorb Ca directly from ambient soil solution. The Ca absorbed by the roots and transported via the transpiration stream (xylem) is unavailable to the pegs and pods of the peanut plant as these subterranean organs do not transpire. Low soil water content in the podding zone can decrease Ca uptake and induce Ca deficiency in peanut leading to empty pods, referred to as ‘pops.’ Calcium, usually applied as gypsum at during early pod set phase, has been widely practiced to increase Ca supply to pods and yield of peanut under drought conditions. Large-seeded Virginia types have been shown to be more sensitive to drought-induced Ca deficiency than smallerseeded Spanish types. Peanuts as other legumes have the unique ability to fix atmospheric nitrogen by forming a symbiotic relationship with Bradyrhizobium bacteria in the root nodules. Inoculation of seeds with effective rhizobia has led to substantial increases in peanut yield in fields that have not previously grown peanuts. It is generally accepted that once a field has successfully grown a peanut crop, it should not require future Rhizobium applications. Estimates of fixed nitrogen as large as 300 kg N ha1 have been reported for well-watered crops, with reports that BNF can supply over 80% of the plants’ total N uptake. Although most of the N in the crop is removed when the pods are harvested, numerous experiments have shown that significant N may be left in the soil for uptake by subsequent crops. A number of studies showed that the N fixation process is extremely sensitive to soil water deficits.

Peanut Products, Quality, and Food Safety Peanut Products Nearly two-thirds of the world production of peanut is crushed for cooking oil, making it one of the world’s leading oil crops. Peanut oil is mostly composed of triglycerides of eight fatty acids. Around 80% of these fatty acids are either oleic acid (monounsaturated, C18:1) or linoleic acid (polyunsaturated, C18:2). Generally, these two fatty acids vary inversely. Of the eight commonly detectable fatty acids in peanut oil, linoleic acid is the only one that is polyunsaturated. The second double bond in a linoleic acid molecule renders it far more susceptible to oxidation. This ‘oxidative rancidity’ generates off-flavors in peanut products and hence limits the shelf life of products in retail outlets. The monounsaturated oil type in peanuts is also known to be ‘heart-healthy.’ It was also found that diets including peanuts and peanut butter lowered cardiovascular disease risk by 21%, whereas the low-fat diet decreased the risk by only 12%. In the late 1980s, researchers at the University of Florida discovered a (naturally occurring) mutant peanut plant with over 75% oleic acid and linoleic acid below 5% of fatty acids, which they subsequently described as high-oleic acid germplasm. This trait has recently been bred into adapted


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commercial varieties, which are currently being released in the United States and Australia. This characteristic will provide even greater benefits to both product shelf life and human health. The increased shelf life is best illustrated by the peroxide value (PV; a measure of shelf life) data shown in Figure 2, which shows how high-oleic acid peanuts maintain low PVs (and hence no rancid off-flavors) during an accelerated aging test.

Nutritional Aspects Peanuts are an excellent source of nutrition for both humans and animals. Tables 3 and 4 give a proximate nutritive composition of peanut kernels and dry peanut hay, respectively. Clearly, they are a rich source of protein, oil, carbohydrate, and minerals. Peanuts are also a good source of niacin, folic acid, phosphorous, vitamin E, and phytosterols.

Bioactives Peanuts contain all nine amino acids essential to humans and nine nonessential amino acids. Recent studies have shown that peanuts also contain many compounds with antioxidant properties such as tocopherols, p-coumaric acid, and t-resveratrol, which can be termed as antioxidants.

products. The human impact, in terms of mortality and morbidity, in peanut-growing countries in developing world is enormous, with estimates of up to 20 000 deaths per year arising from aflatoxin-related illnesses being made in some Southeast Asian countries. In developed countries, consumers are more aware of food safety issues such as aflatoxin and are increasingly demanding peanut products meet strict regulatory standards. Current strategies to reduce aflatoxin levels to below regulatory limits (e.g., 15 ppb in retail products in the United States and Australia) involve a post-farm gate process of selective segregation achieved through blanching and color sorting in shelling plants. In developing countries, aflatoxin regulatory limits for peanut have been stringently applied and have recently affected export of peanut and its products. A number of potential solutions have been proposed to minimize aflatoxin at its source, the farm. The use of agronomic management methods, including pre- and postharvest strategies that minimize aflatoxin contamination by the fungi Aspergillus flavus and Aspergillus parasiticus, has shown to be effective. A number of peanut varieties have been shown to have some aflatoxin tolerance, which seems to be associated with drought avoidance and escape mechanisms. Recent research is also investigating the potential for using a biocontrol approach, where nontoxigenic strains of the Aspergillus flavus fungus are applied to the soil and infect kernels and hence competitively exclude toxigenic strains.

Food Safety

Table 3

Aflatoxin

Principle

Nutrient value

Protein Oil Carbohydrate Dietary fiber Cholesterol Vitamins Folates Niacin Riboflavin Thiamin Vitamin E Electrolytes Sodium Potassium Minerals Calcium Copper

28–30 g 48–49 g 16 g 8.5 g 0 mg

Aflatoxin is a human carcinogen that contaminates peanuts, particularly under end-of-season drought and makes them unsafe for human consumption. Aflatoxin production occurs in peanut kernels particularly under drought conditions consequent to infection by soilborne fungi, Aspergillus flavus and Aspergillus parasiticus. Aflatoxin production can occur during crop growth, during postharvest-drying phase, or during storage. The aflatoxin problem is a worldwide phenomenon but is particularly severe in developing countries in Africa and South and Southeast Asia, where food safety and security systems are not well developed to protect consumers against unsafe food

Peroxide value (meq kg–1)

400

300

Normal-oleic

Nutritional value per 100 g of peanut kernels

240 mg 12 mg 0.135 mg 0.640 mg 8.33 mg 18 mg 705 mg 92 mg 1.14 mg

Source: USDA National Nutrient database.

200

Table 4 100 High-oleic 0

0

100

200

300 400 500 600 Heating time (h)

700

800

900

Figure 2 Peroxide value over time as a measure of oxidation of high- and low-oleic acid peanut oils. Reproduced From O’Keefe, Wiley, and Knauft (1993) Journal American Oil Chemists Society, 70, 489–492.

Nutritional value per kg of dry peanut hay

Principle

Nutrient value of hay (g kg1)

Crude protein Neutral detergent fiber Calcium Phosphorus

105 466 12 1.7

Source: Khan MT, Khan NA, Bezabih M, Qureshi MS, and Rahman A. (2013) The nutritional value of peanut hay (Arachis hypogaea L.) as an alternate forage source for sheep. Tropical Animal Health and Production, 45(3), 849–853.

THE LEGUMES AND PSEUDOCEREALS | Peanuts: Overview Cadmium Cadmium (Cd) is a heavy metal, which can accumulate in some foods and potentially lead to kidney damage if high levels of intake occur over prolonged periods. Recent research has shown that peanut can accumulate high Cd levels on acidic sandy soils, especially where there has been a history of phosphatic fertilizer application, which had contained Cd as a byproduct. A number of management practices have been proposed to minimize Cd accumulation in peanuts, and readers are referred to the following website for more information.

Anaphylaxis Anaphylaxis is a sudden, severe, potentially fatal, systemic allergic reaction to peanuts that can involve various areas of the body (such as the skin, respiratory tract, gastrointestinal tract, and cardiovascular system). Anaphylactic reactions can be mild to life-threatening and seem to have an annual incidence of about 30 per 100 000 persons. A number of the proteins responsible for peanut allergy have already been identified. Among major peanut allergens, Ara h 1, Ara h 2, and Ara h 3, are storage proteins that comprise a substantial proportion of the total protein in the seed. These proteins that are critical for cellular function most likely could not be eliminated without deleterious consequences for plant growth and development. However, breeding or bioengineering research is underway to explore possibilities of substituting a nonallergenic for an allergenic form of proteins.

Breeding and Biotechnology There is a general consensus that further genetic enhancement of crops including peanut for improved adaptation is best achieved by trait-based breeding strategies. While conventional empirical breeding for yield improvement has been generally successful, the rate of genetic gain has been slow and increasingly becoming cost-prohibitive. Recent studies in Australia lead to the development of ‘speed breeding’ strategies, which can potentially half the time taken for the release of a new variety with desirable agronomic traits. There is enormous genetic variability in peanut germplasm for most traits of interest, including host-plant resistance to disease and insects and along with important agronomic and quality traits. This germplasm has been collected and preserved. The most significant collection is housed at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India, where some 12 000 accessions are maintained, along with more than 70 wild Arachis species.

Marker-Assisted Breeding The biotechnology revolution occurring in a range of crops has yet to be realized in peanut. This has been largely due to the lack of polymorphism for allozymes or restriction fragment length polymorphism (RFLP), which has restricted the use of marker technology for improved selection of quantitative traits such as yield. The peanut genome is also very large, around 2800 Mbp, and is classed as a tetraploid. Due to the low number of polymorphic markers available for the cultivated peanut, there has been very little success in marker-assisted breeding in peanut. Where the markers have

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been identified for specific traits such as high oleic acid and nematode resistance, the marker-assisted selection has been successful in the development and commercial release of varieties. The advent of next-generation sequencing (NGS) provides a cost-effective strategy to identify molecular markers, at wholegenome level, associated with traits of interest and can expedite the development of new peanut varieties. The size and complexity of the cultivated peanut genome have previously been considered to be a barrier to progress in molecular breeding research; however, as the cost of NGS continues to decrease, this appears to be no longer the case. The International Peanut Genome Initiative (IPGI) established in 2004 and currently renamed as ’Advances in Arachis through Genomics and Biotechnology’ (AAGB) is aimed to facilitate the rapid discovery of progress in the development of genomic resources across the international peanut community. It is expected that a high-quality reference genome for the cultivated peanut will be available by end of 2015. Several research institutions have been able to transform peanut with exogenous DNA and generate fertile plants from transformed tissues. This technology has opened up enormous possibilities for expanding the genetic diversity of peanut. Recent applications of this technology include genetic transformation for disease resistance to PStV and TSWV.


• • • • • • •

What makes peanut unique compared to other grain legumes? What are the major peanut-producing countries in the world? What is the major food safety issue with peanut? What parts of peanut produce aflatoxin? What factors contribute to aflatoxin production in peanut? How can aflatoxin contamination be minimized? What are allergens? What implications do they have for human health?


• • •

Peanut allergens are becoming a major issue in developing countries only. What could be the possible reasons? Allergens are some specific proteins in peanut kernel. How many proteins are associated with allergens in peanut? What makes molecular breeding of peanut complicated?

See also: Food Grains and the Consumer: Grains and Health; Food Grains: Intolerance, Allergy and Diseases: Cereal Allergens; The Basics: The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Legumes and Pseudocereals: Amaranth: Overview; Beans: Overview; Chickpea: Overview; Grain Legumes and Their Dietary Impact: Overview; Pea: Overview; The Oilseeds: Oilseeds: Overview; Soybean: Overview; Sunflower: Overview.

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Further Reading Ashley JM (1984) Groundnut. In: Goldsworthy PR and Fisher NM (eds.) The Physiology of Tropical Field Crops, pp. 453–494. New York: Wiley. Bell MJ, Bagnall DJ, and Harch G (1991) Effects of photoperiod on reproductive development of peanut (Arachis hypogaea L.) in a cool subtropical environment. II. Temperature interactions. Australian Journal of Agricultural Research 42: 1151–1161. Boote KJ and Ketring DL (1990) Peanut. In: Stewart BA and Nielsen OR (eds.) Irrigation of Agricultural Crops’. Agronomy Monograph 30, pp. 625–717. Madison, WI: American Society of Agronomy. Chu Y, Holbrook CC, Timper P, and Ozias-Akins P (2007) Development of a PCR-based molecular marker to select for nematode resistance in peanut. Crop Science 47: 841–847. Chu Y, Wu CL, Holbrook CC, Tillman BL, Person G, and Ozias-Akins P (2011) Markerassisted selection to pyramid nematode resistance and the high oleic trait in peanut. Plant Genome 4: 110–117. http://dx.doi.org/10.3835/plantgenome 2011.01.0001. IPGI (2013) The Peanut Genome Project. In: Wilson RF (ed.) International Peanut Genome Initiative. http://www.peanutbioscience.com/homepage.html. Isleib TG, Wynne JC, and Nigam SN (1994) Groundnut breeding. In: Smartt JT (ed.) The Groundnut Crop, pp. 552–623. London: Chapman Hall Chapter 14. Nageswara Rao RC, Sheshshayee MS, Nataraja Karaba N, Rohini S, Rama N, Kumaraswamy S, Prasad TG, and Udaykumar M (2012) Genetic approaches to enhance adaptation of groundnut (Arachis hypogaea L.) to abiotic stresses. In: Tetuja N, et al. (ed.) Improving Crop Resistance to Abiotic Stress, pp. 304–360. Germany: Wiley-Blackwell, Wiley-VCH Verlag GmbH & Co Chapter 14. Nigam SN (1992) Groundnut – A global perspective. In: Proceedings of an International Workshop, 25–29 November, 1991, 548 pp. Patancheru, India: ICRISAT Centre. Pattee HE and Young CT (1982) Peanut Science and Technology. Yoakum, TX: American Peanut Research and Education Association.

Reddy PS (1988) Groundnut. New Delhi, India: Publications and Information Division, Indian Council of Agricultural Research. Revoredo CL and Fletcher SM (2002) World Peanut Market: An overview of the past 30 years. Research Bulletin No. 437. The Georgia Agricultural Experiment Stations College of Agricultural and Environmental Sciences, University of Georgia, Athens, GA, May 2002. (www.ces.uga.edu/ES-pubs/RB437.htm). Wright GC and Nageswara Rao RC (1994) Groundnut water relations. In: Smartt JT (ed.) The Groundnut Crop, pp. 281–335. London: Chapman Hall, Chapter 9. Wright GC, Hubick KT, Farquhar GD, and Rao RCN (1993) Genetic and environmental variation in transpiration efficiency and its correlation with carbon isotope discrimination and specific leaf area in peanut. In: Ehleringer JR, Farquhar GD, and Hall AE (eds.) Stable Isotopes and Plant Carbon-Water Relations, pp. 247–268. San Diego, CA: Academic Press.

Relevant Websites http://agnews.tamu.edu/stories/PATH/aflares.htm – Texas A. & M. University, USA. http://www.ars.usda.gov/is/AR/archive/jan02/peanut0102.htm – Aflatoxin Biocontrol. http://www.ars.usda.gov/is/pr/1999/990712.htm – Agricultural Research Service, USDA. http://www.clw.csiro.au/publications/general2002/grain_legumes_brochure.pdf – Cadmium in Grain Legumes. http://cropgenebank.sgrp.cgiar.org/index.php/management-mainmenu-433/stogsmainmenu-238/groundnut/guidelines/viruses – Peanut Viruses. http://www.dpi.qld.gov.au/fieldcrops/3027.html – Managing Aflatoxin. http://www.foodallergy.org – Anaphylaxis in Peanuts. http://www.peanut-institute.org/ – The Peanut Institute. http://www.peanutsusa.com – The American Peanut Council. http://sacs.cpes.peachnet.edu/nprl/oldver/atoxin.htm – National Peanut Research Lab, USA.

Quinoa: Overview SA Valencia-Chamorro, Escuela Politećnica Nacional, Quito, Ecuador ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

Quinoa is an ancient crop from the Andean region. This grain exhibits great adaptability to extreme climate, from sea level to 4000 m, and is able to grow in poor and marginal soils with low annual rainfall. It presents a wide genetic variability with differences in form, in grain color and size, in grain yield and also in terms of its by-products. Quinoa, a very nutritious grain crop, is a unique grain, which contains the correct balance of essential elements and vitamins, and it is gluten-free. The main producers of quinoa are Bolivia, Peru, and Ecuador. However, production is expanding to other continents such as Africa, Asia, Australia, and Europe. Quinoa production is around 80 000 t (8 107 kg) annually. Processed foods from quinoa include a wide range of bread types, pasta, noodles, breakfast cereals, beer, porridge, etc. NASA has designated quinoa as a potential crop for its Controlled Ecological Life Support System (CELSS). Quinoa presents high potential to contribute to food security and nutrition for humankind in several regions worldwide.

Classification

Learning Objectives

• •

To achieve understanding of the adaptability, variability, nutritional quality, and uses of quinoa grain, the ancient crop from the Andean region. To be able to assess the future prospects for quinoa as a major grain crop.

Introduction Quinoa (Chenopodium quinoa, Willd) is an indigenous crop of the Andean region of South America. It is one of the oldest crops of the American continent. Archaeological findings in northern Chile showed that quinoa was used prior to 3000 BCE. In Ayacucho, Peru, evidence has been found that quinoa was cultivated before 5000 BCE. The quinoa plant was widely cultivated in the entire Andean region, in Colombia, Ecuador, Peru, Bolivia, and Chile, before the Spanish conquest. However, habits and traditional foods of the native people were replaced by foreign crops such as wheat and barley. Therefore, quinoa was cultivated either in small plots in rural areas for domestic consumption or as borders for other crops such as potatoes or maize. For that reason, it was classified as food for poor people. Quinoa is grown in the highlands from 5 N in southern Colombia to 30 S in northeastern Argentina. At sea level, it is cultivated between 36 S and 40 S, in central Chile. Thus, Encyclopedia of Food Grains, Second Edition

quinoa is cultivated from sea level in Chile to 4000 m in the Altiplano of Peru and Bolivia. In the late 1970s, the main production areas of quinoa were located in the Andean region. In Peru and Bolivia, this crop was of great importance. It was cultivated not only for domestic consumption but also for export. The cultivation of quinoa then spread from the Andean region to several countries in the world. In the 1980s, quinoa was grown in Canada, Denmark, the United States, and the United Kingdom. In the late 1990s, an American and European project on quinoa to promote the regional interchange of excellent genetic material among research institutes and universities from both continents was undertaken. Today, after more than 20 years of work, quinoa has worldwide distribution. Quinoa is being cultivated in several countries of the Andean region (Colombia, Bolivia, Ecuador, Chile, and Peru), in Africa (Kenya), Asia (China, Japan, the plains of Northern India, and the Himalayas), Australia, Europe (England, Denmark, France, Germany, Italy, the Netherlands, Portugal, Spain, and Sweden), and North America (United States and Canada). Quinoa production is in a process of expansion into different geographic areas of the planet due to its ability to adapt to a wide range of agroecological zones with extreme ecological conditions.

Quinoa belongs to the Chenopodiaceae family, genus Chenopodium. Its botanical name is C. quinoa, Willd. Common names used in the Andean region are ‘quinua,’ ‘kiuna, or’ ‘parca’ in Ecuador, Peru, and Bolivia; ‘supha,’ ‘jopa,’ ‘jupha,’ ‘jiura,’ ‘aara,’ ‘ccallapi,’ or ‘vocali’ in Bolivia; ‘quinhua’ in Chile; and ‘suba’ or ‘pasca’ in Colombia. The classification of quinoa was first made based on the color of the plant and fruits. Subsequently, it was based on the morphological types of the plant. Despite the wide variation observed, quinoa is considered to be one single species. For practical reasons, quinoa, like maize, was classified in terms of races. The most extensive collection of different quinoa races belongs to Peru and Bolivia; each has over 2000 ecotype samples. However, other collections exist in Argentina, Colombia, Chile, Ecuador, England, the United States, and the former Soviet Union. Quinoa collected in Ecuador, Peru, and Bolivia has been classified into 17 races; however, more races may exist. Two types of inflorescence are described: 1. Glomerulates are small groups of flowers (glomeruli) originating from tertiary axes. 2. Amaranthiformes have glomeruli originating mainly from secondary axes. According to this, the races of quinoa are classified as follows: first, glomerulate inflorescence (Cajamarca, Copacabana,

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Cuzco, Challapata, Cochabamba, Sicuani, Junıń, Ancash, Glorieta, and Dulce) and, second, amaranthiforme inflorescence (Achacachi, Puno, Real, Potosi, Puca, Sucre, and Pichincha). Quinoa grows from sea level to the Andean highlands. Thus, one of the most useful classifications is that describing five ecotypes (Table 1): sea level, valley, subtropical, salar, and altiplanic. Quinoa presents a great genetic diversity, with differences in color, form, and size, as well as in quality and quantity of primary elements and secondary metabolites. Quinoa germplasm banks in the Andean region have been in existence since the 1960s. Germplasm collection has continued in several Andean countries. The main quinoa germplasm collection is preserved in Bolivia, which conserves more than 5000 quinoa accessions. Peru, Ecuador, and Chile hold more than 536, 642, and 25 quinoa accessions, respectively.

clustered in different forms – either amaranthiforme or glomerulate. The flowers are incomplete; they do not have petals. Quinoa has both hermaphrodite flowers, located at the distal end of a group, and female flowers located at the proximal end. The fruit of quinoa is an achene. It is covered by perigonium, which is the same color as the plant: white, yellow, gray, light brown, pink, black, or red (Figure 2). It is easily removed when it is dried. It produces small, circular-shaped seeds, range 1.5–4 mm (1.5 10 3–4.0 10 3 m) diameter (250–500 seeds per gram).

Taxonomic and Botanical Description Quinoa is a plant of the Chenopodiaceae family, genus Chenopodium, section Chenopodia, and subsection Cellulata. The genus Chenopodium is the largest in the family Chenopodiaceae and has worldwide distribution, with about 250 species. With regard to botanical description, quinoa is an annual gynomonoecious plant; it can grow up to 3 m high, depending on the variety and the environment (Figure 1). The seeds can germinate very rapidly, in a few hours after being exposed to moisture. Roots can reach depths of up to 0.30 m. The stem is cylindrical (0.03–0.05 m diameter); it can be either straight or with branches, and its color is variable. Depending on the variety, it changes from white, yellow, or light brown to red. The leaves are shaped like a goose’s foot. They are formed by petioles and lamina; petioles are longchanneled on their upper side. The lamina is polymorphous in the same plant: rhomboidal or triangular in the lower lamina of leaves and triangular or lanceolate in upper leaves. Quinoa inflorescence is a panicle, full of bunches (racemose), which emerge on the upper part and do not have branches. The length of the panicle varies from 0.15 to 0.70 m. Flowers can be Table 1

Figure 1 Quinoa plant. Courtesy of Ing. Angel Murillo, INIAP Ecuador.

General ecotypes of quinoa

Ecotypes

Location

Growth altitude (m)

Varieties

Characteristics

Sea level

South of Chile

<500

Chilean varieties

Valley

Andean valley

2000–4000

Blanca de Junıń, Rosada de Junı´, Amarilla de Matangani, Dulce de Quitopamba, Dulce de Lazo

Unbranched, long day plants (<2 m tall), yellow, bitter seeds Big plants (2–3 m tall), branched, short growth period

Subtropical

Subtropical area of Bolivia (Yungas) Bolivian Salares

2500–3000

Salar Altiplanic

Area around Lake Titicaca

3700–3800

Real

3500–4000

Cheweca, Kancolla, Blanca de Julı´

Plants with intense green color that turn orange as they mature; small seeds, white or orange Plants adapted to salty and alkalinic soils; bitter seeds; high saponin content Short plants with straight stems (1–1.8 m tall); short growth period; resistant to frost

Source: Risi J and Galwey NW (1984) The Chenopodium grains of the Andes: Inca crops for modern agriculture. Advances in Applied Biology 10: 145–216. Reproduced from Encyclopedia of Food Sciences and Nutrition, second ed. (2003), p. 4896. Elsevier Ltd.


Figure 2 Quinoa seeds. Courtesy of Silvia Valencia Chamorro.

Two layers enclose the seed. The pericarp adheres to the seed. It contains saponins, which confer the bitter taste characteristic of quinoa. The episperm encloses the seed as a thin layer. The embryo is formed by two cotyledons and a radicle; it comprise about 60% of the volume within the episperm and forms a ring around the perisperm. The high protein content of quinoa, unlike cereals, is explained by the high proportion of embryo.

Cultivation Practices and Production The cultivation of quinoa is related to the crop rotation. In the Andean region, traditional rotation includes maize, faba beans, potatoes, lupin, wheat, and barley. This practice improves quinoa yield and preserves soil fertility. Cultivation of the quinoa plant requires loose soil that can retain an adequate amount of moisture. However, it can be cultivated in different areas in South America with a wide range of rainfall (0.05–2.00 m). Quinoa tolerates a wide range of pH conditions of the soil (from pH 4.8 to 8.5), relative humidity (from 40% to 80%), and temperatures (from 4 to 38 C). Quinoa is frost-resistant. Therefore, quinoa presents great adaptability to extreme climatic and soil conditions. For this reason, quinoa has been ranked among 21 grain species most resistant to climate change along with beans, maize, amaranth, onions, and others. Sowing density may vary according to region. It has been reported from 0.4 to 0.6 g m 2 (4.0 10 4 to 6.0 10 4 kg m 2) in the Bolivian Altiplano, from 0.5 to 2.3 g m 2 (5.0 10 4 to 2.3 10 3 kg m 2) in Puno, and from 1.2 to 1.6 g m 2 (1.2 10 3 to 1.6 10 3 kg m 2), for varieties such as INIAP-Tunkahuan and INIAP-Pata de Venado, in Ecuador. However, sowing density can depend on varieties and climatic conditions of the region where it is cultivated. Quinoa is harvested at physiological maturity. Physiological maturity may be reached within 70–90 days after flowering. Depending on the variety, it takes between 5 and 8 months for a plant to mature. Traditionally, harvesting is done manually. The plants are cut with a sickle and then placed in windows to dry completely. The yield of quinoa can be in the range of 45–500 g m 2

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(4.5 10 2–5.0 10 1 kg m 2) depending on the variety and growing conditions. Quinoa has a seed coat containing saponins, which confer a bitter taste. The saponins must be removed before consumption. External layers are removed using either a wet or a dry process. The traditional wet process used in rural areas is hand scrubbing in alkaline water. This process is used on a commercial scale; it involves abrasive dehulling to remove the external coverings, followed by a thorough washing. However, this method has economic and ecological restrictions: The water demand is high and wastewater is contaminated with saponins, which are toxic to cold-blooded animals. Moreover, wet grains must be dried immediately, or they may germinate after a few hours in wet conditions. In the dry method, grains are scrubbed and polished to remove, as fine powder, their external layers. This method presents several advantages; no water is needed, no heat treatment to dry the seeds is required, and no environmental contamination is produced. This method is best suited to sweet varieties (low saponin content) of quinoa. A combination of dry and wet processes is applied to bitter varieties (with high saponin content) of quinoa. Saponin is first removed by polishing, when most of the saponin is removed. Then, the saponins that remain in the seeds are washed with water, followed by a dry process. Any of the processes described earlier makes the quinoa ready for use by the consumer or for further processing. In the future, a novel enzymatic method for removing saponins utilizing enzymes of Eurysacca quinoae Povolny may be used. However, this method has not yet been commercialized. The most important fungal disease is downy mildew (Peronospora farinosa), which requires high humidity and temperature. The main symptom is chlorotic lesions on the upper surfaces of the leaves, with a white or purple mycelium on the lower surfaces. Another disease is brown stalk rot, which is caused by Phoma exigua var. foveata. The stem often becomes shrunken and the plant may become chlorotic with progressive defoliation toward the apex may occur. Kcona kcona (Scrobipalpula sp.) is probably the most serious pest of quinoa. Larvae first destroy leaves and inflorescences. Later, when the plant is mature, larvae destroy the panicle and grains. Today, where quinoa is cultivated in new agroecological regions, it is probable that it will provide a new host for the local pests and fungi. The production of quinoa is consistently increasing worldwide. The main producers are Bolivia, Peru, the United States, Ecuador, and Canada. In the 6 years, from 2005 to 2011, the cultivated area of quinoa increased by around 47%, from 68 863 to 101 527 ha (6.9 108–1.0 109 m2), and the production increased about 37%, 58 443 to 80 241 t (5.8 107– 8.0 107 kg). However, quinoa is still mainly cultivated in the Andean region: Bolivia, Peru, and Ecuador. Bolivia is the main producer country, with 54% of cultivated area and 51% total production. Bolivia is also the main exporter of the grain, followed by Peru and Ecuador. Several efforts have been made to increase the production of quinoa in the Andean region, for example, in Ecuador, where the potential cultivated area for quinoa production in 2012 was 86 856 ha (8.7 108 m2). Traditional production of quinoa was based on crop rotation. However, in some Andean areas, quinoa is grown as an

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intensive monoculture using mechanization. Thus, some concerns with regard to environmental sustainability have arisen.

Chemical Composition and Nutritional Value The diet of ancient inhabitants of the Inca Empire has generated interest due to its being extremely nutritious. Like cereals, quinoa grains contain carbohydrates, protein, fat, minerals, fiber, and vitamins (Table 2). The chemical composition of quinoa depends on the variety, soil, cultural practices, and environment of its cultivation. Values for the nutritional characteristics of 555 quinoa accessions have been reported: protein (10.21–18.39%), fat (2.05–10.88%), dietary fiber (3.46–9.68%), ash (2.12–5.12%), carbohydrates (52.31–72.98%), and energy (1.31 104–1.68 104 kJ kg 1). Quinoa accessions show wide variability for most of the studied parameters, which is indicative of their genetic potential.

Quinoa Grains Protein The protein content of quinoa grains can vary from 8% to 22%, which on an average is higher than that of common cereals Table 2

grains such as rice, maize, and barley. However, it represents less than half of the quantity of protein in most legumes. In quinoa, most of the protein is located in the embryo. The nutritional value of quinoa varies considerably among varieties, which may depend on soil and fertilization regime. Several studies on the chemical composition of quinoa have been made in the past decades. For instance, in Bolivia, variation in nutritional values of 20 different quinoa accessions from the Banco Nacional de Germoplasma de Granos Altoandinos (BNGA) was reported. The protein content was in the range 12.47–15.48%, which is low. Albumins and globulins are the major protein fraction (44–77% of total protein) in quinoa, which is greater than the prolamins (0.5–7.0%). Thus, quinoa is considered to be a gluten-free grain because it contains very little or no prolamin. Therefore, quinoa provides a nutritional food source, which is of particular relevance to gluten-intolerant people. The good nutritional quality of quinoa is primarily due to its high protein content and quality. Quinoa protein has a good balance of essential amino acids (Table 3). It is exceptionally high in lysine, an amino acid, which is generally not overly abundant in plant foods. It is also a good complement for legumes, which are often low in methionine and cystine.

Chemical composition of quinoa and some cereals and legumesa (10

Protein Fat Ash Carbohydrateb Fiber, total dietary kJ kg−1(104)c

2

kg per kg dry wt)

Quinoa

Barley

Corn

Rice

Wheat

Oat

Rye

Bean

Lupin

Soybean

16.28 7.00 2.74 73.99 8.07 1.54

11.02 1.29 1.23 86.44 17.35 1.47

10.51 5.29 1.34 82.85 8.14 1.53

7.94 2.92 1.53 77.24 3.50 1.55

17.65 2.20 2.17 77.98 13.98 1.34

18.40 7.52 1.87 72.21 11.55 1.63

11.57 1.82 1.76 84.85 16.89 1.41

26.72 0.94 4.34 68.00 28.22 1.39

40.39 10.88 3.66 45.08 21.10 1.55

39.90 21.80 5.32 32.98 10.28 1.87

a

Quinoa, uncooked; Barley, pearl, raw; Corn, yellow; Rice, brown, long-grain, raw; wheat, hard red spring; Beans, kidney, all types, mature seeds, raw; Lupins, mature seeds, raw; Soybeans, mature seeds, raw. b Carbohydrate includes fiber. c kJ kg−1: 4 (%protein + carbohydrates) + 9 (%fat). Source: Adapted from US Department of Agriculture, Agricultural Research Service. 2013. USDA National Nutrient Database for Standard Reference, Release 26. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/nutrientdata (accessed 21-02-2014).

Table 3

Essential amino acids in quinoa and other foodsa (10−3 kg per kg protein)

Histidine Isoleucine Leucine Lysine Methionineb Phenylalaninec Threonine Tryptophan Valine a

Quinoa

Corn

Rice

Wheat

Bean

Milk

FAO/WHO/UNU

29 36 60 54 36 61 30 12 42

11 36 70 32 29 75 31 11 49

25 42 83 38 35 89 37 13 57

21 35 67 26 41 77 28 13 44

51 44 80 69 26 15 42 12 96

30 52 95 84 32 10 43 13 63

15 30 59 45 22 38 23 6 39

Quinoa, uncooked; Corn, yellow; Rice, brown, long-grain, raw; Wheat, hard red spring; Beans, kidney, all types, mature seeds, raw; Milk, whole, 3.25% milk fat, with added vitamin D. Methionine + cystine. c Phenylalanine + tyrosine. Source: Adapted from US Department of Agriculture, Agricultural Research Service (2013). USDA National Nutrient Database for Standard Reference, Release 26. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/nutrientdata (accessed 21-02-2014); World Health Organization (2002). Joint FAO/WHO/UNU Expert Consultation on Protein and Amino Acid Requirements in Human Nutrition. WHO technical report series; no. 935. Geneva: WHO. b

THE LEGUMES AND PSEUDOCEREALS | Quinoa: Overview The nutritional evaluation of quinoa protein has been reported in several studies. The protein efficiency ratio of raw debittered quinoa was 78–93% of that of casein. These figures increased when quinoa was cooked and became 102–105% of that of casein. Thus, the protein quality of quinoa matches that of the milk protein casein.

Carbohydrates and fiber The major component in quinoa is carbohydrates, which varies from 67% to 74% of the dry matter. Starch is about 52–60%. The starch is located in the perisperm of the seed; starch may be as simple units or as spherical granules. The diameter of quinoa starch granules is in the range of 0.4–2.0 mm (4 10 7– 2 10 6 m). Starch granules in quinoa are smaller than those reported for maize (range 1–23 mm (1.0 10 6– 2.3 10 5 m)) and for wheat (2–40 mm (2 10 6– 4 10 5 m)). The gelatinization temperature for different quinoa cultivars was found to be in the range of 55.5–72.0 C. The starch amylose content is about 11%, which is lower than in cereals, for example, rice (17%), wheat (22%), and barley (26%). The total dietary fiber ranges from 11.0 to 13.3% in raw and heat-treated quinoa. The crude fiber content is in the range 2.5–3.9%, and pentosans 2.9–3.6%. “The high content of dietary fiber has many positive health effects, for example, it can reduce the level of cholesterol in the blood and improve digestion. For this reason, consumers in developed countries may also have an interest in including quinoa in their diets.” Other carbohydrates are found in small amounts, such as monosaccharides (2%) and disaccharides (2.3%).

Fat, vitamins, and minerals Quinoa contains from 2% to 10% fat. Quinoa and soy oils exhibit similar fatty acid composition. Thus, quinoa is a rich source of essential fatty acids such as linoleic (18:2n 6: 52%) and linolenic (18:3n 6: 4%). The fatty acid composition is similar to maize germ oil. Quinoa is also a good source of minerals (Table 4). It contains more calcium, magnesium, iron, and zinc than common cereals, and the iron content is particularly high. Polishing and washing quinoa grain reduce the mineral content to some extent, by 12–15% for iron, zinc, and potassium, 27% for copper, and 3% for magnesium. Quinoa contains more riboflavin (B2) and a-tocopherol than rice, barley, or wheat. The concentrations of the natural antioxidants g- and a-tocopherol in quinoa were found to be 797.2 and 788.4 ppm (7.97 10 4–7.88 10 4 kg kg 1), respectively. Thus, quinoa can be a source of vitamin E.

Other components Saponins (after removal), phytic acid, trypsin inhibitors, and tannins are present in quinoa in low levels. As stated, saponin, a bitter-tasting compound, is located in the outer layers of quinoa seeds (at levels of 0.1–5%). It protects the seeds from birds and insects. The amount of saponins present depends on the variety. Bitter-flavor varieties contain more saponin than sweet varieties. Saponins are glycosidic compounds, which occur in two groups. According to the nature of the sapogenin moiety, they are conjugated with hexoses, pentoses, or uronic acids. The sapogenins are steroids (C27) or triterpenoids (C30). Using gas chromatography, the sapogenins oleanolic

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Table 4 Mineral composition (10−5 kg per kg dry wt) and vitamin concentration (10−5 kg per kg dry wt) of quinoa and some cerealsa Quinoa Minerals (10−5 kg per kg) Ca 54.2 Mg 227.2 K 649.2 P 526.9 Fe 5.3 Cu 0.7 Zn 3.6 Vitamins (10−5 kg per kg) 0.42 Thiamin (B1) 0.37 Riboflavin (B2) 1.75 Niacin (B3) Ascorbic acid NR α-Tocopherol 2.81 β-Carotene 0.01

Wheat

Rice

Barley

28.7 142.1 389.7 380.6 4.1 0.5 3.2

25.7 159.5 248.8 371.5 1.6 0.3 2.3

32.3 87.9 311.4 245.8 2.8 0.5 2.4

0.58 0.13 6.55 0.00 1.16 0.01

0.45 0.10 5.68 0.00 1.34 0.00

0.21 0.13 5.12 0.00 0.02 0.01

NR, not reported. a Quinoa, uncooked; wheat, hard red spring; rice, brown, long-grain, raw; barley, pearl, raw. Source: Adapted from US Department of Agriculture, Agricultural Research Service (2013). USDA National Nutrient Database for Standard Reference, Release 26. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/nutrientdata (accessed 21-022014).

acid, hederagenin, 30-o-methylspergulagenate, and phytolaccagenic acid are identified in sweet and bitter genotypes of quinoa. Saponins show hemolytic activity and are in general toxic to cold-blooded animals, which obtain oxygen directly from water. Reduction of plasma cholesterol has been attributed to the presence of certain saponins in the diet. However, some saponins can form insoluble complexes with minerals, such as zinc and iron, which make the minerals unavailable for absorption in the gut. Phytic acid (myoinositol 1,2,3,4,5,6-hexakis dihydrogen phosphate) is found in most cereals and legumes, fruits, and vegetables. In quinoa seeds, phytic acid is located in the external layers as well as in the endosperm. Even small amounts (0.5 mmol g 1 (5.0 10 4 mmol kg 1)) of inositol hexaphosphate (IP6) or pentaphosphate may reduce the solubility of iron. IP6 was mainly found in varieties from Ecuador: sweet INIAP-Tunkahuan (11.3 mmol g 1 (1.1 10 3 mmol kg 1)) and bitter INIAP-Ingapirca (8.6 mmol g 1 (8.6 10 3 mmol kg 1)). These levels were reduced to just 0.3 mmol g 1 (3.0 10 4 mmol kg 1) by fermentation of germinated quinoa flour. At the same time, a five- to eightfold increase in the amount of soluble iron was found. The trypsin inhibitor activity in eight varieties of quinoa (range 1.36–5.04 TIU mg 1 (1.36 10 6–5.04 10 6 TIU kg 1)) was found to be much lower than in soybean (24.5 TIU mg 1 (2.5 10 5 TIU kg 1)). Trypsin inhibitor is a thermolabile protein, which is inactivated by heat treatments. The total phenolic content (using the Folin–Ciocalteu method) of precooked quinoa seeds indicated that bitter seeds contained higher amount of phenolics (range 7.23–10.05 mg gallic acid equivalent per 100 g (7.2 10 5–1.0 10 4 kg gallic acid equivalent per kilogram)) than sweet ones (range

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6.05–9.39 mg/100 g (6.1 10 5–9.4 10 5 kg gallic acid equivalent per kilogram)). Moreover, bitter quinoa precooked seeds exhibited a higher flavonoid content (1.04–1.74 mg catechin equivalent per 100 g (1.0 10 5–1.7 10 5 kg catechin equivalent per kilogram)) than sweet seeds (0.71–0.91 mg/100 g (7.1 10 6–9.1 10 6 kg/kg 1)). Thus, bitter and sweet quinoa seeds varieties are a rich source of antioxidant compounds, the former being higher in antioxidants.

Quinoa Leaves The leaves of quinoa are comparable to spinach as regards flavor. They contain (on a wet basis) carbohydrate 4.8%, protein 3.3%, fat 1.8%, ash 3.3%, and fiber 1.9%. The protein content of quinoa leaves is also similar to spinach. However, its protein contains slightly more isoleucine (5.8% per 100 g protein) and valine (7.5% per 100 g protein). The amount of saturated fatty acids such as palmitic (16:0; 16.7%) and stearic (18:0; 1.3%) is higher than in the grains. Quinoa leaves are a rich source of vitamin A containing 2085 mg RE (retinol equivalents) per 100 g (fresh wt.) (2.9 10 5 kg RE per kilogram (fresh wt.)) and vitamin E 2.9 mg a-TE (alpha-tocopherol) per 100 g (2.9 10 8 kg a-TE (alpha-tocopherol) per kilogram). Fresh quinoa leaves contain more magnesium (83 mg per 100 g fresh wt. (8.3 10 4 kg per kilogram fresh wt.)) and sodium (289 mg per 100 g fresh wt. (2.9 10 3 kg per kilogram fresh wt.)) than spinach leaves. Also, quinoa leaves have low levels of the antinutrients nitrate and oxalate. Sapogenins in the leaves increased as the plant matures. After 120 days of from sowing, the sapogenin content in leaves of sweet genotypes varied between 0.013% and 0.017% (dry matter) and in bitter varieties varied between 0.02% and 0.16% (dry matter). Hederagenin was the major sapogenin present in the leaves.

Uses In Chile, Ecuador, Peru, and Bolivia, the main uses of whole quinoa seeds are in soups, salads, casseroles, and stew. Cooked grains swell to about two or three times their original size.

Quinoa can be eaten as a rice replacement, as a hot breakfast cereal, or boiled in water to make an infant cereal (Figure 3). The grains can even be popped like popcorn. The seeds can be also sprouted. The sprouts need to turn green before they can be added to salads. Quinoa flour can be mixed with maize or wheat flour for making bread and pasta, and it is used for making biscuits, cakes, and pastries in general. Several levels of substitution of quinoa flour have been reported, for instance, in bread (10–13% quinoa flour), noodles and pasta (30–40% quinoa flour), and sweet biscuits (60% quinoa flour). All levels produce quinoa products of excellent quality. Quinoa flour can also be drum-dried and extruded, producing products with good physical, sensorial, and nutritional qualities. Solid-state fermentation of quinoa with Rhizopus oligosporus Saito has been performed, to produce tempeh of good quality. In Bolivia, in 1975, the government adopted a resolution mandating that 5% of quinoa flour must be added to all pastas, crackers, and breads. Quinoa leaves, like grains, can also be cooked, made into a spinach-like dish, or may be served raw in a salad. During four years, from 2002 to 2006, an Andean Quinoa Project was undertaken in three countries, Bolivia, Peru, and Colombia. Research goals included agriculture and agroindustrial activities. Several quinoa enriched quinoa products were developed. Additionally, more than 30 different processed products from quinoa grains and plants have been reported. Quinoa has jumped from a staple food to gourmet kitchen food. Saponins from quinoa, due to their chemical qualities, have multiple purposes. They are used in the manufacture of soap, liquid detergents, shampoos, toothpaste, stain removers, and foam stabilizer; in beverages, especially beer; as an insecticide; in a compound for fire extinguisher; and in photo processing. The grains, the stems, and the leaves have been used for their medicinal properties, for cicatrizing, as an anti-inflammatory, an analgesic, and a disinfectant. The plant-dried stalks are used as fuel or may be used in preparing bleach or dyes or for cardboard and paper. The natural colorant from quinoa (betalains) was traditionally used for cloth dyeing and food preparation.

Figure 3 Quinoa products. Courtesy of Lcdo. Guillermo Tapia, Cereales Andinos Ecuador.

THE LEGUMES AND PSEUDOCEREALS | Quinoa: Overview Because of its excellent nutritional characteristics, NASA has included quinoa as a potential crop for its CELSS project. The CELSS concept utilizes plants to remove carbon dioxide from the atmosphere and generate food, oxygen, and water for the crews of long-term human space missions.

• • •

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What important nutritional characteristics does quinoa have? How can these be exploited in development of new food products? Which environmental concern is related to increased production in the Bolivian highlands? How is quinoa being promoted all over the world? Do you think it has potential to be major grain worldwide?

Future Perspectives Quinoa has long been recognized as nutritious food. The importance that quinoa could play in nutritional behavior is now being emphasized, not only in developing countries but also in the developed world. Quinoa could be a strategic crop used to complement the diet in rural/marginal regions where protein-energy malnutrition affects most of the population. On the other hand, quinoa represents an exotic and healthy rediscovery in the developed world. Germplasm collection should continue in countries of the Andean region. The production of the grain has notably increased in the Andean region. It is also in a process of expansion in other parts of the world. The potential for improving quinoa production seems promising. Therefore, new varieties (precocity, grain size and color, resistance to biotic and abiotic factors, and grain yield) and by-products should be obtained through genetic improvement. Participatory plant breeding for quinoa (including plant breeders, agronomists, communities, farmers, and others) is desirable. Improvement of quinoa yields by improving cultivation practices should be performed. There is need for intensive cultivation of quinoa. This could meet the quantity and quality needs of the food industry. Traditional production of quinoa includes crop rotation. In the Bolivian Southern Altiplano, production is often made without crop rotation. This could lead to very unsustainable production systems. Further research is needed in order to identify the agroecological and social basis of quinoa sustainability in traditional and new cultivation regions. Improving methods for removing saponins without significant modification of nutritive value is encouraged. The selection of sweet genotypes with low saponin content in the seeds is the main breeding goal. Further research is needed to find markers for indirect selection of sweet genotypes. Aggressive promotion campaigns should be carried out to encourage greater consumption of quinoa, as it is a very healthy and gluten-free grain. Quinoa has been spread outside of the Andean region, owing to its great adaptability to different agroecological systems. The year 2013 was declared the ‘International Year of the Quinoa.’ Several international events were carried out all over the world. Quinoa should be promoted as a food of the twenty-first century, as it has a high potential to contribute to food security in several regions worldwide.


• •

What region is the origin of quinoa? Where is most genetic variation to be found? What is the adaptability of this crop to soil and climate conditions? Could quinoa be produced near where live?


• •

Quinoa is a unique food crop, which contains all the essential amino acids in the correct balance. Taking this into account, what are the agro-industrial prospects for this grain? Production of quinoa was originally in Andean countries; now, quinoa is cultivated in other countries. What are the challenges arising from this fact?

See also: Carbohydrates: Carbohydrate Metabolism; Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Glycemic Index, Glycemic Load, and Their Health Benefits; Grains other than Cereals: Non-starch Polysaccharides; Health Effects of b-Glucans Found in Cereals; Resistant Starch and Health; Starch: Analysis of Quality; Starch: Chemistry; Starch: Starch Architecture and Structure; Starch: Synthesis; Fats: Healthy Fats and Oils; Lipid Chemistry; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Cereal Allergens; The Gluten-Free Diet; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Proteins: Nitrogen in Grain Production Systems; Nitrogen Metabolism; Protein Synthesis and Deposition; Proteomic Analysis Relevant to Cereal Grains; The Enzymes Associated with Food Grains and Their Functions in Processing; The Protein Chemistry of Dicotyledonous Grains; Thiolomics of the Gluten Protein Network of Wheat Dough; The Basics: Taxonomic Classification of Grain Species; The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Grains that Feed the World.

Further Reading Brkic M, Garcıá A, 2013 Un cultivo ancestral para apuntalar el futuro. http://www. alimentosargentinos.gov.ar/contenido/revista/pdfs/57/57_04_QUINOA.pdf (accessed 01.10.13.). FAO 2011 Quinoa: An ancient crop to contribute to world food security. http://www.fao. org/fileadmin/templates/aiq2013/res/en/cultivo_quinua_en.pdf (accessed 01.02.13.). Gandarillas H (1979) Historia y distribucioń geogra´fica. In: Tapia M, Gandarillas H, Alandia S, Cardoso A, Mujica A, Ortiz R, Otazu V, Rea J, Salas B, and Zanabria E (eds.) La Quinua y la Kan˜iwa. Cultivos Andinos, pp. 21–44. Bogota´: Centro Internacional para el Desarrollo. Giusti K (1970) El geńero Chenopodium en la Argentina. I. Nu´mero de Cromosomas. Darwiniana 16: 98–105. International Year of the Quinoa. www.fao.org/quinoa-2013 (accessed 13.08.13.). Jacobsen SE, Mujica A, and Ortiz R (2003) The global potential for quinoa and other Andean crops. Food Rev. Int. 19: 39–148. Masterbroek H, Limburg H, Gilles T, and Marvin H (2000) Occurrence of sapogenins in leaves and seeds of quinoa (Chenopodium quinoa Willd). J. Sci. Food Agr. 80: 152–156. Mujica A, Jacobsen SE, Izquierdo J, 1998 Libro de Campo: Prueba Americana y Europea de Quinua (Chenopodium quinoa Willd). Universidad Nacional del

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Altiplano, Puno, Peru; Red de Cooperacioń Tećnica en Producioń de Cultivos Alimenticios de la Oficina Regional de la FAO para Ame´rica Latina y el Caribe. Mujica A, Ortiz R, Bonifacio A, et al., 2006. Proyecto Quinua: Cultivo Multipropo´sito para los Paı´ses Andinos PNUD- PROY/INT/01/K01- Peru- Bolivia- Colombia. Informe Final. Peralta E, Mazoń N, Murillo A, et al., 2012. Manual Agrıćola de Granos Andinos: Chocho, Quinoa, Amaranto y Ataco. Tercera edicioń. Publicacioń Miscelańea No. 69. Programa Nacional de Leguminosas y Granos Andinos. Estacioń Experimental Santa Catalina, INIAP. Repo-Carrasco R, Espinoza C, and Jacobsen S-E (2003) Nutritional value and use of the Andean crops quinoa (Chenopodium quinoa) and Kan˜iwa (Chenopodium pallidicaule). Food Rev. Int. 19: 179–189. Risi J and Galwey NW (1984) The Chenopodium grains of the Andes: Inca crops for modern agriculture. Adv. Appl. Biol. 10: 145–216. Soto JL and Carrasco E (2012) Market potential of Andean grains. In: Giuliani A, Hintermann F, Rojas W, and Padulosi S (eds.) Biodiversity of Andean Grains:

Balancing Market Potential and Sustainable Livelihoods, pp. 25–74. Rome, Italy: Bioversity International. Tapia M (1979) Historia y distribucioń geogra´fica. In: Tapia M, Gandarillas H, Alandia S, Cardoso A, Mujica A, Ortiz R, Otazu V, Rea J, Salas B, and Zanabria E (eds.) La Quinua y la Kan˜iwa. Cultivos Andinos, pp. 11–19. Bogota´: Centro Internacional para el Desarrollo. U.S. Department of Agriculture, Agricultural Research Service, 2013. USDA National Nutrient Database for Standard Reference, Release 26. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/nutrientdata (accessed 21.02.14.). Valencia S, Svanberg U, Sandberg A-S, and Ruales J (1999) Processing of quinoa (Chenopodium quinoa Willd): Effect on the in vitro iron availability and phytate hydrolysis. Int. J. Food Sci. Nutr. 5: 203–221. World Health Organization, 2002. Joint FAO/WHO/UNU expert consultation on protein and amino acid requirements in human nutrition. WHO Technical Report Series: No. 935. WHO: Geneva.


Contents Grain Production and Consumption: Overview Grain Production and Consumption: Africa Production and Consumption of Grains: India Grain Production and Consumption: China and South-East Asia Grain Production and Consumption: Europe Grain Production and Consumption: Cereal Grains in North America Grain Production and Consumption: Oilseeds in North America Grain Production and Consumption in Oceania: Australia and Pacific Countries Grain Production and Consumption: South America

Grain Production and Consumption: Overview T Beta and C Isaak, University of Manitoba, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Wheat, rice, and maize contribute over 90% of global cereal production. World production of wheat, paddy rice, and maize was 652, 701, and 875 million tonnes (Mt) in 2012. The major wheat-producing regions are the EU, FSU, NC America, South America, Oceania, and Asia. The major rice exporters include India, Thailand, Vietnam, the United States, and Pakistan. Maize is the preferred crop in Africa and South America. World oilseed production was 454 Mt in 2012 with soybean as the predominant grain crop.

Learning Objectives

•

Achieve understanding of the major grains that are produced and consumed worldwide.

Introduction The term grain is used to include cereals (wheat, rice, and the coarse grains such as maize, barley, sorghum, oats, and rye), oilseeds, and pulses. World grain production, particularly in wheat and rice, increased substantially between 1961 and 1980 due to the increase in yields per hectare or the ‘Green Revolution’ (Figure 1). Since then, per capita (per person) grain production has not increased much as most of the easily realizable benefits of plant breeding, fertilizer, machinery, and irrigation have already been achieved. Production of


grain per hectare is close to the maximum obtainable through photosynthesis; hence, world grain production has not matched the increase in world’s population. Low grain prices at planting time, high temperatures, and water shortages are the major factors contributing to reduced grain harvests. The fall in production has triggered an increase in the prices of wheat and maize and a corresponding increase in products (bread, breakfast cereals, pasta, and livestock products, including meat, milk, and eggs) derived from these grains. World production of wheat, rice (paddy), and maize in 2012 was 652, 701, and 875 million tonnes (Mt), respectively (Table 1). Total cereal production is shown in Figure 2 as an average of 10-year periods beginning 1961. There was a 30% increase in cereal production during the period between 1971–80 and 1981–90. The rate of increase in cereal production has been slowing since the days of the Green Revolution in the 1970s. Table 1 shows world production of cereals, wheat, rice, maize, barley, sorghum, millet, and rye for the period 2010–12. Data on yields and area harvested are also listed. The world’s wheat was produced in Asia (47%), Europe (29%), and North and Central (NC) America (13%) in 2012. About 90% of the world’s rice was produced in Asia. Africa and South America contributed 4% and 3% to the world’s rice production, respectively. NC America, Asia, South America, and Europe contributed 36, 33, 13, and 11%, respectively, of the world’s maize production. Wheat, rice, and maize contributed to over 90% of global cereal production. World exports and imports of cereals by region in 2009 and 2010 are given in Figures 3(a) and 4(a), respectively. Pulses (including dry beans, dry peas, chick pea, and pigeon pea) were 3% of the total cereal production. Among oilseeds, soybean was 10% of world cereal production.

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GRAINS AROUND THE WORLD | Grain Production and Consumption: Overview

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2800 2600 2400

Production (mt)

2200 2000 1800 Cereals, total (Mt)

1600 1400

Rice, paddy (Mt)

1200

Wheat (Mt)

1000

Maize (Mt)

800 600 400 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

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Figure 1 World grain production for the period 1961–2012. FAOSTAT Database 2013.

Table 1

World cereal production for the period 2010–12 Area harvested (Mha)

Cereals, total 2010 693 2011 707 2012 703 Wheat 2010 217 2011 221 2012 217 Rice, paddy 2010 162 2011 163 2012 163 Maize 2010 164 2011 172 2012 177 Barley 2010 47 2011 48 2012 49 Sorghum 2010 41 2011 42 2012 38 Millet 2010 36 2011 34 2012 31 Oats 2010 9 2011 10 2012 10 Rye 2010 5 2011 5 2012 6 Source: FAOSTAT Database 2013.

Yield (kg ha 1)

Production (Mt)

3571 3660 3622

2547 2589 2474

3003 3175 3115

675 701 652

4336 4429 4395

718 723 701

5187 5154 4944

850 885 875

2606 2747 2684

124 133 132

1439 1384 1535

59 59 58

905 803 820

32 27 26

2163 2348 2179

20 23 26

2374 2565 2617

12 13 15

Wheat Data on world wheat production, area harvested, and yield for the period 2010–12 are given in Table 1. World wheat production decreased by 49 Mt in 2012 from the previous year (Table 1). The area harvested declined by 4 million hectares (Mha) and yields were 60 kg ha 1 less than in 2011. The average global wheat production increased tremendously during the period 1960–80 largely due to an increase in yield. In developed countries, wheat yields tripled between 1950 and 1996 due to new wheat varieties and improved technologies including methods of sowing, irrigation, fertilizer application, moisture retention, and integrated pest management. Potential yields are still to be realized in African and Asian developing countries due to several constraints including inadequate water, infertile soils, poor weather, and lack of inputs. The major wheat-producing countries during 2012 by regions are EU (France, Germany, and the United Kingdom), FSU (the Russian Federation and Ukraine), NC America (Canada), South America (Argentina), Oceania (Australia), and Asia (China, India, Pakistan, Turkey, Iran, and Kazakhstan). Bread wheat is planted on 93% of world wheat-growing area while durum and soft wheat occupy the remainder. Spring types are sown on two-thirds of the land devoted to wheat in developing countries. The five major wheat exporters are France (EU), the United States and Canada (NC America), the Russian Federation (FSU), and Australia (Oceania) (Figure 3(b)). India and Pakistan produce enough wheat to meet their country needs. Developing countries in Africa, Asia, and South America accounted for at least 50% of world wheat imports in 2009 and 2010 (Figure 4). Figure 5 shows consumption of wheat in the EU, FSU, NC America, South America, NE Asia, FE Asia, and Africa in 2009. Most wheat is used for human consumption with a limited amount going into livestock feed. World wheat production and consumption are projected to increase in 2013 and 2014. Exports to China are expected to increase in 2013 due to a


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Average cereal production (Mt) 700 600 400 300 100 0 1961-70

1971-80

1981-90 1991-2000 2001-10

Average wheat production (Mt) 700 600 500 400 300 200 100 0 1961-70

1971-80

1981-90 1991-2000 2001-10

Average paddy rice production (Mt) 700 600 500 400 300 200 100 0 1961-70

1971-80

1981-90 1991-2000 2001-10

Average maize production (Mt) 800 700 600 500 400 300 200 100 0 1961-70

1971-80

1981-90 1991-2000 2001-10

Figure 2 World cereal production, averages for 10-year periods. FAOSTAT Database 2013.

poor quality domestic crop. Wheat dry milling produces flour, semolina, bran, and germ. The primary products of milling are used largely in baking and extrusion to produce breads and pastas. Wheat germ oil and meal are valuable coproducts. The

bran, a by-product of milling, is used in high-fiber foods and as an animal feed ingredient. Wheat is also used as a valuable feed ingredient for milk and beef livestock as it is more nutritious than maize, sorghum, and barley.

ME Asia 6%

Africa 1%

FE Asia 6%

Other 0%

S America 10%

Africa 1%

Other 1%

ME Asia 7% FE Asia 6%

S America 12% EU 25%

EU 26%

NC America 31%

NC America 33%

FSU 15%

FSU 8% Oceania 6%

(a)

ME Asia 3%

Oceania 6%

S America 5%

Other 1%

Other 1%

ME Asia 5%

S America 5%

Africa 0% FE Asia 0%

Africa 0% FE Asia 0%

EU 32%

EU 35%

NC America 29%

FSU 20%

FSU 11%

Oceania 10%

(b)

Other 0%

NC America 32%

Africa 4%

Oceania 11%

S America 9% NC America 10%

ME Asia 19%

Africa 3%

Other 0%

S America 6%

Oceania 0%

ME Asia 22%

Oceania 0% FSU 0%

NC America 12%

FSU 0% EU 6%

EU 5% FE Asia 53%

FE Asia 51%

(c) ME Asia Other 3% 3% FE Asia 2%

EU 16%

Africa 2%

FE Asia 1% S America 18%

FSU 3%

Other 2%

Africa 2%

EU 15% S America 27%

Oceania 0%

FSU 8% Oceania 0%

ME Asia 2%

NC America 48%

NC America 48%

(d)

Figure 3 (a) World exports of cereals by region for 2009 (330 Mt) and 2010 (334 Mt); regional totals exclude processed secondary products. (b) World exports of wheat by region for 2009 (146 Mt) and 2010 (145 Mt); regional totals exclude processed secondary products. (c) World exports of milled rice by region for 2009 (30 Mt) and 2010 (33 Mt); regional totals exclude processed secondary products. (d) World exports of maize (corn) by region for 2009 (101 Mt) and 2010 (108 Mt); regional totals exclude processed secondary products. FAOSTAT Database 2013.


Other 3%

Other 4% Africa 19%

ME Asia 20%

S America 7% NC America 8% EU 21%


FE Asia 23% EU 20%

Oceanla 0% FSU 0%

(a) Other 3%

Africa 24%

FE Asia 17%

NC America 5% Oceanla 0%

EU 23%

S America 9%

EU 23%

FSU 0%

(b)

FSU 0%

NC America 5%

Oceanla 0%

Other 4%

Other 4%

Africa 31%

ME Asia 23%

Africa 29%

ME Asia 24%

S America 4% EU 10% FSU 1%

(c)

S America 4% NC America 7% Oceanla 2%

Other 2%

FE Asia 33%

Oceanla 0%

Africa 26%

ME Asia 17%

S America 7%

FE Asia 15%

ME Asia 12%

FSU 0%

Other 3%

ME Asia 23%

FE Asia 21%

NC America 6%

EU 9% FSU 1%

Oceanla 2%

Other 3% Africa 14%

S America 9%

NC America 12% EU 18%

(d)

Africa 20%

ME Asia 18%

FE Asia 21%

FE Asia 18%

353

Oceanla 0% FSU 0%

ME Asia 13%

Africa 13%


FE Asia 35%

EU 16%

FSU 0%

Oceanla 0%

Figure 4 (a) World imports of cereals by region for 2009 (328 Mt) and 2010 (335 Mt); regional totals exclude processed secondary products. (b) World imports of wheat by region for 2009 (147 Mt) and 2010 (144 Mt); regional totals exclude processed secondary products. (c) World imports of milled rice by region for 2009 (30 Mt) and 2010 (31 Mt); regional totals exclude processed secondary products. (d) World imports of maize by region for 2009 (100 Mt) and 2010 (107 Mt); regional totals exclude processed secondary products. FAOSTAT Database 2013.

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100% 80% 60% 40% 20%

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ld W or

ca Af ri

As ia FE

As ia E M

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Am er ica NC

FS U

EU

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100% 80% 60% 40% 20%

M

ld W or

a ric

ia

Af

E

FE

As

ia As

ica S

Am

er Am NC

(b)

er

ica

U FS

EU

0%

100% 80% 60% 40% 20%

Food

Feed

W or ld

a Af

ric

ia As FE

ia As M E

er ica S

(c)

Am

ica NC

Am

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FS U

EU

0%

Food Manufacturing

Seed

Other

Figure 5 Wheat, maize, and milled rice consumption by regions for 2009 in tonnes. (a) Total wheat consumption in selected regions were 117 (EU 15), 54 (FSU), 46 (NC America), 24 (South America), 170 (ME Asia), 130 (FE Asia), 52 (Africa), and 610 (world). (b) Total rice consumption (milled equivalent) in selected regions were 63 (EU 15), 5 (FSU), 325 (NC America), 59 (South America), 36 (ME Asia), 208 (FE Asia), 62 (Africa), and 770 (world). (c) Total maize consumption in selected regions were 3 (EU 15), 1 (FSU), 5 (NC America), 15 (South America), 130 (ME Asia), 245 (FE Asia), 21 (Africa), and 423 (world). FAOSTAT Database 2013.

Rice World production of paddy rice (unmilled or rough rice) was 701 Mt in 2012, a decrease of 22 Mt from the previous year. The area harvested remained the same but yields decreased by 34 kg ha 1 during the same period. World rice production

doubled from 216 to 448 Mt during the period 1961–83. The increase in average rice production was 15% between the 10-year periods 1981–90 and 1991–2000 and 1991–2000 and 2000–10 compared with 30% for the periods 1971–80 and 1981–90 (Figure 2).

GRAINS AROUND THE WORLD | Grain Production and Consumption: Overview Most of the rice is grown in developing countries. In 2012, Asia was responsible for 93% of the world rice production, 51% of the total crop being produced by China and India. Only small amounts (< 10%) of world rice produced are traded internationally. World exports of rice by region for 2009 and 2010 are given in Figure 3(c). The major rice exporters include India, Thailand, Vietnam, the United States, and Pakistan. Many countries in NC and South America, Europe, and Africa are net importers (Figure 4(c)). Total rice consumption (milled equivalent) for 2009 in Mt was 3 (EU15), 1 (FSU), 5 (NC America), 15 (South America), 130 (ME Asia), 245 (FE Asia), and 21 (Africa), giving a total of 423 (world). Global rice trade is predicted to remain the same in 2013 and 2014 as there are limited opportunities for expansion. Both production and consumption are expected to increase slightly worldwide.

Coarse Grains World production of coarse grains (including maize (corn), barley, sorghum, oats, rye, millet, triticale, buckwheat, and quinoa) was 1153 Mt in 2012 versus 1121 Mt in 2010. Among the coarse grains, maize, barley, and sorghum are the most important in terms of total cereal production. World production of maize, barley, and sorghum was 875, 132, and 58 Mt, respectively, in 2012 (Table 1). Production of other coarse grains was below 30 Mt each. A record of 1295 Mt, an increase of 11.4% from 2012 in global production of coarse grain in 2013, has been attributed to a strong recovery in maize production in the United States following the 2012 droughtreduced level. Leading producers in coarse grain production include the United States, China mainland, EU, Brazil, India, Argentina, the Russian Federation, Ukraine, Mexico, Canada, Nigeria, Indonesia, Ethiopia, Turkey, and South Africa. Major exporters of coarse grains are Argentina, Australia, Brazil, Canada, EU, Russian Federation, Ukraine and the United States.

Maize Maize composes 35% of total cereal production in the world. Maize is the preferred crop in Africa and South America. In Asia, it occupies the third position after rice and wheat. World maize production fell by 10 Mt from 885 Mt in 2011 (Table 1). The area harvested in 2012 was 177 Mha. Yields have remained relatively low in developing countries (1980 kg ha 1) compared with the global average (4944 kg ha 1) due to environmental, technological, and socioeconomic factors. Developed countries make use of adequate inputs and a well-mechanized system for maize production. In 1961, world maize production was 205 Mt. The figure rose to 615 Mt in 1998. After the 1998 peak in world maize production, rising production costs and shortage of foreign exchange in many developing countries have led to diminished production and, consequently, maize trade. There was a 50% increase in average global maize production between the periods 1961–70 and 1971–80 (Figure 2). World exports and imports of maize by region for 2009 and 2010 are given in Figures 3 and 4, respectively. The main maize

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exporters are the United States, Argentina, Brazil, France, Hungary, and Ukraine. The United States accounts for almost half of the world maize exports. China supplies grain to its neighboring countries. Japan and the Republic of Korea are the largest importers, each importing 16 and 9 Mt, respectively, in 2010. Globally, the total domestic supply of maize was 799 Mt in 2009. The primary product of maize milling is the meal used for feed and food purposes. At least 55% of world maize production is used to feed livestock and 14% is used for human food. Other uses include industrial processing and seed. Secondary and derived products are obtained through dry-milling and wet-milling processes. Global maize trade is forecast to reach a 6-year high in 2013 as the demand in China is increasing.

Barley World barley production was 132 Mt in 2012, down by 1 Mt from 2011 (Table 1). The area planted has steadily increased by 1 Mha from 2010 to 2012 but yields declined by 63 kg ha 1 from 2011 to 2012. In 2012, the major producers by region included the EU (Germany 10, France 11, and Spain 6), FSU (Russian Federation 14), NC America (Canada 8 and the United States 5), Asia (Turkey 7), and Oceania (Australia 8). The EU is a major exporter of barley. The Russian Federation and Ukraine have become competitors with the EU in export markets. Exports from the EU also face competition from Australia and Canada especially for supply of malting barley. ME Asia and FE Asia imported 10 and 4 Mt, respectively, of the total 25 Mt traded in 2010. Saudi Arabia, China, and Japan were the major Asian importers along with European countries Germany, Belgium, and the Netherlands. Global domestic supply of barley totaled to 140 Mt in 2009. Feed use accounted for 65% of barley consumption while food use remained very low (4.5%).

Sorghum The area under production for sorghum was 38 Mha in 2012 compared with 42 Mha in 2011 (Table 1). Global yield increased by 151 kg ha 1 from 2011 to 1535 kg ha 1 in 2012. World sorghum production decreased 1 Mt from 2011 to 58 Mt in 2012. Nigeria, Mexico, the United States, India, Argentina, China, and Ethiopia are the leading producers. Most sorghum is produced by small-scale and subsistence farmers in semitropical regions of Africa and Asia and by other farmers in the United States and Latin America. Africa produced 40% of the world total in 2012 on 23 Mha, more than half the world total area. India has the largest area harvested for sorghum, although there has been a significant reduction from 16 Mha in 1989 to 6.3 Mha in 2012. Production decreased in China from a peak of 6 Mt in 1994 to 2 Mt in 2012 due to a decline in area harvested. The United Arab Emirates had the largest average yield in 2012 at 84 667 kg ha 1. World trade of sorghum was 13 Mt in 2010 with the United States and Argentina supplying 3.9 and 1.7 Mt to the export market, respectively. In 2010, Mexico and Japan imported 2.3 and 1.6 Mt, respectively. Mexico, the most important producer of sorghum at 7 Mt in

356


2012, is also the largest importer. Chile, Ethiopia, the Republic of the Sudan, and Spain are also main importers. Sorghum is also an important commercial and export crop for Australia and Argentina. The crop is utilized for feed (43%), food (44%), and other uses (13%). Mexico, the United States, Australia, Brazil, Japan, and Nigeria are principal feed users.

Millets World production of all millets was 26 Mt in 2012 (Table 1), 46% of which was produced in Africa. West Africa (Nigeria, Niger, Burkina Faso, Chad, Mali, and Senegal) produces 75% of the millet output in Africa. Asia and Africa account for 96% of the global output of millet. India, China, Niger, Burkina Faso, and Nigeria are the leading producers of millet. Small-scale farmers produce almost all millet for household consumption and localized trade. Very little millet (0.9 Mt or 3.5% of world millet production) is traded internationally. India, the United States, China, Ukraine, and Austria are the major exporters of millet. The European community accounts for more than 23% of the global imports. Millet is primarily dry-milled to produce cracked grain, grits, meal, and flour from which a number of secondary and derived products are made.

Oats World oat production in 2012 was 21 Mt, down by 2 Mt from 2011 due to a decrease in crop yields (Table 1). The total area harvested was 10 Mha with an average yield of 2179 kg ha 1. World oat production for 2012 by region, in Mt, was 7.9 (EU), 4.7 (FSU), 3.7 (NC America), 1.3 (Oceania), 0.6 (FE Asia), and 0.3 (ME Asia). Russia and Canada are the leading producers followed by the United States and Australia. Canada is the world’s largest exporter with the United States accounting for over 90% of Canada’s oat exports. The next largest export regions are the EU (mainly Finland and Sweden) and Australia. Russia generally consumes its feed quality oats domestically even though it is the world’s largest single producer of oats. The United States dominates global oat imports, accounting for 80%, followed by Germany, Mexico, and Japan. Oats is used primarily for animal feed (71%) and human food (16%). High levels of soluble fiber in oats have contributed to its promotion as a healthy food ingredient.

Rye, Triticale, Buckwheat, Fonio, Quinoa, and Canary Seed World production of rye, triticale, buckwheat, fonio, quinoa, and canary seed was 13, 14, 2.3, 0.6, 0.08, and 0.2 Mt,

respectively, in 2012. These grains composed 1% of total cereal production. Germany, Poland, the Russian Federation, and Belarus are the major producers of rye. World buckwheat production increased between 2010 and 2011 as area harvested and yields grew slightly. Decreases in area harvested resulted in a decline in global canary seed production between 2010 and 2011. Worldwide production of both canary seed and buckwheat remained steady between 2011 and 2012. World quinoa production has steadily increased while global triticale and fonio production has remained fairly constant from 2010 to 2012. Canada contributed 62% of world canary seed production in 2012. Canary seed is currently used almost exclusively as birdseed. Rye, triticale, buckwheat, fonio, and quinoa are used for human food mostly as ingredients in baked products. It is projected that the demand for these grains will grow as whole grains continue to be promoted as healthy foods.

Pulses Table 2 gives data on world pulse production for the period 2010–12. Among pulses, beans were produced at 23.2 Mt followed by chickpeas (10.9 Mt) and peas (10.2 Mt) in 2010. Asia contributes 45% of world pulse production. Pulse production quadrupled in NC America and Africa since 1961. In the EU, pulse production peaked in 1990 at 7.4 Mt and steadily declined to 3.2 Mt in 2012. India, Brazil, and Myanmar are the leading producers of dry beans. The major chickpea producer is India followed by Australia, Turkey, Myanmar, and Ethiopia. Canada leads in both production and export of dry peas in the world. Russia, France, China, and India are also significant producers. World lentil production is 4.6 Mt with Canada (1.9 Mt) and India (0.9 Mt) as leading producers. India is a major importer of dry peas and dry beans. Over 70% of pulse crops are consumed as human food globally. Peas are used for both livestock feed and human food. The proportion for the latter use is higher in Asia and Latin America than in Europe.

Oilseeds Major oilseeds produced include soybean, rapeseed, cottonseed, groundnuts, sunflower seed, palm kernels, and copra. World oilseed production was 454 Mt in 2012 with soybean, rapeseed/canola, cottonseed, groundnuts (unshelled), sunflower seed, and palm kernels making up 53, 13, 10, 8, 8.6, and 3%, respectively, of the total production. World oilseed production has risen tremendously since the 1970s due to the

Table 2

World pulse and oilseed production (Mt) for the period 2010–12

Year

Total pulses

Dry beans

Dry peas

Chickpeas

Cow peas

Pigeon peas

Soybean

Rapeseed

2010 2011 2012

70 68 70

23 23 23

10 10 10

11 12 11

7 5 6

4 4 4

265 262 253

60 63 65

Source: FAOSTAT Database 2013.

GRAINS AROUND THE WORLD | Grain Production and Consumption: Overview expansion of the area planted. Soybean, palm, rapeseed, and sunflower oil each accounted for 27, 32, 15, and 10, respectively, of the world total oil (coconut, cottonseed, groundnut, linseed, olive (virgin), palm, palm kernel, rapeseed, safflower, sesame, soybean, and sunflower) produced (155 Mt) in 2012. However, soybean made up about 70% of the world protein meal consumption (187 Mt).

Soybean World soybean production was 253 Mt in 2012 (Table 2) compared with 26 Mt in 1961 (Figure 6). The United States, Brazil, Argentina, China, and India accounted for 32, 26, 16, 5, and 4.5% of total production in 2012. In general, production has been increasing since the 1950s due to the increase in global area planted and crop yields; however, a decrease in average yields between 2010 and 2012 caused a decline in world soybean production. Soybean production is now worldwide due to the crop’s ability to adapt to different types of soils and climates and versatile end uses. In Europe, production remains limited due to poor climate and soil conditions. Argentina continues to expand soybean-processing capacity as domestic policies continue to encourage value-added activities. Its processing capacity was only half that of Brazil in 1999; however, it has since surpassed that of Argentina with an estimated 175 000 tonnes compared to 169 000 tonnes per day in Brazil. Global soybean production is expected to increase due to an increase in production in the Americas. A growing demand for soybeans in China may lead to a growth in world trade. World soybean exports were at 93 Mt in 2010. Major exporters were the United States (45%), Brazil (28%), Argentina (15%), Paraguay (4%), and Canada (3%). Soybean is grown primarily for its meal in order to satisfy the feed protein requirement of broilers, pork, and aquaculture producers, which are not met by meat and fish meals and meals from other oilseeds. Soybean oil is a secondary product. Derived products (made from soybean, soybean meal, or soybean by-product) include fermented foods (e.g., tofu, soymilk, and soy sprouts) and nonfermented foods (soy sauce, ‘miso,’ ‘tempeh,’ and ‘natto’). Soybean can be used to produce products differing in protein content. Other derived products include soy ice cream, yogurt, burgers, cheese, meat analogs, salad, cooking, and frying oils, and shortening and margarines.

Rapeseed/Canola Rapeseed/canola production was 65 Mt in 2012 compared to 60 Mt in 2010 (Table 2). More than 88% of the world’s rapeseed was produced in Asia, EU, and NC America, that is, 22, 19, and 16 Mt, respectively. China contributed 22% of total rapeseed production. Canada produced 93% of the crop in NC America. Canola is processed into vegetable oil for human consumption and meal for livestock feed. Global rapeseed production is expected to increase; however, this growth may be limited by high prices and tight availabilities.


• • • • • • • •

Identify cereals classified as coarse grains and indicate whether they are major or minor in terms of global production. Why are potential yields of wheat not yet realized in African and Asian developing countries? Which countries are the major exporters of wheat? Globally, which regions or countries produce the most rice? Which continent(s) identifies maize as the preferred crop? What is the predominant use of barley? Which countries are the leading producers of sorghum? What are the major oilseed crops produced globally?


• • • •

Select one region and identify the major cereal crops produced. Are there variations in production among the leading producers over the last 5 years? Oilseeds are important for the production of oil and meal products. How does the current forecast differ from the past year in production and consumption of soybean in North America? Maize is a preferred crop in most South American and African countries. How is maize consumed in those regions? Can sorghum replace maize to produce foods consumed in those regions? Are there minor cereal and oilseed crops that are likely to become prominent in the near future in terms of production and consumption? Give the rationale for your response to this question.

300 Production (Mt)

250 200 150 100 50 0 1960

1970

357

1980

1990 Year

Figure 6 World soybean production for the period 1961–2012. FAOSTAT Database 2013.

2000

2010

358


See also: Grains Around the World: Grain Production and Consumption: Africa; Grain Production and Consumption: Cereal Grains in North America; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Oilseeds in North America; Grain Production and Consumption: South America.

Further Reading Agricultural Statistics (2000) National Agricultural Statistical Service. Washington: US Government Printing Office; United States Department of Agriculture. FAOSTAT (2013) FAO statistical databases. Food and Agriculture Organization of the United Nations. Rome, Italy (website: http://faostat.fao.org). Halweil B (2003) Grain production drops. In: Starke L (ed.) Vital Signs 2003. New York: Norton. IGC (2002) World Grain Statistics 2000/01. London: International Grains Council.

Signposts (2002) Envisioning the Future. Washington, DC: Worldwatch Institute. A Worldwatch CD-ROM Resource.

Relevant Websites http://www.angoc.ngo.ph – Agrarian Reforms in Asia http://www.angoc.org/-Asian NGO Coalition, for agrarian reform and rural development. http://www.igc.org.uk – International Grain Council market reports and grain statistics Password required. http://www.irri.org – International Rice Research Institute world rice statistics. http://www.soystats.com and http://www.unitedsoybean.org– Oilseed and soybean statistics. http://www.fao.org and http://faostat.fao.org – United Nations Food and Agriculture Organization, probably the best single source of general articles, and FAOSTAT, online databases covering international statistics in agriculture. http://usda.mannlib.cornell.edu – USDA Economics, Statistics and Market Information System. http://www.worldwatch.org – Worldwatch research on food and agriculture.

Grain Production and Consumption: Africa JRN Taylor, University of Pretoria, Pretoria, South Africa ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Comprehensive information on the quantities of the various grains (cereals, pulses, and oilseeds) produced in Africa and where they are produced. Review of Africa’s rich culture of traditional grain foods and beverages. Overview of the state of African agriculture and the causes of low agricultural productivity. Focus on the impact of rapid population growth and urbanization on food consumption and grain food security. Information on the grain production and grain food supply situation in Africa with respect to production and imports. Review of major initiatives taking place in Africa to improve agriculture and food security, including the application of biotechnology and grain biofortification.

Learning Objectives

• • • • •

To know which are the important grains (cereals, pulses, and oilseeds) produced in Africa and where they are produced. To understand the factors responsible for the generally low agricultural productivity in Africa. To be aware of Africa’s rich culture of grain foods and beverages. To understand the impact of rapid population growth and urbanization in Africa on food security. To be aware of the major initiatives taking place in Africa to improve agriculture.

Introduction Africa is the second largest continent with an area of 30.3 million square kilometers. It is the only continent that straddles both tropics. Hence, Africa has a predominantly subtropical and tropical climate. Most of North Africa and much of southwestern Africa have a desert climate, with < 250 mm of rainfall a year. The climate in the African tropics varies from warm and dry (rainfall 250–500 mm year 1) to hot with a dry season or two dry seasons (rainfall 500–1000 mm) to the equatorial region, which is hot with rain all year (1000–3000 mm). Only on the northwestern Mediterranean seaboard, the southern Cape, and South African eastern seaboard there is a mild, warm, and wet climate (rainfall 500–1000 mm). Africa’s natural vegetation mainly ranges from desert and semidesert, though savanna, to subtropical and tropical broadleaf forest. One significant exception is the central part of South Africa, which is natural grassland, the ‘grassveld.’ By 2015, Africa’s population would be 1.17 billion (Figure 1). In the past 50 years from 1965 (the date when


most African countries had become independent), it has grown exponentially, increasing 3.6-fold. The population is still increasing rapidly but the rate of growth is slowing somewhat and is now 2.5% per year. Nevertheless, it is predicted that by 2050, the population of sub-Saharan Africa will increase to between 1.5 and 2 billion. Notably, half the world’s increase in population to 2050 will be from sub-Saharan Africa. As can be seen from Figure 1, both the rural and urban populations are increasing, but urbanization is taking place much more rapidly. It is predicted that by 2030, 50% of Africa’s population will live in large towns and cities. Obviously, Africa’s high population growth rate, coupled with rapid urbanization, is currently having and will continue to have a profound impact on the continent’s food security and food utilization. This article examines the grain food situation in Africa, with particular reference to the importance of grains as foodstuffs in Africa, Africa’s major grains and their production, the causes of grain agriculture low productivity, grain consumption, and the impact of rapid population growth and urbanization and concludes by reviewing developments and challenges in grain agriculture and grain handling. The data are from the FAOSTAT database of the Food and Agriculture Organization (FAO) of the United Nations.

Importance of Grains Africa is an exception compared to much of the rest of the world in that quantitatively, cereals are only the second largest foodstuff in terms of production. Starchy roots and tubers are the largest, of which cassava accounts for just over half. The quantities in 2012 were 172 million tonnes (Mt) of cereals and 266 Mt of starchy roots and tubers. However, it should be taken into account that cereal grains contain 70% starch, whereas starchy roots and tubers only contain 35% starch, and hence cereals are the larger contributor to energy intake. Africa is also unusual in that only a relatively small proportion of the cereals produced is used as animal feed, 12.5%. This means that still today, the African diet is predominantly plantbased. This is also reflected by the fact that the production of plant protein, in the form of pulses, 15.9 Mt, is virtually identical to that of meat, 16.4 Mt.

Grain Production Cereal production in Africa is dominated by maize, which is a tropical (C4) cereal, at 70 Mt (2012), some 40% of total cereal production (Table 1). As can be seen, production is very widespread across the continent both geographically and climatically. In fact, maize production is recorded for 50 countries in Africa. However, the top four producing countries South Africa, Nigeria, Egypt, and Ethiopia are responsible for about half of the total production.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00043-7

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360

GRAINS AROUND THE WORLD | Grain Production and Consumption: Africa

1200

Population (millions)

1000 Total

800

600 Rural 400 Urban 200

0 1965

1970

1975

1980

1985

1990 Year

1995

2000

2005

2010

2015

Figure 1 Africa’s population growth from 1965 to 2015. Data from FAOSTAT: http://faostat.fao.org. Population (accessed 21.04.14.).

Table 1

Grains produced in Africa (2012 data)

Grain

Production (t 103)

Cereals Cereals (total) Barley Fonio Maize Millet (mainly pearl millet) Oats Rice (paddy) Rye Sorghum

172 184 6023 587 69 637 16 083 276 26 824 94 23 313 26 24 711

Triticale Wheat Pseudocereals Buckwheat Pulses (grain legumes) Pulses (total) Bambara bean Dry beans (common beans) Broad bean Chickpea Cowpea Lentil Peas (dry) Pigeon pea Pulses (other) Oil-rich legumes Peanuts (groundnuts) (in shell) Soybean Oilseeds Rapeseed Sunflower seed a

Area harvested (h 103)

Yield (t ha 1)

Major producing countries in descending order

(3.5)a (0.3) (40.4) (9.3) (0.2) (15.6) (<0.1) (13.5)

106 955 4997 566 33 710 19 978 199 10 538 52 23 169

1.61 1.21 1.04 2.08 0.81 1.39 2.54 1.80 1.01

(<0.1) (14.4)

13 10 217

2.01 2.42

Nigeria, Egypt, Ethiopia, South Africa Ethiopia, Algeria, Morocco Guinea, Nigeria South Africa, Nigeria, Egypt, Ethiopia Nigeria, Niger, Mali Algeria, South Africa, Morocco Egypt, Nigeria, and Madagascar Egypt Nigeria, Ethiopia, Burkina Faso, and Sudan (former) Tunisia Egypt, Morocco, Ethiopia, and Algeria

11

0.97

Tanzania

10 15 865 159

(1.0)b

24 447 233

0.65 0.68

5070 1505 697 5403 187 596 632 1262

(32.0) (9.5) (4.4) (34.1) (1.2) (3.8) (4.0) (8.0)

7829 670 595 11 043 188 715 754 1890

0.65 1.55 1.17 0.49 0.99 0.83 0.84 0.67

Ethiopia, Nigeria, Tanzania, and Niger Burkina Faso, Niger, Cameroon, and Mauritania Tanzania, Kenya, Ethiopia, and Rwanda Ethiopia Ethiopia Nigeria, Niger Ethiopia Ethiopia and Tanzania Malawi and Tanzania Mozambique, Sudan (former)

10 942

11 823

0.93

Nigeria, Sudan (former), and Tanzania

1986

1638

1.21

South Africa and Nigeria

201 2224

113 1780

1.79 1.24

South Africa, Ethiopia, and Algeria Tanzania and South Africa

Percentage of cereal production. Percentage of pulse production. Data from FAOSTAT http://faostat.fao.org. Production (accessed 21.04.14.). b

GRAINS AROUND THE WORLD | Grain Production and Consumption: Africa Quantitatively, the next most important cereals, in descending order, are rice, wheat, and sorghum, accounting for 15.6%, 14.4%, and 13.5% of total cereal production. Production of these three cereals is also widespread across Africa, with 43 producing countries being recorded for rice, 41 for sorghum, and 31 for wheat. However, there are some important differences with respect to their cultivation. Africa’s production of sorghum, 23 Mt, is 40% of world sorghum production. The area where sorghum is harvested in Africa, 23 M ha, is 60% of the world total. The major production is in the semiarid tropics of North Africa, from Nigeria and Burkina Faso in the west to Sudan and Ethiopia in the east (Table 1). This is probably on account of the fact that sorghum, a tropical (C4) cereal, is indigenous to Africa and is very well adapted to harsh climatic conditions, being able to withstand periods of drought and also waterlogging. Sorghum requires a minimum of only 400 mm of water for cultivation, as opposed to the 500–600 mm needed by maize. In contrast, the production of rice (a tropical C3 cereal) requires much more water and is concentrated in areas of high water availability: the Nile valley of Egypt, tropical Nigeria, and Madagascar. Concerning wheat, which is a temperate C3 cereal, its production is generally highest in countries in Africa on the Mediterranean coast. The top three producers are Egypt, Morocco, and Algeria. Substantial quantities of wheat are also grown in countries in the tropics, in particular Ethiopia and Kenya, with cultivation being carried out at elevated altitudes to attain the required cooler conditions. Africa is the home to a number of millet species, which are all C4 cereals. Millets are, by definition, small grained cereals. The FAO data (Table 1) only specifically record the millet species fonio (Digitaria sp.), also known as acha, or more colloquially as ‘hungry rice’ on account of its ability to produce a crop under extreme hot and dry conditions. Fonio is endemic to the Sahel region of West Africa, in particular Guinea (Table 1). The other millets are lumped together under the general heading ‘millet.’ Millet production in total accounts for 19% of the land area under cereal cultivation in Africa. By far, the most important millet is pearl millet (Pennisetum glaucum), accounting for 87% of millet production in Africa and 8% of the continent’s total cereal production. Pearl millet is uniquely able to produce a crop under very low rainfall conditions, with a minimum water requirement of only 300 mm and very high temperatures (daytime temperatures above 30 C). Pearl millet production is also mainly in the dry areas of West Africa, but it is also cultivated widely across the continent. The other economically important millets in Africa in descending order of production are finger millet (Eleusine coracana), teff (tef) (Eragrostis tef), and guinea millet (Brachiaria deflexa). Finger millet, so-called because the grains are borne on fingerlike panicles (Figure 2(a)), is grown throughout subSaharan Africa. It is an especially important grain with regard to rural food security on account of its excellent storability, being resistant to insect attack on account of its proportionally small germ. Teff production is almost exclusively in Ethiopia and Eritrea. There is also substantial production of barley in Africa, which is produced both for brewing and as a food, the latter especially in Ethiopia. Production of oats, rye and triticale, and the pseudocereal buckwheat is very limited (Table 1).

361

Figure 2 Finger millet and bambara beans. (a) Finger millet under cultivation in Kenya, (b) Bambara beans from Namibia, (c) Bambara beans from Zimbabwe (close up).

As mentioned, pulses are a major food crop in Africa. Total pulse production is 16 Mt per year and is dominated by cowpea (Vigna unguiculata) and dry beans (Phaseolus vulgaris), the production of both being 5 M tonnes per annum (Table 1), and together, they account for 66% of pulse production. Cowpea is indigenous to Africa. The major producing countries are in tropical West Africa, in particular Nigeria and Niger, although production is widespread throughout Africa with significant production recorded in 19 countries. Dry beans (also known as common beans) originated in South America. The major producing countries are in East Africa, with the highest production in Tanzania, Kenya, and Ethiopia. However, there is significant production across the continent in at least 33 countries. Broad bean (Vicia faba) is quantitatively the third most important bean with an annual production of 1.5 M tonnes, with Ethiopia responsible for 63% of Africa’s production. The production of other pulses, including chickpea (Cicer arietinum), pigeon pea (Cajanus cajan), dry pea (Pisum sativum), lentil (Lens culinaris), bambara bean (Vigna subterranea), and other exotic and indigenous pulses such as lablab (Lablab purpureus), yam bean (Pachyrhizus sp.), mung bean (Vigna radiata), and marama bean (Tylosema esculenta) is also of significant importance especially with regard to rural food security and in the case of dry peas and lentils as cash crops. Of particular interest is the bambara bean (Figure 2(b) and 2(c)), also known as the African or bambara groundnut, which is indigenous to Africa. It is widely cultivated across the drier parts of topical Africa, with, according to one authoritative source, Zimbabwe being the center of production, whereas FAOSTAT only records significant production in five countries, all in the Sahel region, with Burkina Faso being the largest producer. The bambara bean can be cultivated where temperatures reach as high as 40 C and is one of the most droughttolerant legume species. It is considered to be one of the world’s most underestimated and neglected crop plants. Total production of oil-containing grains (oilseeds) in Africa is also 16 Mt per year and is dominated by peanuts (groundnuts) at 10.9 Mt (Table 1). This is related to the fact that peanuts are used as both a food and a source of cooking oil.


Production takes place throughout Africa, with 47 countries recorded as significant producers. However, Nigeria produces by far the largest quantity of peanuts, 3.1 Mt. Significant quantities of oil-bearing grains other than peanuts are also produced in Africa. The most important are sunflower and soybean, with a total production of 2.2 and 2.0 Mt, respectively. There is also some production of rapeseed (canola). South Africa is the major producer of both soya and canola.

with an 73% increase over the entire period. In contrast, yield initially increased over the first 10 years and then remained static until the mid-1990s and has subsequently increased substantially in recent years. Over the whole period, yields increased by 83%. Increased area of harvest and increased yields have resulted in a continuous increase in cereal production, which has accelerated since the mid-1990s. Overall, cereal production increased 3.2-fold, keeping pace with but not exceeding the increase in population 3.1-fold. As a consequence, Africa’s cereal imports have grown at a rapid but linear rate over the period, increasing from 11% to 34% of cereal production. Imports of maize now represent some 26% of local production (Table 2). The need to import an increasing proportion of cereal grains is related to the fact that much of Africa’s agriculture is still subsistence farming. However, small-scale commercial and large-scale mechanized farming are widespread and increasing.

Grain Agriculture

Production/area harvested/imports (Mt)

Figure 3 shows the trends in cereal production and imports for Africa over a 45-year period since the mid-1960s when most African countries gained independence, to 2010. Over the period, the area harvested remained more or less constant up until the about 1980 and then steadily but gradually increased, 180

1.80

160

1.60

140

1.40

120

1.20

100

1.00

Yield

80

Area harvested

Production

0.80

60

0.60

40

Yield (tonnes/Ha)

362

0.40

Imports

20

0.20

0 1965

1970

1975

1980

1985

1990

1995

2000

2005

0.00 2010

Year Figure 3 Africa’s cereal production and imports from 1965 to 2010 (data from FAOSTAT5). Data from FAOSTAT. Production: Crops http://faostat.fao. org/ (accessed 21.04.14.).

Table 2

Africa’s domestic grain-based food and beverage supply (2009) (t 103)

Products

Production

Imports

Imports (% of production)

Exports

Cereals (total) Maize Wheat Barley Lager and stout beers Pulses (total) Peanuts (groundnuts) (in shell) Soybeans Sunflower seed Groundnut oil Soybean oil Sunflower seed oil

146 217 57 702 26 074 5827 9758 12 086 9604

55 987 14 995 30 288 1744 510 1262 227

38.3 26.0 116.2 29.9 5.2 10.4 2.4

4065 2132 897 29 188 577 148

2.8 3.7 3.4 0.5 1.9 4.8 1.5

1612 1689 1374 300 597

1133 175 9 1449 596

70.3 10.4 0.7 483.0 99.8

192 14 48 127 90

11.9 0.8 3.5 42.3 15.1

Data from FAOSTAT http://faostat.fao.org. Production (accessed 21.04.14.).

Exports (% of production)

Stock changes

Domestic supply

Domestic supply (% of production)

1163 3498 126 306 199 322 16

199 303 67 067 55 339 7237 9882 12 803 9670

136.3 116.2 212.2 124.2 101.3 105.9 100.7

170 116 16 87 132

2722 1734 1319 1535 971

168.9 102.7 96.0 511.7 162.6


• • • • • • • • • • Figure 4 Grain harvesting in Africa. (a) Manual harvesting of teff in Ethiopia. (b) Combine harvesting of wheat in Kenya.

Unfortunately, the so-called green revolution has barely impacted on the subsistence farming sector. Here, agriculture is characterized by traditional farming practices using manual labor and some draft animal power (Figure 4(a)), low inputs (no inorganic fertilizer or pesticides), and the use of lowyielding traditional varieties or landraces. Taking the example of sorghum, which in Africa is mainly produced by subsistence farmers, yields have only increased marginally over the period from 0.75 to just 1.0 t ha 1. This compares to the sorghum yield of almost 4 t ha 1 in the United States where mechanized, high-input agriculture using hybrid seeds is employed. Where these technologies are also applied in Africa, for example, in South Africa, yields are substantially higher, 2.7 t ha 1. Also, as can been seen from Table 1, agricultural production efficiency in Africa varies very considerably between the grains, with a low of millet at 0.8 t ha 1 among the cereals, and an overall low of only 0.5 t ha 1 for cowpea, and a high of 2.4 t ha 1 for wheat among the cereals. Production efficiency appears to depend, to a considerable extent, on whether the grain is primarily home-processed as in the case of cowpeas or industrially processed as in the case of wheat. In other words, production is driven by the existence and needs of a linked food processing industry, which encourages the development of larger-scale mechanized farming, as, for example, has taken place with wheat in Kenya (Figure 4(b)). Hence, the average yield of wheat in Africa of 2.4 t ha 1 compares reasonably well with the 3.1 t ha 1 in the United States of America.

Grain Food Consumption Africa has a rich culture of traditional grain foods and beverages (Figure 5). The following gives some idea of the huge variety of cereal and legume products:

• •

Roasted snack foods, for example, ‘kollo’ – barley (Ethiopia) Leavened baked wheat flour breads, for example, ‘geish baladi’ (Egypt)

•

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Leavened steamed wheat flour breads, for example, ‘ledombolo’ (South Africa) Flatbreads, for example, ‘kisra’ – sorghum or millet (Sudan) Pancakes, for example, ‘injera’ – tef, sorghum, finger millet, wheat or maize, or combinations (Ethiopia) Dumplings, for example, ‘kenkey’ – maize (Ghana) Whole or dehulled boiled grains, for example, ‘supa mtama’ – sorghum (Kenya) Steamed, granulated foods, for example, ‘couscous’ – wheat, sorghum, or pearl millet (North and West Africa) Stiff porridges, for example, ‘sadza,’ maize (Zimbabwe), and ‘ugali,’ maize, sorghum, and finger millet (East Africa) Soft porridges and gruels, for example, ‘uji’ – maize, sorghum, or finger millet (East Africa) Porridge cooked with wood ash extract making it alkaline, for example, ‘toˆ’ – sorghum or pearl millet (Mali) Porridge, lactic acid-fermented, making it sour, for example, ‘ogi,’ maize, sorghum, or pearl millet (Nigeria), and ‘ting,’ sorghum (Botswana and South Africa) Porridge flavored with tamarind or lemon juice, making it acidic, for example, toˆ – sorghum (Burkina Faso)

Traditional African cereal beverages are both nonalcoholic, for example, ‘mageu’ (southern Africa), and alcoholic, for example, cloudy ‘pito beer’ (Ghana) and opaque sorghum beer (central and southern Africa). The beverages are generally opaque and viscous in consistency, due to the presence of semisuspended starch. They are produced variously from sorghum, maize, pearl millet, and finger millet, either singly or in combination. In the beers, a portion of the cereal is in the form of malt, in order to provide amylase enzymes to hydrolyze the starch into fermentable sugars. A characteristic of many traditional African cereal foods and beverages is that they have undergone a lactic acid bacterial fermentation during processing. This gives the product a characteristic sharp, sour taste and helps preserve it against microbial spoilage. Examples include the pancake ‘injera,’ the dumpling ‘kenkey,’ the firm porridge ‘ting,’ the thin porridge ‘ogi,’ the nonalcoholic beverage ‘mageu,’ and sorghum beer. Legume-based traditional African foods include

• • • • • • • • •

blanched and roasted whole grain snacks, for example, ‘kollo,’ chickpea (Ethiopia); boiled whole grain snacks, for example, ‘nifro,’ chickpea, broad bean, or lentil (Ethiopia); boiled whole grains foods, for example, ‘dikgobe,’ cowpea (Botswana); ‘mayengele,’ dry beans (Uganda); and ‘mtakura,’ cowpea, peanuts, or bambara bean (Zimbabwe), all often mixed and served with boiled maize grains; steamed pastes, for example, ‘moi-moi,’ dry beans (Nigeria), and ‘okpa,’ bambara bean (Nigeria); deep-fried pastes, for example, ‘kose,’ cowpea or dry beans (Ghana); deep-fried bean balls, for example, ‘akara,’ dry beans (Nigeria); fermented pastes, for example, ‘siljo,’ broad bean (Ethiopia); boiled grains made into a sauce, for example, ‘magila,’ cowpea (Uganda); germinated and boiled grains made into a sauce, for example, ‘azifa,’ chickpea, broad bean, or lentil (Ethiopia); and

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Figure 5 Selection of African grain foods and beverages. (a) Kisa flatbread (sorghum) – Sudan, (b) toˆ porridge (maize) with chickpea relish and goat meat – Burkina Faso, (c) Ugali porridge (sorghum) – Kenya, (d) Baladi bread (wheat) – Sudan, (e) Fonio couscous and peanut sauce (Burkina Faso), (f) Mealie bread (maize and wheat) – South Africa, (g) Samp and beans (maize and dry beans) – southern Africa, (h) Opaque sorghum beer (maize and sorghum) – southern Africa, (i) Mageu fermented nonalcoholic beverage (sorghum and maize) – Zimbabwe and South Africa.

•

dry roasted grain milled into powder, spiced, and made into a sauce, for example, ‘shiro,’ pea, broad bean, or chickpea (Ethiopia).

However, food consumption patterns in Africa are changing rapidly as a result of urbanization. The so-called nutrition transition is resulting in a dramatic increase in consumption of Western-style convenience foods, including bread, potato chips (French fries), fried chicken, and beef burgers, and beverages, in particular carbonated soft drinks and lager beer. For example, with regard to convenience foods, the largest South African fast-food franchise company opened 18 restaurants in other African countries in the last quarter of 2012. In the case of lager beer, the figures are if anything even more dramatic. From 2007 to 2012, the largest brewing company in Africa recorded an average annual 12% increase in beer volume. These changing food consumption patterns are severely impacting on the grain food supply situation in Africa. With regard to cereals, the continent is importing as much wheat as is produced locally (Table 2). In the case of barley, imports amount to 30% local production. The situation with regard to soybeans, the most important protein source in formulated animal feeds, is worse, with domestic supply being 170% of production. With regard to seed oils, which are majorly used to manufacture plant-based fats like margarine, the situation is even more dire. Africa is importing nearly five times the quantity of soy oil it produces and as much sunflower seed oil as it produces. Taking the previously mentioned into account, the fact that Africa is essentially self-sufficient in lager and beer

production may seem surprising. Part of the explanation is that a substantial proportion of these beers are now brewed using locally grown sorghum as either the sole or major ingredient, especially in West and East Africa.

Developments and Challenges in Grain Agriculture and Grain Handling The high dependence on imported grains has a very adverse effect on the fragile economies of many African countries. To prevent increasing poverty and malnutrition resulting from rapid population growth and urbanization, it is essential that the effectiveness of African grain agriculture is improved. However, the improvement of agriculture in Africa faces a number of severe challenges. These include the acute need to introduce modern agricultural production technologies and chronic environmental problems such as decreasing soil fertility and desertification, resulting from farming more marginal land. There are also sociopolitical issues. Governmental policies are often not conducive to local agricultural development. As of 2013, only eight countries in Africa had met the UN Millennium Development Goal of halving the proportion of hungry people. Persistent problems include keeping food prices artificially low to subsidize the urban consumer, but at the cost of the farmers’ livelihood, and poorly planned and executed land reforms that disrupt large-scale commercial farming operations.

GRAINS AROUND THE WORLD | Grain Production and Consumption: Africa The application of biotechnology to grain agriculture in Africa has the potential to provide many benefits that could help the continent leapfrog the first green revolution. Genetically modified (GM) crops are currently being commercially cultivated in some countries, notably South Africa and Burkina Faso. For example, some 80% of maize produced in South Africa is GM glyphosate herbicide-tolerant and/or Bt gene insect-resistant. It is stated that latter technology has increased yields by 11%. However, some African countries refuse to even import GM grains, never mind grow them. Notwithstanding this, GM plants with ‘built-in’ specific resistance to pests, tolerance to environmental stresses such as drought and low rainfall, and improved nutritional value to combat malnutrition should be of tremendous value. Biotechnology alone will not be a panacea. In recent years, there have been several major collaborative initiatives to improve Africa’s agriculture, notably the Alliance for a Green Revolution in Africa (AGRA). AGRA aims to develop practical solutions to significantly boost farm productivity and incomes for the poor while safeguarding the environment. Perhaps the most important of AGRA’s projects is the Program for Africa’s Seed Systems (PASS). PASS supports in-country-breeding teams who work closely with farmers to develop new varieties and with local entrepreneurs to establish independent seed companies to produce and distribute the seed. AGRA also supports the training of high-level agricultural scientists, for example, training PhD-level plant breeders through the African Centre for Crop Improvement, hosted by the University of KwaZulu-Natal in South Africa. A notable initiative is the development of biofortified staple crops for smallholder farmer cultivation in Africa. Biofortification is the enhancement of the levels of critically deficient nutrients, particularly micronutrients, in staple food crops such as grains. It can be achieved by conventional breeding and also by recombinant DNA technology (genetic engineering). Probably the most well-known biofortified crop is quality protein maize (QPM), the protein of which is much richer in lysine and other indispensible amino acids than conventional maize. Several studies have shown that consumption of QPM maize has improved the nutritional status of young children, for example, in Ethiopia. Recent biofortified cereals include provitamin A maize, iron- and zinc-rich pearl millet, and Africa Biofortified Sorghum. The latter, which has been developed by genetic engineering, is unique in that the final product will have enhanced multiple nutrients: provitamin A, improved protein quality and protein digestibility, and increased iron and zinc bioavailability. As Africa urbanizes and develops its grain processing industries, a further challenge that still needs to be properly addressed is for countries to dramatically improve their grain handling systems. Lack of adequate grain storage facilities in many countries causes ruinously low prices for farmers when crops are good and acute shortages for consumers when crops are poor (Figure 6(a)). The almost complete absence of railways and lack of good roads in much of Africa mean that the costs of transporting grain from the point of production to where it is processed are very high. This is compounded by high costs of grain assembly, where many small consignments of grain from different small-scale farmers have to be brought to one place to make up a truckload. As a result, locally

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Figure 6 Grain handling challenges in Africa. (a) Outdoor storage of sorghum at harvest time in Burkina Faso. (b) Poorly cleaned smallholder farmer-produced sorghum being unloaded at a factory in Nigeria.

produced grain is often more expensive than imported grain. Additionally, there can also be severe problems with quality that render small-scale farmer-produced grain unsuitable for industrial processing. Consignments of grain may comprise different varieties with differing grain properties such as grain size, and worse, the grain may be heavily contaminated with dirt and stones (Figure 6(b)).


• • • • •

State in descending order which are quantitatively the major cereals, pulses, and oilseeds produced in Africa. Give examples of indigenous African cereals and pulse grains (at least three of each) and state where they are cultivated. Give examples of traditional African grain foods and beverages (at least three of each) and state what type of product they are and from which grain(s) they are made. State which are the major grains and grain products that Africa imports. Explain the reasons for the generally poor agricultural productivity in Africa.

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Explain what is the impact of rapid population growth and urbanization on food security in Africa. Explain the concept of biofortification and its benefits.


• • • • •

Improving smallholder agriculture productivity in Africa using appropriate technologies. Improving grain storage using appropriate technologies. Reduction in the cost of assembly and transport of consignments of grain produced by smallholder farmers. Development of simple but effective grain-quality standards suitable for smallholder farmers. Development of technologies to produce inexpensive but good-quality bread using maize and sorghum.

Further Reading Akalu G, Taffesse S, Gunaratna NS, and De Groote H (2010) The effectiveness of quality protein maize in improving the nutritional status of young children in the Ethiopian highlands. Food and Nutrition Bulletin 31: 418–430. National Research Council (1996) Lost Crops of Africa. vol. 1: Grains. Washington, DC: National Academies Press. National Research Council (2006) Lost Crops of Africa. vol. 2: Vegetables. Washington, DC: National Academies Press.

Popkin BM (2003) The nutrition transition in the developing world. Development Policy Review 21: 581–597. Rohrbach DD (2003) Improving the commercial viability of sorghum and pearl millet in Africa. Afripro Paper 22. http://www.afripro.org.uk (accessed 21.04.14). Saltzman A, Birol E, Bouis HE, et al. (2013) Biofortification: Progress toward a more nourishing future. Global Food Security 2: 9–17. Taylor JRN, Dlamini BC, and Kruger J (2013) 125th Anniversary Review: The science of the tropical cereals sorghum, maize and rice in relation to lager beer brewing. Journal of the Institute of Brewing 119: 1–14. Van Wyk B-E and Gericke N (2000) Peoples Plants: A Guide to Useful Plants of Southern Africa. Pretoria: Briza.

Relevant Websites http://agra-alliance.org – AGRA (accessed 21.04.14.). http://www.fao.org – FAO. 12 June 2013. 38 countries meet anti-hunger targets for 2015 (accessed 21.04.14.). http://faostat.fao.org/ – FAOSTAT. Commodity Balances: Crops Primary Equivalent (accessed 21.04.14.). http://faostat.fao.org – FAOSTAT. Population (accessed 21.04.14.). http://faostat.fao.org/ – FAOSTAT. Production: Crops (accessed 21.04.14.). http://www.financialmail.co.za – Financial Mail. 6 July 2012. SABMiller barrels ahead (accessed 21.04.14.). http://www.fao.org – How to Feed the World 2050: High-level Expert Forum. The special challenge for sub-Saharan Africa (accessed 21.04.14.). http://www.howwemadeitinafrica.co.za – How We Made It In Africa. More than enough potential for restaurants and fast-food in Africa (accessed 21.04.14.). http://education.nationalgeographic.com – National Geographic Education. Africa: Physical Geography (accessed 21.04.14.). http://www.pannar.com – PANNAR Seed. 2013 Product Catalogue (accessed 21.04.14.). http://unhabitat.org – UN Habitat: The State of African Cities, 2012 (accessed 21.04.14.).

Production and Consumption of Grains: India BS Khatkar, N Chaudhary, and P Dangi, G. J. University of Science and Technology, Hisar, India ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

Agriculture accounts for considerable importance in India’s economic development, as it provides food for more than 1.2 billion people and total employment to about 54.6% of the population. India holds the second-largest agricultural land (179.9 million hectares) in the world. Food grain production covers the dominant part of the cropped area (65%) in Indian agriculture. India is the world’s largest producer of millets and secondlargest producer of wheat, rice, and pulses. The highest food grain production of 259.32 million tonnes was recorded in 2011–12. The cereals other than rice and wheat contributed 1 kg per person per month in rural India and 0.8 kg per person per month in urban India in 2011–12. The consumption of all food grains per person in the rural areas is projected to decline from 15.3 kg per month in 2000 to 13.8 kg per month by 2050 and only slightly decrease from 11.8 to 11.6 kg per month in the urban areas. The nongrain food crops and animal products contributed 27% and 8%, respectively, of the total caloric requirement. Meat consumption in India is very low due to cultural and religious reasons, and most of the calories from animal products are obtained from milk and milk products.

Learning Objectives

• • • •

To present past and future prospects of the Indian food grain production. To identify the role of the Indian government in supporting agriculture and food grain production. To understand food grain consumption patterns of the Indian population. To learn the status of changing food grain consumption patterns and the reasons behind these shifts.

Introduction India accounts for only about 2.4% of the world’s geographical area and 4% of its water resources, but has to support about 17% of the world’s human population and 15% of the livestock. India holds the second-largest agricultural land (179.9 million hectares) in the world. Food grain production covers dominant part of the cropped area (65%) in Indian agriculture. According to the FAO world agriculture statistics (2010), India is the world’s largest producer of millets and second-largest producer of wheat, rice, and pulses. Indian agriculture has witnessed wide ups and downs in growth performance during the last six decades. Performance


of Indian agriculture can be divided into six phases viz. pregreen revolution period (1960–61 to 1968–69), early green revolution period (1968–69 to 1975–76), period of wider technology dissemination (1975–76 to 1988–89), period of diversification (1988–89 to 1995–96); postreform period (1995–96 to 2004–05), and period of recovery (2004–05 to 2010–11). The green revolution period was the golden period for Indian agriculture, as it witnessed tremendous growth in agricultural production. During the period of wider dissemination of technology, the spread of green revolution technologies pushed to maintain the increasing rhythm of growth across various regions realized during the previous period. However, a visible deceleration of growth was experienced during the postreform period, as both public and private investments suffered a setback, which resulted in the sluggish performance of the sector. Moreover, yield levels of most of the crops suffered a deceleration because use of primary resources in the sector also slowed down. The descending trend of growth continued up to 2004–05, after which a sharp return was attained that can be attributed to a conscious increment in public and private ventures and substantial improvement in trade in favor of the agricultural sector.

Food Grain Production India is continuously facing pressure on the demand side due to steady population growth, limited land availability, and several other production deterrents, which might also appear as obstacles for the supply of food grains. Indian government policies and planning has always given considerable importance to production of food grains due to which India has been achieving the continued growth despite many constraints. During the last decade (2000–01 to 2010–11), the areas under cereals, pulses, and oilseeds have increased by about 5.7, 6.0, and 4.0 million hectares, respectively, and the area under coarse cereals has declined by 2.6 million hectares. The area under wheat cultivation has accelerated significantly in comparison to other cereals and millets. However, a moderate deceleration in total grain cultivated area in comparison to pulses cultivated area was witnessed during the years of 2005 to 2011. The highest food grain production of 259.32 million tonnes was recorded in 2011–12. Out of the total food grains production, cereals accounted for 242.23 million tonnes and pulses 17.09 million tonnes (Figure 1). Production of rice and wheat was recorded at 105.3 and 94.9 million tonnes, respectively. It was estimated that the agriculture sector in India is likely to grow by 5.2–5.7% in 2013–14. India is one of the largest producers of cereal as well as the largest exporter of cereal products worldwide. India’s export of cereals during 2013–14 stood at Rs. 63452.09 crores. Rice (including basmati and non-basmati) occupies the most sizable share in India’s total cereals export with 64.40% during this period. Countries

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GRAINS AROUND THE WORLD | Production and Consumption of Grains: India

Total Pulses

Coarse Cereals

Total cereals

Total Foodgrains

Production (million tonnes)

300 250 200 150 100 50 0 2010-11

2011-12 Year

2012-13

Figure 1 Production of food grains in India.

40

33.8

Area (percentage)

35 30 25 20

14.8

12.7

15

9.7

8.7

10

7.8 3.5

5

1.8

1.5

1.5

2.8

1.4

O

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States Figure 2 Share of states in India in terms of area under cultivation of wheat.

such as Iran, Saudi Arabia, Indonesia, UAE, and Bangladesh mainly imported cereals from India during 2013–14.

Wheat The area and production under wheat has increased from 27.99 million hectares in 2006–07 to 29.86 million hectares in 2011–12 and from 75.81 million tonnes in 2006–07 to an all-time record high of 94.88 million tonnes in 2011–12, respectively. Figure 2 shows the percent share of states in India in terms of area. Uttar Pradesh, Madhya Pradesh, Punjab, Rajasthan, and Haryana are the leading states in terms of area under wheat cultivation. Uttar Pradesh accounts for the maximum area under cultivation and production, whereas Punjab and Haryana are yielding higher productivity with lesser landholding under wheat cultivation. The increase in production of wheat has been observed in the states of Haryana, Punjab, Madhya Pradesh, and Uttar Pradesh. The normal national productivity is about 2.9 tonnes per hectare. The major wheat-producing states are Uttar Pradesh, Punjab, Haryana, Madhya Pradesh, Rajasthan, Bihar, Maharashtra, Gujarat, Karnataka, West Bengal,

Uttaranchal, Himachal Pradesh, and Jammu and Kashmir (Figure 3). These states contribute about 99.5% of total wheat production in the country. The remaining states, namely Jharkhand, Assam, Chhattisgarh, Delhi, and other northeastern states, contribute only about 0.5% of the total wheat production in the country. Among food grains, wheat in India stands next to rice both in area and production.

Rice India is the second-largest producer and consumer of rice in the world and accounts for 22.3% of global production. Several programs run by the government such as National Food Security Mission (NFSM) launched during 2007–08 and Bringing Green Revolution in Eastern India (BGREI) during 2010–11 increased production and productivity of rice from 96.7 million tonnes and 2202 kg ha 1 in 2007–08 to 105.31 million tonnes and 2393 kg ha 1, respectively, in 2011–12. The NFSM is presently under implementation in 482 districts of 19 states of the country with a view to enhance the production of rice, wheat, and pulses through area expansion and productivity enhancement, restoring soil fertility and


Production (percentage)

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33.7

35 30 25

21.2

20 12.9

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6.2 1.7

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1.2

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States Figure 3 Share of states in India for production of wheat.


25

20

15

4 13

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3 20

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Year Figure 4 Status of maize production in India.

productivity, creating employment opportunities, and enhancing farm level economy to restore confidence of farmers. The basic strategy of the mission is to promote and extend improved technologies that is, seed, micronutrients, soil amendments, integrated pest management, farm machinery, and resource conservation technologies, along with capacity building of farmers with effective monitoring and better management in the high-potential districts to bridge the yield gaps. BGREI aims to increase rice productivity by intensive cultivation through promotion of recommended agriculture technology and a package of practices by addressing the underlying constraints of different agroclimatic subregions. It is under operation in seven states including Uttar Pradesh, Jharkhand, Bihar, West Bengal, Assam, Orissa, and Chhattisgarh. Rice contributes to more than 40% of total food grain production and is cultivated throughout the country. Rice production in India shows a steady upward trend, but it is subjected to wide year-to-year fluctuations compared to wheat, as a significant portion of the crop is not irrigated. Indian Basmati rice is traditionally grown in Punjab, Haryana, and western Uttar Pradesh. With the introduction of high-yielding PUSA 1121 variety, India’s long-grain basmati rice production has been

improving, and its cultivation has spread to other parts of Uttar Pradesh and Madhya Pradesh.

Maize After rice and wheat, maize is emerging as the third-mostimportant crop in India. Its importance lies in the fact that it is used for human food as well as animal feed, and it is also widely used for the starch industry, oil production, baby corns, and so on. However, despite the production strength, Indian corn yields are significantly below the yields in major cornproducing countries. There is immense scope for an increment in India’s corn production by increasing the area under hybrids, adoption of better genetics, and improved agronomic practices. Maize is primarily a kharif crop (summer season’s crop) with 85% of the area under cultivation and accounting for 9% of total food grain production. In India the CAGR (cumulative annual growth rate) of maize production has been 5.5% over the last 10 years from 14 million tonnes in 2004–05 to 23 million tonnes in 2013–14 (Figure 4). There was a decline in the production of maize during 2009–10 due to drought conditions in India.


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Years Figure 5 Yield and area under cultivation of maize. Area (Hectares)


Yield (Kg/Hectare)

3000 2500 2000 1500 1000 500 0

2007-08

2008-09

2009-10

2010-11

2011-12

2012-13

Year Figure 6 Area, production, and yield of barley in India.

In Figure 5 area under maize cultivation, yield, and CAGR of area are mentioned. During the last decade (2004–05 to 2013–14), CAGR of the area under maize cultivation has increased 2.5%, and cultivated area increased from 7.5 million hectares in 2004–05 to 9.4 million hectares in 2013–14. Factors such as adaptability to diverse agroclimatic conditions, lower labor costs, and lowering of the water table in the rice belt of India have contributed to the increase in acreage of maize. Productivity of maize has accelerated at a CAGR of 2.9% from 1.9 million tonnes per hectare in 2004–05 to 2.5 million tonnes per hectare in 2013–14. Yield of maize increased by 20% due to introduction of single-cross hybrid seeds coupled with adequate rainfall in 2007–08. In India 85% of maize production and 80% of the area under cultivation come from nine states viz. Karnataka, Andhra Pradesh, Tamil Nadu, Rajasthan, Maharashtra, Bihar, Uttar Pradesh, Madhya Pradesh, and Gujarat.

Barley Barley is the fourth-most-important and most adapted crop of all cereals. It is used for both feed and food. A shift in the food

habits and lifestyle has reduced the demand for barley for human consumption, thereby causing the area in cultivation of barley to plummet during last few decades. Barley is utilized for beer, food processing, and feed industries apart from direct human consumption in India. Recently, a rise in demand for beer in urban India has directly increased the demand for barley malt from Indian beer manufacturing industries. The country is self-sufficient in barley production, although production is low, besides exporting 0.1–0.2 million tonnes of barley annually. In recent years, India’s annual production has been stagnant at 1.2–1.5 million tonnes, with production in 2012–13 at 1.74 million tonnes against 1.61 million tonnes reported last year. Similarly, the area under cultivation has also remained stable at 600–700 ha, with a per-hectare yield of 2508 kg (Figure 6). In India, major barley-growing states are Uttar Pradesh, Rajasthan, and Madhya Pradesh, with a contribution of 34%, 30%, and 12%, respectively, in total acreage. Compositely, these states hold about 80% of the whole acreage (Figure 7). Rajasthan ranks second in terms of acreage under barley and holds first place in terms of production due to a higher yield level. Rajasthan accounts for 40% of total production of


Uttar Pradesh 16% Rajasthan 34%

4% 4%

Madhya Pradesh

12%

Himachal Pradesh Haryana 30% Others

Figure 7 Area under cultivation of barley in various states of India.

Rajasthan

371

protein, which is almost twice the protein in wheat and three times that of rice. India is the leading producer in the world with 25% of the total share and is also the largest importer and consumer in the world. Major pulses grown in India include Bengal gram or gram, red gram, lentil, black gram, green gram, moth bean, horse gram, cowpea, and faba bean. Most popular among these are Bengal gram, red gram, lentil, black gram, and green gram. Madhya Pradesh, Maharashtra, Uttar Pradesh, Andhra Pradesh, Karnataka, and Rajasthan are the major states growing pulses in India. These six states contribute 70% of total pulse production and area. The country has achieved a record pulses production of 19.57 million tonnes in 2013–14 compared to 18.34 million tonnes in the year 2012–13. Production of all the pulses, as a whole has been increasing year after year except for a downturn in 2011–12. The production of black gram only has been estimated to decline from 1.9 million tonnes in 2012–13 to 1.5 million tonnes in 2013–14.

9% 5%

Uttar Pradesh

Consumption of Food Grains

Madhya Pradesh

In India the rate of growth of population and food grains production for last five decades are illustrated in Figure 9. It has been observed that the population growth rate has seen a downfall from 2.24% to 1.03%. The overall rate of production of food grains has also declined, with a rise only during the period from 1981–91. During 2004–05 total cereal consumption showed a rise of about 100 g per person per month in rural areas and a fall of 350 g per person per month in urban areas. The per capita consumption trend of grains such as sorghum, pearl millet, and maize has been higher in the rural sector as compared to a declining trend in consumption of major grains like rice and wheat. The cereals other than rice and wheat contributed 1 kg per person per month in rural India and 0.8 kg per person per month in urban India in 2011–12. The consumption of all food grains per person in the rural areas is projected to decline from 15.3 kg per month in 2000 to 13.8 kg per month by 2050 and to only slightly decrease from 11.8 to 11.6 kg per month in the urban areas. It has been estimated that due to rapid urbanization, per capita consumption of food grain in India will decrease from 14.4 to 12.7 kg per month over the next 50 years. However, total food grain demand is projected to increase from 16.7 to 19.9 kg per month over the next 50 years due to increment in the demand of feed grain. The total grain demand will increase from 201 million tonnes in 2000 to about 291 and 377 million tonnes by 2025 and 2050, respectively. The major diet of the Indian people is vegetarian, and food grains are considered the main components of their diet, although some variation in diet is found across different parts of India. Wheat is the principal choice of food grain in the north followed by rice. Wheat comprises half of the total grain consumption in the west followed equally by rice and other coarse cereals together. Wheat is the staple food in India mostly consumed in the form of homemade chapattis or rotis (unleavened flat bread) using atta (whole wheat flour). Wheat is also consumed as bakery products like pan breads, cakes, biscuits, cookies, and crackers.

6% 40% 9% Haryana Punjab 31% Others Figure 8 Barley productions in Indian states.

barley followed by Uttar Pradesh (31%), Madhya Pradesh (9%), and Haryana (6%; Figure 8).

Coarse Cereals Crops like sorghum, millets, ragi, and other small millets (kudo, kutiki, sanwa, and foxtail) termed as coarse cereals have been the primary components of the food basket of rural India. Rain-fed regions of India like Karnataka, Maharashtra, Tamil Nadu, Madhya Pradesh, Rajasthan, and Gujarat are best suited for coarse cereal crops, and coarse cereals are therefore cultivated predominantly in these areas. A downturn has been witnessed in the area covered under coarse cereals cultivation from 29.03 million hectares in 2004–05 to 26.42 million hectares in 2011–12. Significant increases in the yield of coarse cereals has been witnessed from 1153 kg ha 1 in 2004–05 to 1591 kg ha 1 in 2011–12. Production of coarse cereals in 2004–05 was 33.46 million tonnes, which increased to a maximal level of 43.40 million tonnes in 2010–11 but decreased slightly to 42.04 million tonnes in 2011–12 mainly because of a shift in area of cultivation to other competing crops.

Pulses Pulses complement the staple cereal in the diet as a gifted source of proteins, essential amino acids, vitamins, and minerals among the vegetarians in India. They contain 22–24%

372


Population

Foodgrain Production

Growth rate (Percentage)

6 5 4 3 2 1 0

1961-71

1971-81

1981-91 Years

1991-01

2001-11

Figure 9 Growth rate of population and food grain production in India.

Rice is consumed as the main food grain in the south and the east followed by wheat in the east and coarse cereals in the south. Rice consumption in 2013–14 was estimated at 95.0 million tonnes compared to 93.5 million tonnes in 2012–13, a modest increase of 1.5%, almost equal to the population growth rate of 1.4% per annum. Monthly rice consumption in India declined to the extent of 400 g in rural and 220 g in urban areas from 6.38 to 5.98 kg to 4.71 to 4.49 kg during, respectively, the period from 2004–05 to 2011–12 in rural and urban areas, respectively. On the contrary, monthly consumption of wheat showed a slight increase of about 100 g per person in rural areas and a fall of 350 g in urban areas during the same period. Direct human consumption of maize has been reduced over the years. In 2012–13, consumption of maize in the form of human food was only 20%, and it is estimated to decline further due to rising per capita income and commercialization, which has made cereals like wheat and rice more preferred and affordable. Maize is the basic raw material utilized for starch manufacturing and increasing commercial demand from poultry and starch industries leading to higher farmer realization. The remarkable portion, that is, 47% of total maize production is used for poultry feed processing because it possesses good nutritional value. Out of the total production of maize, 12% is for starch manufacturing, 14% for cattle feed, and 7% for brewery and food processing (Figure 10). Maize contains 60–65% starch content and hence cannot be easily substituted by other commodities for starch manufacturing. Barley was the staple food for many countries until wheat supplanted it, resulting in the deceleration of human consumption of barley with time. A wide variety of barley products known to be suitable for human consumption includes porridge, muesli, cookies, barley flakes, muffins, breads, and pasta. Barley, being a good source of protein, is used as a feed for livestock. Barley is used as animal feed in the form of rolled, ground, flaked, or pelleted grain. Barley is also used in alcoholic beverages like beer and wine in the form of malt. Apart from this, malted barley is also used as flavors, sweeteners, malt extracts, malt flours, and so on. In India total malt production is around 3.5 lakh tonnes, but the demand of beer and

Poultry

7% 12%

Direct Consumption 47% 14%

Cattle Feed Starch manufacturing

20%

Food Processing

Figure 10 Utilization of maize in India.

malt is increasing at the rate of 10% annually; to meet this demand, the area and production of the barley needs to be increased. Economic growth has continued to fuel increased pulse consumption in recent years. Consumption in 2014–15 is forecasted higher at 22.5 million tonnes compared to 21.5 million tonnes last year on continued strong domestic demand for the rising Indian population. Monthly consumption of pulses and their products increased from 705 to 783 g in the rural sector and from 824 to 901 g in the urban sector for this period. The growth in the pulses consumption was attributed mainly to the increase in the consumption of split gram, whole gram, peas, and besan (Bengal gram flour) to the extent of 69 g in the rural sector and 57 g in the urban sector. The nongrain food crops and animal products contributed 27% and 8%, respectively, of the total caloric requirement. The meat consumption in India is very low due to cultural and religious reasons, and most of the calories from animal products are obtained from milk and milk products.

Future Consumption Trend The emerging food consumption trends in India have been illustrated by many authors. They have claimed that in recent decades there has been a clear transition from grain

GRAINS AROUND THE WORLD | Production and Consumption of Grains: India consumption to nongrain food and animal product consumption. Rath suggested that the per capita grain consumption will further decrease due to the reduction in physical labor requirement in rural areas due to the adoption of more mechanized and modernized agriculture. Furthermore, improving medical facilities and infrastructure also contribute to the reduction in energy requirements and thus less cereal consumption. It has been suggested that a reduction in the intake of food grains on this account should not be taken as deterioration in human welfare. Sustained economic growth and changing lifestyles are accounting for a significant shift in Indian food culture that is inclined toward high-value horticultural and animal products and away from staple food grains. Rising per capita income and urbanization are leading to a dietary transition primarily from cereals with low-price calorie foods (foods such as wheat and rice with low price and rich in carbohydrates) toward highprice calorie foods like livestock products and processed or ready-to-eat products. The transitions are also attributed to farming patterns, as farmers are adopting new technologies that have resulted in an increase in farm productivity. In accordance with Engel’s law, as the earnings of people rise, the cheaper source of energy for living, which comes from the staple food consumption, is likely to drop. A decline in cereal consumption is substituted with the increased consumption of high-value commodities. Over time the shifting of cereal consumption pattern will be prominent across all households in different expenditure groups. The devolution in cereal consumption can also be credited to the diversification of food production, easy access of high-value commodities, and switching tastes and preferences. This agrees with the arguments by Kumar and Mathur that the demand for food is not only influenced by the income of a person but also by differences in urban and rural lifestyles, the development of more advanced marketing systems, and occupational changes are closely linked with increasing per capita income. Tastes and preferences are also moving toward high value commodities. With the availability of cash money and high-value commodities in the food basket, the decline in calories by reduced cereal consumption is partly compensated for by intake of highly nutritive and vitamin-rich food products. Some other studies have also attributed the change in per capita consumption of cereals to economic growth, rise in per capita income, urbanization and preferences, market integration, and many more as the dominating factors.

Exercise for Revision

• • • •

How has Indian agriculture been successful in changing its face postindependence? In what ways has the Indian government contributed to the growth of agriculture in India? What factors govern the changing consumption patterns of food grains in India, and how is it changing? What is the total production of different grains in India, and which are the major grain-producing states?

373


• • •

Why are India’s food grain production and productivity still lagging behind? What would be the implications of economic development and urbanization on the food grain consumption patterns of the Indian population? What would be the effects of switching consumption patterns on the future production estimates of grains?

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Grains Around the World: Grain Production and Consumption: Overview; The Basics: The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Maize: Overview; Rice: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Amarasinghe UA, Shah T, and Singh OP (2007) Changing consumption patterns: Implications on food and water demand in India. Colombo, Sri Lanka: International Water Management Institute, 43 p. (IWMI Research Report 119). Annual Report, 2011–12. Department of Agricultural Research (DARE) & Education/ Indian Council of Agricultural Research (ICAR). Bansil PS (1999) Demand for foodgrains by 2020 AD. New Delhi: Observer Research Foundation. Directorate of Economics and Statistics, 12–13. Department of Agriculture and Cooperation, Ministry of Agriculture, Government of India, New Delhi. Kumar P and Mathur VC (1996) Structural changes in demand for food in India. Indian Journal of Agricultural Economics 51(4): 664–673. Kumar P and Mathur VC (1997) Agriculture in future: Demand and supply prospective. In: Desai BM (ed.) Agricultural Development Paradigm for the Ninth Plan Under New Economic Development. New Delhi, India: Oxford and IBH Publishing. Mittal S (2007) What affect changes in cereal consumption? Economic and Political Weekly: 444–447, February. National Sample Survey (NSS)-68th round July 2011-June 2012. Household consumption of various goods and services in India, Government of India. Radhakrishna R and Ravi C (1990) Food Demand Projections for India. Hyderabad: Centre for Economics and Social Studies. Radhakrishna R and Ravi C (1992) Effects of growth, relative price and performances of food and nutrition. Indian Economic Review 27: 303–323. Rao CHH (2000) Declining demand for foodgrains in rural India: Census and Implications. Economic and Political Weekly, January 22. Rath N (2003) Linking of rivers: Some elementary arithmetic. Economic and Political Weekly: 3032–3033, July. Singh SK (2014) Grain and feed annual, India. Global Agricultural Information Network (GAIN) report-IN4005. The Economic Survey 2014–15, Agricultural and Processed Food Products Export Development Authority (APEDA). The Tribune, Chandigarh, February 21, 2014. Sale of beer on the rise, scientists for contract farming of barley.

Relevant Websites faostat.fao.org – FAOSTAT, data.

Grain Production and Consumption: China and South-East Asia H Corke and YZ Cai, The University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition volume 2, pp 77–86, ã 2004, Elsevier Ltd.

Topic Highlights

• •

• •

Asia is characterized by high and increasing populations, and limited and declining areas of arable land. Asian countries have to balance a desire for food selfsufficiency requiring great agrotechnical and social resource commitments, with an openness to import staple grains which carries political risks such threat of sanctions or boycott. The Green Revolution of the 1960s, greatly increasing rice and wheat yields in Asia, and transforming India into a grain exporter, led to greater optimism about longterm prospects for food production. China’s production and consumption, and China’s increasing demand for meat and other animal products, will continue to be a major driver of global grain production and marketing.

The General Problem

Learning Objectives

• • •

To understand the scale of Asian grain production, the population and land pressures, and the necessity for most Asian countries to pursue substantial self-sufficiency in grain production. To understand the significance of the Green Revolution for Asian grain production. To understand the relationship between demand for meat and demand for grain. Without agriculture, there is no stability, without grain, there is chaos. Deng Xiaoping

Introduction Several factors make Asian grain production and consumption key to understanding the global balance of grain exports, imports, and food sufficiency. Asia has the world’s two most populous countries, China with 1.2 billion people, and India with 1 billion and on track to exceed China in population within 20–30 years. Asia is the dominant producer of rice, yet an insignificant amount enters world grain trade. Asia is a major net importer of wheat and soybeans, thus influencing decisions about quality priorities in exporting countries. Asian countries have tended to aim for grain self-sufficiency for reasons of agrarian stability, foreign currency conservation, and independence from political restrictions on their imports from major western producers. Major successes in grain production over recent decades have increased confidence in regional capability

374

to seek continuing technological solutions to create everincreasing productivity. This confidence has been dented by stalling yield gains, especially in overexploited rice soils, and by industrialization and urbanization, which absorb agricultural land and compete for water resources. This article will discuss these issues, focusing on three major themes: (1) statistical patterns of grain production, import, and export; (2) the impact and aftermath of the Green Revolution in wheat and rice production; and (3) the role of China as a consuming giant in an era where small-scale grain production makes less economic sense, and where increasing prosperity drives demand for grainintensive animal product consumption. Asia is a diverse region with many countries of widely differing land area, population, and specific problems. These will not be discussed separately, but the main issues will be presented by discussion of the few of the biggest countries.

Although rice is the staple crop for half the population of the world, only 2% of total production is traded on international markets. The principle of national production for domestic consumption has driven most Asian countries to aim primarily for self-sufficiency (although some countries such as Thailand and India are rice exporters). In many countries, such as Philippines, self-sufficiency is difficult to achieve. Populations are increasing; people are increasingly moving off the land to the cities; water supply is not sufficient to produce the possible three harvests per year on the rice paddies; every flat arable piece of land is already in production, so major land-use changes tend to be those taking land out of production. In the Philippines and elsewhere, rice has in many areas been grown continuously in the same fields for centuries. It had long been supposed that atmospheric and water-borne mineral and trace element additions to the soil are sufficient to allow indefinite maintenance of soil fertility, requiring only macronutrients and water for each new crop. But results of long-term field experiments analyzed at the International Rice Research Institute (IRRI) near Manila showed that across Asia, for irrigated rice systems, the soil base has been depleted of nutrients by continuous monoculture. The result of this is that the same variety responds less to the same level of added nitrogen. In other words, improved varieties and production methods are needed simply to maintain current yield levels. In future, expanded use of hybrid rice varieties using Chinese technology may increase yield per unit area but also further increase mineral depletion and biomass removal from the field. Philippines has achieved approximate self-sufficiency in rice in 2004 but this may be transient; demand will continue to increase, and energyintensive inputs will still be required. Farmers who produce rice on small pieces (typically 2 ha) of rented land will continue


http://dx.doi.org/10.1016/B978-0-12-394437-5.00045-0

GRAINS AROUND THE WORLD | Grain Production and Consumption: China and South-East Asia to seek lives with less physical hardship and better incomes elsewhere. In a 1996 interview, K. Lampe, then Director General of IRRI, summarized the problems of developing tropical Asian economies such as Philippines.

In 30 years from now we will have for example in the Philippines 120 million people, 60 million more than today. How to feed them, nobody seems to care. Over the last 30 years rice has had to increase to such an extent that 600 million people can eat rice today who otherwise would not be able to. Another 30 years and we are predicting a world population of more than 8 billion people. More than half of them will be rice eaters. A prediction from United Nations data is that about 400 million people will move over the next 10 years from rural areas in Asia to the big cities. What will happen is that the belt of poverty around these mega-urban conglomerations will become most probably unbearable. And what we will face is most probably social unrest of unprecedented magnitude. Our task is to grow more rice on less land with less fertilizer, less pesticides, and less labor, because producing rice is one of the most tedious tasks for a farmer.

Production Statistics Using the Food and Agriculture Organization of the United Nations (FAO) definition of “Asia,” the population of Asia has more than doubled in the past 40 years (Figure 1), and is dominated by its two most populous countries (China and India). The population of China is more or less under control, such that India is likely to overtake it as the world’s most

Population (million)

5000

China India Kazakhstan Saudi Arabia Indonesia Iran Mongolia Pakistan Turkey Myanmar Others 0

20

0

40

40 60 Land area (10 Mha)

80

100

160

200

Pakistan Indonesia Thailand Iran Myanmar Bangladesh

Asia

4000 3000 2000

China

Others

1000

India

0 1950 1965 1980 1995 2010 2025 Years Land area (ha per capita)

populous nation in the not too distant future. The limited land supply (an index of population density) in China is going to be matched across Asia as a whole as the population of the rest of Asia continues to increase (Figure 1). Although the population density of India is greater than China, the supply of arable land is also greater (Figure 2). Widely quoted figures are that China has 22% of the world’s population but only 7% of the world’s arable land. This creates a stark problem – how to feed 5 billion Asians in 25 years time without increased supply of high-quality land (indeed, with high-quality land continuing to be lost to urbanization and industrialization). Six Asian countries had populations of 100 million or more in 2001 (Figure 2). Their agricultural populations accounted for 43–66% of their total population, except for Japan, which had only 3.6% of its people engaged in agriculture. Japan, as a highly advanced economy which is already committed to food import rather than food self-

India China Turkey Kazakhstan

6000

1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 0.3 0.1 1950

375

2040

2055

China India

total pop. (M) agric. pop. (M) 0

1980

1995 2010 Years

2025

120

China India Indonesia Pakistan Bangladesh Japan Vietnam Philippines Iran Turkey Others

Aisa

1965

80

Arable land (Mha)

2040

2055

Figure 1 Estimated population (1950–2001) and land area per capita (1961–2000) of all Asia, China, and India, with projections till 2050.

200

400

600

800

1000

1200

1400

Population (million)

Figure 2 Land area, arable land, and total and agricultural populations of top ten population countries in Asia in 2001. (Data from FAOSTAT Database).

376

GRAINS AROUND THE WORLD | Grain Production and Consumption: China and South-East Asia

sufficiency, has substantially different problems from other Asian countries. It focuses on managing the quality and suitability of its imports, and on maintaining a domestic agricultural sector (e.g., a meat industry using imported grain), which competes poorly on price but which is politically and socially important. China produces 41% of Asian grain on 26% of the area under cultivation; India produces 22% on 30% of the area (Figure 3). This reflects a wider adoption of intensive cultural practices and some favorable environmental factors in China. Indonesia, another highly populous country, also has greater production per unit area than the average for Asia, whereas Thailand shows below-average production. These figures can be used to indicate possible areas for greater technology adoption and hence increased production using existing land under cultivation. How is Asia’s one billion tonnes (Gt) annual grain production distributed across crops? Asia is well-known for rice production, and for the widespread dietary cultures based on rice consumption. Indeed, more than half of Asian grain production is rice (Table 1, Figure 4) with 523 million tonnes (Mt) in 2002. Other than for India, Asia is less well known as a wheat producer, yet more than 44% (Table 2) of global wheat production is from Asia, and China is by far the largest wheat producer in the world. Maize production at 166 Mt, again

India China Indonesia Turkey

predominantly in China, is substantial. China ranks second to the US in maize production. It is interesting that the center of origin of maize is in America (Mexico) but it has become globally widespread and successful, including in Asia. However, soybean, a crop originating in Asia, is more commercially significant in the US than in Asia. Sorghum and millets are significant crops in arid parts of Asia, typically areas of China and India too dry for maize production. Many local traditional uses of these cereals have developed, for example typical use of sorghum in China is in distilled alcoholic beverage production. Buckwheat also has a significance beyond its relatively small production, with uses in traditional “soba” (Japanese buckwheat noodles) and some Chinese traditional foods such as noodles, vermicelli, and fermented vinegars. Barley is a substantial crop, fourth after maize, partly reflecting China’s rise to rank first in the world for beer production. Asia’s grain imports in 2001 were worth about US$ 25 billion, and exports about $8 billion (Table 2). Imports were dominated by wheat, maize, and soybean, and exports by rice. Industrial, processed food, and feed uses predominate for maize and soybean. The unique properties of wheat flour make it impossible to substitute with any other grain. Strong demand for wheat supplies exists for traditional uses (e.g., noodles and steamed bread in northern China and other temperate Asian countries). Economic development also tends to

29.7% 26.4% 4.9% 4.6%

Pakistan

3.9% 3.9% 3.7%

Bangladesh Thailand

2.7%

Vietnam

2.2% 2.1%

Myanmar Philippines

14.1%

Others 0

20

40 60 Harvested area (Mha)

80

China

100

40.8%

India

21.7%

Indonesia

6.2%

Bangladesh

4.0%

Vietnam

3.7% 3.2%

Turkey Thailand

3.1%

Pakistan

2.7% 2.3%

Myanmar Philippines

1.8% 10.5%

Others 0

90

180

270

360

450

Grain production (Mt) Figure 3 Harvested area and grain production of top ten grain-producing countries in Asia in 2002. Data from FAOSTAT Database. Percentage (%) is based on total harvested area or total grain production in Asia.

GRAINS AROUND THE WORLD | Grain Production and Consumption: China and South-East Asia Table 1

377

Area, production, and yield of grains (cereals, soybeans, and pulses) in Asia (2002)a Area harvested

Production

Crop

Mha

% of Asia total

Mt

% of Asia total

% of world total

Yield (kg ha 1)

Countries (number)

Cereals, total Paddy rice Wheat Maize Barley Millet Sorghum Buckwheat Rye Oats Triticale Others Soybeans Pulses, total

307 131 96.1 42.7 11.8 11.4 11.4 0.9 0.7 0.7 0.5 0.2 17.1 36.3

100 42.6 31.3 13.9 3.8 3.7 3.7 0.3 0.2 0.2 0.2 0.1

986 523 253 166 19.4 9.1 11.0 1.4 1.1 1.1 1.2 0.2 23.7 25.6

100 53.1 25.6 16.8 2.0 0.9 1.1 0.1 0.1 0.1 0.1 0.0

48.6 90.8 44.1 27.5 14.7 39.0 20.2 65.2 5.2 4.3 10.9 2.6 13.2 46.4

3209 3998 2629 3884 1645 803 959 1451 1467 1543 2320 2641 1385 706

47 30 37 39 33 20 20 6 11 15 1 11 25 40

a

Data from FAOSTAT Database.

400 350

250

China Bangladesh India Indonesia

200 Rice production (t)

Total grain production (t)

450

300 250 200 150 100

China India Thailand

Bangladesh Indonesia Vietnam

150

100

50

50 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years 140

100

China Iran Pakistan

India Kazakhstan Turkey

120 Maize production (t)

Wheat production (t)

120

80 60 40 20

100

China Indonesia Thailand

India Philippines Turkey

80 60 40 20

0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

Figure 4 Trends of yield production in major Asian countries producing principal cereal crops from 1961 to 2002. (Data from FAOSTAT Database).

increase demand for wheat products (e.g., baked bread) at the expense of rice consumption. Thus, many tropical Asian countries that do not produce any wheat require substantial imports (e.g., Philippines, Indonesia, Malaysia). Country data (Table 3) show that Japan is the largest net importer of grain in Asia. Its demand is likely to be stable, due to constant (or slightly declining) population and its advanced economic status

(far past the rapid growth stage) and therefore stable dietary patterns. China was a major importer but also a significant exporter (in 2001). But its import–export pattern is highly variable, as slight percentage changes in its large production base, will cause dramatic changes in its import needs and export capacity (Figure 7). India was a net exporter in 2001, and should be able to maintain this capability in the short

378


Table 2

Quantity and value of grain imports and exports to/from Asia in 2001

Crop

Imports – qty (Mt)

Imports – value (1000 US$)

Exports – qty (Mt)

Exports – value (1000 US$)

Cereals Maize Wheat Barley Rice Sorghum Rye Oats Buckwheat Millet Triticale Others Soybean Pulses

106 478 996 40 913 789 40 238 186 10 117 996 9 426 314 2 015 717 381 226 112 604 104 668 65 854 251 3 102 391 28 045 849 4 463 201

16 732 160 5 076 869 6 760 921 1 490 596 2 623 935 233 845 46 196 20 100 25 227 15 188 74 439 209 6 025 734 1 468 603

38 394 615 7 013 319 7 906 977 436 870 19 798 418 20 587 15 983 5597 104 491 45 735 25 528 3 021 110 366 951 2 636 496

7 057 804 759 271 896 782 40 048 4 902 134 3061 2065 701 20 365 9099 5653 418 625 109 096 1 065 219

Table 3

Top ten Asian countries of grain (cereal and soybean) imports and exports in 2001 Import quantity

Export quantity Top ten export countries

Asia, total 1. Japan 2. China 3. Korea 4. Iran 5. Indonesia 6. Saudi Arabia 7. Malaysia 8. Philippines 9. Iraq 10. Israel

134.5 31.1 26.3 13.7 10.4 5.9 5.1 4.4 4.2 4.0 3.6

100.0 23.1 19.6 10.2 7.7 4.4 3.8 3.3 3.1 2.9 2.6

25.8

19.2

Asia, total 1. China 2. Thailand 3. India 4. Vietnam 5. Kazakhstan 6. Pakistan 7. Turkey 8. Myanmar 9. Japan 10. United Arab Emirates Others

Others

term. Other countries have adopted a policy that will see sustained dependence on imports, some not having any economic reason or climatic suitability to pursue self-sufficiency (e.g., Saudi Arabia). Sustained import markets are the easiest for exporters to deal with – they can develop relationships with the buyers to understand quality needs and develop long-term policies to meet these needs. Erratic, but large purchases, on international markets are more difficult to handle efficiently. Total cereal production has risen fairly steadily across Asia as a whole since 1960 (Figure 4) (despite Chinese production in the last 5 years, although high, has been more variable than in the past). This reflects improved varieties and agronomic practices (under the Green Revolution, discussed below), but also expansion of cultivated area under the multipronged approaches adopted to cope with vast increases in demand. The situation has become rather less stable in more recent years (Figures 4 and 5), with substantial drops in production of cereal grains other than the big three, namely, rice, wheat, and maize. In fact, between 1992 and 2002 total production (output) increased only 6%, whereas area harvested

Mt

Percentage (%)

Top ten net import countries

Mt

Percentage (%)

38.8 9.3 8.2 5.4 3.8 3.6 3.4 1.6 1.0 1.0 0.5

100.0 23.9 21.2 14.0 9.8 9.2 8.6 4.0 2.7 2.6 1.3

Asia, total 1. Japan 2. China 3. Korea 4. Iran 5. Indonesia 6. Saudi Arabia 7. Malaysia 8. Philippines 9. Iraq 10. Israel

95.8 30.1 17.1 13.7 10.4 5.8 5.1 4.3 4.2 3.9 3.6

100.0 31.4 17.8 14.3 10.8 6.1 5.4 4.4 4.4 4.1 3.7

1.1

2.8

2.3

2.4

Others

30 Change during 1992–2002 (%)

Percentage (%)

20 10

harvested area grain production

0 –10 –20 –30 –40 –50 –60

er ea l Ri s, t ce ot , p al ad d W y he a M t ai ze Ba r So ley rg hu m M Bu ille ck w t he at Ry e O at Tr s iti ca O le th er s

Mt

C

Top ten import countries

Net import quantity

Cereal crops in Asia Figure 5 Change in Asian grain production and harvested area of total cereals by crop over the past decade (1992–2002). (Data from FAOSTAT Database).

GRAINS AROUND THE WORLD | Grain Production and Consumption: China and South-East Asia decreased 8%. Although this reflects a healthy improvement in yield per unit area, it underscores worrying trends. One is the diversion of agricultural land to noncereal uses, offering higher returns to farmers, and another is the steady loss of high-quality agricultural land. In many places, such as in parts of China, production of grain on small family-based farm units is no longer economically attractive. Other agricultural activities – vegetables, meat production such as ducks, or even flower production may be preferable. In some cases, land may be left idle while the landholder pursues nonagricultural business activities. These shifts are often beneficial in raising the living standards of rural families. But they also show that more or less open markets, keeping grain prices near world levels, are certainly incompatible with full self-sufficiency in grain.

The Green Revolution “India has all the food it needs, but half of it is currently being eaten by rats,” according to a western aid official quoted in a Financial Times report of December 2002. In the three years up to 2002, India’s reserve of rice and wheat increased from 20 to 60 Mt, relative to an annual production of 220 Mt. Half of Indian children are underweight, and many are malnourished. India has seemingly solved one problem – the technological problem for which the solution began with the Green Revolution – only to be left with a perhaps more intractable problem, that of creating an economic system that distributes food equitably and without undue wastage. Development of dwarf wheat that could sustain high fertilizer inputs and thus produce high grain yields without lodging began at International Center for the Improvement of Maize and Wheat (CIMMYT) in Mexico in the early 1960s. At that time, India’s wheat production was low ( 10 Mt per year) and static, showing only random seasonal fluctuations from year to year. Like most low-income, high-population countries, population growth was much more rapid than growth in food production, and a social catastrophe seemed imminent. The dwarf wheat from Mexico was introduced to India, through a system of demonstration fields and a supporting package of technology that emphasized to farmers the uniqueness of the new varieties, and the necessity of growing them with the high inputs of water, fertilizer, and other agricultural chemicals. From the mid-1960s, wheat production in India began to increase rapidly, outstripping growth in population – and leading to the present day problem of distribution of excess production. Over a 20-year period (1961–80), overall food production increased 3.6% per year in Asia as a whole, from 1981 to 2000 (sometimes referred to as “Late Green Revolution”), it increased 2.1% per year. Thus, we should consider the adoption of high-yielding, high-input wheat varieties as the beginning of an agricultural transformation, and not as an abrupt one-time revolution. Present-day technologies may be seen as contributors to the same continuum of progress. If production increases in the range of 2–3% a year, clearly limiting the population growth to less than this is the key to increased production per person. Shortly after the dwarf wheat varieties came into use, a parallel development started with dwarf rice varieties, distributed from IRRI Philippines. G. S. Khush, the IRRI plant breeder

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responsible for much of development of these rice varieties, summarized their biological features:

• • • • • •

reduction in plant height (improved harvest index) and higher biomass, photoperiod insensitivity (can grow any time of year) and short growth duration (110 days), increased yield stability through disease and insect resistance (biotic stresses), tolerance to adverse soil conditions (abiotic stresses), eating quality, and comprehensive agronomic knowledge on crop management, e.g., nutrient requirements, water management, mechanization techniques, and equipment.

These technical inputs alone were not enough. As with wheat in India, production conditions had to be improved. The main factors associated with this are:

• • •

Increased provision of irrigation facilities, Availability of inorganic fertilizers, and Supportive government policies

The Green Revolution is a high-input system. There is no “free lunch” or nonenergy intensive way to produce such dramatic increases in production. Central to this is farmer knowledge and participation in a system with higher risks (e.g., use of credit to finance the required inputs) but better rewards (higher economic returns).

The Crisis Grain Supply in China Chinese tradition and the political leadership have a clear understanding of the importance of grain production, from the proverb “Of all things food is the foremost necessity of the people” to the comment by Deng Xiaoping “Without agriculture, there is no stability, without grain, there is chaos.” This has an impact even in relation to Hong Kong: “As long as the overall political situation in China is stable and the economy develops further, we will stand by our agreements and principles agreed with Britain” Qiao Shi (quoted 8 January 1995). This was in relation to the agreed transfer of sovereignty of Hong Kong from the United Kingdom to China from 1997, where substantial autonomy would be granted to Hong Kong (as a “Special Administrative Region”) for a period of 50 years. Pragmatically speaking, if a government cannot feed its population, it cannot maintain the credibility to stay in power and carry out its normal obligations. This issue is all the more pressing in China with its large population, limited area of arable land, and recent memory of the disastrous famine of the early 1960s, which caused the deaths of over 30 million people.

Money, Meat, and Grain The book “Who Will Feed China?” by US environmentalist L. R. Brown, (1995), was perhaps the most influential early study in drawing the attention of western policy-makers to a fairly obvious problem, i.e., grain trade and capacity for global


increases in grain production are limited, economic prosperity increases demand, industrialization reduces production, and the huge population of China makes it the key country where these issues converge. Industrialization and urbanization have many effects on agriculture: 1. Loss of agricultural land to urbanization takes out the productive farmland, and of course that nearest to the centers of population; 2. Increased use of motor vehicles – particularly new opportunities for personal ownership of cars, creates need for expanded highways, roads, and parking systems, which also absorb agricultural land; 3. Competing demands for water reduces that available for agriculture and increases the relative cost; 4. Bringing inferior land under cultivation on the peripheries of existing arable land use results in lower average yields, and increased susceptibility to erosion, salinization, and other environmental problems; 5. The movement of people from rural to urban areas in search of better paying jobs reduces agricultural production capacity; and 6. Intensive land use requires ever-greater input of agricultural chemicals and other energy-based inputs, simply to maintain production. Brown’s book had pointed out that “the entire world cannot reasonably aspire to the US standard of living” and “we cannot afford to keep adding 90 million people a year indefinitely.” In food production terms, the difference between the US and other countries is the total per-person demand for grain. Consumption of animal products – with the animals consuming grain-based feed – makes US per capita grain consumption 800 kg per year. Even Italy, an affluent country with many cultural affinities with the US, has a consumption of only 400 kg per person (and a healthier diet with less obesity). Prediction of China’s future grain consumption – currently 330 kg per person – is the key to preparing to meet future demand. An earlier study “Grain in China” published by the Department of Foreign Affairs and Trade, Australia (1992), had set out in some detail the technical issues related to this. In general, increased prosperity does not lead to large increases in the direct consumption of grain, assuming basic adequacy in dietary energy intake. However, increases in disposable incomes do lead to marked changes in dietary composition, first in the direction of more diversity, and particularly more meat products (and dairy, eggs, fish, etc.). Further increases in incomes will increase consumption of processed foods, meals prepared outside the home, and other convenience options. Taiwan, with a Chinese population of similar dietary customs, can be used as proxy for studying future dietary changes with increased incomes in the Chinese mainland. As mainland China reaches the purchasing-power-adjusted GDP per capita prevailing in Taiwan in the past, the demand for particular food products should also match Taiwan’s at that stage of development. Using data up to 1990, Figure 6 shows that an increase in mainland China’s GDP per capita from $1000 to $2000 would be expected to increase demand for meat by 10 kg per person per year. Such figures are the basis for concern about China’s future needs. An increase in demand from 2003 onwards of a

30 25 Meat (kg)

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20 15 Taiwan China

10 5 200

500

800

1100

1400

1700

2000

2300

GDP (1987 US$) Figure 6 Per capita GDP and meat (pork, beef, and mutton) consumption in China (1977–90) and Taiwan (1952–75). GDP for China is increased threefold to adjust for purchasing power. (Adapted from Garnaut R and Ma G (1992) Grain in China, 151 pp. Canberra: East Asia Analytical Unit, Department of Foreign Affairs and Trade, Commonwealth of Australia).

further 10 kg would represent a need for perhaps 40 Mt of grain (depending on feed conversion ratios and the proportion of grain used in the animals’ diet). Naturally, one way to proceed is to greatly increase meat imports, with the US and Brazil representing source countries with further potential. However, this, to some extent, just shifts the burden of grain production elsewhere (away from Asia), and would deprive farmers in China of added income if they were simply to produce lowcost commodity grain (at low production efficiency) while imports satisfied needs for higher value products. For Asia’s two biggest countries, we can summarize that China’s main driver of demand, for grain, is shifting food consumption patterns (toward meat), whereas India’s main driver of demand is increasing population.

“Food Price Rises May Herald a World Crisis” This November 2003 news item published in the South China Morning Post, Hong Kong, quoted Lester Brown “Sudden food price rises on the [Chinese] mainland could be the sign of a coming world food crisis. I view these as the warning tremors before the earthquake.” Four consecutive years of world grain harvest decline, and historically low world grain stocks since records were kept, could lead to soaring grain prices worldwide. In 2003, wheat prices in northeastern China rose 32%, maize prices by 100%, and rice by 13%. China faced a 40 Mt shortfall in 2003, and the rest of the world, 56 Mt. In an era of global grain trade (Figure 7) and heightened expectations of diminishing barriers to trade, all consumers (nations) will increasingly compete – on price – for the basic staples necessary for survival. Virtually all major grain producers still use price-distorting mechanisms such as farm subsidies (in some countries, payments not to produce grain; in others, artificially high domestic prices, usually coupled with tariffs and quotas to restrict trade). “More than just a hill of beans” headed a Washington Post article of November 2003 (published in The Standard, Hong Kong). This illustrated the complex relationship among farmer


Quantity of imports and exports (Mt)

160

(a)

Imports

Quantity of imports and exports (Mt)

Net imports

140 120 100 80 60 40 20 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years 35

(b)

Exports

Imports

Exports

Net imports

30 25 20 15 10

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General Discussion Is Biotechnology the Answer? Biotechnology can provide plant varieties that are more stressresistant, responsive to appropriate inputs, resistant to pests and diseases (removing the necessity for energy-costly treatments), and are suited to specific end uses. Biotechnology cannot change food production from a “water, dirt, and energy” business into an environmentally stress-free selfsustaining system. Massive increases in food production are needed in the next several decades to keep pace with present demographic trends. Hopefully, population growth will slow and the new plateau in food production will prove to be sustainable. In some ways, biotechnology is distracting governments from the true nature of the problem and from their obligations to act on realistic solutions. Biotechnology has served poorly – if at all – in increasing yields relative to energy inputs. Yield increases over the 40 ongoing years of the Green Revolution have been due to development of varieties that can better sustain such inputs. Limits to population and limits to demand are keys to global food security. Food supply has become too politicized for governments to feel secure placing their fundamental food security in the hands of the most efficient producers. Perhaps the time has come to develop an international treaty guaranteeing free and unimpeded trade in basic foods and medicines, no matter what the prevailing conditions of political conflict or even war between nations.

5 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

Figure 7 Changes in grain (cereals and soybean) imports and exports in Asia (a) and China (b) from 1961 to 2001.

needs, urban consumer needs, and development of grainprocessing facilities in producing-yet-importing markets (China) and exporting but price-distorting markets (the US). Recent Chinese restrictions on soybean imports have increased domestic prices, benefiting farmers in Heilongjiang, the main soybean-producing province. Limited supplies of soy meal have increased prices of pork, and soybean oil has also become more expensive, affecting urban shoppers across the country. Rising meat consumption in China has led to development of a soybean feed-processing industry employing 250 000 people. Restricted imports, for whatever reason, affect their livelihoods. China’s estimated consumption of soybean is 33 Mt, which is projected to rise to 50 Mt within 5 years; in the face of current production of only 17 Mt. Expectations of free trade under World Trade Organization (WTO) are commonly undermined by nontariff barriers. Clearly Chinese imports of soybean – from the US – should continue and a mutually beneficial trade will result. The reasons for the restrictions (safety standards for genetically modified soybeans, and phytosanitary regulations concerning phytophthora) obviously have a strong policy overtone. However, they may be placed in context of the widespread demands from developing economy nations for US farm subsidies and tariffs to be reduced in the same spirit of free trade.

The Future Asia is the key to world prosperity, food security, and stability; or the alternative of massive regional famines. Large increases in grain prices will not much affect consumers in the industrialized west. Like oil-price fluctuations, these will be absorbed into the economy. Grain raw material prices are a small percentage of most consumers’ monthly food costs in these countries. Most Asian countries will be able to absorb any such structural increases in grain prices – albeit with some economic pain during the readjustment. Most of the poorer Asian countries are more or less self-sufficient in grain, or with increasing prices will have the motivation and capability to become selfsufficient. Rapidly industrializing and developing economies – such as China – will combine continued substantial domestic grain production with the capacity to import additional needs through the strength of their export-focused manufacturing industries. Perhaps long-term grain price increases will enable major producers (in North America and Europe) to remove farm subsidies and move to more effective free-market production. An additional 100 Mt, for example, of grain entering world trade (at far higher prices than today) will be an attractive prospect to marketing boards and farmers’ organizations in the US, Canada, and Australia. But these major exporting countries have to look carefully at the environmental costs of meeting such increased demand. The food supply crisis, although arising from western production constraints and Asian demands, will have its most serious consequences in countries, many in Africa, which have limited production, rapidly rising populations, and few competitive exports. Many of these are the same countries that suffered most in

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the oil price crises of the past few decades. With grain more than with oil, the impact of the crisis will be more immediate and drastic on the health and survival of the people of these countries.

Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America.


• • •

Can and should China feed itself? Was the Green Revolution really a success? Argue the pros and cons, focusing on the effect on rural populations in India. How much grain is required to produce one kg of each major meat product?


• • •

How can new storage and supply chain technologies reduce grain losses from farm to consumer? What are the prospects for a new Green Revolution based on genetic engineering? Why is Vietnam a major rice exporter, yet Philippines struggles to feed itself?

See also: Grains Around the World: Grain Production and Consumption: Cereal Grains in North America; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania:

Brown L (1995) Who Will Feed China?, p. 163. New York: W.W. Norton and Company. Cassman KG and Pingali PL (1995) Extrapolating trends from long-term experiments to farmers’ fields: the case of irrigated rice systems in Asia. In: Barnett V, Payne R, and Steiner R (eds.) Agricultural Sustainability: Economic, Environmental and Statistical Considerations, pp. 63–84. London: Wiley. Garnaut R and Ma G (1992) Grain in China, p. 151. Canberra: East Asia Analytical Unit, Department of Foreign Affairs and Trade, Commonwealth of Australia. Kaosa-ard MS and Rerkasem B (2000) The Growth and Sustainability of Agriculture in Asia, p. 303. Oxford: Oxford University Press. Khush GS (1999) Green Revolution: preparing for the 21st century. Genome 42: 646–655. Khush GS (2001) Green revolution: the way forward. Nature Reviews: Genetics 2: 815–822. Wittwer S, Yu Y, Sun H, and Wang L (1987) Feeding a Billion, p. 462. East Lansing, Michigan: Michigan State University Press.

Relevant Websites apps.fao.org http://apps.fao.org – The FAO database on agricultural production and trade statistics is a comprehensive resource and invaluable to researchers working in this area. It has been extensively used in preparation of this article. irri.org http://www.irri.org – Website of the International Rice Research Institute, Philippines. Information and links on sustainable rice production in Asia. worldwatch.org http://www.worldwatch.org – Website of Worldwatch Institute, for “independent research” for an enviornmentally sustainable and socially just society.

Grain Production and Consumption: Europe MG Lindhauer, Max Rubner-Institut (MRI), Detmold, Germany ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • •

Europe is one of the most important cereal producers of the world. Within Europe, the European Union is the dominant cereal producer. Soft (bread) wheat and maize, and to a lower extent barley, rye, oats, and triticale, are the most important grain cereals. In some parts of Europe, rye is the basis for bread making. Other cereals are rice, sorghum, millet, and buckwheat (pseudocereal). The per capita consumption of cereals varies significantly between European countries. Cereal consumption and preference for individual cereals are very much dependent on cultural traditions in diet. Europe is an important producer of pulses (beans, broad beans, peas, and lentils) and to a lower extent of soybeans. Rapeseed and sunflower are important oilseeds. The majority of grains harvested are used for animal feed.

Learning Objective

•

To get an overview of the agronomically important grain species grown in Europe and of their importance in human consumption and other utilization.

Introduction In Europe, grain crop production has a long tradition, and grains of different plant origins are substantial constituents of the human diet and of animal feed since ancient times. For the cultivation of grain crops, of cereals especially, Europe has excellent prerequisites because of its climatic and pedological conditions and its overall efficient agricultural systems. Preference for specific grain crops varies very much among European countries and larger geographic regions owing to the wide cultural multiplicity and ethnic diversity in nutritional habits. Rye may serve as an example. It is a cereal very specific to Europe and hardly grown not only anywhere else in the world but also within Europe; it is projected as a bread-making cereal and animal feed. It is grown almost exclusively in central, northern, and northeastern countries of Europe. Another point of consideration while recording statistical data is that because the European Union (EU) is politically very diverse, it dominates all the markets including the agricultural one. This is the case, although the EU as yet does not include countries like Russia and other countries of the former Soviet Union.


Consequently, data have been prepared and presented with respect to this given political situation but concentrating more on the ‘main players’ to ensure clarity.

Grain Production Cereals In Europe, cereals are by far the most important agricultural crops (Tables 1–4) and among these, wheat is the principal crop (Table 1). Wheat accounts for nearly half of the total quantity harvested in 2012. Grain maize and barley and, to a distinctly less degree, oats, rye, and triticale are also of significance. Triticale, the result of crossbreeding wheat and rye, is in demand in those cultivation areas where normally rye is grown and where farmers are looking for alternatives. All other cereals are of minor importance. The pseudocereal buckwheat – a plant belonging botanically to the Polygonaceae family – was grown throughout Europe until the early 1900s. It had mostly been grown in areas with poor soils and served for the production of grits and for specific traditional dishes such as pancakes and crepes. It has survived as a kind of specialty crop, for example, in Northern Germany, Russia, Austria, and individual Balkan states. In very recent years, there has been a certain rekindling of interest in buckwheat as a functional food in modern nutrition systems because of constituents such as dietary fibers that have been scientifically proved to improve health and avoid diseases in human (animal) metabolism. Rice is produced only in those parts of Europe that have a suitable climate, for example, Spain, southern France, Italy, or Southern Russia. On the European continent, the EU, with its 28 member countries, is the most important cereal producer accounting for almost far more than half of the production of all the cereals, wheat, barley, maize, and rice (Table 2). Most of the triticale is grown in the EU. Among EU member countries, France is the main cereal producer, followed by Germany, Poland, the United Kingdom, Spain, and Italy (Table 3). Variance of data between individual harvest years is due to specific climatic conditions as, for example, in 2010 and 2011 where drought periods during the growth period in major production countries (e.g., France and Germany) resulted in significantly lower cereal yield. Also, it has to be taken into consideration that data generation may differ between individual member states, making comparison of data from different sources sometimes difficult. Growing of cereals is a long-standing tradition in the Russian Federation and in Ukraine, though both countries are yet to utilize their full agronomic capacity (Table 4). Also, when studying production data for single cereals of Russia and Ukraine (Table 4), the role of wheat as the most preferred cereal is underlined. Barley is in the second position

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GRAINS AROUND THE WORLD | Grain Production and Consumption: Europe

Table 1 year 2013

Cereala production (Mt, millions of tonnes) in Europe in the

Wheat, totalb Barley Rye Oats Maize Triticale Sorghum Millet Rice, paddy Buckwheat Mixed grain Cereals, nesc Total cereals

225.486 85.838 14.945 14.526 117.454 13.546 1.156 0.635 3.895 1.333 3.673 0.665 483.138

a

Including the pseudocereal buckwheat. Soft þ durum þ spelt wheat, respectively. c Including inter alia amaranth and quinoa species. Source: FAOSTAT: FAO Statistical Division (2014). b

Table 2 Cereala production (Mt, millions of tonnes) in the European Union (EU-28) in the year 2013 Wheat, totalb Barley Rye Oats Maize Triticale Sorghum Millet Rice, paddy Buckwheat Mixed grain Cereals, nesc Total cereals

225.486 59.844 10.239 8.414 65.056 11.430 0.689 0.113 2.787 0.289 3.652 0.584 306.487

Table 3 Total cereal production (1000 tonnes) in EU member countries in selected years Member country

2009

2010

2011

2012

Austria Belgium Bulgaria Croatia Cyprus The Czech Republic Denmark Estonia Finland France Germany Greece Hungary Ireland Italy Latvia Lithuania Luxemburg Malta The Netherlands Poland Portugal Romania Slovenia Slovakia Spain Sweden The United Kingdom EU-28

5748 3324 6384 3442 57 7832 10 117 874 4261 69 862 49 748 4609 13 579 2063 15 892 1663 3806 189 – 2089 29 827 957 14 801 533 3330 16 914 5250 21 618 298 161

5144 3105 7079 3007 66 6878 8748 678 2989 65 555 44 039 3869 12 256 2040 16 941 1436 2797 166 – 1888 27 228 849 16 651 569 2554 18 941 4287 20 946 280 380

4818 2944 7461 2828 74 8285 8794 772 3668 63 681 41 920 4416 13 669 2509 18 226 1412 3262 150 – 1685 26 767 972 20 777 608 3714 21 167 4646 21 485 291 559

4876 3012 6941 2729 74 6596 9460 994 3687 68 335 45 397 4069 10 299

2125 4657 153 – 1775 28 544 991 12 563 570 3036 16 412 5106 19 515 27 7218a

a

COCERAL (2013). Source: Federal Ministry of Food and Agriculture (ed.) (2013) Statistisches Jahrbuch u¨ber Erna¨hrung, Landwirtschaft und Forsten der Bundesrepublik Deutschland, 57. Jhrg. Landwirtschaftsverlag GmbH Mu¨nster-Hiltrup.

a

Including the pseudocereal buckwheat. Sum of soft þ durum þ spelt wheat, respectively. c Including inter alia amaranth and quinoa species. Source: FAOSTAT: FAO Statistical Division (2014). b

in Russia, and in the Ukraine, it is maize. Rye has a certain importance in Russia but nearly none in the Ukraine. Yields for cereals as a whole and for individual cereal species reveal a higher cultivation efficiency within the EU (Table 5) when compared with respective data calculated on the whole-Europe basis (Table 6) or with data from Russia or Ukraine (Table 7). The reasons for the more efficient agricultural system in most of the European member countries are multifold. Without a doubt, in the majority of the countries, farmers are well educated and experienced and can rely on well-established governmental and private consulting systems. They have unlimited access to production means like fertilizers, pesticides, high-value varieties, and modern technical equipment. After revision of the EU common agricultural market policy in 2007 and thus unlike as in former decades, grain intervention, that is, buying for a fixed threshold price and storing surpluses from the market, has practically come to an end. It has been restricted to the cereal species soft wheat, durum

Table 4 Cereal and pseudocereal production in Mt (millions of tonnes) in the Russian Federation and Ukraine in the year 2012

Wheat Maize Rye Oats Triticale Barley Sorghum Millet Rice, paddy Buckwheat Cereals, total

The Russian Federation

Ukraine

37.72 8.21 2.13 4.03 0.46 13.95 0.05 0.33 1.05 0.80 68.77

15.76 20.96 0.01 0.01 – 6.94 <0.001 0.001 0.002 0.002 45.67

Source: FAOSTAT: FAO Statistical Division (2014).

wheat, maize, and barley. But due to an increasing demand with coinciding high prices achievable on the world market, cereal intervention has nearly lost its importance. In large parts of the EU, the climate and soil are very favorable for cereal cultivation. In the main cereal production

GRAINS AROUND THE WORLD | Grain Production and Consumption: Europe Table 5 Cultivation area (1000 ha) and average yield (tonnes ha1) a of cereals in the European Union (EU-28) in the year 2013 Species

Cultivation area

Yield

Wheat Barley Rye Oats Maize Triticale Sorghum Millet Rice, paddy Buckwheat Mixed grain Cereals, nesb Total cereals

25 683 12 339 2583 2645 9685 2676 137 61 430 159 1201 119 57 721

5.6 4.8 4.0 3.2 6.7 4.3 5.0 1.9 6.5 1.8 3.0 4.9 5.3

a

Including the pseudocereal buckwheat. Including inter alia amaranth and quinoa species. Source: FAOSTAT: FAO Statistical Division (2014). b

Table 6 Cultivation area (1000 ha) and average yield (tonnes ha1) a of cereals in Europe in the year 2013 Species

Cultivation area

Yield

Wheat Barley Rye Oats Maize Triticale Sorghum Millet Rice, paddy Buckwheat Mixed grain Cereals, nesb Total cereals

57 582 24 569 4978 6143 18 874 3418 328 495 648 1265 1208 183 119 791

3.9 3.5 3.0 2.4 6.2 4.0 3.5 1.3 6.0 1.1 3.0 3.6 4.0

a

Including the pseudocereal buckwheat. Including inter alia amaranth and quinoa species. Source: FAOSTAT: FAO Statistical Division (2014). b

Table 7 Area harvested (1000 ha) and average yield (tonnes ha1) of cereals and buckwheat in the Russian Federation and in Ukraine in the year 2012 The Russian Federation

Wheat Barley Rye Oats Maize Triticale Sorghum Millet Rice, paddy) Buckwheat Cereals, total

Ukraine

Area

Yield

Area

Yield

21 278 7641 1423 2853 1938 0.2 0.04 0.03 0.02 1030 36 988

1.77 1.83 1.50 0.14 4.24 2.08 1.04 1.02 0.05 0.77 1.86

5630 3293 0.3 0.3 4372 – 0.06 0.02 0.03 0.03 14 412

2.80 2.11 2.27 2.09 4.79 – 2.23 1.03 6.19 0.87 3.17


385

countries in Western and Central Europe, precipitation is rather high and equally distributed throughout the year. Temperatures are moderate, being, on average, not too low during winter for the growth of winter-type cereals (winter wheat, winter rye, etc.). These cereals have a prolonged vegetation period and are thus higher in yield. In recent years, however, there seems to be a tendency towards more frequent unusual weather events like drought and very high temperature in spring and during the main growth period, respectively, and more frequent heavy thunderstorms with huge amounts of rainfall that may be taken as indications of climate change, the consequences of which for cereal production in quantity and processing quality are hard to assess at present. Also, among EU member countries, yields of different cereals are varying significantly. Data for bread wheat yield in 2013 (data not shown) may serve as an example. The average yield ranged from 8.6 tonnes ha1 in Belgium to 1.9 tonnes ha1 in Portugal. In countries like Belgium/Lux., Denmark, France, Germany, Ireland, the Netherlands, and the United Kingdom, yields much higher than the EU average are standard. To a limited degree, there is also a variation in yield within these countries. These phenomena are the result of differences in climate, soil conditions, utilization of production means, and a question of the choice of varieties among which there is a broad range in genetically determined yieldforming potential.

Wheat Additional detailed information on wheat has been provided because of its overall predominance in production and consumption. Data presented in Tables 1, 2, and 4 refer to wheat as a single entity. These statistical data do not distinguish between different wheat species. As mentioned in the preceding text, the so-called soft aestivum wheat (botanical name – Triticum aestivum) is the most important wheat species in Europe and worldwide. Two types of T. aestivum wheat are cultivated: winter wheat and spring wheat, where winter wheat is by far the most preferred due to its higher yield performance. Spring-type wheat are chosen when they specifically fit into the crop rotation system or in those countries (e.g., Scandinavia) where the climate in winter and the growth period are too uncomfortable for winter-type wheat. In the main wheat-producing countries, the contribution of spring wheat to the total wheat harvest is distinctly less than 1%. T. aestivum wheat are covering the wide range of feed and food applications, whereas the species T. durum, known as durum or hard wheat, is specifically grown for pasta production. (This does not mean that pasta production would not be possible from soft wheat, too!) Durum wheat is more adapted to warmer climatic conditions. Consequently, it is preferably grown in countries with Mediterranean climates, namely, in Italy, France, and Spain (Table 8). Since a couple of years, however, durum wheat varieties more adapted to moderate climates are successfully grown in smaller quantities in the Czech Republic, in Germany, and in Austria. In regions with suitable growth conditions within these countries, durum wheat means a production alternative for farmers and a local supply of durum mills with produce.

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Table 8 Cultivation area, yield, and production of durum wheat in the European Union (EU-28) in the year 2013 Member country

Area (1000 ha)

Yield (tonne ha1)

Production (1000 tonnes)

Austria France Germany Greece Italy Portugal Spain Cyprus The Czech Republic Hungary Malta Slovakia Romania Bulgaria EU-28

12 335 9 535 1240 7 342 6 40

5.1 5.2 5.9 1.9 3.2 2.1 2.6 1.7 4.8

63 1742 53 1000 4005 15 903 10 192

12 2 20 5 27 2592

4.5 4.6 4.6 2.0 3.5 3.2

54 9 92 10 95 8243

Source: COCERAL (2013).

In some parts of France, Switzerland, Germany, and Austria, cultivation of spelt wheat (T. spelta) has been conserved through the centuries for specific use in certain foods and for brewing a special beer. In recent times, people have become more and more conscious of the important role of a healthy nutrition, and it is of benefit for health to consume multifold foods and among them those with functional constituents (such as dietary fiber/functional food), and in this context, emmer (T. dicoccum), small spelt (T. monococcum), and Kamut (T. polonicum) are gaining certain renewed recognition. This is more so in the case of organic farming and its niche clientele. However, the production rates are negligibly low. In addition, only baked spelt wheat goods, mainly bread, are more frequently available in specialized bakeries.

Rye Rye is a very important cereal for Europe and – more precisely – for central, east, and northeast European countries, and it is hardly grown anywhere else in the world (Tables 1, 2, and 4). This has a historical basis. Rye is assumed to have originated from Southwest Asia (Turkey, Iran, and Iraq). From there, it is said to have moved to Central Europe as a weed along with wheat and barley. But ancient farmers learned to appreciate this ‘weed’ as it turned out to be often more stable and efficient in yield performing better than the originally sown cereal, especially on poor sandy soils. Rye has a better drought resistance and efficiency of nutrient uptake from poor substrates. Also, it is much more tolerant of low temperatures during winter. Consequently, rye was very widely grown in Europe. In some parts, for example, in the United Kingdom, it has been replaced again by wheat. But in other parts, it remained of utmost importance in the human diet, primarily for bread making.

Table 9 2012

Production of selected cereals (1000 tonnes) in Europe in

Austria Belgium Bulgaria Croatia Cyprus The Czech Republic Denmark Estonia France Finland Germany Greece Hungary Italy Ireland Latvia Lithuania Luxemburg Malta The Netherlands Poland Portugal Romania Slovenia Slovakia Spain Sweden The United Kingdom EU-28 Iceland Norway Switzerland The Republic of Macedonia Turkey

Wheata

Maizeb

Barley

Ryec

1276 1835 4455 1000 23 3519 4525 485 37 921 887 22 409 1569 4011 7767 708 1540 2999 79 – 1302 8608 59 5298 188 1275 5190 2289 13 261 134 476 – 235 512 215 16 807

2351 734 1718 1341 – 928 75 – 15 614 – 5515 2010 4742 8195 – – 79 2 – 245 3996 849 5949 272 1170 4115 11 23 60 079 – – 149 119 4600

663 364 662 235 48 1617 4059 342 11 348 1578 10 391 326 996 960 1152 249 742 38 – 203 4180 21 971 85 471 5977 1705 5522 54 901 15 550 185 90 7100

219 3 22 2 – 148 384 57 160 66 3878 28 78 312 – 124 157 6 – 9 3163 15 19 3 49 256 140 33 9332 – 5 11 7 371

a

Including spelt wheat. Kernel maize including corn cob mix. c Including maslin. Source: EUROSTAT (2013); Federal Ministry of Food and Agriculture (ed.) (2013) Statistisches Jahrbuch u¨ber Erna¨hrung, Landwirtschaft und Forsten der Bundesrepublik Deutschland, 57. Jhrg. Landwirtschaftsverlag GmbH Mu¨nster-Hiltrup. b

According to the 2012 databases, Germany is the most important rye producer, followed by Poland (Table 9) and Russia (Table 4). In the Baltic states and in the Nordic countries, rye and rye products are important constituents of the human diet and animal feed, though also in these countries, there is a tendency to lower rye in favor of increased wheat consumption.

Pulses and Oilseeds In comparison with cereals, the production of pulses is of lesser importance in Europe (Tables 10–12). It is mainly the EU, the Russian Federation, Ukraine, and some other European countries where the production of specific legumes plays a remarkable role. Table 11 provides details of the highest amounts being reported for individual pulses and, for some countries, soybeans. Preference for individual species differs very much between countries, depending strongly on traditional diet as

GRAINS AROUND THE WORLD | Grain Production and Consumption: Europe far as human consumption is concerned and on recipes of optimized feedstuff mixtures in modern animal production. At this point, it should be mentioned that there is a strong tendency not only in Europe, namely, in Russia and Ukraine, but also in Mediterranean countries to grow soybeans. Even in countries like Austria or Germany where the climate was considered so far to be too unfavorable for this species, attempts are made to establish soybean production. Making use of respective progress in breeding the underlying idea is to have a further feedstuff raw material from home production. The majority of the huge amounts of soybeans used, however, will remain to be imported from overseas. Soybean may be used not only as protein source for food and feedstuff but also as oil production raw material. The statistics, however, reveal rapeseed and sunflower as oilseeds of importance in European agriculture (Tables 12 and 13).

Table 10 Production of pulses and soybeans (1000 tonnes) in total in Europe, the European Union (EU-28), Russia, and Ukraine in the year 2012

Total pulses Beans, dry Chickpeas Cowpeas Lentils Peas, dry Pulses, nesa Soybeans

Europe

EU-28

Russia

Ukraine

6485 488 89 23 91 3420 1186 5515

3173 139 36 <1 62 1272 850 863

2220 7 <1 – 28 1160 321 1806

473 <1 – – <1 <1 <1 2410

a Including inter alia: hyacinth bean (Dolichos ssp.), jack or sword bean (Canavalia spp.), and winged bean (Psophocarpus tetragonolobus). Source: FAOSTAT: FAO Statistical Division (2014).

Table 11

387

Both plants are of tremendous significance, whereas other species like linseed, for example, are specialty crops in specific countries. Basically, for oilseeds, too, it has to be stated that they are of lesser importance, although they may contribute to a large extent to agricultural production as in France, Germany, or the United Kingdom, for instance.

Consumption and Utilization Consumption and utilization of grain seeds in Europe are greatly influenced by factors as varied as climate, soil conditions, preference for specific crops based on tradition and ethnic peculiarities, economics, and governmental regulations. These factors are further compounded by the diversity in regions and countries found in the European continent at large. As it is impossible to discuss every grain species in detail or take into consideration the entire range of diversities, an attempt will be made to focus on major trends and to outline the main fields. Nearly all grain seeds or components of them serve as food and feed raw materials, and these are by far the most important fields of utilization. Furthermore, these crops or components derived thereof may be used as basic materials for chemical or technical purposes in the nonfood or feed industry. For example, starch is applied for the synthesis of adhesives.

Consumption of Cereals Statistically, the EU as a whole is a self-supplier of cereals. Individual countries, however, especially the main grainproducing ones like France (200%), Germany ( 140%), and the United Kingdom (125%), produce much more cereal in total than can be consumed by the national population. However, there are also countries within the EU like, for

Production of pulses and soybeans (1000 tonnes) in selected European countries in 2013

Albania Austria Belgium Bulgaria The Czech Republic Denmark Finland France Germany Greece Hungary Italy Poland Portugal Serbia Spain Sweden Switzerland The United Kingdom Russia Ukraine

Beans

Broad beans

27.0

0.2 13.65 2.20

0.82 1.13

Lentils

1.30 1.80

7.55 25.00 0.22 8.53 31.33 2.37 33.79 10.00 1.05

7.06 25.80


245.55 59.70 3.32 0.20 49.42 0.28 20.00

22.73

28.10

24.00

1.10 200.00 7.56 4.00

16.63 0.70

3.20 0.02 1.54

Peas 17.60 1.50 2.00 30.70 14.60 10.50 498.94 129.50 0.75 43.60 8.60 33.23 31.70 177.70 40.70 12.30 107.00 1350.17 275.00

Total pulses

Soybeans

30.02 41.39 4.52 6.80 40.16 24.60 10.50 788.92 228.80 46.77 44.37 118.28 375.71 23.07 109.64 373.30 41.75 13.59 737.00 2084.34 371.50

0.10 82.78 0.60 13.47

110.28 2.00 4.00 82.10 472.4

385.21 1.40

1636.00 2774.30

388


example, Italy (40%) or Spain ( 70%) that lack sufficient production. This means a compensation of surpluses and demands, respectively, not only within the EU but also from outside. As a whole, the EU is one of the big players in worldwide cereal trade; this is specifically valid for major grainproducing member states like France or Germany where there is a strong pressure for export outside the EU or for alternative utilization of cereals. The latter aspect, however, is diversely discussed and may steadily lose importance with respect to world population growth and therefore increased demand for cereals for human consumption. In more recent years, Russia and Ukraine have also become significant cereal exporters (especially wheat) on the world market, the available amounts Table 12 Total production of pulses (1000 tonnes) and oil crops (1000 tonnes) in Europe in the year 2013

Total Europe EU-28 Russia Ukraine

Pulses

Oil crops

6212 3165 2084 372

27 240 15 137 5294 5948

Source: FAOSTAT (2012).

Table 13 Production (1000 tonnes) of rapeseed and sunflower seed in the European Union in the year 2012

Austria Belgium Bulgaria Croatia Cyprus The Czech Republic Denmark Estonia France Finland Germany Greece Hungary Italy Ireland Latvia Lithuania Luxemburg Malta The Netherlands Poland Portugal Romania Slovenia Slovakia Spain Sweden The United Kingdom EU-28

Rapeseed

Sunflower seed

149 48 271 26 – 1109 485 163 5483 73 4821 1 401 25 – 304 633 15 0 7 1862 – 159 17 213 52 323 2564 –

53 – 1388 90 0 57 0 – 1575 0 63 160 1302 186 0 0 0 0 – 0 – 10 1389 0 197 0 0 0 –

–, Data not available. Source: Federal Ministry of Food and Agriculture (ed.) (2013) Statistisches Jahrbuch u¨ber Erna¨hrung, Landwirtschaft und Forsten der Bundesrepublik Deutschland, 57. Jhrg. Landwirtschaftsverlag GmbH Mu¨nster-Hiltrup.

of cereals, however, being much dependent on yearly fluctuations in total production quantities. The majority of the yearly cereal harvest is used for feedstuff. Germany may serve as an example: Out of c.26 million tonnes of wheat produced per year round, about 7 million tonnes is milled for human consumption. Food use is dominated by bread production and the production of other baked goods like pastries and cakes. Breakfast cereals also contribute to the total consumption of cereals, though in comparison with bread making, this segment is small, with a permanently increasing tendency. The significance of grain food use is demonstrated in Table 14 as consumption of cereals per capita and year in selected EU member states. Consumption differs a lot between individual countries, with, for example, Greece having extraordinarily high consumption rates. In the large majority of the European countries, the production of bread or comparable foodstuff means production from wheat. This is also true for central, eastern, and northeastern countries, but here in addition, rye is also used as a raw material for bread making. The extent to which rye is used is quite different between individual countries. For example, in Germany, 850 000 tonnes of rye is milled for bread production; however, this tendency is slowly decreasing. Bread making does not only mean utilization of pure rye flour. Most breads offered on the market are made of mixtures of rye and wheat flour. In relation to wheat, rye has higher proportions of dietary fiber. Actually, this health benefit is used in arguing in favor of increased rye consumption again. Health aspects are also the reason of increased interest in the so-called ‘old’ wheat species as spelt, emmer, or einkorn. With steadily increasing amounts, wheat and maize serve as raw materials for starch production (Table 15). The advantage of these raw materials is based on marketable by-products like germ for oil extraction or protein for feed (maize) or gluten for food use (and feed) from wheat. The so-called vital gluten from wheat starch plants is used in a wide range of feed and food applications, as a flour improver in the bread industry, for example. The main product of the starch industry, starch, is mainly used in food applications (Table 16). Table 14 Per capita consumption of cereals (kg year1) in selected European countries in the economic year 2011/2012

Austria Estonia Germany Greece Hungary Latvia Lithuania Luxemburg The Netherlands Romania The United Kingdoma a

Cereals, total

Soft þ durum wheat

Other cereals

90.9 62.3 95.0 313.0 106.6 112.0 92.2 60.0 109.9 159.2 80.8

64.4 38.0 69.9 308.1 89.9 82.9 74.4 57.3 99.3 120.3 76.9

26.5 24.3 25.0 4.8 16.8 29.0 17.8 2.7 10.6 38.9 3.9

Data of 2009–10. Source: Federal Ministry of Food and Agriculture (ed.) (2013) Statistisches Jahrbuch u¨ber Erna¨hrung, Landwirtschaft und Forsten der Bundesrepublik Deutschland, 57. Jhrg. Landwirtschaftsverlag GmbH Mu¨nster-Hiltrup.

GRAINS AROUND THE WORLD | Grain Production and Consumption: Europe Table 15 Total raw material processed, starch production, and the respective contribution of specific plant groups in Europe in selected years Year

2001

2005

2008

2010

Total raw material (Mt) Potato (%) Maize (%) Wheat (%) Starch produced (Mt) Potato (%) Maize (%) Wheat (%)

21.2 41 31 28 9.0 20 46 34

22.6 39 31 30 9.6 18 46 36

21.6 35 33 32 9.4 16 47 37

22.0 32 34 34 9.9 14 48 38

Mt, millions of tonnes Source: German Starch Industry Association (2012).

389

In European tradition, maize as such is of little interest for food use, though actual development reveals the so-called Mexican food to become a segment of diet, at least in some European countries. Minor quantities of grain maize are used for grits production, as raw material for snacks, while the great majority of grain maize is used in feed. Because of their b-glucan content with health benefits, oats are processed to a certain amount to produce special food like flakes and extruded products. But the majority of the production is used for feed. This is also valid for barley, though a notable quantity of barley is used for beer brewing. Barley is also rich in b-glucan, a reason why it should be treated as cereal, the potential of which for food production is underestimated.

Consumption of Pulses and Oilseeds Table 16 Utilization of starch and starch derivatives in Europe in selected years

Total utilization (Mt) Native starches (%) Modified starches (%) Saccharification products (%) Food uses (%) Nonfood uses (%)

2001

2005

2008

2010

8.3 23 17 60 55 45

9.0 23 20 57 58 42

8.8 23 21 56 60 40

9.0 25 20 56 62 38

Mt, millions of tonnes Source: German Starch Industry Association (2012).

Table 17

To a limited extent and varying very much between individual areas and countries within Europe, pulses are used for human nutrition (Table 17). Mostly, they are components of feedstuff mixtures. This is also true for soybeans. Food use is in oil and protein (tofu) extraction. The quantity outlined for certain countries like Germany, for example, does not necessarily indicate home products but may represent imports. Oilseeds are mainly used for oil production and the protein-rich residues serve as feedstuff ingredients. The oil, especially of rapeseed, is of high nutritional value and therefore used in human nutrition. However, the bulk is used for technical applications, for example, as energy for motor cars.

Food supply quantity (1000 tonnes) and consumption per capita (kg) of pulses and soybeans in selected European countries in the year 2011 Beans

Albania Austria Belgium Bulgaria The Czech Republic Denmark Finland France Germany Greece Hungary Italy Poland Portugal Serbia Spain Sweden Switzerland The United Kingdom Russia Ukraine

Peas

Pulses (others)

Pulses (total)

Soybeans

1000 tonnes

kg

1000 tonnes

kg

1000 tonnes

kg

1000 tonnes

kg

1000 tonnes

kg

15.00 1.60 8.23 12.00 1.85 0.74 0.12 52.70 8.00 30.83 7.83 115.07 36.67 23.03 45.62 46.12 2.56 2.00 10.00

4.8 0.2 0.8 1.6 0.2 0.1 0.0 0.8 0.1 2.8 0.8 1.9 1.0 2.2 4.8 1.0 0.3 0.3 0.2

0.00 3.99 13.00 1.00 20.00 4.00 6.00 30.18 59.18 1.53 24.39 45.76 40.51 3.39 42.64 215.89 12.00 10.54 118.95 260.00 69.82

0.0 0.5 1.2 0.1 1.9 0.7 1.1 0.5 0.7 0.1 2.4 0.8 1.1 0.3 4.4 4.6 1.3 1.3 1.9 1.8 1.5

0.91 1.27 2.06 3.46 6.42 1.00 0.23 44.04 19.00 20.50 5.63 130.43 2.99 10.36 0.59 141.44 2.83 2.28 21.65 1.14 1.09

0.3 0.2 0.2 0.5 0.6 0.2 0.0 0.7 0.2 1.8 0.3 2.2 0.1 1.0 0.1 3.0 0.3 0.3 0.4 0.0 0.0

16.00 7.00 23.00 16.00 28.00 6.00 6.00 127.00 86.00 53.00 35.00 291.00 81.00 36.00 90.00 403.00 18.00 15.00 151.00 261.00 71.00

5.1 0.8 2.1 2.2 2.6 1.1 1.1 2.0 1.0 4.8 3.5 4.8 2.1 3.4 9.4 8.7 1.9 1.9 2.4 1.8 1.6

0.04 14.39 0.65 0.31 6.30 0.35 0.28 3.53 52.33 0.16 0.05 0.63 0.27 0.14 0.04 0.69 1.23 1.03 5.42 5.40 0.61

0.0 1.7 0.1 0.0 0.6 0.1 0.1 0.1 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.0 0.0


390



• • • • • • • • •

Which are the main cereals produced in Europe as a whole and in the EU? What are the main cereal-producing countries in Europe? What cereal species is a specialty in Europe and hardly grown elsewhere in the world? What are the main pulses grown in Europe as a whole and in the EU? What are the main oilseeds produced in Europe? What are the cereal species preferably used for human consumption in Europe? What is the significance of soft wheat in bread making in Europe? Are there differences in the significance for bread making between individual European countries? Are there differences among countries in the preference for the use of pulses?

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Labelling of Grain-Based Foods; Food Grains and Well-being: Functional Foods: Overview; Grains Around the World: Grain Production and Consumption: Overview; Non-food Products from Grains: Cereal Grains as Animal Feed; Utilization of the Whole Cereal Plant to Maximize its Value; Processing of Grains: Evaluation of WheatGrain Quality Attributes; Grain Quality Attributes for Cereals Other than Wheat; Starch: Uses of Native Starch; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Durum Wheat: Overview; Rye Grain: Its Genetics, Production, and Utilization; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview; Pseudocereals: Overview; The Oilseeds: Oilseeds: Overview; Soybean: Overview; Wheat Processing: Gluten and Modified Gluten; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.


• • •

Compare the significance of cereal grains versus pulses in human nutrition. Select different countries for their preference in utilization of different cereal species for bread making. Identify regions of Europe where rye is the predominant bread cereal.

Further Reading FAOSTAT: FAO Statistical Division (2014). Federal Ministry of Food and Agriculture (ed.) (2013) Statistisches Jahrbuch u¨ber Erna¨hrung, Landwirtschaft und Forsten der Bundesrepublik Deutschland, 57. Jhrg. Landwirtschaftsverlag GmbH Mu¨nster-Hiltrup.

Grain Production and Consumption: Cereal Grains in North America JA Fox and LL Ward, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

North America’s relatively low population density and abundant arable land contribute to its position as a major grain producer and exporter. The US dominates global maize production, widely uses GM maize, and in recent years has further increased production to meet demand for bioethanol. Maize is the most important cereal crop in Mexico (70% of production area), and wheat is in Canada (60% of production area). North America produces only 2% of the world’s rice, but is still a significant exporter.

Learning Objective

•

To provide perspective on the role of North America in global production and trade for the covered grains.

Introduction According to worldstat.info, the North American continent (herein defined as comprising the United States, Canada, and Mexico) has 17% of the world’s arable land and 6.6% of the world’s population. Given the relative abundance of arable land (0.52 ha per person vs. world average of 0.2 ha per person), the continent is a major producer and exporter of several grain crops including barley, maize, oats, rice, sorghum, and wheat. This article updates an earlier Encyclopedia of Grain Science chapter on the North American grain sector (Lukow and McVetty) with data covering the 12-year period from 2002 to 2013. Like the earlier chapter, which covered the period from 1992 to 2001, we provide an overview of production, consumption, and trade for the major North American grains. Unless otherwise noted, all data are drawn from the Food and Agriculture Organization (FAO) FAOSTAT database. We begin with a brief overview of grain production on the continent and then provide additional detail for each of the major cereal grains. Figure 1 shows the total hectares of cereal grains (barley, maize, oats, rice, sorghum, and wheat) harvested annually in the United States, Canada, and Mexico between the years 2002 and 2013. During the 12-year period between 2002 and 2013, an average of 82.2 Mha of cereals was harvested in North America, accounting for almost 13% of the world’s harvested area (640 Mha). With higher yields, however, North America accounted for 20% of world cereal production during the same period. Within North America, the United States, with an average harvested area of over 57 Mha, accounted for about 70% of the total harvested area, with Canada having 18% and Mexico 12%.


Maize is the most commonly grown crop on the continent, accounting for almost half of the area in cereals (Figure 2) followed by wheat with about one-third. Less than 2% of North American cereal area is in rice production compared to almost 25% for the world. Between 2002 and 2013, the area in North American cereal production increased by about 6.6 Mha (8.5%). Most of the increase (5.7 Mha) occurred in the United States, where the area in maize (corn) increased from 28 Mha to over 35 Mha. The net increase in US cereal area was partially a result of a 3 Mha reduction in the Conservation Reserve Program (USDA Farm Service Agency) and reductions in other crops, primarily hay (down 2.5 Mha) and cotton (down 1.4 Mha) (USDA, QuickStats). During the same period, the area in oilseeds (soybeans, rapeseed, sunflower, and linseed) in North America, the main alternative to cereal crops, also increased by about 6 Mha from 36 Mha in 2002 to 42 Mha in 2013. Most of the net increase in oilseed area occurred in Canada where the area in rapeseed (canola) production more than doubled from about 3.6 Mha in 2002 to over 8 Mha in 2013. Figure 3 shows total cereal production in North America between 2002 and 2013. During that period, production increased from 361 million tonnes (mt) to 535 mt, an increase of over 48%. Production increased in all three countries: by 47% in the United States, by 86% in Canada, and by 15% in Mexico. On average, the United States accounted for 82% of North American cereal production over the 12-year period, with Canada contributing 11% and Mexico 7%.

Maize (Corn) Table 1 provides data on North American and world maize production from 2002 to 2013. Maize is the most important cereal grain in North America accounting on average for 49% of harvested cereal acres and 71% of cereal tonnage produced. Maize is also the world’s top cereal crop with over 1 billion tonnes produced in 2013. On average, North America produced almost 42% of the world’s maize between 2002 and 2013, on 25% of the world’s harvested maize area. Yields in North America averaged 8.2 mt ha1 compared to the overall world average (including North America) of 4.9 mt ha1. The United States is the world’s leading producer, accounting for 90% of North American production, with Canada contributing 3% and Mexico 7%. US yields averaged 9.3 mt ha1 over the 12-year period, compared to 8.6 mt ha1 in Canada and 3.0 mt ha1 in Mexico. Drought in the US Midwest during the 2012 growing season resulted in yields declining to 7.7 mt ha1, the lowest average yield during the 12-year period. Average yields trended upward in each country during the 12-year period, by 0.03 mt ha1 per year in the United States, by 0.18 mt ha1 per year in Canada, and by 0.04 mt ha1 per year in Mexico.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00048-6

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392

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America

Harvested area – cereals 100 000 000 90 000 000 80 000 000 70 000 000 60 000 000 50 000 000 40 000 000 30 000 000 20 000 000 10 000 000 0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 US

Canada

Mexico

Total N.Am.

Figure 1 Harvested area of barley, maize, oats, rice, sorghum, wheat (hectares).

Cereal area distribution 60%

N. America World

49%

50% 40%

36%

30%

25%

34%

25%

20% 10%

6%

8%

5% 7%

2% 2%

0%

Barley

Maize

2%

Oat

Rice

Sorghum

Wheat

Figure 2 Cereal area distribution: North America versus world.

Cereal production 600 000 000 500 000 000 400 000 000 300 000 000 200 000 000 100 000 000 0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 US

Canada

Mexico

Total N.Am.

Figure 3 Production of barley, maize, oats, rice, sorghum, and wheat (tonnes).

Since the introduction of genetically modified (GM) crops in the late 1990s, both the United States and Canada have experienced widespread adoption of GM maize. In 2013, GM varieties of maize accounted for 90% of the planted area in the United States (USDA, ERS) and 98% of the area in Canada

(GMO Compass). GM maize is not grown commercially in Mexico and its possible introduction is the subject of ongoing legal challenges (Nature.com). The area of maize harvested in the United States increased by over 25% between 2002 and 2013, from 28 Mha to over

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America Table 1

Maize production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

393

Area 28 057 28 710 29 798 30 399 28 587 35 014 31 797 32 169 32 960 33 990 35 359 35 478 31 860

Prod. 227 765 256 227 299 874 282 261 267 501 331 175 307 142 332 549 316 165 313 949 273 820 353 699 296 844

Canada Area 1283 1226 1072 1085 1061 1369 1169 1142 1203 1202 1418 1480 1266

Prod. 8999 9587 8837 9332 8990 11 649 10 592 9561 11 715 10 689 13 060 14 194 10 600

Mexico Area 7120 7521 7688 6606 7295 7333 7354 6223 7148 6069 6924 7096 7031

35 Mha, with its share of US cereal area increasing from 52% to over 60%. Higher yields, in conjunction with the increase in area, resulted in a 55% boost in production over the same period. The acreage increase can be attributed largely to increased demand for ethanol production spurred by the US renewable fuels mandate introduced in the 2005 Energy Policy Act (US Environmental Protection Agency) and the attendant increase in maize price. US maize production is concentrated in the Midwest ‘corn belt’ states, with Iowa and Illinois typically accounting for around one-third of the US crop. The recent expansion has boosted production in other states such as Kansas where the area under maize increased from 1 million to 1.6 million hectares between 2002 and 2013 (USDA, Quick Stats). Approximately 15% of US corn harvested area is irrigated (USDA, Census of Agriculture). Maize is by far the most important cereal crop in Mexico, accounting for over 70% of the area under cereals, with production occurring throughout the country. The total area in maize was stable during the period under review, with almost identical areas harvested in 2002 and 2013. Higher yields resulted in a 17% increase in production between 2002 and 2013 but productivity gains have been limited by structural problems. More than 85% of Mexico’s 2 million corn growers have fewer than 5 ha and have limited access to improved genetics, fertilizer, etc. (USDA, FAS). In Canada, maize is a relatively minor crop, accounting for an average of only 8.2% of the area in cereals, with production concentrated in Ontario and Quebec (Statistics Canada). The area in maize increased slightly from 1.28 Mha in 2002 to 1.48 Mha in 2013, but higher yields contributed to an overall increase in production of about 58%.

Consumption and Trade Table 2 provides 10-year average balance sheet data on production, consumption, and trade for maize in North America for the period 2002 to 2011. In the balance sheet, domestic supply is calculated as production þ imports þ stock changeimports. Thus, a negative stock change corresponds to a reduction in domestic supply. Because total supply accounts for stock change, the total use number corresponds to total supply. Using FAO definitions for the various use categories, feed refers

Prod. 19 298 20 701 21 670 19 339 21 893 23 513 24 320 20 143 23 302 17 635 22 069 22 664 21 379

North America Area 36 460 37 457 38 558 38 089 36 942 43 716 40 319 39 534 41 311 41 260 43 701 44 054 40 117

Prod. 256 062 286 516 330 381 310 932 298 384 366 337 342 054 362 253 351 181 342 273 308 949 390 557 328 823

World Area 137 609 144 701 147 454 148 035 146 741 158 390 162 689 158 743 164 030 172 257 178 552 184 192 158 616

Prod. 604 872 645 165 728 971 713 682 706 847 790 115 830 611 820 203 851 271 887 855 872 792 1 016 736 789 093

to livestock feed, processing is the amount used for manufacture of processed food items (e.g., high-fructose corn syrup), food comprises amounts not detailed otherwise in the balance sheet that are available for human consumption, while other uses comprise quantities used for the manufacture of nonfood products (e.g., ethanol). In the United States and Canada, maize is grown primarily for livestock feed and ethanol with relatively small amounts used for human food consumption. In Mexico, however, white maize targeted toward human consumption (e.g., tortillas) accounts for two-thirds of production (USDA, FAS). Over the 10-year period from 2002 to 2011, food use accounted for 63% of maize produced in Mexico, compared to 6% in Canada and only 1.3% in the United States. Mexico has traditionally been a major importer of feed corn for its domestic livestock sector, particularly the poultry sector, with imports coming primarily from the United States. Over the 10-year period from 2002 to 2011, average imports of 7.3 mmt were equal to 34% of average domestic production. In 2002, Mexico imported 5.2 mmt and ranked as the world’s third largest importer after Japan and South Korea. In 2011, imports had doubled to 11.2 mmt, with Mexico as the #2 ranked import market after Japan. Between 2002 and 2011, Canada was a net maize importer, but as maize production increased, the country gradually shifted from being a relatively small net importer to a relatively small net exporter. In 2002 and 2003, Canadian net imports amounted to 3.6 mmt and 1.7 mmt, respectively, while in 2011, net imports had fallen to 0.4 mmt. For 2012 and 2013, Canada was estimated to have net maize exports of between 1 and 1.25 mmt. In the United States, the growth of the ethanol sector during the past decade consumed an increasing share of the US maize crop. Of the US maize crops produced in 2002 and 2003, an average of 27 mmt (11% of total usage) was used for ethanol production. Of the 2010 and 2011 crops, the average amount used for ethanol was 127 mmt, equivalent to 40% of total use (USDA World Agricultural Outlook Board). The United States has long been the world’s top-ranked maize exporter and, despite increasing ethanol production, has maintained the top export ranking due to increased domestic production. Throughout the 10-year period, the United States, on average,

394 Table 2

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America Maize production, trade, and use (mt)

Production Imports Stock change Exports Domestic supply Use Feed Seed Waste Processing Food Other uses Total use

The United States

Canada

Mexico

North America

293 460 800 566 349 2 678 290 50 552 700 246 152 739

9 995 000 2 562 245 (94 500) 641 963 11 820 778

21 181 430 7 283 827 280 889 308 182 28 437 950

324 637 230 10 412 421 2 864 679 51 502 844 286 411 467

138 788 400 555 280

9 357 673 12 840 371 117 1 213 531 647 500 218 127 11 820 788

10 081 009 396 066 3 208 635 1 409 676 13 296 600 45 968 28 437 953

158 227 082 964 185 3 579 752 24 959 737 17 836 830 80 843 984 286 411 570

22 336 530 3 892 730 80 579 890 246 152 830

10-year average (2002–2011).

Table 3

Wheat production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

Area 18 545 21 474 20 222 20 277 18 940 20 639 22 541 20 191 19 271 18 496 19 798 18 274 19 889

Prod. 43 704 63 803 58 697 57 242 49 216 55 820 68 016 60 366 60 062 54 413 61 677 57 967 57 582

Canada Area 8711 10 215 9389 9404 9682 8636 10 032 9638 8269 8544 9497 10 442 9371

Mexico Prod. 15 961 23 049 24 796 25 748 25 265 20 054 28 611 26 848 23 167 25 261 27 205 37 530 25 291

Area 635 605 517 635 646 692 802 828 679 662 579 634 659

exported around 17% of domestic maize production. During the 2002/03 crop marketing year, the United States exported 40.3 mmt compared to total world exports of 78.2 mmt, a market share of 51.5%. The second ranked exporter was Argentina with 11.2 mmt. During the 2011/12 crop year, US exports of 39.2 mmt accounted for a 50.2% share of the 77.8 mmt export market. The second ranked exporter was Brazil with 24.3 mmt, followed by Argentina with 17.1 mmt.

Wheat Following maize, wheat is the second most commonly grown cereal in North America, accounting for about one-third of the area in cereals. Worldwide, average annual wheat production between 2002 and 2013 was 640 mmt, with North America accounting for around 13%. Table 3 provides data on North American and world wheat production from 2002 to 2013. Between 2002 and 2013, the area harvested in North America remained relatively stable at about 30 Mha, peaking at 33.3 Mha in 2008 with production peaking at over 100 mmt in the same year. Since the early 1990s, however, the area in wheat has dropped significantly with the 29.5 Mha harvested

Prod. 3236 2716 2321 3015 3378 3515 4019 4116 3677 3628 3274 3357 3354

North America Area 27 890 32 293 30 128 30 315 29 268 29 967 33 374 30 658 28 218 27 702 29 874 29 350 29 920

Prod. 62 901 89 568 85 814 86 005 77 860 79 390 100 647 91 329 86 906 83 302 92 157 98 854 86 228

World Area 213 817 207 700 216 569 219 573 211 195 216 710 222 279 224 634 216 965 220 196 217 320 218 461 217 118

Prod. 574 743 560 129 632 144 626 739 602 332 612 874 683 207 686 720 649 325 699 389 671 497 713 183 642 690

in 2013 representing a decline of over 25% on the 40.1 Mha harvested in 1992. Between those years, the US area in wheat declined by about 7 Mha, and the Canadian area by about 3 Mha. Wheat is the primary cereal crop in Canada, occupying over 60% of the area in cereals and over 20% of the total arable land. Most of Canada’s wheat production is in the Prairie Provinces comprising Alberta, Saskatchewan, and Manitoba. Canada Western Red Spring (CWRS) is the most commonly produced class accounting for about 60% of the wheat area, followed by Canada Western Amber Durum (CWAD) with around 15%. The United States harvested an average of just under 20 Mha of wheat during the 12-year period, equivalent to about one-third of the country’s cereal acreage and slightly more than 10% of the arable land. In 2013, about one-third of US wheat was hard red winter (HRW), grown primarily in the Central and Southern Great Plains. Hard red spring (HRS), grown in the Northern Great Plains, and soft red winter, grown in the eastern and southeastern states, each accounted for about a quarter of production. White wheat accounted for around 12% of production, and durum around 3%. Wheat is a relatively minor crop in Mexico, occupying only about 7% of the area in cereals and <3% of arable land, with durum being the predominant class (USDA, FAS).


average exports of over 30 mmt representing more than half of domestic production, the United States is the world’s leading wheat exporter, accounting in recent years for a 20% share of the world’s trade. Most of the domestic wheat supply is for human food consumption, with only 13% used for animal feed. Canada is also a major wheat exporter with average exports of 16.7 mmt representing over 70% of production. Canada is typically one of the top five wheat exporters with the other major exporters being the EU, Australia, and Russia. In contrast to the United States, almost half of Canada’s domestic supply is used for animal feed. Mexico is a net importer of wheat with average imports exceeding domestic production. Imports doubled from an average of 1.8 mmt per year in the period from 1991 to 2000 to an average of 3.6 mmt in period from 2002 to 2011. Approximately two-thirds of Mexico’s domestic wheat supply is for food use.

In 2013, the United States was the world’s fourth largest producer (after the EU, China, and India) and, with annual production of around 57 mmt, generally accounts for about two-thirds of North American production. Of the remainder, Canada, with an average of about 25 mmt, accounts for about 30%, with only 4% produced in Mexico. A bumper crop in Western Canada in 2013 saw the Canadian share of North American production rise to 38%. North American wheat yields averaged 2.8 mt ha1 over the 12-year period, slightly below the world average of 2.9 mt ha1. Within North America, average yields were highest in Mexico at 5.1 mt ha1 compared to 2.9 mt ha1 in the United States and 2.7 mt ha1 in Canada. Higher yields in Mexico are due to the fact that much of Mexican wheat production is done under irrigation. Average yields trended upward in each country during the 12-year period, by 0.05 mt ha1 per year in the United States, by 0.1 mt ha1 per year in Canada, and by 0.07 mt ha1 per year in Mexico.

Sorghum

Consumption and Trade Table 4 summarizes wheat production, consumption, and trade in North America for the period 2002 to 2011. With Table 4

395

Grain sorghum is grown in Mexico and the United States, but because maturity requires higher temperatures, there is no

Wheat production, trade, and use (mt)


The United States

Canada

Mexico

North America

57 134 020 3 660 880 898 696 30 429 360 31 264 250

23 875 980 684 010 (97 472) 16 732 450 7 730 067

3 362 165 3 611 733 0 1 117 632 5 856 267

84 372 165 7 956 623 801 224 48 279 442 44 850 584

4 128 683 2 133 622

3 663 790 905 600 22 630 14 021 2 796 166 382 608 7 784 814

78 109 72 173 487 267

7 870 582 3 111 395 509 897 14 021 31 577 935 1 821 479 44 905 308

0 25 000 220 1703 31 264 229

3 781 549 1 437 168 5 856 265

10-year average (2002–2011).

Table 5

Sorghum production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

Area 2883 3156 2637 2321 1999 2748 2943 2234 1948 1590 2005 2630 2425

Prod. 9163 10 446 11 523 9981 7032 12 636 11 998 9728 8779 5447 6272 9882 9407

Canada Area 0 0 0 0 0 0 0 0 0 0 0 0 0

Mexico Prod. 0 0 0 0 0 0 0 0 0 0 0 0 0

Area 1744 1973 1833 1599 1600 1775 1838 1691 1768 1728 1820 1689 1755

North America Prod. 5206 6462 7004 5524 5519 6203 6611 6108 6940 6429 6970 6308 6274

Area 4627 5128 4470 3921 3600 4523 4781 3924 3716 3318 3825 4319 4179

Prod. 14 369 16 908 18 528 15 505 12 550 18 839 18 609 15 836 15 720 11 876 13 242 16 190 15 681

World Area 41 316 44 609 40 832 46 362 43 366 44 818 45 382 40 945 41 583 42 312 38 158 42 120 42 650

Prod. 53 496 59 037 58 117 59 633 57 772 62 810 66 524 56 938 60 056 58 243 57 030 61 385 59 253

396


commercial grain sorghum production in Canada (AgAnnex). Some sorghum is harvested for silage, but the area is small, typically around 5% of the US area. Table 5 provides sorghum production data for the United States and Mexico. Between 2002 and 2013, sorghum occupied about 5% of North America’s area in cereals, far less than the shares taken by maize (49%) and wheat (36%). It is, however, the second most commonly grown cereal crop in Mexico, with 1.7 Mha accounting for about 18% of harvested cereal acreage. As the US area in maize has expanded, the area in sorghum has fallen, and the 2.6 Mha harvested in 2013 represented a 46% decline on the 4.8 Mha harvested in 1992. North America’s area in sorghum averaged 4.1 Mha between 2002 and 2013, just under 10% of the world total. With higher yields, averaging 3.9 mt ha1 in the United States and 3.6 mt ha1 in Mexico compared to a world average of 1.4 mt ha1, the continent accounted for more than a quarter of world production. Interestingly, US sorghum yields declined from an average of 4.1 mt ha1 in the 10-year period from 1992 to 2001 to an average of 3.9 mt ha1 between 2002 and 2013. During the same periods, Mexican average yields rose from 3.2 to 3.6 mt ha1. In most years, the United States and Mexico are ranked among the top four sorghum-producing nations along with Nigeria and India, with each typically producing between 10% and 15% of the world’s total sorghum crop. In 2013, the United States was the top-ranked producer with 9.8 mmt representing 16% of world production, while Mexico ranked third with 6.3 mmt. In the United States, the largest sorghumproducing states are Kansas and Texas, which jointly account for almost 80% of production (USDA, Crop Production). In Mexico, sorghum is produced throughout the country and approximately one-third of the planted area is irrigated (USDA, FAS).

Consumption and Trade Table 6 summarizes sorghum production, consumption, and trade in North America for the period 2002 to 2011. With exports averaging 4.6 mmt per year comprising almost half of domestic production, the United States is the world’s leading Table 6

sorghum exporter. Over the 10-year period summarized in Table 6, US exports accounted for 76% of total world trade, but its share declined throughout the period as domestic use, including some for ethanol production, increased and exports from Argentina, the second ranked exporting country, grew from < 0.5 mmt in 2002 to over 1.8 mmt in 2011. Most of the US domestic supply is used for animal feed. Despite being a major producer, Mexico is also the world’s leading sorghum importer, accounting in some years for more than half of world imports. Until 2013, when sorghum was imported from Argentina, imports were sourced exclusively from the United States. Mexican sorghum use is for animal feed, with the poultry industry being the major consumer (USDA, FAS). Canada’s domestic supply, which is also used exclusively for animal feed, is imported from the United States.

Barley Similar to wheat, barley has both spring and winter growth forms, but North American production is predominantly of the spring form (Lukow and McVetty). North America produces about 11% of the world’s barley supply, and the crop occupies about 6% of the North American area in cereals. Table 7 provides data on barley area harvested and production. Between 2002 and 2013, the EU was the world’s largest barley producer, accounting for about 40% of production, with North America contributing about 11%. Other leading producers included Russia, Ukraine, and Australia. Canada is the largest producer in North America, supplying about twothirds of the continent’s barley, equivalent to about 7% of world production. Canada is typically among the top five producing countries. After wheat, barley is the second most commonly grown cereal in Canada, occupying about 20% of the cereal area. Canadian acreage declined by 20% during the 12-year period described in Table 7, and the 2013 harvested area of 2.6 Mha was 30% below the 1992 figure of 3.8 Mha. Barley is a relatively minor crop in both the United States and Mexico, occupying between 2% and 3% of the cereal area. In the United States, barley is grown primarily in northern states, with Idaho, Montana, North Dakota, and Washington combining to account for almost 80% of the US harvested area.

Sorghum production, trade, and use (mt) The United States

Production Imports Stock change Exports Domestic supply Use Feed Seed Waste Processing Food Other uses Total use 10-year average (2002–2011).

9 673 297 879 89 501 4 650 196 5 113 491 3 777 720 21 971

Canada

Mexico

North America

6 200 727 2 746 408 0 65 8 947 068

15 874 024 2 752 313 89 501 4 650 375 14 065 471

4912

8 739 151 28 974 178 943

4912

8 947 068

12 521 783 50 945 178 943 1 068 700 245 100 0 14 065 470

5026 114 4912

1 068 700 245 100 5 113 491

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America Table 7

397

Barley production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

Area 1669 1913 1627 1323 1194 1417 1529 1260 998 906 1313 1214 1364

Table 8

Barley production, trade, and use (mt)


Prod. 4940 6059 6091 4613 3923 4575 5230 4949 3925 3392 4796 4683 4765

Canada Area 3342 4397 3841 3634 3223 3998 3502 2918 2387 2365 2060 2652 3193

Prod. 7468 12 164 12 557 11 678 9573 10 984 11 781 9517 7605 7756 8012 10 237 9944

Mexico Area 282 365 326 306 315 286 311 239 268 218 328 297 295


Area 5293 6675 5794 5263 4733 5701 5342 4416 3652 3489 3701 4163 4852

Prod. 13 145 19 308 19 579 17 052 14 365 16 211 17 792 14 985 12 203 11 635 13 840 15 514 15 469

World Area 55 270 57 736 57 567 55 357 56 386 55 860 55 533 53 956 47 368 48 488 49 573 49 781 53 573

Prod. 136 724 142 565 153 905 138 680 139 522 134 175 154 788 151 782 123 683 132 951 133 507 144 755 140 586

The United States

Canada

Mexico

North America

4 769 556 762 430 (81 203) 886 840 4 563 943

10 108 280 125 464 (124 100) 2 280 319 7 829 327

749 564 365 608 1886 8442 1 108 616

15 627 400 1 253 503 (203 417) 3 175 600 13 501 886

1 282 117 138 151

6 963 198 328 400 1530 529 539 6659 0 7 829 326

331 106 16 496 25 319 735 115 580

8 576 421 483 047 26 849 4 246 814 168 754 0 13 501 884

2 982 160 161 514 0 4 563 941

1 108 616

10-year average (2002–2011).

As in Canada, the US area in barley has also declined – from 2.9 Mha in 1992, to 1.7 Mha in 2002, and down to 1.3 Mha in 2013, a reduction of over 55% in 22 years. The decline can largely be attributed to the expansion of corn production. In Mexico, the area in barley has been stable, averaging 295 000 ha. Average yields are highest in the United States, at 3.5 mt ha1, and lowest in Mexico at 2.5 mt ha1, while Canadian yields averaged 3.2 mt ha1 over the 12-year period. Average yields increased slightly in the United States and Canada, by 0.06 and 0.1 mt ha1 per year, respectively, between 2002 and 2013, but showed no growth in Mexico. Overall production of barley in North America is trending downward, however. In 2012 and 2013, average production was 14.7 mmt compared to an average of 21.8 mmt in 1992 and 1993.

Consumption and Trade Table 8 summarizes production, consumption, and trade in barley in North America between 2002 and 2011. During that period, almost two-thirds of the domestic supply was used for animal feed, with another third used in processing – mostly as malt for beer-brewing industry, with smaller amounts used for

food and seed. Usage for animal feed has declined in step with reduced production, while the amounts used for processing have been fairly steady. North America is a net exporter of barley, with exports accounting for around 12% of average annual production. Canada, with exports averaging about 2.2 mmt, is typically one of the top five exporting countries. Of its remaining domestic supply, almost 90% is used for animal feed. In the United States, however, only 30% of the available supply goes to animal feed, with the majority of the crop going to the malting sector. In 2011, for example, malting varieties accounted for 75% of the acreage planted in Idaho (USDA, NASS, Idaho Barley Varieties) and over 90% of the acreage in North Dakota (North Dakota Barley Council).

Oats Oats, like barley, are minor cereals in North America and, with an average of 1.9 Mha harvested per year, accounts for < 3% of cereal acreage. The distribution of oats in North America is very similar to that of barley, with Canada accounting for 65% of

398 Table 9

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America Oat production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

Area 833 898 723 738 633 609 567 558 511 380 423 417 607

Table 10

Oat production, trade, and use (mt)


Prod. 1684 2096 1679 1667 1357 1313 1294 1351 1178 779 987 1016 1367

Canada Area 1379 1415 1234 1271 1537 1816 1448 980 906 1030 985 1107 1259

Mexico Prod. 2911 3377 3467 3283 3852 4696 4273 2906 2480 2997 2812 3888 3412

Area 42 46 67 77 76 72 100 72 67 52 47 49 64

Prod. 64 94 103 127 152 125 148 130 111 51 84 91 107

North America

World

Area 2254 2360 2024 2086 2246 2497 2115 1610 1484 1461 1455 1574 1930

Area 12 436 12 128 11 663 11 250 11 661 11 990 11 279 10 195 9096 9638 9580 9759 10 890

Prod. 4658 5567 5249 5077 5362 6134 5714 4388 3769 3826 3884 4995 4885

Prod. 25 424 26 541 26 036 23 697 22 612 25 806 25 863 23 345 19 723 22 316 21 312 23 821 23 875

The United States

Canada

Mexico

North America

1 439 809 1 980 072 (234 800) 99 493 3 085 586

3 424 110 35 045 (47 726) 1 754 758 1 656 673

110 464 144 953 0 390 255 027

4 974 383 2 160 070 (282 526) 1 854 641 4 997 286

1 774 544 138 004

1 491 643 147 220 900

190 960 3782 1970

1 173 038

16 909

58 315

3 457 147 289 006 2870 0 1 248 262

3 085 586

1 656 672

255 027

4 997 285

10-year average (2002–2011).

the area, the United States with 31%, and Mexico < 4%. Table 9 provides data on oat production between 2002 and 2013. Worldwide, oats accounted for only 1.7% of the area in cereals, and between 2002 and 2013, the harvested area declined by more than 20%. North America accounts for about 20% of the world’s production. The EU and Russia are the leading oat producers, accounting for roughly 35% and 20% of production, respectively. Canada is the third ranked producer with around 15% of world production (Agriculture and Agri-Food Canada). In Canada, oats occupy about 8% of the area in cereals, a share similar to that of maize. In the United States and Mexico, its share is much lower at 1.1% and 0.6%, respectively. Mirroring the trend in world acreage, between 2002 and 2013, the area in oats declined in both the United States and Canada. The decline has been sharpest in the United States where the 416 Tha harvested in 2013 represented half the area harvested in 2002 and less than a quarter of the 1.8 Mha harvested in 1992. In the United States, oats are grown primarily in the North Central states, with Minnesota, North and South Dakota, Wisconsin, and Iowa jointly accounting for more than half of the US harvested area. In Canada, most of the production is in the Prairie Provinces (Alberta,

Saskatchewan, and Manitoba). Yields in the United States averaged 2.3 mt ha1 between 2002 and 2013, compared to 2.7 mt ha1 in Canada and 1.7 mt ha1 in Mexico. Yields in the United States and Canada evidenced a slight upward trend over the period, but as was the case with barley, there was no similar upward trend in Mexican yields. The area in oats in Mexico ranged from 42 000 ha in 2002 to 100 000 ha in 2008, with most production in the northwest of the country.

Consumption and Trade Table 10 summarizes production, consumption, and trade in oats in North America between 2002 and 2011. As with barley, oats are used primarily for animal feed. Of the average domestic supply of 5 mmt, around 3.5 mmt or 70% was used for animal feed, with most of the remainder used for human consumption. The amount of oats used for human food has remained relatively constant – averaging 1.3 mmt per year in the period between 1992 and 2001 and 1.25 mmt between 2002 and 2011. As production declined, the amount used for animal feed also declined, averaging 3.5 mmt per year between 2002 and 2011, compared to 4.9 mmt between 1992 and 2001.

GRAINS AROUND THE WORLD | Grain Production and Consumption: Cereal Grains in North America Trade in oats is fairly limited with exports from Canada to the United States accounting for between 55% and 65% of annual world trade, making Canada the world’s largest exporter and the United States the largest importer. Canada’s exports averaged 1.7 mmt, equivalent to half of domestic production, while US imports exceeded its own domestic production. Mexico also imports more oats than it produces domestically with imports coming primarily from Canada.

Rice Data on North American and world rice production (paddy equivalents) from 2002 to 2013 are provided in Table 11. The United States accounts for over 95% of North American rice acreage and production. Mexico harvests about 50 000 ha annually accounting for < 0.5% of its cereal area. Because the climate is unsuitable, no rice is grown in Canada. Combined, the United States and Mexico account for < 2% of world production. Global production is concentrated in Asia, with China and India combining for over half the world total. Another 20% of production comes from Thailand, Vietnam, Indonesia, and the Philippines. Table 11

399

The US area in rice declined by over 20% between 2002 and 2013, from 1.3 Mha to just under 1.0 Mha. An average yield increase of 0.08 mt ha1 per year tempered the decline in production to about 10% over the 12-year period. The leading rice-growing state is Arkansas with about 44% of the total US area, followed by California with 22%. Rice is also grown in Louisiana, Mississippi, Missouri, and Texas. Rice is classified as either long grain, medium grain, or short grain depending on the shape and length of the grain. US production is predominantly long grain, which is grown mostly in Arkansas and the other southern states and accounts for over 70% of US production. Medium and short grain types are grown almost exclusively in California, although Arkansas does have some medium grain production.

Consumption and Trade Table 12 provides data on rice production, consumption, and trade (in paddy equivalent tonnes, not milled) in North America between 2002 and 2011. Although the United States is relatively small in terms of global production, it is a major exporter. On average, over the 10-year period considered in Table 12, the United States exported over half of its domestic production and,

Rice production: Area harvested (000 ha) and production (000 mt) The United States

Year 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Avg.

Area 1298 1213 1346 1361 1142 1112 1204 1256 1463 1059 1084 1000 1211

Table 12

Rice production, trade, and use (mt)

Production Imports Stock change Exports Domestic supply Use Feed Seed Waste Processing Food Other uses Total use 10-year average (2002–2011).

Prod. 9569 9067 10 540 10 108 8826 8999 9241 9972 11 027 8389 9051 8613 9450

Canada Area 0 0 0 0 0 0 0 0 0 0 0 0 0

Mexico Prod. 0 0 0 0 0 0 0 0 0 0 0 0 0

Area 50 60 62 57 70 71 50 54 42 34 32 33 51


Area 1348 1273 1408 1419 1212 1183 1255 1310 1505 1093 1116 1033 1263

Prod. 9796 9340 10 818 10 399 9163 9293 9466 10 235 11 244 8562 9230 8793 9695

World Area 147 628 148 509 150 554 154 989 155 581 155 040 159 993 158 130 161 189 162 800 162 317 164 722 156 788

Prod. 571 388 587 031 607 986 634 444 641 207 656 978 688 415 686 958 701 999 726 122 738 188 745 710 665 535

The United States

Canada

Mexico

North America

9 573 761 1 164 158 (122 019) 5 482 877 5 133 021

611 334 (5) 147 972 463 357

257 963 843 477 (794) 43 982 1 056 664

9 831 724 2 618 969 (122 817) 5 674 831 6 653 042

3451 48 726 74 417 927 595 2477 1 056 665

0 176 565 1 000 591 768 572 4 477 181 246 159 6 669 069

173 115 938 409 694 156 3 129 554 213 814 5 149 047

13 457 420 033 29 868 463 358

400


with an 11% share of world exports, was the fourth largest exporter following Thailand, Vietnam, and India and ranking marginally ahead of Pakistan. Mexico is the largest export market for US rice with other important markets including Japan, Turkey, and a number of Central American and Caribbean countries. The United States also imports rice, but imports are mostly aromatic varieties that are not grown domestically, such as jasmine from Thailand and basmati from India and Pakistan (USDA, ERS, Rice). Canada’s domestic supply is all imported with about half coming from the United States. Mexico is also reliant on imports, which account for close to 80% of its supply. Those imports come primarily from the United States, but Mexico also imports from Uruguay and Pakistan (USDA, FAS, Mexico Grain and Feed Annual). In North America, rice is used predominantly for human food with some use in food manufacturing (rice starch, beer, or alcoholic beverages).

of maize for as many years as possible. Subtract the US and Canadian data from the world data to facilitate comparison between the United States, Canada, and the rest of the world (RoW). Divide production by area harvested to obtain average yield, and plot the average yield over time for the United States, Canada, and the RoW. Comment on the trends.

Further Reading Lukow OM and McVetty PBE. Grain production and consumption: Cereal grains in North America. Encyclopedia of Food Grains, 1st edn. United States Department of Agriculture (USDA), Foreign Agricultural Service (FAS). (2013) Global Agricultural Information Network (GAIN) Report Number MX3024. Grain and Feed Annual, Mexico. http://gain.fas.usda.gov/Recent%20GAIN% 20Publications/Grain%20and%20Feed%20Annual_Mexico%20City_Mexico_315-2013.pdf.


• •

• • •

• •

Use the data in the tables to construct pie charts describing the 2013 allocation of cereal hectares among the six grains for each of the three North American countries. Again, using the data provided, create line graphs showing the trend for the North American share of world production for each of the six grains between 2002 and 2013. For which of the grains is there a noticeable upward or downward trend in the North American share of global output? If the decline in US oat production continues at the same rate as occurred between 2002 and 2013, in what year will oat production cease in the United States? Within Europe, what are the leading oat-producing countries? Compare the trends in world average yields for oats and barley. Compare the trends in US, Mexican, and world sorghum yields between 2002 and 2013. Are there any noticeable differences? (Hint – for a cleaner comparison, first subtract US and Mexican area and production from the world numbers before calculating the average yield for the rest of the world). Estimate the trend growth in US maize yields (with and without the drought year of 2012). What is the predicted maize yield for 2020 using both models? Compare the trends in US and Canadian average yields for maize and wheat.


•

• •

Investigate the importance/share of organic production for each of the major grains. What are the recent trends in production of organic corn and soybeans in the North American countries? Is North America a net imported or exported of organic grains? Investigate the prospects for rice production, particularly wild rice, in Canada. Can you find data on wild rice production? How significant is production of wild rice in relation to Canadian rice imports? Use the FAOSTAT database to obtain data on US, Canadian, and world area (hectares harvested) and production (tonnes)

Relevant Websites http://www.agannex.com/research/sorghum-in-canada – Ag Annex “Sorghum in Canada”. http://www.agr.gc.ca/eng/industry-markets-and-trade/statistics-and-marketinformation/by-product-sector/crops/crops-market-information-canadian-industry/ market-outlook-report/oats-situation-and-outlook-august-2010/? id¼1378843401619 – Agriculture and Agri-Food Canada. Oats: Situation and Outlook. http://www.agcensus.usda.gov/Publications/2012/Online_Resources/Ag_Atlas_Maps/ Crops_and_Plants/ – United States Department of Agriculture (USDA), Census of Agriculture. http://barley.idaho.gov/pdf/quality_reports/2011varieties.pdf – United States Department of Agriculture (USDA), National Agricultural Statistics Service (NASS). Idaho Barley Varieties. http://www.epa.gov/otaq/fuels/renewablefuels/ – United States Environmental Protection Agency, Renewable Fuel Standard. http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-inthe-us.aspx – United States Department of Agriculture (USDA), Economic Research Service (ERS). http://www.ers.usda.gov/topics/crops/rice/trade.aspx – Adoption of Genetically Engineered Crops in the U.S. http://www.fsa.usda.gov/FSA/webapp?area¼home&subject¼copr&topic¼rns-css – United States Department of Agriculture (USDA), Economic Research Service (ERS). Rice. http://faostat3.fao.org/download/Q/*/E – FAOSTAT, Food and Agriculture Organization of the United Nations. http://gain.fas.usda.gov/Recent%20GAIN%20Publications/Grain%20and%20Feed% 20Annual_Mexico%20City_Mexico_3-15-2013.pdf – United States Department of Agriculture (USDA) Farm Service Agency, Conservation Programs. http://www.gmo-compass.org/eng/agri_biotechnology/gmo_planting/ – GMO Compass. http://www.nature.com/news/gm-maize-splits-mexico-1.15493 – Nature.com “GM maize splits Mexico”. http://www.ndbarley.net/barleystatistics/ – North Dakota Barley Council. http://www.statcan.gc.ca/pub/96-325-x/2014001/article/11913-eng.htm – Statistics Canada. “Corn: Canada’s third most valuable crop”. http://quickstats.nass.usda.gov/ – United States Department of Agriculture (USDA), National Agricultural Statistics Service (NASS), Quick Stats. http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID¼1000. United States Department of Agriculture (USDA) National Agricultural Statistics Service (NASS), Acreage http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID¼1046 – United States Department of Agriculture (USDA), National Agricultural Statistics Service (NASS), Crop Production. http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID¼1194 – United States Department of Agriculture (USDA), World Agricultural Outlook Board. World Agricultural Supply and Demand Estimates, Various Issues. http://en.worldstat.info/ – Worldstat.

Grain Production and Consumption: Oilseeds in North America PBE McVetty, University of Manitoba, Winnipeg, MB, Canada OM Lukow, Agriculture and Agri-Food Canada, Winnipeg, MB, Canada LM Hall, University of Alberta, Edmonton, AB, Canada I Rajcan, University of Guelph, Guelph, ON, Canada H Rahman, University of Alberta, Edmonton, AB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

The major oilseeds grown in North America are canola, soybean, linseed/flax, and sunflower. Whereas sunflower is native to North America, the other species have been introduced. Statistics are provided for disposition and consumption of these oilseeds as 10-year means, as well as historical and recent annual figures for acreage and production for Canada, the United States, and Mexico. Canola (Brassica napus) has increased in area because it is adapted to cool Canada’s climate and has been bred to have low levels of erucic acid in seed oil and glucosinolates in seed meal. Canada is the major producer of canola with much of it being exported. The United States is the major producer of soybeans, with much of it being used domestically. Linseed and sunflower are relatively minor crops in North America.

Learning Objectives

• •

To achieve understanding of the origins and production of the major oilseed species in Canada, the United States, and Mexico. To understand the uses of these species and the extent of their involvement in world trade.

Introduction

Canola (Double-Low Rapeseed)

North America is the major production area for oilseeds and is a primary or secondary producer in the world of many of the oilseeds reviewed in this article. Major oilseeds grown in this continent include canola, soybean, linseed/flax, and sunflower. These oilseeds are grown, to greater or lesser extent, in three countries comprising this continent, Canada, the United States, and Mexico. Several of the major oilseeds, such as canola, soybean, and linseed/flax, currently grown in North America were introduced in the last few centuries, whereas sunflower is native to this continent. All the current major oilseeds in this continent have grown from small beginnings to their major field crop status today based on successful research and development in cultivar development, production practices, market development, and new use development. This article will review the area used to produce each of these major oilseeds and their production in


each North American countries and on the continent since 1960s. The last 10-year mean disposition and consumption of each of these major oilseeds in each of the countries and on the continent will also be reviewed. All comments regarding crop disposition and consumption refer to averages of the 2000s, unless specifically stated otherwise. Area and production data for all crops relate to crops harvested for dry grain only. For disposition and consumption of commodities, the definitions of the listed elements are taken primarily from the Food and Agriculture Organization (FAO) of the United Nations. Values given for production relate to the total domestic production. Imports cover all movements into the country of the commodity. Stock variation is the changes in stocks at all levels between the production and the retail levels. A negative sign indicates increases in stocks (add to stock) and no sign means net decreases (from stock). Exports cover all movements by the crop commodity out of the country. Domestic supply is defined as (production þ imports) (exports þ changes in stocks). Feed is the amount of the commodity in question fed to livestock, whether domestically produced or imported. Seed comprises the amount of commodity used for reproduction. Waste includes the amount of crop commodity lost in processing, storage, and transportation. Processing is the amount of commodity used for the manufacture of processed products that cannot be converted back to their originating primary commodities. Food available for human consumption comprises the amounts of the commodity not detailed otherwise in the balance sheet. Other uses comprise quantities of the commodity used for manufacture of nonfood products.

Introduction Rapeseed includes the Brassica oilseed crop species Brassica napus and Brassica rapa, while Brassica juncea is commonly called mustard. These oilseed crops collectively contribute about 15% of the world’s total supply of vegetable oils and became the third-leading source of oil in the world after soybean and palm. Brassica oilseeds contain about 40–46% oil (in some cases up to 50%) and the seed meal remaining after oil extraction contains about 40% protein. Worldwide, this meal is the second most important (after soybean) economical protein source used in animal feed. Brassica oilseed crops are primarily grown to produce edible oil and meal for animal feed; however, small quantities are used directly for feed and planting seed. Because of the ability of the Brassica seeds to germinate and grow at low temperatures, these oilseed crops are among the

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few oil crops that can be grown in the temperate regions of the world. Among these, B. napus is predominantly grown in North American countries; however, B. rapa and B. juncea can also be found on limited areas (<1%). B. rapa is more suited to short growing season areas, while B. juncea is more suitable to the hotter and drier regions. B. napus exists in both spring and winter growth habit forms, but it is the spring form that predominates in North American production; winter form is grown on very limited areas in the United States. This oilseed crop was first introduced in Canada and grown at a commercial scale during the Second World War. Traditional rapeseed and mustard seeds contain a high level of erucic fatty acid in oil (>40% of the total fatty acids) and a high level of glucosinolates in seed meal (>100 mmol g1). The erucic acid is undesired in edible oil, while the seed meal containing a high level of glucosinolate is undesirable for use of this meal as protein source in animal feed. The oil and meal quality of these oilseed crops has been dramatically improved (virtually eliminated erucic acid in oil and reduced glucosinolate content to <30 mmol g1 seed meal) in 1960s–1970s through research, and the name ‘canola’ for this qualityimproved-type Brassica oilseed crops has been adopted in most parts of the world. The term ‘double-low rapeseed’ or ‘rapeseed’ or ‘oilseed rape’ is still being used for this qualityimproved type in some countries as well as in some articles. Most of the world production of Brassica oilseeds including the production acreages in North American countries has transferred to canola quality type; therefore, the word ‘canola’ will be used in this article. Currently, most of the canola grown in North American countries is hybrid cultivars. About half of the canola crop is Roundup (glyphosate) herbicide-tolerant and half Liberty (glufosinate) herbicide-tolerant; Clearfield (imidazolinone) herbicide-tolerant crops cover a small acreage (<5%).

Area Harvested Canada has harvested canola on an average from about 6.2 million hectares (Mha) (14.4% of Canadian arable land) during the period of 2003–12 (Table 1). Since 1980s, canola production area in Canada has increased more than twofold with a sharp increase in the recent years (>8 Mha in 2012) (Table 1). The vast majority of canola production area in Canada is in the Prairie Provinces Alberta, Saskatchewan, and Manitoba, while small production areas can be found in Ontario and British Columbia. The United States started to grow canola from the late 1980s. This country on an average has harvested canola from about 453 725 ha (0.3% of American arable land) annually during the period of 2003–12 (Table 2); this is more than a twofold increase since the 1990s. The vast majority of canola production area in the United States is the northern state of North Dakota where spring canola is grown. Small production areas can also be found in Minnesota, Montana, Idaho, Oregon, Washington, and Oklahoma. Recently, winter canola has captured about 15% of the canola production area in the United States, primarily grown in Oklahoma and small areas in the Pacific Northwest region. Mexico is a very small canola producer, harvesting on an average from only about 2000 ha (0.01% of Mexican arable

Table 1

Area harvested (ha) for major oilseeds grown in Canada

Year

Canola

Soybean

Linseed

Sunflower

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

473 395 1 269 886 1 311 010 2 296 424 2 695 840 3 060 920 4 692 620 4 653 100 4 689 200 4 867 000 5 175 400 5 238 200 6 327 600 6 494 400 6 513 300 6 848 300 7 471 300 8 379 900 6 200 460

104 650 139 534 178 307 296 980 403 880 555 400 855 900 1 027 500 1 048 600 1 173 500 1 165 200 1 201 200 1 171 500 1 195 400 1 383 300 1 476 800 1 542 400 1 668 400 1 302 630

721 569 830 993 532 374 621 610 647 360 508 800 679 520 690 180 728 400 518 000 732 600 785 200 524 000 625 200 623 300 353 300 273 200 360 000 552 320

23 253 49 768 34 845 116 520 46 660 58 360 58 060 75 580 105 600 55 400 70 800 76 900 78 900 68 800 63 500 51 400 13 800 40 000 62 510

Italicized ¼ 5- or 10-year means. Source: Food and Agriculture Organization of the United Nations (FAO).

Table 2 Area harvested (ha) for major oilseeds grown in the United States Year

Canola

Soybean

Linseed

Sunflower seed

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

0 0 0 0 3060 38 960 163 604 515 835 432 695 338 240 451 634 413 593 468 070 400 160 329 780 579 880 422 620 700 560 453 723

13 775 857 17 268 909 21 679 194 27 309 878 24 741 123 23 432 403 25 261 600 29 199 730 29 330 310 29 930 060 28 834 570 30 190 680 25 959 245 30 222 654 30 906 980 31 003 300 29 856 410 30 798 530 29 703 274

1 078 310 827 732 571 738 286 500 230 500 93 014 60 464 202 993 237 958 206 797 386 480 310 397 141 237 137 595 127 070 169 160 70 010 135 980 192 268

37 669 146 238 472 853 1 653 180 1 078 720 831 596 1 183 810 1 157 571 889 104 692 425 1 056 240 716 300 814 236 969 640 790 560 758 310 589 960 745 030 802 181


land) annually in the last 10 years (Table 3). The area of canola harvested in Mexico has varied widely during the years. Canola production area in Mexico has reduced to less than half in the recent years when compared with 1970s (Table 3). This variation in harvested area is typical for any small-volume crop. The vast majority of canola production area in Mexico is in the central area of the country. For the entire North American continent, canola was harvested from an average 6.7 Mha (2.9% of North American

GRAINS AROUND THE WORLD | Grain Production and Consumption: Oilseeds in North America Table 3

Area harvested (ha) for major oilseeds grown in Mexico

Table 5

403

Production (tonnes) for major oilseeds grown in Canada

Year

Canola

Soybean

Linseed

Sunflower

Year

Canola

Soybean

Linseed

Sunflower

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

5800 6400 5800 3600 807 177 1025 3200 1000 1000 4000 5000 3000 2000 2181 0 185 10 1838

41 925 151 696 288 624 297 419 421 432 315 880 166 454 75 084 67 880 88 840 96 266 54 211 62 580 75 767 64 740 153 473 155 513 142 329 96 160

17 623 17 340 10 262 4795 683 85 27 367 1350 2900 1400 8500 10 300 7300 2600 3600 2600 2500 4305

0 13 415 3354 9905 9545 4098 1295 470 124 90 22 175 3 4 216 1878 1850 1280 564

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

429 557 1 257 833 1 403 862 2 697 258 3 430 320 3 758 120 6 120 800 6 636 900 6 771 200 7 673 600 9 483 300 9 000 300 9 601 100 12 642 900 12 889 200 12 773 300 14 164 500 15 409 500 11 040 890

202 003 278 264 374 759 663 476 978 700 1 309 720 2 260 540 2 438 280 2 273 300 3 043 900 3 155 600 3 465 500 2 695 700 3 335 900 3 506 800 4 345 300 4 246 300 4 870 160 3 493 846

518 155 689 302 443 500 609 519 757 940 546 360 887 780 820 740 754 400 516 900 990 600 988 800 633 500 861 100 930 100 423 000 368 300 489 000 695 570

15 310 41 111 36 893 142 980 57 440 85 100 76 340 122 840 142 300 52 200 84 400 157 300 124 800 112 200 101 900 67 600 19 800 73 600 93 610



Table 4 America

Production

Area harvested (ha) for major oilseeds grown in North

Year

Canola

Soybean

Linseed

Sunflower

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

479 195 1 276 286 1 316 810 2 300 024 2 699 707 3 100 057 4 857 249 5 172 135 5 122 895 5 206 240 5 631 034 5 656 793 6 798 670 6 896 560 6 845 261 7 428 180 7 894 105 9 080 470 6 656 021

13 922 433 17 560 138 22 146 124 27 904 277 25 566 435 24 303 683 26 283 954 30 302 314 30 446 790 31 192 400 30 096 036 31 446 091 27 193 325 31 493 821 32 355 020 32 633 573 31 554 323 32 609 259 31 102 064

1 817 502 1 676 065 1 114 375 912 904 878 543 601 899 740 011 893 539 967 708 727 697 1 120 480 1 104 097 675 537 770 095 752 970 526 060 345 810 498 480 748 893

60 922 209 421 511 051 1 779 605 1 134 925 894 054 1 243 165 1 233 620 994 828 747 915 1 127 062 793 375 893 139 1 038 444 854 276 811 588 605 610 786 310 865 255


arable land) annually during the period of 2003–12 (Table 4); this production area constitutes about 22% of the world’s Brassica oilseeds crop acreage. The canola production area in this continent has doubled in the recent years when compared with the production area in the 1990s (Table 4). Of the total North American canola harvested area during the period of 2003–12, Canada’s share was 93.1%, the United States 6.8%, and Mexico <0.5%.

Canada has produced on an average about 11 Mt canola annually during the period of 2003–12 (Table 5). Canola production in Canada has varied by a factor of about 2 during the 2000s (Table 5). This variation resulted from the increase in harvested area as shown in Table 1 and about a 25% increase in yield with the introduction of hybrid cultivars. The average yield of canola in Canada has reached to 1.78 tonnes ha1 in the recent years as compared to 1.35 tonnes ha1 in 1990s. The United States has produced on an average 754 943 tonnes of canola annually during the period of 2003–12 (Table 6). Canola production in this country has increased by about 1.5-fold in recent years when compared with production in the 1990s (Table 6). The average yield of canola in the United States has reached 1.66 tonnes ha1, similar to the Canadian average yield. Mexico has produced on an average 2746 tonnes canola annually during the period of 2003–12 (Table 7). The production of this crop in Mexico has reduced to almost half in the 2000s when compared with 1970s (Table 7). The average yield of canola in Mexico has been 1.49 tonnes ha1, slightly lower than Canada and the United States. For the entire North American continent, average annual canola production was 11.8 Mt during the period of 2003–12 (Table 8); this is about 22% of the world’s production of Brassica oilseeds. In North America, there has been a sharp increase in production in the last 10-year period – mostly reflecting Canadian production. Canada has produced 93.6%, the United States 6.4%, and Mexico <0.3% of the North American canola during the period of 2003–12. In terms of global production, North America has produced about 22% of the world’s Brassica oilseeds during the period of 2003–12. The share of world canola for Canada, the United States, and Mexico in the last 5 year average is 22.0%, 1.4%,

404


Table 6 States

Production (tonnes) for major oilseeds grown in the United

Table 8 America

Production (tonnes) for major oilseeds grown in North

Year

Canola

Soybean

Linseed

Sunflower

Year

Canola

Soybean

Linseed

Sunflower

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

0 0 0 0 2450 57 918 242 190 769 017 686 462 612 533 718 484 632 948 649 519 655 610 669 340 1 113 390 698 910 1 112 230 754 943

22 592 554 31 646 150 40 105 814 55 071 062 51 579 882 52 119 203 63 292 800 75 110 850 66 781 392 85 013 945 83 504 928 86 998 898 72 857 739 80 748 700 91 417 300 90 605 460 84 191 930 82 054 800 82 417 509

682 119 626 942 344 966 233 298 209 340 81 928 64 184 247 081 267 117 263 358 500 273 279 894 149 764 145 192 188 550 230 030 70 890 146 360 224 143

40 319 155 861 596 032 2 256 880 1 395 300 1 089 000 1 692 246 1 726 263 1 208 930 929 690 1 822 151 972 330 1 301 298 1 552 570 1 377 320 1 240 830 924 550 1 263 570 1 259 324

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

433 357 1 263 433 1 409 662 2 700 858 3 433 783 3 816 190 6 364 140 7 410 317 7 458 662 8 288 133 10 206 784 9 641 248 10 254 619 13 302 510 13 561 821 13 886 690 14 863 440 16 521 880 11 798 579

22 874 598 32 206 247 40 979 377 56 278 439 53 326 233 54 051 454 65 843 445 77 667 860 69 180 698 88 191 192 86 847 763 90 545 511 75 641 810 84 237 622 95 045 000 95 118 425 88 643 464 87 172 460 86 062 395

1 215 535 1 339 214 804 955 848 497 967 827 628 429 952 010 1 068 078 1 022 477 782 258 1 491 833 1 274 694 790 464 1 011 392 1 120 450 655 530 440 990 637 060 922 715

55 629 205 349 635 980 2 407 590 1 461 224 1 176 857 1 769 907 1 849 665 1 351 385 982 122 1 906 582 1 129 808 1 426 105 1 664 775 1 479 552 1 312 227 947 176 1 338 478 1 353 821



Table 7

Table 9 Canada 10-year averages for disposition and consumption (tonnes) 2000–09

Production (tonnes) for major oilseeds grown in Mexico

Year

Canola

Soybean

Linseed

Sunflower

1963–67 1968–72 1973–77 1978–82 1983–87 1988–92 1993–97 1998–2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2003–12

3800 5600 5800 3600 1013 152 1150 4400 1000 2000 5000 8000 4000 4000 3281 0 30 150 2746

80 042 281 833 498 804 543 900 767 651 622 531 290 105 118 730 126 006 133 347 187 235 81 113 88 371 153 022 120 900 167 665 205 234 247 500 151 039

15 261 22 970 16 488 5680 547 141 46 258 960 2000 960 6000 7200 5100 1800 2500 1800 1700 3002

0 8376 3056 7730 8484 2757 1321 562 155 232 31 178 7 5 332 3797 2826 1308 887


and 0.003%, respectively. Currently, Canada ranks in the top five countries of the world for canola production.

Disposition and Consumption During 2000–09, of the average annual 8.6 Mt canola produced in Canada and the 200 832 tonnes imported, 3.9 Mt was used domestically and 4.8 Mt was exported (Table 9). Thus, Canadian production was more than double the quantity of

Crop

Canola

Soybean

Linseed

Sunflower

Production Imports Stock change Exports Domestic supply Feed Seed Waste Processing Food Other uses

8 609 150 200 832 84 000 4 799 534 3 926 448 288 376 45 593 266 662 3 280 738 45 080

2 815 060 479 988 4000 1 242 257 2 056 791 336 197 122 440 27 000 1 549 250 21 804

695 570 13 000

115 560 21 823 1850 82 127 57 106 5142 954

530 570 178 000 30 260

51 010 8900 131 720

Statistics Canada, 2014. Source: Food and Agriculture Organization of the United Nations (FAO).

canola used domestically. About 85% of the canola used domestically in Canada was used for processing and food manufacture, 7% for feed, and small amount for planting seed (Table 9). Of the average annual 737 320 tonnes canola produced in the United States and the 536 768 tonnes imported each year during 2000s, 965 542 tonnes was used domestically and 309 171 tonnes was exported (Table 10). Of the total domestic supply in the United States, almost the whole amount was used for processing and food manufacture (Table 10) and a small amount for planting seed. Mexico’s domestic supply of canola is heavily dependent on imports. During 2000–09, the country imported on an average 1.1 Mt annually while producing only 5017 tonnes per year (Table 11). About 99% of the Mexico’s domestic supply was used for processing and food manufacture (Table 11).

GRAINS AROUND THE WORLD | Grain Production and Consumption: Oilseeds in North America Table 10 US 10-year averages for disposition and consumption (tonnes) 2000–09 Crop

Canola

Soybean

Sunflower


737 320 536 768 625 309 171 965 542

79 605 515 215 039 1 420 000 29 835 045 51 405 509 1 272 200 2 433 077 1 736 721 45 952 100 11 413

1 343 461 71 636 21 070 147 185 1 246 842 353 400 11 042

4159 17 177 897 800 72 469 49 830

625 100 265 400

Source: Food and Agriculture Organization of the United Nations (FAO).

Table 11 Mexico 10-year averages for disposition and consumption (tonnes) 2000–09 Crop

Canola

Soybean

Sunflower


5017 1 087 017 680 440 1 090 914

120 053 3 859 942 0 871 3 979 124 867 170 3365 119 359 2 185 877 1353 802 000

175 25 472 700 42 26 304

23 11 026 1 072 080 7785

23 790 2514


Table 12 North America 10-year averages for disposition and consumption (tonnes) 2000–09 Crop

Canola

Soybean

Sunflower


9 351 487 1 824 617 84 055 5 109 144 5 982 905 288 376 49 775 294 865 5 250 618 125 334 49 830

82 540 628 4 554 969 1 424 000 31 078 173 57 441 424 2 475 567 2 558 882 1 883 080 49 687 227 34 570 802 000

1 459 196 118 931 18 520 229 354 1 330 252 358 542 11 995 699 900 267 914


Of the average 9.4 Mt canola produced annually in North America during the period of 2000–09, 6.0 Mt was used domestically (Table 12). About 90% of the canola used domestically in North America was used for processing and food manufacture (Table 12). A small amount was used directly for feed and planting seed as well.

405

Soybean Introduction Soybean (Glycine max [L.] Merr.) was domesticated as a forage crop in China about 3000 BC from its wild progenitor, Glycine soja. It became a commercially viable oilseed crop in the 1940s due to the development of shatter and disease-resistant new cultivars and the need for a domestic source of edible oil and protein for feed while trade was disrupted during World War II. There are only spring growth habit forms. By origin, the soybean progenitor is a subtropical plant, the cultivated soybean has wide adaptation to various climatic and soil conditions. As a photoperiod-sensitive short-day plant, it is divided by latitude into 13 maturity groups (000–10). While soybean has been grown in China as a food crop for thousands of years, it is grown throughout the world and used primarily as a source of edible vegetable oil and high-protein meal for animal feed (Table 9). Recently, soybean has also been used as a source of biodiesel and bioproducts for the manufacturing industry such as the automotive sector. Small quantities of soybeans are also used directly as animal feed, food (‘tofu,’ ‘miso,’ ‘natto,’ soymilk, and soy sauce), and planting seed.

Area Harvested Canada has harvested soybean from about 1.3 Mha (10 year average, 2003–12, 2.9% of Canadian arable land) annually (Table 1). The area of soybean harvested in Canada has varied by a factor of 3 during the 1990s, from about 555 000 ha to over 1.67 Mha (Table 1). Until the mid-1990s, the majority of soybean production area in Canada was in southwestern Ontario, whereas today, about 70% of soybean is grown in Ontario with the remainder being grown in Manitoba, Quebec, and a small amount in Prince Edward Island. The United States has harvested soybean from about 29.7 Mha (16.2% of American arable land) annually during the period of 2003–12 (Table 2). The area of soybean harvested in the United States has increased since the 1990s, beginning the decade at 23.6 Mha and ending it in 2012 at about 30.8 Mha (Table 2). The vast majority of soybean production area in the United States is in the midwestern US ‘corn belt’ states of Iowa, Illinois, Nebraska, Minnesota, Indiana, Kansas, Wisconsin, and South Dakota and the lower Mississippi Delta. Mexico is a very small soybean producer, harvesting soybean from only 96 160 ha (0.4% of Mexican arable land) annually during the period of 2003–12 (Table 3). The area of soybean harvested in Mexico has varied widely during the 1960s to 2000s, from a low of 41 000 ha to a high of 315 000 ha, with a trend toward decreased harvested area during the 1990s, which was replaced by an increasing trend in the late 2000s (Table 3). This variation in harvested area is typical for any small-volume crop. Soybean production occurs in central Mexico. For the entire North American continent, soybean was harvested from an average 31.1 Mha (12.1% of North American arable land) annually during the period of 2003–12 (Table 4). The area harvested has varied slightly since 1990s, from a low of 24.0 Mha to a high of 32.6 Mha (Table 4). Canada’s average soybean harvested area was 4.6%, the United States 94.9%, and Mexico <0.5% of the North American harvested area.

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Production Canada has produced on an average 3.5 Mt of soybean annually during the period of 2003–12 (Table 5). The production of soybean in Canada has varied by a factor of almost 3 during the 1990s and 2000s (Table 5), paralleling the variation in harvested area for soybean in Canada shown in Table 1. The average yield of soybean in Canada has been 2.8 tonnes ha1. The United States has produced on an average 82.4 Mt of soybean annually during the period of 2003–12 (Table 6). Soybean production has increased by more than 40% in the United States during the 1990s, from 52.1 Mt at the beginning of the 1990s to 90.6 Mt at the end of the 2000s (Table 6). The average yield of soybean in the United States has been 2.9 tonnes ha1, similar to the Canadian average yield. Mexico has produced on an average 151 000 tonnes of soybean annually during the period of 2003–12 (Table 7). The production of soybean in Mexico has varied by a factor of 8 during the 1990s, from a low of 81 000 tonnes early 1960s to a high of 622 000 tonnes in early 1990s (Table 7). This variation in production is typical for any medium volume crop. The average yield of soybean in Mexico during the 1990s has been 1.7 tonnes ha1, lower than the soybean yields seen for Canada and the United States. Soybeans are grown in Mexico under water-limiting rain-fed conditions. For the entire North American continent, average annual soybean production during the period of 2003–12 was 86.1 Mt (Table 8). There has been a year-to-year variation in production, with a trend toward increased production, not only mostly in the United States in recent years but also in Canada. In terms of North American production proportions, Canada has produced an average 4.6%, the United States 94.9%, and Mexico <0.5% of the soybean produced in North America. In terms of global soybean production, North America has produced on an average 33.0% of the soybean produced in the world. The share of world soybean production for Canada, the United States, and Mexico is 1.0%, 32.5%, and <0.2%, respectively. The United States is the top soybean producer of the world; however, it falls behind Brazil and Argentina, which represent almost a half (49%) of world production combined.

was used domestically and 871 tonnes was exported during the period of 2000–09 (Table 11). Approximately 55% of the soybean used domestically in Mexico was used for food processing (Table 11). Another 20% of the soybean domestic supply was used as animal feed and 20% was used in other uses. Minor amounts were used for planting seed and food (<3%). Of the average annual 82.5 Mt of soybean produced in North America and the 4.5 Mt imported, 57.4 Mt was used domestically, and 31.1 Mt was exported during the period of 2000–09 (Table 12). Over 60% of the soybean used domestically in North America was used for food processing (Table 12). Small amounts were used for feed, seed, food, and other uses (<8%).

Linseed (Flax) Introduction Linseed (Linum usitatissimum), also known as flax in North America, is one of the earliest cultivated field crops, initially grown for its fiber. In North America, in the last two centuries, linseed has been grown primarily for its oil. It is a spring annual, adapted to a wide range of soil and climatic conditions in the cool temperate zones of the northern hemisphere. Linseed in North America is used primarily to produce industrial oil and animal feed meal. Linseed oil is a drying oil used in paints and varnishes and for the manufacture of linoleum flooring. A trend toward bioproducts has increased this market in the 2000s. Because linseed oil contains alpha-linolenic acid (ALA), an essential omega-3 fatty acid, it has a variety of uses. Whole linseed is fed to poultry to produce omega-3 fatty acidenriched eggs. Linseed meal is a component of rations fed to pets, poultry, and animal. Small quantities of linseed are also used in food products (breads and breakfast cereals), but a significant number of products are being developed using linseed, in response to the variety of health benefits, including reducing heart disease and cancer risk. Additional products have been created based on the health and nutrition claims of linseed oil, lignans, and antioxidant flavonoids. Small quantities of linseed are used for (re)planting seed.

Disposition and Consumption

Area Harvested

Of the average annual 2.8 Mt of soybean produced and 480 000 tonnes imported by Canada, 2.1 Mt was used domestically and 1 242 000 tonnes was exported during the period of 2000–09 (Table 9). Approximately 55% of the soybean used domestically in Canada was used for food processing, mainly edible oil production (Table 9). Another 12% of the soybean domestic supply was used as animal feed. Minor amounts were used for planting seed and food (5%). Of the average annual 79.6 Mt of soybean produced in the United States and the 215000 tonnes of soybean imported, 51.4 Mt was used domestically and 29.8 Mt was exported during the period of 2000–09 (Table 10). Approximately 64% of the soybean used domestically in the United States was used for food processing, mainly edible oil production (Table 10). Small amounts were used for feed, planting seed, and food (<5%). Of the average annual 120 000 tonnes of soybean produced in Mexico and the 3.9 Mt of soybean imported, about 3.9 Mt

Canada has harvested linseed from an average of 552 000 ha (1.25% of Canadian arable land) annually between 2003 and 2012 (Table 1). The area of linseed harvested in Canada has varied widely, from a low of about 273 000 ha to a high of 785 000 ha (Table 1). The vast majority of linseed production area in Canada is in the Prairie Provinces (Alberta, Saskatchewan, and Manitoba). The United States has harvested linseed from about 192 000 ha (0.14% of American arable land) annually, averaged between 2003 and 2012 (Table 2). The area of linseed harvested in the United States has varied widely during the 2000s, from a low of about 70 000 ha to a high of 386 000 ha (Table 2). The vast majority of linseed production area in the United States is in the north-central states of North and South Dakota, Minnesota, and Montana. Only a small amount of linseed is grown in Mexico, averaging 4300 ha between 2003 and 2013.

GRAINS AROUND THE WORLD | Grain Production and Consumption: Oilseeds in North America For the entire North American continent, linseed was harvested from an average 748 000 ha (0.32% of North American arable land) annually between 2003 and 2012 (Table 4). The area harvested has varied widely during the 2000s (Table 4). Canada’s average linseed harvested area was 73.7%, United States 25.6%, and Mexico 0.6% of the total North American linseed harvested area.

Production Canada has produced on an average 695 570 tonnes of linseed annually between 2003 and 2012 (Table 5). The production of linseed in Canada has varied widely during the 2000s, from a low of 368 000 tonnes to a high of 0.99 million tonnes (Mt) (Table 5), paralleling the widely varying production area for linseed harvested in Canada as shown in Table 1. The average yield of linseed in Canada between 2003 and 2012 was 1.26 tonnes ha1. The United States has produced on an average 224 000 tonnes of linseed annually (Table 6). The production of linseed in the United States has varied widely during the 2000s, from a low of 71 000 tonnes to a high of 500 000 tonnes (Table 6), paralleling the widely varying production area for linseed harvested in the United States shown in Table 2. The average yield of linseed in the United States has been 1.02 tonnes ha1, slightly lower than the Canadian average yield. For the entire North American continent, average annual linseed production was 923 000 tonnes annually between 2003 and 2012 (Table 8). In terms of North American production proportions, Canada has produced an average of 75%, United States 24%, and Mexico 0.3% of the linseed produced in North America. In terms of global linseed production, North America has produced on an average 43.6% of all the linseed produced in the world. The share of world linseed production for Canada and the United States is 32.8% and 10.5%, respectively. Canada was the top linseed producer in the world in the 2000s, dropping from 34.8% in the 1990s due to the identification of low-level presence (LLP) of genetically engineered flax seeds.

Disposition and Consumption Canada is a net exporter of linseed. Of the average annual 695 570 tonnes of linseed produced in Canada and the 13 000 tonnes imported into Canada, 178 000 t was used domestically and 530 570 tonnes was exported, primarily for industrial oil uses (Table 9). Of the linseed used domestically in Canada, only small amounts of linseed (<5%) were used for food, while 74% was used for other uses combined (seed crushed for industrial oil and meal production for feed), and 17% was used for planting seed (Table 9). An average of 304 000 tonnes was retained on farm, for either seed or temporary storage (Statistics Canada 2014). Canada is a major exporter of linseed to the world (530 570 tonnes), with significant exports to Europe, the United States, Japan, South Korea, and China. Canada currently supplies nearly 60% of the linseed used in the United States. The United States is a net importer of linseed but exports 80% linseed to either Belgium or Canada. Because linseed is a relatively minor bioproduct crop, internal disposition of flax is not tracked by USDA or FAO.

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Sunflower Introduction Sunflower (Helianthus annuus) was domesticated as a food crop in North America, perhaps as early as 3000 BC. This was introduced to Europe in the 1600s and was successfully developed as an oil crop in Russia in the early 1800s. Russian plant breeders were able to increase the oil content in sunflower seed from less than 30% to over 50% – the major factor permitting the development of sunflower as oil crop for the temperate areas of the world. Sunflower is used primarily for edible vegetable oil and the seed meal is used for animal feed (Table 10). Moderate quantities of sunflower are directly used for animal feed and food manufacture (confectionary and bakery products) (Table 10). Small amounts are used for planting seed (<5%).

Area Harvested Canada has been growing sunflower commercially since the early 1940s; however, the production area remains small. During the period of 2003–12, Canada on an average has harvested sunflower from about 62 500 ha (about 0.1% of Canadian arable land) annually (Table 1). The area of sunflower harvested in Canada varied greatly during the years since the 1960s from a low of <15 000 ha to a high of >100 000 ha (Table 1), which is typical for a small-volume crop. The vast majority of sunflower production area in Canada is in the Prairie Province of Manitoba. The United States on an average has harvested sunflower from about 0.8 Mha (0.5% of American arable land) annually during the period of 2003–12 (Table 2). This is about a 15-fold increase in the production area when compared with the production area in 1960s; this is, however, about a 30% reduction when compared with the 1990s. The vast majority of sunflower production area in the United States is in the central Plains states (from Dakotas to Texas, with North Dakota being the predominant production area state). Mexico has been growing sunflower since early 1970s. During the period of 2003–12 the country on an average has harvested sunflower from only 564 ha (0.002% of Mexican arable land) annually (Table 3); this is <10% of the production area when compared with the acreage of this crop in the 1970s and 1980s. The area of sunflower harvested in Mexico has varied widely since 1970s; the crop almost vanished in mid-2000s (Table 3). The greater part of the sunflower production area is in central Mexico. For the entire North American continent, sunflower was harvested from an average 0.9 Mha (0.4% of North American arable land) annually during the period of 2003–12 (Table 4); this constitutes about 3.6% of the total sunflower production area in the world. The area harvested in North America has varied greatly in the last 50 years (Table 4). Of the total sunflower harvested area in this continent during 2003–12, Canada’s share is 7.2%, the United States 92.7%, and Mexico only 0.07%.

Production Canada has produced on an average 93 610 tonnes of sunflower annually during the period of 2003–12 (Table 5). The

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production of sunflower in Canada has varied greatly from a low of <20 000 tonnes to a high of >150 000 tonnes (Table 1) – reflecting the variation in harvested area. The average yield of sunflower in Canada has been 1.5 tonnes ha1. The United States has produced on an average 1.3 Mt of sunflower annually during the period of 2003–12 (Table 6) with an average yield of 1.6 tonnes ha1 (similar to the Canadian average yield). Compared to the 1990s, the country has produced about 20% less sunflower in the last 10 years. Mexico has produced on an average 887 tonnes of sunflower annually during the period of 2003–12 (Table 7). The production of sunflower in this country has varied greatly; this is primarily due to the variation in production area (Table 1). The average yield of sunflower in Mexico has been 1.6 tonnes ha1, very similar to the yields for Canada and the United States. For the entire North American continent, average annual sunflower production was 1.4 Mt during the period of 2003–12 (Table 8). This is about 23% reduction in production when compared with the production in the 1990s. In terms of North American production proportions, Canada has produced 6.9%, the United States 93.0%, and Mexico <0.1% of the total sunflower produced in North America during 2003–12. In terms of world sunflower production during 2003–12, North America has produced 4.2% of all the sunflowers produced in the world (Canada’s and Mexico’s share is <0.4% and the United States’s share is 3.9%).

Disposition and Consumption Of the average annual 115 560 tonnes of sunflower produced and the 21 823 tonnes of sunflower imported in Canada during the period of 2000–09, 57 106 tonnes was used domestically and 82 127 tonnes was exported (Table 9). About 89% of the sunflowers used domestically in Canada were utilized in processing and food manufacture, 9% was used as animal feed, and a small amount was used as planting seed (2%) (Table 9). Of the average annual 1.3 Mt of sunflower produced and the 71 636 tonnes of sunflower imported in the United States in the 2000s, 1.2 Mt was used domestically and 147 185 tonnes was exported (Table 10). About 70% of the sunflowers used domestically in the United States were utilized in processing and food manufacture, 28% were used as animal feed, and 1% were used for planting seed (Table 10). Mexico’s average annual domestic supply of sunflower in the 2000s was about 26 300 tonnes of which only 1% was produced within the country and the rest being imported (25 472 t) (Table 11). All domestic supply of the sunflower in Mexico was used in processing and food manufacture (Table 11). Of the average annual 1.5 Mt of sunflower produced and the 118 931 tonnes of sunflower imported in the North American countries during the period of 2000–09, about 84% of this supply was used domestically (Table 12). Over 70% of the sunflower used domestically in North America was used for processing and food manufacture, 27% was used as animal feed, and 1% was used for planting seed (Table 12).


• • • •

Describe the contrasts in the origins and cultivation of these major oilseed species in North America. Explain the role of plant breeding in the improvement of these crop species. What features distinguish oilseed production, quality, and consumption in your region from these factors in North America (or choose one of the North American countries)? Compare and contrast the utilization of the products of these four major oilseeds.


• • • •

Flax is a minor but significant crop in North America, where it is primarily grown for its seed. Find out about the possible use of the traditional product of flax as a fiber. Find out the differences in composition and properties between the oils obtained from these four oilseed species. Find out the differences in composition and properties between the residues (meal) left after oil removal obtained from these four oilseed species. Obtain details of oilseed-production areas of North America for each of the species. How similar (or different) are the respective growing sites in each of these countries?

See also: Agronomy of Grain Growing: Canola: Agronomy; Soybean: Agronomy; Breeding of Grains: Canola/Rapeseed: Genetics and Breeding; Soybean: Germplasm, Breeding, and Genetics; Fats: Healthy Fats and Oils; Lipid Chemistry; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Canola: Harvest, Transport, and Storage; Grains Around the World: Grain Production and Consumption: Cereal Grains in North America; Nonfood Products from Grains: Cereal Grains as Animal Feed; Oilseed and Legume Processing: Canola: Processing; Soybean: Processing; Soybean: Soy Concentrates and Isolates; The Oilseeds: Canola: Overview; Linseed: Overview; Oilseeds: Overview; Soybean: Overview; Sunflower: Overview.

Further Reading Robbelen G, Downey RK, and Ashri A (eds.) (1989) Oil Crops of the World, p. 554. Toronto: McGraw-Hill. Slinkard AE and Knott DR (eds.) (1995) Harvest of Gold: The History of Field Crop Breeding in Canada, p. 367. Saskatoon, Saskatchewan: University Extension Press/ University of Saskatchewan.

Relevant Websites http://www.canolacouncil.org/ – Canola Council of Canada. http://www.canadasunflower.com/ – National Sunflower Association of Canada (NSAC). http://faostat3.fao.org/faostat-gateway/go/to/download/Q/*/E – Food and Agriculture Organization of the United Nations. http://www.sunflowernsa.com/ – National Sunflower Association. http://www.statcan.gc.ca/start-debut-eng.html – Statistics Canada. http://www.uscanola.com/ – U.S. Canola Association. http://usda.gov – United States Department of Agriculture (USDA).

Grain Production and Consumption in Oceania: Australia and Pacific Countries CW Wrigley, University of Queensland, Brisbane, QLD, Australia RJ French, University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Food and Agriculture Organization lists 26 countries in the Oceania region – the South Pacific – including the main grain producers Australia and New Zealand. Maize and rice are produced in tropical countries such as New Caledonia, the Solomon Islands, New Caledonia, Vanuatu, and Fiji. The introduction of cereal grains to Australia since 1788 has been difficult with inappropriate varieties and ‘upsidedown’ seasons. Australia produced the world’s first wheat breeder–cereal chemist combination (Farrer–Guthrie) in the 1890s. Farrer and other breeders have greatly improved the yields and grain quality of Australian wheats. Grain yields differ considerably between grain species and between Australia and New Zealand. Grain yields are expected to increase as atmospheric levels of CO2 rise in coming decades; the protein content will decrease as a result.

Learning Objective

•

To extend knowledge about the production and utilization of grains around the world by learning about the countries in the Oceania region

Introduction The Oceania region includes the many islands of the southern Pacific Ocean, including Australia (classed as both an island and a continent), New Zealand (two major islands), Papua New Guinea, and many smaller islands. Those smaller islands that produce significant amounts of grain are listed in Table 1. Others include the Cook Islands, French Polynesia, Nauru, Samoa, and Tonga, most of them in the tropics. The Food and Agriculture Organization (FAO) lists 26 countries in Oceania in its statistics of agricultural products. Of these countries, the main grain producers are Australia, New Zealand, and Papua New Guinea (Table 2). Australia produces by far the greatest volume and diversity of grains, being also by far the largest in area, although much of its land area is not suited to grain production (Figure 1). None of the grains of economic significance are native to any of the countries of Oceania. These grains have been introduced by the first European colonists whose arrival in the southern Pacific is only a little over two centuries ago. The first settlers in Eastern Australia (the Sydney of 1788) found themselves trying to grow wheat under conditions in the


southern hemisphere that were completely different from those of their homeland, England. The first wheat crop, grown at the current site of Sydney’s Royal Botanic Gardens, yielded little more than the few bushels that were sown. In contrast to those early days, Australia is now a major exporter of wheat and of many other grains. Wheat and wool have been important for Australia’s (early) prosperity. Their importance has been acknowledged on the first bank notes issued in 1966 at the commencement of decimal currency (Figure 2). New Zealand was colonized at a time and under circumstances similar to those of Australia. Grain production in New Zealand is now also significant (Table 2), but generally not to the extent of being involved significantly in grain export. In contrast, the many nations of the Pacific Islands are importers of grain and flour products. For these reasons, much of this article relates to grain production in Australia.

Historical Perspective In its early decades, the Australian grain-growing industry fluctuated from underproduction through self-sufficiency to occasional periods of excess (Table 3). Wheat was the main grain grown, being needed for bread making. Farmers had to contest dry conditions, poor soil in some of the areas cultivated initially, attack by the rust pathogen, the reversal of seasons from their previous experience in the northern hemisphere, and varieties that were poorly adapted to the new continent. The problem of inappropriate wheat varieties was realized in the latter half of the nineteenth century by far-sighted farmers, by staff of ‘experimental farms,’ and by an amateur, William Farrer, whose profession as a surveyor took him into the heart of the wheat-growing regions. Whereas farmers attempted to develop improved varieties by selecting seed from plants that looked better than the rest of the crop, Farrer set about the (then) new technique of crossbreeding to increase the genetic diversity from which to select better genotypes. Figure 3 is an artist’s impression of Farrer among his small plots of crossbred wheats. The tall plants contrast with the much shorter wheats of more recent times. An example of the selection method is given in Table 3: the extension of wheat growing into drier regions was attributed to the selection of ‘Purple Straw’ (an earlier-maturing wheat) from a field of ‘Red Straw’ by a South Australian farmer in about 1860, just before the introduction of crossbreeding. The recent use of crossbreeding to produce new wheat varieties is shown in Figure 4. In most cases, crosses have been made, but there are still a few new varieties that have arisen as selections from an already existing variety, such as the selection of ‘Meering’ from the former wheat ‘Condor,’ which was presumably released as a mixture of a few genotypes.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00049-8

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GRAINS AROUND THE WORLD | Grain Production and Consumption in Oceania: Australia and Pacific Countries

Table 1 Production, in kilotonnes, of grains according to categories in crop year 2012 for countries of Oceania where there is significant production Country

Cereal grains

Oilseeds

Pulses

Australia Fiji Micronesia New Caledonia New Zealand Papua New Guinea Solomon Islands Vanuatu

43 372 9 0.3 3 1168 16 4 0.8

5291 0.3

2956 2.4

5 1.4

23 4 6

3

Source: http://faostat.fao.org.

Table 2 Production, in kilotonnes, of grain crops for the 2012 crop year in Australia, New Zealand, and Papua New Guinea (PNG) Crop Cereals Barley Maize Millet Oats Phalaris, canary seed Rice, paddy Rye Sorghum Triticale Wheat Oilseeds Cottonseed Linseed Peanuts Rapeseed Safflower Soybeans Sunflower seed Pulses Beans (various) Chickpeas Lentils Lupins Peas Vetches

Australia

New Zealand

PNG

8221 451 45 1262 6 919 40 2239 285 29 905

439 211

10

1694 7 25 3427 5 86 47

18

Diversification of Markets for Australian Wheat 1.2 4.5

489

2.4 1.4 2.7

4 475 673 463 982 343 20

improvement of grain quality for all grain species. A world-first innovation of that time (1890s) was the development of a very small-scale flour mill, suited to evaluating the milling quality of the small samples of grain coming from Farrer’s wheat breeding (Figure 5). Subsequent years brought the excess production of wheat that justified Farrer’s vision of export to England, largely as a result of the development of new wheat varieties (Table 3). These contributions by Farrer were recognized by the issue of $2 bank note when Australia changed to decimal currency in 1966 (Figure 2). However, the greatest expansion in wheat production occurred in the second half of the twentieth century, with production expanding from about 2 million tonnes (Mt) in 1940 to a high of about 25 Mt in 1999/2000. Nevertheless, production has fluctuated on occasions due to drought. The high of 2000 contrasts with the drought year of 2002/2003, when the national wheat crop was only a little over 10 Mt, less than half of the crops either side (about 24 Mt in both 2001/ 2002 and 2003/2004). Similar reductions in production were experienced for all grains in the 2002/2003 drought year. More recently, fluctuations have not been so great (Table 4) and total wheat production has continued to grow, with the production of nearly 30 Mt in 2012.

3 20

Gaps indicate insignificant production. Source: http://faostat.fao.org.

Farrer’s use of crossbreeding was partly aimed at developing wheats with grain quality suited for export to England by combining the dough quality of Canadian Fife wheats with the drought tolerance of wheats introduced from countries such as India, Palestine, and South Africa. This vision led him to enlist the help of the agricultural chemist, Frederick Guthrie, to evaluate the milling and baking quality of the small samples of his many crossbred lines. Thus, there was a start to the development of small-scale test methods and (probably) the world’s first breeder–chemist association, a combination that is now an integral part of the

Further improvements in the quality of wheat varieties and in management practices through the early twentieth century extended opportunities for grain exports. Initially, these exports were to England, where the grain was used for traditional products, mainly bread. This situation changed dramatically in the second half of the twentieth century. In recent decades, Australia has produced about four times more than its domestic needs, so that 70–80% of the wheat harvest is exported. Exported wheat goes to a wide range of countries, including Egypt, Indonesia, Iran, Iraq, Japan, and China. In the early days of this expansion, there was minimal diversification of the crop on the basis of grain quality. ‘Fair average quality’ was the basis of assessment of quality for most of the crop, although the region of origin of the ‘FAQ’ wheat provided a good indication of quality (Figure 6). The 1960s brought the realization that export markets for Australian wheat included a diversity of foods that could then be classed as ‘exotic’ (to Australians), such as ‘Arabic’ flat breads in the Middle East and a range of noodles and steamed breads in Asian countries. Furthermore, in countries such as Indonesia, even the manufacture of leavened bread involved nontraditional methods that required wheat of quality different from the English market. Accordingly, experts were brought to cereal chemistry laboratories in Australia from the new export markets to demonstrate the production of these exotic products. Figure 7 shows an expert from the Middle East with experimental Arabic ‘pocket’ breads, from both normal-scale baking and smallscale baking. As a result of seeking this expertise, it was possible for wheat breeders to select new varieties that would suit these diverse quality requirements. The resulting research led to the establishment of specifications for the wide range of wheatbased products made around the world. With the publication


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Australian wheat growing regions Wheat terminals Australian premium white wheat area Predominantly Australian premium white and hard wheat area Predominantly hard wheat area

Northern Territory Queensland

Western Australia

South Australia New South Wales

Victoria

Tasmania Figure 1 Wheat-growing areas of Australia. Reproduced from Australian Crop Report, 2007, Australian Bureau of Agricultural and Resource Economics, Canberra.

Figure 2 The $2 bank note, introduced with Australia’s decimal currency in 1966, featured William Farrer – the wheat breeder responsible, in the period 1890–1910, for providing farmers with new varieties adapted to Australian conditions.

of these findings, advantages of the knowledge have flowed to the importing countries involved and to other exporters. Another form of diversification came with the challenge presented to wheat growers by the sandy soils of Western Australia, due to the lack of soil nitrogen. An efficient solution to this problem was the introduction of grain-legume crops in agronomic rotation with wheat. The ability of the legumes to fix atmospheric nitrogen led to the provision of a natural source of nitrogen fertilizer, plus the welcome harvest of other grains, particularly lupins and various pea and bean

crops (Table 2). These pulses have only emerged as important crops since the 1980s. Expansion of production has depended significantly on the growth of export markets. Recent expansions in wheat and pulse production have warranted the enlargement of terminal storage facilities in Perth, Western Australia (Figure 8). Another form of agricultural diversification accompanied the downturn in wheat prices during the 1980s. In addition to growing grain legumes, a valuable crop was supplied in the form of canola (rapeseed). Production of canola continued,

Table 3

Historical developments in the Australian wheat industry

I. Period of foundations 1788–92 1788 Eight acres is sown to wheat at Farm Cove, Sydney 1790 James Ruse grows ‘bearded’ wheat on a few acres at Rose Hill, Parramatta, in Western Sydney 1792 About 200 acres is cultivated to wheat in the colony II. A wheat market is established 1793–1824 1793 The colony is self-sufficient in wheat and maize 1803 Rust destroys wheat crops in Sydney’s Dundas Valley 1804 Abundant yields of ‘Common Brown’ wheat in the Sydney district bring self-sufficiency again, but prices are low 1810þ ‘White Lammas’ and ‘Red Lammas’ wheats from England and Scotland are cultivated, mainly in coastal regions. ‘White Lammas’ was latematuring and poor in baking quality 1811 James Ruse makes himself a plow; previously most tillage was by hoe 1822 Various wheats are introduced by the newly established Royal Agricultural Society of New South Wales from England, South Africa, India, and Egypt III. Period of insufficient expansion 1825–55 1850 ‘Red Straw’ and ‘White Essex’ (a Lammas type) are introduced IV. Period of declining yield 1855–96 1860þ South Australia’s climate and geography favor quality-wheat production, and grain is exported to England 1860 ‘Purple Straw’ (an early-maturing wheat) is selected, probably from a field of ‘Red Straw’ by a South Australian farmer. This selection starts an extension of wheat growing into drier regions 1880 Introduction of Ganz steel roller mills from Hungary alters quality requirements 1881 ‘Du Toit’s’ wheat, early-maturing and rust-resisting, is introduced from South Africa by Dr. Schomburgk, director of the Adelaide Botanic Gardens. From this introduction, James Ward, of Port Pirie, selects a rust-resisting high-yielding wheat named ‘Ward’s Prolific’ 1882 Correspondence with ‘The Australasian’ newspaper prompts the English-born surveyor W. J. Farrer to make plans for wheat improvement by crossbreeding and selection, thereby going beyond the previous practice of selection only for wheat improvement 1889 Farrer’s first crosses are attempted at his property, Lambrigg, near Canberra. The variety ‘Blount’s Lambrigg’ is selected from crossbred material provided by A. E. Blount of Colorado, the United States 1890 Disastrous wheat losses, due to rust, prompt the first rust-in-wheat conference to be convened. Farrer’s letter to the conference calls for crossbreeding as a means of improving both rust resistance and grain quality 1893 F. B. Guthrie, recently appointed chemist with the Department of Agriculture of the Colony of NSW, devises small-scale tests of milling and baking quality for selecting suitable parents and crossbreds from Farrer’s breeding program. Improvement of quality is thereby made possible 1893 Hugh Pye produces ‘Improved Steinwedel’ at Dookie College, Victoria, by making the cross (Steinwedel Purple Straw) Steinwedel 1893 A date suggested as the origin of cereal chemistry as a discipline, due to breeder–chemist collaborations in Australia and overseas 1895 Farrer’s ‘Yandilla’ is the first of a new generation of wheats, designed to combine Fife quality with the drought resistance and earliness of Indian wheats V. Period of rapid expansion 1896–1930 1896 Local millers are forced to modify their machinery to suit imported North American Fife wheats due to local shortages. They are thus more ready to accept Farrer’s stronger wheats, which they had previously rejected 1898 Farrer is appointed officially as ‘wheat experimentalist’ to the NSW Department of Agriculture on an annual salary of £350 1900 Release of ‘Bobs,’ reportedly obtained by crossing a selection from ‘Blount’s Lambrigg’ with ‘Bald Skinless Barley’ by Farrer in 1896. It became popular throughout Australia and represented a breakthrough in the production of ‘strong’ wheat 1901 Export of 25 million bushels of wheat and flour 1901 Release of ‘Federation,’ selected by Farrer from his cross in 1895 between ‘Purple Straw’ and ‘Yandilla.’ Though it fell short of his quality and disease-resistance goals, its yield made it the most popular wheat in Australia from 1910 to 1925. It was also widely grown in the United States, India, and other countries 1906 Death of Farrer and suspension for some years of quality-directed breeding 1911 NSW ‘Strong White Wheat’ class is established to segregate Farrer’s strong wheats. Export of 64 million bushels of wheat and flour of all classes. The contrast between this harvest and that of 10 years before is due largely to Farrer wheats such as ‘Federation’ 1924 Release of ‘Ghurka,’ bred by G. S. Gordon in 1916, becoming a leading Victorian variety in its own right and also a parent of many important soft wheats 1929 The variety ‘Bencubbin’ commences its phenomenal rise to popularity, not only in Western Australia, where it was bred by E. J. Limbourn, but also throughout Australia VI. International marketing expansion 1930–48 1936 The Gepp Royal Commission recommends that breeders should ‘endeavor to produce new varieties that have the quality of strength’ 1945 Availability of ‘Gabo’ wheat saves many farmers from ruin due to rust. It starts Australia’s reputation for high-protein baking-quality wheat 1946 Introduction of ‘Insignia,’ selected for tiller survival, permits further extension of the wheat belt into drier areas VII. Grain quality targeted to specific market needs 1949–70 1950þ Segregation of specific truckloads of high-protein wheat of selected varieties as prime-wheat grades by the Prime Wheat Association, in northern New South Wales 1956 Release of ‘Dural,’ the first Australian-bred durum wheat 1957 Passage of the Wheat Research Act through federal parliament and the consequent formation of the Wheat (Industry) Research Council, later to be replaced by the Grains R&D Corporation with responsibility for research on the wide range of agricultural grains 1960 Naming of ‘Gamenya,’ derived from ‘Gabo’ by I. A. Watson. Though bred in the east, its greatest impact was in Western Australia and as an ideal noodle wheat 1960þ Growing market awareness, involving an active acknowledgment that about three-quarters of the Australian wheat crop is exported for ‘exotic’ uses, leading to research initiatives on noodles, flat breads, and steamed bread 1967 ‘Timgalen,’ issued by the University of Sydney, offers excellent quality with high-protein potential, disease resistance, and agronomic qualities that earned it a continuing unrivaled position for prime-wheat production 1970þ Introduction of near-infrared spectroscopy revolutionizes the analysis of protein and moisture in grains


Figure 3 Artist’s impression of the 1890s wheat breeder William Farrer among his small plots of crossbred wheats.

tripling in the period 1996–99; cottonseed also increased with the expansion of cotton production (Table 2).

Wheat The Australian Wheat Board was given responsibility for marketing the wheat crop since its formation in 1939. In July 1999, its status changed from an Australian government statutory marketing authority to a private company called AWB Limited. Since then, there has been further diversification of marketing, with the result of general deregulation. Wheat yields in Australia are relatively low by world standards (Table 5) largely because production is mainly dryland, with only a small extent of irrigation, reflecting Australia’s character of being the world’s driest continent. Wheat varieties registered in Australia are virtually all whitegrained, in contrast to the red-grained wheats that are common in other wheat-producing countries. This policy direction, taken in the very early days of the industry, has been recognized as a marketing advantage. For many years, only whitewheat varieties have been grown. In addition, the dry climate of Australia’s wheat belt (mainly inland) ensures that the grain produced is very dry. Furthermore, marketers and

413

bulk-handling corporations set rigid standards for the cleanliness of export wheat. Consequently, Australian wheat has regularly been marketed as ‘clean, white, and dry.’ These three characteristics offer millers the triple promise of high flour extraction, namely, the lack of nonmillable material (clean), the white grain permitting a higher extraction rate before flour color is compromised, and dry grain offering less moisture to be paid for at the price of grain (if sold on ‘as is’ weight). Because of the high proportion of the Australian wheat crop that is exported, marketing strategies must take into account the wide range of products for which it is used. Several of these are shown in Figure 9. The main products domestically are the many conventional forms of leavened bread. This type of baked product is in a minority for export uses, which are more likely to include products such as various Arabic flat breads, Chinese steamed breads, many types of noodles (made from hexaploid wheats), and pasta (made from tetraploid durum wheats). Durum wheats make up a small proportion of the crop, but this proportion is increasing. To meet the wide range of quality specifications for these various products, there are many wheat grades with tight specifications. Varietal identity is an important part of the quality specifications, with a small group of varieties of similar quality type being permitted for each grade. Other specifications cover aspects of the plumpness of the grain, absence of contaminants and of insects, cleanliness, soundness, the absence of defects, and, importantly, protein content. This approach to grading and marketing is in great contrast to the FAQ era of the earlier part of the twentieth century. The maintenance of grain quality in the current range of grades and classes requires strict systems for assessing grain quality when it is delivered. It is common for grain to be delivered directly from the field to the local silo (grain elevator or storage site), although on-farm storage is becoming more common. At the point of delivery, it is critical for the range of quality attributes to be determined quickly, to allow for the grain to be dumped into the storage cell appropriate to the grade to which it is allocated. In addition, grain samples are kept to represent the deliveries of each grower and to indicate the composition of the storage cells. These samples can be further analyzed subsequent to delivery. Identification of variety is also needed for the payment of royalties, based on deliveries, according to plant breeders’ rights.

Rice Rice production and export has been a significant industry for Australia, but production has been reduced in recent seasons by drought. Table 4 shows the low point of less than 200 000 tonnes of paddy rice in 2010, but production has since risen again. It is grown within the irrigation areas of the Murrumbidgee and Murray River systems in southern NSW, with some further areas of production in Victoria, Western Australia, Queensland, and the Northern Territory. Farming operations are entirely mechanized. In the irrigation area, sowing occurs in September and October into dry seedbeds. Sometimes, sowing involves the aerial dispersal of pregerminated seed into shallow water. After about 4 months, water is drained

414


Raven Aroona WW15

Condor… Meering 2*

2* WW80

Brochis ‘S’ Banks

PWTH

Batavia Janz

Cook

Winglen

4*

3Ag3 Timgalen

AKMS

3Ag14

Madden 2*

Kite

Sunstate

Pavon‘S’ …Hartog

Amber mutant Sonora 64 Spica BT-Schomburgk Ciano Barunga Molineux Gallo Frame Dagger

Sabre Insignia RAC177 Vereanopolis

Condor

Sunvale

4* 2* Sunbrook

Blade

MEC3

Sonora 64

Sunco 5* VPM1

Machete

2*

Yaqi54

3*

SUN9E-27 4*

Gabo

TPP

Cunningham WW15

Spear 3* 3*

Suneca Wilgoyne Wren

Stiletto Gaboto Dollarbird Kalyansona

Heron

Rosella

Bluebird

Farro Lunga WW33G

WW33B TA3PNB3P AUS10894 Bencubbin Insignia

Cocamba

4*

Ouyen

TM56 Takari

Siete Cerros

Bodallin

Bokal

Gabo 6* Mentana

Gamenya

2* Kenya 117a

Eradu

Ciano Gallo Noroeste

Wilgoyne Zambesi

Sunfield 51b Cunderdin Cranbrook

Wren

Perenjori

Sword

Bencubbin

2* Lr21-SrX Jacup

Khapstein Gluyas…Gluyas Early Clubhead

2* Centrifen

Mexico Gabo

PI0522B WW15

Chile 1B

3Ag3-Condor

Insignia

Halberd 3*

Madden

3*

Gluclub Tincurrin

Amery

Shortim

Charter Kenya C604

3*

Hyden

Inia 66

Raven 4*

Datatine

Aroona Tadorna 3*

Cadoux Falcon-EMS Sharbarti Sonora 64

Kalannie

Cascades

Inia 66

Falcon Figure 4 Pedigrees of recent prominent varieties of wheat grown in Eastern and Western Australia. Pedigrees are read from left to right. For example, Raven was crossed with the line WW15 to produce the variety Aroona. The line WW15 was crossed with WW80 and then crossed again (double backcross, 2*) to produce the variety Condor. The variety Meering was selected from Condor. Condor was a parent entering into the pedigrees of Banks and Cook. A sister line of Condor was a parent that also entered into the pedigrees of Banks and Cook.


Figure 5 A quarter-scale model of the small-scale flour mill used by Guthrie to evaluate the milling quality of the small amounts of grain coming from Farrer’s wheat breeding program. It is now on show beside the commercial-size roller Ganz mill in the Foundry Museum in Budapest. Table 4 Production, in kilotonnes, of major cereal crops in Australia for successive crop years Crop

2010

2011

2012

Wheat Barley Oats Maize Triticale Sorghum Rice, paddy

22 138 7294 1374 328 502 1598 197

27 410 7995 1128 357 284 1935 723

29 905 8221 1262 451 285 2239 919


415

allowing the beds to dry prior to mechanical header harvesting. Yields are high by world standards, averaging over 9 tonnes per hectare (Table 5), with some growers achieving 13 tonnes per hectare. Rice is generally delivered at relatively high moisture (20–22%) to avoid cracking of the kernels. Aerated storage is used to further reduce the moisture to about 15% prior to milling. All deliveries are sampled on delivery and are analyzed for moisture and protein contents by near-infrared transmission spectroscopy. Samples are also checked for variety and for defects. Most of the rice grown in Australia is from medium- and long-grain Indica varieties. The long-grain varieties include the fragrant types. The hulls that are removed in the milling process are converted by incineration to high-carbon ash, which is used by the steel industry in Australia and overseas. The ash is used to coat the surface of open-hearth furnaces, thus trapping the heat and improving fuel efficiency. Fireproof building materials have also been developed using this ash as a starting material. Rice accounts for about 8000 tonnes of the 9000 tonnes of cereal-grain production in Fiji (Table 1).

Coarse Grains Barley Barley is second in importance to wheat, based on volume and quality (Tables 2, 4, and 5). Like wheat, yields of barley are moderate by world standards (Table 5). Export markets are mainly China, the Middle East, and Japan. Australia is the second most important country in world malting-barley trade, depending on seasonal fluctuations. The premium use of barley is for malting to produce beer. In addition to the export of malting barley, malt produced in Australia is exported for beer production overseas. Varieties are bred specifically for the purpose of malting, based especially on the production of brewery extract for fermentation purposes after

Prime Hard and Hard Hard and Fair Average Quality Fair Average Quality — some Hard Fair Average Quality Soft and Fair Average Quality Export terminal. Figure 6 Types of wheat quality according to the ‘fair average quality’ system of the mid-twentieth century in Australia. Map provided by John Moss.

416

GRAINS AROUND THE WORLD | Grain Production and Consumption in Oceania: Australia and Pacific Countries Table 5 year

Mean yields of crops in tonnes per hectare for the 2012 crop

Crop

Australia

New Zealand

World

Wheat Barley Rapeseed Sorghum Seed cotton Rice (paddy) Maize Oats Peas (dry)

2.1 2.2 1.5 3.4 4.8 8.9 6.5 1.7 1.4

8.9 6.7 1.1

3.1 2.7 1.9 1.5 2.2 4.4 4.9 2.2 1.5

10.9 4.7 3.1


Figure 7 Arabic ‘pocket’ breads baked experimentally by an expert from the Middle East in the laboratories of the Bread Research Institute of Australia in the 1970s. This type of flat bread comes from the oven puffed into a sphere. On cooling, it returns to its flat-bread form. Advice from such experts has assisted Australia in recent decades in providing wheat of the quality suited to specific market requirements.

Figure 8 The grain-storage facility in Perth, Western Australia. The very large storage capacity of this recent construction was warranted by the recent increase in grain production in Western Australia. The many storage cells are designed to accommodate the diversity of grain species and grades.

Figure 9 The range of food products made from Australian wheat. In addition to the many forms of leavened bread, Australian export wheat is used for products such as Chinese steamed bread (white sphere at lower left), Arabic flat breads (lower left), noodles (at right), crisp breads (lower center), and pasta (lower right).

malting. These are all two-row types; Australian six-row barleys are of feed quality. Animal feed is the destination of barley that does not meet the stringent requirements of the malting grades, due to failures in meeting specifications for variety, protein content, or absence of defects. Feed barley, together with sorghum and downgraded wheat are the main grains for the animal-feed industry, their importance being greater because of the lower production of maize in Australia. Barley is also used for human food purposes both domestically and in export markets. Japan has emerged as a major user of food-grade barley. Much of the food use involves pearling, to remove the bran and husk layers. In other cases, flour is produced and some of this is becoming used to produce highfiber pasta products, taking advantage on barley’s high-fiber content in its cell walls (b-glucans and pentosans). The production of distilled beverages is another significant use of foodgrade barley.

GRAINS AROUND THE WORLD | Grain Production and Consumption in Oceania: Australia and Pacific Countries Oats Most of the oat crop (Tables 2, 4, and 5) is used within Australia. It may serve on-farm as a forage crop to be grazed when plants are young, with the option of allowing the plants to mature and produce harvestable grain. Some varieties are suited to milling and processing for food purposes, but much of the oat crop is used as animal feed in its various forms – forage, hay, and grain.

Sorghum Sorghum is a feed grain. Much of the crop is exported for this purpose. The main customers are Japan and Taiwan. Production is mainly confined to the warmer subtropical parts of Australia.

Cereal Rye Flour produced from rye grain is used in Australia for European-style breads, biscuits, crispbreads, multigrain breakfast cereals, muesli bars, pet food, and special dietary foods that provide higher lysine, pentosan, and b-glucan content than other cereals. Production is minor in volume.

Triticale The wheat–rye hybrid triticale has enjoyed reasonable popularity in Australia. Annual production varies, recently peaking in 2010 at about half a million tonnes (Table 4), making Australia the world’s fourth largest producer of triticale, depending on seasonal fluctuations. Triticale’s attraction has mainly been as an alternative to wheat for the stockfeed industry, which is the major domestic end user. However, efforts have been made to develop niche markets for human food.

Maize Maize is a relatively minor crop in Australia, with annual production ranging up to half a million tonnes (Table 4), less than the production figures for the major cereal grains. However, grain yields are good. About 10% of the maize crop is exported. About one-quarter of the crop is used domestically as human food, mainly for breakfast cereals, sweet corn/vegetable uses, corn-based foods, and industrial manufacture of corn starch. The remainder is used domestically as stockfeed. Industrial use of maize is minor compared to northernhemisphere maize use, because Australian starch production is mainly based on wheat. Maize processing into starch relates mainly to special products such as high-amylose starch.

Pulses Pulse production in Australia has expanded greatly since 1980 in response to changing farming systems and increasing world demand for vegetable protein. The main species are lupin, chickpea, lentil, field pea, and faba bean (Table 2). Lupin and field pea have been grown in Australia since the nineteenth century when they were used mostly as animal feed. There was little plant breeding effort at this time: one

417

of the pea varieties grown in the early twentieth century, Dun, was still being grown in the 1980s. This began to change with the work of John Gladstones on lupin at the University of Western Australia and later in the WA Department of Agriculture beginning in the 1950s, in which he took what was essentially a wild plant, Lupinus angustifolius, and by gradually incorporating genes for low seed alkaloids, soft seed, nonshattering pods, white flowers, and early flowering, created the modern crop-type narrow-leafed, or Australian Sweet, lupin beginning with the release of Uniwhite in 1967. Field pea breeding resumed in Australia in the 1970s, and chickpea and lentil breeding began in the 1980s. All of these pulses are susceptible to devastating diseases, and improving disease resistance has been an important objective of these breeding programs, as well as improving adaptation to Australian conditions. Pulses in Australia are grown in rotation with cereals and improve production by providing fixed N and reducing cereal disease levels. Production expanded rapidly in the 1980s and 1990s as cereal production intensified, whereas legume-based pastures, which had formerly played a similar rotational role, declined in response to the changing economic environment of Australian farming. There are geographic differences in pulse production across the country. Narrow-leafed lupin is the predominant pulse in Western Australia; white or albus lupin (L. albus) is grown mainly in southern New South Wales, desi chickpea in northern New South Wales, and the other species in South Australia, Victoria, and southern New South Wales. Production of lupin, field pea, and lentil declined between 2000 and 2012 in response to changing grain prices relative to wheat and canola, which has displaced pulses to some extent. Increasing weed control costs as herbicide-resistant weeds become more prevalent has contributed to declining lupin production in Western Australia, and more frequent drought during the past decade has also been important. On the other hand, production of chickpea has more than quadrupled in the same period. A high proportion of Australian pulse production is exported. Field pea, lentil, and chickpea mostly go to the Indian subcontinent where they are used in human food, although a significant proportion of field pea is used domestically in pig and poultry rations, especially in Eastern Australia. Australia produces more than 70% of the world’s lupin and about 50% of this is exported. Most goes to Europe or northern Asia where it is used for animal feed. Australian lupin is also used for aquaculture feed, and there has been considerable effort over the past decade to develop human food uses for lupin, including fiber and protein additives, which can be used in a wide range of manufactured foods. However, these are currently only minor uses.

Oilseeds The canola (rapeseed) crop has expanded dramatically since the 1990s, production having tripled in the period 1996–99. It was about 2.4 Mt in 1999, rather less than the figure given in Table 2 for 2012, and is now the third-largest crop in Australia after wheat and barley. It performs a similar role in crop

418


rotations to pulses (although it does not fix atmospheric N), and its expansion has to some extent been responsible for the stagnation of pulse production in the past decade. Canola is one of the two crops in which genetically modified (GM) varieties are approved for commercial production in Australia (the other is cotton). Currently, between 10% and 20% of production is from varieties with the Roundup Ready® trait. In recent years, about two-thirds of Australian production has been exported, and Australia is the world’s second-largest exporter of canola after Canada. Cottonseed production is the volume of ‘white seed,’ after allowing for delinting and dehulling. About a quarter of this is crushed domestically for oil production. Yields are good (Table 5). Production volumes are modest for sunflower and soybean (Table 2). Peanut production is well below these at about 25 000 tonnes. Lesser oilseeds include linseed and safflower. Australia is a significant exporter of oil crushed from these various oilseeds, especially cottonseed. The residues from oilseed crushing make important contributions to the stockfeed industry.

Consumption Australians consume about 70 kg of wheat flour per person per year, mainly in the form of baked goods, but flour also goes into many processed foods. A significant part of this ‘consumption’ (based on statistics) is due to the importance of the starch–gluten industry, which processes dough to separate the starch fraction, using the ‘A’ starch for paper manufacture. Wheat starch is also a significant food ingredient. The remaining gluten is dried and used as an additive for bread manufacture (both domestically and as a significant export commodity) and also for incorporation in a range of foods. The residue of starch is fermented to ethanol for blending with petrol for vehicle fuel. Another significant use of grains in Australia is the breakfast-cereal market, which is valued at $800 million. These and other grain-based foods represent an important part of Australia’s exports of manufactured foods, primarily to the Pacific Islands and to Asia.

New Zealand Significant volumes of wheat, barley, and maize are produced in New Zealand, as is shown in Table 2. Grain yields are very high by world standards (Table 5). Deregulation of the wheat industry some years ago accounted for significant changes in the structure of the industry, increasing competition and the likelihood of importation of grain. In contrast to Australia, adequate on-farm storage for the crop is common (Figure 10), so that the grain buying and transport systems are different from those in Australia. Most of the New Zealand harvest is later than in Australia, where early deliveries may start in October. On the other hand, harvest time in the south of the New Zealand South Island may be as late as Easter time (late in the southern-hemisphere autumn).

Figure 10 Wheat field and on-farm storage in the south of the South Island of New Zealand. As late as April (autumn), the standing grain is still waiting to be harvested.

Future Prospects The future for international grain trading is difficult to predict, largely due to the entry of new exporting nations and the deregulation of marketing strategies in several other countries. Looking further ahead, climate-challenge issues will affect production and quality characteristics. Likely climate changes include more frequent heat episodes and rainfall that is variable and less reliable. One of the results may be the need to move away from traditional growing regions for some grain species. Rising sea levels may reduce the amounts of arable land in Pacific Islands nations. It is inevitable that there will be a continuing rise in the level of carbon dioxide in the Earth’s atmosphere, although the causes and the rate of increase are subject to discussion at present. Many studies have already shown that the resulting ‘carbon fertilizer’ effect produces increased yields of grain and biomass, accompanied by lower protein content for the resulting grain. For grains like wheat, a significant reduction in protein content may require changes in baking procedures, such as the use of added gluten to bolster dough properties or use of the Chorleywood bread process, which was developed originally to accommodate low-protein wheat in the United Kingdom. Wheat breeders may also need to incorporate gluten genes associated with greater dough strength. The many experimental trials of elevated CO2 have provided a basis for modeling to extrapolate predictions of future effects to a wider range of environments. For example, Figure 11 illustrates expectations for the state of Victoria in southeastern Australia. It takes into account the rising levels of CO2 together with other expectations, such as heat episodes, rainfall, and known soil types. Although large areas are expected to enjoy higher crop yields in 70 years’ time, there are significant areas where that result may not be expected. Research and development is ongoing, especially in Australia and New Zealand, with outcomes expected to benefit both grain yield and quality. New quality types include the production of low-glycemic-index wheats (based on highamylose wheats) that will address chronic health issues such as diabetes, obesity, and cardiovascular disease. Research on


N

419

Crop yield still increasing by year 2070

Decreasing crop yield by year 2070



0

98

196


kilometers Figure 11 Predicted changes in crop yields for the Australian state of Victoria, based on modeling of rising levels of CO2 together with other expectations, such as heat episodes, rainfall, and known soil types. Illustration, courtesy of G. O’Leary and coworkers.

canola is providing lines capable of producing omega-3 fatty acids. The ‘mining of novel genes’ is being facilitated by the establishing the Australian Grains Genebank in Horsham, Victoria. It houses about 300 million seeds from around the world, for use in current and future plant breeding programs.


• • • • •

What features distinguish grain production, quality, and consumption in your region from these factors in Oceania (or choose one of the Oceanian countries). What advantages are claimed for Australian export wheat? What are the reasons for determining the variety identity in the Australian wheat harvest? Name some of the improvements made to Australian wheats by breeding and selection. What uses of barley and wheat are described?


• • • • •

What factors could account for the differences in grain yields for the various grain species in Table 5, contrasting Australia, New Zealand, and world averages? Find out about the development and expansion of wheat in your region. How did their early times contrast with the origins of the Australian wheat industry? How would starch from wheat (as is usual in Australia) differ from the commercial production of starch from maize in many northern-hemisphere countries in production methods and in quality? Find out about the relative advantages of the oilseeds mentioned with respect to the amount and quality of the oils produced. How does the value of the respective residues after oil removal affect the overall economics of oilseed utilization?

See also: Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Grain Marketing and Grading:

Identification of Varieties of Food Grains; Wheat: Grading and Segregation; Wheat: Marketing; Non-food Products from Grains: Fuel Alcohol Production; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Oilseeds: Canola: Overview; Cottonseed: Overview; Wheat Processing: Gluten and Modified Gluten.

Further Reading Anonymous (1994) Australian Grains. Melbourne, VIC: Morescope Publishing. O’Brien L and Blakeney AB (eds.) (2000) An Introduction to the Australian Grains Industry. Melbourne, VIC: Royal Australian Chemical Institute. O’Brien L, Morell M, Wrigley C, and Appels R (2001) Genetic pool of Australian wheats. In: Bonjean AP and Angus WJ (eds.) The World Wheat Book, pp. 603–640. Paris: Lavoisier Publishing. O’Leary G, Christy B, Weeks A, et al. (2011) Downscaling global climatic predictions to the regional level: A case study of regional effects of climate change on wheat crop production in Victoria, Australia. In: Shyam S, Yadav RJR, Hatfield JL, Lotze-Campen H, and Hall AE (eds.) Crop Adaptation to Climate Change, pp. 12–26. Chichester: Wiley. Quail KJ (1996) Arabic Bread Production. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW (1978) W.J. Farrer and F.B. Guthrie: The unique breeder-chemist combination that pioneered quality wheats for Australia. Records of the Australian Academy of Science 4: 7–25. Wrigley CW (1981) Farrer, William James. In: Nairn NB and Serle AG (eds.) Australian Dictionary of Biography: 1891–1939, pp. 471–473. Melbourne: Melbourne University Press. Wrigley CW (1983) Guthrie, Frederick Bickell. In: Nairn NB and Serle AG (eds.) Australian Dictionary of Biography: 1891–1939, vol. 9, pp. 143–144. Melbourne: Melbourne University Press. Wrigley CW (2005) Contributions by Australians to wheat quality research. In: O’Brien L and Blakeney AB (eds.) An Introduction to the Australian Grains Industry, pp. 33–41. Melbourne: Royal Australian Chemical Institute. Wrigley CW and Rathjen A (1981) Wheat breeding in Australia. In: Carr DJ and Carr SGM (eds.) Plants and Man in Australia, pp. 96–135. New York: Academic Press. Wrigley CW, To¨mo¨sko¨zi S, and Be´ke´s F (2011) Hungarian-Australian collaborations in flour milling and test milling over 120 years. Cereal Research Communications 39(2): 216–225. http://dx.doi.org/10.1556/ CRC.39.2011.2.5.

Grain Production and Consumption: South America OR Larroque, CSIRO Agriculture Flagship, Canberra, Australia JC Catullo, INTA, Buenos Aires, Argentina ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

Brazil and Argentina are the major producers and traders in the region. Farmland will continue to increase as more virgin land is transformed for agriculture use. GMOs are widely used in South America. Technological advances in mechanization (i.e., no-tillage) proved crucial to farming success. Soybean will continue to be the major cash crop in the region. Constant monitoring to assure sustainability is needed. Cereals are an important part of the South American diet. Breakfast cereals are not widely consumed. Pseudocereals like quinoa and amaranth are becoming more popular.

Learning Objectives

•

Current status of South American production, trading, and consumption of grains.

Prologue Since the onset of the 2008 global economic crisis, investors favored more secure alternatives than the crumbling financial sector options. As a result of that and on the back of increasing international food prices, agriculture became an attractive investment option worldwide and particularly in South America. South America is one of the regions with greater aptitude for providing food and renewable energy to the rest of the world. The whole region possesses plenty of arable land and renewable water resources. Increases in harvested area (Table 1) and improvements in average yields of the major crops (Table 2) have boosted the region’s production (Table 3) in the last decades. This was possible thanks to better seed varieties, mechanization, no-tillage farming, and widespread and more efficient agrochemicals and fertilizer usage. Fifty-one percent of the world’s soybean production and 11% of maize are harvested in South America (average 2010–12) per year. Wheat accounts for just over 5% of the world production. While maize and wheat increased their share in the last decade by 1.3% each, soybean’s share of the global market production increased by a whopping 7%. The agricultural boom has prompted the governments of the region to adapt their policies to the emerging situation in grain trading. For example, Argentina implemented measures since 2007 to unpeg high global food prices from local prices. The country increased soybean export taxes and limited exports

420

(namely, wheat and maize) in order to secure a well-supplied local market. Cereals’ share in total food supply varies in the region from 29.0% in Argentina to 48.3% in Guyana. Argentina, Bolivia, Brazil, Chile, Peru, and Uruguay have wheat as the main staple cereal component of their diets, while maize is the prevalent cereal component in Colombia, Paraguay, and Venezuela. Rice is the more ubiquitous cereal component of the diet in Ecuador, Guyana, and Suriname (Figure 1).

Argentina The Argentine Republic is the second grain producer and the main grain exporter of South America (Figure 2). Technological advances, better seed quality, genetic improvement, and better crop management were all important factors in the resurgence of agriculture as one of the main driving forces of the country’s economy. From a total continental area of 273 670 000 hectares, Argentina dedicates 38 000 000 hectares to agriculture (2011). Ten years ago, the arable land was 27 000 000 hectares. In contrast, rural population continues to decrease (10.73% of total population in 1996; 7.27% in 2012). The share of agriculture value added in total GDP is gradually returning to increase (from a lowest value of 4.79% in 1999) although not to the levels of 20% that they had up to half a century ago. Agriculture value added (% of GDP) in Argentina was 10.61 as of 2011. Wheat, maize, sunflower, and soybean account for 90% of all the grain produced in the country, making the top ten world producers’ and the top five exporters’ list for each of the crops. Other important grain crops are sorghum (5 200 000 tonnes in 2012) and barley (5 500 000 tonnes in 2012). Argentina ranks fifth in the world, with more than 8% share of sorghum’s global production, and is the second largest exporter behind the United States. Chile, Japan, Colombia, Peru, Germany, and Ecuador are the main buyers of Argentine sorghum. In the last 15 years, there have been steady increases in exports of most of the grains, particularly coarse grain and oil crops. The main production area is the Pampas, once called the ‘Granary of the World,’ a rich humid plain in the central eastern part of the country, which concentrates 80% of grain production. Wheat is the top overall commodity available for consumption (2009) with 678 kcal per capita per day. Maize and rice are the joint second grain and sixth overall (81 kcal per capita per day). Cereals account for 29.0% of the total food supply (2009). Total wheat flour consumption is 94 kg per capita from which 64 kg corresponds to continental bread, 10 kg to pasta, 7 kg to crackers, and 4 kg to sliced bread, according to statistics from the Milling Industry Federation (FAIM).


http://dx.doi.org/10.1016/B978-0-12-394437-5.00050-4

GRAINS AROUND THE WORLD | Grain Production and Consumption: South America Table 1

421

Grain-cultivated area in South American countries

Country Argentina Bolivia, Plurinational State of Brazil Chile Colombia Ecuador French Guiana Guyana Paraguay Peru Suriname Uruguay Venezuela, Bolivarian Republic of World

Barley

Beans, dry

1121 53

274 52

3384 331

227 6

92 17 3 25

3275 11 116 46

13 375 127 510 370

175 97 3 1

1

151

61 81

3 812 493

11

2

64

5 55

105 664

23

48 401

30 040

170 865

9462

Maize

Oats

Quinoa 64

101

Rice, paddy

Sunflower seed

Sorghum

Soybean

Triticale

Wheat

236 178

971 105

18 749 1012

1687 182

2615 24 488 365 3 132 70 36 55 180 245

703

24 078

72 3

13 9

33 44

24 380

2826

104 1

572 151

32 243

952 23

5 62

373 1

162 759

40 410

104 283

24 681

4189 175 45 23

2071 260 6 8

3842

218 197

Average 2010–12 (thousands of hectares). Source: FAOSTAT.

Table 2

Yield of major producers of grains in South America

Country/yield 2003 and 2012

Maize 03

Argentina Bolivia, Plurinational State of Brazil Chile Colombia Paraguay Peru Uruguay Venezuela, Bolivarian Republic of World

Maize 12

Wheat 03

Wheat 12

6.48

7.34

2.54

2.97

3.73 10.00

5.01 10.72

2.40 4.32

2.32 4.95

2.38

3.90

2.20

2.46

3.43 4.46

4.29 4.94

Rice 03

Rice 12

Soybean 03

Soybean 12

3.25

4.81

2.80 2.32 2.80

2.66 2.20 2.63

6.79

7.72 2.85

2.78

5.86

4.14 2.55

2.65 2.37

2.77

2.85

2.70

3.12

3.95

4.39

2.28

Rice, paddy

Sorghum

Soybeans

Sunflower seed

1520 454

4429 401

51 019 2206

3078 238

12 035 125 2001 1583 10 582 368 2825 227 1405 1334

1834

69 757

95 6

59 13

72 72

148

8040 3

165

1421 220

122 481

2119 38

6 54

1167

58 578

260 075

36 418

Years 2003 and 2012 (tonnes per hectare). Source: FAOSTAT.

Table 3

Grain production in South American countries

Country/production avg 2010–12 Argentina Bolivia, Plurinational State of Brazil Chile Colombia Ecuador French Guiana Guyana Paraguay Peru Suriname Uruguay Venezuela, Bolivarian Republic of World þ (total)

Barley

Beans, dry

Maize

Oats

Quinoa

4180 49

340 61

24 059 915

492 6

280 98 5 18

3 20 133 13

60 774 1430 1643 1004

387 465 4 1

1

210

53 91

5 3178 1578

12

42

210

3 47

455 2421

129 693

23 173

Average 2010–12 (thousands of tonnes). Source: FAOSTAT.

870 060

37

47

21 114

80

713 984

Triticale

Wheat 13 656 235

110 108

13 652

5414 1438 11 7

453 350

422

GRAINS AROUND THE WORLD | Grain Production and Consumption: South America

100

90

80

70

60

% 50

Wheat Rice (milled) Maize

40

30

20

10

0 Argentina Bolivia

Brazil

Chile

Colombia Ecuador Guyana Paraguay Peru Suriname Uruguay Venezuela

South America + (Total)

Figure 1 Share of main cereals in the South American diet. Source: FAOSTAT (2009).

According to the same source, the country has 33 000 bakeries where artisan continental bread is baked daily. Argentina is currently the fifth largest world exporter of wheat flour. Argentina’s undernourishment figures are not significant, comprising <5% of the population in 2010–12.

Bolivia, Plurinational State of Landlocked Bolivia is the least developed country of the region, with a large proportion of its population living in rural areas (32.54% in 2012). Arable land has increased in recent years from 2.59 million hectares in 1996 to 3.84 million hectares in 2011. This increase was mainly made at the expense of forest cover. Agriculture employs 40%of the workforce (down from 45% in 1997). While the GDP has doubled between 2005 and 2010, the share of agriculture value added in total GDP has decreased, continuing a trend that saw its figures going down from nearly 20% in 1995 to just above 10% in 2010. In recent decades, this Andean country has consolidated a strong growth in oilseed crop production, particularly soybean with planted areas exceeding 1 000 000 hectares and total production of 2 298 857 tonnes in 2011–12. Soybean is the largest agricultural export and the third largest Bolivian export. Santa Cruz de la Sierra is the main producing area with an average production yield of 1600–2400 k ha1. There are two crops per year: the most important in summer (November/ December) and also in winter (June/July). The second most important grain crop is maize (1 006 000 tonnes in 2012) followed by sorghum (478 000 tonnes) and paddy rice (440 000 tonnes).

Wheat is the top commodity available for consumption (2009) with 406 kcal per capita per day. Maize is the second (302 kcal per capita per day) and rice third (280 kcal per capita per day). The prevalence of undernutrition is very high at 24% (2010–12). Dry bean production in 2012 was 60 000 tonnes. Bolivia is also the largest producer and exporter of quinoa, a high-protein grain native to South America that was the staple food of the Incas. The UN declared 2013 the Year of Quinoa. Unfortunately, higher international prices for the crop are leaving the poorest segments of the population unable to purchase quinoa anymore.

Brazil The South American giant is the largest economy of the region and the major grain producer. Brazilian agriculture has changed dramatically in the last 30 years. From being a major food importer (Figure 3), the country also became a top grain exporter (Figure 1). Brazil is the first of the big exporters to be in a tropical area and not a temperate area (like it is the case with the United States, Canada, Australia, Argentina, and EU). The arable land has increased from 57 860 000 ha in 1996 to over 70 000 000 ha in 2011. It corresponds to 8.3% of the total country area. Furthermore, it has over 400 000 000 ha of potentially arable land, the largest area for any country in the world according to FAO. Most of this land is in the Brazilian savannah (the Cerrado).


423

35 000 32 986

30 000 26 832 25 000

20 000

15 806

Thousands of tonnes 14 355

15 000

10 820 9487

10 000

8411

5010 5000

4417

0 Soybean Soybean cake Brazil

Argentina

Maize

Soybean cake

Soybean

Maize

Wheat

Soybean

Soybean oil

Argentina

Brazil

Argentina

Brazil

Argentina

Paraguay

Argentina

Figure 2 Major grain commodities exports South America. Source: FAOSTAT (2011).

The most recent data show that primary agriculture accounted for 5% of Brazil’s GDP and agricultural population nears 20 000 000 people (12% of total population). Brazil is second largest producer of soybean oilseed (88 000 000 tonnes) and the third largest producer of maize (70 000 000 tonnes) in the world, behind the United States and China. In 2011, maize exports accounted for 9 486 914 tonnes (second in the region and third in the world), and soybean exports were just below 33 000 000 tonnes (number one exporter in the world). The country is the sixth largest importer of wheat (5 740 753 tonnes in 2011) although it also exports (2 350 000 tonnes in 2011). Brazil is the third largest producer of pasta in the world. Rice is a staple food in the country (352 kcal per capita per day), so its consumption is correlated with the population growth. Most of Brazilian rice is cropped in uplands, particularly in the northern and midwestern regions. Production of rice (milled) was 8 200 000 tonnes in 2011. Brazil is the ninth world producer. Other grain commodities available for consumption are wheat (384 kcal per capita per day), soybean oil (336 kcal per capita per day), maize (209 kcal per capita per day), and beans

(151 kcal per capita per day). Brazil’s traditional, basic meal consists of rice and beans (‘feijoada’). Brazil is the second world producer of dry beans, behind India. Production figures for 2012 were nearly 3 000 000 tonnes. Consumption of 16.30 kg per capita per year was recorded for 2009. Although the importance of breakfast cereals in the region is limited, Brazil and Venezuela show some increase in consumption. From 2011 to 2016, it is predicted that Brazil’s market will increase by 27%. Increase in consumption is associated with upper and middle-upper income segments of the population. On the other end of the spectrum, breakfast cereals are still very expensive for lower-income earners when compared with traditional breakfast meals. The prevalence of undernutrition has dropped from 12% in 1999–2001 to 7% in 2010–12. The Zero Hunger Program launch in 2001 by the then-presidential candidate Lula da Silva has successfully helped in the improvement of these figures. Family farming, the main pillar of food security in the country, is responsible for the domestic production of 70% of beans, 46% of maize, 34% of rice, and 21% of wheat. Brazil legislation now permits the use of GMOs. Since the full lifting of the ban in 2005, Brazil has turned into the second largest producer of GM crops in the world, behind the United


424

7000

6000

5740

5000

4000

Thousands of tonnes 2820

3000

1908

2000

1684

1535 1299

1215 1014

1004

1000

0 Wheat Brazil

Maize Colombia

Maize Peru

Wheat Peru

Wheat Colombia

Maize Venezuela

Soybean cake Soybean cake Wheat Venezuela Colombia Peru

Figure 3 Major grain commodity imports into South American countries. Source: FAOSTAT (2011).

States. Over 80% of the soybean crop is GM, and they are planning to bring to the market a GM bean with resistance to the golden mosaic virus.

Chile Located on the western coast of the continent, facing the Pacific, the Republic of Chile occupies a narrow strip of land between the sea and the Andes mountains. The share of agriculture value added in total GDP is very little (<5%) and the rural population is just above the 10% mark. The arable land has diminished in the last years, from 2 000 000 hectares in 1996 to 1 320 000 hectares in 2011. The main grain crop is wheat (1 575 822 tonnes in 2011). A quarter of this production comes from 40 000 small farmers (subsistence group, no or little alternative crop to grow). A little over 550 farmers produce 50% of the wheat and around 5000 farmers are considered medium size producers. Maize (1 493 292 tonnes in 2012) is the second crop in importance. Chile is the top producer of oats (450 798 tonnes in 2012) in the region and within the top five in the world. To fulfill internal demand, wheat (655 527 tonnes), maize (668 151 tonnes), and sorghum (636 112) are three of the most imported commodities in the country (2011).

Wheat is the top overall commodity available for consumption (2009) with 850 kcal per capita per day. Maize is the second grain and third overall (211 kcal per capita per day) and rice the third and eighth, respectively (90 kcal per capita per day). Cereals account for 42.3% of the total food supply (2009). Chileans consume an average of 86 k of bread per capita per year (2001–10), making them the largest consumers of bread in the region and second in the world, behind Germany. The most consumed types are the soft bread ‘marraquetas’ and the flat round ‘hallullas.’ Chile fortifies basic food (in this case, wheat flour) with micronutrients (iron). Chile’s undernourishment figures are not significant, comprising <5% of the population in 2010–12. In 1990–92, 8.1% of the population was undernourished.

Colombia Situated in the northwestern part of South America, Colombia is the fourth largest country of the region, after Brazil, Argentina, and Peru. The arable land fluctuates around 2% of the total area of the country. The eastern plains region called the ‘Altillanura’ has potential for future agricultural expansion. The share of agriculture value added in total GDP has abruptly dropped from the turn of the millennium. In 2011,

GRAINS AROUND THE WORLD | Grain Production and Consumption: South America Colombia’s agriculture contributed nearly 7% of total GDP. Nevertheless, agriculture continues to be an important source of employment (24% of the economically active population). The most important grain crop is rice (paddy 2 000 000 tonnes; milled 1 320 000 tonnes in 2011), which ranks sixth among the top ten commodities produced in Colombia. Most of the crop is grown under irrigation. The harvested area averages just over 400 000 ha in recent years. Maize contributed with a production of 1 700 000 in 2011. The harvested area remains steady at 500 000 ha in recent years. Around 10% of the planted area uses biotech seed and is expected to increase in the future. Colombia is the second largest importer of the region, behind Brazil. Maize imports have been well above 3 000 000 tonnes in recent years (3 900 000 tonnes in 2013) positioning the country as the largest maize importer in South America. Ninety-five percent of maize imports (mainly yellow) are used in the feed industry. Soybean is being used in rotations with maize, but production is not significant (86 634 tonnes in 2012) Wheat imports average 1 500 000 tonnes per year. Bread production demands 75% of the wheat, while the pasta industry requires 15% and the cookies and pastry industry the remaining 10%. Rice (358 kcal per capita per day), maize (333 kcal per capita per day), and wheat (222 kcal per capita per day) are the main commodities available for consumption. Colombia is the third largest producer of beans in South America (133 000 tonnes in 2012) and ranks fourth in consumption with 3.5 kg per capita per annum. Prevalence of undernutrition (2010–12) remains steady at 13%.

Ecuador The Republic of Ecuador has borders with Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. Arable land accounted for 1 160 000 hectares in 2011 (4.7% of the total area). Agricultural population is still high at almost 20% of the total population, but the numbers have decreased quite constantly at a rate of 1% of the population size per year. The share of agriculture value added in total GDP is 10%. Rice (paddy, 1 655 535 tonnes in 2012) and maize (864 445 tonnes in 2011) are the main crops grown in Ecuador. This satisfies internal rice demand (which is a very sensitive issue in Ecuador), but not maize, which is also imported to fulfill demand (543 817 tonnes in 2011). Imported maize is used mainly by the feed meal compound industry and the related poultry, egg, and pork industry. Recent crop forecasts predict large increases in maize harvest (over 1 200 000 tonnes) and subsequently less need for imports. Ecuador imports most of its wheat (565 523 tonnes in 2011). Despite government measures tending to boost wheat production, domestic-grown areas are still insignificant. The importation of soybean cake amounted for just over 600 000 tonnes in 2011 (the fourth importer in the region, after Peru, Venezuela, and Colombia). Sorghum imports amounted for 26 264 tonnes in 2011.

425

Dry beans production averaged 13 000 tonnes for 2010–12. The main grain commodities available for consumption in 2009 were rice (milled) at 431 kcal per capita per day and wheat (295 kcal per capita per day). Soybean oil availability for consumption was 120 kcal per capita per year. Cereals’ share was 34.4% in total food supply (2009). The prevalence of undernutrition was one of the highest in the region with 18% for the period 2010–12, slightly down from an average of 21% (1999–2009).

French Guyana Agriculture is concentrated in coastal areas (10 000 hectares of arable land). Rural population accounts for 23% of the total population. The main and almost only grain crop grown in the country is rice, with a production of 9587 tonnes in 2011 (130th in the world). Production has dramatically decreased in the last decade (31 000 tonnes in 2001).

Guyana Annual crops are grown on the narrow coastal strip. Arable land represents 2% of the total country area. Rice is almost the only grain produced, with nearly 600 000 tonnes harvested in 2011. There are two crops per year. Agricultural value added in total GDP decreased from around 40% in 1995 to just over 20% in 2010. The main grain commodity available for consumption in 2009 was rice (796 kcal per capita per day) followed by wheat (483 kcal per capita per day). Cereals account for 48.3% of the total food supply (2009), the highest in the region.

Paraguay Paraguay is landlocked between the two South American powerhouses: Brazil and Argentina. Agriculture, including subsistence farming, is the main economic activity. From a population of nearly 7 million in 2012, agricultural population represented 28% of the total and 24% of the total labor force. The share of agriculture value added in total GDP was 23.1% as of 2011, positioning the country in the first place for this indicator in the region. Gross domestic product and gross national income per capita have both dramatically increased since 2005. In 2013, the Paraguayan economy is expected to have the largest GDP growth (13%) of the region. Arable land has increased mainly at the expense of forest cover and permanent crops. Like in other countries in the region, this was mainly due to the economic importance of cash crops. The eastern region is the major production area in the country, with a mixture of traditional small farms and wellequipped medium/big farms. Main producing states are Alto Paranaa´, Itapuá, and Canindeyu´. Soybean is the main agricultural commodity in both production (8 309 793 tonnes in 2011) and value. Constant increases in planted areas and excellent yields have skyrocketed

426


this crop in detriment of maize (third place, 3 345 877 tonnes), wheat (fifth place, 1 461 020 tonnes), rice, and sorghum. Paraguay is the fourth most important exporter of soybeans in the world. Maize is the top commodity available for consumption (2009) with 509 kcal per capita per day. Wheat is the second (216 kcal per capita per day) and beans third (54 kcal per capita per day). Per capita consumption of beans ranks second in the region (5.8 kg). The prevalence of undernutrition is very high at 26% (2010–12), a sharp increase from figures of 13% to 17% recorded in the previous 10 years.

Peru The birthplace of the Inca’s empire is located on the western coast of the continent, facing the Pacific. Peru has three distinctive environments: the coastal region, the Andes, and the eastern jungle of the Amazon basin. Almost one-fourth of the population (23% in 2012) is dedicated to agricultural activities. There has been a steady decline in the evolution of rural population at a rate of 1.5% per year in the last decade. Arable land has remained at around 3 650 000 hectares in the last 10 years, which represents 2.8% of the total area of the country. Permanent crops have increased in area from 500 000 hectares in 1996 to 850 000 hectares in 2011. The share of agricultural value added in total GDP is low, when compared with other countries in the region. In the last decade, agriculture GDP never exceeded 5%. The main grain crops are rice (paddy) with a production of 3 019 316 tonnes in 2012 and maize (1 679 333 tonnes in 2012). Quinoa’s production was 44 000 tonnes (2012). Peru produces around 90 000 tonnes year1 (2010–12) of dry beans and exports an average of 34 000 tonnes year1. Peru is a large importer of grains (third in South America). In 2011, maize and wheat imports accounted for 1 907 853 tonnes (the second largest maize importer in the region and fifteenth in the world) and 1 683 702 tonnes, respectively. Rice is the top grain commodity available for consumption (2009) with 524 kcal per capita per day. Wheat is the second (345 kcal per capita per day) and maize fifth (184 kcal per capita per day). Cereals account for 42.9% of the total food supply (2009). Peru is one of the largest pasta consumers in the region with 250 000 tonnes year1. The prevalence of undernutrition is 11% (2010–12), a sharp decrease from figures of 23% recorded more than a decade ago in 1999–2001.

Suriname Most of the agricultural products are cultivated on reclaimed land in the coastal region. Almost all the country is covered by forest. Arable land average just 60 000 hectares (0.4% of total area), and rural population accounted for 29.78% of total population.

The share of agriculture value added in total GDP was 10.8% in 2012. The main crop is rice, which accounts for almost all the harvested grain (paddy rice 220 000 tonnes) according to FAO statistics for 2012. Rice availability for consumption (2009 data) was 629 kcal per capita per day of the milled equivalent. Wheat accounted for 413 kcal per capita per day and soybean oil for 263 kcal per capita per day. Cereals’ share in total food supply was 41.6%.

Uruguay Located on the southeast coast of South America, most of Uruguay’s landscape is a mixture of flat plains and ranges of low hills, known as ‘Cuchillas.’ It has the largest proportion of arable land (10.3%) and agricultural land (20.8%) in the region, employing 10.99% of the total labor force in agriculture. Uruguay, although small in area, manages to export most of its grain and oilseed crop productions. The agricultural sector as a whole has mimic in many ways the evolution that happened in Argentina and the south of Brazil, where contractors (mainly from neighboring Argentina) use traditional livestock lands to produce cash crops such as soybean (1 180 000 hectares sown in 2012) in short-term leases using the latest technology (no-till machinery, GMOs, and fertilizers). As a result of this, soybean production evolved from < 70 000 tonnes in the year 2000 to 3 000 000 tonnes in 2012. Wheat and rice are the cereal largest crops, with harvests of 1 000 000 tonnes and 1 490 000 tonnes (paddy), respectively, in 2012. Uruguay is the second producer of barley (235 000 tonnes) in the region and the third of sorghum (105 000 tonnes). Exports of soybean (1 810 000 tonnes in 2011) and wheat (900 000 tonnes in the same year) are the most valuable for the country, only surpassed by boneless meat exports of veal and beef. Wheat is the top grain commodity available for consumption (2009) with 891 kcal per capita per day. Rice (milled) at 192 kcal per capita per day and maize (177 kcal per capita per day) rice are also important. Cereals account for 45.6% of the total food supply (2009). Together with Argentina, Chile, and Venezuela, Uruguay has a consistently low number of the population undernourished. Undernourishment is under 5%, while in 1990–92, was 7.3%.

Venezuela, Bolivarian Republic of Agriculture is concentrated in the ‘Llanos,’ a vast tropical grassland plain, and does not constitute a major component of the Venezuelan economy. Even though there have been domestic production increases in rice, corn and sorghum in recent years, the country heavily relies on grain imports. Share of agriculture value added in total GDP was 3.9% in 2012. Arable land represents 2.9% of the total country area and has remained stable in the last decade. Rural population has dropped from 11.58% in 1997 to just over 6% in 2012.

GRAINS AROUND THE WORLD | Grain Production and Consumption: South America Maize (mostly white) is the most important cereal in Venezuela, constituting the main source of energy in the Venezuelan diet. Refined, precooked maize flour is the basic ingredient for the preparation of ‘arepas,’ a popular type of corn cakes. The availability for consumption in 2009 was 429 kcal per capita per day. Other top ten grain commodities available for consumption were wheat (371 kcal per capita per day) and milled rice (308 kcal per capita per day). The Venezuelan government is committed to increase the production of maize, particularly white. For the period 1992–2012, the average production of maize had been 1 709 294 tonnes. Production figures for 2011 were over 2 118 000 tonnes and 3 000 000 tonnes for 2012 (FAOSTAT, unofficial data). Rice (paddy) average production (1992–2012) was 915 724 tonnes. Wheat is imported, on average, at a rate of 1 600 000 tonnes annually. Domestic production is almost inexistent, due to unsuitable climate and soil conditions. Pasta and bread are low-cost basic staples of the Venezuelan diet. In terms of pasta consumption, Venezuela ranks second in the world (12.3 kg per capita in 2011), behind Italy (26 kg per capita) (Figure 4). Beans production was 47 000 tonnes in 2012. Consumption averaged 5.3 kg per capita per year in 2009, the third largest in South America, behind Brazil and Paraguay. ‘Pabellon’ is a national dish, which consists of rice, beans, beef, and fried plantains. Undernourishment is under 5%, while in 1990–92, was 13.5%.

Future Prospects Brazil and Argentina are likely to maintain and even expand their leadership in grain production and trade in the region. Spare farmland will continue to become available for increasing grain and oilseed crop production, particularly in ‘El Cerrado,’ Brazil. According to USDA, Brazil will duplicate its soybean harvest in 10 years, but they will need to solve urgent infrastructure shortcomings. Yield gains are still possible in the region, continuing with the success achieved in the last decades. This would not be restricted exclusively to large farms; small and medium producers may also benefit from improved efficiency in the management of their production systems. No-tillage technology and GMOs together with adequate cultural practices have proved to be key factors for the success of the agricultural sector in the region. All the previously mentioned factors built on the bases of a very strong agricultural research and technology sector, both government-driven and private. Nevertheless, more actions are needed to secure sustainability of the model. For example, broadening the use of irrigation would help to increment agricultural productivity and crop diversification. On the matters and nutrition and food security, FAO and Mercosur have joined forces to strengthening family farming in the region, which accounts for nearly 40% of Brazil agricultural production,30% in Uruguay, 25% in Chile, 20% in Paraguay, and 19% in Argentina.

14

12.3 12

kg per capita per year

10 8.4

8.2

8

7.9

6.2 6 4.8 3.9

4

3

2

0 Venezuela

Chile

Peru

Argentina

427

Brazil

Bolivia

Figure 4 Pasta consumption in South American countries (2011). Source: www.internationalpasta.org.

Ecuador

Colombia

428


Climate changes in the region may negatively impact from an economic and social perspective if not properly addressed.


• • • • • • • • • •

What pseudocereals are native to South America? What is the social cost of the agricultural economic boom in the region? What strategy is Brazil using to mitigate hunger in its population? Colombia is one of the major importers of maize in the region. What is it mainly used for? How is Ecuador planning to increase its maize production? Why are breakfast cereals not popular in the region? Where is ‘El Cerrado’ located and what is its importance? Name the countries where wheat is not the main staple cereal in the region. Find a recipe for ‘Feijoada’ and ‘Pabellon’ on the Net. What grain components do they share? What were the main economic and political reasons behind the 2008 farmers’ strike in Argentina?


• • •

Sustainability of the soybean production models Brazil agriculture before and after lifting the ban on GMOs No-tillage and postharvest technology in the region

See also: Agronomy of Grain Growing: Precision Agriculture; Soybean: Agronomy; Wheat: Agronomy; Non-wheat Foods: Maize: Foods from Maize; The Legumes and Pseudocereals: Amaranth: Overview; Quinoa: Overview; The Oilseeds: Oilseeds: Overview; Wheat-Based Foods: Breads; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.

Further Reading Cereal marketers race for global bowl domination http://adage.com/article/news/cerealmarketers-race-global-bowl-domination/236738/ (accessed 17/12/13). Quinoa boom a mixed blessing for Bolivians http://www.aljazeera.com/indepth/features/ 2013/07/201371013540775237.html (accessed 12/12/13).

Brazil says ‘yes’ to genetically modified food, Mexico says ‘no’ http://www. businessweek.com/articles/2013-10-30/brazil-says-yes-to-genetically-modifiedfoods-dot-mexico-says-no (accessed 12/12/13). Nutrition Profile Bolivia http://www.childinfo.org/files/nutrition/DI%20Profile%20-% 20Bolivia.pdf (accessed 12/12/13). Nutrition Profile Paraguay http://www.childinfo.org/files/nutrition/DI%20Profile%20-% 20Paraguay.pdf (accessed 15/12/13). Why is Argentina so efficient? http://cornandsoybeandigest.com/tillage/why-argentinaso-efficient (accessed 15/11/13). Dros JA (2004) Managing the soy boom: Two scenarios of soy production expansion in South America. Amsterdam: AIDEnvironment. The miracle of the cerrado http://www.economist.com/node/16886442 (accessed 17/12/13). Ecuador 2013 maize production estimated at record levels http://www.thecropsite.com/ news/15111/ecuadors-2013-maize-production-estimated-at-record-levels (accessed 4/1/14). Current status of adoption of no-till farming in the world and some of its main benefits http://www.fao.org/ag/ca/CA-publications/China_IJABE.pdf (accessed 14/11/13). Brazil tries to fill the potholes in its path to growth http://www.ft.com/cms/s/0/ 7dd98ed6-059f-11e3-ad01-00144feab7de.html#axzz2xV094L00 (accessed 31/3/14). Pasta Consumption http://www.internationalpasta.org (accessed 1/11/13). Family Agriculture in the Mercosur http://www.reafmercosul.org/reaf (accessed 13/12/13). Sunny side up for Latin America breakfast cereals http://www.just-food.com/analysis/ sunny-side-up-for-latin-america-breakfast-cereals_id97594.aspx (accessed 17/12/ 13). GMOs a global debate: Brazil, second largest GMO producer in world http://www. theepochtimes.com/n3/162906-gmos-a-global-debate-brazil-second-largest-gmoproducer-in-world/?photo¼2 (accessed 18/12/13). Value Added (%GDP) in Colombia http://www.tradingeconomics.com/colombia/ agriculture-value-added-percent-of-gdp-wb-data.html (accessed 12/12/13). Vergara W, Rios A, Trapido P, and Malarin H (2014) Agriculture and future climate in Latin America and the Caribbean: Systemic impacts and potential responses. InterAmerican Development Bank Discussion Paper No. IDB-DP-329.

Relevant Websites http://www.faim.org.ar/ – Argentinean Milling Industry Federation (In Spanish). http://odepa.gob.cl – Chilean Office of Studies and Agricultural Policies (In Spanish). http://www.embrapa.br/english – Embrapa (Brazilian Agricultural Research Corporation). http://www.reafmercosul.org/reaf/ – Family Agriculture in the Mercosur. http://faostat.fao.org/site/291/default.aspx – FAOSTAT. http://inta.gob.ar/ – INTA (Argentinean National Agricultural Technology Institute) (in Spanish). http://www.iica.int/Eng/Pages/default.aspx – Inter-American Institute for Cooperation on Agriculture. http://www.thecropsite.com/reports/?id¼2556 – The Crop Site. http://www.rlc.fao.org/en/publications/zero-hunger/ – The Fome Zero (Zero Hunger) Programme.


Contents Research Organizations of the World: CGIAR Research Organizations of the World: Europe and North America Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East Research Organizations of the World: Global Trends and the Commercial Sector Scientific Societies Associated with Grain Science

Research Organizations of the World: CGIAR JH Skerritt, University of Queensland, St Lucia, Australia ã 2016 Elsevier Ltd. All rights reserved. This article includes some content from the previous edition article by F.J.B Reifschneider & S. Hussain, volume 3, pp 26–36, ã 2004, Elsevier Ltd.

Topic Highlights

• • •

The CGIAR international agricultural research centers provide a significant contribution to grains research, particularly for the developing world. The CGIAR centers have traditional strengths in germplasm development, agronomy, quality assessment, biotechnology, pathology, natural resource management, and economics. In 2011–12, much of the research undertaken within the CGIAR system was organized into major research programs. Five CGIAR Research Programs have a primary emphasis on improvement of yields and profitability of grain crops, dryland cereals, grain legumes, maize, rice, and wheat, while other programs focus on farming systems, crop nutritional characteristics, production sustainability, soil and water management, and climate change.

To identify and understand the role and major priorities of the CGIAR, particularly its centers that focus on grains research.

Current and Future Challenges Agriculture is inextricably linked to the broader development agenda. Most of the world’s poor people depend directly or indirectly on agriculture for their livelihoods although almost one billion people in the world are undernourished. The Earth’s ecosystems are under stress: Almost half of land has already been irreversibly transformed or degraded by human actions and agricultural activities. Most of the world’s water is


• • • • •

Learning Objective

•

used for irrigation, and agriculture frequently accounts for 70% of freshwater withdrawals and agricultural activities are one of the leading causes of climate change, contributing 20% of all greenhouse gases. Globally, the agricultural sector is set to face pressing challenges in the future: World population is expected to reach nine billion by 2050. Over the same time frame, demand for food is set to more than double, with most of the increased demand coming from developing countries. Erosion, salinization, compaction, and other forms of soil degradation affect 30% of the world’s irrigated lands, 40% of rainfed agricultural lands, and 70% of rangelands. Most of the world’s freshwater is used for irrigation and water use is expected to increase by 50% by the 2030s. Arable land per person in developing countries was 0.32 ha in 1961–63, but is expected to drop to 0.16 ha by 2030. Cereal productivity growth increases (i.e., rises in cereal yields per ha) have slowed.

Given these challenges, science-based agricultural development will continue to be an important method for promoting economic growth and addressing current and future food and environmental challenges and poverty. Concern about hunger and the world’s ability to feed growing populations has been a recurring theme throughout history. In modern times, the Irish famine and the famines of the twentieth century in Bengal (1943–44), Bangladesh (1974–75), China (1959–61), and Holland (1944–45) and during the 1970s–80s in large parts of Africa (Ethiopia, Sudan, Mozambique, Nigeria, Niger, Somalia, and Zaire) caused millions of deaths. Famines can result from breakdowns in food grain production and distribution and from a restricted flow of income with which people buy food. Shocks in the agricultural sector (plant disease as in the case of Irish famine and extreme weather events

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such as droughts and floods) and human-induced conflicts and civil wars can all trigger famines. The 1960s marked a period when deep-rooted pessimism about food availability surfaced anew. However, scientists working with farmers successfully averted the worst Malthusian specter by ensuring abundant agricultural yield. The story of wheat improvement in England is compelling. It took nearly 1000 years for wheat yields to increase from 0.5 to 2 tonnes per hectare (mt ha 1), but only 40 years to climb from 2 to 6 tonnes ha 1, illustrating the ability of modern grain science to increase agricultural productivity.

However, the benefits of the green revolution were spread unevenly and largely bypassed Africa. On average, crop yields in Africa are one-third of those achieved by Asian farmers. Less than 4% of Africa’s arable land is irrigated. There is enormous potential for growth-led productivity in sub-Saharan Africa where agriculture provides 70% of employment, 40% of exports, and one-third of gross domestic product. However, productivity benefits for Africa are now starting to emerge, particularly for maize, roots, and tubers.

Grains Research Centers in the CGIAR Mobilizing Grain Science for Development The Consultative Group on International Agricultural Research (CGIAR) was established in 1971. A group led by The Rockefeller Foundation, Ford Foundation, Food and Agriculture Organization, The World Bank, and others created the CGIAR. The founding objective was based on a profound belief in the ability of science, especially grain science, to increase food supply in low-income countries facing severe food scarcity. At that time, the central idea of mobilizing grain science internationally to meet food and development needs, within a public goods framework, was novel. The CGIAR system is supported by the World Bank and a range of national governments, usually through their overseas development assistance programs. In 2013, the CGIAR’s research investment exceeded $US 1 billion for the first time and represented the single largest effort in mobilizing science for agricultural development. The CGIAR is best known for the ‘green revolution,’ a term used to refer to the set of agricultural innovations (new high-yielding varieties of wheat, rice, and maize, increased investments in irrigation, easy availability of farm inputs such as fertilizers and pesticides, improved grain distribution, and food policies in developing countries) that helped boost grain yields and incomes of farmers in poor, agrarian economies. The green revolution transformed agriculture in developing countries especially in India, Mexico, Pakistan, and the Philippines. Cereal crop yields and food production more than doubled between 1960 and 1985. The new varieties of rice, wheat, and maize increased daily calorie supply in developing countries by 25%, from under 2000 calories per person in the early 1960s to 2500 calories per person by the 1990s. Without the productivity growth in basic food crops, the number of poor and hungry would have been far greater. Critics of the green revolution have argued that the new crop technologies favored farmers in well-endowed areas, worsened pollution through excessive use of fertilizers and pesticides, threatened biodiversity, promoted monocultures, and required higher input costs from impoverished farmers. While a comprehensive discussion of these issues is beyond the scope of this article, subsequent studies and analyses have increased understanding about the effects of the new technologies. A range of subsequent policy interventions (e.g., increased credit, improved marketing and seed distribution facilities, land reforms, and strengthened emphasis on pesticide safety, and others) have helped poor farmers to benefit from green revolution technologies.

CGIAR achieves its mission through the work of 15 international agricultural research centers (IARCs, Table 1) that work with national agricultural research systems, the private sector, and civil society. The IARCs are autonomous institutions, linked by a common commitment to promoting agricultural development in developing countries; 13 IARCs are headquartered in developing countries. Improving the sustainable productivity of food grains (including cereals, legumes, and pulses) is a major objective of CGIAR research. Nine of the IARCs have specific crop improvement mandates. More specifically, the CGIAR centers have traditional strengths in germplasm development, providing much of the germplasm for development of the modern varieties that are now utilized throughout most of the developing world (as well as in some developed countries with similar production environments such as Australia). To support this work, centers have strengths in agronomy, quality assessment, biotechnology, pathology, natural resource management, and economics. For the purposes of this paper, only eight IARCs have crop improvement mandates that correspond to the definition of grains cited earlier, the exception being root and tuber crops, including potato. Even though Bioversity (formerly known as International Plant Genetic Resources Institute) does not have a plant breeding program, its mandate to serve as a world center for conserving plant genetic resources is germane to the focus of this article.

The International Agricultural Research Centers Several of the centers have a grain science focus, including the Centro Internacional de Mejoramiento de Maı´z y Trigo (The International Maize and Wheat Improvement Center (CIMMYT) www.cimmyt.org). CIMMYT is based in Mexico but has programs in Latin America, Africa, Central and West Asia, and North Africa. Three centers carry out studies on rice improvement. The International Rice Research Institute (IRRI, www.irri.org) is the main one, and its work aims to develop new rice varieties and crop management techniques to help farmers improve the yield and quality of rice in a sustainable way. The semidwarf rice varieties and management packages developed by IRRI were central to the successes of the green revolution in the 1960s and 1970s. Two other centers undertake rice breeding and management in Latin America and Caribbean (International Center for Tropical Agriculture

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: CGIAR Table 1

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CGIAR Centers with crop improvement mandates

Center International Center for Tropical Agriculture (CIAT) International Maize and Wheat Improvement Center (CIMMYT) International Center for Agricultural Research in the Dry Areas (ICARDA) International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) International Institute of Tropical Agriculture (IITA) International Plant Genetic Resources Institute (now called Bioversity) International Rice Research Institute (IRRI) International Potato Center (CIP) West Africa Rice Development Association (now called AfricaRice)

Year founded

Host country

Mandate crops

1967 1966

Colombia Mexico

Cassava, beans, rice, tropical forages Maize, wheat (bread and durum wheat, triticale)

1975

Syriaa

1972

India

Barley, wheat (durum species), lentil, chickpea, faba bean, forage legumes Sorghum, pearl millet, groundnut, chickpea, pigeon pea

1967 1974

Nigeria Italy

Cassava, yams, maize, soybean, cowpea Genetic resources, cocoa, coconut/Musa species

1960 1970 1975

Philippines Peru Cote d’Ivoireb

Rice Potato, sweet potato Rice

a

Currently Lebanon. Currently Benin.

b

(CIAT) ciat.cgiar.org in Cali, Colombia) and West Africa (AfricaRice, www.africarice.org, in Cotonou, Benin). Other CGIAR centers with a strong grains focus include the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT, www.icrisat.org) in Patancheru, India (focussing on sorghum, pearl millet, chickpea, pigeon pea, and peanut), and the International Center for Agricultural Research in the Dry Areas (ICARDA, www.icarda.cgiar.org) long established in Syria, but now headquartered in Beirut, Lebanon (focussing on barley, wheat, lentil, faba bean, chickpea, and forage legumes). The CGIAR centers have traditional strengths in germplasm development, providing much of the germplasm for development of the modern varieties that are now utilized throughout most of the developing world (as well as in some developed countries with similar production environments such as Australia). To support this work, centers have strengths in agronomy, quality assessment, biotechnology, pathology, natural resource management, and economics. At CIMMYT, wheat breeding and maize breeding (agronomy and quality evaluation programs) are backed up by programs in economics, natural resource management, and biotechnology. ICRISAT has a geographic emphasis on South Asia and sub-Saharan Africa, and its research addresses water scarcity through natural resource management (rainwater conservation and utilization) and plant breeding to improve water-use efficiency and drought tolerance. ICARDA has a geographic emphasis on central West Asia and North Africa, but its germplasm is utilized worldwide. ICARDA focuses on agriculture in tropical dry areas, while ICRISAT emphasizes temperate and subtropical dry areas. It also has an emphasis on watersoil management in integrated farming systems for lowrainfall areas. The International Institute of Tropical Agriculture (IITA) with headquarters in Nigeria focuses on germplasm (including cowpea, maize, and soybean), pest management, and crop-based farming systems for smallholder farmers of sub-Saharan Africa. Some work on processing quality is carried out by the centers, but little work on grain storage and other postharvest technologies.

Evolving Research Agenda The CGIAR’s role and mission has evolved over time and this is reflected in its structure. When the CGIAR was founded, four IARCs (CIAT, CIMMYT, IITA, and IRRI) were brought under its umbrella. Thus, at that time, it was largely an alliance of grains research organizations, and in the 1960s, the research agenda was clearly around maize and rice productivity. During the 1970s, new IARCs were established to pioneer improvements in key food crops (legumes, roots, tubers, and other cereals), livestock health, and ecological regions (dry, semiarid, and tropical regions). In the 1980s, the mandate (and structure) was expanded to encompass food policy and strengthening of national agricultural research systems and in the 1990s further expanded to conduct research on pressing issues involving agroforestry, forestry, water management, and aquatic resources. During the 1990s and early-mid-2000s, the research programs undertaken in the CGIAR were organized around five focus areas:

• • • • •

Increasing productivity (of crops, livestock, fisheries, forestry, and the natural resource base) Strengthening national systems (joint research, policy support, training, and knowledge sharing) Protecting the environment (by developing new technologies that make more prudent use of land, water, and nutrients and help reduce agriculture’s adverse impacts on ecosystems) Saving biodiversity (collecting, characterizing, and conserving genetic resources) Improving policies (with a major impact on agriculture, food, health, the spread of new technologies, and the management and conservation of natural resources).

In summary, over 50 years, the CGIAR’s research portfolio evolved from the original focus on increasing productivity in individual critical food crops. The current approach recognizes that saving biodiversity, protecting the environment, improving food policies, and strengthening scientific capacities of developing countries through training and knowledge sharing are all key

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components in the drive to enhance sustainable agricultural productivity. The CGIAR’s focus on the fundamentals remains as strong as ever: Agricultural growth and increased farm productivity in developing countries creates wealth, reduces poverty and hunger, and protects the environment. Recognizing the complexity of the challenges faced in developing world agriculture and the importance of establishing sufficient capacity, the CGIAR was reorganized effective 2010. The CGIAR Consortium (www.cgiar.org/cgiar-consortium) “integrates the research of the 15 centers to increase the effectiveness and relevance of the work of the CGIAR; enhance the impact of the research by setting common objectives and planning concerted action; and to take advantage of opportunities for the CGIAR to become more relevant, more effective, and more efficient.” In 2011–12, much of the research undertaken within the CGIAR system was organized into major research programs (www.cgiar.org/our-research/cgiar-research-programs), which typically involve several CGIAR centers as well as universities, NGOs, and government agencies from both developing and developed countries. The CGIAR Consortium coordinates CGIAR Research Programs across research centers, which are members of the CGIAR Consortium and partner. Five CGIAR Research Programs have a primary emphasis on improvement of yields and profitability of grain crops:

• • • • •

Dryland cereals (such as barley, sorghum, finger, and pearl millets) in South Asia and Africa Grain legumes (addressing major biotic and abiotic stresses, nitrogen fixation, and opportunities to use grain legumes to intensify cropping systems) Maize (focussing on the productivity of maize-based cropping systems) Rice (focussing on genetic diversity, development of new varieties, rice-based farming systems, quality, and marketing) Wheat (wheat-based cropping systems, pest, diseases, and nutrient management, yield, and seed systems)

In addition, two programs (Integrated Systems for the Humid Tropics and Dryland Systems) aim to improve the productivity, profitability, sustainability, and resilience of entire farming systems; one program (Agriculture for Nutrition and Health) includes a thrust on grains nutritional composition, while a further program underpins the CGIAR crop (particularly grain) germplasm collections. Further two programs aim to improve production sustainability and environmental integrity and adapt to and mitigate climate change – namely, the CGIAR Research Programs on Climate Change, Agriculture and Food Security and Water, Land and Ecosystems.

Collaboration with National Agricultural Research and Extension Systems As comparatively small, research-oriented centers focussed on international public goods, the tension between addressing this mission and achieving practical impacts at the national level and in the shorter term has been present since the

formation of the CGIAR and its forerunners over 50 years ago. Another continuing challenge is the level of skills and resourcing within the National Agricultural Research and Extension Services (NARES) as this affects the ability of national organizations in poorest countries to be able to effectively partner. Centers with an ecoregional focus, such as ICARDA, have traditionally had a more extensive program of collaboration with the NARES in their region than those with a global crop mandate. The NARES themselves have recognized the importance of leveraging off CGIAR research and trying to do so in a more structured manner than in the past. For example, the Asia-Pacific Association of Agricultural Research Institutions (APAARI) has recently developed a strategy for strengthening partnerships in South Asia between the NARES and the CGIAR (www.apaari.org/publications/nars-cgiar-proceedings.html). Various approaches have been used to develop or strengthen relationships between centers and the NARES in developing countries. One of the most effective and enduring has been development of mechanisms by each of the grains centers to ensure that developing country breeders are trained at their centers and that grains breeding programs have access to materials. This has typically involved provision of germplasm and advanced lines (but not usually finished varieties), although the level of crossing from the materials made available by the centers depends on the resources available in the particular NARES as well as the extent of further work required to ensure that the material is sufficiently locally adapted. Translation (or extension) of agronomic research results from CGIAR centers to the NARES is necessarily more complex – by definition, it involves practice change rather than having ‘the technology embedded in the seed.’ Apart from the expected approaches of short- and long-term training and development of publications and other written materials, a challenge has been to develop longer-term partnerships that achieve impact while not distracting from the core function of knowledge generation at the centers. To facilitate such partnerships, a number of individual national and multilateral donors have funded major partnership projects, which through the provision of ‘restricted funding’ (now called bilateral funding) can fund the extension of CGIAR crops research results through formal, funded partnership projects. For example, the African Development Bank is currently supporting a major collaboration between AfricaRice, ICARDA, and IITA to enhance the productivity and income of four priority value chains (cassava, maize, rice, and wheat) on a sustainable basis. The importance of partnerships with the NARES has also been recognized in the design of most of the new CGIAR Research Programs and most projects that involve not only several CGIAR centers but also the NARES and universities in both developed and developing countries. Finally, capacity building of the NARES organizations has itself been a focus of the CGIAR over many years. This led to the formation of a specialized CGIAR center, the International Service for National Agricultural Research (ISNAR, in the Netherlands), although it merged into the IFPRI in 2004. Some controversy remains, however, as to whether the CGIAR is weakening the NARES capacity rather than building it as in some regions the most able, internationally trained

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: CGIAR scientists are hired to work for the CGIAR institutes. In addition, where the NARES are weak, there has in the past been a tendency for the CGIAR to assume the NARES role of developing and testing technologies at plot and field scale. This returns us to the challenge of demonstrating impact versus seeing the CGIAR as an intermediary.

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improved germplasm, and a unique set of wild crop relatives. These include wheat, barley, oats, and other cereals; food legumes such as faba bean, chickpea, lentil, and field pea; and forage crops, rangeland plants, and wild relatives of each of these species.

Rice

Selected Impacts of CGIAR Grains Research There have been several published analyses of the overall impacts of CGIAR research, and most of them have shown an overwhelmingly positive return on investment. In the initial studies, the point was made that in some countries, the benefits from modern varieties developed by the CGIAR centers had favored poor urban food consumers and large farmers rather than poor smallholder farmers, although it was pointed out that small farmers do tend to adopt modern varieties but later than large farmers. Evenson and Gollin published an extensive study of CGIAR crop research impacts across a wide range of crops and continents. Renkow and Byerlee assessed the impacts of more recent GIAR research – that published since 2000 – and argued that impacts of CGIAR crops genetic improvement research have continued to be strongly positive even some decades after the green revolution. Lastly, Raitzer and Kelley attempted to undertake a benefit–cost meta-analysis of investment in CGIAR research and concluded benefit–cost ratios of between 1.9 and 17.3, depending on the stringency of demonstration of causality of benefits from particular research activities. However, they concluded that “the true benefits arising from the CGIAR is probably in excess of even the upper bounds of these results as only a small subset of system impacts have been quantified.”

Wheat CIMMYT has a global mandate for wheat improvement (bread and durum species). In the late 1960s, about one-third of all wheat varieties in developing countries were CIMMYT crosses. By the 1990s, these numbers rose to about half from CIMMYT crosses and another quarter from varieties that had a CIMMYT parent. Worldwide, around 90% of all spring bread wheat releases had at least one CIMMYT ancestor; the percentage for durum wheat was even higher with nearly all spring durum wheat releases having a CIMMYT ancestor. In 1970, semidwarf wheat varieties were important only in Asia. By the 1990s, semidwarf wheat varieties covered 80% of world wheat area, with adoption rates of 90% and higher in Asia and Latin America. More recently, across Afghanistan, Bangladesh, Ethiopia, Egypt, Nepal, and Pakistan, high-yielding wheat varieties resistant to Ug99, a highly virulent disease, have protected the livelihoods and food security of 500 000 farming families. ICARDA’s wheat improvement research focuses on spring bread and durum wheats in the West Asia–North Africa region. ICARDA grain scientists have made major advances in identifying new sources of resistance to abiotic stresses (drought, heat, and cold) and biotic stresses (rusts, Septoria diseases, and Hessian fly), in broadening genetic diversity and in selecting for grain quality. ICARDA’s genebank holds over 135 000 accessions from over 110 countries: traditional landraces,

IRRI began rice improvement in the 1960s. Expanding on the successes in wheat improvement, IRRI scientists successfully introduced semidwarfism into two indica rice varieties (IR5 and IR8). The latter variety would lay the foundations of the green revolution in Asia. IRRI has made substantial contributions toward improvement of rice varieties. Of the estimated 2040 rice varieties released over 40 years by national rice research systems of South and Southeast Asia, 219 were direct IRRI lines. Of the 2021 varieties, 31% had originated from one or more parents developed at IRRI. This number rises to 46% when the IRRI-developed varieties are included. In the 1970s, the release of IRRI-related varieties peaked at 60%, subsequently stabilizing at 40% of all varieties released. Since that time, the increase in rice production has been enormous. More recently, ‘Scuba rice’, which can survive under water for 2 weeks, is protecting the harvests, incomes, and food security of poor farmers and consumers across monsoon Asia. AfricaRice conducts rice improvement research in West and Central Africa, focussing on three distinct rice ecologies: upland, rainfed lowland, and irrigated land. Using interspecific hybridization techniques, Africa Rice successfully combined the ruggedness of the local African species of rice (Oryza glaberrima) with the phenomenally high productivity traits of Asian rice (O. sativa) (common rice) that was the mainstay of the green revolution. The new rice varieties, NERICA or New Rice for Africa, resist droughts and pests and are able to thrive in poor soils. CIAT has a mandate to promote sustainable increases in rice production and productivity in Latin America and the Caribbean region.

Maize CIMMYT has a global mandate for maize improvement, and it targets lowland tropical, subtropical, midaltitude, and tropical highland environments throughout the developing world. Mexico, where CIMMYT headquarters are located, is a center of origin for maize. The use of CIMMYT germplasm has increased over time, with about two-thirds of public sector varietal releases containing CIMMYT germplasm. Estimates of economic benefits from CIMMYT’s maize research vary, but based on the earlier results (21.2 Mha planted to CIMMYTrelated varieties) and a conservative estimate of farm-level maize prices (US$120 per tonne, on import parity basis), gross benefits range from US$1.3 billion to US$4 billion per year. These benefits take into account both germplasm improvements and better crop management practices. CIMMYT also developed quality protein maize (QPM), a product of 30 years of research. QPM looks and tastes like normal maize but has nearly twice the amount of lysine and tryptophan, two amino acids essential for protein synthesis in humans. QPM is now being planted on 1 Mha in 20 countries, boosting food, nutrition, and income security. More recently,

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drought-tolerant maize has increased farmers’ yields by 20–30%, benefiting 20 million people in 13 African countries. IITA has a regional maize improvement mandate mainly targeting humid tropical and moist savannah zones of Western and Central Africa. Maize accounts for more than 20% of domestic food production in Africa.

The CGIAR, with greater emphasis on the centers working together with each other – and with partners in developed and developing countries to leverage complementary skills and resources expect a number of significant impacts from the new CGIAR Research Programs. Some of the planned impacts from the new programs related to grains (www.cgiar.org/ourresearch) include the following:

Other Crops

•

Two significant achievements involving ICRISAT should be mentioned. Breeding and disseminating micronutrient-rich crop varieties through biofortification are potentially a costeffective strategy to increase micronutrient intake such as iron and zinc. India has some of the world’s worst malnutrition rates, resulting from a lack of essential vitamins and minerals in the diet. This affects the survival and development of women and children in particular. About three quarters of children under three and half of women suffer from anemia, mostly caused by iron deficiency. Pearl millet is a nutritious but underutilized staple crop, eaten by 50 million people in dry rural areas of India. As well as being rich in B vitamins, calcium, iron, potassium, magnesium, and zinc, it is well adapted to drought, poor soils, and high temperatures. It is much higher in iron than wheat, rice, or maize. ICRISAT is developing drought-tolerant pearl millet varieties with even higher levels of iron. This is part of a larger biofortification initiative coordinated through HarvestPlus and IFPRI and reviewed in Saltzman et al. Another significant impact involves partnership with agribusiness on the microdosing of fertilizer to resource-poor farmers in sub-Saharan Africa. This involves using only 8–10 kg of nitrogen per hectare but applying it precisely to the roots three to 4 weeks after planting. In Zimbabwe, ICRISAT has recorded yield increases of 30–50% among farmers adopting the technique. With evidence that precision agriculture techniques can work, the challenge is creating appropriate enabling environments to encourage take-up. In addition, ICRISAT has been active in developing agribusiness incubators, but the involvement of other centers in agribusiness has been variable.

Conserving Biodiversity For more than 30 years, CGIAR scientists have been collecting, characterizing, and conserving biodiversity. Currently, the CGIAR holds over half a million samples of crop, forage, and agroforestry genetic resources in 11 gene banks around the world. Since the 1980s, CGIAR gene banks have distributed well over one million germplasm samples worldwide, and the vast majority of requests came from developing countries. In 1994, CGIAR signed an agreement with FAO, placing the collections in public trust, available to researchers worldwide. Recognizing the challenge of creating a sustainable funding base for conservation activities, the Global Crop Diversity Trust (GCDT) was established in association with the CGIAR to support global conservation of biodiversity. More recently, the Svalbard Global Seed Vault has been established as a secure seedbank in Norway, only 1300 km from the North Pole. It maintains duplicate samples of seeds held in other genebanks worldwide, as an attempt to insure against the loss of seeds in other genebanks during large-scale crises.

• • •

By 2035, research on rice will increase farmers’ yields and lower prices for poor consumers, lifting 150 million people out of poverty and reducing the number of undernourished people in Asia by 62 million. By 2020, 12 million households in Africa will have access to sustainable irrigation, thanks to research on water, land, and ecosystems. By 2022, research will help increase harvests of grain legumes – a key source of protein for the poor – in lowincome countries in five regions, improving their nutrition from 2.1 million tonnes of extra protein. By 2018, 50 million people will have access to staple food crops specifically bred to be rich in key vitamins and minerals – namely, iron, zinc, and vitamin A – in an effort to combat malnutrition.


• • • •

Which CGIAR centers have a mandate for rice research? What has been the main shift in research organization in the CGIAR centers over the last 3–5 years? What are some of the approaches that have been used to facilitate the extension of research results from CGIAR centers to the NARES? What has been implemented to provide a ‘back up’ in the event of a CGIAR center’s genebank being destroyed through war or civil unrest?


• • •

What are the main research activities of IRRI? How are they funded and what is their relationship with major research organizations in the developed world? How do developed countries benefit from the results of CIMMYT research? Which centers provide the enabling science in natural resources management to underpin the work of the cropsspecific centers? How do they collaborate to support each other?

Acknowledgments Some of the text, particularly in the ‘Current and Future Challenges’ and ‘Mobilizing Grain Science for Development’ sections, has been adapted from an article for the first edition of the encyclopedia, by F.J.B. Reifschneider and S. Hussain, formerly of the CGIAR office in Washington DC.

See also: Agronomy of Grain Growing: Implication of Climate Changes; Wheat: Agronomy; Breeding of Grains: Barley: Genetics

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: CGIAR and Breeding; Maize: Breeding; Rice: Breeding; Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grains Around the World: Grain Production and Consumption: China and South-East Asia; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; Production and Consumption of Grains: India; Scientific Organizations Related to Grains: Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; WheatBased Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Alston JM and Pardey PG (1996) In: Making Science Pay – The Economics of Agricultural R&D Policy, p. 203. Washington, DC: American Enterprise Institute. Baum WC (1986) Partners Against Hunger: Consultative Group on International Agricultural Research. Washington, DC: The World Bank. Binswanger H and McCalla A (2010) In: Pingali P and Enenson R (eds.) Handbook of Agricultural Economics, pp. 3571–3712. Amsterdam: Elsevier. Bouman BAM, Hengsdijk H, Hardy B, Bindraban PS, Tuong TP, and Ladha JK (2002) Water-wise rice production. In: Proceedings of the International Workshop on Water-wise Rice Production, 8–11 April. Los Banõs, Philippines: International Rice Research Institute. Brown LR (1995) Who Will Feed China? Wake-up Call for a Small Planet. Washington, DC: Worldwatch Institute. Bruinsma J (2009) The resource outlook by 2050: How much do land, water and crop yields need to increase by 2050? Expert Meeting on How to Feed the World in 2050, Food and Agriculture Organization of the United Nations, ftp://ftp.fao.org/docrep/ fao/012/ak971e/ak971e00.pdf.

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Conway G (1999) The Doubly Green Revolution – Food for All in the 21st Century. London: Penguin Books. Evenson RE (2003) In: Evenson RE and Gollin D (eds.) Crop Variety Improvement and its Effect on productivity – The Impact of International Agricultural Research, pp. 71–108. Wallingford, UK: CABI Publishing. Hazell P (2003) Green revolution. In: Mokyr J (ed.) The Oxford Encyclopedia of Economic History UK: Oxford University Press. Hazell P and Ramasamy C (1991) The Green Revolution Reconsidered: The Impact of High-yielding Rice Varieties in South India. Baltimore, MD: Johns Hopkins University Press. Hoekstra AY and Mekonnen MM (2012) The water footprint of humanity. Proceedings of the National Academy of Sciences of the United States of America 109: 3232–3237. Kiple KF and Ornelas KC (2002) The Cambridge World History of Food. Cambridge, UK: Cambridge University Press. Lipton M and Longhurst R (1985) Modern Varieties, International Agricultural Research and the Poor. CGIAR Study Paper Number 2, Washington DC, USA: The World Bank. Lipton M and Longhurst R (1989) New Seeds and Poor People. Baltimore, MD: Johns Hopkins University Press. Newman LF (1990) Hunger in History: Food Shortage, Poverty, and Deprivation. Cambridge, UK: Basil Blackwell. Pingali PL (2012) Green revolution: Impacts, limits, and the path ahead. Proceedings of the National Academy of Sciences of the United States of America 109: 12302–12308. Raitzer DA and Kelley TG (2008) Benefit-cost meta-analysis of investment in the International Agricultural Research Centers of the CGIAR. Agricultural Systems 96: 108–123. Ravallion M (1997) Famines and economics. Journal of Economic Literature 35: 1205–1242. Renkow M and Byerlee D (2010) The impacts of CGIAR research: A review of current evidence. Food Policy 35: 391–402. Saltzman A, Birol E, Bouis HE, et al. (2013) Biofortification: Progress towards a more nourishing future. Global Food Security 2: 9–17. Tilman D, Balzer C, Hill J, and Befort BL (2012) Global food demand and the sustainable intensification of agriculture. Proceedings of the National Academy of Sciences of the United States of America 108: 20260–20264. Timothy JD and Guei RG (2003) Productivity gains from rice genetic enhancements in West Africa: Countries and ecologies. World Development 31: 359–374.

Research Organizations of the World: Europe and North America JH Skerritt, University of Queensland, St Lucia, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

•

While maintaining a systems and sustainability focus, there has been renewed emphasis on research directed at improving grain yields in many countries. The formation of networks between grain research investors, research institutes, and industry increasing in Europe and North America. A greater proportion of agricultural (including grains) research is carried out in universities in Europe and North America compared with developing countries, where it is largely within government-funded research institutes. Significant increase in commercial involvement in grain breeding and biotechnology, particularly where strong intellectual property protection and end point royalty systems are in place. Farmer organization-led grain research is also becoming more important. Research to underpin grain utilization for animal feed and for biofuels is important in several countries.

Learning Objectives

•

To understand the structure and major roles of public sector grain research organizations within Europe and North America.

Introduction Compared to the long history of cultivation of grains (many thousands of years), the use of research principles to address constraints is a comparatively recent approach. Agricultural societies were established in the United Kingdom, France, and Germany in the mid-1800s (e.g., The Royal Agricultural Society of England (1839), La Socie´te´ des Agriculteurs de France (1850), and Deutsche Landwirtschafts-Gesellschaft (1885)) and by the mid-to late nineteenth century, agriculture experiment stations were appearing in Europe and North America. The tradition of government-funded grain research is the longest established in Europe and North America, although similar initiatives were started in the late nineteenth century in a number of European colonies. Government-funding bodies have shown a greater interest in assessing the economic and social impacts of research that they fund – research funding is increasingly viewed as an investment rather than as ‘grants.’ The most significant trend in terms of research intensity is the very significant growth over the last couple of decades in the level of grain (especially cereals) R&D carried out by the private sector or alternatively funded by the private sector but carried out in universities or government organizations. Most publicly funded agricultural research in North America and Europe is concentrated in

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the United States, France, and Germany, with Canada and particularly the United Kingdom having smaller public sector roles. There is also a greater proportion of agricultural (including grains) research carried out in universities in Europe and North America compared with developing countries, where it is largely within government-funded research institutes. Grain R&D carried out by commercial and industry organizations is reviewed in a separate article, so the emphasis of this article is on major public sector (government and university) grain science organizations.

The United States Although the United States has very large private sector (seed companies; milling, baking, brewing, and oilseed processing companies; and biotechnology companies) involvement in grain R&D, government investments are also significant. A wide range of temperate grain crops are targeted – especially not only wheat, barley, maize, and oilseeds but also pulses and subtropical rice, with most resources dedicated to maize and wheat research. State and federal governments invest roughly equally in agricultural research. The Agricultural Research Service (ARS, www.ars.usda.gov) is the principal research agency of the (national) US Department of Agriculture (USDA), and together with the ‘land grant’ universities, they form the main research centers that conduct grain research. The development of a single strategic plan and national program structure by USDA–ARS in recent years has increased the amount of coordination between the 800 or so individual USDA projects underway in different centers. Crop Production and Protection is the third national program described in USDA–ARS’s 2012–17 strategic plan and “delivers science-based information, genetic resources, and technologies for increased crop productivity, economically and environmentally sustainable methods of crop production, and protection from plant diseases and pests.” There are six subprograms, each relevant to grain research: Plant Genetic Resources, Genomics and Genetic Improvement; Plant Biological and Molecular Processes; Plant Diseases; Crop Protection & Quarantine; Crop Production; and Methyl Bromide Alternatives. The two major goals under area 3 are firstly to “Protect, expand, and enhance the United States’ crop genetic resource base, increase scientific knowledge of crop genes, genomes, biological processes and systems, and deliver economically and environmentally sound technologies that improve the production efficiency, quality, health and value of the nation’s crops” and secondly to “Develop knowledge, strategies, systems and technologies that maximize the production efficiency of our annual, perennial, greenhouse and nursery cropping systems. Develop new technologies and tools contributing to improving these systems to meet current and future food crop


http://dx.doi.org/10.1016/B978-0-12-394437-5.00056-5

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: Europe and North America production needs of diversified consumers, while ensuring economic and environmental sustainability and production efficiency, health, and value of our nation’s crops.” The Natural Resources and Sustainable Agricultural Systems program cluster is also relevant. Some USDA centers are free-standing multidisciplinary research centers, while smaller ones are typically colocated on university campuses. Many centers have the mandate to carry out research directed at the particular agroecological zone in which the institute is based. For example, wheat is grown in many parts of the United States, but there are different quality types suited for different locations – soft red winter wheat in the Midwest, Virginia, and North Carolina; hard white and some hard red winter wheat in Pacific Northwest; hard red winter varieties in the Great Plains, from Texas to Montana on the Canadian border; and spring varieties in northern central states such as Minnesota, North and South Dakota, and Montana – and appropriately located USDA centers develop germ plasm and agronomy packages for the different types of varieties. Some of the USDA centers carrying out grain research are based in the following:

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• • • • • • • • • • • •

Aberdeen, ID – Small Grains and Potato Germplasm Research Albany, CA (Western Regional Research Center) – Genomics and Gene Discovery and Crop Improvement/utilization Research Ames, IA – Corn Insects and Crop Genetics Research Beltsville, MD (Beltsville Agricultural Research Center) – Sustainable Agricultural Systems Laboratory, Instrumentation and Sensing Laboratory, National Germplasm Resources Laboratory, Soybean Genomics and Improvement Laboratory, and Food Quality Laboratory College Station, TX (Southern Plains Agricultural Research Center) – Crop Germplasm Research and Insect Control and Cotton Disease Research Colombia, MO – Plant Genetics Research Corvallis, OR – Forage Seed and Cereal Research Fargo, ND – Cereal Crops Research and Hard Spring and Durum Wheat Quality Laboratories Fort Collins, CO – National Center for Genetic Resources Preservation Ithaca, NY – Plant Genetic Resources, Plant Protection Research, Plant, Soil and Nutrition Research Lane, OK (South Central Agricultural Research Laboratory) – Genetics and Production Research Lincoln, NE – Grain, Forage, and Bioenergy Research Lubbock, TX – Cropping Systems Research Laboratory and Plant Stress and Germplasm Development Research Madison, WI – Cereal Crops Research Manhattan, KS (Center for Grain and Animal Health Research) – Grain Quality and Structure Research, Stored Product Insect Research, and Hard Winter Wheat Genetics Research Peoria, IL (National Center for Agricultural Utilization Research) – Cereal Products and Food Science Research, Plant Polymer Research, Mycotoxin Research, New Crops and Processing Research, Crop Bioprotection Research, and Bacterial Foodborne Pathogens & Mycology Research

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Pullman, WA (Pacific West Area) – Wheat Genetics, Quality Physiology and Disease Research, Land Management and Water Conservation Research, and Root Disease and Biological Control Research Raleigh, NC – Soybean and Nitrogen Fixation Research and Plant Science Research Laboratories Shafter, CA – Western Integrated Cropping Systems Research Sidney, MT – Agricultural Systems Research Unit Stillwater, OK – Wheat, Peanut, and Other Field Crops Research, Plant Science and Water Conservation Research Stoneville, MS – Crop Genetics & Production Research Unit St Paul, MN – Midwest Area Cereal Disease Laboratory and Plant Science Research Stuttgart, AR – Dale Bumpers National Rice Research Center Tifton, GA – Crop Genetics and Breeding Research and Crop Protection and Management Research Urbana, IL – Soybean/maize Germplasm, Pathology, and Genetics Research West Lafayette, IN – Crop Production And Pest Control Research Wooster, OH – Corn, Soybean and Wheat Quality Research Wyndmoor, PA – Crop Conversion Science & Engineering Research Unit

USDA also has Economic Research Service (www.ers.usda. gov), which carries out research and communication activities in many areas relevant to grains, including farm-level risk management, commodity outlook research, and economic and statistical research on marketing and production sustainability. The USDA National Institute of Food and Agriculture (NIFA, www.nifa.usda.gov) replaced the Cooperative State Research, Education, and Extension Service in 2009 and is intended to consolidate all federally funded agricultural research (including federal support to land grant universities) and have overarching federal coordination of extension work done through USDA. The ‘land grant’ college system was established in 1862 – the name is derived from the fact that the colleges were originally endowed by grants of public lands in the expanding western United States. The 1887 Hatch Act established the agricultural experiment station system to enable these colleges to undertake research, and the 1914 Smith–Lever Act established the cooperative extension system. This unique system has the advantage of linking state government R&D and extension activities to university research. The greatest emphasis for state government efforts is on breeding new cultivars and adapting crop production approaches to local conditions and on education. The universities usually have experiment stations at different locations in their state, again often corresponding to different agroecological zones but also requiring researchers to carry out a local outreach function. There are usually a balance of applied grain research on constraints to productivity in a particular state and a proportion directed toward more fundamental research. Cooperative extension systems from land grant universities have a state development mandate and often involve location of farm advisors in counties throughout the state. The continued involvement of the government and public funding in agricultural extension in the United States is in contrast with the winding back or exiting

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SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: Europe and North America

of state or national government staff from extension roles in other countries such as the United Kingdom, Australia, and New Zealand. A summary of some of the main US universities that carry out grain research is provided in Table 1. Land grant Table 1

universities are usually predominantly state-funded, but with significant federal funding as well. In 2011, the US government commenced the president’s global hunger and food security initiative (www.feedthefuture.

Some US universities undertaking significant grain research

University (website)

Grain research emphasis

Colorado State University, Fort Collins, CO (www.agsci.colostate.edu) Cornell University, Ithaca, NY (www.cals.cornell.edu)

Genomics, biotechnology, dryland farming systems, wheat breeding, precision agriculture

Iowa State University, Ames, IA (www.ag. iastate.edu) Kansas State University, Manhattan, KS (www.k-state.edu)

Michigan State University, East Lansing, MI (www.maes.msu.edu) Montana State University, Bozeman, MT (www.montana.edu/agriculture) North Carolina State University, Raleigh, NC (www.cals.ncsu.edu) North Dakota State University, Fargo, ND (www.ag.ndsu.nodak.edu) Oklahoma State University, Stillwater, OK (www1.dasnr.okstate.edu) Ohio State University, Columbus, OH (www.oardc.ohio-state.edu) Pennsylvania State University, University Park, PA (www.research.cas.pse.edu) Purdue University, West Lafayette, IN (www.agriculture.purdue.edu/arp) Rutgers University, New Brunswick, NJ (www.foodsci.rutgers.edu/caft) NJ Agricultural Experiment Station (www.cook.rutgers.edu) Texas A&M University, College Station, TX (www.agresearch.tamu.edu; www. agrprogram.tamu.edu) University of Arkansas, Fayetteville, AR (www.uark.edu/admin/aes) University of California, Davis (www.ucanr. org; www.caes.ucdavis.edu)

University of Illinois, Urbana–Champaign, IL (www.web.aces.uiuc.edu) University of Idaho, Aberdeen, ID (www. ag.uidaho.edu) University of Minnesota, St. Paul, MN (www.maes.umn.edu) University of Missouri, Colombia, MO (www.cafnr.missouri.edu) University of Nebraska, Lincoln, NE (www.unl.edu)

Washington State University, Pullman, WA (www.cahe.wsu.edu)

Genetics, biotechnology, basic plant science, maize breeding, seed science, cereal pathology, cereal product rheology. Wheat variety development, genetics research, disease resistance, and crop management. Particular emphasis on breeding methodologies, disease resistance, comparative genomics, association mapping, allele characterization, and genomic selection methods Corn and soybean breeding, nonfood crop products, corn quality, basic plant sciences, crop genomics, seed technology Wheat, soybean, and sorghum breeding; cereal (wheat, corn, sorghum, and millet) agronomy and physiology, entomology, cereal chemistry, milling and baking, livestock feeds. Wheat genetics, development of genomics resources and high throughput genotyping technologies, wheat breeding, germ plasm development Grain crop breeding, cereal chemistry, genomics Winter wheat, barley, durum, pulses, canola, and soybean breeding, precision agriculture, integrated pest management Bioinformatics, integrated pest management Basic research on wheat quality and processing; milling; pasta production; brewing; farming systems, pathology, and entomology Baking, grain protein chemistry, oilseed chemistry, plant diseases Maize production systems, cereal and oilseed quality, soft red winter wheat and soybean agronomy and breeding, soy protein functionality Starch chemistry, entomology Plant stress physiology, biotechnology, integrated pest management, precision agriculture, new grain products, carbohydrate research Cereal processing, plant biotechnology

Precision agriculture, farming systems, plant genomics, grain food processing

Rice, wheat, oat, and soybean breeding; agronomy and physiology, rice processing Genetic resources conservation, genetics of cereals and legumes, agronomy, wheat breeding, entomology, plant pathology, rice breeding Breeding, Marker-Assisted selection, Positional cloning of agronomic genes, Dissection of flowering and disease resistance regulatory pathways Maize and soybean breeding and agronomy, cereal diseases, starch chemistry Grain breeding and agronomy (wheat, oilseeds) Cereal structure, wheat and barley breeding and pathology, soybean diseases, precision agriculture, cereal food processing Tillage, soybean, sorghum, and corn cropping systems and soybean breeding, basic grain science, maize genome mapping Processing of grain starches, cereal breeding, genomics. Wheat breeding and genetics of winter hardy, disease and insect resistant, high-yielding cultivars. Fundamental research in wheat virology, fungal disease control, biochemistry, statistical approaches, and breeding methodology including transformation. Grain crops breeding and genetics, pathology/entomology, soil science, processing

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: Europe and North America gov/approach), which includes the ‘Feed the Future’ research strategy. This is a major international development assistance initiative managed through USAID. Investments under this strategy range from longer-term research to address major global challenges to applied and adaptive research guided by host-country priorities for nearer-term impact. A number of US research laboratories within USDA and the university sector are involved – given the central role of grains in food security, it is not surprising that several initiatives support grain research. Within three broad research themes (advancing productivity, transforming production systems, and enhancing food safety and nutrition), these include work on wheat stem rust, abiotic stress tolerance, genetic resources, marker-assisted technologies, legume productivity, and management of mycotoxin contamination in stored grains.

Centre, Quebec (for cool, wet production systems), Atlantic Cool Climate Crop Research Centre (St John’s, Newfoundland), Crops and Livestock Research Centre (Charlottetown, Prince Edward Island), Brandon Research Centre, and Semiarid Prairie Agricultural Research Centre (Swift Current, Saskatchewan). Several universities carry out grain research in Canada, often working closely with Agriculture and Agri-Food Canada scientists. These include the following:

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Canada The majority of wheat breeding and research in Canada is conducted by the public sector, although private sector breeding is gaining momentum and Syngenta has released wheat varieties in Canada since 1993. Several public–private partnerships exist between industry and most publically funded research institutions. Agriculture and Agri-Food Canada (www.agr.gc.ca/science and innovation/research centers) carries out grain research at several of its 19 research centers across the country. Cereal research is carried out mainly at the Winnipeg (Manitoba) Cereal Research Centre, which is colocated with the University of Manitoba and emphasizes six areas: cereal diseases, cereal germ plasm and genomics, pulse germ plasm, nutrition and functional foods, bioprospecting from grains, and grain storage research. The Eastern Cereal and Oilseed Research Centre (Ottawa, ON) develops new varieties of spring and winter wheat, barley, corn, oats, and soybeans and has the central biodiversity mandate for Canada. There is a strong emphasis on gene isolation, gene transfer, and the study of gene expression in grain crops, bioprospecting for new bioactives, and study of Fusarium resistance. Wheat breeding is also carried out at the Semiarid Prairie Agricultural Research Centre (Swift Current, Saskatchewan, along with breeding of other cereals) and the Lethbridge Research Centre (Alberta). The Lethbridge Research Centre also carries out bean and forage crop breeding and research on water, soil, crop, and manure management for prairie conditions. There is an emphasis on disease and disease resistance and agronomy. The Brandon Research Centre (Manitoba) is the main site of barley breeding along with a strong soil science focus, while the Lacombe Research Centre (Alberta) undertakes oat-varietal improvement research, along with barley breeding (disease resistance focus) and farming systems research. The Saskatoon Research Centre (Saskatchewan) is the main center of breeding programs for canola and mustard for prairie conditions. Some canola breeding and breeding for other short-season grain crops also take place at the Lacombe Research Centre, while the Greenhouse and Processing Crops Research Centre in Harrow, Ontario, also carries out soybean breeding. Agronomy research for grain production is undertaken at the Soils and Crops Research and Development

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University of Saskatchewan (www.usask.ca) with research emphasis on wheat, barley, oat, canola, and legume (lentil, pea, dry bean, and chickpea) breeding and agronomy, plant genetic engineering, molecular marker development, and malting and brewing science. University of Alberta, Edmonton (www.afns.ualberta.ca), studies grain and oilseed crops for Western Canada – breeding, disease resistance, agronomy, and livestock feed utilization. In wheat, it focuses on conventional breeding and genetic research with an emphasis on adaptation of wheat to the short growing season on the Canadian prairies and agronomy and breeding of grains for organic agricultural environments. University of Manitoba, Winnipeg (www.umanitoba.ca/ afs/plant_science), carries out research on canola and wheat breeding and postharvest technology, grain storage technology, cereal chemistry, baking technology, pulse food science, functional foods, and cereal agronomy including precision agriculture, genetics and wheat breeding, agronomic production systems, pathology, breeding methodologies, and end-use quality. University of Guelph, Ridgetown, Ontario (www.ridgetownc.com/index.cfm), emphasizes grain crops breeding (soybean, barley, wheat, and canola), agronomy, pathology, and genome mapping. McGill University, Quebec, Ontario (www.mcgill.ca), is involved with basic plant science, biotechnology, and some grain food processing research.

The National Research Council (NRC) Plant Biotechnology Institute in Saskatoon (www.pbi.nrc.ca) carries out basic research in genomics and proteomics and has a special interest in the modification of oil composition and of agronomic traits of oilseeds and in cereal and legume molecular marker and transformation technology. Some individual provinces also have agencies that carry out applied agriculture and food research. For example, the Field Crop Development Centre is funded in part by the province of Alberta and conducts breeding and development programs focussed on feed and malting barley, spring and winter triticale, and winter wheat. The Canadian Grains Commission in Winnipeg, Manitoba, regulates grain handling and establishes and maintains grain quality standards for Canada. Its Grain Research Laboratory (www.grainscanada.gc.ca/cgc-ccg/grl-lrg/ grlm-mlrg-eng.htm) has emphasis on research to understanding the genetic, environmental, structural, and biochemical basis on end-use quality of major grains, how grading factors affect end-use qualities, and investigating new uses for Canadian grain. The Canadian International Grains Institute (www.cigi.ca), also in Winnipeg, has a technical training and information dissemination role.

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Mexico In Mexico, maize is the main grain crop, but the national program played an important role in semidwarf wheat breeding ahead of the establishment of Centro Internacional de Mejoramiento de Maiz y Trigo, International Wheat and Maize Improvement Center (CIMMYT). Most federal government agricultural research is carried out by the Instituto Nacional de Investigaciones Forestales Agrıćolas y Pecuarias (INIFAP, www.inifap.gob.mx); some of the state governments have small grain research activities. There is also significant activity within the higher education and science and technology ministries Consejo Nacional de Ciencia y Tecnologıá (CONACYT, www.conacyt.mx), with grain research being carried out in several of their regional centers (Centro de Investigacioń en Alimentacion y Desarrollo (CIAD), AC, Centro de Investigacioń y Assistencia en Tecnologıá y Diusenõ del Estado de Jalisco (CIATEJ), Centro de Investigaciones Biolo´gicas del Noroeste (CIBNOR), and El Colegio de la Frontera Sur (ECO SUR)). Postgraduate colleges, within the universities managed under the agriculture secretariat (SAGAR), along with the agronomy faculties in autonomous universities in different Mexican states, are also active. Mexico is home to a number of national seed companies (maize, sorghum, and wheat), along with subsidiaries of foreign (especially the United States) seed companies, and these carry out a variety of trials and agronomy work.

Europe The Seventh Framework Programme for Research (www.ec. europa.eu/research/fp7/index_en.cfm) provided € 50 billion for collaborative research from 2007 to 2013 across ten thematic areas, one of which is bioeconomy, encompassing food, agriculture and fisheries, and biotechnology (www.ec.europa. eu/research/bioeconomy/index_en.htm). Grain research features in several projects and programs with the bioeconomy area, including improved feed utilization of grain crops, cropping system resilience under climate change, value addition to crops through biotechnology and food quality and safety, and a range of major basic plant science and biotechnology projects. In Western Europe, yields of most major cereals are high, and it is clear that there has been a shift away from research on increasing production to an emphasis on environmentally friendly production and managing variability under climate change. While biotechnology programs are strong, there is limited work on crop genetic transformation due to lack of acceptance of commercial genetically modified (GM) food crops by many European governments. Other areas of grain research emphasis across Europe include quality and processing technologies, including value-addition and nonfood uses of grains; food safety, nutrition, and health (with grains, the main emphasis is on mycotoxins, nutraceuticals, dietary fiber, and allergies and intolerances); traceability (e.g., of GM cereals); and breeding, genomics, and diagnostic technologies. Among the UK government institutes, the Biotechnology and Biological Sciences Research Council (BBSRC, www.bbsrc. ac.uk) emphasizes research on grains within several institutes:

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John Innes Centre, Norwich – prebreeding and basic research on breeding technology for yield and quality, plant biotechnology, and biology of cereals and brassica crops Rothamsted Research – grain crop performance, farming systems, seed science, GM wheat trialing, and plant bioscience Institute of Biological, Environmental and Rural Sciences (at Aberystwyth University) – genome diversity analysis, breeding methodologies, oat breeding, and biofuels The Genome Analysis Centre

The James Hutton Institute in Scotland (www.hutton.ac.uk) conducts research on the genetics of quality relationships in barley and wheat, farming systems, weeds, pests, and diseases. Major British universities carrying out research in grain science include the University of Reading (www.apd.rdg.ac.uk); University of Nottingham, Sutton Bonington (www.nottingham.ac. uk); University of Bristol, Long Ashton; University of East Anglia, Norwich (www.uea.ac.uk); Heriot-Watt University, Edinburgh; University of Plymouth, Devon; University of Leeds; University of Manchester; Institute of Science and Technology; Satake Centre for Grain Process Engineering (www.ce.umist.ac.uk); and Queen’s University Belfast–School of Agriculture and Food Science (www.qub.ac.uk). The Home-Grown Cereals Authority (www.hgca.com) is an organization funded on grower levies to support research and provide market information and extension information for British grain farmers. Campden BRI (www. campdenbri.co.uk) provides technical and research support for industry and incorporates three former centers – the Chorleywood Food Research Association, Brewing Research International, and Campden Food Research Institute. In Ireland, the Irish Agriculture and Food Development Authority’s (TEAGASC, www.agresearch.teagasc.ie) Oak Park Crops Research Centre emphasizes research on grain crops, especially aiming for more efficient production systems for cereals, grain lupins and rape oilseed. There are a strong emphasis on the management of fungal and viral diseases of cereal crops and an increasing focus on nonfood uses for grain crops. The main university for production research on grain crops is University College Dublin, while University College Cork emphasizes grain processing research. In Switzerland, the major government grain research institutes are the Federal Office for Agriculture, Swiss Federal Research Station for Plant Production, and Swiss Federal Research Station for Agroecology and Agriculture, while in the university sector, the Swiss Federal Institute of Technology in Zurich carries out most of the applied grain sciences research. In France, the Institut National de la Recherche Agronomique (INRA, www.inra.fr/en) is the main government research organization in agriculture and grain research within four divisions: Genetics and Plant Breeding, Plant Health and Environment, Environment and Agronomy, and Science and Process Engineering of Agricultural Products. Major areas of grain research at INRA are structural and functional genomics, analysis of genetic diversity, plant breeding, host–pathogen interactions, and grain development and quality. INRA has a large center in Nantes with a research emphasis on agriculture and food processing. There is an additional emphasis on cereal food and nutritional quality and nonfood uses, with a strong emphasis on processing technologies and basic protein and starch molecular sciences

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organizations of the World: Europe and North America related to cereals. At INRA Montpellier, there is an ongoing research on processing technology, grain crop production systems, plant protection, and genetic resource conservation as well as more basic studies on grain crop development. Several French universities have Ecole Nationale Superieure Agronomique, for example, in Paris Grignon, (the Institut National Agronomique (INA-PG)), Montpellier, Rennes, Nancy, and Toulouse. ARVALIS Institut du ve´ge´tal (www.arvalisinstitutduvegetal.fr/en) is responsible for applied research on cereals, maize, pulses, potato, and forage crops. The activities of this technical institute, which is run and financed by farmers, include sustainable cropping systems, precision farming, remote sensing, satellite images, biotechnology, farm economics, quality assurance, safety quality, traceability, human food, animal feed, and technology transfer. CETIOM (www. cetiom.fr) is responsible for similar topics on oil crops. Ce´reáles Valleé (www.cereales-vallee.org) is a government ‘competitiveness cluster’ established in 2005. It supports the development of applied cereal research projects through collaboration between a number of public and private partners in France. There are four programs that in turn address sustainable cereal production, cereals for human nutrition and health, cereals for animal feed, and cereals for agromaterials. Breeding of new cereal cultivars in Germany is aimed at increased yields, improved resistances to biotic and abiotic stress, and high quality and like many other European countries is now conducted by private breeding companies, with government researchers carrying out prebreeding activities. Cereal research is conducted at the following:

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Universities, for example, the Technical University of Munich, Technical University of Berlin, Martin Luther University Halle-Wittenberg, Justus Liebig University Giessen, Humboldt State University, and the Universities of Bonn, Go¨ttingen, Hohenheim, Kassel, Kiel, Rostock, and Paderborn. Federal research institutes, for example, the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK, www. ipk-gatersleben.de/en); the Julius Ku¨hn Institute (JKI, www. jki.bund.de/en); Federal Centre for Cereal, Potato, and Lipid Research (BAGKF, Detmold, www.mri.bund.de/en/ de/max-rubner-institut/geschichte/bundesanstalt-fuergetreide-kartoffel-und-fettforschung.html); the Federal Research Centre for Plant Breeding (BAZ, www.genres.de); and the Institute of Agricultural Engineering (ATB, Potsdam-Bornim, www.atb-potsdam.de/en.html). Max Planck Institute for Plant Breeding Research (MPIPZ, www.mpipz.mpg.de/2169/en). German state research centers in agriculture – several of these carry out grain research, sometimes in conjunction with universities (e.g., Bavarian State Research Centre for Agriculture and State Plant Breeding Institute of the University of Hohenheim (Baden-Wu¨rttemberg)).

The ‘proWeizen’ initiative was recently founded and is coordinated by the German Federation of Private Plant Breeders (GFP). Its aim is to coordinate and foster German wheat research. It consists of leading research institutes and private companies and organizations involved in wheat breeding and growing. In the Netherlands, two institutes within the Dienst Landbouwkundig Onderzoek (DLO), a private nonprofit research

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institute that is now part of Wageningen University and Research Center, carry out grain research, including the Agrotechnology and Food Sciences Group and Plant Research International (www.pri.wur.nl/uk) who focus on crop protection, crop ecology, agricultural systems, genetics, and reproduction. The Netherlands Organisation for Applied Scientific Research (TNO) conducts research on cereal processing. Wageningen University (www.wageningenur.nl/en/wageningen-university.htm) is the main university research center for grain research. In Belgium, there are relevant government agricultural research centers in Gent and Gembloux, while at least four universities carry out some aspects of grain production and processing research – Ghent University, Catholic University of Leuven, Gembloux Agricultural University, and Catholic University of Louvain. The Italian government Ministry of Agricultural, Food and Forestry Policies has several research institutes covering grain research, including various Research Institutes for Cereal Research (ISC, www.sito.entecra.it/portale/cra_dati_istituto. php?id¼205&lingua¼EN) and the Industrial Crops, Plant Nutrition, Plant Pathology and Food and Nutrition (IMRAN). The NRC (CNR, www.cnr.it) has a separate system of research institutes, and some of these also carry out grain research. Many major states in Italy host universities that have agriculture faculties, and most of these carry out at least some grain research – the Universities of Turin, Milan, Padua, Udine, Bologna, Piacenza, Florence, Pisa, Ascoli, Perugia, Viterbo, Naples, Bari, Potenza, Reggio Calabria, Catania, Palermo, and Sassari. The Cereal Institute, National Agricultural Research Foundation (NAGREF, www.nagref.gr), Thessaloniki, Greece, is the Greek government research institute responsible for cereal breeding and cereal food product development. However, the Ministry of Agriculture has a separate research service with a network of institutes in different parts of the country. At least three universities carry out some grain research work – Agricultural University of Athens, Aristotle University of Thessaloniki, and the Mediterranean Agronomic Institute at Chania. In Hungary, the Ministry of Agriculture and Rural Development manages the Central Food Research Institute (KEKI) and the Agricultural Biotechnology Center (MBK), as well as the Cereal Research Institute in Szeged. The Hungarian Academy of Sciences has several institutes relevant to grain science – the Agricultural Research Institute, the Research Institute for Soil Science and Agricultural Chemistry, and the Plant Protection Institute. Universities with research areas most relevant to grain science are the Technical University of Budapest (grain processing) and the Universities of Agricultural Sciences at Go¨do¨llo, Debrecen, and Pannon. In Austria, the Federal Ministry of Agriculture, Forestry, Environment and Water Management has research institutes for general agriculture and an institute of cereal processing, applied soil science, and agricultural engineering. There is also the University of Natural Resources and Life Sciences in Vienna. The International Association for Cereal Science and Technology (www.icc.or.at) is headquartered in Vienna and has evolved from being a professional organization of cereal scientists to also hosting a number of EU (Seventh Framework)funded grain research projects. These include projects on food-related disease prevention, bioactives and food supplements from cereal grains, food allergens and allergy risk

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management, and mycotoxin analysis. In the Czech Republic, relevant Ministry of Agriculture research institutes include the Food Research Institute, Research Institute of Crop Production, Research Institute for Soil and Water Conservation, and Research Institute of Agricultural Engineering. There are semicommercial institutes responsible for cereals (Agricultural Research Institute Kromeriz Ltd.), oilseed crops (Oseva Ltd.), and brewing and malting. Two universities – Mendel University of Agriculture and Forestry and Czech University of Agriculture – are relevant to grain research. In Spain, the Ministry of Agriculture, Fisheries and Food runs the National Institute for Agriculture and Food Research and Technology (INIA, www. inia.es), while the Polytechnic University of Madrid has a large faculty involved with research in agriculture. There is also an INIA in Portugal, while agricultural research is carried out at the Technical University of Lisbon, the Universidade de Tra´s-osMontes e Alto Douro, and Universidade dos Açores. In Sweden, the government Swedish Institute for Food Research and the Swedish Institute for Food and Biotechnology (SIK, a joint industry/government body) carry out grain processing research. Production research and basic scientific investigations within universities include the Swedish University of Agricultural Sciences at Svalov and Lund University. Three main institutes in Norway carry out grain research. Within the government Ministry of Agriculture, there is the State Agricultural Research Station (SFL) and the Agricultural University of Norway at Aas, while the Norwegian Food Research Institute (Matforsk) is a nonprofit organization. In Finland, the Ministry of Agriculture and Forestry has the Agricultural Research Centre of Finland and Plant Breeding Institute, while VTT Biotechnology in Espoo carries out cereal technology research in close collaboration with industry. The University of Helsinki is the main higher education center dealing with grain research. In Denmark, the Ministry of Food, Agriculture and Fisheries has Institutes of Agricultural Sciences and Agricultural Engineering. The Royal Veterinary and Agricultural University also carries out grain research. Activities related to the Carlsberg laboratory are described in the article “Research Organizations of the World: Global Trends and the Commercial Sector”. In Russia, the Russian Academy of Agricultural Sciences (www.euracadagri.com/eng/members/russia.php) comprises many dozen institutes. These include All-Russia Research Institutes (e.g., All-Russia Research Institute of Plant Quarantine (Bykovo), Plant Protection (St. Petersburg), and Biological Protection of Plants (Ekaterinburg), which carryout entomology research related to grains) and regional research institutes in former republics. The latter often cover a range of agricultural disciplines and some have an almost 100-year history; many have significant grain breeding and seed distribution programs. Three of the All-Russia Research Institutes most relevant to grains are the Institute of Legumes and Groat Crops (Streletskoye), Institute of Sorghum and Cereals (Zernograd), and N.I. Vavilov Institute of Plant Industry (www.vir. nw.ru). The latter institute, based in St. Petersburg, but with a number of experimental stations throughout Russia, is the main internationally renowned Russian institute emphasizing the conservation and study of plant genetic resources, including grain crops. Most states have state agrarian universities, and there are a small number of specialist agrarian academies including Moscow Agricultural Academy.

After separation from Russia in 1991, national agricultural research systems developed in most of the former Soviet republics using the institutional assets left by the former USSR; several of these have a crop emphasis although resources for research are very limited and it has been difficult (and often undesirable) to maintain the staff numbers and infrastructure left behind. They have had to develop their priority setting to match specific requirements of their various agroecological zones and the changed policy/economic environment including a greater emphasis on markets rather than a central procurement and distribution system.


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What are some of the major institutional trends in grain research in North America and Europe over the last decade? How do the major grain research priorities differ between now and 30 years ago? What are the major priorities globally for biofuel research? Name three of the countries within Europe and North America that have the highest proportion of publicly funded agricultural R&D. Why are agricultural universities in the United States called ‘land grant colleges’?


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Explore the major grain research projects funded under the Seventh Framework Programme of the European Union. What are the common themes? What have been the major achievements of the N.I. Vavilov Institute of Plant Industry in Russia over the last century? What areas of grain research from the Netherlands major agricultural university in Wageningen have had global impact?

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Soybean: Agronomy; Wheat: Agronomy; Breeding of Grains: Barley: Genetics and Breeding; Canola/Rapeseed: Genetics and Breeding; Maize: Breeding; Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Development of Genetically Modified Grains; Genome Mapping; Genomics of Food Grains; Grain Marketing and Grading: Barley: Grading and Marketing; Wheat: Grading and Segregation; Wheat: Marketing; Grains Around the World: Grain Production and Consumption: Cereal Grains in North America; Grain Production and Consumption: Europe; Grain Production and Consumption: Oilseeds in North America; Grain Production and Consumption: Overview; Non-food Products from Grains: Biodiesel; Cereal Grains as Animal Feed; Fuel Alcohol Production; Scientific Organizations Related to Grains: Scientific Societies Associated with Grain Science; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.


Further Reading Fox JA and Ward LL (2016) Grain production and consumption: Cereal grains in North America. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 391–400. Elsevier Ltd. Grassini P, Estraidge KM, and Cassman KG (2013) Distinguishing between yield advances and yield plateaus in historical crop production trends. Nat. Commun. 4: 2918. http://dx.doi.org/10.1038/ncomms3918. Lindhaeur MG (2016) Grain production and consumption: Europe. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 383–390. Elsevier Ltd.

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Pardey RG and Beintema NM (2001) Slow Magic: Agricultural R&D a Century after Mendel. Washington DC: International Food Policy Research Institute. McVetty PBE, Lukow OM, Hall LM, Rajcan I, and Rahman H (2016) Grain production and consumption: Oilseeds in North America. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 401–408. Elsevier Ltd. Ray DK, Mueller ND, West PC, and Foley JA (2013) Yield trends are insufficient to double global crop production by 2050. PLoS One 8(6). http://dx.doi.org/10.1371/ journal.pone.0066428. Skerritt JH (2016) Research Organizations of the World: CGIAR. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 429–435. Elsevier Ltd.

Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East JH Skerritt, University of Queensland, St Lucia, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Countries in regions other than North America and Europe vary significantly in their grains research capacities. Within these regions, Australia, Brazil, China, and India have the greatest grains research capacity. Global grain price spikes in the last few years have increased the emphasis on grains research for food security in developing countries.

To identify and understand the major priorities of the major organizations in grains research in countries other than North America and Europe

Introduction Many of the trends in North American and European grains research and grains research organizations are reflected in the developed and major developing economies within the AsiaPacific, Latin American, African, and Middle Eastern regions, but to varying degrees. In Australia and India, there has been a move toward formation of networks between research institutes, often being a requirement of funding program design. In Australia, China, and Brazil, the private sector has significantly increased its role, particularly in breeding. Other trends in Australia include the greater importance of levies from grain growers in supporting research in a number of countries and the increase in commercial involvement in grains breeding and biotechnology. Across each of the regions reviewed in this article, a shift in focus of many of the grain R&D institutions took place in the 1990s and first few years of the twenty-first century from a largely production focus to an emphasis on environmental issues such as water-use efficiency and sustainability of farming systems. However, with grain price spikes that occurred over the last few years, several Asian countries have reintroduced a food security imperative to the top of their national agricultural R&D agenda. Within Asia, exports of grains such as rice are significant contributors to national incomes for countries such as Thailand and Vietnam, while grain import requirements have critical balance of payments and thus political imperatives for India, China, Indonesia, and the Philippines. While significant exceptions exist, an institutional challenge for developing countries is the typically inadequate levels of collaboration between research institutes within and between countries – especially when comparing the performance of different lines in different agroecological zones. For the developing countries that benefited from the higher-yielding varieties of the ‘green revolution,’ sustaining the productivity gains through more efficient use of water and

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Major Public Sector (Government and University) Grain Science Organizations Australia and New Zealand

Learning Objectives

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prevention of erosion, waterlogging, salinity, and acidification is now critical. Also critical is research on grain quality and addressing market requirements, as grain production in several of these countries struggles to compete with subsidized European and US agriculture.

There are three main public sector providers in grains research in Australia – state government departments, Commonwealth Scientific and Industrial Research Organisation (CSIRO), and universities. Unlike in many countries, the national Department of Agriculture (www.agriculture.gov.au) does not conduct laboratory or field research in agriculture. In the last 10–15 years, there has been a shift in emphasis of many state departments from an overwhelming emphasis on production agriculture to sustainable production, and over the last decade, as budgets become more constrained, a decrease in research resources. In this period, grains breeding in Australia, particularly of wheat, has moved into the private sector, with public research agencies instead carrying out germplasm development and prebreeding activities. While one company (LongReach Plant Breeders) is freestanding, the three others (Australian Grain Technologies, InterGrain, and HRZ Wheats) are consortia involving private industry and state or national research agencies. Some of the states retain strong capacity in grains prebreeding and agronomy and in soil science and farming systems research. Information on their research programs is available as follows:

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NSW Department of Primary Industries (www.agric.nsw. gov.au) Department of Economic Development, Jobs, Transport and Resources (www.economicdevelopment.vic.gov.au) Queensland Department of Agriculture, Fisheries and Forestry (www.dpi.qld.gov.au) South Australian Research and Development Institute (SARDI) (www.sardi.sa.gov.au) Department of Agriculture and Food, Western Australia (www.agric.wa.gov.au) Department of Primary Industries, Parks, Water and Environment, Tasmania (www.dpiwe.tas.gov.au) Department of Primary Industry and Fisheries, Northern Territory (www.nt.gov.au/d/Primary_Industry)

All state governments have formed various formal agricultural research alliances with universities – some include joint appointment of staff and a single organizational structure, while others mainly are based on colocation with universities.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00057-7

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organisations of the World In some cases, the alliances cover most areas of grains research; in others, specialized areas such as biotechnology. Examples relevant to grains research include the Queensland Alliance for Agriculture and Food Innovation (QAAFI, involving the University of Queensland, www.qaafi.uq.edu.au); the EH Graham Centre for Agricultural Innovation (involving Charles Sturt University, www.csu.edu.au/research/grahamcentre); the Primary Industries Innovation Centre in NSW (involving the University of New England, www.dpi.nsw.gov.au/research/alliances/primary-industries-innovation-centre); AgriBio in Victoria (involving La Trobe University, www.latrobe.edu.au/agribio); the South Australia Research and Development Institute, colocated with the University of Adelaide (www.sardi.sa.gov.au); the Western Australian State Agricultural Biotechnology Centre, located at Murdoch University (www.sabc.murdoch.edu.au); and the Tasmanian Institute of Agriculture (www.tia.tas.edu.au). While Queensland and Victoria retain reasonable capacity, an increasing proportion of extension services, formerly provided by the state governments, are now provided to farmers on a commercial basis by the private sector and/or incorporated farmers’ (‘growers’) groups. Within the national research organization CSIRO (www. csiro.au), much research (including grains research) is now being conducted in cross divisional ‘flagship’ programs. The Food Futures Flagship is using advanced genetics to create differentiated grain, food, and feed products, focussing on wheat barley with improved processing quality and oilseeds with enhanced oil content and improved nutritional value. Other flagships carrying out grains research include biosecurity, sustainable agriculture (natural resource management and farming systems focus), and climate adaptation flagships. A small amount of grains-related research is conducted outside flagships, by the Divisions of Plant Industry; Animal, Food and Health Sciences; Ecosystem Sciences; and Land and Water. Some independent nongovernment grains research organizations exist including GrainGrowers (www.graingrowers. com.au), their expertise including milling, near-infrared reflectance technology, baking science and technology, and Asian wheat foods. The Australian Grains Centre (www.cbh.com.au/ our-business/operations/grain-quality/australian-grain-centre. aspx) and Agrifood Technology (www.agrifood.com.au) emphasize testing services. Relevant grains research is carried out at several universities. This includes the following:

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University of Adelaide – bread and durum wheat and barley prebreeding, molecular markers, cereal root diseases, cereal pathology, biotechnology, weed management, malting, and brewing biochemistry University of Sydney – prebreeding for rust resistance in barley and wheat, cereal diseases, cereal genomics, precision agriculture, soil science, and crop modeling University of Melbourne – research to underpin the sustainability of temperate grain crop production, with emphasis on agronomy and farming systems, and protection of natural resources University of New England – agronomy and soil science, plant nutrition, crop protection, weed science, and integrated pest management University of Queensland – production systems and postharvest handling of cereals, grain legumes and oilseeds, weed management, plant protection, and molecular biology

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University of Western Australia – grain crop science and molecular genetics Charles Sturt University – agronomy, irrigation, and plant pathology Curtin University– agronomy, precision agriculture, and grains processing Murdoch University – molecular markers for barley and wheat, grain legume genome mapping, transgenics, diseases, and viruses University of New South Wales – grain storage engineering University of South Australia – agricultural machinery research and design University of Southern Queensland – plant–pathogen interactions, cereal genetic engineering, marker-assisted breeding, and canola breeding University of Tasmania – cereals, grain legumes, and oilseeds as break and rotation crops

Over the last 20 years, there has been a significantly increased emphasis on establishment of more formal links between research organizations. This has been driven to a significant extent by the advent of the Cooperative Research Centres (CRCs, www.crc.gov.au) program and encouragement by funders. At present (January 2014), there are only two CRCs that have relevance to grains research (Future Farm Industries CRC and the Plant Biosecurity CRC) – many fewer than earlier in the program. The Grains Research & Development Corporation (www.grdc.com.au) facilitates and manages funding for research and assists in communicating results. Government and industry R&D levies co-fund this research. The main New Zealand organization undertaking grains research is Plant & Food Research (www.plantandfood.co.nz), one of several government-owned Crown Research Institutes. Its program includes wheat and barley genomics, breeding and production systems, and food processing. Universities with research interests in grains include Massey University (Palmerston North, www.massey.ac.nz) with a research emphasis on food science and engineering. Lincoln University (Christchurch, www.lincoln.ac.nz) carried out research on grain foods composition, crop agronomy, seed science and technology, and some biotechnology. Although wheat is one of the major cereals, the growing environment is very different from that in Australia, requiring rather different varietal characteristics. Further information on grain production and consumption in Oceania is discussed elsewhere in this Encyclopedia.

North Asia In Japan, much of the grains research is carried out in institutes managed under the Agriculture, Forestry, and Fisheries Research Council of the Ministry. National Agriculture and Food Research Organization’s (www.naro.affrc.go.jp/english/ index.html) Institute of Crop Science in Tsukuba conducts research on the breeding of rice, wheat, barley, soybean, sweet potato, and industrial crops such as sesame and on the development of new technologies for breeding. Research activities also cover the understanding of basic mechanism of agronomic and physiological traits regarding crop quality, photosynthesis, and productivity. The NARO Agricultural

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SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organisations of the World

Research Center, also headquartered in Tsukuba, focuses on rice and soybean systems, agronomy, soil fertility, crop nutrition and rotations, pest management, and biofuels. There are four main regional research centers. The National Institute of Agrobiological Sciences (www.nias.affrc.go.jp/index_e.html, also headquartered in Tsukuba) is the largest agricultural research institute in Japan for basic life sciences, and a number of its programs focus on grain crop/genomics and genetic research. Major universities with agriculture faculties include Tokyo University of Agriculture and Technology, Tohoku University, Kyoto University, Kyushu University, Hokkaido University, Kagoshima University, Yamaguchi University, Tottori University, and Nagoya University. Several universities carry out research in grains processing. The Korean Rural Development Administration of the Ministry of Agriculture, Food and Rural Affairs has a series of national research institutes, including the National Institute of Crops Science (www.nics.go.kr/english) with a focus on rice, wheat, maize, soybean, and maize breeding, agronomy and applied biotechnology, and postharvest technology; National Academy of Agricultural Science in Suwon (www. naas.go.kr/English/naas_main.asp) with relevant work on crop protection and agro-ecology; National Institute of Agricultural Biotechnology (www.niab.go.kr); and several provincial agricultural and extension institutes. Grains research is strongly rice-focussed, but with an increasing environmental protection and biotechnology emphasis. Of the ten ‘Flagship Korean National Universities,’ eight have agriculture colleagues that undertake grains research to varying extents, including Chonbuk, Chonnam, Chungbuk, Chungnam, Gyeongsang, Kangwon, Kyungpook, and Seoul National Universities. China has the largest national agricultural research systems (NARS) in the world and also the most geographically and administratively decentralized. The government has placed a high priority on developing research capacity and infrastructure over the last decade, and private sector expenditure in research has also increased. Because of the large range of production environments, research on both temperate and tropical grains is important, and some institutes undertake pioneering grains research, for example, in the development of high-yielding rice varieties, rice functional genomics, and transgenic crops. In recent years, the Chinese government has been making major investments in R&D physical infrastructure and equipment, and there has been a move to retain or attract back eminent scientists from the Chinese diaspora. There is an increasing shift in emphasis in China from research aimed at increasing grain production to increasing quality and ensuring that production is environmentally sustainable, especially in view of the increasing pressure on water resources for agriculture in China. Grains research is carried out in five main types of organizations. The Chinese Academy of Agricultural Sciences (CAAS, www.caas.net.cn/en) under the Ministry of Agriculture has the largest number of grains research projects. There are 32 research institutes (employing over 5000 research staff directly affiliated with CAAS; another nine are hosted jointly with universities and provincial governments), with a growing emphasis on environmental safety and sustainability, rather than just higher yields. CAAS has recently consolidated its vast array of research projects into eight disciplinary clusters.

The Crop Science crop germplasm resources cluster addresses genetics and breeding, molecular biology, cultivation and physiology, molecular breeding, functional genomics, proteomics, metabonomics, and bioinformatics – participating grains institutes include the Institute of Crop Sciences, Biotechnology Research Institute, China National Rice Research Institute, and the Oil Crops Research Institute. The Agricultural Resources and Environment cluster addresses plant diseases, insect pests, weeds and rodents, dryland and water-efficient agriculture, soil sciences, and plant nutrition, and participating grains institutes include the Institute of Plant Protection, Institute of Environment and Sustainable Development in Agriculture, Biotechnology Research Institute, the Farmland Irrigation Research Institute, China National Rice Research Institute, and the Agro-Environmental Protection Institute. Grains research is also undertaken within the Agricultural Mechanization and Engineering; Agro-Product Quality, Safety, and Processing; and Agricultural Information and Economics clusters. The Agricultural Science and Technology Innovation Program (ASTIP), launched in early 2013, funds four crosscutting objectives – supporting long-term and interdisciplinary research, capacity building, expanding research support facilities and infrastructure, and fostering international cooperation – over the next 13 years. The Chinese Academy of Sciences (www.english.cas.cn), under the Ministry of Science and Technology, also carries out some research relating to grains, at the Institute of Botany and Institute of Genetics and Developmental Biology (Beijing; basic plant biology and biotechnology), Institute of Zoology (Beijing; pest management), Institute for Soil Research (Nanjing), National Centre for Genetic Research (Shanghai; rice genomics), Chengdu Institute of Biology (cereal breeding), Institute of Soil and Water Conservation (Yangling; agronomy), NW Institute of Plateau Biology (Qinghai; crop assessment), and Shijiazhuang Institute of Agricultural Modernization (Hebei; farming systems for the North China plain) among others. Several provincial academies of agricultural science have strengths in grains research including Jiangsu, Sichuan, Guangdong, Fujian, Henan (for wheat), Shandong, Liaoning, and Gansu. The State Administration of Grain (www.chinagrain. gov.cn/english/Scientific%20Research.html) also carries out grain storage research, including through the Grain Storage Research Institute in Chengdu. In recent years, much of the increase in research capacity has come from the universities. Each province has at least one agricultural university, but the three strongest universities in agricultural science are Nanjing Agricultural University, Zhejiang University, and Huazhong Agricultural University. Other agricultural universities carrying out grains research are South China Agricultural University (Guangzhou), Shenyang Agricultural University, Southwest Agricultural University (Chongqing), and Northwest A&F University (Yangling). Further information on grain production and consumption in China is discussed elsewhere in this Encyclopedia.

South Asia India also has one of the largest NARS in the world and a traditional strength in crops research, particularly grain

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organisations of the World sciences, given the ongoing national focus on food security. Most grains research is done within the Indian Council of Agricultural Research (ICAR, www.icar.org.in) and state agricultural universities. Of the 45 ICAR Central Research Institutes, most of the grains research institutes are within the Crop Science Division. Major thrusts include development of grain varieties resistant/tolerant to a range of abiotic and biotic stresses, hybrid technology, application of molecular techniques, plant genetic resources conservation, and farming systems research. The main ICAR institutes carrying out grains research include

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the Indian Agricultural Research Institute (emphasis on more strategic research); the Indian Institute of Pulses Research; the National Bureau of Plant Genetic Resources; the National Research Centres for Groundnut, Rapeseed Mustard, Sorghum and Soybean; the National Centre for Integrated Pest Management; the National Research Centre on Plant Biotechnology; the Central Institute of Post-Harvest Engineering and Technology; the Central Soil Salinity Research Institute; the Central Arid Zone Research Institute; the Central Research Institute for Dryland Agriculture; the Indian Institute of Soil Science; Directorates of Wheat Research, Sorghum Research, Oilseeds Research, Soybean Research, Rice Research, and Weed Science Research.

Several smaller project directorates covering biological control, oilseeds, rice, wheat, and maize. All India Coordinated Research Projects attempt to link institutes as a mechanism to build nationwide coordinated interdisciplinary research networks – increasing the level of interinstitutional collaboration is currently a high priority of the Indian government. The second significant resource is the 55 state agricultural universities (SAUs). Some of the SAUs with strong grains research programs include Acharya NG Ranga AU (Andhra Pradesh), CCS Haryana AU, GB Pant AU (Uttar Pradesh), Punjab AU, and Tamil Nadu AU. The Council for Scientific and Industrial Research (CSIR) has the Central Food Technological Research Institute (CFTRI, Mysore, www.cftri.com) has a department that researches cereal (especially wheat) milling, baking, and biochemistry. A number of private sector companies undertake research into crop breeding and plant protection. Further information on grain production and consumption in India is discussed elsewhere in this Encyclopedia. Pakistan also has one of the largest numbers of grains researchers in the developing world. The main institute of the Pakistan Agricultural Research Council (PARC, www.parc.gov. pk), the National Agricultural Research Centre in Islamabad, covers soil fertility; wheat, rice, sorghum, and millet; farm machinery; water resources; agricultural biotechnology; vertebrate pests; crop diseases; crop production; land resources; plant genetic resources; technology transfer; and seed sciences. There are a separate tropical agricultural research center at Karachi and four arid zone research centers in different regions of Pakistan. There are several agricultural universities in Pakistan that carry out grains research, the largest being the

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Pakistan Agricultural University at Faisalabad. Sindh Agriculture University, the University of Arid Agriculture (Rawalpindi), and the Northwest Frontier Agricultural University (Peshawar) are all smaller, but with a similar range of activities. The Ministry of Science and Technology manages the Pakistan Council of Scientific and Industrial Research, which carries out grains postharvest research. There is also a separate National Institute for Biotechnology and Genetic Engineering (Faisalabad) as well as the NARC Institute of Agricultural Biotechnology and Genetic Resources. State departments of agriculture in Balochistan, Punjab in particular, carry out some grains research. Elsewhere in South Asia, the Bangladesh Agricultural Research Council has a central Bangladesh Agricultural Research Institute (which carries out significant amounts of grains research) together with satellite institutes covering soils and rice. The largest university conducting grains research is Bangladesh Agricultural University.

Southeast Asia The major Indonesian government agricultural research and development agency is the Indonesian Agency for Agricultural Research and Development (IAARD, www.en.litbang.deptan. go.id). Research institutes working on grains (unlike plantation crops) are publicly funded and those focussing on grains include the Centers for Food Crops R&D (Bogor, W Java), Rice Research (Subang, W Java), Agricultural Engineering R&D (Serpong, W Java), and Postharvest R&D (Bogor, W Java). Typically smaller research institutes work on legume and tuber crops (Malang, E Java), cereals (particularly maize) (Makassar, S Sulawesi), and soils (Bogor, W Java). Adaptive research is carried out by Assessment Institutes for Agricultural Technology (under IAARD, but located in each province). Major agricultural universities include Bogor Agricultural University (IPB), Gadjah Mada University, Hasanuddin University, University of Mataram, Sam Ratulangi University, Sebelas Maret University, Andalas University, Haluoleo University, Brawijaya University, and Padjadjaran University. Under the Philippine Department of Agriculture (DA), there is a national rice research center (PhilRice in Munõz, Luzon, www.philrice.gov.ph), addressing both research and technology dissemination, and the Bureaus of Plant Industry, Soil and Water Management (www.bswm.gov.ph), and Postharvest Research and Extension (which includes an emphasis on grain storage research). The Food and Nutrition Research Institute (www.fnri.dost.ph) and the research planning and funding body, the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (www. pcaarrd.dost.gov.ph), sit under the Department of Science and Technology. There are also Regional Integrated Agricultural Research Centers – there is one organization in each of the 15 regions, but some have 2–3 research stations and several focus on grain crops. The universities have a far greater share of research capacity than DA. The strongest university in agriculture including grains research is the University of Philippines at Los Banõs, which has specialized institutes of plant breeding and of farming systems research. These include Benguet State University, Central Luzon State University, Visayas State University College of Agriculture, Don Mariano Marcos State

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University, Central Mindanao University, and the University of Southern Mindanao. There are also several others with some strengths in agriculture (Mindanao State University, Bicol University, and Central Visayas State College). Some of the universities have regional research and development centers and also have quite good extension/outreach systems. While significant private sector research enterprises are present in horticulture, grains research remains in the public domain. The Thailand Department of Agriculture (DOA, www.doa. go.th/en) is responsible for crops and farm mechanization research, while the Department of Agricultural Extension (DOAE) is responsible for transfer of technology to farmers. While there are experiment stations in every region of the country, most research is carried out in Bangkok. DOA has programs covering agricultural chemistry, agricultural engineering, plant pathology and microbiology, entomology and zoology, soil science, botany, and weed science, crop protection, and specialist rice and field crops institutes (there is reasonable research capacity in maize and legumes research). The Land Development Department conducts research in relation to land improvement and soil and water conservation. Grains postharvest technology is carried out within the Thailand Institute of Scientific and Technological Research (TISTR, www.tistr.or.th/tistr_en) in Bangkok. One of the three research centers with National Science and Technology Development Agency is Genetic Engineering and Biotechnology (BIOTEC, www.biotec.or.th/en), which carries out some rice biotechnology work. Kasetsart University in Bangkok, Khon Kaen University, Chiang Mai University, Prince of Songkla University (Hat Yai), and King Mongkut’s Institute of Technology in Bangkok are all involved in grains research, the latter having a special focus on grains postharvest technology. In Malaysia, agricultural R&D spending as a percentage of production value (research intensity) remains comparatively high. The Rice and Industrial Crops Research Centre of the Malaysian Agricultural Research and Development Institute (MARDI, www.mardi.gov.my) researches rice, maize, and groundnuts as well as several nongrain crops. The most relevant activity is development of high-quality rice varieties with disease resistance and accompanying agronomy. The food technology research center does work on the development of rice-based snacks and other food products. The major universities carrying out grains science research is the Universiti Putra Malaysia and Universiti Kebangsaan Malaysia. Most grains research in Vietnam is conducted under the Ministry of Agriculture and Rural Development (MARD, www.agroviet.gov.vn). Other relevant ministries are education and training (university sector), science and technology (www. most.gov.vn), which has some excellent crop biotechnology and plant protection research facilities, and the Ministry of Industry (which has an Oil Plant Research Institute – with the mandate for peanut, soybean, sunflower, and sesame). While most institutes are located in either Hanoi or Ho Chi Minh City, many maintain ‘research centers’ in more remote locations. The key MARD institutes in grain science are the Food Crops Research Institute, National Institute for Plant Protection, National Institute for Soils and Fertilizers, Institute of Agricultural Engineering and Post Harvest Technology, Institute of Agricultural Science in the South, Vietnam Agricultural Science Institute, Agricultural Genetics Institute, National

Maize Research Institute, and Mekong Rice Research Institute. The Department of Plant Protection of MARD is also becoming an important applied research organization. The main universities with research interests in grain science include Hanoi Agricultural University, Hanoi University of Science (also known as Hanoi College of Sciences), Nong Lam University, Hue University of Agriculture and Forestry, Thai Nguyen University, and Can Tho University. Further information on grain production and consumption in Southeast Asia is discussed elsewhere in this Encyclopedia.

Central and South America The major grains R&D capacity in Central America is within Mexico. Initially, it was focussed in several of the Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias (INIFAP, www.inifap.gob.mx) crops institutes based on different agroecological zones (www.inifap.gob.mx), but it is now spread across a range of universities and other government agencies. Grains food research and biotechnology is carried out in the Consejo Nacional de Ciencia y Tecnologia (CONACYT, www.ciad.mx). Grains research is carried out in the Universidad Autońoma Chapingo, the Instituto Politećnico Nacional, and over a dozen regional universities. In South America, Brazil has a well-developed NARS, with more agricultural researchers than any other country in Latin America. Many centers fall under EMBRAPA (Empresa Brasileira de Pesquisa Agropecua´ria, www.embrapa.br), a specialized science agency of the Agriculture Ministry. Brazil has the largest NARS of any Central or South American country, followed by Mexico; Brazil also has an advanced university system. In addition, 16 of Brazil’s 26 states operate agricultural research institutes, with Sao Paulo the largest. There are separate EMBRAPA institutes relating to genetic resources and biotechnology (CENARGEN), upland rice and beans (CNPAF), corn and sorghum biotechnology (CNPMS), soils technology transfer (CNPS), soybean and sunflower (CNPSO), wheat, barley, oats, soybeans, and biotechnology (CNPT), temperate climate agricultural research (CPACT, irrigated rice), and food technology (CTAA), as well as at least 12 regional centers. There are also nonprofit centers – Foundation Center for Wheat Experimentation and Research (FUNDACEP, www.fundacep.com. br), the Central Agricultural Cooperative of Technology Development and Economics (COODETEC; soy, maize, and wheat), and the Rice Institute of the Rio Grande do Sul (IRGA). Several universities carry out grains research – the federal universities of Goia´s (www.agro.ufg.br), Lavras, Paraiba, Pelotas (www. faem.upfel.edu.br), Rio Grande do Sul, Rural do Rio de Janeiro (www.la.ufrrj.br), Santa Catarina (www.cav.udesc.br), Saõ Carlos (www2.ufscar.br), Santa Maria, Viçosa, and Brasilia as well as several state universities (Santa Catarina State, Paulista, Campinas, Sul de Santa, and Saõ Paulo). Some Brazilian companies, such as Agroceres, DuraFlora, Mogiana, and Braskalb, carry out breeding and agronomy research to support seed distribution businesses. The Argentine Government Instituto Nacional de Tecnologia Agropecuaria (INTA, www.inta.gov.ar) is under the Agriculture Ministry, and capacity has increased significantly over the last decade due to significant increase in government

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Research Organisations of the World investment. There are also a large number of programs and centers relevant to grains research under CONICET (Consejo Nacional de Investigaciones Cientificas y Tećnicas, www.conicet.com.ar), which is under the Culture and Education Ministry. This includes a number of crop breeding, agronomy, and natural resource (CADIC and CEFYBO), plant protection (CEAVE and IFEVA), postharvest technology (CEFOBI and CRILAR), and plant physiology and molecular biology (INFIVE and INGEBI) centers. Several national universities have agronomy science faculties – Buenos Aires, Buenos Aires Province, Catamarca, Comahue, Cordoba, Cuyo, Entre Rios, Jujuy, La Pampa, La Plata, Litoral, Lomas de Zamora, Mar del Plata, Noredeste, Rio Cuarto, Rosario, Santiago del Estero, de Sur, de Salta, Tucuman, and de Formosa. The Chilean Ministry of Agriculture has an Instituto de Investigaciones Agropecuarias (INIA, www.inia.cl), which undertakes some grains research, although overall agricultural research is much more limited than in Brazil or Argentina. There are also agronomy departments at several universities – Austral University (www.agrarias.uach.cl), the University of Conception (www.chillan.udec.cl), the University of La Frontera, the University of La Serena (www.userena.cl), the University of Magallanes, the University of Talca, the University of Tarapaca´ (www.uta.cl), Universidad de Chile, and Universidad Iberoamericana de Ciencias – as well as the Catholic universities (Temuco (www.uctemuco.cl), Valparaiso (www.ucv.cl), and Maule). In Colombia, the main government crops research agency is CORPOICA (www.corpoica.gov.co); but much more research is now carried out through the producer association, Asociacioń Nacional de Acuicultores de Colombia (ACUANAL); there are research groups working on rice. Apart from the campuses of the national university in Bogota, other universities with grains agronomy faculties include Cordoba (www.unicordoba.edu.co) and Tolima (www.ut.edu.co). The main research agency in the Ecuador agriculture ministry is INIAP (Instituto Nacional Autonomo de Investigaciones Agropecuarias); universities in most regional centers have small agronomy departments. In Uruguay, the government Instituto Nacional de Investigacion Agropecuaria (INIA, www.inia.org. uy) is the largest crops research institute. Further information on grain production and consumption in South America is discussed elsewhere in this Encyclopedia.

Africa and the Middle East South Africa has the best-developed NARS of the African countries, although its capacity has declined over the last decade. South Africa maintains reasonable research capacity in maize (the main grain crop), sorghum, and some experience in wheat and a little in barley. The Agricultural Research Council (www.arc.agric.za) is the main agricultural research structure and has a series of research institutes, several carrying out grains research – particularly the Grain Crops Institute and the Small Grains Institute, with some other institutes carrying out supporting natural resource management research. The nine provincial departments also carry out selection and agronomy research to varying degrees. There are some well-resourced grains research programs at the Universities of Pretoria (www.web.ip.ac.za), KwaZulu-Natal

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(www.sasa.ukzn.ac.za), the Free State (www.ufs.ac.za), and Stellenbosch (www.acadmic.sun.ac.za/agric/). In the 1990s, there has been a significant shift in research emphasis in South Africa to accommodate the needs of the wider population, rather than just white commercial agriculture, to include emerging farmers and subsistence farmers in former homelands. Private companies such as Monsanto and Pannar carry out seed and fertilizer research. In Zimbabwe, most crops research is carried out by the Department of Research and Specialist Services in the Ministry of Lands (www.drss.gov.zw) and Agriculture, Mechanization and Irrigation Development, with the University of Zimbabwe (www.uz,az.zw) maintaining reasonable strength. The Kenya Agricultural Research Institute (KARI, www.kari. org) is comparatively strong in crops and livestock and the Kenyan government agricultural research system one of the strongest in Africa. In the grains area, mandate crops include cereals (wheat, maize, sorghum, millets, and rice) and grain legumes with efforts ranging from plant breeding for adaptation to different agroecological zones and stress resistances, agronomy, postharvest technology, and cooking quality. Almost all Kenyan grain production is rain-fed. The breeding and postharvest research is backed up by a soil and water management research program. The Kenya Industrial R&D Institute (www.kirdi.go.ke) also carries out some postharvest research. Some grains research is carried out at various universities (Jomo Kenyatta University of Agriculture and Technology (www.jkuat.ac.ke), Egerton University (www.egerton. ac.ke), Moi University (www.mu.ac.ke), the University of Eastern Africa (www.uaeb.ac.ke), and the University of Nairobi (www.ounbi.ac.ke). The Ethiopian Institute of Agricultural Research (www.eiar.gov.et) has national and regional centers emphasizing maize, plant protection, soils, and agricultural mechanization. Crops research is carried out at Hawassa University (www.hu.edu.et), Haramaya University (www.haramana.edu.et), Jimma University (www. ju.edu.et), and Mekelle University (www.mu.edu.et). In Uganda, most grains research capacity is within the main government National Agricultural Research Organization (NARO, www.naro.go.ug) and at Makerere University (www. agric.mak.ac.ug). In Nigeria, the Ministry of Agriculture through the Agricultural Research Council of Nigeria (www.arcnigeria.org) has a series of research institutes – National Cereals Research Institute, Lake Chad Research Institute (www.icresmaid.org), and the Institute for Agricultural Research (www.abu.edu.ng). Postharvest technology research is carried out under the Ministry of Industry at the National Stored Products Research Institute (www.nspiilofin.com), while the Ministry of Science and Technology has established a National Centre for Genetic Resources and Biotechnology (www.nacgrab.gov.ng). Universities with relevant research programs include the University of Ibadan (www.agric.ui.edu.ng), University of Nigeria (www.unn.edu. ng), Bayero University, Ahmadu Bello University (www.abu. edu.ng), and Obafemi Awolowo University (www.oauife.edu. ng). In Zambia, the Zambia Agricultural Research Institute (www.zari.gov.zm), Postharvest Food Processing and Nutrition Institute (www.nsirir.org.zm), and the University of Zambia (www.unza.zm) are the main grains research providers. In Tanzania, it is the Directorate of Research and Development of

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the Ministry of Agriculture and Food Security (www.agriculture.go.tz) along with the Sokoine University of Agriculture (www.suanet.az.tz); in Botswana, the Department of Agricultural Research (www.dar.gov.bw), while in Ghana, the Crops Research Institute of the Council for Scientific and Industrial Research (www.cropsresearch.org), along with the University of Ghana (www.ug.edu.gh) and the Kwame Nkrumah University of Science and Technology (www.knust.edu.gh), are the main crops research providers. Further information on grain production and consumption in Africa is discussed elsewhere in this Encyclopedia. The Israeli NARS is reasonably well resourced. Within the Agricultural Research Organization (www.agri.gov.il), the Institute for Plant Sciences has programs on cereal crop agronomy to overcome drought, disease, and heat stress. There are separate institutes for plant sciences, soil water and environmental sciences, postharvest and food sciences, and agricultural engineering, which also carry out grains-related research. Universities carrying out grains research include Technicon (Israel Institute of Technology (Haifa)) and the Ben-Gurion University of Negev. Egypt also has a large government agricultural research system, within the Agricultural Research Center (ARC, www. arc.sci.eg), within the Ministry of Agriculture and Land Reclamation. In ARC, there are separate programs for plant protection, plant pathology, food technology (bread and pasta research), agricultural genetic engineering, and farming systems research relating to wheat, barley, maize, rice, sorghum, legumes, and oil crop production. Universities with agriculture faculties include Alexandria, Cairo, Ain Shams, Al-Azhar, Suez Canal, Zagazig, Assiut, Mansoura, Minia, Menoufia, Tanta, and South Valley. Further information on grains research in other West Asian and North African countries is discussed elsewhere in this Encyclopedia.


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What is the largest national agricultural research system in the world? In what regions of the world is grains research capacity thought to have decreased over the last decade? Name three countries where the involvement of the private sector in grains breeding has increased significantly over the last decade. What role does the national Australian government have in grains R&D delivery? What are the two major organizations or systems undertaking grains research in India?


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How do agricultural research in Brazil contributed to the export success of its grains industries?

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How do the priorities of grains research for the Indian state agricultural universities differ when they are based in different geographic zones of India? Being a small country, why doesn’t New Zealand simply adopt the grain varieties and agronomy research findings of its larger neighbor, Australia?

See also: Agronomy of Grain Growing: Implication of Climate Changes; Wheat: Agronomy; Breeding of Grains: Barley: Genetics and Breeding; Canola/Rapeseed: Genetics and Breeding; Maize: Breeding; Rice: Breeding; Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grains Around the World: Grain Production and Consumption: China and South-East Asia; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; Production and Consumption of Grains: India; Scientific Organizations Related to Grains: Scientific Societies Associated with Grain Science; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Beintema NM and Stads G-J (2010) Public agricultural R&D investments and capacities in developing countries: Recent evidence for 2000 and beyond. Background note for the Global Conference on Agricultural Research for Development, Montpellier, France, March 28–31. Beintema N and Stads G-J (2011) African Agricultural R&D in the New Millennium: Progress for Some, Challenges for Many. Washington, DC: International Food Policy Research Institute. Cassas J, Sohl M, and Hafaz H (1999) The National Agricultural Research Systems in the West Asia and North Africa Region. Aleppo, Syria: ICARDA, p. 278. Corke H and Cai YZ (2016) Grain production and consumption: China and South East Asia. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 374–382. Elsevier Ltd. Flaherty K, Stads G-J, and Srinivasacharyulu A (2013) Benchmarking Agricultural Research Indicators Across Asia-Pacific. Washington, DC: International Food Policy Research Institute. Khatkar BS, Chaudhary N, and Dangi P (2016) Production and Consumption of Grains: India. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 367–373. Elsevier Ltd. Pardey PG and Alston JM (2006) Agricultural R&D in the Developing World: Too Little, Too Late? Washington, DC: International Food Policy Research Institute. Roseboom J, Cremers M, and Lauckner B (2001) Agricultural R&D in the Caribbean: An Institutional and Statistical Profile. The Hague: International Service for National Agricultural Research, ISNAR Research Report No. 19. Taylor JRN (2016) Grain production and consumption, Africa. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 359–366. Elsevier Ltd. Wrigley CW and French RJ (2016) Grain production and consumption in Oceania: Australia and Pacific Countries. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 409–419. Elsevier Ltd.

Research Organizations of the World: Global Trends and the Commercial Sector JH Skerritt, University of Queensland, St. Lucia, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Greater emphasis on demand-driven rather than sciencedriven research Increasing emphasis on topics such as production sustainability, crop–livestock systems, systems modeling, and the use of techniques from molecular and information sciences but also a return to treatment of research on grain productivity and yield. Specialization into particular areas common as well as clearer identification by funders and institutes about how near to market Greater collaboration between disciplines and between research institutes as well as increased private sector has greater involvement in agricultural R&D Major commercial groups involved in grains and grain product research

Learning Objectives

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To obtain a better understanding of global trends in grains research and grains research undertaken by the commercial (biotechnology, seed, crop protection, milling and baking, brewing, and cereal foods) sector.

Grains Research in the Commercial Sector The private sector has greater involvement in agricultural R&D, especially in linkages between seed business and biotechnology/life science concerns. Pardey and Beintema had calculated that since the mid-1990s, in developed countries, expenditures from the private sector in agricultural research have exceeded public expenditure. While bakery and grains processing companies have always engaged in research to support new product development, a particular focus of their research over the last decade has been in the development of grain food products that promote health and well-being. Despite the health benefits, there are challenges to increasing consumption of whole grain foods including taste preferences and convenience of these foods. In addition, there is a growing tendency for increasing numbers of people to avoid cereals in their diets because of perceived health issues, even though the documented prevalence of celiac disease and cereal allergy is comparatively low. Development and marketing of gluten-free foods has thus become a significant business opportunity.

Grains Processing Companies Most of the research carried out by these companies is concerned with practical applications (e.g., new product


development) aimed to support their flour milling and bakery product businesses (including breakfast cereals), but some carry out more basic research and their staff contribute actively to research conferences and the scientific literature. Major examples in the United States include ConAgra Foods in Omaha, NE (www.conagrafoods.com), General Mills in Minneapolis, MN (www.generalmills.com), Kellogg Company in Battle Creek, MI (www.kelloggcompany.com), and Nabisco, New Jersey (www.snackworks.com). Nabisco Research carries out fundamental studies on dough rheology and physical properties. Riceland Foods (www.riceland.com, Stuttgart, AR, the United States) and Riviana Foods (www.riviana.com, Houston, TX, the United States) are two large manufacturers of rice- and soy-based food ingredients and undertake applied research to support their markets. The National Starch and Chemical Company, Bridgewater, NJ (www.nationalstarch. com), focuses on cereal starch-based polymers and supports a significant research program including work on new adhesives, specialty food starches, and biodegradable packaging materials. Cargill has wheat flour milling and maize wet milling divisions and provides grains-based feeds for livestock. Through Cargill Health and Food Technology (www.cargillfoods.com), it focuses on nutraceuticals research, especially on developing products derived from soy. In Japan, two large milling companies, Nisshin Flour Milling (www.nisshin.com/english/group) and Nippon Flour (www.nippn.com), have played an important role over the last few decades in increasing the consumption of wheat in Japan. They also carry out a significant amount of research. In the United Kingdom, Rank Hovis (www.rankhovis.co.uk), ADM Milling (www.adm.com/en-US/MillingUK/Pages/ default.aspx), Associated British Foods, Allied Bakeries, and British Bakeries are among the largest milling and baking companies, and they conduct some in-house research and technology development. Barilla (www.barillagroup.com/corporate/en/home/lavora-con-noi/organization-and-job-families/research-development-quality.html) has a large cereal products research center in Italy, while in Australia, Goodman Fielder (www.goodmanfielder.com.au) and GWF (www.georgewestonfoods.com.au) have active technology development programs. Other companies within the oilseed crushing and animal feeds industry also have applied research programs.

Baking Industry Associations Industry associations are also an important provider of research and technical services in the grains industry. In the United Kingdom, Campden BRI (www.campdenbri.co.uk), Chipping Campden (Gloucestershire) and Nuffield (Surrey), is a membership-based organization that provides research and consultancy services for cereal-processing companies. Leatherhead Food Research (www.leatherheadfood.com) started as a UK food-industry association but has evolved

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into an independent provider of food research and market information. In France, ARVALIS Institut du ve´ge´tal, a farmers’ organization, carries out research on grains to satisfy the demands of markets and consumers. AIB International (www.aibonline.org), in Manhattan, KS, the United States, was founded by the North American baking industry to apply research findings to the industry in the United States and internationally. Emphasis of the research includes cereal science, baking technology, nutrition, and food safety. BRI Australia Ltd. (formerly the Bread Research Institute) has now become part of GrainGrowers (www.graingrowers. com.au), an independent Australian organization supported by the industry through membership fees and by competitive government and industry research grants. It carries out applied research in flour milling, baking, and Asian foods. The Japan Institute of Baking Technology in Tokyo also plays a similar role.

Seed and Grain Biotechnology Companies In a large number of cases, these two sectors have merged since the 1990s. A brief description of some of the largest multinational companies is in Table 1. Many of the companies were initially agrochemical suppliers, but the development of transgenic, herbicide-resistant grain crops provided them with an opportunity to market the seed and agrochemical together as a package. Several companies have an obvious leadership role in the development of agrochemicals and transgenic crops. However, the merger of many of these enterprises with seed companies increased their importance in breeding and agronomy and, more significantly, resulted in the consumer benefiting from research on transgenic crops. Genetic engineering has been carried out mostly on maize, cotton, soybean, and canola – with limited commercial progress with barley and wheat because of consumer resistance and in some cases technical challenges. To achieve resistance to herbicides and insecticidal activity, genes for Bacillus thuringiensis toxin were incorporated. For example, Monsanto Company’s products (St. Louis, MO) include herbicide-resistant soybeans, canola, and corn and insect-protected corn. Several of the companies also have broader genomics and gene-discovery programs. Refer to the papers by King and O’Brien for reviews of barley and wheat breeding, respectively, and by Gill and Henry for reviews of genome mapping and genomics, respectively. Research and development budgets of several of these companies run into several hundreds of millions of dollars, comparable with the government agricultural R&D budgets in some medium-sized developed countries. Over the last decade, early commercial impact in the cotton industry has translated into significant market share for grains, particularly maize and soybean. Consumer resistance and technical challenges mean that significant commercialization of genetically modified wheat and barley is lagging. Industry describes the products of biotechnology as ‘seed with trait’ – meaning traits such as herbicide or insecticide resistance. Of these, herbicide resistance (enabling particular herbicides to be sprayed in a standing grain crop) is the main trait for relevant grain crops, while insect resistance through B. thuringiensis (Bt) technology is second in importance. Some other ‘stacked’ traits provide tolerance to abiotic stresses, diseases, and control pollination.

Brewing Companies These form a second large group of private sector companies carrying out grains research. The largest brewing industry supported research organization is Campden BRI (www.campdenbri.co.uk) in the United Kingdom, which was formed out of merger between the Campden and Chorleywood Food Research Association and Brewing Research International. It undertakes research on behalf of members worldwide on aspects of food safety, barley and malt quality, fermentation, and beer quality. In addition, a number of the major brewery companies have significant in-house R&D activities, such as the giant US–European brewing conglomerate ABInBev, SABMiller in the United Kingdom, and Tepral (Strasbourg, France) as well as smaller brewing companies worldwide. Applied research on barley and malt composition and quality is carried out. The research activities of Carlsberg Brewers spread much further than malting and brewing. Since the establishment of research laboratories in 1875, Carlsberg has made major contributions to fundamental chemistry and such as the development of the Kjeldahl protein analytic method. The Carlsberg Laboratory (www.carlsberglab.dk) emphasizes both basic research and applied research on barley grain protein and carbohydrates and their reactions during brewing and genetic and biochemical studies on amino acid transport, protein-folding seed germination, barley mutants, starch synthesis, and yeast physiology.

The Private Sector in Asia and Africa Over the last decade, there has been increasing recognition by governments and by aid donors that private sector involvement in research can impact on poverty and increase production in Asia and Africa. While poorly developed compared with the United States, Europe, and Australia–NZ, despite challenges with regulatory and policy settings, private company involvement in applied grains research in varietal development and selection, crop protection, and crop processing has significantly increased in recent years. Indian private sector agribusiness investment is now quite significant, being over $250 million in 2008/09. This includes biotechnology and seed systems R&D to develop and disseminate maize, wheat and rice cultivars, and rice, pearl millet, and sorghum hybrids that provide superior yield under challenging conditions. Private sector investment in African applied grains R&D has also increased over the last decade and is growing rapidly, coinciding with the development of more favorable policy environments at a time when public funding for research has stagnated, in several sub-Saharan countries. The primary focus is the seed industry and plant variety development, in particular maize (both proprietary and genetically modified hybrids). In addition, private sector-bred varieties of wheat, sorghum, barley, soybeans, and sunflower have dominated over publicly bred varieties of the same species in terms of recent crop registrations for the Republic of South Africa.

Major Trends among Grains Research Organizations Improvements in grain crop yields over the last five decades are the overwhelming reasons that despite a 120% increase in

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Global Trends and the Commercial Sector Table 1

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Major international life sciences and seed companies carrying out grains research

Company/locations

Product/technology R&D emphasis

Website

Monsanto Company St. Louis, MO, USA Agracetus (part of Monsanto) Middleton, WI, USA ADM (Archer Daniels Midland) Decatur, IL Pioneer Hi-Bred (a Du Pont Company) Des Moines, IA, USA BASF Limburgerhof, Germany Raleigh, NC, USA Bayer Crop Science Akeno and Yuki, Japan Frankfurt, Germany Kansas City, MO, USA Lyon, France Syngenta Jealott’s Hill, UK Research Triangle Park, USA Saint-Sauveur, France Uberlandia, Brazil Beijing, China Dow Agrosciences Indianapolis, IN, USA Mycogen Indianapolis, IN, USA Cargill Ft Collins, CO, USA Elk River MN, USA Minneapolis, MN, USA Vilvoorde, Belgium KWS UK Thriplow, UK Limagrain Auvergne, France Biogemma Clermont Ferrand and Mondonville, France

Maize, soybean breeding, hybrids, herbicide, insect and wilt resistance, agrochemicals, seeds, and genomics Crop plant transformation, therapeutic protein expression in plants

www.monsanto.com

Food ingredients; oilseeds; soy-based foods; feed ingredients; bakery science; nutraceuticals; biofuels; extrusion research

www.adm.com

Seeds, grain additives Crop management, precision farming Grain seeds, especially hybrid maize (also millet, rice, sorghum, wheat) Crop protection products Transgenic crops with stress tolerance, high oil content, and pathogen tolerance

www.pioneer.com

Crop protection

www. bayercropscience. com

Crop protection, seeds, and crop genetics Genomics, biotic stress tolerance, fungal diseases, insect and nematode control, markerassisted breeding, maize, rice and soybean breeding, and transgenics

www.syngenta.com

Plant genetics and biotechnology; agrochemicals; seeds (hybrid and GM), traits (sunflower, corn, and soybean) and oils; crop protection Breeding of sorghum, hybrid corn, sunflower, soybean, and canola

www.dowagro.com

Cereals for animal feed, biofuels; novel traits; oilseed breeding; biotechnology

www.cargill.com

Wheat, barley, maize, and canola varieties

www.kws-uk.com

Cereal breeding; seeds; plant genome analysis; transgenesis; biotechnology; maize, wheat, rapeseed, sunflower, soybean, barley, peas; baking technology Maize, wheat, rapeseed, sunflower breeding plant genome analysis; drought tolerance; disease resistance

www.limagrain.com

global populations, food security is higher than ever. This is because grain yields almost tripled in the same time, this growing faster than population (http://faostat.fao.org). Successful grains research, together with irrigation in favored areas and favorable policy setting, is largely responsible for averting starvation over the last half century. As emphasized in the articles on taxonomy of grains research systems, the last few years have seen a reemphasis of food security, particularly for developing countries, and thus a return to treatment of research on grain productivity and yield as a priority. Also, specialization into particular areas – sometimes driven in a ‘top-down’ sense by funding bodies – and clearer identification by funders and institutes about how near to market they are, that is, whether the institute’s focus is on variety development, precompetitive applied research, or enabling plant science, have emerged as trends.

www.agracetus.com

www.basf.de/en; www.basf.com

www.mycogen.com

www.biogemma.fr

Increased Planning and Collaboration Since the 1980s, there have been significant changes in the organization and management of grains research. There has been a greater degree of planning and an increased degree of focus in the programs of many research organizations. Much of the increased focus has been on market needs – it is hard to criticize the important influence this has had on breeding programs, grains chemistry, and processing research. Greater linkages between research on grain production and marketing are important so that the research facilitates farmers who engage in market-specified production, as opposed to research to underpin increased production of grain as a bulk commodity. Over the last couple of decades, research centers have often moved from being provided with guaranteed government allocations to being dependent on competitive funding. Research

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planning exercises have been in favor in a number of commercial and government organizations across the globe. It is unclear to what extent individual creativity has been affected by these trends – certainly, there may be less scope for curiosity-driven grains research. The greater focus on markets by farmers and ‘producing for a particular market’ is reflected in research. An overarching trend has been the greater level of cooperation between research organizations; funding networks such as those established by the European Commission and Australian Government CRC system have facilitated this trend, as well as organizational changes in major government departments such as US Department of Agriculture. However, it is probably true that US grains research is less well coordinated at a national level – although locally, the close interactions between a number of USDA-ARS facilities and land grant universities are very productive. The increased importance of networks in many areas of science is a response to the increased cost of carrying out research plus an increasing realization that problems are multidimensional and are best addressed through multidisciplinary approaches. There has also been pressure from governments and funding bodies for research providers to network more, in part to avoid duplication of research and also to ensure that particular subprojects are carried out by the most qualified group. In the developing world, development banks such as the World Bank and Asian Development Bank have funded reform programs that encourage rationalization in the number of research providers as well as greater coordination. In addition, since the spike in global grains prices in 2007–08, development agencies and banks have had a resurgence of interest in funding agriculture including grains-related research. Scientist-to-scientist collaboration across institutional and national boundaries has been greatly facilitated by the communications revolution – the ability to e-mail (or more recently, use cloud computing for) large amounts of data and draft manuscripts for immediate receipt and prompt publication online has totally changed the possibilities for collaboration compared with 20 years ago. Globalization in industry – through both development of alliances between commercial research providers in different countries and increased emphasis on grains breeding for export markets – has also become a more important force. Markets are becoming more differentiated so there is an increased emphasis on grain quality – with targets for breeding efforts being additional yield and disease resistance – and on research aimed at improving the understanding of the genetic, chemical, and structural factors underpinning grain quality. An increased focus on impact assessment, better understanding of the concept of spillover but recognition of the lag between successful R&D and adoption – claimed to be 15–25 years for much public agricultural R&D. While such lag periods have been documented for early and mid-twentieth-century innovations such as hybrid maize and semidwarf cereals, respectively, the lag period may persist – it is two decades since the first genetically engineered grain crops were grown commercially, and yet for food grains, these still represent only a minority of grains produced globally. So grains research requires a longer-term view to be taken, both by aid donors who fund grains R&D in developing countries through commercial investors in advanced economies.

Changes in Research Subject Matter Grains agronomy programs have had to develop a stronger research emphasis on sustainability of production in recent years, responding to a shift in community values as well as serious scientific concerns about the long-term impact of some grain farming practices. Concerns about effects of irrigation, salinity, acidification (especially with certain legume crops), loss of soil, and of soil structure have led to an increase in research on reduced tillage, water conservation, and weed control and maintenance of soil fertility. Molecular breeding approaches have been implemented through the development and release of new varieties – a move from the laboratory to the field over the last decade. Impacts on climate variability and change and adaptation to variable climates have proved a significant focus for grains research over the last decade. However, the shift in research resources from productivity to other areas has been controversial – Alston et al. demonstrated that a shift in research investment in productivity or yield-related outcomes has coincided with a plateauing in global yields for major cereals. Indeed, the major factor underpinning sustainable agriculture has been the ability to feed the world’s increasing population through enhanced yields, and with the exception of a few communities, grains, especially cereals, are the central element of almost diets. Since the 1940s, there has not been a significant increase in the area of land available for agriculture. However, it is true that with the expansion of irrigation systems and with new varieties and increased fertilizer use in the middle of the twentieth century, there was an expansion of grain-growing areas. Since the 1980s, the expansion of irrigated areas has largely ceased and so production increases must come from increases in yield. In suitable ecologies, there has been a shift toward more frequent harvests, especially in irrigated areas that may accommodate three irrigated rice crops per year, as well as also improved rainfed rotations, for example, between a winter cereal and a legume, rather than leaving the soil fallow over summer. On the other with the recognition that breeding targeted toward ideal high yield environments does not provide varieties that perform well under normal farm conditions, a greater focus on breeding for representative environments and on abiotic stress tolerance has emerged. Therefore, the key contributor to sustainability in grain production will continue to be productivity; increases are important for both developing and developed country farmers, as the terms of trade for farmers continue to become poorer. An even greater challenge to developing countries is how North American and European governments shield their grain farmers from market realities through subsidies. Livestock are becoming a very significant consumer of grains worldwide; the trend is especially noticeable in developing countries, where meat consumption has increased significantly through the 1980s and 1990s, from a low base. Many of these animals are now grain-fed, so research has had to underpin the increased importance of grains for feed rather than food applications. This research is also driven by increased intensification of monogastric animal production, including in developing countries. In many countries, farmers are not solely grain growers or cattle or sheep farmers, but manage a mixed enterprise. There has been a more active development of systems-based research to address their needs.

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Global Trends and the Commercial Sector Another grains research area focused on Africa and South and South East Asia is biofortification. There are several international projects focused on biofortification of staple cereals with micronutrients such provitamin A, iron, and zinc. Some approaches involve the use of genetic engineering technology to transfer biosynthetic genes (e.g., for vitamins) into the grain species, while other programs focus on exploration of natural variation for the desired micronutrient in a grain species or in primitive relatives of a target grain species followed by introgression of the desired characteristics into high-yielding, highquality locally adapted varieties. Consumer trends provide critical direction for many of the commercial milling and baking organizations that conduct research, including on product development. The trend toward cooking less at home and convenience foods is continuing; there is increasing popularity of gluten-free diets (whether or not they are indicated on medical grounds) and greater consumption of weight loss and diet snacks that have improved taste. In addition, a focus on high-protein/low-fat and lowcarbohydrate grain products and emergence or niches for some ancient grains such as spelt and nongrains/pseudocereals such as quinoa and buckwheat used in traditionally grain foods have also driven industry cereal foods product research and development. In parallel, whole grain and whole fiber, specialty baked goods, have emerged as an increasingly important sector for bakery research. Biofuel research continues to be important in certain countries as demands grow – for example, in 2010/11, 40% of the US corn crop and 14% of soybean oil were used for biofuels in the United States.

Institutional Trends Another major change in the nature of agricultural research since the 1980s, particularly in the United States and Europe, has been the shift in balance of research to a greatly increased role for the private sector. And within government systems, the greatly increased resourcing and impact of Chinese, Indian, and Brazilian grains researchers and their work are being felt globally. Different countries also have different types of involvement of universities in grains breeding, although in the process of training the next generation of grains breeders, some universities have developed significant breeding programs and have become a mainstay of breeding efforts for a country. Several interdependent factors have given rise to greater commercial involvement in grains breeding, including the increased importance of plant breeders’ rights, development and application of biotechnology in grains science, shrinkage of government support for agricultural research, and the increased importance of intellectual property protection. In some cases, privatization of former public sector plant breeding institutes has taken place. In some parts of the world, such as Europe, there has been a long history of significant plant breeding efforts being carried out by industry; in others, such as Australia (with the exception of hybrid cereals), almost all plant breeding was formerly carried out by government and universities. Nowadays, Australia and several other countries separate the responsibilities for prebreeding and breeding between public and private sector organizations, respectively. The other industry group that has become more involved in grains research has

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been farmers themselves. Farmer-driven groups now often have a key role in identifying research priorities as well as being a vehicle for dissemination of research results – in a number of countries, farmer groups directly manage on-farm adaptive research trials on technologies such as rotations, weed control, and reduced tillage, but some are also adopting a wider perspective. Realizing that both small and large farms are often diversified enterprises, grains research has a much greater emphasis on farming systems than in previous years. The influence of farmers is important in fitting grains research into a wider farming systems context. Organizations that use farmers’ levies to fund research such as the Home Grown Cereals Authority in the United Kingdom or the Australian Grains Research and Development Corporation have also been instrumental in encouraging greater farmer involvement. Grains science is carried out within formal institutional structures, most of which have evolved from a range of historical and political situations, rather than having been developed with a consideration of whether the institutional structures fit the needs of the twenty-first century. In many state- or provincial-based departments, there remains a close collaborative linkage between cereal breeding and cereal chemistry, and the scientists involved carry out a service function as well as independent research – often creating a tension between the time spent on the two, but with the advantage that the research objectives are informed by genuine industry problems. There are few grains science institutions globally that cover all of cereals, legumes, and oilseeds. Instead, there may be research clusters within university agronomy or agriculture faculties or grains researchers within plant science or crops research organizations. It is more usual for postharvest technology institutions or grain storage research laboratories to consider various issues relating to a wider range of cereals and other grains together, on the basis that the storage and handling of grains as durable commodities have common research challenges. Over the last decade, there has been a decrease in postharvest grains research globally, given that there is a prevailing view that the main priority is now adoption of established technologies. Some institutes do cover several cereals or grains more broadly, although usually with a focus on those crops relevant for their country or targeted region. For example, wheat and barley are often studied together. Some of the equipment and techniques are common, while others specialized – for example, while Falling number is used as a measure of postharvest sprouting for both wheat and barley, dough rheology testing is specific to wheat. Specialized grains science departments are found in a small number of US and European universities, but their numbers are decreasing. Arguments for this model are the critical mass of researchers and ability of students to train in aspects from grains breeding to postharvest technology. On the other hand, such departments can lack linkages to emerging or discovery science and to the broader range of disciplines in agriculture and science. One of the lessons of modern molecular biology is that techniques such as those in functional genomics are often readily transferable between grains, other crops, microorganisms, and animals. This aspect has very much been exploited in recent years as whole genome sequencing becomes faster and much less expensive, and its use to understand disease

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resistance and quality associations becomes more widespread. The high degree of synteny tells us that gene structure and function are conserved across cereals and the great similarity of their physiological and biochemical processes often makes it simple to utilize research ideas and techniques between different grain crops. There are no definitive answers to the issue of an optimal institutional structure for grains research other than to assume that earlier structures need not necessarily be more important than ever for breeders, agronomists, crop protection scientists, and researchers of processing quality to interact. Finally, institutional structures can coevolve with the evolution of technology. With the growth of networks of researchers collaborating nationally and globally and able now to exchange large data sets through cloud computing, the establishment of formal institutional structures and a prerequisite for geographic colocation to foster collaboration has become less important. But humans will remain social animals, and it is hard to envisage a world where face-to-face collaboration will become irrelevant.


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What are some of the factors leading grains research to be more ‘demand-driven’? How has greater collaboration between research institutes been encouraged by governments and funding agencies? What type of research do grains processing companies in Europe and North America predominantly carry out? What opportunities stimulated agrochemical companies to get involved in grains breeding? What are the main areas of subject matter emphasis for commercial grains research and development in India and Africa? What factors have led to greater commercial involvement in grains breeding?


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Explore the similarities and differences between focus areas for wheat and barley research. Why are some areas similar yet others quite different? How do priorities for research relating to irrigated wheat and rice differ from those for rainfed (or dryland) wheat and rice? Compare and contrast the role, organization, and business models of farmers’ organizations undertaking grains research in a developed country and a developing country.

See also: Barley, Rice and Maize Processing: Barley: Malting; Breeding of Grains: Barley: Genetics and Breeding; Canola/ Rapeseed: Genetics and Breeding; Maize: Breeding; Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains

and the Consumer: Consumer Trends in Grain Consumption; Genetically Modified Grains and the Consumer; Grains and Health; Genetics of Grains: Development of Genetically Modified Grains; Genome Mapping; Genomics of Food Grains; Processing of Grains: Cereals: Breakfast Cereals; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Breads; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Pasta.

Further Reading Alston JM, Pardey PG, and Smith V (1999) Paying for International Productivity. Baltimore/London: Johns Hopkins University Press. Alston JM, Beddow JM, and Pardey PG (2009) Agricultural Research, productivity and food prices in the long run. Science 325: 1209–1210. Cuesta-Marcos A, Kling JG, Belcher AR, Filichkin T, Fisk SP, Graebner R, et al. (2016) Barley: genetics and breeding. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 4, pp. 287–295. Elsevier. DePauw R and O’Brien L (2016) Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation. In: Wrigley C, Seetharaman K, Corke H, and Faubion J (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 4, pp. 279–286. Elsevier Ltd. Evenson RE and Gollin D (2003) Assessing the impact of the Green Revolution, 1960–2000. Science 300: 758–762. Henry RJ (2016) Genomics. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 4, pp. 360–364. Elsevier Ltd. Jetter KM and Cassady DL (2006) The availability and cost of healthier food alternatives. American Journal of Preventative Medicine 30: 38–44. Jones JM and Sheats DB (2016a) Grains and Health: Misinformation and Misconceptions. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 2, pp. 23–28. Elsevier Ltd. Jones JM and Sheats DB (2016b) Consumer Trends in Grain Consumption. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 2, pp. 29–34. Elsevier Ltd. Pardey RG and Beintema NM (2001) Slow Magic: Agricultural R&D a Century after Mendel. Washington, DC: International Food Policy Research Institute. Pray C, Gisselquist D, and Nagarajan L (2011) Private investment in agricultural research and technology transfer in Africa. Agricultural R&D: Investing in Africa’s future, ASTI-FRA Conference, Accra, Ghana, 5–7 December, Working paper 13. Pray CE and Nagarajan L (2012) Innovation and Research by Private Agribusiness in India. Washington, DC: International Food Policy Research Institute IFPRI Discussion Paper 01181. Ray DK and Foley JA (2013) Increasing global crop harvest frequency: Recent trends and future directions. Environmental Research Letters 8: 044041. http://dx.doi.org/ 10.1088/1748-9326/8/4/044041 10 pp. Saltzman A, Birol E, Bouis HE, et al. (2013) Biofortification: Progress toward a more nourishing future. Global Food Security 2: 9–17. Skerritt JH (2016a) Research organizations of the world: Europe and North America. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1, pp. 436–443. Elsevier Ltd. Skerritt JH (2016b) Research organizations of the world: Asia-Pacific, Central-South America, and Africa-Middle East. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 1. pp. 444–450. Elsevier Ltd. Tiwari VK, Faris JD, Friebe B, and Gill BS (2016) Genome mapping. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edn., vol. 4, pp. 365–375. Elsevier Ltd. US Energy Information Administration (2012) Biofuels Issues and Trends, October 2012, US Department of Energy, Washington (www.eia.gov/biofuels/issuestrends/ pdf/bit.pdf).

Scientific Societies Associated with Grain Science SC Nelson, AACC International (AACCI), St. Paul, MN, USA CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Large numbers of scientists and technologists are involved with food grains worldwide. These people have formed scientific associations, based on their specific interests, to facilitate interactions and information sharing. These interactions involve working collaborations and the exchange of ideas via conferences, publications, standardizing analytic methods, and explaining grain science to the general public. Two such associations, originally based in the United States and in Europe (the AACCI (American Association of Cereal Chemists International) and the ICC (International Association for Cereal Science and Technology)), have become international. Other associations have regional memberships. Some of these associations specialize in specific aspects such as seeds, breeding, agronomy, soil science, and grainrelated health benefits.

Learning Objectives

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Achieve understanding of the need for and the activities of scientific associations that have been established to facilitate collaboration and exchange of ideas between scientists and technologists involved in the breeding, growing, harvesting, marketing, and processing of food grains and nutritionists and consumer groups.

Introduction The industries that grow, harvest, and process grain are big businesses worldwide, involving large numbers of people, including many scientists and technologists. It is important that all these professionals should have opportunities to interact with one another, to exchange ideas, to learn from one another, and to develop grain-testing methods that are accepted internationally. In addition, they need to interact more broadly with consumers, the media, and government agencies. Opportunities for these various activities are provided by specialist societies and associations (‘learned societies’), with grain scientists as members, formed for the purposes of interacting with one another in their areas of expertise. Many such scientific societies have been formed for grain scientists, covering the wide range of aspects of grain science, from breeding, to agronomy and farming, to the chemistry of the harvested grain, to marketing, processing, and retailing. Some of these societies are selected for description in the


succeeding text, but the range covered is by no means comprehensive. In addition to scientific societies, there are also trade associations, formed for the purposes of interaction at the technical and commercial levels and for lobbying purposes. A list of many scientific and trade associations of the food industry has been assembled by www.stagnitomedia.com and www. hoovers.com. The activities of the scientific associations include the organization of conferences at which lectures are presented, as shown in Figure 1. In addition to lectures, there are poster presentations, involving the author standing beside the description of a research project on a large poster board for discussion with conference delegates (Figure 2). Conferences also serve the purpose of providing opportunities for personal interactions to occur; these face-to-face situations complement the less personal interactions by phone and Internet at other times. Trade exhibits (Figure 3) at conferences provide information about the latest equipment and resources. These learned societies use conference time for making awards to their members who have excelled in aspects of the science and technology relevant to the society’s activities. Figure 4 shows the recent presentation of several awards at a meeting of AACCI. The Thomas Burr Osborne Medal (Figure 5) is one of these awards. Other activities include the dissemination of information via journals, books, and other publications; the establishment of professional standards of conduct and training; and the development of standard methods of analysis. A related activity is the provision of ‘check samples’ – characterized subsamples, such as grain or flour, that are provided to many cooperating laboratories for them to establish that standard methods of analysis are providing similar results across various regions. The provision of reliable scientific information is becoming an important function, thereby advising decision-making bodies and the general public; these activities may even border on lobbying when it becomes apparent that misinformation is prevailing.

The Range of Societies Prominent among these learned societies are those relevant to the quality and processing of grain. In particular, AACCI has a worldwide membership of scientists involved in grain production and processing. The ICC, based in Vienna, Austria, is an international association committed to international cooperation through disseminating information and developing standard methods relevant to grain production and processing. There are also national bodies with similar objectives, such as the Chinese Cereals and Oils Association (CCOA), based in Beijing, China, and the Australasian Grain Science Association

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SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Scientific Societies Associated with Grain Science

Figure 1 A major activity of scientific associations is the organization of conferences at which lectures are presented to inform members about recent developments in their field of grain science.

Figure 4 Scientific societies honor members who excel in their field of study by the presentation of awards.

Figure 2 Poster sessions provide an alternative to lectures at conferences. The author of the information on the poster is available to discuss its contents with other delegates.

Figure 5 The Thomas Burr Osborne Medal, awarded for ‘research in the field of cereal chemistry that has contributed significantly to the progress of the science.’ The medal commemorates an important research pioneer of cereal chemistry early in the twentieth century.

Figure 3 Trade exhibits at conferences help members become familiar with the latest equipment and resources.

(previously the Cereal Chemistry Division of the Royal Australian Chemical Institute (RACI)). Other societies have been formed for those involved in specific aspects of chemical analysis or individual classes of chemical compounds. For example, the American Oil Chemists’ Society (AOCS), comprising some 5000 members

worldwide, provides ‘a global forum for the science and technology of fats, oils, surfactants, and related materials.’ Furthermore, AOAC International is an ‘internationally recognized organization with 130 years of experience in validating and approving analytic methods for foods and agriculture.’ In these cases, involvement goes well beyond the analysis of grains, but grains are a significant part of their broader scope. The American Society of Agronomy, the Crop Science Society of America, and the Soil Science Society of America attract scientists involved in plant growth and production. While their interests include grain production, the involvement of these societies covers the full breadth of plant-based agriculture. Complementary to this aspect of grain science is the International Seed Testing Association (ISTA), concerned with the earliest stage of plant production, namely, the provision of pure seed. Again, the scope of this society extends well beyond food grains to cover all types of plant seeds.


AACC International (AACCI) AACCI is one of the largest international nonprofit organizations dedicated to creating opportunities for providing and exchanging knowledge and advancing innovations across the broad disciplines of cereal grain science by facilitating research, education, collaboration, technical service, and advocacy efforts. AACCI was founded in 1915 for the purpose of standardizing methods of analysis among cereal laboratories. Today, the association’s mission is to be the global authority in cereal grain science and technology. The association now provides a comprehensive and respected collection of grain science methods. All methods go through a rigorous approval process by an AACCI technical committee. AACCI’s technical committees are composed of scientists chosen for their specific areas of expertise. Today, as industry issues arise, AACCI strives to provide science-based approaches and responses to address current needs and trends. The diverse membership provides the creative and scientific strength to help provide creative solutions and quality recommendations in reaction to a dynamic industry and world environment. Through its activities in methods validation, AACCI is acknowledged as a scientific authority when proposing definitions and providing comments to regulatory agencies worldwide. Key definitions developed include dietary fiber, whole grain, oat bran, glycemic carbohydrates, and aleurone. Additionally, AACCI has provided comments on whole grain label statements; proposed guidance on food allergens, food labeling, and nutrition with respect to gluten-free foods; and health claims relating to the consumption of certain oat products to a reduced risk of coronary heart disease. In 2013, AACCI’s Whole Grains Working Group approved its characterization of a whole grain. The characterization states that a whole grain food product must contain 8 g or more of whole grain per 30 g of product. Volunteers have also organized ad hoc internal committees to examine key issues affecting the science and developed action plans to address these issues. AACCI’s strategic initiatives include (1) generating and disseminating the highest quality of science and information on cereal grains and their products; (2) driving scientific communication, collaboration, and innovation; (3) providing professional development for its members; (4) facilitating the interface of the many disciplines involved in cereal and grain science; and (5) ensuring a vital organization in future years. In 2015, AACCI commemorated its centennial year by examining the major advances made in cereal grain science through the association’s 100 years. AACCI produced a series of feature articles in its publication, Cereal Foods World, examining the advances by category and explaining the importance of these advances in science today. Centennial activities also included the creation of a timeline of historic advances and key moments in AACCI history, which is currently available on AACCI’s website. AACCI’s 2015 Centennial Meeting included additional scientific content and a speaker who looked to how today’s understanding of cereal grain science will inform the future of the science and its impact on the world.

The Activities of AACCI Members Many AACCI members are involved in food manufacturing using grains, one of the fastest-growing, most dynamic

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segments of the food industry. They are responsible for producing some of the most popular and profitable products, such as new types of cracker, cookies, pretzels, or other snack foods. Bringing such products into the market involves design, development, and marketing skills. Breads, tortillas, frozen doughs, and dry mixes all rely on cereal chemists for their success in the marketplace. Other AACCI members are involved in the ‘upstream’ of the food industry. They may be associated with plant-breeding programs, with responsibility for ensuring that the grain from new varieties is suited for specific marketing and processing requirements. Research activities are prominent for other cereal chemists, with the objectives of elucidating the chemical and molecular bases of grain quality, thereby laying a foundation for the development of improved testing methods for grain quality. Other research activities are likely to lead to the development of new grain types with better processing and nutritional attributes.

AACCI Resources AACCI has provided resources in grain science for a century, supporting members’ professional needs in private industry, academia, and government. The association provides an avenue of bringing together and disseminating scientific information and technical research on cereal grains and related materials and their processing and utilization. This information is made available through annual meetings, through continuing education courses, and in publications. The range of published materials includes scientific journals, books, electronic newsletters, and data provided on the website. AACCI publishes Cereal Chemistry, a journal with peerreviewed, original research on raw materials, processes, and products that relate to the utilization of cereal grains, oilseeds, and pulses and analytic procedures and methods in the grains area. AACCI also publishes Cereal Foods World, which includes feature articles and original research that focus on advances in grain-based food science and the application of these advances on current practices in baking, snack foods, breakfast foods, and other grain-based products. In addition to these two journals, AACCI has published more than 80 titles on various foodscience topics. Some titles are technically focused while others are more general. The AACCI handbook series offers a single source of practical information for the major ingredients used in food processing. AACCI’s website offers members the opportunity to obtain information and resources in one common location. The website features an online catalog of books, special reports, membership directory, a calendar of events, and online symposia. AACCI journals and electronic copies of publications can be found in the AACCI online Grain Science Library. This content platform delivers a large and growing collection of resources, including Cereal Chemistry, Cereal Foods World, and AACCI PRESS online books. AACCI’s continuing education programs offer professional development services for food industry professionals at any level in a variety of food-related industries. Core services include short courses taught by experts that offer comprehensive training and tools for real-world applications. AACCI’s continuing education programs also focus on emerging issues and strategies for the future success in the food

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industry. Members receive special rates on technically focused, hands-on training. Courses are offered globally.

AACCI Meetings AACCI’s annual meetings are attended by an international audience of more than 1000 grain-based professionals, providing a rich scientific program and networking opportunities for the global grain industry. Presenters have the opportunity to share the latest research on topics such as biotechnology, functional foods and ingredients, health and nutrition, structure and function of food components, and quality enhancements. The annual meeting also provides students with numerous opportunities to display their research, including product development and research paper competitions. The annual meeting features a trade show, typically composed of approximately 250 exhibits. AACCI recognizes excellence through its awards program (Figure 4). AACCI awards include the Alsberg–French–Schoch Memorial Lectureship, the C. W. Brabender Award, the Edith A. Christensen Award, the Excellence in Teaching Award, AACCI Fellowships, the Phil Williams Applied Research Award, the Texture Technologies Quality Research Awards, the Thomas Burr Osborne Medal (Figure 5), the William F. Geddes Memorial Award, the Young Scientist Research Award, and Honorary Memberships. In addition, the AACCI Foundation provides scholarships and fellowships annually for students majoring in disciplines related to cereal science. Student and young professionals receive travel assistance grants to attend the annual meeting through the Student Travel Award program and the Cecil F. Pinney Travel Award. Members have the opportunity to attend local section meetings, connecting them to other professionals within their own region. AACCI also has several subject-matter divisions focused on basic research and development areas. The Student Association, in conjunction with the Professional Development Panel, provides students with professional development opportunities such as showcasing their research (with lectures and poster presentations; Figures 1 and 2), interacting with well-respected members of the scientific community through mentorships, and building professional leadership skills through the competitions mentioned previously. Students also have opportunities to attend hands-on workshops including the AACCI Breakfast Cereals and Europe Section’s European Young Cereal Scientists and Technologists Workshop and the Young Cereal Chemists Meeting.

The International Association for Cereal Science and Technology The ICC is an independent, internationally recognized organization of experts specializing in the milling of wheat and other cereals, bread making, and the production of other cerealbased foods from around the world. In more recent times, the ICC has expanded its focus to address issues that contribute to improved food quality, food safety, and food security for the health and well-being of all people. The ICC is

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an apolitical forum for all cereal scientists and technologists; a publisher of international standard methods and a scientific journal; an organizer of major national and international events in the field; a promoter of international cooperation on a global, regional, and national level; a significant player in the coordination and participation in international research projects.

Objectives The ICC is a nonpolitical, nonprofit-making organization. Membership is open to all interested countries, corporations, and institutions that are prepared to offer their cooperation and to support the aims and ideals of the association.

A Short History of the ICC The ICC was founded in 1955 on the occasion of the third International Bread Congress in Hamburg, Germany, as the ‘International Association for Cereal Chemistry’ (ICC). The original objective of the ICC was the development of internationally approved and accepted standard testing procedures for cereals and flour. Today, the ICC is one of the foremost international organizations in the field of grain science dedicated to international cooperation, the dissemination of knowledge, and the improvement in safety and quality of cereal-based foods. The association has its headquarters and its General Secretariat in Vienna, Austria. At present, some 30 countries from five continents are represented in the ICC.

ICC Mission Statement ICC is the preeminent international association in the field of cereal science and technology, committed to international cooperation through the dissemination of knowledge, conducting research, and developing standard methods that contribute to advance innovation and improve food quality, food safety, and food security for the health and well-being of all people.

National Cereal Chemistry Societies Many countries have formal and informal associations of professionals in grain science. In addition, international associations, such as the AACCI, have regional sections and branches that provide opportunities for members to hold ‘local’ meetings.

The Chinese Cereals and Oils Association The CCOA, based in Beijing, China, provides opportunities for interaction for a large number of Chinese scientists working with grains, edible oils, and related commodities. While its activities are mainly centered within China, the association also hosts international conferences, thereby involving the

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Scientific Societies Associated with Grain Science wider range of grain scientists. The CCOA has over 6000 individual members and has over 570 organization members. The CCOA is a member of the ICC. The CCOA is divided into four subassociations, namely, grain storage, grain food, edible-oil processing, and animal-feed production. The CCOA publishes a journal, the Journal of the Chinese Cereals and Oils Association. The Chinese version is published every 2 months, while the English version appears annually.

461

commemorates the pioneering wheat research of Australian Frederick Bickell Guthrie, who formed the world’s first chemist–breeder collaboration with the wheat breeder William Farrer commencing in the 1890s. Throughout the life of AGSA and the Cereal Chemistry Division, presentations at annual meetings have been recorded in published form, in recent years under the titles Cereals 2016, Cereals 2015, Cereals 2014, etc. Details of these publications and other activities are provided on the AGSA website (http:// ausgrainscience.org.au).

Australian and New Zealand Grain Scientists The Australasian Grain Science Society (AGSA) is currently the main association for cereal chemists and other grain scientists in Australia, New Zealand, and nearby regions. AGSA, now a stand-alone society, has grown out of the Cereal Chemistry Division, which was a part of the RACI, based in Melbourne, Australia. In addition, many Australian grain scientists are members of the AACCI’s Downunder Section. AGSA provides opportunities for scientists and technologists to exchange information and to interact with colleagues internationally, especially at annual meetings. These annual meetings continue the series of annual Australian Cereal Chemistry Conferences, which commenced in 1950, so that the 2016 annual meeting is the 66th conference in this series. At regular intervals, these meetings are combined with other international societies, especially the AACCI and the ICC. Other activities include workshops and training seminars on specific aspects of grain science, the provision of standard methods of analysis, and facilities for checking samples with known analytic results by which laboratories are able to compare the results of their analytic methods with others. AGSA has several awards to acknowledge special contributions to grain science. The Guthrie Medal (Figure 6)

Figure 6 The Guthrie Medal, originally awarded by the Cereal Chemistry Division of the Royal Australian Chemical Institute, is now awarded of the Australasian Grain Science Association. It is awarded for ‘outstanding contributions in the field of grain science.’ The medal commemorates an Australian cereal chemist of the 1890s and 1900s.

Societies Involved with Grain Growth The International Seed Testing Association The ISTA is a worldwide, nonprofit association, whose main activity is to provide methods and services for the testing of seed traded internationally. The primary purpose of the association is thus to develop, adopt, and publicize standard methods for sampling and testing seeds of all types, not only the edible grains. ISTA’s secondary purpose is to promote all areas of seed science and technology. These purposes are largely served by the publication of relevant handbooks and bulletins, scientific journals (Seed Science and Technology and Seed Symposium Abstracts), proceedings of symposia and workshops, and training booklets. The primary ISTA ‘instrument’ for promoting uniformity of seed-testing procedures is the International Rules for Seed Testing, a publication that is updated annually with amendments and additions resulting from ISTA meetings. The ISTA Secretariat is based in Bassersdorf, Switzerland.

The American Societies of Agronomy, Crop, and Soil Science Founded in 1907, the American Society of Agronomy is ‘dedicated to the development of agriculture enabled by science, in harmony with environmental and human values.’ The society supports scientific, educational, and professional activities to enhance communication and technology transfer among agronomists and those in related disciplines on topics of local, regional, national, and international significance. The Crop Science Society of America is an educational and scientific organization composed of more than 5000 members dedicated to the advancement of crop science. The motto is ‘Plant science for a better world.’ Founded in 1955, the society is international in scope with members in more than 100 countries who are advancing the discipline of crop science by acquiring and disseminating information about crops in relation to genetics and plant breeding, crop physiology and production, germplasm resources, and environmental quality. An important function of the society is the production of its main journal Crop Science. The Soil Science Society of America, established in 1936, is the professional home for over 6000 professionals throughout the world involved in soil science. Their claim is ‘Soils sustain life.’ The primary purpose of the society is to advance the discipline and practice of soil science by study and education concerning soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management and recycling, and wise land use.

462


Societies Involved with Grain Analysis AOAC International AOAC International is ‘a globally recognized, independent, third party, not-for-profit association’ with 130 years of experience in validating and approving analytic methods for foods and agriculture. It has over 3000 members worldwide. The organization was founded in 1884 as the Association of Official Agricultural Chemists, under the auspices of the US Department of Agriculture. Its initial role was to adopt uniform methods of analysis for fertilizers. In the following year, a convention established the AOAC as an independent organization, but membership was restricted to analytic chemists in state and federal positions of the US government, and this membership requirement remained for a century. In 1965, to recognize the expansion of AOAC’s scope of interest beyond agricultural topics, the association’s name was changed to the Association of Official Analytical Chemists. During the 1970s, membership was extended to scientists outside the United States and to nongovernmental scientists, with many members working in industrial laboratories. During the 1980s and 1990s, the scope of analyses expanded and there was increasing demand for quality control of laboratories and international laboratory accreditation. Consequently, the name of the association was changed to AOAC International, thereby retaining the initials by which the association had been known for 130 years, while eliminating reference to a specific scientific discipline or profession. The scope of the AOAC includes methods not only for the analysis of grains but also for a much wider range of materials. AOAC provides a number of key publications (especially its Official Methods of Analysis), hosts technical meetings and conferences, and offers training courses in the areas of laboratory management, quality assurance, accreditation, statistics, and measurement uncertainty.

The American Oil Chemists’ Society The AOCS (‘Your Global Fats and Oils Connection’) is another American scientific association that has become international, growing and expanding in scope since its origins in 1915. This scope now includes oil- and fat-related commodities, oilseeds, oilseed meals, and edible fats. Grains are thus prominent in this range of materials for analysis, but the scope goes beyond grains, including other sources of edible fats, such as fish and animals. The AOCS technical services are based in Champaign, IL, the USA.

Societies Relating to Food Grains and Health Grains for Health Foundation The people working with Grains for Health Foundation include scientists, business leaders, educators, and health professionals working together at the grassroots level encouraging all sectors, disciplines, and communities to use their expertise to improve public health. The Grains for Health Foundation provides publications, resources, and events within the grains and health

communities. Membership helps shape this foundation’s objectives and foster integral conversations that create practical change. The Grains for Health Foundation actively seeks both sponsor members and partner members. Grains for Health Foundation goals include redesigning the food supply by facilitating the development, delivery, and consumption of grain-based foods in order to promote a healthy body weight, reduce chronic disease, and curb healthcare costs. These bridges ignite the necessary conversations around making healthy, grain-based foods accessible. Grains for Health Foundation measures its success to the extent that contributions help build and maintain the crucial relationships needed between the whole grain food supply and the researchers and policy makers that regulate the distribution and education surrounding grain-based foods. Measures of success include the following:

• • • • • •

Foods with healthy grains are available in your grocery, school, or business. Health-care professionals recommend whole grains as a means of reducing chronic illness. Policy makers design legislation leading to healthier grain products. Scientists create grains able to feed our communities. Rates of chronic diseases decline. Cost of health care is lowered.

Grains for Health Foundation undertake strategic and transformative work on all levels of the grain chain from connecting growers to scientists to politicians to distributors to educators to health-care professionals. The cross-disciplined work builds a vast community needed to create the positive change in public health so you can be assured access to healthy, grainbased foods.

The HEALTH GRAIN Forum This association was founded in May 2010 to continue promotion of science and communication for production and consumption of healthy cereal foods, as a follow-up of the HEALTHGRAIN Forum of the European Union. There are currently members from 19 countries. The organizational structure includes a board and four task forces to plan activities, interacting via telemeetings on a regular basis. Two annual workshops are organized to provide opportunities for interaction. The mission of the HEALTHGRAIN Forum is to promote science-based concepts fully, unlocking the health-promoting potential in the entire grain food production chain to obtain healthy, convenient, and appealing foods. The vision is to assist consumers in health maintenance worldwide, help reduce health-care costs, and provide added value for companies in the production chain. The motto is ‘The best of the grain for consumer well-being.’

Celiac Societies Celiac societies have been formed in many countries and regions by people with celiac disease and related forms of dietary intolerance to gluten. These are not associations of

SCIENTIFIC ORGANIZATIONS RELATED TO GRAINS | Scientific Societies Associated with Grain Science professionals only, but rather of people with celiac disease, together with their relatives and friends. They may, in turn, rely on scientists and medical workers to provide advice in the forms of publications, consultation, and conference presentations for the benefit of the members. A few web addresses are provided in the list in the succeeding text, but there are many more such societies worldwide.

•

Future Prospects Into the future, grain science professionals will continue to need opportunities to interact and collaborate. Scientific societies can continue to provide scientists not only with validated and archived information but also with the essential feature of contact with other scientists. While today’s technology provides new options for frequent and instant communications, it continues to be important for scientists to meet face to face for effective dialogue. Some means of interaction will progressively change, largely due to changes in the range of novel electronic media. Already, traditional means of print publication are being duplicated or replaced by various electronic means. The value of face-to-face meetings and conferences cannot be readily replaced.

•

463

other examples can you find? Think, for example, of associations involving breeders, geneticists, grain growers, health professionals, nutritionists, and consumers. Find out the costs of membership, of conference attendance, and of other forms of involvement for some of these associations. Try to assess the value for money in terms of professional benefits to be gained by members. To what extent do you reckon that benefits depend on involvement via publications (only), conference attendance (only), and/or volunteering for direct participation in association affairs? Look for indications that these associations have recently been involved in advising decision-making bodies with respect to their areas of expertise.

See also: Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Scientific Organizations Related to Grains: Research Organizations of the World: Asia-Pacific, Central–South America, and Africa–Middle East; Research Organizations of the World: CGIAR; Research Organizations of the World: Europe and North America; Research Organizations of the World: Global Trends and the Commercial Sector.


• • •

What features distinguish the associations described in this article from other types of associations in society in general? Which of the associations described would be the most appropriate for you, depending on your location and your area of grain science (e.g., breeding, farming, milling, food processing, and advising about nutrition)? List the range of activities and opportunities provided by membership of a scientific society that would not be otherwise available.


•

There are even more associations relevant to grain science than the prominent examples given in this article. What

Relevant Websites http://www.aaccnet.org – The AACC International. http://www.agronomy.org – The American Society of Agronomy. http://www.aoac.org – AOAC International. http://www.aocs.org – The American Oil Chemists’ Society. http://www.asbcnet.org – The American Society of Brewing Chemists. http://www.ccoaonline.com – Chinese Cereals and Oils Association. http://www.coeliac.org.au – The Coeliac Australia. http://www.crops.org – The Crop Science Society of America. http://www.csaceliacs.org – The Celiac Support Association, USA. http://www.icc.or.at – The International Association for Cereal Science and Technology (ICC). http://seedtest.org – The International Seed Testing Association. http://www.nopa.org – The National Oilseed Processors’ Association. http://www.soils.org – The Soil Science Society of America. http://www.spcouncil.org – The Soy Protein Council.




NUTRITION AND FOOD GRAINS EDITORS




{

deceased


Academic Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB 225 Wyman Street, Waltham MA 02451 First edition 2004 (as Encyclopedia of Grain Science) Copyright © 2016 Elsevier Ltd. All rights reserved The following articles are US government works in the public domain and are not subject to copyright: Grain Crops, Overview; Maize Overview. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers may always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library SET ISBN 978-0-12-394437-5 VOLUME 1 ISBN 978-0-12-803537-5 VOLUME 2 ISBN 978-0-12-803536-8 VOLUME 3 ISBN 978-0-12-803535-1 VOLUME 4 ISBN 978-0-12-803538-2

For information on all publications visit our website at http://store.elsevier.com Printed and bound in the UK.


CONTENTS Preface

xvii


xix


xxiii xxv xxvii


1

The Basics

1


1



13

H Corke


16

RA Graybosch


22

CW Wrigley


31



41

H Corke


51

J Wyatt

The Cereal Grains

73


73

CW Wrigley


86

LA Morrison

Maize: Overview

99



105

CW Wrigley

v

vi

Contents


117


Rice: Overview

125

BO Juliano


130



140



147



153

A Cruickshank


159


Triticale: Overview

168

BJ Furman

Oats: Overview

173

PK Zwer

Coix: Overview

184



190

JRN Taylor


199


Teff: Overview

209

G Bultosa

The Oilseeds

221

Oilseeds: Overview

221

RJ Mailer

Soybean: Overview

228

K Liu

Canola: Overview

237

VJ Barthet


242

E Hernandez

Sunflower: Overview

247



254

C Hall III

Linseed: Overview

259

S Cloutier


265


265

TE Michaels

Contents


vii

274

RJ Fletcher

Lupin: Overview

280

DS Petterson

Amaranth: Overview

287


Beans: Overview

297

SK Sathe

Buckwheat: Overview

307


Chickpea: Overview

316


Pea: Overview

324


Peanuts: Overview

334


Quinoa: Overview

341



349


349

T Beta and C Isaak


359

JRN Taylor


367



374

H Corke and YZ Cai


383

MG Lindhauer


391

JA Fox and LL Ward


401



409



420



429


429

JH Skerritt


436

JH Skerritt


444

viii

Contents


451

JH Skerritt


457



1


1


1

G Bultosa


11

G Bultosa


17

AM Fehily


23


23



29



35



43

CM Rosell


50



57

JM Jones

Grains and Health

63



72

Cereal Allergens

72

AS Tatham


77

KJ Carpenter

Celiac Disease

83



91


Proteins

98


98



109

Contents


ix

115


Nitrogen Metabolism

123

CA Atkins


129



138



146



154


Carbohydrates

161


161


Starch: Chemistry

174

FL Stoddard

Starch: Synthesis

181



190



198



208

GB Fincher


224

L Ramsden


230

A Evans


236



241

D Dan Ramdath

Fats

248

Lipid Chemistry

248

L Day


257



268


268

HD Sapirstein


277

x

Contents


283


Mycotoxins

290



297


297

CW Wrigley


300



308



1

Wheat-Based Foods

1


1

CF Morris

Breads

8

TR Moore


19

KJ Quail


25

SP Cauvain


30

DE Ortiz


37

SP Cauvain


44



51



59


Noodles: Starch

64



72


Pasta

79

M Sissons

Tortillas

90


Non-wheat Foods

97


97

SO Serna-Saldivar

Contents


xi

110

S Lu


116



124

DK O’Toole


134

DK O’Toole


144


144



154



161



166

JS Bao


176


176

BJB Wood


183

JRN Taylor


193

GH Palmer


206

DK O’Toole


215


215

JL Black

Pet Foods

223

RCE Guy


228

L Munck


235


Biodiesel

245

Y Yan


251


251

CF Morris


257

xii

Contents


262



268

RCE Guy


274

JW Lawton


282

JN BeMiller


287

MS Izydorczyk

Wheat Processing

299


299


Wheat: Dry Milling

307



320


Oven Technologies

325

CE Walker


335



343

B Dobraszczyk

Frozen Dough

354


Refrigerated Dough

359



367

TS Palav


375



384



396

L Day


403



408



414

MN Riaz


423

Barley: Malting

423



434

Contents


xiii

446

L Pallas


453

JS Godber

Maize: Dry Milling

458


Maize: Wet Milling

467



482


482

C-Y Ma

Soybean: Processing

489

T Wang

Canola: Processing

497



1


1


1


Wheat: Marketing

9



16



25



29



42


42



50

RJ Henry


54



62

JJ Mayko


68

SA Barton


74



83

xiv

Contents


99

PC Annis


105



110

PC Annis


117

F Fleurat-Lessard


126

F Fleurat-Lessard


140


140

S Ceccarelli


144

L Munck


154



162

EC Leonard


168

SA Barton

Wheat: Agronomy

176


Barley: Agronomy

186


Maize: Agronomy

194

ED Nafziger


201

WL Rooney

Canola: Agronomy

207


Chickpea: Agronomy

216


Lentil: Agronomy

223


Lupin: Agronomy

231

RJ French

Field Pea: Agronomy

240

RJ French

Soybean: Agronomy

251

ED Nafziger


257



264

Contents


xv

273


Breeding of Grains

279


279



287


Maize: Breeding

296


Rice: Breeding

304



311


Lentil: Breeding

317


Lupin: Breeding

325



333


Genetics of Grains

343


343

L Privalle


350

RD Shillito


360

RJ Henry

Genome Mapping

365


Wheat Genetics

376

RA McIntosh


382

E Akhunov


388



393


Rice: Genetics

398

JS Bao and H Corke

Maize: Genetics

407

EA Lee


420

JS Li and SK Vasal


425

xvi

Contents


433



450



460


Glossary

467

Index

491




xvii

xviii

Preface


• Members of the Editorial Advisory Board; • Authors who have shared their special knowledge and experience; • Elsevier staff who have provided extensive advice and administrative services, especially Donna de Weerd-Wilson, Simon Holt and Rachel Gerlis (successive Supervisory Staff) and Gemma Tomalin, Gemma Taft, Joanne Williams and Mark Harper (successive Content Project Managers). The Editors Harold Corke, Jon Faubion, Koushik Seetharaman, and Colin Wrigley




xix

xx






xxi





xxiii










xxv




















xxvii

xxviii

Contributors















Contributors






xxix


xxx

Contributors















Contributors


xxxi








CK Madsen Aarhus University, Slagelse, Denmark RJ Mailer Australian Oils Research, Lambton, NSW, Australia JT Manful Africa Rice Center, Cotonou, Republic of Benin AG Marangoni University of Guelph, Guelph, ON, Canada DJ Mares University of Adelaide, Glen Osmond, SA, Australia L Marquart University of Minnesota, St. Paul, MN, USA; Grains for Health Foundation, St. Louis Park, MN, USA A Marti Universita` degli Studi di Milano, Milan, Italy

CS Moffat Curtin University, Bentley, WA, Australia ES Monyo ICRISAT, Nairobi, Kenya TR Moore AIB International, Manhattan, KS, USA MK Morell International Rice Research Institute, Los Banõs, Philippines CF Morris USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA LA Morrison Oregon State University, Corvallis, OR, USA

B Maschoff Grains for Health Foundation, St. Louis Park, MN, USA

WK Mousa University of Guelph, Guelph, ON, Canada; Mansoura University, Mansoura, Egypt

A Mathiowetz University of Minnesota, St. Paul, MN, USA; Rochester, MN, USA

K Mrva University of Adelaide, Glen Osmond, SA, Australia







xxxii

Contributors















Contributors


xxxiii










xxxiv

Contributors

















NUTRITION AND FOOD GRAINS Food Grains and Well-Being

Contents Functional Foods: Overview Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics Nutrition: Soy-Based Foods

Functional Foods: Overview G Bultosa, Botswana College of Agriculture, Gaborone, Botswana; Haramaya University, Dire Dawa, Ethiopia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

Functional food concepts/definitions. Bioactive compounds. Chronic diseases and functional foods. Gluten-free foods for celiac patients.

Learning Objectives

• • •

To achieve understanding on the concepts/definitions of functional foods. To achieve understanding of bioactive compounds used in functional foods, grain dietary sources, and potential effects on health. To impart processing principles on grain-based functional foods.

Introduction Humankind has progressed from a hunter-gather approach to food consumption to sedentary agriculture, progressing through the industrial revolution to our current knowledge-based society with advances in food processing. There is now enormous evidence about the limitations of consuming specific food component(s) on human health. The twenty-first century of humankind is marked by lifestyle changes resulting in the consumption of diets high in calories, fat, cholesterol, and sodium and inadequate intakes of calcium, iron, zinc, and dietary fibers and an increased resistance of pathogens to drugs. These factors, coupled with less physical exercise, aging populations, and more leisure time, have exposed much of the world’s population to cancers and various metabolic syndrome-related diseases, osteoporosis, dementia, etc. Some genetically predisposed individuals are also affected by diet-caused allergens. Encyclopedia of Food Grains, Second Edition

Consumption of an adequately balanced diet is a means of body structure formation, energy generation, and health. More than 2500 years ago, ‘Let foods be our medicine and medicine be our foods’ was stated by Hippocrates. This shows that consumption of diets with health-promoting effects is not new. But evidence on the relationship between dietary chemical component(s) and health is on evolutionary development as technology and human comprehension advance. Within such evolution, the concept of functional foods was started in the 1980s as Foods for Specified Health Use (FOSHU) in Japan. Foods, when consumed as a regular diet that supplies one or more bioactive components beyond basic nutrients and offer health-promoting effects, are today branded as functional foods. Functional foods are not prescribed drugs, dietary supplements, medical foods of therapeutic effects, traditional medicines, or nutraceuticals. Functional foods are distinct from macronutrient and micronutrient supplements targeted to achieve balanced diets and to treat nutrient deficiency syndromes. Functional foods thus comprise whole foods, fortified, enriched, or enhanced foods bearing bioactive compounds beyond macro- and micronutrients. Sources of bioactive ingredients include whole grains, flaxseed, sesame seed, psyllium seed husks, legumes (soybean and fenugreek), fruits, vegetables, herbs, spices, and fermented foods. The nature of bioactive compounds derived from such sources is variable even though similarities also exist. Those recognized bioactive compounds include phenolics; carotenoids; dietary fibers; b-glucans and inulin-type fructans; o-3 fatty acids; probiotics, prebiotics, and synbiotics; phytoestrogens; soy proteins; plant stanols and sterols; isothiocyanates; polyols; and some minerals and vitamins. In some respects, there is an overlap with food bioactives recognized to be functional ingredients and micronutrients such as in the case of vitamins and minerals. Most bioactive compounds present in functional foods are not necessarily essential for life but are recognized contributors toward good health.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00071-1

1

2

FOOD GRAINS AND WELL-BEING | Functional Foods: Overview

The World Health Organization (WHO) recommends to the public to move toward healthful diets. The functional-food expansion across the globe is enormous with the current market size estimated from 7 to 190 billion USD. The ever-increasing health-care costs and public awareness on roles of diet on health are contributing factors for such expansion. Functional-food development involves evaluation of the roles, safety, and consumer acceptance of bioactive compounds. For foods that have no history of consumption as regular diets (novel foods), the evaluation and regulatory requirements are rigorous and are required to be substantiated by scientific evidence for their efficacy and safety. As a result, even though a number of novel foods were developed in the past, their wider expansion was limited. Various grain-based functional foods are today on the market in the form of whole grain snacks, baked foods, extruded products, ready-to-eat breakfast cereals, fermented cereals, beverages, and gruels. Other products are: dietary fibers, inulintype fructans, b-glucans, carotenoids, o-3 fatty acids, plant sterols, and/or stanols-fortified products. There are also indigenous foods that are a heritage of a given community and their record as safe diet is lost in antiquity and yet most of them fulfill what is expected of functional foods. In this article, functional food definitions, distinction from related concepts, recognized bioactive ingredients, dietary sources, health benefits, and processing principles are described giving emphasis on grains. Read also functional foods: dietary fibers, prebiotics, probiotics, and synbiotics as these are not covered here.

Functional Food: Concepts and Definitions So far, there is no global consensus on the definition of functional foods. The Codex Alimentarius Commission only issued guidelines (CAC/GL 23–1997) on nutrition and health claims to be used through consultation with country policy. However, food regulatory agencies and various professional societies in different countries have described closely related concepts/ working definitions. Definitions offered from various sources for functional foods, features, and requirements on what constitute to be nutrition, health, and structure/function claims are listed under the Further Reading section. According to the ADA, “all foods are functional at some physiological level because they provide nutrients or other substances that furnish energy, sustain growth, or maintain/ repair vital processes. However, functional foods are recognized to provide additional health benefits that may reduce disease risks and/or promote optimal health. Functional foods include: (1) conventional foods or whole foods, (2) modified foods, (3) medical foods, and (4) foods for special dietary use.” According to Functional Food Science in Europe, “Functional foods are those satisfactorily demonstrated to affect beneficially one or more target functions in the body, beyond adequate nutritional effects, in a way that is relevant to either an improved state of health and well-being and/or reduction of risk of disease when consumed as part of normal food pattern.” Thus, functional foods include: a natural, unmodified food; a food in which one of the components has been enhanced through special growing conditions, breeding, or biotechnological means; a

food to which a component has been added to provide benefits; a food from which a component has been removed by technological or biotechnological means so that the food provides benefits not otherwise available; a food in which a component has been replaced by an alternative component with favorable properties; a food in which a component has been modified by enzymatic, chemical, or technological means to provide a benefit; a food in which the bioavailability of a component has been modified and combination of any of the above. In Japan, FOSHU refers to foods consumed as part of an ordinary diet, containing functional ingredients and exerting health or physiological effect. FOSHU requires that safety assessment, health functions, and claims must be approved by the Ministry of Health, Labour, and Welfare. Functional foods are also required to have three other fundamental features: (1) nutritional functions, (2) sensory functions, and (3) physiological functions such as regulation of biorhythms, the nervous system, the immune system, and body defense beyond nutrient functions. As of April 2011, in Japan, 955 products were approved as FOSHU. Based on extensive literature review and expert consultation, “A functional food is, or appears similar to be, a conventional food. It is part of a standard diet and is consumed on a regular basis, in normal quantities. It has proven health benefits that reduce the risk of specific chronic diseases or beneficially affect target functions beyond its basic nutritional functions.” Even though there are slight variations, the following are reflected on definitions given by different sources: (1) functional foods should be consumed as part of regular safe diet not as drugs; (2) they are required to bear functionally bioactive adequate ingredient(s) beyond basic nutrients; (3) diet with its functionally bioactive ingredient(s) should impact positive health in an individual by either (i) decreasing occurrences of disease(s), (ii) decreasing disease-causing factor(s), or (iii) promoting positive human physiological functions for optimal health such as by maintaining body homeostasis and/or through bolstering body immune systems; (4) they should improve quality of life; and (5) if there is no history of consumption as a regular diet, they must pass a strict regulatory evaluation process for their safety and for beneficial claim(s) declared substantiated with sound scientific evidence.

Other Concepts Related to Functional Foods Nutraceuticals These are distinct from functional foods and defined as a product isolated or purified from foods generally sold in medicinal forms (i.e., as pills, powder, syrups, or other medicinal forms) that have specific health benefits.

Dietary Supplements These are products other than tobacco intended to supplement diet, which contain one or more of the following dietary ingredients: vitamin, mineral, herb or other botanical, amino acid, concentrate, metabolite, constituent, extract, or combinations of these ingredients; they are ingested in pill, capsule, tablet, or liquid form; they are not represented for use as conventional food or as a sole item of diet.

FOOD GRAINS AND WELL-BEING | Functional Foods: Overview Novel Foods These are defined as raw foods or food materials with no history of safe use, for example, genetically modified foods; foods produced by algae, fungi, or microorganisms; foods isolated from plants and animals without a history of safe use; and foods that have been processed where the process has dramatically changed the food.

Bioavailability This refers to a fraction of a given compound and/or its metabolite that reaches systemic circulation and involves gastrointestinal digestion, absorption, metabolism, and tissue distribution. Bioavailability encompasses bioaccessibility and bioactivity.

Bioaccessibility This refers to the quantity or fraction of a bioactive that is released from a food matrix in the gastrointestinal tract and becomes available for absorption. It includes digestive transformations, absorption/assimilation into intestinal epithelium cells, and also the presystemic metabolism (both intestinal and hepatic).

Bioactivity This refers to a specific response, biomarker, or effect observed upon exposure to the bioactive substance. It includes tissue uptake and the subsequent physiological response.

Recognized Bioactive Compounds in Functional Food Phenolics (Polyphenolics) Phenolics are ubiquitous in plants and more than 8000 compounds are known. Dietary phenolics can be broadly divided into flavonoids (anthocyanins, flavonols, flavones, flavanones, isoflavones, flavan-3-ols, condensed tannins or proanthocyanidins, lignans, chalcones, coumarins, coumestans, and aurone) and nonflavonoids (simple phenols, phenolic acids (hydroxybenzoates and hydroxycinnamates), and stilbenes) (Figure 1). Flavonoids are the largest group and more than 6000 compounds have been identified. Hydrolyzable tannins are derivatives of gallic acids. They exert deleterious effects and may be found at trace levels in some edible foods. Flavonoids often exist as glycosides with sugar molecules attached often at position 3, sometimes at 5, 7, 40 , 30 , and 50 and hydroxyls at 40 , 5, and 7 on the flavonoid basic structure. Flavonoids without sugars are called aglycones. Phenolic acids and various flavonoids in whole grains and bran fractions (pericarp, aleurone layer, testa, and germ) are extensively documented. Bran is removed during cereal grain milling for production of refined flours. Among phenolic acids, ferulic acids are dominant (about 80% to 90%) in cereal grains. Sorghum is known to have unique 3deoxyanthocyanins. Other unique phenolics documented in grains are alkylresorcinols in rye, wheat, triticale, and barley, avenanthramides in oats, and g-oryzanols (ferulic cid esters of

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phytosterols and triterpene alcohols) in rice (Figure 2). Alkylresorcinol metabolites are currently studied for use as biomarkers of whole-grain intake. Bran also contains vitamins, phytosterols, minerals, proteins, lipids, carotenoids, tocols, and phytic acids. Consumption of grain foods along with their bran is beneficial due to the presence of various bioactive compounds. Functional roles documented for phenolics include: bolstering of cellular antioxidant defenses, protection from cardiovascular disease (CVD) risks, brain wellness, antineurodegenerative, antiulcer, anticarcinogenic, antimutagenic, anti-inflammatory, antimicrobial properties; and improvement of eye health and vision, muscle performance, and immune responses. Phenolics are generally partially bioavailable and their properties are influenced by their structures and solubility. Most soluble phenolics are found unbound, whereas insolubles are found bound to cell wall polysaccharides or proteins where they form stable complexes. Insoluble phenolics are not absorbed in the small intestine, but they are fermented by colon microbiota yielding largely ferulic acid followed by p-coumaric acid. Within cells, phenolics suppress reactiveoxygen (ROS) and nitrogen species (RNS) by donating hydrogen atoms or electron, quenching free radicals, and activating endogenous antioxidant enzymes. They also chelate metal prooxidants. Oxidative stress can happen when generation of oxidants exceeds the natural antioxidant systems. Oxidative stress causes damages to DNA, RNA, lipids, proteins, and carbohydrates and leads to different types of chronic diseases. In cereal grains, anti-oxidant potentials follow pigmented grains (tannin sorghums, black rice, brown and black sorghums, teff, millets, blue maize) > non-pigmented grains (white-sorghum, wheat, rice). Even though, phenolics are shown to suppress cancers in in vitro in cells and in vivo in animal models, studies in human intervention are less clear. The synergetic effects are believed to have a role. Phenolics are also used as antimicrobial food preservatives, food colorants, and flavor imparters. Tannins, despite having high antioxidant activity, are antinutritional and inhibit digestive enzymes and mineral absorptions.

Phytoestrogens Phytoestrogens are nonsteroidal plant compounds with structures and biological activities similar to steroid hormone estrogen, 17b-estradiol (Figure 3). Functional roles documented include: influence on growth and functioning of female and male reproductive tissues; maintenance of skeletal and central nervous systems; cardio-protection; suppression of colon, breast, and prostate cancers and skin aging; and relief from menopausal symptoms. At low concentration, they act like estrogens (agonists) and at high doses as blockers (antagonists). Phytoestrogens are potential endocrine disrupters and become cytotoxic at high dose. Groups of compounds recognized as phytoestrogens are lignans, isoflavones, coumestans, and stilbenes.

Lignans These are 18-carbon skeleton compounds composed of two phenylpropanoid units with various functional groups connected to benzene rings (Figure 4). Secoisolariciresinol,

4


OH

O

Derivatives of simple phenol

C

OH

Derivatives of hydroxybenzoic acid

Gallic acid: R1=H, R2=R3=R4=OH Phenol: R1=R2=R3=H R1 Gentisic acid: R1=R4=OH, R2=R3=H Catechol: R1=OH, R2=R3=H Salicylic acid: R1=OH, R2=R3=R4=H R3 Resorcinol: R1=R3=H, R2=OH R4 p-(OH) Benzoic acid: R =R =R =H, R =OH R2 1 2 4 3 Phloroglucinol: R1=H, R2=R3=OH Protocatechuic acid: R1=R4=H, R2=R3=OH R3 OH Syringic acid: R1=H, R2=R4=OCH3, R3=OH Derivatives of hydroxycinnamic acid C Vanillic acid: R1=R4=H, R3=OH, R2=OCH3 Cinnamic acid: R1=R2=R3=R4=H O o- Coumaric acid: R1=OH, R2=R3=R4=H m- Coumaric acid: R1=R3=R4=H, R2=OH R4 p- Coumaric acid: R1=R2=R4=H, R3=OH R3 Caffeic acid: R1=R2=H, R3=R4=OH Ferulic acid: R1=R2=H, R3= OH, R4 =OCH3 Sinapic acid: R1=H, R2=OCH3, R3=OH, R4=OCH3

R1 R2

R1 R2

Phenolic acids

Stilbene

2` 8 7 6

3`

1

O

4`

O

5`

2

O

O

6`

Flavan-4-o1

3

OH 5 4 Flavan-3-o1 Flavonoid basic structure OH

O

OH Flavonol

OH O

O OH +

O O

OH Anthocyanidin Isoflavone O OH

O

O Coumarin

O

O

O

Aurone

O

Chalcone

Flavanone

Flavone

O

O

HO

O

Lignan

O Coumestan

Basic structures of main class flavonoids and related structures (aurone, lignan) OH OH O

HO R

HO

+O

OH OH

OH OH HO

OH

O OH OH

OH Sorghum 3-deoxyanthocyanidins (Apigenindin, R=H and Luteolinidin, R=OH)

OH HO

OH

O OH OH

Figure 1 Structures of phenolics.

n:0 to many

Proanthocyanidins


R1

O

OH

R2

N H O C OH HO

R

R3

Avenanthramides (more than 35 forms are identified) Avenanthramide 2p, R1=R3=OH, R2=H Avenanthramide 2f, R1=R3=OH, R2=OCH3 Avenanthramide 2c, R1=R2=R3=OH

Alkylresorcinols (R = alkyl chain, odd carbon C15 to C27) O C OR

CH3O

O C O

CH3O

HO Gamma-oryzanol (ferulic acid esters, R = phytosterols or triterpene alcohols)

HO Gamma-oryzanol (campesteryl ferulate)

Figure 2 Structures of alkylresorcinols, avenanthramides, and gamma-oryzanols.

OH

OH

O OH

H

H H

H

H

H HO

HO 17 beta-Estradiol

H

H HO Estrone

Estriol

Figure 3 Structures of mammalian endogenous estrogens.

HO H CH3O

H CH2OH CH3O H CH2OH

HO

CH3O

O HO

O O

HO

O

H

O Sesamol

OH HO

O

Enterolactone

OH Figure 4 Structures of common lignans.

O H

O O

OH

H

O

O Sesamin

OH Enterodiol

O

O

H

H HO

O

OH O

OH

OH

O

O Sesamolin

O

OCH3

OH

O

O

Matairesinol

HO

OH OCH3 Secoisolariciresinol diglycoside

OH

OH H

OH

OH

OCH3 Secoisolariciresinol

CH2O H CH2O

HO

OH O

O

5

6


matairesinol, sesamin, and sesamolin are typical examples. When two glucose molecules are attached to the hydroxyl groups of the propanol chain of secoisolariciresinol, the compound is called secoisolariciresinol diglucoside (SDG). Lignans have higher antioxidant potential than vitamin E. Lignans are implicated to have potential use in hormone replacement therapy, to maintain good cognitive function in postmenopausal women, and to have anticancer activities (breast, prostate, colon, and skin cancers). They may contribute to the reduction of hypercholesterolemia, atherosclerosis, and diabetes. SDG is converted by bacteria in the human colons to mammalian lignans enterodiol and enterolactone, which are also antioxidants. Enterodiol and enterolactone are purported to reduce growth of cancer tumors, especially hormone-sensitive ones. Grain sources of lignans include oilseeds (flax, rapeseed, and sesame), whole-grain cereals (wheat, oats, rye, barley, and millets), and legumes (soybean). Flaxseed is the richest source of SDG and also contains other lignans (matairesinol, pinoresinol, lariciresinol, and isolariciresinol). Baked products and salad dressings fortified with flax and sesame seeds can be considered as functional foods rich in lignans

Isoflavones Isoflavones are often found as glycosides. Common isoflavones include daidzin, genistin, biochanin A, and formononetin (Figure 5). The glycosides are converted to aglycones by gut microflora. Among isoflavones, studies with genistein on breast cancer cell lines show cell proliferation at low doses and inhibition at high concentrations. Isoflavones are also recognized as mild antioxidants. Isoflavones are exclusively documented in leguminosae of which soybean is the richest source. Other sources are kidney, navy, pinto, red, small white, and mung beans and chickpeas, split peas, peanuts, sunflower seed, and walnut. Raw soybeans can contain 1.2–4.2 mg g1 dry weight isoflavones, while highprotein soy flour may contain up to 1.1–1.4 mg g1 dry weight. Diets rich in soybeans are implicated to improve cognitive abilities, prevent osteoporosis and various cancers, improve immune

R1

HO

O

O

R2

Geinstein Daidzin Biochanin A Formononetin

Isoflavones R1

R2

OH H OH H

OH OH OCH3 OCH3

function and maintenance of menopausal health in women, and also suppress CVD by lowering total cholesterol and LDL cholesterol and raising HDL in the blood vessels. However, the isoflavone content of soybean products varies with processing. Water- and alcohol-extracted soybean protein concentrate and soybean oils have insignificant levels of isoflavones.

Coumestans Coumestans are less abundant than isoflavones in human diets. They are known to have stronger estrogenic activity than isoflavones. Typical examples are coumestrol and 40 methoxycoumestrol (Figure 6). Coumestrol and genistein have higher binding affinities to ERb than other phytoestrogens. Coumestrol has been reported to inhibit bone resorption and stimulate bone mineralization by in vitro studies. Among grains, chief sources are soy sprouts, mung bean, and sunflower seeds.

Stilbenes Stilbenes are C6–C2–C6 compounds with –H,–OH, and –OCH3 as substituents on their two benzene (C6) rings (Figure 7). Stilbenes are known to be anticarcinogenic, antioxidative, antimutagenic, antitumor, and antiosteoporotic. Diets rich in resveratrol, which exists in both trans and cis isomers of the stilbene, are purported to prevent CVD, neurodegenerative disorders such as Parkinson’s and Alzheimer’s disease, and various cancers. Resveratrol has stronger antioxidant activity than propyl gallate, vanillin, phenol, 2,6-di-tert-butyl-p-hydroxytoluene (BHT), and a-tocopherol. Among grains, stilbenes are found in Fabaceae and Poaceae. Other good sources are peanuts, grape skins, and notably some sorghum varieties.

Phytosterols Phytosterols are natural components of human diets, are cholesterol-like and lipophilic, and comprise sterols and stanols. Stanols are hydrogenated products of sterols. Of more than 250 sterols and stanols known to exist in nature, only six (campesterol, campestanol, stigmasterol, sitosterol, sitostanol, and brassicasterol) are dominant in seed oils (rapeseed, soybean, corn, and sunflower oils), other grains (corn, rye,

R

HO R

R Stilbenes,R = H, OH or OCH3

Figure 5 Structures of isoflavones.

Figure 7 Structures of stilbenes.

OH

O

HO

O Coumestrol

O

Figure 6 Structures of coumestrol and 40 -methoxycoumestrol.

HO

O

O O 4`-M ethoxycoumestrol

OCH3

OH HO Resveratrol


18

R

R 20

12 11 1 2 5 3

4

18 11

1

(a)

4

H 13 14 8

5 3

21

22

24

25

27

Brassicasterol

Sitosterol/stanol

R20 17

9 10

26

27

12

2

25 24

Cholesterol/stanol

6 19

HO

21 20 22 23

21 20 22 23 24 25 26 27

7

Sterols

26 23

20

15

8

10

HO

16

17

13 H 14 9

19

7

7

16 21 20 22 23

25

26

21 20 22 23 24

24

15

25 26 27

27

Campesterol/stanol

Stigmasterol/stanol

6

Stanols

H

C O Sitosteryl stearate O H H3CO HO

CH

CHCOO Sitostanyl ferulate H

CH2OH O OH

O

HO O

Steryl glycoside (SG) OH H

C O CH 2 O OH HO (b)

O Acylated steryl glycoside (ASG)

OH

Figure 8 (a) Structure of plant stanols and plant sterols. (b) Conjugated structure of plant stanols and plant sterols.

wheat, barley, millets, rice, oats, and peanuts), and tree oils (Figure 8(a)). In plant tissues, sterols and stanols can exist as conjugates often esterified with fatty acids, oleic, or linoleic in five forms (Figure 8(b)). Plant sterols and stanols are known to attenuate absorption of low-density lipoprotein cholesterol (LDLC), a risk factor for premature atherosclerosis and CVD. Consumption of 2 g d1 of plant sterols or stanols as part of diet is known to lower LDLC plasma levels by about 10%. Consumption of low cholesterol and saturated fat along with high stanols or sterols can reduce LDL by 20%. Statin medication along with sterols or stanols is more effective in lowering LDL than doubling statin dose. Ranking toward blocking of cholesterol absorption is as follows: free-form stanols > stanol esters > free-form sterols > sterol esters due to structural and metabolic reaction differences toward gut microorganisms. The precise mechanisms of cholesterol-lowering effect by individual compounds in

humans remain largely unknown. Plant sterols/stanols are also implicated to have mild anti-inflammatory effects and are not toxic at physiological concentrations.

Carotenoids Carotenoids are lipid-soluble tetraterpene hydrophobic compounds, which impart yellow, orange, or red colors, and found associated with lipid portions in human cells. Carotenoids are divided into two groups (Figure 9): carotenes (hydrocarbons) and xanthophylls (oxygenated carotenes). Carotenoids bear conjugated double bonds in their structures, which are responsible for color formation and reactive oxidant stabilization. Carotenoids are antioxidants, and functional foods processed from carotenoids are helpful for prevention of CVD and cancers. b-carotene, a-carotene, and b-cryptoxanthin are provitamin A compounds.

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CH3

CH3

CH3

CH3 CH3

CH3

CH3

CH3

CH3

CH3

HO

CH3

CH3

CH3

H3C

HO

CH3

CH3 OH

H3C

CH3

H3C

CH3

O Retinyl palmitate

CH3

Vitamin A compounds

O CH3 H3C

H3C CH3 O

CH3

CH3

Examples of xanthophylls

OH

H3 C

CH3

CH3 CH3

CH3

H3C

Lutein*

CH3 H3C

H3C

CH3

Zeaxanthin*

CH3

CH3

CH3

H3C

CH3

CH3

H3C

CH3

Beta-cryptoxanthin

CH3

H3C

H3C

CH3

CH3

HO

CH3

H

CH3 H3C

Examples of carotenes

H3C

CH3

Alpha-carotene

CH3

H3 C

H3C

Beta-carotene

CH3

H3C

OH Retinoic acid CH3 H3C

CH3

CH3 O

CH3

H3C

CH3

CH3

H

OH Retinol

Retinal CH3

CH3

CH3

Figure 9 Structures of carotenoids (*not provitamin A).

Of more than 700 carotenoids identified in nature, 24 occur commonly in human foods and 40 have been detected in human milk, serum, and tissues. Among grains, chief sources are yellow maize, durum wheat, einkorn, and golden rice. Carotenoid contents can vary depending on varieties, cultivation conditions, geographic locations, part of plant utilized, maturity stage, food processing, and storage conditions used. Heating, cooking, and mechanical disruption and the presence of fats/oils can enhance bioavailability of carotenoids. Carotenoid activities can be destroyed by isomerization and oxidative reactions. Lutein and zeaxanthin are not synthesized by humans. They can be supplied from grains (yellow maize, durum wheat, golden rice, and einkorn), vegetables (basil, parsley, spinach, kale, leek, and red pepper), yellow egg yolks, and human milk. Along with their metabolite meso-zeaxanthin, both are

protective against age-related macular degeneration and cataracts, a leading cause of eye blindness. Cereal-based lutein and zeaxanthin-containing functional foods processed from yellow maize, durum wheat, golden rice, einkorn, and maize bran include high-lutein bread, high-lutein cookies, high-lutein muffins, corn tortilla, corn chips, and extruded products.

Omega (v)-3 Fatty Acids Omega-3 fatty acids are long-chain polyunsaturated fatty acids (PUFA) (C18-C22) commonly designated as o-3 fatty acids (Figure 10). The o-3 and o-6 fatty acids are essential nutrients. Alpha-linolenic acids (ALA, o-3) derived from plant sources are precursors for physiologically important longer-chain


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O ALA (C18:3Δ 9,12,15)

EPA (C20:5Δ 5,8,11,14,17) DHA (C22:6Δ 4,7,10,13,16,19)

C OH O C OH O C OH

Figure 10 Omega-3 fatty acids: ALA, EPA, and DHA.

PUFAs: eicosapentaenoic (EPA, o-3) and docosahexaenoic acid (DHA, o-3). Omega-3 fatty acids are components of cell membranes. Their documented health benefits include suppressions of CVD, cancer, type 2 diabetes, depression and stress, inflammatory diseases, and (6) Alzheimer’s disease. They are also beneficial in infant nutrition for normal brain, eye, and mammalian nervous system development and function. Omega-3 fatty acids are available as supplements from pharmaceuticals. However, consumers prefer o-3 fatty acids from diets. In this respect, there is high opportunity for o-3 fatty acid-containing functional foods. The main source of ALA is flaxseed. Other sources are canola, soybean oils, and walnuts. In flaxseed, bioavailability of ALA is as follows: oil > milled > whole flaxseed. Despite fish oil being a major source of EPA and DHA, it is sensitive to autoxidation, and there is also a possibility for methyl mercury toxicity since fish has potential for contamination with this toxin. Where consumption of fish oil is limited and methyl mercury toxicity is a possibility, EPA and DHA are required to be supplied from ALA even though conversion of ALA to EPA and DHA is known to be inefficient. Baked foods like bread and injera and various cereal grain snacks processed by incorporating flaxseed oils and/or milled flaxseed flours are an alternative way of supplying o-3 fatty acids.

Gluten-Free Foods In some genetically predisposed individuals, gluten proteins from wheat, rye, barley, and triticale when ingested will lead to celiac disease (CD). Oats are also not considered free, because of potential contamination and the possibility that some people who are intolerant to gluten are not immune to it. CD involves interactions between genetic susceptibility (HLADQ2 and HLA-DQ8 alleles), gluten proteins, and an immunologic response that causes small intestinal mucosal damage characterized by complete loss of absorptive villi to maldigestion and malabsorption of nutrients. Such effects lead to chronic diseases like skin lesions, anemia, diarrhea, weight loss, osteoporosis, fatigue, infertility, and cancer. About 1% of the world population is estimated to be gluten-intolerant. There is no drug for CD, and the remedy is a complete adherence to a gluten-free diet (GFD). The Codex Alimentarius Commission and FDA have set standards for GFD to be <20 mg kg1 gluten. Gluten proteins are vital for production of aerated baked products to which consumers are attracted. The use of baked products from gluten-free cereal grains (teff, maize, rice, sorghum, and the millets) particularly those processed from whole grains is a remedy for CD. Teff grain is one

such best candidate because it is always consumed as whole grain often fermented as injera with insignificant antinutrients in it and in many respects it supplies better nutrients for celiac patients. Other approaches to gluten-free bread quality improvements are the use of gluten-free flours and starches, incorporation of nutritional ingredients, and use of structure modifier additives and processing technologies that will change the allergenic glutens. Other bioactive compounds to be noted include tocols (tocopherols and tocotrienols) from cereal germ and aleurone layers; betaine and choline from wheat, barley and rye germ, and brans; and benzoxazinoids from whole-grain wheat and rye. Some bioactive compounds known for their antinutritional effects tend to portray beneficial effects under specific conditions. They include glucosinolates from rapeseed, phytic acids from germ and aleurone layers of grains, and lectins (hemagglutinins) from legumes and whole cereal grains.

Conclusions Opportunities for grain-based functional foods are high because grains are sources of many bioactive compounds that are located in specific anatomical structures. However, bioavailability can be influenced by many factors including forms of existence, processing technology, and food matrices that prevail during consumption. Functional foods are recognized to be consumed as varied regular diets. However, the absence of a definition that has received global consensus potentially poses various risks such as inaccurate health claims, adverse reactions, poor quality control during manufacturing, allergic reactions, and carcinogenicity. Novel foods in particular may pose unprecedented risks because they do not have a long history as diets to populations of different genetic background. A distinction between novel and functional foods may help to reduce such effects. Misuse of functional foods can lead to adverse effects such as anti-nutritional, thyroid toxicity, drug interactions, allergic reactions and geno-toxicity/ carcinogenicity. A given diet is believed to bear more than 25 000 bioactive constituents. Minimum dietary intake that would lead to desirable health effect and maximum intake to avoid adverse effects are yet not available for most bioactive compounds. A distinction is yet to be clearly established for most bioactive compounds whether a desirable outcome is caused by a single compound or by synergic effects. Since they are consumed as regular varied diets for health promotion, designing functional foods for synergic effects of bioactive compounds seems beneficial. While designing for an optimum supply for those health effects is established, caution is also required not to

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affect other components used to be served in a given regular diet. With an accurate definition in place, functional foods can be better regulated to improve health and well-being.

Diseases: Celiac Disease; Cereal Allergens; The Gluten-Free Diet; The Basics: Grain: Morphology of Internal Structure.


Further Reading

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Bagchi D (ed.) (2014) Nutraceutical and Functional Food Regulations in the United States and Around the World. NW, USA: Elsevier Inc. Capriles VD and Areâs JAG (2014) Novel approaches in gluten-free bread making: interface between food science, nutrition, and health. Comp. Rev. Food Sci. Food Saf. 13: 871–890. Doyon M and Labrecque J (2008) Functional foods: a conceptual definition. Br. Food J. 110(11): 1133–1149. Dykes L and Rooney LW (2007) Phenolic compounds in cereal grains and their health benefits. Cereal Foods World 52: 105–111. Fraga CG (ed.) (2010) Plant Phenolics and Human Health: Biochemistry, Nutrition, and Pharmacology. Hoboken, NJ, USA: John Wiley & Sons, Inc. Gogus U and Smith C (2010) n-3 Omega fatty acids: a review of current knowledge. Int. J. Food Sci. Technol. 45: 417–436. Gylling H, Plat J, Turley S, Ginsberg HN, Ellega˚rd L, Jessup W, Jones PJ, Lu¨tjohann D, Maerz W, Masana L, Silbernagel G, Staels B, Boreń J, Catapano AL, De Backer G, Deanfield J, Descamps OS, Kovanen PT, Riccardi G, Tokgo¨zoglu L, and Chapman MJ (2014) Plant sterols and plant stanols in the management of dyslipidaemia and prevention of cardiovascular disease. Atherosclerosis 232: 346–360. Hasler CM and Brown AC (2009) Position of the American dietetic association: functional foods. J. Am. Diet. Assoc. 109: 735–746. Howlett J (2008) Functional Foods: From Science to Health and Claims. Belgium: ILSI Europe. Malla S, Hobbs J, and Sogah EK, (2013) Functional Foods and Natural Health Products Regulations in Canada and Around the World: Nutrition Labels and Health Claims. Report Prepared for the Canadian Agricultural Innovation and Regulation Network (CAIRN), Canada Mohamed S (2014) Functional foods against metabolic syndrome (obesity, diabetes, hypertension and dyslipidemia) and cardiovascular disease. Trend Food Sci. Technol. 35: 114–128. Ndolo VU and Beta T (2014) Comparative studies on composition and distribution of phenolic acids in cereal grain botanical fractions. Cereal Chem. 91(5): 522–530. Peterson J, Dwyer J, Adlercreutz H, Scalbert A, Jacques P, and McCullough MJ (2010) Dietary lignans: physiology and potential for cardiovascular disease risk reduction. Nutr. Rev. 68(10): 571–603. Sajilata MG, Singhal RS, and Kamat MY (2008) The carotenoid pigment zeaxanthin—a review. Comp. Rev. Food Sci. Food Saf. 7: 29–49. Taylor JRN, Belton PS, Beta T, and Duodu KG (2014) Review: Increasing the utilization of sorghum, millets and pseudocereals: Developments in the science of their phenolic phytochemicals, biofortification and protein functionality. J. Cereal Sci. 59: 257–275.

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Provide three features that you think useful to describe functional foods. Describe how functional foods are different from dietary supplements, prescribed drugs, traditional medicines, and nutraceuticals. List various grain-based bioactive compounds. Provide factors that may influence bioaccessibility, bioavailability, and bioactivity of bioactive compounds. List potential safe diets for celiac patients. Name indigenous foods consumed in your communities believed to have health-promoting effects.


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Explore the possibility of extending the earlier lists of bioactive compounds in various grains. What metabolites are produced from the partial degradation of some of the bioactives listed? Find out if these are still active. Investigate what innovative processing technologies might provide optimum utilization of grain bioactive compounds. Could these technologies also ensure that food safety issues are addressed because bioactive compounds are located in unique grain anatomical parts? Research the possibilities in plant breeding to enhance the presence and availability of bioactives. Investigate the possible exploitation of indigenous foods relevant to your region. Their consumption as safe diets has been known for ages, so their potential to grow in the functional foods spectrum should be considerable.

See also: Appendix 3: Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease; Bioactives and Toxins: Bioactives: Antioxidants; Bioactive Compounds in Wheat Bran; The Antinutritional Components of Grains; Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Grains other than Cereals: Non-starch Polysaccharides; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Fortification of Grain-Based Foods; Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Grains and Health; Labelling of Grain-Based Foods; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Food Grains: Intolerance, Allergy and

Relevant Websites http://www.biomedcentral.com/content/supplementary/1475-2891-9-3-S1.PDF – University of Oslo. http://www.glnc.org.au/wp-content/themes/glnctheme/images/home.png http://www.google.co.bw/url? http://www.nutritionj.com/content/9/1/3.

Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics G Bultosa, Botswana College of Agriculture, Gaborone, Botswana; Haramaya University, Dire Dawa, Ethiopia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Dietary fiber (DF) and whole grain functional foods. Prebiotic, probiotic, and synbiotic functional foods. Metabolic syndrome-related diseases and cancers. Lactose intolerance.

suppressing various diseases including colon cancers, allergy, asthma, celiac disease, HIV infection, inflammatory bowel diseases, hypertension, gastrointestinal pathogen infections, peptic ulcer, diarrhea, obesity, necrotizing enterocolitis, rheumatoid arthritis, and liver diseases. In this article, the nature and sources of DFs, prebiotics, probiotics, and synbiotics for functional foods are described with emphasis on grains.

Learning Objectives

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To achieve understanding of the definitions of DFs, whole grain foods, prebiotics, probiotics, and synbiotics. To achieve understanding of DF and prebiotic grain sources. To impart principles of DFs, prebiotics, probiotics, and synbiotics with respect to the processing of functional foods. To explain linkages of the intake of DFs, prebiotics, probiotics, and synbiotics to health.

Introduction Functional foods processed from DFs are linked to various health benefits. Soluble fibers and b-glucans in particular are known to modulate hyperlipidemia, hyperinsulinemia, hyperglycemia, and obesity, which are risk factors for chronic diseases including cardiovascular diseases (CVDs), diabetes mellitus, and cancers. Soluble fibers are rapidly fermented by gut microbiota. Adequate intake (AI) of insoluble fibers is also linked to the reduction of colon cancers and improved gastrointestinal health (GIH), reduced CVD, and obesity. Cereal grain fibers and legume cotyledons are included in bread, extruded products, cakes, cookies, and fermented and other ready-to-eat breakfast cereal (RTE) products. Consumption of whole grain foods is encouraged for AI of DF. Healthpromoting effects of DF are imparted by nonstarch carbohydrates, resistant starches, and closely associated/attached compounds. Those DFs that selectively promote growth and/ or activities of probiotics and promote host health are prebiotics. Arabinoxylans, fructans, inulin, resistant starches, bglucans, and a-galactooligosaccharides are fermented by probiotics to short-chain fatty acids (SCFAs): butyrate, propionate, and acetate that are absorbed in the colon to furnish additional energy for the host. Prebiotics are also known to improve the absorption of calcium and magnesium and to suppress colon cancers and absorption of triglycerides and cholesterol. Cellulose and water-insoluble arabinoxylans are major contributors to laxative effects and fecal bulking. Barley, wheat, rye, oats, triticale, maize, einkorn, chickpea, and lentils are notable sources of prebiotics. Intake of prebiotics is also achieved through consumption of whole grains like teff, millets, sorghums, and brown rice. Dietary intake of probiotic bacteria mainly from the genera of Lactobacillus and Bifidobacterium is linked to improved immune capacity and GI health and to


Dietary Fibers and Whole Grains Dietary Fibers DFs are a structurally diverse group of compounds. Various regulatory bodies and professional societies – American Association of Cereal Chemists International (AACCI), Institute of Medicine (IOM), Food Standards Australia and New Zealand (FSANZ), FAO/WHO Codex Alimentarius Commission, European Food Safety Authority, and Health Canada – have offered definitions for DF primarily based on the physiological roles and analytical methods used to isolate and quantify them. According to Codex, DFs are carbohydrate polymers with 10 or more monomeric units (decision on whether to include carbohydrates of 3–9 monomeric units should be left up to national authorities), which are not hydrolyzed by the endogenous enzymes in the small intestine of humans and comprise the following: (1) Edible carbohydrate polymers naturally occurring in the food as consumed. When derived from a plant origin, DF may include fractions of lignin and/or other compounds – protein fractions, phenolic compounds, waxes, saponins, phytates, cutin, vitamins, phytosterols, minerals, etc. – when such compounds are associated with the polysaccharides in the plant cell walls and extracted together. (2) Carbohydrate polymers, which have been obtained from food raw materials by physical, enzymatic, or chemical means and which have been shown to have a beneficial physiological effect to health as demonstrated by generally accepted scientific evidence to competent authorities. (3) Synthetic carbohydrate polymers, which have been shown to have a beneficial physiological effect to health as demonstrated by generally accepted scientific evidence to competent authorities. The Codex definition is expected to be used in all jurisdictions. Currently, there is wider consensus that the AACCI definition is reconciling with Codex definition. AACCI defines DF as edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. DFs include polysaccharides, oligosaccharides, lignin, and associated plant substances. DFs promote beneficial physiological effects including laxation and/or blood cholesterol and glucose attenuations. DFs thus comprise the following:

http://dx.doi.org/10.1016/B978-0-12-394437-5.00245-X

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FOOD GRAINS AND WELL-BEING | Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics

i. Nonstarch polysaccharides and resistant oligosaccharides: cellulose, b-glucans, hemicellulose (arabinoxylans and arabinogalactans), polyfructoses (inulin and oligofructans), galactooligosaccharides, gums, mucilages, and pectins ii. Analogous carbohydrates (indigestible dextrins/resistant maltodextrins from corn and other sources and resistant potato dextrins), synthesized carbohydrate compounds (polydextrose, methylcellulose, and hydroxypropyl methylcellulose), and resistant starches iii. Lignins iv. Substances associated with the nonstarch polysaccharides and lignin complex in plants (waxes, phytates, cutins, saponins, suberin, polyphenols, tannins, vitamins, minerals, alkylresorcinols, carotenoids, betaine, etc.) The classification of DFs as soluble (gums, oligosaccharides, pectins, water-soluble arabinoxylans, b-glucans, galactomannans, psyllium fibers, and alginates) and insoluble (cellulose, lignins, and water-insoluble arabinoxylans) also continues to be in use. DFs for human nutrition are largely derived from cereal grains 44%, vegetables 21%, fruits 13%, and legumes 10%. The outer pericarp of cereal grains, endosperm cell walls, seed coat and cotyledons of legumes, psyllium husks, and fruit and vegetable skins are rich sources of DF. Diets rich in bran (pericarp, aleurone layer, and testa) and germ are known to have high antioxidant activities than diets based on refined white flours largely due to associated DF–phenolics, tocols, and carotenoid antioxidants. Functional foods containing DFs are currently widely available in the form of breads; extruded products like pasta, cakes, and cookies; and fermented and other RTE products. Although incorporation of DF to some levels has produced products comparable to those processed from refined flours, increased DF contents have been associated with reduced consumer acceptance (color, texture, and taste). Currently, improvements being researched include the use of enzymes and other physicochemical means to modify fiber structures and incorporation of fibers from fruits and vegetable skins. The beneficial physiological effects conferred by AI of DF include attenuation of blood cholesterol and blood sugars, suppression of CVD diseases (coronary heart disease, stroke, and hypertension), weight control, improved insulin sensitivity and suppression of type 2 diabetes mellitus, improvement of GIH, improved laxation, suppression of cancers such as colon and breast cancers, improved immunity, and contribution to the overall longevity. The physiological roles of DF can vary depending on nature of the compound. Properties of DF such as viscosity, molecular weight, molecular size, solubility, water-holding capacity, and fermentation characteristics by gut microbiota are known to play a role in the physiological effects of DF-based functional foods. Increased intake of soluble fibers is known to suppress hyperglycemia and to improve insulin sensitivity in nondiabetic and diabetic individuals. Cardiovascular protective roles of DF are imparted by attenuation of blood cholesterol levels specifically by interfering and limiting cholesterol fractions transported by LDL. The viscous characteristics of fiber are implicated to have a dominant role in this regard. Energy load reduction and weight control are imparted by (1) displacing available energy and nutrients from the diet; (2) increasing chewing, limiting intake, and promoting

secretion of saliva and gastric juice resulting in an expansion of the stomach and increased satiety; and (3) reducing absorption efficiency of the small intestine. Diets with high DF contents are known to have slow nutrient digestion and gastric emptying rates. This action leads toward attenuation of blood glucose and helps in the control of type 2 diabetes mellitus. Some DFs are fermented (prebiotic) completely or partially by the symbiotic microorganisms of the large intestine to SCFAlike butyrate, which is the preferred energy source for mucosa cells. Inulin and oligofructans are not used by potential pathogenic bacteria but are the preferred substrate for beneficial Bifidobacteria and thus help to maintain and restore the balance of healthful gut microbiota. Beta-glucans and the presence of magnesium in whole grains and/or bran-rich DF are known to lead to improved insulin sensitivity to suppress type 2 diabetes and other metabolic syndrome diseases. Psyllium (or ispaghula; Plantago ispaghula or Plantago ovata) fibers and oat and barley b-glucans are used in functional foods targeted at lower cholesterol and blood sugars for improved cardiovascular health, control of type 2 diabetes, and weight reduction and maintenance. Cereal grain DFs are generally recognized to be more potent than fruits and vegetable fibers in the many beneficial physiological roles of the DF functional foods. Excessive DF intake through functional foods or other regular diets may lead to deleterious effects because it contributes to reduced absorption of some vitamins, minerals, proteins, and energy. It may also lead to diarrhea, flatulence, bloating, and abdominal discomfort. Children less than 1 year old and older people, in particular, are advised not to consume higher than recommended DF levels. The recommended AI for total DF is 19–25 g day 1 for children aged 1–8 years, 31–38 g day 1 for boys aged 9–18 years, 38–30 g day 1 for males greater than 19 years old, 26 g day 1 for girls aged 9–13 years, 25–21 g day 1 for females greater than 19 years old, 28 g day 1 at pregnancy, and 29 g day 1 during lactation.

Whole Grains Whole grains are defined by AACCI in 1999 as “consisting of the intact, ground, cracked or flaked caryopsis, whose principal anatomical components – the starchy endosperm, germ, and bran – are present in the same relative proportions as they exist in the intact caryopsis.” Thus, whole grains are good sources of various nutrients, starch, proteins, lipids, DF, vitamins (thiamine, riboflavin, niacin, pantothenic acid, vitamin B6, folate, and vitamin E), minerals, and phytochemicals such as various phenolic compounds, phytosterols, tocols, lignans, and carotenoids. AI of whole grain foods has been associated with GIH and reduced risk of various metabolic syndrome-related diseases (obesity, diabetes, hypertension, and dyslipidemia) and various cancers. For example, consumption of two to three servings per day (about 48 g) of whole grains is preventive of the risks of CVD, type 2 diabetes mellitus, overweight, and obesity. Whole grain intake results in greater intake of diverse nutrients. Although whole grain has been defined, it remains challenging for researchers, industry, regulatory authorities, and consumers to clearly identify what constitutes whole grain foods. Following a review of evidence from various epidemiological, interventions, animals, and human clinical studies on relationship of whole grain intake and the many benefits

FOOD GRAINS AND WELL-BEING | Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics on health and wellness, an expert panel of whole grain working committee in 2014 has recommended that ‘8 g of whole grain per 30 g serving (27 g per 100 g), without a fiber requirement, be considered a minimum content of whole grains that is nutritionally meaningful and that a food providing at least 8 g of whole grains per 30 g serving be defined as a wholegrain food.’ This definition also reconciles with the one offered by AACCI that ‘whole grain food product must contain 8 g or more of whole grain per 30 g of product.’ Sources of whole grain functional foods include whole wheat and rye flours, barley and whole barley flour, whole grain maize meal, grits and popcorn, teff, sorghum, oat groats, whole grain millets, brown rice, quinoa, amaranth, buckwheat, and wild rice. Thus, whole grain foods (whole grain snacks and extruded, fermented, and baked foods) can be regarded as functional foods rich in DF and phytochemicals. Many African traditional diets and other indigenous foods around the globe are based on whole grains being consumed as boiled, cooked, fermented, and baked as in injera from grain teff in Ethiopia. Such diets can be described as functional foods and they have been serving communities since folklore.

Probiotics, Prebiotics, and Synbiotics Human organs particularly the gastrointestinal tract (GIT) are known to be host for vast numbers of microbes ( 1015 bacterial cells), which are designated as microbiota, microflora, or normal flora. These microbiota are today extensively exploited for GIT health and beyond under probiotic and synbiotic functional foods. Consumption of such diets is actually not new because a range of naturally occurring prebiotics and probiotics primarily from the genera Lactobacillus, Bifidobacterium, and Saccharomyces are consumed throughout the world in the indigenous fermented foods since folklore. Probiotics and prebiotics are also available commercially in the form of dietary supplements and clinical therapeutics to be delivered orally or nonorally.

Probiotics The word probiotics is derived from the Greek term ‘pro bios’ meaning ‘for life.’ The widely accepted definition of probiotics

Table 1

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given by FAO/WHO (2001) as “Live microorganisms which when administered in adequate amounts confer a health benefits on the host” was recommended in August 2014 by International Scientific Association for Probiotics and Prebiotics (ISAPP) to be used with minor rewording as “Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” Major bacterial strains commonly used in probiotics are lactic acid bacteria (LAB) from the genera of Lactobacillus and Bifidobacterium (Table 1). Other LAB reported are from Pediococcus, Lactococcus, Leuconostoc, Streptococcus, and Weissella. Certain yeast and fungal strains are also recognized for probiotic effects. The ISAPP restricted the term probiotic to be used only on products that deliver live, safe microorganisms with suitable viable counts ( 106 colonyforming units per gram of a product) of well-defined strains with a reasonable expectation of delivering benefits for wellbeing of the host. Ability to survive, proliferate, and colonize the gut is also a criterion although some cultures lack such ability like traditional yogurt starter cultures (S. salivarius subsp. thermophilus and L. delbrueckii subsp. bulgaricus), which are recognized as probiotics because of their production of b-galactosidase that helps lactose digestion in maldigesters. ISAPP has divided live cultures into two: (1) probiotic (nonoral probiotic foods, probiotic drugs, probiotic medical foods, nonoral probiotics, defined microbial consortia, probiotic dietary supplement, probiotic infant formula, and probiotic animal feed) and (2) not probiotic (fermented foods with undefined microbial content and undefined consortia including fecal microbiota transplant). The various beneficial functions of probiotics are (1) structural and histological such as the development of healthy structure and morphology of the gut; (2) metabolic such as in the synthesis of B vitamins, vitamin K, amino acids, SCFA, antioxidants, and bacteriocins and in the biotransformation of bile, which help to modulate glucose and cholesterol homeostasis; and (3) protective from colonization by pathogens such as through production of antimicrobial compounds, by competing for nutrients and attachment sites on gut lining. The various health benefits documented for probiotic diets include suppression of (1) obesity and type 2 diabetes through modulating glucose metabolism; (2) allergic inflammation and atopic dermatitis; (3) liver disease; (4) hypercholesterolemia and CVD

Microbial species used as probiotics

Species

Strain

Lactobacilli

L. acidophilus, L. bulgaricus, L. casei, L. delbrueckii ssp. bulgaricus, L. fermentum, L. johnsonii, L. crispatus, L. salivarius, L. bifidus, L. reuteri, L. plantarum, L. helveticus, L. casei subsp. rhamnosus, L. gallinarum, L. brevis, L. gasseri, L. cellobiosus, L. vitulinus, L. collinoides, L. cremoris, L. ruminis, L. dextranicum, L. lactis, L. rhamnosus, L. curvatus, L. faecium, L. paracasei B. bifidum, B. adolescentis, B. brevis, B. longum, B. animalis, B. infantis, B. thermophilum, B. breve, B. essencis, and B. lactis B. coagulans (GanedenBC30), B. lactis DR10, B. licheniformis, B. subtilis R0179, B. subtilis (natto) OUV23481 P. acidilactici, P. pentosaceus, P. halophilus L. lactis subspp. lactis and cremoris L. mesenteroides subsp. dextranium, paramesenteroides, or lactis S. diacetilactis, S. cremoris, S. lactis, salivarius subsp. thermophilus, S. faecium, S. equinus W. cibaria and confusa Saccharomyces cerevisiae, S. cerevisiae var. boulardii Aspergillus oryzae, Scytalidium acidophilum

Bifidobacteria Bacillus Pediococcus Lactococcus Leuconostoc Streptococcus Weissella Yeast Fungi

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through modulating cholesterol, LDL-cholesterol, and triglyceride metabolisms; (5) various cancers such as colon, bladder, and cervical cancers; (6) inflammatory bowel disease; (7) diarrhea; (8) lactose intolerance; (9) renal diseases; (10) hormonal immune response failure; and (11) ingestion of toxic compounds. Although probiotics containing dairy products are dominant, probiotic-fermented cereals and soy beverages, flakes, baked goods, soups, and traditional fermented cereals are also available. Microencapsulation of probiotics is currently being researched to enable incorporation into various grain products. Fermented grain products containing probiotics have the following advantages: the possibility of grain components to be prebiotic sources, multimedia characteristics of the grain products, and their lactose- and cholesterol-free natures.

Prebiotics The current consensus definition given is “A dietary prebiotic is a selectively fermented ingredient that results in specific changes, in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health.” Compounds recognized as prebiotics include inulin-type fructans (inulin fructooligosaccharides, and oligofructose), lactulose, galactooligosaccharides, isomaltooligosaccharides, lactosucrose, xylooligosaccharides, glucooligosaccharides, sugar alcohols, resistant starches, and modified starches. Resistant starches, fructans, arabinoxylans, arabinoxylan oligosaccharides, and b-glucans are reported in various grains such as in wheat, rye, maize, barley, oat, and maize. Prebiotic food products are available in the market as beverages (soy milk, smoothies, and juice), bakery products (snack bars, biscuits/cookies, waffles, and pancakes), breakfast cereal (extruded cereals and instant oatmeal), confectionery (chocolate and gummy candy), dairy products (yogurt, ice cream, and frozen yogurt), desserts (pudding and jelly/jello), fruit products (fruit preparations), and infant and toddler foods and in specialty liquid nutrient supplements. Inulintype fructans are popular prebiotics. Even though fructans are present in grains, good sources are from Jerusalem artichoke, chicory, garlic, and onion. Prebiotics are fermented to SCFA acetate, propionate, and butyrate. Other bacterial end products include lactate, ethanol, succinate, formate, valerate, caproate, isobutyrate, 2-methyl butyrate, and isovalerate. Bacterial fermentation takes place in the cecum and colon, where SCFAs are absorbed, stimulating absorption of vitamins, water, and minerals (calcium and magnesium). The SCFAs have been known to have a protective effect on the intestinal epithelium. The colonic bacteria prefer butyrate as their sole source of energy and are also metabolized by the colonic epithelium where it regulates cell growth and differentiation. Butyrate is known to induce secretion of mucin, antimicrobial peptides, and other factors, which reinforces the defense barrier in the colon. Butyrate limitation leads to inflammation characteristics of the ulcerative colitis. Acetate and propionate are found in portal blood and are eventually metabolized by the liver (propionate) or peripheral tissues, particularly muscle (acetate). Acetate and propionate might also play a role as modulators of glucose metabolism. Absorption of such SCFAs is implicated to result in low glycemic responses and to ameliorate insulin sensitivity.

Synbiotics are a combination of probiotics and prebiotics when administered together. There is synergy between probiotics and prebiotics resulting in more effectiveness than using either one because it favors competitive advantage for probiotic rapid adaptation in the GIT. Synbiotics are currently available as combinations of bifidobacteria and fructo-oligosaccharides (FOS), lactobacillus GG and inulins; bifidobacteria, lactobacilli and FOS or inulins.

Functional Foods for Lactose Intolerance Lactose intolerance is the inability to utilize lactose from milk because of limited lactase enzyme production in the small intestine in some individuals. Infants can produce adequate lactase enabling them to utilize lactose of milk, which is the sole carbon source for the newborn. The ability to generate lactase enzymes diminishes with age. For individuals with limited lactase production, lactose will be transferred to the large intestine intact where it is hydrolyzed and fermented. The hydrolyzed products cause secretion of water into the intestinal lumen to balance the osmolarity pressures. This accumulation of water produces dehydration and electrolyte imbalance on the systemic side and watery stools on the intraintestinal sides. The fermentation of the sugar adds gaseous components (carbon dioxide, hydrogen, and methane) leading to bloating, cramping, and flatulence. The limited calcium supply through inadequate milk intake may lead to osteoporosis. Probiotics containing Lactobacillus strains are known to recover the lactose tolerance. The various nondairy probiotic functional foods and drinks developed include the following: (1) Soy-based (nonfermented soy-based frozen desserts, fermented soymilk drink, and soy-based stirred yogurt-like drinks). (2) Cereal-based puddings; rice-based yogurt; oat-based drink; oat-based products; yosa, an oat-bran pudding; mahewu, a fermented maize beverage; maize-based beverage; probiotic beverages fermented from wheat, rye, millet, maize, teff, sorghum, and other cereals; malt-based drinks; boza fermented from cereals, maize, and sorghum; millet malt-fermented probiotic beverages; and millet or sorghum flour-fermented probiotic beverage. (3) Fruit- and vegetable-based drinks; fermented banana pulp and fermented banana juice; beet-based drink; tomatobased drink; many dried fruits; green coconut water; peanut milk; cranberry, pineapple, and orange juices; ginger juice; grape and passion fruit juices; cabbage juice; carrot juice; noni juice; onion puree; probiotic banana puree; nonfermented fruit juice beverages; and blackcurrant juice. (4) Others (starch-saccharified probiotic drink, probiotic cassava-flour product, meat products, and dosa (rice and Bengal gram)).

Conclusions Various DFs are available from whole grains, which are also sources of other nutrients and phytochemicals. The healthpromoting effects of DF (GIH, cancer prevention, and suppression of metabolic syndrome-related diseases) are widely acknowledged. Functional foods containing DF are available

FOOD GRAINS AND WELL-BEING | Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics as baked, extruded, fermented foods and beverages. Many components of DF have prebiotic effects. The healthpromoting effects of prebiotics are known by their selective growth promotion of probiotics, fermentation to SCFA, prevention of various cancers, and enhancement of mineral absorption. They also suppress CVD, obesity, and diabetes. Prebiotic functional foods are available as beverages, whole grains, fermented cereal foods, bakery products, and RTE, infant, and toddler foods and in specialty liquid nutrient supplements. Probiotics are known to have various healthful effects (enhancement of gut immunity, anti-inflammation, prevention of pathogenic infection, and suppression of irritable bowel syndrome (IBS), cancers, CVD, diabetes, rheumatoid arthritis, liver diseases, lactose intolerance, and diarrhea). Currently, nondairy probiotic functional foods and drinks such as soy-based foods, fermented cereals, and extruded and baked foods are on the rise. Microencapsulation is one option to incorporate probiotics in grain products. A combination of prebiotics and probiotics as synbiotics has synergetic healthpromoting effects. Many traditional fermented grain foods with live or active cultures if fully characterized have huge potential to be used as probiotic functional diets. Development of grains with desirable DF profiles of prebiotic potential and improved phytonutrients can advance prebiotic, probiotic, and DF functional foods. The bioactives used in DF, whole grains, and prebiotic functional foods are concentrated in the outer portions of the grains, which may be contaminated by toxicants that can pose food safety challenges. Good agricultural practices, good manufacturing practices, hazard analysis critical control points, and adequate grain drying, cleaning, scouring, and/or removal of very small portion of outermost layers of grains during milling can suppress such food safety challenges and also preserve functional ingredients.


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Provide definitions of DFs, whole grain foods, prebiotics, probiotics, and synbiotics. List up to seven different compounds regarded to be DFs. List up to four different compounds regarded to be prebiotics. Provide genera of microbial species widely used as probiotics. Provide essential characteristics of probiotics. Provide at least two health beneficial effects of DFs, whole grain foods, prebiotics, probiotics, and synbiotics. List up to four indigenous fermented foods consumed in your communities believed to have the effects of prebiotics, probiotics, and synbiotics. List potential safe diets for lactose-intolerant individuals.


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What innovations in grain-processing technology can you envisage to preserve grain bioactive ingredients used to deliver optimum DFs, prebiotics, and probiotics?

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How would you provide further characterization of specific DF components from grains for their health benefits and prebiotic effects? Suggest further improvements that may be made to traditional fermented grain foods to promote their probiotic value.

Explore possibilities for developing grains using conventional breeding or through genetic manipulation to provide desirable DF profiles for prebiotic potential, like inulin-type fructans and b-glucans.

See also: Beverages from Grains: Fermentation: Foods and Nonalcoholic Beverages; Bioactives and Toxins: Bioactives: Antioxidants; Bioactive Compounds in Wheat Bran; Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Glycemic Index, Glycemic Load, and Their Health Benefits; Health Effects of b-Glucans Found in Cereals; Resistant Starch and Health; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Fortification of GrainBased Foods; Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Grains and Health; Labelling of Grain-Based Foods; Food Grains and Well-being: Functional Foods: Overview; Nutrition: Soy-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; The Basics: Grain: Morphology of Internal Structure.

Further Reading AACCI Dietary Fiber Definition Committee (2001) The definition of dietary fiber. Cereal Foods World 46(3): 112–126. Anderson JW, Baird P, Davis Jr. RH Jr., Ferreri S, Knudtson M, Koraym A, Waters V, and Williams CL (2009) Lead article: Health benefits of dietary fiber. Nutr. Rev. 67(4): 188–205. Binns N (2013) Probiotics, Prebiotics and the Gut Microbiota. Belgium: ILSI Europe. Birkett AM and Cho SS (2013) Cereal fiber and health: Current knowledge. Cereal Foods World 58(6): 309–313. Cho SS and Finocchiaro ET (2010) Handbook of Prebiotics and Probiotics Ingredients Health Benefits and Food Applications. Boca Raton, FL: CRC Press, Taylor & Francis Group. Corona-Hernandez R, Alvarez-Parrilla E, Lizardi-Mendoza J, Islas-Rubio AR, de la Rosa LA, and Wall-Medrano A (2013) Structural stability and viability of microencapsulated probiotic bacteria: A review. Comprehen. Rev. Food Sci. Food Saf. 12: 614–628. Dwivedi S, Sahrawat K, Puppala N, and Ortiz R (2014) Plant prebiotics and human health: Biotechnology to breed prebiotic-rich nutritious food crops. Electron. J. Biotechnol. 17: 238–245. Ferruzzi MG, Jonnalagadda SS, Liu S, Marquart L, McKeown N, Reicks M, Riccardi G, Seal C, Slavin J, Thielecke F, van der Kamp JW, and Webb D (2014) Developing a standard definition of whole-grain foods for dietary recommendations: Summary report of a multidisciplinary expert roundtable discussion. Adv. Nutr. 5: 164–176. Foschia M, Peressini D, Sensidoni A, and Brennan CS (2013) Review the effects of dietary fibre addition on the quality of common cereal products. J. Cereal Sci. 58: 216–227. Granato D, Branco GF, Nazzaro F, Cruz AG, and Faria JAF (2010) Functional foods and nondairy probiotic food development: Trends, concepts, and products. Comprehen. Rev. Food Sci. Food Saf. 9: 292–302. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, Morelli L, Canani RB, Flint HJ, Salminen S, Calder PC, and Sanders ME (2014) Consensus statements: The International Scientific Association for Probiotics and Prebiotics consensus

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statement on the scope and appropriate use of the term probiotic. New York: Macmillan, Expert Consensus Document, 11, 506-514. Jones JM (2014) CODEX-aligned dietary fiber definitions help to bridge the ‘fiber gap’. Nutr. J. 13(34): 2–10. Marsha AJ, Hill C, Rossa RP, and Cotter PD (2014) Fermented beverages with healthpromoting potential: Past and future perspectives. Trends Food Sci. Technol. 39: 135–145. Poutanen K, Sozer N, and Valle GD (2014) Review: how can technology help to deliver more of grain in cereal foods for a healthy diet? J. Cereal Sci. 59: 327–336. Saad N, Delattre C, Urdaci M, Schmitter JM, and Bressollier B (2013) An overview of the last advances in probiotic and prebiotic field. LWT- Food Sci. Technol. 50: 1–16.

Slavin J, Tucker M, Harriman C, and Jonnalagadda SS (2013) Whole grains: Definition, dietary recommendations, and health benefits. Cereal Foods World 58(4): 191–198.

Relevant Websites http://wholegrainscouncil.org/whole-grains-101/existing-standards-for-whole-grains – Whole Grains Council. http://www.isapp.net/Home – ISAPP.

Nutrition: Soy-Based Foods AM Fehily, Tinuviel Software, Warrington, UK ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 348–354, ã 2004, Elsevier Ltd.

Topic Highlights

Nutrients

•

Soybeans contain protein, fat, carbohydrate, vitamins, minerals, and fiber.

• • •

Soy is a widely used protein source in Asian cuisine, and the source for most texturized vegetable protein and vegetarian meat substitutes. Soy isoflavones may have significant effects on cholesterol (and hence on coronary heart disease) reduction; on cancer risk; and on reduction in menopausal symptoms. Soy isoflavones, as phytoestrogens, may have negative effects if consumed at high levels. Soy contains antinutritional constituents such as lectins, goitrogens, and phytic acid.

Learning Objectives

• • •

To understand the chemical composition of soybean and its nutritional and antinutritional effects. To understand the health consequences of isoflavone consumption. To be aware of the dietary significance of soy proteins.

Protein Soybeans are a good source of protein, containing 14 g per 100 g. This is more than the protein content in most other vegetables and in most other legumes (typically 5–9 g per 100 g), the exception being peanuts which contain 26 g of protein per 100 g. In terms of protein quality, soy contains substantial amounts of most essential amino acids. When compared with a reference protein (egg), soy protein, like other legumes, is deficient in sulfur-containing amino acids (the essential amino acid methionine and the nonessential amino acid cystine) and has a higher content of lysine. Combining legumes with cereals provides a meal with a high protein quality, as cereals have adequate amounts of sulfurcontaining amino acids but are deficient in lysine.

Carbohydrate Soybeans contain 5 g of carbohydrate per 100 g. This is lower than that of many other legumes. Of the total carbohydrate content present, 37% is starch, 41% sugars, and 22% oligosaccharides. The sugars present are sucrose, fructose, and glucose.

Use of Soy in Foods Soybeans are perhaps the most versatile of plants, providing the source for a wide range of ingredients. In the Far East, soybeans are used to produce foods such as ‘tofu,’ ‘miso,’ ‘tempeh,’ and soy sauce. In Western countries, soybeans have become widely used in recent years in the production of a range of very diverse ingredients, e.g., soy flour, soy protein, soy oil, soy lecithin, and mono- and diglycerides of fatty acids. These ingredients are widely used in foods. For example, soy flour and soy protein are used in foods such as breads, pizza bases, other cereal products, and some meat products. Soy protein is often used to make vegetarian alternatives to meat products, e.g., textured vegetable protein (TVP) in vegetarian burgers, vegetarian sausages, etc. Soy oil is used as a vegetable oil both in domestic cooking and by the food industry. Soy oil is also used in the manufacture of spreadable fats. Soy lecithin and mono- and diglycerides of fatty acids are used as emulsifiers in many foods, e.g., breads, fat spreads, and ice cream. Vegan alternatives to cow’s milk, cheese, and yogurt are produced from soy. Soy is also used to produce infant formulas for those infants who are intolerant to lactose or cows’ milk protein.

Fat Soybeans contain 7 g of fat per 100 g. This is more than the fat content in other legumes, most of which are low in fat. The exception to this is peanuts, which contain 46 g of fat per 100 g. The fatty acid composition of soy has a high ratio of unsaturates to saturates. Of the fatty acids, 16% are saturates, 24% are monounsaturates, and 60% are polyunsaturates. The polyunsaturated fatty acids present are the essential fatty acids – linoleic acid (18:2n–6) and a-linolenic acid (18:3n–3).

Minerals Soybeans contain significant amounts of several minerals: calcium, iron, magnesium, potassium, phosphorus, and zinc (see Table 1). One hundred grams of soybeans provides 12% of the daily reference nutrient intake (RNI) (UK) for calcium, 20% for iron, 23% for magnesium, 15% for potassium, 45% for phosphorus, and 13% for zinc (see Figure 1).

Vitamins

Composition Soybeans contain a wide range of nutrients. They contain some ‘antinutrients’ and also other components, e.g., isoflavones, which may have beneficial effects on health.


Soybeans contain a number of water-soluble vitamins: thiamin, riboflavin, niacin, vitamin B6, and folate (see Table 1). One hundred grams of soybeans provides 15% of the daily RNI (UK) for thiamin, 8% for riboflavin, 21% for niacin, 19% for vitamin B6, and 27% for folate (see Figure 1). Soybeans also contain vitamin E: 1 mg per 100 g.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00066-8

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FOOD GRAINS AND WELL-BEING | Nutrition: Soy-Based Foods

18 Table 1

Vitamin and mineral composition of soybeans Amount per 100 g as consumed

Sodium Potassium Calcium Magnesium Phosphorus Iron Copper Zinc Manganese Selenium Iodine Vitamin A (retinol equivalents) Vitamin D Vitamin E Thiamin Riboflavin Niacin equivalents Vitamin B6 Vitamin B12 Folate Pantothenate Biotin Vitamin C

1 mg 510 mg 83 mg 63 mg 250 mg 3.0 mg 0.32 mg 0.9 mg 0.7 mg 5 mg 2 mg 1 mg 0 mg 1.13 mg 0.12 mg 0.09 mg 2.7 mg 0.23 mg 0 mg 54 mg 0.18 mg 25.0 mg Trace

(lectins, goitrogens, and digestive enzyme inhibitors). These substances are, however, inactivated by appropriate cooking of the beans or, in the case of goitrogens, counteracted by adequate iodine intake.

Lectins Lectins, also known as haemagglutinins, are present in raw soybeans and in other legumes. They are, however, heat labile and are inactivated when the beans are properly cooked. In experimental animals these polymeric proteins have been shown to cause damage to red blood cells and intestinal mucosa, and thereby impaired nutrient utilization and loss of body weight. In humans, these compounds can result in nausea, vomiting, diarrhoea, and abdominal pain.

Goitrogens Enlargement of the thyroid gland has been shown to occur in rats fed soybean meal. The goitrogenic agent in soybeans is unknown. However, the effect is counteracted by adequate iodine intake.

Digestive enzyme inhibitors

Data from Royal Society of Chemistry and Ministry of Agriculture Fisheries and Food (1991) McCance and Widdowson’s The Composition of Foods, 5th edn. Cambridge, UK: Royal Society of Chemistry. Crown copyright is reproduced with the permission of the Controller of Her Majesty’s Stationery Office.

Folate Vitamin B6 Niacin Riboflavin Thiamin Zinc

Raw soybeans contain certain proteins (protease inhibitors) which react with digestive enzymes (trypsin, chymotrypsin or salivary, and pancreatic a-amylase), thereby interfering with the digestion of protein and starch. In humans, raw soy or isolated protease inhibitors increase levels of cholecystokinin (CCK) and pancreatic secretion. It is thought that chronic pancreatic stimulation may lead to pancreatic hypertrophy, hyperplasia, and possibly to cancer. In rats, raw soy has been shown to increase risk of pancreatic cancer. However, protease inhibitors present in raw soy are inactivated by heat and are therefore not a problem in cooked beans. For example, in countries such as Japan where soy foods are widely consumed, the incidence of pancreatic cancer is similar to or less than that for Western countries where soy forms a relatively small component of the total diet.

Phosphorus

Phytic acid

Potassium Magnesium Iron Calcium 0

10

20

30

40

50

Figure 1 Vitamin and mineral composition of soybeans – in relation to reference nutrient intakes (% of reference nutrient intake (RNI) provided by 100 g). (Reproduced from (2003) Encyclopedia of Food Sciences and Nutrition, 2nd edn, p. 5393. Elsevier Ltd.)

Phytic acid is present in soybeans and also in other fibercontaining foods. It has been suggested to reduce the absorption of calcium, iron, zinc, and vitamin D from the diet. However, these effects have been observed in in vitro experiments and not in in vivo studies, even at fiber intakes at the upper limit of the normal human consumption range. In addition, levels of micronutrients tend to be higher in fiberrich foods than in fiber-poor foods. Thus, adverse effects of phytic acid on nutrient absorption are likely to be unimportant at the levels of fiber normally consumed in the human diet.

Fiber Soybeans are a valuable source of fiber in the diet: 6 g of nonstarch polysaccharides (NSP) per 100 g. Of this, 44% is soluble fiber and 56% insoluble fiber. One hundred grams of soybeans provides 33% of the daily ‘dietary reference value’ (UK) for fiber.

Antinutrients Raw soybeans contain a number of substances which may have detrimental effects on digestion and other metabolic processes

Isoflavones Soybeans contain isoflavones, a group of compounds that are structurally similar to oestradiol (phyto-oestrogens). Soybeans contain higher amounts of the isoflavones – genistein and daidzein (see Figure 2) and smaller amounts of glycitein, primarily in the form of glycosides: genistin, daidzin, and glycitin (total isoflavone content of 180 mg per 100 g). The glycosides are hydrolyzed in the gut by a bacterial enzyme, glucose being removed to produce the aglycone forms


OH O

HO

Daidzein

O

OH OH

HO

O

O

Genistein

Figure 2 Chemical structure of the main isoflavones present in soy – daidzein and genistein. (Reproduced from (2003) Encyclopedia of Food Sciences and Nutrition, 2nd edn, p. 5394. Elsevier Ltd.)

(genistein, daidzein, and glycitein). Daidzein and genistein have been shown to have weak oestrogenic activity and are able to bind with low affinity to oestrogen receptors, the affinity being greater for b-receptors than for a-receptors. Compared with 17b-oestradiol (the main oestrogen produced by the body), daidzein and genistein have been reported to have much less potency in producing oestrogenic effects, by about 1000-fold or more. In the 1940s, it was reported that phyto-oestrogens may exert adverse effects on uterine and ovarian function. This was because sheep grazing on pastures, containing a particular type of clover (Trifolium sp.) rich in formononetin, which is converted to daidzein in the rumen, developed a widespread infertility. An infertility syndrome has also been described in captive cheetah, as a result of soybean use, the syndrome being reversed by removal of soy from the food. No adverse effects of soybeans on human fertility have been reported. More recently, it has been recognized that isoflavones may act either as weak oestrogens or as antioestrogens, competing for oestradiol at the receptor complex, yet failing to stimulate a full oestrogenic response after binding to the nucleus. This fact has stimulated much research into whether isoflavones may have a protective role in hormone-related diseases such as breast cancer.

Role of Soy in the Diet Soy has been a staple in the diet of many Far Eastern countries for centuries, e.g., foods such as tofu, tempeh, and miso. These traditional soy foods are not very widely consumed in Western countries, but are sometimes used as an alternative to meat. As soybeans are extremely versatile, as described earlier, consumption of foods containing soy has increased in Western countries over the last 50 years. Nevertheless, the amount of soy consumed in Western countries such as the USA and UK is much less than in countries such as Japan and

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China. The Food and Agriculture Organisation (FAO) food balance sheets provide data for the amounts of various foods available for human consumption in different countries. These show that the amount of soybeans available for use in foods for humans is 8.5 kg per person per year in China and 7.9 kg per person per year in Japan. This compares with less than 1 kg per person per year in countries such as the USA and UK. In fact, of the soybeans grown worldwide, only 10% of the total is used in foods for humans, the majority is used as feed for animals. Soybeans can be an important component of a normal healthy diet as they are low in saturates, provide a source of fiber, and contain a wide range of other nutrients. Soybeans are also the main source of phyto-oestrogens in the diet. In addition, soybeans may have a number of potential health benefits and these are discussed in the following sections. For vegetarians, and particularly for vegans who eat no animal products, soybeans play a very important role in the diet. They provide a valuable source of protein that can be of high quality if soybeans are combined with cereals, since the amino acid compositions are complementary. They also provide an important source of iron. Low iron intake can lead to iron-deficiency anemia. Ensuring adequate iron status can be difficult for vegetarians as, in general, iron from vegetable sources is less well absorbed than that from animal sources. However, soybeans provide a source of iron that can be absorbed as well as that in meat. For infants intolerant to cow’s milk protein or to lactose, soy-based infant formulas can be an invaluable alternative to cow’s milk-based formulas. For older children and adults who are allergic to cow’s milk or intolerant to lactose, drinks and other foods made from soy can be very important components of the diet, helping to ensure that nutrient intakes are adequate for the maintenance of health. In common with other legumes, soybeans are also of agronomic importance, as they increase the nitrogen content of the soil. Although green plants cannot utilize nitrogen in the atmosphere, there are several species of bacteria, fungi, and blue-green algae that are able to transform nitrogen in the air into a form that can be used by plants. An important genus of nitrogen-fixing bacteria is Rhizobium, which forms nodules in the roots of legumes. These bacteria live symbiotically with the legumes, the bacteria obtaining food from the green plant and the legumes obtaining abundant usable nitrogen compounds from the bacteria.

Soy and Coronary Heart Disease Coronary heart disease (CHD) is a major cause of death in many countries. For example, in the UK, CHD accounts for 30% of male deaths and 23% of female deaths. The level of cholesterol in the blood is a major risk factor for CHD. Soy protein substituted for animal protein in the diet results in reductions in total plasma cholesterol (by 9% on average), low-density lipoprotein cholesterol (LDL-C) (by 13% on average), and triacylglycerols (by 11% on average). High-density lipoprotein cholesterol (HDL-C) is unchanged or may be slightly increased. The amount of reduction in blood

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lipids tends to be greater among those with the highest plasma cholesterol levels at baseline. A great deal of research has been done to identify the component(s) of soy protein that is responsible for its effect on blood lipids. Studies using a mixture of amino acids that duplicate the amino acid profile of soy protein have found that this does not have the same effect on blood lipids as the intact protein. However, studies of soy protein with isoflavones intact have shown that this has a lipid lowering effect, whereas soy protein with isoflavones removed has no significant effect. It has therefore been suggested that the isoflavones present in soy protein are largely responsible for the lipid lowering effect of soy protein. The benefits of isoflavones present in soy protein on cholesterol lowering have been suggested to be mediated through upregulation of LDL-receptor activity. Nevertheless, studies of isolated and purified isoflavones have failed to show that these have a lipid lowering effect. Soy may reduce risk of CHD through several mechanisms in addition to its ability to lower blood lipids (see Figure 3). For example, soy isoflavones are known to act as antioxidants and have been suggested to reduce oxidative damage to LDL-C. A decrease in oxidized LDL particles, which are considered atherogenic, may reduce the risk of atherosclerosis. A study of young cynomolgus monkeys showed that the size of atherosclerotic lesions was 70% less in those fed on a diet containing soy protein with isoflavones present compared with those fed on a diet containing soy protein with isoflavones removed. This suggests that isoflavones may inhibit atherogenesis. In another study of surgically postmenopausal cynomolgus monkeys, soy protein with isoflavones intact was found to reduce the progression of atherosclerosis. The magnitude of the effect was reported to be comparable to that of postmenopausal oestrogen therapy. Soybean isoflavones, in particular genistein, impact beneficially on vascular reactivity. Genistein has also been shown, in vitro, to have a number of other effects whereby the

development of atherogenesis may be delayed: inhibition of the migration and proliferation of smooth muscle cells; inhibition of platelet activation and aggregation; and reduction in platelet serotonin uptake. In 1999, in response to the available evidence on the benefits of soy protein, the USA Food and Drug Administration (FDA) announced that it would allow food manufacturers to label products containing 6.25 g of soy protein per serving as helping to reduce risk of heart disease, as part of a balanced diet low in fat and saturates.

Soy and Cancer Cancer is a major cause of morbidity and mortality. For example, in the UK about one in three people will develop cancer at some time during their life and cancer accounts for about one in four of all deaths. There are marked differences in death rates from several types of cancer between Asian countries and many Western countries. The differences are more striking for hormone-dependent cancers of the prostate, breast, and colon/rectum. For example, the risk of dying from prostate cancer among Japanese men is only one-fifth that of men in the USA and Japanese women have a breast cancer mortality rate that is only a quarter of that of women in the USA. Countries where mortality from prostate and breast cancers is low have considerably higher intakes of soy than those countries where mortality from these cancers is high. In animal models, studies investigating the effects of soybeans on prostate cancer or breast cancer have shown reduced tumorigenesis. In humans however, evidence is inconclusive. Epidemiological studies of prostate cancer conducted in Japan and in Japanese migrants to Hawaii have shown no significant effect of soy consumption. However, a recent study in the USA reported that men who drank one cup of soy milk per day had a risk of developing prostate cancer that was 70% lower than that of controls. For breast cancer, although some studies have shown Upregulate LDL receptor activity

Soy isoflavones

Reduce oxidative damage to LDL-C

Inhibit migration & proliferation of smooth muscle cells

Beneficial effects on vascular reactivity

Inhibit platelet activation & aggregation

Reduce platelet serotonin uptake

Delay progression of atherosclerosis

Reduce blood lipids

Reduce CHD risk Figure 3 Mechanisms through which soy could reduce risk of coronary heart disease (CHD).

FOOD GRAINS AND WELL-BEING | Nutrition: Soy-Based Foods that soy can help prevent breast cancer, others have found no significant effect. An increase in menstrual cycle length has been observed in some studies, in response to soybean consumption, although no change was observed in others. Such an effect is of potential relevance to the hypothesis that soy may be protective against breast cancer, because some data indicate that longer cycles, which are typical of Asian women, are associated with a reduced risk of breast cancer. For colo-rectal cancer data are also inconclusive: some studies showed no significant effect, some reported a protective effect of soy, and others observed an increased risk with soy consumption. For cancers at other sites, data tend to show that increased soybean consumption may be protective against lung and stomach cancer. Much more research is needed to confirm whether soy has a protective effect against cancer in humans. Isoflavones appear to be the components of soy that would be most likely to account for any protective action of soy against cancer, especially in inhibiting the initiation stage of carcinogenesis (see Figure 4). Genistein has been shown to suppress the growth of a wide range of cancer cells. It inhibits certain enzymes that could affect the onset of cancer or the growth of tumors: tyrosine protein kinase, mitogen-activated protein (MAP) kinase, and ribosomal S6 kinase. Genistein also inhibits the DNA repair enzyme topoisomerase II and acts as an antioxidant, thus potentially preventing oxidative DNA damage. It increases in vitro concentrations of transforming growth factor b, which is thought to inhibit the growth of cancer cells. In addition, genistein has also been shown to inhibit angiogenesis, the formation of new blood vessels, an abnormal event that occurs as part of the growth and expansion of malignant tumors. However, many of these effects have been shown with very high concentrations of genistein and not in cells treated with levels likely to be achieved in plasma of human subjects eating soy foods.

Soy and Bone Health Osteoporosis is a clinical condition in which there is a reduced amount of bone per unit volume and an increased susceptibility to fractures, particularly fractures of the vertebrae, distal forearm (Colles fracture) and hip. Of these, hip fracture is the most severe, since patients require a prolonged hospital stay, there is a high mortality rate (about 20% within six months of the fracture) and of those who survive may suffer permanent disability and dependency. Osteoporosis is a major health

problem in many Western countries, although not in Asian countries. A number of factors are known to increase risk of osteoporosis, including insufficient dietary calcium, low physical activity, and lack of oestrogen. In women, bone mass reduces at a rapid rate in the first few years after the menopause, due to the reduction in oestrogen. Hormone replacement therapy (HRT) is well known to reduce bone loss in postmenopausal women. However, HRT is not appropriate for all women. Since soy may have oestrogenic effects, it has been hypothesized that it may provide an alternative to HRT. Soy protein containing isoflavones has been reported to reduce bone loss due to oestrogen deficiency in ovariectomized rats. Soybean isoflavones have also shown a protective effect on bone loss in ovariectomized rats, suggesting that the beneficial effect of soy protein is due to isoflavones. The effect of isoflavones on bone loss in rats has been reported to be similar to that for oestrogen. The bone sparing effect of soy protein isoflavones has been suggested to be due to a reduction in bone resorption and/or to an increased osteoblast activity (increasing bone formation). In humans, most but not all studies indicate that soy protein containing isoflavones favorably affects bone turnover and bone mineral density in the lumbar spine of perimenopausal and postmenopausal women. Treatment with ipriflavone, a synthetic isoflavone, has also been reported to have bone conserving effects in postmenopausal women with low bone mass, confirming that the beneficial effect of soy protein is likely to be due to isoflavones. In addition to the effect of soy protein on bone mineral density, it has also been suggested that soy protein, when substituted for animal protein, may indirectly enhance bone strength. Another effect of soy protein is that it helps to conserve calcium by reducing urinary calcium excretion. This is due to the lower sulfur amino acid content of soy protein. Soy protein therefore appears to have modest beneficial effects on bone density. However, studies to date have been short term and have involved only small numbers of subjects. In addition, no study has investigated whether soy protein containing isoflavones has an effect on fracture risk.

Soy and Menopausal Symptoms Hot flushes (also known as hot flashes) are a common symptom among menopausal women in Western societies, but are

Soy isoflavones

Women: increase menstrual cycle length

Inhibit activity of various enzymes

Prevent DNA damage

Reduce initiation of cancer & growth of cancer cells Figure 4 Mechanisms through which soy could reduce risk of cancer.

21

Inhibit angiogenesis

22


reported to be much less common in Japan. Whether this difference is due to the higher consumption of soy in Japan is not clear. Hormone replacement therapy (HRT) generally alleviates hot flushes and other menopausal symptoms such as vaginitis. There is much research interest in the possibility that soy may provide an alternative to HRT in this regard. Evidence of benefit of soy in menopausal women is conflicting. Some researchers have reported an improvement in the frequency of hot flushes in women taking soy protein daily. Others have reported no effect of soy protein on the number of hot flushes experienced but found a reduction in the severity of symptoms. Others have reported a reduction in both the incidence and severity of hot flushes with soy protein or an isoflavone extract compared with a control group. Others have reported no difference in either the frequency or severity of hot flushes in the intervention group compared with the control group. Two studies have investigated the effects of phyto-oestrogen supplements on vaginal cytology and found an increase in cell proliferation (an indication of oestrogenic activity) and reversal of menopausal atrophy. Others have reported no significant effect. There are difficulties in interpreting the results of these studies. This is because there are differences in the amounts of soy protein and isoflavones used and differences in the duration of the studies. Interpretation is also complicated by the fact that reported frequency and severity of symptoms tends to reduce in the control group as well as the intervention group. Thus, much more research needs to be done before soy protein can be proposed as a potential alternative to HRT for the control of menopausal symptoms.


• •

Complile a summary of the effects of phytoestrogens on young adult men and women. What are the effects of high temperature processing on soy nutritional characteristics?


•

Investigate further the current state of knowledge on the effect of soy isoflavones on a medical condition of interest to you.

•

How would you ‘design’ a soybean for optimum nutritional and nutraceutical composition.

See also: Agronomy of Grain Growing: Soybean: Agronomy; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara; Oilseed and Legume Processing: Soybean: Processing; Soybean: Soy Concentrates and Isolates; The Legumes and Pseudocereals: Beans: Overview; Grain Legumes and Their Dietary Impact: Overview.

Further Reading Anderson JJB, Anthony M, Messina M, and Garner SC (1999) Effects of phyto-oestrogens on tissues. Nutrition Research Reviews 12: 75–116. Anderson JW, Johnstone BM, and Cook-Newell ME (1995) Meta-analysis of the effects of soy protein intake on serum lipids. New England Journal of Medicine 333: 276–282. Bingham SA, Atkinson C, Liggins J, Bluck L, and Coward A (1998) Phyto-oestrogens: where are we now? British Journal of Nutrition 79: 393–406. Lissin LW and Cooke JP (2000) Phytoestrogens and cardiovascular health. Journal of American College of Cardiology 35: 1403–1410. Messina MJ (1999) Legumes and soybeans: overview of their nutritional profiles and health effects. American Journal of Clinical Nutrition 70(suppl): 439S–450S. Messina M and Messina V (2000) Soyfoods, soybean isoflavones and bone health: a brief overview. Journal of Renal Nutrition 10: 63–68. Messina M, Persky V, Setchell KDR, and Barnes S (1994) Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutrition and Cancer 21: 113–131. Potter SM (2000) Soy – new health benefits associated with an ancient food. Nutrition Today 35: 53–60. Royal Society of Chemistry and Ministry of Agriculture, Fisheries and Food. (1991) McCance and Widdowson’s. The Composition of Foods, 5th edn. Cambridge, UK: Royal Society of Chemistry.

Relevant Websites nutrition.org.uk http://www.nutrition.org.uk – British Nutrition Foundation. food.gov.uk http://www.food.gov.uk – Food Standards Agriculture Organisation. apps.fao.org http://apps.fao.org – Food and Agriculture Organisation (FAO). ajcn.org http://www.ajcn.org – American Journal of Clinical Nutrition.


Contents Grains and Health: Misinformation and Misconceptions Consumer Trends in Grain Consumption Cultural Differences in Processing and Consumption Fortification of Grain-Based Foods Genetically Modified Grains and the Consumer Labelling of Grain-Based Foods Grains and Health

Grains and Health: Misinformation and Misconceptions DB Sheats and JM Jones, St. Catherine University, St. Paul, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

•

•

• • • •

•

•

• Claims suggest that wheat is the product of genetic research and that we are eating genetically altered wheat. In reality, genetically modified wheat is not sold legally anywhere in the world. Claims suggest that wheat and its gluten have changed and that is why celiac disease, an autoimmune disorder, is on the rise. While celiac disease rates are increasing, and theories abound, as to why. Claims suggest that wheat is addictive. There are no data to support claims that removing wheat from the diet results in withdrawal symptoms. Claims suggest that wheat causes uncontrollable overeating. Existing data show that ingestion of wheat protein causes the release of satiety hormones. Claims suggest that wheat ingestion leads to a host of mental health issues. There are scanty scientific data to support these claims. Claims suggest that wheat causes obesity and diets that eliminate wheat and other carbohydrates are the most effective way to lose weight. In reality, any significant weight loss that occurs with these diets is due to the reduction in total calories from any source, not just wheat or carbohydrates. Claims suggest that the elimination of wheat from the diet results in the cure or improvement of many health conditions. In reality, many of these conditions are made better by weight loss and not specifically the elimination of wheat. Claims suggest that the nutrient contribution of wheat and grains can easily be obtained from other food groups. While it is true that these nutrients are found in other foods, studies on nutritional quality indicate that diets without whole and enriched grains are often lacking in these nutrients.


Food and nutrition professionals need to be able to counter unfounded theories about wheat and other grains with sound science and unbiased, critical thinking.

Learning Objectives

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To identify current controversies surrounding wheat, grains, and health. To describe scientific evidence regarding wheat, grains, and health. To understand the important role that food and nutrition professionals play in dispelling common misinformation and misconceptions about wheat and grains.

Introduction Recently, grain consumption, especially wheat, has been blamed for obesity, diabetes mellitus, other chronic diseases, food addiction, and impaired brain function. Popular press books such as Wheat Belly by William Davis, the Paleo Diet by Loren Cordain, and Grain Brain by David Perlmutter and other authors and food bloggers claim that eliminating grains is the key solution to improving health. A review of nutrition and medical literature suggests a different scenario. This article provides a review of the scientific evidence regarding grains and health to dispel misinformation and misconceptions. This piece will focus on wheat because it has been subject to the most misinformation.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00078-4

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FOOD GRAINS AND THE CONSUMER | Grains and Health: Misinformation and Misconceptions

Wheat Breeding and Genetics Wheat originated in the Middle East thousands of years ago. According to the Food and Agriculture Organization (FAO), wheat is grown on more land area than any other commercial crop and continues to be the most important food grain source for humans. Together, rice, wheat, and maize provide over half of the world’s calories. Popular press authors and food bloggers suggest that wheat is the product of genetic research, and today, we are eating genetically altered wheat. They contend that wheat and its gluten have changed and our bodies can no longer digest the modified grains of today, and that is why people are having so much difficulty digesting wheat and why celiac disease, an autoimmune disorder, is on the rise. It is alleged that modern wheat has changed to be less healthy because of breeding practices. In fact, wheat breeding is an age-old practice. Significant advances in plant breeding occurred in the 1940s with the work of Norman Borlaug and others, using traditional techniques (non-genetically modified organisms). Lines selected provide increased yield through disease, drought, and insect resistance, especially in developing countries. Despite assertions to the contrary, these lines were produced by crossing wheat varieties with other wheat varieties from all over the globe. In 1970, Dr Borlaug with his so-called Green Revolution won the Nobel Peace Prize for his wheat and grain breeding programs, which produced grains with high yields that grow under a wide variety of conditions and help address world food supply challenges. It is also alleged that genetic modification of wheat has made it less healthy and has changed the gluten proteins. This is untrue for two reasons. First, no ill effects can come from genetically modified wheat because there is none sold legally anywhere in the world. Second, recent studies from USDA labs and labs at the University of Saskatchewan and studies in Europe using grains from seed banks going back as far as Canadian Red Fife in 1857 show wheat gluten has not changed. Concern has been raised about the use of hybrid dwarf wheats. They now comprise 99% of the wheat grown worldwide. Short-straw naked (dwarf) wheats are one of the advances that were part of the green revolution. They increased yield for two reasons: (1) wheat varieties with long, spindly straws lodge, meaning that the kernel head is heavy and falls to the ground, making harvest difficult, and (2) shorter straw means that inputs, for example, water and nutrients, go into making wheat kernels rather than straw. Popular press authors imply that new wheat varieties and their proteins are unique or harmful in some way. Further, they posit that 5% of the proteins in wheats are unique, meaning they are found in neither parent, and that this unexpected genetic rearrangement results in altered proteins with potentially toxic effects. It is important to consider that plants can only express proteins that they have the genetic code to produce. Creating a unique protein requires a mutation of the DNA or RNA. While environmental conditions can promote or inhibit the expression of certain proteins, it cannot code for proteins that are not in the genome. Therefore, hybridization of wheat does not create unique proteins.

Ancient wheats such as einkorn are held as models of what we should eat because they have not been hybridized and because of their protein makeup. In fact, one author says that einkorn contains 28% protein compared with average protein contents of 12–15% in modern wheats and that ancient wheats did not cause the symptoms that new varieties do. However, studies carried out at the University of Saskatchewan where ancient and other varieties of wheat were grown on adjacent plots actually show that the crude protein content of einkorn is 18% and that of other ancient and modern varieties had protein values ranging from 16.3% to 17.5%. This fits well with the USDA World Wheat Collection, which shows approximately a threefold variation in protein content of wheat from 7% to 22%, with one-third of this under genetic control and two-thirds of this controlled by environmental conditions.

Celiac and Related Disorders Celiac disease is on the rise, as are other autoimmune diseases, in Western countries. This fact is documented in the scientific literature. Studies by Mayo Clinic gastroenterologist Joe Murray and colleagues compared celiac titers in blood samples from the recent US Air Force recruits with stored blood samples taken from recruits more than 50 years ago. The analysis showed 0.2% of recruits had the gene for celiac disease in 1950 compared with 0.9% of recent recruits, which is a quadrupling of the incidence rate. Data from Finland also show an increase from 1% to 2% or a doubling of the rate of celiac disease incidence in that population. While celiac disease rates are increasing, it is uncertain whether this is due in part to better identification and awareness of the disease, as well as a myriad of other dietary, immunologic, and environmental changes, especially those that impact the microorganisms and integrity of the gut. Some theories include the ‘clean’ theory, poor diets overall, overuse of antibiotics and other drugs especially acid-lowering drugs, lack of breast-feeding, and frequent use of Cesarean sections. Davis and other popular press authors posit that the reason for the increase in celiac disease is attributed to the fact that celiac disease-triggering proteins are expressed at higher levels in current wheat varieties than found 50 years ago. Such authors suggest that high-molecular-weight (HMW) glutenins and higher levels of gliadin of modern wheat are the problem. While studies show that the immune system reacts to breakdown products of HMW glutenins, data are lacking that show that these proteins trigger more reactions than those of ancient wheats or even wheat varieties from 50 years ago. Interestingly, gliadins are found in higher amounts in ancient versus modern wheats. Gluten-containing grains are also implicated in non-celiac gluten sensitivity (NCGS). This newly recognized disorder has no medically agreed-upon test to confirm a diagnosis, and therefore, its existence and incidence are subject to much debate. The best estimates are that 4–6% of the population may have NCGS. NCGS is thought to be present in about 5% of irritable bowel syndrome cases and may cause the rash, dermatitis herpetiformis, which can be seen in some celiac patients.


Allergens Wheat has long been categorized as one of the ‘big eight’ allergens (the most common allergens in Western countries). Despite beliefs that the incidence is much higher, only 0.5% of children and adults in the United States suffer from wheat allergy, which can be caused by any number of proteins in wheat. Glutenins are the most frequent allergens, but gliadins, especially gamma-gliadin, result in the most severe allergic reactions. A particular protein, omega-5 gliadin, is responsible for wheat-dependent, exercise-induced anaphylaxis and may be the offending protein in the wheat allergies of young children. There are also reported allergies to albumins, globulins, and enzyme inhibitors. Interestingly, delayed introduction of solid foods including grains such as wheat and rye has been found to be responsible for greater allergic sensitization in young children.

Addiction and Overconsumption of Food Popular press authors and bloggers suggest that wheat is the world’s most destructive dietary ingredient because during its digestion, it breaks down into peptides that act as exorphins (exogenous opioids). These authors assert that wheat is unique in this role. Studies conducted by the National Institutes of Health (NIH) in 1979 show that digestion of wheat proteins can produce peptides that interact with opioid receptors. However, the claim that wheat is unique in this regard is incorrect, as these same studies show that other food proteins also produce peptides that interact with opioid receptors. Hydrolysates of milk proteins (alpha-, beta-, or kappa-casein; alpha-lactalbumin; beta-lactoglobulin; and lactotransferrin) show the highest opioid activity. In addition to milk proteins and wheat gluten, rice albumin, bovine serum albumin, and even a protein from spinach all produce peptide fragments capable of interacting with opioid receptor ligands. It is important to consider that the studies indicating wheat’s possible opioid potential were conducted either in vitro or by feeding the preformed peptides, not by feeding wheat itself. Studies feeding wheat foods, not hydrolysates, must be conducted to determine the actual effects of peptides from gluten digestion. Some studies have also reported beneficial effects of these peptides. If bioavailable, they have the potential to help control blood pressure and to improve learning performance. Another theory promulgated by popular press authors and bloggers is that wheat opioids are highly addictive causing individuals to lack control of their eating, with subsequent removal of wheat from the diet producing withdrawal symptoms. The controls over hunger and satiety are complex being affected by many mechanisms from physical feelings of fullness (stomach distention) to neuroendocrine, psychosocial, and sensory factors. While some suggest specific foods such as sugars and fats are addictive, supporting evidence is weak and scarce, with no human data. Similarly, there are no data to support claims that removing wheat from the diet results in withdrawal symptoms. Claims from Davis and others that wheat causes uncontrollable overeating conflict with existing data that show wheat

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protein ingestion causes the release of satiety hormones cholecystokinin and glucagon-like peptide 1. Wheat and pea proteins show a stronger ability than other sources to stimulate the release of both hormones. Some data suggest that consumption of proteins such as those in gluten may be a good dietary strategy for weight management.

Mood, Mental ‘Fogginess,’ Autism, Attention-Deficit/ Hyperactivity Disorder, and Schizophrenia A common assertion in the popular press is that wheat ingestion alters mood and causes mental ‘fogginess.’ There are little data showing that wheat consumption alters mood or mental acuity. In a small study of patients with celiac disease, a glutenrestricted diet failed to improve neurological symptoms. In contrast, increased serotonin is associated with a sense of well-being and elevates mood. In a study of malnourished Indian primary school children, wheat biscuits added to their diets actually improved cognitive ability. There are data suggesting adding lysine to grain-based diets may reduce measures of anxiety. In a study of Syrians with marginal diets based primarily on wheat, the addition of lysine, wheat’s limiting amino acid, reduced symptoms of anxiety. This study supports the fact that complementary plant proteins are needed in grainbased diets low in complete proteins. Wheat is also alleged to cause of autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD), and schizophrenia. Case reports and other narratives suggest there may be a link between autism and celiac disease. However, documentation in the medical literature is scarce. Regarding autism, there is only one randomized clinical trial and its findings showed no significant difference in symptoms due to gluten removal from the diet. A review considered the ‘gold standard’ in the medical literature concluded that further large-scale, randomized-controlled trials are needed. According to Fasano, a noted celiac disease researcher at the Center for Celiac Research in Baltimore, MD, while the gluten-free, casein-free diet is one of the most popular diets for the treatment of autism, the efficacy of this diet is inconclusive. Similarly, studies examining the relationship between wheat and ADHD are lacking, even though sensitivity to a range of foods, including wheat, has been suggested in a number of case reports. Studies with very small numbers of subjects show no improvement in ADHD symptoms with a gluten-free diet. Screenings for celiac disease in a clinical report (no control group) involving 67 people diagnosed with ADHD showed the incidence to be slightly higher than the population as a whole with 1 out of 7 (vs. slightly < 1 in 10) having celiac disease. These celiac disease-positive participants showed a significant decrease in ADHD symptoms. Schizophrenia’s link to gluten was noticed during World War II when a British physician observed decreased admissions for this disorder. Dr. Dohan theorized that this decrease correlated with decreased wheat consumption imposed by rationing and postulated links between wheat, celiac disease, and schizophrenia. Part of the theory suggests that wheat ingestion affects tight junctions and reduces the gut’s capacity to prevent the entry of exogenous substances, thus allowing the development of schizophrenia and other mental conditions. It is also

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known that schizophrenia incidence increases in the presence of any autoimmune disease or a history of severe infections. It is thought that the antibodies produced can impact the brain. In some studies, a subset of schizophrenia patients show elevated gliadin antibodies. However, classic celiac disease diagnostics, either antibodies or gene markers, were not found in higher rates in schizophrenia patients than in the public at large. A comprehensive review looking at the connection between gluten and schizophrenia showed that gluten withdrawal resulted in a drastic reduction or full remission of symptoms but only among a small subset of schizophrenia sufferers. Thus, in a small group of schizophrenia patients, removal of wheat may be helpful but not the miracle cure indicated by Davis and others.

Obesity and Weight Loss Obesity rates have increased dramatically around the world since the 1970s. Obesity rates in the United States have increased by 214% since 1950. Davis and other popular press authors note that obesity was rare in the 1950s and cited increased wheat consumption as a cause. It is true that wheat consumption increased from 1970 to 2000; however, it dropped between 2000 and 2014. Importantly, these authors failed to note that during this same period, portion size and caloric intake have increased dramatically while physical activity has decreased and screen time has increased. In fact, in 2008 in the United States, there were on average 600 more calories available per person than in 1970. Food bloggers and popular press authors suggest that the proliferation of wheat products in the diet parallels increased weight and central obesity. Central obesity, also known as visceral adipose tissue (VAT), has increased in the population and is a cause for concern due to its association with higher rates of diabetes, high blood pressure, heart disease, and certain forms of cancer. While VAT has increased, it is not true that wheat causes this condition or that the elimination of wheat will cure this condition. It is well documented that no one food or food group is responsible for VAT. Instead, ingesting too many calories of any kind coupled with too little exercise will result in VAT. Recent data from the Framingham Heart Study cohort refute claims that wheat increases VAT. Those who had the least VAT ate two servings per day of refined grains and three servings per day of whole grains. For many years, various low-carbohydrate diets have been recommended as the most effective way for individuals to lose weight. It is not surprising that eliminating wheat from the diet has recently been considered to be the ‘holy grail’ of weight loss regimens using low-carbohydrate diets. While it is true that lowcarbohydrate diets have been shown to cause more rapid weight loss than other diets in the first 6 months, these diets do not result in greater weight loss over time. In addition, low-carbohydrate diets often result in more dropouts than other diets that are more balanced and do not eliminate entire food groups. Any significant weight loss that occurs with these diets cannot be attributed to the ‘magic’ of eliminating grains, but instead, it is due to the reduction in total calories from any source.

Grain Foods and the Glycemic Index The glycemic index (GI) is a measure that compares the blood glucose response produced by 50 g of available carbohydrate from a food with the blood glucose response produced by 50 g of glucose. Popular press authors and food bloggers correctly noted that wheat bread has a GI that is higher than table sugar. However, GI is most often misunderstood because it is used to compare very different amounts of food. For example, 50 g of table sugar (approximately three tablespoons) would yield 50 g of available carbohydrate. In contrast, 50 g of available carbohydrate from whole wheat bread is much more than 50 g of bread since bread is not all carbohydrate and not all the carbohydrate is available. Thus, it would take 144 g of whole wheat bread (5.1 slices at 28 g per slice) or 111 g of white bread (3.9 slices) to yield 50 g of available carbohydrate.

Grain Foods and Other Diseases Popular press authors and bloggers claim that elimination of wheat from the diet results in the cure or improvement of many conditions including diabetes, coronary heart disease, multiple sclerosis, rheumatoid arthritis, asthma, acid reflux, irritable bowel syndrome, ulcerative colitis, acne, and other rashes. However, many of these conditions are made better by weight loss, so attributing improvement to wheat removal is overly simplistic and is likely an inaccurate deduction. A number of meta-analyses and reviews show that those who eat grains and whole grains have lower risk or most chronic diseases with a recent one showing a reduction in both the risk of cardiovascular and all-cause mortality.

Nutrient Composition of Wheat and Grains Many diet authors bashing grains and wheat assert that the nutrient contribution of wheat and grains can easily be obtained from other food groups. While it is true that most of the constituents of grains can be found in other foods, there are some issues. For example, grains provide many of the B vitamins. While it is true that these are found in other foods, studies on nutritional quality indicate that diets without whole and enriched grains are often lacking in these nutrients. The concern is especially important for folate. Folate fortification of grains has decreased neural tube defects and other neurological problems in North American populations by 50% since fortification of grains was mandated. Other compounds such as betaine are found in wheat and wheat bran and germ, the highest sources of this important phytochemical. Betaine is not widely distributed in the foods supply and has importance in human nutrition. Diets without grains can have significant problems getting adequate dietary fiber and a good mix of fiber types. Wheat bran/fiber is used as the standard against which government agencies test the efficacy of a fiber in terms of laxation, as it is the fiber with significantly greater effect on laxation than fibers from fruits and vegetables. The same fiber in barley and oats with proved cholesterol-lowering properties is not widely found

FOOD GRAINS AND THE CONSUMER | Grains and Health: Misinformation and Misconceptions in many fruits or vegetables, and when found, its structure is such that it does not have cholesterol-lowering properties. Further epidemiological studies show that cereal fiber reduces the risk of certain gut cancers while fruit and vegetable fibers do not. These data suggest that balance as prescribed in USDA MyPlate provides the best diet.

Conclusion Numerous health problems including obesity, diabetes mellitus, other chronic diseases, food addiction, and impaired brain function have been attributed to grains such as wheat. A review of nutrition and medical literature reveals that there are little evidence to support claims that wheat and grains cause adverse health effects and chronic disease and much evidence to show that a balanced diet that includes wheat and grains, especially whole grains, reduces chronic disease risk and lowers overall mortality. Popular press authors and food bloggers claim that eliminating wheat grains is essential for optimal health for all. While it is true that wheat and other gluten-containing grains must be eliminated for those with reactions to gluten and wheat because of celiac disease, allergies, or other conditions, it is not true that wheat and grain elimination is best for all. Further, it is also true that many diets contain too many calories and grain-based desserts and snacks contribute to excess calories, and it is not true that the grains and wheats are the culprit. Rather, it is the poor food choices that should be addressed. Data for elimination of grains for all are, at best, scanty and do not show scientific rigor. Food and nutrition professionals need to be able to counter unfounded theories about wheat and other grains with sound science and unbiased, critical thinking. This article provides a review of the scientific evidence regarding grains and health to dispel common misinformation and misconceptions.


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Take a specific wheat controversy and describe the scientific evidence to support or refute this claim. Model a diet with and without grains. Calculate the nutritional value of the model diet using a computer analysis to show what nutrients might be at risk. Show what foods would need to be consumed in larger quantities. If this were done, what would happen to calories? Calculate the calories for 3 days of diets with wheat or grains included and the calories of that same diet without the wheat or grains. Show how much weight would likely be lost with the elimination of these products. Go to a store and compare the cost, nutritional value, and eating quality of products that are labeled as gluten- or wheatfree with their gluten- or wheat-containing counterparts.


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Why is misinformation around diet so readily accepted? Show the evidence supporting the use of wheat and grains in preventing any one of the chronic diseases. Assess this evidence in and evaluate evidence for their nonuse.

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Assess the evidence associated with grains, carbohydrates, and brain function. How does this evidence compare with other nutritional impacts on the brain? Use the GI tables and look up the values for wheat and grain staples such as sourdough and whole grain bread basmati rice and pasta. Explain why such products often with the same ingredients have varying GIs. Then look at the amount eaten for 50 g of carbohydrate and compare that and the nutritional quality of indulgent and other foods with lower GIs such as candy or chocolate cake. Using this research, explain when the GI might be useful for food selection and when it might not yield optimal nutrition choices.

See also: Appendix 3: Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease; Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Food Grains and the Consumer: Grains and Health; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Cereal Allergens; The GlutenFree Diet; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Abdel-Aal E-SM, Hucl P, and Sosulski FW (1995) Compositional and nutritional characteristics of spring einkorn and spelt wheats. Cereal Chemistry 72: 621–624. Aune D, Chan DS, Lau R, et al. (2011) Dietary fibre, whole grains, and risk of colorectal cancer: Systematic review and dose–response meta-analysis of prospective studies. BMJ 343: d6617. Benros ME, Nielsen PR, Nordentoft M, Eaton WW, Dalton SO, and Mortensen PB (2011) Autoimmune diseases and severe infections as risk factors for schizophrenia: A 30year population-based register study. American Journal of Psychiatry 168: 1303–1310. Bolotin D and Petronic-Rosic V (2011) Dermatitis herpetiformis. Part I. Epidemiology, pathogenesis, and clinical presentation. Journal of the American Academy of Dermatology 64: 1017–1024. Burke SJ, Gibney MJ, O’Dwyer NA, and McCarthy SN (2005) The influence of cereal and dairy consumption on the Irish diet: Implications for developing food-based dietary guidelines. Public Health Nutrition 8: 227–237. Cascella NG, Kryszak D, Bhatti B, et al. (2011) The gluten connection: The association between schizophrenia and celiac disease. Schizophrenia Bulletin 37: 94–100. Centers for Disease Control and Prevention (2014) Adult Obesity Facts. Atlanta, GA: CDC. Published online at: http://www.cdc.gov/obesity/data/trends.html (accessed 1/14). Choi S, Disilvio B, Fernstrom MH, and Fernstrom JD (2009) Meal ingestion, amino acids and brain neurotransmitters: Effects of dietary protein source on serotonin and catecholamine synthesis rates. Physiology and Behavior 98: 156–162. Corsica JA and Pelchat ML (2010) Food addiction: True or false? Current Opinion in Gastroenterology 26: 165–169. Corwin RL and Grigson PS (2009) Symposium overview – Food addiction: Fact or fiction? Journal of Nutrition 139: 617–619. Craig SA (2004) Betaine in human nutrition. American Journal of Clinical Nutrition 80: 539–549. Crider K, Bailey LB, and Berry RJ (2011) Folic acid food fortification – History, effect, concerns, and future directions. Nutrients 3: 370–384. Dohan FC (1966) Wheat "consumption" and hospital admissions for schizophrenia during World War II. A preliminary report. American Journal of Clinical Nutrition 18: 7–10. Fasano A (2014a) Gluten-Related Disorders. Philadelphia, PA: Lippincott, Williams and Wilkins, p. 10. Fasano A (2014b) Gluten-Related Disorders. Philadelphia, PA: Lippincott, Williams and Wilkins, p. 44.

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Fewtrell M, Wilson DC, Booth I, and Lucas A (2011) Six months of exclusive breastfeeding: How good is the evidence? BMJ 342. http://dx.doi.org/10.1136/bmj. c5955. Foster-Powell K, Holt SH, and Brand-Miller JC (2002) International table of glycemic index and glycemic load values 2002. American Journal of Clinical Nutrition 76: 5–56. Genuis SJ and Bouchard TP (2010) Celiac disease presenting as autism. Journal of Child Neurology 25: 114–119. Geraedts MC, Troost FJ, Tinnemans R, So¨derholm JD, Brummer RJ, and Saris WH (2010) Release of satiety hormones in response to specific dietary proteins is different between human and murine small intestinal mucosa. Annals of Nutrition and Metabolism 56: 308–313. Grains. http://www.choosemyplate.gov/food-groups/grains-why.html (accessed 1/14). Gregorini A, Colomba M, Ellis HJ, and Ciclitira PJ (2009) Immunogenicity characterization of two ancient wheat a-gliadin peptides related to coeliac disease. Nutrients 1: 276–290. Hsu CL, Lin CY, Chen CL, Wang CM, and Wong MK (2009) The effects of a gluten and casein-free diet in children with autism: A case report. Chang Gung Medical Journal 32: 459–465. Jenkins DJ, Kendall CW, Vuksan V, et al. (1999) The effect of wheat bran particle size on laxation and colonic fermentation. Journal of the American College of Nutrition 18: 339–345. Jenkins DJ, Wolever TM, Taylor RH, et al. (1981) Glycemic index of foods: A physiologic basis for carbohydrate exchange. American Journal of Clinical Nutrition 34: 362–366. Kalaydjian AE, Eaton W, Cascella N, and Fasano A (2006) Prevalence of celiac disease and gluten sensitivity in the United States clinical antipsychotic trials of intervention effectiveness study population. Acta Psychiatrica Scandinavica 113: 82–90. Kramer T (1979) Environmental and genetic variation for protein content in winter wheat (Triticum aestivum L.). Eyphytica 28: 209–218. Likes R, Madl RL, Zeisel SH, and Craig SA (2011) The betaine and choline content of a whole wheat flour compared to other mill streams. Journal of Cereal Science 46: 93–95. Lohi S, Mustalahti K, Kaukinen K, et al. (2007) Increasing prevalence of coeliac disease over time. Alimentary Pharmacology and Therapeutics 26: 1217–1225. McKeown NM, Troy LM, Jacques PF, Hoffmann U, O’Donnell CJ, and Fox CS (2010) Whole-and refined-grain intakes are differentially associated with abdominal visceral and subcutaneous adiposity in healthy adults: The Framingham Heart Study. American Journal of Clinical Nutrition 9: 1165–1171. Meisel H (2004) Multifunctional peptides encrypted in milk proteins. BioFactors 21: 55–61. Millichap JG and Yee MM (2012) The diet factor in attention-deficit/hyperactivity disorder. Pediatrics 129: 330–337. Millward C, Ferriter M, Calver S, and Connell-Jones G (2008) Gluten- and casein-free diets for autistic spectrum disorder. Cochrane Database of Systematic Reviews CD003498. Molberg Ø, Solheim Flaete N, Jensen T, et al. (2003) Intestinal T-cell responses to high-molecular-weight glutenins in celiac disease. Gastroenterology 125: 337–344. Mo¨ller NP, Scholz-Ahrens KE, Roos N, and Schrezenmeir J (2008) Bioactive peptides and proteins from foods: Indication for health effects. European Journal of Nutrition 47: 171–182. Nazni P, Pradheepa S, and Hasan A (2010) Effects of weaning biscuits on the nutritional profile and the cognitive development in preschool children. Italian Journal of Pediatrics 36: 18. Niederhofer H (2011) Association of attention-deficit/hyperactivity disorder and celiac disease: A brief report. The Prim Care Companion for CNS Disorders 13(3). Nwaru BI, Erkkola M, Ahonen S, et al. (2010) Age at the introduction of solid foods during the first year and allergic sensitization at age 5 years. Pediatrics 125: 50–59.

Othman RA, Moghadasian MH, and Jones PJ (2011) Cholesterol-lowering effects of oat b-glucan. Nutrition Reviews 69: 299–309. Palosuo K, Varjonen E, Kekki OM, et al. (2001) Wheat omega-5 gliadin is a major allergen in children with immediate allergy to ingested wheat. Journal of Allergy and Clinical Immunology 108: 634–638. Putnam J, Allshouse J, and Kantor LS (2002) U.S. per capita food supply trends: More calories, refined carbohydrates, and fats. Food Review 25(3). http://ers.usda.gov/ publications/foodreview/dec2002/frvol25i3a.pdf. Ravindra CN, Hucl P, Briggs C, Irvine C, Ba˚ga M, and Graf RJ (2014) Canadian ancestral and present wheat varieties have similar protein concentration. Abstr./ poster. Canadian Nutrition Society. June 2014. St. John’s Newfoundland, Canada. Reicks M, Jonnalagadda S, Albertson AM, and Joshi N (2014) Total dietary fiber intakes in the US population are related to whole grain consumption: results from the National Health and Nutrition Examination Survey 2009 to 2010. Nutrition Research 34: 226–234. Rubio-Tapia A, Kyle RA, Kaplan EL, et al. (2009) Increased prevalence and mortality in undiagnosed celiac disease. Gastroenterology 137: 88–93. Samaroo D, Dickerson F, Kasarda DD, et al. (2010) Novel immune response to gluten in individuals with schizophrenia. Schizophrenia Research 118: 248–255. Siqueira Neto JI, Costa AC, Magalha˜es FG, and Silva GS (2004) Neurological manifestations of celiac disease. Arquivos de Neuro-Psiquiatria 62: 969–972. Smriga M, Ghosh S, Mouneimne Y, Pellett PL, and Scrimshaw NS (2004) Lysine fortification reduces anxiety and lessens stress in family members in economically weak communities in Northwest Syria. Proceedings of the National Academy of Sciences of the United States of America 101: 8285–8288. Sponheim E (1991) Gluten-free diet in infantile autism. A therapeutic trial. Tidsskrift for den Norske Lægeforening 111: 704–707. Stevens LJ, Kuczek T, Burgess JR, Hurt E, and Arnold LE (2011) Dietary sensitivities and ADHD symptoms: Thirty-five years of research. Clinical Pediatrics (Philadelphia) 50: 279–293. Teschemacher H (2003) Opioid receptor ligands derived from food proteins. Current Pharmaceutical Design 9: 1331–1344. USDA Wheat Yearbook. Verdu EF, Armstrong D, and Murray JA (2009) Between celiac disease and irritable bowel syndrome: The "No Man’s Land" of gluten sensitivity. American Journal of Gastroenterology 104: 1587–1594. Wei J and Hemmings GP (2005) Gene, gut and schizophrenia: The meeting point for the gene-environment interaction in developing schizophrenia. Medical Hypotheses 64: 547–552. Wilson GT (2010) Eating disorders, obesity and addiction. European Eating Disorders Review 18: 341–351. Wu H, Flint AJ, Qi Q, et al. (2015) Association between dietary whole grain intake and risk of mortality: Two large prospective studies in US men and women. JAMA Internal Medicine 175: 373–384. http://dx.doi.org/10.1001/ jamainternmed.2014.6283. Yoshikawa M, Takahashi M, and Yang S (2003) Delta opioid peptides derived from plant proteins. Current Pharmaceutical Design 9: 1325–1330. Zioudrou C, Streaty RA, and Klee WA (1979) Opioid peptides derived from food proteins. The exorphins. Journal of Biological Chemistry 254: 2446–2449.

Relevant Websites http://www.choosemyplate.gov/grains-why.html. http://gowiththegrain.org. http://wheatfoods.org.

Consumer Trends in Grain Consumption JM Jones and DB Sheats, St. Catherine University, St Paul, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Trend drivers in developed countries are different from those in emerging markets and developing countries, but each can influence the other. Grain consumption worldwide is increasing, but direct consumption is decreasing as wealth increases and animal foods are selected. Gluten-free is needed for wheat allergy and celiac disease and related disorders but is unnecessary and expensive. It may be lower in nutrients especially dietary fiber and folate for those who do not need to adopt this diet. Low-carbohydrate, antigrain, and other fad diets impact grain consumption. Underconsumption of whole grains and overconsumption of grain-based desserts and snacks are trends that need to be addressed in many regions. The selection of alternate grains and sprouted grains is another emerging trend.

International Consumer Trends

Learning Objectives

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To identify drivers that affect grain consumption and be able to show how those are different in different regions and economies, To name a number of sources of data, which track grain production and consumption, To describe drivers of grain consumption for specific grains, To distinguish between drivers that are trends and those that are fads and to attribute causes for both.

Introduction Taste, cost, availability, convenience, and nutrition have a strong impact on consumer behavior and consumption with regard to food and grains. Many new trend drivers have been added or are exerting more influence than in the past. These include environmental concerns, concerns about food sustainability, the food–environment and food–fuel connections, food provenance and the ‘locavore’ movement, social norms that affect attitudes toward growers and producers of food including concerns about large agribusiness and spawning the growth of local markets and consumer-supported agriculture, the role of women in the society, the importance of food and the time spent devoted to food in a culture, the attitudes toward maintaining food traditions versus encouraging the use of new foods and methods of production and cookery, globalization of foods, fear and misunderstanding of technologies and practices involved in food production, distrust of long esteemed food staples such as grains, and worries about the rise in obesity and certain other diseases. All of these must be


balanced with the looming specter of inadequate food supplies to feed the anticipated population of 2050. Consumer attitudes and ideas change continually, but these changes seem to occur at a faster rate in the age of social media, blogs, battling experts, 24 h news cycles, and talk shows, all which report the latest research findings sometimes with varying degrees of accuracy. If these voices persist, the information – regardless of its veracity – causes changes in food and grain consumption. Perception is reality and consumer beliefs and trends drive the marketplace. Thus, it is important that those producing and manufacturing grain in planning for the long term be able to (1) differentiate between fads and trends, (2) to tailor food product development and market launches so that product introduction and supply meet consumer expectations, and (3) to predict changes in the future that allow innovation and are ready with supply chain and production to meet these changed demands.

The trend toward consumption of higher-value food products across all income levels has risen in many countries in recent years due to higher disposable incomes. While changes in income affect consumption patterns, increased urbanization is an important driver. It often results in higher levels of education, in more women working outside the home, and in shifts from jobs that require much energy expenditure to more sedentary ones, and it may alter incomes and food choices both positively and negatively. Those trapped in urban ghettos may shift their diets to cheap, readily available calorie sources that may be poor choices in terms of nutrient density. However, consumers thriving in emerging economies such as China and Mexico shift their food purchases away from traditional diets and grains and other carbohydrate-rich staple foods to more expensive sources of calories, such as meat and dairy products, more packaged foods such as breakfast cereals and other frozen, instant or ready-to-eat options, and more foods prepared away from home. According to MarketsandMarkets, the most rapid rate of growth in the breakfast cereal category is expected to occur in the Asia Pacific region because of some of the aforementioned factors. Some consumption trends affect health either positively or negatively. The trend reflecting the demand for healthier cereals and cereal products is happening in many regions. However, there is also the trend away from healthy, grainbased staples to increased consumption of grain-based desserts, pastries, and snacks, which may add little in terms of nutrition and may add many unneeded calories. In terms of food and grains, urbanization often also means a mixing of people from various regions and ethnic groups introducing new foodstuffs and tastes and creating the

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availability of a wide array of food products. Many jobs also require travel that introduces the population to more tastes, different grains, and different ways of using grains. Many multiethnic cities have markets and restaurants that offer an array of grain products from amaranth cereal, to buckwheat groats, to corn tortillas, to porridge (oat meal), to quinoa pilaf, to rye crisp, to sorghum beer, to rice noodles, to breads from all over the world.

Tracking Consumer Trends Governments have traditionally tracked the supply and availability of grain-based foods. This is done in a variety of ways. Government and international food and agriculture bodies such as WHO/FAO collect statistics that give information on types and varieties of grain and other products grown; cost and availability of seeds and inputs; stores of grain; weather, environmental, and other factors that affect crop planting, yield, and market availability; food disappearance and consumption; health issues; and economic factors. Data are usually country- or region-specific, but trends in one region may influence consumption in another region. Food consumption data collected by governments, academia, and industry monitor what has been eaten. If collected in a consistent manner, they document changes in patterns of food intake. These may also be useful in predicting what will be needed in greater or lesser quantities in terms of nutrition and the marketplace and may help distinguish between what might be a fad and a trend. Trend watchers and marketers conduct and scan material from books, media, blogs, and other social media, especially in areas that intersect with food such as cooking, health and medicine, energy and the environment, employment and income factors, and agricultural economics. Pronouncements about nutrition by various authoritative bodies impact food choices and messaging about food. Government regulation also impacts what may be sold and what may be said about it. For example, in Mexico, breakfast cereals are being rated with a tax as a measure to address obesity. This causes cereal manufacturers to reformulate to meet government guidelines and to launch more high-fiber or reduced-sugar versions. Understanding how these factors interact can help predict consumer food trends.

Trends in Grain Usage and Its Impact on Consumers Data on supply and disappearance of grains are followed in many regions. For example, the Economic Research Service (ERS) of the US Department of Agriculture (USDA) report consumer demand for food by US households. This may influence the types of crops that farmers grow; the prices farmers receive; how crops are grown, handled, and manufactured; and ultimately what grain products are produced. ERS data on acres planted, yields, stores, and other vital data for the major food grains (wheat and rice) and the major feed grains (corn, barley, oats, and sorghum) also give an idea of grain supply and stores to assess food security for a population. The ERS working with the Census

Bureau and other government agencies. Publicly available databases play a key role in assessment of nutrient intakes and evaluation of the risks related to possible hazards in food (Figure 1).

Trends in Worldwide Wheat Consumption In the 1990s and the first decade of the 2000s, world wheat consumption continued to expand in response to rising population and incomes. Rising wealth fosters increased consumption of meat, meaning that more wheat and grains are being used as animal feed, thus boosting total usage. However, in some countries, direct human consumption of wheat is decreasing. For example, wheat consumption in the United States has decreased since 1997. The pattern of wheat consumption is shown in Figure 2. Per capita wheat use declined from a high in 1879 when one in every four was on the farm and many engaged in hard physical labor, making the per capita consumption 102.27 kg. For nearly 100 years, until the 1970s, wheat use dropped to a low of 50 kg per capita as energy required for both work and play decreased, wealth increased, and diets became more diversified. By 1997, wheat use had rebounded to 66.72 kg per capita. The overall growth in per capita use that occurred between 1973 and 1997 reflected changes that included (1) the boom in away-from-home eating and fast foods with their buns or other grain-based food items, (2) an increase in ready-to-eat options such as breakfast cereals, (3) widespread dietary guidance that promoted diets low in fat and high in carbohydrates and grains for controlling coronary disease, and (4) a wider recognition of health benefits stemming from eating bran, oat bran, and other high-fiber, grain-based foods. The 30-year pattern of increased wheat consumption ended in 1997. There are many reasons for this trend: (1) the decrease in energy expenditure, (2) concern about increases in rates of overweight, obesity, and rising chronic disease, and (3) a number of missteps with the introduction of low-fat products, often

Production + beginning stocks + imports

minus

Exports + farm and industrial use + ending stocks

equals

US food consumption (disappearance) Figure 1 Estimation of food available for consumption (disappearance data) in the United States. Data from USDA/Economic Research Service.


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U.S. per capita wheat flour use, 1964–2012 Pounds/person 150

140

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100 1968

1972

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1980

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1996

2000

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Source: USDA, Economic Research Service calculations using data through the second quarter of 2011 from U.S. Department of Commerce, Bureau of the Census’ Flour Milling Products (MQ311A) and U.S. Department of Commerce, Bureau of Economic Analysis’ Foreign Trade Statistic. Subsequent flour milling calculations are based on data from the North American Millers’ Association.

2008

2012

ERS

Figure 2 US per capita wheat flour use, 1964–2012.

formulated with grains, that failed to either address overweight or add nutrient quality. Thus, around the turn of the millennia, consumers switched from low-fat diets to low-carbohydrate diets of various types such as the Dr. Atkins Diet Revolution and the South Beach Diet. Some of these ketogenic diets allowed only 200 cal from all carbohydrates, so that there was a decrease in consumption of all carbohydrates and grains. This switch reduced per capita wheat and grain consumption. Consumer interest in low-carbohydrate diets spiked after 2000, although this trend continues because of medical literature showing that it is a successful diet pattern for some dieters. ERS estimated per capita wheat flour use at 60.22 kg in 2011. New allegations about wheat and wheat products from blogs and books bashing gluten, wheat and wheat breeding, and grains in general continue to keep wheat consumption at lower levels than in 1997.

Whole Grains, Carbohydrate Quality and Glycemic Response as Trend Drivers The type of grain and wheat products is also changing. Since 2000, emerging science around the health benefits of whole grains was translated into dietary guidance in many countries with recommendations to substitute a portion of refined and enriched grain staples with whole grain breads and cereals, for example, to ‘make half your grains whole.’ Across many continents, this effort is reflected in groups such as Australia and New Zealand’s Grains and Legume Nutrition Council or

the HEALTHGRAIN project in the EU. Nordic efforts to increase rye and oats and other whole grains are part of a healthy eating advice. In Italy and France, there also has been a modest increase in whole grain products with successful launches of whole grain pastas and other products. The Whole Grains Council, which has international reach, has documented a marked increase in the number of whole grain foods and a shift to whole grain offerings in all categories. Data show that consumers in Western countries eat too many refined grain servings and too few whole grain servings such that their calories exceed their energy needs. Grain-based desserts and snacks provide nearly as many calories as sugarsweetened beverages in the US diet of children and teens. Since many of these grain foods offer little in the way of nutrition, it is critical that health professionals and the food industry work together to both improve the nutritional contribution of such products and promote their consumption in the correct serving sizes and as special treats. Concern about the glycemic impact of foods including wheat and grain products has caused some to use glycemic index (GI) in as part of dietary advice, especially for diabetics. Either some governments have allowed (Australia) GI labeling or some merchants (the United Kingdom) have voluntarily labeled foods including grain-based foods with GI. Some government bodies such as Health Canada have decided that the GI is not appropriate for food labeling because of problems with measurement and lack of consumer understanding. When used, dietary guidance in these countries encourages consumers to select products in the same category with GIs

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deemed low to moderate. In some cases, foods carried a GI label, and then, for a variety of reasons, the voluntary labeling was withdrawn. Such labeling can impact the type of grain foods selected and has become a driver in the selection of many carbohydrate foods.

Gluten-Free and Wheat and Grain Avoidance Trends Gluten-free and the avoidance of wheat, gluten, and grain have become both a fad and a trend in some developed countries in the last few years. The trend is also being exported and adopted in some emerging economies. Data published in 2008 changed the thinking in health professions regarding the incidence of celiac disease. These data showed that the incidence, instead of being 1 in 2500, is around 1 in 133, and it is underdiagnosed. And data from the United States, Finland, and even Asia Pacific countries – where the overall incidence is low – show that celiac disease incidence is increasing. Nonceliac gluten sensitivity has been proposed as a glutenrelated disorder. The condition has no medically vetted diagnostic test and no agreement about its incidence, but is characterized by a cluster of symptoms including gas and distention. Beyond these conditions, the trend toward reduced wheat and grain consumption is driven by books and blogs suggesting that modern wheat and grains are addictive leading to overconsumption of grains and are causing obesity and other chronic diseases and health conditions. These same sources demonize not only high sugar intake but also wheat and grains, especially refined grains. Some make consumers believe that foods labeled as gluten- or wheat-free are more nutritious than their gluten-containing counterparts. Summing of all those who need to avoid gluten – those with wheat allergy, celiac disease, and nonceliac gluten sensitivity – means that around 6–8% of the population needs to avoid gluten. In 2014, as many as 30% of the North American population said that they sometimes avoid wheat and gluten. This is also a trend in Australia and New Zealand with 10% of the population indicating that they are avoiding gluten. In terms of markets, the United Kingdom has the biggest gluten-free market in all Europe, but Germany has the largest market on the continent. Italy and Scandinavia also have a sizeable market. Yet, all of these countries have about 1% of consumers with celiac disease. Compared to other European countries, sales of gluten-free foods are on the low side in both France and Spain. In terms of trends, the gluten avoidance fad will have an impact for a while and will likely diminish. However, there will be a baseline trend for those with celiac disease, allergies, and other gluten issues that will remain and may increase. Concern over carbohydrate quality will remain high, and changes in types of carbohydrates and grain-based foods will serve as another trend driver.

Rice Rice supplies around 20% of the calories consumed worldwide and is a staple for nearly half of the world’s 7 billion people.

More than 90% of the world’s rice is consumed in Asia, where it is a staple for a majority of the population, including some of the world’s poorest populations. Developing countries have long depended and continue to rely on rice’s versatility, protein availability, and high caloric value. From the 1960s to the 1990s, Asia’s per capita rice consumption went from 85 kg per year to nearly 103 kg. In that same period, per capita consumption rose from 50 to 65 kg per year. The rising per capita consumption plus the growing population more than doubled global rice consumption during this period from 150 to 350 Mt. Changes in the standard of living have altered rice consumption patterns. Increased wealth in countries such as India and China slowed the rate of growth in rice consumption due to a switch to foods with higher value such as meat and produce. In some countries such as Japan and Taiwan, there is decreasing rice consumption due to Westernization of the diets, a decline of family size, increasing participation rate of women in labor market, and aging populations. However, rice consumption continues to rise in Southeast Asia (the Philippines and Indonesia), South Asia (India and Bangladesh), and many parts of Africa. After Asia, the second largest rise in rice consumption occurs in sub-Saharan Africa. Overall, the rising populations of emerging and developing economies cause a rise in overall rice consumption. For those needing to avoid gluten, rice has become an important substitute. Recently, concern about arsenic in rice has been raised as an issue and may impact consumption. In summary, increasing wealth in some countries may shift consumers away from rice and grains to other foods afforded by higher-income consumers, but the increases in population in many countries offset any decline in worldwide consumption. Worldwide rice production was 600 Mt in 2000. It is predicted to increase 1.5 times by 2030, to 904 Mt with gains in production in nearly all areas.

Maize, Oats, Sorghum, and Barley Maize (corn), sorghum, barley, and oats are used more as feed grain than as human food. Maize contributes one-third of the world’s cereal output. Demand for maize as a feed grain will increase. Globally, maize production has increased by nearly 50% due to expansion in Asia and high-yielding varieties including genetically modified corn (bT-corn). Differences in consumer attitudes to the GM corn around the world have dramatically affected its acceptance. The challenge this creates for international trade of maize and future production must be addressed and can sharply impact trends in its use as a feed or food grain. Only 15% of maize is processed for human food to become a variety of milled grain products and starch, sweeteners, corn oil, and alcoholic beverages. Direct use of maize as human food is unlikely to change significantly, even in countries where maize is an integral part of local diets. Oats are an important foodstuff in northern climates because they tolerate cooler summers and more rain than many grains. Oat production has remained steady for the past 10 years. The EU region is the largest producer of oats, but Canada is the largest exporter. The United States is the

FOOD GRAINS AND THE CONSUMER | Consumer Trends in Grain Consumption world’s largest importer of oats, even though it is the world’s fourth largest oat producer. Mexico is the world’s second largest oat importer, followed by Japan. Per capita consumption of oats is high in former colonies of the United Kingdom with Canada and Australia topping the consumption charts. Russia, the United States, Poland, the United Kingdom, and Scandinavia are countries with a higher consumption of oats than many countries. In the United Kingdom, oats comprise 3% of the crops cultivated, but half the oat crop is used as human food where about 50% of the population eat porridge (oatmeal). Among the grains, oats is viewed as a healthy grain. This trend began with the ‘oat bran’ craze of the late 1980s when research documented the health benefits of oats. Its status as a whole grain and high nutritional marks, with its micronutrients, phytochemicals, and protein content ranking high among the grains, continue to lure consumers. The real driver for oats consumption is its viscous fiber b-glucan. The data on its cholesterol-lowering ability are so well documented that it has a health claim in a number of countries. The first of many claims was in the United States in 1997 with other countries following. Interest in the health value of oats is expected to continue as consumers continue to want good-tasting, high-fiber whole grains. Emerging research on benefits of oats for blood glucose control and satiety keeps consumers interested, and the production of gluten-free oats for celiacs is driving demand for oats. The only concern is that oats is the only major world crop where production has shown a steady decrease since 1970. The decline amounts to a total of about 60%.

Barley Only 2% of the barley crop is used directly for human food. Malt production for beer takes over 40% of the crop. Barley, like oats, contains the soluble fiber b-glucan, which has been associated with maintaining healthy cholesterol levels and healthy heart. In 2005, FDA amended its health claim for soluble oat fiber and coronary heart disease to include barley. Studies indicate that barley may also have potential in modifying glycemic response in humans. Also, the vitamin E of the outer layers of whole barley may be important. There is a trend by consumers to romanticize ancient grains, and barley is considered part of this ill-defined category. Use of barley as sprouted grains is also showing some consumer interest.

Trends in Consumer Consumption

accounting for at least half of this amount. Using ERS’s lossadjusted food availability data from 2005, it is estimated that more grain servings than recommended (8.1 oz-eq of grains per person per day versus the 6 recommended) were consumed. Instead of half of these as whole grains, nearly 90% was as refined grains. Consumption data for children and teens show that nearly as many calories emanate from consumption of grain-based desserts and snacks as do from sugar-sweetened beverages. Thus, Americans, on average, overconsume refined grains with added sugar and fat and underconsume whole grain staples. Only a small percentage of the population was eating the recommended amount of whole grain. Efforts to bring total amount of grain eaten in line with recommendations while substituting whole grains for refined grains must continue in order to reverse current trends. It is difficult to predict what economic and agronomic conditions and policies, geopolitical climates, and technical advances will affect food pricing and availability and costs especially with population, fuel, and environmental pressures. Trend drivers such as new health research, social media with food fads and scares, changing social norms, adoption of foods from other countries, and other issues related to consumers will continue to affect consumption but are hard to predict. Trend watchers and available data sources can track trends and may be used to help answer critical questions about food choices.

Summary Consumption data for grains and grain-based foods relate to a number of trends. Major factors that affect trends around the world include demographics (age, household size, household income, women in the labor force, amount of education, geographic location, and ethnic background), diverse lifestyles, and consumer attitudes (toward food habits and food preferences). Consumer trends that affect movement of grain-based foods through the food system include food marketplace trends, food processing/manufacturing trends, and agricultural trends. Major trends in the food system include niche marketing, development of grocery stores to improve food shopping convenience, increased demand for and development of convenience foods, and the growing demand for food away from home.

Exercise for Revision

• In many countries throughout the world, calorie intake has increased since 1970. Despite charges to the contrary that excesses are due to one food group such as grains, data from ERS suggest that food availability and consumption for all major food groups have increased. The ingestion of more energy over the last three decades has not been translated into more people meeting dietary recommendations for certain food groups and nutrients. The 2005 Dietary Guidelines for Americans recommend (for those on a 2000-calorie-per-day diet) the consumption of 6 ounce equivalents (oz-eq) of grains per day with whole grains

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Compare the effects of agriculture policy in a country from the developed world and developing world and see how it affects grain consumption trends. Follow two different grain food fads within a country and see what caused the fad, how long they lasted, and at what rate they rose and fell, and compare the drivers of the trend. Compare a grain food fad in different countries and see what is similar and different. What are the trend drivers needed to change attitudes regarding grains produced using biotechnology? Examine the trend behind distrust of traditional breeding among some sectors.

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Discuss impacts of inputs (water, fuel, fertilizer, etc.) on trends in grain consumption in a region. Study the interaction of food trends such as the locavore movement, the Paleo diet, and other meat-based antigrain diets and the organic movement on grain and food production and the ability to feed a growing world population.

See also: Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Health Effects of b-Glucans Found in Cereals; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Grains and Health; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Grains Around the World: Grain Production and Consumption: Overview; The Cereal Grains: Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Maize: Overview; Oats: Overview; Rice: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Abbassian A (2007) Maize international market profile. http://siteresources.worldbank. org/INTAFRICA/Resources/257994-1215457178567/Maize_Profile.pdf (accessed January 2015). Economic Research Service (ERS), U.S. Department of Agriculture (USDA). Food Availability (Per Capita) Data System. http://www.ers.usda.gov/Data/ FoodConsumption; http://ers.usda.gov/topics/food-choices-health/foodconsumption-demand/food-consumption.aspx.

Kubo M and Purevdorj M (2004) Future of rice production. Journal of Food Distribution Research 35(1): 128–142, http://ageconsearch.umn.edu/bitstream/27145/1/ 35010128.pdf (accessed January 2015). Lin BH and Yen ST (2007) The U.S. Grain Consumption Landscape: Who Eats Grain, in What Form, Where, and How Much? ERR-50. U.S. Department of Agriculture, Economic Research Service. Mohanty S (2013) Trends in rice consumption. http://irri.org/rice-today/trends-inglobal-rice-consumption (accessed January 2015). Rice Outlook/RCS-14l/December 12, 2014 Economic Research Service, USDA. Wells HF and Buzby J (2008) Dietary Assessment of Major Trends in U.S. Food Consumption, 1970–2005. Economic Information Bulletin No. 33. Economic Research Service, U.S. Department of Agriculture. World Agricultural Supply and Demand Estimates WASDE-537 – January 12, 2015.

Relevant Websites http://www.agr.gc.ca/eng/industry-markets-and-trade/statistics-and-marketinformation/by-product-sector/crops/crops-market-information-canadian-industry/ market-outlook-report/oats-situation-and-outlook-august-2010/? id¼1378843401619. www.barleyfoods.org (accessed January 2015). http://www.efsa.europa.eu/en/datex/datexfoodcdb.htm. http://ers.usda.gov/data-products/food-availability-%28per-capita%29-data-system/. aspx (accessed December 2014). http://ers.usda.gov/data-products/food-availability-%28per-capita%29-data-system/ food-availability-documentation.aspx. http://ers.usda.gov/topics/food-choices-health/food-consumption-demand.aspx. http://www.ers.usda.gov/topics/crops/wheat.aspx. http://www.ers.usda.gov/topics/crops/wheat/usda-wheat-baseline,-2014-23.aspx. http://www.ers.usda.gov/topics/international-markets-trade/global-food-markets/ international-consumer-retail-trends.aspx. http://irri.org/rice-today/trends-in-global-rice-consumption. http://www.just-food.com/management-briefing/germany-canada-australia-amongother-growth-markets_id123020.aspx. http://www.nationmaster.com/country-info/stats/Agriculture/Grains/Oats/ Consumption-per-million (accessed January 2015).

Cultural Differences in Processing and Consumption AMR Hayes, St. Catherine University, Lafayette, MN, USA JM Jones, St. Catherine University, Arden Hills, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights


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Cereal grains are staple foods among many cultures. They can be consumed separately or in combination with other foods. Each variety of cereal grain contributes unique nutrients, mainly providing carbohydrates, protein, dietary fiber (DF), and vitamins and minerals such as B vitamins, vitamin E, magnesium, and iron. Additionally, different processing techniques can affect the bioavailability of certain nutrients in cereal grains. The aims of this article are to discuss the place of grains in the diet, the effects of processing on grain nutriture, some specific types of grains, and the overall impact of cultural practices of grain consumption on diet.

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Consumption of cereal grain varies by cultural practice and country, and each variety contributes unique nutrients that can be affected by different processing techniques and preparation methods. The processing techniques used in different countries impact starch digestion and energy yield of cereal grains; most minimally processed grains are digested slowly, and highly refined grains provide slightly more calories than less refined types. Cereal grains are incomplete sources of protein but can be paired with other foods containing the amino acids they lack to provide a complete source of protein, as is evident in the traditional dishes of many countries. Processing can either inhibit or promote the bioavailability of minerals and toxic compounds, affecting nutrient needs in certain regions. Wheat is the most common cereal grain in the majority of Western countries; refined or enriched flours are popular in the United States, Europe, Latin America, South Asia, and much of Australia. Rice contributes approximately half of the calories for half of the world’s population and is common in regions of South and Southeastern Asia, Japan, Latin America, the southern part of the United States, and the Philippines. Discussions of cereal grains (teff (tef), oats, rice, corn/ maize, barley, rye, millets, sorghum, and triticale) and ‘pseudocereal’ grains (amaranth, buckwheat, and quinoa) provide insight into their histories and current uses. Increasing globalization and promotion of specific foods, such as those that are gluten-free or whole grain (WG), are altering the types and roles of cereal grains in the diet of many regions.

Learning Objectives

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To identify general variations in energy, protein, and nutrient requirements among cultures. To recognize and understand some of the changes in cereal grains that occur with certain processing techniques or cultural preparation methods. To gain insight into the diverse histories of distinct cereal grains, their nutritional qualities, and some of their current uses. To attain an understanding of cereal grains that promotes the exploration for future applications addressing changes in dietary habits.


Cultural Differences in Consumption Energy requirements Cereal grains can provide over 50% of both energy and protein in parts of the developing world because they comprise the fundamental components of most diets. Since nutrient requirements, food availability, and cultural practices vary by country, the role of cereal varies. For example, abundant supplies of food in developed countries result in cereals comprising a smaller percentage of the diet and energy intake. The protein contribution of cereal grains is less important for individuals in the developed world than those in the developing world. Exceptions may be for those who are vegetarian or flexitarian. Cereal grains that are highly refined may contribute to more available carbohydrate and slightly more calories than unrefined varieties. This is partly due to structures in the outer layers of grain trapping some of the starch and making its form resistant starch (RS) type 1. Germ and bran phytochemicals may inhibit the activity of amylases and proteases, thus reducing the total number of calories available. High levels of tannin in some grains such as tannin-containing sorghum varieties can have a significant impact on calorie availability in countries where this grain is a staple. Refined grains may be beneficial in developing countries, where calories are in high demand. Alternatively, in developed countries where excessive caloric consumption is widespread, the inclusion of WGs – with their slightly reduced carbohydrate contribution – may be advantageous.

Protein Each cereal grain is characterized by distinct nutritional qualities. When the cereal grain is a major food source in a culture or region, its nutritional characteristics are of notable importance. In developed countries, protein quality and quantity of grains

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are less important because other protein-rich foods are more available and constitute a higher percentage of the diet. Processing methods impact protein nutritional quality of cereal grains. Milling, fermentation, and germination increase the digestibility and bioavailability of protein and certain essential amino acids. Germination also increases the synthesis of the amino acids lysine and tryptophan. When cooking and ‘dehulling’ (debranning or decortication) accompany fermentation of grains such as sorghum and millets, protein digestibility is increased because antinutrients such as tannins are reduced. In the case of tannins, this means that tannin’s binding of protein and inhibition of digestive enzymes (proteases) are reduced. Cereal grains are generally incomplete sources of protein, as they are limited in the amino acid lysine. Corn (maize) is also limited in tryptophan, while wheat, barley, and rye are low in threonine. Through pairing cereal grains with other foods containing the limiting amino acids, a complete protein can be achieved. This protein complementation is exemplified throughout the world by national dishes that pair cereal grains with legumes. Cereal grains contribute methionine, which is generally limited in legumes, while legumes contribute lysine and other amino acids. Some regions use a grain-based dish with a very small amount of animal protein such as cheese or meat. The following are a few examples of popular dishes:

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Ethiopia: Kik alicha wot (spiced cooked split peas) with injera (teff flatbread) India/Sri Lanka: Chapati (cereal unleavened flatbread) with dhal (legumes, often lentils) Middle East: Pita wheat bread with hummus (garbanzo bean–tahini spread) China: Congee (rice porridge) with toppings of tofu, fish, and sometimes meat Mexico: Corn tortillas, beans, and rice, sometimes with a little meat or cheese Southern Africa: Samp (porridge from coarse milled maize) with whole common beans or cowpeas The United States: Peanut butter on whole wheat bread The United States: Macaroni and cheese

Carbohydrates, including DF Starch Energy from cereal grains is primarily from starch. Processing impacts starch digestion and energy yield. When grain is milled into flour, energy yield is increased. This is important in areas of nutrient and energy deficiency. Germination and fermentation result in the partial degradation of starch, which promotes starch digestibility. Grains that are cooked whole or are minimally processed may be digested slowly, therefore slowing glucose release into the bloodstream, referred to as slowly available glucose (SAG). This may be advantageous for satiety and control of blood glucose and lipid levels. Processing can alter the ability of digestive enzymes to access the starch. For example, the compact structure of an al dente pasta impedes access of the digestive enzymes to the starch, lowering the glycemic response (GR), but not as much as is seen, for example, in a spa¨tzle noodle from Germany. With the porous structure of breads, even WG ones, amylases have easy access to the starch and thus elicit a rapid GR.

Lowering the pH as occurs through a sourdough process changes the activity of the amylase and lowers the GR. Cultural practices of adding acid, as with oil and balsamic vinegar on bread or vinegar in Japanese sushi, also lower the glycemic impact. Using fats such as oils or butters on bread or using legume and nut accompaniments also lowers the GR.

Resistant starch Processing techniques can impact starch digestion. Processing can affect the degree to which a starch is digested and absorbed and can increase or decrease the content of RS. The following processes increase RS: extrusion at high temperatures, as in the making of cornflakes, followed by cooling to induce crystallization of the starch molecules. Thus, amylase enzymes do not readily penetrate the starch, which means some starch is undigested. Treatments of repeated heat and moisture, such as is practiced in Africa where maize porridges are repeatedly heated and cooled, also create RS (type 3). Cooked kernels and bulgurs, as is popular along the Mediterranean, trap starch in the grain matrix and make it unavailable to digestive enzymes resulting in RS (type 1). Microwave cooking shortens starch chains in many foods and speeds digestion by having more rapidly available glucose (RAG) and less RS. Germination and fermentation not only may decrease RS but also may change the levels of RAG and SAG The following processes increase RS:

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Steam cooking Autoclaving Parboiling Baking Extrusion cooking (some studies show it decreases it slightly also) Coarse milling

Cultural preferences for grain varieties or grain processing can dramatically impact carbohydrate availability and the GR. For example, the amount of RS and SAG in rice varies by processes such as parboiling and variety. High-amylose varieties, such as ‘basmati’ preferred in India, have lower GR. Conversely, varieties high in amylopectin, such as glutinous rice preferred in parts of China and Japan, have high GR. Most forms of processing, notably parboiling, often reduce GR.

Dietary fiber A growing body of evidence suggests that inadequate DF intake is associated with decreased gut motility and increased risks of heart disease, diabetes, and certain types of cancer. Diets in many countries are characterized by inadequate intake of DF and WG. Extraction rate, or the degree of milling, impacts the nutritional quality of cereal grains. Higher rates retain more bran and germ and therefore have a higher level of DF and grain phytochemicals. Countries that regularly use higher extraction rates, such as Norway, have increased DF and grain phytochemical intakes. DF intake is higher in countries that regularly include WG in the diet. For example, regular consumption of WG products made from whole wheat, rye, oats, and barley as occurs in Scandinavia and parts of northern Europe contributes to higher DF intakes than in many European nations. In parts of

FOOD GRAINS AND THE CONSUMER | Cultural Differences in Processing and Consumption Asia where white rice is the staple, the DF contribution of cereal grains is frequently low. In a traditional rural Mexican diet with its staple of WG corn tortillas and beans, DF intake is high, whereas in the urban areas, DF may be lower due to a Westernized diet pattern. The specific types of cereal grain typically consumed by various cultures also affect nutriture, as each grain offers various fiber types and phytochemicals. Rye, a common choice among Germans and Scandinavians, is relatively high in arabinoxylans. Wheat, which is common in North America and southern Europe, contains fewer arabinoxylans than rye, but its cellulosic bran is associated with gut health and improved laxation. b-Glucans, which are found in barley and oats, are often consumed in northern Europe. In parts of the world where high-tannin cereals such as sorghum are the staple, nutrient availability, especially that of minerals, is compromised. Additionally, some hull materials may be bowel irritants or can damage the gut tissue (e.g., oat hulls with their razor-sharp pieces).

Micronutrients The bran and germ portions of cereal grain contain the majority of the vitamins and minerals. Overmilling and high degrees of extraction even as practiced in producing white bread flour can remove the aleurone layers of grains, along with germ-rich vitamins, minerals, and other grain phytochemicals. Thus, limited extraction and the inclusion of WG foods as is part of traditional cultural food patterns may help maximize micronutrient amount contributed by grains. However, consumption does not always equal absorption, as certain microcomponents may be bound or unavailable. While milling reduces the overall number of micronutrients, it also makes them more absorbable. Heat treatment of some grains not only increases shelf life but also is critical to preventing rancidity of all fats including essential fatty acids, fat-soluble vitamins, and antioxidants within the bran. Rice bran and oats are just examples of grain or grain components that are typically subjected to heat treatment in order to inhibit lipase activity of the grain and germ. However, severe heat treatments may destroy vitamins, bind nutrients, and potentially promote rancidity. B vitamins in grains are particularly affected by processing. Since thiamin is among the most heat-labile of the vitamins, it is easily reduced through heating in alkaline pH. Thus, the thiamin content of chemically leavened (baking soda) baked products, such as Irish soda bread, can be decreased by over 70%. Conversely, processing via germination and fermentation can increase B vitamins. In the case of nixtamalization (the process of liming corn), the tightly bound niacin is released from niacytin to make it available to the body. Thus, in countries where maize was traditionally limed, pellagra (niacin deficiency) was not endemic. Enrichment and fortification are used in many countries to replace some of the vitamins and minerals lost during milling. Such techniques are used to address nutrient deficiencies and their corresponding health consequences. For example, pellagra was eliminated in the southeastern United States by niacin enrichment of corn. In countries with mandatory folate fortification of grain products, birth defects such as spina bifida are reduced, in some cases, by over 50%. However, it is important

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to note that enrichment and fortification efforts can be negated by cultural practices. For example, washing rice prior to cooking it or cooking it in large amounts of water, which is then discarded, washes away much of the vitamin-rich talc added to enrich the rice. Fermentation and malting processes can alter nutrient quality. Fermentation typically results in increased levels of vitamin B, but the extent of increase depends on the type of grain and the particular process. Malting or germination of grains and pulses has been found to increase vitamin C and phosphorus availability. Such practices are especially important in parts of the world such as India and Africa. Mineral status is largely impacted by the grain choice and processing of a certain culture. Ligands in grain, such as tannins and phytates, bind iron, zinc, and other metals, rendering them less bioavailable and leading to mineral deficiencies. However, absorption of some minerals can be improved through processing techniques. Notably, milling with debranning removes most of the tannin and some of the phytate, increasing mineral bioavailability. The crushing and pulverization of the grain may also increase bioavailability. Traditional lactic acid (sourdough-type) fermentation can facilitate the phytase reaction, releasing the tightly bound zinc in many grains. The longer the fermentation process, the longer the phytase enzyme is allowed to degrade phytate, thus improving mineral status. In the 1970s, hypogonadal dwarfism was shown to be due to zinc deficiency, due to diets where 85% of the energy needs came from whole wheat pocket bread. With efforts to increase the bioavailability of zinc in food and improve overall diet, the incidence of this health condition has been greatly reduced.

Toxic compounds Aside from nutrient-binding phytates and tannins, cereals and other plant foods can contain toxic or antinutritional substances. However, processing techniques such as milling can remove a majority of these:

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Protease and amylase inhibitors found in cereal bran are lost or reduced during milling, germination, or fermentation processes. Grain soaking or heating as practiced in some cultures may also reduce the activity of these inhibitors. Saponins that occur, for example, in some pseudocereals not only can cause growth inhibition and are known for their hemolytic activity but also may have anticancer impacts on the colon. Again, the cultural practices of soaking, fermentation, and germination may reduce these. Mold toxins can affect any grain, especially those grown in humid climates or harvested with high moisture levels. Grain grading and inspection processes used in various regions are in place to prevent various mycotoxins from entering the food supply. Milling may remove mycotoxins in the outer grain layers but not those contaminating the endosperm. Industrial milling practices have steps that remove unsound grains or incorrectly colored grains in early points of the milling process as an attempt to remove any infected grains. Fermentation and nixtamalization may further reduce levels of aflatoxins, due to either an opening of the lactone ring or a loss of the toxins into soaking liquid.

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Cultural Uses of Specific Grains and Their Impact on Nutritive Qualities Wheat and Its Parent/Derivative Grains and Products Wheat Wheat and its related grains such as durum spelt and other wheat parents are used as flour, wheat berries, bulgur, cracked wheat, and coarsely milled fractions such as farina or semolina. All types of wheat can be used for pastas, but durum makes the optimal product. In most Western countries, more foods are made with wheat than with any other cereal grains. While WGs are used, refined or enriched varieties are popular in the United States, Europe, Latin American, South Asia, and much of Australia and Africa. Breads, pastries and small cakes, breakfast cereals, and pastas are just some of the ways wheat is used. Noodles are found around the world in various forms. In many countries, they are made from durum wheat. Couscous, while often mistaken for a grain, is a steamed semolina, which is a staple of cooking in North African countries such as Morocco, Algeria, Tunisia, Libya, and Egypt. To produce couscous, yellow granules of semolina, which are made from durum wheat, are parcooked and then dried. Its culinary uses as a salad or pilaf base, an addition to soups, an accompaniment for meats and vegetables, or a dessert make it like other small grains and some pastinas. Both plain and flavored varieties of couscous exist.

Bulgur Whole wheat kernels that are broken to become cracked wheat. If they are soaked, precooked, and then dried, they become bulgur. Evidence indicates bulgur has been eaten by Arab, Israeli, Egyptian, and Roman civilizations as early as 1000 BC, while the Chinese consumed bulgur as early as 2800 BC. Currently, bulgur can be sold as a pilaf or tabouli, taboule, tabbouleh, or tabouleh mix.

Grano Grano is a specialty durum that has been cultivated in Italy since the fifth century BC. Its origins in Sicily and Puglia make it a popular food choice on certain holidays, but it is a newly emerging product in the United States. Firm and chewy in consistency, grano is made from specially selected durum wheat. Although it most resembles barley, its bran has been removed, making the starch more accessible. Grano can be cooked like arborio rice in dishes similar to risotto and either used as a hot accompaniment with pasta or served cold in salads.

Einkorn/farro/emmer Einkorn and its cousin farro are hulled wheat. They were two of the first types of wheat to be domesticated about 11 millennia ago in Georgia, Armenia, and Turkey. Its name, however, is from the German meaning ‘first grain.’ Farro/emmer is known by different names depending on the region, with the most common ones being farro and emmer. Nutritionally, einkorn is somewhat higher in protein than modern wheat or farro, but all have lysine as their limiting amino acid. Einkorn contains somewhat higher levels of phosphorus, potassium, iron, and

magnesium than wheat or farro. Like many ancient wheat relatives, the lower yields and greater costs of einkorn and farro make them less widely available. They can be used in any way that wheat is used, and they are now being sought as a specialty grain for variety.

Kamut Kamut, a relative to durum (also known as khorasan), was originally cultivated in the Fertile Crescent, and is still used along the Mediterranean. Given its naturally higher sugar content, kamut has a sweet nutty flavor. It provides B vitamins, selenium, and magnesium; is higher in zinc, magnesium, and selenium than modern wheat; and provides a higher amount of protein but a similar amino acid profile compared to hard red wheat. Kamut can be used as whole kernels for pilafs or ground into refined WG flour to be used in breads, pasta, and other grain-based foods.

Spelt Spelt is known as ‘dinkel’ to Germans and ‘farro’ (but different from emmer, also called farro) to Italians. It dates back to 7000 BC. Like modern wheat, this ancient parent has winter and spring varieties as well as hard and soft types. It is mainly used in breads and pastas. Its protein content is only slightly higher than modern wheat, but it is higher in selenium, phosphorus, and magnesium than most cereal grains. Spelt WG flours and doughs contain significantly higher amounts of RS and give less available starch. However, baking or other processes affect this, with breads showing the highest starch availability and cookies the lowest. All of the grains related to wheat contain gluten and must not be used in the preparation of products for the gluten-free market.

Teff (Tef) Teff, a tiny, slightly sweet-flavored grain, is so small its name means ‘lost grain.’ The bran and germ compose a larger percentage of the grain than other grains, and it has high levels of RS. Teff provides fiber and B vitamins, has a higher overall mineral content than most other cereal grains, and is known for its levels of iron and calcium. However, it may not be as high in iron as was once thought. Currently, it is also being grown more widely in India, Australia, and Canada. Traditionally, teff is ground into flour and fermented to make spongy sourdough bread called injera (an Ethiopian flatbread resembling a spongy large pancake). Teff’s use in some other countries has expanded into foods featuring ancient grains or multigrain blends, such as tortillas, pizza, crackers, pasta, pancakes, snacks, breads, cereals, and many other products. Its application into gluten-free products is expanding.

Oats Oats are a popular grain in regions where they thrive, including Russia, Canada, North America, Finland, Poland, and the United Kingdom. In countries that were once part of the British Commonwealth, porridge was standard breakfast fare with steel-cut or pin-milled oats being preferred for their chewy texture and nutty flavor. While this is still a breakfast option,

FOOD GRAINS AND THE CONSUMER | Cultural Differences in Processing and Consumption changing habits have caused a decrease in the intake of porridge and an increase in oats in beverages, as additions to yogurt and as the basis of ready-to-eat cereals and breakfast and energy bars. For other parts in the British Isles and most of Scandinavia, oats are found in many foods such as oatcakes, biscuits, crackers, and even soup thickeners. In the United States, most groats are steamed and flattened into rolled oats (‘old-fashioned’ or regular oats, quick oats, and instant oats). The higher the degree of flattening and steaming, the quicker the cooking time and softness of the end oats. In Germany, Switzerland, and other parts of Europe, muesli-type cereals, based on uncooked, rolled oats with a combination of nuts, fruits, and other grains, are popular. Part of oats’ popularity is due to their nutrition and satiety properties. They contain more than 20 unique polyphenols called avenanthramides. They have high antioxidant, antiinflammatory, and anti-itching activities. They are high in b-glucans. These fibers have been proven to lower serum cholesterol and help maintain a healthy blood glucose level. A number of countries have health claims that tout these benefits.

Rice Rice’s roots date back to South Asia. It has been dispersed and cultivated in a wide variety of habitats and consumed by humans for centuries. It is grown on every continent except Antarctica. Rice provides about half the calories for up to half of the world’s population, especially in South and Southeastern Asia, Japan, Latin America, the southern part of the United States, and the Philippines. Rice has a role in religious and ceremonial occasions and medicine in many cultures. It is so important in certain regions that saying ‘Hi. How are you?’ is literally asking ‘Hi. Have you eaten rice today?’ Among various parts of the world, the type of rice desired can be very different. Rice is classified by texture, color, and size: long-, medium-, or short-grain varieties. Short-grain varieties can be referred to as ‘sticky’ because of their higher amylopectin content (starch), while brown rice (WG rice) is known for its higher levels of vitamins and minerals, and colored rices are prized for their variety and antioxidant capacity, the latter being due to their high anthocyanin content. Among the diverse rice uses throughout the world are Chinese stir-fries, Spanish ‘paellas,’ Japanese ‘sushi,’ Indian ‘biryani,’ Thai ‘salads,’ Middle Eastern ‘pilafs,’ Italian ‘risottos,’ Mexican beans and rice, Senegalese ‘yassa,’ Norwegian rice pudding, American ‘gumbos,’ and so many more. Wild rice is not actually a kind of rice. Instead, it is a semiaquatic grass historically grown in lakes, tidal rivers, and bays. Native Americans traditionally harvested the wild rice in northern lakes and processed it by parching the green seeds in large pots over open fires and then packing them away in birch-bark baskets. Commercially, wild rice farmers ‘cure’ the rice until the chlorophyll dissipates, and then while the kernel is still in the hull, it is dried. The inedible hull is removed mechanically, leaving the kernel exposed. All these processes give wild rice its signature nutty, smoky flavor. It is slightly higher in protein than most other WGs and is a good source of fiber, folate, magnesium, phosphorus, manganese, zinc, vitamin B6, and niacin. Native Americans mixed it with berries and used it

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with game. It is often mixed with other rice and can be used any way that rice may be.

Corn/Maize Corn, also known as maize, is a staple in parts of Central America, Africa, India, and China. It can be used alone or in combination with other foods and is the most widely grown crop in the Americas. The domestication of corn occurred over 9000 years ago in Mexico. Corn was carried from the Americas to Europe and Africa by early explorers and traders, so it became important in the cuisines of many countries throughout the world. Maize contains a small amount of provitamin A (which can contribute up to ten times the content of other grains) and is high in antioxidants and carotenoids associated with eye health (lutein and zeaxanthin). Its protein quality is poor and niacin tightly bound, so it is associated with pellagra in marginal diets based on corn. Nixtamalization, a process used in Latin America, releases the niacin and improves amino acid availability in order to prevent pellagra. This process of soaking the grain in lime (calcium oxide) gives it a flavor that characterizes the Latin kitchen. Traditional dishes mixing corn with beans and rice in many cultures provide amino acids to make a complete protein. Flour from the nixtamalized corn is masa harina, which is made into tortillas, enchiladas, and many other dishes. In the United States, corn was originally soaked in lye to remove the pericarp. It was then dried to make hominy and hominy grits. Hominy and corn meal are popular throughout the southern and southwestern United States with foods such as corn pone and hush puppies. Cheese and grits are popular in the southeastern United States and spicier corn dishes and hominy lamb stews (posole) are popular in the Southwest. Corn-based breads and hot cakes are used throughout the United States and can be made of corn alone or have wheat added to them. The method and ingredients vary across the country. In Italy and Spain, corn is used for dishes similar to polenta. Ugali in Kenya and mealie porridge in South Africa are just a few of the corn dishes that are also important in Africa.

Barley Barley’s use as human food is small despite its being the grain with the fourth highest production in the world. The amount of milling required to make the barley edible varies by whether the grain is hulled or hulless (naked). Like chaff of the wheat, the outermost layers are not digestible and must be removed by processing. For hulless varieties, the outer hull is loosely attached so very little polishing is required for its removal. Whether hulled or hulless, most barley is polished (pearled) to some degree, varying from regular to medium to fine to baby pearled barley. On average, pearled barley is about one-third lower in micronutrients than unpearled. Pot barley (also called scotch barley) has the hull polished off, but the polishing process is least invasive. Barley’s nutritional contribution is similar to wheat with a few differences. It is highest in fiber of all the WGs, containing on average 17 g of fiber/100 g, with a range from 12 to 40 g/100 g. The fiber in barley is b-glucans, and unlike in

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other grains, it is distributed throughout the grain. Barley’s bglucans have a health claim in the United States and in other countries. Barley contains twice as many fatty acids as wheat, which accounts for its slightly higher calorie content. Barley’s lysine content is higher than most other grains, giving it a better amino acid profile. It is a gluten-containing grain. Barley’s prime use is for feed and beer, but it is also used for making a tea in parts of Asia. Barley can be malted to make a sweet syrup or addition to milk as in products such as milo or malted milk powder. Additional applications include processing barley into flakes and other ready-to-eat cereals, porridge, pancakes, and flatbreads; using it as pilafs and sides; and adding it to hearty soups in areas of the British Isles to northern and Central Europe.

Rye Rye is grown in regions with colder climates, such as Russia, the Baltics, parts of Germany, Poland, Scandinavia, Canada, Argentina, China, and Turkey. Rye came to the Americas with European settlers in the sixteenth and seventeenth centuries and spread to South Africa and Australia during the mid-nineteenth century. Like other grains, it is used to some extent in many regions, but is most popular in northern and eastern Europe where it has many uses and is popular in peasant-style breads. Rye contains gluten, but much less than wheat, making many rye breads heavy as in the classic German pumpernickel bread. Rye mixed with wheat improves the texture and volume. Sourdough ryes are popular in a number of countries. Rye berries may be soaked for several hours, added to a small amount of sourdough rye culture, and baked; eaten hot as a cereal; used in sides such as pilaf; added to soups; or used in a grain salad. Rye can be flaked or added in other forms to ready-to-eat cereals, and thin crisp rye breads are very popular.

Millets Millet actually refers to several different small-seeded cereal grain species, the major ones being pearl millet, foxtail millet, proso millet, finger millet, and teff (although the latter is usually considered separately). Millets are thought to have been the staple grain in Asia before rice, so their cultivation is over 10 000 years old. They are an important food source in many parts of the world and are used widely in developing counties. They are generally drought- and temperaturetolerant, making them well suited for cultivation in semiarid tropics in Asia and Africa, especially in India, China, Nigeria, and Niger. Millet seeds are small, round, and relatively soft, of varying colors and are generally rich sources of antioxidants. Finger millet is notably rich in calcium. Millets can be eaten as a breakfast porridge in regions such as Africa and China. They can be added to soups and stews, popped as corn, or made into sides such as pilafs and couscous. Millets are used in breads, breakfast cereals, cookies, and crackers. Millets are gluten-free grains so they used for foods in this growing market. In India, ragi (finger millet) is used to make roti (staple flatbread). In Africa, millets are also used for brewing beer and in China, for ‘wine.’

Sorghum Sorghum originates from Africa around 8000 BC. It thrives in adverse conditions, making it versatile and popular. Sorghum is known by many names – milo or guinea corn (West Africa), mabela (South Africa), dura (Sudan), mtama (eastern Africa), jowar (India), or kaoliang (China). Since sorghum’s hull (actually pericarp) is edible, it can be eaten with all its outer layers and thus retains the majority of its nutrients. WG sorghum contains essential B vitamins, minerals, fiber, antioxidants, other phytonutrients, and policosanols. The latter are thought to impact cardiac health. In Africa and parts of Asia, sorghum is used primarily as a human food. The light color and neutral flavor of white tanplant (the so-called food-grade) sorghum varieties easily enable their substitution for wheat flour, wheat-based, and gluten-free and multigrain baked goods including muffins, breads, pizzas, pastas, casseroles, cookies, cakes, and pies. Sorghum’s gluten-free, non-GMO WG status has increased its use in the West. It works well in gluten-free baking mixes, cereals, and breads and provides a WG option. Region-specific applications include the following:

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North Africa: couscous and flatbreads Bangladesh: boiled like rice to produce kichura Honduras: used to make tortillas Sub-Saharan Africa: porridges and traditional beers India: flatbreads China: distilled spirits and vinegar

Triticale A hybrid of wheat and rye, triticale is barely over one century old. It offers the advantages of wheat for product development and the hardiness of rye to thrive in colder climates. Since it requires few pesticides, reduces soil erosion, captures soil nitrogen, and capitalizes on the nutritional advantages of its wheat and rye parents, it may be important in the future. It can be used in most applications that its parent grains can be used.

Pseudocereal Grains These are actually the seeds of dicotyledonous plants, but are starch-rich, like cereal grains.

Amaranth Amaranth not only was a staple grain of the Mayans and Aztecs in Mexico but also has historical importance in Africa, India, and Nepal. It has been grown in China, Russia, Thailand, Nigeria, and parts of South America. Its name originates from the Greek word amarantos, meaning ‘one that does not wither’ or ‘the never-fading.’ This tiny grain contains enough lysine to blend it with other grains to improve protein quality. It contributes iron, phosphorus, magnesium, potassium, and folic acid, but it is noted for its calcium contribution. Thus, this gluten-free grain is a welcome addition to traditional and gluten-free formulations for cereals, breads, muffins, crackers, and pancakes to add

FOOD GRAINS AND THE CONSUMER | Cultural Differences in Processing and Consumption additional texture and flavor. Some amaranth applications are listed as follows:

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South American countries: sold on the streets (like popcorn) India, Mexico, Nepal, and Peru: traditional ingredient for breakfast porridge Mexico: dulce de alegria, a sweet cookie-confection dessert

Buckwheat The origins of buckwheat can be traced to about 8000 BC in Tibet and northern China. Despite ‘wheat’ in its name, it is in the same family as rhubarb and sorrel but its seeds are used and cooked as cereals are. The triangular-shaped, dark-hulled groat and flour made from the entire groat are considered WG. Buckwheat is used to make everything from pancakes to noodles. Buckwheat noodles are important in Tibet, northern China, Japan, and Korea and northern Italy as pizzoccheri. The fact that these noodles contain no gluten makes their preparation and manufacture different from noodles made with wheat. Roasted buckwheat groats, kasha, are popular in eastern Europe, particularly Russia and Poland, where it is used as a pilaf, mixed with pasta, added to filling for knishes and blintzes, and used in soups and other dishes. Sprouted groats can be eaten raw or cooked as porridge. Delicate buckwheat pancakes (blini), sometimes raised with yeast, are eaten in several countries, while heartier buckwheat hotcakes are eaten in North America. In Ukraine and other regions, yeast rolls are made from buckwheat. In Nepal, a doughy mixture of buckwheat with grains such as maize and millet called dhedo is popular. A buckwheat, wheat, and maize mixture makes a type of polenta eaten in northern Italy. Buckwheat is a source of higher-quality protein than cereal grains and is high in magnesium and potassium. It is glutenfree, so it is also used in these applications.

determines the presence and bioavailability of micronutrients and macronutrients. In most developed countries where overweight is a problem, consumption of WGs may be advantageous, whereas refined grains remain popular and may benefit areas where calories are in short supply. With increasing globalization, grains and foods specific to one region are spreading across the globe and enriching the diets of many both nutritionally and culturally. The resurgence of plant-based and gluten-free diets has made traditional and alternative cereal grains important dietary contributors.


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In one continent, take a sampling of counties from various sectors and outline the main grains used and characteristic dishes that show protein complementarity. Compare a population where one staple grain is used with another where a different grain is used and show the advantages and disadvantages for each area. If northern climates get hotter and dryer, discuss how grain staples would change and suggest some cultural adaptations of customary dishes in the region to be prepared with these alternate grains. Show how milling practices in two regions affect nutrition outcomes in these regions. What are the cultural issues that cause resistance to changing preferred grain and processing techniques? How can various grains impact DF intake? If the diet is based on a grain with a low-fiber content, what are some dietary strategies to address this? Some components in certain grains are antinutritional or other concerning components. How can processing and cultural practices minimize the impact of these?

Quinoa


Quinoa was a sacred staple food of the Incas. It is related to beets and spinach. Over 120 varieties exist, but the white, red, and black types are commercialized. Most of the quinoa consumed within the United States is imported from South America. Quinoa is gluten-free, provides high-quality protein, and contains potassium, folic acid, and vitamin E. Its bitter saponin-containing outer coating offers natural protection against pests, aids in drought resistance, and is an antioxidant. It has a distinctive taste with mild notes of corn and bean flavor. Frequently added to pilafs, stews, salads, or bread, quinoa is found in gluten-free products and gourmet food applications.

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Conclusion The variety of ways in which cereal grains are processed and consumed around the world is both interesting and important in terms of providing calories and contributing to nutrients to the diet. The extent of grain refinement and cultural practices

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With an increasingly globalized world, how are the traditional cultural uses of cereal grain changing? How can cultural preparation methods and practices be altered to improve diet? How can processing techniques and cultural preparation methods be applied to provide optimal nutrient availability in cereal grains? What implications do the expanding gluten-free and WG markets have on cultural practices? Discuss how alternate grains can be utilized in diets that are gluten-free or wheat-free. Cross-reference to gluten-free, sorghum, millets, teff, and quinoa. Show how WG inclusion in a diet where the cultural practice to choose refined grain can improve nutrient intake. Cross-reference to WGs; see specific grains.

See also: Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Processing of Grains: Starch: Uses of Native Starch.

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Further Reading Abdel-Aal E and Rabalski I (2008) Effect of baking on nutritional properties of starch in organic spelt whole grain products. Food Chemistry 111(1): 150–156. Jones JM (2012) Glycemic index: The state of the science, Part 1 – The measure and its variability. Nutrition Today 47(5): 207–213. Molina J, Sikora M, Garud N, et al. (2011) Molecular evidence for a single evolutionary origin of domesticated rice. Proceedings of the National Academy of Sciences 108(20): 8351. Mosley BS, Cleves MA, Siega-Riz AM, et al. (2009) Neural tube defects and maternal folate intake among pregnancies conceived after folic acid fortification in the United States. American Journal of Epidemiology 169(1): 9–17. Schroeder N, Gallaher DD, Arndt EA, and Marquart L (2009) Influence of whole grain barley, whole grain wheat, and refined rice-based foods on short-term satiety and energy intake. Appetite 53(3): 363–369. http://dx.doi.org/10.1016/j. appet.2009.07.019.

Shewry PR (2007) Improving the protein content and composition of cereal grain. Journal of Cereal Science 46(3): 239–250.

Relevant Websites http://www.grdc.com.au/ http://www.homebaking.org/hbamembers/ http://hsc.csu.edu.au/food_technology/issues/ http://www.ifst.org/learninghome/helpforteachers/lessonplantopics/cereals/ http://www.kswheat.com/ http://wbc.agr.mt.gov/ http://www.wheatfoods.org/ http://wholegrainscouncil.org/whole-grains-101/

Fortification of Grain-Based Foods CM Rosell, Institute of Agrochemistry and Food Technology (IATA-CSIC), Paterna, Valencia, Spain ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Since fortification is a broader term, it will be used here while referring to the addition of nutrients.

Fortification is a way of supplementing the diet through the intake of some nutrients to combat deficiencies. Foods selected as vehicles for fortification must meet criteria of availability and price. Cereals are the best carriers for food fortification, mainly in the case of vitamins and minerals. Chemical compounds must be carefully selected for ensuring micronutrient bioavailability after processing. Fortification is legislated in different countries.

Learning Objective

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Criteria for Food Fortification Minerals and vitamins may be added to foods only for the purpose of (1) restoration of nutrients lost during processing, (2) nutritional equivalence of substitute foods, (3) fortification, and (4) ensuring the appropriate nutrient composition for a special purpose food. Some considerations should be taken into account prior to addition of any nutrient to foods:

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Understand the meaning of fortification and the role of cereals and cereal-based foods in fortification.

Introduction Fortification can be defined as the addition of one or more vitamins and/or minerals to a food, regardless of their usual content in the food. Additions are carried out based on generally accepted scientific knowledge of the role of vitamins and minerals in attaining good health. Foods are fortified for the following reasons:

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to prevent or correct a demonstrated deficiency of one or more vitamins and/or minerals in the population or specific population groups; and to improve the nutritional status of the population and dietary intake of vitamins or minerals due to changes in dietary habits.

Enrichment is a term usually interchanged with fortification. The term ‘enriched flour’ was coined during the World War II when the American government decided to improve the soldiers’ diet by including different nutrients in bread. Initially, the enrichment consisted of the addition of the three major B-vitamins (thiamine, riboflavin, and niacin) and iron, despite the scarce scientific information concerning the real nutritional improvement obtained through that proposal. Later, numerous scientific studies have been conducted for verifying the utility of those measures. Ideally, enrichment should be equivalent to restoration. This means that the addition of vitamins and minerals, present in the edible portions of the food, will restore the levels lost during manufacturing, storage, and handling. The other relevant term in this subject is ‘nutritional equivalence,’ which means ‘being of similar nutritive value in terms of quantity and bioavailability of vitamins and minerals.’


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The nutrient added should be present at a level that will not result in either an excessive or an insignificant intake, considering the amount provided from other dietary sources. The maximum safe amount to be added should be set considering the levels established by generally accepted scientific data and bearing in mind the diverse degree of sensitivity shown by different consumer groups. Nutrients should not be added to fresh products including meat, fish, fruits, and vegetables, neither to beverages containing more than 1.2% by volume of alcohol. The nutrient added should be biologically available from the food and should not interfere with the metabolism of any other nutrient. The nutrient added should be sufficiently stable during packaging, storage, distribution, and end use and should not affect both the sensory characteristics and the shelf life of the food. Technology and processing facilities should be available to permit the addition of the nutrient and also methods of measuring and controlling the levels of nutrient added. Fortification should not be used as a tool for providing nutrients in substitution of the natural nutrient sources, as this would lead to a change in the dietary patterns and thus jeopardize good dietary practices.

It is clear that the policy for food fortification has a completely different objective when considering developed and developing countries. In developed countries, the social changes (industrialization, high per capita income, consumption of fast food outside the home) over the years have led to increasing consumption of more highly processed foods. This has been used to justify the necessity of food fortification for ensuring the adequate intake of nutrients, mainly vitamins and minerals. However, there is no general consensus about the extent to which food fortification should be allowed. There are differing opinions that manufacturers could use fortification as a promotional tool, resulting in an excessive intake of certain nutrients that would represent a risk for consumer

http://dx.doi.org/10.1016/B978-0-12-394437-5.00074-7

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FOOD GRAINS AND THE CONSUMER | Fortification of Grain-Based Foods

health. An uncontrolled food fortification program could result in excessive intake of certain nutrients, thus creating nutrient imbalances, and in consequence representing a risk to the health of consumers. It must be had in mind that while deficiencies provoke diseases, the intake of too much of a vitamin or mineral also may cause health problems. In fact, too much vitamin A can cause birth defects, too much folate can hide symptoms of a vitamin B12 deficiency which can lead to damage of the nervous system, and too much calcium can induce kidney problems. In developing countries, food fortification is one approach toward solving nutrient deficiencies, and so far the implementation of these programs has been very successful in correcting nutritional deficiencies of large segments of the population within a very short period. In these countries, care should be taken that the food selected as a medium for the nutrient addition is stable and routinely consumed by the population at risk, and that the amount of nutrient added is sufficient to correct the possible deficiency. However, in any case fortification programs should include adequate Quality Assurance and Quality Control (QA/QC) at production level, regulatory monitoring of the nutrient content of fortified foods, as well as assessment methods to document the nutritional and health effectiveness when implementing fortification strategies.

Cereal-Based Products as Vehicles of Minerals and Vitamins One of the most critical decisions concerning food fortification is the selection of the appropriate food to act as a carrier of the nutrient. The basic criteria for identifying the food products for fortification include selecting a food that is regularly consumed by the target population group, affordability, and availability all through the year. Cereals and cereal-based products constitute a major component of diet around the world. Cereals have been used as the basis of human diet from the ancient times and their implication in the human diet is still very significant. Globally, cereals account for 48% of total energy intake and they are a cheap source of proteins compared to animal proteins. Although their relative contribution to human diet greatly depends on the production and the cultural differences, the popularity of cereals, mainly rice and wheat, in the diet worldwide make them the most appropriate vehicles for fortification strategies. Additionally, it must be remarked that cereals are not directly consumed as grains; processing is generally required to transform the grain prior to its consumption, with the subsequent reduction in nutrients and micronutrients that are mainly concentrated in the outer layers and germ. In the conversion of cereal grains to white flour, 20 or more ingredients (such as thiamin, riboflavin, niacin, pyridoxine, folate, panthothenate, biotin, vitamin E, calcium, copper, iron, potassium, magnesium, manganese, phosphorus, zinc, chromium, fluorine, molybdenum, and selenium) are lost to the extent of 50–90% during the milling process. Cereal fortification methods have been developed to restore the nutrients that have been removed during milling and to improve the nutrient intake level of specific population.

Table 1

Vitamins and minerals that may be added to foods

Vitamins

Minerals

Vitamin A Vitamin D Vitamin E Vitamin K Vitamin B1 Vitamin B2 Niacin Pantothenic acid Vitamin B6 Folic acid Vitamin B12 Biotin Vitamin C

Calcium Magnesium Iron Copper Iodine Zinc Manganese Sodium Potassium Selenium Chromium Molybdenum Fluoride Chloride Phosphorus

Once the food or carrier to be fortified is selected, the nutrient deficiencies affecting the population must be determined. There are only certain vitamins and minerals that may be added to foods (Table 1). Nevertheless, the main micronutrients recognized as being of concern to the health of the population are iron, folic acid, B-vitamins, vitamin A, and zinc, although in developed countries calcium also is considered. In general, the population of all the rice-consuming countries have vitamin A deficiency, which is associated with corneal lesions that can lead to partial or total blindness, and with reduced resistance to infectious diseases. This would, in consequence, lead to an increase in morbidity and mortality. Another deficiency associated with people of rice-consuming countries is anemia due to iron deficiency. This has been linked to reduced resistance to infection and also affects the cognitive development and physiological functions in children and, in severe cases, causes maternal deaths. Iodine constitutes the third major deficiency in rice-consuming countries. This mineral is necessary for proper fetal development and also for normal physical and mental activities in adults. In developed countries, iron supplementation has been a measure adopted to reduce the prevalence of iron-deficiency anemia. B-vitamins (thiamine, riboflavin, and niacin) and calcium are also supplemented in developed countries to ensure the adequate intake of those nutrients. Lately, some studies confirming the role of folates in congenital malformations (neuronal tube defect) and the development of chronic diseases like Alzheimer’s in elderly people have recommended the supplementation of folic acid in cereal-based foods. However, the effectiveness of this fortification program in the decrease of homocysteine concentration and its relationship with a reduction in the incidence of cardiovascular disease is still under research. Selenium is an essential micronutrient for humans and may reduce the risk of degenerative diseases, including cancer, but its deficiency has been detected in at least a billion people worldwide, although wheat is a major source of dietary selenium in humans.


Methods for Cereal Fortification Cereal fortification methods are mainly addressed to restore the nutrients that have been removed during milling and to improve the nutrient intake level of specific population. In addition, some efforts have focused on enhancing the nutritional quality of the crops because half of the world population suffers from malnutrition with respect to iron, zinc, and selenium.

Biofortification Biofortification, the increase of micronutrients in the edible parts of the plants, can be achieved by either mineral fertilization or plant breeding. Biofortification by mineral fertilization is a common practice in some countries that applied seleniumcontaining fertilizers as a short-term solution for improving selenium content of wheat. Biofortification through plant breeding consists of the development of micronutrient-enhanced crop varieties through conventional breeding. Nevertheless, the implementation of this type of biofortification requires the identification of genetic resources to determine the interaction of genotype and environment, to define the desired level of micronutrient increase, and finally to assess the cost-effectiveness. So far, it seems a sustainable and cost-effective approach for reaching biofortification in zinc and iron.

Rice Fortification Rice requires special methods for fortification as it is commonly consumed as a whole grain and is extensively washed prior to cooking or strained after cooking. There are different methods for rice fortification; the earliest one was the production of parboiled rice. In the parboiling process, rice is steamed under pressure to gelatinize the starch within the kernel; this process allows the transference of nutrients from the bran layer to the starchy endosperm. Other methods currently used are the powder and grain enrichment methods. A powder preblended with mixtures of vitamins and minerals is added to the rice. For white parboiled rice, the blend is added immediately after milling because the heat and moisture content of the grain surface at that moment facilitates the adherence of the powder mixture. However, the

45

nutrient supplementation in this method can be washed off if the grains are rinsed before cooking. The grain enrichment method involves the addition of a powdered mixture of vitamins and minerals and a subsequent coating of the grain with a water-insoluble substance. Usually, grains enriched by this method contain a high nutrient concentration, and they are mixed in a proportion of 0.5% with normal milled rice to finally obtain an enriched product that meets the required standard levels. Different variations of these methods have been developed through the years. For instance, the powdered mixture can be sprayed onto the rice and then coated with ethanol, isopropanol, palmitic acid, or cellulose derivatives. This method has been effective for enriching rice with niacin, thiamin, pyridoxine, vitamin A, vitamin E, folic acid, iron, and zinc by adding alternative layers of nutrients and coatings. Synthetic rice obtained by extrusion of rice flour to a rice kernel shape in the presence of vitamins and minerals also covers the fortification objective. The fortified simulated grains are then mixed with normal milled rice, although the consumer often notices and removes those grains before cooking. This is obviated by dyeing them with a distinct color, so that the consumer clearly knows that it should be present.

Flour and Bakery Products Fortification of flour is usually carried out in mills, where the nutrient mixture is blended with the flour. In this practice, the definition of the nutrients and the levels to be added must be based on the nutritional needs and deficiencies of the population, the common consumption of the fortifiable flour, the sensory and physical aspects, and economic cost. The addition of B-vitamins, iron, and calcium is a common practice in some developed countries. However, the nutrient added must have good stability during storage, and in defining the levels to be added must be considered the extraction rate during milling. In fact, some recommendations have been established for wheat flour fortification (Table 2). Fortification can even take place during the breadmaking process. Different yeast strains have been suggested for obtaining enriched baked goods. A selenium-enriched yeast has been used for increasing the content of selenium in bread, obtaining wheat bread rolls that can provide 25% of the recommended daily allowance in the form of selenomethionine, which is the best form of selenium for human consumption.

Table 2 Average levels of nutrients to consider adding to fortified wheat flour based on extraction, fortificant compound, and estimated per capita flour availability Level of nutrient to be added (ppm) by estimated average per capita wheat flour availability (g day1) Nutrient

Flour extraction rate

Compound

<75

75–149

150–300

>300

Iron

Low

NaFeEDTA Ferrous sulfate Ferrous fumarate Electrolytic iron NaFeEDTA

40 60 60 Not recommended 40

40 60 60 Not recommended 40

20 30 30 60 20

15 20 20 40 15

High

Source: WHO, FAO, UNICEF, GAIN, MI, and FFI (2009) Recommendations on wheat and maize flour fortification. Meeting Report: Interim Consensus Statement. Geneva: World Health Organization. http://www.who.int/nutrition/publications/micronutrients/wheat_maize_fort.pdf (accessed 10.12.13).

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Pasta Fortification In pasta-consuming countries, pasta and noodles are used for fortification. The production of fortified pasta or noodles requires only the addition of the nutrient at the mixing stage prior to the dough extrusion process, or instead previously fortified flour can be used for this purpose. Some vitamin losses are produced during the drying process, although the extent of that loss depends on the temperature reached during drying.

Table 3 vitamins

Compounds that may be added to cereals as a source of

Vitamins

Chemical compound

Vitamin A

Retinol Retinyl acetate Retinyl palmitate Beta-carotene Thiamin hydrochloride Thiamin monohydrate Riboflavin Riboflavin 50 phosphate Nicotinic acid Nicotinamide D-Pantothenate, calcium D-Pantothenate, sodium Pyridoxine hydrochloride Pyridoxine 50 phosphate Pyridoxine dipalmitate Cyanocobalamin Hydroxocobalamin Ascorbic acid Sodium ascorbate Calcium ascorbate Ascorbyl 6-palmitate Tocopherol Tocopheryl acetate Tocopheryl acid succinate Pteroylmonoglutamic acid

Vitamin B1 Vitamin B2

Breakfast Cereal Fortification The fortification of ready-to-eat breakfast cereals is a wellestablished practice. In fact, this plays an important role in ensuring the adequate intake of nutrients by the US population. Vitamins, like niacin and riboflavin, are added to the basic ingredients prior to processing when the breakfast cereal is heat stable or sprayed onto the processed breakfast cereal in the case of addition of heat-labile vitamins (vitamin A, C, and thiamine), ensuring the uniformity of the coverage. Hydrophobic vitamins (e.g., vitamins A and D) need special consideration as emulsions need to be sprayed on the cereals. In these products, the packaging material is very important, as the moisture content should be below 5% to avoid the texture modification of the product.

Niacin (B3) Pantothenic acid (B5) Vitamin B6

Vitamin B12 Vitamin C

Vitamin E

Folic acid

Compounds Used as a Source of Vitamins and Minerals Three different requirements should be considered when selecting the source of nutrients: the chemical compound (1) should be stable during packaging, storage, distribution, and end use; (2) should not modify the sensory characteristics (appearance, texture, taste, and aroma); and (3) should ensure the bioavailability of the nutrient. Different chemical compounds are used as a source of vitamins (Table 3) and minerals (Table 4) to be added to cereals. Nutrient stability is very important in the case of vitamin fortification. Vitamins are sensitive to heat, oxidizing and reducing agents, light, and other physical and chemical stress. For instance, vitamins are stable when added to flour but the combination of high humidity and temperature adversely affects the stability of the vitamin A. This vitamin is labile to high temperature and unstable in the presence of oxygen and light, due to its susceptibility to oxidation. Therefore, a protection and appropriate conditions of storage should be used in order to reduce the vitamin A loss. Encapsulation in a more hydrophilic coat is a common practice in order to obtain a more water-dispersible product. The supplementation of B-vitamins to flour is affected by low stability of these compounds during storage. Hence, higher effectiveness is obtained when B-vitamins are added at the bakery rather than at the mill. The bioavailability of added nutrients, particularly iron, varies widely depending on the iron compound used for fortification and the physical and chemical properties of the food to be fortified. The selection of the iron form is based on organoleptic considerations, bioavailability, cost, and safety. Iron powders are extensively used in flour fortification, but

they are poorly absorbed and their absorption is highly dependent on the meal served (phytates, calcium, and polyphenols decrease the bioavailability of iron). Ferrous sulfate is preferred for enriching wheat flour because of its high bioavailability but it often leads to unpleasant colors and flavors due to reactions with other components of the food matrix. Some of these interactions with other food components can be avoided by coating the iron form with hydrogenated oils or ethyl cellulose. Iron fortification of flour is generally regulated in most countries by specifying a minimum iron level in the flour resulting from the sum of the added and native iron. Nevertheless, Hurrell et al. reviewed the effectiveness of the iron fortification programs in 78 countries and concluded that they are likely to be ineffective. Legislation needs to be updated in many countries so that flour is fortified with adequate levels of the recommended iron compounds to meet population requirements.

Legislation Concerning Cereal Fortification Although cereal fortification can be an effective means of improving micronutrient status, there are some barriers to the general implementation. These include concerns related to a proliferation of the fortified foods if the fortification is voluntarily practiced by manufacturers, which would lead to a simultaneous replacement of the nonfortified foods in the diet. The success of fortification programs always depends on good control, so they should be set up, regulated, and enforced by the national governments.

FOOD GRAINS AND THE CONSUMER | Fortification of Grain-Based Foods Table 4 minerals

Compounds that may be added to cereals as a source of

Minerals

Chemical compound

Calcium

Calcium carbonate Calcium chloride Calcium salts of citric acid Calcium gluconate Calcium lactate Calcium hydroxide Cupric carbonate Cupric citrate Cupric gluconate Cupric sulfate Sodium and potassium iodide Sodium and potassium iodate Ferrous carbonate Ferrous citrate Ferric ammonium citrate Ferrous gluconate Ferrous fumarate Ferrous lactate Ferric diphosphate Elemental iron (carbonyl þ electrolytic þ hydrogen reduced) Hydroxocobalamin Magnesium acetate Magnesium carbonate Magnesium chloride Magnesium salts of citric acid Magnesium oxide Magnesium sulfate Manganese carbonate Manganese sulfate Manganese chloride Manganese citrate Calcium salts of orthophosphoric acid Zinc acetate Zinc chloride Zinc oxide Zinc sulfate Zinc carbonate

Copper

Iodine Iron

Magnesium

Manganese

Phosphorus Zinc

The addition of nutrients is generally practiced by manufacturers either voluntarily or because it is compulsory under national rules. In general, vitamins and minerals may be added in conformity with the legislation of the country in which the product is being sold, which must regulate the list of foods to which vitamins and minerals may be added, the vitamins and minerals permitted, and the levels at which they may be added. The Economic and Social Department of FAO has elaborated a review about the legislation status concerning rice (Table 5) and wheat flour (Table 6) fortification. Rice fortification is voluntary in the United States; however, most of the rice sold is fortified, and lately folic acid is also being added to the enriched rice. In Canada, fortification of rice is also voluntary, and when labeled as enriched, it contains vitamin B1, vitamin B3, and iron. Moreover, in Canada, the addition of vitamins B5 and B6 and folic acid is optional. Fortification of rice in Philippines has a long tradition, and there is a mandatory regulation for the addition of vitamin B1.

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There are currently 14 countries with legislation or regulations that mandate the fortification of wheat flour, whereas in countries such as Finland, New Zealand, and Norway law prohibits the addition of nutrients to wheat flour. In the United States, the Food and Drug Administration approves the supplementation of four B-vitamins (thiamine, niacin, riboflavin, and folic acid) and iron to the wheat flour, for obtaining ‘enriched flour,’ although this practice is regulated by Federal law. The US government adopted a mandatory regulation concerning folic acid fortification. In the United Kingdom, it is mandatory for the restoration of all the nutrients removed with the bran in all types of flours, with the exception of whole meal. From 1997, the Organizacioń Panamericana de la Salud (OPS) is supporting the supplementation of iron to wheat flour due to its low cost and extensive consumption. Some countries from South and Central America have implemented this measure for reducing the incidence of iron-deficient anemia. The levels of nutrients to be added are also regulated by national governments. At the international level, GAIN’s (Global Alliance for Improved Nutrition) National Fortification Program, which began in 2003, has expanded to support 19 countries with high levels of vitamin and mineral deficiencies. A broad coalition of governments, businesses, international organizations, and civil society partners, known as National Fortification Alliances, support GAIN’s projects. Those projects aim to fortify foods and condiments including wheat and maize flour, sugar, vegetable oil, milk, soy sauce, and fish sauce. Vitamins and minerals used to fortify foods include vitamin A, vitamin D, iron, zinc, folic acid (B9), thiamin (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), and cobalamin (B12).

Future Prospects Currently, in the developed countries the term ‘functional foods’ or ‘nutraceuticals’ seems to be old-fashioned, and the cereal-based products surely may be one of the best carriers of different compounds related to physiological functions. Therefore, the near future in nutrition could be the use of cereal-based products as carriers of o-fatty acids and probiotic compounds such as fructo-oligosaccharides, inulin, etc.


• • • • • •

What requirements should the nutrients to be used in fortification meet? When and where would food fortification be recommended? Which cereals would be the selection for food fortification? When using wheat white flour as a fortification carrier, which chemical compounds would be advisable to be added? Cross reference to wheat milling chapters. Which cereal-based foods are usually fortified? Considering iron deficiencies and consumption intake, justify where would be recommended iron food fortification.

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Table 5

Summary of voluntary and mandatory fortification of rice

Country

Law status

Angola Australia Canada Costa Rica Cuba El Salvador Ethiopia Finland Gambia Haiti Hungary Mauritania Morocco New Zealand Norway Peru Philippines Sweden Tanzania Turkey United Kingdom Uruguay United States Vietnam

Table 6

Prohibited Voluntary Voluntary Voluntary

Legislation

Known nutrient deficiencies

No

Vitamin A, I, Fe

B1, B3 No No No No Restoration allowed No No 1 serving must contain 1/3 of RDA No No In process of reviewing the legislation

Prohibited

Voluntary Voluntary Prohibited Prohibited Voluntary Voluntary

I, Fe Fe, vitamins B1, C, and A Vitamin A, I, Fe Vitamin A, I, Fe I, Fe, Ca, folic acid, vitamin B2

I, Fe, folic acid Vitamin A, I, Fe

No Legislation for B1, B3, Fe May be allowed with special permission No In accordance with Codex Must be safe No B1, B2, B3, folic acid No

Voluntary Voluntary Voluntary Voluntary

Vitamins A, B1, and B2, I, Fe Fe, I, folic acid, vitamin A Fe, I, Ca, vitamins B2, B6, C, and D Fe, I, vitamin D Vitamin A, I, Fe

Summary of voluntary and mandatory fortification of wheat flour

Country

Law status

B-vitamins

Vitamin E

Folic acid

Iron

Zinc

Magnesium

Australia Canada

Voluntary Mandatory Voluntary Mandatory Mandatory Mandatory Mandatory Mandatory Prohibited Mandatory Mandatory Voluntary Voluntary Prohibited Mandatory Prohibited Mandatory Voluntary Mandatory Voluntary Voluntary Mandatory

B1, B2, B3, B6 B1, B2, B3 B5, B6 B1, B2, B3 B1, B2, B3 B1, B2, B3 B1, B2, B3 B1, B2, B3

þ

þ

þ þ

þ

þ

Chile Costa Rica Dominican Republic Ecuador El Salvador Finland Guatemala Honduras Hungary Malta New Zealand Nigeria Norway Panama Philippines Saudi Arabia Sweden Switzerland United Kingdom Uruguay United States Venezuela

Mandatory Mandatory

B1, B2, B3 B1, B2, B3

þ

þ þ

þ þ þ þ þ

þ

B1, B2, B3

þ

B1, B2, B3

þ þ þ þ þ þ þ þ þ

þ

þ

þ þ

B1, B2, B3

B1, B2, B3 B1, B2, B3, B6 B1, B2, B3 B1, B3 B1, B3 B1, B2, B3 B1, B2, B3

þ

Calcium

þ


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Further Reading

•

Allen L, Benoist B, Dary O, and Hurrell R (2006) Guidelines on Food Fortification with Micronutrients. Geneva: World Health Organization and Food and Agriculture Organization of the United Nations. http://www.who.int/nutrition/publications/ guide_food_fortification_micronutrients.pdf (accessed 10.12.13). Baurenfiend JC and DeRitter E (1991) Foods considered for nutrient addition: Cereal grain products. In: Baurenfiend JC and LaChance PA (eds.) Nutrient Additions to Food, pp. 143–209. Connecticut: Food and Nutrition Press. Hurrell R, Ranum P, de Pee S, et al. (2010) Revised recommendations for iron fortification of wheat flour and an evaluation of the expected impact of current national wheat flour fortification programs. Food and Nutrition Bulletin 31 (1 supplement): S7–S21. http://www.ncbi.nlm.nih.gov/pubmed/20629349. Ranum P, Lynch S, Bothwell T, et al. (2001) Guidelines for Iron Fortification of Cereal Food Staples. Washington, DC: SUSTAIN. Published online at www.sustaintech. org/publications/pubm7.pdf. Rosell CM (2008) Vitamin and mineral fortification of bread. In: Hamaker B (ed.) Technology of Functional Cereal Products, pp. 336–361. Cambridge: Woodhead Publishing Ltd. Rosell CM (2012) The nutritional enhancement of wheat flour and related products. In: Cauvain S (ed.) 2nd edn., Bread-Making: Improving Quality, 2nd edn., pp. 687–710. Cambridge: Woodhead Publishing Ltd. WHO, FAO, UNICEF, GAIN, MI, and FFI (2009) Recommendations on wheat and maize flour fortification. Meeting Report: Interim Consensus Statement. Geneva: World Health Organization. http://www.who.int/nutrition/publications/micronutrients/ wheat_maize_fort.pdf (accessed 10.12.13).

• •

The cereal composition changes after milling. What would be the minerals and vitamins that must be restored after milling? Cross reference to cereal processing chapters. Select some cereal-based goods and determine which chemical compound would be advisable for their fortification in minerals. Select several countries and identify their regulations regarding fortification of wheat flour.

See also: Barley, Rice and Maize Processing: Barley: Milling and Processing; Rice Processing: Beyond the Farm Gate; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Labelling of Grain-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Nutrition: Beriberi, A Deficiency Related to Grains; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grains Around the World: Grain Production and Consumption: Overview; Processing of Grains: Cereals: Breakfast Cereals; Wheat Processing: Wheat: Dry Milling; Wheat-Based Foods: Breads.

Genetically Modified Grains and the Consumer A Mathiowetz, University of Minnesota, St. Paul, Rochester, MN, USA JM Jones, St. Catherine University, Arden Hills, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

•

• • • • • •

• • •

The purpose of genetically modified (GM) grains is to improve yield, increase resistance to plant pests and diseases, help plants adapt to stressful environmental conditions, confer resistance to certain herbicides, reduce spoilage mechanisms, and improve the nutrient profile of a crop. GM grains may help address nutritional deficiencies in the developing world. The scientific community agrees that GM foods present no greater safety risk than conventionally grown crops. Despite prevailing scientific evidence, consumers remain wary. Awareness of GM foods is increasing among consumers, as is skepticism too. European, Mexican, and some African consumers are the most outspoken against GM foods, while consumers in the United States are the most open to the idea. Consumer perception is dependent on understanding of safety, perceived ratio of risks to benefits, religious/moral values, intended use of GM foods, scientific literacy, trust in regulatory organizations, price, and social economic status. Yield gains through GM technology are critical for the developing world to meet growing population, but monetary benefits often occur in developed countries. Maize, soy, and rice are commercially grown and sold worldwide, but GM wheat has not been commercialized. Labeling is mandatory on all GM foods and foods containing GM ingredients in 21 EU countries, Australia, Brazil, Russia, China, and Japan. Individual states in the United States are considering GM labeling.

Learning Objectives

• • •

•

To understand the purpose of GM grains and their application to the greater majority of the world. To recognize common factors that influence consumer perception of GM grains. To compare and contrast consumer perception of GM foods/grains across varying regions of the world and to observe differences in the perceptions of the scientific and consumer communities. To understand the movement for labeling of GM foods: Where is labeling already mandated, who are its proponents/opponents, and what is the fundamental argument?

Introduction Genetically modified (GM) foods and grains create varied reactions around the world. Some see the use of this technology as

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a way to feed the rapidly rising population against a background of significant pressure on land, water, and other valuable resources. At the other end of the spectrum are those who think that the use of this technology is ‘playing God’ and have dubbed GM foods ‘frankenfoods.’ GM grains refer to those that contain a gene introduced by recombinant DNA methods to confer a desired trait. The ability to pick a specific gene for a desired trait is an outgrowth of standard breeding practices that have been used for centuries where plants or animals with desired traits were bred together in hopes of perpetuating the trait. For many grains, this would be a 10-year process. The use of genetic modification, also called biotechnology, has been used since the 1970s. It can shorten the time required to achieve the same outcome as standard breeding process and can be much more precise than traditional hybridization. Traits have been introduced to grain foods to improve yield, to increase resistance to plant pests and diseases, to help adapt to stressful environmental conditions such as drought or extremes of temperature, to confer resistance to certain herbicides, to reduce spoilage, and to improve the nutrient profile of a crop. Since the introduction of commercially available biotech crops in 1996, the global use of GM crops have sustained a growth rate of 6% or 10 million hectares per year. Thus, between 1996 and 2012, there has been nearly a 100-fold increase in acreage. Farmers in North America grow the most GM crops with Brazil in second place. GM soybeans, maize, cotton, and rapeseed were planted on 170.3 million hectares worldwide in 2012, according to figures from the International Service for the Acquisition of Agri-biotech Applications (ISAAA). In developing countries, biotech grains accounted for 52% of all biotech crops planted in 2012 worldwide. This is up from 50% 1 year earlier. In contrast, Europe grew < 0.1% of the world’s biotech grains. Scientific bodies around the world continue to evaluate evolving data and continue to aver that there are no health risks in consuming foods including grains that are produced by biotechnology. The US National Academy of Sciences concluded “no adverse health effects attributed to genetic engineering have been documented in the human population. ”Similarly, the International Council for Science, which includes 111 national academies of science and 29 scientific unions, concluded that there is “no evidence of any ill effects from the consumption of foods containing GM ingredients.” The World Health Organization also issued a response stating, “No effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved.” In 2010, a European Commission review of 50 studies on the safety of biotech crops found “no scientific evidence associating GMOs (Genetically Modified Organisms) with higher risks for the environment or for food and feed


http://dx.doi.org/10.1016/B978-0-12-394437-5.00075-9

FOOD GRAINS AND THE CONSUMER | Genetically Modified Grains and the Consumer safety than conventional plants and organisms.” The American Medical Association’s Council on Science and Public Health stated that “Bioengineered foods have been consumed for close to 20 years, and during that time, no overt consequences on human health have been reported and/or substantiated in the peer-reviewed literature.” Despite acceptance by farmers and diverse expert scientific panels around the world, consumer attitudes to GM foods and grains vary markedly by geographic region. Various degrees of activism, prevailing public opinion, and the extent of economic development strongly influence attitudes toward GM foods. However, two overarching factors seem to influence public opinion of GM grains worldwide: (1) the risk–benefit perception related to the personal and family situations and needs of the country and (2) ambivalence or fear about the safety of GM foods, often resulting from either a lack of information or misinformation generated by some inaccurate media. Often, media reports fuel fears of some untoward consequence that may not be accurately predicted. In terms of risk and benefit, some feel that the consumer bears a disproportionate share of the risk while large companies reap the monetary benefit. In terms of adopting biotech crops, the farmers are as divided as public opinion. Subsistence farmers worry about planting biotech crops because they fear they may be unable to feed their families or earn a living. In contrast, other farmers are lured by the promise of fewer inputs of water, fertilizer, and pesticides and thus lower costs and higher yields. The view is strongly influenced by region.

Perceptions of GM Grains by Region GM Foods in the United States and Canada Farmers in North America have dramatically increased their planting of GM grains between 1996 and 2013. This has been driven by farmers’ expectations of higher crop yields and/or lower production costs, a reduction in time devoted to crop care and management, and other benefits including farm sustainability. Reduced input, lower use of pesticides and herbicides, less acreage and tilling required, and fewer crop diseases are among some advantages cited. As a result, currently 93% of the soybeans and 80% of the corn, according to the United States Department of Agriculture (USDA), grown in the United States are GM. (Despite allegations to the contrary, no GM wheat is grown commercially in any part of the world.) Consumer acceptance of GM food in the United States has increased slowly but steadily and somewhat parallels the increase in number of hectares of biotech crops. It also reflects a less disparaging reaction to the technology by the press and the public. This is reflected in the International Food Information Council’s 2012 survey on ‘Consumer Perceptions of Food Technology,’ which shows that 74% of consumers have, at minimum, heard ‘a little’ about biotechnology and as many as 38% of US consumers are ‘somewhat or very favorable toward plant biotechnology.’ 44% asserted they were ‘somewhat or very favorable’ regarding the use of biotechnology in grains specifically. Overall, consumers were likely to be more accepting biotechnology if the benefits of the technology were clearly communicated and especially if consumers were

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convinced that the technology could increase yields for developing countries. Variability in consumer perception is influenced by demographics of the consumer. Older consumers are more likely to accept the use of biotechnology that affords health benefits, not as likely to accept it for benefits of increased freshness or flavor. Those with more education are more likely to try GM crops. Women are more resistant to the use of biotechnology than men. Canadians are also divided regarding the concept of GM foods. Less than a third of Canadian consumers say they oppose the use of GM in food. This is a change in attitude with more respondents in 2011 stating that they ‘strongly support’ or ‘somewhat support’ the use of GM in food production than in 2001. Regulation in various countries often reflects public opinion. Health Canada regulates GM foods and requires that developers show that the seeds and plants have no untoward effect on the environment or human health. Receiving approval from Health Canada can take 10 years and be very costly. However, once approved, Canada does not require labeling on all GM foods, unless there are any health or safety concerns such as a food containing an allergen. The United States currently only has voluntary labeling guidelines for foods produced by biotechnology. However, the Food and Drug Administration (FDA) outlines certain circumstances where labeling is required, including foods that have significantly altered nutritional makeup, allergens, or toxic levels of an ingredient as a result of GM. Regulatory policies on GM foods are enforced by the FDA, Environmental Protection Agency (EPA), and USDA. The federal law regarding GM voluntary labeling does not reflect the results of several polls indicating that over 90% of US consumers want GM foods to be labeled. This is reflected in bills on GM labeling being introduced at the state level. Approximately half of US states have pending legislations requiring labeling of GM foods to some extent. Maine and Connecticut have passed laws mandating labeling of all GM foods, and many states are likely to follow suit. Those in favor of labeling argue that they have a right to know what is in their food, some for ethical or religious reasons and some for health or environmental reasons. Much of the argument for labeling is simply transparency. Americans claim a right to have immediate access to information on their food’s content, so they can make a personal decision. Organic foods cannot contain GM ingredients, so some consumers used the organic label as a proxy for a label saying ‘GMO-free.’ Many manufacturers and sellers of organic foods oppose the use of GM products. This meets the wishes of many organic consumers, but lack of GM labeling supports their own economic interests. The calls for legislation on labeling of GM foods have dismayed those in agribusiness as well as some scientists and consumers. Considering that 60–70% of processed foods in the United States contain at least one GM ingredient, experts worry that the reaction of consumers to such labels will cause them to reject use of GM products and seeds, turning back gains made in yields along with profits. Food economists suggest that not only it is these large corporations that will be burdened with the negative consequences of labeling but also

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FOOD GRAINS AND THE CONSUMER | Genetically Modified Grains and the Consumer

consumers would likely see increased prices and changed availability. Groups who do not favor labeling often reference scientific literature, arguing that there is no significant difference in the safety of GM foods and non-GM foods. They also note that manufacturers are required to alert consumers of any material difference in GM foods that could affect safety such as the presence of allergens or potential toxins or decreased nutritional quality. Those who oppose GM labeling state that consumers wishing to avoid GM ingredients have the option to purchase foods labeled ‘organic,’ which precludes their use.

GM Foods in Europe Strong resistance to GM foods pervades Europe. This occurs despite numerous decisions regarding the safety of GM foods by bodies such as the European Commission (EC). However, regulators dealing with GM foods in Europe invoke the ‘precautionary principle,’ which states that if there are any unresolved concerns, they will not accept the food process or additive in the food supply. This principle aims at minimizing any perceived or theoretical threats. It fails to consider any potential benefits where the science is indeterminate. It also is problematic as safety cannot be proven, only lack of safety. Consumer resistance to GM foods and belief in the ‘precautionary principle’ have led at least 21 European Union (EU) countries to require labeling of GM foods or foods with GM components. The overall sentiment in Europe is that the benefits must outweigh the risks. Furthermore, consumers and experts hold wholly different viewpoints toward GM foods, specifically regarding safety, ethical tradeoffs, benefits, and international trade. What might be seen as a benefit to experts is often viewed as a risk to consumers. When GM foods were first introduced into the European market, consumers did not perceive that there was a benefit of these products in that they were not cheaper, did not seem tastier, and did not offer other added value. The higher yields per hectare did not reduce prices for consumers due to a general increase in prices for fuel and other inputs that affect food prices. Food scares in Europe in the 1990s eroded confidence in food regulatory bodies and the food supply. This influenced discussions regarding the acceptability of GM foods. Consumers continue to question aspects of consumer health, environmental risks that may occur over time, and economic effects on small European farmers. There are also fears of allergenicity and the development of microbial resistance to GM traits just as has occurred with pesticides and herbicides. Farmers are wary of GM food as most of the GM food is imported, so there is an economic concern as well. Countries who produce GM products have contested the use of the precautionary principle as a trade barrier. Yet organizations such as the World Trade Organization are reluctant to impinge on the authority of various member states. Despite over 25 years of use and no environmental or other problems, European consumers claim they have insufficient and inconclusive information. They state that their confidence could be improved if more definitive scientific information be made more readily available to the public. Acceptance of GM foods varies among the countries with some of the strongest resistance found in the United Kingdom.

2013 surveys carried out by the UK government showed that only 21% of the UK public support GM foods and less than half of UK farmers believe GM technology is a good innovation. Over 40% of people stated that they ‘were completely against’ the government promoting GM technology. European acceptance of GM food, while limited, may be increasing. A poll of European consumers conducted between 2002 and 2005 showed an increase of 6% in positive attitude toward GMOs. 80% of EU consumers did not intentionally discriminate against GM foods when shopping. Thus, European consumers’ stance on GM food may not be affecting purchasing behavior. Recent research indicates that acceptance of GM food is much improved if the consumer benefits such as ‘produced with fewer sprays’ and ‘higher levels of a needed component such as omega-3 fats’ are clearly communicated to the consumer.

Asia-Pacific Nations-Developed Countries In Australia, consumer acceptance of GM foods has fallen since 2007, following a steep rise in consumer acceptance between 2005 and 2007. However, the acceptance level among the general public is still at 67%. Approval ratings of biotechnology in food and drink have consistently remained lower than approval ratings of biotechnology in medicines, vaccines, and stem cells, as well as for the purpose of creating pest-resistant plants. Awareness of biotechnology in food is at a commendable 82%, and a solid two-thirds of the Australian public thinks the use of biotechnology in food crops could be useful. Less than half of the population finds the application risky, but GM-containing foods must be labeled. A study of 2000 New Zealand consumers sought to determine whether consumers would purchase GM foods. Slightly more than 30% of the over 700 who returned the survey said that they would not purchase any of the GM foods listed on the survey, which included bread from GM wheat and maize altered to resist insects. However, not all information from New Zealand shows attitudes toward it to be negative, especially when the science is applied sensibly and consumers see it involves no great risks. Further biotechnology would be acceptable in New Zealand if (1) the consumer is given a choice, (2) the benefits hold greater weight than the risks, (3) the benefits are shared by the consumer as well as agribusiness, (4) the practice is environmentally friendly, and (5) the technology is safe, practical, and cost-effective. Concern and reasonable doubt certainly exist in New Zealand regarding GM foods, but not to an extent that completely stifles acceptance. Japan and Brazil, Russia, and China mandate labeling of all GMO-containing foods. While Japanese resistance to GM is not as strong as that in Europe, Japanese consumers continue to remain unwilling to accept GM products. This was recently highlighted after finding of GMO wheat in Oregon. This revived the issue and Japan’s Ministry of Agriculture, Forestry and Fisheries opted for temporary import suspension and called for urgent greater GM inspection on imports to Japan.

Asia-Pacific Nations-Developing Countries In Malaysia, almost 90% of consumers surveyed were aware of GM foods. However, the fraction of Malaysian consumers who

FOOD GRAINS AND THE CONSUMER | Genetically Modified Grains and the Consumer accept GM foods may not be as high. The study revealed large concerns over food safety and perceived risk–benefit ratio. Other factors affecting consumer opinion were media influence and lack of information. Filipinos, in general, trust the international agencies responsible for conducting studies and disseminating information on topics such as GMOs. This may be true due to the work of the International Rice Research Institute (IRRI) and the work of the International Maize and Wheat Improvement Center (CIMMYT). Citizens are less confident in the government than university scientists. Overall, Filipinos believe the nutritive qualities of GM grains could prove beneficial, but they remain guarded about safety. A study conducted in the Philippines analyzed the attitudes of 423 Filipinos, who worked in a variety of careers. The majority were middle-aged, educated males with an allegiance to Roman Catholicism. Attitudes were affected by education level and religious affiliation; those with higher education held more of a positive view on GM foods, while the strongly religious had moral concerns about GM technology. Many Filipinos across various disciplines claimed insufficient information on GMOs. Those who received information from the scientific community were more likely to have positive opinions of the technology than those who received information from popular media. Even without easy access to literature on biotechnology, Filipinos are less likely to have extreme attitudes toward GM food. However, an anti-GMO group of 400 interfered in 2013 with a GM trial on ‘Golden Rice,’ a variety of rice intended to decrease the prevalence of vitamin A deficiency.

India In India, most consumers are aware of GM crops, some to a greater extent than others. While a whopping 96% of Indian consumers deem biotechnology to be beneficial and worth further exploration, < 33% currently support the implementation of GM crops and hardly any want GMOs in their own food supply. Although awareness is high and an overwhelming majority views them as a promising prospect for the future, consumers do not necessarily trust the use of GMOs in their food currently. They are more open to their use in medicine. The Supreme Court in India has just called for an indefinite moratorium on field trials for new GM food crops. Just next door, Bangladesh is allowing the planting of GM staples.

China Chinese consumers remain divided over the use of GM foods but are more accepting than consumers in Japan. A study published in 2010 by Zhang et al. recognized Chinese consumers as belonging to one of four categories: neutral (risks posed by GMOs are equal to benefits), relaxed (benefits of GMOs outweigh the risks), skeptical (risks outweigh the benefits), and uninterested (no perceived risks or benefits). Social status and income level strongly influenced the particular category. Although variability in degree of acceptance exists across China, results of the Zhang study suggest that more people accept biotechnology than object to it. When asked to rate nutrition-improved GM rice on a scale from ‘completely acceptable’ to ‘strongly opposed,’ 25% of 1000 surveyed said

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it was completely acceptable, 42% deemed it ‘relatively acceptable,’ 21% pleaded neutral, 5% were relatively opposed, and only 1% were strongly opposed. The acceptance rate of folate-enhanced rice was found to be > 60% in a study of nearly 1000 consumers. Again, results were most strongly affected by perceived risk–benefit ratio.

Africa Attitudes regarding GMOs in many countries in Africa are influenced by those in the rest of the world. Some developed nations and world food organizations encourage the use of GM crops for the purpose of alleviating hunger and tackling food insecurity. Not all Africans are convinced that GMOs would be a helpful strategy in addressing food insecurity. In fact, many are distrustful despite a backdrop of decreased agricultural productivity throughout most of the continent. The Center for Strategic and International Studies (CSIS) noted that despite 70% of Africans working in agriculture, Africa imports a quarter of its food. Across Africa as a whole, the mood toward GM foods can be summarized as ambivalent, with some nations more resistant and others more welcoming. Tanzania, Uganda, Malawi, Mali, Zimbabwe, Nigeria, and Ghana have at least begun to consider the possibility of growing GM plants, and many are conducting research and field studies. Awareness and acceptance vary dramatically across Africa. For example, the awareness level for GMOs in Ghana has been calculated at around 60%, meaning more than half of the population of Ghana has heard to some extent of GM foods. However, increased awareness does not assuage fear; rather, it may lead to increased uncertainty. Part of the uncertainty stems from the perception that the safety of GMOs is still in question. Another part stems web posts and media stories that may inaccurately portray or overstate the risks and fail to tout the benefits and the numerous consensus statements averring their safety. Similar trends have been observed in other developing nations, even ones in the throes of a hunger crisis. Tens of thousands of tonnes of corn donated by the United States was rejected by Zambia’s president, who called it ‘genetically modified poison.’ One stated rationale noted that since Europe objects to its use, it must not be safe. While a large number of Zambians are not welcoming to the idea of GMO, an increasing fraction is warming (ever so slowly) to the possibility of someday growing GMOs. However, ‘someday’ sits far off on the horizon as existing legislation all but bans the use of GM seeds and proponents have yet to unify and work toward acceptance. A larger portion of Kenyans compared to those from other nations in Africa are more accepting regarding the use of GMOs partially due to wider acceptance by prominent political and scientific leaders in Kenya. Greater acceptance and use of GM crops are aided by two factors. First, the British left behind a relatively advanced research center giving Kenyans in direct contact with the latest scientific data on GMOs. Second, commercial interests are exceptionally strong in Kenya, and they promote the development and use of GM crops. If Kenya is one of the more progressive nations regarding GMO use, South Africa is the most progressive, and GM crops

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have been grown in South Africa since 1997. As with Kenya, South Africa’s educational system is built on deep scientific roots. Local scientists affirming GMOs safety and benefits help promote consumer acceptance of biotechnology. South Africa, Egypt, Sudan, and Burkina Faso are the four nations in Africa that sell GM crops commercially.

Latin America Widespread production of GM crops in Brazil and Argentina means that approximately one-third of the world’s acres planted in GM crops occur in South America. GM maize leads the production, but GM versions of cotton, soybean, and canola are also grown in South America. The widespread production of GM crops does not mean South American consumers readily accept GM technology. Interestingly, the countries with high production – Brazil and Argentina – also have high resistance. Arguments against GMs use include a lack of human resources and appropriate equipment in the region, concerns about viability of small farmers, disputes about seed ownership, and fears that regulation surrounding GMOs is inadequate. Peru and Colombia, in particular, are actively protesting GMOs and resisting the efforts of multinational seed companies. Countries such as Mexico have actually banned the growing of GM crops. In 1998, it became illegal to grow GM maize after the seeds were introduced into Mexico either through accidental cross contamination or through illegal intent. However, the law has been loosely enforced. Reiteration of the ban in 2013 by a judge may change this. Vocal leaders emphasize corn’s essentiality and identity as Mexico’s national crop and describe GM corn as a ‘threat to their sovereignty and identity.’ Mexico faces opposition from such bodies as the United Nations Food and Agriculture Organization, which argue in favor of GMOs to eliminate hunger. Thus, across Latin America, mass scale production of GMO crops occurs while there are bans and widespread resistance, sometimes within the boundaries of the same country.

GM Foods in Developing Countries: A ‘Beacon of Hope?’ In most developing countries, GM grains promise many agronomic benefits. With the worldwide population expected to double by 2050, food security is of great concern. Biotechnology can be one of the most sustainable ways for ensuring adequate agricultural yields and value-added and nutritionally enhanced products. Statements such as those in the journal GMO Biosafety Research dub the technology a ‘beacon of hope.’ Biotechnology protects food security via three primary methods: increasing yields on existing land and optimizing other limited resources, advancing food quality and safety, and potentially bettering the economic status of local farmers. GM grains can offer numerous nutritional advantages, such as fortification to address nutrient gaps or extreme deficiencies in developing countries. For example, WHO estimates that 250 million preschool children are vitamin A-deficient and an estimated 250 000 to 500 000 vitamin A-deficient children become blind every year, half of them dying within 12 months.

GM-produced ‘golden rice’ adds vitamin A to help mitigate this tragic public health problem. No matter what the region, it is important that GM foods and technologies address needs of local and subsistence farmers, as well as respect cultural, dietary, and religious importance of certain crops. In some cases, GM versions of familiar crops may have greater acceptance than an unfamiliar crop. While this is true in all regions, it may be especially true for those in developing nations. Judicious use of GM crops in developing nations means that efforts must be directed to ensure that the use of this technology does not exacerbate the economic divide. Care must be exercised to ensure that the benefits of GM crops help address the problem of food security and improve the environment in the region and that economic or other risks are minimized.

Conclusion The practice of biotechnology began in the 1970s, and grains such as maize were some of the first commercially available GM foods. Biotechnology has been employed with grains to heighten the ability to withstand stress and resist pests, disease, and herbicides; enhance the nutrient profile, freshness, or flavor of the plant; and reduce spoilage and improve yield. Most crops available up until now have increased benefits to farmers and this indirectly can help contain food costs for consumers. Soon, foods with increased flavor and nutrient profiles will be on the market. Perception and acceptance of GM foods vary. The scientific community concludes that GM foods, including GM grains, are safe and pose no more risks than do conventionally grown foods. Consumers remain wary despite the large body of scientific evidence and numerous scientific and government bodies deeming them safe and a possible way to address future food needs. Attitudes toward GM foods strongly influence perception of benefit and safety. Such attitudes are influenced by media, legislation, science literacy, trust in regulatory organizations, price, religion and morality, and social economic status. It is exceptionally difficult to capture an entire population’s sentiment in one study, let alone a few sentences. Scientific literature shows a lack of consensus, even within a region. It is even more difficult to mention or represent every country’s perspective. Despite limitations, this article divulges consumer perception as it was most commonly portrayed in the scientific literature. Overall, awareness of GM foods has increased significantly worldwide. In the developing world, GM grains offer the prospect of closing nutritional gaps, but still meet significant resistance. Many in the developing nations remain wary of biotechnology. Wariness is increased because most biotechnology initiatives emanate from multinational companies. This fact means that not only there may not be adequate understanding of the consumers in a region but also there is worry about motives of the multination and about who will reap economic gains. Acceptance of biotechnology may increase when goals of

FOOD GRAINS AND THE CONSUMER | Genetically Modified Grains and the Consumer developed countries align with those of developing countries, and the benefits are made reciprocal and equal. In some regions, the technology is slowly gaining and more hectares are being planted. The developed world is divided over the use of GM foods. The United States, parts of South America, and South Africa currently have large areas devoted to GM-crop production. Australia and New Zealand place great weight on the benefits and who reaps the benefits. In most regions, GM approval continues to be higher in medicine than food, but GM food approval still is relatively high in these regions. The most vehement opposition comes from parts of Europe. Where GM crops are allowed, many jurisdictions require labeling and regulation of crops produced by biotechnology. Mandated labeling on all GM foods and foods containing GM ingredients is currently enforced in several countries in Europe, Japan, Australia, Brazil, Russia, and China. In countries where no labeling of GM foods is required, labeling has become a heated issue. Many consumers claim they have the right to know what is in their food, and the government has an obligation to make such information readily accessible. Those opposed to labeling of GM foods cite consensus statements of government agencies and health organizations stating that food grown from GM seeds is not materially different from food produced conventionally; therefore, there is nothing to disclose. The US consumer population is largely in favor of labeling, but federal labeling guidelines are voluntary. The global status of labeling on GM foods may change in the coming years, as consumers continue to demand transparency from their governments. It may be interesting to observe how consumer perception and purchasing behaviors of GM foods are altered in response to increased transparency. Encouragement of GM crops as a way to address the needs of the world population in 2050 by humanitarians such as those working for the Gates Foundation could have a dramatic effect on attitudes and acceptance of GM foods in many parts of the world. Further, open and transparent communication on the benefits of GM foods and the availability of foods with specific consumer benefits may help to address the concerns of many consumers and improve acceptance.


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In one continent, take a sampling of countries from various sectors and show in detail how these countries vary in their acceptance and regulation of GMO. Take a country or region and define the major concerns regarding acceptance of GMO. Take a country or region and suggest communication strategies that would be convincing for the acceptance of GMO. What additional scientific information is needed for a certain population to accept GMO? What world events or program backing has the potential to impact GMO acceptance? What problems has golden rice faced on its journey and how could such things be avoided in the future?

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To what extent do countries have access to scientific literature concerning biotechnology and how does it affect their overall consumer perception? How well do GM grains address nutritional deficits in the developing world? How does labeling affect consumer perception of GM foods?

See also: Food Grains and the Consumer: Labelling of GrainBased Foods.

Further Reading American Medical Association, AMA (2013) Report of the Council on Science and Public Health: Labeling of Bioengineered Foods. http://www.ama-assn.org/ama (accessed 01.14.). American Council for Science and Health (2014) The co-existence of organic and GMO foods. http://acsh.org/2014/04/co-existence-organic-gmo-foods/ (accessed 4/2014). Center for Food Safety (2013) US Polls on GE Food Labeling. http://www. centerforfoodsafety.org/issues/976/ge-food-labeling/us-polls-on-ge-food-labeling (accessed 01.14.). DeSteur H, Gellynck X, Storozhenko S, et al. (2010) Willingness-to-accept and purchase genetically modified rice with high folate content in Shanxi Province, China. Appetite 54(1): 118–125. EuropaBio (2013) Abc stresses overwhelming weight of evidence on safety of GM crops. http://www.europabio.org/news/abc-stresses-overwhelming-weightevidence-safety-gm-crops (accessed 01.14.). European Commission (2006) Eurobarometer 66: Public Opinion in the European Union. http://ec.europa.eu/public_opinion/archives/eb/eb66/eb66_highlights_en. pdf (accessed 01.14.). Hart J and Herrmann R (2009) Do they always say no? German consumers and secondgeneration GM foods. Agricultural Economics 40(5): 551–560. Herath D (2001) Evolving Consumer Acceptance of Biotechnology Applications in Canada: Evidence from the Public Opinion Surveys in 2001 (fifth wave) and 2011 (seventh wave). http://ageconsearch.umn.edu/bitstream/150525/2/Herath8_1AAEA. pdf. International Council for Science, ICSU (2003) New Genetics, Food, and Agriculture Scientific Discoveries – Societal Dilemmas. http://www.icsu.org/publications/ reports-and-reviews/new-genetics-food-and-agriculture-scientific-discoveriessocietal-dilemas-2003/ (accessed 01.14.). International Food Information Council (2012) Consumer Perceptions of Food Technology Survey. http://www.foodinsight.org/Content/5438/FINAL%20Executive %20Summary%205-8-12.pdf. International Service for the Administration of Agri-Biotech Applications, ISAAA (2013) ISAAA Brief 44–2012: Press Release. http://www.isaaa.org/resources/publications/ briefs/44/pressrelease/ (accessed 01.14.). Kaye-Blake W, Saunders C, and Fairweather J (2007) GM food and New Zealand Consumers. http://www.biotechlearn.org.nz/themes/ new_zealand_views_on_biotech/gm_food_and_new_zealand_consumers (accessed 01.14.). Myhr AI (2007) The precautionary principle in GMO regulations. In: Traavik T and Lim LC (eds.) Biosafety First Norway: Tapir Academic Publishers (accessed 01.14.). http://genok.no/wp-content/uploads/2013/04/Chapter-29.pdf. The National Academy of Sciences, NAS (2004) Safety of Genetically Engineered Foods: Approaches to Assessing Unintended Health Effects. http://dels.nas.edu/Report/ Safety-Genetically-Engineered-Foods-Approaches/10977?bname¼ (accessed 01.14.). Nielsen T (2012) How do concerns about pesticides impact consumer willingness to buy genetically modified french fries in Germany? Results from a purchasing experiment. 2012 International European Forum, 13–17 February, 2012. Austria: Innsbruck-Igls. Paulsen T GM food fight: Why the Gates Foundation wants to make rice golden. http:// www.humanosphere.org/basics/2013/09/gm-food-fight-why-the-gates-foundationwants-to-make-rice-golden/.

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Torres CS, Suva MM, Carpio LB, and Dagli WB (2006) Public Understanding and Perception of the Attitude Towards Agricultural Biotechnology in the Philippines. ISAAA. SEARCA and CDC-UPLB. http://www.isaaa.org/programs/supportprojects/ (accessed 01.14.). USDA, Economic Research Service (2013) Adoption of Genetically Engineered Crops in the U.S. www.ers.usda.gov/data-products/adoption-of-genetically-engineeredcrops-in-the-us/recent-trends-in-ge-adoption.aspx#.U0FCRMf95lk (accessed 01.14). Vinter R (2013) Livestock 2013: Survey shows consumer resistance to GMs. Farmers Weekly. http://www.fwi.co.uk/articles/03/07/2013/139866/livestock-2013-surveyshows-consumer-resistance-to.htm (accessed 01.14.). World Health Organization, WHO (2014) 20 questions on genetically modified foods. http://www.who.int/foodsafety/publications/biotech/20questions/en/ (accessed 01.14.). Zhang X, Huang J, Qiu H, and Huang Z (2010) A consumer segmentation study with regards to genetically modified food in urban China. Food Policy 35(5): 456–462.

Relevant Websites http://www.agbioworld.org/ – AgBio World, Peer Reviewed Publications on the Safety of GM Foods. http://dels.nas.edu/ – National Academy of Sciences, Division on Earth and Life Studies. National Research Council (U.S.). http://edis.ifas.ufl.edu/fe934 – Evans, EA Ballen, FH. A synopsis of US consumer perception of genetically modified (biotech) crops. University of Florida Extension. http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-cropsinthe-us/ – Fernandez-Cornejo J, 2011 U.S. Economic Research Service, Adoption of Genetically Engineered Crops in the U.S. http://www.gmo-compass.org/eng/agri_biotechnology/gmo_planting/ – GMO Compass. http://www.icsu.org/ – International Council for Science. http://www.isaaa.org/ – International Service for the Acquisition of Agri-biotec.

Labelling of Grain-Based Foods JM Jones, St. Catherine University, St. Paul, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Basic label requirements are similar across jurisdictions with the ingredient statement and contact information being critically important. Label terminology used to describe grain processing, milling, and grain fractions is understood by industry, but not by consumers. Further, it is not standardized across jurisdictions and is confusing to consumers. Nutrition labeling of grain-based foods is mandatory in many countries. Whether required or voluntary, the format is specified but formats vary across jurisdictions. Regulation for labeling of organic and genetically modified grains and other label descriptors such as ‘fresh’ and ‘natural’ vary across jurisdictions. Procedures and rules regarding the approval and use of nutrient-content claims, structure–function claims, and health claims in grain-based foods depend on the jurisdiction. Issues regarding the labeling of whole-grain foods are complicated due to varying recommendations for whole-grain intake across regions, issues about the amount of dietary fiber or detractor nutrients that are in the whole-grain food, and the use of wet or dry weight for calculation of the whole grain.

Learning Objectives

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Label Descriptors for GBF

To be able to outline and define various requirements and terms associated with labeling grain-based foods. To compare various label descriptors, nutrition labels, and types of nutritional claims used on grain-based foods in various jurisdictions. To delineate issues associated with labeling of whole grains and whole-grain foods within and across jurisdictions.

Overview Grain-based food (GBF) labels allow consumers to select and purchase products with desired characteristics, ingredients, and nutritional profiles. Labels act as both marketing tools and transmitter of legally required information. They must name and accurately describe the food and list the ingredients in descending order by weight. The ingredient statement is critical for most consumers as it delineates what is in the product and gives the consumer an idea of the relative amounts of the various components in a product, since they must be listed in order by weight from the most to the least prevalent. In some countries, percent labeling is required, so that a precise amount of a specific ingredient is declared. Interested consumers can carefully scrutinize the ingredient statement for components or additives that they wish to include or avoid in their diets.


Coded or overt dates and lot numbers are required both to track shelf life and to allow for product recalls. The manufacturer contact information enables consumers to make queries and to state complaints and facilitate recalls, if necessary. The net weight allows price and value comparisons of competing products and ensures the consumer receives a fair measure. Some jurisdictions may require the country of origin labeling, warning statements about allergens or ingredients of concern, and advisory statements on safe handling of the product. Nutrition labeling, usually with a prescribed format, is mandatory in many jurisdictions, while others allow or encourage it voluntarily. Statements and visuals on the package and advertising must not be misleading. Foods for special dietary or medical use such as cereals or bars that have functional ingredients that reduce blood sugar may have more extensive nutrition labeling requirements. Nutrient-content, structure–function, and health claims are allowed in some jurisdictions, but specific claims and rules regarding them vary across jurisdictions. GBFs also carry label descriptors about the size, shape, and processing of the grain. In many cases, the terminology is familiar only to those in the cereal industry. Thus, consumers are confused about definitions surrounding grain fractions, whole grain (WG), and especially the definition of a wholegrain food (WGF). This article will discuss these and other issues specific to GBF.

Label descriptors for GBF can be those that are more general such as ‘fresh’ and those that communicate aspects regarding the product, form, and level and type of processing specific to grain such as the method and degree of milling, the particle size, and other processing aspects. While these industry terms associated with GBF are understood by industry, they can leave consumers confused. Terms such as ‘medium pearled’ or ‘degermed’ are not always as clear or as easy to operationalize as terms for other common foods, such as ‘canned sliced peaches in syrup,’ where most of these terms need little further clarification. Nonetheless, this information is needed for selecting the grain form for the best culinary use and for choosing desired nutritional characteristics. Terms such as ‘fresh,’ ‘natural,’ ‘homemade,’ ‘artisan,’ ‘traditional,’ ‘ancient,’ and ‘stone-ground’ are popular with marketers and consumers alike but have come under scrutiny by various regulatory bodies. For the consumer, such terms give products a ‘goodness halo’ that may or may not be justified, so some jurisdictions have prescribed ways such terms can be used. In areas where there is no legal definition, the expectation is that such terms are not misleading. Terms such as ‘natural’ or ‘fresh’ may or may not be defined depending on the jurisdiction. In some jurisdictions, the term ‘fresh’ for bread is defined to mean ‘prepared at the venue and sold there

http://dx.doi.org/10.1016/B978-0-12-394437-5.00076-0

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shortly after baking.’ Preprepared dough off-site and baked on the premises cannot be labeled as ‘fresh’ in some regions. It is easy to understand why terms are confusing because the term ‘fresh’ for pasta denotes that the pasta is not dried. Designations such as ‘light,’ ‘low-calorie,’ ‘very low sodium,’ ‘high in,’ or ‘free from’ may be strictly defined or not allowed. For example, in the United States, rice cakes with under 40 cal might be labeled as a naturally ‘low-calorie’ food and cannot be labeled as ‘low-calorie rice cakes’ implying that they are lower in calories than other rice cakes. In certain jurisdictions, a GBF formulated to reduce an attribute such as calories, sodium, or fat must be reduced by a specific percent and must be labeled and compared to either the original food or the average of foods in the category. Claims that a food is ‘high in x’ may need to follow rules for nutrient-content claims and may not be allowed for components that are not nutrients such as WG or antioxidants. In some jurisdictions, ‘free from’ labeling is specified in that foods that have never had component x cannot be labeled as ‘free from x.’ Statements about ‘gluten-free’ must follow rules of the jurisdiction. The CODEX regulations, followed in a number of areas, require < 20 ppm gluten, but a few regions also allow ‘low gluten’ with higher levels of gluten. Allergen labeling may be required, and so GBF would have the required disclosures of wheat, nuts, milk, eggs, and other common allergens. Organic labeling for GBF aids consumers wishing to purchase products that are produced without additives, pesticides (other than those allowed by organic rules), and chemical fertilizers and did not undergo genetic modification (GM) or irradiation. Some regions require official certification at all stages of the process in order to label products as organic. Table 1 shows a gradation in organic that is allowed in the United States with products where 95% or more of the product is organic can bear an official seal. If a product has < 70% organic ingredients, it cannot use ‘organic’ on the main package label, but individual ingredients listed as ‘organic’ on the ingredient statement. If GM grains are allowed, many countries require their labeling. In the United States, labeling of GM grains is not required because the USFDA views that there is neither a material difference nor a safety or environmental issue associated with these products. However, deeply held beliefs by some consumers have prompted a number of state legislators to sponsor bills requiring GM labeling. To date, all such initiatives have failed.

The Nutrition Label The nutrition labeling of packaged foods, including GBF, is mandatory in many countries of the world. Where voluntary, Table 1

most countries have regulated formats. The nutrition label in most countries requires a declaration of energy in calories or joules, total fat, saturated fat, trans fat, cholesterol, sodium, total carbohydrates, dietary fiber (DF), sugars, and protein. Rules about saturated fat, trans fat, and calories from fat vary across jurisdictions. Similarly, the list of micronutrients required and allowed varies as does the percent daily value (DV) standard. In most jurisdictions, labeling becomes compulsory if a nutrition claim regarding a specific nutrient is on the label or in advertising. Nutrition labeling is harmonized throughout the European Union and some regions; however, this is often not the case. DF values in GBF may vary depending on which DF definition and analytic method have been officially accepted. The acceptance of Codex Alimentarius and aligned DF definitions and methods by Europe, Canada, and many other jurisdictions has helped harmonize fiber labeling across many jurisdictions. Energy values may also vary depending on what calorie value is assigned to certain fibers in various regions. In most countries, nutrition labels are based on 100 g of food, but some countries use dual labeling. Nutrient values are listed per 100 g of food and also for a serving size appropriate to the food and the country. In the United States, the nutrient values are based only on government-mandated serving sizes called reference amounts commonly consumed (RACCs). The system using 100 g portions has the advantage of allowing easy comparison of products and enables consumers to easily calculate the percent of various macronutrients. However, some consumers cannot envision how 100 g of a specific product a serving can be eaten. The following examples illustrate this confusion. A slice of bread is usually 30 g so labeling per 100 g would be the nutrient value for three slices of bread. Ready-to-eat cereals vary dramatically so a 30 g serving of a dense granola is 1/3c, whereas it is two cups of a puffed grain cereal. Unfortunately, many consumers are not able to use the nutrition label effectively as they are unable to apply the listed values to the amount they have eaten. The nutrition label must list the nutrients in the package as sold, regardless of how the food is commonly ingested. Thus, some products have two values – the one required for the food as packaged and the one that gives nutrition information of the product as prepared or ingested. Thus, cereal labels often give values for the cereal as purchased and as consumed with 120 g (½c) of low-fat milk. A similar type of dual labeling may be on packaged foods such as cake or pasta mixes, which have an additional column giving nutrient values for the food prepared according to package directions. Dual-language (or multilanguage) labeling of GBF enables their sale in countries such as Canada with more than one national language or in a region such as Southeast Asia.

The USDA organic label definitions

100% organic Organic Made with organic ingredients Some organic ingredients

Must contain only organically produced ingredients At least 95% of the product’s ingredients must be organic Must contain at least 70% organic ingredients Products contain <70% organic ingredients

Labelling of the Various Grain Components Grains have been processed since before biblical times to remove the outer inedible husk, and in many cases, outer layers may be removed. Grains may then be broken into particles of various sizes, sifted into various streams, and kept separate or recombined, and the various fractions may be processed further. The specific terminology used to describe grain

FOOD GRAINS AND THE CONSUMER | Labelling of Grain-Based Foods components from various stages of milling and processing is on the label, but consumers do not know if a meal is different from a grit and may think that degermed is a sterilization, and not a milling, process. In many parts the world, GBFs are most commonly made from refined or enriched grains. These foods have mostly the endosperm of the grain, or in the case of enriched, the endosperm has some nutrients lost in milling added back. Current nutrition research suggests that WGs are advantageous in terms of more DF and reduced risk of chronic disease. Thus, some consumers are trying to replace refined and enriched grain foods with WGFs, which makes the understanding of GBF label terms so important. Enriched and Refined Grains: If the various parts of a kernel have been removed, it is a refined grain. If some vitamins and minerals lost in milling are added back, the grain is enriched. Various food authorities decide if enrichment is allowed and, if so, the specific nutrients added and the amount allowed. If enriched flour is used in packaged food products, the nutrients added not only must be reflected on the nutrition facts panel but also may be reflected on the ingredient statement. The ingredient statement might read ‘Ingredients: Sugar, Enriched Bleached Flour (wheat flour, niacin, iron, thiamine mononitrate, riboflavin, folic acid). . ..’ Grains may also be fortified to address nutritional inadequacies in the region. Thus, the nutrient levels of fortified products may be higher than enriched products. Often, 25% of the DV is added, but some products have more. These additions are reflected on both the ingredient statement and the nutrition facts panel. If fortification levels in some GBF meet the daily requirement, for example, 100% of the DV, the product must be labeled as a multivitamin and mineral supplement GBF. The intake of these fortified cereal products increases intakes of nutrients of concern. In the case of folic acid fortification of grains, there has been a reduction of neural tube defects, and certain birth defects have been decreased by 50–70% in various countries. Yet some fear that such a policy could put some groups at risk for excess folic acid intake, even though most data do not indicate that this might be a problem. WG was first defined by the American Association of Cereal Chemists (now AACCI) in 1999 as follows: Whole grains shall consist of the intact, ground, cracked or flaked caryopsis, whose principal anatomical components – the starchy endosperm, germ and bran – are present in the same relative proportions as they exist in the intact caryopsis.

WGs have subsequently been defined by other organizations. The Whole Grains Council (WGC) created a more consumer-friendly definition. It reads as follows: Whole grains or foods made from them contain all the essential parts and naturally-occurring nutrients of the entire grain seed. If the grain has been processed (e.g., cracked, crushed, rolled, extruded, lightly pearled and/or cooked), the food product should deliver approximately the same rich balance of nutrients that is found in the original grain seed.

The European HEALTHGRAIN (HG) workshop (2008) defined WG as follows:

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Wholegrain is defined as intact and/or processed (e.g., de-hulled, cleaned, ground, cracked, flaked or the like) grains, where the fractions endosperm, bran and germ are present in the same proportion as found in the least processed traditional forms of the edible grain kernel of the same species.

All three definitions do not require that the grain remain as an intact kernel, but rather that all of its components be present. However, a few countries using the terminology require that ‘whole’ defines the intact kernel. Each definition varies slightly in terms of both consumer friendliness and allowable loss of outer layers. The WGC definition is more consumerfriendly than the AACCI definition that uses the botanical term ‘caryopsis.’ The HG definition allows some removal of a small amount of grain such as that occurs in traditional processes such as making bulgur or nixtimalizing corn or those that make the grain healthier. Examples include the scoring of the outer kernel to increase availability of nutrients or nixtimalizing to reduce mycotoxins in the outer layers. Some countries equate whole-wheat or wholemeal flour; others allow the removal of some of the outer layers and still call it wholewheat flour. This does create confusion. Definitions of WG help processors formulate food and help consumers describe WGFs that are all WG such as porridge oats (oatmeal) or WG flours. However, the consumer has great difficulty determining which foods are WGF or determining the number of servings of WG to ingest in products that are partly WG. Each current strategy for finding WGFs in the marketplace has a disadvantage. One strategy suggests that a food is WG, if the first ingredient in the ingredient statement is WG. While this may correctly identify a WGF, it may not if the food has many ingredients. This is explained by the following examples. The ingredient statement from a bread mix is as follows: enriched flour, whole-wheat flour, brown rice flour, rolled oats, nonfat dry milk, yeast, and salt. This could be a bread mix with 90% enriched flour and 10% other ingredients making it not a WG bread mix. On the other hand, the ingredient statement could reflect 35% refined flour, 30% whole-wheat flour, 30% brown rice flour, 3% rolled oats, and 2% other ingredients. This bread mix would clearly be a WGF even though refined flour was the first ingredient. A 30 g serving of granola could have 5 g of whole oats; 4 g each of peanuts, almonds, pecans, and walnuts; and 5 g of raisin paste, honey, and salt. The granola, while contributing WG and many nutritious ingredients, may not give a dietarily significant amount of WG. Some suggest that combining the ingredient statement with the product’s DF levels could identify WGFs, but this approach works only if the formulation contains high-fiber WGs. Low-fiber WGs such as brown rice would have a lowfiber level on the nutrition panel. Achieving international agreement on the amount of WG that should be in a product to call it a WG serving is very difficult. There is no international agreement regarding the recommended daily intake of WG. Some regions make no recommendations. For those that do, recommended intakes vary from 48 to 115 g day 1. This wide range makes agreement on the amount of WG in a product to call it a WGF-difficult. Some jurisdictions allow manufacturers to label ‘statements of fact,’ which means statements such as ‘YXZ’ product gives xx grams of WG per serving. The difficulty is that most consumers

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do not know the amount of WG recommended per day, so such labeling could easily be misinterpreted. Similarly labeled banners such as ‘made with whole grain,’ ‘whole-grain goodness,’ and ‘multigrain’ and even ‘high-fiber’ make some consumers think that the food meets one of the recommended WG servings. The WGC stamp has high consumer recognition, is easy to understand, and is used internationally. The WGC has a stamp on the food label that indicates the product has 8 g of more of WG per labeled serving or RACC. The stamp has two disadvantages. First, it causes some consumers to deduce that only those products bearing the stamp are WG. This may occur because consumers are unaware that some companies may not use the stamp because of its cost. Its second disadvantage is that the stamp gives an unfair advantage to products with low moisture or large serving sizes. This creates a scenario where a dough made into a 25 g bun would not have the needed 8 g of WG to receive the stamp, but the same dough in a 55 g bagel would. Since a clear WG characterization was suggested as being important to the goal of eating more WG, AACCI and HG tried to respond by putting forward a way to identify WGFs. The following questions were laboriously considered in the WGF determination: 1. Should the WG characterization apply only to products that are in the grain group? 2. Should it be based on a serving of food or be proportional and therefore serving size-neutral? 3. Should it be based on a wet (as served) or dry weight basis? (Use of wet weight favors dry products and penalizes cooked oatmeal, bread, and soup with pasta or barley.) 4. Should it apply only to the grain portion of the food? If so, should there be a minimum level or grain, even if all the grain is WG? 5. Should it indicate that the food would deliver a certain amount of DF or not have a certain level of detractor nutrients such as sugar, salt, fat, or saturated fat? 6. Should it apply to the entire meal in a frozen or other dinner where the side of grain would meet the requirements but would fail to do so when all the food entreé and other meal components are factored into the calculation? 7. Should half the grain in the product be WG? The AACCI Whole Grain Working Group put forward a WG characterization that suggests a proportionality of 8 g of WG per 30 g of food. This addresses problems created by small and large serving sizes, but leaves some unanswered questions such as WG pasta in a soup or side in a ready-to-eat meal. The 8 g/ 30 g does not specify that the product must have ‘half of the grain be WG.’ Rather, it places a WG minimum, which allows formulators of GBF to increase the other grain fractions such as bran, germ, or aleurone, which technically are not WG but carry many nutritional attributes of WG. Some are concerned that the characterization could allow products to have higher levels of refined grain component than WG. This could be true but the intent of using the 8 g per 30 g is that with the recommendation of six 30 g servings of GBF needed for most calorie levels, a person would get a minimum of 48 g of WG, an amount thought to be dietarily important.

It should be noted that it is merely a characterization and does not speak of the nutritional attributes such as DF or detractors like sugar or fat in the product. For some consumers, any designation of a food as WG is misinterpreted and creates a ‘halo effect’ causing consumers to think such foods have more DF, fewer calories, and detractor ingredients than they do. Further, this characterization is only voluntary and the net result is that there can be many package statements claiming WG content and consumer confusion.

Nutrient Content, Health, and Structure–Function Claims Nutrient-content claims are allowed in some jurisdictions provided that they are factual and use terminology in ways specified in the regulations. In many cases, a serving of a food carrying a nutrient-content claim must provide a certain minimum percentage of the DV, often 10% in a normal serving. For example, ‘Acme cereal is a significant source of folic acid.’ Structure–function claims are popular in some countries. Japan was the first to enfranchise these and allow a number such claims. Such claims are also allowed in North America, Europe, Australia, and parts of Asia. Structure–function claims may point out the association with health but must not claim to cure a disease. Claims such as ‘Acme cereal is a significant source of vitamin A, which has been associated with skin and eye health,’ and ‘Bran fiber in Acme cereal helps maintain bowel regularity’ are allowed in some jurisdictions. As with structure–function claims, the amount of nutrient needed to make a nutrient-content claim is often the same. Some countries prohibit any claims if the food also contains the so-called detractor nutrients, such as saturated fat. If a claim is allowed, the detractor nutrient must also be prominently labeled in the same place as the positive claim. In order to have claims on a food that ‘diagnose, mitigate, treat, cure, or prevent a disease or specific class of diseases,’ officially approved health claims are used. Health claims are accepted only after significant scientific agreement by the regulatory authorities in the region. The only exception is that of classical nutrient deficiency diseases. Table 2 gives a sampling of health claims for GBF.

Health Claims Regarding Blood Glucose The Swedish Nutrition Foundation (SNF) allows the following claim about blood glucose: ‘oat bran ß-glucan reduces blood glucose and insulin response.’ EFSA allows a claim on a lowered glucose response if 14 g of resistant starch is substituted for 14 g of available starch.

Summary Labeling of GBF informs consumers when making grain purchases, enables industry to comply with rules regarding GBF and grain components, and helps regulators ensure consumer

FOOD GRAINS AND THE CONSUMER | Labelling of Grain-Based Foods Table 2

Health claims for grain-based foods in various jurisdictions

Fiber-containing grain products, fruits, and vegetables and cancer Sample claim: ‘Low-fat diets rich in fiber such as Acme Bread may reduce the risk of some types of cancer, a disease associated with many factors’ Requirements: GBF must meet criteria for ‘low fat’ and, without fortification, be a ‘good source’ of dietary fiber Fruits, vegetables, and grain products that contain fiber, particularly soluble fiber, and the risk of coronary heart disease Sample claim: ‘Diets low in saturated fat and cholesterol and rich in fruits, vegetables, and grain products that contain some types of dietary fiber, particularly soluble fiber, may reduce the risk of heart disease, a disease associated with many factors’ Requirements: GBF must meet criteria for ‘low saturated fat,’ ‘low fat,’ and ‘low cholesterol.’ They must contain, without fortification, at least 0.6 g of soluble fiber per reference amount, and the soluble fiber content must be listed Folic acid and neural tube defects Sample claim: ‘Healthful diets with adequate folic acid may reduce a woman’s risk of having a child with a brain or spinal cord birth defect’ Requirements: Enriched GBF must meet or exceed criteria for ‘good source’ of folic acid, that is, at least 40 mg of folic acid per serving (at least 10% of the daily value) Dietary soluble fiber, such as that found in whole oats, barley, oat bran, and Oatrim or psyllium seed husk and coronary heart disease and cholesterol lowering Sample claim: ‘Diets low in saturated fat and cholesterol that include 3 g of soluble fiber from whole oats per day may reduce the risk of heart disease. One serving of this whole oat product provides xx g of this soluble fiber’ Requirements: Foods must meet criteria for ‘low saturated fat,’ ‘low cholesterol,’ and ‘low fat.’ Foods that contain whole oats must contain at least 0.75 g of soluble fiber per serving. Foods that contain psyllium seed husk must contain at least 1.7 g of soluble fiber per serving Typical foods: GBF made with whole or rolled oats, oat bran, or whole oat flour; barley; psyllium seed husk; and isolated or modified b-glucans from barley and oats Note: The European Food Safety Authority (EFSA) allows the claim ‘Oat beta-glucan has been shown to lower/reduce blood cholesterol. Blood cholesterol lowering may reduce the risk of heart disease.’ The Swedish Code of Practice allows ‘Soluble fiber from oat bran may help reduce cholesterol.’ The United Kingdom allows ‘The inclusion of oat bran can help reduce cholesterol as part of a diet low in saturated fat and a healthy lifestyle.’ The Netherlands Nutrition Centre (Voedingscentrum) allows ‘One daily portion of ACME oat bran-based bread reduces cholesterol within 3 weeks and helps maintain healthy arteries and blood vessels.’ And Switzerland BAG ‘Oat bran favorably impacts cholesterol levels’ Whole grain and heart disease ‘Diets rich in whole-grain foods and other plant foods and low in total fat, saturated fat, and cholesterol may reduce the risk of heart disease and some cancers’ Dietary fiber content of at least 1.7 g per 35 g serving Typical foods: Whole-grain breads and cereals (USFDA claim) WG claims not been approved in many other jurisdictions because of inadequate characterization of the ingredients and rulings of inadequate evidence Vitamins B12, B6, and folic acid and reduced risk of heart disease Sample claim: Foods containing vitamin B12, as well as B6 and folic acid, may reduce the risk of coronary heart disease Typical foods. Fortified GBF may make such claims in the United States

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protection and fair marketing of GBF. Understanding label terms for any food is challenging, but terms for GBF, which describe grain forms, particle size, degree of milling and specific milling and processing treatments of various grain types, and fractions, add to consumers’ confusion. This is compounded because terms vary across regions and among grains for a similar process. Terms such as enriched and refined are applied to grains and not to most other foods. General label terms such as ‘fresh’ and ‘organic’ apply to GBF, but these may or may not be defined in a jurisdiction. If defined, definition even within a jurisdiction may vary among products with ‘fresh’ on bread meaning something different than ‘fresh’ on pasta. Some use organic labeling as a way to avoid chemicals and GMFs. Nutritionally labeled products are found in many regions and help consumers meet individualized nutritional needs, although many consumers are confused by many terms on the nutrition and grain label. GBF can carry a number of nutrient-content, structure–function, and health claims. Each region has specific rules regarding their approval and use. Various health promotion agencies are suggesting the ingestion of more WG. However, the ability of consumers to make informed choices as to what is a WGF is difficult. Even experts disagree on the best and fairest strategy for such labeling. Various strategies have been proposed for the identification of labeling WGFs, but each has some drawbacks. Most recently, AACCI has put forward a WG characterization, which is a proportional minimum of 8 g or WG/30 g of product. Labeling of GBF is important and complicated. It varies across regions due to nonstandardized use of terms, varying nutritional requirements, differing regulations by food authorities, and varying degrees of consumer understanding, needs, and perceptions.


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Take a country or region and compare the nutrition label and general labeling requirements for GBF. Compare the various terms used to describe the milling process of various grains such as pearling, polishing, pin milling, and rolling and resultant particulate fractions such as kernels, groats, grits, meals, and flours. Compare health claim approval and use for GBF in various countries. Compare the labeling of WGs and WGFs across jurisdictions. Compare the rules for using the terms ‘natural,’ ‘fresh,’ and ‘organic’ across jurisdictions. What contributions do enriched, refined, fortified, and WGs make to the diet of a particular country or subpopulation?


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Label marketing statements, grain and processing terminology, and nutrition labeling are confusing to consumers. Suggest some strategies to diminish confusion.

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FOOD GRAINS AND THE CONSUMER | Labelling of Grain-Based Foods What activities and labeling initiatives can be undertaken to help consumers identify WGFs and increase their WG intake? Percent ingredient labeling is used in some countries for all foods including GBF. Does this improve consumer understanding of what is in the food?

See also: Food Grains and the Consumer: Fortification of GrainBased Foods; Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Scientific Organizations Related to Grains: Research Organizations of the World: Global Trends and the Commercial Sector; Scientific Societies Associated with Grain Science; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Maize: Overview; Oats: Overview; Rice: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading AACCI’s Whole Grains Working Group Unveils New Whole Grain Products Characterization (2013). http://www.aaccnet.org/about/newsreleases/Pages/ WholeGrainProductCharacterization.aspx.

Barr SI, DiFrancesco L, and Fulgoni 3rd VL 3rd (2013) Consumption of breakfast and the type of breakfast consumed are positively associated with nutrient intakes and adequacy of Canadian adults. Journal of Nutrition 143(1): 86–92. Berry RJ, Bailey L, Mulinare J, Bower C, and Folic Acid Working Group (2010) Fortification of flour with folic acid. Food and Nutrition Bulletin 31(Supplement 1): S22–S35. FDA Wants Consumers to Truly Get the ’Whole Grain’ (2014). http://usgovinfo.about. com/od/consumerawareness/a/wholegrain.htm. Grieger JA and Cobiac L (2012) Comparison of dietary intakes according to breakfast choice in Australian boys. European Journal of Clinical Nutrition 66(6): 667–672. Hamner HC, Tinker SC, Berry RJ, and Mulinare J (2013) Modeling fortification of corn masa flour with folic acid: The potential impact on exceeding the tolerable upper intake level for folic acid, NHANES 2001–2008. Food and Nutrition Research 57, 19146. Holmes BA, Kaffa N, Campbell K, and Sanders TA (2012) The contribution of breakfast cereals to the nutritional intake of the materially deprived UK population. European Journal of Clinical Nutrition 66(1): 10–17. Yang Q, Cogswell ME, Hamner HC, et al. (2010) Folic acid source, usual intake, and folate and vitamin B-12 status in US adults: National Health and Nutrition Examination Survey (NHANES) 2003–2006. American Journal of Clinical Nutrition 91(1): 64–72.

Relevant Websites http://wholegrainscouncil.org/whole-grains-101/definition-of-whole-grains – HealthGrain Forum. Definition and analysis of whole grain. http://wholegrainscouncil.org/whole-grains-101/definition-of-whole-grains – Whole Grains Council. Definition of whole grains.

Grains and Health R Korczak, University of Minnesota, St. Paul, MN, USA D Hauge and B Maschoff, Grains for Health Foundation, St. Louis Park, MN, USA L Marquart, University of Minnesota, St. Paul, MN, USA; Grains for Health Foundation, St. Louis Park, MN, USA P Jacques, Tufts University, Boston, MA, USA R Lindberg, Minneapolis Heart Institute Foundation, Minneapolis, MN, USA R Menon, The General Mills Bell Institute of Health and Nutrition, Minneapolis, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Abbreviations AFH CBPR CDC PHAD

Away from home Community-based participatory research Centers for Disease Control and Prevention Practical, healthier, affordable, and desirable

Topic Highlights

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Innovative approaches are necessary to address the complex and dynamic health-related issues facing food scientists, nutrition and health, and community involvement. Systems thinking is one approach to view ‘problems’ as parts of an overall system, rather than reacting to a specific part, outcome, or event. For example, how will we address the complexity of what and how to deliver healthy grain-based foods that consumers find acceptable and will include in their daily diet? At minimum, public health officials are being asked to consider not only the overall roles of each player within the food system and how they work together to create the food environment but also the significance of community and citizen representation in identifying and filling the gaps, such as research projects that help meet the diverse and complex demands of the public. In order to increase consumer intake of these grain-based foods with higher whole grain content, it will require the development of tools, methods and approaches, systems, and necessary infrastructure to successfully develop and deliver these foods into the marketplace. Public and private partnerships can create a collaborative environment that maximize cross-disciplinary expertise among government, academic, and industry researchers to help solve complex research problems. Food and ingredient industries are uniquely positioned with the technical expertise to make gradual product formulation changes that are well accepted by consumers.

Learning Objectives Among the few major learning outcomes expected from studying this article, the reader will be able to


PPP USDA-ARS

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Public and private partnerships United States Department of Agriculture Agricultural Research Service Whole grain

identify challenges facing current research approaches used to investigate the efficacy and use of grain-based foods by consumers; understand systems thinking for problem identification and use collective solutions for increasing healthier grainbased foods in the marketplace; discuss the pros and cons of public and private partnerships for advancing grain-based research; describe the process of undertaking public and private partnerships from (1) achieving a common purpose among individuals, disciplines, and sectors; (2) sharing of knowledge in a safe environment; and (3) arriving at collective solutions; outline one project that meets the public and private partnership criteria related to grain-based foods issue.

Introduction This article provides one perspective about our initial approaches to address research initiatives relative to grainbased foods that might benefit both industry interests and nutrition-related public health issues. Research is proposed to be accomplished through public and private partnerships (PPPs) where the government and industry collaborate and work toward collective solutions while comingling funding sources from public and private sectors. Systems thinking approaches and public nutrition policy will be addressed relative to identifying research initiatives that fill crucial gaps in the supply chain, food environment, and local community. Three proposed grain-based projects will be presented with rationale for potential support through public and private research efforts. Further discussion will focus on the appropriateness of these projects as opportunities for PPP research initiatives. This article is based on the initial steps leading to a 35-member PPP research meeting focusing on healthier grain-based foods December 2014 in Washington, DC.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00067-X

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Moving from Traditional Research and Analytic Thinking to Include Systems Approaches Traditional nutrition research, from a biological and physiological dimension, has been primarily explored through in vitro, animal, observational, and experimental approaches where reductionism is considered the gold standard. Analytic thinking has been the mainstay for scientific investigation and remains an important aspect of our current scientific practice. These traditional approaches were extremely effective in addressing nutrient deficiencies in the late nineteenth and early twentieth centuries, up until the 1950s and 60s when chronic diseases became a major issue of concern for food and nutrition researchers. As our society moves into a new millennium, innovative approaches are necessary to address the complex and dynamic health-related issues facing scientists through food technology, nutrition and health, and community involvement. Unfortunately, we are routinely taught throughout our academic careers and professional lives on how to solve problems, but rarely taught how to identify problems. According to Russell Ackoff, “We fail more often not because we fail to solve the problems we face, but because we fail to face the right problem.” For example, how will we address the complexity of what and how to deliver healthy grain-based foods that consumers find acceptable and will include in their daily diet? One solution, as recommended by the 2010 Dietary Guidelines for Americans Committee, is for the sectors of government, industry, and nonprofits (including both large and small businesses) to come together in order to develop a system that would allow for health-promoting dietary patterns. At minimum, public health officials are being asked to consider not only the overall roles of each player within the food system and how they work together to create the food environment but also the significance of community and citizen representation in identifying and filling the gaps, such as research projects that help meet the diverse and complex demands of the public. For example, one way to fulfill the gap(s) and meet the demands of the public is to develop a grain-based food that is practical, healthier, affordable, and desirable (PHAD) such that consumers will eat it in a restaurant setting. Yet the food must be ‘practical’ for supply chain stakeholders along with chefs and clientele in restaurants. A grain-based food might be described as ‘healthier,’ such that whole grain (WG) wheat is incrementally or ‘gradually’ increased if the food/product meets PHAD criteria and restaurant clientele actually eat it. ‘Affordability’ throughout the supply chain and in the food preparation and restaurant setting can be a limiting factor. Overall ‘desirability’ of these grain foods by supply chain stakeholders, restaurant chefs, staff, and clientele along with community norms needs to be taken into account. In order to increase consumer intake of these grain-based foods with higher WG content, it will require the development of tools, methods and approaches, systems, and necessary infrastructure to successfully develop and deliver these foods into the marketplace. The successful outcome of this effort might be underpinned via research initiatives that focus on increasing WG ingredients in grain-based foods for restaurant service. Ideally, these inherent research problems and solutions are conceived and tested within the context of a complex grain

foods supply, which interfaces with a community of clients who frequent the food environment, such as restaurants whereby these ‘healthier’ grain-based foods are served and potentially consumed. Systems thinking is one approach to view ‘problems’ as parts of an overall system, rather than reacting to a specific part, outcome, or event. It is about understanding and seeing through the complexity and managing interdependency of sectors, disciplines, and individual contributions. The process encourages understanding of the big picture by sensing its large-scale patterns and responding to them. We might benefit by carefully crafting a process for defining problems and only then designing collective solutions. Ultimately, this reflects design thinking in bringing more healthful ingredients, foods, and products into the kitchen and/or marketplace that consumers demand, by taking into account the influences of the overall food system, food environment, and community. A systems approach will require multicultural representation to come around a specific initiative to prioritize, focus, and leverage the strengths of individuals throughout the various sectors and diverse disciplines of study.

Partnerships to Achieve a Common Goal around Healthier Grain-Based Foods According to Rowe et al., PPPs can create a collaborative environment that maximize cross-disciplinary expertise among government, academic, and industry researchers to help solve complex research problems. Leveraging the proficiencies and competencies of a broad range of stakeholder experts could maximize available expertise and collectively achieve the best research outcomes while extending and enhancing limited financial and other resources. Figure 1 addresses 12 proposed principles of PPPs, offered in no strict chronological order because each partnership has unique characteristics.

It Starts by Defining Shared Value and Vision Our vision is to bring together the various sectors, including government, industry, nonprofit, academia, and activist groups, to begin articulating the needs, desires, and demands for targeting research dollars. The acquisition of research dollars will help fill a void, which increases our ability as a society to cost-effectively deliver healthier grain-based foods into the marketplace. This is a vision of operation whereby sharing of intimate information, goals, and objectives makes it challenging to establish a common shared value leading to a common purpose, which drives this network of individuals toward a common outcome and benefit for business and society.

Vision Increase the availability of grain-based foods that are PHAD with the intention of making the healthy choice the easy and natural choice for citizens.

FOOD GRAINS AND THE CONSUMER | Grains and Health Figure 1 PPPs should do the following: 1. Have a clearly defined and achievable goal to improve the health of the public 2. Articulate a clear statement of work, rules, and partner roles, responsibilities, and accountability, to build in trust, transparency, and mutual respect as core operating principles – acknowledging there may be ‘deal breakers’ precluding the formation of an effective partnership in the first place 3. Ensure that objectives will meet stakeholder partners’ needs, with a clearly defined baseline to monitor progress and measure success 4. Considering the importance of balance, ensure that all members possess appropriate levels of bargaining power 5. Minimize conflict of interest by recruiting a sufficient number of partners to mitigate influence by any single member and to broaden private sector perspectives and expertise 6. Engage partners who agree upon specific and fundable research question(s) to be addressed by the partnership 7. Enlist partners who are committed to the long-term goals as well as to the sharing of funding and research data 8. Along with government and the private sector, include academics and other members of civil society as partners 9. Select objective scientific measurements capable of providing common ground for both public and private sector research goals 10. Adopt research questions and methodologies established by partners with no vested financial interest in them, ideally in the precompetitive space 11. Be flexible and ensure ongoing transparent communications 12. Consider a third-party convener to ensure equality at the table, clarify rules, establish operational guidelines, and specify funding arrangements

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Alignment among stakeholders through gauged, coordinated, and prioritized research efforts that bridge the gaps between research and consumer solutions A sustainable infrastructure guided by industry profitability while gradually improving the availability and consumer acceptance of ‘healthier’ food products Targeted, prioritized research efforts that allow scientists to address the food attribute gaps related to quality, cost, convenience, and efficacy, translating science into food Research that ranges from fundamental to product application of functional foods and health, including enhanced delivery of bioactives Research that focuses on the successful development, delivery, and enhanced consumer intake of healthier food ingredients (this knowledge can provide insight on what innovation opportunities are feasible)

Who Will Guide This Process? Assemble the right minds

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The PPP will be composed of an expanded network of working partners across all sectors and disciplines of the food supply, closely linked to consumer groups. We are asking stakeholders to be a part of a PPP, which will be formed to identify and to convene these participants and to solidify the project scope and the overall approach.

Why Participate? Values Values are integral in the roles that individuals play through the group process and dynamics, clarity of objectives, mutual trust, cooperation, and expected outcomes.

PPP members will be uniquely positioned to

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Why Is There a Need for a PPP? Food and ingredient industries are uniquely positioned with the technical expertise to make gradual product formulation changes that are well accepted by consumers. These gradual product formulation changes will not only improve the product nutritional profile but also move consumers toward dietary recommendations:

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How can we fund research initiatives that guide food formulation and product development to make it easier for consumers to eat in a way that supports dietary guidance? Is there a research approach that simultaneously encourages new ingredient and innovative technology development, supports a profitable industry business model, and delivers products with enhanced nutritional value that appeal to consumers?

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steer the fundamental research path from the ground floor, before it becomes available to the greater grain-based food industry/community; view firsthand the output of this fundamental and translational research, which can feed research and development efforts to reach targeted customer segments such as schools, restaurants, home, and retail; leverage the resulting innovation and new processing technologies.

How Will This PPP Function? 1. Key representatives, from across the food supply, will convene to identify and prioritize research issues and gaps. 2. Meaningful collaboration will occur through application of collective knowledge and targeted research. 3. Mutually beneficial collective solutions for business and for society will result, ultimately positively influencing public health outcomes.

What Are the First Steps?

What Makes This PPP Approach Unique?

New research is needed to support system-wide changes and to assure continuity from science (theory) to consumers (practice) throughout the food delivery system. This integrated and multifaceted process would deliver the following:

This will be an innovative and a gradual shift in the way we think about our food supply resulting in a shared and coordinated approach to research with the following governing guidelines:

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• • • •

FOOD GRAINS AND THE CONSUMER | Grains and Health Open and safe environment to share ideas Time to identify research gaps that limit availability of healthier foods in the marketplace Supporting infrastructure to implement the changes Freedom to innovate and to conduct the targeted research necessary to transform science into food

What Will Success Look Like? Short term to midterm Coordinated and comprehensive plan that identifies research gaps through an integrated and gradual approach so that basic, applied, and translational research can be targeted toward the development and delivery of healthier grain-based foods that deliver the attributes of a food product that are appealing to consumers.

Follow-up from the meeting will be posted on the Grains for Health Foundation’s website (Whole Grains Summit 2012 Events Page: http://grainsforhealth.org/news-and-events/ events/2012-whole-grain-summit). Further discussions with representatives from industry, government, grain organizations, and academic institutions that proposed research initiatives/projects include I. standardized approaches and methods to WG research, II. WG impact on the microbiome project, III. community WG farm-to-fork intervention in New Ulm, MN.

Standard Protocol for WG Intervention Studies of Intermediate Metabolic End Points (Proposed Project I) Purpose

Long term Sustainable infrastructure in place that supports a coalition across the food supply chain, developing a unified strategy that leads to increased availability of grain-based foods that meet dietary guidance and resulting in a model that meets both business and societal needs.

Overview of Foods Research and Public Health Figure 2 summarizes the formation of partnerships/collaborative processes of convening the sectors and disciplines in the top portion of the diagram. On the far right side, key consumer issues are identified and prioritized related to food environments, such as schools, restaurants, or retail. Moving to the left, specific food attributes for grain-based food categories are then discussed relative to overcoming supply chain barriers and challenges through product development. The food attributes of grain-based foods should ideally meet standards for PHAD by customers. Based on right to left movement from the food environment, to food attributes, to supply chain challenges, the research input is identified and targeted through the supply chain and focused on key audiences in schools, restaurants, and retail. Based on the 2012 Whole Grain Summit, Minneapolis, MN, five recommendations were established. Summit participants issued a call for a unified direction for the global grains and health communities to

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promote communication and unify leadership among organizations in both grains and health, encourage the delivery of consistent WG messages to consumers, support development of new products through targeted research on both the health-related efficacy of WG and technology for improved product development, improve the consumer environment for choosing WG foods through new product development by grain-based food companies as a main means of increasing WG consumption, encourage wider adoption of governmental policies supportive of an effective approach toward greater WG availability in the marketplace.

The main objective is to develop a standardized protocol whereby future intervention studies of WG and surrogate end points would contain very specific research methods. Identifying the appropriate methods of WG intervention studies would allow for easier comparisons across studies of similar WG and of studies that investigate different types of WG. Conducting a meta-analysis would then be more easily performed to adequately address the role of WG in prevention of chronic disease.

What Problem(s) Does the Proposed Project Address and for Whom? The current body of evidence supporting the role that WG plays in promoting health is largely composed of observational studies. Intervention studies have yielded inconsistent results when examining WG and health end points, such as insulin resistance and Body Mass Index (BMI). The existing intervention studies are not truly amenable to meta-analyses to help address the issue of small sample size because of the variability in the populations studied, variability in the WG interventions (sources and quantity), and lack of standardization in measuring surrogate endpoints. The end result is a lack of comparability across many of the existing randomized trials. Developing a standard protocol for WG intervention studies of intermediate metabolic end points would have a huge impact on the scientific community. Researchers would be able to pool individual study results together for stronger metaanalysis. This would not only reduce the need for a single, large-scale intervention but also save researchers time and money. Altogether, a better understanding of the role that WG plays in health would ultimately benefit citizens and communities, providing clearer nutrition education and implementation.

Why a PPP for This Project? 1. Does the research have the potential for significant public health impact? A clearer investigation of the role WG plays in health could provide industry better direction in production, delivery, and labeling of WG foods. This ultimately


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OVERVIEW FOR

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HEALTHY CHOICE IS THE EASY CHOICE. Figure 2 An overview of public and private partnerships for food research and public health.

provides the consumer with more informed and healthier options. When the science gets better, everyone wins. 2. Does it have implications across many different food and/or beverage categories? Over the last decade, WGs have made their way in to almost every food and beverage category (cereal, bread, pasta, smoothies, grab and go salads, snack bars, crackers, etc.), and this is a trend that is forecasted to continue as restaurants begin to incorporate WGs onto their menus. Additionally, the grains research community currently struggles to deliver a consistent message on the benefits of

WG. Some grain groups focus on communicating the benefits of enriched grains, some on the fiber benefits, and some on WG. Building a stronger science base will allow for clarity in messaging to product developers, health professionals, and the consumer. 3. Is it precompetitive in nature and what does this mean for the food industry? Yes, the question is precompetitive. The investigation and subsequent inquiry would benefit any/all players in the grain food industry. A stronger science base for the


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food industry would provide clarity in product development, ingredient procurement, packaging messages/marketing claims, etc. A common protocol for WG research means less money spent on research that does not deliver the final clarity that industry is looking for and more ‘mileage’ out of the money that is spent on individual interventions.

Who As suggested by Rowe et al. “Partners with complementary capability, capacity, resource access, and experience should bear the risk appropriate to their contribution and share fairly in the benefits from the research based on the value they bring to the partnership.” Partners might include the US Department of Agriculture Agricultural Research Service (USDA-ARS) and industry interested in clarifying the role of WG in health, the Centers for Disease Control and Prevention (CDC) and/or the National Institutes of Health, and leading academic research centers, such as Tufts University and University of Minnesota.

Where USDA-ARS research centers and National Institute of Food and Agriculture external funding sources may help fund and participate in this effort.

WG Impact on the Microbiome: PPP (Proposed Project II)

Why A number of epidemiological studies have established that WG consumption is associated with positive health benefits. Although reductionist experimental approaches have provided some insights into the components of WG that might explain these associations, a thorough understanding of the impact on WG consumption on host metabolism would be incomplete without addressing the role WG plays in modulating host metabolism through its impact on gut microbial communities. This project has the potential to further our understanding of the positive benefits of WG consumption to human health. The project would have applications across several food categories (cereals, snacks, etc.). This research may strengthen the evidence-based justification for increasing our consumption of WG foods in the face of rising popular sentiments against grain-based foods.

Who The participation of both academia and industry will be essential to explore the benefits of WG on gut microbial communities and their impact on human health. The food industry’s knowledge and experience in creating food products with meaningful quantities of WG without compromising taste would be an essential complement to the academic institution’s capabilities for assessing the impact of such foods on gut microbial communities and health (Figure 3).

Community WG Farm-to-Fork Intervention in New Ulm, MN (Proposed Project III)

Purpose There is increasing evidence that microbial communities that reside in the gastrointestinal tract play a crucial role in health and disease. It is also becoming increasingly evident that diet, among other factors, may be an important variable in the establishment and maintenance of a microbial ecosystem that supports and promotes health.

Purpose To create a healthful, sustainable local grain food supply within a Minnesota community using a PPP model to leverage diverse expertise to address WG intake. This proposal will focus on WG foods in away from home (AFH) eating establishments. Ecological and community-based participatory research

What are the characteristics of a “healthy” microbiota?

PROJECT SCOPE

DIET Genetics Lifestyle Life stage Other

How does a whole grain diet influence the gut microbiota?

Gut Microbiome

HEALTH

How does the gut microbiota influence health?

Figure 3 The possible scope of a collaborative research project to assess the impact of whole grain foods on the gut microbial communities.

FOOD GRAINS AND THE CONSUMER | Grains and Health (CBPR) approaches will be utilized to increase WG availability, sustainability, and consumption of AFH foods by increasing the number of WG offerings and percent WG content in grainbased foods found in restaurants and grocery store eateries. This supply chain intervention will start in New Ulm, Minnesota, as part of GrainUP!, a grassroots WG consumer awareness campaign that encompasses the crucial industryfacing supply chain work to create a road map for increasing WG menu offerings AFH. The proposed study will test the following hypothesis: increasing the WG food offerings by 25–50% (depending upon the AFH setting and food category) and gradually introducing an increase in the WG content of popular grain-based items in New Ulm’s AFH food environment (restaurants and grocery store eateries). The hypothesis is that this will increase AFH WG consumption from an average of one-third serving per day to 1 serving per day, thus contributing to the Dietary Guidelines for Americans’ overall recommended three daily servings of WG. We aim to address availability, consumption, and sustainability at a systems level.

Why For almost a decade, the Dietary Guidelines for Americans have recommended that Americans consume at least three ounce equivalents (servings) of WG foods daily for optimal health. WG foods improve heart health and weight management and lower risk of certain cancers. Yet in spite of health benefits and Dietary Guidelines for Americans recommendations, the average American consumes only 0.8 servings per day. Low WG consumption may be linked to the food environment and consumption of foods outside of the home. Today, the average American spends 42% of his or her food budget on AFH foods, which constitutes about 35% of daily calories. These foods tend to be lower in nutritional quality – often high in calories, fat, sodium, and cholesterol – and offer less than one-third ounce of WG per day. Eating AFH as little as one meal per week can lead to approximately two extra pounds of weight each year for adults. Modifying the food environment where adults frequently eat is a promising approach to bringing about sustainable improvements in nutrition behaviors at a population level so that when consumers are faced with making food choices, the healthier choice – WG foods – is the easier and preferred choice. Recent research examining the ‘relative healthfulness’ of restaurant menus has shown that of 34 restaurants assessed in New Ulm, fewer than 26% offered a WG bread option. According to Rebecca Lindberg, researcher of Hearts Beat Back: The Heart of New Ulm Project, feedback from restaurant owners and chefs involved in trying to improve the healthfulness of their menu offerings has indicated that the WG category is one of the most difficult menu items to change (oral communication, 17 March 2014). Recent restaurant and grocery store eatery assessments demonstrated that increasing AFH WG menu choices remains difficult to influence when compared to other healthful restaurant practices.

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Yes, this has potential for significant public health impact. Investigating the current barriers to a sustainable WG supply chain consistently delivering healthier WG options to AFH settings benefits the consumer. By allowing chefs, manufacturers, researchers, and policy makers to understand the barriers, challenges, and opportunities to increasing WG consumption AFH, steps can be taken to make the WG choice the easy choice. This supports the Dietary Guidelines for Americans recommendation of eating at least three servings of WG a day. 2. Does it have implications across many different food and/or beverage categories? Grains are present in most AFH food categories, from appetizers to dessert. In addition, their appearance usually includes other food groups, such as fruits and vegetables, meats and legumes, and dairy. Grains can serve as the perfect vehicle for healthier foods AFH and provide an opportunity to address portion sizes and added sugars and fats. 3. Is it precompetitive in nature and what does this mean for the food industry? This proposal provides the opportunity for both ingredient and consumer packaged goods manufacturers to develop and pilot products and supply chain strategies, in a precompetitive, collaborative environment. This applied research model holds the potential to streamline processes, reduce costs, and ensure technology transfer that can be applied to other cities and communities.

Who This proposal involves the resources and expertise of the Hearts Beat Back Project (Minneapolis Heart Institute Foundation, Allina Health, and the community of New Ulm, MN), food industry, academics at the University of Minnesota, and project management from the Grains for Health Foundation. The Hearts Beat Back Project has previously received a USDA Farmers Market Promotion Program grant, so has relationships with farmers/producers, and is currently finishing a CDC Community Transformation grant (expanding their work to the rest of Brown County, MN).

Where The intervention will support current work of the Hearts Beat Back Project, a 10-year population-based demonstration project designed to deliver interventions at individual, institutional, and community levels that reduce the rate of heart disease risk factors in adult residents of New Ulm. Minneapolis restaurants will be the next intervention site(s), once a sustainable supply chain approach and model is established, with eventual rollout to other nationwide cities and communities.

Why a PPP for This Project

When

1. Does the research have the potential for significant public health impact?

Project work will occur over a 2-year period starting July 2014, in the four phases listed in the succeeding text:


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Phase 1: Environmental scan for assessments and establishment of AFH community forums Phase 2: Gradual implementation of intervention using the CBPR approach Phase 3: Social marketing and promotion Phase 4: Final assessments and evaluation of likelihood intervention outcomes will be sustained

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How Typically, the last mile of the AFH food supply chain is where many of the complications with WG foods reaching the consumer occur. Given this, intervention will occur at various points along the food supply chain (miller, baker, food manufacturer, and AFH eating environment) to address WG food quality, affordability, and desirability. An ecological framework and the CBPR approach will be used to assess, implement, promote, and measure a gradual increase in WG offerings and percent WG content of current grain offerings. WG foods of varying refined grain/WG content will gradually be introduced in these establishments, along with technologies to help reduce rancidity and enable tracking of shelf life of WG flours to ensure the delivery of a fresh, safe, nutritious, and palatable final product. The goal is that the increased consumer acceptance and consumption of WG foods in AFH setting will become permanent and sustainable.

Conclusions New research is needed to support system-wide changes and to assure continuity from science (theory) to consumers (practice) throughout the food delivery system. Public and private research is one approach to explore ways of identifying research initiatives that might help fill gaps in the food supply chain, food environment, and community settings to more successfully deliver healthier grain-based foods into the marketplace that consumers demand and readily consume. A process is necessary to examine the issues, problems, and gaps that exist relative to the development, delivery, and consumer intake of healthier grain-based foods. Each research project has merit as it relates to enhancing the development, delivery, and consumption of grain-based foods made with WG ingredients. Each project is complex in its own way and affects different aspects of the food system and food environment along with community input and influence. We began to address these research initiatives during a PPP meeting held on 3–4 December 2014, in Washington, DC. The outcomes of this meeting will be discussed in another communication venue.


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Why are public and private partnerships needed to support grain-based research? What kind of thinking looks at parts of an overall system? How is this helpful in grain-based research? What is the benefit of a PPP in terms of solving complex research problems?

Public and private partnerships combine what type of sectors and disciplines?

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Identify the challenges and opportunities (gaps) related to the substitution of WG wheat flour (50% whole wheat flour) in a restaurant pizza. Track the pizza (1) through the supply chain from field to fork and (2) in the food environment, such as in a restaurant, and explore the characteristics of the community patrons who frequent this local restaurant. How might a flour milling or packaged foods company use this information related to the gaps in the food supply, food environment, and community patrons? What type of training programs might colleges, universities, and industry consider in training of students and young professionals to understand more about the food system, food environment, and surrounding community who purchase and use their products?

Further Reading Ackoff RL (1981) Creating the Corporate Future: Plan or Be Planned for. New York: Wiley. Andersson A, Tengblad S, Karlstrom B, Kamal-Eldin A, Landberg R, Basu S, et al. (2007) Whole grain foods do not affect insulin sensitivity or markers of lipid peroxidation and inflammation in healthy, moderately overweight subjects. Journal of Nutrition 137: 1401–1407. Beauman C, Cannon G, Elmadfa I, Glasauer P, Hoffmann I, Keller M, et al. (2005) The principles, definition and dimensions of the new nutrition science. Public Health Nutrition 8(6A): 695–698. http://dx.doi.org/10.1079/PHN2005820. Bodinham CL, Hitchen KL, Youngman PJ, Frost G, and Robertson MD (2011) Shortterm effects of whole-grain wheat on appetite and of intake in healthy adults: A pilot study. British Journal of Nutrition 106: 327–330. Ferruzzi M, Jonnalagadda S, Liu S, Marquart L, McKeown N, Reicks M, et al. (2014) Developing a standard definition of whole grain foods for dietary recommendations: Summary report of a multidisciplinary expert round table discussion. Advances in Nutrition 5(2): 164–176. Gharajedaghi J (2011) Systems Thinking: Managing Chaos and Complexity: A Platform for Designing Business Architecture, 3rd edn. New York: Elsevier. Giacco R, Clemente G, Ciriano D, Luongo D, Viscovo D, Patti L, et al. (2010) Effects of the regular consumption of wholemeal wheat foods on cardiovascular risk factors in healthy people. Nutrition, Metabolism, and Cardiovascular Diseases 20: 186–194. The Giessen declaration. Public Health Nutrition (2005) 8(6A): 783–786. Grains for Health Foundation, Whole Grains Summit 2012: http://grainsforhealth.org/ news-and-events/events/2012-whole-grain-summit. Hassel CA (2014) Reconsidering nutrition science: Critical reflection with a cultural lens. Nutrition Journal 13: 42. http://dx.doi.org/10.1186/1475-2891-13-42. Jacobs Jr. DR Jr., Meyer KA, Kushi LH, and Folsom AR (1998) Whole grain intake may reduce the risk of ischemic heart disease death in postmenopausal women: The Iowa Women’s Health Study. American Journal of Clinical Nutrition 68: 248–257. Jacques P, Hauge D, Voth K, Hermann M, Maschoff B, and Marquart L (2013) Overcoming the challenges of translating the US Dietary Guidelines into healthier grain-based foods. Nutrition Today 48(6): 254–259. Lankinen M, Schwab U, Kolehmainen M, Paananen J, Poutanen K, Mykka¨nen H, et al. (2011) Whole grain products, fish and bilberries alter glucose and lipid metabolism in a randomized, controlled trial: The Sysdimet Study. PLoS One 6: e22646. Lin BH and Guthrie J (2012) Nutritional Quality of Food Prepared at Home and Away From Home, 1977–2008. Washington, DC: USDA, ERS EIB No. 105. Liu S, Manson JE, Stamfer MJ, Rexrode KM, and Hu FB (2000) Whole grain consumption and risk of ischemic stroke in women: A prospective study. JAMA 284: 1534–1540. Liu S, Willett WC, Manson JE, Hu FB, Rosner B, and Colditz G (2003) Relation between changes in intakes of dietary fiber and grain products and changes in weight and

FOOD GRAINS AND THE CONSUMER | Grains and Health development of obesity among middle-aged women. American Journal of Clinical Nutrition 78: 920–927. Marquart LF, Jonnalagadda SS, van Klinken BJ-W, Clemens R, Jensen G, Arndt E, et al. (2013) Delivering healthy and affordable whole grain foods: How can the food industry produce whole grain products that consumers will eat? Food Technology 67(7). McKeown NM, Troy LM, Jacques PF, Hoffmann U, O’Donnell CJ, and Fox CS (2010) Whole- and refined-grain intakes are differentially associated with abdominal visceral and subcutaneous adiposity in healthy adults: The Framingham Heart Study. American Journal of Clinical Nutrition 92: 1165–1171. Minkler MNW (2003) Introduction to community based participatory research. In: Minkler MNW (ed.) Community Based Participatory Research for Health. San Francisco, CA: Jossey-Bass. Pereira RF, Sidebottom AC, Boucher JL, Lindberg R, and Werner R (2014) Assessing the food environment of a rural community: Baseline findings from the Heart of New Ulm Project, Minnesota, 2010–2011. Preventing Chronic Disease 11: 130291. Reed GE (2006) Leadership and systems thinking. Defense AT&L 35: 10–13. Reicks M, Jonnalagadda S, Albertson AM, and Joshi N (2014) Total dietary fiber intakes in the US population are related to whole grain consumption: Results

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from the National Health and Nutrition Examination Survey 2009 to 2010. Nutrition Research 34: 226–234. Rowe S, Alexander N, Kretser A, Steele R, Kretsch M, Applebaum R, et al. (2013) Principles for building public-private partnerships to benefit food safety, nutrition and health research. Nutrition Reviews 71(10): 682–691. Story M, Kaphingst KM, Robinson-O’Brien R, and Glanz K (2008) Creating healthy food and eating environments: Policy and environmental approaches. Annual Review of Public Health 29: 253–272. Tighe P, Duthie G, Vaughan N, Brittenden J, Simpson WG, Duthie S, et al. (2010) Effect of increased consumption of whole grain foods on blood pressure and other cardiovascular risk markers in healthy middle-aged persons: A randomized controlled trial. American Journal of Clinical Nutrition 92: 733–740. Todd JE (2014) Changes in Eating Patterns and Diet Quality Among Working-Aged Adults, 2005–2010. Washington, DC: USDA, ERS Report No. 161. U.S. Department of Agriculture and U.S. Department of Health and Human Services (2010) Dietary Guidelines for Americans 2010, 7th edn. Washington, DC: U.S. Government Printing Office. Ye EQ, Chacko SA, Chou EL, Kugizaki M, and Liu S (2012) Greater whole grain intake is associated with lower risk of type 2 diabetes, cardiovascular disease, and weight gain. Journal of Nutrition 142: 1304–1313.


Contents Cereal Allergens Nutrition: Beriberi, A Deficiency Related to Grains Celiac Disease The Gluten-Free Diet

Cereal Allergens AS Tatham, Cardiff Metropolitan University, Cardiff, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Wheat, maize, and rice are major contributors to human diets. The cereals contain proteins (albumins, globulins, and prolamins) that are implicated in food allergy and intolerance. Four major types of wheat allergy are described, associated with proteins that are part of protein ‘superfamilies.’ These superfamilies account for the cross-reactivity observed between the cereals and between botanical species. Currently, there are no treatments of cereal allergy (apart from treating the attendant symptoms). Patterns of cereal allergy are changing as patterns of cereal consumption change.

Learning Objective

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To achieve understanding of the types of cereal allergy, allergens, clinical manifestations, and treatment.

Introduction The most common allergic foods associated with immunoglobulin E (IgE)-mediated reactions on a worldwide basis are fish, peanuts, soybeans, milk, eggs, crustaceans, tree nuts, and wheat. These foods commonly account for over 90% of food allergies. Food allergies are increasing in prevalence and are currently estimated to affect 2–8% of the population. The reasons for this increase remain unexplained, as do the mechanisms by which food proteins become capable of inducing an allergic response in an individual. The prevalence of cereal allergies is low, a figure of 2% of the population often being quoted. Wheat allergy is defined as an adverse (IgE-mediated) reaction to wheat, as distinct from intolerance (celiac disease), which is a cell-mediated inflammatory reaction in the intestinal lining. Wheat allergy can be divided into wheat-dependent exercise-induced anaphylaxis (WDEIA), bakers’ asthma

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(occupational asthma) (both of which have well-characterized allergens), classic food allergy (affecting the skin and gastrointestinal and respiratory tracts), and contact dermatitis (where the allergens are less well defined). Wheat, rice, and maize constitute the ‘big three’ cereal crops, with the cereals forming the staple of many diets. It is, therefore, perhaps unsurprising that cereal allergies, arising either through ingestion or through exposure to cereal flours and dusts, are increasing.

Symptoms and Pathology IgE-mediated food allergies can elicit life-threatening reactions. Allergy refers to an adverse immune reaction to food proteins that are normally tolerated by the immune system. IgE acts as a mediating antibody in the development of inflammatory responses. These reactions, occurring in the lungs, skin, or digestive tract, include asthma, rhinitis (hay fever), oral allergies, food and contact allergies, and anaphylaxis; the most severe form of allergic response involves a whole-body reaction, which in some cases can lead to death. The development of an allergic response involves several steps. The first is sensitization, where the allergen stimulates the production of antigen-specific IgE antibodies that can bind to mast cells. This does not induce an allergic response, but repeated contact with the antigen on subsequent ingestion binds to the IgE, inducing the mast cells to release chemicals, such as histamine, that cause the various symptoms of food allergy (inflammation and anaphylaxis). Some individuals are referred to as atopic, where they produce relatively high amounts of IgE and are prone to becoming sensitized and developing an allergy.

Cereal Proteins The proteins found in cereals fall into a limited number of protein superfamilies that are characterized on the basis of


http://dx.doi.org/10.1016/B978-0-12-394437-5.00085-1

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | Cereal Allergens their highly conserved sequence regions, structures, and functions and account for the cross-reactivity of allergens that are found within the cereals. The prolamins (defined as aqueous alcohol-soluble seed storage proteins) of wheat, barley, and rye, and to some extent oats, are related; those of maize, millet, sorghum, and rice are in part related but differ significantly from wheat, barley, rye, and oats. Other protein families include the pathogenesis-related (PR) proteins, which are involved in the defense systems of plants against a host of different pathogens, and also albumins and globulins that can be involved in storage functions and metabolic proteins. Understanding these relationships can be critical in understanding cross-reactivity in cereal allergy and intolerance. Allergic reactions to wheat can be divided into inhalational allergy (bakers’ asthma), ingestion (WDEIA), and also wheat allergy and contact dermatitis, caused by skin contact with wheat proteins. In bakers’ asthma and WDEIA, the allergens are well characterized, whereas the allergens involved in wheat allergy and contact dermatitis appear to be related to a range of proteins that vary between individuals.

Bakers’ Asthma Bakers’ asthma is one of the most common forms of occupational asthma, caused by the inhalation of wheat and cereal flours and of dusts and other substances commonly found in bakeries and flour mills. In bakery and flour-handling workers, studies indicate 5–10% suffer from asthma and 10–20% from rhinitis, making it one of the most common occupational allergies. Studies have shown that multiple allergens are present in cereal flours that are recognized by IgE from patients’ sera. One group, the a-amylase inhibitors, contains the major allergens, with other allergens (including the lipid-transfer proteins (LTP), peroxidase, thioredoxin, and serine proteinase inhibitors) showing the strongest IgE reactivates in wheat flour; the prolamins, thaumatin-like proteins, and acyl-CoA are also implicated. In addition, a range of flour improvers/additives contribute to the allergenic potential of cereal flours. The a-amylase inhibitors consist of 12–16 kDa polypeptides with 4–5 intrachain disulfide bonds, which are tightly folded, making them thermally stable and difficult to digest. They are encoded by multigene families in wheat, barley, and rye, giving rise to marked heterogeneity in their composition. In addition, they can occur as monomers, homodimers, and tetrameric aggregates. They are active against the a-amylase of insects and in the cereals are active in plant defense. Homology between the proteins found in wheat, barley, and rye accounts for the cross-reactivity between the flours from these cereals. They are panallergens, being present in the flours of other cereals. In addition, LTPs constitute a family of panallergens; their main function is in plant defense against phytopathogens (fungi and bacteria); they are classified as PR proteins. They have been identified as the major allergens in many fruits in the Rosaceae family (e.g., peach, plums, and apples). In bakers’ asthma, they are major allergens. In addition to the water/salt-soluble allergens, which constitute the major classes of allergens in bakers’ asthma, the prolamins are also implicated. Patients’ sera have shown

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binding to the a-, g-, and o-type gliadins and low-molecularweight subunits of glutenin. Detailed studies of sequentially extracted wheat flour, into salt-soluble (albumins and globulins) and alcohol-soluble gliadins and glutenins, indicate that patients’ sera recognize multiple allergens. Other ingredients are used as flour/bakery additives, often starch-cleaving enzymes, and some of these have been found to be allergenic. Fungal a-amylase from Aspergillus oryzae is added to digest starch and is allergenic, as are cellulases and xylanases from Aspergillus niger, added to flour to digest fiber. Soy flour, added to wheat flour as a source of lipoxygenase to whiten flours, is responsible for food and inhalational allergies. Soybean allergy has been implicated in bakers’ asthma.

Wheat-Dependent Exercise-Induced Anaphylaxis Food-dependent exercise-induced anaphylaxis (FDEIA) is defined as when food intake, followed by exercise, results in the display of allergic symptoms (from urticaria to anaphylactic shock). When food intake and exercise are taken independently of each other, no symptoms are observed. Ingestion of the causative food and exercise within 2–3 h (moderate to strenuous) are required for the allergic response to occur. Wheat is reported, along with crustaceans, to be one of the foods most commonly reported to be associated with FDEIA. The incidence of FDEIA is difficult to evaluate but estimated to account for 5–15% of all anaphylactic cases; of this, one-third to one-half are estimated to arise from FDEIA. In a Japanese study, the incidence was found to be 0.017% and 0.031% for cases of FDEIA and EIA, respectively. The major allergens associated with WDEIA have been identified as the o5-gliadins (from the B genome of wheat) and the high-molecular-weight (HMW) subunits of wheat. In one study, 80% of patients had IgE reacting to o5-gliadins, the remainder to HMW subunits. The g-35 and g-70 secalins of rye and the g-3 hordeins of barley cross-react with wheat allergic sera, but no cross-reactivity with the avenins of oats has been reported. In wheat, the epitopes (amino acid sequences that cause the allergic response) are well characterized. Four immunodominant epitopes in the o5-gliadins of wheat have been identified (QQIPQQQ, QQFPQQQ, QQSPEQQ, and QQSPQQQ). Mutational analysis, using synthetic peptides, indicated that Gln at positions 1, 5, 6, and 7 and Pro at position 4 of the heptapeptides were critical for IgE binding. Omega gliadins, derived from the A and D genomes of wheat, do not contain these epitopes and are not implicated in WDEIA. Three IgE-binding epitopes, in the repetitive domains of the HMW subunits of wheat, have been identified, QQPGQ, QQPGQGQQ, and QQSGQGQ, using synthetic peptides. Aspirin increases the levels of gliadin-derived peptides circulating in the bloodstream and upregulates the allergic response to specific foods, including wheat. Wheat–exercise and wheat–aspirin challenges increased the levels of gliadinderived peptides in the blood, indicating that both exercise and aspirin facilitate allergen absorption from the intestine. The specificity of the association between o5-gliadin and WDEIA has led to the development of diagnostic tests measuring the levels of IgE directed against recombinant o5-gliadins.

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FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | Cereal Allergens

Wheat Allergy

Maize Allergy

Wheat allergy caused by the ingestion of wheat proteins can give rise to a range of symptoms including urticaria, atopic dermatitis, and anaphylaxis. Wheat allergy in children, similar to egg and milk allergies, is outgrown by the majority of children by the age of 3–5. In children, the most common symptoms are atopic dermatitis. In adults, wheat allergy is less frequently observed. Studies have shown that the IgE fractions for both adults and children react with gliadin (a-, g-, and o-types) and glutenin fractions, albumins, and globulins, the latter two groups being strongly correlated with atopic dermatitis. Similar studies have shown differences in the pattern of IgE recognition related to age and symptoms. Patients who showed anaphylactic reactions, similar to those with WDEIA, had IgE to the o5-gliadins. Patients with this form of allergy often show IgE to multiple allergens, and diagnosis, other than by food challenge, is problematic. Wheat-specific IgE concentrations do not appear to be good indicators of the outcomes of provocation (food challenge) tests, so even with a low or negative outcome, wheat allergy cannot be excluded without a challenge test, if clinical symptoms suggest wheat allergy.

Maize allergy has been reported in countries where maize forms a staple in the diet, such as Africa, Central and South America, and southern Europe. In the United States, the prevalence of allergy to maize and maize-derived sweeteners is low (estimated at 0.016% of the population); the incidence elsewhere is thought to be higher. Maize allergy is linked to occupational asthma and contact dermatitis through handling maize flour and food allergy by maize ingestion. The major allergens are LTPs and a-amylase inhibitors; the LTPs show cross-reactivity with LTPs from barley and rice; minor allergens include thioredoxins, g-zein (an alcoholsoluble seed storage protein), and trypsin inhibitors.

Contact Dermatitis Contact dermatitis is an inflammation of the skin caused by coming into direct contact with an allergen. This form of wheat allergy mainly occurs in bakery workers and others coming into occupational contact with wheat flours and dusts. More recently, contact dermatitis has been reported from cosmetics where hydrolyzed wheat proteins have been used as an ingredient to improve hydration properties, although their occurrence is uncommon. Oats, also used as an ingredient in cosmetics, have also been reported to cause contact dermatitis. There are few studies on the allergens responsible; a-amylase inhibitors, albumins, and globulins and gliadins have all been implicated.

Rice Allergy Rice allergy is common in Eastern Asia where rice forms a staple in the diet; it is less common in western countries. The most frequently observed symptoms are atopic dermatitis, eczema, asthma, and less commonly anaphylaxis. There are few reports of rice allergy, and little is known of the incidence or prevalence of rice allergy in Asian countries. Considering the importance of rice in the diet of a large part of the world’s population, this allergy lacks detailed studies on prevalence. The major allergens are the a-amylase inhibitors, which are implicated in 90% of patients exhibiting food-related atopic dermatitis. Rice-induced anaphylaxis has been linked to the LTP proteins, and cross-reactivity has been reported with LTPs from peach and apple. Rice is also linked to occupational asthma and contact dermatitis in workers handling rice and rice-derived products.

Allergies to Minor Cereals and Pseudocereals Food and inhalational allergies have been reported for millets and sorghum and for the pseudocereals buckwheat, amaranth, and quinoa. These crops are recommended for inclusion in gluten-free diets for celiac sufferers.

Effects of Food Processing on Allergenicity Cereals are often consumed after being subject to a variety of processing conditions, which may alter the epitopes in the proteins responsible for their allergenic properties. Processing can result in a reduction, no change, or an increase in the number of epitopes in the protein or an increase in their stability to digestion. The effects of thermal processing on wheat proteins have been reported, with different conclusions. Some studies have reported a reduction in allergenicity on heating extracted isolated proteins in solution or extracting them from heated gluten and analyzing their IgE binding. Others have reported similar IgE reactions from wheat proteins extracted from flour then heated and cooled or from flour and water heated and cooled and then extracted. In food challenges, some patients responded to a lower dose of cooked flour than unprocessed flour, which suggested an increase in the number of allergen epitopes. The effects of proteolysis (enzymatic digestion) to produce hypoallergenic wheat have been developed, using enzymes that digest known epitopes; however, these seriously affect the functional properties of the proteins. Severe allergic responses have been shown in hydrolyzed wheat proteins used in cosmetics, where the unmodified protein did not induce the response. This indicates that the process may introduce epitopes. In addition, deamidation of the glutamine residues of the prolamins may increase their allergenic potential; it is known that deamidation of glutamine residues in the celiac-active motifs enhances their activity. Allergic responses have been reported from beers brewed from barley and wheat and from barley malt. The major allergen was identified as an LTP, which retained allergenicity after being unfolded and chemically modified.


Diagnosis of Cereal Allergy If a cereal allergy is suspected, a number of tests can be performed for an accurate diagnosis. Skin prick tests (SPTs) involve applying allergens, in solution, subcutaneously. In an allergic individual, these will provoke mast cells to release histamine and produce inflammation within about 15 min. Blood tests measure IgE levels in vitro in blood serum. These tests measure sensitization, and not necessarily a clinically relevant allergy. The most reliable tests involve food challenges, which are used for immediate wheat allergy detection. Although diagnostic in vitro IgE and SPT assays are known to be unsatisfactory, they are extensively used. The CAP system has a predictive value for wheat of < 75%. The recent use of recombinant o5-gliadin for the diagnosis of WDEIA patients was reported to be around 80%, and children with high concentrations of IgE specific to o5-gliadin had a higher risk of failing a wheat challenge. The tests may, in some part, be unsatisfactory due to the allergen mixtures that are used. The albumins and globulins are relatively easy to extract from wheat flour; the prolamins are less so, due to their poor solubility in aqueous media and possible presentation in the IgE-binding assay.

Safe Amounts of Wheat Proteins for Patients with Wheat Allergy There is an inherent difficulty in determining the minimum eliciting doses that will cause an allergic reaction. Individuals will differ in their sensitivity to different allergens, and often, multiple allergens are present; a combination of these may be required to elicit a response. In children with wheat allergy, 8–10 g flour has been shown to induce symptoms, whereas in another study, it required < 2 g; children generally have a lower tolerance than adults due to their smaller body mass. WDEIA appears to be triggered by larger amounts of flour (60 g), which may be related to the allergen being present in small amounts, but there are few reported studies. There are ethical issues with feeding cereal flours to individuals with wheat allergy (as you are inducing a clinical response), but further study is required.

Management of Allergies to Cereals Managing cereal allergy involves reducing the risk of an allergic reaction by avoiding the allergen and by medical treatments to reduce symptoms. Allergen avoidance is an essential step in managing food allergies, for which there are currently no cures. Allergen labeling on packaged foods is a legal obligation in many countries. However, the use of ‘may contain’ places the onus on the customer to make a decision whether to purchase and consume the food. There is an increasing market for ‘free-from’ food products, especially ‘gluten-free,’ providing a wide range of products with similar textural properties to wheatcontaining products. Hidden allergens remain a problem, where wheat gluten is used in a wide range of products. Studies

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suggest that wheat gluten and wheat starch are found in more than 30% of packaged supermarket foods. Allergy medications control the symptoms and reactions to allergens but do not cure the allergy. Antihistamines are the most common form of allergy medication. During an allergic reaction, the immune system releases histamine, which starts the cascade effect of allergy symptoms, including swelling or edema, a drop in blood pressure, and itching. Antihistamines work by blocking the action of histamine, and they work best if taken before an allergic reaction has started, but they can block the further release of histamine after a reaction has started. Emollient lotions and creams, used for eczema and dry skin, may contain antibiotics to reduce the risk of infection and steroids to reduce inflammation. Adrenaline is used as an emergency treatment for anaphylactic shock, where sudden high levels of histamine released during the allergic reaction cause difficulty in breathing. Adrenaline alleviates the symptoms of the reaction and can be delivered by an autoinjector before further emergency treatment.

Application of Genetic Modification The use of genetic engineering to downregulate gene expression has been demonstrated in a number of cereal crops, particularly in relation to reducing the levels of specific proteins that contain celiac disease-activating epitopes. These approaches have the potential to reduce allergens in cereals. Hypoallergenic rice has been developed with downregulation of the gene family encoding a-amylase inhibitors, which are major food allergens in Japan. These approaches reduced the levels of the inhibitors down to about 20% of their levels in control plants. Wheat has been transformed to silence the o5gliadins (active in WDEIA), resulting in complete or substantially reduced levels relative to untransformed controls, with the retention of technological properties. These approaches could be used to reduce allergenicity by introducing stable heritable changes in the cereal genome.

Conclusions The major allergens associated with bakers’ asthma and WDEIA have been identified. The a-amylase inhibitors are most important in bakers’ asthma but less important in food allergy. The prolamins appear important in food allergies, particularly the o5-gliadins in WDEIA, and less so in bakers’ asthma. Several other minor allergens have been identified and their clinical relevance needs to be determined. There is a lack of information relating to rice allergy and to a lesser extent maize allergy. With the wider use of minor cereals and pseudocereals in the diets of cereal-allergic patients, it might be expected that there will be an increase in the incidence of allergy to these cereals as they become established foodstuffs. More reliable diagnostic methods are being developed for cereal allergies based on the major allergens, and advances are being made for their removal/reduction in transgenic crops. The wider availability of ‘free-from’ and ‘gluten-free’ will give the allergic consumer greater choice and, with legislation

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related to labeling, greater confidence in the foods that they consume.


• • • •

What are the major types of allergy associated with wheat? Why are patterns of cereal allergy changing worldwide? What are the major classes of proteins in cereal grains? What are the main types of wheat allergy and their causative allergens?


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Which groups of proteins account for cross-reactivity between botanical species? What are the potential uses of GM technology in reducing cereal (and general) food allergies? What are pseudocereals? How can they contribute to the diet of cereal allergy and intolerance sufferers?

Further Reading Altenbach SB and Allen PV (2011) Transformation of the US bread wheat ’Butte 86’ and silencing of omega-5 gliadin genes. GM Crops 2: 66–73. Gilissen LJWJ, van der Meer IM, and Smulders MJM (2014) Reducing the incidence of allergy and intolerance to cereals. Journal of Cereal Science 59: 337–353. Hischenhuber C, Crevel R, Jarry B, et al. (2006) Review article: Safe amounts of gluten for patients with wheat allergy or coeliac disease. Alimentary Pharmacology and Therapeutics 23: 559–575. Inomata N (2009) Wheat allergy. Current Opinion in Allergy and Clinical Immunology 9: 238–243. Matsuo H, Kohno K, Niihara H, and Morita E (2005) Specific IgE determination to epitope peptides of omega-5 gliadin and high molecular weight glutenin subunit is a useful tool for diagnosis of wheat-dependent exercise-induced anaphylaxis. Journal of Immunology 175: 8116–8122. Pastorello EA, Farioli L, Pravettoni V, et al. (2009) Maize food allergy: Lipid transfer proteins, endochitinases, and alpha zein precursor are relevant maize allergens in double-blind placebo-controlled maize-challenge-positive patients. Analytical and Bioanalytical Chemistry 395: 93–102. Salcedo G, Quirce S, and Diaz-Perales A (2011) Wheat allergens associated with bakers’ asthma. Journal of Investigational Allergology and Clinical Immunology 21: 81–92. Sheffer AL and Austen FA (1980) Exercise-induced anaphylaxis (1980). Journal of Allergy and Clinical Immunology 66: 106–111. Tada Y, Nakase M, Adachi T, et al. (1996) Reduction of 14–16 kDa allergenic proteins in transgenic rice by antisense gene. FEBS Letters 391: 341–345. Tatham AS and Shewry PR (2008) Allergens in wheat and related cereals. Clinical and Experimental Allergy 38: 1712–1726.

Nutrition: Beriberi, A Deficiency Related to Grains KJ Carpenter, University of California, Berkeley, CA, USA ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 318–325, ã 2004, Elsevier Ltd.

Topic Highlights

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Beriberi, a name meaning ‘great weakness’ is due to B-vitamin (thiamin) deficiency, commonly associated with milled rice consumption. White rice alone, absent a diverse diet providing varied sources of vitamins, is severely deficient in thiamin. There is no easy, convenient food source that provides high thiamin. Parboiling of rice is beneficial, as is enriching rice with synthetic vitamins.

struggling to understand this disease that led to the discovery of the class of micronutrients that now is known as vitamins. It is a complicated story with many false leads, but it provides a valuable lesson in how science does eventually advance, and the dangers of over-simplification of the problems of the real world. It also shows how it finally proved possible, as a result of collaboration between industry and academia, to “enrich” highly milled grain products so that they still provided a good contribution of vitamins and minerals.

Occurrence in Asia Learning Objectives

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To understand the etiology of beriberi and the history of its dicovery. To understand the effect of grain processing on thiamin levels and hence on propensity to induce beriberi. To understand the effects of other dietary habits, e.g. excessive alcohol consumption, on thiamin deficiency.

Introduction Grains have been the major source of both energy and protein for the world’s population for millenia. However, it is now realized that, when the diet lacks a variety of other foods, the grains are also needed to supply a considerable number of other essential micronutrients if those eating them are to remain healthy. But the processing of grains to remove the bran and germ, in addition to its favorable effects of increasing shelf life by removing much of the oils that can become rancid, and providing foods with a smoother feel by removing most of the fiber, does also cause the loss of a large proportion of their other nutrients. It now appears that the emergence of the disease pellagra amongst communities in the southern states of the USA from around 1910 is explained by the introduction of machinery that allowed the replacement of stone-ground “whole corn meal” with “de-germed meal,” and that this, combined with white wheaten flour and little in the way of lean meat, eggs, and milk, resulted in a diet deficient in the vitamin niacin. Until this came to be understood in the 1930s, several thousand people died and even more suffered a miserable and humiliating disease. The following article summarizes the way in which another disease, beriberi, that was causing huge suffering in the Far East, particularly in the earlier period 1870–1910, came to be understood as the consequence in most cases of people having polished white rice as their staple food with little in the way of supplementary foods. It was the work of the pioneers


The first Western physicians allowed to work in Japan in the 1870s were surprised to discover the existence of a serious disease previously unknown to them and “second only to smallpox in its ravages.” In Japan, it was known as “kakke´,” but was soon recognized as being identical to the disease known in South-east Asia as “beriberi,” a native name now universally adopted, which may originally have meant “great weakness.” Characteristically, it began with a feeling of weakness in the legs and a loss of feeling in the feet. Then, in many but not all cases, the legs and then the trunk would swell with retained water. Finally, the heart would be affected so that the subject gasped for breath, and would die from heart failure. Older records from both Japan and China showed that it had been known for some centuries, although it had been the opinion of two eighteenth century Japanese physicians that the disease had become worse after 1750. The early records also indicated that it was largely a disease of the wet summer months and could attack even the well-off.

Infection or Malnutrition? Those most at risk were men in the newly modernized Japanese army and navy, and also prisoners. As these were all people living together in large groups, and with the excitement in this period at other diseases being traced to the transmission of pathogenic bacteria, this seemed a likely cause for beriberi also. Yet, it was difficult, on this basis, to explain the frequent observation that a naval ship would leave its base with all its crew in good health, yet, after a month or more in isolation at sea, the disease would sweep through the crew. Kanehiro Takaki, a surgeon on the naval staff, was directed in 1878 to work on the problem. He knew that the ships had been built in Britain and that they followed the general practices of the British navy where there was no beriberi. The only difference that caught his attention was in the rations issued to the men: the Japanese issues contained less protein and did not meet the high standard in force at that time in Europe. He therefore persuaded his superiors to permit a trial of modified rations with a proportion of the rice being replaced by meat,

http://dx.doi.org/10.1016/B978-0-12-394437-5.00080-2

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condensed milk, vegetables, and barley. The change was a complete success, and it was found that even just the use of barley in place of one half of the rice staple was enough to prevent the disease, which Takaki now believed to have resulted from a deficiency of protein in the earlier rations. The Japanese army, perhaps as the result of interservice rivalry, did not follow the navy and in the short Russo-Japanese war of 1904–05, some 100 000 of their soldiers had to be invalided home from Manchuria suffering from beriberi.

A Disease in Chickens Meanwhile, the disease had become an equally serious problem in the Dutch East Indies (now Indonesia) (Figure 1). After a punitive military expedition had to be withdrawn because of a beriberi epidemic, the Dutch government dispatched a small commission to try to identify the bacteria responsible for the disease. After a few months, it was thought that the microorganism had been found, and Christiaan Eijkman, a young Army physician, remained behind to confirm its activity in animal models. Some of the chickens that Eijkman had injected with blood from beriberi patients developed signs of leg weakness, but so did some of his uninjected controls, suggesting that the condition was so infectious that it could “jump” from cage to cage. Autopsies of the affected birds showed degenerated peripheral nerves. But in the following months, none of the next batch of birds developed the condition. Eijkman discovered that when the leg weakness had appeared, the man in charge of the birds had been feeding them on cooked white rice left over from feeding the beriberi victims in the adjoining hospital, instead of buying rough, feed-grade rice.

A long series of feeding trials confirmed that birds fed on white rice would become sick with leg weakness, whereas those given supplements of rice polishings (still present in feed-grade rice) remained healthy. This was only an animal disease, but a survey by the medical inspector of prisons in Java showed that prisoners who had been receiving white rice as their staple issue were susceptible to beriberi, whereas those receiving brown rice were not.

The Concept of a Vitamin Eijkman, who believed that the disease was a kind of starch poisoning, now had to be invalided home with malaria. His successor, Gerrit Grijns, found that birds became sick even when fed on meat that had been autoclaved. After further work, his statement in 1901 was perhaps the progenitor of the “vitamin era” in nutritional research: “there occur in various natural foods substances which cannot be absent without serious injury. . .they are easily disintegrated. . .and cannot be replaced by simple chemical compounds.” The work of Eijkman and Grijns was confirmed by British investigators in Malaysia and by Americans in the Philippines, and attempts began to extract the active material from rice polishings and to concentrate it. There are moving accounts of scientists in Manila being implored by local doctors to bring a few spoonfuls of extracted syrup to save the lives of infants with beriberi, and of the babies’ spectacular recoveries. Women themselves seemed less susceptible to beriberi than men, but when mothers were receiving a diet of low thiamin content, their breast-fed babies were at a high risk of dying with acute infantile beriberi.

Isolation of Thiamin

Figure 1 Two prisoners in Java with beriberi and needing assistance to walk. (Reproduced with permission from Vorderman (1897) Onderzoek naar het gevangenissen op Java en Madoera en het voorkomer van beri-beri order de geintemeerden. Batavia: Jav. Boekh & Drukkerij.)

Isolation of the active factor proved very difficult. Each stage of extraction, and then further partitioning by reprecipitation involved biological assays with birds. Eventually, the next generation of Dutch workers in Indonesia was successful, obtaining a few milligrams of active crystalline material after starting with one-third of a tonne of rice polishings and going through at least 16 separation stages in which much of the vitamin was lost. It was found that adding just 2 ppm of the crystals to white rice was enough to keep birds healthy. In 1931, the crystals were found to contain sulfur as well as carbon, hydrogen, nitrogen, and oxygen, and the chloride salt was shown to have the empirical formula C12H18N4SO2Cl2. There were, of course, almost innumerable ways in which these atoms could be combined. By good fortune, Robert R. Williams in the USA found that adding sodium sulfite to a solution of the vitamin led to its division into two roughly equal halves. Further work at a number of centers showed that one of these compounds contained a pyrimidine and the other a sulfathiazole ring. By 1937, a synthesis of the active molecule was achieved. It was named “thiamin or thiamine” (i.e., the sulfur-containing vitamin) and soon began to be produced and marketed as a pharmaceutical.


The Analysis of Foods Thiamin can be oxidized to a highly fluorescent derivative, “thiochrome.” This property is used to measure the thiamin contents of different foods, even at levels of less than 1 ppm. The procedure is specific, and no other naturally occurring compounds have been found that give the thiochrome reaction. However, thiamin can react with polyphenols and a compound present in garlic to give derivatives that are still biologically active (as will be referred to again) but do not give the thiochrome reaction. The analytical procedure may therefore underestimate the efficacy of a product. It is essential, therefore, to have a confirmatory bioassay before knowing for certain that any kind of processing has caused significant loss of thiamin.

Rice and Other Staples Figure 2 illustrates the thiamin levels in the world’s major staple foods, both when fully milled and when minimally processed. In the case of grains, the latter means removal of the husk (or hull) but no more. It is clear that, for each grain, the full milling that removes both the bran and germ results in the loss of a major portion of the thiamin originally present. White rice is not that much lower than white wheat flour in its content of the vitamin, but after the grains have been prepared for consumption, the difference is increased. White rice is normally washed several times, and this alone can remove half the thiamin present, and boiling in excess water can again halve the level of remaining vitamin. In contrast, white wheat flour is most commonly baked into bread with yeast as the raising agent, and this causes little loss of thiamin.

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There is no evidence that cooked white rice has any positively harmful qualities, but if it is the major item in a diet that contains only small amounts of foods that are richer in thiamin, so that the diet as a whole provides no more than about 0.25 mg per 1000 kcal, it is not surprising that beriberi should gradually develop. The data in Figure 2 also explain the Japanese experience that serious problems with beriberi in their navy in the late 1800s disappeared when one-half of their rice ration was replaced by barley. The same figure also shows the low thiamin content of tapioca prepared from cassava roots. This explains the existence of beriberi in Brazil at the same period among even well-off people whose favorite foods were tapioca and molasses. Their preferred protein supplement was dried, salted cod, which had to be soaked for several days to leach out most of the salt, which also removed most of the vitamin. The very first reports of beriberi to reach Europe came from Portuguese priests working in the Molucca Islands (at the Eastern end of Indonesia) in the 1500s. Their staple was the locally produced sago meal, now realized to be almost pure starch, and the priests correctly attributed their weakness to a lack of “something” in this food and asked to be provided by their superiors with wheat flour. Beriberi was also a serious problem in early spring in isolated communities in Newfoundland in the early years of the twentieth century. Their families, who would be cut off for the winter, had to buy 6 months of supplies, with white flour as their staple. They were also apparently not familiar with using yeast to leaven bread, but cooked their flour with baking soda, and it is known that much of the thiamin present would be destroyed under the alkaline conditions during this procedure.

Figure 2 Representative analytical values for the thiamin content of different staple foods: (1) after husking only ( ) and (2) after full processing ( ), as explained in the text, and also for some staple root crops, etc. Sago meal is not shown, as it contains only an insignificant level of thiamin. (Reproduced with permission from Carpenter KJ (2000) Beriberi, White Rice and Vitamin B. Berkeley, CA: University of California Press.)

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The Improvement of Rice Once the association of beriberi with white rice in Asia had been established, attempts were made to replace it in some way with other foods. As already mentioned, barley was an economic and well-accepted alternative in the diet of the Japanese armed forces. In the Philippines, a proposal was made to enforce the use of brown rice by the local military. This, of course, is rice from which the husk has been removed but not the entire bran layer and germ (embryo and scutellum) (Figure 3). This was the traditional staple of villagers in South-east Asia who had no access to mechanical rice mills. They would pound their paddy (i.e., rice still in the husk) in some kind of bowl and then winnow the product so that the lighter husks blew away, and the grains fell in a pile. This procedure was time-consuming but created no problems when only enough was pounded for immediate use in the next 24 h. However, it was repeatedly found that in the tropics, brown rice on storage would become infested with insects of different kinds, and the oil in the bruised germ would become rancid. Since large organizations, or an army on the move, needed large-scale supplies ready for cooking, brown rice did not provide a practicable staple. The early workers who discovered the association of beriberi with white rice had assumed that the important micronutrient was concentrated in the bran of the grain. However, it was later realized that more was present in the germ area (Table 1). Japanese millers then attempted to modify their machinery so as to remove the bran without removing the germ from the grain. The so-called “germ rice” that they were able to produce proved to be both palatable and an improved source of thiamin. However, millers were only able to produce

it with certain varieties of rice, and not with the bulk of the rice favored in Japan. A traditional method of processing rice common in Bengal is called parboiling. It had been found that if rice in the husk were to be steeped for a period in hot water and then allowed to dry in the sun, the husks cracked off more easily on pounding, and there was less breakage of the grains. Broken grains had a lower commercial value. In Malaysia, where many immigrant groups were employed as laborers but living on their habitual diets, it was realized in 1910 that Bengalis were remarkably free from beriberi, and studies in a mental hospital showed that replacing ordinary white rice with polished rice prepared from parboiled grains relieved the inmates from the disease. After thiamin had been identified, analyses showed that the initial soaking of the grain caused thiamin to diffuse into the endosperm and to remain there as the grains dried out. Again, this does not appear to be something that could be applied more widely. The traditional soaking and sun-drying leaves the rice with a characteristic musty flavor and slight discoloration, which is acceptable only to people who have grown up with it. The process can be modernized, with controlled autoclaving and vacuum-drying for so-called “conversion” of the rice, but this makes it too expensive for mass consumption in developing countries. The final procedure for the production of “enriched” rice is to fortify it with the synthetic vitamin. For a flour, such as white wheat flour, this is relatively simple, requiring only very careful mixing of the traces of vitamin with a small quantity of flour, then the blending of the premix to larger batches. This is familiar, and indeed compulsory practice, in the USA and UK, together with other vitamins and trace minerals. As a powder, thiamin cannot be blended with grains of white rice. However, methods have been developed of preparing vitaminrich granules with the size and appearance of rice grains, and blending these in the ratio of one granule to 200 grains, so that the mix has at least the thiamin content of brown rice. To reduce loss of the vitamin during washing and cooking, the granules are coated with a nontoxic resin at the final stage of their production. This method of enrichment has been tested in an area of the Philippines where beriberi was endemic and has proved successful in greatly reducing its incidence. Unfortunately, where widely separated villages each had a small electric mill, there were practical problems in persuading millers to pay for the premix when the product appeared unchanged, but the price had to be a little higher.

Supplementing Foods

Figure 3 Dissection of a dehusked rice grain. (Reproduced with permission from Carpenter KJ (2000) Beriberi, White Rice and Vitamin B. Berkeley, CA: University of California Press.)

Unfortunately, there is no convenient food that is extremely rich in thiamin. Dried brewers yeast contains 15 mg per 100 g, but many people cannot tolerate it in more than extremely small regular doses. Of the meats, pork is richest with lean pork containing 1 mg per 100 g. Beef has only about one-tenth as much. Dry peas and beans contain about 0.5 mg per 100 g. Potatoes are another useful supplement – on a dry matter basis, they have slightly more thiamin than brown rice. In practice, reaching a desirable intake of thiamin comes usually from eating a wide variety of foods. Nineteenth-century

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | Nutrition: Beriberi, A Deficiency Related to Grains Table 1

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Thiamin contributed by the different parts of a sample of dehusked rice grains Thiamin

Dissected parts of rice grain

Proportion by weight (%)

Concentration in fraction (mg per 100 g)

Contribution to 100 g grain (mg)

Pericarp þ testa þ aleurone layers Germ area Embryo Scutellum Endosperm Total

6

3.1

0.186

1 1 92 100

5.9 18.9 0.05 —

0.046 0.480

0:059 0:248 0:189

Reproduced with permission from Carpenter KJ (2000) Beriberi, White Rice and Vitamin B. Berkeley, CA: University of California Press.

Japanese believed that consumptions of most foods other than rice during the summer months caused “heat.” Hence, food consumption was almost entirely restricted to rice consequently leading to an increase in beriberi during these months.

Is there an Antithiamin Problem? There are many references in the literature to at least a suspicion that certain foods and beverages may be responsible for beriberi appearing in people whose intake of thiamin would otherwise be adequate.

Thiaminases Many species of fish contain enzymes in their viscera that split thiamin molecules at the junction between its two ring structures. This was discovered when foxes, being reared for their fur and fed on a mix containing a large proportion of whole raw fish, developed a form of paralysis that responded to injections with thiamin. A similar condition was seen later in cats that had been fed on a canned food containing a large proportion of whole fish. It was believed that the thiamin in the mix had been largely destroyed after the mix had been prepared and was waiting to be autoclaved. These experiences led to investigations as to whether humans could be similarly at risk, but it appears not. The enzymes are not present in fish muscles (i.e., fillets), and even where small fish are eaten whole, they are not ground up with other items of diet before being cooked. Lastly, it was found in animal studies that a subsequent meal with different constituents was not affected by thiaminases being present in an earlier meal. Another source of thiaminases was found to be bracken, and their presence explained the condition known as “staggers” that occurs in horses that have been feeding on bracken. Cooked bracken, in which the thiaminase was inactivated, proved harmless to horses. The only known case of thiaminase poisoning in humans occurred in a group exploring the interior of Australia in the 1860s. Running out of provisions on their return journey, they lived on the sporocarps in the fronds of a particular fern that is now known to contain a high level of a particularly heat-resistant thiaminase. All four men developed leg weakness and lassitude; three died, and the survivor remained lame even after his safe return.

Heat-Stable Antithiamins? It has been found that when the thiamin in a food comes into contact with polyphenols such as caffeic acid, it no longer gives a fluorescent product in the usual thiochrome procedure for the estimation of thiamin. This led some workers to suppose that drinking large quantities of tea or coffee, or chewing betel nut – all sources of polyphenols – might induce a condition of thiamin deficiency. However, biological assays have indicated that the vitamin is still fully available. When thiamin is incubated with garlic extracts, it undergoes a reaction with the allicin present in which the thiazole ring opens, and the sulfur atom in the ring links to the alkyl sulfide to form a disulfide compound. This is not measured in the thiochrome reaction, but in the body it is reduced to re-form the active vitamin. In fact, compounds of this type can be absorbed more efficiently by alcohol-damaged intestinal walls than ordinary thiamin. Thiamin tetra-hydrofurfuryl disulfide in particular is approved for this purpose in some countries. Although there is no confirmed evidence of naturally occurring heat-stable compounds that inactivate thiamin, chemists have synthesized such materials. One, named “oxythiamin,” has the amino group attached to the pyrimidine group in thiamin replaced by a hydroxy group. Giving it to animals results in the more rapid production of some of the signs of thiamin deficiency, although it differs from thiamin in being unable to pass the blood–brain barrier.

Acute Deficiency in the West With the discovery that autoclaving yeast powder would destroy the thiamin, whereas the other B-vitamins were retained, it was possible to place volunteers on an artificial diet essentially free of thiamin. To the surprise of investigators, some subjects had lost appetite within 2 weeks and became nauseated and dizzy, with other mental symptoms, by 6 weeks, but with no sign of peripheral nerve damage or cardiac abnormality, which are characteristic of classic beriberi. Trials using pigeons and rats with very deficient diets also produced appetite loss and death before any sign of leg weakness had developed. It appeared that in both humans and animals, acute deficiency of thiamin resulted in damage to the central nervous system. With slightly higher intakes, the

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CNS had priority, whereas peripheral nerves gradually degenerated.


• Deficiencies in Total Parenteral Nutrition There are many reports of people recovering from surgery of the gastrointestinal tract who have developed acute thiamin deficiency. They had been fed intravenously with a solution providing energy, amino acids, and minerals, but no vitamins. This is adequate for a short period, but thiamin is the first vitamin to become depleted. In a number of cases where this type of parenteral feeding has continued for some weeks, a condition called “Wernicke’s encephalopathy” has developed. Patients are confused and have characteristic involuntary eye movements. Where patients have died, autopsies have shown brain lesions analogous to those found in acutely deficient animals. The same outcome has been seen in subjects voluntarily fasting for long periods or being unable to take food because of persistent vomiting in pregnancy.

Alcoholism One material that can be responsible for the production of thiamin deficiency is ethanol (i.e., “alcohol” in everyday speech). In developed countries where nearly everyone can afford a well-balanced diet, most of those diagnosed as being thiamin-deficient are “alcoholics.” The continued ingestion of high levels of alcoholic beverages has many undesirable effects. In the present context, two are relevant. First, the alcoholic typically no longer bothers to eat a normal range of foods, partly because the beverages provide a large portion of their calorie needs and partly from nothing but their next drink being of immediate interest. Second, the high level of alcohol ingestion damages the intestinal wall so that thiamin is absorbed less efficiently, and the requirement for the vitamin increases. Unfortunately, a small proportion of such victims develop Wernicke’s encephalopathy, which may lead in turn to Korsakoff’s psychosis. Such people, sometimes referred to as suffering from the Wernicke–Korsakoff syndrome, are at present incurable and have to be maintained in a mental hospital for the rest of their life. The cost of this to the state is such that some specialists have argued that it would actually be cheaper to have all beer and wine fortified with thiamin as a preventive. There may be a genetic factor making some Western people susceptible to the cerebral form of beriberi and the Wernicke–Korsakoff syndrome, since it was seen even in Western prisoners of the Japanese in the Second World War who had white rice but no alcohol, but apparently has not been seen in Asian subjects.

•

In your community, what dietary habits are most likely to result in insufficient thiamin consumption? What are the mandatory (and common voluntary) enrichments of cereal grain products in your country? Do you think the regulations make sense in relation to current typical dietary patterns?


• •

What methods are used to measure thiamin content? How stable is thiamin after typical food processing operations? Are there any potential genetic solutions to low thiamin content in milled rice?

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Non-wheat Foods: Rice: Chinese Food Uses; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure.

Further Reading Carpenter KJ (2000) Beriberi, White Rice and Vitamin B. Berkeley, CA: University of California Press. Cook CC, Hallwood PM, and Thomson AD (1998) B vitamin deficiency and neuropsychiatric syndromes in alcohol misuse. Alcohol and Alcoholism 33: 317–336. Eijkman C (1929) Antineuritic vitamin and beriberi. In: Nobel Lectures: Physiology or Medicine, pp. 1922–1941. Amsterdam: Elsevier. Hinton JJC (1948) The distribution of vitamin B1 in the rice grain. British Journal of Nutrition 2: 237–241. Jansen BCP and Donath WF (1926) On the isolation of the anti-beriberi vitamin. Koninklijke Akademie von Wetenschappen, Amsterdam, Proceedings 29: 1390–1400. Sauberlich HE, Herman YF, Stevens CO, and Herman RH (1979) The thiamin requirement of the adult human. American Journal of Clinical Nutrition 32: 2237–2248. Shimazono N and Katsura E (1965) Review of Japanese Literature on Beriberi and Thiamine. Kyoto: Vitamin B Research Committee of Japan. Takaki K (1906) The preservation of health amongst the personnel of the Japanese army and navy. Lancet i: 1369–1374. Truswell AS and Apeagyei F (1982) Alcohol and cerebral thiamin deficiency. In: Jelliffe EF and Jelliffe DB (eds.) Adverse Effects of Foods, pp. 253–258. New York: Plenum Press. Williams RR (1961) Toward the Conquest of Beriberi. Cambridge, MA: Harvard University Press. Williams RR and Cline JK (1936) Synthesis of vitamin B1. Journal of the American Chemical Society 58: 1504–1505. Wuest HM (1962) The history of thiamine. Annals of the New York Academy of Sciences 98: 385–400.

Celiac Disease P Koehler, H Wieser, and KA Scherf, Deutsche Forschungsanstalt fu¨r Lebensmittelchemie, Leibniz Institut, Freising, Germany ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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• • • • •

Celiac disease (CD) is an inflammatory disease of the upper small intestine triggered by dietary gluten from wheat, rye, barley, and oats and has a prevalence of 1:300 to 1:100 individuals. CD patients present with intra- and/or extraintestinal symptoms with villous atrophy as the classical clinical feature. Gluten proteins are resistant to gastrointestinal digestion and activate the adaptive and innate immune responses in the lamina propria. Other gluten-dependent diseases are dermatitis herpetiformis, gluten ataxia, wheat-dependent exercise-induced anaphylaxis, and non-celiac gluten sensitivity. CD diagnosis is based on symptoms, serology, small intestinal histology, and response to a gluten-free diet, which is the current essential treatment. Testing for CD toxicity may be done by in vivo challenge of CD patients, by in vitro tests with tissues and cells of CD patients, or with animal models.

Learning Objective

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Attain understanding of symptoms, epidemiology, genetics, pathogenesis, diagnosis, and therapy of celiac disease and of its precipitating factor, gluten.

Introduction Celiac disease (CD) is a permanent intestinal intolerance to dietary wheat, rye, barley, and oat proteins (gluten) that produce mucosal lesions and nutrient malabsorption in genetically susceptible individuals. The current essential therapy is a strict lifelong withdrawal of gluten from the diet. The prevalence of CD was underestimated for a long time; with the development of sensitive serological tests, more and more evidence is emerging that CD is one of the most frequent food intolerances in many parts of the world. An overview of extensive research on CD is provided.

Definition

Historical Review CD was already noted by the Roman physician Aretaeus of Cappadocia as early as the second century AD, who wrote that “if diarrhea does not proceed from a slight cause of only one or two days duration and if, in addition, the general system be debilitated by atrophy of the body, the celiac sprue of chronic nature is formed.” However, it was not until 1888 that the English physician Samuel Gee described the classical account of CD features. He recognized that “if the patient can be cured at all, it must be by means of the diet.” Thereupon, the dietary treatment of CD was continued more or less successfully. For example, all sources of carbohydrates such as bread, cereals, and potatoes were excluded or a banana diet was recommended. Such extreme dietary treatments were then used for many years. In 1950, Willem K. Dicke, a Dutch pediatrician, observed a decline in CD in the Netherlands during the grain-deprived years of the Second World War. A clear association between CD and the ingestion of wheat and, later on, of rye and barley was established. The fractionation of wheat flour and testing led to the conclusion that gluten was toxic, whereas starch and the water-soluble albumins were not. Since that time, a ‘GFD’ has been the conventional treatment of CD, which excludes products containing wheat, rye, and barley, only excepting pure starches produced from these cereals. The celiac toxicity of oats has been judged controversially. With the introduction of peroral biopsy of the intestinal mucosa, the abnormalities of the small intestinal mucosa tissue of CD patients were demonstrated, and among others, this diagnostic procedure is the criterion standard of diagnosis to this day.

Symptoms and Pathology

CD, also known as celiac sprue or gluten-sensitive enteropathy, may be defined as an inflammatory disease of the upper small intestine (duodenum and jejunum) in genetically susceptible individuals. CD is a permanent food intolerance induced by ingestion of storage proteins (gluten) from certain cereals (wheat, rye, barley, and oats) that cause damage to the enterocytes and, as a consequence, malabsorption of important nutrients. CD patients develop a flat jejunal mucosa with the


absence of normal villi, a cellular infiltrate of the lamina propria, and an increase of the number of intraepithelial lymphocytes (IELs). The mucosa improves morphologically on treatment with a gluten-free diet (GFD) and relapses when gluten is reintroduced. The clinical features of CD are highly variable and can be divided into intestinal symptoms (e.g., diarrhea, steatorrhea, and vomiting) and extraintestinal complaints (e.g., osteoporosis, anemia, and constant fatigue). Therapeutically, a lifelong GFD is necessary.

A range of symptoms may be associated with CD, and these can be divided into intestinal disorders and extraintestinal features caused by malabsorption of essential nutrients such as deficiencies of vitamins and minerals. In infants, classical symptoms appear after weaning and introduction of cereals into the diet: diarrhea, abdominal distension, failure to thrive, vomiting, muscle wasting, and apathy. Older children tend to

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have more varied symptoms. Besides diarrhea or constipation, features such as anemia, loss of appetite, and short stature may be predominant. Diarrhea is the main presenting feature of adults; in some patients, anemia, osteoporosis, abdominal pain, loss of weight, and weakness may be found. A minor number of patients present psychological or psychiatric symptoms such as depression, epilepsy, autism, or schizophrenia. Frequently, the disease may be clinically silent or masked by associated diseases like type 1 diabetes, although the patients exhibit the full mucosal lesion. They are discovered only when intestinal studies are undertaken. Around 2–5% of CD patients develop a resistance to a strict GFD. This condition, called refractory celiac disease (RCD), is characterized by a constant inflammatory process in the intestinal mucosa accompanied by persistent diarrhea, abdominal pain, and weight loss. RCD carries a significant burden of morbidity and mortality, mainly from malnutrition and lymphoma. The small intestinal lesion of CD has a highly characteristic morphology, but it may vary from patient to patient depending on the severity and extent of disease. Patients show a wide variation of mucosa appearance from a complete flat to a convoluted pattern. The parameters usually assessed for the measurement of intestinal mucosa are villous height, villous width, villous height to crypt depth ratio, mucosal thickness, epithelial cell height, crypt mitotic activity, and number of IELs. Electron microscopy demonstrates fewer microvillous intramembrane particles and abnormal tight junctions (TJs) between epithelial cells. In untreated CD, serological antibodies to gliadin, deamidated gliadin peptides, reticulin, endomysium, and tissue transglutaminase (TG2) are present.

Epidemiology and Genetics CD is prevalent mostly in Europe and those countries to which Europeans have emigrated including North and South America and Australia. However, CD is also known to occur in many other parts of the world. In the past, CD was considered a comparatively uncommon disorder with prevalence rates of 1 in 2000 to 1 in 1000. Several recent studies using serological screening followed by small intestinal biopsy have shown a much higher prevalence, and it is now estimated that CD may affect as many as 1 in 300 to 1 in 100 individuals. The iceberg is a common model to describe the epidemiology of CD. The tip of the iceberg is formed by patients who have been diagnosed by conducting a biopsy demonstrating a flat mucosa. Below the waterline, there is a big group of undiagnosed patients with a flat mucosa, but with no or weak symptoms (undiagnosed silent CD). At the bottom of the iceberg, there is a small section of patients with a normal mucosa but with the genetic predisposition and increased levels of celiac-specific antibodies. These subjects may develop clinically overt CD later in life (undiagnosed potential CD). The occurrence of CD among first-degree relatives of CD patients is fairly strong with a prevalence of 10–15%. The concordance between dizygotic twins is reported to be in a range of 11–20% and that between monozygotic twins 75–80%. CD can occur at any age, but in adults, the peak incidence is in the fifth decade. Females are more commonly affected than males with a suggested ratio of around 2:1.

CD is associated with histocompatibility complex class II alleles HLA-DQ2 and HLA-DQ8. Almost all CD patients ( 97%) possess one of these HLA genes. The large majority of patients ( 90–95%) are DQ2-positive, and the remainder are DQ8-positive. Two isoforms DQ2.5 (predominant) and DQ2.2 (rare) were identified among DQ2 alleles. HLA-DQ genes encode protein heterodimers with a- and b-chains, both responsible for the CD-specific binding of gluten peptides by intestinal antigen-presenting cells. The HLA-DQ2.5 genotype is associated with a very high risk for developing CD, followed by DQ8 (high) and DQ2.2 (low). However, about 30% of the healthy population carry DQ2 and will never develop CD. Thus, HLA-DQ genes alone do not explain the development of CD, and additional factors such as non-HLA genes and environmental factors need to be involved in disease development. Further, CD-specific genome research, mainly focused on non-HLA genes, indicated little consensus, and the contribution of all non-HLA genes, known up to now, has been estimated to account for less than 10%. Different environmental factors have been considered to be important for the development of CD. For example, infections by a variety of pathogens, an imbalanced intestinal microbiota, the amount and timing of gluten exposure, and breastfeeding during first gluten intake have been associated with developing CD in infants.

Pathogenesis The development of CD is induced by the oral intake of gluten present in wheat, rye, barley, and oat products. A daily intake of more than 20 mg of gluten is estimated to be not tolerable for CD patients. This approximately correspond to onehundredth of a slice of bread. In contrast to most other food proteins, gluten proteins are highly resistant to complete proteolytic digestion within the gastrointestinal tract due to their high proline content. Thus, relatively large protein fragments (peptides) accumulate in the small intestine and reach the intestinal brush border (step 1 in Figure 1). However, the poor digestibility of gluten proteins is not sufficient to cause CD, and there is no known difference between healthy individuals and CD patients in their (in)ability to digest these proteins. Changes in the mucosal permeability for gluten peptides are supposed to be the first pathogenic event in the development of CD. Gluten peptides are bound to the intestinal mucosa before passing through the enterocyte layer either transcellularly or paracellularly (Figure 1, step 2). The most important structures of the paracellular route are the epithelial pore-forming TJs. They are composed of a number of proteins (e.g., zonulins, claudins, and occludin) that regulate paracellular permeability. Zonulin 1, known to enhance permeability and to be upregulated during the acute phase of CD, has been proposed to be one of the initial factors of the pathogenesis of CD. When crossing the epithelium via the transcellular pathway, gluten peptides are differently degraded in the intracellular compartments of the enterocytes of CD patients. The transcellular permeability is much higher for intact CD-active peptides compared with nonactive peptides. After passing through the epithelium, CD-active peptides arrive at the lamina propria and induce two different immune responses: the adaptive and the innate responses. Within the


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I 1

E

II

E

2

E

E

3 5 III

IFN TNF MMP

T

A P C

4

B

T T

B

P 6

B

T

IgA IgG

B

Th 1 Th 2

gluten peptide deamidated gluten peptide TG2/deamidated gluten peptide conjugate

TG2

TG2/gluten peptide conjugate

Figure 1 Schematic representation of the adaptive immune response in the intestinal lymphatic tissue and destruction of enterocytes in the pathogenesis of celiac disease. I, intestinal lumen; II, epithelium; III, lamina propria; APC, antigen-presenting cell; B, B cell; E, enterocyte; IFN, interferong; Ig, immunoglobulin; MMP, matrix metalloproteinase; P, plasma cell; T, CD4þ T cell; TG2, tissue transglutaminase; Th, T helper; TNF, tumor necrosis factor. For steps 1–6, see text. Reproduced with permission from Wieser H, Koehler P, and Konitzer K (2014) Celiac Disease and Gluten: Multidisciplinary Challenges and Opportunities, 1st edn. London, Waltham, San Diego: Academic Press.

adaptive mechanism, gluten peptides are specifically modified by TG2 (Figure 1, step 3) either by partial deamidation of glutamine residues leading to negatively charged glutamic acid residues or by cross-linking to TG2 by isopeptide bonds between glutamine residues of the peptides and lysine residues of TG2. Particularly, deamidated peptides are selectively bound to DQ2/ DQ8 heterodimers on the surface of antigen-presenting cells (dendritic cells, macrophages, and B cells) and then presented to the T cell receptor of gluten-sensitive CD4þ T cells. The stimulation of T cells leads to the secretion of proinflammatory T helper (Th-1) cytokines (Figure 1, step 5), in particular interferon-g, tumor necrosis factor, matrix metalloproteinase, and nitric oxide, which lead to premature senescence of small intestinal enterocytes, shedding of these cells, and, in turn, the observed small intestinal enteropathy. Simultaneously, T cells provide help for the production of IgA and IgG antibodies to gluten proteins and autoantibodies to TG2 (Figure 1, step 6). In contrast, the rapid innate immune system is characterized by the massive increase in IELs, one of the hallmarks of CD, which can be observed very early before the onset of villous atrophy. Two subsets of IELs bearing the abT cell receptor or the gdT cell receptor are linked to CD innate immunity. Interleukin-15 (IL-15) has been considered a central player in this part of the gluten-induced immune response. IL-15 is produced by epithelial and lamina propria cells in active CD, but not by T and B cells involved in the adaptive immune response. Recently, it has been suggested that amylase-trypsin inhibitors (ATIs) present in cereal flours are coactivators of the innate immune system. How the cross talk between innate and adaptive immunities is orchestrated is an outstanding question that will need to be addressed.

Associated Diseases Dermatitis herpetiformis, a skin disorder, is associated with CD, because some degree of gluten-sensitive enteropathy is

common to both conditions. It appears as patches of itchy red papules and blisters on the extensor surface and pressure areas; healing up results in pigmentation. Histologically, there is infiltration of the dermal papillae with inflammatory cells. The dermal histology is similar to that of the small intestine in CD, but the abnormalities tend to be milder and patchier. In many cases, a GFD results in a significant improvement. Gluten ataxia is one of the neurological manifestations attributed to gluten intake. All these patients present gait ataxia, and the majority have limb ataxia and evidence of cerebellar atrophy. The current diagnostic recommendation is a serological screening for antigliadin, anti-TG2, and antiTG6 antibodies. Patients positive for these antibodies should follow a GFD. Wheat-dependent exercise-induced anaphylaxis (WDEIA) is a severe IgE-mediated allergic reaction provoked by the combination of wheat ingestion with intense physical exercise over the next few hours. Aspirin and ethanol, together with wheatcontaining food, are further cofactors for WDEIA. Peptides derived from o5-gliadins and high-molecular-weight (HMW)glutenin subunits have been identified to be critical for IgE binding. Non-celiac gluten sensitivity (NCGS) is a gluten-mediated disorder characterized by gastrointestinal complaints including bloating, diarrhea, weight loss, and abdominal pain. The small intestine of patients is usually normal, and serum antibodies typical for CD are absent. ATI or fermentable oligo-, di-, and monosaccharides and polyols may be implicated in NCGS, but to date, there is too little knowledge on responsible triggers of this currently underrecognized and undertreated disorder. Recent screening studies have shown an increased prevalence of CD in autoimmune disorders such as type 1 diabetes, thyroid disease, primary biliary cirrhosis, and Sjo¨gren’s syndrome. Moreover, IgA deficiency, chronic fibrosin alveolitis, other interstitial lung diseases, and concomitant distal ulcerative colitis have been reported in association with CD. In other

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instances, there are unexpected associations such as epilepsy and various undefined neurological disorders. A small number of patients with CD have exhibited symptoms of various psychiatric disorders, such as schizophrenia. A lymphoma of the small intestine is the classical malignancy associated with CD. The prevalence of carcinoma of the small intestine, esophagus, or pharynx, crypt hyperplasia, villous atrophy, and mucosal hypertrophy also increases with CD. It has been reported that a strict GFD helps safeguard against these malignancies.

Diagnosis The diagnosis of CD is complex and tends to require a high level of clinical suspicion. The diagnostic approaches have changed during the last decades, and recommendations for the procedures are still different. In summary, the diagnostic scheme may consist of the following points: (1) clinical history and symptomatology, (2) serology, (3) small intestinal histology, (4) response to a GFD, and (5) HLA status. Classical intestinal symptoms should prompt the primary doctor to initiate a serological test. Extraintestinal symptoms are more difficult to interpret, and medical specialists (e.g., dermatologists, dentists, and neurologists) should be aware of possible CD. For initial testing, a quantitative test detecting IgA class antiendomysium, anti-TG2, and antideamidated gliadin peptide antibodies from a blood sample is recommended. To achieve the clinical demand for both maximal sensitivity and specificity, the combination of different tests is recommended. In case of IgA deficiency, IgG class antibodies have to be used. The histological judgment of small intestinal mucosa is commonly regarded as the gold standard for the reliable diagnosis of CD. Biopsy specimens of active CD demonstrate a flat mucosa with the absence of intestinal villi, a cellular infiltrate of the lamina propria, and an increase in the number of IELs. In the ESPGHAN guidelines revised in 2012, the omission of the small intestinal biopsy is only tolerated in children and adolescents with distinct signs and symptoms suggestive for CD and very high anti-TG2 antibody titers with levels exceeding ten times the upper limit of normal. Genetic tests based on HLA-DQ2 and DQ8 alleles cannot be used to confirm CD, because they are common in the general population (around 30%). In the case of doubtful diagnostic results, however, HLA-DQ genotyping can be used to rule out the existence of CD, because of its high negative predictive value. If a patient is negative for HLA-DQ2/8, CD can be excluded lifelong and no further investigations and follow-up are needed. The final confirmation of CD is established by a clinical, serological, and histological response to a GFD. When keeping a strict GFD, patients show a rapid improvement of symptoms within weeks. Histological regeneration is slower and complete recovery can take months or years.

Therapy After the diagnosis of CD has been established, permanent withdrawal of gluten from the diet is the current essential treatment. The GFD involves avoiding products containing

wheat, rye, and barley. Starches of these cereals are permitted, if the gluten level is lower than 20 mg kg1 (Draft Revised Codex Standard 2008). The toxicity of oats has been discussed controversially, but recent studies have provided strong evidence that only a very small subgroup of CD patients cannot tolerate oats. The daily intake of gluten should not exceed 20 mg. Since small amounts of gluten are hidden in many foods, dietary counseling is absolutely necessary. In most countries, celiac societies are an invaluable help in providing dietary guidelines and food lists. The prognosis for patients who are correctly treated is excellent, whereas failure to implement a strict diet may result in continuing symptoms and in the two major complications: osteoporosis and malignancy. CD patients may consume gluten-free foods from two different categories. Firstly, they are allowed to eat a wide range of common products such as meat, fish, milk, fruits, and vegetables. In the case of composite foods, however, it is difficult to recognize whether they are gluten-free or not. Labeling of gluten as an allergen is mandatory in the framework of CODEX Alimentarius and in the European Union. Secondly, patients consume dietetic food that is gluten-free according to the CODEX Alimentarius standard. The current standard and legislation in the United States, Canada, and the European Union set a gluten level of 20 mg kg1 food as the threshold for a gluten-free claim. In some countries, foods containing up to 100 mg gluten/kg, such as wheat starch, can be labeled as low in gluten. For gluten analysis, extraction with 60% ethanol and an immunochemical method for quantitative determination (enzyme-linked immunosorbent assay (ELISA) with monoclonal or polyclonal antibodies) are recommended. Dietetic gluten-free foods are mostly substitutes of products usually containing wheat, rye, and barley, such as bread, other baked products, pasta, and beer. Common raw materials used for these products are flours from corn, sorghum, rice, buckwheat, quinoa, teff, and chestnut, and common thickening agents are locust bean gum, guaran gum, and hydroxypropyl methyl cellulose. Owing to the enormous increase of knowledge about the pathomechanism of CD, a number of novel strategies for the prevention and treatment of CD have been developed. Usually, CD-toxic peptides derived from digested gluten survive the normal digestive process. Supplementation with additional peptidases may degrade CD-toxic epitopes to avert an immune response. Peptidases from bacteria, fungi, and germinating cereals have been proposed for oral therapy. Some of these approaches are already in phase 1 and 2 clinical trials. Moreover, inhibitors of zonulin, a key molecule for intestinal permeability; inhibitors of TG2, the autoimmunogen of CD; inhibition of gluten peptide presentation by HLA-DQ2 antagonists; and modulation or inhibition of proinflammatory cytokines have been proposed as alternative therapies. However, the risks, benefits, and costs of alternatives have to be carefully weighed, and the conditions and indications under which such alternative therapies might be warranted have to be accurately defined.

Toxicity Testing Numerous in vivo and in vitro methods have been used to identify CD toxicity and immunogenicity of different cereal

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | Celiac Disease and noncereal materials, proteins, and peptides. The tests can be differentiated into (1) in vivo challenge of patients, (2) in vitro tests with tissues and cells of patients, and (3) animal models. Most investigators would agree that in vivo testing is the ‘gold standard’ for assessing CD toxicity of proteins or peptides. Early workers established toxicity in a series of feeding tests based on the production of symptoms such as steatorrhea or on tests such as malabsorption of fat or xylose. However, an important impediment was that CD patients differed widely in their sensitivity to gluten and, consequently, the optimal amount of gluten equivalent used to challenge patients and the duration of challenge were uncertain. In any case, 10–100 g of gluten equivalent was necessary for the testing of each patient, and such large amounts were the most crucial limiting factor for feeding tests of purified proteins or peptides. Direct instillation into the small intestine followed by biopsy allows the reduction of required amounts to 1 g equivalent of gluten. Biopsies are taken from patients in remission at the beginning and after several hours of testing. Changes in enterocyte height, ratio of villous height to crypt depth, and the number of IELs are considered to be reliable parameters for toxicity assessment. Because in vivo tests require large quantities of substances and only a limited number of test patients are available, a series of in vitro tests has been developed. The organ culture of human small intestine, which requires only milligram equivalents of gluten, provides the most reliable in vitro approach. The intestinal tissue from patients with active CD is removed as part of the diagnostic procedure and incubated in a culture medium. The tissue shows improvement of enzyme activity and morphology in the medium alone, but not in the presence of CD-toxic substances. Apart from human material, tissue cultures with fetal rat and chicken intestine have been used. T cell lines and clones raised against gluten are useful for performing a large number of experiments and readily demonstrate the T cell response to stimuli. Gluten-sensitive T cells can be isolated from intestinal biopsies cultured and stimulated in vitro or can be found in the blood of treated CD patients after oral gluten challenge. A frequently used test is the T cell proliferation assay performed by incubation of intestinal CDsensitive T cells, the putative antigen ( 100–200 mg ml1) treated with TG2, antigen-presenting cells (e.g., B cells), and tritiated thymidine. The proliferation of T cells determined by scintillation measurements is a parameter for immunogenic effects. Additionally, the production of IFN-g or interleukins can be measured. T cell tests have been used widely to compare the level of immunogenic effects. Generally, it should be mentioned that T cells do not necessarily reflect the small intestine in vivo, because they lack any connection to other cell types present in the intestine. In addition, T cells are frequently different in their reaction to antigens; application of several simultaneous T cell lines from different patients is therefore needed. Moreover, immunogenicity does not always correspond to toxicity demonstrated by in vivo or organ culture tests. In any case, in vivo testing ultimately will be necessary to evaluate conclusions on in vitro testing. Among animals, there are three models that spontaneously generate glutendependent diarrhea: the Irish setter dog, the rhesus macaque, and the horse. However, the animal model that reproduces all important aspects of CD still awaits development.

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Toxicity of Cereals The relationship between CD and the ingestion of wheat flour was established in 1950. Soon after, a series of investigations led to the conclusion that rye and barley were also harmful, whereas corn, rice, buckwheat, and potatoes were not. There has been disagreement about the toxicity of oats; the reason for that could have been that commercial oat flour is frequently contaminated with small amounts of wheat, rye, or barley. Most clinical studies indicate that pure oats do not activate CD and it is proposed that only a very small subgroup of CD patients is sensitive to oats. Accordingly, CD is closely related to the taxonomy of cereals: only species found in the tribe Triticeae within the grass family Poaceae are likely to trigger CD. All wheat species besides bread wheat such as durum wheat, spelt, emmer, einkorn, and kamut have been suggested to be toxic for CD patients due to homology of their storage proteins to wheat.

Toxicity of Cereal Proteins Immediately after wheat was established as the CD-activating cereal, fractionation of the flour and in vivo testing led to the conclusion that gluten is toxic, whereas starch and albumins are not. Gluten is the rubbery protein mass that remains when wheat dough is washed with water to remove starch granules and other soluble constituents. Wheat gluten proteins can be divided according to their solubility in aqueous alcohols into the soluble gliadins and the insoluble glutenins. Toxicity tests indicated that the gliadin fraction was the most toxic factor, whereas the effect of the glutenin fraction was described either nontoxic, weakly toxic, or as toxic as gliadins, but on very inadequate evidence. More recent studies on pure glutenin subunits indicated that the glutenin fraction is also harmful for CD patients. Flour protein fractions of rye and barley have not been tested for celiac toxicity until now, but equivalent to the gliadin fraction of wheat, the corresponding prolamin fractions of rye (secalins) and barley (hordeins) are associated with CD. Although the prolamin fractions of cereals are crude mixtures of different proteins, their amino acid compositions (Table 1) show a close relationship to both taxonomy and CD toxicity. Toxic gliadin, secalin, and hordein fractions are characterized by the highest contents of glutamine (35–37 mol%) and proline (17–23 mol%). Both amino acids have been considered to be important for CD toxicity. The prolamins of rice, millet, and corn are lower in glutamine and proline, but rich in alanine (9–14 mol%) and leucine (12–19 mol%). Oats are in an intermediate position, the glutamine content being similar to the Triticeae prolamins and the values of proline and leucine in agreement with those of other species. Among the prolamin fractions, only wheat prolamin (gliadin) has been investigated in detail. The digestion with pepsin and trypsin alone or followed by pancreatin resulted in the retention of toxicity, and a peptide mixture with a molecular mass less than 2000 was still toxic. Also, the breakdown of the disulfide bonds by oxidation or heating during the baking process did not abolish toxicity. In consequence, the

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Table 1

Partial amino acid composition (mol%) of prolamins of different cereals

Amino acid

Wheat (gliadin)

Rye (secalin)

Barley (hordein)

Oats (avenin)

Rice (oryzin)

Millet (kafirin)

Maize (zein)

Glx Pro Leu Ala Met Lys Trp

37.1 16.6 6.9 2.8 1.1 0.8 0.4

35.4 18.4 5.8 3.0 1.0 1.0 0.4

35.3 23.0 6.1 2.3 0.9 0.5 0.6

34.1 10.2 10.6 5.5 2.1 1.0 0.3

19.6 5.1 11.8 9.1 0.5 0.5 0.5

21.8 7.8 13.4 13.5 1.7 0.0 1.5

19.4 10.2 18.5 13.6 1.1 0.0 0.0

Table 2

Amino acid sequences of peptides tested for CD toxicity by instillation and organ culture tests

Amino acid sequence

Source

Position

Toxicitya

VPVPQLQPQNPSQQQPQEQVPL VQQQQFPGQQQPFPQQPYPQPQPFPSQQPY VRVPVPQLQPQNPSQQQPQEQVPLVQQQQF LGQQQPFPPQQPYPQPQPFPSQQPY LGQGSFRPSQQN LGQQQPFPPQQPYPQPQPF LGQQQPFPPQQPY PQPQPFPSQQPY LQLQPFPQPQLPYPQPQLPY SQQPYLQLQPFPQPQLPYSQ

Gliadin Gliadin A-Gliadin A-Gliadin Synthetic Synthetic Synthetic Synthetic Synthetic Synthetic

a3–24 a25–55 a1–30 a31–55 a206–217 a31–49 a31–43 a44–55 a56–75 a51–70

þ (OC) þ (OC) þ (OC) þ (OC) þ (IN) þ (IN, OC) þ (IN) þ (IN) þ (IN) þ (OC)

a

IN, instillation; OC, organ culture.

three-dimensional structure of gliadin proteins is not important for the toxic effect. The complete degradation into free amino acids by acid hydrolysis, however, rendered it harmless, as did extensive deamidation of glutamine side chains with a limited cleavage of peptide chains. Subsequent in vivo and in vitro studies demonstrated that all gliadin types produce toxic effects. In contrast, the major protein types of the glutenin fraction, lowmolecular-weight (LMW)-glutenin subunits have not been tested in vivo until now. However, in vivo studies with HMW glutenin subunits confirmed their toxicity for CD patients. Currently, approaches aimed at reducing or abolishing CD toxicity of wheat are underway. Beside the strategy to reduce the toxicity of wheat by conventional breeding approaches, the recombinant production of completely safe gluten proteins is an additional aim based on currently gained knowledge on the elimination of the toxic fragments. The first approach is based on the assumption that the dose of exposure to gluten-derived CD-active epitopes will contribute to a general reduction of the prevalence of CD and of symptom severity in the population. Barley is a diploid cereal with pure inbred cultivars available and is, therefore, attractive for use in genetic approaches to detoxification. Barley lines lacking B-, C-, and D-hordeins gave gluten concentrations of 4–5 mg kg1 after quantitation by ELISA and liquid chromatography-mass spectrometry (LC-MS). Test with peripheral blood mononuclear cells activated by oral hordein challenge demonstrated that the immunogenicity of these lines was reduced 20-fold compared with that of wild-type barley. Therefore, the creation of hordein-free barley seems to be a realistic goal. However, the quality of products (e.g., beer) derived from hordein-free barley lines has still to be demonstrated.

Toxicity of Peptides The discovery that gliadins are enzymatically degraded without loss of toxicity and subsequent studies on gluten digestion and immune response clearly revealed that gluten peptides are, in fact, the precipitating factors of CD. Therefore, research on CD toxicity has been focused on peptides either isolated from protein digests or synthesized. In vivo instillation tests and in vitro organ cultures enabled the study on peptides in milligram and even microgram amounts. With the exception of one peptide (a206–217), toxic peptides are contained in the N-terminal domain of a-gliadins characterized by sequences rich in glutamine (Q) and proline (P) (Table 2). Since the end of the 1990s, the search for CD-active peptides has shifted toward epitopes that stimulate intestinal gluten-sensitive T cell lines of CD patients, and peptides from gliadins, glutenins, secalins, and hordeins were investigated. A small selection of the first generation (1999–2005) of immunogenic peptides is presented in Table 3. Given the heterogeneity of wheat, rye, and barley proteins, it is not surprising that a large number of T cell epitopes exist. The major part of peptides is HLA-DQ2 restricted and is derived from the glutamine- and proline-rich sequence domains. A number of studies have shown that patients respond heterogeneously to different epitopes and that there also are differences between children and adults. The Food Allergy Research and Resource Program of the Department of Food Science and Technology, University of Nebraska–Lincoln, the United States, has compiled a database of CD-active gluten peptides. It includes more than 1000 native or deamidated peptides described in more than 60 publications. These peptides have their origins in all types of

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | Celiac Disease Table 3 Amino acid sequences of selected gluten peptides stimulatory for intestinal T cells of CD patients Protein

Amino acid sequencea

a2 a20 g5 g5 LMW 156 LMW 17 HMW 2 HMW 2 Sec a2 Sec a9 Hor a2 Hor a9 Av a9A Av a9B

LQLQPFPQPQLPYPQPQLPYPQPQLPYPQPQPF PFRPQQPYPQPQPQ FLQPQQPFPQQPQQPYPQQPQQPFPQ QFSQPQQQFPQPQ QQQQPPFSQQQQSPFSQQQQ QQPPFSQQQQQPLPQ GQQGYYPTSPQQS QGYYPTSPQQSG QPFPQPQQPFPQSQ PQQPFPQPQQPFPQ QQFPQPQQPFPQQP PQQPFPQPQQPFRQ QYQPYPEQQEPFVQ QYQPYPEQQQPFVQ

a

Glutamine (Q) residues targeted by TG2 are in bold. Source: Wieser H, Koehler P, and Konitzer K (2014) Celiac Disease and Gluten: Multidisciplinary Challenges and Opportunities, 1st edn. London, Waltham, San Diego: Academic Press, with permission.

wheat gliadins and glutenins, rye secalins, barley hordeins, and oat avenins. Some authors have subdivided CD-active peptides into ‘toxic’ peptides generating an innate immune response and ‘immunogenic’ peptides generating an adaptive immune response. The discrepancy between the numbers of immunogenic peptides identified by T cell tests and of toxic peptides identified by in vivo or organ culture tests is extraordinary: 1014 peptides have been classified as immunogenic, 10 peptides as toxic, and 5 peptides as both toxic and immunogenic. The question of whether immunogenicity corresponds to toxicity in any case remains to be answered. In summary, a common feature among toxic/immunogenic peptides is the presence of multiple proline and glutamine residues, which gives rise to four unique structural and functional properties: 1. These peptides are exceptionally resistant to peptidolysis by gastric, pancreatic, and intestinal digestive peptidases because of their high proline content. As a result, a high intestinal concentration of potentially immunogenic peptides is maintained following a gluten-containing diet. 2. Selected glutamine residues in these gluten peptides are deamidated or transamidated by TG2 under physiological conditions, leading to enhanced immunogenicity. 3. The proline-rich gluten peptides naturally adopt a lefthanded polyproline II helical conformation, which is the preferred conformation of all bound major histocompatibility complex class II ligands. 4. Large peptides that contain multiple HLA-DQ-binding epitopes have a greater T cell stimulatory activity than small peptides containing only one epitope.

Future Prospects A standardization of criteria for prevalence determination and a differentiation into cases of active, silent, and potential CD

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would be helpful to establish a more precise epidemiological picture of CD. Little is known on the complex interplay between genetic and environmental factors leading to CD development, and it will be a major area of research to understand their respective contributions and develop possible prevention strategies. Further studies are required to allow a better diagnostic differentiation between CD, NCGS, and irritable bowel syndrome, because the symptoms and nonspecific findings may be similar in patients. While the role of gluten peptides in the adaptive immune response is well characterized, much less is known regarding the innate immune response. Elucidating the mechanism of the innate immune response will contribute to a better understanding of the CD pathomechanism. Gluten-sensitive T cell assays are used to compare the level of immunogenic effects, but immunogenicity measured by T cell tests does not necessarily correspond to toxicity revealed by in vivo or organ culture tests. This is the reason why it would be of interest to test immunogenic peptides by in vivo assays. The GFD will remain the preferred therapy of CD in the future. Regarding alternative therapies, CD patients have expressed the wish to have access to a vaccine against CD or to a pill that would occasionally allow them to eat glutencontaining food. Such alternative therapies are still in the early stages of development, and they will have to undergo safety and toxicology testing before they can enter the market.


• • • • • •

What is the primary environmental trigger for CD and which cereals are harmful? What other gluten-related disorders are there? What are the steps in the diagnostic scheme to identify CD and what is the essential treatment once the diagnosis has been established? What methods can be used to measure CD activity? What foods are allowed to be consumed by CD patients? What are the characteristic properties of CD-toxic/ immunogenic peptides?


• •

•

CD patients need to adhere to a strict GFD. Compare the characteristics of wheat bread to those of gluten-free breads. The increased knowledge about the pathomechanism of CD has led to the development of novel treatment strategies, such as oral peptidase therapy. Look at the different proposed treatment options and identify which steps in the pathomechanism are targeted. Take a look at the database of CD-active gluten peptides of the Food Allergy Research and Resource Program of the Department of Food Science and Technology, University of Nebraska–Lincoln, the United States (www.allergenonline.org/celiacbrowse.shtml), and find the CD-active peptides derived from alpha-gliadins.

See also: Appendix 1: Nutrient-Composition Tables for Grains and for Grain-Based Products; Appendix 2: Lists of Standardized Testing

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Methods for the Analysis of Grain and Grain-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Cereal Allergens; The Gluten-Free Diet; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; The Composition of Food Grains and Grain-Based Products; Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units; Proteins: Protein Synthesis and Deposition; Proteomic Analysis Relevant to Cereal Grains; The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Grain Crops: An Overview; ; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Oats: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: Gluten and Modified Gluten; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

Further Reading Abadie V, Sollid LM, Barreiro LB, and Jabri B (2011) Integration of genetic and immunological insights into a model of celiac disease pathogenesis. Annual Review of Immunology 29: 493–525. Arendt EK and Dal Bello F (2008) Gluten-Free Cereal Products and Beverages, 1st edn. Burlington, San Diego, London: Academic Press. Catassi C, Fabiani E, Iacono G, D’Agate C, Francavilla R, Biagi F, et al. (2007) A prospective, double-blind, placebo-controlled trial to establish a safe gluten threshold for patients with celiac disease. American Journal of Clinical Nutrition 85: 160–166.

Dicke WK, Weijers HA, and van de Kamer JH (1953) Coeliac disease. II. The presence in wheat of a factor having a deleterious effect in cases of coeliac disease. Acta Paediatrica 42: 34–42. Husby S, Koletzko S, Korponay-Szabo IR, Mearin ML, Phillips A, Shamir R, et al. (2012) European Society for Pediatric Gastroenterology, Hepatology, and Nutrition guidelines for the diagnosis of coeliac disease. Journal of Pediatrics Gastroenterology and Nutrition 54: 136–160. Kasarda DD (1994) Toxic cereals in coeliac disease. In: Feighery C and O’Farelly C (eds.) Gastrointestinal Immunology and Gluten-Sensitive Disease, pp. 203–220. Dublin: Oak Tree Press. Lindfors K, Rauhavirta T, Stenman S, Maeki M, and Kaukinen K (2012) In vitro models for gluten toxicity: Relevance for celiac disease pathogenesis and development of novel treatment options. Experimental Biology and Medicine 237: 119–125. Ludvigsson JF, Leffler DA, Bai JC, Biagi F, Fasano A, Green PH, et al. (2012) The Oslo definitions for coeliac disease and related terms. Gut 62: 43–52. Richey R, Howdle P, Shaw E, and Stokes T (2009) Recognition and assessment of coeliac disease in children and adults: Summary of NICE guidance. British Medical Journal 338: b1684. Sapone A, Bai JC, Ciacci C, Dolinsek J, Green PHR, Hadjivassiliou M, et al. (2012) Spectrum of gluten-related disorders: Consensus on new nomenclature and classification. BMC Medicine 10: 13. Schuppan D, Junker Y, and Barisani D (2009) Celiac disease: From pathogenesis to novel therapies. Gastroenterology 137: 1912–1933. Sollid LM, Qiao S-W, Anderson RP, Gianfrani C, and Koning F (2012) Nomenclature and listing of celiac disease relevant gluten T-cell epitopes restricted by HLA-DQ molecules. Immunogenetics 64: 455–460. Wieser H (2007) Chemistry of gluten proteins. Food Microbiology 24: 115–119. Wieser H and Koehler P (2008) The biochemical basis of celiac disease. Cereal Chemistry 85: 1–13. Wieser H, Koehler P, and Konitzer K (2014) Celiac Disease and Gluten: Multidisciplinary Challenges and Opportunities, 1st edn. London, Waltham, San Diego: Academic Press.

The Gluten-Free Diet V Zevallos, Johannes Gutenberg Mainz, Mainz, Germany I Herencia, Universidad Politecnica de Madrid, Madrid, Spain ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Human nutrition and the gluten-free diet (GFD). GFD, celiac disease (CD), and other inflammatory conditions. Gluten and nongluten wheat proteins. Grains with and without gluten. Legislation of gluten-free products. Nutritional and technological developments of gluten-free products.

Learning Objectives

• • •

To understand the origin and current situation of a GFD. To understand the effects of a GFD on health and disease. To know the current nutritional and technological developments of GF products.

Introduction The human diet has changed throughout the years, motivated mostly by an adaptation to the surrounding environment. From hunter-gatherers to sedentary populations, the human diet has evolved, adapted, and changed affecting and influencing health and disease. Agriculture was one of the main factors influencing the human diet; for instance, the success of Roman Empire was arguably supported by agriculture, particularly wheat production. However, having a diet mostly based in one staple (wheat) had detrimental effects as indirectly suggested by Aretaeus from Cappadocia, a physician that in AD 200 described a malabsorptive syndrome with chronic diarrhea that was the first account for what is currently known as CD, an enteropathy affecting mostly the small intestine architecture in genetically predisposed individuals. In around 1700, two books described a gastrointestinal condition characterized by diarrhea (white flux) and the term sprue from the Dutch spruw was used. At the end of the nineteenth century, Samuel Gee accurately outlined the typical features of CD and even highlighted the importance of diet in the treatment; one of his first dietary intervention was the use of mussels in a child with suspected CD who relapsed after the mussel’s season ended. Haas described “Some years ago I treated a child, aged 3 years, who suffered from a severe case of anorexia nervosa. She had reached a serious state of depletion and weakness from her self imposed starvation, refusing all food and regurgitating that fed to her by gavage (tube feeding). She finally accepted a banana, with the result that other food was taken in a more or less normal amount within 48 h. There was a complete relapse when the banana was withheld and food was taken normally only with bananas.”


According to this observation, Haas described a treatment of ten celiac patients, eight of which were cured with the banana diet and two of which died. The banana diet and other diets based on fruit and vegetables were the best treatment for celiac patients, but during the Second World War, those items were unavailable, and therefore, another dietary treatment was necessary. At that time, Dicke (Figure 1) and collaborators were the first to establish a clear link between diet and CD by concluding that wheat and rye flours caused anorexia, increased fecal output, and steatorrhea in CD patients, setting up the basis for an effective treatment. Further studies confirmed their initial hypothesis by identifying gluten from wheat and related cereals as the storage proteins triggering CD. Thus, giving rise to what is currently known as a GFD, this diet includes naturally occurring gluten-free foods such as fruit, vegetables, unprocessed meat, fish, and poultry. Products such as pasta, bread, breakfast cereals, crackers, and snack foods that are usually manufactured with gluten-containing cereals (wheat, barley, and rye) are replaced with flour from glutenfree cereals such as maize, rice, millet, buckwheat, and sorghum. The recent increased prevalence in CD and related conditions (nonceliac gluten sensitivity (NCGS) and inflammatory bowel syndrome (IBD)), the rediscovery of forgotten highly nutritious staples (quinoa and amaranth), and a recent social dietary trend have facilitated the expansion of the glutenfree market. Current reports indicate that the global gluten-free market has reached an estimated value of more than $6 billion with a projected annual growth rate of 10.2% by 2018 (http://www. marketsandmarkets.com/Market-Reports/gluten-free-productsmarket-738.html), suggesting a rapid expansion beyond the traditional dietary treatment for CD to a global dietary choice that will compete with traditional food industries. This article aims to provide an overview about the effects of a GFD on health and disease, gluten and nongluten proteins and plant sources, legislation of gluten-free products, and the nutritional value of a GFD.

Celiac Disease CD is a gluten-sensitive enteropathy that affects mainly the villous architecture of the proximal small intestinal in genetically predisposed individuals (Figure 2). CD is now being considered a multiorgan autoimmune disease characterized by an inappropriate immune response triggered by the ingestion of amino acid sequences found in seed storage proteins or prolamins of wheat, barley, and rye. The prevalence of CD ( 1%) was traditionally higher in Europe, where glutencontaining cereals are frequently cultivated and consumed. However, increased migration and similar agricultural and

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Figure 1 Professor Willem-Karel Dicke at the Wilhelmina Children’s Hospital, Utrecht. Reproduced from van Berge-Henegouwen GP and Mulder CJ (1993) Pioneer in the gluten free diet: Willem-Karel Dicke 1905–1962, over 50 years of gluten free diet. Gut 34(11): 1473–1475.

dietary patterns have widen the demographic distribution of CD with similar prevalence in United States, Australia, South America, and North Africa where children of Arab-Berber origin had 5.6% prevalence of antiendomysial antibody. Other regions (Japan and China) where CD was historically rare are starting to report new CD cases, which correlates with an increase in wheat consumption, suggesting that the population was genetically susceptible but simply did not manifest disease due to the absence of the environmental factor (dietary gluten) that is essential to develop CD. The typical clinical manifestation of CD in adults includes generalized malabsorption, weight loss, and continuous, intermittent, or alternated diarrhea with periods of constipation. In children, classical symptoms such as anorexia, vomiting, and anemia are observed during the first months of age, followed by loss of appetite, failure to thrive, behavioral problems, abdominal distension, small stature, muscle wasting, and enamel defects during the first years. Moreover, milder cases characterized by the partial absence of symptoms or atypical signs are becoming increasingly common, particularly since CD is a complex condition that is associated with many diseases, not only mainly autoimmune diseases but also reproductive, neurological, and dermatologic disorders. The current serological gold standard is IgA endomysial antibody (EMA), with a specificity that approaches 100% and a sensitivity of 90%. The titer of EMA correlates with the

degree of mucosal damage. Enzyme tissue transglutaminase (tTG) was recognized as being the autoantigen for the EMA allowing the development of an IgA anti-tTG enzyme-linked immunoassay with less specificity than the IgA EMA test (95–99%) but more sensitivity (93–90%). However, histological assessment of the small intestine remains the gold standard in the diagnosis of CD. The celiac lesion predominantly affects the mucosa of the proximal duodenum with lessening damage occurring toward the distal part; multiple biopsies using standard size forceps are needed due to the patchy nature of the villous changes. The diagnosis of CD is based on genetic predisposition (human leukocyte antigen (HLA)-DQ2 or HLA-DQ8), gastrointestinal symptoms, and positive serological and histological abnormalities at duodenal level on a gluten-containing diet. Once CD has been diagnosed, the main treatment involves following a strict GFD that consists of eating naturally occurring gluten-free foods such as fruit, vegetables, unprocessed meat, fish, and poultry. Products such as pasta, bread, breakfast cereals, crackers, and snack foods that are usually manufactured with gluten-containing cereals (wheat, barley, and rye) are replaced with flour from gluten-free cereals such as maize, rice, millet, buckwheat, quinoa, and sorghum. A full list of gluten-free products is available in Appendix 3. ‘Grains, Foods, and Ingredients Suiting GFD for CD.’ Fortunately, the gluten-free industry has experienced a significant development over the last years. However, this rapid growth has been accompanied by variations in labeling standards and in the amount of gluten that can be safely tolerated depending of the country or region, for example, 20 ppm is considered a safe threshold in Europe. Furthermore, a strict GFD can only be achieved with difficulties when patients are traveling and have to eat outside, heavily relying on third parties (restaurants and shops). In addition, adherence to the GFD depends mainly on factors such as palatability, availability, age, social/peer pressure, and cost. Also, celiac patents that are extremely sensitive to gluten can have persistent symptoms despite following a GFD due to consumption of foods containing ‘hidden’ sources of gluten such as wheat thickeners, malted barley with unsafe levels of gluten/ambiguous labels, and other ingredients such as fermentable starches or some gluten-free ingredients. CD requires strict adherence to a GFD for life and hence the importance to maintain regular contact with a multidisciplinary team formed by the gastroenterologist, GP, dietician, and nutritionist that can provide ongoing support to the celiac patients. Failing to maintain a strict GFD could lead to a persistent stage of inflammation that could be associated to increased mortality. It is also very important to continue the development of new products and ingredients to improve the quality of the GFD.

Other Inflammatory Conditions There is growing evidence that a GFD has the potential to become an alternative treatment for gastrointestinal and extragastrointestinal inflammatory conditions such as irritable bowel syndrome (IBS), NCGS, rheumatoid arthritis (RA), diabetes mellitus (DM), and neurological and dermatological


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Figure 2 Villous architecture of the proximal intestine in a treated (a) and an untreated (b) CD patient, using scanning electron microscopy (left) and histology (right). Reproduced from Gasbarrini G and Mangiola F (2014). Wheat-related disorders: a broad spectrum of “evolving” diseases. United Eur. Gastroenterol. J. 2(4): 254–262.

disorders. The pathogenesis of IBS, Crohn’s disease, and ulcerative colitis remains to be fully elucidated, but genetic predisposition, microbiome, and environmental/dietary triggers are the most important factors involved in the onset of disease. Furthermore, in vivo experiments using HLA-DQ8 mice sensitized with gluten show that an altered barrier function could be a critical step in facilitating exposure of the mucosal immune system to dietary antigens that subsequently will trigger an immune response. Thus, a GFD recommended to patients with IBD-like symptoms resulted in improved symptoms, suggesting the potential role of a GFD as adjunctive therapy. Nonceliac gluten/wheat sensitivity (NCGS) is a condition that significantly improves on a GFD, initially reported in the late 1970s; NCGS can be defined as a reaction to gluten-containing grains without involvement of allergy or autoimmune mechanisms. It is associated with gastrointestinal (bloating, diarrhea, abdominal pain, and nausea) and predominantly nongastrointestinal symptoms (headache, ‘foggy mind,’ chronic fatigue, joint and muscle pain, numbness of leg and arms, and anemia). The prevalence of NCGS is between 1% and 5% and seems to be more common in females and young/middle-aged adults although the prevalence in children needs further investigation. The pathogenic mechanism is still unclear, but the innate immune response to wheat, particularly part of the

nongluten fraction (amylase trypsin inhibitors, ATIs), seems to play a significant role in the onset of disease. RA increases the risk of atherosclerosis and cardiovascular disease; it has been shown that a gluten-free vegan diet decreased total cholesterol. It is antiatherogenic and significantly reduces disease activity and the levels of antibodies to b-lactoglobulin. Type I DM is also affected by gluten and having a GFD has beneficial effects on the preservation of Bcell function. Wheat consumption also affects neurological dysfunctions, although the precise mechanism on the nervous system is still unclear. Thus, a GFD has been shown to improve and stabilize ataxia by preventing irreversible loss of Purkinje cells in the cerebellum and improve neuronal sensory action potential and headaches. Furthermore, there are reports indicating that a GFD has a positive effect on symptom reversal of multiple sclerosis. Dietary trends are an important cultural factor often associated with health and disease; in recent years. Being on a GFD has become ‘fashionable’ in most Western societies. In the United States, it is considered the most trendy diet with 1.5 million citizens (without any underlying medical condition) consuming gluten-free products. This proportion is similar in other Western countries and is predicted to increase even more in the coming years. The popularity of gluten-free products is

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partly motivated by the association with healthy eating, weight loss, and a recent negative perception of wheat as an overutilized staple of the Western diet.

Gluten and Nongluten Wheat Proteins The storage proteins are the main immunogenic components of wheat, barley, and rye kernels. These proteins are located in the endosperm of kernels and can be subdivided according to their solubility in water, salt, alcohol, and alkali into albumins, globulins, prolamins, and glutelins, respectively. For wheat, the gluten–protein complex can readily be purified by making a dough with wheat flour and water and kneading the dough under running water. The starch and water-soluble proteins wash out and a cohesive ball of gluten remains. The cohesive properties of wheat gluten are the reason why only wheat flour is well suited to bread making. The storage proteins of barley and rye are similar to those of wheat, but they lack the doughforming properties of wheat gluten. For dietary purposes, the storage proteins of wheat, barley, and rye can be considered as gluten, being a mixture of both prolamins and glutelins. Prolamins are alcohol-soluble storage proteins characterized by their higher content of proline and glutamine, which in combination could constitute between 30% and 70% of the total amino acid composition. The molecular weight of prolamins ranges from 10 to 100 kDa and prolamins are a significant source of nitrogen, sulfur, and carbon for the developing embryo and they are known as gliadins in wheat, hordeins in barley, and secalins in rye. According to their decreasing electrophoretic mobility, gliadins can be divided into a, b, g, and o gliadins. Based on their N-terminal amino acid sequences, gliadins can be categorized into a, g, and o. There is another classification based on the amount of sulfur, o gliadins are sulfur-poor and a and g gliadins are sulfur-rich. The first prolamin to be fully sequenced was A-gliadin (an a-type) using direct protein sequencing; the remaining amino acids were sequenced using cloned DNA, facilitating the development of synthetic peptides. Other studies using different wheat, barley, and rye cultivars found that purified prolamins from rye (g and o secalins) and from barley (o hordeins and C-hordeins) could be identified using chromatographic methods. Prolamins are also present in other plants but at a different proportion and with different amino acid sequences than in wheat, barley, and rye. The glutelin protein of wheat is termed glutenin. It consists of alcohol-soluble subunits that are cross-linked by interchain disulfide bonds to form alcohol-insoluble polymeric glutenin. These subunits have been classified according to their electrophoretic mobility into high-molecular-weight (HMW) and low-molecular-weight groups. The HMW glutenin subunits make a major contribution to dough formation. Specific subunits are identified according to the relevant genes, such as 1Dy10, 1Dx5, 1Dx4, and 1Dy9. Rye and barley have equivalent glutelin fractions (HMW secalins and D-hordeins, respectively) but they are less suitable for dough formation. Immunogenic gluten (prolamins and glutelins) peptides trigger an adaptive immune response in CD. These peptides reach the lamina propria via a combination of defective tight

junctions, a paracellular pathway, epithelial transcytosis, and direct sampling by dendritic cells. Internalized gluten peptides are then deamidated by the enzyme tTG II, increasing negatively charged peptides that can be accommodated in binding pockets of the heterodimeric HLA class II alleles encoding for HLA-DQ2 and HLA-DQ8. This increase in antigenicity accelerates the secretion of interferon-g (IFN-g) by gluten-specific CD4 þ T-helper cells, contributing to the expansion of cytotoxic T cells and fibroblasts and the release of metalloproteases to degrade the extracellular matrix of enterocytes at the lamina propria and also to start secretion of anti-tTG by glutenspecific plasma cells into the lamina propria and then to the bloodstream. The other major grouping of wheat-grain proteins is the water-/salt-soluble proteins referred as nongluten wheat proteins, the most relevant in terms of innate inflammation being the ATIs. Some of these proteins play a significant role as a plant defense mechanism against pests and during the metabolic process of seed development. Wheat ATIs were identified as contaminating proteins within pepsin–trypsin gliadin digests; they represent between 2% and 4% of total grain protein compared to 70–80% for gluten. ATIs are resistant to proteolytic digestion due to their compact secondary structure that includes five intrachain disulfide bonds. ATI subfamilies can be monomeric or form noncovalently linked dimers or tetramers. There are up to 17 ATI species of around 150-amino acid length with a variant primary structure and conserved secondary structure. ATIs engage the toll-like receptor 4 (TLR4)-MD2-CD14 complex and lead to upregulation of maturation markers and release of proinflammatory cytokines in myeloid cells of celiac patients. In vivo feeding experiments in mice showed that ATIs increased intestinal and systemic release of cytokines and chemokines like IL-8, TNF-a, and CCL-2 within 2–12 h, and ex vivo celiac biopsy studies demonstrated an adjuvant effect of added ATIs for the gluten-specific T-cell response. Therefore, ATIs appear to be the sought triggers of innate immunity in CD and NCGS.

Gluten-Containing and Gluten-Free Plants Gluten-containing cereals are part of the Gramineae family, also known as Poaceae due to its association with the type genus Poa. This family includes 12 subfamilies, in which two are more relevant to CD: Pooideae that includes wheat, rye, and barley, which are considered toxic for celiac patients, and Panicoideae that includes maize, millet, and sorghum, which are considered suitable for the GFD. The food product ‘corn gluten’ is a misnomer; it is the protein washed from maize (corn) grain during wet milling. It is not related to wheat gluten. The taxonomic plant classification proposed by Kasarda provided a simple guidance to separate safe from unsafe grains. Monocotyledonous plants, members of the Gramineae family, and the Triticeae tribe (wheat, barley, and rye) were considered celiac-toxic, while dicotyledonous plants such as Chenopodiaceae and Amaranthaceae (quinoa and amaranth) and those from other tribes (maize, rice, and tef) are considered safe for celiac patients.

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | The Gluten-Free Diet Early studies on oats, probably contaminated with gluten, indicated that oats were unsuitable, but recent feeding studies comparing a GFD with and without oats concluded that moderate amount of oats (50–70 g per day) can be safely added to the GFD of celiac patient. Another study assessing the longterm effects of large amount of oats (up to 100 g per day) found that histology, serology, and well-being were constant throughout the study. However, there have also been reports that activation of CD with morphological deterioration occurred after oats challenge. They described T-cell lines reactive to avenin (the storage protein of oats) from duodenal mucosa of five patients consuming oats as part of their GFD that were positively stimulated by avenin peptides rich in proline and glutamine residues. Other reports indicated withdrawals from some large feeding studies, which added to the T-cell data, suggest that for a minor proportion of the celiac population, oats are unsuitable. Furthermore, gluten-containing plants (wheat, rye, barley, and their earlier ancestors) rich in ATIs have a strong innate stimulatory capacity that contrasts with a rather minimal innate stimulatory effect of ATIs from gluten-free plants. Thus, gluten-free plants are also ATI-free. The average amount of wheat flour consumed per adult/day is 250 g, indicating that around 1 g of ATIs could be enough to trigger a moderate innate immune response in the gut of people affected by CD or NCGS, also having an effect on nongastrointestinal organs. The morphological effect of ATIs is discrete and characterized by an increase in inflammatory cells in accordance to histological changes observed in NCGS patients. Furthermore, the effect is dose-dependent, and therefore, a reduction (80–90%) of daily ATI consumption may be sufficient to eliminate the stimulatory effect, and therefore, a strict GFD does not need to be maintained. Over the last decades, an increased prevalence of allergies and autoimmune diseases has been observed, particularly in developing countries. This can be partly explained by a parallel increase in wheat (ATIs) consumption since traditional (gluten-free) staples were replaced by more affordable alternatives (modern wheat).

Legislation of Gluten-Free Products The denomination ‘gluten-free’ theoretically implies without any amount of gluten; however, having such a diet will be impractical and very difficult to implement since gluten is a ubiquitous ingredient and therefore will be almost inevitably present in trace amounts within any diet. Furthermore, compliance to a GFD is mainly related to palatability and the availability of gluten-free products. This difficulty was partly addressed by the addition of wheat starch flour to the glutenfree list, particularly in Scandinavia and the United Kingdom where patients consumed traces up to 200 ppm without clinical evidence of exacerbation of the disease. However, there is an individual level of tolerance to gluten and even small amounts of gluten can be of relevance for a group of celiac patients. The other alternative to increase palatability and reduce the risk of nutritional imbalance is to include alternative ‘naturally gluten-free’ ingredients. However, there is a risk of gluten contamination that could occur from harvest to packaging, for example, samples of millet, sorghum, and soy heavily

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contaminated with gluten (up to 3000 mg kg1). Although these products were not labeled as gluten-free, they still represent a risk for celiac patients, particularly since clinical studies have suggested that 100 mg kg1 of gliadin or more can trigger an inappropriate immune response leading to histological damage of the intestinal mucosa in diagnosed patients. Similarly, it was found that the daily intake of gliadin at 4–14 mg did not produce the same effects for most celiac patients. The codex standard for gluten-free foods (Codex Stand 118, 1981) regulates the level of gluten in gluten-free foods and is often reviewed by a special FAO/WHO committee. The last review of Codex Alimentarius Commission (2008) indicates that the maximum gluten level for gluten-free products is 20 mg kg1. In 2012, new legislation based on these guidelines was issued by the European Commission, and the 20 mg kg1 threshold was applied to all GF products, that is, naturally GF (maize, rice, and uncontaminated oats) and derived from wheat starch. Other organizations such as the Food and Drug Administration have adopted similar a similar threshold level (20 ppm), and the Food Standards Australia New Zealand has chosen a more strict approach considering no detectable amount of gluten or as low as 3–5 ppm (www.standards.gov. au; www.coeliac.org.au).

Nutritional Value of the GFD Restrictive diets such as a GFD tend to have an inherent risk of nutritional deficiency. Previous studies mostly agreed that a GFD is nutritionally inadequate, but other studies did not reach the same conclusion (http://www.food.gov.uk/science/ research/allergy-research/t07053), and in general, information about the nutrition adequacy of a GFD is still rather limited. There is evidence that adults following a GFD have increased levels of cholesterol, altered homocysteine levels, and a potentially high risk of developing cardiovascular disease. Furthermore, another study showed that gluten-free products, particularly breads and pasta, have low protein, high saturated fat, sodium, and cholesterol compared to gluten-containing products, reflecting the nutritional consequences (low protein/high fat) particularly in females. This nutritional imbalance can be due to the ingredients used. For instance, wheat starch requires an industrial process that inevitably alters the macro- and micronutrient composition of wheat, a source of protein, iron, and vitamins (thiamin, riboflavin, folate, and niacin). In addition, replacing traditional gluten-free products for alternative naturally gluten-free products such as Andean grains (quinoa and amaranth) can increase variety, palatability, and most importantly significant amounts of nutrients such as protein, fiber, iron, calcium, vitamins, and polyunsaturated fatty acids. Baking gluten-free products remains a challenge mainly because the main ingredient, gluten, cannot be easily replaced. Most of the gluten-free flours lack the viscoelastic properties of wheat dough when kneaded in water and usually require more water to form a dough, which is difficult to handle. It is often referred to as a batter. The main problem arises when the mixture of water, yeasts, gluten-free flours, and starches forms few coherent structures because the gases from fermentation are not entrapped, directly affecting quality parameters, having

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reduced volume and crumbly structure, with poor texture, mouthfeel, and flavor. However, the gluten-free baking industry through food technologists and nutritionists maintains a continuous process of quality development, particularly by the addition of novel ingredients and new technologies. Thus, the main goal is to create gluten-free products with similar quality standards to the gluten-containing counterparts that will ultimately help to improve the quality of life of people affected by wheat-related conditions.

Conclusion and Future Developments Patients affected by wheat and related cereals benefit from a GFD. There is clear evidence that gluten proteins exacerbate celiac disease. However, non-gluten proteins as activators of innate immunity might also play a significant role in CD and other inflammatory conditions. Health care professionals support patients on a GFD by improving their psychological wellbeing, reducing social restrictions, developing new products to meet nutritional targets, and ultimately improving their quality of life. The increased number of people benefited from a GFD as well as a recent social trend indicates that the gluten-free market is projected to grow significantly over the coming years.


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Describe the most common symptoms of CD for children and for adults. What are the screening tests and the ‘gold standard’ tests to diagnose CD? Outline the taxonomic groupings of grain species that are celiac-toxic or not. Refer to the encyclopedia’s article on the taxonomy of grain-bearing plants. Summarize the development of legislation to assist consumers in choosing gluten-free foods, also considering the means of communication, mainly via product labeling.


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Investigate the recorded evidence for oats being harmful or not in CD. Refer to recommendations in Appendix 3, and examine articles such as the following: - Kemppainen, T.A. et al., 2008. Unkilned and large amounts of oats in the coeliac disease diet: a randomized, controlled study. Scandinavian Journal of Gastroenterology, 43(9), pp. 1094–1101. - Lundin, K.E.A. et al., 2003. Oats induced villous atrophy in coeliac disease. Gut, 52 (11), pp. 1649–1652. In recent years, a GFD has become ‘fashionable’ in many societies. Investigate the existence of this ‘fashion’ in your region. Determine the extent to which this trend, if apparent, has a cultural-fashion basis or if it may be associated with valid health and disease reasons. In parallel, investigate the availability of gluten-free foods in your region, considering over-the-counter goods and packaged foods in the local shops.

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Investigate the methods used to determine the amount of gluten in food products and ingredients. Start with the encyclopedia’s articles on the standardization of methods for analyzing grains and Appendix 3, which lists testing methods.

See also: Appendix 3: Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Grains and Health: Misinformation and Misconceptions; Labelling of Grain-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Cereal Allergens; Proteins: The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Catassi C, et al. (1993) Dose dependent effects of protracted ingestion of small amounts of gliadin in coeliac disease children: A clinical and jejunal morphometric study. Gut 34(11): 1515–1519. Catassi C, et al. (1999) Why is coeliac disease endemic in the people of the Sahara? Lancet 354(9179): 647–648. Catassi C, et al. (2013) Non-celiac gluten sensitivity: the new frontier of gluten related disorders. Nutrients 5(10): 3839–3853. Ciacci C, et al. (1999) Low plasma cholesterol: A correlate of nondiagnosed celiac disease in adults with hypochromic anemia. Am. J. Gastroenterol. 94(7): 1888–1891. Dicke WK, Weijers HA, and Van De Kamer JH (1953) Coeliac disease. II. The presence in wheat of a factor having a deleterious effect in cases of coeliac disease. Acta Paediatr. 42(1): 34–42. Dieterich W, et al. (1997) Identification of tissue transglutaminase as the autoantigen of celiac disease. Nat. Med. 3(7): 797–801. Dupont FM, et al. (2011) Deciphering the complexities of the wheat flour proteome using quantitative two-dimensional electrophoresis, three proteases and tandem mass spectrometry. Proc. Natl. Acad. Sci. U. S. A. 9: 10. Ejderhamn J, Veress B, and Strandvik B (1988) The long-term effect of continual ingestion of wheat starch-containing gluten-free products in coeliac patients. In: Kumar PJ (ed.) Coeliac Disease: One Hundred Years, pp. 294–297. Leeds: Leeds University Press. Gasbarrini G and Mangiola F (2014) Wheat-related disorders: a broad spectrum of “evolving” diseases. United Eur. Gastroenterol. J. 2(4): 254–262. Haas SV (1924) The value of banana in the treatment of celiac disease. Arch. Pediatr. Adolesc. Med. 28(4): 421. Hadjivassiliou M, et al. (2003) Dietary treatment of gluten ataxia. J. Neurol. Neurosurg. Psychiatry 74(9): 1221–1224. Hafstro¨m I, et al. (2001) A vegan diet free of gluten improves the signs and symptoms of rheumatoid arthritis: The effects on arthritis correlate with a reduction in antibodies to food antigens. Rheumatology 40(10): 1175–1179. Hager AS, et al. (2012) Investigation of product quality, sensory profile and ultrastructure of breads made from a range of commercial gluten-free flours compared to their wheat counterparts. Eur. Food Res. Technol. 235(2): 333–344. Herfarth HH, et al. (2014) Prevalence of a gluten-free diet and improvement of clinical symptoms in patients with inflammatory bowel diseases. Inflamm. Bowel Dis. 1–4. Junker Y, et al. (2012) Wheat amylase trypsin inhibitors drive intestinal inflammation via activation of toll-like receptor 4. J. Exp. Med. 209(13): 2395–2408. Kasarda DD (1994) Toxic cereal grains in coeliac disease. In: Feighery C and O’Farrelly C (eds.) Proceedings of the 6th International Symposium on Coeliac Disease, pp. 203–220. Dublin: Oak Tree Press. Kasarda DD, et al. (1984) Nucleic acid (cDNA) and amino acid sequences of alpha-type gliadins from wheat (Triticum aestivum). Proc. Natl. Acad. Sci. U. S. A. 81(15): 4712–4716. Kemppainen TA, et al. (2008) Unkilned and large amounts of oats in the coeliac disease diet: a randomized, controlled study. Scand. J. Gastroenterol. 43(9): 1094–1101.

FOOD GRAINS: INTOLERANCE, ALLERGY AND DISEASES | The Gluten-Free Diet Lee AR, et al. (2009) The effect of substituting alternative grains in the diet on the nutritional profile of the gluten-free diet. J. Hum. Nutr. Diet. 22(4): 359–363. Lo W, et al. (2003) Changing presentation of adult celiac disease. Dig. Dis. Sci. 48(2): 395–398. Lundin KEA, et al. (2003) Oats induced villous atrophy in coeliac disease. Gut 52(11): 1649–1652. Miranda J, et al. (2014) Nutritional differences between a gluten-free diet and a diet containing equivalent products with gluten. Plant Foods Hum. Nutr. 69(2): 182–187. Molberg O, et al. (1998) Tissue transglutaminase selectively modifies gliadin peptides that are recognized by gut-derived T cells in celiac disease. Nat. Med. 4(6): 713–717. Osborne TB (1907) The Protein of the Wheat Kernel. Washington, DC: Carnegie Institute of Washington, 84. Pastore MR, et al. (2003) Six months of gluten-free diet do not influence autoantibody titers, but improve insulin secretion in subjects at high risk for type 1 diabetes. J. Clin. Endocrinol. Metabol. 88(1): 162–165. Pengiran Tengah CDSNA, et al. (2004) Multiple sclerosis and occult gluten sensitivity. Neurology 62(12): 2326–2327.

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Peraaho M, et al. (2003) Wheat-starch-based gluten-free products in the treatment of newly detected coeliac disease: prospective and randomized study. Aliment. Pharmacol. Ther. 17(4): 587–594. Schuppan D, Junker Y, and Barisani D (2009) Celiac disease: from pathogenesis to novel therapies. Gastroenterology 137(6): 1912–1933. Shewry PR and Tatham AS (1990) The prolamin storage proteins of cereal seeds: structure and evolution. Biochem. J. 267(1): 1–12. Stern M (2000) Comparative evaluation of serologic tests for celiac disease: a European initiative toward standardization. J. Pediatr. Gastroenterol. Nutr. 31(5): 513–519. Størsrud S, et al. (2003) Adult coeliac patients do tolerate large amounts of oats. Eur. J. Clin. Nutr. 57(1): 163–169. Zanini B, et al. (2013) Impact of gluten-free diet on cardiovascular risk factors. A retrospective analysis in a large cohort of coeliac patients. Dig. Liver Dis. 45(10): 810–815. Zevallos VF, Herencia LI, and Ciclitira PJ (2014) Gastrointestinal effects of eating quinoa (Chenopodium quinoa Willd.) in celiac patients. Am. J. Gastroenterol. 109(2): 270–278.

Proteins

Contents The Protein Chemistry of Cereal Grains The Protein Chemistry of Dicotyledonous Grains Protein Synthesis and Deposition Nitrogen Metabolism Nitrogen in Grain Production Systems The Enzymes Associated with Food Grains and Their Functions in Processing Proteomic Analysis Relevant to Cereal Grains Thiolomics of the Gluten Protein Network of Wheat Dough

The Protein Chemistry of Cereal Grains F Be´ke´s, FBFD PTY LTD, Beecroft, NSW, Australia CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

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Worldwide, plant proteins contribute more than half of our dietary supply of protein. Over 200 million tonnes of protein are harvested each year in the form of cereal grains, based on FAO statistics (http://faostat.fao.org). This protein harvest includes that derived from the three major cereal grains, wheat, rice, and maize, and also less widely grown species: barley, rye, triticale, and sorghum. In some developing countries, a single cereal species may be the major or sole source of protein in the diet. In many countries, cereal proteins enter the diet in various forms, including wheaten breads and pastries, noodles, fried rice dishes, rye crispbreads, cookies, biscuits, pearl barley, pasta, corn tortillas, breakfast cereal, oatmeal porridge, couscous, and many more foods. Most obviously, cereal grain proteins are eaten directly in these many processed forms. The second route is indirect, in the form of animal products, such as meat, milk, and eggs, following the feeding of cereal grains to animals. Whereas the protein part of the grain is important nutritionally, it also serves functional purposes, relevant to the processing of the grain. Of these, wheat and rye are unique because of the dough-forming properties of their storage proteins, known as ‘gluten’ when formed into dough.

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The importance of dietary protein from cereal grains – rice, wheat, maize, and others. The purification of wheat gluten from dough – as an experiment in the kitchen and as a commercial product. The simple structure of proteins – a linear polymer of amino acids – produces the diversity of properties of enzymes, hormones, hair and horn, silk and sinew, and gluten together with the many other grain storage proteins. Folding and cross-linking of the amino acid polymer gives three-dimensional structure that is needed for many protein functions, such as enzymatic activity. Osborne’s solubility-based protein classes: water-soluble albumins, salt-soluble globulins, prolamins extractable with 70% aqueous ethanol, and the residual glutelins. Protein quantity is determined by various methods, especially by near-infrared spectroscopy, based on total nitrogen content. Protein quality relates to its nutritional value and its contribution to functional uses. The specific proteins are described for wheat, rye, triticale, barley, rice, maize, and sorghum.

The Discovery of Protein Structure

Learning Objective

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Cereal Proteins in Prehistory

To achieve an understanding of proteins as critical components of the grains of cereal species and their function for the plants and for our dietary needs.

Historically, the proteins of the cereal grains have played a significant part in the civilization of mankind, through their role in providing a reliable source of amino acids, the essential


http://dx.doi.org/10.1016/B978-0-12-394437-5.00101-7

PROTEINS | The Protein Chemistry of Cereal Grains

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dietary compounds that are the building blocks of proteins in the body. Grains as a source of dietary proteins could be obtained via agriculture, permitting the establishment of a permanent dwelling place, providing an important change from the nomadic existence of the hunter-gatherer way of life. The establishment of permanent towns led, in turn, to specialization of occupation and to opportunities for mankind to pursue cultural pursuits and scientific inquiry. However, it is only in recent centuries that the chemistry of proteins has been elucidated.

Early Concepts The word ‘protein’ was proposed by the French scientist Berzelius, writing to the German scientist Mulder, with the appropriate meaning of ‘primary substance,’ as recently as 1838, long after the acceptance of the terms for specific types of proteins, such as ‘gluten,’ ‘zymom,’ and ‘fibrin.’ Early concepts of protein chemistry imagined it to have the complex formula C20H31N5O6, meaning that 20 molecules of carbon (C) were compounded with 31 molecules of hydrogen, five molecules of nitrogen, and six molecules of oxygen. The dogma of those early days also maintained (incorrectly) that this complex was absorbed (unchanged) directly by the intestine. It is now known that dietary proteins are hydrolyzed to the component amino acids for absorption into the bloodstream.

Wheat Gluten: The First Purified Protein One of the first proteins to be obtained in reasonably pure form was gluten, because it could be prepared so readily (by the washing of dough made from wheat flour). This important experiment, first reported by the Italian scientist Beccari in 1729, can be simply performed in the home kitchen. To do so, a dough is mixed by adding water, a little at a time, to wheat flour until a cohesive mass is formed. This dough is kneaded between the fingers under a gentle stream of water from the tap. If a glass is placed underneath, a milky-white stream of starch can be caught in the glass, while the dough in the fingers becomes smaller and tougher. The gluten ball held in the fingers is mainly protein, separated very simply from the starch that settles at the bottom of the glass. Strictly speaking, gluten is a protein–lipid–carbohydrate complex formed as a result of specific covalent and noncovalent interactions from flour components during dough making as the components are hydrated and energy from mechanical input from the mixing process is provided. This gluten-washing procedure has since become very big business internationally, because the gluten thus isolated is needed for bolstering the protein content of a wide range of food products – bread, especially, and also breakfast cereals, meats, cheeses, snack foods, and texturized products – or consumed directly as ‘seitan.’ Nonfood applications include pet and aquaculture feeds, biodegradable plastics, films, coatings, adhesives, inks, cosmetics, and pharmaceuticals. Late in the nineteenth century, the American scientist Thomas Osborne studied the proteins of many edible grains, using a succession of solvents to extract diverse classes of proteins from the crushed grain. As a result, he proposed the generic names of ‘albumin’ (extracted with water), ‘globulin’ (extracted subsequently by salt solution), ‘prolamin’ (extracted

Figure 1 The cover of one of Osborne’s early publications (1912) on the proteins of cereal grains.

by 70% aqueous ethanol), and ‘glutelin’ (extracted finally by a dilute acid). Subsequently, the prolamins of wheat have been understood to be single polypeptides, whereas wheat glutelins (known as glutenins) have been shown to be disulfide-linked polymers built up of glutenin subunits. The cover of one of Osborne’s famous publications appears in Figure 1. In many cereal grains, the metabolic proteins are albumins and globulins, many of these being the residual enzymes that have functioned in synthesizing the components of the maturing grain, plus others that are present in preparation for germination. On the other hand, the cereal storage proteins are often of the prolamin and glutelin classes; their water insolubility offers the advantage that they will be retained when the grain becomes waterlogged in the germination process. Osborne’s names for these major protein classes have since continued in use, but their definitions have been refined, and it has become clear that any one of these protein classes contains a large number of distinct but related proteins. The modern classification of cereal proteins is based on their genetics, also based on the chromosomal location of their coding genes. The term ‘prolamin’ in this nomenclature system covers all the polypeptides soluble in ethanol, independently whether they exist in the grain in monomeric or polymeric form. In the case of wheat (Figure 2), this prolamin group is subdivided into three

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Wheat proteins

Soluble proteins

Gluten proteins

Monomeric gliadin

Albumins

Globulins

ω gliadins

Polymeric glutenin

LMW

α gliadins β gliadins glutenin subunits γ gliadins

S-poor prolamins

S-rich prolamins

HMW prolamins

HMW glutenin subunits

HMW prolamins S-poor prolamins

HMW glutenin subunits

ω gliadin

γ LMW glutenin subunits

gliadin

β gliadin α gliadin

S-rich prolamins

Figure 2 Classification of the proteins of the wheat grain, showing the electrophoretic patterns for some of them.

groups as sulfur-rich, sulfur-poor, and high-molecular-weight (HMW) prolamins, representing the a-, b-, and g-gliadins plus the low-molecular-weight (LMW) glutenin subunits, the o-gliadins, and finally the HMW glutenin subunits, respectively, in the old classification system.

So What Is a Protein? A protein molecule is simply a linear polymer of amino acids. The structure of protein molecules also depends on the folding and cross-linking of the polymers, giving a three-dimensional structure that is especially important for functions such as enzymatic activity. It is no wonder that these early protein chemists wrestled with reaching this understanding, when we now see that this relatively simple chemical structure can produce the great diversity of properties that are found in proteins, such as enzymes and epidermis, hair and horn, feathers and flagella, silk and sinew, and even spider’s web. The diversity depends on the selection and sequence of the amino acids plus the length of the protein (polypeptide) chain. Further diversity is provided by cross-linking between polypeptide chains and from linking to accompanying molecules (lipids, carbohydrates, or metal ions). The resulting protein molecules are large compared with many biological compounds, with molecular weights often in the range of 10 000–100 000 Da (1 Da being equivalent to the mass of a hydrogen atom). Some proteins are even larger, the largest glutenin proteins of wheat gluten having sizes extending up to tens of millions of Daltons.

There are about 20 different amino acids, each of them having the combination of an acidic group (COOH) and a basic group (NH2) and each having a distinct side chain that provides the functional differences between them all. The amino acids are joined together by peptide bonds to form a polypeptide chain, by the following formula (for two amino acids, R1 and R2): R 1 COOH þ H2 N R 2 ! R 1 CO NH R2 þ H2 O The sequence and specificity of the amino acids are ‘spelled out’ exactly in the genetic code of the genes, thereby ensuring that the protein will be made in the same manner each time in the specific species and tissue. For this reason, the determination of grain protein composition is a valuable means of establishing the identity of a variety within a grain species.

Many Different Cereal Grain Proteins In the past century, we have come a long way from Osborne’s concept of four classes of proteins to realize that within each of his classes, there are a large number of proteins differing in charge and size; this great diversity and heterogeneity can readily be shown by fractionation methods such as gel electrophoresis. Each of the horizontal lines (‘bands’) in the electrophoretic patterns in Figure 3 represents a separate protein component (more than one in many cases). The combination of gel electrophoresis and gel isoelectric focussing as used in proteomics, provides a two-dimensional display of spots (Figure 4), each being a distinct protein (polypeptide, meaning polymer of amino acids).


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Figure 3 Lab-on-a-chip analysis of the composition of prolamin proteins extracted from grains of wheat varieties (L to R: Halberd, Janz, Frame, and Yitpi) and of barley varieties (Excalibur, Sloop, Schooner, Flagship, Gairdner, and Baudin). Each protein extract was applied to a small lab chip for microfluidic capillary electrophoresis. Each analysis took about 50 s. The elution patterns were manipulated to simulate gel electrophoresis patterns.

kDa 130

3

pH

10

10 Figure 4 Proteome map of the polypeptides (reduced proteins) extracted from mature wheat grain (cv “Rosella”). Fractionation involved isoelectric focussing between pH 3 (left) and pH 10 followed by SDS gel electrophoresis in a gradient from 8% (top) to 18% polyacrylamide. After in-gel digestion with trypsin, 315 protein spots (as numbered) were excised and identified by MALDI-TOF and LC–MS/MS. Adapted from Mak, Y., Willows, R. D., Roberts, T. H., Wrigley, C. W., Peter Sharp, P., and Copeland, L., 2009. Germination of wheat: A functional proteomics analysis of the embryo. Cereal Chemistry 86 (3), 281–289.

The diversity of grain protein composition is such that differences in composition can readily be demonstrated between closely related varieties of a grain species. This is evident in Figure 3 where each column of bands represents

Crude protein

Crude fat

Crude fiber

Crude ash

Starch

Cellulose

Figure 5 Chemical composition typical of a whole cereal grain.

the prolamin proteins extracted from grain samples of specific varieties of wheat and of barley. Each of the two sets of varieties has a distinct pattern of bands, while all the wheat patterns differ from all the barley patterns. This type of analysis is thus useful for the identification of varieties in the practical situation of grain delivery when identity must be established to define quality type and royalty payment for distinct varieties.

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Why Is Protein So Important in Grains? The protein component of the grain is critical to the grain’s role as a seed – the beginning of a new plant. The grain protein has the natural purpose to serve as a reserve of amino acids for the embryo (germ) to draw upon during germination, while the roots and shoots are growing until the leaves can support growth and development via photosynthesis. The protein component of the grain is important nutritionally as a source of amino acids, especially the essential amino acids that we cannot synthesize ourselves. The amino acids that are essential include lysine, methionine, leucine, isoleucine, and several more. On the other hand, grain protein is important for the grain processing industry, because it is often the most important part of the grain in determining processing quality and nutritional value. In grain composition, protein is next in abundance after starch Table 1 Approximate protein content of the more common cereal species, as percentages of the ‘as is’ weight of whole grain, except for rice (milled grain) Cereal species

Protein content

Barley Maize (corn) Oats (as groats) Rice (milled) Rye Wheata

9–12 8–12 12–15 8–11 12–15 9–16

a

Durum wheat, a distinct species from common wheat, generally requires a higher protein range, say, 12–16%.

and the fiber components (Figure 5). The protein content of cereal grains ranges from 8% to 15% of the grain weight (Table 1). Even within a grain species, the actual protein concentration may cover a range of values, depending on the genetic potential of a specific variety of that grain species, on the nutritional status of the plant, and on climatic and other environmental factors. Most of the protein is in the grain’s endosperm (the part that becomes white flour after milling the cereal grain), the endosperm being the largest part of the grain by mass. However, the proportion of protein may be higher in some of the non-endosperm tissues of the grain, especially in the germ (the embryo, which will become the new plant after germination). The barley grain is taken as an example of this in Figure 6. Figure 7 shows the chemical composition of wheat grain, with respect to the distribution of protein (and other components) in its various anatomical parts. The importance of protein content is seen in the valuation of grain shipments. The ‘single figure’ of the protein content of a grain sample is an important specification in the marketing of most cereal grains. In general, grain of higher protein content commands a higher value. For wheat, a higher protein content indicates better baking quality, and a higher protein content for feed grains provides a richer supply of essential amino acids (irrespective of the proportion of essential amino acids in their storage protein). However, malting barley is an exception to the rule that high protein content is desirable, because of the need to have a high starch content to provide a correspondingly high extraction of fermentable sugars in the malting process. Nevertheless, even for malting barley, there is a minimum level of protein (8%), to ensure that there is an adequate supply of the hydrolytic enzymes needed throughout the malting process.

Crude protein Crude fat Crude fiber Crude ash Nitrogen-free extract Cellulose

Crude fiber

20

Crude fat

15

Crude protein

5

13.5

4

13.0 12.5

3

12.0

10 2 5

1

0

0 Whole

Pearled

Hulls

11.5 11.0 10.5 Whole

Pearled

Hulls

Figure 6 Chemical composition of the barley grain; distribution between the different parts.

Whole

Pearled

Hulls


12% 2% 60% 2% 6% 2% 2%

% of grain 0 Embryo

Scutellum

50 Pericarp

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Protein Lipids Starch Red. sugars Pentosans Cellulose Ash

Aleurone

100 Endosperm

Protein Lipids Starch Red. sugars Pentosans Cellulose Ash Figure 7 Chemical composition of the wheat grain; distribution between anatomical parts. ‘Red. Sugars’ means reducing sugars, such as glucose.

Table 2 Methods used to determine the protein content of cereal grain, especially wheat Process

Material assayed

Assay method

Grain Flour/meal

NIR NIR

Mill # Wash (for wheat only) # Extract

Gluten

Weight (wet or dry)

Protein in solution

# Hydrolyze

Biuret or dye-binding reaction

Amino acids

Gas or liquid chromatography

Amide N

Titrate ammonia released

Ammonia or nitrogen

Kjeldahl or Dumas method

# Alkaline digestion # Acid digestion

Analysis of Protein Content Today, the routine determination of protein content of all grain species generally involves the use of near-infrared (NIR) spectroscopy, applied to whole grain, milled grain, or flour, based on correlations to total nitrogen analyses (Table 2). In the case of wheat only, protein content can also be determined by washing out the gluten protein and weighing its wet mass. Even though gluten protein is less than 80% of the total grain protein, this approach can be used if appropriate correlations are established between the level of washed gluten and ‘true’ grain protein content. Further possibilities include colorimetric methods (e.g., the biuret reaction) or the amide distillation procedure (Table 2). The standard (‘true’) method for protein determination involves the complete digestion of the grain or flour to its

elements and determination of the proportion of the element nitrogen. This figure is multiplied by 6.25 to obtain the protein content or by a factor of 5.7 in the case of wheat. This procedure assumes that virtually all the nitrogen in the grain is in the form of protein. A lower multiplication factor is used for wheat because its protein contains a high proportion of the amino acid glutamine, giving its protein unusually high nitrogen content (Figure 8). The total nitrogen content is used as an absolute value in establishing correlations for the routine method of NIR spectroscopy to determine the protein content of whole grain or of milled products (Table 2).

Protein Quality The ‘single figure’ of protein content, however, does not take into account the quality of the protein. This quality is indicated for nutritional purposes by analysis of the levels of essential amino acids after hydrolysis of the peptide bonds. For wheat, however, the quality of the protein also relates to the dough strength provided by the particular combination of gluten proteins present, determined partly by the genotype (the variety) and also by the growth conditions. For the animal feed industry, the amino acid composition is especially important, due to the need to ensure an adequate supply of essential amino acids. The protein of cereal grains is a good source of most of the essential amino acids, with the exception of lysine and possibly tryptophan, which are lower in the cereal grains than in most animal proteins. The amino acid composition for wheat is shown in Figure 8, with respect to the major classes of wheat proteins. The amino acid compositions of whole grains of several cereals are compared in Table 3.

Comparison of the Proteins of Cereal Species The various cereal species differ in the composition of their grain proteins. Just as the various cereal species are related

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Albumin

Globulin

Prolamin

Glutenin

Ile Leu Lys Met Cys Phe Tyr Thr Trp Val Arg His Ala Asp Glu Gly Pro Ser NH3 Figure 8 Amino acid composition of the Osborne fractions of wheat.

Table 3 The amino acid compositions of whole grains of several cereals, expressed as grams per 16 g of nitrogen Amino acid

Wheat

Rice

Corn

Barley

Oats

Alanine Arginine Aspartic acid Cysteine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

3.6 4.6 4.9 2.5 29.9 3.9 2.3 3.3 6.7 2.9 1.5 4.5 9.9 4.6 2.9 1.1 3.0 4.4

6.0 8.3 10.3 1.1 20.6 5.0 2.5 3.8 8.2 3.8 2.3 5.2 4.7 5.4 3.9 1.2 3.5 5.5

7.5 4.2 6.3 1.6 18.9 3.7 2.7 3.7 12.5 2.7 1.9 4.9 8.9 5.0 3.6 0.6 3.8 4.8

4.0 4.7 5.7 2.3 23.6 3.9 2.1 3.6 6.7 3.5 1.7 5.1 10.9 4.0 3.3 1.5 3.1 5.0

4.5 6.3 7.7 2.7 20.9 4.7 2.1 3.8 7.3 3.7 1.7 5.0 5.2 4.7 3.3 1.3 3.0 5.1

genetically, these genetic similarities and distinctions are reflected directly in the amino acid sequences of their storage proteins. Both the relevant gene sequences and the corresponding amino acid sequences also reflect the taxonomic relationships among the cereal species, as is illustrated in Figure 9. To a large extent, these differences explain how the storage proteins of the respective cereal grains make their distinct contributions with respect to their food uses. The most obvious example is wheat, whose gluten-forming storage protein is unique among the cereals in suiting wheat flour for bread making. Furthermore, the proteins of the rice grain contribute to its eating quality. The storage proteins of

the cereal endosperm have been given the specific names according to each cereal genus, as listed in Figure 9.

The Proteins of Wheat, Rye, and Triticale Wheat and rye are closely related; triticale is a man-made hybrid between wheat and rye. The genetic control of the storage proteins of these cereals is detailed in the specific articles on wheat, rye, and triticale. Their protein compositions are thus similar to a limited extent, but the dough-forming quality of rye and triticale is much poorer than that of wheat. The popularity of rye-based foods is not so widespread as that of foods made from wheat. Rye is especially popular in Eastern European and Scandinavian countries. Baked products are commonly crispbread and varieties of bread, including pumpernickel. Whereas ‘true’ rye bread is made from 100% rye, it is common for rye bread to be made from a blend of rye and wheat flours, the contribution of the wheat gluten being needed to provide the baking quality that is lacking in the rye flour. The poorer dough-forming characteristics of rye gluten are largely due to the lower level of the glutelin-type protein, combined with the more hydrophilic (water-loving) properties of the rye secalins, compared with the corresponding classes of protein in wheat. The water-soluble proteins of rye contain the albumin and globulin classes of protein, similar to those in wheat, but for rye, there is generally a higher level of amylase enzymes than in wheat because of the greater susceptibility of rye to preharvest sprouting and the consequent production of starch-degrading enzymes. The essential amino acid composition of rye is slightly better than that of wheat, because of the lower content of prolamin-type proteins in rye (Figure 9). The properties of triticale are intermediate between those of rye and wheat, reflecting the genetic origins of triticale.


Globulins

7S

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Prolamins

11/12S

Maize, oats, rice, barley, rye, wheat

Wheat

Oats

7S globulin

T riticin

Globulin

Other prolamins

Rice

Maize

Glutelin

The prolamin superfamily

Sorghum

Maize

Rice

Kaffirin

Oats

Triticeae: barley, wheat, rye

Avenin 16 kDa 10 kDa 13 kDa

-Zein

-Zein

-Zein

-Zein HMW S-rich S-poor

Embryo, aleurone

Endosperm

Figure 9 Storage protein classes in cereals. Adapted from Shewry, P. R., Tatham, A. S., and Halford, N. G., 1999. The prolamins of the Triticeae. In: Shewry, P. R. and Casey, R. (Ed.), Seed Proteins. Kluwer Academic, The Netherlands, pp. 35–78.

Table 4

Classes of barley proteins (hordeins) and corresponding loci

Hordein class

Loci

Gene copy number

Proteins present in the cv ‘Carlsberg’

MW (kDa)

Corresponding wheat prolamin

B C D g

Hor 2 Hor 1 Hor 3 Hor 5

20–30 20–30 1 Low

10 9 1 7

36–45 50–60 105 36–45

LMW glutenins o-Gliadins HMW glutenins g-Gliadins

The Proteins of the Barley Grain The protein concentration of cultivated barley ranges from 9% to 12%. For barley, the protein content is generally calculated as total nitrogen content multiplied by the factor of 6.25. The protein content of hull-less (naked) barley genotypes is generally higher (even up to 18%) because of the absence of the outer hull layers (the glumes – the palea and lemma), which contain relatively little protein. The production of the enzymes of germination is an important part of a good malting barley, but paradoxically, high protein content (e.g., over 11%) is not necessarily desirable for the best malting quality. This is because the ultimate test of malting quality is the extent of ‘extract’ produced during the mashing process. The amount of extract determines how much beer can be produced from a given amount of malt. ‘Extract’ represents the amount of soluble fermentable sugars from the hydrolysis of starch, resulting from the combination of very active amylases and high starch content. For this reason, a low protein content (i.e., less than 8%) is also undesirable, as it may have the consequence of inadequate enzyme production. Consumption for human food is a traditional use of barley, but this now accounts for only 5% of total barley consumption worldwide. Feed use predominates, amounting to 75% of barley use. The amino acid composition of barley does not provide a consistently better balance nutritionally than other

cereal grains, still being deficient in lysine, methionine, and threonine. Nevertheless, it is a popular source of protein and energy in feedstuffs, in combination with other sources of energy. High-lysine barley genotypes have been developed, analogous to those in maize, the first of these being the Hyproly line. The hordein polypeptides show considerable polymorphism, like the prolamins of wheat and rye. A large proportion of the barley prolamins are disulfide-linked (both intra- and interchain linkages) with naturally occurring polymers of high molecular weight. Unlike the glutenin polymers of wheat, these are not desirable for the processing of barley. Because they generate problems in the malting process and downstream, they are likely to produce haze in the final product (i.e., beer) if they have not been adequately hydrolyzed during processing. The hordein polypeptides are classified into groups (A, B, C, and D hordeins) according to their decreasing mobilities during SDS gel electrophoresis. The C hordeins have analogy to the omega-gliadins of wheat, having a general absence of the sulfur-containing amino acids. They are coded by genes (locus Hor 1) on the short arm of barley chromosome 1H, as indicated in Table 4. The genes (Hor 2 and Hor 5) for the sulfur-rich B and gamma-hordeins are also coded on chromosome 1H. The D hordeins, which occur as disulfide-linked polymers, are analogous to the HMV subunits of wheat glutenin; like them,

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their genes (Hor 3) are located on the long arm of the corresponding barley chromosome (1H).

The Proteins of the Rice Grain The proteins of rice are a contrast to those of wheat and barley, being predominantly of the globulin class. As a protein source, milled rice contains the lowest amount of protein (about 5%) among the major cereals. Moreover, this protein is not easily digestible by humans and monogastric animals. However, compared with that of other cereal proteins, the overall amino acid composition of rice protein is significantly more balanced due to the relatively higher level of lysine content. This unusual amino acid composition results because rice is one of the few cultivated plants in which there are significant levels of globulins and prolamins. These are the two major classes of storage proteins in the seeds of higher plants. Unlike other cereals that accumulate prolamins as their primary nitrogen reserve, the major storage proteins in rice are the glutelins, which are homologous at the primary sequence level to the 11S globulin proteins (Figure 9), a class that is the dominant form of nitrogen deposition in legumes. Rice prolamin proteins have a number of characteristics that are different from the prolamins present in most other cereals. The most important characteristic of the deposition of nitrogen in the rice kernel is that there are three kinds of protein bodies in the rice endosperm, namely, large spherical, small spherical, and crystalline protein bodies. Each of these is surrounded by a single continuous membrane. Although the spherical protein bodies form within vacuoles, the proteins are synthesized in the endoplasmic reticulum and in the Golgi apparatus and are then transported to the vacuoles via vesicles. Removal of the husk (hull) from rough (paddy) rice yields the kernel. This is composed of the pericarp, seed coat, aleurone, endosperm, and the germ and is known as ‘brown rice.’ It has a protein content of 9–10%, with a significantly higher nutritional value than the most commonly utilized rice product – white polished (milled) rice, whose protein content is 8%. The milling process for paddy rice results in 40–55% white milled rice, together with three major by-products, namely, husks (20%), bran (10%), and brokens (10–22%). These byproducts have protein contents of 3%, 17%, and 9%, respectively. The aleurone layer, the tissue with the highest level of proteins and nutritionally important minor components, is removed during the rice milling process. The subaleurone region of the rice grain plays an important part because of its nutritional value. It is a globulin-rich layer, being several cell layers thick. Its lysine content is much higher than that of the proteins located in the rice endosperm. Thus, rice should be milled as lightly as possible to retain as much as possible the subaleurone layer. The albumin fraction of rice is highly heterogeneous, containing biologically important components. It can be separated into four subfractions, based on the molecular size of its proteins. More than 50 individual polypeptides were observed in the albumin fraction, using isoelectric focussing. As for cereal grains in general, the albumins are mainly enzymes and enzyme inhibitors.

Like the prolamins from other cereals, rice prolamins are readily soluble only in alcohol/water mixtures. However, the classical extraction procedure had not been useful in early studies. More recently, these estimates of prolamin content have been shown to be low. Using 55% propan-L-ol and reducing agents, higher yields of prolamins (20–25% of the total protein) have been obtained. Rice prolamins are 10–16 kDa in molecular weight. Thus, their molecular size range is significantly smaller than the prolamins of other cereals. They are highly variable between rice cultivars, based on their electrophoretic and isoelectric focussing fingerprints. According to the Osborne classification system, the least soluble proteins of the rice grain are oligomeric globulins representing up to 80% of the total protein fraction (Figure 9). They have been difficult to study because of their general insolubility in all solvents except dilute alkali, due to their high molecular weight and their heterogeneity. When analyzed by gel filtration chromatography, the purified globulin subunits were resolved into three subunits, linked by disulfide bonds, which varied in stoichiometry depending on the report and on the rice variety used. Despite their general insolubility, rice glutelins are homologous in structure to 11S globulins (Figure 9). The structural relationship is evident when comparing the N-terminal amino acid sequences and using immunologic methods. The extent of homology between the rice glutelin and legume 11S globulins is 30–35%. Structural similarity is evident in the primary sequences of homology to a motif common in wheat, rye, barley, and maize prolamins.

The Proteins of Maize Maize (or corn), often classed in world trade as one of the ‘coarse’ grains, is an important source of protein in the diets of many people in countries such as Africa and South America. In addition, maize is used extensively as a feed grain and in a range of industrial processes. The process of corn starch manufacture produces the grain protein as a by-product. It is sometimes referred to as ‘corn gluten’ in the trade, but this name is inappropriate, because maize protein has no relationship to the gluten of wheat and is safe for consumption by those susceptible to celiac disease. Like the other cereal grains, maize protein is slightly deficient in lysine. This limits its utilization as an animal feed. This nutritional imbalance is largely due to the low lysine content of ‘zein,’ the major group of maize proteins (Figure 9). The development of the ‘opaque-2’ and ‘floury-2’ mutations has led to the development of maize genotypes with higher levels of lysine, due to a lower content of zein and more of the nutritionally superior albumin type of protein. Although these new maize types offer nutritional advantages, they carry a grain yield penalty. The zein protein of maize can be isolated by extraction of the crushed endosperm (the starchy part of the grain) with 70% aqueous ethanol, after breaking disulfide bonds. Maize zein has been further fractionated into subclasses of proteins, designated alpha-, beta-, gamma-, and delta-zeins. The genes for their synthesis have been mapped to maize chromosomes 6 and 7.


The Proteins of Sorghum


The major storage proteins of sorghum, termed ‘kafirins’ (Figure 9), are fractionated by a procedure similar to that for the zeins of maize. Alpha-kafirin, composing about 80% of the overall kafirin content, can be further subdivided into two proteins with molecular weights of about 23 000 and 25 000 Da. Three beta-kafirins and one gamma-kafirin have been identified, all of them having molecular weights in the range of 16–28 kDa. Like maize, high-lysine mutants of sorghum have been developed.

• • • •

Future Prospects Our current understanding of grain protein chemistry contrasts strongly with the rudimentary knowledge of the early twentieth century. That knowledge has progressed from the recognition of only a few distinct grain proteins to fractionating and characterizing thousands of proteins from all the tissues of the cereal grain – the endosperm, germ, scutellum, and bran. This knowledge permits more efficient selection for improved processing quality in the breeding of new varieties. The knowledge is also being applied to testing for protein quality after the grain is harvested, so that grains of specific quality can be segregated for appropriate marketing and processing. Knowledge at the chemical level is now complementing new genetic insights, so that breeders and molecular geneticists can employ conventional and novel methods to create quality types that have previously not been possible – varieties with new protein functionality. Thus, the future holds great promise for grains that will be processed more efficiently with nutritional advantages. For example, it has been possible to incorporate purified gluten proteins into rice dough, thus to monitor their effects on the mixing properties. The protein content of the cereal grains has always been important for marketing and processing. The generally desirable trait of high-protein concentration has often been inversely proportional to grain yield. Improvements in genetics and agronomic practice have tended to reduce grain protein levels, because high yield has been a common goal for farmers. The coming decades will bring a new factor that will further erode protein levels – the rising concentrations of carbon dioxide in the atmosphere. For whatever reason, it is inevitable that CO2 levels will continue to rise, although the rate of increase is difficult to predict. Many experiments have been conducted to simulate effects of future levels of CO2. They have consistently indicated increased yields of grain and biomass, together with decreased levels of grain protein content. The higher atmospheric concentration of CO2 acts as a carbon fertilizer, with consequent increases in starch synthesis but little change in protein synthesis. There will thus be a need to rethink the role of protein in cereal grains if it will gradually become lower in concentration. At the manufacturing level, there is increasing interest in providing greater protein content for cereal-based snacks and breakfast foods. Cereal proteins are also undergoing texturization and extrusion with the aim of creating synthetic meat products.

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How did the early chemists’ views on protein chemistry differ from our present knowledge? Why were they unaware of the great heterogeneity of grain proteins? What are the aspects of protein composition that explain the great differences between the various proteins in their properties? Prepare a table of differences and similarities between the major cereal species with respect to their protein compositions. What are the nutritional deficiencies of cereal grain proteins with respect to the essential amino acids? Describe the genetic achievements that have partially overcome these deficiencies.


•

•

•

•

Examine the taxonomic relationships between the major cereal species, as provided in this encyclopedia. Compare the associations between the proteins of these grains in Figure 8. Look at the genus names to see the origins of the grain-specific protein names. Obtain the amino acid compositions of the grain proteins for the major cereals. What are the main differences? How would these differences account for functional and nutritional differences between these grain species? Contrast the differences in function for an enzyme (to catalyze a specific reaction) versus a storage protein (a source of amino acids for the new plant). Why would both types of protein be produced under the same strict genetic control? Compare the various methods of determining the amount of protein in a grain or flour sample (Table 2 and elsewhere). Which would you expect to be the most accurate?

See also: Genetics of Grains: Maize: Other Maize Mutants; Maize: Quality Protein Maize; Grain Marketing and Grading: Identification of Varieties of Food Grains; Proteins: Protein Synthesis and Deposition; Proteomic Analysis Relevant to Cereal Grains; The Enzymes Associated with Food Grains and Their Functions in Processing; The Basics: Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Bailey HC (1941) A translation of Beccari’s lecture “Concerning Grain” (1729). Cereal Chem. 18: 555. Bushuk W (ed.) (2001) Rye: Production, Chemistry and Technology, second ed. St. Paul, MN: American Association of Cereal Chemists. Dendy DAV (ed.) (1995) Sorghum and Millets: Chemistry and Technology St. Paul, MN: American Association of Cereal Chemists. Hartley H (1951) Origin of the word protein. Nature 168: 244. Henry RJ and Kettlewell PS (1996) Cereal Grain Quality. London: Chapman and Hall. Islam S, Ma W, Yan G, Be´ke´s F, and Appels R (2011) Modifying processing and health attributes of wheat bread through changes in composition, genetics and breeding.

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In: Cauvain SP (ed.) Bread making. Improving quality, second ed. Boston, New York: CRC Press. Juhasz A, Bekes F, and Wrigley CW (2014) Wheat proteins. In: Ustunol Z (ed.) Applied Food Protein Chemistry, Chapter 11, pp. 219–304. West Sussex, UK: Wiley-Blackwell, John Wiley & Sons. Juliano BO (ed.) (1985) Rice: Chemistry and Technology, second ed. St. Paul, MN: American Association of Cereal Chemists. Kent NL (1975) Technology of Cereals, with Special Reference to Wheat, second ed. Oxford, UK: Pergamon. Lasztity R (1999) Cereal Chemistry. Budapest, Hungary: Akade´miai Ko¨nyvkiado´. McGregor AW and Bhatty RS (eds.) (1993) Barley: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Mertz ET (ed.) (1992) Quality Protein Maize. St. Paul, MN: AACC International. Pomeranz Y (ed.) (1988) Wheat: Chemistry and Technology, third ed. St. Paul, MN: American Association of Cereal Chemists. Seneweera S, Fernando N, Panozzo J, Tausz M, Norton RM, Fitzgerald GJ, Myers S, and Nicolas ME (2014) Intra-specific variation of wheat grain quality in response to elevated [CO2] at two sowing times under rain-fed and irrigation treatments. J. Cereal Sci. 59(2): 137–144. Shewry PR and Casey R (eds.). (1999) Seed Proteins. The Netherlands: Kluwer Academic.

Shewry PR and Miflin BO (1985) Seed storage proteins. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology vol. 7, pp. 1–83. St. Paul, MN: American Association of Cereal Chemists. Sikorski ZE (2001) The Chemical and Functional Properties of Food Proteins. Lancaster, PA: Technomic Publishing. Watson SA and Ramsted PE (eds.) (1987) Corn: Chemistry and Technology St. Paul, MN: American Association of Cereal Chemists. Webster FH (ed.) (1985) Oats: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW (2012) Proteins – the basis of life. Teach. Sci. 58: 56–59. Wrigley CW and Batey IL (eds.) (2010) Cereal Grains: Assessing and Managing Quality Oxford, UK: Woodhead Publishing Ltd.

Relevant Websites http://www.aaccnet.org – American Association of Cereal Chemists. http://www.campden.co.uk – Campden & Chorleywood Food Research Association. http://www.icc.or.at – International Association for Cereal Science and Technology. http://www.usda.gov – United States Department of Agriculture. http://www.wheat.pw.usda.gov – Grain genes.

The Protein Chemistry of Dicotyledonous Grains PR Shewry, Rothamsted Research, Harpenden, UK; University of Reading, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

The major types of storage proteins present in seeds of dicotyledonous (noncereal) crops are globulins and albumins. Two types of storage globulin are recognized with sedimentation coefficient S20,w values of 7 and 11. 7S and 11S globulins have related structures and belong to the ‘cupin’ superfamily of plant proteins. 2S albumin storage proteins are related to other types of small sulfur-rich proteins and belong to the ‘prolamin’ superfamily, which includes cereal seed storage proteins.

Learning Objectives

•

To understand storage protein composition and properties in dicotyledonous crops in relation to evolutionary relationships and biological roles.

Introduction The protein contents of dicotyledonous grain crops vary widely, from less than 20% of the dry weight in the pseudocereals to 50% in some lines of soybean (Table 1). Extraction and separation of ‘total’ protein fractions show that all comprise highly complex mixtures, with many components being present in small amounts. However, in all cases, a small number of components are present in substantial amounts: these correspond to the seed storage proteins and usually account for half or more of the total seed proteins. Although specialized storage protein types occur in some species, for example, lectins in some legume seeds, most of the storage proteins present in dicotyledonous seeds fall into three groups, which are defined on their solubility and S20,w values (sedimentation coefficients determined by sedimentation equilibrium ultracentrifugation), which are a measure of their molecular masses. The characteristics of these three types of proteins are discussed, followed by brief descriptions of the storage proteins present in the major dicotyledonous species covered in this encyclopedia.

Types of Storage Protein

7S globulins 7S globulins typically have molecular masses of 150–200 kDa and have a trimeric structure comprising three nonidentical subunits of mass 50–70 kDa. The subunits contain no cysteine residues and hence do not form disulfide bonds, and noncovalent forces stabilize the trimeric proteins. However, this simple structure may be modified after protein synthesis in two ways. First, glycosylation (addition of oligosaccharides) may occur on one or two asparagine residues in one or more subunits of the trimer. This results in an increase in mass of the subunits and lower mobility when separated by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) with partial glycosylation resulting in additional heterogeneity. Second, in some species (e.g., pea and field bean), some, but not all, 7S globulin subunits are proteolytically processed at one or two sites, giving rise to polypeptide chains ranging in mass from processed products of 12 kDa in pea and 18 kDa in bean to unprocessed subunits of 50 kDa. The processed products remain associated in the trimeric complexes until released by denaturation. The role of this proteolytic processing is not known and it does not occur in some species such as soybean and common or navy bean (Phaseolus vulgaris). Although typically trimeric in structure, the 7S globulins may undergo reversible aggregation into hexamers depending on ionic strength.

11S globulins

Globulins Globulins are defined as proteins that are soluble in dilute salt solutions, usually taken as 0.5–1.0 M NaCl. Storage globulins with S20,w values of 7 and 11 are widely distributed in dicotyledonous plants. However, they have been most widely studied from legume seeds. Hence, 7S globulins are sometimes called vicilins after the Viciae tribe of legumes, and 11S


globulins are called legumins after the family Leguminosae. The individual types of 7S and 11S globulins in different crops are also often given specific trivial names, as listed in Table 1. It has long been recognized that members of these two protein groups also vary in their precise S20,w values, with legumin-like globulins often having values of 12 or more (e.g., the 13S lupin globulin) and vicilin-like globulins 8 (e.g., in peanut). Furthermore, not all 11S globulins are readily soluble in dilute saline, with notable exceptions being 11S storage globulins of cereals, which are either insoluble in saline (rice) or only soluble at higher concentrations (0.8–1.0 M) of NaCl (oats). Consequently, the term 11S is used in this article to describe storage proteins with a legumin-like structure and the term 7S to describe vicilin-like proteins.

11S globulins typically have masses of 300–400 kDa and are hexamers of six nonidentical subunits. Each subunit is synthesized as a precursor protein that is proteolytically processed to release acidic (also called A or a) and basic (B or b) polypeptide chains, which correspond to the N-terminal and C-terminal parts of the precursor protein, respectively. The masses of the acidic chains vary in the range of 20–60 kDa but are typically

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PROTEINS | The Protein Chemistry of Dicotyledonous Grains

Table 1 Protein contents and types of storage proteins in major legume, oilseed, and pseudocereal crops Species

Protein content (% DW)a

Legumes Soybean

30–40

Pea

25

Peanut

16–36

Lupin

26–42

Oilseeds Oilseed rape/ canola Linseed/ linola Sunflower Safflower Cottonseed

36–44

12S glycinin, 7S b-conglycinin, 2S albumin 12S legumin, 7S vicilin/convicilin 2S PA1 13S arachin, 8S conarachin, 2S albumin 11–12S conglutin a, 7S conglutin b, 2S conglutin d 12S cruciferin, 2S napin

20–24

12S globulin

15–20 15 16–22

12S helianthinin, 2S albumin 12S carmin, 2S albumin 11S globulin, 7S globulin, 2S albumin

Pseudocereals Quinoa 15 Amaranth 13–18 Buckwheat

Storage proteins

13.5

11S chenopodin, 2S albumin 13S amaranthin, 8S conamaranthin, 2S albumin 11S globulin, 8S globulin, 2S albumin

The S20,w values listed are only approximate with a range of values having been reported for some components. a % Dry weight.

Table 2 Polypeptide molecular masses (Mr 103) of 7S and 11S globulins present in species

Legumes Soybean Pea Peanut Lupin Oilseeds Oilseed rape/ canola Sunflower Pseudocereals Quinoa Amaranth Buckwheat

7S

11S acidic chain

11S basic chain

50, 80 12–50, 70 23–75 15–60

10–40 25–40

20 21–22

14–48 25–63

21 21

30–40

20

32–34

22–27

32–39 30–37 32–43

22–23 18–27 20–23

15–90 16–66

The terms 7S and 11S refer to vicilin-like and legumin-like proteins, respectively, and do not imply that all of the proteins listed have these precise S20,w values. In fact, the true values vary ( 7–8S and 11–13S, respectively). It should also be noted that widely different values for polypeptide masses have been reported and those presented here have been selected by the author. The 7S polypeptides include whole subunits and chains released by proteolysis. The acidic and basic 11S chains are generated by proteolysis of a single precursor subunit.

Slime molds

Plants

Prokaryotic protogermin protein

Spherulins

40 kDa, while the basic chains usually have masses of 20 kDa. Thus, a typical 11S globulin comprises six subunits of mass 60 kDa, each consisting of 40 and 20 kDa polypeptide chains. The basic and acidic chains are covalently linked by a single disulfide bond formed in the precursor protein. Whereas the 7S globulins are rapidly assembled into their mature trimeric structure, the 11S globulin precursors are not immediately assembled into their mature hexameric structure but into an intermediate trimer with the hexamer forming only after proteolytic processing occurs to release the basic and acidic chains. The polypeptide (i.e., subunit and chain) masses of the 7S and 11S globulins discussed in the succeeding text are summarized in Table 2.

Structures of 7S and 11S Globulins Simple comparisons of the amino acid sequences of 7S and 11S globulins show little or no evidence of homology, but more sophisticated comparisons (in which the properties of the amino acids and their propensity to form similar structures are also considered) do indicate some relatedness, particularly between the C-terminal parts of the 7S subunit and the basic chains of 11S subunits. Similar comparisons also show internal homology between the N- and C-terminal parts of the 7S subunits. These observations, and the more detailed structural comparisons discussed in the succeeding text, indicate that the 7S and 11S globulin subunits have evolved from a single

Duplicated ancestor

Germins- and germin-like proteins

Fern vicilin-like protein

acidic

basic

11S globulins (legumins)

N C 7S globulins (vicilins)

Figure 1 Hypothetical pathway for the evolution of germins and globulin storage proteins from an ancestral ‘protogermin’ protein. Reproduced with permission from Shewry, P.R., Jenkins, J., Beaudoin, F., Mills, E.N.C., 2003. The classification, functions and evolutionary relationships of plant proteins in relation to food allergens. In: Mills, E.N.C., Shewry, P.R. (Eds.), Plant Food Allergens. Blackwell Science, Oxford, UK.

ancestral protein that initially underwent a duplication to give two homologous domains, which diverged to form the 7S N-terminus/11S basic chain and 7S C-terminus/11S acidic chain, as shown in Figure 1. Comparisons of the three-dimensional structures of 7S globulin trimers (phaseolin from common bean, canavalin from jack bean, and b-conglycinin from soybean) and the intermediate trimer of proglycinin (the 11S globulin of


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α-Helical domain 2

α-Helical domain 4 Domain 3 Domain 1

Figure 2 Structure of the 7S globulin canavalin from jack bean (Canavalia ensiformis) seeds. The protein is trimeric, with a single subunit shown in lighter gray. Domains 1 and 3 are b-barrels and domains 2 and 4 a-helical. Reproduced with permission from Shewry, P.R., Jenkins, J., Beaudoin, F., Mills, E.N.C., 2003. The classification, functions and evolutionary relationships of plant proteins in relation to food allergens. In: Mills, E.N.C., Shewry, P.R. (Eds.), Plant Food Allergens. Blackwell Science, Oxford, UK.

soybean) confirm this scheme and show remarkable conservation of structure. Each protein consists of three subunits arranged around a threefold axis (Figure 2), with each subunit consisting of two closely related structural modules and each comprising an antiparallel b-barrel domain and an a-helical domain. The subunits of 7S and 11S globulins have similar structures, as shown by the overlay in Figure 3, and the mature hexameric 11S globulin protein is considered to be a ‘dimer of trimers.’ The similarity in the structures of the 7S and 11S globulins is consistent with the observation that both proteins can exist in trimeric forms (the mature 7S and intermediate 11S globulins) and in hexameric forms (the mature 11S globulins and the mature 7S globulins under specific conditions). It is also consistent with the fact that the 7S and 11S proteins appear to be stored as a homogeneous mixture in protein bodies in seeds of legumes and other dicotyledonous species. A final point of interest is that both 11S and 7S globulins may be allergenic, notably in soybean and peanut.

Albumins Albumins are defined as proteins that are soluble in water. Consequently, albumin fractions extracted from most plant tissues comprise complex mixtures of largely unrelated components. However, the seeds of many dicotyledonous plants

contain a well-defined family of albumin storage proteins with S20,w values of 2. These ‘2S albumins’ are major storage proteins in a number of dicotyledonous crops (e.g., oilseed rape/ canola and sunflower) and minor components in others (e.g., soybean). Although they have not yet been identified in some dicotyledonous crops, this may reflect lack of study rather than true absence, and they may well prove to be ubiquitous in dicotyledonous seeds. A preliminary report of the presence of 2S albumin storage protein in seeds of one monocotyledonous species (yucca) has not been confirmed by more detailed studies, but they are known to be structurally related to several other families of low-molecular-mass sulfur-rich proteins including nonspecific lipid transfer proteins and trypsin/aamylase inhibitors of cereal grain. A typical 2S albumin consists of two subunits of Mr 8–10 kDa and 4–5 kDa, which are associated by two disulfide bonds. However, these two subunits are initially synthesized as a single precursor polypeptide, and hence, by analogy with 7S and 11S storage globulins, they should perhaps be called polypeptide chains. Nevertheless, the term subunit is widely used and will be retained here. The proteolytic processing to release the 2S albumin subunits may result in the loss of short peptide sequences from the N- and C-termini of the proteins and from between the two subunits (‘linker’ peptides). Furthermore, this proteolysis only occurs after the proproteins are folded and four disulfide

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Figure 3 Overlay of the backbone structures of single subunits of proglycinin (11S globulin precursor) from soybean (black) and phaseolin (7S globulin) of bean (gray). Reproduced with permission from Shewry, P.R., Jenkins, J., Beaudoin, F., Mills, E.N.C., 2003. The classification, functions and evolutionary relationships of plant proteins in relation to food allergens. In: Mills, E.N.C., Shewry, P.R. (Eds.), Plant Food Allergens. Blackwell Science, Oxford, UK.

Signal peptide removed cotranslationally −21 NH2 S

157 A

B

Small subunit N-terminal prosequence

C

COOH

Large subunit C-terminal prosequence

Linker peptide Peptides removed by proteolysis in vacuole

Figure 4 Schematic sequence of the precursor protein of napin (the 2S albumin of oilseed rape) indicating peptides removed by proteolysis and the large and small subunits of the mature protein.

bonds formed between eight highly conserved cysteine residues. Two of these become interchain bonds linking the two subunits and two intrachain bonds within the large subunits. This processing is shown schematically in Figure 4. The mature proteins have a compact tightly folded structure comprising five a-helices in a right-handed fold (Figure 5). The vast majority of 2S albumins have two-chain structures similar to that described earlier. However, single-chain forms (i.e., without proteolytic processing into two chains) also occur, notably in sunflower. Of particular interest in relation to grain nutritional quality is the presence in some species of 2S albumins that are rich in methionine or, less commonly, cysteine, the two sulfurcontaining amino acids that are frequently limiting in legume and other dicotyledonous seeds. These albumins have been studied in most detail in Brazil nut and sunflower. Although they were initially considered to provide an attractive target for use in genetic engineering to increase seed sulfur content, it is now known that both are allergenic, as are 2S albumins from a number of other species (e.g., mustards, castor bean, walnut, sesame seeds, and peanut).

Figure 5 Schematic structure of the 2S albumin from oilseed rape. Alpha helices are shown as cylinders and numbered 1–5. Reproduced with permission from Shewry, P.R., Jenkins, J., Beaudoin, F., Mills, E.N.C., 2003. The classification, functions and evolutionary relationships of plant proteins in relation to food allergens. In: Mills, E.N.C., Shewry, P.R. (Eds.), Plant Food Allergens. Blackwell Science, Oxford, UK.

PROTEINS | The Protein Chemistry of Dicotyledonous Grains Storage Proteins of Legumes Many leguminous species store 7S globulin, 11S globulin, and 2S albumin proteins, but the proportions of these vary and exceptions do occur. For example, Phaseolus contains 7S but not 11S globulins. Additional types of storage protein also occur in some species, including various lectins and protease inhibitors, which can have negative impacts on nutritional quality. Soybean is the most widely studied legume species. It contains major groups of 11S (glycinin) and 7S (b-conglycinin) globulins, in ratios ranging from 1:1 to 6:1 depending on the genotype, with only small amounts of 2S albumins. In addition, a number of other proteins can each account for up to 5% of the total protein in some lines, notably Kunitzand Bowman–Birk-type protease inhibitors, lectins, urease, and lipoxygenase. Sedimentation coefficients and masses for glycinin have been reported to range from 11.8S to 13.1S and from 30 to 380 kDa and for b-conglycinin from 6.7S to 8.0S and from 105 to 330 kDa. Glycinin has a typical hexameric 11S globulin structure, with subunits comprising basic chains of Mr 20 kDa linked to acidic chains varying in mass from 10 to 40 kDa. Glycinin is also unusual in that the hexamer can undergo reversible dissociation into trimers, depending on the ionic strength. b-Conglycinin comprises various combinations of three major subunits – a (Mr 80 kDa), a0 (Mr 80 kDa), and b (Mr 50 kDa) – resulting in seven major forms. Both 7S and 12S globulins of soybean are also thought to be allergenic. Pea seeds contain legumins (12S to 13S, Mr 330–420 kDa) and vicilins (7S to 8S, Mr 150–190 kDa). The legumin subunits consist of acidic chains of Mr 25 kDa and 40 kDa linked to basic chains of Mr 20 kDa. The 7S vicilins comprise subunits of Mr 50 kDa, but proteolysis at one or two sites and glycosylation at a single site may occur, resulting in polypeptide chains varying in Mr (12–50 kDa). Larger subunits of Mr 70 kDa also occur, which form a second trimeric 7S protein called convicilin. Pea seeds also contain two major albumins, PA1 and PA2, of which the former may be a 2S storage albumin. PA1 accounts for 10% of the total seed protein but half of the total sulfur, in the form of cysteine ( 11 mol.%). The dominant peanut proteins are arachin (13S–14S, Mr 330–400 kDa) and conarachin (8S to 9S, Mr 140–190 kDa). The subunits of arachin comprise acidic chains of Mr 14–48 kDa linked to basic chains of Mr 21.4 kDa, whereas conarachin comprises polypeptide chains ranging in Mr from 23 to 75 kDa. It is probable that both large and typical conarachin subunits are present, as in soybean and pea, with proteolytic processing contributing to the polymorphism. Both proteins also exhibit complex association/dissociation behavior, depending on the ionic strength. The major peanut allergen Ara h 1 is a glycosylated 7S globulin with Mr 63.5 kDa, whereas Ara h 3 is an 11S globulin. Most of the knowledge of peanut albumins comes from the analysis of genomic clones and is related to their role as allergens (Ara h 2, 4, 6, and 7). They show high homology to 2S albumins from other legumes (soybean and lupin) and are presumed to have a typical heterodimeric structure. The salt-soluble (i.e., albumin and globulin) proteins of lupins are called conglutins. The major component is usually

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the 7S conglutin b, with slightly less conglutin a (11S globulin) and 25% of the 2S albumin conglutin d. Conglutin a has a mass of 336 kDa and readily dissociates to a trimeric form (7.1S, Mr 170 kDa) at low ionic strength or high pH (8.8). It comprises acidic chain varying in Mr (within and between species) from 25 to 63 kDa linked to basic chains of Mr 21 kDa. Conglutin a is unusual among 11S legumintype globulins in that it is glycosylated on a single site. Conglutin b comprises polypeptides that range in mass between and within species from 15 to 60 kDa. Little detailed work has been carried out on the other legumes/pulses discussed in this article. Both chickpea and lentil contain 11S and 7S storage globulins (in a ratio of 6:1 in chickpea). In addition, chickpea contains a major albumin of Mr 20 kDa, which comprises subunits with Mr 10 and 12 kDa. Adzuki bean is rich in 7S globulins with major components of Mr 55 kDa, but small amounts of 11S globulins and 2S albumins are also present.

Storage Proteins of Oilseeds The two most intensively studied oilseeds are sunflower and oilseed rape (canola). Both contain predominantly 11S-type globulins with some 2S albumins. The 12S globulins (cruciferin) of oilseed rape account for 40% of the total seed proteins and have Mr of 30–360 kDa. They have a typical hexameric structure with acidic chains of Mr 30–40 kDa linked to basic chains of Mr 20 kDa. The 2S albumins of oilseed rape (napins) also have a typical structure. The major napins have masses of 14.5 kDa (subunit Mr of 9 and 4 kDa) but minor forms of Mr 12.5 kDa also occur. Napin processing includes the loss of N-terminal, C-terminal, and linker peptides, as discussed earlier. Sunflower, a member of the family Compositae, contains 12S globulins (helianthinin) and 2S albumins in a ratio of 2:1. The Mr 300 kDa helianthinin comprises acidic chains of Mr 32–34 kDa (a and a0 chains) linked to basic chains of Mr 22–27 kDa (b chains). Sunflower 2S albumins comprise 11–13 components with masses of 10–18 kDa. All are singlechain proteins (i.e., they lack a proteolytic cleavage site between the putative large and small subunits), but most are synthesized as pairs, two albumins being released from a single precursor protein by proteolysis. One sunflower albumin that is synthesized from a separate precursor protein is called SFA8. This contains 16 methionine and 8 cysteine residues in a mature protein of 103 residues (i.e., a total of 23 mol.% of sulfur-containing amino acids). Safflower, a related member of the family Compositae, also appears to contain major groups of 12S globulin (called carmin) and 2S albumin storage proteins, but little detailed work has been carried out. Cottonseed is unusual among nonleguminous dicotyledonous species in containing 7S globulin storage proteins as well as 11S globulins and 2S albumins, with most of the knowledge being based on DNA-derived sequences with little direct analysis of the seed proteins. Linseed (and linola) has not been widely studied but the major seed protein is reported to be a 12.7S globulin of Mr 250–300 kDa. SDS-PAGE showed six nonidentical subunits.

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Storage Proteins of Pseudocereals Pseudocereals are not true cereals but three dicotyledonous crops that produce small grain-like seeds. Consequently, their seed proteins are similar to those of other dicotyledonous plants rather than related to cereal seed storage proteins. Seeds of amaranth (Amaranthus spp., Amaranthaceae) contain 13S legumin-type globulins (amaranthin) and 8S vicilin-type globulins (S20,w value of 8.6) (conamaranthin). In addition, albumin proteins with S20,w values of 2 are present, with SDS-PAGE showing major bands of Mr 9 kDa and 4 kDa. This is consistent with the presence of typical 2S albumins. Two methionine-rich proteins with Mr 18 kDa have also been reported. Quinoa (Chenopodium quinoa, Chenopodiaceae) seeds also contain 11S globulins (chenopodin), of Mr 320 kDa, and 2S albumins, the latter being rich in cysteine (15.6 mol.%) but low in methionine. In buckwheat (Fagopyrum esculentum, Polygonaceae), the major 13S legumin-like globulin is located in the cotyledons with smaller amounts of putative 8S globulins in the perisperm. Methionine-rich ( 9 mol.%) 2S storage albumins are also present.

Conclusions The 2S albumins, 7S globulins, and 11S globulins are major groups of storage proteins that are widely distributed in seeds of dicotyledonous plants, although their relative amounts vary and other types of storage proteins also occur in some species. Consequently, they largely determine the nutritional quality and processing properties of the seeds. A detailed knowledge of their structures and properties is therefore essential in order to elucidate structure–function relationships. This will facilitate the optimization of seed quality for traditional and novel products with improvement using classical genetic or genetic engineering approaches.


•

Compare the structures and properties of albumin and globulin storage proteins.

• •

Compare the contents of albumin and globulin storage proteins in the major types of dicotyledonous crops: legumes and pulses, oilseeds, and pseudocereals. What are the relationships of albumin and globulin storage proteins to other grain proteins?


• •

How do the structures and compositions of storage proteins determine the functional properties of the seeds for food processing and their role in the human diet? How can these structures and properties be manipulated (by breeding or GM technology) to improve their quality for nutrition and processing and to reduce adverse reactions in humans (allergies and intolerances)?

See also: Oilseed and Legume Processing: Canola: Processing; Soybean: Soy Concentrates and Isolates; Proteins: Protein Synthesis and Deposition; The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Legumes and Pseudocereals: Amaranth: Overview; Beans: Overview; Buckwheat: Overview; Chickpea: Overview; Lupin: Overview; Pea: Overview; Pseudocereals: Overview; Quinoa: Overview; The Oilseeds: Oilseeds: Overview; Sunflower: Overview; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Pulses, Overview.

Further Reading Bewley JD and Black M (1999) Seeds Physiology of Development and Germination. New York: Plenum. Black M and Bewley JD (2000) Seed Technology and its Biological Basis. Sheffield: Academic Press. Boulter D and Croy RRD (1997) The structure and biosynthesis of legume seed storage proteins: a biological solution to the storage of nitrogen in seeds. Adv. Bot. Res. 27: 1–84. Salunkhe DK, Chavan JK, Adsule RN, and Kadam SS (1992) World Oilseeds Chemistry, Technology, and Utilisation. New York: Van Nostrand Reinhold. Shewry PR (1995) Plant storage proteins. Biol. Rev. 70: 375–426. Shewry PR and Casey R (eds.) (1999) Seed Proteins. Dordrecht: Kluwer. Shewry PR, Jenkins J, Beaudoin F, and Mills ENC (2003) The classification, functions and evolutionary relationships of plant proteins in relation to food allergens. In: Mills ENC and Shewry PR (eds.) Plant Food Allergens. Oxford: Blackwell Science.

Protein Synthesis and Deposition PR Shewry, Rothamsted Research, Harpenden, UK; University of Reading, Reading, UK P Tosi, University of Reading, Reading, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

Synthesis, Folding, Processing, and Deposition of Seed Storage Protein

Seed storage proteins are synthesized on the endoplasmic reticulum (ER) and cotranslationally transported into the lumen. Protein folding, assembly, and posttranslational modifications occur in compartments of the endomembrane system: the ER, Golgi apparatus, and vacuole. Proteins may be deposited in protein bodies derived from the ER (many cereal prolamins) or vacuole (albumins, globulins, and some cereal prolamins). Seed storage protein genes are under complex regulation, which ensures their tissue and temporal specificity of expression but allows modulation related to the environment and nutrition.

Learning Objective

•

To understand the pathways and mechanisms of storage protein synthesis, processing, trafficking, and deposition in the endomembrane system of the seed.

Introduction The protein content of seeds varies widely, from 10% of the dry weight in cereals to 40% in soybean. The number of individual protein components present is vast, but all seeds contain well-defined groups of storage proteins, which account for half or more of the total proteins. The storage proteins are largely responsible for the nutritional quality and processing properties of the grain and will, therefore, be the focus of this article. Four types of storage proteins occur widely in seeds, which were initially defined based on their solubility properties and molecular masses measured by sedimentation equilibrium ultracentrifugation. The latter allows the calculation of sedimentation coefficients (S20,w values) with higher values indicating greater mass. Alcohol-soluble prolamins form the major storage protein fraction in most cereal grain and two types of globulins (7S and 11S), the major fractions in most dicotyledonous species, including legumes and oilseeds. However, many of the latter also contain 2S albumin storage proteins. Similarly, all cereals also contain storage globulins, with proteins related to the 11S globulins of dicotyledonous plants forming the major storage protein group in oats and rice. The characteristics of these four types of proteins are summarized in Table 1 and the trivial names used for different species in Table 2. This article will focus on their synthesis and deposition.


The vast majority of the proteins present in the mature cereal grain, including all of the major groups of storage proteins, are encoded by genes present on the chromosomes in the nucleus. Smaller genomes are also present in two organelles, the mitochondrion and plastid, but these do not encode any major seed proteins. Initiation of gene transcription is regulated by the interactions between promoter elements located upstream of the gene-coding regions and transcription factors, which are proteins that interact with the promoter elements and with the RNA polymerase enzyme that catalyzes the synthesis of messenger RNA (mRNA) from the DNA template in the gene. The mRNA is initially synthesized as a precursor form, which is processed in the nucleus prior to being transported through the nuclear membrane to the cytoplasm for translation. Protein synthesis involves the translation of the nucleotide sequence of the RNA (which is initially derived from that of the genomic DNA) into the amino acid sequence of the protein. This occurs on structures called ribosomes, which comprise complexes of ribosomal RNA and proteins. Transfer RNAs bearing amino acids and mRNAs are brought together on the ribosome resulting in the formation of peptide bonds between adjacent amino acids leading to the synthesis of the polypeptide chain. Attachment of the mRNA to the ribosome occurs in the cytoplasm and the translated protein may subsequently be released into the cytoplasm. However, many proteins are synthesized with an N-terminal signal peptide, which directs them into the endomembrane system. This is because the translation of the signal peptide causes the ribosome to attach to the outer surface of the endoplasmic reticulum (ER), allowing the signal peptide to direct the nascent (newly synthesized) protein through the ER membrane into the lumen. The major events in protein synthesis, and the way that the sequence of nucleotides in the genomic DNA ultimately determines the sequence of amino acids in the protein, are summarized in Table 3. More detailed and highly readable accounts of the various stages of protein synthesis are given in Buchanan et al.

Seed Storage Proteins Are Products of the Endomembrane System Seed storage proteins are present in the cells in dense protein bodies. These originate from the endomembrane system of the cell, which comprises the ER and structures derived from this, including the Golgi apparatus and various types of vesicle, which transport components to and from specific cellular destinations. The parts of the endomembrane system that are relevant to storage protein synthesis and deposition are shown schematically in Figure 1, while the processing events are summarized in Table 4. It should be noted that trafficking of

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PROTEINS | Protein Synthesis and Deposition

Table 1 2S albumins

7S globulins

11S globulins

Prolamins

Summary of the characteristics of albumin, globulin, and prolamin storage proteins Soluble in water Molecular mass (Mr) typically 10–15 kDa Processed posttranslationally to give large and small subunits Two intrachain bonds within the large subunit and two interchain disulfide bonds Not glycosylated Specific components are rich in methionine Soluble in dilute salt solutions Typically trimeric proteins of Mr 150–190 kDa Subunit Mr varies from 40 to 80 kDa but is typically 50 kDa Subunits may be proteolytically processed and glycosylated Contain little or no cysteine and methionine Soluble in dilute salt solutions Typically hexameric proteins of Mr 300–450 kDa. Subunits typically of Mr 60 kDa are posttranslationally processed to give Mr 40 kDa (acidic) and Mr 20 kDa (basic) chains associated by one interchain disulfide bond Low in cysteine and methionine Vary widely in structure, with subunit Mr ranging from 10 to 100 kDa Include monomeric forms and high Mr polymers stabilized by interchain disulfide bonds Presence of repeated sequences and regions (domains) rich in specific amino acids results in unusual amino acid compositions Rich in proline and glutamine, poor in lysine and, in some cases, tryptophan, threonine, and methionine No glycosylation or proteolytic processing Soluble in alcohol/water mixture when native and/or reduced

Source: Shewry PR (2000) Seed proteins. In: Black M and Bewley JD (eds.) Seed Technology and Its Biological Basis, pp. 42–84. Sheffield: Blackwell Science and Sheffield Academic Press, with permission.

Table 2 Types of major storage proteins present in seed crops and their trivial names Species

Protein type

Trivial name

Cereals Wheat (Triticum spp.)

Prolamin

Gliadin/ glutenin Hordein Secalin Zein Kafirin Avenin

Barley (Hordeum vulgare) Rye (Secale cereale) Corn (Zea mays) Sorghum (Sorghum bicolor) Oats (Avena sativa) Rice (Oryza sativa) Legumes Soybean (Glycine max) Broad bean (Vicia faba)/pea (Pisum sativum) French bean (Phaseolus vulgaris) Peanut (Arachis hypogaea)

Oilseeds Cottonseed (Gossypium hirsutum)

Sunflower (Helianthus annuus) Oilseed rape/canola (Brassica napus)

Prolamin Prolamin Prolamin Prolamin Prolamin 11S globulin Prolamin 11S globulin

Glutelin

7S globulin 11S globulin 7S globulin 11S globulin 7S globulin 7S globulin 11S globulin 2S albumin

b-Conglycinin Glycinin Vicilin Legumin Phaseolin Conarachin Arachin

11S globulin 7S globulin 2S albumin 11S globulin 2S albumin 11S globulin 2S albumin

Gossypin Congossypin Helianthinin Napin Cruciferin

Source: Shewry PR (2003) Plant proteins. In: Thomas B, Murphy D, and Murray B (eds.) Encyclopaedia of Applied Plant Science, pp. 889–896. London: Elsevier Science.

Table 3 Summary of the major events in protein synthesis from nuclear genes Genomic DNA in the chromosomes of the nucleus consists of a linear sequence of four nucleotides (bases). Individual genes comprise protein-coding sequences flanked by regulatory sequences. Coding sequences specify the amino acid sequences of proteins in series of three bases called codons. The correspondence of codons to amino acids is called the genetic code. Regulatory sequences control gene expression by interactions with regulatory proteins (transcription factors) and RNA polymerase enzymes # Transcription of gene gives messenger (m)RNA with codon sequence reflecting that in the gene # mRNA is processed in the nucleus and transported via nuclear membrane to cytoplasm # mRNA binds to ribosome in the cytoplasm. Transfer RNAs bearing amino acids recognize and bind to specific codons allowing the amino acids to be linked in a specific sequence by peptide bonds. Thus the sequence of codons determines the amino acid sequence of the protein # Translation of a signal peptide directs the ribosome to the endoplasmic reticulum (ER) allowing translocation of the nascent protein into ER lumen

proteins through the endomembrane systems is a highly regulated process with the destinations of individual proteins being determined by the presence of specific sequences or structural features. In the absence of such signals, the protein is secreted from the cell by fusion of ‘secretory vesicles’ derived from the Golgi apparatus with the plasma membrane. Hence, secretion is often referred to as the default destination.


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Storage protein synthesis occurs on ribosomes attached to ER RER Smooth ER

Transport in vesicles Golgi apparatus

Protein body formation within RER

Protein body formation Secretory vesicle Plasma membrane

Within vacuole

Figure 1 Schematic summary of storage protein synthesis, processing, trafficking, and deposition in the endomembrane system of the cell. Table 4 Processing of seed storage protein in the endomembrane system of the cell ER 2S albumins

7S globulins

11S globulins

Prolamins

Folding, disulfide bond formation Folding, Nglycosylation, formation of trimers Folding, disulfide bond formation, formation of intermediate trimers Folding, disulfide bond formation, polymer assembly

Golgi apparatus

Vacuole Proteolytic processing

Glycan modification

Glycan trimming, proteolytic processing Proteolytic processing to give acidic and basic chains, formation of hexamers

Synthesis, Folding, and Disulfide Bond Formation Occur Simultaneously on the ER Seed storage protein is synthesized by mRNA associated with polyribosomes present on the rough ER. The protein translated from the mRNA differs from that deposited in protein bodies in the presence of a short N-terminal extension (the signal sequence

that is usually 20 amino acids) whose role is to lead the newly synthesized (nascent) polypeptide through the ER membrane into the lumen, thus entering the endomembrane system. This occurs by specific interaction of the signal sequence with a complex of proteins called the translocon. Once the nascent polypeptide emerges into the ER lumen, the signal sequence is removed by a specific enzyme (a signal peptidase) and the polypeptide chain commences to fold into its three-dimensional structure. These events, translocation, signal peptide cleavage, and folding, occur when the protein is still undergoing synthesis and hence are termed cotranslational. Protein folding is almost certainly assisted by a complex of proteins and other factors, the most well known of which is the ‘molecular chaperone’ BiP (binding protein). In addition to assisting protein folding, BiP also binds to malfolded proteins to prevent their escape from the ER. Thus, it is often present in higher amounts in mutants in which seed protein synthesis is affected (e.g., floury-2 and defective endosperm – B30 of maize) as well as during the period of maximum storage protein synthesis and deposition. Most proteins synthesized on the ER also contain interchain and/or intrachain disulfide bonds. These bonds also form in the ER as an integral part of protein folding, and this may be assisted by the enzyme protein disulfide isomerase (PDI), which catalyzes the formation, exchange, or reduction of disulfide bonds, depending on the substrate and conditions.

Storage Albumins and Globulins Are Deposited in Storage Vacuoles The 2S albumin and 7S and 11S globulin storage proteins are transported via the ER lumen, Golgi apparatus, and vesicles to specialized storage vacuoles where they form dense deposits.

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These vacuoles may subsequently divide to form protein bodies. However, all three types of storage protein may also undergo modification, either in the vacuole or during their passage through the ER and Golgi apparatus. The 2S albumins are synthesized as precursor proteins, which undergo folding and disulfide bond formation in the ER lumen. The precursors are then proteolytically processed in the vacuole to generate the mature two-subunit structure. This processing involves cleavage adjacent to specific asparagine residues and the loss of one or more short peptide fragments (from the protein N-terminus and C-terminus and between the two subunits). The 7S and 11S globulin subunit is also folded in the ER lumen with the formation of a single intrachain disulfide bond in the latter (7S globulins lack cysteine residues and hence have no disulfide bonds). Both types of subunits are then assembled into trimeric structures stabilized by noncovalent forces. There has been considerable debate about the extent to which globulin storage proteins are modified by the addition of oligosaccharides (glycosylation). It is now established that this rarely, if ever, occurs for 11S globulins but that some 7S globulin subunits are modified by glycosylation of specific asparagine residues (N-glycosylation). This occurs in several stages, with the initial attachment of a high-mannose sugar occurring cotranslationally (i.e., concurrent with folding and disulfide bond formation). Subsequently, enzymes present in the ER and Golgi apparatus may act to remove or add further sugar residues to give a more complex structure with final ‘trimming’ occurring within the storage vacuole. Once within the vacuole, the 11S globulins are proteolytically cleaved at an internal asparagine residue to give acidic and basic chains that remain associated by the single disulfide bond formed in the ER. After this proteolytic processing, the ‘intermediate dimers’ formed in the ER are able to assemble to form the mature hexameric structure. The 7S globulin subunits may also be proteolytically processed in the vacuole, but this depends on the species and the precise protein subunit. For example, in bean (Phaseolus vulgaris) and soybean (Glycine max), the 7S globulin subunits do not undergo any proteolysis, while in pea (Pisum sativum), some subunits are processed at one or two sites to give polypeptide chains ranging in mass from 12 to 35 kDa, in addition to unprocessed chains of mass 50 kDa. However, the trimeric structure is not affected by these processing events.

Cereal Prolamins Are Deposited in Two Types of Protein Body Cereal prolamins do not undergo glycosylation or proteolytic processing (except for cotranslational removal of the signal sequence), but some subunits are assembled into highmolecular-mass polymers stabilized by interchain disulfide bonds. In wheat, these glutenin polymers may have masses of between 1 and 10 MDa, and it is not known how such complex multisubunit structures are assembled. However, it is probable that assembly and interchain disulfide bond formation occur rapidly after synthesis within the ER lumen. Subsequently, prolamins are deposited in two discrete types of protein body.

In rice and maize (and probably also in sorghum and millets), prolamins accumulate directly within the lumen of the ER to form a population of protein bodies surrounded by a membrane of ER origin, which may remain studded with ribosomes. In contrast, it appears that two separate pathways occur in wheat, barley, and rye, with some prolamins being trafficked through the ER and Golgi apparatus and deposited in storage vacuoles (as described earlier for albumin and globulin storage proteins), while others are retained in the ER as in maize and rice. It has been suggested that the polymeric prolamins are preferentially retained in the ER and monomeric forms transported to vacuoles, but it seems likely that the division is not so clear-cut. It is also probable that the relative amounts of prolamins deposited in the two types of protein body vary with the rate of protein synthesis and with the developmental state of the tissue. Thus, it can be envisaged that high levels of protein synthesis would lead to a high level of accumulation within the ER lumen and that this route would also be favored as the cells become distended with deposits of starch and proteins. In wheat, the individual protein bodies collapse during the later stages of seed maturation forming a continuous matrix in the cells of the mature grain.

What Determines the Destination of Storage Proteins in the Endomembrane System? As discussed earlier, trafficking through the endomembrane system is a highly regulated process with the destinations of proteins being determined by their sequences and structures. The retention of storage proteins within the ER or their transport to the vacuole should, therefore, result from the presence of specific signals. A number of proteins are permanently resident in the lumen of the ER, including PDI and BiP. In these cases, retention results from the presence of a specific ER retention signal, which is a tetrapeptide located at the protein C-terminus. The two most widespread tetrapeptides are KDEL and HDEL, which correspond to the amino acids lysine or histidine, aspartic acid, glutamic acid, and leucine. There is no evidence that such a retention signal is present at the C-termini of prolamins that are retained in the ER, and a different mechanism must therefore be sought. It has been suggested that BiP plays a role in rice, by transiently binding to prolamins and retaining them in the ER to allow assembly into protein bodies. However, this mechanism has not so far been shown to be applicable to other cereals. An alternative explanation is that retention results from the insolubility of the proteins in aqueous environments (i.e., the ER lumen) and their propensity to form aggregates under such conditions. It can be envisaged that such aggregates would accumulate directly in the ER lumen and then be ‘budded off’ to form protein bodies. Some proteins are targeted to the vacuole by the presence of specific ‘prosequences’ that are removed by posttranslational proteolysis once the protein arrives in the vacuole. These prosequences may be at the protein N-terminus, as in the barley cysteine proteinase aleurain and the sweet potato storage protein sporamin (which is stored in tubers) or at the C-terminus as in lectins; more rarely, a noncontiguous series of residues form a tridimensional structure in the mature protein, which acts as a vacuolar sorting signal. None of the 2S albumins, 7S globulins, 11S globulins, or prolamins that are deposited in


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vacuolar protein bodies have cleavable prosequences that are involved in vacuolar targeting. However, it has been proposed that aggregation of 7S and 11S globulins into electron-dense aggregates in the Golgi is a prerequisite for ensuring that they are sorted into dense vesicles and ultimately deposited into the vacuole, whereas other proteins are sorted into different types of vesicles with different destinations. This sorting may require the presence of specific hydrophobic residues, which mediate the protein–protein interactions. However, the precise mechanisms that determine the final destination of seed storage proteins, whether to ER-derived or vacuolar protein bodies, are still poorly understood.

Organization of Storage Proteins in Protein Bodies (a)

The 7S and 11S globulins have similar three-dimensional structures with the 11S hexamers essentially corresponding to dimers of the trimeric 7S proteins. This similarity presumably facilitates their efficient packaging in the same protein bodies. However, protein bodies may also contain separate phases, or inclusions, containing specific proteins or other components. For example, the protein bodies of castor bean consist of a matrix of 2S albumins and other proteins (including lectins) with crystalline inclusions of 11S globulins and noncrystalline globoid inclusions consisting of phytin (calcium and magnesium salts of myoinositol hexaphosphoric acid). Phytin globoids are also present in protein bodies of other dicotyledonous seeds and in aleurone cell protein bodies of cereals. The different routes, taken by prolamins and glutelins (11S globulin homologues) in rice lead to the formation of two separate populations of protein bodies called PB-I (ER-derived containing prolamins) and PB-II (vacuolar-derived containing glutelins). However, in wheat and oats, these two types of protein are located in the same protein body, with prolamin inclusions in a globulin matrix in oats and vice versa in wheat (Figure 2). This segregation has been suggested to result in oats from the fusion of ER-derived protein bodies containing prolamins with vacuolar protein bodies containing globulins. It has also been shown that different types of prolamin (zein) are concentrated in the outer and inner parts of protein bodies of maize, although in this case, the location appears to result from the pattern of development of the bodies in the endosperm cells.

Assembly of Glutenin Polymers in Wheat Polymer assembly is of particular interest in wheat as the formation of high-molecular-mass glutenin polymers underpins the processing properties of flour, by conferring elastic properties to dough. These polymers comprise of two major types of subunit, called high-molecular-weight (HMW) and low-molecular-weight (LMW) subunits. These subunits are linked by interchain disulfide bonds that are presumably initially formed during folding in the ER (as discussed earlier). The complexity and size of the glutenin polymers have limited attempts to determine their precise structures, but current evidence is consistent with a model in which the HMW subunits form the ‘backbone,’ linked mainly ‘head to tail,’ while the LMW subunits form branches. In addition, glutenin polymers

(b)

(c)

Figure 2 Protein bodies in developing starchy endosperm cells of cereals. (a) Rice at 7 days after flowering, showing two populations of protein bodies. PB-Is are spherical vesicles delimited by a single unit membrane derived from the ER and contain prolamins. PB-IIs are amorphous, derived from vacuolar deposition and contain globulins/ glutelins. Reproduced from Yamagata H and Tanaka K (1986). The site of synthesis and accumulation of rice storage proteins. Plant and Cell Physiology 27: 135–145, with permission. (b) Oats at 8 days after anthesis showing light-staining deposits of prolamin (labeled with 10 nm colloidal gold) as inclusions in protein bodies containing globulins (5 nm colloidal gold). Reproduced from Lending CR, Chesnut RS, Shaw KL, and Larkins BA (1989). Immunolocalization of avenin and globulin storage proteins in developing endosperm of Avena sativa L. Planta 178: 315–324, with permission. (c) Wheat at 11 days after flowering showing inclusions of triticin (dark staining, labeled I) within a matrix of prolamin (M). The bars are 1.0 mm in (a) and 0.5 mm in (b) and (c). Reproduced from Bechtel D, Wilson JD, and Shewry PR (1991). Immunocytochemical localization of the wheat storage protein triticin in developing endosperm tissue. Cereal Chemistry 68: 573–577, with permission.

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interact strongly with each other and with the monomeric gliadins by noncovalent forces, particularly hydrogen bonds. This combination of covalent and noncovalent interactions, together with the intrinsic structures of the individual subunits, results in the viscoelastic properties associated with wheat dough and gluten. The limited information that is available indicates that glutenin polymers have defined structures, with specific interactions between individual subunits. Similarly, it is clear that some allelic forms of HMW subunits are associated with the formation of larger polymers, leading to positive effects of quality. However, the mechanisms responsible for defining specific structures are not known. Finally, the proportion of high-molecular-mass glutenin polymers increases dramatically during the desiccation phase of grain development, suggesting that polymer formation is also driven by dehydration. This is consistent with the model that glutenin polymers are stabilized by strong arrays of hydrogen bonds, but rearrangements of disulfide bonds may also occur.

Regulation of Storage Protein Synthesis

storage tissue(s) and cease when these cells mature and desiccate. The onset and duration of the phases vary widely between species and genotypes and are greatly affected by the environmental conditions. In small grain cereals (wheat and barley) grown in the United Kingdom, storage protein synthesis is usually first detected in appreciable amounts at 12–14 days after pollination and is most active over the next 2–3 weeks. However, synthesis may be initiated as early as 6 days in plants grown in hot and dry climates. In maize (corn) grown in North America, storage protein synthesis occurs between 3 and 7 weeks after pollination. Storage protein fractions are, of course, not single proteins but mixtures of components, which may be encoded by several multigene families. In general, these genes show highly coordinated patterns of expression, with only small differences in their timing and relative levels of expression during development. For example, in sunflower, the expression of genes for 11S globulin storage proteins (helianthinins) is detected slightly before that of genes for 2S albumins, but in wheat and barley all groups of prolamin storage proteins show similar expression patterns.

Tissue Specificity

Environmental Control

Storage protein synthesis in seeds is strictly regulated with respect to timing, tissue specificity, and, to a lesser extent, nutrient availability. In addition to the embryo, which is a diploid zygotic tissue that gives rise to the seedling, all seeds also contain an endosperm, which is triploid and is derived from a second fertilization event. However, the size of the endosperm varies greatly, forming 80–90% of the mature cereal grain but being largely broken down during development in soybean and many other seeds. Similarly, whereas some seeds such as quinoa and amaranth contain a perisperm (derived from the maternal nucellar tissue), this fails to develop and is absorbed in most species. In all seeds, at least one of these three tissues functions as a storage tissue, and in some cases, more than one. The central part of the endosperm is the major storage tissue in cereals, accumulating protein (prolamins with varying amounts of 11S-type globulins), and starch. However, 7S globulins and oil are also stored in the outer cells of the endosperm (the aleurone layer) and the single cotyledon (scutellum) of the embryo. The cotyledons of the embryo form the major storage tissue in grain legumes (including soybean, peanut, lupin, and pea), sunflower, and oilseed rape/canola, while proteins and oil are stored in the endosperm and embryo of quinoa with starch being stored in the perisperm. It should also be noted that the synthesis of seed storage proteins has never been detected in nonseed tissues of the plant, whether by determination of gene expression (i.e., mRNA populations) or by protein accumulation.

Environment has a major impact on seed development, including storage protein synthesis, with higher temperatures generally increasing the rate of development. In addition, specific heat-shock effects may occur when temperatures exceed 35 C: these can result in detrimental effects on the quality of wheat grown in Australia and some other parts of the world. The most dramatic effect of environment on storage protein synthesis is that of nutrition. It is well established that the protein content of seeds is regulated by the availability of nitrogen, with storage protein acting as a sink for nitrogen, which is not required by the plant for other purposes. For example, increasing the total nitrogen content of barley grain from 1% to 3% is associated with an increase in prolamin (hordein) storage proteins from 35% to 50% of the total grain nitrogen. This effect can be exploited to grow grain with defined protein contents for specific end uses (e.g., low protein for malting barley and high protein for bread-making wheat). However, almost all storage proteins also contain sulfur in the form of the amino acids cysteine and methionine. Many species are able to adjust to variation in the relative availabilities of nitrogen and sulfur by having specific types of seed storage proteins with high and low contents of sulfur amino acids. Thus, the 2S albumin storage proteins of oilseed rape and sunflower have higher contents of cysteine and methionine than the globulin storage proteins, and the synthesis of the former is therefore reduced under conditions of low sulfur availability (Figure 3(a) and 3(b)). Similarly, restricted availability of sulfur favors the synthesis of the sulfur-poor C hordeins of barley (Figure 3(c)) and o-gliadins of wheat over other more sulfur-rich prolamins, which can have adverse consequences for grain quality in the latter species.

Temporal Regulation Seed development proceeds through a series of genetically programmed stages, starting with cell division and differentiation to establish the basic structure of the component organs and tissues (i.e., the embryo and endosperm). The synthesis and accumulation of storage products, including proteins, occur during the subsequent expansion of the cells of the

Regulation of Storage Protein Gene Expression The regulation of seed storage protein genes usually occurs at the level of gene transcription, although some ‘fine-tuning’ can


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maize, which binds the protein encoded by the Opaque 2 locus. Mutation of this locus results in reduced a-zein synthesis and a ‘high lysine’ phenotype. Although several other proteins that bind to regulatory sequences of storage protein genes have also been identified, the precise mechanisms of storage protein gene regulation remain poorly understood.

2

Conclusions 3

(a)

+

–

(b) +

–

(c)

+

–

Figure 3 The effect of sulfur on the total seed proteins of oilseed rape (a) and sunflower (b) and on the prolamin (hordein) proteins of barley (c). Note the presence of S-rich low-molecular-mass proteins (probably 2S albumins) in oilseed rape and sunflower (bracket) and of S-poor C hordeins (2) in barley. Parts (a) and (b) are reproduced from Spencer D, Rerie WG, Randall PJ, and Higgins TJV (1990). The regulation of pea seed storage protein genes by sulfur. Australian Journal of Plant Physiology 17: 355–363, with permission. Part (c) is reproduced from Shewry PR, Franklin J, Parmar S, Smith SJ, and Miflin BJ (1983) The effects of sulfur starvation on the amino acid and protein composition of barley grain. Journal of Cereal Science 1: 21–31, with permission.

occur at the level of translation of the mRNA into proteins. Consequently, interest has focused on the identification of regulatory sequences present upstream of the gene sequences that encode storage proteins (called 50 upstream sequences) and of specific proteins that bind to these (transcription factors). This has led to the identification of short conserved nucleotide sequences (often called boxes) that regulate expression of the genes. Comparison of the 50 upstream sequences of a number of genes encoding 11S storage globulins has led to the identification of a 28 base pair (bp) ‘legumin box.’ Deletion of a central 7-nucleotide motif from the center of this box resulted in a drastic reduction in the gene expression in transgenic plants, demonstrating its importance. Related ‘boxes’ are also present in the 50 upstream sequences of 7S globulin and 2S albumin genes. However, further studies have demonstrated the presence of several additional upstream regulatory sequences that may modulate storage globulin gene expression. Similar studies have shown that many prolamin genes also contain a conserved sequence of 30 bp located about 300 bp upstream of the gene-coding region. This is called the ‘endosperm box’ or ‘prolamin box’ and is unrelated in sequence to the ‘legumin box.’ The ‘prolamin’ box actually comprises two conserved sequences separated by a more variable region. One of these conserved sequences is thought to be responsible for conferring endosperm specificity, while the other may play a role in the regulation of the gene. However, additional regulatory sequences are undoubtedly also present including a short sequence (the E motif) in the a-zein genes of

It is clear that we still have much to learn about the precise mechanisms of storage protein synthesis, trafficking, and deposition, although the broad principles are now understood. A detailed understanding of these mechanisms is important as interactions (i.e., between proteins and with other grain components) established during synthesis and deposition may ultimately affect the functional properties of the proteins in food products. Furthermore, it is becoming clear that the synthesis, assembly, deposition, and interactions of seed proteins may be affected by environmental factors that ultimately impact on seed quality. Identifying the major sites of these effects and the critical stages of seed development should allow them to be predicted and ultimately manipulated to give a higher level of stability. It is also important to understand the mechanisms of seed protein synthesis, trafficking, and deposition in order to facilitate the application of genetic engineering to improve grain quality. It is essential that any novel or mutant proteins expressed in transgenic plants should be ‘accepted’ by the secretory system as authentic and transported to their correct destination. Any errors in folding or failure to contain the correct targeting information could lead to protein turnover or accumulation in incorrect compartments (e.g., ER instead of storage vacuoles in dicotyledonous seeds) with adverse effects on grain development, quality, and yield.


• • •

Summarize the compartments of the endomembrane system of the plant cell in relation to the trafficking and processing of seed storage protein. Discuss the origins of protein bodies in cereal and dicotyledonous seeds. Discuss the pathways and mechanisms of processing and deposition of different types of storage proteins: albumins, globulins, and prolamins.


• • •

Identify the structure/sequences that determine storage protein targeting and trafficking in the endomembrane system. Determine the organization and interactions of storage proteins within protein bodies. Determine the precise mechanism of storage protein gene regulation in the context of grain development, the nutritional status of the plant, and abiotic stress.

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See also: Proteins: The Protein Chemistry of Cereal Grains; The Protein Chemistry of Dicotyledonous Grains; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Bechtel D, Wilson JD, and Shewry PR (1991) Immunocytochemical localization of the wheat storage protein triticin in developing endosperm tissue. Cereal Chemistry 68: 573–577. Bewley JD and Black M (1995) Seeds Physiology of Development and Germination, 2nd edn. New York: Plenum Press. Buchanan BB, Gruissem W, and Jones RL (2000) Biochemistry and Molecular Biology of Plants. Rockville, MD: American Society of Plant Physiologists. Larkins BA and Vasil IK (1997) Cellular and Molecular Biology of Plant Seed Development. Dordrecht: Kluwer Academic. Lending CR, Chesnut RS, Shaw KL, and Larkins BA (1989) Immunolocalization of avenin and globulin storage proteins in developing endosperm of Avena sativa L. Planta 178: 315–324. Muntz K and Shutov AD (2002) Legumains and their functions in plants. Trends in Plant Science 7: 340–344.

Shewry PR (2000) Seed proteins. In: Black M and Bewley JD (eds.) Seed Technology and its Biological Basis, pp. 42–84. Sheffield: Blackwell Science and Sheffield Academic Press. Shewry PR (2003) Plant proteins. In: Thomas B, Murphy D, and Murray B (eds.) Encyclopaedia of Applied Plant Science, pp. 889–896. London: Elsevier Science. Shewry PR and Casey R (1999) Seed Proteins. Dordrecht: Kluwer Academic. Shewry PR and Halford NG (2002) Cereal seed storage proteins: Structures, properties and role in grain utilization. Journal of Experimental Botany 53: 947–958. Shewry PR, Franklin J, Parmar S, Smith SJ, and Miflin BJ (1983) The effects of sulphur starvation on the amino acid and protein compositions of barley grain. Journal of Cereal Science 1: 21–31. Shewry PR, Halford NG, Tatham AS, Popineau Y, Lafiandra DL, and Belton PS (2003) The high molecular weight subunits of glutenin and their role in determining wheat processing properties. Advances in Food and Nutrition Research 45: 221–302. Spencer D, Rerie WG, Randall PJ, and Higgins TJV (1990) The regulation of pea seed storage protein genes by sulphur. Australian Journal of Plant Physiology 17: 355–363. Tosi P (2012) Trafficking and deposition of prolamins in wheat. Journal of Cereal Science 56: 81–90. Yamagata H and Tanaka K (1986) The site of synthesis and accumulation of rice storage proteins. Plant and Cell Physiology 27: 135–145.

Nitrogen Metabolism CA Atkins, The University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 287–292, ã 2004, Elsevier Ltd.

Topic Highlights

• • •

stage we must infer the commonality of processes that are so far only adequately documented for a few species.

Mature plant seeds contain nitrogen-based nutrient reserves, particularly proteins. Nitrogen is transported into grain or seed, where it is metabolized into amino acids. Most nitrogen entering the seed is sued to synthesize storage proteins, which are utilized by the germinating seedling (or enter into food processing).

Learning Objectives

• • •

To understand the dynamics of nitrogen metabolism that results in the storage of useful plant proteins in the mature grain. To understand the transportation of nitrogen-containing solutes into the seed, in relation to the concept of sink strength. To understand the metabolism of nitrogen within the seed and the formation of storage reserves.

Introduction The success that flowering plants enjoy is in no small way a consequence of the effectiveness of their seed as a perennating organ. The embryo is in a metabolically dormant state and is accompanied by a reserve of nutrients that can be mobilized on germination to support the activated meristems of the new plant. The diversity of composition exhibited by mature seeds reflects variation in the size and nature of this stored reserve. Some are high in carbohydrate, others in protein, and others in oil. Yet all are viable and are able to convert the reserves into translocatable solutes with a balance of C and N that supports the active root and shoot meristems before uptake from soil provides an alternative source of nutrients and before the seedling is autotrophic for C through photosynthesis. The reserves are fashioned from organic assimilates that supply C, N, and S through the long distance translocation channels of the vegetative structure of the plant. Metabolism of N has been studied in a restricted range of seed types, mostly those of cereals, legumes, and oilseeds of agricultural importance and more recently in the model species Arabidopsis thaliana. Because of the high proportion of protein stored in legume seeds these have received most attention in this regard. However it is well to realize that plants produce an almost bewildering array of N-containing compounds, many of which are amino compounds that accumulate in seeds and are likely to impart unique nutritional, toxicological and pharmacological properties. Our understanding of this whole area in angiosperms is thus limited and fragmentary, and at this


Nitrogen Nutrition of Developing Seeds Before considering seed nutrition it is useful to review the basic structural features of seeds and the consequences of this structure to solute import into and transfer within the component tissues of a seed as it develops. The outer seedcoat tissues are maternal while the endosperm and embryo within this coat are filial. There is no vascular connection between the two. Thus, whether stored reserves of the seed accumulate in the endosperm, the embryo, or associated tissues, in all cases solutes that supply C and N (assimilates) pass across an apoplastic compartment. It follows that in receiving translocated solutes before they pass to the embryo the seedcoat may regulate both the rate and nature of solute transfer. Although developing seeds and their surrounding supporting structures may have the capacity for photosynthesis during early stages of development, this is limited. Consequently their major source of C is assimilates translocated in phloem and xylem. These are principally in phloem as sucrose, longer raffinose-based oligosaccharides, or in some species cyclitols, like mannitol and sorbitol. The same translocation streams supply N but typically phloem contains 10–20 times more N than xylem. However, even though both streams may carry a wide array of amino acids, as well as other N-solutes (e.g., proteins, nucleic acids, plant growth regulators), usually one or two low molecular weight organic compounds predominate. For many dicotyledonous species, including temperate legumes, these are the amides, glutamine and asparagine or their parent acids, glutamate, and aspartate, especially in cereals. In some species arginine, proline, or non-protein amino compounds like homoserine, ornithine, citrulline, canavanine, and putrescine predominate. In others, particularly nodulated legumes of tropical origin, the ureides, allantoin, and allantoic acid, account for almost all the N in xylem and a significant component in phloem-N. There are some very unusual N-solutes that translocate the bulk of N, for example djenkolic acid (two cysteines bridged at their S groups by a methylene) occurs at very significant levels in the xylem of some Acacia spp., and no doubt the plant kingdom employs many other forms of translocated N that have yet to be discovered. Thus protein synthesis in sink organs does not receive a mixture of amino acids that can be simply used to form protein, but rather a mixture in which just one or two solutes provide the bulk of N that has to be metabolized to generate the appropriate proportions of the 20 protein amino acids. In their passage from sites of phloem unloading to the embryo, N-solutes may be transiently stored, for example in the

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seedcoat, and are metabolized in highly specific ways within the tissue compartments they traverse. There seems little doubt that almost all the N entering seeds is in an organic form. Although the literature records quite high levels of ammonium ion in both xylem and phloem, it is not likely that this is the norm and may, in many cases, be a consequence of hydrolysis of the amide groups of glutamine and asparagine during or subsequent to collection of vascular exudates. Xylem transports considerable quantities of nitrate from the root system to the major transpiring surfaces of the shoot but negligible quantities of this inorganic ion are transferred to phloem. As a result, fruit tissues and especially developing seeds are unlikely to receive significant levels of nitrate and consequently exhibit low or negligible capacity for its assimilation. Early in legume fruit/seed development when a significant proportion of translocated N is delivered in xylem, the C:N ratio of incoming solutes is more narrow than that required by the developing tissues, and ‘excess’ N is transiently stored. The endosperm in many dicotyledonous seeds accumulates a significant proportion of this N as ammonium ion and levels approaching 0.1 M have been recorded for periods of 3–4 weeks in white lupin (Lupinus albus) seeds. Although the ammonium is promptly reassimilated when the developing embryo expands to fill the endospermic apoplast, such high levels are normally regarded as extremely toxic and mechanisms that prevent this ammonium entering the embryo to any great extent must be functioning at this time. In pea (Pisum sativum), the major forms of accumulated N in the endosperm are homoserine, glutamine, and alanine, in cowpea (Vigna unguiculata) endosperm there is negligible ammonium ion but 30–55% of the N is histidine, while in chickpea (Cicer arietinum) ammonium and citrulline predominate. The significance of ammonium or other N solutes that accumulate to such high levels in endosperm when embryo development is characterized by cell division is unknown, but it is interesting to note that coconut endosperm (‘milk’), used in pioneering studies of plant cell and tissue culture, contains high concentrations of N, including ammonium ion, along with plant growth regulators. A positive correlation has been established between rates of ammonia emission (i.e., N loss) and ammonium concentration in leaves. There are no emission data available for developing seeds/fruits, but given the high levels of ammonium ion that may accumulate in liquid endosperm it seems possible that transient periods of N loss occur due to its volatilization. It is perhaps not too surprising then that the highest rates of ammonia emission in barley occur during grain filling. The mix of solutes in phloem is not constant during reproductive growth, the C:N ratio changing to more closely match the C and N requirements of the developing seed. In white lupin, sucrose levels in phloem decline progressively after anthesis while the concentration of amino compounds increases, almost doubling over the period of grain filling. This pattern of change is consistent with a declining rate of photosynthesis and increasing senescence of leaves, with release of protein-N as amino compounds, during reproductive development. However, further studies with lupin have shown that in fact the phloem N level also increases to narrow the C:N ratio as a consequence of solute specific mechanisms that achieve an enrichment of phloem with asparagine as the

translocation stream passes through stem segments immediately before entering the inflorescence. Similar specific exchanges of amino acids have also been found for developing cowpea fruits/seeds. The precise tissue or cellular site where these transfer mechanisms act and the molecular basis for their regulation is unknown but a role for transfer cells has been inferred. The developing seed is supported on or within fruiting structures that not only bear the vasculature which brings the translocation streams to the seed but which serve also as intermediate sites for metabolism and transient accumulation of nutrients, including N. For example, in the period from anthesis to 11 days after anthesis, in cowpea fruits 21 mg N enters in phloem and 17 mg N in xylem. Of this N less than half (15 mg) reaches the developing embryo and endosperm, the rest is sequestered into the pod wall (16 mg) and the testa (7 mg). Importantly, however, the incoming N-solutes are metabolized extensively before being transferred to the embryo. At this early stage of development xylem-N is 70% ureide and phloem-N 20% ureide, but ureides account for less than 20% in the podwall and testa and no more than 2% of soluble-N in the liquid endosperm or embryo. Later in development (12–22 days after anthesis) phloem accounts for 80% of N entering the fruit and, although the ureide level is low, ureide-N accumulates preferentially in the seedcoat. Despite this enrichment literally no ureide is transferred to the apoplast surrounding the embryo. Rather, ureide-N is converted to glutamine and this is the major source of N for protein synthesis. Similar observations have been made for soybean, another plant that translocates significant levels of ureide-N in xylem and to a lesser extent in phloem. In pea a major N-solute entering the seedcoat in phloem is homoserine and, although this may accumulate transiently in endosperm, most is converted to threonine and glutamine in the seedcoat during embryo expansion. Even in species that have an asparagine-rich phloem stream reaching the seedcoats, a significant proportion of asparagine-N is converted to glutamine-N during passage to the apoplast and embryo. Whether this apparent preference for N as glutamine in the embryo’s nutrition reflects some metabolic requirement or the specificity of transporters involved in transferring solutes across tissue compartments of the seed has yet to be clearly resolved. In maize the endosperm of the developing kernel supplied assimilates through the pedicel and even though the major phloem N-solute is aspartate this is largely metabolized with its N being transferred to glutamine. The maize pedicel expresses a unique cytosolic form of glutamine synthetase, GSp1, which is developmentally regulated, increasing as storage protein synthesis increases. Glutamine is the major amino acid released from the pedicel to the apoplast surrounding the endosperm and a transporter expressed in the basal endosperm transfer cells apparently enhances its uptake. Thus specificity of both metabolism and transport combine to ensure that a preferred N-solute reaches the embryo tissues.

Transport of N-Solutes within Seeds Rates at which solutes that supply C and N to the embryo are transported are likely to contribute to determining the

PROTEINS | Nitrogen Metabolism potential accumulation of assimilates or ‘sink strength’ of seeds and consequently grain yield and harvest index. Studies with four cultivars of bean (Phaseolus vulgaris) that differed in their rates of seed growth found that although sink size, as assessed by surface area and volume of cotyledons, were major determinates of growth rate, the rate of transfer of dry matter was also a contributing factor. Not surprisingly, maximal sucrose fluxes into cotyledons were positively correlated with levels of expression of the sucrose/Hþ symporter and accompanying Hþ-ATPase in the dermal cells facing the apoplast between the cotyledons and the seedcoat. Specifically in relation to N nutrition, activity of amino acid transporters has been suggested to regulate the rate of seed protein synthesis. Although most research into solute unloading from phloem and transport within developing seeds has involved sucrose, some of the amino acid transporters expressed in seed tissues have been identified and their location studied in relation to likely function. In pea, two cDNA clones (PsAAP1 and 2) belonging to the AAP (amino acid permease) family of Hþ/amino acid co-transporters have been isolated from cotyledons. Like the sucrose transporter, PsAAP1 is highly expressed in specialized epidermal transfer cells abutting the seedcoat and shows broad specificity, mediating transport of acidic, neutral, and basic amino acids. Similar broad-spectrum members of the AAP family have been described for developing Arabidopsis and castor bean seeds. In Arabidopsis AtAAP1 is localized to endosperm and cotyledons while AtAAP2 is restricted to the vasculature of siliques and the funiculus. Thus, AtAAP2 is thought to mediate exchange of amino acids from xylem to phloem. Such an exchange has been identified as a specific asparagine transfer in the upper stem segments and raceme of lupin to enrich phloem with N, narrowing the C:N ratio to match more closely seed demands for these commodities. The broad substrate specificity found for most plant amino acid transporters does not conflict with the idea that translocated N is characterized by just one or two amino acids. Most of the amino acid transporters from plants have been characterized by yeast mutant complementation or functional analysis in Xenopus oocyte assays and specificity in vivo may be quite different. Indeed, differences in affinity for amino acid species have been described. Furthermore, specific transporters are likely to be found when more extensive genomic data is available for a wider range of plants. As noted above seed tissues produce and may transiently accumulate significant amounts of ammonium ion. It appears that this is a feature of their metabolism throughout development, raising the question of transport mechanisms for the ion within seed tissues. Preliminary data indicates that genes homologous to the high affinity ammonium transporter family (AMT), AtAMT1 from Arabidopsis, are not expressed in the seedcoat and cotyledons of developing lupin seeds. However, the recently described high affinity AMT2 transporter gene is expressed in Arabidopsis siliques and this may be the transporter that functions in seeds. In view of the widely diverse levels of ammonium that form in seed tissues at different stages of development it seems likely that other transporters/channels with quite different kinetic features are also involved.

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The Arabidopsis genome has revealed transporters for other types of N-solute that are expressed and could have significant roles in seed metabolism. These include oligopeptide transporters, such as AtPTR2-B, that might be responsible for the movement of peptides released from storage proteins during germination to new meristems or in the transport of signal peptides from sites of synthesis to sites of action. The possible importance of peptide transport in seed development was highlighted in a study where antisense lines for AtPTR2-B were generated in Arabidopsis. The transgenic plants showed normal silique development but formed fewer, larger seeds than controls. Specifically about half of the embryos were arrested at an early stage of their development, suggesting peptide transport was essential for N nutrition at this time or that transfer of some bioactive peptide, essential for embryogenesis, was limiting. Plants also express high affinity transporters specific for purines and purine derivatives (PUPs) including bases, nucleosides, purine alkaloids, and cytokinins. Northern analysis for AtPUP1 in Arabidopsis has however shown only a low level of expression in developing siliques compared to other tissues and their functional significance in seed development or in the mobilization of N during germination remains to be established. A novel superfamily of transporters has recently been described for allantoin and other oxidized derivatives of heterocyclic N solutes in Arabidopsis. In view of the predominance of ureide-N in translocation streams serving developing fruits in certain tropical legume species, but with the metabolic requirement that ureide-N is not transferred from the maternal tissue to the embryo, it will be interesting to see whether or not fruit and seed tissues express these transporters. Enzymes of purine oxidation (urate oxidase and allantoinase) have been demonstrated at elevated levels during germination of a number of seeds, and it has been inferred that purines are released due to intense nucleic acid hydrolysis. If indeed allantoin provides a supplementary source of translocated N to the newly formed root and shoot apices then the novel allantoin transporters may be important in phloem loading at this time.

Primary N Metabolism The primary pathways of N metabolism in seeds are the reactions that utilize incoming N-solutes to form the 20 protein amino acids. As noted above N-solutes translocated to tissues surrounding a developing seed or to the embryo itself are characterized by one or two predominant compounds. Among these asparagine and glutamine appear to be the most common. Although some incoming asparagine is incorporated directly into seed protein the majority is metabolized (in white lupin more than 80% over 13 weeks of development). Supplying 15N (amide)-labeled asparagine to developing lupin fruits in phloem resulted in label being recovered in 15 amino acids following hydrolysis of seed protein. In addition to asparagine, glutamine, aspartate, and glutamate, those labeled included arginine and histidine, those derived from pyruvate (alanine, leucine and valine) and 3-phosphoglycerate (glycine and serine), those of the aspartate family (lysine and

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isoleucine) as well as aromatic amino acids (tyrosine and phenylalanine). Clearly seeds express all the major pathways for synthesis of protein amino acids. There are two potential pathways releasing asparagine-N to amino acid synthesis. Hydrolysis of the amide-group by asparaginase produces ammonia and aspartate, the latter providing an amino donor to the many aminotransferases (AT) that have been detected in seeds. The second pathway utilizes an asparagine-AT that transfers the amino group to glyoxylate forming glycine and 2-oxosuccinamic acid. The acid is reduced to 2-hydroxysuccinamate and deamidated to ammonia and malate. Although both potential pathways are expressed in developing pea fruits, asparagine-AT is largely confined to pod tissue and is very low in developing seeds. Asparaginase on the other hand is expressed at high levels in seedcoats early in development, transiently in endosperm and in filling cotyledons of legume seeds. The same could be said for predominant non-amino acid solutes like the ureides. Although there are a number of enzymic routes for the degradation of allantoin that are expressed in different plants, differing even between cultivars, the N is released as ammonia. Thus reassimilation of ammonia is a major activity of seed tissues whether in the seedcoat, endosperm, or the components of the embryo. Not surprisingly, both glutamine synthetase (GS) and glutamate synthase (GOGAT) activities are expressed in seed tissues, providing a high affinity utilization mechanism for ammonia that is likely to function in reassimilation throughout seed development. Seeds express glutamate dehydrogenase (GDH) activity and this may also participate in reassimilation. While the role of GDH has been the subject of considerable debate and conflicting opinion the consensus view that has emerged for most tissues appears to be one of oxidation of glutamate rather than synthesis. However, the very high concentrations of ammonium ion that form transiently in the endosperm of some seeds would be kinetically favorable for GDH to function, for a short while at least, in its assimilation. Among the protein amino acids that are synthesized largely in situ to meet the needs of seed storage protein accumulation are those of the aspartate family; namely lysine, threonine, isoleucine, and methionine. Not surprisingly expression of the first committed step in the aspartate pathway, catalyzed by a bifunctional aspartate kinase (AK)-homoserine dehydrogenase (HSDH) in Arabidopsis, is coincident with storage protein synthesis in the embryo. Cereals are deficient in lysine and in some, threonine and tryptophan, while legume seeds are poor sources of S-amino acids, particularly methionine. As a consequence there has been considerable research into regulation of the pathway for these ‘essential’ amino acids. There have also been numerous attempts to exploit this knowledge to enhance the nutritional and/or processing qualities of both cereal and pulse grains. AK activity is subject to feedback inhibition by pathway products, specifically lysine or threonine. However, in the high lysine opaque-2 mutants of maize very significant levels of the aspartate family accumulate as a pool of free amino acids in the mature endosperm. Accumulation results in part from lysine degradation being compromized, because lysine-ketoglutarate reductase activity is suppressed, but other studies have identified changes in sensitivity of the monofunctional AK (Ask2) to feedback regulation by lysine as a major genetic determinant of free amino acid content. In a

mapping population with the mutant Ask2 was a good candidate gene for a quantitative trait locus (QTL) affecting free amino acid content in the harvested grain. Dihydropicolinate synthase (DHDPS) converts the product of AK (aspartate 4 semialdehyde) to an intermediate in lysine synthesis and is also subject to feedback inhibition by lysine during seed development. Specific features of C metabolism within the developing seed are required to accommodate some aspects of amino acid synthesis. Phosphoenolpyruvate carboxykinase (PEPCK) is present in a wide range of developing seeds. In grape seeds, PEPCK is expressed in the inner layer of the seedcoat, in the chalaza and in cells at the boundary of the storage tissue; expression coinciding with maximum deposition of storage reserves. Feeding asparagine to developing grape seeds caused a strong induction of PEPCK indicating that the enzyme functions in the metabolism of N-solutes after unloading from phloem. These data are consistent with an anaplerotic role for PEPCK in supplying acetyl-CoA when the TCA cycle is involved in the interconversion of C skeletons for 4C and 5C amino acids. Because seeds are formed within enclosing structures that limit gas exchange the concentrations of respired CO2 within the structures may build up to quite high levels and refixation of some of this C is achieved through RubisCO (Ribulose bis P carboxylase/oxygenase) and especially PEP carboxylase. In lupin embryos some of this refixed C is incorporated in sugars and TCA cycle intermediates (malate, isocitrate, and citrate), but as much as one-third provides C for a range of amino acids, principally alanine, aspartate, and serine, but also glutamate, glutamine, asparagine, glycine, valine, leucine, and isoleucine. In Vicia faba PEP carboxylase is up-regulated in cotyledons during grain filling. Again this suggests an anaplerotic role for the provision of 5C skeletons to the TCA cycle functioning in amino acid synthesis in an intensely respiring tissue.

Synthesis of Stored N Reserves in Seeds The major dietary sources of plant protein are seeds of cereals and legumes. Legumes and some oilseeds typically contain 30–50% dry weight as protein while cereals are lower, 10%. The ‘storage’ proteins constitute up to 90% of the seed’s protein at maturity and as a consequence it is this group that largely determines the nutritional and processing qualities of grain. Features of the synthesis, localization, and properties of the major storage proteins have been reviewed extensively and, more recently, details of the regulatory mechanisms that determine their synthesis in response to changes in plant nutrition and environmental conditions are being revealed. While most of the incoming N is used for protein synthesis, seeds may also accumulate quite a significant pool of free protein amino acids that persists to maturation and constitutes a ‘store’ at maturity. The amides glutamine and asparagine are common constituents of this soluble-N pool but other amino acids may predominate in some species. One of these soluble reserves is arginine. In soybean arginine is synthesized in developing cotyledons as well as being supplied from the seedcoat to the embryo through the apoplast. Its accumulation to more than 60% of the free amino acid pool apparently occurs because arginase is not expressed

PROTEINS | Nitrogen Metabolism in the embryo. The accumulation of lysine and other amino acids of the aspartate family in maize endosperm was noted above and doubtless there are numerous other examples that occur in nature. Seeds accumulate significant quantities of non-protein amino acids. Some of these, such as homoserine, are intermediates in the synthesis of the 20 protein amino acids while others are accumulated as end products of metabolism. Some, such as the arginine analogue canavanine, are highly toxic to insects and other potential herbivores apparently serving to protect the developing or mature grain. Canavanine can reach levels that are 6% of the dry weight in the seeds of Canavalia ensiformis and so represent a significant stored reserve of N. Mature groundnut (Arachis hypogea) seeds contain high levels of g-methylene-glutamine that is mobilized to the developing seedling following germination but is not metabolized to any great extent, apparently accumulating again in the next generation of seed. There are hundreds of nonprotein amino and imino acids formed by plants with the overwhelming majority of these accumulated in seeds. Many of these occur in sufficient amounts that they could be construed as a stored reserve but the physiological and biochemical studies to confirm this role have yet to be undertaken.

Mobilization of N Reserves in Germinating Seeds While the N reserves in seeds are principally in the form of storage proteins, as germination proceeds N from nucleic acids or metabolic proteins that might have been formed before dehydration or subsequently following imbibition is also available. The possibility that allantoin is formed from nucleic acid catabolism has been indicated earlier. Additionally seeds mature with what can be a significant soluble N pool and this appears to have a specialized role in the first few hours/days of germination when the newly activated meristems of the embryo begin to grow rapidly. Arginine has been recognized as a common constituent that fulfils this role. Its accumulation as the seed matures results from suppression of an enzyme, arginase, which would normally catabolize the amino acid. However, within a day after imbibition arginase transcript level and activity increase sharply in the cotyledons to release urea and, as a result of urease activity, ammonium ion for reassimilation and translocation to the new meristems. It is likely that the translocated N-solute at this time is glutamine. Thus arginine is a ‘compact’ form of stored N (C:N ratio of 1.5) that provides an almost instant N source, and is no doubt used in this role in a wide range of species (e.g., pumpkin and pea seeds). Whether other soluble N-compounds that accumulate in maturing seeds function as initial sources of N for germination is not known. Ammonia released from oxidation of free and mobilized amino acids can account for 50% of the N made available during germination of Arabidopsis seeds indicating, as during seed development, a central role for GS/GOGAT in reassimilation. QTLs for enhanced germination efficiency in maize have been identified that are co-localized with two of the GS1 (cytosolic forms of glutamine synthetase) structural genes, gln3 and gln4, emphasizing the importance of ammonia

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reassimilation in regulating the germination process. Such markers offer the potential to breed for complex traits related to seed N metabolism in grain improvement program.

Future Prospects Despite the wealth of knowledge about the composition of seeds and the nature of their stored reserves, factors that determine which reserves are formed and stored and the roles of environmental cues in these processes have yet to be established. Clearly there is tissue-specific and temporal expression of genes that encode biosynthetic enzymes but the nature of the mechanisms that integrate metabolism so that stored N-reserves are generated to maximize the available resources of C, N, and S need to be resolved. Although functional genomic or proteomic analyses have been applied to developing seed tissue they have yet to reveal new information about more detailed aspects of the pathways and regulation of N metabolism and transport. As genomic analysis is extended to a wider range of plants this information will become available providing new tools for both understanding and manipulating grain development. Significant changes to grain composition through selection from germplasm collections, conventional breeding and the exploitation of direct genetic engineering will be an ongoing area for research as novel, more nutritious and health promoting food ingredients are sought. Because plants engage in a bewildering diversity of N metabolic end products, many of which accumulate in seeds, it is important that critical studies of N metabolism are extended beyond the handful of species for which information is currently available.


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Draw up a flow chart showing the movement of nitrogen from the farmer’s field to the final grain-based food product. Investigate further the concepts of source and sink in relation to carbon and nitrogen metabolism in cereals. How useful are these concepts?


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Investigate the current understanding of nitrogen metabolism in relation to endosperm protein formation in a selected cereal grain. What techniques are available to study nitrogen fluxes in cereal plants? What are the energetic limitations to increased protein content in cereals?

See also: Carbohydrates: Carbohydrate Metabolism; Starch: Chemistry; Proteins: Protein Synthesis and Deposition; The Enzymes Associated with Food Grains and Their Functions in Processing; The Protein Chemistry of Dicotyledonous Grains; The Basics: Grain: Morphology of Internal Structure; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

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Further Reading Editorial (1995) The plant cell – special review issue on plant biochemistry. Plant Cell 7: 795–1111. Atkins CA (2000) Biochemical aspects of assimilate transfers along the phloem path: N-solutes in lupins. Australian Journal of Plant Physiology 27: 531–537. Azevedo RA, Arruda P, Turner WL, and Lea PJ (1997) Review Article Number 121: The biosynthesis and metabolism of the aspartate derived amino acids in higher plants. Phytochemistry 46: 395–419. Bewley JD and Black M (1985) Seeds. Physiology of Development and Germination. NY: Plenum Press. Kozlowski TT (ed.) (1972) Seed Biology, vol I. Importance Development and Germination. NY: Academic Press.

Lea PJ and Ireland RJ (1999) Nitrogen metabolism in higher plants. In: Singh BK (ed.) Plant Amino Acids, pp. 1–47. NY: Marcel Dekker. Murray DR (1987) Nutritive role of seedcoats in developing legume seeds. American Journal of Botany 74: 1122–1137. Rosenthal GA (1982) Plant Nonprotein and Imino Acids. NY: Academic Press.

Relevant Websites mpiz-koeln.mpg.de http://www.mpiz-koeln.mpg.de. dijon.inra.fr http://www.dijon.inra.fr.

Nitrogen in Grain Production Systems XM Zhou, McGill University, Ste-Anne-de-Bellevue, QC, Canada BL Ma, Agriculture and Agri-Food Canada, Ottawa, ON, Canada DL Smith, McGill University, Ste-Anne-de-Bellevue, QC, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 277–286, ã 2004, Elsevier Ltd.

Topic Highlights

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The nitrogen cycle refers to the dynamic flow of nitogen from the atmosphere to plants and animals and its recycling. Nitrogen is fixed through nitrogen (atmospheric fixation), biological fixation, and industrial fixation through the Haber-Bosch process. Nitrate and ammonium are taken up and assimilated by plants, and produce amino acids and thence the storage proteins of the grain. Inappropriate use of fertilizers may result in nitrate run-off to surface water, and consequent environmental health risks.

most common inorganic forms include dinitrogen (N2) gas, nitric acid (HNO3), nitrate (NO 3 ), nitrite (NO2 ), ammonium þ (NH4 ), gaseous nitrous oxide (N2O), gaseous nitric oxide (NO), gaseous nitrogen dioxide (NO2), and gaseous ammonia (NH3). The most common N-containing biomolecules belong to one of the following three chemical families: proteins (including enzymes) and related compounds (including peptides and amino acids), nucleotides (largely RNA and DNA), and porphyins (e.g., cytochromes and chlorophyll). Although N constitutes only 1–7% (w/w) of plant dry matter, it is the element most frequently limiting the plant growth. Sufficient nitrogen is fundamental for crop growth, development, and yield. Improvement in N use-efficiency is thus the key to produce safe and high-quality food and feed in an environmentally responsible way.

Learning Objectives

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To understand the fixation of nitrogen from the atmosphere and its processing into storage proteins of the grain or seed. To understand the importance of crop management practices in reducing environmental harm caused by nitrogen runoff.

Introduction Nitrogen (N) is the largest component of the Earth’s atmosphere, comprising 78% (by volume) of the air we breathe. It is usually present in the atmosphere as a dinitrogen gas (N2), which is colorless, odorless, tasteless, and relatively inert at room temperature. Nitrogen was first identified by the chemist and physician Daniel Rutherford in 1772. It is now known to be present in a vast range of materials encountered in our day-to-day existence; foods, fertilizers, poisons, and explosives are a few general examples. Some specific examples are: nitrogen gas is used as a blanketing medium during the production of electronic components, as an agent for annealing stainless steel, in beverage processing, as a refrigerant for food protection and preservation, and as a major fertilizer in crop production. Atmospheric nitrogen is also responsible for the orange-red, blue-green, blue-violet, and deep violet colors of the aurora. More importantly, N is a component of a wide range of biological compounds, being fourth in abundance after carbon (C), hydrogen (H), and oxygen (O). Nitrogen exists in organic and inorganic forms in the atmosphere, biosphere, hydrosphere, and geosphere. It can be present in gas, liquid (dissolved in water), or solid phases. The


The Nitrogen Cycle Nitrogen is a dynamic element and is recycled continually by plants and animals. It can be transformed from one oxidation state to another through processes that comprise the N cycle (Figure 1). The term ‘cycle’ is really a misnomer as the pathways of N in the biosphere are actually a simple web. Nitrogen moves among oxidation states, with ammonia (NH3) being the most reduced and nitrate (NO 3 ) the most oxidized. The tremendous chemical stability of dinitrogen (N2) gas makes the conversion of this compound into ammonia (NH3) or oxides of N (NO 3 ) energetically expensive and the ratelimiting step in this part of the ‘cycle.’ This causes N2 to accumulate in the atmosphere. Thus, cycling of nitrogen by various biological entities determines a major part of the composition of the Earth’s atmosphere. It is a paradox that while 78% of the Earth’s atmosphere is N2 gas, and plant stems, leaves, flowers, and fruits are immersed in this gas, biologically available N is generally the most limiting nutrient element for crop production. A solution to this problem evolved in the exquisitely adaptable prokaryotes. A limited number of microorganisms are able to react N2 with electrons to form NH3, which they then incorporate into various biomolecules. When these microorganisms die, N is mineralized to simple forms (NH3, NO 3 ) through decomposition by other microorganisms. In these forms, N is available to higher plants. Nitrogen is taken up by crop plants, which become food for animals, including human beings, and energy sources for bacteria or fungi; N is then cycled back to the soil when dead cells and tissues of organisms (plant debris for example) or N-containing waste products (such as animal urine and feces) are broken down by soil microbes.

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Removal N from harvest

Gaseous losses N2, NOx into atmosphere

Chemical fertilizer Rainfall (HNO 3) and fertilizer NH4+

Animal and plant residues

Denitrification Soil organic matter R-NH2

Plant uptake Symbiotic and nonsymbiotic N2 fixation

Mineralization

Nitrates NO3 Nitrification

Soluble and exchangeable ammonium NH4+

Nitrites NO2

Micelle fixation

Nitrification Metal and clay organic complexes

Leaching Figure 1 A diagram of the N ‘cycle’ in a typical grain crop containing agri-ecosystem.

In natural ecosystems, N changes from one form to the other, but most of it remains within the nearly closed system in a dynamic balance. In agricultural systems, humans often add chemical N, fixed through industrial processes, a significant portion of which is eventually removed from the field in harvested material. Food, fiber, and livestock are now often produced primarily in one location and transported to other regions of the world for consumption, making crop production fields into nutrient flow-through systems. Nitrogen input into agriculture production systems is largely from chemical fertilizers, or N-fixing crops (including those grown as green manures). There are other minor sources, such as biosolid waste products, which are sometimes added to croplands. A small amount of N comes with precipitation, sometimes associated with lightning discharges, which reacts the N2 and O2 in the atmosphere. There is some N-cycling within agricultural systems, with livestock manures constituting the major component of this process. Nitrogen outputs from crop production systems include removal of harvested grains and forage biomass from production systems and losses of various N forms through runoff (surface water), leaching (to ground water), denitrification (production of gaseous N2O), and volatilization (generally NH3). Because of leaching and gaseous losses, and aspects of plant N physiology, only 50% of the N applied to crop

production systems is taken up by the plants, with the remainder being unusable or lost. Globally, various forms of N are in a dynamic balance. Soil microbes play a wide range of roles in the N cycle. Because of this, these processes are dependent on temperature, moisture, and the quality and quantity of soil organic matter available to them. It is microbes that break down most of the organic material, leading to ‘mineralization’ of organic N. Microbial populations in the soil can take up large amounts of N released from decomposing plant tissues, as long as there is sufficient reduced carbon available, leading to ‘immobilization’ of N. The conversion of ammonium (NHþ 4 ) to nitrite (NO 2 ) and to nitrate (NO3 ) is referred to as nitrification. All forms of N in the soil (except N2 gas) can be converted to NO 3 by soil microorganisms, under aerobic conditions when soil temperatures are above freezing. The amount of nitrification is controlled by the supply of NHþ 4 which is, in turn, controlled by decomposition rates, plant and microbial growth, and soil pH, or by N-fertilizer addition rates. Nitrate can be converted back into N2, or into nitrous oxide (N2O), through denitrification. This process often takes place under anaerobic (generally water saturated) soil conditions. In this process, soil NO 3 can be reduced to N2 gas through a series of intermediate steps [NO 3 ! NO2 ! NO (gaseous nitric oxide) ! N2O] and finally to N2 (gas). The

PROTEINS | Nitrogen in Grain Production Systems intermediate and final products of denitrification, are released into the atmosphere. Denitrification may lead to the loss of 4–5% of soil NO 3 each day when soil remains water saturated. Microbes play a key role in most aspects of the N cycle, generally extracting energy by converting forms of N out of equilibrium with the oxidation state of their environment into forms that are in equilibrium, and extracting a reasonable portion of the energy liberated through this process. This causes N to move among forms that are biologically available or unavailable, mobile or immobile, oxidized or reduced, gaseous or solid.

Nitrogen Sources Nitrogen exists in inorganic or organic forms in our environ ment. Inorganic forms include NO 3 , NO2 , NH3, and N2 whereas organic N is found in a wide range of biomolecules. Protein is one of major classes of biomolecules and generally the largest repository of organic N in the biosphere. RuBisCo, the plant protein responsible for the uptake of CO2 by C3 plants, is the most abundant protein on the planet. The other two most abundant classes of biocompounds, carbohydrates, and lipids, generally have little N associated with them. Over 90–99% of N in the surface (or tillage layer; 0–25 cm) layer of most soils is in organic forms. Although there is an abundant potential supply of N in the Earth’s atmosphere (N2 gas), the unique geometry of the triple bond between the two N atoms results in a very stable compound that is very energetically expensive to break. Thus, this form of N cannot be used directly by most organisms. Whenever dinitrogen is converted into other forms, a large input of energy is involved. The major sources of this energy are: (1) lightning in the case of atmospheric fixation, which accounts for 5–8% of total N fixed and potentially available to the biosphere. This process results in the combination of oxygen from the atmosphere with dinitrogen, causing the formation of N oxides. These compounds dissolve in rain water and are carried to Earth; (2) reduced carbon and adenosine triphosphate (ATP) in the case of biological N fixation, conducted by certain prokaryotes alone or in symbiotic relationships with plants and sometimes animals; and (3) fossil fuels for industrial fixation. Industrial fixation relies on the Haber–Bosh process, developed during the First World War for the production of explosives. This process uses a catalyst, high pressure, and high temperature (600 C), to combine N from the atmosphere with hydrogen (usually derived from natural gas or petroleum) to produce ammonia (NH3). Ammonia can be used directly as fertilizer, reacted with CO2 to form urea ((NH2)2CO), and/or oxidized to form nitrate (NO 3 ) which can be salted with other compounds (such as ammonium, NHþ 4 ) to form other types of N fertilizers (e.g., ammonium nitrate). The large requirement for energy makes N fertilizer easily the largest component of fossil fuel consumption in crop production, being close to 50% of the total for crops such as maize. The bulk of the soil N in noncropland systems comes from fixation by symbiotic bacteria (largely genera associated with legumes and collectively referred to as rhizobia and species of Frankia, usually symbiotic with woody plants), fixation by free-living bacteria and mineralization of organic matter

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(N released as decomposition of plant and animal residues). The potentially available N (90–99%) in the soil is in organic forms, the rest being in inorganic (or mineral) forms. The organic forms are not immediately available for plant use and have to be decomposed by soil microorganisms through mineralization. In addition, a very small amount of organic N may exist in relatively small soluble compounds, such as urea or amino-sugars, which may be slightly available to plants. Symbiotic (largely legume) N-fixation and mineral fertilizer N are the major sources of N for grain production systems, with animal and green manures, crop residues, composts, sludges, soil micro- and macro-biota being the other possible sources. Again, organic N must be mineralized before it is available to plants. Sodium nitrate (NaNO3) and potassium nitrate (KNO3) are formed by the decomposition of organic matter. In certain dry areas of the world, these saltpeters are found in quantity and are used as fertilizers. Other inorganic N compounds are ammonia (NH3), nitric acid (HNO3), the N oxides (NO, NO2, NO3, N2O), cyanides (CN), etc. However, inorganic N in soil generally comprises only a small portion of soil N. Hence, despite N being one of the most abundant elements on the biosphere, N deficiency is probably the most common nutritional problem affecting crop plant production worldwide.

Nitrogen Availability to Crop Plants The availability of N sources is a fundamental requirement for metabolism as it allows N assimilation into amino acids (for which photosynthetically produced carbon compounds are also required) and their availability for protein synthesis. An adequate supply of N allows leaf growth and photosynthesis. Inorganic (or mineral) forms of N, such as NHþ 4 and NO3 , comprise the majority of plant-available N. Other forms of N must be converted to one of these compounds by either natural or artificial means before they can be utilized by plants. When N is first released from organic matter, it is in the form of gaseous NH3, which is volatile and can be lost to the atmosphere. When NH3 dissolves in water, it acquires a proton and becomes ammonium (NHþ 4 ), which carries a positive charge and is attracted by the soil clay colloids and soil organic matter, which carry negative charges. Once attached to the soil matrix, NHþ 4 becomes part of the cation-exchange process whereby plants exchange a hydrogen ion (Hþ) for one of the positively charged molecules in the soil. Only a small portion of the soil þ NHþ 4 exists in the soil solution; this NH4 is available to crop plants. On the other hand, NO3 carries a negative charge, and so is not bound by clay particles. Thus, NO 3 molecules are free to move with the soil water and are more readily available to crop plants than NHþ 4 . However, in coarse textured or watersaturated soils, NO 3 is much more prone to leaching into groundwater than NHþ 4 ; once in ground water NO3 becomes a potentially serious pollutant.

Nitrogen Fixation A symbiotic relationship between leguminous plants and N-fixing bacteria allows for plant-based biological N fixation.

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The major conversion of N2 into NH3 (a biologically available form) is the biological N-fixation process, carried out by singlecelled prokaryotes. This process requires a great deal of energy, supplied as ATP, which is derived from the breakdown of organic matter, or through photosynthesis (e.g., cyanobacteria). It is estimated that biological N fixation accounts for the annual production of as much as 250 109 kg of ammonia, which is twice the amount produced by the Haber–Bosch process. Biological N fixation can be described as the following equation: N2 þ 8Hþ þ 8e þ 16ATP ¼ 2NH3 þ H2 þ16ADP þ 16Pi This reaction is conducted by prokaryotes only (eubacteria and archea) through the enzyme dinitrogenase, and the closely associated dinitrogenase reductase. Dinitrogenase contains both iron and molybdenum in a cofactor referred to as FeMoco. The fixation of N is carried out while N2 is bound to dinitrogenase. Dinitrogenase reductase (the Fe protein) is reduced by electrons donated by a protein generally containing ferredoxin. Reduced dinitrogenase reductase (Fe protein) binds ATP and reduces dinitrogenase (molybdenum-iron protein), which provides electrons to N2 resulting in its reduction to 2NH3. Due to its economic importance and agronomic value, the legume-rhizobia symbiosis is the most investigated process of biological N fixation. Many grain legumes are important crops due to this symbiotic relationship; these include soybean, bean, mung bean, faba bean, peanut, and pea as well as forage legumes such as alfalfa, clover, sainfoin, fenugreek, and vetch. During the establishment of this symbiotic process, rhizobia infect the roots of legume plants and cause the formation of nodules. It is in these nodules that the bacteria fix N and supply it to the plant. The plant provides reduced carbon (sugars) to the nodules, where it is converted to organic acids and supplied to the bacteria as an energy source. In most cases, the symbiosis can supply all N required for normal growth and development of the plant. The amount of N fixed by legume plants is estimated to range from 11 to 250 kg N ha1 year1. When fertilizer N is supplied, N fixation is inhibited through several long and short-term mechanisms, so that adding N fertilizer to N-fixing legumes does not increase the amount of N available to the plants. For grain legumes, however, a small amount of starter N fertilizer greatly helps crop growth prior to the time when nodules become functional and begin to supply N. The simplest approach for evaluating whether nodules in fieldgrown legumes are able to fix N is to observe their interior color: effective nodules contain leghemoglobin and are bright red, while nodules not yet functional are generally white and those that are no longer functioning are generally greenish. Leghemoglobin carries oxygen into N-fixing (rhizobia containing) nodule cells, ensuring the availability of large quantities of oxygen, but in a very controlled fashion, to the noduleenclosed rhizobia. On the other hand, all field crops in the grass family, such as the grain crops maize, sorghum, rice, and wheat, as well as forage grasses, and also nonleguminous broadleaf field crops (e.g., sunflowers, potatoes, sugar beets, cotton, etc.) are unable to form N-fixing root nodules. Therefore, these plants must obtain their required N from the soil and other exogenous sources.

Table 1

Annual N inputs and outputs of typical agricultural land N (kg ha1)

Inputs Plant residues Biological N fixation Natural fertilization through precipitation Chemical fertilizer Outputs Volatilization of NH3 Dinitrification Leaching Crop harvest

10–100 10–250 0–50 0–400 0–60 10–70 10–70 10–150

At present, almost 90 genera of diazotrophic bacteria, which can reduce atmospheric dinitrogen to ammonia with varying efficiencies, are known. Biological N fixation can be carried out by a wide range of prokaryotes, alone or in symbiosis, including cyanobacteria free living and in symbiosis in lichens, cycades, the fern Azolla or the angiosperm Gunnera; and free-living soil bacteria. These types of N fixation contribute significant quantities of NH3 to natural ecosystems, but not to most cropping systems, with the exception of paddy rice. Their contributions are generally less than 5 kg N ha1 year1. Table 1 indicates the general annual input and output of N in agricultural ecosystems.

Symbiotic Signals Nitrogen fixing root nodules are the result of symbiotic interactions between leguminous plants and rhizobia. This begins with a recently elucidated signal exchange between the two symbiotic partners. Initially, the roots of leguminous plants secrete flavonoid compounds into the soil. These compounds activate a set of genes in the appropriate rhizobia. A structurally diverse mixture of lipo-chitooligosaccharides (LCOs) is produced by rhizobia after induction with flavonoids. LCOs consist of a chitooligosaccharide backbone of b-1,4-linked N-acetyl-d-gluconsamine (GlcNac) and a fatty acyl group attached to the nonreducing saccharide. Diversity of the fatty acyl substituents (length and degree of unsaturation) contributes to the diversity of LCOs. In addition, various groups can be added to the chitin backbone. The nodE gene determines the nature of the fatty acyl moiety, a major determinant of host range. LCOs are considered to be key factors in the specific recognition processes that underlie the formation of leguminous root nodules and their bacterial infection; in these associations only appropriate legume and rhizobium matches can come together and create a specific symbiosis.

Uptake þ Nitrate (NO 3 ) and ammonium (NH4 ) are the two major mineral forms of N taken up and assimilated by plants. These compounds enter the plant roots by diffusion through the space between root cells until they cross the plasma lemma and enter the plant cell interior. Once inside the symplast

PROTEINS | Nitrogen in Grain Production Systems (for a review of the ‘symplast,’ see www.worldreference.com) these compounds can be stored in vacuoles, assimilated into amino acids or proteins or moved into the stele (xylem) for transport elsewhere in the plant. Movement among the cells that make up the symplast is through the plasmodesmata that connect plant cells. All mineral N must enter the symplast before entering the stele. This can happen at any point in the root cortex, but must happen by the time mineral N molecules reach the casparian strip. During the course of the vegetative þ growth, both NO 3 and NH4 enter the plant root and are transported via the xylem to the leaf (Figure 2). Once it reaches the leaf, nitrate reduction takes place, leading to the production of amino acids. Most of the newly formed organic acids are then translocated to the root where carboxyl groups are exchanged for an ammonium and the newly assimilated N is incorporated largely into leaf N compounds (protein). When a large quantity of N is required by developing fruits and filling seeds (reproductive growth stage), leaf proteolysis occurs and a great deal of the amino N in the leaf is ultimately exported to the filling fruits where it is accumulated as seed storage proteins (Figure 2). As a result, the phloem is enriched with amino compounds, which repress nitrate uptake and diminish the rate of nitrate reduction. Improved crop yield due to increased fertilizer N application suggested that the availability of N (usually nitrate in agricultural soils) is often the limiting factor in plant growth. The absorption of NO 3 by roots is not only determined by the N demand of the plant, but also by its availability in the soil environment. Nitrate absorbed via roots is either reduced in situ into ammonium, imported into vacuoles (by high- and low-affinity transport systems) for storage, or transported via the xylem to the shoot where it can either be metabolized or stored as a reserve. A low-affinity root NO 3 uptake system may play a greater role in nitrate uptake. In some cases, a high-affinity system has been shown to be the major mode of nitrate uptake through uptake competition studies and membrane voltage change studies. The low affinity transport system (LATS) (possibly a carrier system or an anion channel), and the inducible, high affinity transport system (HATS) are regulated by cellular energy supply, intracellular nitrate levels, and a proton electrochemical gradient. The latter is regarded as an Hþ/anion cotransport carrier system that produces transient plasma membrane depolarization upon addition of nitrate. The depolarization is counteracted by the plasma membrane Hþ-ATPase. The plasma membrane proton ATPase is induced by nitrate. In addition to the nitrate uptake system, plants have an inducible nitrate efflux system, requiring both RNA and protein synthesis. The efflux system, however, has a much slower rate than the uptake system. In the agricultural soils of tropical and temperate regions (except paddy rice fields), nitrate accounts for 70–90% of soil mineral N. Nitrate in the soil solution is 10 times more mobile þ than NHþ 4 . Two reserves of soil NH4 exist: a small portion of is in the soil solution, and a large portion of NHþ NHþ 4 4 is adsorbed on soil colloids. Only water soluble NHþ 4 is available for plant uptake. Depending on the plant species, the bulk of the nitrate entering the plant is reduced to ammonia and assimilated into organic compounds in the roots or in the þ leaves. Plants can take up either NO 3 , NH4 , or mixtures of the two. In most cases, crop plants perform better when the

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þ mixture of NO 3 and NH4 fertilizer is provided than either one alone. Uptake of NO3 by roots is governed by the concentration of NO 3 in the soil solution, the volume of soil exploited by roots and root density within that volume, and plant demand for N, the latter being largely related to plant growth, development, and production. The root uptake efficiency of N is affected by metabolic demand, N concentration around the roots, and conditions such as temperature. Ammonium is mainly assimilated in roots. It or alanine, formed by organic acid ammonization, is the main form of N exported from symbiotic N2-fixing microorganisms to their host plants. In soil, NHþ 4 comes mainly from the mineralization of organic matter. When NO 3 levels in the soil are low or completely exhausted, plants can rely on NHþ 4 released from cation-exchange sites or through mineralization of organic matter. During NHþ 4 assimilation in the root, excess þ Hþ is generated (3NHþ 4 ¼ 3R NH2 þ 4H ) and released directly to external solution. While NO3 assimilation occurs excess OH is produced (3NO 3 ¼ 3R NH2 þ 2OH ). This excess OH may be neutralized by carboxylation or by HCO3 released from the roots. Thus an Hþ neutral synthesis of plant materials can occur with a ratio of assimilation of 1NHþ 4 per 2NO3 . This is why many plant species grow optimally with a mixture of mineral N compounds (NO 3 and þ þ NHþ 4 ). With a mixed N solution (NO3 and NH4 ), NH4 is often the form of N preferentially taken up by the plant. Many forest species take up primarily NHþ 4 , since forest soils are relatively acidic, inhibiting the development of populations of bacteria that cause nitrification. The average NHþ 4 concentration in well-aerated soil is 10–100 times lower than NO 3 , rarely exceeding 0.1–2 ppm. However, absorption of NHþ 4 by plant roots can occur at very high rates, due to the presence of transport systems in the root plasma membrane þ with high substrate affinities. Like NO 3 , NH4 uptake by roots is diurnally regulated, with maximum uptake during the light period. Uptake is stimulated by sugar supply, implying that the greater uptake during the day is related to the availability of photosynthate.

Assimilation of Nitrogen Both nitrate and ammonium are taken up and assimilated by plants. In general, NO 3 is the predominant form of inorganic N taken up by grain crop plant roots (except paddy rice). Under most circumstances, absorbed nitrate is reduced to ammonium in roots and/or leaves, and is then utilized in the synthesis of amino acids and proteins. Whatever the source of ammonium in plants, this ion is first converted into amino acids, the building blocks of protein. Nitrate is assimilated into organic compounds by GS/ GOGAT (GS – glutamine synthetase/glutamate synthase; GOGAT – glutamate oxidase, glutamine amino tranferase). The GS/GOGAT pathway is considered the major pathway for incorporating reduced N into organic molecules. This pathway recycles glutamate; amino groups are eventually transferred to other amino acids and utilized for protein synthesis and also for synthesis of other key biomolecules such as RNA, DNA, and porphyrins.

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Ammonia assimilation Proteins

Proteins

Seeds

Mitochondrion NH1

Albumins Globulins Prolamins (cereal)

AA

Chloroplast

GS2 NIR NH4+

NH1

NO2–

Vacuole NH4+

NH4+

HNO3–

NH+4 Leaf

Stem NO3–

Phloem

NO2–

Nitrate reduction (cytoplasm) NR

HNO–3 NO3–

NO2–

NH+4 NO3–

Nitrite reduction (plastid) NO2– NIR NH+ 4

Xylem

Amino acid (AA)

Root

Symbiotic nitrogen fixation NO3–

NH+4 HNO–3

AA

NH+4

Protein

Plasma membrane GS2 Plastid AA NIR – + NH4 NO2 GS1 Vacuole NH+4 NH+4

NH+4

N2 + 3H2

2NH3

Nitrate reduction (cytosol) NR NO3–

HNO–3

NO3–

Figure 2 A diagrammatic summary of N metabolism in a grain crop.

GS and GOGAT are located in the cytosol (for a review of the ‘cytosol,’ see www.worldreference.com) and the chloroplast (for a review of ‘chloroplast,’ see www.worldreference. com). Their activity in particular plant tissues is closely linked to specific primary N assimilation, NH3 recycling during photorespiration, or general N remobilization. There are two pathways for incorporation of N into amino acids: (1) Direct

incorporation where glutamate dehydrogenase is involved: a-ketoglutarate þ NH3 þ NADH ! glutamate þ NADþ; (2) GSGOGAT cycle: GS catalyses the ATP-dependent conversion of glutamine utilizing ammonia as substrate and is represented by two protein groups, plastid (GS1) and cytosolic (GS2) isoenzymes; GS1 is located exclusively in chlorophyllous tissues while GS2 is located predominantly in roots, nodules, and floral

PROTEINS | Nitrogen in Grain Production Systems organs. GOGAT catalyzes the conversion of glutamine and a-ketoglutarate to glutamate: glutamine þ a-ketoglutarate þ NADPþ H þ Hþ ! 2 glutamate þ NADPþ. The assimilation of NH3 may be by either glutamate dehydrogenase or GS/GOGAT; the first of these requires quite high concentrations and the bulk of uptake is thought to be through GS/GOGAT. Following the incorporation of NH3 into glutamine, N can be transferred directly to the same position in asparagine by asparagine synthetase. Amino transferase can transfer the amino group to aspartate, which is converted to asparagine. It has been suggested that the reaction catalyzed by Fd-GOGAT is the key regulatory element controlling N partitioning and redistribution during plant growth and development. To date, research has focussed on modifying ammonia assimilation in transgenic plants and this has demonstrated that the amplification or shifting of ammonium assimilation in a particular organ or tissue has strong effects on plant growth and development. Thus, there appears to be great potential for improving N-use efficiency in crop plants.

Reduction of Nitrate and Nitrite Once NO 3 enters the root symplast, it may follow five pathways: 1. efflux back to the apoplast [for a review of ‘apoplast’ see www.worldreference.com]; þ 2. reduction of NO 3 to NO2 , then NH4 by nitrate reductase (NR) using the reduced form of nicotinamide adenine dinucleotide (NADH) and by nitrite reductase (NIR) using ferredoxin (Fd) in root cells, leading to the production of amino acids; 3. accumulation into vacuoles of root cells, involving transport across the tonoplast [for a review of ‘tonoplast’ see www.worldreference.com]; 4. secretion into xylem vessels for long distance transport to the shoots; and 5. reduction of NO 3 in the leaves, often using excess reductant in upper, CO2 limited, leaves. High concentrations of nitrate can be found in vacuoles, indicating that nitrate not only acts as a nutrient but also participates in osmotic maintenance. The first step in the nitrate assimilation pathway is the reduction of nitrate to nitrite, catalyzed by assimilatory NR. When reduction occurs in leaves, the nitrite formed by NR activity is then translocated to the chloroplast, where it is further reduced to NHþ 4 by NIR. During the nitrate reduction process, NR activity appears to be the rateþ limiting step in the conversion of NO 3 to NH3/NH4 , because it is (1) the first enzyme in the pathway NO3 of assimilation, (2) substrate inducible, (3) relatively unstable, and (4) it’s activity – relative to other enzymes in the NO 3 assimilation pathway – is low and its Km (related to binding affinity) for NO 3 is high. Further, there is evidence that when nitrate is the dominant N source, nitrate reductase activity (NRA) is the limiting factor to the growth of many plants. NR has therefore been intensively studied in order to understand it’s catalytic efficiency and regulation. Nitrite is reduced to NHþ 4 by NIR

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using ferredoxin (Fd). Nitrite reductase is located in plastids and possesses Fe–S and heme cofactors. Subsequently, the is incorporated into carbon compounds: amides NHþ 4 (amino acids) and ureides. Nitrate reduction occurs mainly within the chloroplasts of green leaves, but can also occur within plastids of roots. Induction and the rate of nitrate uptake depend on the external nitrate concentration, light, pH, temperature, the concentration of other ions, anaerobic conditions, metabolic inhibitors, and biological genotypes. Since nitrate reductase contains Mo, Mo deficiency can cause N deficiency.

Nitrogen Storage Seed storage proteins comprise 70% (up to 100% in some developing countries) of total intake of dietary protein by humans. It also provides the major protein source in the diet for nonruminant livestock. The amino acids in the leaves, produced from assimilated NO 3 with energy and carbohydrates produced by photosynthesis, are transported to the embryo and the cotyledons via mass flux in phloem vessels of the leaf. The main transport forms of amino acids are: glutamine, asparagine, serine, alanine, glutamate, and aspartate. As a result, storage proteins are the products of the secretary pathway, which resides within the endomembrane system of the cell. In general, N assimilates available to developing grains are mainly used for the synthesis of proteins. These proteins then are accumulated and stored in specialized tissues such as the endosperm of cereals, other endospermic monocotyledons, or the cotyledons of the embryo for the pulse legumes and other nonendospermic dicotyledons. Grains of cereal crops usually contain 7–19% protein while the seeds of legume crops contain up to 40% protein, in both cases on a dry matter basis. Tuber crops are rich in soluble carbohydrates and low in protein. For example, the crude protein concentration in sweet potato is twice that of potato (12.1% versus 5.4%). Thus, when tuber crops are used as human food or animal feed, they are a good source of energy, but require protein supplementation. Almost all storage proteins in the seeds of major crops can be grouped into three categories according to their functions: (1) globulins (soluble in dilute saline solutions), the most common storage proteins, are present in all angiosperm seeds; (2) albumins (soluble in water); (3) prolamins (soluble in dilute alcohol) and restricted to the seeds of Gramineae (grass) family. This protein represents the main storage protein in cereals such as wheat (gliadins), barley (hordeins), oat (globulins), rice (glutelins), rye (secalins), and maize (zeins). Both albumins and globulins have biological functions. This is particularly true of enzymes during seed germination. In most cases, storage proteins have no biological activity and only act as a source of N, sulfur, and carbon skeletons for the developing seed. Thus, storage proteins are not as evolutionarily constrained as those of other proteins, such as enzymes, although there is a requirement that proteins should be efficiently synthesized, packaged, and stored, and then remobilized during the process of seed germination.

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Interactions between Nitrogen and Carbon Metabolism The products of photosynthesis are the building blocks of agricultural production. From a production point of view, the efficiency of photosynthesis is mainly determined by the availability of light, CO2, water, heat (temperature), and key elements in the soil, with N being the most likely to be limiting. Precipitation is outside management control in crop production systems, although irrigation may provide reliable water where water resources are available. Nitrogen application, including aspects such as quantity, timing, and method is part of most crop management regimes. Grain yield is largely a function of accumulation of photosynthetic assimilates. The interactions between carbon dioxide (CO2) and nitrate assimilation and their dynamics are key elements of crop production. As a result, an adequate supply of N, its assimilation into amino acids (for which photosynthetically produced carbon compounds are required), and their availability for protein synthesis, are essential for metabolism. Nitrate is reduced to NH3 by NR and NIR using electrons from photosynthetic electron transport. The NH3 is then converted into amino acids by the GS/GOGAT reaction (the main pathway by which plants convert ammonia into amino acids), and the ‘carbon-skeletons’ are provided as organic acids derived from the tricarboxylic acid cycle. Carbohydrates for organic acid synthesis, ultimately from photosynthetic CO2 assimilation, and ATP for the GS/GOGAT reaction are produced by photosynthesis and respiration. Thus, there is close interaction in the very earliest phases of N and carbon metabolism, both using light energy, with some 10% of the electron flux in photosynthesizing leaves used for N reduction. During the last 4–6 decades grain yields of major field crops have increased 2.5 fold, largely due to an increase in the production and storage of carbon in grains by efficient crop varieties and increased use of N fertilizer. Although large variations in grain protein concentrations exist among varieties within a species, an increase in yield has generally resulted in a slight to severe decrease in the protein/starch or oil ratio. For example, in the case of maize, the increase in the genetic-based yield potential after 1967 was, on average, accompanied by a decrease in the concentration of protein ( 1.5%) and an increase in that of starch ( 2%). In the case of soybean, genetic selection leading to a seed yield increase of 100 kg ha1, increased seed oil yield by 1 kg ha1, and decreased protein yield by 2–3 kg ha1. For wheat, an increase in yield of 2 kg ha1 led to a decrease in the protein concentration of more than 2% of the dry weight. Plant geneticists and breeders continually make efforts to break this relationship, hoping for increases in yield without decreases in quality.

Nitrogen and Environmental Health Nitrate accumulation in plants occurs when the speed of nitrate uptake exceeds the rate of reduction and subsequent assimilation into amino acid and proteins for growth. A high nitrate accumulation in edible parts of plants consumed as vegetables is a potential health hazard. Although nitrate itself

is not toxic, it can easily be reduced, internally, to the toxic compound nitrite. Reduction to nitrite in vegetables can occur postharvest as well as after ingestion, in saliva and in the gastrointestinal tract. One of the symptoms of nitrite toxicity is methemoglobinaemia, in which NO 2 binds tightly to hemoglobin reducing the ability of the blood to carry oxygen and leading to respiratory dysfunction. Chronic nitrite toxicity may lead to the formation of carcinogenic nitrosamines. The frequency of gastric cancer could be reduced by avoiding high intake of nitrate. According to the International Fertilizer Association, annual world consumption of N fertilizer is equivalent to 83 million tonnes (Mt). North America accounts for 15% of this total world consumption. Nitrogen that is not taken up by plants may lead to gaseous loss to the atmosphere, or an increased level of nitrate in the soil. This nitrate is vulnerable to run off in surface water or leaching into groundwater, causing significant environmental pollution. High concentrations of NO 3 in drinking water due to surface and ground water contamination can also lead to methemoglobinaemia. Nitrous oxide (N2O) is a greenhouse gas with a heattrapping capacity that is 310 times greater than that of CO2. Since the last century N2O emission has been increasing 0.3% year1. Emissions of N2O from cultivated lands are estimated at 3.0–3.5 Mt N2O-N year1. The bulk of current N2O emissions are caused mainly by the application of fertilizer N and biomass burning. When soils become anaerobic, or sometimes during the conversion of NHþ 4 to NO3 , N2O is produced. N2O escapes the soil as a gas and accumulates in the atmosphere where it is both an agent of stratospheric ozone destruction and a very potent greenhouse gas. High levels of soil organic matter and nitrate combined with low oxygen levels promote rapid denitrification. Increasing emissions of greenhouse gases are likely to accelerate global climate change. Average global surface temperature is expected to rise 0.6–2.5 C (33.1–36.5 F) in the next fifty years, and 1.4–5.8 C (34.5–42.4 F) in the next century. Reducing the contamination of drinking water associated with excess application of inorganic fertilizer and manure in agriculture production is a high priority. There is an urgent need to develop new crop production systems that maximize N use efficiency and are less hazardous to the environment. However, the reduced application of fertilizers conflicts with the need for greater crop yields to feed rising world populations. Crop yields would drop to a very low level if N-fertilizer applications were to cease. Many countries that use substantial amounts of fertilizers and export agricultural produce would barely be able to feed their own population in the absence of N-fertilizer applications. To overcome the potentially dangerous social problems of food shortage, environmental degradation and pollution, agricultural yields per unit land area must be increased at the same time as dependence on applied fertilizers is decreased. Agriculture uses N fertilizer very inefficiently (even in developed countries), in part because other environmental conditions are often limiting. Thus, understanding the process of N uptake and assimilation, and mechanisms associated with increased N-use efficiency by crops would be a benefit not only in the context of environmental concerns but also crop quality. Consequently, selection of superior genotypes with efficient N-use and development of sustainable

PROTEINS | Nitrogen in Grain Production Systems production systems for specific regions will solve or at least reduce the negative impact of fertilizer N use on the environment.

Conclusions and Prospects Nitrogen is essential to the growth and reproduction of all plants, and animals. Improved understanding of N dynamics in the biosphere is of both economic and environmental importance in developing sustainable N management strategies for crop production. Absorption of nitrate and ammonium by plant roots is the primary pathway for the entry of N into our food chain. Nitrate and ammonium enter plants through the cell walls and root membranes. This mineral N has to be incorporated into carbon-nitrogen compounds in order to build cellular metabolites, especially protein. Some leguminous plants can convert atmospheric N to bio-available forms through a symbiotic relationship with specific soil bacteria. This rhizobia-legume symbiosis plays a major ecological and economical role on a global scale. A major recent achievement in understanding the rhizobia-legume symbiosis has been the characterization of signal molecules produced during initial communication between leguminous plants and N-fixing bacteria. The specific lipo-oligosaccharide (LCO) signal compounds, also called Nod factors, secreted by rhizobia, are considered to be a new class of growth regulator, affecting plant growth and development and ensuring the formation of N-fixing nodules. Consequently, a better understanding of the whole plant system, from genes, to plantmicrobe relationships, to biomass production, partitioning and grain yield formation might achieve the long-term objective of improved crop N-use efficiency, leading to increased grain crop yield with reduced impact on the environment. For cereals and other nonleguminous grain crops, development of superior genotypes and sustainable production systems with efficient N use continues to be one of the major goals for plant geneticists, crop physiologists, agronomists, grain crop producers, environmental scientists, and policy makers.

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• •

Compare nitrogen use in leguminous and in cereal grain crops. Explain the environmental effects of large-scale nitrogen use in crop agriculture.


• •

What is the current supply situation for nitrogenous fertilizers? What are the constraints to increasing production capacity? How can nitrogen be used more efficiently in agriculture? How can waste be reduced? How important is precision agriculture to the development of solutions in this regard?

See also: Agronomy of Grain Growing: Organic Grain Production and Food Processing; Carbohydrates: Starch: Synthesis; Processing of Grains: Cereals: Breakfast Cereals; Proteins: Nitrogen Metabolism; Protein Synthesis and Deposition; The Protein Chemistry of Dicotyledonous Grains.

Further Reading Follett RF and Hatfield JL (eds.) (2001) Nitrogen in the Environment: Sources, Problems, and Management. New York: Elsevier. Lea PJ and Morot-Gaudry JF (eds.) (2001) Plant Nitrogen. Berlin: Springer. Morot-Gaudry JF (ed.) (2001) Nitrogen Assimilation by Plants: Physiological, Biochemical and Molecular Aspects. Enfield, NH: Science Publishers.

Relevant Websites sws.uiuc.edu http://www.sws.uiuc.edu – Illinois State Water Survey. fertilizer.org http://www.fertilizer.org – International Fertilizer Industrial Association. hort.purdue.edu http://www.hort.purdue.edu – University of Purdue.

The Enzymes Associated with Food Grains and Their Functions in Processing DJ Mares and K Mrva, University of Adelaide, Glen Osmond, SA, Australia GB Fincher, Australian Research Council Centre of Excellence in Plant Cell Walls, University of Adelaide, Glen Osmond, SA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

Enzymes involved in the synthesis and degradation of endosperm cell wall polysaccharides. Synthesis of enzymes during grain development and germination that are involved in the breakdown of starch and protein stored in grain endosperm tissue. Enzymes present in ripe grain that affect the quality, storage, or nutritional value of wheat and wheat-based end products. Endogenous enzyme inhibitors.

Learning Objective

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To achieve a better understanding of the role of specific enzymes in the development, utilization, and storage of cereal grains.

Introduction Enzymes are biological catalysts that direct complex biochemical reactions at temperatures relevant to living organisms and the environments in which they exist. The proteinaceous nature of these molecules allows for a myriad of threedimensional (3-D) structures that will accommodate different substrate specificities and respond to the presence of other ‘regulatory’ molecules, changes in ionic environment, pH, temperature, and hydrophobicity. These interactions often result in alteration to the conformation of the enzyme protein that in turn impacts on binding of substrates, activators, inhibitors, and cofactors or the efficiency of the catalytic activity. In addition to the mechanisms for controlling enzyme activity, the actual amount of enzyme protein in a cell can be controlled via a balance of synthesis and degradation, thus allowing for many tiers of regulatory control. Cells in grains contain a multitude of enzymes that are common to all living cells, including animals and microorganisms, albeit with minor variations in structure and specificity depending on the species. These enzymes, which are essential for general cellular metabolism and function, will not be discussed here, and the reader is referred to any of the numerous plant biochemistry and general biochemistry texts that are readily available. Rather, this article focuses on some of the enzymes that are critical to the specific functions and structures of cereal grains or those that influence the end use of cereal grains or the quality of cereal end products. One of the major functions of cereal grains is to synthesize and sequester starch, protein, and lipid in the endosperm tissue, which can subsequently be mobilized in the germinated grain to support growth of the developing seedling. In this article, discussion

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of enzyme activities in cereal grains will be presented in the context of synthesis and degradation of endosperm cell walls in relation to the specific functions of this specialized storage tissue and synthesis by grains of enzymes that affect processing, end-product appearance, nutritional value, or storage of grain.

Enzymes Involved in the Synthesis and Degradation of Endosperm and Aleurone Cell Walls Cell Walls in Cereal Endosperm Cell walls are central to the growth and development of the endosperm of cereal grains and the remobilization of the stored reserves during germination. They are also important contributors to many quality characteristics of cereal grains. The enzymes responsible for the synthesis and degradation of cell wall polysaccharides are therefore critical not only to the normal biological functions of the endosperm but also to the subsequent utilization of cereals by humans. The endosperm consists of two distinct tissues, the aleurone and the starchy endosperm, that have different roles. The starchy endosperm forms the bulk of the grain. It is the storage organ for starch, protein, and some lipids, and by the time grains are ripe and ready for harvest, it is a nonliving tissue incapable of synthesizing new enzymes. By contrast, the aleurone is the layer of cells that surrounds the starchy endosperm and responds to signals from the germinating embryo to synthesize and secrete the key hydrolytic enzymes required to initiate degradation of the stored endosperm reserves. The aleurone remains a living tissue throughout development and long periods of storage and also retains some integrity during the early stages of germination to enable the programmed dissolution of the endosperm to proceed. Subtle variations in the fine structures of major wall polysaccharides can have a dramatic effect on the functional and rheological properties of cereal-based products. The major wall components in the endosperm of cereal grains are arabinoxylans and (1,3;1,4)-b-glucans; other wall components include cellulose, protein, other minor polysaccharides such as heteromannans, and some phenolic acids, chiefly ferulic acid (Table 1). Endosperm walls generally lack lignin. Although cell wall components account for only 5–10% by weight of the grain, they can have a disproportionately large impact on grain technology, utilization, and nutrition.

Biosynthesis of Cell Wall Polysaccharides in Cereals Given the central role played by cell wall polysaccharides in cereal processing, there has been considerable interest in the enzymes that mediate their biosynthesis, particularly in the developing grain. Cellularization of the starchy endosperm early in grain development involves ‘atypical’ growth of cell walls around individual nuclei in a multinucleate syncytium.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00102-9

PROTEINS | The Enzymes Associated with Food Grains and Their Functions in Processing Table 1

Composition of cell walls in cereal endosperm

Cereal

Source of walls

Major polysaccharides

Barley

Aleurone

71% Arabinoxylan 26% (1,3;1,4)-b-Glucan 2% Cellulose 2% Glucomannan 75% (1,3;1,4)-b-Glucan 20% Arabinoxylan 2% Cellulose 2% Glucomannan 65% Arabinoxylan 29% (1,3;1,4)-b-Glucan 2% Glucomannan 2% Cellulose 70% Arabinoxylan 20% (1,3;1,4)-b-Glucan 7% Glucomannan 4% Cellulose 27% Arabinoxylan 20% (1,3;1,4)-b-Glucan 28% Cellulose 3% Pectin 15% Xyloglucan/mannans

Starchy endosperm

Wheat

Aleurone

Starchy endosperm

Rice

Starchy endosperm

The fertilized endosperm mother cell divides for 70 h to form up to 2000 free, individual nuclei in the cytoplasm of the central cell. Walls subsequently grow between the free nuclei. After a lag phase, further expansion of the cellular endosperm occurs through meristematic activity of peripheral cells that eventually differentiate to form the aleurone. In barley, the major components of the starchy endosperm walls, (1,3;1,4)-b-glucan and arabinoxylan, accumulate steadily between 13 and 40 days post anthesis (dpa). Despite the importance of cell wall biosynthesis as a determinant of final cereal grain quality, polysaccharide synthases involved in wall synthesis have proved very difficult to purify by conventional biochemical procedures, mainly because they are membrane-bound enzymes and can be rapidly inactivated in vitro. A key breakthrough in this area occurred when cellulose synthase genes (CesA) were identified in higher plants; subsequently, multiple CesA genes and multiple groups of cellulose synthase-like (Cs1) genes have been identified. It has now been demonstrated that the CslF, CslH, and CslJ genes encode (1,3;1,4)-b-glucan synthases and that the CslF group is probably the most important in cereal grain development. Indeed, mutations of the CslF6 gene result in grain with little or no (1,3;1,4)-b-glucan, and when the CslF6 gene is overexpressed in developing barley grain, (1,3;1,4)-b-glucan levels increased significantly, as did dietary fiber content of the grain. Nevertheless, it is becoming increasingly apparent that other proteins and enzymes are also required for (1,3;1,4)b-glucan synthesis and regulation. Identification of the xylan synthase genes in cereals has been particularly challenging, and although genes encoding enzymes from the glycosyltransferase (GT) GT43 and GT47 families have been implicated in the synthesis of the (1,4)-bxylan backbone of cereal grain arabinoxylans, precise details of the roles of these enzymes are now yet available. Enzymes encoded by the GT61 family appear to mediate the addition

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of arabinofuranosyl residues to the xylan backbone. There have been suggestions that xylan synthesis might also involve enzymes of the cellulose synthase or cellulose synthase-like enzyme families, given the structural similarities between cellulose and the xylan backbone of arabinoxylans. As the genomes of more cereal species are sequenced, it is clear that most genes involved in cell wall polysaccharide synthesis are members of multigene families.

Enzymic Hydrolysis of Wall Polysaccharides in Germinated Grain Most of the enzymes involved in (1,3;1,4)-b-glucan and arabinoxylan degradation in the endosperm of germinated grain have been characterized in detail, particularly in barley, wheat, and maize. In each case, a battery of hydrolytic enzymes is required to completely depolymerize the polysaccharides. The enzymes responsible are generally synthesized de novo in the aleurone layer or the scutellum and subsequently secreted into the starchy endosperm. Walls of the starchy endosperm are completely degraded during this process, but a thin inner layer of the aleurone cell walls appears to resist degradation, presumably to maintain the structural integrity of the aleurone cells while enzyme secretion is in progress. The (1,3;1,4)-b-glucans of endosperm cell walls are depolymerized by (1,3;1,4)-b-glucan endohydrolases, of which there are one or two isoforms in most cereal species. The (1,3;1,4)-b-glucan endohydrolases release low-molecularmass (1,3;1,4)-b-oligoglucoside products that can be further hydrolyzed by exohydrolases such as b-glucan glucohydrolases and b-glucosidases. The gene families that encode these enzymes are generally larger, with five or more members. A second, distinct class of (1,3;1,4)-b-glucan endohydrolase has been reported in germinated barley and in maize coleoptiles. The enzymes release (1,3;1,4)-b-glucans with degrees of polymerization of 60–100, but the enzymes have not been characterized in detail. Their action patterns are consistent with a cellulase, but there remains some doubt as to their precise role in (1,3;1,4)-b-glucan depolymerization in germinated grain. Arabinoxylan depolymerization in germinated cereal grains also requires the concerted action of a range of different hydrolytic enzymes. (1,4)-b-Xylan endohydrolases hydrolyze glycosidic linkages in the (1,4)-b-xylan backbone of the polysaccharide and probably require a short, unsubstituted region of the (1,4)-b-xylan chain for activity. Genes and cDNAs encoding barley (1,4)-b-xylan endohydrolases have been isolated and used to define the expression patterns and chromosome locations of the genes. There is another class of enzymes that can hydrolyze polymeric arabinoxylans from cereal cell walls. These enzymes hydrolytically remove single a-arabinofuranosyl substituents from the (1,4)-b-xylan backbone of the polysaccharide and have been designated arabinoxylan arabinofuranohydrolases (AXAH). They are probably responsible for the removal of arabinofuranosyl residues prior to (1,4)-b-xylan endohydrolase action in germinated grain but might also be involved in the modification of arabinoxylan fine structure during wall deposition, maturation, or expansion. Despite these possibilities, there has not been any definitive description of the role of the AXAHs in cereal grain

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PROTEINS | The Enzymes Associated with Food Grains and Their Functions in Processing

development or germination. Complete depolymerization of oligoarabinoxylosides released from cell wall arabinoxylans by (1,4)-b-xylan endohydrolase requires the action of aarabinofuranosidases and b-xylosidases, both of which have been detected in germinated cereal grains. Enzymes with dual aarabinofuranosidase/b-xylosidase activity have been described and again these hydrolases are encoded by multigene families.

Enzymes in Grains That Affect Processing, End-Product Appearance, Nutritional Value, or Storage of Grain This section will focus primarily on wheat that is a staple food in many parts of the world and unique in terms of the myriad of end products that are consumed.

a-Amylases in Developing and Ripe Wheat Grains Starch constitutes up to 80% of the material in the endosperm of cereal grains and is stored in a highly crystalline form in granules that are laid down during development and ripening. a-Amylase is a critical enzyme in remobilization of the endosperm since it initiates hydrolysis of the starch granules, reducing the large, complex molecules of starch to smaller units as already described. Wheat and barley grains can synthesize two groups of a-amylases, or a-amylase isoenzymes, that differ in genetic control, temporal pattern of synthesis, and physical and chemical properties. Perhaps, the most important group in grains are the high-pI (germination or malt) a-amylases that are products of the a-Amy1 genes that are normally only synthesized in the grains during the early stages of germination. The second group, low-pI (pericarp or ‘green’) a-amylases, are products of the aAmy2 genes. They are present in the pericarp of immature grains, at low levels in mature grains, and are also synthesized during the later stages of germination. In comparison with other cereal enzymes, the a-amylases are relatively thermostable and remain active at temperatures above 60 C where the starch is gelatinized and becomes extremely sensitive to enzymic hydrolysis. Under ideal growth conditions, ripe wheat grains contain a small amount of low-pI a-amylase and no high-pI a-amylase, and following milling, the flour can be used to produce a vast array of processed foods including pan breads, flat breads, noodles, cakes, and biscuits as well as industrial products. For leavened products such as western-style pan breads, some aamylase is required to produce the fermentable sugars needed by the yeast. This a-amylase, often microbial in origin, is normally added in measured amount during mixing particularly in the highly automated bread-making plants that require strict adherence to specifications to maintain quality and efficient production. Under nonideal growing conditions, or as a result of adverse genotype environment interactions, variable amounts of either, or both, groups of a-amylases may be retained or synthesized prior to harvest and as a consequence the grain may be unsuitable for processing. Wheat with unacceptably high levels of a-amylase is commonly downgraded in quality, often to be restricted to animal feed, and attracts substantial financial dockages. While some of the a-amylase is removed with the bran and germ during milling, at progressively higher levels of activity, more of the enzyme will have been transported into the endosperm and will be recovered in the flour. Excess levels of a-amylase in wheat have a disastrous

effect in long fermentation processes, which applies to most types of western-style pan breads and leads to sticky dough that is harder to handle, a sticky crumb, dark-colored crust and loaves with large holes that are difficult to slice and may jam slicing machines. During cooking or baking, the starch becomes increasingly susceptible to attack by a-amylase, and even small amounts of enzyme can cause dramatic differences in starch viscosity and product texture. Flat breads, ‘chapatis,’ and sourdough breads are more tolerant to a-amylase, whereas Japanese-style (‘udon’) noodles are very sensitive. Irrespective of the end product, appearance and quality deteriorate as aamylase activity increases. High levels of a-amylase activity in ripe wheat grain can arise via a number of mechanisms. First, the low-pI a-amylase that is synthesized in the green (chlorophyllous) pericarp of immature grains may be retained rather than being gradually degraded as the grain matures (Figure 1). Frost damage to partially developed grains and conditions of high humidity and low light intensity during ripening have been associated with this abnormal retention of low-pI a-amylase. Second, some bread and durum wheat genotypes contain a genetic defect referred to as late-maturity a-amylase (LMA) or prematurity a-amylase (PMAA) that may be result in the synthesis of high-pI a-amylase in the aleurone tissue during the mid to later stages of grain development (Figure 1). Induction of high-pI a-amylase synthesis in LMA-prone varieties may be constitutive, in tall wheat varieties and in semidwarf varieties grown under mild conditions free from moisture stress, or require a cool temperature shock in semidwarf varieties ripening under warm to hot conditions. LMA, unlike germination or sprouting, is not dependent on rain and does not appear to involve changes in, or signals from, the embryo. Finally, adverse weather conditions (rain accompanied by high humidity) at maturity and prior to harvest may trigger grains to commence germination while still in the spike. This phenomenon, known as preharvest sprouting (Figure 2), is relatively common in many parts of the world. Preharvest sprouting-resistant varieties in which the grain is still dormant at harvest ripeness have been developed to combat this problem. The sequence of events that occurs during sprouting follows very closely those observed in isolated grain that is germinated under more controlled conditions. a-Amylase synthesis begins adjacent to the embryo or germ end of the grain and progresses in a wave toward the distal end. The system has been very widely studied by plant biochemists endeavoring to understand the intricacies of control of enzyme synthesis and the role of plant hormones. Initially, only high-pI isoenzymes are synthesized; however, as germination progresses, the low-pI groups are also produced. While LMA and sprouting are readily distinguished both in genetic control and in the pattern of enzyme distribution within the grain, the a-amylase isoenzymes involved are similar, as are the effects on the quality of end products. In contrast to LMA, where only high-pI a-amylase appears to be synthesized, sprouted grains may contain elevated levels of a range of hydrolytic enzymes including endoproteases, lipases, and cell wall-degrading enzymes.

Endoproteases in Developing and Ripe Wheat Grains Endoproteases attack the internal peptide bonds of proteins and may make them more accessible to exoproteases that


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50 45

α-Amylase activity

40 35 30 25 20 15 10 5 0 0

5 10 15 20 25 30 35 40 45 50 Days after anthesis

Sprouted

70

Figure 2 Sprouted (left) and nonsprouted (right) spikes of wheat.

60 α-Amylase activity

Nonsprouted

critical to the production of high-quality end products such as bread and noodles.

50

Enzymes Involved in Determining the Color and Appearance of End Products such as Asian Noodles

40 30 20 10 0 0

24

48

Time (h) Figure 1 Diagrammatic representation of a-amylase synthesis in wheat grains during development, ripening, and preharvest sprouting. Low-pI a-amylase is synthesized in the pericarp during the early stages of grain development and then declines to very low levels at maturity in all genotypes (a), while new low-pI a-amylase is synthesized by the aleurone later in grain germination or sprouting (b). High-pI a-amylase is synthesized in the aleurone during later stages of grain development in LMA-prone cultivars (a) and in the aleurone during the early stages of germination of all cultivars (b). Low-pI a-amylase (thick line), high-pI a-amylase (thin line).

Large quantities of the wheat used in Southeast Asia, Japan, Korea, and China are consumed as noodles and increasingly these products are also finding a place on tables in western societies. As the markets for noodle products develop and become more quality-sensitive, greater emphasis has been placed on improving appearance, consistency of color, and color stability, because these characteristics strongly influence customer appeal. Asian noodles made from wheat flour come in a wide range of forms, although there are two basic recipes used for production. These are referred to as white salted noodles (WSN), made from flour, water, and varying amounts of salt, and yellow alkaline noodles (YAN), prepared using flour, water, and alkaline salts such as potassium and sodium carbonate. For both types, initial color should be clean and bright and there should be minimal darkening in the time between preparation and cooking. WSN vary from white to cream in color, while YAN have a yellow color that is often enhanced with artificial coloring agents or eggs.

Synthesis of Flavonoids and Xanthophylls cleave amino acids from the amino or carboxyl terminals of peptides and proteins. There are at least four groups of endoproteases in wheat grains that differ in their tissue location, their temporal control during grain development or germination, and their substrate specificity. Three of these are present in various tissues in developing grains, but it is not clear whether they can degrade the major grain storage proteins. In contrast, acidic thiol endoproteases that are low in developing grain are synthesized during germination. These endoproteases can attack the gliadin and glutenin proteins responsible for the unique rheological and processing properties of wheat that are

The creamy color of WSN and a part of the yellow color of YAN are dependent on natural yellow pigments, xanthophylls (primarily lutein), present in the germ and endosperm of wheat grains. Lutein is a member of the carotenoid family of compounds that are found in all plants and are synthesized from isopentenyl phosphate via a biosynthetic pathway commencing with geranylgeranyl pyrophosphate synthase. The additional yellow color that develops in the presence of alkaline salts in YAN is attributed to flavonoid compounds such as flavone glycosides that are found in the germ and seed coat but not the endosperm, as well as unidentified chromophores that appear to be located in the endosperm and associated with

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protein. The starting point for synthesis of flavonoids is phenylalanine and the enzyme phenylalanine ammonia lyase, which leads into a biosynthetic pathway that produces a vast array of structures including flavones, cinnamic acids and lignins, anthocyanins, and tannins. Xanthophylls and flavonoids accumulate during the early to middle stages of grain development, depending on the activity of the enzymes in the respective biosynthetic pathways. In the case of xanthophylls, the levels decline markedly as the grain ripens. Lutein may also be converted to mono- and di-fatty acid esters during storage of ripe grain or flour. The concentrations of xanthophylls and flavonoids in flour are a product not only of the balance of synthesis and degradation during grain development but also of the milling process, in particular the efficiency of separation of starchy endosperm from other grain tissues such as the germ and seed coat.

Lipoxygenase Lipoxygenases (LOX) catalyze the oxidation of polyunsaturated fatty acids such as linoleic and linolenic acid to hydroperoxides. Fatty acid radicals produced during the intermediate steps in the reaction can initiate oxidative degradation of pigments such as lutein and b-carotene. As a result of this cooxidation, lutein and lutein ester pigments may decline during dough mixing in preparation for the production of WSN and durum pasta, leading to poor color stability. Loss of pigment can be reduced by the addition of compounds such as a-tocopherol that inhibit LOX activity or by using bread and durum cultivars that have been selected for zero LOX activity. In addition to its effects on color, LOX has been associated with the formation of compounds with undesirable odors and flavors in a range of products. Loss of lutein and carotene is also undesirable due to the role these compounds play in the health of our eyes, in iron uptake in the intestinal tract, and as general scavengers of peroxy radicals that reduce oxidative damage to tissues.

Polyphenol Oxidase Polyphenol oxidases (PPO) catalyze the oxidation of phenolic compounds to produce brown pigments on the cut or damaged surfaces of fruits and vegetables and can cause major economic losses. PPO located in the seed coat of ripe wheat grains is able to hydroxylate certain phenols in the s-position adjacent to the existing –OH group to form orthodiphenols.

The orthodiphenols are oxidized further by PPO to s-benzoquinones, which in turn polymerize nonenzymatically to melanins (brown pigments). Fortunately, most of the PPO in wheat grains is removed with the bran during milling, but sufficient enzyme is carried through in the flour of many wheat cultivars to present problems with the color stability of products that are not cooked immediately. While the endogenous substrate of PPO in grains has not been identified, the role of PPO in darkening of WSN, YAN, and durum pasta is now clear. Addition of exogenous substrates such as tyrosine, catechol, and L-DOPA (L-3,4-dihydroxyphenylalanine) enhances noodle darkening, whereas darkening is greatly reduced in the presence of specific PPO inhibitors or in cultivars selected for low or zero grain PPO activity (Figure 3). Variation in PPO activity explains most of the genetic difference in noodle darkening between cultivars, but is only responsible for a portion of the total darkening that occurs. Physical effects and other unidentified oxidation reactions also contribute to the reduction in noodle brightness over time.

Peroxidases and Hydrogen Peroxide Synthesis and Catalysis Peroxidases are oxidoreductases widely distributed in higher plants and have been shown to oxidize many compounds, including phenolics, in the presence of hydrogen peroxide. Oxidation of phenolic compounds by these enzymes can lead to the formation of brown pigments similar to those formed by PPO, and consequently, they have also been implicated in browning or darkening of noodles and pasta. In the case of peroxidase, the situation is complicated by the presence of a number of forms with different substrate specificities that are localized in embryo, endosperm, and seed coat tissues of wheat grains and by the interaction with systems that either generate H2O2 (superoxide dismutase and NADH oxidation) or catalyze (catalase) its destruction. In addition to its possible role in product darkening, peroxidase has been implicated in the development of symptoms of a grain quality defect known as ‘black point.’ Both wheat and barley are prone to this defect, which manifests as a dark stain in the seed coat or husk, respectively, at the embryo end of the grain and is associated with warm, humid conditions during ripening (Figure 4). Unfortunately, this pigmented tissue fragments during milling and black specks are carried through into wheat flour or semolina. While it has no effect on processing properties or texture, the specks are visible in

Figure 3 Yellow alkaline noodle sheets: from left to right – control (2% sodium carbonate), 10 mM tyrosine (polyphenol oxidase substrate), and 10 mM tyrosine plus 10 mM tropolone (specific polyphenol oxidase inhibitor).


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Figure 4 Sound and black point affected wheat grains.

noodle and pasta products and high levels of black point result in downgrading and substantial economic losses. The enzymes discussed in this section all have specific functions within the tissues of developing grains, although in some instances the exact role has not been identified unequivocally. Their physiological functions are quite distinct from their effects on processing and end-product appearance. While in many cases it is possible, or at least conceivable, to develop germplasm with extremes of variability for levels of these enzymes, some caution is required in case such dramatic changes have adverse effects on plant growth, disease resistance, or grain yield.

Enzymes that Are Active in Ripe, Quiescent Grains Despite the low moisture content of ripe cereal grains and the death of the seed coat and starchy endosperm tissues during grain ripening, it is clear that respiration and some other enzyme-catalyzed reactions continue at a slow rate during storage of harvested grain. Some of these activities result in the modification of the structure of grain constituents and secondary metabolites, while others may impact on the storage quality or the capacity to maintain freshness and palatability. In addition, ripe grains contain a range of enzymes such as exopeptidases and b-amylase that are sequestered in active or inactive form. These enzymes can spring into action once endo-acting enzymes, synthesized during germination or sprouting, catalyze the initial depolymerization of protein and starch. At maturity and depending on the genotype and growing conditions, wheat grains contain varying levels of xanthophyll (hydroxy carotene) present primarily as free lutein. During storage of wheat grain and wheat flour, and again depending on genotype as well as temperature and humidity, considerable proportions of the free lutein (up to 60%) may be converted to mono- and di-fatty acid esters. A specific GDSL-lipase (the prefix GDSL is added to distinguish this group of lipases from common lipases and refers to specific sequence of amino acids at the active site of this group of lipases), coded by a gene located on chromosome 7D, appears to be responsible for esterification possibly acting as a trans-esterase to transfer linoleic and palmitic acids from membrane phospholipids to the hydroxyl groups of lutein. The lipase is synthesized during the early to middle stages of grain development but does not catalyze esterification of lutein until the ripe grain is stored under warm, dry conditions. Esterification does not occur in

durum wheat that lack the D-genome ‘Wheat Genomics’ or in a small number of bread wheat cultivars that contain a nonfunctional version of the gene. Since adequate lutein intake is associated with a reduction in the incidence of glaucoma and macular degeneration, a major cause of blindness in elderly people, this modification may have implications for absorption, bioavailability, and attempts to improve eye health through dietary supplementation. Enzymes have been implicated in the deterioration in quality of rice during storage. This deterioration may be linked to lipid peroxidation, peroxidative changes in polyunsaturated fatty acids that in turn are governed by the balance of production and dissipation of reactive oxygen species. Peroxidases are key scavengers of reactive oxygen species and recent studies have indicated that the activity of this enzyme declines during storage of rice.

Endogenous Enzyme Inhibitors Cereal and legume grains contain inhibitors against a range of enzymes such as proteinase, a-amylase, endoxylanase, and limit dextrinase. While some inhibitors are only effective against exogenous enzymes of microbial or insect origin, others are capable of inhibiting endogenous grain enzymes. The physiological function of these inhibitors is not certain but it has been suggested that they may be involved in plant defense mechanisms, protecting the stored reserves in the seed from invading microbes and insects, and/or play a regulatory role in plant development and metabolism. A role in the plant defense mechanisms seems plausible given the effectiveness of many endogenous inhibitors against hydrolytic enzymes from microbial and insect sources. Support for a regulatory role is less plausible and requires unequivocal evidence that the inhibitors reduce the activity of particular endogenous grain enzymes at physiological concentrations and that the inhibitors are located in the same tissue as the target enzyme. Most of the proteinase inhibitors that have been characterized to date are inhibitors of a particular class of protein hydrolases, the serine proteinases. As yet, there has been no conclusive demonstration of serine proteinases of the chymotrypsin family or their genes in plants. In the case of the bifunctional a-amylase/subtilisin inhibitor that is common in barley grains, there is clear evidence that it can significantly reduce the activity of endogenous high-pI a-amylase extracted from germinated or malted grain and ameliorate

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some of the deleterious effects of high-pI a-amylase on loaf volume and structure. However, recent studies of gene expression have indicated that the inhibitor is primarily located in the maternal seed coat tissues of barley grains rather than endosperm. Similarly, whereas proteins of the ‘serpin’ superfamily are localized in both vegetative and endosperm tissues of barley grains, they only inhibit specific mammalian serine proteinases. Limit dextrinase inhibitors isolated from barley inhibit the activity of endogenous limit dextrinase and appear to be ineffective against a number of other enzymes capable of hydrolyzing a-1,6-linkages in dextrins. In theory at least, these inhibitors could interfere with the malting process although a role in commercial malting has not been demonstrated. Two groups of endoxylanase inhibitors (XIP-type and TAXItype) have been isolated from cereal grains that are effective against fungal endoxylanases and both bacterial and fungal endoxylanases, respectively. Microbial endoxylanases are commonly used in bread making to improve loaf volume. Irrespective of possible roles in plant defense and regulation, significant numbers of inhibitors are active either against endogenous enzymes that are important in processing or against exogenous enzymes, usually of fungal or bacterial origin, that are added as ingredients to improve processing and quality of end products. In these instances, the inhibitor and the enzyme are brought into contact as a result of milling or deliberate physical admixture and there may be important implications for industrial applications.

Future Prospects Many cereal products and processes depend on, or are adversely affected by, specific enzymes either that are present in grains at maturity or that develop as the result of interactions between grains and the environment. As more of these enzymes are recognized, and their impact quantified, many opportunities will be presented to improve products and to develop new and novel products and processes. In many cases, there is already sufficient genetic variation within existing germplasm or near relatives for the selection of lines with enzyme levels more appropriate to the particular end-use process, while in other instances, it may be possible via mutation, genetic engineering, or modification of milling techniques to extend variation beyond that currently available. Genetic engineering, in particular, opens up the possibility of introducing genes encoding novel enzymes into cereal grains, overexpressing genes controlling synthesis of existing enzymes, or synthesizing enzymes in tissues such as the starchy endosperm where they are currently absent. As an example, identification of the genes should reveal potential strategies for the manipulation of cell wall (1 ! 3,1 ! 4)-b-D-glucan and arabinoxylan levels, for the enhancement of cereal quality and productivity. The 3-D structure of one of the barley (1,3;1,4)-b-glucan endohydrolases has been solved and the structural information used to rationally design mutated forms of the enzyme with enhanced thermostability. The increased thermostability of this barley (1,3;1,4)-b-glucan endohydrolase could have commercial potential through its ability to overcome filtration problems and other difficulties encountered in the malting and brewing industries. Increasingly sophisticated and high-throughput

genomics technologies, coupled with rapid functional analysis systems, are now available to researchers. These new technologies can be confidently expected to identify more genes and reveal potential strategies for further manipulation of enzyme and grain constituent levels relevant to the grains industries in the near future.


• • • • • •

What enzymes are important in the development and breakdown of endosperm cell walls? What enzymes are important during germination? When are the different a-amylase families synthesized in wheat grains? Which enzymes present in ripe wheat grains affect endproduct quality? What methods are used to overcome the deleterious effects of some enzymes on the quality of wheat-based end products? What is black point and does it affect end-product quality?


•

•

•

Fully characterize all the gene families involved in endosperm (aleurone and starchy endosperm) cell wall synthesis and degradation, develop a better understanding of their respective roles and interactions, and explore ways of modifying their activity to improve products and processing. Genetic and molecular characterization of late-maturity aamylase in wheat to assist in the development of varieties that maintain low a-amylase activity and to provide new insights into the processes involved in the control of grain development. Utilize genetic and molecular techniques to optimize the grain content of enzymes and constituents that impact on end-product quality and grain storage without compromising productivity.

See also: Barley, Rice and Maize Processing: Barley: Malting; Carbohydrates: Cereals: Chemistry and Physicochemistry of Nonstarchy Polysaccharides; Starch: Synthesis; Fats: Lipid Chemistry; Genetics of Grains: Wheat Genetics and Genomics; Proteins: Protein Synthesis and Deposition; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wheat-Based Foods: Noodles: Asian Wheat Flour Noodles.

Further Reading Asenstorfer RE, Appelbee MJ, and Mares DJ (2009) Physical-chemical analysis of nonpolyphenol oxidase (non-PPO) darkening in yellow alkaline noodles. Journal of Agricultural and Food Chemistry 57: 5556–5562. Chen TF and Chen CL (2003) Analysing the freshness of intact rice grains by colour determination of peroxidase activity. Journal of the Science of Food and Agriculture 83: 1214–1218. Dominguez F and Cejudo FJ (1996) Characterization of the endoproteases appearing during wheat grain development. Plant Physiology 112: 1211–1217.

PROTEINS | The Enzymes Associated with Food Grains and Their Functions in Processing Fincher GB (1989) Molecular and cellular biology associated with endosperm mobilization in germinating cereal grains. Annual Review of Plant Physiology and Plant Molecular Biology 40: 305–346. Fincher GB and Stone BA (1986) Cell walls and their components in cereal grain technology. Advances in Cereal Science and Technology 8: 207–295. Fuerst EP, Anderson JV, and Morris CF (2006) Delineating the role of polyphenol oxidase in the darkening of alkaline wheat noodles. Journal of Agricultural and Food Chemistry 54: 2378–2384. Garcia-Olmedo F, Salcedo G, Sanchez-Monge R, Royo J, and Carbonero P (1987) Plant proteinaceous inhibitors of proteinases and a-amylases. Oxford Surveys of Plant Molecular and Cell Biology 4: 275–334. Hidalgo A and Brandolini A (2012) Lipoxygenase activity in wholemeal flours from Triticum monococcum, Triticum turgidum and Triticum aestivum. Food Chemistry 131: 1499–1503.

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Howitt C and Pogson BJ (2006) Carotenoid accumulation and function in seeds and non-green tissues. Plant, Cell and Environment 29: 435–445. Mares D and Mrva K (2008) Late maturity a-amylase: low falling number in the absence of preharvest sprouting. Journal of Cereal Science 47: 6–17. Shirley BW (1998) Flavonoids in seeds and grains: Physiological function, agronomic importance and the genetics of biosynthesis. Seed Science Research 8: 415–422. Stewart RJ, Varghese JN, Garrett TPJ, Hoj PB, and Fincher GB (2001) Mutant barley (1 ! 3,1 ! 4)-b-glucan endohydrolases with enhanced thermostability. Protein Engineering 14: 245–253. Williamson PW (1997) Black point of wheat: In vitro production of symptoms, enzymes involved and association with Alternaria alternate. Australian Journal of Agricultural Research 48: 13–19.

Proteomic Analysis Relevant to Cereal Grains A Juha´sz, Centre for Agricultural Research of the Hungarian Academy of Sciences, Martonva´sa´r, Hungary R Haraszi, Campden BRI, Gloucestershire, UK F Be´ke´s, FBFD PTY LTD, Beecroft, NSW, Australia DJ Skylas, Grain Growers Limited, North Ryde, NSW, Australia CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Definition of the concept of proteomics versus other types of ‘-omics’. Display of the proteome as a two-dimensional map of spots, using gel-based technology. Gel-free proteomic analysis and LC fractionation. Qualitative and quantitative identification of the polypeptides. Mass spectrometry-based proteomics. Proteome mining and functional proteomics.

Learning Objectives

• •

To achieve an understanding of proteomics and its relationships to genomics and to the functions of individual cereal grain polypeptides. To understand how proteomics can provide greater insights into the physiological functions of the cereal grain and into the utilization of grains.

Introduction Elucidation of grain composition at the molecular level is needed to permit ongoing genetic improvements to grains with respect to their efficient production and processing. This information is especially needed concerning the proteins of the grain, because they are the primary molecules in implementing the ‘directions’ from the relevant genes, under the further control of environmental conditions. There is thus an important interaction between genotype (the variety, comprising the set of genes) and growth conditions (Figure 1), and this interaction determines the synthesis of the individual proteins that are needed to conduct all the functions of the plant cells.

Background to Proteomics The study of proteins and their functions has long been an accent of biochemical research, but it has been only in the 1990s that the concept of ‘proteomics’ has been introduced to this study. Proteomics is a powerful approach to the analysis of gene expression in biological systems, with the term ‘proteome’ indicating the full complement of proteins expressed by the genome of an organism (e.g., wheat) in a tissue (e.g., leaf, endosperm, or embryo) at a particular stage of development and under specific growth conditions. Even

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though there is only one definitive genome of an organism, it can code for multiple expressed proteomes. The expression of a single protein largely depends on the environment and is a result of combined events including transcription, translation, and protein turnover and posttranslational modifications (PTMs). The specific genes that are active are also determined by the growth conditions, as shown in Figure 1. The first activity of the genes is transcription, that is, the production of messenger ribonucleic acid (mRNA), with a nucleotide sequence based on that of the stretch of DNA that constitutes the particular gene. Analysis of the mRNA (the ‘transcriptome’) provides information about which proteins are to be synthesized in the next stage of translation, as shown in Figure 1. Routinely, analysis of the proteins (the proteome) is preferred over study of the mRNA, because the mRNA molecules are transitory, being degraded after their role in protein synthesis is completed. Therefore, the mRNA transcripts may not be a true indicator of protein expression and often do not correlate with protein levels. The transcriptome and the proteome are thus subsets of the wider range of mRNA and protein molecules that might have been produced, given the full extent of the genome. In summary, the study of the proteome tells us about the range of proteins that relate to the specific tissue under study (root or shoot or mature grain), as it was grown under the particular environmental conditions existing at the time for the genotype involved.

Methods of Proteomic Analysis Sample Preparation Seed tissues, such as bran and seed endosperm, contain a large number of diverse proteins, with different chemical characteristics that resulted in the development of special extraction and purification requirements. To extract seed proteins in a satisfactory amount and purity, there are several basic criteria that need to be considered. For cereal grains, the major storage components are starch and different carbohydrates that have an adverse effect on the extractability of proteins. Compared to other plant tissues, extraction of seed proteins first requires the mechanical breakage of the hard structure of the mature seed using grinding or milling. This can be followed by the subsequent solubilization-based Osborne fractionation or the use of either proteolytic enzymes or special chemicals in order to further break down or fractionate polypeptides. Purification and protein enrichment can be essential steps, too, which also require the use of sophisticated and expensive chemicals. Due to frequent interference between chemicals and sensitive


http://dx.doi.org/10.1016/B978-0-12-394437-5.00107-8

PROTEINS | Proteomic Analysis Relevant to Cereal Grains

Genomics

DNA

Transcriptomics

Gene expression

RNA

Proteomics

Proteins

Metabolomics

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Discovery

Biological function Phenotype

Modified proteins

Translation Post-translational modifications

Metabolites Sugars, nucleotides, amino acids, lipids

Environment Figure 1 Newly emerging technologies to elucidate genome and proteome interactions.

Figure 2 Workflow of the gel-based and gel-free methods of proteomic analysis.

detection techniques (e.g., NaCl ionization in the ESI of a mass spectrometer suppresses the peptide ionization), they need to be removed at a proper time of analysis. Starch and complex carbohydrates can also seriously reduce protein extraction, which might be a primary problem in proteomic analyses of maize or rice seeds, however. The ideal extraction method should be compatible with downstream protein analysis by

gel electrophoresis, liquid chromatography, and mass spectrometry and subsequent protein identification (Figure 2).

Gel-Based Methods Gel-based proteomics is still the main approach used in grain proteomics. For decades, one-dimensional gel electrophoresis

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(1-D GE) was the most popular method in protein chemistry due to its ability to determine and compare the molecular weights of proteins. It was used in different approaches, such as to compare and determine the number and size of seed storage proteins in wheat. It is also used in immunodetection or Western blotting. Today, it is most often used as the second dimension in two-dimensional gel electrophoresis. Twodimensional gel electrophoresis (2-D GE), introduced in 1975, is the most widely used gel-based technique to separate proteins. The first dimension involves isoelectric focusing (IEF), in which proteins are fractionated based on their isoelectric points (pI) across a specific pH range using commercially available immobilized pH gradient (IPG) gel strips. The second-dimension of fractionation resolves the proteins on the basis of their molecular mass, using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The SDS detergent binds to the denatured proteins, overriding any intrinsic charge differences, to provide a uniform charge-tomass ratio, allowing proteins to resolve according to their respective sizes. Due to its excellent resolving power, the technique is suitable to separate over 1000 proteins on a single gel. The 2-D GE proteomic map in Figure 3 represents the proteins of immature wheat grain flour. It shows the polypeptides extracted from the immature endosperm of the soft wheat variety ‘Wyuna,’ the endosperm being the floury part of the grain, excluding the germ, embryo, and bran layers. The proteome map of Wyuna appears in two parts, reflecting two different pH ranges used in IEF. Protein extracts were fractionated in both acidic (pH 4–7) and basic ranges (pH 6–11). The proteomic pattern is thus a map of pI, in the horizontal dimension increasing from left to right, and of molecular size, in the vertical dimension. SDS-PAGE provides fractionation on the general basis of the size of the protein molecules, from largest (top) to smallest (bottom). After separation, the proteins in the gels must be visualized. There are various stains available for protein visualization,

including Coomassie or silver staining, but the more common and routinely used stains now are fluorescent dyes, such as SYPRO Ruby protein stain or CyDyes (Cy2, Cy3, and Cy5). Two-dimensional Fluorescence Difference Gel Electrophoresis (2-D DIGE) was developed to overcome problems related to moderate gel-to-gel reproducibility observed in 2-D gel electrophoresis. In this approach, two protein samples and an internal standard are labeled prior the gel electrophoresis with one of the three size- and charge-matched, spectrally resolvable fluorescent dyes. The three samples are then mixed and uploaded onto a single IPG strip followed by SDS-PAGE. The simultaneous separation of multiple fluorescent-labeled samples, together with an internal standard, results in fewer gels needing to be analyzed in a significantly shorter time frame. Using the internal standard, the gel-to-gel variation can be eliminated as no technical replicates are needed to confirm differences in protein abundance.

Gel-Free Methods: LC-MS and LC-MS/MS Methods In proteomics, high-throughput protein identification is usually done by mass spectrometry (MS) or coupling it with more sensitive methods. Shotgun or bottom-up proteomic approaches are targeting the analysis of a peptide mixture that is a derivative of the target proteome. Proteolytic enzymes or specific chemicals can be used to digest proteins before chromatographic separation that is followed by peptide ionization and detection. The general use of trypsin digestion failed in the case of gluten, which contains low level of arginine and lysine. Replacement by chymotrypsin was first shown to effectively produce peptides suitable for chromatography. A novel combination of direct enzymatic digestion–LC-MS/MS (ESI ion trap) method was developed for the semiquantification of gluten traces in food samples, which applies a two-step multienzymatic digestion. Recent studies are more and more acknowledging the odd nature of cereal proteins and

Wyuna cultivar-endosperm proteome maps pH

4

pH

76

11

1 4 5 2

6

3

Figure 3 The acidic and basic proteome maps of immature (17 days postanthesis) wheat grain endosperm of the soft Wyuna variety. Protein spots were characterized by N-terminal amino acid sequencing and identified from protein-sequence database interrogation.

PROTEINS | Proteomic Analysis Relevant to Cereal Grains demonstrating the need to use unconventional proteomic approaches for proteins like gluten. Top-down proteomics involves the gas-phase ionization of intact proteins and subsequent high-resolution mass measurement of intact protein ions followed by their direct fragmentation inside the mass spectrometer without prior digestion. Topdown approaches enable a more complete characterization of protein isoforms and any PTMs than the bottom-up approaches but are not exempt from limitations (e.g., high purity, HPLC separation, and high molecular weight (>50 kDa)). New methodological advances with ultra high performance liquid chromatography (UHPLC) and mass spectrometers with ion mobility are opening up new ways for top-down approaches in the proteomics field. Matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) can be used for indirect quantification of cereal proteins like gliadins even in processed foods and the direct identification and exact molecular mass determination of cereal proteins without prior separation. MALDI-MS–PMF (peptide mass fingerprinting) is a combination, which involves enzymatic digestion of proteins resulting in peptide fingerprints. Sensitivity and resolution of LC-MS methods (e.g., MALDITOF and ESI-Q) can be increased with the application of coupled (tandem MS) techniques like ESI-QqQ and ESI-QTOF, where selected ionized peptides are fragmented before entering the detector of the mass spectrometer. The monitoring of specific mass transitions as SRM (single reaction monitoring) or multiple reaction monitoring (MRM) provides a unique identification and quantification tool for the analysis of complex mixtures including overlapping peptide characteristics.

Identification and Characterization of Protein Gel Spots This procedure of 2-D GE has been available for some decades, providing proteomic maps such as in Figure 3. Six spots are numbered as examples of polypeptide identification. Table 1 shows the results from excising these six spots from these gels for identification by N-terminal sequencing. As a result of matching these sequences to databases, the identities could be determined for five of these six spots.

Table 1 examples

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The relatively novel aspect of proteomic analysis is the subsequent stages of postseparation microcharacterization of the individual protein spots. The ability to characterize and identify proteins in a high-throughput manner is a critical factor in proteome projects. Two widely used proteincharacterization methods are N-terminal amino acid sequencing and MS, with the latter being the preferred method of choice used in proteome projects. N-terminal amino acid sequencing has been a popular method for characterizing proteins in the past. The most common form of this method is the traditional Edman degradation chemistry, which can be used to sequence proteins from gels, or it can be carried out on proteins electroblotted from the proteome gel to a polyvinylidene difluoride membrane. In either case, Edman chemistry involves the reaction of phenyl isothiocyanate with the free amino group of the protein; derivatives are cleaved and then converted to phenylthiohydantoins, which differ in their amino acid side chain, allowing them to be characterized by retention time using reversedphased high-performance liquid chromatography. This is not the preferred method in high-throughput large-scale proteome projects, due to the relatively low number of samples that can be processed in parallel (generally only three or four samples), its low sensitivity, and the time and cost for analysis. A gel spot can be directly ionized by MALDI and detected with a TOF or can be destained, reduced, enzymatically digested, and then extracted (in gel digestion) in order to have a peptide mixture, which then can be analyzed with LCMS or LC-MS/MS for protein composition. Peptides and proteins are identified from the recorded and processed mass spectra with a peptide matching algorithm and against a protein database. Besides experimental conditions including the chromatographic separation, the precision of peptide identification is highly depending on the quality of the mass spectra and the database. Peptides with completely different amino acid sequences and functionality may coelute during LC separation, have identical or very similar masses, and may fragment similarly. This is particularly true for proteins belonging to a protein family like alpha-gliadins and low molecular weight (LMW)

N-terminal amino acid sequence characterization of immature wheat endosperm proteins, taking the six numbered spots in Figure 3 as

Spot no.

N-terminal sequence

Gene product

Identity (%)

Matched organism

1

XATFTLPD

Superoxide dismutase (EC 1.15.1.1)

87.5% in 8 aa

Wheat

2

SGPWMCYV

100% in 7 aa

Wheat

3

MKLIAAYL

100% in 8 aa

Wheat

4, 5

NMQVDPSG

a-Amylase inhibitor WDAI-3 60S acidic ribosomal protein P2 (ribosomal protein ‘A’) g-Gliadin

100% in 8 aa

Wheat

6

DILRSDQP

Comments and accession no. N-terminal sequence starts at residue 22 of O82571 with residues 1–21 possibly being a signal sequence or truncated. Also matches to P93606 and Q96185 P10846 (fragment). Also matches other a-amylase inhibitors P01084 and P01085 Subunits P1 and P2 exist as dimers at the large ribosomal subunit P05390 N-terminal sequence starts at residue 20 of P21292 as signal sequence of precursor is residues 1–19 No close matches

Protein sequences were used to interrogate SWISS-PROT and TrEMBL databases via FASTA algorithm.

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glutenin subunits. Additionally, the protein content in a gel spot is usually so little that without sufficient sensitivity and resolution, the detection and identification of their peptides are not possible. Generally, marker peptides are used for the quantitative detection of proteins. The first step is to do discovery work in order to map the most unique and detectable peptides using a high-resolution mass spectrometer like an ESI-Q-TOF or a software tool such as Skyline or the ProPepper database, which provides the starting point in the marker selection process. After selecting a potential pool of peptides, the next step is the experimental optimization of the quantification method using, for example, an ESI-QqQ and synthetic peptides in order to tune up the mass spectrometer for the accurate detection of specific predefined mass transitions of the targeted peptides. The size of a database due to false-positive hits and the accuracy of entries (proper annotations) are further critical factors in the relation of peptide matches to the protein source. This is relevant in the discovery phase and especially complex for the seed proteome, where the plant genomes are not fully sequenced yet. In targeted shotgun proteomics, the design of an SRM for protein quantification needs to fulfill the criteria that the amount of peptides and that of proteins are equimolar, which is not the case for, for example, gluten, where the high level of homology and the multiple prevalence of sequences limit the establishment of quantitative relationships between a detected peptide, its individual protein source, its protein family, and its plant origin.

The Potential Value of Proteomics to Grain Science Using proteomic analysis, we can identify the individual proteins that are responsible for specific aspects of the phenotype,

that is, the many different characteristics of the plant and of the grain produced from it. There are different subdivisions of proteomics that use different approaches and targets to answer different questions related to protein identification, expression, function, interactions, etc. These different types are summarized on Figure 4.

Proteome Mining The water-soluble albumins and salt-soluble globulins of wheat grain comprise mainly metabolic and protective proteins, while at least some of the insoluble structural proteins may be extracted with dilute acid or alkali in the glutenin fraction. Albumins and globulins, each accounting for 10% of total flour proteins, are known to be soluble enzymes and proteins soluble in polar solution, respectively. More than 2000 protein spots can be extracted from flour with salt solution. The structure of the wheat grain can be categorized simply into three distinct fractions, the outer layers, the germ, and the endosperm. The endosperm plays the most important role from a human consumption point of view and is the fraction studied in most detail, identifying a large number of proteins in the developing grain. The proteins located in the wheat endosperm determine the characteristics of elasticity, extensibility, and gas-holding ability of the wheat dough. Particularly important are the proteins within the gluten complex, the low- and high-molecularweight glutenin subunits, proteins, and the diverse group of gliadins. This group of proteins shows extensive polymorphism across wheat genotypes. Wheat also contains smaller amounts of other storage proteins such as globulins and triticins and proteins such as amylase and protease inhibitors

Protein identification Subproteome isolation Organelle composition

Phosphorylation Glycosylation Ubiquitination Polymerization

Proteome mining

Posttranslational proteomics

Proteomics Functional and expressional proteomics

Protein interactions Signaling pathways Metabolic pathways Biological processes Environmental responses Gene silencing Introduction of genes

Computational and structural proteomics Structure – function relations Protein – ligand interactions Enzyme complex analyses 3D protein modelling Database and bioinformatic analyses

Figure 4 Proteomic approaches used in grain science. Adapted from Juha´sz J, Moolhuijzen P, Bellgard M, Appels R, and Be´ke´s F (2013) Wheat grain proteomics for the food industry. In: Toldra´ F and Nollet LML (eds.) Proteomics in Foods. Principles and Applications. Food Microbiology and Food Safety, vol. 2, pp. 341–379. New York: Springer.

PROTEINS | Proteomic Analysis Relevant to Cereal Grains that may protect against insects and fungi. A range of enzymes exist in very small amounts. Amphiphilic proteins are detergent-soluble membrane proteins and together with gluten proteins play an important role in wheat quality. Some of them, like puroindolines, are lipidbinding proteins and are strongly linked to dough-foaming properties and to fine crumb texture. The proteomic investigation of the wheat amyloplast can be carried out on whole amyloplasts or purified amyloplast membranes, identifying the total number of 171 and 108 proteins, respectively. The largest class of proteins with a known function (24%) was found to be starch synthesis and storage enzymes. Affinity electrophoresis using glucan (cornstarch or amylopectin) as affinity substrate has been utilized successfully in the identification of enzyme-type proteins, especially the proteins related to starch biosynthetic and hydrolyzing enzymes and their inhibitors. Achievements of proteomic research on bran and germ tissues are described by Juhasz et al.

Functional Proteomics Functional proteomics aims to characterize how changes in protein localization, expression, and interaction are affected in the different developmental stages or by different environmental cues. These processes include germination and seedling development, tillering, stem elongation, head emergence, flowering, seed development, and dormancy. Functional proteomics is suitable to determine the dynamics of how proteins are related into complex networks and how their expression influenced by coexpressing proteins or other biomolecules present in the tissue. The approaches used are based on quantitative analyses of the proteome, combining approaches such as analytical chemistry, biochemistry, MS, and bioinformatics. For instance, large-scale proteomic experiments enable us to understand the key players and mechanisms involved in grain filling and seed maturation (i.e., the expression of cereal grain proteins) in order to understand how environmental stresses affect wheat quality. These mechanisms determine regulatory principles of transcriptional activation and protein turnover in response to abiotic or biotic stresses as well as to differences in developmental processes in the different cereal species or cultivars.

Expression Proteomics Quality attributes of a flour sample are defined by the allelic composition of gluten proteins (the high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits together with gliadins) as well as their relative expression levels. Proteomic analysis, used to monitor the expression of gluten proteins during grain development, specially the glutenin subunits, provides useful information about polymer formation and helps in relating protein composition to quality attributes. Nongluten proteins encompass smaller percentages of the seed protein content; however, they play a crucial role in different metabolic processes during grain development, ripening, and desiccation, and they can have a relevant role in defense mechanisms against biotic and abiotic stresses.

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Numerous studies have been carried for the identification and mapping of wheat proteins. Studies, for example, on kernel responses to heat stress have enabled identification of many of the enzymes in kernel of wheat. However, the majority of soluble proteins still need to be identified and mapped. Proteomic research activities have been reviewed describing applications of proteomics in wheat research: dough quality, starch properties, puroindoline, chromosomal location of coding genes, effects of growth environment, insect damage to wheat grains, and genotype identification. The review of Juha´sz el al. provides a table listing 38 application areas in 113 publications, using the different techniques of proteomics in both plant biology and food science. The development of techniques to improve extraction and separation and to identify proteins and peptides is facilitating functional proteomics, together with the analysis of subproteomes from small amounts of starting material, such as seed. The combination of proteomics with structural and functional analysis is increasingly applied to target subsets of proteins. These ‘next-generation’ proteomic studies differentiate between special subproteomes and functional subproteomes and contribute to understanding the processes controlling cereal grain development, nutritional and processing characteristics, and the changes caused by biotic and abiotic stresses. The importance of abiotic stresses caused by global climate change has particular significance in the future of agriculture and food industries. Advances in crop proteomics provide the basis for interpreting changes in the grain as a result of climatic factors including photosynthetic stress, air pollutants, thermal stress including heat and cold, osmotic stress (drought, salt, and flooding), and metal stress to help to eliminate or to reduce the negative effects of these factors on the food production chain

Posttranslational Proteomics Polypeptides produced during translation often undergo different posttranslational alterations by modifications of amino acid side chains through the addition of a wide range of molecules, mostly carbohydrates, lipids, phosphate, nitrate, or methyl groups. These modifications are covalent processing events that can modulate the activity, localization, turnover, and interaction of many seed proteins. The resulted modifications, such as glycosylation, phosphorylation, methylation, ubiquitination, and deamidation, of the proteins are often associated with changes in the protein functions. PTM results in changes in the molecular weight, charge, and hydrophobicity of proteins. The modified subproteomes can be studied at both protein and peptide levels using different gel-based analysis techniques, as well as MS. Glycosylation and phosphorylation are two common forms of modifications affecting about 40% and 60% of the seed proteins. Glycosylation events are characteristic on all secreted and membrane proteins, while phosphorylation is often linked to proteins related to enzyme metabolism, stress responses, and growth. Storage proteins of the cereal seeds are rich in amino acids like proline or glutamine. Deamidation of glutamine-containing proteins into glutamic acid results in higher water-binding capacity. Polymer formation of storage proteins in wheat gluten may result from PTM events, by which sulfur-containing amino acids are

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bound to each other via disulfide bonds, so that a stabile chemical interaction is formed. These abilities of cereal and especially wheat grain proteins are important in the structure– function relationship analysis of wheat gluten for food products and also for nonfood uses.

Computational and Structural Proteomics Structural proteomics deals with the complex information hidden in the amino acid sequence of a protein. It determines how the order and characteristics of the constituent amino acids influence the secondary and tertiary structure of a protein and how these features determine the ability of these proteins to function as interacting partners in protein complexes. The major challenge of structural proteomics is to assign structure data determined by x-ray or NMR crystallography or in silico modeled to protein sequences obtained from genome and transcriptome sequencing projects by the use of highthroughput characterization of the 3-D structure. Structural proteomic studies of cereal grains can be used to analyze enzyme complexes present in the seed, to identify receptor functions by the analysis of different protein–ligand interactions, to predict how pathogens (including viruses, fungi, or insects) interact with the host plant, or to identify and predict allergen components present in the seed. Structural proteomics strongly builds on computational biology utilizing the potential of sequence data analysis and 3-D modeling. Computational proteomics is a term generally describing a broad range of computational tools, including algorithms, bioinformatics techniques, and data acquisition models to analyze protein or peptide related sequence data. The collection and evaluation of data from protein databases, combined with gelbased and MS-based or immunoanalytical computational analyses, can deliver outputs in drug discovery, food-safety analyses, and even the development of personalized medicine.

combined with Western blotting may be used to overcome this challenge. The power of proteomics used for the identification and characterization of protein components in the grain is greatly magnified when combined with other postgenomic techniques such as metabolomics. Such multidisciplinary analyses, including tools of proteomic, metabolomic, and bioinformatic analyses, can provide direct evidence of the effects of protein expression. The next major challenge toward this aim is to identify the constituents of the cereal grain proteome in order to understand the cereal genome. Of particular importance will be the deciphering of protein alterations between normal and stressed conditions to permit the identification and prioritization of agronomically important targets. Proteome analysis aims to identify changes not only in protein expression but also in PTMs, protein–protein interactions, cellular and subcellular distribution, and temporal patterns of expression. The power of proteomics as a tool for the discovery of biological pathways and processes related environmental changes is now well established. Indeed, proteomics has already uncovered many potential targets for specialized quality purposes or different biotic and abiotic stress conditions. The current era of proteomics is now beginning to investigate how this technology can serve the breeders, the food industry, and the consumer for high-throughput identification and prognostic applications.


• •

Improving on Current Proteome Technology

• The successful completion of wheat genome and genomesequencing projects of related grain species will lead us to better understand mechanisms involved in the stages of plant development, such as seed development, maturation, seed dormancy, and germination. Additional insights will come from using genome sequences combined with genotype-level information, plus additional achievements in protein separation and identification techniques. Results can be expected in genotype-level complex information about what features are responsible for specialized end-use quality attributes, for sustainable quality under different environmental conditions, and for the complexity of wheat-allergen proteins. To study these mechanisms, projects need to involve multidisciplinary approaches, such as genomics, proteomics, metabolomics, and bioinformatics. Currently, proteomics receives criticisms related to its low reproducibility, evidenced by gel-to-gel variations between laboratories. By the standardization of extraction and separation protocols, these issues will be improved. Identification of weakly expressed molecules via MS remains problematic, although techniques such as protein and peptide chips

• •

Develop an extended definition of the proteomics concept, including mention of the genome, growth conditions, tissue identity, stage of maturity, and functional relationships. Explain the relative advantages and disadvantages of gelbased and gel-free technologies for proteome analysis. Which is better suited for polypeptide identification and for eventually elucidating the functions of the many polypeptides? Several distinct versions of proteomics are described: expression, structural, functional, posttranslational proteomics, etc. Explain the differences between these concepts and their successive roles in understanding the sequence of events from genes to mature grain. Describe some practical applications of proteomics in grain science. Construct a diagram (and explanation) showing relationships between genomics, various forms of proteomics, and other ‘-omics.’ Describe their relevance to grain science. Consider thiolomics and zymomics, as examples (but not economics). The following reference provides an introduction to zymomics: Kosar-Hashemi B, Irwin JA, Higgins J, Rahman S, and Morell MM (2006) Isolation, identification, and characterization of starch-interacting proteins by 2-D affinity electrophoresis. Electrophoresis 27: 1832–1839.


•

It is stated that the results of proteomic analysis of grain proteins have ‘wide-ranging implications for research on


•

• •

structure–function relationships’ for grain proteins. Find out about some examples of proteomics being used to demonstrate how specific proteins influence significant aspects of grain development and utilization. Develop some diagnostic applications of proteomic analysis, based on the knowledge that specific polypeptides distinguish one cereal variety from others (variety identification), or one grain tissue from another (milling) or one grain genus from another, or grain tissue from that of a predator. Investigate applications of proteomics in plant breeding to achieve aims such as improved pathogen resistance and better grain quality. Construct a diagram (and explanation) showing relationships between genomics, various forms of proteomics, and other ‘-omics.’ Describe their relevance to grain science. Consider thiolomics and zymomics, as examples (but not economics). The following reference provides an introduction to zymomics: Kosar-Hashemi B, Irwin JA, Higgins J, Rahman S, and Morell MM (2006) Isolation, identification, and characterization of starch-interacting proteins by 2-D affinity electrophoresis. Electrophoresis 27: 1832–1839.

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Development of Genetically Modified Grains; Genomics of Food Grains; Wheat Genetics and Genomics; Grain Marketing and Grading: Identification of Varieties of Food Grains; Proteins: Protein Synthesis and Deposition; The Protein Chemistry of Cereal Grains; Thiolomics of the Gluten Protein Network of Wheat Dough; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

Further Reading Branlard G and Bancel E (2007) Protein extraction from cereal seeds. In: Thiellement H, Zivy M, and Damerval C (eds.) Plant Proteomics Methods and Protocols. Methods in Molecular Biology, vol. 355, pp. 15–27. Totowa, NJ: Humana Press. Camafeita E, Solıs J, Alfonso P, Lopez JA, Sorell L, and Mendez E (1998) Selective identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of different types of gluten in foods made with cereal mixtures. Journal of Chromatography A 823: 299–306. Colinge J and Bennett KL (2007) Introduction to computational proteomics. PLoS Computational Biology 3(7): e114. http://dx.doi.org/10.1371/journal. pcbi.0030114. Cramer R and Westermeier R (eds.) (2012) Difference Gel Electrophoresis (DIGE). Methods and Protocols. In: Methods in Molecular Biology, vol. 854. Totowa, NJ: Humana Press. Dupont FM, Vensel WH, Tanaka CK, Hurkman WJ, and Altenbach SB (2011) Deciphering the complexities of the wheat flour proteome using quantitative two-

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dimensional electrophoresis, three proteases and tandem mass spectrometry. Proteome Science 9: 10. http://dx.doi.org/10.1186/1477-5956-9-10. Finnie C, Sultan A, and Grasser KD (2011) From protein catalogues towards targeted proteomics approaches in cereal grains. Phytochemistry 72: 1145–1153. Gao L, Wang A, Li X, et al. (2009) Wheat quality related differential expressions of albumins and globulins revealed by two-dimensional difference gel electrophoresis (2-D DIGE). Journal of Proteomics 73: 279–296. Gao L, Ma W, Chen J, et al. (2010) Characterization and comparative analysis of wheat high molecular weight glutenin subunits by SDS-PAGE, RP-HPLC, HPCE, and MALDI-TOF-MS. Journal of Agricultural and Food Chemistry 58: 2777–2786. Hashiguchi A, Ahsan N, and Komatsu S (2010) Proteomics application of crops in the context of climatic changes. Food Research International 43: 1803–1813. Jorrin-Novo JV, Komatsu S, Weckwerth W, and Wienkoop S (eds.) (2014) Plant Proteomics Methods and Protocols. In: Methods in Molecular Biology, vol. 1072. Totowa, NJ: Humana Press. Juha´sz J, Moolhuijzen P, Bellgard M, Appels R, and Be´ke´s F (2013) Wheat grain proteomics for the food industry. In: Toldra´ F and Nollet LML (eds.) Proteomics in Foods. Principles and Applications. Food Microbiology and Food Safety, 2: pp. 341–379. New York: Springer. Kav NNV, Srivastava S, Yajima W, and Sharma N (2007) Application of proteomics to investigate plant-microbe interactions. Current Proteomics 4: 28–43. Manjasetty BA, Bu¨ssow K, Panjikar S, and Turnbull AP (2012) Current methods in structural proteomics and its applications in biological sciences. 3 Biotech 2(2): 89–113. Martıńez-Maqueda D, Hernańdez-Ledesma B, Amigo L, Miralles B, and Go´mez-Ruiz J (2013) Extraction/fractionation techniques for proteins and peptides and protein digestion. In: Toldra´ F and Nollet LML (eds.) Proteomics in Foods. Principles and Applications. Food Microbiology and Food Safety, vol. 2, pp. 21–50. New York: Springer. McLaffety FW, Breuker K, Jin M, et al. (2007) Top-down Ms, a powerful complement to the high capabilities of proteolysis proteomics. FEBS Journal 274: 6256–6268. Miernyk JA and Hajduch B (2011) Seed proteomics. Journal of Proteomics 74: 389–400. Pappini D, Hojrup P, and Bleasby A (1993) Rapid identification of proteins by peptidemass fingerprinting. Current Biology 3: 327–332. Sealey-Voyksner JA, Khosla C, Voyksner RD, and Jorgenson JW (2010) Novel aspects of quantitation of immunogenic wheat gluten peptides by liquid chromatographymass spectrometry/mass spectrometry. Journal of Chromatography A 1217: 4167–4183. http://dx.doi.org/10.1016/j.chroma. 2010.01.067. Shewry PR, D’Ovidio R, Lafiandra D, Jenkins JA, Mills NF, and Be´ke´s F (2009) Wheat grain proteins. In: Khan K and Shewry PR (eds.) Wheat Chemistry and Technology, pp. 223–298. St Paul, MN: AACC Press. Skylas DJ, Mackintosh JA, Cordwell ST, et al. (2000) Proteome approach to the characterisation of protein composition in the developing and mature wheat-grain endosperm. Journal of Cereal Science 32: 169–188. Skylas DJ, Copeland L, Rathmell W, and Wrigley CW (2001) The wheat-grain proteome as a basis for more efficient cultivar identification. Proteomics 1: 1542–1546. Skylas DJ, Van Dyk D, and Wrigley CW (2005) Proteomics of wheat grain. Journal of Cereal Science 41: 165–179. Tasleem-Tahir A, Nadaud I, Girousse C, Martre P, Marion D, and Branlard G (2011) Proteomic analysis of peripheral layers during wheat grain development. Proteomics 11: 371–379.

Relevant Websites http://expasy.org – Proteomics tools. http://propepper.net – ProPepper is a protein, peptide and epitope analysis suitable for cereal prolamin analysis. www.uniprot.org – Uniprot is a comprehensive database and analysis tool used protein science. http://wiley-vch.de – Proteomics is a scientific journal specializing in articles on proteomics.

Thiolomics of the Gluten Protein Network of Wheat Dough F Bonomi and S Iametti, University of Milan, Milan, Italy ã 2016 Elsevier Ltd. All rights reserved.

Abbreviations 2-ME 5-IAF DTT HMW-GS

2-Mercaptoethanol 5-Iodoacetamidofluorescein Dithiothreitol High-molecular-weight glutenins

Topic Highlights

• • • • • • • • • •

Cysteine thiols and disulfides play key roles in the formation and stabilization of gluten network. Disulfides may be inter- or intramolecular. Intramolecular disulfides are typical of gliadins; intermolecular, of glutelins. The pattern of free cysteines and of disulfides is typical of individual components in both gliadins and glutelins. Accessibility of cysteine thiols to suitable reagents depends on structural features of the protein(s). Denaturing agents cause changes in the accessibility of cysteine thiols to specific reagents. Accessible thiols in individual polypeptides may be studied after they are covalently labeled with a fluorescent reagent. Separation of covalently labeled polypeptides by 2-D electrophoresis allows to identify species- and variety-specific accessibility patterns. Image analysis of thiol-stained and protein-stained 2-D electrophoretic patterns forms the basis of ‘thiolomics.’ Thiolomics combines data on the occurrence/abundance of individual proteins with those on the accessibility of their cysteine thiols in the presence/absence of chaotropes.

Learning Objectives

• • • •

To understand the role of thiols and disulfide in the establishment of intra- and intermolecular covalent bonds among cereal proteins. To acquire knowledge on how individual proteins in cereals may contribute to process-induced formation of a protein network through disulfide exchange reactions. To get acquainted with methodologies used to study the accessibility of free thiols in cereal proteins and processrelated changes in their accessibility pattern. To get an overview of how proteomics-based approaches can be combined with chemical labeling of accessible thiols, in order to evaluate the possible contribution of individual species to the desired product properties.

Relevance of Thiols and Disulfides to Protein–Protein Interactions Formation of a viscoelastic network involving wheat gliadins and glutelins (and similar proteins in related cereals) is a

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LMW-GS PAGE SDS-PAGE

Low-molecular-weight glutenins Polyacrylamide gel electrophoresis Sodium dodecyl sulfate polyacrylamide gel electrophoresis

crucial step in the production of an extremely diverse variety of common wheat-based foods. Gliadins and glutelins represent two classes of water-insoluble proteins found in wheat flour and semolina. The so-called gluten network formed by these two protein classes contributes to these systems an array of features that have a deep impact on the consumer appreciation of the final product, be that due to retention of gas bubbles in bread and baked products or to entrapment of swollen starch in pasta. The interactions leading to the formation of the viscoelastic network in gluten are of two main types, namely, (1) hydrophobic contacts among proteins (or within individual proteins) and (2) intra- and intermolecular disulfides. Most often, these bonds are present in the original molecules, but they are rearranged in processes that require protein structural flexibility (made possible by the addition of water prior to the mixing steps) and the action of shear forces that act as ‘mechanical denaturants’ during mixing. Covalent bonds form as a consequence of oxidation of spatially closed cysteine thiols to form a disulfide bridge or – more commonly – in the so-called ‘disulfide exchange’ reactions, which in turn require the presence of free and accessible cysteine thiols and of a preexisting disulfide in specific proteins. Disulfide exchange among proteins upon structural modification is a common occurrence in many processed foods, from hard-boiled eggs to heat-treated milk. Given the relevance of disulfides and thiols to gluten properties, chemical and biochemical oxidants and reductants have often been used as ‘ameliorants’ of wheat flour. Oxidants (such as bromate/iodate or hydrogen peroxide that may also be produced in situ by appropriate enzymes) promote the formation of disulfides, whereas reducing agents (such as ascorbate, cysteine, and free or protein-bound glutathione) increase the number of free thiols and could facilitate thiol–disulfide exchange reactions. In common practice, the amount of proteins in wheat flour or semolina and the glutelin/gliadin ratio in wheat flour are considered key parameters to predict their best possible use. Proteomics-based studies have provided a comprehensive and detailed view of the protein patterns in wheat, but attempts at finding correlations with the processing performance seldom indicated evident connections. Also, environmental and agronomic issues may affect either protein expression or protein structure after proteins are deposited in the seed. Among the many other parameters that need to be considered in a comprehensive approach to ‘protein quality’ are those


http://dx.doi.org/10.1016/B978-0-12-394437-5.00108-X

PROTEINS | Thiolomics of the Gluten Protein Network of Wheat Dough related to structural issues in these proteins. These include (1) the role of noncovalent (mostly hydrophobic) interactions in network formation; (2) the availability of thiols and disulfide to exchange reactions, as determined by overall and local protein flexibility, in turn related itself to protein solvability and to the intensity of physical deformation; and (3) the possible role of low-molecular-weight thiols and of low-abundance thiol-rich proteins in facilitating thiol– disulfide exchange reactions. Structural studies on proteins that cannot be solubilized without resorting to the use of denaturants (alcohols or detergents) are intrinsically complicated. Methods capable of evaluating protein surface hydrophobicity in systems made up of water-insoluble proteins have been developed and applied to protein characterization in cereal-based starting materials and products without resorting to protein separation that necessarily uses solvent systems that affect protein structure and interactions or to standard ‘proteomics’ or ‘peptidomics’ approaches, in which a combination of separative techniques is used to clarify the whole pattern of proteins and peptides and to quantitate their relative abundance. Protein solubility in the absence/presence of chaotropes and in the absence/presence of disulfide reductants, such as dithiothreitol (DTT) and 2-mercaptoethanol (2-ME, also known as beta-mercaptoethanol), has been used to study hydrophobic and covalent interactions among proteins and their impact on the rheological properties of dough. These properties are reportedly affected by agents that block the reactivity of thiols in wheat proteins, thus preventing many of the permanent structural changes that occur during further processing. The ‘thiolomics’ approach described in what follows aims at combining information about the amount of thiols present (and accessible under native or denaturing conditions) in individual protein components in a complex system such as grain proteins. This approach offers the advantage of combining information about thiols on individual proteins along with their location on specific components (which may be identified by further proteomics analysis), thus contributing to a more comprehensive assessment of the molecular determinants of grain performance.

Protein Thiols in Cereal Systems Wheat proteins will form the basis of the discussion here, as the occurrence and relevance of thiols in small molecules (the so-called low-MW thiols that include free and protein-bound glutathione and free cysteine itself) and in the water-soluble albumin/globulin components of flours will be discussed elsewhere. It has to be noted that some of the processes used to convert some cereals into foods (including fermentation, as in the case of sorghum) result in a significant decrease of the total content of reactive cysteines that appear to be preferentially metabolized by the involved microorganisms. These effects on protein thiols are not as evident in other pretreatments of cereal and noncereal grains (e.g., germination and/or malting). As summarized in Figure 1, wheat gliadins are monomeric proteins with a relevant role in the development of the gluten intermolecular network through the formation of hydrogen bonds, of hydrophobic bonds between nonpolar amino acid

155

side chains, and of thiol–disulfide exchange reactions. Gliadins also interact with the flour lipids or with added lipids, and there is a general consensus on their role in determining dough extensibility. Gliadins have molecular masses ranging from 30 to 45 kDa and had been subdivided into a/b, g, and o fractions, according to their mobility in polyacrylamide gel electrophoresis (PAGE) at acid pH. Alpha- and b-gliadins are currently considered a single gliadin (a/b type) and contain six Cys residues in their C-terminal domain. Eight Cys residues are found in the C-terminal domain of g-gliadins, whereas no cysteine is present in o-gliadins. The glutenin fraction in wheat consists of protein aggregates from about 60 000 to more than 10 millions Da. Glutenin subunits have been divided into high-molecular-weight glutenins (HMW-GS) and low-molecular-weight glutenins (LMW-GS). HMW-GS represent 5–10% of gluten proteins, but dough properties are reportedly strongly influenced by their relative abundance. The bread-making quality of wheat genotypes appears to be determined by the expression of specific HMWGS genes. The N- and C-terminal domains in HMW-GS contain cysteine residues that form inter- and intrachain disulfide bonds, whereas the central domain comprises repeated sequences that may promote intermolecular hydrogen bonding. In particular, the x-type subunit includes four cysteines; three at the N-terminal and one at the C-terminal. The y-type subunit has seven cysteines; five in the N-terminal domain, one within the repetitive domain, and one close to the C-terminus. These proteins promote the formation of larger glutenin polymers by forming intermolecular disulfides with other glutenins. LMW-GS are classified into B (42–51 kDa), C (30–40 kDa), and D types (55–70 kDa), the B type being the most abundant. D-type LMW-GS correspond to a o-gliadin-like protein with an additional cysteine that allows interchain disulfide bond formation in the glutenin polymer. C-type LMW-GS have a structure similar to a/b- and g-gliadin but contain an extra unpaired cysteine residue thought to be involved in an interchain disulfide. The presence of an odd number of cysteines makes the C- and D-type LMW-GS behave as terminators of the growing glutenin polymer chains, with a presumed negative effect on flour quality. B-type LMW-GS are subdivided in LMW-s, LMW-m, and LMW-i types, on the basis of the first amino acid in the mature polypeptide being Ser, Met, or Ile, LMW-s-type subunits being the most abundant. The sequences of LMW-s and LMW-m consist of a short N-terminal region including the first cysteine, a glutamine-rich repetitive domain, and a C-terminal region containing seven cysteines. Mature LMW-m and LMW-s contain eight cysteines, of which the first and seventh are involved in intermolecular disulfide bonds, whereas the others participate in intramolecular bonds. LMW-i contain the typical eight cysteine residues, all in the C-terminal domain and all involved in interchain disulfide bonds. The ability of LMW to form a variable number of intermolecular disulfide bonds defines their role as chain extenders or chain terminators. B-type LMW-GS allow the extension of glutenin polymers (‘chain extenders’). LMW-GS of the C type and D type behave as chain terminators, in what they block further extension of the disulfide network, as they lack the additional free cysteine residues required for formation of further interchain linkages.

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PROTEINS | Thiolomics of the Gluten Protein Network of Wheat Dough

N-TER

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C-TER C

2

3

6

4

C

C

C

C1

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C5

REP

γ

C-TER C2 C3 C4 C5

C6

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Gliadins HMW REP

N-TER 1

2

C C C

C4

N-TER 1

2

C C C

REP

3

C5

C

REP 6

CC C C C

7

C

C

SH

SH

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C7

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REP

s-and m-type

C-TER 3

4

C

6

C

8

C

C

C5

C2

N-TER

y-type

C-TER

1 2 3 4 5

C

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4

N-TER

LMW

x-type

C-TER

3

REP

i-type

C-TER C2

C3

C4

C5

C6

C8

C

C

SH

SH

Glutenins Figure 1 Location of cysteine residues and of disulfide bonds in wheat gliadins and glutelins.

Thiol Accessibility as a Protein Structural Probe Accessibility of thiols to common colorimetric or fluorescent reagents has been studied as a function of added denaturing agents (urea, thiourea, guanidinium ions, and detergents) and of reaction time to assess overall and local rigidity of proteins in either the starting material or the finished products. This approach could to some extent be combined with solubility and compositional data, in an attempt to gather a unifying vision of individual molecular features that contribute to the properties of these systems. The approach presented here relies on the observation that thiols buried within the structure of a protein (or a protein aggregate) often become available to suitable reagents only upon protein denaturation by physical or chemical agents. Accessibility of the target thiol(s) is thus determined by steric factors, in particular when bulky reagents are used. From a methodological standpoint, readily accessible thiols may be assessed in the absence of suitable protein denaturants, whereas the addition of denaturing agents should permit the detection of all free thiols in the investigated proteins. Simple spectrophotometric assays rely on using 5,50 -dithiobis-(2-nitrobenzoic acid) (DTNB, see Figure 2) that releases a

colored thionitrobenzoate anion upon reacting with an SH group. This method can be applied – in principle – regardless of the solubility of the proteins being investigated, but it is not suitable for ‘permanent’ (i.e., covalent) labeling of thiols, in view of the lability of the resulting mixed disulfide. Other reagents can form much more stable bonds with protein thiols, generating species that may resist the chemically severe conditions used for resolving individual components in OH O N+

O O HO –O

S

O–

S

+

N

O NO2

O R

SH + HO O2N

S

NO2

OH

S O

R

S

OH

S O

NO2 +

OH

HS O

Figure 2 Structure of 5,50 -dithiobis-(2-nitrobenzoic acid) (DTNB) (Ellman’s reagent) and its reaction with thiols, leading to the formation of the yellow-colored (A412 ¼ 13 700) thionitrobenzoate anion.

PROTEINS | Thiolomics of the Gluten Protein Network of Wheat Dough protein mixtures. There are three fundamental types of chemical reactions that can be used for this purpose (see Figure 2), involving (1) mercuric derivatives, (2) N-ethylmaleimide derivatives, (3) iodinated compounds, such as monoiodobimane or iodoacetamide derivatives. Selected examples of compounds in each of these classes of reactivity are presented in Figure 3.

Mapping the Pattern of Thiol Exposure in Individual Cereal Proteins (Thiolomics) The possibility of covalently labeling any exposed thiol prior to separation of individual polypeptides has been exploited to assess the pattern of thiol exposure also in the insoluble components of wheat flours and semolina. By introducing denaturing and disulfide-reducing steps at appropriate points in the thiol-labeling procedure, it is possible to use 2-D electrophoresis techniques to obtain a visually informative ‘thiolomics’ map of the conditional accessibility of thiols in individual proteins in the materials under investigation. These maps provide information as for the type of proteins where thiols are available and on the relative abundance of proteins and reactive thiols on them (Figure 4). In the original procedure, thiols in wheat flour or semolina proteins were covalently labeled by 5-iodoacetamidofluorescein (IAF) in the absence or in the presence of 4 M urea, allowing to evaluate thiols accessibility before and after protein unfolding and as related to the dissociation of noncovalently linked protein complexes. Proteins labeled under either condition were then separated by SDS-PAGE and/or by 2-D electrophoresis. Visual inspection and quantitative comparison of the maps for proteins and for accessible thiols in different and variously treated starting materials were then carried out to identify specific proteins or protein classes whose thiol functions may specifically contribute to specific traits of the material. Only readily accessible protein thiols should be labeled in flour samples treated with IAF in the absence of urea, whereas O I

Iodoacetamide NH2 O

O N

H3C

CH3 Monobromobimane

N

CH2Br

H3C

O N-Ethylmaleimide

N O O

CH3

Hg O

Phenylmercury acetate

Figure 3 Examples of common thiol reagents suitable for covalent labeling of proteins.

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additional thiols buried in the hydrophobic regions of proteins or at hydrophobic interfaces among proteins should become available to the labeling agent if denaturants were added prior to IAF. As stated earlier, measurements based on thiol accessibility may be carried out regardless of whether the involved proteins are soluble or insoluble (as is the case for most of wheat proteins) in the conditions used for labeling. As indicated by electrophoretic separation of IAF-labeled wheat proteins in the presence of sodium dodecyl sulfate (SDS-PAGE; see an example in Figure 5), treatment with IAF in the presence of urea gave the expected increase in the intensity and number of fluorescent bands, as a consequence of increased thiol exposure in the presence of the chaotrope. The SDS-PAGE tracings in Figure 5 also allow to appreciate some specificity of the labeling procedure in wheat flour and in semolina and a different sensitivity of otherwise similar proteins in each of the samples to the presence of urea during the labeling step. In the case of soft wheat, labeling in the presence of urea apparently modifies only the intensity of the fluorescence associated with all protein bands, and no additional bands were present in the sample labeled in the presence of urea. In the case of durum wheat semolina, the fluorescence intensity of specific protein bands was sensibly increased when labeling was carried out in the presence of urea, and the effect of the denaturant on the accessibility of thiols was most evident in the largest polypeptides. This may be taken as an indication of the presence of multiple thiols on the involved proteins and of changes in their accessibility to the reagent in the presence/absence of urea. Given the possible ambiguities associated with identification of specific components from SDS-PAGE gels, 2-D electrophoretic maps were also obtained, similar to those used in classic ‘proteomics’ studies. In this technique, proteins are made soluble by unfolding in urea and reduction with DTT and are separated first according to their isoelectric points (pI) in an immobilized pH gradient. The second run is performed in an orthogonal direction with respect to the first separation step and separates them by molecular mass. A comparison of protein-stained 2-DE maps obtained in the presence and absence of treatment with the fluorescent thiol probe confirms that covalent binding of the probe may introduce some alterations in the pI of labeled proteins, although the impact of this substitution on the acidic proteins that are predominant in wheat does not impair analysis of the resulting maps. Typical 2-D maps of the IAF-labeled polypeptides in various wheat samples are shown in Figure 6. These maps can be easily analyzed by standard image analysis techniques that may be used to convert positive and negative images (the original fluorescence maps had bright spots against a black background) and to transform halftone images into very informative and/or easily read ‘landscape plots’ (see the example presented in Figure 7). This type of graphical rendition makes it easier to appreciate (both visually and on a quantitative basis) compositional and/or structural differences among samples as reflected in their thiol accessibility maps. It has to be noted that the very same 2-D gel can subsequently be stained for proteins by any of the procedures used in standard proteomics studies (see Figure 8). Image analysis of the protein-stained gel can provide additional information on not only the occurrence and abundance of specific protein


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O O

I

OH O

N H

O

OH

Iodoacetamide fluorescein (IAF) Cysteine thiols Interprotein disulfide bonds Hydrophobic contact regions Native, no denaturant

Denaturant present

Covalently bound fluorophor

Labeled species present after denaturing/reducing treatments

Figure 4 A graphical rendition of the events related to covalent binding of the fluorescent probe IAF to wheat protein thiols in the absence/presence of denaturants.

Urea

+

−

Urea

+

Soft wheat

−

Urea

−

Urea

−

+

+

Semolina

Figure 5 SDS-PAGE patterns for proteins reacted with IAF under various conditions. In each figure, the left panel is Coomassie bluestained, and the right panel is the corresponding fluorescence image. Letters on individual lanes indicate whether the treatment with IAF was carried out in the presence (þ) or in the absence () of 4 M urea.

components but also comparison with the fluorescence labeling maps allowing information to be gathered on the presence and exposure of thiol groups in each of them. Furthermore, since labeling with IAF does not to compromise identification of specific protein components by standard mass spectrometric

No urea

+ urea

Figure 6 2-DE pattern of IAF-labeled proteins in soft wheat flour. Labeling with IAF was carried out in the absence or presence of urea, as indicated. Images are digitally generated negatives from the original fluorescence maps. Dashed areas indicate artifacts.

techniques, it is possible to identify individual proteins – present with exposed or buried thiols – in materials of different technological performances or in products obtained through different processes. In conclusion, ‘thiolomics’ represents – along with other ‘omics’ approaches – a potentially powerful tool to assess features of grain proteins that may be relevant to their technological performance. In comparison with approaches based on the analysis of individual proteins, it offers the advantage of


(a)

Hard wheat

(b)

159

Soft wheat

Figure 7 Landscape plots obtained after image analysis of IAF-labeled 2-D electrophoretic patterns.

•

Silver–Coomassie

Fluorescence

Figure 8 2-DE pattern of IAF-labeled proteins in hard wheat flour. Treatment with IAF was carried out in the presence of urea. The 2-DE gel was stained for proteins with silver–Coomassie blue (left) after acquiring the fluorescent image (right). Green arrows indicate examples of proteins that were present in marginal amounts but had a high content of reactive thiols. Red arrows indicate examples of proteins present in substantial amounts, but with no reactive thiols.

offering a comprehensive view of both the protein and the thiol pattern in a complex system and of discriminating between protein structures of different accessibilities.


• • • • • •

Define the relevance of covalent and noncovalent interactions among proteins as for establishing a stable network. Why is the pattern of exposed thiols expected to be different in native and denatured proteins? Do you expect protein thiols to be more accessible in pizza or in spaghetti? What could happen if all the free thiol groups in wheat proteins were blocked (e.g., by chemical reagents) prior to mixing cereal flours? Provide a rationale for the observation that the pattern of thiol-labeled proteins in a 2-DE analysis of wheat flour does not overlap the pattern of proteins. Why is the pattern of thiol-labeled proteins different when the necessary dissociating step is carried out prior to the labeling procedure?


•

Extension of thiol accessibility/labeling studies to systems containing proteins other than those of cereal origin may

•

provide interesting insights into their participation in the establishment of an interprotein network. Discuss. Thiol accessibility/labeling studies may also help to understand the behavior of those systems (e.g., germinated grains or fermented flours) where cereal proteins may undergo proteolytic events and where a mechanical denaturation step (as in mixing/kneading) is not present. Propose a specific study to investigate this. The ‘thiolomics’ approach as reported here could be further improved and adapted to studies on the relevance of individual steps in specific processes (e.g., by using other protein dissociating agents and/or other thiol-specific reagents). Design an appropriate study.

See also: Proteins: Protein Synthesis and Deposition; Proteomic Analysis Relevant to Cereal Grains; The Protein Chemistry of Cereal Grains; Wheat Processing: Analysis of Dough Rheology in Breadmaking; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

Further Reading Belton PS (1999) On the elasticity of wheat gluten. Journal of Cereal Science 29: 103–107. Bonomi F, Mora G, Pagani MA, and Iametti S (2004) Probing structural features of water-insoluble proteins by front-face fluorescence. Analytical Biochemistry 329: 104–111. Bonomi F, D’Egidio MG, Iametti S, et al. (2012) Structure–quality relationship in commercial pasta: A molecular glimpse. Food Chemistry 135: 348–355. Bonomi F, Iametti S, Mamone G, and Ferranti P (2013) The performing protein: Beyond wheat proteomics? Cereal Chemistry 90: 359–366. Field JM, Shewry PR, and Miflin BJ (1983) Solubilization and characterization of wheat gluten proteins; correlations between the amount of aggregated proteins and baking quality. Journal of the Science of Food and Agriculture 34: 370–377. Goesaert H, Brijs K, Veraverbeke WS, Courtin CM, Gebruers K, and Delcour JA (2005) Wheat flour constituents: How they impact bread quality, and how to impact their functionality. Trends in Food Science and Technology 16: 12–30. Iametti S, Marengo M, Miriani M, Pagani MA, Marti A, and Bonomi F (2013) Integrating the information from proteomic approaches: A “thiolomics” approach to assess the role of thiols in protein-based networks. Food Research International 54: 980–987. Joye IJ, Lagrain B, and Delcour JA (2009) Endogenous redox agents and enzymes that affect protein network formation during breadmaking. Journal of Cereal Science 50: 1–10. Mamone G, Addeo F, Chianese L, et al. (2005) Characterization of wheat gliadin proteins by combined two-dimensional gel electrophoresis and tandem mass spectrometry. Proteomics 5: 2859–2865.

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Mamone G, De Caro S, Di Luccia A, Addeo F, and Ferranti P (2009) Proteomic-based analytical approach for the characterization of glutenin subunits in durum wheat. Journal of Mass Spectrometry 44: 1709–1723. Morel MH, Redl A, and Guilbert S (2002) Mechanism of heat and shear mediated aggregation of wheat gluten upon mixing. Biomacromolecules 3: 488–497. Shewry PR, Tatham AS, Forde J, Kreis M, and Niflin BJ (1986) The classification and nomenclature of wheat gluten protein: A reassessment. Journal of Cereal Science 4: 97–106. Shewry PR, Halford NG, Tatham AS, Popineau Y, Lafiandra D, and Belton PS (2003) The high molecular weight subunits of wheat glutenin and their role in determining

wheat processing properties. Advances in Food and Nutrition Research 45: 219–302. Singh H and MacRitchie F (2001) Application of polymer science to properties of gluten. Journal of Cereal Science 33: 231–243. Skylas DJ, Van Dyk D, and Wrigley CW (2005) Proteomics of wheat grain. Journal of Cereal Science 41: 165–179. Veraverbeke WS and Delcour JA (2002) Wheat protein composition and properties of wheat glutenin in relation to bread-making functionality. Critical Reviews in Food Science and Nutrition 42: 179–208. Wieser H (2007) Chemistry of gluten proteins. Food Microbiology 24: 115–119.

Carbohydrates

Contents Carbohydrate Metabolism Starch: Chemistry Starch: Synthesis Starch: Starch Architecture and Structure Starch: Analysis of Quality Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides Grains other than Cereals: Non-starch Polysaccharides Resistant Starch and Health Health Effects of b-Glucans Found in Cereals Glycemic Index, Glycemic Load, and Their Health Benefits

Carbohydrate Metabolism RN Chibbar, S Jaiswal, M Gangola, and M Ba˚ga, University of Saskatchewan, Saskatoon, SK, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Carbohydrates are one of the major components of food grains. Carbohydrates are mainly categorized on the basis of their degree of polymerization, structure, and function. Biosynthesis of different sugars occurs in different plant cell organelles. Carbohydrates support seed germination and early seedling development. Carbohydrates, besides being an energy source, also provide structural integrity to plant cells. Carbohydrate biosynthesis can be targeted to improve food grain quality for human consumption. Carbohydrates are also involved in abiotic stress tolerance.

Learning Objectives

• •

To achieve understanding of the structural diversity of grain carbohydrates, their biosynthesis, storage in grains, and mobilization during seed germination. To appreciate the influence of structural diversity of grains on their end use for human food, animal feed, and industrial applications.

Introduction Carbohydrates are one of the most important nutrients for both plants and animals. In plants, carbohydrates constitute


two-thirds to three-quarters of dry matter and are the major components of storage organs. Cellulose, the most abundant plant carbohydrate, provides structural integrity to plants and is used for fiber and fuel by humans. In seeds, carbohydrates provide energy and substrates required for the germination and initial growth of seedlings. Carbohydrate in the form of starch is the major reserve polysaccharide present in grains. Carbohydrates like starch and cellulose form the basis of several important industries in the food, feed, and fuel sectors. They also provide renewable and environmentally friendly raw materials for industrial applications such as biodegradable plastics, adhesives, and ethanol-based fuels. With the development of genetic modification technologies, the biosynthesis of carbohydrates can be altered in planta to generate novel products for various food and industrial applications. This article will describe the structure, occurrence, and distribution of some of the common storage and structural carbohydrates present in the grains of major crops. The biochemical reactions occurring during the biosynthesis of carbohydrates and their utilization during seed germination will be discussed.

Carbohydrates Definition and Classification The term carbohydrate, or hydrates of carbon, is derived from its basic elemental formula [Cx(H2O)y], in which carbon is joined to hydrogen and oxygen present in the same ratio as in water. Chemically, carbohydrates are polyhydroxy aldehydes or ketones, their simple derivatives, or their polymers. Carbohydrates in grains are classified based on their chemical structures

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CARBOHYDRATES | Carbohydrate Metabolism

or their digestibility when consumed by humans as food or by livestock as feed. Based on the polymeric nature of carbohydrates, they are classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides (Figure 1). Monosaccharides are the simplest of all sugars, contain at least three carbon atoms, and are the building blocks of all carbohydrates. The most common monosaccharides in grains are the hexoses (fructose, glucose, and galactose) and the pentoses (arabinose and xylose). Two sugar moieties joined by a glycosidic bond (an oxygen bridge) form

a disaccharide. Upon hydrolysis of disaccharides, the glycosidic bond is split into yield the component monosaccharides. Sucrose and maltose are the most commonly occurring disaccharides in the majority of grains. Oligosaccharides include the sugars that contain 3–20 sugar molecules joined by glycosidic bonds. The most common oligosaccharides are soluble a-galactosides, characterized by galactose moieties joined by a(1,6) linkages. In legumes, raffinose, stachyose, and verbascose are the most common oligosaccharides and constitute 6–18% of the legume

Monosaccharides

O

H O

H O

O

O

H O

H

O

O

H

O

H

O

H

O

H

O

H

O

H

O

O

O H

H

H

α-D-Glucose

O

H

O

O

O

H

O

H

O

O

O

H H

H

O H

O

O

H

H

α-D-Xylose

β-D-Fructose

O

α-D-Galactose

α-L-Arabinose

Disaccharides H

H

O H

H

O

O

H

O

O

H

H

O

O

H

O

H

O

O

H O

H

O

O

O O

O

H

O

H

H

O

H

O

H

O

O

O

O

H

H

H

O

H

H

O

O

H

α-D-Maltose

Sucrose

O

O

H

O

O

O

O

H

O H

O

O

H

O O

H

H

O

O

H

O

O

O

H

H

O H

Galactinol

H

O

Lactose

Oligosaccharides HO

HO H O H H

OH

H O

H O O

O O

O O

O

H O H H

OH O

H

H

Raffinose

O H

H

Manninotriose

O O H

O H

O

H

O

O

O O

O H O O

Lychnose

O

O O H

O

O

O H H

H

O

H

O

H

OH O

O H

HO

H O O

O

O O

O O

O

H O

O O H

O O

Mediose

H

H

H

H H

OH

HO

O

O O

O O

Verbascose

O O

O

Stellariose

HO

O

O H

OH

O H

H O

O

H H

HO

O

O

H O

H O H

H O

HO

O

H

O

O

O O

O

HO

O O

OH

O O

O

H O

O

H O

O

O

H

O

O H

OH

H O

O H H

O

H H O

O

HO

HO

OH

H O

Stachyose

O

O H

Figure 1

H O

H

O

H

H

O

O

O

H

H

O

O O

H

H O

H O

O

OH

HO H O

O

H

O

O

O H

O

O

O

HO O H

H

H O

H O

O

O

O O

H O

HO

O

OH

O H

HO

O O H

H O OH


163

Polysaccharides H H Main chain CH2OH O

CH2OH O OH

O

H

H O

OH

O O

n

α-D-Glc(1→4) linkage

O

O

O

O

O

O

OH

OH

OH

CH2

CH2

OH

O

O

O

CH2

OH

CH2 O

O

H

H

O-H H

O H

HO

Amylose

O

O

O

O

O

O

O

HO

H CH2

CH2 O CH2OH O

CH2OH O

Branch

OH

O

O

OH

O

OH

O

O

O

O

O OH

OH

O OH OH

OH

OH

OH

α-D-Glc(1→4) linkage

O

O

OH

OH

OH

Main chain

O

OH

O

H

CH2OH O

CH2

CH2OH O

OH

H

OH O α-D-Glc(1→6) branch point

OH CH2OH O

O

Cellulose units linked with inter and intra chain H bonds

OH

O

O

OH

H O

OH

OH

OH

OH

β-1, 3-Xylan

n

Amylopectin

Fructans CH2OH

O OH

CH2OH CH2OH OH

O

CH2OH O

O

OH CH2O

OH O

OH

CH2O

OH

OH

OH

CH2OH CH2OH

(n)

OH

OH O

CH2

OH OH

CH2OH

O

CH2OH O

O

OH

CH2

O

O

OH

(n)

OH O

OH

CH2OH

CH2OH

OH

OH

Fructan-levan type

Fructan-inulin type

Sugar alcohols H

O H O

O

O H

O

O O

O

H

H

H

H O

O

H

H

O

O O

O O H

O H

O H

O

H

H

O

O

H

O

H

H

O O O

O

H

H

O

H

O

H

H

O H

Ciceritol

Sorbitol

Mannitol

Figure 1 (Continued) Classification and chemical structures of representative carbohydrates found in grains of crops. Structure database source: http://www.ncbi.nlm.nih.gov/pccompound. CID number reference: a-D-glucose, 79025; b-D-fructose, 439709; a-D-xylose, 6027; a-D-galactose, 439357; a-L-arabinose, 641630; sucrose, 5988; a-D-maltose, 439341; galactinol, 11727586; lactose, 6134; raffinose, 439242; manninotriose, 440660; stachyose, 439531; verbascose, 441434; lychnose, 25079986; stellariose, 46926270; mediose, 46926113; ciceritol, 44237401; sorbitol, 5780; and mannitol, 6251.

seed dry weight. The presence of these flatulence-causing a-galactosides is one of the major reasons restricting consumption of legume-based food products. The absence of a-galactosidase in the intestinal tract of humans causes fermentation of a-galactosides by intestinal bacteria that contribute to the flatulence effect. Polysaccharides are polymers with more than 20 monosaccharides joined together by glycosidic linkages. These are complex molecules because of the diversity in monosaccharide units and type of linkages present in the polysaccharides.

Some of the most common polysaccharides present in grains are starch, cellulose, and xylans such as pentosans, b-glucans, and arabinoxylans. In relation to human and animal nutrition, carbohydrates are often classified as available and unavailable. The available carbohydrates represented by sugars and starches are broken down and absorbed in the human and animal digestive tracts to provide energy for the body. Structural cell wall carbohydrates such as cellulose, hemicellulose, and nonstarch complex carbohydrates, for example, xylans, are categorized as

164


Table 1 Chemical composition of seeds of some important grain crops Composition (percentage dry weight) Crop Cereal crops Wheat (Triticum aestivum) Barley (Hordeum vulgare) Corn (Zea mays) Rice (Oryza sativa) Oat (Avena sativa) Sorghum (Sorghum vulgare) Rye (Secale cereale) Teff (Eragrostis tef) Pearl millet (Pennisetum glaucum) Foxtail millet (Setaria italica) Finger millet (Eleusine coracana) Kodo millet (Paspalum scrobiculatum) Proso millet (Panicum miliaceum) Canary (Phalaris minor) Triticale (xTriticosecale) Cereal like non-Poaceae family grains Buck wheat (Fagopyrum esculentum) Quinoa (Chenopodium quinoa) Pulse crops Lentil (Lens culinaris) Pea (Pisum sativum) Chickpea (Cicer arietinum) Kidney bean (Phaseolus vulgaris) Mung bean (Vigna radiata) Pigeon pea (Cajanus cajan) Soybean (Glycine max) Cowpea (Vigna unguiculata) Lupin (Lupinus albus) Oilseed crops Rape (Brassica napus) Sunflower (Helianthus annuus) Flax (Linum usitatissimum) Peanut (Arachis hypogaea) Sesame (Sesamum indicum) Hemp (Cannabis sativa)

Carbohydrate

Protein

Lipid

82 80 84 88 67 82 82 83 81 82 88 84

14 9 10 8 28 12 14 11 12.5 9.9 7 11.5

2 1 5 2 1 4 2 2.5 5 2.5 1.7 1.3

82 61 72

10.6 20.3 13

4 11 2.1

83

11

2

78

14.5

5.2

65 68 65 70 69 65 32 60 37

27 27 23 24 26 21 38 24 38

1 2 5 2 1 1 20 1 20

25 48 32 25 19 27

23 20 26 27 20 29

48 29 38 45 54 41

unavailable carbohydrates because they are not assimilated by the digestive tract. The unavailable carbohydrates are also often referred to as dietary fibers.

Distribution in Important Grains In general, carbohydrates dominate as the major constituent of the dry weight of seeds (Table 1). However, in oilseed grains, such as Brassica spp., lipids and proteins exceed carbohydrates as the major storage components by comprising three-quarters of grain dry weight. In cereal grains, the total concentration of mono-, di-, and oligosaccharides varies from < 1% to 3% (Table 2). Corn kernels contain the highest percentage of glucose and fructose, whereas in barley, sucrose is the major free sugar. Wheat grains have the highest concentration of raffinose among the cereal grains (Table 2). Legume crops in general have a higher concentration of di- and oligosaccharides as compared with

cereal grains (Table 3). Chickpeas especially have a high concentration of soluble sugars, of which sucrose is the major component. Lentils and peas have higher concentrations of stachyose and verbascose as compared with other legumes. Starch is the major storage carbohydrate in cereal grains, where it forms twothirds to three-quarters of the dry weight. However, in oats, the starch concentration is slightly less, ranging from 50% to about 60%. Legume seeds also contain 50% starch, except lupins and soybeans in which only 0.5–1.4% of the dry weight is starch. The structural carbohydrates or functionally unavailable carbohydrates (dietary fibers) range in distribution from slightly above 5% in rice to almost one-third of the grain dry weight in barley. In grain legumes, chickpeas have a higher concentration of total nonstarch polysaccharides, whereas the concentration of total dietary fiber corresponds to that of other legumes (Table 3). The major nonstarch complex carbohydrate in grain legumes is cellulose, which represents about one-eighth of the grain dry weight in most of the grain legumes (Table 3).

Metabolism Autotrophic plants have the ability to convert simple nutrients such as carbon dioxide, water, and inorganic ions into intermediates leading to the biosynthesis of complex molecules, such as nucleic acids, proteins, lipids, polysaccharides, and secondary metabolites needed for growth and development (Figure 2). Through the process of photosynthesis, plant cells capture light energy to fix reduced carbon dioxide and water into a simple carbohydrate backbone, CH2O. The reaction takes place in chloroplasts, wherein CO2 entering the Calvin cycle is incorporated into 3-phosphoglycerate (3-PGA) molecules, which are subsequently converted to triose phosphates. In addition, the absorbed light energy is used for extracting reducing equivalents from water and ATP production required for processes involved in plant growth and development. The reactions associated with light absorption are diurnal, which results in large variations in nutrients available to plants during light and dark periods. However, plants have developed considerable flexibility in their metabolism to cope with fluctuations in nutrient concentration. Plant cells can be envisioned to have a series of metabolic intermediate pools, which are interconnected to each other through enzyme reactions or transport mechanisms that are often reversible (Figure 2). According to the physiological need(s) of a plant, metabolites can be added to or withdrawn from these pools. Two metabolite pools of the reductive pentose phosphate pathway and its intermediates are (1) the triose phosphate (3-PGA and dihydroxyacetone phosphate (DHAP)) and (2) the hexose phosphate (glucose 1-P, glucose 6-P, fructose 1-P, and ADP-glucose) pools (Figure 2). The triose phosphates are either transported by triose phosphate transporters to the cytosol or converted to other phosphorylated compounds, such as fructose 6-phosphate, in the plastid. The plastidial fructose 6-phosphate is used for both regenerating ribulose-1,5-bisphosphate and producing glucose 1-phosphate. Glucose 1-phosphate is converted to ADPglucose by ADP-glucose pyrophosphorylase (AGPase), the immediate precursor for starch biosynthesis. Starch biosynthesis occurs inside plastids, but its functionality depends on the plastid type (chloroplast/amyloplast) and source plant tissue. Starch synthesized in the chloroplast during the day is known as

CARBOHYDRATES | Carbohydrate Metabolism Table 2

165

Carbohydrate composition of some cereal grains Free sugar (%)

Starch (%)

Nonstarch complex carbohydrates (%)

Crop

Total

Glucose

Fructose

Sucrose

Raffinose

Total

Amylose

Total dietary fiber

Wheat Barley Rice (brown) Teff Sorghum Pearl millet Finger millet Foxtail millet Proso millet Corn Oats Rye Canary Triticale Quinoa

1.4–1.3 2.0–3.0 1–1.1

0.02–0.03 0.1–0.2 0.12–0.13

0.02–0.04 0.1 0.11–0.13

0.57–0.80 1.9–2.2 0.6–0.66

0.54–0.70 0.59 0.1–0.2

63–72 57–59 66

23–28 22–26 16–33

14.6 19–23 3.9

6.6 5.9 1.2

1.4 3–7 0.11

2.0 4.3 1.7–2.0

1.8 1.3–2.5 2.2–2.8

0.73 0.2–1.1 0.08–0.16

0.47 0.6–1.6 1.3–1.8

0.62 0.15–0.39 0.65–0.84

NA 63 53–70

73 24 20–32

20–26 6 13.3

8 NA NA

NA NA NA

NA NA NA

NA NA NA

0.59–0.69

0.14–0.19

0.20–0.24

0.06–0.08

55.7–63.4

14.4–38.6

18

NA

NA

NA

NA

0.46

0.10

0.15

0.04

52–69

11.2–32

NA

NA

NA

NA

NA

NA

NA

0.66

0.08

61–68

17.2–32.6

NA

NA

NA

NA

NA

1.0–3.0 1.4 3.2 1.75 NA 2.9

0.2–0.5 0.05 0.08 0.06 0.23 0.02

0.1–0.4 0.09 0.10 0.07 3.1 0.02

0.9–1.9 0.64 1.9 0.83 0.2–1.9 NA

0.1–0.3 0.19 0.4 NA NA NA

64–78 43–61 69 61 59–70 63

24 16–27 24–31 17.2 23 11–12

13.4 9.6 14.6 6.0 13–16 9.6

5.8–6.6 7.7 8.5 NA NA NA

0.1 3.9–6.8 1.9–2.9 1.1–2.3 0.5–1.0 NA

2.1 6.0–12.9 1.5 NA 1.7–2.5 NA

transitory starch, as it is degraded to maltose, glucose, hexose phosphates, and triose phosphates at night. This periodical starch degradation involves two major steps: initiation, which involves the activation of starch, and starch digestion. Transient starch degradation is mainly attributed to b-amylases, and the product of its action is transported back to the cytosol, where it undergoes further modifications. Some of the starch degradation products are converted to sucrose, the major transport sugar. Sucrose through symplastic or apoplastic transport enters the phloem, through which it is mobilized to the storage tissues, where symplastic or apoplastic uptake into sink cells takes place. The transported sucrose is further converted to substrates that give rise to the diverse carbohydrates present in grains of different crops as described earlier. The hexose phosphate pool also plays an important role in starch and sucrose utilization by plants. In the glycolytic pathway, which acts in reverse of the triose phosphate synthetic pathway during photosynthesis, starch and sucrose are oxidized to provide energy and hexose phosphates that on phosphorylation contribute to the hexose phosphate pool. In addition, the glycolytic reactions provide several intermediates that contribute to the synthesis of proteins, lipids, and organic acids (Figure 2). These compounds are important grain components and are described in other articles. The hexose phosphate pool is an important converging point for both carbohydrate synthesis and degradation and thus is considered to play an important role in carbohydrate metabolism in plants. The main components, glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate, are readily interconvertible when present in the same system. However, in plants, the hexose phosphates are compartmentalized to the plastids and cytosol. In photosynthetic tissues, the plastidial and cytosolic hexose phosphate pools are independent of

Pentosan

b-Glucan

Cellulose

each other, and their exchange is often restricted. Therefore, the regulation of carbohydrate metabolism in plants is more complex than in other organisms, where such subcellular compartmentalization of hexose phosphates is not present.

Sucrose Sucrose is the most abundant disaccharide and the major product of photosynthesis. It is a nonreducing sugar with limited chemical reactivity and thus is utilized as a transport and storage molecule in most plants. Sucrose synthesis is predominant in leaves, but the ability to synthesize sucrose is fairly widespread among plant cells. Sucrose is synthesized in the cytosol by the consecutive activities of two enzymes: sucrose-phosphate synthase (SPS) and sucrose phosphatase (SPP). SPS catalyzes the reversible transfer of glucosyl units from UDP-glucose to fructose 6-phosphate, synthesizing sucrose 6-phosphate that is dephosphorylated by SPP to yield sucrose in an irreversible reaction. SPS is the key regulating step of sucrose biosynthesis. In plants, SPS can be activated allosterically by glucose 6-phosphate and inhibited by inorganic phosphate (Pi). In addition, SPS also contains several regulatory phosphorylation sites. Sucrose synthase (SucS), present in both soluble and membrane-bound forms, is responsible for catalyzing both the synthesis and degradation of sucrose. However, sucrose degradation is mainly attributed to SucS in sink tissues participating in sucrose degradation. The translocation of synthesized sucrose from source to sink tissues is essential for proper plant growth and development. Sucrose can be translocated either symplastically (through plasmodesmata) or apoplastically (through apoplasts with the help of sucrose transporters). In sink tissues, sucrose can be stored inside cell vacuoles through transporters located

166

Carbohydrate composition of some grain legumes Soluble carbohydrates (%)

Crop Common bean Peas Lentils Chickpeas Faba beans Mung bean Black gram Red gram

Starch (%)

Nonstarch complex carbohydrates (%)

Total soluble sugars

Sucrose

Raffinose

Stachyose

Verbascose

Total galactosides

Total

Amylose

Polysaccharides

Dietary fiber

Hemicellulose

Cellulose

2.0–9.6

1.6–3.9

0.2–2.5

0.2–3.9

0.1–1.8

0.4–8.0

51–51.9

22.1–36.0

6.4–20.4

11.2–27.5

0.5–5.6

3.2–13.1

3.5–13.8 3.3–9.5 4.6–14.2 2.2–8.5 3.9–7.2 3.0–7.1 3.5–10.2

0.9–5.4 1.1–3.0 2.8–6.9 0.1–3.8 0.3–2.0 0.7–1.5 2.7

0.4–2.3 0.1–0.8 0–0.3 0.1–1.5 0.3–2.6 0.0–1.3 1.0–1.1

0.3–4.2 1.1–4.0 0.4–2.0 0.2–1.6 1.2–2.8 0.9–3.0 2.7–3.0

0–4.3 0–6.4 trace–0.4 1.1–2.4 1.7–3.8 3.4–3.5 4.0–4.1

2.3–9.6 1.8–7.5 2.0–7.6 1.0–4.5 NA NA NA

24.7–57.4 40.1–57.4 43.0–59.0 39.2–47.2 37.0–53.6 32.2–47.9 40.4–48.2

23.5–33.1 20.7–45.5 31.8–45.8 22.0–35.0 13.8–35.0 43.9 38.6

NA 6.9–14.7 5.5–35.4 17.5 NA NA NA

16.1–21.6 11.0–21.4 8.2–24.0 17.1–23.8 15.7 22.4 18.7

0.9–12.4 1.2–15.7 0.6–16.0 1.6–8.9 0.3–9.1 10.7 10.1

0.9–13.3 3.5–14.8 1.1–13.7 8.3–14.3 2.5–4.6 5.0 7.3

Black gram: Vigna mungo; red gram: Cajanus cajan; faba bean: Vicia faba.


Table 3


Cell-wall carbohydrates, e.g., cellulose, β-glucan, xylans

Starch

Light Glucose

Hexose-phosphate pool • ADP-glucose • Glucose-1-phosphate • Glucose-6-phosphate • Fructose-6-phosphate

Sucrose Fructose Raffinose Fructan

Ribulose5-bisphosphate

Ribulose-1,5bisphosphate

Photosynthesis (Calvin cycle reduction phase) Glyceraldehyde-3-phosphate

Tryglycerides Amino acids

Pentose phosphate pathway Glycolysis pay-off phase

Citric acid cycle

Other amino acids, proteins, nucleic acids, alkaloids Other amino acids, proteins

CO2 H2O

Purines Triose-phosphate pool 3-PGA, GAP, DHAP

Nucleic acids

Aspartic acid

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NADH FADH2

Tryglycerides

ATP

Amino acids

Glutamic acid

NADH

Delta-aminolevulnic acid

Oxidative phosphorylation

Chlorophyll, Cytochrome, phytochrome

Purines

Purines Tryglycerides Amino acids

NAD+ FAD ATP

Figure 2 A schematic overview of the carbohydrate metabolism and its interrelationship with other biochemical pathways to show the production of major plant cell constituents.

at tonoplasts or can be hydrolyzed by invertase providing glucose and fructose to the cell. The translocation of sucrose from source to sink tissues is very active during grain development when storage carbohydrates are synthesized in the grains. A boost in sucrose concentration in seeds is observed during seed germination when stored carbohydrates are broken down to provide energy to the germinating embryo.

Alpha-Galactosides Alpha-galactosides are low-molecular-weight, nonreducing oligosaccharides and rank next to sucrose among abundant soluble sugars. These sugars constitute about 6–18% of the dry weight of mature legume seeds. Alpha-galactosides are sucrosylgalactosides and are characterized by the presence of an a(1! 6) linkage between the galactosyl residue and the C-6 of the glucose moiety of sucrose. Alpha-galactosides can further be classified into two groups. Raffinose family oligosaccharides (RFOs) constitute the first group, and the first member of this group, raffinose (degree of polymerization (DP) ¼ 3), is the main RFO in most monocotyledon seeds, while its higher homologues, stachyose (DP ¼ 4), verbascose (DP ¼ 5), and ajugose (DP ¼ 6), accumulate predominantly in seeds of dicotyledons. Higher members like ajugose are generally found in trace quantities in seeds. Some alternative RFOs such as lychnose, stellariose, mediose, and manninotriose have been recently reported from

Caryophyllaceae and Lamiaceae plants (Figure 1). The second group of a-galactosides includes galactosyl cyclitols. Ciceritol is the most common of the galactosyl cyclitols and was first reported from chickpea (Cicer arietinum), followed by lentil (Lens culinaris). RFO biosynthesis occurs in the cytosol and begins with the formation of galactinol from myo-inositol and UDP-galactose in a reaction catalyzed by galactinol synthase. In the next step, raffinose synthase supports galactinol to donate its galactosyl unit to sucrose yielding raffinose. Raffinose and stachyose, together with galactinol, synthesize stachyose and verbascose in two separate reactions catalyzed by stachyose synthase and verbascose synthase, respectively. In a galactinol-independent pathway, already present RFOs react with each other to synthesize higher members of RFOs. Galactan/galactan galactosyltransferase is the sole enzyme catalyzing the reaction. RFOs participate in plant physiological processes like seed desiccation tolerance, seed germination, photosynthate translocation (mostly in Cucurbitaceae, Verbenaceae, Lamiaceae, Oleaceae, and Scrophulariaceae families), and stress tolerance. However, in the human diet, food rich in RFOs causes stomach discomfort, flatulence, and diarrhea in humans and monogastric animals, as they lack a-galactosidase, a hydrolyzing enzyme needed for RFO breakdown. RFOs when consumed in lower concentrations are considered as prebiotic and support the growth of beneficial intestinal microflora.

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Fructans In contrast to tropical and subtropical grasses, which accumulate sucrose and starch as storage carbohydrates, grasses of temperate and cool regions mainly store fructans, the fructose polymer. Fructans serve as soluble storage carbohydrates in about 12–15% of all flowering plants belonging to the Asterales, Poales, and Liliales. Fructans can be found as long-term reserves such as in bulbs and tubers or as temporary stocks in leaves, stems, and seeds. In cereals, fructans can be found in young internodes, from which fructan-derived carbohydrates are mobilized to kernels during grain filling, especially during challenging environmental conditions. In addition, fructans contribute to regulating osmotic balance, maintaining sink strength, and providing tolerance against cold and drought stresses. Fructans are also designated as low-calorie sweeteners, fat replacers, and prebiotics (fructans with low DP) in the human diet. Fructans, on the basis of glycosidic linkage, are categorized into five groups: (a) inulin having b(2 ! 1) linkage, (b) levan/ phlein having b(2 ! 6) linkage, (c) graminin (having inulin or levan backbone with 1 short branch), (d) inulin neoseries (like inulin but one glucose unit between two fructose moieties), and (e) levan neoseries (like levan but one glucose unit between two fructose moieties) (Figure 1). Fructan biosynthesis is sensitive to photosynthetic demand and sink sucrose concentration. It is synthesized in vacuoles by fructosyltransferase enzymes utilizing sucrose as the primary substrate. As the first step of fructan biosynthesis, a fructose unit from one sucrose molecule is transferred to another synthesizing b(2! 1) or b(2! 6) linkage in sucrose/sucrose 1-fructosyltransferase (1-SST)- or sucrose/fructan 6-fructosyltransferase (6-SFT)-catalyzed reactions yielding 1-kestose (inulin type) or 6-kestose (levan type), respectively. Some plant species also synthesize 6G-kestose by transferring a second fructosyl unit of 1-kestose to the glucose molecule of sucrose in a reaction catalyzed by fructan/fructan 6G-fructosyltransferase (6G-FFT). These trisaccharides, 1-kestose, 6-kestose, and 6G-kestose, serve as precursors for higher members of the fructan family. Elongation of the inulin- or levan-type backbone is mediated by fructan/fructan 1-fructosyltransferase (1-FFT; uses fructosyl oligosaccharides as fructosyl unit donor) or 6-SFT (uses both sucrose and fructosyl oligosaccharides as fructosyl unit donor), respectively.

Sugar Alcohols Sugar alcohols are primary photosynthetic products that accumulate temporarily in leaves during the light period and translocated to other plant organs at night. As compared with the corresponding sugar, sugar alcohols have an additional hydroxyl group and therefore are designated as polyols, polyalcohols, or polyhydric alcohols. Mannitol and sorbitol (or glucitol) are the main sugar alcohols that have been studied in plants. These compounds are rare in monocots but contribute significantly to transported and stored carbon in some horticultural plants, such as members of the Rosaceae, Rubiaceae, and Plantaginaceae families. Sugar alcohols have been implicated in abiotic stress tolerance. In comparison with sucrose, sugar alcohols are more metabolically sequestered, and this has important implications

in their physiological role in the translocation and storage of carbohydrates. Sugar alcohols are synthesized from hexoses or hexose phosphates, through the consecutive action of reductases and phosphatases. Mannitol biosynthesis begins in the cytosol with the formation of mannose 6-phosphate from fructose 6-phosphate in a phosphomannose isomerase-catalyzed reversible reaction. Mannose 6-phosphate is first reduced to mannitol 1-phosphate and converted to mannitol in reactions catalyzed by mannose 6-phosphate reductase and mannose L-phosphate phosphatase, respectively. Sorbitol is similarly reduced and dephosphorylated from glucose 6-phosphate by the action of a glucose 6phosphate reductase and a sorbitol (glucitol) 6-phosphate phosphatase.

Starch Starch is the most abundant storage polysaccharide in seeds, fruits, tubers, and roots of higher plants. Cereal and tuber starch contribute about 50% of the calories in the human diet. Besides being an important energy source in the human diet and animal feed, its amenability to modification led to many nonfood applications including paper, pulp, textile production, cosmetics, packaging, biodegradable plastic films, construction, and mining. Since starch is a renewable and biodegradable resource, it has received increased interest for the production of environmentally friendly biomaterials. However, environmental concerns and costs associated with chemical modifications are major constraints to completely utilizing starch as an industrial raw material. Starch is a complex macromolecule composed of two glucan polymers, an essentially linear-chain amylose and a highly branched amylopectin. Starch is normally made up of one-quarter amylose, with the remaining three-quarters being amylopectin. The two components are arranged in a three-dimensional, semicrystalline structure – the starch granule. Starches from different sources differ in their overall properties due to differences in granule size distribution and shape, amylose and lipid contents, distribution of chain length in amylopectin, phosphorylation, and crystallinity. For example, native starches from pulse crops generally have a higher percentage of amylose as compared with cereal starches (Tables 2 and 3). Most of the gelling and pasting behavior of extracted starch is determined by the amylose/amylopectin ratio, amylopectin structure, and starch granule size distribution. Genetically altered starches derived from mutagenesis and breeding programs have already been commercialized. The biosynthesis of starch is a complex biochemical process. The basic biochemical mechanism is the same for transitory starch synthesis in the chloroplasts in green organs or storage starch in amyloplasts of storage organs. Starch biosynthesis can be divided into four basic steps: (i) availability of substrates for starch synthesis, (ii) priming of starch granules, (iii) chain initiation and elongation, and (iv) introduction of branches. In chloroplasts, when photosynthetic carbon fixation is greater than the amount of sucrose being exported, triose phosphates are converted to fructose 1,6-bisphosphate and become part of the hexose phosphate pool by undergoing a reaction with fructose 1,6-bisphosphatase. Its further processing by phosphoglucoisomerase and phosphoglucomutase results in the

CARBOHYDRATES | Carbohydrate Metabolism formation of glucose 1-phosphate. In storage tissues, sucrose is converted into glucose 6-phosphate in the cytosolic region from where it is imported into the amyloplasts through a hexose phosphate/Pi antiporter. The glucose 6-phosphate is converted to glucose 1-phosphate, which acts as a substrate for AGPase, to synthesize ADP-glucose as in chloroplasts and act as the primary building block required for chain elongation to initiate starch synthesis. AGPase is an allosterically regulated enzyme, whose activity is generally stimulated by 3-PGA and inhibited by Pi. This allosteric regulation is further influenced by plant species, plastid type, and subcellular location. Studies of starch mutants have so far produced a general consensus that AGPase, soluble starch synthases (SSs), starchbranching enzymes (SBEs), starch-debranching enzymes (DBEs; pullulanase and isoamylase), and possibly disproportionating enzyme (D-enzyme) catalyze the final steps leading to amylopectin synthesis. The five major classes of SS include GBSSI, SSI, SSII, SSIII, and SSIV, of which all but SSIV have been shown to have distinct roles in determining starch composition and structure. Granule-bound starch synthase 1 (GBSSI) is the only enzyme committed to amylose synthesis with limited contribution toward amylopectin as indicated in some recent reports. Since several of the enzymes exist in different isoforms, some of which vary in their subcellular distribution, enzyme specificity, temporal activity, and interaction with other enzymes; the starch biosynthesis pathway is complex. Hilum, also known as starch granule core, indicates the presence of a priming mechanism for starch granule formation. The priming mechanism for starch glucan polymerization in plants is unclear, but it likely involves short-chain maltodextrins that are extended and branched by the action of GBSSI, SBEI, and SSI to form a molecule with an amylopectinlike backbone. Glycogenin-like self-glycosylating protein has also been proposed. The primary glucan polymer is further polymerized through cycles of chain extensions and branching catalyzed mainly by SSI and SBEII. DBEs have been proposed to play a role in starch biosynthesis by trimming the ends of the water-soluble preamylopectin molecules to produce amylopectin that can be crystallized and packaged into granules. Two distinct DBE families (isoamylase and R-enzyme/pullulanase/ dextrinase) with substrate specificity have been identified in plants. DBEs are also suggested to degrade water-soluble glucans synthesized by starch synthases and starch-branching enzymes to prevent accumulation of phytoglycogen, which cannot form granules. Observations made in Chlamydomonas suggest that the D-enzyme is also involved in starch synthesis and granule formation in addition to starch degradation. The polymerization of amylose is initiated from soluble maltooligosaccharides that serve as primers for GBSSI. Starch biosynthesis can be visualized as a wavelike formation, where high and low nodes result in the formation of regions of different crystallinities visible as growth rings (e.g., potato starch). Many reports have indicated that the presence of starch biosynthetic enzymes as protein complexes and positioning of SS, SBE, and DBE in these complexes influence amylopectin architecture. Amylopectin chains distributed in polymodal patterns form clusters with architectural specificity. These chains are designated as A-chains (DP 6–12), the outermost chains; B-chains, named B1, B2, and B3 depending on their degree of polymerization (DP 13–24 up to 50), which support A-chains

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or other B-chains; and the central C-chain. The backbone of starch, that is, the C-chain from which B-chains are connected within a granule, is oriented toward the center or hilum of the granule. Amylopectin glucan chain length distribution influences functional properties like gelatinization, retrogradation, and pasting properties of starch.

Cellulose Cellulose is the major component of cell walls and accounts for 28–30% of dry matter in forage grasses and 42–45% of wood. This extracellular polysaccharide-based outer matrix of the plant cell is complex and dynamic and has enormous strength. It is the most abundant renewable biomass synthesized on Earth and has since the early days of human civilization been used for fuel, timber, fiber, and forage. Today, cellulose has additional uses as a raw material for the production of paper, pulp, and many chemicals. Cellulose has a paracrystalline structure formed by b-(1 ! 4)-D-glucan chains, formed individually and crystallized to form cellulose microfibrils (an average thickness of 36 chains through inter- and intramolecular hydrogen bonds and van der Waals forces). The chains contain a few thousand glucose units giving an individual length of 2–3 mm, but the chains start and end at different points of the microfibril, thus extending the length of the microfibril to hundreds of micrometers. The length, angle, and crystallinity of these microfibrils influence plant cell wall strength. In higher plants, cellulose synthesis occurs in a plasma membrane-bound complex known as ‘rosette TC.’ The structure contains six subunits, each composed of six glucan (cellulose) synthase molecules that are symmetrically arranged into a rosette. The subunits of the complex simultaneously synthesize 36 1,4-b-D-glucan chains that are bundled into a microfibril emerging from the rosette TC. The basic biochemical understanding of cellulose synthase (CesA) has mainly been obtained from studies of the bacterium, Acetobacter xylinum. In plants, the number of CesA genes varies depending upon the species. CesAs categorized under the glycosyltransferase-2 (GT-2) superfamily with eight-transmembrane topology consist of at least two subunits, one with a catalytic role and the other with a regulatory role. The catalytic subunit of CesA is a progressive glycosyltransferase that binds the substrate, UDP-glucose, derived from sucrose by the action of a membrane-bound SucS. Recent studies proposed that these subunits are placed in the loop between transmembrane domains 2 and 3 with a D, D,D,QXXRW motif. The present model of cellulose synthesis postulates that the first two conserved aspartic acid residues interact with UDP, the third aspartic acid residue forms the catalytic base for the glucan extension, and the last QXXRW residues form a binding site for the terminal glucan parts of the chain. At the initiation of polymerization, two UDP-glucose molecules are present in the substrate-binding site, and as the chain elongates, glucose is added to the nonreducing end of the chain. In addition to Ces genes, plants have a number of cellulose synthase-like (CSL) genes that share homology with Ces and belong to the GT-2 superfamily. CSLs are grouped into ten families designated from A to J. Many of these are associated with b-glycan polymer synthesis, for example, CSLF for b-(1 ! 3;1 ! 4) glucans.

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In addition to Ces, membrane-anchored endo-1,4b-glucanases may also play a role in cellulose biosynthesis, based on studies with the Arabidopsis KORRIGAN mutant and the cellulose-producing bacterium Agrobacterium tumefaciens.

Other Cell Wall Carbohydrates Other important polysaccharide components of the cell wall include cross-linking glycans, which are hydrogen-bonded to cellulose microfibrils. These glycans coat the cellulose microfibrils and link two or more cellulose microfibrils to form a network in the primary cell walls of all plants. The two major classes of the cross-linking glycans are xyloglucans (XyGs) and glucuronoarabinoxylans (GAXs), of which XyGs are present in the cell walls of most dicots and almost half of all monocot species. The XyGs are made up of linear chains of 1,4-b-D-glucan with numerous a-D-Xyl units linked to the O6 position of the glucan units. In some cases, the xylosyl units are further substituted for by arabinose or galactosyl units. In addition to the two xyloglucans, some members of the Poaceae family, which includes the majority of cereal crops, such as wheat and barley, contain a third cross-linking glycan, bglucan. This is a linear polymer that consists of 3-Dglucopyranosyl monomers joined by both (1 ! 3) and (1 ! 4) linkages, normally in a 2:1 ratio. In comparison with other cereals, barley and oat grains are enriched with b-glucans. The b-1,4-linked molecules cellotriose (DP3) and cellotetraose (DP4) are randomly joined by b-1,3 bonds, which results in the formation of kinks in the molecule. The DP3/DP4 ratio affects polymer solubility. The highest content of soluble (1,3;1,4)-b-glucan is associated with DP3/DP4 ratios in the 1.5–2.5 range. Both the ratio and concentration of b-1,4-linked molecules in the grain cell wall, especially in oat and barley, influence their end use in food, feed, or industrial applications.

Arabinoxylans and b-glucans affect the quality and utilization of cereal grains due to their presence in the endosperm cell walls. The predominant component of starchy endosperm cell walls in barley, oats, and maize is b-glucan, whereas arabinoxylans are the major component found in rye and wheat. These compounds have a significant impact on the utilization of the grains for both food and animal feed. In wheat flour, pentosans absorb water and significantly affect the quality of baked products. The cell wall carbohydrates are not completely digested in the stomach or small intestine of humans or other monogastric animals but are broken down by bacteria in the large intestine. They tend to reduce the absorption of mono- and disaccharides in the gut by raising the viscosity of the gut contents, thus decreasing the levels of blood glucose and insulin. b-Glucans have been shown to significantly reduce blood cholesterol levels, when present in the diet at high concentrations. In addition, they have also been shown to have antibacterial and antiviral effects and accelerate wound healing. In animal feed, both glucuronoarabinoxylans and b-glucans have antinutritional effects, as these may decrease the absorption of nutrients due to their high viscosity and indigestibility. Cell wall polysaccharides are synthesized from sucrose through the action of SucS, UDP-glucose dehydrogenase, UDPglucuronate decarboxylase, xylan synthase, and arabinosyltransferase that sequentially give rise to UDP-glucose, UDP-glucuronate, UDP-xylose, 1,4-b-xylan, and arabinoxylan, respectively. The action of three epimerases further converts UDP-glucose to UDP-galactose, UDP-glucuronate to UDP-galacturonate, and UDP-xylose to UDP-arabinose.

Carbohydrate Breakdown Germination is initiated when the dry seed imbibes water, and the process is completed with the elongation of the embryonic axis (Figure 3). One of the first signs of metabolic Husk Pericarp Testa Aleurone Endosperm GA receptor

H2O

α-amylase

GA

Starch Maltose

GAMyb Aleurone cell

Glucose α-amylase GA

H2O

Scutellum

Scutellum Embryo

Coleoptile Shoot Radicle Coleorrhiza Root

Figure 3 A generalized diagram of a germinating cereal grain to show the various parts of a grain and the major biochemical activities during germination.

CARBOHYDRATES | Carbohydrate Metabolism activity in a germinating seed is the activation of enzymes that hydrolyze storage reserves. This process has been well characterized in cereal grains (Figure 3). A group of plant growth regulators known as the gibberellins (GAs) are the first to be synthesized in the scutellum of the embryo. The GAs diffuse into the aleurone layer and induce the production of hydrolytic enzymes such as a-amylases active on the starch granules in the endosperm. The GA-inducible R2R3MYB transcription factor known as GAMYB was first identified in the cereal aleurone. It has been proposed that a GA receptor present on the aleurone membrane binds to GA, which induces GAMYB activation, which further binds to the GA response element (GARE), 50 AACA/TA-30 , to activate hydrolase genes including a-amylase involved in starch breakdown and mobilization for embryo growth. The hydrolysis products are taken up by the embryo to initiate its growth. Carbohydrates stored in the endosperm or cotyledons are the primary source of energy in the developing embryo until it forms leaves, and the photosynthetic process takes over to supply the necessary energy and chemical constituents for the developing plantlet.

Starch Breakdown In cereal grains, starch is the major carbohydrate that is broken down during germination. Starch degradation occurs in three distinct phases: (1) reduction of starch granules to soluble maltodextrins, (2) degradation and debranching of larger maltodextrins to glucose and glucose 1-phosphate, and finally (3) transport of the glucose or glucose 1-phosphate from the storage organs to the hexose phosphate pools of developing plant cells for further metabolism into chemical constituents and energy. In germinating seeds, the initial degradation of starch granules is associated with an increase in the a-amylase activity. Intact starch granules are attacked by a-amylase resulting in the formation of random pits on the granules. During the a-amylase attack, a(1,4) bonds in both amylose and amylopectin are randomly broken to release large glucan polymers. Subsequent degradation occurs with assistance from b-amylases, phosphorylases, maltases, and starch DBEs. a-Amylase action on amylopectin, which contains both a(1,4) and a(1,6) glucan linkages, results in maltose and branched dextrins of short chain length as a-amylase cannot break the a(1,6) linkages. b-Amylases first act only on the nonreducing ends of the glucan polymer and hydrolyze starch into b-maltose, which is rapidly converted into natural mixtures of a- and b-isomers by mutarotation. Starch phosphorylases are a group of phosphorolytic enzymes that degrade starch molecules from the nonreducing end of the glucan chain. The reaction results in the complete breakdown of amylose to glucose 1-P units, but in amylopectin, the degradation stops within a few glucose residues of the branch point to give dextrins. Like plant amylases, starch phosphorylases are also widely distributed in plants and have an important role in starch degradation in leaves and seeds of many plants. However, in germinating cereal grains, starch phosphorylase activity is not detected, giving the a- and b-amylases a dominant role in starch degradation. In the seeds of other species and in leaves, starch phosphorylases also contribute toward starch degradation.

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The a(1,6) glucan linkages in the starch molecule are hydrolyzed by starch DBEs, which have also been implicated in starch synthesis as described earlier. This group of enzymes hydrolyze a(1,6) linkages, thus producing additional end groups for action by amylases and phosphorylases. Concerted action of these enzymes results in the production of maltose, glucose, or glucose 1-phosphate. Maltose rarely accumulates during starch digestion as it is broken down to glucose by maltase. Starch breakdown is influenced by its structure and composition. Amylopectin fine structure and amylose both play important roles in effecting its breakdown by metabolic enzymes.

Raffinose Family Oligosaccharide RFOs, accumulated in seeds by phloem loading and transport, are rapidly utilized during the early stages of seed germination. Alpha-galactosidase cleaves the terminal nonreducing a(1 ! 6)-linked galactose residues of a-galactosides, thus providing readily available energy and carbon to the germinating seed. Two types of a-galactosidases have been reported – (1) acidic (found in protein storage vacuoles (PSVs)) and (2) alkaline (active in cytosol). Acidic a-galactosidase (activated by the pH shift during seed imbibition) was proposed to be responsible for the breakdown of RFOs in PSVs during the early stages of seed development, providing the main energy sources for seed metabolism. The resulting increase in sucrose concentration during the transition phase, from germination to plant growth, was attributed to the induction of expression of alkaline a-galactosidase, resulting in the mobilization of the remaining RFOs. The galactose unit is thereafter phosphorylated by a galactokinase to produce a-D-galactose 1-P, which is further metabolized through UDP-galactose to produce either UDP-glucose or glucose 1-P, which enters the cellular hexose phosphate pool. Depending on the metabolic activities of the tissues, the carbon may flow into the respiratory pathways as in the case of germinating tissues or to the synthesis of starch, sucrose, oligosaccharides, or other cellular components such as glycolipids or glycoproteins (Figure 2) in young meristematic tissues. Most of the RFO-degrading enzymes have been purified from seeds of pulse crops, and increased activities have been shown to be associated with seed germination. However, strategies to modulate the activities of RFO-degrading enzymes are complicated by the presence of two distinct pathways for the metabolism of galactose 1-P to UDP-glucose and glucose 1-P.

Fructans Fructans are hydrolyzed by fructan 1-exohydrolases (1-FEH) or fructan 6-exohydrolases (6-FEH) that cleave the terminal b(2,1)- or b(2,6)-linked fructosyl moiety, respectively. These enzymes are also proposed to participate in fructan biosynthesis by modulating the chain length and branching pattern of the polymer. A b-fructofuranosidase from Jerusalem artichoke tubers successively cleaves fructose units from inulin until a mixture of fructose and the terminal sucrose unit remains. Fructose can directly enter the respiratory pathway, whereas sucrose must be broken down to glucose and fructose first.

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Sucrose Invertase and SS are the two enzymes capable of cleaving sucrose present in plants. Invertases catalyze the irreversible hydrolysis of sucrose to free glucose and fructose. Based on optimum pH of their activity, invertases are grouped into acidic (optimum pH 4.0–5.5) and alkaline/neutral types (optimum pH 7.0–8.0). Acidic invertases are mainly found in cytosol and occasionally in cell walls, whereas alkaline/neutral types are abundant in vacuoles and cell walls. Alkaline/neutral invertases have recently been reported in chloroplasts and mitochondria. Alkaline invertases are sucrose-specific, while neutral invertase from carrot can also mediate raffinose and stachyose hydrolyses. The cell wall invertases hydrolyze the incoming translocated sucrose into glucose and fructose molecules. SucS catalyzes the reversible reaction converting sucrose and UDP to fructose and UDP-glucose. Fructose is available for respiration and the UDP-glucose can enter the hexose phosphate pool for further metabolic processes. SS, compartmentalized in the cytosol, is the main enzyme that degrades sucrose in starch storage organs such as developing seeds or in rapidly growing tissues that are converting sucrose to cell wall structural polysaccharides. In slow-growing and mature cells, invertase is the major enzyme hydrolyzing sucrose, which provides substrates for respiration.

and abiotic stresses. It is often found that a single reaction in the carbohydrate metabolic pathways is catalyzed by multiple isoforms of an enzyme. Differences in the temporal and spatial expression of genes encoding these isoforms present several challenges to modifying the carbohydrate metabolic pathways by genetic engineering. To date, it has been possible to alter the expression of genes encoding starch biosynthetic enzymes to produce crops with modified grain carbohydrates that have health benefits for human beings and/or grain processing advantages. Some advances have also been made in changing the cell compartment and/or tissue in which a specific polysaccharide is stored. As knowledge of the carbohydrate metabolic pathway expands, novel strategies to alter the carbohydrate biosynthetic or degradation pathways will emerge, which can be utilized to develop crop cultivars with novel products in the grain. These new crops will diversify the uses of the grain to benefit both the producers and consumers.

Learning Outcomes

• • •

Cell Wall Polysaccharides The cell wall polysaccharides have a physiologically different role in seed germination. The process of germination and seedling development requires the participation of several endo- and exohydrolases that degrade or modify the cell wall structure. During germination, (1,3)- and (1,4)-b-D-glucan endohydrolases hydrolyze the (1,4) linkages adjacent to the (1,3)-b-D-glucosyl residues to release large oligosaccharides. The resulting oligosaccharides are further hydrolyzed by broad-specificity exohydrolases to produce glucose, which can subsequently be used in numerous ways (Figure 2). Some other cell wall polysaccharides, such as arabinoxylans, can be degraded to oligosaccharides that subsequently follow the oligosaccharide degradation pathway as described earlier.

Concluding Remarks In most grains, carbohydrates are the major components that provide the energy needed during seed germination and early seedling development. Carbohydrates also play a major role in determining the quality of the grain and its subsequent use by human beings. Carbohydrate metabolism in plants differs from most other organisms as it occurs in two distinct cellular compartments, the plastid and the cytosol. Most of the biosynthetic activities take place in the plastids, chloroplasts in leaves, and amyloplasts in the storage organs. The carbohydrate metabolism in the cytosol communicates with that of the plastids through metabolic carriers in the plastid envelope. The stationary nature of the plant forces it to withstand changes in the external environment, and therefore, plants have developed inherent flexibility in their metabolism to cope with both biotic

• •

Hexose phosphate pool serves as a central component of carbohydrate metabolism. Sucrose and raffinose family oligosaccharides maintain source–sink relationship by photosynthate translocation. Starch, the most abundant storage polysaccharides, in plants exists as a temporary/transient form in leaves and a stable storage form in grains and tubers. Cellulose and glycans are important for structural integrity of cell wall. Complex and highly regulated enzymatic machinery is involved in structural and storage carbohydrate biosynthesis and metabolism. Its key modulator steps with possibilities of genetic alterations provide ample opportunities of crop improvement for food and industrial usage.


• • • • • •

Question 1: Differentiate oligosaccharide from polysaccharide with example. Which group of food grains has the highest concentration of oligosaccharides? Question 2: What are dietary fibers and what role do they play in human nutrition? Question 3: Describe two major metabolite pools of the reductive pentose phosphate pathway with their major functions inside the plant system. Question 4: Describe the major steps of starch biosynthesis, with emphasis on the enzymes involved in each step. Question 5: In a germinating seed, what is the major starchmetabolizing enzyme and how is it activated? Question 6: How do tropical grasses differ from temperate grasses in carbohydrate storage?


•

How do plant–environment interactions affect carbohydrate metabolism in plants?


• • • •

What are the mechanisms attributed for stress tolerance by sugars? How does genetic modification of one biosynthetic pathway affect the hexose phosphate pool and the biosynthesis of other carbohydrates? What are the critical limits (minimum and maximum) of carbohydrates’ concentrations required for normal plant growth and development? How are sugars involved in the genetic regulation of metabolic pathways?

Acknowledgments We gratefully acknowledge the following for supporting our research: Canada Research Chairs, Natural Sciences and Engineering Research Council, Western Grains Research Foundation, Saskatchewan Winter Cereals Development Commission, Winter Cereals Manitoba Inc., Agriculture and Agri-Food Canada, Saskatchewan Pulse Growers, and Saskatchewan Agriculture Development Fund.

See also: Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Grains other than Cereals: Non-starch Polysaccharides; Starch: Analysis of Quality; Starch: Chemistry; Starch: Synthesis; Fats: Lipid Chemistry; Processing of Grains: Starch: Modification; Starch: Uses of Native Starch; Proteins: Protein Synthesis and Deposition; The Basics: The Grains that Feed the World.

Further Reading Aoki N, Hirose T, and Furbank RT (2012) Sucrose transport in higher plants: From source to sink. In: Eaton-Rye JJ, Tripathy BC, and Sharkey TD (eds.) Photosynthesis: Plastid Biology, Energy Conversion and Carbon Assimilation. Advances in Photosynthesis and Respiration, vol. 34, pp. 703–729. Berlin: Springer Science þ Business Media B.V. Blo¨chl A, Peterbauer T, Hofmann J, and Richter A (2008) Enzymatic breakdown of raffinose oligosaccharides in pea seeds. Planta 228: 99–110.

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Buchanan BB, Gruissem W, and Jones RL (eds.) (2002) Biochemistry and Molecular Biology of Plants. Rockville, MD: American Society of Plant Physiologists. Burton RA, Collins HM, Kibble NAJ, et al. (2010) Over-expression of specific HvCslF cellulose synthase-like genes in transgenic barley increases the levels of cell wall (1,3,1,4)-b-D-glucans and alters their fine structure. Plant Biotechnology Journal 9: 1–19. Chibbar RN, Ambigaipalan P, and Hoover R (2010) Molecular diversity in pulse seed starch and complex carbohydrates and its role in human nutrition and health. Cereal Chemistry 87: 342–352. Chibbar RN and Ba˚ga M (2003) Genetic modification of primary metabolism – Carbohydrates. In: Thomas B, Murphy DJ, and Murray BJ (eds.) Encyclopedia of Applied Plant Sciences, pp. 449–459. Oxford: Elsevier. Cui SW and Wang Q (2009) Cell wall polysaccharides in cereals: Chemical structures and functional properties. Structural Chemistry 20: 291–297. Cummings JH and Stephen AM (2007) Carbohydrate terminology and classification. European Journal of Clinical Nutrition 61: S5–S18. Edwin JR, Emilie AR, Ve´ronique A, Lailiang C, and Robert T (2009) Phloem loading strategies in three plant species that transport sugar alcohols. Plant Physiology 149: 1601–1608. Hedley CL (2001) Carbohydrates in Grain Legume Seeds: Improving Nutritional Quality and Agronomic Characteristics. Wallingford: CABI Publishing. Hrmova M and Fincher GB (2001) Structure-function relationships of b-D-glucan endoand exohydrolases from higher plants. Plant Molecular Biology 47: 73–91. Jaiswal S, Ganeshan S, Ba˚ga M, and Chibbar RN (2010) In Planta modification of starch quantity and quality. In: Singh BP (ed.) Industrial Crops and Uses, pp. 236–258. Wallingford, UK: CAB International. Lunn JE (2008) Sucrose metabolism. In: Encyclopedia of Life Sciences. Chichester: Wileyhttp://dx.doi.org/10.1002/9780470015902.a0021259. Martinez-Villaluenga C, Frias J, and Vidal-Valverde C (2008) Alpha-galactosides: Antinutritional factors or functional ingredients? Critical Reviews Food in Science and Nutrition 48: 301–316. McFarlane HE, Do¨ring A, and Persson S (2014) The cell biology of cellulose synthesis. Annual Review of Plant Biology 65: 69–94. Yan D, Duermeyer L, Leoveanu C, and Nambara E (2014) The functions of the endosperm during seed germination. Plant and Cell Physiology 55: 1521–1533. Zeeman SC, Kossmann J, and Smith AM (2010) Starch: Its metabolism, evolution and biotechnological modification in plants. Annual Review of Plant Biology 61: 209–234.

Relevant Websites http://www.chem.qmul.ac.uk– International Union of Pure and Applied Chemistry and International Union of Biochemistry and Molecular Biology; IUPAC-IUBMB Joint Commission on Biochemical Nomenclature (JCBN) – Nomenclature of Carbohydrates. http://www.fao.org– Includes classification and chemistry of carbohydrates, carbohydrate metabolism in fish, factors affecting it and energy transformation.

Starch: Chemistry FL Stoddard, University of Helsinki, Helsinki, Finland ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

Starch is a widespread polymer in the plant kingdom, composed of chains of a-1,4 linked glucose in helices, bridged by a-1,6 bonds. It develops in granules within chloroplasts and amyloplasts. Two classes of starch molecule are recognized, highly branched amylopectin and poorly branched amylose. Packing of amylopectin double helices confers diagnostic x-ray diffraction patterns. Starch granule morphology differs between families of plants. In the presence of heat and moisture, starch helices open and the granules are disrupted. Cooked, cooled starch forms a paste or gel with properties that depend on amylose and amylopectin concentration and structure. Cooked starch gradually recrystallizes (retrogrades), losing water (syneresis). Industry requires starches with different compositions (granule size, amylose content, and amylopectin chain length) for different uses.

Learning Objectives

•

To understand the role of chain length, branching pattern, and association in starch, as these affect economically important industrial and food uses

Introduction Starch is the major energy reserve of higher plants and hence a major energy source in the diet of humans and many other animals, including livestock animals grown for their meat and milk and pest animals that consume grains in storage. Starch comprises 70% of the dry matter of the endosperm of a mature cereal grain and 16% of the fresh matter of a mature potato tuber. Starch may be loosely defined as a polymer of glucose that is distinguished from other glucans by a number of key features. First, it is a-linked, unlike cellulose and other b-linked glucans. The majority of these links are a-1,4 (also written as a-(1 ! 4)), leading to chains of varying lengths, and the chains are joined together by a-1,6 linkages. These branching points occur in a highly ordered fashion, leading to double-helix formation and a type of crystallinity, minimizing waterholding capacity. This feature is in significant contrast to glycogen, an a-(1 ! 4), (1 ! 6) mixed-link glucan found in animals and bacteria. Ordering in glycogen is very limited, so it holds much more water than an equivalent mass of starch.

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It is thus not as efficient an energy store where water availability is limited, such as in a dry, dormant seed. Starch is deposited in granules between 1 and 100 mm in diameter within membrane-bound organelles. In the actively photosynthetic parts of the plant, these organelles are the chloroplasts, and in storage organs, they are the modified chloroplasts called amyloplasts. Granule structure has a number of features that are consistent across species, while granule size, morphology, and composition vary widely among species. These aspects and starch composition affect the processing properties of the starch.

The Monomer and Linkages The building block of starch is D-glucose, in its hexagonal pyranose ring conformation (Figure 1). Carbon 1 of this ring is a highly reactive, aldehydic, ‘reducing’ end. Most commonly, during polymer formation in a plant, it attaches to carbon 4 of another glucopyranose residue (Figure 2). When the monomers are a-D-glucopyranose, the resulting polymer is a chain of starch, and when they are b-D-glucopyranose, it is a chain of cellulose. An a-1,4 linked glucan is at its most stable in a left-handed helix, with a complete turn taking six residues (Figure 3) and occupying 2.1 nm. Hydrogen bonding between adjacent glucose residues helps to stabilize the helix. The helix can allow a second parallel helix to fit into it, creating a double helix. The helical structure of starch is an important factor in its processing properties and in its enzymatic degradation during digestion. Cellulose, in contrast, is highly crystalline and ribbonlike rather than helical, and relatively few organisms have the appropriate enzymes to hydrolyze it. The presence of a-1,6 bonds (Figure 2) allows the development of much larger and less soluble polymers through the introduction of branching points connecting glucose chains of various lengths. Starch is an excellent example of the evolutionary conservation of a successful structure throughout the plant kingdom.

Starch Polymer Types Two classes of starch, amylose and amylopectin, have been widely recognized, differing in chain length, branching pattern, and overall mass. Both have a single reducing group per molecule and a variable number of nonreducing ends. Most plant starches comprise about one-fifth to one-third amylose and the remainder amylopectin (Table 1). Plant breeders and geneticists have considerably enhanced this range since the beginning of the twentieth century. Amylose is usually described as being ‘essentially linear.’ A typical amylose molecule comprises 2–11 chains of 200–700


http://dx.doi.org/10.1016/B978-0-12-394437-5.00093-0

CARBOHYDRATES | Starch: Chemistry

H

6

CH2OH

4

OH

O

H

5

H

H

3

2

OH

OH

1

H

OH

Figure 1 D-Glucopyranose in its a-conformation. In the b-conformation, the hydroxyl group and hydrogen attached to carbon 1 are in the opposite orientation.

O

O

α 1

O O

1

α

4

6

O

O

α

1

O

4

O O

O Figure 2 An a-1,4 linked glucose polymer with an a-1,6 branching point.

O

O

O O

O O O O O O O

O O

Figure 3 Helix of a-1,4 glucose residues, seen from above.

a-1,4 linked glucose residues. The chains are connected by a1,6 bonds, leading to an overall polymer size of 1000–5000 glucose residues and a molecular mass of (1.6–8) 105. Chain length and branch number are species-specific. Within the starch granule, the amylose chain is present as a single helix. This is demonstrated by the ease with which it may be leached out of the granules by water at moderate temperatures and its full release at 60–80 C, whereas an amylose double helix should not be released until the temperature greatly exceeds

175

100 C. The single helix retains a hydrophobic channel or lumen along its axis, into which a fatty acid, for example, may interpolate. These amylose–lipid complexes have critical effects on the processing properties of the starch, as described in the succeeding text (starch-bound lipids). Amylose concentration increases during the course of starch deposition in the storage organ and, in maize, is greater in proximal than in distal grains. Amylopectin is a much more complex entity and is usually described as ‘highly branched.’ The overall molecular mass is of the order of 106–108, making this polymer one of the largest known in nature. Chain length distribution is multimodal and there are three main types of chain. The A-type chain is the outermost in the branching pattern and contains 15–30 a-1,4 linked D-glucose residues. It is attached to a B-type chain by an a-1,6 bond between the reducing C1 of the A-chain and a C6 of the B-chain. The A-chain/B-chain ratio is commonly 1–1.5:1. The B-chain has one to several A-chains attached to it and is itself attached either to other B-chains or to the C-chain, which carries the reducing end of the polymer. The B-chain is classified as B1–B4, with the numeral indicating how many crystalline lamellae, or zones of the starch granule, it passes through. A B1-chain passes through only one lamella and is similar in chain length to the A-chains. A B2-chain passes through two such lamellae and has a chain length of 45–50 glucose residues. The B3- and B4-chains are correspondingly longer and rarer. The currently accepted model, supported by a range of analytic methods, is that the branching points are clustered within any given molecule and also coordinated in adjacent molecules, rather than random (Figure 4). The model shows double helices, often of an A-chain and a B1-chain, as the state of the outermost branches. The lumen of a double helix is smaller than that of a single helix and hence less likely to include guest molecules. In potato amylopectin, phosphate groups are attached to some of the hydroxyl groups of the glucose residues. This is associated with greater hydrophilicity and may contribute to the high swelling power of potato starch, which is ten times that of many other starches. Numerous biochemical tests have been devised to evaluate the relative proportions of amylose and amylopectin in a starch. One of the most common involves the use of iodine, which may be quantified in two ways. Amylose can bind 20% of its mass in iodine, whereas amylopectin binds <1%. This may be measured accurately, if slowly, by potentiometric titration. In a more approximate and considerably more rapid method, the light absorption of the solution may be measured. Chains of triiodide ions bound by the amylose helix absorb strongly at longer wavelengths of light, 600–640 nm, causing the starch–iodine solution to appear blue. Each turn of the helix holds about two iodine atoms. Shorter chains infrequently included in amylopectin helices absorb at a lower wavelength, 530–550 nm, and confer a tan, reddish, or purplish color to the solution. Any lipid molecules in the solution compete with the triiodide ions for the amylose helices and thereby reduce the apparent amylose concentration. Simultaneous measurement of absorbance at 2–6 wavelengths across the visible spectrum generally increases the accuracy of this method over the traditional measure at a single wavelength in the 600–640 nm range. High-pressure size exclusion

176 Table 1

CARBOHYDRATES | Starch: Chemistry Typical properties of some common starches

Source

Granule average diameter (mm)

Amylose concentration (%)

Lipid concentration (%)

Protein concentration (%)

Maize (corn) Wheat, barley, and rye A-granules Wheat, barley, and rye B-granules Rice Oat Amaranth Quinoa Canary grass Pulses or grain legumes Potato Cassava

15 25

25 27

0.80 0.90

0.35 0.40

5

24

0.90

0.40

3 5 1.5 1.5 2 25 30–40 8

20 27 20 9 17 33 20 17

0.62 1.10 1.10 0.11 0.02 0.10 0.10 0.10

0.60 0.80 0.49 0.91 0.20 0.50 0.10 0.10

Data from a variety of sources.

Flexible spacers in the amorphous lamella (~2.7 nm)

B2 chain

Amylopectin double helices in the crystalline lamella (~6.3 nm)

C chain Figure 4 Representation of the amylopectin molecule as a liquid crystal. The shaded blocks represent double helices. In the dry state (left), they are disordered, and in the hydrated state (right), they are aligned. Adapted from Donald AM, Perry PA, and Waigh TA (2001) The impact of internal granule structure on processing and properties. In: Barsby TL, Donald AM, and Frazier PJ (eds.) Starch: Advances in Structure and Function, pp. 45–52. Cambridge: Royal Society of Chemistry, with permission.

chromatography is a modern method for amylose determination with a reasonable balance of throughput and accuracy. ‘Intermediate material’ was a term used in maize starch chemistry for many years, for polymers having some of the features of amylose and others of amylopectin due to the combined effects of different mutations in starch-synthesizing enzymes, for example, amylopectin-type branching but with much longer chains. Phytoglycogen is found in certain plant mutants such as sweet corn. It is due to a mutation in the gene for starchdebranching enzyme or isoamylase. Its structure is very comparable to that of animal glycogen, and its lack of higher-order structure, such as double helix formation, allows it to remain largely water-soluble. This aspect limits the amount of storage

polysaccharide that can accumulate in a grain, so when it dries down at maturity, it is shrunken and wrinkled.

Levels of Organization The next order of structure is an alignment of the short, stiff double helices of the amylopectin molecules. This takes place in two ways. First, they align parallel to each other, along the radius of the starch granule. This is what gives the polarization of light, leading to a characteristic ‘Maltese cross’ appearance when starch granules are viewed between crossed polarizers in a microscope. Second, the double helices pack together in an energy-minimizing fashion (Figure 5). In some starches,


177

Figure 5 Packing of amylopectin double helices: left, monoclinic crystal giving A-type x-ray diffraction pattern; right, open crystal giving B-type x-ray diffraction pattern.

generally those from tubers and stems, the packing is hexagonal with a lumen in the center, which leads to a consistent pattern, termed B-type, in x-ray diffraction. In other starches, mostly those from grains, the double helices pack much more closely, without a lumen, leading to a different, A-type, x-ray diffraction pattern. Starches from grain legumes and from most roots have an intermediate diffraction pattern, termed C-type, which implies that some of the hexagons have a lumen and others do not. A final x-ray diffraction pattern, V-type, is given by amylose that encloses a lipid chain. High-amylose maize gives a B-type diffraction pattern, suggesting that amylose does not pack as tightly as amylopectin. Some species of yam (Dioscorea) show A-type diffraction patterns and some B-type. Starches with the B-type pattern generally retain or take up more water than those with an A-type pattern. The crystalline double helices are thus aligned in a crystalline lamella. This alignment is possible because the branches in amylopectin are clustered, leading to an amorphous (noncrystalline) region (Figure 4). The thickness of this amorphous/ crystalline ring is commonly 9 nm. This is commensurate with a helix of 18 residues (6.3 nm) plus a few more residues to join with the B-chain in the amorphous lamella. This, in turn, accounts for the 15–30 unit length of the majority of amylopectin chains. Alteration of packing can occur in the presence of gentle hydration, leading to the model that in the hydrated starch granule, the rodlike double helices on their flexible attachments function as a liquid crystal (Figure 4). Stacks of 16 amorphous/crystalline lamellae form semicrystalline layers of 140 nm in thickness. These layers are separated by amorphous layers of comparable thickness. This level of order was visible in early electron micrographs and considered to be growth rings. Early research found that they disappeared in wheat grown in continuous light, but this is not always the case and they are generally attributed to physical mechanisms. Most starch granules show the alternating semicrystalline and amorphous layers across their entire cross section. Certain double mutants in maize, however, show clearly biphasic growth. In ae du and ae wx lines, the core 30–60% (by volume) of the starch granule shows the typical concentric rings, but the remaining outer mass of the granule is shapeless and disorganized. It was proposed that there was a change in the relative expression of the starch synthetic enzymes and in substrate concentration.

Starch Granule Morphology Starches of wheat, rye, barley, and many of their wild relatives in the cereal tribe Triticeae have biphasic granule initiation, rather than biphasic growth. One major starch granule, termed A-type, originates in each amyloplast. About 15 days into grain filling, membrane tubules appear around the equator of the A-granule and several subsidiary, B-type, granules form. At grain maturity, the A-granules are approximately lenticular or lentil-shaped, with a long diameter about twice the short diameter and with a detectable equatorial groove. Mean A-granule diameter can be as low as 15 mm in diploid wheats such as Triticum monococcum or as large as 30 mm in some tetraploid and hexaploid Aegilops species but is 20–25 mm in cultivated rye, barley, durum wheat, and common wheat (Table 1). The B-granules are roughly spherical and average 5–6 mm in diameter in most of these species. There are other differences between A- and B-granules. B-granules lack the central cavity or hilum found in A-granules and also in the granules of other species. They also lack at least one granule-bound protein, and they can have amylose contents 2–4% lower than A-granules. With their greater surface area, they adsorb more water per unit mass than A-granules. The factors determining A-granule size and B-granule concentration or initiation are the subjects of continuing research. Many scientists view a third population of small B-granules as a distinct C-granule type. This bimodal (or trimodal) granule size distribution is not found in any other group of plant species. In maize, starch granules are spherical when isolated from ‘mealy’ regions of the mature grain where there is space between the granules but are polyhedral when isolated from ‘vitreous’ regions where the granules have been in close physical contact since partway through grain filling. Faceted granule surfaces are thus attributable to restricted growing space rather than active differences in granule development. A-type granules of wheat and barley often show indentations where other granules have impinged on them during development. Oat and rice have compound starch granules. Grain legume starch granules are generally ovoid or elliptical, and root or tuber starches are usually round to ovoid. Zero-amylose (waxy) starches have a fairly normal gross morphology. Granules of high-amylose starches, in contrast, such as those of amylomaize, pure-amylose barley, or wrinkled pea, are shapeless, fissured, and nonbirefringent.

178


These features demonstrate the critical role of amylopectin in determining granule crystallinity and the much less critical role of amylose.

The total protein concentration of extracted starch is higher in cereal grains than in roots or tubers (Table 1), although the exact figure depends heavily on the extraction method.

Starch-Bound Lipids

Dissociation Chemistry

As mentioned in the preceding text, long amylose chains and lipids can form complexes. The concentration of lipid in starch is very strongly correlated with the amylose concentration of the starch. The amylose–lipid complexes resist both their own leaching from the starch granule and also the entry of water into the granule. This latter aspect may be the biological importance of starch-bound lipids in the quiescent or germinating seed. Starch processing properties are also affected by the presence of bound lipid that increases gel temperature and the temperature of maximum viscosity, decreases gel strength, and delays staling by interfering with retrogradation. Removal of lipids lowers gel temperature and increases peak viscosity. Starch-bound lipids are generally either free fatty acids (commonly linoleic) or lysophospholipids. The ratio of these two classes differs among species in the cereals (Table 2), but there is much less information on the pulses and pseudocereals. The lipid concentration of extracted starch varies up to tenfold depending on the extraction method.

Gelatinization has been defined as ‘the collapse (disruption) of molecular order within the starch granule, manifested in irreversible changes in properties such as granule swelling, native crystalline melting, loss of birefringence, and starch solubilization.’ Pasting is what happens after gelatinization – ‘granule swelling, exudation of molecular components from the granule, and, eventually, total disruption of the granules.’ Starch granules in cold water can reversibly absorb 30% of their weight in water. When starch is heated in an excess of water, a sequence of events occurs as the kinetic energy of the polymer increases and the hydrogen bonds rupture. At the pasting or gelatinization temperature, between 60 and 70 C, energy is absorbed in decrystallizing the crystalline regions of the molecule. It also leads to an endotherm, as seen in the differential scanning calorimeter (DSC), due to the absorption of energy. Typical values of the heat of gelatinization or gelatinization enthalpy are 8–12 J g1 but are as high as 32 in amylomaize. The loss of crystallinity leads to a rapid swelling of the granule combined with a considerable loss in structure, as seen in a rapid increase in viscosity in a pasting curve (Figure 6). Amylose leaches from the granule but amylopectin remains associated. Further heating without stirring in an enclosed vessel, such as a DSC, causes dissociation of amylose from lipid. This process also absorbs energy and shows as an endotherm between 102 and 110 C. If, however, the heating is in the presence of stirring in a nonpressurized container, such as a Brabender Visco-AmyloGraph or a Rapid Visco Analyzer (RVA), the viscosity of the suspension continues to increase as the amylose molecules get more dispersed and the granules become more porous, gelatinized, and swollen. Further stirring at a high temperature results in shear thinning, where the molecular entropy is not enhanced but granule structure is gradually further destroyed until a new plateau is reached. This phase is known as breakdown. As the paste is cooled and stirred, viscosity reaches a final value. The RVA takes 15 min for the process, instead of about an hour for the Visco-Amylo-Graph. The RVA has the significant advantage that it gives readings in SI units (cP), in contrast to the arbitrary units of older models and the ViscoAmylo-Graph. In a set of rice starches of equivalent amylose content, most RVA parameters were not significantly affected, but breakdown was correlated negatively with the proportion of long amylopectin chains and positively with the proportion of short. In a separate study, increased firmness of cooked rice was associated with increased content of long amylopectin chains. The short chains are types A and B1, the long B2–B4. Perhaps, the presence of more interconnections between crystalline lamellae, given by a higher content of B3 and B4 chains especially, helps to maintain structure of the gelatinized starch granule. Furthermore, the radius of rotation of the chain increases with its degree of polymerization, and the viscosity increases as the

Starch-Bound Proteins Numerous types of protein are found in close association with starch granules, some on the surface and others bound within. The biological functions of some of these proteins remain to be determined. The surface proteins tend to be smaller than the internal proteins. Altered sequences in the tryptophan-rich surface proteins, puroindoline-a and puroindoline-b, have been strongly linked with difference in grain hardness, but their causative role in this difference is controversial. Granule-bound starch synthase (GBSS), which has a relative molecular mass of 60 kDa, is responsible for synthesizing amylose and is thus absent from the so-called ‘waxy’ mutants identified in a wide range of crops including maize, barley, wheat, rice, pea, and cassava. Confocal laser scanning microscopy of fluorescent-dyed proteins has shown that GBSS is localized in concentric spheres coinciding with the amorphous layers of the growth rings in the starch granules of maize, wheat, and potato. Other unidentified proteins were shown by this method to be concentrated in the hilum of the granule. A large, 140–152 kDa form of starch branching enzyme I (SBE) was found to be associated only with A-granules, not B-granules, of wheat. Table 2

Composition of starch-bound lipids of several cereals

Species

Free fatty acids

Lysophospholipids

Wheat, barley, and rye Rice and oat Millet and sorghum Maize

10 30 45 60

90 70 55 40

Data from a variety of sources.


179

Figure 6 Starch pasting profile, as determined with an RVA (Newport Scientific Pty Ltd., Warriewood, NSW, Australia). Key measurements are named on the graph. The thin black line shows temperature profile and the thick green line shows viscosity profile. Table 3

Classification of resistant starch

Type

Description

Example

1 2 3

Physically inaccessible Native granules Retrograded after heat/moisture treatment Chemically or thermally modified

Grain fragments Uncooked banana Cooled, cooked potato Acetylated starch

4

cube of the radius, so small increases in chain length can lead to large increases in viscosity.

Reassociation Chemistry As stated earlier, the minimum energy state for an a-1,4 linked glucan is as a double helix with another such chain. As a starch solution cools, the chains reassociate in a process termed ‘retrogradation.’ Long amylose chains have a considerable radius of rotation and freedom of movement in a solution and may thus entangle with many other long chains at concentrations as low as 1–1.5%. Amylose retrogradation thus entraps a lot of water, involves many molecules, makes a clear hard gel, and is essentially complete when the cooked product has cooled to room temperature. The double helices are generally limited to a few dozen (perhaps 50) glucose residues, leaving great lengths of single helix that can entrap enough iodine to give a strong blue color. Amylopectin retrogradation, in contrast, is more likely to involve chains from the same molecule that are already much shorter than their amylose counterparts. This process can take up to several days and makes a translucent, soft paste. Loss of water from the gel or paste during storage is termed ‘syneresis.’ Some of the components of a retrograded starch are so well crystallized that they are resistant to enzyme attack and are known as ‘resistant’ starch (Table 3). These can contribute to dietary fiber. Recrystallized autoclaved amylomaize starch is sold as resistant starch by at least two manufacturers. Similar

material is used as an additive to white bread by an Australian bread manufacturer in order to increase insoluble dietary fiber content without adversely affecting the color or texture of the product.

Mutant Starches Starch synthesis mutants have been well characterized in several species. These have been valuable not only as industrial and food components but also for elucidating the relative roles of amylose and amylopectin in starch functionality. GBSS-null mutants do not synthesize amylose (or do so to only a limited extent), so the starch is 100% amylopectin and is known as ‘waxy’ on account of the appearance of the cereal grains. These wx mutants have long been known in barley, maize, and rice (‘glutinous’) and have more recently been developed in common wheat and pea. The gel temperature is usually lower and peak viscosity higher in waxy starches than in their normal counterparts. In many cases, final viscosity is higher as well. The isolation of further waxy starches, for example, from other grain legumes and pseudocereals, may give us even more interesting properties. High-amylose starches have been harder to develop, even though one has been known for a very long time and was an important part of Mendel’s original elucidation of the principles of genetics. The distinction between ‘round’ and ‘wrinkled’ peas, called ‘rugosus,’ is now known to be due to a mutation in SBE I. The wrinkled phenotype is associated with an amylose concentration of up to 80% in a reduced mass of starch. Highamylose barley (amo-1) is 45% amylose, whereas high-amylose maize starch can exceed 85% amylose. A barley containing no amylopectin was developed by RNA interference with the SBEs. Amylose appears to be digested more slowly than amylopectin in the gut of monogastric animals. High-amylose starches have been associated with increased satiety (i.e., reduced desire for food), reduced glycemic index, and reduced insulin release in comparison with normal-amylose starches. High-amylose foods are thus an attractive option for people with diabetes

180


and other metabolic problems related to insulin, glycemia, or obesity. Many mutations affect maize starch synthesis, including ae (amylose extender), du (dull), h (horny), sh1 and sh2 (shrunken), and su1 and su2 (sugary). The double mutant ae wx maize has no true amylose, owing to the wx mutation, but has longer amylopectin chains (average 52 instead of 30 glucose residues) than the wild type due to the ae mutation. Starches of other double or triple mutants of maize have desirable properties that emulate or exceed those of chemically modified starches. These include good freeze–thaw stability (wx sh1) and low viscosity when hot during processing but high viscosity when cool, which is desirable for canning (du h, du ae, du su2, and ae su2). Starch of the ae du wx triple mutant has high paste viscosity, shear resistance, and acid resistance, and the paste has a creamy texture making it a suitable fat substitute. Chemical analysis of chain length and branching pattern has not yet been at sufficiently high resolution to provide mechanistic explanations of these differences in processing properties.

Conclusions Numerous techniques have been used to elucidate aspects of the physical and functional chemistry of starch. Although it is a homopolymer consisting entirely of glucose, its structure is extremely variable, showing differences in chain length, branching pattern, and the incorporation of other molecules such as proteins and lipids. These differences lead to a wide range of processing properties. Aspects of the nomenclature may be confusing to the novice, in particular the use of the letters A, B, and C to indicate such diverse traits as different types of amylopectin chain, granule size, or x-ray diffraction pattern. Many questions remain to be answered about the various levels of organization within the starch granule, including the nature of the initiation of the starch granule itself.


• • • •

Distinguish between amylose and amylopectin. What happens to starch during gelatinization and retrogradation? Describe the ABCs of starch granule size, chain length, and x-ray diffraction. Describe the various levels of crystallinity in a starch granule.


•

How are we manipulating the genes of starch synthesis to make new types of starch for food and industrial purposes? See articles on starch synthesis, uses of native starch, and

• •

functional foods and various articles on breeding and genetics of cereals, pulses, and pseudocereals. What are the starch quality requirements (e.g., granule size and amylose content) for bread, or biscuits, or noodles, or pasta? See articles on the relevant food item. The initiation of starch granules, particularly of the secondary starch granules in wheat, barley, and rye, remains an enigma, as does the regulation of granule size and shape.

See also: Barley, Rice and Maize Processing: Barley: Malting; Breeding of Grains: Barley: Genetics and Breeding; Maize: Breeding; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Carbohydrates: Carbohydrate Metabolism; Resistant Starch and Health; Starch: Synthesis; Food Grains and Well-being: Functional Foods: Overview; Genetics of Grains: Maize: Genetics; Rice: Genetics; Processing of Grains: Starch: Modification; Starch: Uses of Native Starch; The Cereal Grains: Durum Wheat: Overview; Maize: Overview; Oats: Overview; Rice: Overview; Rye Grain: Its Genetics, Production, and Utilization; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Amaranth: Overview; Beans: Overview; Chickpea: Overview; Grain Legumes and Their Dietary Impact: Overview; Pea: Overview; Pseudocereals: Overview; Quinoa: Overview; Wheat Processing: Chemistry of Cake Manufacturing; Wet Milling of Wheat; Wheat: Dry Milling; Wheat-Based Foods: Noodles: Starch; Pasta.

Further Reading Atwell WA, Hood LF, Lineback DR, Varriano-Marston E, and Zobel HF (1988) The terminology and methodology associated with basic starch phenomena. Cereal Foods World 33: 306–311. BeMiller JN and Whistler RL (2009) Starch Chemistry and Technology, 3rd edn., 904 pp. New York: Academic Press. Bertolini AC (2009) Starches: Characterization, Properties and Applications, 288 pp. Boca Raton, FL: CRC Press. Donald AM, Perry PA, and Waigh TA (2001) The impact of internal granule structure on processing and properties. In: Barsby TL, Donald AM, and Frazier PJ (eds.) Starch: Advances in Structure and Function, pp. 45–52. Cambridge: Royal Society of Chemistry. Morrison WR (1995) Starch lipids, starch granule structure and properties. In: Schofield JD (ed.) Wheat Structure, Biochemistry and Functionality, pp. 261–270. Cambridge: Royal Society of Chemistry. Parker R and Ring SG (2001) Aspects of the physical chemistry of starch. Journal of Cereal Science 34: 1–17. Sonnewald U and Kossmann J (2013) Starches – From current models to genetic engineering. Plant Biotechnology Journal 11: 223–232.

Relevant Websites http://www.corn.org – Corn Refiners Association, Inc, Washington DC, USA. http://www.jic.bbsrc.ac.uk – The John Innes Centre, Norwich, UK. http://www.mri.bund.de/en/de/institute/sicherheit-und-qualitaet-bei-getreide.html – Department of Safety and Quality of Cereals, Max-Rubner Institut, Detmold, Germany. http://www.starch.dk – International Starch Institute, Aarhus, Denmark. http://eu.wiley.com/WileyCDA/WileyTitle/productCd-2041.html – Starch/die Sta¨rke (Journal home page), Wiley Interscience Publishing.

Starch: Synthesis A Regina, CSIRO Food Futures National Research Flagship, Canberra, ACT, Australia; CSIRO Plant Industry, Canberra, ACT, Australia S Rahman, Monash University Malaysia, Bandar Sunway, Malaysia Z Li, CSIRO Food Futures National Research Flagship, Canberra, ACT, Australia; CSIRO Plant Industry, Canberra, ACT, Australia MK Morell, International Rice Research Institute, Los Banõs, Philippines ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

• • •

Starch is the major component of grains. It is important for human nutrition and also as raw material for various domestic and industrial products. Starch is a polymer of glucose with two different types of linkages and other modifications. Different plant starches can vary considerably in some of their characteristics such as the size and shape of the granule, ratio of different linkages, and proportion of modifications. Starch biosynthesis is carried out in special compartments of the plant cell. Many enzymes are involved in starch biosynthesis and the roles of all of these enzymes have not yet been clarified. Further knowledge of starch biosynthesis will enable the production of starch more precisely tailored to specific needs.

Learning Objectives

• • •

To appreciate the chemical nature of starch. To appreciate the complex nature of the biosynthesis of starch. To appreciate gaps in knowledge and the potential for targeting starch for specific end uses.

Introduction Starch makes up by far the largest component of cereal grains and is also found in fruits, roots, tubers, and leaves. It is a very important source of energy in our diets. Most starch is easily digested; however, some starches termed resistant starch are digested only after they reach the large intestine, and recent research shows that this type of starch has positive attributes for bowel health. Starch also performs two basic roles in the food industry: as a stabilizer providing viscosity, texture, mouthfeel, and consistency to food products and as a processing aid to facilitate manufacturing. As a consequence of its low cost and diverse functionality, starch is used in a range of food and nonfood industries. Starch is a polymer of glucose monomers linked by a-1,4 and a-1,6 linkages, so it is a glucan. Cellulose is also a glucan; however, the single type of glucose linkage between the glucose molecules (b-1,4) provides very different properties. The a and the b refer to different spatial relationships between the glucose residues. In starch, the frequency of a-1,6 linkages defines the two major components of starch – amylose and amylopectin.


Amylose and amylopectin differ in their degree of polymerization (DP) or number of glucose residues and branching frequency. Amylose is mainly linear with <1% a-1,6 linkages and a DP of 500–5000, whereas amylopectin is highly branched with 4–6% a-1,6 linkages and a DP of 50 000–500 000. The amylose/amylopectin ratio and the details of the branching (such as the length of the branches and distance between branches) are important determinants of the suitability of starch for specific end uses. Generally, the amylose content of starch is 25%, but it can vary from 0% to 90% depending on alterations in the starch biosynthetic pathway. In nature, starch is found in granules. x-Ray diffraction studies have revealed a crystalline structure for such granules, with alternating crystalline and amorphous zones. The x-ray diffraction pattern is determined by the proportion of the external chains that are aligned in crystalline arrays and by the packing in the array. Amylopectin molecules are radially arranged with their nonreducing ends pointing toward the surface. The location of amylose chains within this structure is unclear, and it has been suggested that it is present in the amorphous region and/or interspersed in the amylopectin crystalline region. Starch is synthesized in plants within organelles that are either photosynthetic (such as the chloroplast of leaf cells) or nonphotosynthetic (such as the amyloplast of cereal endosperm cells). The starch in chloroplasts is synthesized during the day and broken down at night, and it is often termed transitory starch. In contrast, the starch synthesized in seeds is broken down only on germination, and the starch is termed reserve starch. There are some differences in the detail of biosynthesis between the two types of starch. This article is mainly concerned with the starch deposition within the nonphotosynthetic amyloplast.

Starch from Different Cereals Starch granules in the reserve tissues vary widely in size distribution and shape between species (see Table 1 and Figure 1). Maize and rice starches exhibit a unimodal granule size distribution ranging from 5 to 20 mm for maize and 2 to 5 mm for rice. Starches of wheat, barley, and rye are characterized by a bimodal distribution composed of an A granule population of 10–35 mm diameter, which are lenticular in shape with a characteristic equatorial groove, and a B granule population of generally spherical granules with a diameter less than 10 mm. In barley, a trimodal distribution of starch granules with ‘C’ granules of diameters less than 5 mm is also reported. In wheat, the larger granules, which are initiated during the early stages of endosperm development, constitute 70–80% of the starch

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182 Table 1

CARBOHYDRATES | Starch: Synthesis Typical properties of starch from different sources

Source

Starch granule size range (mm)

Starch granule size distribution

Apparent amylose content

Gelatinization onset temperaturea( C)

Wheat Barley Rice Maize

3–35 2–35 2–5 5–20

Bimodal Trimodal Normal Normal

25 22 18 28

57 56 70 64

a

Gelatinization temperature measured by differential scanning calorimetry using starch mixed with water in a ratio of 2 parts of water to 1 part of starch. The heating rate was 10 C min1 over a temperature range of 25–150 C. Source: Data compiled from Jane J, Chen YY, Lee LF, et al. (1999) Effects of amylopectin branch chain length and amylose content on the gelatinization and pasting properties of starch. Cereal Chemistry 76: 629–637; Rahman S, Li Z, Batey I, Cochrane MP, Appels R, and Morell M (2000) Genetic alteration of starch functionality in wheat. Journal of Cereal Science 31: 91–110.

by weight, and the more numerous smaller granules, which are started later, contain only 20–30% of the total starch in grain. There have been some reports of slight variation in amylose content between the A and B granules and between different regions of the granule. The amylose/amylopectin ratio does not normally vary greatly between sources, with a ratio of 1:3 being common. However, mutations where amylose is completely missing are fairly common and such starches are known as waxy starches. In some food preparations, such starches are preferred, for example, in the preparation of many Asian sticky rice desserts.

Waxy starches are also often preferred as thickeners because of the greater solubility of starches without amylose. In cereals, high-amylose starches are best known in maize among cereals where amylose content to 90% has been achieved. More recently, high-amylose wheat, barley, and rice have also been developed. The starch granules with elevated amylose content appear to be distorted. High-amylose starches are in demand because such starches are useful starting points for the production of resistant starches in foods and can be used in packaging materials and adhesives. An important property of starch granules is the gelatinization onset temperature, the temperature at which the granules begin to lose internal order and crystallinity. The gelatinization temperature of starches can vary considerably, from 57 C for barley starches to over 75 C for rice. Mutations in some of the starch synthases (SSs) (GBSS and SSIIa) have been shown to lower the gelatinization onset temperature to 46 C in mutants of SSIIa in wheat and barley. On the other hand, the suppression of starch branching enzyme (SBE) IIa and IIb tends to increase gelatinization onset temperature to 60 C. The differences in gelatinization correlate with the differences in the branch lengths of starches from different sources and in the packaging of branches in the granule. Another important property is the viscosity of the gelatinized starch. This is related to phosphate content and is a principal difference between starches from cereals and tubers. Potato starches have 0.5% phosphorylated glucose residues compared with 0.05% for cereal starches. Usually, the phosphate is linked to the carbon at position six in glucose molecules. The difference in the phosphorylation imparts

Wheat

Barley

Maize

Rice

Figure 1 Starch granules from common cereals. Scanning electron micrographs by CSIRO Plant Industry by scanning electron microscopy.

CARBOHYDRATES | Starch: Synthesis tuber starches with properties significantly different to cereal starches in terms of viscosity and flow properties. It has also been shown that starches with more short and intermediate glucan chains have a high starch viscosity. The lipid content of cereal starches is low, 1%. However, even this can be divided into three operational classes: nonstarch, surface, and internal lipids. The internal lipids of wheat consist entirely of lysophospholipids, which are complexed inside linear glucan chains. The fatty acid composition of lipids differs slightly between wheat and rice, with wheat being richer in 18:2 (linoleic acid) and rice having more 16:0 (palmitic acid) fatty acids. How lipids accumulate in cereal starches is not yet clear, but the hydrophobic environment in the interior of the glucan chain leads to complexes of lipids with amylose.

Pathway from Sucrose to Starch Granule Pathway Preceding Starch Biosynthesis Starch synthesis requires a hexose phosphate supply. Plants produce sugars in photosynthetic tissues (e.g., leaves and pericarp of the grain) where they can support starch synthesis. Some of these sugars are exported as sucrose. In the endosperm, incoming sucrose is either converted into uridine diphosphate (UDP)–glucose and fructose by a UDP-dependent sucrose synthase or converted to hexoses by invertase, as observed in maize. The UDP–glucose or hexose phosphate derived from fructose is interconverted to glucose-1-phosphate by other enzymes such as UDP–glucose pyrophosphorylase, hexokinase, and phosphoglucomutase. This glucose-1-phosphate can be used in various metabolic pathways; however, once the glucose-1-phosphate is utilized to form adenosine diphosphate (ADP) glucose (ADPG), a commitment is made to the synthesis of starch.

Biochemistry of Starch Biosynthesis A consensus view of starch biosynthesis in cereal endosperm is shown in Figure 2. Starch biosynthesis requires four types of enzymes, which are as follows:

Isoamylase SBE IIb SBE IIa SBE I 75% Amylopectin

ADPG PPase

SS III SS II ATP PPi SS I G1P ADPG

25% Amylose

ADP ADPG

GBSS

Amyloplast Figure 2 A consensus view of the starch biosynthetic pathway in cereals.

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(1) ADPG pyrophosphorylase, which produces ADP-glucose from glucose-1-phosphate and ATP. (2) SSs, which elongate glucan chains by using ADP-glucose to add a glucose residue at the nonreducing end. (3) SBEs, which introduce a-1,6 branches to the glucan chain. These branches can then be extended by SSs. (4) Debranching enzymes remove branches from starch molecules. The role of debranching enzymes in starch synthesis is still being debated, although the genetic evidence for a role for these enzymes is unambiguous. Other enzymes are also capable of influencing the properties of the starch produced and these will be discussed later. Maize has been the most extensively characterized model system for the isolation of mutations affecting starch biosynthesis. Analysis of these mutants (along with those from other model systems such as Arabidopsis and Chlamydomonas) has greatly contributed to the exploration of the key enzymes and their isoforms involved in starch biosynthesis. In maize, mutations in genes affecting starch synthesis such as the waxy and amylose extender mutations can be brought about by the insertion of transposable elements, a DNA sequence capable of moving from one location to another within a genome. Such mutations often lead to alterations in the structure and properties of starch. Specialty maize varieties such as waxy (granule-bound starch synthase (GBSS) I mutant), amylose extender (SBEIIb mutant), sugary-2 (SSIIa mutant), sweet corn (sugary-1, isoamylase mutant), and dull (SSIII mutant) find applications for specific food and industrial uses.

ADPG Pyrophosphorylase ADPG pyrophosphorylase is believed to be the key enzyme that determines the rate of starch synthesis in leaves. Genetic engineering has been used to introduce the ADPG pyrophosphorylase from Escherichia coli (which is not subjected to feedback inhibition) into potatoes, and tubers with a higher content of starch were obtained. It is not clear, however, whether ADPG pyrophosphorylase is also the rate-limiting enzyme for starch biosynthesis in the grain, as the purified enzyme from leaves and grains shows differences in properties. ADPG pyrophosphorylase from both leaves and endosperm is composed of four subunits, in which two of each type are large and small. The large subunit has a mass of 55 kDa, whereas the small subunit is slightly smaller, 50 kDa. The sequence of amino acids of these subunits is 50% identical. Mutations in the sequence of either of these subunits can destroy or reduce the activity of the enzyme, and then grains or seeds with a shrunken appearance (due to decrease in starch synthesis) are produced. Such mutations in ADPG pyrophosphorylase were given the names brittle-2 (mutation in small subunit) and shrunken-2 (mutation in large subunit) when they were discovered in maize (Table 1). Recent evidence shows that ADPG pyrophosphorylase in the cereal grain exists in both the cytoplasm and amyloplast of endosperm cells; however, most of it is in the cytoplasm. This enzyme in the cereal grain differs from that in the seeds of dicots and leaves of all the plants investigated so far, where ADPG pyrophosphorylase appears to exist exclusively in the

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CARBOHYDRATES | Starch: Synthesis

plastids. Evidence from both monocots (such as barley and maize) and dicots (such as peas) suggests that there is more than one gene for the large and small subunits of ADPG pyrophosphorylase, and different versions of these may code for the forms that are expressed in the cytoplasm and in the plastid. The annotation of the rice genome sequence also indicates multiple gene sequences coding for ADPG pyrophosphorylase. The transfer of ADP-glucose from the cytoplasm of endosperm cells to the amyloplast is important as the other enzymes in the process are located there. The Brittle-1-encoded ADPG/ ADP antiporter facilitates this transfer in maize. Mutations are known where this transfer is affected and this too produces grain where starch synthesis is affected (Table 2). ADPG pyrophosphorylases exhibit complex regulatory properties that vary depending on the species and tissue

Table 2

source. The enzymes from the leaves of all plants examined, maize endosperm, and potato tubers are allosterically activated by 3-phosphoglyceric acid and inhibited by inorganic phosphate. Pea and bean embryo and wheat and barley endosperm ADPG pyrophosphorylases, on the other hand, are much less sensitive, or insensitive, to modulators compared with their leaf counterparts. The allosteric properties of ADPG pyrophosphorylases are of potential importance in determining its role in controlling the rate of starch synthesis. Altered starch biosynthetic rates resulting from altered allosteric properties due to mutations in ADPG pyrophosphorylase subunits have been demonstrated in maize, barley, and the green algae Chlamydomonas. Alterations in the properties of ADPG pyrophosphorylase have been utilized in the plants grown in the greenhouse to increase starch production and thus seed weight.

List of selected starch mutants

Mutant

Phenotype

Plant species

Causal mutations/only enzyme affected

Brittle-1 (bt1) Shrunken-1 (sh1) Rugosus 4 (rug4) Rugosus 3 (rug3) Rb Brittle-2 (bt2)

Low starch Low starch

Maize Maize

Adenylate transporter Sucrose synthase

Low starch

Pea

Sucrose synthase

No starch

Pea

Phosphoglucomutase

Decreased starch content and increased levels of sucrose Low starch

Pea Maize

Shrunken-2 (sh2) Waxy (wx)

High levels of sucrose and low levels of starch

Maize

Zero amylose

Maize, wheat Pea

ADPG pyrophosphorylase Small subunit of ADPG pyrophosphorylase Large subunit of ADPG pyrophosphorylase GBSSI

Low amylose (lam) Shrunken (shx) Sugary-2 (su2) Rugosus 5 (rug5) Dull (du1) Amylose extender (ae) High amylose (amo1) Floury-2 (flo-2)

Low level of amylose Reduced starch content, altered granule size distribution Altered granules, high sugar Granules with deeply divided lobes, reduced amylopectin synthesis, altered amylopectin chain length Mature kernels with tarnished, glassy, and dull appearance. High apparent amylose content High levels of amylose

Barley Maize Pea

SSI (not known to be casual) Starch synthase IIa (?) SSII

Maize

Mutation at SSIII, SBEIIa affected secondarily SBEIIb, RBEIII

Higher level of amylose

Maize, rice Barley

Soft, white endosperm that crumbles easily into powder. High amylose content

Rice

SbeIIa::mu Sbe1::mu Rugosus (r) Sugary-1 (su1)

No endosperm phenotype, altered leaf starch No known phenotype Wrinkled seed, lowered starch, and enhanced amylose, sucrose, and lipid levels Low starch, phytoglycogen accumulation

Soft starch (h) SGP-1 Isoamylase mutant Sex6

Loosely packed, large granules Abnormal starch granule morphology. High amylose content Phytoglycogen accumulation. No B granule initiation

Maize Maize Pea Maize, rice Maize Wheat Barley

Decreased amylopectin synthesis, shortened amylopectin chain length distribution, reduced gelatinization temperature

GBSS

Barley

Source: Data compiled from the references in ‘Further Reading’ section. ‘?’ – not clear if the gene responsible has been identified.

Unknown RBEI, RBEIII, and GBSS (not known to be casual) BEIIa BEI SBEI Isoamylase Unknown SSII Isoamylase SSIIa


Starch Synthases SSs elongate preexisting glucan chains in the amyloplast by adding the glucosyl moiety from ADP-glucose to the nonreducing end of an existing a-1,4-glucan. Ten different SS genes have been identified in plants that encode two classes of SSs. One class of SS is only found bound to starch granules and these are known as GBSS. The other class of SS is present either in the amyloplast stroma alone or distributed between the stromal and granular fractions, and these are known as soluble SSs. Four types of soluble SS have been reported in crop plants: SSI, SSII, SSIII, and SSIV. In monocots, the SSII has been further subdivided into the IIa and IIb forms, SSIII into SSIIIa and SSIIIb forms, and SSIV into SSIVa and SSIVb forms. The primary structures of soluble SSs from different sources share a distinguishing feature, an N-terminal extension with little homology between sequences from different sources. Comparison of the deduced amino acid sequences of SSs revealed that maize SSI, SSIIa, SSIIb, and SS IIIa contained N-terminal extensions of 93, 176, 144, and 656 amino acids, respectively, compared with GBSS. Pea SSII also contains a ‘flexible’ 162-amino acid N-terminal arm. It has been shown through expression analysis using N-terminally truncated SSII that the N-terminal extension is not essential for the catalytic activity of the enzyme but is probably related to substrate binding. There are two types of GBSSs: I and II. GBSSII is similar in amino acid sequence to GBSSI but is not expressed in the grain. GBSSI is a single polypeptide, 60 kDa in mass. If the grain lacks an active GBSSI, then starch is composed almost entirely of amylopectin. Such starch is called waxy starch (Table 2). Clearly then, GBSSI is essential for the synthesis of amylose and the other SSs cannot substitute for it. The hexaploid nature of wheat allows a range of starches of intermediate amylose content to be developed, an opportunity not possible in diploids such as barley. In wheat, the GBSSI gene has been mapped as a triplicate set of single-copy homeoloci on chromosome arms 7AS, 4AS, and 7DS. A reduction in the proportion of amylose is observed when the GBSSI activity is reduced, and these starches are known as low-amylose or partial waxy starches. The loss of only one of the three isoforms, the 4A form of GBSS, has clearly been shown to yield a starch with increased ability to swell in water on heating. This property is desirable for udon noodle production, and such low-amylose starches from wheat are preferred for this end use. The soluble SSs are also all single polypeptide enzymes. SSI is 75 kDa in mass and is found both free in the amyloplast and bound to the starch granule. Starches of SSI mutants of Arabidopsis and rice and SSI RNAi silenced wheat have reduced amounts of amylopectin, low peak viscosities, and high peak gelatinization temperatures. Studies in these modified lines have shown that SSI is involved in the synthesis of short chains of the amylopectin (DP 8–12). SSII has been subdivided into IIa, IIb, and IIc forms on the basis of gene sequence comparisons; however, the IIb and IIc forms appear not to be expressed or expressed at very low concentrations in the cereal endosperm. The IIa form is 85 kDa in mass, although the wheat enzyme appears to be over 100 kDa by electrophoresis. Barley and wheat lines lacking SSIIa have been produced, and the starch from these lines is

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clearly different from normal. The barley mutants have high amylose (70%); the wheat mutants, less so (35%). It is not clear if there are differences in the structure of the amylose. The starch granules are of distorted appearance and have a lower gelatinization temperature. The proportion of branches of 7–25 glucose units in length is decreased, while the proportion of branches of 4–6 glucose units in length is increased. There are also effects on the abundance of other starch biosynthetic enzymes, so it is difficult to know how many of the effects on starch properties are the direct result of the lack of this enzyme and how many are due to the other enzymes affected. The differences in the starch between indica and japonica rice cultivars appear to be due to a combination of alterations in SSIIa and GBSS. SSIII has been subgrouped into SSIIIa and SSIIIb. SSIIIb is mainly expressed in the pericarp and does not appear to be easily detected in the endosperm. SSIIIa is a polypeptide of 180 kDa. The absence of this enzyme in maize leads to a slightly higher amylose content, and the starch looks dull compared with normal. Mutants in rice and barley have a reduced amylopectin content, a reduced starch content, but an increased amylose content. The mutation of SSIIIa increases the expression of SSI and GBSSI in the endosperm. An intermediate glucan fraction ( 15%), which is distinguished from amylose and amylopectin, occurs in starch from maize lines missing SSIIIa. SSIV has been subdivided into SSIVa and SSIVb isoforms in cereals. Both isoforms are expressed in the endosperm, although SSIVa is expressed at a higher concentration than SSIVb in rice. The importance of either of the SSIVs for starch synthesis in the endosperm is unknown at present. Mutation of SSIV in Arabidopsis dramatically reduces the number of starch granules per plastid, leading to a large increase in starch granule size in the leaf, and it appears that SSIV has a critical role in regulating the number of starch granules.

Starch Branching Enzymes SBEs, as their name suggests, are required for the addition of branches to linear glucans. Their impact is clearly more on the synthesis of amylopectin than amylose, although branching enzymes may also have a subtle role in amylose synthesis. There are two broad types of SBEs: SBEI and SBEII. Expression of these enzymes in bacteria has shown that SBEI adds longer branches than SBEII. They are both single polypeptide chains of 85 kDa. SBEI and SBEII share 60% sequence identity over the middle third of the molecules. The importance of SBEI for starch biosynthesis in the grain is not clear. Mutations in SBEI in maize and wheat did not produce a clear phenotype. A number of isoforms of SBEI may exist in wheat. However, in rice, an SBEI mutant contains amylopectin with significantly decreased proportions of long chains of DP 37 and above and short chains of DP 12–21. However, the proportion of short chains of DP 10 and below and intermediate chains of DP 24–34 increased. Starches from the rice SBEI mutant had a low gelatinization onset temperature. SBEI in rice may also play a crucial role in the synthesis of

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amylopectin molecules by interacting with phosphorylase 1 to form branched maltodextrin primers. SBEII is divided into two isoforms in cereals: IIa and IIb. The amino acid sequences of IIa and IIb isoforms are very similar (over 80% sequence identity within a species). In maize, the IIb form makes up 90% of the starch branching enzyme II activity in the endosperm, but the proportion of the two isoforms is nearly equal in wheat. Maize lines lacking starch branching enzyme IIb produce a very high (70% and higher) proportion of amylose. Rice SBEIIb mutants also contain high-amylose starch, but the proportion is much lower (40%) than in maize. In wheat and barley, suppression of SBEIIb expression using RNAi technology has no effects on starch amylose content. Suppression of both SBEIIa and SBEIIb is required for the production of amylose (>70%). In rice suppression of SBEI, IIa and IIb are required to achieve amylose contents of more than 50%. High-amylose starches are linked to the formation of resistant starches in products. Resistant starch has been shown to have very beneficial effects if present in the diet.

Debranching Enzymes Debranching enzymes remove branches from branched glucans. Two types of debranching activities, pullulanase and isoamylase, have been described from developing endosperms of rice and maize. They differ in the type of glucan they can debranch – with pullulanase debranching more efficiently open structures (e.g., pullulan) and isoamylase debranching the more branched structures (e.g., glycogen). The role and importance of these enzymes for starch biosynthesis are still being debated. Pullulanase is a single polypeptide enzyme of 100 kDa in mass. Grains from a rice pullulanase mutant contain starch with a reduced proportion of short chains (DP 13 and below) and a slightly lower gelatinization temperature (lower by 1–3 C). Such mutations in rice do not change the amylose content. A pullulanase mutant in maize contains significant quantities of low-molecular-mass a-1,6-polyglucans in the endosperm. Similar to rice, mutants in maize pullulanase contain starch with unaltered amylopectin structures and amylose/ amylopectin ratios. Isoamylase activity in plants is controlled by three gene products, designated as ISA1, ISA2, and ISA3. Of these, ISA1 and ISA2 are involved in starch biosynthesis and ISA3 is involved in starch breakdown. ISA1 is more catalytically active than ISA2 and can form complexes with it. ISA1 is a single polypeptide enzyme of 90 kDa in mass. It can debranch highly branched structures like amylopectin and glycogen. The lack of this enzyme in rice and maize is associated with the production of a very highly branched and unusual polysaccharide called phytoglycogen. Such lines also contain high levels of free sugars and are known as sugary mutants. However, there is also a reduction in the level of pullulanase in these sugary mutants, so it is difficult to know which of the effects are directly due to the lack of ISA1. The effect of the loss of ISA2 is slight in rice. There are differences between the isoamylase mutants described in rice, maize, and barley. In rice, different phenotypes

were observed for the sugary mutants ranging from no starch and only phytoglycogen to starch in the outer layer of the endosperm and phytoglycogen internally. In contrast, in barley, both phytoglycogen and starch were reported in the same endosperm cells. The maize sugary mutants also contain both phytoglycogen and starch. In barley, it has been reported that the lack of isoamylase leads to an alteration in the initiation pattern of starch granules. While it is established that isoamylase plays a significant role in starch biosynthesis, the mechanism by which it acts is not resolved. Two mechanisms have been proposed. One proposal known as the ‘glucan trimming’ mechanism suggests that isoamylase removes moderately and loosely spaced branches from a soluble preamylopectin structure that interferes with the crystallization of amylopectin and promotes the formation of a stable amylopectin structure with regularly packed glucose units. In the absence of isoamylase activity, the preamylopectin structure is further branched by branching enzymes and results in the production of phytoglycogen. The second model is based on the assumption that a competition exists between polysaccharide aggregation into starch and the nonproductive formation of water-soluble polysaccharides (WSPs), in turn resulting in a competition for both carbon source and soluble enzymes involved in amylopectin synthesis. The role of isoamylase here would be to clear the stroma of WSPs and prevent phytoglycogen formation. A role in starch granule initiation and growth, apart from phytoglycogen suppression, for isoamylase is also suggested based on the analysis of barley isoamylase mutants.

Other Enzymes with Potential Roles in Synthesis Many of the new insights into starch synthesis have come from the study of simpler systems, such as Chlamydomonas and Arabidopsis. Such studies have indicated other loci that are important in starch synthesis in these organisms. It is possible (although by no means certain) that genes encoded by such loci are also important for starch synthesis in the grains of cereals. D-Enzyme or disproportionating enzyme has the property of breaking a glucan chain and adding one portion to the nonreducing end of a preexisting chain. In this way, one chain is made shorter but the other one is made longer. In Chlamydomonas mutants where the gene for D-enzyme is affected, the starch produced appears to have somewhat more amylose. These mutants are required to be grown in constant light. Genes for D-enzyme have been described from Arabidopsis, rice, maize, barley, and wheat. Starch phosphorylase is another enzyme that could have an impact on starch biosynthesis in the grain. This enzyme breaks down starch and was originally considered to be important for degradation. There are at least two isoforms in the plant – a cytosolic form and a plastidic form; however, Chlamydomonas appears to contain three isoforms. The lack of one of these isoforms leads to a starch excess phenotype and the production of larger starch granules. In rice, the same phenotype is observed, but this is more obvious at low growth temperatures (20 C). In wheat, plastidic phosphorylase appears to be

CARBOHYDRATES | Starch: Synthesis associated with leaf and seed endosperm accumulation, not with the degradation of reserve starch. The initiator protein for glycogen is called glycogenin. Glycogenin is an autocatalytic glycoprotein, and the glucose residues provide the starting point for glycogen synthesis. By analogy, with this, a number of glycogenin-like proteins have been described from plants, but again, the importance of these proteins to starch biosynthesis in the grain is yet to be elucidated. The R1 protein is important for starch phosphorylation in potatoes. If this protein is downregulated in potatoes, then the starch produced is sharply reduced in phosphate content and increased in amylose content. The peak viscosity was also reduced. As cereal starch contains naturally far less phosphate, the importance of this protein for cereal starch biosynthesis needs to be ascertained. However, sequences similar to the gene for the R1 protein are found in the cereal genome. In Arabidopsis, potato, and wheat, the absence of the R1 protein leads to a decrease in starch breakdown and the consequent production of the starch excess phenotype.

Protein Interactions in Starch Biosynthesis Recent studies in maize and wheat have shown that the key enzymes involved in starch biosynthesis congregate into protein complexes during starch biosynthesis. These complexes may act as functional units to perform the task of granule formation. Several such interactions are now known. For example, SSIIa forms a complex with SSI and SBEIIb in maize. The composition of such assemblies may change when there are changes in the expression of key enzymes. For example, in the amylose extender mutant of maize, in which the SBEIIb activity is lacking, SBEI, SBEIIa, and starch phosphorylase are recruited into the complex involving SSIIa and SSI.

Genes and Genetics in Wheat The structure of the genes for the principal starch biosynthetic enzymes mentioned earlier has been described from wheat (Figure 3). The genes are all complex in intron/exon structure. The genes differ considerably in length, varying from 6 to 11 kb. GBSS SSI SSII SSIII SBEI SBEIIa SBEIIb Isoamylase 0

2

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Figure 3 Structure of wheat starch biosynthetic genes (data from authors’ laboratory). Exon sequences are illustrated by the thick lines; intron sequences by the narrow line.

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The processing of the initial transcript to the final RNA is clearly a complex process. Many of the mutants in GBSSI are due to errors or inefficiencies in the processing of the RNA. In barley, the waxy mutations have been reported that produce low amylose, rather than zero amylose. In these mutant starch granules, the outer cell layers of the endosperm contain more amylose than the inner layers. Investigation of these mutants revealed that the change in expression of GBSSI in these lines is due to a 413-bp deletion of part of the promoter and 50 untranslated region of the gene. Two other barley waxy families analyzed have no detectable level of amylose due to a 1-bp alteration in the GBSS gene that completely eliminates GBSS activity. In rice, a single nucleotide polymorphism at the leader intron 50 splice site of the GBSS gene has been shown to be associated with changes in amylose content due to altered efficiency of GBSS mRNA processing. A sequence of AGGTATA at this site is found to be associated with cultivars having an amylose content of above 18% as against a sequence of AGTTATA that is present in cultivars having lower amylose content. The locations of most of the starch biosynthetic enzyme genes are known in wheat and shown in Figure 4. Many of these genes are on chromosome 7. In rice, the locations of the gene are known from the genome sequence, and the locations of the wheat genes are consistent with the established relationships of the chromosomes in these two grasses.

Future Work Genomics has essentially provided the whole genome sequence of Arabidopsis and rice. The sequencing of the wheat and barley genomes is also nearing completion. It should soon be possible to identify all putative starch biosynthetic enzyme genes in the genomes of these species. The function of such putative candidate genes can be analyzed by performing conditional knockouts of selected genes, and powerful RNAi technology can be used. TILLING has also been used to obtain desired mutants in starch biosynthesis. Additionally, more sophisticated gene-editing techniques using DNA nucleases based on technologies such as TALENs and CRISPRs may be applicable for such experiments. Conversely, gene inactivation through tagging will also yield information about the role of candidate genes. This can arise either through the identification of the tagged gene and analysis of the phenotype or by observing a phenotype and then identifying the gene inactivated. Both approaches will be highly informative. Analysis of expression of all of the genes in a tissue by means of microarrays and transcriptomics can also be performed. The ability to study the pattern of transcription of the whole genome by means of ‘chips’ and the transcriptome will facilitate the study of linked genes and pathways. If tagged mutants are compared with the wild type, then the total changes in transcription can be identified, and pathways can begin to be deciphered. For untagged mutants or natural phenotypes, all the genes affected in a particular phenotype can be identified from microarray or sequence abundance analysis of the expressed genes in bulked segregants differing in the phenotype studied.

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WxB1 WxA1

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Figure 4 Chromosomal location of wheat starch biosynthetic genes. Data from authors’ laboratory observations and from the suggested readings.

New Starches in Cereals It is clear that with increasing knowledge of the enzymes involved in starch biosynthesis, the ability to alter the starch produced is also gained. New products and processes will need to be developed to capture any advantages occasioned by these new starches. Although such new phenotypes can be produced most easily by using transgenic technology, current public opinion would make it prudent to also produce starches by conventional breeding. The development of molecular markers and rapid breeding technologies (such as the production of doubled haploids and embryo culture and the ability to quickly extract DNA from small samples) will undoubtedly also speed up the production of novel types of starch by conventional breeding strategies.

able to precisely manipulate the starch structure and functionality to suit specific end uses.


• • • • • •

Why is starch important for our daily life? How many classes of enzymes are involved in starch synthesis? Which starch synthetic enzymes are important in the determination of starch structures? Which starch synthetic enzymes are important in the determination of starch properties? How can novel starches be produced in cereals? What approaches can be used for the study of the roles of the enzymes in starch synthesis?

Conclusion


The involvement of four classes of enzymes – ADPG pyrophosphorylase, SSs, SBEs, and debranching enzymes – in starch biosynthesis is clearly established, although the precise roles of isoforms in many cases are not clear. Other enzymes may also have roles in starch biosynthesis. Starch phosphorylase and disproportionating enzyme (D-enzyme) are examples. The role in starch degradation of both of these enzymes is well known. However, their involvement in starch synthesis, although demonstrated from a few studies, is a matter requiring further research. The priming of polysaccharide synthesis and granule formation during starch biosynthesis is still unresolved. Although it is evident that mutations in the core genes lead to specific starch phenotypes over a variety of species, speciesspecific characteristics are observed that are often significant and of practical importance. Understanding the complex nature of starch biosynthesis has always been facilitated and accelerated through investigations on model systems such as Chlamydomonas and Arabidopsis and increasingly rice. However, attempts should also be focused on individual species to be

• • •

The roles of different isoforms of starch synthetic enzymes in the determination of starch structures and properties. Interaction of the isoforms of starch synthetic enzymes in starch synthesis. Regulation of the isoforms of starch synthetic enzymes in starch synthesis.

See also: Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Grains other than Cereals: Non-starch Polysaccharides; Starch: Analysis of Quality; Starch: Chemistry; Processing of Grains: Starch: Uses of Native Starch; Wheat-Based Foods: Noodles: Starch.

Further Reading Buleon A, Gallant DJ, Bouchet B, et al. (1997) Starches from A to C: Chlamydomonas reinhardtii a model system to investigate the biosynthesis of the plant amylopectin structure. Plant Physiology 115: 949–957.

CARBOHYDRATES | Starch: Synthesis Gilbert RG, Wu AC, Sullivan MA, Sumarriva GE, Ersch N, and Hasjim J (2013) Improving human health through understanding the complex structure of glucose polymers. Analytical and Bioanalytical Chemistry 405: 8969–8980. James MG, Denyer K, and Myers AM (2003) Starch synthesis in the cereal endosperm. Current Opinion in Plant Biology 6: 215–222. Jane J, Chen YY, Lee LF, et al. (1999) Effects of amylopectin branch chain length and amylose content on the gelatinization and pasting properties of starch. Cereal Chemistry 76: 629–637. Morrison WR (1988) Lipids in cereal starches: A review. Journal of Cereal Science 8: 1–15. Morrison WR (1993) Seed storage compounds: Biosynthesis, interactions and manipulation. 12. Cereal starch granule development and composition. In: Shewry PR and Stobart K (eds.) Seed Storage Compounds-Biosynthesis, Interaction and Manipulation. Proceedings of the Phytochemical Society of Europe, pp. 175–190. Oxford: Oxford University Press. Nakamura Y (2002) Towards a better understanding of the metabolic system for amylopectin biosynthesis in plants: Rice endosperm as a model tissue. Plant Cell Physiology 43: 718–725. Shewry PR and Morell M (2001) Manipulating cereal endosperm structure, development and composition to improve end-use properties. In: Shewry PR, Lazzeri PA, and Edwards KJ (eds.) Advances in Botanical Research Incorporating Advances in Plant Pathology Biotechnology of Cereals, vol. 34, pp. 165–236. San Diego: Academic Press. Tetlow IJ (2011) Starch biosynthesis in developing seeds. Seed Science Research 21: 5–32. Thitisaksakul M, Jimenez RC, Arias MC, and Beckles DM (2012) Effects of environmental factors on cereal starch biosynthesis and composition. Journal of Cereal Science 56: 67–80.

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Topping DL and Clifton PM (2001) Short-chain fatty acids and human colonic function: Roles of resistant starch and nonstarch polysaccharides. Physiological Reviews 3: 1031–1064. Tuncel A and Okita TW (2013) Improving starch yield in cereals by over-expression of ADPglucose pyrophosphorylase: Expectations and unanticipated outcomes. Plant Science 211: 52–60. Utsumi Y, Utsumi C, Sawada T, Furjita N, and Nakamura Y (2011) Functional diversity of isoamylase oligomers: The ISA1 homo-oligomer is essential for amylopectin biosynthesis in rice endosperm. Plant Physiology 156: 61–77. Yu TS, Kofler H, Hausler RE, et al. (2001) The arabidopsis sex 1 mutant is defective in the R1 protein, a general regulator of starch degradation in plants, and not in the chloroplast hexose transporter. Plant Cell 13: 1907–1918. Zeeman SC, Kossmann J, and Smith AM (2011) Starch: Its metabolism, evolution, and biotechnological modification in plants. Annual Review of Plant Biology 60: 209–234.

Relevant Websites http://www.ncbi.nml.nih.gov – A resource for molecular biology information. http://www.tigr.org/tdb – Provides databases containing DNA and protein sequences and gene expression, protein family and taxonomic data for microbes, plants and animals.

Starch: Starch Architecture and Structure V Vamadevan, University of Minnesota, St. Paul, MN, USA; Agriculture and Agri-Food Canada, Guelph, ON, Canada Q Liu, Agriculture and Agri-Food Canada, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Granule morphology, structure, and composition of starches from different genetic backgrounds. Organization of glucan chains at different structural levels of starch granules. Cluster model of amylopectin versus building block backbone model. Unit chain categories of amylopectin. Branching point distribution pattern in amylopectin. Structural parameters of amylopectin.

Learning Objectives

• • • •

To understand the complex hierarchical structure of starch granules. To understand the concepts underlying proposed amylopectin models. To understand the internal structure of amylopectin. To identify unresolved structural aspects of starch granules.

common. Cereal starches are generally small and have round or polyhydric shapes with a concentric hilum and a unimodalsize distribution. Wheat, triticale, barley, and rye starches, however, exhibit bimodal size distributions, with large (A-type) and small (B-type) granules. Starch granules from tubers are usually large and oval-shaped with an eccentric hilum. Pulse starches are normally medium-sized, with a beanlike or ovoid shape and an elongated or starred hilum. Highamylose starches generally appear as irregular, filamentous, or rod-shaped granules (Figure 1). Corn, sorghum, millet, wheat, rye, and barley starch granules are characterized by nonuniformly distributed surface pores. Some granules have numerous pores, others feature only a few, and the starch granules of rice, oat, pulse, potato, tapioca, canna, yam, and arrowroot appear to have none at all. In some starch granules, such as maize, sorghum, and millet, radially oriented channels that connect to a central cavity have been observed. Which biomechanism determines the size of the granules in different plants and how the pores and channels are formed are still unclear.

Introduction Produced by plants as an end product of the photosynthetic process, starch is one of the most abundant renewable biopolymers on Earth. It serves as a major energy source in the human diet and an important functional ingredient in many food and nonfood products. Principal sources are cereal grains (e.g., wheat, maize, rice, and barley), tubers (e.g., potato), roots (e.g., cassava), and pulses (e.g., pea, chickpea, and bean). Starch is stored in the form of granules whose morphology, structure, and composition are dependent on the genetic background of the source. Starch is synthesized in organelles called amyloplasts, and the so-called hilum is thought to be the initiation point of the biosynthesis of the starch granule. The position of the hilum in the granule varies according to the botanical source. Starch granules are classified as simple, compound, or semicompound types depending on how many granules are initiated in each amyloplast. In simple starch granules (e.g., maize, wheat, and barley), one granule is initiated in each amyloplast, whereas compound granules (e.g., rice and oat) are composed of multiple granules, known as subgranules, that are initiated simultaneously in a single amyloplast. Semicompound granules (e.g., wrinkled pea) have two or more fused subgranules. The molecular mechanism underlying starch granule initiation is still largely unknown.

Starch Granule Morphology The diameter of starch granules varies from 0.1 to 200 mm. However, granules in the range of 2–100 mm are the most

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Structural Components Starch is synthesized as semicrystalline granules made up of two principal types of glucan polymers: amylose and amylopectin. Both are composed of anhydrous glucopyranose units connected through a-(1,4)- and a-(1,6)-glycosidic linkages. A third type of glucan polymer, known as an intermediate material, is found in amylose extender (ae) maize mutant starches and in some regular starches and starches derived from developing or immature grains. Most starches consist of 20–30% amylose and 70–80% amylopectin, with a very low amount of intermediate material content. However, amylose-free waxy starches contain essentially 100% amylopectin, and high-amylose starches consist of < 50% amylopectin. The frequency of the a-(1,6)-linkages (degree of branching) constitutes the basis for the characterization and definition of the glucan components. Amylose is a relatively long, linear polymer with few branches (1% a-(1,6)-linkages), whereas amylopectin is a large, highly branched molecule, composed of about 5% a-(1,6)-linkages. The structure of the intermediate material falls in between those of amylose and amylopectin. The molecular weight ranges of the amylose and amylopectin are in the order of 105–106 g mol 1 and 107–109 g mol 1, respectively. While the location of the amylose and its contribution to the granular architecture are still largely unknown, it is thought to be present primarily in the amorphous region of the granules. Amylose chains that pass through both the crystalline and amorphous layers are referred to as tie chains.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00095-4

CARBOHYDRATES | Starch: Starch Architecture and Structure

(a)

(b)

(c)

(d)

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Figure 1 Light micrographs (1000 ) of maize (a), canna (b), mung bean (c), and Hylon VII maize starches (d).

Amylopectin Structure Over the years, a number of models have been employed as a means of visualizing the organization of amylopectin glucan chains. Currently debated structural models include the traditional cluster model and the two-directional backbone model. The traditional cluster model was originally proposed independently by both French and Nikuni and was subsequently modified by Hizukuri. In this model, short adjacent linear amylopectin chains are paired as double helices tightly registered in parallel alignment to form clusters, which are interconnected through long chains. According to this model, long amylopectin chains are part of the crystalline and amorphous lamellae (Figure 2(a)). The model is based primarily on indirect evidence drawn from the amylopectin unit chain profile. Another argument that supports this model stems from the molecular structure of lintners (acid-treated starch). This indirect evidence suggests that the group of short chains builds up the crystalline region, whereas long chains interconnect the clusters. In the two-directional backbone model, the direction of the short chains in the clusters is perpendicular to the direction of the long chains, which are present mainly in the amorphous lamellae. According to this model, long chains do not pass through the crystalline region (Figure 2(b)). Interestingly, the two-directional backbone model can also be defended based on the indirect evidence and arguments put forward for the traditional model. Unfortunately, no direct experimental verification yet exits to enable the validity of either model to be tested, and none of the amylopectin models developed are based on the function of isozymes during starch biosynthesis.

The molecular structure of amylopectin from individual starches can be differentiated according to both the unit chain profile and the organization of the internal chains. The unit chain profile describes the chain length (CL) distribution pattern, or average composition, of the chains in the whole amylopectin molecule, whereas the organization of the internal chains primarily identifies the nature of the branching pattern.

Amylopectin Unit Chain Profile After hydrolyzation of the a-(1,6)-linkages using debranching enzymes, isoamylase and pullulanase, the unit chain profile of amylopectin can be obtained through high-performance sizeexclusion chromatography (HPSEC) or high-performance anion-exchange chromatography (HPAEC). Unit chains are broadly categorized into three major groups: A, B, and C. A-chains carry no other chains and are linked with the rest of the molecule by a-(1,6)-bonds, whereas B-chains carry one or several other chains (A- and/or B-chains). A C-chain carries the sole reducing end of each amylopectin molecule. Hizukuri described the polymodal distribution pattern of amylopectin based on the observed periodicity of the CL and subdivided the B-chains accordingly into B1, B2, B3, and B4 categories. These chains differ with respect to their length and the number of clusters they span. B1-chains (with a degree of polymerization (dp) 20 to dp 24) are short chains, which build up the clusters in partnership with A-chains (dp 11 to dp 14), whereas B2- (dp 42 to dp 48), B3- (dp 69 to dp 75), and B4- (dp > 75) chains are long B-chains (dp > 36). The numerals


f

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(a) C

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Figure 2 (a) Schematic representations of the cluster model (adapted from Robin JP, Mercier C, Charbonnie`re R, and Guilbot A (1974) Lintnerized starches. Gel-filtration and enzymatic studies of insoluble residues from prolonged acid treatment of potato starch. Cereal Chemistry 51: 389–406) and (b) the backbone model of amylopectin (reproduced from Chauhan F and Seetharaman K (2013) On the organization of chains in amylopectin. Starch/Sta¨rke 65: 191–199.).

associated with B-chains indicate the number of clusters they span (Figure 3). According to the divisions obtained by Hizukuri using HPSEC, the periodicity of the CL is approximately dp 27 to dp 28, and the average CL is dp 17 to dp 26. Hanashiro et al. observed a shorter periodicity (dp 12) with HPAEC and named the chain fractions fa- (dp 6 to dp 12), fb1(dp 13 to dp 24), fb2- (dp 25 to dp 36), and fb3- (dp > 36) chains, which presumably represent A-, B1-, B2-, and B3chains, respectively. Using this division, B2-chains are considered a subdivision of the B1-chains categorized by Hizukuri. The very shortest amylopectin chains consist of six glucose residues. The limit dextrin profile of amylopectin reveals that A-chains (fa-chains) overlap with B1-chains (fb1-chains), so the fa fraction therefore represents only part of the A-chains. A-chains consist of a subgroup of chains called fingerprint A-chains (dp 6 to dp 8), which are too short to form double helices and can cause structural defects within the crystalline lamellae. On a molar basis, the ratio of short to long unit chains varies from 4 to 19, depending on the starch source. Although the unit chain profile is useful for describing many of the structural features of the amylopectin molecule, it fails to explain how glucan chains are organized within the amylopectin molecule.

Organization of Amylopectin Internal Chains The organization of the unit chains in amylopectin determines the unique architecture of the starch granule. Unit chains can be categorized as either external or internal chains. External chains are composed of A-chains and a portion of the B-chains. The A–B-chain segment that has branching points is designated an internal chain. External chains participate in the formation

of the crystalline lamellae, whereas internal chains are present primarily in the amorphous lamellae. The internal unit chain profile can be obtained from f,b-limit dextrins by removing the external amylopectin chains using the exo-acting enzymes phosphorylase and b-amylase. Since exo-acting enzymes cannot bypass branching points, the resulting limit dextrin represents the internal amylopectin structure. In f,b-limit dextrins, all A-chains and the external segments of B-chains appear as maltosyl and glucosyl stubs, respectively. The characterization of A- and B-chains from f,b-limit dextrin provides a relatively accurate estimate of the ratio of A-chains to B-chains, which, on a molar basis, is typically in the range of 0.8–1.5. The internal amylopectin structure consists of two major groups of B-chains: short B-chains (dp < 24) and long B-chains (dp > 24). Short internal B-chains (BS chains) are subdivided into ‘fingerprint’ B-chains (Bfp) with dp values 7 and a major group of short B-chains (BSmajor) with dp values from 8 to 25. Long internal B-chains are classified as B2-chains (dp 26 to dp 50) or B3-chains (dp > 50). Short B-chains are part of clusters, and long internal B-chains function as cluster-connecting chains. Based on the quantity and distribution pattern of the short and long internal B-chains, amylopectin from different botanical sources is one of four different types: type 1, type 2, type 3, or type 4 (Figure 4). Type 1 amylopectin is characterized by large numbers of short internal chains, mainly BSmajorchains, with a broad distribution pattern, whereas type 4 amylopectin has a large number of long internal chains. Types 2 and 3 represent intermediate distributions. Type 2 amylopectin exhibits a significant number of Bfp chains in clusters. Based on this grouping, cereal starches are considered to be types 1 and 2, and root and tuber starches to be primarily types 3 and 4.


A-chain

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Figure 3 Chain categories of amylopectin. Adapted from Hizukuri S (1986) Polymodal distribution of the chain lengths of amylopectins, and its significance. Carbohydrate Research 147: 342–347.

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Degree of polymerization (DP) Type 1 (A-and C-crystalline): e.g., barley, rye, oat, Andean yam Type 2 (A-and C-crystalline): e.g., maize, rice, sago, kudzu Type 3 (A-and C-crystalline): e.g., cassava, arrowroot, mung bean Type 4 (B-crystalline): e.g., potato, canna, lesser yam

Figure 4 Internal unit chain profile of debranched f,b-limit dextrins from four different types of amylopectin, as obtained by high-performance anion-exchange chromatography (HPAEC). Adapted from Bertoft E, Piyachomkwan K, Chatakanonda P, and Sriroth K (2008) Internal unit chain composition in amylopectins. Carbohydrate Polymers 74: 527–543, with permission.

The cluster structure of amylopectin is examined primarily with the use of enzymatic methods. Clusters, or macro a-limit dextrins, are isolated from amylopectin using limited hydrolysis with a-amylase. These clusters are defined as groups of short chains separated by internal chain segments with dp values < 9. This definition is somewhat arbitrary because the hydrolysis pattern is dependent on the source of the a-amylase and its kinetics as well as on experimental conditions. Clusters from different types of amylopectin differ with respect to size and CL and are made up of tightly branched units, known as building blocks. Building blocks are micro a-limit dextrins, which are released from clusters through extensive hydrolysis with a-amylase. The size of the building block is determined

based on the number of chains (2, 3, 4, or more) in the unit. Adjacent building blocks within the cluster are connected by interblock chain segments, which are in the range of 5–8 glucose residues. Computer simulation and crystalline stability studies have revealed that the CL between adjacent building blocks is one of the most critical parameters governing the alignment of the external chains and the crystalline packing. The number of building blocks within the cluster, the interblock chain length (IB-CL), and the cluster size and the number of chains in the cluster and the length of the external chains are all used to characterize different types of amylopectin. A schematic model illustrating the internal structure of amylopectin is provided in Figure 5. Cereal starches

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Figure 5 Schematic illustration of the building block structure of amylopectin.

generally have a higher number of building blocks, a shorter IB-CL, and larger cluster sizes than tuber and root starches. The two-directional backbone model of amylopectin is based primarily on the structure of experimentally isolated clusters and building blocks.

B-type

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Structural Polymorphism of Amylopectin The double helices of amylopectin in the crystalline lamellae are organized into different types of polymorphs. Starch granules exhibit two main types of polymorphic patterns: A-type and B-type. They differ primarily with respect to packing arrangement and degree of hydration. The A-type polymorph is packed with monoclinic unit cells and consists of four H2O molecules/unit cell, whereas the B-type has a hexagonal unit with 36 H2O molecules/unit cell (Figure 6). Polymorphic patterns can be characterized with the use of wide-angle x-ray scattering (WAXS). Most starches derived from cereals exhibit an A-type polymorphic pattern with characteristic main peaks at 15 2y and 23 2y and an unresolved doublet at around 17 2y and 18 2y. Characteristic of tuber, ae maize, and retrograded starches, the B-type polymorphic pattern shows primary reflection intensities at 5.5 2y, 14–15 2y, and 17 2y, as well as a well-resolved doublet centered at 22 2y–24 2y. Root, pulse, and some fruit and stem starches exhibit a C-type polymorphic pattern, which is a mixture of A- and B-crystalline types (Figure 7). The type of polymorphic pattern is thought to be related to the amylopectin CL (A-type CL < 20 and B-type CL 22). Interestingly, a B-type polymorph has also been observed in some starches (e.g., Arabidopsis leaf and immature wheat grain) that have shorter amylopectin CLs than B-type endosperm starches. This finding suggests that the polymorphic patterns of starches cannot be explained based solely on the average CL of the amylopectin.

Amylose Structure Starches generally contain both linear and branched fractions of amylose. Incomplete b-amylolysis indicates the presence of branched fractions, which consist of 5–17 chains linked by a-(1,6)-linkages. The conformation of amylose in an aqueous solution is highly speculative. Since its random coil conformation is unstable, amylose tends to form single helices with guest molecules (lipid, iodine, alcohols, and dimethyl sulfoxide

Figure 6 Unit cell structure of B- and A-type starches. Each green circle represents the upper view of the double helix; the red dots indicate water molecules. Adapted from Imberty A, Chanzy H, Pe´rez S, Buleon A, and Tran V (1988) The double-helical nature of the crystalline part of A-starch. Journal of Molecular Biology 201: 365–378.

(DMSO)) or double helices with adjacent chains in the absence of complexing agents. Single-helix amylose is referred to as V-amylose and is characterized by six glucose units per turn. However, the helical structure and number of glucose units per turn are controlled by the size of the inclusion complex. In WAXS pattern, a peak centered at 20 2y generally reflects V-type crystallinity. Reflection intensities of 7.5 2y and 13 2y can also be considered indicative of a single-helix structure. Double helices of amylose are found in A- or B-polymorphic form and are similar to the crystallites formed by amylopectin.

Semicrystalline Structure of Starch Granules Starch is known to have a hierarchically ordered structure with characteristic periodicity. Its levels of organization are granule, growth ring, blocklet, lamella, and glucan chains (Figure 8). Each level has been characterized and defined with the use of a variety of imaging and analytic techniques. However, the structural connections between these levels of order are still far from completely understood. The organization of glucan chains at different levels of order determines the architecture of starch granules, which consists of alternating amorphous and semicrystalline growth rings that develop outward from the hilum by apposition. The thickness of the growth rings generally varies from 120 to 400 nm. The number and thickness of growth rings formed during granule development are dependent on the botanical source of the starch. Growth ring formation is thought to be subject to the diurnal cycle, with semicrystalline rings being deposited during


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A-type B-type C-type

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Figure 7 Wide-angle x-ray scattering patterns of A-, B-, and C-type starches.

Amorphous background

Crystalline lamella (C) Amorphous lamella (A)

9 nm

Maize/HCl/2.2M/ 80% hydrolysis

Starch granule (1 – 100 mm)

Growth rings (120 – 400 nm)

Blocklets (20 – 100 nm)

Cluster

Double helix

C 9 nm

2.1 nm

5 – 6 nm

A 3 – 4 nm Figure 8 Schematic representation of the structural levels of starch.

the daytime and amorphous rings being formed during the night. However, whereas constant light treatment has been shown to affect ring formation in barley and wheat, it has no effect on ring formation in potatoes. While this finding suggests that a circadian rhythm related to biological mechanisms influences ring formation, no definite explanation has yet been established for the occurrence of alternating zones of growth rings in starch granules. While the detailed structure of amorphous growth rings is still to be determined, such rings are thought to consist of

amylose and disordered amylopectin. A semicrystalline growth ring consists of a number of alternating crystalline and amorphous lamellae with a repeat distance of 8.5–11 nm. Amorphous lamellae are thought to contain amylose plus long chains and branching points of amylopectin. Crystalline lamellae are formed primarily from the double helices of short amylopectin chains. Each double helix consists of six anhydroglucopyranose units per turn with a pitch height of 2.1 nm2. The birefringence pattern of starch granules revealed under polarized light microscopy is attributable to their

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(a)

(b)

Figure 9 Bright-field microscopy (a) and polarized microscopy (b) of iodine-treated waxy potato starch granules.

semicrystalline nature, and the distinctive Maltese cross indicates that the ordered amylopectin chains in the crystalline lamellae are radially oriented (Figure 9). Images obtained using high-resolution scanning electron and atomic force microscopy indicate another level of organization called a blocklet, which appears to be present in both semicrystalline and amorphous growth rings. Blocklets are more or less spherical, with sizes varying from 20 to 100 nm, depending on the location of the granule and the botanical source. Potato starch blocklets are generally larger than those in cereal starches. The presence of the larger blocklets, coupled with its semicrystalline nature, is commonly linked to the relative resistance to enzymatic hydrolysis of the potato starch granule. According to the blocklet concept, growth rings are organized in the form of blocklets that occur in a semicrystalline growth ring consisting of a stack of lamellae. However, the exact nature of both the blocklet and its relation with the rest of the structural levels of a starch granule remains open to speculation.

biosynthetic enzymes, and the structure–function relationship of starch in a variety of applications.


• • • •


• Conclusion In starch granules, amylopectin chains are organized into a hierarchical structure. Although existing sophisticated imaging and analytic techniques have enabled the observation of different levels of order in starch granules, a substantial knowledge gap remains with respect to understanding how glucan chains are arranged in amylopectin and how the structural levels are interconnected. The crystalline lamellae and unit CL distribution of amylopectin have been more extensively analyzed than other structural features. However, the organization of glucan chains cannot be explained based on the average composition of the unit chains. Detailed analysis of the internal amylopectin structure is therefore of paramount importance for providing insight into the crystalline stability, the polymorphic pattern, and the architecture of the building blocks, which are considered to be the fundamental structural unit in amylopectin. Enhanced knowledge of the granular architecture will provide additional opportunities for uncovering the processes that govern the initiation of starch synthesis, the control mechanism involved in

How does amylopectin build up the semicrystalline lamellae? Define the structural parameters of amylopectin. Explain how a,b-limit dextrin has improved the unit chain analysis of amylopectin. How does the internal structure of amylopectin determine the glucan chain alignment in crystalline lamellae?

• • • •

How can the validity of the proposed amylopectin models be tested? Does the nature of the branching pattern influence the polymorphic pattern? Does amylose influence the assembly of crystalline lamellae? How does the molecular structure of amylopectin in the semicrystalline region of starch granules differ from the amylopectin in the amorphous region? Do blocklets build up the super helical structure of starch granules?

See also: Carbohydrates: Starch: Analysis of Quality; Starch: Chemistry; Starch: Synthesis; Genetics of Grains: Maize: Other Maize Mutants; Processing of Grains: Starch: Modification; Starch: Uses of Native Starch.

Acknowledgment The authors thank Dr Eric Bertoft for his critical review of this article.


Further Reading Bertoft E (2013) On the building block and backbone concepts of amylopectin structure. Cereal Chemistry 90: 294–311. Bertoft E, Piyachomkwan K, Chatakanonda P, and Sriroth K (2008) Internal unit chain composition in amylopectins. Carbohydrate Polymers 74: 527–543. Buleón A, Colonna P, Planchot V, and Ball S (1998) Starch granules: Structure and biosynthesis. International Journal of Biological Macromolecules 23: 85–112. Chauhan F and Seetharaman K (2013) On the organization of chains in amylopectin. Starch/Sta¨rke 65: 191–199. French D (1984) Organization of starch granules. In: Whistler RL, BeMiller JN, and Paschall EF (eds.) Starch: Chemistry and Technology, 2nd edn., pp. 183–207. San Diego, CA: Academic Press. Hanashiro I, Abe J, and Hizukuri S (1996) A periodic distribution of the chain length of amylopectin as revealed by high-performance anion-exchange chromatography. Carbohydrate Research 283: 151–159. Hizukuri S (1986) Polymodal distribution of the chain lengths of amylopectins, and its significance. Carbohydrate Research 147: 342–347. Imberty A, Chanzy H, Pe´rez S, Buleon A, and Tran V (1988) The double-helical nature of the crystalline part of A-starch. Journal of Molecular Biology 201: 365–378.

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Nikuni Z (1978) Studies on starch granules. Starke 30: 105–111. O’Sullivan AC and Pe´rez S (1999) The relationship between internal chain length of amylopectin and crystallinity in starch. Biopolymers 50: 381–390. Pe´rez S and Bertoft E (2010) The molecular structures of starch components and their contribution to the architecture of starch granules: A comprehensive review. Starch 62: 389–420. Robin JP, Mercier C, Charbonnie`re R, and Guilbot A (1974) Lintnerized starches. Gel-filtration and enzymatic studies of insoluble residues from prolonged acid treatment of potato starch. Cereal Chemistry 51: 389–406. Shannon JC and Garwood DI (2009) Genetics and physiology of starch development. In: Whistler RL and BeMiller JN (eds.) Starch: Chemistry and Technology, 3rd edn., pp. 25–86. San Diego, CA: Academic Press. Thompson DB (2000) On the non-random nature of amylopectin branching. Carbohydrate Polymers 43: 223–239. Vamadevan V, Bertoft E, and Seetharaman K (2013) On the importance of organization of glucan chains on thermal properties of starch. Carbohydrate Polymers 92: 1653–1659. Zobel HF (1988) Starch crystal transformations and their industrial importance. Starch 40: 1–7.

Starch: Analysis of Quality A Gunaratne and H Corke, The University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 202–212, ã 2004, Elsevier Ltd with revisions made by the editor.

Topic Highlights

• • • •

•

• •

•

Starch as the main constituent of food grains and the reason for many of the functional properties of grains. Starch occurs as granules in the endosperm of cereal grains; granule shape is distinctive for the species. The functional properties of starch are affected by botanical source, structure and physicochemical properties, and pretreatments during processing. The two major compounds of starch are amylose (mainly linear polymers of a(1–4)-linked glucose) and amylopectin (usually the major component, being highly branched polymers). Amylose forms a distinctive blue color complex with iodine. Better analysis is provided by high-performance size-exclusion chromatography (HPSEC) and various other methods. Near-infrared (IR)-reflectance analysis can be used to determine amylose content rapidly for mutant lines that differ significantly in amylose:amylopectin ratio. Direct testing of starch function involves the pasting test whereby viscosity changes are monitored for a starch suspension heated in excess water, using equipment such as the Viscoamylogram or the Rapid ViscoAnalyzer. Starch retrogradation is the key physical change associated with bread staling.

Learning Objectives

• •

Understand the chemical properties of starch that affect its functional utilization. Understand how and when to apply the range of testing procedures for starch chemistry and function.

Introduction Starch is the main polysaccharide produced in photosynthetic tissues. Recently, there has been a growing demand for starch in both food and nonfood industries because of its wide array of applicability in diverse systems. Functionality is the key for the industrial utilization of starch. Functional properties can be defined as the characteristics that govern the behavior of a food component during processing, storage, and preparation. Factors such as botanical source, structure and physicochemical properties, and pretreatments of starch directly affect functional properties of starch. Analysis of starch-related functionality should provide a clear picture of the relevant property that will allow better use of starch in food and nonfood systems, for example, to maintain consistent quality and functionality of starch-based products in every batch, otherwise the product

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will not survive in the competitive market. Methods that are implemented for the analysis of starch functional properties should be simple and fast, technically feasible, nondestructive, and able to provide reproducible results with high accuracy. Although several methods have been developed recently to monitor some of the functional properties, individual methods are sometimes not capable of providing adequate data on all the dimensions of a functional property, especially in the determination of retrogradation and gelatinization. Therefore, it is often worth applying at least two methods to get complementary data. This article aims to discuss some functional properties of starch from the perspective of the applicability of methods that are currently employed to determine those properties.

Properties, Functions, and Analysis of Starch Macromolecules Amylose The two major compounds of starch are amylose and amylopectin. The two polymers are structurally different, the minor component, which is linear, consisting mainly of a(1–4)linked glucose. However, in some starches, amylose chains have shown a slight degree of branching. Incomplete conversion to maltose by b-amylase suggests the presence of branched points in the amylose polymer. The branched chains can also act similar to unbranched chains. Amylose isolated from tuber and root starches such as potato and cassava has a larger molecular weight than that isolated from cereal starches such as maize and wheat. Although amylose is a linear molecule, its conformation tends to change due to the large number of hydroxyl groups that can produce higher hydrogen bonding capability with strong internal forces. The conformation of amylose has been the subject of controversy and has been shown to vary from helical to an interrupted helix, to a random coil. In alkaline solutions (KOH) and dimethyl sulfoxide (DMSO), amylose probably has an expanded coil conformation, while in water and neutral aqueous potassium chloride solutions, it is a random coil with short, loose helical segments. Although helical conformation is common in amylose, double helices form when different helices are packed together. The helical arrangement of amylose forms a hydrophobic core inside the amylose molecule, which permits complexing with guest molecules such as lipids and iodine. The amount and molecular characteristics of amylose have a significant influence on starch functionality. Higher amylose content decreases the granular swelling power, whereas increasing amylose concentration decreases the gel stickiness but increases the gel firmness. Reassociation of amylose chains on cooling of a starch paste shrink the starch gel resulting in water


http://dx.doi.org/10.1016/B978-0-12-394437-5.00092-9

CARBOHYDRATES | Starch: Analysis of Quality Table 1

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Some physical and chemical properties of common starches

Starch

Granular size (mm)

Granular shape

Amylose (%)

Barley Maize Regular Waxy High amylose Potato Rice Rye Sago Sorghum Tapioca Wheat Oats

2–35

Round, elliptical, lenticular

22

5–25 5–25

Round, polygonal Round, oval Round Egg-like, oyster indentations Polygonal clusters Elliptical, lenticular Egg-like, some truncate forms Round, polygonal Round, oval, truncated on side Round, elliptical, lenticular Polygonal, compound

26 1 Up to 80 22 17 23 27 26 17 25 27

15–100 3–8 2–35 20–60 5–25 5–35 2–35 2–10

Swelling power at 95 C

Solubility at 95 C

Taste Low

24 64 6 1000 19

25 23 12 82

97 22 71 21

Low Low Low Slight Low Low Low Low Fruity Low Low

22 48 41

Adapted from Collado LS and Corke H (2003) Starch properties and functionalities. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 473–506. New York: Marcel Dekker.

accumulation on an aging gel, which decreases the storage stability and usually the quality of an affected starch-based food product.

Table 2 Amylose content in maize mutant starches as estimated with size exclusion chromatography (SEC), Concanavalin (Con. A), differential scanning calorimetry (DSC), and iodine binding capacity (IBC) Amylose (%)

Methods used in amylose estimation Conventional quantitative determination of amylose is based on its ability to form a deep blue color complex with iodine. Amylose content of starch therefore can be quantified either by spectrophotometric means or by potentiometric titration. Table 1 shows amylose content of some common starches. However, interference from amylopectin and other intermediate materials in the blue color formation reaction biases the estimation of actual content of amylose. Amylopectin–iodine complex is not stable due to shorter unit chain length of amylopectin, but long chains of amylopectin, e.g., long B chain of waxy maize amylopectin can bind with iodine in a similar way to amylose. This would lead to an overestimation. Despite shortcomings such as this, and the time-consuming nature of the assay, the amylose–iodine reaction is still the basis of the most widely used method to determine amylose content of starch because of its accuracy, reproducibility, and easy operation. However, the excessive time needed limits its use in quality control applications. Instead of conventional thermal dissociation of amylose in DMSO, low-temperature gelatinization in CaClB2B could be employed to reduce the time requirement. High performance size exclusion chromatography (HPSEC), that has shown a good correlation with blue value measurements of amylose content, can be employed to separate starch and de-branched starch. Ability to directly monitor the effect of de-branching on the molecular size distribution of starch and high-molecular weight linear amylose content from this technique provides the estimation of long-chain amylopectin chains that contribute to the apparent amylose content. Recently another technique that is able to eliminate the effect of long-chain amylopectin in the estimation of amylose content has been introduced. In this method, starch completely dissolved in DMSO is subjected to de-fatting with ethanol. The precipitate after de-fatting is dissolved in acetate/ salt solution. A special reaction mixture (concanavalin-A) is then added to the solution to precipitate the amylopectin

Starches

SEC

Con. A

DSC

IBC

ae wx Du su2 du su2 ae du Ae

nd 27 24 34 30 54

7 45 50 58 56 63

nd 55 58 66 64 60

14 45 45 60 56 63

nd: not detected. Source: Planchot V, Gerard C, Bertoft E, and Colonna P (2001) An approach to structural analysis of granules using genetically modified starches. In: Barsby TL, Donald AM, and Frazier PJ (eds.) Advances in Structure and Function, pp. 104–128. UK: The Royal Society of Chemistry.

component and the resulting supernatant after centrifugation contains only the amylose component. However, a comparative study of size exclusion chromatography (SEC), differentialscanning calorimetry, iodine-binding capacity (IB), and concanavalin-A, where SEC was used as the reference method, has revealed that IB, differential-scanning calorimetry (DSC), and concanavalin-A resulted in an overestimation in the determination of amylose content of mutant maize starches (Table 2). As other alternative methods to the conventional iodine–amylose complex formation, spectroscopic methods have been developed recently. These techniques provide advantages such as ease of sample preparation, speed, and applicability to online monitoring in the process control situation compared with other techniques. Near-infrared (IR)-reflectance analysis has been successfully introduced in determining the amylose content of waxy, normal, and high amylose maize, unground brown or milled rice, and whole grain maize samples. Raman spectroscopy on the other hand is becoming more popular as a quantitative analytical technique in the food industry and has shown potential applicability in the estimation of amylose content in maize starches.

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CARBOHYDRATES | Starch: Analysis of Quality

Amylopectin Amylopectin, the highly branched molecule, is usually the major component in the starch granule with a(1–4)-linked glucose linear chains and a(1–6)-linked branch points. Crystalline domains of the starch granules are due to the clustered branches of amylopectin chains that are packed together, whereas the free amylose, amylose complexed with lipids, and branch points of the amylopectin are found in the amorphous region. Alternative arrangement of crystalline and amorphous region was proposed for the semicrystalline starch granule. However, there is no clear demarcation between amorphous and crystalline regions. Crystalline region is less susceptible to enzymatic hydrolysis, water penetration, and other chemical reactions than amorphous region. Amylopectin has a lesser tendency to gelation, retrogradation, and syneresis because of the branched structure. The amount of amylopectin varies among different starches. Waxy varieties contain almost 100% amylopectin. The extent of functional characteristics of starch (viscosity, gelatinization, solubility, texture, gel stability, retrogradation, shear resistance) are directly affected by the amylose/amylopectin ratio. Although amylopectin is the major component of the starch granule, there is no convenient method developed for direct estimation of amylopectin and studies on amylopectin are dependent on development of enzymatic and instrumental methods. Average structural properties of whole molecule and impact of internal structure of clusters on crystallization have been studied by means of enzymatic and SEC. It has been shown that the combined application of preparative and analytical size exclusion chromatography with multiple detection, precipitation techniques, and enzymatic de-branching provides the most detailed analytical insight on the microstructural properties of amylopectin.

Function Related to Morphological Characteristics of Starch Granules Granules are the basic physical structural unit of starch. The size, shape, and other morphological characters of starch granules are extremely diverse (Table 1). The shape of the starch granule can be spherical, disk, polygonal, or elongated. In general, cereal starches have smaller granules compared to tuber and root starches. Most tuber and root starch granules have a simple size distribution. In some starches, such as barley and wheat, two different granular size populations exist, i.e., a bimodal distribution. Granular size and morphology have recently received more attention, e.g., the size of granules is important in determining taste and mouth feel of some starchbased fat mimetics. Some specific industrial applications of starch are related to size and the size distribution of starch granules. For example, the small size of rice starch granules makes it highly suitable for laundry use. Most of the physicochemical properties of native starch are highly correlated with the size of the starch granules. Larger size granules tend to swell more than smaller granules, whereas smaller size granules are more susceptible to enzymatic hydrolysis. The outer surface of starch granules also plays a key role in many applications of starch. Electron microscopic images have revealed that tuber

and root starches show no sign of any pores on the granular surface. However, pores are present on the surface of maize, sorghum, and millet starch granules. Pores on granule surfaces increase accessibility of a-amylase to the granule interior resulting in increased enzymatic hydrolysis. Microscopic analysis provides information on surface features and size of starch granules.

Characterization and Analysis of Starch Thermal Properties Gelatinization Gelatinization is one of the most important processes affecting starch. It occurs when starch is heated in excess water, when irreversible granular swelling, native crystallites melting, loss of granular order, loss of birefringence, and starch solubilization take place. The extent of these changes depends on type of starch, starch concentration, temperature, presence of other solutes, and shear applied during the gelatinization process. As a result of the above changes during gelatinization, the starch paste develops viscosity, the basis of most technological usefulness of starch as an ingredient in food and nonfood applications. In the majority of food applications, starch functions (e.g., imparts texture on consumption) in a gelatinized form. Several concepts have been proposed to explain the gelatinization process. Granular swelling acts primarily as a driver to destabilize the starch crystallites. Recently, a model was proposed to explain the phenomena involved in gelatinization and hydration of starch based on the side-chain liquid crystalline. In this model, lamellae in starch are considered in terms of three components – (1) backbone, (2) side-chain, and (3) double helices. The degree of mobility of these three components, coupled with the helix–coil transition, give starch its distinctive properties in gelatinization. Gelatinization is influenced by many factors such as, botanical source of starch, water content, and added solutes. Several methods have been proposed to study the effect of water content on thermal stability. Depending on the water content available during gelatinization, changes in endothermic transition have been detected in terms of number and the position of the differential scanning calorimetric endotherms. Only one endotherm is detectable at higher levels of moisture content while two endothermic transitions are reported at the low-moisture-content level for some starches where low temperature and higher temperature endotherms are designated as G1 and M1 respectively (Figure 1). In addition to two endothermic transactions at lower moisture content, peaks are shifted to higher temperature, indicating need for higher thermal energy to melt the starch crystallites at low moisture content. If there is sufficient water available in gelatinization, then crystallites melt cooperatively, resulting in a single endotherm. Two endothermic transition peaks in insufficient water could be attributed to the differences in the stability of starch crystallites, which melt over different temperatures, less stable crystallites melt first and the others are next causing the second endotherm. Redistribution of water between crystalline domain and gelatinized starch could also result in two endothermic transitions, in which the first endotherm could be attributed to melting of starch crystals in excess water. Much research has been conducted to investigate the


201

Temperature (°C)

To

Tc

Endothermic heat flow

ΔHcx ΔHgel

M2

Tcx M1

G

Tm

Figure 1 Schematic representation of DSC thermograms obtained for wheat starch heating. (Eliasson A-C (2003) Utilization of thermal properties for understanding baking and salting processes. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 65–115. New York: Marcel Dekker.) Table 3

Gelatinization parameters of some starches measured by differential scanning calorimetry

Starch

Starch–water ratio

To

Tp

Tc

To

Wheat Maize normal Maize waxy Potato Cassava Sweet potato Taro True yam (Dioscorea)

1:3 1:3 1:3 1:3 1:3 1:3 1:3 1:3

57.0 65.3 62.9 59.6 63.0 60.0 76.8 75.0

62.0 71.3 72.8 66.3 71.5 69.0 83.0 80.0

67.0 80.9 84.3 76.0 81.5 82.5 95.2 90.2

10.0 15.6 21.4 16.4 18.7 22.5 18.4 16.5

Tc

DH 9.7 11.0 13.6 16.3 12.3 7.1 14.5 17.8

To onset temperature ( C); Tp peak temperature ( C); Tc conclusion temperature ( C). DH enthalpy (J g 1). Sources: Gunaratne A and Hoover R (2002) Effect of heat-moisture treatment on the structure and physicochemical properties of tuber and root starches. Carbohydrate Polymers 49: 425–437; and Hoover R, Vasanthan T, Senanayake NJ, and Martin AM (1994) The effects of defatting and heat-moisture treatment on the retrogradation of starch gels from wheat, oat, potato, and lentil. Carbohydrate Research 261: 13–24.

influence of added solutes such as sugars, emulsifiers, and electrolytes (such as sodium chloride), which are widely applied in food industry on starch behavior. Sugars have shown to increase the gelatinization temperature but not to affect endothermic heat absorption. Quality of various food products, bread and cakes, thickening and gelling of sauce, pie filling, and extrusion of cereals are highly dependent on starch–water interaction. Increased gelatinization, when sugars are added to starch paste could be due to decrease of water availability for the gelatinization, binding water to sugar molecules. However, it was reported that sugar acts as an antiplasticizer rather than gelatinizer through the effect on waterbinding capability. Increased sugar concentration decreases the plasticization effect requiring more heat energy to achieve the gelatinization. The extent of the influence of sugars on gelatinization, swelling, and viscosity differs depending on the type of sugars and salts used when compared on a molar basis. Monosaccharides are less effective than disaccharides except maltose; among disaccharides, sucrose is more effective.

Methods in the analysis of starch gelatinization There are several methods to analyze the gelatinization process, such as DSC, Kofler hot-stage microscopy, light microscopy, electron microscopy, X-ray crystallography, enzymatic analysis, nuclear magnetic resonance (NMR), pulsed nuclear magnetic

resonance, small angle X-ray scattering, and small angle neutron scattering, Brabender viscoamylography (BV), and Rapid Visco Analysis. DSC, the most widely used method, measures the dissociation parameters, TBoB (onset), TBpB (peak), TBcB (conclusion), and DH (endothermic heat absorption), of starch crystallites in gelatinization (Figure 1). DH is the area below the transition endotherm. Gelatinization parameters of starches from different botanical sources measured by DSC are presented in Table 3. In addition, DSC can be used to study the glass transition temperatures of various starchy food products. Gelatinization temperatures are influenced more by the granular architecture than the amylose–amylopectin ratio and depend on the degree of starch crystallite perfection, whereas endothermic heat absorption reflects the quality and amount of starch crystallites. Analysis of gelatinization parameters of starch using DSC was first reported in 1971. Gelatinization parameters measured by DSC can be affected by sample preparation, baseline application, pan selection, method of adding water, sample mass, heating rate, and moisture equilibration time. Thermal behavior of amylose–lipid complex as well as formation of amylose–lipid inclusion with various molecules such as fatty acids and emulsifiers can also be detected by DSC. Characterization of amylose–lipid complex in cereal starches and influence of amylose–lipid complex on starch properties are well documented. Some of the internal lipids in cereal


starch is thought to be complexed with amylose to form the amylose–lipid complex, which is dissociated at higher temperature (M2 endotherm in Figure 1) than that of normal starch crystallites (Figure 1 and Table 4). Although DSC is widely used to study gelatinization, the small sample size used can limit its real applications. In a comparative study of maize starch gelatinization with DSC and NMR, it was reported that NMR could provide much better performance in the analysis of gelatinization for larger samples than DSC. Gelatinization temperature of Peruvian carrot, potato, and maize starch measured by Rapid Visco Analyzer (RVA) and BV, and DSC have shown different values for different methods. This indicates the need for multiple analytical techniques for a meaningful understanding of gelatinization along with careful specification (and preferably standardization) of experimental conditions used. Table 5 shows the differences in gelatinization parameters measured by different techniques for the same starch.

Pasting properties Starch heated in excess water undergoes various changes as a result of heat and moisture transfer. Gelatinization and pasting occur in the same system and have often been used to describe all the changes that occur. Gelatinization may be used to refer to early changes whereas pasting includes later changes. Starch gelatinization is defined as the collapse of the starch granule manifested in irreversible melting, loss of birefringence, and starch solubilization. The point of gelatinization, and the range over which it occurs is governed by starch concentration, Table 4 starches

Measurement of pasting properties The BV is the most widely established method for determining pasting properties, although it has some methodological and geometrical shortcomings. This apparatus measures the development of viscosity when a starch–water suspension is subjected to a programmed heating and cooling cycle under a shear force. The temperature at which viscosity begins to increase is termed pasting temperature. With further heating, granular swelling increases the viscosity to reach a peak. Further heating at elevated temperature under shear force tends to disintegrate the swollen granules resulting in decrease of viscosity. Upon cooling the starch paste in the next stage, there is a tendency, mainly due to amylose chain reassociation, to increase viscosity. Therefore, a typical pasting profile exhibits

DSC parameters of amylose–lipid complex of some cereal

Starch

Condition

Tcx

DHcx

Wheat Rye Barley High-amylose barley

50% water 50% water 50% water 50% water

110.1 107.8 110.3 110.8

1.4 0.8 1.8 2.8

Tcx (peak temperature); DHcx (transition enthalpy). Source: Fredriksson H, Silverio J, Andersson R, Eliasson A-C, and Aman P (1998) The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches. Carbohydrate Polymers 35: 119–134.

Table 5

method of observation, granular type, and heterogeneity. Pasting is defined as the phenomena following gelatinization in the dissolution of starch, involving granular swelling, exudation of molecular components from the granule, and eventually total disruption of the granules. The schematic representation of granular changes and viscosity development that occurs during pasting is shown in Figure 2.

Viscosity

202

Time/temperature Figure 2 Schematic representation of granular changes and viscosity development during starch pasting (Daniel JR and Whistler RL (1985) Principal changes in starch during food processing. In: Richardson TR and Finley JW (eds.) Chemical Changes in Food During Processing, pp. 305–326. Westport, CT: Avi Publishing Co.).

Gelatinization temperature range of some starches as measured with different techniques: DSC, NMR, BV, and RVA Gelatinization temperature range

Starch Maize Waxy maize Potato Cocoyam Peruvian carrot a

Starch–water ratio

DSC

NMR

1:2 1:2 1:2 1:2 1:2

58.1–79.6 56.4–81.3 49.2–73.9 74–87 56–73

59–67 60–67 53–60

BVa

RVAb

76–86 78–95 62–95

75–86 85–95 68–95

Starch concentration (4%) except Peruvian carrot (6%). Starch concentration (8%). Sources: Perez EE, Breene WM, and Bahnassey YA (1998) Gelatinization profiles of cassava, sagu, and arrowroot native starches as measured with different thermal and mechanical methods. Starch/Starke 50: 14–16 and Gonera A and Cornillon P (2002) Gelatinization of starch/gum/sugar systems studied by using DSC, NMR, and CSLM. Starch/Starke 54: 508–516. b

CARBOHYDRATES | Starch: Analysis of Quality three distinct viscosity developments, peak viscosity, hot paste viscosity, and cold paste viscosity (Figure 3). Pasting curves vary according to botanical source of the starch, starch concentration, and the programmed heating–cooling cycle chosen. Among the native starches, potato shows the highest peak viscosity, and generally, low peak viscosity and higher setbacks can be detected in normal cereal starches compared to tuber and root starches. Waxy cereal starches, on the other hand, behave more like the tuber and root starches (Figure 4). According to the characteristics of pasting curves, starch has been categorized into four groups as, high swelling starch (potato, cassava, waxy cereals, ionic starch derivatives), moderate swelling starch (normal cereal starch), restricted swelling starch (cross-linked starch), and highly restricted starch

250

100 Cool paste viscosity Peak viscosity

Viscosity (RVU)

200

Setback

Breakdown

150

100

60

40

Hot paste viscosity

20

50

0

0 0

3

6 9 Time (min)

12

(starches >55% amylose). The above four different categories of starch exhibit the following pasting properties respectively: high peak followed by rapid and major thinning during cooking; lower peak and much less thinning; no peak but maintain high viscosity during cooking; and no swelling to gave a viscous paste at normal concentration. Because of some technical shortcomings with the BV, such as large sample size requirement and inability to program the temperature profiles, a more recent equipment, the RVA, has become popular for analyzing pasting properties. The RVA differs from the Brabender instrument due to rapid heating rate and stronger mixing action. However, controlled heating rate to 1.5 C min 1 in RVA provides similar results to those observed in the BV. Comparative study of pasting properties of cassava, ‘sago’ (sagu), and arrowroot using Brabender and RVA has shown that both techniques provide similar pasting patterns (Table 6). Pasting curves of some of the starches determined by BV and RVA is presented in Figures 4 and 5.

Swelling and Solubility

80

Peak time

Temperature (°C)

Temperature profile

203

15

Native starch granules are insoluble in water. Although small amounts of water can be absorbed at room temperature, granular swelling is limited in intact granules. During heating in excess water, after the onset of gelatinization, granules begin to swell rapidly, losing the polarization crosses. The extent of the swelling power and solubility depends on the magnitude of the starch chain interaction within the amorphous and crystalline domain, size of the starch granules, amylose content, bound lipids, starch damage, temperature, and molecular characteristics and the amount of amylose–amylopectin ratio. Table 1 presents the swelling and solubility of some starches at 95 C. High amylose content lowers the swelling whereas larger granules show greater swelling. The swelling power and solubility provide information on the relative strength of bonding within the granules.

Figure 3 Characteristics of a typical pasting curve.

Methods used to analyze starch swelling

Time 0

30

60

90

120

150

180 min

3000 2500

5% starch by weight

Potato

2000

Viscosity (BU)

1500 Maize

Tapioca

1000

Waxy maize 500 Wheat

0 50

95 Heat

95 Hold

95

50 Cool

50 Hold

50 °C

Temperature

Figure 4 Brabender Viscoamylogram of starches from different botanical sources.

Swelling volume, swelling power or swelling factor, all measure the extent of granular swelling at a given temperature, when starch is heated in excess water. However, swelling factor measures only the intergranular water content and hence reflects the true swelling of starch granules at a given temperature. Swelling power measures the weight of swollen starch sediment relative to the initial starch dry weight, and is expressed as the ratio of the wet sediment to the initial weight of the dry starch. Measuring the soluble carbohydrate that dissolved in the supernatant either by oven drying or colorimetric method enables solubility, the ratio between the amount of soluble carbohydrate to the initial weight of dry starch to be obtained. Swelling volume is a modified version in which programmed shaking of starch suspension is used instead of stirring, and measurement is of the volume expanded due to granular swelling. Swelling factor is the ratio of volume of swollen starch granule to the volume of the dry starch. Swelling factor measures only the intragranular water content. Calculation of the swelling factor is based on starch weight adjusted to 10% moisture assuming the density of 1.4 mg ml 1. The basic principle of this method is the measurement of the volume of water absorbed by starch granules


204 Table 6

Pasting properties of cassava, sago, and arrowroot as determined by BV and RVA

Starch

Method a

Cassava Sago Arrowroot

BV RVAb BV RVA BV RVA

GT

PV

FV at 95 C

V at 50 C

BD

SB

Consistency

68–90 73–90 68–90 73–95 75–90 79–92

50 23 300 60 150 30

40 9 460 22 150 14

40 17 660 37 170 18

10 14 160 38 0 16

10 6 360 23 20 12

0 8 200 15 20 4

GT – gelatinization temperature range; PV – peak viscosity; FV – final viscosity; V – viscosity; BD – breakdown; SB – setback. a Starch concentration 4.3%. b Starch concentration 8%. Source: Perez EE, Breene WM, and Bahnassey YA (1998) Gelatinization profiles of cassava, sagu, and arrowroot native starches as measured with different thermal and mechanical methods. Starch/Starke 50: 14–16.

600

Potato Sweet potato 300

60

Maize

150

Temperature (⬚C)

80

450 Viscosity (RVU)

Effect of retrogradation on quality of starch-based food products

100

Retrogradation has desirable as well as undesirable effects on quality of starch-based food products. Mostly it is undesirable. Bread staling is one of the main undesirable effects of retrogradation. Although several factors contribute to bread staling, it has been found that retrogradation is the key physical change associated with bread staling. Retrogradation sometimes aids processing in some food products such as hardening of parboiled rice and to improve textural characteristics of certain types of noodles.

40

Determination of starch retrogradation Wheat

0 0

5

10 15 Time (min)

Rice 20

25

Figure 5 Pasting curves obtained for different starches from Rapid Visco Analyzer.

heated in excess water, based on the observation that blue dextran dye (molecular weight 2 10P6P) will dissolve in supernatant and interstitial water. The advantages of this method over the others are the ability to measure the true swelling and the high accuracy.

Retrogradation Reassociation of starch polymers via hydrogen bonding in gelatinized starch on cooling is generally termed retrogradation, and is time- and temperature-dependent. Starch gels tend to undergo structural changes during storage as they are metastable and nonequilibrium systems. Both amylose and amylopectin are involved in retrogradation, where rapid amylose aggregation causes a short-term development of starch gel providing initial firmness. Branched amylopectin recrystallization, particularly outer branches of amylopectin molecule, is correlated with long-term development of starch gel. Several factors influence starch retrogradation, such as, starch concentration, storage temperature, initial heating temperature, chain length distribution of amylopectin, molecular size of amylose, lipids, and physical and chemical modification of starch.

Several methods have been developed to determine starch retrogradation, because of its great influence on industrybased food and nonfood products, such as DSC, X-ray analysis, rheological methods, and spectroscopic methods.

Differential scanning calorimetry Several studies on retrogradation behavior have been examined using DSC techniques. DSC is probably the best thermal analysis method to study the starch-aging process for different systems. However, dissociation parameters of stronger crystals that formed due to the association of amylose are usually difficult to detect using DSC, since those crystals dissociate at higher temperature (>120 C). Therefore, DSC usually measures the melting of recrystallized amylopectin, that occurs at the same temperature interval as gelatinization (Figure 6), when reheating of retrograded starch gel, in which heat absorption, the area under the endotherm (DH), and transition temperatures can be detected (Table 7). Crystals formed by the association of amylose chains would be possible to detect using DSC pans, that can withstand a higher temperature range (Figure 7). Characteristic smaller endosperms were usually reported for the retrograded gel compared with the gelatinization endotherm of their native counterpart. However, it was reported that retrograded starch crystals melt over a wide range of temperature indicating the more heterogeneous crystal perfection than those of native starch crystals. Melting temperature indicates the perfection of recrystallized amylopectin, the quality and heterogeneity. Although DSC has some advantages especially that it is not time consuming, has a wide range of applications, and measures directly, it has some weakness particularly its small


205

Heating steps Bread crumb 1 2 Endothermic heat flow

Wheat starch

Endothermic heat flow

3 Amylopectin

Amylose 0.05 mcal s–1

40

60

80

4

5

60

100

Temperature (°C)

(To

Wheat

6/6 6/30 6/306/30 6/40 6/40/6/40 6/6 6/30 6/30/6/30 6/40 6/40/6/40

40.4–63.3 48.5–64.7 49.3–65.4 58.0–68.5 58.2–69.0 35.2–78.2 48.8–78.3 49.7–78.1 59.2–78.3 60.7–79.5

Potato

Tc)

180

Figure 7 DSC curves obtained for amylose retrogradation. (Eliasson A-C (2003) Utilization of thermal properties for understanding baking and salting processes. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 65–115. New York: Marcel Dekker.)

Table 8 Table 7 DSC characteristics of amylopectin retrogradation of wheat and potato starch gel (1:1) under different storage conditions Storage conditiona

140

Temperature (°C)

Figure 6 Differential scanning calorimetric curves for different retrograded food systems. (Eliasson A-C (2003) Utilization of thermal properties for understanding baking and salting processes. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 65–115. New York: Marcel Dekker.)

Starch

100

DH (J g

1

AMP)

8.1 7.7 9.4 4.5 5.9 13.3 11.7 13.1 9.9 10.6

To Tc – transition temperature range; DH – enthalpy; AMP – amylopectin. a Each number indicates the temperature for one day of storage; 6/40 means one day at 60 C, followed by one day at 40 C. Source: Silverio J, Fredriksson H, Andersson R, Eliasson A-C, and Aman P (2000) The effect of temperature cycling on the amylopectin retrogradation of starches with different amylopectin unit-chain length distribution. Carbohydrate Polymers 42: 175–184.

sample size and inability to determine retrogradation in dilute starch paste. More often DSC coupled with X-ray analysis provides better performance in characterizing retrogradation.

X-ray analysis X-ray analysis can be applied to detect the presence and nature of crystallinity in native starch granules as well as crystals formed in aging starch gels. In native starch, the crystallinity is due to the amylopectin components and the crystal domains are constructed mainly of A chains and outer B chains of amylopectin. Native starches can be categorized into three groups according to their X-ray diffraction pattern. The A type

X-ray pattern and crystallinity of different starches

Starch

X-ray pattern

Crystallinity

Rice Oat Wheat Rye Amylomaize Corn Waxy rice Potato Cassava True yam (Dioscorea) Taro Sweet potato

A A A A B A A A C B A C

38 33 36 34 15–22 40 37 30 37 32 31 38

Sources: Zobel (1988b) and Gunaratne A and Hoover R (2002) Effect of heat-moisture treatment on the structure and physicochemical properties of tuber and root starches. Carbohydrate Polymers 49: 425–437.

crystallinity is found mainly in cereal starches. Most tuber and root starches exhibit typical B type X-ray pattern and C type is intermediate between A and B types, shown in legumes, cassava, and some varieties of sweet potato (Table 8). X-ray analysis of retrograded starch has shown that aging gels form B-type crystals irrespective of the native starch. Some research using wide range and small angle X-ray diffraction, shows that crystalline formation in starch paste occurred primarily due to amylopectin aggregation, whereas amylose provides a template effect and highly ordered amylose aggregation does not necessarily possess a crystalline nature but accelerates the amylopectin reassociation. Recently, more information on bread staling has been revealed by X-ray analysis. Aggregation of starch polymers that formed crystals in bread staling was shown from X-ray analysis; however, NMR and FTIR techniques are better

206 Table 9

CARBOHYDRATES | Starch: Analysis of Quality Gel textural properties of maize starches differing in amylose content

Sample

Probe type

Hardness (g)

Adhesiveness

Springiness

Cohesiveness

Regular Waxy High amylose Waxy High amylose

5 (mm)

75

219

0.94

0.51

20 (mm)

19 28 128

18 18 160

0.61 0.94 0.85

0.031 0.81 0.35

Starch paste after RVA analysis kept at 25 C for 24 h Source: Liu H, Ramsden L, and Corke H (1999) Physical properties and enzymatic digestibility of hydroxypropylated ae, wx, and normal maize starch. Carbohydrate Polymers 40: 175–182.

at detecting minor differences of starch polymer aggregation than X-ray analysis.

•

Rheological methods

•

Measurement of pasting parameters, analysis of textural properties of starch paste using texture analyzer, and small deformation dynamic techniques oscillatory rheometry can be applied to the behavior of starch. Pasting behavior of starch indicates the trend of starch retrogradation. In a typical pasting profile, the magnitude of setback reflects the tendency of mainly amylose polymer reassociation in a starch paste. Several investigations have been performed to study the properties of aging breads using viscometry and have observed a tendency of decreased peak viscosity when bread staling progresses. Recently there is a growing interest, especially in industry, in use of texture analyzers that can directly and rapidly measure the textural properties such as hardness, stickiness, cohesiveness, adhesiveness, fracturability of starch paste (Table 9). Long-term reliability and accuracy, direct measurement, time saving, and technical feasibility of the texture analyzer increases its attractiveness among food technologists. The main issue which requires continuing work is that of instrumental to sensory correspondence, i.e., whether the texture analysis profile is adequately predictive of the sensory traits important to the consumer. Many additional methods can be employed to detect retrogradation. No individual method is able to fully characterize all the events of the starch-aging process. DSC measures only the transition of heat energy in the melting of crystal aggregates, X-ray measures the presence and characteristics of retrograded starch crystals, and texture analysis provides textural parameters for the aged starch gel. Therefore, it is clear that a multiple analytical technique approach for the advance detection of retrogradation behavior is necessary. For example, a study of bread staling with multiple techniques, DSC, FTIR, and NIR, led to greater understanding of the process than would be possible with each individual technique used alone.


• • •

What are the chemical and functional differences between amylose and amylopectin? Explain the terms ‘waxy’ and ‘non-waxy’ in terms of starch composition and function. Describe the range of methods available to determine amylose:amylopectin ratio. What situations might suit the use of one of these methods versus another?

•

Describe the process of ‘starch pasting’ and the methods for its analysis. How does this property affect the uses of starch in the food industry? What is meant by ‘starch retrogradation’? Explain the resulting beneficial and undesirable consequences for food products. What are the events of the ‘starch-aging process’? How do these phenomena affect the functional use of starch in food and non-food uses?


•

•

•

Explore the range of mutant types of grain species for which wide differences in amylose:amylopectin ratio have been developed. What are the resulting differences in functional properties and thus in applications in utilization? ‘Starch is insoluble in water.’ Do you agree with this statement? Under what circumstances and for which forms of starch is the statement true and untrue? Explain how the ‘solubility’ (or not) of starch is critical to its utilization. Explore how the presence of starch-degrading enzymes (such as amylase enzymes) increases starch solubility and thus its functional properties. What lessons might be learned from research into the chain lengths and degree of branching of the various starch molecules.

See also: Carbohydrates: Carbohydrate Metabolism; Glycemic Index, Glycemic Load, and Their Health Benefits; Resistant Starch and Health; Starch: Chemistry; Starch: Starch Architecture and Structure; Starch: Synthesis; Food-quality Testing: Noodles: Testing for Quality; Pasta: Quality Testing Methods; Rice: Eating Quality; Genetics of Grains: Maize: Other Maize Mutants; Maize: Quality Protein Maize; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; The Composition of Food Grains and Grain-Based Products; Processing of Grains: Starch: Modification; Starch: Uses of Native Starch; Wheat Processing: Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties.

Further Reading Collado LS and Corke H (2003) Starch properties and functionalities. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 473–506. New York: Marcel Dekker.

CARBOHYDRATES | Starch: Analysis of Quality Daniel JR and Whistler RL (1985) Principal changes in starch during food processing. In: Richardson TR and Finley JW (eds.) Chemical Changes in Food During Processing, pp. 305–326. Westport, CT: AVI Publishing Co. Eliasson A-C (2003) Utilization of thermal properties for understanding baking and salting processes. In: Kaletunc G and Breslauer KJ (eds.) Characterization of Cereals and Flours, pp. 65–115. New York: Marcel Dekker. Fredriksson H, Silverio J, Andersson R, Eliasson A-C, and Aman P (1998) The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches. Carbohydrate Polymers 35: 119–134. Gonera A and Cornillon P (2002) Gelatinization of starch/gum/sugar systems studied by using DSC, NMR, and CSLM. Starch/Starke 54: 508–516. Gunaratne A and Hoover R (2002) Effect of heat-moisture treatment on the structure and physicochemical properties of tuber and root starches. Carbohydrate Polymers 49: 425–437. Hoover R, Vasanthan T, Senanayake NJ, and Martin AM (1994) The effects of defatting and heat-moisture treatment on the retrogradation of starch gels from wheat, oat, potato, and lentil. Carbohydrate Research 261: 13–24. Jane J, Kasemsuwan T, Leas S, Zobel HF, and Robyt JF (1994) Anthology of starch granules morphology by scanning electron microscope. Starch/Starke 46: 121. Karim AA, Norziah MH, and Seow CC (2000) Methods for the study of starch retrogradation. Food Chemistry 71: 9–36. Liu H, Ramsden L, and Corke H (1999) Physical properties and enzymatic digestibility of hydroxypropylated ae, wx, and normal maize starch. Carbohydrate Polymers 40: 175–182. Perez EE, Breene WM, and Bahnassey YA (1998) Gelatinization profiles of cassava, sagu, and arrowroot native starches as measured with different thermal and mechanical methods. Starch/Starke 50: 14–16.

207

Phillips DL, Xing J, Liu H, Pan DH, and Corke H (1999) Potential use of Raman spectroscopy for the determination of amylose content in maize starch. Cereal Chemistry 76: 821–823. Planchot V, Gerard C, Bertoft E, and Colonna P (2001) An approach to structural analysis of granules using genetically modified starches. In: Barsby TL, Donald AM, and Frazier PJ (eds.) Advances in Structure and Function, pp. 104–128. UK: The Royal Society of Chemistry. Praznik W, Huber A, Watzinger S, and Beck RHF (1994) Molecular characteristics of high amylose starches. Starch/Starke 46: 88–94. Silverio J, Fredriksson H, Andersson R, Eliasson A-C, and Aman P (2000) The effect of temperature cycling on the amylopectin retrogradation of starches with different amylopectin unit-chain length distribution. Carbohydrate Polymers 42: 175–184. Tester RF and Morrison WR (1990) Swelling and gelatinization of cereal starches 1. Effects of amylopectin, amylose and lipids. Cereal Chemistry 67: 551–557. Yu L and Christie G (2001) Measurement of starch thermal transitions using differential scanning calorimetry. Carbohydrate Polymers 46: 179–184. Zobel HF (1988) Molecules to granules: a comprehensive starch review. Starch/Sta˜rke 40: 44–50.

Relevant Website starch.dk http://www.starch.dk – Website of the International Starch Institute, Denmark, with useful links to other starch-related sites.

Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides GB Fincher, Australian Research Council Centre of Excellence in Plant Cell Walls, University of Adelaide, Glen Osmond, SA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Structure and function of cell wall polysaccharides. Fine structure of wall polysaccharides and how these vary in different tissues and at different stages of development. How fine structure affects physicochemical properties, including viscosity, solution behavior, and gelation. Genes involved in the biosynthesis, remodeling, and degradation of cell wall polysaccharides. The importance of solubility and viscosity in cereal processing and human health. The benefits of dietary fiber from cereal grains in reducing the risk of serious human diseases, including type II diabetes, colorectal cancer, and cardiovascular disease.

Learning Objectives

• • •

To know how chemical structure affects solution properties. To understand how cell wall polysaccharides contribute to dietary fiber. To know the structure–function relationships in cereal processing and nutrition.

Introduction The nonstarchy polysaccharides of cereal grains include cellulose, (1 ! 3, 1 ! 4)-b-D-glucans, heteroxylans (arabinoxylans), glucomannans, xyloglucans, pectic polysaccharides, callose, fructans, and arabinogalactan proteins (AGPs). With the exception of the fructans and the AGPs, all are key components of the walls of cells in the various tissues that comprise the grain. In this article, the chemistry and physicochemical properties of nonstarchy polysaccharides from cereal grains, which are important in human and animal nutrition and which have an impact in grain utilization and in cereal technology, will be described. The cells of grain tissues have diverse functions during development, during dormancy, and after germination. The pericarp and seed coat tissues are concerned with the protection of the seed during development and dormancy. However, at grain maturity, these tissues are nonliving and consist almost entirely of cell wall residues. The nucellar tissue between the seed coat and the aleurone surface is involved in the transfer of nutrients to the developing grain but collapses at maturity to leave compressed cell wall remnants in the mature grain. Cells of the starchy endosperm are nonliving in the mature grain, but are packed with starch and storage protein and, in most cereal species, have relatively thin cell walls. In contrast, the thick-walled, nucleated, aleurone cells are living at grain maturity and are packed with membrane fragments, protein bodies, and lipid droplets. The living embryonic tissues of the grain are at least partly differentiated into functional cell types

208

that are eventually found in shoots and roots. At the interface of the embryo and the starchy endosperm lies the scutellum, which delivers nutrients to the developing endosperm and plays a dual role during germination; in the first instance, the scutellar epithelial layer secretes degradative enzymes into the proximal region of the starchy endosperm, but later, it translocates digestion products of the endosperm reserves into the developing embryo. The cell wall compositions and organization of the cell types found in the tissues of the grain reflect these different functions and, in turn, determine the nutritional impact and behavior of various grain parts in technical operations during grain utilization and processing. Together, the nonstarchy polysaccharides usually constitute <10% by weight of the grain (Table 1) but can nevertheless be key determinants of grain quality. Although the precise physical relationships between individual nonstarchy polysaccharides and other wall components have not been described, it is generally considered that in the wall, microfibrils of cellulose are embedded in a matrix phase that consists mainly of noncellulosic polysaccharides and smaller amounts of protein. Lignification of walls in the outer layers of the grain is observed, but little or no lignification is found in most cells of the endosperm and embryo. Wall integrity is maintained predominantly through extensive noncovalent interactions, especially hydrogen bonding, between the matrix phase and the microfibrillar constituents. In the walls of some grain tissues, covalent associations between heteroxylans, lignin, and proteins are present. Indeed, there have been several recent reports of previously unrecognized covalent linkages between noncellulosic polysaccharides of plant cell walls more generally. The extent of covalent associations between components also varies with the wall type and genotype. The relative ease of extraction of noncellulosic polysaccharides from the different wall types in cereal grains is strongly influenced by both noncovalent and covalent interactions. Cell walls have been isolated and analyzed from some cereal grains, in particular aleurone and starchy endosperm walls from wheat and barley (Table 1). Noncellulosic polysaccharides, especially heteroxylans and (1 ! 3, 1 ! 4)-b-D-glucans, constitute a relatively high proportion of the walls of the aleurone and starchy endosperm and probably also of the scutellum. Cellulose contents are correspondingly lower (Table 2). The generally low cellulose content of these walls, together with the fact that the walls of the endosperm contain no lignin, might be related functionally to a limited requirement for structural rigidity of walls in central regions of the grain and to a requirement for rapid depolymerization of wall components following germination of the grain. There is some indirect information on the composition of starchy endosperm walls from rice, which are extremely thin and appear to consist mostly of cellulose and heteroxylans. The (1 ! 3, 1 ! 4)-b-D-glucan levels appear to be low, and varying amounts of pectin, xyloglucan, and glucomannan have been reported in rice endosperm walls.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00090-5

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides Table 1

209

Composition of cell walls of cereal grains (% by weight) Component

Cereal

Origin of cell wall

Cellulose

Glucomannan

Wheat (Triticum aestivum L.)

Aleurone Starchy endosperm Bran (pericarp, seed coat, and aleurone) Beeswing bran (outer pericarp) Aleurone Starchy endosperm Bran Bran (pericarp, seed coat, and aleurone)

2 2 29

2 2

Barley (Hordeum vulgare L.) Rice (Oryza sativa L.) Maize (Zea mays L.)

(1 ! 3, 1 ! 4)b-D-Glucan

Heteroxylan

29 20 6

65 70 64

8.3

9.2

60

12

6

12

6 5 8

30 2 2 9 23

2 2 3

26 75 6

Pectin

Lignin

Proteina 1

71 20 60 67

8

a

Values for protein may include cellular proteins.

Table 2

Content of (1 ! 3, 1 ! 4)-b-D-glucan and heteroxylan in whole cereal grains (gram per 100 g DW) (1 ! 3, 1 ! 4)-b-D-Glucan

Arabinoxylan

Cereal

Total

Water-extractable

Total

Water-extractable

Wheat (Triticum aestivum L.) Durum (Triticum durum) Spelt (Triticum aestivum ssp. spelta) Barley (Hordeum vulgare L.) Hull-less Waxy hull-less Rice (Oryza sativa L.) Sorghum (Sorghum bicolor L.) Rye (Secale cereale L.) Rye-derived wheats (1B/1R translocations) Maize (Zea mays L.) Oats (Avena sativa L.) Triticale

0.5–2.3 0.5–0.6 0.57 2–10 3.9–5.4 6–15 0.13 1.1–6.2 1.0–2.0

0.02 0

4.0–9.0 ? ? 4–8

0.3–0.9

0.8–1.7 3.8–6.1 0.34–1.8

Up to 50% 1.0–2.7 0.03

3.7–5.0 0

? ? 7.1–12.2 5.2–5.5 5.1–6.8 2.2–4.1 5.8–7.4

0.4

0.6–2.4 4.6 0.2

?, data unavailable.

In walls of cells in the multiple tissue layers of the maternally derived, pericarp–seed coat, which provides protection for the embryo and endosperm and which is not mobilized during germination, cellulose and lignin contents are much higher and the concentrations of noncellulosic polysaccharides are correspondingly lower.

Cellulose Cellulose is a component of all cell walls in cereal grains. However, its concentration varies widely. Cellulose is usually a minor constituent of the primary walls of starchy endosperm and aleurone cells of cereal grains, but its content is much higher in secondary walls of the pericarp and seed coat cells (Table 1). It is a linear homopolymer composed of b-D-glucopyranosyl residues, all of which are (1 ! 4)-linked (Figure 1(a)). Individual molecules have a degree of

polymerization of up to 6000 in primary walls and 14 000 in secondary walls. The molecular chains have an extended, ribbonlike conformation that allows parallel packing of chains into three-dimensional, fibrillar aggregates stabilized by extensive intermolecular hydrogen bonding and van der Waals interactions (Figure 1(b)). These aggregates, termed microfibrils, are easily visible under the electron microscope and may reach diameters of 3 nm in primary walls and 5–10 nm in secondary walls. Within microfibrils, individual cellulose molecules are mostly packed into parallel, highly ordered, crystalline arrays, although there are usually regions where molecular alignment is less ordered. In particular, the surface molecules may have a different conformational and hydrogen-bonding arrangement compared with molecules within the more crystalline interior. Long-held views that the cellulosic microfibrils of higher plant walls contain about 36 individual cellulose molecules have recently been challenged, and it appears likely that the number of individual cellulosic chains per microfibril is considerably lower than originally believed.

210

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides

Figure 1 Cellulose structure. (a) Portion of a cellulose molecule. (b) Crystal structure of cellulose I: (i) projection down the fiber axis c showing the layers (sheets) of cellulose chains hydrogen-bonded in the ac plane but lacking intersheet bonding. The intersheet bonding involves van der Waals interactions between the hydrophobic faces of the glucose units. (ii) View of a layer approximately perpendicular to the ac plane showing the two intramolecular hydrogen bonds in the direction of the fiber axis c and the interchain hydrogen bonds. Reproduced from Kroon-Batenburg LMJ and Kroon J (1995) The crystal and molecular structures of cellulose. Carbohydrates in Europe 12: 15–19, with permission.

Cellulose microfibrils may also associate with water and matrix polysaccharides such as the (1 ! 3, 1 ! 4)-b-D-glucans, heteroxylans (arabinoxylans), and glucomannans. Cellulose is insoluble in water but swells in concentrated sodium hydroxide solutions and may be brought into solution by powerful hydrogen bond-breaking reagents such as N-methylmorpholine N-oxide. Thermal and shear treatments, followed by alkaline peroxidation and shearing to remove lignin, have been used to convert cellulose-rich maize bran (Table 1) to a cellulosic gel for use as a dietary fiber supplement.

(1 ! 3, 1 ! 4)-b-D-Glucans (1! 3, 1 ! 4)-b-D-Glucans, also referred to as mixed-linkage or cereal b-glucans, occur almost exclusively in members of the monocotyledon family Poaceae, to which the cereals and grasses belong, and in related families of the order Poales (sensu stricto). They are important constituents of the walls of the starchy endosperm and aleurone cells of many cereal grains, where they can account for up to 70% by weight of the walls (Table 1). The concentration of (1! 3, 1 ! 4)-b-D-glucans in cereal grains varies across the grain and depends on the genotype, the position of the grain on the spike and environmental factors such as planting location, climatic conditions during grain development, and soil nitrogen. Barley, oat, and rye grains are rich sources of (1! 3, 1 ! 4)-b-D-glucans, whereas wheat, rice, and maize have lower concentrations of the polysaccharide (Table 2). The (1! 3, 1 ! 4)-b-D-glucans are relatively minor components of walls in vegetative tissues of cereals and grasses. A structurally related (1! 3, 1 ! 4)-b-D-glucan, lichenin, is found in the walls of the fungal component of the lichen,

Iceland moss (Cetraria islandica). There have been recent reports of the presence of (1! 3, 1 ! 4)-b-D-glucans in the walls of the horsetail fern (Equisetum spp.), in some bryophytes, various algal species, and the walls of certain fungal pathogens.

Structure (1 ! 3, 1 ! 4)-b-D-Glucans are linear, unbranched polysaccharides in which b-D-glucopyranosyl monomers are polymerized through both (1 ! 4)- and (1 ! 3)-linkages (Figure 2(a)). The ratio of (1 ! 4) to (1 ! 3)-linkages is generally fairly constant, and in the range 2.2–2.6:1, although in the (1 ! 3, 1 ! 4)-b-Dglucan from sorghum endosperm, the ratio is 1.15:1. The two types of linkages are not arranged in regular, repeating sequences. Single (1 ! 3)-linkages are usually separated by two or more (1 ! 4)-linkages. Regions of two or three adjacent (1 ! 4)-linkages predominate, but there is no regularity in the arrangement of these units. Thus, cereal (1 ! 3, 1 ! 4)-b-Dglucans may be considered as (1 ! 3)-b-linked copolymers of cellotriosyl (G4G4GRed), cellotetraosyl (G4G4G4GRed) units, and longer (1 ! 4)-b-D-oligoglucosyl units (Figure 2(b)). The ratio of tri- to tetrasaccharide units varies between cereal species, as follows: wheat (3.0–4.5:1), barley (2.9–3.4:1), rye (2.7:1), and oats (1.8–2.3:1). The ratios vary according to the temperature and conditions of extraction. However, up to 10% of the chain may consist of longer stretches of 5–20 adjacent (1 ! 4)-linkages, and at low frequency, single (1 ! 4)-linkages are detected. An important point related to (1 ! 3, 1 ! 4)-b-D-glucan structure is that the single (1 ! 3)b-D-glucosyl residues will introduce molecular ‘kinks’ into the main chain of the polysaccharide and thereby interrupt what would otherwise be an extended, straight cellulose molecule


211

Figure 2 (a) Portion of a (1 ! 3, 1 ! 4)-b-D-glucan molecule. (b) Distribution of linkages in a (1 ! 3, 1 ! 4)-b-D-glucan. (G, b-glucosyl unit); 3 (1 ! 3)-linkage, 4 (1 ! 4)-linkage; red, reducing end, arrows, site of hydrolysis by (1 ! 3, 1 ! 4)-b-D-glucan endohydrolase (EC 3.2.1.73). (c) Perspective drawings of computer-generated, instantaneous conformations of b-glucans: (i) (1 ! 4)-b-D-glucan (cellulose), (ii) (1 ! 3)b-D-glucan (callose), (iii) (1 ! 3, 1 ! 4)-b-D-glucan, (○) (1 ! 4)-linked residues, and (•) (1 ! 3)-linked residue. Reproduced from Fincher GB and Stone BA (1986) Cell walls and their components in cereal grain technology. Advances in Cereal Science and Technology 8: 207–295, with permission.

(Figure 2(c) (i) cf. Figure 2(c) (iii)). First-order Markov chain analyses have been used to show that the DP3 and DP4 units of the water-soluble barley (1 ! 3, 1 ! 4)-b-D-glucan are arranged at random (Figure 3), which means that the molecular ‘kinks’ imposed by (1 ! 3)-b-D-glucosyl residues in the main chain of the polysaccharide will also be irregularly spaced.

..G 3 G 4 G 4 G 3 G 4 G 4 G 4 G 3 G 4 G 4 G 3 G .. 1– p p

Cellotetraosyl

Cellotriosyl

1– q

q

Solubility The extractability of (1 ! 3, 1 ! 4)-b-D-glucans from walls of cereal grains is partly a function of their degree of selfassociation and their association with other wall polysaccharides and proteins. In addition, extractability depends on the molecular mass and linkage distribution in the (1 ! 3, 1 ! 4)b-D-glucan chains. Extensive association with other polymers and very high molecular masses will render the (1 ! 3, 1 ! 4)b-D-glucans more difficult to extract from the grain. The average molecular masses reported for cereal (1 ! 3, 1 ! 4)-b-D-glucans range from 48 000 (degree of polymerization, DP, 300) to 3 000 000 (DP 1850), depending on the cereal species, cell wall type, extraction procedure, and the method used for molecular mass determination. It is likely that in many cases, the DP of the polysaccharide has been overestimated, particularly where gel permeation chromatography is used for size determination, because standards used to calibrate the columns often have a more globular conformation than the

r=p+q r = autocorrelation (interdependence between DP3 and DP4 units) Figure 3 Determination of the arrangement of cellotriosyl (DP3) and cellotetraosyl (DP4) residues in a water-soluble (1 ! 3, 1 ! 4)b-D-glucan from barley grain. The polysaccharide was hydrolyzed (vertical arrows) with a specific (1 ! 3, 1 ! 4)-b-D-glucan endohydrolase until the penultimate oligosaccharides of DP6, DP7, and DP8 predominated. The autocorrelation coefficient (r) is defined in terms of the probabilities that a cellotriosyl residue is followed by another cellotriosyl residue (p) or a cellotetraosyl residue (q), which can be estimated from the abundance of the oligosaccharide products. If the polysaccharide is treated as a first-order Markov chain, a r value of þ1 indicates an adjacent arrangement of DP3 and DP4 units, a r value of 1 indicates an alternating arrangement of DP3 and DP4 units, and a r value of 0 indicates a random arrangement of DP3 and DP4 units. Values very close to 0 were obtained for two barley (1 ! 3, 1 ! 4)-b-D-glucans.

212


highly asymmetrical wall polysaccharides. The (1 ! 3, 1 ! 4)-bD-glucans are invariably polydisperse with respect to molecular mass, and this is illustrated by a weight average to number average molecular mass ratio (Mw/Mn) of 1.18 for barley (1! 3, 1 ! 4)-b-D-glucan. Certain barley (1 ! 3, 1 ! 4)-b-Dglucans are covalently associated with small amounts of protein and have estimated molecular masses of up to 40 000 000. Apart from their molecular mass, the fine structure of the (1 ! 3, 1 ! 4)-b-D-glucans is a key determinant of their solubility. There are two components of fine structure that need to be considered in this context. Firstly, the longer stretches of 5–20 adjacent (1 ! 4)-linkages in the polysaccharide will be ‘cellulosic’ in nature and would allow intermolecular aggregation and hence reduced solubility. However, these longer blocks of adjacent (1 ! 4)-linkages are not abundant and their effects on solubility have not been quantitated. The second and probably more important element of polysaccharide fine structure that will affect solubility is the relative proportions of the major subunits of the (1 ! 3, 1 ! 4)-b-D-glucans, namely, the cellotriosyl (DP3) and cellotetraosyl (DP4) units (Figure 2(b)). The ratio of these tri- to tetrasaccharide units (DP3:DP4 ratio) as illustrated in Figure 2(b) is proving to be a useful predictor of (1 ! 3, 1 ! 4)-b-D-glucan solubility, insofar as the polysaccharide appears to become less soluble in aqueous media as the ratios move away from 1:1. As the number of DP3 units in the (1 ! 3, 1 ! 4)-b-D-glucan increases, the molecular kinks imposed by the single (1 ! 3)-b-D-glucosyl residues will become more evenly spaced, and the polysaccharide chains will be able to align over longer regions. Thus, solubility will decrease as the DP3:DP4 ratio increases to larger values. Similarly, as the number of DP4 units in the (1 ! 3, 1 ! 4)-b-D-glucan increases, the molecular kinks imposed by the single (1 ! 3)-b-D-glucosyl residues will again become more evenly spaced, and solubility will decrease as the DP3: DP4 ratio decreases to low values. This key argument for explaining (1 ! 3, 1 ! 4)-b-D-glucan solubility in terms of DP3:DP4 ratios only holds if the major DP3 and DP4 units of the polysaccharide are arranged in an essentially random fashion along the (1 ! 3, 1 ! 4)-b-D-glucan chain. This has been demonstrated for very few (1 ! 3, 1 ! 4)-b-D-glucans, but a random arrangement of the DP3 and DP4 units does occur in a water-soluble (1 ! 3, 1 ! 4)-b-D-glucan from barley grain (Figure 3). The variations in the DP3:DP4 ratios between (1 ! 3, 1 ! 4)-b-D-glucans from different tissues and at different development stages indicate that the biosynthetic enzymes responsible for (1 ! 3, 1 ! 4)-b-D-glucan synthesis are able to adjust the fine structure and hence the physicochemical properties of the polysaccharide. There is circumstantial evidence that the amount and solubility of (1 ! 3, 1 ! 4)-b-D-glucan in grain are correlated (Table 3). However, it needs to be emphasized that the solubility of the (1 ! 3, 1 ! 4)-b-D-glucan will also depend on intermolecular interactions with other (1 ! 3, 1 ! 4)-b-Dglucan molecules and with other polysaccharides and proteins in the grain during cereal processing, as noted earlier. A portion of the (1! 3, 1 ! 4)-b-D-glucan from barley, oat, and rye flours is extracted by water at pH 7.0 and 40 C. These flours consist predominantly of aggregates from starchy endosperm cells. Further fractions can be solubilized at higher temperatures. The proportion of total (1 ! 3, 1 ! 4)-b-D-glucan

Table 3 Adoption of (1 ! 3, 1 ! 4)-b-D-glucan in grain is correlated with fine structure Species Oats (Avena sativa)

Barley (Hordeum vulgare)

Wheat (Triticum aestivum)

Typical properties of (1,3;1,4)-b-glucans in grain Ratio in grain 2:1 80% soluble in water (40 C) 6–8% (w/w) grain Ratio in grain 2.8:1 20% soluble in water (40 C) 4–10% (w/w) grain Ratio in grain 3.2:1 0% solubility in water (40 C) 0.5–2.3% (w/w) grain

As the DP3:DP4 ratio increases, the solubility of the (1 ! 3, 1 ! 4)-b-D-glucan decreases and the amount in the grain also appears to decrease.

that is water-soluble at 40 C varies within and between species. For example, waxy (high-amylose) barleys have a higher proportion of water-soluble (1 ! 3, 1 ! 4)-b-D-glucan than normal barleys. (1! 3, 1 ! 4)-b-D-Glucans extracted from barley at 40 C have a slightly lower tri- or tetrasaccharide ratio (1.7:1) than those extracted at 65 C (2.0:1). Complete extraction of cereal (1! 3, 1 ! 4)-b-D-glucans from grain requires the use of alkaline extractants such as 4 M NaOH or aqueous Ba(OH)2, containing NaBH4 to prevent alkali-induced degradation from the reducing terminus. Alkali-extracted barley (1 ! 3, 1 ! 4)b-D-glucan fractions have higher molecular masses, higher ratios of (1! 4):(1 ! 3)-linkages, more contiguously linked (1 ! 4)linked segments, and higher trisaccharide–tetrasaccharide ratios than their water-extractable counterparts. Other extractants, such as dimethyl sulfoxide, hot perchloric acid, trichloroacetic acid, N-methylmorpholine N-oxide, and dimethylacetamide– LiCl, have also been used to solubilize (1 ! 3, 1 ! 4)b-D-glucans, but all are liable to cause some depolymerization or degradation of the polymer. Thus, care must be exercised in comparing structural differences in cereal (1 ! 3, 1 ! 4)b-D-glucans extracted using different solvents. Once extracted with hot water or alkali, the (1 ! 3, 1 ! 4)-b-D-glucans are soluble at neutral pH and room temperature. However, upon cooling, the (1! 3, 1 ! 4)-b-D-glucans slowly aggregate and precipitate.

Molecular Conformations In aqueous media barley (1 ! 3, 1 ! 4)-b-D-glucans adopt a partially extended, somewhat rigid, reptate (snakelike) chain conformation (Figure 2(c)) with a cross-sectional diameter of 0.45 nm and a length–width (axial) ratio of 100. It is likely that other (1 ! 3, 1 ! 4)-b-D-glucans adopt a similar conformation in aqueous media, but there are insufficient conformational data available for (1 ! 3, 1 ! 4)-b-D-glucans from a range of sources to allow meaningful comparisons. It would be particularly interesting to compare the molecular conformations of (1 ! 3, 1 ! 4)-b-D-glucans with different DP3:DP4 ratios. In the solid state, x-ray fiber diagrams of the water-soluble barley, (1 ! 3, 1 ! 4)-b-D-glucan can be interpreted as a (1 ! 3)-linked cellotriosyl polymer with a threefold screw

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides axis and a fiber repeat of 4.2 nm. The shape of the chain is reminiscent of cellulose in the cellotriosyl and longer cellooligosaccharide units, but the (1 ! 3)-linkages provide some helical character.

Viscosity of Solutions of (1 ! 3, 1 ! 4)-b-D-Glucans The intrinsic viscosities of (1 ! 3, 1 ! 4)-b-D-glucan solutions are dependent on the cereal species from which the polysaccharide is extracted and on the solvent used. Intrinsic viscosity values for barley (1 ! 3, 1 ! 4)-b-D-glucans in water range from 4.6 to 6.9 dl g1 and from 2.0 to 9.6 dl g1 for oat (1 ! 3, 1 ! 4)-b-D-glucans. The extractability, solubility, and viscosity characteristics of cereal (1 ! 3, 1 ! 4)-b-D-glucans can be understood by reference to their fine structures, as noted earlier. Long runs of adjacent (1 ! 4)-b-D-glucosyl units in the (1 ! 3, 1 ! 4)-b-D-glucan chain will form extended ribbonlike cellulosic stretches, but the insertion of a (1 ! 3)linked glucosyl unit between them causes a ‘kink’ in the molecule (Figure 2(c)). Chain flexibility arises principally from the isolated (1 ! 3)-b-linkages. Because the (1 ! 3)-linked b-glucosyl units do not occur regularly along the chain, the polysaccharides are not able to align over extended regions and hence remain ‘dispersed’ and soluble in aqueous media. The overall extended polysaccharide conformation is due to the predominance of (1 ! 4)-linkages and results in the occupancy of a high volume of solvent (high hydrodynamic volume). This results in aqueous solutions of high viscosity. The viscosity of solutions of cereal (1 ! 3, 1 ! 4)-b-Dglucans depends strongly on concentration. At concentrations of oat (1 ! 3, 1 ! 4)-b-D-glucan where the total volume occupied by the chains is, in aggregate, less than the total volume of the solution, there is contact between individual chains, but the viscosity of the solution is independent of shear rate. At concentrations above the critical overlapping concentration, there is interpenetration of the chains in response to increasing space occupancy. The viscosities of such aqueous solutions are reduced with increasing shear rate, a phenomenon known as ‘shear thinning.’ These different concentration-dependent rheological properties of (1 ! 3, 1 ! 4)-b-D-glucan solutions may be of significance in their physiological responses as food ingredients and in their use in food formulations.

Gelation (1 ! 3, 1 ! 4)-b-D-Glucan solutions at concentrations of 5% (w/v) or more form elastic gel networks. The gels are thermoreversible, exhibit broad melting transitions, and show syneresis. Their melting temperatures depend on the source of (1 ! 3, 1 ! 4)-b-D-glucan as follows: lichenin, 73 C; barley, 65 C; and oats, 62 C. These values are again related to trisaccharide–tetrasaccharide ratios, which in these examples are 22:1, 3:1, and 2:1, respectively. In the gel state, the (1 ! 3, 1 ! 4)-b-D-glucan chains interact to form three-dimensional networks. Association between chains at junction zones, through pairs of consecutive cellotriosyl units, is proposed. This accounts for the higher melting temperature of lichenin gels, where cellotriosyl units make up most of the molecule. In the cereal (1 ! 3, 1 ! 4)-b-D-glucans, consecutive cellotriosyl units are less frequent, although the longer runs of adjacent

213

(1 ! 4)-b-D-glucosyl units, not present in lichenin, may also participate in junction zone formation. The induction time for gelation depends on mobility and diffusivity. It increases with the molecular mass of (1 ! 3, 1 ! 4)-b-D-glucan and decreases as the concentration increases. Gelation is repressed at high and low temperatures, where molecular motion is high and low, respectively. Gelation may be induced by homogenization, centrifugation, and freezing and thawing.

Structure–Function Relationships in Cereal Processing and Nutrition The viscosity-generating properties of soluble cereal (1 ! 3, 1 ! 4)-b-D-glucans are critical determinants in many aspects of cereal processing. For example, incompletely degraded (1 ! 3, 1 ! 4)-b-D-glucans from malted barley and cereal adjuncts can contribute to wort and beer viscosity and are associated with problems in wort separation and beer filtration. In other applications, (1 ! 3, 1 ! 4)-b-D-glucans can be cast as biodegradable films, have foam- and emulsionstabilizing ability, and, when used as a flour supplement, increase water absorption in doughs. Soluble cereal (1 ! 3, 1 ! 4)-b-D-glucans have ‘antinutritive’ effects in monogastric animals such as pigs and poultry. The ‘antinutritive’ effects have been attributed to the increased viscosity of gut contents, which is believed to slow both the diffusion of digestive enzymes and the absorption of degradative products of enzyme action. This, in turn, leads to slower growth rates. Moreover, in dietary formulations for poultry, high (1 ! 3, 1 ! 4)-b-D-glucan concentrations are associated with ‘sticky’ feces, which are indicative of the poor digestibility of the (1 ! 3, 1 ! 4)-b-D-glucans and which may present major handling and hygiene problems for producers. Cereal (1 ! 3, 1 ! 4)-b-D-glucans are important components of dietary fiber in human and animal diets. Humans and monogastric animals produce no enzymes that degrade (1 ! 3, 1 ! 4)-b-D-glucans, although there are indications that some depolymerization occurs in the stomach and small intestine, presumably due to the activity of commensal microorganisms. By comparison, the soluble (1 ! 3, 1 ! 4)b-D-glucans and other nonstarchy polysaccharides are readily fermented by colonic microorganisms and make a small contribution to digestible energy. In contrast to their ‘antinutritive’ effects in monogastric animals, oat and barley (1 ! 3, 1 ! 4)b-D-glucans at high concentrations in human foods have beneficial effects, especially for noninsulin-dependent diabetics, by flattening glucose and insulin responses that follow a meal. High concentrations of (1 ! 3, 1 ! 4)-b-D-glucans (20% w/v) in food have also been implicated in the reduction of serum cholesterol concentrations, by lowering the uptake of dietary cholesterol or resorption of bile acids from the intestine. There is now a good deal of information on the microbiota of the human large intestine, on how the relative abundance of constituent microorganisms is controlled by the carbon source embodied in dietary fiber, and on how the fermentation products of specific bacteria affect bowel health and reduce the risk of serious human diseases, including type II diabetes, cardiovascular disease, and colorectal cancer. More recently, connections between dietary fiber and protection against inflammatory diseases are emerging.

214


(1 ! 3, 1 ! 4)-b-D-Glucans, in common with a number of other polysaccharides, in particular (1 ! 3)-b-D-glucans, modify immunologic responses in humans by a process that is mediated through binding to receptors on cells of the reticuloendothelial system (leucocytes and macrophages). In addition, they may have the capacity to activate the proteins of the human complement pathway, a system that is invoked as a first line of defense before circulating antibodies are produced.

Analysis and Detection Specific reagents for the analysis and detection of cereal (1 ! 3, 1 ! 4)-b-D-glucans include enzymes, fluorochromes, and monoclonal antibodies. The (1 ! 3, 1 ! 4)-b-D-glucan endohydrolase (EC 3.2.1.73) from Bacillus subtilis has been adopted for the specific quantitation of (1 ! 3, 1 ! 4)-b-D-glucan in grain or grain extracts. This enzyme cleaves only (1 ! 4)linkages that adjoin (1 ! 3)-substituted glucosyl units in the glucan chain and therefore liberates a series of oligoglucosides with (1 ! 3)-linked reducing units (Figure 2(b)). These may be quantified by b-glucosidase cleavage and measurement of the released glucose with the glucose oxidase–peroxidase reagent, by separation and quantitation by high-performance liquid chromatography (HPLC), or by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS). The latter procedures allow an assessment of the profile of oligosaccharides making up the primary structure of the (1 ! 3, 1 ! 4)-b-D-glucan and, in particular, the trisaccharide– tetrasaccharide ratio. b-D-Glucans, including (1 ! 4)-b-D-glucan, cellulose, (1! 3)-b-D-glucan, callose, and cereal (1 ! 3, 1 ! 4)-b-D-glucans, form complexes with the diphenyldiazo dye, Congo red, and members of the calcofluor family of diaminostilbene sulfonates. These reagents complex poorly with heteroxylans and AGPs. Irradiation of the complexes induces a brilliant red fluorescence in the case of Congo red (emission lmax, 590 nm; green excitation, 470 nm) and a bright blue fluorescence with calcofluor (emission lmax 420, 442 nm; blue excitation, 350 nm). The fluorochromes complex with and precipitate soluble b-glucans. Although complexing with the fluorochromes is not specific for (1! 3, 1 ! 4)-b-D-glucans, it is nevertheless useful in quantifying soluble (1! 3, 1 ! 4)-b-D-glucans with molecular weights of > 10 kDa in grain extracts and in products such as wort, where cellulose will not be present. The fluorochromes and a (1 ! 3, 1 ! 4)-b-D-glucan-specific monoclonal antibody can be used to locate (1 ! 3, 1 ! 4)b-D-glucans in tissue sections in histological studies. Although near-infrared reflectance (NIR) spectra of polysaccharides are complex, making their direct interpretation difficult, principal component analysis of the spectra of different polysaccharides enables characteristic NIR wavelengths to be determined. NIR spectroscopy has been applied to the determination of (1 ! 3, 1 ! 4)-b-D-glucans in ground barley grain and this method forms the basis of rapid, routine (1 ! 3, 1 ! 4)-b-D-glucan estimation.

Genetics (1 ! 3, 1 ! 4)-b-D-Glucan concentrations in grain are influenced by both genotype and environment. Quantitative trait

locus (QTL) mapping has enabled regions of the barley genome that control (1 ! 3, 1 ! 4)-b-D-glucan concentrations to be identified and placed on high-density genetic maps. Furthermore, the conservation of gene order (synteny) across cereal genomes means that regions controlling (1 ! 3, 1 ! 4)b-D-glucan concentrations in cereals other than barley can often be deduced from the genetic positions of barley QTLs. Using a comparative genomics approach based on barley QTLs and the rice genome sequence, it has been shown that (1 ! 3, 1 ! 4)-b-D-glucan synthesis in the cereals is mediated by the cellulose synthase-like (Csl) genes of the CslF, CslH, and CslJ clades. The CslF gene subfamily is the largest of these clades. There are ten CslF genes in barley and similar numbers in wheat, sorghum, and rice. The CslH and CslJ gene subfamilies are generally much smaller. The multiple members of the CslF gene subfamily are distributed across cereal genomes, although there is a cluster of CslF genes on chromosome 2H of barley and in syntenic regions of other cereal genomes. The function of the gene cluster is not known. Expression analyses indicate that the CslF6 gene is the most highly transcribed member of the gene subfamily in developing barley grain and in most other tissues of barley. The CslF6 gene also appears to be important in most other cereals. Overexpression of the CslF6 gene in transgenic barley led to significantly elevated levels of (1 ! 3, 1 ! 4)-b-D-glucan in the grain and to increased dietary fiber values. This work also suggested that different CslF isoenzymes synthesize (1 ! 3, 1 ! 4)-b-Dglucans with different fine structures, as measured by DP3:DP4 ratios. Genome-wide association studies are showing that additional genes are likely to participate in the regulation of (1 ! 3, 1 ! 4)-b-D-glucan levels in grain.

Heteroxylans The cereal heteroxylans, or pentosans, are of two main types: the arabinoxylans and the glucuronoarabinoxylans. They are characteristically abundant in walls of vegetative tissues of cereals and grasses, where they represent the ‘core’ noncellulosic polysaccharide in walls of the Poaceae. The arabinoxylans are the major noncellulosic polysaccharides in walls of the starchy endosperm cells and of the aleurone layer of cereal grains, whereas the glucuronoarabinoxylans are characteristically found in walls of the pericarp–seed coat tissues (Table 1). Within a cereal species, heteroxylan concentration is influenced by both genotypic and environmental factors.

Structure Cereal heteroxylans have a (1 ! 4)-b-D-xylan backbone that has the same shape as the (1 ! 4)-b-D-glucan, cellulose (Figure 1). The b-xylopyranosyl (Xylp) units of the xylan backbone are modified by side-chain branching (substitution) (Figure 4). The major side chains comprise single a-Larabinofuranosyl (Araf) units, situated predominantly at C(O)3, but in certain species also at C(O)2 of the Xylp units. In some cases, Araf substitutions occur at both C(O)3 and C(O)2. The frequency of Araf substitution depends on the cereal species and wall type and is reflected in a very wide range of Xylp:Araf ratios. The Xylp units of cereal arabinoxylans

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides may be acetylated. In sorghum heteroxylans, acetyl groups are present on both the C(O)2 and the C(O)3 of xylopyranosyl residues. Heteroxylans from cell walls in vegetative tissues, especially lignified walls such as those from parenchyma, sclerenchyma fibers, and the pericarp–seed coat tissues that are found in cereal brans, have low degrees of Araf substitution and therefore high Xylp:Araf ratios. On the other hand, heteroxylans from the aleurone layer and starchy endosperm have relatively low Xylp:Araf ratios. The distribution of Araf units along the xylan chain is not regular. In one wheat arabinoxylan fraction, three major types of substitution patterns have been identified in different regions of the xylan backbone (Figure 5). In region I, isolated unsubstituted Xylp units are separated by one or two mono- or disubstituted units. Region II contains high amounts of Araf units linked at C(O)3 and region III contains high amounts of contiguous (up to six and possibly more) unsubstituted Xylp units.

HO O

HO

O

OH

O

OH O

O

O

O OH

O

O

OH O

O CH2

Other monosaccharides found on the xylan backbone include D-glucuronic acid (GlcAp) and its 4-O-methyl ether, linked to the C(O)2 of Xylp units. GlcAp units are found on endosperm and bran heteroxylans of rice and sorghum and on bran heteroxylans of wheat, rye, and maize. The barley husk arabinoxylan has 4% by weight GlcAp. Various oligomeric chains are also found as substituents on arabinoxylans (Table 4). Characteristically, a proportion of the Araf units in the arabinoxylans of cereals, grasses, and several other families of monocotyledons are esterified with the hydroxycinnamic acids, ferulic acid (FA), and, to a lesser extent, its nonmethoxylated analog p-coumaric acid (pCA) (Figure 4). These hydroxycinnamates are found at C(O)5 of Araf units that are linked to C(O)3 of the Xylp units. Hydroxycinnamates constitute 1.8% (w/w) in walls of wheat aleurone cells and the FA:pCA ratio is 9:1. In contrast, walls of the starchy endosperm cells contain only 0.04% (w/w) FA, with a trace of pCA. During wall formation, enzyme-catalyzed, radical (oxidative) coupling of feruloyl units on neighboring arabinoxylan chains occurs and leads to their cross-linking. At least five different cross-linking FA dehydrodimers are encountered in fiber from wheat, barley, rye, spelt, oats, rice, and millet. Their structures are shown in Figure 6. In walls of pericarp and seed coat tissues, dehydrodiferulate bridges also cross-link arabinoxylans, and in lignified walls, the arabinoxylans are cross-linked to lignin through FA and dehydrodiferulate ester–ether bridges (Figure 7). Thus, the lignified

OH Table 4

H3CO

215

OH

Figure 4 Structure of portion of a (1! 4)-b-D-xylan chain substituted at O3-L-arabino of one residue with a 5-O-trans-feruloyl-L-arabinofuranosyl substituent. Reproduced from Fincher GB and Stone BA (1986) Cell walls and their components in cereal grain technology. Advances in Cereal Science and Technology 8: 207–295, with permission.

Region I

Substituents on xylan backbone of heteroxylans

a-L-Araf-(l4-Me-D-GlcpA-(lD-GlcpA-(lb-D-Galp-(l ! 5)-L-Araf-(lb-D-Xylp-(l ! 2)-L-Araf-(lb-D-Xylp-(l ! 3)-L-Araf-(lb-D-Galp(l ! 4)-b-D-Xyl-(l ! 2)-L-Araf-(l-(or L) 4Me-D-GlcA-(l ! 4)-D-Xylp-(l ! 4)-D-Galp-(l-

~

~

>

Region II

~

~

>

Region III ~

~

> Figure 5 Model of distribution of substituents on an arabinoxylan fraction from wheat endosperm showing three regions with different substitution patterns. Reproduced from Izydorczyk MS and Biliaderis CG (1995) Cereal arabinoxylans – Advances in structure and physico-chemical properties. Carbohydrate Polymers 28: 33–48, with permission.

216


O

O

O

Ara O 5

O

O

Ara O H

Ara

8 O 4

OMe

5

O

Ara O

Ara O

O

Ara

O H

8 H

OMe

5 O

OMe

OH OH OMe

OMe OMe

OH 1 (5-5⬘)

OH

2 (8-O-4⬘)

3(8-5⬘)

OH OMe Ara H

Ara H Ara

8 O

Ara

4 5 OMe O OH OMe

MeO OH

O

O

8 O

O

O

O

O

4 (8-8)

5 (4-O-5⬘)

Figure 6 Ferulated arabinoxylan chains in cell walls of grasses become cross-linked by radical coupling of ferulate monomers into ferulate dehydrodimers (structures 1–6). Dotted arrows indicate potential sites for further radical coupling with hydroxycinnamyl alcohols or lignin oligomers, resulting in cross-linking of arabinoxylans to lignin. ‘Ara’ is an arabinofuranosyl residue on an arabinoxylan. Reproduced from Grabber JH, Hatfield RD, Ralph J, Zon J, and Amrhein N (1995) Ferulate cross-linking in cell walls isolated from maize cell suspension cultures. Phytochemistry 40: 1077–1082, with permission.

OH

Direct ether linkage

Direct ester linkage

Lignin O

=

O

O

C=O O

OH

Lignin

Hydroxycinnamic O acid ether C (e) O H

O O

=

Ferulic acid bridge

de

O

C

=

ari

O H (g)

: p-Coumaroyl

: Feruloyl

hari sacc

=

ch

O=C O O C O

OH

O

Poly

ac

de

(h)

Po

Dehydrodiferulic acid diester-ether bridge

de

(f)

O

lys

ari

(c) C=O

OH

C

O

ch

=

acch Polys

(d)

O O C

Hydroxycinnamic acid ester

OH

O

(a)

O=C O Po lys ac

(b)

=

aride

O C

(c)

Dehydrodiferulic acid diester bridge : Dehydrodiferuloyl

Figure 7 Schematic diagram showing possible covalent cross-links between polysaccharides and lignin in walls. (○) p-Coumaric acid; ( ) ferulic acid; ( ) dehydrodiferulic acid. (a) Direct ester linkage; (b) direct ether linkage; (c) hydroxycinnamic acid esterified to polysaccharide; (d) dehydrocinnamic acid esterified to lignin; (e) hydroxycinnamic acid etherified to lignin; (f) ferulic acid ester–ether bridge; (g) dehydrodiferulic acid diester bridge; and (h) dehydrodiferulic acid diester–ether bridge. Reproduced from liyama K, Lam TB-T, and Stone BA (1994) Covalent cross-links in cell wall. Plant Physiology 104: 315–320, with permission.

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides walls in the pericarp–seed coat layers and husk of cereal grains contain significant concentrations of lignin–heteroxylan complexes. Wheat bran, which consists largely of pericarp–seed coat and aleurone, contains 0.09–0.18% (w/w) diferulate residues. This arises almost exclusively from the pericarp–seed coat, because the contribution of FA dimers from the aleurone is very low (0.03% w/w). The heteroxylans in maize bran contain 1.3% (w/w) dehydrodiferulates, which represent 15 dehydroferulate cross bridges per heteroxylan molecule. Lignin–heteroxylan associations through ester–ether FA and di-FA cross-links also occur in lignified walls in stem tissues of cereals and grasses. In walls of wheat aleurone, highly branched arabinoxylan appears to be covalently associated with protein, possibly through ester-linked FA that is linked to tyrosine in wall proteins by radical coupling. Heteroxylans in maize and rye brans are also covalently associated with protein. The covalent bridges between heteroxylans, wall proteins, and lignins are important determinants of the cohesiveness of the wall fabric and of the resistance of lignified walls to digestion by polysaccharide and ester hydrolases.

Molecular Parameters Average molecular masses of cereal heteroxylans range from 65 000 to 5 000 000 (DP 500–38 000) and, as is the case with the (1 ! 3, 1 ! 4)-b-D-glucans, the value depends on the cereal species, cell wall type, extraction procedure, and the method used for molecular mass determination. The cereal heteroxylans are highly polydisperse with respect to molecular mass as indicated by Mw/Mn values that range from 1.3 to 4.2 for alkalisoluble wheat arabinoxylan, 4.1 for water-extractable wheat arabinoxylan, and 8.5 for rye arabinoxylan. As with the (1 ! 3, 1 ! 4)-b-D-glucans, a portion of the arabinoxylans from walls of cereal grains is soluble in water at 40 C and higher temperatures, but other extractants are required to bring all the arabinoxylan into solution. Whereas 0.05 MNa2CO3, 8 M urea, and dimethyl sulfoxide extract only a small part of the water-insoluble arabinoxylan, most can be extracted with 1 M NaOH, 1 M hydroxylamine hydrochloride, saturated Ba(OH)2, or 4-methylmorpholine N-oxide. Of these, saturated Ba(OH)2 containing NaBH4 is the most successful extractant. Oxidative degradation with chlorite or alkaline H2O2 is effective in extracting arabinoxylan cross-linked to lignin from cereal brans. Arabinoxylans extracted under alkaline conditions may lose all or part of their acetyl and hydroxycinnamate substituents.

Solid-State and Solution Conformations Unsubstituted (1 ! 4)-b-D-xylans can adopt a twofold, helical conformation with only one hydrogen bond (O50 –H-O30 ) between adjacent Xylp units. This conformation is more flexible than the twofold helix of the (1 ! 4)-b-D-glucan, cellulose, which has two hydrogen bonds (O20 –H-O60 and O50 –H-O30 ) between adjacent glucosyl units (Figure 1(b)). The absence of cooperative interresidue associations in xylans allows the molecules to be conformationally more versatile. Indeed, in the solid state, the unsubstituted (1 ! 4)-b-D-xylan chain preferentially exists as a fully extended, threefold (i.e., three Xylp units per helical turn), left-handed helix or a ‘slowly twisted ribbon’

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(Figure 8(a)). Araf substitution of the backbone Xylp units does not substantially change the basic threefold helical conformation (Figure 8(b) and 8(c)). However, substituted arabinoxylans cannot assume the twofold helical conformation in solution because of significant steric interactions between the Araf units and the xylan backbone. Nevertheless, (1 ! 4)b-D-xylans with low degrees of substitution interact reversibly with the surfaces of cellulose microfibrils and may do so in the twofold helical conformation. With increased Araf substitution, the affinity for cellulose decreases, presumably due to the shift from twofold to threefold helical conformation, which would be unfavorable for association with cellulose, and because of the steric hindrance to interaction imposed by the substituents themselves. The length of the backbone chains of arabinoxylans is 3–5 nm. In solution, the arabinoxylans behave as partially stiff, wormlike, cylindrical molecules whose flexibility is largely unaffected by Araf:Xylp ratios, which are generally in the range 0.39–0.82:1.

Solution Properties The intrinsic viscosities of wheat arabinoxylans range from 0.8 to 5.5 dl g1, depending on the degree of substitution. These values may be compared with 0.21 dl g1 for dextran, 0.19 for beet arabinan, 0.12–0.25 for gum arabic, and 4.6–6.9 and 2.0–9.6 for barley and oat (1 ! 3, 1 ! 4)-b-D-glucans, respectively. The behavior of the arabinoxylans in solution is influenced not only by the overall asymmetry of the molecules and their DP but also by the specific arrangement of Araf units along the xylan backbone. Thus, stretches of unsubstituted Xylp units may permit intermolecular alignment over these sequences and lead to the formation of chain associations that are stabilized by hydrogen bonds. As with (1 ! 3, 1 ! 4)b-D-glucans, the properties of arabinoxylan solutions are strongly concentration-dependent. At low concentrations, their viscosities are not shear-dependent but become so at higher concentrations. This behavior is typical of polysaccharides with extended, asymmetrical conformations. Removal of Araf units, either by dilute acid or by a-L-arabinofuranosidase action, leads to aggregation and precipitation of the residual (1 ! 4)-b-D-xylan or of partially substituted arabinoxylan molecules.

Gelation At high concentrations, arabinoxylan solutions form thermoreversible gels that are stabilized by noncovalent interactions. Gelation of arabinoxylan solutions can also be induced by dimerization (cross-linking) of feruloyl units on neighboring arabinoxylan chains by radical coupling (Figure 6). The dimerization can be catalyzed by peroxidase/hydrogen peroxide, manganese-dependent peroxidase, laccase, ammonium persulfate, ferric chloride, and other metal chlorides, halogens, and linoleic acid/lipoxygenase, but not by iodate or bromate. Welldeveloped, three-dimensional gel networks are obtained with arabinoxylans containing high FA contents, high molecular masses, and relatively unsubstituted xylan backbones. The latter facilitate the initial contact between feruloyl groups on neighboring arabinoxylan chains. The rate of gelation depends

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Figure 8 Arabinoxylan conformations. Projections perpendicular (top) and parallel (bottom) of (a) (1 ! 4)-b-D-xylan backbone, (b) backbone with single arabinofuranosyl side groups, and (c) backbone with two arabinofuranosyl side groups. Hydrogen bonds are shown by dotted lines. In each case, the backbone is a left-handed, threefold helix. Reproduced from Atkins EDT (1992) Three dimensional structure, interactions and properties of xylans. In: Visser J, Beldman G, Kusters-van Someren MA, and Voragen AGJ (eds.) Xylan and Xylanases, 576 pp. Amsterdam: Elsevier, with permission.

on temperature, pH, and concentration of oxidizing agent. The gel-forming abilities of water-extractable arabinoxylans from rye and barley are higher than for those from wheat and triticale, presumably because of fine chemical differences of the type listed earlier. Covalently cross-linked arabinoxylans may hold up to 100 g water per 1 g polysaccharide. Gels formed by treatment of maize bran with peroxide/peroxidase are brittle, probably due to the high content of cellulose.

Structure–Function Relationships in Cereal Processing and in Nutrition Arabinoxylans, together with (1! 3, 1 ! 4)-b-D-glucans, contribute to wort and beer viscosity, which may impede wort separation and beer filtration. Arabinoxylans are also components of some beer hazes. The water-soluble arabinoxylans in barley, rye, and wheat contribute an ‘antinutritive’ effect in dietary formulations for poultry. In human diets, cereal arabinoxylans are components of the dietary fiber fraction. Waterextractable fractions from rye, wheat, and spelt (Triticum spelta)

are mainly arabinoxylan, whereas those from barley and oats are mainly (1! 3, 1 ! 4)-b-D-glucans. Ingestion of arabinoxylanenriched, wheat flour by-products reduces the glucose response following a meal in normal subjects. Water-extractable cereal fractions have a very low content of dehydrodiferulate and are partially fermented by anaerobic bacteria in the colon to produce short-chain fatty acids. Water-unextractable cereal fractions contain variable proportions of dehydrodiferulate; maize and millet have the highest content and oat wheat and spelt the lowest. Water-unextractable cereal fractions are poorly fermented in the colon, which may be related to the relatively high diferulate cross-linking of arabinoxylan chains that prevents swelling and attack by bacterial polysaccharide hydrolases or, more generally, because of lower rates of pentose fermentation. High concentrations of water-unextractable fractions in the diet are effective in increasing stool weight, through its bulking capacity. In recent pig feeding trial experiments, diets supplemented with wheat arabinoxylans were associated with increased viscosity of small intestine digesta, changes in large intestine microbiota composition that led to large increases in

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides short-chain fatty acids, reduced damage to DNA from colonocytes, and reduced serum triglyceride levels. These changes can be linked with human health benefits that are attributed to dietary fiber, including reduced glycemic index, reduced risk of colorectal cancer and cardiovascular disease, and reduced risk of type II diabetes. Arabinoxylans have well-demonstrated impacts in bread making. Added water-extractable arabinoxylans have positive effects on the water absorption of doughs, especially after oxidative gelation, and also enhance loaf volume. In both cases, the amounts and molecular masses of the added arabinoxylan are important. Added water-extractable arabinoxylans are reported to slow starch retrogradation and to produce less firm breadcrumbs. The effect on breadcrumb texture is attributed to the increased moisture content of the samples. Waterextractable arabinoxylans from wheat bran are good emulsion stabilizers. They increase the strength and elasticity of gluten– starch films surrounding gas bubbles in doughs. This leads to a higher retention rate of CO2 in the bubbles and produces a positive effect on the fineness and homogeneity of crumb texture. On the other hand, water-unextractable arabinoxylans have detrimental effects on dough rheology and loaf volume. Water-extractable rye arabinoxylans are inhibitors of ice crystal growth and are thus candidate cryostabilizers. Arabinoxylan– lipid mixtures may be cast as films.

Analysis and Detection The determination of arabinoxylans in cereal and cereal products relies on the phloroglucinol–HCl or orcinol–HCl colorimetric reactions that show a high, but not absolute, specificity for pentoses. In addition, NIR can be used to estimate arabinoxylan content in grain, and NIR peak intensity ratios at 1164 and 990 cm1 allow the degree of Araf substitution in arabinoxylans to be defined. Arabinoxylans in grain tissues can be sensitively detected by UV-induced, bright blue fluorescence (lmax, 415–445 nm; excitation, 310 nm) due to esterified FA residues. Lignins also fluoresce under UV irradiation but may be distinguished from ferulate esters by examining walls at a high pH, where the lignin continues to fluoresce blue, but ferulate esters fluoresce green. Arabinoxylans may also be located in tissue sections through immunogold labeling with polyclonal antibodies raised against 4-O-methyl glucuronoxylan or arabinoxylan or with gold-labeled xylanases. Polyclonal antibodies raised specifically against highly or sparsely substituted glucuronoarabinoxylans can also differentiate these types of arabinoxylan in cell walls.

Genetics As high-density genetic maps for barley and wheat have become available, QTLs for arabinoxylan (or pentosan) content in grain have been mapped. A QTL accounting for 35% of variation in both Araf: Xylp ratio and extract viscosity has been found on the long arm of chromosome 1B of bread wheat. The observation that there is no apparent change in arabinoxylan concentrations in the wheat 1BL/1RS translocation lines suggests that the genes involved are located outside the segment of that chromosome that was introgressed from rye. A total of five QTLs controlling acid detergent fiber (ADF)

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Table 5 Genes that have been implicated in heteroxylan biosynthesis in higher plants, including proposed roles in xylan backbone synthesis and the addition of the numerous substituents of the backbone chain Gene family

Proposed role

GT8 (IRX8 and GAUT) GT43 (IRX9 and IRX14) GT47 (IRX10 and IRX7) GT61 BAHD/PMT acyltransferases DUF579 (IRX15) AXY

GluA transferases (1,4)-b-Xylan synthase (1,4)-b-Xylan synthase Ara transferases or Xyl transferases Feruloyl transferases O-Methyl transferase (GluA) O-Acetylation

have been identified in barley, and although ADF consists predominantly of cellulose and lignin from the pericarp–seed coat, some of the effects might be related to arabinoxylan and/or (1! 3, 1 ! 4)-b-D-glucan content. Three QTLs, with relatively large effects, map close to one another on chromosome 2H, whereas the other two QTLs are on chromosomes 4H and 1H. Overall, however, interpretation of the QTL data in terms of identifying genes involved in the biosynthesis of arabinoxylans has usually been complicated by the phenotyping assays. For example, QTLs for water-extractable arabinoxylans might be attributable either to xylan synthase activity or to arabinofuranosidase/glucuronidase activity, because solubility will be affected by the degree of substitution of the xylan backbone. Phenotyping on the basis of Araf or Xylp levels or Araf:Xylp ratios can also be misleading, because both monosaccharides will be found in polysaccharides other than arabinoxylans, such as xyloglucans, pectin, and AGPs. Based largely on the analyses of Arabidopsis mutants, a number of genes have been implicated in heteroxylan biosynthesis (Table 5). However, the roles of these genes in arabinoxylan synthesis in cereal grains have not always been defined and the identification of genes that mediate the biosynthesis of the (1 ! 4)-b-D-xylan backbone of cereal arabinoxylans still requires confirmation.

Glucomannans Glucomannans are linear copolymers of b-D-glucopyranose ( 30%) and its 2-epimer, b-D-mannopyranose ( 70%), joined by (1 ! 4)-linkages (Figure 9(a)) to form linear chains with DPs ranging from < 100 to several thousand. In some examples, the backbone has (1 ! 6)-linked b-Dgalactopyranosyl substituents and is generally esterified with acetyl groups. The shape of the glucomannan polymer is similar to cellulose (Figure 1(a)), and it has therefore been suggested that the chains may associate strongly with surfaces of cellulose microfibrils. The glucomannans are extractable from walls with alkaline borate solutions that act by complexing with the mannopyranosyl units. Glucomannans are minor constituents of walls of most aleurone and starchy endosperm cells of cereals (Table 1), but in certain Oryza indica rice cultivars, values of up to 17% glucomannan have been reported in the endosperm walls. The CslA genes have been shown to mediate glucomannan biosynthesis in some plants.

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Gal 6 --Man 4 Man 4 Glc 4 Man 4 Man 4 Man 4 Man 4 Man 4 Man 4 Glc 4 Glc 4 Man-6 Gal Man = β-D-mannopyranosyl unit Glc = β-D-glucopyranosyl unit Gal = a-D-galactopyranosyl unit 4 = (1→4)-linkage (a) 6 = (1→6)-linkage Fuc Fuc 2 2 Gal Gal 2 2 Xyl Xyl Xyl Xyl 6 6 6 6 --Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc 4 Glc-6 6 Xyl Xyl Glc = β-D-glucopyranosyl unit Xyl = a-D-xylopyranosyl unit Gal = β-D-galactopyranosyl unit Fuc = a-L-fucopyranosyl unit 4 = (1→4)-linkage 6 = (1→6)-linkage 2 = (1→2)-linkage (b)

R R R 4 4 4 --4 Gal A 2 Rha 4 Gal A 2 Rha 4 Gal A 2 Rha 4-Gal A = β-D-galaclopyranosyl unit Rha = a-L-rhamnopyranosyl unit 4 = (1→4)-linkage 2 = (1→2)-linkage R = (1→4)-linked β-D-galactopyranosyl chain

(c)

or (1→3,1→6)-linked β-D-galactopyranosyl chain or (1→5)-linked a-L-arabinofuranosyl chain with (1→2) and (1→3)-side-branching

Figure 9 Structural features of three noncellulosic polysaccharides found as minor constituents in cell walls of cereal grains: (a) glucomannans, (b) xyloglucans, and (c) pectic polysaccharides.

Xyloglucans Xylo-(1 ! 4)-b-D-glucans (xyloglucans) are a family of side chain-branched heteroglycans (Figure 9(b)) consisting of a cellulose-like (1 ! 4)-b-D-glucan backbone side-branched at regular intervals by a-D-xylopyranosyl units at C(O)6 of the glucosyl residues. Some side-branch xylosyl units carry b-Dgalactopyranosyl and a-L-fucopyranosyl substituents, and the unsubstituted glucosyl residues of the backbone chain can be acetylated. Compared with xyloglucans from dicotyledonous plants, those from the cereals are less substituted with xylose, contain little galactose, and have stretches of unsubstituted backbone. Xyloglucans have DPs of 600–700 and readily associate with surfaces of cellulose microfibrils. After extraction with dilute alkali, they are water-soluble. Xyloglucans are generally considered to be of minor significance in walls of cereal grain tissues, although procedures used in earlier analyses may have underestimated their relative abundance in wall preparations.

Pectic Polysaccharides The pectic polysaccharides are a diverse group of side chainbranched heteroglycans. The backbone is a copolymer of alternating (1 ! 4)-linked a-galacturonosyl and (1! 2)-linked a-L-rhamnopyranosyl units (Figure 9(c)). The rhamnogalacturonans are variously side-branched on the rhamnosyl units by arabinan, arabinogalactan, and more complex branched oligosaccharides. In addition, variable amounts of (1 ! 4)-a-linked homogalacturonan may be present in the same backbone chain.

There is also variable methyl esterification and hydroxyl acetylation of the galacturonosyl units. The homogalacturonan domain complexes with Ca2þ, which promotes gelation by forming Ca2þ bridges between unesterified galacturonosyl units on adjacent chains. Pectic polysaccharides are minor constituents of the walls of vegetative tissues and grains of cereals, although measurable amounts have been reported in the walls of rice endosperm cells (Table 1).

Callose Callose is a (1 ! 3)-b-D-glucan. Like cellulose, it is a linear homopolymer and is insoluble in water. However, callose is soluble in dilute NaOH. Callose can be recognized in tissue sections by an intense yellow, UV-induced fluorescence (lmax, 495 nm; excitation, 380 nm) when associated with the aniline blue fluorochrome, a sulfonated 4,40 -dianilinobenzophenone, or by its binding to a specific monoclonal antibody. In mature barley endosperm, callose occurs as small bead-like deposits on the inner surfaces of walls throughout the starchy endosperm but especially at the aleurone/subaleurone interface. The deposition of callose is a well-known consequence of stress and wounding. Thus, the endosperm deposits may arise as a consequence of plasmolysis during the drying of the grain. The callose content of barley endosperm wall preparations is 1%. Callose is found in the developing walls of rice and barley endosperm during the early stages of cellularization, but is not a component of mature walls. It is also found in the nucellar projection and in the vascular tissue of the crease of developing barley but at maturity remains only in the vascular

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides tissue. In the nucellar projection and the vascular tissue, callose deposition might be related to the control of assimilate transport into the developing endosperm.

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specific enzymatic procedure, and their size distribution determined by HPLC or MALDI-TOF-MS.

Arabinogalactan Proteins

Fructans Fructans from cereals consist of short chains of up to 4–5 b-Dfructofuranosyl units in (2 ! 6)-b-linkage to the fructosyl residue of the disaccharide sucrose. Some branching through (2 ! 1)-b-linkages may also occur. Cereal fructans are soluble in water and in boiling 80% (v/v) ethanol. During the early development of wheat grain, fructans can account for as much as 20% dry weight. In mature grains, the contents are low and variable: wheat, 1.3–2.5%; rye, 4.6–6.6%; barley, 0.8%; and oats, 0.1%. In the grain, fructans are found in both the endosperm and the pericarp/embryo, with higher concentrations in the latter fraction. Fructans are important carbohydrate reserves in the vegetative tissues of temperate cereals, particularly in young seedlings where they can account for 70% of the dry weight. Cereal fructans are not digested in the monogastric stomach or small intestine but are readily fermented by microorganisms in the lower gut. Thus, they may be considered to be components of cereal dietary fiber. Fructans may be quantified by NIR or by a

AGPs are widely distributed in plants. They consist of a protein backbone that is rich in hydroxyproline and to which arabinogalactan polysaccharides are covalently attached, although there are many structural subclasses, some of which are membrane-anchored. In wheat grains, the major AGP is an arabinogalactan peptide, with a peptide backbone that is much smaller than most AGPs. The arabinogalactan peptide from wheat flour constitutes 0.27–0.38% on a dry-weight basis and has an average molecular mass of 22 000, although highermolecular-mass AGPs have been detected in other cereal grains, including barley. The polysaccharide portion of the wheat arabinogalactan peptide constitutes 92% of the molecule and consists of branch-on-branch b-D-galactosyl units (Galp) linked by (1 ! 3)- and (1 ! 6)-linkages (Figure 10). The branched b-D-galactan backbone is substituted by single a-L-arabinofuranosyl units. The arabinogalactan has an Araf:Galp ratio of 0.63–0.72:1. In wheat endosperm, the arabinogalactan component of the molecule is covalently linked to a peptide of molecular mass 7800 at

H3N Tyr Ala Glu Val Hyp Ser Hyp Ala Ala Gly Ala Hyp Thr Ala Asp COO–

+

Figure 10 Structure of wheat arabinogalactan peptide. (○) (1 ! 3)-Linked-b-D-galactopyranosyl unit, ( ) (1 ! 6)-linked b-D-galactopyranosyl unit, and ( ) terminal a-l-arabinofuranosyl unit. Structure based on data of Fincher GB, Sawyer WH, and Stone BA (1974) Chemical and physical properties of an arabinogalactan-peptide from wheat endosperm. Biochemical Journal 139: 535–545; Van den Bulck K, Looseveld A-MA, Courtin CM, Proost P, Van Damme J, Robben J, Mort A, and Delcour JA (2002) Amino acid sequence of wheat flour arabinogalactan-peptide, identical to part of grain softness protein GSP-1 leads to improved structural model. Cereal Chemistry 79: 329–331.

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each of the three hydroxyproline residues in the peptide sequence. The same peptide sequence is found at the NH2terminus of a protein associated with the surface of wheat starch granules. Among eight Canadian wheat cultivars, the peptide constituted between 6.5% and 14.3% of the AGpeptide molecule. The wheat AG peptide is very soluble in water and is not precipitated at saturating ammonium sulfate concentrations. Its solutions are of low intrinsic viscosity (0.045–0.062 dl g1). Neither its subcellular location in the endosperm nor its physiological function is known. The wheat AG peptide, unlike its larger AGP counterparts, does not bind to the phenylazo dye, b-glycosyl Yariv reagents. The effects of wheat AG peptides on bread-making properties are of equivocal significance.

Concluding Remarks There is a great deal of information available on the chemistry and physicochemistry of nonstarchy polysaccharides in cereal grains. This is directly attributable to the central importance of these polysaccharides in large-scale food processing activities that include brewing, baking, and stock feed manufacture. Moreover, the nonstarchy polysaccharides of cereals have attracted renewed interest in recent years because of their potentially beneficial effects in human nutrition. Despite this interest, there remain major gaps in our knowledge of the genes and enzymes that control nonstarchy polysaccharide biosynthesis in the cereal grain, particularly the genes that control arabinoxylan biosynthesis. In the case of cereal (1 ! 3, 1 ! 4)-b-D-glucans, where genes involved in the biosynthesis of the polysaccharide have been identified, attention is now turning to genes that regulate levels of grain (1 ! 3, 1 ! 4)-b-D-glucan and eventually to an understanding of the factors that control fine chemical structure of the polysaccharides and hence their solubility and general solution behavior during cereal processing. This information can be confidently expected to provide additional molecular markers through which breeders will track key genes in their breeding programs, to allow breeders to improve quality characteristics related to nonstarchy polysaccharides in commercially important processes, and to further enhance the role of cell wall polysaccharides as components of dietary fiber that carry human health benefits.


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What differences would you expect in the solubility of wheat flour arabinoxylans with xylose–arabinose ratios of 1.2 and 1.5, respectively, and how would you rationalize those differences in terms of chemical fine structure? What differences would you expect in the solubility of barley (1 ! 3, 1 ! 4)-b-D-glucans with DP3:DP4 ratios of 2.5 and 3.0, respectively, and how would you rationalize those differences in terms of chemical fine structure? Cereal grains produce noncellulosic cell wall polysaccharides, such as arabinoxylans and (1 ! 3, 1 ! 4)-b-D-glucans, that will not form microfibrils of the type produced by cellulose. What are the two different chemical strategies

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used to prevent microfibril formation in arabinoxylans and (1 ! 3, 1 ! 4)-b-D-glucans? Summarize current knowledge on the genes that mediate arabinoxylan and (1 ! 3, 1 ! 4)-b-D-glucan biosynthesis in cereal grains. Summarize the functions of arabinogalactan peptides in wheat grains. Show the detailed metabolic pathways leading to the structures shown in Figure 7.

Exercises for Readers to Explore the Topic Further Although there have been significant advances in our understanding of the metabolism of cereal grain nonstarchy polysaccharides, there remain a number of unanswered questions that will undoubtedly attract research attention in the immediate future. Examples of these key questions include the following:

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What is the precise molecular mechanism through which (1 ! 3, 1 ! 4)-b-D-glucans are synthesized and how are the fine structures and hence physicochemical properties altered in response to changing functional requirements? What genes are involved in the biosynthesis of arabinoxylans in cereal grains? Can we identify regulatory genes that control and amounts and fine structures of (1 ! 3, 1 ! 4)-b-D-glucans and arabinoxylans in cereal grains? Can we define the cellular aspects of (1 ! 3, 1 ! 4)-b-Dglucans and arabinoxylan synthesis, including sequential assembly events and the organelles involved? Is there evidence for the two phase assembly of cell wall polysaccharides, whereby oligosaccharides are synthesized first and subsequently assembled into polysaccharides?

See also: Carbohydrates: Health Effects of b-Glucans Found in Cereals; Food Grains and the Consumer: Grains and Health; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Atkins EDT (1992) Three-dimensional structure, interactions, and properties of xylans. In: Visser J, Beldman G, Kusters-van Someren MA, and Voragen AGJ (eds.) Xylan and Xylanases, p. 576. Amsterdam: Elsevier. Bamforth CW (1994) b-Glucans and b-glucanases in malting and brewing: Practical aspects. Brewers Digest 69: 12–16. Belobrajdic DP, Bird AR, Conlon MA, et al. (2011) An arabinoxylan-rich fraction from wheat enhances caecal fermentation and protects colonocyte DNA against dietinduced damage in pigs. British Journal of Nutrition 107: 1–9. Burton RA, Collins HM, Kibble NAJ, et al. (2011) Over-expression of specific HvCslF cellulose synthase-like genes in transgenic barley increases the levels of cell wall (1,3;1,4)-b-D-glucans and alters their fine structure. Plant Biotechnology Journal 9: 117–135. Burton RA, Gidley MJ, and Fincher GB (2010) Heterogeneity in the chemistry, structure and function of plant cell walls. Nature Chemical Biology 6: 724–732. Burton RA, Wilson SM, Hrmova M, et al. (2006) Cellulose synthase-like CslF genes mediate the synthesis of cell wall (1,3;1,4)-b-D-glucans. Science 311: 1940–1942.

CARBOHYDRATES | Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides Carpita N and Gibeaut D (1993) Structural models of primary cell walls in flowering plants: Consistency of molecular structure with the physical properties of the walls during growth. Plant Journal 3: 1–30. Collins HM, Burton RA, Topping DL, Liao M-L, Bacic A, and Fincher GB (2010) Variability in the fine structures of non-cellulosic cell wall polysaccharides from cereal grains: Potential importance in human health and nutrition. Cereal Chemistry 87: 272–282. Cui SW (2001a) Cereal non-starch polysaccharides I: (1 ! 3) (1 ! 4)-b-D-glucans. In: Cui SW (ed.) Polysaccharide Gums from Agricultural Products, pp. 104–165. Lancaster: Technomic Publishing. Cui SW (2001b) Cereal non-starch polysaccharides II: Pentosans/Arabinoxylans. In: Cui SW (ed.) Polysaccharide Gums from Agricultural Products, pp. 167–227. Lancaster: Technomic Publishing. Evers T and Millar S (2002) Cereal grain composition and development: Some implications for quality. Journal of Cereal Science 36: 261–284. Fincher GB, Sawyer WH, and Stone BA (1974) Chemical and physical properties of an arabinogalactan-peptide from wheat endosperm. Biochemical Journal 139: 535–545. Fincher GB and Stone BA (1986) Cell walls and their components in cereal grain technology. Advances in Cereal Science and Technology 8: 207–295. Grabber JH, Hatfield RD, Ralph J, Zon J, and Amrhein N (1995) Ferulate cross-linking in cell walls isolated from maize cell suspension cultures. Phytochemistry 40: 1077–1082.

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Harris PJ and Fincher GB (2009) Distribution, fine structure and function of (1,3;1,4)-bglucans in the grasses and other taxa. In: Stone BA, Bacic T, and Fincher GB (eds.) Chemistry, Biochemistry, and Biology of (1,3)-b-Glucans and Related Polysaccharides, pp. 621–654. Philadelphia, PA: Elsevier. Iiyama K, Lam TB-T, and Stone BA (1994) Covalent cross-links in the cell wall. Plant Physiology 104: 315–320. Izydorczyk MS and Biliaderis CG (1995) Cereal arabinoxylans – Advances in structure and physico-chemical properties. Carbohydrate Polymers 28: 33–48. Kroon-Batenburg LMJ and Kroon JJ (1995) The crystal and molecular structures of cellulose. Carbohydrates in Europe 12: 15–19. Skendi A, Biliaderis CG, Lazaridou A, and Izydorczyk MS (2003) Structure and rheological properties of water soluble b-glucans from oat cultivars Avena sativa and Avena bysantina. Journal of Cereal Science 38: 1–17. Stone BA and Clarke AE (1992) The Chemistry and Biology of (1 ! 3)-b-Glucans. Victoria: Latrobe University Press. Van den Bulck K, Looseveld A-MA, Courtin CM, et al. (2002) Amino acid sequence of wheat flour arabinogalactan-peptide, identical to part of grain softness protein GSP1 leads to improved structural model. Cereal Chemistry 79: 329–331. Vinkx CJA and Delcour JA (1996) Rye (Secale cereale L.) arabinoxylans – A critical review. Journal of Cereal Science 24: 1–14. Visser J, Beldman G, Kusters-van Someren MA, and Voragen AGJ (eds.) (1992) Xylan and Xylanases, p. 576. Amsterdam: Elsevier.

Grains other than Cereals: Non-starch Polysaccharides L Ramsden, University of Hong Kong, Hong Kong, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Plant Cell Walls

•

In common with all plant tissues, the tissues forming a grain are composed of cells, each of which is defined by a cell wall. The cell is the basic structural unit of plants and cellulose is the basic structural component of the plant cell wall. All plant cell walls contain not only cellulose but a number of other polysaccharides that are important in maintaining the structural integrity of the wall and controlling wall permeability. Other components may be involved in interactions with neighboring cells and the environment. The cell walls of plants display a composition that is characteristic of the taxonomic group in which the plant is found. In the angiosperms, there are consistent differences in the pattern of wall polysaccharides present between dicots and monocots. Thus, cereal plant cells possess walls typical of monocot grasses, and this also applies to the endosperm cells in the cereal grain. The cell wall is formed from two types of wall, the primary and the secondary. Primary walls are those first laid down after a cell is formed and are thinner and more flexible than secondary walls that are found in mature cell types. Both primary and secondary walls contain cellulose, but the cellulose fibrils of the primary wall are thinner and more loosely arranged; in the secondary wall, the cellulose fibrils are closely packed into organized layers that are linked to each other by cross-links. Endosperm cells are typically larger and have thinner walls than other tissues in the plant so the proportion of cellulose present can be lower than that in other tissues. Seed-bearing plants deposit energy-containing reserves to support growth of the embryo within the seed. While the major reserve polysaccharide is indisputably starch, there are a number of other polysaccharides that are used particularly within the legume plant family (Fabaceae). Starch reserves are stored in the cytoplasm inside amyloplasts, but the non-starch reserve polysaccharides in seeds are deposited in highly thickened walls of endosperm cells without a structural function.

• • • •

Non-starch polysaccharides (NSP) have a diverse composition and are widely distributed in plants, are all indigestible, but can strongly influence texture. Different types of NSP are produced in monocots and dicots. NSP may be accumulated as a reserve polysaccharide independently or as part of the cell wall. NSP may influence the absorption of carbohydrates, lipids, and proteins. The legume family is an important source of non-cereal grains.

Learning Objective

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To appreciate the diversity, abundance, and potential value of NSP resources in non-cereal grains.

Introduction All plant tissues contain a large variety of polysaccharides, many of which serve structural or reserve functions in the plant. However, the most important polysaccharide obtained from grain crops is starch and the focus in starch producing grain crops is naturally on the yield of starch. Any other polysaccharides present are considered to be of secondary importance as ‘non-starch polysaccharides (NSPs),’ a term that covers a great variety of biological functions and chemical structures. There is a growing awareness that these polysaccharides can have considerable value both in human nutrition and for the food industry. In particular, non-cereal grains show an interesting diversity of polysaccharides that are less familiar than the better studied NSPs of the cereal grain. Non-cereal grains include a great variety of potential species, many of which have not been analyzed for NSP content. Consequently here, it is only possible to present a limited selection together with some details of the structure and their value in products derived from grains. Polysaccharides in a grain can serve two major biological functions. They can act as the energy reserve in the endosperm or cotyledons or they may be involved in forming the structure of the grain tissues. Other functions in which polysaccharides can play essential roles are in the regulation of water balance during dormancy and imbibition and in the protection of the seed against predation and attack by pathogens. In cereals, only starch has a major reserve function, but in dicot grains, other polysaccharides are found to act as reserves, often together with starch.

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Distribution of Grain NSPs There is a clear distinction between monocot- and dicot-grain NSPs, which reflects the differences between the monocot and dicot cell walls. The actual levels present in any grain sample can also vary dependent on the growth conditions and particular genotype. The distribution of NSPs in dicot grains is more difficult to assess due to the variability in designation of what constitutes a dicot grain. In dicots, the major monocot NSPs, the mixed linkage b-glucans, are absent (Figure 1), and arabinoxylans, though they may be present in dicot cell walls, should generally be expected to be largely replaced by xyloglucan that is the main hemicellulose in dicots. Xyloglucans can be found as a reserve polysaccharide in a number of seeds. Galactomannans are found as seed reserve polysaccharides in


http://dx.doi.org/10.1016/B978-0-12-394437-5.00091-7

CARBOHYDRATES | Grains other than Cereals: Non-starch Polysaccharides

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β1–3 glucose

β1–4 glucose Figure 1 The sequence of glucose units in a mixed linkage (1–3)(1–4)-b-glucan.

several dicot families; though their commercial importance as food additives is derived from their presence in large tree seeds, they are also present in many smaller grains.

Uses of Grain NSPs The presence of high levels of NSPs in grain products will reduce the nutritional value of the grain, a factor which is of significance in the animal feed industry. An important feature of NSPs is their ability to bind water that allows them to act as hydrocolloids and disproportionately influence the rheology of aqueous systems. In baking, the NSPs of wheat can enhance water retention and texture of bread and cakes. Purified NSPs can be used as raw materials for the food additive industry that is a major user of polysaccharide texture modifiers, stabilizers, and gelling agents. Currently, traditional grains are not major sources of industrial polysaccharide hydrocolloids, but high demand on traditional supplies makes this a competitive area for development of new sources. However, one of the major benefits of NSPs arises after they have been consumed as part of the diet, when they contribute to the dietary fiber.

Dietary Fiber The NSPs together form the major part of the dietary fiber of grain crops. Dietary fiber is the fraction of a food consumed that is not degraded in the small intestine, and as human digestive enzymes can only cleave a1–4 glucan bonds, all polysaccharides other than starch are part of the dietary fiber. Dietary fiber can be both soluble and insoluble dependent on the molecular structure of the polysaccharides. There are also a smaller number of other polymers present in plant tissues, such as lignin, which also form part of the dietary fiber. However, the simplest available measure of the quantity of NSP in grains is the level of dietary fiber present (Table 1), and often, this is the only figure available for many grains that have not been analyzed in adequate detail for polysaccharide composition. Although unable to contribute to human nutrition in terms of provision of energy, the dietary fiber is well recognized to form an important component of our diet for the correct functioning of the digestive system. Polysaccharides through their high water-binding capacity play an important part in providing bulk to the gut contents to allow easy passage through the intestine. The human digestive system developed to cope with a diet rich in high fiber plant material with a large volume and is

Table 1

Dietary fiber in cereal and legume grains Total fiber

Wheat Barley Rice Sorghum Millet Maize Oats Rye Triticale Chickpea Black gram Mung bean Pigeon pea Soybean Lupin Lima bean Kidney bean Faba bean Sunflower

14.6 22.6 2.4 10.1 8.5 13.4 9.6 14.6 18.1 13.5 7.1 12.8 8.1 4.96 4.0 6.3 6.2 8.0 4.2

Figures given are the highest levels reported. Actual values may vary considerably depending on the variety grown and the cultivation conditions. Data from Shelton DR and Lee WJ (2000). In: Kulp K and Ponte JG (eds.) Handbook of Cereal Science and Technology, 2nd edn., pp. 385–415. New York: Marcel Dekker; Sathe SK (1996). In: Nwokolo E and Smartt J (eds.) Food and Feed from Legumes and Oilseeds, pp.12–32. London: Chapman & Hall.

less well suited to the modern high-fat, energy-rich, low-volume diets of industrialized countries. This deficiency in the modern diet can be overcome through the consumption of grain products high in dietary fiber. NSP can lower the availability and glycemic index of starch by complex formation and restricting access for digestive enzymes. Polysaccharides can also bind to dietary lipids and reduce their uptake into the body, a factor that has been observed in the ability of high-fiber diets to lower blood lipid levels with potentially beneficial consequences for the incidence of cardiovascular disease.

Insoluble Cell Wall Polysaccharides The main structural component of any cell wall is cellulose, a b1–4 linked polymer of glucose (Figure 2). It is the world’s most abundant polymer, followed by its sister glucan starch, with the

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β1–4 glucose Figure 2 The sequence of sugar units in the b1–4 glucan cellulose.

key difference that it cannot be degraded by human digestive enzymes and cannot therefore contribute directly to our nutrition. Cellulose chains are long flat linear ribbons of glucose units, the number of which can exceed 10 000 and with molecular weights of over 1 000 000. Because the b1–4 linkage between the glucose units holds the chain in a flat conformation, it is possible for cellulose chains to align next to each other and form numerous hydrogen bonds between the sugar hydroxyl groups. The chains can stack together to form larger microfibrils, which makes cellulose highly insoluble and tough, an ideal building material for plants. The quantity of cellulose that is found in grains can vary from species to species and is largely a consequence of the thickness of the husk and seed coat that tends to have stronger thicker cell walls that contain more cellulose. The cells of seed endosperm contain only thin cell walls, and in a well-filled grain, the proportion of cellulose to starch or other reserve polysaccharides should be low. Other insoluble polysaccharides such as glucomannans can occur in the walls of some plants, but quantities are typically low, and although levels of up to 2% in some grain walls have been indicated, these would not have a major impact on grain properties.

Soluble Cell Wall Polysaccharides All plant cell walls contain more soluble polysaccharides known as pectins and hemicelluloses with a variety of different structures that serve various functions. These polymers contain a number of different sugar units and are classified according to their composition and solubility. The pattern of soluble polysaccharides present is characteristic of groups and species of plants. The pectins are a major class of highly soluble wall-related polysaccharides that are accumulated in fruits but not to a great extent in most seed grains. Pectins are charged, acidic polysaccharides with a variety of structures based on rhamnogalacturonans, polymers of rhamnose and galacturonic acid together with a number of other sugar substituents. Purified hemicelluloses can show varying degrees of water solubility dependent on their size and structure, but all hemicelluloses are strongly bound to the intact cell wall either by hydrogen bonding or by cross-linking to cellulose. The major function in the plant of hemicelluloses is to increase the rigidity and impermeability of the cell wall.

Dicot Arabinoxylans Arabinoxylans can be found in many dicots but usually only at low levels. An exception is in linseeds, the seeds of the flax

plant (Linum usitatissimum). Linseed is a traditional crop valued for the oil that can be expressed from the seeds. The seeds readily hydrate to form an arabinoxylan mucilage that can easily be extracted by incubation in cold water. High levels of arabinoxylans are known to occur in seeds of various species of genus Plantago. The arabinoxylan is present in the seed coat and can be extracted with boiling water and yields are increased under mild alkaline conditions. The structure of the psyllium arabinoxylan is based on a xylan backbone substituted with arabinose and some uronic acids (Figure 3). Solubility in water is not high and the polysaccharide swells to give a weak gel. The gel shows a broad melting range around 80 and is susceptible to syneresis on freezing/ thawing but shows good stability over a range of ionic concentrations. Psyllium arabinoxylan is a soluble dietary fiber that is effective in lowering plasma cholesterol levels and that has traditionally been a component in laxatives where its high swelling power and mucilaginous gel ease the passage of gut contents. Another abundant arabinoxylan is obtained from seeds of the quince tree (Cydonia oblonga). Seeds can be directly extracted with hot or cold water, and a mucilage is readily released that is a mixture of cellulose microfibrils dispersed in a matrix composed principally of xylose and arabinose. The polysaccharide is easily soluble in cold water and forms a highly viscous mucilage but is not gel-forming. Dispersions show good stability with respect to pH, salt concentration, and temperature. Quince seed arabinoxylan is mainly used for cosmetics applications in Middle Eastern countries. A number of food uses have been suggested such as for use as a stabilizer in ice cream, but these have not been commercialized due to the high cost and poor availability and variable quality of the gum.

Dicot Xyloglucans The major hemicellulose of the dicot cell wall is a xyloglucan formed from a b1–4 linked chain of glucose units substituted with a1–6 xylose units. Some of the xylose units may be joined to an a1–2 linked galactose unit (Figure 4). Most legume grains contain a major proportion of xyloglucan in the cell wall as a structural hemicellulose. Less often high levels of xyloglucans are found in the seeds of some plants where they appear to have a reserve function such as in nasturtium (Tropaeolum majus) and the tamarind tree (Tamarindus indica). Tamarind seeds can be ground to flour that is hot watersoluble to form a mucilaginous gel. The main polysaccharide is a xyloglucan with a b1–4 glucan backbone carrying 1–6 linked xylose and arabinose and galactose substituents in a ratio of galactose/xylose/glucose of approximately 1:2:3. Tamarind xyloglucan can form a gel under acid conditions, which remains stable at alkaline pH. Gels can also form in the presence of ethanol where cross-links arise due to the low solubility of some chain regions allowing aggregates to form. Tamarind gels are used in India for a range of traditional confectionery products. Xyloglucans are used as food additives in Japan for a wide range of products.


β1–4 Xylose

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α-Glucuronic acid

α-Arabinose Figure 3 The arrangement of sugar units in arabinoxylan. a-Arabinose and a-glucuronic acid linked 1–2 or 1–3 to a backbone chain of b1–4 xylose units.

β1–4 glucose

β–Galactose

α–Xylose Figure 4 The arrangement of sugar units in xyloglucan. a-Xylose linked 1–6 to a backbone chain of b1–4 glucose units, with some b-galactose linked 1–2 to the xylose units.

Reserve Polysaccharides Seed-bearing plants deposit energy-containing reserves to support growth of the embryo within the seed. While the major seed reserve polysaccharide is without doubt starch, there are a number of other polysaccharides that are used as reserves, particularly within the legume family. Unlike starch, which is stored in amyloplasts in the cytoplasm, the major non-starch reserve polysaccharides in seeds are deposited in the cell wall but do not serve a structural function. Apart from starch, there is only one other major polysaccharide used by plants as a reserve outside the cell wall. These are polymers of fructose, the fructans, which can have chain lengths of up to 250 sugar units but are generally shorter and highly water-soluble. Many grasses are known to use fructans for storage and for frost resistance. Potentially, fructans may occur in the grains but there is little evidence for significant quantities and most sources of fructans are from tubers or stem tissue.

Galactomannans Many seeds of the legume family contain high levels of reserve galactomannans. The seed galactomannans all possess the same basic structure of an a1–4 linked mannan backbone chain with varying degrees of substitution with a1–6 linked

galactose residues (Figure 5). The ratio of galactose to mannose is roughly constant for a given species. The distribution of galactose along the mannan chain is not uniform but tends to be clustered in blocks of high substitution (rough regions) that are separated by intervening stretches with few galactose residues (smooth regions). Purified galactomannans for industrial usage are obtained from four main plant sources in the legume subfamily Caesalpinioideae that are well characterized. There are guar gum from the seeds of Cyamopsis tetragonoloba, locust bean gum from seeds of Ceratonia siliqua (carob tree), tara gum from seeds of Caesalpinia spinosa, and cassia gum from seeds of Cassia obtusifolia. Extraction of galactomannans involves dehulling of seeds and crushing to remove the embryo, followed by milling of the endosperm to produce a crude flour. The flour can be purified by dissolving in hot water, followed by filtration and precipitation with isopropanol to remove impurities. The properties of galactomannans from different sources vary, depending on the structure of the galactomannan that is characteristic of the source species. The use of locust bean galactomannan (LBG) in the Mediterranean and the Middle East has been part of traditional food preparation for hundreds of years. LBG has a galactose to mannose ratio of 1:4 and a molecular weight of around 300 000. The cold water solubility of LBG is low and dispersions need to be heated to 85 C to achieve good dissolution,

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β1–4 mannose α1–6 galactose Figure 5 The arrangement of sugars in galactomannan. a-Galactose linked 1–6 to a backbone chain of b1–4 mannose units.

concentrations of up to 5% w/v being possible. Low solubility is due to the tendency for the linear mannan chains to strongly hydrogen bond to each other in unsubstituted regions of the chain, limiting opportunities for interaction with water molecules. Though LBG does not itself form gels, it can be used together with other hydrocolloids to give rise to gels, such synergistic gel formation being observed with other nongelling polysaccharides such as xanthan gum. This property is attributed to the ability of the nonsubstituted regions of the linear mannan backbone being able to hydrogen bond to helical regions of the other hydrocolloids and generate crosslinking. LBG is widely used as a thickener and stabilizer in many foods such as ice cream, cheese spreads, salad creams, processed meats products, and pie fillings. It can also be used to prepare a chocolate substitute, carob chocolate. A major use of LBG, and guar, is in ice cream where it can act as a stabilizer to prevent ice crystal growth at low temperatures. Guar galactomannan has long been used as a food ingredient in India. Guar is a linear b1–4 mannan with a higher proportion of galactose substituents than LBG, having a galactose/mannose ratio of 38:62, and this is reflected in the easier dispersion of guar when compared with LBG. Guar can be dissolved at lower temperatures (20 ) as the extent of unsubstituted regions of mannan chain is lower, reducing opportunities for interchain hydrogen bonding that would lead to aggregate formation and prevent hydration. The rheology of guar is similar to that of LBG, pseudoplastic and decreasing with temperature, with good pH stability. Gel formation is only observed when other polysaccharides are added but the ability of guar to participate in synergistic actions is lower than that of LBG. Again, this is attributed to the reduced extent of galactose-free regions of the mannan chain that could form close hydrogen bonding with another polysaccharide. Galactomannan from tara seeds has a galactose/mannose ratio of 27:73, intermediate between those of LBG and guar. The rheological properties are similar to those of LBG. Cassia galactomannan has an average galactose/mannose ratio of approximately 18:82 and can only be solubilized after boiling when a high-viscosity solution can be obtained. The structure of the gum is rather variable and fractions of different solubilities are obtained due to varying degrees of galactose substitution. Like the aforementioned tree seeds of the legume subfamily Caesalpinioideae, the major grain legumes in the Papilionoideae can also contain galactomannans as well as arabinoxylans.

The Papilionoideae include all the main bean crops of agriculture including soya beans (Glycine max), Phaseolus spp., Vicia faba, and Vigna spp. and may contain levels of total fiber from 20% to 50% with percentages of monosaccharides indicative of arabinoxylans and galactomannans. One particular example is fenugreek (Trigonella foenum-graecum), a legume from the Mediterranean region that contains high levels of a seed endosperm galactomannan with a galactose mannose ratio approaching 1:1. Fenugreek galactomannan is cold-water-soluble forming solutions with lower viscosity than the other galactomannans. It has potential as an emulsifier and can show good ability to stabilize oil/water interfaces. Soybeans contain a trace amount of seed galactomannan with a galactose/mannose ratio approaching 1:2, while lupin seeds (Lupinus albus) are unusual in containing an unrelated reserve galactan (or arabinogalactan) with a main chain of b1–4 linked galactose. Bean dietary fiber in various forms is now available commercially as a by-product of oil or protein extraction processes; however, the composition is not well characterized and can contain high levels of cellulose from the seed coat or husk. It is also marketed as bean bran or hull flour for use as an ingredient to add dietary fiber to bakery products.

Identifying NSPs As new species are tested for potential as grain producers, investigation for the presence of NSPs should be a component in any study. It is relatively simple to ascertain the presence of any unusual polysaccharides where these contain different sugar units from those in known polymers. From the analysis of the monosaccharide composition of a grain sample after total acid hydrolysis, it will often be possible to infer the presence of polysaccharides from the ratios and quantities of monosaccharides present. Monosaccharide analysis is conducted by HPLC or gas chromatography after generation of volatile sugar derivatives. Where the polysaccharides differ more subtly by variation in the linkages between similar monosaccharides than the method of choice is usually methylation analysis, requiring the production of methylated sugar derivatives reflecting the positions of glycosidic linkages that can then be analyzed by GC/MS. Where soluble polysaccharides are under investigation clear signals reflecting the position of linkages can sometimes be obtained relatively rapidly by NMR analysis. The aforementioned analytic techniques will usually be complemented by prior separation of polysaccharides present into different fractions depending on their solubility in different solvents. Using the water solubility/insolubility of a polysaccharide is a rapid way to simultaneously extract polysaccharides from a sample and distinguish among those present in the grain.

Conclusion An enormous diversity of NSPs are potentially present in seeds. The polysaccharides of the major cereal crop grains are well known, but as the exploitation of grain resources expands to include new and often diverse dicot plant resources, new NSPs

CARBOHYDRATES | Grains other than Cereals: Non-starch Polysaccharides will be encountered. Many of these new grains have not been fully investigated for the composition of minor polysaccharides present in the endosperm that may have a significant impact on the properties of grain-derived products. In particular, grain legumes as well-developed crops with high levels of NSP would have potential for further investigation to establish the composition of dietary fiber fractions and permit exploitation as defined NSP sources. Similarly, there are opportunities for the development of grain crops to obtain NSP resources that are presently obtained from related species with much lower yields. Eventually, we may see NSPs no longer being regarded as a nuisance reducing the value of the grain but instead representing the major economic product.


• • • • • •

What is a non-cereal grain? Give examples from different plant groups. Give examples of where NSP may be found in plant tissues. What is the difference between NSP and dietary fiber? What are the common chemical structures found in noncereal grain NSP? Which non-cereal grain NSPs are exploited commercially by the food industry? What by-products from the agriculture industry may contain NSP?


• •

Consider the various by-products available from legume crop processing and suggest if any could be used to extract NSP. Examine the geographic distribution of non-cereal grains and cereal grains and consider to what extent they represent complementary resources.

•

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Using literature sources, try and find a new non-cereal grain crop that is not currently exploited for NSP and predict from DF content if it would be a useful source.

See also: Carbohydrates: Carbohydrate Metabolism; Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Health Effects of b-Glucans Found in Cereals; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Functional Foods: Overview; Processing of Grains: b-Glucans: Measurement and Processing; The Basics: Grain: Morphology of Internal Structure; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview; The Oilseeds: Oilseeds: Overview.

Further Reading Brett C and Waldron K (1996) Physiology and Biochemistry of Plant Cell Walls, 2nd edn. London: Chapman Hall. Cui SW (2001) Polysaccharide Gums from Agricultural Products. Pennsylvania, PA: Technomac. Eliasson A-C (ed.) (1996) Carbohydrates in Food. New York: Marcel Dekker. Harris PJ and Smith BG (2006) Plant cell walls and cell-wall polysaccharides: Structures, properties and uses in food products. International Journal of Food Science and Technology 41(s2): 129–143. Hedley CL (ed.) (2001) Carbohydrates in Grain Legume Seeds. Wallingford: CABI Publishing. Loewus FA and Tanner W (eds.) (1982) Plant Carbohydrates I. Encyclopedia of Plant Physiology, vol. 13A. Berlin: Springer. Nwokolo E and Smart J (eds.) (1996) Food and Feed from Legumes and Oilseeds. London: Chapman & Hall. Ouhida I, Pe´rez JF, and Gasa J (2002) Soybean (Glycine max) cell wall composition and availability to feed enzymes. Journal of Agricultural and Food Chemistry 50(7): 1933–1938. Phillips GO and Williams PA (eds.) (2000) Handbook of Hydrocolloids. Florida: CRC Press. Tharanathan RN and Mahadevamma S (2003) Grain legumes – A boon to human nutrition. Trends in Food Science and Technology 14(12): 507–518. Tosh SM and Yada S (2010) Dietary fibres in pulse seeds and fractions: Characterization, functional attributes, and applications. Food Research International 43(2): 450–460.

Resistant Starch and Health A Evans, Tate and Lyle, Hoffman Estates, IL, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

What is resistant starch? Resistant starch intake; measurement and consumption. Effect of resistant starch intake on gut health. Metabolic effects of resistant starch intake.

Learning Objectives

• •

To get a basic understanding of what resistant starch is and where it is found. To learn about how its consumption has been linked to a variety of potential beneficial health outcomes in the area of gut health and various metabolic effects such as blood glucose, insulin, and lipid levels.

What Is Resistant Starch? Starch is the major source of carbohydrates in the human diet. Starch is present in many different fruits, vegetables, roots, and grains. Starch and starch derivatives are a nutritive, abundant, and economical food source. Starch can be consumed unprocessed in the form of raw fruits and vegetables or in the form of more shelf-stable processed foods. Food starches contribute to the characteristic viscosity, texture, mouthfeel, and consistency of many food products. In the human body, starch is digested by a-amylases. First, salivary a-amylase in the mouth catalyzes the hydrolysis of amylose to maltose, maltotriose, and maltotetraose and the hydrolysis of amylopectin to the same products plus two a-limit dextrins. The partially digested starch then passes into the stomach. After some resident time in the low pH environment of the stomach, the partially hydrolyzed starch then passes into the small intestine where it is neutralized. The majority of hydrolysis of the starch is then accomplished by pancreatic a-amylase that is secreted from the pancreatic duct via a multiple attack mechanism. a-Amylases hydrolyze the starch into small mono-, di-, and oligosaccharides that then need to be further broken down to be absorbed as glucose. Two other enzymes are necessary to convert the hydrolysis products of the a-amylases into glucose, which can be actively transported across the small intestine membrane. These two enzymes are the brush-border glucogenic enzymes maltase– glucoamylase and sucrase–isomaltase. The resulting D-glucose is then actively transported across the luminal membrane of the small intestine and passes into the blood via the sodium– glucose cotransporter, which is located at the luminal surface of enterocytes. Several factors influence the rate and extent of starch digestion. The main hydrolysis of starch is performed by the a-amylases. Starch digestion by a-amylases requires a series of

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steps. First, the enzymes diffuse into the starch matrix of the food. In the second step, the enzymes bind to the substrate, and finally, the enzymes cleave the a-1,4-glycosidic linkages of the substrate (starch). The structure of the food matrix and the structure of the starch itself influence the kinetics of the amylase hydrolysis. Resistant starch (RS) has been defined as “the starch and products of starch digestion that are not absorbed in the small intestine of healthy individuals.” Based on the source of the enzyme resistance, RS has been classified into five different types (Table 1). In type 2, type 3, and type 5 RS, the enzyme resistance is due to the physical structure of the starch molecules. Type 2 RS is found in raw starch granules and the enzyme resistance is due to the natural organization of the starch within the starch granules. Significant amounts of type 2 RS can be found in green banana, potato, and high-amylose maize. In type 3 RS, the enzyme resistance is due to the physical structure of starch chains that have undergone some type of restructuring due to retrogradation or heat treatment. Different factors, such as amylose/amylopectin ratio, chain length, lipid content, and processing conditions, have been shown to influence the amount and quality of type 3 RS. Annealing and heat moisture treatment are two types of heat treatments that are often used to create RS. Both of these treatments, as well as gelatinization, either fully or partially melt crystalline structure present in the native starch granules. After heat treatment, linear amylose molecules and linear regions of amylopectin molecules can organize into a mix of amorphous and crystalline areas with varying degrees of enzyme resistance. Formation of the crystalline structures usually takes place above the glass transition temperature and below the melting temperature, and any components present that influence the glass transition temperature can therefore be expected to influence the formation (yield and quality) of the formed type 3 RS. The amylose content of starch has been positively correlated with RS yield and the formation of type 3 RS is strongly related to the crystallization of amylose. The amount of RS formed is also dependent on the water content and temperature used during the heat treatment. Water does act as a plasticizer in the system and a minimum water content is necessary to achieve the chain mobility needed to form crystalline structure resistant to enzyme digestion. At high-starch concentrations, the starch chains interact more easily, leading to increased crystal and RS formation. The presence of lipids has been shown to decrease the formation of type 3 RS due to formation of amylose–lipid complexes (type 5 RS). The enzyme resistance in type 5 RS is due to the molecular structure of amylose–lipid complexes that can be either present in the native starch or formed by controlled reactions using nongranular starch and lipids to form the resistant amylose–lipid complex. The enzyme resistance in type 4 RS is due to chemical modification of the starch. Chemical modification of starch creates


http://dx.doi.org/10.1016/B978-0-12-394437-5.00097-8

CARBOHYDRATES | Resistant Starch and Health Table 1

Classification of resistant starch (RS)

RS type

Source of enzyme resistance

Examples

1 2

Whole grains Raw starch granule structure

3

Structures formed on reassociation or retrogradation of starch after heat treatment Chemical modifications of the starch Starch lipid complex

Seeds, grains Green banana, high amylose, potato Cooked pasta, cooked potato

4 5

Modified starch Amylose-containing starch

chain irregularities or branches in the starch chains. Crosslinking of starch covalently links two starch chains together, in effect creating a branch point on both chains. Chemical substitution introduces a bulky side group to the starch chains. The introduction of these chemical groups may create a steric hindrance to one or more human digestive enzymes.

RS Intake Quantification of RS To determine the effect of RS intake on health, it is important to determine the amount of RS consumed as accurately as possible. Ideally, RS consumption would be determined in vivo by quantification of undigested starch in healthy individuals. This is, however, very difficult to do. Several in vivo approaches have been used for measurement of RS. These in vivo methods include the breath hydrogen test, direct collection of ileal effluent from ileostomy patients, and direct collection of the ileal effluent from healthy subjects using a long triple lumen tube. The measurement of breath hydrogen to determine the amount of RS in a diet is based on the concept of fermentation of dietary fibers including RS. When RS enters the colon, it may be fermented by the colon microbiota that leads to the production of short-chain fatty acids (SCFAs) (acetate, butyrate, and propionate) and gases like hydrogen (methane and carbon dioxide). Most of the gases produced by colonic fermentation are absorbed into the circulation, but about 10% is present in the breath on exhalation. Since breath hydrogen is not specific for only RS fermentation, but does indeed measure fermentation from any dietary fiber source, care has to be taken when interpreting these results for RS content in a food/diet. Direct collection of ileal effluents would be expected to give more accurate results than breath hydrogen measurement especially when different forms of dietary fibers and RS may be present in a diet. Analysis of the ileal effluent allows for quantification of undigested carbohydrate and potential identification of the different sources of dietary fiber within the effluent. Most ileostomy models are, however, based on the use of patients that had their colon removed due to health issues and their digestive patterns may therefore not be representative of a healthy population. Analysis of ileal effluent from healthy individuals should provide the most accurate

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data, but these measurements are difficult and intrusive and can therefore not be done on large scales. It is generally accepted that any in vitro method used to measure RS should give values in line with those obtained with ileostomy patients. In 1986, Berry developed a new in vitro method by modification of a method previously developed by Englyst, Wiggins, and Cummings in 1982. This modified method was subsequently confirmed to give results in line with healthy ileostomy subjects. In 1992, Englyst developed a method that could measure rapidly digestible starch (RDS), slowly digestible starch (SDS), and RS. This method employed incubation of the samples at 37 C with pancreatic amylase and amyloglucosidase and measures the amount of RS by subtracting the sum of RDS and SDS from the total starch present in the sample. Several new methods for the measurement of RS were developed during the European Research Program EURESTA. Even though many different methods were developed during the 1990s for the measurement of RS, none of these methods were successfully subjected to interlaboratory evaluation to be adopted as an official AOAC method of analysis. In 2002, McCleary and Managhan developed a new RS method by modifying existing methods to obtain a method that would yield robust, reproducible results that correlated with results from ileostomy patients. This method underwent interlaboratory evaluation and was later adopted as AOAC Official Method 2002.02. An Integrated method for the measurement of total dietary fiber was later developed and was published in 2007. This method allows the accurate measurement of all dietary fibers including RS. The enzymatic incubation step uses pancreatic a-amylase and more closely simulates digestion in the human digestive tract and yields RS values in line with those obtained with AOAC Official Method 2002.02 and with results from ileostomy patients. This method was accepted as AOAC Method 2009.01.

Sources of RS and Intake Levels Of all unprocessed foods, the green banana has the highest RS content of between 47% and 57%. While flour can be prepared from green bananas and incorporated into different foods as a source of RS, it is important to keep in mind that food processing methods such as cooking may gelatinize the starch granules and destroy the structures responsible for the enzyme resistance originally present and responsible for RS formation. Raw potato starch is also high in RS, but since raw potato starch is seldom consumed, it is not a good source of RS. However, cooling of cooked potatoes or potato products can lead to retrogradation of the starch and may lead to formation of new RS (type 3) if the right conditions (heat, moisture, time, and starch concentration) are met. The level of RS in different legumes can vary widely and RS content in the legumes as consumed depends on processing and legume variety. Murphy et al. examined the RS intake in the United States by comparing reported RS contents of different foods with dietary recall records from participants in the 1999–2002 National Health and Nutrition Examination Survey. They showed that the RS concentration varies greatly, even within the same food category. This could be due to natural differences (cultivar), differences in food preparation methods, and

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also differences in analytic methods used to determine the amount of RS present. The RS content of different breads varied between 0.1% in wheat rolls and 4.5% in pumpernickel bread. Ready-to-eat breakfast levels contained between 0% (rice cereal) and 6.2% (puffed wheat) of RS and cookies/crackers had between 0.2% (oatmeal) and 2.8% (crackers and crisp bread) of RS. The category of cooked cereal and pastas had the widest range of RS contents between 0.4% (noodles and chow mein) and 11.3% (oats and rolled uncooked). Within the vegetable category, the lowest RS content was shown for sweet corn (cooked/canned) and potatoes (slow-cooked) with 0.3% while the highest content was observed for fried potatoes with 2.8%. In the legume category, RS content ranged from 0.6% for chickpeas (cooked/canned) to 4.2% for white beans (cooked/canned). Comparison of the RS content of different foods and the food intake records showed that Americans on average consumed an estimated 3–8 g of RS per day. In Europe, the intake of RS has been estimated to be between 3 and 6 g per day while the intake in developing countries has been estimated to be between 30 and 40 g per day.

Health Benefits of RS Gut Health By definition, RS escapes digestion in the human small intestine. RS therefore passes into the colon where like other dietary fibers, it may be fermented. Fermentation of carbohydrates in the colon leads to the production of SCFAs. SCFAs are the metabolic products of anaerobic bacterial fermentation and consist of butyrate, propionate, and acetate. The SCFAs produced by bacterial fermentation in the human gut are the preferred fuel for the cells lining the colon (colonocytes) and have been shown to lower luminal pH, increase the excretion of bile acids, and help prevent the development of abnormal colonic cells. A lower pH has been associated with protection against colorectal cancer and has been shown to inhibit the conversion of primary to secondary bile acids. Secondary bile acids are thought to promote tumors as they are cytotoxic to colonic cells. It is therefore reasonable to assume that RS may confer health benefits to gut health by production of SCFA, which in turn have a positive effect on pH and reduced production of secondary bile acids. A low pH has also been found to suppress the growth of potentially pathogenic organisms and reduce the absorption of toxic compounds (such as ammonia). Individual SCFAs have also been shown to have more specific actions in the colon. Most RS is readily fermented into SCFA and many are a good source of butyrate. Butyrate is a preferred energy source for colonocytes and helps drive the uptake of electrolytes and water. Intake of butyrate producing RS as part of oral rehydration solutions has been shown to significantly reduce the recovery time for children with watery diarrhea. Butyrate has also been shown to help maintain barrier function in the gut by enhancing mucin production. The barrier function is important to reduce bacterial translocation, which may be a key element in the development of diseases such as inflammatory bowel disease (IBD). Intake of RS has been suggested to be beneficial for the reduction of IBD.

Butyrate has been shown to induce apoptosis, decreasing the risk of cancer development. Animal studies have shown that an increased supply of butyrate to the large bowel decreases the induction of large bowel tumors in rats. However, despite the fact that the data strongly suggest the link between butyrate and reduced risk of colonic cancer, studies examining the link between RS intake and colonic cancer have not been able to prove such a relationship. One reason for this may be the importance of RS intake levels. Studies examining the butyrate production from RS intake have shown significant increase in fecal butyrate when 22 g of RS was consumed per day, but no changes in butyrate or pH levels were observed when 12.5 g of RS was consumed per day. The level of butyrate produced may also depend on the type of RS consumed. Another aspect of gut health often linked to dietary fibers is laxation and fecal bulk. An increase of fecal bulk is thought to be beneficial and is often reported as a potential health benefit of different dietary fibers. Increases in fecal mass are important for relief of constipation and prevention of diverticulosis and other disorders such as hemorrhoids. The effect of RS on fecal bulk has been studied and an increase of fecal output was reported from different studies. Phillips et al. reported an average increase in fecal output of 42% and also showed that the fecal output increased with increased RS intake. This increase fecal output could be due to increased water in the fecal material, undigested and unfermented starch and dietary fibers, or possible bacteria from the digestive tract. Increased fecal nitrogen was observed in diets high in RS indicating either an increase in bacterial mass or protein excretion.

Metabolic Effects Several studies have shown that replacement of digestible carbohydrate with RS leads to a reduced blood glucose response. This has formed the basis for approval of a European Food Safety Authority (EFSA) claim for RS (EFSA, ID 681, April 2011). While this claim was granted, there was insufficient evidence for the effects of RS when the glycemic load (amount of digestible carbohydrate) remains constant. In 2012, Robertson reviewed several studies on the effect of RS addition to the diet when the available carbohydrate load was held constant and noted a significant inconsistency between the studies reviewed. While some found no effect of RS on glycemia and significant reduction in insulin secretion, others found the opposite, that is, a reduction in glycemia and an elevation in postprandial insulinemia. The difference in these results could be due to differences in the RS tested or simply be due to the difficult relationship between glucose absorption, clearance, and hepatic release, which makes accurate measurements and conclusions difficult. Another important factor to consider is the sources of RS used in different studies. RS can come from foods such as beans, high-amylose corn starch, or potatoes, and these foods all have different physiochemical properties that can affect the response to RS ingestion. The fat content of the diets is also important as fat is known to have a significant impact on the glycemic response to a meal. A careful review of studies with appropriate fat and protein levels showed that RS consumption does indeed lead to a small decrease in postprandial glycemia and a larger attenuation of postprandial insulinemia. These acute changes in plasma

CARBOHYDRATES | Resistant Starch and Health glucose and insulin concentrations caused by the addition of RS to the diet could have important metabolic implications. Both hyperglycemia and hyperinsulinemia are affected in the development of insulin resistance. Increases in plasma glucose concentrations have been linked to increased concentrations of free fatty acids. Glucose uptake in the muscles and increased glucose uptake in the adipose tissue have been linked to hyperinsulinemia. The potential chronic effects of RS intake on metabolism and associated diseases are even more interesting than the acute effects discussed earlier. There are animal data showing a significant relationship of RS inclusion in the diet and improved insulin sensitivity. Decreased insulin sensitivity, or insulin resistance, has severe metabolic consequences as it is strongly associated with several diseases known as metabolic syndrome. Metabolic syndrome describes diseases such as type 2 diabetes, obesity, coronary heart disease, hypertension, and dyslipidemia. Even if RS only leads to reduction in blood glucose response when digestible carbohydrates are replaced, such an effect may have significant benefits to human health. Diabetes affects about 8% of US population and is increasing globally. Diabetes is characterized by hyperglycemia that can subsequently lead to systemic tissue toxicity. Risk factors for diabetes include increased glucose response (both fasting and postprandial), decreased insulin sensitivity, and obesity. These risk factors may be reversible with lifestyle modifications that have been shown to be effective in delaying the onset of type 2 diabetes. One lifestyle change could be to reduce the glycemic load of the diet that could be achieved by replacing ordinary starch in foods with RS. RS has been shown to have significant effects of serum triglyceride and cholesterol concentrations. Several animal studies have shown significantly lower plasma cholesterol and triglyceride concentrations when RS is included in the diet in replacement of digestible starch. A decrease in fasting cholesterol and triglycerides was observed when RS was consumed chronically (5–14 weeks). The mechanism responsible for these effects seems to be increased bile acid excretion caused by consumption of RS, but some study showing reduced plasma cholesterol and triglyceride concentrations even compared to the bile acid sequestrant cholestyramine suggests that the effects of RS extend beyond just bile acid secretion. The effects of RS on cholesterol and blood triglyceride levels seem to be mediated through a combination of enhancement of bile acid secretion, a significant decrease in cholesterol absorption, and an increase in hepatic LDL receptor expression. Both high blood lipid and cholesterol levels are associated with coronary heart disease and the effects of RS consumption may therefore have important health ramifications. The effects of RS consumption on satiety and weight management are not as clear. One major reason for the current global obesity epidemic is the overconsumption of energy, and therefore, strategies that can manage the energy intake may be successful in reducing obesity. Dietary fiber is one way to decrease the energy value of foods if it is used to replace digestible carbohydrates that have a higher caloric value. Some dietary fibers have also been linked to increased satiety and lower BMI, but not all fibers have the same effects. RS is a type of dietary fiber and it would therefore be reasonable to

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expect some effect on satiety and/or total energy intake when RS is used to replace digestible starch in the diet. Animal studies have shown the production of satiety hormones GLP-1 and PYY when RS was added to the diet, which suggests an effect of RS on satiety. However, only a few human studies have been conducted to examine the effect of RS on satiety and the results were mixed. Some studies have shown an increase in satiety after RS consumption, but others have shown little or no effect. Satiety seems to be linked to changes in plasma glucose concentrations and studies that showed a decrease in plasma glucose/insulin response to a high RS meal also showed an increase in satiety while those studies that showed no change in plasma glucose also showed no difference in satiety. Overall, there is indication that there is at least a weak association between RS consumption and satiety. Some animal studies have shown reduced energy intake when RS was added to the diet. Aziz et al. showed that body weight was reduced by 40% in obese rats that were fed with a diet high in RS compared with rats fed with a low-RS diet. While this study seems to indicate a real positive effect of RS on energy intake and potentially obesity management, the levels of RS used for this study (23.4%) may not be realistic in a human diet. Long-term studies in humans with realistic RS inclusion levels are required to get a better understanding of the potential for RS to help in the management and reduction of the current obesity epidemic.

Summary/Conclusions RS is a dietary fiber and can be used to replace digestible starch in foods. Many animal studies have been conduced to examine the effect of RS consumption. RS may be fermented in the colon and the resulting SCFA production has been linked to a number of health benefits such as reduced pH, which has been associated with the suppression of growth of potentially pathogenic organisms and reduction of the absorption of toxic compounds. Fermentation of RS has been shown to produce relatively high levels of the SCFA butyrate that has been linked to reduced risk of colon cancer. RS fermentation has also been linked to benefits in the risk reduction of IBD by strengthening of the gut barrier via increased production of mucin. RS has been shown to increase fecal bulk, which is important for relief of constipation and prevention of diverticulosis and other disorders such as hemorrhoids. An EFSA claim was granted in 2011 for reduced blood glucose response when RS is used to replace digestible carbohydrate in the diet (EFSA, ID 681, April 2011). The effect of RS on glycemia and insulinemia is less clear, and studies have shown that different effects are possible due to study designs (e.g., amount of fat and protein in diets) and amount of RS tested. Overall, it does seem that RS consumption does indeed lead to a small decrease in postprandial glycemia and a more significant attenuation of postprandial insulinemia that could have important metabolic implications. Both hyperglycemia and hyperinsulinemia are affected in the development of insulin resistance, which in turn has been linked to several diseases known as metabolic syndrome, for example, type 2 diabetes, obesity, coronary heart disease, hypertension, and dyslipidemia.

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RS has been shown to have significant effects on serum triglyceride and cholesterol concentrations. The effects of RS on cholesterol and blood triglyceride levels seem to be mediated through a combination of enhancement of bile acid secretion, a significant decrease in cholesterol absorption, and an increase in hepatic LDL receptor expression. Both high blood lipid and cholesterol levels are associated with coronary heart disease and the effects of RS consumption may therefore have important health ramifications. The effects of RS consumption on satiety and weight management are not as clear. RS is a type of dietary fiber and it would therefore be reasonable to expect some effect on satiety and/or total energy intake when RS is used to replace digestible starch in the diet. Only a few human studies have been conducted to examine the effect of RS on satiety and the results were mixed. Overall, there is indication that there is at least a weak association between RS consumption and satiety, but long-term studies in humans with realistic RS inclusion levels are required to get a better understanding of the potential for RS to help in the management and reduction of the current obesity epidemic.


• • •

What are the different types of resistant starch? What is the link between resistant starch consumption and colon cancer? How does resistant starch affect insulin sensitivity and why is this important?

Exercises for Readers to Explore the Topic Further While many animal studies have been conducted examining the relationship of resistant starch intake and various health benefits, a more limited number of human clinical studies have been conducted. The results of these clinical studies are sometimes contradictory, and strong conclusions on the health benefits of resistant starch are therefore difficult in some areas. More human studies with careful study designs are needed in the future.

See also: Carbohydrates: Carbohydrate Metabolism; Health Effects of b-Glucans Found in Cereals; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Grains and Health: Misinformation and Misconceptions; Grains and Health; Food Grains and Well-being: Functional Foods: Overview; Grains Around the World: Grain Production and Consumption: Overview; The Basics: The Grains that Feed the World.

Further Reading Abell GCJ, Cooke CM, Bennett CN, Conlon MA, and McOrist AL (2008) Phylotypes related to Ruminococcus bromii are abundant in the large bowel of humans and increase in response to a diet high in resistant starch. FEMS Microbiology Ecology 66: 505–515. Asp N-G (1992) Resistant Starch. Proceedings from the second plenary meeting of EURESTA: European FLAIR concerned action no. 11 on physiological implications

of the consumption of resistant starch in man. European Journal of Clinical Nutrition 46: S1–S148. Aziz AA, Keeney LS, Goulet B, and Abdel-Aal ES (2009) Dietary starch type affects body weight and glycemic control in freely fed but not energy-restricted obese rats. Journal of Nutrition 139: 1881–1889. Berry CS (1986) Resistant starch: Formation and measurement of starch that survives exhaustive digestion with amylolytic enzymes during the determination of dietary fibre. Journal of Cereal Science 4: 301–314. Bird AR, Colon MA, Christophersen CT, and Topping DL (2010) Resistant starch, large bowel fermentation and a broader perspective of prebiotics and probiotics. Beneficial Microbes 1(4): 423–431. Birt DF, Boylston T, Hendrich S, et al. (2013) Resistant starch: Promise for improving human health. Advances in Nutrition 4: 587–601. Brayer GD, Sidhu G, and Maurus R (2000) Subsite mapping of the human pancreatic alpha-amylase active site through structural, kinetic, and mutagenesis techniques. Biochemistry 39: 4778–4791. Brown IL, Yotsuzuka M, Birkett A, and Henriksson A (2006) Prebiotics, synbiotics and resistant starch. Journal of the Japanese Association of Dietary Fiber Research 10: 1–9. Cummings JH, Beatty ER, Bingman SM, Bingham SA, and Englyst HN (1996) Digestion and physiological properties of resistant starch in the human large bowel. British Journal of Nutrition 75: 733–747. Cummings JH, Macfarlane GT, and Englyst HN (2001) Prebiotic digestion and fermentation. American Journal of Clinical Nutrition 73(supplement 2): 415S–420S. Czuchajowska Z, Sievert D, and Pomeranz Y (1991) Enzyme-resistant starch. IV. Effects of complexing lipids. Cereal Chemistry 68: 537–542. Davie JR (2003) Inhibition of histone deacetylase activity by butyrate. Journal of Nutrition 133: 2485S–2493S. Dysseker P and Hoffem D (1994) Estimation of resistant starch intake in Europe. In: Proceedings of the Concluding Plenary Meeting of EURESTA. Wageninger, pp. 84–85. European FLAIR-Concerted Action No. 11 (COST 911). Eerlingen RC and Delcour JA (1995) Formation, analysis, structure and properties of type III enzyme resistant starch. Journal of Cereal Science 22: 129–138. Englyst HN, Kingman SM, and Cummings JH (1992) Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition 46: S33–S50. Finnie IA, Dwarakanath AD, Taylor BA, and Rhodes JM (1995) Colonic mucin synthesis in increased by sodium-butyrate. Gut 36: 93–99. Ghodke SK and Ananthanarayan L (2008) Health benefits of resistant starch. Agro Food Industry Hi-Tech 19: 37–39. Giczewska A and Borowska J (2003) Nutritional value of broad bean seeds. Part 1: Starch and fibre. Food 47(2): 95–97. Gork AS, Usui N, Ceriati E, et al. (1999) The effect of mucin on bacterial translocation in I-407 fetal and Caco-2 adult enterocyte cultured cell lines. Pediatric Surgery International 15: 155–159. Hasjim J, Lee S-O, Hendrich S, Setiawan S, Ai Y, and Jane J (2010) Characterization of a novel resistant starch and its effects on postprandial plasma glucose and insulin responses. Cereal Chemistry 87: 257–262. Higgins JA (2004) Resistant starch: Metabolic effects and potential health benefits. Journal of AOAC International 87: 761–768. Jacobasch G, Schmiedl D, Kruschwski M, and Schmel K (1999) Dietary resistant starch and chronic inflammatory diseases. International Journal of Colorectal Disease 14: 201–211. Jenkins DJA, Vuksan V, and Kendall CWC (1998) Physiological effects of resistant starches in fecal bulk, short chain fatty acids, blood lipids and glycemic index. Journal of the American College of Nutrition 6: 609–616. Keenan MJ, Zhou J, and McCutcheon KL (2009) Effects of resistant starch, a non-digestible fermentable fiber, on reducing body fat. Obesity (Silver Spring) 14: 1523–1534. Knowler WC, Barrett-Connor E, Fowler SE, et al. (2002) Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine 346: 393–403. Mazur AK and Nakatani H (1993) Multiple attack mechanism in the porcine pancreatic alpha-amylase hydrolysis of amylose and amylopectin. Archives of Biochemistry and Biophysics 306: 29–38. McCleary BV (2007) An integrated procedure for the measurement of total dietary fibre (including resistant starch), non-digestible oligosaccharides and available carbohydrates. Analytical Bioanalytical Chemistry 389: 291–308. McCleary BV and Monaghan DA (2002) Measurement of resistant starch. Journal of the Association of Official Analytical Chemists 85: 665–675. Moore CO, Tuschhoff JV, Hastings CW, and Schanefelt RV (1984) Applications of starches in foods. In: Whistler RL, BeMiller JN, and Paschall EF (eds.) Starch: Chemistry and Technology, pp. 575–590. New York: Academic Press.

CARBOHYDRATES | Resistant Starch and Health Murphy MM, Spungen Douglass J, and Birkett A (2008) Resistant starch intakes in the United States. Journal of the American Dietetic Association 108: 67–78. Nichols BL, Avery SE, Sen P, Swallow DM, Hahn D, and Sterchi EE (2003) The maltaseglucoamylase gene: Common ancestry to sucrase-isomaltase with complementary starch digestion activities. Proceeding of the National Academy of Sciences in the United States of America 100: 1432–1437. Nugent A (2005) Health properties of resistant starch. Nutrition Bulletin 30: 27–54. Pencek RR, Koyama Y, and Lacey DB (2002) Transporter-mediated absorption is the primary route of entry and is required for passive absorption of intestinal glucose into the blood of conscious dogs. Journal of Nutrition 132: 1929–1934. Phillips J, Muir JG, Birkett A, Lu ZX, Jones GP, and O’Dea K (1995) Effect of resistant starch of fecal bulk and fermentation-dependent events in humans. American Journal of Clinical Nutrition 62: 121–130. Ramakrishna BS, Venkataraman S, Srinivasan S, Dash P, Young GP, and Binder HJ (2000) Amylase-resistant starch plus oral rehydration solution for cholera. New England Journal of Medicine 342: 308–313. Robertson MD (2012) Dietary-resistant starch and glucose metabolism. Current Opinion in Clinical Nutrition and Metabolic Care 15: 362–367. Robyt JF (1984) Enzymes in the hydrolysis and synthesis of starch. In: Whistler RL, BeMiller JN, and Paschall EF (eds.) Starch: Chemistry and Technology, pp. 87–118. New York: Academic Press. Rodriguez S, Islas JJ, Agama E, Tovar J, and Bello LA (2008) Characterization of a fibre-rich powder prepared by liquefaction of unripe banana flour. Food Chemistry 107: 1515–1521. Roediger WEW (1989) Short chain fatty acids as metabolic regulators of ion absorption in the colon. Acta Veterinaria Scandinavica. Supplementum 86: 116–125. Rumessen JJ (1992) Hydrogen and methane breath tests for evaluation of resistant carbohydrates. European Journal of Clinical Nutrition 46(supplement 2): S77–S90. Sharma A and Yadav BS (2008) Resistant starch: Physiological roles and food applications. Food Reviews International 24: 193–234.

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Sievert C and Pomeranz Y (1990) Enzyme-resistant starch. II. Differential scanning calorimetry study on heat-treated starches and enzyme-resistant starch residues. Cereal Chemistry 68: 86–91. Silvester KR, Englyst HN, and Cummings JH (1995) Ileal recovery of starch from whole diets containing resistant starch measured in vitro and fermentation of the ileal effluent. American Journal of Clinical Nutrition 62: 403–4113. Smirnov A, Perez R, Amit-Romach E, Sklan D, and Uni Z (2005) Mucin dynamics and microbial populations in chicken small intestine are changed by dietary probiotic and antibiotic growth promoter supplementation. Journal of Nutrition 135: 187–192. Swallow DM, Poulter M, and Hollox EJ (2001) Intolerance to lactose and other dietary sugars. Drug Metabolism and Disposition 29: 513–516. Swinburn B, Sacks G, and Ravissin E (2009) Increased food energy supply is more than sufficient to explain the US epidemic of obesity. American Journal of Clinical Nutrition 90: 1453–1456. Tester RF, Karkalas J, and Qi X (2004) Starch – Composition, fine structure and architecture. Journal of Cereal Science 39: 151–165. Topping DL, Bird AR, and Young GP (2009) Effect of aspirin or resistant starch on colorectal neoplasia in the Lynch syndrome. New England Journal of Medicine 360: 1462. Wanders AJ, van den Borne J, and de Graaf C (2011) Effects of dietary fibre on subjective appetite, energy intake and body weight: A systematic review of randomized controlled trials. Obesity Reviews 12: 724–739. Wolever TM, Robb PA, and Thomas MS (1992) Effect of guar, pectin, psyllium, soy polysaccharide, and cellulose on breath hydrogen and methane in healthy subjects. American Journal of Gastroenterology 87: 305–310. Worthley DL, Le Leu RK, and Whitehall VL (2009) A human, double-blind, placebo-controlled, crossover trial of prebiotic, probiotic, and synbiotic supplementation: Effects on luminal, inflammatory, epigenetic, and epithelial biomarkers of colorectal cancer. American Journal of Clinical Nutrition 90: 578–586.

Health Effects of b-Glucans Found in Cereals SM Tosh, Agriculture and Agri-Food Canada, Guelph, ON, Canada S Shea Miller, Agriculture and Agri-Food Canada, Ottawa, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Mixed-linkage b-glucans are found almost exclusively in members of the grass family. Endosperm cell walls of oats and barley contain the highest amounts of mixed-linkage b-glucans. The b-glucan from oats, barley, rye, and wheat differs in size and structure. Solubility and viscosity are largely responsible for b-glucan’s physiological effects. Consumption of oat or barley products moderates glucose response after a meal. Over time, oat or barley reduces LDL cholesterol in hypercholesterolemic individuals. b-Glucan fermentation by colonic flora is associated with improved gut health.

Learning Objectives

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Mixed-linkage b-glucans are found almost exclusively in the cell walls of members of the grass family, with the endosperm cell walls of oats and barley containing the highest amounts. The b-glucan from oats, barley, rye, and wheat differs in molecular weight, as well as ratios of (1 ! 3) and (1 ! 4) linkages. Differences in size and linkage ratios affect the solubility and viscosity of b-glucan in solution which are largely responsible for its physiological effects. Consumption of products containing b-glucan from oats or barley has been demonstrated to moderate the glucose response after a meal. Consumption of products containing b-glucan from oats or barley over time has been demonstrated to decrease LDL cholesterol in hypercholesterolemic individuals. Because of the b-linkages, b-glucan is not digested by the enzymes of the upper digestive tract, but is fermented by colonic flora to generate butyrate, propionate, and acetate, short-chain fatty acids that are associated with improved gut health.

Introduction In Western society, chronic diseases including type 2 diabetes and cardiovascular disease are becoming major concerns. It is recognized that dietary factors contribute to the risk of developing these diseases and that obesity is also associated with their incidence. Therefore, there is an interest in foods and bioactive components of foods that could reduce the likelihood of developing type 2 diabetes or cardiovascular disease. In the early 1980s, a relationship between the consumption of oats and oat bran and reduction of LDL cholesterol, a risk factor for cardiovascular disease, was recognized. Subsequent research identified the soluble fiber (1 ! 3)(1 ! 4)-b-D-glucan,

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commonly called b-glucan, as the bioactive component. It also reduces the blood glucose response following a meal. Significant amounts of soluble b-glucan are also found in barley and have been shown to have similar effects to oat b-glucan.

Distribution b-Glucan is a mixed-linkage polysaccharide found almost exclusively in the cell walls of members of the grass family or Poaceae, which contains a large proportion of the world’s economically important crops. Cereals, including oats and barley, are members of the grass family, which belongs to the subclass of monocots. Although b-glucans are present in the cell walls of both vegetative and reproductive tissues, the highest amounts are located in the endosperm cell walls of oats and barley, followed by rye and wheat, in decreasing order (Figure 1). Only oats and barley are considered to have economically (and physiologically) significant amounts. The b-glucans in these four cereals differ in molecular weight and in the ratios of oligosaccharides and linkages making up the polymer and thus in solubility as well (Table 1). Rice and corn do not contain significant amounts of mixed-linkage b-glucan, while the dicots, including legumes, pseudocereals, and nuts, do not have any. The oat endosperm cell wall is approximately 85% b-glucan, and within the oat endosperm, the greatest concentration of bglucan is found in the thick cell walls of the subaleurone layer (Figure 1(a)). The walls of the central endosperm are much thinner (Figure 1(b)), and there is a correspondingly lower concentration of b-glucan in that area of the kernel. In barley, the cell walls, which are also high in b-glucan ( 70%), are typically a uniform thickness throughout the endosperm, so the b-glucan is much more evenly distributed (Figure 1(c) and 1(d)). In rye, the predominant cell wall polysaccharide is arabinoxylan, with the b-glucan being found mostly in a layer on the inside of the wall (Figure 1(e) and 1(f)). In the rye endosperm cell walls shown in Figure 1(f), it can be seen that the staining of b-glucans in the walls is less intense than that of the oats and barley shown in (b) and (d), indicating a lower b-glucan content. Wheat is unique, in that the b-glucan is found in highest concentration in the aleurone cell walls (Figure 1(g)), with smaller amounts in the endosperm cell walls just inside the aleurone layer (Figure 1(h)). In oats, barley, and rye, a thin layer of bglucan can also be detected on the inside of the aleurone cell walls (e.g., Figure 1(a), 1(c), and 1(e)). The main mixed-linkage b-glucan found in fungi, such as mushrooms and yeast, is structurally different. It is a branched polysaccharide with a b-(1 ! 3) backbone and b-(1 ! 6) linkages at the branch points. So, although they have similar names, the biological functions of supplements containing yeast and mushroom b-glucans are quite different.


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CARBOHYDRATES | Health Effects of b-Glucans Found in Cereals

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Figure 1 Fluorescence micrographs of glycol methacrylate sections of cereals. (a), (c), (e) and (g) stained with Congo red to show b-glucan (red) in the endosperm and aleurone cell walls, as distinguished from the autofluorescence of phenolics (blue) in the aleurone cell walls (oriented at the top of each micrograph). (b), (d), (f), and (h) stained with calcofluor white to demonstrate b-glucan in the cell walls of the central endosperm (blue–white fluorescence). Bars in (a)–(c), (d), and (g) represent 20 mm. Bars in (e), (f), and (h) represent 10 mm. (a) and (b) oat; (c) and (d) barley; (e) and (f) rye; (g) and (h) wheat.

Table 1

Oats Barley Rye Wheat

Content and characteristics of mixed-linkage b-glucan found in major cereal grains b-Glucan content (% of kernel)

Molecular weight (106 g mol1)

Trisaccharide/tetrasaccharide ratio

2–8% 2–10% 1.5–2.5% 0.5–1.5%

2.5–3 1.8–2.5 1–1.3 0.3–0.7

1.7–2.4 2.9–3.4 2.7–3.6 3.7–4.8

Chemical Structure Mixed-linkage b-glucan is a linear homopolymer of glucose, similar in structure to cellulose ((1 ! 4)-b-D-glucan). However, there are single b-(1 ! 3) linkages interspersed with the b-(1 ! 4) linkages that make up about 30% of the linkages. Because the b-(1 ! 3) linkages are not regularly spaced, b-glucan does not form crystalline structures and fibrils like

cellulose; thus, it is much more soluble in water than cellulose (Figure 2). Of all the cereals, the b-glucan in oats tends to have the longest molecules (highest molecular weight). In the native grain (Table 1), the molecular weight is generally around 2–2.5 million g mol1 (12 000 glucose units). Approximately 40% of the b-glucan in uncooked oatmeal, oat bran, or oat flour is soluble in water at 37 C in the presence of digestive

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Cellotetraosyl unit

Glucose monomer

β-(1→ 4) linkage

Cellotriosyl unit

β-(1→ 3) linkage

Figure 2 Schematic diagram depicting the chemical structure of a portion of a b-glucan molecule.

Health Benefits Cholesterol Reduction It has been well established that daily consumption of soluble b-glucans can reduce total and LDL cholesterol. A recent metaanalysis determined that persons with mildly elevated serum cholesterol levels (3.0–5.0 mmol l1) who consumed at least 3 g of oat b-glucan per day experienced an average reduction in LDL cholesterol of 0.24–0.29 mmol l1. Similar benefits have been demonstrated with the consumption of barley b-glucan. Barley and b-glucan isolated from barley lowered LDLcholesterol concentrations by 0.21–0.39 mmol l1 compared with control. Health claims are permitted on food products containing physiologically significant levels of b-glucans from oats or barley in the United States, Canada, the European Union, and Malaysia. The viscosity generated by the b-glucan in the gut increases excretion of cholesterol and bile acids. Bile acids are released into the small intestine to emulsify fat in ingested food. Normally bile acids are reabsorbed lower down in the digestive tract and recycled, but viscous fibers tend to physically entrap them and carry them out of the body. To replenish what was lost, in preparation for the next meal, the liver converts stored cholesterol into bile acids, thus lowering the total cholesterol levels.

8 Whole wheat Blood glucose conentration (mmol l−1)

enzymes. Cooking or extrusion can increase the solubility. The b-glucan in barley tends to be slightly smaller, about 1 million g mol1, but has a higher ratio of cellotriosyl (trisaccharide) to cellotetraosyl (tetrasaccharide) units than that in oats (trisaccharide/tetrasaccharide ratio ranges from 2.9 to 3.4 for barley, compared with 1.7–2.4 for oats). Wheat and rye contain b-glucans of even lower molecular weight, and while rye has a similar trisaccharide/tetrasaccharide ratio to barley, that of wheat (3.7–4.8) is significantly higher than the other cereals (Table 1). Higher trisaccharide/tetrasaccharide ratios and lower molecular weight have been associated with increased elasticity of b-glucan gels.

Oat bran

7

6

5

4

3 0

20

40

60 Time (min)

80

100

120

Figure 3 Glycemic response to oat bran muffin containing 4 g of b-glucan and whole-wheat muffin containing <0.1 g of b-glucan. After consumption of the oat bran muffin, blood glucose levels increased more slowly, peaked at a lower level, and returned to baseline more slowly than after consumption of the whole-wheat muffin.

enzymes with food, inhibiting the release of glucose from starch. Intact cell walls in cooked whole kernels (including pearled and pot barley), steel-cut oat, and milled flakes also protect starch from digestive enzymes. Sugars, inherent in a meal or released from starch, take longer to reach the intestinal wall in a high viscosity mass than in low viscosity environment because of the slow mixing and diffusion rates. Therefore, glucose enters the bloodstream at a slower rate and over a longer section of the small intestine. The protracted release of glucose into the bloodstream results in a beneficial reduced insulin response; repeated spikes in insulin concentrations increase the risk of developing glucose intolerance that in turn may lead to type 2 diabetes.

Attenuation of Glycemic Response

Increased Satiety and Weight Management

Oat and barley foods have been shown to reduce blood glucose concentrations after a meal compared to control foods and the bioactive component has been demonstrated to be b-glucan (Figure 3). Approximately 4 g of b-glucan per serving is required to observe a significant physiological effect. In the stomach, viscosity generated by b-glucan impedes the mixing of food with gastric fluids and slows gastric emptying rate. In the upper intestine, it hinders mixing of digestive

Increased satiety and delayed hunger have been observed after a meal containing oat or barley foods compared with foods containing refined wheat flour. Although the mechanism is not well established, the effect appears to be related to slower gastric emptying and digestion rate, which is also responsible for reduced glycemic response. In addition, changes in gut hormone responses have been observed following consumption of oat and barley foods. Despite changes in satiety, results


A

*

A

* A

*

A (a)

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(b)

(c)

Figure 4 In vitro digestion and fermentation of oat bran. (a) Suspension of oat bran in buffer, stained with calcofluor to demonstrate b-glucan. Note sheets of aleurone cells (A) and endosperm cell walls (*). (b) Suspension of oat bran after in vitro digestion with a-amylase and proteases to mimic digestive enzymes, stained with calcofluor. Note that aleurone cell wall sheets (A) are unchanged by digestive enzymes but that the b-glucan in the endosperm cell walls has been solubilized and appears as an amorphous blue mass (*), although some endosperm cell wall structure is visible (arrow). (c) Suspension of oat bran/feces after in vitro fermentation, stained with calcofluor. The b-glucan has been completely fermented by the fecal flora. Some autofluorescence of phenolics is visible in vascular elements from other plant-based foods (arrow), as well as in small fragments of blue cell walls embedded in the larger fecal particle. Bars in (a)–(c) represent 100 mm.

for studies measuring changes at a subsequent meal have been mixed. Some studies observed a significant drop in calories consumed while others did not.

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Fermentation and Laxation Oat and barley fiber are not broken down by enzymes in the upper intestine and arrive in the colon intact. Intact oat bran contains particles of aleurone and endosperm cells, which are easily seen with the fluorescence microscope due to the autofluorescence of phenolics in the aleurone layer and the blue fluorescence of b-glucans stained with calcofluor (Figure 4(a)). After an in vitro digestion with a-amylase and proteases meant to mimic conditions in the upper GI tract, the b-glucans have been mostly solubilized, as demonstrated by the loss of discernible cell wall structures and the appearance of amorphous blue-staining material in Figure 4(b), but are still present in the digesta. Because of its solubility, b-glucan is susceptible to enzymes produced by gut microbiota and rapidly fermented, as demonstrated by the loss of calcofluor-stained material in the digesta (Figure 4(c)). During fermentation of b-glucan, gut bacteria produce increased levels of butyrate, propionate, and acetate, the short-chain fatty acids associated with improved gut health (and possibly satiety as well, in the case of acetate). Oat bran improves laxation mainly because of the insoluble fiber portion. Wheat bran is more effective at promoting laxation because of its high insoluble fiber content.

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Oat and barley b-glucans are not absorbed into the bloodstream. How are they able to influence concentrations of glucose and cholesterol in the blood? b-Glucan is a dietary fiber. What is the definition of dietary fiber? What functions do soluble and insoluble dietary fibers play in maintaining health? If wheat contains b-glucan, why does it not reduce cholesterol?


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How do different types of food processing affect the effectiveness of b-glucan? Does it matter whether oats and barley are consumed in extruded breakfast cereals, cooked cereals, breads, soups, snack bars, desserts, or beverages? How can consumers be encouraged to increase their intake of oat and barley foods to take advantage of their health benefits? Oat and barley foods have been reported to increase and extend satiety after a meal? Is the satiety effect related to bglucan or glycemic response modulation?

See also: Carbohydrates: Carbohydrate Metabolism; Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Glycemic Index, Glycemic Load, and Their Health Benefits; Food Grains and the Consumer: Grains and Health; Food Grains and Well-being: Functional Foods: Overview; Processing of Grains: b-Glucans: Measurement and Processing; The Cereal Grains: Oats: Overview.


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Where are b-glucans mainly found? Name the plant family. Which food ingredients are the main sources? Draw a schematic diagram of a b-glucan molecule including two tetrasaccharide and two trisaccharide segments. Identify the 1 ! 3 and 1 ! 4 linkages. What are the linkage differences between cereal b-glucans, cellulose, and starch? What are the implications for structure and physiological effect? What four health benefits have been attributed to oat and barley b-glucans?

Further Reading Abdel-Aal EM and Wood PJ (eds.) (2005) Specialty Grains for Food and Feed. St. Paul, MN: AACC International. AbuMweis SS, Jew S, and Ames NP (2010) b-Glucan from barley and its lipid-lowering capacity: A meta-analysis of randomized, controlled trials. European Journal of Clinical Nutrition 64(12): 1472–1480. A˚man P (2006) Cholesterol-lowering effects of barley dietary fibre in humans: Scientific support for a generic health claim. Scandinavian Journal of Food and Nutrition 50(4): 173–176. Anderson JW (1987) Dietary fiber, lipids and atherosclerosis. American Journal of Cardiology 60: 17G–22G.

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Braaten JT, Wood PJ, Scott FW, et al. (1994) Oat b-glucan reduces blood cholesterol concentration in hypercholesterolemic subjects. European Journal of Clinical Nutrition 48: 465–474. Chu Y-F (ed.) (2013) Oat: Nutrition and Technology. Chichester: Wiley. El Khoury D, Cuda C, Luhovyy BL, and Anderson GH (2012) Beta glucan: Health benefits in obesity and metabolic syndrome. Journal of Nutrition and Metabolism, Article number 851362. Kale M, Hamaker B, and Bordenave N (2013) Oat b-glucans: Physicochemistry and nutritional properties. In: Chu Y-F (ed.) Oat: Nutrition and Technology. Chichester: Wiley. Newman RK and Newman CW (2008) Barley for Food and Health: Science, Technology, and Products. St. Paul, MN: AACC International. Othman RA, Moghadasian MH, and Jones PJH (2011) Cholesterol-lowering effect of oat b-glucan. Nutrition Reviews 69(6): 299–309. Shewry PR and Ullrich SE (eds.) (2014) Barley: Chemistry and Technology, 2nd edn. St. Paul, MN: AACC International. Tosh SM (2013) Review of human studies investigating the post-prandial bloodglucose lowering ability of oat and barley food products. European Journal of Clinical Nutrition 67: 310–317.

Truswell AS (2002) Cereal grains and coronary heart disease. European Journal of Clinical Nutrition 56: 1–14. Webster FH and Wood PJ (eds.) (2011) Oats: Chemistry and Technology, 2nd edn. St. Paul, MN: AACC International. Whitehead A, Beck EJ, Tosh SM, and Wolever TMS (2014) Cholesterol-lowering effects of oat beta-glucan: A meta-analysis of randomized controlled trials. The American Journal of Clinical Nutrition 100: 1413–1421. Wood PJ (2010) Oat and rye b-glucan: Properties and function. Cereal Chemistry 87(4): 315–330. Wood PJ (2011) Oat b-glucan: Properties and function. In: Webster FH and Wood PJ (eds.) Oats: Chemistry and Technology, 2nd edn., pp. 219–254. St. Paul, MN: AACC International. Wood PJ, Arrigoni E, Shea Miller S, and Amado` R (2002) Fermentability of oat and wheat fractions enriched in b-glucan using human fecal inoculation. Cereal Chemistry 79: 445–454. Wu¨rsch P and Pi-Sunyer FX (1997) The role of viscous soluble fiber in the metabolic control of diabetes: A review with special emphasis on cereals rich in b-glucan. Diabetes Care 20: 1774–1780.

Glycemic Index, Glycemic Load, and Their Health Benefits D Dan Ramdath, Agriculture and Agri-Food Canada, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Carbohydrates are required as part of a healthy diet, but they vary in the rate at which they increase blood glucose following ingestion. Glycemic index (GI) is a numeric physiological basis of classifying carbohydrate foods initially used to improve blood glucose control in persons with diabetes. Glycemic load is the product of the carbohydrate content per serving of food and its GI. Measurement of GI requires experienced users and a method that is accurate and valid. Glycemic response is the blood glucose response following consumption of digestible carbohydrate and is measured as the area under the blood glucose response curve. Several food characteristics may affect derivation of GI values. Regular consumption of diets that are low in GI and GL is associated with lower risk for type 2 diabetes (T2DM) and cardiovascular disease (CVD).

Learning Objectives

• • • • • • •

To describe the different types of carbohydrates in the human diet and their effects on blood glucose. To describe the concept of glycemic index and glycemic load and their role in management of diabetes and health promotion. To understand the derivation, required methodology, and classification of GI. To calculate the GI and GL of a mixed meal. To understand the food characteristics that may affect derivation of GI values. To outline the difference between GI, GL, and glycemic response. To examine human studies on the role that GI and GL might play in reducing risk for T2DM and CVD, and promoting satiety and weight loss.

Introduction Carbohydrates provide approximately 50–60% of energy intake in the normal human diet, and this requirement is met through regular consumption of starchy foods such as cereals, fruits, and vegetables. Following consumption, carbohydrates are progressively broken down by digestive enzymes in the gastrointestinal tract where degraded starch structures give rise to glucose, which is then actively transported to various tissues to meet cellular energy requirements. About four decades ago, it was recognized that carbohydrates differ in the rate at which they are digested and consequently vary in


their effects on blood glucose levels. In 1981, the glycemic (or glycaemic) index (GI) was proposed as a numeric physiological basis of classifying carbohydrate foods in order to improve blood glucose control in persons with diabetes. Studies that preceded this concept demonstrated that different carbohydrate foods raised blood glucose by varying amounts, which could not be predicted from chemical analysis. Indeed, differences were measured among foods belonging to the same food group. It is now widely accepted that the blood glucose raising potential of carbohydrate-rich foods can be ranked in a standardized matter using GI, and this feature can be used as an adjunct in the dietary management of persons with diabetes. In 1997, a joint Food and Agriculture Organization/World Health Organization Expert Consultation defined GI as the incremental area under the blood glucose response curve (AUC) elicited by a 50 g available carbohydrate (AC) portion of a test food expressed as a percentage of the response elicited by the same amount of AC from a standard food (either white bread or glucose) taken by the same person. GI is therefore a measure of how much a standard quantity of a food raises blood glucose compared with a standard quantity of glucose or white bread, with a value of 100 having been assigned to glucose. In practical terms, GI is derived from repeated testing of a carbohydrate food in at least ten research participants, with the reference food tested at on 2 occasions (see eqn [1]). Although the significance of GI in managing persons with diabetes is widely accepted, there have been numerous debates on the derivation of GI, including the accuracy and precision of the method and its universal application to public health promotion campaigns to guide healthy food choices: Glycemic index food ¼ AUCfood =mean AUCreference 100 [1] The derivation of GI is based on the amount of available (or preferably glycemic) carbohydrates present in a carbohydraterich food. GI compares equal quantities of carbohydrate and provides a measure of carbohydrate quality but not quantity. It has been argued that GI is a property of carbohydrate-rich foods, which is independent of age, gender, body mass index, ethnicity, and glucose tolerance status but may be influenced by factors such as food variety, cultivars, processing, preparation, and storage effects, among others. Using standardized methodology, the GI of carbohydrate-rich foods can be assessed with a standard deviation of about 9, and the resulting values can be classified (with glucose as the standard) as high (GI 70), medium (GI ¼ 56–69), or low (GI 55). See Table 1 for a sample listing of GI values of different foods. Diets containing high amounts of refined carbohydrates have been shown to increase plasma levels of triglyceride and reduce high-density lipoprotein. Assessing this type of relationship in human studies required an understanding of carbohydrate quality (i.e., GI) and the quantity eaten in a meal or during the course of the day. The concept of glycemic load (GL) was therefore introduced in 1997 by researchers at

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242 Table 1

CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits Glycemic index values for various foods (glucose ¼ 100)

Fruits

Root vegetables

Apple, Golden Delicious Banana (Canada) Cherries, dark, raw Kiwi Mango Orange (South Africa) Papaya Pineapple

39 3 62 9 63 6 58 7 51 3 33 6 56 6 66 7

Legumes

French fries, baked (OreIda) Mashed potato, instant (Canada) Parsnips, peeled, boiled Potato, Irish, peeled, baked Potato, Irish, boiled Sweet potato, peeled, boiled Taro (China) White yam, boiled (Jamaica)

Dairy

64 6 80 13 52 5 83 6 59 4 46 5 48 5 79 4

High-carbohydrate foods

Ice cream, vanilla (Sara Lee) Milk, full-fat (Canada) Milk, skim (Canada) Soy milk, VitasoyW organic Yogurt, white peach (Finest) Yogurt, Greek style, plain Yogurt, frozen, vanilla Blue Menu™ Yogurt, natural, fat-free

38 3 34 6 32 5 43 3 34 7 12 4 46 5 19 5

All-Bran™ (Canada) Cornflakes™ (Canada) Rice, Basmati, boiled 8 min Rice, brown Rice, sticky Rolled oats, cooked 20 min Spaghetti, white, durum wheat Wonder™, white bread

40 5 38 3 22 5 51 5 42 5 21 7 25 4 14 2

Baked beans in tomato sauce Chickpeas, canned Chickpea hummus Kidney beans, dried, soaked overnight, boiled 45 min Lentils, brown, canned Lentils, red, dried, boiled Mung bean, germinated Soya beans, canned (Canada) Snacks 51 5 80 6 69 6 66 5 87 2 49 8 58 7 72 4

Chips (Doritos™ original) Chips, potato, plain, salted Chocolate, dark, DoveW Chocolate, milk, DoveW Jelly beans (Allen’s) Mars BarW Mixed nuts, roasted, salted Sports bar, Clif barW, Brownie

42 4 51 7 23 3 45 8 80 8 62 8 24 10 57 6

Low GI ¼ < 55; medium GI ¼ 55–69; high GI ¼ 70. Source: Atkinson FS, Foster-Powell K, and Brand-Miller JC (2008) International tables of glycemic index and glycemic load values: 2008. Diabetes Care, 31, 2281–2283.

Harvard University to quantify the overall glycemic effect of a portion of food (see eqn [2]). GL is defined as the product of the carbohydrate content per serving of food and its GI. As such, dietary intakes of carbohydrates can be weighted to provide the GL, which is a summative value of the quantity of a carbohydrate-rich food ingested and the quality of the food and allows for a better understanding of how different-sized portions of carbohydrate foods compare in terms of their blood glucose raising effect. The higher the GL, the greater the expected elevation in blood glucose and in the insulinogenic effect of the food. Foods can be classified as having GLs that are low (GL 10), medium (10 < GL < 20), or high (GL 20). Glycemic loadfood ¼

GIfood available carbohydrate ðgÞ=serving 100

[2]

GI Derivation and Methodology The method for derivation of GI has evolved considerably over the last two decades with many improvements in the techniques and prerequisites for testing. In an attempt to standardize and improve the precision of the method used to determine GI, two multilaboratory studies were undertaken with each lab analyzing the same foods. These studies concluded that variation in the GI values obtained by established laboratories could be accounted for by differences in data analysis and within-subject variation of glycemic responses. Several improvements in the methodology were suggested, including duplicate measurements of fasting blood glucose, use of capillary blood sample, and pretest restrictions on exercise and alcohol consumption. Many of these improvements have

been included in the current International Organization for Standardization methodology (ISO 26642:2010) for determining the GI of foods. This well-defined set of guidelines include mandatory procedures, recommendations for characteristics of study participants and pretesting preparation, and internal validity checks, such as the use of a method to measure blood glucose with an analytic variation of <3% and exclusion of outliers. Typically, the ISO GI method calls for a minimum of ten healthy research participants who, following an overnight fast, are randomly fed a 50 g AC portion of the test or reference food (white bread or glucose) using a randomized block design. Before consumption of the test meal, two fasting blood samples are obtained via the finger prick method, and additional blood samples are collected at 15, 30, 45, 60, 90, and 120 min after the first bite is taken. Persons with type 2 diabetes (T2DM) or glucose intolerance can be included as research participants, in which case additional blood samples are taken at 150 and 180 min. Finger prick capillary blood is preferred because (i) it is easier to obtain, (ii) the rise in blood glucose is greater than in venous plasma, and (iii) results for capillary blood glucose are less variable than those for venous plasma. As such, differences in the blood glucose response between foods are larger and easier to detect statistically using capillary blood glucose. Changes in the blood glucose concentrations above fasting are calculated as the incremental area under the glucose response curve using the trapezoid rule. The reference food is eaten by each research participant on at least two separate occasions to derive a mean AUC for that individual. The AUC of each participant after each test food is expressed as a percentage of the mean AUC elicited by the reference food in the same participant. Next, the mean of these values for all participants is calculated as the food GI. If white bread is used as the reference food, the GI values are multiplied by 0.71 to convert them to the glucose scale

CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits (i.e., the GI of glucose ¼ 100). The concept of GI testing and derivation is illustrated in Figure 1. Given the care required to produce accurate and valid GI value, it is advisable that new investigators adhere closely to the ISO method and perform a minimum of three tests on the reference food. From the protocol outlined in the preceding text, it becomes clear that GI is not a simple ratio of two values, but rather a summation of 3 or 4 values from each volunteer and may be expressed mathematically as Xx¼1 x 100 Fx =G n [3] GI ¼ n where Fx is the incremental blood glucose response (AUC) in participant x elicited by 50 g AC from the test food and Gx is the mean AUC in participant x elicited by 50 g glucose (or the equivalent white bread) tested on two or three separate occasions. In the hands of experienced investigators, this approach with 12 healthy adult volunteers usually provides a power of 80% to detect a 22% difference in AUC. Further, among 28 centers participating in an interlaboratory study on GI methodology, the between-laboratory standard deviation of the GI values was 9. In order to reduce unnecessary repetition in the testing of individual foods and to promote wider research and application, an international table of GI and GL values was compiled from the scientific literature in 1995 and updated in 2002 and 2008 to contain 2487 separate entries from 205 published articles. Further, GI values derived from studies of 5 persons are listed separately, and caution is given in using these values. This resource, a sample of which is shown in Table 1, has been instrumental in improving the quality of research examining the relation between GI, GL, and health. It has been used by researchers in many human cohort and interventional studies and in supporting dietary guidelines for high-fiber, low-GI foods for individuals with diabetes as a means of improving postprandial glycemia and weight control. However, others have been more reluctant to putting advice about GI values into practice over concerns about potentially adverse effects on food choice and fat intake. Limitations in the use of the international GI table include the fact that it was compiled

Plasma glucose (mmol l–1)

10

before the existence of a standardized method for GI and that in some instances, the GI values of the same food item have relatively large variation. Some of this variation could be attributed to foods being tested in 10 persons; however, differences in GI values of the same food category may also be explained by differences in processing, in determining the digestible carbohydrate content of the test foods, in GI testing, inherent botanical differences and growing conditions, etc. Indeed, derivation of GI values is affected by many food factors (see Table 2), and this has been the focus of many disagreements on the relevance and application of GI to human health.

Glycemic Carbohydrates An imperative of GI testing is that both the reference foods and test foods must contain the same amount of available or glycemic carbohydrate; typically 50 or 25 g portions are consumed by participants. The method used for determining available Table 2

Food characteristics that may affect derivation of GI values

Food factor

Effect on GI

Presence of monosaccharides • Glucose; fructose; galactose

Formulations with glucose will have higher GI than those containing sucrose or high-fructose corn syrup

Type of starch • Relative abundance of amylose and amylopectin

Amylopectin has branched structure containing a1-6 linkages, which is digested faster and has higher GI

Storage • Ripening • Moisture • Temperature • Retrogradation

Many fruits and vegetables undergo ripening during which starch content decreases and sugars increase Moisture influences retrogradation and formation of resistant starch Cold storage after cooking can promote recrystallization of the starch chains

Processing • Starch particle size • Cell wall integrity

Different cultivars often have different starch structures Large starch granules have larger surface areas and higher GI Disruption of cell wall during processing

Cooking • Same product with different ingredients • Ingredients processed differently • Recipe variation; flour used, moisture content, cooking time

Differences in the rate of carbohydrate digestion and hence the GI value Degree of starch gelatinization and consequently the GI values

Other food components • Dietary fiber and resistant starch • Antinutrients • Organic acids

Soluble viscous fiber associated with lower GI Presence of a-glucosidase inhibitors Delayed gastric emptying

50 g glucose standard

8

50 g AC Test food

6

4 0

30

60 Time (min)

Figure 1 Derivation of Glycemic Index

90

120

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CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits

carbohydrate is therefore critical. In fact, there have been suggestions that glucose should be used as the only reference food because of the ease of measuring 50 g of glucose. AC is defined as the fraction of carbohydrate that can be digested by human enzymes, is absorbed, and enters into intermediary metabolism. It does not include dietary fiber, defined as intrinsic plant cell wall polysaccharides, which can be a source of energy only after colonic fermentation in the large intestine. It has been recommended that the term ‘AC’ be replaced by ‘glycemic carbohydrate.’ Using this terminology, glycemic carbohydrates will include most monosaccharides and disaccharides, some oligosaccharides (maltodextrins), and rapidly digested starches. Slowly digested starches, which are digested less rapidly to release glucose, are also considered to be glycemic carbohydrates. In contrast, ‘nonglycemic carbohydrates’ include oligosaccharides, nonstarch polysaccharides (defined as ‘macromolecules consisting of a large number of monosaccharide residues joined to each other by glycosidic linkages’), and resistant starch. Resistant starch (RS) is defined as ‘the sum of starch and products of starch digestion (such as maltose, maltotriose, and a-limit dextrins) that are not absorbed in the small bowel’ and can be classified into four types: RS I, physically inaccessible starch mostly present in whole grains; RS II, RS granules (B-type starches); RS III, retrograded starch (after food processing); and RS IV, modified starches. It is possible that earlier GI studies relied on generic foodcomposition tables, data from food manufacturers, or even food labels, which are insufficient to obtain an accurate measurement of glycemic carbohydrate. Accurate laboratory measurement of glycemic carbohydrate should be undertaken prior to embarking of GI testing. Typically, this involves analysis of moisture, fat, ash, and protein from which total carbohydrate P is obtained as ½100 ð ash þ protein þ moisture þ fatÞ. In addition, measurement of total dietary fiber is required. Glycemic carbohydrate is then calculated as [total carbohydrate by difference total dietary fiber]. This approach does not take into account resistant starch, which is difficult to

measure routinely. There are suggestions that it may be more accurate to quantitate glycemic carbohydrates directly, rather than by difference; however, this measurement is only available in specialized laboratories.

GI Versus Glycemic Response One of the central issues driving the debate on the derivation and application of GI to human health is possibly an appreciation of the difference between glycemic response and GI. As shown in Figure 1 and outlined in eqn [3], a test or reference food will produce an individual glycemic response, defined as the blood glucose response following consumption of digestible carbohydrate and measured as the AUC. As outlined before, the food GI obtained in an individual is derived by dividing the test food AUC by the mean glycemic response obtained from 2 or 3 tests of the reference food in the same individual. The food GI is then taken to be the average of the GI obtained in at least ten individuals. This approach reduces variation and provides a more precise estimate of the true mean. Studies have shown that when healthy or diabetic volunteers repeatedly consume carbohydrate foods (e.g., spaghetti, rice, and bread) on different occasions, significant variation in their glycemic response is observed, but mean GI values remain similar. Figure 2 probably best illustrates the difference between glycemic response and GI and the effect of individual variation on the derivation of these indices. Following the consumption of 50 g AC portions of five different foods (sucrose, instant potato, bread, rice, and barley) by persons with varying levels of glucose tolerance, significant differences in their blood glucose response were observed, but the between-individual variation in GI of the foods studied remained relatively constant. As such, it may be concluded that GI is a property of the food, whereas the glycemic response is a variable individual characteristic. The ecological validity of dietary GI and GL has been assessed in a randomized trial of lifestyle modification in

Partitioning of variance Variance (×106)

800

Within-subjects Between-subjects Food

8

AUC GI

4 0

AUC

GI

120

400

80

Glycaemic index (%)

AUC (mmol min l–1)

1200

12

40 0

1

3

5

7

9

11 13 15 17 19 21 23 25 27 29 31 Subject ID number

0

Figure 2 Comparison of variance associated with AUC and GI in persons with varying glucose tolerance. Incremental AUC and estimates of GI in 31 study participants (9 normal, 12 hyperinsulinemic, and 10 with type 2 diabetes) elicited by 50 g avCHO portions of five different carbohydrate foods (instant potato, white bread, spaghetti, barley, and sucrose); values are mean s.d. for the five test meals in each participant. AUC differs significantly among participants, but GI does not. Inset: the amounts of variance in AUC and GI due to the different foods, the different study participants (i.e., between individuals), and day-to-day variation (within participants) from repeated-measures analysis of variance. Expressing results as GI reduced variation between participants by 95%. Figure re-drawn using data derived from Lan-Pidhainy X and Wolever TMS (2011) Are the glycemic and insulinemic index values of carbohydrate foods similar in healthy control, hyperinsulinemic and type 2 diabetic patients? European Journal of Clinical Nutrition, 65, 727–734.

CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits free-living overweight and obese individuals with T2DM, using continuous glucose monitoring to measure the glycemic response to foods. In this study, participants consumed foods in self-selected amounts, at self-selected times, and in self-selected combinations. Participants kept 3-day dietary diaries from which intakes of energy, fat, protein, carbohydrates, sugar, and fiber were obtained and GI and GL calculated. After controlling for energy and carbohydrate intakes, dietary GI accounted for 10–18% of the variance in the glycemic response indices assessed. Further, when dietary intake was adjusted for energy, GL and GI were significantly correlated with the glycemic response. The authors concluded that GI was the strongest and most consistent independent predictor of glycemic response and variability. Less invasive studies have also shown that the predominant determinants of the glycemic response to a mixed meal are the amount of carbohydrate and meal GI, which explain 90% of the variation in mean AUC. In fact, the glycemic response is dependent on the relative amounts of carbohydrates and the amounts and types of fat and protein in the mixed meal. For example, it has been shown that addition of fat to a potato test meal reduces the glycemic response by about 50%. Other factors affecting glycemic response include nature of monosaccharide components, starch structure and relative abundance of amylose and amylopectin, degree of ripening of fruits and vegetables, and cooking and processing. It is therefore reasonable to conclude that eating a food as part of a mixed meal alters the glycemic response, but not its GI; this differentiation therefore allows for the calculation of the GI of a meal containing several carbohydrate foods as outlined in Table 3.

similar names (e.g., bread, cookies, and cakes) may have different ingredients (e.g., type of flour used) or may have used different processing methods (e.g., different cooking times resulting in different moisture contents), which could influence the degree of starch gelatinization and rate of digestion and ultimately the GI value. Starch type and structure and relative abundance of amylose/ amylopectin in different varieties of rice and potato can influence their GI. Amylose is a form of starch with a long, straight chain structure, whereas amylopectin is highly branched and allows easier access by the digestive enzymes and is therefore associated with higher GIs. Various factors affect the amylose and amylopectin content of foods; many of these influence retrogradation and resistant starch formation and include moisture, cooking and storage temperature, reheating, and ripening. These factors are discussed in detail in other articles. Many fruits

Table 4 Glycemic index of a sample of relatively unprocessed foods from different countries Food item

Country

GI (mean SEM if available)

White flour

The United Kingdom Canada South Africa Italy India China Canada Australia Canada South Africa Canada Australia The United Kingdom Canada Australia Canada New Zealand Australia China The United States South Africa

59 11 69 5 71 7 89 12 43 83 1 72 9 47 5 62 9 70 5 29 3 37 3 21 7 15 5 20 3 14 2 37 12 48 55 2 60 62 5

Rice

Banana

Lentils

Effect of Food Processing on GI/GL Soya beans

Examination of published data will show that some foods (e.g., rice and potatoes) have a wide variation in their GI values (Table 4). This is likely due to inherent botanical differences from country to country, compositional and processing differences, and possibly methodological differences in deriving GI values (see Table 2). The majority of available GI values were derived from commercially processed foods, and changes by the food manufacturers in the ingredients or processing methods used will influence the GI. Manufactured foods with

Table 3

245

Sweet corn

Source: Atkinson FS, Foster-Powell K, and Brand-Miller JC (2008) International tables of glycemic index and glycemic load values: 2008. Diabetes Care, 31, 2281–2283.

Method for calculation of the glycemic index of a mixed meal Mathematical formula

Practical example

Food

GI

CHO (g)

Meal GI

Food

GI

CHO (g)

Meal GI

a b c d e Sum

GIa GIb GIc GId GIe

ga gb gc gd ge G

[GIa ga]/G [GIb gb]/G [GIc gc]/G [GId gd]/G [GIe ge]/G Meal GI

Roast beef White bread Peas and carrots Margarine Apple juice Sum

– 71 74 – 38

0.0 50.0 5.7 0.0 23.6 79.3

0.0 44.8 5.3 0.0 11.3 61.4

GI values are based on the glucose scale, using GI of glucose ¼ 100. CHO, AC. Source: Wolever TMS (2013) Is glycaemic index (GI) a valid measure of carbohydrate quality? European Journal of Clinical Nutrition, 67, 522–531.

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CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits

and vegetables undergo ripening during which starch content decreases and sugars increase; this will produce higher GI. Moisture influences retrogradation and formation of resistant starch, whereas cold storage after cooking can promote recrystallization of the starch chains, which delays amylase activity. In this regard, potato that was precooked, refrigerated overnight, and reheated before consumption was shown to have a significantly lower GI than potato that was cooked and eaten immediately. Processing of grains and cereals disrupts the outer germ layer, cell wall integrity, and starch granules, which in turn influences starch particle size and exposes starch to enzymatic digestion, thereby affecting GI. In the case of finely milled particles, starch is more available to amylase compared to larger or intact grains. Similarly, a given food might be processed differently to produce different products (e.g., whole fruit, whole fruit puree, and fruit juice). During the varied processing methods needed to produce these items, there will likely be changes in starch structures, particle size and relative abundance of starch fractions; these will result in different GI values. The influence of food fiber content on GI is not well defined with many studies showing some or no effect. This relationship is complicated by observations that soluble and insoluble fiber appear to have varying effects on GI. In randomized controlled trial (RCT), treatment with a low-GI diet for 6 months resulted in lower HbA1c levels (a valid marker of glycemic control) compared with a high-cereal fiber diet. Examination of dietary interventions in persons with T2DM shows that high-fiber diets improve glycemic control. However, it was apparent that those incorporating purified viscous fibers more frequently lowered fasting blood glucose and total cholesterol than interventions with purified nonviscous fibers. These effects have been directly attributed to the viscosity of purified fibers and the resulting effects on digestion and absorption in the small intestine.

GI, GL, and Health Outcomes Epidemiological Studies Examination of epidemiological cohort studies in human populations consistently shows an inverse association between dietary whole grains and incident cardiovascular disease (CVD). Current guidelines recommend that diets rich in minimally processed whole grains may lower risk for T2DM. However, the relationship between GI, GL, and T2DM seems to differ by geographic location. In the United States, a recent meta-analysis of three large studies confirmed previous findings that dietary GI and GL are associated with increased risk of T2DM. Further, the combination of low-GI or low-GL diets with high cereal fiber intakes was associated with reduced relative risk of T2DM. In fact, persons who consumed diets with high GI or high GL, along with a low cereal fiber intake, had 40% higher risk of T2DM than persons who consumed low-GI or low-GL diets and had a high cereal fiber intake. This analysis also showed that obese persons who consumed highGI or high-GL diets had a >10-fold higher risk of T2DM. Further, a meta-analysis of ten studies on GI and T2DM and 14 on GL and T2DM, conducted in the United States (n ¼ 6), Europe (n ¼ 4), and 1 each in the United Kingdom, China, and Japan, showed that persons with the highest dietary GI and GL

had significantly higher relative risk of T2DM: 1.19 (CI 1.14–1.24) and 1.13 (CI 1.08–1.17), respectively. In contrast, a cohort study in eight European countries found no relationship between GI, GL, and T2DM. This difference may be attributed to the dietary assessment tools and methods used to assess dietary intakes but may also reflect the limitations in using the international table of GI and GL values. As discussed earlier, inherent botanical differences and growing conditions of crops and differences in formulation and composition of manufactured goods may limit the generalizability of GI values derived in one geographic region and used in another.

Randomized Controlled Trials There are many limitations in examining diet–disease association through epidemiological studies; this is overcome by conducting randomized clinical trials, which is widely accepted as an unbiased assessment of the effectiveness of an intervention. Numerous RCTs have been conducted to examine the efficacy of low-GI and low-GL diets in reducing risk factors for T2DM and CVD and their effects on satiety and weight loss. Over the past 5 years, several systematic reviews have been conducted in order to assess the overall effectiveness of interventions with low-GI and low-GL diets in persons with diabetes. These metaanalyses showed that interventions of at least 4 weeks in duration consistently resulted in improved glycemic control, with additional benefit seen when intake of unavailable carbohydrates is high. Similar reviews of existing RCTs have shown that insulin sensitivity is improved by consumption of lower-GI, lower-GL diets containing higher unavailable carbohydrates. In terms of CVD risk factors, after adjusting for confounding factors such as dietary fat intake, low GI was shown to reduce fasting triacylglycerol, which is one of the two major lipids found in blood. Conversely, high dietary GI is positively associated with triglycerides and negatively associated with HDL–cholesterol. When legumes are included in low-GI dietary interventions, clinically significant reductions in HbA1c are achieved, along with reductions in blood lipids, blood pressure, and body weight. There is inconsistency in the relationship between low-GI or low-GL dietary interventions and weight loss, although most studies show a nonsignificant trend that favored these diets. When unavailable carbohydrate is taken into account interventions with low GI or low GL, high legume diets are significantly associated with reductions in body weight and are probably linked to an associated reduction in energy intake. In fact, preliminary evidence suggests that low-GI or low-GL diets may have superior satiety effects, which may influence dietary energy intake.

Summary GI can be used to classify the blood glucose raising potential of carbohydrate-rich foods, but its derivation can be influenced by many food factors. As such, several precautions must be taken in order to obtain valid GI values. This could be achieved within a regulatory framework where there is scrutiny over the generation of GI values. Widespread utilization of GI in public health promotion message has been limited due to concern that increasing consumption of low-GI or low-GL diets could

CARBOHYDRATES | Glycemic Index, Glycemic Load, and Their Health Benefits lead to increased consumption of total and saturated fats, thereby increasing CVD risk. However, recent evidence indicates that lower AC intake following reductions in GI was not accompanied with increased fat intake. Rather, they are associated with improved satiety and lower dietary energy intakes.


• • • • • • •

Define glycemic index (GI) and explain the rationale for its utilization. Define glycemic load (GL) and explain the rationale for its utilization. Outline the method and precautions needed to derive the GI value for a food. Explain the derivation of the GI of a mixed meal. Outline the food factors that may influence the GI value of a food. Discuss the precautions required to achieve accurate and valid GI values. Compare the findings of epidemiological and interventional studies that have focused on the health benefits of low-GI diets.


• • • • •

What additional steps are required to improve the method for GI so that it is universally accepted as being valid and reproducible? What is required to allow the widespread inclusion of GI values on food labels? How can GI values be better used for public health promotion of healthy eating? Is there a need for further human trials of low-GI foods? If yes, what outcomes would be relevant? What is the evidence that low-GI diets can influence brain function, cognition, and satiety?

Acknowledgments This article is supported by Agriculture and Agri-Food Canada RBPI #1503, RBPI #2834/Agri-Innovation Program #068 with Pulse Canada, and #T4.H29.V1 cluster program with Pulse Canada. Prof. Thomas Wolever kindly provided Table 3 and Figure 2. Emily Padhi assisted with preparation of the other figures and tables.

247

See also: Carbohydrates: Carbohydrate Metabolism; Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Grains other than Cereals: Non-starch Polysaccharides; Resistant Starch and Health; Food Grains and the Consumer: Grains and Health; Grains and Health: Misinformation and Misconceptions; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics.

Further Reading Atkinson FS, Foster-Powell K, and Brand-Miller JC (2008) International tables of glycemic index and glycemic load values: 2008. Diabetes Care 31: 2281–2283. Bhupathiraju SN, Tobias DK, Malik VS, et al. (2014) Glycemic index, glycemic load, and risk of type 2 diabetes: Results from 3 large US cohorts and an updated metaanalysis. The American Journal of Clinical Nutrition 100: 218–232. http://dx.doi. org/10.39345/ajcn-079533. Fabricatore AN, Ebbeling CB, Wadden TA, and Ludwig DS (2011) Continuous glucose monitoring to assess the ecologic validity of dietary glycemic index and glycemic load. The American Journal of Clinical Nutrition 94(6): 1519–1524. Food and Agriculture Organization of the United Nations (1998) Carbohydrates in Human Nutrition. Rome: Food and Agriculture Organization of the United Nations Food and Nutrition, Paper 66. International Organization for Standardization (2010) Food products – Determination of the glycaemic index (GI) and recommendation for food classification. International Organization for Standardization, September 23, 2010 (ISO 26642:2010). Available from: http://www.iso.org/iso/catalogue_detail.htm? csnumber¼43633 (cited 18 August 2014). Jenkins DJA, Wolever TMS, Taylor RH, et al. (1981) Glycemic index of foods: A physiological basis for carbohydrate exchange. American Journal of Clinical Nutrition 34: 362–366. Lan-Pidhainy X and Wolever TMS (2011) Are the glycemic and insulinemic index values of carbohydrate foods similar in healthy control, hyperinsulinemic and type 2 diabetic patients? European Journal of Clinical Nutrition 65: 727–734. Li SS, Kendall CW, Souza RJ, et al. (2014) Dietary pulses, satiety, and food intake: A systematic review and meta-analysis of acute feeding trials. Obesity (Silver Spring) 22(8): 1773–1780. http://dx.doi.org/10.1002/oby.20782. Livesey G, Taylor R, Hulshof T, and Howlett J (2008) Glycemic response and health – A systematic review and meta-analysis: Relations between dietary glycemic properties and health outcomes. The American Journal of Clinical Nutrition 87(1): 258S–268S. Mirrahimi A, Chiavaroli L, Srichaikul K, et al. (2014) The role of glycemic index and glycemic load in cardiovascular disease and its risk factors: A review of the recent literature. Current Atherosclerosis Reports 16(1): 1–10. Salmeron J, Manson JE, Stampfer MJ, Colditz GA, Wing AL, and Willett WC (1997) Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA 277: 472–477. Sluijs I, Beulens JW, van der Schouw YT, et al. (2013) Dietary glycemic index, glycemic load, and digestible carbohydrate intake are not associated with risk of type 2 diabetes in eight European countries. Journal of Nutrition 143(1): 93–99. Venn BJ and Green TJ (2007) Glycemic index and glycemic load: Measurement issues and their effect on diet–disease relationships. European Journal of Clinical Nutrition 61(Suppl. 1): S122–S131. Wolever TMS (2013) Is glycaemic index (GI) a valid measure of carbohydrate quality? European Journal of Clinical Nutrition 67: 522–531. Wolever TMS, Brand-Miller JC, Abernethy J, et al. (2008) Measuring the glycemic index of foods: Interlaboratory study. The American Journal of Clinical Nutrition 87(1): S247–S257.

Fats

Contents Lipid Chemistry Healthy Fats and Oils

Lipid Chemistry L Day, AgResearch Ltd., Palmerston North, New Zealand ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

The major lipid class in cereal grains and oilseeds is triacylglycerols. The minor complex lipids are phospholipids, glycoglycerolipids and sterols. The composition of the lipids (or oil) in oilseeds determines its food or non-food applications. Extraction and quantification of different lipid classes are achieved by solvent selections and various chromatographic methods. Supercritical fluid carbon dioxide with or without cosolvent is now applied for lipid analyses and for industrial extraction of oils. Mass spectrometry is increasingly being used for the determination of lipids. Lipids play an important technological role in cereal production, storage, processing and quality of cereal-based foods. Plant lipids contain more essential polyunsaturated fatty acids than animal fats, and their inclusion in food is positive from a nutritional point of view.

Learning Objective

•

To understand lipid classes in grains and oilseeds, their analysis, their technological properties in processing, and nutritional values of plant lipids.

Introduction After protein and carbohydrate, lipids (commonly known as fats or oils) are the third most important macronutrient in human and animal diets. Although lipids are relatively minor constituents in food grains, they play an important technological role in the quality of grains upon storage: and in most aspects of processing, including milling, brewing, baking and

248

extrusion. On the other hand, oilseeds are primarily grown for their oil content. Thus, the composition of the lipids (or oil) in various oilseeds is an essential consideration in determining the use of the oil. Lipids are also essential for the nutrition and consumer acceptance of finished food products as they are carriers of fat-soluble flavor compounds and vitamins. The terminology of lipid chemistry is largely dependent on the extraction conditions, including the solvents used and temperature, and quantification methodologies.

Classification Lipids can be classified based on their physical properties at room temperature (oils are liquid and fats are solid) or their polarity (neutral lipids include fatty acids (FAs), glycerides, and sterols and polar lipids include glycerophospholipids (phospholipids) and glyceroglycolipids (glycolipids)). The most common classification of lipids is based on their structure – simple or complex. Simple lipids, composed of FAs and alcohol, include acylglycerols, ether acylglycerols, sterols and their esters that can be hydrolyzed to two different components – usually an alcohol and an acid. Complex lipids include phospholipids, glycolipids and sphingolipids, which yield three or more different compounds on hydrolysis. The FAs (carboxylic acids) are the main building blocks in lipid structures. Only a small portion of the total lipid fraction consists of free carboxylic acids, or free fatty acids (FFAs). Most of the carboxylic acids in the lipid fraction are found as esters of glycerol, that is, as triacylglycerols (TAGs), commonly known as triglycerides (Figure 1). The most common TAGs are those with long-chain carboxylic acids (C14–C22). The positions of carboxylic acids in TAGs are also important to their properties and utilization. The saturated forms of FAs are the most stable against oxidation. They also have high melting temperatures in comparison with unsaturated FAs with the same number of carbon atoms. In plant TAGs, unsaturated FAs are predominantly located in the 2 position. Monoacylglycerols (MAGs) contain only one long-


http://dx.doi.org/10.1016/B978-0-12-394437-5.00099-1

FATS | Lipid Chemistry

Glycerol Carbon Position 1

O C R O

2

H C OH + H O

3

H C

OH + H

H C O

C R O

C R′ O

H C O

C R′ O

R″

H C O

C

O C

H Glycerol

Compositions and Distribution of Lipids in Cereal Grains and Oilseeds

Ester Linkage H O

O

H H C OH + H

R″

H Fatty acid

Triglyceride

Figure 1 Triacylglycerol synthesis: R, R0 , R00 are usually long-chain alkyl groups and R, R0 , R00 are typically all different and may also contain one or more carbon–carbon double bonds.

Table 1 General classification of lipids and their commonly used abbreviations Lipid class Simple lipids: compounds with two types of structural moiety Glyceryl esters: esters of glycerol and fatty acids (see Figure 1) Triacylglycerols: 3 fatty acids Diacylglycerols: 2 fatty acids at any 2 positions Monoacylglycerols: 1 fatty acid at any position Sterol esters: esters of sterol and fatty acids Waxes: esters of long-chain alcohols and fatty acids Complex lipids: compounds with more than two types of structural moiety Phospholipids: glycerol esters of fatty acids, phosphoric acid, and other groups containing nitrogen Phosphatidic acid: diacylglycerol esterified to phosphoric acid Phosphatidylcholine: phosphatidic acid linked to choline Phosphatidylethanolamine Phosphatidylserine Phosphatidylinositol Lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol Glycoglycerolipids: 1,2-diacylglycerol joined by a glycosidic linkage through position sn-3 to a carbohydrate moiety Monogalactosyldiglyceride Digalactosyldiglyceride Monogalactosylmonoglyceride Digalactosylmonoglyceride

249

Abbreviation

TAGs DAGs MAGs SEs

PC PE PS PI LPC, LPE, LPS, LPI

MGDG DGDG MGMG DGMG

chain FA (saturated or unsaturated) at either the 1, or 2, or 3 position. Similarly, diacylglycerols (DAGs) have two FA chains at any of the two positions. However, the phosphoric acid residue of phosphoglycerides (PLs) and the first glycosidic residue of glycosylglycerides (GLs) are always in the 3 position. The general classification of the principal lipids found in cereal grains and oilseeds, brief descriptions of their basic structures, and their common abbreviations are listed in Table 1.

Cereal Grains Lipids are minor components of the cereal grains. Wheat, barley, brown rice, rye and sorghum have lower lipid contents than other cereal crops such as oats, pearl millet, and maize. All cereal grain lipids are richer in nonpolar lipids than in polar lipids. Wheat contains the highest level of glycolipids among all cereal grains, followed by triticale, rye, and barley; millet, maize, and sorghum lipids contain the lowest glycolipid content. In general, phospholipids are more abundant in wheat, triticale and rye lipids and slightly lower in the lipids of barley, maize, oat, sorghum and rice. Approximate lipid contents and the proportions of nonpolar lipids and polar lipids (separated into glycolipids and phospholipids) in each cereal are listed in Table 2. TAGs are the major nonpolar lipids in cereal grains, representing from 50% of the total nonpolar lipids in wheat and barley to as high as 90% in maize. They are deposited in spherosomes (oil droplets) bound by a monolayer membrane and are usually stored by plants in this form. The remainder of the nonpolar lipids are mainly di- and monoglycerides, FFAs, and sterol esters. The major phospholipids in cereal grains are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Monoacyl PLs, or lysophospholipids (prefix L added to LP abbreviation, Table 1), are usually regarded as degradation products of PL. The GLs are quantitatively the major components of the glycolipids in whole cereal grains and starchy endosperm. The principal sugar in the GLs is galactose, and glucose is either a minor component or absent. The main galactosylglycerides are monogalactosyldiglyceride (MGDG) and digalactosyldiglyceride (DGDG). Small amounts of galactosylmonoglycerides (monogalactosylmonoglycerides (MGMG)) and digalactosylmonoglycerides (DGMG) are also found in the endosperm of some mature cereal grains. Polar lipids are found in all membranes including the amyloplast membrane. Apart from these major acyl lipids, the other lipids in cereals include sterols and lipid-associated compounds such as carotenoids and tocopherols. Although carotenoids are very minor constituents in cereal grains, color contributed by carotenoids is an important factor in the use of cereal grains in food production, particularly in the use of durum wheat for pasta making. The lipid content in cereals is influenced by the water content, the stage of maturity, and the variety of the grain crop. Lipids are also unevenly distributed in various parts of cereal grains. For example, in the wheat grain, the germ comprises only 4% of the total grain, by weight, but it has the highest lipid content and the highest proportion of polar lipids (Table 3), whereas the endosperm, the major fraction of wheat grain, has significantly lower lipid content than the other fractions. Lipids in flour (except whole meal) can be subdivided into nonstarch and starch lipids (Figure 2). The nonstarch lipids are further divided into free lipids and bound lipids based on the extractability of lipids by solvents. The lipids that are easily extractable from flour or freeze-dried dough, with a nonpolar solvent such as hexane, ether, or petroleum ether, are called free lipids. Bound lipids refer to the nonstarch lipids that are only extractable with a very polar

250 Table 2

FATS | Lipid Chemistry Approximate lipid contents and the distribution of lipid classes of the total lipids in cereal grains Lipid class (% w/w of TL)

Cereal grains

Total lipids (% w/w in whole grain)

NL

GL

PL

Barley Maize/corn Millet Oats Rice (brown) Rye Sorghum Triticale Wheat

2.5–4.7 5.1–6.0 1.7–11.0 4.5–10.3 0.9–3.1 3.5 3.6–6.0 2.6–4.6 2.1–3.8

65–78 88–96 75–94 66–80 78–87 63–71 77–86 53–67 60–72

7–26 3 1–15 6–10 4–12 10–12 2–6 10–18 12–22

9–26 5 1–14 12–26 8–10 18–25 11–17 17–29 14–26

TL, total lipids; NL, nonpolar lipid; GL, glycolipid; PL, phospholipid.

Table 3

Distribution and compositions of lipids in wheat grain fractions Lipid class (% w/w of TL)

Grain fraction

Grain composition (%)

Lipid distribution (%)

Total lipids in each fraction (% w/w)

NL

GL

PL

Whole grain Germ Bran Endosperm Nonstarch lipid Starch lipid

100 4 4 92

100 30–35 2–5 60–70

2.1–3.8 25–35 2–4 1.5–2.5

60–72 79–85 72–80

12–22 0–3.5 6–10

14–26 14–17 13–18

33–46 4–6

30–38 1–5

24–34 90–95

TL, total lipids; NL, nonpolar lipid; GL, glycolipid; PL, phospholipid.

Wheat flour lipids

Nonstarch lipids (1.4%)

Free lipids (0.8%)

Bound lipids (0.6%)

Nonpolar lipids Polar lipids (0.6%) (0.2%)

TAG, DAG, MAG, FFA, SE

Starch lipids (1.0%)

GL, PL

Nonpolar lipids (<0.1%)

Polar lipids (0.9%)

LPC

Figure 2 The subdivision of wheat flour lipids. TAGs, triacylglycerols; DAGs, diacylglycerols; MAGs, monoacylglycerols; SEs, sterol esters; GLs, glycolipids; PLs, phospholipids; LPC, lysophosphatidylcholine.

solvent such as chloroform or water-saturated n-butanol from the flour with free lipids already removed. When free and bound lipids are extracted from flour and freeze-dried dough, the free lipid fraction in dough is only one-third of the amount of flour-free lipids. This is because two-thirds of the flour lipids become bound, mainly to gluten during dough mixing. The nonstarch lipids, which consist of all the endosperm lipids, excluding those inside starch granules, contain more GL than

PL, whereas starch lipids are predominantly PL and almost exclusively lyso-PL in which LPC is the main lipid component. The distribution of lipid classes in other cereal grains is qualitatively similar to those in wheat. The germ is the richest source of lipids among all cereal grain fractions; more than one-third of the total lipids is in the germ. In particular, maize has a larger proportion of germ in the grain, 11–25%, by weight, with an exceptionally high lipid content, 39–47% by weight, containing mostly TAGs, with a small amount of PL and traces of GL. Maize germ is, therefore, more suited for edible oil production than any other cereal, after it has been separated from the starch endosperm. The FA composition of cereal lipids is generally similar for wheat, barley, triticale, maize, and sorghum (Table 4). All cereal grain lipids are rich in unsaturated FAs. Palmitic acid (16:0) is a major saturated FA, and linoleic acid (18:2) is a major unsaturated FA for all cereals expect for brown rice. Rye lipids contain slightly higher levels of linolenic acid (18:3) than those of other cereals. Oat lipids are similar to those of brown rice; both are rich in oleic acid (18:1).

Oilseeds Unlike the cereal grains, lipids (oils) are the main constituent of the oilseed crops. Oilseeds such as canola/rapeseed, safflower and sunflower are grown for their oil. On the other hand, oil is produced as a by-product from other crops such as soybeans, which are grown primarily for their protein-rich content, and cottonseed grown for its fiber. Peanut, a

FATS | Lipid Chemistry Table 4

251

Common FA compositions of total lipids in cereal grains Fatty acid (wt%)

Lipid source

Palmitic (16:0)

Stearic (18:0)

Oleic (18:1)

Linoleic (18:2)

Linolenic (18:3)

Wheat Barley Oats Rye Maize/corn Brown rice Sorghum Triticale

17–24 21–24 7–26 12–19 11–37 14–26 10–17 16–20

1–2 1–2 1–4 1–2 1–5 1–3 1–2 1–2

8–21 9–14 22–48 12–16 11–24 36–52 21–27 8–14

55–60 56–59 31–52 57–65 46–63 25–39 42–58 57–60

3–5 4–7 1–4 3–12 1–6 1–4 1–5 4–6

Table 5

Oil contents in oilseeds

Oilseeds

Oil in dry seed (% w/w)

Canola Rapeseed/mustard Cottonseed Linseed Peanut Safflower Soybean Sunflower

40–50 30–50 15–25 35–45 36–56 12–47 15–22 25–50

leguminous oilseed, is used not only for edible oil production but also for direct consumption in various human foods, being a good source of protein and oil. Another oilseed crop, linseed, produces oil that is not extensively used for food, but it is nevertheless an important industrial oil. Lipid contents vary among the oilseed crops, shown as oil contents in Table 5, ranging from about 15% to 25% in soybean and cottonseed, to as high as 50% in sunflower and canola/rapeseed, to 56% in peanut. It must be emphasized that both oil content and component FA proportions in an oilseed are subject to quite a wide variation. Such variations arise from genetic manipulation of seed varieties, climatic factors and cultivation practices. Lipids in oilseeds are predominantly TAG, 90% or more of total lipids, and phospholipids being the main polar lipids. Other minor lipid constituents are FFAs, sterols, hydrocarbons, etc. The FA composition of lipids is the main influence in terms of the ‘quality’ and the uses of the oil. Cottonseed oil has high levels of saturated FAs among the oilseeds, 18–25% palmitic acid, and a small amount (1–3%) of myristic acid (Table 6). The main unsaturated FAs are linoleic acid (32–52%) followed by oleic acid (10–32%). Cottonseed oil has a significant storage stability not only due to its lesser amount of unsaturated FAs content but also due to the presence of enough tocopherols to reduce lipid peroxidation. Among the common oilseeds, safflower, sunflower, and peanut oils contain high levels of unsaturated FAs. Sunflower oil is characterized by its high concentration of linoleic acid (60–70%) followed by oleic acid (15–35%). The high proportion of polyunsaturated FAs makes sunflower oil a popular source of essential FAs in the diet. Sunflower, safflower and soybean oils are the oils containing the highest levels of

linoleic acid (C18:2). The FA composition of safflower oil is similar to that of sunflower. The oil of commercial safflower cultivars contains 55–81% linoleic acid and 7–42% oleic acid as major FAs, followed by stearic acid (1–10%) and palmitic acid (2–10%) as minor FAs. In peanut oil, oleic and linoleic acids constitute 33–71% and 12–46% of the total FAs, respectively. A high proportion of unsaturated FAs in an edible oil, however, does decrease its storage stability and quality, due to oxidation reactions associated with the double bonds in unsaturated FAs. In addition, more and more nutritional studies are showing that linoleic acid is not necessarily good for your health. A new type of sunflower that has about 65–71% oleic acid has been produced to replace the traditional sunflower. Unlike other oilseeds, FA composition in rapeseed oil is unusual in that it contains substantial amounts of long-chain FAs, in particular a significant amount of erucic acid (22:1) as 20–50% of total lipids (Table 6). Major changes in the FA composition of rapeseed oils have arisen as a result of selective breeding for low levels of erucic acid. This is because of some indications that erucic acid had antinutritional properties. Consequently, varieties of rapeseed (called ‘canola’) have been developed in which the level of erucic acid is virtually zero. Canola varieties are also characterized by markedly increased levels of oleic acid with smaller increases also in linoleic and linolenic acid content compared with those of the former rapeseed varieties due to the substantial reduction of erucic acid content (Table 6). Canola is the oil with the lowest content of saturated FAs. Linolenic acid content has also been reduced in some canola varieties in favor of linoleic acid, through selective breeding. Low-linolenic acid content canola varieties could have less than 2% linolenic acid and resemble olive oil in terms of their monounsaturated FA contents more than the high linolenic acid content oil variety (conventional canola varieties). Linseed oil is characterized by high levels of linolenic acid (52–60%), which undergoes autoxidation to give thin, crosslinked, and tough films, making it unsuitable for edible purposes. It is, however, an important drying oil used to produce oil-based paints.

Extraction and Quantification of Lipids Accurate and precise analyses of lipids are important, not only for the determination of their nutritive values for human

252


Table 6

FA compositions of total lipids in oilseeds Fatty acid (% w/w)

Lipid source

Palmitic (16:0)

Stearic (18:0)

Oleic (18:1)

Linoleic (18:2)

Linolenic (18:3)

Canola Rapeseeds Cottonseed Linseed Peanut Safflower Soybean Sunflower

3–5 1–3 18–25 5–7 8–14 2–10 6–12 5–7

1–1.5 0.7–1 1–2 3–4 2–6 1–10 2–5 2–6

57–60 12–14 17–38 18–20 37–56 7–42 20–34 15–35

10–20 11–22 45–55 15–17 25–40 55–81 46–56 60–73

10–12 8–10

health benefits, but also for the understanding of the structural characteristics and functional properties of lipids, which may allow the development of tailor-made products that are designed for a particular function or application. Analyses of lipids involve several steps which usually include preparation of the sample, solvent extraction of the lipids, removal of the solvent and separation of the lipids into classes for qualitative or quantitative analyses. Sample preparation mainly involves particle-size reduction of plant tissues or seed materials using methods such as grinding. The purpose of this step is to increase surface area and facilitate subsequent lipid extraction. In some cases, acid hydrolysis may be required to release lipids which are covalently bound to proteins and carbohydrates.

Solvent Extraction The choice of organic solvents for lipid extraction largely depends on both the chemical nature of the sample and the type of lipids to be extracted, that is, total lipids, starch lipids, and polar or nonpolar lipids. Neutral lipids are hydrophobically bound and can be extracted readily by nonpolar solvents, whereas polar lipids, such as glycolipids and phospholipids, which are predominantly bound by electrostatic forces and hydrogen bonding, require polar solvents capable of breaking such bonds. Hexane (petroleum ether) is the preferred solvent for extracting nonpolar, neutral lipids such as triglycerides and is the main solvent used for oilseed crushing/extraction for the industrial production of crude oil from oilseeds because of its low cost. However, cereal grains and milled flour contain relatively large amounts of glycolipids and phospholipids, and large amounts of cereal lipids (about half of the total lipids) are bound to polypeptides or polysaccharides. Therefore, more polar solvents such as chloroform, alcohol, or chloroform–methanol (2:1) mixture are needed for extraction. Hexane combined with an acid hydrolysis will give a complete extraction of the lipids from cereals. Removal of the solvent from lipid extracts is normally conducted under vacuum in a rotary evaporator at or near room temperature. Care must be taken to minimize lipid oxidation during sample preparation, solvent extraction and storage of lipids. Cereal lipids characteristically contain large proportions of polyunsaturated FAs together with carotenoids and tocols, all of which are highly susceptible to autoxidation. The lipids are only slowly oxidized while the grain tissues are intact, but once the tissues have been disrupted, oxidation must be

Others 20–50% erucic (22:1) 1–3% myristic (14:0)

52–60

5–12

minimized by keeping lipids in solvents such as chloroform and under a nitrogen atmosphere as well as by working at low temperatures if possible.

Supercritical Fluid Extraction Supercritical fluid extraction (SFE), which utilizes the solvation power of the gases when compressed above critical point fluids at pressure and temperature, has been applied for lipid analyses and for industrial extraction of oils. Carbon dioxide (CO2) is the most widely used supercritical fluid. The preparation of the sample before extraction is extremely important. For solid materials, for example, grains, seeds, flours, or meals, the material needs to be ground to produce smaller particles in order to increase surface area and promote more efficient extractions. Supercritical CO2 is generally considered a more selective solvent than hexane. The fact that supercritical CO2 is a good solvent for nonpolar and moderately polar compounds makes it an excellent choice for extracting lipids without extracting other more polar nonfat components. In this way, it is possible to extract nonpolar TAG without the coextraction of PL. However, polar lipids such as PL can also be extracted by the supercritical CO2 method with the use of solvent modifiers such as ethanol, which increases the polarity of the supercritical CO2. The SFE method uses no hazardous solvents, so it is well suited for the process-control environment. The SFE-based test methods have been approved as an official method by AOCS for the determination of processscale extractable oil or determination of total oil. The method has two parts involving extraction with supercritical CO2 alone or plus 15% ethanol. Although SFE has been used for wheat lipid extraction, there is no official SEF-based method for extraction of lipids from wheat and other similar cereal grains. Lipid extracts are complex mixtures of individual classes of compounds and require further separation. Many chromatographic and spectroscopic techniques are in use to separate and quantify individual lipid components. The most commonly used techniques are thin-layer chromatography (TLC), highperformance liquid chromatography (HPLC) and gas chromatography (GC).

Thin-Layer Chromatography TLC provides the separation of a wide variety of compounds with different polarities on a single plate and has long been


Triglycerides

Free fatty acids

253

lipids. In most cases, glycolipids overlap phospholipids in TLC systems that separate phospholipids. More complex GLs or PLs are preferentially separated by two-dimensional TLC, using a neutral/basic solvent such as in the first dimension and an acidic solvent in the second dimension. TLC offers a much higher sample throughput due to the possibility of performing separations simultaneously, and it can handle ‘not-so-clean’ samples since the separation medium is used only once. TLC is a cost-effective, simple, and easy chromatographic technique.

High-Performance Liquid Chromatography

Glycolipids

Phospholipids

1

2

3

Figure 3 Separation of wheat flour lipids by TLC on a silica gel G plate (20 20 cm) developed in chloroform/methanol/water (90:20:2 v/v/v). Wheat flour was collected from different mill streams (1–3: early–late), where more TAGs were detected in the later mill streams as progressively more bran materials were being incorporated into flour.

used for the separation of cereal lipids. Silica is still the stationary phase material preferred. Small amounts of lipid material are spotted on a plate. The plate is then developed in a lidcovered glass chamber containing a mixed solvent system, which behaves like a gradient elution during travel on a plate. The separation of lipids is based on relative affinities of the components to the TLC adsorbent. When the solvent front is close to the top of the plate, the plate is removed from the chamber and residual solvent is evaporated under an inert atmosphere. The separated lipid spots can be visualized as brown spots (temporarily) by exposing to iodine vapor or under UV light after spraying with fluorescent agents or as dark spots (permanent) by spraying with sulfuric acid (10–50% in ethanol v/v) and subsequently charring above 160 C. The advantage of using a temporary nondestructive detection is that the lipid spots may be recovered from the silica gel for preparative or analytic proposes. Lipids, after separation on a silica plate, may also be quantitated by densitometric or fluorimetric scanning. Cereal lipids can be separated into various classes by TLC. As an example, Figure 3 shows the separation of wheat flour lipids extracted by chloroform from different flour mill streams, where more TAGs were detected in the later mill streams (lane 3) as more bran materials were being incorporated into flour. Straightforward unidimensional TLC is adequate for the separation of nonpolar lipids and some polar

In principle, separations by HPLC are carried out by essentially the same separation principle as TLC. Using HPLC, it is easier to generate large numbers of ‘theoretical plates’ (a measure of resolution efficiency); HPLC is simpler to automate than TLC. However, HPLC is much more expensive than TLC in terms of both equipment and running costs. HPLC separation occurs in a stainless steel column packed with a very uniform, finely divided, microspherical adsorbent material of controlled porosity and degree of hydration. A high-pressure pump ensures adequate and constant flow of solvent, the ‘mobile phase,’ through the column, and a flow-through detector continuously monitors the column eluate. Adsorption chromatography with columns of silica gel is commonly used for the separation of lipids. Elution of the column may be carried out either with a solvent mixture of constant composition or by gradient elution, in which the solvent composition is varied linearly or in a stepwise fashion with both binary and ternary solvent systems. The choice of the elution systems is sometimes restricted by the use of the detection system. For example, a solvent mixture of constant composition with low UV absorbance may be essential for a UV detector. Although gradient solvent systems can be used with an evaporative lightscattering detector (ELSD), the choice of solvents is constrained by the need for sufficient volatility for evaporation in the detector under conditions that do not cause evaporation of the solute. Complicated programs (up to eight steps) are sometimes required to achieve the desired separations. However, ELSD has presently become the detection method used most often in the separation of lipids by HPLC. HPLC for analysis of all simple lipid classes in one chromatographic run has not yet been used widely, probably because TAGs (major components in all cereal grains and oilseeds) dominate the system. HPLC methods have been devised more for specific analysis of individual components. The use of HPLC for the separation of complex lipids has increased. Separation of glycolipids MGDG and DGDG, along with several phospholipids from wheat flour lipid extracts at analytic scale (Figure 4), as well as preparative scale, has been achieved.

Gas Chromatography GC is the most useful tool for the analysis of the FA composition in lipids. Derivatization of FAs is required to increase their volatility. Fatty acid methyl esters (FAMEs) may be prepared by different transmethylation techniques and then separated on GC columns and detected by a flame ionization detector (FID). The gas phase for GC is usually nitrogen, hydrogen, or helium.


900 800

1000

700

200

300

100

0 10

15

20

25 30 Time (min)

35

40

Figure 4 HPLC analysis of wheat flour polar lipids extracted by chloroform. Separation was carried out on a PVA-Sil threaded guard column (23 4.0 mm i.d.) with gradient elution at 0.5 ml min1 and detected by a ELSD. Four steps of gradient were used for the separation – 0–10 min, 100% eluent A (2,2,4-trimethylpentane); 10–20 min, 90% eluent A þ 10% eluent B (tert-butylmethylether); 20–35 min, 100% eluent B; and 35–40 min, 100% eluent C (methanol/n-ethylmorpholine/ glacial acetic acid (500:4.2:1.5 v/v)). For abbreviation of lipids, see Table 1.

Since the principal FAMEs in cereal and oilseed lipids are 16:0, 16:1, 18:0, 18:1, 18:2, and 18:3, heptadecanoic acid (17:0) can be used as an internal standard. Identification and quantification of individual FAs can be achieved by comparing and calibrating with relatively cheap FAME standards. Figure 5 shows a typical GC profile of FA compositions in canola oil. FA compositions in lipid classes can also be obtained by GC analysis of lipids in each class separated or prepared by TLC or other column chromatographic techniques. Lastly, mass spectrometric detection is being used increasingly for the detection and analysis of complex lipids. The technique can be used with direct inlet injection or linked to HPLC or GC systems where the mass spectrometer serves both to detect lipids and to obtain information on their molecular structure.

Functionality of Lipids in Bakery Products Apart from being used directly as a source of human food and animal feed, a large proportion of cereal grains are milled to flour, which is then used for producing various food products. Wheat has been the predominant cereal grain used for baked goods, largely due to its ability to form dough when flour is mixed with water. Rye ranks next in importance while other cereals assume a role in specialized products and in the preparation of composite flours. The rheological properties of doughs made from wheat flour are principally determined by the gluten protein, and lipids (naturally occur in cereal grain, excluding added fat) appear to make little contribution. When protein is removed from flour, dough and bread-making properties are lost. In contrast, good dough properties and bread-making capacity are retained after removal of the nonstarch lipids. However,

18:2 linoleic

400

200

PC

PG

400

500

18:0 stearic

600

600

16:1 palmitic

800

Response (mV)

MGDG

Response (mV)

18:1 oleic

1200

18:3 linolenic

DGDG

254

0 20

25

30

35

Time (min) Figure 5 GC analysis of a canola oil. FAs methyl esters separated using a capillary GC column (SP2560, Supelco) and detected by an FID at 240 C.

flour lipids do affect the loaf volume and crumb texture of bread. Fractions of polar and nonpolar lipids have opposite effects on baking performance. Incremental addition of the extracted lipid to a defatted flour produces an unusual effect on the loaf volume and texture in a rapid baking test in which exogenous lipid is omitted. Loaf volume decreases to a minimum at a lipid content intermediate between those of the defatted flour and untreated flour and thereafter increases. At high lipid contents (above the inherent lipid content of the flour), the loaf volume–lipid curve tends to plateau. The changes in volume are paralleled by changes in crumb grain, which, at first, also deteriorates and then improves. Fractions of polar and nonpolar lipids affect loaf volume and crumb grain in opposite ways. The polar lipid fraction has generally beneficial effects, whereas the nonpolar fraction has deleterious effects. Thus, if the ratio of polar to nonpolar lipid is increased, the minimum of the loaf volume–lipid content curve is shifted to lower lipid contents. If the percentage of polar to nonpolar lipid in a flour is varied from 0 to 100 at a constant lipid level, test-bake loaf volume increases approximately in a linear manner. The addition of different lipids to test their effects on dough has shown that the unsaturated FAs such as linoleic acid are the components that mainly contribute to the deleterious effects of the nonpolar fraction. Higher loaf volume and better crumb texture in bread are favored by a high ratio of polar/nonpolar lipid and a high content of flour lipid. However, the variation in loaf volume that can be attributed to lipid is relatively small, and by far, the greatest variation is imposed by the effect of gluten protein quality. The role of the polar lipid appears to act as a complex mixture of components with surface activities in stabilizing or destabilizing the gas bubble structure during expansion of the loaf and thus the final texture. Upon heating (i.e., during baking), the dispersed lipids provide an interfacial film at the surface of gas cells, thus helping to modulate the growth, expansion and coalescence of air cells. In addition to their effects in influencing volume and texture of baked products, lipids also play a role in staling mechanisms. Generally, the

FATS | Lipid Chemistry presence of lipid reduces bread staling and enhances shelf life. This is largely due to the interaction between lipids and starches. When monoacyl lipid monomers are present to form the lipid–starch complex, an insoluble amylose–lipid film is likely to be formed on the surface of the starch granules. Such a film is capable of acting as a barrier against water transport involved in the staling process. The effects of lipids have also been studied for Arabic bread, steamed bread, cakes and biscuits. Despite differences in processing, the general features with respect to lipids have much in common. It is the crumb texture that is influenced most, and, like bread, differences in lipids have not been found to account for major variations in quality. However, the contribution of the lipid component to flour quality should not be ignored when considering parameters to be used as a basis for selection in plant breeding programs even though protein composition appears to be the major factor that determines flour quality. The ‘quality factors’ in flour lipid, as presently known, are a high nonstarch lipid content, a high ratio of polar to nonpolar lipid, and a low free fatty acid content.

Nutritional Values Lipids are the richest source of energy on a weight basis. They are essential components of our diet and play vital physiological and biochemical roles in human health and well-being. Lipids also increase palatability, including taste, aroma, and texture of food, because they are carriers of fat-soluble flavors. Fats and oils are also good carriers of fat-soluble vitamins such as vitamins A, D, E, and K. Plant lipids contain tocopherols and tocotrienols, which are the most important sources of vitamin E. Appropriate intake of lipids is essential for health maintenance. However, a high consumption of fat, especially saturated FAs, may be connected with several chronic diseases, such as heart disease and obesity. Of the lipid components of a normal diet, the most important FAs are linoleic acid (n-6) and a-linolenic acid (n-3), the two primary essential polyunsaturated fatty acids (PUFAs). They play a role in stabilizing biological membranes by creating physical properties that are optimal for the transport of substances across the membrane and for the biochemical reactions occurring in the membrane. Through metabolism, they are converted into a whole range of oxygenated compounds which exert a range of profound physiological activities involving lowering plasma cholesterol, aggregating red blood cells, and smoothing muscle performance, all attributes that are required for good health. However, studies have shown that too much linoleic acid (C18:2) can have adverse effects on health, especially causing inflammatory conditions. Since the human body is unable to synthesize them, they must be obtained from dietary sources. Since plant lipids contain more essential PUFAs than animal fats, their inclusion in food is positive from a nutritional point of view. The important source of the essential FAs is oilseeds. Although cereal grains contain high amounts of linoleic acid, due to the generally low total lipid content of the grain, they are unlikely to have much contribution to the essential FA intake in the human diet, except when the lipids are extracted from the lipid-rich germ and produced as oil, such as maize, or rice germ oil or wheat bran oil.

255

Oils extracted from oilseeds, however, have a sufficient influence in the total fat intake of the human diet since they are used directly for frying foods, as cooking ingredients, and as spreads. Recent developments in plant molecular biology now allow the engineering of oilseeds with increased omega-3 long-chain PUFAs through complex multigene biosynthetic pathways. Such development can have a considerable potential to increase the nutritional values of plant-based oils.


• • • • • • •

What are the different classes of lipids in cereal grains and oilseeds? What are the most common fatty acids in cereal grains and oilseeds? What are the different solvents used for the extraction of nonpolar or polar lipids? What is the most common gas used in the SFE-based test methods and how can the SFE extraction be used for the determination of nonpolar TAG and total oil? How to prepare lipid samples for gas chromatographic analysis? What are the functional properties of lipids in bakery products? What are the different roles of nonpolar and polar lipids in cereal processing? Which polyunsaturated fatty acids are most common in plant-based lipids?


•

• •

The multiple interactions of lipids with other constituents (i.e., proteins during dough mixing and starch) are important for the processing and quality of cereal foods. How do different classes of lipids, for example, nonpolar and polar lipids, influence the functions of gluten proteins and the starch-gelatinization mechanism? How can mass spectrometry be used to improve the detection and identification of lipids? How can generic breeding increase the nutritional values of plant-based oils?

See also: Agronomy of Grain Growing: Soybean: Agronomy; Barley, Rice and Maize Processing: Oil from Rice and Maize; Breeding of Grains: Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Carbohydrates: Starch: Starch Architecture and Structure; Fats: Healthy Fats and Oils; Grain Marketing and Grading: Soybean: Grading and Marketing; Oilseed and Legume Processing: Soybean: Processing; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; The Legumes and Pseudocereals: Peanuts: Overview; The Oilseeds: Cottonseed: Overview; Oilseeds: Overview; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Gluten and Modified Gluten; Ultrastructure of the Wheat Grain, Flour, and Dough.

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Further Reading AOCS (2000) In: Official Methods and Recommended Practice of the American Oil Chemists Society. Champaign, IL: The Society. Barnes PJ (1983) Lipids in Cereal Technology. London: Academic Press. Christie WW (2010) Lipid Analysis – Isolation, Separation, Identification and Structural Analysis of Lipids, 4th edn. Bridgwater: The Oily Press. Chung OK (1986) Lipid–protein interactions in wheat-flour, dough, gluten, and protein-fractions. Cereal Foods World 31: 242–244, 246–247, 249–252, 254–256. Chung OK and Ohm JB (2000a) In: Lorenz KJ and Kulp K (eds.) Handbook of Cereal Science and Technology, 2nd edn., pp. 417–477. New York, NY: Marcel Dekker. Chung OK and Ohm J-B (2000b) Cereal lipids. In: Karel K and Ponte Jr. JR (eds.) Handbook of Cereal Science and Technology, 2nd edn. New York, NY: Marcel Dekker. Chung OK, Ohm JB, Ram MS, Park SH, and Howitt CA (2009) Wheat Lipids. St. Paul, MN: American Association of Cereal Chemists Inc (AACC). Damude HG and Kinney AJ (2008) Engineering oilseeds to produce nutritional fatty acids. Physiologia Plantarum 132: 1–10. Eliasson A-C and Larsson K (1993) Cereals in Breadmaking. A Molecular/Colloidal Approach. New York, NY: Marcel Dekker. Gunstone FD (1996) Fatty Acid and Lipid Chemistry. Glasgow: Chapman and Hall. Hubbard JD, Downing JM, Ram MS, and Chung OK (2004) Lipid extraction from wheat flour using supercritical fluid extraction. Cereal Chemistry 81: 693–698. King JW (2002) Supercritical fluid technology for lipid extraction, fractionation, and reactions. In: Lipid Biotechnology, pp. 663–687. New York, NY: Marcel Dekker.

King JW (2004) Critical fluid technology for the processing of lipid-related natural products. Comptes Rendus Chimie 7: 647–659. Macritchie F (1981) Flour lipids – Theoretical aspects and functional-properties. Cereal Chemistry 58: 156–158. Morrison WR (1978a) Cereal lipids. Advances in Cereal Science and Technology 2: 221–348. Morrison WR (1978b) Wheat lipid-composition. Cereal Chemistry 55: 548–558. Morrison WR (1978c) Cereal lipids. In: Pomeranz Y (ed.). Advances in Cereal Science and Technology, vol. II, pp. 221–348. St. Paul, MN: American Association of Cereal Chemists. Morrison WR, Tan SL, and Hargin KD (1980) Methods for the quantitative-analysis of lipids in cereal-grains and similar tissues. Journal of the Science of Food and Agriculture 31: 329–340. Papantoniou E, Hammond EW, Scriven F, Gordon MH, and Schofield JD (2001) Isolation of polar lipid classes from wheat flour extracts by preparative highperformance liquid chromatography. Cereal Chemistry 78: 663–665. Rocha JM, Kalo PJ, Ollilainen V, and Malcata FX (2010) Separation and identification of neutral cereal lipids by normal phase high-performance liquid chromatography, using evaporative light-scattering and electrospray mass spectrometry for detection. Journal of Chromatography A 1217: 3013–3025. Salunkhe DK, Chavan JK, Adsule RN, and Kadam SS (1992) World Oilseeds – Chemistry, Technology, and Utilization. New York: Van Nostrand. Tweeten TN, Wetzel DL, and Chung OK (1981) Physicochemical characterization of galactosyldiglycerides and their quantitation in wheat-flour lipids by highperformance liquid-chromatography. Journal of the American Oil Chemists Society 58: 664–672.

Healthy Fats and Oils SM Ghazani and AG Marangoni, University of Guelph, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Healthy minor components in fats and oils. Fatty acids and triglyceride profiles of different oil sources. Classification of fats and oils. Major vegetable oils and beneficial components in them. Oil refining and its effects on healthy minor components.

Learning Objectives

• • • •

To understand healthy minor components in oils. To categorize oils and fats based on fatty acid composition. To diagnose differences between desirable and undesirable minor components in oils. To realize the main purpose of oil refining.

Introduction Fats and oils are considered an important part of our daily diet intake because they provide a concentrated source of energy and essential fatty acids. They are carriers of fat-soluble vitamins (A, D, and E) and make fundamental parts of cell walls and other biological structures. In addition to biological functions and nutritional properties, they exhibit key functionality by playing an important role in the final quality of food products. Fats and oils can naturally be found in different sources, but only a few of these sources are of economic importance. Oils and fats may mainly originate from plants (seeds, beans, and fruits), animals (lard, tallow, fish oil, and milk fat), and microbial sources (yeasts, algal, and bacteria). Edible oils are mainly obtained from beans, seeds, and fruits by mechanical and/or solvent extraction. Based on USDA statistical reports, total world vegetable oils production for 2012/2013 was 160.7 million tonnes. Meanwhile, the production levels of four main vegetable oils in that period were palm oil (55.8 million tonnes) followed with soybean oil (42.8 million tonnes), canola oil (24.9 million tonnes), and sunflower oil (13.5 million tonnes). In that period, the total amount of produced animal fats from four main sources (lard, tallow, fish oil, and milk fat) was about 25 million tonnes (Table 1). It is important to consider two important points. First, some part of produced oils is used for nonedible applications (e.g., oleochemical industry, biodiesel, cosmetic), and second, daily dietary intake of fats and oils may go above the total amount of produced oils because other lipid-containing food sources such as nuts, meat, and dairy products should be considered in the diet as a source of fats and oils. Recent studies in biotechnology and plant molecular biology led to the introduction of numerous types of engineered oilseeds and microbial sources to produce novel fats and oils with new fatty acid and triglyceride compositions and with a higher oil yield. New


sources are important for their unique quality of healthy minor components, fatty acid profile, or triacylglycerol composition (e.g., high oleic oils for frying oil or omega-3-enriched oils). As fats and oils are the highest source of energy in the human diet and their main contribution is palatability of many food products, selecting a good source of fats and oils based on the daily calorie need is important. Choosing an appropriate source of oil and monitoring the energy intake may be helpful in controlling obesity, which is considered a risk factor for many chronic diseases such as diabetes, cancer, and cardiovascular diseases (CVDs).

Health and Nutrition Properties of Fats and Oils Because fats and oils have different composition when it comes to health, interest in specifying a fatty acid profile and healthy minor components has been emerging. Oils and fats are predominantly a mixture of triacylglycerols as main organic components that provide energy (9 kcal g1) accompanied by other minor components that could be nutritionally important such as tocopherols, tocotrienols, sterols, polyphenols, phospholipids (PLs), sphingolipids, and hydrocarbons. Also, other minor components are available and mostly removed during refining steps like waxes, free fatty acids, mono- and diacylglycerols, flavoring, and coloring agents. More than the source of fats and oils, many other factors such as varieties, growing conditions, maturity of seeds or fruits, harvesting time, storage conditions, handling, and processing settings (extraction and refining oil) may affect the level of healthy minor components in oils. Based on current recommendations, adults should get 20–35% of daily calories from fats and oil sources. Currently we are emerging with two trends in food intake—first, increasing consumption of processed foods and snacks, and second, increased demand for virgin or cold-pressed oils. As oils in the snack foods made up a relatively large portion intake of energy in industrialized countries, choosing snacks could directly affect the health. In this article, first nutritional properties of healthy minor components will be discussed followed by a comparison between fatty acid composition of fats and oils, and main sources of fats and oils will be reviewed.

Healthy Minor Components Phospholipids PLs are organic components with both hydrophilic and hydrophobic moieties in molecule structures. They can be found in all plant and animal cell membranes. The main food sources of PLs are egg yolk (8–10%), butter (0.5–1.2%), and crude vegetable oils (0.5–3.7%). The six major types of PLs in vegetable oils are phosphatidic acid (PA), phosphatidylcholine (PC),

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FATS | Healthy Fats and Oils

Table 1

World main vegetable oils production, 2009/10–2013/14 (million tonnes)

Oil type/year

2009/10

2010/11

2011/12

2012/13

2013/14a

Coconut Cottonseed Olive Palm Palm Kernel Peanut Rapeseed Soybean Sunflower Total

3.52 4.59 3.08 46.04 5.60 4.89 22.56 38.80 12.28 141.36

3.70 4.96 3.25 48.73 5.73 5.33 23.52 41.30 12.42 148.94

3.41 5.25 3.24 51.95 6.14 5.32 24.22 42.59 15.34 157.46

3.65 5.27 2.67 55.77 6.51 5.55 24.90 42.81 13.53 160.66

3.54 5.11 3.28 58.43 6.86 5.67 25.76 44.66 15.67 168.98

a

Forecast, Source: USDA, Foreign Agricultural Service, Oilseeds: World Markets and Trade.

phosphatidylethanolamine (PE), phosphatidyl glycerol, phosphatidylserine (PS), and phosphatidylinositol (PI). PLs showed great positive functionality in several diseases such as liver diseases, neurological disorders, CVDs, and hepatic and colon cancers. They also have immunological functionality for body system, and they can improve physiological and mental performances. The amount of PLs in crude oils depends on the oil sources and extraction method. Solvent-extracted oils have higher phosphatides than mechanically extracted oils. PLs have been shown to have effects on lowering blood cholesterol and TAG levels in serum. Many studies have shown that in athletes, PS can improve performance and decrease muscle damage during some sports like cycling, weight training, golf, and endurance running. Among PLs, PI and PE are more effective than PC in increasing oxidative stability of oils as a synergistic function with a-tocopherol. In the digestive tract, PLs play an important functionality in the metabolism of lipids and other digestive fluids. Although PLs have health-promoting properties, from an industrial viewpoint, they are considered undesirable components. In the neutralization process, they work as an emulsifier, hinder the separation of oil and water phases, and help to increase the oil loss in this step. Also, they may interfere with bleaching clays, poison nickel catalysts throughout hydrogenation, darkening oil during deodorization and decreased shelf life of refined oils. PLs can be almost completely removed from oil through the degumming stage of oil refining; only they can be found in virgin or cold-pressed oils in different levels.

Sterols Sterols comprise of the main part of unsaponifiable matter of fats and oils. In fats and oils, they can be in two forms of free and esterified sterols. Free sterols can commonly esterify with fatty acids, glycosides, and/or ferulic acid to make sterol esters. The amount of phytosterols in most of common vegetable oils is usually between 1000 and 5000 ppm (1–5 g kg1). However, higher levels could be found in rapeseed oil (5000–11 000 ppm) and in corn oil (8000–22 000 ppm). The major phytosterols in common vegetable oils are brassicasterol, campesterol, stigmasterol, b-sitosterol, and avenasterol. Canola oil, corn oil, sesame oil, and soybean oil are good sources of phytosterols between vegetable oils. Some sterol

esters, for instance g-oryzanol in rice bran oil, have unique nutritional properties such as antioxidant activity, hypolipidemic effects, and stimulation of growth and hypothalamus activity. Hypocholesteremic properties of phytosterols have been studied, and based on the guidelines, 2 g of phytosterols per day, along with 10–25 g soluble fibers, was recommended. In animal fats, the main sterol is cholesterol. Although a trace level of cholesterol 20–50 ppm could be found in vegetable oils, it is much lower than the levels reported for animal fats (up to 1000 ppm), fish oils (up to 7000 ppm), dairy fats (2000–3000 ppm), and egg yolk (12 500 ppm). It is important to note that cholesterol is not primarily associated with the storage adipose (tallow or lard), so lowering the level of total fat in meat (using lean or extra-lean meats) will not greatly decrease the cholesterol content because it is a necessary membrane component. In the human blood system, there are two main types of cholesterol named high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol. HDL cholesterol is ‘good cholesterol’ because excess HDL cholesterol is carried to the liver and then metabolized. LDL cholesterol is ‘bad cholesterol’ because it remains in the blood plasma and can start to produce plaques in the arterial wall and lead to obstruction of heart blood artery, causing a heart attack. So elevated total and HDL cholesterol levels are considered risk factors for the development of coronary heart disease that is one of the main health problem in developed countries. Phytosterols in vegetable oils can inhibit cholesterol absorption. Intake of phytosterols at the level of 1.5–3 g day1 can bring total blood cholesterol and LDL cholesterol lower by 10–15%. Phytosterols usually have a lower absorption rate in the digestive tract than cholesterol; for example, only 5% of b-sitosterol of the food supply can be absorbed, so phytosterols in foods can compete with cholesterol absorption and leads to an increase in bile secretion and inhibition of cholesterol absorption from the gut. Much research has shown that phytosterols, especially b-sitosterols, inhibited cancer growth and may offer protection from colon, prostate, and breast cancers. Besides cholesterol, ergosterol (precursor of vitamin D2) can also be found in animal fat sources such as fish oil and butter fat. Phytosterols are stable molecules, but after as long time being heated or exposed to oxygen during food processing

FATS | Healthy Fats and Oils and storage, they are susceptible to oxidation, and oxidized phytosterols (oxyphytosterols) are absorbed from digestive tract. Oxyphytosterols could be mutagenic and be a source of free radicals, so they can affect cell viability, stimulate inflammation, cause oxidative changes in the retina, and affect hormonal activity. So monitoring the amount of oxidized phytosterols, especially in long heated or fried foods, would be necessary.

Tocopherols The tocols (tocopherol and tocotrienol molecules) are natural fat-soluble organic components with antioxidant properties. Many factors may influence the concentration of tocols in oilseeds such as the amount of unsaturated fatty acids, climate conditions, and genotype. In extracted oils, the method of oil extraction has a great influence on tocol concentration in crude oils. For example, solvent-extracted oils usually contain higher amounts of tocopherols than cold-pressed oils. In crude oils, the concentration of tocopherols and tocotrienols varies between 200 and 1200 ppm. Tocopherols are free or esterified molecules found in four homologues, namely, a-, b-, g-, and d-tocopherols. In living organisms (in vivo systems), a-tocopherol shows the highest vitamin E activity and the most effective antioxidant properties compared to the other isomers, whereas in the food system (in vitro) the antioxidant activity of the tocopherol isomers decreases in the order: d > g > b > a. A single molecule of tocopherol can react with more than 100 molecules of singlet oxygen, and this specific property is related to their ability to transform to their active form after oxidation. Tocotrienols have more antioxidant activities than tocopherols. They also have health benefits such as hypocholesterolemic, antithrombic, and antitumor properties. Tocoterienols, especially g- and d-, have cholesterol-lowering properties, probably by inhibiting cholesterol biosynthesis. The recommended dietary allowances daily intake of a-tocopherol (vitamin E) for adults is 11–15 mg. Intake of unsaturated fatty acids determines the dietary requirement of vitamin E, for example, for 1 g intake of oleic, linoleic, linolenic acids about 0.1, 0.6, and 0.9 mg a-tocopherol, respectively, are required. Both natural and synthetic forms of vitamin E are absorbed in digestive tract, but the concentration of a natural form in the blood system was significantly higher than the synthetic form.

Polyphenols Polyphenols are organic components that mainly influence flavor and stability of crude oils. At high concentration (more than 300 ppm), they cause a bitter taste in olive oil. Several studies have shown that polyphenols have antioxidant and antimicrobial properties. They showed radical scavenger properties in the body system, and they may contribute to the lower incidence of CVD and some types of cancer. Among different polyphenols, hydroxyltyrosol has the highest antioxidant properties, and it is more effective than synthetic butylated hydroxyl toluene. There are a large variety of polyphenols in crude oils. Virgin olive oil and cold-pressed canola oils are good sources of polyphenols.

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Hydrocarbons Saturated and unsaturated hydrocarbons in aliphatic or terpenic forms can be found in fats and oils. Two major well-known unsaturated terpenic hydrocarbons are carotenoids and squalene. Squalene can be found in olive oil, palm oil, rice bran oil, and in animal fats (shark liver oil). Squalene is a natural antioxidant, and it also has antitumor, antibacterial, and anticarcinoma properties. Carotenoids are yellowish to red color natural family pigments found in most oils. b-Carotene (pro-vitamin A) and lycopene are good examples of carotenoids. b-Carotene exhibits vitamin A activity and, along with other carotenoids, acts as a strong antioxidant in the presence of light. Research showed that b-carotene and a-tocopherol have a synergistic antioxidant effect. Red palm oil is the richest source of carotenoids, whereas butter and cod liver oil have large amounts of carotenoids in animal fats. Research showed that a high level of carotenoids in red palm oil has an anticarcinogenic effect. Vitamin A deficiency is common worldwide and leads to eye diseases, severe infection, and death in many people, especially children and women. The body can make vitamin A from carotenoids in oils. The recommended daily intake of vitamin A (retinol) for females is 700 mg and for males 900 mg. The main functionalities of vitamin A are in visual system, growth, immune system, epithelial cellular integrity, and reproduction.

Fatty Acids and Triacylglycerols Compositions More than 1000 types of fatty acids have been identified. However, not all of them are important from nutrition and health points of view. The main differences between fatty acids are the number of carbon atoms and the number and position of double bonds. Fatty acid double bonds occur in two geometric isomers either in the cis form that is the natural form of fatty acids (hydrogens on the same side of the plane), or trans configuration (hydrogens on opposite sides of the plane), which form during hydrogenation or high temperature exposure during deodorization. Some fatty acids have special functional groups such as hydroxyl, epoxy, keto, or ring groups. The fatty acids are classified as short-chain fatty acids (C2–C4), medium-chain fatty acids, (C6–C10), and long-chain fatty acids (C12–C24) and saturated (without double bonds), mono-unsaturated (one cis or trans double bond), and polyunsaturated (two and more cis or trans double bonds). Numbering of fatty acids could be based on the omegareference system that indicates the number of carbons, the number of double bonds, and the position of the double bond for the carbon atom of x, starting from the terminal methyl group and designated as (nx) for example C18:3 (n 3). The main saturated fatty acids are butyric acid, C4:0; caproic acid, C6:0; caprylic acid, C8:0; capric acid, C10:0; lauric acid, C12:0; myristic acid, C14:0; palmitic acid, C16:0; stearic acid, C18:0; arachidic acid, C20:0; behenic acid, C22:0; and lignoceric acid, C24:0. The main monoenoic fatty acids are lauroleic acid, C12:1 (n 3); myristoleic acid, C14:1 (n 5); palmitoleic acid, C16:1 (n 7); oleic acid, C18:1 (n 9); gadoleic acid, C20:1 (n 11); cetoleic acid, C22:1 (n 13); and erucic acid, C22:1 (n 9).

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OH O O β-Carotene

Sesamol

Squalene HO H3C

O CH3

γ-Tocopherol

HO Cholesterol

Polyunsaturated fatty acids (PUFAs) can be characterized based on a methylene group that can be central, conjugated, or unconjugated. For instance, linolenic acid (C18:3) can be found in two forms of a-linolenic -9, 12, 15-oic acid, (n 3) or g-linolenic-6, 9, 12-oic acid (n 6). Eicosapentaenoic acid (EPA) C20:5 (n 3) and docosahexenoic acid (DHA) C22:6 (n 3) found in oily fishes are examples of PUFAs with nutritional characteristics. Triacylglycerols comprise more than 95% of fats and oils composition. Each triacylglycerol molecule consists of three fatty acids that attached to the glycerol molecule with ester bonds. Normally triacyglycerols can categorize to simple triglycerides with only one type of esterified fatty acid, for example, triolein (OOO); di-acid triglycerides with two types of fatty acids esterified to glycerol molecule, for example, dipalmito 1,3 olein 2 (POP); and tri-acid with three types of acyl groups, for example, palmito 1, oleo 2, and stearin 3 (POS). Glycerol molecules can also esterify with only one fatty acid to form monoacyl glycerols or with two same or different fatty acids to make diacylglycerols. The physical, chemical, biological, and physiological properties of fats and oils related to triacylglycerol composition and presence of healthy minor components. The reason for the importance of triacylglycerol composition is that two oils with the same fatty acid profile may have different physical, chemical, and physiological properties. Also the position of fatty acids on glycerol molecules has health and physiologically importance. For instance during fat digestion, because human lipase is specific (hydrolyzing only fatty acids in positions 1 and 3 of TAGs), the fatty acids attached to carbon number 2 of glycerol structure (the sn-2 position) are especially absorbed as the 2-monoacylglycerol

HO β-Sitosterol

and serve as the template for re-esterification by intestinal cells to reform triacylglycerols. In vegetable oils, unsaturated fatty acids are esterified in the sn-2 position, whereas in animal fats saturated fatty acids are in this position. In addition, selective distribution of fatty acids on glycerol backbone is an important factor that leads to triacylglycerols diversity. For example, palm oil contains six types of fatty acids, but only 14 diverse triacylglycerols can be detected. Omega-3 and omega-6 PUFAs have different physiological properties in the human body system. Whereas n 3 fatty acids have anti-inflammatory, antithrombotic, antihypertensive, and anti-arrhythmic derivatives, n 6 fatty acids cause inflammatory, thrombotic, hypertensive, and arrhythmic metabolites. That is the reason for the importance of the ‘n 6/n 3 ratio’ balance in human diet. The impact of saturated fatty acids on LDL cholesterol depends on the number of carbon atoms in the fatty acid chain with lauric acid > myristic acid > palmitic acid > stearic acid. Clinical studies showed that saturated fatty acids lead to an increase in total blood cholesterol and LDL cholesterol, whereas mono-unsaturated and more effective polyunsaturated fatty acids lead to a decrease in the total serum cholesterol and LDL cholesterol and increasing HDL cholesterol in the bloodstream. The risk of coronary heart disease in the societies in which people consume olive or canola oil (good source of oleic acid) and fish oil (good source of omega-3 fatty acids) is lower. Studies have shown that consumption of n 3 fatty acids (fish oil, walnut oil, and flaxseed oil) reduces mortalities related to CVDs by lowering triacylglycerol accumulation in the liver and circulation.


Classification of Oils and Fats Based on Fatty Acid Profile Medium-Chain Fatty Acids (C6:0 to C10:0) Subgroup This group of oils (MCTs) is important in the case of providing an instant source of energy for the body. These fatty acids have small size and higher solubility and are mainly transported directly via portal circulation and metabolized in the liver, whereas longer-chain fatty acids are absorbed via the lymphatic system after micellar transport at the intestinal wall. MCTs are neutral on LDL-, HDL-cholesterol or triacylglycerol concentration in serum and may be beneficial in controlling obesity.

Lauric Acid and Myristic Acid Subgroup Among saturated fatty acids, lauric acid and myristic acid are the most blood cholesterol and LDL-cholesterol increasing fatty acids. Although, the effect of myristic acid is higher than lauric acid, the position of fatty acids on the glycerol backbone needs to be considered. Coconut oil and palm kernel oil are categorized in this subgroup.

Palmitic Acid Subgroup The effect of palmitic acid on increasing serum cholesterol and LDL cholesterol is lower than lauric acid and myristic acid. Palm oil and lard are good examples of this group.

Stearic Acid Subgroup Among saturated fatty acids, stearic acid exhibited as quite neutral with no deleterious effect on plasma lipids. Cocoa butter and shea butter can be in this subgroup because they contain up to 40% of stearic acid.

Oleic Acid Subgroup (>60%) Olive oil is the best representative oil of this subgroup, which contains about 80% of oleic acid and then canola oil with about 65% oleic acids. In nuts oil, hazelnut oil and macadamia oil are rich in oleic acid.

Linoleic Acid Subclass (>60%) The common vegetable oils gathered in this group are grape seed oil, evening primrose oil, and safflower oil. As the human body cannot synthesize linoleic acid from food components, presence of this fatty acid is essential for good health and termed an essential fatty acid. As mentioned earlier, the inflammatory effect of consuming n 6 fatty acids should be considered and n 6/n 3 ratio should be balanced in the diet.

Linoleic Acid þ Saturated Fatty Acids Subgroup Cottonseed oil and watermelon seed oil are clustered in this group. Their fatty acid profiles mainly contain linoleic acid, associated with saturated fatty acids (especially palmitic acid).

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Linoleic Acid þ Oleic Acid Subgroup Sunflower oil, corn oil, sesame oil, pumpkin seed oil, and borage oil are good examples of this subgroup. In this group, borage oil has a high amount of g-linoleic acid (about 22% of the total fatty acids).

Conjugated Linoleic Acid Conjugated linoleic acid (CLA) is a term used for positional and geometric isomers of linoleic acid that can be found in animal fats such as beef, lamb, and dairy foods. CLA are produced by microbial fermentation of PUFAs and isomerization of linoleic acid in the rumens of ruminants. Whereas double bonds in linoleic acid are between the ninth and tenth carbons and the twelfth and thirteenth carbons, CLA has conjugated double bonds at carbon atoms 10 and 12 or 9 and 11, with possible cis and trans combinations. Many clinical studies have shown that conjugated linoleic acid may have physiological effects, including anticarcinogenic, antiatherogenic, improvement of type II diabetes, and immunomodulating properties of CLA. Some clinical studies on animals showed that conjugated linoleic acid is quite effective to inhibit the growth and metastasis of breast and prostate cancers.

Trans Fatty Acids Two types of trans fatty acid (TFAs) isomers can be found in fats as naturally and industrially produced fatty acids. The presence of TFAs in animal fats was revealed some time ago. TFA in tallow and milk fat is vaccinic acid C18:1 (n 7t). This TFA is naturally produced during biohydrogenation and isomerization of PUFAs in rumen guts. Catalytic hydrogenation is an industrial modification process that is applied to reduce the amount of polyunsaturated fatty acids and leads to improvement in oxidative stability of oils and increasing hardness. This industrial process produces TFA, which are almost unavailable in natural fats. TFA levels and isomeric distribution depend on processing factors (nickel catalyst type and concentration, hydrogen pressure, stirring speed, and reaction temperature), fatty acid composition of original oil, and degree of saturation (partially or fully hydrogenation). Partial hydrogenation produces mostly geometrical and positional trans-18:1 isomers (mainly elaidic acid) while reducing the amount of PUFA. During deodorization of edible oils, a small amount of trans-linoleic and trans-linolenic acid are produced. A positive correlation between intake of a high amount of TFAs in a diet with increased risk of chronic diseases such as cardiovascular, inflammatory, autoimmune diseases, and cancer have been found. TFAs raise the amount of LDL cholesterol and lower the level of HDL cholesterol, thus resulting in doubly detrimental effects. New regulations on TFA labeling, which led to a ban on industrially produced trans fats in foods, caused a dramatic reduction in TFAs in food products, but they still can be found in some foods such as confectionery coatings and fillings, biscuits (cookies), pie crusts, toffees, and analogs of dairy products such as butter, cream, and toppings.

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Using naturally saturated fats such as palm oil and/or applying fully hydrogenated oils or vegetable oils from new varieties such as high oleic oils could be solutions for food industries to substitute TFAs in their products.

Omega-3 Fatty Acids The omega-3 fatty acids consist of a-linolenic acid, EPA, and DHA. Several clinical studies showed a positive correlation between consumption of omega-3 fatty acids in the diet and an improved prognosis of CVD and nonalcoholic fatty liver disease. The main sources of a-linolenic are flaxseed oil and walnut oil and oily fishes such as tuna, menhaden, anchovies, sardines, and mackerel are the main sources of EPA and DHA.

Major Vegetable Oils This section is mainly focused on the main sources of vegetable oils that would cover more than 95% of total vegetable oils consumed in the word (Table 1).

Palm Oil Palm oil is the main vegetable oil produced in the world. During 2013–2014 about 53.4 million tonnes of palm oil were produced (Table 1). Palm oil originated from South Africa

Table 2

and was introduced to East Asia in 1884. Currently, Indonesia and Malaysia are the two main palm oil producers in the world. Palm oil is rich in healthy minor components such as carbohydrates (carotenoids and squalene) and tocols. Crude palm oil has about 400–1000 ppm carotenoids (pro-vitamin A) but after physical refining, the amount of carotenoids decreased to nondetectable levels. The squalene content in crude palm oil is between 200 and 500 ppm, which is dramatically higher than other common vegetable oil sources. Total tocols in crude palm oil are about 800 ppm, 70% of which are tocotrienols. The distribution of tocopherols in palm oil is a-tocopherol 22%, and b-, g-, and d- tocopherols represent 20%, 46%, and 12%, respectively. Crude palm oil contains 210–620 ppm of phytosterols. The main phytosterols in palm oil are b-sitosterol (120–370 ppm), campesterol (46–150 ppm), and stigmasterol (26–66 ppm). Palm oil is a good source of carotenoids. Based on the carotenoid content, crude palm oil color varies from yellowish to dark red. The main carotenoids in palm oil are a-carotene (24–42%) and b-carotene (50–60%). Palmitic acid and oleic acid are the main fatty acids in palm oil (more than 80% of total fatty acids and almost in equal amount). Normally, palm oil is fractionated into different derivatives (palm olein, palm stearin, palm super olein, and palm mid fraction) with specific physical and chemical characteristics (Tables 2 and 3). Because of fatty acid composition (about 50% saturated fatty acids and 50% oleic acid), crystallization in the form of b0 and the

Fatty acid composition of palm oil and its derivatives

Fatty acids (%)

Palm oil

Palm olein

Palm super olein

Palm top olein

Palm stearin

Palm mid fraction

12:0 14:0 16:0 16:1 18:0 18:1 18:2 18:3 20:0

0.2 1.1 44.1 0.2 4.4 39.0 10.6 0.3 0.2

0.3 1.1 40.9 0.2 4.2 41.5 11.6 0.4 0.4

0.3 1.0 35.4 0.3 3.8 45.1 13.4 0.3 0.3

0.2 1.0 28.8 0.3 2.5 52.0 14.6 0.4 0.2

0.1–0.3 1.1–1.7 49.8–68.1 0.05–0.1 3.9–5.6 20.4–34.4 5.0–8.9 0.1–0.5 0.3–0.6

0.0–0.3 0.8–1.4 41.4–55.5 – 4.7–6.7 32.0–41.2 3.6–11.5 0.0–0.2 0.0–0.6

Malaysian Palm Oil Board (MPOB) (2009) Pocketbook of Palm Oil Uses, pp. 3–41.

Table 3

Fatty acid composition of main vegetable oils

Fatty acids (%)

Soybean oil

Canola oil

Sunflower oil

Cottonseed oil

Corn oil

Peanut oil

Olive oil

12:0 14:0 16:0 16:1 18:0 18:1 18:2 18:3 20:0 20:1 20:2 22:0 24:0

– 0.1 11.0 0.1 4.0 23.4 53.2 7.8 0.3 – – 0.1 –

– – 4.3 0.2 1.8 62.3 19.4 9.2 0.6 1.2 0.1 – –

– – 5–7 <0.4 4–6 15–25 62–70 <0.2 <1 <0.5 – <1 –

– 0.5-1.3 17–31 <1 1–3 13–21 34–60 <1 0.2–0.5 – – – –

– <0.1 8–13 <1 1–4 24–32 55–62 <2 <1 <0.5 – <0.5 –

– – 8–13 <0.3 3–4 48–66 14–28 <0.3 1–2 1–2 – 2–4 1–2

– <0.1 7.5–20 0.3–3.5 0.5–5 55–83 3.5–21 <1 <0.8 – – <0.3 <1

FATS | Healthy Fats and Oils presence of natural antioxidants (tocols), this oil is widely used in the food industry as a main part of base stock to formulate margarines, shortenings, frying oils, and confectionary fats.

Soybean Oil Soybean is the main oilseed produced in the world, and soybean oil is the second-largest-produced vegetable oil after palm oil (Table 1). The world’s major producers of soybean oil are the United States, China, Argentina, Brazil, EU-27, and India. Crude soybean oil is a good source of phosphatides that after extraction and purification steps can be used as a natural emulsifier (lecithin) in various food products. The three major phosphatides in crude soybean oil are PC, PE, and PI present in the ratio of 55%, 26%, and 18%, respectively. Concentration of phytosterols and tocopherols in soybean oil is 2350–4050 ppm and 1257–1370 ppm, respectively. In soybean oil, b-sitosterol (47–59%) and g-tocopherol (44–60%) are the major phytosterol and tocopherol in soybean oil. Soybean oil contains about 6–8% a-linolenic acid. Research showed that soybean oil consumption led to a reduction in total blood serum cholesterol and LDL cholesterol. The major triacylglycerols in soybean oil are OLL (20%), LLL (19%), and PLL (13%). Crude solvent extracted soybean oil typically has about 2%PLs. The main phytosterols in soybean oil are b-sitosterol (52%), campesterol (25%), and stigmasterol (23%). Two major hydrocarbons in soybean oil are squalene and hexahydrofarnesyl acetone.

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(100–386 to 189–753 ppm, respectively; data adapted from Codex Alimentarius, 2010). Green color of crude canola oil is related to the presence of chlorophylls (5–50 ppm). Plant breeders have developed canola oil with new fatty acid composition such as high oleic canola oil (oleic acid raised to about 85%), high lauric canola oil (up to 31% lauric acid), and high stearic acid canola oil (stearic acid content increased to about 28%).

Sunflower Oil Russia, Ukraine, Turkey, European countries, and Argentina are the main producers of sunflower oil. During 2013–2014, about 15.7 million tonnes of sunflower oil were produced (Table 1). Linoleic acid as an essential fatty acid (62–70%) and oleic acid (15–25%) are predominant fatty acids in this oil. These amounts for new mutant of high oleic sunflower oil are 2–17% and 75–91%, respectively. The main triglycerides in regular sunflower oil are LLL (36%) followed by OLL (29%). Sunflower oil normally has about 3200–5100 ppm phytosterols (58–64% b-sitosterol) and 440–1200 ppm tocopherols (91–97% a-tocopherol). It is also considered a good source of squalene (150–200 ppm). Crude sunflower oil has 0.5–1.2% PLs and around 180 ppm of total polyphenols. The main polyphenols in crude sunflower oil are caffeic acid, vanillic acid, and chlorogenic acid.

Canola Oil

Cottonseed Oil

Canola oil was first produced in Canada in 1974. Genetic modifications of rapeseed oil led to a reduction in the concentration of erucic acid and glucosinolate. The currently rapeseeds in use have erucic acid and glucosinolates less than 0.1% and 8.5 mM g1, respectively. After palm oil and soybean oil, canola oil is the third major vegetable oil produced in the world (Table 1), and China, EU-27, Canada, India, and Japan are the main producers. Canola oil in Canada is extracted mainly from the seeds of genetically modified Brassica napus L., but a small part of extracted canola oils are from Brassica rapa L. Canola oil is the only known vegetable oil with a sulfur atom in some fatty acid structures that are responsible for the sulfur flavor in the oil. Many dietitians believe that canola oil could be considered the healthiest edible oil. Canola oil has unique characteristics such as fatty acid composition and levels of tocopherols, phytosterols, and polyphenols. Canola oil contains about 12% a-linolenic acid (omega-3) and about 65% oleic acids. Also, it contains a low amount of saturated fatty acids (<7%) compared to other common vegetable oils. This oil has a high amount of polyphenols (113 ppm gallic acid), and the predominant polyphenols in crude canola oil are vinylsyringol, 4-vinylsyringol dimer, sinapic acid, and sinapine. PA is the main phospholipid in crude canola oil (around 44%). Canola oil lecithin is usually used as an animal feed ingredient. After soybean oil and corn oil, canola oil has the highest amount of tocopherol isomers, whereas the a- and g-tocopherols are the major tocopherols with a 1:2 ratio

Cottonseed oil extraction plants are mainly in China, India, Pakistan, the United States, Brazil, and Turkey (5 million tonnes per year production; Table 1). Typically the three main fatty acids in this oil are palmitic acid, oleic acid, and linoleic acid with an average percentage of 22, 20, and 54, respectively. Four major triacylglycerols in cottonseed oil are PLL (27.5%), LLL (19%), POL (14%), and OLL (12.5%). Cottonseed oil has unique types of fatty acids—malvalic and sterculic acids, which are called cyclopropenoid fatty acids. Both malvalic and sterculic acids have one double bound at the propene ring and some toxicity properties, but after deodorization the amount of total cyclopropenoid fatty acids will reduce to 0.04%. Typically, PLs content in crude cottonseed oil is about 0.7–0.9%. Cottonseed oil is also exceptional for the presence of a toxic polyphenolic component named gossypol. This pigment gives a dark red color to crude cottonseed oil. Most parts of the gossypol are removed during neutralization, and at the end of refining a safe level of 1–5 ppm would be present in oil. Although gossypol shows toxicity effects, recent research showed that this component has bioactive properties such as antimicrobial, antioxidant, and anticancer activities. b-Sitosterol is the most abundant sterol in cottonseed oil followed by campesterol, stigmasterol, and D5-avenesterol. Cottonseed oil is a rich source of tocopherols. The total tocopherol content in crude cottonseed oil is about 1000 ppm, and a- and g-tocopherols account for 41% and 58%, respectively. The presence of a high level of natural antioxidants, a relatively high percentage of saturated fatty acids, and a special nutty flavor makes this oil one of the best choices to use as a frying oil.

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Corn Oil Corn oil is a by-product of corn meal- and starch-making companies. Fatty acid composition of corn oil comprises a relatively high level of linoleic acid (58–62%). The major triacylglycerol molecules in corn oil are LLL (25%), LLO (22%), LLP (15%), OOL (11%), and PLO (10%). In vegetable oils, corn oil is categorized as one of the richest source of phytosterols (8300–25 500 ppm) and tocopherols (1130–1830 ppm). The main phytosterol and tocopherol in corn oil are b-sitosterol (63–70%) and g-tocopherol (68–89%), respectively. Numerous clinical studies showed a correlation between corn oil consumption and total serum cholesterol reduction that may be related to a high concentration of phytosterols in this oil. Research showed that a high ratio of g-tocopherol in corn oil has health benefits such as a protection effect against DNA damage, blood pressure, platelet aggregation, and diabetes.

Peanut Oil China and India are the main producers of peanut oil. Phospholipid content of crude peanut oil is 0.6–2%, depending on the maturity of peanuts. The main fatty acids in peanut oil are oleic acid (45–53%), linoleic acid (27–32%), and palmitic acid (11–14%). This oil specifically has long-chain saturated fatty acids such as arachidic acid (1–2%), behenic acid (1.5–4.5%), and lignoceric acid (0.5–2.5%). The main triacylglycerols in peanut oil are OOL (19%), OLL (18%), POL (13%), OOO (12%), and POO (7%). Crude peanut oil contains about 3400 ppm total phytosterols, whereas the main phytosterols are b-sitosterol (64%), campesterol (15%), stigmasterol (11%), and D5-avenesterol (8%). Tocopherols concentration in peanut oil ranges from 130 to1300 ppm with the composition of a-tocopherol (47–65%) and g-tocopherol (30–50%). This oil also has a high level of squalene (400–700 ppm).

Olive Oil Olive oil has been used for a long time as a food and a medicine. The world average annual production of olive oil is about 3 million tonnes mainly in Mediterranean countries. Many epidemiological studies have shown that the lower rates of breast, ovarian, and colorectal cancers in Mediterranean countries may be related to consumption of olive oil. There are two kinds of olive oil in the world: one with a high amount of oleic acid and low amount of linoleic acid (European origin) and another with the opposite ratios (North African origin). This diversity caused a wide range of fatty acid and triacylglycerol composition to be considered for this oil. In general, three major fatty acids in olive oil are oleic acid (55–83%), palmitic acid (7.5–20%), and linoleic acid (3.5–21%). The greenish color of virgin olive oil is related to the presence of chlorophyll in this oil, and their level ranges from 10 to 30 ppm. a-Tocopherol is the major tocopherol (up to 95%) in olive oil, and it has a range from 100 to 300 ppm. The level of squalene in olive oil is relatively high and in most of samples reported in the range of 200–500 ppm. Research

showed that squalene in olive oil may have a preventive effect on breast cancer, and it also has cardioprotective properties. Total phytosterol content in virgin olive oil is between 980 and 1840 ppm; meanwhile the main phytosterol is b-sitosterol (75–90%). Virgin olive oil is considered a rich source of polyphenols. The amount of polyphenols in virgin olive oil changes from 100 to 300 ppm. Polyphenols in virgin olive oil (tyrosol, hydroxytyrosol, and oleuropein) have very strong free radical scavenger properties and antioxidant activity. Research showed that they may correlate with decreasing the risk of CVDs and cancer. The level of phosphatides in olive oil is lower than common seed oils (40–135 ppm). Clinical studies have shown that olive oil consumption has lots of preventive effects against chronic diseases such as obesity, CVDs, inflammatory diseases, and cancer.

Coconut Oil Average annual production of coconut oil is 3–4 million tonnes, mainly in the Philippines, Indonesia, and India. Normally, coconut oil is extracted after sun or fire drying of the coconut kernel. Dried kernel is named copra, and it has about 65% oil. Coconut oil contains high levels of saturated fatty acids mainly lauric acid and myristic acid (more than 60% of total fatty acids). Coconut oil and palm kernel oil are the richest natural source of medium-chain fatty acids. Because the major fatty acids in coconut oil are saturated, the total tocopherol level in this oil is very low (55 ppm). The main fatty acid and triacylglycerol in coconut oil are lauric acid (48%) and trilaurin (19%), respectively. The special flavor of coconut oil is related to the presence of d- and g- lactones. The range of total phytosterol in this oil is between 800 and 2300 ppm. The major sterols are b-sitosterol (45%), D5avenasterol (30%), and stigmasterol (14%). The amount of hydrocarbons in coconut oil is high, whereas it only has a small amount of squalene (20 ppm), but the level of polycyclic aromatic hydrocarbons (PAHs) could reach to about 3000 ppm as result of contamination of oil with petroleum oil or during fire drying. The main difference between fatty acid composition of coconut oil and palm kernel oil is that although the level of medium-chain fatty acids (caprylic and capric acids) in coconut oil is higher than palm kernel oil, the amount of oleic acid in palm kernel oil is higher than coconut oil. These oils have a sharp melting point that makes them highly suitable to formulate different food products such as confectionary fats, ice creams, and icings (Table 4).

Sesame Oil For a long time, sesame was used as an oilseed crop because of high levels of oil (50%) and protein (20–25%) in this seed. Sesame oil is produced mainly in China, Japan, India, Singapore, and Mexico. In sesame oil, oleic acid and linoleic acid are the main fatty acids with the same ratio (around 40%). The major triacylglycerols in this oil are LLO (25%), LLL (20%), and LOO (15%). Total phytosterols and tocopherols contents in sesame oil are 5400–6300 ppm and 200–500 ppm, respectively. b-Sitosterol and campesterol are the main phytosterols in this oil (more than 80% of total sterols), and g-tocopherol comprises more than 96% of

FATS | Healthy Fats and Oils Table 4

Fatty acid composition of lauric oils

FA (%)

Palm Kernel

Coconut

6:0 8:0 10:0 12:0 14:0 16:0 16:1 18:0 18:1 18:2 18:3 20:0 20:1

<0.8 2–5 3–5 44–51 15–17 7–10 <0.1 2–3 12–18 1–4 <0.7 <0.3 <0.5

<0.1 6–10 5–10 39–54 15–23 6–11 <2 1–4 4–11 1–2 <0.1 <0.2 <0.2

Karkeskind A (1996) Sources of the main fats and relevant monographs. In: Oils and Fats Manual, pp. 117–323. Paris: Lavoisier Publishing.

total tocopherols. Sesame oil has a good oxidative stability. More than tocopherols, the stability of this oil is related to the presence of the unique natural phenolic antioxidants of sesamol and sesamolin (totally around 5000 ppm). In many countries, sesame oil is used as frying oil because of its high stability and also its nutty flavor.

Rice Bran Oil Rice bran oil is mainly produced in Japan, Thailand, India, China, and Vietnam. The major fatty acids in rice bran oil are oleic acid, linoleic acid, and palmitic acids (typically, 42%, 32%, and 20%, respectively). Activity of lipase during rice bran oil extraction leads to an increase in the amount of FFA, mono-, and diacylglycerols. Triglycerides totally comprise 83–86% of total neutral lipids, whereas PLO, PLL, and OOO are predominant triacylglycerols in this oil. The concentration of phytosterols in rice bran oil is higher than common vegetable oil (32 000 ppm) with the composition of 54% of b-sitosterol, 20% of campesterol, and 11% of D5-avenesterol. Rice bran oil is a good source of tocopherols, and the average of tocopherol content in rice bran oil is 860 ppm. Research has shown that rice bran oil has health benefits such as lowering serum cholesterol level, inhibiting platelet aggregation, increasing fecal bile excretion, and decreasing early atherosclerosis.

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oils, but g-tocopherols is the major tocopherol in chestnut, pecan, walnut, heartnut, cashew, and Brazil nut oils. Macadamia nut oil is rich in tocoterienols (about 60 ppm). Walnut oil has the highest amount of total phytosterols (3000 ppm) followed by peanut and pecan oils (2800 ppm) and almond oil (2700 ppm). Macadamia oil has the lowest level of phytosterols (1280 ppm). Based on clinical studies, regular nut consumption or using nut oils as salad oil is associated with reduced risk of coronary heart disease, diabetes, and cancer.

Fats and Oils Refining The main purpose of crude oil refining is to remove undesirable minor components and contaminants from oils. Free fatty acids, oxidation products, chlorophyll, waxes, and trace metals from oils are generally undesirable because they may decrease the quality of refined oil through darkening, foaming, smoking, precipitation, development of off-flavor, and decreasing oxidative stability or be potentially dangerous to health. The source of oil contamination could be from oilseeds during harvesting and storage with trace metals, dioxins and polychlorobiphenyls from industrial wastes, polycyclic aromatic hydrocarbons, or mineral oil from vehicle exhausts. Another source of oil contaminants could be the trace amount of insecticides, fungicides, or herbicide extracted from oilseeds and transferred to oils. Although most of these chemicals are removed during refining, oil refining may also lead to the formation of another group of degraded products such as polycyclic aromatic hydrocarbons (PAHs) or 3-monochloropropane-1,2-diol (3-MCPD) esters and glycidolesters. Another important fact about oil refining is related to the loss of micronutrients during refining. Fully refining (degumming, neutralization, bleaching, and deodorization) of oils leads to change not only in the level of healthy components but also in their chemical structure and composition by isomerization or polymerization. Research showed that traditional refining leads to about a 20% loss in total amount of tocopherols and 24% in phytosterols level in canola oil. A typical specification for fully refined oil in general could be as taste (bland), moisture (max. 0.05%), phosphorus (max. 5 ppm), free fatty acids (max. 0.1%), peroxides (max. 3 meq/kg), iron (max. 0.5 ppm), copper (0.05 ppm), lead (max. 0.01 ppm), hexane (max. 5 ppm), benzopyrene (max. 2 ppb), dioxins (0.75 pg), aflatoxins (6 ppb), and mineral oil (LOD).

Nut Oils The main world’s most popular nuts are peanut, almond, cashew, pistachio, walnut, hazelnut, and pecan. The oil content of nuts varies from 0.8% for chestnuts to 67% for Brazil nuts. Fatty acid composition of nut oils is very diverse. The highest amount of saturated fats belongs to Brazil nut oil (around 23%), and the lowest level of saturated fat belongs to heartnut oil (about 5%). Hazelnut oil and pistachio oil have the highest amount of oleic acid (more than 75%), and walnut oil has the highest amount of n 3 and n 6 PUFAs. a- and g-Tocopherols are the main tocopherols in nut oils. a-Tocopherol is the predominant tocol in hazelnut, pistachio, almond, and peanut

Conclusion Although fats and oils contribute to palatability of many food products, consumers are nowadays paying more and more attention to their health and well-being. Based on WHO recommendation for dietary intake of fats and oils for adults, it is suggested that we get 20–35% of our energy from fats and oils sources. In a selection of healthy oil sources, many factors should be considered such as fatty acid composition, healthy minor components, process of oil extracted (solvent extracted, hot-pressed or cold-pressed), and minimally refined or fully

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refined oil. Other factors such as availability, price, food application, and stability should be considered. It is also important to know that in the food industry oil or fat used in a food product has been carefully chosen for its unique physical or functional characteristics that are not always a healthy one. This has been a challenge for food companies to offer a healthy food with a delicious taste.


• • • •

What makes an oil or fat healthy? Canola oil is a healthy oil, but is it suitable for deep-frying foods? What is the main difference between essential fatty acids and omega-3 fatty acids? Is it true to say cold-pressed oils have higher levels of healthy minor components compared to solvent-extracted oils?


• • •

Microbial fats and oils sources and their health benefits. New genetically modified oils. Structured lipids and their health functionality.

See also: Barley, Rice and Maize Processing: Maize: Wet Milling; Oil from Rice and Maize; Oilseed and Legume Processing: Soybean: Processing; The Oilseeds: Canola: Overview; Oilseeds: Overview; Soybean: Overview.

Further Reading Alasalvar C and Pelvan E (2011) Fat-soluble bioactives in nuts. European Journal of Lipid Science and Technology 113: 943–949. Amri IN (2013) The lauric (coconut and palm kernel) oils. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 169–197. West Sussex: Wiley-Blackwell. Beardsell D, Francis J, Ridley D, and Robards K (2002) Health promoting constituents in plant derived edible oils. Journal of Food Lipids 9: 1–34. Bockisch M (1998) Composition, structure, physical data, and chemical reactions of fats and oils and their associates. In: Fats and Oils Handbook, pp. 53–120. Champaign, IL: AOCS Press. Boskou D (2013) Olive oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 243–271. West Sussex: WileyBlackwell. Brompone MA (2006) Sunflower oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 655–730. Hoboken, NJ: Wiley-Interscience. Canapi EC, Agustin YTV, Moro EA, Pedrosa E, and Bendano MLJ (2006) Coconut oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 123–146. Hoboken, NJ: Wiley-Interscience. Caramia G, Gori A, Valli E, and Cerretani L (2012) Virgin olive oil in preventive medicine: From legend to epigenetics. European Journal of Lipid Science and Technology 114: 375–388. Choe E (2008) Effects and mechanisms of minor compounds in oil on lipid oxidation. In: Akoh CC and Min DB (eds.) Food Lipids, Chemistry, Nutrition, and Biotechnology, 3rd edn., pp. 449–474. New York: CRC Press. Dawd MK (2013) Cottonseed oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 199–224. West Sussex: Wiley-Blackwell.

Dean LL, Davis JP, and Sanders TH (2013) Groundnut (peanut) oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 225–242. West Sussex: Wiley-Blackwell. Dubois V, Breton S, Linder M, Fanni J, and Parmentier M (2007) Fatty acid profiles of 80 vegetable oils with regard to their nutritional potential. European Journal of Lipid Science and Technology 109: 710–732. Dunford NT (2004) Oil-and oilseed-based bioactive compounds and their health effects. In: Nutritionally Enhanced Edible Oil and Oilseed Processing, pp. 1–24. Champign: AOCS Press. Elmadfa I and Park E (1999) Impact of diets with corn oil or olive/sunflower oils on DNA damage in healthy young men. European Journal of Nutrition 38: 286–292. Fernholz KM, Seifert JG, Bacharach DW, Burke ER, and Gazal O (2000) The effects of phosphatidyl serine on markers of muscular stress in endurance runners. Medicine and Science in Sports and Exercise 32: S321. Firestone D (2006) Olive oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 303–331. Hoboken, NJ: Wiley-Interscience. Garcıá-Gonza´lez DL, Aparicio-Ruiz R, and Aparicio R (2008) Virgin olive oil – Chemical implications on quality and health. European Journal of Lipid Science and Technology 110: 602–607. German JB (1990) Muscle lipids. Journal of Muscle Foods 1: 339–361. Grompone (2013) Sunflower oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 137–167. West Sussex: Wiley-Blackwell. Gunstone FD (1998) Movement towards tailor-made fats. Progress in Lipid Research 37: 277–305. Gunstone FD (2013) Composition and properties of edible oils. In: Hamm W, Hamilton RJ, and Calliauw G (eds.) Edible Oil Processing, 2nd edn., pp. 1–39. West Sussex: Wiley-Blackwell. Hammond EG, Johnson LA, Su C, Wang T, and White PJ (2006) Soybean oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 577–653. Hoboken, NJ: Wiley-Interscience. Harwood J and Yaqoob P (2002) Nutritional and health aspects of olive oil. European Journal of Lipid Science and Technology 104: 685–697. Hernandez E (2012) Lipids, pharmaceutical and cosmetic use. In: Kirk-Othmer Encyclopedia of Chemical Technology. New York: Wiley. Hernandez ME and Kamal-Eldin A (2013a) Current trends in the consumption of fats and foods. In: Processing and Nutrition of Fats and Oils, pp. 1–16. West Sussex: John Wiley. Hernandez ME and Kamal-Eldin A (2013b) New developments in micronutrients and lipids. In: Processing and Nutrition of Fats and Oils, pp. 137–154. West Sussex: John Wiley. Hernandez ME and Kamal-Eldin A (2013c) Biochemical and bioactive properties of fats and oils. In: Processing and Nutrition of Fats and Oils, pp. 39–64. West Sussex: John Wiley. Howell TJ, MacDougall DE, and Jones PJH (1998) Phytosterols partially explain differences in cholesterol metabolism caused by corn or olive oil feeding. Journal of Lipid Research 39: 892–900. Kamal-Eldin A (2008) Micronutrients in cereal products: Their bioactivities and effects on health. In: Hamakar BR (ed.) Technology of Functional Cereal Products, pp. 86–111. Boca Raton, FL: CRC Press. Karkeskind A (1996) Sources of the main fats and relevant monographs. In: Oils and Fats Manual, pp. 117–323. Paris: Lavoisier Publishing. Kochhar SP (2013) Minor and specialty oils. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 291–341. West Sussex: Wiley-Blackwell. Ku¨llenberg D, Taylor LA, Schneider M, and Massing U (2012) Health effects of dietary phospholipids. Lipids in Health and Disease 11: 1–16. Lacoste F (2014) Undesirable substances in vegetable oils: Anything to declare? OCL 21: A103. Lin SW (2013) Palm oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 25–58. West Sussex: WileyBlackwell. Marie-Pierre St-Onge M, Aban I, Bosarge A, Gower B, Hecker KD, and Allison DB (2007) Snack chips fried in corn oil alleviate cardiovascular disease risk factors when substituted for low-fat or high-fat snacks. American Journal of Clinical Nutrition 85: 1503–1510. Mirzaee Ghazani S and Marangoni GA (2013) Minor components in canola oil and effects of refining on these constituents: A review. Journal of American Oil Chemistry Society 90: 923–932. Mirzaee Ghazani S, Garcia-Liatas G, and Marangoni A (2013) Minor constituents in canola oil processed by traditional and minimal refining methods. Journal of American Oil Chemistry Society 90: 743–756.

FATS | Healthy Fats and Oils Mirzaee Ghazani S, Garcia Llatas G, and Marangoni A (2014) Micronutrient content of cold pressed, hot-pressed, solvent extracted and RBD canola oil: Implication for nutrition and quality. European Journal of Lipid Science and Technology 116: 380–387. Monteiro J, Michael Leslie M, Moghadasian MH, et al. (2014) The role of n 6 and n 3 polyunsaturated fatty acids in the manifestation of the metabolic syndrome in cardiovascular disease and non-alcoholic fatty liver disease. Food & Function 5: 426–435. Monteleone P, Maj M, Beinat L, Natale M, and Kemali D (1992) Blunting by chronic phosphatidylserine administration of the stress-induced activation of the hypothalamo-pituitary-adrenal axis in healthy men. European Journal of Clinical Pharmacology 42: 385–388. Moreau RA (2013) Corn oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 273–289. West Sussex: WileyBlackwell. Osborn HT and Akoh CC (2002) Structured lipids–novel fats with medical, nutraceutical, and food applications. Comprehensive Review in Food Science and Food Safety 3: 110–120. Pande G and Akoh CC (2013) Enzymatic modification of lipids for trans-free margarine. Lipid Technology 25: 31–33. Pattee HE (2005) Peanut oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 431–463. Hoboken, NJ: Wiley-Interscience.

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Pattee HE (2006) Peanut oil. In: Shahidi F (ed.) Bailey’s Industrial Oil and Fat Products, 6th edn., pp. 431–463. Hoboken, NJ: Wiley-Interscience. Przybylski R (2013) Canola/rapeseed oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 107–136. West Sussex: Wiley-Blackwell. Rocha M, Banuls C, Bellod L, and Jover A (2013) The effect of phytosterols on cholesterol metabolism and addressing issues. Recent Research Developments in Lipids 9: 1–18. Spanova M and Daum G (2011) Squalene-biochemistry, molecular biology, process biotechnology, and applications. European Journal of Lipid Science and Technology 113: 1299–1320. Talbot G, Favre L, and Thorig L (2007) Palm oil: The healthy alternative to trans fats. INFORM 18: 198–200. Wang T (2013) Soybean oil. In: Gunstone F (ed.) Vegetable Oils in Food Technology: Composition, Properties and Uses, 2nd edn., pp. 59–105. West Sussex: WileyBlackwell. Wang X, Beckham TH, Morris JC, Chen F, and Gangemi JD (2008) Bioactivities of gossypol, 6-methoxygossypol, and 6,60 -dimethoxygossypol. Journal of Agricultural and Food Chemistry 56: 4393–4398. Wester I (2000) Cholesterol-lowering effect of plant sterols. European Journal of Lipid Science and Technology 102: 37–44. Wisont K (1999) Lipids and cancer. INFORM 10: 380–397.


Contents Bioactive Compounds in Wheat Bran Bioactives: Antioxidants The Antinutritional Components of Grains Mycotoxins

Bioactive Compounds in Wheat Bran HD Sapirstein, University of Manitoba, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

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Wheat, eaten as bread and other baked products, has been a staple of the human diet for several thousand years. Wheat is a globally important agricultural commodity and ubiquitous food ingredient mainly because it is the only cereal grain capable of being processed into leavened bread, an attribute that derives from its unique gluten protein composition. While the use of whole wheat for food waned significantly in the early part of the twentieth century in favor of baked goods made with refined flour, the past several decades have seen a remarkable resurgence in the consumption of whole wheat and whole grains in general. This has been sparked by increasing consumer interest in healthful eating and awareness of the importance of the health-protecting and health-promoting effects of whole grains. The functional properties of whole wheat for health extend well beyond its nutritional properties and derive for the most part from bioactive compounds in the bran fraction. Those compounds provide a significant source of dietary fiber and micronutrients, along with a substantial complement of phytochemicals including those thought to have a role in reducing the risk of chronic diseases such as atherosclerosis, obesity, diabetes, and cancer. This article presents a compilation and discussion of the diverse array of major bioactive compounds that reside in wheat bran. These compounds in wheat are generally qualitatively similar across different cereal grains, but specific proportions and distribution in the kernel can be very different. The health efficacies of these compounds are not substantially discussed as several excellent reviews or books on the topic are available for further reading.

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The structure of the wheat kernel is described. There is an important difference between wheat bran as it exists in the seed, which can be hand-dissected, and wheat bran commonly obtained by milling. Food-grade bran is not a standardized product and can vary in purity and composition of bioactive compounds due to genetic factors (different wheat varieties or types), the wheat growing environment, and also how the milling is carried out. The unique protective role of bran from a seed’s perspective reflects its complement of bioactive compounds, particularly those in fiber tissues. Bran is the most complex physical component of the wheat kernel containing many layers of tissues with more or less distinct composition of bioactive compounds, particularly between the outer pericarp and inner aleurone. The aleurone layer of bran has a high concentration of the fiber compound arabinoxylan and many other bioactive phytochemical compounds such as minerals, B vitamins, phytic acid, and ferulic acid. Bran is a heterogeneous mixture of several different types of nonstarch polysaccharides, which together constitute the fiber fraction of bran that represents most of the fiber in whole wheat. The typical contents of bioactive compounds that are significantly enhanced in bran compared to levels found in whole wheat are presented.

Learning Objectives

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Structure of the Wheat Kernel and the Distinctiveness of Bran

To recognize and understand the diversity of bioactive compounds that are contained in wheat bran, along with their heterogeneous distribution in the different bran tissue layers, and the degree to which these bioactive compounds are enhanced compared to flour or whole wheat.

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Like all cereal grains, the wheat kernel is defined botanically as a caryopsis, that is, it contains the seed for generation of a new plant, plus external tissues, collectively referred to as the pericarp, which is fused to the seed coat and represents the ripened ovary


http://dx.doi.org/10.1016/B978-0-12-394437-5.00109-1

BIOACTIVES AND TOXINS | Bioactive Compounds in Wheat Bran

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Hairs of brush

Endosperm (~82%)

Crease

Aleurone cells (6-9%) Nucellar tissue Seedcoat (testa) Tube cells Cross cells Inner and outer Hypodermis pericarp Epidermis

Bran (~15%)

Germ (3%)

Scutellum

Figure 1 The structure of the wheat kernel sectioned longitudinally (left) and transversely (right). There are six bran layers plus the aleurone, which is invariably part of conventionally milled bran. The crease, which runs the full length of the kernel, prevents fully efficient separation of bran from endosperm. Typical weight proportions contributed by bran, germ, and endosperm are shown. Adapted from Dexter JE and Sarkar AK (2004) Wheat: dry milling. In: Wrigley C, Corke H, and Walker C (eds.), Encyclopedia of Grain Science, pp. 363–374. Oxford, UK: Elsevier Science.

Table 1 Proximate and select nutrient composition of the three different components of whole wheat grain, with flour, bran, and germ being products of commercial millinga Nutrients a

Moisture Proteina Total lipida Ash (minerals)a Total carbohydrates (by difference)a Total dietary fibera Sugarsa Total bioactive phytochemicalsb

Whole wheat (%)

Refined flour (endosperm %)

Bran (%)

Germ (%)

10.5 13.4 2.1 1.6 72.3 11.5 0.41 1.2

11.9 10.3 0.98 0.47 76.3 2.7 0.27 nd

9.9 15.6 4.3 5.8 64.5 47.8 0.41 6.2

11.1 23.2 9.7 4.2 51.8 13.2 37.6 nd

a

Data source: USDA National Nutrient Database for Standard Reference (US Department of Agriculture, 2015). Carbohydrates includes total dietary fiber (TDF), starch, and sugars; the sugar value for germ ¼ carbohydrates – TDF. b Values for whole wheat and bran (not determined, ‘nd’ for endosperm and germ) correspond to the sum of major phytochemicals considered and reported in this article in descending order of content in bran: phytic acid, betaine, ferulic acid þ ferulic acid dehydrodimers, alkylresorcinols, choline, phytosterols, sum of other phenolic acids, total B vitamins, and lignan.

wall of a wheat floret. The pericarp, which represents about 50% of the thickness of bran, should not be confused with the hull or husk of the grain. Modern wheat has evolved as a free-threshing grain, that is, the caryopsis is naked and does not include the highly fibrous hull, which is easily removed as chaff in mature wheat when threshed or harvested. In this way, wheat is distinct from some other grains like most barley types, as well as oats and rice, whose kernels naturally include the hull. The three major components of the wheat kernel are the germ, bran, and endosperm (Figure 1). Based on research involving careful wheat kernel dissection, endosperm, bran (pericarp, testa, and aleurone), and germ (embryo and

scutellum) have been found to represent about 83%, 13–15%, and about 3% by weight of the whole grain, respectively. These three fractions of the wheat kernel are relatively distinct in basic chemical composition (Table 1). The endosperm is energy-rich as it is predominantly composed of starch but contains less than 10% of the nutritive value (minerals, vitamins, and dietary fiber) of whole grain. Germ is distinct in its relatively high protein and lipid content and exceptionally high concentrations of sugars. Bran contains nearly all the bioactive compounds of wheat, that is, it is enriched in fiber components (nonstarch polysaccharides and lignin), minerals, B vitamins, and other phytochemical compounds (Table 2).

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From the seed’s perspective, the germ contains the embryonic plant and an organ called the scutellum, which separates the embryo from the endosperm. During germination of the seed, the scutellum absorbs nutrients from the endosperm to provide food for the germinated seed and growing seedling. The biological function of bran is very different, which reflects its complex and multilayered structure as well as chemical composition; it is to protect the seed from microorganisms and insects and from adverse weather conditions. The wheat kernel, as with all cereals, contains a crease that runs parallel to its long axis, which covers about 25% of its surface. This crease affects the utilization of wheat for food, such that the endosperm can only be freed from bran by conventional roller milling using relatively low flour extraction rates. The low extraction rate, in the context of milling, minimizes significant ‘contamination’ of the flour by bran and germ and results in the production of refined flour, which is used to make the so-called ‘white’ bread. Low extraction rates in flour milling also result in the exclusion of the full complement of the great many bioactive compounds, which are Table 2 Average concentration of phytochemicals enhanced in wheat bran compared to whole grain (mg/100g)a Phytochemicals

Whole grain

Bran

Lignan Phytosterols Betaine Choline B vitamins, total B1 (thiamin) B2 (riboflavin) B3 (niacin) B5 (pantothenic acid) B6 (pyridoxine) B9 (folate)

0.4 78 156 111 9.02 0.56 0.18 6.5 1.35 0.38 0.05

4.75 158 868 172 33.5 0.65 0.51 28 3.15 1.0 0.23

a

Proportion of vitamin retained (%)

Values are means of range data in Table 2 of Fardet A (2010) New hypotheses for the health-protective mechanisms of whole-grain cereals: What is beyond fibre? Nutrition Research Reviews 23: 65–134.

Thiamine Pantothenic acid Riboflavin Folic acid Niacin Pyridoxine

100 80 60 40 20 0 40

50 60 70 80 90 Milling extraction rate (%)

100

Figure 2 The effect of wheat roller milling on the retention of selected B vitamins in flour. The figure illustrates the invariably uneven distribution of bioactive compounds in the wheat kernel using B vitamins as an example. Adapted from Figure 8 of Akyroyd WR and Doughty J (1970) Wheat in Human Nutrition. Rome: FAO.

concentrated in commercial wheat bran, which includes the bioactive-rich aleurone layer that represents about 50% by weight of total bran (Figure 1). It is important to point out that commercial wheat bran is not the same as botanical bran, that is, as it exists in the original grain, which excludes the aleurone layer, which developmentally forms the outer part of endosperm (Figure 1). Wheat bran can be derived from various stages of the milling process and, depending on the setup of the mill in terms of flour extraction, can vary in purity, that is, endosperm contamination, and hence can vary in its content of fiber, starch, protein, and other constituents, due to milling effects alone and also due to genotype, wheat hardness, and environmental conditions during wheat kernel development. Wheat bran is therefore not a standardized product of milling and can be produced from conventional dry roller milling or a combination of conventional milling and abrasion processing similar to that used in rice polishing. An example of how the degree of flour extraction in commercial milling affects the retention of the B vitamin group of bioactive compounds is shown in Figure 2. A milling extraction rate of 100% is the equivalent of whole wheat flour.

Nature of Variation in the Content of Bioactive Components in Bran It is clear from the literature that there is considerable variation in the content of bioactive components in wheat or bran depending on the type of wheat or variety (genotype effect) and the environment in which the wheat is grown. Recent science has nicely documented this variation for European wheats and has shown that whole grains can vary from about 1.5- to 4-fold depending on the specific compound and more importantly that some compounds have ample heritability to allow breeders to further increase levels if that is desired. Regarding bran, however, there is another source of variation that creates issues in accurately documenting bioactive component content, that is, milling. As noted in the previous section, wheat bran is not a standardized product of milling. While it is possible to obtain pure bran or even isolate specific bran tissues by hand dissection, this is not the form of bran available to consumers. It is impossible to obtain 100% pure wheat bran by any manner of mechanized milling or grinding procedure due to the tight bond that exists between the aleurone cell layer of the wheat kernel and endosperm cells that lie immediately inward of the aleurone. Depending on the type of wheat or genotype, and milling procedure, roller-milled bran can contain from 5% to 20% of adhering endosperm, which is enriched in starch. Typically, the harder the wheat, the more pure the resulting bran will be. This variation in endosperm content of milled bran accounts in part for the wide variation in content of fiber and bioactive components that has been reported in the scientific literature.

Structure of Bran and the Distribution of Bioactive Components Bran represents the outermost portion of the grain, which surrounds the starchy endosperm. Bran can be divided into


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nucellar tissue & seed coat outer pericarp

aleurone

cross cells endosperm

different tissue layers, more than what is depicted in Figure 1. Accordingly, bran is the most complex physical component of the wheat kernel. Bran basically comprises the outer and inner pericarp, seed coat (often referred to as testa), and a layer of large and thick-walled cells called the aleurone (Figures 3 and 4). In the mature wheat seed, the aleurone consists of living tissue, one cell thick that surrounds the endosperm. During germination, aleurone cells have an important enzyme secretion function; they respond to the embryo’s release of the hormone gibberellic acid, to synthesize and secrete enzymes such as a-amylase and proteases, which hydrolyze endosperm starch and protein to sugars and amino acids, respectively, to support the early growth of the embryo into a developing seedling. Quantitatively, the predominant bioactive component of wheat bran is fiber. Fiber is not a distinct chemical compound, but a heterogeneous mixture of various nonstarch polysaccharides plus lignin and other compounds. Ranked in order of decreasing content, the major bran fiber bioactive compounds are arabinoxylans, cellulose, lignin, fructans, and b-glucans (Figure 5). Together, these compounds comprise over 90% of the fiber content of wheat (Figure 5) and from 45 to 55% of the fiber content of bran. In contrast, refined wheat flour depending on type (e.g., cake flour or all purpose) contains from 1.5 to 3% fiber (Table 1). Lignin is molecularly different from the other fiber components as it is a complex polyphenolic compound that does not contain any sugar molecules. All the fiber components of bran reside in the cell walls of the tissue layers (e.g., Figure 4, which depicts the distribution of arabinoxylans and b-glucans in aleurone cell walls) and include small molecules such as phenolic acids (Figures 3 and 6). Wheat bran phenolic acids and

Figure 4 Double labeling of arabinoxylan (AX) and b-glucans in aleurone cell walls from wheat grain. Polyclonal antixylan and monoclonal anti-b-glucan antibodies were used with a second-stage goat antirabbit (orange-red fluorescence) and a second-stage goat antimouse (green fluorescence) antibody, respectively. Yellow fluorescence indicates the presence of both b-glucans and AX. The light-colored circular structures within the vacuoles of the aleurone cells are storage protein bodies that contain dark-stained inclusion bodies or globoids in which the phytochemical phytin is concentrated. Reprinted from Saulnier et al. (2007) Plant cell wall polysaccharides in storage organs: Xylans (food applications). In: Kamerling J, Boons G-J, Lee Y, Suzuki A, Taniguchi N, and Voragen AGJ (eds.) Comprehensive Glycoscience, vol. 2, pp. 653–689. Oxford: Elsevier Science Ltd.

30 25 g/100 g

Figure 3 Fluorescence microscopy image showing the outer endosperm and different tissue layers of bran revealing the distribution of ferulic acid and other minor phenolic acids in wheat bran and endosperm. Aleurone contains the highest concentration of phenolic acids in the wheat kernel. Bar ¼ 50 mm. Adapted from Ndolo VU, Beta T, and Fulcher RG (2013) Ferulic acid fluorescence intensity profiles and concentration measured by HPLC in pigmented and non-pigmented cereals. Food Research International 52: 109–118, with permission.

24.0

Whole wheat

21.4

20

Bran

15 10 5

5.9

5.2 2.0

2.3

2.3

3.9

2.3 2.0

0

Figure 5 Components of fiber in whole wheat and bran. Data compiled from a variety of sources showing typical values averaged across wheat genotypes and/or samples.

ferulic acid most notably are important bioactive phytochemicals that have a structural role to cross-link the nonstarch polysaccharides with other cell wall components including lignin, thereby increasing the physical integrity of cell walls, and also provide a barrier to invading pathogenic fungi and other microorganisms, which are naturally present in the pericarp of wheat bran. Similarly, the seed coat that separates the pericarp from aleurone and endosperm appears to be chemically inert and waterproof. This latter property of the seed coat


500 410

mg/100 g

400

296

300 200 117

100

25

Whole wheat Bran

20

mg/100 g

272

73

20.0

Whole wheat Bran

15 10

9.0 6.3 3.7

5

1.5

3.5

1.3

3.2 0.7

2.2

0

0 Ferulic + dimers Alkylresorcinols (a)

(b)

Figure 6 Phenolic compounds significantly enhanced in wheat bran compared to whole grain. Ferulic acid plus ferulic acid dehydrodimers and alkylresorcinols (a) are the predominant phenolic compounds, each having at least tenfold higher concentration compared to the total of all other phenolic compounds including simple phenolic acids (b) and flavonoids (not shown). Phenolic acid data compiled from a variety of sources. Alkyresocinol values are the mean of those reported by Fardet (2010). Reproduced from Mattila et al. (2005) Contents of phenolic acids, alkyl- and alkenylresorcinols, and avenanthramides in commercial grain products. Journal of Agricultural and Food Chemistry 53: 8290–8295.

5 4 g/100 g

likely derives at least in part from the presence of a distinct group of phenolic lipid compounds called alkylresorcinols, which contain long hydrophobic alkyl chains similar to saturated fatty acids. Botanically, the aleurone layer of wheat is part of the endosperm, but because of its high adherence to the seed coat, which is likewise strongly bonded to the pericarp, aleurone is mainly found in bran fractions after milling. Wheat as noted has a single-cell aleurone layer. In contrast, barley aleurone has two to four cell layers. The thicknesses of wheat bran’s tissue layers also vary. The aleurone is the thickest layer (up to 65 mm), a feature that can be clearly seen in microscope images (e.g., Figures 3 and 4). The outer pericarp is of intermediate thickness (15–30 mm), and the seed coat is the thinnest layer (5–8 mm). Variation in bran thickness in an individual wheat grain is believed to be due to the irregularities of thickness of aleurone cells affecting the separation of bran from endosperm during milling. Thus, flour yield during milling depends in part on bran thickness, size of grain (bran and endosperm content), and crease characteristics. An interesting question is whether reported differences among different wheats in phenolic acid content and antioxidant capacity are due, at least in part, to variation in thickness of the aleurone layer and therefore concentration of constituent phytochemicals such as ferulic acid. There appears to be no science to answer this question at the present time. From a bioactive phytochemical perspective, the aleurone is the most significant tissue in the wheat kernel. It contains in its thick cell walls relatively high levels of fiber components (Figure 4). Aleurone cell walls are also rich in phenolic compounds such as ferulic acid and r-coumaric acid (Figure 3) and therefore contribute the highest antioxidant capacity of any wheat tissue. Aleurone cells are also enriched in B vitamins (B3, or niacin; B2, or riboflavin; B5, or pantothenic acid; B6, or pyridoxine; and B9, or folate), minerals (e.g., phosphorus, potassium, magnesium, manganese, and iron), and choline and betaine to a lesser extent. In addition, wheat aleurone has a very high content of phytic acid, which is the

Whole wheat

4.2

Bran

3 2 1

0.7

0 Phytic acid Figure 7 Phytic acid content in whole wheat and bran. Values are the mean of those reported by Fardet (2010).

predominant storage form of phosphorus in the seed. Phytic acid, also known as inositol hexaphosphate, is the phytochemical in highest concentration in whole wheat (0.3–1.5%) and wheat bran (2.3–6%) (Figure 7). Phytic acid is typically complexed in the seed with minerals such as calcium or magnesium, and in this form, it is called phytin. Phytin exists within the cavity or vacuole of aleurone cells and can be seen in microscopic images (e.g., Figure 4) as numerous darkstained inclusions within circular storage protein bodies. While phytate has been traditionally viewed as an antinutrient because of its mineral-binding properties, it is also known to have compelling anticancer properties. Molecular structures of several of the major bioactive compounds in bran as discussed are shown in Figure 8.

Brief Descriptions of Some of the Major Bioactive Compounds in Wheat Bran A common physiological role for many of the fiber-bound bioactive compounds that are enhanced in wheat bran, notably nonstarch polysaccharides, oligosaccharides (fructans),


273

OH -O

OH

P

O

O

R = CnH2n+1 n = 15, 17, 19, 21, 23, 25

OH

O

O P O

R

O-

P

O

O O

OO-

P

O

O-

P

Alkylresorcinol

O-

OH

O(a)

OO-

O

O O

P

Phytic acid

(b)

OH OH HO

HO

A

A HO O O

OH HO O

X O

HO

O HO

O O

X

O

O O O HO A

OH

O H3CO

F (c)

O

O

X

O

X

O OH

OH O

Arabinoxylan

HO

R3 Cinnamic acid derivatives ferulic acid, R1 = OCH3; R2 = OH CH = CH- COOH sinapic acid, R = OCH ; R = OH 1 3 2 p-coumaric acid, R2 = OH

R2

R1 R3

R2

Phenolic acids

COOH

Benzoic acid derivatives vanillic acid, R1 = OCH3; R2 = OH syringic acid, R1 = R5 = OCH3; R2 = OH p-hydroxybenzoic acid, R2 = OH

R1 (d)

Figure 8 Basic molecular structures or portions of the structure of four types of bioactive compounds in wheat bran: alkylresorcinol (a); phytic acid (b); arabinoxylan (c) showing xylose (X) backbone with substituted arabinose (A) molecules, some of which are linked to the phenolic acid ferulic acid (F); phenolic acids (d). (Figure 8c adapted from Saulnier et al. (2007) Plant cell wall polysaccharides in storage organs: Xylans (food applications). In: Kamerling J, Boons G-J, Lee Y, Suzuki A, Taniguchi N, and Voragen AGJ (eds.) Comprehensive Glycoscience, vol. 2, pp. 653–689. Oxford: Elsevier Science Ltd.)

and lignin (Figure 5), is to promote intestinal health. There are an amazing number of bacterial cells in the colon in particular, and estimates run from 1011 to 1012 cells per gram. This huge population of cells, often referred to as the microbiome, is gaining considerable importance in science due to an increased understanding of the profound health effects, both positive and negative, that good or poor gut health, respectively, can contribute.

Wheat bran (fiber) is particularly relevant in this discussion as it is highly indigestible, yet fermentable by bacteria in the colon, which have enzymes necessary to hydrolyze the polymeric compounds in bran such as polysaccharides. It has been known for a long time that the stimulation of fermentation caused by consuming these fiber bioactives leads to an increase in bacterial mass and consequently fecal mass, which has a positive effect on laxation and regularity. What is only being

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understood very recently is that fermentation causes alterations in the microbiome, which in turn alters bacterial metabolites (short-chain fatty acids), modulates inflammatory responses, and likely leads to a decreased risk of inflammation-associated and other metabolic abnormalities such as atherosclerosis and type II diabetes. Also, by producing short-chain fatty acids, most notably butyric acid, and other metabolites, the intestinal microbiome is believed to contribute to a gut environment that resists the proliferation of pathogenic bacteria.

Arabinoxylans and Ferulic Acid Arabinoxylans, which are part of a group of nonstarch polysaccharides compounds, originate in the cell walls of bran tissues. Pentosans, a term still used in the current literature synonymous with arabinoxylans, represent nonstarch polysaccharides composed of five-carbon or pentose monosaccharides, xylose, and arabinose (Figure 8). More precisely, arabinoxylans consist of a xylose polymer backbone with frequent branching of arabinose residues. Significantly from the standpoint of structure and bioactivity, arabinoxylans contain the phenolic compound ferulic acid, which is covalently bound to arabinose residues. Arabinoxylans are quantitatively the most important bioactive compound in wheat and can represent as much as 30% of the content of bran (Figure 5). Ferulic acid is the main cell wall-bound phenolic acid in all cereal grains and in wheat it is found almost exclusively associated with arabinoxylans. Arabinoxylans are very diverse in structure and relative content of arabinose, xylose, and ferulic acid molecules. They differ in this way from those found in the endosperm, which tend to be more soluble than arabinoxylans in bran, which are highly insoluble. Arabinoxylans are known to have a prebiotic function in the gut, that is, they can stimulate the growth of healthful bacteria such as Bifidobacterium and, in this way and others, contribute to gut health. The socalled dehydroferulic acid dimers (diferulates) have an important structural role to cross-link and therefore stabilize arabinoxylan polysaccharides and hence the cell walls in bran. Consequently, diferulates may be partly responsible for the insoluble nature attributed to the dietary fiber of wheat bran. Importantly, the antioxidant potency of extracts of wheat and bran is predominantly determined by the high content of ferulic acid in bran (Figure 6), which is enriched in the aleurone fraction. The antioxidant capacity of biomolecules such as ferulic acid is associated with the scavenging of free radicals, many of which are reactive oxygen molecules, which are often toxic to cells causing inflammatory responses and damage to lipids, proteins, and nucleic acids.

b-Glucan b-Glucans are so-called b-linked polysaccharides of glucose monomers. b-Glucans are a diverse group of molecules that can vary with respect to molecular mass, solubility, and viscosity. In wheat, b-glucan is found mainly in the aleurone cell walls of wheat bran but are distributed more widely in the grain of other cereals. In oats, b-glucans are concentrated in

the subaleurone layer, while in barley and rye, b-glucans are located mainly in the endosperm. The b-glucan levels of wheat bran are low (2%) and represent <1% of the total dietary fiber content of whole wheat. Because of its low concentration in wheat, b-glucans likely contribute relatively little by way of health attributes, compared to oats and barley. In these latter grains, b-glucan is considered to be an important soluble fiber that is associated with lowering serum cholesterol levels and attenuating glycemic response. These effects originate in the upper gastrointestinal tract and probably are related to the viscosity of b-glucan.

Cellulose Cellulose is a very abundant cell wall polysaccharide in the outer pericarp and intermediate layers of wheat bran. Cellulose consists of glucose units linked together by b-1–4 glycosidic bonds to form a linear polysaccharide. Cellulose comprises about 21% of wheat bran on a 14% moisture basis (Figure 5), which is substantially enhanced compared to whole wheat at (2%); however, estimates vary widely. Cellulose is considered to be very resistant to intestinal microbial fermentation when compared with the noncellulosic fiber polysaccharides such as arabinoxylans and especially b-glucans whose digestibility is relatively high. Nevertheless, bacteria in the colon are known to contain cellulase enzymes, which can break down cellulose leading to its fermentation and likely beneficial effects for health.

Lignin Lignin is a complex polyphenolic polymer residing in the pericarp and seed coat cell walls of wheat bran. Lignin is a nonpolysaccharide cell wall component that is a polar polymer. Whole wheat has a lignin concentration of 2% of dry material that is only moderately enhanced in wheat bran to levels of about 5% (Figure 5). The distribution of lignin in wheat has been reported to range from about 2 to 9% in different bran layers but is not found in aleurone according to the literature. Ferulic acid, together with dehydroferulic acid, is a component of lignocelluloses, serving to cross-link the lignin and polysaccharide, thereby conferring rigidity to the cell walls. Like cellulose, lignin is fermented at low levels by bacteria in the colon and is able to increase fecal bulk. Also, lignins lower intestinal transit time, which is important to reduce exposure time of dietary carcinogens adsorbed in fiber. Lignins also possess in vitro antioxidant activity and may mitigate oxidative DNA damage and development of diseases in relation to increased oxidative stress.

Fructans Fructans are a category of functional food carbohydrates that encompass naturally occurring plant oligosaccharides and polysaccharides containing fructose. Fructans are different in

BIOACTIVES AND TOXINS | Bioactive Compounds in Wheat Bran nature and classified according to linkage and origin. Fructooligosaccharide is a subgroup of inulin, consisting of linear chains of fructose sugar monomers linked by b-(1–2) bonds with a low degree of polymerization (10). Whole wheat grain and bran fructan contents are similar to those reported for lignin. Fructans are classified as a functional fiber that are believed to be extensively fermented, but with little effect on stool weight. Fructans are known to have positive effects on calcium uptake in the gut and hence calcium bioavailability.

Phenolic Acids Phenolic acids are a very noteworthy constituent of wheat bran. Apart from flavonoids, which are found to a large extent in wheat germ and in relatively low concentration in bran, virtually all other phenolic compounds (phenolic acids and phenolic acid esters) reside in wheat bran tissues, most notably aleurone. Phenolic acids can be subdivided into two major chemical groupings: hydroxybenzoic acids and hydroxycinnamic acids (Figure 8). Hydroxybenzoic acids of significance in bran, although levels are relatively low (Figure 5), include vanillic acid, synergic acid, and r-hydroxybenzoic acid. They are typically components of complex compounds like lignins and tannins. The concentration of hydroxybenzoic acids in wheat and bran is low compared to hydroxycinnamic acids, which includes r-coumaric, and ferulic acid, which form links to cell wall structural components such as arabinoxylans, cellulose, and lignins through ester bonds. By far, the predominant phenolic acid in wheat is (trans) ferulic acid, which comprises more than 90% of total phenolic acids in wheat bran. Wheat bran is one of the richest sources of ferulic acid with levels as high as 1400 mg/100g being reported. Ferulic acid is predominant in wheat aleurone, pericarp, and embryo cells, while only trace amounts can be found in starchy endosperm. Aleurone cells are associated with the highest concentration of ferulic acid (Figure 3). The seed coat layer of wheat bran contains significant quantities of ferulic acid, higher than those in the pericarp. Total ferulic acid concentration in wheat bran is typically about four times higher than that in whole wheat grain (Figure 5). There is considerable scientific evidence that ferulic acid, like other phenolic compounds, has antioxidant, anticarcinogenic, and anti-inflammatory properties. The great majority of these studies are based on animal or cell models. The types of antioxidant activities possessed by phenolic acids include radical scavenging, metal ion chelation, and inhibition of prooxidant enzymes. Ferulic acid has been extensively studied for its in vitro antioxidant effects and has been shown to be effective. However, in vivo studies of phenolic acids from cereals like wheat and fractions like wheat bran are few. Cereal grains such as wheat that have significant quantities of ferulic acid and other phenolics require in vivo studies to determine if high enough levels of these bioactive compounds become bioavailable when consumed in food to provide health benefits.

Alkylresorcinols Alkyresorcinols are phenolic lipids that are present exclusively in bran and specifically in the outer layer of the seed coat.

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Compared to simple phenolic acids, alkylresorcinols represent a very distinct group of phenolic compounds in terms of molecular properties, that is, they are amphiphilic, meaning they have both polar and nonpolar properties. This bioactive compound consists of a phenolic ring with two hydroxyl groups and a hydrophobic and mostly saturated alkyl chain that can contain from 15 to 25 carbons (Figure 8). Wheat bran is a rich source of alkylresorcinols and has been reported to contain levels of about 0.3%, which is fourfold higher than its content in whole wheat (Figure 6). Refined flour contains essentially no alkylresorcinol content. Accordingly, alkylresorcinols can be used as biochemical markers of whole wheat and bran in foods. Several studies have reported that alkylresorcinols have the ability to protect cellular lipid components from oxidative processes. Accordingly, alkylresorcinols appear to behave as antioxidant compounds, but they are generally known as weak antioxidants, based on their hydrogen-donating and radicalscavenging abilities, compared to some other bioactive compounds such as a-tocopherol (vitamin E). Their antioxidant potential depends on their chain length, which affects their amphiphilic behavior and incorporation into cell membranes; studies have shown that the shorter the chain length, the higher the inhibitory level of lipid oxidation. Also, membrane incorporation of alkylresorcinols could accommodate a biological effect given their high concentration in wheat and bran, but limited data on alkylresorcinol’s effective dose levels require further studies on risk modulation of cancer and cardiovascular disease. Alkylresorcinols are absorbed through the lymphatic system and have been recovered from rat adipose tissue, human lipoproteins (the main transporter), human erythrocyte membranes, and human plasma. Animal studies have shown that alkylresorcinol is highly bioavailable, which indicates that apparently, the indigestible bran matrix does not greatly inhibit absorption.

Phytic Acid Perhaps the most notable phytochemical constituent of wheat bran is phytic acid, which is composed of a simple sugar (inositol) with phosphate groups attached to each of the six carbons in the sugar molecule (Figure 8). It is typically found in food sources high in fiber content, although wheat bran may be the richest source in nature. Phytic acid represents the main storage form of phosphorus in wheat and other cereal grains. Phytic acid represents the most highly concentrated phytochemical in wheat and wheat bran in particular with average levels of 0.7% and 4%, respectively (Figure 7). By contrast, endosperm tissue of wheat contains very little phytic acid. Phytic acid has traditionally been considered to be an antinutrient associated with its ability to bind minerals with positively charged ions (i.e., cations) such as iron, as well as magnesium and calcium. This binding of minerals therefore reduces their bioavailability, but only for poorly nourished people consuming predominantly whole grains in their diet. Many animal studies have shown phytic acid to be capable of antineoplastic activities on multiple types of cancers of the breast, colon, liver, prostate, skin, and skeletal muscle. Potential mechanisms suggested for phytic acid’s anticarcinogenic properties include cell cycle inhibition, antioxidant ability (metal chelation), gene alteration, and increased natural killer cell activity.

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Summary and Conclusions The nature of wheat’s value for human health derives from its structure, biochemical composition, and functionality of its components. Because wheat consumption as bread and other foods is so significant, whole wheat and the bran it contains have the potential to deliver to the diet considerable amounts of fiber and constituent bioactive compounds whose functionality extends well beyond the role of nutrients, which are essential for growth and maintenance of life. There is now ample scientific evidence that consumption of adequate amounts of bran in whole wheat is associated with lowering the risk of many chronic diseases, although the specific actions of individual biologically active compounds in bran have been only studied using animal and cell models. A more thorough discussion of the potential health efficacies of the major bioactive compounds of wheat bran is well beyond the scope of this article. Many excellent books or review papers have been published and a few are offered at the end of this article as suggestions for further reading. These articles are based on a foundation of hundreds of research studies, and the science in this area continues to expand in scope and knowledge. Most exciting perhaps is the microbiome-related research on the fermentation of fiber and bran that is gaining momentum. Wheat bran is generally considered to be one of the best, if not the best, sources of fiber for fecal bulking and laxation. This sort of bioactivity represents the traditional health benefit ascribed to bran, but it also suggests that wheat bran interacts strongly with the microbiome and that this area of research has enormous potential for greater understanding of mechanisms underlying the more compelling health efficacies generally associated with the consumption of whole wheat and bran and its constituent bioactive compounds.


• • •

Are there wheat milling procedures that can generate bran of higher purity that is more concentrated in bioactive compounds? What is the function of the bioactive compounds in wheat bran from the perspective of the wheat seed? How much wheat bran is typically produced in a large milling operation and how much of that bran is destined

• •

for food use and how much for feed? How do these proportions vary in major wheat producing countries? Are there wheat genotypes or varieties that have bran with enhanced levels of bioactive compounds? How does the wheat growing environment affect the content of bioactive compounds in bran?


• • •

How do bioactive compounds in the bran or whole grain of other cereals compare to wheat, especially oats, given its reputation for having dietary benefits? Select a few fruits or vegetables that are commonly associated with health benefits. How similar or different are the bioactives in those foods compared to wheat bran? Apart from eating whole wheat bread or pasta, think of other ways to increase your consumption of wheat bran that would appeal to you.

See also: Bioactives and Toxins: Bioactives: Antioxidants; Carbohydrates: Cereals: Chemistry and Physicochemistry of Nonstarchy Polysaccharides; Food Grains and the Consumer: Grains and Health; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Functional Foods: Overview; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; The Basics: Grain: Morphology of Internal Structure.

Further Reading Anson NM, Hemery YM, Bast A, and Haenen GR (2012) Optimizing the bioactive potential of wheat bran by processing. Food and Function 3: 362–375. Fardet A (2010) New hypotheses for the health-protective mechanisms of whole-grain cereals: What is beyond fibre? Nutrition Research Reviews 23: 65–134. Marquart L, Jacobs Jr. DR Jr., McIntosh GH, Poutanen K, and Reicks M (eds.) (2007) Whole Grains and Health. Oxford: Blackwell. Okarter N and Liu R (2010) Health benefits of whole grain phytochemicals. Critical Reviews in Food Science and Nutrition 50: 193–208. Shewry PR, Charmet G, Branlard G, et al. (2012) Developing new types of wheat with enhanced health benefits. Trends in Food Science and Technology 25: 70–77. Slavin J (2013) Fiber and prebiotics: Mechanisms and health benefits. Nutrients 5: 1417–1435.

Bioactives: Antioxidants T Beta, University of Manitoba, Winnipeg, Manitoba, Canada KG Duodu, University of Pretoria, Pretoria, South Africa ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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of bioactive antioxidants albeit in relatively lower levels compared to other food sources.

Grain bioactives that exert antioxidant effects include phenolic compounds, carotenoids, tocols, sulfur compounds, betaine, choline, policosanol, melatonin, g-oryzanol, saponins, and phytates. Chemical and biological measurements of antioxidant properties demonstrate varying degrees of activity among grains, grain fractions, and constituents. Grain bioactive antioxidants are proposed to potentially ameliorate the fundamental processes of oxidative stress that tend to be precursors for many chronic diseases of lifestyle. The mechanisms of action of grain bioactives are proposed to be mainly via either exertion of antioxidant effects or modulation of the activity of various enzymes involved in the cellular and molecular pathways and reactions associated with chronic diseases.

Learning Objectives

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To achieve understanding of the major bioactive compounds in grains that exert antioxidant effects when measured using chemical and biological assays. To achieve an understanding of the role of grain bioactive compounds in offering antioxidant protection against major chronic diseases and the mechanisms of action of the bioactives.

Introduction In addition to major and minor nutritional components, cereal grains including maize, rice, wheat, barley, sorghum, rye, oats, triticale, buckwheat, and millets contain a wide range of bioactive phytochemicals associated with antioxidant effects. Grain phenolics, carotenoids, tocopherols, phytates, and phytosterols are among the list of candidates displaying antioxidant properties. Some bioactive antioxidants are unique to certain grains such as avenanthramides in oats; xanthophylls in yellow endosperm maize, wheat, and, sorghum; and anthocyanins in blue, red, and purple grains. The literature on antioxidant effects of grain bioactives is not easily comparable due to the lack of uniformity of the assays in use. However, there has been an attempt to establish systematic databases such as the Phenol-Explorer database on polyphenol content of foods. In vitro antioxidant measurements have been applied to a lesser extent on non-phenolic bioactive constituents in grains, while in vivo measurements using humans are largely lacking. Since grains are staples around the world, they are a notable source


Cereal Grains and Grain Products Cereal grains include maize, rice, wheat, barley, sorghum, rye, oats, triticale, buckwheat, and millets. The glumes/husks cover some grains such as oats. Once dehusked, the cereal caryopsis is made up of the endosperm, which includes the aleurone layer, germ, testa or seed coat, and outer pericarp layers as the main botanical parts. Carbohydrates, proteins, and lipids make up the major chemical components while minerals and vitamins are considered minor nutrients in grains. Phytochemicals including bioactives in grains make up the remainder of the minor constituents. The distribution of nutrient components and phytochemicals varies among the different botanical parts of the grain as exemplified by whole-grain wheat, wheat bran, and wheat germ (Table 1). Following harvest, cereal grains are stored and processed for human food. Grain processing includes dry and wet milling, boiling, lime cooking, steaming, baking, frying, extrusion, flaking, roasting, fermentation, malting or sprouting, and brewing. Storage and processing affect the chemical constituents of grains including bioactives resulting in an alteration of the phytochemical profiles of the resultant products. Qiu et al., for example, demonstrated a much lower total phenolic content in quick-cooking wild rice than in uncooked wild rice varieties. Whole-grain cereal, germ, and bran (aleurone, testa, and outer pericarp layers) obtained during dry milling or hand dissection often display higher phytochemical levels than the endosperm. Several phytochemicals, exerting antioxidant effects, have been identified in grains. Consumption of whole-grain cereals can potentially protect the human body against increased oxidative stress.

Reduction and/or Prevention of Oxidative Stress Cellular redox processes in the body lead to the formation of highly reactive free radicals, generally in the form of reactive oxygen species or reactive nitrogen species. Some examples of such radicals that are of importance in living organisms include hydroxyl (OH ), superoxide (O2 ), nitric oxide (NO ), and peroxyl (RO2 ). It is postulated that at high concentrations, these reactive species cause the condition known as oxidative stress, which is harmful to cell structures. Oxidative stress is a term used to describe the condition where there is an imbalance between the generation of reactive oxygen or nitrogen species and the activity of the natural antioxidant defense systems of the body. Severe oxidative stress can cause cell damage and death, and it is implicated in various human l

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BIOACTIVES AND TOXINS | Bioactives: Antioxidants Antioxidants in whole-grain wheat, wheat bran, and wheat germ

Bioactive: antioxidant

Whole-grain wheat

Wheat bran

Wheat germ

Reduced glutathione Methionine Cystine Lignins Phytic acid Fe Zn Mn Se Cu Mg Thiamin (B1) Tocols (E) Total tocopherols Total tocotrienols Total carotenoids b-Carotene Lutein Zeaxanthin b-Cryptoxanthin Total phenolic acids Bound phenolic acids Total ferulic acid Total dehydrodiferulic acid Total dehydrotrimer FA Total flavonoids Anthocyanins Lignans Alkylresorcinols Betaine Total choline Phytosterols Melatonin

1.04–5.74 mg/100 g 0.17–0.24 g/100 g 0.19–0.40 g/100 g 0.9–2.8 g/100 g 0.28–1.50 g/100 g 1.0–14.2 mg/100 g 0.8–8.9 mg/100 g 0.9–7.8 mg/100 g 0.0003–3.000 mg/100 g 0.09–1.21 mg/100 g 17–191 mg/100 g 0.13–0.99 mg/100 g 2.3–7.1 mg/100 g 1.06–2.89 mg/100 g 1.09–4.49 mg/100 g 0.044–0.626 mg/100 g 0.005–0.025 mg/100 g 0.026–0.383 mg/100 g 0.009–0.039 mg/100 g 1.12–13.28 mg/100 g 16–102 mg/100 g 14–78 mg/100 g 16–213 mg/100 g 1.5–76.0 mg/100 g 2.6–3.5 mg/100 g 30–43 mg CE/100 g 0.45–52.60 mg CE/100 g 0.199–0.619 mg/100 g 11.6–128.8 mg/100 g 22–291 mg/100 g 27–195 mg/100 g 57–98 mg/100 g 0.2–0.4 mg/100 g

1.7–19.4 mg/100 g 0.20–0.29 g/100 g 0.32–0.45 g/100 g 2.2–9.0 g/100 g 2.3–6.0 g/100 g 2.5–19.0 mg/100 g 2.5–14.1 mg/100 g 4–14 mg/100 g 2–78 mg/100 g 0.84–2.20 mg/100 g 390–640 mg/100 g 0.506–0.800 mg/100 g 9.5 mg/100 g 2.4 mg/100 g 7.1 mg/100 g 0.25–1.18 mg/100 g 0.03–0.010 mg/100 g 0.050–0.180 mg/100 g 0.025–0.219 mg/100 g 0.018–0.064 mg/100 g 761–1384 mg/100 g 148–340 mg/100 g 138–631 mg/100 g 13–230 mg/100 g 15–25 mg/100 g 14.9–40.6 mg/100 g 0.9–48.0 mg/100 g 2.8–6.7 mg/100 g 215–323 mg/100 g 230–1506 mg/100 g 74–270 mg/100 g 121–195 mg/100 g

19.4–245.7 mg/100 g 0.39–0.58 g/100 g 0.35–0.61 g/100 g 1.3–1.6 g/100 g 1.3–2.2 g/100 g 3.9–10.3 mg/100 g 10–18 mg/100 g 9–18 mg/100 g 1–79 mg/100 g 0.70–1.42 mg/100 g 200–340 mg/100 g 0.8–2.7 mg/100 g 23.1–31 mg/100 g 21.5–30.6 mg/100 g 1.3–1.6 mg/100 g – 0.062 mg/100 g – – – – – 7–124 mg/100 g 9 mg/100 g – 300 mg RE/100 g – – – 306–1395 mg/100 g 152–330 mg/100 g 410–450 mg/100 g

Source: Fardet A (2010) New hypothesis for the health-protective mechanisms of whole-grain cereals: What is beyond fibre? Nutrition Research Reviews 23: 65–134.

diseases including cancer, cardiovascular disease, type 2 diabetes, and even cataractogenesis. It is hypothesized that bioactives from cereal grains could offer potential health benefits by protecting against diseases associated with oxidative stress. A lot of in vitro evidence has emerged that shows the ability of cereal bioactives to protect cell constituents against oxidative stress and oxidative damage of biological tissues. This observed protective effect has been attributed to various mechanisms. These include the suppression of the formation of reactive oxygen species by either inhibiting enzymes or chelating trace elements involved in free radical production, scavenging reactive oxygen species, or upregulating or protecting antioxidant defense systems.

Antioxidants from Whole-Grain Cereals Whole-grain cereals serve as sources of antioxidants that include sulfur compounds, minerals, B vitamins, phytic acid, tocols, carotenoids, phenolic compounds, lignins, lignans, alkylresorcinols, betaine, choline, policosanol, melatonin, g-oryzanol in rice bran, avenanthramides, and saponins in oats as reviewed by Fardet. These antioxidants differ in their

structure and mechanism of action, which can be direct or indirect. Mechanisms may involve direct free radical scavenging or Fe chelation. Indirect antioxidants such as Fe, Zn, Cu, and Se act as cofactors of antioxidant enzymes. Very few studies have examined the antioxidant hypothesis; hence, in vivo investigations are needed to determine the complex and synergistic mechanisms taking place in human subjects.

Sulfur Compounds Total methionine and cystine contents of whole-grain wheat, wheat bran, and wheat germ are 0.5%, 0.6%, and 1.0%, respectively (Table 1). Other cereal varieties may contain higher levels. Methionine and cystine contents of commercially prepared whole-wheat bread based on USDA database are, respectively, 155 and 214 mg/100 g, contributing an average 47 and 64 mg day1 when a 30 g slice of bread is consumed. Significant amounts of at least 280 mg methionine and 380 mg cystine per day can be obtained by following USDA food guide pyramid that recommends between 6 and 11 daily servings of wholegrain cereal products. The two sulfur-containing amino acids are both precursors of reduced glutathione (GSH), an intracellular antioxidant that controls cell oxidative status by participating in

BIOACTIVES AND TOXINS | Bioactives: Antioxidants

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gene expression through the modification of the thiol redox status. GSH is also present at levels of 1.04–5.74, 1.7–19.4, and 19.4–245.7 mg/100 g in whole-grain wheat, wheat bran, and wheat germ, respectively, although its absorption in humans is deemed negligible in its free form.

ADP–Fe–oxygen complexes that initiate lipid peroxidation. Phytic acid may play a role in the prevention of various cancers including colon cancer.

Minerals

Lignins range from 0.9% to 2.8% in whole-grain wheat, 1.9% to 5.6% in wheat bran, and 1.5% in wheat germ. They have been shown to have antioxidant effects on ex vivo fresh lymphocytes. They account for 26–32% of the enterolactone (a mammalian lignan) formed from cereal bran. Mammalian lignans are antioxidants in vitro at concentrations of 10–100 mM achievable in vivo, particularly in the colon. Lignans make up 0.2–06, 2.8–6.7, and 0.49 mg/100 g of whole-grain wheat, wheat bran, and wheat germ, respectively (Table 1). Lignins are neither absorbed nor fermented in the human GIT. Only 0–4% of lignins are apparently absorbed in rats following the consumption of raw and processed wheat bran. Their antioxidant activity due to the phenolic hydroxyl group may contribute to the prevention of colon cancer.

The contents of Fe, Zn, Mn, Mg, Cu, and Se in whole-grain wheat, wheat bran, and wheat germ are shown in Table 1 as reviewed by Fardet. Low levels of 3.8% Fe are absorbed in humans following the consumption of wheat bran rolls. About 17–20% and 19–95% of zinc is absorbed in humans and rats, respectively, following the consumption of wholegrain wheat. There is limited literature on apparent absorption of Mn in humans, although levels are known to reach 14–18 mg/100 g in wheat bran and wheat germ compared to 0.078–0.079 mg/100 g for selenium in respective fractions. Studies have shown a 60–85% absorption of selenium in rats following the consumption of wheat and sodium selenite. Fe, Zn, Cu, and Se act as cofactors of antioxidant enzymes and therefore serve as indirect antioxidants. Cu exerts its antioxidant effect mainly as superoxide dismutase cofactor. Mg displays antioxidant effects by acting against lipid peroxidation. Se protects cell membranes from damage caused by lipid oxidation.

Thiamin and Riboflavin Both thiamine (B1) and riboflavin (B2) are present in grains including wheat (Table 1). The two B vitamins exert antioxidant effects in addition to their several well-documented physiological functions.

Phytic Acid Phytic acid (myoinositol hexakisphosphate) can reach up to 6% in the bran of certain wheat varieties. It displays strong in vitro antioxidant activity; however, it has been considered an antinutrient due to its ability to chelate minerals such as Zn, Fe, Ca, and Mg, reducing their bioavailability. Processing procedures such as the preparation of sourdough to produce bread can activate endogenous phytases and lower pH, thereby reducing the chelation of minerals by phytic acid. Phytic acid can also chelate Fe and limit the oxidative damage caused by the Fenton reaction, which would otherwise lead to the production of the very reactive free radical OH . Strategies are required that prehydrolyze phytic acid so as to maximize mineral bioavailability while simultaneously enhancing its antioxidant effect against free radicals in the gastrointestinal tract (GIT). Phytic acid is poorly absorbed in humans. In the absence of the enzyme phytase, phytate is not likely to be absorbed at the intestinal level in humans. About 58–60% of phytate is degraded into lower myoinositol phosphates in ileostomates following the consumption of raw wheat bran and only 5% following the consumption of phytase-deactivated wheat bran. As an antioxidant, phytic acid chelates various metals including the suppression of damaging Fe-catalyzed redox reactions, inhibits xanthine oxidase, suppresses oxidant damage to the intestinal epithelium, and interferes with the formation of l

Lignins and Lignans

Lipotropes and Methyl Donors (Betaine, Choline, and Folates) Whole-grain wheat, wheat bran, and wheat germ contain about 0.28%, 1.04%, and 1.09% of betaine and choline, respectively, and about 51, 231, and 420 mg folates/100 g. Betaine, choline, and folates are lipotropic compounds together with methionine and myoinositol that prevent excess fat deposition in the liver by hastening fat removal or by limiting lipid synthesis. Whole-grain wheat, wheat bran, and wheat germ can supply 0.51, 1.31, and 1.59 g lipotropes/100 g, respectively. Betaine is likely to be more bioavailable as it is not bound to cell wall constituents as is the case with ferulic acid. Data on apparent absorption of betaine and choline are not available.

g-Oryzanols g-Oryzanols or phytosteryl ferulates mainly found in rice bran have been reported to have antioxidant activity. They are considered more effective than tocopherols and tocotrienols in the prevention of cholesterol oxidation. They have the ability to scavenge radicals in multiphase lipid systems and inhibit UV irradiation-initiated linoleic acid oxidation.

Avenanthramides in Oats Avenanthramides are found only in oats, particularly in the outer layers. Avenanthramides or hydroxycinnamoyl anthranilinate alkaloids are amides of various cinnamic acids with different anthranilic acids. Avenanthramides 2p, 2f, and 2c are the most abundant among over 35 forms identified to date. Oat grain contains 4–13 mg avenanthramides 1/100 g (the major avenanthramide), while oat bran contains 1.3–12.5 mg/100 g according to the type of avenanthramide considered. The inclusion of avenanthramide-2c (N-(30 ,40 -dihydroxycinnamoyl)-5-hydroxyanthranilic acid) in rat diets altered oxidant–antioxidant balance in various tissues. It resulted in selective reduction in the production of exercise-induced reactive oxygen species and lipid peroxidation in the rats. This is related to the ability of the avenanthramides to modulate

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antioxidant enzyme systems such as superoxide dismutase and GSH reductase activities.

Saponins in Oats Saponins are glycosides with a steroid or triterpenoid aglycone. Oats synthesize two families of saponins, the steroidal avenacosides and the triterpenoid avenacins. The saponin content varies from 0.02% to 0.13% (DW) in oat endosperm. Saponins exert their antioxidant effects through the activation of transcriptional activity of Cu–Zn superoxide dismutase gene, scavenging of superoxide radicals, and reduction of lipid peroxidation.

Phenolic Compounds Pe´rez-Jimeńez et al. indicated 29 phenolic acids, 33 flavonoids, 6 lignans, and 2 other polyphenols as being present in various cereal grains and cereal products.

Phenolic acids Using the Phenol-Explorer database, Li and Beta identified cereal and cereal products in which high maximum values (>100 mg/100 g) have been reported for the sum of individual phenolic acids. The list includes whole-grain maize, refined maize flour, hard wheat semolina, common wheat germ, whole-grain rye flour and bread, hard wheat whole-grain flour, common wheat whole-grain flour, whole-grain oat flour, refined rye flour, and whole-grain rice. Phenolic acids occur as hydroxylated derivatives of benzoic and cinnamic acids. The hydroxycinnamic acids are more common than hydroxybenzoic acids. Hydroxycinnamates identified in grains include ferulic, caffeic, p-coumaric, and sinapic acids. Ferulic acid is the most abundant cinnamic acid derivative in cereal grains. Dehydrodimers of ferulic acid also exist including 5-80 -dehydrodiferulic, 8-O-40 -dehydrodiferulic, and 5-80 -benzofuran dehydrodiferulic acids. Phenolic acids occur as free, conjugated (soluble), and bound (insoluble) forms with concentrations in the order of bound > conjugated > free. The bound form makes up more than 80% of the total phenolic acids. Phenolic acid composition is similar, but concentrations of individual phenolic acids vary significantly in grain botanical fractions of corn, wheat, oat, and barley. Vanillic, p-coumaric, ferulic, sinapic, and syringic acids are present in all grain fractions. Phenolic acids are unevenly distributed even within the grain fractions of pericarp, aleurone, germ, and endosperm obtained from the same cereal kernels. Ferulic acid levels in whole-grain wheat, wheat bran, and wheat germ are 16–213, 138–631, and 7–124 mg/100 g, respectively (Table 1). While absorption of ferulic acid is very low following the consumption of whole-grain wheat or wheat bran, 2.0–5.7% urinary excretion has been reported in humans and rats. Small intestinal esterases may release very small amounts of the bound ferulic acid. Absorption of free and conjugated ferulic acid is reported as high in the rat small intestine; however, 27.8–78.9% is excreted through the urine in humans. Insoluble fiber plays a role in delivering antioxidant-bound phenolics to the colon thereby potentially aiding in the prevention of colon cancer and contributing to gut health.

Flavonoids Using the Phenol-Explorer database, Li and Beta reported the sum of individual flavonoids (mg/100 g) of selected cereals and cereal products as 51.5–108.4 for common wheat wholegrain flour, 16.4–63.4 for whole-grain buckwheat flour, 32.7–39.0 for whole-grain barley flour, 13.2–26.3 for common refined wheat flour, 1.7–17.0 for refined buckwheat flour, and 4.0–13.4 for buckwheat thermally treated groats. The major flavonoids include apigenin arabinoside–glucoside and apigenin galactoside–arabinoside in common wheat whole-grain flour; quercetin 3-O-rutinoside and apigenin 6-C-glucoside in whole-grain buckwheat flour; prodelphinidin dimer B3, procyanidin dimer B3, and (þ)-catechin in whole-grain barley flour; apigenin galactoside–arabinoside and apigenin arabinoside–glucoside in common refined wheat flour; and quercetin 3-O-rutinoside in refined buckwheat flour. Proanthocyanidin polyphenols with degree of polymerization (dp) greater than 10 (1307.3–1767.0 mg/100 g), dp 7–10 (150.0–325.0), and dp 4–6 (85.1–253) are present in some varieties of whole-grain sorghum. Due to their antioxidant properties, phenolic compounds are believed to potentially play a role in protecting the body against oxidative stress and its effects. Free and bound phenolic compounds in grains may directly mitigate oxidative stress by increasing plasma total antioxidant capacity or do so indirectly through cell signaling. It is suggested that phenolic compounds can modulate the GSH radical scavenging system to improve plasma total antioxidant capacity. In this radical scavenging system, GSH peroxidase is used to metabolize hydrogen peroxide to water by using reduced GSH as a hydrogen donor. The ability of reduced GSH to scavenge free radicals can be compromised if oxidized GSH is not converted back to GSH by GSH reductase or if the activity of GSH peroxidase is reduced. Some in vitro evidence suggests that flavonoids can alter the expression of genes responsible for the synthesis and regulation of GSH. Furthermore, it is reported that flavonoids can increase plasma total antioxidant capacity by increasing plasma uric acid levels, which has reducing and free radical scavenging activities.

Alkyresorcinols Alkyresorcinols are found in higher concentration in rye (320 mg/100 g) compared to wheat (12–129 mg/100 g) (Table 1). The phenolic lipids consist of a phenolic ring with two hydroxyl groups and long (typically C15–C25) nonisoprenoid side chain attached at the C5 position. The major alkylresorcinols include 5-heneicosylresorcinol, 5-heneicosenylresorcinol, 5-nonadecylresorcinol, and 5-heptadecylresorcinol in rye and wheat products. About 60–79% of alkylresorcinols are absorbed in the small intestine of pigs following the consumption of whole-grain rye bread. The 1,3-dihydroxybenzene derivatives are absorbed (45–71%) within the small intestine of ileostomates following the consumption of baked rye products. They are considered potential biomarkers of whole-grain rye and wheat intake for epidemiological research and observational studies. Although they are known to exert antioxidant effects through the modulation of lipid oxidation, their biological activity is multifactorial.

BIOACTIVES AND TOXINS | Bioactives: Antioxidants Carotenoids Carotenoids found in grains include beta-carotene, betacryptoxanthin, lutein, and zeaxanthin. Table 1 shows the total carotenoid, beta-carotene, lutein, zeaxanthin, and betacryptoxanthin content of whole-grain wheat and wheat bran. Only beta-carotene content of wheat germ is included. Although the composition of carotenoids is similar among cereals (wheat, oat, corn, and barley), concentrations vary significantly. Total carotenoid content ranges are 0.88–2.27 and 14.17–31.35 mg kg1, respectively, in corn and non-corn (wheat, oat, and barley) cereal endosperm fractions. The aleurone layer, which botanically is the outer part of the endosperm, has zeaxanthin contents two- to fivefold higher than lutein. Lutein and zeaxanthin contents are higher in the germ of non-corn cereals than in corn germ. The germ is the most concentrated source of carotenoids in cereals. There is a high correlation between %DPPH free radical scavenging and total lutein and zeaxanthin content. Beta-carotene, betacryptoxanthin, lutein, and zeaxanthin exert antioxidant effects. Lutein and zeaxanthin quench singlet oxygen, neutralize photosensitizers, and inhibit lipid peroxidation.

effects have other physiological functions. Unraveling the cumulative mechanisms involved beyond antioxidant effects will provide strong evidence for consumption of whole grains concentrated in bioactives.


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Tocopherols and Tocotrienols

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Policosanols Policosanols are present at low levels in the germ of wheat (1.01 mg/100 g), while wheat bran (0.11–3.00 mg/100 g) and whole-grain wheat (0.30–5.62 mg/100 g) contain lower levels (Table 1). They exert antioxidant effects through the reduction of low-density lipoprotein and membrane lipid peroxidation.

Melatonin Melatonin constitutes 0.2–0.4 mg/100 g of whole-grain wheat. There is no data on melatonin absorption in humans following the consumption of whole-grain wheat. Melatonin exerts its antioxidant effects through several mechanisms. It increases gene expression for antioxidant enzymes. It is reported to protect against lenticular protein oxidation enzymes. Melatonin is considered the most potent physiological scavenger of hydroxyl radical (OH ). l

What are the major grain bioactives? Explain briefly how bioactives can be altered through grain processing. What is meant by the term ‘oxidative stress’ and what is its significance in relation to chronic diseases of lifestyle? Which phenolic acid is predominant in grains? How are phenolic compounds purported to protect the body against oxidative stress and its effects? Briefly explain how minerals in grains serve as antioxidants. What are the major carotenoids in grains?


• Tocopherols and tocotrienols (vitamin E vitamers) are lipidsoluble micronutrients found in grains. Table 1 shows the content of total tocols, tocopherols, and tocotrienols in wheat. Through the exertion of their strong intracellular antioxidant effects, tocols protect against oxidative damage of polyunsaturated fatty acids within cell membranes and in lipoproteins, DNA nucleotidic bases, and proteins. The tocotrienols are considered stronger antioxidants than tocopherols.

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The content of major phytochemicals such as phenolic acids and flavonoids may be high in grains; however, these antioxidants are tightly bound to the cell wall matrix. Explore the extent of their bioavailability taking into consideration those studies that have shown harmful effects on human health of some antioxidants under certain conditions. Several approaches are used to assess antioxidant capacity of bioactive components in grains. Discuss the limitations of chemical- and cellular-based models in establishing the optimum doses to be taken daily to achieve beneficial effects on human health. There is a need for ex vivo and in vivo studies to confirm the efficacy and site of action of grain bioactives in animals including humans. Investigate a selected bioactive in depth, and propose what further detailed studies would be required to achieve a fuller understanding of its action. Synergistic mechanisms and modes of action among bioactives and with other grain components in whole-grain products are little understood. Moreover, bioactives may exert their effects through mechanisms other than antioxidant action. Can you suggest general approaches to identify suitable biomarkers to conduct such mechanistic studies in a holistic manner?

See also: Bioactives and Toxins: Bioactive Compounds in Wheat Bran; Food Grains and the Consumer: Grains and Health; Food Grains and Well-being: Functional Foods: Dietary Fibers, Prebiotics, Probiotics, and Synbiotics; Functional Foods: Overview; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.

Future Prospects The antioxidant effects of bioactive compounds from whole grains are potentially beneficial in delaying or preventing the development of diseases in relation to increased oxidative stress. However, the same compounds that exert antioxidant

Further Reading Adom KK, Sorrells ME, and Liu RH (2005) Phytochemicals and antioxidant activity of milled fractions of different wheat varieties. Journal of Agricultural and Food Chemistry 53: 663–671.

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Aruoma OI (1998) Free radicals, oxidative stress, and antioxidants in human health and disease. Journal of the American Oil Chemists’ Society 75: 199–212. Belodrajdic DP and Bird AR (2013) The potential role of phytochemicals in wholegrain cereals for the prevention of type-2 diabetes. Nutrition Journal 12: 62. Fardet A (2010) New hypothesis for the health-protective mechanisms of whole-grain cereals: What is beyond fibre? Nutrition Research Reviews 23: 65–134. Grassi D, Desideri G, and Ferri C (2010) Flavonoids: Antioxidants against atherosclerosis. Nutrients 2: 889–902. Li W and Beta T (2013) Food sources of phenolics compounds. In: Ramawat KG and Merillon JM (eds.) Natural Products: Phytochemistry, Botany and Metabolism of Alkaloids, Phenolics and Terpenes, pp. 2527–2558. Berlin, Heidelberg: Springer-Verlag. Ndolo VU and Beta T (2013) Distribution of carotenoids in endosperm, germ, and aleurone fractions of cereal grain kernels. Food Chemistry 139: 663–671.

Ndolo VU and Beta T (2014) Comparative studies on composition and distribution of phenolic acids in cereal grain botanical fractions. Cereal Chemistry 91: 522–530. Neveu V, Perez-Jimeńez J, Vos F, et al. (2010) Phenol-Explorer: An online comprehensive database on polyphenol contents in foods. Database. doi:10.1093/ database/bap024. Version 1.5.2. http://www.phenol-explorer.eu. Okarter N and Liu RH (2010) Health benefits of whole grain phytochemicals. Critical Reviews in Food Science and Nutrition 50: 193–208. Pe´rez-Jimeńez J, Neveu V, Vos F, and Scalbert A (2010) Systematic analysis of the content of 502 polyphenols in 452 foods and beverages: An application of the Phenol-Explorer database. Journal of Agricultural and Food Chemistry 58: 4959–4969. Ryan D, Kendall M, and Robards K (2007) Bioactivity of oats as it relates to cardiovascular disease. Nutrition Research Reviews 20: 147–162.

The Antinutritional Components of Grains CK Madsen and H Brinch-Pedersen, Aarhus University, Slagelse, Denmark ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Antinutritional compounds interfere with the utilization of nutrients and energy. The major antinutritionals of grains are phytate, proteinaceous inhibitors of digestive enzymes, tannins, and nonstarch polysaccharides. Antinutritionals may also offer nutritional benefits that have to be balanced against their negative effects. The significance of antinutritionals depends on species and nutritional status of the human or animal consuming it.

Learning Objectives

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To achieve an understanding of the chemistry, occurrence, and antinutritional mechanism of the major antinutritional compounds in grains. To gain an overview of strategies to counter antinutritionals.

Introduction Antinutritionals are compounds that reduce the bioavailability of essential nutrients or energy in the diet. This leads to discrepancies between the formal and actual nutritional values of a food or feed. It is therefore most important that both nutrients and antinutritionals are part of the equation when the nutritional value of a food item is evaluated. Moreover, it is important to notice that some antinutritionals may also possess positive dietary properties and that nutritional goals in human and animal nutrition can be very different, that is, with respect to weight gain. Antinutritionals that are deleterious for the calorie yield of a diet may be used to counter obesity in a human diet, whereas they result in poor resource use efficiency in animal husbandry. The use of the term antinutritionals is inconsistent in the scientific literature and may sometimes refer to compounds that are considered overall unhealthy (i.e., allergens, irritants, and toxins). Such compounds are beyond the scope of this article.

Phytate Phytic acid or myo-inositol-(1,2,3,4,5,6)hexakisphosphate (IP6) is the major phosphorus (P) storage compound in plants. IP6 is hexaphosphorylated myo-inositol. At physiological pH, it adopts a conformation with two phosphates in the axial position and the remaining five phosphates in the equatorial position. IP6 interacts with a range of cations through the


negatively charged phosphate groups (Figure 1). The strength of the interactions depends on the charge of the cations (Me3þ > Me2þ > Meþ) and to a lesser extent other parameters such as ionic radius. At acidic pH, the metal cations compete with Hþ and interactions with most metal cations are insignificant below pH 5. In grains, IP6 typically accounts for 2/3 of the total P content (see Table 1 for exact values). This IP6 is found as an insoluble mixed salt with cations called phytin. In many grains including cereals and legumes, phytin forms spherical inclusions called globoids inside protein storage vacuoles. Not only are the globoids the principal site of P, K, and Mg in the mature cereal grain, but also they contain Ca, Fe, Zn, Cu, Mn, and Na. Globoids are predominantly found in the aleurone layer of small grain cereals and in the embryo of maize, tissues that are the main contributors to millers’ bran fraction. Accordingly, the IP6 contents in bran and white flour are higher and lower, respectively, than those in whole grain. IP6 is resistant to most phosphatases, whereas the lower inositol phosphates are substrates of a wider range of phosphatases. Phosphatases that can initiate dephosphorylation of IP6 are known as phytases. All plants express phytases to assist in their IP6 metabolism but the phytase activity in mature seed varies several orders of magnitude, even in closely related species. This is in sharp contrast to the modest variation in total and proportional content of IP6 (Table 1). The Triticeae tribe of cereals (such as wheat, barley, rye, and triticale) stand out with exceptionally high mature grain phytase activity. This is caused by the relatively recent duplication of a purple acid phosphatase phytase gene whose archaic function was to be expressed during germination. Following the gene duplication, one copy has changed expression pattern so it is expressed during grain filling. The reported intake of IP6 for adults ranges from 180 to 5577 mg day1. Omnivorous Westerners are in the low range of the interval (usually less than 1000 mg day1). Vegetarians and people in developing countries are in the high range (>1000 mg day1). The highest value (5577 mg day1) has been reported for a group of Trappist monks on a lacto-ovo vegetarian diet. The utilization of IP6 by humans and most nonruminants is negligible unless the meal has sufficient phytase activity. Fast-growing animals on a high phytate containing feed without P supplements may suffer from P deficiency. The low retention of IP6 affects not only the molecule per se but also its chelation partners. Because of the chemical properties discussed earlier in the text, IP6 will release chelated metals in the low pH of the stomach but recruit ions again from the food matrix as pH reaches neutral during the duodenal passage. Therefore, IP6 from one source exerts an antinutritional effect on the entire meal. In vivo, this has been shown to affect zinc, iron, calcium, magnesium, copper, and manganese bioavailability. Zinc/IP6 represents perhaps the simplest system as zinc absorption can be predicted to a large extent by zinc and IP6 intake alone (Figure 2).

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Iron is a complex system, where heme iron and ferritin iron are unaffected by phytate and ferrous and ferric ions have different affinities for IP6. Ascorbate has been shown to counter the negative effect of IP6 on iron absorption. Apparently, this is achieved by reducing the iron into its ferrous state and by forming a bioavailable complex with it. Thus, the significance of IP6 on iron bioavailability is highly dependent on the source of iron (meat vs. vegetable) and other components of the food matrix such as ascorbate. The most severe impact of IP6 on iron absorption occurs with an overreliance on grain staples as seen in the developing world. At least six different strategies have been developed to deal with phytate in animal feed:

Fe3+ HPO4HPO4-

HPO4HPO4HPO4-

HPO4-

Zn2+ Figure 1 Phytic acid in the conformation and degree of protonation found at physiological pH. Examples of how a zinc and a ferric ion may be chelated are also sketched. Table 1

Wheatb Wheatc Wheatd Barleyb Barleyc Barleyd Ryeb Ryec Ryed Triticaleb Triticalec Oatsb Oatsc Oatsd Maizeb Maized Ricee Soybeand Peasb Field beansc Lupinc

1. Incubation with water to initiate germination and thereby activate endogenous phytases (steeping and malting) 2. Supplementation with exogenous phytase, that is, industrially produced microbial phytases 3. Development of low phytate cultivars by mutational breeding 4. Genetic modification of crop plants to produce high phytase levels in the grain 5. Breeding for the highest phytase activity in Triticeae cereals supported by the recent discovery of the responsible genes 6. Genetic modification of farm animals to secrete phytase in their digestive tract The first strategy has been used in traditional agricultural systems but is currently less used because of hygienic and technical challenges. Option two, on the other hand, has been widely used since the 1990s when technical enzymes became affordable. Further motivation to use this strategy happened in the beginning of the new millennium where meat and bone meal as a cheap feed additive for monogastrics was banned in Europe as a control measure for bovine spongiform encephalitis. Strategies three and four have been demonstrated in a series of major grains. The phytase expressing pig has only been generated for experimental purposes and cereal breeding for high phytase activity has only been practical for a few years. The three strategies for plant improvement could also benefit human nutrition; however, for strategies four and five, the potential inactivation of the phytases during cooking should be taken into account. Heat-stable phytases have successfully been introduced in crop plants by genetic transformation, whereas the Triticeae phytases are heat-labile. Nevertheless, Triticeae phytases are active during the leavening of bread where they can greatly reduce the IP6 content under favorable

Total P, IP6-bound P, proportion of IP6-bound P, and phytase activity in some grains n

Total P (% of dry matter)

Total IP6 P (% of dry matter)

Percent IP6 out of total P

Phytase activity (FTU/kg)a

13 18 30 9 15 21 2 13 6 6 12 6 6 9 11 7 1 4 11 11 14

0.33 0.02 0.40 0.04 0.29 0.03 0.37 0.02 0.42 0.4 0.31 0.03 0.36 (0.35–0.36) 0.36 0.02 0.34 0.03 0.37 0.02 0.40 0.03 0.36 0.03 0.37 0.01 0.29 0.02 0.28 0.03 0.32 0.01

0.22 0.02 0.29 0.04 0.23 0.03 0.22 0.01 0.26 0.03 0.19 0.02 0.22 (0.20–0.23) 0.24 0.2 0.20 0.01 0.25 0.02 0.28 0.03 0.21 0.04 0.25 0.02 0.17 0.03 0.19 0.03 0.18 0.01

67 4.8 73 8.1 79 0.07 60 2.4 63 3.5 61 0.04 61 (56–66) 67 5.0 59 0.02 67 3.7 70 5.4 59 11 67 5.4 59 0.07 68 5.9 78 0.01

0.73 0.01 0.38 0.02 0.57 0.09 0.57 0.15

0.33 0.01 0.17 0.03 0.39 0.08 0.35 0.09

45 0.01 45 6.2 70 5.2 63 3.7

1193 223 2886 645 1637 275 582 178 2323 648 1016 330 5130 (4132–6127) 6016 1578 5147 649 1688 227 2799 501 42 50 496 35 84 39 15 18 70 7 72 32 2.5 116 54 290 78 324 59

The number of samples is n and denotes the standard deviation. The range is given if n 2. Variations are caused by the use of different cultivars and methods by the investigators. a One FTU is the amount of enzyme that liberates 1 mmol of inorganic phosphorus per minute from sodium phytate at pH 5.5 and 37 C. Values from bEeckhout and De Paepe (1994), cSteiner et al. (2007), dViveros et al. (2000), eLucca et al. (2001).

5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

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5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 −1 ) 1000 2000 day g (m 3000 ate 4000 hyt p y tar Die Absorbed zinc (mg day−1)

Absorbed zinc (mg day−1)


16

14

12 10 8 6 Dietary zinc (mg da

4 y−1)

2

0

Figure 2 Three-dimensional graph of the trivariate model for zinc absorption proposed by Hambidge et al. Amounts are given as milligrams per day (mg day1). Actual data points from various sources are shown as points and the stems show their deviation from the model. Reproduced from Hambidge KM, Miller LV, Westcott JE, and Krebs NF (2008) Dietary reference intakes for zinc may require adjustment for phytate intake based upon model predictions. Journal of Nutrition 138: 2363–2366.

conditions. The IP6 hydrolysis is favored by high phytase activity in the flour, pH 4.5–6, temperatures of 35–55 C, and long incubation times. For the reasons discussed earlier, it is also possible to remove most IP6 from flour by removing the bran fraction during milling. Unfortunately, bran also contains most of the micronutrients and dietary fibers of the grain, so this method comes at a nutritional cost. Other food processing options mainly for legumes are germination and fermentation whereby endogenous or microbial phytases reduce the phytate content.

Proteinaceous Digestive Enzyme Inhibitors Grains contain a wide array of proteinaceous inhibitors of hydrolytic enzymes. These include amylase inhibitors, protease inhibitors, and xylanase inhibitors. In general, the inhibitors can be seen as defense compounds that have evolved to protect the storage compounds from being utilized by external pests. Many inhibitors are specific for microbial enzymes. However, others (trypsin and chymotrypsin inhibitors and certain aamylase inhibitors) affect human and animal digestive enzymes.

Protease Inhibitors Protease inhibitors are major antinutritional factors for the digestibility of protein. Most legumes possess high levels of trypsin and chymotrypsin inhibitors. In soybean, approximately 6% of the total seed protein content is constituted by these inhibitors, which can be grouped into either the Bowman–Birk or the Kunitz families. The Bowman–Birk inhibitors are single-chain polypeptides of approximately 8 kDa with seven disulfide bridges. They have two active domains for the inhibition of trypsin and/or chymotrypsin. Bowman–Birk inhibitors were first isolated from soybean but they are major inhibitors in most legumes, and related proteins (with different activities) are also found in cereals. The Kunitz family consist of larger, 20 kDa, single-chain polypeptides with

only two disulfide bridges. They bind trypsin in a 1:1 complex. Also, the Kunitz inhibitors were first isolated from soybean where they contribute significantly to the trypsin inhibitory potential. They are also present in other legumes, for example, pea and chickpea, but at lower levels than soybean. Low Kunitz inhibitor soybeans have been bred and shown to be advantageous in feeding experiments with pigs and chicks. In ileal-cannulated pigs, the low Kunitz inhibitor soybeans resulted in higher apparent amino acid digestibility. However, growth depression is also observed when trypsin inhibitors are present in diets consisting of only free amino acids. This is believed to be caused by increased secretion of digestive enzymes and the associated metabolic burden and loss of sulfur-containing amino acids. A study with soybean trypsin inhibitors in pig diets concluded that the nitrogen balance was affected more by the loss of endogenous amino acids than by impaired absorption of dietary amino acids. In humans, soybean Bowman–Birk inhibitors caused a two- to threefold stimulation of the production of trypsin, chymotrypsin, elastase, and amylase. This points to a negative feedback inhibition of pancreatic exocrine secretion. Long-term animal feeding studies have given conflicting results regarding the pancreatic pathology. Thus, pancreatic enlargement, lesions, neoplasia, and tumors have been observed in some species but not in others. The risk to humans remains unclear. Legumes are generally heat-treated before consumption to inactivate lectins and this can to some extent also inactivate protease inhibitors. However, the heat treatment must be mild, not to compromise the chemical integrity of the amino acids. Thus, in commercial soy meals, up to 20% of the inhibitors persist after the heat treatment. Alternatively, heat treatment with reagents that break disulfide bridges, for example, cysteine, can completely inactivate the inhibitors. Cereals possess a multigene family of trypsin/a-amylase inhibitors or CM proteins. The latter term refers to their presence in chloroform/methanol extracts of flour. As the first name suggests, the gene family includes inhibitors of trypsin and/or a-amylase. They contain 120–160 amino acid residues and five disulfide bridges. The trypsin/a-amylase inhibitors

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were first and most extensively studied in wheat and barley but they have also been found in maize and rice. Most of the research has focused on their role in plant defense and as allergens, and there is a paucity of studies on their importance as antinutritionals. Nevertheless, it is known that trypsin inhibitory activity persists in bread (in rye bread with up to 15% of the original activity). The antinutritional effects of these inhibitors must be assumed to have similar effects as the legume inhibitors.

Amylase Inhibitors Inhibitors of digestive a-amylases can potentially interfere with the utilization of the major energy source in many food and feed items, starch. Some members of the cereal trypsin/aamylase inhibitor family (discussed in the preceding section) are inhibitors of human and higher animal a-amylases. As for the trypsin inhibitors in the family, some a-amylase inhibitor activity persists after heating (e.g., in bread baking) but their nutritional significance has not been thoroughly investigated. Nevertheless, their effect seems to be minor given the high glycemic index of bread. Legumes including soy and the common bean (Phaseolus vulgaris L.) are more potent sources of aamylase inhibitors. The common bean contains three isoforms of amylase inhibitors, aAI1, aAI2, and aIL, of which the aAI1 isoform inhibits human a-amylase. The aAI1 isoform attracted attention in the 1980s as a counter-obesity supplement (‘starch blocker’) but was soon discredited because of disappointing clinical results. However, the quality of the inhibitor preparations used in the experiments was questioned and the aAI1 isoform attracted research attention again. Active aAI1 preparations reduce postprandial plasma glucose and insulin levels and increase breath hydrogen. This suggests that human a-amylase is indeed inhibited and that starch is fermented by the intestinal microflora instead. This should result in less metabolizable energy from the meal and ultimately weight loss. Some studies have found modest weight losses, whereas others have not. The aAI1 isoforms have also been expressed in transgenic peas as a measure to control the pea weevil. The inhibitor was effective at that but feeding experiments with pigs and broiler chickens demonstrated reduced ileal digestibility of starch and consequently low apparent metabolizable energy.

Tannins Tannins are plant compounds named after their use in tanning of leather. They are soluble phenolic compounds, with molecular weights between 500 and 3000 Da, interacting with proteins, in many cases precipitating them. This attribute is the key to the tanning process, the astringent taste of tannin-rich foods and some of their antinutritional characteristics. They are classified into hydrolyzable and nonhydrolyzable tannins, the latter also known as condensed tannins, flavolans, or proanthocyanidins. Hydrolyzable tannins are esters of phenolic acids and polyols such as glucose. They can be either gallotannins (if gallic acid is the phenolic) or ellagitannins (if the phenolic is derived from oxidation of galloyl residues). Hydrolyzable tannins have not been found in monocots and they are also absent from many legumes. Condensed tannins

are polymers of flavan-3-ols and/or flavan-3,4-diols. They yield anthocyanidins when heated in acidic solution, hence the name proanthocyanidins. Tannins have been associated with decreased weight gain in poultry, swine, mice, hamsters, and rats. This may be explained by their ability to inhibit salivary enzymes. However, other studies suggest that this inhibition is countered by the secretion or proline-rich proteins (PRPs). The metabolic burden of producing these proteins may be the direct reason for causing the reduced weight gain. In humans, the PRPs comprise about 70% of the saliva protein and their main function has been suggested to be detoxification of tannins by precipitation. Another protein–tannin interaction believed to be important is the formation of insoluble less digestible complexes with the dietary proteins themselves. The effect of tannins on ruminants is very different from that on monogastrics. The tannins inhibit the utilization of protein by microorganisms in the rumen, thus increasing the amount of protein and peptides that escape the rumen and reach the small intestine. Since the small intestine is the principal site of amino acid uptake, tannins result a net improvement of amino acid absorption contrary to the situation in monogastrics. Tannins are also good chelators of the ferric ion and to a lesser extent aluminum (III) and copper (II). This makes tannins an antinutritional factor for iron absorption under the same conditions as phytate, that is, when the diet contains little heme iron and ascorbate. The tannin content can be modified by plant breeding. For instance, tannin-free barley has been bred for malting purposes and the tannin content is significantly reduced in the majority of elite sorghum lines. Wheat has traditionally been grouped into white and red varieties. The pigments of red wheat are derived from tannins. Thus, white wheat cultivars lack the tannins. A similar but stronger variation exists in rice and various beans where some cultivars have colored pericarp because of tannin-derived pigments, whereas tannins are absent or very low in white-seeded cultivars (Figure 3).

Nonstarch Polysaccharides The group of nonstarch polysaccharides (NSPs) consists of cellulose, pectins, arabinoxylans (pentosans), heteroxylans, xyloglucan, inulin, fructooligosaccharides, and b-glucans. For a detailed discussion of the chemistry of NSPs, refer to Chapters 00090 and 00091. NSPs are found in varying amounts and compositions in grains where they act mainly as cell wall components. NSPs are not digested by the endogenous enzymes of monogastrics and proceed to the large intestine where they become substrates for the intestinal microflora. The NSPs constitute the major part of the dietary fiber. In the nutritional context, it is useful to distinguish between soluble and insoluble NSPs. They behave very differently in the digestive tract and the distinction reduces the chemical complexity of the discussion. In humans, NSPs are largely considered beneficial. This is not the case in animal science where growth depression and sticky droppings have long been associated with the use of barley and rye in poultry feed. The negative effects have been shown to originate from the higher content of the soluble NSPs b-glucan (barley) and arabinoxylans (rye) in these cereals compared to wheat (Table 2). Experiments with


-Proanthocyanidins

287

+ Proanthocyanidins

Rice

Beans

Figure 3 The dark red color of some rice and bean cultivars is an indicator of the proanthocyanidin content.

broilers fed with diets supplemented with varied amounts of arabinoxylans demonstrated a negative effect on the digestibility of starch, protein, and (most prominently) lipids. Growth depression is also observed in pigs but the effect is less severe and varies with the stage of growth. This difference may be explained by the pig’s larger capacity to ferment the soluble NSPs. The antinutritional effect of the soluble NSPs is believed to be caused by different concerted mechanisms. Soluble NSPs increase the viscosity of the feed matrix. This slows down the passage time in the digestive tract and may ultimately reduce feed intake. Furthermore, high viscosity reduces diffusion rates of macromolecules in the feed matrix, thus compromising the interaction of digestive enzymes with their substrates and the contact between nutrients and the mucosa. Another mechanism is the interaction of soluble NSPs with bile acids, lipids, and cholesterol that may compromise their action in lipid metabolism and their recirculation in the organism. Ultimately, this may modify the gut physiology by the enlargement of the digestive organs and increased secretion of digestive juices as observed in long-term feeding studies. The third mechanism is the modification of the gut microflora induced

through the availability of the NSPs as an energy source and their effect on gut passage time, which in turn affect oxygen tension and pH. The antinutritional effect of soluble NSP has prompted the widespread implementation of xylanases and b-glucanases as feed enzymes for poultry and pigs. The effects of insoluble NSPs are less severe and may be positive or negative depending on processing and context. As cell wall components, they may interfere with the accessibility of the digestive enzymes to the nutrients. This can to a large extent be overcome by feed processing. However, coarse insoluble NSP feed constituents, for example, oat hulls, can decrease the gut passage time, which at least to some extent is a positive effect.


• •

Define antinutritionals as opposed to toxins or food allergens. What are the major antinutritionals in grains?

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Table 2

Content in % of dry weight of the total and some major NSPs in various grains

Wheat Barley Rye Triticale Sorghum Maize Rice (pearled) Soybean Chickpeas Peas Navy bean Pinto bean Rapeseed Sunflower seeds Lupin seeds

Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble

Arabinoxylans

b-Glucans

Cellulose

Total NSP

1.8 6.3 0.8 7.1 3.4 5.5 1.3 9.5 0.1 2.0 0.1 5.1 – 0.2 No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data

0.4 0.4 3.6 0.7 0.9 1.1 0.2 1.5 0.1 0.1 – – 0.1 – No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data

– 2.0 – 3.9 – 1.5 – 2.5 – 2.2 – 2.0 – 0.3 – 4.4 No data No data No data No data No data No data No data No data No data No data – 8.7 – 1.2

2.4 9.0 4.5 12.2 4.6 8.6 1.7 14.6 0.2 4.6 0.1 8.0 0.3 0.5 2.7 16.5 3.3 7.4 2.5 32.2 5.7 1.7 6.3 13.1 11.3 34.8 4.5 23.1 4.6 32.0

The NSPs are divided into soluble and insoluble fractions. Values from Choct (1997).

• • • •

Which populations or groups of people are more likely to experience deficiencies where grain antinutritionals contribute? Explain for each of the major antinutritionals which nutrients they compromise. Outline the strategies to counter an antinutritional compound of your choice. Give an example of a compound (or group of compounds) that causes problems as an antinutritional in one context but offers health benefits in another context (explain).


•

• •

Endogenous phytase from wheat and its closest relatives (Triticeae) can significantly reduce phytate during food processing under conditions outlined in the preceding text. Which processes offer such conditions and which do not? Polishing and certain milling processes can greatly reduce the phytate content of rice and flours. How is this done and what are the disadvantages? Examine the chemical structure of nonstarch polysaccharides. Consider or discuss the differences between grains with respect to nonstarch polysaccharides.

• •

Compare the effect of b-glucans in humans and monogastric animals. Why are they more desirable in the human diet? Choose an antinutritional compound and explore the possibilities to reduce the content in grains by breeding or genetic modification.

See also: Carbohydrates: Cereals: Chemistry and Physicochemistry of Non-starchy Polysaccharides; Glycemic Index, Glycemic Load, and Their Health Benefits; Grains other than Cereals: Non-starch Polysaccharides; Health Effects of b-Glucans Found in Cereals; Food Grains and the Consumer: Grains and Health; Food Grains: Intolerance, Allergy and Diseases: Nutrition: Beriberi, A Deficiency Related to Grains.

Further Reading Barth CA, Lunding B, Schmitz M, and Hagemeister H (1993) Soybean trypsin inhibitor(s) reduce absorption of exogenous and increase loss of endogenous protein in miniature pigs. Journal of Nutrition 123: 2195–2200. Bethke PC, Swanson SJ, Hillmer S, and Jones RL (1998) From storage compartment to lytic organelle: The metamorphosis of the aleurone protein storage vacuole. Annals of Botany 82: 399–412. Boisen S and Djurtoft R (1981) Trypsin inhibitor from rye endosperm: Purification and properties. Cereal Chemistry 58: l94–l98.

BIOACTIVES AND TOXINS | The Antinutritional Components of Grains Brinch-Pedersen H, Sorensen LD, and Holm PB (2002) Engineering crop plants: Getting a handle on phosphate. Trends in Plant Science 7: 118–125. Brinch-Pedersen H, Madsen CK, Holme IB, and Dionisio G (2013) Increased understanding of the cereal phytase complement for better mineral bio-availability and resource management. Journal of Cereal Science 59: 373–381. Choct M (1997) Feed non-starch polysaccharides: Chemical structures and nutritional significance. Feed Milling International 191: 13–26. Dionisio G, Madsen CK, Holm PB, et al. (2011) Cloning and characterization of purple acid phosphatase phytases from wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), maize (Zea maize L.) and rice (Oryza sativa L.). Plant Physiology 156: 1087–1100. Eeckhout W and De Paepe M (1994) Total phosphorus, phytate-phosphorus and phytase activity in plant feedstuffs. Animal Feed Science and Technology 47: 19–29. Friedman M and Brandon DL (2001) Nutritional and health benefits of soy proteins. Journal of Agricultural and Food Chemistry 49: 1069–1086. Hambidge KM, Miller LV, Westcott JE, and Krebs NF (2008) Dietary reference intakes for zinc may require adjustment for phytate intake based upon model predictions. Journal of Nutrition 138: 2363–2366. Herkelman KL, Cromwell GL, Stahly TS, Pfeiffer TW, and Knabe DA (1992) Apparent digestibility of amino acids in raw and heated conventional and low-trypsininhibitor soybeans for pigs. Journal of Animal Science 70: 818–826. Jansman AJM (1993) Tannins in feedstuffs for simple-stomached animals. Nutrition Research Reviews 6: 209–236. Lajolo FM and Genovese MI (2002) Nutritional significance of lectins and enzyme inhibitors from legumes. Journal of Agricultural and Food Chemistry 50: 6592–6598. Li X, Higgins TJ, and Bryden WL (2006) Biological response of broiler chickens fed peas (Pisum sativum L.) expressing the bean (Phaseolus vulgaris L.) a-amylase inhibitor transgene. Journal of the Science of Food and Agriculture 86: 1900–1907.

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Lucca P, Hurrell R, and Potrykus I (2001) Genetic engineering approaches to improve the bioavailability and the level of iron in rice grains. Theoretical and Applied Genetics 102: 392–397. Madsen CK, Dionisio G, Holme IB, Holm PB, and Brinch-Pedersen H (2013) High mature grain phytase activity in the triticeae has evolved by duplication followed by neofunctionalization of the purple acid phosphatase phytase (PAPhy) gene. Journal of Experimental Botany 64: 3111–3123. Min BR, Barry TN, Attwood GT, and McNabb WC (2003) The effect of condensed tannins on the nutrition and health of ruminants fed fresh temperate forages: A review. Animal Feed Science and Technology 106: 3–19. Obiro WC, Zhang T, and Jiang B (2008) The nutraceutical role of the Phaseolus vulgaris a-amylase inhibitor. British Journal of Nutrition 100: 1–12. Schlemmer U, Frølich W, Prieto RM, and Grases F (2009) Phytate in foods and significance for humans: Food sources, intake, processing, bioavailability, protective role and analysis. Molecular Nutrition and Food Research 53: S330–S375. Siegenberg D, Baynes RD, Bothwell TH, et al. (1991) Ascorbic acid prevents the dosedependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption. American Journal of Clinical Nutrition 53: 537–541. Smits CH and Annison G (1996) Non-starch plant polysaccharides in broiler nutritiontowards a physiologically valid approach to their determination. World’s Poultry Science Journal 52: 203–222. Steiner T, Mosenthin R, Zimmermann B, Greiner R, and Roth S (2007) Distribution of phytase activity, total phosphorus and phytate phosphorus in legume seeds, cereals and cereal by-products as influenced by harvest year and cultivar. Animal Feed Science and Technology 133: 320–334. Viveros A, Centeno C, Brenes A, Canales R, and Lozano A (2000) Phytase and acid phosphatase activities in plant feedstuffs. Journal of Agricultural and Food Chemistry 48: 4009–4013.

Mycotoxins MT Fletcher and BJ Blaney, The University of Queensland, St Lucia, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

Mycotoxins are substances produced by fungi and that are poisonous to humans and other animals if consumed in sufficient quantities. Fungi can produce mycotoxins in grains if they parasitize the host plants during growth or else grow as saprophytes on grains during harvest and storage. Different mycotoxins can disrupt critical hormonal systems, damage organs, compromise the immune system, or cause cancer. Mycotoxin contamination can be managed by disseminating knowledge about mycotoxins, predicting and preventing contamination, detecting mycotoxins in grains, effective use of contaminated grain, and breeding crops for fungal resistance.

Learning Objective

•

To understand what mycotoxins are, the potential impacts on human health and on livestock, the causes of contamination of various crops, and how to minimize their impact on food safety/security.

Introduction Mycotoxins are substances produced by fungi that are poisonous or ‘toxic’ to mammals. The Greek prefix ‘myco’ alludes to fungus – hence, ‘mycotoxin.’ The term mycotoxin is usually restricted to secondary metabolites of those fungi (microfungi or molds) that are either parasites or saprophytes of our food plants or livestock forage, including members of the fungal genera Aspergillus, Penicillium, Fusarium, and Claviceps. Mycotoxins are classed as ‘secondary’ metabolites, because they are not considered essential for the ‘primary’ purpose of growth and reproduction in fungi. Nevertheless, secondary metabolites have important roles, such as helping the fungus to invade plant tissue and as defense against insect predators or competing fungi. Of a vast range of secondary metabolites produced by fungi, only some are regarded as mycotoxins, and these can affect an array of food and feed, especially cereals, forages, grain, fruits, and manufactured products. Mycotoxin contamination is of significant concern worldwide with a range of regulatory restrictions in place in different countries and consequently impacts on trade as well as human and animal health. In this article, we concentrate on the most important mycotoxins associated with food grains, the diseases they cause, and how to minimize their impact on health and food security. Of these grain crop mycotoxins, ergot alkaloids, aflatoxins, and trichothecenes have been clearly shown to cause diseases of epidemic proportion in both humans and livestock (Table 1). Some others including ochratoxins, fumonisins,

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zearalenone, and phomopsins certainly cause disease in livestock, but while these might have been associated with human diseases, conclusive scientific proof remains elusive. Other mycotoxins (cyclopiazonic acid, sterigmatocystin, mycotoxins of Alternaria alternata, and citrinin) that have been identified as occurring in food grains, but not proved to cause significant disease in either humans or livestock in natural circumstances, have not been included in this article.

Ergot Alkaloids The ergot fungi (Claviceps species) have been known to be toxic to humans for thousands of years, with early mentions including reference to ‘noxious pustule in the ear of grain’ on an Assyrian tablet from around 660 BC and regular epidemics in Europe through the Middle Ages and up until last century. Ergot fungi infect grain crops during flowering, when the pollen tube is open to receive pollen. If an ergot fungal spore enters the pollen tube, it will infect the ovary, and after a growth cycle characterized by release of copious quantities of sticky honeydew (modified plant sap), the fungus produces a hard body (sclerotium) where the seed would normally be. The shape of the fungal sclerotium growing on rye grain was perceived as similar to a rooster’s spur (or ‘argot’ in Old French), from which was derived the name ‘ergot.’ Ergots contain a range of toxic alkaloids (Table 1). Before the risk was understood and steps taken to recognize and remove ergots from grain, they were often milled into flour and baked into bread. The fungal genus Claviceps contains 36 different species, known to parasitize over 600 plants, including grains and forage grasses. The most important ergot parasites of cereal grains are C. purpurea, C. fusiformis, and C. africana (Table 1). Two types of ergotism from C. purpurea in humans have been described, ‘convulsive’ and ‘gangrenous,’ but are not well differentiated. Differences in signs and symptoms are probably due to variation in the alkaloid profile and dose consumed and individual susceptibility. Early symptoms are common to both types of ergotism and include slight giddiness, feeling of frontal pressure in the head, fatigue, depression, nausea, and pain in the limbs and lumbar region. A more severe symptom with larger doses is ‘formication’ or tingling of the skin – according to sufferers “as if ants were crawling over it.” Convulsions and seizures are common with large doses, and hallucinations are frequently reported, often involving demons or strange animals, and severe depression. The history of human ergotism makes fascinating reading. Around 20 000 people (half the population) of Aquitane in southern France were reported to have died from ergot poisoning in AD 944–945. Around 50 years later, 40 000 people were reported to have died from ‘holy fire.’ Another major outbreak occurred in 1089, and in 1093, a monastic order was founded to care for the victims of ergotism, with the patron saint St. Anthony of Egypt, who was venerated for his legendary


http://dx.doi.org/10.1016/B978-0-12-394437-5.00112-1

BIOACTIVES AND TOXINS | Mycotoxins Table 1

291

Important grain mycotoxins, most common fungal source, main grain affected, and some of the effects on humans and other animals

Mycotoxins

Fungal species

Grain

Effect on humans and livestock

Claviceps purpurea

Rye, barley, wheat, oats, and triticale

Impaired lactation, impaired heat regulation, gangrene of extremities in humans and livestock

Agroclavine Setoclavine Chanoclavine Elymoclavine

Claviceps fusiformis

Millet

Impaired lactation in pigs, gastroenteritis and convulsions in humans

Dihydroergosine Dihydroelymoclavine

Claviceps africana

Sorghum

Impaired lactation in pigs and cattle, impaired heat regulation and reduced growth in cattle

Aflatoxins Aflatoxin B1 Aflatoxin G1

Aspergillus flavus Aspergillus parasiticus

Maize, rice, peanuts, and oilseeds

Liver damage, human and livestock carcinogen. Impaired immunity, stunting

Ochratoxins Ochratoxin A Ochratoxin B

Aspergillus ochraceus Penicillium verrucosum

Barley, maize, and sorghum

Kidney damage in pigs, possible human carcinogen

Fusarium verticillioides Fusarium proliferatum

Maize

Liquefaction of brain in horses, fluid accumulation in lungs of pigs, possible human carcinogen

Fusarium equiseti Fusarium poae Fusarium sporotrichioides

Wheat, oats, and barley

Fusarium graminearum Fusarium culmorum Fusarium crookwellense

Maize, wheat, barley, and triticale

Fever; gastroenteritis; bleeding from the nose, throat, and gums; exhaustion of the bone marrow in humans and livestock Vomiting, feed refusal in pigs and other livestock; nausea, diarrhea in humans

Zearalenone

Fusarium graminearum Fusarium culmorum Fusarium equiseti

Maize, wheat, barley, and sorghum

False estrus in pigs, infertility in cattle and sheep

Phomopsin

Diaporthe toxica

Lupins

Liver disease in livestock

Ergot alkaloids Ergotamine Ergocryptine Ergocornine Ergocristine Ergovaline

Fumonisins Fumonisin B1 Fumonisin B2 Fumonisin B3 Trichothecenes T-2 toxin HT-2 toxin Scirpentriol Neosolaniol Deoxynivalenol Nivalenol

suffering and perceptions of being tormented by malevolent demons. Ergotism subsequently came to be called “St. Anthony’s Fire,” with notable outbreaks occurring over the centuries. In 1926–27, over 11 000 cases of ergotism were reported near the Ural Mountains in Russia. In 1951, convulsive ergotism from heavily contaminated flour occurred in a small French village (200 affected, 5 deaths). In Ethiopia, there was an outbreak of gangrenous ergotism in 1977–78 (93 cases, 47 deaths), and in 2001 (18 cases, 3 deaths), gangrenous ergotism resulted when barley crops were contaminated with ergotized wild oats. Ergot alkaloids have structures with some stereochemical similarities to the biogenic amines dopamine, serotonin, and noradrenaline (Figure 1) and interfere with the action of these neurotransmitters on receptors. This interference produces a cascade of physiological effects, including reduced peripheral blood circulation, reduced circulating prolactin concentration, and central nervous effects. Reduced blood supply to extremities produces two effects: firstly, coldness and anesthesia of

hands and feet, which can progress to gangrene and loss of the limb, and secondly, reduced heat loss via the skin and a rise in core body temperature. In addition, there is evidence of effects of ergot on the central nervous system, including tremors, excitability, hallucinations, and depression. It is not hard to imagine the human sufferer having delusions of being ‘consumed by flames’ or burning up with ‘holy fire.’ The effects on livestock are species-dependent. In cattle, reduced blood circulation to the skin and extremities leads to very high temperatures in warm conditions or gangrene of extremities in cold conditions (both associated with reduced feed intake and growth rates). Interference with dopamine receptors inhibits prolactin excretion and consequently milk production of sows, ewes, cows, and mares, with high mortality of dependent offspring. Poisoning of livestock by rye ergot (C. purpurea) is a sporadic problem in Europe, Canada, and other cooler regions of North America and occasionally also in Australia, New Zealand, and South Africa. This fungus can infect wheat,

292

BIOACTIVES AND TOXINS | Mycotoxins

H N

O

R¢

OH O N O

H

N

HN

H

N O

R

Ergotamine: R = Benzyl, R¢ = CH3 Ergocristine: R = Benzyl, R¢ = CH(CH3)2 Ergovaline: R = CH(CH3)2, R¢ = CH3 Ergocornine: R = CH(CH3)2, R¢ = CH(CH3)2 Ergocryptine: R = CH2CH(CH3)2, R¢ = CH(CH3)2

Figure 1 Rye ergot alkaloids of C. purpurea.

barley, and rye crops directly, but the source of contamination can also be from infection of annual ryegrass (Lolium rigidum), as in southern Australia. Livestock can be affected by grazing infected ryegrass directly or from eating grain containing sclerotia. Annual ryegrass can grow as a weed among cereal crops, and the ryegrass sclerotia can then be inadvertently harvested with the wheat or barley. Human ergotism is not limited to C. purpurea, with C. fusiformis growing on millet, poisoning 78 people in India in 1975, with gastrointestinal symptoms, convulsions, and other effects on the central nervous system. C. fusiformis produces clavine alkaloids (Figure 2) that are related but different from C. purpurea alkaloids so the symptoms are somewhat different. While the toxicity of rye ergot has been known for centuries, the toxicity of a closely related fungus, sorghum ergot (Claviceps africana) was only recognized in grain crops in Australia and America in the mid-1990s despite the fungus being widespread in Africa and Asia. Sorghum ergot infects only sorghum and related plants, like Johnson grass, but now occurs wherever sorghum is grown. The ergot sclerotium is of similar size to the sorghum grain itself but generally thinner, slightly pointed, and with a scaly, lustrous surface under magnification. Prevalence is dictated largely by weather conditions in that cold, wet weather around flowering time reduces pollen production and favors infection by ergot. Crops planted later at cooler parts of the year are more at risk. Sorghum ergot sclerotia contain alkaloids with a saturated piperidine ring, predominantly 9,10-dihydroergosine (Figure 3), which are dihydro derivatives of rye ergot alkaloids. These dihydro derivatives had in the past been considered far less toxic than the parent compounds and in some cases to counteract their effects. Indeed, dihydroergotamine is a human drug used to combat migraine headache. However, extensive studies with sorghum ergot demonstrated a similar effect in depressing prolactin (and consequently lactation of sows and cows) as rye ergot alkaloids. Consumption of infected sorghum also produces severe hyperthermia and reduced growth rates of cattle, especially in feedlot conditions, but the risk to humans is unknown. Once the risk is recognized, management of ergot contamination in wheat and barley is relatively easy in bulk grain, as the ergot sclerotia are darker and different in size and weight to grain and so can be removed using gravity grading equipment. It is more difficult in dark rye grain but achievable. Sorghum ergot can also be physically graded out of sorghum, albeit with less efficiency and some loss of the lighter grain fractions. All of these grading processes should be supported by assay of alkaloids in the cleaned grain, since grain dusts and fragments can still harbor contamination.

OH

R HO H

H N H HN Agroclavine, R = H Elymoclavine, R = OH

N H HN Setoclavine

H N H

HN Chanoclavine

Figure 2 Clavine alkaloids of C. fusiformis.

Aflatoxins Aflatoxins are highly oxygenated heterocyclic compounds characterized by dihydrodifurano moieties fused to a substituted coumarin (Figure 4). These toxins are produced mainly by Aspergillus flavus and A. parasiticus, greenish or gray molds that thrive in warm (15–40 C), moist conditions, such as grain and oilseeds stored without sufficient drying. These fungi are regarded as saprophytes or weak pathogens, attacking summer crops like maize and peanuts under growing stress from heat, insufficient moisture, and/or insect invasion. A. flavus produces mainly aflatoxins B1 and B2, while A. parasiticus produces aflatoxins B1, B2, G1, and G2. Aflatoxins were first identified in the mid-1960s in Britain, as the cause of serious epidemics in housed poultry (Turkey X disease) associated with imported peanut (groundnut) meal in the diet. In humans and livestock, aflatoxins primarily attack the liver. Ducklings, turkeys, young pigs, and dogs are very susceptible; older pigs, cattle, sheep, and horses are intermediate; and chickens are relatively resistant. In livestock, aflatoxins cause reduced production, poor feed conversion and growth, and impaired immunity to infectious diseases. Aflatoxin B1 is one of the most potent liver carcinogens known and has been associated as a cocarcinogen with hepatitis B in the high incidence of human liver cancer in parts of Africa and Southern Asia. Aflatoxins can also cause acute poisoning, such as that occurred in Kenya in April 2004 when consumption of aflatoxin-contaminated maize affected 317 people, with 125 deaths, and in India in 1974 when similar maize contamination resulted in 397 recognized cases and 106 deaths. Although aflatoxins can contaminate just about any commodity, they are most prevalent in peanuts (groundnuts) and maize.


293

OH H N

O

O H

N

OH O

O

H

H

H N H

N H NH

N H NH

NH 9,10-Dihydroergosine

8a,9-Dihydroelymoclavine

Festuclavine

Figure 3 Dihydro alkaloids of sorghum ergot (Claviceps africana).

O H O H O

O

O

O

H

OMe

Aflatoxin B1

O H O

O

O

O

H

OMe

O H O

O

O

O

OMe

Aflatoxin G1

Aflatoxin B2

O

O H O H O

O

O

OMe

Aflatoxin G2

Figure 4 Aflatoxins B1 and G1 together with their dihydro analogs B2 and G2.

Aflatoxin was first detected in the 1960s in peanut meal from South America and Africa but has since been found to be a problem everywhere peanuts are grown. A. flavus and A. parasiticus invasion of the developing peanut kernel occurs with premature drying of the developing kernel under drought conditions, insect damage (boring into the pod), and delays in drying the mature nuts to safe storage moisture levels. In more developed countries such as Australia and North America where the industry is coordinated, systems of aflatoxin assay, segregation, and grading have been implemented to control aflatoxin levels in finished peanut product. Irrigation, droughtresistant peanut varieties, and biocontrol using competition with nonaflatoxigenic species of A. flavus are also available, but all of these processes are costly. In less-developed countries, where peanut growing is often at village levels, aflatoxin is very difficult to manage. Maize is highly susceptible to aflatoxin and suffers from extensive contamination in hotter regions of Southeast Asia, Africa, and parts of Australia and the United States. Factors affecting contamination include insect damage and microcracks in the kernels from high temperature and inadequate moisture allowing fungal entry to the developing kernel. Delays in drying the mature kernels to moisture levels inhibit fungal growth and then allow the fungi to produce aflatoxins. Climate plays a large part in contamination – crops planted at a time when very high temperatures affect the developing seeds will be more susceptible to invasion by Aspergillus, while timing of rainfall or inadequate irrigation and soil depths are also contributing factors. Predictive models linking contamination to climate, combined with regular aflatoxin testing, are necessary to manage aflatoxins in maize. Extensive literature on aflatoxins in maize/corn is available, including the USDA Aflatoxin Handbook (http://www.gipsa.usda.gov) and through the Maize Association of Australia website (http:// www.maizeaustralia.com.au/mycotoxin.html). Rice has been shown to be commonly contaminated with aflatoxin in India and Southeast Asia. The causes have been less

investigated, but storage at high temperatures and humidity is clearly implicated. Sorghum also is susceptible to contamination, but infected, lightweight grain tends to be removed during harvest, and significant contamination is usually only associated with storage without adequate drying. Summergrown oilseeds like sunflower and safflower are also susceptible, but as aflatoxins are not soluble in oil, the contamination remains in the oilseed cake or meal remaining after oil extraction (also applies to peanut meal and to gluten extracted from maize). The human health risks then depend on whether the aflatoxin-contaminated meals are used for human food or for livestock feeds. Practically, any commodity can develop high aflatoxin concentrations during storage at high moisture contents, but summer crops (particularly peanuts, maize, rice, sorghum, some oilseeds, coconut, and tree nuts) are far more susceptible than winter crops, barley and wheat, since aflatoxin-producing fungi do not compete with other fungi in cooler, wetter conditions.

Ochratoxins In cooler climates (e.g., northern Europe and Canada), the major producer of ochratoxins is Penicillium verrucosum, which has a growth range of 0–31 C, optimally 20 C. This can cause serious contamination of barley and other stored grains and kidney damage in pigs fed with such grain. In a warm and moist environment (e.g., Southeast Asia, northern Australia, and southern United States), ochratoxins are produced by Aspergillus ochraceus – a mold found in a variety of commodities, including maize and sorghum. A. ochraceus has a growth range of 8–37 C, with an optimum for ochratoxin production of 30 C and 30–40% moisture. Consequently, most contamination occurs during storage. A. ochraceus can co-occur with aflatoxin-producing fungi in such grains, but usually at lower frequency, and its significance tends to be overshadowed by aflatoxin.

294


Ochratoxin A is a substituted coumarin derivative with an acidic carboxyl group (Figure 5). Ochratoxin B usually occurs in conjunction with ochratoxin A but at lower concentrations, and ochratoxin B is much less toxic to laboratory animals. Ochratoxin A is known to cause severe kidney damage in pigs (porcine nephropathy) and other animals, immunosupression, and can induce kidney tumors in laboratory rats at high dosages. Early studies in the 1980s suggested a link between ochratoxin A and Balkan endemic nephropathy – clusters of endemic human kidney diseases and rare tumors in regions along the tributaries of the Danube and Sava rivers in the Balkan Peninsula – but this link has not been compellingly established. Evidence from animal models in 1993 was sufficient for the International Agency for Research on Cancer to classify ochratoxin as a possible human carcinogen and to justify monitoring and surveillance to limit consumption. Apart from cereal grains, ochratoxin A also occurs in the kidney, liver, and blood from farm animals ingesting ochratoxin-contaminated feed, and so it can be detected in small goods made from those tissues (e.g., liverwurst and bloodwurst). Management of ochratoxin in cereals follows similar principles to managing aflatoxins – awareness, predicting and preventing contamination, early detection, and distribution of contaminated material away from human food toward livestock feed, and further processing.

Fumonisins Fumonisins are produced by Fusarium verticillioides and F. proliferatum, the most common fungi associated with maize. These fungi are present in maize with no visible damage and do not reduce grain yield in normal circumstances (compared with other diseases of maize). Consequently, they were not targeted for eradication in early maize breeding programs, and as the fungi are transmitted in seed, they are widespread wherever high-yielding maize hybrids are grown. However, if the maize becomes stressed, for example, through irregular water availability, microcracks can appear in some kernels, O

OH O

OH O O

N H Ochratoxin A, R = CI Ochratoxin B, R = H

facilitating mold growth leading to kernel rot. Excessive moisture during grain maturation will then favor accumulation of fumonisins in the infected kernels. Ingestion of ear-rotted maize has been known for some time to be the cause of equine leukoencephalomalacia (ELEM – liquefaction of the brain in horses, mules, and donkeys). First reported as moldy corn toxicosis in the United States in 1891, this disease was subsequently reported in Argentina (1945), China (1957), Egypt (1968), South Africa (1970), and Australia (1993) in horses fed with large amounts of maize. Following an outbreak of ELEM in South Africa in 1970, studies were undertaken to assess the toxicity of fungi associated with the maize and possible links to a high incidence of human esophageal cancer in the Transkei region. Maize is a dietary staple in this region, being consumed in various forms, from ground-meal porridge to maize beer. F. verticilliodes was the dominant fungus in the maize and was shown in animal trials to cause ELEM and fluid accumulation in the lungs of pigs (porcine pulmonary edema or PPE). It also caused heart damage, liver damage, and liver cancer in rats. Several mycotoxins were identified in the fungus, including moniliformin and fumarins, but the main carcinogenic toxin remained elusive until the fumonisins were finally discovered in 1988. About 15 different fumonisins have since been reported, but fumonisins B1, B2, and B3 (Figure 6) are regarded as the most important. Fumonisin B1 induces apoptosis (programmed cell death) and is a liver and kidney toxin in all animal species tested, with horses, pigs, and rabbits being the most susceptible. Fumonisins have since been shown to cause both ELEM and PPE, with both diseases involving disturbed sphingolipid metabolism (which severely impacts on nerve cells) and cardiovascular dysfunction. Not surprisingly, given the widespread prevalence of the fungi, fumonisins have been detected in maize wherever advanced hybrids are grown, including North America, Africa, Australia, Southeast Asia, and Europe. There is as yet no direct scientific evidence that fumonisins cause adverse effects in humans, but fumonisin B1 is still regarded by scientific authorities as a possible human carcinogen, and Codex has set a limit of 2 mg kg1 fumonisins in maize for human consumption. Apart from detection and regulation, fumonisin management over the long term will require development of maize hybrids with increased resistance to the producing fungi.

Trichothecenes

CH3

R

Three broad groups of trichothecenes are recognized: type A (e.g., T-2 toxin, HT-2 toxin, neosolaniol, and scirpentriol), type

Figure 5 Ochratoxins A and B.

O

COOH COOH

O

R O O

COOH COOH

Figure 6 Major fumonisins in Fusarium verticillioides and F. proliferatum.

R¢

OH

NH2 Fumonisin B1: R = OH, R¢ = OH Fumonisin B2: R = H, R¢ = OH Fumonisin B3: R = OH, R¢ = H


H

H O

H R¢¢

H O

R

295

R¢¢

O R¢

R¢

Type A Trichothecene

Type B Trichothecene

T-2 toxin: R = OCOCH2CH(CH3)2 R¢ = OCOCH3 R¢¢ = OCOCH3 HT-2 toxin: R = OCOCH2CH(CH3)2 R¢ = OCOCH3 R¢¢ = OH Neosolaniol: R = OH R¢ = OCOCH3 R¢¢ = OCOCH3 Scirpenetriol: R = H R¢ = OH R¢¢ = OH

Deoxynivalenol: R¢ = OH R¢¢ = H Nivalenol: R¢ = OH R¢¢ = OH

Figure 7 Type A and type B trichothecenes present in grain crops.

B (e.g., nivalenol, deoxynivalenol, and their acetyl derivatives), and macrocyclic types. Both type A and type B trichothecenes (Figure 7) affect grain crops, but macrocyclic trichothecenes are mostly found on cellulose-rich substrates (straw, paper, etc.) rather than cereal grains. Type A trichothecenes are produced by several Fusarium species, including F. sporotrichioides and F. poae, primarily restricted to cereal grains grown in cold climates, and F. equiseti, which is more ubiquitous. Type B trichothecenes are most prevalent because the main source fungi, Fusarium graminearum, F. crookwellense, and F. culmorum, are common in wheat, maize, and rice grown in temperate climates. However, certain species are recorded as producing both types A and B trichothecenes. In Russia during 1942–48, over 100 000 people died from a mysterious epidemic, initially called ‘septic sore throat’ and subsequently alimentary toxic aleukia (ATA). Symptoms include fever; gastroenteritis; bleeding from the nose, throat, and gums; exhaustion of the bone marrow leading to pancytopenia (loss of all blood cells); and opportunistic bacterial infections. The disease mostly occurred in the Orenburg district near the Caspian Sea, where up to 60% of the population were affected in some localities and up to 10% died. The disease has since been shown to have occurred previously in Russia in 1932 and 1913. Eventually, it became clear that the cause was consumption of bread and other cereal products made from grain, which was left in the fields over winter, due to wartime labor shortages. However, it was not until the 1970s that it was shown that type A trichothecenes (T-2 toxin, HT-2 toxin, and neosolaniol) were produced by F. sporotrichioides and F. poae in the grain during cycles of freezing and thawing. ATA was probably produced by these trichothecenes, but definitive proof is lacking. ATA has not been seen since the late 1940s, probably due to improved grain handling and nutrition. F. sporotrichioides has also been implicated in several diseases of livestock, including scabby grain intoxication in Japan and moldy corn toxicosis in the United States. In the 1960s and 1970s in the state of Indiana in the United States, widespread ear rot in maize due to Gibberella zeae (F. graminearum) was associated with refusal of pigs to consume infected maize and vomiting in many that did. Both effects were later shown to be caused by deoxynivalenol (also called ‘vomitoxin’). In some cases, there were estrogenic effects in young pigs, later found to be associated with the fungal estrogen zearalenone, also produced by this fungus. The syndrome of feed refusal, vomiting, and pseudoestrogenism was also produced by F. graminearum-infected wheat – a condition known as head scab, head blight, or red mold. The disease in pigs

OH

O

HO Zearalenone

O

Figure 8 The fungal estrogen zearalenone.

has occurred in many other countries of the world – pigs are most susceptible, but other species can be affected at higher doses. In the late 1960s, several human cases were reported in Japan of disease associated with consumption of wheat and barley affected with akakabi-byo (red mold). The syndrome included nausea, mouth ulceration, vomiting, headache, gastroenteritis, diarrhea, and convulsions and had some similarity to ATA. Analysis of the grain consumed revealed F. graminearum and the mycotoxins nivalenol, acetylnivalenol, and diacetoxyscirpenol. These trichothecenes are more acutely toxic than deoxynivalenol and have less emetic action, but cause leukopenia (reduced white cell numbers), in common with type A trichothecenes. Two distinct ‘chemotypes’ of F. graminearum are now recognized as either deoxynivalenol producers or nivalenol producers. Both chemotypes co-occur in Japan and New Zealand, while deoxynivalenol producers are most common in Canada and the United States. In Australia, there is some regional separation with deoxynivalenol producers dominating in wheat, maize, and sorghum in more southern regions and nivalenol producers in maize in far northern Queensland. Both chemotypes also produce zearalenone. Management of trichothecenes should follow similar principles as with mycotoxins previously discussed, but breeding grain hybrids for resistance to F. graminearum and related fungi is of high priority.

Zearalenone F. graminearum, F. culmorum, and F. equiseti are the major source in grains of the fungal estrogen zearalenone, a substituted resorcyclic lactone (Figure 8). Zearalenone competitively binds to estrogen receptors and consequently causes a false estrus in pigs and infertility in sheep and cattle. Zearalenone can have a major effect on reproductive productivity of livestock, but there is doubt that it should be considered a serious mycotoxin. Minor mortalities in pigs associated with

296


• O

O

H N

NH

MeHN

•

O N

HO O CI

OH

H

N H

H N

COOH COOH

Phomopsin

Effective use of infected grain by feeding to resistant livestock Improving resistance of plants to mycotoxigenic fungi

With appropriate amendment, this is a useful model for management of other food safety and trade-related problems associated with mycotoxins.


Figure 9 Phomopsin produced by Diaporthe toxica in lupins.

zearalenone tend to be due to secondary factors such as infection of vulval or rectal prolapses or to other trichothecenes cooccurring in the feed.

• • •

Phomopsins Phomopsins are very potent cytotoxic and antimitotic substances that primarily target the liver. They are produced by the fungus Diaporthe toxica, which infects and colonizes most parts of the lupin plant. Phomopsin contamination occurs across southern Australia where over a million hectares of lupins (Lupinus angustifolius) can be planted annually. Livestock consuming infected lupins can contract lupinosis, an often fatal liver disease. Lupinosis can occur when the stubbles of lupin crops or screenings from harvested lupins are fed to cattle and sheep. The release of Phomopsis-resistant lupins in 1989 has greatly reduced its incidence, but it remains a serious problem. Phomopsin A is regulated in Australia to 0.005 mg kg1 in lupins for human consumption (Figure 9).

•


•

•

Future Developments The mycotoxins described in the preceding text include all those occurring in food grains that have had the most serious impact on human health or livestock production. There are hundred more mycotoxins, which have been identified in the laboratory, but the significance of which remains unknown. Further investigation may well show that they have widespread but subtle impact on important disease syndromes. Increasing interest also focuses on the so-called masked mycotoxins where mycotoxins such as deoxynivalenol are present in a bound form that can be released during digestion but may escape detection in grain unless specific detection methods are used. Climatic changes from global warming, and continually changing cropping systems, affect the crop–fungus interaction and can increase mycotoxin contamination from season to season. Managing this problem requires a coordinated effort from all participants in our food production systems. A strategic management plan was used in Australia to successfully deal with a serious incursion of sorghum ergot into the country and also to manage mycotoxin contamination of the national maize crop. The plan has the following five main elements:

• • •

Communication and coordination at a national level Prediction, prevention, and management of disease outbreaks in crops Detection and rapid assessment of mycotoxin contamination

What is meant by the term ‘mycotoxin’? Name several mycotoxic fungi, and discuss their different characteristics and occurrence in food grains. Which group of mycotoxins are formally classed as human carcinogens? What food crops are most susceptible to contamination? Under what conditions is contamination most likely to occur? What mycotoxins produce a disease once called St. Anthony’s Fire? What are a few of the signs and symptoms, and why was it given that name? Is the disease common in present days – why?

•

How might authorities responsible for regulating mycotoxins in food grains approach this task? What principles might guide their assessment of the risk to human health posed by specific mycotoxins? Investigate the occurrence of mycotoxins in different regions around the globe. What are some of the most important factors that determine the occurrence of mycotoxins in food consumed in different countries? Consider food grains consumed, climate, and socioeconomic factors. Investigate the occurrence of mycotoxins in your own country. How are mycotoxins managed in your country – could this be improved?

See also: Grain Harvest, Storage and Transport: Contaminants of Grain.

Further Reading EFSA (2014) Evaluation of the increase of risk for public health related to a possible temporary derogation from the maximum level of deoxynivalenol, zearalenone and fumonisins for maize and maize products. EFSA Journal 12: 3699, 61 pp. EFSA Panel on Contaminants in the Food Chain (CONTAM) (2012) Scientific opinion on Ergot alkaloids in food and feed. EFSA Journal 2012(10): 2798, 158 pp. EFSA (2004) Opinion of the CONTAM Panel related to Aflatoxin B1 as undesirable substance in animal feed. EFSA Journal 2004(39): 1–27. Kubo M (2012) Mycotoxins Legislation Worldwide. Available at: http://services. leatherheadfood.com/eman/FactSheet.aspx?ID¼79.

Relevant Websites http://www.efsa.europa.eu/en/topics/topic/mycotoxins.htm – See this website for other similar documents.


Contents The Composition of Food Grains and Grain-Based Products Standardized Test Methods for Grains and Grain-Based Products Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units

The Composition of Food Grains and Grain-Based Products CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Contents of the Composition Appendix (No 1)

•

The large body of data on food composition requires an appendix because of its length. The information is arranged in two tables, based on a serving portion of specified weight, indicating energy value, the contents of protein, carbohydrates, fat and fiber, plus a full range of minerals and vitamins. Appendix No 1 covers the range of food grains and the many foods derived from grains in the following categories:

• • •

Data on food composition are available in the Grain Composition Appendix. For practical reasons, single figures are provided, even though in reality there may be significant variations in nutrient values of a specific food-nutrient combination. These variations arise from differences in genotype, growth environment and food processing. There are specific dietary components that must be provided in our diet; these include essential amino acids and fats, plus all the minerals and vitamins.

Learning Objectives

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Appreciate the potential value of nutrient-composition data. The need to realize that single-figure data may be an oversimplification of reality.

Introduction “We are what you eat”. But how do we select our food and drink? How do we make our food choices? Generally we decide on the basis of our upbringing, our culture, hunger, advertising, on costs and our ability to pay; and ultimately on the very subjective bases of taste and mouth-feel. Perhaps it is less often that we base these food choices on the composition of the foods. How often do we consult a table of food composition? It is more likely that we will glance at the label of the food package for information about its composition. However if we wish to select foods, before buying, according to composition then we really do need composition tables. That is what is provided in this encyclopedia as Appendix 1. “NutrientComposition Tables for Grains and for Grain-Based Products”.


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Grains, flours, and cooked cereals (including enriched or fortified nutrients) Pasta and rice (including enriched nutrients) Cereal, ready-to-eat (including fortified nutrients) Baby food cereals (including fortified nutrients) Breads and other related products (including enriched nutrients) Crackers (including enriched nutrients) Cookies (including enriched nutrients) Cakes, pastries, and other desserts (including enriched nutrients) Granola and cereal bars (including fortified nutrients) Snacks and chips (including enriched nutrients) Legumes Meat substitutes Alcoholic beverages Ingredients used in grain products

As indicated above, most categories include foods that are fortified or enriched in some way. For these cases, the specific nutrient is shown in bold italics. The primary reference foods are of American origin, as the grain nutrient composition table has been developed by the Nutrition Coordinating Center (NCC) at the University of Minnesota. The tables contain values compiled from scientific literature, the USDA Nutrient Database for Standard Reference, manufacturers’ information, and estimated data. The data include both analytic and estimated values. Estimated values were derived from (1) a

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different form of the same food (e.g., raw to cooked), (2) a similar food, or (3) calculation of recipes or formulations.

Not Just a Single Figure, but a Range for each Food-Component Combination Although the appendix tables specify a single figure for each combination of a foodstuff and a component, it must be realized that in each case this is a notional value; a range of values around this would be obtained if several samples of this food were to be analyzed. For example, the protein content of hard red wheat is given as 15.4% (6.93 grams in a 45-gram portion of grain). In contrast, soft red winter wheat is given as 10.4% protein (4.66 grams of protein in a 45-gram portion of grain). This difference in protein content reflects the distinct utilization of these wheat grades, respectively, a higher protein content for bread-making (hard) wheat and a lower protein content for cookie-making (the soft wheat). However, there may be some samples of hard red wheat with protein content as low as 10.4% and vice versa, soft wheats with a protein content as high as 15.4%. The article on cereal proteins provides ranges of protein content for the various cereals; the articles on grain receival and marketing show ranges of protein content for specific grades of grain. These variations are due to differences in the variety (genotype) of the grain involved, in the growth conditions, and in the processing conditions (for the derived foods).

Variations in Composition due to Genetic Factors There are multiple varieties (even species) of all agricultural grains, and these genetic variants differ in their genetic potential to accumulate protein, fat, fiber, minerals and all other aspects of composition. In many such cases, considerable breeding effort has been expended to select greater genetic potential to achieve higher (even lower) levels of specific components. The hard and soft wheats mentioned above are specific cases where breeders have intentionally selected for the genetic potential for higher or lower protein content. Even greater differences in protein content have been produced by the development of mutants for some grain species, especially for maize as described in the relevant articles in this encyclopedia.

Variations in Composition due to Environmental Factors Differences in composition also arise due to variations in growth conditions, such as climate, rainfall, fertilizer use, diseases and various aspects of farm management. Growth conditions are likely to contribute considerably to the examples above of hard and soft wheats. In fact, farm management practices and growth sites would have been selected to achieve the desired outcomes with respect to protein content. The effects of growth conditions of grain composition are expected to become greater under the influence of rising levels of carbon dioxide and the consequent aspects of climate

change (such as altered rainfall and temperatures). Experimental field trials have shown that grain yields will rise significantly due to the “carbon fertilizer” effect of increased carbon dioxide in the atmosphere. As the yield increase is mainly due to greater starch synthesis, grain-protein levels will be reduced. In addition, simulated field experiments with increased atmospheric levels of carbon dioxide have indicated increased concentrations of some minerals in cereal grains, especially zinc, manganese and copper.

Variations in Composition due to Processing Factors Considerable changes in composition obviously accompany grain processing. For example, flour milling is generally designed to remove the outer husk and bran layers of grains, thereby also removing fiber components and some of the minerals and vitamins of the original grain. Heat treatments may also alter aspects of food composition. On the other hand, fortification and enrichment procedures are often undertaken during processing, with consequent improvements in food nutrition. Cases of specific enrichment appear in the Composition Appendix in bold italics.

Conclusion The amazing diversity of grain-based foods that we eat can be reduced to specific amounts of the various biochemical components – protein, fat, carbohydrate, minerals and vitamins. Yet even for grain-based foods there are hundreds of alternatives to suit our palates, our cultures and our ability to pay. Reducing our favorite foods to numbers and biochemical components may appear to detract from the allure of our foods, but in the process of this type of analysis, we are able to reach the realization about how our dietary needs are satisfied with respect to these components. Nevertheless, it is also amazing that our bodies can function on a very wide range of foods, forming such a contrast to our automobiles, which do not function unless we tank up with just the right type of fuel. Whilst our metabolism is quite capable of transforming ingested sugars into fats, for example, there are specific dietary components that must be provided in our diet; these include essential amino acids and fats, plus all the minerals and vitamins. When we need to ensure that these essentials are in our diet, the Composition Appendix is a valuable reference with respect to the important place that the grains have in our diet.


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Why is it an over-simplification to provide only one number for the composition of one nutrient in one food source? What are the most useful applications of a table of nutrients for food sources? Explain the reasons for variations in the nutrient content of specific foods. What are the main aspects of food composition that determine its energy value?

GRAIN COMPOSITION AND ANALYSIS | The Composition of Food Grains and Grain-Based Products


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Use the Composition Appendix to compare the nutritional values of the three major cereal grains (maize, rice and wheat). Which grain species provides the best balance of nutrients? What is the range of foods made from each of them? Which would you prefer as a food source if you had access to only one of them? If the best food for a small bird is provided in an egg; if the best food for a calf is provided in cow’s milk; if the best food for a human baby is provided in mother’s milk; then the best nutrition for a plant seedling is provided by the seed. We choose to eat all these sources of food, but according to this logic, we might not expect to have our nutrient needs provided by grains. In what regards (if any) are grains a lessthan-optimal source of nutrition for humans? Hint: also examine the levels of essential amino acids (see Protein Chemistry article).

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See also: Food Grains and the Consumer: Fortification of GrainBased Foods; Grains and Health; Labelling of Grain-Based Foods; Food Grains and Well-being: Nutrition: Soy-Based Foods; The Basics: The Grains that Feed the World; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Coix: Overview; Maize: Overview; Rice: Overview; Sorghum Grain, Its Production and Uses: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Amaranth: Overview; Grain Legumes and Their Dietary Impact: Overview; Lupin: Overview; The Oilseeds: Oilseeds: Overview; Soybean: Overview; The Basics: The Grain Crops: An Overview.

Standardized Test Methods for Grains and Grain-Based Products AR Bridges, AACC International, St. Paul, MN, USA CW Wrigley, University of Queensland, Bribane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Test methods are needed to determine the quality of all types of grain and grain-based products. Methods developed and standardized for these purposes are listed. The testing procedures listed have been developed via collaborations between scientists as members of learned societies for final approval by the societies’ procedures. The range of situations that require test results covers the entire ‘grain food and feed chain’ from breeding, through production and harvest, to processing, retailing and nutrition. There are multiple versions of some tests, depending on whether the test must be performed in a laboratory situation or ‘in the field,’ where there may be minimal facilities for testing. Examples are provided of the testing of grain composition and sprouting damage for grain deliveries after harvest.

Learning Objectives

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AACC International AACCI (formerly the American Association of Cereal Chemists) is based in St. Paul, MN, United States. It has a worldwide membership of over 4000 scientists involved in grain production and the grain-based food industry. AACCI celebrated its hundredth anniversary in 2015. The logo is provided in Figure 1. AACCI validates testing methods and guidelines to internationally recognized criteria for applications in all areas of the grains industry. They are published in an online manual. The methods are used internationally and recognized by other standards organizations including Codex Alimentarius.

The ICC

To understand the need for approved testing methods to analyze grains, related foods, and ingredients. To become familiar with the range of tests available, the means of their development, and the situations where the tests are needed.

Introduction You have just come home with some grocery items from the supermarket. You pick up one of them, maybe a packet of cake mix, and you examine the table of ‘nutritional information.’ Do you consider how ‘they’ come up with all of those analyses – the amounts of protein, fat, carbohydrates, sodium, vitamins, etc.? Who are the ‘they?’ What tests are conducted by the ‘they?’ How do the tests work? What is the range of materials to be tested? How far up the grain production and processing chain are testing methods needed? Read on; here are the answers to these questions.

Origins of Testing Methods for Grain and Grain-Based Products

The International Association for Cereal Science and Technology (ICC), based in Vienna, Austria, is an international association committed to international cooperation through disseminating information and developing standard methods for the well-being of all people. The ICC logo appears in Figure 2. The foundation of ICC in 1955 met the need for internationally approved and accepted standard testing procedures for cereals and flour. In the early smaller European Community, ICC standard methods were the basis for the grain market and this still applies in the much bigger European Community. ICC also cooperates with the European Committee for Standardization (CEN), an association that brings together the National Standardization Bodies of the 33 European countries. Historically, in the global cereals industry, when companies produced grain-testing equipment, they applied for standardization of methods validated to measure the reliability and reproducibility of the test method associated with the equipment.

The Wider Range of Organizations

Test methods are needed for all types of grain and grain-based products – bread, pasta, rice, beer, bioethanol fuel, animal feedstuffs, canola oil, and ingredients in grain-based foods. For the many consumer products and for the intermediate materials of their processing, there is the need for laboratory

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test methods to evaluate their quality characteristics and to monitor the processing quality of the final products. This article introduces many methods that have been devised to provide these testing requirements. The methods are those developed and published by two major associations of grain scientists, the ICC and AACC International (AACCI), respectively.

In addition, standard methods of grain testing have been developed by other organizations, including the following:

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The American Oil Chemists’ Society (AOCS) comprises nearly 5000 members worldwide, providing ‘a global forum for the science and technology of fats, oils, surfactants, and related materials.’


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Methods from these organizations are recognized by Codex Alimentarius.

Examples of Testing Procedures Protein Content

Figure 1 Logo for test methods in the early times of the American Association of Cereal Chemists. Illustration reproduced with permission from AACC International.

Figure 2 Logo of the International Association for Cereal Science and Technology (ICC). Illustration reproduced with permission from the ICC.

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The International Seed Testing Association (ISTA) is a worldwide, nonprofit association whose ‘main activity is to provide methods and services for the testing of seeds moving in international trade.’ AOAC International is an ‘internationally recognized organization with 120 years of experience in validating and approving analytical methods for foods and agriculture.’ The Australasian Grain Science Association (AGSA), formerly the Cereal Chemistry Division of the Royal Australian Chemical Institute. See reference to Westcott and Ross (2002) in ‘Further Reading.’ The American Society of Agronomy (ASA) is ‘dedicated to the development of agriculture, enabled by science, in harmony with environmental and human values. The Society supports scientific, educational, and professional activities to enhance communication and technology transfer among agronomists and those in related disciplines on topics of local, regional, national, and international significance.’ The Grain and Feed Trade Association (GAFTA) is an organization that provides guidance and certification of methods and testing for the international grain trade. International Organization for Standardization (ISO) is an internationally recognized organization for a wide range of products and situations including grains and they have close cooperation with the European Committee for Standardization (CEN).

When you read the protein content on the packet of cake mix or of any other grain-based product, you may wonder what procedure has been used to determine the amount of that component. You may even wonder what a protein is. The protein class of biochemical compounds includes a wide range of materials – milk casein, blood albumin, egg white, spiderweb, wool, silk, hair, and the storage proteins of grains, for example, gluten. Amazingly, all these forms of protein have the same basic composition, that is, they are all linear polymers of amino acids, which are characterized by having an amino group containing the element nitrogen (N). Protein is the main constituent of grains that contain nitrogen, so the most basic method for protein analysis is to determine the amount of nitrogen in the test material. This involves digesting the sample to its elemental content and determining the nitrogen content, either as ammonia (after Kjeldahl digestion) or as nitrogen gas (by the Dumas and other combustion methods). Some variations of the Kjeldahl method are provided in the AACCI method group 46. The nitrogen gas methods are described in the ICC method 167 and AACCI method 46-30.01. To obtain a result for actual protein content, the level of nitrogen is multiplied by 6.15 for most sources of protein. However, for wheat, the factor of 5.7 is used to convert percentage nitrogen to percentage protein because most of wheat grain’s protein is gluten, which has an unusually high content of nitrogen, being rich in glutamine (an amino acid with two nitrogen atoms). Compared to the analysis of nitrogen, there are more convenient (secondary) methods to determine protein content. The most commonly used involves spectroscopic scanning in the near-infrared part of the spectrum. However, this group of methods must first be calibrated using a set of relevant samples that have already been analyzed for protein based on their nitrogen content (reference method usually by Kjeldahl or a combustion analysis). Near-infrared reflectance (NIR) analysis involves scanning the surface of a ground sample. Most simply, near-infrared transmittance (NIT) analysis of grain involves scanning whole grain, poured into an instrument, as indicated by the cutaway diagram in Figure 3. Both NIR and NIT methods provide instant results.

Near-Infrared Analysis for Moisture and Oil Content These near-infrared methods are also used to determine moisture in grains generally and oil content in oilseeds (e.g., AACCI method group 39 and ICC methods 159 and 202). The speed and convenience of these methods have revolutionized the determination of grain composition, so that samples from trucks may be analyzed on receival to permit on-the-spot segregation of grain into separate storage silos, based on protein and/or oil content. Moisture content is an important attribute because of the greater risk of insect or mold attack for moist grain in storage.

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Figure 3 Cutaway diagram of the workings of equipment for near-infrared transmittance (NIT) analysis of grain for protein content of moisture. Whole grain is poured into the instrument while being scanned at several wavelengths in the infrared part of the spectrum. Reproduced with permission from MultiSpec.

Maximum moisture levels are therefore set for the postharvest delivery of all grains, generally in the range of 12–15%. On the other hand, moisture content is an added financial concern for grain growers if they are paid on the usual basis of the mass of grain as delivered. In the hot dry weather of harvesting, grain may be harvested at very low moisture content (as low as 8%), so that a lower price is paid on a dry-weight basis. Growers have therefore obtained NIT equipment that allows oil, protein, and moisture levels to be monitored (and possibly adjusted) for harvested grain prior to delivery to an elevator or mill.

grain receival, so a new method was subsequently developed, named the ‘stirring number’ test, based on novel equipment, the Rapid Visco Analyzer (RVA). As a result, stirring number methods were developed (AACCI method 22-08.01 and ICC method 161). This example shows how there may be a range of methods able to achieve similar results, because the various methods are suited to different situations. Furthermore, the RVA, developed initially to determine sprout damage, has been adopted for its use in characterizing starch attributes (AACCI method 7621.01 and ICC method 162).

Sprouted Grain A potential defect of harvested cereal grain is premature sprouting caused when there is rain at harvest. However, in some global areas, sprouted grains are desired for the changed nutritional profile, being used in breads and other baked grain products. When sprouting is severe at harvest time, roots and shoots are seen emerging from the grain’s germ, but these visible signs may not be evident for incipient sprouting, even though rain has triggered the production of the starch-degrading enzyme, a-amylase. The resulting wheat and rye grain are unsuitable for normal milling and baking. Incipient sprouting in barley may reduce its storage life for malting quality. The traditional test for sprout damage is the ‘falling number’ test (AACCI method 56-81.02 and ICC method 107/1) that involves the rate of falling of a plunger through a heated ‘porridge’ of a wholemeal suspension. Alternative methods involve laboratory testing of enzymatic activity by colorimetric means (AACCI method group 22 and ICC method 108). A few decades ago, there was an unusually wet harvest in Australia with levels of sprout damage rarely seen previously. It was difficult to deploy the traditional methods at the sites of

Method Development This story about the sprout-damage testing only partly indicates the painstaking and laborious process needed to establish the many methods. The process may start with the realization that there is the need for a specific method of analysis. So a group of researchers may study the best means of achieving the desired aim. It may take a year or two of research to achieve their initial goal. When they reckon that they have a viable method, they would probably describe it in a research article that is submitted to a suitable scientific journal. The methods being developed may call for microscopy as a means of identifying foreign material in cereal-based foods, such as is seen in Figure 4. Alternatively, microbiological methods may be needed to test for the risk of fungal or bacterial infection (Figure 5). The relevant journal may be one that covers topics of grain science, such as Cereal Chemistry and Cereal Foods World (both published by AACCI) or the Journal of Cereal Science (published by Elsevier Science, United Kingdom). Alternatively, they may choose to submit their paper to a journal that deals more


Figure 4 The use of microscopy as a means of identifying foreign material in cereal-based foods. Illustration provided by AACC International.

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of these referees, the editorial staff may accept the article for publication; alternatively, it may be rejected, or it may be returned to the authors for revision until it is acceptable for publication. Other research groups may read the new published method and realize its value, evaluating it as a procedure that would suit their analytic needs. If they find it suitable, they might add some improvements of their own. These research groups might communicate with the original group of scientists, suggesting the need for collaborative evaluation of the method, either in its original or in its modified form. A common forum for such collaborative evaluation is provided within scientific associations with common interests, such as the AACCI or ICC. Regular scientific meetings of the technical methods committees within these associations provide additional opportunities for the exchange of ideas and for arranging collaborative development and evaluation of new methods. Further steps in the formal development of an approved method (standard) are the agreement on the need for the method, on a draft method, and on the process for evaluation of the method. If the method is new to most users, a precollaborative study with a limited number of expert laboratories will be used to determine any problems in the draft method and make recommendations for improvement. The method is then validated for the range of matrices and analytic values using an international collaborative study (or ‘ring trial’). This process involves the preparation of a set of samples (representing the different matrices and analyte range for the final use of the method) for distribution to all of the participating laboratories. Results obtained using these samples and the draft method are returned to a central coordinator for statistical evaluation (ISO standard 5725) here using guidelines provided in ICC method 203 and an AACCI Report published in Cereal Foods World (see ‘Further Reading’). The results of this study are used to write the final method and report the performance characteristics of the method for specific matrices and range of analytes. These include the accuracy, precision, reproducibility, and repeatability factors. The final step for adoption as ‘an approved or standard method’ of the association requires review and approval by experienced analysts and statisticians.

Publication of Standard Methods

Figure 5 Microbiological methods in use to test for fungal or bacterial infection. Illustration provided by AACC International.

broadly with food science or agriculture or more specifically with analytic methodologies. On receipt of their research article, the editorial staff of the journal would send out the manuscript for ‘peer review,’ that is, the paper is sent for critical assessment separately by two or more independent scientists who are recognized experts in the specific field covered by the paper. Depending on the opinions

Following adoption, the details of the method are added to the association’s set of standard methods. In the past, hard-copy manuals were used; in some cases, the manuals were loose-leaf to facilitate updating from time to time as new methods were added (and also superseded methods were removed). More recently, standard methods are published in an edition on the respective websites of the societies and identified by their ‘doi’ numbers. This simplifies the process of adding new methods and revision. This greatly helps the laboratories following standards of laboratory procedures (ISO/IEC 17025:2005) that require the latest version of an approved method. This general process of method development has been followed, in some form or other, for the methods listed in ‘Methods.’ Inevitably, there is some duplication between

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associations in the methods developed. In some cases, the method developed by one organization is adopted (possibly with style modification) by another organization. In addition, lists of approved methods are developed by individual research organizations, by analytic laboratories, or by companies. These lists form part of the standard operating procedures of the laboratory or organization. Standard methods are developed according to the needs and analytic techniques available at any given moment in time. Some analytic methods change, with the passage of time, as improvements in methodology and equipment are introduced. In some cases, changes may be accommodated within an existing standard method and result in the modification of the original, while in other cases, completely new standard methods are developed and published.

The Range of Methods The diversity of procedures covers the needs for information about grains and grain-based products (including the associated ingredients) throughout the grain chain from breeding through production and processing to the consumer and nutritional labels. Additional to these are the many analytic tests used in the earlier stages of grain production, such as soil and plant testing. Further details of these agronomic needs can be accessed on relevant websites and via ‘Further Reading.’

Sampling Methods Are Critical A critical first step for any of the methods is taking the sample. If the sample taken for analysis is not representative of the whole consignment that was sampled, then there is little point in performing the required analysis. The sample plan will determine the ‘limit of detection’ of the test method. At least, there must be an awareness of the relationship of the sample for testing to the whole consignment that it is intended to represent. Therefore, attention has been given to sampling procedures (see recommended sampling methods in the ICC methods (101, 120, 130, and 138) and in the AACCI method group 64). Government standards for export trade often prescribe the sampling process to be used.

Grain Testing after Harvest In the sequence of grain production and processing, the analysis of the harvested grain comes first. Initial tests involve the determination of bulk density (as ‘bushel weight’ in AACCI method 55-10.01) and of nongrain material, called ‘extraneous matter’ in the AACCI method group 28 and ‘besatz’ in ICC methods 102 and 103. Grain analysis also involves the determination of possible defects, such as mycotoxins (AACCI method group 45) and the presence of grain contaminated with ergot (AACCI method 42-56.01) or smut (AACCI methods 42-70.01 and 42-71.01).

Chemical Composition Next in importance is the chemical composition of the grain, involving moisture content for all grains, protein content for most grains, and oil content for the oilseeds. Routine analyses of these constituents generally involve NIR spectroscopy (AACCI method group 39 and ICC methods 159 and 202), but these procedures require reference sets of samples whose composition has been determined by the basic methods of oven drying for moisture (AACCI method group 44 and ICC method 109), elemental analysis of nitrogen content for protein (ICC method 167 and AACCI method group 46), and solvent extraction for oil and fat (ICC method 136 and AACCI method group 30). These methods have also been adapted to the analyses of milled and baked products. For flour and food products, a wider range of compositional analyses may be required, including the content of starch (AACCI method group 76 and ICC methods 122, 123, and 128), nonstarch polysaccharides and fiber of various types (ICC methods 113, 140, and 156 and AACCI method group 32), specific types of lipids (fats and oils) (AACCI method group 58), vitamins (ICC methods 111, 112, 117, and 119 and AACCI method group 86), and heavy metals (ICC methods 141 and 154).

Simulation of Grain Processing Many of the methods of analysis are designed to predict how a consignment of grain or flour can be expected to perform in processing. The most obvious are methods that are small-scale versions of the real process. For example, equipment and procedures have been developed for laboratory-scale milling (AACCI method group 26). Following milling (laboratory- or full-scale), a common method to determine the quality of the resulting flour is to assay the flour for its ash content (AACCI method group 08 and ICC methods 104 and 157), that is, the mineral residue remaining after burning off the combustible materials, such as protein, fat, and starch. Likewise, small-scale versions are available for the analysis of wheat to mimic the processes of making bread, pasta, noodles, and other food products. Predictive of these product-related methods are the significant aspects of flour performance that influence processing, especially dough properties (ICC methods 114, 115, 121, and 126 and AACCI method group 10). Further groups of methods determine specific aspects of composition that are known to provide a correlation to performance in the real process. These include gluten strength (ICC methods 155 and 158 and AACCI method group 38) and sedimentation tests (AACCI methods 56-60.01 to 56-63.01, and 56-70.01 and ICC methods 116, 118, and 151).

Methods for Food Processing Further methods describe the means of testing the quality of a range of ingredients that may be used in the preparation of grain-based foods (AACCI method groups 20 and 58). Test bakers (in wheat-breeding programs) are interested in replicating the finished food process using much smaller quantities of flour and will use a guideline like AACCI method 10-12.01 to evaluate their results. This method includes illustrations of


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Plant Breeding

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Figure 6 Illustrations of ‘pup loaves’ as a basis for evaluating baking quality for small flour samples according to the external-appearance scores and volumes of ‘pup loaves.’

small-scale ‘pup loaves’ in Figure 6 as a basis for evaluating external-appearance scores and loaf volumes. Other methods relate to the evaluation of finished products according to their color (AACCI method group 14) and their taste and mouth feel (sensory analysis; AACCI method 3350.02). Paramount for food production is the need to test for food safety, that is, the need for assurance of the absence of pathogenic microorganisms (ICC methods 125, 133, 134, 139, 144, 147, and 206 and AACCI method group 42).

Methods for the Diversity of Grains The main accent in the AACCI and ICC methods is on wheat and wheat-based foods, but there are also analyses of product and processing quality for rice (these mainly involve the quality of rice starch; AACCI method group 61), corn, oats, barley, and pulses. Methods for barley testing are provided by the European Brewing Commission and the American Society of Brewing Chemists (http://methods.asbcnet.org/toc.aspx).

Oilseed Methods Greater accent on fats and oils is provided by the standard methods of the American Oil Chemists’ Society (AOCS). These have been available as a loose-leaf manual of 1200 pages but now online at the AOCS website. Their methods include sections on vegetable-oil source seeds (Section A), oilseed by-products (Section B), commercial fats and oils (Section C), and various other methods for the wider range of fats, oils, and surfactants. Specific methods of relevance to oilseed analysis include the following:

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The determination of oil content in oilseeds Oil content of oilseeds by nuclear magnetic resonance Oil in oilseeds: supercritical fluid extraction method The determination of oil, moisture, and volatile matter and protein by NIR analysis Total hexane content in extracted meals

Many of the cereal grain and seed testing methods are also essential to plant breeders, who must evaluate the suitability for specific end uses of the many new crossbred lines coming through their breeding programs, whatever the grain species. In the late stages of breeding, there may be no more than a kilogram of grain for advanced lines. For wheat breeding, for example, this amount must be sufficient for test milling and test baking if the breeder’s aim is to produce a bread-making wheat. Examples of ‘pup-loaf’ testing are shown in Figure 6. In the earlier stages of breeding, the amount of grain is much less, and very small-scale methods have been devised to suit these specific purposes, so that lines that perform poorly for end-use quality can be eliminated from the breeding program, thereby avoiding the unnecessary propagation of poor lines.

Ongoing Method Development Method development is an ongoing task, as new results are needed and as novel principles and procedures become available. Annual meetings of grain science associations provide the opportunity for collaborators to meet face to face. At a recent AACCI meeting, 260 individuals involved with the 22 technical committees met to discuss the issues, successes, and overall progress in developing new methods and enhancements for method users. For example, a new method was approved for determining the gelatinization temperature of rice flour. Gelatinization temperature and amylose content are common measures of rice cooking quality. This method provides a rapid and simple method for determining the gelatinization temperature of a small sample of rice flour using an RVA, making it particularly suited to rice breeders. The method was developed by members collaborating in the Rice Milling and Quality Technical Committee. It was examined and subsequently approved by the Approved Methods Technical Committee, which has general oversight. The new method was added to the list of standard methods and the collaborative trial report of the method was published in AACCI’s Cereal Foods World. At the same meeting, the Bread-Baking Methods Committee checked a new video illustrating the Optimized StraightDough Bread-Making Method (AACCI method 10-10.03) as a means of assisting operators in different locations to perform the method in a uniform manner. This committee also discussed the development of a new procedure – a baking method for whole-grain flour. Once finalized, this method will be presented to the committee, where it will be discussed and considered for approval as an AACCI method. Furthermore, a new pancake method was approved for inclusion in AACCI’s Approved Methods of Analysis, 11th edition. This method outlines a procedure for the production of pancakes in a laboratory setting to gain information about the potential performance of a flour used in general batter-based product applications. The formulation eliminates many common ‘biological’ ingredients such as soy flour, buttermilk, nonfat dry milk, and egg to minimize the variability in measurement each adds to the resulting product.

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Check Samples for Interlaboratory Comparisons The primary purpose of developing and publishing standard methods is to ensure that laboratories in different locations can produce results that are directly comparable because they are using the same procedures or validated equivalent method procedures. However, they still need to establish that the results really are comparable. This comparison is achieved using ‘check samples’ that are sent to subscribing laboratories. For example, one sample (from a single lot) of flour is divided into many portions and distributed to laboratories for them all to perform an agreed set of analyses. The results are then assembled and compared. Analysts compare their results to the mean of all the results for each analyte and use this information to compare their laboratory’s performance to that of other laboratories. Sometimes this process enables them to identify modifications that they may have made to the standard method. There is the need to see what causes a biased result or perhaps to find out why a laboratory is trending out of specification. This review process is called proficiency testing and is often provided as part of a check sample service. Check sample services are available from the several scientific societies already mentioned in the preceding text. Check sample services may also highlight the need for an updated standard method. This may require additional collaborative work to be completed, for example, if new ingredients are included in the food matrices or when new manufacturing processes are introduced.

See also: Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Labelling of Grain-Based Foods; Foodquality Testing: Rice: Eating Quality; The Application of Sensory Science to the Evaluation of Grain-Based Foods; Genetics of Grains: Detection of Genetically Modified Grains; Grain Composition and Analysis: Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units; Grain Harvest, Storage and Transport: Cereals: Grain Defects; Grain Marketing and Grading: Identification of Varieties of Food Grains; Processing of Grains: bGlucans: Measurement and Processing; Scientific Organizations Related to Grains: Scientific Societies Associated with Grain Science; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.


• • • •

Describe the steps leading to the final approval and publication of a testing method. Why might there be different methods to achieve the same analytic results? What is the range of grain constituents covered by the many methods in ‘Methods?’ Which ingredients are included for making grain-based foods? How does the use of check samples help a laboratory check their results against other laboratories and measure their quality performance?

Future Trends


Suitable methods of analysis are essential to the ongoing development of the grain-processing industries, both internationally and locally. These methods permit the comparison of test results between laboratories and between countries. Without this ability, it would be impossible to establish international codes for the hygiene and composition of grains and of foods made from them. A decade or so ago, printed methods books had progressed to loose-leaf folders. This change allowed new methods to be inserted or replaced with modified procedures. Now, it is usual for methods to be available on the Internet, further facilitating ready access for laboratories and allowing the timely revision of older procedures and the addition of new methods. New methods are now taking advantage of the biotechnology era, as well as addressing the challenges of biotechnology. For example, AACCI methods in the biotechnology group (11) provide the means for determining the presence of genetically modified corn, using methods from the new biotechnology, namely, protein (immunological) and DNA assays. In addition, ISO Technical Committee 34/SC16 provides guidelines and standards for new biotechnology methods. These parallel trends are likely to expand, with the increasing need to identify and segregate grains that have resulted from genetic modification. On the other hand, molecular biology is delivering a wide range of efficient testing methods, whereby analysis can be conducted by targeting the presence or absence of specific marker genes or marker proteins.

• • •

Check through the lists of methods. Can you think of any test missing that would be relevant to grain processing? Check through the many methods in ‘Methods’ and see how many have the name of a person, presumably the originator of the method. Examine the ‘nutritional labeling’ details on some supermarket packets. Do you see methods to obtain these results?

Further Reading AACC International. AACC International Methods of Analysis, 11th edn. St. Paul, MN: AACC International. AOAC (2005) Official Methods of Analysis, 18th edn. Gaithersburg, MD: AOAC International. AOCS (2007) Official Methods and Recommended Practices of the AOCS, 6th edn, 3rd printing. Champaign, IL: American Oil Chemists’ Society. AOCS (2002) Standard Methods of the American Oil Chemists’ Society. Champaign, IL: AOCS. CCFRA (2010) Manual of Methods for Wheat and Flour Testing, 4th edn. Chipping Campden, Gloucester: CCFRA Technology Ltd. Guideline No. 3. International Association for Cereal Science and Technology (2002) Standard Methods. Vienna, Austria: International Association for Cereal Science and Technology (ICC). ISTA and International Seed Testing Association (1999) International Rules for Seed Testing. Zurich, Switzerland: International Seed Testing Association. Nelsen TC and Wehling P (2008) Collaborative studies for quantitative chemical analytical methods. Cereal Foods World 53: 285–288. http://dx.doi.org/10.1094/ CFW-53-5-0285 http://www.aaccnet.org/publications/plexus/cfw/pastissues/2008/ Documents/CFW-53-5-0285.pdf.

GRAIN COMPOSITION AND ANALYSIS | Standardized Test Methods for Grains and Grain-Based Products Westcott T and Ross D (eds.) (2002) Official Testing Methods of the Cereal Chemistry Division of the Royal Australian Chemical Institute. Melbourne, Australia: Royal Australian Chemical Institute. Wrigley CW, Booth RI, Bason ML, and Walker CE (1996) Rapid visco analyser: Progress from concept to adoption. Cereal Foods World 41: 6–11.

Relevant Websites http://www.aaccnet.org – AACC International.

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http://www.agronomy.org – American Society of Agronomy. http://www.aoac.org – AOAC International. http://www.aocs.org – Standard Methods of the American Oil Chemists’ Society. http://asbcnet.org – American Society of Brewing Chemists (ASBC). http://www.codexalimentarius.org – Codex Alimentarius Food Standards. http://www.gafta.com – Grain and Feed Trade Association. http://www.icc.or.at – International Association for Cereal Science and Technology. http://www.seedtest.org – International Seed Testing Association (ISTA). http://www.iso.org – International Organization for Standardizations.

Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units W Huang, Jiangsu Academy of Agricultural Sciences, Nanjing, China CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• •

• • • •

There is a need for conversion tables to permit the ‘translation’ of measurement units between the different systems. Three significant systems are used worldwide, namely, ○ the imperial system used in the United States, ○ the traditional Chinese system, and ○ the International System of Units (Syste`me Internationale d’Unite´s) – the metric system. There are also differences between the imperial systems as used in the United States and the United Kingdom. Conversion tables are provided to facilitate transferring measurements in one system to another. The origins of these systems are described. Units of measurement specific to grain science analysis are also explained.

Learning Objectives

• •

To realize that there are systems of measurement different from those used in your local situation. To understand how these diverse systems came into existence and how they can be harmonized by using conversion tables.

Introduction Until the whole world shares one common ‘language’ for units of measurement, there will be a need for conversion tables, such as are provided in this article. There is a bewildering array of units, many of them are no longer in common use; examples of confusing units in the English language include tons and tonnes, fathoms and furlongs, pennyweights and hundredweights, stones and scruples, gills and grains, drams and pecks, poles and perches, rods and roods, and leagues and bags. In the range of traditional Chinese units, the same term (e.g., the fen [分] and the li [厘]) is used for units of length, area, and mass. The English word ‘ounce’ denotes a different measure depending on whether it is a dry or liquid measure and depending on whether it is a troy ounce, an apothecaries’ ounce, or an avoirdupois ounce! Agreement on the units of measurement is no less important today for grain science, in the many disciplines that make their contributions, than such agreement has been through the ages. Throughout this encyclopedia, the standard is to quote units as metric, and indeed, this is usual throughout the

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scientific community worldwide, including China. However, it is appropriate that there should be the provision of conversion tables between metric and US units in this article, because the metric system of units is still not in common use in some English-speaking countries. This is especially so for the United States, although the United States is officially on the metric system. All US units are defined in terms of the International System of Units (Syste`me Internationale d’Unite´s) (Table 1). The use of ‘customary US units’ continues to be permitted in trade, but they are not mandated. In many cases, including consumer foods, for example, canned foods and packaged baking mixes, there is dual labeling in US customary units and in the metric equivalent. In medicine, metric units are used almost exclusively. Metric units are also used for some alcoholic beverages. The provision of conversion tables is also needed for many of the current and older generations in countries that have adopted the metric system relatively recently, as they may still think in imperial terms for infrequently used units. Added problems for the use of units of measurement relate to the lack of standardization of units in nonmetric systems. Many of the British imperial units are differently defined in the United States. Some of these problems are discussed and explained in the succeeding text. Table 1 is confined to conversion between the US and metric units. Table 2 provides the added feature of equivalence with traditional Chinese units. In addition, explanation is needed for a range of nonstandard units used in some branches of grain science. Such instances are discussed in this article, thereby providing a focus for this information, which is also spread throughout the encyclopedia.

Historical Perspective: The Metric System Agreement on units of measurement has been necessary since the beginning of civilization. For example, it was all very well for the cubit to be used to measure short lengths, based on the distance from the elbow to the fingertip, but when accuracy mattered, whose elbow and whose fingertip? According to the Oxford dictionary, this measurement ranged from 18 to 22 in. So, presumably, the matter of standardization was resolved by decree: the standard elbow and fingertip would be the king’s arm! Anatomical origins obviously also apply to the English foot (French pied), still in use in England and the United States, but discontinued in France following the French Revolution of 1789. Prior to that date, the familiar unit was the pied du roi (king’s foot), similar, but not identical, to the British foot. However, even within France, the pied du roi varied from province to province. The foot of Paris was 11% longer than that in


http://dx.doi.org/10.1016/B978-0-12-394437-5.00115-7

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance Table 1 units

Conversion between metric units (mostly SI units) and US

Metric units

US units

Length 1 centimeter (cm) 25.4 millimeters (mm) 1 meter (m) 0.3048 m 1m 0.9144 m 1 kilometer (km) 1.6093 km

0.3937 inch (in) 1 in 3.2808 feet (ft) 1 ft 1.094 yard (yd) 1 yd 0.6213 mile 1 mile

Area 1 square centimeter (cm2) 645.2 square millimeters 1 square meter (m2) 1 m2 1 m2 1 hectare (ha) 0.4047 ha 1 ha 259.0 ha

0.1550 square inch (in ) 1 in2 10.76 square feet 1.196 square yard 0.0002471 acre (ac) 2.471 ac 1 ac 0.00386 square mile 1 square mile (1 ‘section’)

Volume 1 cubic centimeter (cc) 16.38 cc 1 milliliter (mL or ml) 29.57 mL (or ml) 1 liter (L or l) 3.785 l (or l) 1 hectoliter (hL or hl) 1 hL (or hl) 35.24 L (or l) 1 L (or l) 0.9463 L (or l)

0.0610 cubic inch (in3) 1 in3 0.3382 fluid ounce 1 fluid ounce 0.2642 US gallon 1 US gallon 26.42 US gallons 2.838 US bushels 1 US bushel 0.02838 US bushel 1 quart (liquid)

Mass 1 gram (g) 28.35 g 1 kilogram (kg) 0.4536 kg 1 quintal (q) (100 kg) 45.36 kg 1 tonne (t) (metric ton) 0.9072 t 1t 1.016 t

0.0353 ounce 1 ounce 2.205 pounds (lb) 1 lb 220.5 lb 1 US hundredweight (cwt) (100 lb) 1.102 US short ton (2000 lb) 1 US short ton 0.9843 US long ton (2240 lb) 1 US long ton

Grain yield 1 q ha1 0.1235 tonne/hectare (t ha1) 1 t ha1 6.73 t ha1 1 t ha1 1 t ha1

0.79 cwt/acre 1 bag/acre 14.86 bushels/acre for wheat 100 bushels/acre for wheat 13.87 bushels/acre for maize 11.89 bushels/acre for barley

Bulk density 1 kilogram/hectoliter (kg hl1) 1.287 kg hl1

0.7770 lb/US bushel 1 lb/bushel

Power 1 kilowatt (kW) 0.7457 kW

1.341 horsepower (hp) 1 hp

2

Table 1

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(Continued)

Metric units

US units

Energy 1 joule (J) 4.187 J 1 kilojoule (kJ) 1.055 kJ

0.239 calorie (cal) 1 cal 0.945 British thermal unit (BTU) 1 BTU

Temperature 0 C (Celsius) 20 C 100 C

32 F (Fahrenheit) 68 F (about ‘room temperature’) 212 F

Pressure 100 pascals (Pa)

1 millibar (mbar)

Dynamic viscosity 1 pascal second

1 poise

Strasbourg, but 10% shorter than the foot measure in Bordeaux. Such impediments to trade were addressed by the French scientific community following the French Revolution. The French Acade´mie des Sciences was given the responsibility of producing a unified system of weights and measures by act of Parliament in 1790. Although France and England were officially at war at the time, the decree of 1790 stated that the King of England should be approached for England to join in the process of standardizing the system of weights and measures. It is still unclear whether this invitation was ever relayed to the English or, if it was, what response was provided. If Anglo-French cooperation had proceeded at that time, we would probably be a more unified world a few centuries later, in view of the subsequent spread of the British imperial system. Furthermore, the basis of the unit of length might also be much simpler, because a pendulum system was proposed for the joint action with the Royal Society of Britain. According to this system, the basic measure was the length of a pendulum with a period of 1 s (as familiar as the grandfather clock) giving a system of kilopendules, millipendules, and cubic pendules. Instead, however, the Acade´mie des Sciences settled for the meter as one ten-millionth part of one-quarter of the Earth’s meridian. Initially, this was to be based on accurate measurement of the distance from Dunkirk to Barcelona. The interim project, begun in 1793, involved measurement only to Collioure in the south of France. This measure has stood the test of time much better than others in the original package, such as a 10 h clock, a circle divided into 400 grades (still finding some use), and a French Republican Calendar, starting on 22 September (the autumnal equinox in the northern hemisphere) with 12 months, each divided into three 10-day periods, plus a 5-day holiday period (or 6-day holiday period in a leap year).

Imperial Units: The British and US Versions

(Continued)

Following the transfer of the British imperial system of weights and measures to the United States a few centuries ago, separate

310 Table 2

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance Chinese units equivalent to metric (SI) and US units

Chinese units

Metric units

US units

Length 1 hao (毫) 1 li (厘) 3.333 li (厘) 1 fen (分) 3.3333 fen (分) 1 cun (寸) 1 chi (尺) 3 chi (尺) 1 zhang (丈) 1 li (里) 2 li (里)

0.0333 millimeter (mm) 0.3333 mm 1 mm 0.3333 centimeter (cm) 1 cm 3.3333 cm 0.3333 meter (m) 1m 3.3333 m 0.5 kilometer (km) 1 km

0.0013 inch (in) 0.0131 in 0.0394 in 0.1312 in 0.3937 in 1.3123 in 1.094 feet (ft) 1.094 yard (yd) 3.647 yd 0.3107 mile 0.6213 mile

Area 1 square li (平方厘) 9 square li (平方厘) 90 square hao (平方毫) 1 square fen (平方分) 9 square fen (平方分) 1 square cun (平方寸) 1 square chi (平方尺) 9 square chi (平方尺) 1 square zhang (平方丈) 1 square li (平方里) 0.04 square li (平方里) 1 li (厘) 1 fen (分) 1 mu (亩) 15 mu (亩) 1 qing (顷)

0.1111 square millimeter (mm2) 1 mm2 1 mm2 0.1111 square centimeter (cm2) 1 cm2 11.111 cm2 0.1111 square meter (m2) 1 m2 11.111 m2 25 hectare (ha) 1 ha 6.666 m2 66.666 m2 666.66 m2 1 ha 6.666 ha

0.0002 square inch (in2) 0.0015 in2 0.0015 in2 0.0172 in2 0.1550 in2 1.722 in2 1.195 square feet 1.196 square yard 13.289 square yard 61.775 acre (ac) 0.00386 square mile 7.973 square yard 79.733 square yard 797.33 square yard 0.00386 square mile 0.0257 square mile

Volume 1 cuo (撮) 1 cuo (撮) 1 shao (勺) 1 he (合) 1 sheng (升) 1 dou (斗) 1 shi (石)

1 cubic centimeter (cc) 1 milliliter (ml) 10 ml 100 ml 1 liter (l) 10 l 1 hl

0.0610 cubic inch 0.3382 fluid ounce 3.382 fluid ounce 33.82 fluid ounce 0.2642 US gallon 2.642 US gallon 2.838 US bushels

Mass 1 hao (毫) 0.2 hao (毫) 1 li (厘) 1 fen (分) 1 qian (钱) 0.2 qian (钱) 1 liang (两) 1 jin (斤) 2 jin (斤) 1 dan (担) 1 dan (担) 1 dan (担) 20 dan (担)

5 milligram (mg) 1 mg 50 mg 500 mg 5 gram (g) 1g 50 g 0.5 kilogram (kg) 1 kg 50 kg 0.5 quintal (q) 0.05 tonne (t) (metric ton) 1t

0.0001765 ounce 0.0000353 ounce 0.001765 ounce 0.01765 ounce 0.1765 ounce 0.0353 ounce 1.765 ounce 1.1025 pounds (lb) 2.205 lb 110.25 lb 1.1025 US hundredweight (cwt) 0.0551 US short ton 0.9843 US long ton

Grain yield 1 kg mu1 (公斤/亩) 6.66 kg mu1 (公斤/亩) 1 t mu1 (吨/亩) 15 t mu1 (吨/亩) 1 t qing1 (吨/顷) 6.666 t qing1 (吨/顷)

0.15 q ha1 1 q ha1 15 t ha1 1 t ha1 0.15 t ha1 1 t ha1

0.1185 cwt/acre 0.79 cwt/acre 12.35 bag/acre 8.097 bag/acre 1.215 bag/acre 14.86 bushels/acre for wheat

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance evolution has occurred on either side of the Atlantic Ocean, introducing further inconsistencies between the two versions of what is known as the imperial system of units. The differences include the following examples:

• •

• • •

The US gallon (3.785 l (liter)) is smaller than the British gallon (4.546 l). The US ‘short’ ton of 2000 pounds (lb) (907.2 kg (kilogram)) is a ‘shorter’ measure than the ‘long’ ton of 2240 lb (1016 kg), made up of 20 British hundredweights (cwt) of 112 lb each. The US bushel (35.24 l) consists of 32 dry quarts, or 8 US gallons, or 4 pecks. It differs from the British ‘Winchester’ bushel (8 British gallons), which is 36.37 l. The British ‘bag’ of 3 bushels (0.109 m3 (meters squared)) is not in general use in the United States, but it is a farmers’ unit in former British colonies such as Australia. The US hundredweight (cwt) (45.36 kg) is 100 lb (as the name suggests), significantly less than the British hundredweight of 112 lb (50.80 kg), made up of 8 stones, each being 14 lb.

One story to explain the hundredweight anomaly refers to the shipping of wool from Australia to Britain in the nineteenth century. Bales of wool started as 100 lb on the dry Australian sheep station, but they gained moisture during the long ocean voyage in the wool clippers to become about 112 lb on arrival in Britain. To the extent that metric units have been used in the United States, there have been differences in spelling to further confound the possibility of standardization. For example, the tonne, litre, metre, and gramme of the SI metric system are the metric ton, the liter, the meter, and the gram in US use, respectively. Potentially, international adoption of the SI metric system is a unifying principle to overcome these anomalies, but habitual use of traditional systems dies hard. On the assumption that the use of nonmetric units is more prevalent in the Unites States than elsewhere, the table of conversions to metric units (Table 1) relates primarily to US units, using US spelling for the metric units.

The International System (SI) of Units The SI metric system of units is the modern version of the metric system. The General Conferences on Weights and Measures (1954–71) agreed on seven base units for seven basic quantities as the foundation of the SI metric system. These are

• • • • • • •

meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current intensity, kelvin (K) for thermodynamic temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity.

A much longer set of derived SI units was based on these. The basic SI units for area and volume are thus obtained by raising the unit for length to the second and third powers, respectively. A more complex case is the set of derived units for energy, which may be expressed as the meter squared kilogram per

311

second squared (m2 kg s2), also called the joule (J), the newton meter (N m), and the volt ampere second (V A s). These three terms for energy are equivalent; the user may choose which is appropriate to use in a specific context. The General Conferences on Weights and Measures (1960–75) adopted a set of decimal multiples as SI prefixes. The more common ones are

• • • • • • • • •

giga (G) for 109, mega (M) for 106, kilo (k) for 103, hecto (h) for 102, deci (d) for 101, centi (c) for 102, milli (m) for 103, micro (m) for 106, and nano (n) for 109.

The Chinese System of Units During China’s long history, many different units of grain measurement have been used. For example, a famous book in the Zhou dynasty, ‘Yili, Dowry eighth,’ described the measurement units of grain in ancient times. It said that 10 dou (斗) are equal to 1 hu (斛), 16 dou (斗) equal to 1 shu (籔), 10 shu (籔) equal to 1 bing (秉), 4 bing (秉) equal to 1 ju (筥), 10 ju (筥) equal to 1 ji (稯), 10 ji (稯) or 400 bing (秉) equal to 1 cha (秅). In different dynasties and various places, the units of grain may be not uniform. But, with historical changes, most of these units are no longer used. Now, in most cases, SI units are used in China. Nevertheless, some Chinese traditional units are still used. For length units, there are hao (毫), li (厘), fen (分), cun (寸), chi (尺), zhang (丈), and li (里). For the area units, there are square hao (平方毫), square li (平方厘), square fen (平方分), square cun (平方寸), square chi (平方尺), square zhang (平方丈), and square li (平方里). For units of area, there are li (厘), fen (分), mu (亩), and qing (顷). For mass units, there are hao (毫), li (厘), fen (分), qian (钱), liang (两), jin (斤), dan (担), and ton (吨). The unit liang (两) used now is not equal to what it was in the past. Now, 1 jin (斤) is equal to 10 liang (两), but in the past, 1 jin (斤) was equal to 16 liang (两). For volume units, there are cuo (撮), shao (勺), he (合), sheng (升), dou (斗), and shi (石). The relationship between Chinese metric (SI) and US units is shown in Table 2.

Standard Measures in Grain Science Units of Grain Harvesting In science, generally, and in grain science, specifically, the SI metric system of units is happily accepted. Yet, at harvest, farmers might still measure their grain yields in ‘bushels per acre,’ or even in ‘bags to the acre,’ with grain volume given in US bushels, Winchester bushels, hectoliters, or quintals. In ‘dry measure’ of volume, the US bushel is 2150 cubic inches or 8 gallons or 4 pecks or 32 dry quarts. One dry quart

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GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance

equals 67.20 cubic inches or 1.101 l. In the metric system, grain yield is measured in tonnes per hectare (t ha1), that is, units of mass per unit of area. However, the US tradition has been to measure yield in bushels per acre, that is, units of volume (not mass) per unit of area. The use of volumemeasurement units for grain in the United States makes it difficult to provide direct conversion between metric and US units for grain yield. To overcome this problem, the US government has defined the bushel for grains in commerce in terms of weight, irrespective of the true test weight. Standard volume–mass values for the various cereals are

• • • • •

1 bushel of wheat ¼ 60 lb, 1 bushel of maize ¼ 56 lb, 1 bushel of oats ¼ 32 lb, 1 bushel of barley ¼ 48 lb, and 1 bushel of rye ¼ 56 lb.

Thus, it is possible to convert grain yields, depending on the grain being considered. When the grain in question is wheat, 100 bushels per acre is 6000 lb per acre equal to 2723 kg for 0.4047 ha, or 6.73 t ha1. A rough ‘rule of thumb’ is to take the yield of wheat in pounds per acre and increase it by 10% to get kg ha1. Correspondingly, 1 t ha1 equates to 14.86 bushels per acre for wheat, 13.87 bushels per acre for maize, 7.92 bushels per acre for oats, 11.89 bushels per acre for barley, and 13.87 bushels per acre for rye. With the British ‘bag’ measuring 3 bushels, 1 t ha1 (15 bushels per acre) approximates to five bags to the acre – a farmer’s on-the-spot measure of wheat yield.

Units for Temperature Temperature is another case of difficulties for conversion, because the Fahrenheit and Celsius (centigrade) scales do not correspond at any reasonable temperature (they equate at 40 ). Conversion between the scales involves taking into account the differences between the scales in the slope (ratio of 9:5) and the freezing point of water (0 C and 32 F). To convert a temperature from Celsius to Fahrenheit, multiply C by 9, divide the result by 5, and add 32. To convert a temperature from Fahrenheit to Celsius, deduct 32 from the temperature in F, multiply by 5, and divide by 9.

Cereal-Based Foods and Nutrition Several articles in this encyclopedia relate to the food end of the grain production–utilization chain. It is thus necessary to explain units in this area, which eventually involves the home kitchen. These articles use units such as cups (CU), tablespoons (TB), teaspoons (tsp), and fluid ounces (FO). This last unit is defined in Table 1. Household units are more difficult to define. Their use in this encyclopedia is provided later in the text. These US measurements may use the same word for two measurements that are different. An ounce can be one-sixteenth of a pound (weight measure) or one-sixteenth of a pint (volume measure). A fluid ounce and an ounce of weight may be two different amounts, depending on the density of the ingredients being measured. In countries outside of the United States, cooks usually measure solid ingredients by weight. US measurements are based on fluid measures used for water or milk, for dry

ingredients such as flour and sugar, and for solid ingredients such as shortening. Commonly used equivalents are

• • • • •

1 tablespoon (TB) ¼ 3 teaspoons ¼ 15 ml, 1 teaspoon (tsp) ¼ 1/3 tablespoon ¼ 5 ml, 8 tablespoons ¼ ½ cup or 4 ounces or 1 teacup, 16 tablespoons ¼ 1 cup, and 1 cup (CP) ¼ ½ pint or 8 fluid ounces ¼ 237 ml.

The names of some British units have the same names as US measurements, but are not identical to US units. Overall, weights are equivalent but volumes differ. An English measuring cup (English breakfast cup) is 32% larger than the US cup, measuring 312 ml.

Chemistry Units Standard chemical units are used throughout the encyclopedia. These include estimates of the amounts and sizes of molecules, especially macromolecules, such as proteins. The mole (abbreviated to mol) is described in the preceding text as one of the seven basic units of the SI metric system, being (approximately) the amount of the substance expressed as its molecular mass in grams. The size of a molecule is given as its molecular mass in daltons (abbreviated to Da) or its relative molecular mass (Mr with no units). In both the cases, the number indicates approximately the size of the molecule as a multiple of the size of the hydrogen atom, taken to be 1 Da. More correctly, however, the unit is taken to be one-twelfth of the mass of the carbon nuclide 12C. The svedberg unit (S) is a less common unit used in relation to estimating the size of macromolecules. In particular, it is an estimate of the size of a protein molecule, based on how fast it sediments under the very large centrifugal force of the ultracentrifuge. This rate of sedimentation is measured in sedimentation units. One svedberg unit equals 1013 sedimentation units. The svedberg unit is often used, for example, to characterize the proteins of the legume grains. Examples are vicilin and legumin, which are indicated to be 7S and 11S, respectively.

Units for Cereal Chemistry Testing It is still normal practice for cereal chemists to measure the resistance to extension of a dough in Brabender units and to determine the activity of a-amylase (the enzyme that hydrolyzes starch) in Farrand units or in stirring number units. Such nonstandard units may not be a problem to people working in the same topic area; they have worked during the development of these methods of analysis. In some cases, these units may be intentionally perpetuated, because a manufacturer or inventor sees the names for these units as a valuable means of advertising. Although these units are meaningful and familiar for those who are using the test systems all the time, standard units would be more appropriate for the newcomer to the field. The adoption of standard units would also be conducive to international standardization of the method. This surely is the main reason for the use of SI units, namely, that they form a sound basis of universal understanding of what analytic results mean from one time to another and from one laboratory to another. In this encyclopedia, there is therefore the need to explain the basis for the nonstandard units of grain science,

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance as well as providing conversion tables for interchange between the metric and US units.

The Moisture Basis for Grain and Flour Data Irrespective of what units are used, it is important to be aware of the moisture basis on which composition data are based for grain and flour samples. For example, protein content may be quoted in various forms, namely, on a dry-weight basis, on a specified moisture content basis (e.g., 14.5% moisture), and on an ‘as is’ basis (the moisture content of the sample as it was at the time of testing). Figure 1 provides the means of converting values for protein content from a known moisture basis to either 11.0 or 13.5% moisture content. Furthermore, when flour milling is under consideration, ‘extraction’ terms may need to be clarified. For example, some mills base 100% extraction and mill capacity on the dry weight of wheat, whereas others base such estimates on the weight of wheat after the process of tempering, also known as conditioning, during which its moisture content is adjusted to a suitable level, often 14.5% moisture. Alternatively, mill capacity may be based on the production capacity for all flour products. A US flour mill making 78 000 lb of flour from 100 000 lb of wheat grain would be described as a 780 cwt mill in the United States, but not in Europe.

Measurement Units of Dough Testing Resistance Units and the Mixograph When American scientists Swanson and Working developed the mixograph, a recording dough mixer, in the early 1930s, the vertical axis of the mixograph trace was left unlabeled, providing no quantitative indication of the resistance of the

313

dough to mixing. In their 29-page article, they described how an early version measured watts of electric power to the mixer, not dissimilar to the direct-drive mixograph, developed in the 1990s with electronic data collection. In the first reports of the latter, the vertical axis was again labeled as ‘arbitrary units,’ but subsequently, procedures were developed to express the vertical (resistance) axis in grams of force for the conventional moving-bowl mixograph by attaching a pulley and calibration weights to the moving arm. Not only is this approach valuable, but also it can be complicated by the design of some mixographs to measure dough samples of differing sizes; as a result, the scale can be simply labeled as ‘% of full scale.’

Traditional and Newer Dough-Testing Equipment The Brabender Farinograph and Extensograph use a combination of SI units and ‘Brabender units’ (BUs) in the testing of various aspects of dough testing. No standard units have become adopted for the BU, so it remains as a measure that is meaningful for cereal chemists, who regularly use the equipment, or for those who are involved in interpreting the results, for example, wheat breeders. Recently developed research instruments for emulating the dough-testing processes of the Brabender Farinograph and Extensograph with very small dough samples (a few grams) have been designed specifically for automatic data capture, to correlate with the results from more traditional instruments, and to provide results in SI units, namely, in grams force (vertical axis of the mixing curve) and centimeters (horizontal axis). Other recently developed dough-testing instruments are calibrated and read out in SI units. In the case of the doughLAB (Figure 2), an instrument similar to the Brabender Farinograph, data are reported in either newton meters (N m), or

Figure 1 Conversion graph to permit the alteration of the protein content of a cereal grain sample from a known moisture basis: (a) to an 11% moisture basis or (b) to a 13.5% moisture basis. To do so, a ruler is used to join the observed protein content of the sample on the left-hand scale to the moisture content of the sample (right-hand scale). The point where the ruler crosses the inner scale is the protein content of the sample, based on either (a) 11% or (b) 13.5% moisture. Adapted from the Cereal Chemistry Division Official Methods, Royal Australian Chemical Institute, Melbourne, Australia.

314

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance

6000

Torque (mNm)

5000

4000

3000

2000

1000

0 0.00

2.00

4.00

6.00

8.00

10.00 12.00 Time (min)

14.00

16.00

18.00

20.00

Figure 2 (a) (Upper illustration) The doughLAB equipment, designed to provide dough-testing results in SI units (newton meters). Dough is mixed in the tiny chamber in front. (b) (Lower illustration) Mixing curve for a strong flour from the doughLAB, showing the vertical axis in millinewton meters. The mixing action produces a broad band of torque, whose width is indicated by the two outer traces. The inner trace shows the mean of the mixing curve. Resistance to mixing starts from zero and rises as the dough forms, reaching a maximum (for this sample) after mixing for 6 min. Thereafter, the resistance to mixing decreases only slightly, showing that this dough would have a good tolerance to overmixing in the bakery. A much greater decrease in ‘breakdown’ after the peak would be indicative of a weak flour, which would also have a shorter time to the peak of mixing torque. Illustrations provided by Perten Instruments, Sydney, Australia.

Farinograph units (‘FU’). The relationship between these units is unfortunately not constant, but differs with the choice of bowl, namely, that for the 300 g bowl, 500 FU ¼ 4.90 N m and for the 50 g bowl, 500 FU ¼ 0.98 N m.

Measurement Units of Enzymatic Activity and Starch Viscosity The Falling Number Unit One of the strange names for units in grain science is the ‘falling number unit,’ akin to the (also strange) stirring number

unit. The falling number method was developed in Sweden in response to the need for a means of quantifying the degree of sprout damage to grain as a result of premature germination caused by rain at harvest. It provides a measure of the enzymatic action of a-amylase on the endogenous starch for the germinating grain. It is applicable to several cereal species, especially wheat and rye. The results are provided as the number of seconds taken for a plunger to fall through a heated mixture of ground grain and water; a short falling time, for example, 100 s, indicates extensive sprout damage. One falling number unit is thus simply equal to 1 s of falling time, but nevertheless, the name falling number unit is still in common use in grain trading.

GRAIN COMPOSITION AND ANALYSIS | Grain Science and Trade: US, Chinese, and Metric Units Equivalance The Stirring Number Unit The ‘stirring number method’ was developed in 1984 and 1985 following widespread rain damage to the Australian wheat crop. Research was initiated to develop an instrument that could detect this damage, like the established falling number method, but would be robust and rapid, thus better suited to the harsh conditions of the Australian silo (grain-receival site). The instrument produced was called the Rapid Visco Analyzer (RVA), and a 3 min test was devised to detect sprout damage. The test works by using stirring action to mix and measure the viscosity of a slurry of wheatmeal and water as it is heated. Apparent viscosity is measured continuously as the power requirement of the stirring motor. The viscosity of raindamaged samples is markedly lower than that of undamaged grain because of starch hydrolysis by the sprouting enzyme. The stirring number unit (later renamed the ‘rapid visco unit’) was chosen for routine output from the method to provide results in a range that would make the measurement easily accessible to farmers and grain traders. The range chosen was near zero (poor-quality damaged grain) to 150 (goodquality sound grain).

The Rapid Visco Unit and Centipoise Nevertheless, at the outset of developing the RVA, the use of standard units of viscosity was seen as essential. Initially, the RVU was devised as a unit for the more general use of the RVA in characterizing starch properties. This unit of apparent viscosity can be related to international units through the relationship 1 RVU ¼ 12 centipoise (cP). Traceable calibrations were then developed for the RVA, which now provides data in centipoise (1 centipoise ¼ 1 millipascal second (an SI unit) abbreviated to mPa s).

Conclusion While there may be general agreement that it is desirable to standardize units of measurement, the world is still far from uniform in this respect. There may be less general agreement that the SI metric system is the only one by which standardization can be achieved; there is no other real contender. Until international standardization is adopted in practice, it will be necessary to provide conversion tables, such as are given in Tables 1 and 2. Nevertheless, the general agreement in the scientific community on SI units sets an example for the rest of the world, demonstrating the added efficiency of uniformity in units of measurement.

315


• • • •

With what system of units are you most familiar? Take some of the most familiar (and least familiar) units in that system and convert them into the other systems given here. Find a recent statistical report provided in your region and convert the units into the systems that are less familiar to you. Speculate on what today’s world of measurement might be like if Anglo-French cooperation had proceeded to success in the 1790s. Find and study the official publication on standard units for your country.


• • •

See if you can determine the present state of affairs with respect to the general worldwide adoption of the SI metric system of units, especially in the United States and China. What impediments to international grain trading are provided by the lack of agreement about measurement units? Are you aware of any significant incidents in grain science and trade caused by confusion about units of measurement?

See also: Food Grains and the Consumer: Labelling of GrainBased Foods; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; The Composition of Food Grains and Grain-Based Products; Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading International Standards Organization (1993) ISO Standards Handbook: Quantities and Units, 3rd edn. Geneva, Switzerland: International Standards Organization. Lentner C (1981) Geigy Scientific Tables. Volume 1. Units of Measurement, Body Fluids, Composition of the Body, Nutrition. Basle, Switzerland: Ciba-Geigy Ltd. Standards Australia (1998) The International System of Units (SI) and Its Application. AS ISO 1000–1998. Standards Australia, Sydney, Australia. Wrigley CW (2010) Equivalence between metric and US units for the grain industry. Cereal Foods World 55: 32–34. http://dx.doi.org/10.1094/CFW-55-1-0032.




GRAIN-BASED PRODUCTS AND THEIR PROCESSING EDITORS




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deceased


Academic Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB 225 Wyman Street, Waltham MA 02451 First edition 2004 (as Encyclopedia of Grain Science) Copyright © 2016 Elsevier Ltd. All rights reserved The following articles are US government works in the public domain and are not subject to copyright: Grain Crops, Overview; Maize Overview. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers may always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library SET ISBN 978-0-12-394437-5 VOLUME 1 ISBN 978-0-12-803537-5 VOLUME 2 ISBN 978-0-12-803536-8 VOLUME 3 ISBN 978-0-12-803535-1 VOLUME 4 ISBN 978-0-12-803538-2

For information on all publications visit our website at http://store.elsevier.com Printed and bound in the UK.


CONTENTS Preface

xvii


xix


xxiii xxv xxvii


1

The Basics

1


1



13

H Corke


16

RA Graybosch


22

CW Wrigley


31



41

H Corke


51

J Wyatt

The Cereal Grains

73


73

CW Wrigley


86

LA Morrison

Maize: Overview

99



105

CW Wrigley

v

vi

Contents


117


Rice: Overview

125

BO Juliano


130



140



147



153

A Cruickshank


159


Triticale: Overview

168

BJ Furman

Oats: Overview

173

PK Zwer

Coix: Overview

184



190

JRN Taylor


199


Teff: Overview

209

G Bultosa

The Oilseeds

221

Oilseeds: Overview

221

RJ Mailer

Soybean: Overview

228

K Liu

Canola: Overview

237

VJ Barthet


242

E Hernandez

Sunflower: Overview

247



254

C Hall III

Linseed: Overview

259

S Cloutier


265


265

TE Michaels

Contents


vii

274

RJ Fletcher

Lupin: Overview

280

DS Petterson

Amaranth: Overview

287


Beans: Overview

297

SK Sathe

Buckwheat: Overview

307


Chickpea: Overview

316


Pea: Overview

324


Peanuts: Overview

334


Quinoa: Overview

341



349


349

T Beta and C Isaak


359

JRN Taylor


367



374

H Corke and YZ Cai


383

MG Lindhauer


391

JA Fox and LL Ward


401



409



420



429


429

JH Skerritt


436

JH Skerritt


444

viii

Contents


451

JH Skerritt


457



1


1


1

G Bultosa


11

G Bultosa


17

AM Fehily


23


23



29



35



43

CM Rosell


50



57

JM Jones

Grains and Health

63



72

Cereal Allergens

72

AS Tatham


77

KJ Carpenter

Celiac Disease

83



91


Proteins

98


98



109

Contents


ix

115


Nitrogen Metabolism

123

CA Atkins


129



138



146



154


Carbohydrates

161


161


Starch: Chemistry

174

FL Stoddard

Starch: Synthesis

181



190



198



208

GB Fincher


224

L Ramsden


230

A Evans


236



241

D Dan Ramdath

Fats

248

Lipid Chemistry

248

L Day


257



268


268

HD Sapirstein


277

x

Contents


283


Mycotoxins

290



297


297

CW Wrigley


300



308



1

Wheat-Based Foods

1


1

CF Morris

Breads

8

TR Moore


19

KJ Quail


25

SP Cauvain


30

DE Ortiz


37

SP Cauvain


44



51



59


Noodles: Starch

64



72


Pasta

79

M Sissons

Tortillas

90


Non-wheat Foods

97


97

SO Serna-Saldivar

Contents


xi

110

S Lu


116



124

DK O’Toole


134

DK O’Toole


144


144



154



161



166

JS Bao


176


176

BJB Wood


183

JRN Taylor


193

GH Palmer


206

DK O’Toole


215


215

JL Black

Pet Foods

223

RCE Guy


228

L Munck


235


Biodiesel

245

Y Yan


251


251

CF Morris


257

xii

Contents


262



268

RCE Guy


274

JW Lawton


282

JN BeMiller


287

MS Izydorczyk

Wheat Processing

299


299


Wheat: Dry Milling

307



320


Oven Technologies

325

CE Walker


335



343

B Dobraszczyk

Frozen Dough

354


Refrigerated Dough

359



367

TS Palav


375



384



396

L Day


403



408



414

MN Riaz


423

Barley: Malting

423



434

Contents


xiii

446

L Pallas


453

JS Godber

Maize: Dry Milling

458


Maize: Wet Milling

467



482


482

C-Y Ma

Soybean: Processing

489

T Wang

Canola: Processing

497



1


1


1


Wheat: Marketing

9



16



25



29



42


42



50

RJ Henry


54



62

JJ Mayko


68

SA Barton


74



83

xiv

Contents


99

PC Annis


105



110

PC Annis


117

F Fleurat-Lessard


126

F Fleurat-Lessard


140


140

S Ceccarelli


144

L Munck


154



162

EC Leonard


168

SA Barton

Wheat: Agronomy

176


Barley: Agronomy

186


Maize: Agronomy

194

ED Nafziger


201

WL Rooney

Canola: Agronomy

207


Chickpea: Agronomy

216


Lentil: Agronomy

223


Lupin: Agronomy

231

RJ French

Field Pea: Agronomy

240

RJ French

Soybean: Agronomy

251

ED Nafziger


257



264

Contents


xv

273


Breeding of Grains

279


279



287


Maize: Breeding

296


Rice: Breeding

304



311


Lentil: Breeding

317


Lupin: Breeding

325



333


Genetics of Grains

343


343

L Privalle


350

RD Shillito


360

RJ Henry

Genome Mapping

365


Wheat Genetics

376

RA McIntosh


382

E Akhunov


388



393


Rice: Genetics

398

JS Bao and H Corke

Maize: Genetics

407

EA Lee


420

JS Li and SK Vasal


425

xvi

Contents


433



450



460


Glossary

467

Index

491




xvii

xviii

Preface


• Members of the Editorial Advisory Board; • Authors who have shared their special knowledge and experience; • Elsevier staff who have provided extensive advice and administrative services, especially Donna de Weerd-Wilson, Simon Holt and Rachel Gerlis (successive Supervisory Staff) and Gemma Tomalin, Gemma Taft, Joanne Williams and Mark Harper (successive Content Project Managers). The Editors Harold Corke, Jon Faubion, Koushik Seetharaman, and Colin Wrigley




xix

xx






xxi





xxiii










xxv




















xxvii

xxviii

Contributors















Contributors






xxix


xxx

Contributors















Contributors


xxxi








CK Madsen Aarhus University, Slagelse, Denmark RJ Mailer Australian Oils Research, Lambton, NSW, Australia JT Manful Africa Rice Center, Cotonou, Republic of Benin AG Marangoni University of Guelph, Guelph, ON, Canada DJ Mares University of Adelaide, Glen Osmond, SA, Australia L Marquart University of Minnesota, St. Paul, MN, USA; Grains for Health Foundation, St. Louis Park, MN, USA A Marti Universita` degli Studi di Milano, Milan, Italy

CS Moffat Curtin University, Bentley, WA, Australia ES Monyo ICRISAT, Nairobi, Kenya TR Moore AIB International, Manhattan, KS, USA MK Morell International Rice Research Institute, Los Banõs, Philippines CF Morris USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA LA Morrison Oregon State University, Corvallis, OR, USA

B Maschoff Grains for Health Foundation, St. Louis Park, MN, USA

WK Mousa University of Guelph, Guelph, ON, Canada; Mansoura University, Mansoura, Egypt

A Mathiowetz University of Minnesota, St. Paul, MN, USA; Rochester, MN, USA

K Mrva University of Adelaide, Glen Osmond, SA, Australia







xxxii

Contributors















Contributors


xxxiii










xxxiv

Contributors

















GRAIN-BASED PRODUCTS AND THEIR PROCESSING Wheat-Based Foods

Contents Cereals: Overview of Uses: Accent on Wheat Grain Breads Flatbreads of the World Sour Dough Technology Cakes, Muffins and Bagels Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics Cookies: A Diverse Family of Baked Goods Wafers: Methods of Manufacture Cookies and Crackers: Commercial Production Noodles: Starch Noodles: Asian Wheat Flour Noodles Pasta Tortillas

Cereals: Overview of Uses: Accent on Wheat Grain CF Morris, Washington State University, Pullman, WA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

The major cereals are wheat (bread wheat, soft wheat, and durum), rice, maize, barley (malt and feed), sorghum, millets, oats, rye, and triticale. Individual quality traits are variably affected by genetics and the environment. Wheat is the most complex cereal in terms of end-use quality and variety. Major categories of wheat foods include fermented breads, steamed breads, flat breads, crackers, cookies, cakes, noodles, ready-to-eat (RTE) cereals, pasta, and couscous.

The ‘fruit’ of cereal plants is a ‘caryopsis,’ wherein the seed coat is fused to the fruit wall. The caryopsis may be referred to as a kernel and, in mass, is referred to as grain. Cereal plants go through a preprogrammed physiological death, associated with crop ‘maturity.’ Cereal grains are harvested as soon after maturity as possible and, depending on the climate, may be artificially dried to a safe storage moisture content, usually below 12%. The uses of cereal grains are a direct interaction between the physical and chemical compositional attributes of cereals and human nutritional, cultural, and aesthetic features. Consequently, to understand cereal quality, one must appreciate the array of end uses of the various cereals. The major cereals and their uses are presented in Table 1. The remainder of this article focuses on the uses of wheat.

Learning Objective

•

To know the major cereals and what ‘defines’ a cereal, understand why cereals are important for food and feed, and know the major uses of wheat.

How Are Cereals Used? Cereals are grass species of the Poaceae family, in general, monocotyledonous annual flowering plants grown in monoculture.


General Considerations The success of cereals as food and feed crops stems from the ability to store easily the grain produced from them for a long period of time. Compare this feature to fruits, vegetables, and meats. Add to this the productivity and broad adaption of most cereal crops and their relatively high nutritive characteristics, and it is clear why cereals play a prominent, central role in agriculture. The prominence of the major cereal crops is evidenced by their production: about 962 Mt annually for maize,

http://dx.doi.org/10.1016/B978-0-12-394437-5.00142-X

1

2

WHEAT-BASED FOODS | Cereals: Overview of Uses: Accent on Wheat Grain

Table 1

Major cereals and their uses

Common name Wheat Bread wheat

Genus and species Triticum aestivum L.

Soft wheat

Triticum aestivum L.

Durum wheat

Triticum turgidum L. subsp. durum (Desf.) Oryza sativa L. Zea mays L.

Rice Maize (corn, US) Dent, floury, flint

Popcorn Sweet corn Barley Malting barley Feed barley Rye Triticale Oats Grain sorghum Millet(s)

Major uses Many styles of pan breads, hearth breads, noodles, starch and gluten, animal feed Cookies (biscuits), cakes, pastries, noodles, animal feed Pasta, couscous

Polished rice (staple food) Animal feed, dry milling (production of grits), wet milling Snack food As a cooked vegetable

Hordeum vulgare L.

Secale cereale L. Triticosecale sp. (Wittmack) Avena sativa L. Sorghum bicolor (L.) Moench Various species

Beer and brewing Animal feed Animal feed, bread Animal feed Animal feed, porridge, snacks Animal feed, food, brewing Food, animal feed

708 Mt for wheat, 473 Mt for rice (milled), 141 Mt for barley, 63 Mt for sorghum, 31 Mt for millets, 23 Mt for oats, 16 Mt for rye, and 14 Mt for triticale. Since all of the cereal grains are botanically related, and all of the grains are technically caryopses, some general descriptions of cereal grains can be made. All cereal grains are composed primarily of an endosperm attached to a germ (embryo) via a scutellum, all of which are enclosed in several layers of tissues collectively referred to as the bran. These three different parts have quite different biological roles and hence quite different compositions and structures. Because of these differences, humans utilize each in markedly different ways. The endosperm is the key feature of cereal grains. For the cereal crops of significance, most have endosperms composed of starch (60–75%), protein (6–19%), fiber (3–8%), and oil (1–4%). In contrast to most grain legumes, tree nuts, and horticultural crops, cereal crops store most of the energy for germination and seedling emergence in the form of starch. Nitrogen reserves are deposited in the grain in the form of protein ‘bodies’ and ‘matrix’ protein, the latter surrounding the starch granules and protein bodies. Cereal germs are relatively rich in oil. In the case of wheat, millers desire to remove the germ because its oil contributes to rancidity of flour. In maize, the germ contributes to the feeding value (energy) of the whole grain and is the source of food oil in the milling process. Cereal bran is a rich source of vitamins, minerals, and phytochemicals. Although ‘whole grain’ foods are receiving greater consumer interest, traditionally, the bran of wheat

and rice – the two leading cereals of the Old World – was removed during a milling process. In the case of rice, bran removal converts ‘brown’ rice to ‘polished’ rice. In the case of wheat, bran is removed during roller milling. Additionally, cereal grains may be enclosed in vegetative tissues, the lemma and palea, collectively referred to as the hull, which can be fused to the caryopsis (in the case of barley), or simply be mechanically resistant to removal such that the harvested ‘grain unit’ is the caryopsis enclosed in the hull (as in the case of rice, oats, and the hulled wheats spelt, emmer, and einkorn). The hull is of little direct value since it is largely cellulose and is undigestible by humans and most livestock. Consequently, the hulls are removed during processing for human food. However, the husk is an important part of the filtration process in brewing with barley malt and can protect the seed – especially the germ – from mechanical damage during harvest as in the case of oats and einkorn.

Wheat The end-use quality of wheat is by far the most complex of all the cereal grains. This complexity reflects the tremendous diversity of the genetics of wheat, the tremendous diversity of the uses of wheat, and the central role that wheat plays in the diet of much of humankind. Wheat has distinguished itself from all other cereals and grain legumes because of the unique properties of its endosperm storage proteins. These proteins, classified as glutenins and gliadins, when hydrated and mixed (by hand or machine), form ‘gluten.’ Gluten is unique in that it exhibits both viscous and elastic properties. These properties allow gluten to form a continuous membrane, which can retain the gases produced in fermenting doughs. The retention of these gases greatly decreases the density of doughs, and upon baking, this light, airy structure is fixed. A simple model describes a dough ‘foam’ transformed to a ‘sponge.’ An almost limitless number of foods are made from wheat. Wheat flour, starch, bran, etc., are also important food ingredients. Table 1 lists the major uses of wheat and flour. The quality of a particular flour is not necessarily low or high until it is judged in the context of a particular end use. For example, a flour that exhibits very high bread baking quality generally also has very poor cookie or cake baking quality. Therefore, wheat quality is defined by an almost infinite number of different food products that contain flour, starch, gluten, bran, whole and cracked grain, sugar, fats, oils, etc. The majority of wheat is first milled into flour, and consequently, the miller is in a central and critical position in the utilization of wheat as a food. The miller takes a raw material of biological origin and converts it into a food ingredient for countless numbers of diverse food products. Much of the day-to-day success of the baker is a direct result of the miller’s technical ability and expertise. In this regard, the overriding aspect of flour quality is consistency of performance. This endeavor is by no means simple or straightforward. Wheat is a biological entity and as such can vary dramatically over geographic locations, over years, and importantly, among different cultivars. In one sense, it is the miller’s task to remove this variation and thereby produce a consistent product.

WHEAT-BASED FOODS | Cereals: Overview of Uses: Accent on Wheat Grain The various categories of wheat foods described in this article include pan, hearth and other fermented (leavened) breads, steamed breads, flat breads and crackers, cookies, cakes and other soft wheat products, noodles, breakfast foods, and pasta and durum wheat products.

Fermented (Leavened) Breads Leavened breads include traditional white pan, variety, hearth and sourdough breads, sweet goods including yeast-leavened doughnuts, and bagels. Rolls are simply smaller-sized products and may be similar to other, larger breads and sweet goods. Leavened breads are characterized by a crumb texture that is light, airy, and porous, yet chewy. One of the primary determinants of this texture is the quantity and quality of the gluten protein. By far, the most common type of leavened bread in the West is white pan bread made from straight-grade or patent flours of hard spring and winter wheats. White pan breads require high flour water absorption, medium to strong dough mixing strength, extensible gluten, and good fermentation and mixing tolerances. Large loaf volume and fine, smooth crumb grains are desirable. A smaller version of pan bread is the sandwich bun. Variety breads are embellished versions of white pan. These breads are prepared using whole-wheat flour and/or as many as a dozen different ancillary ingredients. Hearth breads were the forerunners of pan breads. Hearth breads are baked on the oven floor or sole. As a consequence, they range from having an ovate or nearly spherical shape to one approximating a horizontal cylinder. In addition to affecting the shape, the absence of baking pans exposes the entire bread surface to the oven environment. This large, exposed surface area produces the greater crust-to-crumb ratio characteristic of hearth breads. Perhaps, the most famous hearth bread is the French baguette. Many hearth breads are characterized by long fermentation and no antistaling additives. Sourdough bread is similar to white hearth bread except for its characteristic sour, acidic flavor and extra chewy texture. Sweet goods, on the other hand, are characterized by rich formulas high in fat and sugar and contain milk solids and eggs. These products are more varied but generally require flours similar to other leavened breads. Products include yeasted doughnuts, cinnamon rolls, coffee cakes, Danish and puff pastries, and French brioche. Doughnuts are of two general types: yeast-leavened and cake. The unique characteristics of doughnuts are their traditional ring shape and the method of frying in hot oil. Yeastleavened doughnuts are similar to bread in that they are made from yeast-fermented doughs. Bagels are doughnut-shaped rolls. The word ‘bagel’ comes from the Austrian–German word bugel, meaning stirrup. Bagels were invented over 300 years ago to honor Jan Sobieski, king of Poland and famed equestrian. Bagel doughs are retarded for up to 20 h and then boiled just prior to baking. Retarding refers to a secondary fermentation conducted at low temperature, i.e., by placing the dough under refrigeration. A traditional style of bagels has a very chewy texture, whereas many commercial styles have the texture of pan bread.

Steamed Breads Asian steamed breads are simply breads that are steamed, rather than baked. As such, they lack the brown crust that is

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characteristic of oven-baked breads. They may be plain or with a sweet bean paste or savory meat filling. Steamed breads are traditional wheat foods in China, Japan, the Philippines, and other East Asian countries. Two main types are consumed in China: northern style and southern style. Northern style is larger and chewier and is made from the higher-protein, stronger gluten wheats of that region. Southern style is smaller, of lower density, and often sweeter.

Flat Breads and Crackers Flat breads, crackers, and tortillas are usually no more than 6 cm and often less than 3 cm thick. Most flat breads and tortillas are higher in water content than crackers and are therefore chewy as opposed to crisp. Tortillas and most crackers have no discernible crumb and crust. The majority of flat breads are consumed in North Africa, the Middle East, and the Indian subcontinent. Major types include ‘chapati,’ ‘roti,’ ‘naan,’ ‘paratha,’ ‘poori,’ ‘balady,’ ‘pita,’ and ‘barabri.’ These breads typically have high crust-to-crumb ratios and limited crumb. They are generally baked at very high temperatures for very short time periods (e.g., 550 C for 30 s). Flat breads are typically produced from high-extraction (75–90%) or wholewheat flours. Due to the higher bran content of these flours, white wheat is preferred for a lighter color. Much less gluten strength is required compared to pan and hearth breads for two reasons: (1) The limited crumb does not require much gasholding capacity, and (2) many of these breads are prepared by hand and weaker gluten is easier to mix and handle. Due to their geometry and structure, tortillas, pizza crust, English muffins, crumpets, and pretzels can be considered flat breads. Tortillas are flat breads traditionally made from wheat flour or maize and are indigenous to Mexico, Central America, and the southwestern United States. Particularly in the United States, tortillas are used in many convenience foods, more similar to sandwiches, and are commonly referred to as ‘wraps.’ Pretzels are unique because they receive an intermediate processing step. Two types of pretzels are popular. The first tends to be small (about 10 cm) and may be in the characteristic twisted shape or other configurations such as short, straight sticks or rings. These products are baked and then dried to about 2–3% moisture content and have a crunchy texture and a relatively long shelf life. The second type, soft pretzels, tends to be much larger, up to 30 cm, with the baked dough piece diameter about 2–4 cm. Moisture content is higher and the texture resembles chewy bread. In addition to the characteristic twisted shape, the feature that sets pretzels apart is the use of caustic lye (usually 1.25% NaOH). The dough pieces are immersed briefly in hot lye solution, baked, and then sprinkled with coarse granular salt. Pizza crusts in the United States are typically made from higher-protein, stronger gluten flours. English muffins and crumpets are flat breads characterized by a coarse, open grain, grilled top and bottom with light sides, and a flat disk geometry. Crackers are characterized by a thin geometry, low water content, and crisp, crunchy texture. Crackers are popular in North America, Europe, and Australia. Products include soda crackers, cream crackers, water biscuits, graham crackers, sprayed crackers, and savory crackers. Soda crackers, or

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saltines, are the most definitive cracker product. They are prepared by a sponge–dough system with a long sponge ferment. Fermentation is partially accomplished by lactic acidproducing bacteria, which lower the pH to the point where flour proteases become active and lead to a partial hydrolysis and weakening of the gluten polymer. Sodium bicarbonate (hence the name soda cracker) is added at the dough stage to neutralize the drop in pH. Sheeting of doughs is accomplished by a system wherein multiple layers of dough are combined and then ‘docked.’ Steam expansion between dough layers results in the characteristic flaky texture.

Cookies, Cakes, and Other Soft Wheat Products Soft wheat is used in many diverse food products. In some, it is the major ingredient, but in others, it ranks second or third. Soft wheat is used in these applications because (1) the stronger gluten and higher-protein levels of hard wheat reduce product quality, (2) soft wheat flours have lower levels of starch damage and consequently lower water absorption and dough viscosity, (3) soft wheat flours generally have a finer texture or smaller particle-size distribution, and (4) soft wheat is often cheaper than hard wheat and thus reduces ingredient costs. Often, a blend of the two types provides an intermediate level of gluten strength. As opposed to hard wheat flour, where the inherent strong viscoelasticity of gluten is the primary reason for its use, soft wheat flour usually has weak, extensible gluten. This lower strength of gluten translates into the soft, tender texture of soft wheat products. The major food uses of soft wheat flour are chemically leavened crackers, pie crust, cookies (biscuits), American-style biscuits, scones, moon cake, products made from batters such as sugar wafer cookies, ice cream cones, pancakes and waffles, cakes, tempura, breadings, and soup thickeners. Chemically leavened crackers are similar to fermented crackers except for their method of leavening, which is usually sodium bicarbonate with an acidifying salt. Pie crust has a high fat content and little structure; it is usually sheeted. Cookies (biscuits) generally have limited threedimensional structure, a high content of sugar and fat, and generally a low moisture content. Most are chemically leavened to reduce product density and impart a desirable texture. The major types of cookies (from lowest to highest water content) are rotary-molded, cutting machine, wire-cut, and deposit varieties. In the United Kingdom and its former colonies, chemically leavened cookie doughs are classified as short-dough sweet biscuits (sweet biscuits, short doughs, or short sweet doughs) and hard-dough semisweet biscuits. ‘Marie’ and ‘Rich Tea’ are popular examples of hard-dough semisweet biscuits. In these products, gluten is partially developed. Shortdough sweet biscuits may be classified according to the US system. In rotary-molded cookies, the dough is pushed into dies cut on the surface of a smooth cylinder, excess dough is scraped off, and the cookie is released onto a canvas conveyor and moved to the oven. The dies produce three-dimensional raised designs, which are maintained after baking. Often, a cream filling is deposited between two cookies (i.e., ‘sandwich’ cookies). Cutting machine cookies are produced from a sheeted

dough. Various shapes are cut from the dough sheet and baked. The wire-cut cookie is the most common commercial cookie in the United States. A popular variation includes chocolate chips. Wire-cut cookies are produced by passing a taut wire through a stream of extruded dough. Individual dough pieces drop onto a belt and are conveyed to the oven. Deposit cookies are made from higher-moisture doughs, some approaching the viscosity of cake batters. Deposit cookies are produced by extruding the dough through nozzles where reciprocating cutters release the dough onto the conveyor or oven band. Popular variations are the vanilla wafer and Danish butter cookie. Batter products include some low-moisture, crisp products such as wafer cookies and ice cream cones, griddle cakes such as pancakes and waffles, a vast array of higher-volume cakes, and coatings such as tempura. Pancakes are relatively thin, round cakes prepared by cooking batter on a hot griddle or pan. Oil on the griddle surface fries the outer surface of the pancake to a golden brown. Waffles are prepared from similar batters but are cooked in a two-sided griddle, which imparts the characteristic three-dimensional structure and crisp texture. Where pancakes are fried in a thin layer of oil, doughnuts are completely immersed in hot cooking oil. Cake doughnuts, in contrast to yeast-leavened doughnuts, are made from a formula similar to a standard layer cake, which uses both chemical leavening and incorporated air to obtain the desired low product density. Cakes are baked foams and usually have substantially higher proportions of fat and sugar compared to breads. Cakes derive their light, porous texture through the use of leavening agents such as sodium bicarbonate and/or through the entrapment of minute air bubbles. Like cookies, cakes exhibit little gluten development; gluten development is detrimental to cake quality and imparts an undesirable tough chewy texture. In contrast to cookies that have generally less than 2–3% moisture, cakes are formulated to produce tender, moist textures. Cakes, depending on type, may have amounts of sugar, eggs, and fat in their formula that exceed the quantity of flour. In high-ratio cakes, as the name implies, sugar-to-flour ratios may range from 1 to as high as 1.2. In the case of angel food cake, sugar and egg whites may each exceed flour by a ratio of 2.75. Cakes are made from batters with substantially lower viscosity than cookies or bread doughs. Consequently, the stable entrapment of minute air cells is critical to cake volume and texture. The formation of emulsions with formula fat or egg lipids is crucial for the entrapment of air bubbles and for preventing the establishment of a continuous gluten network. In many cakes, the structureforming role of egg white or whole egg protein is important. Cakes are often highly flavored with high proportions of chocolate, fruit, and other ingredients. Some of the main classifications of cakes are high-ratio, pound, chocolate, yellow layer and white layer, sponge, Swiss roll, chiffon, angel food, cupcakes and muffins, and Japanese castella varieties. Tempura is a traditional Japanese batter used to coat seafood and vegetables prior to deep-fat frying. Breadings, like tempura, are used to coat foods and often to impart a crunchy texture. Soup thickeners are used to provide a high viscosity to soups. Therefore, starch plays the most important role and flours must be free of amylases associated with preharvest sprouting.


Noodles In this article, differentiation is made between noodles prepared from common, or hexaploid, wheat flour and pasta prepared from durum semolina. Noodles may be generally defined as boiled ‘strings’ of unleavened wheat dough. However, this definition has many exceptions and caveats due to the tremendous diversity of noodle products. Most noodles are produced and consumed in Eastern Asia, and as such, their use runs parallel to bread consumption in the West. Noodles are the traditional form in which wheat is consumed and predates recorded history. In addition to rice, noodles form the foundation of the carbohydrate-based diets in that part of the world. Although tremendously diverse, the vast majority of noodles are prepared from very simple formulas: flour, water, and salts. Because of this, wheat flour quality is particularly critical in determining noodle quality and consumer acceptance. For the purposes of classification and discussion, noodles may be grouped according to formulation (primarily, type of salts), noodle geometry, method of preparation, post-preparation processing, method of packaging, and manner in which they are consumed. Based on formulation, noodles may be classified as white salted, alkaline, ‘soba,’ or egg. Additionally, ramen or instant noodles are noteworthy. A number of noodle-like sheeted products include egg roll, pot sticker, and wonton wraps. The three main features of white salted noodle quality are color, appearance, and texture. Noodle color should be clear and bright, not dull or dark. The leading factor in good color is the absence of discoloring enzymes called polyphenol oxidases. The noodle should appear smooth with a glossy surface and should have square, well-defined edges, rather than rounded ones. Texture and biting characteristics vary according to cultural preference: For Japanese udon, the texture should be soft and elastic. For Mandarin Chinese (‘gan mian’) and Cantonese (‘kon mien’), the texture should be firm and chewy. Wheat and flour quality characteristics that contribute to these desired quality traits include good milling characteristics with ease of bran separation, bright endosperm, and flour color. For udon noodles, weak but extensible gluten, relatively high starch paste viscosity, low amylase activity, and lower starch amylose content are desirable. Usually, soft white wheat is preferred. For white salted Chinese noodles, high-protein, stronger gluten flours are preferred, similar to those used in bread. In this case, a normal level of starch amylose contributes to a firmer texture. Alkaline noodles, as the name implies, are prepared using alkaline salts. A typical formulation would include 1–3% NaCl and 1–3% alkaline salts (flour weight basis). Alkaline salts, often referred to as kansui (‘can soo-ee’ or ‘can-swee’), may be composed of combinations of potassium and sodium salts of carbonate (K2CO3 and Na2CO3) and/or sodium hydroxide. Like white salted noodles, the main quality attributes of alkaline noodles are color, appearance, and texture. Color should range from creamy white to yellow. Appearance should be bright, not gray or dull, with as few specks as possible. The color should be stable and should not deteriorate during storage. Texture should be elastic, rather than weak and soft, and should not soften or deteriorate during storage. Milling

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quality, endosperm color, gluten characteristics, and starch pasting quality all contribute to alkaline noodle quality. Alkaline noodles are typically prepared from higher-protein, stronger gluten hard wheats, similar to those used for bread. Two popular variations on the basic, simple formula include buckwheat and egg noodles. Buckwheat noodles, called soba, are made from wheat flour and buckwheat (Fagopyrum esculentum Moench): about three parts wheat flour to one part buckwheat flour. Egg noodles, as the name implies, are prepared using eggs and may be prepared using whole fresh eggs as the only source of formula liquid. In the United States, dry egg noodles contain at least 5.5% egg solids. Convenience is an important force that drives consumer spending. In the United States, Japan, and Korea, instant noodles, which have been fried in hot oil, cooled, and packaged, provide a quick and easy meal. Some are packed in ready-toserve cups or bowls and almost all come with a seasoning sachet and often include dehydrated vegetables and meat.

‘Ready-to-Eat’ Cereals and ‘Breakfast’ Foods Although many rolls, breads, noodles, etc., are eaten at the first meal in the morning, ‘RTE’ cereals and breakfast foods are popular in many parts of the world. RTE foods are cerealbased foods, which require no cooking. Generally, flaked, extruded, steamed, puffed, or shredded process gelatinizes starch, denatures protein, and develops texture. These processes often dramatically reduce the bulk density of the product. Most of these foods have very low moisture content and consequently can be stored for long periods of time. A high proportion of these products are sweetened and flavored to appeal to consumer tastes. Popular brands are produced by General Mills, Kellogg’s, Nestle´, Post, Uncle Tobys, Malt-OMeal, and other companies. These and similar products are made from wheat, rice, maize, and other cereals. Soft white wheat grain with large kernels is preferred for easy flaking and better color after roasting. More traditional wheat-based ‘breakfast’ foods include products similar to oatmeal porridge and other cooked cereals.

Pasta and Durum Wheat Products Alimentary paste, or ‘pasta,’ is prepared from extruded dough pieces of various shapes and sizes, usually dried during production and later boiled and consumed. A common classification is based on whether the pieces are long or short (e.g., spaghetti vs. macaroni). In contrast to the noodles described earlier, pasta is prepared from durum (Triticum turgidum subsp. durum) semolina. Although Italian in origin, pastas – such as spaghetti, macaroni, lasagna, and fettuccine – are now a common part of culture and language in the United States and worldwide. Some pasta products contain fillings, such as tortellini and ravioli with cheese or meat. The production of semolina is the primary goal of durum wheat milling. Semolina is simply larger-sized pieces of endosperm (compared to flour), free of adhering bran. Semolina size ranges from about 130 to 550 mm. In addition to the particle size of semolina, color, vitreousness, and protein quantity and quality are key quality traits. Higher levels

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(>13%) of strong gluten are preferred. The protein must form a continuous matrix to entrap the starch granules so that the pasta surface does not become sticky during cooking. In most cases, the addition of hexaploid wheat to pasta is considered undesirable and is illegal in some countries. As mentioned earlier, pasta is an extruded product. Semolina is first mixed with water in an approximate ratio of 30:100 (water/semolina) into a stiff dough. The dough is forced at high pressure through a die to produce the desired shape and size. The pasta is then collected and dried. Mixing, kneading, and drying are critical steps to successful pasta manufacture. Other nonpasta durum wheat products include primarily bread, couscous, and bulgur. Durum bread is prepared from durum flour, rather than semolina. The salient differences between typical hexaploid and durum wheat flours are coarser particle size, higher starch damage, higher water absorption, strong gluten with low extensibility, high dough stability, and yellow color of durum flour. Due to the high levels of damaged starch and water absorption of durum flour, durum bread stales much more slowly and consequently has an extended shelf life, compared with hexaploid wheat bread. Couscous and bulgur are precooked, unleavened foods traditionally consumed in North Africa and the Middle East. Couscous is prepared from semolina by hydrating, mixing, steaming, drying, and size fractionating the resultant particles. Couscous is then rehydrated with oil and meat and/or vegetable sauce when eaten. Bulgur, on the other hand, is prepared from whole or cracked kernels by soaking in water, parboiling, drying, and grinding. Prior to eating, bulgur is boiled or steamed.

Starch and Gluten Wheat starch and gluten each have unique compositions and properties. Consequently, it is useful to isolate each in a relatively pure form. Separation is accomplished through one of the three general methods: Martin and batter processes and differential centrifugation. All three typically employ rollermilled flour, usually harder, higher-protein, stronger gluten wheats. The Martin process mixes flour and water into a dough and then washes out the starch and water-soluble constituents. Usually, NaCl is included to promote gluten agglomeration. Small aggregates of agglomerated gluten are recovered by sieving. In both the Martin and batter processes, starch is recovered through centrifugation/hydrocyclones. Differential centrifugation separates nonaggregated gluten from starch, the main advantage being reduced wash water. Once separated, most gluten is dried and sold as a free-flowing powder. The primary reason for starch–gluten isolation is to obtain vital gluten. ‘Vital’ refers to the fact that the isolated gluten retains its functional viscoelastic (and therefore breadimproving) properties. The main use of vital gluten is in yeast-leavened bread products, especially variety breads where the load of nonfunctional ingredients is relatively high and flour protein is diluted. Vital gluten helps maintain product volume and internal structure. During isolation, controlled drying is key to maintaining the functionality of vital gluten. Excessive heat denatures gluten and renders it nonvital. Nonvital gluten, though of little value in baking, does find application in pet foods and other uses.

In the United States and other countries with large quantities of maize, wheat starch is of minor importance, gluten being the primary reason for starch–gluten separation. In countries such as Argentina and Australia, however, starch is an important coproduct. After isolation, starch is usually further processed into sugar syrups, ethanol, and specialty modified starches. In this regard, wheat starch use parallels maize.


• • • • •

What is a working definition of ‘quality’? What are the major cereals and approximately how much of each is grown worldwide? What are the major constituents of the cereal grain? What determines the major uses of cereals? What is starch and vital gluten, and why are they isolated?


• • •

What are the concepts of ‘phylogeny’ and ‘synteny’ in cereal genetics? Which cereals are more closely related? Rank the cereals in terms of genome size.

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Contaminants of Grain; Non-food Products from Grains: Cereal Grains as Animal Feed; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; Grain Quality Attributes for Cereals Other than Wheat; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Durum Wheat: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wheat: Dry Milling; Wheat-Based Foods: Breads; Flatbreads of the World.

Further Reading Bonjean AP and Angus WJ (eds.) (2001) The World Wheat Book. A History of Wheat Breeding. Secaucus, NJ: Lavoisier and Andover Hampshire: Intercept. Bushuk W (ed.) (2001) Rye: Production, Chemistry, and Technology, second ed. St. Paul, MN: American Association of Cereal Chemists. Campbell GM, Webb C, and McKee SL (eds.) (1997) Cereals, Novel Uses and Processes, Proceedings of an International Conference on Cereals: Novel Uses and Processes, 4–6 Jun 1996 (1997) Manchester, UK . Canadian International Grains Institute, 1993. Grains and Oilseeds, Handling, Marketing, Processing, fourth ed. Canadian International Grains Institute, Winnipeg, MB. Champagne ET (ed.) (2004) Rice: Chemistry and Technology, third ed. St. Paul, MN: American Association of Cereal Chemists. Delcour JA and Hoseney RC (2010) Principles of Cereal Science and Technology, third ed. St. Paul, MN: AACC International. Dendy DAV (ed.) (1994) Sorghum and Millets: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Faridi H and Faubion J (eds.) (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. Gooding MJ and Davies WP (1997) Wheat Production and Utilization Systems, Quality and the Environment. Wallingford: CAB International. Henry RJ and Kettlewell PS (1996) Cereal Grain Quality. London: Chapman and Hall.

WHEAT-BASED FOODS | Cereals: Overview of Uses: Accent on Wheat Grain Heyne EG (ed.) (1987) Wheat and Wheat Improvement, second ed. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Hill LD (1990) Grain Grades and Standards. Urbana, IL: University of Illinois Press. Kulp K (ed.) (1994) Cookie Chemistry and Technology. Manhattan, KS: American Institute of Baking. MacGregor AW and Bhatty RS (eds.) (1993) Barley: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Marshall HG and Sorrells ME (eds.) (1992) Oat Science and Technology. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Murphy CF and Peterson DM (eds.) (2000) Designing Crops for Added Value. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Olson RA and Frey KJ (eds.) (1987) Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Posner ES and Hibbs AN (2005) Wheat Flour Milling, second ed. St. Paul, MN: AACC International. Pyler ER and Gorton LA (2009) Baking Science and Technology, fourth ed. Kansas City, MO: Sosland Publishing. Rasmusson DC (ed.) (1985) Barley. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Shewry PR and Khan K (eds.) (2009) Wheat: Chemistry and Technology, fourth ed. St. Paul, MN: AACC International. Simmonds DH (1989) Wheat and Wheat Quality in Australia. Collingwood, Australia: CSIRO.

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Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) (2012) Durum Wheat: Chemistry and Technology, second ed. St. Paul, MN: AACC International. Sprague GF and Dudley JW (eds.) (1988) Corn and Corn Improvement, third ed. Madison, WI: The American Society of Agronomy – Crop Science Society – Soil Science Society of America. Webster FH and Wood PJ (eds.) (2011) Oats: Chemistry and Technology, second ed. St. Paul, MN: AACC International. White PJ and Johnson LA (eds.) (2003) Corn: Chemistry and Technology, second ed. St. Paul, MN: American Association of Cereal Chemists. Yamazaki WT and Greenwood CT (eds.) (1981) Production, Breeding, Milling, and Uses. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.aaccnet.org – Website of the AACC International. http://www.aibonline.org – Website of the American Institute of Baking. http://www.aoac.org – Website of the AOAC International. http://www.crops.org – Website of the Crop Science Society of America. www.icc.or.at – International Association for Cereal Science and Technology. http://www.irri.org – Website of the International Rice Research Institute. http://www.knowledgebank.irri.org/rice.htm – Rice Knowledge Bank of the International Rice Research Institute (IRRI). http://www.wsu.edu/wwql/php/ – Website of the USDA-ARS Western Wheat Quality Laboratory.

Breads TR Moore, AIB International, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The simplest bread can be made from just wheat flour and water. Bread types vary greatly across the globe due to differing expectations of the consumer. Consumer requirements for longer shelf life have introduced new ingredients to the bread formulation. High-speed equipment has allowed modern-day bakers to produce many types of bread in large quantities to meet increasing demand. Bread can be made with any of several different doughmaking processes, each tailored to produce the desired baked product attributes.

early on, only two ingredients are necessary to make palatable bread, those being flour from grain and water. Almost by accident, it was learned that what we now recognize as yeast added desirable flavor and lightness to bread. Later, it was discovered that salt added more flavor. Today, additional ingredients are used in bread to meet the demands of the modern-day consumer, namely, better keeping qualities, better flavor, softer (or firmer) texture, and other physical and sensory improvements. As mentioned previously, geographical and cultural differences exist between breads, meaning that ingredients that are commonly used in North American, British, and Australian pan breads may not be used in German rye bread, French baguettes, or Arabic bread, for example. See Table 1 for common ingredients and their functions.

Learning Objective

Equipment

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The modern commercial bakery houses many pieces of specialized equipment. The goal of using modern automated equipment is to carry out the basic steps of the dough production process in bulk quantities and to do it profitably. The design, construction, and usage of machinery to make bread are truly global, with bakers all over the world buying and using equipment made in foreign countries. See Table 2 for an overview of the equipment used for modern bread production. While automated (or semiautomated) production is common throughout the world, it must not be forgotten that suitable types of bread can also be made using nothing more than a bowl and a hot stone.

Attain knowledge of bread types, ingredients used, and process steps.

Introduction Bread, in all its various forms, has served as humanity’s staff of life for centuries. Its ability to provide nourishment to the human body is undeniable, and the pure enjoyment of eating fresh bread is unquestioned. While many people around the globe think of bread as simply a small part of their daily diet, it is much more than that to many others. To the wheat breeders, farmers, millers, and bakers of the world, bread is a means of providing for themselves and their families, a product to be proud of, and practically a way of life. As would be expected of a product that has been in existence for so long, bread has evolved over the years such that it means different things to different people. Indeed, the geographical and cultural differences in the product known as ‘bread’ are quite broad, as evidenced by the tremendous array of bread varieties available today in the developed economies of the world. Pan breads, hearth breads, buns, rolls, and flat breads are increasingly available around the world, even if they are not indigenous to the consumer’s homeland. Simply stated, the differences between breads are largely a function of the ingredients used and the manner in which those ingredients are processed into the final product. Consumers enjoy the bread products they eat, whether they were made using an ancient process or came from the most modern high-speed production bakery.

Ingredients

Whether bread is made by hand or by machine, certain steps of the bread-making process are the same. Mixing of the dough, for example, can be done either mechanically or manually, and good bread can result. Bread owes its uniqueness not only to the ingredients and equipment used in its manufacture but also to the different processes by which dough is made. Most of these processes are of geographical or cultural origin and are still used in the regions of their invention today. However, with globalization of trade and world travel, consumers now demand products that were not familiar to them in the past. It is not difficult to find authentic French bread in America, flour tortillas in Australia, or pita bread in Hong Kong. However, achieving the unique characteristics of different breads often requires that a specific dough-making process be used.

Straight Dough Process

Various ingredients are used in bread formulas to manipulate the characteristics of the finished product. As humanity learned

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Dough-Making Processes

As noted in Figure 1, this is an uncomplicated process whereby all the ingredients are loaded ‘straight’ into the mixer. The


http://dx.doi.org/10.1016/B978-0-12-394437-5.00116-9

WHEAT-BASED FOODS | Breads Table 1

Functions of bread ingredients

Ingredient

Function(s)

Wheat flour

Forms structure and provides body Contributes gluten-forming proteins Contributes starch for heat-induced formation of crumb Hydrates flour protein and damaged starch Acts as solvent for other ingredients Controls dough temperature Contributes pan flow Contributes to shelf life Enhances flavor of product Strengthens gluten network Controls fermentation rate Provides leavening Metabolizes fermentable sugars into CO2 and alcohol Fermentation products contribute to bread flavor Serve as food source for yeast Enhance flavor of product Contribute to crust coloration Act as product tenderizer Contribute to shelf life Lubricates dough system Facilitates easier expansion of gas cells in dough Tenderizes crust Facilitates easier slicing Contributes to shelf life Contribute to nutrition profile of product Provide dough buffering Enhance flavor of product Contribute to crust coloration Strengthens dough Increases water absorption Provides greater baked loaf volume Enhances fermentation process Provides yeast nutrients Acts as water conditioner Conditions dough (with optional oxidant) Improve production process and finished product quality Convert starches into fermentable sugars Shorten dough mixing time Strengthen dough Provide greater baked loaf volume Retard mold growth Contribute to shelf life

Water

Salt

Yeast

Sweeteners

Shortening

Dairy products

Wheat gluten (dry)

Yeast food

Enzymes

Preservatives

dough is mixed and then allowed a bulk fermentation period of 60 min to 4 h, during which the dough is ‘punched down’ or purposely deflated to control expansion. After the fermentation period, the dough proceeds to ‘make up,’ a bakery term for the process of cutting and forming smaller dough pieces.

No-Time Straight Dough Process This process is a variation of the straight dough method. It does away with the bulk fermentation period, substituting in its place chemical dough development, or the use of oxidizing agents and mix time reducers. A slightly modified version of this process is used for the manufacture of frozen dough

9

products, which are used extensively by supermarket bakeries in North America, Europe, and elsewhere.

Sponge–Dough Process This process is dominant in North America for the production of pan breads and buns and also finds use in other countries where pan breads are popular. The sponge is a thick stiff mass, ‘plastic’ in texture, which contains most of the formula flour, water, and yeast. After mixing, the sponge is allowed to ferment for 3–4 h and is then remixed with the remaining dough ingredients added. A short rest period, or ‘floor time,’ is given to the finished dough before it proceeds to the makeup stage, as shown in Figure 2. Breads made in other parts of the world can use a similar process, but the names are different. For example, Italian breads such as ciabatta and pugliese can be made with a biga, which is very similar to a North American sponge except for the longer fermentation time it is given. French breads, including baguettes and batards, can be made with poolish, a liquid version of the sponge that actually originated in Poland, or with levain, a sourdough-like starter used as a leavening and flavoring agent.

Liquid Sponge Process This is a close relative of the sponge–dough process, but as the name implies, it is liquid in form, containing at least as much water as flour. This enables the fermentation process to take place in stainless steel tanks, as shown in Figure 3, with the chilled liquid sponge pumped to the dough mixer, a great production advantage. The fermentation time is shorter for liquid sponges than for plastic sponges, usually on the order of 60 min to 3 h.

Continuous Mix Process This process enjoyed great popularity in North American commercial bakeries in the 1960s and 1970s, particularly for sliced white pan bread. As the name implies, this process produced bread dough continuously, rather than in individual batches. Ingredients were metered into a high-speed developer head, which mixed the dough and deposited it into baking pans. This process, while economical, eventually fell out of favor due to the lack of flavor and crumb strength in the bread. See Figure 4 for a schematic representation.

Chorleywood Bread Process Developed by the British Baking Industries Research Association at Chorleywood, England, this process is used around the world to produce bread from lower-protein flours. For this reason, it has not gained great acceptance in North America, where higher-protein flours are the norm. It relies on a shorttime, intensive mixing, sometimes with partial vacuum in a Tweedy mixer, after which the developed dough is sent to the makeup stage, as depicted in Figure 5.

WHEAT-BASED FOODS | Breads

10 Table 2

Common wholesale bread bakery equipment

Equipment

Purpose

Comments

Dough mixer

Imparts mechanical shear to flour proteins and water to form gluten and develop dough mass ‘Divides’ large dough mass into loaf-sized pieces

Capacity of up to 1400 kg. Can be horizontal or vertical. Mixer bowl can be refrigerated Types include ram and knife, rotary, single pocket, vacuum, extrusion Skin on exterior of dough ball helps to retain gas Dough balls ride on trays or belts

Divider Rounder Intermediate proofer Sheeter–molder

Forms divided dough piece into smooth, tight ball Relaxes rounded dough balls Expels gas from and flattens dough balls with sheeting rollers, curls dough sheet into cylinder, and seals seam Drops molded dough pieces into pans on conveyor below Allows panned dough to rise to proper height prior to baking Bakes dough, kills yeast, gelatinizes starch, and colors the crust Cools baked loaves prior to slicing Slices loaves prior to packaging Pulls poly bag over sliced loaf

Panner Proofer Oven Cooler Slicer Bagger

Horizontal mixer

All ingredients

Divider

Rounder

1–4 h

10–25 min

50–60 min

Intermediate proofer

Sheeter

Molder

Proofer

16–30 min

Traveling tray, belt, spiral, rack Band, reciprocating Bags closed with tie or clip

Bulk fermentation

xx

Oven

Straight grain, cross grain, and curling molders all commonly used Can index dough pieces into pans with seams on bottom Employs controlled temperature and humidity Tunnel, lap, rotary, deck, rack steam required for hearth bread

Panner

2–15 min

Figure 1 The straight dough process. Adapted from AIB Science of Baking Correspondence Course, Module III Breads and Rolls (2001) Dough Mixing and Development, pp. 6–8. Manhattan, KS: AIB International.

Remaining ingredients Flour, Yeast, water

Sponge mixer

Sponge fermentation

Horizontal mixer Divider Floor time

xx 2–4 min

Oven

16–30 min

Proofer

50–60 min

3–4 h

Molder

Panner

8–20 min

Sheeter

0–30 min Intermediate proofer

Rounder

2–15 min

Figure 2 The sponge–dough process. Adapted from AIB Science of Baking Correspondence Course, Module III Breads and Rolls (2001) Dough Mixing and Development, pp. 3–5, 7. Manhattan, KS: AIB International.


Remaining ingredients Flour, yeast, water

Liquid sponge mixer

Fermentation tank

Heat exchanger

11

Horizontal mixer

Refrigerated holding tank

xx 8–20 min

1–3 h

Molder

Proofer


Sheeter

Panner

50–60 min

Divider

Rounder

2–15 min

Oven

16–30 min Figure 3 The liquid sponge process. Adapted from AIB Science of Baking Correspondence Course, Module III Breads and Rolls (2001) Dough Mixing and Development, pp. 5–7. Manhattan, KS: AIB International.

Water, yeast, flour or sugar

‘Brew’ mixer

Remaining ingredients Heat exchanger

‘Brew’ tank

Premixer

xx

Oven

Proofer

16–30 min

50–60 min

Developer/divider

Panner

1 min

Figure 4 The continuous mix process. Adapted from AIB Science of Baking Correspondence Course, Module III Breads and Rolls (2001) Dough Mixing and Development, pp. 6–7. Manhattan, KS: AIB International.

All ingredients

Tweedy mixer

Divider Rounder

xx

Oven

16–30 min

3–5 min

Proofer

50–60 min

Molder

Panner

Sheeter


2–15 min

Figure 5 The Chorleywood process. Adapted from AIB Science of Baking Correspondence Course, Module III Breads and Rolls (2001) Dough Mixing and Development, pp. 7, 9. Manhattan, KS: AIB International.

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Sourdough Process This is the oldest and most time-consuming of the methods discussed and is used to produce breads with rich and complex flavor and texture. More European in nature, sourdough breads are leavened with a sour ‘starter,’ which consists only of flour and water. The starter is allowed to ferment spontaneously, that is, with only the naturally occurring microorganisms present in the flour (mainly wild yeast and lactic acid-producing bacteria). There is no added bakers’ yeast. To keep the starter active for daily use, it must be replenished or ‘fed’ periodically with added flour and water. Given proper feeding, a starter can last many years.

made with a blend of white and whole-wheat flours (Table 4). These types of pan breads often need to be supplemented with dough strengtheners, as the inclusion of significant amounts of whole-wheat flour weakens the gluten network and results in bread of lower baked volume. Other types of pan breads fall

Bread Products As mentioned, bread can take many shapes and sizes and can have fairly diverse sensory characteristics. In addition to the ingredients, equipment, and processes just mentioned, the various physical and organoleptic differences between bread products available today are attributable to cultural, geographical, and philosophical differences between the people who consume them. Generally, certain bread types are prevalent in certain cultures and not in others. This is changing, however, with the world gradually becoming smaller with the advent of jet travel, wireless communication, and international trade.

Figure 6 A round-top ‘strap’ pan, background; sliced white bread, left; unsliced white bread, center; sliced cracked wheat bread, right.

Pan Breads Loosely defined, these are simply breads that are baked in pans, either open or closed. These breads are very common in North America, Eastern and Western Europe, Australasia, and other industrialized areas of the world. Most of the pan bread baked on these continents is produced in large wholesale baking plants, using automated or semiautomated equipment. It is almost always sold presliced in polyethylene bread bags and can be found in supermarkets, convenience stores, and other retail outlets. In many of the aforementioned regions, pan breads are available as either ‘round-top’ or ‘Pullman’ loaves. Round-top bread is baked in a pan with an open top, so that the baked loaf has the characteristic round crown when viewed in profile (Figure 6). Pullman bread, commonly called ‘sandwich’ bread, is baked in a rectangular pan, usually longer in length than a round-top pan, and has a lid placed over it after proofing and before baking (Figure 7). The lid prevents expansion of the dough in the oven and results in a baked loaf having a nearly square profile. This bread is usually sliced slightly thinner than round-top bread for the North American market, the thought being most sandwich consumers want more of the filling per bite and less of the bread. Both round-top and Pullman loaves are available in several different varieties in most global markets. The most common include white bread, made with white refined wheat flour (Table 3), and wheat or ‘whole-grain’ bread, made with whole-grain or whole-meal wheat flour. In the United States, ‘whole-wheat’ bread may be made only with 100% wholewheat flour, while the more generic ‘wheat’ bread may be

Figure 7 A Pullman ‘strap’ pan and lid, background; sliced white sandwich bread, left; sliced honey bran sandwich bread, center; sliced multigrain sandwich bread, right. Table 3

Sponge and dough white pan bread

Ingredient

Sponge (%)

Dough (%)

Bread floura Water Yeast, compressed Salt Sweetener (solids basis) Shortening Yeast food Milk replacer Fungal protease Mono- and diglycerides Calcium propionate

70.0 40.0 3.0

30.0 22.0 (variable) 2.0 8.0 3.0

0.5 2.0 0.5

All ingredients are given in bakers % (flour ¼ 100%).

a

0.5 0.2

WHEAT-BASED FOODS | Breads under the ‘variety’ bread category – including multigrain bread, made with several cereal grains in whole-wheat dough; fiber bread made with varying types of high-fiber ingredients; and the ever-popular raisin bread (Figure 8). To respond to the consumer’s desire for greater selection and to gain market share, bakers have developed pan breads that contain a wide array of specialty ingredients, including oats, crushed wheat, flaxseed, sunflower seeds, cinnamon, fruit, honey, and nuts. Additionally, toppings can be added to the surface of the proofed loaves prior to baking. Some of these include wheat bran, wheat flour, crushed wheat, sesame seed, flaxseed, sunflower seed, and other differentiating ingredients. A common practice for North American round-top breads is to split the surface of the proofed dough lengthwise with a water jet and apply melted butter in the cavity, thus creating the ‘butter top’ variety (Figure 8). Pan breads can be formulated to be lean, rich, or somewhere in between, depending on the consumer’s taste. Most white breads tend to be soft and somewhat sweet, containing high amounts of water, shortening, and crumb softeners, along with higher sweetener levels. Whole-meal breads tend to be slightly dryer than white bread, chewy, and not as sweet. Common in many markets around the globe is the practice of producing similar bread varieties at different price points, or perceived quality levels, for supermarket sale. Terms such as ‘value priced,’ ‘private label,’ ‘branded,’ ‘premium,’ and ‘super premium’ illustrate the practice. The differences are usually Table 4

Sponge and dough wheat pan bread

Ingredient

Sponge (%)

Bread floura Whole-wheat flour Water (variable) Yeast, compressed Yeast food Salt Shortening Molasses Sweetener (solids basis) Vital wheat gluten Calcium propionate

60.0 15.0 42.0 2.5 0.5

Dough (%) 25.0 18.0

2.0 3.0 4.0 4.0 2.0 0.2

Wheat flour þ whole-wheat flour ¼ 100%.

a

higher-quality ingredients, a richer formula, possibly the use of a pan with a slightly different shape, and more elaborate packaging graphics.

Hearth Breads Historically, hearth breads, also referred to as artisan breads or rustic breads, have been made from relatively stiff and dry doughs so that they could be baked directly on the hearth, or floor, of the oven, without the benefit of a pan to impart shape or structure to the loaves. Today, the best-quality hearth breads are still made this way, especially by European bakers. While French and Italian bakers have traditionally been recognized for excellent hearth bread quality, a similar product can increasingly be found in all corners of the world. In North America, this type of baking has enjoyed a true renaissance, with hundreds of small- and medium-sized bakeries turning out French baguettes, batards, and boules, Vienna bread, and crusty hard rolls. Bakeries in Japan, Korea, Hong Kong, and Thailand offer their customers a similar product, as do those in Ireland, Israel, and Argentina. The best known of the hearth breads is generically referred to as French bread. However, the term does not do justice to the broad array of bread products produced in France. Indeed, the French take their bread so seriously that the government found it necessary to legally define baguette and to regulate the various methods of bread making that are employed there. In France, French bread is made with wheat flour, salt, and water, with fermentation carried out by levain, direct addition of fresh yeast, or the addition of prefermented dough. In North America, certain compromises have been made to adapt French bread to the consumer’s palate and to the producer’s balance sheet. For example, shortening and a small amount of sweetener are sometimes added to make the bread softer and sweeter tasting and to extend the shelf life beyond the usual few hours (Table 5). Interestingly, the inclusion of these two ingredients in French bread is not legal in France. True French bread, whether it is made in France or elsewhere, is available in several shapes and sizes. Baguette is the term for a long, narrow loaf with rounded ends, measuring 60– 70 cm in length and weighing 250 g. It has seven characteristic slashes applied to the top surface after the proofing step, which helps control bursting during baking. A batard is similar to a baguette in weight but measures only 35–40 cm in length and carries only three slashes. Ficelle is smaller still, weighing 125 g with a length of 40–45 cm. It usually has five surface slashes. Table 5

Figure 8 Left to right: raisin bread, split and topped seven-grain bread, double-split and topped fiber bread, butter top wheat bread.

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Sponge and dough white hearth bread and hard roll

Ingredient

Sponge (%)

Dough (%)

Bread floura Water (variable) Yeast, compressed Yeast food Salt Sweetener (solids basis) Shortening Nondiastatic malt

60.0 30.0 3.0 0.5

40.0 25.0


a

2.0 2.0 2.0 1.0

14


Parisian is a large loaf weighing 400 g and measuring 60– 70 cm in length. It has five to seven surface slashes. Boules are circular loaves and can be of varying weights and diameters. Various surface designs are applied via slashing in order to give the boule a distinctive appearance (Figure 9). The crust of these breads should be relatively thin, crispy, and blister-free, courtesy of the steam introduced into the oven chamber during baking. Crust color can vary from pale brown to practically black, depending on the region and consumer taste. Internal characteristics are just as unique as the external appearance. The crumb color is usually creamy to pale yellow, with a very open and irregularly shaped cell structure. There are normally several moderately sized holes in each slice, giving the crumb surface a rough texture. The crumb will be slightly chewy in the mouth. Flavor will be characteristically well rounded, fermented, and slightly salty. Several different processes can be used to produce French bread, including the previously mentioned straight dough, sponge–dough, and sourdough processes. In the United States, a close relative of French bread originated in the San Francisco, California region, during the gold rush period of the late 1840s and early 1850s. Called San Francisco sourdough bread, it was a mainstay of the diets of gold miners. Today, it is still a fairly unique product in the American marketplace, in that it has a very characteristic sour flavor, open grain, and substantial crust (Figure 10). Many specialty sourdough bakeries have opened across the United

States to capitalize on the growing consumer demand for this product. As the name indicates, the bread is made with a sour starter, also called a mother sponge (Table 6). Another type of hearth bread is rye bread, which takes its name from the inclusion of flour from the cereal grain rye. Rye bread has been produced around the world for centuries and has gained great popularity for its distinctive flavor and dense, chewy crumb. In Northern and Eastern Europe, rye bread is a highlight of the meal, rather than an accompaniment. The types of rye bread are many, including American rye, Jewish rye, German rye, Russian rye, and Swedish rye, to name a few (Figure 10). The differences are largely due to the ingredients and consumer taste indigenous to the producing region. Rye flour differs greatly from wheat flour in that its protein does not form gluten. As such, it contributes nothing to the strength of the dough or the volume of the bread. Therefore, the amount of rye flour that can be used in rye bread dough is limited, with the majority being wheat flour. Rye flour is available as light rye, medium rye, and dark rye; rye meal, rye flakes, and cracked rye are also available. Generally, rye breads are differentiated based on the amount of wheat flour used and the type of rye flour that is chosen (Table 7). This creates rye breads having different crumb color, crumb density, and flavor. In some types, it is common practice to include ground or whole caraway seed in the formula to further accentuate the flavor of the bread. Rye bread is generally made with the sponge–dough process. The traditional pumpernickel bread, a dark and heavy version of rye bread, uses a sour made of whole rye meal. German sour rye bread is also produced with a sour.

Buns and Rolls

Figure 9 French-style stick loaves and boule.

These are simply small individual units of baked bread, normally eaten with a meal or as the bread component of a sandwich. In North America, buns are usually sweeter and richer in formulation than white pan bread (Table 8), while rolls tend to be made from leaner formulas (Table 5). Both products can be panned and baked either as single units or in clusters, depending on the intended users’ desires. Buns and rolls can be made from the same types of dough as used for bread loaves. White, wheat, rye, and sourdough buns and rolls are common. The most popular usage of buns is for the ubiquitous hamburger and hot dog, as their respective buns are shaped and sliced specifically to accommodate those specialty meat items (Figure 11). Hamburger and hot dog buns are most Table 6

Sourdough bread Dough starter

Figure 10 San Francisco sourdough boule, left; European sour rye bread, right.

Dough

Ingredient

Amount (kg)

Ingredient

Amount (kg)

High gluten flour Water (variable) Starter

45.4

High gluten flour

136.0

22.7 11.4

Water (variable) Starter Salt Yeast, compresseda

81.6 25.0–34.0 2.7 0.17

a

Optional.


Sponge and dough rye bread

Ingredient Sponge Flour: cleara Patent Light rye Water Yeast, compressed Yeast food Diastatic malt Dough Flour: clear Light rye Dark rye Water Yeast Salt Shortening Molasses Caraway seed Syrup Nonfat milk solids

American (light)

Swedish

70.0

66.0

34.0 2.5 0.5 0.5

Jewish

40.0 20.0 36.0 2.0 0.25 0.5

36.0 2.5 0.5 0.5

5.0 25.0

10.0 30.0

24.0 10.0 28.0

30.0 2.0 3.0 2.0 1.0

32.0 0.25 2.0 1.0

2.0 4.0

12.0 4.0

Wheat flour þ rye flour(s) ¼ 100%.

a

Table 8

Sponge and dough hamburger and hot dog buns

Ingredient

Sponge (%)

Dough (%)

Bread floura Yeast, compressed Water Sweetener (solids basis) Salt Vegetable oil Protease enzyme Yeast food Vital wheat gluten Crumb softener Calcium propionate

70.0 3.5 40.0

30.0 24.0 12.0 2.0 4.0

0.5 0.5 2.0 0.5 0.3


15

usually made in wholesale bakeries on automated high-speed equipment in large quantities. Also popular in North America are the kaiser rolls, made from a lean bread dough formula (Figure 11). The dough balls are flattened slightly after forming, with a characteristic ‘star’ pattern subsequently stamped into the top surface. The proofed rolls are baked with steam injected into the baking chamber to form the light, slightly crispy crust that is expected of the product. As opposed to the North American preference for soft rolls, European rolls are traditionally of the hard type, made with lean formula dough and baked with steam in the oven to facilitate the formation of a crispy crust (Figure 12). Hard rolls are also available in other areas of the world and are of good quality as long as two things are present in their manufacture – strong protein flour and oven steam. Other types of rolls include croissants and brioche, both of which are of European origin and very popular all over the world. The croissant (Figure 12) is made with laminated Danish pastry-type dough, that is, the dough is actually composed of many individual layers of dough and fat, usually unsalted butter. The dough is continually reduced in thickness through a series of sheeting steps, after each of which, it is folded and sheeted again. This procedure is repeated until the proper number of laminations has been obtained. It is common for croissant dough to have anywhere from 36 to 72 dough/fat layers. These layers serve to trap moisture and carbon dioxide produced during fermentation. On exposure to oven heat, the moisture turns to steam that, in conjunction with the carbon dioxide gas, causes the croissant dough to ‘bloom’ in the oven. This blooming action results in the formation of the light and flaky texture for which croissants are known. Brioche is a light, sweet, yeasted roll that is made from a rich formula high in eggs, sugar, milk, and butter. As such, it finds favor as a dessert item and is popular for holiday celebrations. It is usually made with the sponge–dough process but can also be made with either the straight dough or sourdough method. As the term ‘brioche’ can apply just as easily to the dough as to the individual baked product, the rolls can take on many different shapes and sizes. In Europe, the appearance of brioche is often based on the regional preference of the baker and his clientele.

a

Flat Breads These are the most widely consumed of all bread types, eaten daily by many millions of people all over the globe. While this

Figure 11 ‘Cluster’ hamburger buns, left rear; ‘cluster’ hot dog buns, right rear; assorted kaiser rolls, front.

Figure 12 Assorted hard rolls surrounded by croissants.

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number may seem questionably large at first, it is put into proper perspective by considering the wide selection of products available, many of which are not familiar or available to those outside of certain regions. Generally, flat breads can be divided into the single-layered and double-layered types. Single-layered flat breads are consumed universally. For most North and Central Americans, the flat bread of choice is the tortilla. Indeed, for many people, it is the bread accompaniment at most every meal. While the corn tortilla is the more traditional product, wheat flour tortillas have gained great acceptance in the United States and Canada, especially for the fast-food trade (Figure 13). See Tables 9 and 10 for representative formulas. In many non-Hispanic homes in the United States, tortillas have become as common as sliced white pan bread. Tandoor bread is another single-layered flat bread that is widely consumed, especially in parts of the Middle East, India, and Pakistan. While it may be given slightly different names in different regions (taftoon in Iran and tanoori in Afghanistan), it is essentially the same product, with similar ingredients and processes used. It is made of wheat flour, soda (sodium bicarbonate), yeast, and water, with optional ingredients being salt

and date syrup in certain types. Sourdough can be used in place of the yeast. It is baked into thin, oblong shapes. Ciabatta is Italian in origin and in fact translates to ‘slipper bread.’ It has gained a large following in Europe and North America (Figure 14). It is baked from lean formula sponge– dough, usually consisting of wheat flour, water, yeast, and salt. Olive oil is sometimes added, especially in Italy. High amounts of water are added to the dough to give the baked bread its characteristic open and irregular crumb structure. Similar to ciabatta, focaccia (Figure 14) uses the same basic ingredients but is prepared with the straight dough procedure, often with a long bulk fermentation period for added flavor. The dough is traditionally flattened in a shallow pan with the fingertips and then topped with various items such as onions, peppers, tomatoes, and seasonings. A short proof is given after which the dough is baked. Topped focaccia is seen as an upscale type of pizza in North America and is a very popular item in boutique bakeries and cafes. Pizza is a universally popular type of flat bread enjoyed all over the world. While pizza is usually distinguished by the toppings applied to it, the crust itself is subject to variation in thickness, texture, and added flavorings, depending on the particular geographical region in which it is served. Thickness can range from very thin and cracker-like (0.5 cm) to thick and hearty (upward of 5 cm). Crust texture is manipulated by the ingredients chosen, including flour strength, and the process used to manufacture the dough. Toppings vary widely and are limited only by the imagination. Traditional US toppings include tomato sauce, mozzarella cheese, olive oil, and various herbs, vegetables, and meats. Chapati, also known as roti, is estimated to be the most widely consumed flat bread in the world. The people of Tibet, India, Pakistan, Afghanistan, and other countries eat it as their

Table 10

Figure 13 Large and small wheat flour tortillas, left; corn tortillas, right. Table 9

Straight dough wheat flour tortilla

Ingredient

% a

Bread flour Vital wheat gluten Soy flour Water Salt Shortening Gums Yeast, compressed Baking powder Oxidizersb,c Mold inhibitorsc,d

100.0 0–5 0–5 45–60 1–2.5 5–12 0–4 0.1–1 1–1.5 Variable Variable

All ingredients are given in bakers % (flour ¼ 100%). Can include azodicarbonamide, potassium bromate, and/or ascorbic acid. c Please note that not all specified additives are permitted for food use in all countries. d Can include potassium sorbate surface spray, calcium sorbate, sodium propionate, calcium propionate, and 100-grain vinegar.

Corn tortilla

Ingredient

%

Yellow corna White corn Water Lime Soy flour Sodium hydroxide Calcium hydroxide Buffers/preservativesb

85–100 0–15 25–30 1–2 0–10 1–4 0.25–1 Variable

Yellow corn þ white corn ¼ 100%. Monocalcium phosphate, sorbic acid, citric acid, fumaric acid, calcium propionate, potassium sorbate, etc. a

b

a

b

Figure 14 Ciabatta, left; focaccia, center; pita bread, right.


Straight dough Arabic (pita) bread

Ingredient a

Flour Yeast (active dry) Salt Water

% 100.0 0.5 1.5 50.0


17

equipment design, product shelf life, and distribution techniques will almost certainly give the bread baker advantages his ancestors never had. Implementing this technology to create wholesome and appetizing breads that are also safe and profitable will prove advantageous for bakers and consumers alike.

a

daily bread. It is unleavened, round in shape, and made with whole-wheat flour and water. The most recognizable double-layered flat bread is Arabic bread, also known as pita bread (Table 11). This product is lean in formulation and round in shape and has a characteristic ‘pocket’ inside that defines the product (Figure 14). This pocket is formed largely by a second proofing (rising) step that is not given to single-layered flat breads. The second proof allows the formed dough surface to dry slightly. The resultant dough skin allows the product to balloon during baking, forming the internal pocket. Baking is carried out at high temperatures, normally 400 C, for short periods of time, usually 90– 100 s. The combination of high temperature and short time helps emphasize pocket formation by quickly converting internal dough moisture to steam, which, along with residual CO2, accentuates the separation between the top and the bottom of the bread.

Gluten-Free Breads An emerging product category in North America and Europe, gluten-free bakery products are formulated without the gluten proteins found in wheat, barley, and rye. Ingestion of these proteins by those suffering from celiac disease causes an immune response in the small intestine. Over time, this reaction causes inflammation that damages the lining of the small intestine, preventing the absorption of nutrients. In children, malabsorption interferes with proper growth and development patterns, and in adults, stomach pain, weight loss, and bloating are common indications. Absent a cure, celiac sufferers can avoid the symptoms only by adhering to a strict diet devoid of gluten. To the baker interested in serving the celiac customer, this means that wheat flour, the very backbone of yeast-raised breads and rolls, cannot be used in the product formulation. Instead, the current technology generally requires that a combination of ‘flours’ made from beans, sorghum, corn, white rice, brown rice, and other sources be substituted for the wheat flour, along with various starches, food gums, and other hydrocolloids. This approach imparts a distinctly non-gluten-like characteristic to the rheology of the dough, which is more correctly described as a batter. The resulting baked product, while acceptable to many celiac sufferers, does not approximate the visual or organoleptic qualities of its gluten-containing counterpart.

Future Considerations As it has with most things, technology will continue to affect the baking industry. Further advances in ingredients,


• • • • • • • • •

What differentiates the various types of pan bread available? What is a Pullman loaf, and how does it differ from roundtop bread? Are there any formulation differences between white pan bread and hamburger buns? What is the most popular dough-making process currently used? What does sourdough bread rely on for its unique flavor? Structurally speaking, what is the most important ingredient in a loaf of pan bread? Is shortening an allowable ingredient in an authentic French baguette (produced in France)? How is the ‘pocket’ formed in pita bread? What ingredients are called for in replacing wheat flour in gluten-free bread?


• • •

What pressures may be exerted on the wholesale bread industry in the future, regarding nutrition and health? How can the wholesale baking industry continue to adapt to the needs of those suffering from allergies and celiac disease? How is it that such divergent baked products can be made from just a few common ingredients?

See also: Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Frozen Dough; Milling and Baking: History; Wheat: Dry Milling; Wheat-Based Foods: Flatbreads of the World; Sour Dough Technology; Tortillas.

Further Reading Bilheux R, Escoffier A, Herve D, and Pouradier J (1989) Special and Decorative Breads. New York: Van Nostrand. Calvel R (2001) The Taste of Bread. Maryland: Aspen Publishers. Doerry WT (1995a) In: Baking Technology. Breadmaking, vol. 1. Manhattan, KS: American Institute of Baking. Doerry WT (1995b) In: Baking Technology. Controlled Baking, vol. 2. Manhattan, KS: American Institute of Baking. Jenkins S (1975) Bakery Technology Book 1, Bread. Toronto: Lester and Orpen Limited. Kulp K and Lorenz K (eds.) (2003) Handbook of Dough Fermentations. New York: Marcel Dekker. Kulp K and Ponte Jr. J Jr. (eds.) (2000) Handbook of Cereal Science and Technology, 2nd edn. New York: Marcel Dekker.

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Matz S (1999) Bakery Technology and Engineering, 3rd edn. McAllen, TX: Pan-Tech International. Pyler EJ (1988) Baking Science and Technology, 3rd edn. Merriam, KS: Sosland. Pyler EJ (1994) Bakers Handbook. Merriam, KS: Sosland. Qarooni J (1996) Flat Bread Technology. New York: Chapman and Hall. Williams A (ed.) (1975) Breadmaking: The Modern Revolution. London: Hutchinson Benham.

Relevant Websites http://www.aibonline.org – Aibonline.org; AIB International, formerly the American Institute of Baking, located in Manhattan, Kansas, USA, was founded in 1919 as a service and education organization for the American wholesale baking industry.

Today, the Institute’s influence is worldwide, with services ranging from seminars and short courses to contract research facilities to food safety auditing. http://www.baking.ca – Baking.ca; The Baking Association of Canada serves members of the wholesale, retail, and in-store baking segments, as well as those in the allied trades. http://www.bbga.org – Bbga.org; The website of the Bread Bakers Guild of America, offering content of interest to artisan bakers, along with information and formulas from the Team USA baking team which placed first in the 1999 and 2005 Coupe du Monde de la Boulangerie, and second in the 2002 and 2012 competitions. http://www.campden.co.uk – Campden.co.uk; Located in the United Kingdom, the Campden and Chorleywood Food Research Association conducts research and development on food and beverage products for clients worldwide, and is the UK’s largest independent membership-based organization.

Flatbreads of the World KJ Quail, Grain Growers Limited, North Ryde, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Flatbreads are a staple food product of the Middle East, North Africa, and the Indian subcontinent. Types of flatbread are also consumed in Central America, China, and Europe. A high proportion of the world’s flatbread is still produced using traditional methods; however, a growing number of these breads are manufactured in industrial bakeries throughout the world. Flatbreads have been categorized under three major types including single-layered breads baked on a hot plate, singlelayered breads baked in an oven, and two-layered breads baked in an oven. The shelf life of flatbreads with low fat levels is limited. The nutritional contribution of flatbreads for over 1.5 billion people is extremely important.

Learning Objective

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To achieve an overall understanding of the various types of flatbreads, of the procedures for their production, of quality attributes and nutrition, and of shelf life limitations.

Within this broad definition, flatbreads may be produced with or without yeast, may be baked dry, or retain moisture levels of over 35%. The definition of a flatbread can become difficult to distinguish with biscuit-style products such as crispbreads, which are baked to produce a dry, crisp product that may include high levels of added fat. This article will focus on flatbread products manufactured from a wheat flour-based dough, where the final product has a moisture content over 20% and a fat content of < 10%. In general, this includes most of the flatbreads consumed as food staples. It does not include products such as the Scandinavian crispbread products; these products have been described elsewhere. There are three main production methods for the manufacture of flatbreads. These production methods provide a framework to consider the many different products consumed around the world, although it is acknowledged that there is some overlap between the methods. Within each broad production method, there are often variations that contribute to the distinct style of breads from different regions. By describing the major production techniques and the resulting bread styles, it is possible to understand the principles of flatbread production and apply this knowledge to the many unique and varied products identified globally. These production methods can also be applied to new product development to adapt traditional flatbreads to supply convenience foods for urban consumers.

Introduction Flatbreads were the first baked cereal products prepared and consumed by early human society. Today, flatbreads are arguably the most widely consumed bread category in the world. An estimated 1.5 billion people consume traditional flatbreads as a food staple, and many people throughout the world are also consuming newer forms of products based on flatbread technology, such as take-out pizzas or sandwich wraps. Traditional flatbreads include those consumed in the Middle East, North Africa, the Indian subcontinent, Central America, China, and Europe. In many of these countries, flatbreads are an important food staple. For example, in Egypt, Iran, Azerbaijan, and Kazakhstan, flatbread consumption is over 130 kg per person per year. In Iran, traditional flatbreads typically represent over 50% of the daily energy requirements. Despite the importance of flatbreads globally, there has been significantly less literature published on this product category when compared with pan or volume breads. This article aims to describe a diverse range of flatbread products and to outline the production technology used for their manufacture. Given the dietary importance of these products, a section has also been allocated to the nutrition of flatbreads. The diverse category of flatbreads includes many products from around the world. Providing a definition of what constitutes a flatbread can, however, be difficult. Common features are a low specific volume and a high crust-to-crumb ratio.


Production Methods Single-Layered Flatbreads Cooked on a Hot Plate Rather Than Baked in an Oven Breads cooked on a hot plate are typically very thin and may be made using a dough that is sheeted before cooking on a hot plate or using a batter that is poured onto the hot plate. Products produced on a hot plate may contain small amounts of yeast but more typically contain chemical leavening agents; however, some products are made without leavening. Chapatis are widely consumed in Afghanistan, India, Pakistan, and Bangladesh. Chapati is typically produced by mixing a high-extraction wheat flour, typically 90%, with a high ash level, referred to as atta, and water together to form a dough. Small additions of salt or oil are sometimes added to the dough as well. The cohesive dough mass is rested for a short time before dividing into small dough balls, which are rounded before sheeting (using either a rolling pin or paired roller to flatten the dough piece) to form a thin round dough piece. Each dough piece is then placed on a flat hot plate at 220 C. The first side of the chapati is cooked for 45 s before turning to cook the other side for a further 90 s. The chapati can be consumed without further processing or placed in a hot oven 350 C to puff the bread. Ideally, the finished chapati is soft and flexible when consumed. Rao et al. developed a test

http://dx.doi.org/10.1016/B978-0-12-394437-5.00125-X

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WHEAT-BASED FOODS | Flatbreads of the World

method for the evaluation of chapati. This method has been used to evaluate preferred wheat types for the production of this bread style. The flatbread saaj also known as markouk or rogag is consumed widely in the Middle East. It is a paper-thin product traditionally manufactured as a circular loaf 70 cm in diameter. It is typically prepared from a high-extraction wheat flour (100%), sugar (1–3%), salt (0.5–1.5%), and oil (1–2%) and may have added yeast (0.1%). Water is added to make a stiff or dry dough, which is bulk fermented for 30–60 min. The dough is divided to form 200 g dough balls, which are then sheeted using a roller. The sheeting results in a very thin dough that is stretched over a domed hot plate and heated to 250 C. The bread is turned over after 90 s to be cooked on the second side for a similar time.

Sheeted Single-Layered Flatbreads Baked in an Oven Flatbread styles baked in ovens are prepared using dough pieces that are either sheeted or pressed to produce a flat piece of dough. The sheeted dough piece, considered in this section, must be docked before baking to avoid large blisters or complete separation of the dough into two layers, referred to as pocketing. Docking of flatbreads can range from firm pressing of the dough to form defined furrows to, more typically, puncturing the dough with a spiked roller. Single-layered flatbreads manufactured with a sheeting process represent the most culturally diverse style of flatbreads. This style of flatbread has lent itself to high-speed automated production. Automation has been a contributing factor to the popularity of some singlelayered flatbreads in nontraditional markets. Examples include tortilla from Central America, pizza from Italy, and lavash from Azerbaijan and Iran. Tortilla and pizza bases are covered elsewhere in this publication. Barbari bread is a single-layered flatbread that is usually an oblong shape, 70–80 cm long, and 25–35 cm wide with a thickness of 2–3 cm. It has a shiny glazed surface and has deep furrows on the upper surface that run the length of the bread. Barbari bread is most popular in Northern Iran. A typical formula for barbari bread is wheat flour 77% extraction (100%), baking soda (0.35%), salt (2.0%), sourdough (40%) or yeast (1.0%), and water (60%). The dough is mixed and a bulk fermentation of 2 h is used. Dough is divided into 800–900 g pieces, which are rounded and allowed to rest for 15 min. The dough balls are flattened into an oval shape, and then a mixture of flour, sugar, and boiled water is rubbed onto the surface of the dough as a form of glaze. The dough is then docked and grooved with fingers to form five or six 1 cm deep rows; this stops the formation of large blisters and serves to decorate the bread. It is then proofed for 15 min. The bread is baked on the hearth of a dome-shaped oven heated by a burner on the side of the oven. Baking is 5–8 min at 250–300 C. The production of barbari has been automated with the process following similar steps to those of manual production. Specific innovations required for automated production include specifically designed rollers to dock the bread, simulating the handmade appearance of the traditional product. Lavash is a thin single-layered flatbread. It is typically a large rectangular loaf 60–70 cm long, 30–40 mm wide, and 2–3 mm thick. The bread originates in the northern parts of the Middle

East and is often associated with Armenia and Iran. For traditional production, flour of high extraction (100%) is mixed with salt (1%), yeast, or sourdough and water (45%) to form a dry or tight dough. A poorly developed dough is then allowed a bulk fermentation of 30–180 min before dividing to form dough pieces of 300 g. The dough is then sheeted using a hand roller to form a thin rectangular dough. The dough is docked with a spiked roller and then immediately spread over a cushion, which is used to stick the dough against the internal wall of the oven. The oven is typically an egg-shaped barrel on a 45 angle with a gas or oil burner at the base. The oven operates at 300 C and the bread is baked for 30–40 s. The production of lavash bread has been mechanized successfully. Similar ingredients are mixed to form a stiff, lowmoisture dough. The dough is extruded and sheeted through a series of rollers to form a thin, flat continuous dough. The dough is then docked with a spiked roller, and dough pieces of the correct size and shape are cut using a die on a roller. The dough pieces have about a minute on a conveyor before entering the oven. The dough pieces are carried through the oven on either a steel mesh or band conveyor and are baked at 320 C for 40 s. A form of lavash bread is now used for making sandwich wraps indicating a successful modern application for this product. Tanoor or tandoor bread, otherwise known as taftoon in Iran, is baked as either a circular- or triangular-shaped loaf. The bread is about 30 cm in diameter and 5–6 mm thick. It is mostly consumed in Southern Iran, the Gulf countries, Iraq, Syria, and Afghanistan. Traditional production of this bread is still common in small bakeries that follow similar procedures. High-extraction flour (85%), salt (1%), leavening, and water (60%) and an optional ingredient date syrup (2.5%) are mixed to form a dough. In the past, sodium bicarbonate and sourdough starters were used for leavening, but this has largely been replaced with yeast. A bulk fermentation of 60 min is allowed before the dough is divided into 300 g dough pieces. An intermediate proof of 10 min is allowed before the dough pieces are flattened either by hand or using a roller. The dough is docked using a spiked roller and then stretched over a cushion and then stuck to the wall of an oven. The ovens are commonly built of clay and are a barrel-shaped, either placed vertically in the floor or placed at 45 with an opening at bench height. The burner, which is usually oil, heats the oven to 350–400 C.

Two-Layered Flatbreads Baked in an Oven Two-layered flatbreads are formed when a flattened dough piece separates into two distinct layers during baking. Arabic bread is popular in many countries and is known by the following names: khobz, shami, mafrood, burr, bairuti, Lebanese, pita, and pocket. It is a round two-layered flatbread. Formation of the two layers occurs when the bread ‘pockets’ during baking at high baking temperatures of 350–600 C. Made most commonly with a moderate ash white flour (76–80% extraction), it is also produced with high-extraction flours and meals. The bread can range from very thin (4 mm) to quite thick (20 mm). A typical formula would be flour 100%, yeast 1%, salt 1.5%, and water 56%. The dough is

WHEAT-BASED FOODS | Flatbreads of the World ideally mixed to full development and may be processed immediately or allowed a bulk fermentation period of approximately an hour. After scaling, the dough is rounded and rested before sheeting. On an automated line, the sheeting is usually completed with three sets of rollers. The first roller gently flattens the dough to allow the dough pieces to enter the second roller, which flattens the dough in the same direction but more aggressively on this occasion. The dough is then turned at right angles for the third sheeting. The final roller is set to produce the desired final thickness, and also by sheeting at right angles, this typically produces a round thin dough piece. The sheeted dough piece is then proofed for 20 min. During the proof, a fine cell structure develops and a thin dry skin forms on the surface of the dough. The dough is then baked at a high temperature, with thinner dough pieces requiring higher baking temperatures for shorter baking times. Oven temperatures can be over 600 C with baking times < 20 s. During the baking period, the very hot temperature forms a crust of ungelatinized starch on the surface of the dough piece, which provides a barrier to gas transfer. Gases within the cell structure expand and steam is generated. The gases spread through the now discontinuous cell structure, and once the gas pressure is adequate, it forces the upper and lower layers of the bread apart. Ideally, the layers are of even thickness, and this is largely achieved through a similar heating rate from the top and the bottom as this sets the crumb structure before the layers are separated. Alternative dough preparation methods have been suggested for the production of Arabic bread including the use of a sponge and dough system. In this study, bread produced with the sponge and dough method was considered to have improved eating quality and shelf life. Arabic bread although originating in the Middle East has now become popular in many other countries including the United States, England, and Australia. Mechanization of production has been a key to the successful adoption of this bread in so many countries. Baladi (balady) is also a round, two-layered flatbread. It is made with high-extraction wheat flour and is distinguished from Arabic bread by the higher baking absorption used for production. Although baladi accounts for up to half of Egypt’s wheat flour consumption, it is still largely produced by hand. This is attributed to the difficulty of processing the soft and sticky dough using automated equipment, especially once the dough has been flattened. The bread has a rough appearance with irregular edges. There is bran on the bottom of the dough, which is used to reduce sticking during processing. The upper surface often has dark blisters. The internal crumb has an open structure and is moist. A high-extraction flour (100%; extraction 85%), with clearly visible bran particles, is mixed with salt (1.5%), water up to 80%, and a starter dough or yeast. Mixing is of low intensity and there is little gluten development. After mixing, the soft and sticky dough is allowed 30 min of bulk fermentation. Dividing is done by hand, and scaled dough balls are deposited in boxes heavily dusted with wheat bran. After 10 min, the dough piece is pressed flat; after a further 15 min, the dough is baked. As the dough is removed from the proofing box, it is flattened further and stretched by hand to give a diameter of 200 mm for a 200 g dough piece. An

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oven peel is used to place the dough on the oven hearth for baking at 350 C for 2 min. The bread pockets in the oven in a similar fashion to that described for Arabic bread.

Product Quality It is important to acknowledge that the product quality criteria for flatbreads are quite different to pan or Western-style bread. Many of the products were used traditionally as an eating utensil. In this case, they were torn, and pieces of the bread were used to pick up other foods, often high in moisture. For this application, the breads require a degree of strength and flexibility. In other cases, such as lavash, the breads are used to wrap around other fillings, and again, this requires strength and flexibility to hold and form the shape required. Although the specific characteristics of the breads may vary, there are common attributes of softness, flexibility, and strength. Various bread scoring and assessment systems have been described for some of the flatbreads. These quality scoring systems include characteristics of product appearance and functionality. Appearance factors include crust and crumb color, presence of blisters, and uniformity of shape. The functionality is typically measured as a rolling or folding test. The bread is typically rolled around a cylinder or folded and assessed for cracking or tearing of the crust. Other assessments of softness or tearing resistance are more subjective in their assessment. In some cases, it has been possible to replace subjective assessment with instrumental testing including the measurement of tearing and puncturing to measure product strength.

Shelf Life Traditionally, flatbread was purchased and consumed within 4 h of baking. This was supported by the production of breads in small bakeries, with consumers purchasing bread directly from their local bakery. In some cases, the bread is still baked at home. With changing lifestyles, urbanization, and the use of these products in nontraditional markets, centralized largescale production has become more common. Centralized production requires a distribution system and the use of dispersed retail outlets that require extended shelf life of the products. The shelf life of flatbreads is limited by two considerations, namely, spoilage and staling.

Spoilage The moisture content of flatbreads tends to be lower than most pan or Western-style bread products. This is a result of the large surface area-to-volume ratio. However, the water activity is still typically high enough in these products to be prone to spoilage by mold and bacteria. A survey of flatbread types from an Australian supermarket that included tortillas with extended shelf lives, chapati, and Arabic bread indicated a range of water activity from 0.88 to 0.96 (unpublished). With such water activity, the bread held at 22 C is susceptible to the development of mold within 72 h unless specific actions are taken. When bread emerges from the oven, it is free from viable mold organisms. During cooling and packaging,

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contamination can result from either airborne inoculum or contact with contaminated surfaces. Flatbreads are particularly vulnerable due to their large surface area-to-volume ratio. Good bakery sanitation and hygiene should form the primary approach to reducing the degree of contamination. Some bacterial spores can survive the baking process, or contamination can occur before packaging is complete. Either way, it is difficult to produce bread that is totally free from mold or bacteria at the point of packaging. There are four main strategies used to extend the mold-free shelf life of flatbreads, and discussion of these follows.

reported on the partial baking and frozen storage of chapati to extend shelf life. The rebaking of the frozen parbaked chapati was found to produce better product texture than fully baked chapati, which was thawed for consumption.

Combined treatments By combining either MAP or vacuum packaging with an oxygen scavenger sachet and the use of bread preservatives, it is possible to achieve mold-free shelf life of over 6 months. This practice is widely used for the distribution of tortillas in supermarkets that require extended shelf lives.

Modified atmosphere packaging Trials were conducted by Avital and Mannheim on the application of modified atmosphere packaging (MAP) to extend the shelf life of flatbread. Samples of bread were packed in a range of carbon dioxide and nitrogen concentrations. A high barrier laminate utilizing ethylene vinyl alcohol as the barrier layer was used as packaging. This package had an oxygen permeability of 0.45 ml/m2/24 h and carbon dioxide and water, 3.5 g/m2/24 h. The total thickness of the laminate was 10 mm. When flatbread was packed in polythene without modification of the atmosphere, the bread was spoiled by microbial activity after 3 days. When packed with the inert gas nitrogen, the shelf life was extended to 5 days. A combination of 73% carbon dioxide and 27% nitrogen extended the shelf life to 14 days. In a study by Black et al., microbial spoilage was prevented for up to 28 days in packs flushed with 100%, 40%, and 15% carbon dioxide, and the inclusion of either an oxygen scavenger or ethanol-generating sachets. In this study, the inclusion of the sachets had the effect of doubling the shelf life of the breads.

Vacuum packaging An alternative to MAP is to draw a vacuum when packaging flatbreads. This has commonly been applied to the packaging of tortillas. The packaging used should have a low oxygen permeability to avoid leakage over time. It is also recommended that to extend the value of vacuum packaging, an oxygen scavenger is used. This is because it is difficult to remove the gas from the crumb of the bread when drawing a vacuum. The scavenger sachet will remove any remaining oxygen and significantly extend shelf life.

Preservatives Chemical mold inhibitors in the form of acetic, sorbic, and propionic acids or their potassium or calcium salts are widely used to extend the shelf life of baked products. Other acids including fumaric, phosphoric, and citric may also be used. The limiting factor in the use of these acids is often their impact on aroma and flavor. Perhaps, the most effective combination is to use acetic acid with propionic acid. This combination will generally extend the shelf life by up to 5–7 days without other measures.

Freezing Freezing flatbread soon after packaging will stop microbial spoilage. Frozen storage is expensive and is not typically used for the commercial distribution of flatbreads. Gurjal et al.

Staling Bread staling is a process of chemical and physical changes. These changes to the bread result in a loss of consumer acceptance. The major changes to occur after baking are moisture redistribution, drying, starch retrogradation, increased bread firmness, increased bread fragility, and loss of flavor and aroma. For flatbreads, the high crust-to-crumb ratio is highly significant when the impact of moisture redistribution is considered. For flatbreads, one of the key characteristics to change during staling is the loss of product flexibility, and as this is such an important quality feature of these products, it typically becomes the limiting factor for shelf life. After several hours of storage, most traditional flatbreads become stiff and are more fragile. For the extension of shelf life for pan or Western-style bread, it is common to use the addition of emulsifiers or fats to produce softer bread crumb. For flatbreads, the impact of these ingredients needs to be carefully managed as the softening effect often reduces the strength of flatbreads. Typically, emulsifiers are suitable at half to one-third the addition level when applied to flatbreads as compared with their use in pan breads. In the case of the Iranian flatbread, taftoon, improvements in dough properties, water absorption, and bread shelf life were achieved with the addition of mono- and diglyceride and lecithin. The results suggest a level of 0.2% monodiglyceride provided the best total bread score. Shaikh et al. studied the staling of chapati at room temperature and using refrigerated storage. They found that chapati texture, measured using a puncture test, was the most widely correlated factor with other indicators of staling. This suggests that by managing the texture of chapati, it will be possible to extend sensory acceptance. Shaikh et al. found that the addition of maltodextrin, guar gum, and alpha-amylase was effective at reducing the staling of chapatis as measured by changes in product texture. Another approach to shelf life extension was taken by Tavakolipour and Kalbasi-Ashtari using the addition of hydrocolloids. They found that the addition of carboxymethyl cellulose at 0.5% increased the shelf life of lavash bread by more than 45%. The extended shelf life achieved for tortillas requires high levels of fat addition and in some cases hydrocolloids. The high fat level does weaken the strength of the product to some extent, but it allows the tortilla to remain flexible to achieve an extended shelf life. This high fat content is not suitable for many other styles of flatbread as it significantly reduces the strength of the product.


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Nutrition

Minerals

The nutrition of flatbreads is most relevant where they make a significant contribution to the total nutrient intake. This is possibly most important in the Middle East, North Africa, and regions of the Indian subcontinent. The average per capita bread consumption per day has been reported as 355 g in Saudi Arabia, 277 g in Kuwait, and 444 g in Egypt. In the case of Kuwait, flatbread accounted for 30% of energy, iron, and thiamine intake and up to 50% of protein for the 1420 people surveyed. The nutrition of flatbread is similar to other bread types. However, the high temperatures used for baking and the high crust-to-crumb ratio do create some differences to Western-style pan breads. The use of high-extraction flour is very common for some flatbread types, such as chapati, but less common for Arabic bread.

For diets with a high intake of flatbreads, the benefit of fiber intake may be counterbalanced by the phytate content of wheat bran. Phytate binds minerals including Fe, Zn, Mg, and Ca by forming insoluble compounds that reduce bioavailability. Therefore, diets high in wholemeal or whole-wheat flatbreads could have mineral deficiencies. A study by Khan et al. showed that supplementing chapati flour with 24% soy flour increased the mineral content of chapati for Fe, Zn, Cu, Mn, Ca, and Mg. The study also found that the baking process used for chapati production decreased the level of phytate in the finished bread. However, the study did not include an assessment of bioavailability or compare the efficiency of this approach to flour fortification with mineral nutrients, which is widely supported for countries with poor total nutrition. Other studies of flatbread production indicate that between 22% and 32% phytate is lost during fermentation. It is suggested that Middle Eastern diets typically have low dairy intake and may be deficient in calcium. Ziadeh et al. identified sensory thresholds for the addition of calcium salts to support fortification. Fortification at half the sensory detection level was expected to provide between 61% and 125% of the recommended daily intake for calcium. Iron deficiency is considered the most common nutritional disorder and affects some 2 billion people worldwide. Fortification with ferrous iron can influence the sensory properties of foods. In the case of fortified flatbreads in Pakistan, fortification of whole-wheat flour with 50 ppm ferrous iron was more acceptable than breads prepared with 75 ppm. World Health Organization guidelines recommend iron and zinc fortification is determined by daily consumption and the type of iron compound used. Given the need for improved dietary levels of micronutrients for many of the world’s population dependent on flatbreads as a significant dietary component, it is recommended that further studies are completed to assess the optimum levels of flour fortification for the production of traditional flatbreads to ensure consumer acceptance.

Protein The protein content of flatbreads is almost exclusively contributed by the wheat flour used for production. This may vary within a small range but would typically represent 12% of the bread on a dry matter basis. Perhaps, more important than the total contribution is the quality of the protein. The essential amino acid composition of flatbread was assessed by Hallab et al. and Sawaya et al. It was identified that lysine was the most limiting of the amino acids. It was reported in 1968 by Maleki and Djazayeri that some Middle Eastern diets were deficient in lysine. This could be expected when flatbreads accounted for between 50% and 90% of energy intake in Iran. Trials with the addition of soy flour and chickpea flour to increase lysine content were published as far back as 1972 by Hallab et al. This study demonstrated that bread produced with 10% soy and up to 20% chickpea flour had good organoleptic acceptance and significantly improved the protein score. However, there has been very little uptake of such bread fortification. This suggests that bread habits in these regions are very traditional and that change in the use of bread ingredients is difficult to achieve, especially if it adds cost to the bread.

Dietary Fiber Cereals provide an excellent source of dietary fiber. Fiber helps prevent constipation and may also protect against diseases such as diverticulitis, hemorrhoids, and colon cancer. Breads produced from high-extraction flours contain more bran, which is the major fiber component. A survey of Australian supermarkets indicates that white Arabic bread typically has 2.8% dietary fiber, and wholemeal Arabic bread 6.8% (unpublished). Several studies demonstrate that flatbreads, in a similar manner to other bread styles, are suitable carriers for added fiber products. The addition of 20% of barley fiber-rich fraction was demonstrated to provide health benefits of two-layered flatbread by increasing the levels of total and soluble dietary fibers. Alviola et al. added up to 15% cross-linked wheat-resistant starch to significantly increase tortilla dietary fiber without negatively affecting dough handling and final product quality.

Vitamins Bread is a major source of the vitamins thiamine, riboflavin, and niacin. Higher levels of these vitamins are contained in the bran; therefore, higher-extraction flour provides a better source of these vitamins. A study by Maleki and Daghir found that white Arabic bread made from 65% extraction flour had 0.2 mg/100 g of thiamine, while Arabic bread made from 85% extraction flour had 0.7 mg/100 g. They also found that the levels were consistent across a range of baking conditions. Other flour fortification recommendations by the World Health Organization include folic acid, vitamin B12, and vitamin A. These recommendations would be considered important for flour used for flatbreads when they represent a significant contribution to total energy consumption.


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List five examples of flatbreads.

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WHEAT-BASED FOODS | Flatbreads of the World What are the steps in producing a single-layered flatbread baked in an oven? Describe how the two layers of Arabic bread are formed in the oven. What is ‘docking’ when referring to the production of flatbreads? List important nutrients supplied by flatbreads when they are considered a dietary staple.


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Compare the advantages (and disadvantages) of making flatbreads from wholemeal versus refined white flour (e.g., 60–70% extraction), considering nutritional, appearance, and taste aspects. What changes in mixing and baking procedures do you suggest to provide products that are optimized for all these aspects of quality? Leavened breads are baked daily in some regions (even at home), but the trend worldwide has been for factory production of leavened breads for sale in supermarkets with several days’ shelf life. Do you see these trends extending to flatbreads? Which types? What aspects of flatbread quality would need to be altered to achieve an outcome similar to that for leavened breads? How could these improvements be achieved? Which type is your favorite flatbread? Do you have a ‘wish list’ of how it could be even better? How might this dream be achieved? Could this dream involve the addition of savory or sweet additives?

See also: The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Breads; Tortillas.

Further Reading Abu-Ghoush M, Herald TJ, Dowell F, Feng X, Aramouni FM, and Madl R (2008) Effect of additives on the shelf life extension of chapatis. International Journal of Food Science and Technology 43: 357–364.

Amr A and Ajo R (2005) Production of two types of pocket forming flat bread by the sponge and dough method. Cereal Chemistry 82: 499–503. Avital Y and Mannhein CH (1988) Modified atmosphere packaging of pita (pocket) bread. Packaging Technology and Science 1: 17–23. Azizi MH, Rajabzadeh N, and Riahi E (2003) Effect of mono-diglyceride and lecithin on dough rheological characteristics and quality of flat bread. LWT – Food Science and Technology 36: 189–193. Black RG, Quail KJ, Reyes V, Kuzyk M, and Ruddick L (1993) Shelf-life extension of pita bread by modified atmosphere packaging. Food Australia 45: 387–390. Faridi HA and Finney PL (1980) Technical and nutritional aspects of Iranian breads. Bakers Digest 34: 14–20. Gujral HS, Singh GS, and Rosell CM (2008) Extending shelf life of chapatti by partial baking and frozen storage. Journal of Food Engineering 89: 466–471. Hallab AH, Khatchadourian HA, and Jabr I (1974) The nutritive value and organoleptic properties of white Arabic bread supplemented with soybean and chickpea. Cereal Chemistry 51: 106–112. Malaki M and Daghir S (1967) Effect of baking on retention of thiamine; riboflavin and niacin in Arabic bread. Cereal Chemistry 44: 483–498. Mousa EI, Ibrahim RH, Shuey WC, and Maneval RD (1979) Influence of wheat classes; flour extractions and baking methods on Egyptian balady bread. Cereal Chemistry 56: 563–566. Qarooni J, Wootton M, and McMaster GJ (1989) Factors affecting the quality of Arabic bread – Additional ingredients. Journal of the Science of Food and Agriculture 48: 235–244. Qarooni J (1993) Wheat flour tortillas. American Institute of Baking Technical Bulletin XV(5). Qarooni J (1996) Flat Bread Technology. New York: Chapman and Hall pp. 1–176. Quail KJ, McMaster G, Tomlinson D, and Wootton M (1990) Effect of baking temperature/time conditions and dough thickness on Arabic bread quality. Journal of the Science of Food and Agriculture 54: 99–110. Quail KJ, McMaster G, and Wootton M (1991) Flour quality tests for selected wheat cultivars and their relationship to Arabic bread quality. Journal of the Science of Food and Agriculture 54: 99–110. Quail K (1996) Arabic Bread Production. St Paul, MN: American Association of Cereal Chemists, pp. 1–148. Sawaya WN, Jehangir K, Khatchadourian HA, and Al Mahmoud MM (1984) Nutritional evaluation of various breads consumed in Saudi Arabia. Nutrition Reports International 29: 1161–1170. Simon A (2003) Foreign Agricultural Service GAIN Report Kazakhstan. Republic of Food Processing Ingredients Sector Report. Rao H, Leelavathi PK, and Shurpalekar SL (1986) Test baking of chapatti-development of a method. Cereal Chemistry 63: 297–303. Reza G and Khaniki J (2005) Determination of zinc content in Iranian flat breads. Pakistan Journal of Nutrition 4: 294–297. Shaikh IM, Ghodke SK, and Ananthanarayan L (2007) Staling of chapatti (Indian unleavened flat bread). Food Chemistry, 101: 113–119. WHO (World Health Organisation) (2009) Recommendations on wheat and maize flour fortification meeting report: Interim consensus statement. www.who.int/nutrition/ publications/wheat_maize_fort.pdf (accessed 09/10/2012).

Sour Dough Technology SP Cauvain, BakeTran, Witney, OX, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Sour dough breads have a long history of production and are based on spontaneous fermentation. Naturally occurring bacteria and wild yeasts are involved in a symbiotic process. The breads are characterized by acetic and lactic acid flavor notes. The creation of a ‘mother’ or ‘starter’ dough is a key first step. Periodic replenishment of the starter is necessary. There are many individual types of starter and production methods.

Learning Objective

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To attain a knowledge of sour dough bread types, their important characteristics, and methods of production.

Introduction The manufacture of dough using spontaneous fermentation is undoubtedly of great antiquity. Early breads were manufactured using (by today’s standards) crudely crushed grains mixed with water to form a porridge-like mixture that was stiff enough that it could be shaped before baking. If such a mixture is left for any length of time in warm conditions (typically around 20 C) before it is baked, then any wild yeast spores and bacteria, which may be present in the mixture, begin to break down the starch in the grains. The result of these actions is fermentation and with it the release of carbon dioxide gas, some of which may be trapped in the mixture causing the resulting dough to rise and resulting in bread with a lighter and more aerated texture. It is considered that the cultivation of wheat grains for human consumption is likely to have started in the Turkey/ Iran border regions, and so, it is reasonable to assume that bread making also began in the same area. However, it is the ancient Egyptians who are credited with the manufacture of the first deliberately leavened breads. The discovery of spontaneous fermentation is likely to have been accidental with a portion of dough having been left for a longer period of time than normal before being used. Human curiosity was bound to take over and translate into some form of experimentation to see what changes could be induced in the final bread by prolonging the fermentation period. It cannot have taken long for people to recognize that the light and aerated texture of the baked products obtained with fermentation made their normal daily fare more pleasant to consume, especially for those whose teeth had been ground down by the grit and sand in the flours from the milling technologies of the time.


Thus, the concepts of modern sour dough technology have their origins many thousands of years ago. Today, the fundamental principle of sour dough technology is still based on the preparation of a ‘starter’ or ‘mother’ dough, which exploits the principles of spontaneous fermentation. Since the fermentation process cannot proceed without the presence of cereal starch as a food source for the microbial activity, it would eventually come to an end, and so, it is necessary to ‘top up’ the food source with more flour (source of starch) in order to sustain the process. This means that the basic microflora of most mother doughs has been there a long time, though of course, they are not the original starting cells that will have long died away but have left behind many active ‘offspring’ as the result of reproduction and multiplication. Thus, each mother dough has its own unique starting culture of microorganisms, which brings its own special character, not least with respect to flavor profile in the finished bread. Today, there are bakers who manufacture and maintain their own mother dough in the time-honored fashion, and there are those who work with a more controlled environment to ensure that the variability in their product is limited and the uniqueness of the microflora content is maintained. At a larger scale, sour dough bread production may well be based on a traditional starter culture, but the benefits of modern technology are sometimes used to deliver consistent and safe products to consumers. This means that in some cases, sour dough breads utilize specialist-prepared sours that have been dried for supply to bakers who do not wish to manufacture and maintain their own starter. Rye bread concentrates (providing the sour component) are also available and can be blended with wheat flour to yield a less acidic flavored bread for those consumers who prefer it.

Some Common Types and Forms of Starter The most common starter is usually only a mixture of flour and water, which is replenished on a daily basis with new flour as required. However, since the starter is based on spontaneous or natural fermentation by microflora in the flour or from the atmosphere, it could be argued that each starter is unique. In addition, the ratio of flour in the starter may vary according to the preferences of the baker (see the succeeding text). The two most common forms of sour are those based on wheat and those based on rye. While their preparation is based on similar principles, the technical rationale behind their use is quite different. Some of the common sours may be described as follows:

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Levain is the term commonly used to describe a sour dough starter, that is, based on spontaneous fermentation ascribed collectively to ‘wild yeasts,’ a poorly defined group of microorganisms almost certainly belonging to the Saccharomyces (S.) and Candida (C.) genera, and the presence of Lactobacilli (L.).

http://dx.doi.org/10.1016/B978-0-12-394437-5.00117-0

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WHEAT-BASED FOODS | Sour Dough Technology A variation on the levain starter is the levain de pate or preleavened dough where the addition of bakers’ yeast (Saccharomyces cerevisiae) plays a role in the preparation of a ‘mixed’ sponge. The daily preparation of an acidic sponge is still required. The San Francisco sour dough is a very well-known process, not only within the United States but also in many parts of the world. This particular sour dough process is associated with L. sanfranciscensis because it was in San Francisco, the United States, that the microorganism concerned was first isolated and identified from dough. However, the organism concerned has a much wider geographic spread, and it is the method of preparation of the sour that separates this particular product from other sour dough products. One particular difference between this and other sour dough processes is the usually greater proportion of the total flour used in its preparation. The poolish (polish-style sponge) is a relatively liquid system comprising equal parts of flour and water. It is leavened with bakers’ yeast (S. cerevisiae) in advance of dough mixing. As its name suggests, it was developed in Poland, probably sometime in the middle of the nineteenth century, and later adopted in Vienna and subsequently France. The overall flavor profile is less acid (fewer acetic acid notes) than bread prepared with levain. Biga is a stiffer dough compared to poolish and commonly used in Italy with the addition of baker’s yeast. Typically, it is fermented overnight (12–16 h) to develop its flavor. The application of sours in the production of rye bread is common. However, in the case of rye flours, the level of gluten formation is much less than that of wheat flour, and so, the main structure-forming components are the starch and the pentosans, and the technological importance of the sour is probably the same as that of flavor development (see the succeeding text).

Sour Dough Fundamentals and the Generation of Flavor Profiles The essence of the sour dough is based on a symbiotic relationship between the specific bacteria and yeasts, which are present in the flour or which arrive as airborne spores. Fermentation is based on the ability of yeasts to break down sugars and generate carbon dioxide and ethanol by the actions of a suite of enzymes contained with the yeast cells. The carbon dioxide gas, which is generated, is then retained within the gluten matrix, which has been developed during mixing by means of using the trapped air (nitrogen gas) bubbles as nucleating sites. As more carbon dioxide gas is generated and held, the bulk of the dough increases and the final product becomes more aerated in texture. Yeasts are relatively fussy feeders, and the process of fermentation is driven by the enzyme maltase, which converts the sugar maltose into glucose, a sugar that yeast can metabolize. In wheat flour, the presence of a- and b-amylases progressively breaks down the starch into maltose molecules, and so, in prolonged fermentation periods, the supply of food for the yeast is replenished until all the available starch is used up. However, the enzymatic conversion of starch to maltose has its limits, not

least of which is the level of a-amylase present. This can be limited and in turn may limit the ability of the so-called wild yeasts to sustain fermentation. In bread-making methods that employ S. cerevisiae-based dough, baking technologies have evolved to ensure that sufficient fermentation can be sustained. In the sour dough culture, the symbiotic relationship between bacteria and yeast is important in sustaining fermentation. This is because the bacteria ferment the more complex (larger-molecular-weight) sugars that the yeasts cannot use. Indeed, the fermentation is only sustained in sour dough because the yeast can metabolize the by-products of the bacterial fermentation. This symbiotic relationship is complex depending on the composition of the microflora in the sour and, most importantly, the conditions under which fermentation takes place. Each microorganism present in the microflora mix has a set of conditions in which it works best, with the major impact coming from the pH of the matrix and the temperature at which the sour is held. While the basic principle of the sour relies on symbiosis between bacteria and yeasts, there is also a competitive element to the relationship in that if storage conditions favor one organism more than another, the favored organism may multiply to limit the potential of others. This complex mixture of symbiosis and competition lies at the heart of the control of sour fermentation conditions and the development of specific flavor profiles in the final product. The flavor profile of sour dough is dominated by acetic and lactic acids, and the balance of the two acids is driven by the conditions under which the starter is prepared and held. Starters with a lower moisture content tend to have less bacterial activity relative to yeast activity, and the balance of acid formation is biased toward acetic acid. With an increase in moisture level and holding temperature, the balance tends to swing toward bacterial activity with an increase in lactic acid relative to acetic acid. While both yeasts and bacteria prefer acidic conditions, once the pH drops below 4.0, the activity of acid-tolerant yeasts is favored above that of Lactobacilli. Since the pH of the sour can play an important role in flavor development, it is worth noting that ‘external’ factors can play a role in limiting flavor development. In particular, the practice of fortification of flour for nutritional reasons with calcium carbonate (as required by law in the United Kingdom and other parts of the world) buffers or limits the rate and degree of acid development, which can be achieved, especially, with shorter fermentation times. Control of the microflora in any starter is an important part of delivering the final product quality, and so, once the process is underway, it is important to protect the starter from external contamination with unwanted microorganism, which may affect the flavor profile but may deliver unwanted ‘off-notes’ or catastrophic changes in behavior in the final dough, including its potential to reduce the ability of the dough to retain sufficient gas to yield an aerated product.

Processing Impacts of the Application of Sour Dough In wheat flour dough, the development of a gluten network to trap the carbon dioxide gas, which evolves during fermentation, is an important part of aerating the structure of bread. The

WHEAT-BASED FOODS | Sour Dough Technology formation of a strong gluten network can be affected by pH and the presence of natural reducing agents. In general, the application of sours has a negative effect on the gas-holding capacity of the dough, and the density of sour dough breads tends to be greater than those obtained with other forms of bread production. To reduce the density of the resultant bread, the baker may use a flour with a higher protein or wet gluten content or even supplement the recipe with dried vital wheat gluten. However, in Europe, general consumer perception is that sour dough breads will be denser than their nonsour equivalents. The same is essentially true in the United States though in general, sour dough breads are less dense than their European equivalents. As noted in the preceding text, there are differences between the application of starters in rye dough and those in wheat flour dough because of the limited gluten formation in the rye. Amylase activity in rye continues to higher temperatures than experienced with wheat flour, and so, there is a greater overlap between the gelatinization of the rye starch and the inactivation of the amylases, which, in turn, results in greater breakdown of the starch and has a greater negative impact on subsequent bread structure. In the case of rye flour, the pHlowering effect of the sour is important in restricting the degree to which the bread structure is degraded.

Wheat Sour Dough Recipes and Methods In the manufacture of wheat sour dough breads, it is the conditions of preparation of the sour that are probably the most critical quality control point, if only in terms of flavor. As noted in the preceding text, there are a number of variations in the manner in which the sours are prepared in terms of the ratio of flour to water and the fermentation conditions employed. Commonly, the sour is a mixture of only wheat flour and water, but there are cases where other ingredients may be added according to particular local tastes and traditions. However, the sour is prepared; its replenishment with more flour (fermentation substrate) is critical, but here again, there are many local variations in practice. Thus, it is not possible to define only one recipe or set of conditions for the manufacture of the sour, rather just a set of guidelines to general principles employed and a practical example. In general terms, higher inoculation (refreshment) ratios are associated with greater microbial stability and lower pH, which, in turn, lead to more acid flavor development though the impact of fermentation temperatures and times cannot be ignored. As long as the sour is replenished, it will remain active and the periods of time between replenishments are important. Such times may vary from daily to once every 3 days. As a general principle, reducing the period of time between replenishments increases the rate of carbon dioxide gas production in the starter. A typical sour recipe and method may be described as follows: Creating the starter or mother dough from scratch:

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Mix a suitable flour (e.g., strong bread flour) with about half its weight of water to form a stiff dough. Do not be tempted to add too much water as the dough will naturally soften as spontaneous fermentation proceeds. Store the dough in a warm environment, typically 25– 30 C, for about 2 weeks.

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Approximately every 24 h, add a little more flour to the dough to maintain fermentation and make sure that this is well mixed in.

Using the starter:

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Mix by mass, 1 part by starter, 1.3 parts flour, and approximately 0.75 parts water on low speed for 6–12 min to yield a final dough temperature around 25 C. Ferment for 4–6 h.

Creating the final dough:

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• •

Blend the starter with the other ingredients in the ratio of – 1.0 kg starter, – 1.10 kg wheat flour, – 0.10 kg rye flour, – 0.73 kg water. Mix for 6–10 min on low speed to final dough temperature around 25 C. Ferment for 4–6 h.

The final dough may be used to make a variety of bread shapes and types according to the local traditions. Some interesting examples of local variations to starters include the additions of (organic) grape skins, sugar, and milk (Amish friendship bread), whole wheat flour (Flemish Desem bread), teff flour (Ethiopian injera), and soaked basil leaves (Greek sour dough). Diastatic, enzyme-active malt flour may be used to encourage activity, which might otherwise be low, for example, because of low cereal a-amylase levels (high falling numbers) in the flour.

Rye Sour Dough Recipes and Methods Acidification is an important step in improving the baking capability of rye flour, and the use of sour dough is one means by which the beneficial improvement may be achieved. In addition to the tradition of using spontaneous fermentation, a number of other methods have been evolved to deliver improvements to the baking qualities of rye dough in a more controlled manner.

Three-Phase Method With portion of a sour dough starter, the ‘three-phase’ method for rye sours proceeds as follows: 1. The preparation of the Anfrisch sour held at 26 C for 2–4 h to encourage the multiplication of the yeast 2. The preparation of the basic sour using the Anfrisch sour and the addition of more rye flour, held at slightly cooler temperature (typically 2 C lower) for 5–8 h to develop the acid flavors 3. And finally, the formation of the full sour, that is, fermented under warmer conditions (typically around 28 C) for 2–3 h

Two-Phase Method This method forgoes the use of the Anfrisch sour and is based on the preparation of only the basic sour and full sours

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WHEAT-BASED FOODS | Sour Dough Technology relatively thick crust and a large surface area for their bulk. In all bread products, there is a moisture gradient between the dry crust and relatively moisture crumb. During post-baking storage, there is a general equilibration between crust and crumb, with the rate of equilibration depending on the conditions under which the products is held (e.g., type of wrapping material and storage temperature). Bread crust is sterile when the product leaves the oven but quickly becomes contaminated during cooling. However, it is not until the moisture content (water activity) is high enough that the contaminating microbial spores can begin to form visible mold colonies. Since the overall moisture content of sour dough breads is lower than that of many wheaten breads, it takes longer for favorable moisture (water activity) conditions to develop and encourage the formation of visible mold colonies.

Figure 1 Sour dough breads.

(Figure 1). The advantages of this less complicated method are easier calculation of the quantities of materials required and that it is less labor-intensive.

Single-Phase Methods


• • • •

What are the key characteristics of sour dough breads? How is the flavor varied? What microorganisms are important in sour dough bread manufacture? What is the importance of replenishment of the starter dough? What are the differences between sour dough production methods?

There are a number of single-phase methods, which may be used in the manufacture of rye bread. They include the following:

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The Berliner short sour method, that is, based on a single fermentation stage or around 3 h with the dough held at 35 C and produces a less acid flavor in the bread. The Detmolder one-phase method that utilizes a single fermentation stage of 15–20 h. Variations from 100% rye to 100% wheat and temperatures in the range 20–28 C may be used. The Weinheimer one-phase method that uses a low level of flour in the starter (typically around 2% of the total flour weight) with temperatures starting around 28 C and falling to around 23 C with resting periods of 15–30 h. The Monheimer salt–sour method, that is, based in taking a 2% starter and then making the acid dough component with 2% salt (based on total flour weight). The addition of the salt delays the acidification of the sour and inhibits the proliferation of unwanted microorganisms. The method uses high sour dough temperatures (typically 35 C decreasing to 23 C) and long fermentation times, 22–24 h.

Shelf Life of Sour Dough Breads The mold-free shelf life of sour dough breads tends to be longer than that of many wheaten bread products. This is the result of the lower pH of the final product coupled with a lower overall moisture content (water activity). Because of the way in which they are manufactured, many sour dough breads have a

• •

What might be the opportunities to introduce flours from other grains into the production of sour dough breads? Could the principle of spontaneous fermentation be applied to any other bakery products?

See also: The Cereal Grains: Rye Grain: Its Genetics, Production, and Utilization; Wheat Processing: Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Milling and Baking: History; Wheat: Dry Milling; Wheat-Based Foods: Breads; Flatbreads of the World.

Further Reading Bojean B and Guillaume L-D (2003) Yeasts in bread and baking products. In: Boekhout T and Robert V (eds.) Yeasts in Food. Cambridge, UK: Woodhead Publishing. Cauvain SP (2007) Other cereals in breadmaking. In: Cauvain SP (ed.) Technology of Breadmaking, 2nd edn., pp. 371–388. New York: Springer Science þ Business Media LLC. Cauvain SP (2012) Breadmaking: Improving Quality, 2nd edn. Cambridge, UK: Woodhead Publishing. Cauvain SP and Young LS (2008) Bakery Food Manufacture and Quality: Water Control and Effects. Oxford, UK: Wiley-Blackwell. Clavel R, Wirtz RL, and MacGuire JJ (2001) The Taste of Bread. Gaithersburg, MA: Aspen Publishers.

WHEAT-BASED FOODS | Sour Dough Technology Gobbettei M and Ganzle M (2013) Handbook of Sourdough Biotechnology. New York: Springer ScienceþBusiness Media LLC. ICC Method 106 (2009) Working method for the determination of wet gluten in wheat flour. In: The ICC Handbook of Cereals, Flour, Dough & Product Testing; Methods and Applications, p. 230. Lancaster, PA: DEStech Publishing.

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Schunemann C and Treu G (2001) Baking: The Art and Science, 2nd edn. Calgary, Canada: Baker Tech. Williams T and Pullen G (2007) Functional ingredients. In: Cauvain SP (ed.) Technology of Breadmaking, 2nd edn., pp. 51–92. New York: Springer ScienceþBusiness Media LLC.

Cakes, Muffins and Bagels DE Ortiz, W. K. Kellogg Institute, Battle Creek, MI, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Cakes, muffins, and bagels, which are a diverse product group with differing needs for flour quality. Flour improvers and their global differences. Finished food differences in cakes, muffins, and bagels. Discussion about different leavening types (chemical vs. biological). Brief discussions about shortenings and sweeteners as they impact the formulas for these foods. Differences between doughs and batters.

Learning Objectives

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To be able to identify differences in formula and finished food qualities for cakes, muffins, and bagels. To be able to identify several critical factors of flour quality for cakes, muffins, and bagels and compare and contrast them. To be able to identify other critical formula ingredients, basic quality parameters for those ingredients, and how they interact with flour in the food.

Introduction Cakes, pastries, muffins, and bagels are a rich and diverse topic. It is probably easiest to think of cakes and muffins in one group of chemically leavened, batter-based products and pastries and bagels as a separate group of dough products, some yeastleavened and some not leavened. All of these products are sold at the local grocery store and bakery and also have been taken to high art forms by pastry chefs and artisan bakers. These products have also been successfully scaled up to production lines churning out thousands of pieces an hour. Many of these large production lines produce elegant versions of these products with very little handwork.

Cakes

Flour for Cakes

The variety of cake products and formulations across the globe is quite large. In the United States, many industrially baked cakes are baked using a high-ratio formula (more sugar than flour) and chlorine-treated cake flour. Due to regulatory restriction, most of the rest of the global cake bakers do not use chlorinetreated cake flour. For example, many European cake formulas use a lower level of sugar and soft pastry flour (Table 1). Bakery items classified as cakes are generally batter products that are relatively high in sugar, fats, eggs, dairy ingredients (such as milk or sweetened milk), and flavorings. Baking powder and air incorporation are common leavenings. Although

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there are a few savory-flavored products that could be labeled as cakes, in general, cakes are sweet-flavored and have a soft, tender texture. In the United States, there is a subclass of pastries called ‘coffee cakes’ or Danish pastries. These products will be addressed in the section on pastries as most of these products are yeast-leavened instead of chemically leavened. Cakes are generally categorized by their ingredients and mixing procedure. The most common cake is the ‘butter’ cake that is mixed by creaming shortening together with granulated sugar to incorporate air. Air is further entrapped with the addition of eggs to the creamed mixture and more mixing. Foamtype cakes such as angel food or sponge cakes rely heavily on the eggs in the system to incorporate the air cells. In the past, these products were made by whipping eggs or egg whites separately from the rest of the batter ingredients and then carefully folding the whipped eggs into the system. With the advent of current emulsifying systems, sponge cakes can be made as a single-stage mix by adding hydrated, blended emulsifiers. Batters contain more water or fluid ingredients than doughs. The separation between doughs and batters is not a clear line, but usually, batters are pourable and flowable in a short period of time measured in seconds. Doughs often require cutting to separate a portion of the dough from the mass. And, although doughs flow over time, they cannot be easily poured and their flow is generally measured in minutes or hours. One of the earliest recorded recipes for cakes was a household recipe for pound cake that contained a pound each of flour, butter, sugar, and eggs. Many early bakeries essentially followed this outline for years with individual bakers modifying the formula to vary the butter and egg level and adding milk. After the advent of finely milled ‘patent’ flours that were chlorine-treated in 1930s America, formulas were more dramatically altered to have higher levels of sugar than flour. This was the advent of the ‘high-ratio’ layer cakes. These high-ratio cakes contain between 100% and 140% granulated sugar on a flour weight basis as compared to a sponge-type cake with 30–45% sugar on flour weight basis. Patent flours are lowash flours created from the millstreams taken from the center of the wheat endosperm.

Cake flour in the United States is generally milled from soft red wheat grown in the Ohio River Valley states (Ohio, Indiana, Illinois, and Michigan). Some of this wheat is also grown in some more southern states like Missouri, Arkansas, Tennessee, and Texas. The millstreams collected for cake flour are typically those lowest in ash content with an extraction rate of between 50% and 75%. This flour has a small particle size compared to a bread-type flour and can be treated with gaseous chlorine, which lowers the flour pH from 6 to 4.5–5. Most importantly for cakes, the gluten must be of a quality that aids in the forming of films for trapping gas in small air bubbles, but


http://dx.doi.org/10.1016/B978-0-12-394437-5.00118-2

WHEAT-BASED FOODS | Cakes, Muffins and Bagels Table 1 Sample high-ratio cake formulas (percentages in flour weight basis) Ingredient

Yellow

Sponge

Devil’s food

Flour, chlorine-treated cake Sugar Shortening Milk, nonfat dry Eggs, dry whole Eggs, dry whites Eggs, liquid whole Baking soda Baking powder, double-acting Salt Cocoa, alkalized red Water Hydrated sorbitan monostearate Invert sugar

100.0 135.0 55.0 4.0 12.0 3.0

100.0 45.0 – 3.0 – – 100.0 1.0 – 1.5 – – 4.0

100.0 135.0 50.0 4.0 12.0 3.0 – 2.0 2.0 1.5 16.0 180.0 – 15.0

– 0.6 1 – 130 – –

not the quality that lends the toughness/chewiness commonly found in bread flours. Gaseous chlorine is used as an improver for soft wheat flour for cakes in the United States alone. Gaseous chlorine reacts with nearly all of the components in flour and has profound effects on many of them. Some of the effects of chlorine on flour include bleaching of pigments by addition across conjugated double bonds; lowering pH of a flour slurry by freeing of hydrogen ions from pigments, lipids, proteins, and starch; and oxidizing and depolymerizing starch. Most of the chlorine gas reacts first with the lipid- and water-soluble fraction. The end result of the addition of gaseous chlorine is that the cake batters are better able to expand during baking and collapse less upon removal from the oven. In the European Union and other parts of the globe, regulations ban the use of chlorine gas to treat flour. Alternative treatments such as heat, light, and ozone treatments have been investigated, and currently, some cake flour is heat-treated to ‘improve’ the baking quality of the flour. This improvement gives small changes in the flour quality to improve the cake baking quality but not the dramatic changes seen with chlorine gas.

Shortenings The other major ingredient technology improvement was the advent of emulsifiers and new emulsified shortenings, which were much more consistent than their simpler nonemulsified counterparts. Air cells cannot be added to the mass by any means other than mechanical agitation. The gases created by chemical leavening or by steam add to the volume of the air cell created during mixing, but creation of cells all comes during mixing. The industry has found several methods for aiding in the formation of these cells and protecting them once formed by changing the surface tension of the material at the cell/mass interface. Emulsifiers are one method that protects air cells by changing the surface properties of the interface. Common emulsifiers for cakes like lecithin or mono- or diglycerides have a hydrophilic and hydrophobic region on the molecules. This allows the materials in the batter to interact more closely and in thinner sheets. This results in

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better dispersion of the emulsified shortening throughout the entire batter, forming smaller, more uniform air cells, which in turn produce a tender cake with a fine texture.

Sweeteners In most of the world, where granulated sugar prices are low, granulated sugar is the exclusive sweetener found in cakes. Granulated sugar imparts sweetness and tenderness to the texture of the finished cake. The crystalline structure and granulation size of the sugar help in the formation of air cells in the batter and contribute to the viscosity of the batter. In the United States, where sugar prices are higher, it is common to substitute part or all of the sugar with high-fructose corn syrup (HFCS) or other corn-based sweeteners. When this change is made, there are many formulation changes that are required to make a similar cake. Because liquid sugars introduce more liquid to the cake batter, as well as reducing sugars, the cake formula must be altered. These changes include changing the fat level and/or type, changing the emulsifier level and/or type, and changing the liquid levels. The risk one takes when making these changes is that the high level of reducing sugars in the presence of the protein in the eggs and milk common to most cakes will give a product that is darker in both crust and crumb. Low in sugar or ‘no sugar’ can also be made in several ways. The first is by adding one of the several high-intensity sweeteners coupled with a bulking agent like polydextrose or maltodextrins. Another method is to substitute sugar alcohols such as sorbitol or xylitol for the sugar in the formula. Lastly, a new variety of sweeteners that are based on sugar (i.e., sucralose and modified starches) can reportedly be substituted one-for-one for sugar. All of these methods will likely require some modification of the formula ingredients and process to compensate for the changes in viscosity and eating character of the cake when sugar (sucrose) is removed.

Leavening Leavenings are a critical factor in aiding the formation of the aerated structure one expects to find in cakes and cake batters. Chemical leavenings commonly found in cake formulations are blends of leavening acids and sodium bicarbonate. The action of the acid portion of the leaveners is largely dependent on the temperature at which the acid will go into solution and react with the sodium bicarbonate, as well as the level of bicarbonate present. Some acids that are quick to solubilize are leaveners like monocalcium phosphate monohydrate and some of the fast-acting sodium acid pyrophosphates (SAPPs). These largely react in the mixing bowl to add gas to the batter, thus adding volume and viscosity to the batter while it is being mixed. Other acids require the higher temperatures of the oven to fully solubilize. These include the most common second acid in double-acting baking powders, sodium aluminum phosphate (SALP), some slow-acting SAPPs, and sodium aluminum sulfate. Double-acting baking powders are designed to include both acids that solubilize at room temperature during mixing and secondary acids that solubilize in the oven at elevated temperatures. When designing leavening systems for cakes or any other chemically leavened food products, it is important to balance

32

WHEAT-BASED FOODS | Cakes, Muffins and Bagels

the alkaline component (sodium bicarbonate) with the acid component or components to achieve complete neutralization in the finished food. Leavening blends may be formulated by mathematical calculation using an equation called the ‘neutralizing value’ (NV). NV is defined as the weight of sodium bicarbonate required to completely react with 100 parts by weight of a leavening acid. This is captured by the following equation: NV ¼

g of sodium bicarbonate 100 100 g of acidic salt

NVs for many common leavening acids have been included in Table 2.

sodium bicarbonate only to ensure that the pH stays in the alkaline region.

Pastries Pastries are defined as any products made from any of several different doughs that include fats, flour, and water. Examples of pastry include puff pastry, pie dough, and paˆte sucreé (a sweet short pastry). Pastries can also be a general term for sweet baked goods such as Danish pastries or coffee cakes. This is a broad and diverse category of bakery products. It is easiest to divide pastries into dough products that are laminated and those that are not (Table 3).

Other Cake Ingredients

Laminated Doughs

There are a number of minor ingredients and flavoring ingredients that are used in modern cake production. It is difficult to find a cake produced in the United States without a modified starch or a gum. Modified starches and gums help to add viscosity during processing. This helps stabilize the air cells and thus helps to produce a fine-textured, soft cake. These ingredients also act as a tenderizer by diluting the flour and help maintain moistness in the cake throughout storage. There are also very few cakes made without vanilla or vanillin or other flavoring ingredients. One very important additive is cocoa or chocolate. Melted chocolate can be added to many cakes during the creaming stage of mixing along with the shortening and sugar. These cakes can be labeled in the United States as chocolate cake. More often, cocoa is used to impart the ‘chocolate’ flavor and color so desired by consumers. These cakes cannot be labeled as ‘chocolate.’ But there are several common names that are used for these cakes like ‘devil’s food’ or ‘fudge.’ Cocoa is commonly added to cakes either in the creaming stage or in the last stage of mixing along with the flour. In the latter method, the cocoa is usually sifted with the flour to prevent clumping of the cocoa, as it is a rather hydrophobic ingredient. The cocoa used in cakes is usually treated with alkali to produce Dutched cocoa, and therefore, controlling the pH of the finished cakes is very important because it affects the color and flavor of the finished product. Natural or untreated cocoa is often used in frostings, icings, and fudge. Control of the pH in all ‘chocolate’ cakes has a large impact on the flavor and color of these cakes. As a result, many of them are baked with

Laminated dough products can be further subdivided into those that contain yeast and those that do not. The products without yeast are commonly referred to as ‘puff pastry.’ The products that do contain yeast include the broad category known as Danish pastries as well as croissants. In both of these types of products, development of gluten structure is important to the finished product quality. The dough for all of these products must be able to tolerate the stresses in multiple passes through reduction rollers without breaking. In general, the yeasted laminated products are made from flour with slightly lower protein content than the puff pastry products. But for all of these products, flour quality and laminating shortening quality are of equal importance. Processing conditions and resting of the dough between times of stress also play an important role in the manufacture of great laminated dough. Flours used for puff pastry vary from region to region. In the United States and EU, it is not uncommon for pastry chefs to use ‘bread’ flour with a protein level of 11–12% for their puff pastry. This high-quality flour with a relatively high protein level allows the dough to sheet into very thin layers between the layers of fat. In the United Kingdom, where flours tend to have less gluten strength, it is not uncommon for the flour to be supplemented with additional vital wheat gluten to give the final dough the strength that is needed to form the products. This practice may be frowned upon by traditional pastry chefs, who roll their laminated doughs by hand, but with the rigors of

Table 2

Types of leavening acids and their neutralizing value

Leavening acid Dicalcium phosphate dihydrate Monocalcium phosphate Monopotassium tartrate Sodium acid pyrophosphate Sodium aluminum phosphate Sodium aluminum sulfate

Common abbreviation

Neutralizing value

DCP

33

MCP Cream of tartar SAPP SALP

80 45 72 100

SAS

100

Table 3

Sample pastry formula (percentages in flour weight basis)

Ingredient

Puff

Danish

Paˆte sucreé

Flour, pastry Flour, bread Sugar, granulated Sugar, powdered Eggs, liquid whole Egg yolks, liquid Water, cold Salt Shortening or butter Yeast Milk, nonfat dry Vanilla extract

100.0 – – – – – 50.0 2.0 75.0 – – –

25.0 75.0 20.0 – 20.0 – 50.0 2.0 20.0 7.0 6.0 –

100.0 – – 38.0 0.5 32.0 – 1.5 45.0 – – 0.1

WHEAT-BASED FOODS | Cakes, Muffins and Bagels mechanical sheeting, doughs have different levels of stress placed on them and fortification with gluten may be required to handle the added stress. Some processors of laminated doughs mix the flour, water, and other minor ingredients into a well-developed gluten structure prior to mixing in fat to the dough. They believe that this helps shield the proteins from abuse during sheeting. More likely, it just shortens the mix time by allowing the gluten protein matrix to develop before the shortening is added. Shortening lubricates the flour and protects it from absorbing water as quickly, slowing hydration of the gluten proteins, and therefore usually requires longer mix times to develop the gluten. Fats or shortenings are used in two ways in laminated doughs. ‘Dough fat’ is the shortening that is added to the flour and water and other ingredients that comprise the dough. ‘Laminating fat’ is the shortening or butter that is formed into thin layers between the thin dough layers during the sheeting and folding of the dough. This laminating fat is also often referred to as ‘roll-in’ shortening. The laminating fats used in Danishes and puff pastries can be butter, margarine, or vegetable shortening. In any case, the laminating shortening must be relatively plastic at the cool temperatures used to make most of the doughs (10–20 C). The laminating shortenings must also have a controlled melt point of between 39 and 44 C so that they do not taste waxy upon consumption. Some roll-in margarines and butter contain a significant amount of water, but many commercial bakers prefer the control and crisper texture that they get with butter, lard, or shortenings that are devoid of water. Water is very important in laminated products for the formation of dough as well as acting to aerate the products through steam expansion. As steam leaves the dough or the laminating fat during the heat of baking, it pushes against a solid barrier layer of the laminating shortening, pushing the layers of dough apart to create the height and flakiness desired in the product. Increasing water level in the dough of laminated products has little effect on the finished product but can affect the sheetability and handling properties of the dough. If too little water is added to the dough, this can restrict the dough during proofing and baking and give a final product that is low in volume. Sugar, egg, and milk added to the dough of laminated products can greatly influence the final finished product. Sugar not only increases the sweetness of the dough and finished product but also can decrease finished height while increasing shrinkage when added at levels up to 20% flour weight basis (FWB). In general, adding sugar to doughs tends to soften the dough, increasing dough stickiness and difficulty in sheeting. Sugar also contributes to the color of the finished product. One important consideration when using high levels of sugar in yeasted pastry doughs is that the high sugar levels may inhibit the yeast fermentation by elevating the osmotic pressure on the yeast. On the other hand, levels of sugar below 12% (FWB) have not been reported to inhibit fermentation for most common yeasts used in baking. Small levels of egg added to pastry doughs can provide some additional protein support to the products as well as the emulsifying benefits of indigenous lecithin. Pastry products with up to 3% egg yolk tend to bake higher and are tenderer. At higher levels of egg, the color and flavor of the egg become

33

evident and can contribute to inappropriate browning and offflavor development. Much of what makes the laminated doughs so popular with consumers is the shaping and forming of the doughs with added fillings and toppings. It is not uncommon in local bakeries and full-scale production facilities to see croissants made not just plain but with fillings such as chocolate, apple, sweet almond paste, raspberry, and cream cheese or a full-scale breakfast like scrambled eggs and cheese. Coffee cakes are often braids of these sweet, laminated doughs with apple filling and streusel topping. Many of the dough formulas vary little, but the shapes, fillings, and toppings are endless.

Short Doughs, Pie Doughs, and Paˆte Sucreé Short doughs and pie doughs are slightly sweet, very rich doughs containing high levels of fats. Paˆte sucreé is also very rich dough, but it is also very high in sugar, similar to a shortbread cookie. Paˆte sucreé can be up to 50% butter (FWB) and 30% sugar (FWB). Paˆte sucreé and paˆte sableé are both short doughs with similar formulas. The difference between these two doughs is the production method. Many short doughs and paˆte sucreé are made in similar fashion. The first step is creaming of the shortening or butter with the sugar. The second step is creating an emulsion with the liquid ingredients, including eggs. And the last step is the addition of dry ingredients, including flour and leavenings. Pie doughs and paˆte sableé are made differently. With this product, the shortening is cut into the dry ingredients including the flour and sugar until fine, and then, the liquid ingredients are added last. The two different mixing procedures give different finished products with the short doughs and paˆte sucreé having a less tender bite and the pie doughs and the paˆte sableé having more tender and, in the case of pie doughs, flaky texture.

Muffins The history of the bakery item that we call ‘muffins’ today is not clear. There are several distinct foods that bear the muffin moniker. ‘English’ muffins are toastable rounds that are split in the center and generally served as a toast replacement. The ‘English’ muffin is generally baked in a round form on an oven band and has a simple formula with little additional sugar and fat. The bakery muffins that are addressed in this article are readily identifiable by their shape. The muffin shape comes from baking in a ‘cupcake’ or ‘muffin’ pan. They are a recognized by their stout ‘mushroomlike’ shape. Muffins can also be identified by formulation. Most muffins are baked from a chemically leavened batter into a moist, course-grained minicake. Muffins range in formula from those that are rather low in fat, sugar, eggs, and milk to those that are richer than many cakes in fat and sugar. Ingredients commonly found in muffins include flour, sweeteners, fats, eggs, milk, chemical leavening, salt, and identifying ingredients such as bran, fruits or fruit pieces, corn meal, chocolate chips, or chopped vegetables. The flours commonly used in muffins have to withstand the high levels of sweeteners and particulates. Although there are some muffin

34


formulations that use the chlorine-treated cake flour used in high-ratio layer cakes, most muffin formulas are better suited to a blended flour of pastry flour and bread flour otherwise known as ‘all-purpose’ flour. Some formulas even specify higher-protein bread flour. The addition of the higher-protein flour helps create a product that is slightly chewier and coarser in crumb than a cake. Most American muffin consumers would expect this chewier, coarser texture (Table 4). There are some other carbohydrate-based ingredients that are added to some muffin formulas. Some modified starches and gums are added to lengthen shelf life by helping maintain a higher-moisture product. In some muffin batters with large particulates or significant quantities of particulates, batter viscosity can be increased by adding a small amount (0.05–0.2% FWB) of a gum like xanthan or guar. This increase in viscosity helps the particulates stay evenly dispersed throughout the batter during processing. The most commonly used sweetener for muffins produced in a small-scale bakery is granulated sucrose. Other sugars may be used in these bakeries for specific uses such as honey or molasses to contribute a specific flavor profile or color. Corn syrup may also be used to help contribute color. In large-scale bakery operations, corn syrup or HFCS may be used to lengthen the shelf life of the muffin products. When adding these reducing sugars, care must be taken not to overbrown the products. As with cakes, nearly every muffin formula has a substantial quantity of eggs and milk or other dairy ingredients. In bakery mixes, these ingredients may be added as dry, powdered ingredients to the mix, thus reducing the likelihood of a mistake made by the baker and guaranteeing a more consistent product. Eggs are added to muffins to contribute their flexible proteins to the structure of the muffin. Also, eggs contain a natural lecithin that aids in mixing of the batters. Milk or milk constituents are added in large part because of the contribution that the lactose and milk proteins make to the browning of the finished product. Most muffins are deceptively high in fats. The average consumer is likely not aware that muffins can be upward of 40% fat (FWB). Many muffins are made with vegetable oil rather Table 4

Sample muffin formulas (percentages in flour weight basis)

Ingredients

Simple

Blueberry

Bran

Flour, all-purposea Sugar, granulated Shortening Baking powder Baking soda Nonfat dry milk Whole egg powder Salt Bran Molasses, light brown sugar Honey Water Blueberries, fresh whole

100.0 80.0 30.0 5.0 – 4.0 10.0 1.5 – – – 65.0 –

100.0 115.0 85.0 2.0 1.5 4.0 7.5 2.0 – – 10.0 70.0 80.0

75.0b 50.0 35.0 2.0 3.0 10.0 5.0 1.5 25.0b 25.0 25.0 100.0 –

a

All flour is all-purpose type except for the blueberry muffin that would require a chlorine-treated cake flour. b For the bran muffin, wheat-based ingredients (flour plus bran) equal 100%.

than with a hydrogenated shortening, but muffins still contain a substantial amount of fat. Most muffin formulas do not require an added emulsifier unless very little egg is used in the formula. When emulsifiers are added, they are likely to be lecithin or the mono- and diglycerides found in emulsified shortening. Chemical leavenings used in muffins range from the addition of simple sodium bicarbonate to a complex double-acting baking powder. Most muffins are rather simple in their mixing, with little air incorporation by whipping. Most of the air is trapped in large air cells, thus adding to the coarse texture of a muffin. There are some muffins made using a more cake-like formula and production method that will give a smaller air cell and a finer texture. Most often, muffin formulas rely on a lateacting acidulant such as SALP to aid in the formation of the cell structure. Leavening is also one of the major influences on the finished shape of the muffin. Most muffins either have a mushroom top or have a simple peak top. Mushroom-topped muffins have a leavening balanced to force the batter to expand and flow before a crust is formed on the top surface of the muffin pan. Additional leavening, in the form of a late-acting acidulant, remains to push the center of the muffin up, thus forming the mushroom cap effect. These mushroom-topped muffins also are frequently richer in formula and have more batter in the cup than a peak-topped muffin. The peak-topped muffins are usually baked at a higher temperature (above 400 F), and the leavening is designed to act early in the baking process so as not to crack the top after the top crust is formed. One of the characteristics of muffins is the addition of fruits, nuts, chips, wheat or oat bran, or other strongly flavored particulates. These additives can be added as fresh fruit (blueberries, peach, or apple chunks), whole or chopped nuts, chocolate or other flavored chips, or fabricated bits of flavored material. The addition of these ingredients adds to the perception of quality and overall wholesomeness of the muffin. Also, the particulates act to break up the structure of the muffin and change the texture. Toppings are also common with muffins and can be as simple as a cinnamon/sugar blend or as complex as a nut streusel. Some toppings are also materials meant to ‘sink in’ to the muffin creating a ‘filling’ such as the addition of a sweet cream cheese mixture. Again, this topping adds to the complex nature of the muffin, creating changed in texture and flavor as the consumer eats the product.

Bagels Bagels are a unique bakery good both by history and by formulation. The word bagel comes from the Yiddish word, beygel. Bagels are thought to have originated in Poland where Polish bakers, in an effort to honor their victorious horseriding king, made a stirrup-shaped roll and boiled it before baking. This boiling helped keep the shape of the roll during subsequent baking. Jewish immigrants who moved to the northeastern United States brought bagels to America. Bagels were made ubiquitous in the United States by a successful Polish-American baker, Harry Lender, and his sons who used humor in advertising to reach out to middle America with a traditionally ethnic,

WHEAT-BASED FOODS | Cakes, Muffins and Bagels northeastern food. Bagels have now become more readily available in some other parts of the EU, Japan, and other parts of Southeast Asia. In general, bagels have a very simple formulation. The formula is very similar to simple bread or roll formulas: flour, salt, yeast, and water. What separates the bagel from the rest of the rolls are the flour quality and the processing. Traditional bagels were made with very high-protein, spring wheat flour. The flour for bagels is often still between 13% and 16% protein. Spring wheat grown in the northern plains of the United States, Canada, part of Russia, and China produces most of the flour used in baking traditional bagels made today. Many major manufacturers of bagels use less expensive flour in the 12.4–13% protein range but still are forced to pay a premium for the higher protein content. The high protein content of the flour and the mixing of that flour to full development help give bagels their characteristic chewy texture (Table 5). The other significant distinction for bagels is the processing. Traditional bagels develop much of their flavor and distinct crust characteristics from a long, cold fermentation step called retardation. Among large-scale bagel makers, this retardation step has been either a bulk retardation of the whole dough mass or an individual fermentation of preformed bagels. The bulk retardation has more effect on flavor and internal crumb character than on crust characteristics. Piece retardation not only has effects on flavor and crumb characteristics but also has a significant effect on the crust characteristic. The air cells on the surface of the bagel collapse and the surface dries somewhat giving a thick, chewy crust after baking. This collapse and coalescence of cells is also seen in the crumb. Bagels that have been through a retardation process tend to have a coarser, thick-walled cell structure than a nonretarded bagel. The dough for bagels in high-speed production is divided in one of the many typical methods found in roll production. The formation of the ring structure is rather unusual and there are very fewer manufacturers of the equipment necessary to make the rings. One method deposits a dough ball on the end of a belt that moves the ball under a plate to form the dough into a cylinder and then around a mandrel to form the ring. These are called horizontal formers. The second method in a vertical former where the dough ball in dropped into a series of hinged cups that form the dough around a mandrel. The last processing distinction for traditional bagels is the boiling process. The setting of the structure of the dough ring

can be achieved through the application of moisture to the dough surface either through steam injection into the first zone of a tunnel oven or by moving the dough rings through a boiling water bath. This bath water can contain malt or sometimes a sugar, but often, it is just simple water that becomes saturated with starch and dextrins. There are advantages to both methods of water application, but the finished food is different. Boiled bagels tend to have a more distinct hole and a thicker, chewier, shiny crust. Steamed bagels tend to have a softer crust. Bagels may, and often do, contain other ingredients. Bagels can be made with a variety of added grains, fruit and vegetable pieces, nuts, spices, eggs, garlic, cheeses, etc. Bagels often contain dough modifiers like fats, emulsifiers, malt, enzymes, and other processing aids similar to those typically found in roll or bread formulations. Shelf-stable bagels frequently contain the typical preservative systems of breads (e.g., Ca or Na propionate) and crumb softening systems. The crumb softening systems are usually a combination of starch-modifying enzymes and moisture-‘holding’ ingredients like gums or modified starches. In general, bagels are lower in fat than some other baked goods, but sometimes, bakers make up for this by the addition of fat-containing ingredients such as cheeses. Bagels are also often baked with toppings on them such as seeds, finely chopped onion, or salt. These toppings help contribute some of the characterizing flavor and appearance of flavored bagels. The toppings are often coated on the top of the bagels after boiling and before baking. If the bagels are baked using a steam-injected oven, the toppings may be adhered to the surface of the dough using a wash like a modified starch or a gum that acts as an adherent to keep the toppings on the bagels’ dough. In summary, there are many different products that can be classified as a cake, pastry, muffin, or bagel. They are an interesting and diverse set of baked products that present the baker with many options to personalize the products. And this personalization will continue to keep the bakers’ consumers well fed.


• • •

Table 5

Sample bagel formula (percentages in flour weight basis)

Ingredient

Plain

Egg

Onion

Flour, high-proteina Yeast, dry Yeast food Salt Sugar, granulated Waterb Egg, whole powdered Onion, dry toasted

100.0 0.5 1.5 3.0 5.0 65.0 – –

100.0 0.5 1.5 3.0 5.0 70.0 4.0 –

100.0 0.5 1.5 3.0 5.0 70.0 – 2.0

• •

Describe the differences between cake flour in the United States and the rest of the globe. Describe the finished food differences between cakes, muffins, and bagels. Compare and contrast the processes for making cakes, muffins, and bagels. Briefly describe differences between chemical leavening and biological leavening (yeast). Discuss the rheological differences between doughs and batters.


• •

a

Flour should have added malted barley flour. b Water varies by flour requirements and by levels of dry ingredients requiring some hydration.

35

•

How might chemical leavening be replaced in the future? Is it by processing changes or altering formulas? How might the United States alter the flour quality for cakes to remove chlorine treatments? Is it possible to use one flour specification for every product – even on a high-speed line?

36


Further Reading Atwell WA (2001) Wheat Flour. St. Paul, MN: Eagen Press. Benson RC (1988) Muffin technology. Technical Bulletin 10(6), American Institute of Baking, Manhattan, KS. Cauvain S (2002) Laminated bakery products: Influencing the outcome. European Baker, March/April, 48–53. Daniel AR (1963) Bakery Materials and Methods, 4th edn. England: Elsevier Applied Science. Hoseney RC (1995) Principles of Cereal Science and Technology, 2nd edn. St. Paul, MN: American Association of Cereal Chemists. Knight JB and Kotschevar LH (2000) Bakeshop production. In: Knight JB and Kotschevar LH (eds.) Quantity Food Production, Planning and Management, 3rd edn. New York: Wiley.

Manley D (2000) Technology of Biscuits, Crackers and Cookies, 3rd edn. Boca Raton, FL: Woodhead Publishing Limited and CRC Press LLC. McWilliams M (2001) Baking applications. In: McWilliams M (ed.) Foods: Experimental Perspectives. Upper Saddle River, NJ: Prentice Hall. Pyler EJ (1988) Baking Science and Technology, 3rd edn. Merriam, KS: Sosland Publishing Company. Townsend GM (2001) Cookies, cakes and other flour confectionary. In: Dendy DAV and Dobraszczyk BJ (eds.) Cereals and Cereal Products: Chemistry and Technology. Gaithersburg, MD: Aspen Publishers. Willyard M (2000) Muffin technology. Technical Bulletin 22(10), American Institute of Baking, Manhattan, KS.

Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics SP Cauvain, BakeTran, Witney, OX, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

•

Cookies, biscuits, and crackers are characterized by their low moisture content, their crisp or hard-eating properties, and their long microbial shelf life. Products’ shapes, sizes, and textures vary greatly. The category includes both sweet and savory forms. Flour, fat, and sugar properties all play key roles in determining final product character. Methods of dough processing are diverse and mostly carried out in large-scale automated plants.

Learning Objective

•

To attain knowledge of cookie, biscuit, and cracker types; ingredients used; and process steps required.

Introduction Cookie-, biscuit-, and cracker-like products have been made for hundreds of years. The word biscuit is derived from either the Latin bis coctus or the Old French ‘bescoit,’ meaning twicebaked. The name refers to the practice of first baking the products in a hot oven and then transferring them to a cooler oven to complete the drying-out process. The low moisture content of these products makes them generally free from microbiological spoilage and gives them a long sensory shelf life, provided that they are protected from the uptake of moisture from the atmosphere. Shelf life may be limited by fat rancidity. The long shelf life, together with their high energy density, has made them popular with travelers and explorers over the years, and they still form a significant proportion of emergency food supplies. However, today, most of the products in this diverse category are considered to be a sweet snack (Figure 1) or an accompaniment in savory-based meals. In a few cases, the role that these products can play in delivering specific nutritional requirements through fortification has been recognized, and ranges of products that meet the needs of certain medical conditions have also been developed, for example, for diabetics and celiac sufferers (gluten-free). This diverse group of products can be classified under five major headings according to the type of dough used in their manufacture:

•

•

Cookies (or short-dough biscuits) that contain high levels of sugar and fat together with low recipe water levels, yielding doughs with very little gluten development and short, crumbly textured final products. Hard-dough (semisweet) biscuits having lower fat and sugar levels and higher recipe water levels than shortdough biscuits. The doughs are extensible and have some gluten development.


•

Crackers prepared from yeasted or unyeasted dough with low fat levels, generally with no added sugar and having a high water level. The gluten in the dough is well or fully developed. Laminated biscuits in which the fat is incorporated into the dough as a series of more or less discrete layers with the dough having significant gluten development.

The manufacture of all of these products is most commonly carried out in large-scale automated bakeries manufacturing, assembling, and wrapping many thousands of units per hour. Smaller-scale operations tend to use smaller versions of the same processing equipment but concentrate on specialized products, for example, gluten-free.

Production of Cookies (Short-Dough Biscuits) Cookies have high levels of fat and sugar in the recipe (Table 1) and relatively low water levels that yield short crumbly doughs with almost no developed gluten network. The digestive biscuit (Table 2) is popular in the United Kingdom and elsewhere and is also sold half-coated with chocolate. Oat-based digestive biscuits are also very popular, often with a chocolate coat.

Rotary Molding Rotary molding is the process commonly used in the production of cookies. It relies on pressing the dough into molds to form the pieces. In the machine, the dough coats a feed roller and more dough is forced into the engraved molds of the molding roller, a knife scrapes excess dough from the backs of the molds, and the dough pieces are extracted onto a fabric band by the pressure of an extraction roller. The technique cannot normally be used for sticky doughs as they are difficult to extract from the molds. The doughs are usually processed soon after mixing. There is no waste to recycle.

Extrusion Soft and sticky cookie dough may be extruded by forcing the dough under pressure through a nozzle. Three main types of machine are used:

•

Wire-cut

The extruding nozzle used is the diameter or shape of the dough piece required. As the dough is slowly extruded vertically downward, a piano wire or blade is moved quickly through it just below the nozzle outlet and cuts the dough to the required dough piece thickness. The top surface of the product is formed by the cutting wire so it is not possible to impose any design on the biscuit. However, the rough surface normally bakes into quite an attractive appearance.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00119-4

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WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics

38

•

•

Rout press

The dough is extruded continuously as a ribbon and the nozzle is shaped to suit the cross section of the dough piece. The dough can be cut vertically into pieces either before entering the oven or after baking depending on the product required. The basic operation of a rout press is similar to that for a wire-cut machine. A typical recipe for rout press cookies is given in Table 3.

Fig Newton (roll) extruder

The Fig Newton (Table 4) is made with a special form of rout press in which two materials are coextruded; one forms a tube around the other. This requires a double hopper and double feed unit, one for each material, coming together at the nozzle concentric within the larger dough nozzle. A similar system can also be used to make biscuits from two colors or types of dough. The dough pieces undergo further shaping and cutting after extrusion. Chewy or soft-eating cookies may be formed by extruding two slightly different dough types (Table 5). The outer dough is similar to a regular cookie recipe, whereas the inner dough contains a very high substitution of high-fructose corn syrup for sucrose. Fructose is a powerful humectant, which means that it is difficult to remove water during baking. The result is a product with a soft, chewy, high-moisture-content center with a crispy exterior. It is possible to obtain similar textural characteristics for a few days after baking by adjusting the relative

Table 3

Flour Fat Sugar Skimmed milk powder Salt Ammonium bicarbonate Sodium bicarbonate Acidulant Water

Figure 1 Examples of cookies and short-dough biscuits. Table 1

Short-dough cookie recipe

Table 4

Flour Fat Sugar (pulverized) Skimmed milk powder Salt Acidulant Sodium bicarbonate Water

100 48 52 1.75 0.9 0.4a 0.8 19

a

Level depends on the choice of acidulant (see the succeeding text).

Table 2

Recipes for digestive biscuits

Flour Wholemeal flour Oats, rolled Fat Sugar Demerara sugar Golden syrup Salt Malt extract Tartaric acid Sodium bicarbonate Ammonium bicarbonate

Recipe for rout press cookies

Regular

Oat

78 22 0 31 8.3 16 7.1 1.1 1.2 0.7 1.6 0.4

40 40 60 31 33 0 5 1.1 0 0 1.6 0.4

100 28 28 1 0.5 0.2 0.6 0.3 17

Recipe for Fig Newton (Fig roll)

Flour Fat Sugar Glucose syrup Invert syrup Skimmed milk powder Sodium bicarbonate Ammonium bicarbonate Figs Water

Table 5

Outer case

Filling

100 16 43 0 7 0.4 0.5 0.4 0 16

0 0 80 10 0 0 0 0 100 variable

Recipe for soft-eating cookies

Flour Fat Sucrose High-fructose corn syrup Salt Sodium bicarbonate Milk powder Water Chocolate chips

Outer crisp layer

Inner chewy layer

100 45 85 20 1.4 1.4 4 17 0

100 58 36 95 1.5 1.5 0 0 75

WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics proportions of sucrose and high-fructose corn syrup (or invert sugar syrup) in regular cookies. However, the products tend to flow more and the surface becomes much smoother. This type of product is commonly made for immediate sale in retail outlets, and the dough may arrive in frozen form for bake-off. Some short-dough cookies may be further processed by assembling them in pairs (shells) with very low-moisture, fatbased creams or low-water jams placed as a layer in the twobiscuit sandwich (Figure 2). In many cases, the creams contain no moisture other than what might be contributed by the ingredients used. The low moisture content and low water activity of the filling are essential to prevent moisture migration from the filling to the biscuit shell; otherwise, the latter would lose its hard-eating character and go soft during storage.

Production of Hard-Dough, Semisweet Biscuits This group includes products that have higher fat and higher water levels (Table 6) that, together with the mixing regime, permit the development of a limited gluten network during mixing.

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Processing These doughs are mixed to a temperature around 40 C and have enough recipe water to produce a hydrated and developed gluten network. However, the strength of the developed gluten is modified either by using sodium metabisulfite (SMS) (see the succeeding text) or by adding about 25% extra water and using a higher work input (about 120 kJ kg 1 as compared with 90 kJ kg 1 for a sulfited dough). Once mixed, the dough is allowed to rest for up to 30 min in either a mixer or a tub before sheeting. During this time, the stored energy in the gluten is partly dissipated to give a ‘relaxed’ dough. The dough passes into a presheeter but is mainly processed through three pairs of gauging rollers with decreasing gaps. The gluten strands tend to line up in the machined direction, and an attempt is made to relax the dough just prior to cutting using a transfer web running at a slightly lower speed than the sheeting web. The sheet forms a series of standing waves a few centimeters high at the junction between the webs. Once the final sheet is formed, the dough is cut with rotary cutters or vertical reciprocating cutters. The process results in varying proportions of scrap related to the shape of the dough piece with respect to the overall dough sheet. This scrap must be recycled to an early stage in the process to either the presheeter or the first pair of gauging rollers with the fresh dough on top.

Production of Crackers and Laminated Biscuits Crackers (Figure 3) form a varied group of products that include saltine, chemically leavened, savory, and yeastleavened products (Table 7). The high water level hydrates the proteins during mixing and develops a gluten structure. The recipes typically have a low yeast level for a long fermentation process (see the succeeding text). Speciality crackers include savory crackers, which are sprayed with fat and dusted with salt and other materials. They can be unyeasted and may include either an SMS or a protease enzyme to modify the protein characteristics during dough formation.

Figure 2 Examples of cream sandwich cookies.

Table 6 Range of formulations for sheet and cut hard-dough, semisweet biscuits Ingredient Flour Fat Sugar Glucose Salt Acidulant Sodium bicarbonate Ammonium bicarbonate Sodium metabisulfite Water

100 16–20 21–25 1–2 1–1.2 0.15–0.20 0.5 1.0 0–0.022 19–24

Figure 3 Examples of crackers.

40 Table 7

WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics Recipes for soda and cream crackers Soda cracker

Flour Fat Salt Sodium bicarbonate Yeast Water (about) Yeast nutrients Fermentation

100 9.5 0.9 0.63 0.23 31 18

Cream cracker 100 12.5 1.4 0.1 1.4 32 Vary 4

100 12.5 1.4 0.1 1.8 32 0.5

Laminated (puff) biscuits are manufactured in a similar manner to crackers with the exception that the layering of the fat is more critical. In part, this is controlled by the choice of fat (see the succeeding text) and the number of fat layers created.

Mixing and Fermentation The preparation of cracker dough usually involves a period of fermentation after mixing. Commonly, this involves making an initial sponge with part of the flour, water, yeast, and salt and leaving this mixture to stand in temperature-controlled conditions for a fixed period of time, 12–24 h. After the sponge has fermented, it is mixed with the rest of the recipe ingredients and the final dough may be further rested for 1–6 h, depending on individual preferences. All-in dough processes may be used with a fermentation period of 4–16 h. All-in, short fermentation periods with increased yeast and continuous liquid fermentation systems may be used.

Sheeting, Laminating, and Cutting The most common method of delivering the fat for the lamination of crackers is by means of a ‘cracker dust,’ a mixture of flour and fat sprinkled into the sheeted surface of the dough before lamination. Once dusted, the lamination of crackers is carried out with either horizontal or vertical lapping machines. At each change of travel direction, there is a double thickness of dough outside. This tends to give crackers in lanes that are different in properties from those across the rest of the plant. Other laminators work on the cut and lay principle in which the dough sheet is cut to the full width of the plant and laid as a sheet across it. This eliminates the double thickness of dough at the edges and the dough sheet also has a chance to relax during the layering. The layered dough is reduced to about 1–2 mm thickness usually with three pairs of gauging rollers. This process tends to produce a uniform gluten structure in all directions in the dough. Cutting is quite critical in that the pressure used during cutting and docking (pricking of the surface) affects the formation of blisters on the finished cracker surface.

Key Ingredients Flour Cookie and biscuit manufacturers use flours derived from both soft and hard milling wheats, depending on the processing and textural characteristics required. Products manufactured with hard wheat flours alone tend to be denser, thinner, and harder-

eating than those made from soft wheat flours. They also require a higher water level to produce a processable dough, and more energy is used in the baking process. The main criteria for cookie and cracker flours are as follows:

• • • • •

Moisture – should not exceed 14% to avoid mold growth during storage. Protein – for short-dough and semisweet biscuits 8–9.5% and for crackers 9.5–10.5%. Starch damage – flours with lower water absorption capacities are generally desirable, and so low levels of damaged starch are preferred. Water absorption – may be measured as for bread making, but for biscuit doughs, it is more meaningful to assess the consistency of doughs made using biscuit recipes. Extension testing – dough rheology tests may be used to assess flour characteristics, especially for hard-dough and cracker production.

Biscuit dough fats Biscuit fats should have low solids in the range 20–35 C for processing and very low solids up to 40 C to avoid unpleasant greasy palate cling or waxy tastes. Fats may be received from the supplier as a liquid at temperatures around 45–55 C. In some products, for example, crackers, where the final dough temperature at the end of mixing is above the softening range of the chosen fat, liquid fat can be used directly. However, for shortdough products where the temperature at the end of mixing is within the softening range of the fat (20–30 C) and where the fat plays an important structural role in the dough, more complex processing is required to ensure that a constant proportion of solid material in the correct crystal state of fat is present in the dough mixer. This processing is known as plasticizing the fat and is carried out using a scraped surface crystallizer. The fat blend is cooled to 30–35 C and then passed through a chiller. It should leave this unit at around 22 C in a partially crystallized state. The product is stored in waterjacketed silos at around 28 C for 6–24 h when further recrystallization takes place. After storage, the solid fat crystals should be of the ‘b’ polymorphic form, a dispersion of small crystals and a matrix of chain-like structures to contain the liquid oil components. Increasing the level of fat in recipes produces softer-eating products but can alter other biscuit characteristics. For example, higher fat levels in short dough induce flow during baking, leading to thinner biscuits with larger diameters.

Puff biscuit and cracker fats In puff biscuits, the laminating fat must be sufficiently firm yet pliable to keep the dough layers separate and relatively undamaged. The important feature is the solid fat index (SFI) and the size of the crystal. Both contribute to the hardness of the fat; optimally, the SFI should be high and the crystal size small. Puff biscuit fats have a higher SFI in region of 30–35 C compared with short-dough biscuit fats but should have a low SFI at body temperature. Large fat crystals interrupt the dough layers and so there will be poor separation. In contrast, small fat crystals will give good separation of the layers, resulting in a flakier product. The characteristics of cracker fats are similar to

WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics those of puff biscuit fat even though it is not required to form discrete fat layers to the same extent.

Butter Butter gives biscuits a distinctive flavor, but as a shortening agent, it is less functional because its dilatation characteristics are not ideal and it is more susceptible to rancidity. The flavor of butter comes from a compound called diacetyl, which is present in butter in quantities ranging from 0.5 to 2.0 parts per million. Standard butter and margarines contain around 15% water. Therefore, when changing recipes containing butter or margarine as shortening, it is essential to reduce the level of shortening by 15%. It may also be necessary to increase the recipe water level.

semisweet but only 10% of that for short-dough biscuits; the remainder of the increase is due to steam generated by the dough water during baking. Leavening agents used include the following:

•

Sugars Sugars affect product dimensions, color, hardness, structure, surface finish, and sweetness. White and brown sucrose, glucose, glucose syrup, golden syrup, invert sugar syrup, and highfructose corn syrup are all used in. At low levels, the sugar goes into solution during heating and forms a glass-like structure when cooled. This results in an open texture when no gluten has been developed. The hard-eating properties of crunch biscuits are due to their high sugar content: for example, gingersnaps contain upward of 34% sugar, compared with 19% in shorter-eating digestives. Sugar inhibits gluten development by competing with the flour for the recipe water. In short-dough biscuits, which have high sugar and low recipe water levels, some of the sugar dissolves in the water to form a saturated sugar solution, leaving no free water to hydrate the flour protein to form gluten. Many biscuit manufacturers mill crystalline sugar to change the particle size distribution. When a crunchy, coarse-eating product is desirable, a proportion of granulated sugar is added. Particle size affects the rate of solution of sucrose during mixing and in short-dough biscuits affects biscuit dimensions and texture. Larger-particle-sized sugar produces doughs that flow less during baking, meaning that the biscuits produced are shorter, wider, and thicker. Large sugar particles increase in biscuit hardness. A proportion of granulated sugar is essential in gingersnap biscuits to give them their characteristic cracked surface. Large sugar particles, which have not dissolved during mixing, melt to form a glass on the surface during the early stages of baking. As the dough expands, the glass cracks, resulting in the typical cracked surface appearance. Sugar contributes to color via Maillard browning reactions, which require the presence of both reducing sugars and amino acids. Sucrose is not a reducing sugar but is partially hydrolyzed to glucose and fructose (reducing sugars) during baking. Some of the compounds produced by Maillard reactions contribute to biscuit flavor. Brown sugars contribute to biscuit flavor and color both via Maillard reactions and due to small quantities of aromatic compounds from the molasses.

Leavening in biscuits Leavening (raising) agents decrease biscuit bulk density to give a softer-eating product. The extent to which bulk density is affected depends on the type of biscuit. For instance, raising agents account for about 50% of the increase in thickness of

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•

•

Ammonium bicarbonate often referred to as ‘Vol’ breaks down on heating to give ammonia and carbon dioxide gases. It decomposes very fast at about 60 C when the product is being heated in the oven though it is volatile at all temperatures and will react with acids. A major advantage of using Vol is that there are no solid residues at the end of baking. It should not be used in very thick or high final moisture content products as some of the ammonia released on decomposition dissolves in the dough water and some may remain in the finished product, giving a slightly bitter flavor. Vol has low solubility so it should always be added to the dough in water to avoid small pimples from undissolved salts forming on the biscuit surface. Sodium bicarbonate is widely used by itself or in conjunction with an acid. There is always a residue in the biscuit of sodium carbonate from thermal decomposition or a sodium salt of the acid used. Acids can be used in conjunction with sodium bicarbonate. Some examples are shown in Table 8 with an indication of their speed of reaction and the amount needed to neutralize one part of sodium bicarbonate. The first three on this list are the most commonly used. Glucono-delta lactone is not an acid but is converted to gluconic acid when heated in the presence of water in the dough and also has potential for use in prepared mixes or chilled or frozen doughs.

Other ingredients

•

• •

SMS may be used to modify the rheological characteristics of sheeted dough. Used at low levels, SMS reduces the disulfide bonds in the glutenin fraction of wheat gluten and makes the dough less elastic. Where SMS is not permitted or used, then an increase in the added water level in dough making is the practical alternative (see the preceding text). L-Cysteine hydrochloride may be used as an alternative to SMS but is commonly considered to be only about half as effective at typical levels of addition. Proteases (enzymes) may be added to randomly hydrolyze proteins and reduce dough elasticity. In general, they are not effective agents in semisweet recipes because of the low level of available water in dough but are used in snack

Table 8

Acids used with sodium bicarbonate

Acid Acid calcium phosphate Potassium acid tartrate Sodium acid pyrophosphate Tartaric acid Sodium acid aluminum phosphate hydrate Glucono-delta lactone

Speed of reaction

Amount to neutralize 1 part of NaHCO3

Fast Medium Medium Medium Slow

1.25 2.25 1.33 0.95 1.0

Slow

2.12

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•

•

•

• •

• •

WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics crackers to modify the dough handling characteristics and give a more tender-eating cracker. Emulsifiers may be added as part replacement of the recipe fat. Their action reduces the surface energy between the oil and water interfaces in the dough. Less energy is required to spread the fat throughout the dough, and the mixture behaves as if extra fat had been added. Emulsifiers found to have such an effect are sodium stearoyl-2-lactylate (SSL), citric acid esters of monoglycerides (CAEM), diacetyl tartaric acid esters of monoglycerides (DATEM), and lecithin. The level of fat that can be replaced by adding 0.25% (flour weight) of an emulsifier into a short-dough recipe is given in Table 9. Polyhydric alcohols are used in the manufacture of cookies for diabetics. They are produced by hydrogenating sugars, and their use in foods is limited because of their laxative effect. Salt improves flavor and is particularly important in sweet biscuits (typical level about 1% on flour weight). It can be used in the dough of all biscuit types and dusted onto fatsprayed crackers. Milk products may be used to deliver flavor and color. Cocoa powder and chocolate may be used in dough or creams for both flavor and color. When using cocoa, it is necessary to add extra water to the formulation. Chocolate chips are commonly added to manufacture wire-cut cookies. Peanuts, almonds, hazelnuts, pecans and coconut, and finely chopped dried fruits can be used to flavor biscuits and change texture. Liquid egg products may be used in the manufacture of some specialty products.

Mixing cookie, cracker, and biscuit dough Mixing has to produce a homogenous dough from the ingredients. The flour particles will absorb water and the proteins hydrate if there is enough free water. Cookie dough tends to have low water content by comparison with bread dough, and there is significant competition coming from the recipe sugar and to a lesser extent (because of the lower level of addition) the salt. The dough characteristics change with time after mixing and often they become stiffer. Where doughs have a significant gluten network, the tendency is to rest them before processing (commonly 10–40 min) to enable easier processing and limit potentially adverse impacts on biscuit shape. The main types of mixing processes may be described as follows:

•

All-in where all of the ingredients are added to the mixer at the start. This is best for doughs with some gluten Table 9

Emulsifiers as fat replacers

Emulsifier

Fat replaced by 0.25% (flour weight) of emulsifier in the recipe (%)

SSL DATEM CAEM Lecithin

20 20 13 5

•

•

development. If used for short doughs, extra water is needed to achieve a standard consistency. Two-stage, usually called creaming, where all of the ingredients apart from flour and materials such as nuts are mixed to a cream, and then the flour is added and mixing continued to form the dough. Multistage where the flour may be added in more than one portion. If used, nuts, fruits, or chocolate chips are added in a third stage by blending them in on slow speed.

The common types of mixers used are as follows:

•

• •

• •

Vertical spindle machines with two or three spindles in a large tub. They may hold up to 1 tonne of dough. The spindles turn at speeds up to 25 rpm, and long mixing times are used, especially for hot doughs. They are used mainly for all-in processes. Horizontal spindle machines, often referred to as highspeed mixers, though they mix to only 75 rpm. They usually have two bars of varying shape. Horizontal mixers with two beaters and a central metal sprag (bar) between the mixer arms. The rate of work input is higher compared with parallel arm mixers and results in shorter mixing times and more gluten development. Double Z-blade mixers with two blades running counterrotating. Continuous mixers that are often dedicated to a single product and processes. They require a very high standard of metering equipment, and it is a normal practice to dissolve minor ingredients in some of the recipe water before addition.

Changes in biscuits during baking The baking of biscuit products is usually carried out in a few minutes, typically around six, but may range from 2 to 15 min. Industrial ovens are commonly 60–100 m in length and 1–2 m wide. The aims of the baking process can be summarized as follows: 1. Development of the biscuit structure 2. Setting of the biscuit structure by partly drying it 3. Completion of drying and coloring of the biscuit structure The dough piece enters the first section of the oven at temperatures around 25 C and water content 10–30% depending on type. On entry to the oven, the dough pieces are below the dew point of the oven (typically 55 C for a gas-fired oven), and water in the oven atmosphere condenses on the dough piece surface, transferring its latent heat to it. The condensed water aids the development of a smooth finish in semisweet biscuits and a cracked surface on high-sugar cookies; however, effects on other product types are limited. The surface water soon evaporates and the dough piece starts to lose water. As the piece increases in temperature, the following processes happen:

•

The fat melts and any undissolved sugar goes into solution in the dough water, the viscosity of the dough piece is reduced, and it begins to flow.

WHEAT-BASED FOODS | Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics

•

• • •

•

•

•

Ammonium salts lose carbon dioxide rapidly at temperatures up to about 60 C; the ammonia released dissolves in the dough water and is lost during the remainder of the baking time. Sodium bicarbonate starts to produce carbon dioxide by thermal decomposition or by reaction with acids in the dough. The dough piece expands due to reduced internal viscosity and gas pressure developed by the leavening and water evaporation. In the case of crackers, most of the increase in thickness is due to the separation of the dough layers and blister formation. This is caused by steam generation and increases in thickness of the individual layers. Biscuits tend to reach a maximum volume some time before the end of the bake, which cannot be sustained by the internal gas pressure, and hence, they decrease rapidly in thickness. At this stage of baking, the biscuit can be considered as having a set structure due to an increase in viscosity in the dough as the moisture content decreases. Other factors influencing setting are the dissolved sugar, protein denaturation, and starch gelatinization. The sugar solution becomes saturated and increases in viscosity, as the moisture is lost because it behaves like a molten glass. Proteins will denature at temperatures from about 70 C and lose their flexibility. Starch will gelatinize from about 60 C upward depending on dough water level and the sugar content; starch swells and absorbs water as crystalline regions in the granules melt, giving an increased viscosity in the dough piece. The temperatures for protein denaturation and starch gelatinization increase for increasing sugar concentration. In short-dough biscuits, there is little starch gelatinization, and in semi-sweet biscuits, up to about 20%. Browning of the surface takes place late in the baking process with yellow tones formed first at temperatures above 110 C. Red tones form at higher temperatures giving rise to a brown color on the biscuit surface. These reactions coincide with biscuit moisture contents of about 6% downward. If baking is prolonged or the biscuits packed at much above ambient temperature, the crumb will also color.

Because coloring is normally seen toward the end of baking, it is a common practice to increase the temperature (and hence heat flux) in the final zones of the oven to increase color when needed. Some direct-fired ovens are fitted with ribbon burners above the band and down the last few meters of the oven for this purpose.

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techniques on both final and intermediate products can deliver more consistent product dimensions and qualities. It is inevitable that there will be a strong focus on the potential for reducing energy consumption for the manufacture of cookies in bakeries. This will include more efficient oven design and operation, the recovery of useful heat from the oven exhaust system, and improvements in process control so that wastage is reduced. The manufacture of products with specific nutritional profiles will continue to grow as consumers seek healthier products. This will involve further reformulation and process changes to enable the incorporation of ingredients that may be higher in fiber and with the addition of particulates, such as nuts and dried fruits, all of which interfere in the intrinsic structure of the dough and structural integrity of the final product.


• • • • • • •

What are the key characteristics of cookies, biscuits, and crackers? What differentiates the various types of cookies, biscuits, and crackers? What are the main requirements for biscuit flours? What are the main requirements for cookie and cracker fats? How does the particle size of sugar affect product characteristics? What is the role of leavening agents? What are the structural changes that occur during baking?


• •

What opportunities might exist for reducing fat and sugar levels in cookie and cracker products? What opportunities might exist for fortifying cookies and crackers to deliver specific benefits?

See also: Food Grains and the Consumer: Fortification of GrainBased Foods; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; The Gluten-Free Diet; Wheat Processing: Chemistry of Cake Manufacturing; Oven Technologies; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wheat: Dry Milling; WheatBased Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Future Considerations Changes in raw materials, their properties, and availability will continue to drive the development of improved practices in the manufacture of cookies, biscuits, and crackers. Though current production is highly automated, there is still room for improved process control; in particular, online imaging

Cauvain SP (2009) The relevance of testing to the manufacture of biscuits (cookies), cakes and pastries. In: Cauvain SP and Young LS (eds.) The ICC Handbook of Cereals, Flour, Dough & Product Testing; Methods and Applications. Lancaster, PN: DEStech Publications Inc. Cauvain SP and Young LS (2001) Baking Problem Solved. Cambridge, UK: Woodhead Publishing Ltd. Manley D (2000) Technology of Biscuits, Crackers and Cookies. Cambridge, UK: Woodhead Publishing Ltd.

Cookies: A Diverse Family of Baked Goods S Zydenbos and V Humphrey-Taylor, (Retired) New Zealand Institute for Crop Food Research Limited, Christchurch, New Zealand CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by S. Zydenbos, V. Humphrey-Taylor and C. Wrigley, volume 1, p. 313–317, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • • •

‘Cookies’ are a family of small, flat, baked products, often sweet, made from wheat flour. Cookies are also known as biscuits (meaning twice-cooked) because historically, they were double cooked to provide a very dry food with a long shelf life. While wheat flour is the common base ingredient, other grain species are often involved, such as oatmeal cookies. Biscuits are often chemically leavened; some crackers are yeast-fermented. The major ingredients are flour, sugar, shortening, emulsifiers, and water, each having a specific role. Minor ingredients include salt, flavors, colors, eggs, dairy products, malt, and leavening agents. The baking process is usually fast, given their flat shape, resulting in loss of water and weight reduction.

Learning Objectives

•

Achieve understanding of the family of biscuits, cookies, and crackers, with respect to their formulation, processing, chemistry, shelf life, and potential for an even wider range of types.

Introduction There is a great diversity of baked goods in the family typified by cookies, biscuits, and crackers. This diversity is evident on the shelves of a Western-style supermarket, but worldwide, the diversity is even greater. These family favorites are also well known in home baking because of their simplicity. They are characterized by a low moisture content (below 5%) and a cereal-flour base of at least 60%. The flour is usually from wheat, but it may also involve oats, barley, rye, maize, or rice to some extent. The other major ingredients are shortening and sugar. Obviously, water is also added but usually much less than for breads and cakes. This article describes the history and usage of cookies, biscuits, and crackers and the classification of the various types. An overall range of types is illustrated in Figure 1.

Historical Origins The terms ‘cookie,’ ‘biscuit,’ ‘cracker,’ ‘biscotti,’ and ‘zwieback’ refer to a family of small, flat, baked products, often sweet, made from cereal flour, usually wheaten. ‘Cookie’ obviously derives from the general verb to ‘cook,’ but it may also derive from the Dutch word ‘koekje’ (meaning little cake). The name ‘biscuit’ comes from Latin, where ‘bis coctus’ means twice-

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baked. There is also an Old French word, ‘bescoil,’ that has a similar meaning. The sound of a cracker being eaten probably led to the use of that name. There is a consistent meaning of twice-cooked in the words ‘biscuit,’ ‘biscotti,’ and ‘zwieback,’ respectively, with French, Italian, and German origins. As used now universally, cookies no longer have the twicebaked connotation, but originally, this form of preparation was applied literally. After the initial baking, the product was dried out further in a slow oven to ensure a very dry product, which would ensure a long shelf life. ‘Hardtack’ was the extreme product of this type; it was baked more than twice to ensure long life on the early sailing voyages. A similar dry food was used by the Roman legions on long marches two millennia ago. Whereas the original process consisted of baking the biscuits in a hot oven and subsequently drying them in a cool oven, it is rare to find this double-baking technique in modern biscuit production. However, a special type of microwave oven may be connected after a gas-fired oven in factories. Biscuit, as defined earlier in the text, is a term used in the United Kingdom (and in New Zealand, Australia, and South Africa). A historic version dating back to seventeenth-century England is the ‘Digestive’ (Figure 2). The ‘Scotch Finger’ (Figure 3) is another traditional biscuit, but having higher fat and sugar contents than the Digestive. The word biscuit is also used for a different baked product in the United States, namely, a leavened bread-like product that is similar to the English scone; it is not considered a part of the cookie family that is discussed in this article. In the United States, the word ‘cookie’ describes the same type of products that are called biscuits in the United Kingdom. Oatmeal and chocolate-chip cookies (Figures 4 and 5), though manufactured, are made to simulate the home-baked product. ‘Cracker’ is a generic term used throughout the world and refers to products with low sugar and fat contents. The cracker is usually associated with cheese and savory dips (Figure 6). The common cracker is circular, with a serrated edge, ‘docking points,’ and some variegation in color between the docking holes (Figure 7). Larger and rectangular is the Graham cracker (Figure 8) more common in the United States. A further variation is the cream cracker (Figure 9), which is made by a process of lamination of successive layers of dough, resulting in a multilayered cross section. The cheese crackers in Figure 10 may involve a spray of oil and dusting with flavored particles. A variation of the sweet cookie is the formation of a creamfilled sandwich, such as that appears in Figures 11 and 12. The name ‘Melting Moments’ has been given to the cookies in Figure 12 because the cooked part is equivalent to shortbread. The word ‘short’ refers to the crumbling texture of the cookie because of the high fat content; shortbread traditionally has a recipe consisting of sugar, butter, and flour in the approximate proportions of 1:2:3 by weight. Enrobing with chocolate is a


http://dx.doi.org/10.1016/B978-0-12-394437-5.00250-3

WHEAT-BASED FOODS | Cookies: A Diverse Family of Baked Goods

Figure 1 Biscuits come in a wide range of shapes, sizes, textures, flavors, and colors. Reproduced from Wrigley C, Corke H, and Walker C (eds.) (2004) Encyclopedia of Grain Science, first ed. Vol. 1, pp. 313–317, Elsevier Ltd.

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Figure 4 Oatmeal cookies are commonly baked at home.

Figure 2 The English ‘Digestive’ biscuit, classed as a semisweet biscuit, made with chemical leavening.

Figure 5 Chocolate-chip cookies illustrate the possibility of incorporating other foods in the cookie dough before baking.

Figure 3 The classical ‘Scotch Finger’ approximates to being shortbread because of its higher fat content.

Figure 6 Crackers are traditionally served with cheese and a savory paste into which the crackers are dipped before being eaten.

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Figure 7 The common circular cracker (‘Jatz cracker’). The top-right cracker is turned over to show the imprint of the traveling wire belt from baking.

Figure 10 Cheese crackers have been sprayed with oil and dusted with a flavoring agent.

Figure 8 The common rectangular cracker (‘Graham cracker’). The imprint of the traveling wire belt is shown for the cracker at the bottom. Figure 11 Cream sandwich cookies, with spots of cream and of raspberry jam between the two cookies.

Figure 9 Cream crackers are produced from a laminated dough, giving a multilayered texture to the baked cracker.

Figure 12 ‘Melting Moments.’ Cream-filled shortbread.

WHEAT-BASED FOODS | Cookies: A Diverse Family of Baked Goods further enhancement, as shown in Figure 13 with chocolatecovered biscuit sticks. Figure 14 illustrates a variation in which a mixture of sultanas and berries is surrounded by a soft biscuit-cake covering. The low moisture content of biscuits, cookies, and crackers means that these products have a relatively low risk of spoilage by microorganisms. This has led to a history of usage in epic journeys, such as the flight of the Israelites from Egyptian slavery and the sea voyages of the fifteenth-century explorers. British and European traditions usually served biscuits in a semiformal situation with tea or coffee between main meals, especially in the afternoon. Small biscuits were usually made so that a range of appearances and flavors could be eaten without a large intake of food. Modern biscuits, cookies, and crackers are often used as a casual snack food, especially in the United States. Many of these are much larger than traditional biscuits, as they are sometimes eaten to replace meals by consumers who have busy lifestyles.

Figure 13 Biscuit sticks enrobed with chocolate are one variation of the many possibilities of enrobing the basic biscuit.

Figure 14 Garibaldi-type biscuits containing a sultana–berry mix as the filling.

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Classification Geographic location plays an important role in the classification of biscuit and cookie names. In particular, distinct names are used in the United Kingdom and the United States, while in other parts of the world, the distinction between biscuits or cookies and cakes is not as clear; these products are often classified as small confectionery products. For example, biscuits in France are often classified under the title ‘petits fours sec.’ These words literally translate as small oven dry, giving the implication that these are small, dry baked goods. However, petits fours secs may also encompass other products that are outside the biscuit definition given in the preceding text, such as cake-, meringue-, and pastry-based products. Biscuits that are too large to be put in the mouth at one time would be called ‘les petits gaˆteaux secs,’ meaning small dry cakes. A similar distinction exists in Germany where biscuits are called ‘kekse’ or ‘konfekt,’ but only if they are small. In the United Kingdom, biscuits are classified on their formulation, the two major categories being hard and short doughs. Hard doughs are similar to bread doughs but have a much stiffer consistency. With hard doughs, the threedimensional gluten network is well developed during the mixing process, so the dough is both elastic and extensible. The formula for hard doughs is very lean, as the content of fat and sugar relative to flour is very low. Crackers are made from hard doughs, as are semisweet, unsweetened, and savory biscuits. Short doughs are more closely related to cake doughs than bread doughs, although they have less water than a standard cake formula. Short doughs are so named for their higher content of shortening or fat than hard doughs. They also have a higher sugar content. The increased levels of fat reduce dough extensibility, causing this type of biscuit or cookie to break easily. The flour in short doughs is given very little mixing, so the development of a gluten network is minimized. The consistency of short doughs has been compared with wet sand; they hold together under pressure but crumble easily. Short doughs have a subgroup called soft doughs that have higher levels of fat and sugar, resulting in a dough with an even softer consistency. Biscuit classification in the United States is based on the method of processing and, in particular, the way the biscuits are shaped. The four main categories are sheeting or cutting (sometimes called cutting machine doughs), rotary molding, wire cutting, and depositing. Sheeting is used for doughs that would be classified as hard doughs in the United Kingdom and is always used for making crackers. The dough is passed through a series of rollers until it reaches the required thickness. The biscuit or cracker shapes are then cut out of the dough sheets using a plastic or metal die. It is important that the dough is strong and elastic so that the biscuits and cracker shapes do not deform when excess scrap dough is removed from around the shapes. Rotary molding is used for short doughs and requires a dough with a relatively stiff consistency that is not too sticky. The dough is compressed into dies mounted on the surface of a roller, and any excess dough is scraped off. The molded dough piece retains its shape as it is pushed out of the die on to the baking sheet or band. Short doughs may also be shaped by wire cutting, which involves extruding the dough through a die and slicing it with a

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tight wire at appropriate intervals. The tension placed on the dough during extrusion and the thickness of the wire will vary for different types of doughs. Because soft doughs are similar to a batter, having a semifluid consistency and lacking cohesiveness, they are shaped by depositing. The dough is extruded through a nozzle and dropped on to the baking sheet or band. To achieve uniformity in size and shape of the biscuits or cookies, the flow of dough is cut off at regular intervals.

Types of Crackers Attributes that distinguish crackers are very low levels of fat and sugar (Figures 6–10). They are often used as a basis for a savory topping, such as cheese or tomato, but the modern snack cracker, with its tasty coatings and flavors, may be eaten without additions. Crackers may be further subdivided into those that are fermented, including soda crackers, saltines, and cream crackers, and those that are chemically leavened like the popular snack cracker. Soda crackers have been popular in the United States for over 150 years. They are typically 4 mm thick and 50 50 mm square. The shortening content is 8–10%. Saltines are a smaller, daintier type of soda cracker with an increased amount of shortening. Traditional soda cracker manufacture involves long fermentation using a sponge starter. Soda crackers have a significant amount of sodium bicarbonate added to the dough (1%), which increases the alkalinity and is the reason for the name of the cracker. Once the dough is mature, it is sheeted to about 4 mm and then laminated 6–8 times. The cracker is cut by making lines of perforations and baked as a whole sheet, a process that minimizes the amount of waste dough. A feature of soda crackers is the nine-hole docking pattern on each cracker, set out in a 3 3 grid pattern. After baking, the sheet of crackers is split along the perforation lines, usually to make a block of four crackers for packaging. The final product is quite flaky but crisp. The spring between the docking holes on the top of the cracker should be even, and the bottom surface should be almost flat with numerous small blisters. Because soda crackers are quite dry and bland, they are not usually eaten alone and are often used as an accompaniment to soup. In the United Kingdom, soda crackers are rare, and cream crackers fill a similar market niche (Figure 9). Despite their name, cream crackers contain no cream! They have a slightly higher fat content (12–18%) than soda crackers. Cream crackers generally have a 65 75 mm rectangular shape and are slightly thicker than soda crackers with about 6.5 mm between biscuits stacked in a column. Unlike soda crackers, they are usually produced as individual units. While, traditionally, the long sponge and dough fermentation process was used for manufacturing cream crackers, modern techniques involve a single-stage mixing and fermentation process, which takes from 4 to 16 h. As with soda crackers, cream crackers are sheeted and laminated. A feature of cream crackers is the laminating ‘dust,’ consisting of flour, shortening, and salt, that is applied between the layers of dough. This causes the laminations to lift apart during baking, giving an extra flaky structure. The movement of the laminations and subsequent surface blistering are quite irregular, giving the cream cracker its characteristic uneven surface. Blisters are present on both

the top and bottom surfaces. Cream crackers have a final moisture content of 3–4%, which is quite high for a cracker, and along with the increased fat content, the cracker is relatively soft, will not crumble, and should ‘melt in the mouth.’ Without chemical leavening, cream crackers are bland but have a slightly nutty flavor. They are mostly eaten with a savory topping and are often buttered. Snack or savory crackers have a more recent history than soda and cream crackers. They have two distinguishing characteristics. The first is that the cracker is sprayed with hot oil as it leaves the oven, and the second is that a topping is applied to the crackers to add flavor (Figure 10). Snack crackers usually contain some sugar (4–10%), which also adds flavor and texture. They are usually chemically leavened, but some snack crackers are made from fermented doughs. Because snack crackers do not have the long fermentation to mature the dough, proteolytic enzymes or sulfites are used to relax the doughs so that the crackers do not deform during sheeting and cutting. Snack crackers come in a wide range of shapes and sizes but are often round and have docking holes to allow an even lift during baking. Only snack crackers produced by fermentation are laminated. Toppings are generally applied before baking and include herb, cheese, salt, chicken, and smoke flavors. Sometimes, the crackers are decorated with small seeds, such as poppy, sesame, or celery. Snack crackers have a dense texture and are quite soft. The hot oil spray improves the mouth feel and gives an attractive appearance to the finished product.

Cookies and Biscuits Made from Hard Doughs Sweet and semisweet biscuits (e.g., Figure 2) made from hard doughs are generally more popular in the United Kingdom than the United States. While the gluten network is relatively well developed by mixing, the higher amounts of sugar (about 20% of flour) and fat (16–20%) than in cracker doughs make the gluten less elastic and more extensible. Chemicals, such as sodium metabisulfite or other chemical derivatives of sulfur dioxide, can also be used to condition and relax the dough to facilitate processing. Unlike cracker doughs, most hard sweet and semisweet biscuit doughs are chemically leavened. After mixing, the dough is sheeted and formed into shapes. The individual biscuits are cut out of the dough sheet, leaving a web of scrap dough to be removed and incorporated back into the main batch of dough. These biscuits are generally docked and marked with a name or pattern before baking. Sometimes, a milk or egg/milk wash is applied to enhance their appearance after baking, and occasionally, a garnish of sugar or other granular material is applied. Baked biscuits should have a smooth, even surface with a pale color. The texture of the biscuit is open and even, giving a delicate bite, although this is somewhat dependent on the formula – lower levels of sugar result in a harder bite. The ingredients in sweet and semisweet biscuits are quite plain, so the flavor is usually a mild vanilla, caramel, or buttery flavor. The biscuits are generally served without accompanying food and are eaten with tea or coffee. There are some interesting variations of sweet and semisweet biscuits, such as those that are processed after baking to incorporate a cream sandwich (Figures 11 and 12) or chocolate coating (Figure 13). The

WHEAT-BASED FOODS | Cookies: A Diverse Family of Baked Goods Garibaldi fruit sandwich biscuits (Figure 14) have a layer of currant or small sultana filling between layers of hard dough.

Cookies and Biscuits Made from Short Doughs Most of the biscuits and cookies consumed worldwide are made from short doughs, and consequently the range of shapes, sizes, flavors, and ingredients is huge. Formulas are correspondingly variable, but there are some consistent requirements. Flour is usually weak, with less than 9.5% protein. While there are no rules for the proportions of fat and sugar, which can range up to 100% and 200% of flour weight, respectively, the quality of these ingredients is important since they make up such a large proportion of the dough. Short doughs are usually mixed in a two-stage process with an initial creaming of the fat and sugar, although modern techniques tend to use the ‘all-in’ mixing method. The doughs are cohesive and plastic but lack extensibility and elasticity. The consistency of the dough will vary according to the requirements of the machinery used to form and shape the biscuits. As described earlier in the text, the two main processes for forming short dough biscuits and cookies are rotary molding and wire cutting. Rotary molding originated from the simple wooden molds often used in monastery kitchens to produce biscuits and cookies containing inscriptions. With a rotary mold, dough is continually fed from a hopper and forced into a metal die on a rotating roller. The formed dough shape is pressed out of the mold on to the baking band as the roller rotates. Unlike hard doughs, which tend to shrink during baking, short and soft doughs generally spread because of the high sugar and fat content. This is a particular disadvantage of rotary molding as the inscription can become blurred. Tight control of the formula is necessary to reduce spread. Rotary cookies should be thin and smooth with no surface cracks or irregularities. Because of their regular size and shape, rotary cookies may be used to make cream sandwiches in the same way as hard sweet biscuits. Wire cutting is a form of extrusion; the dough passes through a die and is sliced at intervals by a tight wire so that the formed dough shape drops on to the baking band. Doughs intended for wire cutting are usually softer than rotary molding doughs; more chunky ingredients, such as chocolate chips, nuts, or raisins, may be incorporated. A variation of the wirecutting process is a rout press that extrudes dough continuously. The dies on a rout press are designed to produce strips, which are cut into short lengths before baking. Both these techniques can be adapted to coextrude by having two different doughs or a dough and a filling coming from separate hoppers into a single die that forms a dual-layer cookie (e.g., chocolate/ vanilla) or a dough tube often filled with a fruit paste of similar consistency.

Cookies and Biscuits Made from Soft Doughs Soft doughs have a pourable consistency, are typically rich in fat (65–76% of flour weight), and may be based on whipped egg whites (15–25%). Sugar is 35–40% of the flour weight. Weak flour is used, and mixing is in a two-stage process. The flour and other dry ingredients are added last, and only minimal mixing takes place to prevent the dough from becoming

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tough. Often, rich, expensive ingredients, such as ground almonds, coconut flour, or cocoa, are used in soft doughs. However, coarse particles are avoided, because they may block the nozzles during depositing. Dough temperatures are important to achieve the correct consistency for forming the specific type of biscuit or cookie required. Temperatures generally range between 10 C and 17 C. The dough flows from the hopper through a nozzle on to the baking band. The nozzles may be of different shapes and sizes to alter the appearance of the cookie, but because the dough flows a little after depositing, these designs may be rather irregular. Some depositor heads can be rotated to make swirls and circular shapes, while two or more depositors may be synchronized to combine doughs of different flavors or colors within the same biscuit or cookie. Soft dough biscuits and cookies have a soft, delicate texture and a ‘melt-in-the-mouth’ feel (e.g., Figure 12). However, these properties make them fragile and subject to breakage, and packaging can also be difficult because of the irregular shapes.

Decorating Biscuits and Cookies The nature of the final product can be further altered by secondary processing after baking. A wide range of processes are used to finish and decorate biscuits, cookies, or crackers, some of which have already been referred to. Two of the most popular are cream sandwiches (Figures 11 and 12) and chocolate coating or enrobing (Figure 13). In a cream sandwich, the cream usually makes up about 30% of the final biscuit weight and consists of sugar, fat, and flavorings, such as fruit acids, cocoa powder, and skimmed milk powder. The cream is either poured into a stencil positioned over the top of the biscuit base or deposited directly on to the base. Working with chocolate is technically difficult because of the necessity to control the temperature accurately. The properties of chocolate are quite variable and depend on the ingredients that were used to make the chocolate. Various methods of fully enrobing or partially dipping the biscuit or cookie into a chocolate bath are used, depending on product specifications. Icings, made from icing sugar, water, and sometimes fat or a gelling agent such as gelatin, are another popular finishing on biscuits. Jellies, jams, marshmallow, caramel, fruit, seeds, and nuts may also be used to enhance the taste and texture of biscuits, cookies, or crackers.


• • • •

Summarize the range of major ingredients that go into the manufacture of biscuits and related products. What are their respective functions? Describe the types of flour best suited for the various types of cookies. Explain how they differ from flour types used for conventional breads, noodles, and pasta. Salt and sugar are relatively minor ingredients, but they have various roles. What are these contributions? Salt and sugar may seem to be opposite in taste sensation. How can their roles be compatible and even attractive?

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• •

WHEAT-BASED FOODS | Cookies: A Diverse Family of Baked Goods Describe the respective types of dough used for cookie-type baked goods, namely, hard, soft, and short. What are the reasons for these different dough types? What are the various processing factors and ingredients that contribute to the external and internal color of biscuits and related products?


•

•

•

•

Compare home baking of cookie-type goods with factory production. What are the relative advantages and disadvantages of each of these approaches to making cookies? Make suggestions about how to overcome the inherent disadvantages of either approach. Explore the concept of shape for biscuits and related foods, thinking of variations in the surface features as well as the shape, seen from the preceding text. What further novelty features may be possible? What are the restrictions in exploring extreme shapes? Cream-filled sweet biscuits are common. Explore the possibility of using the cracker type of biscuit for the production of a savory-based cream-filled sandwich. What problems might arise? Chocolate enrobed biscuits are also common. Explore the possibility of using other materials that might be used in this way.

See also: Carbohydrates: Starch: Chemistry; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Food-quality Testing: The Application of Sensory Science to the Evaluation of Grain-Based Foods; Grain Composition and Analysis: Standardized Test

Methods for Grains and Grain-Based Products; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; Extrusion Technologies; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Cereal Food Production with Low Salt; Chemistry of Cake Manufacturing; Oven Technologies; Snack Foods: Processing; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wheat-Based Foods: Cookies and Crackers: Commercial Production; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Wafers: Methods of Manufacture.

Further Reading Faridi H and Faubion J (1995) Wheat End Uses Around the World (1995). St Paul, MN: American Association of Cereal Chemists. France WJ and Small M (1986) The New International Confectioner, fifth ed. London: Virtue and Co. Kulp K (1994) Cookie Chemistry and Technology. Manhattan, KS: The American Institute of Baking. Manley D (2000) Technology of Biscuits, Crackers and Cookies, third ed. Cambridge, UK: Woodhead. Matz SA (1992) Cookie and Cracker Technology, third ed. McAllen, TX: Pan-Tech International. New Zealand Institute for Crop & Food Research (1999) Biscuit Production. Baking Distance Learning Course. Christchurch, New Zealand: New Zealand Institute for Crop & Food Research. Newman RK and Newman CW (2008) Barley for Food and Health: Science, Technology, and Products. St. Paul, MN: American Association of Cereal Chemists. Smith WH (1972) Biscuits, Crackers and Cookies. vol. 1 and 2. London: Applied Science. The American Institute of Baking (1999) The Science of Baking Correspondence Course. Saltines/Snack Crackers. Manhattan, KS: The American Institute of Baking. The Biscuit and Cracker Manufactures Association (1979) The Cookie and Cracker Manufacturing Correspondence Course. Unit IV Crackers. Washington, DC: The Biscuit and Cracker Manufacturers’ Association. Wade P (1988) The Principles of the Craft. Biscuits, Cookies and Crackers. vol. 1. London: Elsevier.

Wafers: Methods of Manufacture K Tiefenbacher, (Retired) Kansas State University, Manhattan, KS, USA CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by K. Tiefenbacher and C. Wrigley, volume 1, pp. 300–307, ã 2004, Elsevier Ltd.

Topic Highlights

The Main Features of Wafers

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Wafers are baked as sheets, cones, and sticks or with different fancy shapes. The characteristic features with respect to other bakery products are as follows:

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Wafers are in our everyday foods, as crisp low-fat products made of wheat flour. The two basic types are no- or low-sugar wafers and highersugar wafers. Manufacturing steps involve – batter preparation and deposition onto the baking mold; – baking, usually between heated plates, often carrying engraved markings; – water release and cooldown; – conditioning from the release moisture content (about 1–4%) to minimize cracking; – final enhancements, such as cutting, creaming, book building, or enrobing. Wafer manufacture usually involves an automatic production line of specialized machinery.

Learning Objective

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Achieve understanding of the manufacturing process for making wafers in their many forms.

1. Wafers are very thin biscuits; the overall thickness is usually between < 1 and 5 mm. They often have a typical ‘wafer pattern’ on one surface or on both. The surfaces are smooth and precisely formed, with the dimensions and all the details – engravings, logos, etc. – of the baking molds. These features may be seen in the examples in Figures 1–3. 2. Wafers are cereal-based low-fat products made of wheat flour, sometimes with the addition of other flours or starches. The product density is in the range of 0.10–0.25 g cm3. In cross section, the wafer matrix is highly aerated and primarily of gelatinized starch. 3. Wafers, by their typical delicate and crisp texture, combine well with different fillings (cream, ice cream, and foam) and coatings. There is sometimes confusion in terminology between the crisp ‘wafers’ as described here and ‘waffles,’ which are of a soft, cakelike texture but show some kind of wafer pattern, too.

The Main Types of Wafers

Introduction

There are two basic types of wafers: Wafers are thin, crisp, and precisely shaped products, generally made from the flour of wheat, occasionally incorporating other cereals. The ice-cream cone is the most familiar member of the wafer product group. Like many uses of wafers, the ice-cream cone (Figure 1) is the ultimate illustration of the concept of providing food in an edible container. Indeed, wafers often serve the function of being edible carriers of an added food. However, the crispness of the wafer enhances the appeal of the added food, making the wafer much more than an inert carrier. Wafers are a special member of the biscuit/cookie/cracker family of cereal products. The ‘wafer book’ (Figure 2) verges on being called a biscuit with flat wafer sheets being interleaved with cream fillings. The diversity of wafer shapes (illustrated in Figure 3) includes flat wafers, hollow wafers, molded cones, rolled wafer cones, and wafer sticks. In addition, these many forms of wafer are enhanced by their use, for example, in sandwich format with cream fillings and by enrobing with chocolate. They may be made from quite different formulas, using a diversity of manufacturing equipments, and destined for a variety of uses. However, they share the same fundamental sequence of manufacturing steps detailed in this article. To understand the manufacturing process, the concepts of water activity and of glass transition are of critical importance.


1. No- or low-sugar wafers. After baking, these contain from zero to a very low percentage of sucrose or other sugars. Typical products are flat and hollow wafer sheets, molded cones, cups, and fancy shapes. 2. Higher-sugar wafers. Well over 10% of sucrose or other sugars are responsible for the plasticity of the hot, freshly baked sheets. These are formed into different shapes before sugar recrystallization occurs. Typical products are rolled sugar cones, rolled wafer sticks or tubes, and deep-formed fancy shapes. As in both wafer types, the main ingredient is flour; wafers fit very well into current dietary recommendations to consume more cereals. They are high-carbohydrate, low-fat products. The baking of ‘wafers’ between hot metal plates has been known since medieval times, but these first wafers were more similar to our waffles or pancakes in their high fat and egg contents and their texture. Modern wafers are low-fat cereal products, very similar to the altar breads for Christian churches, and are basically made out of flour and water. The first wafer ovens were used after the First World War, but more automatic manufacturing lines have been available since the mid-1950s.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00251-5

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WHEAT-BASED FOODS | Wafers: Methods of Manufacture

Figure 1 Probably the most popular form of wafer technology – the ice-cream cone.

Figure 3 Some of the varieties of wafer products. From top to bottom: (a) molded cones; (b) flat wafers, creamed/enrobed; (c) hollow wafer pieces; and (d) wafer sticks. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 539, Elsevier Ltd.

Figure 2 Flat wafers sandwiched with chocolate or strawberry fillings forming a ‘wafer book.’

in minor ingredients in the formula. The use of wholemeal flour is possible, and in some regions, other cereals such as rice or corn are used for wafer production. Table 1 lists the common ingredient ranges for both types of wafer.

The Main Formulas for Wafers There are two questions to be answered before deciding upon a wafer formula:

In-Line Manufacturing of Wafer Biscuits

1. What is the end use of the wafer? If it is part of a creamfilled, chocolate-covered biscuit, where contributing a crisp texture element is far more important than the taste of the wafer itself, formulas with few components are recommended. If the wafers are consumed directly as wafer bread or wafer sticks, more sophisticated formulas are chosen. 2. What kind and quality of raw materials are available? Lowto medium-protein soft wheat flours with a low water absorption work best, especially for no-sugar wafers. Problems with suboptimal flours must be balanced by variations

Wafer biscuits are the most important products by volume. The different steps of manufacture are illustrated in Figure 4.

Batter Preparation Wafers are made from a fluid batter with a typical viscosity in the range of 300–2000 mPs. First, the water-soluble components are dissolved. By adding the farinaceous ingredients, a homogenous suspension, the ‘wafer batter,’ is obtained within a few minutes of mixing (Figure 4, process 1).

WHEAT-BASED FOODS | Wafers: Methods of Manufacture Batter Transport and Depositing

The baking process

From an intermediate tank via a ring main, the batter is pumped to the oven and spread on to the baking molds by a depositor head (Figure 4, process 2).

Wafer Sheet Baking The baking of wafer sheets is performed in ‘tongs,’ that is, pairs of cast-iron metal plates with a hinge and latch on opposite sides. Baking plate sizes up to 350 730 mm are available. The precisely machined baking plates carry reedings or other engravings. We call the resulting wafers ‘flat’ wafer sheets, with an overall thickness of no more than 2–5 mm (Figure 4, process 3). But such baking plates can also carry special figures (nuts, sticks, hemispheres, and fancy shapes) up to a depth of about 20 mm, thus yielding the so-called ‘hollow’ wafer sheets. Modern wafer-baking plates often are surface-plated, for example, with chromium for easier release and reduction of cleaning stops. The plates are edged with metal strips to give a closed baking mold, except for small venting channels for steam release. Wafer-baking ovens frequently have 32–104 pairs of plates, continuously circulating on a chain. They are mostly gas, sometimes electrically heated and operate at mold temperatures between 160 and 190 C. Table 1

Wafer batter ingredient ranges (weight parts, flour ¼ 100)

Wheat flour Water Starch Sucrose Oil/fat Milk powder Soy lecithin Salt Sodium bicarbonate

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No (low)-sugar wafer

Higher-sugar wafer

100 120–160 0–12 0–4 0.5–2 0–2 0.2–1 0–0.6 0.1–0.5

100 100–140 0–5 25–75 1–6 0–2 0.2–1.5 0–0.6 0–0.3

Optional minor ingredients: other cereal flours, soy flour, other sugars and syrups, egg-based ingredients, whey powder, yeast, caramel color, cocoa powder, colors, ammonium bicarbonate, enzymes. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 540, Elsevier Ltd.

Within a few seconds after batter deposition, the baking molds close and are locked. At first, the batter is distributed mechanically, but then, the mold is filled completely by the steam that evolves. A small quantity of batter is extruded as baking waste ‘bobbles’ through the venting channels. As gelatinization of starch starts immediately, the pressurization of the mold by steam occurs at the right moment, resulting in a well-aerated starch foam. When most of the water has been driven off, the glass temperature of the wafer matrix rises, and the stable structure is formed. The temperature of the wafer increases to 160–190 C, that is, to the temperature of the baking mold. Then, from Maillard reactions, the typical wafer color and flavor develop. The overall baking times are between 1.5 and 2.5 min, depending on the wafer thickness and baking temperature. During the wafer-manufacturing process, there is no substantial degradation of starch molecules compared with other bakery products such as extruded cereals. Therefore, wafers have two unique textural properties: 1. Extreme crispness on biting and initial chewing 2. Good mouthfeel during prolonged chewing and swallowing due to the absence of sticky, glutinous stimuli

Wafer Release and Cooldown At one end of the oven, the plates open to release the baked sheets and to spread fresh batter and then reclose very quickly. The sheets are cooled to room temperature while passing over an arch-type sheet cooler (Figure 4, process 4).

Wafer Conditioning Next, the wafers optionally pass a conditioning unit, where the moisture content of the sheets is carefully increased so as to achieve some stability in both the texture and size of the wafer (Figure 4, process 5).

Moisture sorption and wafer texture After baking, the residual moisture is 0.8–1.5%. Looking to the sorption isotherm, this corresponds to a water activity of about

Figure 4 Manufacturing line for creamed and enrobed wafer biscuits from flat wafers. (1) Batter preparation, (2) batter transport and depositing, (3) wafer sheet baking, (4) wafer sheet cooling, (5) conditioning of sheets, (6) creaming and wafer book building, (7) cooling and cutting of books, (8) enrobing, (9) cooling of enrobed pieces, and (10) packaging. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 540, Elsevier Ltd.

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0.1 or even lower. As both the water activity of the air in the production area and the water activity of filling creams or coatings are well above that, wafers pick up moisture very easily. In line with this sorption, the dimensions of the sheet increase by 0.2–0.3% for every 1% of additional moisture. This can result in cracking of the coating in enrobed wafer biscuits. To compensate for the low water activity, humidity conditioning up to about 4.5% wafer moisture is possible. This is recommended, especially if enrobed or chocolate molded wafer products are made, in order to anticipate this first dimension increase and to avoid any cracking of the coating during its shelf life. Moreover, with increasing water activity, the wafer texture changes from a soft to a harder crispness, accompanied by a higher mechanical stability, which is good both for handling and for the final product texture. Up to 5–6% moisture content, the wafer sheets keep their typical crisp texture, but higher moisture levels will result in most cases in inadequate, tough, or even soft and soggy textures (see Table 2 for details).

Enrobing or Molding in Chocolate, Cooling The cut biscuits may be enrobed with chocolate-type coatings, sometimes after the application of chopped nuts or crispies to the top wafer. Molding in chocolate is another possibility. After a final cooling step, the biscuits are ready for packaging (Figure 4, processes 8 and 9).

Packaging The biscuits have to be packed tightly to protect not only against humidity but also against oxygen and light to prevent oxidative deterioration and to ensure a shelf life of 6–9 months. Inadequate packaging-film moisture barriers and bad sealing are the most frequent reasons for later complaints by customers. Laminated or specially coated films are used for the typical wafer product packaging in flow packs, boxes, or bags (Figure 4, process 10).

Manufacturing of Molded Wafer Cones Creaming and Book Building The sheets then pass the creaming station, where a layer of a sugar- and fat-based cream is applied to one side. The type of cream flavor liked most varies regionally, but chocolate, vanilla, hazelnut, milk, strawberry, and lemon are the most common. Creaming is done at temperatures of 30–40 C either by contact spreading or by depositing a preformed cream film (Figures 2 and 4, process 6). For flat wafers, several creamed sheets together with a noncreamed top sheet form a so-called wafer book. For hollow wafers, the cream is added to the hollow parts either by spreading or by controlled single depositing. Again, either two hollow wafer sheets or a hollow and a flat sheet are combined to form a ‘book.’

Other types of ‘hollow’ wafers, cones, cups, and fancy shapes with up to 185 mm in length are produced in cast-iron molds. Holes for four to six items are provided in each of these molds, and 12–72 molds are circulated in one oven. The lower part of the mold is made of two symmetrical halves that open to release the baked pieces. After their reclosure, they take up a fresh batter deposit, and finally, the ‘core,’ the upper part of the mold, closes the mold for a new baking cycle. The baked cones are cooled down and stacked for packaging. With respect to the formula, there are two groups of molded cones:

Cooling and Cutting

1. No- or low-sugar cones, generally known as ‘cake cones,’ have formulas that are similar to those for sheets (see Table 1). 2. The so-called molded sugar cones have an intermediate sugar content, usually below 20 parts of sucrose for 100 parts of flour.

The wafer books pass a cooling tunnel to set the cream, after which they are wired or saw-cut into small biscuits (Figure 4, process 7).

Recent Developments in Molded Wafer Cones

Table 2

Water activity, water content, and texture of wafers

Wafer condition

Wafer texture

Water activity, approx.

Moisture (%), approx.

Freshly baked

Very tender, crisp Crisp, harder

<0.1

<2

0.3

4.5

0.5/0.55

6

0.7

12

0.85

> 20

After conditioning Limit of crispness Wafers, foamfilled Collapse of structure

Crisp to tough Soft to flexible Very soft, shrinks

Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 541, Elsevier Ltd.

Whereas traditionally molded cones have flat tops and regular, symmetrical reedings now for a few years, molds for more sophisticated products can be manufactured. We now see cones and cups in the market showing curvilinear tops and artfully designed outsides. Figure 5 shows the first of these, which comes from a Japanese cone manufacturer.

Manufacturing of Rolled Wafer Cones ‘Rolled sugar cones’ need a concentration of more than 20% of sucrose or other sugars in the finished product. The first three steps of rolled sugar cone manufacturing are rather similar to no- or low-sugar wafer sheet baking with the exception of reduced steam pressure as there are no baking ledges to build up pressure and to extrude ‘bobbles.’ The deposit is just to form an oval or circular sheet (see Figure 6):

WHEAT-BASED FOODS | Wafers: Methods of Manufacture 1. Batter preparation (Figure 6, process 1). 2. Batter transport and depositing (Figure 6, process 2). 3. Wafer sheet baking (Figure 6, process 3). Nowadays, equipment is available to manufacture up to 13 000 cones per hour. 4. Wafer takeoff, rolling, and cone release (Figure 6, process 4). When, after baking, the mold reopens, the sheet is automatically stripped off the plate and rolled immediately on tapered mandrels to form the finished cone. A series of rolling devices mounted on a round table operates continuously: sheet removal, rolling, release, etc.

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Glass Transition and Formability During the rolling procedure, the wafer temperature is still above the glass transition point. The molten sugar acts as a plasticizer, and so any rolling or deep-forming operation can be performed. Besides the rolled cones, three more types of products are manufactured by the same principle: 1. Wafer ‘rolls.’ Wafer sheets of rectangular shape are baked, stripped off the baking plate, and rolled into a sugar wafer ‘rod’ without a center hole (different from wafer ‘sticks’ with a center hole discussed later). The rod is later cut into smaller cylindrical pieces. Typically, these pieces are finally partially enrobed with chocolate-type coatings. 2. ‘Deep-formed’ wafers (cups and shells), where the hot, flat wafer piece is introduced into a forming tool, sometimes with an additional embossing or stamping device, which defines the final shape. 3. Rolled wafer sticks. These are discussed in a separate section later in the text.

Cone Cooling The fresh cones pass through a cooling section, where ambient or cooled air is applied. Here, sugar recrystallization finishes to give the final strong and brittle texture (Figure 6, process 5).

Cone Sleeving and Stacking

Figure 5 Molded wafer cone: example for new, non-flat-top design. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 542, Elsevier Ltd.

Now, paper sleeves are applied automatically, and these form the packaging material for the typical end product, industrially manufactured ice-cream cones. Next is automatic cone stacking and packaging. Later in the ice-cream plant, the wafer cones are sprayed inside with chocolate and filled, and finally, the paper cone is closed (Figure 6, process 6).

Figure 6 Manufacturing line for rolled sugar cones. (1) Batter preparation; (2) batter transport and depositing; (3) wafer sheet baking; (4) takeoff, rolling, and cone release; (5) cooling of cones; and (6) cones sleeving, stacking. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd Edition (2003), p. 543, Elsevier Ltd.

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Manufacturing of Rolled Wafer Sticks Rolled wafer sticks are hollow tubes with walls consisting of very thin multiple layers, similar in texture to crunchy cereals. These layers do not carry a wafer pattern and are about 0.5 mm in thickness. But from the formula, the sticks are typical highersugar wafers (see Table 1). In manufacturing, a stripe of batter is applied to a heated drum and baked into a continuous wafer band. The band is rolled immediately while still hot into a continuous still formable tube with an internal diameter of about 6–36 mm. From here, there are several options to create a large family of finished products: 1. The tube is automatically cut into wafer stick pieces and cooled. These are consumed as sweet snacks or with ice cream, for example. Other end uses include intermediate products for confectioners to finish by additional filling or decorating operations. 2. During the rolling operation, the tube is coated inside with compound chocolate or filled with cream, either partially or fully. Then, cutting and cooldown, followed optionally by a coating and/or decorating process, give the finished product. 3. The filled tube is transformed into small pillow-like bits by a combined squeezing–cutting operation. 4. The wafer tube pieces, nonfilled, coated inside, or partially cream-filled immediately after cutting while still hot, pass a pressing station to form oval or even flat pieces. Such flat pieces may form the center of premium-type confectionery items with a chocolate coating, including chopped nuts or cereal crispies. 5. Larger-diameter tubes are pressed flat, and by an embossing and stamping operation, the so-called fan wafers or other elaborate shapes can be generated. The diameter and length of the sticks as well as the number of very thin, ‘glassy’ sheets forming the wall of the stick can be adjusted individually. Rolled wafer sticks have a unique brittle wall texture without being too hard in biting and chewing.

Savory Wafer Products Whereas many end uses of wafers in combination with sweet fillings, coatings, etc. are well known, savory or neutral-tasting wafer products are becoming increasingly popular in some areas. The following are some of the examples: 1. Wafers as crisp bread, delivering a crunchy but softer texture than traditional hard crisp breads. Besides wheat flour, there are several options for other cereal and noncereal flours as raw materials. The products either are neutral in taste to be eaten with sweet or nonsweet toppings or have spices, cheese, and other flavorsome ingredients. 2. Wafers – flat or hollow wafers – with savory fillings, for example, peanut butter or cheese creams. 3. Wafer sticks, a recent development, made from a nonsweet but still rollable material. These are typically combined with savory cream fillings.

Table 3

Which product from which wafer type?

End product

No (low)-sugar wafer

Wafer crisp bread Sugar wafer biscuits, creamed Wafer biscuits, creamed and enrobed or molded in chocolate Containers, e.g., for ice cream

Flat wafer sheet Flat wafer sheet

Confectionery, filled, enrobed, decorated

Hollow wafer or hollow þ flat wafer

Fan wafers

Wafer rolls, partially enrobed Wafer bowls

Higher-sugar wafer

Flat wafer sheet

Molded cake cone

Molded sugar cone, rolled sugar cone Wafer stick or sugar cone, small Wafer stick, pressed, embossed Rolled sheet Deep-formed sheet

Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 544, Elsevier Ltd.

Trends: From the Wafer to a More Sophisticated End Product After discussing the different wafer types and their traditional end uses (for an overview, see Table 3), a sharply increasing number of new confectionery brand products during the last decade are worth mentioning. Here, wafers are only a smaller, but still important, part of the deal. These are small confectionery pieces, mostly in bite-size or sectioned bars, often chocolate-covered, where the wafer has three main functions: 1. To add its typical texture and crispness, for example, to a soft filling cream with a piece of nut and a chocolate cover, thus imparting a multitextured impression 2. To make the overall product ‘lighter’ in calories and nutritious, as the wafer part is of an extremely low density and cereal-based 3. To define the precise structure of the piece, for example, when holding a soft filling, or, for noncoated pieces, to keep the consumer’s hands clean if the filling melts due to warmer conditions Looking to some of the current trends, we see increasing interest in combining lower-fat fillings such as toffee (caramel). Another trend may be newer fat-free fruit-type fillings with water activities that are so low that the wafers stay crisp. Even some new examples of fillings with a higher moisture, resulting in a ‘soft’ wafer part, can be rolled out.

Developments in Wafer-Manufacturing Equipment After a long period of just ‘routine’ technical optimizations, recent years have seen a few new technical concepts in wafermanufacturing equipment:


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Figure 7 New, inductively heated, low-emission oven for rolled wafer stick manufacturing. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn. (2003), p. 545, Elsevier Ltd.

1. The ‘stack oven,’ with the baking plates vertically stacked. Here, the weight of the stack itself eliminates the need for hinges and for closing mechanisms as in the traditional chain oven. Moreover, the floor area needed is greatly reduced. The coming years will show whether that development will find its way into industrial practice. 2. A new ‘low-emission’ heating concept together with a 60% reduction in energy consumption for rolled wafer stick ovens. The key is the replacement of the gas-heated drum by a ring, heated by induction. This results in a new, more consistent and more controllable product quality and results in the elimination of flue gases and a huge reduction in energy consumption for baking, as the first industrial oven prototypes (Figure 7) showed.


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Summarize the types of wafer that are usually made and describe their respective batter formulas and processing methodology required. What is the role of sugar (sucrose), if included? Explain the need for cooling and conditioning of wafers immediately after baking. Include explanation of glass transition in this and other aspects of wafer manufacture. Describe the difficulties of making wafers in their more unusual shapes, such as rolled wafer sticks.

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(semi)liquid fast foods. After consuming the contents, the customer eats the container. What applications can you imagine? Consider sweet and savory, involving fruit, vegetables, soups, and candies. Consider how wafers might substitute for the cookie (biscuit) disks in the wide range of cookie-type baked goods. What novel food types can you envisage? The cream-filled sweet ‘wafer book’ design is reasonably common. Explore the possibility of using a low-sugar flat wafer for a savory equivalent. What fillings would you use? What problems might arise?

See also: Carbohydrates: Starch: Chemistry; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; Extrusion Technologies; Wheat Processing: Bakeries: The Source of Our Unique WheatBased Food, Bread; Chemistry of Cake Manufacturing; Oven Technologies; Snack Foods: Processing; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain; Cookies: A Diverse Family of Baked Goods; Cookies and Crackers: Commercial Production; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics.

Further Reading Exercises for Readers to Explore the Topic Further

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Compare sweet and savory uses of wafers in their various shapes. What different applications and taste sensations can you suggest? Speculate about the possible use of wafer-based food containers, treated to be moisture-resistant, for the sale of

Barron LF (1977) The expansion of wafer and its relation to the cracking of chocolate and “baker’s chocolate” coatings. Journal of Food Technology 12: 73–84. Blanshard JMV, Frazier PJ, and Galliard T (eds.) (1986) Chemistry and Physics of Baking. London: Royal Society of Chemistry. Haas F, Haas J, and Sachsenhofer J (1998) Bakers’ Oven for Producing Thin-Walled Shaped Products with Baking Forms Each Consisting of Two Form Halves Which Open and Close. PCT Patent Application WO 98/51156. Manley DJR (2000) Technology of Biscuits, Crackers and Cookies, 3rd edn., pp. 290–306. Cambridge: Woodhead Publishing.

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Negri G (1984) Waffeln und Verfahren zu deren Herstellung. European Patent 0,022.901. Oliver G and Sahi SS (1995) Wafer batters: A rheological study. Journal of the Science of Food and Agriculture 67: 221–227. Pritchard PE and Stevens DJ (1974) The influence of ingredients on the properties of wafer sheets. Food Trade Review 42(8): 9–15. Roos YH (1995) Phase Transitions in Foods. London: Academic Press. Schwartzberg HG and Hartel RW (eds.) (1992) Physical Chemistry of Foods. New York: Marcel Dekker.

Seibel W, Menger A, Ludewig H-G, Seiler K, and Bretschneider F (1978) Standardisierung eines Backversuches fu¨r Flachwaffeln. Getreide Mehl und Brot 32: 188–193. Stevens DJ (1976) The role of starch in baked goods. Part 1. The structure of wafer biscuit sheets and its relation to composition. Starch 28: 25–29. Tiefenbacher K and Dobrovics M (1999) Mehle fu¨r die Waffelherstellung. Getreide Mehl und Brot 53: 349–353. Wade P (1988) Biscuits, Cookies and Crackers, vol. 1, pp. 139–150. Barking: Elsevier.

Cookies and Crackers: Commercial Production LC Paulson, The Bama Companies, Tulsa, OK, USA CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by L. Doescher Miller and C. Wrigley, volume 1, pp. 295–300, ã 2004, Elsevier Ltd.

Topic Highlights

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Vertical Spindle Mixers

The practice of home baking of cookies has largely been replaced by factory-scale production. Dough mixing, the initial stage of cookie production, may involve vertical mixers, horizontal mixers, or a continuous mixing process. Biscuit doughs generally fall into two broad categories – ‘hard’ and ‘soft’ doughs. The types of dough-forming equipment include wire-cut, rotary-molded, bar-shaped, deposited, and cut or stamped. The baking of a relatively thin disk of dough produces a product with low moisture content; shelf life is good as a result.

Learning Objective

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Achieve understanding of the industrial process for the mixing, forming, and baking of cookies and related baked goods.

Introduction Ask children in Western countries where cookies come from, and their answer today would probably be: ‘From a packet bought in the supermarket’ (with little knowledge of the preceding process). A few generations ago, the answer would probably be: ‘We just make cookies at home!’ Nevertheless, the methodology of production (in home or factory) is similar, involving the essential steps of mixing, shaping and forming, and baking. Obviously, there are major differences in detail involved in the mass-production process, compared to making a small batch of cookies at home. This article describes the processes (mixing, forming, and baking) used to produce the diversity of cookies, biscuits, and crackers prior to their arrival in packets in the supermarket.

Dough Mixing The first step in manufacture involves the blending of the ingredients into a uniform, homogeneous mixture. In the context of cookie and cracker doughs, the term ‘mixing’ takes on a broader meaning in that it also applies to the development of gluten from hydrated flour proteins, the aeration of a mass to give a lower density, and the dispersion of solids in liquids. One or more of the functions are required for the formation of cookie and cracker doughs. These processes are accomplished with three principal types of mixers: vertical spindle mixers, horizontal drum mixers, and continuous mixers.


Vertical mixers were used extensively before the development of the high-speed mixer. Although usage has decreased overall, this type of mixer is still used for crackers and semisweet doughs, for which the vertical spindle design is particularly well suited. The feature that all vertical mixers have in common is the portable dough trough, which serves as the mixing vessel. The trough is usually a wheel-mounted, heavy tub with vertical sides, round ends, and a flat bottom. The trough is designed so that it may be wheeled into position below the mixer head and locked into place. Mounted on an overhead frame are the drive mechanism and spindles with horizontal paddles or arms. Most mixers of this type are equipped with two or three spindles. The spindles are lowered into the trough and move in either a planetary or a stationary, circular motion when activated. The shape of the arms forces the dough upward and downward in the trough, generating a mixing action. The mixer blades are designed to provide a cutting action rather than kneading or stretching of the dough. The advantage of vertical spindle mixers is that they can be used for almost any product. They are very well suited for products such as soda cracker doughs. These doughs require a two-stage mixing sequence separated by a fermentation period. The sponges and doughs do not have to be transferred in and out of the trough at each mixing stage. Instead, they remain in the same trough for the entire mixing/fermentation sequence. Because there is almost no heat generated during the mixing process, this mixer is ideal for doughs that must remain cool. The mixing action is very gentle. Doughs containing ingredients or particulates that are easily damaged may be safely mixed with this mixer type. The primary disadvantage of vertical mixers is their slow operating speed. The spindles rotate over a limited range at two or three speeds, up to a maximum of about 20 rpm. For doughs requiring the development of a gluten network, the mixing time required may be as long as 90 min. Because this is slow relative to the speed of the remainder of the processing line, several mixers may be needed to maintain an uninterrupted dough supply. Other disadvantages include lack of uniformity of the mix and the labor-intensive nature of the system’s design. The latter disadvantage relates to the fact that the dough troughs are very heavy, requiring special equipment to move, lift, and tilt the tubs at each stage of the process.

Horizontal Mixers The feature that all mixers of this type have in common is a horizontal bowl mounted on a rigid frame that encloses the drive motor. The bowl may be stationary with a vertical front wall that slides down so that the dough may be ejected. More commonly, the mixer bowl is designed to tilt, and the dough is

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WHEAT-BASED FOODS | Cookies and Crackers: Commercial Production

ejected from the tilted position. In both designs, the top cover is fixed so that mixing takes place in an enclosed space. The blades of horizontal mixers are mounted on a horizontal shaft and may have any of several different shapes, depending on whether a cutting, scraping, or kneading action is needed. Mixing times for cookie and cracker doughs range from 5 min for soft doughs to 30 min for the hard doughs, which require gluten development. Most mixers of this type are fitted with a jacket surrounding the mixing chamber. This allows a coolant to be circulated, so that dough temperatures can be controlled. Without such control, horizontal mixers can increase the dough temperatures to the point where dough handling and finished product properties are adversely affected. The advantages of horizontal mixers are their high speed, their ability to supply dough to a processing line continuously, their uniformity of the mixes they produce, and their potential for complete automation. Horizontal mixers may be operated at speeds of 15–80 rpm. Commonly, their power train is equipped for two-speed rotation. Unlike most vertical spindle mixers, ingredients may be added with the blades in motion, and the discharge of the dough from the mixer is simple. Accurate control of dough temperature is possible, because there is a continuously circulating refrigerant. Horizontal mixers require that all ingredient-charging spouts be located overhead or that ingredients be added manually. Charging the mixer with ingredients is typically a significant portion of the total mixing cycle time. During mixing, the blades may throw material to the top of the chamber, so that it is never fully incorporated. With the shaft and mixing blades located in the center of the bowl, dough discharge is not always rapid and may occur in several large fragments. Only one operation (charging, mixing, or discharging) may be performed at any one time, so that fast cycling of the dough batches may not be possible. Horizontal mixers usually have capacities of up to 550 kg. The weight and the vibrations generated by their relatively high operating speeds place special design demands on the production facility. In addition to a reinforced floor, special mounts are necessary to secure the mixer in place.

Continuous Mixers Continuous mixers are best described as a rotor or screw operating within a barrel jacketed for temperature control. The ingredients are fed continuously, either from one end of the barrel or in successive ports at intervals along its length. The mixing action may be altered from gentle blending and dispersing to vigorous or high-intensity kneading by varying the arrangement of different mixing arms along the length of the barrel. The amount of work put into the dough during its transit may be controlled additionally by restricting the dimension of the outlet orifice, creating a back pressure inside the barrel. Continuous mixers are favored in some plants because they are capable of providing a constant supply of dough to the production line. Continuous mixers are small in size relative to horizontal mixers and are suitable for complete automation. In spite of this advantage, continuous mixers are not common in cookie or cracker plants, where a single line may be required to produce a variety of products. They are usually used only on high-output lines having a single purpose or similar product types.

The primary disadvantages of this mixer type are its high cost and the additional cost of the associated automated, continuous ingredient-feeding systems. Beyond this, continuous mix systems are not particularly flexible; different products usually require completely different types of machines. In addition, the initial process setup can be difficult, requiring considerable experimentation to determine optimum mixing conditions and sequences. Finally, starting and stopping the process are difficult in the event of any problem along the rest of the production line.

The Dough-Forming Process This step is specific to each product type, whereas the mixing and baking stages may be similar for all types of products. Three processes are used to form cookie and cracker doughs: (1) cutting or stamping from a continuous sheet of dough, (2) rotary molding by shaping dough in die cavities cut into the surface of a metal cylinder, and (3) extruding dough through a shaped die. For each of these methods, the rheology of the dough is different and is designed to be compatible with the process. In general, doughs that are to be sheeted possess a significant gluten network as a result of mixing and are both elastic and extensible. Those destined for rotary molding lack gluten development and are best described as cohesive. Doughs intended for extrusion are soft and frequently high in shortening and spread while baking.

Sheeting and Cutting The most common and versatile method to form cookie and cracker doughs is sheeting and cutting. This method involves the production of a thick sheet of dough, evenly reducing the thickness of the sheet, cutting out the desired shapes, and returning the scrap dough to be reincorporated either in the mixer or early in the sheeting process. This method is used for the production of crackers, semisweet biscuits, and selected soft doughs. After mixing, the dough is fed into a hopper, below which lie the sheeting rollers. There are typically three rollers below the hopper arranged in a triangular fashion (Figure 1). At least one of the top two rollers, known as forcing rollers (labeled (a) in the figure), is cross grooved so that a positive feed is provided to the gauge or gauging roller. The gauging roller (b), which is always smooth, serves to deliver the dough to the conveyor belt (c). The purpose of the sheeting unit is to compact the mass from dough hopper uniformly and provide a sheet of even thickness having the width of the processing line. The relatively thick dough slab from the sheeter then passes through a series of reduction or gauge rollers (d). These are smooth steel rollers used to reduce the dough sheet to the thickness that is desired before cutting of the finished dough piece. The gauge rollers occur in pairs mounted vertically. For products having sticky or adherent doughs, it may be necessary to mount a scraper blade against one or both of the rollers to release the sheet of dough. On most process lines, there are two or three pairs of rollers. This ensures that the thickness is reduced no more than 50% at any one rolling operation.


A

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A F

E B

D

C Figure 1 Sheeting and cutting process. See text for explanation. Reproduced from Macrae R, Robinson RK, and Sadler MJ (eds.) (1993) Biscuits, cookies and crackers: Methods of manufacture. In: Encyclopaedia of Food Science, Food Technology and Nutrition. London: Academic Press.

Some doughs, such as those of saltines and cream crackers, are laminated before cutting. The lamination occurs by lapping the dough back upon itself in the process direction. At the lapper, the takeaway conveyor lies at a 90 angle relative to the line delivering the dough. The number of layers is controlled by the relative rate of the lapper and takeaway conveyor. The lapped dough then passes through several more sets of gauging rollers to bring the dough sheet to the desired thickness prior to cutting. The repeated working of the dough in one direction results in the accumulation of stress. If the dough were cut at this point, the resulting pieces would shrink to relieve the stress, and misshapen or distorted products would result. Therefore, it is normal to relax the dough after reduction and before cutting. The relaxation is accomplished by transferring the dough to a conveyor, still moving in the same direction, but at a slower speed. Once the dough has been relaxed, it passes on to the cutting operation. Two different types of cutting methods exist: reciprocating cutters and rotary cutters. The reciprocating cutters are heavy block cutters that stamp out one or more pieces at a time. The cutter head (e) may have a dual action, whereby the cutter drops first, followed by a docking head or an embossing plate. The equipment operates via a swinging mechanism so that the dough sheet moves at a constant speed and the cutter drops and moves with the dough and then rises and swings back to the original position. The second type of cutter, the rotary cutter, consists of a rotating metal cylinder. On the face of the roll are formed the desired shapes with a sharp metal edge. As the cutter rotates with the dough conveyor, the metal edges cut into the dough sheet to form the product. The product pieces are then conveyed into the oven. As a result of either cutting process, 20–60% of the dough sheet remains as scrap. The scrap dough (f) is lifted away from the cut dough pieces and returned either to the mixer or to the sheeter. Return to the mixer permits uniform incorporation of the scrap into the dough mass. However, most systems route the scrap back into the sheeter either along the full length of the hopper or at the back side of the hopper. If dough is incorporated behind the new dough, imperfections will be on the bottom side of the dough sheet and will not be visible on the finished product.

Rotary Molding The principle of rotary molding is illustrated in Figure 2. Three rollers are placed in a triangular arrangement below a dough

A

B

E

F

D C Figure 2 Rotary molding process. See text for explanation. Reproduced from Macrae R, Robinson RK, and Sadler MJ (eds.) (1993) Biscuits, cookies and crackers: Methods of manufacture. In: Encyclopaedia of Food Science, Food Technology and Nutrition. London: Academic Press.

hopper. A roller, called the forcing or feed roller (a), has deep grooves designed to pull dough down from the hopper. The dough is forced into the cavities of the engraved roller (b) by the forcing roller. A scraper blade (c) is mounted against the engraved roller to remove any excess dough and return it to the hopper via the forcing roller. Beneath the engraved roller is a rubber-covered extraction roller (d) that serves to drive the takeaway belt (e). The extraction roller applies pressure to the engraved roller via the belt, causing the dough to adhere preferentially to the conveyor belt. Dough pieces are dropped from the takeaway belt into pans or directly on to the baking belt (f). The rotary molding process is suitable only for dry, crumbly doughs. This process offers advantages over sheeting and cutting in that there is no scrap to recycle and there are very low labor requirements to run the process.

Extrusion There are two types of devices used in the production of extruded cookies: wire-cut machines and bar/rout-presses. Both systems are very similar in design (Figure 3). A hopper is placed over a system of two or three rollers (a) that force dough into a pressure chamber (b). The rollers may run continuously or intermittently to force dough out of the pressure chamber at the die. For wirecut cookies, the dough is extruded through a row of dies, and a wire or blade (c) mounted on a frame moves through the dough just below the die nozzle outlet. The cut dough pieces then drop into a conveyor band (d) for transport to the oven. The wire usually moves only in one direction through the dough, opposite that of the conveyor. The wire-cut machines operate at rates of up


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A

A B

C

D (a)

(b)

Figure 3 Extrusion process: (a) wire-cut machine; (b) bar/rout-press. See text for explanation. Reproduced from Macrae R, Robinson RK, and Sadler MJ (eds.) (1993) Biscuits, cookies and crackers: Methods of manufacture. In: Encyclopaedia of Food Science, Food Technology and Nutrition. London: Academic Press.

to 100 strokes per minute. Difficulties encountered with this type of production are distortion of the extruded dough piece during cutting and inconsistent placement or drop of the cut piece on to the conveyor. The design of the bar- or rout-press is very similar to that of the wire-cut machine. The hopper rollers and pressure chamber are essentially identical to their wire-cut counterparts. Unlike the wire-cut machine, the base of the pressure chamber has a die plate that is inclined in the direction of the extrusion. A continuous ribbon of dough is extruded from a nozzle, which is shaped to impart the desired finished product design. The dough ribbon can be cut into individual pieces by a vertically operating guillotine before the oven or after baking. If the product can be baked as a continuous ribbon, the dough is extruded directly on to the oven band; otherwise, it is extruded and cut on to a conveyor belt.

Baking The baking of cookies, biscuits, and crackers is performed almost exclusively in band or traveling ovens. The band oven is essentially an insulated, heated tunnel equipped with a continuous conveyor. The ovens vary both in length (from 30 to 150 m) and in band width (from 1.0 to 1.5 m). More modern ovens frequently consist of a series of modular units or zones. Each of the zones is equipped with its own set of controls so that the temperature and airflow may be controlled within that zone. The oven band is typically continuous, passing on to a drive drum at the end of the oven and returning underneath the baking chamber to a tension drum at the feed or input end of the oven. The chamber through which the oven belt returns may or may not be enclosed. Frequently, the oven band serves as the baking surface for the product. Depending on the product type, the oven band may be solid or any of a variety of open wire-mesh types. The choice of mesh is a critical factor in the process, as it affects the heat transfer at the bottom of the product. This, in turn, can have a marked effect on the quality of the finished product. There are three basic types of ovens: direct-fired, indirectfired, and fully indirect-fired. Ovens are usually heated by the combustion of gas, although there are a few manufacturers who use oil or electricity for economic reasons. The most common type is the direct-fired oven, in which gas is burned

inside the baking chamber itself. In these ovens, the burners are placed across the width of the oven at regular intervals, both above and below the oven band. In other oven types, termed ‘indirect ovens,’ the gas or oil is burned outside the baking chamber, and the heated combustion gases are circulated into and throughout the baking chamber. Indirect-fired ovens typically have a single burner for each section. The hot gases from the burner pass along pipes parallel to the length of the oven, both above and below the oven band. The products of combustion are circulated throughout the baking chamber by large fans. Fully indirect ovens are those in which the heat source is independent from the baking chamber and heat transfer occurs via a heat exchanger. None of the products of combustion circulate inside the baking chamber. This type of oven is not common, except when oil is used as a combustible material. If circulated, the products of this type of combustion would impart an unacceptable flavor to the products.

Cooling Products hot from the oven must be cooled prior to packaging for several reasons: the products may not be firm enough to withstand the packaging process while warm, the packaging material may shrink around a warm product, and the quality of the products would deteriorate if palletized while warm because the cooling rate across the pallet would be quite slow. The normal method of cooling products is to place them on an open conveyor and transfer them along a distance 1.5–2 times the length of the oven. The products cool naturally in the ambient factory atmosphere. In a few cases, it is necessary to provide forced air to aid the cooling process.


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Define the following terms and list them in the sequence of their use in the manufacture of cookie-type goods: ingredient charging, cutting, cooling, sheeting, packaging, mixing, docking, lapping, forming, kneading, extruding, molding, laminating, stretching, and baking. Explain the importance of the dough-mixing process. Why do some dough types require more or less mixing? Mixing vertically, horizontally, and continuously – why use one approach to dough mixing versus another of these mixing methods? Describe the operation of the main equipment types for forming dough pieces ready for baking. List some of the potential difficulties of cookie manufacture, and provide the matching solutions that are the most obvious.


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Compare the more common types of dough mixers and ovens. Imagine that you are advising on equipment for a new baking facility for cookie- and cracker-type baked goods. (You choose the factory type, e.g., high-output lines for similar product types or a smaller-scale situation for a wide variety of cookie-type goods.)


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– What mixer types would you recommend? Why? – What oven setup would you recommend? Why? – Make sure that your recommendation will suit your favorite cookie type. (What is it?) Examine the various means used to cool bread and other baked products to see if there are any innovations that could be transferred to cookie production to increase the speed and efficiency of the cooling step.

See also: Wheat-Based Foods: Cookies: A Diverse Family of Baked Goods; Appendix 2: Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; Extrusion Technologies; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Cereal Food Production with Low Salt; Chemistry of Cake Manufacturing; Oven Technologies; Snack Foods: Processing; WheatBased Foods: Cereals: Overview of Uses: Accent on Wheat Grain;

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Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Wafers: Methods of Manufacture; Lists of Test Methods.

Further Reading Almond N (1989) The Biscuit Making Process. Biscuits, Cookies and Crackers, vol. 2. London: Elsevier. Faridi H and Faubion J (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. Macrae R, Robinson RK, and Sadler MJ (1993) Biscuits, cookies and crackers: Methods of manufacture. In: Encyclopaedia of Food Science, Food Technology and Nutrition. London: Academic Press. Manley D (1991) Technology of Biscuits, Crackers and Cookies, 2nd edn. Chichester: Ellis Horwood. Matz SA (1978) Cookie and Cracker Technology, 2nd edn. Westport, CI: AVI. Matz SA (1988) Equipment for Bakers. McAllen, TX: PanTech International. Pyler EJ (1988) Baking Science and Technology, vol. II. Merriam, KS: Sosland, 3rd edn. Smith WJ (1972) Technology, Production and Management. Biscuits, Crackers and Cookies, vol. I. New York: Magazines for Industry. Wade P (1988) The Principles of the Craft. Biscuits, Cookies and Crackers, vol. I. London: Elsevier.

Noodles: Starch LS Collado, The University of the Philippines Los Banos, Laguna, Philippines H Corke, The University of Hong Kong, Hong Kong, Pokfulam, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Starch noodles defined. Starch noodle names, categories, and descriptions. Raw materials: purified starch, nonwheat flours, and mixed substrates. The process of making starch noodles. Nutritional benefits from starch noodles. The future of starch noodles in the food industry and human diet.

Learning Objectives

•

Types of Starch Noodles

To demonstrate an understanding of the raw materials, the process of making, and the nutritional value of starch noodles in the human diet.

Introduction In general, the term noodles is derived from a German word Nudel, which is of unknown origin but means narrow strips of dried dough. It is also closely associated with the Latin word pasta that means dough, pastry cake, or paste, which also used to indicate a glue mixture with reference to gluten used since 1803 to refer to the nitrogenous component of wheat and other grains. The ease by which strips and strands can be made from wheat flour has been attributed uniquely to gluten. By mere addition of sufficient water to wheat flour coupled with kneading, the elastic dough can be developed and flattened to a sheet and cut into strips or strings. The absence of gluten in other crops did not become a hindrance for making dough strips, strings, or ribbons from them. The characteristics of gluten-free starchy raw materials and their suitability for this unique line of food ingredients as they impart distinct sensory attributes as well as nutritive value are the main content of this book chapter. As such, starch noodles are also referred to as nonwheat or gluten-free noodles. Alternatively, noodles are also referred to as vermicelli, an Italian word from the Latin word vermis ‘worm,’ so-called for the resemblance. This may be preceded by descriptive terms such as cellophane, glass, and rain to refer to its characteristic appearance of being transparent and clear. The crop name such as rice, maize, mung bean, sweet potato, or potato from which starch has been extracted is also commonly used with the product. Depending on the dimension and use of the product, sticks, ribbons, and sheet or paper maybe written on product labels. Based on similar references to the appearance and crop names, these products are called by different dialects, regional names, and vernacular terminologies.

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In summary, starch noodles are a category of Asian noodles produced by partial gelatinization of the starch component of the starch-based substrate that maybe purified as in the case of mung bean, sweet potato, potato, tapioca, and canna or its flour as in the case of rice, maize, and buckwheat. The gelatinized starch serves as a binder that enables the development of a dough that can be shaped. Its distinctive attributes are the crystalline structure of the dried noodles and characteristic slippery smooth texture of the cooked noodles. On its own, it is bland tasting, but on rehydration, it readily absorbs the flavors of the other ingredients with which it is cooked.

The main type of starch noodles is that of rice noodles that come in a variety of forms such as thin threads that may be bundled or packed in a compact block. They are also produced as well-separated rice sticks that vary in diameter and are generally straight cylindrical rods. There are also flat noodles or ribbons that are well separated and packed as folded bundles. Distinct characteristics of dried rice noodles are their offwhite color, slight to high opacity, and brittleness of the raw noodles. Although commonly sold as dried products, fresh rice noodles can be found in most Asian wet markets. Instant rice noodles in clear soups are found in many supermarkets and come in thread and ribbon forms. They are either boiled in water or soaked in boiling water for 3 min before being served and are offered with assorted flavors of soup base such as chicken, seafood, and beef. They are also conveniently packed in cups to which boiling water is poured and can be directly consumed after a few minutes. Selected prepared foods from rice noodles and wrapper are presented in Figure 1. Another major type of starch noodles is produced from the legume mung bean. These noodles are much whiter, usually thinner in diameter than most rice noodles, very glossy, clear, and with high tensile strength in both the raw and the cooked forms. The strands are well separated, are bundled neatly, and do not break easily. Another difference between rice noodles and bean thread noodles is the cooking instructions that come in the package. Mung bean vermicelli withstands long soaking and boiling times without adverse effects on the characteristic cooked texture as compared to rice noodles. In Asia, starch noodles from root crops are used in various dishes. Sweet potato starch noodles are a well-known delicacy as both snack food and main dish in China, Korean, and Japan. Unlike clear almost colorless crystalline legume starches, they have thicker strands and it is acceptable for them to have a slightly yellow to brown crystalline structure. The common characteristics they share with legume noodles are that they have well-separated strands and both the raw and the cooked


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WHEAT-BASED FOODS | Noodles: Starch

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Figure 1 Prepared dishes and the starch noodle/wrapper used: (a) rice flat noodles used in beef soup, (b) maize starch noodles in pancit palabok, and (c) rice paper used for steamed spring rolls.

noodles have a high tensile strength. When cooked, they have a slippery mouth feel. Starch sheet wrappers, used in many food preparations, are differentiated from noodles only by their dimension and end use. Steamed Chinese dim sums are normally wrapped in wheat

flour dough sheets but may also be wrapped in starch sheets made from wheat and cassava that provide a nearly transparent skin that shows the mixture of the vegetable and meat fillings of the product. These wrappers may also be mixed with vegetable juices from spinach or carrots to give dim sum dishes

66


diverse natural colors. Starch sheets may also be sold in the dried form and used as spring roll wrappers. Vietnamese steamed or fried spring rolls with mixed vegetable and meat fillings are wrapped in round rice paper. Another fresh variant of this product is starch sheets steamed with either vegetable or meat bits, which are rolled after cooking and served with a sauce.

Raw Materials Starchy crops without gluten are the major raw materials for starch noodles. Rice, maize, and buckwheat noodles are made from their flour, while legume and root crops like potato, tapioca, and canna noodles are produced from purified starches. Noodles from cereal flours are thus higher in nutritive value with higher protein content as compared to the purified starch substrates. Purified starch however confers a higher product storage stability. It is also a common practice to mix these flours and starches to alter and improve quality of the end product. Root crop starches are added to cereal flours or other starches to impart both desirable texture and clarity to the raw and cooked noodles. Research studies have been performed to set starch quality standards/index for suitability for starch noodle production based on starch pasting, swelling, solubility, thermal, and physical starch granule properties.

Cereal Flours and Starches Rice is the staple food in Asia. It is cooked as a whole polished grain by plainly boiling in water or steaming of soaked grains. The trade in whole grains is based on grades in which price is highly dependent on the percentage of head rice and purity of variety. The increase in the percentage of broken rice causes a considerable price downgrade. The content of broken grain could be indicative of grain handling from timing of harvest, maturity of grains, or moisture content during milling. Such broken rice is utilized for other products such as noodles. High-amylose indica rice with 25–35% amylose is suitable for making rice noodles, while glutinous japonica rice is usually added to improve texture. Rice is aged for at least 9 months before being used for noodles. Suitability for noodles is generally based on the sensory quality of the cooked grain as assessed by the skilled processor. The production of many Asian food products like rice noodles could be considered an art in itself.

Purified Starches Traditional starch purification in Asia such as the extraction of root crop starches normally involves the use of a lactic acid fermentation solution. Studies have shown that fermentation confers to mung bean starch significant beneficial thermal properties. Among starches with similar amylose content, those having a higher proportion of long chains in the amylopectin fraction tend to have a higher degree of retrogradation. It is inferred that this is the reason why mung bean starch intended for noodle production is lactic acid-fermented. The extraction of starch for noodles from most substrates is by wet milling, where the main objective is to extract the starch

without recovering other fractions of the grain as typically done in wet milling. However, utilization of the by-products from starch extraction must be incorporated for process efficiency and to reduce environmental pollution.

Cereal Starches Maize starch is now evolving as a cheap substrate for starch noodle production, not to replace mung bean starch but for rice noodles. In the Philippines, it is now being used in part or up to 100% in the production of rice noodle-like products differing in dimensions from thin threads, strips, ribbons, or sticks. Being readily available with a consistent product quality, it is used now extensively to produce both fresh and dried ricelike noodles. Furthermore, it has conferred a certain degree of storage stability to the product being lower in nutritive value with lower protein as well as fat content. Maize starch noodles do not spoil as quickly as pure rice vermicelli.

Legumes Mung bean is native to Asia and is considered the best substrate for starch noodles. It produces noodles that have high tensile strength and do not break easily in the raw form as well as cooked noodles. It has excellent cooking and eating quality. These quality characteristics have been attributed to its starch, which has a high amylose content ranging from 30% to 34% and has restricted swelling during gelatinization and a high shear resistance of its paste. Other legume starches such as red beans, kidney beans, broad beans, lentils, and peas are also utilized in starch noodle manufacture, but they are not as good as starch from mung beans. Pea starch from smooth peas has an amylose content that ranges from 24% to 65%, while starch from wrinkled peas has an amylose content that ranges from 60% to 85%, which exhibit very restricted swelling. A new extrusion process has been developed to utilize pea starch for noodles.

Root Crops Root crop starches are extensively utilized in starch noodle production. These starches are considered as a good, cheaper substitute for mung bean for starch noodle production. Sweet potato, potato, cassava, and canna starches are all used in noodle production in Asia.

Mixed Substrates Cereal flours and starches are mixed often times with root crop starches to impart desirable textural and visual properties to the end product. Fresh starch noodles or wrappers are likewise prepared from a composite of wheat starch and cassava starches to attain a characteristic translucency and texture not possible when the starches are used individually in the formulation. Generally, blending of starches serves to improve texture, which may be reflected as increased strength and elasticity imparted to starch noodle/sheets during processing. This makes the noodle strips less vulnerable to breakage and consequently reduces production losses. Another common recommended noodle improver is ‘konjac’ flour, composed mainly of glucomannan and extracted from elephant’s foot yam

WHEAT-BASED FOODS | Noodles: Starch (Amorphophallus sp.). It may be added at the rate of 3–10% of starch, and its addition not only improves texture but also increases the soluble fiber content of the product. A traditional product from composite flour with wheat is buckwheat noodles. Its structure is partially dependent on the wheat flour component. It is brownish in color and can be found in both the dry and the fresh forms and can be served hot or cold.

Noodle Processing The general procedure by which starch noodles are made is presented in Figure 2. A portion of the flour or starch is gelatinized to serve as binder, which allows formation of dough or batter, which may be extruded or sheeted and further molded into the desired shape. The variations possible in each step in different products are presented in the following sections.

Partial Gelatinization of Moist Starch In the preparation of rice noodle, the grains are soaked overnight, washed, and wet milled to a fine consistency, after which excess water is drained. When purified starch is used as substrate such as in the case of maize, potato, and sweet potato, water is distributed evenly to the dry starch to make 20% moisture content. This initial moisture enables mixing with minimal lumpiness that facilitates easy addition of more

Starch flour

Addition of water and partial gelatinization

Formation into desired shape

Full gelatinization

Retrogradation

Drying

Starch noodles Figure 2 General procedure for the production of starch noodles and sheets.

67

water appropriate for easy handling of dough. For rice and maize noodles, the dough is formed into fist-sized balls and cooked in boiling water for 30 min. The outer layer is cooked in the process, but the inner portion is left uncooked. A kneading process is employed to fully disperse the gelatinized starch in the uncooked portion to produce noodle strands that do not readily break during extrusion. A laboratoryscale production of maize noodles is presented in Figure 3. For jelly noodles from sweet potato and potato, a batter with appropriate flow characteristics is required to enable smooth application on to a metal plate or cloth canvas to form a sheet. The metal sheet conveyor is always kept clean so that the smooth sheet is peeled off easily. The addition of hot water of 70–80 C with simultaneous mixing enables partial gelatinization and development of the right viscosity and smoothness. A potato jelly noodle production line is presented in Figure 4. In a similar manner, Chinese dim sum wrappers from starches are prepared by adding boiling water to wheat starch and cassava starch to enable the formation of dough, which can be formed into a ball and rolled thin to a circular sheet used to enclose the filling.

Shape Formation In rice and maize starch noodles, smooth balls are made from the kneaded dough and loaded into a cylindrical tube holder ready for extrusion by a hydraulic press that forces the dough through a die with a specified opening corresponding to the noodle diameter. For flat noodles, the cutting step is done after sheet formation that is set through gelatinization. In fresh noodle processing, the cutting edge is heavily coated with oil to prevent starch sheet and noodles from sticking to metalcutting surfaces. Dim sum wrappers are formed by carefully picking up the flattened soft pliable circular dough, folding three to five times on one side of the circle, pinching to keep the folds in place, putting a tablespoon of filling into the dough circle, and sealing tightly with another pinch. For dried starch wrappers, the shape is attained when batter is poured on to a shaped mold, normally a round shallow container. Rice spring roll wrapper usually has a delicate weave design that it picks up from the bamboo tray on which it was molded and dried. A Vietnamese dish uses this rice paper as a wrapper for steamed or fried spring roll. The different preparation methods for starch noodles are determined to a great extent by the flow characteristics of the starch dough and are reflected in the finished product. Mixed root crop starches may result in thicker noodle strands even when using the same die opening, compared to the use of pure mung bean, sweet potato, or potato starches. This may be attributed to the difference in the degree of gelatinization of binder, extrusion conditions employed, the unique starch properties of substrate being used, and/or the additive or improver applied. Indeed, the process of making starch noodles remains an art based on experience of the processor.

Full Gelatinization of Shaped Dough The shaped noodles or sheet is fully gelatinized by either boiling or steaming. In rice noodles, the noodle strands may

68


Figure 3 Laboratory-scale production of maize starch noodle showing (a) starch dough, (b) cylindrical dough holder, (c) manual extruder assembly, (d) extrusion of dough into boiling water, (e) drained noodles, and (f) noodles on a drying tray (Food Science Cluster, College of Agriculture University of the Philippines, Los Banõs College, Laguna, the Philippines).

be extruded directly into boiling water in a cooking vat for 2–5 min or steamed on trays in steaming chambers for 15–20 min. Once the extruded noodles are dropped into boiling water, they are removed when sufficiently cooked or when strands begin to float on the surface. This is due to the change in density of the noodle strand as it is cooked or gelatinized. Uncooked hydrated starch granules have a relatively high density, 1.5 g cm3, so that uncooked noodles settle directly to the bottom of the cooking container; but as they gelatinize, starch granules swell as they absorb more water and

consequently float on the surface of boiling water. The extruded noodles can also be steamed in a conveyor for 15 min at 120 C. Full gelatinization of the extruded noodles and subsequent retrogradation serve to set noodle structure. For flat noodles, the starch sheet is steamed through the application of heat under the metal or canvas conveyor, which moves over the heating/steaming components. In effect, the speed by which the sheet moves sets the cooking time. In the processing of canna starch noodles in Vietnam, the steam sheeting of canna starch dough is followed by a stretching


69

Figure 4 Potato starch noodles production showing (a) mixing starch batter, (b) application of batter on a metal sheet, (c) cooked sheet peeled off from metal sheet, (d) drying starch sheet, (e) tempering of starch sheet, (f) sheets in rollers, (g) cutting, (h) drying, and (i) potato noodles (Changchun, People’s Republic of China).

step not found in rice or mung bean/sweet potato jelly sheet noodles. For Chinese dim sum, not only cooking enables setting the wrapper shape, but it also cooks the vegetable and meat fillings.

Retrogradation In the production of starch noodles, processes are employed to enhance retrogradation, such as the low-temperature conditioning step applied after the gelatinization of the noodle strands or sheets. Retrogradation is the process that finally sets the

noodle structure that can withstand normal cooking temperatures in soups and stir-fried meat and vegetable dishes. This may involve freezing and thawing as in mung bean noodles or a simple washing in cold water and conditioning as in rice, potato, and sweet potato noodles at room temperature. It is interesting to note that in village-level production of sweet potato noodles, the conditioning stage is attained naturally since processing is an annual activity during the cold months in October or November when night temperature in Sichuan and Shandong, China, drops to 0–5 C with very low relative humidity. After an overnight conditioning, the noodles are separated and allowed to dry


70

under the sun. In tropical production systems in Asia, favorable conditions for retrogradation have to be provided artificially through appropriately designed processing equipment and facilities to ensure consistent quality.

•

Drying

•

Most starch noodles are traditionally air-dried under the sun, but most commercial productions are now dried in mechanized driers, which are part of a continuous process. In China, in the production of jelly sheet noodles from potato and sweet potato, the gelatinized sheet is scraped and moved on to a fine wire screen conveyor that leads to a heating cabinet, after which the sheet comes out ready for conditioning followed by cutting, drying, and packing.

• •

•


• Nutritional Benefits Starch noodles are a health food being a rich source of retrograded starch, a form of resistant starch (RS) due to the nutritional benefits associated with their consumption. The definition of dietary fiber (DF) has broadened in recent years to include RS. Starch noodles not only provide an alternative to wheat-based pasta for celiac patients but also are now considered a source of DF from retrograded starch. Retrograded starch is left undigested until fermented in the large intestines. Glucose and oligosaccharides are released from retrograded starch over an extended period through the normal digestive process. Studies have shown that extruded noodles from high-amylose rice varieties significantly reduced starch digestibility and the glycemic index in normal individuals. This has been attributed to starch gelatinization and retrogradation during processing. The low glycemic response from noodles implies that these foods may have health benefits to both normal and diabetic individuals through sustained energy level and prolonged satiety. DF is a significant food component that can minimize the risk of colon cancer, cardiovascular disease, and diabetes. Studies demonstrated that RS offers advantages comparable to traditional sources of DF in providing fecal bulk and encouragement of the growth of beneficial microflora. The physiological effects of RS are comparable to those of fermentable DFs. A lower acidity in the colon is attained through the fermentation of carbohydrates by gut bacteria to short-chain fatty acids such as acetic, propionic, and butyric acids. Systemic effects of RS may be important for the treatment of colorectal cancer, amelioration of inflammation, and optimal bowel health. Optimization studies on RS formation in starch noodles with the use of different substrates and process variables may present alternative ways by which RS can be offered as a functional food ingredient in both traditional and nontraditional food products.


• •

What crops are made into starch noodles? What process step is essential to make a starch dough that can be shaped into noodles or food sheets/wrappers?

What is the conditioning step in starch noodle production that sets the structure of the dried noodles? Describe the sensory attributes (visual and textural properties) of starch noodles. How does it differ from wheat noodles? Why are root crop starches added to cereal starches in the production of noodles? What make starch noodles suitable for celiac patients? Starch noodles have RS. What nutritional benefits do RS to human health?

•

•

• •

Starch is composed of amylose and amylopectin components arranged inside the starch granule. When starch is cooked in excess water, gelatinization occurs, and upon cooling, retrogradation consequently happens. Discuss what happens to amylose and amylopectin in starch granules during gelatinization and retrogradation. Describe the wet milling process for the extraction of maize starch. What are the coproducts of starch from the different kernel fractions? Discuss the commercial value of the coproducts in agriculture and food processing. Wheat proteins confer unique properties that make it suitable for bread and pasta? How is wheat dough developed so it can be shaped into different products? Take note how different it is from dough made from gluten-free starch substrates. What are the advantages of using nonwheat flours in starch noodle production? What are the benefits of using purified starch in noodle production? Starch functional properties will continue to evolve to make innovative healthy products. Discuss how starch is being utilized in different food products that can prevent disease and promote health.

See also: Barley, Rice and Maize Processing: Maize: Wet Milling; Carbohydrates: Glycemic Index, Glycemic Load, and Their Health Benefits; Resistant Starch and Health; Starch: Chemistry; Food Grains: Intolerance, Allergy and Diseases: The Gluten-Free Diet.

Further Reading Alden L (2005) The Cook’s Thesaurus. http://www.foodsubs.com/NoodlesRice.html (accessed 14.01.16.). Alden L (2005) The Cook’s Thesaurus. http://www.foodsubs.com/NoodlesAsianOther. html (accessed 14.01.16.). Champ M (2004) Resistant starch. In: Eliasson AC (ed.) Starch in Food: Structure, Function and Applications, pp. 562–564. Boca Raton, Boston, New York Washington DC: CRC Press. Chang YH, Lin CL, and Chen JC (2006) Characteristics of mung bean starch isolated by using lactic acid fermentation solution as the steeping liquor. Food Chemistry 99(4): 794–802. Chen Z, Schols HA, and Voragen AGJ (2003) Starch granule size strongly determines starch noodle processing and noodle quality. Journal of Food Science 68(5): 1584–1589.

WHEAT-BASED FOODS | Noodles: Starch Collado LS, Mabesa LB, Oates CG, and Corke H (2001) Bihon-type noodles from heat moisture treated sweet potato starch. Journal of Food Science 66: 604–609. Harper D (2013) Online Etymology Dictionary. http://www.etymonline.com/index.php? term¼noodle (accessed 14.01.16.). Harper D (2013) Online Etymology Dictionary. http://www.etymonline.com/index.php? term¼vermicelli (accessed 14.01.16.). Higgins JA and Brown IL (2013) Resistant starch: A promising dietary agent for the prevention/treatment of inflammatory bowel disease and bowel cancer. Current Opinion in Gastroenterology 29(2): 190–194. Isleib DR (1958) Density of potato starch. American Potato Journal 35(3): 428–429. Kaczmarczyk MM, Miller MJ, and Freund GG (2012) The health benefits of dietary fiber beyond the usual suspects of type 2 diabetes mellitus, cardiovascular disease and colon cancer. Metabolism 61(8): 1058–1066. Lii CY and Chang SM (1981) Characterization of red bean (Phaseolus radiatus var. aurea) starch and its noodle quality. Journal of Food Science 46: 78–81. Lu ZH and Collado LS (2010) Rice and starch-based noodles. In: Hou GG (ed.) Asian Noodles: Science, Technology and Processing, pp. 393–431. Hoboken, NJ: Wiley. Panlasigui LN, Thompson LU, Juliano BO, Perez CM, Jenkins DJA, and Yiu SH (1992) Extruded rice noodles: Starch digestibility and glycemic response of healthy

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and diabetic subjects with different habitual diets. Nutrition Research 12: 1195–1204. Singh JY, Voraputhaporn UW, Rao PV, and Jambunathan R (1989) Physicochemical characteristics of pigeon pea and mungbean starches and their noodle quality. Journal of Food Science 54: 1293–1297. Singh K, Maninder S, and Mukesh K (2010) Studies on noodle quality of potato and rice starches and their blends in relation to their physicochemical, pasting and gel textural properties. LWT – Food Science 43(8): 1289–1293. Tam LM, Corke H, Tan WT, Li JS, and Collado LS (2004) Production of bihon-type noodle from maize starch differing in amylose content. Cereal Chemistry 81(4): 475–480. Tan HZ, Li ZG, and Tan B (2009) Starch noodles: History, classification, materials, processing, structure, nutrition, quality evaluating and improving. Food Research International 42(5–6): 551–576. Udesky J (1988) The Book of Soba, pp. 21–42. Tokyo: Kodansha International. Wang N, Maximiuk L, and Toews R (2012) Pea starch noodles: Effect of processing variables on characteristics and optimisation of twin-screw extrusion process. Food Chemistry 133(3): 742–753.

Noodles: Asian Wheat Flour Noodles GB Crosbie, Crosbie Grain Quality Consulting, East Fremantle, WA, Australia AS Ross, Oregon State University, Corvallis, OR, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Classification Based on Manufacturing Process A small percentage of noodles are handmade and valued for their fine texture, including types made by stretching, cutting, or shaving of hand-mixed dough. Most noodles are made by machine, with the basic steps of dough mixing, sheeting, combining of sheets, resting, rolling, and cutting being used in most noodle plants. Subsequent treatment varies, and noodles may be manufactured in various final forms for sale, including fresh (raw), semidried, dried, boiled, steamed, steamed and dried, steamed and fried, and frozen types. These types are described in more detail later in this article.

Classification of noodles. Noodle making process. Effects of processing on noodle quality. Raw materials. Effects of raw materials on noodle quality.

Learning Objectives

• • •

To understand various types of Asian wheat flour noodles. To understand noodle manufacturing processes. To learn of factors influencing noodle quality.

Classification of Noodles Noodles are often classified on the basis of raw materials and dimensions of the strands and by the method of manufacture. A similar approach is used here.

Classification Based on Ingredients The main ingredients in Asian noodles are flour, salt (sodium chloride), and water and, in the case of alkaline noodles, solutions of sodium carbonate, potassium carbonate, sodium bicarbonate, or sodium hydroxide. The alkaline solutions are known as lye water or ‘kansui.’ On this basis, noodles can be classified as nonalkaline or alkaline depending on the presence or absence of alkaline salts. There has been a tendency for nonalkaline noodles to be referred to as ‘white salted,’ but this category is not exclusively white and containing sodium chloride. In Japan, a creamy-colored noodle is preferred, and in China, this noodle type is manufactured with and without salt. Also, sodium chloride may be used in addition to alkaline salts in the manufacture of alkaline noodles. While there is also a tendency for Japanese-style white salted noodles to be referred to generally as ‘udon,’ in Japan, there remains a preference for such noodles to be referred to by specific names that relate to noodle strand size – of which udon is one (see succeeding text and Table 3). In addition, ingredients such as starches, gums, phosphate salts, and colorants are commonly used for specific effects in both nonalkaline and alkaline noodle types. ‘Soba’ is a popular noodle consumed in Japan and is usually made from a mixture of buckwheat flour and high-protein wheat flour, water, and salt. The high-protein content of the wheat flour compensates for the lack of gluten-forming protein in buckwheat flour. Basic formulations for various noodle types are given in Table 1.

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Classification Based on Noodle Size Noodles commonly have a rectangular cross section but may be square or round depending upon the thickness of the noodle sheet and the shape and size of the cutting rolls used. In Japan, there are a wide range of nonalkaline types that differ markedly in their width (Table 2). Throughout Asia, an extensive range of noodle types and sizes are manufactured including alkaline and nonalkaline noodles (Table 3).

The Noodle-Making Process and Its Effects on Noodle Quality Basic Processing Steps Mixing Vertical or horizontal dough mixers and a variety of mixing processes are used to blend ingredients and, depending upon the amount of water added, to develop a crumb or dough. Saline or alkaline solutions are usually incorporated with the dry ingredients at levels of 28–35% (based on flour weight) for nonalkaline noodles and 28–34% for alkaline noodles. Moisture additions may increase from 40% to 47% if vacuum is applied during mixing. In forming the initial dough crumb, the main focus is even hydration of the dry ingredients and there is little gluten development. Estimation of optimal water addition is generally based on an assessment of crumb size (for low water additions) and satisfactory sheeting and handling properties. The amount of water added affects almost all processing operations and final product quality. Low water addition and crumb formation are favored in the preparation of noodles that will be dried prior to distribution. The use of higher amounts of water under vacuum mixing has advantages in minimizing gluten damage during subsequent sheeting, combining, and rolling operations, increasing product yield of raw noodles, and reducing cooking time for processes involving boiling or steaming. The maintenance of close control of dough temperature is important in the mixing stage of the noodle process, and too


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WHEAT-BASED FOODS | Noodles: Asian Wheat Flour Noodles Table 1

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Typical noodle formulations Basic ingredients

Noodle type

Country or region

Preferred color of product for marketa

Nonalkaline Udon

Japan

China

Creamy–creamy yellow White–creamy yellow White

SE Asia

Gua mian (dried noodles) Gua mian (dried noodles) Mee sua (steamed and dried) Mee teow (steamed and dried) Alkaline Ramen (raw) Steamed Chinese noodles Cantonese (raw) Hokkien mee (parboiled) Hokkien mee (parboiled) Mee pok (raw) Mee kia (raw) Wanton mee Singapore style (raw) Wanton mee – Hong Kong style (raw) Bamee Instant steamed and fried

Alkali

Flour (parts)

Waterb Parts

NaCl Parts

100

34

2c

100

d

100

25–32

2–3

3

White

e

e

e

4

SE Asia

White

e

e

e

4

Japan

Light yellow

100

32

1

1.0

Japan

Light yellow

100

34

1

1.0

Asia

100

36

1

SE Asia

Light–medium yellow Intense yellow

100

36

SE Asia

Intense yellow

e

SE Asia SE Asia SE Asia

Light yellow Light yellow Intense yellow

SE Asia

Thailand SE Asia

China

Parts

Type

Other key ingredients

Reference 1 2

1.2

Na2CO3:K2CO3 (40:60) Na2CO3:K2CO3 (40:60) Na2CO3

5

2.5

0.8

NaOH

5

e

e

e

NaOH, KOH

4

e

e

e

e

e

e

e

e

e

e

e

e

4 4 4

Intense yellow

e

e

e

e

Intense yellow Light yellow

100 100

28 34–37

3 1.6

1.5 0.2

Na2CO3, K2CO3 Na2CO3, K2CO3 Na2CO3, K2CO3, NaHCO3, KHCO3 Na2CO3, K2CO3, NaHCO3, KHCO3 Na2CO3 Na2CO3:K2CO3 (50:50)

1 1

Eggs or egg white, approved colorant Eggs or egg white, approved colorant Egg Guar gum, polyphosphatesf

4

6 6

a

Ideally, the noodles should also be bright. Higher water levels are added with handmade noodles; also with vacuum mixing, for example, udon–40–43%. c Higher levels of salt in handmade noodles. d Water addition based on farinograph water absorption. e Ingredient listed in main reference but amount not indicated. f A wide range of ingredients and additives are permitted. References: (1) National Foods Research Institute, Ministry of Agriculture, Forestry, and Fisheries, 1985. Quality Assessment of Wheat – Sensory Tests for Noodles, MAFF, Japan; (2) Professional Standard of the People’s Republic of China (SB/T 10137–93); (3) Huang, S., 1996. China – the world’s largest consumer of paste products, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 301–329; (4) Singapore Standard CP64:1996; (5) Commercial source; (6) Hou, G., Kruk, M., 1998. Asian Food Technology. American Institute of Baking, Manhattan, KS; Technical Bulletin, Vol. XX, Issue 12. b

Table 2 Classification of Japanese-style white salted noodles in Japan by width Noodle type

Width (mm)

Cutting roll size

Somen Hiyamugi Udon Hiramen (Kishimen)

1.0–1.2 1.3–1.7 2.0–3.8 5.0–7.5

30–26 24–18 16–8 6–4

Source: Japanese standard JIS, B9201.

low or too high a temperature can have adverse effects on product quality. In experimental studies, the Japanese National Food Research Institute specifies that room temperature should be 25 2 C and the crumb or dough temperature 26 2 C. These specifications could also be used as a guide for commercial noodle manufacture.

Initial sheeting and combining The crumb or dough is split into two and each is passed through a set of sheeting rolls. The two sheets are then combined through a single set of rolls to facilitate gluten development.

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WHEAT-BASED FOODS | Noodles: Asian Wheat Flour Noodles

Table 3

Dimensions of various types of Asian noodles

Noodle type Nonalkaline Udon Gua mian (dried noodles) Gua mian (dried noodles) Mee sua (steamed and dried) Mee teow (steamed and dried) Alkaline Ramen (raw) Steamed Chinese noodles Cantonese (raw) Hokkien mee (parboiled) Hokkien mee (parboiled) Mee pok (raw) Mee kia (raw) Wanton mee–Singapore style (raw) Wanton mee–Hong Kong style (raw) Bamee Instant steamed and fried

Country or region

Final roll gapa (mm)

Raw noodle thickness (mm)

Raw noodle width (mm)

Reference

Japan China China SE Asia SE Asia

1.7 1.0 – –

2.5 Not specified 0.6–1.4 0.8 0.8

3.0 2.0 0.8–6.0 Very fine Fine

1 2 3 4 4

1.1 1.1 0.6 0.9

1.4 1.4 1.0 1.2

1.5 1.4b 1.5 2.0

0.8 1.2 1.0

5.0 1.2 1.0

1 1 5 5 4 4 4 4

SE Asia

0.9

0.9

4

Thailand SE Asia

1.5 0.9

1.5 1.4

6 6

Japan Japan Asia SE Asia SE Asia SE Asia SE Asia SE Asia

c

c

a

Final roll gap is set to give the required noodle sheet thickness. Noodles for the market are made with round-grooved cutting rolls but a square cutting roll is preferred for experimental purposes. c Hokkien mee is manufactured over a range of width and thickness. References: (1) National Foods Research Institute, Ministry of Agriculture, Forestry and Fisheries, 1985. Quality Assessment of Wheat – Sensory Tests for Noodles, MAFF, Japan; (2) Professional Standard of the People’s Republic of China (SB/T 10137-93); (3) Huang, S., 1996. China – the world’s largest consumer of paste products, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 301–329; (4) Singapore Standard CP64:1996; (5) Commercial source; (6) Hou, G., Kruk, M., 1998. Asian Food Technology. American Institute of Baking, Manhattan, KS; Technical Bulletin, Vol. XX, Issue 12. b

At this stage, the sheet is usually rested for periods of up to 1 h, although longer rest periods are used in some plants. The rest period allows for relaxation of the gluten structure and minimizes damage to the gluten during subsequent reductions in sheet thickness. Studies at the Bread Research Institute of Australia that were reported in 1987 showed that rested Cantonese noodle doughs had a more continuous protein matrix, fewer air spaces, and less protein contraction on the sheet surfaces. The better developed protein matrix was considered to result in improved noodle eating quality.

Rolling of the sheet The sheet is then passed through a series of rolls to progressively reduce the sheet thickness. This stage of the process can impact substantially upon noodle eating quality. Important factors include rate of reduction in sheet thickness, moisture content of the sheet, direction of sheeting, and the temperature of the rolls. The reduction in sheet thickness should ideally not be greater than 30% at any pass through a pair of rolls; otherwise, the gluten structure may be damaged and the eating quality of the noodle impaired. The moisture content of the sheet is important with higher moisture levels protecting the gluten structure from damage. The superior texture of handmade noodles has been associated with improved gluten development through a combination of higher dough moisture content and kneading of the dough after mixing. The kneading leads to randomized development of the gluten rather than the unidirectional development achieved through conventional sheeting. New techniques have attempted to achieve the

characteristics of handmade noodles in mechanized production. Strategies employed have included the use of corrugated or waved rolls that are reported to simulate the effects of multidirectional sheeting. The temperature of the sheeting rolls is important, and water-jacketing of the rolls assists in controlling sheet temperature. Changes in temperature also affect sheet elasticity and viscosity. These factors, in turn, influence the roll gap settings required to achieve the desired final sheet thickness. Excessive roll temperatures can lead to surface drying of dough sheets, and the Japanese National Food Research Institute has reported that low roll temperatures cause roughness of the noodle surface.

Cutting After reduction of the noodle sheet to its final thickness, the noodles are cut lengthways through cutting rolls. Cutting rolls are available to produce noodles that vary in width from 1.0 mm to 7.5 mm. The final dimensions of the noodle strands are determined by the cutting rolls and the thickness by the sheeting process. These dimensions influence time taken for drying (for dried noodles) and cooking (for steamed and boiled noodles).

Processing for Specific Noodle Types Dried noodles Drying preserves noodles and prolongs shelf life by reducing water activity to a level that greatly restricts or stops quality

WHEAT-BASED FOODS | Noodles: Asian Wheat Flour Noodles deterioration and microbial growth. The drying of noodles involves close control of temperature and humidity for times that vary according to noodle width and thickness. A typical method for drying ‘udon’ involves an initial drying at low temperature (15–25 C) and relative humidity (60%) over 30–60 min – the aim here is to remove surface moisture quickly, to harden the noodle strands to avoid stretching and breakage when hanging in the drying chamber. The main drying is carried out at slightly higher temperature (about 40 C) and relative humidity (70–75%) for up to 6 h. Finally, the noodles are cooled slowly to room temperature, using as much ambient air as possible, to achieve a final moisture content of less than 14%.

Boiled noodles Several types of noodles are boiled prior to sale. These include boiled udon and the alkaline ‘Hokkien’ noodles manufactured in Southeast Asia. After cooking, boiled udon noodles are rapidly cooled in chilled water, drained, automatically packed, and refrigerated at 5 C. In contrast to boiled udon, Hokkien noodles are only parboiled by the manufacturer and the final cooking is done immediately before eating. Hokkien noodles are cooled by either air or chilled water, drained, sprayed with oil to minimize sticking, and usually packed in plastic bags. Long-life noodles are boiled noodles, which can be stored at ambient temperature for long periods. In this case, the noodles are formed, partly boiled, cooled, soaked in a dilute organic acid solution such as lactic acid, surface treated with oil or a-amylase to stop sticking, and then packed and pasteurized at temperatures exceeding 90 C. Boiling time required varies according to noodle size, but a typical time period for complete boiling would be 20 min for raw udon, with a moisture content of 35% and with crosssectional dimensions of 3.0 mm 2.5 mm. Boiling time decreases with increased moisture content and increases with the size of the noodle strand. The Japanese National Food Research Institute indicates that pH of water used in boiling udon should be maintained at 5.5–6.0 to minimize boiling losses. The pH of the water is not so critical for alkaline noodles, which leach alkaline salts into the boiling water. Where pH control is required, organic acids such as lactic, malic, and citric acids are suitable.

Frozen noodles In the manufacture of frozen noodles, raw noodles are boiled, washed in chilled water, drained, and rapidly frozen at 30 C or below. High-quality frozen noodles are usually made by mixing under vacuum, allowing increased water addition. The additional water improves gluten hydration and development, reduces gluten damage during sheeting, and reduces boiling time by allowing more rapid heat transfer into the noodle. Rapid freezing is also beneficial to ensure formation of small water crystals, which are less likely to disrupt the gluten network than the larger water crystals formed at slower freezing rates. Frozen noodles can have very high quality, approaching that of fresh (raw) noodles. The process is critical and poor results can occur if any of the key steps are not finely tuned.

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Instant steamed and fried noodles Steamed and fried instant noodles were introduced in the late 1950s and early 1960s in Japan and Korea. They have fast rehydration rates on final cooking and this convenience makes them very popular. Their basic processing, up to cutting, is common with other noodle types. Dough moisture should be low enough to promote fast dehydration during frying. However, dough moisture must also be sufficiently high to promote full gelatinization of starch during steaming and adequate development of the gluten structure. Adequate gluten development is needed for its contribution to noodle texture and to minimize excessive softening of noodles in hot soup. The process deviates after cutting. First, the noodles are waved and formed into the appropriate shape for sale. The wave conformation assists in even penetration of steam and frying oil. Various devices ranging from hinged baffles to rubber flaps, both placed immediately after the cutting rolls, are used to form the waved noodles. The devices allow the buildup and release of the noodles that cause the wave pattern to form. The noodles are then steamed, and steaming should be extensive enough to cook the noodles right through, that is, to the disappearance of the doughy core at the center of the noodle strand. This allows full swelling of the starch on rehydration, which is associated with good texture. The frying step simultaneously cooks and dehydrates the product. In addition, frying creates voids through violent steam release, which increases the surface area of noodles and assists in speeding rehydration rates. Frying further gelatinizes the starch, the block of noodles is set into shape to facilitate easy packaging, and a desirable golden color is developed. Instant steamed and fried noodles have a relatively high fat content ( 15–22%) compared with steamed and dried instant noodles (1–3%). Some manufacturers, to decrease oil uptake, take measures such as partially drying the noodles prior to frying or using edible coatings, sometimes polysaccharidederived. Much of this work is the subject of patent coverage.

Instant steamed and dried noodles Instant steamed and dried noodles are manufactured in several forms, with the most popular being a waved form in blocks, similar to instant steamed and fried noodles. These noodles may become increasingly popular with consumers because of their low fat content.

Raw Materials and Their Effects on Noodle Quality Wheat The principal consideration in selecting wheat for the milling of noodle flours is that it be well filled, of good appearance, and not damaged by weather or grain drying. Wheat used for the manufacture of noodle flour should have an appropriate balance of protein content, protein quality (as indicated by dough properties), and starch quality for the targeted noodle type. The presence of excessive levels of a-amylase, either preharvest sprouting a-amylase or late-maturity a-amylase, can have deleterious effects during processing and on the quality of the final product – these include increased boiling losses and reduced eating quality. High levels of protease, associated with rain

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damage, may lead to increased breakage of noodles during drying and poor color in both alkaline and nonalkaline noodles. In addition to having access to sound wheat of high milling quality, the milling process is also important. The highestquality noodle flours are associated with low extraction milling and low ash levels in the flour. This can be achieved either by milling to a low extraction rate or by milling conventionally and utilizing flour streams least contaminated by bran particles.

Flour Typical flour specifications for the different types of noodles are given in Table 4.

Flour attributes and noodle appearance Flour extraction levels and ash contents have a profound influence on noodle appearance. Higher flour extraction levels generally lead to duller noodles with a higher propensity to darken during dough processing. Low flour extraction and ash levels are preferred for the manufacture of noodles that retain a clean, bright appearance after cooking. Raw noodles discolor with time. This is associated with polyphenol oxidase (PPO) activity, flour extraction rate, weather damage, and variety. Wheat breeders in the exporting nations have been working diligently to decrease PPO levels Table 4

Nonalkaline Udon Dried noodles: superfine grade to common grade Dried noodles Alkaline Ramen Cantonese Cantonese (high-quality) Cantonese Wonton Hokkien Hokkien Bamee Instant noodles (ramyun): common to high-quality cup noodles

Instant

Flour and noodle texture The principal characteristics of flour that affect noodle texture are protein content, reflecting the relative proportions of the two main components of the flour, protein and starch, and the

Typical specifications for noodle flours

Noodle type

Instant Instant

and hence raw noodle darkening, in all potential noodle wheat, but noodle darkening is still an issue. In addition to PPO in the flour itself, PPO is preferentially localized in the bran. Higher flour extraction levels lead to higher numbers of bran particles in flour and increased visible speck counts in raw and boiled noodles. If raw noodles are held for too long before cooking, the specks become darker and more visible due to the effects of PPO. Increased flour protein content also decreases noodle brightness in a range of noodle types but has little effect on noodle darkening over time. The yellowness of the flour, mainly due to the presence of xanthophyll pigments, has a significant effect on the color of raw and cooked noodles. In Japan, the main preference is for creamy-colored udon, associated with a moderate level of yellow pigment in the flour. In addition to the effect of yellow pigment in the flour, the yellowness of ramen and other types of alkaline noodles is also influenced by the effect of the alkali on flavonoid compounds in the flour. Flour particle size also influences noodle brightness, with decreased particle size, at equivalent starch damage levels associated with brighter noodles.

Country/region Japan China

Moisture (%)

14.5 14.5

Protein (%) 8.0–10.0

China

9.5–11.0

Japan SE Asia SE Asia SE Asia SE Asia SE Asia SE Asia Thailand Korea

10.5–12.0 12.0 12.0–13.0 10.0–12.0 >13.0 10.5 10.0–11.5 11.5–13.0 10.3–10.6 9.4–10.6 11.0–11.5 11.5–13.0 10.0

Taiwan The Philippines Indonesia

13.5–14.0 13.5–14.0 13.5–14.0

11.0–12.0

Wet gluten (%)

Ash (%)

Falling number (s)

28 26

0.36–0.40 0.55 0.70

200 200

Reference 1 2 3

0.33–0.38

0.46 0.50–0.54 0.40–0.44 0.40–0.45 0.45–0.55

1 4 5 5 5 4 6 7 8

9 9 9

References: (1) Nagao, S., 1996. Processing technology of noodle products in Japan, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 169–194; (2) Chinese National Flour Standard (SB/T 10137–93); (3) Huang, S., 1996. China – the world’s largest consumer of paste products, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 301–329; (4) Moss, H.J., 1984. Ingredient effect in mechanized noodle manufacture, in: Proc. Singapore Inst. Food Sci. and Tech. Conf. Singapore Inst. of Food Sci. and Technology, Singapore, pp. 71–75; (5) Miskelly, D.M., 1996. The use of alkali for noodle processing, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. Am. Assoc. of Cer. Chem.: St. Paul, MN, pp. 227–274; (6) Shelke, K., Dick, J. W., Holm, Y. F., Loo, K. S., 1990. Chinese wet noodle formulation: A response surface methodology study. Cereal Chem. 67, 338–342; (7) Hou, G., Kruk, M., 1998. Asian Food Technology. American Institute of Baking, Manhattan, KS; Technical Bulletin, Vol. XX, Issue 12; (8) Kim, S. K., 1996. Instant noodles, in: Kruger, J.E., Matsuo, R.B., Dick, J.W. (Eds.), Pasta and Noodle Technology. American Association of Cereal Chemists: St. Paul, MN; (9) Nagao, S., 1995. Wheat usage in East Asia, in: Faridi, H., Faubion, J.M. (Eds.), Wheat End Uses Around the World. American Association of Cereal Chemists: St. Paul, MN, pp. 167–189.

WHEAT-BASED FOODS | Noodles: Asian Wheat Flour Noodles compositions of these two components. Flour lipids may also play an important role. Flour protein, in its hydrated form as gluten, provides the basic structure of a noodle strand. Increased protein content in the flour and also increased gluten strength, reflecting the composition of the protein, have significant effects on various aspects of noodle processing and texture. Increased protein content has been related in the literature with increased noodle hardness. However, there is conflicting evidence in the literature regarding the relative importance of protein content and gluten composition. In studies where sample sets with small ranges of protein content have been selected, a clear effect of protein composition on noodle texture can be observed. Where the range of protein content is greater, protein content seems to dominate the effects of gluten composition on noodle texture. In the last few years, study of the effects of gluten composition on noodle texture has become a dynamic area of research, and readers are advised to closely monitor the developments regarding this issue. Starch also has a significant effect on noodle texture. Initial studies on the effect of starch on noodle texture focused on the pasting characteristics of isolated starch and showed that high starch paste peak viscosity and correspondingly high levels of paste breakdown during shear were preferred for Japanese udon. Later studies indicated that the starch component of flour for udon should have high-swelling properties and these could be predicted from flour swelling volume (FSV) tests. The high-swelling starch type was found to be closely linked to the desired soft and elastic texture in udon. Early studies also indicated a possible requirement for low paste breakdown in starch isolated from flour for Japanese ramen. Recent studies have indicated that flour with lowswelling starch is required to give the firmness, lack of stickiness, and other desired characteristics in ramen. However, this may not be a common requirement of all noodles made with the inclusion of alkali. As research has progressed, it has become apparent that the swelling characteristics of flour appear to have a primary effect on boiled noodle yield and texture. Associations between paste viscosity measurements and noodle texture appear likely to reflect the common dependence of these characteristics on flour swelling. More recently, the genetic underpinnings of the main differences in starch characteristics for wheats preferred for udon have been elucidated. The biosynthesis of amylose is controlled by granule-bound starch synthase, which is normally present in three isoforms or isozymes. The isozymes, known as Wx-A1, Wx-B1, and Wx-D1, can be readily identified by gel electrophoresis. There are eight possible combinations of Wx-A1, Wx-B1, and Wx-D1 proteins, and wheat genotypes may be classified as wild-type (all three isozymes present), single-null (any one isozyme absent), double-null (any two isozymes absent), and triple-null (all three isozymes absent). The level of amylose decreases and amylopectin increases as more isozymes are absent, with triple null, full waxy wheat containing 100% amylopectin. The increased relative proportion of the highly branched amylopectin leads to greater swelling of starch granules during gelatinization, which can be detected as increased FSV and as the unique soft and elastic texture desired in udon and some other specialized noodle types. Wheat varieties released in

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Western Australia for the Japanese udon market have been single null types, associated with slightly elevated amylopectin levels.

Effects of salt High levels of salt, up to 8%, are used in some dried noodles, particularly handmade. Salt influences the ease or rate of drying of noodles, modifies enzymatic activity, and prolongs shelf life. It also reduces boiling time, causes a softer mouthfeel, and makes dough handling easier.

Effects of alkali Common alkalies used in the manufacture of alkaline noodles include sodium carbonate, potassium carbonate, and sodium bicarbonate. Mixtures of the alkalies are commonly used, with 1% (flour basis) of a 40:60 mixture of sodium carbonate and potassium carbonate being incorporated with 1% (flour basis) of salt in the Japanese National Food Research Institute method for ramen. In Malaysia and Singapore, sodium hydroxide is sometimes used in the manufacture of Hokkien noodles. Here, the use of this very strong alkali is favored for its positive effects on noodle brightness and yellowness, but this may be offset to some degree by a more rapid deterioration in cooked noodle texture with time. The use of alkali has a strong influence on noodle texture due to its effects on gluten and starch properties, and these differ according to the type of alkali used. Sodium hydroxide has a more substantial effect on starch gelatinization than sodium carbonate, even to the extent of inducing gelatinization of starch at room temperature. Noodles made from sodium hydroxide are reported to have a softer texture than those prepared from sodium carbonate, and this is likely to be associated with increased starch swelling. A consequence of this is that the optimum starch type required for flour used in the manufacture of alkaline noodles may vary according to the type of alkali used.

Effects of other ingredients Ingredients that have been used in noodle formulations include starches, gums, emulsifiers, enzymes, and colorings. For frozen noodles, nonwheat starches are frequently included in formulations. Modified starches designed to enhance freeze–thaw stability or slow retrogradation rates can improve the texture of the final cooked product through a softer but more elastic texture. In instant noodles, potato starch or other modified starches can be used to alter noodle texture and to increase the rate of rehydration on final preparation. There are many types of gums available that currently or potentially have applications in noodles. These include guar and locust bean gums; alginates, including propylene glycol alginate (PGA); carrageenans; xanthan gum; gellan gum; and cellulose gum. Gums are added in low amounts (often between 0.5% and 1.5% of flour weight) and are commonly used to make noodles firmer, increase water-holding capacity in preboiled noodles, increase freeze–thaw stability and reduce ice crystal formation in frozen noodles, and reduce fat uptake in fried noodles. In choosing a gum, one needs to consider the type of gum, the viscosity of the gum, its ease of hydration, and its mesh, or particle size. Hydration and particle size are crucial factors in some noodle formulations because of the low

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water additions used. As a rule, gums should be fully hydrated prior to addition to the flour. Monoglycerides and other emulsifiers can be used to modify dough sheeting and handling characteristics or to restrict starch swelling on cooking. The benefit of the latter is to reduce surface erosion and cooking losses during boiling, but this needs to be balanced against some reduction in cooked noodle yield. More recently, a range of enzymes have been developed for use in noodles. Transglutaminase, which forms glutamyllysine cross-links in gluten, can be used to increase break strength in uncooked dried noodles as well as produce firmer boiled noodles. Lipases that produce monoglycerides and other lipid species in situ have been developed commercially and are claimed to reduce surface stickiness and increase firmness and cooking tolerance of noodles in a similar fashion to the use of monoglycerides. Oxidoreductases, such as glucose oxidase, are claimed to increase noodle firmness and to reduce cooking losses and stickiness. Surface application of amylases is also suggested for reduction of surface stickiness in packaged and precooked noodles. The patent literature and technical literature from enzyme suppliers provide rich sources of further suggestions for the use of enzyme technology in noodle applications. Proteins, such as gluten or whey protein isolates, can also be added to improve noodle firmness. Addition of egg white tends to make noodles both firmer and less elastic. Final noodle color may also be adjusted by the addition of food colorants. a-Carotene is often used as a means of adjusting udon to a creamy yellow color. In Japan, riboflavin (vitamin B2) may be used in alkaline noodles to accentuate the yellow color of ramen. In Southeast Asia, tartrazine is a common colorant used in the manufacture of intensely yellow Hokkien noodles.


• • • • • •

Review flour quality requirements for Japanese udon. Consider factors influencing noodle color and discoloration. Outline the various steps in the manufacture of steamed and fried instant noodles. Explain the effects of starch composition on noodle texture. Consider the possible effects of weather damage on noodle quality. Outline the processing steps in the manufacture of Hokkien noodles.


• •

Review research on the relative contributions of protein content and gluten composition on noodle quality. Based on traditional materials and processes, how would you develop new noodle products with altered texture, appearance, or nutritional value?

See also: Food-quality Testing: Noodles: Testing for Quality; Wheat-Based Foods: Noodles: Starch.

Further Reading Crosbie GB (1991) The relationship between starch swelling properties, paste viscosity and boiled noodle quality in wheat flours. J. Cereal Sci. 13: 145–150. Crosbie G, Miskelly D, and Dewan T (1990) Wheat quality for the Japanese flour milling and noodle industries. J. Agric. West. Aust. 31: 83–88. Crosbie GB, Ross AS, Moro T, and Chiu PC (1999) Starch and protein quality requirements of Japanese alkaline noodles (ramen). Cereal Chem. 76: 328–334. Hatcher DW and Kruger JE (1993) Distribution of polyphenoloxidase in flour mill streams of Canadian common wheat classes milled to three extraction rates. Cereal Chem. 70: 51–55. Hou GH, Otsubo S, Okusu H, and Shen L (2010) Noodle processing technology. In: Hou GH (ed.) Asian Noodles: Science, Technology, and Processing. New Jersey: John Wiley and Sons. Huang S (1996) China – the world’s largest consumer of paste products. In: Kruger JE, Matsuo RB, and Dick JW (eds.) Pasta and Noodle Technology, pp. 301–329. St. Paul, MN: American Association of Cereal Chemists. Miskelly DM (1984) Flour components affecting paste and noodle colour. J. Sci. Food Agric. 35: 463–471. Moss HJ, Miskelly DM, and Moss R (1986) The effect of alkaline conditions on the properties of wheat flour dough and Cantonese-style noodles. J. Cereal Sci. 4: 261–268. Moss R, Gore PJ, and Murray IC (1987) The influence of ingredients and processing variables on the quality and microstructure of Hokkien, Cantonese and instant noodles. Food Microstruct. 6: 63–74. Nagao S (1996) Processing technology of noodle products in Japan. In: Kruger JE, Matsuo RB, and Dick JW (eds.) Pasta and Noodle Technology, pp. 169–194. St. Paul, MN: American Association of Cereal Chemists. National Foods Research Institute, Ministry of Agriculture, Forestry and Fisheries (1985) Quality Assessment of Wheat – Sensory Tests for Noodles. Japan: MAFF. Oda M (1991) Shin Men no Hon (in Japanese),1st ed. Tokyo, Japan: Shokuhin Sangyou Shinbun Sha. Oda M, Yasuda Y, Okazaki S, Yamauchi Y, and Yokoyama Y (1980) A method of flour quality assessment for Japanese noodles. Cereal Chem. 57: 253–254. Ross AS, Quail KJ, and Crosbie GB (1997) Physicochemical properties of Australian flours influencing the texture of yellow alkaline noodles. Cereal Chem. 74: 814–820. Seib PA (2000) Reduced-amylose wheats and Asian noodles. Cereals Food World 45: 504–512. Shirao Y and Moss HJ (1978) Suitability of Australian wheat and flour for noodle production. In: Proc. 28th Aust. Cereal Chemistry Conf., Sydney. Parkville, Australia: Royal Australian Chemical Institute. Wu TP, Kuo WY, and Cheng MC (1998) Modern noodle based foods – product range and production methods. In: Blakeney AB and O’Brien L (eds.) Pacific People and Their Food, pp. 37–90. St. Paul, MN: American Association of Cereal Chemists. Zhao LF and Seib PA (2005) Alkaline-carbonate noodles from hard winter white wheat flours varying in protein, swelling power and polyphenol oxidase activity. Cereal Chem. 82: 504–516.

Relevant Websites http://www.instantramen.or.jp – The home page of instant ramen and the official website of the Japan Convenience Foods Industry Association. Information in English and Japanese on the history of instant noodles, their manufacture, the ingredients used, classification of types, and other instant ramen facts. http://www.wsu.edu – The home page of the Western Wheat Quality Laboratory of the United States Department of Agriculture – Agriculture Research Service. Information on evaluation of the biochemical and genetic bases of the milling and baking characteristics of wheat for commercial food production.

Pasta M Sissons, Tamworth Agricultural Institute, Tamworth, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Brief history of pasta. World production, trade, and consumption. Raw material quality requirements for pasta products. The manufacture of pasta. Assessment of pasta quality. Functional pasta and nutritional value. Further reading.

This article provides a brief overview largely directed at dried pasta. It covers a brief history, the raw material requirements, and the manufacture of pasta from wheat milling to pasta drying. The assessment of pasta quality, its nutritional value, and the use of nonwheat sources to manufacture pasta is also discussed. The reader is encouraged to read the Further Reading section for much more detail on the subject.

Origin of Pasta Learning Objectives

• • •

A brief overview of how durum wheat is converted into dried pasta. Some statistics on which countries produce durum wheat and consume pasta. Important measurements of pasta quality used in industry.

Introduction The word ‘pasta’ is Italian for ‘dough’ and is generally used to describe products fitting the ‘Italian’ style of extruded foods such as spaghetti or lasagne. It is distinguished from the ‘oriental’ style of sheeted and cut foods called noodles. There are over 600 pasta shapes, the most popular being spaghetti, elbow, macaroni, lasagne, and shells. Pasta can be sold fresh (as made in the home or restaurant) or refrigerated but most pasta is dried (with or without eggs), canned, or frozen. There are composite products, such as ravioli, cannelloni, lasagna, etc., in which pasta is combined with meat and vegetables in a tomato-based sauce, but the ingredients for making pasta are principally durum wheat semolina and water. The wheat preferred is durum Triticum turgidum L. subsp. turgidum conv. durum (Desf.) MacKey. Durum wheat, in contrast to common wheat T. aestivum L. which is used to make bread and oriental style noodles, is the hardest wheat. Durum milling produces a coarse particle called semolina, ideal for making pasta and couscous. The key features of durum wheat include its hardness, intense yellow color, and nutty taste. After conversion to pasta, this wheat produces products with good cooking quality and stability to endure overcooking, with unmatchable eating quality. Several countries (Italy, France, and Greece) have decreed that pasta be produced exclusively from durum wheat and that the use of other cereals not mentioned is considered a fraud. In Italy, fresh pasta can be produced from common wheat flour or blends with semolina. Other countries such as Spain, United States, Canada, and Australia traditionally consume, by choice, pasta made from only durum wheat, but do not have a specific law on the matter.


Indications are that pasta originated from China, although there is evidence of pasta use in Italy during the Etruscan civilization (several centuries BC). The earliest written record referring to pasta was in 1279 where pasta was included among the items in a will, referred to as a ‘bariscella plena da macaroni’ (basket full of macaroni). By the sixteenth century, pasta makers in Italy were organized into trade associations and this quickly spread to France and other parts of Europe. Originally the production of pasta involved a batch process of manual kneading, cutting of the dough, and extrusion by hand press, followed by sun drying. In about 1800 the first mechanical devices appeared in Italy, and by the late 1890s equipment comprising mixers, kneaders, hydraulic presses, and drying cabinets became available. It was not until 1934 that the first continuous press system (where semolina and water are converted into wet pasta in a fully automated system) was developed replacing the batch method of pasta preparation and today all presses are of the continuous type. For more details on history see http://www.professionalpasta.it.

World Production and Consumption of Pasta The Mediterranean region is the world’s largest producer of durum wheat (55–60% of world production) followed by North America (30%). Most of the durum wheat traded on the world market comes from North America. The average annual durum wheat production globally over a 20 year period (1990–2010) was estimated to be 34 million tonnes (Mt). This was produced on a harvested area of 14–16 Mha, but this represents only 6–8% of the total global wheat production (Table 1). The major importing and exporting countries amounts to an average trade of 5.4–7.8 Mt (Table 2). Annual pasta production from more than 45 countries amounts to 12.2 Mt (Figure 1). Italy is traditionally the leading producer with the highest per capita consumption (Table 3). Demand in other regions such as South and North America, Oceania, and Asia has been increasing steadily. For more information about production, imports and exports see http://www.fas.usda.gov.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00123-6

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80 WHEAT-BASED FOODS | Pasta

Table 1

Durum wheat production in the major producing countries between 1990 and 2010 (millions tonnes)

Country

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

20 Year average

EU Canada US Turkey Algeria Morocco Tunisia Syria Kazakhstan Other countries Total

7.4 4.3 3.3 5.5 0.6 1.6 0.9

11.3 4.6 2.8 5.0 1.3 2.2 1.4

9.0 3.1 2.6 4.0 1.3 0.7 1.3

7.0 3.4 1.9 4.2 1.1 0.6 1.1

8.0 4.7 2.6 4.0 0.7 2.4 0.4

7.1 4.6 2.8 3.5 1.3 0.4 0.5

8.7 4.6 3.2 3.8 1.6 2.3 1.6

7.2 4.4 2.3 4.0 0.5 0.9 0.7

5.4 29.0

5.8 34.4

6.1 28.1

6.9 26.2

8.8 31.6

2.3 7.2 29.7

2.5 8.0 36.3

2.5 7.7 30.2

9.2 6.0 3.8 4.0 1.5 1.5 1.1 2.6 1.0 6.0 36.7

7.4 4.3 2.7 3.8 0.9 0.8 0.7 2.0 3.0 6.5 32.1

9.1 5.6 3.0 3.0 0.5 0.4 0.7 2.1 2.2 6.9 33.5

6.9 3.0 2.3 3.0 1.2 1.0 0.9 3.1 2.5 7.9 31.8

8.9 3.9 2.2 3.0 1.0 1.0 0.4 2.8 2.6 8.8 34.6

8.2 4.3 2.6 3.2 1.8 1.8 1.6 3.0 2.6 7.7 36.8

11.4 5.0 2.5 3.2 2.0 2.0 1.4 2.5 2.2 8.3 40.5

8.4 5.9 2.8 3.2 1.6 0.9 1.3 2.5 2.4 0.2 37.2

9.1 3.3 1.5 3.0 1.8 2.1 1.1 2.0 2.6 9.2 35.7

8.4 3.7 2.0 2.7 1.8 0.5 1.4 1.8 3.0 9.7 35.0

10.0 5.5 2.3 3.0 0.9 1.0 1.4 1.2 2.5 11.1 38.9

8.8 5.4 3.0 3.1 2.9 1.9 1.4 1.8 2.6 10.1 41.0

8.7 3.0 2.9 2.9 2.2 1.6 0.6 1.6 1.7 9.2 34.4

8.6 4.4 2.6 3.6 1.4 1.3 1.0 2.2 2.4 7.5 34.0

Source: Adapted from The durum wheat market, January 2011 FranceAgriMer.

Table 2

Global trade by country

In thousands of tonnes Imports European Uniona US Algeria Morocco Tunisia Libya Venezuela Exports Canada European Uniona US Turkey Syria Mexico Australia Others Total trade

92/93

93/94

94/95

95/96

96/97

97/98

98/99

99/00

00/01

01/02

02/03

03/04

04/05

05/06

06/07

07/08

08/09

09/10

10/11

214 386 2381 260 12 166 288

540 437 2265 292 33 212 266

765 347 3523 55 516 289 233

1185 221 1457 337 449 147 313

863 408 1758 353 123 247 368

1490 468 2658 520 551 217 287

816 542 1935 477 225 113 315

1100 481 2018 529 248 223 369

816 381 2560 685 519 159 354

1657 589 1841 536 470 281 345

848 350 2150 483 830 103 271

2103 234 1692 629 70 104 462

1753 446 2029 619 89 129 453

1995 508 1962 665 229 33 500

1709 697 1580 739 221 180 473

1909 633 1979 724 444 28 315

1585 643 2131 563 728 105 332

2158 540 1550 550 480 25 350

2100 600 1300 700 700 100 400

2577 2642 1155

2797 1171 1270

3907 1578 1082

3307 235 914

3882 402 1051

250

400 201

232 5520

161 6828

666 5372

114 6050

3786 293 1264 645 50 353 276 95 6762

3386 674 1581 395 50 651 318 312 7367

3608 591 1251 204 345 495 583 345 7422

2912 1304 977 33 450 466 220 406 6768

3376 907 1220 61 600 357 261 298 7080

3408 1436 739 167 250 595 475 224 7294

3871 1181 1095 104 350 456 222 45 7324

4377 1209 1036 12 300 522 115 250 7821

3364 880 1400 10 158 1127 31 248 7218

3675 1100 1100 430 0 820 250 225 7600

3800 800 1400 100

100

3572 287 1427 225 431 96 116 51 6205

3516 1726 510 0

50

4412 285 1507 112 770 277 183 158 7704

6524

900 250 250 7500

WHEAT-BASED FOODS | Pasta

Forecasts at 25/11/10. a European Union of 15 from 1994/95, of 25 from 2003/04 and of 27 from 2007/08. Source: Adapted from “The durum wheat market,” January 2011 FranceAgriMer; IGC.

1130 296 233 7411

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WHEAT-BASED FOODS | Pasta Table 3 Estimate (2009) of pasta consumption among selected countries (kg head1 year1)

Asia

Australia

North Africa

EU

North America

Mexico

Middle East

Russia

South America

Figure 1 Approximate (2009) pasta production by region (% of world total). Adapted from The durum wheat market, January 2011 FranceAgriMer.

Raw Material Quality Requirements for Pasta Products Consumers of pasta are becoming more discerning in their quality requirements and less accepting of product variability. To achieve consistent quality, pasta makers must use raw materials that have the desired characteristics for processing into pasta. Currently, there are no standard measures of quality, and even for accepted parameters (as shown in the succeeding text) there is often disagreement over the methodology employed. Each parameter should not be viewed in isolation but used as part of a ‘picture of the quality’ of the semolina. The important factors are given as follows.

For Wheat Grain Appearance. Visual examination is very important to a buyer of wheat as it indicates how well the wheat will process. Most wheat-producing countries market wheat on the basis of its physical attributes. Test weight. This is the quantity of grain that packs into a fixed volume. High values (>80 kg hl1) indicate plump kernels undamaged by disease or environmental stress and this is correlated to the amount of semolina that can be produced from the wheat. Closely allied with test weight is the weight of 1000 kernels, which is also correlated with semolina yield, since large, plump kernels have more endosperm and hence, when milled, produce more semolina. Physical defects. Grains with black coloration on the tips or in the crease of the grain will create noticeable black specks in the semolina. These specks will appear in the pasta and are especially noticeable in sheeted products. The most common surface discolorations are black point, smudge (fungal infection into the crease), and mildew. Fusarium, another fungal infection, reduces semolina yield due to kernel shriveling and makes pasta redder and duller. Fusarium is also a safety concern because of associated mycotoxins such as deoxynivalenol (vomitoxin). Other fungi include ergot (Claviceps purpurea), Alternaria alternata, and Dreschlera tritici-repentis which produce dark specks in semolina. Vitreousness. Durum wheat kernels should have a translucent, vitreous appearance to ensure good semolina yield. Nonvitreous or starchy kernels tend to produce more flour than semolina upon milling because they are softer. The percentage of vitreous kernels in a sample of wheat is an important

Country

Consumption

Italy Venezuela Tunisia Greece Switzerland Sweden US Peru Chile France Germany Slovenia Hungary Argentina Portugal Canada Brazil Turkey Russia Czech Republic Austria Estonia Slovak Republic Spain Bolivia Netherlands Lithuania Poland Latvia Dominican Republic Israel Australia Panama Costa Rica Finland Mexico Columbia Romania Ecuador United Kingdom Libya Guatemala Denmark Japan Egypt Ireland El Salvador

26.0 12.0 11.7 10.4 9.7 9.0 9.0 8.3 8.3 8.1 7.7 7.5 7.4 7.2 6.7 6.5 6.4 6.0 6.0 6.0 5.6 5.3 5.0 5.0 4.8 4.4 4.4 4.2 4.1 4.0 4.0 4.0 3.8 3.7 3.2 3.0 3.0 2.7 2.6 2.5 2.0 2.0 2.0 1.7 1.2 1.0 1.0

Source: Adapted from The durum wheat market, January 2011 FranceAgriMer.

grading factor used in trading in some countries. Low vitreous percentages are often associated with a low protein content. Moisture content. The moisture content of the wheat will vary from 8% (arid areas) to 14% (temperate areas). The miller needs to know the grain moisture content in order to determine the conditioning profile before milling the wheat to produce semolina with a moisture content of 14–15%. High moisture content leads to greater microbiological growth. Weather damage. Frost exposure of wheat kernels during grain maturation prevents them from completely filling out,

WHEAT-BASED FOODS | Pasta thus reducing semolina yield. Grains that begin to germinate in the head before harvest due to damp, low-temperature conditions, have high levels of the enzyme called a-amylase. This enzyme degrades endosperm starch to produce sugars and can cause extrusion problems resulting in sticky pasta. The extent of sprouting can be measured by assaying for a-amylase or falling number. The latter estimates the thickness of a hot wheat-water slurry by measuring the time (in seconds) for a plunger to free-fall through the paste, where a short time is indicative of weather damage. Protein quantity. The grain protein percentage forms a part of the wheat payments to farmers in some countries (e.g., Australia and Canada). High-protein semolina from durum wheats of good physical condition will generally yield semolina of uniform particle size and will hydrate evenly during mixing to produce pasta that is strong and elastic. When cooked, the pasta swells, leaving minimal residue in the cooking water, and remains firm to the point of serving. Semolina with low protein will produce pasta products deficient in some or all of these characteristics. A minimum protein content for pasta manufacture is 12–15% (dry matter basis). Either the Kjeldahl (acid hydrolysis) or Dumas (combustion) methods are used to determine the nitrogen content in the grain (where % protein ¼ N 5.7).

For Semolina Ash. This is a measure of the mineral content (largely derived from the bran layers) remaining when all the organic content has been removed by combustion at very high temperatures. High extraction rates produce semolina with higher ash (0.9–1.1% dry weight basis) due to contamination by the bran and this reduces semolina’s brightness and yellowness. Protein quality. The protein type present in the grain affects processing properties. Gluten strength is a term used to describe the ability of the proteins to form a satisfactory network that promotes good cooking quality. The continuity and strength of the protein matrix formed during dough mixing and extrusion is important in determining the textural characteristics of the pasta. Compared to weak gluten of the same protein level, strong gluten wheats exhibit less sticky dough with better extrusion properties and superior cooked textural characteristics. Experienced operators can judge the quality of this gluten by its feel in the hands; others need to use various physical tests. These tests include the sodium dodecyl sulfate sedimentation test, gluten index, farinograph, mixograph, and alveograph. Strength is particularly important for instant pastas since these have thinner walls and need more strength during processing. In contrast, popular fresh pastas require a more extensible dough and weaker gluten to improve sheeting properties. Thus, durum wheat or semolina specifications for gluten strength will vary depending on the type of final product being processed. Color. A bright, yellow color in semolina ensures a good color in the pasta which consumers prefer. The main pigments in durum wheat responsible for the yellow color are the carotenoids, which include two classes: the carotenes and the xanthophylls. Lutein represents 86–94% of the total carotenoids. The yellow pigments can be partly degraded by the enzyme lipoxygenase during pasta processing. However, the high

83

temperatures during drying denature the enzyme to make it ineffective. Color is typically measured using CIE (Commission Internationale de l’Eclairage) tri-stimulus values L* (brightness), a* (redness), and b* (yellowness) with a chromameter or spectrophotometer. In addition, a brownish pigment caused by a copper protein complex causes a browning effect on the semolina which leads to a duller appearance in the pasta. Speck count. Specks in semolina are caused by any material with a color (brown or black) that contrasts with the durum endosperm particles. The black specks are easily detected in semolina. They also stand out clearly in the finished pasta. Brown specks arise from bran contamination and high levels indicate poor milling and/or high extraction rates. These are harder to see and their effect on pasta is to dull the appearance giving a gray effect to a normally bright product. It is impossible to completely eliminate these; therefore, an acceptable level is agreed upon between the miller and the pasta manufacturer. Measurement is normally done by visual inspection where the number of specks per unit area is counted. Particle-size distribution. This is important since it affects the amount and uniformity of water absorption during mixing. Coarse particles hydrate slower than fine ones, and if there are too many fine particles in the mix, this will leave the coarse particles starved of water. These manifest as white inclusions in the pasta (white specks), which is unattractive to the consumer. For this reason the particle-size range should not be too broad since mixing time is limited in continuous flow mixers. The typical particle-size distribution has been decreasing since the early 1980s (in the past 630–125 mm) with common ranges now being 350–130 mm resulting in quicker and better water absorption and consequently, shorter mixing times. Nondurum contamination. An acceptable tolerance is typically 3%. New techniques have been developed to accurately determine the levels of adulteration of durum wheat semolina or pasta with common wheat. Typical figures for quality of durum wheat and semolina are best seen in the data for the three grades of Canadian durum wheat (Table 4). The data clearly illustrate what happens to the grade as some of the characteristics deteriorate.

Water The water used should not have off-flavors or smells and needs to be monitored to ensure that it is safe and free from microbiological and chemical contaminants. It should not be too hard, but should have a low content of sodium, magnesium, and calcium ions as these would give an unpleasant flavor and color.

Other Raw Materials Spinach has been used for many years and is usually added as a powder during mixing ( 2% of the final product) to impart color. Tomato has also been used in much the same way. Egg imparts a change in color, texture, and increases protein content. It may be added in a liquid or dry state (four eggs – per kg of pasta). Vitamins are commonly used to fortify pasta in USA.

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Table 4 Quality data of the three grades of Canada Western amber durum wheat for 2000–01

Wheat Wheats of other classes (%) Test weight (kg hl1) Vitreousness (%) 1000 grain weight (g) Falling number (s) a-Amylase activity (units g1) Protein content (% at 13.5%) moisture SDS sedimentation (ml) Semolina yield (%) Semolina Ash content (%) Protein content (%) Wet gluten content (%) Dry gluten content (%) Yellow pigment (ppm) L*(brightness) a*(redness) b*(yellowness) Speck count per 50 cm2 Spaghetti dried at 70 C L* a* b* Cooking quality parameter

No. 1

No. 2

No. 3

0.69 82.0 83 41.7 410 5.5 12.9 42 67.4

0.93 82.1 68 39.5 390 10.5 12.1 34 66.3

1.31 80.5 56 38.3 280 45.5 12.0 31 65.6

0.69 12.0 30.8 10.3 7.2 87.8 2.9 30.6 29

0.67 11.2 28.5 9.7 6.9 87.6 3.0 29.3 31

0.69 11.3 28.3 9.5 7.0 87.4 2.8 28.7 42

77.1 2.6 61.8 47

76.9 2.5 61.3 37

75.6 3.3 56.1 41

Source: Adapted from website www.cgc.com.ca.

These are added as a dry mixture (1 kg t1 semolina) and typically contain vitamin B1, B2, iron, and folic acid. Other additives include: acidifiers to give a sour taste (citric and tartaric acids); acidity correctors to modify pH of a food product (citric and lactic acids); emulsifiers to produce a homogeneous mixture of one or more immiscible phases in a food product (lecithins, fatty acids); preservatives to prolong the validity period of food products, protecting them from deterioration caused by microorganisms (sorbic acid); and flavor enhancers (monosodium glutamate).

The Manufacture of Pasta An overview of the pasta making process is presented, but the reader is referred to more detailed accounts contained in the reference material.

Milling The first step toward the manufacture of pasta is the milling of durum wheat to obtain semolina. The wheat must be cleaned (by specific gravity) to remove impurities such as rocks, iron residues, straw, dust, insect fragments, and eggs. The wheat is then tempered to a moisture of 15–16% for 4 h before milling to toughen the bran. This ensures that the grain does not shatter excessively, as this would make it more difficult to separate bran from the endosperm in the purifier. Corrugated rolls are used to maximize semolina yield. Rolls with flutes aligned sharp-to-sharp further minimize flour production and

maximize shearing during grinding. A long break system is used to allow the gradual release of coarse endosperm particles with a minimum yield of lower priced flour (Figure 2). Many purification passages are required to separate endosperm particles by their size and density. Passage through the rolling mills is alternated with sifting phases carried out by the plansifters and the purifiers. The plansifters, which are made up of superposed oscillating sieves of decreasing mesh size, have the task of separating the ground material according to particle size. The product that comes out of the plansifters is then conveyed, by pneumatic transport devices, to the next phases of the milling process shown in the diagram. As the purifier sieve frame oscillates, an upward air current causes the material to stratify with the lighter bran-rich particles rising to the surface to float over the end of the sieve frame. The heavier endosperm particles fall through the sieve. After some initial purification, the stock is sent to sizing rolls to lightly grind the coarse particles releasing adhering bran and further reducing particle size. This is again purified and any material meeting the size settings is recovered as semolina and the rest goes onto the next sizing roll. A short reduction system is used to recover flour from the stock that is either too fine or too bran rich to be included in semolina. The reduction rolls have a smooth surface and are set closely together to release flour. Good purification is essential since bran or other dark particles are readily visible in the semolina. Commercial mills convert 65–75% of the wheat to semolina with 8–12% flour with the remainder being bran and embryo. For more details the reader is referred to a review of durum wheat milling.

Mixing This step involves combining semolina and water in a premixer. Water in a proportion of 18–25% of the dry raw materials is added at 35–40 C, to achieve a freshly formed dough containing an average of 30–32% moisture. After mixing (10–20 min), the mixture passes to the vacuum extruder (130 mmHg) (Figure 3).

Extrusion Dough is forced through a die in vacuum and at high pressure (80–120 kg cm2) and this gives the pasta its desired shape. The vacuum helps to minimize the oxidation of pigments, reduce enzymatic and oxidative decomposition reactions, and to decrease the likelihood of bubbles being incorporated into the dough, which can cause unsightly appearances in the final pasta. Dough temperature is kept below 50 C to avoid deterioration of the gluten matrix. Rectangular dies are used for long goods (spaghetti, etc.) and circular dies for short goods (shells, macaroni, etc.) (Figure 4). The feed holes of the die inserts are usually teflon coated to produce pasta with a smooth surface while bronze inserts are used to achieve a rougher pasta surface, which helps sauces to stick better to the cooked pasta. Teflon-coated dies achieve much higher throughput rates. After extrusion the pasta is immediately subject to a blast of hot air to minimize strands sticking together. The strands then enter the predryer.


Breaking and grading

Primary purifiers

Sizing purifiers

Sizing 1SZ

1B

1SC

Reduction 1M

2SZ

1P 2B 1P

85

1SC 1SF

2B 1SZ

1SZ

SEMO

2M

1SF

F 2SZ

F SEMO

F 2SZ

2B

3SZ

2P 3B 2P

2M

2SC

2SC 2SF

3B 1SZ

SEMO F 3SZ

F

1SZ

3M

2SF SEMO

F 3SZ

3B

4SZ

3P 4B 3P

3M

3SC

3SC 3SF

4B 2SZ

SEMO F 4SZ

F

1SZ

SH

3SF SEMO

F 4SZ

4B

4SC 5SZ

4P 5B 4P

4SC 4SF

5B 3SZ

4SZ

SEMO 4SF 5SZ

F SEMO

F 5SZ

5B

5S 6SZ

5P 6B 5P

6B

5S 6S

4SZ

SEMO 6S 1M

F

5SZ

SEMO

F 6SZ

6B 6P Duster 6P 2M

SH 1M

5B 1M

5SZ F

F Figure 2 Simplified durum wheat semolina mill flow: B ¼ break roll; P ¼ purifier; SZ ¼ sizing roll; F ¼ flour; S ¼ sizing purifier; SC ¼ coarse sizing purifier; SF ¼ fine sizing purifier; M ¼ middling roll; SEMO ¼ semolina; SH ¼ shorts. Reproduced from Kruger JE, Matsuo RB, and Dick JW (eds.) (1996) Pasta and Noodle Technology, p. 98. St. Paul, MN: American Association of Cereal Chemists International, with permission.

Sheeting by extrusion and rolls

Drying

There are a number of different sheeting die formats. The extruder with a 300 mm head rated at 350 kg h1 gives a flat sheet of 850 mm width. The sheet may be shredded to produce shortcut noodles, folded or presented as pasta Bologna. Such a machine can cut a wide range of different shapes that are stamped out while leaving an open lattice of reworkable material which is delivered to the feed stock of pasta dough.

The final step in the pasta-making process is drying. The purpose of drying is to produce a strong, stable product with a final moisture content of 12.5% with low water activity to ensure a long shelf life. Moisture is removed from the surface of the pasta by a stream of hot air creating a moisture gradient within the pasta. During the drying of pasta, it is essential that the outside surface of the pasta does not dry too quickly,

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1 3

2

4

5 6

10

7

9

8

11 12 Figure 3 Layout of a modern continuous press: (1) doser; (2) premixer; (3) mixer; (4) control gear box for mixers; (5) capsulism device; (6) vacuum mixer; (7) extrusion worm; (8) cylinder; (9) worm control gear box; (10) extrusion head; (11) die; and (12) cutter. Reproduced from Kruger JE, Matsuo RB, and Dick JW (eds.) (1996) Pasta and Noodle Technology, p. 15. St. Paul, MN: American Association of Cereal Chemists International, with permission.

Figure 4 Die for short goods (macaroni, elbows etc.). Reproduced from Kill RC and Turnbull K (eds.) (2001) Pasta and Semolina Technology, p. 155. London: Blackwell, with permission.

otherwise a large moisture difference between the inside and outside of the pasta will occur. This causes ‘checking’ or fracture lines to develop that will lead to breakage during packaging and storage. In severe cases, the strands will fall apart during cooking, destroying its appearance and therefore consumer appeal. The drier heat creates a permanent protein network around the starch granules, enhancing the strength and integrity of the pasta. This will prevent the starch granules from leaching into the cooking water and this will improve the firmness and bite of the cooked pasta. Excessive temperature during drying is undesirable, as it will result in brown discoloration of the pasta due to extreme nonenzymatic browning (Maillard reactions). The pasta moves through a drying chamber and moisture falls from 30% to 12.5% and is then stabilized to ensure that

any remaining moisture is evenly distributed. The product temperature is cooled down to that of the surrounding environment. Long goods which are draped over metal sticks move through the drier and the stick stacker. The pasta is then cut with high-speed stripper saws (Figure 5) to remove the bends (the portion of the strand which curves over the stick), trimming the product to the desired length. There are three different types of drying temperature used: normal temperature drying at 50 C for 18 h; high temperature drying at 60–75 C for 8 h; and ultrahigh temperature drying at 85–105 C for 4–5 h (Figure 6). Ultrahigh temperature drying has become common with benefits to quality such as increased pasta firmness and higher yellowness and higher capacity. The final product is then packaged into cellophane or polyethylene bags or cardboard boxes. Packaging is designed to keep the product free from contamination, protect it from damage during shipment and storage, and display the product favorably while differentiating products. The typical yield for the complete process from milling to pasta is as follows: 140 kg of durum wheat produces 95–105 kg of semolina; 100 kg of semolina produces 98.5 kg of pasta. For more details the reader is referred to a review on pasta manufacture.

Assessment of Pasta Quality In traditional pasta-consuming countries the consumer is concerned about the aroma, color, appearance, texture, flavor, and nutritional value of the pasta. The pasta after cooking should maintain its texture and not become a thick, sticky mass. Mechanical texture is typically described by a range of terms


Semolina mixer

87

Water

Extrusion chamber Die 1

Press/ spreader

Drying zone No. 2

Drying zone No. 1

Drying zone No. 3

Cooling zone

1

Stick stacker/stick magazine

Stripper/saw

100

Product moisture (%)

30

90

25

UHT 80 HT

20

70 15

60 NT

10

50

Drying temperature (°C)

Figure 5 A simple schematic of a long goods pasta line. Reproduced from Marchylo BA and Dexter JE (2001) Pasta production. In: Owens G (ed.) Cereals Processing Technology, p. 113. Cambridge, England: Woodhead Publishing, with permission.

40 0

3

6 9 Drying time (h)

12

Figure 6 Drying diagrams at ultrahigh temperature (UHT), high temperature (HT), and normal temperature (NT) for the drying of long goods. Lines show change in product moisture and hatched areas are the temperature profiles used. Reproduced from Marchylo BA and Dexter JE (2001) Pasta production. In: Owens G (ed.) Cereals Processing Technology, p. 116. Cambridge, England: Woodhead Publishing, with permission.

(firmness, elasticity, stickiness, chewiness, and bulkiness) and can be measured by a sensory panel or by objective tests. Sensory evaluation is regarded as the ultimate test of pasta cooking quality and is the reference for which other methods are compared. However, some difficulties occur related to the different background and experience of the testers. To avoid subjectivity, various testing instruments have been developed

to evaluate texture and all involve a means of deforming a sample and recording the force, time, and compression rate. Another test involves measuring by chemical methods, the total amount of organic matter released from the cooked pasta after immersion in water for a fixed time. This test is highly correlated with sensory evaluation. For more details the reader is referred to a review on methods to assess quality of durum wheat, semolina and pasta and the concept of what quality means to the participants in the durum production chain.

Pasta Products from Nonconventional Raw Materials Although durum wheat semolina is considered the best raw material for pasta making, in some countries other ingredients are used to make pasta. Flours from other cereals such as oat, barley, millet, rye, maize, rice, sorghum, hulled wheat (spelt, emmer, and einkorn), triticale, khorasan, buckwheat, amaranth, or quinoa may be used to make pasta. Alternatively, raw materials from noncereals such as legume flour/starches (of chickpea, bean, pea, soybean, cowpea, and lentil), protein concentrates, and various animal proteins are used. Pasta has been produced from some of these raw materials for centuries in some Eastern countries. In the absence of durum wheat it is necessary to change the processing conditions, because unconventional raw materials have proteins of inferior quality and are not able to form a gluten network. Methods that modify starch structure help to produce a starch–protein matrix (e.g., gelatinization/retrogradation, pregelatinization of starch, and

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extrusion cooking). Other techniques include hightemperature drying to promote a protein network, the addition of selected additives, and fortifying raw materials with proteins. Yellow color can be enhanced by adding riboflavin, sunset yellow, b-carotene, and vitamin E.

Nutritional Value of Pasta Pasta is considered a healthy food being relatively low in fat, high in carbohydrate, and having good protein content. Nutritional improvement of pasta mainly involves increasing protein and dietary fiber content and the fortification with vitamins and minerals (Table 5). High-protein flours (soybean, pea, lupin, and chickpea) can be added to increase the protein content of pasta to > 15% and improve the content of limiting amino acids, particularly lysine. To increase the content of minerals, vitamins, and dietary fiber, incorporation of buckwheat, whole wheat, artichoke, and amaranth pastas all claim health benefits. Several studies have suggested that pasta reduces the increase in blood glucose in humans following a meal compared to an equivalent load of other carbohydrates, such as white bread. This is considered beneficial in reducing the risk of developing type II diabetes. Flavored pastas allow diet conscious consumers to have flavor (basil, garlic, parsley, and red pepper) without the addition of the high caloric sauces. Nutritional improvement of pasta can be achieved by enrichment with protein and dietary fiber and fortification with vitamins and minerals. The raw materials mainly used for improving the amount of protein of vegetable origin include: soybean, pea, lupin, bean, or chickpea and of animal Table 5

Calories (kcal) Protein (g) Fat (g) Carbohydrates (g) Dietary fiber (g) Minerals Calcium (mg) Iron (mg) Phosphorus (mg) Potassium (mg) Sodium (mg) Vitamins Ascorbic acid (mg) Thiamin (mg) Riboflavin (mg) Niacin (mg) Vitamin B6 (mg) Folacin (mg) Vitamin B12 (mg) Vitamin A (iu) Cholesterol (mg)

Vitamin enriched


• •

Nutrition values for different types of pasta Plain

origin: whey proteins, casein, and powdered milk. Whole grains or meals can be successfully used to improve the dietary fiber content of durum wheat semolina pasta (9.4–11% compared to 3.0–3.7% in semolina pasta). Good sources of fiber include: amaranth, barley, buckwheat, bulgur, corn, millet, quinoa, rice, rye, oats, sorghum, teff, triticale, wheat, and wild rice. In the last few years there has been much interest in using cereal by-products in pasta formulations that are rich in substances with beneficial physiological effects (folic acid, dietary fiber, tocols, polyphenols, arabinoxylans, and lignans). These can be obtained from a range of sources such defatted germ, aleurone layer, corn gluten meal, bran from cereal milling and pearling, spent grains, distillers’ dried grains, roots, and yeast from malting, brewing, and distillation. A particular category of tailor-made foods is functional food. The term functional food was coined to describe a food that provides a specific physiological benefit other than a purely nutritional effect. There are now several ‘functional pastas’ that confer these types of benefits and the reader is referred to Marconi and Messia for more details. Pasta as a food represents an inexpensive means of improving diet quality in developed countries and helps to reduce hunger problems in developing countries. The unique combination of properties of cheapness, ease of preparation, versatility, nutritive value, and long shelf life will ensure that pasta will continue to play a role of importance as world demand for cereals increases.

Egg pasta

342 12 1.8 74 2.9

370 12.8 1.6 74 4.2

380 14 4.2 75 4.7

25 2.1 190 250 3

17.5 3.8 149 161 7

29 4.5 214 223 21

0 0.22 0.31 3.1 0.17 34 0 0 0

0 1 0.44 7.5 0.1 17.5 0 0 0

0 1 0.5 8 0.1 30 0.4 61 94

All information per 100 g product. Source: Data from Kill RC and Turnbull K (eds.) (2001) Pasta and Semolina Technology. London: Blackwell.

Why is the vitreousness of the grain important in trading of durum wheat? Which is the more desirable parcel of grain for making pasta in the table below and why?

Grain characteristic

Test weight

Vitreousness

Falling number

Protein content

Sample A Sample B Sample C Sample D

72 79 80 80

95 50 99 99

600 600 550 150

13 10 13.2 13.8

•

Is it better to purchase inferior raw material (grain) for pasta making and use very high temperature drying or use high quality wheat and low-high temperature drying?


• •

Using the further reading suggestions, find out how pasta made with other ingredients can benefit our health. Can debranning of the wheat grain overcome issues like fungal staining and black point in grain?

See also: Agronomy of Grain Growing: Wheat: Agronomy; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Carbohydrates: Starch:

WHEAT-BASED FOODS | Pasta Chemistry; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Genetics of Grains: Wheat Genetics; Grain Marketing and Grading: Wheat: Grading and Segregation; Wheat: Marketing; Processing of Grains: Starch: Modification; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Wheat: Dry Milling; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Dick JW and Matsuo RR (1988) Durum wheat and pasta products, In: (Editor: Pomeranz, Y.) 3rd (eds.). Wheat Chemistry and Technology, 3rd edn., vol. 2, pp. 507–547. St. Paul, MN: American Association of Cereal Chemists. Gruber W and Sarkar A (2012) Durum wheat milling. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 139–160. St. Paul, MN: American Association of Cereal Chemists International. Kill RC and Turnbull K (eds.) (2001) Pasta and Semolina Technology London: Blackwell (major reference work used for “Pasta” article). Kruger JE, Matsuo RB, and Dick JW (eds.) (1996) Pasta and Noodle Technology St. Paul, MN: American Association of Cereal Chemists.

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Marchylo BA and Dexter JE (2001) Pasta production. In: Owens G (ed.) Cereals Processing Technology, pp. 109–130. Cambridge: Woodhead Publishing. Marconi E and Messia MC (2012) Pasta made from non-traditional raw materials: Technological and nutritional aspects. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, pp. 201–211. St. Paul, MN: American Association of Cereal Chemists International. Pollini CM, Panto F, Nespoli A, Sissons M, and Abecassis J (2012) Manufacture of pasta products. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 161–176. St. Paul, MN: American Association of Cereal Chemists International. Sissons M, Abecassis J, Marchylo B, and Cubadda R (2012) Methods used to assess and predict quality of durum wheat, semolina and pasta. In: Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) Durum Wheat Chemistry and Technology, 2nd edn., pp. 213–234. St. Paul, MN: American Association of Cereal Chemists International. Troccoli A, Borrelli GM, De Vita P, Di Fares C, and Fonzo N (2000) Durum wheat quality: A multidisciplinary concept. J. Cereal Sci. 32: 99–113.

Relevant Websites http://www.fas.usda.gov – This website provides information about production, imports, exports for various crops across the world. The site is monitored by the US Department of Agriculture. http://www.professionalpasta.it – This is the website for the Professional Pasta Journal and contains significant amounts of information about pasta processing, history and quality. There are many free downloadable articles available.

Tortillas LW Rooney, Texas A&M University, College Station, TX, USA SO Serna-Saldivar, ITESM-Campus, Monterrey, Mexico ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Historical background. Processes used in production of wheat and corn tortillas. Chemical reactions involved in wheat and corn tortillas formation. Nixtamalized corn made into masa. Masa formed into tortilla and variety of snacks. Table tortillas, wheat or corn: soft or fried. Nutritional value and importance.

Learning Objectives

• • • •

To realize the nutritional importance of grain in the diet. To understand chemical reaction in converting grains into flatbreads. To discuss the difference in wheat and maize flours in production of products. To understand chemical functionality of maize and wheat in food products.

Introduction A tortilla is a flat, round, unfermented bread produced from wheat (Triticum aestivum L.) flour or lime (CaO)-cooked maize (corn – Zea mays L.). Sorghum (Sorghum bicolor L.) is used alone or in mixtures with maize for tortillas in parts of Central America. Processing and characteristics of wheat flour and maize tortillas differ considerably. Both types of tortillas originated in Mexico, where they are considered the national bread and are consumed with other food such as beans, meat, and vegetables. Tortillas, traditionally, are homemade, prepared on a daily basis, and consumed fresh. The technology for maize tortilla production was developed by early Mesoamerican civilizations. Tortillas and ‘masa’ products constitute the staple food for most people in Mexico and Central America. The annual per capita intake in 2001 was 85 kg in Mexico (up to 120 kg in some areas), 6 kg in the United States, and 0.3 kg in Europe. The technology for wheat flour tortillas was developed during the sixteenth century in northern Mexico. Tortillas are increasing in popularity throughout the world. Global sales in 2012 were estimated at $12 billion for tortillas and 10 billion for maize ‘tacos,’ ‘tostadas,’ tortilla chips, and other corn snacks. Mexico accounts for 42% of the world’s production of tortillas, the United States 36%, Central America 9%, and other countries 13%. Maize comprises 98% of the tortillas consumed in Mexico and Central America. In Mexico, 40% of the maize is used for tortillas. The tortilla industry is the fourth largest industry (0.90% of GDP) in Mexico. Wheat flour tortillas are more prevalent than maize tortillas throughout the

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rest of the world. Processing plants for tortillas and alkalinecooked corn snacks are located in almost every continent. Around the world, a large number of different types of flatbreads are made from blends of many cereals. Consumption is increasing because they use local grains and they are used as wraps for a wide variety of foods. The convenience and widespread production of wraps and related products will continue because they are finger foods as well as sophisticated foods. They are widely consumed because they are convenient and can be rapidly reheated and consumed. It is common to take tortillas for lunch, breakfast, and dinner with other items. They vary from upscale products to simply wrapping of meat or vegetables in tacos or many other items.

Wheat Flour Tortillas All wheat tortillas contain flour, water, fat, and salt. Tortillas prepared using these ingredients are leavened by steam generated during baking, have dark toast points, and have areas that are translucent (i.e., not opaque). These tortillas are common in northern Mexico and are 1 mm thick, up to 60 cm in diameter, and contain up to 20% fat (on a weight of flour basis). Most flour tortillas outside of Mexico and Central America contain baking powder for leavening to ‘improve’ flavor, opacity, texture (softness and rollability), and shelf life (1 week to 6 months). Tortillas with good appearance, uniform whiteness or opacity, large diameter, and long shelf stability are prepared using chemical leavening agents, emulsifiers, reducing agents, antifungal agents, acidulants, gums or hydrocolloids, sugar, maltodextrins, proteins, and nonactive yeast. Flour tortillas in Mexico and Central America are usually consumed fresh on the day of production, just as ‘chapatis,’ an unleavened, flatbread in India and southern Asia, is prepared from wheat flour, water, salt, and fat (optional). The formula and processing of flour tortillas in the United States have changed to yield a longer shelf life tortilla, due to the cultural practices of infrequent shopping, refrigerated storage of foods, and preparation and consumption over several weeks. Hot-press, die-cut, and hand-stretch methods are used to form wheat dough into thin disks in the preparation of flour tortillas by the food industry. These methods have replaced the traditional processes of preparing tortilla disks by hand. Each requires different flour specifications, dough preparation, and baking conditions, resulting in distinct tortilla characteristics. Hot-press tortillas (Figure 1) are consumed as gourmet table tortillas, ‘fajitas,’ and soft tacos and are prepared in restaurants for immediate consumption. Hot-press tortillas have a smooth surface, a tender bite, and some elasticity; resist moisture absorption from fillings; and have longer shelf stability than other flour tortillas. Hot-press tortillas are the most popular and account for >90% of the retail market.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00124-8

WHEAT-BASED FOODS | Tortillas

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Figure 1 Processing of flour tortillas using the hot-press method. Note: (a), tortilla dough (D) in bowl with dough hook (H); (b), dough balls; (c), resting chamber for dough and dough balls; (d), dough ball moving on Teflon belt into the hot-press (P) behind inset area (I; arrow indicates press); (e), pressed disk moving on Teflon belt immediately after hot-pressing (arrows indicate direction of movement); (f), tortilla at the end of the first tier of a three-tier oven; (g), tortillas on wire conveyer; and (h), stack of flour tortillas.

Die-cut tortillas are mainly used in ‘burritos,’ frozen Mexican foods, and fried products, for example, taco salad bowls, taco shells, ‘chimichangas,’ and ‘bun˜uelos.’ Die-cut tortillas often have dusting flour on the surface, lower moisture content, and a pasty mouthfeel and are less resistant to cracking during storage. The die-cut method greatly reduces the cost of production of tortillas. Hand-stretch tortillas are consumed as table tortillas and burritos and used to prepare certain fried products. Hand-stretch tortillas have dusting flour on the surface, irregular shapes, moderate elasticity, and a firmer bite than hot-press tortillas. They are more costly to produce and are decreasing in popularity. Tortilla dough is mixed to incorporate micro-ingredients, fat, and water into the flour and form a pliable, extensible dough (Figure 1(a)). The optimum dough temperature should be

32–34 C after mixing and gluten development. Dough properties are primarily modified by flour quality; levels of reducing agent, emulsifier, fat, and water; and dough temperature. The dough is rested 0–20 min (Figure 1(c)) before being divided and rounded into dough balls (Figure 1(b)) for the hot-press and hand-stretch procedures. The dough balls are rested in a warm, moist environment for 2–20 min (Figure 1(c)) to relax the gluten network. Rested dough balls form larger diameter tortillas with more opacity and longer shelf stability. Tortilla dimensions (thickness and diameter), opacity, and shelf stability are affected by the hot-press dough ball pressure, temperature, and duration of hot-pressing (Figure 1(d) and 1(e)). In the hand-stretch procedure, the dough balls pass through two pairs of rollers, set perpendicular to each other, prior to stretching by hand on a hot griddle and baking. The dough for hand-stretch and die-cut

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tortillas is dusted with flour to prevent adhesion to equipment. The dough, in die-cut operations, is pumped and shaped into a sheet that is further thinned by a series of rollers and cross rollers on a moving belt. The thin sheet of dough (0.5–2.5 mm) is cut by a circular die, which forms the tortilla shape. The scrap dough is returned to the dough pump and reprocessed. The formed tortilla disks, regardless of the process, are baked (190–260 C for 18–50 s) in gas-fired ovens (Figure 1(f)) that usually have three tiers. Oven conditions vary depending upon tortilla thickness, type of conveyor (slat or wire), and method of preparation. Puffing of the tortilla occurs near the end of baking and is common in hot-press and hand-stretch tortillas. Tortillas are typically ‘cooled’ to <32 C on conveyors (Figure 1(g)) for 2–5 min prior to packaging in plastic bags. Moisture and heat are lost during this operation. Improper cooling increases not only the microbiological problems but also the ‘stickiness’ of the tortillas. Fresh tortillas (Figure 1(h)) have a soft and pliable texture, which changes to a firmer and less extensible texture during storage. Improvements that make it possible to retain the freshness of hot-press tortillas throughout the storage period are naturally preferred. About 80% of flour tortillas are prepared using the hot-press method even though the die-cut method is more efficient. Hotpress flour tortillas are the preferred ‘bread’ in the space program because of their versatility, functionality, long shelf stability, and lack of crumbs. Consumers prefer hot-press tortillas because they retain their freshness during storage. Nontraditional fillings for breakfast, lunch, dinner, and desserts increase their versatility and convenience. Wheat flour requirements are determined by the desired tortilla characteristics, the formula, processing conditions, and equipment. Wheat flour is usually hard wheat flour with a protein content ranging from 9.5% to 12.5%. Flours for hot-press and hand-stretch tortillas generally contain less protein and gluten strength than flours for die-cut tortillas. Tortillas that are made with flours with poor gluten strength remain pliant for only a couple of days. Hot-press tortillas, which are made with good-quality flours, are generally the ones with smaller diameter and less opacity and tend to remain more pliant during storage. Flour ideal for hot-press tortillas has intermediate gluten strength and levels of protein quality with small amounts of damaged starch. Hater (45–55% of flour weight) is a reaction medium for gluten formation and chemical reactions (leavening) during mixing. Low levels (10–80 ppm) of reducing agents, such as sodium metabisulfite or cysteine, reduce dough mixing time and increase the extensibility of dough during hot-pressing, which yields larger diameter tortillas. Salt (1–2%) is added for taste and to strengthen the gluten complex. Baking powder (0.05–2.5%) causes tortillas to have a less dense, spongy structure, that is, increased whiteness or opacity and greater specific volume. The high dough temperatures (25–40 C) cause premature leavening reactions during mixing and less leavening is available during baking. Leavening acids and bicarbonates that dissolve more slowly and react to form CO2 during latter stages of baking improve tortillas opacity and thickness. Various natural and modified cellulose gums are added at 0.1–0.5% levels to improve dough machinability and decrease the stickiness of baked tortillas. Solid or liquid fats (3–20% of flour weight) are added to improve dough properties by weakening gluten strength. Fats

also contribute to softer and more flexible tortillas by limiting amylose retrogradation during storage. Dough-strengthening emulsifiers, such as sodium stearoyl-2-lactylate, improve dough cohesiveness and integrity of the outside perimeter of hot-press tortillas. Emulsifiers, such as glycerol monostearate, limit amylose retrogradation and improve tortilla softness. Low-fat (<3 g fat per serving) and fat-free (<0.5 g fat per serving) flour tortillas have been developed; these have proved to be extremely popular with sales exceeding $40 million in the United States in 2002. Antimicrobial agents (propionates, sorbates, or mixtures thereof) limit fungal growth and extend shelf life and are used at 0.2–0.6% of flour weight. Optimum antifungal activity occurs at less than pH 5.5. Tortilla pH is lowered by acidulants (citric, fumaric, and phosphoric acids). Soluble acids, however, cause the early release of CO2; hence, granular fumaric acid or fat-encapsulated acids are commonly used to delay their leavening reactions.

Lime-Cooked Maize Products Three basic types of products are industrially produced from lime-cooked maize: table or soft tortillas, corn chips, and tortilla chips. Corn and tortilla chips are primarily produced and consumed in developed countries, where they have an important share of the salted snack-food market. Sales of corn and tortilla chips in the United States in 2002 totaled $12 billion. Modern production of tortilla chips and corn chips has evolved into specialized processes. They are quite different from the original tostadas made by frying stale, maize table tortillas.

Table Tortillas from Maize Tortillas are produced using traditional and industrial processes. Maize (Figure 2(a)), lime, and water are three basic ingredients needed for the production of masa. In the traditional process, maize is lime-cooked in clay pots over a fire, followed by steeping for 8–16 h. The cooking liquor, called ‘nejayote,’ is discarded; then, the ‘nixtamal’ is hand-washed and ground into a fine masa with a stone grinder. The masa is hand-molded or pressed into disks, which are baked on a hot griddle or ‘comal.’ The tortilla disks are baked on each side to seal the surfaces and form steam that causes the tortilla to puff. Traditionally, tortillas are produced on a daily basis. Tortillas vary in thickness from different localities in Central America and Mexico. Fresh maize tortillas have an outstanding flavor and texture, which firms rapidly into an unacceptable product. In Mexico, the bulk of tortillas is consumed fresh daily and leftover tortillas are fried into tostadas and ‘totopos.’ Tacos are soft tortillas wrapped around meat, sauces, beans, and other fruits and vegetables in Mexico. The tacos in the United States, however, are deep-fried tortillas in a U shape, filled with meat, sauces, etc. Other masa-based products include ‘tamales,’ ‘atoles,’ and ‘pozol,’ which is a fermented masa. A popular Mexican soup, ‘posole,’ is made from large, soft, nixtamalized maize kernels. The industrial tortilla process begins when the maize is lime-cooked in agitated open baths, vertical cookers, or steam kettles (Figure 2(b)). The grain is generally mixed with three


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Figure 2 Processing of maize into tortillas and tortilla chips. Note: (a), kernels of maize illuminated from behind, the light areas indicate the hard, vitreous endosperm (H), while the darker areas indicate the soft, floury endosperm (S), and germ (G); (b), maize entering cooking water containing calcium oxide; (c), cooked maize or nixtamal with adhering partially hydrolyzed pericarp (HP) before the washing step; (d), separated grinding stones with nixtamal (center, N) and masa (outside edge, M) in the grooves (arrow); (e), stone-ground masa; (f), sheeting rollers forming disks of masa and a wire mesh belt transferring the disk to the oven (arrow indicates direction of movement); (g), tortilla oven with a tortilla (T) on the third tier leaving the oven; (h), tortillas cooling on a wire conveyer; (i), stack of maize tortillas.

parts water and 1% lime, based on grain weight, and cooked for 15–45 min at temperatures ranging from 85 to 100 C. The nixtamal is then steeped for 8–16 h in the hot lime solution. After steeping, the cooked maize or nixtamal (Figure 2(c)) is pumped with the steep liquor or dropped by gravity to washers. The cooking liquor is drained and the nixtamal washed with pressurized water. Most of the pericarp and lime is removed during this step. The washed, cooled nixtamal is ground using two radially carved, volcanic or synthetic (aluminum oxide) stones (Figure 2(d)) or stainless-steel plates. One stone is stationary and the other rotates at 500–700 rpm. Masa particle size is directly related to the gap and pressure between the stones and the size, depth, and pattern of the grooves. During grinding, the nixtamal is disrupted into an array of

particles from starch granules (10 mm) to endosperm pieces (2 mm). Some starch granules are gelatinized and dispersed by the friction of the stones to produce the glue-like material that causes cohesiveness in the masa. Only a small amount of gelatinization of the starch occurs during cooking and steeping. Grinding produces most of the gelatinized starch that holds the particles of masa together during subsequent pumping and sheeting into unbaked tortillas. The ground particles (Figure 2(e)) are dropped into a masa feeder with augers (masa hog), which move the masa to above the sheeter head. The two rollers of the sheeter compress the masa into a thin layer, which is die-cut into standard size disks, strips, triangles, etc., depending upon the products desired. These formed pieces of masa (Figure 2(f)) are transferred by

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mesh belts into a three-tier, gas-fired oven (Figure 2(g)) to bake on lime-coated, metal slats or mesh belts at 280–302 C for 30–45 s. The tortillas are allowed to cool on open conveyors, counted, stacked, and packaged (Figure 2(g) and 2(h)). Tortillas are formulated with antifungal compounds or by raising the pH to improve their shelf life when merchandized for 3–90 days. Antifungal compounds, sorbates and propionates, along with acidulants are incorporated during grinding or masa kneading. The pH must be reduced to enable the preservatives to function properly. Alternatively, tortillas are preserved by the lime that is not removed during washing. High pH is an effective preservative, if the tortilla pH is > 9.8. Tortilla pieces that are fried immediately do not need preservatives; however, those fried after ambient or refrigerated storage are acidified and preserved. About 40% of the maize tortillas consumed in Mexico are prepared using dry masa flour. More than 2 million tonnes (Mt) of dry masa flour for table tortillas is produced annually in Mexico. These flours are transformed into 3.4 Mt of table tortillas. Dry masa flour is produced by cooking corn with alkali, coarsely grinding the nixtamal with a modified hammermill, drying, and then sifting. The masa is dried in large tunnels, or drying towers, in which warm air flows countercurrently over the ground particles. The particles too large for masa flour are ground by hammer milling and sifted, and the various particle sizes are blended in the correct proportions to produce various dry masa flours for specific products with different particle size, color, pH, and water uptake. The quality and consistency of these products have improved over the years. The particle size of masa for table tortillas is finer because the tortillas hopefully will puff during baking. In the case of fried snacks, the coarser particles in dry masa flour allow water vapor to escape during frying, which improves chip texture. High-quality tortillas and chips are prepared from dry masa flours. A blend of dry masa and fresh masa is sometimes used in many tortillerias. Dry masa flours for table tortillas are usually enriched with thiamin, riboflavin, niacin, folic acid, iron, and zinc. The use of dry masa flour depends upon the processor. However, many new processors use dry masa flour because of its convenience, even though it costs two to three times as much as raw maize. Dry masa flour does not require experienced personnel, space, or equipment to cook, steep, wash, and grind maize, or the expense of effluent disposal. The dry masa flour is shelf-stable if it contains < 10% moisture and only requires water and mixing to form masa. Dry masa flours are mixed with 1.0–1.2 parts water for 3–5 min to produce suitable dough. Dry masa flours usually produce masa with less adhesiveness and higher viscosity, requiring more force on the rollers to form a thin sheet. Properties of rehydrated masa can be changed by modifying cooking and frying procedures or by adding 0.1–0.7% carboxymethyl cellulose. Cellulose makes table tortillas more chewy and improves tortilla flexibility during storage. Vital wheat gluten when added at 0.5–2% improves retention of tortilla flexibility during storage. Other hydrocolloids also increase masa softness but usually not tortilla flexibility. Emulsifiers used at < 0.5% do not usually improve table tortilla quality. Specific amylases soften masa and tortillas and improve processing and product qualities. Combinations of these additives are common in tortillas.

Fried/Snack Products Frying has expanded the market for masa-based foods because the final products have excellent organoleptic properties and long shelf lives. Two popular snacks from masa are corn chips and corn tortilla chips. Corn chips are produced by directly frying extruded or sheeted masa pieces, while masa for tortilla chips is formed into triangles, strips, or circles, baked, equilibrated, and fried. Tortilla chips have less oil, a firmer texture, and a stronger maize flavor than corn chips. Nixtamal for these snack foods is cooked and not steeped as much as the nixtamal for table tortillas. The nixtamal for fried snack foods is ground into coarse masa because the larger particles in the sheeted pieces allow steam to escape through many small pores that develop during baking and frying. This prevents the formation of serious quality defects, such as oily appearance, pillowing, or blistering. Corn chips are prepared by extruding masa through a die, which is cut by rotating knives before frying or by sheeting and cutting into strips. Corn chips have a more friable texture than corn tortilla chips and contain more oil than tortilla chips (Table 1). Products from white maize are fried at higher temperatures and shorter times than those from yellow maize. Beta-carotenes in yellow maize degrade into beta-ionones, which are bitter and off-colored. Frying temperatures and times range from 165 to 195 C for 20–90 s, depending upon maize properties. A blend of yellow and white maize is normally used for corn chips. The moisture content of the masa or tortilla is related to the oil absorption during frying; specifically, the higher the moisture, the higher the oil absorption. As moisture leaves the cooked product during frying, oil is absorbed into and onto the structure of the fried food. The appearance and texture of chips are also affected by masa particle size distribution, tortilla baking equilibration. structure, and maize color in the piece to be fried. Corn and tortilla chips are salted and flavored immediately after frying. The hot chips are conveyed into an inclined rotating cylinder where the flavorings are applied. The most popular flavorings include nacho cheese, hot and spicy, barbecue, French onion, lemon and salt, and jalapenõ. Corn and tortilla chips are packaged in moisture-proof aluminized bags, flushed with nitrogen to protect the product physically and to limit oxidative rancidity. Specialty products include blue chips and reduced-fat snacks. Blue maize tortilla chips, served in specialty restaurants, are available as organic and regular products. Blue maize has a pigmented aleurone that imparts an intense blue color. It has high levels of flavanoids and other phenolics that may have nutraceutical properties. Reduced-fat snacks can be achieved by processing or by using a fat replacer. Baked, low-fat tortilla chips are prepared using air impingement, infrared, and/or microwave ovens. Olestra, a nonabsorbed fat, is utilized to fry tortilla chips and reduce fat content and calories. Sales of low-fat and olestrafried chips have decreased apparently because consumers prefer the taste and texture of full-fat products and/or dislike the perceived gastric side effects. The trends toward organic and natural health products are continuing with a wide variety of organic chips available.

WHEAT-BASED FOODS | Tortillas Table 1

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Nutrient profilea (per 100 g of edible portion) of flour tortillas, lime-cooked maize products, and table bread

Nutrient

Unit

Wheat flour tortilla

Table maize tortilla

Corn tortilla chips

Corn chips

White bread

Water Protein Lipid (fat) Ash Carbohydrate, calc Fiber, dietary Calcium, Ca Iron, Fe Magnesium, Mg Phosphorus, P Potassium, K Sodium, Na Zinc, Zn Copper, Cu Manganese, Mn Selenium, Se Folate, food Niacin Pantothenic acid Riboflavin Thiamin Vitamin A Vitamin B6

g g g g g g mg mg mg mg mg mg mg mg mg mcg mcg mg mg mg mg IU mg

26.80 0.90 8.70 0.58 7.10 0.58 1.80 0.15 55.60 3.3 125 7.5 3.30 0.12 26 1.3 124 7.9 131 7.3 478 24.0 0.71 0.08 0.267 0.14 0.462 0.011 23.4 2.4 12 1.1 3.572 0.135 0.582 0.061 0.293 0.069 0.531 0.025 0 0.050 0.01

44.10 0.66 5.70 0.13 2.50 0.24 1.20 0.06 46.60 5.2 175 7.1 1.40 0.07 65 1.5 314 26.2 154 7.2 161 15.0 0.94 0.08 0.154 0.015 0.402 0.011 5.5 1.1 15 1.3 1.498 0.096 0.194 0.014 0.073 0.008 0.112 0.015 0 0.219 0.03

1.80 0.11 7.00 0.13 26.20 0.49 2.20 0.14 62.90 6.5 154 6.0 1.52 0.09 88 1.4 205 5.4 197 6.5 528 21.2 1.53 0.09 0.120 0.009 0.382 0.010 6.7 0.8 10 1.279 0.051 0.788 0.026 0.184 0.024 0.075 0.008 196 23 0.286 0.01

1.00 0.05 6.60 0.09 33.40 0.28 2.20 0.05 56.90 4.9 127 2.8 1.32 0.03 76 1.2 185 3.6 142 2.8 630 12.9 1.26 0.05 0.161 0.017 0.381 0.014 6.7 0.8 20 1.183 0.057 0.394 0.144 0.010 0.027 0.005 94 11 0.24 0.03

36.70 0.10 8.20 0.05 3.60 0.08 1.90 0.02 49.50 2.3 108 2.6 3.03 0.03 24 0.4 94 1.7 119 2.0 538 8.6 0.62 0.02 0.126 0.003 0.383 0.008 28.2 1.1 34 3.969 0.034 0.390 0.015 0.341 0.006 0.472 0.005 0 0.06 0.01

a

US Department of Agriculture, Agricultural Research Service, 2002. USDA National Nutrient Database for Standard Reference, Release 15. Nutrient Data Laboratory Webpage, http:// www.nal.usda.gov/fnic/foodcomp.

Chemistry of Nixtamalization (Alkaline Cooking) Cooking and steeping maize in lime solution (pH > 11) softens the pericarp, hydrates the endosperm, partially solubilizes proteins and cell walls, facilitates starch swelling, and gelatinizes only a small amount of starch. Significant dry matter is lost in the steep solution especially soluble proteins, sugars, and other components. The breakdown of the cell walls of the pericarp forms gums, which are useful in table tortillas. However, for snacks, the partially solubilized pericarp is removed by washing, as these pieces cause processing problems. The cooking and steeping times vary depending upon the desired products, equipment used, and the maize quality. The quality of maize for alkaline cooking is critically important to produce high-quality products. Whole, sound, mature kernels of maize with a high proportion of hard to soft endosperm (Figure 2(a)) yield more masa and tortillas after nixtamalization. Uniform flat kernels without cracks and broken kernels and intermediate to hard endosperm are preferred. Pericarp removal is affected by genetics and by the environmental conditions during maturation of the maize. The maize must be cooked uniformly to provide adequate hydration and partial solubilization so that grinding produces a nonsticky, cohesive masa that can be formed into a thin disk and baked into a desirable tortilla or fried into chips or tortilla chips. During cooking and steeping, the pericarp is converted into gums and insoluble materials. These materials are washed from nixtamal before grinding, especially for fried products; however, nixtamal for maize table tortillas is not washed as much, since the gum binds water and improves the texture of tortillas. In tortilla chips, the partially hydrolyzed pericarp causes discoloration and darkening of tortillas. However,

extra washing increases dry matter losses and sewage charges since the dry matter losses range from 5% to 10% or higher of the original maize depending on the maize quality and the processing parameters. Table tortillas are excellent when fresh but become rigid after 4–8 h. The firming or staling of tortillas is affected by pH, extent of cooking, moisture content, and storage conditions. Alkaline tortillas retain softness and flexibility longer than regular tortillas because starch retrogradation is inhibited by the negative charges on the starch chains at pH > 9. Many tortillas are acidified (pH 5.0–5.5) to activate the preservatives, but starch retrogradation and staling are not inhibited at this pH. Individually or in combination, the addition of carboxymethyl cellulose, vital wheat gluten, amylases, and waxy maize (100% amylopectin) produces tortillas that retain flexibility longer than normal tortillas. Softness and flexibility of tortillas containing soy flour, barley flour, or beta-glucans from barley flour were retained longer than normal tortillas. The use of emulsifiers, neutral gums, shortening, and modified starches was less effective in limiting firming of tortillas. Quality of end products depends on the nature of manufacturing practices and of raw materials. Specific types of maize hybrids are approved for use in alkaline cooking by processors. Yellow maize and white maize, or mixtures thereof, are commercially manufactured into alkaline products. Food maize suppliers arrange for producers to grow, harvest, store, and deliver clean maize to processors. Premiums are paid to producers to secure maize that is acceptable in terms of kernel hardness, size, cracks and brokens, pericarp removal, and levels of aflatoxins and fumonisins. The ideal grain should be clean, sound, large, uniform, bright-colored, and free of cracks and

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broken kernels and have high test weight with intermediate-tohard endosperm. In addition, the kernels should have a rounded crown and a shallow, unwrinkled dent, and the pericarp should be easily removed during lime-cooking. Broken and cracked kernels cause increased dry matter losses and poor-quality (sticky) masa. The environment affects corn quality significantly. Anything that affects the kernel during maturation affects the processing properties of the grain.


• • •

What are the effects of incorporation other grains into the commercial processes? What effect does the variety of maize and wheat have on final food product? How important is water content and preservatives in the shelf life of wheat and corn tortillas?

Nutritional Value The nutrient composition of some lime-cooked maize foods is compared with white pan bread and wheat tortillas in Table 1. Tortillas, especially wheat flour tortillas, are commonly used as a substitute for pan bread by many people. Flour tortillas are higher in gross and digestible energy because their formula contains more shortening (5–15% based on flour weight). Whole meal flour tortillas have higher amounts of fiber, protein, and ash than white flour tortillas. Maize tortillas are the main source of energy, protein, calcium, and other important nutrients in Mexico and Central American diets. Lime-cooking considerably increases calcium and the bioavailability of niacin and significantly decreases the amount of aflatoxins and fumonisins in contaminated maize. The caloric densities of corn chips and tortilla chips are significantly higher than table tortillas because of the oil absorbed during frying and their low postprocessing moisture contents. Tortillas and snacks produced from enriched dry masa flour contain higher levels of B vitamins, Fe, and Zn than counterparts produced from fresh masa. In Mexico, dry masa flours are enriched by government regulation; some of these flours are optionally fortified with 5% soy flour. Human nutritional studies have demonstrated that fortified and enriched flours significantly upgrade the nutritional status of low-income people, especially children. Quality protein maize (QPM), which contains 50% more lysine and tryptophan, is processed into tortillas in some areas of Mexico. The tortillas have improved protein quality but limited production of QPM restricts its application.

Conclusion Tortilla use around the world has increased rapidly and is expected to continue driven by their wide variety of fillings and use of blends of many different flours to produce excellent products. Fried tortilla snacks and other foods are increasing rapidly around the world. White flour tortillas account for 43%, corn tortilla 42%, and tortilla chips, taco shells, and tostadas 15% of the US market. Pressed white flour tortillas are the most popular process (85%) and white corn is preferred to yellow corn.


• • • •

Research more historical information. Corn tortillas for celiac diet. Incorporation of various grains for health food market. Whole grain tortillas for school lunch programs.

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; The Cereal Grains: Maize: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: Wheat: Dry Milling; Wheat-Based Foods: Flatbreads of the World.

Further Reading Almeida Dominguez HD, Cepeda M, and Rooney LW (1996) Properties of commercial nixtamalized corn flours. Cereal Foods World 41: 624–630. Betran J, Bockholt AJ, and Rooney LW (2001) Blue corn. In: Hallauer A (ed.) Specialty Corns, 2nd edn., pp. 293–301. New York: CRC Press. Bressani R (1990) Chemistry, technology, and nutritive value of maize tortillas. Food Reviews International 62(2): 225–264. Dally V and Navarro L (1999) Flour tortillas: A growing sector in the US food industry. Cereal Foods World 44: 457–459. McDonough CM, Gomez MH, Rooney LW, and Serna-Saldivar SO (2001) Alkalinecooked corn products. In: Lusas E and Rooney LW (eds.) Snack Foods Processing, pp. 73–113. New York: CRC Press. McDonough CM, Seetharaman K, Waniska RD, and Rooney LW (1996) Microstructural changes documented by traditional and environmental scanning electron microscopy in wheat flour tortillas during baking. Journal of Food Science 61(5): 995–999. Rooney LW and Serna-Saldivar SO (2003) Food use of whole corn and dry milled fractions. In: White P and Johnson L (eds.) Corn (Zea mays L.): Chemistry and Technology St. Paul, MN: American Association of Cereal Chemists. Rooney LW and Suhendro EL (1999) Perspectives on nixtamalization (alkaline cooking) of maize for tortillas and snacks. Cereal Foods World 44: 466–470. Rooney LW and Suhendro EL (2001) Food quality of corn. In: Lusas E and Rooney LW (eds.) Snack Foods Processing, pp. 39–71. New York: CRC Press. Serna-Saldivar SO, Gomez MH, and Rooney LW (2001) Food uses of regular and specialty corns and their dry-milled fractions. In: Hallauer A (ed.) Specialty Corns, 2nd edn., pp. 303–337. Boca Ratone, FL: CRC Press. Serna-Saldivar SO and Rooney LW (1994) Quality protein maize processing and perspectives for industrial utilization. In: Larkins B and Mertz ET (eds.) Proceedings of the International Symposium on Quality Protein Maize, pp. 89–120. Sete Lagoas, MG, Brazil: EMBRAPA/CNPMS. Serna-Saldivar SO, Rooney LW, and Waniska RD (1988) Wheat flour tortilla production. Cereal Foods World 23: 855–864. Snack Food Association (2003) Snack Food Association state of the industry report. Snack World, June, pp. 20–45. Waniska RD (1999) Perspectives on flour tortillas. Cereal Foods World 44: 471–473. Waniska RD (2001) Evaluation methods and quality control for snacks. In: Lusas E and Rooney LW (eds.) Snack Foods Processing, pp. 607–629. Lancaster, PA: Technomic Publishing Co.

Relevant Websites http://www.nal.usda.gov – US Department of Agriculture, Agricultural Research Service (2002) website. The Nutrient Data Laboratory Webpage provides information on the USDA National Nutrient Database for Standard Reference, Release 15.

Non-wheat Foods

Contents Maize: Foods from Maize Rice: Chinese Food Uses Sorghum: Utilization Soybean: Soy-Based Fermented Foods Soybean: Soymilk, Tofu, and Okara

Maize: Foods from Maize SO Serna-Saldivar, Centro de Biotecnologıá FEMSA, Escuela de Ingenierıá y Ciencias, Monterrey, Mexico ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Maize is the most important cereal grain in the world in terms of production. Currently, the maize is used as animal feed, for the production of an array of indigenous and industrialized human foods and for bioethanol production. Maize is a staple food for many people and cultures around the globe especially in low socioeconomic groups inhabiting Latin America, Africa, and Asia. Maize may be consumed green (corn on the cob) or prepared from meal in many indigenous or traditional foods prepared daily. Maize has great genetic variability. The most important types are white, yellow, sweet, popcorn, blue, waxy, and quality protein. These types have unique properties in terms of nutritional value, starch functionality, and specialty foods. Maize is widely processed into grits, meals, and flours using dry milling procedures. The refined products are used by the breakfast cereal, snack, baking, and brewing industries. Maize is the main source of starch worldwide. The refined starch is mainly transformed into an array of syrups and sweeteners such as dextrins, maltose, glucose, and high fructose. These sweeteners strongly compete with crystallized sugar for many food applications. Maize is lime-cooked into nixtamal, which is the base for the production of table tortillas and corn and tortilla chips. Tortillas are considered as the most important food for Mexicans and other Latin Americans, whereas corn chips and tortilla chips as the second most important snacks in the world.

Learning Objectives

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The reader will learn the main food uses of maize and the general milling processes to obtain an array of grits, meals,


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flours, starch, fresh masa, and dry masa flour that are further processed into traditional foods, breakfast cereals, extruded snacks, syrups/sweeteners, tortillas, and nixtamalized snacks such as corn and tortilla chips. The reader will learn the main food uses and distinctive characteristics of different sorts of maize genotypes such as white, yellow, blue or pigmented, quality protein, popcorn, waxy, and Cuzco.

Introduction Maize (Zea mays L.) is the leading grain in the world with recent annual production that exceeds 1 billion tonnes and is the staple for large groups of people in Latin America, Africa, North America, and Asia. In contrast to rice and wheat, maize is mainly utilized for animal feeding and first-generation bioethanol, although direct and industrial food uses are increasing. According to the FAO (2013, http://apps.fao.org/) 54, 19, 13.8, and 14% were used for feed, food manufacture, direct food, and bioethanol, respectively. Maize is a crop with a remarkable genetic variability, and both GMO and regular types are planted throughout the planet. Many specialty genotypes are available, the main ones being popcorn, waxy, high-amylose or amylomaize, sweet, blue, Cuzco, and quality protein maizes (QPMs). Maize foods are characterized by their unique distinctive flavor not duplicated by any other cereal. The starchy grain is used for the production of numerous indigenous foods: maize meal, flour, grits, starches, sweeteners, cooking oil, breads, tortillas, breakfast foods, snacks, industrial alcohol, and alcoholic beverages. Processed maize products are manufactured from raw materials obtained from three major milling industries: dry milling, wet milling, and nixtamalization (Figure 1). The dry milling industry produces an array of refined products widely used by the baking, brewing, snack, and breakfast cereal industries. Most of the starch

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NON-WHEAT FOODS | Maize: Foods from Maize

Maize

Storage

Dry milling

Flaking grits Brewing grits Other grits Corn meal/flour Germ Bran

Wet milling

Nixtamalization

Starch Germ Gluten Bran Steep water liquor

Masa Dry masa flour

Food industries Breakfast cereals, snacks, baking, brewing, distilled spirits, oil, sweeteners, table tortillas, corn, and tortilla chips Figure 1 Flowchart of the postharvest management and processing of maize for human foods.

obtained from the wet milling industry is bioenzymatically converted into maltodextrin, maltose, glucose, and highfructose syrups. The alkaline cooking or nixtamalization process of whole maize has become important in the United States and other parts of the world due to the increase in popularity of Mexican foods.

Food Uses of Specialty Maize Specialty maize types have been selected due to their unique properties, the most important being popcorn, sweet, high amylose, waxy, blue, and quality protein (Table 1). Popcorn has been a favorite traditional snack worldwide for more than a century, whereas sweet maize is one of the most popular canned or frozen vegetables in the United States and Canada. Large quantities of waxy maize that contains more than 95% amylopectin are channeled to the wet milling industry with the aim of obtaining starch that has unique functionality (e.g., low retrogradation). QPM was developed from the mutant opaque-2 maize discovered in 1963 and contains almost twice as much lysine and tryptophan compared to regular maize. Thus, QPM-based foods can upgrade the nutritional status of infants, who consume cereals daily in marginal areas around the world. A generation of new biofortified QPM genotypes with high protein quality and levels of carotenoids, iron, and zinc is being researched. Blue maize has a pigmented aleurone that imparts an intense blue color and a unique flavor. It has been traditionally dry-milled for the production of flours or meals and also used for tortillas and chips. Blue maize tortilla chips are often served in specialty restaurants and are also sold as organic food. It has high levels of anthocyanins and other phenolics that may have nutraceutical properties.

Indigenous Maize Foods Regular and specialty maizes are widely consumed in numerous forms in Latin America, Asia, Africa, and the Balkans (Table 2). White maize is generally preferred for foods because it favors the final color of processed foods, but yellow maize is preferred in Brazil, China, Argentina, and some other areas. Most traditional foods are produced from grain that is milled into a meal or flour. The use of fresh or immature maize on the cob is practiced worldwide. Maize cobs with or without husks are boiled in water or cooked over a fire and then flavored with salt, cream, butter, margarine, and other sauces. In most areas, regular maize is used as green maize. In Latin America, maize is processed into tortillas, ‘arepas,’ ‘couscous,’ ‘polenta,’ porridges, and various meals and gruels (Table 2). The traditional method to process maize into tortillas was developed by ancient Mesoamericans. In the traditional process, maize is lime-cooked in clay pots over a fire, followed by overnight steeping. The cooking liquor, called nejayote, is discarded, and then, the nixtamal is hand-washed and ground into a masa with a stone grinder named metate. Masa is hand-molded or pressed into disks, which are baked on a hot griddle or comal. Industrially produced tortillas are mainly used as wraps to prepare tacos that hold different types of fillings (beans, various meats, cheeses, and vegetables). Tacos are the symbol of the Mexican cuisine and are known and consumed worldwide. The Mexicans also inherited many other nixtamalized-derived foods such as tamales, atole, pinole, pozol, and others (Table 2). Arepas, the national maize bread of Venezuela and Colombia, are traditionally produced from white grits or meal that is moistened, cooked in water, and ground to a dough. The dough is hand-shaped into flat disks that are browned on each side and baked in an oven. Arepas are cut in half and

NON-WHEAT FOODS | Maize: Foods from Maize Table 1

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Characteristics and food uses of specialty maizes

Specialty maize

Food uses

Popcorn

Special kind of flint maize (Figure 2). Hybrids or varieties with high proportions of translucent or vitreous endosperm give higher expansion rates. Expansion volume is the most critical quality factor for popcorn. Most commercial popcorn has a 30- to 40-fold expansion. Popping occurs at 177 C (350 F), which is equivalent to a steam pressure of 2.5 t cm 2 (135 psi) inside the kernel. The water in the kernel is superheated and at the moment of popping converts to steam, which provides the driving force for expanding the thermoplastic endosperm after the kernel ruptures. The pericarp and outer layers of the kernel participate directly in the popping action by serving as a pressure vessel enclosing the endosperm. Popped maize with a spherical shape is called mushroom or ball type and is preferred in the confection industry. The butterfly-type popcorn has a higher expansion, lower apparent bulk density, and better mouth feel; it is preferred for onpremises popping These types have improved processing efficiency in dry milling and snack food processing plants. These maizes have high test weight, high density, thousand kernel weight, and a pericarp that is easily removed during processing. In addition, the kernels should come preferably from white cobs. Kernels from pink- or red-colored cobs are high in phenols and yield undesirable off-colors in processed foods QPM has the opaque 2 gene that is combined with modifier genes that significantly improve the hardness and agronomic performance of the crop. The QPM material has been incorporated into high-yielding hybrids in Brazil, Mexico, and other countries, while open pollinated varieties are grown in Africa and Central America. Harder QPM maizes are suited for dry milling and alkaline cooking, while soft hybrids for use in wet milling to produce sweeteners, starches, and alcohol would be desirable since the coproducts would be more valuable Blue corn is a floury or soft endosperm type that generally grows in long ears (8–12 rows). The aleurone layer contains the anthocyanins that impart the blue appearance. Blue corn is especially prized as a ceremonial maize by the North American Indian tribes and is currently being used to produce organic flours and foods such as tortillas and chips. The blue corn contains higher levels of flavonoids that are excellent source of antioxidants for nutraceutical foods Sweet corns have recessive genes (sugary 1 or su1 and sugary 2 or su2) that cause an alteration in the endosperm that results in higher levels of soluble sugars and reduced levels of starch in the kernel. Sweet corn hybrids have been developed specifically to produce maize with desirable color, sweetness, and tenderness Special maize varieties are grown and shucked immediately after pollination when the ears are 1–2 in long. These small ears are used as pickles and other tasty snacks in salad bars. Most of the baby corn used is produced in Thailand and exported to Europe and North America Waxy maize is named for the somewhat waxy appearance of the kernel. Waxy maize starch is composed entirely of amylopectin. It is utilized mainly by the wet milling industry. Waxy starch has a higher hot viscosity and produces softer, more stable, and clearer gels due to its lower retrogradation. It also has a higher freeze–thaw stability Also named amylomaize. Expresses high quantities of linear amylose because of the recessive ae gene located in chromosome 5. Most genotypes contain amylose from 37% to 65%. Although it is not commercially planted, the amylomaize has potential for the paper, textile, corrugating, and adhesive industries. The high-amylose starch produces rigid opaque gels with potential for the confectionery industry and as a thickener in various puddings and processed foods. It can be used as a binding agent for dehydrated potatoes or as a coating to reduce oil absorption of deep fat-fried potatoes. One of the best potential uses of it is for the production of biodegradable packaging materials that resemble polystyrene foam used for ‘plastic peanuts’ The Cuzco maize comes from eight-rowed ears that produce the largest known kernels. Cuzco corn grows at high altitudes and produces white kernels with soft endosperm texture and bland flavor. Cuzco corn is mainly used to manufacture Corn Nuts™ and cacahuacintle kernels for hominy and pozole production Yellow genotypes that have been selected by CIMMYT to contain high levels of carotenoids (vit. A), Fe, and Zn. These genotypes are being tested in Central Africa in order to diminish vitamin A deficiencies, anemia, and malnutrition

Food-grade yellow and white

Quality protein

Blue corn

Sweet corn

Baby corn

Waxy

High-amylose

Cuzco/cacahuacintle

Biofortified

stuffed with meat, cheese, butter, jellies, and other fillings. Stuffed arepas are also fried to produce ‘hallaquitas,’ ‘empanadas,’ and other foods. ‘Chicha’ is a prehispanic sacred fermented beverage prepared in Peru and Bolivia in which ground maize is first treated with amylases from germinated maize or saliva and then naturally fermented. Other alcoholic beverages such as ‘tesguïno’ are consumed in Mexico and ‘pito,’ ‘talla,’ and other related opaque beers in Africa (Table 2). In Africa and Asia, maize is generally dry-milled into grits, meals, and flours for the production of flat breads, unfermented and fermented porridges, steamed foods (couscous), and alcoholic or nonalcoholic beverages. Many of the traditional

foods are produced from fermented or germinated maize, which increases the vitamin content, mineral bioavailability, and protein quality. ‘To,’ ‘pap,’ ‘nshima,’ and ‘sadza’ are popular porridges consumed in Africa (Table 2). The early settlers of North America cooked maize in lye or wood ashes to produce hominy. The alkali effectively removes the pericarp, enhances the palatability and nutritional value of the kernels (Table 3), and transforms the hard raw kernels into a soft, chewable product, which could be stored relatively safely. In Mexico, lime-cooked hominy is commonly used for the preparation of ‘pozole’ and ‘menudo’; both are soups in which the hominy is mixed with condiments and shredded meats (Table 2).

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Table 2

Major uses of maize for preparation of indigenous foods

Food

Description of product and process

Tortillas and tlayudas

Maize is lime-cooked for 5–30 min and steeped overnight. The cooking liquor is discarded and the resulting ‘nixtamal’ rubbed between the hands to remove the bran. The washed nixtamal is hand-ground with a cylindrical stone and a ‘metate’ or flat stone slab to produce a dough or masa. Pieces of masa are patted into thin round disks that are baked for 30–60 s onto a hot clay circular hot griddle or ‘comal’ to produce tortillas. Tlayudas are a sort of tortillas that have larger diameter and lower moisture due to toasting and a different flavor because the masa is salted Maize meal alone or blended with wheat flour is processed into dough with water and/or milk and baked. Chemical leavening agents and flavorings (i.e., sugar and salt) are used in some formulations to obtain better texture, volume, and flavor. Many types of corn bread exist around the world National bread of Venezuela and Colombia. Moistened maize is dehulled and partially degermed in a wooden mortar using a pestle. The meal is cooked in boiling water and stone-ground into masa. Arepas are manually formed into flat disks and baked for 2 min on each side on a clay or metal griddle. Arepas are stuffed with meats, cheese, butter, jellies, or other fillings Staple foods of Africa. Maize meal is cooked in water until completely gelatinized. The porridge is placed in a gourd, cooled for 1 h, and eaten with the fingers and a sauce. Acid (tamarind and lemon), fermentation, or alkali (wood ashes) is added to cooking water to produce acid and alkali porridges. Granulation of the flour, composition, type of sauce, and final consistency vary among countries and tribes Dish widely consumed in Brazil. Canjica is degermed maize kernels cooked with sugar and milk and generally consumed as a dessert or breakfast cereal Prehispanic dishes in which one of the main ingredients is whole nixtamal generally prepared from cacahuacintle (white and large kernels with floury endosperm) maize. It is a spicy soup that generally contains peppers, shredded meats, and other spices. The lime or lye cooked maize is mixed with beef stomach, peppers, spices, and onions to produce a soup called menudo or with shredded pork meat to yield pozole Traditional dish of American Indians of the southwest prepared from a thin batter of blue maize meal, ash, and water. The batter is cooked on a hot flat stone to form a parchment-like product. Piki can be crumbled, salted, roasted, and eaten like chips Prehispanic breakfast gruels or porridges made out of masa that is diluted in water, sweetened with sugar, and flavored with cinnamon, vanilla, orange leaves, and others. Champurrado is produced from cocoa beans, brown sugar, and cinnamon Brazilian porridge. Corn grits are mashed or immature kernels are cooked in water to produce porridges similar to atole Maize kernels are toasted on a hot griddle until attaining a brown-golden color, dry-milled into a meal, and blended with cinnamon, anise, brown sugar, and other flavorings. The resulting shelf-stable mix is diluted with water or milk boiled for 4 min and consumed as a breakfast gruel. Tejate is made by toasting maize meal and blending the resulting product with cocoa (Theobroma cacao), mamey (Mammea americana), and cocoa flour. The blend is used to prepare a beverage Prehispanic beverage made out of fermented masa. Fresh masa is wrapped in banana leaves and allowed to naturally ferment for 3–5 days. The fermented masa is diluted in water and consumed as beverage. It is considered the major source of nutrients and the ‘job beverage’ for some indigenous groups in south Mexico Prehispanic dish widely consumed during festivities. Consists of masa surrounding a filling that has been placed in a wrapper and steamed. In tropical areas, tamales are wrapped in banana leaves; hydrated maize husks are used in the rest of Mexico. The coarse masa is blended with lard, salt, chicken or beef broth, and baking powder. Tamales are steamed in a large pot equipped with a rack in the bottom so as to avoid their contact with the boiling water. The pot should be tightly covered with the lid to prevent vapor loss. Cooking times vary from 1 to 3 h or until the masa does not stick to the wrapper. The most common tamales contain spicy beans, shredded chicken, beef, pork, fish, seafood, cheese, or sweets (fruit pastes, jelly, nuts, and raisins). Tamales or TV dinners are available in the frozen shelves of the major food markets This is the most popular way of consuming table tortillas. Soft tortillas are filled with refried beans, shredded meat or poultry, eggs, guacamole, and vegetables. Quesadillas are tacos filled with cheese, while sincronizadas contain a combination of cheese and ham. Tacos are generally rolled or simply folded Tortillas are filled with shredded meat, rolled into small cylinders, and fried until crisp. Guacamole, sour cream, and/or cheeses with vegetables are usually spread on top of the flautas Masa for table tortillas is blended with coloring agents (mild red pepper extract, paprika, or artificial), molded, and baked into a red tortilla. Tortillas are fried for few seconds and immediately filled with cheese/raw onions. Some people also called enchiladas the red-colored tortillas filled with shredded chicken or other fillings (mashed potato and various types of meats). Shredded fresh cheese and sauces are spread on top of the filled tortillas prior to serving Masa is mixed with salt, lard, and tallow. After blending, the masa is formed into balls, which are allowed to rest for 30 min. Balls are hand-pressed or patted into thick disks, which are baked on a hot griddle. These tortillas are usually furnished with beans/cheese and different fillings. Gorditas, another type of tortillas, are the ones produced by mixing masa with shredded cheese, ground peppers, and refried beans Thick tortillas are filled with refried beans, shredded meats, or poultry with the filling placed underneath the tortilla skin. The product can also be fried. Baked or fried panuchos are generally served with sliced tomato and cooked or cured onions

Corn bread

Arepas

To, sadza, pap, and nshima

Canjica Pozole or menudo

Piki

Atole and champurrado

Mingau Pinole and tejate

Pozol

Tamales

Tacos

Flautas Enchiladas

Tortillas de manteca or gorditas

Panuchos or pupusas

(Continued)

NON-WHEAT FOODS | Maize: Foods from Maize Table 2

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(Continued)

Food

Description of product and process

Sopes, chalupas, or garnachas

Masa, sometimes blended with lard, is formed into a flat thick disk 1 cm thick and 10 cm diameter and, while baking, a 1 cm high peripheral wall is formed by pinching. The sope is filled with a combination of refried beans, cheese, shredded meats, poultry, and vegetables (lettuce, tomato, radishes, and onions) Masa is flattened into thick disks and refried beans placed in the middle of the formed cake. Both sides are folded to cover the beans and to impart the typical tlacoyo configuration (oval-elongated shape). Tlacoyos are baked on both sides onto a hot griddle and usually served with green sauce and dairy cream. Blue maize tlacoyos are very popular in central and south Mexico Masa, sometimes mixed with baking powder, is formed into small balls and pressed into thin disks. The preformed masa is filled with shredded meats, beans, cheeses, and folded. The rim of the folded (half-moon) tortilla is sealed by pressing with a fork and then fried Tostadas are tortillas fried in the flat form and widely used as the base to hold different fillings. For their preparation, nixtamal and red-paprika peppers or annatto is stone-ground into a coarse masa. Today, coloring agents are also used. The red- or orange-colored masa is baked into a tortilla and then fried into a tostada. Tostadas are the base for the preparation of wide array of meals. It is very common to consume tostadas with refried beans, cheese, shredded meats, and vegetables such as lettuce, tomato, onions, peppers, and radish. Taco shells are the American version of tostadas with the only difference that they are usually fried bent (U form) and rarely colored. Regular and low-fat tostadas and taco shells are available in grocery stores in Mexico and the United States Mayan dish. Maize masa is blended with salt and lard and sometimes ground peppers. The masa is formed into thick disks that are baked on a hot griddle previously greased with lard Mayan dish. Black beans are smashed, fried, and sun-dried. Then, they are mixed with masa to form a thick black tortilla disk. The disks are fried and served with picante sauce Mayan dish. Small masa balls are cooked with smashed beans and the resulting blend served with ground squash seeds Mayan dish. Annatto seeds are fried in lard until they release their color. The resulting colored lard is mixed with masa and salt. Alongside, ground meat is cooked with finely ground onion, tomato, and sweet peppers. Masa is hand-formed into an oval shape and the filling placed in the center. The masa is folded, wrapped in banana leaves, and steam-cooked Maize masa is blended with salt and wheat flour. Handmade tortilla disks are fried and then spread on top lettuce or cabbage, shredded poultry, cured onions, and sliced tomato One of the most popular Mexican soups. Contains up to 15 different ingredients in which the main one is fried tortilla strips. Garlic, onion, and tomato are ground into a sauce and diluted and simmered in chicken broth. Salt, peppers, and other seasonings are added. Few minutes before serving, the soup is reheated, and fried tortilla strips, cheese cubes, and avocado are incorporated onto the top of the mix Prehispanic dish very popular in all Mexico. The nahuatl word derives from chilli (peppers) and quilitl (edible) herbs. Chilaquiles are prepared by first producing a sauce based on tomato, onion, peppers, garlic, and salt. Then stale or leftover tortillas cut into pieces and fried until crisp and incorporated into the sauce. Shredded chicken, cream, and cheese are usually placed on top of the dish Prehispanic sacred beverage prepared in Peru and Bolivia. Salivated or germinated maize flour and water are heated to 75 C, thoroughly mixed for 1 h, and cooled. Upon sedimentation, the upper layer called ‘upi’ is placed in another pot and simmered for several hours until it is caramelized. This product called ‘misqui kheta’ is allowed to cool, combined with more upi, and fermented for 48–144 h to produce a clear, yellowish effervescent beverage. Chicha morada is made from blue corn that is cooked in water with sugar for several hours. The mixture is filtered and the purple liquor is blended with fruit juice (i.e., pineapple) and consumed as a beverage Alcoholic beverage produced in Mexico. Maize is soaked in water for several days, drained, germinated, ground, and steeped in water until the mixture turns yellow (8 h). Then, the liquid is filtered; ground leaves, beans, and legumes are added. Fermentation produces an opaque, sour beer with 3–4% alcohol Nigerian alcoholic beverage. Maize is soaked in water, drained, and held in a moist chamber for 5 days’ germination. The maize malt is mashed for 6–10 h, cooled, and sieved. The filtrate sours due to microbial fermentation. Then, it is concentrated and inoculated with starter from a previous batch and allowed to ferment overnight. Pito is a light brown, slightly bitter, sweet–sour alcoholic beverage Ethiopian alcoholic beverage. A slurry of toasted, ground, and cooked maize flour is mixed with flavorings, pieces of freshly baked flat bread, and wheat or barley malt. After a day, the mixture is diluted with water, fermented for 5–7 days, and filtered. Talla has a smoky flavor and a tan to dark brown color Fermented porridges widely consumed in Africa. Maize kernels are steeped and fermented for several days. Steeped grain is wet-milled, slurried with water, and sieved. The slurry is allowed to ferment longer. The fermented sediment is separated and boiled in water to yield ogi porridge that is consumed warm or cooled to form a gel or pudding Popular dish in Italy and South America. Refined maize grits are cooked in water until gelatinized; mixed with tomato sauce, cheese, meat, etc.; and baked Ground maize is kneaded with water until the flour particles agglomerate when forced through a coarse sieve. Then, the particles are steamed. At intervals, the couscous is removed, received, and returned to the steamer. The cooked product is consumed with a sauce. In Africa, ground baobab leaves, peanut butter, okra, etc., are mixed with the couscous during the final stage of steaming when it is to be dried and used as a convenient food

Tlacoyos

Empanadas

Tostadas and taco shells

Pimes Pemoles Joroch Tobi holoch

Salbutes Tortilla soup

Chilaquiles

Chicha morada

Tesguïno

Pito

Talla

Ogi and ugali

Polenta Couscous

102 Table 3

NON-WHEAT FOODS | Maize: Foods from Maize Nutritional value of different types of maize-based foods (100 g) Minerals

Food

Moisture (g)

Miscellaneous products Corn on the cob with 72.1 butter Yellow sweet corn, 76.7 boiled and drained Cooked corn grits 85.3 White hominy, 82.5 canned Corn pudding 72.3 High-fructose corn 24.0 syrup 63.9 Bourbon whiskey, 86 proof Flat and leavened breads Tortillas 44.1 Maize bread 39.1 Corn muffins 32.6 Hush puppies 29.0 Arepas 50.8 Breakfast cereals Corn flakes 3.0 Corn Chex 2.2 Corn Pops 3.0 Kix 3.2 Snack foods Extruded cones 2.0 Extruded puffs, 1.5 cheese flavored Corn Nuts, plain 1.3 Corn chips, plain 1.0 Tortilla chips 1.8 Light tortilla chips, 1.3 nacho flavor Popcorn, oil-popped 2.8 Popcorn, caramel2.8 coated

Energy (kcal)

Protein (g)

Fat (g)

CHO (g)

106

3.1

2.4

21.9

80

2.8

0.4

19.6

60 72

1.4 1.5

0.2 0.9

131 281

4.4 0

250

Dietary fiber (g)

B vitamins

Ca (mg)

P (mg)

Fe (mg)

B1 (mg)

B2 (mg)

B6 (mg)

Niacin (mg)

3

74

0.6

0.17

0.07

0.22

1.49

2.4

4

57

0.4

0.08

0.07

0.13

1.30

13.0 14.2

0.2 2.5

0 10

12 35

0.6 0.6

0.10 0.00

0.06 0.01

0.02 0.01

0.81 0.30

5.0 0

17.0 76.0

3.0 0

39 0

90 0

0.5 0

0.07 0

0.15 0.02

0.13 0

1.03 0

0

0

0.1

0

0

5

0

0

0

0

0.1

222 266 305 337 219

5.7 6.7 5.9 7.7 5.4

2.5 7.1 8.4 13.5 5.4

46.6 43.5 50.9 46.0 37.1

5.2 1.9 3.4 2.8 2.6

175 249 74 278 89

314 169 284 189 117

1.4 2.5 2.8 3.0 1.0

0.11 0.29 0.27 0.35 0.07

0.07 0.29 0.33 0.33 0.04

0.22 0.11 0.08 0.10 0.11

1.50 2.25 2.04 2.78 0.88

361 373 380 389

7.0 7.0 3.7 9.0

0.8 0.9 0.7 2.3

86.0 86.0 90.0 82.6

3.5 2.0 0.8 1.4

7 333 17 125

50 72 31 138

30 30 6.2 28.6

1.30 1.25 1.20 1.3

1.53 1.42 1.40 1.5

1.80 1.7 1.60 1.8

17.9 16.7 16.1 17.6

510 554

5.8 7.6

26.9 34.4

62.9 53.8

1.1 1.1

3 58

44 108

2.5 2.4

0.32 0.26

0.24 0.35

0.04 0.13

1.41 3.23

439 539 501 445

8.5 6.6 7.0 8.7

14.1 33.4 26.2 15.2

73.3 56.9 62.9 71.6

6.9 4.9 6.5 4.8

9 127 154 159

275 185 205 318

1.7 1.3 1.5 1.6

0.04 0.03 0.08 0.22

0.13 0.14 0.18 0.27

0.23 0.24 0.29 0.23

1.69 1.18 1.28 0.41

500 431

9.0 3.8

28.1 12.8

57.2 79.1

10.0 5.2

10 43

250 83

2.8 1.7

0.13 0.07

0.14 0.07

0.21 0.03

1.55 2.20

Source: From USDA (2013). http://ndb.nal.usda.gov

Industrial Processing of Maize for Foods Most of the maize is first industrially processed by wet milling, dry milling, or nixtamalization (Figure 2). Dry milling manufactures refined endosperm fractions of varying particle size (grits, meal, and flour), germ for oil, and sometimes dietary fiber ingredients. Starch and refined dry-milled products are mainly used for the production of snacks, breakfast cereals, syrups, lager beer, and ethanol. Wet milling produces relatively pure starch, protein, fiber, and germ. Nixtamalization produces dry masa flours, tortillas, and related snack foods that are increasing rapidly in popularity in the United States and other countries around the globe.

Food Uses of Starch More than 90% of the commercial starch is from maize due to the low cost of the grain, high starch content, and high value of

the coproducts. The refined starch is channeled to various food industries to be used as additive, or it is enzymatically hydrolyzed into various types of syrups. In addition, the coproducts are highly valued by the feed and vegetable oil industries. The bran is generally used to feed ruminants, although some is finely ground to produce high-dietary-fiber foods. The germ is demanded by oil mills to produce the added-value refined oil and defatted protein meal. Maize oil is widely used as cooking oil because of its stability and high levels of polyunsaturated fatty acids.

Corn Syrups Approximately 11 million tonnes of dry weight of corn syrups were manufactured in the United States in year 2011. About 70% of this production was from high-fructose corn syrups (HFCSs). The production and utilization of maize syrups have increased during the past decades because the soft drink


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mainly used as thickening agents. Regular cornstarch produces haze formation, whereas utilization of waxy starch, more stable syrups. A high-dextrin syrup adjusted to contain 15% solids and pH 5–6 is used as substrate for CGTase for cyclodextrin production. These cyclic oligosaccharides are composed of six, seven, or eight glucose units linked by a-(1–4) linkages to form a-, b-, or g-cyclodextrins, respectively. Cyclodextrins have several useful properties. They have good chemical stability to bases and weak acids and good thermal stability because they melt at temperatures of 270 C. Their hygroscopicity is low, and they are resistant to amylolytic enzymes. In addition, they are used to enhance chemical stability and reduce volatility of complexed molecules and mask unpleasant odors and flavors.

Maltose syrups Figure 2 Popcorn is a special type of maize that possesses a flinty endosperm and a thick pericarp. These grain features allow to expand when exposed to heat. Popcorn has been historically one of the most popular snacks.

industries prefer to use sweeteners instead of crystallized cane or beet sugar. Maize sweeteners are preferred over sucrose because they readily dissolve in water and are easier to incorporate into soft drinks, are easily flavored, and impart a fruit flavor to beverages and foods. The HFCSs containing 90% fructose impart 1.7 times more sweetness than sucrose at equivalent concentrations. The various types of syrups are manufactured from acid hydrolysis or enzymatic conversion or a combination of these two processes (Figures 3 and 4). The industrial production of amylolytic enzymes allowed the production of better-quality low-DE (dextrose equivalents) syrups and the production of glucose syrups with high DE or sweetness. The industry evolved with the commercial availability of heat-stable a-amylase and amyloglucosidase that could transform practically all the starch into glucose. The greatest technological developments were the utilization of immobilized glucose isomerase and the continuous separation of glucose and fructose by moving bed chromatography. With these developments, the industry is capable of producing with high efficiency the popular HFCSs.

Low-DE syrups (maltodextrins) The low-DE or maltodextrin-rich syrups are industrially produced by acid hydrolysis or by a-amylase conversion. These syrups are the easiest to manufacture and are the first step for the production of maltose, glucose, and HFCS. The acid hydrolysis is performed in 35–40% starch suspensions using a 0.02–0.2 N hydrochloric solution in a pressurized reactor. A higher acid concentration or longer process time can yield undesirable compounds such as methylfurfural, formic acid, and/or off-flavors and off-colors. That is the reason why the use of this technology is now limited. The most popular way to convert starch into maltodextrins is via the utilization of aamylases or liquefying enzymes. Today, heat-stable a-amylases are used because they require shorter incubation. Their optimum activity is achieved at pH of 6.5 and temperatures of 90–100 C. These syrups with 10–20 DE are very viscous, rich in maltodextrins, and low in sweetness; therefore, they are

Regular and high-maltose corn syrups are manufactured starting with a low-DE syrup that is treated with b-amylase or a combination of pullulanase and b-amylase (Figure 3). bAmylase works best at pH 5 and 55 C. The utilization of only b-amylase yields a syrup with 50–55% maltose, while the use of debranching pullulanase and b-amylase syrups results in syrups with 80% maltose. Regular and highmaltose syrups are widely used as flavorings for breakfast cereals, beverages, ice creams, and other food products.

Glucose syrups For the production of 90 DE glucose syrups, low-DE syrups are treated with amyloglucosidase or saccharifying enzyme at pH 4.6–5.2 and a temperature of 55–60 C (Figure 3). The syrup is refined and clarified through columns of activated carbon and ionic resins with the aim of removing minerals, pigments, soluble protein, fat, and enzyme-resistant starch. Glucose syrups are utilized as sweeteners for soft drinks, in baking formulations, and as a source of fermentable carbohydrates for light beer, alcohol production, and yeast-leavened baking goods. Crystallized dextrose can be produced by concentrating the syrup to 75% solids, adding glucose, and gradually cooling to drop the temperature to 20–30 C for several days.

High-fructose corn syrups HFCSs are manufactured starting from a 90 DE glucose syrup that is further treated with immobilized glucose isomerase (Figure 3). The refined glucose syrup is deaerated and treated with magnesium sulfate so as to assure oxygen removal and the sequestration of calcium that lowers enzyme activity and halflife. There are three major types of HFCSs: 42, 55, and 90. The 55 and 90 HFCSs are produced from the 42 HFCS. The 42 HFCS is industrially produced by passing glucose syrup through a reactor with glucose isomerase. The optimum operating conditions are pH 7.5–8.2 and 55–60 C. The substrate flow rate is controlled so as to convert 42–45% of the glucose into fructose. The 90 HFCS is obtained after separating fructose and glucose in a moving bed chromatography system that produces two syrups with 90% of each type of sugar (Figure 3). If desired, the glucose-rich syrup can be converted into 42 and 90 HFCS as explained before. The 55 HFCS is manufactured by mixing 42 and 90 HFCSs. The 90 HFCS has 1.7 times more sweetness than the other HFCSs and crystallized sugar. HFCSs are used as substitutes of table sugar

Starch (30–35% solids)

Liquefaction Heat stable a -amylase addition pH 6.5–6.8 and temp. 95–100 ⬚C

Acid hydrolysis Presure cooking, 0.02–0.2 N HCl sol.

Dextrinized syrup (20 DE)

b -Amylase addition pH 4.6–5.2 and temp. 55–60 ⬚C

Maltose syrup

Saccharification Amyloglucosidase addition pH 4.6–5.2 and temp. 55–60 ⬚C

Glucose syrup (90 DE)

Pullulanase and b -amylase addition pH 4.6–5.2 and temp. 55–60 ⬚C

High maltose syrup

Refining, de-aeration, and magnesium sulfate addition

Immobilized glucose isomerase reactor pH 7.5–8.2 and temp. 55–60 ⬚C

42 HFCS

Glucose syrup (90 DE)

Moving bed chromatography

55 HFCS

90 HFCS Figure 3 Flowchart of industrial processes to produce maize syrups.

Figure 4 Maize starch is the main raw material for the production of dextrins, maltose, glucose, and high-fructose syrups.

Figure 5 Dry-milled fractions of maize. Clockwise: maize kernels, bran, flour, brewing grits, flaking grits, and germ.

NON-WHEAT FOODS | Maize: Foods from Maize especially in soft drinks. The main advantage of using HFCS is that they readily dissolve in water, are easily flavored, and impart a sweet fruit flavor to beverages and foods.

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Maize grits are low in fiber and contain < 1% oil. Grits of various granulations are extensively utilized by the snack, breakfast cereal, and brewing industries. In the United States, maize grits are consumed as a side dish for breakfast (Table 3).

The grits are cooked in boiling water for 10–25 min and then seasoned with butter or margarine. Instant or precooked maize grits that require only 5 min cooking are popular. In southern states, white maize grits are preferred over the yellow counterpart because they possess a bland and sweeter flavor. Traditionally, the brewing industry has been the largest user of maize grits. Grits are used as a source of inexpensive fermentable carbohydrates. Brewer grits have a size range that facilitates filtration of the wort. The most desirable grits contain < 1% oil, ash, and fiber and have optimum particle size distribution and high malt extracts. Whole ground maize and refined grits are used to produce alcoholic beverages. Straight bourbon whiskey is obtained from distillation of a fermented mash containing at least 51% maize in the United States. The distillate is aged for 2–10 years in wooden barrels, blended, and bottled. Maize alone or in combination with other cereals and ingredients is often used in ready-to-eat breakfast foods. Grits, meals, or flours are cooked to gelatinize the starch, denature the protein, and produce a dough, which can be processed into flakes, shreds, granules, puffs, or collets. The nutritional value of several maize-based breakfast cereals is summarized in Table 3. Desirable flavor, aroma, and texture are usually obtained by controlled toasting. Currently, most new breakfast cereals are prepared by continuous extrusion and puffing, which has economic advantages. Maize flour or meal is moisturized, combined with starches, flavorings, and coloring agents to prepare a wide array of products. Extruded gun-puffed cereals are still one of the most popular types of ready-to-eat breakfast cereals. The puffing gun is charged with equilibrated collets, sealed, and heated to increase the pressure to 150–200 psi. The pressure is suddenly released and the material explodes from the gun. The degree of puffing varies according to temperature and pressure. The expansion varies from 10 to 16 times. Products that require less expansion are generally oven puffed. Puffing is achieved by exposing the product to radiant heat on a belt or by tumbling it in a rotating cylinder. This process produces a three- to fourfold expansion. The oven puffing operation requires the correct balance of moisture content and oven temperature to achieve the desired puffing.

Figure 6 Traditional cornflakes are manufactured from flaking grits obtained from dry milling.

Figure 7 Extruded corn puffs manufactured from refined grits are one of the most popular snack foods.

Food Uses of Dry-Milled Fractions Endosperm products from maize dry milling, ranging from large grits to flour, are widely used by brewers, snack food, and breakfast cereal processors (Figure 5).

Flaking Grits Flaking grits are large (US 3.5–6 mesh sieves) endosperm particles obtained after maize degerming. These large pieces of endosperm are almost exclusively used to manufacture cornflakes by the traditional way, the most popular ready-to-eat breakfast cereal (Figure 6). The fundamental process has remained relatively unchanged over the past century. Yellow maize is preferred because of its stronger flavor and rich golden color after toasting. The flaking grits are pressure-cooked in rotary cookers for 1–2 h with syrup, sugar, nondiastatic malt, salt, and water. The cooked grits are conveyed to a delumping equipment and dried at 66 C to lower its moisture to 20%. Then, the grits are equilibrated for 6–24 h in a bin and flaked through a pair of counterrotating rollers. The resulting soft flakes are toasted in a gas-fired oven in order to develop the crisp texture, brown color, and the characteristic flavor. The flakes are sprayed with nutrients and equilibrated. The typical nutritional value of cornflakes is presented in Table 3. Sugarcoated flakes are made by the same process, but the sweetener is sprayed onto the flakes after toasting. Cornflakes can also be made from meal or grits that are extruded to produce pellets.

Maize Grits

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Figure 8 Arepas, the national bread from Venezuela, are produced from degermed precooked maize flour.

Water

Extruded snacks are a growing segment of the maize-based snack market. Corn meal or grits are processed through extrusion cooking and puffing to produce maize curls, puffs, and balls (Table 3 and Figure 7). The shape of the puffed extrudate is determined by the die, operational temperature, cutoff knife speed, and other factors. Extrudate expansion is closely related to product texture and is affected by the viscoelastic nature of the material and the amount of moisture in the material flowing through the extruder die assembly. The extrudates are baked or fried, flavored, and packaged to produce the final ready-to-eat product. Mouth feel is affected by oil content of the products. Collets or half products can be produced by conventional methods, that is, macaroni presses, or by using a combination of two extruders. The first extruder cooks the raw ingredients, while the second cools, forms, and sizes the extrudate into dense collets, which are dried, stored, and then baked or fried into the final product called third-generation snacks. Baked collets are crisp with a light, crunchy texture. Deep fat-fried collets are crisp with smoother texture due to the uptake of the oil. Preextrusion moisture content of the meal is critical in determining the characteristics and texture of the product. As the moisture content is increased, extrusion cooking temperatures generally drop, and a dense, less expanded product is obtained. Highmoisture meals produce hard, dense extrudates that are generally fried. Meals with low moisture produce expanded extrudates that are generally baked to form a light-textured puffed snack. Large, state-of-the-art plants commercially produce instant arepa flours that require only hot water to produce the dough.

Lime Ca(OH)2

Maize

Lime cooking, steeping, and washing

Nixtamal (lime-cooked grain)

Grinding

Drying (countercurrent air flow)

Dough or masa (lime-cooked dough)

Sifting and blending

Baking (gas-fired oven) Deep fat frying (160 − 180 ⬚C/50 − 70 s)

Corn chips

Tortilla chips

Table tortillas

Additives (preservatives, gums, emulsifiers) and enrichment mix (vitamins and minerals)

Dry masa flour

Figure 9 General flowchart for the production of table tortillas, corn chips, tortilla chips, and dry masa flour.


107

Maize grits are cooked and then passed through flaking rolls to gelatinize the starch. The flakes are dried and ground into flour with acceptable granulation. With precooked maize flour, arepas can be prepared in 30 min instead of 12–24 h required by the traditional process (Figure 8).

Maize Meal and Flour Maize meals and flours have smaller granulation than grits and are popular products because of their long shelf life, freedom from black specks, and bright color. Maize meal is often enriched with thiamin, riboflavin, niacin, and iron. It is used to produce an assortment of chemically leavened baked and fried products such as corn bread, muffins, pancakes, corn sticks, fritters, hush puppies, and spoon bread (Table 3). Most maize bread formulations contain wheat flour, chemical leavening agents, sugar, salt, milk powder, and other ingredients. Maize does not have a functional gluten so wheat flour is included to give the dough more elasticity and hence produce a more aerated lighter product. Hush puppies are produced from a chemically leavened dough, which contains maize meal, wheat flour, eggs, milk, salt, onions, and tomato. Pieces of dough are deep fat-fried for 2–3 min. Maize flour is also widely used as an ingredient in many formulations, for breadings and batters and as a binder in processed meats.

Food Uses of Nixtamalized Products Three basic types of products are industrially produced from lime-cooked maize: table or soft tortillas, corn chips, and tortilla chips (Figures 9 and 10). Corn and tortilla chips are primarily produced and consumed in developed countries, where they have an important share within the salted snack food market.

Table Tortillas Tortillas and masa products constitute the staple food for large population in Mexico and Central America. Tortillas are produced using traditional and industrial processes. Tortillas are the main source of energy, protein, calcium, and other important nutrients in Mexico and Central America (Table 3). Lime cooking considerably increases calcium and the bioavailability of niacin and significantly decreases the potential for aflatoxins in contaminated maize. The industrial production of maize tortillas is laborintensive and requires considerable equipment. It starts when the grain is lime-cooked in agitated open baths, vertical cookers, or steam kettles. The grain is generally mixed with three parts water and 1% lime, based on grain weight, and cooked for 15–45 min at temperatures ranging from 85 to 100 C. The nixtamal is then steeped for 8–16 h in the hot lime solution. The cooking liquor is drained and the nixtamal washed with pressurized water. Most of the pericarp and excess lime is removed during this step. The cleaned nixtamal is discharged into a stone grinder, where it is disrupted into a plastic and cohesive dough or masa. Masa is then kneaded by mixers or extruders that feed the forming machine or roll sheeters. During forming, the masa is rolled into a sheet, which is cut by a rotating cutter positioned underneath the

Figure 10 Nixtamalized or lime-cooked maize products.

rolls. The formed pieces of masa are fed into a three-tier, gasfired oven for baking (temperature ranging from 280 to 302 C for 30–45 s) and then cooled through a series of open tiers and packaged. Tortillas are generally treated with gums, emulsifiers, and acidulants and antimycotics (e.g., sorbates and/or propionates) to improve textural and microbial shelf life.

Nixtamalized Dry Masa Flours The use of dry masa flour is rapidly growing because of its convenience. Dry masa flour is produced by drying and grinding lime-cooked, coarsely ground masa (Figure 9). The masa is dried in large dryers in which warm air flows countercurrently to the pieces of masa. A wide array of products can be manufactured by selecting and blending streams with different particle sizes and colors. In most cases, resulting flours are enriched with B vitamins and trace minerals. Coarser flours with lighter colors are required for snacks. The flour with < 10% moisture is shelf-stable and only requires water (1.1–1.3 l water per kg flour) to form masa for further processing. Many manufactures use dry masa flour because it does not require much labor, equipment, or space and processors do not have to worry about effluent disposal and control of scheduling and manufacturing practices.

Fried/Snack Products Frying has expanded the market for masa-based foods because the final product has excellent organoleptic properties and a long shelf life. The two most popular snacks, tortilla and corn chips, are usually made from coarsely ground fresh masa or masa flours. Corn chips are produced directly from masa (Figures 9 and 11) and contain more oil than tortilla chips (Table 3). Tortilla chips are baked similarly to tortillas before frying. Tortilla chips absorb less oil and have a firmer texture and a stronger maize flavor than corn chips. Nixtamal for these snacks is generally cooked less than for table tortillas, and it is ground into coarse masa, which allows steam to escape through the many small pores during baking and frying. This prevents the formation of serious quality defects, such as oily appearance and blistering. Masa for corn chips is extruded

108


Figure 11 Corn (left) and tortilla chips (right) are the second most important snack food in the world.

through a die and cut by rotating knives before frying. Masa for tortilla chips is formed into triangles, strips, or circles before baking, equilibrating, and frying. Frying temperatures and times range from 165 to 195 C and from 50 to 90 s. Corn and tortilla chips are often salted and flavored immediately after frying. Most popular flavorings include nacho cheese, hot/spicy, barbecue, lemon salt, and jalapenõ. Special processes to produce baked low-fat tortilla chips that combine air impingement, infrared, and microwaves have been developed.


• • •

• •

•

•

Investigate the nutritional and nutraceutical properties of blue and quality protein maizes. What are the ideal popcorn kernel properties? What are the differences and uses of mushroom popcorn and butterfly popcorn? Briefly describe the key manufacturing steps of the following indigenous foods: (a) Toˆ (b) Atole (c) Pozol (d) Tesguïno (e) Chicha (f) Ogi (g) Couscous What are the optimum maize kernel properties and characteristics for wet milling or starch production? What factors related to the maize kernel affect the optimum sulfur dioxide steep time? Investigate alternative processes to significantly reduce steep time without affecting starch yield and quality. When producing maltose syrups, why does the addition of pullulanase or debranching enzyme significantly increases maltose content? What are the major food uses of maltose syrups? Explain the industrial process to convert low-DE syrups into glucose syrups of more than 90 DE. Compare flowcharts for the production of maize flakes via traditional and extrusion processes. What are the advantages and disadvantages of each process? How can you recognize flakes made via extrusion?

• • •

How does lime-cooking or nixtamalization affect the nutritional value of maize? Why is pellagra virtually unknown in Mexico and other tortilla-consuming countries? What are the major differences between dry masa flour for table tortillas and that for tortilla chips, in terms of degree of starch gelatinization, granulation, and additives? Describe at least two process alternatives to produce low-fat tortilla chips and one to produce fat-free (no added fat) tortilla chips?


•

• •

Select several countries and identify their national foods derived from regular and specialty maizes. Propose some ideas for new product development, building on traditional maize foods, but adapting them for likely preferences of your target market. Investigate the impact of first-generation maize bioethanol production on the food industry worldwide. Crossreference to bioethanol production. Investigate the impact of mycotoxins on the maize-based food and feed industries. Cross-reference to mycotoxins or aflatoxins.

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; Beverages from Grains: Beverages: Distilled; Fermentation: Foods and Nonalcoholic Beverages; Fermentation: Origins and Applications; Food Grains and the Consumer: Fortification of Grain-Based Foods; Grains and Health; Labelling of Grain-Based Foods; Genetics of Grains: Maize: Quality Protein Maize; Processing of Grains: Cereals: Breakfast Cereals; Extrusion Technologies; Wheat Processing: Snack Foods: Processing; Wheat-Based Foods: Tortillas.

Further Reading Duensing WJ, Roskens AB, and Alexander RJ (2003) Corn dry milling: Processes, products, and applications. In: White PJ and Johnson LA (eds.) Corn Chemistry and Technology, 2nd ed. St. Paul, MN: American Association of Cereal Chemists, Chapter 11.

NON-WHEAT FOODS | Maize: Foods from Maize Eckhoff SR and Watson SA (2009) Corn and sorghum starches production. In: Bemiller JN and Whistler R (eds.) Starch: Chemistry and Technology, 3rd ed. New York, NY: Academic Press, Chapter 9. Hallauer AR (2001) Specialty Corns, 2nd ed. Boca Raton, FL: CRC Press. Hobbs L (2009) Sweeteners from starch: Production, properties and uses. In: Bemiller JN and Whistler R (eds.) Starch: Chemistry and Technology, 3rd ed. New York, NY: Academic Press, Chapter 21. Johnson LA (2000) Corn: The major cereal of the Americas. In: Kulp K and Ponte Jr. JG Jr. (eds.) Handbook of Cereal Science and Technology, 2nd ed. New York: Marcel Dekker. Kearsley MW and Dziedzic SZ (1995) Handbook of Starch Hydrolysis Products and Their Derivatives, 1st ed. Cambridge, Great Britain: Blackie Academic and Professional. McDonough CM, Gomez MH, Rooney LW, and Serna-Saldivar SO (2001) Alkaline cooked corn products. In: Lusas E and Rooney LW (eds.) Snack Foods Processing, 1st ed. Lancaster, PA: Technomic Publishing. Rooney LW and Serna-Saldivar SO (2003) Food uses of whole corn and dry milled fractions. In: White P and Johnson L (eds.) Corn Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Serna Saldivar SO (2008) Industrial Manufacture of Snack Foods. London: Kennedys Publications.

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Serna Saldivar SO (2010) Cereal Grains: Properties, Processing and Nutritional Attributes. Boca Raton, FL: CRC Press (Taylor & Francis Group). Serna Saldivar SO (2013) Wet milling and starch extraction. In: Ferreira Guine RP and dos Reis Correia PM (eds.) Engineering Aspects of Cereal and Cereal-Based Products, pp. 241–270. Boca Raton, FL: CRC Press (Taylor & Francis Group), Chapter 11. Serna-Saldivar SO, Gomez MH, and Rooney LW (1990) The technology, chemistry and nutritional value of alkaline cooked corn products. In: Pomeranz Y (ed.) Advances of Cereal Science and Technology, vol. 10. St. Paul, MN: American Association of Cereal Chemists. Steinkraus KH (1983) Handbook of Indigenous Fermented Foods, vol. 9. New York: Marcel Dekker. Wacher MC and Lappe P (1993) Alimentos Fermentados Indigenas de Mexico. Mexico, DF: Universidad Autonoma de Mexico.

Relevant Websites http://apps.fao.org – FAO (2013). http://ndb.nal.usda.gov – USDA (2013).

Rice: Chinese Food Uses S Lu, National Chung Hsing University, Taichung, Taiwan ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 68–74, ã 2004, Elsevier Ltd.

Topic Highlights

• • •

The processing and properties of rice starch (an abundant, small-granule starch with a wide range in amylose content) are presented. A flow diagram for the production of rice crackers, a product common to both China and Japan, is given. A brief description of puffed rice, rice dessert, rice noodle and rice muffin products should enable the reader to identify possibilities for further product development.

Learning Objectives

• •

To understand the characteristics of rice starch that support its use in varied Chinese traditional food products. To outline the diversity and processing requirements of typical Chinese rice food products.

Introduction That rice culture has had a direct and significant impact on Taiwanese, and southern Chinese culture is a historical fact that could not be ignored. The Chinese proverb “Sow in spring, plow in summer, harvest in fall and store in winter” originated from and referred to rice culture which can be traced back to 4000 BC. Of all rice, 90% is consumed as cooked whole kernels, and the rest is milled to produce flour, which is used to make cakes, desserts, and snacks for special feasts or celebrations. In the USA, rice is usually classified by the length of grains, i.e., short, medium, and long. Both medium and long grain rice are produced in southern states and all grain types in California. In Taiwan, short grain japonica nonwaxy rice is produced throughout the island mainly in the southwestern plain area. Of this 10% is of long grain indica rice, waxy indica, and/or waxy japonica varieties. Most short grain varieties are round or bold, and the long grain varieties are slender. The two topics covered in this article will be how to mill rice to flour and an introduction to rice-based foods. Most of the rice foods are made from either nonwaxy indica or waxy japonica rice only, and some others are made from waxy indica type of rice.

Milling and Starch Isolation Rice is milled or ground to flour or a coarse meal in some Asian countries as part of the process for making traditional rice dishes that resemble baked or steamed products. Rice flour used in processed food, which includes cereals, soup, snacks,

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candy and others, is estimated to have been 12.2 million cwt in 1990/91, over 21% of total domestic demand for milled rice. Official Taiwan markets statistics indicates that 0.9 million cwt of rice flour is consumed annually, primarily in desserts and snacks. Of the total production, 30% is used in making noodles, including rice noodles, “Bi-Tai-Ba,” in main dishes. One thousand years of milling history have produced three different milling processes: dry, semi-dry, and wet milling (Figure 1), which, depending on the amount of water used, yield different flour varieties. Properties and textural differences of rice flour are directly related to some of the inherent characteristics of starch, particularly the amylose content. Rice starch has more combinations of physico-chemical properties than other cereal starches. The amylose content of rice starch, which ranges from trace amount in waxy types to more than 30% in some nonwaxy indica varieties, plays an important role when rice flour is used as a thickener in food production. Some indica varieties, because of their higher amylose content (>27%), cause the product to be firmed or thickened, which produces a rigid gel during storage. Thin and wide rice noodle producers and rice cake manufacturers prefer high-amylose indica varieties, such as Tainung Sen 19 and Taichung Sen 17. The starch gel of the flours from medium or short grain japonica variety is more stable than that of high-amylose indica rices and is preferred in the production of puffed rice cakes and rice cracker, such as popular snacks in Japan, “Sen Bei” and “Arare.” The waxy japonica rice demonstrates a stickier cooked product than the waxy indica variety. Viscoamylography, a rapid viscosity analysis (RVA) or a differential scanning calorimeter (DSC), would test and determine the damage starch produced and gelling or pasting behavior. These measurements are important in choosing the type of rice for the manufacturing of the rice flour. In addition to inherent preprocessing starch properties and storage conditions, methods of milling or grinding and pretreated rice kernel profoundly affect the physico-chemical and functional properties of rice flour. Complementary quality control tests – such as protein, ash, and microbial content tests – should be performed on the rice flour, as flour gleaned during the milling process is used to produce other food products, i.e., baby cereal and processed products.

Rice Starch Starch is a reserve carbohydrate found mainly in cereals, roots, tubers, and fruits and sometimes in the pith of plants. Usually it is associated with fats and inorganic salts, such as phosphorus. Rice starch granules are compound starches, varying in size from 3 to 10 mm. A starch granule is a homopolymer of a-Dglucopyranoside units. The linear polysaccharide, amylose, has a degree of polymerization on the order of several hundred


http://dx.doi.org/10.1016/B978-0-12-394437-5.00127-3

NON-WHEAT FOODS | Rice: Chinese Food Uses

Rice

Clean

Soak

Stone mill

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Slurry

Adding water

Remove water

Rice batter

Leach water

Toast or puffing

Dry and mill

Screening

Wet-milled flour

Roller or hammer mill

Screening

Semi-dry milled flour

Mill

Screening

Dry-milled flour

Mill

Screening

Gelatinized flour

Figure 1 The flowchart of dry, semi-dry, and wet milling. (Reproduced with permission from Chen JJ (1995) Studies on the Physicochemical Properties of Waxy Rice Flours by Different Milling Methods. Master thesis, Chung-Hsing University, Taichung, Taiwan.)

glucose residues connected by a-D-(1,4) glucoside linkage. Amylopectin, a branched polymer, has a degree of polymerization on the order of several hundred thousand glucose residues, while the branched points are a-D-(1,6)glucoside linkage. Commercial preparation of rice starch is not a dominant product because of its higher cost, when compared to corn, wheat, and tapioca starches. In Belgium, Remy Industries produce 75% of the world supply of rice starch. Rice starch has more combinations of physico-chemical characteristics than other starches. The amylose content of rice starch, which ranges from trace amounts in waxy types, to more than 30% in some nonwaxy indica varieties, must be considered when using rice flour as a thickener in food production. Some indica varieties, with an amylose content of more than 27%, cause the product to harden or thicken and produce a rigid gel during storage. The common methods of preparing rice starch are by alkali or DOBS extraction. An older process for manufacture of rice starch is dodecylbenzene sulfonate (DOBS) treatment. The newer process of preparing is by NaOH extraction of the protein. Milled or broken rice kernels are steeped in 5 times its weight of 0.1–0.2% NaOH for 24 h at 40 C to soften the kernels and aid protein removal at the first step. Caustic treated kernels are washed and mixed with five parts of 0.1% NaOH and then stirred for 24 h. Soaked rice kernels are ground into flour and cell walls are removed by screening. The starch slurry is allowed to settle and the supernatant solution, which contains most of the protein, is removed. Starch granules are washed with water; decanting is employed to remove soluble materials. Centrifuging dewaters washed starch; complete removal of residual alkali is an important step. The starch slurry is put in an oven to dry-down the moisture to 10%; the rice starch cake is ground to the desired particle size and sieved.

The starch properties measured by differential scanning calorimetry (DSC) showed that gelatinization temperature and enthalpy values were significantly correlated for these flours. The lower enthalpy values for dry-milled flour give an indication of relative high starch damage that occurs during milling.

Rice-Based Food Products This article will not pay attention to the rice crackers, because they are the major and traditional baked snack food in Japan (Figure 2). Instead, the rice food which is consumed by the Chinese or overseas Chinese community will be emphasized. In terms of expanding into industrial scale, several discouraging factors come into play. The main obstacle is the lack of well-formulated machinery manufacturing processes. Other concerns include governmental controls over the distribution and price of rice, which limit the accessibility of raw materials to rice industry. The rice food products are classified into: (1) products using whole grains, such as puffed rice items, and (2) products using flours prepared before and after cooking.

Puffed Rice Puffed rice products are common in Taiwan. The kernel puffing process involves frying or by high pressure.

Gun-puffing and Mi-Hua-Tung Gun-puffing cake and “Mi-Hua-Tung” are typical Chinese rice snacks made from puffed rice mixed and molded with syrup, sugar, peanut, and flavoring. Japonica type nonwaxy as well as waxy rice varieties are preferred for gun puffing. Waxy-type rice has higher water absorption index and water solubility,

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Moisture%

Senbei

Issues

Arare

Rough indica rice

Variety of rice

Rough waxy rice

Polishing

Degree of polishing (91%)

Polishing

Washing, soaking

Hydration

Washing, soaking for 6–12 h

34–38%

Draining

30–34%

Roller milling

Particle size

40–45%

Steaming kneader (110⬚C, 5–10 min)

Degree of starch gelatinization

50%

Draining

Cooling to 60–65⬚C by immersing into water (18⬚ C)

Homogenization

30–34%

Steam cooking (96–100 ⬚C, 15–20 min)

Kneading

Kneading

Moisture%

40%

Quick cooling at 2–5⬚C to harden for 2–3 days

Forming and cutting Forming and cutting 20%

Primary drying (hot air at 70–75⬚C)

Control of temperature and time to yield uniform water distribution

Drying (hot air at 45–75⬚C)

20%

Tempering (10–20 h)

10–12%

Secondary drying (hot air at 70–75⬚C)

3%

Baking at 200–260⬚C

E xpansion affected by temperature, moisture content, material properties

Seasoning or coating

Packaging

Product Figure 2 Manufacturing of “Senbei” and “Arare.” (Courtesy of Yeh AY (2003). Preparation and application of rice flour. In: Champagne E (ed.) Rice: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists.)

resulting in a soggy texture and eating quality, so the best choice for gun puffing is the low amylose content (below 20%) japonica rice. About 600 g of the rice with 14% moisture is fed to the gun, in which pressure is built up to 10–12 kg cm2, and then suddenly released. The gun is preheated for a couple of minutes before the rice is put in. After a short cooking time, the gun is suddenly opened and puffed rice

kernel is caught in a metal hopper. The puffed rice is mixed with sugar syrup or maltose syrup in a pan to make small square pieces, called gun-puffing cakes. For Mi-Hua-Tung, the milled rice or brokens are washed, soaked in water, and passed through a steaming and drying oven. The cooked rice is dried to 10–15% moisture by a rotated dryer, and then fried at a temperature of 240–250 C for

NON-WHEAT FOODS | Rice: Chinese Food Uses 10–12 s for puffing. The puffed rice kernel is mixed with maltose, starch syrup, and other ingredients and put through a molder, metal separator, and then packed.

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and the ratio is 100:80:70 for flour, sugar, and water, respectively (Table 1). The batter is cooked in a steamer for 4–5 h, then cooled and packed.

Guo-Ba For “Guo-Ba,” the rice grain is cooked first. There are two ways to cook the rice. Traditionally, the rice is soaked in water for 30 min, and then boiled or steamed by gas to obtain the whole grain cooked rice. All the water is absorbed by the rice during cooking period. For industry, the milled rice is soaked in an equal amount of water at room temperature for a couple of hours and then steamed in 18 psi pressure for 10 min. Selecting the proper indica waxy rice varieties and controlling the water–rice ratio are important in keeping the cooked rice from being too sticky or too soft. The heating conditions should be controlled to get the gelatinized rice or the cooked rice grain without scorches in the center location. Cooked rice is weighed and cut to rectangular pieces (10 grams each), put into 5 cm squares, and dried to reduce the moisture content down to 12–15%. Dried products are then fried at 220 C by a deep fry conveyor for 4–8 s and then packed.

Indica rice varieties with high amylose content are preferred to make rice noodles because retrogradation is necessary. There are several rice noodle types, such as “Mi-Fen,” “Bi-Tai-Ba,” “Ho-Fen,” etc., which are very popular in Taiwan, Japan, and among the overseas Chinese communities in Southeast Asian countries.

Mi-Fen Mi-Fen is a popular main dish in meals. Generally Mi-Fen is made in the dry state, and it can be steamed or cooked before serving. There are two procedures to make Mi-Fen, process A or B. Either of them can be selected.

Process A

Rice Desserts and Sweets Mogi In Taiwan, to the natives and to some extent immigrants, “mogi” is a very popular rice cake. It is prepared from japonica waxy milled rice (short grain) by washing, soaking, wet milling to flour, steaming at 100 C for 45–60 min, kneading, cooling, dividing, and packing. Traditionally, the rice is pounded by wooden pestles in mortars. During this process, air is removed from the rice cake and a smooth texture is obtained. With mechanical kneading, the air bubbles easily get into the mogi which results in a rough surface of whiter appearance. Mogi is usually produced in a ball shape with mashed red beans or peanut grits inside and eaten as a snack.

New year cake (Nien-Kuo) The short grain waxy rice is preferred to make “Nien-Kuo.” The rice is soaked for a couple of hours and ground by stone mill to get slurry. The slurry is dehydrated either by centrifugation or by draining the slurry in a cotton cloth bag with heavy stones placed on the top of bag. The wet-milled rice flour containing 45% moisture is mixed with sugar and water to get batter, Table 1

Rice Noodle (Bi-Tai-Ba)

Cleaned rice kernels soaked in water for couple of hours are ground into slurry, the rice slurry is filled into a cloth bag, and the filled bag is pressed with a mechanical press or centrifugation to remove water. The dewatered rice solids are put in a heated mixer for 50 min and the rice solids are partially cooked to a soft mass (addition of cornstarch and/or wheat is optional). The soft rice mass is mixed a second time to further soften it. The soft rice mass is transferred to a presser to form thick sheets, followed by extruding the sheets into rice noodles, cooling, and loosening the extruded rice noodles immediately to avoid sticking together. The extruded rice noodles are steamcooked for 50 min, then cut into with a knife when still warm, shaped into bundles or blocks, and loaded onto trays in carts. Finally, shaped rice noodles are dried for 8 h, and cooled thoroughly before packaging into specific containers for retail or storage.

Process B Instead of soaking, grinding, and dewatering the rice, rice flour is used directly in mixing and partial cooking. The rest of the steps are essentially the same as process A.

The quality characteristics of Nien-Kuo with different formula Ingredients ratio (sucrose:water:flour)

Quality characteristics

11:4:10

Hardness Awb pH L A B

3612 56 0.79 0.01 5.66 0.15 26.12 0.35 1.01 0.12 12.34 0.20 a

10:5:10

9:6:10

8:7:10

7:8:10

2245 35 0.81 0.01 5.85 0.04 29.37 0.14 0.56 0.11 9.99 0.21

1801 65 0.86 0.01 5.84 0.11 32.70 0.12 0.45 0.09 9.12 0.16

1587 67 0.87 0.01 6.01 0.13 33.07 0.24 0.31 0.05 9.25 0.12

1432 24 0.90 0.02 6.10 0.10 34.82 0.24 0.05 0.04 10.69 0.11

Mean SD, n ¼ 6. Aw: water activity. Source: Lin JS (1993) Studies on the Quality of New-Year Rice Cake Treated by Different Soaking Conditions and Dehydration Methods. Master thesis, Chung-Hsing University, Taichung, Taiwan. a

b

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Bi-Tai-Ba Bi-Tai-Ba is produced as a wet form of noodles, coarser and shorter. It is eaten with syrup and ice water in the hot season, but it also can be served with meat, green onions, or other seasoning. The traditional procedure to make Bi-Tai-Ba is explained as follows: Soaked rice kernels are wet milled to slurry, centrifuged to dehydrate the batter, heated to pregelatinize one-third of batter, the remaining two-thirds of the batter is extruded to string (3.0 mm in diameter), and finally, steamed, cooled, and packed. Recently, the extruder method has been used to make BiTai-Ba. Dry-milled flour with 38% moisture is fed to a single screw extruder, which has three barrel sections, with temperature set at 130 C, 100 C, and 50 C, respectively.

Rice Cracker Japonica and/or waxy rice varieties are preferred to make rice cracker. Cleaned rice kernels are soaked in water for a couple of hours, and ground in a stamp mill or pulverized in a roller mill. The fine particle rice flour is fed into a steaming kneader or cooked in a steamer for 15–20 min to gelatinize the starch, then cooled down to 60 C, and the dough is sheeted to plate form and cut to pellets. The pellets are dried until only 20% moisture content remains, tempered at room temperature for 1 day, and then dried at a certain temperature until the moisture content drops to 10%. The dried pellets are then baked in an oven at a temperature ranging from 200 to 260 C, thereafter, the expanded final product has a moisture content of 3–5%.

Ho-Fen Ho-Fen making is similar to Bi-Tai-Ba; it is produced in both wet and dry forms of noodle, more thinner (1–2 mm thick) and wider (1 cm) rice stripes. The basic steps in the making of traditional Ho-Fen is described as follows: prepare rice slurry with rice flour and water, put a small amount of oil on stainless trays to coat the trays evenly, pour rice slurry on the trays to form a thin layer ( 1–2 mm thick). Steam the trays of thin layers of rice slurry to gelatinize the starch for 5 min, then remove the trays as soon as possible from the steamer and cool down to the room temperature. Roll up the gelatinized rice sheet from each tray with a spatula ( 10 cm in depth), and cut the layered rice sheets into 1 cm wide stripes. For long-time storage, dry the moisture to 10% water-content with a mechanical oven drier or any such aid.

Miscellaneous Products There are several rice products, which are not major consumption for Asian people, and will not be attempted to introduce in this article. These products include parboiled rice, breakfast rice cereals, canned rice, easy-to-cook brown rice, rice bran oil and yeast-fermented rice cake.

Summary Rice-based food products require specific physico-chemical characteristics to produce the required eating qualities. There are several major factors affecting the cooking or eating qualities as considered by the end user, which include the aging or storage conditions of rice grains, rice varieties, amylose content of starch, degree of milling, as well as milling methods.

Fa-Kuo (Rice Muffin) There is another kind of muffin-style rice food, “Fa-Kuo,” in Taiwan and Southeast Asian countries. Indica rice is preferred to make this kind of food. Dried or wet-milled rice flour (100 g base) is mixed with 50–80% sugar and 3.5% leavening agent with or without red color additive, and water is added to the tune of 120% to make batter. The batter is put into a bowl, steamed for 20 min, and then cooled. Fa-Kuo is prepared from wet-milling flour by two steps of high-speed mixing to get better eating quality than one-speed mixing procedure. The red-colored Fa-Kuo is usually prepared for celebration and festivals, since it is a symbol for luck and promotion in one’s profession. During the time of Chinese New Year every family will have Nien-Kuo and Fa-Kuo.


• •

Discuss the application of the Rapid Visco-Analyzer (RVA) in quality control for a rice food product. Purchase rice products such as those described from you local market and compare their characteristics and properties.


•

Bowl Rice Curd

•

It is a very traditional and popularly consumed breakfast food item in the south of Taiwan. Indica rice flour is preferred to make bowl rice curd. The procedure is as follows: Milled rice kernels, homogenize, take 1/3 of the slurry to heat for partial gelatinization, mix remaining 2/3 portion, put in bowl and add other ingredients (chopped pork, salt, fried red onion, black pepper, seasoning etc.), steam for 15 min and, finally, pack the product.

•

How can the glycemic index properties of rice be utilized in design of nutritionally enhanced food products? How do sensory preferences for rice food products differ regionally? How would the interactions of sugars and salts with starch under high-temperature processing affect the physical properties of rice foods?

See also: Barley, Rice and Maize Processing: Oil from Rice and Maize; Breeding of Grains: Rice: Breeding; Genetics of Grains: Rice: Genetics; The Cereal Grains: Rice: Overview; Wildrice, Zizania:

NON-WHEAT FOODS | Rice: Chinese Food Uses Overview; Wheat-Based Foods: Noodles: Starch; Wheat Processing: Snack Foods: Processing.

Further Reading Bean MM and Nishita KD (1985) Rice flours for baking. In: Juliano BO (ed.) Rice Chemistry and Technology, 2nd edn., pp. 539–556. St. Paul, MN: American Association of Cereal Chemists. Chang SM and Chang TL (1995) The characteristics of explosion puffing rice produced with different amylose contents. Journal of Food Science (Chinese) 22: 465–478. Chen JJ (1995) Studies on the Physicochemical Properties of Waxy Rice Flours by Different Milling Methods. Master thesis, Chung-Hsing University, Taichung, Taiwan. Huang RM, Chou MB, and Lii CY (1998) Effect of the characteristics of rice and the processing conditions on the expansion ratio of dry cooked rice. Journal of Food Science (Chinese) 25: 383–393. Jomduang S and Mohamed S (1994) Effect of amylose/amylopectin, milling methods, particle size, sugar, salt, and oil on the puffed product characteristics of a traditional Thai rice-based snack food (Khao Kriap Waue). Journal of the Science of Food and Agriculture 65: 85. Juliano BO and Sakurai J (1985) Miscellaneous rice products. In: Juliano BO (ed.) Rice: Chemistry and Technology, 2nd edn., pp. 569–618. St. Paul, MN: American Association of Cereal Chemists. Lin JS (1993) Studies on the Quality of New-Year Rice Cake Treated by Different Soaking Conditions and Dehydration Methods. Master thesis, Chung-Hsing University, Taichung, Taiwan.

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Lu S and Lii CY (1989) The influences of various milling processes on the physico-chemical properties of rice flours and the rice flake preparation. Journal of Food Science (Chinese) 16: 22–35. Lu S and Yeh CP (1996) Laboratory preparation of bi-tai-ba by single screw extruder. Journal of Food Science (Chinese) 23: 650–661. Lu S, Lin MS, Lin TC, and Lii CY (1993, 1995) Studies on the quality of bi-tai-ba and its frozen stability addition with commercial starches. Journal of Food Science (Chinese) 20: 64–74. Lu S, Lin JS, and Lin TC (1995) The effects of physicochemical characteristics at different soaking and dehydration conditions on wet-milled rice flour. Journal of Food Science (Chinese) 22: 426–437. Sakurai J (1971) Rice as an Industrial Raw Material for Manufacture of Processed and Ready-to-Eat Rice Products. In: (Proceedings) International Seminar on the Industrial Processing of Rice – Madras, India, p. 65. Vienna: United Nations Industrial Development Organization. Taiwan Provincial Government (1998) Taiwan Food Statistics Book. Republic of China: Department of Food and Agriculture, Taiwan Provincial Government. Yeh AY (2004) Preparation and application of rice flour. In: Champagne E (ed.) Rice: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Yeh AY, Hsiu WH, and Shen JS (1991) Some characteristics in extrusion cooking of rice noodle by twin screw extruder. Journal of the Chinese Agricultural Chemistry Society 29: 340–351.

Relevant Website irri.org http://www.irri.org – Website of the International Rice Research Institute, based in Philippines. Has information and links on rice utilization.

Sorghum: Utilization RD Waniska, LW Rooney, and CM McDonough, Texas A&M University, College Station, TX, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

more than 2% of sorghum with pigmented testa or colored pericarp. Mixed sorghum contains a blend of kernels with and without pigmented testa. The United States also markets ‘food-grade’ white sorghum, a white kernel with tan plant and glume characteristics. The amounts of anthocyanin pigments that darken these grains are less than those from grain with purple or red glumes.

Sorghum grading and classification. Appearance and genetics. Grain structure and properties. Composition. Food uses of the grain. Industrial uses of the grain. Nutritional value. Feed uses of the grain.

Appearance and Genetics of Sorghum

Learning Objective

•

A comprehensive understanding of the structure, composition, processing, and food/feed uses of sorghum.

Introduction Sorghum is utilized as food, feed, and industrial products around the world. About 30–40% of the 62 million tonnes (Mt) produced annually is used in a wide variety of traditional foods mainly in Africa, Asia, and Central America. Industrial production of beer, nonalcoholic beverages, and porridges occurs in Africa, especially Nigeria, South Africa, and Botswana. Small quantities of sorghum are used for foods in the western hemisphere and in Japan. Production, plant characteristics, and related information on sorghum were presented elsewhere in this encyclopedia. The major use for sorghum is as livestock feeds for all species of animals. Sorghum is processed, to improve its feed efficiency, into a wide variety of feeds ranging from floating fish food to steam flakes for ruminants in large feedlots. Sweet sorghums are preferred for syrup and for forage. The forage (fodder) may be more valuable than the grain. The stalks are used for dry fodder for ruminants, and some sorghums are grazed, since the stalk remains green after grain maturation. Most of the comments in this article are on the utilization of sorghum grain, but forage utilization is also important in drier areas of the world.

Grading and Classification Sorghum is marketed according to US grain standards in four classes: sorghum, white sorghum, tannin sorghum, and mixed sorghum. The sorghum class cannot contain more than 3% sorghum with a pigmented testa (undercoat). Tannin sorghums have a pigmented testa beneath the pericarp. The pigmented testa is seen as a dark layer between the light endosperm and the pericarp when the caryopsis is scraped to remove the pericarp. Bleaching using the Clorox bleach test causes the constituents in the pericarp and testa to oxidize and gives a pronounced black color to the bleached kernels, while nontannin sorghums have a white appearance. The white class contains sorghum with a white pericarp without a pigmented testa and cannot contain

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Many factors affect grain appearance: pericarp color and thickness, presence of a pigmented testa, endosperm color, secondary plant, and glume colors and damage by insects and molds affect the appearance and quality of sorghum. Pericarp color is genetically controlled by the R and Y genes. The combination of these genes produces white or colorless (R_yy or rryy), lemon yellow (rrY_), or red (R_Y_) color. The intensifier (I_) gene increases the brightness of the pericarp color in red pericarp sorghums. Sorghums with homozygous recessive (zz) genes have a thick mesocarp containing small starch granules, which causes a chalky appearance that masks the colors of the testa and endosperm. A pigmented seed coat (testa) is present when both B1_ and B2_ genes are dominant. Caryopses with a pigmented testa (B1_B2_) and a recessive spreader gene (ss; type II) or dominant spreader gene (S_; type III) contain condensed tannins and are brown (tannin) sorghums. The tptp genes control testa color, which is brown or purple. Type III sorghums have more tannins than type II sorghums. Type I sorghums do not contain tannins (proanthocyanidins). Yellow endosperm cultivars contain 8–30 ppm carotenoid pigments. Endosperm color affects appearance, especially in caryopses with a thin pericarp and without a pigmented testa where the grain appears to be yellow. A thick mesocarp and colorless pericarp cause a white or chalky appearance. Heteroyellow endosperm sorghum results when sorghums with yellow and nonyellow endosperm colors are hybridized. Bronze sorghums contain a thin, red pericarp with yellow endosperm color, while cream sorghums contain a thin, white pericarp with yellow endosperm. Waxy endosperm cultivars contain three genes (wx) in the recessive form. Heterowaxy genotypes contain one or two of these genes in the dominant form, whereas normal or nonwaxy endosperm sorghums contain all three genes in the dominant form. Waxy cultivars contain nearly 100% amylopectin and the endosperm looks like candle wax. The high-lysine (hl) sorghum from Ethiopia has a soft, floury endosperm texture and a shriveled kernel structure and is susceptible to deterioration in humid environments during and postcaryopsis development. The improved protein digestibility sorghum and the chemically induced, high-lysine sorghum have intermediate-soft to soft endosperm textures; they have reduced grain yield and increased deterioration due to molds and weathering.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00128-5

NON-WHEAT FOODS | Sorghum: Utilization

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Grain Structure and Physical Properties

Composition

The sorghum kernel is considered a naked caryopsis, although some African types retain their glumes after threshing. The kernel weight varies from 3 to 80 mg. The size and shape of the grain vary widely among sorghum races. Commercial sorghum grain has a flattened spherical shape, 4 mm long, 2 mm wide, and 2.5 mm thick, with a kernel weight of 25–35 mg. The volumetric weight and grain density range from 708 to 760 kg m3 and from 1.26 to 1.38 g cm3, respectively. The sorghum caryopsis is composed of three anatomical parts: pericarp, endosperm, and germ (Figure 1(a)). The relative proportion of these structures varies but in most cases is 6%, 84%, and 10%, respectively. The pericarp (Figure 1(b)) is the fruit coat and is fused to the sorghum seed. It originates from the ovary wall and is subdivided into three distinctive parts: epicarp, mesocarp, and endocarp. The epicarp is the outermost layer and is covered with a waxy film. The mesocarp varies in thickness and thick mesocarps contain starch granules. The endocarp is composed of cross and tube cells and plays a major role in transporting moisture and nutrients during germination and development. The true seed consists of the seed coat (testa), endosperm, and germ. The endosperm tissue is triploid, resulting from the fusion of a male gamete with two female polar nuclei. The testa (seed coat) is derived from the ovule integuments; in brown sorghums, it is thick and contains condensed tannins. The testa is pigmented when the genes are B1_B2_. The endosperm is composed of the aleurone layer, peripheral, corneous, and floury areas. The aleurone consists of a single layer of rectangular cells adjacent to the tube cells or testa. Aleurone cells contain a thick cell wall, large amounts of proteins (protein bodies) and enzymes, ash (phytic acid bodies), and oil bodies (spherosomes). The peripheral endosperm (Figure 1(c)) adjacent to the aleurone layer is a hard layer composed of dense cells containing large quantities of protein and small starch granules. These layers affect the processing and nutrient digestibilities of sorghum. Processing of sorghum by steam flaking, micronizing, popping, and reconstitution is designed to disrupt the endosperm structure to improve the digestibility. The corneous and floury endosperm cells are composed of starch granules, protein matrix, protein bodies, and a thin cell wall rich in b-glucans and hemicellulose. In the corneous endosperm, the protein matrix surrounds the starch granules and protein bodies are embedded in the matrix (Figure 1(d)). The starch granules are shaped polygonally and often contain dents from protein bodies. The appearance is translucent and the texture vitreous. The opaque–floury endosperm is located around the geometric center of the kernel. It has a discontinuous protein phase, air voids, and loosely packaged, round– angular starch granules and is opaque to transmitted light (Figure 1(e)). The germ is diploid owing to the sexual union of one male and one female gamete. It is divided into two major parts: the embryonic axis and scutellum. The embryonic axis forms the new plant and is subdivided into a radicle and plumule. The radicle forms primary roots, whereas the plumule forms leaves and stems. The scutellum is the single cotyledon of the sorghum seed. It surrounds the embryonic axis; contains large amounts of oil (spherosomes), protein, enzymes, and minerals; and separates the endosperm and germ.

Sorghum grain composition (Table 1) is significantly affected by genetic and environmental factors. Starch (75–79%) is the major component, followed by protein (9.0–14.1%) and oil (1.5–5.0%). The protein content (N 6.25) of sorghum is more variable and usually 1–2% higher than maize. Approximately 80%, 16%, and 3% of the protein is in the endosperm, germ, and pericarp, respectively. Sorghum generally contains 1% less oil and significantly more waxes than maize.

Starch Sorghum starch is composed of 70–80% amylopectin and 20–30% amylose. Waxy sorghums contain starch with 100% amylopectin; their properties and uses are similar to those of waxy maize. The gelatinization temperature of sorghum starch is slightly higher than that of maize starch; however, it can be used interchangeably with maize starch. Sorghum starch from the hard endosperm is difficult to separate from the protein matrix. The wet milling of food-type sorghums produces excellent prime starch. Sorghum endosperm requires a little longer to cook compared to maize endosperm particles. Sorghum endosperm can be easily extruded into a wide variety of snacks and other ready-to-eat products.

Soluble Sugars Mature kernels contain 2.2–3.8% soluble sugars, 0.9–2.5% free reducing sugars, and 1.3–1.4% nonreducing sugars. Glucose and fructose comprise 0.6–1.8% and 0.3–0.7%, respectively. High-lysine and sugary cultivars contain additional simple sugars and amino acids, which accounts for the flavor they develop during roasting.

Fiber Most of the fiber is present in the pericarp and cell walls. Sorghum contains 6.5–7.9% insoluble fiber, hemicellulose, and cellulose and 1.1–1.2% soluble fiber, b-glucans, and pentosans. Sorghum contains 1.3% pentosans, located mainly in the pericarp. Approximately 70% of the pentosans are alkalisoluble, and 30% are water-soluble. Fibers in cell walls of the aleurone and endosperm are associated with ferulic and caffeic acids. Fibers in the pericarp provide structural and protective functions; therefore, fiber content of sorghum products depends on the extent of pericarp removal during milling. Insoluble dietary fiber increases during food processing due to increased levels of bound protein, mainly kafirins, and enzyme-resistant starch. In tannin sorghum, cooking also forms polyphenol–protein complexes, which increases bulking ability. Sorghum brans do not lower blood cholesterol levels but are excellent bulking agents in rats. Sorghum bran fed to humans increases stool weight, decreases intestinal transit time, and increases the frequency of bowel movement.

Proteins Protein content and composition vary due to agronomic conditions (water availability, soil fertility, temperatures, and environmental conditions during grain development) and genotype. Nitrogen fertilization significantly increases kafirin


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5 µm

Cutin S.A

Aleurone layer Corneous E.

Peripheral endosperm Testa

Floury E. S.

Pericarp E.A.

Epidermis Hypodermis Mesocarp

Germ

Cross cells Tube cells Testa Aleurone layer Peripheral endosperm

Pericarp

Hilum

(c)

(a)

(d)

(b)

(e)

Figure 1 Scanning electron microscopy photos of sorghum microstructure. (a) Cross section of the sorghum caryopsis; (b) a thick pericarp; (c) peripheral endosperm; (d) corneous endosperm; (e) floury endosperm. A, aleurone layer; C, corneous endosperm; CC, cross cells; CW, cell wall; E, epicarp; F, floury endosperm; G, germ; M, mesocarp; PE, peripheral endosperm; P, pericarp; PB, protein body; PM, protein matrix; S, starch granule; SC, seed coat; T, tube cells. Reproduced from Earp et al. (2004) Journal of Cereal Science 39(1): 21–27, with permission.

NON-WHEAT FOODS | Sorghum: Utilization Table 1 grain

Compositiona (%, unless otherwise stated) of sorghum

Component

Value

Range

Protein (N 6.25) Albumins Globulins Prolamins Glutelins Lipid Ash Nitrogen-free extract Fiber Crude Dietary, insoluble Dietary, soluble Acid detergent Sugars

11.6 5.7 7.1 52.7 34.4 3.4 2.2 79.5

8.1–16.8 1.6–9.2 1.9–10.3 39.3–72.9 23.5–45.0 1.4–6.2 1.2–7.1 65.3–81.0

2.7 7.2 1.1 3.3 2.1

0.4–7.3 6.5–7.9 1.0–1.2 2.9–3.6 1.3–2.6

a

All values are expressed on a dry-matter basis. Nitrogen-free extract was calculated by difference. Adapted from Rooney LW and Waniska RD (2001) Sorghum food and industrial utilization. In: Smith WC and Frederiksen RA (eds.) Sorghum: Origin, History, Technology and Production, pp. 689–725. Wiley.

accumulation and protein content. Kafirins (the sorghum prolamin proteins) and glutelins comprise the major protein fractions in sorghum. These fractions are primarily located within the protein bodies and protein matrix of the endosperm, respectively. The alcohol-soluble prolamin fraction comprises 50% of the protein. These proteins are hydrophobic and rich in glutamine, leucine, alanine, and proline; contain little lysine; and are primarily located within protein bodies. Kafirins contain crosslinked proteins that slow digestibility of the protein. Sorghums identified with easier to digest proteins have protein bodies with a modified structure and contain less kafirin and less crosslinked protein after cooking. Glutelins are high-molecularweight proteins, mainly located in the protein matrix. The lysine-rich protein fractions, albumins and globulins, predominate in the germ. Lysine and threonine are the first and second most limiting amino acids in sorghum proteins. Sorghum lysine meets 40% of the recommended level for infants. High-lysine cultivars contain 50% more lysine. They are soft and dented and contain lower levels of kafirins and higher levels of glutelins and salt-soluble proteins.

Lipids The germ contains 80% of the 3.5% lipid in the sorghum caryopsis. The fatty acid composition consists mainly of linoleic (49%), oleic (31%), and palmitic (14.3%) acids. Refined sorghum oil is very similar to maize oil in quality and fatty acid content. The reduced oil content of sorghum compared to maize is an advantage for some applications in food products, that is, extruded whole grains and some brewing operations where whole grains are used with industrial enzymes to produce lager beer without barley. Waxes form protective films on the surface of the leaves, stalks, and pericarp of the grain of sorghum. The surface of the pericarp contains up to 0.5% wax, which has properties and composition similar to carnauba wax. The low amount of wax

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limits commercialization, but the economics could improve as a by-product recovered from distillers grains during alcohol production.

Vitamins and Minerals The germ and aleurone are rich in fat-soluble and B vitamins. Sorghum contains 0.3–0.8 mg g1 a-tocopherols and 9–11.5 mg g1 t-tocopherols. Precursors of vitamin A (carotenes) are found in yellow and heteroyellow endosperm sorghums. Yellow endosperm sorghum caryopses contain 1.5–30 ppm of carotenoids: 36.3% zeaxanthin, 28.6% lutein, 24.7% xanthophyll, and 10.4% b-carotene. Weathering causes sorghum to lose 50% of its carotenoids. Sorghum is an important source of minerals that are located in the pericarp, aleurone layer, and germ. Phosphorus is the mineral found in greatest amounts; its availability is negatively related to the amount bound by phytates. Phytase activity during malting and fermentation significantly increases availability of phosphorus and other minerals as well.

Enzymes The sorghum aleurone layer is not a major source of endosperm-degrading enzymes. The scutellum of sorghum is where a-amylase is formed and diffuses into the endosperm. Sorghum does not respond to gibberellins to enhance production of amylases during malting. The a-amylase activity in sorghum starts 24–36 h after germination. A rapid increase in dextrinase activity is observed 24 h after germination. Limit dextrinases and proteases are found mainly in the endosperm, whereas carboxypeptidases are located primarily in the germ. Sorghum malt has high levels of a-amylase activities but it has reduced b-amylase activities.

Tannins and Phenols Condensed tannins (proanthocyanidins) are not present in all sorghums; however, all sorghums contain phenolic acids, and most contain flavonoids. Kernels that contain condensed tannins have a thick, highly pigmented testa. These sorghums were referred to as brown sorghums but are now classified as tannin sorghums. Tannins protect the kernel against preharvest germination and attack by insects, birds, and molds. Birds consume brown sorghums when other foods are unavailable. Animals fed with tannin sorghum rations eat more feed and produce about the same amount of gain, so feed efficiency is reduced. There are no toxicity problems, but feed efficiency is reduced by the condensed tannins. This situation is grossly misstated in the literature, because there have been numerous feeding trials reporting decreased feed efficiency with only a few instances of other problems. The condensed tannins have a high affinity for prolamin proteins and decrease feed efficiency by 5–15% depending upon the livestock species and processing of the rations. In some areas of Africa, special processes are used to prepare the tannin sorghums to improve their food properties. Tannin sorghums bind enzymes during brewing of sorghum beer and additional malt is required. The tannin sorghums are potent sources of antioxidants. Bran fractions and extracts from them have significantly higher

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Table 2 ORACa levels in sorghum brans and extracts relative to common fruits Sample

ORACa(DM basis)

Black sorghum bran Sumac sorghum bran Tannin sorghum bran Blueberries Strawberries Plums Grapes Watermelon Orange Extracts Sumac sorghum bran Grape skin Red wine concentrate Vitamin C ¼ reference

1008 3120 2400 87–873 356–400 452–600 100 15 80–152 11 200 6124 3200 5000

a

ORAC, oxygen radical absorbance capacity, is a measure of antioxidant potential measured in mmol TE g1, using fluorescein as a probe.

oxygen radical absorbance capacity (ORAC) levels, a measure of antioxidant strength, than most fruits and vegetables (Table 2). Bakery products containing this bran have increased fiber content, higher antioxidant potential, and attractive natural brown or chocolate color. Tannin sorghums can also be transformed into excellent whole grain snacks by extrusion. The extrusion process significantly reduces the degree of polymerization of tannins, which may be beneficial in human foods.

Uses of the Grain Food Uses The major categories of traditional foods are fermented and unfermented flat breads, fermented and unfermented thin and thick porridges, steamed and boiled products, snack foods, and alcoholic and nonalcoholic beverages (Figure 2). Worldwide, the most popular unfermented flat breads from sorghum are ‘roti’ in India and tortillas in Central America. For roti, a portion of the flour is gelatinized, mixed with more flour and warm water, and kneaded into a dough, which is shaped into a circle and baked on a hot griddle. For tortilla production, whole sorghum is lime-cooked, steeped overnight, washed, stone ground into ‘masa,’ shaped into thin circles, and baked on a hot griddle (Figure 2(d)). Sorghum and maize blends are often used in Salvador, Nicaragua, Guatemala, and Honduras. Food-type white sorghums (Figure 2(a)) lighten the color and decrease the off-flavors in many food products. The most popular fermented breads are ‘injera,’ ‘kisra,’ and ‘dosa,’ consumed in Ethiopia, Sudan, and India, respectively. About 80% of the Ethiopian sorghum is used for the production of injera (Figure 2(i)). The sorghum flour is mixed with water and a yeast starter from a previous batch of injera. After fermentation for 24–48 h, the batter is poured onto a greased pan for baking. The resulting product is a flexible, large diameter pancake-like bread containing uniformly distributed fish eyes (air bubbles). It is moist and retains its flexibility for 2–3 days. Dosa is consumed in India and is produced from a mixture of black gram, sorghum, and rice flour. It is used as a wrap for vegetables, sauces, and other foods.

Porridges are popular foods from sorghum (Figure 2(g)). The pH of porridges varies from acid, to neutral, to alkaline depending upon the region or country. ‘Toˆ’ is an unfermented stiff porridge cooked in alkali in Mali, cooked in acid in Burkina Faso, or fermented and cooked. Decorticated sorghum flour is cooked in water acidified with tamarind juice or water made alkaline with the leachate of wood ashes (potash). Popular fermented porridges are ‘ogi’ and ‘nasha,’ widely consumed in West and East Africa, respectively. Whole sorghum is soaked in water and allowed to ferment for 2–3 days. The wet grain is crushed in a slurry of water and sieved to remove the bran. The fine particles are allowed to ferment longer. Excess water is decanted and the resulting slurry cooked in water or milk to make thin or thick porridges. Porridges are consumed with sauces prepared from vegetables, fish or meat, grain legumes, amaranthus leaves, and other materials. For couscous production, sorghum flour is kneaded with enough water, 30%, to form agglomerates. The wet flour is forced through a coarse screen to form large particles, which are steamed. The cooked product is consumed with a sauce or milk. In some cases, the particles are dried after steaming and used as one of the true convenience foods in the Sahelian zone of Africa. Decorticated sorghums are often cooked like rice. Alcoholic beverages are produced from malted sorghum (Figure 2(h)). The high-solids beer is sour, alcoholic, pinkish, and effervescent. The fermentation time is short and the beer is drunk while actively fermenting. The beers vary from sweet to very sour; alcohol and solids contents vary. The most common type in southern Africa, called opaque beer, undergoes souring and yeast fermentation. Sorghum processing into food is a tedious, time-consuming chore done by the housewives several times per week. There are very few processed foods that meet the convenience, taste, flavor, and texture requirements of urban consumers. Grain obtained in the markets is mixed and usually contaminated with sand, trash, and damaged grains. In some areas, valueadded sorghum grain is processed into profitable products for sale in urban areas and local markets. The major challenge is to obtain a consistent supply of good-quality grain for processing. Sorghum grits, meal, and flour can be used alone or mixed with wheat flour to produce an array of baked goods (Figure 2(f)). Sorghum does not contain gluten. Thus, the amounts of sorghum flour in the blends depend on the quality of the wheat flour, baking procedure, formulation, and quality of the baked products desired. New food-type sorghums that produce excellent yields of flour with a bland flavor and light color are available. They can be used to extend wheat-based products without affecting flavor. Sorghum can be puffed, popped, shredded, and flaked to produce ready-to-eat breakfast cereals (Figure 2(b) and 2(c)). Extrusion of sorghum produces acceptable snacks (Figure 2(e)) and precooked products.

Milling For production of most traditional foods, the pericarp is removed by decortication, before it is milled into flour. To decorticate, the grain is usually washed, placed in a wooden mortar, and pounded vigorously with the wooden pestle. The abrasive action separates the pericarp from the kernel at the mesocarp. Grains with thick pericarp, hard endosperm, and spherical shape are preferred because they are easier to mill. A


(a)

(b)

(d)

(e)

(g)

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(c)

(f)

(h)

(i)

Figure 2 Traditional and processed foods prepared using sorghum. (a) White, food-type sorghum; (b) flakes after whole grain was tempered, steamed, rolled, and toasted; (c) air-popped sorghum; (d) tortillas after whole grain was nixtamalized, washed, ground, formed into disks, and baked; (e) collets, whole grain was extruded; (f) wheat bread containing 1.5% tannin sorghum; (g) stiff porridge from sorghum after dehulling, milling into flour, and cooking with water; (h) opaque beer prepared from sorghum and malted sorghum; (i) ‘injera’ prepared from sorghum after decortication, milling into flour, mixing with water, natural fermentation, preparation of a slurry, and baking on a griddle.

thin pericarp requires 1.5–2 times more time to decorticate. The bran (pericarp) is separated from the grain by washing with water or by winnowing the sun-dried grain. Most sorghums are decorticated to remove 10–30% of the original grain weight.

The decorticated kernels are reduced into flour by pounding in the mortar and pestle, with stone mills, or by electric or dieselpowered attrition mills. Flour is sieved to obtain fractions with an acceptable particle size for specific products.

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Commercial milling of sorghum is practiced in several countries. Sorghum is decorticated using mechanical decortication with rice-milling equipment or abrasive disks, followed by degermination and subsequent sieving. The decorticated material is then milled, gravity-separated, and sieved to produce low-fat grits, meal, and flour. In Botswana and South Africa, sorghum is milled using abrasive decorticators followed by grinding the grain using hammer mills or attrition mills. In India, sorghum is cleaned and milled using a stone mill followed by sifting to remove the bran, 1–3% of the original grain. The coarse flour is used for roti and related products. Milling of sorghum with wheat roller mills produces acceptable flour and other products. Small industrial-scale roller mills produced in South Africa are used extensively to process maize, sorghum, and millet into flour and meal. The yields are quite high and the flour has good characteristics. Also, large sophisticated mills based on degermination and gravity separation of the milling fractions exist and produce highly refined grits, meal, and flour. In many areas of Africa, large-scale milling of sorghum has failed because of poor infrastructure and inadequate supplies of food quality grain.

Malting Sorghum and Brewing Nonalcoholic beverages and extracts are produced from malted sorghum, which has replaced the malted barley extracts in Nigeria. Maltabella, Morvite, and a shelf stable opaque beer are popular products consumed in South Africa. Some companies produce ground sorghum malt for sale to consumers who prefer to produce traditional opaque beer for special festivals, weddings, and other occasions. In addition, powders containing pregelatinized maize grits, sorghum malt, and yeast allow consumers to produce beer by adding water and storing overnight.

Sorghum opaque beer In southern, eastern, and western Africa, sorghum malt is used for alcoholic and nonalcoholic beverages, weaning foods, and breakfast foods. Sour–opaque beers are produced commercially in southern Africa. Opaque beer is produced following the basic steps of the traditional process, which involves malting the sorghum, converting the cooked sorghum and maize grits into fermentable sugars, souring the mash, and finally fermenting the sugars into alcohol. The beer is packaged in vented cartons (Figure 2(h)) or transported to beer halls in stainless steel tanker trucks. The beer is drunk while actively fermenting. Opaque beer was the first large-scale, industrial process of sorghum in Africa. Industrial enzymes replace sorghum malt to convert the cooked, soured grits of maize or sorghum into fermentable sugars. The color of the beer has become lighter, due to a greater use of maize as adjunct, and consumption of opaque beer is decreasing because consumers prefer lager beer. Large commercial malting operations steep, germinate, and dry the malted sorghum for the breweries. Malting requires 4–5 days and 15–20% of the initial weight is lost in respiration, rootlets, and shoots. Sorghum malt is produced at 23–25 C during steeping and germination. Malting does not modify the cell walls of sorghum. Special varieties are grown for malting that produce malt with higher diastatic and other malt enzymes. Tannin sorghums are treated with formaldehyde and/or alkali to limit the effects of tannins on diastatic or malt enzymes.

Lager beer (clear beer) Breweries in Africa and Asia use sorghum grits as an adjunct in brewing lager beer. In Nigeria, sorghum and maize are used to produce lager (clear beer) without barley malt. Nigerian breweries produce clear beer from a combination of malted sorghum, ground whole or decorticated sorghum, and/or maize grits with commercial enzymes to convert the starch to fermentable sugars. The quality of clear beer is good; the taste differs from barley malt beer. The modern industrial brewing of beer in Nigeria uses ground whole sorghum treated with commercial enzymes followed by filtration to remove the solids and then fermentation into alcohol. Sorghum malting is a costly process in terms of time with dry-matter losses of 15% or more. The use of ground whole sorghum is a recent innovation, which requires a more efficient filtration procedure. Sorghum is preferred over maize since it has reduced oil content, a thin pericarp, and bland flavor.

Industrial Uses Sweet sorghums contain 20–30% sugar in the juice that is crushed from the stalks, clarified, and concentrated into an amber sorghum syrup (molasses) that is a popular product in the southern United States. It has a strong flavor and is sometimes blended with cane syrup. Sorghum grain and/or sweet sorghum biomass is used for ethanol production. Yields of 182-proof alcohol (387 l t1) from sorghum grain are comparable with maize (372 l t1). The commercial technology to ferment sweet sorghum biomass into alcohol has developed in Brazil. Sorghum grain is a good substrate for industrial and beverage alcohol where it competes with maize and other sources of starch. Several alcohol plants in the United States, India, and other countries use sorghum as an adjunct for alcohol production depending upon availability and cost. In China, a distilled alcoholic beverage from ‘kaoliang’ (sorghum) is exported. It has a unique flavor and aroma and is high in alcohol content. Sorghum flour is used in adhesives, building board, ore refining, and metal casting as an inexpensive source of starch. The sorghum is dry-milled to remove the pericarp and sometimes converted into acid-modified dextrins. Binders that strengthen the durability of pellets for livestock feed are made from sorghum. Sorghum is wet-milled to produce starch in Sudan and India. Sorghum starch has properties similar to maize starch. Commercial wet milling of sorghum in the United States was discontinued in the 1970s due to poor economics.

Nutritional Value Sorghum has proximate composition, amino acid contents, and nutritional value similar to that of maize. However, due to its lower fat content, sorghum usually has a slightly lower gross, digestible, and metabolizable energy. Lysine and threonine are the first and second limiting amino acids. The tryptophan content is higher than that in maize. High-lysine cultivars contain 50% more lysine and promote better weight gains in weaning rats. Fermentation, malting, and other processing methods significantly improve its nutritional value. Proteins in sorghums are 76–82% digestible. This is 5% less digestible than proteins from maize and other cereals as

NON-WHEAT FOODS | Sorghum: Utilization determined by in vivo studies using swine, poultry, and cattle. Proteins in sorghum were reported to be 20–50% less digestible than maize by the in vitro pepsin digestion test. This is based on the reduced digestibility seen when the sorghum was cooked as a gruel without stirring and fed to proteinmalnourished, ill children. Extrusion cooking of sorghum eliminated the reduced protein digestibility in these children. Over the centuries, millions of Africans and Indians have been nourished by sorghum foods. Proper processing of sorghum yields foods with high digestibility and nutrient values.

Livestock Feeds Sorghum is an excellent feed for livestock and companion animals. The feeding value of sorghum for livestock species is generally considered 95% or more of the feeding value of yellow dent maize. Tannin sorghums have 85–95% the feeding value of maize. Sorghum use can result in savings because it is often less expensive than other grains, even when more grain has to be fed. Sorghum must be properly processed to enhance its digestibility. Sorghum can be dry-rolled, steam-rolled, cooked with steam, and flaked into thin flakes; micronized and flaked, roasted, ground, and tempered with water up to 30%; stored under aerobic conditions; or ground or rolled. The two most widely used processes are grinding and steam flaking. Sorghum is hammer-milled or attrition-milled into meal and coarse particles. Steam flaking is used in large feedlots where grain is a major part of the rations. Grinding, steam flaking, micronizing, reconstitution, and popping are used to prepare sorghum grain in beef cattle feedlot rations. Grinding, rolling, crushing, and pelleting are used for poultry and swine feeds. Dairy cattle utilize steamflaked or roasted sorghum grain efficiently, and protein content of the milk is enhanced. The light color and bland flavor of the white-food sorghums are advantages, when color is important in pet or companion animal feeds.

Future Prospects Sorghum will for many centuries continue to be utilized as food, feed, and industrial products. This will be driven by sorghum’s robust agronomic characteristics and good nutritive, processing, and organoleptic properties. Development of reasonably priced, convenience foods containing sorghum will increase the demand for food sorghums. An example of a niche market for sorghum is as a nutraceutical ingredient containing antioxidants. However, decreasing consumer preference for sorghum-based foods and beverages is likely to continue for those who have increased purchasing ability.

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What are the primary food uses of Sorghum in Africa and India? How and why is sorghum processed before inclusion in animal feeds?

Exercises for Readers to Explore Further

• • •

Discover the basis for and solutions to the loss of sorghum protein digestibility due to cooking. Expand the use of naturally occurring antioxidants present in sorghum as food additives. Continue to develop and to expand sorghum based formulations as foods for sufferers of Celiac Disease.

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Barley, Rice and Maize Processing: Oil from Rice and Maize; Beverages from Grains: Fermentation: Foods and Nonalcoholic Beverages; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Non-wheat Foods: Maize: Foods from Maize; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure.

Further Reading Chung KT, Wong TY, Wei CI, Huang YW, and Lin Y (1998) Tannins and human health: A review. Critical Reviews in Food Science and Nutrition 38: 421–464. Earp CF, McDonough CM, and Rooney LW (2004) Microscopy of pericarp development in the caryopsis of Sorghum bicolor (L.) Moench. Original Research Article. Journal of Cereal Science 39(1): 21–27. Moyer RA, Humer KE, Finn CE, Frei B, and Wrolstad RE (2002) Anthocyanins, phenolics, and antioxidant capacity in diverse small fruits: Vaccinium, rubus, and ribes. Journal of Agricultural and Food Chemistry 50(3): 519–525. Rooney LW and Serna-Saldivar SO (2000) Sorghum. In: Kulp K and Ponte J (eds.) Handbook of Cereal Science and Technology, 2nd edn., pp. 149–175. New York: Marcel Dekker. Rooney LW and Waniska RD (2001) Sorghum food and industrial utilization. In: Smith WC and Frederiksen RA (eds.) Sorghum: Origin, History, Technology and Production, pp. 689–725. New York: Wiley. Serna-Saldivar SO and Rooney LW (1995) Structure and chemistry of sorghum and millets. In: Dendy D (ed.) Sorghum and Millets: Chemistry and Technology, pp. 69–124. St. Paul, MN: American Association of Cereal Chemists. Stoskofp NC (1985) Cereal Grain Crops. Reston, VA: Reston Publishing Co. Taylor JRN, Dewar J, Taylor J, and von Ascheraden RF (1997) Factors affecting the porridge-making quality of South African sorghums. Journal of the Science of Food and Agriculture 73(4): 464–470. Waniska RD and Rooney LW (2001) Structure and chemistry of the sorghum caryopsis. In: Smith CW and Frederiksen RA (eds.) Sorghum: Origin, History, Technology and Production, pp. 649–688. New York: Wiley. Waniska RD and Rooney LW (2002) Sorghum grain quality for increased utilization. In: Leslie JF (ed.) Sorghum and Millet Diseases, pp. 327–335. Ames, IA: Iowa State University Press. Weaver CA, Hamaker BR, and Axtell JD (1998) Discovery of grain sorghum germplasm with high uncooked and cooked in vitro protein digestibilities. Cereal Chemistry 75: 665–670.


• • •

How do genetics control the color of the sorghum kernel? How do genetics control the structure and composition of the testa layer? Compare sorghum storage protein digestibility with that of Maize storage proteins.

Relevant Websites http://apps.fao.org – FAO (2003) FAOSTAT Database Data website gives details of yearly production database. http://www.usda.gov – Federal Grain Inspection Service website provides documentation to procedures and policies used to inspect grains.

Soybean: Soy-Based Fermented Foods DK O’Toole, City University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 174–185, ã 2004, Elsevier Ltd.

Topic Highlights

Fermented Whole Bean Products

•

The gross composition of some fermented soybean products is shown in Table 1.

• • •

Characteristics of whole bean, fermented bean paste, and soy milk products. Manufacturing processes and conditions to produce fermented soy products. Okara fermentation for food and nonfood uses. Health benefits of fermented soybean products.

Learning Objectives

• • •

To understand the characteristics of, compositions of, and manufacturing processes for fermented soybean foods To understand the microorganisms responsible for those fermentations. To understand the health benefits conferred by fermented soybean products.

Introduction Unlike other grains, soybeans do not contain large quantities of starch, but they do contain large amounts of good quality protein and oil. However, the protein is not easily digested, and so, it must be made nutritionally available by the first step of soaking and cooking the beans. This step makes the protein more digestible and destroys the antinutritional characteristics of the soybeans. The oil plays little or no part in soybean fermentations. In most food fermentations, easily available mono- and disaccharides, either as the sugars or as breakdown products from starch, are a prerequisite for the fermentation to proceed. In the case of soybean, the amount of carbohydrate is 30% in the dry matter, and about a third of it is soluble. The soluble component consists of sucrose ( 5%), raffinose ( 1%), and stachyose ( 4%); the insoluble carbohydrate ( 2% of the dry matter) is made up of starch (<1%), cellulose ( 4%), hemicellulose ( 1%), and pectin ( 6%). In view of this composition, soybean fermentations are sometimes augmented with small or large quantities of starch from other grains, because it promotes microbial growth. By far, the most important microorganisms for soybean fermentation are the filamentous fungi, rather than bacteria or yeasts. The fungi produce a range of powerful enzymes capable of hydrolyzing protein, starch, and complex carbohydrates, and, despite low starch levels, acid-producing and proteolytic bacteria, as well as yeasts, often play a significant role.

124

Tempeh ‘Tempeh’ is a fermented soybean product and meat substitute that originated in Indonesia. It is probably the first ‘fast food’ in that it can be deep-fried in 3–4 min or cooked in 10 min. The production of tempeh is outlined in Figure 1. In the first step, the soybeans are soaked in water or acidified water at room temperature. During this stage, a partial germination of the soybeans may occur depending on the amount of O2 available to the seed, and acid is produced by bacteria growing in the soak water. Depending on the temperature during soaking, bacteria reach 108–1010 colony-forming units per ml after 24–36 h. The pH drops from 6.5 to 4.5 due to the growth of the acid-producing bacterial species – for example, Lactobacillus casei, Streptococcus faecium, Staphylococcus epidermidis, and Klebsiella pneumoniae – that are present naturally on the soybeans. The acid helps to prevent the growth of undesirable microorganisms, but any partial seed germination can affect the protein properties of the soybean and the subsequent fungal growth phase. The bacteria that grow in the steeping water produce vitamin B12, a significant nutrient in tempeh. The most desirable bacterial species for this stage is K. pneumoniae, but other pure bacterial starter cultures can perform the same function. The soaked beans are dehulled and carefully cooked to avoid overcooking or undercooking of the beans. The soybeans are then drained, cooled below 35 C, and dusted with wheat flour to provide a good source of fermentable carbohydrate, and inoculated. The desirable fungal species for successful tempeh production, whether arising from environmental inoculation or from pure starter inoculation, are Rhizopus oligosporus (e.g., NRRL 2710), R. stolonifer, R. arrhizus, R. oryzae, R. formosaensis, and R. achlamydosporus. The spores of R. oligosporus are produced commercially in Indonesia for industrial-scale tempeh production. During the fungal growth phase, the O2 level must be controlled at a reduced level; otherwise, the fungus will grow too quickly and form black spore masses that degrade the quality of the tempeh. The traditional way to control O2 is to wrap the inoculated beans in banana leaves, but a modern innovation is the use of microperforated polyethylene plastic. The fungus grows and mycelia knit the beans into a firm cake to give the characteristic meaty texture. The enzymes from the fungi transform the soybeans making them more nutritious by hydrolyzing the protein and complex carbohydrates and increasing the levels of the


http://dx.doi.org/10.1016/B978-0-12-394437-5.00129-7

NON-WHEAT FOODS | Soybean: Soy-Based Fermented Foods Table 1

125

The gross composition, g kg1, of some fermented soybean products

Fermented soy product

Moisture

Protein

Fat

Soluble carbohydrate

Fiber

Ash

Sufu (red) Sufu (white) Natto¯ Soybean miso Chianga (chunky) Tempeh

555 565 585 475 486 640

146 144 165 168 116 183

57 112 100 69 52 40

58 48 101 136 272 110

6 7 23 23 21 17

171 124 26 130 74 10

a

The equivalent to Japanese miso. Source: Liu TS (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman and Hall.

Soybeans Purpose

Action Soak in water

Cooks protein, allows acid and vitamin production by bacteria; acid may be added to water

Remove seedcoat Drain and cook Drain and cool Tempeh fungi

Inoculation occurs and incubation under restricted O2 conditions

Wrap in leaves or pack in perforated plastic bag Incubate at 30–38 °C, 20–24 h Tempeh

Figure 1 A flow diagram of the production of tempeh, an Indonesian fermented soybean product. The fungal mycelia knit the soybeans into a cake.

vitamins – riboflavin, niacin, pantothenic acid, and vitamin B6. Tempeh must be consumed fairly quickly. Defects include (1) black patches due to fungal sporulation, (2) slime due to excessive bacterial growth because of too little O2 or a temperature of 42 C, and (3) a yellow color due to growth of toxic fungi. The yellow color indicates that the tempeh is highly toxic and it should not be eaten.

Natto¯ This is produced in Japan, Korea (‘chung kook jang’), and Thailand (‘thua nao’), but not in China. Traditionally, the beans are soaked, boiled, and cooled and wrapped in rice straw and left for 1–2 days at a warm temperature to allow bacteria to grow on the beans and produce a sticky slime. The straw imparts a straw aroma to the fermented beans, as well as being the source of the bacteria for the fermentation, and it absorbs some of the unpleasant aroma of ammonia released during the bacterial growth.

In modern manufacture, bacterial cultures of an obligate aerobe Bacillus subtilis var. natto are used, and the incubation temperature is kept at 38 C for 20 h, followed by cooling (Figure 2). During growth, the bacteria produce a viscous, sticky slime that pulls out into long strings when the soybeans are pulled apart. The viscous substance increases to 2% of the ‘natto¯’ after 48 h and its crude protein content is 80%, of which 20% is the D-isomer of g-polyglutamic acid and the remainder is mostly free amino acids. The bacterial fermentation results in a high concentration of vitamin K2 (menaquinone-7), 100 times more than found in cheese. The fermentation also reduces the ‘beany’ flavor and aroma of soybeans and increases the level of alkyl pyrazines that are responsible for the characteristic odor of natto¯. The amount of volatile compounds rises from 35 mg kg1 wet weight in cooked soybeans to 2–3.5 mg kg1 wet weight in 72 h. Predominant volatile compounds in Japanese natto¯ are 3-hydroxybutanone (acetoin), 2,5dimethylpyrazine, trimethylpyrazine, and tetramethylpyrazine.

Salted Black Beans or Soy Nuggets This product is made in China (‘douchi’), Japan (‘hamanatto’), the Philippines (‘tao-si’), and India (‘tao-tio’). Whole soybeans are soaked and cooked as usual. Under natural conditions, fungi/bacteria grow depending on the ambient temperature, but under controlled conditions, an inoculum of Aspergillus oryzae is used. The Chinese incubate beans for 3–20 days, then wash them to remove fungal spores, mycelium, mold odor, and bitter taste, then mix them with brine (or soy sauce) and spices, which can vary widely (e.g., Indians add sugar), and ferment them in a jar for several months. They are then dried. The Japanese use a soybean-to-wheat flour ratio of 2:1 and incubate them for 50 h. They do not wash the beans but sun-dry them immediately and then place them in brine under pressure for weeks to months. They are then redried and soy sauce and pickled ginger may be added at the final stage.

Soy Milk-Based Products Fermented Tofu The general name for these products is ‘sufu,’ which means ‘molded milk’ in Chinese, and in hieroglyphics, it is known as ‘furu,’ which is its preferred Chinese name. Soy milk is extracted and coagulated to make a curd (‘tofu’) that is then

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NON-WHEAT FOODS | Soybean: Soy-Based Fermented Foods

Soybeans

Whole small seeded soybeans

Soaking and grinding Clean & soak overnight

Filtration

Residue (okara)

Soymilk 70–80 °C Autoclave at 130 °C for 32 min

Calcium salt

Coagulation Soy whey

Pressing Tofu

Cool to 38 °C & inoculate with Bacillus subtilis var. natto

Incubate for 20 h & cool to 5 °C for 24 h to mature

Fresh natto Figure 2 A flow diagram showing how natto¯ is produced. Adapted from Liu K-S (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman and Hall.

Dice, cool Straw mats or mold spore suspension, Actinomucor elegans or Mucor taiwanensis

Inoculation Solid-substrate fermentation Pehtze (Pizi)

Saturated salt solution

Dry salt

Solution of 12% salt + 10% alcohol

Dressing mixture

Dressing mixture

Maturation, ripening

cut into rectangular pieces on which mold is allowed to grow. Mold enzymes hydrolyze the protein, making it more digestible, and the soy oil, producing strong flavors. Tofu was invented by Liu An in 179–122 BC and the first production record dates from the Wei Dynasty in AD 220–265, but the origins of ‘sufu’ are not known. Sufu production in China, domestically and in factories, is 300 000 tonnes per annum. The sufu making process is as follows (Figure 3): Soybeans of suitable quality are processed in the usual way to produce soy milk. The coagulation step involves the addition to soy milk at 70–80 C (in a suitable container) of calcium sulfate or magnesium sulfate at a rate equal to 2.5–3.5% of the dry weight of the soybeans used to produce the milk, which is 20% more than used to produce regular tofu. After briefly stirring the mixture vigorously, it is left quiescent for the coagulum to form in 10–15 min. The curd is then pressed mechanically to remove excess water (soy whey) and cut into rectangular blocks 32 32 16 mm. Moisture content and pH vary between 70% and 79% and 6 and 7, respectively.

Mold stage The next stage, the ‘pehtze’ (pizi) or mold stage, is akin to the ‘koji’ stage in soy sauce and ‘miso’ production. Traditionally, the spores came from straw mats and contaminated the surface, but in modern production methods, spores of a selected pure fungal culture, first isolated and identified in 1920, are applied to the surface of the cubes, followed by incubation. Using pure mold cultures, production time is reduced from 5 to 15 days to 48 h. Preferred mold cultures include Actinomucor elegans and A. taiwanensis used in Beijing and Taiwan, respectively, but Mucor sufu and M. wutungkiao also have

Sufu Figure 3 A flow diagram of the production of sufu, a kind of fermented tofu block. It depends on the growth of fungi on the surface of the tofu blocks to help in the production of flavors. Salting and dressing mixtures favor the development of flavors and introduce flavors to the final product.

desirable characteristics. The mold for the production of the best quality pehtze must have the following: 1. A high proteolytic and lipolytic activity 2. White appearance or at most a slight yellow color that is attractive to consumers 3. The ability to produce a mycelial mat over the tofu surface with a texture that is dense and tenacious and able to retain the tofu block shape during subsequent processes 4. The ability to prevent unwanted bacterial growth and the inability to produce off-odor, astringent taste, and mycotoxins Ideally, temperature and relative humidity should be controlled for pehtze production, because Actinomucor and Mucor species only grow well in the 20–30 C range. The fungal starter culture, as a spore suspension containing 105 colonyforming units per ml, is prepared either by solid-state or by liquid culture in roux bottles. The solid-state culturing medium is bran and water (1:1.3 or thereabouts), and the liquid culture medium is soy whey with added maltose (2–3%) and peptone (1.5–2.0%). The tofu blocks are sprayed with the inoculum and placed on wooden or bamboo strips in plastic trays and transferred to

NON-WHEAT FOODS | Soybean: Soy-Based Fermented Foods an incubation room at 25 C with a relative humidity of 88–97%. Within 8–12 h, a thin layer of mycelia is obvious, and by 36–40 h, it is thick. The temperature is then reduced by aeration of the room and the pehtze observed regularly until a slight yellowish-white color appears. The total incubation time is 48 h, but glutaminase activity that results in glutamic acid production and increased monosodium glutamate (MSG) levels is greatest within 3 days. In the final stage of pehtze production, the mold is flattened by hand.

Salting stage Salting does five things: it imparts a salty taste to the sufu, it prevents the growth of undesirable organisms, it stops the growth of the mold, it releases the proteolytic enzymes bound to the mold mycelia so they can penetrate into the tofu to transform it, and it removes some water from the tofu blocks. Salting can be by dry salting or brine salting. Dry salting takes longer and does not result in a consistent product. The layers of blocks are spread with dry salt and then stored for 6–12 days, during which the salt content of the blocks rises to 16%. The blocks are then removed, washed with water, and transferred to another container for further ripening. Brining is done with a saturated salt solution or an alcoholic brine solution in which the blocks are immersed for 4–5 days, resulting in final moisture levels of 50–65% with 12% salt. The alcoholic brine combines the salting and aging or ripening steps. The ethanol has two effects: First, during ripening, lipolytic enzymes release free fatty acids that combine with ethanol to produce aromatic esters and, second, it seems to interfere with protein degradation when compared with salted sufu so that the sufu does not degrade as much. The final ripening stage of dry-salted pehtze is conducted in various dressing mixtures that result in a range of different sufu products. The salted pehtze is placed in the dressing mixture in jars or bottles ranging in size from 0.25 to 10 l. For red sufu, the dressing preparation commonly used is a mixture of 2% ‘angkak,’ 3–5% of a paste made with flour or soybean, 8–12% of alcohol, and 5–10% of spices. Further flavor variation is obtained by adding flavors such as rose essence for rose sufu or hot pepper to make hot sufu. Traditional ripening periods extend up to 6 months, but modern methods require only 2–3 months. Reducing the size of the tofu cubes, lowering the salt content from 14% to 10%, lowering the alcohol content from 10% to 6%, keeping the ripening temperature higher and constant, and reducing the storage jar size can further reduce the ripening period. The higher salt concentrations are thought to reduce rates of proteolysis and lipolysis, but reduced salt content shortens the shelf life.

Types of sufu Types vary widely throughout China, but four types are distinguished based on the fermentation methods used and four types based on the color and flavor of the product. The four fermentation types are given as follows: 1. Mold-fermented sufu: Use of pure mold culture, brine salting, and aging in a dressing mixture. 2. Naturally fermented sufu: Use of environmental fungi in straw mats and the subsequent process is the same as for (1).

127

3. Bacteria-fermented sufu: The tofu is prepared and presalted, and a pure bacterial culture is used followed by further salting and aging. 4. Enzymatically ripened sufu: Use of mold-based koji (see section ‘Soy Sauce’) at the dressing stage. From the dressing stage, four color and flavor types of sufu are recognized; they are given as follows: 1. Red sufu: Sufu blocks are red to purple outside and yellow to orange inside due to the angkak (‘anka,’ red kojic rice, or red ‘qu’) prepared with the fungus Monascus purpureus that also imparts a specific flavor to the sufu. 2. White sufu: Sufu blocks are light yellow throughout, and manufacture is similar to red sufu but without angkak and with a slightly reduced salt content. 3. Gray sufu: It has a strong pungent odor basically of unknown origin. It is probably derived from the use of a dressing mixture that includes soy whey from the soy milk manufacturing step and salt and spices. 4. Other sufu: Sufu blocks are flavored with a variety of additives including vegetables, rice, bacon, and higher concentrations of alcohol. Sufu may be further classified by size and shape.

Soy Milk Yogurt This is a modern product intended to imitate yogurt, but the beany flavor due to natural n-hexanal and pentanal, and stachyose and raffinose, which cause human flatulence, detracts from the product. Trials with the usual yogurt cultures did not produce good results unless lactose or sucrose was added. However, Bifidobacterium bifidum can metabolize the sugars and the bean flavor substances to produce a satisfactory product thought to be beneficial to human health.

Fermented Soybean Pastes Soy Sauce Soy sauce is an ancient Chinese product whose precursor was mentioned 3100 years ago in the Chinese literature. It was introduced to Japan in AD 552 and has also spread to other East Asian countries (Table 2). Soy sauce was derived from a Chinese food called ‘chiang yu’ that was basically a mash made by growing yellow aspergilli on millet; then mixing the molded grain and salt in an alcoholic liquor with added pieces of animal, poultry, or fish flesh; and storing it for 100 days. (A similar product using soybeans is still made today in China.) A liquid extract from this type of product was first mentioned in the Han dynasty (AD 25–220), and the first mention of the use of soybeans in this kind of mash dates from AD 535. However, it is the Japanese who have established the scientific basis for modern soy sauce production and they call it ‘shoyu.’ In AD 2000, 1800 manufacturers in Japan produced 1.046 million kiloliters of soy sauce, of which 51% was produced by six manufacturers. The best quality soy sauces are naturally brewed, but in practice, some commercial soy sauces may contain added vegetable protein extract prepared by chemical or enzymatic

128


Table 2

The general compositiona of some soy sauces from various parts of the world

Product

Be´

NaCl

TN

RS (IS)

Alcohol

Color

Koikuchi shoyu, Japan Soy sauce, Taiwan Soy sauce, Korea Soy sauce, Hong Kong Soy sauce, the Philippines Soy sauce, Singapore Soy sauce, Malaysia Kecap asin, Indonesia Kecap manis, Indonesia Soy sauce, the United States

23.6 25.6 21.9 28.5 23.3 30.1 23.9

170 156 173 262 247 241 183 72 59 16.5

17 20.5 15 15.4 7.6 19.7 11.7 1.9 1.9 1.65

50.7 59.5 21 42.2 10.6 48.1 85 144.5 111 (581) 37

25 8.6 3.9 0 0.1 0 0.3 0.2 0.9 20.7

þþ þþ þþ þþþ þþ þþþ þþþ þþ þþþ þþ

22.8

Be´ ¼ specific gravity, degrees Baume´; NaCl ¼ sodium chloride (g l1); TN ¼ total nitrogen (g l1); RS (IS) ¼ reducing sugar (invert sugar) (g l1); alcohol ¼ ethanol (ml l1). Source: Yokotsuka T and Sasaki M (1998) Fermented protein foods in the Orient: Shoyu and miso in Japan. In: Wood BJB (ed.) Microbiology of Fermented Foods, 2nd edn., vol. 2, pp. 351–415. London: Elsevier Applied Science.

a

Table 3

Typical percentage composition of the five types of soy sauce recognized in Japan

Soy sauce (shoyu)

NaCl (w/v)

Total nitrogen (w/v)

Formol nitrogen (w/v)

Reducing sugar (w/v)

Alcohol (v/v)

Koikuchi

16.9

1.57

0.94

3

2.3

Usukuchi

18.9

1.19

0.8

4.2

2.1

Tamari

19

2.55

1.05

5.3

0.1

Saishikomi

18.6

2.39

1.11

7.5

Trace

Shiro

19

0.5

0.24

20.2

Trace

Color Deep brown Light brown Dark brown Dark brown Yellow/ tan

Soybean-towheat ratio 1:1

Comment Most popular in Japan, 83% of market

More wheat 10:1

Main Chinese type

1:1

Raw shoyu, not fresh brine, is used

Very high wheat

Specific gravity is from 22 to 29 Baume´; pH is from 4.6 to 4.8. Source: Fukushima D (1989) Industrialization of fermented soy sauce production centering around Japan. In: Steinkraus KH (ed.) Industrialization of Indigenous Fermented Foods, pp. 1–88. New York: Marcel Dekker.

hydrolysis. Briefly, production involves an initial solid-state mold growth phase, followed by steeping in brine solution. Soy sauce is the liquid extract from the aged mixture. The varieties of soy sauces on the market owe their differences to the countries of origin where different processing conditions are used and to the addition of wheat, a source of starch that promotes fungal growth and the production of mold enzymes. The soybean-to-wheat ratios used vary from 1:0 to 1:3. In Japan, there are five main types of shoyu – ‘koikuchi,’ ‘usukuchi,’ ‘tamari,’ ‘saishikomi,’ and ‘shiro’ – based on the soybean-to-wheat ratios and other factors (Table 3). Koikuchi is the most popular in Japan, and the main Chinese type of soy sauce is similar to tamari, but soybean-to-wheat ratios of 2:1 and 1:1 are also common in China. Indonesians have two basic kinds of soy sauce – ‘kecap asin’ and ‘kecap manis’ – and they add sugar to the latter. Koikuchi has an alcohol content of 0.3% because it stabilizes the quality and adds flavor to shoyu, but ethanol is not a significant constituent in soy sauces from other parts of Asia. However, in taste tests, Koreans also favor 3% ethanol in their ‘kanjang.’

Raw materials and their preparation The first stage in koikuchi soy sauce production is the choice of raw materials (soybeans and wheat) and their preparation (Figure 4). The traditional choice is whole beans and whole wheat grains and the beans are cooked and the wheat roasted and cracked. However, the oil content of the beans is insignificant in soy sauce, so in modern production systems, defatted beans are used, as well as wheat flour. Wheat bran is sometimes preferred, because it is a source of ferulic acid, a precursor for 4ethylguaiacol and a desirable flavor component. Also, the pentose in wheat bran enhances darker coloration and color stability but reduces the alcohol content. Best quality soy sauces contain high soluble nitrogen levels, so one of the objectives of production is to maximize the extraction of the bean protein, which is achieved by using heating at far higher temperatures and for much shorter times than in the traditional boiling methods. Following the preparation of the raw materials and cooling them, they are mixed and inoculated with fungi to make the koji. The most desirable fungi are strains of either A. oryzae or A. sojae.


Soybeans 40 kg, soaked in water

or

Defatted soybean, 33 kg + 42 I of hot water

129

Koji mold starter, 0.1–0.2% w/w of raw materials

Wheat 34 kg, roast & crush

Autoclave Mixing mold culture (koji making) Salt 28 kg Water 120 I Temperature control, 15 °C ® 30 °C, slight aeration

48–72 h Mixing (mash making) Fermentation tank

Enzymatic degradation of materials; lactic acid & yeast fermentations; up to 6 months

Aging Pressing

Raw shoyu, 150–160 I

Soy cake 22 kg, about 30% moisture

Pasteurization Sediment Bottling

Refined shoyu, pH 4.7–4.9

Figure 4 A flow diagram of the production of koikuchi shoyu, the most popular type of soy sauce in Japan. The product is a salty extract of the soybean-to-wheat mixture modified by mold growth through the mixture, followed by yeast and bacterial growth in the brine that result in distinctive soy sauce flavors. Adapted from Yokotsuka T and Sasaki M (1998) Fermented protein foods in the Orient: Shoyu and miso in Japan. In: Wood BJB (ed.) Microbiology of Fermented Foods, 2nd edn., vol. 2, pp. 351–415. London: Elsevier Applied Science.

Koji production The ‘tane’ koji, or starter culture for the koji, is prepared by growing the molds through to the sporulation stage on steamed polished rice or wheat bran. Then, 0.1–1.0% w/ w is mixed with the cooked soybean/wheat mixture. In traditional koji production, the inoculated soybean/wheat mixture is placed in a shallow layer ( 3–5 cm) in trays in a koji room and incubated for 2–3 days for mold growth. The fungi require oxygen to grow and produce heat that must be dissipated (Figure 5), but in modern production systems, special koji rooms or machines are used, and conditioned air is mechanically driven through the inoculated layer of soybean/wheat mixture. The fungi produce amylase in the temperature range of 35–40 C, but excessive amylase production results in sticky koji, so the koji must be cooled by mixing at around 18 and 27 h of incubation. Good ventilation is important; however, overcooling can be detrimental. The fungal growth slows at 36 h, and during the last stage, the important proteases begin accumulating below 35 C. The process is stopped before fungal spore formation by gathering up and placing the prepared koji in a brine solution for the long steeping stage. The production processes and names of the processing stages differ from country to country (Table 4). In Korea, during traditional manufacture, instead of koji, a ‘meju’ cake is made. Soybeans are steeped for 24 h, dehulled, steamed for 2 h and cooled to 50 C, and then crushed to a size of 10–15 mesh, and the natural environmental mold is allowed to grow. The molded soybean cakes are dried for 2 days in air and then hung up with rice straw for a further 20–30 days to ferment in a koji room. The cakes are then broken into 12

pieces before immersion in brine. In Indonesia, the koji is sun-dried before steeping.

Moromi stage In the steeping stage, the brine solution is made up with water low in iron and copper, adjusted to pH 6.5–7.0, and cooled to 0 C. A complex enzymatic and fermentation process begins that is controlled by managing the temperature and the addition of air and pure cultures. The high sodium chloride concentration kills the fungi and other incidental salt-sensitive bacteria and yeasts in the koji. The fungal enzymes continue to break down the starch and proteins and cellulose, hemicellulose, and pectin in the soybeans (Figure 6). The objective during this stage is to maximize flavor production, the release of proteins by hydrolysis of cell structural components by macerating enzymes (hemicellulase, pectinase, etc.), and protein hydrolysis. About 300 compounds contribute to flavor, which depends on the sauce pH range being 4–5, but the important ones are glutamic acid (MSG) and ethanol, the characteristic soy sauce compound 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone, 4-ethylguaiacol, and 4ethylphenol. Glutamic acid is produced early by the fungal enzymes and is maximized by retarding the growth of the lactic acid bacterium Tetragenococcus halophilus by keeping the temperature of the moromi low at 15 C for the first few weeks. The ethanol production depends on the growth of a yeast, Zygosaccharomyces rouxii, but the yeast will only grow after the pH of the mixture has been reduced to < pH 5.0 by bacterial growth. To maximize ethanol production, the moromi temperature is raised to 30 C, below which ethanol production

130


First stirring about 38 °C

40

Second stirring about 33 °C 29 °C

Temperature (°C)

35 °C 30

Prepared koji moved to brine stage

25 °C 25 °C

25 °C

20 Room humidity is saturated

Room humidity is unsaturated

10

temp. of koji mixture temp. of koji room

0

9

18

27 36 45 54 Time course of incubation (h)

63

72

Figure 5 The production of koji is an aerobic process that depends on the growth of fungi. This illustrates what happens in a traditional process. The soybean-to-wheat mixture is inoculated and spread in a layer 5 cm deep. The tray is then put in a controlled atmosphere room, and as the fungus grows, it produces heat. This heat must be dissipated to reduce temperature, so the layer is mixed twice, as indicated. The koji is harvested before the mold starts to sporulate when enzyme production is optimum. Adapted from Fukushima D (1989) Industrialization of fermented soy sauce production centering around Japan. In: Steinkraus KH (ed.) Industrialization of Indigenous Fermented Foods, pp. 1–88. New York: Marcel Dekker.

Table 4

The names by which the various stages of the soy sauce production system are known in some East Asian countries

Country

Solid-state fermentation stage

Steeping stage

Final product

Japan Korea Indonesia China The Philippines Thailand

Koji Meju Bungkil Chou

Moromi

Shoyu Kanjang Kecap Chiang yu Toyo See-ieu

Baceman

Protein

Structural carbohydrates

Alkaline Pectin proteinases transeliminase Semialkaline Hemicellulase proteinases Cellulase Neutral Xylanases proteinases Endo-polyAcid galacturonidase proteinases Peptides Acid carboxypeptidase Leucine aminopeptidase

Starch

Amylase Glucoamylase

Glucose

Pentoses, hexoses, phenolic acids

Glutamine Glutaminase

Amino acids Glutamic acid

Figure 6 The fungal enzymes in the koji act on the three main components in the soybean-to-wheat mixture: the proteins, the structural carbohydrates, and starch. The amino acids and glutamic acid are important flavor and nutritive components; the pentoses, hexoses, and phenolic acids are important precursors for flavor compounds; the breakdown of the structural components eases the filtration of mash at the end of aging; the glucose is an important precursor for acids, ethanol, and other flavoring compounds.

NON-WHEAT FOODS | Soybean: Soy-Based Fermented Foods is almost nonexistent. Later, other yeasts, Candida versatilis and C. etchellsii, grow and produce the other characteristic compounds, 4-ethylguaiacol and 4-ethylphenol, from ferulic and p-coumaric acids. All the yeasts are obligate aerobes; so to encourage their growth, the moromi is stirred occasionally by pumping air to incorporate oxygen. The moromi maturation time in Japan is from 6 to 8 months. At the end of 2–3 months, most of the fermentable carbohydrate has been converted to lactate (1% w/v), ethanol (2–3% v/v), and simple sugars (e.g., glucose and xylose). The length of the moromi stage in other countries varies. In Indonesia, it may be from 1 day to 5 months; in Korea, the traditional incubation period is 2 months. In China, one method used involves a defatted soybean meal-to-wheat bran mixture at a 6:4 ratio that is incubated for 24 h for koji production, followed by 3 weeks at a moromi temperature of 40–45 C. Finally, the solid and liquid components are separated, by either drawing off the liquid or drawing off and pressing the residue. In some parts of China, the raw soy sauce is drawn off, and further brine is added to the residual beans for a short period to produce different grades of soy sauce. The raw sauce is placed in a vat exposed to sunlight under a transparent cover for up to 6 weeks. The raw liquid is then heated to develop further flavor compounds in the final product. The heating promotes Strecker degradation reactions and Maillard reactions involving pentoses and amino acids that produce flavors. A biotechnological approach, to reduce the soy sauce production time by employing bioreactors based on immobilized enzymes and microbial cells using ceramics, Chitopearl, and alginate gels as the base, has shown some promise. Production times as short as 2 weeks have been achieved. The koji mixture is produced as usual and the enzymatic hydrolysis stage in the brine is controlled. The hydrolyzed extract is then pumped over the immobilized cells for the fermentation stage.

Miso Miso is made with either added rice or added barley (Figure 7). The carbohydrates are cooked for 40 min, and the soybeans are soaked and cooked at 115 C for 20 min. The koji mold, A. oryzae, is grown only on the rice or barley. It is inoculated and incubated at 35–38 C for 40–48 h to promote amylase production instead of protease production. Salt is added immediately to prevent further mold growth, and the salted rice or barley koji is mixed with the cooked soybeans. Lactic acid bacteria and yeast may be added. The mixture is packed in a tank and covered and incubated at 30 C. During aging, it is moved from one tank to another to mix the contents and to introduce some oxygen to promote yeast growth. The aged miso is then blended, mashed, and pasteurized, and 2% alcohol is added to prevent yeast growth.

Okara The dry matter content of okara, the waste product from soy milk production, contains 26% protein, 12% oil, and 52% complex carbohydrates such as hemicellulose, pectin, and cellulose. It is a waste product of growing significance, and

Milled rice or barley, 60 kg

Soybeans, 100 kg De-hulled

131

Koji starter Aspergillus oryzae, 109 spores/g

Soak in water Soak in water

0.1% in the rice

Steam 45 min Autoclave 115 °C, 20 min

Cool to 30 °C

Koji making, 40–48 h, 35–38 °C Salt 43 kg Mash tank Lactobacilli Fermentation 30 °C, 1–3 months Remove to another tank or vat (2 times) Alcohol to 2% Pasteurization Miso, 330 kg Figure 7 A flowchart for the production of miso. In this case, the koji is prepared with the starch source alone, and a slightly higher incubation temperature is used to promote amylase production over protease enzyme production. Adapted from Yokotsuka T and Sasaki M (1998) Fermented protein foods in the Orient: Shoyu and miso in Japan. In: Wood BJB (ed.) Microbiology of Fermented Foods, 2nd edn., vol. 2, pp. 351–415. London: Elsevier Applied Science.

the high insoluble dietary fiber content is a negative nutritional characteristic.

Fermentation of Okara A traditional Chinese product is ‘meitauza’ – produced with A. elegans. The acid protease enzyme from the mold releases ammonia and increases nonprotein nitrogen eightfold, while pH rises from 5.5 to 7.5. A natto¯-like product has been produced with selected bacterial cultures. Fermentations are usually tempeh-like, so okara cakes are inoculated with fungi and incubated. Using the tempeh fungus, R. oligosporus, and the koji fungus, A. oryzae, the nutritional quality of okara is improved because, on a dry matter basis, there are increases in protein digestibility (80–84%), free amino acids (0.02–0.41%), acid-soluble nitrogen compounds (0.15–0.84%), free sugars (12–18%), and inorganic phosphorus and decreases in fiber content (56.6–49.5%). Phosphorus increase is due to the hydrolysis of phytic acid that binds iron, making the iron unavailable in the diet. Added rice bran improves okara tempeh. The mold Neurospora intermedia used to make Indonesian ‘oncom,’ a fermented groundnut press cake with an orange color, when grown on okara press cake, increases the protein content (22–27%) and decreases insoluble fiber and fat content 15–9%. The texture of fried okara oncom resembles chicken.

132


Citric acid Citric acid is produced from okara with added 0.1% (NH4)2SO4 and using solid-state fermentation with two mold cultures: A. terreus NCIM 653 and A. niger NRRL 330. A. terreus saccharifies the okara, and noncellulolytic A. niger produces the citric acid. Maximum citric acid yields of 5.1 g citric acid per 100 g of dry solids are obtained when A. niger and A. terreus are grown together.

Okara Fermentations for Nonfood Purposes Usually, solid-state fermentations are used. B. subtilis NB22, incubated at 25 C, produces iturin A, a cyclic heptapeptide of a-amino acids connected by long b-amino acids, that is effective against serious plant pathogenic fungi. Up to 11 g kg1 dry weight okara of iturin A has been produced. B. subtilis RB14 growing on okara produces surfactin, a lipopeptide consisting of iso-C15-hydroxy carboxylic acid and a seven-member ring structure of amino acids, that inhibits fibrin clotting and lyses erythrocytes, spheroplasts, and protoplasts and is a powerful biosurfactant able to lower water surface tension from 72 to 27 mN m1. Surfactin production as high as 2.0 g kg1 wet weight was achieved during growth at 37 C. Fibrinolytic enzyme production by some B. subtilis strains was 2.5-fold higher when grown on okara compared with whole soybeans. For Penicillium simplicissimum AK-40, okara was the best medium for the production of some novel compounds with insecticidal properties called okaramine A (C32H32N4O3) and B (C33H34N4O5) and another strain, ATCC 90288, produced the insecticidal agent okaramine D.

Health Benefits of Fermented Soybean Products Fermented soybeans are thought to have some beneficial effects on health. The benefits arise from the fiber components in the products and from metabolically transformed components.

Tempeh Tempeh made with R. oligosporus has high free radical scavenging activity, one-third of which comes from isoflavones released by fungal b-glucosidase from the glycosides and two-thirds from the peptides. One of the antioxidants is 3-hydroxyanthranilic acid (HAA); when it is at high levels in cell culture, it inhibits the production of the dominant membrane lipid, but at low concentration, it accelerates membrane lipid formation. Also, HAA inhibits cell growth and induces apoptosis in a human hepatoma-derived cell line (HuH-7), suggesting that it may have anticancer properties. To study the antioxidative, anti-inflammatory, and antithrombotic properties of tempeh, male Wistar rats were fed with an aqueous tempeh extract for 7 days, and then their femoral arteries were observed using a g-camera. When free radicals were induced in the rats, the animals fed with the tempeh extract had lower interleukin-1 a-plasma levels and reduced plasma thromboxane B2 levels, suggesting a protective effect against atherosclerosis. Okara-based tempeh, when fed to rats, increased the levels of cholesterol and bile acid in the feces and

significantly lowered them in plasma while liver cholesterol levels were lower compared with controls.

Natto¯ The B. subtilis var. natto used to manufacture natto¯ produces enzymes that break down enterotoxins produced by Staphylococcus aureus. Natto¯ has positive effects on osteoporosis. Ovariectomy-induced bone loss in rats was used as the model, and when fed with natto¯ containing added isoflavone (446–924 mg kg1 isoflavone, including genestin, genistein, daidzin, and daidzein) and zinc along with added calcium, serious bone loss in the rats over a 3-month trial period was prevented. A crude antioxidant preparation called NTX from natto¯-fermented okara exerted an anti-inflammatory effect on the gastric mucosa better than a-tocopherol due to the scavenging of the superoxide anion, and in the diet, it repressed edema when induced in rat footpads by subcutaneous injection of croton oil. NTX also lowered the levels of serum thiobarbituric acid-reactive substances, total cholesterol, low-density lipoprotein cholesterol, and triacylglycerol, as well as depressing atherosclerosis in rabbits. Natto¯ intake also increases serum levels of vitamin K2 (menaquinone-7) in humans.

Miso A powerful antioxidant isolated from A. oryzae-fermented soybean is 6-hydroxydaidzein in addition to 8-hydroxydaidzein and 8-hydroxygenistein. However, it was only produced when the soybeans were used to make the koji, not when rice or barley was used. It helps prevent the oxidative deterioration of miso. Protein and fiber components in okara koji made with A. oryzae affect lipid metabolism in rats. Lower cholesterol levels in plasma and liver and lower triglyceride levels were found in rats fed with a diet containing 50% okara protein enriched with A. oryzae compared with a casein-based control diet. The antioxidants in A. oryzae-fermented okara are g- and d-tocopherols; the isoflavones genistin, daidzein, and genistein; and HAA. The antimammary cancer effects of miso were tested in combination with tamoxifen in rats. The tamoxifen was implanted subcutaneously and the miso fed at 10% of the diet. Mammary cancer was induced, and while both the miso group and the tamoxifen group showed reduced cancer rates, the two together showed a synergistic effect. The incidence of tumors in the control group, the miso-fed group, the tamoxifen-implanted group, and the miso þ tamoxifen group was 91%, 77%, 68%, and 10%, respectively. Iron absorption in children can be improved by feeding fermented soybeans. Microbial hydrolysis of the phytate reduces its iron-binding capacity. When fed to 437 children in China for 6 months, the incidence of iron deficiency dropped from 21.7% to 1.25% and the iron absorption rate was 21.8% in the children given fermented soy and only 14.2% in those on the control diet.


• •

What are the primary whole bean fermented products? How is tofu produced?


• •

What class of microorganisms is primarily responsible for soy product fermentations? List the health benefits of any three fermented soy products.


• •

Expanded food uses for okara. Expanded evidence for the health benefits of fermented soy foods.

See also: Food Grains and Well-being: Nutrition: Soy-Based Foods; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Non-wheat Foods: Soybean: Soymilk, Tofu, and Okara; The Oilseeds: Soybean: Overview.

Further Reading Bei Z-H, Rombouts FM, and Nout MJR (2001) A Chinese fermented soybean food. International Journal of Food Microbiology 65: 1–10. Fukushima D (1989) Industrialization of fermented soy sauce production centering around Japan. In: Steinkraus KH (ed.) Industrialization of Indigenous Fermented Foods, pp. 1–88. New York: Marcel Dekker. Liu K-S (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman and Hall. Nunomura N and Sasaki M (1993) The shelf life of soy sauce. In: Charalambous G (ed.) Shelf Life Studies of Foods and Beverages: Chemical, Biological, Physical and Nutritional Aspects, pp. 391–408. Amsterdam: Elsevier.

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O’Toole DK (1997) The role of microorganisms in soy sauce production. Advances in Applied Microbiology 44: 87–152. O’Toole DK (1999) The characteristics and use of okara, the soybean residue from soy milk production: A review. Journal of Agricultural and Food Chemistry 47: 363–371. Sasaki M and Nunomura N (1993) Soy sauce. In: Macrae R, Robinson RK, and Sadler MJ (eds.) Encyclopedia of Food Science, Food Technology and Nutrition, vol. 3, pp. 1786–1795. London: Academic Press. Wang HL and Fang SF (1986) History of Chinese fermented foods. In: Hesseltine CW and Wang HL (eds.) Indigenous Fermented Food of Non-Western Origin. Mycological Memoir No. 11, pp. 23–36. Berlin: J. Cramer. Yokotsuka T and Sasaki M (1998) Fermented protein foods in the Orient: Shoyu and miso in Japan. In: Wood BJB (ed.) Microbiology of Fermented Foods, 2nd edn., vol. 2, pp. 351–415. London: Elsevier Applied Science.

Relevant Websites http://en.wikipedia.org – This is a site with a free, multilingual encyclopedia. Type in the name of a soy product or soy food to search for information. http://www.foodreference.com – A site dealing in general with all aspects of food. It includes daily food and beverage news, a culinary quiz, and a ‘Today in food history’ section. There is a wealth of information. http://www.japanweb.co.uk – A Japanese food and restaurant guide that contains a glossary of Japanese foods including soy foods. Information on the use of soy sauce in various recipes is also given. http://www.soyfoods.com – The US Soyfoods Directory with a free soyfoods guide available for downloading, as well as food recipes, mail order, and new soy research. Descriptions of all kinds of soyfoods are given. http://www.tempeh.info – A general site describing all aspects of tempeh including health aspects and food recipes using tempeh. Producers of tempeh in the United States, Canada, and Belgium are listed and suitable cultures for home production are available.

Soybean: Soymilk, Tofu, and Okara DK O’Toole, City University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 185–195, ã 2004, Elsevier Ltd.

Topic Highlights

Soymilk Production

•

The traditional soymilk production method involves soaking the beans to rehydrate them, rinsing, resuspension in water and grinding of the beans, followed by filtration to separate the soymilk and fibrous residue. The Japanese developed a slight variation in the traditional Chinese method (Figure 2) that improved soymilk yield and improved filtration characteristics but at the cost of a tendency to burn the slurry and the need to use mechanical means to filter the hot mixture, as well as increased energy costs. Usually the ratio of water to beans is in the range from 8:1 to 10:1. About 70% of bean solids, 80% of bean protein, and 89% of the oil end up in the soymilk. The residue left is known by a variety of names: okara, draff, tofukasu, soy pulp, tofu residue, tofu cake, dou zha (Chinese), bejee (Korean), and tempeh gembus (Indonesian). During soymilk production distinctive flavors develop that are variously described as ‘beany,’ ‘painty,’ ‘rancid,’ and ‘bitter.’ People from East Asia are used to the flavor but those in other places are generally not used to it. The flavor is due to the action of a native soybean enzyme, lipoxygenase. The enzyme reacts with the unsaturated fatty acids in the oil (linoleic acid, etc.) in the presence of water, and oxygen, by a process called autoxidation resulting in hydroperoxides (Figure 3) that are then broken down to aldehydes and ketones with strong odors and flavors, e.g., hexanal that has a flavor threshold of less than 1 mg kg1. Normally, in the whole undamaged bean, the oil and the enzyme do not come into contact but, when the beans are ground, contact with the necessary elements of the reaction occurs so that the reaction can proceed. As heat destroys the enzyme, possible processes to prevent bean flavor development include heating the dry beans, grinding the beans in hot water, and blanching the beans, but these processes render some soy protein insoluble, may introduce cooked flavor, and affect soy protein function. However, lipoxygenase is of value for the organoleptic qualities of tofu and soymilk, because tofu made with lipoxygenase-deficient soybeans lacks ‘mouthfulness’ or richness, and soymilk made with similar soybeans results in soymilk with a darker yellow color. Modern continuous production systems try to balance these factors. Recognized processes include:

• •

Soy proteins have special nutritional, antinutritional, and physical properties which are explained in relation to their use in traditional food products. Originating in China, soybean has wide use in processing of a beverage (soymilk) and related solid food products (tofu and okara). The basic process flow diagrams for major soy products are outlined, and the use of fermentation to make additional product variants is discussed.

Learning Objectives

• • •

To understand the composition and properties of soy protein. To understand the basic principles of processing and utilization of major soy food products (soymilk, tofu and okara). To gain an introductory idea of the types of fermented soy foods traditionally produced.

Introduction Soybeans, first cultivated in the Yellow River Valley in China 5000 years ago and on record from sixteenth to eleventh century BC, contain about 34% protein, 20% oil, and about 30% carbohydrate that is comprised of a soluble and an insoluble fraction. The soluble carbohydrate fraction, about 10% of the bean, is a mixture of sucrose (5%), raffinose (1%), and stachyose (4%), and the insoluble fraction consists of pectin (30% of insoluble carbohydrate), hemicellulose (50%), and cellulose (20%), and there is less than 1% starch. Soy hemicellulose consists mainly of arabinogalactan. About 12% of the protein is water soluble. In the beginning soybeans were cooked and eaten but then in the West Han Dynasty, 2000 years ago, Liu An, who dates from 164 BC, is said to have invented tofu that required the extraction of soymilk from the beans. A major problem with soybeans is that they contain a trypsin inhibitor, an antinutritional agent that prevents the intestinal digestive enzymes from breaking down proteins, and that must be destroyed by heating for a few minutes (Figure 1) to obtain maximum nutritional value. Because soybeans have a high protein content, they, and products derived from them, are seen as animal protein substitutes. In their raw state the concentration of nutrients is high, by comparison with beef, eggs, and milk (Table 1), but when prepared for consumption soybean products have significantly lower nutrient concentrations (Table 2). Apart from the fermented products obtained from soybeans, there are four main products and by-products: soymilk, tofu, yuba, and okara.

134

•

•

Cornell method. Soybeans are de-hulled and ground in a hot grinder with hot water at 80–100 C. The slurry is then boiled in a steam-jacketed kettle and constantly stirred for 10 min, followed by centrifugation or filtering to remove okara. Illinois method. Soybeans are de-hulled and either presoaked and placed in boiling water for 10 min, or placed dry in hot water for 20 min, then drained and ground in sufficient cold water to make a slurry with 12% solids that is then heated to 93.3 C and homogenized. Added sodium


http://dx.doi.org/10.1016/B978-0-12-394437-5.00130-3

NON-WHEAT FOODS | Soybean: Soymilk, Tofu, and Okara bicarbonate (0.25–0.5%) in the early stage may be used to hasten enzyme inactivation and has to be neutralized after homogenization. The resulting product, while bland in flavor, unfortunately has a chalky feel in the mouth. Soybean hulls are the only solid waste product.

•

3.1 (PER)

80

2.7

60

2.3

40

1.9

20

(TIA)

0

2

4

6

10 Minutes at 100 ⬚C

1.5

Protein efficiency ratio (PER)

Trypsin inhibitor activity (TIA/mg)

100

•

20

Figure 1 The effect of heating time on the protein efficiency ratio (PER) and its relationship to the trypsin inhibitor activity (TIA) in soybean. As trypsin activity drops, the digestion of the protein improves as shown by increased PER.

•

135

Rapid hydration hydrothermal cooking method. Soybeans are ground into flour, mixed with hot water, okara removed by centrifugation and soymilk pumped to a steam injection head where live steam is injected to increase temperature instantly (UHT conditions, 154 C for 30 s), and the soymilk is held in a holding tube to deactivate trypsin inhibitors. Okara waste results (e.g., the Tetra Alwin™ Soy system). Full fat soy flake method. The process begins with a product called MicroSoy Flakes made by the MyCal group of Iowa, USA, from de-hulled soybeans. Commercial integrated production systems. Some of these systems are designed to be continuous and incorporate steps to minimize ‘beany’ flavor development, such as procedures to minimize incorporation of oxygen that reacts with lipoxygenase.

Large soymilk manufacturers may include a deodorization step at the conclusion of soymilk extraction. The hot soymilk is injected into a chamber under strong vacuum in which volatile off-flavors, such as sulfur flavors, short chain fatty acids and vinyl or sterol compounds, and air in the soymilk, are vaporized and stripped out. The soymilk is also rapidly cooled as it expands into chamber. Whether or not the soybeans should be de-hulled before processing is debatable, because the process can damage the cotyledon thus releasing the enzyme but some benefits include elimination of a ‘green or raw’ flavor, and reduced soaking

Table 1 The gross composition, and vitamin and mineral content of whole soybeans compared with other protein sources from animals in the uncooked state Vitamin contents may change when the foods are cooked Gross composition (g per 100 g)

Vitamins and minerals (mg per 100 g)

Food (kJ/100 g)

Carbohydrate

Protein

Lipid

Retinol

Thiamine

Riboflavin

Niacin

Ca

P

Fe

Soybean (1653) Beef (464) Eggs (631) Cow milk (264)

30a

36.1 21.0 12.3 3.1

17.7 3.0 11.3 3.5

2 5 530 38

660 130 100 40

220 170 300 653

2.2 5.5 0.1 0.2

226 12 73 114

546 224 224 102

8.8 3.2 3.1 0.1

5

a

Nutritionally most of this carbohydrate is not available to humans.

Table 2

The gross composition, and mineral and vitamin contents, of some soybean-based products Gross composition (g per 100 g) a

Minerals and vitamins (mg per 100 g)

Food

Water

Protein

Fat

Carbohydrate

Crude fiber

Ca

Fe

Zn

P

Soymilkb Tonyuc Okara Okarac Tofu Tofuc Yubac Tempeh

93.3 89.4 81.6 78 84.6 86.3 7.1 55.0

2.8 4.5 3.2 5.1 8.1 7.0 46.2 19.0

1.9

1.8

1.1

4 22 80 50 105 78 321 93

0.51

0.23 0.52

78

1.7 4.8

7.7

12.5 1.9

17.0

4.1 0.1

3.0

Kjeldahl N 5.71. Concentration of components in soymilk depends on the soybean:water ratio used to make the slurry. c Values from a Japanese paper, tonyu is the Japanese term for soymilk. a

b

1.30 5.36

2.26

0.6 0.80 0.75 4.08 1.81

Thiamine

Riboflavin

0.16

0.07

0.02

0.02

0.08

0.05

0.13

0.11

86 105 707

136

NON-WHEAT FOODS | Soybean: Soymilk, Tofu, and Okara

Whole soybeans, large 1

Water, 2–3 × bean volume

De-hull

Soak overnight 2 Drain

Waste

Rinse

Waste

Water rinse, 2–3 times

Water : bean ratio − 6 : 1

Chinese method

Japanese method

Grind to produce slurry

Filter to separate soymilk from fibrous residue (okara)

Heat slurry to near boiling temperature Okara to waste

Filter to separate soymilk from fibrous residue (okara)

Boil soymilk for a few minutes

Soymilk

Packaging for sale as a beverage, as it is or as a UHT product

Further processing to coagulate and make bean curd or tofu

Figure 2 A schematic diagram of the production of soymilk by the Chinese and the Japanese methods. Soybeans may be de-hulled before they are put in to soak or the hulls may be removed at the end of the soaking stage, or the hulls may not be removed at all. Okara is a major by-product from the process.

COOH

COOH

Linoleic acid

Lipoxygenase in H2O

CH3 O

13-hydroperoxy-cis-9, trans-11octadecadienoic acid

H

O2

CH3

OOH COOH

An oxo acid

CHO Hexanal

Figure 3 The lipoxygenase enzyme is responsible for the “beany” flavor commonly noted in soymilk. The reaction catalyzed by the enzyme involves water, the unsaturated oil, and oxygen and the end-product hexanal is one of the compounds responsible for the beany flavor.


Soak temperature (⬚C)

2.5

40 50 60 80 70 90 30

70

Hydration ratio

90 50

80

60

2.0

40 30

1.5

1.0

• 0

1

2

3 4 Soak time (h)

5

6

7

Figure 4 The time to maximum water uptake (hydration) by soybeans depends on the temperature of the soak water.

•

time. Soaking time to full soybean hydration is fastest at 80–90 C and much slower at room temperature (Figure 4). During maceration to produce the slurry, the seedcoat does not behave the same way as the cotyledon cells.

• Tofu Tofu resembles a soft white cheese and can be defined as ‘a water extracted and salt- or acid-coagulated soy protein gel with water, soy lipids, and other constituents trapped on its network’ that was developed in China and spread through East Asia. It was introduced into Western cuisine less than 100 years ago. The manufacture of tofu with consistent quality and yield is difficult as many things can affect the outcome. In the production of tofu, various coagulants are used to solidify the soymilk. They include magnesium chloride, calcium sulfate, and glucono-delta-lactone. The general process is outlined in Figure 5. Factors affecting the quality and yield of tofu include:

•

•

•

Size, shape, and color of hilum and cotyledon of the soybean. Light colors are favored and although a large size, 200 mg per seed or larger, is a traditional Japanese requirement, there seems to be no scientific basis for it. Total protein and the 11S–7S protein ratio. Japanese manufacturers prefer soybeans containing 13% moisture with a 38% or greater protein content. The 7S fraction is b-conglycinin and the 11S fraction is glycinin and the concentrations and ratio of these vary with seed cultivar (Table 3). The 11S fraction controls hardness, brittleness, and gumminess of resulting tofu, and the 7S fraction requires more calcium or magnesium for coagulation. Hence, the ratio of these two proteins in a soymilk influences the process and product characteristics. The 11S fraction, the a0 polypeptide of 7S, and the basic polypeptide of 11S seem to each affect tofu yield but they are not related to tofu firmness. However, there is a relationship between tofu firmness and the 11S fraction, the 7S fraction, and their ratio. The effect of the 11S:7S ratio may be modified by the processing conditions. When calcium sulfate is used for coagulation, the concentration of the salt for optimum tofu quality declines from

•

•

•

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0.8% (w/w) to 0.4% as the concentration of protein in the soybeans rises from 31% to 38%. The recommended concentration is 0.02–0.04 mol, but in practice experienced tofu makers know if the amount is correct by whey color and curd texture. If concentration is just right, the whey is transparent with amber or pale yellow color and sweet taste, and if too much coagulating agent is added the whey is slightly bitter and the curd has a coarse texture. As grinding temperature rises from 2 C to 50 C, the firmness of resulting tofu declines. This is due to the activity of the lipoxygenase enzyme whose reaction by-products, the peroxides, oxidize the –SH groups on the soybean protein being released during the grinding and so reduce protein cross-linking. The percentage of total solids in soymilk is related to the water:soybean ratio. The water value used is the total amount of water absorbed by the dry beans plus the final addition of water for grinding plus any rinse waters from the residual okara added back to the slurry. Maximum protein yields are obtained at a ratio of 10:1, water:soybean, but at a ratio of 9:1 pressed tofu has the lowest fresh yield and cohesiveness, and highest brittleness and hardness. The coagulation temperature depends on type and concentration of coagulant, how the coagulant is added in, and tofu type to be produced. Generally, as the temperature used is increased (50–90 C) tofu yield decreases, but at the lower temperatures tofu is soft and at higher temperatures tofu is hard and uneven. Consequently, the optimum temperature range is 70–80 C. If the soymilk is stirred with added coagulant, the resulting tofu has a hard curd and a low fresh yield is obtained. Highspeed stirring favors hard curd production and low-speed stirring for a short time favors softer curds. Although soybean variety affects tofu qualities and yield, the growing season for the production of the soybeans has a major impact on tofu texture, due to the effect of environmental growth conditions on the 11S:7S ratio in the protein. When soybeans are stored under adverse conditions of high temperature and relative humidity, the tofu yield decreases and tofu hardness increases (Table 4).

During the production of tofu, additives are sometimes included to change the tofu characteristics or to improve textural characteristics. Added blood in Japan, algal cells (Chlorella sp.) in Korea, and chitosan have also been used to improve tofu texture. Commercial transglutaminase or glucose at a low level, when added at 5 mg l1 to soymilk to make glucono delta lactone tofu, suppresses retort-induced water release during sterilization at 115 C for 20 min. Tofu is classified into soft (silken), firm, and extra firm varieties. Subsequent processing results in a range of products. Silken tofu contains 88–90% water and 6% protein and is made with soymilk containing 10–12% solids. The curds, when broken and pressed, result in firm and extra firm tofus. The firmness makes it easier to handle the small curd blocks so they keep their shape during slicing and cooking by deep frying or pan frying. Products, depending on subsequent handling, include plain tofu, frozen tofu (a 1000–1500 year old Chinese tradition), dried-frozen tofu, deep-fried tofu, grilled tofu, and

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Soymilk boiled for 10 min

Traditional method

Acid method

Gluconodelta-lactone

Coagulant: choice of gypsum (CaSO4), nigari (MgCl2)

Cool to 78 ⬚C, add solution and stir vigorously for 30 s, quiescent 30 min

Water solution

Cooled soymilk

Dispense in package and seal

Soft or silken tofu is cut into cakes, removed under water and cooled

Heat by immersion in hot water to coagulate with gluconic acid from lactone, 50 min

Curd is stirred and broken, placed in cloth lined forming box and pressed 30 min, then cut into cakes and stored under cold water

Pasteurized silken tofu with no whey separation

Figure 5 A schematic diagram of the production of tofu. Traditionally calcium and magnesium salts have been used as coagulants but a more recent innovation is the use of an acid coagulant, gluconon-delta lactone that slowly hydrolyzes to gluconic acid to cause the coagulation of the proteins. The final product is manipulated in various ways to form the final shape and form of the tofu being produced.

Table 3 Soybean cultivars vary in their protein content and the ratio between the protein fractions 11S and 7S and they have an impact on the tofu yield and tofu firmness Soybean (g per 100 g soybeans) Cultivar

Moisture

Protein

Tofu yield

Vintron-81 S-20 F8 HP-204 IA-2034 Steyer IA-2020 S-2020

9.67 9.40 9.06 9.66 9.71 9.19 9.04

49.6 49.1 48.5 47.9 47.9 45.9 42.9

293 269 320 322 314 343 290

11S/7S ratio in protein

Tofu firmness (N)

3.33 3.57 3.10 1.85 2.40 2.24 2.05

10.02 9.91 8.53 8.19 7.97 7.84 6.93

Table 4 The affect of storage of soybeans under adverse conditions, at 85% relative humidity and 30 C, on phytate concentration in the soybeans and the yield of tofu and the brittleness and hardness of the tofu measured in grams Months of storage

Phytate (g per 100 g of soybeans)

Tofu yield

Brittleness (g)

Hardness (g)

0 1 2 3 4 5 6

1.33 1.21 1.18 1.16 1.10 1.06 1.05

512 505 481 421 389 362 233

1020 1033 923 873 920 945 >5000

2090 2182 2465 2704 3080 3278 >5000


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fermented tofu. Frozen tofu has an interesting characteristic. On freezing the tofu solids congeal into a firm network, and on thawing the water is released from the tofu block leaving behind a product with a sponge-like texture that is tough and chewy but it absorbs flavors easily. The thawed tofu, when dried (dried-frozen tofu), keeps well (up to 12 months), is easily handled and stored, and is a highly concentrated source of protein and energy.

analogs can be marketed as low fat and cholesterol free as well as being vegetarian. Tofu is very versatile and can be used to make very many Western style foods. Tofu has been used to make cheesecake, dips, pies, cream cheese, mayonnaise, Italian meatballs, and almost any Western style food.

Soymilk- and Tofu-Based Foods

About 1.1 kg of fresh okara is produced from every kg of soybeans processed for soymilk. Okara contains 30% of the whole soybean solids, 20% of the bean protein, and 11% of the oil. Huge quantities of okara are produced, e.g., in Japan 700 000 tonnes (t) of okara were produced from the tofu production industry in 1986, and its disposal is a significant problem. The okara is used as an animal food, is dumped in landfills, is used as a fertilizer, and, in Japan, most is burnt. It has been used as a base for a low cost artificial food for silkworms for the first to the third larval instar stages of growth. Research is ongoing to devise uses for okara including the development of other processed human foods. When dry okara is mixed with rice powder in the ratio of 25:75 to prepare a sauce-like product using a soy sauce manufacturing technique, the resulting product has an excellent flavor with a light and bright color, but total amino acids and glutamic acid are lower than found with a 1:1 mixture of defatted soybean meal and wheat. Okara is not suitable for ethanol production.

Although the name ‘soymilk’ is commonly used, there is some resistance to the use of ‘milk’ in the name, because milk has been more commonly associated with the bovine-derived product. Consequently, it is sometimes named ‘soy beverage.’ Many modern products have been referred as secondgeneration soy foods because they are modern inventions as opposed to the traditional products above, but a clear-cut definition of these products is difficult. Broadly, they can be placed into three categories: dairy analogs, meat analogs, and tofu-based foods. The soymilk-based dairy analogs are foods basically the same as dairy products, but soymilk and soy constituents are used instead of milk and milk constituents. Consequently, the soy-based analogs include frozen soy deserts such as soy ice cream and frozen soy yogurt. Generally, dairy ice cream is made from a mixture of ingredients that include water, high fructose corn sweetener (or sucrose), fruits, vegetable gums, salt, and colorant but in soy ice cream the dairy constituents are replaced with soy oil, tofu, isolated soy protein, and soy lecithin. Frozen soy yogurt is basically made from a mix similar to that found in soy ice cream except that it is cultured with the two yogurt lactic acid bacteria and frozen and whipped as for normal ice cream. The product resembles a regular soft serve frozen product. Attempts to make fermented dairy analogs such as cheese and yogurt from pure soymilk have generally failed for a variety of reasons. They include that the soy protein molecules are larger than milk proteins and have different functional groups and characteristics; the fat to protein ratio in tofu is lower than in cheese, 0.55:1 versus 1.1:1, that results in a hard product; sugars in soymilk do not support growth of dairy bacterial cultures; and acid production by the usual dairy microorganisms in soymilk is variable. Consequently, processes used for dairy products manufacture cannot be easily adapted to soymilk. Products similar to cheese can be made but it requires addition of dairy constituents and enzymes to obtain products similar to dairy cheeses. The idea of making meat analogs from soybean dates from the 1950s. There are two basic processes for manufacturing meat burger-like products, namely fiber spinning and thermoplastic extrusion. Fiber spinning is used to make fibrous meatlike products that are used in the production of ‘meat’ pies, casseroles, seasoned vegetables, and sandwich fillings. Flavors such as bacon flavor can be added to the product. Thermoplastic extrusion is used to make textured vegetable protein (TVP) that can be formed into continuous slabs for eventual cutting into desired shapes such as burger shapes. Various flavors and spices can be added to make the product flavorful. These meat

Okara

Preservation of Okara Due to its high water activity and microbial contamination, okara can putrefy quickly so if it is not used immediately it must be preserved. It is desirable that during preservation the okara should retain its white color and ability to easily absorb water. For short-term storage a lactic acid fermentation will suffice, but drying is the preferred solution. Fresh okara tends to be lumpy so there are homogeneity problems during drying. Successful drying systems depend on the initial moisture content of the okara. Dehydration methods include addition of water-absorbing synthetic polymers in various forms to the okara; the use of a patented process involving a pneumatic conveying drier and a pulverizer; or a pneumatic drying system with hot air (208–254 C) at a low velocity (192 m min1) in a large drying tower. Other drying systems include a vibro-fluidized bed under vacuum, and drying in pellet form (3 mm 10 mm) in hot air. Sterilized wet okara can be produced continuously by finely dividing it and feeding it into a scraper-type heat exchanger at not less than 120 C followed by cooling, filling, and sealing aseptically in a suitable container.

Okara Composition The main components of okara are ruptured cotyledon cells and the seedcoat. The proximate composition of the wet okara depends on the water extraction efficiency from the slurry phase and soybean cultivar from which it is extracted, amongst other factors. Okara has a pH of 6.7, and on a dry-weight basis its proximate composition is 27% protein, 10% crude fat/

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oil, and 14% soluble fiber, 42% insoluble fiber, and 3% ash. The proximate insoluble fiber content is 12% hemicellulose, 5.5% cellulose, 11.5% lignin, and 0.2% phytic acid. Other nutritionally important compounds include vitamins: thiamine, riboflavin and nicotinic acid, as well as calcium, phosphate, zinc, iron, copper, and magnesium (Table 5). The phytic acid (inositol hexa-phosphate), when consumed in large quantities in the diet, reduces calcium balance and metal ion availability, and the zinc has low bioavailability. Soluble carbohydrates include sucrose as well as raffinose and stachyose that cause meteorism (flatulence) (Table 6).

Fractionation of Okara Okara, as a waste product, is a cheap resource, so to add value to it various components can be isolated in fractionating steps to produce high-value products such as proteins and carbohydrates that can be used as food additives.

Protein The protein in okara is of better quality than that from other soy products, e.g., the protein efficiency ratio of okara is 2.71 compared with 2.11 for soymilk, but the ratio of essential amino acids to total amino acids is similar to tofu and soymilk. Protein extracted from heat-treated and nonheat-treated okara differs, the latter contains the same basic 7S globulin found in soybeans, unlike the former. Okara protein isolate is similar to commercial soy isolate in having comparable emulsifying, water and fat binding, and foaming properties. Pepsin digests of proteins lower hypertension and blood pressure because they contain peptides that inhibit the angiotensin I-converting enzyme (ACE) that converts angiotensin I to angiotensin II, a substance that constricts arteries leading to hypertension and raised blood pressure. The peptides have IC50 (concentration at which 50% inhibition is found) values between 14 and 53 mmol.

characteristics similar to commercial pectic polysaccharides products. The monosaccharides units in the polysaccharides in the insoluble fiber components, when enzymatically digested, include galacturonic acid, glucose, xylose, arabinose, and galactose.

Human Consumption The dietary fiber content of okara is greater than 50%, so its energy content is only half that of wheat flour. Okara alone has some antinutritional qualities; however, fermented okara may have definite dietary advantages. It can act as a suitable replacement for digestible food in a food prepared to reduce calorie intake, when consumed, it can reduce cholesterol levels in the blood stream, and as a food that contains antioxidant activity, similar to vitamin E, it can reduce the level of free radicals in the body.

Nonfermented products Haarman and Reimer Corp. in the USA developed an okarabased snack bar, and the Japanese National Food Research Institute patented a process for converting okara to a textured soybean product. Biscuits fortified with 60% okara to give protein and dietary fiber contents of 8.72% and 5.98%, respectively, are acceptable to consumers. The Japanese patented a process to produce okara coated with shortening for use as a wheat substitute for making cakes acceptable to consumers. A nougat candy based on peanut, glucose, hydrogenated oil, sugar, and natural essences with added okara has been developed in Argentina. The candy contains 18.3% okara and 27.4% peanut. Acceptable corn tortillas can be made with 10% added okara, and the tortillas have increased lysine and tryptophan levels, amino acids that are nutritionally limited in corn.

Fermented products Okara fiber component Cellulose concentration is higher in the seedcoat than in the cotyledon but hemicellulose is lower in the seedcoat and higher in the cotyledon, and although galactan hemicellulose is present in the two seed components, araban hemicellulose is present in cotyledon and pentosan hemicellulose in seedcoat. Arabinogalactan hemicellulose is the main constituent in the alkaline extract (24% KOH) from okara. Demethylation of okara hemicellulose results in a lowviscosity water-soluble carbohydrate that can be used to stabilize soluble proteins under acid conditions, e.g., in acidified milk beverages. The hemicellulose content of okara can be fractionated into hot-water-soluble, normal-soluble, and alkali-soluble hemicellulose at ratios of 5:19:4 after soaking at 30 C overnight. Hot water extraction from okara has been done by hydrolyzing in an autoclave at pH 4.5 in two volumes of water with or without a chelator (hexametaphosphate or ethylene diamine tetraacetic acid (EDTA)). The extracted polysaccharides, molecular weight of 105, have emulsification properties influenced by the amount of bound protein. The use of sodium hexametaphosphate results in protein-free pectic polysaccharides with

A traditional Chinese product is meitauza that is produced with okara using the fungus Actinomucor elegans in a solidstate fermentation, and another is pickled okara. However, much recent work has to do with using some traditional fungi and bacteria to produce nutritious and flavorsome okara-based products. Okara-based natto has been produced using selected strains of Bacillus natto. Indonesian ontjom (oncom), an orange colored product, has been prepared from okara using the fungus Neurospora intermedia. The resulting product has no soybean flavor, smooth mouth feel, and, when fried, the texture of okara ontjom resembles chicken. The tempeh fungus, Rhizopus oligosporus, and the soy sauce fungus, Aspergillus oryzae, improve protein digestibility, and availability of nutrients in the fermented okara along with its antioxidant activities. In rats fed with a diet containing 50% okara protein enriched with okara koji fermented with A. oryzae, plasmaand liver-cholesterol levels and triglycerides (compared with a casein-based control diet) are lower. The protein and fiber components in okara koji made with A. oryzae and R. oligosporus affect lipid metabolism in rats. Plasma levels of

Table 5

The proximate composition, mineral analysis, and vitamin analysis on a dry matter basis of okara prepared from three cultivars of soybeans Proximate composition (g per 100 g)

Minerals and vitamins (mg per 100 g)

Proteina

Oil

Carbohydrate

Phytic acid

Insoluble fiber

Soluble fiber

Total fiber

Ash

Ca

Mg

Fe

Na

K

Cu

Zn

Mn

P

Thiamin

Riboflavin

Nicotinic acid

Edgar Hutton Prima

28.4 25.4 26.2

9.6 10.9 9.3

5.3 3.8 4.6

0.5 1.2 0.9

42.0 43.6 40.2

14.6 14.5 12.6

56.6 58.1 52.8

3200 3700 3000

260 428 286

163 158 165

6.2 7.2 8.2

16.2 19.1 18.4

1046 1094 1233

1.1 1.1 1.2

3.8 3.5 6.4

2.5 3.1 2.3

396 444 407

0.59 0.49 0.48

0.04 0.03 0.03

1.01 0.82 1.04

Kjeldahl N 5.71.

a


Soybean cultivar

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142 Table 6

NON-WHEAT FOODS | Soybean: Soymilk, Tofu, and Okara Carbohydrate (not fiber) contents on a dry matter basis, of okara from three cultivars of soybeans (g per 100 g) Oligosaccharides

Starch

Soybean cultivar

Monosaccharides (unspecified)

Stachyose

Raffinose

Sucrose

Edgar Hutton Prima

0.7 0.6 0.7

1.4 0.9 0.9

0.3 0.3 0.4

2.3 1.3 1.8

cholesterol and bile acid are significantly lower in okara tempeh fed animals apparently due to cholesterol and bile acid being more strongly bound to okara fiber than cellulose fiber and so they are excreted in the faeces. Dietary fiber, particularly that from the soybean, may be effective in modifying colonic conditions in a positive way. Rats fed with fermented okara absorb more iron than those fed with unfermented okara, possibly due to reduced levels of phytic acid. Fermented okara, compared with unfermented okara, contains more of an antioxidant, called NTX, that has an antiinflammatory effect on gastric injury in the gastric mucosa. In in vitro tests NTX scavenges the superoxide anion, a process that also occurs in vivo. When foot pad edema is induced in rats by subcutaneous injection of croton oil, NTX fed rats exhibit repressed edema but rats fed with a control diet or vitamin E show no repression of edema. The antioxidants in A. oryzae fermented okara seem to be g-and d-tocopherol, the isoflavones genistin, daidzein, genistein, and 3-hydroxyanthranilic acid. In vitamin-E-deficient rats fed with okara supplemented with the oxidized oil, the body weight gain was lower and plasma peroxidase activities lower than in those fed with fermented okara suggesting that the antioxidants in the fermented okara scavenged lipid peroxides in vivo.

Fermentation for Nonfood Products Some unusual and possibly useful chemicals, new and previously described, including iturin A and surfactin, have been produced by some microorganisms growing on okara only but not other substrates in a solid-state fermentation. When growing on okara, Penicillium brasilianum Batista JV-379 produces two compounds, namely brasiliamide A and B, that cause convulsive responses in silkworms. Strains of the fungus P. simplicissimum produce okaramines, some with insecticidal properties. In addition, they produce a unique oleanane triterpene, and another species of Penicillium produces two new dihydroquinolinones, one toxic for the classic toxin indicator Artemia salina at an LC50 value of 20 mg ml1.

Other Products The Japanese have patented a process in which okara is used to make a reinforced ceramic via the pozzolanic reaction. Fly ash (50–70%), clays (10–30%), and okara (10–20%) along with Ca(OH)2 (10–30%) are mixed and heated in an inert gas to 1300–1500 C. The carbonized okara reacts with SiO2 to form silicon carbide that strengthens the ceramic product.

0.59 0.68 0.79

Yuba This product is made in Japan from soymilk. The soymilk is placed in a wide, open pan and brought to and held at a temperature close to boiling, the ideal temperature being 82 2 C. Over time a slowly thickening film forms that can eventually be removed with two sticks. The film is placed on a wire mesh shelf to dry out. From 10 to 20 sheets may be produced from one batch of soymilk. It has a very high protein content and is highly digestible and nutritious (Table 2). It is highly perishable and is best eaten fresh but it is also sold in dried or semi-dried forms. The yield and characteristics of yuba are affected by 11S and 7S proteins in the soymilk. Yuba made with soymilk containing 11S proteins is smooth, opaque, and strong, but that made with 7S soymilk is translucent, full of creases, and weaker by comparison. The pH of the soymilk is important. The normal pH of soymilk is 6.7 but if the pH is below 6.2 the film will not form, and if the pH is 9 the yield and protein incorporation are at a maximum. Generally, a pH of 7–8 is recommended.

Detection of GM Soybean As genetically modified soybeans are of concern, detection of genetically modified soybeans, e.g., Roundup Ready beans, in a batch is of interest. Using a Polymerase Chain Reaction process the Agrobacterium derived enzyme, 5-enol-pyruvylshikimate-3-phosphate synase gene used in the modification process, can be detected at the level of one modified soybean in 5000 unmodified seeds.


• •

Okara is a low-cost high-protein by-product of soymilk processing. Investigate further the properties of okara and suggest additional value-added uses for it. Examine the soymilk, tofu and related products available in your local market. How would you classify them? How many of them are the result of any microbial fermentation?


• •

How much genetic variation is there in the physical properties of soy proteins? What effect could this have on product textural profiles? How can the ‘beany’ taste of soy products be reduced or eliminated?


See also: Agronomy of Grain Growing: Soybean: Agronomy; Food Grains and Well-being: Nutrition: Soy-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Nutrition: Beriberi, A Deficiency Related to Grains; Non-wheat Foods: Soybean: SoyBased Fermented Foods; Oilseed and Legume Processing: Soybean: Soy Concentrates and Isolates; Wheat Processing: Milling and Baking: History.

Further Reading Bourne MC, Clemente MG, and Banzon J (1976) Survey of the suitability of thirty cultivars of soybeans for soymilk manufacture. Journal of Food Science 41: 1204–1208. Hou HJ and Chang KC (2003) Yield and textural properties of tofu as affected by the changes of phytate content during soybean storage. Journal of Food Science 68: 1185–1191. Ikeda S and Murakami T (1995) Zinc chemical form in some traditional soy foods. Journal of Food Science 60: 1151–1156. Kwok KC and Niranjan K (1995) Review: effect of thermal processing on soymilk. International Journal of Food Science and Technology 30: 263–295. Liu K-S (1997) Soybeans: Chemistry, Technology, and Utilization. New York: Chapman and Hall. Ma CY, Liu WS, Kwok KC, and Kwok F (1996) Isolation and characterization of proteins from soymilk residue (okara). Food Research International 29: 799–805. Matsuo M (1997) In vivo antioxidant activity of okara koji, a fermented okara, by Aspergillus oryzae, Bioscience. Biotechnology and Biochemistry 61: 1968–1972. Messina MJ, Persky V, Setchell KDR, and Barnes S (1994) Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutrition and Cancer 21: 113–131. Mujoo R, Trinh DT, and Ng PKW (2003) Characterization of storage proteins in different soybean varieties and their relationship to tofu yield and texture. Food Chemistry 82: 265–273. Ohno A, Ano T, and Shoda M (1995) Production of a lipopeptide antibiotic, surfactin, by recombinant Bacillus subtilis in solid state fermentation. Biotechnology and Bioengineering 47: 209–214. O’Toole DK (1999) The characteristics and use of okara, the soybean residue from soymilk production: a review. Agricultural and Food Chemistry 47: 363–371.

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Van der Riet WB, Wight AW, Cilliers JJL, and Datel JM (1989) Food chemical investigation of tofu and its byproduct okara. Food Chemistry 34: 193–202. Wang HL and Cavins JF (1989) Yield and amino acid composition of fractions obtained during tofu production. Cereal Chemistry 66: 359–361. Yamaguchi F, Ota Y, and Hatanaka C (1996) Extraction and purification of pectic polysaccharides from soybean okara and enzymatic analysis of their structures. Carbohydrate Polymers 30: 265–273.

Relevant Websites vvww.dietobio.com http://vvww.dietobio.com – A combined French and English site concerned with vegetarian foods. Choose language and go to “Articles” for information on soy foods. ellenskitchen.com http://www.ellenskitchen.com – A site dealing with recipes and special diets for those with metabolic dietary problems, as well as vegetarian diets. hcf-nutrition.org http://hcf-nutrition.org – The site of the HCF Nutrition Foundation with a focus on the nutritional aspects of foods, in particular soyfoods, and how they are all related to disease. fao.org http://www.fao.org – The site of the FAO of the United Nations. Type “soybean” in the search window to obtain information. Go to “World Agricultural Information Centre” and under “Engineering, Technology and Research.” Go to the “Post Harvest Operations” to obtain comprehensive information about postharvest treatments of soybeans. The site is multilingual. wishh.org http://www.wishh.org – The site of the World Initiative for Soy in Human Health, an initiative from the United States of America. The site includes news items. soya.be http://www.soya.be – Information on soyfoods including recipes as well as a wide range of foods. News items are also included. aces.uiuc.edu http://www.aces.uiuc.edu – A University of Illinois website dealing with soybeans. foodsubs.com http://www.foodsubs.com – The Cook’s Thesaurus and Encyclopedia covering thousands of recipes and kitchen tools. soyfoods.com http://www.soyfoods.com – The US Soyfoods Directory with a free soyfoods guide available for downloading, as well as food recipes, mail order and new soy research. Descriptions of all kinds of soyfoods are given. soybean.on.ca http://www.soybean.on.ca – From the Ontario soybean growers in Canada and includes information on the nutritive value of soybeans as well as recipes and descriptions of soyfoods.


Contents The Application of Sensory Science to the Evaluation of Grain-Based Foods Noodles: Testing for Quality Pasta: Quality Testing Methods Rice: Eating Quality

The Application of Sensory Science to the Evaluation of Grain-Based Foods LM Duizer and SB Walker, University of Guelph, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

Sensory evaluation is an analytic tool to understand what individuals perceive in grain-based products. Sensory evaluation can be divided into difference tests, affective (consumer) tests, and descriptive analysis (trained panels). Sensory evaluation tests must be set up in a specific way to minimize errors and biases during testing. A sensory evaluation testing facility should be set up to minimize the interactions occurring between participants. Difference tests can be used to evaluate simple differences or attribute differences in grain-based foods. Consumer-based sensory evaluation measures liking of foods and requires large numbers of individuals. Descriptive analysis requires trained tasters to evaluate intensities of attributes found in grain-based foods. All sensory evaluation approaches require knowledge of statistics to analyze the data.

Learning Objectives

• •

To achieve an understanding of how to use sensory evaluation tests to measure sensory properties and liking of grain-based products. To develop an understanding of how to prepare and present samples for sensory testing.

Introduction Sensory evaluation is defined as “a scientific discipline used to evoke, measure, analyze and interpret those responses to products as perceived through the senses of sight, smell,

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taste, touch and hearing” (Stone and Sidel, 2004). It involves collecting responses as food is eaten and, as such, is the only true measure of how people experience the sensory properties of foods. Sensory evaluation can be used in cereal science to find out how much a person likes a food or to describe the intensity of the sensory properties of the food. These are known as subjective and objective tests, respectively. Often, the results collected from these two groups of tests are combined to obtain an overall picture of how the sensory properties of a food affect consumer liking for a food product. This article will outline the various sensory tests that can be used to collect information about the sensory properties of foods. Examples of these tests as they relate to grain-based products will be discussed. Because sensory testing is concerned with understanding how individuals perceive the sensory properties of a product, it is important to carefully control the preparation and presentation of samples. It is also essential that factors other than the sensory properties of a food that may contribute to a response are minimized so that the collected results are a true reflection of an individual’s perception of sensory attributes in the food and not a reflection of some other aspect of the food. Before discussing the types of sensory tests that can be used to measure perceptions, the factors associated with controlling test conditions will be presented.

Sensory Evaluation: Best Practices Best practices of sensory testing can be classified into considerations of sample preparation and of testing environment. Following these best practices ensure that errors and biases associated with poor sample preparation and presentation are minimized and validity and reliability of results are improved.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00134-0

FOOD-QUALITY TESTING | The Application of Sensory Science to the Evaluation of Grain-Based Foods

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Sample Considerations

Testing Environment

Sample preparation

Sample preparation and sample presentation should occur in different rooms. This ensures that panelists are not influenced by packaging, labels, and brands and that their responses are based solely on the sensory properties of the products. An example of the booths and serving area of a sensory testing facility are shown in Figure 1. A well-equipped testing facility should contain individual sensory testing booths to separate panelists from each other and from the preparation area (Figure 1(a) and 1(b)). Interactions between panelists and servers should be minimized. This is achieved using booths with a serving hatch through which samples are presented on trays (Figure 1(c)). If sensory testing booths are not available, panelists should be placed at individual tables, away from others to discourage discussion during testing. Often, it is necessary for individuals to complete paperwork before a test and to receive payment at the end of a test, and these activities should occur in a separate room in order to minimize distraction. Guidance for the proper design of sensory testing facilities is found within document ISO 8589:1988(E) published by the International Standards Organization (1988).

The amount of sample presented to panelists is very important. Panelists must receive enough sample to make an evaluation but should not be given so much that they become fatigued during testing. It may be necessary to cut samples to a smaller size or to weigh out an amount that is suitable for evaluation. Many grain-based products are easy to prepare for testing. For instance, if conducting sensory testing on crackers, they can be served directly from the package. However, brand identifiers should be masked so that panelists evaluate the products solely for their sensory properties and not for their liking of the brand. When working with a product such as bread, other considerations arise. An individual may not require an entire slice of bread to make their evaluation; a half or quarter slice is often sufficient for testing. If evaluating both crust and crumb, ensure that there is consistency across the samples and that individuals are served samples from the same portion of the slice. If conducting a trained panel for attribute intensity, it may be necessary to test the crust of the bread separately from the crumb as sensory properties differ between these two parts of the slice (Challacombe et al., 2012). Testing of grain-based products that require boiling, such as pasta, requires that the boiling and holding times are consistent for all products and all panelists. The temperature of the product during testing should be held constant as product attributes often vary with temperature. If samples must be kept warm or cold, they should be served in a lidded polystyrene container to maintain temperature. If samples are to be served at room temperature, they can be served in plates or in bowls, as required.

Sample presentation During testing, all samples should be labeled with three-digit blinding codes to minimize bias (Lawless and Heymann, 2010). These codes can be generated by a random number generator or by using a random number table. The use of coding other than a three-digit code, such as the numbers one, two, and three or a, b, and c, implies an order of ‘best’ to ‘worst’ that could influence panelists. Randomly generated three-digit codes prevent such associations. Order effects may occur during sample testing, therefore, at a minimum, sample presentation should be randomized (Lawless and Heymann, 2010). Panelists should evaluate samples in a different order from each other. If possible, sample order should also be balanced so that each sample is presented in the same position an equal number of times. This minimizes carry over and contrast effects between samples. When these effects occur, the sensory properties of the food can be perceived as either weaker or stronger than they actually are. Panelists must be provided with palate cleansers during testing. Often, these can be an unsalted cracker and a glass of water. However, if crackers or other baked products are being evaluated, the use of an apple slice can take the place of the unsalted cracker. If the samples that are being evaluated leave a strong taste in the mouth or leave an oily mouth coating, a citric acid rinse can be used to help cleanse the palate.

Types of Sensory Evaluation Tests The types of sensory tests that can be used to evaluate a food product can be divided into three broad categories. These include descriptive analysis, affective testing, and difference testing. The decision about which test to use is based on the objective of the work being conducted. Descriptive analysis involves the use of trained panels to evaluate attribute intensity of samples while affective testing uses consumers to measure liking. Difference testing determines if differences in perception between or among products exist.

Descriptive Analysis Descriptive analysis by a trained panel uses a small number of individuals (between 10 and 15) to measure the intensity of the sensory properties of a food. When conducting descriptive analysis, it is not appropriate to ask individuals about liking or acceptability of the food. This is for two reasons. First, the number of individuals used for descriptive analysis is not a large enough sample size to gauge a population’s liking of a product. Second, individuals are selected and trained to discriminate among small differences in attribute intensities and, because of this, are not representative of a consumer population.

Screening Screening begins by assessing each individual for their availability for and interest in the project. All participants must be able to commit their time for the duration of the project with minimal absences. They should also be in good health with no allergies or aversions to the foods being tested. Individuals should also be assessed for their attitude toward the task. It is undesirable to have participants who are argumentative or who are very quiet as it is necessary to receive input from all panelists during training and to build confidence in the panelists.

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Figure 1 Sensory testing facility with eight testing booths (a) showing partitions between booths (b) from the panelist’s perspective when sitting in the booths (c) from the serving area.

Once appropriate individuals have been identified, the discriminative ability of each participant is assessed. Individuals must be able to discriminate among products and among attributes of those products. Screening tests include acuity testing to determine an individual’s ability to detect differences among products and to describe these differences (Meillgaard et al., 2007). This can be done through a series of triangle tests (as outlined in ‘Discrimination Testing’) where individuals identify the different sample out of three that are presented to them. The differences between the two samples should be easy to detect at the beginning of the screening session and increase in difficulty by the end of the session. Descriptive tests should also be completed where individuals are asked to describe attribute differences among products. As a general guide, individuals who can correctly identify the different sample greater than 70% of the time in triangle tests, as well as having the ability to describe attribute characteristics with specific terms rather than with generic consumer-based terms, are selected to undergo training (Meillgaard et al., 2007).

Training There are a number of steps to a training program. The first step is attribute identification where individuals identify the sensory characteristics of importance in the products. This is typically done in a round table discussion with a panel leader where individuals receive the products that they will be testing and words used to describe the sensory properties of the products are listed and discussed. From this discussion, the terminology to be used during testing is developed. This involves obtaining panel agreement on the words being used to describe and evaluate an attribute and agreement on the evaluation process to be used for each attribute. After the attributes have been identified, they must be carefully defined and an evaluation approach is discussed and agreed upon by the panel. At no point should subjective attributes such as liking or acceptability be included in this list. All attributes must be objective. An example of attributes and definitions generated during the evaluation of whole-grain breads and crackers is shown in Table 1. A good example of descriptors, definitions,

FOOD-QUALITY TESTING | The Application of Sensory Science to the Evaluation of Grain-Based Foods Table 1 Sensory attribute Taste Sweet Salty Sour Bitter Astringent

Example attributes for trained panel evaluation of whole-grain crackers and breads Definition

Reference

Rating scale

The taste sensation perceived on the tongue as stimulated by sucrose and other sugars The taste sensation perceived on the tongue as stimulated by sodium salts, such as chloride, and in part other salts The taste sensation perceived on the tongue as stimulated by acids such as citric acid Basic bitter taste associated with caffeine and other bitter compounds; bitterness lingers long like an aftertaste A sensation that lingers and coats; dries and numbs the mouth, palate, and tongue

3% sucrose solution

0 ¼ not sweet 15 ¼ very sweet 0 ¼ not salty 15 ¼ very salty 0 ¼ not sour 15 ¼ very sour 0 ¼ not bitter 15 ¼ very bitter 0 ¼ not astringent 15 ¼ very astringent

0.2% sodium chloride solution 0.1% citric acid solution 0.01% caffeine solution 0.01% tannic acid solution

Flavor Branny

A grainy note with a light, dusty impression

Bran-based cereal

Oily

A mouth-coating sensation associated with fats and oils

Vegetable oil heated for 1 min

Grainy

Ten grain cereal

Wheaty

A general term used to describe the dusty or musty note associated with grains such as corn, wheat, and oat A light, baked wheat flour note

Starchy

A bland note associated with raw wheat starch

Malty

Sweet, slightly fermented, or sour grain note associated with freshly kilned malt A fermented note associated with yeast dissolved in water

Yeasty

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and reference standards used to conduct descriptive profiling of Asian noodles is found in Janto et al. (1998). After the attributes have been defined and agreed upon, the panel is trained in the evaluation of the intensity of each attribute and the use of appropriate scales. This is completed through presentation of samples exhibiting intensities of the attributes in question. To assist with the evaluation of attributes, reference samples ranging in intensity are used as guides for placement of evaluations on the intensity scale. These references can be commercial products, ingredients, or chemicals that display the attribute of interest. Providing reference samples ensures that panelists have a common frame of reference when making their evaluations and aids in obtaining consistent results among panelists. During training, individuals are also provided with opportunities to practice their evaluations. This is done by presenting samples varying in intensity of the attributes being evaluated. Providing feedback on the intensity scores provided by the panel leads to more consistent scores during testing. A final practice is given at the end of training to ensure that the panel is in agreement and that everyone understands the attributes being evaluated. When the panel is able to consistently discriminate among samples, testing can occur.

Testing Testing takes place over a number of sessions, and during each session, a ballot is presented to the panelists for making their evaluations. Line scales are commonly used during testing with a trained panel. These scales are usually either 10 or 15 cm in

Wheat-based cereal 2 Tablespoons of wheat starch in 250 ml water, cooked for 1 min in microwave A teaspoon of liquid malt in 500 ml of water A teaspoon of yeast in 250 ml of water

0 ¼ not branny 15 ¼ very branny 0 ¼ not oily 15 ¼ very oily 0 ¼ not grainy; 15 ¼ very grainy 0 ¼ not wheaty 15 ¼ very wheaty 0 ¼ not starchy 15 ¼ very starchy 0 ¼ not malty 15 ¼ very malty 0 ¼ not yeasty 15 ¼ very yeasty

length. Each end of the scale is labeled with anchors appropriate to the attributes being evaluated. An example of the ballot used to evaluate the texture of extruded corn-based snacks is found in Figure 2. Replicate testing of all samples occurs during testing to ensure enough data have been collected for statistical analysis of the data. Statistical analysis of trained panel data involves conducting an analysis of variance test to determine if significant differences exist among the treatments. This is followed by a multiple comparison test to identify where the differences exist. Often, the multiple comparison test used when analyzing sensory data is a Tukey’s honestly significant difference test.

Affective Testing Affective or consumer testing is conducted in order to discover what consumers like about a product. This type of testing differs from trained panel testing as it involves a subjective assessment of products. A consumer test is the appropriate type of test to conduct in order to understand preference for products and liking of product attributes. This type of testing may also extend to attributes such as pricing and purchase intent. Sometimes, only the concept of the product will be tested. Consumer testing can also provide feedback on product attributes for activities such as product optimization and reformulation. In consumer testing, the response of a population to a product is inferred by polling a representative subset of that population. In order to account for differences in personal tastes and to ensure that a few individuals do not skew the

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SAMPLE: 576 Hardness:

Sound Duration:

Type of sound:

Place the food between your incisors and bite down. Evaluate the force required to bite through the food with your incisors. H1 – Cream Cheese – (2) H2 – Hard cheddar cheese – (8)

The number of “pops” heard when biting with the incisors. Evaluate on first bite only. D1 – Wafer - (1) D2 – Extruded snack – (6)

The amount of noise produced on first bite with the front teeth. S1 – Commercial extrusion 1 – (1) S2 – Commercial extrusion 2 – (9)

HARDNESS H1(2)

H2 (8)

Soft SOUND DURATION D1(1)

Hard

D2 (6)

Short

Long

TYPE OF SOUND S1(1)

S2(9)

Quiet

Loud

BRITTLENESS Brittleness:

The degree of shatter which occurs when the sample is bitten into with the front teeth. BR1 – Commercial extrusion 1 – (6)

Rate of Breakdown: After biting with the incisors, evaluate the length of time taken to break the sample down in preparation for swallowing. B1 – Commercial extrusion 1 – (2) B2 – Commercial extrusion 2 – (7) Figure 2 Line-scale ballot used during training of a trained panel.

BR1(6) Not brittle RATE OF BREAKDOWN B1 (2) Short

Very brittle

B2 (7) Long


LINE SCALE RATING

FOOD-QUALITY TESTING | The Application of Sensory Science to the Evaluation of Grain-Based Foods results, this type of testing must make use of larger sample sizes of respondents than trained panel testing. Although the number of panelists differs for each affective test, testing should typically involve at least 75–150 consumers per product for statistical validity (Lawless and Heymann, 2010).

•

Selecting consumers The selection of participants for consumer testing is usually targeted by gender, age, geographic region, or other criteria that define a product’s target market. It is important to consider who the consumers in your test are meant to represent and to choose participants appropriately. Unfocused consumer panels are unlikely to give actionable data. To ensure that the ‘right’ people are being selected for consumer testing, an appropriate recruitment and screening strategy must be used. The following guidelines are recommended as best practices for consumer testing:

•

•

•

•

Avoid using the same individuals too many times. Establish a pool, and use individuals only a few times a year. Overuse risks the consumers becoming a group of professional product evaluators who will critically evaluate products differently from the general population. Screen consumers to ensure they are users of the product category, and set parameters for frequency of consumption beforehand. For example, individuals may say that they frequently eat product x; however, ‘frequent’ is openended and can differ by consumer. Consider asking “how often do you eat product x? 2–3 times per week, once a week, once every 2 weeks, once a month, less than once a month, hardly ever/never.” Select individuals only from higher-frequency groups in order to obtain a group of consumers that not only fit your profile but also are familiar enough with the product to provide critical feedback. Pay consumers for attending evaluations, but do not over pay them. Compensation should be provided to cover time and transport costs. This establishes a professional relationship, emphasizes that they are there to do a job, and implies that the test is to be taken seriously. Paying too much may lead to consumers only participating for financial gain. Also, consumers who are very well paid may feel obliged to be less critical and give higher scores to the products they are evaluating than they otherwise would. Use age-appropriate consumers. Test children’s products with a panel of individuals in the same age group. Using caregivers

Name ____________________________

149

is sometimes done as these people are the primary shopper or food gatekeeper. This approach will almost certainly produce a different result than if the actual consumers of the product were polled. Testing of product concepts, packaging and marketing materials on the other hand should be done using caregivers as they are doing the actual purchasing. Using employees in consumer testing is very convenient and cost-effective. However, the opinions of employees may not be representative of consumers. Employees may be overly familiar with the company’s products resulting in their being particularly critical of minor defects or variability in the product that regular consumers may not notice. Conversely, their familiarity makes it more likely that they will be subject to bias as they are more likely to identify their own company’s products. Bias may be positive or negative, for example, an overly positive response to a product they had a hand in manufacturing or a negative response from an employee who feels they should not have to participate in tasting sessions.

Types of Affective Testing There are a number of ways to conduct affective testing. Simple tests, including preference testing, infer liking based on preference. More information on liking and factors affecting liking can be collected using comprehensive consumer testing.

Preference testing Preference tests are carried out to establish which of two products known to be different from each other is preferred by consumers. Subjects are provided with one sample of each product. They are instructed to try each sample in the order provided and to then indicate which of the two they prefer or like the most overall. See Figure 3 for an example of a paired preference ballot. A variant of this test allows for the selection of a ‘no preference’ option. To account for presentation order effects, the sample sets should be presented in the order AB and then BA alternatively. Analysis of these data is straightforward and involves counting the number of participants who selected each sample as their most preferred. Appropriate statistical tables for determining if a significant difference in preference exists can be found in sensory texts such as those by Lawless and Heymann (2010) and Meillgaard et al. (2007).

Date____________________ Paired preference

There are two samples for you to evaluate. Taste each of the coded samples in order from left to right. Circle the number of the sample which is most preferred __375___

___519___

Note: If a no preference option is added, then in the row listing the 3 digit codes, the phrase ‘no preference’ is added to the ballot. In the instructions, individuals are informed to circle the ‘no preference’ option if they have no preference for either of the sample. Figure 3 Paired preference ballot. Note: If a ‘no preference’ option is added, then in the row listing the 3-digit codes, the phrase ‘no preference’ is added to the ballot. In the instructions, individuals are informed to circle the ‘no preference’ option if they have no preference for either of the sample.

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If more than two products are being evaluated for preference, then a ranking test can be used. Subjects are asked to taste each sample and to indicate the order of preference from most to least. Analysis of these data involves calculating rank sums for each sample and comparing the differences between the rank sums to the critical values for differences located in Lawless and Heymann (2010).

Comprehensive consumer testing Consumers can provide more information about products beyond that obtained from simple difference and preference testing. A consumer panel is the recommended tool for discovering consumer liking of a food product overall, as well as degree of liking of various product attributes. The 9-point hedonic scale has been widely adopted as the standard scale for assessing consumer liking. Data obtained using this scale can be used to infer differences in preference. This method also has the advantage of providing a measure of the size of the difference in liking. When designing an evaluation form for a consumer test, care must be taken in interpreting the terms consumers use, as consumer language does not employ the precise definitions used by trained panelists. For example, consumers commonly confuse the terms sour and bitter (O’Mahoney et al., 1979). It is important to establish that consumers understand the attributes they are being asked to evaluate and that consumer-friendly terms are used when developing an evaluation form. An example of an evaluation form used in the testing of whole-grain empanadas formulated with sprouted wheat flour is shown in Figure 4.

Discrimination Testing Discrimination testing is used to determine if perceivable differences exist among products. It is often used with consumers to establish whether the population of interest is able to determine an overall difference between two or more variants of a product. Establishing whether a perceivable difference exists is vital before committing resources to other types of consumer testing. If consumers are unable to tell a difference between products, then they cannot be expected to have a preference. This approach may also be used with trained panelists during the training process as described in the section on training of a descriptive analysis panel. Two categories of difference testing exist: overall difference tests and directional difference tests. The triangle test and duo–trio test are types of overall difference testing. The objective of the triangle test is to establish if there is an overall difference between two products A and B. Subjects are given two samples of a product and one of another. Subjects try all three samples in the order provided and then indicate which of the samples is the odd one out. Figure 5 outlines a sample triangle test ballot. Subjects are told that if they cannot tell which the odd sample is, they are to guess. To account for presentation order effects, sample sets should be presented in multiples of the six possible presentation orders, that is, AAB, ABA, BAA, BBA, BAB, and ABB. A duo–trio test presents subjects with a reference sample followed by each test sample. Individuals are asked to try the reference sample and then each test sample and to identify the sample which is similar to the reference (Lawless and Heymann, 2010). An example ballot is shown in Figure 6. With

this test, a constant reference sample (i.e., only one product is presented as the reference) or a balanced reference sample (both products are presented as the reference an equal number of times) can be used. As with all sensory tests, the presentation of the two test samples must be randomized. A paired comparison test is a directional difference test. Panelists are asked to indicate which sample in the pair of samples presented is greater in intensity for the attribute of interest. A ballot similar to the one used for paired preference testing can be used for a paired comparison test. In the case of a paired comparison test, the panelists are asked to indicate the sample that is higher or stronger in a specific attribute. Analysis of the data collected from these difference tests involves counting up the number of correct responses (for the triangle and the duo–trio test) or the number of times a product is identified as being greater for the attribute of interest (for the paired comparison test) and collated results are compared to published table values. Such tables can be found in sensory texts such as Lawless and Heymann (2010) and Meillgaard et al. (2007).

Examples of the Use of Sensory Evaluation Techniques in Testing of Grain-Based Products Both affective testing and descriptive analysis techniques have been used in the evaluation of a number of cereal-based products, ranging from noodles to breads and crackers (Challacombe et al., 2011; Huang et al., 1995; Jayasena et al., 2010; Mitra et al., 2012; Nkhabutlane et al., 2014; Nwabueze and Anoruoh, 2011; Silva et al., 2013; West et al., 2013; Xue et al., 2010). Often, consumer work is conducted to ensure that ingredient addition to products does not significantly alter their liking. The effect on liking of the addition of lupin flour (to improve protein and fiber content) to instant noodles has been evaluated using a 9-point hedonic scale. From the collected results, it was possible to ascertain the amount of lupin flour that can be added to instant noodles without compromising consumer acceptability of the noodles (Jayasena et al., 2010). Similarly, the amount of oat flour and broccoli powder that can be added to pasta without affecting consumer liking of noodles has been investigated (Mitra et al., 2012; Silva et al., 2013). Some researchers have used consumer testing to study the effects of cereal variety on liking. Noodles made from flour ground from cassava mosaic disease-resistant varieties of cassava have been tested for liking so that the most appropriate variety can be used in the manufacture of noodles (Nwabueze and Anoruoh, 2011). Different colored wheat varieties have also been incorporated into breads and crackers to ascertain the effect of wheat color on consumer acceptability (Challacombe et al., 2011). Descriptive analysis has been used to develop an in-depth profile of important sensory attributes in food products. During descriptive analysis of traditional breads from Lesotho 36, attributes related to aromas, textures, flavors, and aftertastes of breads made with different cereal grains were evaluated by a trained descriptive panel (Nkhabutlane et al., 2014). Descriptive analysis has also been used to characterize the quality of products. An eating quality parameter for steamed bread, a


Name ____________________________

Date____________________

Empanada Product Questionnaire Please look at, but do not eat, the empanada. Then answer the following question. 1.

What is your opinion of the overall appearance of this empanada?

1 Dislike extremely

2 Dislike very much

3 Dislike moderately

4 Dislike slightly

5 Neither like nor dislike

6 Like slightly

7 Like moderately

8 Like very much

9 Like extremely

You will now be given half an empanada to eat. Please sip some water to cleanse your palate before tasting the empanada. 2.

How much do you like / dislike the Flavor of the pastry?

1 Dislike extremely

3.


4 Dislike slightly


6 Like slightly

7 Like moderately

8 Like very much

9 Like extremely

6 Like slightly

7 Like moderately

8 Like very much

9 Like extremely

6 Like slightly

7 Like moderately

8 Like very much

9 Like extremely

7 Like moderately

8 Like very much

9 Like extremely

How much do you like / dislike the saltiness of the pastry?

1 Dislike extremely

4.

2 Dislike very much

2 Dislike very much


4 Dislike slightly


How much do you like / dislike the texture of the pastry?

1 Dislike extremely

2 Dislike very much


4 Dislike slightly


Thinking about the empanada overall (appearance, flavor and texture) 5.

How much do you like / dislike this empanada?

1 Dislike extremely

6.

2 Dislike very much


4 Dislike slightly


6 Like slightly

What do you particularly like about this empanada? ______________________________________________________________________________

7.

What do you particularly dislike about this empanada? ______________________________________________________________________________

Figure 4 Comprehensive consumer testing ballot.

Name ____________________________

Date____________________ TriangleTest

There are three samples for you to evaluate. Two samples are duplicates and one is different. Taste each of the coded samples in the order left to right and identify which is the different sample. Circle the number of the sample which is different. ____612____ Figure 5 Triangle test ballot.

___955____

___873____

151

152


Name ____________________________

Date____________________ Duo-Trio

There are three samples for you to evaluate. One labelled ‘reference’ and two with three digit codes. One of the coded samples is the same as the reference. Taste the reference first and then taste each of the coded samples in the order left to right. Circle the number of the sample which is the same as the reference. ___891___

___622____

Figure 6 Duo–trio test ballot.

staple food for China, has been determined by multiplying intensity scores collected from a trained panel for softness, elasticity, nonstickiness, and cohesiveness – all important characteristics for eating quality of steamed bread (Huang et al., 1995). Quality parameters of noodles have also been examined by a trained sensory panel (Xue et al., 2010).

Relations Between Sensory and Instrumental Testing In order to study the underlying chemical and physical contributors to sensory perception, there is often an attempt by researchers to relate sensory and instrumental measures. One approach for exploring these relations is through the calculation of a correlation coefficient. Such an approach has been used by researchers to determine whether instrumental measures of the texture and color of northern style Chinese steamed bread can be used as an indicator of eating quality (Huang et al., 1995). Using this approach, instrumental stress relaxation results show the best relation with eating quality, thereby leading to the conclusion that it is possible to identify good quality bread through instrumental testing. Because sensory evaluation often involves the measurement of multiple variables, multivariate data analysis is frequently required to aid in interpretation. Partial least squares regression, an approach used to predict a set of dependent variables from a large number of independent variables, has been used to investigate relations between the chemical analysis of various wheat parameters and sensory properties of instant noodles. Dough quality parameters have also been related to sensory properties of instant noodles with the conclusion that it is possible to use chemical and instrumental measures of ingredients and dough to evaluate the eating quality of noodles (Xue et al., 2010). Others, however, have found that results from instrumental testing do not necessarily reflect what is detected by a human. West observed that a texture analyzer was more sensitive at detecting differences in dried pasta than a trained panel evaluating similar pasta (West et al., 2013). Therefore, the use of an instrument as a direct replacement of human testing is not advisable for all situations. It must be remembered that although it may be possible to find relations between instrumental and sensory properties, the only true measure of what individuals perceive in a product and what and how much consumers like a product is to conduct the appropriate type of sensory test.

Conclusion When set up properly, sensory evaluation testing can be a powerful tool for understanding how individuals perceive the sensory properties of grain-based products. Care must be taken to ensure that products are prepared and presented in such a way that there are no errors or biases with the collected sensory data. In this way, liking and preference of products can be determined. The intensity of sensory properties of the grainbased products can also be measured.


• • • • •

What sensory test would you use to study the effects of wheat color on the sensory properties of whole-grain bread? What are the important aspects, from a sample preparation perspective, that must be considered when setting up a test for whole-grain bread? Describe how you would recruit participants to test consumer liking of a high-protein cereal designed for postmenopausal women. Describe the steps you would go through to train a panel to evaluate the sensory properties of whole-grain pasta. Outline a sample questionnaire to be used to evaluate consumer liking of a green tea-infused cookie.


• •

Discuss how sensory evaluation could be used in the development of new functional foods. Identify the types of physicochemical tests whose results can be correlated with sensory testing results.

See also: Beverages from Grains: Beverages: Asian Alcoholic Beverages; Beverages: Distilled; Fermentation: Foods and Nonalcoholic Beverages; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Fortification of Grain-Based Foods; Genetically Modified Grains and the Consumer; Food Grains and Well-being: Functional Foods: Overview; Food-quality Testing: Rice: Eating Quality; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products;

FOOD-QUALITY TESTING | The Application of Sensory Science to the Evaluation of Grain-Based Foods Non-wheat Foods: Maize: Foods from Maize; Rice: Chinese Food Uses; Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara; Processing of Grains: Cereals: Breakfast Cereals; Extrusion Technologies; Wheat Processing: Chemistry of Cake Manufacturing; Snack Foods: Processing; Wheat-Based Foods: Breads; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Flatbreads of the World; Cakes, Muffins and Bagels; Pasta; Sour Dough Technology; Tortillas.

References Challacombe C, Abdel-Aal E-SM, Seetharaman K, and Duizer LM (2012) Influence of phenolic acid content on sensory perception of bread and crackers made from red or white wheat. J. Cereal Sci. 56(2): 181–188. Challacombe CA, Seetharaman K, and Duizer LM (2011) Sensory characteristics and consumer acceptance of bread and cracker products made from red or white wheat. J. Food Sci. 76(5): S337–S346. Huang S, Quail K, Moss R, and Best J (1995) Objective methods for the quality assessment of northern-style Chinese steamed bread. J. Cereal Sci. 21: 49–55. International Standards Organization, 1988. ISO 8589: 1988(E) Sensory analysis – general guidance for the design of test rooms. Janto M, Pipatsattayanuwong S, Kruk MW, Hou G, and McDaniel MR (1998) Developing noodles from US wheat varieties for the far east market: Sensory perspective. Food Qual. Prefer. 9(6): 403–412.

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Jayasena V, Leung PPY, and Nasar-Abbas SM (2010) Effect of lupin flour substitution on the quality and sensory acceptability of instant noodles. J. Food Qual. 33: 709–727. Lawless HT and Heymann H (2010) Sensory Evaluation of Food: Principles and Practices. New York: Springer. Meillgaard M, Civille GV, and Carr BT (2007) Sensory Evaluation Techniques, fourth ed. Boca Raton: Taylor & Francis. Mitra S, Cato L, James AP, and Solah VA (2012) Evaluation of white salted noodles enriched with oat flour. Cereal Chem. 89(2): 117–125. Nkhabutlane P, du Rand GE, and de Kock HL (2014) Quality characterization of wheat, maize and sorghum steamed breads from Lesotho. J. Sci. Food Agric. 94: 2104–2117. Nwabueze TU and Anoruoh GA (2011) Evaluation of flour and extruded noodles from eight Cassava Mosaic Disease (CMD)-resistant varieties. Food Bioprocess Tech. 4: 80–91. O’Mahoney M, Goldenberg M, Stedmon J, and Alford J (1979) Confusion in the use of the taste adjectives ‘sour’ and ‘bitter’ Chem. Senses 4: 301–318. Silva E, Gerritsen L, Dekker M, van der Linden E, and Scholten E (2013) High amounts of broccoli in pasta-like products: Nutrition evaluation and sensory acceptability. Food Funct. 4: 1700–1708. Stone H and Sidel JL (2004) Sensory Evaluation Practices, third ed. San Diego: Academic. West R, Duizer L, and Seetharaman K (2013) The effect of drying and whole grain content on the pasting, physicochemical and qualitative properties of pasta. StarchStarke 65: 645–652. Xue D, Gao H, Zhao L, and Yin J (2010) Relationships between instrumental measurements and sensory evaluation in instant noodles studied by partial least squares regression. J. Texture Stud. 41: 224–241.

Noodles: Testing for Quality VA Solah, Curtin University, Perth, WA, Australia GB Crosbie, Crosbie Grain Consulting, East Fremantle, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Guidelines for the preparation of noodles for sensory evaluation, involving appearance and texture testing, are described. Noodle quality traits are described. Sensory evaluation: the color and texture methods commonly used by flour mill quality control and organizations involved in noodle research or the evaluation of new noodle wheat varieties are described.

Learning Objectives

•

This article aims to develop awareness of the issues, the theory, and the factors that must be considered when testing for quality in noodles.

Introduction Asian wheat flour noodles are manufactured in a vast range of types that vary with respect to formulation, the manufacturing process used, and the dimensions of the noodle strands. The quality characteristics of the wheat flour, other ingredients, and the processing method strongly influence noodle appearance and texture. Testing of flour, raw, and boiled noodles by both sensory and instrumental methods is featured prominently in flour mill quality control and by organizations involved in noodle research or the evaluation of new noodle wheat varieties.

Methods for Testing Quality Preparation of Noodles for Testing The preparation of noodles for testing depends on the type of noodle. One method would be to prepare and test or serve noodles under conditions similar to those used to serve to the consumer, and this is the preferred method in sensory evaluation. In using instrumental methods, noodles should be boiled in a standard way, that is, boiling is optimized so the noodles are fully cooked with no inner, uncooked core or boiled for a specific time to standardize the process. There are three methods recommended to determine the optimum noodle boiling time: sensory evaluation, the glass slide method, and the measurement of apparent boiled noodle yield (ABNY). Boiling of noodles must be carefully controlled so they are fully cooked with no inner, uncooked core to ensure full gelatinization and minimize the loss of starch. Sensory experts can taste noodles to determine if they are fully cooked through to the core. The use of a glass slide

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involves pressing the noodle strands between two glass slides to reveal any uncooked core. This method is described in AACC International Method 66-50.01 as the ‘Pasta and Noodle Cooking Quality—Firmness.’ A preferred method in Japan involves the use of ABNY – here, the noodles are boiled until they reach a standard boiled noodle yield or final moisture content. Boiling white salted noodle (WSN) (udon) for the determined time to give an ABNY of 310 % is recommended by Solah et al. (2007). ABNY is calculated as the weight of boiled disks, expressed as a percentage of the weight of flour (at 13.5% moisture content) within the boiled raw disks, as indicated by the following equation: ABNY* ¼

boiled noodle weight raw noodle weight 100 13:5 100 100 moist content**of raw noodle

*The ABNY is only an approximate value because of the loss of dry matter including salt during boiling. **The moisture content of raw noodle includes the moisture present in the flour plus added water, expressed as a percentage of the total weight of the dough (weight of flour þ added water þ salt).

Sensory Evaluation While subjective consumer-orientated sensory testing for acceptance, preference, and hedonic (or degree of like or dislike) is of interest, it is the objective product-orientated descriptive analysis and numerical scoring systems that are commonly used sensory tests for noodle assessment. Consumers who are untrained are recommended for acceptance, preference, and hedonic sensory tests, and trained panels are recommended for product-oriented tests (Fu and Malcolmson, 2010).

Discrimination sensory analysis Discrimination tests determine whether sensory differences exist. An example of a discrimination test used in noodle testing is the AACC International Method 33-50.02 for ‘Sensory Evaluation—Triangle Difference Test,’ which determines whether a detectable difference exists between two samples in a specific characteristic, such as flavor, texture, color, or odor. Samples should be sourced that are different for one characteristic and the same for all other characteristics. The cause of the difference is not identified. The panelist is asked to determine which two of the three samples are the same. This test is often used in determining suitability for a trained panel because if a panelist is unable to routinely discriminate a poor quality sample from a good one in blind testing, then they should be excluded from the trained panel.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00131-5

FOOD-QUALITY TESTING | Noodles: Testing for Quality Descriptive sensory analysis Descriptive tests identify the nature and magnitude of the different traits. Descriptive tests are the main tests used to evaluate noodle quality. Descriptive qualitative sensory analysis is important in the determination of the traits that are important to quality (Lawless and Heymann, 1998). Descriptive qualitative sensory analysis enables qualitative insight into perceptions and consumption trends and gives descriptive profiles of liking, appearance, or texture.

Descriptive quantitative methods Quantitative sensory methods enable values to be added to the descriptors defined during qualitative analysis. Sensory evaluation is about feelings, and the words used by different people may not convey that they experience the same feeling. Comparable positioning of marks on the scale or score may not mean the panelists feel the same way. Panelists will naturally compare and bring a frame of reference to evaluations (Lawless and Heymann, 1998). Two common methods in noodle sensory evaluation are as follows: 1. A rating system where traits are reported separately. One example is a visual analogue scale (VAS), which is an unmarked or unstructured line, labeled or anchored at its ends with the ‘minimum and the maximum rating’ for a particular variable or quality aspect such as color or gloss or a texture characteristic. Other examples are semistructured line scales and Likert rating scales where there is a fixed descriptor or label along the line. 2. A scoring system that assesses individual components of appearance and texture and the scores can be totaled with a maximum score of 100 such as in the Japanese (Anon., 1985). A weakness in deriving a total score is that this implies that a shortcoming in one characteristic may be offset by a strength in another characteristic. However, in practice, a significant shortcoming in a single characteristic may result in nonacceptance by industry. Researchers may also use a combination of rating scales and scoring system for noodle evaluation (Fu and Malcolmson, 2010). The decision tree in Figure 1 can assist in designing sensory test to determine whether a consumer or trained panel is required. Sensory evaluation using a trained panel is the most reliable method for measuring the quality characteristics of noodles (Fu and Malcolmson, 2010). Standard methods give general guidance for sensory evaluation such as ISO methods (www. iso.org) and Standards Australia (www.standards.org.au). The Japanese noodle testing method for sensory evaluation of udon and ramen described by Nagao (1996) is used worldwide by flour milling companies and noodle researchers. When the research or quality control team decided on the type of sensory test needed, the rules for how to conduct such a test must be considered. When assessing appearance, standardization of the sample preparation, presentation, and panel procedures is required. Individual sensory booths are recommended, and the sensory panel should be comfortable and free from distraction and set

Acceptance e Th sion ci e e D Tre

Yes

No

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Consumer Panel

Analytical question? Yes

Yes

No

Semi trained panel

Same or different ? Re-define No No

Yes

Degree of difference ?

Trained Panel

Figure 1 Decision tree for designing sensory tests (based on Lawless and Heymann 1998).

up as to prevent discussion or interaction during assessment. The physical surroundings including odor, noise, temperature, and hygiene should be controlled. The background color in the sensory booths or viewing area should be pale and neutral, and the light source should be a standard illuminant such as daylight fluorescent. Many researchers use a color assessment cabinet that has different light sources including D65 (VeriVide, the United Kingdom). The use of a color assessment cabinet that meets international standards for visual color evaluation such as ASTM D1729 and ISO3664 is recommended. The light source in sensory booths is commonly set above a panelist so if a sample needs to be assessed for brightness or gloss, the sample position can be adjusted. In summary, the light source (daylight, fluorescent, halogen, or tungsten) must be considered when measuring color, with many researchers using daylight (D65). The influence of background and the variation in noodle thickness must also be considered in measuring noodle color whether raw or boiled. This can be solved by using layers of noodles or infinite optical thickness (IOT) or a standard backing such as a Leneta chart (Form 2C, the Leneta Co., Mahwah, NJ, the United States), which has a standard white side and black side. Standard backing tiles vary from the white tile used in Australia to black tile used by some researchers in Japan, and researchers must clearly describe what method is used to eliminate the effect of background, that is, whether IOT or a backing tile is used.

Defining quality attributes Despite the diverse range of noodle types in Japan, Okusu et al. (2010) described the desired common attributes of boiled noodles: 1. A smooth and slippery surface feel, never rough or adhering; 2. A good balance for texture between softness, elasticity, and degree of stickiness; 3. A bold shape; 4. A lustrous surface; 5. An appearance that is bright and free of bran specks.

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Further guidance on the quality characteristics that should be part of sensory evaluation using a trained panel can be found by studying the Japanese methods. Appearance should be assessed including color, brightness, visual smoothness, speckiness, and gloss. If the noodle has a square or rectangular cross-sectional shape, as with udon, the corners must be sharp. If the is noodle round, a perfectly round shape is needed, not an elliptical shape. Texture should be assessed to include the softness and hardness balance, elasticity, stickiness, and smoothness. Finally, the taste should be assessed, with a normal taste being preferred. The question of the involvement of trained experts in sensory evaluation relates to the research questions being asked. If the research question is an analytic question, which measures the degree of difference, then a trained panel is required. Western definitions for quality have relied on defects (Lawless and Heymann, 1998), but the Japanese also focus on positives in assessment Anon. (1985) so assessment and training of panelists by Japanese sensory experts in the different degrees of positive attributes are important. It is easy to eliminate a sample for an obvious negative trait but difficult to rate it on degrees of a positive trait. Chinese noodle experts also focus on both negative and positive traits. Cross-cultural sensory research is likely to provide a unique insight into the quality aspects of foods. Sensory evaluation panels need to ensure they are assessing the characteristics in the same way as industry experts. In Japan, professional panels are chosen from general panelists (semitrained) who are usually noodle technicians from major wheat milling companies and who show high ability in the assessment of quality assessed by recognition of blind samples. Professional panelists then undergo further training. Standard samples are prepared for comparison. Discriminative ability tests are used in sensory evaluation of noodles and consist of two identical samples in each sensory session, where one sample is a blind sample and one is named as the standard. If a panelist is unable to identify the blind standard, then the results are not included in the evaluation. The official Japanese method using a trained panel for udon involves assessing components of appearance, color, and surface appearance. The maximum score of 25 is given for a creamy white bright color and a 20 for very smooth appearance and with sharp corners. The texture-related maximum score of 10 is given for softness/hardness, 25 for elasticity/stickiness, and 10 for smoothness. A maximum score of 10 is given for taste, if the taste is normal. The control receives a total score of 70, that is, 31.5 for appearance and 31.5 for texture plus 7 for taste. A poor control with minimum score is 40, 18 for appearance and 18 for texture and 4 for taste that is included in sensory evaluation. The relative weightings for appearance and texture have changed in recent times, but a conversion from one system to the next can be made by a simple calculation. Training is important to show what a specific trait looks, feels, or tastes like to researchers investigating quality traits so they can then train a panel for specific traits. The Japanese assessment procedure for boiled noodle appearance is important in understanding quality aspects. For example, assessment of udon appearance is conducted by observing the condition of

the surface (smoothness or roughness) of boiled noodles, which would be difficult to assess without training by experts. Panelists in Australia have undergone extensive training by experts from Japanese milling companies on udon noodle quality assessment (Crosbie, 1991). Sensory agreement is strong between Australian and Japanese panelists in the trained panels responsible for assessing noodle quality (Crosbie, 1991). This reinforces the importance of familiarity in determining preference and differences in sensory quality traits and also highlights the importance of using standard methods for the production of foods being assessed. The compilation of descriptors, by experts, in a specific area of food quality such as noodles, aids the design of quantitative studies and training of Australian panelists in the assessment of Asian products or products with special characteristics aimed at Asian markets. Noodle sensory evaluation in China uses a similar quality scoring system to Japan of 100. He et al. (2010) described a new Chinese system where maximum score of 15 is given for color, and 10 for appearance, 20 for firmness, 30 for viscoelasticity, 15 for smoothness, and 10 for taste and flavor. In a method where the control receives 70, the maximum score of 15 is given for a bright white uniform color, 10 for visual surface smoothness, 20 for medium firmness, 20 for elasticity, 20 for no stickiness, 10 for smoothness in the mouth, and 5 for a fragrant wheat smell (Yimin Wei, Chinese Academy of Agriculture Science, personal communication). The significant cost of training, recruiting panelists, and the time to conduct sensory evaluation means sensory evaluation is not utilized widely in method development. At the very least, researchers should validate new methods using sensory evaluation to provide confirmation that instruments measure what panelists see or feel.

Noodle Color There is no international standard method available for objective noodle color measurement although there has been significant research that has provided guidelines for color measurement. A standard method should be a priority for industry. Noodles should be bright and free of specks or discoloration (Hatcher et al., 2008). Depending on noodle type, noodles should be creamy white for Japanese white salted noodle or slightly whiter for Chinese white salted noodle or yellow for alkaline noodles. Color, gloss, translucency, and texture are an external representation of internal food interactions and structures. Both appearance and texture will be affected by changes to noodle dough density due to the elimination of air or the addition of water to the dough. Color is the result of the varying structure and composition of food that selectively absorbs or reflects incident light. An object appears colored if certain wavelengths of incident light are selectively absorbed, while other wavelengths are reflected and white if all wavelengths are equally reflected. The human eye perceives color in the light wavelengths of 380 nm to 780 nm. White foods reflect light equally over this wavelength range. When white light passes through a food, it is selectively absorbed and the emergent radiation and selective scattering is perceived as color. In reflectance spectrophotometry, light

FOOD-QUALITY TESTING | Noodles: Testing for Quality scatter from a collection of particles is studied. The scatter is a result of reflection, refraction, and/or diffraction. When light penetrates a food, the scattering of light may result in this light being returned to the surface. As the size of particles is reduced, the number of scattering interfaces is increased, and a greater proportion of light is returned to the surface; thus, flour with a smaller particle size results in brighter noodles (Symons and Dexter, 1991). Reflectance may be specular (perfect specular is where light reflects at a single angle as in a mirror) or diffuse (perfect matte is where light reflects at all angles evenly). An understanding of the factors that affect surface characteristics can lead to an ability to change the characteristics of color, gloss, translucency, and texture in a defined way and to study the different aspects of the changes. Sensory evaluation is a reliable method for color assessment. Raw (fresh) and boiled noodle color is routinely measured objectively with a handheld colorimeter due to the ease of measurement. One method involves using CIELAB or Commission International de l’Eclairage CIE L* a* b* color space, which is based on Hunter tristimulus data and involves a threedimensional representation of color, with L* as the center axis ranging from white as 100 to black as zero. The red-green axis is a* with positive a* representing red and negative a* representing green. The blue-yellow axis is b* with positive b* representing yellow and negative b* representing blue (Figure 2). Noodle brightness is negatively correlated with flour protein content, flour milling yield, and flour color grade (Miskelly and Moss, 1985). Yellowness of the raw noodle sheet and boiled noodle yellowness has been shown to be correlated with yellow pigment levels in the flour (Miskelly and Moss, 1985). A visit by a Japanese noodle technologist resulted in the term ‘color stability’ and improved color stability being adopted as a new objective in the breeding of wheat for udon at the Department of Agriculture and Food Western Australia (DAFWA) in 1991. Differences in the level of the enzyme polyphenol oxidase (PPO) have been reported as a major cause of variation in brightness of noodles (Kruger et al., 1994).

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The need for brighter noodles with low discoloration or speckiness has resulted in the development of a method using image analysis by Hatcher (2010). Hatcher (2010) reported that in subjective analysis, panelists misinterpret color if specks are present and exaggerate speck darkness. Image analysis has been successfully used to characterize the degree of darkness contributed by specks (Hatcher, 2010). When measuring color, many factors must be considered such as light source used in the measuring instrument and the preparation of noodles for measurement. After preparation of noodle sheet, the raw sheet (prior to cutting to strands) is usually used in the testing. A single sheet or multiple-stacked sheets or multiple sheets to IOT are placed on standard backing tile. It is recommended to have a standard backing tile even if using multiple sheets. Measurements are then taken over time and vary with 0 h, 0.5 h, 2 h, and up to 24 h used by the various organizations and laboratories. If color stability or discoloration of raw noodle sheets is undertaken, measurements are made at either 0 or 30 min after the sheets are made and again at 24 h later. Solah et al. (2007) recommended measuring color of noodle sheets at infinite optical thickness, where CIE L*, a*, and b* measurements on black and white tiles are the same – this means that the color measurements are unaffected by background color and noodle sheet thickness. Hou et al. (2010) used a Chroma Meter CR-410 (Konica Minolta Sensing, Inc., Japan) equipped with a 50 mm diameter measuring head and stacked three noodle sheets before measurement similar to that described by Kruger et al. (1994). Color of boiled noodles can assessed at infinite optical thickness using a method developed by Crosbie. After boiling, 60 g noodles were held in a covered plastic jar for 30 min and then compressed with an Agtron sample cup (internal diameter 60 mm at the top and 55 mm at the base), and color measurements are taken through the optical glass base of the Agtron sample cup using a Minolta CRC-310 Chroma Meter (Konica Minolta Sensing, Inc.).

The measurement of translucency CIE 1976 L*a*b* Diagram L* = 100

+ b* − a*

− b*

+ a*

L* = 0 Figure 2 CIE L* a* b* color space diagram. Supplied by Nick Harkness Pty. Ltd. Sydney Australia.

Most foods, including noodles, are translucent, where part of the light is transmitted through the food. Translucency is important in specialty Asian noodle types, such as mung bean noodles. Both raw and boiled noodles also vary in translucency, and although this property is rarely assessed, it is likely to influence overall assessments of noodle appearance. Raw and boiled noodle sheets prepared by a standard method are used for translucency measurement. Solah et al. (2007) reported a method where noodle sheets (either raw or boiled) are transferred to the Leneta opacity chart (Form 2C, The Leneta Co., Mahwah, NJ, the United States) and translucency measured using a Minolta CM-508i spectrophotometer and using D65 illuminant. Reflectance is measured and reported as a CIE Y tristimulus value.

Gloss measurement Crosbie et al. (1998) reported the requirement of luster and a glossy surface for udon, and Seib (2000) reported the requirement of sheen for udon.

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Incident ray

Reflected ray

r⬚

i

r

Refracted ray

Figure 4 Light and its relationship to the observer. (a) Incident light from the light source (blue broken line), is mostly specular reflected light (red unbroken line), and minimal scattered light (yellow). (b) Incident light from the light source (blue dotted line), is minimally specular reflected light (green broken line), and mostly scattered light (orange lines).

Figure 3 The reflection and refraction of light. Note: in theory a perfect glossy surface would give a reflected ray angle of r , i ¼ r .

20⬚

Experienced Japanese udon noodle specialists determine a ‘gloss’ factor by adjusting the position of the noodles, so that light reflects from the noodles, but this characteristic is assigned to ‘visual smoothness.’ The failure to meet the requirement of noodle visual smoothness, as assessed by sensory evaluation, would mean a lower quality rating for the noodle being assessed. The main reason for the lack of research on the measurement of gloss in noodles may be the lack of understanding of its importance outside Japan. It may also be due to ) meaning the way the Japanese describe gloss as ‘koutak’ ( ‘light/beam/brilliance.’ High gloss surfaces, such as the BYK-Gardner standard black glass tile, have a refractive index of 1.5672. Refractive index is calculated as sin i/sin r where i ¼ angle of incidence and r ¼ angle of refraction (Figure 3). Different wavelengths of light are interfered with different extents by the particles that make up the food, and so refractive index of food depends on the wavelength and refraction. Refractive indexes for longer wavelengths (red) are lower than shorter wavelength (blue). A perfect glossy surface has a mirrorlike reflection, but this is not possible with most food surfaces. Gloss is affected by the viewing angle, the nature of the particles, its refractive index, and the ability to form a smooth film. Particle size is associated with gloss as pigments and particles that protrude through the surface film will reduce gloss by providing an uneven surface. To assess gloss, the observer or instrument should view or measure from the opposite side of the perpendicular at the same angle as the incident light. To assess color, an observer should avoid specular reflection since gloss masks color (Figure 4). Specular light occurs when the angle of illumination equals the angle of reflection (Figure 5). Specific gloss meters are available such as the BYK-Gardner micro-TRI-gloss meter, and there are instruments that measure color and gloss simultaneously such as the BYK color-guide gloss and spectroguide. After preparation by a standard method, the raw and boiled noodle sheets are placed on a

60⬚

85⬚

Figure 5 Specular light at 20 , 60 and 85 .

standard backing. Gloss is a surface phenomenon, so when measuring gloss, care must be taken not to touch the surface with fingers or the instrument. Time of measurements must be carefully controlled as surface water, especially in boiled noodle sheets, contributes to gloss and drying will affect results. For example, ‘glossy’ may have a positive connotation and ‘not glossy’ a negative connotation. The word ‘matte’ means not glossy but may be a better descriptor as long as there is a reference sample that shows panelists an example of the appearance of ‘matte.’ In the case of noodle gloss or translucency, panelists can be given examples (descriptors) representing the extremes of noodle gloss or translucency being assessed. The word descriptors should not imply a negative connotation.

Noodle Texture During the measurements of texture of noodles, it is critical that sample preparation is consistent and that the many variables are controlled before testing. These variables include the dimensions of the raw or cooked noodles, the time and length of cooking, the time to boiling after rolling and cutting the noodles, and time to testing after boiling the noodles (Ross, 2006). Instrumental measurement of noodles can involve the

FOOD-QUALITY TESTING | Noodles: Testing for Quality compression of the noodle strands with a blunt probe or cutting them such as in AACC International-approved method 66-50.01. Tensile measurements involve deformation and recovery involves clamping and stretching until the noodles break (Ross, 2006). Subjective texture measurement is a sensory property. When testing boiled noodles, the main textural characteristics include firmness, elasticity or springiness, stickiness, and smoothness. Noodles such as udon should be soft but not excessively soft, elastic, or springy and the surface smooth with a slight stickiness. Elasticity is related to the extent of noodle rebound after an applied stress, and if noodles lose this ability to rebound in the early stage chewing, they will be scored as less elastic. Springiness is similar to elasticity but has been linked to the time the noodles take to recover from compression or ‘rebound force.’ In contrast to udon, ramen noodle texture should be firm, springy, and smooth and have a ‘clean,’ nonsticky ‘cutting feel.’ Thus, the major differences in texture between udon and ramen are in relation to firmness and stickiness. After preparation by a standard method, the raw and boiled noodle sheets or strands are transferred to the instrument for measurement of physical properties of Asian noodle related to texture. Objective texture measurement relates to mechanical or physical characteristics. The AACC International-approved method 66-50.01, Pasta and Noodle Cooking Quality— Firmness, provides a method for measuring firmness or hardness using texture profile analysis and a texture analyzer (TA.XT 2 or TA.XT plus) (Stable Micro Systems, London). This method involves standard preparation, boiling, standard size of strands, and number of strands. A 5 mm flat Lexan blade is used to cut the noodles. Physical characteristics related to springiness, cohesiveness, adhesiveness, chewiness, and resilience can also be determined using texture profile analysis. AACC International (Asian Products Technical Committee) is developing a standard method for objective texture testing.


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Setting up your sensory evaluation method. (a) Choose and describe a method for preparing noodles for testing. Will this be a standard or optimum cooking method? (b) What is your research question? Will you use a consumer or trained panel? Why? Compare the sensory quality traits for noodles from Japan and China. How do they differ? Should you use a standard backing tile for all color measurement? Why or why not? Is gloss an important quality trait for noodles? Why or why not? Describe the major difference between udon and ramen noodles? Define the following: (a) A sensory rating system (b) A sensory scoring system (c) Noodle brightness using L* (d) Texture

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•

•

Sensory evaluation is time-consuming and requires considerable resources, including panelists and proper sensory facilities, and so is not always possible in routine quality analysis. Objective methods using instrumentation are well developed and provide an unbiased assessment of quality characteristics; however, there is a lack of standard methods for most aspects of quality. The ideal situation would be to use both sensory evaluation and instrumental methods together. There is a need for further research and international collaboration to develop definitions of quality traits and international standards for their measurement.

See also: Appendix 2: Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods; Carbohydrates: Starch: Chemistry; Food-quality Testing: The Application of Sensory Science to the Evaluation of Grain-Based Foods; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Wheat-Based Foods: Noodles: Asian Wheat Flour Noodles; Noodles: Starch.

References Anon (1985) Quality Assessment of Wheat – Sensory Tests for Noodles. Japan: National Foods Research Institute, Ministry of Agriculture, Forestry and Fisheries. Crosbie GB (1991) The relationship between starch swelling properties, paste viscosity and boiled noodle quality in wheat flours. J. Cereal. Sci. 13: 145–150. Crosbie GB, Huang S, and Barclay IR (1998) Wheat quality requirements of Asian foods. J. Euphytica. 100: 155–156. Fu BX and Malcolmson L (2010) Sensory Evaluation of Noodles. In: Hou GG (ed.) Asian Noodles: Science, Technology, and Processing, pp. 252–260. Hoboken, NJ: John Wiley and Sons. Hatcher DW (2010) Objective evaluation of noodles. In: Hou GG (ed.) Asian Noodles: Science, Technology, and Processing, pp. 227–248. Hoboken, NJ: John Wiley and Sons. Hatcher DW, Edwards NM, and Dexter JE (2008) Effects of particle size and starch damage of flour and alkaline reagent on yellow alkaline noodle characteristics. Cereal Chem. 85: 425–432. He Z, Xia X, and Zhang Y (2010) Breeding noodle wheat in China. In: Hou GG (ed.) Asian Noodles: Science, Technology, and Processing, pp. 1–23. Hoboken, NJ: John Wiley and Sons. Hou GG, Otsubo S, Okusu H, and Shen LB (2010) Noodle processing technology. In: Hou GG (ed.) Asian Noodles: Science, Technology, and Processing, pp. 99–140. Hoboken, NJ: John Wiley and Sons. Kruger JE, Anderson MH, and Dexter JE (1994) Effect of flour refinement on raw Cantonese noodle color and texture. Cereal Chem. 71: 177–182. Lawless H and Heymann H (1998) Descriptive analysis. Sensory Evaluation of Food: Principles and Practices. New York: Chapman and Hall, pp 353–794. Miskelly DM and Moss HJ (1985) Flour quality requirements for Chinese noodle manufacture. J. Cereal Sci. 3: 379–387. Nagao S (1996) Processing technology of noodle products in Japan. In: Kruger JE, Matsuo RB, and Dick JW (eds.) Pasta and Noodle Technology, pp. 169–194. St. Paul, MN: American Association of Cereal Chemists. Okusu H, Otsubo S, and Dexter J (2010) Wheat milling and flour quality analysis for noodles in Japan. In: Hou GG (ed.) Asian Noodles: Science, Technology and Processing, pp. 57–73. Hoboken, NJ: John Wiley and Sons. Ross AS (2006) Instrumental measurement of physical properties of cooked Asian wheat flour noodles. Cereal Chem. 83: 42–51. Seib PA (2000) Reduced-amylose wheats and Asian noodles. Cereal Foods World 45: 504–512.

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Solah VA, Crosbie GB, Huang K, Quail NSy, and Limley HA (2007) Measurement of color, gloss, and translucency of white salted noodles: effects of water addition and vacuum mixing. Cereal Chem. 84: 145–151. Symons SJ and Dexter JE (1991) Estimation of milling efficiency: Prediction of flour refinement by the measurement of pericarp fluorescence. Cereal Chem. 69: 137–141.

Relevant Websites http://www.iso.org/iso/home.html – International Organization for Standardization. www.standards.org.au – Standards Australia.

Pasta: Quality Testing Methods A Marti, Universita` degli Studi di Milano, Milan, Italy MG D’Egidio, Unita` di ricerca per la Valorizzazione Qualitativa dei Cereali, Rome, Italy MA Pagani, Universita` degli Studi di Milano, Milan, Italy ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

The concept of pasta quality includes different aspects having various origins (durum wheat characteristics, milling and pasta-making conditions, and cooking procedures). Gluten proteins of durum wheat are unique in assuring good pasta cooking performances. Both raw and cooked pasta characteristics are important for pasta quality. The pasta cooking procedure is quite simple, but the evaluation of cooking behavior is very complex. Pasta cooking promotes two main phenomena, starch gelatinization and protein coagulation, each playing opposing roles in the quality of pasta cooking. Presently, no objective method (chemical or instrumental tests) can substitute by itself the sensory evaluation of pasta.

Learning Objectives

• •

•

Characteristics of raw and cooked pasta are strictly related to semolina traits and pasta-making conditions. Water absorption during cooking promotes different and opposite phenomena whose varying extents determine the final quality of the product, both in terms of textural and sensory characteristics. The tests presently proposed to evaluate pasta quality mainly deal with examining of the textural properties of the cooked product.

Introduction Pasta is the most interesting product obtained from durum wheat (Triticum durum). Although pasta is no doubt the Italian food product par excellence, it is also a basic food for people living in some countries of Southern Europe and is increasingly appreciated outside of Europe. The reasons for this success are multiple and include its low price, long shelf life, ease of use, and adaptability to the most diverse eating habits. Despite these social–economic aspects, consumer acceptance and frequency of purchase are greatly influenced by the quality of the product. The various aspects concerning pasta quality along the value chain will be presented, focusing on dry pasta and the most widespread methods used for testing product quality before and after cooking.

The Concept of ‘Quality’ Related to Pasta Products Quality is a term commonly used, but not easily definable, to describe a number of features, including hygienic and sanitary,


technological, nutritional, and sensory/textural characteristics, that are often dependent on each other. This is valid for pasta as for other food products, for which the final quality is linked to the characteristics of the raw materials and processing conditions that in the case of pasta include semolina milling, dough extrusion under pressure or sheeting, drying, and cooking of the final product. The cooking behavior is deemed the most important index of pasta quality; however, consumers increasingly base their choices considering not only its sensory and textural characteristics – which they evaluate personally at the time of consumption – but also other parameters, which they cannot immediately detect and which can affect the overall quality of the product (Table 1). Hygienic and sanitary quality, in the pasta field, is a prerequisite that must be guaranteed since it is closely linked to consumer health. It is generally related to a sound and undamaged harvest, free from sprout damage, disease, mold infestations, and insect pests, all of which may be labeled as defects that greatly influence product safety and end-use characteristics. Kernels exhibiting sprout damage have high levels of a-amylase, which negatively modify starch, promoting its solubilization during cooking. Moreover, the presence of aamylase produces higher sugar levels, which, during hightemperature (HT) drying, leads to increases in the Maillard reaction extent with consequences for physical and nutritional properties, as will be discussed later. The presence of sprouted kernels is usually determined by means of the Falling Number (FN) Method (AACC International Method 56-81.03; ICC Standard 107/1) (AACC, 2011; ICC, 2011). The test measures the viscosity changes promoted by the enzymatic hydrolysis of the starch present in a slurry prepared under controlled conditions. Generally, an FN value of 350 s or longer indicates low enzyme activity and very sound wheat. As the amount of enzyme activity increases, the FN decreases. Values below 200 s indicate high levels of a-amylase activity. Among the most common alterations, Fusarium head blight should be mentioned because of its strong impact on food safety due to the potential presence of mycotoxins in infected kernels. In wheat (common wheat or durum wheat), deoxynivalenol (DON) is one of the most frequently detected mycotoxins. The debranning process before milling results in a significant reduction of the DON concentration in durum wheat kernels, improving both the sanitary quality and the refining characteristics of semolina. Technological quality determines the suitability of the raw materials to a specific industrial process. Semolina from durum wheat is recognized as the best raw material for dried pasta production due to the properties of gluten proteins, which are unique in assuring good pasta cooking. High ash content, small particles of fiber, and black particles in the final product are directly linked to the semolina yield during the

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Table 1

Criteria used to assess pasta quality

Step of the chain

Quality aspect

Quality parameter

Grain and Semolina

Hygienic and sanitary quality

Grain soundness Grain safety Microbial contamination

Grain

Semolina

Pasta

Pasta

Technological quality

Visual appearance Weight of 1,000 kernels Total Defects Vitreousness Moisture content Protein quantity and quality Non-durum contamination

Technological quality

Ash content Speck count Colour Particle size distribution Damaged starch Non-durum contamination Protein quantity and quality

Nutritional quality

Sensory quality

Semolina composition Bioactive compounds Recipe and sauces Glycemic Index Heat-damage due to Maillard reaction Visual appearance (yellow color, uniform appearance) Cooking behaviour (cooking loss, water absorption, firmness, stickiness) Flavor

milling process and therefore are related to the extrinsic quality of the raw material. Other parameters – such as protein content, gluten quality, color, particle size, and damaged starch – are mainly related to the intrinsic quality of durum wheat semolina. Both extrinsic and intrinsic quality attributes affect the pastamaking process and thus the quality of the end product. Nutritional quality is mainly related to the chemical composition of raw materials and the presence of bioactive components. Most of the bioactive compounds – such as lignans and antioxidants – are concentrated in the bran layers and in particular in the aleurone fraction of the kernel. It follows that the amount of these bioactive components is a function of the conditions used during the milling process. Moreover, pasta can be combined in many different kinds of sauces – such as protein-rich ingredients from animal origin – so as to suit every taste and to compensate for the deficiency of some essential amino acids in wheat. The Mediterranean diet solved this problem by combining pasta with legumes. As regards the conditions for the pasta-making process, the high structural compactness of the product (mainly related to the pressure extrusion step) influences not only its cooking performance but also its starch digestibility, thus accounting for the low glycemic index (<60) of the cooked product despite its high-carbohydrate content. Drying at high temperatures (80–90 C and over) promotes

extensive heat damage in dried pasta, mainly related to the Maillard reaction. In a system that contains both proteins and reducing sugars, as is the case for pasta, the interaction between reducing sugars and amino groups of lysine results in a decrease in the bioavailability of this essential amino acid. Sensory quality refers to consumer acceptability of the product. Although cooking is strategic in determining quality, evaluation starts at the time of purchase by visual evaluation of the dried product. Good quality dry pasta must have a uniform, amber yellow color. It has been well documented that carotenoid pigments and lipoxygenase activity in the semolina make pasta products yellow. To prevent a darker color from occurring, oxidation of these pigments by peroxidase has to be controlled. All the main producers of pasta-making equipment have dedicated special attention to the elimination of this defect through the use of mixing and extrusion chambers operating under vacuum to minimize oxidation of the carotenoid or xanthophyll pigments. In addition, the vacuum prevents air bubble formation, responsible for an unsightly appearance and physical brittleness in the dried product. The absence of black or brown specks is a quality indicator, too. Brown specks refer to the presence of small particles of bran in semolina, whereas black ones appear in semolina when some tainted grains (i.e., attack of black point and smudge) or other materials elude the cleaning process. Consumers may think that dark and brown specks are contaminants. White specks represent one of the most frequent defects of dried semolina pasta, due to the presence of unhydrated particles during mixing, and are clearly noticeable in the finished product. This defect not only worsens the aesthetic appearance of the product but also is associated with a nonhomogenous structure of the protein network structure, which makes the pasta very fragile both in its dry state and during cooking. The appearance of white specks can be reduced by using fine semolina (diameter of the particles < 300 mm), which have quicker hydration kinetics and produce a homogeneous moistened system (Dalbon et al., 1996). The consumer’s final judgment on pasta quality will surely be based on its behavior when cooked: Only after cooking in boiling water does pasta acquire a palatable structure, easily adaptable to the most varied tastes by adding seasonings. Cooked pasta must meet consumer criteria. In countries where pasta is traditionally consumed, textural attributes (firmness and elasticity and absence of stickiness) play a primary role in determining consumer acceptance, but other factors (good yellow color, appearance, and nutritional value) are also considered (D’Egidio and Nardi, 1996).

Measuring Pasta Quality Over the years, several methods have been developed for measuring pasta quality. These methods, however, consider only a limited number of quality characteristics, as described in the previous section. In Table 2, we propose a criterion for the classification of methods used today for measuring the quality of both dry and cooked pasta. Since most of the methods presented are strictly dependent on the type of format (longshaped or short-shaped pasta), it is recommended to compare samples that are uniform in shape and dimension in order to obtain reproducible results.

FOOD-QUALITY TESTING | Pasta: Quality Testing Methods Table 2

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Parameters and approaches used for evaluating pasta quality

Product

Dry pasta

Quality parameter

Approach

Color

Visual inspection Light reflectance measurement Near-infrared reflectance (NIR) measurement Near-infrared transmittance (NIT) measurement UV−vis measurement

Surface characteristics (heterogeneity)

Image analysis techniques

Strength

Three-point bending test

Cooking loss

Gravimetric method Colorimetric (iodine absorption) Total Organic Matter in the cooked water

Firmness Cooked pasta

Stickiness

1. Dry State Pasta color comes from a desirable yellow component and an undesirable brown and red component. The yellowness of pasta is due to semolina pigments, while the red component is the result of Maillard reactions. Pasta brightness (L) is an indicator of the overall attenuation of the light reflected by spaghetti samples when illuminated by sunlight or overcast daylight. Several analytic techniques have been developed over the years to evaluate color in semolina and pasta. Among them, the main methods have involved visual comparison with standard references (AACC 14-22.01) (AACC, 2011), chemical pigment extraction (AACC 14-50.01) (AACC, 2011), and light reflectance measurements. In the pasta sector, the most popular instruments for measuring color are based on the color space system L*, a*, b* as defined by the Commission Internationale de l’Eclairage (CIE). The success of these automatic techniques can be found in the rapidity and safety of the procedure in addition to the good correlation found between the chemical extraction of pigments and the yellowness expressed by b*, determined by the reflectance measurements. Difficulties in color evaluation can arise when short shapes are considered because the pieces cannot be arranged to form a regular and continuous surface. In this regard, the grinding of dry pasta to a prefixed particle size was proposed (Acquistucci and Pasqui, 1992). In addition, it is important to specify the depth of spaghetti and the color of background when using the color scales (Liu et al., 2013). In recent years, near-infrared reflectance (NIR) and near-infrared transmittance (NIT) and, more recently, UV–Vis spectrophotometers have been used to determine color as a useful parameter in assessing food quality. Surface characteristics are immediately perceived by sight, and it anticipates a specific tactile perception. In addition, roughness is relevant as it affects the ability to retain

Sensory analysis (the force necessary to penetrate pasta with teeth) Texture analyzer (blade probe, Kramer shear cell, firmness/stickiness rig) Sensory analysis (the work necessary to overcome the attractive forces between the surface of pasta and the surface of other materials which come into contact with the food) Texture analyzer (firmness/stickiness rig) Total Organic Matter of the rinsing water

condiments. Recently, Marti et al. (2011) proposed the evaluation of the surface texture of enriched pasta samples before and after cooking by measuring the heterogeneity parameter using techniques of image analysis, in order to gain information on the degree of roughness and, consequently, on the product structure. Samples with high surface heterogeneity also had lower resistance to fracture, thus indicating a looser internal structure that is probably one of the reasons for the irregular surface. The surface properties may also help to explain pasta cooking behavior: Products with high surface heterogeneity expose a greater area to water action during cooking and, consequently, a high amount of material may be released from the pasta surface and, consequently, into the cooking water. This phenomenon is strictly controlled by the quantity and quality of proteins and their ability to contrast starch leaching. Dry pasta has to be elastic and strong enough to resist breakage during cutting, packaging, handling, and shipping. When broken, pasta must make a dry sound and the fracture must appear smooth and glassy with no air bubbles. Bending tests have been utilized to evaluate the mechanical strength of dried pasta products since the 1930s. Today, three-point bending is the most common bending test used for measuring the resistance of pasta to breakage. In particular, the instrument applied a continuously increasing force to a strand of dried spaghetti until the break occurred. The test specimen should be much longer than its thickness and width. Although the test provides an indication of susceptibility of dried pasta to breakage, it does not relate directly to the textural characteristics of cooked pasta. 2. Cooked State The evaluation of the quality of cooked pasta is made even more complicated by variables related to modes of cooking.

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FOOD-QUALITY TESTING | Pasta: Quality Testing Methods

The most common variables include cooking time (‘al dente,’ optimal, established, or overcooked), pasta/water ratio (1:10, 1:20, 1:25, and 1:50), and type of water (tap water, mineral water, distilled, deionized, that can greatly change as far as salt concentration and pH values are concerned). The cooking procedure should be standardized, since all these features greatly affect the results. According to the AACC International Method 66-50.01 (AACC, 2011), pasta is cooked in boiling natural water with no salt added, keeping the pasta/water ratio at least equal to 1:10. Pasta is usually cooked at the optimal cooking time and the water is drained for 30 s. The optimal cooking time is determined by the time required for the dry central core to disappear when gently squeezed between two pieces of clear plastic. Pasta cooking promotes the absorption of large amounts of water (about 1.5–2 times the weight of dry pasta). The product assumes a palatable and pleasant consistency but, at the same time, maintains its physical integrity and high structural compactness. Water absorption is a complex event promoted by the exceptional capacity of protein and starch (from temperatures of 50 C and higher) to solvate and hold water. It is measured as the weight increase in pasta before and after cooking and is expressed as a percentage of weight gained with respect to the weight of uncooked pasta. While water transfer proceeds from the outside to the inside of each piece of pasta, a reverse transfer of material can take place from the pasta to the cooking water. Cooking loss measures the amount of solid material lost in the water during cooking. As an alternative to the gravimetric approach, Matsuo et al. (1992) proposed a quicker method for estimating cooking loss by reacting a clarified aliquot of cooking water with iodine and measuring the absorbance at 650 nm, corresponding to the absorption maximum for the amylose–iodine complex. Water, which acts as a plasticizer and increases polymer mobility, penetrates concentrically toward the center of the pasta during cooking. Nuclear magnetic resonance imaging (MRI) in combination with the measurement of spin–spin relaxation time (T2) has been recently used to evaluate water distribution and water mobility in dry pasta at various cooking times (Bonomi et al., 2012). The hightemperature dried products that scored best from a sensory standpoint showed the highest crosswise gradient of water content and water mobility. This suggested that slight undercooking contributes to the ‘al dente’ sensation due to the unsolvated core portion of the product, at least in hightemperature dried products. Besides the hydration extent of the solid matrix, the textural properties of cooked pasta are closely related to the outcome of two opposite and competitive phenomena, starch gelatinization and protein coagulation, a trend that has been studied by ultrastructural approaches using light and/or SEM and TEM microscopy. Despite their important role in helping to understand these phenomena, these techniques not only are timeconsuming, labor-intensive, and highly expensive but also allow only a qualitative overview and no quantitative evaluation (Resmini and Pagani, 1983). At a macroscopic level, the degree of starch gelatinization and protein coagulation affects the overall cooking quality of the final product, whose textural properties can be defined as follows (D’Egidio and Nardi, 1996):

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•

•

Firmness or hardness: the force necessary to penetrate pasta with the teeth (at the first bite). Cohesiveness or consistency: the extent to which pasta can be deformed before breaking. Elasticity or springiness or recovery: the rate at which a piece of pasta returns to its initial state after a deforming force is removed. Adhesiveness or stickiness: the work necessary to overcome the attractive forces between the surface of the pasta and the surface of other materials that come into contact with the food (e.g., tongue, teeth, palate, and fingers). Chewiness: the time (or the energy) required to masticate a sample at the rate of one chew per second in order to reduce it to a state ready for swallowing; it is related to firmness, cohesiveness, and elasticity. Bulkiness or clumpiness: the adhesion rate of cooked pasta strands with each other; it is related to stickiness.

Sensory approaches are considered to be the most reliable methods for assessing pasta quality. The International Organization for Standardization (ISO) has developed a standard method (TC 34 SC4 7304) (ISO 7304, 1985) using trained assessors for evaluating the firmness and surface condition (stickiness) of cooked spaghetti. A series of reference photographs are used to estimate the surface condition. A routine standard method (ISO 7304.2) (ISO 7304-2, 2008) was also developed for assessing the quality of cooked pasta such as spaghetti and macaroni in terms of firmness and starch release by comparison with reference samples. The general appearance, degree of swelling, and stickiness are taken into account for assessing the overall rating. Scores for firmness and surface condition are assigned using nine-point rating scales. In Italy, the quality of pasta cooked in water without salt is assessed by using the scoring method proposed by D’Egidio and Nardi (1996), for the evaluation of stickiness, bulkiness, and firmness. Each parameter was scored on a 10–100 scale, where 100 ¼ no stickiness and bulkiness and 100 ¼ very good for firmness. An overall quality score is determined by calculating the mean of each of the three scores. An overall score greater than 70 indicates good quality, while a score below 50 indicates poor quality pasta. Sensory evaluation is usually carried out after a fixed cooking time (12–13 min) and in overcooking (D’Egidio and Nardi, 1996). A quantitative description of the events occurring at a macromolecular level can be obtained by using instrumental tests for texture analysis. The texture of cooked long-shaped pasta (such as spaghetti and noodles) is evaluated in terms of maximum force achieved during the cutting cycle (peak force) and work, represented by the area under the curve (AACC International Approved Method 66-50.01; 2000). In order to assess how much variation exists when the same samples are tested, Sissons et al. (2008) compared the results of cooked spaghetti firmness tested by two laboratories according to the AACC standard method by using various load cells, number of strands and their length, texture rig type, and test speed. The study found close agreement among the methods for measuring the texture of cooked spaghetti. However, even using the same instrument to measure firmness (TA.XT2i), the authors found differences for samples that fell between the extremes in firmness, likely due to variations in the instrument settings,

FOOD-QUALITY TESTING | Pasta: Quality Testing Methods cooking method, and sample presentation used by the two laboratories. When a standard method was selected and defined in detail, results from testing ten samples in both laboratories improved the correspondence greatly. Sissons et al. (2008) highlighted that the AACC method does not specify in sufficient detail these conditions, which may account for the differences. An interlaboratory study under the auspices of AACC International is under way. This should help standardize data between laboratories. Most of the studies on pasta texture have been carried out on long-shaped pasta (such as spaghetti or noodles), while very few tests have been proposed for the various pasta shapes available on the market. Recently, Manthey and Dick (2012) investigated the suitability of various texture probes (knife probe, Ottawa cell, modified Ottawa cell, Kramer shear cell, mini-Kramer shear cell, and rectangular compression probe) for determining cooked pasta texture on various kinds of pasta (lasagna, spaghetti, rotini, and macaroni). The study highlighted the importance of measurement of multiple texture attributes, since consistency values do not by themselves accurately represent all the differences in pasta texture. In addition, results differ depending on the probe used; for example, Kramer and mini-Kramer shear cells gave opposite results compared with those of the pasta blade for macaroni. The textural characteristics of cooked pasta can also be evaluated by means of a compression test, even if this is not a standard method. Seven strands of spaghetti are placed on a specific support block and compressed with a rectangular probe for a few seconds before taking the probe from the sample. Two main parameters can be measured: (1) Young’s modulus or modulus of elasticity, calculated from the stress and strain in the initial linear domain of the curve, and (2) adhesiveness, described as the work needed to pull the sample apart and separate it from the compression plate and corresponding to the area under the zero-force line. Chemical methods are useful for evaluating surface characteristics of cooked pasta. D’Egidio et al. (1993) had developed a chemical method for the quantitative determination of the total organic matter (TOM) rinsed from the surface of cooked spaghetti that indicates the quantity of starch released from the protein matrix of cooked pasta and subsequently adheres to the product surface. Thanks to its significant correlation with sensory and instrumental values of firmness, stickiness, and resilience of cooked spaghetti, TOM values were proposed as suitable indexes for predicting the sensory quality of pasta (D’Egidio et al., 1993).


• • • • •

What are the main criteria used to assess pasta quality? What are the main attributes that affect the quality of pasta? What are the main approaches used for evaluating the quality of the uncooked pasta? What are the main approaches used for evaluating the quality of the cooked pasta? What are the main strengths and weaknesses of the current approaches?

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Most of the tests proposed for the instrumental evaluation of pasta texture focus on long-shaped pasta (spaghetti or noodles). However, today’s consumers shop for a wide range of pasta shapes, and for this reason, instrumental methods for short-shaped pasta need to be developed; What novel methods do you suggest? At the moment, there are no chemical or instrumental methods able to satisfactorily measure several sensory parameters at the same time. Consequently, sensory analysis remains the most viable to jointly assess quality parameters. What approaches may help to overcome this problem? There is a great interest in using sensor arrays for the identification of different volatile compounds, various odors, and tastes in food products. The application of the electronic nose (e-nose) and the electronic tongue (e-tongue) to pasta could represent an attractive alternative to sensory tests for quality control and process monitoring in pasta industries. Investigate this issue and suggest methods for implementation.

See also: Food-quality Testing: Noodles: Testing for Quality; The Cereal Grains: Durum Wheat: Overview; Wheat-Based Foods: Pasta.

References AACC (2011) Approved Methods of the American Association of Cereal Chemists. St. Paul, MN: AACC. Acquistucci R and Pasqui LA (1992) Preliminary results of a study on colour changes during pasta making. Nahrung 36: 408–410. Bonomi F, D’Egidio MG, Iametti S, Marengo M, Marti A, Pagani MA, and Ragg E (2012) Structure–quality relationship in commercial pasta: a molecular glimpse. Food Chem. 135: 348–355. D’Egidio MG and Nardi S (1996) Textural measurements of cooked pasta. In: Kruger JE, Matsuo RB, and Dick JW (eds.) Pasta and Noodle Technology, pp. 133–156. St. Paul, MN: AACC International. D’Egidio MG, Mariani BM, Nardi S, and Novaro P (1993) Viscoelastograph measures and total organic matter test: suitability in evaluating textural characteristics of cooked pasta. Cereal Chem. 70: 67–72. Dalbon G, Grivon D, and Pagani MA (1996) Continuous manufacturing process. In: Kruger JE, Matsuo RB, and Dick JW (eds.) Pasta and Noodle Technology, pp. 13–58. St. Paul, MN: AACC International. ICC (2011) Standard Methods of the International Association for Cereal Chemistry. Vienna, Austria: ICC. ISO 7304, 1985. Durum Wheat Semolinas and Alimentary Pasta – Estimation of Cooking Quality of Spaghetti by Sensory Analysis. ISO 7304-2, 2008. Alimentary Pasta Produced from Durum Wheat Semolina – Estimation of Cooking Quality by Sensory Analysis – Part 2: Routine Method. Liu Y, Carter CE, and Manthey FA (2013) Factors that affect CIELAB and Hunter Lab color scales. Cereal Foods World 58: A56. Marti A, Fongaro L, Rossi M, Lucisano M, and Pagani MA (2011) Quality characteristics of pasta enriched with buckwheat flour. Int. J. Food Sci. Technol. 46: 2393–2400. Mathey FA and Dick T (2012) Assessment of probe type for measuring pasta texture. Cereal Foods World 57: 6–62. Matsuo RR, Malcolmson LJ, Edwards NM, and Dexter JE (1992) A colorimetric method for estimating spaghetti cooking loss. Cereal Chem. 69: 27–29. Resmini P and Pagani MA (1983) Ultrastructure studies of pasta: a review. Food Microstruct. 2: 1–12. Sissons M, Ames N, Egan N, and Rhymer C (2008) A comparison of two instrumental techniques used to discriminate the cooking quality of spaghetti. Int. J. Food Sci. Technol. 43: 1323–1329.

Rice: Eating Quality JS Bao, Zhejiang University, Hangzhou, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Acceptance of rice variety by consumers is primarily determined by eating quality characteristics, but eating quality means different things to different people in different regions and with different cultural backgrounds. The criteria or standards for high quality, based on sensory analysis by panels and physicochemical property evaluations facilitate rice processing, breeding, and marketing. The chemical basis of the texture of cooked rice is attributed to amylose content and particularly long B chains of amylopectin; the genetic basis of the texture of cooked rice is attributed to both the waxy and SSIIa genes on chromosome 6. The chemical basis of the popcorn aroma of cooked rice is attributed to the volatile compound 2-acetyl-1-pyrroline (2AP); the genetic basis of the popcorn aroma of cooked rice is attributed to the fragrance gene (fgr) on chromosome 8. Improvement of eating quality may be fulfilled with marker-aided selection of three genes, that is, waxy, SSIIa, and fgr.

Measuring Eating Quality

Learning Objectives

•

To achieve understanding of the chemical and genetic bases of eating quality and uses of genetic tools to improve the eating quality of rice.

The eating quality can be directly characterized and measured with descriptive sensory analysis and textural instruments or indirectly predicted with a series of physicochemical property evaluations.

Sensory Evaluation

Introduction Rice is a staple food for half of the world’s population. However, more than 90% of rice is consumed in Asia, where it is a staple for a majority of the population. Rice consumption in Africa and Latin America is increasing faster than that of any other food staple in the past decade, mainly due to urbanization and changes in eating habits. In addition, European, US, and Australian citizens are eating more rice nowadays, mainly due to an increased interest in Asian cuisine. China and India alone account for over 50% of the world’s rice consumption. Since the early 1990s, strong economic growth in many Asian countries, such as China and India, halted the upward trend in global per capita rice consumption as consumers diversified their diet from rice to high-value products such as meat, dairy products, fruits, and vegetables. Thus, the consumption per capita in these two largest countries and many other Asian countries has recently decreased (Table 1). Some West African countries (Guinea, Sierra Leone, and Guinea-Bissau), Madagascar, and Guyana are in the lists of the top 20 per capita rice-consuming countries (Table 1).

166

The diverse people of different origins and with different cultural backgrounds consume rice, thus making their demands for rice quality diversified. Different countries have different requirements for the quality of rice, and within countries, preferences also vary. However, the eating quality of rice may be the first thing to be considered for consumers to choose rice for consumption. The eating quality depends on the texture and flavor of the cooked rice or rice products. The texture of the cooked rice is a principal consideration in its consumer acceptability and palatability, which is expressed in terms of hardness or firmness (or, its opposite, tenderness) and stickiness or adhesiveness and moistness to touch. The flavor of the cooked rice is expressed in terms of its aromatics, taste, and mouthfeel. The economic value of rice in domestic and international trade is arguably influenced by the eating quality of cooked rice. Understanding the chemical and genetic basis of eating quality will not only promote the circulation of rice in domestic and international business but also facilitate rice quality improvement through breeding to match the needs in the target markets.

Descriptive sensory analysis is an important tool used to characterize and measure traits of the aroma, flavor, and texture of foods by a panel including around ten specialists trained in the principles and concepts of descriptive analysis. The sensory texture profile is composed of 14 attributes that describe the rice texture at different phases of sensory evaluation (Table 2), beginning with the feel of the rice when it is first placed in the mouth and ending with mouthfeel characteristics after the rice is swallowed. During evaluation, each sample will be presented to the panelists twice, following a randomized design in which each session consists of three samples, a standard, and a blind control. The standard presented as the warm-up sample at the beginning of each session is used to calibrate the panel. After the warm-up sample, test samples are presented to panelists individually at 20 min intervals immediately after cooking, holding, and portioning into serving cups. Evaluations are conducted at individual test stations under red masking lights, during which distilled water will be used to cleanse the mouth between samples. The flavor (aromatics, taste, and mouthfeel) of cooked rice is also evaluated by the sensory panel (Table 3). The rice


http://dx.doi.org/10.1016/B978-0-12-394437-5.00133-9

FOOD-QUALITY TESTING | Rice: Eating Quality Table 1

167

Top 20 per capita rice-consuming countries

Country

Consumption (kg/capita/year)

Country

Consumption (kg/capita/year)

Brunei Darussalam Vietnam Laos Bangladesh Myanmar Cambodia The Philippines Indonesia Thailand Madagascar

245 166 163 160 157 152 129 125 103 102

Sri Lanka Guinea Sierra Leone Guinea-Bissau Guyana Nepal Korea, the Democratic People’s Republic of China Malaysia Korea, the Republic of

97 95 92 85 81 78 77 77 77 7

Source: FAOSTAT – http://faostat.fao.org/site/609/DesktopDefault.aspx?PageID¼609#ancor.

Table 2

The lexicon and their definitions used to evaluate cooked rice texture

Phases/attributes

Definition

Phase I Initial starchy coating Slickness Roughness Stickiness to lips Stickiness between grains Phase II Springiness Cohesiveness Hardness Phase III Cohesiveness of mass Chewiness Uniformity of bite Moisture absorption Phase IV Residual loose particles Toothpack

Place 6–7 grains of rice in mouth behind front teeth. Press tongue over surface and evaluate Amount of paste-like thickness perceived on the product before mixing with saliva (three passes) Maximum ease of passing tongue over the rice surface when saliva starts to mix with the sample Amount of irregularities in the surface of the product Degree to which kernels adhere to lips Degree to which the kernels adhere to each other Place 1/2 teaspoon of rice in mouth. Evaluate before or at first bite Degree to which grains return to original shape after partial compression Degree to which the grains deform, rather than crumble, crack, or break when biting with molars Force required to bite through the sample with the molars Evaluate during chew Maximum degree to which the sample holds together in a mass while chewing Amount of work to chew the sample Evenness of force throughout bites to chew Amount of saliva absorbed by sample during chewing Evaluate after swallow Amount of loose particles in mouth Amount of product adhering in/on the teeth

Source: Champagne ET, Bett-Garber KL, Fitzgerald MA, et al. (2010) Important sensory properties differentiating premium rice varieties. Rice 3: 270–281.

Table 3

The lexicon and definitions used to evaluate cooked rice flavor (aromatics, taste, and mouthfeel)

Sewer animal Floral Grain starchy Hay-like musty Popcorn Corn Alfalfa/grassy/ green beans Dairy Sweet aromatic Water-like metallic Sweet taste Sour/silage Astringent

An immediate and distinct pungent aroma in the flavor characterized as sulfur-like and generic animal. The animal aromatic in the flavor can sometimes be identified as ‘piggy’ Aromatics associated with dried flowers, such as lilac and/or lavender. This aromatic is characterized as spicy floral as in an ‘old-fashioned sachet’ A general term used to describe the aromatics in the flavor associated with grains such as corn, oats, and wheat. It is an overall grainy impression characterized as sweet, brown, sometimes dusty, and sometimes generic nutty or starchy A dry, dusty, slightly brown aroma/flavor with a possible trace of musty odor A dry, dusty, slightly toasted, and slightly sweet aroma in the flavor that can be specifically identified as popcorn The sweet aromatics of the combination of corn kernels, corn milk, and corn germ found in canned yellow creamed-style corn A dried, green, slightly earthy, slightly sweet aroma/flavor including grassy and fresh green bean aroma/flavor A general term associated with the aromatics of pasteurized cow’s milk. Most apparent just before swallowing A sweet impression such as cotton candy, caramel, or sweet fruit that may appear in the aroma and or aromatics Aromatics and mouthfeel of the minerals and metals commonly associated with tap water. This excludes any chlorine aromatics that may be perceived Basic sweet taste associated with sugar A sour fermented vegetation aroma/flavor, not decaying vegetation The chemical feeling factor on the tongue, described as puckering/dry and associated with tannins or aluminum

Source: Champagne ET, Bett-Garber KL, Fitzgerald MA, et al. (2010) Important sensory properties differentiating premium rice varieties. Rice 3: 270–281.

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FOOD-QUALITY TESTING | Rice: Eating Quality

lexicon includes 13 unique flavor attributes that are determined by smelling and evaluation in the mouth. The intensities are scored based on a universal scale for all foods, with the maximum rating for rice flavor attributes generally set at about 5. The advantage of sensory evaluation is that it provides direct description of the eating quality (palatability) of rice by consumers, and it may directly determine consumer acceptability. The disadvantage is that the eating quality evaluated by the panels is constrained to the region where the panels live or in the same populations as the panels. Regional difference and cultural background have a great impact on the sensory quality. It is difficult to compare the sensory parameters across different labs and different regions. Needless to say, the cost of training and maintaining a descriptive panel is always high.

25

Kg

20 H1 Height of first curve 15

10

Area first bite Area second bite

5 A1 0

Instrumental Texture Analysis

D1 (4.9 mm)

A2 A3

D2

Area of negative curve

The texture of cooked rice can be measured by different types of textural instruments. Texture profile analysis (TPA) can be conducted with a texture analyzer, for example, the model TA.XT2 texture analyzer (Texture Technologies Corp., Scarsdale, NY). The cooked warm rice grains are arranged in a single grain layer on the base plate. A two-cycle compression, force versus distance program is used to allow the plate to travel, return, and repeat, which simulates human teeth biting the rice grain. A typical texture profile is shown in Figure 1. It should be noted that the texture and flavor of cooked rice may be affected by the water-to-rice ratio during cooking. The amount of water affected 11 of the 14 texture attributes (Table 2). Of these 11, initial starchy coating, slickness, stickiness between grains, cohesiveness, and uniformity of bite increase in intensity with greater amounts of water at cooking, whereas hardness, stickiness to lips, springiness, and chewiness decrease in intensity. However, the flavor attributes across all cultivars are not significantly affected by the water-to-rice ratio. The advantage of the instrumental analysis of the texture of cooked rice is that it provides a relatively objective and easy measurement tool with the characteristics of being cost- and time-consuming and facilitates comparisons of results derived from different labs, regions, and countries. The disadvantage is that it is only a simulation test, which cannot reflect the real sensory attributes of humans so, in many cases, it cannot predict the real eating quality measured by descriptive sensory evaluation.

Physicochemical Property Evaluation Although descriptive sensory analysis methodology is commonly used for evaluating the intensity of the sensory attributes of cooked rice, it is typically time-consuming and only assesses whether the rice cultivar has quality characteristics deemed desirable by a target population or for a specific application, falling short in measuring subtle differences in sensory quality. Amylose content, gel consistency, gelatinization temperature (GT), and pasting viscosity are regarded as traditional parameters to describe the eating quality of rice. All these parameters reflect the properties of the starch that makes

–5 Figure 1 Typical texture profile analysis (TPA) curve of 1 g rice samples. Attributes on curves: H1, hardness (kg), measurement of force at peak of first curve; A1, area under first curve; A2, area under second curve; A4, measured from first data point to first probe reversal point; A5, measured from first probe reversal point to point where force returns to zero; A2/A1, cohesiveness, ratio of area under curves A2/A1; A3, adhesiveness, area of negative force curve, representing work to separate plunger from sample on upstroke after first curve; D2/D1, springiness, ratio of D2 to D1, where D1 is the total distance traveled by plunger on downstroke and D2 is the distance traveled on downstroke by plunger from point of sample contact to end of downstroke.

up 90% of milled rice. For objective traits, the advantage of using these parameters is that they offer possibilities to compare the physicochemical properties among different rices cultivated in different countries/regions, under different environments. The amylose content is measured with a process using I2–KI solution. However, this method always gives an overestimation, due in part to the value being contributed by amylopectin. Thus, the amylose content of starch as determined by reaction with iodine is termed apparent amylose content (AAC). The AAC of milled rice may be classified as waxy (1–2%), very low (5–12%), low (12–20%), intermediate (20–25%), and high (>25%). The AAC is considered the most important determinant of cooked rice texture, but this constituent falls short as a predictor, because cultivars with similar AAC may still differ in textural properties. The actual value of amylose can be obtained by using the size-exclusion chromatography (SEC) method, which separates polymers based on size. Since the size of amylose and amylopectin molecules differs substantially, they may be separated by SEC. This method does not need a calibration curve, but it is low-throughput and so, it is not appropriate for the routine screening of amylose in breeding programs. The gelatinization temperature (GT) is the critical temperature at which starch granules irreversibly lose their birefringence and crystalline order during heating. The GT can be directly measured under polarized light microscopy with a


Score

Grain not affected Grain swollen Grain swollen, collar incomplete, or narrow Grain swollen, collar complete, and wide Grain split or segmented, collar complete, and wide Grain dispersed, merging with collar Grain completely dispersed and disintegrated

1 2 3 4 5 6 7

CPV 90

SB CS

240 Viscosity (RVU)

Description

320 Temperature Profile

PV BD

75

160 HPV 60

Temperature (°C)

Table 4 Description of the ASV for milled rice after soaking in 1.7% KOH for 23 h

169

80

45 0

heating stage to record the temperature when the birefringence is lost. The GT can also be measured by differential scanning calorimetry or indirectly by the alkali spreading value (ASV) test for rice grains. The ASV is the degree of spreading and disintegration values of six milled rice grains after soaking in 10 ml 1.7% KOH for 23 h at 30 C (Table 4). The ASV of 5.5–7.0 is classified as low GT (55–69.5 C); 3.5–5.4, intermediate (70–74 C); and 1–3.5, intermediate-high or high (74–80 C). The ASV test is usually used by rice breeders due to its simplicity and high-throughput characteristics. Gel consistency is used as a parameter to index the tendency of cooked rice to harden on cooling. This method was originally developed to differentiate cooked rice texture among high-AAC rice. It measures the distance traveled by a gel after cooking. According to the gel length, gel consistency can be classified as soft (61–100 mm), medium (41–60 mm), and hard (25–40 mm). Pasting viscosity is another useful parameter to differentiate rice with similar AAC and is popularly measured by a Rapid Visco Analyzer (RVA). The RVA records the viscosity continuously as the temperature is increased, held constant for a time, and then decreased (Figure 2). Briefly, according to the method of The American Association of Cereal Chemists (AACC) 61-02, rice flour slurry is made in the RVA canister consisting of 3.0 g (12% mb) of rice flour and 25 g of distilled water. The heating profile is set as follows: (1) the temperature is held at 50 C for 1 min, (2) the temperature is linearly ramped up to 95 C until 4.8 min, (3) the temperature is held at 95 C until 7.5 min, (4) the temperature is linearly ramped down to 50 C at 11 min, and (5) the temperature is held at 50 C until 12.5 min. A typical RVA profile is shown in Figure 2. It should be noted that the degree of milling affects not only the texture and flavor of cooked rice but also the physicochemical properties. All these measurements for eating quality assume that the optimum degree of rice milling has been applied to obtain the milled rice. Similar to instrumental texture analysis, the advantage of physicochemical property analyses is that they provide a relatively objective measurement tool for the indirect prediction of eating quality. All the analyses are easy and fast and can routinely be conducted in a quality lab. These analyses also facilitate comparisons of results derived from different labs, regions, and countries. However, the disadvantage is that they fall short in predicting the real eating quality measured by descriptive sensory evaluation.

3

6 9 Time (min)

12

15

Figure 2 The RVA pasting viscosity profile of rice starch. The pasting viscosity parameters: PV, peak viscosity; HPV, hot paste viscosity; CPV, cold paste viscosity; PT, pasting temperature. In addition, the secondary parameters of breakdown, setback, and consistency viscosities can be calculated as PV-HPV, CPV-PV, and CPV-HPV, respectively.

In terms of eating quality evaluations, it is suggested to keep some rice with different eating qualities as standard rice and used as controls. These standard rice can be not only used for panel training for sensory evaluation but also used in instrumental texture analysis and physicochemical property evaluations, which may facilitate comparisons of eating quality across different labs in different regions.

Relationship Between Texture Attributes and Physicochemical Properties The AAC has long been considered the most important determinant of cooked rice texture. Cooked rice with a low-AAC cultivar is soft, moist, and sticky in texture, and those with high AAC are dry, firm, and fluffy. The sensory properties of freshly cooked rice measured by panelists using descriptive sensory analysis vary widely, but 11 of 14 parameters correlate well, either positively or negatively, with the AAC, with correlation coefficient values in the range of 0.76–0.92. Particularly, the AAC is positively correlated with hardness (r ¼ 0.90) and negatively correlated with stickiness to lips (r ¼ 0.91), stickiness between kernels (r ¼ 0.91), and cohesiveness of mass (r ¼ 0.92). Grain flavor ranges in intensity from 2.2 to 4.9 and correlates highly and negatively with the AAC (r ¼ 0.88). Some RVA parameters have significant correlations with AAC; it was found that none of the cooked rice textural attributes, whether measured by descriptive analysis or TPA, are linearly modeled with high accuracy by the RVA. The sensory texture attributes cohesiveness of mass, stickiness, and initial starchy coating and TPA attribute adhesiveness have the strongest correlations with RVA measurements. Setback explains most of the variance attributed to models describing these attributes; the strongest correlation is with cohesiveness of mass (r ¼ 0.69). Inclusion of amylose and protein contents in regression analyses do not strengthen models, and exclusion of samples that cook atypically, based on amylose content or GT types, slightly improve the accuracy of RVA measurements for predicting the cooked rice texture.

170


Criteria for Eating Quality Consumer preferences for rice vary in different areas of the world. It is difficult to find a rice cultivar that could meet the demands of consumers around the world. However, global demand for high-quality rice is ever increasing both in local production regions and in regions in which rice is imported. For the promotion of rice trade, it is necessary to have a standard of grain quality for the commodity. To facilitate appraising the eating quality of new rice cultivars in breeding programs, it is also important to set up standards for eating quality evaluation. US Standards for Milled Rice (2009) provide a system of marketing rice by grade that takes into consideration those quality factors associated with cleanliness, soundness, and purity. However, the eating quality of milled rice has not been included in the standards. In Thailand, Thai aromatic rice has long been well known in international markets and is always exported using the name Thai Hom Mali rice, jasmine rice, or Thai aromatic rice. For the benefit of Thai exporters, the Ministry of Commerce, with cooperation of the Ministry of Agriculture, cooperatives, and private sector, established a notification on the subject: Thai Hom Mali Rice Standards B.E. 2544. These standards comprise both physical and chemical analyses and have two points regarding eating quality: (1) Thai Hom Mali rice such as Khao Dawk Mali 105 and RD15 has a natural fragrant aroma depending on whether it is new or aged rice. Its cooked rice kernels have a tender texture, and (2) it has an amylose content of 13–18%. In China, the Ministry of Agriculture released a standard for cooking rice variety quality in 1986 (NY20-1986) for facilitating the breeding, registration, and extension of new rice cultivars with good grain quality. With changes in grain production, processing, and cropping system rearrangement, the standard was revised in 2002 (NY/T593-2002) with concomitant release of three related standards for indica-type cooking rice (NY/T594-2002), japonica-type cooking rice (NY/T595-2002), and aromatic rice (NY/T596-2002). A new version of these standards was renewed in 2013. In addition to the milling quality and appearance quality required for different grades of high-quality rice, this standard (NY/T593-2013) provides the grade for eating quality (Table 5). Two methods are used for the evaluation of eating quality; one is the sensory test, which is regarded as an arbitration method, and the other is physicochemical property evaluation with three common parameters, ASV, GC, and AAC. Sensory evaluations refer to another national standard – Method for sensory evaluation of paddy or rice cooking and eating quality (GB/T15682-2008). This test includes five items; aroma flavor, surface structure, palatability, taste, and texture of cold cooked rice, which accounts for a score of 20, 20, 30, 25, and 5, respectively, in a total score of 100. If rice meets the requirements of any grades in the standard, it is called high-quality rice including grade 3. Otherwise, it is not a high-quality rice. The eating quality parameters used in indica-type cooking rice (NY/T594-2002) and japonica-type cooking rice (NY/T595-2002) are the same as those in NY/T593-2013 (Table 5). For facilitating rice cooking for sensory evaluation, the water-to-rice ratio is stipulated based on the AAC, where the water-to-rice ratios are 1.2, 1.3,

Table 5 Quality requirements for different grades and different types of rice stipulated in the Chinese standard for cooking rice variety quality (NY/T593-2013) Rice type

Grade

Sensory evaluation

ASV

GC (mm)

AAC (%, db)

Indica nonwaxy rice Indica waxy rice

1 2 3 1 2 3 1 2 3 1 2 3

90 80 70 90 80 70 90 80 70 90 80 70

6.0 6.0 5.0 6.0 6.0 5.0 7.0 7.0 6.0 7.0 7.0 6.0

60 60 50 100 100 90 70 70 60 100 100 90

13.0–18.0 13.0–20.0 13.0–22.0 2.0 2.0 2.0 13.0–18.0 13.0–19.0 13.0–20.0 2.0 2.0 2.0

Japonica nonwaxy rice Japonica waxy rice

1.4, and 1.5 for rice with AAC in the range of 15.0, 15.1–20.0, 20.1–25, and >25.0%, respectively. To facilitate paddy rice circulation, marketing, and market management and promote the rearrangement of the cropping system, the General Administration of Quality Supervision, Inspection and Quarantine of China released a national standard for high-quality paddy in 1999 (GB/T17891-1999), which is still in effect now. This standard stipulates the definition, classification, quality requirement, test methods, and requirement for the packaging, transportation, and storage of high-quality paddy commodities. It also provides parameters for eating quality by grade (Table 6). These standards provide the eating quality requirement of rice commodities for breeders, processors, and merchants and also allow both exporters and importers to have the chance to meet the standards of rice quality in the target market.

Chemical Basis of Eating Quality The chemical basis of the texture of cooked rice attracted researchers’ attention in the period between World War II and the mid-1980s, during which the research repeatedly suggested that amylose content is the single largest determinant of its texture. The greater the amylose, the firmer the cooked rice texture is and vice versa. However, it has been realized that amylose is not sufficient to explain why the texture of cooked rice still differs among rice with similar amylose content, especially within high-amylose rice. It was also found that part of the amylose in rice starch is soluble in hot water and that the proportion of the soluble amylose as a fraction of the total amylose content differs widely among different varieties. The insoluble amylose content of rice (total minus soluble amylose) shows a striking correlation with rice texture, particularly in the high-amylose group, which could be divided into three distinct subgroups showing a distinct texture after cooking. Perhaps, it is related to retrogradation, because it is clearly the insoluble amylose that retrogrades and thus provides greater rigidity to the starch granules and hence to the cooked rice grain. The chemical nature of the insoluble amylose was intensively investigated by characterizing the structure of amylopectin. It


171

Table 6 Quality requirements for different grades and different types of rice stipulated in China national standard for high-quality paddy (GB/ T17891-1999) Rice

Grade

AAC (%, db)

Taste

GC (mm)

Color and smell

Indica paddy

1 2 3 1 2 3

17.0–22.0 16.0–23.0 15.0–24.0 15.0–18.0 15.0–19.0 15.0–20.0 2.0

9 8 7 9 8 7 7

70 60 50 80 70 60 100

Normal Normal Normal Normal Normal Normal Normal

Japonica paddy

Waxy paddy (indica and japonica)

was found that amylopectin also binds iodine, which is apparently caused by the presence of some very long chains. The chain length distribution of rice amylopectin also differs among different rice accessions, with high-amylose rice having more very long B chains than low-amylose rice and intermediateamylose rice having in between. The amylose content of starch as determined by reaction with iodine is always overestimated with part of the value being contributed by amylopectin. It is found not only that amylopectin in high-insoluble amylose rice has more long B chains but also that these chains seemed to be largely located externally in the molecule and vice versa. Thus, the texture of cooked rice is closely correlated with the relative abundance of long B chains in its amylopectin. The more long B chains, the firmer the cooked rice is and vice versa. Long B chains in amylopectin strengthen the starch granules through intermolecular interaction, leading to a firm texture of cooked rice. The chemical basis of the flavor and aroma of cooked rice has received attention. More than 200 volatile compounds have been identified in cooked rice, but only a few of them may relate to the aroma and flavor of cooked rice. It is difficult to determine which volatile compounds are responsible for the perceived aroma/flavor of rice. Only one compound, 2-acetyl1-pyrroline (2AP; popcorn aroma), has been confirmed to contribute a characteristic aroma. Furthermore, 2AP is the only volatile compound in which the relationship between its concentration in rice and its sensory intensity has been established. The fragrance gene (fgr) regulating the biosynthesis of 2AP has been cloned. It encodes the betaine aldehyde dehydrogenase 2 (BADH2). A deletion of 8 bp in this gene truncates and makes nonfunctional the BADH2 protein, leading to accumulation of 2AP in the rice grain. Other factors may also contribute to the difference in eating quality among different rice cultivars. Protein is the second most abundant component of rice endosperm and constitutes 6–10% of the dry matter in the milled rice. The protein content of milled rice has a negative correlation with the appearance, flavor, and stickiness of cooked rice. High-protein rice has much firmer texture than low-protein rice. The eating quality of cooked rice decreases as the ratio of protein body I to the content of total rice protein increases. Further, the cooked rice becomes harder, and the aroma and taste deteriorate with the addition of prolamin. As rice grain storage protein prolamin is located in protein body I, it is expected that the eating quality of cooked rice decreases as the ratio of prolamin to the content of total rice protein increases. The granule-bound starch synthase I (GBSSI) protein is positively correlated with

amylose content (r ¼ 0.95) but negatively correlated with cooked rice stickiness (r ¼ 0.85). The effect of protein content on the texture of cooked rice may also contribute to its glass transition (Tg) being slightly lower than that of starch, so when cooked with limited water, for example, in a rice cooker, the higher the protein content, the more water bound by proteins would be, leaving less water for the swelling of starch granules and leaching of amylose. The addition of proteins or its components in a viscosity test demonstrates their ability to modify the viscosity curves. The modification may be through binding water, which causes the concentration of the dispersed and viscous phases of gelatinized starch to increase, and through the agency of a network linked by disulfide bonds. The lipid content and fatty acids of milled rice may also affect eating quality. Rice lipids are generally classified as starch and nonstarch lipids. The lipid content of milled rice ranged from 0.2% to 2%. Rice varieties with high lipid content and linoleic acid content exhibits better appearance and flavor of the cooked rice and high palatability. The fat content of milled rice correlates positively with the sensory characteristics hardness, color, intactness of grains, puffed corn flavor, raw rice flavor, wet cardboard flavor, and hay-like flavor intensity and negatively with the sweet taste, degree of agglomeration, adhesiveness, cohesiveness, and cohesiveness of mass. Rice with high activities of lipase and lipoxygenase exhibits a low palatability. During storage, the appearance, aroma, taste, cohesiveness, and hardness of cooked rice deteriorate, and this deterioration is accompanied by changes in the chemical components of rice, particularly lipid content and composition. Decreased nonstarch lipid and linoleic acid and increased oleic acid and palmitic acid contents may be responsible for the deteriorations of eating quality after storage.

Genetic Basis of Eating Quality The eating quality of rice is under genetic control. The chemical constituents, that is, starch (amylose and amylopectin) and its structural features, protein, and lipid that influence the eating quality, are characteristics of the rice. These chemical constituents are synthesized through some metabolic pathways under the control of a series of genes. One of the most important pathways is starch synthesis since starch constitutes 90% of the milled rice, so it plays the most important role in the formation of eating quality.


172

Amylose is synthesized mainly by GBSSI, and the amylopectin synthesis process is governed by a combination of multiple isoforms of starch synthase, branching enzyme, and debranching enzyme to produce a uniform number of chains per amylopectin cluster. The waxy (Wx) gene on chromosome 6 encoding GBSSI is mainly responsible for the natural variation in amylose content, gel consistency, and RVA pasting viscosity. Five functional markers in the Wx gene, a (CT)n microsatellite (or simple sequence repeat), a 23 bp insertion/ deletion sequence, and three single-nucleotide polymorphism (SNP) markers are well characterized, with different alleles differing in AAC (Figure 3(a)). Among them, the (CT)n microsatellite in the Wx gene located 55 bp upstream of the putative leader intron 50 splice site has many alleles with n ranging from 8 to 22 in diverse rice germplasm (Figure 3(b)). The G/T SNP at the putative leader intron 50 splice site, and a G to T mutation at this site, reduces the efficiency of Wx pre-mRNA processing and thus results in the lower level of spliced mature mRNA, Wx protein, and AAC (Figure 3(c)). Waxy, low-amylose, and some intermediate-amylose rice have the T SNP allele, while some intermediate- and high-amylose rice have the G allele. Over 75% of the total observed variation in the AAC can be explained by the (CT)n microsatellite and the G/T SNP in the nonwaxy rice accessions. The Wx gene is also responsible for biosynthesis of extralong unit chains of amylopectin in rice. Among the high-AAC rice, the exon 10 SNP of Wx gene is responsible for the difference in the gel consistency, the proportion of soluble to insoluble apparent amylose, gel hardness, and RVA pasting viscosity. The rice with SNP allele C at exon 10 produces soft, viscous gels and has a soft texture when cooked, but with high retrogradation, and the rice with SNP allele T gives a short, firm

(CT)n

G/T

gel and has a firm texture when freshly cooked with little change in texture over storage. The SSIIa is a major gene for GT, thermal properties, and amylopectin structure, which elongates the short A and B1 chains with a degree of polymerization (DP) < 10 to form long B1 chains of amylopectin. The GT was negatively correlated with the amount of DP6-11 and positively correlated with the amount of DP12-24 of amylopectin and is positively correlated with the degree of crystallinity of starch. In waxy rice, in which the Wx gene is dysfunctional, SSIIa is the major gene responsible for the variations in pasting, gelatinization, and retrogradation properties. Four functional SNPs in the SSIIa gene have been revealed by several research groups, in which the third site where valine encoded by GTG is replaced by methionine encoded by ATG at 4198 bp position and the fourth site where glycine–leucine encoded by GGGCTC is replaced by glycine–phenylalanine encoded by GGTTTC at 4229/4330 bp are crucial for SSIIa activity (Figure 4(a)). The SSIIa enzyme is inactive when it is A SNP (coding for methionine) no matter which SNP at 4229/ 4330 bp (GC/TT) is present. The GC/TT is most common and is strongly associated with the GT (Figure 4(b)). This GC/TT polymorphism alone can differentiate rice with high or intermediate GT (possessing the GC allele) from those with low GT (possessing the TT allele), explaining 62.4% of the total variation in pasting temperature (Figure 4(c)). Few rice accessions with the GC allele have a low-GT phenotype, which can be explained by their carrying the A SNP allele in the third SNP. However, it should be mentioned that the A allele of the third SNP (G/A) is quite rare in natural populations. In addition to the genetic effects, the eating quality of rice is also affected by the environment. The texture attributes

Exon 2

Exon 6

Exon 10

InDel

A/C

C/T

(a)

Wx

100

AAC (%)

150

35 30 25 20 15 10 5 0 8

10

11

12

17

18

19

20

21

22

(CT)n

T G

AAC (%)

(b) 30 25 20 15 10 5 0

T

G G/T allele

(c)

Figure 3 Relationship between the Wx alleles and apparent amylose content (AAC). (a) Wx gene functional markers, a (CT)n microsatellites, the G/T SNP in intron 1, the 23 bp duplication in exon 2, a A/C SNP in exon 6, and a C/T SNP in exon 10; (b) genotyping the (CT)n microsatellites (left) and comparison of AAC of each microsatellite class; (c) genotyping the G/T SNP and comparison of the AAC of each allele class.


G/C

A/G

173

A/G GC/TT

(a)

F7

F22 GC

82.0

TT R21

80.0

R1

78.0

F7F22/R1 5 6 7 8

F7/R1R21 9 10 11 12 F7F22/R1R2 13 14 15 16

76.0

PT (°C)

F7/R1 1 2 3 4

74.0

TT

GC

72.0 70.0

(b)

TT

68.0

GC

66.0 –50

A

50

150

250

350

450

550

(c)

Figure 4 Relationship between the SSIIa alleles and gelatinization temperature. (a) SSIIa functional SNPs. (b) Strategy for genotyping the fourth GC/TT SNP (up) and gel image showing different PCR products amplified by different combinations of the primers. (c) The relationship between pasting temperature and GC/TT alleles; the blue circle shows some rice with A SNP at the third site.

roughness and hardness and the flavor attributes hay-like, sweet aromatic, sour, and astringent are significantly different between two cropping years, which may be attributed to the variation in the AAC and protein content as affected by the environment. The AAC is increased when rice is grown at a cooler temperature. Wx gene expression is activated reversibly in response to a cool temperature (18 C), and it is the Wx promoter that is responsive to a cool temperature. The G/T SNP at the alternate splicing site is also temperature-dependent. At 25 C and particularly at 32 C, the amount of mature GBSS mRNA in developing seeds is dramatically reduced. This is one of the reasons why low-amylose varieties are particularly temperature-sensitive. The steady-state level of GBSS mRNA is essentially identical over this temperature range for the rice with G SNP allele. Environmental factors also affect the GT, resulting in a difference of up to 10 C between some rice starches. Environmental factors, especially temperature during grain filling, can modify the expression of the SSIIa gene and hence modify the amylopectin chain length. The amount of short chains in the amylopectin increases significantly, whereas the amount of long chains decreases in rice grown at lower temperatures, resulting in a lower GT.

Improvement of Eating Quality The improvement of eating quality is an essential target of current breeding programs designed to meet industry standards or eating characteristics preferred by consumers in domestic or international markets. Three questions need to be answered before breeding for high eating quality is conducted. The first question is what kind of rice is preferred by

people in the region or country? If a new rice is for exporting, the same question is what kind of quality rice is preferred by people of the country or needed in the targeted market. The second question is what kind of traits should be improved. The third question is what kind of tools are available for breeding, what molecular markers could be used at the genomic level at this time? The first question has been answered by the International Network for Quality Rice, which has conducted a survey of consumer preferences for rice quality in different riceconsuming regions. The maps showing regional variation in amylose and GT, consumer’s preferences for texture based on gel consistency, and consumer’s references for aromatic rice are useful for breeders worldwide, particularly for those whose rice is targeted to the international market. The current eating quality status of your rice materials should be surveyed to understand whether the quality matches the consumer preference and to determine which trait needs to be improved. If allele information of the microsatellites of the Wx gene, SNP of SSIIa, and insertion/deletion marker (8 bp) of fgr for eating quality traits are available in your rice materials, it is easy to transfer the allele of these genes from one variety to another by crossbreeding and backcross breeding with the help of molecular marker detection. In F2 lines, the phenotype is matched with its genotype very well when these functional markers are used to improve the eating quality of a highAAC, high-GT, and nonfragrant maintainer rice II32B from another low-AAC, low-GT, and fragrant rice (Figure 5). The breeding practice with marker-aided selection is also called molecular breeding. In addition to use in molecular breeding, these three gene markers can also be used in the diagnosis of quality traits for

174


M P1 P2 1

2 3

4 5 6

7

8 9 10 11 12 13 14 15 16 17 18 19 20

200bp

100bp (a)

500bp

GC

300bp

TT

(b)

300bp

200bp (c)

Figure 5 Segregation of the marker genotypes at three loci in F2 lines: P1: Yixiang B; P2: II-32B; 1–20 F2 individuals; (a) genotypes of Wx marker; (b) genotypes of SSIIa marker; (c) genotypes of fgr marker. GC represents GC SNPs, and TT represents TT SNPs of SSIIa gene.

rice collecting from markets. Since sensory and physicochemical property evaluations may be influenced by processing, milling, and storage, genotyping with molecular markers can avoid the side effects of these factors and can reduce analysis time, cost, and required sample size.


•

• • • •

What kinds of rice are preferred and what are their physicochemical properties in your region? Does your country have standards for high-quality rice and what are the parameters to evaluate the eating quality? Do you think eating quality affects consumer acceptability? What other factors may affect consumer preference? How do you measure the eating quality of rice and their advantages and disadvantages? What are the chemical and genetic bases of the eating quality of rice? How could you use molecular markers to diagnose the eating quality of rice in the supermarket?


• • •

How could you exploit new techniques such as electronic nose and electronic tongue to predict the eating quality of rice? What is known, and what still needs to be determined, about the genetic bases for other volatile compounds? What is the genetic basis of sensory parameters in rice? How will new molecular tools for eating quality contribute to our ability to manipulate the sensory quality of rice?

See also: Barley, Rice and Maize Processing: Rice Processing: Beyond the Farm Gate; Breeding of Grains: Rice: Breeding; Genetics of Grains: Rice: Genetics; The Cereal Grains: Rice: Overview; Wildrice, Zizania: Overview.

Further Reading Ayres NM, McClung AM, Larkin PD, et al. (1997) Microsatellites and a single-nucleotide polymorphism differentiate apparent amylose classes in an expanded pedigree of US rice germ plasm. Theoretical and Applied Genetics 94: 773–781. Bao JS (2012) Towards understanding of the genetic and molecular basis of eating and cooking quality of rice. Cereal Foods World 57(4): 148–156. Bao JS, Corke H, and Sun M (2006) Nucleotide diversity in starch synthase IIa and validation of single nucleotide polymorphisms in relation to starch gelatinization temperature and other physicochemical properties in rice (Oryza sativa L.). Theoretical and Applied Genetics 113: 1171–1183. Bao JS, Xiao P, Hiratsuka M, et al. (2009) Granule-bound SSIIa protein content and its relationship with amylopectin structure and gelatinization temperature of rice starch. Starch-Starke 61(8): 431–437. Bao JS, Zheng XW, Xia YW, et al. (2000) QTL mapping for the paste viscosity characteristics in rice (Oryza sativa L.). Theoretical and Applied Genetics 100: 280–284. Bhattacharya KR (2005) The chemical basis of rice end-use quality. In: Toriyama K, Heong KL, and Hardy B (eds.) Rice is Life: Scientific Perspectives for the 21st Century, pp. 246–248. Philippines: IRRI. Bhattacharya KR (2009) Physicochemical basis of eating quality of rice. Cereal Foods World 54(1): 18–28. Calingacion M, Laborte A, Nelson A, et al. (2014) Diversity of global rice markets and the science required for consumer-targeted rice breeding. PLoS One 9(1): e85106. Champagne ET (2008) Rice aroma and flavor: A literature review. Cereal Chemistry 85(4): 445–454. Champagne ET, Bett-Garber KL, Fitzgerald MA, et al. (2010) Important sensory properties differentiating premium rice varieties. Rice 3: 270–281. Champagne ET, Bett-Garber KL, McClung AM, et al. (2004) Sensory characteristics of diverse rice cultivars as influenced by genetic and environmental factors. Cereal Chemistry 81: 237–243.

FOOD-QUALITY TESTING | Rice: Eating Quality Champagne ET, Bett-Garber KL, Vinyard BT, et al. (1999) Correlation between cooked rice texture and rapid visco analyses measurements. Cereal Chemistry 76: 764–771. Cheaupun K, Wongpiyachon S, and Kongseree N (2005) Improving rice grain quality in Thailand. In: Toriyama K, Heong KL, and Hardy B (eds.) Rice is Life: Scientific Perspectives for the 21st Century, pp. 248–250. Philippines: IRRI. Fitzgerald MA, Bergman CJ, Resurreccion AP, et al. (2009) Addressing the dilemmas of measuring amylose in rice. Cereal Chemistry 86(5): 492–498. Jin L, Lu Y, Shao YF, et al. (2010) Molecular marker assisted selection for improvement of the eating, cooking and sensory quality of rice (Oryza sativa L.). Journal of Cereal Science 51: 159–164. Juliano BO (1998) Varietal impact on rice quality. Cereal Foods World 43: 207–218.

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Tran NA, Daygon VD, Resurreccion AP, et al. (2011) A single nucleotide polymorphism in the Waxy gene explains a significant component of gel consistency. Theoretical and Applied Genetics 123: 519–525. Umemoto T and Aoki N (2005) Single-nucleotide polymorphisms in rice starch synthase IIa that alter starch gelatinization and starch association of the enzyme. Functional Plant Biology 32: 763–768. Umemoto T, Yano M, Satoh H, et al. (2002) Mapping of a gene responsible for the difference in amylopectin structure between japonica-type and indica-type rice varieties. Theoretical and Applied Genetics 104: 1–8. Yoon MR, Rico CW, Koh HJ, et al. (2012) A study of the lipid components of rice in relation to palatability and storage. Journal of the Korean Society for Applied Biological Chemistry 55: 515–521.


Contents Fermentation: Origins and Applications Fermentation: Foods and Nonalcoholic Beverages Beverages: Distilled Beverages: Asian Alcoholic Beverages

Fermentation: Origins and Applications BJB Wood, Strathclyde University, Glasgow, UK ã 2016 Elsevier Ltd. All rights reserved.

Introduction Fermentations are vital in utilizing many grains, pulses, and other seeds. This article will attempt to place fermentation in context with respect to its contributions to improving palatability, digestibility, and other desirable properties of foods derived from these concentrated, but sometimes, rather uninteresting raw materials. The raw materials from which the foods are derived may also contain toxins or ‘antinutritional factors’ and fermentations can help to ameliorate the effects of these substances on the consumer. Archaeology shows that seeds were used as foods from the very beginning of the transition from hunter–gatherer lifestyles to the more settled communities that were needed to support the greater complexities of even the most primitive agricultural systems. Consideration of how fermentations developed to support consumption of seedbased foods is, necessarily, entirely speculative now. It is known that the earliest civilizations had well-developed technologies for making staples such as bread and beer, and that they had taken significant steps in selective breeding to effect the transformation of (for example) wild grasses into more productive cereal crops. They surely lacked any conception of scientific breeding, microbiology, or any other, among the scientific disciplines which is in use in modern research, agriculture, and manufacture. A great respect for their powers of observation and a priori deduction must therefore be felt, leading to palatable and useful products, and to the start of food industries. Obviously the choice of seeds to use in these ways was heavily influenced by climate and other environmental factors. Rice, wheat, and rye have become successively dominant crops from South to North in the northern hemisphere. The hardiness of rye and primitive barley strains (such as the bere barley still grown in the Orkney Islands and remote upland regions of Iran) means that these cereals are found in various regions where the environment is too harsh for more tender crops. This article will necessarily rely more on speculation

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than hard fact, but will make an honest attempt to identify some of the factors underlying the successes of fermentations in processing seed crops.

The Beginnings of Food Fermentation Although it cannot be known how or when the practice of fermentation in relation to food began, all available evidence suggests that it is a very ancient part of human development. In fact, fermentation can be seen as a subset of biodeterioration. All things that can serve as foods for humans (or any other animal) are, by their capacity to act as foods, more or less unstable. If they are food for mammals, then they will also be able to support the life of many types of bacteria, molds, etc. In practice, even such apparently stable materials as wood are open to attack by microbes, insects, etc. There is a powerful drive throughout nature to use the energy and nutrition present in organic materials, eventually mineralizing these materials back to carbon dioxide, water, and simple mineral salts. Attacks by such microorganisms are seen as, primarily, a deterioration, or loss of desirable characteristics. Some such changes, however, turn out to have desirable characteristics. Such changes may produce improvements in flavor, odor, and texture. In addition, there is substantial evidence of improvements in nutritional status and value arising from controlled fermentations. Various studies have shown that even simple fermentations of basic cereal grains with the indigenous (mainly lactic acid bacteria) microflora generate significant increases in the levels of some B-vitamins. There are strong suggestions that plant proteins, which are somewhat difficult for the monogastric digestive system to handle, can be made more digestible through the actions of proteolytic enzymes produced by bacteria and fungi. Many adults are intolerant to lactose, the principal sugar of milk, but fermentations such as those which produce yogurt, reduce or eliminate this problem.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00135-2

BEVERAGES FROM GRAINS | Fermentation: Origins and Applications Fermentations can also reduce or remove toxins and other ‘antinutritional factors.’ Perhaps the most important example of the former is the detoxification of cassava, while an example of the latter is hydrolysis of phytic acid, with removal of sequestering by it of divalent metals. There is also the prospect that fermentation increases the stability of the affected food, increasing its resistance to attack by other organisms. Before the advent of modern methods for food preservation, such as freezing, canning, etc., even a short extension in storage life would be precious. The prolonged storage possible for the main protein in milk (casein) consequent upon conversion to a hard cheese (such as Cheddar) would thus be of immense value. It must also be remembered that availability throughout the year is a very modern phenomenon. In any given region (particularly in the temperate parts of the world) food supply is very seasonal. The idea that tomatoes, apples, ‘new’ potatoes, would be always on sale, would have seemed unreasonable even a couple of decades ago. Now it is taken for granted throughout the industrialized world. In contrast to this prevailing situation with respect to foods rendered inherently unstable (‘perishable’) by virtue of their high water content, seeds were designed by evolution to remain stable and viable until conditions appropriate for germination were encountered. This made them excellent for storage during temperate and high latitude winters and the dry seasons of more tropical climates. Obviously evolution did not design seeds to be palatable to animals because this would defeat their primary role as reproductive agents. It can be seen in, for example, the evolution of seed-eating birds, a competition between the birds’ need to eat, and the seeds’ need to survive to germination, and so to resist being eaten. Thus sorghum and millet have bitter-tasting tannins in their outermost layers, and attempts to breed low-tannin cultivars were more beneficial to the birds than to the farmers. Unfortunately, there are no fermentation strategies available at present that can remove such tannins, although it is conceivable that fungal enzymes could be harnessed for this purpose in the future. On the other hand, antinutritional factors such as trypsin inhibitors are ameliorated by fermentation. Phytic acid presents an interesting situation. It is reasonable to see it as principally a phosphate, reserved for use as required by the developing seedling as germination progresses. However, its capacity to chelate divalent metal ions definitely gives it an antinutritional role, perhaps more particularly for monogastric animals. Also, the lack of phytase in the gastric juices of animals means that its valuable phosphate and inositol are denied to these consumers. Fermentations of ‘uncooked’ seeds permit phytases present in the seed to effect at least a partial hydrolysis of the material, and this may be supplemented by phytases generated by microbes participating in the fermentation.

An Example The existence of small pits (perhaps a cubic meter, or even less) dug into the chalk of southern England, has long been known, but their purpose(s) remain matters for controversy. One suggestion has been that they would have been used to store grain. However, a priori this seems unlikely. In the ground, grain will

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be exposed to moisture. All seeds will take up available water as a preparation for germination, and will then become more easily attacked by microbes than the dry seeds would be. Chalk, being very porous, will readily conduct water. Thus grain storage in pits dug into the surface of chalk would seem to be an inappropriate method for conserving the material. However, experiments showed an interesting sequence of events. Dry grain was packed into pits prepared for the purpose, and the pits were then sealed with a cap of clay or other impervious material. Initially, the grain closest to the clay took up water and was then colonized by a range of fungi and other microorganisms. Eventually this agglomeration of grains, hyphae, etc., formed an impervious layer, preventing further ingress of moisture. In addition, respiration by the stored grain and the microbes feasting in the outer layers of the stored material used up the available oxygen, replacing it with carbon dioxide. Thus, at the sacrifice of the outermost layer of the stored material, the bulk of it was preserved for a long time. This does not correspond with normal ideas of a foodfermentation process. However, it has illustrations for a number of key points. The pit makers could have had no understanding of the processes at work in their pits. Despite this, the prevailing conditions favored growth of microbes in a beneficial way. There was some loss of stored material, but this was an acceptable price for the storage of the rest in useable condition. All of the foregoing is speculation; we can have no certain knowledge of how the pits were used by their makers. The grain storage hypothesis is nevertheless a valid one, and experiments show that the pits would operate as conservation devices.

Historical Background Very often an understanding of how fermentation began is speculation based on the interpretation of the modern process in the light of the knowledge of conditions in the past. Sometimes this is aided by ancient records, such as pictures from Egyptian tombs or continuing oral traditions, but in many cases such evidence is scanty or entirely absent. Thus, there is a great deal of guesswork in our attempts to reconstruct how particular fermentations originated. In most cases this is unimportant, but it can be irritating when faced with a product such as ‘kefir.’ Here the fermentation relies upon structures called ‘grains.’ Modern analyses show that these grains are highly structured arrangements of yeasts and bacteria upon polysaccharide membranes. These organisms can be separately cultivated in the laboratory, but they do not reform into the characteristic kefir grains when cultured together. How did the grains arise? Was this a single event, or did it happen several times (kefir is widespread across Russia and Eastern Europe)? Clearly, it is unlikely ever that the answers to such questions will be known. Even in simpler cases, such as bread making or the conversion of grapes to wine or grain to beer, there are no records showing the beginnings of such activities. Often there are myths showing such knowledge as gifts from gods or other superior intelligences. Also, foods such as bread and wine frequently have a place in sacramental activities. The giving and consumption of bread and wine, central to the Christian Eucharist, is also found in older traditions, such as those associated with the Roman god Bacchus. This infers the great importance

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BEVERAGES FROM GRAINS | Fermentation: Origins and Applications

of such activities at the change from hunter–gatherer economies to the beginnings of settled agriculture. The author suggests that this knowledge was an essential part of that change. The ability to store foods enhanced survival over-winter and in other periods of hardship. Converting dry grains and other seeds into something more appetizing than a gruel must have made agriculture more attractive and valuable. Alcohol, despite its dangers, provided (and still provides), in reasonable moderation, a basis for social interaction. The apparent changes in the nature of consciousness affected by alcohol must have had spiritual significance, and the economic power possessed by those who control its production and distribution remains important to this day. The vital part played by bread in the agrarian economies of Europe is made starkly plain by the draconian laws controlling the activities of medieval bakers, and that of beer by ordinances such as the German pure beer laws. The trade in fish sauces throughout the Roman Empire affords another example. Fish sauces is often associated with the Far East, but it is known that several fish sauces have been produced in the Mediterranean region since ancient times. Archaeological evidence indicates that these products were traded in substantial amounts throughout the Empire, even as far as Hadrian’s Wall. Although it cannot be known for certain their nature, it seems clear that these were important condiments in the Roman kitchen. The value of vinegar, as both a condiment and a preservative, has been recognized since the most ancient times. It also had importance in medicine and healing. While the earliest vinegars were, as the very name strongly suggests, produced by souring of wine, in more Northern climates, wine was probably too scarce and valuable to be used thus wastefully. Thus vinegars based on malted grains became economically significant. However, to achieve slow acetification, these were still produced by the traditional processes originally developed for wine vinegars (hence the name ‘Orleans Process’ through association with the French town of that name). With the rapid transfer of the British population from a mainly rural existence to an increasingly urban one, consequent upon the Industrial Revolution, the enhanced demand for vinegar resulted in development of the ‘Quick’ vinegar process to replace the slow Orleans method.

Physical and Chemical Properties of Raw Materials for Fermentations Appropriate fermentation techniques for given products will be strongly influenced by the physical and chemical properties of the raw material(s) to be used in its preparation. It is therefore useful to attempt a classification of raw materials. What follows will be entirely pragmatic, and is not intended as a formal classification scheme. Instead it will be a grouping by the characteristics most relevant to fermentation procedures. In order to do this, it is first desirable to review the relevant physical and other characteristics. Of the physical properties, probably the most important will be the availability of water, as this will strongly influence the types of organisms whose growth can be supported on a particular medium, and, in the extreme case, whether any organisms at all will grow on the material in question. Water availability can be limited by simple physical dryness, i.e., the

actual absence of water, and by osmotic pressure creating a physiological drought. Salt and/or sugar in foodstuffs most commonly induce the latter. It should be noted that quite low concentrations of salt, well below that which might be expected to induce significant osmotic stress, can strongly influence the course of fermentations. This must have some significance in bread making with yeast, but becomes more significant in certain types of sourdough bread production, for example the German process called the Manheim salt-sour method. This is a rather simple example of how the chemical composition of the fermentable material is of great importance in determining the types of organisms that can grow on it and the outcomes of fermentations which they affect. In some cases, there will be ample supplies of (for example) sugars to give desired levels of organic acids, B-vitamins to support growth of fastidious lactic acid bacteria, amino acids, etc. In many cases, however, there will be insufficient readily usable material. Then, organisms which can produce and export appropriate hydrolytic enzymes (amylases or proteases, for example) will be at an advantage. They may also prepare the way for later growth of less competent organisms such as yeasts and lactic acid bacteria. The part played by chemicals in herbs, onions, garlic, etc. can be particularly interesting. These materials are valued principally as flavors in foods, but many of them also have long traditions as healing agents and medicines. There is increasing evidence that these traditions have a secure basis in scientific fact. The review by Sherman and Flaxman discusses claims that onions, garlic, and many culinary herbs are powerfully inhibitory against bacteria associated with food poisoning. Some baked foods use such herbs and spices, but of more evident importance is their role in foods such as continental sausages, where comminuted meat and cereal products are combined with such spices, and some of which use particularly high levels of garlic (e.g., salami). Sausages are harsh environments even without these inhibitors. Yet bacteria such as species of Carnobacterium and Micrococcus are present in these products, and are thought to be essential for flavor development. How selective is the toxicity of these plant products? There are clearly interesting biochemical challenges here, even if these claims were shown to be fully justified in the field, i.e., in actual food fermentations. It has been pointed out that, for example, salamis, although particularly heavily spiced with garlic, have been associated with serious illnesses due to Escherichia coli. Thus, claims of this type need to be assessed very carefully, with purely laboratory studies and robust trials in actual foods being run in partnership with each other, if the effects on food microflora of herbs and spices are to be fully understood. The foregoing is not intended as a complete discussion of the issues involved here. Rather it is an indication of some of the factors that require consideration when attempting to understand the factors influencing the initial development and subsequent evolution of food fermentations associated with grains and other seeds.

A Classification of Plant Raw Materials The great diversity of plant materials means that any attempt at grouping into classes will be fraught by difficulties caused by

BEVERAGES FROM GRAINS | Fermentation: Origins and Applications overlaps and ambiguities. For example, tomatoes and cucumbers, although obviously fruit, are often placed among the vegetables, while the edible stems of rhubarb are placed alongside fruits. Thus, what follows is entirely arbitrary, reflecting the practical problems in fermenting plant foods.

Leafy Material Grass and other forage materials are converted into silage on an enormous scale as an essential part of modern ruminant farming. Although not normally thought of as ‘food’ fermentation, i.e., not part of the ‘human’ diet, this is probably the most important among leaf fermentations in the wider context. Among materials for direct human consumption, the best known products are ‘kimchi’ and ‘sauerkraut.’ The latter is a highly industrialized process in the major producing nations. Undoubtedly, it was developed principally as a storage process for conserving excess cabbage through the winter in areas where the severe winter weather would destroy cabbage heads left in the fields, while cut heads would quickly deteriorate in store if held as the unmodified material. The key factors for fermentation are provided for by adding 2–3% by weight of salt to shredded cabbage heads, then packing tightly into containers, where the sap withdrawn from the plant tissue by osmotic action of the dissolving salt quickly displaces remaining air from the plant material. Bacteria naturally present on the plant surfaces drive the lactic fermentation, although there is a tendency toward using selected cultures now. This simple process gave a product that could be conserved without deterioration for many months, even in the absence of refrigeration. Obviously, there is no need to continue this process as a means for conserving cabbage in industrialized societies, where advanced storage systems and transportation, which can deliver any food from any part of the world without regard to season, provide complete freedom from the old domination by the solar cycle. However, this has not reduced demand for the fermented product. On the contrary, those accustomed to it have taken its production with them when they have migrated to, and settled in other parts of the world. Consequently its production is, if anything, increasing. The technology is basically the same for the materials discussed in the next section, with the key difference being that they use salt in prepared brine, whereas here dry salt is added to the raw material.

Fruits Cucumbers are perhaps the classical example here, although olives would be cited first in Mediterranean climates. Other examples include tomatoes. Small onions and certain types of radish roots, although not fruits, are processed in the same way. Again the technology is very simple, easily applicable on a village or domestic level, and originally a way to conserve seasonal surpluses of produce against winter shortages. Essentially, the prepared material is immersed in a salt solution (brine) and a spontaneous lactic fermentation develops. In reasonably cool conditions, the products are stable during prolonged storage. The observations about the survival of sauerkraut technology, after the conservation need had passed, apply with equal force here, as do those on industrialization of the processes. Olives are remarkable in the market

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penetration that the fermented product has achieved outside its traditional consumers. Another type of conservation of fruits relies on fermenting the released juices to produce stable liquids. This is a very pedestrian way to describe the delights of wines and the products from apple (cider; USA ‘hard cider’) and pear (perry) juices, but is deliberately done to place them in a specific context. Undoubtedly, the capacity of the products to induce intoxication would have attracted attention as soon as they were discovered. Indeed, there is ample evidence that birds and mammals are attracted to fermenting fruits, and will manifest clear evidence of drunkenness, and even of addiction to ethanol. In many cases, the intoxication became associated with religious experiences among humans. Despite these complicating sociological factors, alcoholic fermentation can properly be seen as a preservation strategy, essentially indistinguishable from those presented in the preceding two sections. Sweet fruits have a very short storage life, although strategies have been developed to permit storing some hard fruits (notably apples and pears) for extended periods. At the other extreme, grapes are so easily bruised that picking them for table-use demands great care; the yeasts always present on the grape skins quickly ferment the fruit juice at the slightest opportunity. The only practical alternative to fermentation is drying to raisins, currants, and sultanas.

Roots, Bulbs, and Tubers In general, root crops are stable enough for their storage in simple systems, and even for them to be left in the ground during winter until required. Thus, with minor exceptions such as the radishes referred to above, root crops are not fermented in temperate climates. Bulbs are also generally stable enough for winter storage, so fermentation in brine is probably done more for culinary than for conservation reasons. The New World has contributed, among many other valuable crops, three novel starchy crops that have now become so indispensable that their origins now forgotten. Of these, one is a cereal (maize) but the other two are root crops, potatoes (Solanum tuberosum) and cassava (Manioc esculenta). Of these two, the author has no knowledge of potatoes being fermented, except in the very limited sense of their being a source of starch for alcohol production. Potatoes can produce various toxins as defenses against predators, but protecting the tubers from exposure to light easily prevents production of the most important of these, and the author is not aware of any evidence that fermentations will reduce toxicity of green tubers. On the other hand, fermentation is absolutely essential for making cassava safe for use. Most varieties are extremely toxic, because of the presence of a cyanogenic glycoside. In the intact tuber this, and the enzyme that can hydrolyze it, are strictly segregated, but mechanical damage brings them into contact, thus releasing the highly toxic hydrogen cyanide. It is clear that even very primitive people from their native habitats had developed techniques for making the tuber comparatively safe to eat. These are not primarily fermentations, depending as they do on the enzymatic action described above to destroy the cyanogenic glycoside. However, the conditions under which the tubers are harvested and prepared for detoxification

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ensure that there is an abundant microbial flora associated with them. Lactic acid bacteria, which do not use iron-containing enzymes, are resistant to cyanide, and their growth on the cassava portions produces acidic conditions that both favor the action of the relevant enzyme and help in removal of the cyanide as the unionized gaseous form. Subsequent processing, such as drying, reduction to granular form and heat treatments such as (in the case of products such as the West African ‘gari’) roasting. Unfortunately, even ‘garification’ will not reliably remove the last traces of cyanide. Although the residual material is below the acutely toxic concentration, it can, by competing with iodide, produce the thyroid gland malfunction known as goiter.

Seeds The plant products discussed so far have been characterized by high water content. This is true even of the firmest products, such as the root crops. This water content means both that any injury leaves the foodstuff liable to fermentation or other microbial attack, and that even the undamaged item has a restricted storage life because eventually water loss will reduce it to a flaccid and uninviting state. However, some vegetables can be made suitable for storage by deliberate, controlled dehydration. With seeds, as already noted their evolutionary development resulted in a very dry, tough, long-lasting product. Seeds are also packed with nutrients placed there by the parent plant to support initial growth of the new plant whose embryo the seed contains. Thus a seed has many characteristics, which make it potentially desirable as a human or animal food. From the human viewpoint however, seeds often have significant disadvantages as foods. As harvested, they are difficult to eat. If processed in the obvious way, by soaking and/or boiling in water, the product is apt to be rather bland and unappetizing. Indeed, of the various grains and seeds harvested by humans, only rice is primarily consumed in this way. Comminution by crushing or grinding can effect some improvements, but the resulting gruels or porridges are still of limited appeal. Much the same is true if the material is formed into a paste and baked or roasted. On the other hand, even the simplest fermentations can effect considerable improvements. For example, a common breakfast dish in Africa is a maize porridge in which the ground maize is left overnight in water, and then boiled next morning, ready for eating. Overnight there is substantial acidification through the action of lactic acid bacteria. Although this is a fairly minor change, the result is a much more appetizing porridge, especially when a little crude sugar is added just before consumption of the cooked material. Most such mixtures of flours and water will develop substantial populations of lactic acid bacteria, alone or associated with yeast cells. Microbial gas production will cause some expansion of the paste or dough, and give a tastier and more appealing product upon cooking. The most obvious example of this type is of course sourdough bread. It seems reasonable to believe that this is a very ancient product, and archaeological evidence is emerging to support this view. At the most basic level leaving the dough overnight will produce a leavening effect. A simple

improvement would be to add a part of a good ferment to a fresh mixture of flour and water. This process, sometimes called ‘back slopping’ remains the basis for much sourdough bread production to the present. Not only does it provide a more reliable fermentation, but also the increased level of microbes present, and the fact that they are already in active fermentation will tend to give enhanced leavening of the bread over that which could be expected from a newly started fermentation. A more dilute mixture of flour and water would give a crude alcoholic drink. The really important development here was the discovery that germinating the seeds greatly increased the alcoholic content, and the general quality of the resulting drink. Beer production in the West further modifies the properties of the drink by drying and heat treatment of the germinated seeds (barley malt). This also permits production of the malt in quantity greater than is immediately required, and its storage for future use. African sorghum beer does not require this added refinement, and it seems reasonable to think that the earliest barley fermentations would have used ‘green’ (undried) malt. Again the fermentations would have used a mixture of lactic acid bacteria and yeasts. It is clear that from fairly early times residual yeast from beer and wine fermentations were used for bread making. Equally, ‘kvass’ fermentation from rye bread and water uses a portion of sourdough bread ferment to start a new brew going, although once started, it is maintained by ‘feeding’ the ferment with additions of bread and water. Rice flour mixed with legume seed flour and water will ferment with leavening provided by carbon dioxide generated by heterofermentative lactic acid bacteria. In parts of India, this simple process yields products such as ‘idli’ and ‘dosa.’ It seems that rice will not malt well, although the author is not aware of any specific reason why this should be so. Certainly it is not fermented by processes involving germination. Instead ‘koji’ processes similar to those used for soy sauce and other legume seed fermentations have long been employed in preparatory stages for subsequent conversion of rice into alcoholic beverages, vinegar, etc. Essentially strains of the koji mold Aspergillus oryzae producing high levels of amylolytic enzymes are employed to saccharify the rice starch, followed by alcoholic fermentation under conditions such that the fugal enzymes remain active during it, so providing a steady supply of fermentable carbohydrates. Thus, seeds rich in starch are converted to many foods and drinks by a range of fermentations that depend on yeasts and lactic acid bacteria, alone or in associations. Fermentations of protein-rich seeds, particularly the soybean (Glycine max) and the ground nut (peanut, monkey nut, Arachis hypogea), of tropical and subtropical origin, together with the seeds of tropical leguminous trees, have provided both staple foods (such as ‘tempeh’ and ‘oncom’ (‘ontjom,’ ‘onjom,’ etc.) and flavoring materials (soy sauce, ‘miso,’ etc.) throughout the tropics and subtropics for many thousands of years. The driving force for such developments was probably the rather bland nature of the starting materials, but it is now known that fermentations can increase the digestibility of constituents of the seeds, particularly the proteins, enrich the products with extra B-vitamins, decrease concentrations of some toxic or antinutritional factors, and increase the availability of essential mineral nutrients. These fermentations are frequently multistage, using mold

BEVERAGES FROM GRAINS | Fermentation: Origins and Applications fungi to manufacture a range of digestive enzymes, then yeasts and lactic acid bacteria to complete the process. The origins of these fermentations are lost in time, but it is known that soy sauce and miso have existed for at least 3000 years. Legume seeds tend to be rather well supplied with antinutritional factors, and detoxification during the fermentation is a significant benefit of the process. Perhaps the most remarkable example of seed detoxification however, concerns the castor bean (Ricinus spp.). This seed contains a wealth of toxic materials, including ricinoleic acid (a powerful purgative), strongly allergenic proteins, ricin, etc. Despite this, in parts of Nigeria the seeds are collected, boiled, de-hulled, wrapped in leaves and allowed to ferment, then used as a food flavoring, apparently without any ill effects on its consumers.

Types of Fermentations It is worth noting the range of fermentation procedures developed for dealing with foods. The simplest are probably the liquid fermentations used in making drinks such as beers, kvass, wines, and some of the milk products such as yogurt and buttermilk. These are sometimes called suspension cultures because the microbial cells float suspended in the surrounding liquid. Another name is stirred tank reactor fermentations. Fermentations involving molds usually require free access to the air, both to meet the organism’s need for abundant oxygen, and to remove the products of the fermentation, principally carbon dioxide and heat. In one case (tempeh), however the process requires a very limited exposure to oxygen, traditionally achieved by wrapping the substrate in banana or teak leaves, although plastic bags pierced with a pattern of fine holes now often replace these. Such fermentations, which do not require free liquid water, are described as solid substrate processes. Some lactic fermentations, for example, of starchy or farinaceous materials, might also be placed here, as might sausage fermentations. When a solid substrate is in free water, it appears that this is just a type of suspension culture, but there is evidence to suggest that the active microbes attach themselves to the solid material to a considerable extent, thus producing some characteristics of a solid substrate process. The kefir grain provides an interesting problem. Attachment of the cells to the polysaccharide membrane suggests solid substrate process, but analysis of the fermentation shows that there are large numbers of cells suspended in the liquid, quite free of the grains, and that the proportions of bacterial species in suspension are radically different from the proportions within the grains. In Orleans vinegar production, the acetification is effected by a layer of bacterial cells growing as a film or skin at the interface between water and air, so exhibiting some characteristics of a solid substrate process. The ‘Quick’ process features a layer of cells on the surface of the wood shavings, irrigated by the recycling liquid, but also supplied with abundant oxygen, thus showing an even closer relationship to solid substrate process. Citric acid production by Aspergillus used to require static growth on the surface of a liquid layer, rather like the Orleans vinegar process. Some processes were described using growth on bamboo supports and a liquid recycle like the ‘Quick’ vinegar process, but it is not clear if these were applied on a production scale.

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The Future for Traditional Fermentation Processes Some very ancient fermentation processes continue to flourish and develop on a very large scale. Soy-sauce production almost seems capable of expansion without limit, as does cheese. Yogurt has been a remarkable success story, with market penetration far beyond its traditional homelands. Vegetable fermentations, such as sauerkraut and olives also seem to grow, although they perhaps do so more slowly than some of the other cases cited. The sourdough bread story is another remarkable one, with the product now on offer at (it seems) every airport in the USA. There does not seem to be any fear for the future of these and a selection of other products. It is also noteworthy that cerealbased products, notably bread and beer, are effectively penetrating markets (such as South-east Asia) where they did not have a traditional role before colonial times. On the other hand, there is substantial concern for some of the more modest traditional fermentation processes found in the developing countries. These have made a significant contribution to the peoples’ nutrition in the past, and the example of tempeh shows how they can substantially improve the nutritional status of the poorest folk. Tempeh itself seems to be robustly addressing the challenge offered by modernizing Indonesian society, but this is an exception. Sorghum beer in South Africa is another example where (in this case with intelligent support from the central government) a traditional food item continues to enjoy a place in an evolving society’s markets. In many cases, however, modernization tends to displace traditional foods with imported ones perceived as more ‘Western’ by precisely those consumers who are least able to afford the change to imported food fashions. The drift from rural to semiurban living exacerbates the situation. The traditional food fermentation processes are essentially rural, low technology processes conducted at an almost domestic level. Hygiene considerations alarm the Western observer, but in general the adapted consumer population seem to suffer no harm from these products. There are exceptions of course. The continuation of poisoning outbreaks caused by consumption of ‘tempeh bonkrek’ in Indonesia, despite the authorities’ efforts to ban its production, demonstrate the kind of danger which exists. On balance, however, the author’s opinion is that loss of traditional knowledge regarding the conduct and management of traditional fermentations will be a serious matter. This knowledge tends to be the preserve of women. Young people are not interested in learning about these matters, and emerging societies tend to place an even lower value on ‘women’s knowledge’ than developing ones do. Courses on food, fermentation, etc., need to place stress on the value of such information. This is perhaps the only way in which this unique knowledge pool can hopefully be conserved.

See also: Barley, Rice and Maize Processing: Barley: Malting; Beverages from Grains: Beverages: Distilled; Fermentation: Foods and Nonalcoholic Beverages; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Non-food Products from Grains: Fuel Alcohol Production; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Wheat Processing: Milling and Baking: History; Wheat-Based Foods: Breads.

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Further Reading Bushell ME (ed.) (1984) Progress in Industrial Microbiology. In: Modern Applications of Traditional Biotechnologies, vol. 19. Oxford: Elsevier. Campbell-Platt G (1987) Fermented Foods of the World: A Dictionary and Guide. London: Butterworths. Dirar HA (1993) Indigenous Fermented Foods of the Sudan. Oxford: CAB International. Hesseltine CW and Wang HL (eds.) (1986) Indigenous Fermented Foods of NonWestern Origin: Mycologia Memoirs, No. 11. New York: New York Botanical Garden. Huang HT (2000) Science and Civilisation in China, 6(v): Fermentations and Food Science. Cambridge: Cambridge University Press. Pederson CS (1979) Microbiology of Food Fermentations, 2nd edn. Westport, CN: AVI.

Reddy NR, Person MD, and Saluniche DK (eds.) (1986) Legume-Based Fermented Foods. Boca Raton: CRC Press. Rose AH (ed.) (1982) Economic Microbiology. In: Fermented Foods, vol. 7. London: Academic Press. Sherman PW and Flaxman SM (2001) Protecting ourselves from food. American Scientist 89(2): 142–151. Steinkraus KH (ed.) (1989) Industrialization of Indigenous Fermented Foods. New York: Marcel Dekker. Steinkraus KH (ed.) (1996) Handbook of Indigenous Fermented Foods, 2nd edn. New York: Marcel Dekker. Sudarmajdji S, Suparmo S, and Raharjo (eds.) (1998) Reinventing the Hidden Miracle of Tempe. Jakarta: Indonesian Tempe Foundation. Wood BJB (ed.) (1998) Microbiology of Fermented Foods, 2nd edn. Glasgow: Blackie.

Fermentation: Foods and Nonalcoholic Beverages JRN Taylor, University of Pretoria, Hatfield, South Africa ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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taken place or could easily take place, and lastly the potential for further development of these products.

What are lactic acid bacteria. The factors that affect the intensity and type of fermentation. The potential nutritional benefits of lactic acid fermentation of cereals. The potential health benefits of lactic acid fermentation of cereals and possible negative effects. The basic types of traditional lactic acid-fermented cereal food and beverage products. Processes for the production of examples of the basic types of lactic acid-fermented cereal products. Commercial developments in lactic acid-fermented cereal products. Potential for innovative health-promoting lactic acidfermented cereal products.

Learning Objectives

• • • • • •

To understand the basic principles of lactic acid fermentations. To understand the nutritional benefits of lactic acid fermentation of cereals. To understand the potential health benefits of lactic acid fermentation of cereals. To be aware of the major different types of traditional fermented cereal foods and beverages. To understand the basic principles involved in the production of traditional fermented cereal food and beverage products. To be aware of the potential for innovative fermented cereal food and beverage products.

Introduction According to Steinkraus, fermented foods (including beverages) can be defined as “food substrates that are invaded or overgrown by edible microorganisms, whose enzymes and metabolic processes modify the substrate producing nontoxic flavors, aromas, and textures attractive to the human consumer.” As grains are the world’s most important foodstuffs, there are several categories of fermented grain foods and beverages. This article, however, will only deal with traditional cereal-based products that are produced with a predominantly lactic acid bacterial fermentation. Specifically, this article will examine the lactic acid bacteria (LAB) responsible for lactic acid fermentation and the fermentation process itself, the nutritional aspects and food safety and health aspects of lactic acid-fermented cereal foods and nonalcoholic beverages, the different types of traditional fermented food and nonalcoholic beverages, the production processes for specific examples where commercialization has already


Lactic Acid Bacteria In these traditional fermented foods and nonalcoholic beverages, the microorganisms responsible are LAB. In contrast, in the case of wheat and rye sourdough bread fermentations, both LAB and yeasts are involved. Lactic acid fermentation is carried out by several different genera of bacteria, collectively referred to as LAB. They are, with some exceptions, grampositive, catalase-negative, nonspore-forming spheres and rods. Currently, the LAB group comprises 11 genera: Carnobacterium, Enterococcus, Lactococcus, Lactobacillus, Lactosphaera, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Vagococcus, and Weissella. The Lactobacilli are probably the most important in fermented cereal foods and beverages. LAB can carry out respiration without oxygen. Carbohydrates such as glucose are partially oxidized with the release of energy in the absence of any external electron acceptors. The final electron acceptors are organic compounds, specifically lactic acid, produced directly from the breakdown of the carbohydrate. Although the process releases much less energy than aerobic respiration, it specifically confers considerable competitive advantage to the LAB in that an anaerobic, lowpH environment is created in which LAB can flourish, whereas most other types of bacteria do not. LAB can be conveniently divided into two groups: homofermentative and heterofermentative. Homofermentative types produce lactic acid as the major or sole product of glucose fermentation, whereas the heterofermentative types produce equal molar amounts of lactic acid, carbon dioxide, and ethanol. Heterofermentative types also produce more of the generally desirable flavor compounds such as acetaldehyde (ethanal) and diacetyl (butanedione). The genera Pediococcus, Streptococcus, Lactococcus, and Vagococcus are all exclusively homofermentative, whereas the important Lactobacillus genus comprises homofermentative and heterofermentative species. The other LAB genera are all heterofermentative.

Factors Affecting Fermentation Most fermented cereal foods and beverages are produced using a natural, mixed microbial culture. The original source of microorganisms is the environment and the cereal food or beverage itself. Some products are produced with a so-called spontaneous fermentation where the product or intermediate is simply incubated at a suitable temperature for up to 72 h. However, in most cases, a culture is maintained and optimized by the process known as ‘back-slopping.’ A portion of the food/ beverage or intermediate that has undergone a successful fermentation is kept back and used to inoculate a new batch. Although apparently crude, back-slopping is highly effective.

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This is because the environmental conditions of the fermentation favor the growth of the desired bacteria strains. Several intrinsic and extrinsic factors affect the intensity and particular type of fermentation. Intrinsic factors include the pH, moisture, redox potential, and nutrient content and composition of the food or beverage. For example, yeasts grow over a wide pH range, although a pH 4–4.5 is favored, whereas LAB will grow at low pH (
Nutritional Aspects There is evidence that LAB fermentation can reduce the viscosity of porridges. The extent of viscosity reduction is affected by factors such as the pH attained and whether the

microorganisms involved possess amylase activity to hydrolyze the cereal starch into dextrins and sugars. Viscosity reduction is greatly enhanced if fermentation is combined with the addition of malted (sprouted) cereal flour (sometimes referred to as power flour), which contains high levels of amylases. Viscosity reduction is especially important in cereal weaning porridges for infants. Porridges where the starch is unmodified can have very high viscosity, making them unpalatable. If they are diluted to reduce viscosity, there is a concomitant reduction in energy and nutrient density. Reduction in viscosity with fermentation and malt addition, as is done in the porridge ‘togwa’ from Tanzania, can improve palatability and enable a porridge of higher energy and nutrient density to be produced without it having excessive viscosity. LAB fermentation has also been found to have several positive effects on the nutritional quality of cereals. It increases starch digestibility and availability. Although the quantity of protein present in cereals is little affected by fermentation (Table 1), the quality in terms of both lysine availability and relative nutritional value is in general significantly improved. These improvements are probably brought about by a combination of the low pH and bacterial proteolytic action, which modifies the structure of the cereal proteins. In sorghum, where cooking to make the porridge reduces protein digestibility, fermentation appears to counteract this effect, improving in vitro protein digestibility. With regard to micronutrients, there is some indication that B vitamins, particularly thiamine, are increased in LAB fermentations. However, the findings are not clear-cut, presumably because of differences in the extent and type of fermentation. The quantity of minerals in cereals cannot be affected by LAB fermentation. However, there is some improvement in their availability since the quantity of phytate (myo-inositol hexaphosphate), a powerful chelator of divalent metal ions such as calcium, magnesium, and iron that occurs in grains, is substantially reduced by fermentation.

Health-Promoting and Food Safety Aspects LAB fermentation of porridge to a pH of 4.0 or below will inhibit the growth of Enterobacteriaceae, including pathogenic bacteria such as Salmonella typhimurium. It appears that the growth of gram-negative intestinal pathogenic bacteria such as enterotoxigenic Escherichia coli, Campylobacter jejuni, Shigella flexneri, and S. typhimurium is strongly inhibited by the low pH caused by the formation of lactic and acetic acids. The inhibition of food-borne pathogens by LAB fermentation is potentially of great benefit in developing countries where even today, many people do not have access to safe water. The World Health Organization (WHO) estimates that 760 000 children under the age of 5 years die annually as a direct result of diarrhea and that it is a leading cause of infant malnutrition. Further, there is evidence that some organisms involved in traditional cereal fermentation, for example, strains of Lactobacillus reuteri and Pediococcus acidilactici, produce bacteriocins (antibacterial proteins) that can inhibit a wide range of pathogens. Arising from these observations, there is a misconception that traditional fermented cereal products are per se probiotics, sources of viable microorganisms that promote or

BEVERAGES FROM GRAINS | Fermentation: Foods and Nonalcoholic Beverages Table 1

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Effect of spontaneous fermentation for 6 daysa on the protein content, available lysine, and relative nutritive value of various cereals

Cereal Barley Nonfermented Fermented 22–25 C Fermented 37 C Maize Nonfermented Fermented 22–25 C Fermented 37 C Millet (species not specified) Nonfermented Fermented 22–25 C Fermented 37 C Oats Nonfermented Fermented 22–25 C Fermented 37 C Rice Nonfermented Fermented 22–25 C Fermented 37 C Wheat Nonfermented Fermented 22–25 C Fermented 37 C

Crude protein (g 100 g1)

Available lysine (mg g1 Proteinb)

Relative nutritive value (%) c,d

9.75 9.62 9.81

19.0 75.6e 96.3e

70 85 (15)f 84 (14)f

9.94 9.81 9.69

17.4 47.4f 51.8f

67 80 (13)e 80 (13)e

11.56 12.31 12.00

3.0 36.0f 45.0f

65 79 (14)e 81 (16)e

10.75 10.31 9.81

15.0 104.6e 113.0e

85 88 (3) 88 (3)

7.87 7.75 8.25

5.0 46.0f 61.0f

63 85 (22)f 82 (19)f

10.75 9.14 9.26

23.3 64.2e 79.8e

72 86 (14)f 86 (14)f

a

The pH fell to pH 3.6–4.1 within 2 days. Determined by Pediococcus cerevisiae procedure after enzyme hydrolysis. c Determined by Tetrahymena pyriformis procedure. Nutritive value relative to casein. d Numbers in parentheses are increase over nonfermented. e Increase significant at P < 0.01. f Increase significant at P < 0.05. Reproduced with permission from Hamad AM and Fields ML (1979) Evaluation of the protein quality and available lysine of germinated and fermented cereals. Journal of Food Science 44: 456–458. b

support a beneficial balance of the microbial population in the gastrointestinal tract. This is not the case. A comprehensive review of African fermented foods has concluded that there is an absence of firm evidence about their probiotic-induced health benefits. However, a real advantage of LAB fermentation of cereal foods and beverages is that the low pH slows down the rate of microbial spoilage of the product caused by other bacteria. The growth of spoilage bacteria is inhibited by the environmental conditions created by the LAB. Hence, LAB fermentation can be considered as a way of extending the safe storage life of foods and beverages. This is of particular importance in the less-developed world where the vast majority of households do not have refrigerators. Hence, the WHO has promoted lactic acid fermentation of such products, together with hygienic food preparation practices, as a way of helping to ensure household food safety. LAB fermentation may have negative health effects. Some LAB, generally mesophiles (bacteria that grow at ambient temperatures), which are the norm in traditional fermentations, produce both optical isomers of lactic acid L(þ) and D(). Since the latter cannot be metabolized by humans, excessive intake may result in acidosis, a disturbance of the acid–alkali balance in the blood. WHO recommends that young babies should not be fed with foods containing DL or D lactic acid.

Types of Fermented Traditional Products Traditional nonalcoholic fermented cereal products can be categorized into flour/meal, pancakes, doughs/dumplings, cakes/ sweetmeats, thick porridges, thin porridges, and beverages (Table 2). This classification is inevitably arbitrary. For example, the difference between thick and thin porridges and the difference between thin porridges and beverages are often simply an issue of the percentage of water in them. Other products, such as ‘koko,’ ‘ogi,’ and ‘pozol,’ are prepared as a dough but consumed as thin porridge or beverages. Another dough product ‘mawe’ is even consumed in a wide variety of forms including dumplings, steamed bread, fritters, couscous, and thick porridges. It can be seen from Table 2 that these products are widely distributed throughout the world, occurring in southeast Europe, right across Asia especially in the Indian subcontinent, throughout Africa, and in northern Latin America. The list is by no means complete and the impression given that the largest number of such products occurs in Africa may not be entirely correct. However, it is probably significant that there are many such products in Africa. Africa is the only continent that straddles both tropics, and the warm ambient temperature facilitates the natural proliferation of LAB in foods left to stand. For example, mesophilic Lactobacilli have a temperature optimum in the range 28–32 C.

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Table 2

Examples of traditional lactic acid-fermented cereal foods and nonalcoholic beverages

Flour/meal Africa Uusila/oufila (PM) Namibia

Pancakes

Doughs/dumplings

Galettes (PM, S) Burkina Faso Injera (FM, S, T) Ethiopia Kisar (S) Chad Kisra (S) Sudan

Kenkey (M) Ghana Maasa/massa/waina (S, PM) West Africa Mawe (M) Benin

Europe, Middle East, and Asia Dosa (R, S þ black gram) India

Khanomjeen (R) Thailand

Cakes/ sweetmeats

Thick porridges

Thin porridges

Beverages

Aceda (S) Sudan Koko (M) Ghana Banku (M) Ghana Ting (S) Southern Africa

Nasha (S) Sudan Ogi (M, PM, S) Benin, Guinea, Nigeria Togwa (M, PM, S) Tanzania Ugi/uji (FM, M, PM, S) East Africa

Hulu-mur (S) Sudan Kunun-zaki (S) Nigeria Mageu/ amahewu/magou (M) Southern Africa Motoho oa mabela (S) Southern Africa Munkoyo (M) Zambia Oshikundu (PM, S) Namibia Boza (B, M, O, R, W) Bulgaria, Turkey

Anarshe (R) India Dhokla (R þ chickpea) India Idli (R þ black gram) India Jalebi (W) India Puto (R þ sugar) Philippines

Latin America Jamin-bang (M) Brazil

Atole (M) Mexico

Pozol (M) Mexico

Agua-agria (M) Mexico

B, barley; FM, finger millet; M, maize; O, oats; PM, pearl millet; S, sorghum; R, rice; T, teff; W, wheat.

The process used to produce a product in each of the categories will be examined.

Flour/Meal In northern Namibia, pearl millet is the staple and is generally eaten in the form of porridge. The traditional process of milling pearl millet involves a steeping (fermentation) step. Fermented pearl millet flour, which is called ‘uusila’ or ‘oufila,’ is produced commercially in small mills as a convenience product (Figure 1(a)), particularly for urban dwellers and institutional feeding. The flour is also used to make a beverage called ‘oshikundu’ and for porridges, cakes, and cookies. The steeping (fermenting) vessels and drying floor of a pearl millet mill in northern Namibia are shown in Figure 1(b) and 1(c), respectively. The process is described earlier. In brief, it involves abrasively dehulling the grain and then steeping it overnight. The steep is also a lactic acid fermentation with a culture being maintained by back-slopping. The bacteria responsible are probably heterofermentative Lactobacillus. The steeped grain is partially dried in the sun, then hammer-milled into a flour, and then fully sun-dried. The fermented flour has a pH between 4 and 5 and a slight acidic taste, which is favored by consumers. The lactic acid fermentation has a number of other positive effects. It lightens and brightens the flour as a result of the low pH decreasing the color of the pearl millet polyphenolic pigments and also leaching some out. The fermentation also facilitates the grain being reduced into a soft flour (particle size <500 mm) during milling, which enables

baked goods of reasonable quality to be produced from it, despite the fact that pearl millet does not contain gluten.

Pancakes ‘Injera,’ a large (50 cm diameter) leavened pancake, is a staple food of Ethiopia. Injera is sour in taste and flexible and spongy in texture with a characteristic honeycomb-like structure (Figure 2(a)). It is served at most meals, generally with a spicy meaty relish. Injera is almost exclusively home-produced and is preferably made from teff and/or sorghum flour, although flour of other cereals may also be added. Injera is thus rather unusual in that it is a leavened bread-like product made from ‘gluten-free’ cereals. The process for making injera is described in detail on the chapter on Teff. In brief, it involves two fermentations. In the first, a starter culture (‘irsho’) from a previous injera batter is added to the flour dough. The fermentation takes up to 72 h, during which time the pH falls to pH 3.8. A portion of the dough, 20%, is then diluted with water and cooked to gelatinize the starch. This product is called ‘absit.’ The absit is then combined with the fermenting dough and a second fermentation of 2 h takes place, during which time gas is generated. The dough is thinned to a batter and then poured in a circular motion over a hot clay griddle (‘mitad’) (Figure 2(b)). The ‘injera’ is then covered and baked and steamed for 2–3 min. During this time, the starch gelatinizes setting the batter, and gas bubbles expand and escape creating the honeycomb-like structure. The microbiology of the injera fermentations is complex. The first fermentation is believed to be initiated by


Figure 1 Manufacture of fermented pearl millet flour (uusila/oufila) in northern Namibia. (a) Bags of flour, (b) steeping (fermentation) vessel, (c) drying steeped (fermented) ‘dehulled’ grain.

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Figure 2 Injera. (a) Sorghum injera showing baking on the clay griddle (mitad). (b) Pouring the fermenting batter onto the griddle.

Enterobacteriaceae, and then LAB including L. mesenteroides, Streptococcus faecalis, Pediococcus cerevisiae, L. brevis, L. plantarum, and Lactobacillus fermentum are involved. Yeasts of the genera Saccharomyces and Torulopsis are involved in the second fermentation that produces the leavening gas.

Cakes ‘Idli’ is a small fermented and steamed cake with a characteristic sour taste and leavened texture, made from rice and black gram (Vigna mungo). It is widely consumed in southern India and Sri Lanka, where it is a breakfast food. Idli is eaten with chutney, pickles, or curry. The combination of a legume and a cereal makes idli highly nutritious with a good essential amino acid balance. As can be seen, the idli-making process (Figure 3) has some similarities with that of injera. However, for idli, it is known that the main fermentation organism is L. mesenteroides. This heterofermentative bacterium produces both lactic acid and carbon dioxide. During fermentation, the pH of the batter decreases from pH 6.0 to 4.3 and the volume increases by 1.6–3.1 times. It is believed that mucilaginous polysaccharides and globulin proteins from the black gram stabilize a gasholding foam. This enables the formation of a leavened cake. Other bacteria found in the idli fermentation include Lactobacillus delbrueckii, L. fermentum, L. lactis, Enterococcus faecalis, and Pediococcus cerevisiae. Several types of yeasts have also been implicated in the fermentation including species of Geotrichum and Torulopsis. As an alternative to steaming, the thick fermented batter can be diluted to a thin batter and seasoned and then fried to produce a pancake called ‘dosa.’

Dumplings ‘Kenkey,’ a staple food in Ghana, is an orange-sized dumpling produced from fermented white maize with a solids content of 35%. It is produced in the home and by street vendors. Kenkey is eaten at main meals, served with a relish often made with oily fish such as herring.

Dehulled black gram (1 part)

Polished white rice (2 parts) Wash then steep for 5–10 h

Water

Wash then steep for 5–10 h

Grind finely in mortar

Combine

Grind coarsely in mortar

Salt (1% w/v)

Mix well into a thick batter Ferment (15–24 h, 30–32 °C) Pour into small cups on griddle Steam (10 min)

Figure 3 Process for making idli. Adapted from Haard NF, Odunfa SA, Lee C-H, Quintero-Ramı´rez R, Lorence-Quinõnes A, and Wacher-Radarte C (1999) Fermented Foods: A Global Perspective. FAO. http://www.fao.org (accessed 14.06.02).

It can be seen that there are in fact two fermentations in kenkey making: the first, steeping the whole maize and, the second, a fermentation of the dough (Figure 4). After the second fermentation, the pH should be pH 4. The main LAB found in the fermenting dough are L. plantarum, L. confusus, L. brevis, and Pediococcus pentosaceus. As the pH decreases and titratable acidity increases, the heterofermentative types are succeeded by the more acid-tolerant homofermenters. As in injera making, part of the dough is cooked to gelatinize the starch and hence bind the dough into a cohesive mass. However, in kenkey, this dough is not leavened by a subsequent fermentation, but simply cooked in water.


Maize grain Water

189

Sorghum meal (1 part)

Steep/ferment (24−48 h) Water (1.3 parts)

Drain then coarse mill

Water

Ferment dough (24−72 h)

Dough

Divide into two

Slurry

Mix together and shape in ball

Cook (Aflata)

Ferment (72 h, room temperature) Pediso (fermented sorghum meal pH 3.8)

Water Boiling water (2.7 parts)

Wrap in maize cob sheaths (Ga-kenkey) or banana leaves (Fante-kenkey)

Cook with gentle heating

Letlhabego (fermented culture) (1 part)

Supernatant

Sour thick slurry

Custard-like intermediate Simmer Figure 5 Process for making ting.

Boil in water (2−3 h) Figure 4 Process for making kenkey. Adapted from Haard NF, Odunfa SA, Lee C-H, Quintero-Ramı´rez R, Lorence-Quinõnes A, and WacherRadarte C (1999) Fermented Foods: A Global Perspective. FAO. http:// www.fao.org (accessed 14.06.02).

Research has been undertaken to simplify the kenkeymaking process for potential industrial manufacture. Developments include accelerating the fermentation process by using a starter culture and producing dried fermented flour (like the pearl millet flour) and pregelatinized fermented flour.

Thick Porridges ‘Ting’ is a firm, fermented sorghum porridge with a solids content of 15% and pH in the range 3.6–4.3. It is widely produced in the home in Botswana and northern South Africa. Ting is eaten as breakfast porridge and is often served at celebratory functions. In South Africa, ting is generally produced from coarse sorghum meal, industrially manufactured for the purpose from red, nontannin sorghum. In Botswana, meal from white sorghum is generally preferred, which may be produced industrially or by small village mills. A ting-making process used in South Africa is shown in Figure 5. To start the process from scratch, a spontaneous fermentation is carried out at room temperature. The meal sours rapidly with some gas production. The fermented meal, called ‘pediso,’ can be used to inoculate more sorghum meal to produce a culture known as ‘letlhabego’ or directly to make ting. Many households maintain a letlhabego, also known as ‘yeast,’ by back-slopping, the use of which shortens the process of ting making. As the letlhabego is so useful, it is traded between producers. Two to four dominant strains of Lactobacillus have been identified in traditional products. The species involved include L. reuteri, L. fermentum, L. harbinensis, L. plantarum, L. parabuchneri, L. casei, and

L. coryniformis. To prepare ting, the pediso or letlhabego is added to boiling water and cooked as shown. An industrially produced ting product made from maize and sorghum has been developed in South Africa. The product was marketed in polythene sachets and had a shelf life of several weeks, due to its low pH. However, it was not commercially successful on account of its high price.

Thin Porridges ‘Ogi’ (northwest Nigeria) or ‘akamu’ (eastern Nigeria) is a thin, sour porridge of solids content between 5% and 8% or higher, depending on the desired consistency. It is a staple food in Nigeria, eaten as breakfast porridge or as a food for infants and the infirm. It is served hot, often accompanied by bean cake. The traditional production process starts with steeping the grain (a first fermentation), wet milling, and sieving to remove coarse material (Figure 6). The throughs are then fermented by a spontaneous fermentation. The precise microorganisms responsible are not known. However, Lactobacillus, Enterobacter, and Leuconostoc species have been found to be present in sorghum ogi fermentations, with the latter being replaced by Corynebacterium species later in the fermentation. The final pH should be pH 4.1–4.5. Traditionally, ogi slurry is pressed into a dough (known as a cake), which is sold commercially by street vendors. To prepare ogi, the dough is made into a smooth slurry with cold water and added slowly to boiling water and cooked for 2 min. It may be sweetened if so desired. Since the dough has a shelf life of only two days, research had been conducted by the Nigerian Federal Institute of Industrial Research to produce shelf-stable product. A long-life powder has been produced by spray drying. However, this product still requires to be cooked. An ‘instant’ powder produced by roller drying has been developed. As it is precooked, it only requires the addition of hot water to prepare the ogi. A further development is a more nutritious composite instant ogi

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Water (1.5−2 parts)

Maize/pearl millet/ sorghum grain (1 part) Steep/ferment (24 h)

Steep water (discard)

Drain

Wet mill (disk mill) Overtails (animal feed)

Wet sieve (310 µm) Throughs Ferment (24−48 h)

Figure 7 Commercial traditional-type mageu and motoho oa mabela.

Maize meal

Dewater by pressing

Cook

Cake (dough) (65% moisture)

Water

Cool Boiling water (5−7 parts)

Cook

Figure 6 Traditional process for producing ogi. Adapted from Holzapfel WH and Taljaard L (2004) Industrialization of mageu fermentation in South Africa. In: Steinkraus KH (Ed.) Industrialization of Indigenous Fermented Foods, 2nd edn., pp. 363–408. New York: Marcel Dekker.

powder incorporating full-fat soya flour. This nearly doubles the protein content, increasing the percentage contribution to the recommended dietary allowance of an infant from 25% to 48%. Additionally, the ogi biological value, protein efficiency ratio, and digestibility are dramatically improved. Soy-ogi has become a popular product, sold in supermarkets.

Beverages ‘Mageu,’ also commonly known as ‘amahewu’ or ‘magou,’ is a southern African maize-based fermented beverage or gruel. A very similar product is ‘motoho oa mabela,’ which is made from sorghum (Figure 7). Mageu is produced in the home and in institutions such as hospitals and mine canteens. It is also produced on a large industrial scale in South Africa and Botswana. Industrially produced mageu has a solids content of 8% with an energy content of 1160 kJ l1 and a pH of 3.5. Mageu is regarded as a nutritious, energy food, ideal for those doing hard manual work. The traditional method of making mageu simply involves preparing a maize meal porridge of 8–10% solids, allowing it to cool to room temperature and then adding a small quantity of wheat flour. The porridge will then undergo a lactic acid fermentation. The wheat flour acts as a source of the bacterial

Inoculum (thermophilic lactic acid bacteria)

Ferment (~24 h, 50 °C)

Wheat flour and/or cane sugar

Add flavorants, sugar and/or artificial sweeteners

Pasteurize

Package (milk-type cardboard cartons or polythene sachets) Figure 8 Industrial process for making mageu.

starter culture and of hydrolytic enzymes, in particular b-amylase, which produces a small amount of maltose that is utilized by the fermenting microorganisms. A modern industrial process is shown in Figure 8. The major differences from the traditional process are the introduction of thermophilic LAB cultures, which only produce lactic acid, extension of the shelf life of the product by pasteurization and/or chemical preservation, and inclusion of sugar and/or artificial sweeteners. It has been stated that the LAB is L. delbrueckii, although there is a strong indication that the cultures are mixed and also contain thermobacterium as they are very heat- and acid-tolerant.

BEVERAGES FROM GRAINS | Fermentation: Foods and Nonalcoholic Beverages Another development in mageu manufacture involves using pregelatinized maize meal. The use of this so-called powder mageu is ideal for institutional feeding as it obviates the need for porridge cooking equipment. The pregelatinized maize meal can produced by ‘dry-cooking,’ either hightemperature, short-time extrusion, or gun puffing, or by conventional wet cooking followed by drum drying. Mageu developments include drinking yogurt-like products, which have a smooth consistency and have artificial banana, cream, pineapple, and strawberry flavors. Motoho oa mabela developments are even more radical in that the products are not actually fermented, but instead acidified with citric acid (Figure 9).

Potential for Development Traditional nonalcoholic fermented beverages seem to be at crossroads. Although remaining very popular as home or small-scale commercially produced products, large-scale industrialization production is limited. Also, as described, some new commercial products, although loosely based on traditional fermented products, are not actually fermented. Further, there is a trend that with urbanization, rising incomes, and changing lifestyles, people in developing countries are turning away from traditional fermented foods to inexpensive Western-style fast foods and carbonated soft drinks. This nutrition transition is viewed with great concern because of its association with dramatically increased rates of the so-called lifestyle diseases, cardiovascular disease and type 2 diabetes. Perhaps this is overstating the case somewhat, but lactic acid-fermented cereal foods and beverages do have unique functional and nutritional benefits that food scientists should exploit through the development of innovative products, which satisfy the needs of today’s consumers in both the lessdeveloped world and more-developed world. For example, injera seems ripe for development into a commercial product

as it is a leavened bread produced from nongluten-containing cereals such as sorghum. Thus, injera could be very suitable for countries in the semiarid tropics where wheat cannot be produced economically, and it could be attractive to people who are sensitive or intolerant to wheat products. Additionally, injera could make a great fast food as it can be used as a ‘wrap’ for meat or vegetable fillings. A nutritional aspect of fermented cereal foods that is already being exploited in Europe is functional foods, foods that have health-promoting properties over and above their basic nutrient content. For example, a range of oat-based, fermented yogurt-like products have been developed based on traditional Finnish oat ‘vellie’ (Figure 10). Three aspects of these products are of note. First, they are entirely cereal and thus is an ideal alternative to yogurt for people who are allergic or intolerant to dairy products. Second, they are rich in oat fiber that has a cholesterol-lowering property, and third, in addition to LAB, they contain the probiotic bacterium Bifidobacterium animalis ssp. lactis. Many benefits have been claimed for Bifidobacteria, but perhaps the most important, especially for the ‘at risk’ in developing counties, is that they are protective against gastrointestinal infections.


• • • • • • •

Figure 9 Modern developments of mageu and motoho oa mabela.

191

What are the differences between homofermentative and heterofermentative lactic acid fermentations? Explain what is back-slopping. What are the intrinsic and extrinsic factors that affect the intensity and type of fermentation? What are the potential nutritional advantages of lactic acid fermentation of cereals? What are the potential health benefits of lactic acidfermented products? Are there any potential health dangers associated with the consumption of lactic acid-fermented products? Draw a flowchart for the production of a traditional fermented food or beverage of your choice and explain the significance of the various production steps.

Figure 10 Commercial oat vellie product. Reproduced with kind permission from Bioferme Oy.

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• • •

Are traditional fermented foods containing live bacteria actually protective against diseases such as diarrhea? Does the consumption of fermented products containing D-lactate actually pose a health risk to at-risk groups such as infants? Will traditional fermented products fermented with probiotic bacteria be acceptable to consumers?

See also: Beverages from Grains: Beverages: Asian Alcoholic Beverages; Beverages: Distilled; Fermentation: Origins and Applications; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara; The Cereal Grains: Millet Pearl: Overview; Teff: Overview; Wheat-Based Foods: Breads; Sour Dough Technology.

Further Reading Anukam KC and Reid G (2009) African traditional fermented foods and probiotics. Journal of Medicinal Food 12: 1177–1184. Biotechnologies in Agro-industry in Developing Countries, 2010. Current Status and Options for Biotechnologies in Food Processing and in Food Safety in Developing Countries. http://www.fao.org (accessed 14.06.02). Chavan JK and Kadam SS (1989) Nutritional improvement of cereals by fermentation. CRC Critical Reviews in Food Science and Nutrition 28: 349–400. Hamad AM and Fields ML (1979) Evaluation of the protein quality and available lysine of germinated and fermented cereals. Journal of Food Science 44: 456–458. Holzapfel WH and Taljaard L (2004) Industrialization of mageu fermentation in South Africa. In: Steinkraus KH (ed.) Industrialization of Indigenous Fermented Foods, 2nd edn., pp. 363–408. New York: Marcel Dekker.

Jay JM (1996) Modern Food Microbiology, 5th edn. New York: Chapman & Hall. Kazanas N and Fields ML (1981) Nutritional improvement of sorghum by fermentation. Journal of Food Science 46: 819–821. Murty DS and Kumar KA (1995) Traditional uses of sorghum and millets. In: Dendy DAV (ed.) Sorghum and Millets: Chemistry and Technology, pp. 185–221. St. Paul, MN: American Association of Cereal Chemists. Olsen A, Halm M, and Jakobsen M (1995) The antimicrobial activity of lactic acid bacteria from fermented maize (kenkey) and their interactions during fermentation. Journal of Applied Microbiology 79: 506–512. Onyekwere OO, Koleoso OA, Teniola OD, and Akinrele IA (2004) Industrialization of ogi fermentation. In: Steinkraus KH (ed.) Industrialization of Indigenous Fermented Foods, 2nd edn., pp. 409–470. New York: Marcel Dekker. Owusu-Kwateng J, Debrah-Tano K, Akabanda F, Nielsen DS, and Jespersen L (2013) Partial characterization of bacteriocins produced from Lactobacillus reuteri 2-20B and Pediococcus acidilactici 0-11A isolated from fura, a millet-based fermented food in Ghana. Journal of Food Research 2: 50–58. Popkin BM (2003) The nutrition transition in the developing world. Development Policy Review 21: 581–597. Poutanen K, Flander L, and Katina K (2009) Sourdough and cereal fermentation in a nutritional perspective. Food Microbiology 26: 693–699. Sekwati B and Ga¨nzle MG (2011) Microbiological and chemical characterization of ting, a sorghum-based sourdough product from Botswana. International Journal of Food Microbiology 150: 115–121. Steinkraus KH (1995) Handbook of Indigenous Fermented Foods, 2nd edn. New York: Marcel Dekker. Steinkraus KH (2002) Fermentations in world food processing. Comprehensive Reviews in Food Science and Food Safety 1: 23–32. Taylor J and Dewar J (2000) Fermented products: Beverages and porridges. In: Wayne Smith C and Frederiksen RA (eds.) Sorghum: Origin, History, Technology, and Production, pp. 751–795. New York: Wiley. Taylor J and Taylor JRN (2002) Alleviation of the adverse effects of cooking on protein digestibility in sorghum through fermentation in traditional African porridges. International Journal of Food Science and Technology 37: 129–138. World Health Organization (1996) Fermentation: Assessment and research. Report of a Joint FAO/WHO workshop on fermentation as a household technology to improve food safety. WHO/FNU/FOS96.1. Geneva: WHO. World Health Organization 2013. Diarrhoeal disease. http://ww.who.int/ (accessed 14.02.06).

Beverages: Distilled GH Palmer, Heriot-Watt University, Edinburgh, UK ã 2016 Elsevier Ltd. All rights reserved.

Glossary

Air rest Period during steeping when water is drained from the grain. Air can be passed through the bulk of grain (aeration) to facilitate germination. Acrospire The shoot of germinated barley that grows on the dorsal surface of the malting grain. Length of growth can be used as an index of malt modification. Artisanal Traditional (craft) activity or skills. Blending of spirits Blending of distilled spirits is the term used to describe the process of skilfully combining distilled spirit products such as Scotch whiskies. As many as forty whiskies (mainly malt and a few grain whiskies) may be blended together to make one brand of Scotch Blended whisky. Blending of malt Process where different types of malted barley are mixed together to arrive at one specification. The blended specification is an average result which can conceal under-modification and over-modification which can cause unexpected problems during the process of malting barley. Charred New oak barrels are usually charred (burned) before distilled spirits are matured in them. Barrels which have matured whiskies for many years can be scraped and re-charred to lengthen their maturation function. Conversion Enzymic hydrolysis of endosperm substances such as starch and proteins into Brewer’s extract (wort/wash) during mashing. Cooking Process where milled (unmalted) grains are cooked in a large vessel until the starch is solubilized. Unmilled grains can be cooked under pressure to achieve the same solubilization results. Diastatic Power Indirect assessment of mainly Beta amylase (maltose producing) activity. Endosperm (malt) modification Progressive action of enzymes that hydrolyze storage substances of the endosperm such as starch, protein, and cell wall. Malt endosperms can therefore be described as under-modified, modified, or over-modified.

Feints The description of the third fraction of the distillate collected from the Spirit still. Foreshots The description of the first fraction of the distillate collected from the Spirit still. Genetically modified Living organisms whose genetic material has been altered by humans are usually described as being genetically modified. Germination When the roots of grains emerge from their pericarp/testa/husk covering layers, they are regarded as having germinated. Kernel Same as corn or grain. Malt Name of malted barely or of Scotch malt whisky. Mashing The hot water extraction/conversion process of milled malt, for malt whisky production or the hot water extraction of milled malt and mainly cooked unmalted cereals, for grain whisky/whiskey production. Maturation The holding of, for example, the middle-cut fraction (see below) of Scotch whisky in a charred oak barrel for at least the statutory period of three years to remove undesirable compounds and to extract desirable compounds. Middle-cut The term used to describe the second fraction of the distillate from the Spirit still which is collected and matured to produce a distinct product. Pre-germination Term used to describe grains in which the germination process has started (usually before it is harvested). Pure Pure means of one kind. Therefore the term ‘pure malt whisky’ can apply to ‘single malt whisky’ or a ‘blend of malt whiskies’. The term cannot be used to describe a blend (mixture) of malt and grain whiskies. Single malt Malt whisky derived from one malt distillery. Vatting Mixing of whiskies in particular vessels. Wash/Wort Sugar-protein rich extract produced from mashed (converted) malt or mashed (converted) malt and cooked cereals. Whisky Spelling usually applies to Scotch whiskies. Whiskey Spelling usually applies to non-Scotch whiskies.

Topic Highlights

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• •

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• • • •

Plant materials and the alcoholic beverages they produce. Ethanol is the main distilled compound of alcoholic beverages. Congeners also result from distillation, are produced in small quantities, but are major flavor compounds. Different processes of distillation and definitions of alcoholic beverages. Barley malt in Scotch malt whisky production. Maize, wheat, and malt in Scotch grain whisky production. Principles of production of different alcoholic beverages. For example, different types of fermentations and stills.


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Amino acids, sugars, and yeasts are important in fermentation. Copper stills are important in distillation. Maturation of whiskies in oak casks. Flavor and quality development. Social and environmental effects of the production and consumption of alcoholic beverages.

Learning Objective

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To develop and increase understanding of the distilled beverage industry.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00233-3

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BEVERAGES FROM GRAINS | Beverages: Distilled

Introduction The distillation process was invented by the Chinese. Ancient Greeks used distillation to produce alcoholic products. Distilled beverages that are sold commercially today are produced from plant materials (Table 1), and their distillation processes (Table 2) are clearly defined. Each product has distinct aromas and flavors, which reflect raw materials, distillation process, and postdistillation treatments such as maturation in wooden (e.g., oak) casks. The flavor compounds in distilled beverages are referred to as congeners. Different beverages can have small differences in congener levels but have large differences in flavor and aroma intensities. Flavor and aroma intensities Table 1 Raw materials used for the production of some major distilled beverages Products

Raw materials

1. Scotch malt whiskiesa 2. Scotch grain whiskiesa 3. Cachaça

100% malted barley Wheat or maize (þmalted barley) Sugar cane juice only. Unlike ‘industrial’ cachaça, which is made from cane products (e.g., molasses) and sugar, only fresh sugar cane juice is used to produce traditional, ‘artisanal’ cachaça Molasses mainly and sugar cane juice 100% malted barley Barley þ malted barley Maize þ malted barley or enzymes Maize or wheat (with malted barley or enzymes for starch conversion into sugars). Pot still distillation of juniper berries and other botanicals or addition of spirit to juniper berries and botanicals or to the essence of these plants Agave (Agave tequilana Weber Var. Azul) plant Agave plant þ sugar or syrup Cereals, grape juice, raisins, molasses, potatoes (with or without enzymes for starch conversion) Maize þ rye (with malted barley, plus or minus commercial hydrolytic enzymes) Maize, rye, and malted barley and malted rye þ amylolytic and glucanolytic enzymes

4. Rum 5. Irish whiskies

6. Gin

7. Tequila (100%) Tequila 8. Vodka

9. American whiskies (bourbon, corn, rye, Tennessee) 10. Canadian whiskey

11. Brandies Cognac Armagnac Eau-de-vie Raki 12. Aquavit

a

Grapes Grapes, e.g., pears, raspberries, cherries, apples, or plums Double distillation (anise-flavored) Grain or potato (with malted barley or enzymes for starch conversion). Neutral spirit from grain or potato is then redistilled with flavorings. Caraway is the main flavoring and citrus peel. Cardamom and anise can be incorporated as well

Japan also produces malt and blended whiskies.

may also relate to the complex modulating effects, which different congeners have on each other, and to the physiological and cultural differences of consumers. In distilled spirit beverages, ethanol is the main compound as regards quantity, and the congeners can be regarded as ‘ancillary products’ of the natural production of ethanol. However, although ‘alcohol consumption’ is of serious concern to the industry (see the succeeding text), in a recent publication (Worldwide Distilled Spirits Conference (2012)), it is evident that the science and technology of spirit yield, flavor development, product quality, and sustainability remain important activities of the distilling industry. The ethanol in distilled beverages is produced from the different sugars derived from the raw materials used. The mechanisms of production of congeners (the minor compounds responsible for the character of distilled beverages) are very complex. Some are produced by yeast during fermentation, others are produced during distillation, and some develop during maturation. In some distilled beverages such as gin, flavor materials are added. The term ‘distilled potable spirits’ relate to distilled products that are eventually packaged and sold as beverages for human consumption (Tables 1 and 2). The production procedures of many distilled beverages are

Table 2

Types of stills used in production of distilled spirit beverages

Products

Stills

1. Scotch malt whisky 2. Scotch grain whisky 3. Cachaça

Usually, two large copper pot stills (wash and spirit) – tube condensers Continuous (patent) still (analyzer and rectifier)

4. Rum

5. Irish whiskey 6. Gin 7. Tequila 8. Vodka 9. American whiskey 10. Canadian whiskey 11. Brandies Cognac Armagnac

Eau-de-vie 12. Aquavit

Small copper pot stills with worm condenser coils. Traditional (e.g., ‘artisanal’) cachaça is produced using pot stills. Single distillation like Armagnac. Continuous stills used to produce ‘industrial’ cachaça Continuous still (analyzer and rectifier) – Puerto Rican (light rum). Distillation in series of two or three copper pot stills (to avoid double distillation in one still). Cooling coil condensers present: Jamaican (high-flavor (heavy) rum) Three copper pot stills (viz., wash, low wine, and spirit). Triple distillation Continuous still (analyzer and rectifier) and then copper pot stills for distillation with botanicals Copper pot still (double distillation) or continuous still (analyzer and rectifier) Continuous still (analyzer and rectifier) Continuous stills or continuous still plus doubler for additional distillation Continuous still with analyzer column, extraction column, and rectifying column. Pot stills Small copper pot still with cooling worm, direct fired instead of internal heating coil. Double distillation Small copper pot still or small single-column continuous still. Single distillation in pot stills, like traditional cachaça Copper pot still – double distillation (analyzer and rectifier) Continuous still (analyzer and rectifier)

BEVERAGES FROM GRAINS | Beverages: Distilled defined by law. For example, Scotch whisky means whisky distilled and matured in Scotland, and Irish whiskey means whiskey distilled and matured in Ireland. Scotch malt whisky is made from malted barley. The blended brands of Scotch whiskies are blends of Scotch malt whiskies and Scotch grain whiskies. Scotch malt whiskies are produced in pot stills, and Scotch grain whiskies are produced in continuous patent stills. Only enzymes from malted barley can be used in Scotch whisky production. Recent changes (2011) to how Scotch whiskies are described are as follows: The term ‘pure malt’ has been banned. Present categories of Scotch whiskies are single-salt Scotch whisky, single-grain Scotch whisky, blended Scotch whisky, and blended grain Scotch whisky. In the United States, bourbon whiskey must be produced from a mash conversion of not less than 51% corn grain and rye whiskey must be produced from not less than 51% rye grain. Cognac or tequila can only be made in respective areas of France or Mexico. In many countries, a minimum age of postdistillation maturation in wooden barrels is designated by law. Also, in this regard, Scotch whisky can only be matured in Scotland in oak barrels. However, bourbon can only be matured in ‘new’ (charred) oak barrels in the United States. Although distilled beverages are associated with large companies and strong brands, major developments in the industry over the last decade include a widening of traditional products and the growth of the microdistilling industry. This suggests that innovation, such as differences in raw materials and maturation, is still an important feature of the commercial viability of distilled beverages.

Historical Background The exact dates of development of many distilled beverages are not known. The Chinese may have developed the distillation process in ancient times. The ancient Egyptians had alembics, which could have produced alcoholic drinks, but it was the Moors who were responsible for distributing the technique and for the derivation of the word ‘alcohol,’ which is derived from the old Arabic word ‘al-kuhl.’ The distillation process is therefore an ancient-world technology and is known to produce a concentrated alcoholic essence of the initial ferment, which contained lower levels of ethanol. A sugar solution of 14– 16% will, after fermentation by yeast, yield 7–8% ethanol. According to Gay-Lussac, 100 lbs (22.18 kg) of glucose should, after fermentation by yeast in ideal conditions, yield 48.89 lbs of carbon dioxide and 51.11 lbs (23.18 kg) of ethanol. But, according to Pasteur, only 95% of these products can be expected in fermentation systems. Ethanol is a simple alcohol. It is a member of a large group of alcohols, some simple, whereas others complex, but all containing carbon, hydrogen, and oxygen and hydroxyl groups, which have replaced hydrogen atoms. Although it has been suggested that the Crusaders brought the technique of distillation to Europe in the eleventh to twelfth centuries, it was not long after this period that distillation activity was discovered in Ireland. The first written record of Scotch malt whisky appeared in 1494. The word whisky is spelt ‘whisky,’ when applied to Scotch, but is spelt ‘whiskey’ when applied to Irish, Canadian, and American whiskeys. In 1931, the Coffey (continuous or patent) still was invented by

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Aeneas Coffey to produce Scotch grain whisky in large quantities. The first blended Scotch whiskies (i.e., mixtures of malt and grain whiskies) were produced by Andrew Usher in 1860. Blended whiskies are now about 90% of the Scotch whisky market worldwide. Malt whiskies sales have grown to about 10% of the market. According to the Scotch Whisky Association of Scotland (2013), Scotch whisky sales have increased by 87% over the last 10 years. Increases in sales have occurred mainly in China, Russia, India, and Africa. However, at present, about 80% of the selling price of a bottle of Scotch whisky is taken as tax, adding £5 billion to the gross value of the UK economy which is more than that added by most industries. According to the World Health Organization, general consumption of distilled spirit beverages occurred at the greatest levels in South Korea, Estonia, St. Lucia, Bosnia and Herzegovina, Dominica, Grenada, Latvia, St. Kitts and Nevis, Guyana, Slovakia, Bahamas, Haiti, Lithuania, and Bulgaria, suggesting that the consumption of distilled spirit beverages is influenced by holiday destination and culture. Although the production of vodka, in Russia, dates back to the twelfth century, significant development of other major spirit beverages such as tequila (Mexico), cachaça (Brazil), and cognac (France) took place in the sixteenth century. A large rum industry, operated by slaves in the West Indies, was very productive in the seventeenth century. Gin was being produced in Holland in the seventeenth and eighteenth centuries. By 1743, the annual consumption of gin in Britain was 70 million liters for a population of 6 million people. The devastating effect of excessive drinking of gin was portrayed in Hogarth’s (1697–1764) famous etchings of gin drinkers. American whiskeys developed in the eighteenth century, and Canadian whiskey appeared in the nineteenth century. Canadian rye whiskey came to prominence in the 1940s. Examples of other localized, smaller-volume products of the distilled spirit market are aquavit (Denmark), arrack (e.g., Turkey), grappa (Italy), marc (France), okolehao (Hawaii), ouzo (Greece), pisco (South America, e.g., Chile and Peru), maotai (China), and mescal (with or without ‘worm’ (Mexico)). As regards the science and technology of distillation, the first study of the distilling process, where a liquid containing many compounds is vaporized, separated, and collected as desirable (drinkable), was made by the French alchemist Arnaud de Villeneuve in 1310. Taxation of distilled spirits is an important source of revenue for many producing countries. For example, the first taxation on Scotch whisky was in 1644 at 40 pence per gallon. That taxation persists today at the impressive figure of about £88 per gallon for pure alcohol. Of all the spirits in the world, vodka sells in the largest volume. Bacardi rum is the largest brand. Scotch whisky earns the largest income of the brown spirits, and cachaça is the spirit product that is consumed in the largest volume in one country (Brazil). It is produced in the largest number of production facilities (c. 18 000).

Malting and Mashing Processes Malting Genetically modified cereals are not used to make Scotch whisky. Pregerminated grains, which carry significant

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quantities of microbial infection, should not be used to make distilled spirits. As in other grain industries, the assessment of the different degrees of pregermination of the grains within a

Barley variety Harversted (18–25% water)

Dried (11% moisture) Protection of embryo viability during storage

Steeped in water (36–48 h, 16°C) (Water content = 46%)

Germination process (5–6 days, 16°C) Enzyme development: hydrolysis of cell walls of starchy endosperm to release starch and soluble proteins Kilning (24 h, air at ~65°C) and peating

Water reduction to 4.5% Enzyme levels reduced increase of flavor compounds and color

Distiller’s malt (dried roots removed) Figure 1 Production of the distillers’ malt.

Scutellar epithelial cells: absorption of endosperm breakdown products

sample is therefore important. Scotch malt whisky is produced from malted barley of known varieties. Malted barley is derived from the malting process (Figure 1). In this process, 25– 500 tonnes of barley are steeped in water and air-rested for 48 h at 16 C. The water is drained and the grains are allowed to germinate (grow) for a period of 5 days at 16– 18 C. The germinated grains are then kilned (dried) at 60– 70 C. During kilning, peat may be burned to ‘peat’ the malt because the smoky-peaty (phenol: 0–50 ppm) flavor of malted barley is an important flavor note of many brands of Scotch whiskies. During the germination process, the plant hormone gibberellic acid is produced in the growing embryo. This natural hormone is transported to the aleurone (bran) layer, which encloses the starchy endosperm (Figure 2). The aleurone is induced by the hormone to synthesize endosperm-degrading enzymes such as cell wall-degrading endo-b-glucanases, storage protein-degrading proteases, and starch-degrading a-amylases. Other enzymes such as b-amylase (maltose producing) and carboxypeptidases (amino acid producing) develop in the starchy endosperm. Together, these enzymes modify (disrupt) the starchy endosperm so that subsequent milling and extraction (mashing) of the malt in hot water can occur readily. During this process, starch is converted into fermentable sugars; amino acids are extracted and produced. Vitamins and minerals are also extracted. These substrates are required, by the growing yeast cells during fermentation, to produce ethanol and flavor compounds (Figure 4). Distillers set laboratory specifications as regards the quality of the malt they require to produce their whisky products. For example, such malts must have a high fermentable extract potential of 68% and fermentability potential of 87%; amino acids (free amino nitrogen) should be 130–140 ppm; and the modification of the malt, assessed in terms of friability, should be at least 90% to enable easy milling and extraction. The homogeneity of malt modification is an important quality

Progression of enzymic breakdown of cells of the starchy endosperm

Shoot

Embryo

Modified endosperm Unmodified endosperm

Roots Breakdown products

Aleurone layer: optimal production and release of endosperm degrading enzymes

Cell well

Figure 2 Progression of endosperm breakdown by endosperm-degrading enzymes during the malting process (34).

BEVERAGES FROM GRAINS | Beverages: Distilled parameter. It relates to a balanced modification where a malt of good corn (kernel) size and low nitrogen gives optimal fermentable extract/brewers’ extract and high a-amino nitrogen and spirit yield. The spirit yield of specified malt is still of vital importance to the producers of Scotch whisky because the alcohol content, like the flavor quality of the product, is a vital part of the profitability of the product. In this regard, spirit yield expectations of distillers’ malts have increased from 300 l of alcohol per tonne of malt in 1986 to 460 l of alcohol per tonne of malt in 2011. Nitrosamines and ethyl carbamate are natural carcinogenic compounds, which develop during the kilning and distilling processes, respectively. Very low levels of nitrosamines are specified (none or 1 ppb max). Glycosidic nitrile is also specified at very low levels (3.0 g tonne1 of malt) because it is the precursor of ethyl carbamate. Acrylamide (formed from a reaction between asparagine and reducing sugars in cooked foods, e.g., cereals) is another carcinogenic compound that the grain industry monitors to ensure that levels are within food standard guidelines. Like similar compounds, the margins of exposure to the consumers of alcoholic drinks are within published guidelines. Only malted barley can be used to produce Scotch malt whisky. In Scotch malt or grain whisky production, all the enzymes required to convert the starch and proteins to sugars and amino acids must be derived from the malt. By law, no extraneous enzymes can be added. Also, contaminating compounds (e.g., volatile compounds) should be kept away from barley or malt at all stages of the processes of production and storage. If this is not done, the contaminated grain may release off flavors into the finished product.

and 65 C, temperatures at which malt starches (i.e., large starch granules) will gelatinize. Malt contributes starch-degrading enzymes such as a-amylase, limit dextrinase, and b-amylase during mashing. a-Amylase liquefies gelatinized starch molecules; b-amylase hydrolyzes these molecules to maltose – the main sugar of cereal-derived worts. Malt is an important source of amino nitrogen, which yeast requires not only for growth but also for the production of flavor compounds. Shortage of amylolytic enzymes in the mash can be corrected by adding commercial amylolytic enzymes, if permitted. Malt contains vitamin B and phytic acid. The latter helps to cause an acidic pH during mashing, which favors the activities of amylolytic and proteolytic enzymes. Amino acids also add buffering capacity to the wort. Unmalted cereals also contribute amino acids and small assimilable peptides to the wort, albeit at significantly lower levels than malted barley. However, they can release high levels of b-glucans and pentosans into the wort. Undermodified malt grains from inhomogenous malt can cause unexpected problems such as slow wort separation, low extract yield, and low spirit yield.

Scotch whisky By law, only the enzymes of malted barley can be used to convert (hydrolyze) the starches of all malt mashes for malt whisky production and the enzymes of cooked maize or wheat used for grain whisky production. Whole grains of maize or wheat are cooked at 140 C under pressure. Grits of maize or milled wheat are cooked at 105 C under pressure. After these

The Mashing Process: Starch Degradation and Sugar Extraction Process Cereal grains (Tables 1 and 3) used in whisky (whiskey) production contain significant quantities of starch and cell wall polysaccharides such as b-D-glucans and pentosans. Cooking solubilizes both the large (10–30 mm) and the small (<5 mm) starch granules (Figure 3). Heating of raw starch granules beyond their gelatinization temperatures is necessary before they can be converted optimally into sugars by amylolytic enzymes. The large starch granules of wheat, barley, and rye gelatinize between 63 and 65 C. The gelatinization temperature of rye starches can extend to 70 C. Small starch granules will gelatinize at 80 C. Maize and sorghum starches (10 mm) gelatinize at above 70 C and are usually cooked. Malt also contains starches, which must be gelatinized to realize the extract that malt can contribute to the mash. Therefore, when malt is being used to convert cooked or gelatinized starch, the mashing temperature must be between 63 Table 3

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l

s-p p p s-p

cw l s-p p l

cw

l

p

Figure 3 Scanning electron micrograph of wheat starchy endosperm showing large and small starch granules and protein matrix. l, large starch granules; p, protein matrix; s–p, small starch granules and protein matrix; cw, endosperm cell wall.

Constituents of some cereals (%)

Cereals

Starch

Gelatinization temperature ( C)

Protein

Lipid

b-D-glucan

Pentosan

Barley Wheat Rye Maize Sorghum

65 64 60 70 70

63 60 65–70 >70 >70

10.0 11.0 13.0 11.0 10.0

3.0 3.0 2.5 5.0 3.0

3.5 0.5 1.5 0.3 0.3

9.0 8.5 9.0 3.5 3.0

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cereals are cooked and then cooled to 63 C, a slurry of 9– 10% milled green or dried malt is added to effect starch conversion into sugars. The sugary wort required for Scotch malt whisky production is derived from a mash of 100% milled malt (e.g., 8– 10 tonnes). The malt is mashed in a water/malt ratio of 4:1, at 63–64 C for at least 1 h. After the sugary wort is ‘run off,’ the malt bed is washed, two or three times with hot water (80– 100 C), to ensure that all the fermentable sugars are extracted. Although some grain distilleries collect and ferment the sugary worts, others ferment the entire mash. To start the fermentation process, yeast is added to cooled worts (20 C) or to cooled unfiltered maize–malt or wheat–malt mashes (20 C). About 50% of the fermentable sugars of distillers’ sugary worts are maltose. This sugar is mainly produced by b-amylase during mashing. However, a-amylase and limit dextrinase enzymes also assist in the hydrolysis of gelatinized (cooked/ heated) starch – these enzymes facilitate the activity of the bamylase enzyme. b-Amylase is more heat-labile than a-amylase. b-D-glucans are present in the cell walls of the endosperm. Barley contains 3.0% b-glucan. Malt should contain less than 0.4% b-glucan to ensure that during mashing, wort ‘run-off’ rate and starch release are optimal. Cell wall b-D-glucans and pentosans can limit water removal from spent grains required for animal feed production. Appropriate treatment of spent grains with b-glucanase assists dewatering.

Irish whiskey In Ireland, a mash can contain only malt for malt whiskey production, or the mash may have 60% of hammer-milled barley and 40% malt, or it may comprise 90% hammer-milled maize and 10% malt. The 10% malt may be replaced by hydrolytic enzymes. Commercial enzymes can only be added to the production of grain whiskey. The different spirits produced are used to produce a wide range of distilled products such as malt whiskies or blends of malt and grain whiskies made in pot stills or continuous stills.

Canadian whiskeys For Canadian whiskey, maize grains are milled and cooked at 140 C. The mash is cooled to 100 C and amylase is then added. Malts containing amylases and commercial amyloglucosidases are added at 63–65 C to optimize fermentability. For Canadian rye whiskey, the mash contains milled rye alone or, more commonly, rye and other cereals such as maize and/or wheat. Heat-stable amylase and b-glucanase enzymes are added as the mash is heated up to 85 C where the grain meal is held for 20 min. It is then cooled to 63– 65 C and amylases and amyloglucosidases are added to give optimal release of sugars. Finally, the mash is cooled and yeast is added. Fermentation starts at 20–30 C. Yeast may have been subjected to lactic souring.

Gin and vodka The spirits used for the production of gin or vodka are usually neutral spirits. These are mainly highly distilled ethanol (minimum 96%) and are almost free of congeners. The main flavor product is ethanol. The lowest limit of ethanol for a neutral spirit (96%) is usually higher than the 94% taken for the production of Scotch grain whisky. In this regard, Scotch grain whisky has more flavor congeners than the spirits used for gin and vodka production. Neutral spirits are produced from mashes of milled/cooked cereals, potatoes, molasses, fruits, or sugars. Mashes containing cereals and potatoes require the addition of malt enzymes or external enzymes to convert starches into sugars as described for whisky/whiskey production.

Cachaça For traditional cachaça, for example, ‘artisanal,’ no mashing process is necessary because the fermentation sugar, sucrose, is squeezed from washed, freshly harvested, stems as sugar cane juice. Many varieties of sugar canes are used; some reflect crosses of standard varieties such as Saccharum officinarum L. with other varieties. Sugar content of the juice is 12–16%.

Rum American whiskeys Bourbon must be produced from a mash of not less than 51% corn, but typically, a bourbon mash contains 70% corn, 15% rye, and 15% malted barley. A rye whiskey mash can contain 51% rye, 39% corn, and 10% malted barley. The Tennessee whiskey can be made from a mash of 80% corn, 10% rye, and 10% malt. Different milling systems are used to mill the raw grain. The milled grains and malt or enzymes are heated and cooked and then cooled. An additional quantity of milled malt is mashed in at temperatures not exceeding 64 C. Highly enzymic malts are used. The quantities added are usually lower than those used in Scotch grain whisky production. During mashing, natural enzymes of the malt and commercial enzymes produce optimal conversion of starch to sugars. Conversion (mashing) time varies from 15 to 60 min. The term ‘sour mash’ describes the acidic nature of the mash. Long mashing times can encourage the development of microbial infection. At the end of the mashing process, the mash bed (spent grains) is washed with hot water to optimize sugar release, as in other whisky-making processes.

The fermentation sugar, sucrose, is derived primarily from high- or low-sugar molasses. Sugar cane juice is also used. Molasses have a higher mineral and nitrogen content than sugar cane juice and impart a different flavor to the final product. Molasses of high sugar content ( 22–24% sucrose) tend to produce a spirit of 10–12% ethanol, whereas sugar cane juice (12–16% sucrose) tends to produce a postfermentation alcohol content of 6–8% alcohol. Rum produced from sugar beet molasses gives a very different flavor from rum produced from sugar cane molasses. Tasting trials showed that the sugar cane product is generally preferred.

Tequila Tequila and mescal (with or without the ‘worm’ in the bottle) are both produced from the agave plant. However, tequila is produced in Tequila and its vicinity from Agave tequilana Weber var. azul, whereas mescal is produced from Agave potatorum. Agave head is harvested and cut into pieces for cooking. During cooking, the inulin polymer is hydrolyzed to produce fructose, which is sweeter than sucrose – this process

BEVERAGES FROM GRAINS | Beverages: Distilled can take 2 days. Autoclave cooking will produce a sugar syrup of 10%. The cooked agave is milled in small sugar cane mills, and the milled product and sugary juices are collected. For the production of 100% tequila, only agave sugar can be used. For other kinds of tequila, cane sugar, molasses, or corn syrups can be added to levels of 49%. The sugary worts used to produce 100% tequila have sugar concentrations that range from 4% to 10%. For other tequilas, sugar concentration can range from 8% to 16%.

dextrins 13%. Excluding sucrose, these sugars are the products of amylolytic hydrolysis of gelatinized starch during mashing. In contrast, sucrose is the only major sugar of cane juice. In fruit mashes and juices, glucose and sucrose are the major sugars, and in tequila mashes, fructose is the dominant sugar. Total sugar levels of distillers’ wort range from 10% to 16%. Yeast requires a nitrogen source to effect expected growth from which ethanol and flavor compounds are produced (Figure 4). The raw materials used usually satisfy the nitrogen requirements of the fermenting yeast. A malt whisky wort can contain 250 mg l1 of a-amino nitrogen, whereas a grain whisky mash of 90% wheat can contain 100–120 mg l1. In malt whisky production, there is an exceptionally high level of amino acids, which may contribute to the production of esters and other flavor compounds. The role of amino acids in the formation of flavor compounds is complex. However, optimal levels of these nitrogenous compounds will assist in the optimal production of esters. Suboptimal levels of amino compounds may encourage the production of higher (fusel) alcohols. With regard to fusel oil production, the slower metabolism of amino acids such as valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, and methionine contributes to the levels of fusel oils found in the wort (wash) at the end of the fermentation period. The levels of slow and fast metabolizable amino acids in the wort (wash) and yeast vitality may help to determine the quality of the distilled product. However, even at optimal levels of amino nitrogen compounds, different levels of esters can be produced suggesting that other factors influence ester production, such as yeast type, wort concentration, lipid content, and fermentation temperature. Special mention is made of esters because they are important flavor compounds that contribute different flavors to distilled spirits. In this regard, the total ester content does not convey the individual or the

Brandies 1. Cognac derives its name from the town Cognac. The base wine for cognac production comes mainly from the St. Emilion grape although Folle blanche and Colombard grapes are authorized. The glucose of the acidic wine is fermented without the addition of yeast for 3–5 weeks. The acidic wine is then distilled in small pot stills. 2. Armagnac comes from the Armagnac region, and there is written reference to this brandy in 1411, two centuries before cognac was produced. Grape sugar (glucose) is fermented to produce, like cognac, low-alcohol wines. These are then concentrated by distillation without prior removal of grape residues (lees). 3. Eau-de-vie is associated with the Alsace region. Soft fruits are mashed (unheated or preheated) and their sugars are converted to alcohol during fermentation. Alcohol is concentrated in pot stills. Calvados brandy, which is made from apple mashes, specifically comes from the provinces of Brittany, Normandy, and Maine.

Fermentation Cereal (malt) worts can have the following composition of sugars and dextrins: fructose 1%, glucose 10%, sucrose 5%, maltose 50%, maltotriose 15%, maltotetraose 6%, and

Malt-Wort extract

Fatty acids

Sugars

Vitamins

Minerals

Keto acids

Sugars

Organic acids

Amino acids

Amino acids

New flavor compounds

Organic acids Fatty acids

Alcohols Organic acids

Esters

Fatty acids

Esters

Precursor (flavor) compounds

Cell wall

Aldehydes

Aldehydes

199

Alcohols

Figure 4 Fermentation: production of low percentage of spirit (6–8%) from plant sugars and nutrients prior to distillation.

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complementary contribution of different esters to the overall flavor. Insufficient nitrogen nutrients can limit yeast growth, resulting in the production of unexpected or undesirable flavors. One of the main distinctions in fermentation systems is fermenter size. Cachaça and brandies such as cognac and Armagnac are produced from small fermentation volumes ( 1500–3000 l), whereas rum and tequila are derived from larger volumes in the order of 10 000–12 000 l. In malt distilleries, fermentation vessels can range in size from 4000 to 20 000 l. In grain distilleries, these vessels can be as large as 250 000 l. Yeast is usually added to initiate and advance fermentation in gin, vodka, rum, and whisky production. Residual postfermentation yeasts may be used to start new fermentations of spirits such as cachaça, tequila, and some brandies. However, in cognac, wine is allowed to self-ferment for 3–5 weeks. For ‘artisanal’ cachaça, naturally trapped yeast is added initially to effect fermentation. In the production of heavy Jamaican rum, natural inoculation is encouraged but can be supplemented by yeast additions. In Scotch whisky production, fresh yeast is added to new fermentations. Fermentation temperatures vary. Unlike beer fermentation, which usually takes place below 15 C, distillery fermentations range from 20 to 40 C. Since there is no temperature control, whisky/whiskey fermentations can start at 20 C and rise to 30 C over a short 48 h period of fermentation. Most distillery fermentations are usually completed by 48 h, compared with beer fermentations, which can extend to 5 days. However, in tequila and American whiskey production, slow fermentations may exceed 72 h. The high fermentation temperature and the high yeast-pitching rate are mainly responsible for the fast fermentation rates of most of these spirits. Pitching rates for yeast (Saccharomyces cerevisiae) vary and can range from 10 to 20 million cells per milliliter. Distillers use either residual postfermentation yeast, company-cultured yeast, or purchased yeast to effect fermentation. Yeast under cold storage tends to be more viable than yeast stored at warm temperatures. Although great efforts are made to control bacterial infection during fermentation, the by-products of the metabolism of lactic acid bacteria and Clostridium saccharobutyricum in heavy rum production can be essential congeners of the expected flavor profile of fermented worts and mashes. General monitoring of levels of the presence of bacteria can be carried out using a flow cytometer. Specific tests such as enzyme-linked immunosorbent assay and polymerase chain reaction can be used to detect unusual contaminating bacteria. In general, during fermentation, sugars such as sucrose, glucose, fructose, maltose, maltotriose, and maltotetraose are fermented to ethanol, and nutrients (e.g., zinc and amino acids, vitamins, fatty acids) and some malt flavor compounds are used by the yeast to grow and form a wide range of flavor compounds characteristic of the spirit to be produced. These flavor compounds include simple alcohols and higher alcohols (fusel oils), esters, organic acids, aldehydes, ketones, sulfur compounds, and aromatic flavor compounds such as acetals, which tend to develop in acid conditions and high ethanol medium. At the end of the fermentation process, the chemical composition of mashes and worts could be similar. However, intraspirit and interspirit differences become distinct after the distillation process has isolated, separated, and combined the

congeners that define particular spirit products. Fermented worts, derived from different raw materials, will produce different spirit products. However, within a product type, differences will be caused by differences in still sizes, shapes, and modes of operation. In this regard, distillation is as important as raw material in defining spirit type and spirit quality. Here, quality is defined as meeting the expectations of the customer.

Distillation Distilling Using Copper Pot Stills The fermented worts or mashes of many distilled spirits contain 6–8% ethanol. The purpose of distillation is to vaporize the compounds present in worts and mashes and effect their separation and concentration. Still size can vary from 5000 to 25 000 l in capacity. Volatile compounds are derived from the contents of the still. New volatile compounds are also formed during distillation. If specific cyanidecontaining precursors are present, unacceptable compounds such as ethyl carbamate are produced. Cereal spirits should have an upper limit of 150 mg l1 of ethyl carbamate; fruit spirits should have no more than 500 mg l1. Most stills are heated by heating coils. Cognac stills are fired directly. In the production of Scotch malt whisky, double distillation is involved but triple distillation occurs on a limited scale. The situation is similar for rums. For Irish whiskeys, triple distillation is standard. Single distillation is also used to produce products such as cachaça and Armagnac. Double distillation usually takes place in wash and spirit stills. The distillate of the wash still (the low wine) is very high in congeners, and ethanol is concentrated from 6–8% to 23%. In the spirit still, the low wine is fractionated into ‘foreshots’ (heads), ‘middle cut’ (spirit), and ‘feints’ (tails). Single-distillation pot stills operate in a similar manner to spirit stills, separating the ferment into three factions. After maturation in wooden (e.g., oak) casks, the ‘middle cut’ (spirits) will be transformed into the distilled product (Table 2). In the triple distillation system, as used for Irish whiskey, the late portion of the distillate of the wash still is removed and redistilled in a low-wine still. The early portion of the wash still distillate and the early portion of the low-wine still are added to the spirit still for fractionation in ‘heads,’ ‘middle cut,’ and ‘tails.’ As is the case for spirits such as Scotch whiskies and brandy, the congener levels of traditional cachaça are higher than those of rum or bourbon. However, this may not be the case for all ‘industrial’ cachaça, produced in continuous stills. The overlap of ‘foreshots’ into the ‘middle cut’ (i.e., the spirit) and the overlap of the ‘middle cut’ into the ‘feints’ can change the expected flavors of the spirit. High levels of ‘foreshot’ compounds in the spirit can be detected by making a 50/50 mixture of spirit and water. If cloudiness develops, the ‘foreshot’ content of the spirit is usually too high, and adjustments to the ‘spirit cut’ time should be made. ‘Foreshots’ contain very volatile compounds, which can confer ‘solvent-like’ character to the spirit. In contrast, ‘feints’ contain low-volatile compounds that give the spirit a distinct stale, metallic odor. During pot still distillation, ethanol concentration rises during the ‘foreshot’ collection but declines during the ‘middle cut’ collection. Depending on still type, the total ‘middle

BEVERAGES FROM GRAINS | Beverages: Distilled cut’ spirit fraction can contain 50–70% alcohol. Extended collection of the spirit fraction will lower its alcohol content and increase the possibility of having ‘feints’ in the spirit. As regards the volatility of congeners, acetaldehyde, diacetyl (butanedione), methanol, and some sulfur compounds are congeners of high volatility; esters of various kinds are congeners with medium volatility; fusel oils (i.e., higher alcohols) such as propanol, isobutanol, furfural, and isoamyl alcohol have lower volatility than many esters but are usually more volatile than fatty acid congeners such as propionic, isobutyric, isovaleric, hexanoic, and octanoic acids. Despite differences in volatility, all these congeners can be found in the spirit, at levels that characterize the spirit type. The duration of collection of fractions containing these compounds is crucial as regards the distinctiveness and quality expectations of the spirit product. Still size, shape, and distillation volume also affect the composition and levels of congeners present in the ‘middle cut’ (i.e., spirit). The insertion of a water-cooled ‘purifier’ between the neck of the still and the condenser also acts to reduce congener levels and lightens the spirit. The single distillation of cachaça into ‘foreshots,’ ‘middle cut,’ and ‘feints’ in small pot stills with cooling worms makes the middle cut spirit of cachaça a distinctly different product from rum, which is double-distilled or triple-distilled. Rums tend to have lower levels of flavor congeners. In general, in many spirits, the fusel oils are in high concentration but do not dominate the overall aroma and taste because they are counterbalanced by esters and aldehydes. Esters confer fruity and floral aromas to spirits, and although esters are lost in the ‘foreshots,’ the levels retained in the ‘middle cut’ (the spirit) are vitally important. In this regard, butanol, propanol, and aldehydes play important parts in giving distinctiveness to different spirits, but when these congeners are balanced with esters and other flavor compounds, a more complex spirit is achieved. Phenol, cresol, and guaiacol compounds are derived from peated malts. These substances are distilled into the spirit and confer medicinal, smoky, and phenolic aromas and taste to Scotch malt whisky. The intensities of these compounds are balanced by congeners such as esters. Methanol is regarded as an undesirable compound in spirits but is produced in high quantities in noncereal mashes of plant tissue (e.g., potato, agave, and fruits; Table 2). This highly volatile compound is dangerous to health and is absent from most distilled spirits but is present in ‘safe levels’ in eaude-vie. It is a very volatile compound and should be removed in ‘foreshots,’ but fruit mashes contain high levels of pectin from which significant quantities of methanol are derived during mashing (extraction). Preheating of fruits to destroy the enzymes that release methanol or the fermentation of fruit juices instead of mashed fruits significantly reduces the levels of methanol produced.

Properties of copper in distilling The patina, which forms on the internal surface of pot stills, can function to reduce the levels of off-flavor sulfur compounds, that is, sulfides (e.g., dimethyl sulfide and mercaptans) from the spirit. Although copper can be detected in some spirits, the levels are within safe food levels.

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Distillation Using Continuous Stills Continuous stills are large vertical constructions. They contain internal sheets of copper, which perform the same function as the copper in pot stills. In the Coffey stills, there are two columns, the rectifier and analyzer. The 6–8% ethanol ferment or mash is heated as it passes down the rectifier. This heated mash then passes to the analyzer where steam is blown through it. Ethanol and flavor congeners are driven off. These pass back into the bottom of the rectifier and are collected at their designated heights from the lower plates to the higher plates of the rectifying column. For example, plates may ascend from 1 to 39: Plate 7 is rich in isoamyl alcohol (fusel oils), plate 14 is rich in isobutyl alcohol, plate 23 is rich in n-propyl alcohol, and plate 32 is rich in ethanol at 94%. Ethanol concentration increases from plate 1 to plate 32. Volatiles such as methanol, sulfur compounds, and acetaldehyde are found in plates 35–39. An alternative type of continuous still is the column still. This comprises a beer stripper where the 6–8% ethanol ferment is heated using stem, as in the analyzer. The vapors pass to the bottom of the concentrator, which, like the rectifying column, fractionates the vaporized compounds at appropriate plates, for example, plate 5 (fusel oils, e.g., isoamyl alcohol), plate 8 (propanol), plate 35 (ethanol, 95%), and the topmost plate 40 (methanol and volatile sulfur compounds). In all stills, condensers are connected to condense vapors that leave the still. American whiskeys are produced in continuous stills. They cannot be distilled above 80% ethanol and therefore contain more congeners than Scotch grain whisky at 94% ethanol and vodka and gin spirit at 96% ethanol. Canadian whiskeys are produced from maize, rye, malted barley, and malted rye. Spirit fractions are collected between 65% and 95% ethanol and are used to produce different distilled products. Vodka and gin spirit (94% alcohol) may be passed through an extractive (water/steam) column still, which removes traces of volatiles such as methanol and diacetyl. The spirit is then concentrated in a rectifier where fusel oil is drawn off lower down the rectifier. The spirit is now at least 96% ethanol and is passed finally through a demethylizer to remove the last traces of methanol. In some plants, neutral spirit for vodka production is passed through charcoal to assist the purification process. During mashing, glycerol can be converted by lactic acid bacteria to acrolein, which escapes during distillation causing an irritating pepper-like odor in the distillery.

Maturation As indicated in Figure 5, distilled spirits are usually matured in wooden barrels for minimum periods of time. Some spirits are not matured such as vodka and gin, whereas, by law, Scotch whisky spirit and Irish and Canadian whiskey spirits are matured in oak casks for a minimum period of 3 years. American whiskeys are matured for a minimum time of 2 years. The maturation periods for rums are variable – from not at all for some light rums to weeks or years for heavy rums. Cachaça of the highest quality is matured in wooden barrels, especially oak, and for at least 2 years. Brandies (e.g., cognac) are matured in oak barrels and, like Scotch whisky, can be matured for over

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Oak barrel (charred inner surface 2–4 mm)

Alcohols (volatiles)

Sulfides (dimethylsulfide) Arabinose Glucose Xylose Fructose Galactose (sugars)

(Distilled substances) Alcohols

Esters

Acids Color (sherry)

Maltol Glycerol Furfural

Polysaccharides

Polyphenolics (Tannins) Aromatic aldehydes (Vanillin)

Lignin

Lactones terpenes

Volatile oils

Figure 5 Maturation of distilled spirit (‘middle cut’) in oak barrels.

20 years. Maturation can take place in new, charred, wooden barrels (e.g., cognac or American bourbon whiskeys) or in oak barrels previously used for sherry or bourbon. Port, Madeira, and a variety of sherry barrels are now being used by some distillers to ‘finish’ the maturation periods of their whiskies for wider brand appeal. Legally, tequila must be matured in oak casks for 2 months (rested tequila) or 1 year (aged tequila). Different oak species are used for barrel construction, for example, Quercus robur (English), Quercus petraea (Spanish or French), or Quercus alba (the United States). Barrel staves are sawn so that the normal tangential loss of water from the tree stem is avoided. Different spirits are filled into barrels at different strengths of ethanol. Spirit strengths of 63.5% ethanol are most extractive. Temperature conditions influence maturation rate and maturation results. High temperature accelerates ethanol loss from barrels. For Scotch whisky, which can only be matured in oak casks, a loss of 2% (‘the angels’ share’) of the contents of the barrel occurs each year. In such maturation conditions, from an initial fill of 63.5% ethanol, 58% ethanol will remain after a maturation period of 12 years. During maturation, unpleasant compounds are extracted by the barrel; pleasant compounds are released into the spirit, and various important flavor compounds such as esters are formed in the spirit (Figure 5). The active charred inner surface of the barrel contains carbon, which absorbs the unpleasant flavors of dimethylsulfide, dimethyldisulfide, methional, and methional acetate from the whisky, but not dimethyltrisulfide, which, even at low concentrations of 4 ppb, can be detected organoleptically (i.e., by taste or smell). From the scorched subsurface, important wood complexes are released into the spirit, adjusting its flavor and aroma and increasing its color. Hydrolyzable tannins released into the spirit promote oxidative reactions such as ester formation between alcohols and acids. Lignin is the strengthening material of wood and is a complex polymer, which, when scorched by charring, releases

aromatic aldehydes into the spirits such as vanillin and coniferaldehyde. Vanillins confer vanilla-like aromas to the spirit. Vanillin levels are very high in new barrels after charring and are characteristic flavors of bourbons and cognac. Other spirits that are matured in ex-bourbon casks also have detectable levels of vanilla-like aroma and taste. Low-level sweetness is conferred by the release of simple compounds such as glycerol and monosaccharide sugars such as xylose, arabinose, and glucose. Dry toasted malting flavors come from the release of furfural and maltol. American oak barrels release more lactones into the spirit than Spanish oak barrels. Cis-lactones confer desirable woody aromas and sweet, smooth, coconut flavors. Components of tannins such as gallic acid and ellagic acid can contribute astringency and can be oxidized to give color and fragrant compounds. The solid matter content of whisky increases by 2.5 g l1 over a period of 12 years. Some of this material is lipid material (fatty acid esters) that will form hazes when water is added to matured spirit products, if such products are not cold filtered. Cask strength Scotch whiskies, which are not filtered, tend to form hazes when water is added. Metal ions can also form flocs, which are removed by filtration of the product. Pieces of charcoal that are dislodged from the charred surface of the barrel are also removed during filtration. The sherry flavors and vanilla flavors of distilled products are derived from the barrels in which they are matured. Sherry barrels also contribute color to maturing spirits. Repeated use of a barrel will deplete its reservoir of colorproducing materials and flavor compounds and its ability to remove undesirable compounds such as sulfides. Such barrels are rejuvenated by scraping away the inner carbon surface and recharring the newly exposed wood. A barrel may last as long as 40 years. However, its effectiveness declines over these years. Maturation moderates the volatility and increases the smoothness of the spirit. This is particularly important in high congener spirits.


Blending and Bottling Before blending or vatting, the spirit is checked before the casks are emptied and collected in tanks. In general, whiskies, cachaça, rums, brandies, or tequilas are vatted and left to ‘marry’ before being reduced with water of low mineral content to bottling strength. The ethanol levels of vodka and gin are also reduced using low mineral water. Judicious vatting (mixing) of cognac of different ethanol concentrations is effected to arrive at the bottling strength required. The mixing of generic spirits can be referred to as vatting. However, blending is used to describe the mixing of different kinds of spirits (e.g., malt and grain whiskies). In this regard, malt whiskies can be described as ‘pure’ single malts (malt whisky from one distillery), ‘pure’ malts (mixture (vatting) of different malt whiskies), or ‘blends’ of malt and grain whiskies. Here, pure is taken to mean of one kind. The mixing of cachaça products from different production operations is equivalent to the vatting of single malts because the cachaça products used are different in character but are produced traditionally and are therefore of one kind. In contrast, in America, blended whiskies will contain grain whiskey, neutral spirit, or light whiskey and a complement of heavy whiskey or whiskies such as bourbon or maize whiskey. These heavy whiskies are called ‘straights’ if matured for more than 2 years. As in Ireland, the mash bill and still type determine the types of whiskeys that are blended, such as products of high congener levels (malt or high malt whiskies) and products of low congener (high grain whiskies) levels. In Canada, light whiskeys, made from rye and malted barley and malted rye, in continuous stills are blended with high-flavor corn whiskeys (65–80% ethanol), made from 60% corn (maize), rye, and malted barley in either pot stills or continuous stills. Some Canadian whiskeys are blended with wines, sherries, brandies, rums, bourbons, and malt whiskeys to create different flavors and aromas. Lighter whiskeys may be used in larger quantities than heavier spirits; they may not only add lightness but also add flavor notes of freshness, which are crucial to the ‘drinkability’ of blended whiskeys. Since blended whiskies, for example, Scotch blends, can contain as many as 30–40 malt whiskies and 6–8 grain whiskies, the overall complexity is greater than any comparable single malt. Blending extends product range and provides the possibility of arriving at new products, which the public may prefer. This can take a long time; but the opportunity of developing new products should not be ignored. The levels of important congener compounds (e.g., esters) may not be reduced by blending because very highly flavored whiskies in the blend can compensate for the reduction of esters by dilution with grain whiskies, which have low congener levels. In this regard, some blended Scotch whiskies can have similar ester contents to malt whiskies, even though a malt whisky may have four to five times as many esters as a grain whisky. Blending is the high art of distilled beverage production, providing the customer with consistency and complexity without losing the high traditional qualities of a wide range of individual products, which are blended together to extend drinkability.

Alcohol Consumption At present, there is a worldwide debate concerning the relationship between alcohol consumption and poor health and antisocial behavior. The distilling beverage industry sells

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brands, not pure alcohol. The general use of the term ‘alcohol’ has ignored one of the important reasons why people drink different commercially made alcoholic products. Customers drink brands, not pure alcohol. Alcohol is a part of the constituents of the products. However, since the debate is about alcohol consumption, this term will be used. In the European Union in 2011, distilled spirits accounted for 21% of alcohol consumed, beer 37%, and wine 42%. Recent developments in the consumption of spirits include an increase in consumption of premium brands and basic brands of white spirits such as vodka. Some of this increase in consumption has come from increased consumption of cocktails. In the United Kingdom, the Scottish government is the only government that has passed a minimum price law. The law states that the alcohol in alcoholic drinks should be sold at a minimum price of 45 pence per unit. This law has not yet been introduced because it is being challenged in court by the Scotch Whisky Association. A unit of alcohol is defined as 10 ml or 7.9 g of spirit in the United Kingdom. The number of units in an alcoholic drink is calculated as follows: volume of drink alcohol percentage in alcohol by volume/by 1000. The advice of the UK medical authority is that a man should not consume more than 3–4 units of alcohol per day and a woman should not consume more than 2–3 units per day. The units of alcohol present in distilled beverages in the United Kingdom are usually stated on their labels. However, the nature of freshly mixed cocktails makes it difficult to assign units to them. Problems relating to minimum price for alcohol include the observation that the law was, in part, derived from a ‘model’ that indicated that increased price would reduce consumption of alcoholic beverages, which, in turn, would reduce alcoholrelated diseases and antisocial behavior. Objections to the proposed minimum price law state that such laws are against free trading and they penalize the poorest customers. The poorest customers consume about 10% of the alcohol consumed in the United Kingdom. Since richer customers also purchase cheap alcoholic products but can afford to buy more expensive products, minimum price will have a greater financial affect on the poorest sector of society and is therefore disproportionate in its financial effect. The relationship between alcoholic drinks and, for example, liver disease requires scientific research to determine the direct effects that alcohol and lifestyle have on health and social behavior. It has been stated that the effects of caffeinated alcoholic drinks on health and social behavior should also be assessed. Education about drinking, the implementation of existing licensing laws, and ‘sensible drinking’ as the industry’s approach are likely to be more effective than implementing minimum price in controlling alcohol abuse.

Environmental Strategy Environmental strategy is an important objective of the distilled beverage industry. An example of this strategy is that published by the Scotch whisky industry report of 2012. In this report, it is stated that in 2010, for 101 malt and seven grain operational distilleries, 990 000 tonnes of cereals (malted barley and other cereals such as wheat and maize) was used to make Scotch whisky. Over 93% of the malted barley and other cereals used were of local Scottish origin. Total industry CO2

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(equivalent) emissions from energy use were about 698 000 tonnes (down 14% on 2008 levels). Primary energy usage was 3 367 178 455 kWh, equivalent to 0.13% of total UK primary energy consumption. Nonfossil fuel energy use was 6%, up 3% from the level in 2008. The industry’s total water usage was 37 020 430 m3. On average, 79% of the water used in malt distilleries is returned to the environment. The average weight of packaging materials was 6.61 kg per 9 l case, 32% of packaging was reused or recycled, and 7% of industry packaging waste from packaging operations was sent to landfill. In terms of research that links the management of grain quality to environmental changes, partnership research is in progress to develop wheat varieties that will grow and yield optimally on reduced levels of nitrogen fertilizers to improve grain quality in terms of starch percentage yield and to reduce nitrogen pollution of the land. In addition, the author has developed a new, single-grain, amylase pregermination test that determines pregermination in individual grains to overcome the inaccuracies of positive/ negative tests and average analysis tests. This pregermination test may give some indication of the potential of individual cereal grains to form acrylamide (see the preceding text).

Conclusion Reference has not been made to the by-products of the distillation process. In some plants (e.g., Scotch grain whisky), carbon dioxide is collected and sold; spent grains from the mashing process and spent materials from the distillation process (stillage) are dried and sold as animal feed. Wastewater (backset), in some American distilleries, is kept hot (e.g., 65– 95 C) and reused as part of the mashing-in liquor or part of the cooking liquor. This liquor contains lactic acid. It is acidic and nutritious and is a contributing factor to the term ‘sour mash’ in American whiskey production. In addition, fusel oils are collected during the production of grain whisky and sold to the perfume industry. Waste sugar cane skins and fiber (bagasse) are used as fuel. These practices show that the distilling process is ‘environment-friendly’ because most of the products of the process are protected, recovered, transformed (e.g., into bioethanol), and sold. Copper in the stillage can be problematic in animal feed, but this is primarily a problem for single-gut animals. The use of caramel of the highest quality is permitted in the industry to adjust the color of spirit products to expected levels. In most cases, very small levels are used compared with the very high levels used in, for example, chocolates, cola, and gravy mixes. In general, distilled beverages are ethanol-based products, which are made with sound science and high art and, from the levels of their sales worldwide, not only are pleasant to drink but also play an important part in defining the culture from which they originate. Those who produce them are proud of their distinctiveness and quality. An example of such pride can be found in Robert Burns’ poem, ‘John Barleycorn,’ which accurately describes the production of Scotch whisky and glorifies its virtues – virtues that Burns described collectively as a ‘cup of kindness’ in the universal New Year’s song, ‘Auld Lang Syne.’ He believed passionately that whisky and ‘freedom’ went together. Maybe, the same beliefs could be extended to other

spirit beverages that reflect historical custom and practice (culture). In order to protect standards of production and cultural heritage, the essential features of production of distilled spirit beverages should be enshrined in the law, as is the case for many of the distilled beverages described in Tables 1 and 2. In this regard, original place of production, raw material used, production process employed, and overall aroma and taste should be taken into consideration. The spirit industry has always encouraged sensible (moderate) drinking because it is fully aware that excessive alcohol consumption can cause health and social problems. The value of moderate consumption of alcohol, as regards improved cardiovascular function, is still being researched, but the results so far are encouraging. Although the production of distilled spirit beverages sustains many jobs and creates high tax returns to various governments, their contribution to the culture of celebration is probably their most important merit in society.


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List plant materials and relate to beverage type. List still types and relate to beverage type. What did Andrew Usher do? Outline the different stages of the malting process. Describe major changes that occur during fermentation. What is maturation? Why is it important? Outline some of the differences between white spirits, for example, vodka, tequila, and gin, and brown spirits, for example, whisky, whiskey, and cognac. Describe social factors relating to alcohol production and consumption.


•

Select research concepts from the text, relate them to references, and design relevant research. Also, contact the industry and relevant research establishments.

See also: Beverages from Grains: Beverages: Asian Alcoholic Beverages; Fermentation: Foods and Nonalcoholic Beverages; The Basics: The Grains that Feed the World.

Further Reading Agu RC, Bringhurst TA, and Brosman JM (2006) Production of grain whisky and ethanol from wheat, maize and other cereals. Journal of the Institute of Brewing 112: 314–323. Agu RC and Palmer GH (2013) Evaluation of the potential of millet, sorghum and barley with similar nitrogen content malted at their optimal germination temperatures for use in brewing. Journal of the Institute of Brewing 119(4): 258–264. Craig HC (1994) The Scotch Whisky Industry Record. Scotland: Index Publishing. Dolan T (2013) Applying science for 50 years. Brewing and Distilling International 9(4): 35–41. Gray AS (2011) The Scotch Whisky Industry Review, Annual Review of the Industry, 34th edn. Sunderlands: Edinburgh Publication. Hazelwood LA, Daran J-M, van Maris AJA, Pronk JT, and Dickinson JR (2008) The Ehrlich pathway for fusel alcohol production: A century of research on

BEVERAGES FROM GRAINS | Beverages: Distilled Saccharomyces cerevisiae. Applied and Environmental Microbiology 74(8): 2259–2266. Jacques KA, Lyons TP, and Kelsall DR (1999) The Alcohol Textbook, 3rd edn. Nottingham: Nottingham University Press. Lachenmeier DW, Przybylski MC, and Rehm J (2012) Comparative Risk Assessment of Carcinogens in alcoholic beverages. International Journal of Cancer 131: E995–E1003. Lee MK-Y, Paterson A, and Piggott JR (2001) Origin of flavours in whiskies and a revised flavour wheel: A review. Journal of the Institute of Brewing 107: 287–313. Lindsay R (2009) Focus on fermentation factors. Brewer and Distiller International 45–48. Ludbrook A (2010) Purchasing patterns for low price off sales alcohol: Evidence from the expenditure and food survey, http://www.shaap.org.uk/images/UserFiles/File/ Reports%20and%20Briefings/Briefing%20-%20Purchase%20of%20low-price% 20alcohol%20analysis.pdf. May, pp. 1–16. Nykanen L and Lehtonen P (1984) Flavour Research of Alcoholic Beverages, vol. 3. Helsinki: Foundation for Biotechnical and Industrial Research. Owens B, Andrews B, Faulkner A, and Sands G (2011) 99 Pot Stills, pp. 1–101. American Distilling Institute: White Mule Press. Palmer GH (1989) Cereal Science and Technology. Scotland: Aberdeen University Press. Palmer GH (1997) Scientific review of scotch malt whisky. Ferment 10: 367–397. Palmer GH (1998) A wee dram of chemistry. Education in Chemistry 35(2): 40–42. Palmer GH (1999) Achieving homogeneity in malting. In: Proceedings of the European Brewing Congress, Cannes, pp. 323–363. Palmer GH (2006) Malting. In Bewley DJ, Black M, and Halmer P (eds.) The Encyclopedia of Seeds: Science, Technology and Uses, CABI, pp. 396–405.

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Palmer GH (2010) Time for a sober look at alcohol. Evening news, Edinburgh, Scotland, 23.8.2010. Palmer GH (2012) New pre-germination test. Brewing and Distilling International 8(8): 5. Palmer GH and Wang Y (2005) New b-glucan method which measures malt modification. The Brewer and Distiller 1: 50–53. Russell I (2003) Whisky: Technology, Production, Marketing. Handbook of Alcoholic Beverage SeriesLondon: Academic Press. Scotch Whisky Industry (2012) Environmental Strategy Report, 3. Scottish Whisky Briefing 30th April 2012 (/news-media/media – press/publications/). Time (2012) Small business: A booze of one’s own: Micro distilling boom, http:// business.time.com/2012/04/06/craft-distillers/. United Kingdom Bartenders’ Guild (1981) International Guide to Drinks. London: Hutchinson. Walker GM, Goodall R, Fotheringham R, and Murray D (2013) Worldwide Distilled Spirits Conference, Science and Sustainability, Proceedings of Worldwide Distilled Spirits. Nottingham: Nottingham University Press, pp. 1–397. WHO (World Health Organization) (2004) Global Status Report on Alcohol. Geneva: Department of Mental Health and Substance Abuse.

Relevant Websites http://spirits.eu/page.php?parent_id¼11&id¼58 – Spirits.eu – Consumption. http://en.wikipedia.org/wiki/List_of_countries_by_alcohol_consumption – List of countries by alcohol consumption.

Beverages: Asian Alcoholic Beverages DK O’Toole, City University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp. 86–96, ã 2004, Elsevier Ltd.

Topic Highlights

• • • •

Many traditional alcoholic beverages are made in Asia by fungal fermentation of cereal grains. The best known rice wine is Japanese sake´, which requires both Aspergillus and yeast fermentation. China has a diversity of sorghum-based distilled liquors, usually produced in batches by complex traditional processes. Understanding the traditional processes is the first step toward modernizing and adapting them for uniform highthroughput continuous production systems.

Learning Objectives

• • •

To understand the product diversity and characteristics of Chinese and Japanese grain-based alcoholic beverages produced from fungal fermentation. To understand the roles of fungal starter culture and yeast fermentation during processing. To develop an insight into the complexities of adapting traditional production methods for large-scale modernized processing.

For many centuries, China and other East Asian nations have used a mold-based system for the production of alcohol from grains. This mold-based system has also been adapted to the production of other fermented products such as soy sauce. The foundation of the system is ‘koji’ (Japan), or ‘jiuqu’ (China). Grain is prepared and mold allowed to grow on it. The mold enzymes include a-amylase, gluco-amylase, as well as proteases. To produce rice wines such as ‘sake´’ and Chinese rice wines, the molded grains are mixed with rice, and in a complex process the rice is converted to an alcoholic beverage. The distilled sorghum liquors depend on a semisolid fermentation followed by steam distillation. This is done up to 8 times with the same batch of sorghum with ‘daqu’ being added after each distillation.

Introduction Yeasts can only produce alcohol from soluble monosaccharides and disaccharides, most commonly from glucose and maltose. Two sources of these sugars are fruit juices and starch, but the starch is insoluble and the sugars are in polymeric form and so generally unavailable to yeasts. In the West, this unavailability problem was solved by using sprouted barley to release enzymes that breakdown the insoluble starch in the grain to sugars for yeast growth. However, in China, after an attempt 3000 years ago to use sprouting grain to brew ‘Li’

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from ‘Nie’ in a process similar to beer brewing, the idea was dropped in favor of a microbial-based system in which ‘Jiu’ was brewed with ‘Qu’ Modern beer making was only introduced to China in 1900 at Harbin by Russians. The ancient Chinese system depends on growing mold on grain, essentially a solid-state fermentation for enzyme production, mixing the molded grain with cooked grain and water, then soaking it in water to allow the enzymes from the mold to breakdown the starch, followed by a yeast fermentation to produce alcohol. Rice wine or Japanese sake´ are the modern descendents of this technological innovation. The molded cereal-based system starts with wet grain, cooked or uncooked, so that molds grow on the grain to produce carbohydrate degrading enzymes. In Japan, this molded product is called koji, in China it is qu or jiuqu, in Korea it is ‘nuruk’ (or ‘nuluk’). In Southeast Asian countries, a similar powdered-rice product is made and they go by the names ‘bubod,’ ‘ragi,’ ‘lakpaeng,’ ‘men,’ and ‘mochikouji,’ but rice is not necessarily the source of sugar. In the Philippines, the wet form of koji is called ‘binubudan’ and sugar cane juice is fermented. Koji is used to produce a variety of foods, apart from alcoholic beverages, throughout east Asia. This microbial-based system of alcohol production has a long history, dating back to the Xia Dynasty, 4000 years ago, but archeological artifacts associated with the technology have been dated to over 5000 years ago. Jiuqu has been specifically mentioned in Chinese literature dating from the Zhou Dynasty (770–221 bc). As with beer in the West, for centuries in China, and even now, some alcoholic beverages are thought beneficial to health. In China, this mold-based system is used to make grainbased distilled liquors and wines, e.g., from rice, corn, millet, and sorghum. The Japanese have developed sake´-brewing systems based on the scientific study of the organisms and processes while Chinese systems tend to be more traditional and far more complex.

Sake´ Brewing The Japanese rice wine production began 300 BC and today there are 10 000 brands of sake´ produced in 2000 factories. The Japanese have developed pure fungal and yeast culture based systems for rice wine production as opposed to the traditional rice wine making systems mostly used in China. Sake´ is classified according to the degree of polishing of the rice used to make the wine (Table 1). Rice grain weight reduction is from 25–35%. Generally, ‘ginjo sake´’ is made with highly polished rice while ‘honjozo sake´’ is made with rice not polished below 60%. Less highly polished rice results in a higher level of inosinic acid that is responsible for the characteristic flavor of sake´.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00234-5

BEVERAGES FROM GRAINS | Beverages: Asian Alcoholic Beverages Table 1 Types of sake´ are based on the Seimaibuai classification that relies on the percentage of original rice left after the rice has been polished. The lesser the percentage of original rice, the lighter and more delicate is the flavor of the sake´. Seimaibuai classification (% of rice left after polishing)

Type of sake´ Junmai dai ginjo Junmai ginjo Tokubetsu junmai Junmai

50 60 60 70

Comment Highest grade of sake´, light dry type Sweeter, heavier than above ‘Special Junmai,’ a marketing product Means ‘pure sake´,’ no added alcohol, with heavier, fuller flavor

Polished rice: steamed and cooled

Koji-making room, piled and covered to equilibrate

Spread and mix with koji mold, 10–100 g per 100 kg dry polished rice

Reheap inoculated rice and cover with cloth

After 10–12 h remix rice and cover again

After a further 10–12 h, rice is mixed again and divided into 1.5–2.5 kg lots on shallow koji trays

Each lot stirred 6–8 h later, temperature ∼35 ⬚C

Stirred again, after 8–10 h, to expel CO2 and cool, spread 4–5 cm deep

After 10 h, temperature is 40–42 ⬚C, koji is removed from koji room Figure 1 Koji production for sake´ manufacturing is an intensive process designed to maximize enzyme production.

Koji Production for Sake´ Brewers favor large rice grains with soft kernels so that water uptake is rapid and mold mycelia can penetrate the kernels more easily (Figure 1). The mineral content of the water influences sake´ quality, iron levels must be low and potassium,

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phosphorus, and magnesium are required for mold growth, and calcium and chlorine improve fungal amylase extraction. The pH should be neutral to alkaline, of medium hardness (German scale 3–7) and highly chlorinated. After washing off loose bran, the grains are steeped to take up water equal to 25–30% of the milled rice weight. The drained, steeped rice is then steamed in shallow open vessels for 30 min to 1 h, in batch systems, for a shorter period in continuous systems, so that the weight of the grains increase a further 8–12%. The rice is then cooled to 34–36 C and transferred into the koji-making room where temperature and relative humidity can be controlled, and piled on an insulated bed and covered with cloth to allow equilibration with the room. The grains are then spread evenly and inoculated with ‘tane-koji,’ a seed culture of Aspergillus oryzae that has been grown for up to 6 days to maximize sporulation. It is inoculated at 10–100 g per 100 kg of polished rice, reheaped and covered with a cloth. The temperature rises as the fungus grows so the inoculated rice must be manipulated and mixed to control temperature. The way the mold mycelia grow through the resulting molded grain influences the quality of the sake´ produced. If mold growth is confined to the outer layers of the grains, excessive breakdown of grain protein reduces sake´ quality. The fungus produces 50 kinds of enzymes including proteases and amylases. Of particular importance are a-amylase (amylo-1,4-dextrinase) and S-amylase (amyloglucosidase), the former breaks down the starch molecules to smaller fragments to decrease viscosity, the latter removes glucose units.

Moto Production In effect, this is the beginning of the brewing process because ingredients are added to the ‘moto,’ after it has been made, to make the sake´. In moto production, yeast is prepared by a complex process that is, however, simpler than traditional methods. Water (200 l), rice-koji (60 kg), and steamed rice (120 kg) are mixed and held at 13–14 C for 3–4 days with occasional stirring. The temperature drops to 7–8 C. During this stage, the koji enzymes begin the breakdown of the starch in the rice, and some wild bacteria and yeasts begin growing in the mix. However, lactic acid bacteria (Leuconostoc mesenteroides var. sake´ and Lactobacillus sake´) begin growing and lower the pH. These acid conditions, along with the high levels of sugars, eventually kill off these organisms. The temperature rises to 15 C and by 15 days a pure culture of sake´ yeast, a strain of Saccharomyces cerevisiae but with some unique characteristics (Table 2), is added to give a population of 105–106 g1 that rises to 108 g1 as temperature also rises to 20–23 C. A variation on this system is to add lactic acid to the moto mix to bring the pH down to 3.6–3.8 to prevent the wild microbial activity but the sake´ yeast must be added soon after. The characteristics of the water phase at yeast inoculation are: specific gravity, 1.124–1.128; reducing sugar, 26–28%; amino acid as glycine, 0.5–0.8%; total acid as lactic acid, 0.3–0.4%. Traditionally, it took 25–30 days to produce suitable moto.

Rice Wine Production The wine-making process is basically a batch-fed system, the fermentation process is begun and further raw materials are fed

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BEVERAGES FROM GRAINS | Beverages: Asian Alcoholic Beverages

Table 2 Some cultural characteristics that distinguish sake´ yeast and S. cerevisiae Response Characteristic

Sake´ yeast

Growth in vitamin-free medium Growth in biotin-free medium Tolerance to ethanol (% concentration) Habitat

þ

Saccharomyces cerevisiae

þ 20–23

16–19

Found only in sake´ brewing

Widely found in fruits and other environments

into the ‘moromi’ as it progresses (Figure 2). (Moromi is a general term to describe a fermenting mash based on grains on which fungi have grown.) The moromi stage of the process involves putting moto, at 12–13 C, in a vessel 6–18 kl in size along with steamed cool rice, rice-koji and water (Table 3). By this stage, the water phase of moto has a specific gravity of 1.028–1.043, an ethanol content of 12–15%, amino acid content of 0.45–0.65% and total acid content of 0.9–1.0%. The saccharolytic enzymes from the koji release the glucose from the rice starch thus making it available for the yeast to ferment. There are three additions of water, rice-koji, and steamed rice to the vessel containing the moto, and as each addition is made the temperature is lowered by adjusting the temperature of the steamed rice and water so that by the fourth day the temperature

Rice (soft kernel, large grain) Water (with P, Mg, Ca, K, neutral pH)

Polished rice

Bran to waste

Wash ×1, steep 1–6 h Water to waste

Heat

Aspergillus oryzae , koji mold

Steamed, cool rice

Koji production

Water

Moto production: steamed rice, water, and koji, up to 30 days

Lactic acid

Day 0, 12 ⬚C 1st day 3rd day 4th day, 7 ⬚C

Moromi agitated twice daily, fermentation becomes vigorous, temperature rises to 13–18 ⬚C then cools, fermentation ends at 21 days

Moromi is allowed to settle, then filtered, settled again, then passed through activated carbon filter and pasteurized

Spent grain

Figure 2 Sake´ production is a complex process involving the production of koji that is used to make a relatively small batch of starter material, the moto, to which is added further batches of steamed rice, koji, and water. Acid conditions to prevent growth of spoilage organisms are important; so in some cases lactic acid is added instead of relying on the natural growth of lactic acid bacteria in the moto. Temperature control is also important.

BEVERAGES FROM GRAINS | Beverages: Asian Alcoholic Beverages Table 3 The raw materials added progressively to the prepared moto to ferment the rice for sake´

Table 4

The Chinese classification of rice wines

Wine type

Sugar (g per 100 ml, as glucose)

Ethanol (%, v/v)

Total acid (g per 100 ml, as succinic acid)

Dry type Semidry type Semisweet type Sweet type

<0.5 0.50–3.00 3.00–10.00 >10.00

>14.5 >16.0 >15.0 >13.0

0.45 0.45 0.55 0.55

Cumulative totals Preparation stage Motoa 1st addition 2nd addition 3rd addition Total

Day 0 1 3 4

Total rice (kg)

Steamed rice (kg)

Rice-koji (kg)

Water (l)

180 510 1020 1710 3420

120 360 830 1350 2640

60 150 210 360 780

270 500 1230 2329 4329

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a

Moto production takes 2–4 weeks to complete before the actual wine production begins.

is 7–8 C. The lower temperature controls wild microbial growth. The moromi is then agitated twice daily and by 3–4 days, the water phase composition is: specific gravity, 1.051–1.058; ethanol, 3–4%; total acid as succinic acid, 0.06–0.07%. The yeast concentration reaches about 2.5 108 per g and the fermentation becomes more vigorous and temperature rises to about 13–18 C in 6–9 days, where the temperature is held for a further 5–7 days until the ethanol content is 17.5–19.5% and the temperature begins to decline. In the final stage, further additions may be made to the moromi. Pure distilled ethanol may be added to bring ethanol to 20–22%, 7–8% steamed rice allows production of excess glucose to sweeten the wine but pure glucose may be added, lactic acid and succinic acid may be added as well as glutamic acid. By 21 days, the density of the water phase is 1.004–1.000, reducing sugar is 3–2%, ethanol is 18.5–19.5% and the acid content as succinic acid is 0.14–0.16%. The moromi is allowed to stand for a few days to settle and it is then filtered and again allowed to settle for 5–10 days. If the period is too long, the sake´ quality begins to deteriorate. It is then passed through an activated carbon filter, pasteurized, and stored at 13–18 C to mature before bottling.

Scientific Basis of Process The wine-brewing process is conducted as a parallel fermentation, and is best conducted at low temperatures. Further, the development of low pH due to acid production by lactic acid bacteria or addition of lactic acid retards growth of spoilage organisms and permits the growth of yeasts. The parallel fermentation is unique in that while the enzymes are releasing the glucose from the starch, the yeasts are fermenting it to produce ethanol unlike beer where the soluble sugars are first released and then the fermentation is conducted. From studies conducted in Japan, it is known that the release of the sugars initially from the steamed rice occurs rapidly. However, the increased glucose concentration suppresses a-amylase activity, so release of glucose declines until significant yeast activity reduces glucose and produces ethanol. The breakdown of the rice-koji in the moromi is more complex. The mold growth in the outer layers of the rice grain solubilizes the outer layer of starch rather quickly leaving variable amounts of a core of the rice grain that breaks down

much more slowly under the action of the a-amylase. The breakdown of this inner core is dependent on the variety of rice used in the manufacturing.

Chinese Rice Wine Production Unlike modern Japanese sake´ preparation methods, the Chinese traditional methods of preparation did not distinguish between the mold stage and the yeast stage, they were combined into one process that was very complex and varied enormously from place to place. However, pure cultures have been isolated and are increasingly being used but traditional methods are still used. In addition, constituents apart from rice may be used in the preparation so instead of steamed rice, barley, and millet are also used as the main source of starch. Generally, Chinese rice wines are classified according to the residual sugar level, namely dry type, semidry type, semisweet type, sweet type, and extrasweet type (Table 4). They are also classified according to the production method. The four basic methods and their names (Table 5) are: 1. ‘Ling fan jiu,’ e.g., ‘yuan hong’ wine is a dry type wine. The hot steamed rice is cooled by drenching it with cold water then mixing the rice with jiuqu starter. It is commonly used as starter for inoculating more mash. It can be drunk after fermentation for several days. 2. ‘Tang fan jiu,’ e.g., ‘jia fan’ wine that is a semidry type wine. The steamed rice is spread onto bamboo rafts to cool and then mixed with jiuqu, and acidified rice-steeping liquid. 3. ‘Wei fan jiu,’ e.g., ‘san niang’ wine that is a semisweet type wine. This rice wine is produced using a fed batch fermentation method similar to sake´ production. The fermentation is begun as in the first process, but then steamed rice is added intermittently during the fermentation period, usually in three batches. 4. Fortified rice wine, e.g., ‘xiang xue’ wine that is a sweet type wine. Aged rice wine or spirits distilled from refermented spent grains from rice wine are added before the main fermentation ceases. The final alcohol concentration is above 20%, consequently the microorganisms in the mash are inhibited, but the saccharification of the remaining dextrin to sugar in the main mash continues slowly, resulting in high residual sugar contents. A general outline of the manufacturing process of Chinese rice wine is given in Figure 3.

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Table 5

The ingredients and chemical composition of four kinds of Chinese rice wine Types of rice wine

Component Proportions of components used to make the rice wine (kg) Glutinous rice Wheat koji Seed mash Acidified rice-steeping water Freshwater Distilled spirit Composition of rice wines Specific gravity Ethanol (%, v/v) Extracts (g per 100 ml) Sugar (g per 100 ml) Total acids (g per 100 ml) Volatile acids (g per 100 ml) Nonvolatile acids (g per 100 ml)

Yuan hong

Jia fan

San niang

Xiang xue

144 22.5 8–10 84 112

144 25 8–9 50 68.6 5

144 25 15 50 100a

100 10

0.992 15.6 3.325 0.38 0.48 0.06 0.42

0.995 17.8 4.450 0.78 0.46 0.027 0.43

1.0349 16.7 15.65 6.50 0.46 0.054 0.406

1.073 19.4 24.44 20.00 0.28 0.056 0.22

100b

a

This is yuan hong wine. This is 50% distilled spirit. Adapted from Xu G and Bao TF Grandiose survey of Chinese alcoholic drinks and beverages (http://www.sytu.edu/zhgjiu/umain.htm).

b

Jiuqu Production Chinese rice wine making begins with the preparation of a starter material called qu or jiuqu. The preparation is designed to encourage the growth of molds on prepared masses of grains and along with it yeasts also grow. The mold growth results in the production of enzymes in the jiuqu. The molded mass of grains is then shaped and dried for use as an inoculum in rice wine making. When the jiuqu is then added to prepared grains, such as steamed rice, the enzymes breakdown starch in the steamed rice just as malted grains can be used to breakdown adjuncts in beer production. However, unlike beer production, the jiuqu also fills the fermenting function, due to the presence of yeasts (S. cerevisiae) in the prepared jiuqu. The actual number of types of jiuqu used for the production of alcoholic beverages in China is unknown. However, there are three broad types of jiuqu, based on the raw material used, and within each broad type there are subtypes based on the color, presence of additives, and size of the molded masses or molded pancakes produced. The names of various jiuqus based on the raw materials rice and wheat are in Table 6. One is also made from wheat bran, called ‘fu qu,’ that is used for alcohol production. The manufacturing processes also vary which also influence the resulting jiuqu. These processes include the use of pure or mixed cultures, a high temperature or a medium temperature, incubation of jiuqu in a thin or a thick layer, hanging in the air in a suitable small container, and wrapping the jiuqu in straw. Consequently, for a given mass of jiuqu, the enzyme activity varies widely. In addition, jiuqu is prepared to suit the product to be manufactured.

Shenqu Historically, the most active wheat-based jiuqu for making rice wine, was ‘shenqu.’ It was made by milling wheat, splitting it into three portions, one of which was roasted, another steamed, and the other left uncooked. The three portions

were then mixed thoroughly with added water to a consistency that was less than a slurry. The mixture was transferred to an incubation room, and spread on the floor. Moisture content and temperature were critical and these were managed by opening windows to lower temperature and heaping the mixture to raise temperature. The first three days required high-moisture content, to promote growth of mycelia, and lower-water content was required for the subsequent incubation period up to 49 days. After this time, the shenqu had a yellowish to yellowish-green color. The primary fungi for this preparation were Aspergillus species and pure cultures have been isolated and are now used. Preparation methods today with pure cultures differ from the traditional method in that incubation may be on the floor, as in the traditional method, or in a compartment similar to the germinating compartment used for malting barley, or in trays similar to koji trays. Using the compartment, the steamed, cooked wheat grits are inoculated with fungal spores and piled in a heap for 3 h. The wheat is then spread in a 30 cm layer over the perforated plate in the compartment. The temperature and moisture content are controlled, and oxygen supplied for the fungi deep in the pile, by blowing air suitably conditioned for temperature and water content through the layer. Generally, the temperature is kept to a maximum of 30 C.

Daqu Daqu, meaning ‘large qu,’ is used for the manufacture of some Chinese spirits and its manufacture is different from shenqu. There are two basic kinds, depending on the temperature reached during manufacture. One kind is high temperature that is allowed to rise above 55 C, perhaps as high as 65 C, and the other is kept below 55 C. The raw materials are wheat flour, barley flour, and pea flour mixed together in proportions, depending on the manufacturer. One manufacturer, Yanghe Distillery, uses the following proportions and procedures. The wheat:barley:pea proportions are 5:4:1. The


Glutinous rice

Xiaoqu, 0.4–0.5%

Polished rice Water

Wheat qu, 8–10% Bran to waste

Wash ×1, steep Heat

Water to waste

Steamed, cool with water drench

Seed mash

1st addition and stir as needed

2nd addition and stir as needed

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moisture content is brought to 40% and the resulting dough kneaded and eventually packed into a wooden mold with dimensions of 195 138 75 cm. Traditionally, the packing was done by human treading by ten people with a gradation in body weight to get the dough at just the right firmness in the mold (Figure 4). In modern production systems, mechanical pressing devices are used to prepare the blocks. The block is then removed from the wooden mold and placed in the incubation room, with other blocks, in two layers on bamboo rods giving a space of 2 cm between the layers covered with straw. Incubation is for 4 weeks and has three phases. In the first phase of 9 days, there is a rapidly rising temperature due to the growth of fungi and yeasts. The dominant fungi are Aspergillus species and Rhizopus species, namely R. oryzae and R. chinensis. The humidity is initially high and is reduced by opening windows. The temperature of the whole batch is controlled to the temperature range 30–45 C by turning and rearranging blocks 6 times in the 9-day period. In the second phase, of 8 days’ duration, the temperature of the batch is allowed to rise smoothly a little further but within the range 30–45 C. In this phase, more of the moisture evaporates and its loss is controlled so that it is not lost too quickly. In the third phase, the room temperature is allowed to decline and moisture loss from the blocks allowed to increase so that they

Primary fermentation of lao ends at 1 week

Secondary fermentation: transfer lao with 13–14% ethanol to narrow-necked jars that are sealed and left to mature for 70–80 days

Flavor and aroma improve, ethanol in lao rises further 2–4%, lao is squeezed, clarified, pasteurized, and packaged

Spent grains

Figure 3 The production of a Chinese rice wine. The name ‘lao’ is equivalent to moromi in sake´ manufacturing. In this case, there is a secondary fermentation in which the lao is put into a jar and sealed up for months to allow the production of flavors and aromas.

Table 6

Figure 4 An ancient image of daqu production in China. In the early stage, the ‘dough’ is shaped into rectangular blocks by men pressing the dough into a mold with their feet. The weight of the men pressing a block progressively increases. The block is then managed to encourage mold and yeast growth, before drying the blocks. (Data from Xu G and Bao TF Grandiose survey of Chinese alcoholic drinks and beverages (http://www.sytu.edu/zhgjiu/umain.htm))

Types of Chinese qu, based on the base grain employed to make alcoholic beverages from rice and other grains

Rice

Wheat

Qu name

Comment

Qu name

Comment

Xiao qu Yao qu Bai qu Hong qu Hei qu Wu yi hong qu

White, small dimension, made with Rhizopus spp. Herbs added White Red color, due to Monascus fungus Black, due to Aspergillus niger Red and black color

Mai qu Da qu Shu mai qu Seng mai qu Bing qu Dou qu

Wheat qu, made with Aspergillus flavum Dimension large Wheat steamed or roasted Fresh wheat used Pancake shape Added pea or bean, and rice or wheat flour

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weigh less. If at the end the moisture has not been reduced to 12%, the blocks are piled and recovered with straw to raise the temperature and accelerate moisture loss.

Glutinous rice soaked for several days and steamed

Spread rice in ceramic vat, cool to 27–30 ⬚C

Xiaoqu A further important jiuqu is ‘xiaoqu.’ The traditional method is similar to that used for daqu production except only steamed and powdered rice is used, the water used is flavored with steeped herbs, and the freshly made blocks are cut into smaller cubes and formed into balls. Selected old jiuqu is used as a seed culture to inoculate the outer surface of the balls. The old jiuqu is a kind of selected starter culture. As the dominant fungi involved have been isolated, a pure culture method is now used in its preparation as follows. The Rhizopus species are grown on rice meal or wheat bran and the yeast, a Saccharomyces species, is cultured on an extract of a special jiuqu and harvested by centrifugation. Then the Rhizopus culture and yeast concentrate are mixed in a 50:1 ratio. This mixture is used to make a seed mash for rice wine. This particular approach to rice wine making significantly reduces the time to make the wine.

Chinese Rice Wine Making Although Chinese rice wines are usually made with rice, they are also made with maize and millet. When made with rice, 230 kg of rice wine is produced from 100 kg of rice. The jiuqu in rice wine manufacturing has two functions: to supply amylolytic enzymes and to supply yeast for ethanol production. In some modern production systems, commercially manufactured enzymes are used to carry out the saccharification step. For various types of wines different portions of ingredients are used (Table 5). One of the ingredients in the mix is traditional seed mash, and the ingredients used to make this seed mash are 125 kg of glutinous rice that is soaked for several days and then steamed. The steamed rice is then spread in a ceramic vat and after it cools to 27–30 C, half of the xiaoqu jiuqu is mixed through the rice (Figures 3 and 5). The rice is then stacked around the sides of the vat to form a hollow in the middle of the rice and the rest of the xiaoqu powder is sprinkled onto the surface (0.187–0.25 kg total). This maximizes the surface exposure to encourage growth of Rhizopus species (that produce lactic and fumaric acids) to lower the pH, discourage the growth of undesirable organisms, and encourage yeast growth. In addition, the amylase and glucoamylase in the jiuqu saccharify the rice. After about 2 days a pool of liquid containing sugars, etc., gather in the hollow. Then 19.5 kg of jiuqu is added, mixed through the fermenting rice mix and freshwater added to bring the total water content, including that taken up by the rice during steeping and steaming, to 230 kg.

Water and Acidified Rice Steeping Liquid The water used in wine brewing should have a hardness in the range of 2–6, pH 7, and should have a low-iron content. The acidified rice-steeping liquid is traditionally prepared by steeping the polished rice in the water for periods of 10–20 days, preferably 13–20 days. During the steeping, lactic acid bacteria grow and lower the pH. This traditional liquid, when added to the final brew, helps to inhibit the germination of bacterial

Sprinkle about 120 g xiaoqu on rice and mix

Stack rice on the sides of vat, sprinkle about 120 g

After 2 days, liquid pools at the vat bottom, jiuqu is then added, along with water Figure 5 The production of seed mash used in the manufacture of Chinese rice wines. Table 7 Some of the jiuqu mold preparations used in the manufacture of Chinese distilled liquors and the names of liquors based on distinctive aromas and flavors and their characteristic flavor impact compounds Jiuqu used

Aroma and flavor

Flavor-impact compound

Daqu Xiaoqu Fuqu

Maotai Luzhou Fen Rice

Ethyl hexanoate and ethyl butyrate Ethyl acetate Ethyl lactate and ethyl acetate

spores and growth of vegetative cells, provides amino acids and vitamins, lowers the pH for yeast growth, and helps improve the flavor of rice wines. However, alternatives to this include using diluted vinegar solution or a broth made with wheat flour, but lactic acid is now commonly added.

Chinese Distilled Liquors Chinese distilled liquors are classified according to the jiuqu used, the type of aroma and flavor developed, the fermentation state for ethanol production, the quality, the ethanol content and the raw materials used. Important types are in Table 7 along with the characteristic flavor impact compounds. Many Chinese liquors are based on sorghum and contain 53–55% ethanol. They have characteristic aromatic fragrance due to the presence of 4-ethylguaiacol, vanillic acid, and vanillin. The hexanoic acid needed to result in ethyl hexanoate comes from the metabolic activity of anaerobic bacteria in the fabric of the fermentation pits. A difference between Chinese-distilled sorghum liquor and Western-distilled grain liquors is the use of external mold enzymes from koji-like products. The production processes vary. For rice spirit, the rice is washed, steamed, cooled, inoculated with xioaqu, and placed in a ceramic vat to allow the enzymes to breakdown the starch. Then water is added and the vat covered for 7 days to allow yeast growth and then the fermented liquid is distilled. For sorghum, the grains are crushed, mixed with hot water,

BEVERAGES FROM GRAINS | Beverages: Asian Alcoholic Beverages steamed, cooled, and further water added. Daqu is added to the cooled mixture in a ceramic vat or mud pit or stone pit and sealed. The fermentation is allowed to proceed for 3–4 weeks and the steamed sorghum husks added and the mixture distilled. The spent sorghum is then remixed with daqu and sealed in a vat and left for 3–4 weeks whereupon steamed husks are added again and the mixture distilled again.

Wheat daqu, prepared at >55 ⬚C

213

The production system in Taiwan is of rather shorter duration. The typical ‘wine cake’ (or juiqu) for spirit production is produced with cracked wheat, contains up to five varities of yeasts (including S. cerevisiae and S. fibuligera); four molds (including Mucor and Rhizopus species); and six types of bacteria, including a Clostridium species. The level of activity of hydrolytic enzymes is usually low.

Sorghum grain

Spent grain from previous fermentation

Crush grain Water at 90 ⬚C Soak, 4–5 h Distilled spirit Steam Water ∼35 ⬚C Cool with water drench

Poorly flavored distilled spirit

Mixed and heaped for fermentation

Crushed fresh sorghum

Ferment in clay or stone pit 1 month

Steam distillation

Cool spent grain, mix and ferment 1 month

Steam distillation

Cooling, mixing with new daqu, fermenting for 1 month at a time, then steam distilling, is continued 5 more times

Cool spent grain, mix and ferment 1 month

Steam distillation Spent grains Figure 6 The traditional Chinese method of preparation of sorghum-based distilled liquors. The amount of daqu and sorghum used is 1:1. The traditional pit used for the fermentation is the source of particular flavors for some liquors due to associated bacterial activity. Eventually, the completely spent grain is discarded.

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The steamed sorghum is spread out on the floor to a thickness of 5 cm and powdered wine cake mixed through it. The moisture content of the sorghum is 55%. The fungi grow on the cool and dry surface, whereas bacteria and yeasts grow within the wet mass of sorghum. After 24 h, the sorghum is piled into heaps that encourage growth of yeast in an anaerobic and warm environment (prefermentation). The size of the pile is restricted because the internal temperature of the pile must not be allowed to rise above 40 C, and the heat produced metabolically is not easily dispersed. The Taiwanese put the inoculated sorghum into stainless steel tanks or boxes and cover them with polythene sheet to prevent moisture loss and reduce aeration. Microbial growth and metabolism is allowed to progress for up to 10 days after which the mixture is put through a steam distillation to remove the ethanol. The pile of sorghum is reinoculated to encourage further growth and when ready the sorghum is distilled again. Each heat treatment, or steaming, causes partial hydrolysis of starch, carbohydrates, and protein. Steaming also removes the alcohol that prevents yeast cell growth in the thin film of water surrounding sorghum grains. Alcohol is collected by condensation of the distillate and the ethanol yield is 22.53 kg per 100 kg of sorghum. Microbial cells grow slowly on sorghum due to low availability of fermentable substrates, and this leads to the production of secondary metabolites mentioned above, which contribute to the characteristic strong aromatic fragrance of sorghum liquor. In mainland China, the production of sorghum liquor is much more complex and it takes about 1 year to complete the distillations. The process begins with sorghum that is crushed, soaked in hot water, spent grain from a previous fermentation added and then the entire mix is steamed. Spirit of lower quality and the inoculum of daqu is added to the cooled mixture (Figure 6). It is heaped to allow the fermentation to begin and then placed in a fermentation pit for up to a month to allow the fermentation process to take place. The mixture is then steam-distilled, more daqu added, and the fermentation conducted all over again. With slight variation the process is conducted up to 8 times.


• •

Write out a detailed process flow diagram for a selected product from this chapter. Identify all possible sources of variability in final product quality. Suggest methods for identifying and controlling the microbial strains present at each stage of processing.


• •

Investigate the marketing of Asian sorghum-based distilled liquors – what factors influence pricing? What is known about sensory testing and preferences for the beverages discussed in this chapter.

See also: Beverages from Grains: Beverages: Distilled; Fermentation: Origins and Applications; Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing.

Further Reading Fleet GH (1998) The microbiology of alcoholic beverages. In: Wood BJB (ed.) Microbiology of Fermented Foods, vol. 1, pp. 217–262. London: Blackie Academic and Professional. Kodama K (1993) Sake´-brewing yeasts. In: Rose AH and Harrison JS (eds.) The Yeasts London: Academic Press. Lisdiyanti P and Kozaki M (2003) Rice wine in Southeast Asian countries: Thailand, Laos, Vietnam and Myanmar. The First International Symposium on Insight into the World of Indigenous Fermented Foods for Technology Development and Food Safety Organized by Department of Microbiology Faculty of Science Kasetsart University, and the National Research Council of Thailand International Cooperation, Ministry of University Affairs, August 13–14, 2003 at the Microbiology-Genetics (MG) Building, Department of Microbiology. Bangkok, Thailand: Kasetsart University. http://plantpro.doae.go.th. Steinkraus KH (1995) Handbook of indigenous fermented foods. Food Science and Technology. New York: Marcel Dekker, series no. 73. Xu G and Bao TF Grandiose survey of Chinese alcoholic drinks and beverages (http:// www.sytu.edu/zhgjiu/umain.htm). Yoshida T (2003) Technology development of sake´ fermentation in Japan. The First International Symposium on Insight into the World of Indigenous Fermented Foods for Technology Development and Food safety Organized by Department of Microbiology Faculty of Science Kasetsart University, and the National Research Council of Thailand International Cooperation, Ministry of University Affairs, August 13–14, 2003 at the Microbiology-Genetics (MG) Building, Department of Microbiology. Bangkok, Thailand: Kasetsart University. http://plantpro.doae.go.th.

Relevant Websites enonline.sh.cn http://www.enonline.sh.cn – Shanghai online. sytu.edu.cn http://www.sytu.edu.cn – A site of the Southern Yangtze University in China. Contains an English translation of a wide-ranging survey of alcoholic drinks and beverages in China from an historical viewpoint to the technology used as well as aspects of the legal and regulatory side of the industry. foodreference.com http://www.foodreference.com – A site dealing in general with all aspects of food. It includes daily food and beverage news, a culinary quiz and a ‘Today in food history’ section. There is a wealth of information. Use of search function to search for ‘rice wine.’ internationalrecipesonline.com http://www.internationalrecipesonline.com – Recipes for using rice wine are available on the site using the search function.


Contents Cereal Grains as Animal Feed Pet Foods Utilization of the Whole Cereal Plant to Maximize its Value Fuel Alcohol Production Biodiesel

Cereal Grains as Animal Feed JL Black, John L Black Consulting, Warrimoo, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• •

•

•

• •

•

Cereal grains are fed to livestock for energy because of their high starch content. Energy from grains available for metabolism and productivity in animals (MJ d 1) is determined by both the energy released during digestion (digestible energy content, MJ kg 1) and the amount of grain consumed when incorporated into a diet (kg d 1). There is little relationship between digestible energy content (MJ kg 1) and digestible energy intake (MJ d 1) when cereal grains are fed to animals. The former depends primarily of the diffusion rate of digestive enzymes determined by grain chemical composition, endosperm morphology, and processing conditions, whereas the latter depends on the rate of passage of digesta, which is influenced by indigestible fiber and large grain particles and the ileal brake stimulated by partially digested nutrients in the distal intestines. Thus, both digestible energy content and digestible energy intake are needed to fully define the energy value of a grain for animals. Value to an animal of energy released during digestion depends on whether digestion is by animal or microbial enzymes. Microbial digestion (fermentation) results in loss from the animal of 15% of digested energy through methane release, heat of fermentation, and voided microbes. However, microbial digestion is essential for the breakdown of the nonstarch, fibrous components of the grain hull (pericarp) and endosperm cell walls. A large variation exists across cereal species, cultivars, individual grain samples, and animal type in the amount of energy available to animals from grains following ingestion. Anatomy of the animal digestive tract, particularly whether microbial fermentation predominates before or after animal enzyme digestion, has a large impact on the energy value of a specific grain sample. Hence, individual grain samples are best suited to one animal type over another.


•

The energy value of a specific cereal grain for an individual animal type is not related closely to physical characteristics of the grain such as test weight (kg Hl 1) or screening percentage because the internal morphology of a grain has a major impact on the energy released. Alternative methods (e.g., near-infrared (NIR) spectroscopy) have been developed to predict the digestible energy content and digestible energy intake index for cereal grains when offered to different animal types.

Learning Objective

•

To understand how the characteristics of a cereal grain sample and the digestive physiology of an animal determine the energy value of grains for different animal types.

Introduction Cereal grains are used widely as animal feed. Some plant species such as maize (corn), sorghum, millet, triticale, and oats are grown predominantly for animal feed, whereas others including wheat, barley, and rice are grown mainly for human consumption with grains not meeting market specifications frequently being fed to livestock. These latter grains are often small grains from screenings, broken grains, or grains damaged by weather. Cereal grains have a high content of starch relative to other ingredients used as animal feed such as forages or pulses and are offered to animals as a source of readily available energy. Consequently, cereal grains are fed predominantly to intensively reared livestock such as dairy cows, feedlot cattle and sheep, pigs, and poultry and may represent 60–80% of the ration, although they are also used for subsistence in times of poor pasture growth.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00231-X

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NON-FOOD PRODUCTS FROM GRAINS | Cereal Grains as Animal Feed

There is a large variation across cereal species, cultivars, individual grain samples, and animal types in the amount of energy available to animals from grains following ingestion. The variation between grains in energy availability is due in part to heritable characteristics, but much is due to the particular environmental conditions in which the grain was grown. From an understanding of the factors determining the availability of energy for each animal type, it is possible to identify grain characteristics that could be changed by plant breeding or specific processing methods to increase their energy value to animals. Although cereal grains provide amino acids, minerals, and vitamins to livestock, these nutrients are of minor importance in grains relative to other dietary ingredients and are not discussed.

Definition of Available Energy and the Digestive Process The value of a grain as an energy source to an animal depends on the total amount of energy made available for metabolism (MJ d 1), which is determined by the energy released during digestion along the whole digestive tract (digestible energy content, MJ kg 1) and the amount of grain consumed when incorporated into a diet (kg d 1). Digestible energy content is determined by subtracting the energy in feces from energy in each kg of grain consumed. However, in poultry, it is defined as apparent metabolizable energy content (MJ kg 1), because the material excreted from the end of the digestive tract includes uric acid from the kidneys and fecal material. Digestible energy content and digestible energy intake must both be known to fully describe the energy value of a grain for livestock. Animal performance is driven by the total intake of digestible energy (MJ d 1), whereas feed conversion efficiency is determined predominantly by not only digestible energy content (MJ kg 1) of the grain but also by energy intake relative to that required for maintenance of the animal. The digestible energy content of a grain is also used during the formulation of diets for animals. The value of digested energy to an animal varies depending on whether the digestive process is a result of animal enzymes or enzymes of microbial origin. In the latter case, the digestive process is frequently termed microbial fermentation, which results in the conversion of dietary carbohydrates and proteins into growing microbes, volatile fatty acids used as an energy source by the animal, and other compounds, with the release of methane, ammonia, and heat of fermentation. The fermentation process within the digestive tract can result in the loss from the animal of 10–20% of the energy in the digested dietary material, depending on the composition of the diet, conditions of fermentation, and types of microbes present. Nevertheless, the fermentation process is important for animals, because microbial enzymes can cleave chemical bonds in plant material that cannot be broken by enzymes secreted by mammals and birds. Glucose units in grain compounds are commonly linked by a-(1–4), a-(1–6), or b-(1–4) glycosidic linkages. The a-(1–4) bonds, found predominantly in starch, can be hydrolyzed by animal digestive enzymes, whereas the b-(1–4) linkages, found in cellulose, require microbial enzymes for cleavage. The a-(1–6) glycosidic linkages are resistant to animal amylases but are cleaved by an

intestinal brush-border enzyme, a-dextrinase. The a-(1–4) and a-(1–6) bonds are also cleaved by microbial enzymes from gut-inhabiting organisms. Starch digested by animal enzymes is used more efficiently than that digested by microbial enzymes. However, the nonstarch polysaccharides in grains including cellulose and endosperm cell wall constituents, arabinoxylans, xylans, and (1–3, 1–4)-b-glucans can be digested only by microbial enzymes. Although some energy is lost from the animal through the breakdown of these compounds during the fermentation process, 80–90% of the energy released is available for metabolic processes in the animal. The lignin content of grains, which consists of a range of phenolic polymers, is indigestible by animal enzymes and most intestinal microbes. The anatomy of the digestive tract (Figure 1) and the digestive process vary widely between domestic livestock species. Pig

Oe

S

D

I

Ca

Co Re

An

Re

Cl

Fowl

Oe

Cr

P

D

G

I

Ca

Cow

Oe

Rt Ab

Om D Ru

I

Ca

Co

Re An

Figure 1 Diagrammatic representation of the digestive tracts of pigs, poultry, and ruminants (An, anus; Ab, abomasums; Ca, cecum; Cl, cloaca; Co, colon; Cr, crop; D, duodenum; G, gizzard; I, ileum; Oe, esophagus; Om, omasum; P, proventriculus; Re, rectum; Rt, reticulum; Ru, rumen; S, stomach). Reproduced from McDonald P, Edwards RA, and Greenhalgh JFD (1988) Animal Nutrition, 4th edn. Essex, UK: Longman Scientific technical, with permission.

NON-FOOD PRODUCTS FROM GRAINS | Cereal Grains as Animal Feed Feed consumed by ruminants is subjected to microbial fermentation within the rumen-reticulum before it passes to the small intestines where animal enzymes are secreted. The starch in cereal grains is therefore first subjected to microbial digestion and, if degraded rapidly, can result in a significant increase in acid production and fall in rumen pH. Lactic acidosis caused by a rapid increase in the concentration of lactic acid and low pH disrupts the balance of microbes in the rumen; reduces digestion of other dietary constituents, particularly plant fiber; and can severely limit feed intake, health, and productivity of the animals. The rate of starch fermentation in the rumen is influenced by the characteristics of the grain and particle size. The latter depends on the extent of breakdown of grain during mastication and the effectiveness and type of grain processing. Sheep masticate grains more thoroughly than cattle, and often, grains are not processed before feeding to sheep, whereas cereal grains are frequently processed (cracked, rolled, and steam-flaked) before being fed to cattle. Although horses and pigs do not have a compartment like the rumen-reticulum within the stomach for the fermentation of feed, their hind gut contains a large microbial population that digests much of the nonstarch polysaccharide component of their diet. In these animals, the starch component of cereal grains is first subjected to degradation by the animal enzymes. However, if a large quantity of starch passes through the small intestines undigested, it is fermented in the hind gut and can cause laminitis in horses through a lowering of pH and an increase in the susceptibility of pigs to enteric diseases such as swine dysentery and Escherichia coli scours. Pigs masticate their feed poorly, and unless the grain is processed before ingestion, large quantities of starch, protein, and fiber in grain particles can be fermented in the hind gut. Poultry do not have a significant microbial population within the digestive tract, and there is normally insignificant digestion of the nonstarch polysaccharide components in grain. However, poultry have a gizzard within their digestive tract, and the intense muscular contractions of this organ are extremely effective for physically breaking the grain into small particles and disrupting the integrity of the endosperm cell walls and the protein matrix. However, the high dry matter content of poultry digesta and the short transit time of digesta through the gut mean that nonstarch polysaccharides, particularly long-chain molecules, increase digesta viscosity and reduce accessibility of enzymes to the starch granules.

Variation in the Energy Value of Cereal Grains across Animal Types Although there have been many studies around the world examining the effects of grain species and cultivars on energy availability in animals, relatively few have evaluated the same grains across different animal types. The most comprehensive study has been undertaken in Australia where over 3500 cereal grains (wheat, barley, oats, triticale, and sorghum) with a wide range of chemical and physical characteristics have been collected from germplasm archives, plant breeders, and farmers and selected because of drought, frost damage, or preharvest germination. Approximately 350 grains selected on variation in NIR spectroscopy scans and in vitro (laboratory)

217

fermentation/digestion assays were fed to sheep, cattle, pigs, broilers, and layers, and 40 individual grain samples were offered across all animal types. The grains were dry-rolled for ruminants, hammer-milled and cold-pelleted before feeding to pigs and poultry. The energy from grains made available following digestion was measured in all animal types, and voluntary intake was measured in cattle, pigs, broilers, and layers. A comprehensive chemical and physical analysis was conducted on all grains fed to animals.

Digestible Energy Content The range in digestible energy content (MJ kg 1) of several cereal grain species following digestion by different animal types from the Australian research is shown in Table 1. The range in digestible energy tended to be large (3–4 MJ kg 1) for pigs and poultry offered with wheat, barley, triticale, and oats, but less (1 MJ kg 1) for those offered with sorghum. In contrast, the range in available energy content was lower for ruminants than monogastric animals offered with wheat, barley, and triticale (1 MJ kg 1) because activity of microbes in the rumen reduced the impact of variation in grain morphology. The variation in digestible energy content was high for oats fed to ruminants. The range in energy content for sorghum was closer to monogastric animals for sheep, but not for cattle, where the range was 3 MJ kg 1, with the high value coming from a waxy (low-amylose) sorghum isoline. Commonly, cattle extract only around 60% of the energy from dry-rolled sorghum compared with poultry. The low range in digestible energy content for sorghum found in the Australian research is contrary to other studies where ranges of 2–4 MJ kg 1 have been observed when broiler chickens and pigs were offered with a wider variety of cultivars differing in color, tannin content, and seed size. The effect of animal type on the digestion of energy is illustrated more clearly in Figure 2, where individual grain samples were fed to cattle, pigs, broilers, and layers. Barley tended to have the lowest available energy content for pigs and poultry, whereas sorghum had the highest values. Sorghum had the lowest energy content of all grain species for cattle. For most wheat, barley, and triticale samples, pigs tended to extract more energy from the grains than the other animal species, whereas cattle tended to extract the least. Pigs have the advantage of an effective animal enzyme digestion to Table 1 Range obtained from Australian experiments in the available energy content of cereal grains following digestion by different animal types Digestible energy contenta (MJ kg

1

DMb)

Animal type

Wheat

Barleyc

Oatsc

Triticale

Sorghum

Sheep Cattle Pigs Broilers Layers

12.7–13.7 12.2–13.1 12.4–15.0 12.4–15.6 13.1–17.1

11.5–13.9 12.2–13.2 10.6–14.7 11.2–13.7 11.0–14.8

11.2–15.7 10.8–13.4 – 12.6–14.6 12.7–16.4

12.3–13.4 12.9–13.2 12.3–16.5 11.0–14.6 11.6–14.4

13.6–14.3 10.2–13.2 15.5–16.6 15.2–16.5 15.5–16.3

a

Digestible energy measured as energy disappearance throughout the digestive tract. Dry matter. c Naked grain samples included. b

218


Wheat

18

Barley

Oats

Sorghum Triticale

Digestible energy (MJ kg−1 DM)

17 16 15 Cattle

14

Pigs

13

Layers 12 Broilers 11 10 9 8 0

2

4

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Grain number

Figure 2 Digestible energy content of individual grains offered to four animal types. Grain 28 was a sample of naked oats. Reproduced from Black JL (2008) Premium Grains for Livestock Program: Component 1 – Coordination. Final Report. Grains R&D Corporation, Canberra, Australia http://ses. library.usyd.edu.au/handle/2123/1912.

utilize starch followed by a hind gut fermentation to breakdown fiber. There was considerable variation in the available energy content within grain species for all animal types. The smallest within grain species variation was observed for cattle and the largest for broilers. The most important observation from Figure 2 is that the relative digestible energy content of grains by different animal types was not constant across grain samples. For example, wheat sample one had the lowest available energy content for cattle, the highest for broilers, and a relatively high value for pigs and layers when all wheat samples were compared. In contrast, wheat sample five had intermediate energy content for cattle but was low for pigs, broilers, and layers. Wheat sample six was intermediate for cattle, high for pigs, and low for poultry, whereas sample nine had the highest values for both cattle and pigs and was also reasonably high for poultry. Similar variation between animal types can be seen for individual grains within all grain species examined. Correlations between animal types for the available energy content of grains are shown in Table 2 for wheat, barley, and sorghum. The large number of low and negative correlations confirms the observations made in the preceding text that there are considerable differences between animal types in their capacity to digest individual grain samples, with some being relatively more digestible by ruminants, some by pigs, and others by broilers or layers. These observations suggest that individual grain samples are better suited for digestion by one animal type than another.

Digestible Energy Intake The intake of diets containing 70% grain was measured in cattle, pigs, broilers, and layers for many of the same grains for which available energy content was measured. The correlation coefficients relating diet intake to digestible energy content

Table 2 Correlation coefficients between animal types in the digestible energy contenta (MJ kg 1 DMb) of all grains fed to animalsc

Wheat Layers Pigs Cattle Barley Layers Pigs Cattle Sorghum Layers Pigs Cattle

Broilers

Layers

Pigs

0.551* 0.188NS 0.284NS

– 0.422* 0.001NS

– 0.207NS

0.774** 0.562* 0.092NS

– 0.869** 0.712*

– 0.714*

0.928** 0.55* 0.771*

–

0.285NS 0.810*

– 0.607*

NS

, Not significant *, P < 0.05 **, P < 0.01 a Digestible energy measured as energy disappearance throughout the digestive tract. b Dry matter. c Adapted from Black JL (2008) Premium Grains for Livestock Program: Component 1 – Coordination. Final Report. Grains R&D Corporation, Canberra, Australia. http:// ses.library.usyd.edu.au/handle/2123/1912.

for all grains fed to an animal type were 0.07, 0.34, 0.39, and 0.24 for cattle, pigs, broilers, and layers, respectively. These low and negative correlations suggest that characteristics of grains responsible for determining intake differ from those that determine the extent of digestion. A similar conclusion is reached by results shown in Table 3, where five wheat samples for which digestible energy content had been measured were offered in diets to young pigs. There was a small significant difference in digestible energy content across the grains (0.57 MJ kg 1, 4%) but a large difference in intake (302 g d 1, 44%). The grain

NON-FOOD PRODUCTS FROM GRAINS | Cereal Grains as Animal Feed Table 3 Digestible energy (DE) content of wheat grain cultivars and intake by young pigs of diets containing the same wheat samples Wheat cultivar

DE (MJ kg 1)

Diet intake (g d 1)

Currawong Dollarbird Rosella Thriller Lawson

14.96a1 14.51b 14.49b 14.39b 14.87ab

389a 537b 551b 691c 691c

Letters differing within a column signify significant difference P < 0.05. Reproduced from Cadogan DJ, Choct M, Campbell RG, and Kershaw S (1999) Effect of new seasons’ wheat on the growth performance of young male pigs. In: Cranwell PD (ed.) Manipulating Pig Production VII, p. 40. Werribee: Australasian Pig Science Association. 1

samples from the Currawong and Lawson cultivars had statistically similar digestible energy content but produced the extremes in feed intake. These observations confirm that grains with high available energy content may not necessarily promote high intake of digestible energy or high animal productivity. In the Australian study, intake of digestible energy (MJ d 1) was calculated for each grain and animal type from the respective digestible energy content and grain intake values. These intake values were then converted to a digestible energy intake index. The index was calculated by dividing the digestible energy intake value for each grain sample offered across an animal type by the highest value for that animal type and multiplying by 100. The intake index values therefore potentially ranged from 0 to 100. The index was developed because it provided an indication of the relative total energy availability between grains for each animal type and is more meaningful for comparing between grains than results for intake in MJ d 1, which varies each day as an animal grows or its physiological state changes. The index values are not directly comparable between animal types because they were calculated within an animal type. However, the relativity of within grain values for the different animal types when compared across grains provides evidence that some grains are better at supplying digestible energy (MJ d 1) to one animal type than to others and vice versa. This difference in the suitability of individual grains for specific animal types is further confirmed when the index values are correlated across animal types (Table 4). There were not sufficient grains fed to all animal types to develop a full correlation matrix as shown by the missing values in Table 4. Nevertheless, the large number of low and negative correlations, even between broilers and layers, suggests that the specific grain characteristics that determine intake of available energy differ for each of the animal types examined. Thus, individual grain samples can be chosen to provide greater rates of production for one animal type compared with another.

Reasons for Differences between Grains and Animal Types Extent of Grain Digestion The extent of grain digestion by an animal depends first on whether there are enzymes capable of cleaving the chemical bonds of the specific grain components and the concentration

219

Table 4 Correlations between animal types in the digestible energy intake index (0–100)a for grains fed to animalsb Broilers Wheat Layers Pigs Cattle Barley Layers Pigs Cattle Triticale Layers Pigs Sorghum Layers

Layers

Pigs

0.270NS 0.148NS 0.033NS

–

0.076NS 0.466* 0.706*

–

0.018NS IDc

– 0.302NS

0.332NS 0.832*

– 0.290NS

–

0.747**

–

0.035NS IDc

– 0.116NS

NS

, Not significant *, P < 0.05 **, P < 0.01 a See text for definition of digestible energy intake index. b Adapted from Black JL (2008) Premium Grains for Livestock Program: Component 1 – Coordination. Final Report. Grains R&D Corporation, Canberra, Australia. http://ses. library.usyd.edu.au/handle/2123/1912. c Insufficient data.

of these enzymes. As outlined earlier, intestinal microbes alone provide enzymes for degrading fibrous and cell wall components of grains, whereas starch can be digested by enzymes of animal and microbial origins. Accessibility of enzymes to specific grain components is the second important determinant of the extent of starch digestion. There is strong evidence supporting the concept that the predominant factor influencing starch digestion is the diffusion rate of amylase into the grain. Similarly, the rate of grain protein digestion is determined by the diffusion rate of proteases. Enzyme diffusion rate is influenced by the chemical composition and morphology of a grain. It appears to be faster in open-structured grains than in tightly packed grains. For example, the diffusion rate of amylase is approximately twice as fast in barley than it is in sorghum or four and nine times slower than the rate of diffusion of water through these grains, respectively. Similarly, amylase diffusion rate is faster in soft wheat samples than in hard wheat samples. Many grain processing procedures alter the diffusion rate of enzymes and rate of digestion. Doubling grain particle size has been shown to decrease amylase diffusion rate and rate of starch digestion fourfold in both barley and sorghum samples. Gelatinization of starch and germination of grains increase enzyme diffusion rates, whereas starch retrogradation and surface hardening of manufactured feed pellets decrease enzyme diffusion rates and rate of starch digestion. The amount of energy released during digestion of grains is influenced by the relative proportions of major chemical constituents because of differences in the extent of digestion or the energy density of the constituent. Lipids have a higher energy density than carbohydrates or proteins but are generally at relatively low concentrations in cereal grains. The aggregation of results from the Australian studies shows digestible energy content of grains for all animal types to be positively correlated with starch content and negatively correlated with fiber content (Table 5).

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Table 5 Correlations between the starch or neutral detergent fiber content of cereal grains and digestible energy content or digestible energy intake for broilers, pigs, and cattlea Chemical component

Broilers

Pigs

Cattle 1

Starch NDFb Starch NDFb

Available energy content (MJ kg ) 0.77 0.65 0.42 0.59 0.62 0.47 Available energy intake (MJ d 1) NSc NSc 0.77 0.68 0.49 0.58

a

J. L. Black unpublished. Neutral detergent fiber. c Not significant (P > 0.05). b

The composition, thickness, and integrity of cell walls within the endosperm of grains have a major impact on the digestible energy content of grains for the different livestock types. The cell walls, composed of a cellulose skeleton impregnated with soluble and insoluble arabinoxylans and b-glucans, must be disrupted by processing, mastication, or microbial fermentation to expose the starch granules to digestive enzymes. Endosperm cell walls are particularly thick in barley and thin in sorghum, rice, and oats, with wheat and triticale having intermediate thickness. Cell wall characteristics vary widely between cultivars and with plant growing conditions. Endosperm cell walls have only a minor effect on the overall accessibility of starch from cereal grains fed to ruminants because they are degraded readily by rumen microorganisms. Thick cell walls take longer to break down than thin walls and slow the rate of starch digestion within the rumen, alter the rate of acid production, may reduce the susceptibility of animals to acidosis, and increase starch digestion in the small intestines. Cereal grains with thick cell walls are therefore beneficial to ruminants because they reduce the chances of developing lactic acidosis and allow more starch to be digested by animal enzymes. Endosperm cell walls can have a marked effect on the energy value of cereal grains for monogastric animals by reducing amylase diffusion rates and contact with starch granules either by acting as a physical barrier or by increasing the viscosity of the digesta. Endosperm cell walls act more as a physical barrier to the digestion of starch for pigs than for poultry. Grains eaten by birds are subjected to intense grinding in the gizzard, and most endosperm cell walls are ruptured. However, pigs appear to rupture few cells during mastication, and the availability of energy from cereal grains is increased substantially by fine grinding. Cell walls influence starch digestion in poultry through the soluble arabinoxylans and glucans. These compounds increase the viscosity of digesta, reduce the diffusion of digestive enzymes through the digesta, and reduce the rate of substrate digestion. Chain length of these soluble nonstarch polysaccharide polymers appears to be more important for reducing the digestible energy content of wheat for broilers than is the total content of soluble nonstarch polysaccharides because of the greater increase in digesta viscosity, which reduces the digestion of starch, amino acids, and fatty acids. Enzymes that cleave soluble nonstarch polysaccharide compounds are now regularly added to diets for poultry to

reduce the viscosity of digesta and increase the access of enzymes to dietary substrates within the small intestine. The protein matrix in which starch granules in the endosperm of cereal grains are inserted to varying degrees can also influence enzyme diffusion rates and starch digestion. In some grains like sorghum, the protein matrix and embedded protein bodies in the corneous endosperm can form a contiguous layer encapsulating each starch granule. Proteins surrounding the starch granules must be degraded or disrupted to expose the starch to amylases. The protein matrix surrounding the starch granules in sorghum grain contains a high concentration of a, b- and g-kafirins. These proteins contain increasing amounts of cysteine as they progress from the a- to g-types and are rich in disulfide bonds that are resistant to cleavage by some enzymes. There is strong evidence that the low availability of energy from sorghum grain for cattle is due to the inaccessibility of amylolytic enzymes to the starch granules encapsulated by the protein matrix. Waxy sorghum grains appear to have less protein matrix with a lower proportion of g-kafirins than normal cultivars. The marked difference in digestion of sorghum starch by cattle compared with sheep and pigs is possibly due to differences in the concentrations and capacity of proteases from the different animal species to degrade the high-disulfide bond proteins in the matrix surrounding the starch granules. The grinding action of the gizzard in poultry physically disrupts the protein capsule and releases the starch for digestion, which would explain the high digestion of energy observed at the end of the small intestine in poultry. The composition of cereal starch can also affect rate of digestion. Cereal starch is composed primarily of amylose and amylopectin. The tight helical structure of the long chains of glucose in the amylose molecule makes it less accessible to amylases than amylopectin with its branched a-(1–6) linkages. The a-(1–6) glucose branches provide a more open structure to the starch molecule, which increases the accessibility to amylolytic enzymes.

Grain Intake Physical and chemical characteristics of a diet can have a major impact on feed intake of animals. Feed intake is stimulated as the rate of passage of digesta, particularly through the stomach and small intestine increases. Physical characteristics of the diet that cause mild distension stimulate the rate of stomach emptying and propagative peristaltic contractions in the gastrointestinal tract and increase feed intake. However, excessive distension inhibits these responses, slows rate of passage, and induces satiety in all animal types, but particularly in ruminants. Table 5 illustrates the relative impact of increasing starch and fiber content of grain-based diets on energy intake by poultry, pigs, and cattle. Energy intake for broiler chickens and pigs was not significantly correlated with starch content, but was positively correlated with fiber content. On the contrary, energy intake by cattle was positively correlated with starch content and negatively correlated with fiber content. Rumen capacity is known to be a major determinant of intake by sheep and cattle, and increase in indigestible fiber is a potent limiter to intake. Increasing the amount of indigestible fiber or large grain particles in a diet for pigs or poultry initially

NON-FOOD PRODUCTS FROM GRAINS | Cereal Grains as Animal Feed increases feed intake but then decreases intake as gut distension continues. Excessive distension of the gastrointestinal tract in these animals can also be caused by highly viscous diets containing soluble, nonstarch polysaccharides and other highly viscous compounds. Feed intake is also controlled in pigs, to some extent in poultry, but not in ruminants by the so-called ileal brake. The presence in the distal ileum and colon of partially digested dietary compounds and products of microbial fermentation stimulates the release of several hormone peptides from the gut and pancreas that slow the rate of passage of digesta and reduce feed intake. These peptides, particularly PYY (peptide tyrosine tyrosine) and GLP-1 (glucagon-like peptide-1), slow the rate of digesta passage by reducing the number and strength of peristaltic contractions in the stomach and intestines and also through direct action on the satiety center of the brain. Only partially digested nutrients stimulate the ileal brake, with the effect of the slowed rate of passage increasing the time substrates that are in contact with enzymes and obtaining more energy from the food. Thus, in pigs and poultry, increasing the amount of indigestible fiber in a grain can tend to increase intake by stimulating the rate of passage, but when starch is not completely digested in the proximal small intestine, an increased flow of partially digested material to the distal ileum will stimulate the ileal brake and tend to reduce intake. Thus, there can be a strong interaction between the effects of indigestible fiber tending to increase intake and reduced grain digestion in the small intestine tending to reduce intake.


Estimating the Energy Value of Cereal Grains for Animals

•

Traditionally, the energy value of cereal grains for animals has been estimated from test weight (kg Hl 1) and/or the percent of grains passing through a set sieve screen size. Results from the Australian studies, where the actual digestible energy content and digestible energy intake have been measured on many grains, show poor relationships between the measured digestible energy values and physical properties of the grains. Although there is an overall positive relationship between measured energy values and test weight, the relationships are influenced greatly by low-test weight, high-fiber, lowstarch-containing grain samples. For grains with higher test weights, there is no relationship between test weight and the measured energy values for any animal type. These traditional approaches do not provide an accurate assessment of the true energy value of individual grains because the internal morphology of the grain has a larger impact on the value to animals than its packing weight in a set volume. Results from the Australian research have now been used to develop NIR calibrations for estimating the digestible energy content of cereal grains for pigs, broiler chickens, sheep, and cattle and a digestible energy intake index for pigs and broilers. NIR calibrations have also been developed for an acidosis index, which predicts the relative probability of a grain causing lactic acidosis in cattle. These calibrations have reasonable accuracy and robustness and are commercially available.

•

• • • • • • • •

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Why are cereal gains fed to livestock? What is needed to fully describe the energy value of a cereal grain for livestock? What is the impact of microbial fermentation on the energy released from grain digestion and why is microbial fermentation important to an animal? Why are individual grain samples best suited to one animal type or another? What are the main reasons why grains vary in digestible energy content for animals? What are the main reasons why grains vary in digestible energy intake by different animal types? How suitable are physical measures of grains such as test weight for assessing the energy value of cereal grains for animals? What is a suitable replacement for physical tests to obtain more accurate assessments of the energy value of grains for individual livestock types?


• •

How might information in this article lead to new selection criteria for breeding cereal grains? Will there be separate criteria for specific animal types? What new grain processing techniques may increase the energy value of cereal grains for ruminants, pigs, and poultry? What is the best way to make new NIR calibrations predicting the energy value of cereal grain for each animal type available to the cereal growers, livestock producers, and stock feed manufacturers? Can the information and NIR calibrations be used to develop more scientific methods for trading cereal grains for livestock?

Acknowledgments The author acknowledges the contribution made by the research within the Premium Grains for Livestock Program (funded in part by the Australian Grains Research and Development Corporation, Meat and Livestock Australia, Australian Pork Limited, Australian Egg Corporation Limited, and the Rural Industries Research and Development Corporation’s Chicken Meat and Ridley Agribusiness) and the Pork CRC Limited, Australia. Much of the research reported was conducted by the collaborating scientists within these programs, and their work is gratefully acknowledged.

See also: Non-food Products from Grains: Pet Foods; The Basics: Grain: Morphology of Internal Structure; The Grain Chain: The Route from Genes to Grain-Based Products; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

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Further Reading Al-Rabadi GJ, Gilbert RG, and Gidley MJ (2009) Effect of particle size on kinetics of starch digestion in milled barley and sorghum grains by porcine alpha–amylase. Journal of Cereal Science 50: 198–204. Bedford MR and Schulze H (1998) Exogenous enzymes for pigs and poultry. Nutrition Research Reviews 11: 91–114. Black JL (2004) Feed grain. In: Wrigley C, Walker C, and Corke H (eds.) Encyclopedia of Grain Science 1: pp. 11–20. Oxford, UK: Elsevier. Black JL (2008) Premium Grains for Livestock Program: Component 1 – Coordination. Final Report. Grains R&D Corporation, Canberra, Australia. http://ses.library.usyd. edu.au/handle/2123/1912. Black JL, Williams BA, and Gidley MJ (2009) Metabolic regulation of feed intake in monogastric animals. In: Torrallardona D and Roura E (eds.) Voluntary Feed Intake in Pigs, pp. 189–213. The Netherlands: Wageningen Academic Press. Black JL, Hughes RJ, Diffey S, et al. (2014) Rapid assessment of feed ingredient quality. In: Proceedings of the Australian Poultry Science Symposium 25: 23–30. Cadogan DJ, Choct M, Campbell RG, and Kershaw S (1999) Effect of new seasons’ wheat on the growth performance of young male pigs. In: Cranwell PD (ed.) Manipulating Pig Production VII, p. 40. Werribee: Australasian Pig Science Association.

Choct M and Annison G (1992) Anti-nutritive activity of wheat pentosans in broiler chickens: Roles of viscosity and gut microflora. British Poultry Science 33: 821–834. Duke GE (1994) Anatomy and physiology of the digestive system in fowl. In: Proceedings of the 21st Annual Carolina Poultry Nutrition Conference. 7–8 December 1994, Charlotte, NC, pp. 46–51. Gidley MJ, Flanagan B, Sharpe K, and Sopade PA (2011) Starch digestion in monogastrics: Mechanisms and opportunities. In: Cronje´ P (ed.) Recent Advances in Animal Nutrition – Australia. Armidale, Australia: University of New England. McDonald P, Edwards RA, and Greenhalgh JFD (1988) Animal Nutrition, 4th edn. Essex, UK: Longman Scientific Technical. Roche JR, Blanche D, Kay JK, Miller DR, Sheahan AJ, and Miller DW (2008) Neuroendocrine and physiological regulation of intake with particular reference to domesticated ruminant animals. Nutrition Research Reviews 21: 207–234. Sullins RD and Rooney LW (1975) Light and scanning electron microscope studies of waxy and nonwaxy endosperm sorghum varieties. Cereal Chemistry 56: 361–366. Tinus T, Damour M, Van Riel V, and Sopade P (2012) Particle size-starch-protein digestibility relationships in cowpea (Vigna unguiculata). Journal of Food Engineering 113: 254–264.

Pet Foods RCE Guy, Campden and Chorleywood Food Research Association, Chipping Campden, UK ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 445–450, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • •

•

The range of animals included as ‘pets’ for these food types. Dry pet foods have offered the advantages of being lighter in weight for the pet-owner to carry home. Traditional biscuit-making technology and extrusion cooking have facilitated the production of dry pet foods. The recipes have been largely cereal-based with small additions of meat, fat, and bone meal. Extrusion-produced pet foods are often enriched with proteins from meat meals, soy meal and flour. Wet pet foods (often canned) consist of meaty chunks surrounded by a meaty gravy or jelly, but the chunks may alternatively be made of reformed meat meals or vegetable proteins. A pet-food product can be made to be storable at room temperature for several months, with a water activity reduced to <0.7, a low pH of 4–5 and pasteurization.

Learning Objectives

•

Achieve an understanding of the ways in which production and retail methods have contributed to the growth of the pet food market, largely drawing upon grains as raw materials.

Introduction What Are Pet Foods? Pet foods have been manufactured since the 1940s in the USA and Europe, and today there are manufacturing plants in most developed countries. They originated from nutrition-based animal feedstuffs that were manufactured for livestock. The close relationship between pets and owners led to the development of certain sensory requirements to attract the consumer. The products were made with more attractive shapes and colors to satisfy the owners and with special flavorings to ensure that the animals were happy. However, the core products are nutritionally well balanced to give a complete diet for an animal so that they can live a healthy life if fed only on the pet food. There are also some special products known as ‘treats’ that may be more highly flavored, or have a special chewy texture. These products are aimed at providing an enjoyable experience for the animal and its owner, and are not necessarily so well balanced nutritionally. There are many types of pets in the modern world, but cats and dogs dominate all the production in the pet food market by a large margin with sales of over five billion pounds worldwide. The next levels of pet foods are for fish, small mammals such as rabbits, guinea pigs, and ferrets, birds, and then the


products begin to merge with animal feeds for farm animals and reptiles. In this article only the products made for cats and dogs are described in detail, and some of the products made for fish and small mammals are briefly mentioned.

Types of Foods The manufacture of pet has taken two main forms in the past century; these may be described as wet and dry types. Using the mature UK market as an example, the proportions of each type of product sold in 2001 are shown in Table 1. Wet pet foods were developed originally as canned products that had moisture contents of 65–70% w/w, similar to cooked meat and gravy, or raw meat. They could be used straight from the tin and were easily digested by the animals. In the retail market, cans were sold mainly in 400 and 800 g sizes. These were satisfactory for cats and small dogs, but were a little small for large dogs. The packs of cans became very heavy and new forms were developed, such as the intermediate-moisture products with much less water (20–30% compared with 65–70% w/w for cans) that could be sold in large plastic tubes. The food could be easily sliced from the roll to provide the meals. However, they were not very successful and it was the dry products, with moisture content of about 10% that were preferred as the main alternative to canned pet foods. More recently, laminated plastic and foil pouches have been introduced with individual meals that are lighter than cans but offer the same types of wet pet foods. In the market for cats they have captured 20% of the wet sales. Initially dry products were developed as biscuits that could be added to supplement meals prepared at home. These might have been made up of meat and bones from the butcher, or the scraps from a family meal. However, with the advent of the new technology of extrusion cooking, it became possible to prepare a dry food from a well-balanced range of ingredients and was a complete meal. This new type of dry food had considerable advantages in weight for the shopper, removing 60% of the water in canned products plus the tin. The remaining dry solids, which were sold in paper or laminated plastic sacks had a long shelf life and were liked by the pets. Therefore, they began to replace the wet foods in several markets. However, the wet foods were still preferred by many customers for other reasons that the successful introduction of the small individual meal pouches of wet foods has helped to maintain market share for this form of pet food. For other animals such as fish and small mammals, most foods are sold as dry foods, except for some intermediate moisture products for fish. The dry products may be in the form of flakes, extruded rods or pellets, and simple mixtures of different forms of grains, pellets, and flakes.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00140-6

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NON-FOOD PRODUCTS FROM GRAINS | Pet Foods

Table 1

Table 2

UK market for different types of pet foods

Recipes for dog biscuits

Type of pet food

Cat market (%)

Dog market (%)

Ingredients

%

%

%

Wet Dry Semi-moist Treats Mixers

76 21 1.5 1.5 0

39 40 1 14 6

Wheat flour Wheat meal Crumb Bone meal Meat solids Salt Malt Fat Soda Corn meal Yeast

50.7 0 30.8 9.1 5.4 0.7 0 2.5 0 0 0.7

31.3 31.3 0 3.1 1.9 0.6 0 0 0.6 31.3 0

71.5 0 20.0 0.0 5.7 0.6 1.7 0.0 0.3 0.0 0.1

Dry Pet Foods Biscuit Technology Two manufacturing processes are used for dry pet foods, traditional biscuit-making technology or extrusion cooking. Originally, biscuit making was developed by transferring knowledge from the bakery industry. Basic equipment was available to mix, sheet and cut out the shapes, and bake dough into a dry biscuit texture. In some cases, the dough was sheeted by forming extrusions with wide fan-shaped slit dies to produce a sheet, rather than rollers. In most processes the waste dough and biscuit material was added back into the mixer to form the new dough. The recipes for the biscuits were largely cereal-based products (Table 2) with a small addition of meat, fat, and bone meal to provide flavor rather than nutrition. Some of the doughs were also allowed to ferment overnight (e.g., cracker doughs) to develop flavor, but generally they were mixed and allowed to stand for a few hours. The dough produced by mixing the above recipes with water at a low level of 20–30% w/w was often stiff and crumbly, which could be sheeted out by extrusion and cut to form the biscuit shapes. These were usually simple geometric forms such as ovals and squares, but could also be formed into the well-known bone shape. After the pieces were shaped, the baking process was set up to give some aeration to the dough structure by rapid vapor creation, and then to dry out the biscuit to create their hard texture and color. This was not easy to achieve for dog biscuits, because of their size and the time available in the oven. Generally, biscuits were baked with a dry outer region and a moister center that would equilibrate with dry regions over several days, to give an average moisture <10% w/w (Figure 1). At this moisture level, the starchy structure would have a crunchy texture and good shelf life in the packs. Occasionally, this baking method caused problems because of the stresses created in the biscuits. The products could crack along lines of weakness and the biscuits could break into two or more pieces. The traditional dog biscuit had a limited scope for development because of the long baking process. It also had other shortcomings, in that it had a fairly slow production rate and occupied a large factory area. Therefore, the development of extrusion cooking as an alternative method for dry pet-food production seized the imagination of manufacturers worldwide.

Extrusion Cooking Technology Extrusion cookers were invented in the 1940s to manufacture snacks from maize grits, but by the 1950s they were being

Figure 1 Baked biscuits.

adapted for the production of pet foods. At first the machinery was fairly crude and not well understood, and had a relatively small throughput of a few 100 kg h 1. The recipes were still based on a high level of cereals, such as wheat and maize. Later, they were enriched with proteins from meat meals and soy meal and flour (Figure 2 and Table 3). The potential that could be envisaged for extrusion cooking provided the driving force for its development, and the equipment manufacturers strove to meet the needs of the pet food industry. Extrusion cookers are continuous processing units that transform a dry mix feedstock into a plastic fluid with the addition of 10–20% w/w of water, within their barrels. This fluid can be shaped and expanded from the dies at the end of the machine and cut into pieces with a rotating knife. The benefits of using extruders, compared with biscuit technologies, were as follows:

• • • • • • •

continuous processing with low manpower requirements; small factory space; range of shapes and sizes created with different dies; low moisture process to reduce energy in drying (baking); sterile products; short residence time for control of thermal history of materials; and efficient processing.


225

Table 4 Guy’s classification system for ingredients by their functional effects in extrusion cooking Number

Functional group

Typical examples

1 2

Starch, soy, and gluten Soy, bran, and uncooked starch

4 5

Structure forming Dispersed phase fillers Plasticizer/ lubricants Soluble solids Nucleants

6 7

Coloring materials Flavoring materials

3

Figure 2 Extruded dry dog food.

Table 3

Recipe for extruded dog food

Corn for maize Soybean meal Wheat flour Bone and Meat meal Premixes Fats

44% 17% 16% 17% 1% 5%

The improvements in manufacturing units and understanding of the process by operators have both been enormous since the 1960s with production rates doubling every 10 years or so, to reach an amazing 5–10 tonnes per hour (t h 1) on the best modern plant.

Water and oils Sugars, dextrins, salt Calcium phosphates and carbonates, fibers Added and Maillard reactants Added and Maillard reactants

and the extrusion and expansion phenomena at the die has led a diverse range of products and greater control of their quality. There is one problem with dry extruded pet foods because of the starch content. Cats in particular are not suited to a starch-rich diet and they have problems with the digestion of starch. Generally, the pet foods are made in dense form with a low degree of cooking, or dispersion of granular starch.

Extrusion machinery – preconditioning The powder mix for the extrusion cooking process can be metered directly into the extruder barrel and processed without difficulty. However, the extruder manufacturers have developed a secondary unit to warm the powders and to add water and fats prior to processing in the main barrel. This additional treatment has been shown to increase processing rates and reduce energy and wear costs. Little or no gelatinization of the starch occurs in these units because they operate at <100 C and the moisture being usually <30% w/w is too low to reach the melting temperature, Tm, for starch.

Extrusion machinery – extrusion cookers Extrusion cooking – raw materials The basic process starts with the recipe and its components. These are selected for the qualities of flavor and nutrition, their interaction in the process, and their price. In all extrusion cooking processes, the raw materials interact with the processing variables of screw design, rotational speed, barrel temperature, die dimensions, and feed inputs to create the system variables within the machines and eventually the product characteristics of the extrudate. This complex multivariate process was difficult to study in the early machines because they were sealed systems. It was only in the 1980s that CCFRA with its split barrel APV MPF 50 twin screw machine was able to provide good information on the processing of cereals. Most dry pet foods are based on the transformation of starch by a combination of high temperature and powerful shearing forces into a dispersed polymer fluid. Therefore, the starch content of a recipe is very important in determining the physical characteristics of the extruded products. All raw materials have some effect in the process and they may be viewed in terms of their potential in an extrusion process using Guy’s classification system (Table 4). The development of the current understanding of the role of raw material components on the transformation of starch

The heart of the process is an extrusion cooker where the recipe is transformed and prepared for forming into products as it is extruded. M. Riaz describes the various types of extruders, including single and twin screw designs that are available in the market and explains the differences between various types. There have been at least 30 companies selling machines in the market worldwide, but today one or two large single screw machines and three large twin screw machines dominate the world markets. In all these extruders the moist mix of powder and water is compressed and sheared so that it becomes hot enough (120–160 C) to melt the crystalline structures within native starch granules. Once softened, the starch granules are partly dispersed by the shearing action of the screws or paddle elements in the machine, to give an expandable cell-wall material for gas bubble expansion at the die exit. The differences in commercial machines depend on their production capacity and their ability to control the process in terms of the temperature and the degree of starch dispersion. In pet foods, the starch dispersion is relatively low after the melting of starch has been achieved. This gives a fairly dense extrudate with an expansion of 1.5–2 ml g 1 specific volume for the extrudate. The ideal extruder is one with a short

226


residence time in the hot shearing zone and a variable speed screw, which operates independently of the throughput rate at the lowest possible moisture. This type of extruder can be set to disperse starch to the required level at the lowest temperature and fastest throughput. Most extruders offer a compromise between these ideals and running costs, but the latest machines appear to offer more benefits and efficiency than the older models.

Extrusion machinery – coating and drying Once cut, the extrudate can be coated by spraying with a gravy and then dried in a moving or fluidized bed to its final moisture content of <10% w/w. The size of the dryer is dependent on the throughput and the moisture level, which may vary from 18% to 30% at the die exit, according to the process and the extruder.

Wet Pet Foods The basic concept for wet pet food is a plate of meaty chunks surrounded by a meaty gravy or jelly. In practice, the meaty chunks may be made from reformed meat meals or vegetable proteins, such as soy or wheat gluten, or mixtures of both. The gravy is carefully thickened with gums and starches to control its physical character, both when hot and cold. Methods for forming the chunks have changed during the 1990s and now include the use of extrusion cooking to texturize proteins, and simpler thermal methods to gelatinization of starch within meat slurry.

Formation of Meat Chunks – Extrusion Cooking The earliest method for the economic production of meat chunks was the texturization of soy flour by extrusion cooking. In this process the protein is hydrated to 35–40% moisture w/ w and heated to 160 C in a high shear field to produce a fluid melt, similar to the polymer melt of starch developed in dry extrusion cooking. Soy proteins have a tendency to aggregate when denatured and disrupted by heating above their denaturation points of 75–100 C. The use of high shear fields in the extruder prevents this from occurring until they are pumped into the die channels. In long die channels, laminar flow can occur at the normal flow rates with only small shearing forces. This allows the protein molecules to align and form hydrogen and hydrophobic bonds to create layers of fibrous material not unlike meat fibers. The extrusion through the die channels is usually at 120–140 C, and at the exit some water vapor evaporates from the matrix to open up the texture and leave an alveolar structure in the chunks that are cut at the die. Texturized vegetable protein (TVP) can be made with a minimum of 45% soy protein, but becomes stronger and tougher with increasing protein levels up to 90%. The material made from flours or concentrates is satisfactory for pet foods and can carry other materials within its continuous phase. Generally, some starch is used to form a dispersed phase within the smooth continuum of the protein. Other proteins and meals can also be added to enrich the chunks that too will be dispersed in the main soy protein phase.

If the secondary protein becomes dominant in the recipe, it may replace the soy as the continuum. Thus, when wheat gluten is used at 40–50% of a mixture, it may become the continuous phase. This protein has been used extensively in chunks for cat food because cats prefer it to soy products. In the development of texturized proteins, a new type of process has been developed by Clextral of Firminy in France. This process is based on the use of higher moisture (60–80%) in the melt and a long cool die in which the proteins are allowed more time to form their fibrous structure without evaporation of water vapor to disrupt them.

Formation of Meat Chunks – Thermal Gelling of Starch In this process, wheat flours or other cereal flours are mixed into meat slurry to form a paste. The wheat proteins hydrate to provide sufficient viscosity to help keep the solids in suspension until the paste is heated to gelatinize the starch granule of the flour. At this point the slurry becomes a solid gel whose strength increases on cooling and can be cut into small slices or chunks as required. This simple process may be carried out with special equipment to make it more efficient. In a continuous process the slurry is pumped through a forming tube, which is heated to warm the slurry and eventually gel the starch before it is extruded and cut. This type of product and the texturized protein chunk must be stable in a canning process where the chunk is heated in gravy to 110–120 C for a period of 15–20 min. It was shown by that soy proteins must have a well-texturized protein structure to survive. In starch systems the presence of retrograded starch and some cross-linking may help the granules to retain the structure of the chunks.

Intermediate Moisture Products The final type of wet cat and dog food was developed as a longlife product that could be stored at ambient temperatures and packed in light plastic bags or sleeves. Normally, a wet product will decay and be spoiled by microbiological growth once it has been removed from its can or pouch. However, if the water activity is reduced to <0.7 with a low pH of 4–5 and the product is pasteurized, it will remain in good condition for several months. It can be sold in plastic packs in normal retail outlets at ambient temperatures, alongside the dry and canned pet-food products (Table 5).

Treats and Other Foods This section covers a set of products generally called ‘treats’ and some other dry foods. Treats may be made in many forms but are usually dry products that for dogs can be carried by the owner and dispensed to the animals during their walk. The products may take the form of chewy leathery items, or individual biscuits can be made into bone shapes or produced by co-extrusion as mini-beefsteaks or ‘marrow’ filled bones. The extrusion cooking units are very well suited to producing interesting shapes and being able to use special recipes to manufacture tasty products. For cats the treats are given in the house or

NON-FOOD PRODUCTS FROM GRAINS | Pet Foods Table 5

•

Intermediate moisture products

Ingredients

%

Poultry meal Maize Maize gluten Soybean meal Corn syrup/beet fiber Beet fiber Potassium sorbate Propylene glycol Phosphoric acid Vitamin/mineral mix Fats

32.0 17.8 10.0 8.0 12.0 4.0 0.2 8.0 2.0 3.0 3.0

garden. Again, one relies on special shapes and colors to please the owners, and on strong flavors and crunchy textures to satisfy the pet. For the other pets that are kept in the home, the foods are not so well defined and are made as animal feedstuffs, with less thought about shape and color and more on nutrition and wholesome character. Some foods may be shaped into pellets by a forming extruder or pelleting press and some may be flaked as grain by flaking rolls or shaped as wet flour slurry on a roller dryer. The last mentioned method is used for the thin flakes fed to pet fish. To summarize, it can be seen that the pet-food industry is dynamic and full of invention to increase efficiency and improve its products. The market has grown at a fast rate since the 1990s and there appears to an overall increase in the pet population with a slight movement toward cats instead of dogs.


•

• • •

What are the relative advantages of the various approaches to the manufacture of pet foods, including canned wet foods, biscuit foods, extruded foods and moderatemoisture preparations? What are the functions of the various ingredients in extruded pet foods? How do differences between the species of pets affect the required formulations? Describe the various approaches to formulating ‘meat chunks’ for pet foods.


•

What lessons might be learned from research with pet foods in order to improve foods for humans?

• •

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What human-food packaging corresponds to the intermediate-moisture products for pets? Study the ingredient lists (if provided) for a range of pet foods. What are the most common grain species used? Investigate the manufacturing processes for texturized vegetable protein (TVP). How are these products well suited for pet foods, and also for the human diet?

See also: Food Grains and the Consumer: Fortification of GrainBased Foods; Labelling of Grain-Based Foods; Non-food Products from Grains: Cereal Grains as Animal Feed; Processing of Grains: Extrusion Technologies; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; WheatBased Foods: Cereals: Overview of Uses: Accent on Wheat Grain; The Basics: The Grain Crops: An Overview.

Further Reading Frazier PJ, Crawshaw A, Stirrup JE, Daniels NWR, and Eggitt PWR (1980) Factors affecting texture formation during extrusion cooking. Proceedings of 2nd International Congress on Engineering and Food. London: Applied Science Publishers. Guy RCE (1986) Extrusion cooking versus conventional baking. In: Blanshard JMV, Frazier PJ, and Galliard T (eds.) Chemistry and Physics of Baking, pp. 227–235. London: The Royal Chemical Society. Guy RCE (2001) Extrusion Cooking: Technologies and Applications. Cambridge: Woodhead Publishing. Guy RCE (2001) Raw materials for extrusion cooking. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 5–27. Cambridge: Woodhead Publishing. Guy RCE (2001) Understanding extrusion. Food Engineering and Ingredients 26: 29–31. Guy RCE and Horne AW (1987) Extrusion cooking and coextrusion of cereals. In: Blanshard JMV and Mitchell JR (eds.) Food Structure – Its Creation and Evaluation, pp. 331–350. London: Butterworths. Riaz MN (2001) Selecting the right extruder. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 29–49. Cambridge: Woodhead Publishing. Rokey GJ (1994) Pet food and fish food extrusion. In: Frame ND (ed.) The Technology of Extrusion Cooking, pp. 144–189. Glasgow: Blackie Academic and Professional. Smith WH (1972) Biscuits, Crackers and Cookies. London: Applied Science Publishers.

Relevant Websites http://www.aaccnet.org – American Association of Cereal Chemists. http://www.webofscience.com– Web of Science. http://www.campden.co.uk– Campden & Chorleywood Food research Association. http://www.waltham.com– Waltham Nutrional Foundation. http://www.hillspet.com– Hills Petfoods and Nutrion.

Utilization of the Whole Cereal Plant to Maximize its Value L Munck, University of Copenhagen, Frederiksberg C, Denmark ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • •

Whole crop harvesting, drying, and fractionation. Agricultural biorefinery. Connection between agriculture and industry. Value-added sorting. Energy self-sufficiency. From monoculture to utilization of a range of crops. Extended plant growth period and machine utilization. Integrated food, feed, and nonfood production. Increased biodiversity and soil sustainability. Local employment.

Learning Objectives

•

The whole plant utilization concept implies a break in present thinking within agriculture and industry where economic reductionism has divided the market into separate sectors one for each commodity instead of promoting an economy in the integrated production. This has triggered the present crises with regard to environment, energy resources, and sustainability. The introduction of the agricultural biorefinery implies introduction of new technology that could take care of a diversified plant production and utilization as a whole and extend the total plant growth period and yield. Value-added fractionation of seeds and straw could increase economy. Now, the criterion is not the economy of the individual crops added together but that of the integrated production system as a whole. This includes the benefits of a sustainable environment reducing pests, sprays, and synthetic fertilizers that is decreasing the biological diversity and increasing production vulnerability. What was earlier considered as agricultural and human organic waste is now brought to the fields as plant fertilizers and as a biogas fuel for energy. Such investments in an improved infrastructural network would imply a new way of economic thinking linking local agriculture with the central urban industrial concept in a sustainable way producing an increase in living standard and local employment.

Introduction In subsistence plant husbandry, all overground parts of the grain crops were needed for survival, and, therefore, the whole plant was carefully utilized for food, feed, and nonfood purposes. Introduction of the monetary economy ended the isolation of the agricultural village. It was integrated into a national and later an international economy, leading to increased competition and specialization. The dramatic change from a local to a more global economy increased production and created competition for each individual class of products. It brought about a specialization,

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economically favoring farmers who had a local production advantage for a given specific product without caring of negative effects on biological diversity and environment. Specific monocultures were, thus, regionally favored. At the same time, a range of traditional, agricultural nonfood products were phased out by substitutes produced and supported by gas, oil, and coal. There has from the 1970s been an increased awareness of the importance of system research and sustainability. Research programs were introduced by governments, universities, industry, and international organizations to study renewable production systems that take care of the whole plant in a balanced utilization for food, feed, and nonfood purposes. One asked how would it be possible to close the open production chains to reduce waste and overconsumption of fossil fuels. It would imply a recycling effort based on capturing solar energy in plants and plant products instead of burning the now expensive fossil energy, avoiding an increase of carbon dioxide in the atmosphere, that may contribute to a climatic change. Today, the result is an overwhelming number of positive local, focused potential technological solutions; most of them, however, remain to be implemented. The problem of realizing the new technological options together in the production–consumption network driven by photosynthesis that would improve sustainability is discussed in the article 00204.

Value-Added Fractionation of Whole Plant Crops The coarse botanical components of the cereal plant can be divided into the internode (stem or stalk), nodes (divisions between internodes at the insert position of leaves), leaves, husks (or cobs from maize), and seeds. Straw is defined as the remains (leaves, internodes, and nodes) that are left in the field after combining. Internodes may contain marrow, which is especially well developed in maize and sorghum. Internodes, nodes, leaves, husks, and cobs are lignocellulose products. These contain large amounts of cellulose and hemicellulose bound to lignin with protein as a minor component. Each overground grain crop is, in essence, botanically and chemically inhomogeneous and may be fractionated into a range of different components. Thus, straw can be coarsely milled in a simple disk mill to produce flour from leaves, marrow, and chips from internodes and nodes, which are separated by a sifting machine yielding fractions with entirely different chemical and physical properties (see Figure 1). Unfractionated straw has a mediocre value for feed as well as for paper. However, the leaf fraction has improved protein and energy value for feed, and the internode part has as high a content of a-cellulose as wood used for paper. There should, therefore, be an economic incentive for a value-added fractionation of straw, tailored to different uses. The total amount of


http://dx.doi.org/10.1016/B978-0-12-394437-5.00141-8

NON-FOOD PRODUCTS FROM GRAINS | Utilization of the Whole Cereal Plant to Maximize its Value the world production of cereal grains amounts to about 2.2 billion tonnes (Gt) of grains (2012) and at least a similar tonnage of straw, which implies about 1.1 Gt of internode chips and 0.9 Gt of leaf and marrow meal. There is thus a great future for expanding the industrial utilization of agricultural lignocelluloses instead of grains that are designated for foods.

The Botanical, Chemical Composition, and Productivity of Whole Grain Crops Plant-breeding efforts have increased cereal seed yield more than the whole crop output, because new varieties have been bred for increased grain-to-straw ratio, changing the proportions of the whole plant produce by favoring seeds. In Table 1, indicative Danish data regarding yield and composition of whole crops from barley, wheat, rye, oats, and maize show a variation between extreme samples in grain-to-straw w/w index from 0.52 in barley to 1.74 in maize. The average values indicate that short straw breeding to favor grain yield has apparently been most successful in

Coarse chips

Medium chips

Marrow (feed)

Fine chips Figure 1 Dried stem of maize separated by disk milling and sieving into a meal fraction from the marrow and into different sizes of chips from the cell walls of internodes and nodes.

Winter wheat

Spring oats Maize

Today, most of the whole plant products are utilized for food, feed, and energy. The consumption of cereals and cereal products for the nonfood sector is relatively small (about 12% of world production 2012) compared to that of food and feed, although in absolute terms, millions of tonnes of starch, oil, and lignocelluloses are consumed globally by the industry for nonfood purposes. Research on agricultural, nonfood substitutes for import was high during the Second World War, especially in the United States within the USDA. After the energy crisis in the 1970s–1980s, research on developing renewable resources for products and energy was again initiated in countries such as the United States, Holland, and England and in the Scandinavian countries, as well as in the present European

Yield and botanical composition of whole cereal grain crops grown in Denmark

Spring barley

Winter rye

barley, followed by wheat, maize, rye, and oats. Winter wheat and maize, despite the fact that the latter crop is not fully adapted to the Danish climate, produced most grain (top yield 9.1 and 6.9 t ha 1, respectively) and straw (top yield 8.5 and 10.6 t ha 1, respectively). The straw from each sample of the cereal material in Table 1 was hand-dissected into internode, leaf, and node, and the fractions were weighed and analyzed (see results in Table 2). The internode is, on an average, the largest component of straw, ranging from 68.7% in rye to 40.4% in maize. The leaf portion ranges from 48.4% in barley to 20.7% in rye, while the node fraction is relatively high in maize (max 16.6%) and low in barley (min 1.0%). It is also seen in Table 2 that a-cellulose is generally higher in the internode (42.2–38.3%) than in the leaf (30.3–28.2%). The leaf fraction has the highest protein content of 3.5–8.3% compared to 2.0–3.7% for internodes. The leaf fraction shows constantly higher values with respect to ash and silicon than internodes. Ash and silicon contents depend to a great extent on the soil conditions, with high content in loamy soils compared to sandy. The silicon in the internode fraction in several samples grown in sandy soils is below 0.1%, which is a great advantage in the manufacture of chemical paper pulp and paper. In vivo and in vitro digestibility trials give 20–30% higher values with cereal leaf compared to internode (e.g., barley in vivo 51.3% versus 41.0%). Leaf meal energy value for fuel varies from 16.8 MJ kg 1 d.m. in barley to 17.0 MJ kg 1 d.m. in barley straw pellets compared to 18.4 MJ kg 1 d.m. in wood.

Products from Whole Grain Plant Fractions

Parent product

Table 1

229

Mean Range Mean Range Mean Range Mean Range Mean Range

Grain yield (t ha 1)

Straw yield (t ha 1)

Grain/straw ratio (w/w)

5.1 6.3–3.6 6.9 9.1–3.8 4.9 5.4–4.6 4.2 5.4–3.1 6.2 6.9–5.7

3.9 5.5–2.8 6.1 8.5–3.7 6.4 7.5–5.3 5.7 7.1–4.2 6.6 10.6–4.5

0.78 1.01–0.52 0.92 1.63–0.68 1.31 1.58–1.10 1.34 1.36–1.32 1.06 1.74–0.72

Reproduced with permission from Bjørn Petersen, P., Munck, L., 1993. Whole crop utilization of barley including new potential uses. In: MacGregor, A.W., Batty, R.S. (Eds.), Barley: Chemistry and Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 437–474.

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NON-FOOD PRODUCTS FROM GRAINS | Utilization of the Whole Cereal Plant to Maximize its Value

Table 2

Analysis of hand-dissected botanical components of straw from Table 1 Weight distribution % of total harvested straw (w/w)

Spring barley

Winter wheat

Winter rye

Spring oats

Maize

Internode Leaf Node Internode Leaf Node Internode Leaf Node Internode Leaf Node Internode Leaf Node

Mean composition (% d.m.)

Mean

Max/min

a-Cellulose

Protein

Ash

Silicon

50.4 41.6 5.4 55.0 38.7 4.8 67.7 23.9 5.2 50.4 42.1 4.4 46.6 42.1 11.9

55.1/44.7 48.4/33.9 4.0/1.0 63.0/49.8 44.2/31.6 7.0/3.4 68.7/66.7 25.4/20.7 6.5/2.8 53.4/47.3 45.5/38.7 5.1/3.7 52.0/40.4 46.4/34.3 16.6/8.7

38.3 28.2

2.0 3.9

4.5 6.3

0.5 1.4

42.2 29.3

3.0 5.2

4.6 8.4

1.0 2.3

41.3 29.8

3.0 5.9

3.7 5.7

0.5 1.2

39.2 30.3

2.6 3.5

4.6 7.4

0.2 1.9

39.5

3.7 8.3

6.3 7.9

0.2 1.4

Reproduced with permission from Bjørn Petersen, P., Munck, L., 1993. Whole crop utilization of barley including new potential uses. In: MacGregor, A.W., Batty, R.S. (Eds.), Barley: Chemistry and Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 437–474.

Union. The most important driving force was the steadily increasing surplus in cereal production in industrialized countries at the end of the twentieth century. There was, thus, a clear governmental interest in nonfood cereal products that could eliminate the surplus while providing income to farmers. From the 1990s, the rising concern about man-made influence on climate and the global resources of planet earth has taken over. It is obvious that global caring for maintaining photosynthesis in plants from agriculture and wildlife, as the only renewable hydrogenated carbon resource, is the most important counterweight to the negative effects caused by man as a major consumer on the planet. Starch, cellulose, and oil are the major chemical components of industrial interest. Figure 2 gives the whole plant utilization potential of maize as an example. Very large-scale industrial units for maize grain utilization are a significant component. These units feature dry and wet (starch) milling of maize, where oil (from germ) and gluten protein (for feed) come as coproducts from starch manufacturing. There is a wealth of possibilities for utilizing the starch polymer after modification by means of organic chemistry or microbiological transformation to, for example, plastic molds, ethanol, acetone, and butanol. Starch from maize, wheat, and potatoes is consumed in large amounts by the paper industry. Here, starch derivatization with ionizing chemicals is used in the form of cation and anion starches as additives to increase paper strength as well as for coating. Graft polymers with vinyl and acrylic monomers can be produced from granular and gelatinized starch for the production of plastic films, molded products, etc. Such a solid polymer of starch with acrylonitrile can absorb many hundred times its weight in water without being dissolved. These ‘superslurpers’ could be used for applications in hygienic products and medical care, as well as in agriculture for coating seeds and to conserve water under arid conditions. Starch xanthates can be used as carriers for encapsulation of seeds with pesticides.

The lignocellulosic fractionation options demonstrated in Table 2 regarding stem and leaves are sparsely utilized today. The current world production of paper pulp is in the order of 150 million tonnes (Mt), of which 12 Mt comes from cereals and grasses corresponding to about 30 Mt of whole straw. Existing fractionation and treatment technology can exploit the lignocellulose resources of cereals much more effectively than is the case today. Most of the straw produced today is either burned in the open or collected and used as bedding material for animals and as low-quality feed. Straw can be pelleted into a high-grade fuel. It can be instantly treated with alkali and steamed in a pellet press to loosen the lignin bonds, which greatly improves the physiological energy utilization of feed for ruminants. The same alkali-treated pellet can be used as semimanufactured material for paper pulp. Short hardwood fibers from birch, etc., and internode fibers are similar in length, but the latter are much more slender. The smaller diameter of the straw fiber seems to have no adverse effect on the technological properties of the paper derived from it. The fiber length from lignocelluloses in the leaf fraction is shorter than that from the internode fraction. The latter is preferable for paper-pulp processing because of its high content of acellulose and low level of silicon. Silicon may be a problem when straw is used as raw material in the paper-pulp industry, because it prevents recycling of the alkali – black liquor – due to gelling and insulation of the cooker. The use of straw fractions for particleboards is an overlooked application today. The internode fraction from, for example, wheat, rye, maize, and sorghum straw compressed with synthetic glues yields a product strength as high as that of particle boards from wood chips. The texture of this type of boards can be varied, by using different size fractions from internodes, making an appealing natural product. Starch can substitute formaldehyde in phenolic polymers, which can be used as binders in particle boards. Bran from phenol-rich sorghum varieties can also be used for glue making. Another


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Enzymes Feed

Steeping residue

Fermentation

Germs

Oil extraction

Feed industry

Grain

Harvest

Storing

Wet milling separation

Dry milling separation

Separation

Corn gluten feed

Feed industry

Starch

Hydrolysis

Brewing grits

Pharmaceuticals Amino acids Organic acids Vegetable oil

Human consumption

Germ oil cake

Feed industry

Glucose syrup

Stem + cobs

Storing

Fuel Particle board industry Paper and board industry Feed industry

Hydrogenation

Sorbitol

Isomerization

High fructose syrup

Fermentation

Organic acids Alcohol etc.

Paper industry Textile industry Plastic industry

Flour

Chemical industry

Polyol Sweetener Vitamins Food Beverage Industry

Food industry

Modification

Starch derivatives

Plastic industry Textile industry Paper industry

Figure 2 Whole plant utilization with maize as an example. Reproduced from Munck, L., 1993. On the utilization of the renewable plant resources. In: Hayware, M.D., Bosemark, N.O., Romagosa, I. (Eds.), Plant Breeding. Principles and Prospects. Chapman and Hall, London, pp. 500–522.

more elegant solution for glue is enzyme treatment of the lignocellulose matrix of the internode material. This enables the use of the natural component lignin as a binder by introducing free radicals before pressing. Most of the vegetable oils from grains (e.g., rape, sunflower, and maize) are used in the food sector. There is, however, a significant nonfood market for these vegetable oils in soaps and detergents, paint and varnish (emulsifiers and drying oils), lubricants, greases, cosmetics, and pharmaceuticals. Rapeseed oil for driving diesel engines in, for example, tractors and buses is at present used in the public sector in Europe in an effort to reduce pollution and improve carbon dioxide recycling. This is more effective per unit of biomass, compared to using ethanol for motor fuel, obtained microbiologically from hydrolyzed starch or lignocellulose, because the fermentation process involves liberation of large amounts of carbon dioxide.

Whole Plant Utilization Production Systems: Integrated Conversion in Agricultural Biorefineries It may be concluded that there are great opportunities in utilizing whole plants in a variety of food, feed, and nonfood applications. A major obstacle is, however, local organization of the necessary links between decentralized agriculture and centralized industry, for a flexible whole plant utilization of a range of different crops, simultaneously, in accordance with signals from the market. The local cultural role of farms and farmers in society based on traditions has prevented the integration of the local production of vegetative materials and the centralized processing industry. Such an integration has, however, taken place in the forestry industry. Oil palm and cane/ beet sugar extraction plants as well as lucerne and grass dryer and pelleting stations for feed are examples of industries that are closely connected to the agricultural production. They

exercise within a defined crop a whole plant utilization strategy. Since the 1960s, the idea of local agricultural preprocessing stations or agricultural whole plant biorefineries, as a necessary link between agriculture and industry, began to emerge in countries such as Denmark, Sweden, Holland, and the United States. In the following section, the Danish research applicable for northern European conditions is cited as an example. In the 1960s, machine stations and cooperatives for manufacturing of lucerne and grass pellets by high-temperature, oil-heated drum dryers demonstrated the needs and possibilities in changing the structure of local agriculture. Grass and lucerne was harvested as a whole crop by self-propelling choppers (Figure 3(a)) several times during the growing season. These were then brought in containers (Figure 3(b)) to the drying station where they were dried and pelleted for sale to the feed industry. A number of very wet harvesting seasons in the 1960s stimulated the use of the whole crop harvesting strategy for other crops such as barley, wheat, broad beans, and maize. The whole biomass was dried in the drum dryer and afterward separated into seeds and straw. The straw could then be treated in the pellet press of the drying station by steam, sodium hydroxide, and urea to produce high-quality feed for ruminants. In Denmark, in the 1960s–1970s, a major oil company subsidiary ran this type of biorefinery in a limited sense in Jutland, where whole crop harvesting of lucerne, grass, and cereals from farmers in the area was integrated with a large milking cow unit. On the island of Bornholm, a demonstration and research agricultural biorefinery unit, financed by EU projects, has been in operation since 1988. It is located adjacent to a feed factory with a drum dryer and a chipboard factory for wood chips. Large-scale trials were performed with fractionation of wheat and rape straw into internodes and leaf meal. High-quality chipboards were produced from internodes chips. In


232

(a)

(b)

Figure 3 The principle of whole plant harvesting exemplified by barley: (a) self-propelling harvesting chopper loading the coarsely chopped plants into a container; (b) when the container is full, it is transported by truck to the biorefinery for drying and separation of the crop components and further processing.

cooperation with chemical and paper industries, an EU production chain project was implemented (see ref. website: Cascade refining of European wheat) whereby a cation starch product was developed from bran-separated wheat flour in an environmentally closed dry process. The performance of this resource-saving product in paper production was fully comparable to that of the more expensive cationic wheat starch. The quality factors for performance were monitored throughout the production chain with near-infrared spectroscopy (NIRS) interpreted by chemometric (multivariate) data analysis. On the basis of the NIRS analysis, the quality of wheat optimized for the whole process could be defined and predicted, at the raw material stage. After the oil crisis in 1973, Denmark’s lucerne- and grassdrying and pelleting industry, one of the largest in the world at that time, vanished due to high oil prices. Some companies survived by switching to coal. In drying cereals as a whole crop, the pelleted leaf fraction is enough for sustaining the drying process. The implementation of this possibility is dependent on the price of straw. The Danish experience, applicable to the wet and tempered production and harvesting conditions in northern Europe, is contained in the agricultural biorefinery concept demonstrated in Figure 4, comprising a machine station, a drum dryer, crop fractionation equipment, and a feed factory serving a few thousand hectares. Compared to the present farm system with individually run units of

Straw + grain

Harvesting and chopping

Straw-chopping Center Strawmalepressing

ed flak ips De w ch stra ed eat i-tr bs l a Alk w co stra Gra in

Pulp mill and particleboard plant

bs co str aw ted

n

tei

Pro

Oil extraction plant ain Gr

Alk Gr ali-t ain rea

ds

ee

Farmer

ls

Composite feed

Oi

Alkali-treated straw cobs Leaf fraction Grain

Trade elevators Harvesting and threshing

Protein Local feed mill at the center

Starch plant

Figure 4 The agricultural biorefinery concept as a link between agriculture and industry for implementing whole plant utilization technology. Reproduced with permission from Bjørn Petersen, P., Munck, L., 1993. Whole crop utilization of barley including new potential uses. In: MacGregor, A.W., Batty, R.S. (Eds.), Barley: Chemistry and Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 437–474.

NON-FOOD PRODUCTS FROM GRAINS | Utilization of the Whole Cereal Plant to Maximize its Value 50–100 ha, the integrated agricultural biorefinery organization for food, feed, nonfood, and energy products would imply the following advantages: 1. The economic success of the agricultural biorefinery should not be judged on the basis of individual products, but on the integrated total output from a flexible diversified production. 2. Because of whole overground plant harvesting (Figure 3(a) and 3(b)) and its dryer, the agricultural biorefinery organization is independent of harvesting weather. Therefore, a wider selection of whole crops can be safely harvested, separated, and processed as semimanufactured products, ensuring a high quality. 3. The diminished monoculture will lead to improved fertility and less costs for pest control. 4. The field is cleared in one step and a higher yield of both grain and straw is achieved. 5. Harvesting machines and agricultural biorefinery equipment will be able to be used most of the whole year, which will improve economy. It will, thus, be able to support a permanent staff, thereby creating local working opportunities. 6. The system can be run by locally produced bioenergy. 7. Transport costs will be minimized. Locally produced highquality feed pellets from straw and grass will stay in the area, while surplus grains and internode fractions are sent to larger centralized industries outside the area producing, for example, wheat flour for food, starch, and vegetable oil, chipboards, and paper pulp. 8. The benefits of the agricultural biorefinery principle could only be fully utilized in a network of agricultural biorefineries and cooperating industries, which would stimulate sustainable crop utilization and recycling of waste. Local animal and human manure could be collected and used in biogas units, as is done in a few communities in Denmark today. These units could be integrated with the biorefinery. The processed manure products could be recycled to the local agricultural land or sold and exchanged as a hygienic dry product. Thus, the land fertility problem potentially caused by removing too much organic matter (e.g., from straw) from the fields could be solved by reestablishing the biological production chain through recycling the manure. The whole plant utilization technology included in the agricultural biorefinery concept, described here, focuses on using agriculture as a vehicle for the integrated development of a differentiated agroindustrial production pattern for food, feed, and nonfood products, optimizing the use of local natural resources in closed biological production chains. The principle can be adapted to include widely different cases in industrial as well as developing countries, taking local conditions into account. The concept of biorefineries in research later during this century seems to have drifted away from the integrated perspective of the agricultural refinery presented here, to focus on developing more specific nonfood industrial biorefinery options (see ref. website: University of Wageningen). It is important in a widened perspective to focus on global integrated networking in an agricultural–industrial–social–economical perspective to move towards the ideal of ecological sustainability.

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Economy and Future of Integrated Whole Plant Utilization The cost-effective use of biological material for nonfood purposes in present economy should now benefit from the fact that the price for cereal grain (e.g., maize) versus oil w/w has decreased sixfold since 1973. The world market price of pure starch is not far from that of crude oil. However, extensive use of starch-rich grains (maize) for nonfood purposes, for example, for ethanol (as today in the United States), now competes with food and feed uses that press up the price of foods. Because of the increasing demand of grain to feed the increasing world population, nonfood uses of grains are not sustainable in the longer perspective. However, the use of the lignocellulose parts of the cereal plant for nonfood products is attractive because it does not directly compete with food uses. Synthetic low-density polyethylene from fossil fuels as well as paper pulp (lignocellulose) is in the order of 2–3 times more expensive than starch. The high price of paper pulp today reflects the high energy and machine costs in the forestry industry. There should be considerable energy savings, compared to the forestry industry, by using existing machinery in agriculture to take care of the abundant internode fraction from plants for paper pulp and chipboards. It should be advantageous for farmers in countries with existing straw-based paper-pulp factories to sell the internode fraction to these industries while retaining the leaf fraction as feed. Agricultural lignocelluloses for paper and chipboards should be a valuable produce in many developing countries with vanishing forestry resources. Even if several of the previously discussed plant use applications are shown to be profitable today, there are economical, structural, and psychological constraints in a system change from fossil products to renewable plant resources. In many countries such as in Denmark, a major share of cereal lignocelluloses (straw bales) is today used in great scale in electricity power stations and for heating in direct competition with fossil fuels. Near 30% of Denmark’s energy consumption now comes from renewable resources with the target of 50% in 2020. For a change in straw use in Denmark from energy (at present) to other nonfood applications (ethanol, paper, fiber boards, etc.), one has to pay a higher price for straw than that is currently given for energy. The price of oil during the economic crisis 2008–09 underwent a record peak of 145 US$/bbl (July 2008). However, in December 2014, the oil price has decreased to about US$ 60/bbl. This is primarily due to the recent exploitation of new shale gas sources in North America by introducing new cracking technology. This production is likely to have a stabilizing effect on oil (energy) prices for some time to come. However, in the longer time perspective, oil prices are likely to increase considerably when resources are scarce. It is clear that to stimulate the nonfood whole plant utilization option, oil prices should be kept at a stable higher level, than that at present, during several decades. In conclusion, a wide range of new whole plant utilization options have been developed during the last 50 years. Retrospectively, these research results stand as a sort of insurance to be mobilized if needed to meet an unpredictable future. They now most often rest in the laboratory because of lack of understanding on how they, many together, could fit in

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an evolution process of the total global network of the world’s agricultural and industrial production and consumption towards economic, social, and ecological sustainability. Such an integrated structural evolution has to be driven by the monetary system and the market in hard competition with old technologies and vested interests. Without concerted initiatives for an international change by governments and institutions and for public awareness in such a multicomponent amplified system, an evolution towards ecological sustainability is bound to be an extremely slow, erratic, and unlikely process.

See also: Agronomy of Grain Growing: Precision Agriculture; Sustainable Grain Production and Utilization; Grain Harvest, Storage and Transport: Handling from Farm to Storage Terminal; Wheat: Harvesting, Transport, and Storage; Non-food Products from Grains: Biodiesel; Cereal Grains as Animal Feed; Fuel Alcohol Production; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Grain Chain: The Route from Genes to Grain-Based Products; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.


•

•

How could an infrastructural structural evolution in whole plant utilization and agricultural biorefineries by modern available technology be driven by the present monetary system and the market in hard competition with old technologies and vested interests. What is the alternative?

Exercises for Readers to Explore the Topic Further Since the Second World War science has created a huge collection of new options for a balanced utilization of the world’s resources but very few have reached commercial realization. There is therefore a need to introduce a new science of integrated systems development where economic incentives – instead of chopping up productions chains – are connecting the technological options to produce networks that compete on the basis of their integrated economy. Such a huge undertaking can only be financed as demonstration projects by generous investments from international bodies and governments organized by local innovators.

Stimulate Further Thinking on the Topic by Setting a Few Questions, Especially Concerning Where the Topic Might Be Heading in the Future

• • • •

What is the role of the individual consumer in securing a sustainable agriculture? What is the role of science? How are the new options explained as a whole integrated change of the infrastructure to the masses instead of the present focus on single issues adding one by one? Who is going to take the initiative and how should finance be promoted to such a fundamental change in infrastructure in hard competition with the present conventional technology?

Further Reading Bjørn Petersen P and Munck L (1993) Whole crop utilization of barley including new potential uses. In: MacGregor AW and Batty RS (eds.) Barley: Chemistry and Technology, pp. 437–474. St. Paul, MN: American Association of Cereal Chemists. Gomez MI and Munck L (1993) Whole cereal crop utilization. In: Taylor JRN, Randal PG, and Viljoen RH (eds.) Cereal Science and Technology Impact on a Changing Africa, pp. 653–688. Pretoria: The Council for Scientific and Industrial Research (The CSIR). Hugo S, Gooding MJ, Barton SA, and Smith GP (2001) Wheat – still finding alternative uses? A review. Aspects Appl. Biol. 64: 31–38. Lynd LR, Wyman CE, and Berngross TU (1999) Biocommodity engineering. Biotechnol. Prog. 15(5): 777–793. Munck L (1993) On the utilization of the renewable plant resources. In: Hayware MD, Bosemark NO, and Romagosa I (eds.) Plant Breeding. Principles and Prospects, pp. 500–522. London: Chapman and Hall. Munck L (1995) Whole plant utilization by milling and separation of the botanical and chemical components. In: Dendy DAV (ed.) Sorghum and Millets, pp. 223–281. St. Paul, MN: American Association of Cereal Chemists. Munck L, Rexen F, Petersen B, and Bjørn Petersen P (1989) A new agricultural system for Europe? In: Pomerantz Y (ed.) Wheat is Unique, pp. 49–70. St. Paul, MN: American Association of Cereal Chemists. Munck, L.; Rexen, F., 1990. Agricultural Refineries – A Bridge from Farm to Industry. Commission of the European Communities. Report EUR 11583 EN. Brussels, Luxembourg. Munck L and Møller Jespersen B (2011) Adapting cereal plants and human society to a changing climate and economy merged by the concept of self-organization. In: Ullrich SE (ed.) Barley: Production, Improvement, and Uses, pp. 563–602. Ames, IA, USA: Wiley-Blackwell.

Relevant Websites http://www.nnfcc.co.uk/external-resources/crops-database-ienica – IENICA, the website of the Interactive European Network for Industrial Crops and their Applications started by EU. The site contains representative references to websites all over the world. http://cordis.europa.eu/projects/FAIR961105 – Cascade refining of European wheats. http://www.wageningenur.nl/en/Research-Results/Themes/theme-biobased-economy/ Biorefinery.htm – University of Wageningen.

Fuel Alcohol Production YN Guragain, Kansas State University, Manhattan, KS, USA KV Probst, Kansas State University, Manhattan, KS, USA; Grain Processing Corporation, Muscatine, IA, USA PV Vadlani, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by C.C. Maningat & S.D. Bassi, volume 1, pp. 405–414, ã 2004, Elsevier Ltd.

Topic Highlights

• • •

•

Fuel alcohol production started more than a century ago; its production surged in the last decade and reached 23.4 billion US gallons of global production in 2013. Cereal grains (starch-rich biomass) and sugarcane (sugarrich biomass) are the major feedstocks for current global fuel alcohol production. Fuel alcohol production from lignocellulosic biomass, known as second-generation bioethanol, has also recently been initiated to meet the future renewable energy demand without significantly affecting global food supply. Fuel alcohol production consists of a series of processing phases, which are broadly divided into three major steps: (i) Release of monomer sugar from feedstocks – the processing technologies are remarkably different for sugarrich, starch-rich, and lignocellulosic biomass. (ii) Fermentation – to convert sugars to ethanol using various yeasts and bacteria. (iii) Product recovery – the ethanol in fermentation broth (4–18%) is first concentrated to around 95% and further dehydrated to obtain absolute (100%) alcohol to use as vehicle fuel by blending with gasoline.

Learning Objective

•

To understand global scenario of fuel ethanol production from renewable resources and fermentation and recovery methods for ethanol production.

Introduction The production of ethanol or ethyl alcohol is one of the oldest known biotechnologies. In recent years, the fuel ethanol production industry has grown remarkably as a result of government policy and as a global movement toward displacing petroleum with renewable fuels. Many countries have adopted ethanol-blended fuels to replace toxic octane-enhancing ingredients, improve carbon recycling, reduce harmful emissions, and displace fossil fuels. Currently, the majority of the ethanol is produced from first-generation technologies. Firstgeneration ethanol comes from arable crop feedstocks, such as starch-based grains and sugars from sugarcane and sugar beets, and is produced using known mature technologies. Second-generation ethanol, which comes from plant-based biomass and other nonfood-based feedstocks, has recently been commercially implemented. As the production of fuel ethanol continues to evolve as a renewable source of energy,


appropriate technological advances are required along with the broad feedstock range to meet the rising energy demand. This article covers current global fuel ethanol production statistics, fuel ethanol production processes, and future outlook of this emerging industry.

Global Fuel Ethanol Industry Global production of ethanol has increased vastly over the past 15 years. In 2013, annual global ethanol production was 23.4 billion US gallons. As shown in Figure 1, in 2013, the United States was the largest producer with 57% of global output followed by Brazil (27%), Europe (6%), and China (3%).

Ethanol Production in North America In 2013, the US ethanol industry had 192 ethanol manufacturing plants with a production output of about 13.3 billion gallons valued around 40 billion dollars. Corn is used as the major feedstock for ethanol production with the major corn growing midwestern states serving as the top ethanol producers, namely, Iowa (30%), Nebraska (14%), Illinois (10%), and Minnesota (8%) (Table 1). From 2001 to 2011, US ethanol production has increased exponentially as a result of government policy and mandatory fuel blending laws (Figure 2). Early on, ethanol was introduced into fuel as a result of the Clean Air Act Amendments of 1990, which established an oxygenated fuel program and reformulated gasoline in an attempt to control carbon monoxide and ground-level ozone emissions. Upon phaseout of methyl tertiary-butyl ether, a fuel oxygenate responsible for groundwater contamination lawsuits, and the passing of the 2005 Energy Policy Act, which established the first renewable fuel standard (RFS) requiring 7.5 billion gallons of renewable fuel to be blended into gasoline by 2012, the ethanol production industry saw considerable growth. Amendments to the RFS program via the Energy Independence and Security Act (EISA) of 2007 increased the requirement to 9 billion gallons by 2008 and 36 billion gallons by 2022 sparking tremendous growth from 2007 to 2011. Production has since stabilized in 2012 and 2013 as a result of high corn prices ($6–7 per bushel in 2011 and 2012), challenging market conditions, and blending limitations. As a result of the market challenges, ethanol exports have increased considerably (up to 4.7% of total production); this has been an important contributor toward preventing stagnant growth in 2013. In the United States, fuel-grade ethanol is currently blended into conventional gasoline at various levels. E10, classified as a blend of 10% (v/v) ethanol, accounts for roughly 95% of all

http://dx.doi.org/10.1016/B978-0-12-394437-5.00137-6

235

NON-FOOD PRODUCTS FROM GRAINS | Fuel Alcohol Production

236

545 696

United States

523 727

Brazil

1371

Europe China 13300 6267

India Canada Others

Figure 1 Global fuel ethanol production (million gallons) in 2013. Adapted from RFA (2014) Renewable Fuels Association, Ethanol Industry Outlook. http://www.ethanolrfa.org/pages/annual-industry-outlook (accessed on January 22, 2015). Table 1

gasoline in the United States. Adoption of higher blends such as E85, which contains 51–83% (v/v) ethanol intended for flexible fuel vehicles built and designed to handle any ethanol–gasoline blend, has been limited due to poorer fuel mileage and competition from cheaper gasoline. Adoption of higher ethanol blends such as E15, which has been approved by the Environmental Protection Agency for use in vehicles newer than 2001, will be key for preventing a blend wall and meeting future RFA mandates. Canada’s ethanol industry has been active in the past 5 years though at a much smaller scale compared to the United States. In 2013, Canada produced 457 million gallons of ethanol; the industry has been steadily increasing mainly due to Canadian Environmental Protection Act of 1999 that established a 5% renewable fuel requirement in gasoline and blend rate mandates for many of the provinces. Canada is the largest producer of wheat-based ethanol in the world converting roughly 1 million tonnes of wheat annually in 2013.

Top US ethanol and corn-producing states in 2013

State

Million gallons

Refineries

Corn (million bushels)

Ethanol Production in South America

Iowa Nebraska Illinois Minnesota South Dakota Indiana

3958 1897 1384 1129 1019 936

42 26 15 22 15 14

2162 1624 2100 1304 809 1035

Ethanol production in South America has been dominated by Brazil, the second-largest producer of ethanol in the world generating about 6 billion gallons in 2013 (Table 2). It began its fuel ethanol program in 1976, which has been widely adopted throughout the country as a transportation fuel having displaced over 50% of gasoline in the fuel market. Over the years, the mandatory blend has varied between 18% and 25% (v/v) and was recently set to E25 in 2013. Over 90% of the vehicles have flex-fuel capabilities, some even capable of using E100, making Brazil the only country in the world where neat

Source: RFA (2014) Renewable Fuels Association, Ethanol Industry Outlook. http:// www.ethanolrfa.org/pages/annual-industry-outlook (cited on January 22, 2015); NCGA (2014) National Corn Growers Association, World of Corn, 2014. http://ncga.com/ upload/files/documents/pdf/woc-2014.pdf (accessed on January 23, 2015).

16 000

14 000

Millions of gallons

12 000

10 000

8000

6000

4000

2000

0

* 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 19 19 19 19 19 19 19 19 19 19 20 20 20 20 20 20 20 20 20 20 20 20 20 20

Figure 2 US ethanol production from 1990 to 2013. *Forecast. Adapted from RFA (2014) Renewable Fuels Association, Ethanol Industry Outlook. http://www.ethanolrfa.org/pages/annual-industry-outlook (cited on January 22, 2015).

NON-FOOD PRODUCTS FROM GRAINS | Fuel Alcohol Production Table 2

237

Production of ethanol in South America

Country

Million gallons

Feedstocks

Blend rate (%)

Refineries

Brazil Argentina Colombia Peru Paraguay

6436 125 102 63 48

Sugarcane, molasses Sugarcane, molasses, grains Sugarcane, cassava Sugarcane Sugarcane

52 5.8

399 12 6 2 12

6.4 26.4

Source: USDA-GAIN (2014) United States Department of Agriculture (USDA), Foreign Agricultural Service, Global Agricultural Information Network (GAIN). Biofuels Annual – Brazil (GAIN report number BR14004), EU-28 (GAIN report number NL4025), China (GAIN report number CH14038), India (GAIN report number IN4055), Canada (GAIN report number CA14109), Japan (GAIN report number JA4018), Australia (GAIN report number AS1415), Indonesia (GAIN report number ID1420), Thailand (GAIN report number TH4057). http:// gain.fas.usda.gov/Pages/Default.aspx (cited on January 20, 2014).

Table 3

2013 fuel ethanol production in the EU

Country

Million gallons

Benelux (Belgium, the Netherlands, and Luxembourg) Germany France Spain The United Kingdom Austria Poland Others

287 217 200 119 74 61 57 342

Source: USDA-GAIN (2014) United States Department of Agriculture (USDA), Foreign Agricultural Service, Global Agricultural Information Network (GAIN). Biofuels Annual – Brazil (GAIN report number BR14004), EU-28 (GAIN report number NL4025), China (GAIN report number CH14038), India (GAIN report number IN4055), Canada (GAIN report number CA14109), Japan (GAIN report number JA4018), Australia (GAIN report number AS1415), Indonesia (GAIN report number ID1420), Thailand (GAIN report number TH4057). http://gain.fas.usda.gov/Pages/Default.aspx (cited on January 20, 2014).

ethanol (E100) can be purchased for fuel purposes. Similar to other countries, its growth in ethanol production has been driven by government policy aimed at reducing the national dependence on imported fossil oil and boosting the domestic fuel programs. Unlike the United States, Brazil uses sugarcane as the major feedstock for ethanol production. Sugar mills, which produce refined sugar as the major product, often coproduce ethanol from molasses, a by-product of the sugar refining process. Furthermore, the sugarcane bagasse leftover after crushing is often burned to cogenerate electricity to provide power for the sugar mills. The production of ethanol from sugarcane has been reputed as being more sustainable and energy efficient compared to grain-based production method, such as from corn or grain sorghum.

Ethanol Production in Europe The European Union (EU) is the third-largest producer generating roughly 1.4 billion gallons of ethanol per year valued at 8 billion euros. EU production is led by Germany, France, and Spain (Table 3). EU fuel ethanol is produced from sugar beets and grains (wheat, corn, barley, and rye). Similar to the United States, government policy has been driving the implementation of biofuels in the transportation fuel market. The Renewable Energy Directive, a part of the EU energy and climate change package, has set forth goals to reduce greenhouse gas emissions, improve energy efficiency, and increase renewable energy market share. All gasoline in the EU is a blend of E5,

while E10 and higher blends including E85 are available in some countries, but adoption of these has been minimal. Fuel ethanol has not been as successful in the EU as the United States and Brazil mainly due to the fact that automobiles using diesel/biodiesel account for a majority of usage. Additionally, another contributing factor to the stagnant EU fuel ethanol production is the lower cost of imported ethanol (up to 15%) from the United States/Brazil.

Ethanol Production in Asia Ethanol production in Asia has become more prevalent in recent years as countries follow up to increasing production trends set by the United States and Brazil. Several countries including Thailand, India, and the Philippines have implemented policy to meet production targets for renewable fuels. In 2013, total production was about 1.5 billion gallons with the Asian market being dominated by China, India, and Thailand (Table 4).

Fuel Ethanol Production Process Fuel ethanol production from biomass consists of a series of processing steps, which can be broadly grouped into three major steps: sugar release from feedstocks, fermentation, and product recovery (Figure 3). The fermentable sugars are first released from carbohydrate polymers present in cereal grains and biomass resources using appropriate processing and

238 Table 4

NON-FOOD PRODUCTS FROM GRAINS | Fuel Alcohol Production 2013 fuel ethanol production in Asia

Country

Million gallons

Feedstock

Blend rate (%)

Refineries

China India Thailand The Philippines Japan

696 543 251 19 7

Corn, wheat, cassava Molasses Sugarcane, cassava Sugarcane Sugar beet, wheat, rice

2 1 12 8 0.2

6 115 21 4 34

Source: USDA-GAIN (2014) United States Department of Agriculture (USDA), Foreign Agricultural Service, Global Agricultural Information Network (GAIN). Biofuels Annual – Brazil (GAIN report number BR14004), EU-28 (GAIN report number NL4025), China (GAIN report number CH14038), India (GAIN report number IN4055), Canada (GAIN report number CA14109), Japan (GAIN report number JA4018), Australia (GAIN report number AS1415), Indonesia (GAIN report number ID1420), Thailand (GAIN report number TH4057). http://gain.fas.usda.gov/Pages/Default.aspx (cited on January 20, 2014).

Sugars release

Biomass

Sugar-rich biomass

Grains

Lignocellulosic residues

(Sugarcane, sweet sorghum)

Starch

Sucrose

Fermentation

Fructose

Glucose

Hemicellulose

Xylose, arabinose, mannose ...

Pyruvate

Ethanol

Product recovery

Cellulose

Distillation

Dehydration

~ 10% ethanol

~ 95% ethanol

100% ethanol

Figure 3 Fuel ethanol production processes from biomass.

enzyme-based technologies. The released sugars are processed via microbial fermentation to produce ethanol. Finally, the ethanol is recovered from fermentation broth and dehydrated. The absolute (100%) alcohol, also called ‘gasohol,’ is used as fuel by blending with gasoline at a proportion determined by local or national government policies. The biomass feedstocks for fuel ethanol production can be broadly classified into three main types: sugar-rich biomass, starch-rich biomass, and lignocellulosic biomass. The sugar-rich biomass, such as sugarcane, sugar beets, and sweet sorghum, contains high amounts of fermentation sugars, including sucrose, fructose, and glucose. In this type of feedstock, the biomass is crushed and milled to extract juice containing fermentable sugars, which are fermented to ethanol using yeasts. The starch-rich biomass contains starch as the major component and includes corn, sorghum, wheat, cassava, potatoes, and barley as examples. In this type of feedstock, the starch is first enzymatically

hydrolyzed to obtain desired concentration of glucose; the released glucose is fermented to ethanol. The lignocellulosic biomass contains cellulose and hemicellulose polymers strongly bound by lignin, and examples include wood, straw, and grasses. For lignocellulosic biomass, an energy-intensive deconstruction (also called pretreatment) processing step is required to separate lignin from the cellulose and hemicellulose prior to fermentable sugar hydrolysis. Fuel ethanol produced from sugar-rich and starch-rich feedstock is called first-generation ethanol, and lignocellulosic biomass is called second-generation ethanol. The United States alone produces 57% of global ethanol production (Figure 1), and most of the US ethanol is produced from corn (Table 1). Therefore, corn-based ethanol is one of the established industries in the world. Production and recovery technologies for corn ethanol will be discussed further in this article. There are two types of processes for corn ethanol production: the wet-milling process and the dry-grind process. The dry

NON-FOOD PRODUCTS FROM GRAINS | Fuel Alcohol Production grind covers almost 70% of total corn ethanol production. The wet-milling process consists of preprocessing of corn to separate fiber, germ, and gluten prior to hydrolysis of starch to glucose for ethanol fermentation. In case of the dry-grind process, the corn is hammer-milled and then directly enzymatically hydrolyzed (in a series of steps) to glucose, which is fermented to ethanol using yeast. Therefore, wet milling is more capital- and energy-intensive process and produces a number of high-valued by-products, including corn oil, corn gluten meal, and corn gluten feed along with fuel and foodgrade ethanol. On the other hand, the dry-grind process mainly focuses on producing ethanol at the lowest possible cost. The main coproduct of dry-grind process is called distillers’ dried grains with solubles (DDGS), a protein-rich solid material produced by combining the solids, spent

residues leftover after distillation of fermentation broth, and the evaporated thin stillage from the centrifugation step. This product is sold as a supplementary animal feed and is an important part of the profitability of the dry-grind process. Corn ethanol production from the dry-grind process will be discussed later. A schematic diagram for fuel ethanol production from corn using the dry-grind process is given in Figure 4. The corn kernel is ground using hammer mills to a proper particle size, generally less than 2 mm. The whole corn flour is mixed with water in a ‘slurry tank’; around 22 gal mash is generated from each bushel of corn. The slurry is cooked in a ‘jet cooker’ using steam at around 4 bar (110 C). During cooking, the starch granules swell excessively due to water absorption generating a highly viscous and gelatinous mash; the process is called

Steam

α-Amylase

Glucoamylase

Water

Slurry tank

Jet cooker

Corn grain

Gelatinization Hammer mill

Liquefaction

~190 proof ethanol

Mash cooling Yeast

Saccharification CO2

nts

trie

Nu

Steam

Distillation system

200 Proof ethanol

200 proof ethanol Backset (10−50% of thin stillage)

Dehydration system

Thin stillage (5−10% solids)

~ 5% ethanol

Evaporator

Whole stillage (5−15% solids)

Fermentation

Centrifuge Wet cake (35−50% solids) Syrup (25−55% solids)

239

Dryer Distiller’s dried grains with solubles (DDGS)

Figure 4 Schematic diagram for fuel ethanol production from corn using the dry-grind process.

240


Germ dryer Germ

Germ clones Fine grinding (degermination mill) Quick germ process Soaking

Grinding (degermination mill)

Slurry tank Corn grain

Dry grind process

Grinding (hammer mill)

Figure 5 Schematic diagram for the modification of dry-grind process for quick germ process in corn ethanol production.

‘gelatinization.’ The jet cooking also sterilizes the mash. The cooked mash is then allowed to cool to 80–90 C, and ‘a-amylase’ enzyme is added at around 0.082% (w/w) of dry corn and incubated at 85 C for at least 30 min. The a-amylase enzyme randomly breaks a-1,4 glycosidic amylose and amylopectic linkages, leading to a reduction in the size of starch polymers and a decrease in the viscosity of the mash; the process is called ‘liquefaction.’ The liquefied mash is cooled to around 30 C and adjusted to a pH of 4.5. Then, ‘glucoamylase’ enzyme is added, which converts the partially hydrolyzed starch polymers (dextrin) into sugar monomers (glucose); the process is called ‘saccharification.’ The glucose solution is then pumped into a fermentation tank, and yeast culture (Saccharomyces cerevisiae) grown in a separate seed vessel is inoculated into the tank. Supplementary nutrients, including nitrogen sources (e.g., urea) and other growth factors, are also added to the fermentation tank. The yeast ferments glucose to ethanol and carbon dioxide. It also produces a number of other minor secondary products, including acetic acid, glycerol, butanol, methanol, and acetaldehyde. The main strategic focus of the fermentation is to minimize secondary metabolites and maximize ethanol yield per gram of glucose. In recent years, the saccharification is commonly carried out in the fermentation tank itself, a process known as ‘simultaneous saccharification and fermentation (SSF).’ The fermentation process will be discussed in more detail in the ‘Ethanol Fermentation’ section. The fermentation broth containing around 5–18% ethanol is distilled through a distillation column to produce around 95% (190 proof) ethanol, which is further dehydrated to produce absolute (100%) alcohol. The distillation and dehydration process will be discussed in more detail in the ‘Ethanol Recovery’ section. The slurry obtained from the bottom of the distillation column is called ‘whole stillage’ (5–15% solids), which consists of nonfermentable parts of corn kernel,

including germ, fiber, protein, and residual starch. The whole stillage is centrifuged to separate the solid part, called ‘wet cake’ (35–50% solid), and liquid part, called ‘thin stillage’ (5–10% solid). The wet cake, also called distillers’ wet grains (DWG), is either directly sold to the cattle feedlots within the locality or dried to sell as distillers’ dried grain. A part of thin stillage (between 10% and 50%) is recycled through the process, called ‘backset,’ and the remaining part is evaporated to produce condensed distillers’ solubles, which is also called ‘syrup.’ At most of the ethanol plants, the syrup is mixed with DWG and dried to produce DDGS. DDGS is a bulk granular material (less than 10% moisture content), which is physically similar to other dry feed ingredients, like soybean meal. A modified dry-grind process, called the ‘quick germ’ process, was proposed by Singh and Eckhoff by combining drygrind and wet-milling processing technologies to improve the economic advantages of corn ethanol by recovering high-value germ as a coproduct with minimum additional capital investment in existing dry-grind facilities. The hammer milling (grinding) step in dry-grind process is replaced by grinding and degermination processes in ‘quick germ’ process. The grinding and degermination steps in the quick germ process consist of a series of four steps, including soaking of corn (1–3 h at around 60 C), coarse grinding, germ separation, and, finally, fine grinding, as shown in Figure 5.

Ethanol Fermentation The released sugars from biomass are fermented to ethanol using several types of yeasts (Saccharomyces, Pichia, Candida, and Kluyveromyces) and bacteria (Zymomonas, Thermoanaerobacterium, and Escherichia coli). The most common yeast for ethanol fermentation is S. cerevisiae, which produces ethanol via the Embden–Meyerhof–Parnas (EMP) pathway, also known as the glycolytic pathway. Many bacteria, including Zymomonas,


EMP pathway

241

ED pathway

Glucose

Glucose

ATP

ATP

ADP

ADP

glucose-6-phosphate

glucose-6-phosphate

NAD NADH2

fructose-6-phosphate

6-phosphogluconate

NAD NADH2

fructose-1,6-diphosphate

glyceraldehyde-3-phosphate

2-keto-3-dexoy-6-phosphogluconate

glyceraldehyde-3-phosphate

NAD

NAD

NADH2

NADH2

1,3-dipphosphoglycerate


ADP

ADP

ATP

ATP

Glyceraldehyde-3-phosphate

Pyruvate

NAD

CO2

NADH2

Acetaldehyde


NADH2

ADP

NAD

ATP

Ethanol

3-phosphoglycerate

3-phosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

2-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

phosphoenolpyruvate

phosphoenolpyruvate

ATP

ATP

pyruvate

pyruvate

CO2 Acetaldehyde

CO2 Acetaldehyde

ATP

pyruvate

CO2 Acetaldehyde

NADH2

NADH2

NADH2

NAD

NAD

NAD

Ethanol

Ethanol

2 ADP

Ethanol Overall reaction:

Overall reaction:

Glucose

ADP

ADP

ADP

ADP

2 ATP

2 Ethanol + 2 CO2

Glucose

ATP

2 Ethanol + 2 CO2

Figure 6 Embden–Meyerhof–Parnas (EMP) and Entner–Doudoroff (ED) pathways for ethanol fermentation.

produce ethanol via the Entner–Doudoroff (ED) pathway. In these pathways, each glucose molecule produced two pyruvate molecules, which are converted to two ethanol and two carbon dioxide (CO2) molecules as shown in Figure 6. Since the ED pathway releases only half as much ATP per glucose molecule as the EMP pathway, Zymomonas produces less cell biomass than Saccharomyces, thereby funneling more carbon to ethanol fermentation; the ethanol yield by Zymomonas is 5–10% more than Saccharomyces. Additionally, specific ethanol productivity by Zymomonas is 2.5 times higher than Saccharomyces. However,

industries prefer S. cerevisiae than Zymomonas mobilis because of the hardiness of yeast. The stoichiometric calculations for ethanol production from sugars (Table 5) show that the theoretical maximum ethanol yield (g ethanol per gram sugar) from both pentose and hexose is 51.1%, whereas it is 53.8% from sucrose, a disaccharide of fructose and glucose. However, the actual achievable yield is always lower than the theoretical value because a portion of the sugars are utilized for microbial cell growth and maintenance. Additionally, a number of secondary

242 Table 5

NON-FOOD PRODUCTS FROM GRAINS | Fuel Alcohol Production Stoichiometry and theoretical maximum ethanol yield from sugars

Sugar

Stoichiometry

Maximum ethanol yield (%, g/g sugar)

Hexose ðGlucose, fructose, and mannoseÞ Pentose ðXylose and arabinoseÞ Sucrose

C6 H12 O6 ðHexose-180Þ ! 2 C2 H5 OH ðEthanol-46Þ þ 2 CO2 3 C5 H10 O5 ðPentose-150Þ ! 5 C2 H5 OH ðEthanol-46Þ þ 5 CO2 C12 H22 O11 ðSucrose-342Þ þ H2 O ! 4 C2 H5 OH ðEthanol-46Þ þ 4 CO2

51.1 51.1 53.8

products are produced during fermentation along with ethanol, depending upon the fermentation conditions, media composition, and culture type. Saccharomyces and Zymomonas are predominant microbes for first-generation fuel ethanol production due to high yield and ethanol tolerance. However, both of these microbes lack the ability to utilize pentose sugars, the major sugars from hemicellulose hydrolysis. So, these microbes are not suitable for second-generation fuel ethanol production without genetic modification. Candida shehatae and Pichia stipitis are potential yeasts, and Pachysolen tannophilus and E. coli are potential bacteria for pentose fermentation; but they have very low ethanol tolerance. Similarly, some thermophilic yeasts (like Kluyveromyces marxianus) and bacteria (like Thermoanaerobacterium thermosaccharolyticum and Clostridium thermocellum) are capable of pentose fermentation even at 52 C; but they also offer a low tolerance to ethanol. Therefore, genetic engineering of robust ethanol-fermenting microbes to express pentose metabolizing genes would be highly valuable for coutilization of both hexose and pentose sugars for ethanol production. The engineering of yeasts and bacteria for pentose utilization has been extensively studied in the last two decades. Remarkable successes have been made in S. cerevisiae and Pichia stipitis cultures among yeasts and E. coli, Klebsiella oxytoca, and Z. mobilis among bacteria. The industrial xylosefermenting strains of engineered S. cerevisiae (the most robust ethanol producing yeast) demonstrated that ethanol production from lignocellulosic biomass is economically feasible. Fermentative activities of native xylose-metabolizing P. stipitis have also improved in its engineered strains and hence considered as one of the more promising yeasts for ethanol fermentation from biomass hydrolysates. Among bacteria, engineered E. coli has several advantages, including the capability to utilize a wide spectrum of sugars, with minimal supplementary nutrients and a sequenced genome useful for further strain improvement. However, it is less robust than yeast and has a very narrow pH range (6.0–8.0) for growth. The neutral pH requirement is more problematic for SSF process because the optimum pH for most of the commercially available cellulase enzyme is 4.8–5.0. The engineered K. oxytoca and Z. mobilis are better in this regard because their optimum pH is 5.5. Additionally, these engineered bacteria can ferment both xylose and arabinose, the major pentose sugars in the hemicellulose portion of lignocellulosic biomass. Therefore, engineered bacteria are more promising than engineered S. cerevisiae because the latter lacks the ability to utilize arabinose.

Ethanol Recovery Fermentation broth usually contains 4–18% ethanol, depending upon the method of fermentation and type of culture used.

A series of processes is used to recover pure ethanol from the broth; an absolute (100% or 200 proof) alcohol is required to blend with gasoline. Conventionally, the distillation/rectification method is used to produce 95% or 190-proof ethanol. The distilled alcohol is further dehydrated using molecular sieve system to produce absolute alcohol. In the distillation column, the fermentation broth is fed into a tray near the middle of the column, known as the ‘feed tray,’ as shown in Figure 7. The section of the column above the feed tray is called the ‘rectifying/ enriching section’ and below the feed tray is called the ‘stripping section.’ The feed flows down to the bottom of the column and is vaporized in the reboiler. The vapor, consisting of a mixture of ethanol and water, rises up the column, and a part of water vapor is condensed in each tray due to cold liquid feed as well as reflux falling down the column. This process leads to a gradual increase in alcohol concentration in the vapor phase and, finally, reaches around 95% at the top of the column. The ethanol cannot be further concentrated in such distillation system due to the formation of an azeotropic mixture of water and ethanol. The enriched vapor released from the top of the column is condensed, and part of it is refluxed back to the column; the remaining part is recovered as the distilled alcohol. The distillation technology is well matured and has many advantages, including high alcohol recovery, high concentrating factor, energy efficiency at moderate feed concentration, and scalability. However, it is not free from drawbacks. Due to the formation of an azeotrope at 95% ethanol concentration, additional separation steps, like adsorption using hydrophilic molecular sieves, are required to obtain absolute (100%) alcohol. The energy requirement significantly increases if the alcohol concentration in fermentation broth is less than 4%. In order to overcome the limitations of the distillation process, a number of alternative separation processes are available now, including extractive distillation, membrane separations, pervaporation, adsorption, liquid–liquid extraction, and some complex hybrid separation methods, like pervaporation–bioreactor hybrid. These processes operate at lower temperature and hence are less energy-intensive than conventional distillation processes. However, these processes are less mature and are not as common as conventional distillation process in commercial applications. Due to the formation of minimum-boiling azeotropic mixture of water–ethanol solution at 89.4 mol% ethanol and 10.6 mol% water at standard atmospheric pressure, the recovery of dry ethanol in a single process is very difficult. The boiling point of water, ethanol, and the azeotropic mixture of water–ethanol is 100.8, 78.4, and 78.2 C, respectively. Fortunately, water is a more polar and smaller molecule than ethanol; therefore, separation of residual water from the concentrated ethanol can be done by exploiting adsorption


243

Enriched vapor Condenser

Distillate (~95% ethanol)

Rectifying section

Reflux

Stripping section

Feed (~5% ethanol)

Vapor

Bottom products Re-boiler Figure 7 Schematic diagram for distillation column.

and diffusion phenomena. For example, some processes used for the production of anhydrous ethanol are adsorption, liquid–liquid extraction, pervaporation and vapor permeation, and diffusion distillation. The absolute alcohol stream is suitably blended with a denaturant at a desired concentration, such as gasoline, and sold as fuel ethanol product.

Future Outlook In the last two decades, the corn ethanol industry in the United States and the sugarcane ethanol industry in Brazil have significantly improved their production efficiencies as well as valueadded applications of coproducts/by-products, thereby leading to significant cost improvements and additional revenue streams. Further, the government mandates and subsidies favoring renewable fuels, and societal requirement for clean and sustainable transportation fuels, have provided the right impetus for the rapid growth of the biofuels industry. However, highly volatile crude oil prices, new technologies to source crude oil from shale and deep-sea drilling, fluctuating corn and other feedstock prices, and unclear policies of local, national, and international governments have challenged the nascent biofuels industry. Therefore, the biofuels industry is yet to survive on its own, still relying on the governmental intervention in the form of tax exemptions and subsidies. Additionally, the rising concern for food security due to fuel production from food materials and insignificant benefits (as compared to petroleum) in greenhouse gas emission and net energy balance from sugar- and starch-based ethanol have

encouraged the search for alternatives, shifting from sugarand starch-based ethanol to cellulosic ethanol. However, the development of efficient low-cost technologies to convert lignocellulosic biomass to ethanol at competitive costs seems distant. Deconstruction of biomass to separate all biopolymers with minimal degradation, cost of enzymes, and fermentation of pentose sugars are some of the daunting challenges for cellulosic ethanol production. To date, only a few companies have begun commercial production of cellulosic ethanol with heavily supported government programs. Therefore, production of sugar-and starch-based fuel ethanol will continue in the near future, at least until cost-competitive technologies for producing ethanol from lignocellulosic biomass are developed.


• • • •

State the principal steps involved in fuel ethanol production from (i) corn kernels, (ii) corn stover, and (iii) sugar beet. What are the top ethanol producer states in the United States? Calculate ethanol yield (g ethanol/g corn) based on their ethanol production and corn consumption data. What are the key differences in the enzymes used in fuel ethanol production from cereal grains and lignocellulosic biomass? How is the wet-milling process different from the dry-grind process for corn ethanol production? How does the quick

244

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•


germ process incorporate good features of both the wetmilling and the dry-grind processes? Why is the ED pathway of glucose metabolism more efficient than the EMP pathway for ethanol production? Calculate the amount of ethanol produced from 250 g of (i) glucose and (ii) sucrose. Assume 10% sugar is utilized for combined microbial cell growth and maintenance and no secondary metabolites are produced. Why can absolute alcohol not be obtained from a conventional distillation system?


•

•

•

Based on land availability for feedstock production, process efficiency, and the effect on climate change, predict and compare US corn ethanol and Brazil sugarcane ethanol production in the coming decades. DDGS is an important coproduct/by-product of corn ethanol plant. Based on its physical and chemical composition, suggest appropriate alternative use of DDGS for its highvalue application. In glucose metabolism via the ED pathway, glucose-6phosphate is converted to 6-phosphogluconate instead of fructose-6-phosphate in EMP pathway. What is the enzyme (s) responsible for these different pathways? Why is the ethanol yield from glucose different from that of sucrose?

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; Beverages from Grains: Beverages: Distilled; Fermentation: Origins and Applications; Carbohydrates: Carbohydrate Metabolism; Non-food Products from Grains: Utilization of the Whole Cereal Plant to Maximize its Value.

Further Reading Alternative Fuels Data Center, Department of Energy, USA. http://www.afdc.energy.gov/ fuels/ethanol_blends.html (cited on January 23, 2015). Baeyens J, Kang Q, Apples L, Dewil R, Lv Y, and Tan T (2015) Challenges and opportunities in improving the production of bio-ethanol. Progress in Energy and Combustion Science 47: 60–88. Bothast RJ and Schlicher MA (2005) Biotechnological processes for conversion of corn into ethanol. Applied Microbiology and Biotechnology 67: 19–25. Chandel AK, Chandrasekhar G, Radhika K, Ravinder R, and Ravindra P (2011) Bioconversion of pentose sugars into ethanol: A review and future directions. Biotechnology and Molecular Biology Reviews 6(1): 8–20. Dien BS, Cotta MA, and Jeffries TW (2003) Bacteria engineered for fuel ethanol production: Current status. Applied Microbiology and Biotechnology 63: 258–266.

ePure (2014) European Renewable Ethanol, State of the Industry Report 2014. http:// www.epure.org/sites/default/files/publication/140612-222-State-of-the-IndustryReport-2014.pdf (cited on January 22, 2015). Franceschin G, Zamboni A, Bezzo F, and Bertucco A (2008) Ethanol from corn: A technical and economical assessment based on different scenarios. Chemical Engineering Research and Design 86: 488–498. Guragain YN, Wilson J, Staggenborg S, McKinney L, Wang D, and Vadlani PV (2013) Evaluation of pelleting as a pre-processing step for effective biomass deconstruction and fermentation. Biochemical Engineering Journal 77: 198–207. Hahn-Ha¨gerdal B, Karhumaa K, Fonseca C, Spencer-Martins I, and GorwaGrauslund MF (2007) Towards industrial pentose-fermenting yeast strains. Applied Microbiology and Biotechnology 74: 937–953. Huang HJ, Ramaswamy S, Tschirner UW, and Ramarao BV (2008) A review of separation technologies in current and future biorefineries. Separation and Purification Technology 62: 1–21. Jeffries TW (2006) Engineering yeasts for xylose metabolism. Current Opinion in Biotechnology 17: 320–326. Jeffries TW and Jin YS (2004) Metabolic engineering for improved fermentation of pentoses by yeasts. Applied Microbiology and Biotechnology 63: 495–509. Kumar S, Singh N, and Prasad R (2010) Anhydrous ethanol: A renewable source of energy. Renewable and Sustainable Energy Reviews 14: 1830–1844. Lin Y and Tanaka S (2006) Ethanol fermentation from biomass resources: Current state and prospects. Applied Microbiology and Biotechnology 69: 627–642. Madhavan A, Srivastava A, Kondo A, and Bisaria VS (2012) Bioconversion of lignocellulose-derived sugars to ethanol by engineered Saccharomyces cerevisiae. Critical Reviews in Biotechnology 32(1): 22–48. NCGA (2014) National Corn Growers Association, World of Corn, 2014. http://ncga. com/upload/files/documents/pdf/woc-2014.pdf (cited on January 23, 2015). Quintero JA, Montoya MI, Sanchez OJ, Giraldo OH, and Cardona CA (2008) Fuel ethanol production form sugarcane and corn: Comparative analysis for Colombian case. Energy 33: 385–399. RFA (2014) Renewable Fuels Association, Ethanol Industry Outlook. http://www. ethanolrfa.org/pages/annual-industry-outlook (cited on January 22, 2015). Rosentrater KA, Ileleji K, and Johnston DB (2012) Manufacturing of fuel ethanol and distillers grains – Current and evolving processes. In: Lie K and Rosentrater KA (eds.) Distillers Grains Production, Properties, and Utilization. New York: CRC Press, Chapter 5. Shihadeh JK, Huang H, Rausch KD, Tumbleson ME, and Singh V (2014) Vacuum stripping of ethanol during high solids fermentation of corn. Applied Biochemistry and Biotechnology 173: 486–500. Singh V and Eckhoff SR (1997) Economics of germ preseparation for dry-grind ethanol facilities. Cereal Chemistry 74(4): 462–466. Sorda G, Banse M, and Kemfert C (2010) An overview of biofuel policies across the world. Energy Policy 38: 6977–6988. USDA-GAIN (2014) United States Department of Agriculture (USDA), Foreign Agricultural Service, Global Agricultural Information Network (GAIN). Biofuels Annual – Brazil (GAIN report number BR14004), EU-28 (GAIN report number NL4025), China (GAIN report number CH14038), India (GAIN report number IN4055), Canada (GAIN report number CA14109), Japan (GAIN report number JA4018), Australia (GAIN report number AS1415), Indonesia (GAIN report number ID1420), Thailand (GAIN report number TH4057). http://gain.fas.usda.gov/Pages/ Default.aspx (cited on January 20, 2014). Vane LM (2008) Separation technologies for the recovery and dehydration of alcohols from fermentation broths. Biofuels, Bioproducts and Biorefining 2: 553–588. Vleet JH and Jeffries TW (2009) Yeast metabolic engineering for hemicellulosic ethanol production. Current Opinion in Biotechnology 20: 300–306. Walker GM (2011) 125th anniversary review: Fuel alcohol: Current production and future challenges. Journal of the Institute of Brewing 117: 3–22.

Biodiesel Y Yan, Huazhong University of Science and Technology, Wuhan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Chemical structure and properties of biodiesel from grain oils. Methods to produce biodiesel from grain oils. Parameters affecting yield of biodiesel from grain oils. Development of biodiesel from grain oil in the world. Advantages of combustion emissions of biodiesel.

Learning Objectives From this section, you will acquire knowledge of the following:

• • •

Chemical structure and properties of biodiesel, a green and sustainable fuel, from grain oils and how biodiesel is prepared. How many advantages can biodiesel bring? What does the future hold for biodiesel?

Introduction Besides fuel alcohol, oil from grain can also be easily converted into a fuel. Given the depletion of fossil oil and deterioration of the environment, renewable and clean energies, such as biodiesel, are becoming very important for the sustainable development of mankind. Biodiesel as one promising alternative to fossil fuel for diesel engines has become increasingly important due to the environmental consequences of petroleum-fueled diesel engines and the diminishing petroleum resources. Biodiesel is a mixture of mono-alkyl esters produced from renewable biological sources, such as vegetable oils, animal fats, waste cooking oil, and algae oil. In recent decades, biodiesel has been drawing wide attention for its ability to replace fossil fuels, which are likely to get exhausted in the future. Additionally, the environmental issues caused by the emission of gases from the combustion of fossil fuels have also encouraged the production of biodiesel, which is considered to be a carbon-neutral fuel as its carbon content is originally fixed from the atmosphere. It is therefore of great significance to develop biodiesel from grain oils.

Chemical Structure and Properties of Biodiesel from Grain Oils It is established that Grain oils mainly consist of triglycerides with a small fraction of diglycerides and monoglycerides. They have long chains with multiple branches leading to large-size molecules. The molecular weight of grain oils ranges from 850 to 995. The kinematic viscosity and density of grain oils are much higher than those of diesel due to their higher molecular weight and complex structure. To reduce the viscosity of oil,


methyl or ethyl alcohol is used to replace glycerol through transesterification reaction. Biodiesel can be synthesized by chemically combining any natural oil or fat including grain oils with an alcohol such as methanol or ethanol via catalysis by an alkali/acid or a lipase (see Figure 1). Methanol has been the most commonly used alcohol in the commercial production of biodiesel. Several researchers on biodiesel have proved that the fuel made by grain oil can be used effectively on diesel engines. Moreover, the energy density of biodiesel is quite close to regular diesel. Similarities between the combustion properties of biodiesel and petroleum-derived diesel have made the former one of the most promising renewable and sustainable fuels for the automobile. Catalysts for the transesterification reaction can be roughly classified into two categories – chemical and enzymatic. Chemically, the transesterification reaction can be acid- or basecatalyzed. The reaction can also be catalyzed by lipases. Though biodiesels are esters of natural oils, different oils retain similar chemical and physical properties when they are transesterified. Table 1 is a list of fatty acid profiles of possible biodiesel feedstock of grains, such as maize, rapeseed, soybean, sesame, peanut, sunflower, peanut, rice bran, wheat grain, crambe, linseed, safflower seed, and cottonseed.

Methods to Produce Biodiesel from Grain Oils According to the history of biodiesel, there are four mainstream approaches for the preparation of biodiesel from natural oils. They are summarized as follows.

Direct Use and Blending In the 1980s, the concept of employing vegetable oil as fuel was already in place. Bartholomew fully discussed the concept of using food oils for fuel and proposed that vegetable oil, alcohol, and some form of renewable energy must begin to take the place of nonrenewable resources. In 1980, Caterpillar Brazil used precombustion chamber engines with a mixture of 10% vegetable oil to maintain total power without any change to the engine. A blend of 20% vegetable oil and 80% diesel fuel proved to burn out successfully, but a substitution of 100% vegetable oil for diesel fuel was not as successful. Some shortterm experiments use up to a 50:50 ratio. At that time, the effects of vegetable oil fuels on engine performance and durability were a focus. Anon even reported that a diesel fleet was powered with filtered, used frying oil with a blend of 95% used cooking oil and 5% diesel fuel. However, preheating was needed to compensate for cooler ambient temperatures. No coking and carbon buildup problems took place. The only problem was lubricating oil contamination causing viscosity increase owing to the polymerization of polyunsaturated vegetable oils. Altogether, the advantages of vegetable oils as diesel

http://dx.doi.org/10.1016/B978-0-12-394437-5.00138-8

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NON-FOOD PRODUCTS FROM GRAINS | Biodiesel

fuel are liquid nature portability, with 80% of diesel fuel heat content, ready availability, and renewability. The disadvantages are higher viscosity, lower volatility, and the reactivity of unsaturated hydrocarbon chains. Problems appear only after the engine has been operating on vegetable oils for longer periods of time, especially with direct injection engines. The problems include (1) coking and trumpet formation making fuel atomization to occur improperly or as a result of plugged orifices, (2) carbon deposits, (3) oil ring sticking, and (4) thickening and gelling of the lubricating oil resulting from contamination by vegetable oils.

Microemulsions In order to solve the problem of the high viscosity of vegetable oils, microemulsions with solvents, for example, methanol, ethanol, and 1-butanol, have been studied. Microemulsion is defined as a colloidal equilibrium dispersion of optically isotropic fluid microstructures with dimensions generally in the 1–150 nm range formed spontaneously from two normally immiscible liquids and one or more ionic or nonionic amphiphiles. Microemulsions are capable of improving spray characteristics through explosive vaporization of low-boiling constituents in the micelles. Short-term performances of both ionic and nonionic microemulsions of aqueous ethanol in soybean oil were similar to that of No. 2 diesel, despite the lower cetane number and energy content. However, to date, the durability has not yet been determined. Ziejewski et al. made an emulsion of 53% (vol) alkali-refined sunflower oil, 13.3% (vol) 190-proof ethanol, and 33.4% (vol) 1-butanol. This nonionic emulsion had a viscosity of 6.31 cSt at 40 C, a CH2-OOC-R1

CH2-OH

R1-COOR’ Catalyst

CH-OOC-R2

+ 3 R’OH

R2-COOR’

CH2-OOC-R3 Triglycerides

Short chain alcohols

+

CH-OH

R3-COOR’

CH2-OH

Fatty acid methyl esters

Glycerol

Figure 1 Formula of biodiesel production with short-chain alcohols as acyl acceptors. Table 1

cetane number of 25, and an ash content of < 0.01%. With the increase of 1-butanol, lower viscosities and better spray patterns were obtained. In a 200 h laboratory test, no marked deteriorations in performance occurred, but irregular injector needle sticking, heavy carbon deposits, incomplete combustion, and an increase in lubricating oil viscosity were observed.

Thermal Cracking Using 100% pure vegetable or animal fats as diesel fuel has many drawbacks: high fuel viscosity, low power output, thickening and gelling of the lubricating oil, oxidative stability, and low volatility resulting from carbon deposits due to incomplete combustion. Pyrolysis may be a possible way to solve these problems. Pyrolysis is defined as the conversion of one substance into another by means of heat or by heat with the aid of a catalyst. It involves heating in the absence of air or oxygen and cleavage of chemical bonds to generate small molecules. The pyrolyzed material can be any oil such as vegetable oils, animal fats, natural fatty acids, and methyl esters of fatty acids. The first pyrolysis to synthesize petroleum from vegetable oil happened in World War I. During that time, many investigators had studied the pyrolysis of vegetable oils to obtain products suitable for fuel. In 1947, Chang and Wan reported a large scale of thermal cracking of tung oil calcium soaps. Tung oil was first saponified with lime, then thermally cracked to obtain a crude oil, and further refined into diesel fuel and small amounts of gasoline and kerosene. Approximately 68 kg of saponified tung oil could produce 50 l of crude oil. Catalysts, mainly metallic salts, were applied in several studies. The generated products were paraffins and olefins similar to those present in petroleum sources. Soybean oil was also thermally decomposed and distilled with a standard American Society for Testing and Materials (ASTM) distillation apparatus. Sunflower oil was used as a high oleic oil control. The total identified hydrocarbons obtained from the distillation of soybean and high oleic oils in sunflower were 73–77% and 80–88%, respectively. The main compositions were alkanes and alkenes, accounting for 60% of the total oil weight. Carboxylic acids accounted for another 9.6–16.1% of the total weight.

Fatty acid composition of possible feedstock for biodiesel from grain species

Oils

C16:0

Maize Rapeseed Soybean Peanut Sesame Rice bran Wheat grain Sunflower Peanut Crambe Linseed Safflower Seed Cottonseed

11.7 3.5 11.4 11.4 13.0 11.7–16.5 20.6 7.1 8.5 2.1 5.0 7.3 28.3

C16:1

C18:0

C18:1

C18:2

C18:3

C20:0

25.2 64.4 20.8 48.3 53.0 39.2–43.7 16.6 25.5 51.6 18.9 20.0 13.5 13.3

60.6 22.3 53.8 32.0 30.0 26.4–35.1 56.0 62.4 26.0 9.0 18.0 77.0 57.5

0.5 8.2 9.3 0.9

0.2

1.0

1.9 0.9 4.4 2.4 4.0 1.7–20.5 1.1 4.7 6.0 0.7 2.0 1.9 0.9

0.1

0.3 1.3

C20:1

C22:0

C22:1 n9

2.5

C24:0

Others

1.2

0.4–0.6

0.4–0.9

2.9

1.8 0.3

6.9 55.0

2.1

0.8

58.5

1.1 0.2

NON-FOOD PRODUCTS FROM GRAINS | Biodiesel Transesterification Transesterification, also called alcoholysis, is the reaction of a fat or oil with an alcohol to yield esters and glycerol. The reaction is shown in Figure 1. A catalyst is usually employed to enhance the reaction rate and yield. Due to the reversible nature of the reaction, excess alcohol is often used to shift the equilibrium to the product side. Methanol, ethanol, propanol, butanol, and amyl alcohol are conventionally used in the transesterification process, while methanol and ethanol are the most frequently used, especially methanol because of its low cost and its physical and chemical advantages of being polar and the shortest chain alcohol. It can quickly react with triglycerides, and the catalyst NaOH can be easily dissolved in it. Generally, to stoichiometrically complete a transesterification, a 3:1 molar ratio of alcohol to triglycerides is needed. Practically, the molar ratio must be much higher in order to drive the equilibrium to a maximum yield of ester. The reaction can be catalyzed by alkalis, acids, or enzymes. The alkalis include NaOH, KOH, carbonates, and the corresponding sodium and potassium alkoxides, such as sodium methoxide, sodium ethoxide, sodium propoxide, and sodium butoxide. Sulfuric acid, sulfonic acid, and hydrochloric acid are usually used as acid catalysts. Alkali-catalyzed transesterification is much faster than acidcatalyzed transesterification and is most frequently used commercially. However, chemical technologies have some obvious shortcomings, such as high requirement of large amount of energy and for equipment, pollution emission, and complex downstream processes. Most of these disadvantages can be avoided by using biotechnological biodiesel production. Therefore, there is current interest in using lipases as the biocatalyst to commercially convert vegetable oils and fats to Fatty Acid Methyl Ester (FAME) as biodiesel fuel, since it is more efficient, is highly selective, involves less energy consumption (reactions can be carried out in mild conditions), and produces less side products or waste (environmentally favorable). Most of the recent research has involved determining the best enzyme source and optimizing the reaction conditions (substrate molar ratio, solvent or no solvent, temperature, water content, free fatty acid level, percent conversion, acyl migration, and substrate flow rate in packed bed bioreactors) to

Table 2

247

improve the yield of biodiesel comparable with base-catalyzed reactions and for possible industrial scale-up and use. Lipases conventionally used in biodiesel production are mainly obtained from bacteria, yeast, and filamentous fungi (see Table 2). Among all the bacterial lipases employed in transesterification, the most widely reported one is Burkholderia cepacia lipase (BCL). The immobilized form of this enzyme has been used for biodiesel production in isooctane and solvent-free systems. Another typical bacterial lipase is Pseudomonas fluorescens lipase, and in our previous research, the free enzyme was used for biodiesel production. Other bacterial lipases reported for biodiesel production include Photobacterium lipolyticum lipase and Chromobacterium viscosum lipase. Candida antarctica lipase B (CALB) is the most widely applied lipase from yeast. With the aim of creating a powerful lipase for transesterification, this enzyme has been subjected to different immobilization methods and numerous chemical modification strategies. Another extensively used yeast lipase is the one obtained from Candida sp. 99–125 (also Yarrowia lipolytica lipase 2), which has been immobilized on textile and used for biodiesel production in China. In addition, Candida rugosa lipase has also been used for biodiesel production with different feedstocks in various media. Examples of lipases obtained from filamentous fungi and used in alcoholysis include Thermomyces lanuginosus lipase, Rhizopus oryzae lipase, Penicillium expansum lipase, and Geotrichum sp. lipase. In addition, porcine pancreatic lipase (type II) has also been used for biodiesel preparation, which produced a low transesterification yield of only 18.60%. A major problem with lipase reaction with alcohols is enzyme inactivation caused by the volumes of alcohol. This problem has been studied and presumably solved by stepwise addition of methanol. This technique could alleviate the methanol inactivation of Candida antarctica lipase and resulted in 90% yield of FAME from waste oil. The enzyme is kept stable for 100 days and could be recycled 50 times without a significant loss of original activity. A few studies have considered the nature of the alcohols used in the transesterification reaction. Liu et al. studied the effect of monohydric alcohols on enzymatic transesterification for biodiesel production and found lipase presented different kinetic patterns with respect to the monohydric alcohols in solvent-free and t-butanol systems.

Gene resources of lipases for biodiesel production

Source of lipases

Branch name

Supplier

Source of oil

Yields (%)

Burkholderia cepacia Pseudomonas fluorescens Photobacterium lipolyticum Chromobacterium viscosum Candida antarctica Candida sp. 99-125 Candida rugosa Thermomyces lanuginose Rhizopus oryzae Penicillium expansum Geotrichum sp. Porcine pancreatic lipase (type II)

Lipase PS Lipase AK None None Novozym 435

Amano Amano None None Novozymes

Lipase AY Lipozyme TL IM Rhizopus oryzae lipase None None None

Amano Sigma Novozymes Sigma Leveking None Sigma

Soybean oil Soybean oil Waste oils Jatropha oil Olive oil Various oils Rapeseed soap stock Crude palm oil Various oils Maize oil Waste cooking oil Palm oil

98.0 83.8 70.0 92.0 90.0 >87 63.6 96.2 >92 86.0 85.0 92.2

248


The addition of cosolvents such as t-butanol (the so-called solvent engineering) appeared to prevent methanol inactivation of the lipase. Li et al. have investigated biodiesel preparation catalyzed by compound lipase in cosolvent. The treatment accelerated the solubility of methanol in oil and dissolved glycerol, which helped maintain lipase activity. The yields of biodiesel in cosolvent markedly exceeded those in the pure organic solvents. The mixture of cosolvent with 60% acetonitrile and 40% t-butanol (v/v) proved to be the optimum. It has been shown that enzyme-catalyzed alcoholysis reactions can be performed in the presence or absence of a solvent, depending on different types of lipases. It also requires less energy and practically no purification to obtain FAME compared with acid–base-catalyzed alcoholysis, where soap formation presents a downstream processing challenge. Biocatalyst removal, if immobilized lipase is used, is by simple filtration or is not required if a packed bed bioreactor is used for the continuous production of biodiesel. Generally, enzyme catalysts at 4–10 wt% result in FAME yields of 50–99% in 3–96 h at 40–60 C.

Parameters Affecting Yield of Biodiesel from Grain Oils The Effects of Moisture and Free Fatty Acids Generally, the substrates used for the alkali-catalyzed transesterification of glycerides should match certain specifications. The acid value of glycerides must be < 1, and all substrates should be absolutely anhydrous. If the acid value is beyond 1, more NaOH is needed to neutralize free fatty acids. Moisture can cause saponification resulting in the consumption of catalysts and reduction of catalyzing efficiency. The resulting soaps can increase viscosity and form gels, which will make downstream glycerol separation very difficult. If the reactants do not meet the earlier requirements, the yield of esters will significantly decline. Sodium hydroxide or sodium methoxide can also react with CO2 in moist air, leading to the reduction in catalyzing effectiveness.

The Effect of Molar Ratio The molar ratio of alcohol to triglyceride is one of the most important variables affecting yield of esters in the transesterification reaction. The stoichiometric ratio required in transesterification is 3 mol of alcohol to 1 mol of glyceride to generate 3 mol of fatty acid esters and 1 mol of glycerol. The molar ratio depends on the type of catalyst used. An acid-catalyzed transesterification requires a 14–16:1 ratio of methanol to soybean oil, while for alkali-catalyzed reactions, only a 6:1 ratio is required to achieve the same ester yield in a given reaction duration. The practical range of molar ratio is from 3.25 to 5.50:1 methanol to vegetable oil. For example, the ratio of 4.8:1 resulted in a yield of 97–98%, depending upon the quality of the oils. If a threestep process was adopted, the ratio could be lowered to 3.3:1. Methanol loading over 1.75 equivalents tends to block glycerol separation through gravity, risking in adding more production cost. Rapeseed oil was methanolyzed with 1% NaOH or KOH, and a 6:1 ratio of methanol to oil gave the best conversion of more than 98%. If a higher volume of free fatty acids is present in oil substrate, the molar ratio will run as high as 15:1 when

catalyzed by acid. The studies on the effect of the molar ratio (from 1:1 to 6:1) on the ester conversion of vegetable oils, such as soybean, sunflower, peanut, and cottonseed oils, showed similar results and achieved the highest conversions of 93–98% at a molar ratio of 6:1.

The Effect of Catalyst The catalysts of transesterification are of three types: alkali, acid, and enzyme. Alkali-catalyzed transesterification reaction is much faster than acid-catalyzed. However, if a glyceride contains higher free fatty acids and more moisture, acidcatalyzed transesterification is more selective. The acids can be the condensed H2SO4, H3PO4, HCl, or organic sulfonic acid. Alkalis include NaOH, CH3ONa, KOH, CH3OK, NaNH2, NaH, KNH2, and KH. CH3ONa is more effective than NaOH due to the assumption that a small quantity of water will be produced upon mixing NaOH and CH3ONa. NaOH is generally applied to catalyze the transesterifications in large-scale processing because it is much cheaper. Ester conversions at the 6:1 ratio of methanol to oil catalyzed by 1% NaOH or 0.5% NaOCH3 are almost the same in 60 min. The transesterification between soybean oil and methanol, ethanol, and butanol was catalyzed with 1% concentrated H2SO4, and a 30:1 ratio resulted in high conversions to methyl ester. In 1996, an immobilized lipase was used to catalyze the methanolysis of corn oil in flowing supercritical carbon dioxide, resulting in an ester conversion of more than 98%.

The Effect of Reaction Duration The conversion rate will rise with increment of reaction time. Peanut, cottonseed, sunflower, and soybean oils were transesterified with 0.5% CH3ONa at a 6:1 ratio of methanol to oil and 60 C, and an approximate yield of 80% was obtained for soybean and sunflower oils after 1 min. The conversions were almost the same for all four oils (93–98%) within 1 h. For acidcatalyzed transesterification, the optimal reaction duration is 6 h. However, with respect to lipase-catalyzed transesterification, the reaction time may run as long as 8–36 h. Generally, free lipases need longer time than immobilized ones. However, using immobilized lipases on nanoparticles, the reaction duration could be even shortened to < 3 h.

The Effect of Reaction Temperature Transesterification reaction can be carried out at different temperatures, depending on the oil substrates used. Castor oil could be satisfactorily methanolyzed at 20–35 C with a molar ratio of 6:1–12:1 and 0.005–0.35% (w/w) of NaOH catalyst. Using 1% NaOH as catalyst, refined soybean oil could be transesterified with methanol at 6:1 at three different temperatures (32, 45, and 60 C). The ester yields were, respectively, 94%, 87%, and 64% for 60, 45, and 32 C after 30 min, while ester formation was even identical for 60 and 45 C and only slightly lower for 32 C after 1 h. For lipasecatalyzed transesterification, the reaction often occurs at 35–60 C, depending on the thermostability of the lipase used for the reaction. For example, BCL can function at 60 C and even 70 C. The higher the temperature, the more esters

NON-FOOD PRODUCTS FROM GRAINS | Biodiesel will be converted within the optimum temperature range. As can be seen, the temperature clearly influenced the reaction rate and yield of esters.

Development of Biodiesel from Grain Oil in the World As predicted by the International Energy Agency, the global energy demand will be more than 50% higher than the current requirement in 2030. From 2006 to 2030, the energy consumption in the Asia Pacific region is estimated to increase at 2.75% per year or grow 32% faster than the average demand of the world. In order to meet the fast-growing energy consumption, the emerging biofuel industry requires tremendous development within a short period of time. At the same time, the development of the biodiesel industry can provide jobs, cause economic growth, reduce reliance on fossil oil, and eliminate air pollution and greenhouse gas emission. Therefore, many countries such as the United States, Brazil, Germany, Japan, and India have explored and commercially used biodiesel in the blends for vehicles. So far, various kinds of feedstock, such as vegetable oils, animal fats, waste oils, and greases, which contain free fatty acids and/or TGs, could be easily converted into biodiesel via alkali- or acidcatalyzed or lipase-catalyzed preparation technologies. The feedstock used for biodiesel production differs from one country to another. For example, in the United States, corn and soybean oils are widely used. In the European countries, flaxseed and rapeseed oils are commonly employed, while in the Asian countries, palm and waste oils are usually used. In 2013, over 130 million gallons of biodiesel has been produced in the United States. In Europe, biodiesel is currently the most important biofuel, and 82% of the biofuel production is biodiesel. More than 40% of biodiesel is produced by Germany, which is the biggest producer, followed by France and Italy. In the European Union, around 1.4 million hectares (ha) of arable land is used for biodiesel production, and over 40 biodiesel plants have been established. Yet, the number of biodiesel plants is growing rapidly, and most of them are located in Germany, Italy, the Czech Republic, Austria, France, and Sweden. In South America, a biodiesel plant with a production of 120 000 kg day 1 has been established in Rio Grande do Sul, south of Brazil. The trial results have been successful, paving the way for the large-scale industrial production of biodiesel. In Asian countries, biodiesel development is being given great attention. For example, in China, two demonstration assembly lines with a capacity of 10 000–20 000 t year 1 of lipasecatalyzed biodiesel production have been set up in Yiyang City of Hunan province, Shanghai, and Qinhuangdao City of Hebei province, where the technology employed is more environment friendly. Thus, biofuel production has a potential to become a more vital, prosperous industry, when compared with the fossil oil industry, which had played an important role in the history of mankind. Nevertheless, with the severity of food crisis, edible oil used for biodiesel feedstock threatens human food, especially in developing countries and/or populous countries, like India and China. Therefore, developing nonedible oil as biodiesel feedstock, such as microbial oil, wood oil, and waste oil, becomes more attractive. Additionally, with the ability to

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capture renewable energy through photosynthesis and produce high yields from controlled microbial cultivation, microalgae are potentially valuable organisms for economic and industrial-scale production processes. Currently, microalgae are becoming the focus of a promising approach to produce vast volumes of oil feedstock for biodiesel preparation.

Advantages of Combustion Emissions of Biodiesel Biodiesel as a green energy can be a suitable alternative for fossil fuel. It can prevent air pollution via reducing the emission of CO2, SO2, CO, and HC. The carbon cycle of biodiesel from sustainable resources is a zero budget regarding the photosynthetic process and combustion emission as a whole, particularly due to the fact that plants absorb more CO2 than those discharged by the biodiesel combustion process. Thus, using biodiesel can more effectively reduce the emission of CO2, protect the natural environment, and maintain the ecological balance, when compared with the use of fossil fuel. The emission of SO2 in the combustion process of biodiesel is also much lower than normal diesel oil because of its low sulfur content. Thus, the use of biodiesel instead of normal diesel oil will effectively reduce acid rain, which represents a serious threat to the environment and human infrastructure, such as acidification of soil, surface, and groundwater, damage to forest and vegetation, and corrosion of buildings and historical monuments made from calcium-containing stones. Furthermore, CO, HC, and particulate matter will be less discharged, because ester compounds in biodiesel contain oxygen, promoting clean burning. The use of biodiesel in a conventional diesel engine results in a substantial reduction of hydrocarbons, aromatic hydrocarbons, carbon monoxide, alkenes, aldehydes, ketones, and particulate matter. Nitrogen oxide emissions are slightly increased if the engine management remains unchanged. However, this can be optimized using special software and biodiesel sensors. It has been estimated that soy biodiesel reduces carbon dioxide by 78% on a life cycle basis. In addition, biodiesel is the first alternative fuel that has fully completed the health effects testing requirements of the Clean Air Act of the United States.


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Explain, in your own words, the chemical structure and properties of biodiesel from grain oils. Describe briefly, in your own words, the direct use and blending methods used to produce biodiesel from grain oils. Describe briefly, in your own words, the microemulsion techniques used to produce biodiesel from grain oils. Describe briefly, in your own words, the thermal cracking methods used to produce biodiesel from grain oils. Describe briefly, in your own words, the transesterification methods used to produce biodiesel from grain oils. Explain, in your own words, the parameters that affect yield of biodiesel from grain oils. Discuss, in your own words, the development of biodiesel from grain oil worldwide.

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State, in your own words, the advantages of the combustion emissions of biodiesel.


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Although humankind has made a great breakthrough in the production of biodiesel from grain oils, developing biodiesel from grains is increasingly contradictory to the development of food, considering the shortage of food worldwide, especially in the developing countries. How can mankind find effective solutions to this contradiction? To develop nonedible forestry oils or/and microalgal oils may be a good alternative way, but what needs to be done next? Moreover, plants utilize solar energy less effectively, but how can this be improved? In addition, at present, catalysts or well-controlled conditions are employed to produce biodiesel from grain oils. In the future, can an artificial organism be developed to directly secrete biodiesel so as to eliminate the preparation procedure, thereby saving on the production cost?

See also: Non-food Products from Grains: Fuel Alcohol Production.

Further Reading Ahmad AL, Yasin N, Derek C, and Lim JK (2011) Microalgae as a sustainable energy source for biodiesel production: A review. Renewable and Sustainable Energy Reviews 15: 584–593.

Anonymous (1982) Filtered used frying fat powers diesel fleet. JAOCS 59: 780A–781A. Bartholomew D (1981) Vegetable oil fuel. JAOCS 58: 286A–288A. Chang CC and Wan SW (1947) China’s motor fuels from tung oil. Industrial and Engineering Chemistry 39: 1543–1548. da Cunha ME, Krause LC, Moraes MSA, et al. (2009) Beef tallow biodiesel produced in a pilot scale. Fuel Processing Technology 90: 570–575. Janaun J and Ellis N (2010) Perspectives on biodiesel as a sustainable fuel. Renewable and Sustainable Energy Reviews 14: 1312–1320. Li Q, Zheng JJ, and Yan YJ (2010) Biodiesel preparation catalyzed by compound-lipase in co-solvent. Fuel Processing Technology 91: 1229–1234. Liu Y, Tan H, Zhang X, Yan YJ, and Hameed BH (2010) Effect of monohydric alcohols on enzymatic transesterification for biodiesel production. Chemical Engineering Journal 157: 223–229. Rakopoulos CD, Antonopoulos KA, Rakopoulos DC, Hountalas DT, and Giakoumis EG (2006) Comparative performance and emissions study of a direct injection diesel engine using blends of diesel fuel with vegetable oils or bio-diesels of various origins. Energy Conversion and Management 47: 3272–3287. Schwab AW, Bagby MO, and Freedman B (1987) Preparation and properties of diesel fuels from vegetable oils. Fuel 66: 1372–1378. Schwab AW, Dykstra GJ, Selke E, Sorenson SC, and Pryde EH (1988) Diesel fuel from thermal decomposition of soybean oil. JAOCS 65: 1781–1786. Sharma YC, Singh B, and Upadhyay SN (2008) Advancements in development and characterization of biodiesel: A review. Fuel 87: 2355–2373. Sonntag NOV (1979) Reactions of fats and fatty acids. In: Swern D (ed.) Bailey’s Industrial Oil and Fat Products, vol. 1, p. 99. New York: Wiley 4th edn. Yan YJ, Li X, Wang GL, et al. (2014) Biotechnological preparation of biodiesel and its high-valued derivatives: A review. Applied Energy 113: 1614–1631. Ziejewski M, Kaufman KR, Schwab AW, and Pryde EH (1984) Diesel engine evaluation of a nonionic sunflower oil-aqueous ethanol microemulsion. JAOCS 61: 1620–1626.


Contents Evaluation of Wheat-Grain Quality Attributes Grain Quality Attributes for Cereals Other than Wheat Cereals: Breakfast Cereals Extrusion Technologies Starch: Uses of Native Starch Starch: Modification b-Glucans: Measurement and Processing

Evaluation of Wheat-Grain Quality Attributes CF Morris, USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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understand the analysis of cereal quality, one must appreciate the array of end uses of the various cereals.

Quality is defined as the ‘degree of excellence’ or suitability of a cereal grain for a specific food or end use. Individual quality traits are variably affected by genetics and the environment. Wheat is the most complex cereal in terms of end-use quality and variety. Major categories of wheat foods include fermented breads, steamed breads, flat breads, crackers, cookies, cakes, noodles, ready-to-eat cereals, pasta, and couscous. Quality tests can involve end-product tests such as bread or component tests such as gluten.

Learning Objective

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To achieve an understanding of what constitutes end-use quality of cereals, how to evaluate the key factors of quality, and where variation in quality originates.

Why Is the Quality of Cereals Analyzed? Quality of cereals is analyzed because cereal grains (and the products derived from them) are biological entities and can vary dramatically. Further, the ways in which different samples of the same cereal grain vary can have a profound impact on processing, nutrition, and consumer appeal. So, if it is important to analyze quality, what is ‘quality’? Quality in this context is ‘the degree or grade of excellence.’ Quality may also be thought of as suitability. Consequently, to


General Considerations Cereal quality can be considered at two levels: (1) characteristics of grain lots or samples and (2) the intrinsic quality of the grain itself that results from an interplay of genetics and the weather, management, postharvest storage, pathogens, insects, etc. The first of these characteristics of grain lots includes not only the intrinsic quality of the cereal grains themselves but also such things as the presence of seeds of other species and seeds of different types of the same species (e.g., soft red wheat contamination in hard white wheat) and the presence of dirt, stones, chaff, animal filth, or insects. This article assumes that a given lot of grain has been cleaned and is free of these sorts of contaminants. However, in practice, the complete removal of some of these factors is either physically impossible or economically impractical. Consequently, standards for inspecting and grading grain often severely penalize these factors. The second level of quality consideration is at the intrinsic level. As mentioned in the preceding text, all intrinsic properties result from the interplay of the genetic makeup of the plant and the way in which it interacts with (or responds to) external factors. Some external factors exert a very dramatic effect on quality, and the range of effects may be an order of magnitude greater than that observed among a group of varieties. In the other extreme, the expression of some quality genes is essentially minimally affected by external influences such that variation among grain lots is essentially controlled by differences in genes. Between these two extremes is a full range of quality

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traits that have greater or lesser degrees of genetic versus environmental influence. Table 1 lists a few examples of quality traits that are variously affected by external factors.

Assessment of Flour Quality

Wheat The analysis of the quality of wheat is by far the most complex of all the cereal grains. This complexity reflects the tremendous diversity of the genetics of wheat, the tremendous diversity of the uses of wheat, and the central role that wheat plays in the diet of much of humankind. Wheat has distinguished itself from all other cereals and grain legumes because of the unique properties of its endosperm storage proteins. These proteins, classified as glutenins and gliadins, when hydrated and mixed (by hand or machine) form ‘gluten.’ Gluten is unique in that it exhibits both viscous and elastic properties. These properties allow gluten to form a continuous membrane that can retain the gasses produced in fermenting doughs. The retention of these gasses greatly decreases the density of doughs, and upon baking, this light, airy structure is fixed. A simple model describes a dough ‘foam’ transformed to a ‘sponge.’ An almost limitless number of foods are made from wheat. Wheat flour, bran, etc. are also important food ingredients. Table 2 presents the major uses of wheat and flour. The quality of a particular flour is not necessarily low or high until it is judged in the context of a particular end use. For example, a flour that exhibits very high bread baking quality generally also has very poor cookie or cake baking quality. Therefore, wheat Table 1 Quality traits in cereals that range from highly to minimally affected by external factors Quality traits highly influenced by external factors Test weight Moisture content Protein content Presence of mycotoxins Preharvest sprouting ‘Bug’ protease (Eurygaster spp.) Frost damage

Intermediate Seed size Vitreosity Milling quality Dough rheology Baking quality Malt extract

Quality traits minimally influenced by external factors Seed color Starch composition Protein composition Grain hardness Tannin content Polyphenol oxidase Rice aroma

Table 2

Major uses of wheat

Common name

Genus and species

Major uses


Many styles of pan breads, hearth breads, noodles, starch and gluten, animal feed Cookies (biscuits), cakes, pastries, noodles, animal feed Pasta, couscous

Wheat Bread wheat Soft wheat Durum wheat

quality is defined by an almost infinite number of different food products that contain flour, starch, gluten, bran, whole and cracked grain, sugar, fats, oils, etc.

Triticum aestivum L. Triticum turgidum L. subsp. durum Desf.

The main reason for assessing wheat flour quality is to predict its performance in commercial applications – either processing traits or end-product traits. Assessment of flour quality can be classified into two categories: end-product tests and component tests. Both have their own merits and are described in the succeeding text. End-product tests tend to produce a summation of quality – the sum total of all the components of quality and their interaction, if any. For this reason, end-product tests are generally considered the best predictors of commercial endproduct quality. However, end-product tests usually require more personnel, time, flour, and equipment compared with component tests. Component tests tend to assess one or more fundamental properties or components of flour, such that endproduct quality may be predicted. The advantage of component tests is that they are generally conservative of resources, quick, and amenable to large numbers of samples. Component tests also have the advantage of more precisely identifying why a particular flour may have better or poorer quality. The main shortcoming of component tests is their limited ability to capture all aspects of commercial end-product quality.

End-Product Tests End-product tests typically use a scaled-down, semiautomated or nonautomated procedure that mimics the large-scale industrial process. Product formula may match exactly that of the commercial product or may be a simplified, standardized test product. Commonly used standardized end-product tests include pan bread, cookies, cakes, and pasta. Additionally, laboratory-scale end-product tests have also been developed for steamed bread, flat breads, bagels, and noodles. Flour quality is assessed on the characteristics of the prepared product, for example, the volume and internal crumb appearance of bread loaves, the diameter of cookies, and the cooking loss of noodles and pasta.

Component Tests The use of component tests for flour quality assessment is founded on the premise that end-product (or processing) quality can be predicted from one or more attributes of the flour. Beyond predicting end-product quality, there is the practical necessity of determining the processing properties of flour so that plant production runs smoothly and efficiently. Endproduct quality and processing quality are closely linked. It is the inherent, fundamental physical and chemical properties of wheat flour that make it the single most important and diverse food in the world’s diet. It is also these fundamental properties that are characterized, and by doing so, the processing and end-product quality of a flour are predicted. In this context, these properties, or components, of wheat flour may be grouped as protein, starch, water relations, and color. Each of these will be dealt with in the following section.

PROCESSING OF GRAINS | Evaluation of Wheat-Grain Quality Attributes The quality and quantity of wheat flour are important basic properties. As discussed earlier, it is the viscoelastic nature of gluten that allows gasses produced during fermentation to be trapped in the dough, thereby increasing the volume and producing the appealing texture of bread. Likewise, it is these same gluten proteins that can impart a tough or undesirably chewy texture to many cakes, cookies, and pastries. The quantity of protein is often important to predicting end-use quality. Two main approaches are most common: determination of elemental nitrogen with an empirical conversion to protein and an empirically derived prediction of protein based on spectroscopy using specific wavelengths of light in the near-infrared (NIR) region. The techniques include Kjeldahl and combustion methods of elemental nitrogen determination (‘Dumas’) and NIR reflectance and transmission spectroscopy. The quantitative assessment of protein ‘quality’ or gluten functionality is substantially more challenging and usually empirical. Standard methods exist for the determination of gluten contents (not all protein is gluten and gluten is not all protein). Two other approaches to gluten quality include dough mixers and machines that record and characterize the elasticity and extensibility of doughs. In the first category are the mixograph and farinograph. In the second category are the extensigraph and alveograph. Recording dough mixers produce a curve from which assessments of gluten hydration, development, strength, and stability can be derived. Additionally, an assessment of optimum flour–water absorption can be made. The extensibility of gluten in doughs is assessed by the extensigraph by uniaxially stretching a dough piece to the point of failure. The alveograph biaxially stretches a dough piece by blowing a bubble using air pressure. The bubble volume is likewise increased to the point of failure. Recently, Brabender introduced the GlutoPeak that measures the torque of a continuously mixed hydrated sample. The time–torque curve is used to characterize the strength and mixing properties of the gluten. Starch can undergo profound physical–chemical changes. These changes relate primarily to the events known as gelatinization and gelation. During the gelatinization process, starch can interact with several times its own weight in water and, in doing so, forms a gel structure. The viscosity of the gel is highly dependent on the temperature, the proportion of water, and the presence of other ingredients. The characteristics of this gel are critical to the structure, texture, and quality of many foods. In many instances such as soup thickeners, the concomitant increase in viscosity associated with gelatinization is the main purpose for including wheat flour as an ingredient. Conversely, the hydrolysis of starch to simple sugars provides a ready source of fermentable carbohydrates for yeast fermentation. An important consideration in food processing related to gelatinization and gelation is the phenomenon known as ‘pasting’ that relates to the thermal transition of starch from an intact semicrystalline granule to a highly disordered hydrated structure. In the presence of water, heating causes starch hydrogen–hydrogen bonds to be replaced by water–starch hydrogen bonds. As such, a very large amount of water can interact with pasted starch. This process dramatically changes the viscosity of food systems. These starch gels are fragile structures and highly susceptible to shear thinning. As the amylose content of starch is altered

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genetically (see the succeeding text), starch pasting also changes. In the extreme, waxy wheat starch with zero amylose has dramatically different processing properties, especially in the context of puffing and extrusion processing. Wheat flour is about 75–80% starch on a dry weight basis. The starch content of flour can be measured directly using specific starch-degrading enzymes. The functional performance of starch–starch quality, primarily the gelatinization, gelation, and viscosity properties, is usually of much greater interest than the quantity of starch. Two common methods available for assessing starch quality are the Brabender Micro ViscoAmylo-Graph and the Perten Instruments Rapid Visco Analyzer (RVA). Both work on starch–water or flour–water slurries and record viscosity as a function of resistance to stirring during gelatinization and gelation during an operatorcontrolled heating regimen. In wheat, the factor primarily responsible for differences in starch quality is the ratio of amylose to amylopectin. In hexaploid wheat, three genes code for the enzyme responsible for the biosynthesis of amylose (this enzyme is termed ‘granulebound starch synthase’). When all three copies of the gene are present, a ‘normal’ amount of amylose is present, about 23–27% (starch basis). When all three genes/enzymes are absent, amylose is < 1% and the grain is referred to as ‘waxy’ (Figure 1). The presence of one or two genes produces an amylose content of about 18 2% or 21 2%, respectively. Very small changes in amylose content are associated with dramatic changes in starch functionality. Sometimes, the functional performance of starch has less to do with starch quality per se as it does with the presence and activity of starch-degrading enzymes. These enzymes may be of two sources: endogenous, the result of preharvest sprouting, or exogenous, in the form of malt flour or commercial fungal sources that are often added to pan bread formulas. The Micro Visco-Amylo-Graph and RVA can assess existing starch damage and can also assess potential in situ starch damage, which might occur during processing. Similarly, they can assess the potential effects of added amylase. The Perten Instruments ‘Falling Number’ test is widely used to estimate sprout damage and is based on viscometry during gelatinization. A weighted plunger is allowed to fall through a gelatinizing sample of ground grain or flour. Aimed primarily at assessing sprout

Figure 1 ‘Waxy’ (left) compared to ‘normal’ (right) amylose content wheat starch gels. Equal amounts of starch of each type were heated (c. 95 C) with water under constant stirring in a Rapid Visco Analyzer and then allowed to cool to room temperature. Waxy starch contains no amylose and produces gels that are more translucent, weaker, and viscous.

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damage, the method also incorporates inherent differences in starch gelatinization properties. Starch quality and performance are also affected by mechanical starch damage. As noted previously, damaged starch absorbs more water and is more susceptible to enzymatic attack. Although the level of starch damage is highly influenced by grain hardness, milling procedures have a major impact and different millstreams will differ markedly in damaged starch. Quantitative measures of starch damage rely on the susceptibility of granules to a-amylase attack or ability to bind I2/KI. CHOPIN Technologies SDmatic uses iodine absorption to measure starch damage. The third fundamental aspect of flour functionality relates to water relations. Even though gluten hydration during mixing and starch gelatinization are major contributors to water relations, water relations are often examined independently because (1) there are additional, often poorly characterized sources of water uptake and (2) often the simple sum total

Figure 2 Handheld color meter used to objectively measure food product color in the triaxial color space (L*a*b*) system. When analyzing raw noodle sheets, it is critical to use a standardized color tile for background, as shown.

expression of these various components is of immediate interest to the food processor. Assessment of water relations can be made by observing properties of doughs or from the way in which flour interacts with excess water or various solvents. As noted in the preceding text, most of the methods used to assess gluten strength also provide an estimate of the optimum hydration level of a dough. ‘Solvent retention capacity’ (SRC) tests now include methods that employ water, ethanol–water, sucrose–water, and Na–carbonate–water. The amount of solvent retained by the flour after hydrating and centrifuging is diagnostic of flour constituents. CHOPIN Technologies is introducing an automated instrument for measuring SRC. Finally, color is an important consideration, because food must be appealing to the eye and the other senses. Color in the sense of end-product quality may be considered in the context of the production or maintenance of desirable color or the prevention or reduction of undesirable color. A few examples are the golden-brown color of bread crust that results from Maillard reaction, the bright yellow color of pasta, and the prevention of darkening of Asian noodles. Although visual assessment of color is often satisfactory, the development of handheld reflectance colorimeters has made triaxial quantitation of color common (Figure 2). The importance of inherent color systems associated with wheat and flour varies, depending on the particular end product. For example, the whiteness of a soft wheat flour may be crucial to the appeal of an angel food cake, whereas it may matter little in a chocolate cake. Two products where color is especially important are pasta and noodles. Pasta requires high levels of yellow pigments to impart a bright, deep yellow appearance. Loss of color during boiling should be minimized. Noodles, on the other hand, must be bright, not dull, and should be creamy white at neutral pH and yellow at alkaline pH. Off-colors are unacceptable and generally result from chemical or enzymatic changes. Due to the importance of noodle color (especially brightness) and due to the tremendous range in noodle brightness produced from different wheats, noodle brightness has received considerable attention. A leading culprit in the loss of noodle brightness is the enzyme polyphenol oxidase (PPO). Small-scale assays exist that quickly assess PPO levels in grain (Figure 3).

Figure 3 Small-scale assay for assessing PPO levels in wheat grain. PPO activity is associated with noodle darkening; consequently lower levels of PPO are preferable and selected for among breeding lines. Shown are six small (2 ml) tubes that contain 1.5 ml of buffered L-dopa solution and five wheat kernels. The apparatus rotates the samples slowly for 30 min after which the amount of pink product (produced by PPO) is measured spectrophotometrically or judged visually.

PROCESSING OF GRAINS | Evaluation of Wheat-Grain Quality Attributes Lastly and beyond these four major categories of component traits, there are specific traits unique to certain foods or processes. Additionally, there are three practical considerations that are highly dependent on milling and on whether the wheat is hard or soft. These are flour moisture content, ash content, and particle-size distribution. Flour in the United States is targeted to 14% moisture content, and there are several methods for its accurate measurement, similarly ash. Ash is an old but extensively used method of assessing milling extraction and therefore things such as protein quality and color. The central part of the kernel is low in ash, while the bran is high. Flour from the central endosperm generally contains more functional protein (better protein quality) as opposed to flour from near the bran or outer portion of the kernel. By contrast, the outermost, subaleurone portion of the kernel usually has a higher absolute protein content. The production and composition of flours is dependent on the imperfect separation of the bran from the other anatomical structures of the wheat kernel. Similarly, bran often contributes undesirable colors. Soft wheats produce flours of smaller particle size and lower starch damage; durum wheats are at the other end of the scale, producing coarse semolina. Hard hexaploid wheats are intermediate. An interesting development is ‘soft durum,’ wherein the puroindoline genes from soft wheat have been translocated into durum. Kernel texture (see the succeeding text) is equivalent to soft hexaploid wheat.

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Figure 4 Cookies baked from soft (left) and hard (right) wheats that differ only in their Hardness gene. Near-isogenic soft (Ha) and hard (ha) wheat lines were milled and their flours baked using a standard AACC International cookie formula.

Intrinsic Quality of Wheat Grain and Grain Lots Grain hardness (kernel texture) is arguably the single most important aspect of wheat utilization (Figure 4). Durum wheats lack the genes responsible for softness and consequently are very hard, whereas hexaploids may be soft or hard, depending on the allelic state of these genes. Also, overlaid on this genetic system is the variation due to the environment. Measures of grain hardness are empirical but commonly used. A physical method, referred to as particle-size index, relies on the fact that upon grinding, soft wheats produce finer meals and flours. By sifting and weighing, wheats may be classified as soft or hard or assigned a quantitative numerical value. More recent developments in the assessment of grain hardness include an NIR spectrophotometric method and a single-kernel crushing device, the Perten SKCS 4100 (Figure 5). In addition to hardness, kernel mass and morphology affect end-use quality. Generally, millers prefer uniformly large, wellfilled (plump) kernels. The measurement of kernel mass is typically expressed in terms of thousand kernel weight, whereas kernel morphology is approximated using bulk density (hectoliter or bushel weight). The Perten SKCS 4100 device provides measures of kernel weight and outer dimension and hardness and moisture. Protein quantity and quality were discussed in the preceding text for flour. Since there is a strong and direct relationship between flour protein and grain protein, assessing these traits in grain is often desirable. The quality of protein is primarily controlled by genetics. The quantity of protein, however, is highly influenced by the environment including cultural practices, most notably nitrogen fertilizer. A range of 7–17%

Figure 5 Perten Single-Kernel Characterization System SKCS 4100. This instrument weighs individual wheat kernels before crushing them between a rotor and load cell-mounted crescent. The load cell interprets the crush characteristics as a quantitative measure of kernel hardness. Kernel outer diameter and moisture content are also measured. The computer monitor shows the four different stepped histograms of weight, diameter, hardness index, and moisture. The standard method measures 300 kernels in less than 5 min (courtesy of Perten Instruments).

protein is possible within one cultivar. The methods of determining grain protein are similar to those employed for flour. Whole-grain NIR methods are particularly convenient and obviate the need for grinding. Moisture content determines the storability of grain, the relative concentration of other kernel constituents (e.g., protein), and the amount of additional water needed during tempering before milling. For safe storage, wheat must have no more than 12–13% moisture content. The reason grain moisture is critical for safe storage relates to the growth of various molds. In this regard, moisture, time, and temperature, all interact to affect grain storage. An intrinsic quality trait of grain is soundness or sprouting. Preharvest sprouting occurs when rains and high humidity coincide with grain maturation and delayed harvest. The reason that sprouted grain is often considered to be of inferior quality relates to the presence of carbohydrases, proteases, and other hydrolytic enzymes normally associated with germination. The two main methods of assessing sprout damage are by

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visual inspection of kernels (noting pericarp rupture over the embryo or other signs of germination) and the Falling Number assay (see the preceding text). Other methods used for flour or starch or specific to the detection of individual enzymes are amenable, though not commonly used for the analysis of grain. Finally, the quality of grain and grain lots may be reduced by the presence or prior activity of molds, insects and rodents, seeds of other species, nonmillable material, stones, etc. The presence of pesticide residues is increasingly an important issue. The presence of mycotoxins produced by Fusarium fungi and proteases resulting from Eurygaster insect are of particular concern to wheat in certain regions.


• • • • •

What is a working definition of ‘quality’? What are the major constituents of the cereal grain? What are major uses of wheat, and how do those uses determine definitions of quality? What is starch and vital gluten, and why are they isolated? What are some advantages of ‘component’ tests?


• • •

What are some of the individual biosynthetic genes controlling wheat-grain composition and kernel texture? How can new varieties be bred and developed using DNA markers for these genes and alleles? What is the current and future role of GMO (genetic modification) in wheat quality and improvement?

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Genetics of Grains: Wheat Genetics and Genomics; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Contaminants of Grain; Non-food Products from Grains: Cereal Grains as Animal Feed; Processing of Grains: Grain Quality Attributes for Cereals Other than Wheat; Proteins: The Protein Chemistry of Cereal Grains; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Durum Wheat: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Breads; Cereals: Overview of Uses: Accent on Wheat Grain; Flatbreads of the World.

Further Reading AACC International (2014) Approved Methods of Analysis, 11th edn. St. Paul, MN: AACC International. AOAC International (2012) Official Methods of Analysis of AOAC International, 19th edn. Gaithersburg, MD: AOAC International. Bonjean AP and Angus WJ (eds.) (2001) The World Wheat Book. A History of Wheat Breeding. Andover, Hampshire/Secaucus, NJ: Intercept/Lavoisier. Campbell GM, Webb C, and McKee SL (eds.) (1997) Cereals, Novel Uses and Processes. Proceedings of an International Conference on Cereals: Novel Uses and Processes, Manchester, UK, 4–6 Jun 1996. CCFRA (2002) Manual of Methods for Wheat and Flour Testing, 3rd edn. Chipping Campden, Gloucestershire: CCFRA Technologies Guideline, No. 3. Delcour JA and Hoseney RC (2010) Principles of Cereal Science and Technology, 3rd edn. St. Paul, MN: AACC International. Gooding MJ and Davies WP (1997) Wheat Production and Utilization Systems, Quality and the Environment. Wallingford: CAB International. CIGI (1993) Grains and Oilseeds, Handling, Marketing, Processing, 4th edn. Winnipeg, MB: Canadian International Grains Institute. Henry RJ and Kettlewell PS (1996) Cereal Grain Quality. London: Chapman and Hall. Heyne EG (ed.) (1987) Wheat and Wheat Improvement Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America, 2nd edn. Hill LD (1990) Grain Grades and Standards. Urbana, IL: University of Illinois Press. Faridi H and Faubion J (eds.) (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. International Association for Cereal Science and Technology (2002) Standard Methods. Vienna, Austria: ICC. International Seed Testing Association (1999) International Rules for Seed Testing. Zurich, Switzerland: International Seed Testing Association. Kulp K (ed.) (1994) Cookie Chemistry and Technology Manhattan, KS: American Institute of Baking. Murphy CF and Peterson DM (eds.) (2000) Designing Crops for Added Value Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America. Olson RA and Frey KJ (eds.) (1987) Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America. Posner ES and Hibbs AN (2005) Wheat Flour Milling, 2nd edn. St. Paul, MN: AACC International. Pyler ER and Gorton LA (2009) Baking Science and Technology, 4th edn. Kansas City, MO: Sosland Publishing Company. Shewry PR and Khan K (eds.) (2009) Wheat: Chemistry and Technology. St. Paul, MN: AACC International 4th edn.. Simmonds DH (1989) Wheat and Wheat Quality in Australia. Australia: CSIRO. Sissons M, Abecassis J, Marchylo B, and Carcea M (eds.) (2012) Durum Wheat: Chemistry and Technology. St. Paul, MN: AACC International, 2nd edn. Yamazaki WT and Greenwood CT (eds.) (1981) Production, Breeding, Milling, and Uses. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.aoac.org – Website of the AOAC International. http://www.aaccnet.org – Website of the AACC International. http://www.aibonline.org – Website of the American Institute of Baking. http://www.crops.org – Website of the Crop Science Society of America. http://www.irri.org – Website of the International Rice Research Institute. http://www.wsu.edu/wwql/php/ – Website of the USDA-ARS Western Wheat Quality Laboratory. http://www.icc.or.at – International Association for Cereal Science and Technology. http://www.seedtest.org – International Seed Testing Association (ISTA).

Grain Quality Attributes for Cereals Other than Wheat CF Morris, USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Quality is defined as the ‘degree of excellence’ or suitability of a cereal grain for a specific food or end use. Rice, maize, barley (malt and feed), sorghum, millets, oats, rye, and triticale are major cereal crops. Individual quality traits are variably affected by genetics and the environment.

Learning Objectives

•

To achieve an understanding of what constitutes end-use quality of cereals, how to evaluate the key factors of quality, and where variation in quality originates.

General Considerations Quality may be defined as ‘the degree or grade of excellence.’ Quality may also be thought of as suitability. Consequently, to understand the analysis of cereal quality, one must appreciate the array of end uses of the various cereals. The major cereals and their uses are presented in Table 1. The success of cereals as food and feed crops stems from the ability to store easily the grain produced from them for a long period of time. This article covers the analysis of quality of the major cereal crops other than wheat.

Rice Rice is the third leading cereal in terms of world production and is the staple food for over half the world’s population. The rice kernel, when harvested, has an adhering lemma and palea (husk) and is referred to as ‘paddy’ or ‘rough’ rice. The husk, which represents about 20% of paddy rice, is removed during the first stage of milling and produces what is known as ‘brown’ rice – the ‘naked’ kernel with the brown bran layers present. The second stage in rice milling is called ‘polishing’ or ‘whitening’ and aims to remove the bran and germ and improves the appearance while minimizing kernel breakage. Polishing produces the resultant white ‘polished rice’ that is commonly eaten after boiling. According to the International Rice Research Institute, depending on whether the rice is short grain or long grain, it may receive three to four individual processes including ‘abrasive,’ ‘friction,’ and ‘polishing.’ Botanical classification of rice includes japonica (short grain) and indica (long grain), although a range of kernel lengths are observed. In the United States, short-, medium-, and long-grain rice varieties are developed, each with a specific set of quality criteria. Rice is classified also according to amylose content, gelatinization temperature, and whether it is


‘aromatic’ – indicating that it additionally has desirable aroma components. Rice quality is assessed in terms of grain appearance, milling quality, and cooking quality. Kernel size and shape, length, length/width ratio, whiteness, gloss, translucency, uniformity, and moisture content are quality criteria applied to rice grains. Rice milling removes the hull, bran, and germ while minimizing kernel breakage. The majority of rice is consumed in polished form, even though removing the bran greatly decreases the nutritional content of the grain. Milling quality is based primarily on the yield of whole grain polished rice (‘head rice’). Broken grain is strongly disfavored by consumers in many markets. Breakage results from primarily checking and chalky grain. Checking results when harvesting and threshing are delayed or when drying is too rapid and fissures develop in the kernel. The preferred texture and flavor and other cooking characteristics of rice vary among consumers. Usually, short- and medium-grain varieties become somewhat sticky upon cooking, whereas long-grain rice is harder and maintains the integrity of individual kernels. Generally, cooking quality is evaluated directly with measures of water uptake, optimum cooking time, volume expansion, solid loss to the cooking water, etc. Stickiness and other eating quality parameters are evaluated by sensory analysis directly or via instrumental analysis. Due to the inherent subjectivity and time-consuming nature of these cooking and eating quality tests, predictive tests have been developed and are extensively used. These often attempt to relate the chemical and physical properties of the grain to the desired subjective characteristics of the cooked rice. The two most important physicochemical properties related to cooking quality in rice are gelatinization temperature and amylose content of the starch. Starch composes about 90% of the total dry polished rice. Starch exists in compound granules similar to oats. The determination of amylose content and gelatinization temperature and the relationship between these two factors have been the major indirect means of selecting for cooking quality in rice breeding programs. The use of the amylograph and rapid visco analyzer has been extensive in rice breeding to assess starch gelatinization and pasting behavior. Other tests include alkali spread, gel consistency, and protein content.

Maize The vast majority of maize produced worldwide is used as animal feed, and that use is reviewed later. Of the remainder, sizable quantities are used in the wet and dry milling industries, which are described below. In addition, some maize is ground directly for human consumption and some is ground simply as a preparatory step in starch conversion for ethanol

http://dx.doi.org/10.1016/B978-0-12-394437-5.00248-5

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Table 1

Major cereals and their uses

Common name

Genus and species

Major uses

Wheat Bread wheat


Many styles of pan breads, hearth breads, noodles, starch and gluten, animal feed Cookies (biscuits), cakes, pastries, noodles, animal feed Pasta, couscous

Soft wheat Durum wheat Rice Maize (corn, the United States) Dent, floury, flint Popcorn Sweet corn Barley Malting barley Feed barley Rye Triticale Oats Grain sorghum Millet(s)

Triticum aestivum L. Triticum turgidum L. subsp. durum (Desf.) Oryza sativa L. Zea mays L.

Polished rice (staple food)

Animal feed, dry milling (production of grits), wet milling Snack food As a cooked vegetable Hordeum vulgare L.

Secale cereale L. Triticosecale sp. (Wittmack.) Avena sativa L. Sorghum bicolor (L.) Moench. Various species

production. In the Americas, maize has long been a staple food, and a traditional means of preparing maize is through the production of masa, wherein maize is steeped in lime water and ground and the majority of bran is separated and discarded. White maize production is estimated at 65–70 mmt and is used mostly for food. For all food uses, common quality criteria include mold and mycotoxin concerns and the general physical health of the grain. A vast amount of world maize production is not directly consumed. Government policy and energy demands have had a significant influence on maize production in developed economies. As an illustration, the United States produces one-third of the world’s maize (equal to 355 mmt). Of this, the majority goes into animal feed. However, nearly one-third, 118 mmt, was used to produce fuel alcohol, 12.5 mmt for high-fructose corn syrup, 7.2 mmt for glucose(dextrose), 6.3 mmt for starch, 5.3 for RTE cereals and other products, 3.6 mmt for alcohol for beverages and manufacturing, and 0.6 mmt for seed. Maize is a single species but has several important kernel types resulting from simple genetic systems. By far, the most important commercially is yellow dent. Other types include flint, floury, pop, sweet, white, and pod. Some endosperm mutations, which involve alterations in starch biosynthesis, include the sweet corns, high-amylose maize, and waxy maize.

Wet Milling The primary aim of wet milling is the recovery of starch, which is used to make sweeteners, ethanol, modified and unmodified industrial and food starches, etc. Wet milling, as the name implies, involves steeping maize kernels in water and sulfur dioxide to loosen the bran and germ from the endosperm. The germ is recovered and used to isolate oil; afterward, the remaining germ tissue is approximately one-fifth protein and is

Beer and brewing Animal feed Animal feed, bread Animal feed Animal feed, porridge, snacks Animal feed, food, brewing Food, animal feed

valuable as a feed product. Starch is separated from cell wall material (fiber) and endosperm protein through a process of grinding, hydrocyclones, and filtration. The yield of starch is about 65–68%, fiber 11–13%, germ 7–8%, gluten meal 5–6%, and the remainder steep water and loss. Maize for wet milling should have a high starch content and be low in mycotoxins. Kernels should be well filled; low test weight indicates poor grain filling, whereas high test weight indicates that kernels have a high vitreous to starchy endosperm ratio. Vitreous endosperm, such as that found in flint maize and a portion of yellow dent maize, is undesirable due to the slower steeping and processing time required. Mechanically damaged and broken kernels are also undesirable. Lastly, the drying regimen of maize after harvest is critical to highquality grain – too high and steeping rates drop, grinding is more difficult, and there is a loss of protease activity and starch release. Endogenous proteases, along with sulfur dioxide, contribute to starch release. Some waxy maize (having 0% starch amylose) is grown on contract for the wet milling industry.

Dry Milling The primary aim of dry milling is the production of flaking grits – the most valuable product. Flaking grits are large pieces of vitreous endosperm. Naturally, not every maize kernel yields a couple of flaking grits and even those that do also produce some quantity of smaller pieces of endosperm. Depending on the size of the particle, it may be classified as coarse or regular grits or meal or flour. To maximize the yield of flaking grits, the maize kernel is tempered for a short time to loosen the bran and germ (to about 18–24% moisture and < 1 h). The first stage of the grinding process is to remove and recover the germ. Oil is generally extracted from the germ as a coproduct; the remaining tissue is rich in protein and is used as animal feed. All the unrecoverable material from dry milling, primarily

PROCESSING OF GRAINS | Grain Quality Attributes for Cereals Other than Wheat bran recovered by aspiration and spent germ, becomes ‘hominy feed.’ The primary quality criteria for dry milling are a high proportion of vitreous endosperm in a yellow dent variety, free of mold and mycotoxins. Stress cracks from poor drying are undesirable because they reduce the recovery of grits. Even though flint maize is entirely vitreous, it is actually less desirable for dry milling because its more spherical kernel morphology is not conducive to producing grits.

Popcorn and ‘Sweet Corn’ All maize kernels have some propensity to ‘pop’ – that is, explode when superheated steam inside the lumen (hilum) of each starch granule reaches sufficient pressure to cause the pericarp to suffer a catastrophic failure. However, specific varieties of popcorn have been bred to maximize these physical phenomena. Popcorn kernels tend to be nearly spherical and have uniformly vitreous endosperms. The pericarp must be sufficiently strong to facilitate a high internal pressure before failing. However, once popped, the pericarp is undesirable from the consumer’s standpoint and therefore, its thickness is held to a minimum. Quality criteria include the lowest possible levels of mold, mycotoxins, and insect damage, hard endosperm with high test weight, and high popping volume with low percentage of nonpopped kernels. ‘Sweet corn,’ sweet maize, is simply vegetable corn that is eaten prior to full kernel maturity; its flavor is enhanced through a number of endosperm mutations that increase the sugar content at the expense of starch biosynthesis. Sweet corn may be eaten as ‘corn on the cob’ after boiling or cooking or as a canned or frozen vegetable. Hominy is a maize product produced from white- or yellow-kernel maize using alkali to remove the bran. It is popular in the southeastern United States and has a unique chewy texture.

Barley Barley has three distinct end uses: feed, alcoholic beverages, and human foods. The vast majority is used for feed followed by malt and lastly food. About 75% of the world’s barley production is used for feed, whereas only about 5% is consumed as food. Morphologically, there are two major types of barley, two-row and six-row, which refer to the number of vertical rows of kernels on the spike (ear). Two-row barley tends to have plumper, more uniform kernels and therefore may have an advantage in malting. Six-row barley tends to yield better. However, these generalizations have many exceptions depending on the region and the past history of breeding. Specialty types of barley include hull-less, high-amylose, and waxy. Feed barley quality is reviewed in the section given later. Malt quality is related to kernel size uniformity, kernel plumpness, and color. Additionally, protein content and germination rate and uniformity are critically important. Germination should be preferably over 95%, approaching 100%. Like all cereals, there is a concern for microbial contamination including mycotoxins. Naturally, the grain lot should be free of extraneous material, weed seeds, stones, filth, etc.

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Generally, barley malt is made from pure varieties, specifically bred for malt production. Occasionally, a carefully controlled blend of two malt varieties may be used. The two leading roles of barley malt in brewing are to supply a high quantity of hydrolytic enzymes produced during the germination process and a high level of ‘extract,’ which provides the fermentable substrates during brewing. The hydrolytic enzymes break down the starch, protein, and b-glucan during fermentation. The amount of soluble extract is directly related to the amount of beer that can be produced from a given quantity of malt. A negative correlation exists between barley protein and the amount of extract produced from malt. Malt should additionally have low levels of undesirable compounds such as b-glucan, polyphenols, and dimethyl sulfide precursor. The most common method for testing the potential malting quality of a barley sample remains the malting of the sample. Micro- and pilot-scale malting procedures are used. Afterward, analyses typically measure the amount of extract that malt will deliver into solution under standard conditions, amount of solubilized protein, and amount of enzymes. Other useful tests measure moisture and protein contents, germination, kernel size, and plumpness. Varietal purity is also of interest but is technically more challenging. Currently, some major exporters are testing and verifying the varietal composition of barley malt shipments using the polymerase chain reaction, which can exploit unique DNA sequences. The leading use of food barley is pearled barley kernels added to soup. Minor uses include barley flour, rice extenders (Japan), and couscous. Barley for pearling should have a white endosperm color, colorless aleurone, and should be uniformly floury or vitreous (not a mixture).

Sorghum and Millets The United States is the leading producer of grain sorghum, followed by Mexico, Nigeria, and India. In the United States, essentially all sorghum is used as animal feed, similar to maize. Feed use is covered in the section given later. In other parts of the world, sorghum is an important food. Sorghum is drymilled into grits and flour for baking, brewing, porridge, snack foods, malt, and other minor uses. A key quality trait in sorghum is the presence or absence of tannins and pigments in the outer layers of the kernel. Pericarp color is controlled by two genes and confers brown, yellow, or red colors. Testa color is controlled by one gene and can be brown or purple. Yellow endosperm cultivars have a high level of carotenoid pigments. Pericarp thickness affects how these various kernel colors are perceived. Tannins and other phenolics found in some sorghum cultivars are distinctly antinutritional. However, these compounds afford some protection against insects and birds, especially near harvest, features that outweigh their disadvantages in some locales. Nevertheless, white sorghums generally produce higher quality foods. Quality criteria are similar to maize and include kernel hardness, density, and ease of pericarp removal. Millets include a number of distinct grass species and are generally grown in harsh, dry climates by subsistence farmers. India is by far the leader in millet production, followed by

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Nigeria. Common type names include pearl, foxtail, finger, and proso millets. Most are consumed after decorticating by hand in a large mortar and pestle. Decortication is a traditional mechanical process that aims to loosen the pericarp so that it can be separated from the endosperm pieces via winnowing and sieving. Consequently, pericarp removal should be easily achieved and the endosperm should be hard and vitreous; color should be white with low pigment and low tannin contents.

quality criteria of rye are similar to other cereals: the absence of mycotoxins and molds. Additionally, because of rye’s biology and area of production, sprouting and ergot are primary concerns. Triticale is essentially an animal feed. When triticale does find its way into human foods, its quality criteria are similar to those of rye and wheat.

Oats

In terms of animal feeds, cereal grains are primarily a source of energy. Since energy is the most expensive component of feeds, cereals play a central role in rations, especially those for monogastric animals such as poultry and swine. For the major cereals, metabolizable energy (ME) ranges from about 11 to 14 MJ kg 1. Over 80% of this ME comes from starch. Cereals also make an important contribution to protein needs as well. Although cereals may contribute over one-third of the protein required in swine and poultry rations, they are all notoriously deficient in the amino acids lysine, methionine, and threonine. Alternative sources of protein, such as soybean meal, which include higher relative quantities of these amino acids, are required. Various strategies have been developed to address the shortcomings of cereals as feeds. With the exception of maize, cereals are deficient in the essential fatty acid linoleic acid. High oil content maize provides a more concentrated form of energy. Opaque-2 and other types of maize have altered and more balanced protein compositions. The starch of waxy maize, wheat, and barley may have greater digestibility. Generally, with these variants, the cost of production and segregation must be considered against the benefit to the feeder. With the exception of potassium and phosphorus, cereals are deficient in minerals essential for animal growth and reproduction. Potassium is readily available, phosphorus much less so (to monogastrics). However, researchers now have mutations that free up most of the grain’s phosphorus, which is normally ‘locked up’ in the form of phytic acid.

Oats, like rice, are harvested with an adhering hull (lemma and palea), which is removed during processing. The ‘naked’ kernel is referred to as a ‘groat.’ Oats notably have a high oil content (6–8% lipid in the endosperm compared with about 1% for wheat) and are rich in b-glucan. Most are used for feed; an estimate in the 1990s placed food usage at about 25% of world production. The primary food uses of oats are rolled oats, steel-cut groats, quick oats, oat flakes, oat bran, and oat flour. Because of the high oil content and the presence of lipiddegrading enzymes (lipase, lipoxygenase, and peroxidase), oats and oat products are heat-treated to inactivate these enzyme systems. Rolled oats are produced by passing whole groats through steel rollers, which produce flakes. Steel-cut oats are simply groats cut into two to four pieces. The pieces are in turn generally also flaked, producing quick oats and oat flakes. The primary food use of oats is a hot porridge. Consumer interest in convenience has generated ‘instant’ forms of this traditional food. Oats are also used to make ‘breakfast’ cereals (see RTE cereals earlier); perhaps, the most notable in the United States is the extruded product ‘Cheerios.’ The primary quality criteria for oats include the undesirable presence of other cereals in grain lots, especially barley, because the barley kernel is so similar that it is very difficult to remove. Barley contaminates the oat product with its hull, which is highly objectionable to consumers. Other criteria include test weight, percentage of hulls (groat yield), presence of mold and mycotoxins, ‘thins’ (grains that pass through a 1.98 19.05 mm screen), and free fatty acid content (an indicator of prior kernel damage, poor storage, etc.).

Rye and Triticale Most rye is produced in northern Europe and Russia where it remains a traditional, staple food. Germany, Russia, and Poland produce over two-thirds of the world’s production of rye. Production of triticale, which is a man-made species derived by crossing wheat and rye, parallels rye. Germany, Poland, and France are the leading producers and account for over 50% of world triticale production. The unique feature of rye is its high content of nonstarch carbohydrates (formerly referred to as ‘pentosans’). These carbohydrates, predominantly arabinoxylans of the cell walls, impart high water-holding capacity and viscosity to the dough, which allow rye to be baked into bread. Rye is essentially the only cereal besides wheat that has traditionally produced a yeast-leavened loaf of bread. Rye bread, however, is very dark and very dense (consumers choose rye bread for these specific attributes). Often, rye and wheat flours are blended to prepare ‘light rye’ and ‘dark rye’ breads. The primary

Feed Uses of Cereals

Specific Issues Wheat arabinoxylans (a subclass of pentosans) are considered to be an antinutritional factor, especially for poultry. Similarly for barley, the issue is b-glucan and is mostly a problem associated with poultry. Tannins are antinutritional factors for brown sorghums. With the exception of white-kernel varieties, maize is high in carotenoids. Maize gluten meal is a concentrated source of carotenoids and is a primary source of these pigments for the poultry industry, which often desires a highly yellow yolk or yellow carcass fat. During wet milling, carotenoids are concentrated 12-fold in this gluten meal. Barley hulls reduce the ME of rations for monogastrics but are of little concern for ruminants; the hulls may actually be beneficial by reducing the rate of rapid starch breakdown, which causes acidosis or ‘bloat.’ Hull-less barley has nutritional qualities similar to wheat. Oats have been traditionally an animal feed. Although they have a good balance of protein, fat, and carbohydrate, they have been largely displaced by cheaper alternatives. The hulls reduce energy concentration by about 25%. However, oats are

PROCESSING OF GRAINS | Grain Quality Attributes for Cereals Other than Wheat still the preferred feed for horses. For race horses, quality criteria of buyers may be more exacting than those of food processors. Opinion varies as to whether hulled or hull-less oats are better.

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Versatile Cereal Grain with Many Food and Feed Uses; Oats: Overview; Rice: Overview; Rye Grain: Its Genetics, Production, and Utilization; Sorghum Grain, Its Production and Uses: Overview; Triticale: Overview; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Quality Criteria Cereal grain for feed should be low in mold and mycotoxins and lower for monogastrics than for ruminants. Grain should also be low in smut and bunt (Tilletia sp.) spores. The primary means of assessing feed quality is through proximate analysis: moisture, protein, and ash. Measures of ME and protein digestibility are substantially more involved (requiring live animals) and not amenable to grain receival stations. The test weight and general appearance of the grain are crude indicators of feed value and can be used to reject individual lots. Naturally, grain lot contaminants pose a variable level of concern based on their nature (e.g., kernels of other cereals vs. stones or chaff). For most poultry and swine rations, cereals are hammermilled, because smaller particle size increases digestibility. The proportion of vitreous versus nonvitreous yellow dent maize kernels affects grinding energy. Barley and sorghum are often steam-flaked for feedlot cattle. In addition to the use of the entire cereal kernel in feeds, it should be remembered that the processing of all cereals for human foods or industrial products generates by-products, which largely become animal feeds. Examples include wheat bran, maize gluten feed, and brewers’ spent grains.


• • • •

What is a working definition of ‘quality’? What are the major cereals and approximately how much of each is grown worldwide? What are the major constituents of the cereal grain? What are major uses of cereals and how do those uses determine definitions of quality?


• • •

What are the individual biosynthetic genes controlling cereal grain composition and kernel texture? How can new varieties be bred and developed using DNA markers for these genes and alleles? What is the current and future role of genetically modified organisms in cereal quality and improvement?

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Contaminants of Grain; Non-food Products from Grains: Cereal Grains as Animal Feed; Non-wheat Foods: Maize: Foods from Maize; Rice: Chinese Food Uses; Sorghum: Utilization; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a

Further Reading AACC International (2014) Approved Methods of Analysis, 11th edn. St. Paul, MN: AACC International. American Oil Chemists’ Society (2013) Official Methods and Recommended Practices of the AOCS, 6th edn. Champaign, IL: American Oil Chemists’ Society. AOAC International (2012) Official Methods of Analysis of AOAC International, 19th edn. Gaithersburg, MD: AOAC International. Bushuk W (ed.) (2001) Rye: Production, Chemistry, and Technology. St. Paul, MN: American Association of Cereal Chemists, 2nd edn. Campbell GM, Webb C, and McKee SL (eds.) Cereals, Novel Uses and Processes. Proceedings of an International Conference on Cereals: Novel Uses and Processes, Manchester, UK, 4–6 Jun 1996 (1997). Champagne ET (2004) Rice: Chemistry and Technology, 3rd edn. St. Paul, MN: American Association of Cereal Chemists. Delcour JA and Hoseney RC (2010) Principles of Cereal Science and Technology, 3rd edn. St. Paul, MN: AACC International. Dendy DAV (ed.) (1994) Sorghum and Millets: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. CIGI (1993) Grains and Oilseeds, Handling, Marketing, Processing, 4th edn. Winnipeg, MB: Canadian International Grains Institute. Henry RJ and Kettlewell PS (1996) Cereal Grain Quality. London: Chapman and Hall. Hill LD (1990) Grain Grades and Standards. Urbana, IL: University of Illinois Press. International Association for Cereal Science and Technology (2002) Standard Methods. Vienna, Austria: International Association for Cereal Science and Technology (ICC). International Seed Testing Association (1999) International Rules for Seed Testing. Zurich, Switzerland: International Seed Testing Association. Juliano BO and Villareal CP (1993) Grain Quality Evaluation of World Rices. Manila, The Philippines: International Rice Institute. MacGregor AW and Bhatty RS (eds.) (1993) Barley: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Marshall HG and Sorrells ME (eds.) (1992) Oat Science and Technology. Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America. Murphy CF and Peterson DM (eds.) (2000) Designing Crops for Added Value. Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America. Olson RA and Frey KJ (eds.) (1987) Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement. Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America. Rasmusson DC (ed.) (1985) Barley. Madison, WI: The American Society of Agronomy/ Crop Science Society/Soil Science Society of America. Sprague GF and Dudley JW (eds.) (1988) Corn and Corn Improvement. Madison, WI: The American Society of Agronomy/Crop Science Society/Soil Science Society of America 3rd, edn. Webster FH and Wood PJ (eds.) (2011) Oats: Chemistry and Technology. St. Paul, MN: AACC International, 2nd edn. White PJ and Johnson LA (eds.) (2003) Corn: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists, 2nd edn. Yamazaki WT and Greenwood CT (eds.) (1981) Production, Breeding, Milling, and Uses. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.aoac.org – Website of the AOAC International. http://www.aaccnet.org – Website of the AACC International. http://www.crops.org – Website of the Crop Science Society of America. http://www.irri.org – Website of the International Rice Research Institute. www.icc.or.at – International Association for Cereal Science and Technology. http://www.knowledgebank.irri.org/rice.htm – Rice Knowledge Bank of the International Rice Research Institute (IRRI). http://www.seedtest.org – International Seed Testing Association (ISTA).

Cereals: Breakfast Cereals EF Caldwell, AACC International, Roseville, MN, USA JD McKeehen, Cereal Partners Worldwide, Minneapolis, MN, USA RS Kadan{ ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by E.F Caldwell & R.S Kadan, volume 1, pp. 201–205, ã 2004, Elsevier Ltd.

Topic Highlights

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The breakfast cereal industry is important globally, with 2013 sales of $31.8 billion. Breakfast cereals are either ready-to-eat (RTE) before or after adding milk or ready-to-cook, known as hot cereals (HC). RTE cereals are 86% and HC, 14% of the industry. RTE cereals use primarily corn, rice, wheat, oats, barley, or mixtures, plus other ingredients. The major HC are rolled oats in various forms, farina, or corn grits, with minimal processing. Flaked RTE cereals are rolled from cooked whole or parts of grains or from extruded pellets. Puffed wheat or rice are cooked at a high temperature and pressure and expanded by a sudden release of pressure. Shredded RTE cereals are made by rolling cooked grains between grooved rolls and forming shreds into shapes prior to toasting. Expanded RTE cereals result from single- or twin-screw extrusion and toasting. BC can be fortified with vitamins and minerals or protein isolates and preserved with BHT.

Learning Objectives

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Achieve a general understanding of the nature and scope of the breakfast cereal industry, its products, the grains used, and how they are processed.

Introduction The breakfast cereal industry, in its history of over 120 years, has emerged as an important segment of the food industry globally. According to Euromonitor, worldwide sales of breakfast cereals in 2013 were about US$31.8 billion, showing a 5-year compound annual growth rate of about 2.5%. This remarkable progress has been achieved through a combination of knowledge gained in human nutrition, creative formulation, innovative progress in cereal processing technology, and imaginative marketing. The chief driving force has been the continued market for new, convenient, nutritious, and affordable foods, with special appeal to both children and adults in a discriminating, affluent, and mobile society. Breakfast cereals have been defined as ‘processed grains for human consumption.’ The major grains used in their manufacture are corn, rice, wheat, oats, and barley. Breakfast cereals {

Deceased.

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can be divided into the following: (1) those that are RTE before or after adding milk and (2) those that are ready-to-cook, also known as hot cereals (HC). RTE cereals are frequently made from mixtures of one or several grain components with other ingredients; they require extensive processing, are usually fortified with vitamins and minerals, and are specially packaged to protect their flavor, texture, and nutrition during storage as well as display their contents in such a way as to visually appeal to and entice the consumer. In comparison, HC products are typically made from a single grain component by using relatively simple processing and packaging technologies and usually require stove top cooking or microwave heating before eating. Packaged RTE breakfast cereals account for the majority (86%) of breakfast cereal sales at 3.6 million global tonnes, while the remaining portion (14%) represents a growing consumption of HC at 0.8 global million tonnes. As purchased, both RTE and HC products offer compelling breakfast choices versus traditional breakfast alternatives based on affordability by serving size. In the United States, any large grocery store may stock over 200 different packaged grain-based breakfast cereal products. A typical single-serving size of RTE cereal (typically ranging between 28 and 55 g) costs at retail between $0.23 and $0.42, while a serving of HC (also ranging between 28 and 55 g) costs consumers between $0.08 and $0.29. Reflecting continued innovation and investment in the breakfast cereal industry, over the last decade, more than 26 500 new breakfast cereals were introduced globally. Approximately 2/3 of breakfast cereal sales are derived from consumption in North America, Western Europe, and Australia. The remaining 1/3 of sales represent increased consumption across Latin America, Asia, Eastern Europe, the Middle East, and Africa. This growth is spurred on and accelerated by both indigenous manufacture and marketing and the nutritional relevance of breakfast cereals. The growth potential and trend of breakfast cereal consumption is often assessed by comparing per capita annual consumption of different markets. The United Kingdom and the United States may be viewed as proxies for mature, developed breakfast cereal markets, with some of the higher per capita annual consumptions of RTE cereals at 6.7 kg (14.8 lb) and 4.1 kg (9.1 lb), in the United Kingdom and the United States, respectively. These markets have shown a small and steady decline in overall RTE cereal consumption in recent years as consumers move to an array of breakfast alternatives. HC consumption in these same markets, while significantly lower at 1.4 and 0.7 kg (3.1 and 1.5 lb) per capita (the United Kingdom and the United States, respectively), is showing renewed interest and growth, largely due to consumer perception of the healthy nature and satiety of hot cereals, the convenience and portability of single-serve offerings, and the proliferation of a greater variety of hot cereals being


http://dx.doi.org/10.1016/B978-0-12-394437-5.00143-1

PROCESSING OF GRAINS | Cereals: Breakfast Cereals introduced. Similar annual per capita consumption for RTE and HC data exists across Ireland, Canada, Australia, and New Zealand, while a further 16 identifiable RTE cereal markets collectively consume at least 1 kg per capita. Both RTE cereals and HC continue to be adapted and introduced into undeveloped and emerging markets at an accelerated rate.

Methods of Manufacture RTE Cereals RTE breakfast cereals are primarily grain formulations, suitable for human consumption without further cooking. Manufacturing technology varies according to the type of cereal, whether flaked, puffed, shredded, granola, extruded, expanded, or baked, but all are ‘ready-to-eat’ because the grain formulations have been ‘cooked’ by the manufacturer instead of the consumer. Representative samples are shown in Figure 1.

Flaked cereals Flaked RTE breakfast cereals can be divided into two groups: flakes rolled from whole grains or parts of the whole grains and flakes made from more finely ground materials that are first extruded into pellets and then rolled into appropriate size flakes. The whole grains (typically wheat or rice) or major components (such as grits from degermed yellow maize or corn) are cooked with flavorings such as sugar, salt, and malt; they are then dried and tempered to a firm but slightly plastic state, flaked by passing between rolls, and toasted or dried to a final specified moisture content. Cooking of grits or whole grains for traditional flakes is usually done in batches. The moisture content of the cooked mass at the end of cooking is usually 28%. The cooked material should not be mushy, soft, or sticky. After cooking, the mass of material is cooled, dried at 120 C, and tempered (held) for several hours at a final equilibrated moisture content of 10–18%, depending upon the grains. The tempering process is important, not only to allow equilibration of moisture

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within the cooked grains or pellets but also to allow sufficient starch recrystallization or retrogradation to provide a suitable texture for flaking (or for shredding, as discussed next). Flaked RTE cereals are also made from extruded pellets, rather than cooked grits or whole grains. A variety of floury or finely ground grain products such as whole wheat or oat flour can be mixed with sugar, salt, and malt syrup or other flavoring and coloring ingredients to form a dough. This is then extruded to form pellets about the same size as cooked grits or whole grains, the cooking having taken place in the extruder. Pellet moisture is in the range of 18–24%. Conditioning or tempering prior to flaking may or may not be required. Whether consisting of cooked grits, cooked whole grains, or extruded pellets, the tempered material is then flaked. Tremendous pressures are necessary to flatten the prepared material into thin flakes, which traditionally are toasted by keeping them suspended in hot air between 270 and 330 C for 90 s. Certain properties of the finished flakes can be modified by a heating or steaming step immediately before flaking (e.g., infrared heating immediately before flaking will increase the tendency of the flakes to crinkle, rather than remain flat), while other properties – such as blistering, color, crispness, tenderness, and flavor of the final product – are influenced by toasting conditions. The moisture content of the finished product is 1–3%.

Puffed cereals The predominant grains used for making puffed cereals are wheat and rice. The milled rice that is used for puffing is either short- or medium-grain white rice. Such rice usually requires no pretreatment other than the hull and bran removal that occurs during milling or pearling. Wheat, on the other hand, is usually decorticated (bran removed), either by pretreatment with concentrated brine solution or by pearling. In the pearling operation, the grain is passed through a revolving cylinder and abraded against a surface made of mounted silicon carbide or carborundum stones.

Figure 1 Some common RTE cereals. Clockwise from the top left, they are, respectively, flaked, puffed, shredded (bite-size), granola, extruded expanded, and baked products.

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Usually, hard wheat, preferably durum, is used for puffing. A grain flour mixture can also be formed into desired shapes by an appropriate extrusion process and dried to a moisture content of 9–12% for subsequent gun puffing. Puffing guns are vessels capable of holding very hightemperature and high-pressure steam. The critical feature of any puffing gun vessel or barrel is a quick-opening lid that seals the vessel. Operation of a simple single-shot gun consists of placing the grain in the vessel, closing the lid, and raising the pressure and temperature in the vessel to 1380 kPa (200 psi). The quick-opening lid is then activated, causing rapid pressure drop, which in turn instantaneously causes moisture in the grain to ‘flash off’ as steam and the kernels of grain or preformed pellets to expand to as much as 16 times their original volume. Modern puffing guns can be multiple-shot automatic or can be continuous in operation. In the latter case, the grain kernels or preformed pellets are conveyed through a pressure vessel to which they are admitted and from which they are ejected via an orifice or mechanical device without loss of pressure inside the vessel. Another group of RTE products is made by oven puffing. Specially prepared rice or corn grains or their mixtures are oven-heated to 290–340 C in order to puff them. Puffed rice cereal marketed in the United States is either oven-puffed (e.g., Rice Krispies, prepared from short-grain rice) or gun-puffed (e.g., puffed rice). Whether gun- or oven-puffed, the grains are then screened to remove any unpuffed kernels, loosened bran, fine dust, and broken kernels, and the product is heated to lower the final moisture to 1–3%. Processes such as sugar coating or the addition of vitamin enrichment can be carried out during this drying operation.

Shredded cereals Shredded wheat, one of the oldest mass-produced breakfast cereals, is still an important product. Soft white wheat is the primary grain used. Other classes of wheat, as well as other cereal grains such as rice, corn, or oats or mixtures thereof, can also be used to make shredded products. The grains are cleaned, cooked in boiling water, partially dried, and tempered. The shredding operation consists of passing the tempered grain between two rolls. One roll is grooved and the other is smooth. Strong forces in the range of 7000 kPa (1000 psi) along the roll length are often required to maintain the rolls in very close or actual tight contact. The tempered kernels are squeezed into the grooves of the roll and emerge as strands roughly 1 mm in diameter. These strands are accumulated in multiple layers below multiple pairs of rolls and formed into biscuits or bite-sized pieces. A refinement of the shredding process is the use of a roll with added cross grooves to provide lateral strands that can tie the shreds together in a coherent sheet. Alternatively, mixtures of ground cereal products with sugar, salt, malt, and flavoring can be cooked by extrusion, formed into pellets, tempered, and then shredded in the same way as cooked whole-grain kernels. The formed biscuits or pieces are oven-dried and baked to desired color, texture, and moisture. The baking procedure is done in a specialized manner to impart a fluffy texture, particularly for products containing rice or corn. Other minor ingredients – such as sweetening or other flavorings, nutrients, or antioxidants – can also be added prior to drying and baking.

Granola cereals The main grain used to make granola cereals is either regular or quick-cooking (thin-flaked) rolled oats. The cereal products are mixed with other desired ingredients such as nut pieces, coconut, corn syrup, brown sugar, honey, malt extract, dried milk, dried fruits, and vegetable oil. Liquid and dry ingredients are prepared separately and then mixed together and spread in a uniform layer on the band of a continuous oven, with baking temperatures in the range of 150–220 C. When the product is uniformly toasted to a light brown color and the moisture is reduced to 3% after baking, the product is broken into small pieces and packaged.

Extruded expanded cereals Successful application of extrusion technology for producing RTE cereal products from grain flours or meal mixtures by formulating, continuous preconditioning, extrusion cooking, and forming has been an important achievement of the breakfast cereal processing industry. The extruders can be single screw, twin screw, low shear, high shear, and combinations of these or other features. Extrusion technology was developed to produce flaked, puffed, shredded, and expanded breakfast cereals. For extruded expanded cereals, cereal flour mixtures having 25–30% moisture are preconditioned, cooked, and extruded. Perforations in the die and design of the cutoff knives at the end of the extruder, as well as temperature, pressure, dwell time, and shear in the extruder barrel, all influence the shape, size, and texture of the final product. The sudden change from high pressure and temperature to ambient conditions as the product exits the extruder imparts the necessary expansion, texture, and other characteristics. The extruded products may be coated with solutions of vitamins and minerals, and with sweetening and flavoring materials to enhance their sensory appeal, and are then oven-dried to desired moisture levels.

Other RTE cereal types A breakfast cereal can be manufactured using essentially baking or cookie technology to form and cook the pieces. Another type is compressed-flake biscuits, formed from the compression of previously cooked and flaked grains, usually wheat flakes with added sugar, salt and malt, or other flavorings as described in the preceding text. The so-called muesli RTE cereals are mechanical mixtures of several ingredients. In Europe, the major ingredient is quick-cooking rolled oats mixed with sweetening and flavoring components but not otherwise processed. In the United States, a major component can also be processed and toasted flakes from various grains. Either kind is eaten with added milk and sugar.

Hot Cereals HC are products of a single grain or a simple mixture that require cooking or heating in water before consumption. The main such products are rolled oats and related oat products, farina and other wheat fractions, and corn grits. After cleaning, oat kernels are dehulled by an impact process. The resulting groats are steamed, primarily to deactivate lipolytic enzymes, and then rolled, dried, and packaged. Quickcooking rolled oats are made by steel cutting groats into four or five pieces before the steaming and flaking process. Instant

PROCESSING OF GRAINS | Cereals: Breakfast Cereals oatmeal is made by subjecting groats to a special process that results in rapid cooking extra-thin flakes. Incorporation of 0.1–1.0% of an edible gum during processing helps to achieve this objective. Distribution of the gum and necessary salt without damaging the flakes is accomplished during portion control packaging. Such instant products require only the addition of boiling water, stirring, and a short standing time to make the product ready for consumption. The industry has successfully incorporated dried fruits, nuts, and other flavorings to make instant oatmeal products more attractive to consumers. Wheat farina is another important HC. In the United States, farina and enriched farina must meet respective legal standards of identity. Farina is basically wheat endosperm, preferably obtained from hard red spring or winter wheat, the granules of which stay intact during cooking at home. Farina is normally obtained by drawing off chunks of endosperm during milling of wheat into bread flour. In the United Kingdom, it can also be called semolina, but in the United States, that term is reserved for a similar product from durum wheat intended for macaroni and other pasta products. Farina is heated at 60 C for 15 min before packaging, to enhance flavor and head off infestations. Quick and instant farina products are prepared by using disodium phosphate, enzymes, and other treatments including precooking and drum drying. Wheat germ, bran, malted barley, cocoa, and other flavorings can be mixed into farina to enhance the consumer appeal. Other important HC products include wheat products such as cracked wheat and bulgur and corn grits. Grits and bulgur are generally used as cereal accompaniment to other meal menu components such as eggs, sausage, meat, and related preparations, whereas cracked wheat products are cooked for breakfast. Grits usage is mostly in the southern parts of the United States, garnished with butter and salt, rather than with sugar and milk as for traditional breakfast cereals. Grits are produced by dry milling of white degermed corn and can be fortified with vitamins and minerals. Bulgur or parboiled wheat is one of the oldest cereal-based foods and has been consumed for centuries in Turkey, Syria, Jordan, Lebanon, and Egypt. To prepare it, common hard or soft wheat varieties are soaked in water and heated to 90 C for 2–3 h. The cooked wheat is then cooled, dried, moistened, peeled (optional), redried, cleaned, and sized. Bulgur has good shelf life, because cooking destroys insects present in harvested crops and distributes nutrients uniformly throughout the kernel. It does not render the final product quick-cooking or ‘instant.’

Significance in the Diet and Fortification Breakfast cereals are one of the most highly fortified foods in both vitamins and minerals. One serving often can supply up to 25% of the daily values (DVs) of most vitamins and trace minerals as these are defined in the United States for labeling purposes. Some products supply 100% of all established DVs, making them as much nutritional supplements as breakfast foods. The cereal industry justifies these practices on the basis that they fulfill a genuine need to improve the overall nutritional needs of consumers, and in most countries, fortification of RTE cereals is heavily regulated with maximum limits established for vitamins and minerals. Past food consumption surveys showed

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that some of the US population had inadequate intakes of several vitamins and minerals, particularly vitamin A, folic acid, calcium, and iron and possibly vitamin B6, zinc, and magnesium. In the United States, the practice of enrichment of cereal foods started in 1941, when the Food and Drug Administration (FDA) established a standard of identity for enriched flour to include the addition of thiamin, niacin, and iron. Riboflavin was subsequently included, and addition of calcium and vitamin D was optional. Although the initial concept was one of restoration of nutrients lost in processing, recommendations leading to actual fortification were developed after extensive discussions by various committees of the American Medical Association and hearings sponsored by the FDA and the Food and Nutrition Board. As a result, the following criteria for fortification of foods were recognized: 1. The intake of the nutrient is below the desirable level in the diet of a significant number of people. 2. The food used to supply the nutrient is likely to be consumed in quantities that will make a significant contribution to the diet of the population in need. 3. The addition of the nutrient is not likely to create imbalance of essential nutrients. 4. The nutrient added is stable under proper conditions of storage. 5. The nutrient is physiologically available from the food. 6. There is reasonable assurance against excessive intake to a level of toxicity. Various studies have confirmed that fortification of breakfast cereal foods is appropriate and has contributed significantly to improving overall nutrition. Fortification of flour and other grain-based foods with folic acid became a requirement in the United States in 1998 because of evidence that it may help prevent neural tube defects and because these are staple foods that are often consumed daily. Many nutritionists consider eating breakfast regularly as one of the important health habits associated with subsequent favorable health status and reduced mortality. People who had breakfast were found to do significantly more work in the morning than those who did not. Children and the elderly (above 65 years old) are the largest consumers of breakfast cereals. Half or more of the school-age children in the United States prepare their own breakfast, because most of their parents work outside the home. These groups are more likely to skip breakfast. Studies have confirmed that consumers of RTE breakfast cereals are likely to skip fewer breakfasts and that they obtain higher levels of vitamins and minerals than others. Some products contain up to 5 g of dietary fiber per serving. Some high-fiber products can even provide 10 g or more of fiber and thus help consumers to improve their dietary fiber intake to meet recommendations of 25–30 g daily dietary fiber intake. Oat-based breakfast cereals containing sufficient betaglucan soluble fiber to provide 3 g or more of that substance daily, or other products containing sufficient bran with psyllium seed husk to provide up to 7 g of soluble fiber from that source daily, have been shown to decrease blood cholesterol by a small but significant amount, and the United States may carry label health claims to that effect. Studies have also shown that diets rich in whole-grain foods (such as breakfast cereals with whole grains as a major constituent) and other plant foods that

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are low in total fat, saturated fat, and cholesterol may reduce the risk of heart disease and cancer. Most breakfast cereals are not naturally high in protein, and recently, manufacturers have introduced breakfast cereals formulated with various protein isolates (soy, cereal, legume, and dairy) to boost protein content and offer a more complete and balanced nutrition profile. RTE cereals as marketed may also contain sugar and/or salt (sodium) and may contain added fat but with milk and fruit still make an inexpensive, nutritious, and easy-to-prepare breakfast.

•

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• Packaging, Storage, and Spoilage The industry over the years has developed efficient processing, packaging, storage, and shipping technologies to supply consumers with cereal foods that routinely have 6 months or longer shelf life. It is indeed quite a feat to provide an ambient stable, wholesome product with a desirable flavor and texture and such an array of vitamins and minerals (which often interact with each other). Novel techniques have been developed for vitamin preservation and for the incorporation of antioxidants such as BHT or mixed tocopherols directly or via the packaging material. The package not only protects the product against moisture, oxygen, and insects during shipping and storage but also provides attractive consumer appeal at the point of purchase. The industry has accomplished this by following ‘good manufacturing practices’ and other quality control measures and by instituting Hazard Analysis and Critical Control Point (HACCP) systems for food safety purposes. Computer control of processing and attention to environmental issues also characterize most breakfast cereal manufacturing operations and certainly the newer ones.

Future Developments The Nutritional Labeling and Education Act of 1990 and subsequent amendments in the United States undoubtedly contributed to reevaluation of product development, marketing, and advertising strategies by the breakfast cereal industry as a result of stricter control of nutrient claims, ingredient listing, and other label data. Among other moves, the industry has developed new products made from whole grains that are also low in fat, sugar, and salt (sodium), with encouragement provided by the FDA approval of a health claim for products containing one or more whole grains as a majority constituent. Other product developments or modifications are likely to be influenced by such regulatory developments, advances in technology, or nutritional knowledge, as well as by evolving consumer behavior and lifestyle choices.


• •

Describe the main technologies employed for RTE cereals. Which (if any) are best suited to each of the major grain species used for RTE cereals? Explain how fortification and flavorings are provided for RTE cereals.

Breakfast cereals have been defined as “processed grains for human consumption.” Give examples of breakfast cereals (RTE and HC) that have the least and the most processing. Do you think that the examples of greater processing justify the greater input? Explain how the hot cereals have been made easy and quick to prepare.

•

Compare a cross section of breakfast cereals (both RTE cereals and HC) based on several important attributes: the contents of sugar, fats, fiber, and sodium, the extent of fortification with vitamins and minerals, pricing, packaging and advertising, and your personal preferences. Decide for yourself whether to take into account the milk and sugar that might usually be added to several of these cereals. – Do you see obvious correlations across any of these factors? If possible, arrange quantitative scorings or rankings so that statistical correlations can be conducted. – Do the HC stand out from the RTE cereals? On what attributes mainly? Try to define the word ‘healthy’ with respect to foods generally and breakfast cereals specifically. Use your definition to allocate ‘healthy’ scores to the earlier cross section of breakfast cereals.

See also: Appendix 1: Nutrient-Composition Tables for Grains and for Grain-Based Products; Carbohydrates: Resistant Starch and Health; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Fortification of Grain-Based Foods; Labelling of Grain-Based Foods; Processing of Grains: Extrusion Technologies; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.

Further Reading Bemiller JN (2007) Carbohydrate Chemistry for Food Scientists, second ed. St. Paul, MN: AACC International. Champagne ET (ed.) (2004) Rice: Chemistry and Technology, third ed. St. Paul, MN: AACC International. Cho S, DeVries J, and Prosky L (1997) Dietary Fiber Analysis and Applications. Gaithersburg, MD: AOAC International. Cho S and Samuel P (eds.) (2001) Fiber Ingredients and Health Benefits. Boca Raton, FL: CRC Press. Corlett DA (ed.) (1998) HACCP User’s Manual. New York: Springer. Delcour JA and Hoseney RC (2010) Principles of Cereal Science and Technology, third ed. St. Paul, MN: AACC International. Fast RB (1999) Origins of the US breakfast cereal industry. Cereal Foods World 44: 394–397. Fast RB and Caldwell EF (eds.) (2000) Breakfast Cereals and How They Are Made, second ed. St. Paul, MN: AACC International. Khan K and Shewry PR (eds.) (2009) Wheat: Chemistry and Technology, fourth ed. St. Paul, MN: AACC International. McCleary B and Prosky L (2001) Advanced Dietary Fibre Technology. St. Paul, MN: AACC International. Nelson AL (2001) High-Fiber Ingredients Handbook. St. Paul, MN: AACC International. Newman RK and Newman CW (2008) Barley for Food and Health. Hoboken, NJ: Wiley. Van der Kamp JW, Jones JM, McCleary BV, and Topping DL (eds.) (2010) Dietary Fibre – New Frontiers for Food and Health. Wageningen, The Netherlands: Wageningen Academic Publishers.

PROCESSING OF GRAINS | Cereals: Breakfast Cereals Webster FH and Wood PJ (2011) Oats: Chemistry and Technology, second ed. St. Paul, MN: AACC International. White PJ and Johnson LA (eds.) (2003) Corn: Chemistry and Technology, second ed. St. Paul, MN: AACC International.

Relevant Websites http://www/aaccnet.org – AACC International.

http://www/asbe.org – American Society of Bakery Engineers. http://www/fdli.org – Food and Drug Law Institute. http://www/gmabrands.com – Grocery Manufacturers of America. http://www/ift.org – Institute of Food Technologists. http://www/ilovepasta.org – National Pasta Association.

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Extrusion Technologies RCE Guy, Campden and Chorleywood Food Research Association, Chipping Campden, UK ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp. 366–371, ã 2004, Elsevier Ltd.

Topic Highlights

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through the dies into the atmosphere. An extrusion cooking process has a number of key features:

Extruding moist food materials along a barrel, with heating, and through a die for shaping, is a powerful way to create complex foods. As a continuous process, subject to multivariable control of outcomes, great precision and uniformity can be achieved, along with immense product variation. Extrusion, particularly twin-screw extrusion, has its main applications in animal feeds, snack foods, and ready-to-eat breakfast cereals.

Learning Objectives

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To understand the basic principles of twin screw extrusion and its use to transform food biopolymers (such as starch). To be aware of the range of major food and feed products commonly made by extrusion.

Introduction Extrusion cooking technologies for foods and feeds grew out of a process developed by the Adams Company in the 1940s to manufacture snack foods from maize grits. They are derived from the earlier extrusion technologies used to form and extrude sausage meats and pasta. These processes involved conveying, mixing, and compressing of moist materials to form doughs that could be extruded as simple rods, or in the case of pasta, as well-defined shapes. In extrusion cooking, a feedstock of moist powders is also conveyed, mixed, and compressed before shaping at a die (Figure 1). However, the dough temperature is raised to much higher levels compared to pasta making, in the range from 110–200 C on screws confined within a tubular barrel. This means that any water present is superheated within the dough but remains in the liquid state. The high temperatures also cause changes in the structures and form natural biopolymers, such as starch and soy globulins. Simple physical interactions, such as hydrogen and hydrophobic bonds that hold the subunits together, can be broken at high temperatures and the new forms of the polymer can be released and used to create novel structures for foodstuffs. A particular feature of extrusion cooking is the ability of the processing unit to manipulate these polymers at low moistures and to form doughs or fluid systems from them with the minimum of moisture. The basis of the technology is the screw system, confined within a barrel that conveys the dough toward small openings at the end of the barrel called dies. In the confined space of the barrel, the dough is compressed and heated to high temperatures, while subjected to high pressures, before being extruded

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• • • •

the feeding devices supplying the raw material feedstocks, the design of the screw system and its barrel, the dimensions and number of the dies, and the devices that handle the extrudates.

Extrusion cooking is a continuous process in which the raw material feedstocks are metered into the screws at a constant rate and the machinery maintains a steady state equilibrium. This is achieved by balancing the forward flow produced by the screws against the back pressure caused by the resistance of the dies. It is a multivariate process depending on all the independent variables (those not affected by each other) of the machinery and the raw materials such as the screw speed, feed rate, and barrel temperature of the extruder, and the particle size, hardness, and composition of the raw materials. These variables produce a range of dependent variables (those determined by others) in the barrel, such as the material temperature, the pressure, and the mechanical energy input and a further range of dependent variables in the extrudates and products, such as the size, shape, crumb texture, and moisture levels. The consequence of varying one independent variable may be to change several of the product characteristics. Therefore, a good systems approach must be used to control such a process. The range of products manufactured by extrusion cooking can be divided into two groups, food and industrial products. In the food sector, there are both animal products and human foods. The animal products themselves, include basic feeds for stock animals, marine feeds for freshwater and saltwater fish, shrimps, or prawns. They also include large markets for both dry and canned dog and cat foods and treats, and a number of products for other pets and for wild and tame birds. Human foods include the original maize snacks and many new forms including modern versions of prawn crackers, potato chips, tortillas, and other traditional snacks. There are many breakfast cereals products formed in balls, hoops, and flakes from all the major cereal flours and bran-rich recipes, which have large traditional markets in USA and UK and growing markets in many other areas. Similar expanded pieces of rice and maize are used in chocolate confectionery bars. These products called ‘bullets’ of cereal are also used in other products where a crisp expanded foam particle is required, such as museli and granola bars, biscuits, and even in ice cream. The range of extruded foods has been extended to coatings, such as breadings and flakes. These are used on fried foods, particularly frozen fish and chicken portions. Extruded products have replaced some of the traditional baked crumbs. They are made by expanding cereal extrudates and slicing them into crumbs. This process may be taken a step further in the


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PROCESSING OF GRAINS | Extrusion Technologies

←pumping

←shearing

←conveying

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←conveying

←mixing

Figure 1 Diagram of the development of raw materials in a twin screw extrusion cooker.

manufacture of baby foods from extruded feedstocks of cereals and milk powders. For these products, the extrudates are ground to a fine powder, sieved, and used to replace the powders manufactured by the more expensive roller drying process. Industrial products manufactured from grain include ranges of adhesives or glues and more recently, in biodegradable packaging materials such as expanded loose fill from wheat and maize derivatives and films of polylactic acid derived from maize.

Raw materials Mass in

Mass out Extruder barrel Pressure

Pressure

Figure 2 Extrusion cooking showing the balance between mass flow, pressure, and heat flow.

Principles of Extrusion Cooking

Maximum expansion

Overall Balance of Forces The extrusion cooking process is used to transform raw material into hot fluid dough and to continue to change the physical nature of this dough until it is forced out of the die. At that stage, the dough must have attained the ideal form to create a structure in the extruded product. This transformation of the native raw materials has an optimum range for most product types. For some products, only small changes in native biopolymers are required, whereas for others a very high degree of change must be achieved. For each individual product type, the process must be maintained in a balance between the independent input variables to obtain the ideal conditions within the barrel to achieve this level of transformation (Figure 2). A good view of an extrusion cooking process is given by F Meuser and B van Lengerich. They showed that the relationships between the independent process inputs from the machinery and raw materials created a series of dependent variables within the barrel of the extruder. Most notable of these are residence time, temperature, pressure, moisture level, applied mechanical energy, and mass flow rate. Guy and Horne showed that biopolymers in raw materials, such as starch, are affected by these variables so that their physical form changes and dominates the physical characteristics of the fluid dough. As the dough is extruded, the new forms of biopolymers influence the expansion process both in puffing and die swell. Thus, they influence the shape, extent of expansion, and the foam texture of the extrudates. An important principle that must be understood for this is that the continuous extrusion cooking process is in a metastable steady state. Roberts and Guy showed that all extrusion cooking processes fluctuate as the balance is maintained between the independent inputs of the process. A fluctuation in an independent input that causes a perturbation of the equilibrium balance may either die away or grow and cause a larger fluctuation in the outputs and therefore in the product quality. Therefore, it is important to minimize fluctuations in the input variables, such as powder and liquid feed rates, raw material distribution, and quality.

Heat

Stabilisation Stabilization Fluid

Figure 3 Side view of screw system for a twin screw extruder used at CCFRA showing functions of the elements.

The Screw Design The screws of an extrusion cooker are designed to convey a powder or viscous fluid from the feed port to the die and to force the material through the die (Figure 3). Single screws were used in the early machines for production rates of 100–200 kg h 1, leading on from the pasta equipment, although twin screws were known and used by sausage makers. More recently, pairs of corotating intermeshing twin screw machine have been adapted from the plastics industry to become important machines for the food and feed industries. For conveying materials, the screws are designed with a pitch of 0.5–1 times its diameter and a small clearance between the leading edge and the wall. This design will provide a screw with excellent conveying power for viscous fluid and powders. However, its ability to process raw materials is very small. The second feature for an extrusion cooking screw system is designed to apply high levels of mechanical shear to the feedstock being conveyed along its length. In the single screw, this is achieved by reducing the depth of the flights as the material approaches the die and by introducing cuts in the flights to increase back-leakage. In twin screw machines, special sections are added in which the flights are reversed to give a backpressure pump acting against the main flow. These sections are made weaker by cutting gaps in the flights, so that the main pumping screws overcome them, thus achieving a steady flow of the powders and melt fluids though the reversing section under shear. In general, the feed material entering the reversing section will be

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in the form of a moist or dry powder. This will be compressed and heated by mechanical energy plus barrel heating to a high temperature in a short distance. If the temperature is sufficient to melt the crystallites in the raw material it will become soft and form a fluid, otherwise it will remain as a powder and may be extruded without any expansion such as opaque compressed powder from the die. The fluids will lose the air bubbles before reaching the die and become translucent but have the ability to retain bubbles of steam and may expand to develop alveolar structures. A special form of reverse section can be constructed from elliptical paddles placed on each shaft in a series. If successive pairs are placed at an angle to the upstream pair, a screw-like structure can be formed. This type of section acts on the fluid as it passes through, kneading the fluid against walls and the other elliptical paddles. An important feature of such a section is that it is set up as a reversing screw to ensure that all the paddles are full of fluid. If they are not full, they have little or no shearing effect on the fluid. The final role of the screws is to push the fluid melt through the dies in a controlled manner. Normally, the extruder is run with the final sections completely full, so that pressure is transmitted from the main conveying screws to the dies. In those cases where reverse sections are used, there may be a pressure drop after the reverse section and a final section of conveying screw can be used to pump the fluid through the die. In most processes, where the extrusion melt fluid has a temperature >100 C, the pressure in the die will need to be higher than the water vapor pressure. This will ensure that the fluid emerges from the die and expands in the air rather than in the die cavity. Normally, the pressure at the die for good control of hot melt extrusions will be >40 bar. The progress in the machinery has been remarkable and the largest machine currently can process 10-30 t h 1, more than 100 times the rate of the early machines.

The Transformation of Biopolymers The main feature of extrusion cooking is the transformation of the biopolymers in a raw material feedstock. In 90% of the extruded products manufactured, the active biopolymer is starch, and for the remainder, it is a protein from oilseeds, such as soy, or wheat gluten. Physical transformation is necessary to obtain a more suitable form of the biopolymer for structure creation in the postextrusion expansion processes (Figure 1). Starch is found in many of the world major crops, cereals, such as wheat, rice and maize, and in important tubers such as potato and manioc. In all cases, it is found as partially crystalline granules, ranging from 5–100 mm in maximum dimension. The polymers can be released from the granules (Figure 4) either by melting their crystalline regions and applying large shearing forces, or by gelatinizing (melting at 60–75 C and swelling) them in an excess of water (>30–35%). For extrusion cooking at low moistures, 15–20%, the melted starch must be dispersed purely by mechanical shear to obtain a melt fluid of partially, or fully dispersed aggregates. At moistures >30%, the granules swell and are readily dispersed. The melting temperature for starch granules in a low moisture feedstock may be in the range of 120–160 C. Therefore, it is necessary to heat the feedstock to this temperature by the dissipation of mechanical energy and barrel heating. In systems with <25% moisture, the action of the screws on the powders being compressed to a density of 1.4 g ml 1 will normally achieve the required temperature by frictional heating and the dissipation of mechanical energy from the drive motor. The second part of the transformation of the starch is subtler. It has been shown that the major polymer in starch, amylopectin, is highly branched and has a molecular weight range of 108–109 Da. This size range is too large for good flow

Native starch

Melted and compressed

Early shear dispersal

Moderate shear dispersal

Figure 4 Stages in the transformation of starch in an extruder.


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properties in fluids at the concentrations found in the melt fluids. It interferes with the expansion process and reduces the extensibility of the starch films in cell walls. However, the application of high shear inputs to the fluid using reversing screws and high compression ratios can degrade the starch to a much smaller range of 1–5 106 Da. This material is much more extensible and gives a more expanded range of products. The principle of extrusion is to transform the biopolymers by heat and shearing forces to new forms. This may be a completely dispersed form, in which the native granular structures have all been destroyed leaving the polymers to form a continuous fluid in water. Such processed starch would be suitable for forming films that can retain gases during expansion to form fine foams. In examples with proteins, the polymers may be dispersed in a fluid and then allowed to aggregate during laminar flow through long dies to form sheets or fibers in a texturization process. The processing of starch may be set up to produce any type of starch structure from the native granules to the fully dispersed and degraded forms. If the range is divided into a number of stages as in Figure 4, the type formed at each stage may be associated with a different product in the list discussed earlier.

inhibit digestion such as lectins and trypsin inhibitors in soybeans and dough ball forming elastic glutenins in wheat flours.

Miscellaneous Reactions and Physical Effects

Snack Foods

The extrusion cooker is a chemical reactor which can cause interactions between some of the ingredients such as amino acids and reducing sugars to take part in Maillard reactions and similar degradative and condensation reactions. These reactions produce color and flavor compounds and may also reduce amino acid and vitamin contents. Extrusion cooking also has a unique action which serves to sterilize the materials being processed when their processing temperatures are >100 C. The time spent in the extrusion processing zone is short, only 45–120 s in most processes but the high shear fields and temperatures of 140–160 C in the shear zone help to reduce the viable cells and spore counts to low levels. Finally, the explosive release of superheated water from within cells rupture their structure and kills off the remaining viable cells.

The snack foods are made in several forms by either direct expansion, or by the expansion of dense cooked pellets. In direct expansion, the feedstock may be formed from a cereal or potato base mix containing 75–85% starch. The extrusion process is high shear at low moisture to give highly degraded starch with no granular structure and a large amount of molecular degradation. This allows an expansion to a very low specific density of 0.14–0.20 g ml 1. Directly extruded snacks may be formed as tubes at the die and injected with a cream or jam through the center to manufacture a coextrusion or coextruded snack. The simple product is coated with oil and flavorings to complete the process. For the pellet process, a similar feedstock is processed at low shear to melt the starch crystalline regions but to retain its granular structure. The cooked melted fluid is cooled to 95–100 C after cooking, before extruding as the final shape. This soft dense extrudate is cut into pellets and dried to <12% moisture. As it cools to ambient temperatures, it becomes a glassy structure and is known as an intermediate pellet or halfproduct. A snack is formed by heating the half-product for a few seconds in hot oil or hot air at 190 C. Recent developments have seen the production of such products in two layers with a half-product. On frying, this forms a large central cavity and has been called a 3D snack.

Extrusion Cooking Product Technologies Animal Feedstuffs The basic stock feeds are made with cookers and pelleting presses operating at 20–50 t h 1. This does not gelatinize the starch and merely pasteurizes and compacts the material as loose pellets. The second level of processing is obtained with expanders that add steam to an open screw system feeding pelleting presses. This process also fails to gelatinize more than a small amount of starch, until a die is used and the equipment becomes a full extrusion cooker. Feedstuffs with gelatinized and dispersed starch are made for special weaning foods and for all the marine feeds for fish and shrimps. In these products, the pellets are held together by the melted dispersed starch so that a strong structure is formed. Extruders are also used to improve the nutritional value of oilseed and other protein stocks by denaturing proteins, which

Pet Foods Dry pet foods are made from an extruded feedstock of cereals, fortified with protein-rich materials such as dried meat meal, chicken digest, and similar materials. They tend to be fairly dense products with a specific density of 0.35–0.45 g ml 1. The structural material is normally starch, which is supplied by a cereal such as wheat or maize for standard products, and rice for special dietary feeds. There may also be higher levels of oils and fats and minerals to provide a balanced diet for the animals. Many processes incorporate a preconditioning unit (Figure 2) in which the bulk of the feedstock is conveyed and mixed with oil and steam to produce a hot feedstock at 80 C for the extruder. This enables a higher throughput of materials to be processed by the extruder. Processes containing high oil contents must be balanced with materials, which absorb oil and prevent slippage in the machinery. Alternatively, the oil can be sprayed onto the extrudates post extrusion.

Breakfast Cereals A simple form of breakfast cereal is made from a cereal feedstock of wheat, maize, or rice flours and some small additions of sugar, salt, and proteins. The feedstock is processed at 20–25% moisture to a medium expansion at 150 C, to give a specific density of 0.22–0.28 g ml 1. The desired products are formed with a coarse cellular texture and thick cell walls, so

272


that they remain crisp in milk for a few minutes. This is achieved by melting the starch granules and degrading 50% of the granular structures. The recipes for directly expanded breakfast cereals may be varied to form single cereal varieties, such as crisp rice or corn pops, or to form multigrain cereals from blends of wheat, rice, maize, barley, and oats. A unique form of the expanded breakfast cereal is the highbran product in which wheat bran may be used at levels of 70–75%. In this product, a small amount of starch (15–20%) is used to bind the bran fibers together in a cellular structure. The starch must be melted and completely dispersed to achieve this effect. The second major form of extruded breakfast cereal is the flaked product, such as cornflakes or multigrain flake. This product is similar in its processing requirements to the half product snack in that it is made from a cereal feedstock at 120–130 C at low shear. The starch granules are melted, but not dispersed to any significant level. In the process, the cooked cereal feedstock is extruded as a dense fluid at 90 C and cut into small beads. Each bead forms the basis for a flake when rolled out to a thickness of 0.5–0.7 mm. This process occurs under temperature control at 40–60 C and is followed by a toasting process at high temperature of 240 C for a few seconds to blister and dry out the flakes. The degree of processing of the starch is very important for the quality of the flakes when they are consumed in milk as a breakfast cereal. If the starch is sheared too much, the flakes take up water too quickly and become limp and flabby in the bowl.

Breadings and Coatings Traditional breadcrumbs are manufactured by making loaves of bread, shredding, and drying their crumb to produce a small range of products. Several extrusion cooking processes have been set up to make similar products from the same materials and a wider range from other ingredients, which cannot be used in traditional bread. The extrusion of a wheat flour feedstock at 28–35% moisture at temperatures of 110–120 C at low shear produces expanded extrudates with cellular textures similar to breadcrumb. Starch granules within the structure should be melted to lose their crystalline structure, but only dispersed to a small degree to give material for expansion. The extrudates may be cut while still warm and moist to form crumbs, and then dried to <10% to form the glassy structure required for coating crumbs. The recipe for coating crumbs may be based on wheat flour and modified with some chalk to increase the number of cells. Other cereals such as maize and rice may be used with, or instead of, wheat flour to give a variety of products. Maize adds an attractive yellow color to products, while rice gives whiter crumbs.

Baby Food Extrusion cooking has been used to produce expanded baby foods from rice and vegetable flours such as peas and carrots. These products are similar to snack foods in that the starch must be well dispersed to give good expansion and a light

texture. The process must be controlled in terms of temperature to keep the mass temperature as low as possible <130 C during processing. The second form of baby foods is more important because it represents a larger amount of production. It was developed to match the roller-dried instant baby food, which is consumed as porridge, prepared by mixing water or milk with a dry instant powder. The extruded product is made by processing a feedstock of cereals with milk solids under conditions of medium shear input and controlled temperature. The aim is to melt the starch granules, but to retain their structures to a large extent. This gives a high paste viscosity when added to water or milk and produces a more attractive porridge. It is also important to control the temperature of the fluid to reduce any browning reactions that would discolor the products and reduce the nutritional quality of the proteins.


• •

Develop a new product concept relying on extrusion technology, and outline how you would choose and test equipment and processing conditions to develop it. Survey some of the grain products in your local supermarket and determine which are (or could be) made by extrusion.


• •

Investigate in more depth the variants available in extrusion technology and their applications. How is digestibility of starch and protein affected by extrusion?

See also: Non-food Products from Grains: Cereal Grains as Animal Feed; Pet Foods; Processing of Grains: Cereals: Breakfast Cereals; Wheat Processing: Snack Foods: Processing.

Further Reading Blanshard JMV (1995) The glass transition, its nature and significance in food processing. In: Beckett ST (ed.) Physico-Chemical Aspects of Food Processing, pp. 17–48. London: Blackie Academic and Professional. Bouvier J-M (2001) Breakfast cereals. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 133–161. Cambridge: Woodhead Publishing. Bredie WLP, Mottram DS, and Guy RCE (1998) Aroma volatiles generated during extrusion cooking of maize flour. Journal of Agricultural and Food Chemistry 46: 1479–1487. Bredie WLP, Mottram DS, Hassell GM, and Guy RCE (1998) Sensory characterisation of the aromas generated in extruded maize and wheat flour. Journal of Cereal Science 28: 97–106. Bredie WLP, Mottram DS, and Guy RCE (2002) Effect of temperature and pH on the generation of flavour volatiles in extrusion cooking of wheat flour. Journal of Agricultural and Food Chemistry 50(5): 1118–1125. Frame ND (1994) The Technology of Extrusion Cooking. Glasgow: Blackie Academic and Professional. Guy RCE (1998) Measurement of the physical change in starch during extrusion cooking. In: Chang YK and Wang SS (eds.) Advances in Extrusion Technology: Aquaculture/Animal Feeds and Foods, pp. 243–252. Lancaster: Technomic Publishing.

PROCESSING OF GRAINS | Extrusion Technologies Guy RCE (2001) Extruded snack foods. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 161–181. Cambridge: Woodhead Publishing. Guy RCE (2001) Extrusion Cooking: Technologies and Applications. Cambridge: Woodhead Publishing. Guy RCE (2001) Understanding extrusion. Food Engineering and Ingredients 26: 29–31. Guy RCE and Horne AW (1987) Extrusion cooking and co-extrusion of cereals. In: Blanshard JMV and Mitchell JR (eds.) Food Structure–Its Creation and Evaluation, pp. 331–350. London: Butterworths. Kazemzadeh M (2001) Baby foods. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 182–198. Cambridge: Woodhead Publishing.

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Kokini JL, Ho C-T, and Karwe VK (1991) Food Extrusion Science and Technology. New York: Marcel Dekker. Mercier C, Linko P, and Harper JM (1989) Extrusion Cooking. MN: American Association of Cereal Chemists, St. Paul, 435–462. Meuser F, Gimmler N, and van Lengerich JL (1992) A systems analytical approach to extrusion. In: Kokini C-T, Ho , and Karwe VK (eds.) Food Extrusion Science and Technology, pp. 619–630. New York: Marcel Dekker. Roberts SA and Guy RCE (1987) Meta-stable states in a food extruder. Journal of Food Engineering 6: 103–112. Riaz MN (2001) Selecting the right extruder. In: Guy RCE (ed.) Extrusion Cooking: Technologies and Applications, pp. 29–49. Cambridge: Woodhead Publishing.

Starch: Uses of Native Starch JW Lawton (Retired), ARS-USDA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

modified organisms) status of cornstarch reduces its use in some parts of the world.

The industrial uses of starch. Where starch is used in food. What the functional properties of starch are Where starch is used in the paper production. How starch is used in corrugated board and bag manufacturing. Types of physical starch modifications for food.

Learning Objectives Achieve an understanding of:

• • • •

where native starch is used in nonfood application. the main function of starch in food applications. why starch needs modification for use in food and nonfood applications. types of nonchemical modifications being used to modify starch and why these nonchemical modifications are needed.

Production Plant materials high in starch have always been an important part of the human diet. Traditionally, these materials have found their way into either human or animal food. Because of the abundance of these starchy natural materials, it is not surprising that applications other than caloric value have been found for starch. Early in human history, starch was used to coat papyrus and Romans documented the production of paste from white flour and vinegar. The variation found in the different sources of starch gives it great versatility in the type of uses. Starch can contribute to adhesion, viscosity, film forming, binding, and moisture retention, just to name a few. Starch is an attractive industrial material because of its abundant supply, low cost, renewability, and ease of modification. Commercially, available starches are mostly isolated from either cereals (corn and wheat) or tubers and roots (potato and cassava). The United States is the largest producer of starch, producing over 51% of the world’s supply. Approximately 71 million tonnes of starch was produced worldwide in 2011. Of this, about 33 million tonnes were sold as primary starches, with 25 million tonnes being native starch and 8 million tonnes being modified. Of the total world production, 76% comes from corn, which can be native or modified. Figure 1 shows the global supply of starches. Less than 2% of the starch comes from sources other than corn in the United States. Cornstarch is the main native starch produced worldwide, which accounts for 52% of the global supply (Figure 2). However, on a global scale, more native cassava starch is traded. This occurrence is because the United States consumes its own native cornstarch and the GMO (genetically

274

Composition and Properties Starch is deposited in the plastid of higher plants in the form of granules. The size and shape of the granules vary with botanical source (Table 1). The density of these granules is 1.5 g cm 1. The granules are composed of two polymers of D-glucose: amylose and amylopectin. Amylose is a lightly branched polymer, with a molecular weight ranging from 105 to 106, depending on the botanical source. Amylopectin is highly branched and its molecular weight ranges from 107 to 108. The ratio of amylose to amylopectin varies with botanical source. Most starches contain 17–27% amylose and 72–82% amylopectin. Some cultivars contain up to 70% amylose, whereas others contain no amylose. Botanical sources of corn containing only amylopectin were referred to as waxy corn. The waxy corn containing only amylopectin does not contain more wax; it is only an appearance description of the cultivar. Other botanicals that contain only amylopectin also use the description waxy such as potato. Native starch granules are partially crystalline where the amount of crystallinity depends on its botanical source. Amylopectin is the polymer that provides the partial crystallinity of starch, whereas amylose is completely amorphous. The native crystalline nature of amylopectin consists of parallel-stranded double helices. Native starch granules also contain small amounts of protein, lipid, and minerals. Generally, the amounts of these minor constituents of starch make up less than 2% of the granule of cereal starches and less than 1% for tubers and root starches. Gelatinization is the process of disrupting the molecular structure within the starch granule as it is heated in the presence of water. During the gelatinization process, the viscosity is increased as the granules absorb water and swell. Pasting is the influence of further heating after gelatinization. Additional heating causes the granules to become distorted; soluble starch is released into the solution and eventually, total disruption of the granules occurs. Many applications of starch rely on the rheological and textural properties of the starch paste. The properties of the paste depend on many factors including botanical source, amylose content, amylose/amylopectin ratio, degree of granular disruption, additives, temperature, time, and chemical modification. Figure 3 illustrates the starch paste viscosity of different starches. Tubers and root starches swell more rapidly and have higher paste viscosity and solubilities than cereal starches. As the starch paste cools, amylose separates and retrogrades (crystallizes) quickly, whereas amylopectin requires a longer amount of time to retrograde. Viscosity of the paste increases on cooling and starches containing greater amounts of amylose have a greater increase in viscosity due to amylose retrogradation. Starch paste containing amylose will generally gel on cooling while pastes made from waxy starches, which contain no amylose, will remain fluid on cooling.


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PROCESSING OF GRAINS | Starch: Uses of Native Starch

Wheat, Potato, 4%

Other, 2%

5%

Corn, 44%

Cassava , 22%

Modified, 23%

Figure 1 World production of starch.

Other, 2% Wheat, 5% Potato, 7%

Corn, 52% Cassava, 34%

Figure 2 Global production of native starch.

Nonfood Uses of Starches Starch is used in many different industrial products (Table 2) and its function ranges from being an adhesive, binder, flocculent, filler, and fermentation ingredient to being a viscosity modifier.

Starch Used in Paper Production It is estimated that about 5 million tonnes of starch is used worldwide in the paper industry annually, with paper

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containing about 1.5% starch on average. Starch consumption in North America is estimated to be 3.8 billion pounds annually. Starch content in paper depends on the type of paper and its quality. For example, tissue-grade paper contains low amounts of starch, whereas fine writing paper can contain up to 10% starch. Corn-based starches account for 95% of the starch used in paper in the United States, where 76% of it is modified. In contrast, Asian and African paper industries use less than 60% and 35% modified starches, respectively. The largest starch source for paper manufacture in the United States is corn, but other starch sources can be and have been used. Most of the starch used in paper manufacturing needs to be modified. It can be either modified at the paper mill or purchased premodified. Currently, over 75% of the starch used in paper manufacturing is chemically modified, but in the past, large amounts of unmodified starch were used in paper production. Starch used in paper manufacture is generally separated into three application areas: wet-end internal sizing, surface sizing, and coating. Wet-end internal sizing is used to influence dewatering and the retention of fillers and fiber during paper production. Wet-end internal sizing can be divided into acid, alkaline, and neutral sizes. Alkaline sizing is the prominent system used in the wet end of paper production. Alkaline conditions yield stronger paper, which allow the mills to use more fill and less fiber, thereby saving money. Increases in the use of alkaline sizing have led to an increase in the use of starch. Before the switch to alkaline sizing, manufactures of uncoated paper used 4 kg of starch per tonne of paper. Mills using alkaline technology average between 4.5 and 8 kg of starch per tonne of paper. The overall market for starch in wet-end internal sizing in North America was 317 million kg in 2000. Waxy corn starch holds half the maker for paper starches used in the alkaline process. Starch is used in the wet end to improve strength and product appearance. Starches used for sizing may be unmodified or specially modified, uncooked, cooked before addition, or pregelatinized and dried. Cationic starches, which are starch derivates, are the preferred wet-end starch. By being positively charged, they are attracted to the negatively charged cellulose and fillers. This event increases fiber-to-fiber and fiber-to-filler bonding, thereby increasing the strength and filler retention. These starches provide strength and drainage improvement, as well as improved filler retention, in contrast to using native cornstarch. The largest volume of starch used in paper production is for the purpose of surface sizing. Surface sizing improves the paper’s finish, gives a better writing and printing surface, and minimizes lifting. Sizing is accomplished by running the paper through a sizing solution and then through sizing rolls. These rolls press the sizing into the paper and remove the excess from the surface of the paper. To make the sizing solution, paper mills usually purchase unmodified and unconverted starch and convert the starch at the mill. Preconverted starches such as acid-modified, oxidized, acetylated, and hydroxyethylated are also widely used. Cooked unmodified starch is too high in viscosity for most sizing operations. Consequently, the viscosity of the starch is usually reduced. This is normally done at the mill by enzyme conversion, thermal conversion, or thermochemical conversion. Paper coating refers to the addition of pigment, adhesives, and other materials to the surface of the paper. The procedure is


276 Table 1

Structure and composition of native starches High-amylose corn

Property

Dent corn

Waxy corn

Granule size (mm) Average granule size (mm) Granule shape

5–30 15 Round, polygonal

5–30 15 Round, polygonal

Amylose (%) Amylose DP a Amylopectin (%) Crystallinity (%) Gelatinization temperature ( C)

27 800 72 27 62–74

0 NA 99 28 63–72

5–30 10 Round, polygonal, irregular 50–70 700 30–50 – 95–130

Wheat

Potato

Cassava

1–45 25 Round, lenticular

5–100 40 Oval, spherical

4–35 25 Oval, truncated, kettledrum

27 800 72 20 52–64

25 3000 74 24 59–69

27 3000 82 24 52–64

a

DP, average degree of polymerization. Source: Shogren RL (1998) Starch properties and materials applications. In: Kaplan DL (ed.) Biopolymers from Renewable Resources, pp. 30–46. New York: Springer; Whisler RL and BeMiller JN (1997) Starch. In: Carbohydrate Chemistry for Food Chemistry, pp. 117–151. St. Paul, MN: Eagan Press; Rapaille A and Van Hemelrijck J (1992) Modified starches. In: Imeson A (ed.) Thickening and Gelling Agents for Foods, pp. 171–201. London: Blackie Academic and Professional; Stevens ES (2002) Green Plastics. Princeton, NJ: Princeton University Press; Thomas DJ and Atwell WA (1999) Starches Practical Guides for the Food Industry. St Paul, MN: Eagan Press.

RVA viscosity (cps)

Temperature Profile

80

9000 Potato

60

6000 40

Corn Tapioca

3000

Wheat

20

Temperature (⬚C)

100

12000

Waxy Corn

0

0

3

9 6 Time (min)

12

0 15

Figure 3 Pasting profiles of unmodified native starch. The pasting viscosity and temperature time profiles were determined using a Rapid Visco Analyzer (RVA).

commonly called color coating. Some older literature refers to the procedure as pigment coating. The coating is done to provide whiteness, brightness, gloss, and opacity, as well as adequate surface for printing. The adhesive must not only act as a binder for the pigments but also act as a carrier for the pigments. Coating starches need to have lower viscosity than other starches used in the paper industry. This is because there needs to be a significant amount of starch present to bind the pigments, but the coating still needs to be applied as a fluid. Due to the higher starch solids, there is a greater potential for retrogradation to occur. Therefore, chemically modified starches, such as hydroxyethyl starch, which has a lower tendency to retrograde, are used as coating starch. However, higher cost usually limits the use of chemically modified starches in conventional coatings. Most starches used in paper coating applications have been enzymatically converted at the mill to achieve higher starch levels. Continuously enzyme-converted starch has lower viscosity and a more stable paste than batch-converted starch of the same solids content. Thermochemical conversion of starch with oxidants is capable of producing high solids coating binder at low cost. Compared with other binders such as latex, starch has lower adhesive strength, but is less expensive. Some coatings

contain a mixture of starch and more expensive binders to obtain a compromise between adhesive strength and cost. Corrugated board manufacturers are large consumers of starch in the paper industry. Nearly all corrugated board produced uses starch as the adhesive component. Corrugated board is a combination of liners (flat) and fluted paper. The paper to be fluted is first softened by heat and moisture and then passed through corrugated rolls to form flutes. Adhesive is applied to the tips of the flutes and to the face of the line. The two are brought together under heat and pressure to form a single-facer web. A second liner is added to the single-facer web under similar conditions to form a flute double backer that is used in the familiar shipping containers (boxes). Additional single facers can be applied to double backers to build double and triple wallboard. Various weights and thicknesses of liners are used to produce corrugated boards of different strengths for various applications. The substance used to join the liners and flutes of corrugated board is usually a two-phase starch adhesive. The liquid or carrier phase contains cooked (15–20% of the total starch) starch, sodium hydroxide, and water. The solid phase contains raw starch and borax. The total solids of the adhesive are about 20%. The sodium hydroxide is added to increase the wetting of the cellulosic fiber and reduce the gelatinization temperature of the starch. The borax is used to cross-link the carrier starch and increase water-holding capacity. When the adhesive is applied to the heated flute tips, the raw starch is gelatinized in place. Then, the fluted tips are brought into contact with the liners and passed through a roll to bond the material permanently. Large amounts of starch or starch-based adhesives are used in the manufacture of paper bags and sacks. The three types of bag adhesives used are side seam, bottom paste, and cross paste. The formulations of the adhesives for the three types of adhesive operations are quite different. During production of a single-layer bag, the paper is formed into a tube and the tube is held together with a side-seam adhesive. This adhesive needs to be slow-drying, nonpenetrating, and made up of low solids having a high dry-bond strength. Side-seam adhesives usually contain white dextrin or acid-modified starch, so the viscosity

PROCESSING OF GRAINS | Starch: Uses of Native Starch Table 2

Industrial products using native starch

Domestic products Briquettes Diapers Typewriter ribbons Trash bags Twine, cord, string Misc. industrial Explosives Filters Fireworks Drilling fluids Plastics Rubber Tires Fermentation Alcohol, fuel, and potable Beer Lactic acid Building materials Ceramics Coatings Cardboard Wallboard Linoleum Fiberboard Ceiling tile Wallpaper Cork products Chemicals Coating (food and drug) Dispersing agent Industrial alcohol Organic solvents Acetic acid Surgical dressing Sorbitol Dextrose (glucose) Paper and paper-related products Abrasive paper and cloth Bookbinding Labels Paper Straws Paste, adhesive Adhesives Binders Glues Gums Paste Textile Cord polishing Dyes Oil cloth Printing Sizing Window shades

will not be high. The adhesive needs to have low viscosity, because it is pumped to the applicator. Bottom-paste adhesive is used to close the bottom of the tube (bag). This adhesive needs to have greater tack than the side-seam adhesive so as to keep the bag from reopening at the bottom seam. The bottom

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paste can be made from either white dextrin or starch and has a greater viscosity than side-seam adhesive. The cross paste is only used in the production of multiwall bags. It is similar to the side-seam adhesive, but with the added requirement of it not bleeding through to the other layers. Other ingredients added to a side-seam adhesive to produce a cross paste are minerals and poly(vinyl acetate) to reduce bleed-through and urea–formaldehyde or poly(vinyl alcohol) for water resistance.

Starch-Based Adhesive Adhesives are used in a variety of applications, with more than 1000 different types of natural and synthetic adhesives used to manufacture many materials. With industries looking for green alternatives for adhesives, natural adhesives and sealants are increasingly being used. Natural adhesives account for only about 5% of the adhesive market. However, large amounts of natural material are used in petroleum-based adhesive formulations. Natural materials account for about 30% of all components in adhesive formulations. Natural adhesives are derived from corn and wheat starch, lignin, vegetable oils, and plant and animal proteins. Starch-based adhesives make up the largest segment of natural adhesives. Approximately 60% of the natural adhesives produced and consumed in the United States were derived from corn and wheat starch. Environmental concerns have spurred the use of natural adhesives that are renewable, have lower volatile organic compounds, and are biodegradable. The success of some of the starch-based adhesives can be directly related to solid-waste disposal problems and recycling operations. Starch-based adhesives are now preferred in some types of automated systems because of easy equipment cleaning and flow characteristics. Starches must be converted from their natural state before they can be used as an adhesive. Methods of conversion include heating, oxidation, and alkali and acid treatment. Dextrins are a starch conversion product. They are produced by dry-roasting starch with an acid catalyst. Starches such as potato, cassava, and sago are generally easier to convert to dextrins. However, due to the low cost of cornstarch, it is most often used to produce dextrins in the United States. Dextrins can be divided into three categories based on their manufacture: white dextrins, yellow dextrins, and British gums. White dextrin is roasted for a shorter time and at a lower temperature than yellow dextrin or British gum. British gum is roasted for the longest time and at the highest temperature. The roasting times and temperature determine the degree of polymerization of the dextrins. Dextrins are used as adhesive components in bag manufacture, lamination, carton seals, stamps, labels, envelope flaps, and tape.

Other Uses of Starch There are numerous other uses of starch that make up many niche markets. Starch is an excellent binder and is used in the manufacture of charcoal briquettes, ceramics, sand molds, gypsum board, crayons, and chalk. It is also used as a binder in foundry applications and is expected to grow to over 61 million kg per year. By using starch in ceramics, fewer

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hazardous air pollutants are released during firing, in contrast to the pollutants released by bitumen, pitch, or lignin sulfate. Starch needs to be modified so it is cold water-soluble to be used as molding sand binder. Starch has a long history in the textile industry, but has declined in use as the industry has moved out of the United States. About 80% of the starch consumed in textiles is used in warp sizing. Most of the starches used in warp sizing are modified. Acid-modified starch is the predominant starch used for warp sizing, although some oxidized starch is used. Warp sizing liquid is coated onto yarn to increase strength and abrasion resistance during weaving. The sizing is removed from the finished fabric by washing (desizing). Starches are also used for textile finishing. The finishes are intended to improve the appearance, ‘feel,’ and draping qualities of the material. Starches are used in oil-field applications as viscosity modifiers and to prevent drilling-fluid losses. Drilling fluids are thixotropic solutions that are used to cool the drilling bit and to suspend solids for movement away from the bit. High viscosity is needed at low shear to suspend solids, and low viscosity is needed at the high shear region around the drill bit where rapid fluid movement is needed to cool the bit. High viscosity is needed to reduce drilling-fluid losses. Starch uses in drilling fluids are restricted because of its instability above 107 C. It is highly susceptible to bacterial degradation, and starch solutions have reduced permeability when injected into cores. Chemicals are produced from starch by either fermentation or biochemical reactions. Because starch yields pure glucose upon hydrolysis, it is now being used in many fermentation processes. Ethanol is the chemical produced in the greatest quantity from starch. Other chemicals produced from glucose fermentation include acetic acid, citric acid, lysine, lactic acid, and gluconic acid. The fermentation of glucose to lactic acid, from a mass balance point of view, is as effective as the fermentation of glucose to ethanol. The molar yield of lactic acid is two moles of lactic acid per mole of glucose where commercial strains are used in anaerobic fermentations. Alcohols other than ethanol can also be fermented from converted starch or glucose, such as butanol and isopropanol. Butanol and acetone can be produced by one of the oldest industrial bacterial fermentation processes (Weizmann process) dating back to 1916. The yield of product and the ratio of butanol to acetone vary depending on the bacterial species used. Other chemicals such as butyric acid, formic acid, and acetaldehyde can also be produced from glucose derived from starch. Polyhydroxy compounds can be made from starch. Glucose is the most common polyhydroxy compound obtained from starch. Yields of glucose obtained from acid or enzymatic depolymerization of starch are 90–95%. Glucose can be chemically converted to a variety of cyclic and acrylic polyols, aldehydes, ketones, esters, and ethers. The most widely used polyol made from glucose is sorbitol. Its functional properties (e.g., sweeteners, humectants, and bulking agents) make it suitable for a variety of applications.

biodegradable polymers. Plastics intended for one-time uses such as food packaging are difficult to recycle and constitute more than 7.7 billion kg a year market in the United States alone. Recycling efforts around the United States have improved in recent years, but some items such as foodcontaminated plastic are still difficult to recycle. Other items such as plastic bags are being banned, because of their perceived effect on the environment. Because of starch’s biodegradability, relative low cost, and ready availability, it has received considerable attention as an additive to impart biodegradability to single-use plastic. Starch can be used to make plastic-like materials in several ways. A loose-fill packaging material containing 95% starch was first introduced more than 20 years ago. Expanded packaging foams (peanuts) are made by extruding moist starch where the water content of the starch serves as the blowing agent. The original starch foam was prepared from a slightly hydroxypropylated high-amylose cornstarch. A small amount of poly(vinyl alcohol) was coextruded with the starch in the presence of 16% water. The commercial starch-based loose-fill foams on the market generally contain more than 90% starch. These foams have now captured 15–20% of the 4 million kg per year loosefill market and will likely continue to grow. Starch-based loosefill foam has two main drawbacks when compared to expanded polystyrene: (1) It is not as resilient and (2) it has a greater bulk density. The greater bulk density of starch-based foams makes it more expensive per volume basis. It also adds more weight to the freight cost, as more is needed to cover the same volume. Starch-based loose fill does have the advantage of being biodegradable. It is also water-soluble and therefore can be disposed of by dissolving in water and discarded into the wastewater system. Starch-based loose fill has the unexpected property of being antistatic and is used for shipping of electronics. Thin-walled molded articles such as plates, cups, trays, and packaging cushioning (Figure 4) can be prepared by cooking raw starch and water in a mold. This technology is similar to waffle manufacture in the food industry. An article is prepared by feeding aqueous starch batter into a heated mold, with subsequent heating and evaporation of the water. The rapidly evaporating water acts as the blowing agent and expands the starch into the shape of the mold. Molded articles can be made that contain 100% starch, but plant fibers, minerals,

New and Future Uses of Starch For over 30 years now, there has been a keen interest in replacing petroleum-derived disposable plastic articles with

Figure 4 Starch-foamed articles manufactured by baking technology.

PROCESSING OF GRAINS | Starch: Uses of Native Starch plasticizers, and other biodegradable polymers are usually added to improve the physical properties. Potato is the starch most often used in the manufacture of these foamed articles, because of its greater foaming ability and lack of order. Cereal starches can be used but usually need other additives to achieve the same amount of foaming. Some items are already on the market in Europe and the United States. McDonald’s® even test-marketed clamshells that used this technology. Gelatinized starch, referred to as destructured starch, is used to make starch-based plastic. The term ‘destructurized’ describes starch that is extruded at 5–30% moisture under elevated pressures and at temperatures that are above its glass transition temperature and melting temperature. Starch prepared in this manner is thermoplastic and will flow upon heating. Thermoplastic starch resins usually contain various synthetic polymers (poly(vinyl alcohol), poly(ethylene-coacrylic acid), polycaprolactone, and poly(ethylene-co-vinyl alcohol)), plasticizers, and lubricants that improve the properties of the resin and/or the properties of the final product. Thermoplastic starch resins generally contain at least 60% starch. These starch-based resins can be injection-molded into cutlery and golf tees, as well as blown into leaf and lawn compost bags and mulch film. The resins can also be blowmolded into bottles and other containers. Unfortunately, starch-based resins have not made much of an impact on the market because of higher cost and inferior physical properties compared to synthetic resins. Granular starch has been used as a filler in some types of plastic since the 1970s. Generally, starch allows for or increases the biodegradation and/or lowers the cost of the final plastic product. In these systems where starch is a filler in a composite, it is diluting the resin, which is the continuous phase. This can lead to the reduction of some of the physical properties of the composite such as tensile strength, impact strength, and elongation. This reduction in physical properties usually limits the granular starch content in the composite to 40% or less. Much of the early work was done using granular starch as filler in nonbiodegradable synthetic polymers such as polyethylene and polyvinyl chloride. In the early 1990s, new biodegradable polymers were produced such as poly(b-hydroxybutyrate-cohydroxyvalerate), poly(e-caprolactone), and poly(lactic acid). These new polymers had excellent properties but were more expensive than their nonbiodegradable counterparts. Because of starch’s biodegradability and low cost, it was naturally thought of as a filler in these new polymers to reduce the overall cost of these new resins. These starch-filled composites suffer from the same problem as the nonbiodegradable-filled synthetic polymer in that their physical properties are compromised.

Food Uses of Starches Currently, less than 30% of the starch produced in the United States and Europe is used in food, whereas a greater amount of the starch produced in third-world countries is used in food. Starch serves many functions in food such as thickeners, gelling aids, texturizers, emulsifiers, bulking agents, adhesives for coatings, water-binding, and fat substitutes. Table 3 lists the food

Table 3

Food products using native starch

Baking snack foods Baking powder Biscuits Bread and roll Cakes Cookies Cracker Frosting Pies Pretzels Canning Berries Fruits Fruit fillings Soup Tomato sauce Vegetables Confectionery Chewing gum Chocolates Dusting powders Marshmallows Nougats Condiments Catsup Gravies Mayonnaise Mustard Salad dressing Sauce mixes Fats and oil Margarine Pan coatings Frozen desserts Frozen puddings Ice cream or milk Powder mixes Sherbets Meat products Bologna Fish, seafood Mincemeat Sausage Surimi Misc. food Baby food Cheese spread Coffee whitener Precooked frozen meals Powder beverage mixes Pudding Mixes, prepared Cake Coating and breading Cookies, brownie Dessert Frosting Gravy Instant breakfast foods Quick bread Seasoning Soup

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280 Table 4

PROCESSING OF GRAINS | Starch: Uses of Native Starch Properties of native starch paste

Property

Dent corn

Waxy corn

Wheat

Potato

Cassava

Paste viscosity Paste stability shear Paste stability acid Paste stability freezing Retrogradation rate Water-binding capacitya Texture Clarity

Medium Medium low Low Low High 15 Short Low

Medium high Medium low Low Medium Very low 22 Long Medium high

Medium low Medium high Medium low Low High 13 Short Low

Very high Medium Very low Low Medium low 24 Long Very high

High Medium low Low Low low 20 Long High

a

Grams of water per parts of dry native starch to give the same hot viscosity. Source: Whisler RL and BeMiller JN (1997) Starch. In: Carbohydrate Chemistry for Food Chemist, pp. 117–151. St. Paul, MN: Egan Press; Rapaille A and Van Hemelrijck J (1992) Modified starches. In: Imeson A (ed.) Thickening and Gelling Agents for Foods, pp. 171–201. London: Blackie Academic and Professional; Maurer HW (2001) Manufacture and composition of unmodified starch. In: Starch and Starch Products in Surface Sizing and Paper Coating, pp. 25–28. Atlanta, GA: TAPPI Press.

application of starch in food. Using starch as a food ingredient requires that the functional properties of the starch match a particular application. Table 4 lists some of the functional properties of native starches. Granular starch is commonly used as dusting agents for candy, as starch molds for gumdrops, and as a carrier for baking powder. Smaller granular starches or starches with particles ranging from 1 to 2 mm have been used as fat substitutes, because at that size, they resemble fat micelles for mouthfeel. Most food uses of starch require that the granular structure be disrupted and the starch polymer released. Native starches, although widely used in the food industry, have limited resistance to the physical conditions used in processing. To improve the effectiveness of starch as a functional ingredient, native starches are chemically and physically modified. Starch can be physically modified in a number of ways such as using different heating and drying processes. Pregelatinized starches can be prepared by cooking a starch solution and drying. A cold water swelling starch can be prepared by heating the starch in 60–70% aqueous alcohol to 160 C for 5 min. The starch maintains its granular structure but loses it crystallinity. Heat–moisture treatment and annealing are physical modifications that heat the starch in the presence of water at temperatures below the glass transition temperature but below its gelatinization temperature. Annealing takes place with excess water, whereas the heat–moisture treatment uses less than 35% water. The heat–moisture treatment has no effect on granule size but does alter the wide-angle x-ray pattern for tuber and root starches. Heat–moisture treatment of high-amylose starch can be used to produce type 3 resistant starch. Combinations of different starches are also employed to achieve the functional effectiveness needed to meet processing requirements. Native starches that are not chemically modified are now finding greater acceptance in food products due to consumer demands for natural products. Consumers desire foods with simple nonchemical-sounding ingredients (clean label). This has led to using new unmodified starches such as pea and chickpea starches and modifying traditional starches without chemicals. Clean label starch modifications include heat– moisture treatment, annealing, dry roasting, spray drying, and enzyme treatment. Wrinkled pea starch, because of its

high-amylose content, is being considered as an alternative to modified starches for thickening applications. Chickpea starch is of interest for foods requiring hot viscosity such as soup. Starch manufactures have developed native waxy starches that can withstand extremes in heat and shear used in food processing. These native starches can be used in hot retorts and hot filled foods. They also work well in dressings, soups, condiments, yogurt, and puddings. The primary function of a starch in the food industry is to control viscosity. It is used to thicken, to add texture, and to control viscosity in a variety of prepared foods ranging from canned foods and salad dressings to pie fillings and puddings. Starches used during retort are fill viscosity starches designed to impart viscosity during the initial mixing and filling process of canning. The viscosifying starch is used to retain viscosity during retort and as such cannot break down at high temperatures and when high shear is applied. For salad dressing, starch is needed for both texture and viscosity control. Highamylose starches are used to provide the set (or spoonable nature) and mouthfeel, whereas a waxy starch would provide the viscosity control. Pourable salad dressing uses starch to modify the viscosity, shorten the texture, and add creaminess. Starch is used in fillings to modify the viscosity, add stability, and give a smooth texture. The starch should also not mask or alter the flavor of the filling. For fruit fillings, it is important that the starch gives a clear gel.


• • • •

What is the starch content of different starch-containing plants? All cereals contain starch and other plants also contain starch. Why are only certain plants used to obtain starch on an industrial scale? What methods are used to industrially recover starch from plants? Does starch have the same functionality within a food system when not used alone, for example, can wheat flour or corn flour be used as a thickener?



• • • •

Can starch be used to produce foods that contain fewer chemicals but are still acceptable to consumers? Can new starches find industrial application without being chemically modified? Are there new ways to physically modify starch to give it functionality similar to chemical modification? Is it still acceptable to use starch (a food source) for industrial purposes?

See also: Carbohydrates: Resistant Starch and Health; Starch: Chemistry; Starch: Starch Architecture and Structure; Processing of Grains: Starch: Modification.

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Kennedy HM (1989) Starch and dextrin-based adhesives. In: Hemingway RW and Conner AH (eds.) Adhesives from Renewable Resources. Washington, DC: American Chemical Society. Maurer HW (2001) Manufacture and composition of unmodified starch. In: Starch and Starch Products in Surface Sizing and Paper Coatings, pp. 25–28. Atlanta, GA: TAPPI Press. Nordquist CE (2001) Corrugated Adhesives Preparation, 5th edn. Atlanta, GA: TAPPI Press. Radley JA (1976) Industrial Uses of Starch and Its Derivatives. London: Applied Science Publishers. Rapaille A and Van Hemelrjck J (1992) Modified starches. In: Imeson A (ed.) Thickening and Gelling Agents for Foods, pp. 171–201. London: Blackie Academic and Professional. Shogren RL (1998) Starch: Properties and materials applications. In: Kaplan DL (ed.) Biopolymers from Renewable Resources, pp. 30–46. New York: Springer. Stevens ES (2002) Green Plastics. Princeton, NJ: Princeton University Press. Thomas DJ and Atwell WA (1999) Starches, Practical Guides for the Food Industry. St. Paul, MN: Eagan Press.

Further Reading

Relevant Websites

BeMiller JN and Whistler RL (2009) Starch: Chemistry and Technology. New York: Academic Press. Eliasson AC (2004) Starch in Food. Cambridge: Woodhead Publishing. Jarowenko W (1976) Starch based adhesives. In: Skeist I (ed.) Handbook of Adhesives, pp. 192–211. New York: Van Nostrand.

www.adhesives.org – Global Trade Association. www.corn.org – Corn Refiners. www.pulpandpaper-technology.com – Pulp and Paper Technology. www.starch.dk – International Starch Institute. www.tappi.org – Technical Association of Pulp and Paper.

Starch: Modification JN BeMiller, Purdue University, West Lafayette, IN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Most starch used in processed food and other industrial applications has been modified. Modification is done to enhance the starch’s desirable attributes, to minimize its undesirable characteristics, or to add a new functionality. Modifications can be chemical and/or physical. Cross-linking is the most important modification of a food starch. Stabilization is important for both processed food and nonfood applications. Hydroxyethylated starches and cationic starches are widely used in the paper industry.

Learning Objectives

• • •

To identify the major means of modifying starch chemically and physically. To name some properties that can be modified by each type of modification. To point out some major applications of modified starches.

Introduction Commercial sources of starches include cereal grains such as corn/maize (including waxy maize and high-amylose corn), wheat, and rice (various types). (The sago palm and roots and tubers, such as potato, cassava/tapioca, and arrowroot, are other sources.) Corn is by far the principal source of starch, with cornstarch making up 80% of the world’s commercial supply of starch. An additional 8% is obtained from wheat. The largest industrial use of starch is the production of fuel ethanol and glucose and high-fructose syrups. The remaining isolated starch is used in processed food and other industrial applications, most often after being chemically and/or physically modified in at least one way and often in multiple ways. Modification is done to enhance the starch’s desirable attributes and to minimize its undesirable characteristics. Of the starch that is used industrially (in the United States), the greatest amount is used in papermaking, which (in the United States) consumes approximately two-thirds of the remaining starch. This article emphasizes modified food starch. Starch to be used in papermaking undergoes modifications different than those to be used in food applications. Nevertheless, modified food starches exemplify why and how starches are modified.

Background Food processors generally require starches with better behavioral characteristics than are provided by native starches. Cereal

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starches produce weak-bodied, cohesive, rubbery pastes and undesirable gels when cooked. However, the functional properties of starches can be greatly improved via small amounts of modification. Modification is done to introduce specific functionalities; to make resultant cooked products better able to withstand the conditions of heat, shear, and pH (acid) associated with processing conditions; or to improve the stability of the product in which the starch is used as an ingredient. The final products are abundant, functional, and useful food ingredients, generally macroingredients. Modifications can be chemical, physical, or genetic (not covered in this article). Chemical modifications are oxidation, cross-linking, stabilization, and depolymerization. Commercial physical modifications are various types of thermal treatments. Chemical modifications have the greatest effects on functionalities. Modifications can be single modifications, but modified starches are often prepared by combinations of two, three, and sometimes four processes. Ether and ester derivatives found in modified food starches (in the United States) are the following: 1. Stabilized starches a. Hydroxypropyl starches (starch ether) b. Starch acetates (starch ester) c. Starch octenylsuccinates (monostarch ester) d. Monostarch phosphate (ester) e. Starch succinate (ester) 2. Cross-linked starches a. Distarch phosphate b. Distarch adipate 3. Stabilized and cross-linked starches a. Hydroxypropylated distarch phosphate b. Phosphorylated distarch phosphate c. Acetylated distarch phosphate d. Acetylated distarch adipate Some property improvements that can be obtained by chemical modifications include the following: 1. Cross-linked starches a. Increased gelatinization and pasting temperatures b. Increased shear resistance c. Increased acid stability d. Decreased setback of pastes and gels (improved paste stability) e. Increased viscosity of pastes 2. Stabilized starches a. Lower gelatinization and pasting temperatures b. Improved freeze–thaw stability of pastes and gels c. Decreased setback of pastes and gels (improved paste stability) d. Greater clarity of pastes and gels e. Easier redispersibility when pregelatinized 3. Hydrolytic cleavage a. Acid-modified starches


http://dx.doi.org/10.1016/B978-0-12-394437-5.00147-9

PROCESSING OF GRAINS | Starch: Modification i. Decreased viscosity of pastes ii. Lower gelatinization and pasting temperatures iii. Increased solubility iv. Increased gel strength v. Increased clarity of gels b. Dextrins i. Highly water-soluble ii. Better film formation 4. Hypochlorite-oxidized starches a. Lower gelatinization and pasting temperature b. Decreased maximum paste viscosity c. Softer, clearer gels d. Whiter 5. Cross-linked and stabilized starches a. Lower gelatinization and pasting temperatures b. Increased paste viscosity c. Other attributes of stabilized and cross-linked products Any starch (corn, wheat, rice, potato, tapioca/cassava, etc.) can be modified, but modification is practiced significantly only on corn (both normal corn and waxy maize) and potato starches and, to a lesser extent, on wheat and tapioca/cassava starches. This article is written primarily from the point of view of normal corn and waxy maize starches.

Methods of Production and Applications Cross-linked and/or stabilized starch products are prepared by chemical derivatization of a starch, most often in an aqueous slurry in a batch process. In such a process, a slurry of 30–45% solids (starch) as obtained from the wet-milling operation is introduced into a stirred reaction tank. Sodium sulfate or sodium chloride is added to inhibit granule swelling. The pH is adjusted with sodium hydroxide (to values of 8.5 to 11.3, depending on the reaction). A chemical reagent is added. Reactions may be done at controlled temperatures up to 50 C, but pasting must be avoided to allow recovery of the modified starch in granule form by filtration or centrifugation. Because the gelatinization temperature may be lowered by the modification, there may be, and often is, a limit to the degree of substitution (DS) that can be made in this manner. (The DS is the average number of hydroxyl groups per a-D-glucopyranosyl unit (the monomeric unit of starch) that have been derivatized, the maximum being 3.) In some reactions, the pH needs to be controlled by the metered addition of dilute sodium hydroxide solutions. Following modification to the desired level, the reaction mixture is neutralized and the starch is recovered by centrifugation or filtration, washed, and dried. Chemical reactions currently both allowed and used to prepare modified food starches in the United States are as follows:

•

• • •

Esterification with acetic anhydride, succinic anhydride, the mixed anhydride of acetic and adipic acids, 2octenylsuccinic anhydride, phosphoryl chloride, sodium trimetaphosphate, sodium tripolyphosphate, or monosodium orthophosphate Etherification with propylene oxide Acid modification with hydrochloric or sulfuric acids Bleaching with hydrogen peroxide, peracetic acid, potassium permanganate, or sodium hypochlorite

• •

283

Oxidation with sodium hypochlorite Various combinations of these reactions

Other reagents may be used in other countries. The most important are cross-linking with epichlorohydrin, acetylation by transesterification with vinyl acetate, and oxidation with hydrogen peroxide plus copper(II). The first two are allowed modifications in the United States, but are not practiced. Waxy maize starch modifications are especially popular in the US food industry because the inherent properties of waxy maize starch are preferred over modifications to normal corn starch.

Cross-linking Cross-linking is the most important modification of a food starch. Cross-linking occurs when starch granules are reacted with bifunctional reagents to connect hydroxyl groups on two different molecules within the granule. Cross-links reinforce the granule and reduce both the rate and the degree of granule swelling and subsequent disintegration, that is, reduce sensitivity to processing conditions (high temperature, extended cooking times, low pH, and high shear during mixing, milling, homogenization, and/or pumping). Cooked pastes of most cross-linked starches are more viscous, heavier-bodied, shortertextured, and less likely to break down with extended cooking times, greater acidity, or severe agitation than are pastes of the native starches from which they are prepared. Only a small amount of cross-linking is required to produce a noticeable effect. Most cross-linked starches contain less than one crosslink for every 1000 a-D-glucopyranosyl units. At this very low level of cross-linking, both the rate and the degree of granule swelling are reduced, paste stability is increased, and both the viscosity profile as the starch is cooked and the textural characteristics of its paste are improved, giving products in which the starch is used as an ingredient desirable bulk and body. By far, the most common cross-links are distarch phosphate esters. These distarch phosphates are prepared primarily by reaction with phosphorus oxychloride (phosphoryl chloride). To prepare cross-linked starches with phosphorus oxychloride, the reagent is added to an aqueous starch suspension of pH 8–12. Sodium trimetaphosphate or mixtures of sodium trimetaphosphate and sodium tripolyphosphate may also be used to make distarch phosphates. To cross-link a starch with sodium trimetaphosphate, it is slurried in a solution of the reagent at pH 5.0–8.5; the suspension is filtered, and the starch is dried and heated. Some cross-linked starch is made by reaction of corn starch with the mixed anhydride of adipic and acetic acids in an aqueous alkaline suspension.

Stabilization The process of introducing stabilization to a starch is sometimes called substitution. Derivatization of a starch with monofunctional reagents reduces the intermolecular associations that result in gelation of its paste and/or precipitation of the starch polymers. (The combined processes are termed retrogradation or setback.) The use of a stabilized starch product

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improves both the texture and the appearance of the food product in which it is used as an ingredient. Pastes of unmodified normal starches generally will gel, and the gels will usually be cohesive, rubbery, long-textured, and prone to syneresis. (Waxy maize starch pastes gel to a limited extent at room temperature, but will become cloudy and chunky and exhibit syneresis when stored under freezing or refrigerated conditions.) Stabilization/substitution of starch lowers its gelatinization temperature, an indication of a weakening of granules. Upon cooking, a higher peak viscosity is obtained due to greater granule swelling. Upon cooling of the resulting paste, the viscosity becomes lower than that obtained from the unmodified starch, an indication of improved stability, that is, less retrogradation, and the product changes less with time, even under refrigerated or freeze–thaw conditions. Derivatives most often employed for starch stabilization are the hydroxypropyl ether, the acetate ester, and the monostarch phosphate ester. Hydroxypropyl ether derivatives of starches are prepared by reacting a starch with an alkaline (pH 11.3) slurry containing a swelling-inhibiting salt. The reactor is charged with propylene oxide and sealed. Reaction is continued for 24 h at 49 C. In the United States, 0.2 (7.0% of hydroxypropyl groups) is the maximum allowable moles of substitution (MS). (MS is the moles of hydroxypropyl ether groups per a-D-glucopyranosyl unit. A MS value of 0.2 indicates an average of two hydroxypropyl groups per ten glucosyl units. In the context of these stabilized starch products, DS and MS are essentially the same.) Acetylation is accomplished by treating a starch slurry with acetic anhydride at pH 7–11, the optimum pH depending on the reaction temperature. Acetylated starches with an acetyl content of up to 2.5% (DS, 0.09) can be used in food products (the United States). (A DS of 0.09 indicates an average of nine acetyl groups per 100 a-D-glucopyranosyl units.) The acetate ester linkage is less stable than the hydroxypropyl ether linkage. Sodium phosphate monoesters are prepared by impregnating the starch with a solution of sodium orthophosphate. After adjustment of the pH to 5.0–6.5, the slurry is mixed and then filtered, and the filter cake is dried and heated. Monostarch phosphates produce stable pastes that are clear and have a long, cohesive texture. Paste viscosity can be controlled by varying the concentration of phosphate salt, time of reaction, temperature, and pH. Increasing substitution lowers the gelatinization temperature; products become cold-water-swelling at DS 0.07. Cornstarch phosphates of DS 0.01–0.03 produce pastes with hot viscosity, clarity, stability, and texture more like those of a potato starch. Starch phosphates are good emulsion stabilizers and produce pastes with improved freeze–thaw stability. Sodium tripolyphosphate may be used to make products of up to 0.002 DS (one phosphate group per 500 a-Dglucopyranosyl units), the maximum allowed in the United States. The process for this reaction is essentially the same as that using orthophosphate except that the pH is 5.0–8.5. Starch succinate half-esters are prepared by reacting starch with succinic anhydride.

Starches with Hydrophobic Groups Reaction of starch with 2-octenylsuccinic anhydride introduces hydrophobic substituent groups. Such derivatives can be used

as both emulsifiers and emulsion stabilizers in products based on oil-in-water emulsions, such as pourable dressings and flavored beverages. Flavor oil emulsions containing a thinboiling starch or dextrin (see later text) derivatized with 2octenylsuccinate ester groups may be spray-dried. The flavor oil in the resulting powder is protected against oxidation, and the emulsion will reform when the powder is stirred into an aqueous medium. Higher-DS products are nonwetting and are used as release agents for dusting on dough sheets and as processing aids. The maximum DS level allowed in the United States is 0.02.

Hydrolytic Cleavage Acid-modified (also known as thinned, thin-boiling, fluid, and fluidity) starches are prepared by treating a suspension of a native or derivatized starch with dilute mineral acid at a temperature below its gelatinization temperature. When a product that gives the desired cooked paste viscosity is produced, the acid is neutralized, and the product is recovered by centrifugation or filtration, washed, and dried. Even though only a few glycosidic bonds are hydrolyzed, granules disintegrate more easily and after only a small degree of swelling. Acid-modified starches form gels with improved clarity and increased strength, even though their pastes are less viscous. They are used as film formers and adhesives in products such as pancoated nuts and candies and in processed cheese loaves and whenever a strong gel is desired, for example, in gum candies such as jelly beans, jujubes, orange slices, and spearmint leaves. To prepare especially strong and fast-setting gels, a high-amylose corn starch is used. More extensive modification with acid produces dextrins. Dextrins are both more extensively depolymerized and more highly branched and, hence, are more water-soluble than are thin-boiling starches. They find use as encapsulators and carriers of flavors, especially spray-dried flavors, and in coatings, the latter because of their film-forming and adhesive properties. Yet more extensive hydrolysis, done with various amylases, produces maltodextrins, cyclodextrins, various types of glucose syrups, and high-fructose syrups.

Oxidation Depolymerization, viscosity reduction, and decreased pasting temperature can also be achieved by oxidation with sodium hypochlorite (chlorine in an alkaline solution). Oxidation also reduces the association of amylose molecules, that is, results in some stabilization, via the introduction of small amounts of carboxylate and carbonyl groups. Because the starch polymer molecules of hypochlorite-oxidized starches are reduced in molecular weight, that is, depolymerized, to some extent, such oxidized starches have some of the characteristics of acid-modified products. Oxidized starches produce intermediate-viscosity pastes and soft gels and are used when these properties are needed. They are also used to improve adhesion of starch batters to fish, meat, and vegetables and in breadings. Mild treatment with sodium hypochlorite, hydrogen peroxide, or potassium permanganate simply bleaches the starch and reduces the count of viable microbes.

PROCESSING OF GRAINS | Starch: Modification Pregelatinization Pregelatinized starches are precooked starches that can be dissolved in water at temperatures below the gelatinization temperatures of the parent starches; thus, these ‘instant’ starches need no cooking. Two processes are used to prepare a pregelatinized starch. In one, a starch slurry is simultaneously cooked and dried on hot rolls. In the other, a starch slurry is heated and subjected to high shear in the presence of less moisture in an extruder. Both types of products are then milled to the desired mesh size. Because pregelatinized starch products are powders prepared from dried pastes, generally few intact granules are present, although granule fragments may be. Both chemically modified and unmodified starches can be pregelatinized. If chemically modified starches are used, the properties introduced by the modification(s) are found in the pregelatinized products; thus, paste properties, such as freeze–thaw stability, can be characteristics of pregelatinized starches. Several physical forms of pregelatinized starches are produced. For example, some will produce smooth solutions; others will produce pulpy or grainy dispersions and find use in fruit drinks and tomato products. Pregelatinized starches are often used in dry mixes, as are maltodextrins, because they disperse readily, even when mixed with other ingredients. Starches that are not pregelatinized are known as cook-up starches.

Cold-Water-Swelling Starches Products that are gelatinized starches, that is, starches that have lost their crystallinity, but that retain their granular form, in contrast to standard pregelatinized starches, are called coldwater-swelling starches or cold-water-soluble starches, even though standard pregelatinized starches are generally even more soluble in unheated water. There are two ways that such products are prepared commercially. One way is to heat a normal starch in an aqueous alcohol solution with sufficient water to allow gelatinization and sufficient alcohol that granule integrity is maintained. The other way is to quickly heat a starch slurry in a special spray-drying nozzle and dry the droplets in a spray dryer. Cold-water-swelling products swell rapidly and thicken unheated aqueous systems. (A granular, cook-up starch requires heating a slurry to its pasting temperature before thickening occurs.) They are particularly useful in making gum candies. Both types of pregelatinized starches are useful when no heat is available, thickening is desired before heating the formulation, no step utilizes sufficient heat to cook a starch, or heat cannot be applied because of the thermal lability of another ingredient.

Other Thermal Treatments Heat-moisture treatment (HMT) involves heating starch granules with a moisture content of <35% at 80–140 C (above the starch’s glass transition temperature, but below its gelatinization temperature, at the moisture content employed). When HMT starches are cooked, they exhibit a higher pasting temperature, reduced granule swelling, reduced paste viscosity, and reduced leaching of amylose and an increase in hardness of the resulting gel. Slowly digestible starch (SDS) and resistant starch (RS) contents are somewhat increased (RS > SDS). HMT may also be practiced with flours.

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Annealing occurs when granular starch is heated in water close to, but below, the temperature at which the onset of gelatinization occurs. Annealing results in an increase in granule stability, the pasting temperature, and the hardness of any resulting gel and a decrease in granule swelling, amylose leaching, and retrogradation. The content of RS often increases. Because there are so many variables involved (type of starch, moisture content, time and temperature of heating, and heating method) in HMT and annealing, there is a wide range of attributes possible in both products. Starches with acid-, shear-, and temperature-tolerance profiles similar to those of chemically cross-linked starches can be prepared by heating a starch with a low (<15%) moisture content at a temperature above 100 C, but below that which effects thermal degradation. Drying to <1% moisture before heating and a pH of 8.0–9.5 helps change the properties of the starch. This process is practiced to increase the contents of RS and SDS and thereby to increase the content of dietary fiber in food products.

Multiple Modifications Modified food starches are tailor-made for specific applications. Most modified food starches are made by cross-linking, introduction of monosubstituent groups (stabilization), or a combination of these two approaches. Many products, in fact, have received two or more modifications. For example, a modified food starch may be a cross-linked and stabilized waxy maize starch; another may be a stabilized, acid-thinned, and pregelatinized normal corn starch. Characteristics that can be controlled/improved by multiple modifications include, but are not limited to, one or more of the following:

• • • • • • • • • • • • • • • • • • • •

Adhesion Clarity of solutions/pastes Color Emulsion stabilization Film formation Flavor release Hydration rate Moisture retention and control in product Mouthfeel of product Oil migration control in product Paste texture/consistency Product form (liquid, semisolid, and solid) Sheen of product Shelf stability of product Stability to acids Stability to heat Stability to shear Tackiness Temperature required to cook Viscosity (hot paste and cold paste)

Digestion and Metabolism Various regulations concerning reagents that may be used and the maximum allowable modification of a starch for food use, alone or in combination with another modification, are in

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effect around the world. Generally, the level of substitution in a derivatized food starch is below DS 0.1 and in the range DS 0.002–0.2. Because of this low level of modification, the digestion, metabolism, and caloric values of modified food starches are reduced only to a minor, usually unmeasurable, extent as compared to native starches. Because only monosaccharides (D-glucose in this case) are absorbed, fragments containing esterified, etherified, or oxidized a-D-glucopyranosyl units should not be absorbed from the small intestine.

• •

Modifications for Nonfood Applications

•

The papermaking industry uses modified starches not approved for food use. In addition to hypochlorite-oxidized starch (approved for food use), starches oxidized with ammonium persulfate are used as a surface size. Hydroxyethyl ethers of starches, made by reacting a starch with ethylene oxide, are the products of choice for surface sizing and coating binding. Cationic starches are substituted with ether groups that contain a quaternary ammonium group. They are used in the formation of the paper sheet as retention or drainage aids. Carboxymethyl starch is an anionic derivative used as a thickener for coating colors and a coating binder. (When used in the pharmaceutical industry as a tablet disintegrant, carboxymethyl starch is called sodium starch glycolate.) Amphoteric starches may also be employed in papermaking. Graft copolymers, such as starch-g-styrene–butadiene latex, have been made for coating paper. Starch-g-polyacrylate/acrylamide is a superabsorbent and forms hydrogels. Dialdehyde starch is used as a wet strength agent in the production of tissue. Some of the same and similar modified starches are used in oil and gas production and in other applications.


• • • •

What property improvements can be obtained by the following modifications: cross-linking, stabilization, acidmodification, dextrinization, and oxidation? What property changes can be imparted by pregelatinization, HMT, and annealing? What is the principle of making cold-water-swelling starch? What is the principle behind cross-linking?

What is the principle behind stabilization? Why are starches often modified in more than one way?


• •

•

•

What are the names and general structures of the starch polymers? What are the differences between a normal, waxy, and highamylose starch (e.g., in maize)? What are the meanings of the following starch terms: gelatinization, gelatinization temperature, pasting, pasting temperature, breakdown, setback, and retrogradation? Each native starch is unique. What are general characteristics of the following starches: normal corn/maize, waxy maize, high-amylose maize (amylomaize), wheat, rice, potato, and cassava/tapioca? What is the wet-milling process by which corn starches are isolated from kernels?

See also: Barley, Rice and Maize Processing: Maize: Wet Milling; Carbohydrates: Resistant Starch and Health; Starch: Chemistry; Starch: Starch Architecture and Structure; Genetics of Grains: Maize: Genetics; Maize: Other Maize Mutants; Rice: Genetics; Wheat Genetics and Genomics; Non-food Products from Grains: Fuel Alcohol Production; Processing of Grains: Starch: Uses of Native Starch; The Cereal Grains: Maize: Overview; Rice: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading BeMiller JN (2007) Carbohydrate Chemistry for Food Scientists. St. Paul, MN: American Association of Cereal Chemists. BeMiller JN and Whistler RL (eds.) (2009) Starch: Chemistry and Technology, third ed. New York: Academic Press. Bertolini AC (ed.) (2010) Starch. Boca Raton, FL: Taylor & Francis. Eliasson A-C (ed.) (1996) Carbohydrates in Food. New York: Marcel Dekker. Light JM (1990) Modified food starches. Cereal Foods World 35: 1081–1092. Thomas DJ and Atwell WA (1997) Starches. St. Paul, MN: Eagen Press. Whistler RL, BeMiller JN, and Paschall EF (eds.) (1984) Starch: Chemistry and Technology, second ed. Orlando, FL: Academic Press. Wurzburg OB (ed.) (1986) Modified Starches: Properties and Uses. Boca Raton, FL: CRC Press.

b-Glucans: Measurement and Processing MS Izydorczyk, Canadian Grain Commission, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Molecular structure of b-glucans. Analytic methods for the determination of molecular structure and molecular weight of b-glucans. Analytic methods for the quantification of b-glucans in grain and grain products. Production of commercial b-glucan isolates by wet extractions. Production of b-glucan-enriched fractions by dry-grain fractionation. Production of b-glucan-enriched food products. Ensuring efficacy of b-glucans in food products.

Learning Objective

• • •

To achieve understanding of analytic methods to quantify and characterize the molecular structure of b-glucans. To achieve understanding of processes and strategies used to produce b-glucan-rich food products. To ensure efficacy of incorporated b-glucans.

Introduction The mixed-linkage (1 ! 3)(1 ! 4)-b-D-glucans (b-glucans) are unique plant cell wall components that possess a number of technological and physiological functionalities important for food systems and human health. Common cereal grains are excellent sources of b-glucans, with newer oat and barley genotypes containing up to 7% and 11% of b-glucans, respectively. Cereal b-glucans can be used in the food industry as fat replacers, stabilizers, and thickening agents. However, much of the interest in the use of cereal b-glucans has stemmed from their use as functional dietary fiber constituents. b-Glucans have been demonstrated to provide a remarkable range of health benefits and are especially important against two of the most prevalent diseases in industrialized countries, namely, cardiovascular disease and diabetes. On the basis of numerous clinical studies, various global jurisdictions approved health claims that oat and barley b-glucans at a level of 3 g day1 may reduce cholesterol and lower the risk of coronary heart diseases. Mounting evidence also indicates that increased b-glucan intake could be useful in preventing and/or controlling certain metabolic syndromes, including appetite control, hypertension, gut microbiota composition, and modulating immune functions. Such evidence should encourage increased efforts toward the development and consumption of b-glucan-containing functional foods with the goal of preventing and reducing disease prevalence and decreasing healthcare costs. However, continuous scientific efforts to understand structural and physicochemical features


of b-glucans, structure/function relationships, and mechanisms behind their health benefits are needed to ensure and optimize the physiological efficacy of b-glucan-enriched foods.

Molecular Structure of Cereal b-Glucans b-Glucans are homopolysaccharides consisting of b-Dglucopyranosyl residues linked via a mixture of single (1 ! 3) and consecutive (1! 4) glycosidic linkages. The linkages are not distributed randomly along the polymeric chain. Rather, about 90% of the chain is made of cellotriosyl (containing two successive (1 ! 4) linkages) and cellotetraosyl units (containing three successive (1! 4) linkages) joined by single (1 ! 3) linkages (Figure 1). Longer celluloselike oligomers with 5–25 glucose units (or even longer) make up the remainder of the polymeric chain; these longer celluloselike oligomers are interspersed within the polymer and are connected by single (1 ! 3) linkages. b-Glucans are, therefore, linear and unbranched polymers. The presence of (1 ! 3) linkages and the random distribution of cello-oligosaccharides along the polymer chain contribute to the water solubility of b-glucans. Long blocks of adjacent b-(1 ! 4) linkages may exhibit a tendency for interchain aggregation (and hence lower solubility) via strong hydrogen bonds along the celluloselike segments; the b-(1 ! 3) linkages break up the regularity of the b-(1 ! 4) linkage sequences, making them more soluble and flexible. Long sequences of consecutive cellotriosyl units were also shown to form conformationally stable motifs (helical segments) capable of aggregation through interchain cooperative H-bonding, leading to aggregation and insolubility. Thus, the random distribution of the cello-oligosaccharides in b-glucan chains prevents these interchain interactions and formation of highly ordered structures.

Analytic Methods for the Determination of Molecular Structure and Molecular Weight of b-Glucans Glycosidic Linkages Methylation analysis of purified b-glucans followed by analysis of partially methylated alditol acetates by capillary gas–liquid chromatography with flame-ionization detection (GLC-FID) and GLC with mass spectrometry (GLC-MS) affords identification and quantification of specific glycosidic linkages in these polymers. The analysis reveals relatively large quantities of 2,4,6-Me3-Glc and 2,3,6-Me3-Glc residues, indicating !3 (Glcp)1! and ! 4(Glcp)1! linkages, respectively. Minor amount of 2,3,4,6-Me4-Glc is indicative of a relatively small number of terminal glucose units [(Glcp)1!] in the polymeric chain. Carbon-13 nuclear magnetic resonance (13C-NMR) is another method often employed in the determination of bglucan structure. An example of a 13C-NMR spectrum for

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Cellotriose unit 4G 1

Cellotetraose unit

4G 1 3G 1

4G 1

Cello-oligosaccharide unit (n≥3)

4G 1 3G 1

4G 1

4G 1

4G 1 3G 1

4G 1

n

4G 1 3G 1

4G 1

Lichenase hydrolysis

4G 1

4G 1

4G 1

4G 1

4G 1

4G 1

n

4G 1

3G 1

3G 1

DP 3

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DP≥5

DP 4

Figure 1 General molecular structure of b-glucans and hydrolysis products obtained upon digestion of b-glucans with lichenase.

C-1

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79.5 PPM

79.0

C-3

C-6

C-4

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79.5 79.0 PPM

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Figure 2 13C-nuclear magnetic resonance spectra obtained at 125.77 MHz in deuterated dimethyl sulfoxide (DMSO-d6) from oat b-glucan (a). Water-insoluble product from lichenase treatment of oat b-glucan (b). C-1 is resonance from anomeric carbon. Reproduced with permission from Wood PJ, Weisz J, and Blackwell BA (1994) Structural studies of (1 ! 3)(1 ! 4)-b-D-glucans by 13C-nuclear magnetic resonance spectroscopy and by rapid analysis of cellulose-like regions using high-performance anion-exchange chromatography of oligosaccharides released by lichenase. Cereal Chemistry 71: 301–307.

b-glucan is presented in Figure 2. The single resonance at 103.9 ppm is due to C-1 of 4-O-substituted Glcp residues engaged in b-(1 ! 3) linkages, whereas the doublet at 102.5 ppm is from 3-O- and 4-O-substituted Glcp engaged in b-(1 ! 4) linkages. Integration of resonances at 103.9 and 102.5 ppm allows the estimation of the ratio of (1 ! 3)/ (1 ! 4) linkages in b-glucan chains. The single resonance at

86.5 ppm assigned to glycosidically attached C-3 gives another indication of single (1 ! 3) linkages in cereal b-glucans. Three distinct resonances (79 ppm) from glycosidically attached C-4 arise from the three different environments possible for this carbon. The two more intense resonances at 79.4 and 79.6 ppm arise from b-(1 ! 4)-linked Glcp residue flanked on either the reducing or nonreducing end by b-(1 ! 3)-linked

PROCESSING OF GRAINS | b-Glucans: Measurement and Processing glucose residue. The lower-intensity resonance at 79.3 ppm is from the celluloselike blocks in the polymer chain, in which b-(1 ! 4)-linked glucose residue is surrounded on both sides by other b-(1 ! 4)-linked glucose residues. The resonance at 79.3 ppm is a rough measure of the proportion of sequences with three or more consecutive (1 ! 4) linkages.

weight response factors for each oligomer and is complicated by the fact that the sensitivity of PAD may decrease with increasing DP of oligosaccharides. Typical HPAEC profile of oligosaccharide released from lichenase-digested b-glucans previously extracted with water at 65 C from barley endosperm cell walls is shown in Figure 3. The two most abundant oligomers are 3-Ob-cellobiosyl-D-glucose (DP3) and 3-O-b-cellotriosyl-D-glucose (DP4), representing about 88–92% of soluble oligosaccharides present in the digest. The abundance of oligomers with DP 5–11 decreases with the increasing DP, except for DP9 oligomer that shows atypical abundance compared to other cello-oligomers. Cello-oligosaccharides with DP > 11 are also released during lichenase digestion of b-glucans; however, they are more difficult to detect and quantify because of their lower abundance and their tendency to aggregate and precipitate out of solution once released from the polymer chains. The insoluble precipitate generated during enzymatic hydrolysis of b-glucans can be partially dissolved in solvents capable of breaking H-bonds, such as dimethyl sulfoxide, and their analysis by HPAEC-PAD reveals the presence of cello-oligomers with DP up to 28 and again shows the preponderance of DP9 (Figure 4). Specific fractions of b-glucans extracted with water from barley and subsequently hydrolyzed with lichenase were shown to yield between 3% and 5% of these insoluble cello-oligosaccharides (based on the amount of the unhydrolyzed b-glucans). The products of lichenase digestion can also be analyzed by fluorophore-assisted capillary electrophoresis (FACE). The reducing ends of the liberated oligosaccharide chains are derivatized with the fluorescent dye (8-amino-1,3,6-pyrenetrisulfonic acid), separated by capillary electrophoresis, and monitored with a laser-induced fluorescence detector. Figure 5 shows an electropherogram obtained from capillary electrophoresis separation of lichenase-hydrolyzed oat b-glucan with well-resolved

Distribution of Glycosidic Linkages and Building Units in b-Glucan Chains The distribution of glycosidic linkages and the relative amount of cello-oligomers in the b-glucan chain can be construed from the enzymatic hydrolysis of these polymers with (1 ! 3)(1 ! 4)-bD-glucan-4-glucanohydrolase (EC 3.2.1.73). The enzyme, commonly known as lichenase, specifically cleaves the (1 ! 4) linkage of the 3-O-substituted glucose unit in the b-glucan chain. The hydrolysis generates mostly oligosaccharides with degrees of polymerization (DPs) of three and four – 3-O-b-cellobiosyl-Dglucose (DP3) and 3-O-b-cellotriosyl-D-glucose (DP4) – which originate from the cellotriose and cellotetraose units in the polymeric chain (Figure 1). Longer celluloselike fragments with DP 5 are also generated during the enzymatic hydrolysis, as shown in Figure 1. Several techniques have been used to analyze the oligosaccharides from lichenase-hydrolyzed b-glucans, including high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), reversephase chromatography, capillary electrophoresis, and MS. HPAEC-PAD was first used by Wood et al. to characterize oligosaccharides from lichenase-hydrolyzed barley b-glucans and became the most frequently used technique for revealing the molecular structure of cereal b-glucans. Proper quantification of oligosaccharides by HPAEC-PAD requires the knowledge of 3

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Figure 3 High-performance anion-exchange chromatograms with pulsed amperometric detection of water-soluble oligosaccharides released from barley b-glucans upon digestion with lichenase. Inset shows oligosaccharides with longer degree of polymerization. Adapted from Lazaridou A, Chornick T, Biliaderis CG, and Izydorczyk MS (2008) Sequential solvent extraction and structural characterization of polysaccharides from the endosperm cell walls of barley grown in different environments. Carbohydrate Polymers 73: 621–639.

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21 176

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Figure 4 High-performance anion-exchange chromatograms with pulsed amperometric detection of oligosaccharides in the precipitate released from barley b-glucans upon digestion with lichenase. Inset shows oligosaccharides with longer degree of polymerization. Adapted from Lazaridou A, Chornick T, Biliaderis CG, and Izydorczyk MS (2008) Sequential solvent extraction and structural characterization of polysaccharides from the endosperm cell walls of barley grown in different environments. Carbohydrate Polymers 73: 621–639.

Figure 5 Electrophoregram obtained from capillary electrophoresis separation of products of completely hydrolyzed oat b-glucan at 2 mg ml1 with 1 U lichenase/mg b-glucan, after 24 h of reaction. Reproduced with permission from Colleoni-Sirghie M, Fulton DB, and White PJ (2003) Structural features of water soluble (1 ! 3)(1 ! 4)-b-D-glucans from high-b-glucan and traditional oat lines. Carbohydrate Polymers 54: 237–249.

oligomers with DP up to 10. A key advantage of the reductive amination technique is that a single fluorophore is attached per reducing end and the detector response remains constant as the oligomeric chain length increases, thus enabling a molar quantification. The molar ratios of DP3/DP4 ranging from 1.6 to 1.7 were obtained for three different oat lines analyzed by this method; these values were slightly lower than values of 2.1–2.4 reported by Wood et al., who obtained their results by HPAEC-PAD and with no correction for differences in response factors. Matrix-assisted laser desorption/ionization MS (MALDI-MS) was used by Jiang and Vasanthan to analyze lichenase-digested water-soluble barley b-glucans. Samples were cocrystallized with matrix (2,5-dihydroxybenzoic acid), desorbed and ionized by a

nitrogen laser pulse (337 nm), and then accelerated under 20 kV with time-delayed extraction before entering the time-of-flight mass spectrometer. Quantification of oligosaccharides (DP3 to DP12) using MALDI-MS was achieved through the standard addition method (using maltoheptaose as an added standard). Figure 6 shows the MALDI-MS spectrum of oligosaccharides from lichenase-hydrolyzed water-soluble barley b-glucans. MALDI-MS appears to provide a rapid and sensitive method for quantification of oligosaccharides with DP3 to DP12, although the results had higher standard deviation compared to results obtained by HPAEC-PAD used in the same study. Also, the molar ratios of DP3/DP4 for b-glucans extracted with water from waxy, normal, and high-amylose barley were very similar to those determined by HPAEC-PAD (Table 1).


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Figure 6 MALDI-MS spectrum of oligosaccharides from lichenase-hydrolyzed water-soluble barley b-glucan passed through desalting procedure. DHB was used as the matrix. 1. [DP3 þ Na]þ; 2. [DP3 þ K]þ; 3. [DP6 þ Na]þ; 4. [DP7 þ Na]þ; 5. [DP8 þ Na]þ; 6. [DP9 þ Na]þ; 7. [DP10 þ Na]þ; 8. [DP11 þ Na]þ; 9. [DP11 þ Na]þ. Reproduced from Jiang G and Vasanthan T (2000) MALDI-MS and HPLC quantification of oligosaccharides of lichenase-hydrolyzed water-soluble b-glucan from ten barley varieties. Journal of Agricultural and Food Chemistry 48: 3305–3310. Table 1

Molecular features of cereal b-glucans Oligosaccharides released by lichenase digestion

Source Oat

Barley

Pericarp Aleurone Endosperm Wheat Rye

Detection method HPAEC-PAD HPAEC-PAD HPAEC-PAD FACE HPAEC-PAD MALDI-MS HPAEC-PAD HPAEC-PAD

HPAEC-PAD HPAEC

DP3 þ DP4

Molar ratio DP3/DP4

Linkage ratio (1 ! 4)/(1 ! 3)

Molecular weight

References

92.0 89.2–94.1 89.9–93.1 89.2–90.3 91.5 81.7–94.0 79.9–91.7 94.3–94.7 90.5–93.7 91.3–92.0 88.3 91.3–91.4

2.3 2.1–2.2 2.0–2.1 1.6–1.7 2.8–3.4 2.3–2.8 2.1–2.8 3.4–4.2 3.8–4.1 2.7–3.2 3.7 3.3–3.5

2.4 – 2.3–2.6 2.4 2.4 – – –

– 360 000–3 100 000 180 000–850 000 – 1 700 000–2 700 000 – – –

Wood et al. (1994) Doublier and Wood (1995) Skendi et al. (2003) Colleoni-Sirghie et al. (2003) Wood et al. (1994) Jiang and Vasanthan (2000) Jiang and Vasanthan (2000) Izydorczyk (2010)

209 000 800 000–1 300 000

Lazaridou et al. (2006) Wood (2010)

Despite some uncertainty as to definite quantification of the oligosaccharides generated upon hydrolysis with lichenase, it has been consistently shown that about 85–92% of cereal b-glucans are composed of b-(1 ! 3)-linked cellotriosyl and cellotetraosyl units and that the ratio of DP3 to DP4 increases in the order: oats 1.5–2.3 < barley and rye 2.7–3.9 < wheat 3.8–4.8. Differences in DP3/DP4 ratios within the same genera of cereals can be attributed to genotypic and environmental factors. Furthermore, differences have also been found according to the location of the b-glucans within the grain. For example, Izydorczyk showed that DP3/DP4 ratios of b-glucans extracted from the outer layers of barley (pericarp and aleurone) were much higher (3.4–4.2) compared to b-glucans extracted from the endosperm cell walls (2.7–3.2).

The ratio of DP3/DP4 and the presence of celluloselike fragments in b-glucan chains are important determinants of their solubility, extractability, and rheological properties. Two possible mechanisms for intermolecular associations between b-glucan chains have been proposed. One involves the side-byside associations of celluloselike segments of more than three contiguous b-(1 ! 4)-linked glucosyl units, leading to the formation of aggregates, and the other refers to the interactions of chain segments with consecutive cellotriosyl units linked by b-(1 ! 3) bonds that might form extended junction zones. The latter has been supported by findings that a helix made up of at least three consecutive cellotriosyl residues could constitute a stable ordered motif in b-glucan chains, as shown by x-ray analysis, and that the b-(1 ! 3) linkages could be directly


involved in the ordered conformation of barley b-glucans, as revealed by CP/MAS 13C-NMR spectroscopy. Lazaridou et al. showed that an increasing DP3/DP4 ratio increases the tendency of cereal b-glucans to form aggregates and enhances their gelation potential. Moreover, high ratios of DP3/DP4 and large amounts of long celluloselike fragments (DP 5) in b-glucan chains have been associated with decreased solubility or extractability of these polysaccharides from cereal grains.

Determination of Molecular Weight of b-Glucans The weight average molecular weight (Mw) and Mw distribution of b-glucan chains are important physicochemical properties of these polysaccharides directly related to their health benefits and functional properties in food products. In general, b-glucans are high-molecular-weight polysaccharides, which exhibit a broad distribution of molecular weights and structural polydispersity. A method of choice for the determination of b-glucans Mw and their distribution is size-exclusion chromatography, where polymers are separated according to their hydrodynamic volume. After separation, b-glucans are usually detected fluorometrically with calcofluor-white. Calcofluor-white has been known to bind and specifically to precipitate b-glucan from alkaline solution. The method provides, therefore, a convenient way of detecting b-glucans in extracts without any prior purification steps. It assumes that the fluorescence intensity from the calcofluor-white/b-glucan complex is not dependent on the Mw of b-glucans. However, the binding of calcofluor-white to b-glucans decreases for Mw below 20 000, rendering this method less reliable for analyzing low Mw b-glucan fractions. The method requires also a calibration of the size-exclusion columns with standards (preferably polysaccharides of similar conformation) of known molecular weight, usually determined by other preferably absolute methods. The molecular weight of b-glucans is often determined by using the peak retention time of the standard. This, however, is not recommended because b-glucans are polydispersed polymers with a broad distribution of molecular weights; Rimsten et al. recommended using the whole area under the curve to determine molecular weight averages. HPSEC coupled with multiangle laser light scattering, differential refractive index (RI), and viscosimetric detection can also be used to determine the Mw and Mw distribution of b-glucans. The method is based on the relationship between Mw and the angular dependence of the light scattered by a polymer in solution at a certain concentration. This method determines the absolute weight average molecular weight (Mw) and number average molecular weight (Mn); it also provides information about the radius of gyration, conformation of polymers, and their intrinsic viscosity. In this method, however, the RI detector detects the species being eluted from the column, and since the RI detector does not discriminate b-glucans from other unwanted impurities, it is essential that b-glucan preparations are relatively pure in order to accurately determine their Mw. The Mw of cereal b-glucans, reported in the literature, range from 200 000 to several millions (Table 1). Such a range is partially explained by genotypic and environmental factors; however, extraction and purification techniques can also considerably affect the results. Several different methods for extraction of b-glucans from grain or grain products before the

determination of their molecular weight have been developed. The most common include alkaline or water extractions with varying temperatures and extraction times. The extraction conditions (pH and ionic strength of solvents, temperature, time, and particle size) will affect the yield and molecular weight of the isolated b-glucans as different populations of these polymers are solubilized with different solvent and conditions. Complete inactivation of endogenous and exogenous b-glucanases in samples prior to extraction is probably the most important step to retain the original molecular weight of b-glucans during extraction, analysis, and storage. Autoclaving, boiling in 50–75% ethanol, steaming, or calcium chloride treatments reduce b-glucanase activity in samples and result in higher molecular weight of extracted b-glucans (Figure 7).

Quantification of b-Glucans A wide variety of assays for quantification of cereal b-glucans have been developed in recent years. One of the standard and frequently used methods for routine quantification of b-glucan content in cereal grains is based on the enzymatic assay developed by McCleary and Glennie-Holmes. The method involves hydration and gelatinization of ground grain samples at 100 C followed by hydrolysis of b-glucans to soluble fragments with highly purified (1 ! 3)(1 ! 4)-b-D-glucanase (lichenase) from Bacillus subtilis. After the separation of insoluble grain residue by filtration, the volume and pH of the filtrate are adjusted. The soluble b-gluco-oligosaccharides in the filtrate are hydrolyzed to D-glucose with another highly purified enzyme, b-glucosidase. The enzyme is devoid of any contaminating enzymes, such as amyloglucosidase, a-glucosidase, or invertase, that could release additional glucose from other grain constituents (starch, sucrose, and maltooligosaccharides). The resulting D-glucose originates only from b-glucans and is measured with glucose oxidase–peroxidase reagent. The free glucose in the sample is measured by treating 2.5 Differential Weight Fraction (1/log(g/mol)

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2.0

steamed at 100 C untreated grain

heat-treated at 75 C

1.5

1.0

0.5

0.0

100,000

500,000

1,000,000

Molar Mass (g/mol)

Figure 7 Molecular weight distribution of b-glucans extracted and purified from untreated barley grain, heat-treated grain (75 C, 45 min), and steamed-treated grain (100 C, 10 min). Izydorczyk MS, unpublished results.

PROCESSING OF GRAINS | b-Glucans: Measurement and Processing the lichenase digest directly with glucose oxidase–peroxidase reagent, and the content of free glucose is subtracted from the total amount. The method can be used for routine determination of b-glucans in grain samples, grain products, malt, wort, and beer. This enzymatic assay has been adopted as the standard method for measuring b-glucans by AACCI (Method 3223), AOAC (Method 995-16), European Brewery Convention (EBC) (Methods 3.11.1, 4.16.1, and 8.11.1), and ICC (Standard Method No. 166). Another method for measuring b-glucans is based on the specific binding of the fluorochrome calcofluor-white to bglucans. Although the exact mechanism by which the calcofluor-white/b-glucan complex develops is not known, the binding probably involves H-bonding, van der Waals forces, and hydrophobic interactions. The binding results in an increased fluorescence intensity that is proportional to the concentration of b-glucans. An automatic analysis measuring calcofluor-white/b-glucan complex formation by flow injection analysis (FIA) has been developed for the determination of b-glucans in solutions, for example, wort and beer. The method measures b-glucans in solution without any pretreatment of the samples, making it suitable for routine b-glucan determination in quality control laboratories. There are, however, some restrictions in employing calcofluor-white/FIA method for the determination of b-glucans. This method measures only the high-molecular-weight b-glucan fractions as calcofluor-white does not bind to b-glucans with molecular weight below 10 000. The high-ionic strength buffers enhance the fluorescence of the low-molecular-weight b-glucans, thereby extending the detectable low-molecular-weight limit. Higher-molecular-weight b-glucans may form aggregates with calcofluor-white, and although the aggregate formation itself does not normally interfere with the fluorescence measurements, prompt measurements are usually recommended to improve accuracy of the method. The method can be extended for measuring b-glucans in grain products provided that bglucans are made soluble. This is usually accomplished by extraction of b-glucans with mild acid solutions to ensure their complete solubilization without extensive depolymerization. The EBC recommends the calcofluor-white/FIA as the standard method for the determination of b-glucans in barley, malt, wort, and beer. The development of monoclonal antibodies against chemically modified b-glucans created an opportunity to use them in ELISA for the detection and quantification of b-glucans. Presently, however, the assay has a limited linear range and is appropriate for solutions with very low b-glucan levels (<20 ng ml1). The high-sensitivity and low-detection level maybe beneficial in some applications, but for the detection of b-glucans in grain, very large dilutions are required to bring b-glucan samples into the correct range for accurate measurements. The results of the assay are negatively affected by the presence of other cosolutes in the extract solutions (e.g., proteins, enzymes, other polysaccharides, and phenolics); this makes the extraction procedures very tedious and the whole assay lacks robustness and reliability at the present time. Other methods for measuring b-glucans that could be adapted for high-throughput screening of the b-glucan content in grain samples have also been developed in recent years; these include methods based on measuring viscosity of raw flour

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slurries to quickly predict b-glucan content in grain or nearinfrared spectroscopy.

Processing Consumers’ interest in b-glucans and healthy foods has created demand and opportunity for innovative b-glucan isolates/ ingredients and their incorporation into new and traditional food products. However, producing b-glucan isolates/concentrates and b-glucan-containing food products that fulfill expectations in terms of sensory appeal and indeed deliver the expected health benefits is challenging and requires innovative approaches and careful attention throughout the manufacturing steps. The health benefits of b-glucans are dose-dependent, and selecting ingredients and formulating food products with sufficient amount of these polysaccharides are challenges from processing and sensorial perspectives. In addition, the physiological benefits of b-glucans are associated not only with their amount but also with their viscosity-building properties linked to the high molecular weight of these polymers. Several clinical studies reported no significant benefits upon consumption of various food products containing b-glucans. The most plausible explanations relate the absence of positive effects with poor solubility and/or reduced molecular weight of b-glucans in the consumed food, which would impede the formation of viscous environment in the gut.

Chemical and Physical Processes for the Production of b-Glucan Isolates and b-Glucan-Enriched Grain Fractions as Functional Food Ingredients The production of b-glucan concentrates using wet extractions Cell walls of aleurone and starchy endosperm in cereal grains are particularly rich sources of b-glucans, and extensive efforts have been made to isolate them on a large scale. The process usually involves the (1) inactivation of endogenous enzymes in the grain, (2) extractions with water or alkali solutions, (3) removal of contaminating protein and starch using hydrolytic enzymes and/or selective adsorption, and (4) precipitation of b-glucans from the purified solutions with alcohol and freezedrying or alternatively drum- or spray-drying of the extracts. The resulting isolates may contain between 33% and 87% of high-molecular-weight b-glucans; however, the processes are impractical for commercial manufacturing because of high costs and low yields. Recently, new simplified and potentially less-expensive methods of b-glucan extraction and enrichment have been introduced. A series of products carrying the suffix ‘trim’ (Oatrim, Nutrim, and C-Trim; acronym for ‘technical research involving metabolism’) were developed in the United States in the 1990s from oats and barley. Oatrim is one of the earliest oat b-glucan products used as fat replacement due to the unique rheological properties of the mixture of b-glucans and maltooligosaccharides. It was produced by enzymatic (a-amylase) hydrolysis of oat flour or bran, followed by jet cooking at 140 C and centrifugation. Clinical studies showed that daily consumption of 5 g of b-glucan from Oatrim can lower total blood cholesterol and help to control body weight. A new generation of soluble b-glucan product, called Nutrim, was

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prepared by subjecting an aqueous suspension of barley flour to a high-temperature mechanical shearing in the presence of thermostable a-amylase, followed by centrifugations and drum-drying of the supernatant. Nutrim may contain 5–15% of b-glucans. Nutrim and Nutrim-OB, prepared in a similar way but from oat flour, can be used to replace fat, and they impart moisture, softness, and cohesiveness in baked products, cheese, and Asian noodles. Nutrim-OB was shown to contain b-glucans with lower molecular weight than b-glucans extracted from the unprocessed material, but was still effective in lowering plasma cholesterol in hamsters. Three newer oat bglucan isolates, C-Trim20, C-Trim30, and C-Trim50, contain between 20% and 50% b-glucans. They were also obtained through thermal shearing, but contain lower amount of starch compared to other ‘trim’ isolates. An additional centrifugation step prior to jet cooking eliminates a considerable proportion of starch; centrifugation and sieving steps after jet cooking can increase the content of b-glucan in the products. Glucagel, a commercial product from Australia, was obtained by hot water extraction of ground barley and precipitation of b-glucans via repetitive freezing and thawing cycles. The process did not involve inactivation of b-glucanase, but rather made use of the enzymes naturally associated with the grain (endogenous or of microbial origin) to achieve a partial hydrolysis of b-glucans. As a result, the product with average molecular weights between 50 000 and 150 000 and thermoreversible gelling properties is obtained. Glucagel has been recommended as a source of dietary fiber, as a food texture modifier, as a fat replacer, and as an ingredient in edible films. However, in clinical studies, Glucagel had no effect on cholesterol or glucose concentration, due to a substantially reduced molecular weight of b-glucans. Other recently developed b-glucan isolates include the following: an enzymatically produced concentrated oat or barley b-glucan product with high viscosity, called Viscofiber®; a warm-water-extracted product containing 70–90% b-glucans, called Cerogen™; an alkaline-extracted and intensively purified product via centrifugation, ultrafiltration, and drumdrying called, OatVantage™; and a preparation containing submicron particles obtained by nanofiltration of highly concentrated oat b-glucan extracts. Some of these commercial products contain substantial amounts of b-glucans and have been demonstrated to deliver positive results and specific health benefits in clinical studies. Most of the products have generally recognized as safe status, and in the United States, they qualify for the FDA health benefit claim. In Canada, however, the current health claims for oat and barley b-glucans exclude b-glucan products obtained by wet extractions.

Production of b-glucan-enriched products by dry-grain fractionation The nonuniform distribution of b-glucans in cereal grains creates an opportunity for their separation by dry-grain fractionation, for example, by milling. Such products obtained by physical grain fractionation have an appeal of being produced by more ‘natural’ or ‘green’ processes and may be more desirable and attractive food ingredients for health-conscious consumers than products obtained through chemical processes. The concentration of b-glucans in these grain fractions is not as high as in the isolates described earlier in the text, but an

important advantage of products generated by dry-grain fractionation is that they contain fragments of pericarp, aleurone, and/or endosperm cell walls with their natural constituents including other dietary fiber constituents (arabinoxylans, cellulose, mannose, and galactose-containing polysaccharides), vitamins, minerals, and phenolic compounds, in addition to b-glucans. b-Glucan-enriched grain fractions are eligible to carry health claims. A classic example of an oat grain product enriched in bglucans is oat bran, a product commercially available since the late 1980s and recognized for its role in lowering the blood cholesterol. The procedures involved in oat bran production may vary among various processors, but they essentially involve dry grinding and sifting operations. The enrichment factor of b-glucan in oat bran compared to whole grain usually ranges from 1.3 to 1.7 and can be controlled by varying the milling processes. OatWell® products are similar to oat bran, also produced by dry-grain milling, but purified by multiple air classification to achieve 14–22% concentration of b-glucans in the final grain fractions. More recently, an innovative high-bglucan product – ‘organic natural oat fiber’ – has been produced by mechanical and hydrothermal treatments that also convert crystalline cellulose to an amorphous form and, as a consequence, impart smooth mouthfeel and increased water absorption to the product. Compared to oats, processing of barley to produce fraction enriched in b-glucans does not have a long history. Nevertheless, several b-glucan-enriched products have been developed and the processes are described in detail in this Encyclopedia.

Production of b-Glucan-Enriched Food Products: Challenges and Strategies to Ensure Product Quality and b-Glucan Efficacy The incorporation of b-glucan into various food products has the potential to improve their health benefits; however, its addition at the level recommended by various global jurisdictions – that is, 0.75–1 g of b-glucan per serving – has proved to be a challenge, resulting often in products with lower quality and acceptance. This is especially true for traditional wheatbased products, such as bread, pasta, and noodles, for which consumers have high expectations in terms of appearance, color, taste, and texture. In bread and pasta making, the incorporation of sufficient amount of b-glucans to ensure beneficial physiological impact is often associated with replacing large amounts of wheat flour, and the resulting detrimental technological effects are caused by dilution of functional gluten proteins. The use of fiber preparations with a high concentration of b-glucans eliminates the necessity of high-supplementation levels to achieve the desired b-glucan content in the final product; b-glucan-enriched fiber fractions are, therefore, preferred over whole-grain barley or oats flours. Incorporation of b-glucan-containing ingredients usually increases water absorption and mixing time during dough development. The high water-binding properties of b-glucans interfere with proper hydration of gluten, resulting in underdeveloped gluten networks, a decrease in loaf volume and height, and increased hardness of bread crumbs. Some differences in the loaf volume were also observed upon supplementation of wheat bread with


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Figure 8 Bread prepared (remix-to-peak process) from Canadian Western Red Spring (CWRS) wheat flour (control) (left) and supplemented with 2% of high-molecular-weight (Mw 800 000) (middle) and low-molecular-weight (Mw 200 000) b-glucan preparations. Reproduced from Izydorczyk MS and Dexter JE (2008) Barley b-glucans and arabinoxylans: Molecular structure, physicochemical properties, and uses in food products – A review. Food Research International 41: 850–868, with permission.

2% of high-molecular-weight (Mw 800 000) and lowmolecular-weight (Mw 200 000) preparations of b-glucans (Figure 8). The adverse technological effects in bread manufacture associated with high contents of b-glucan fiber can be counteracted to some degree with the use of strong gluten flours, addition of vital gluten or surfactants, or the incorporation of hemicellulases. Jacobs et al. reported that the addition of xylanase to the sponge-and-dough formulas improved the loaf volume, appearance, and crumb structure of bread fortified with barley b-glucan-rich fractions. The authors also reported that the method of bread production strongly influenced bread quality; the best quality b-glucan-enriched bread was obtained by the sponge-and-dough process because the gluten network was allowed to fully develop during the 4 h sponge stage and the barley b-glucan fractions were incorporated only at the dough stage. Good results were also obtained when bread was prepared according to a short-baking process (e.g., the Canadian short process) with about 6–12% of wheat flour being replaced with barley b-glucan-enriched fractions to achieve 0.75 g of b-glucan per serving (Figure 9). The addition of barley fractions enriched in b-glucans to pasta and noodle products at up to 25% resulted in products with acceptable cooking and sensory qualities, but substantially decreased brightness and ‘speckiness’ (Figures 10 and 11). Compared to pan or hearth breads, the production of bglucan-fortified flatbreads is less challenging. Generally, consumers have greater tolerance for different color and taste of these products, and their appeal is not derived from the aerated structure. Thondre and Henry supplemented whole-wheat flour with a commercial barley b-glucan isolate to produce palatable chapatis with reduced glycemic index and 4 g of b-glucan per serving. Izydorczyk et al. produced b-glucanenriched two-layer flatbread by replacing 20% of wholewheat flour with barley b-glucan-enriched fractions, obtained by dry-grain fractionation. The water absorption of the dough was increased and its strength was weakened, but the dough exhibited good handling characteristics at the dividing and sheeting stages, and the appearance, diameter, layer separation, crumb structure, and aroma of the bread were indistinguishable from the whole-wheat flour controls (Figure 12). The flatbreads provided between 1.9 and 3.0 g of total and between 0.6 and 1.4 g of soluble b-glucans per serving. In addition, the breads were also enriched in arabinoxylans, another valuable constituent of dietary fiber, and have substantially reduced in vitro digestibility of starch (Table 2). In another study,

Figure 9 Loaves of bread prepared by Canadian short process procedure: 100% white flour (left); 100% whole-wheat flour (middle); white flour bread supplemented with 6% of barley fiber-rich fractions from waxy barley cultivar CDC Fibar (right). Izydorczyk MS, unpublished images.

pitas prepared by replacing 50% of wheat with whole-grain barley flour were shown to provide about 1 g of total b-glucan per serving. A major consideration during the production of b-glucanenriched food products is the prevention of b-glucan depolymerization that may occur due to the presence of b-glucanase in ingredients used in product formulation, presence of specific food additives (e.g., ascorbate that depolymerizes b-glucans via oxidative–reductive reactions), or high-temperature processing. Since b-glucans are easily degraded by b-glucanases, care has to be taken during production of b-glucan-rich fiber to completely inactivate b-glucanases in grain or grain fractions by certain heat treatments (e.g., autoclaving and steam treatments). Detrimental changes to the molecular weight of bglucans were also shown to occur during the bread-making processes such as mixing and fermentation; keeping these steps as short as possible can reduce the risk of degradation of b-glucans due to their shorter contact with b-glucanases present in wheat flour. Processing such as fresh pasta preparation, production of fermented soups, pancake batter, or functional drinks can also result in extensive degradation of b-glucans. Furthermore, during the typical pasteurization conditions of acidic liquid products, such as fruit or tomato juice, a

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Figure 10 Images of raw white salted noodle sheets at 2 h after processing. Left: control, Canada Prairie Spring White wheat flour (‘Vista’); middle: sheet of raw white salted noodles supplemented with 25% of fiber-rich fraction obtained by dry milling of waxy barley; right: sheet of raw white salted noodles supplemented with 25% of fiber-rich fraction obtained by dry milling of high-amylose barley. Izydorczyk MS, unpublished images.

Figure 11 Appearance of dry pasta. (a) Control, 100% semolina; (b) 100% whole-wheat semolina; (c) 100% semolina supplemented with 10% waxy barley fiber-rich fractions; (d) 100% semolina supplemented with 15% waxy barley fiber-rich fractions. Izydorczyk MS, unpublished results.

Figure 12 Appearance of two-layered pita breads. Control bread prepared from blends of 80% wheat flour and 20% whole-wheat flour (a); pita breads supplemented with 20% fiber-rich fractions obtained by milling barley with normal starch (b), waxy starch (c), and high-amylose starch (d). Izydorczyk MS, unpublished images. Table 2 Contents of b-glucans, arabinoxylans, and digestible starch in two-layered flatbreads supplemented with fiber-rich fractionsa from hull-less barley b-Glucan (g/serving)b

Digestible starch (g/g)c

Flatbread

Total

Water-soluble

Arabinoxylans (g/serving)

15 min

60 min

Controld þ20% N-FRF þ20% N-FRFpm þ20% W-FRF þ20% W-FRFpm þ20% HA-FRF þ20% HA-FRFpm

0.23 1.85 1.84 2.70 2.74 2.91 2.97

0.09 0.58 0.62 1.22 1.10 1.31 1.43

2.40 4.90 4.50 3.70 3.90 4.47 4.20

0.203 0.184 0.172 0.177 0.161 0.180 0.164

0.436 0.374 0.368 0.384 0.352 0.352 0.348

a

N-FRF, W-FRF, and HA-FRF: fiber-rich fractions obtained by dry milling from hull-less barley with normal (N), waxy (W), and high-amylose (HA) starch characteristics. PM: FRFs were additionally pin-milled to reduce particle size. b Single flatbread constituted one serving. c Results expressed as gram of starch released upon digestion with amylase per gram of available starch in the flatbread. d Control flatbreads were prepared by blending 80% straight-grade wheat flour and 20% whole-wheat flour. Source: Izydorczyk MS, Chornick TL, Paulley FG, Edwards NM, and Dexter JE (2008) Physicochemical properties of hull-less barley fibre-rich fractions varying in particle size and their potential as functional ingredients in two-layer flat bread. Food Chemistry 108: 561–570.

PROCESSING OF GRAINS | b-Glucans: Measurement and Processing Table 3

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Characteristics of soluble b-glucans in in vitro extract of control and extrudeda oat bran samples Oat bran

Extract viscosity (mPa s) b-Glucan concentration (mg ml1) Soluble b-glucan (% of total) Peak molecular weight

280 14 3.13 0.1 38.7 1.5 2 537 000 30 000

Extruded oat bran – 3H

Extruded oat bran – 4M

Extruded oat bran – 4L

2900 800 9.9 1.1 66.8 7.3 2 213 000 235 000

1700 160 11.2 0.9 80.2 6.9 847 000 80 000

131 12 14.5 1.5 101.7 5.0 211 000 13 000

Extruded oat bran – 3H: extrusion temperature (T ) ¼ 181 C, water content ¼ 18.7%, standard mechanical energy (SME) ¼ 135 Wh kg1; extruded oat bran – 4M: T ¼ 220 C, water content ¼ 14.5%, SME ¼ 125 Wh kg1; extruded oat bran – 4L: T ¼ 237 C, water content ¼ 7%, SME ¼ 148 Wh kg1. Source: Tosh SM, Brummer Y, Miller SS, et al. (2010) Processing affects the physicochemical properties of b-glucan in oat bran cereal. Journal of Agricultural and Food Chemistry 58: 7723–7730.

a

reduction of molecular weight of incorporated b-glucans occurred probably due to acid hydrolysis. There has been much speculation about the negative effects of extrusion on the physicochemical properties of b-glucans incorporated into food products. Indeed, when the extrusion conditions are severe (high-temperature, high-shear, and low-moisture), some depolymerization and disintegration of b-glucans can occur. However, more moderate extrusion conditions (e.g., 180 C, 19% moisture content) were shown not to decrease the molecular weight of b-glucans from oat bran, but to substantially increase their solubility (Table 3). The solubility of b-glucans in foods is also a concern related to their efficacy, as b-glucans not solubilized under the physiological conditions will not produce adequate viscosity in the aqueous lumen of the gut. The solubility of b-glucans in various food products varies depending on their molecular weight, processing history, the structure of food matrix, and storage.


• • • • •

What is the molecular structure of b-glucans? How do you determine the molecular structure of b-glucans? How do you determine the molecular weight of b-glucans? What processes are used to produce b-glucan-enriched ingredients? How do you ensure the efficacy of b-glucans incorporated in food products?


• • •

Quantification of oligosaccharides obtained by lichenase digestion of b-glucans. How do you improve palatability and sensory properties of b-glucan-based food products? How can new trends in the consumption of functional foods encourage consumer to use more b-glucan-enriched foods in their diet?

See also: Barley, Rice and Maize Processing: Barley: Milling and Processing; Carbohydrates: Health Effects of b-Glucans Found in Cereals.

Further Reading Bellatto S, Del Frate V, Redaelli R, et al. (2011) Use of near infrared reflectance and transmittance coupled to robust calibration for the evaluation of nutritional value in naked oats. Journal of Agricultural and Food Chemistry 59: 4349–4360. Bohm N and Kulicke WM (1999) Rheological studies of barley (1 ! 3)(1 ! 4)-b-Dglucan in concentrated solution: Mechanistic and kinetic investigation of the gel formation. Carbohydrate Research 315: 302–311. Colleoni-Sirghie M, Fulton DB, and White PJ (2003) Structural features of water soluble (1 ! 3)(1 ! 4)-b-D-glucans from high-b-glucan and traditional oat lines. Carbohydrate Polymers 54: 237–249. Colleoni-Sirghie M, Jannink J-L, Kovalenko IV, Briggs JL, and White PJ (2004) Prediction of b-glucan concentration based on viscosity evaluations of raw oat flours from high b-glucan and traditional oat lines. Cereal Chemistry 81: 434–443. Doublier JL and Wood PJ (1995) Rheological properties of aqueous solutions of (1 ! 3)(1 ! 4)-b-D-glucan from oats (Avena sativa L.). Cereal Chemistry 72: 335–340. Fincher GB and Stone BA (1986) Cell walls and their components in cereal technology. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, pp. 207–295. St. Paul, MN: American Association of Cereal Chemists. Inglett GE and Stevenson DG (2009) Converting oats to high-fibre products for use in functional foods. In: Hamaker BR (ed.) Technology of Functional Cereal Products, pp. 476–494. Cambridge: Woodhead Publishing Ltd. Izydorczyk MS (2010) Variations in content and molecular structure of barley nonstarch polysaccharides associated with genotypic and cellular origin. Cereal Chemistry 87: 376–384. Izydorczyk MS, Chornick TL, Paulley FG, Edwards NM, and Dexter JE (2008) Physicochemical properties of hull-less barley fibre-rich fractions varying in particle size and their potential as functional ingredients in two-layer flat bread. Food Chemistry 108: 561–570. Izydorczyk MS and Dexter JE (2008) Barley b-glucans and arabinoxylans: Molecular structure, physicochemical properties, and uses in food products – A review. Food Research International 41: 850–868. Izydorczyk MS, Macri LJ, and MacGregor AW (1998) Structure and physicochemical properties of barley non-starch polysaccharides – I. Water-extractable b-glucans and arabinoxylans. Carbohydrate Polymers 35: 249–258. Jacobs MS, Izydorczyk MS, Preston KR, and Dexter JE (2008) Evaluation of baking procedures and wheat flours for incorporation of high dietary fibre fractions into bread. Journal of the Science of Food and Agriculture 88: 558–568. Jiang G and Vasanthan T (2000) MALDI-MS and HPLC quantification of oligosaccharides of lichenase-hydrolyzed water-soluble b-glucan from ten barley varieties. Journal of Agricultural and Food Chemistry 48: 3305–3310. Jorgensen K and Aastrup S (1988) Quantification of high molecular weight (1 ! 3) (1 ! 4)-b-D-glucan using calcofluor complex formation and flow injection analysis. II. Determination of total b-glucan content in barley and malt. Carlsberg Research Communications 53: 287–296. Kivela R, Nystrom L, Salovaara H, and Sontag-Strohm T (2009) Role of oxidative cleavage and acid hydrolysis of oat beta-glucan in modelled beverage conditions. Journal of Cereal Science 50: 190–197. Lazaridou A, Biliaderis CG, and Izydorczyk MS (2003) Molecular size effects on rheological properties of oat b-glucans in solution and gels. Food Hydrocolloids 17: 693–712. Lazaridou A, Biliaderis CG, and Izydorczyk MS (2006) Cereal b-glucans: Structure, physical properties, and physiological functions. In: Biliaderis CG and Izydorczyk MS (eds.) Functional Food Carbohydrates, pp. 1–72. Boca Raton, FL: CRC Press.

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Lazaridou A, Chornick T, Biliaderis CG, and Izydorczyk MS (2008) Sequential solvent extraction and structural characterization of polysaccharides from the endosperm cell walls of barley grown in different environments. Carbohydrate Polymers 73: 621–639. Malcolmson L, Lukie C, Swallow K, Sturzenegger T, and Han J (2014) Using barley flour to formulate foods to meet health claims. Cereal Food World 59: 235–242. McCleary BV and Glennie-Holmes M (1985) Enzymic quantification of (1 ! 3)(1 ! 4)b-D-glucan in barley and malt. Journal of the Institute of Brewing 91: 285–295. Morgan KR (2002) Beta-glucan products and extraction processes from cereals. US Patent 6,426,201. Munck L, Jorgensen KG, Ruud-Hansen J, and Hansen KT (1989) The EBC methods for determination of high molecular weight b-glucan in barley, malt, wort, and beer. Journal of the Institute of Brewing 95: 79–82. Rampitsch C, Ames N, Storsley J, and Marien L (2003) Development of monoclonal antibody-based enzyme-linked immunosorbent assay to quantify soluble b-glucans in oats and barley. Journal of Agricultural and Food Chemistry 51: 5882–5887. Rimsten L, Stenberg T, Andersson R, Andersson A, and Aman P (2003) Determination of b-glucan molecular weight using SEC with Calcofluor detection in cereal extracts. Cereal Chemistry 80: 485–490. Skendi A, Biliaderis CG, Lazaridou A, and Izydorczyk MS (2003) Structure and rheological properties of water soluble b-glucans from oat cultivars of Avena sativa and Avena bysantina. Journal of Cereal Science 38: 15–31.

Thondre PS and Henry CJK (2009) High-molecular-weight barley b-glucan in chapatis (unleavened Indian flatbread) lowers glycemic index. Nutrition Research 7: 480–486. Tosh SM, Brummer Y, Miller SS, et al. (2010) Processing affects the physicochemical properties of b-glucan in oat bran cereal. Journal of Agricultural and Food Chemistry 58: 7723–7730. Vaikousi H and Biliaderis CG (2005) Processing and formulation effects on rheological behavior of barley b-glucan aqueous dispersions. Food Chemistry 91: 505–516. Wood PJ (2010) Oat and rye b-glucan: Properties and function. Cereal Chemistry 87: 315–330. Wood PJ, Weisz J, and Blackwell BA (1994) Structural studies of (1 ! 3)(1 ! 4)b-D-glucans by 13C-nuclear magnetic resonance spectroscopy and by rapid analysis of cellulose-like regions using high-performance anion-exchange chromatography of oligosaccharides released by lichenase. Cereal Chemistry 71: 301–307. Wood PJ, Weisz J, and Fedec P (1991) Potential for b-glucan enrichment in brans derived from oat (Avena sativa L.) cultivars of different (1 ! 3)(1 ! 4)-b-D-glucan concentrations. Cereal Chemistry 68: 48–51. Wyatt PJ (1993) Light scattering and the absolute characterization of macromolecules. Analytica Chimica Acta 272: 1–40.

Wheat Processing

Contents Milling and Baking: History Wheat: Dry Milling Wet Milling of Wheat Oven Technologies Bakeries: The Source of Our Unique Wheat-Based Food, Bread Analysis of Dough Rheology in Breadmaking Frozen Dough Refrigerated Dough Chemistry of Cake Manufacturing The Gluten Proteins of the Wheat Grain in Relation to Flour Quality Ultrastructure of the Wheat Grain, Flour, and Dough Cereal Food Production with Low Salt Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies Gluten and Modified Gluten Snack Foods: Processing

Milling and Baking: History CE Walker{ WD Eustace, (Retired) Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 268–274, ã [2004], Elsevier [Ltd], with revisions made by the Editor.

Topic Highlights

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Milling and baking scenes have been found on walls of Egyptian tombs dating from 2600 BC. The earliest milling involved back-and-forth motion with a saddle stone. Later (800 BC) came the quern, involving rotary motion with circular stones, powered by hand, by water, by wind, or by animals. Improved flour quality was obtained by adjusting the gap between the millstones, providing gradual reductions in flour particle size and better separation of bran by sieving. Crude sifting was originally used to separate bran particles from the fine white flour. Later (1775) came ‘purifiers’ using air currents blown through falling stock to separate bran from heavier endosperm particles. Roller milling, introduced progressively in the 1800s, provided better throughput and flour quality than millstones. The baking of moistened flour provided a palatable food, readily digestible, that could be kept for a period without spoilage.

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Equipment for baking gradually evolved from bare coals or hot rocks to the concept of an enclosed oven. Today’s bread comes from various baking situations – home baking, hot-bread shop, in-store bakery, and largescale plant bakery. Baking goes beyond yeasted bread to include cookies, cakes, pies, pastries, pizzas, and many more foods. Bakeries may involve various sources of heat, many physical arrangements, and a variety of food types.

Learning Objectives

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To consider the origins and evolution of grain milling and baking into foods. To gain a more thorough understanding of the present-day equipment and procedures.

Introduction The histories of milling and baking parallel each other, as have developments in their technologies. Mutually dependent upon each other, they originated together and remain inextricably

http://dx.doi.org/10.1016/B978-0-12-394437-5.00158-3

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linked, even though the two fields have specialized and separated to the point that many people no longer consider them together.

Flour Milling Volumes have been written on the history of milling and how it parallels the development of civilization. So much has been written that we can only hit the high points without much detail. It has been said that if we compare mankind’s time on earth to a 60 min period, milling started 55 min after his appearance. Agriculture started 4 min later and recorded history 30 s after agriculture. These observations lead one to believe that grain milling may be the oldest manufacturing process in the world. Man probably used stones to break up nuts, berries, grains, and bones to produce food that was easier to chew. The basic process of pounding or rubbing between two stones went on for thousands of years. A saddle stone was found in an Egyptian tomb built around 3660–80 BC. Milling and baking scenes have been found on walls of Egyptian tombs dating from 2600 BC. The drawings show grinding with saddle stones and separating the meal with sieves made of papyrus or horsehair. Saddle stones produce a rubbing or attrition action, making a better separation of bran from endosperm as compared to pounding, which pulverizes the entire kernel. The use of sieves with saddle stones became a popular means to separate the meal from the bran particles. Many versions of the saddle stone have appeared, but the back-and-forth motion required hours of backbreaking labor to produce enough meal to feed a small family. Saddle stones are still used in many parts of the world.

Rotary Motion Around 800 BC, rotary motion was applied to a device called a quern, which is made up of two horizontal circular or conical

stones with one on top of the other. A device called a rind supported the upper stone, allowing a slight gap between the two grinding surfaces. The upper stone was turned, while the lower stone remained stationary. Going from reciprocating to rotary motion was a tremendous step forward. The advantage of rotary motion was the continuous application of force in one direction using wind, water, animals, or people as a source of power. Water was used to turn millstones around 19 BC by the Roman architect Vitruvius. The millstones were 2–3 ft in diameter and 6 in. thick. The application of water power through a gear mechanism laid the foundation for heavy industry. Gears had been described by Aristotle in 400 BC. Ctsesbus in 200 BC used gears in various clock movements where the forces were very light. The mill by Vitruvius was the first recorded use of gears in a massive mechanism designed to do productive work. Figure 1 shows the evolution of stone mills. The millstone became a machine capable of working for extended periods of time, instead of being a hand tool producing large quantities of flour. This meant that the strength of the people or that of animals was not a limiting factor anymore. It is interesting to note that, except for subtle differences in design, the millstone has remained unchanged for over 2000 years. Windmills were utilized in eastern Iraq by CE 644. A mill of this type is most efficient when built in an area that has winds blowing without changing direction. Western Europe had windmills by CE 1145. The use of windmills increased in number until the invention of the steam engine by James Watt in 1769. Steam engines were applied to stone mills in 1786; that allowed the construction of mills in areas that did not have reliable water or wind sources. Milling with stones was a ‘sudden death’ or ‘low grinding’ process in which the wheat kernel was reduced to meal in one pass through the millstones. Some bran might be removed by sifting but a large amount would be reduced to meal or flour size and included with the final product. This was more of a problem with hard wheat than soft wheat.

Saddlestone Slab mill Push mill Lever mill

Hourglass mill

Delian mill Quern Millstones Figure 1 The evolution of the stone mill, from the hand-operated saddle stone to powered millstones. Reproduced with permission from Storck P and Teague WD (1952) Flour for Man’s Bread, 76 p. Minneapolis, MN: University of Minnesota Press.

WHEAT PROCESSING | Milling and Baking: History High Grinding: Gradual Reduction Toward the close of the sixteenth century, the French miller Pigeaud developed a new system. Instead of passing the wheat once through the millstones, he ground it three or four times with sifting between each pass. On the first grinding, the upper millstone was raised slightly giving a larger gap. Sizings and middlings were produced with minimum flour. After sifting, the ‘overs’ of the reel or sieve were ground again with a slightly smaller gap to remove the coarser endosperm particles. The endosperm collected was ground with a very close gap to produce as much flour as possible. This procedure gave higherquality flour than single-pass ‘sudden death’ milling. Because of the better quality flour produced, the method of ‘high grinding’ spread rapidly in Europe and America. This was the start of the gradual reduction system. The Hungarians improved the system by using a purifier developed by Ignaz Paur in 1807 to grade middlings produced on the first several passes through the millstones. This was especially desirable for hard wheat, which tended to produce coarser endosperm particles than soft wheat. With the Hungarian system, workers collected the product from each machine and transferred it by hand in buckets to the next operation. This required a lot of hand labor that was supervised by the miller who made the decision where each separation was sent. At that time, the Hungarian system was the most complicated milling process, but it produced the best flour. The development of particle size classification ranged from handpicking, hand sieves, oscillating sieves, shaking sleeve bolters, cloth-covered reels with internal brushes, polygonal and cylindrical sieving reels, to centrifugals, which are slowly revolving reels with rapidly revolving internal beaters. The Egyptians used hand sieves, but their capacity was limited. The brush sifter was a stationary inclined reel that had revolving brushes inside that forced the fine stock through the screen. John Milene patented this particular machine in England in 1765. Reels varied from 12 to 28 ft (3.6–8.5 m) in length and 20– 36 in. (0.5–0.96 cm) in diameter rotating from 30 to 35 rpm. Their capacity varied from 300 to 2800 lbs (136–1270 kg) per hour depending on mesh size and type of stock being sifted. Reel efficiency was low because only about one-third of the surface was used as the reel rotated. Rotating centrifugals had higher capacity than stationary centrifugals. Plansifters made their appearance around 1880. Karl Haggenmaker of Switzerland built the first serious plansifter in 1888. The early plansifters were only three or four sieves high and were not free-swinging. Free-swinging self-balancing sifters were developed in the United States and Europe in the early part of the twentieth century. These sifters now come with 12, 17, 22, or 27 sieves per section. A carpenter working in a French mill around 1775 invented what is regarded as the first purifier. This machine and others after it used air currents blown through falling stock to separate bran particles from heavier endosperm particles. These machines generated a lot of dust in the mill. In 1855, another Frenchman, Cabane, used air-aspirated sieves as a purifying device. The sieves separated sizings and middlings according to size and removed bran by air. The development of the purifier allowed the miller to produce white flour from hard wheat that would compete with soft wheat flour in terms of color.

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George Christenson had Edmund La Croix install a purifier in the Washburn mill in Minneapolis, Minnesota, in 1870. This machine was different from the previous purifiers because it used a reciprocating sieve with air drawn through the cloth by negative pressure rather than positive pressure. This particular arrangement was based on a patent held by a Frenchman, Perrigault. The only problem with the Perrigault purifiers was the lack of a way to keep the sieve meshes clean. A mill employee, G. J. Smith, developed a traveling brush to clear the meshes and obtained a patent on the change in 1877. Since then, improvements on the basic purifier include air adjustments, drives, number of decks, cloth cleaners, sieve construction, clothing, feeding arrangements, and internal lighting. About the same time that the purifier was being developed, Oliver Evans, an inventor unfamiliar with milling, contracted to build a mill near Wilmington, DE, the United States. He wanted to build a mill that was better than any other previously constructed. He concentrated on using waterpower to drive conveyors moving stock in the mill. This would greatly reduce the manual labor requirements in milling. His mill, using bucket elevators, screw conveyors, and gravity spouts to move stock during processing, was the beginning of automatic milling. This allowed the miller to concentrate more on the milling process. The Evans mill started running in 1785 and eventually became the model for mechanized large-scale mills in the nineteenth century (Figure 2).

Roller Mills When the purifier came into general use, it started what was called ‘new process’ milling because of the millers’ ability to produce flour superior to any previously produced. Combining the purifier and Evans automatic mill started a revolution in American milling that spread to Europe. About this time, roller mills were starting to appear. The concept for the roller mill is credited to Giovanni Torriano in 1558 in Spain. It consisted of a hand-powered corrugated cone working inside a curved corrugated shell. Recorded history shows nothing else about roller mills until 1774 when a patent was granted in England for a roller mill to grind corn. However, nothing was mentioned historically until Helfenberger built his first roller mill in 1820. This attempt was not very successful. Muller, a Swiss in Warsaw, Poland, made progress with improvements on the roller mill design in 1822. He constructed an all-roller flour mill in 1833 that failed almost immediately because of improper placement of equipment in the flow. Another Swiss engineer Jakob Sulzberger was assigned to reconstruct the mill. His changes were so successful that numerous other flour mills were constructed to use roller mills. The mills used both roller mills and millstones in the flow. The break stages used rollers, while the reductions used millstones. Apparently at that time, millstones were more efficient for grinding sizings and middlings than were rollers. Roller mill development in relation to milling took place in Europe, particularly in Hungary, around 1877. The early roller mills were not very effective until high grinding or multipass grinding, which started in France, developed further. Later, roller mills gave better control over grinding because of even distribution of stock to the nip of the rolls. Also, the gap

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Crane spout

Descender

Spiral conveyer

Elevator

Hopperboy

Elevator

Fan Y X Conveyer with lifters

Conveyer with flights

Drill

Figure 2 Oliver Evans 1785 ‘mechanized’ flour mill, showing mechanical conveyors. Reproduced with permission from Storck P and Teague WD (1952) Flour for Man’s Bread, 76p. Minneapolis, MN: University of Minnesota Press.

between the rolls could be controlled more accurately to maintain even grinding. Early roller mills had steel rolls from 4.5 to 9 in. (114–229 mm) in diameter. Porcelain rolls were tried but they wore out more quickly than steel. Today’s modern roller mills are set up to engage when stock is coming to the roll stand or disengage when the stock runs out. Feeder rolls automatically increase or decrease the stock to the rolls to maintain an even load to the length of the rolls. Newer roll stands can be programmed to automatically change roll gap when changing mill mixes. Double high roller mills are being used on selected break and reduction passages. This helps to eliminate sifting. When roller mills were first introduced in mills using millstones, problems arose. First, the capacity of the early roller mill was at least double that of a millstone. This required more handling and processing equipment. Reels could not handle the load, so the miller had to install more reels or go to plansifters both of which were more costly. Increasing capacity to cover the cost led to increased competition among the mills, driving many small operations out of business. Milling was rapidly becoming a narrow-margin, highvolume manufacturing process. That trend has continued unabated until today.

Grain Cleaning Grain cleaning was slower in developing, as compared to milling. Early man probably removed some impurities by hand before and after grinding grain. Sifting of the meal after stone grinding probably removed more impurities. A specific reference to grain cleaning was made by Oliver Evans in the mill he designed and built in 1783. Evans mill design scoured the grain

between two stones and then sent it through a revolving cylinder screen that had a fan for aspiration. Frederick Kick, in 1888, discussed several grain-cleaning methods, one of which was throwing the grain into the air by shovel or hand. When the grain was thrown, the heaviest kernels flew the farthest, while chaff and light kernels traveled the least distance. If a current of air blew across the airborne grain, the separations were cleaner. This process took a lot of practice and was not suitable for large quantities of grain. Kick classified grain-cleaning machines at that time into three categories: 1. Dressing machines with sieves 2. Machine separating round seeds from wheat 3. Machines for sorting grain Category 1 used sieves with air blowing through the grain as it passed through the sieve. Grain and impurities larger than wheat passed over the screen, while wheat and impurities the same size or smaller than wheat passed through the screen. Air blowing on the material through the sieve removed chaff and dust. Category 2 used inclined surfaces to separate round seeds from wheat. Revolving cylinders with the first half perforated and the last half with indented areas are also included in this category. The perforations removed impurities smaller than wheat, while the indents lifted round seeds that were the same diameter as wheat and dropped them into a trough in the cylinder above the grain flow. Category 3 was an inclined reel made of perforated sheet metal or wire with the smallest openings at the head end and largest openings at the discharge end. Wheat tempering (adding water to the mill grist to toughen the bran so it would not shatter) was also practiced but

WHEAT PROCESSING | Milling and Baking: History moisture control was difficult. Moisture determination of grain was time-consuming and the control of moisture added was almost nonexistent. Kick observed that corrugated rolls became dull because of the sand and small stones that were always in the wheat. This observation indicated that grain cleaning at that time had a lot of room for improvement.

Baking The history of baking dates back to well before written history, far back into antiquity. No one knows exactly when and where baking (and hence the oven) was discovered, but the Egyptians had well-designed ovens operated by skilled career bakers. The origin of milling may have preceded baking, probably coinciding with early nomadic tribes grabbing grass seeds, predecessors of the present-day oats, barley, rye, and wheat, to chew on as they wandered across the savannas. Eventually, they discovered that rubbing some of the husks off (the origin of milling) and then soaking the seeds in water made them easier to chew and more palatable. Perhaps someone accidentally splattered some thin gruel on a hot stone to make a crisp, tasty snack. Or perhaps someone left a pot of porridge to set and some wild yeast, probably mixed with lactic acid bacteria, fell into it. The owner may have drunk it that way or perhaps let it dry up in the pot while it was sitting in the coals, forming a flavorful hard cake. The dried cake did not spoil. It could be carried on the hunt, softened in water, and eaten without taking time to gather grains. It could even be stored in the cave to eat when prey was difficult to find. At any rate, harvesting cereal grains, milling, baking, and brewing appear to have a common ancestor and are closely related even today.

Ovens Baking gradually evolved from bare coals and hot rocks into the more sophisticated practice we know today. Archaeologists

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have discovered the remains of ovens, grain bins, and grinding slabs dating from 7000 to 5600 BC in the Jordan Valley of Jericho and of Hacilar in Turkey. Just as in nearly all other forms of technology with which we are familiar today, when civilization developed new baking equipment and techniques, it left some people behind who did not adopt it, keeping the ancient forms alive. Someplace in the world today, a woman is still baking her family’s daily bread using a rock sitting in a bed of coals. Perhaps someone is still following the ancient nomadic practice by baking their bread on dried camel dung, providing the hearth and the fuel source all in one. By 3000 BC, the organized and agrarian Egyptians were using thick earthen jars sitting in coals to bake bread. And as before, the heated earthen jar evolved into the tandoor ovens still in common use in India and the Middle East. A piece of fermented dough is slapped onto the inside of the hot jar. When it falls off, it is baked. At 1000 years BC, the same time that bakers learned to preserve their sour dough for the next day’s production, they developed the ancestral beehive oven design (Figure 3). A stone or clay domed roof sat on top of a flat stone hearth. First, a fire was built inside until the oven was extremely hot throughout. Then, the fire was scraped out, the inside swept free of ashes, and the fermented dough pieces placed on the hearth to bake. Ovens changed slightly in form, but did not leave the basic ‘hearth inside a chamber’ design until the 1800s, only two centuries ago. The Egyptians passed their technology to the Greeks who in turn passed it to the Romans. The Romans understood milling, sifting, fermentation, and baking and distributed the knowledge throughout their empire, spreading it to Europe. The bakers were sometimes highly regarded and skilled people, and at other times, they were slaves to the wealthy. Most bread was still baked at home or in communal ovens. Little change in baking technology occurred from the fall of the Roman Empire through the middle ages. Civilized society nearly vanished from Europe until the eleventh-century crusades brought the travelers into contact with other cultures, exposing travelers to their baking methods.

Figure 3 Beehive-shaped ovens have been used to bake breads for thousands of years. Reproduced with permission from Varilek PS and Walker CE (1983). Baking and ovens: History of heat technology. Part I. Baker’s Digest 57(5): 52–54, 56–57, 59.

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By the late eighteenth century, the beehive oven had evolved into the ancestral ‘deck’ oven and, for larger capacity, the deeper ‘peel’ oven. Both designs live on today, baking pizzas and hearth breads. About this time, though, the heating methods begin to change. For thousands of years, the fire was placed directly in the oven to heat it, the fire was removed, and the bread baked as the oven gradually cooled (Figure 4). A huge advance occurred when the fire was located in a separate firebox, removing much of the soot, ashes, and dirt from the bakery. By 1900, large commercial bakeries were producing 25% of the bread in the United States, mostly in large peel ovens as much as 6 m (20 ft) long. A long-handled paddle (peel) was used to place the dough pieces onto the hearth, loading the oven from the back to the front. The same peel was then used to remove the baked bread, from front to back. The result, of course, was that the loaves received a different bake, depending upon where in the oven they were placed. By the late nineteenth century, bakeries began to mechanize and a wide variety of ovens evolved, finally breaking away from the hot masonry chamber into which loaves had been loaded and removed, one at a time, for many centuries past.

Baking Classifications Baking today may be classified by several methods: scale, food being baked, physical arrangement, and energy source.

Scale Today’s small ‘corner hot-bread shop’ or ‘in-store bakeoff’ may use small batch ovens that only operate a few hours per day, perhaps baking only a hundred loaves. The ‘baker’ only needs to put the loaves (sometimes frozen doughs or even par-baked loaves) into the oven and remove them when the buzzer

sounds. Larger-scale bakers are probably using rack or reel ovens, still manually loading them a batch at a time. They may bake a few hundred to a few thousand loaves per day. More judgment and skill are required on the part of the baker because the entire operation is probably a ‘scratch’ bakery, preparing doughs and batters from individual ingredients, not from mixes or frozen items. Finally, modern large-scale high-speed plant bakeries produce 100 loaves per minute on each of several lines.

Food being baked Except in very small bakeries, breads are baked in different ovens from sweet doughs, such as yeast-leavened pastries. Cookies and crackers will be baked on a different design, and cakes and pies require still different designs. While smaller bakers may use a ‘one for all’ oven, by far, the best results will be obtained using an oven designed for the specific food type.

Physical arrangement Different physical arrangements for ovens began with the descendents of the primitive beehive ovens, such as hearth or deck ovens, rotary hearth, rotary rack, reel, traveling tray ovens with single or multiple laps, and finally today’s long, continuous tunnel ovens used for crackers and cookies.

Heat sources Except for small or primitive bakers and a few ‘boutique’ bakers, wood is seldom used today. Refined petroleum, natural gas, and electricity are the most commonly used heat sources. Individuals living in very hot and sunny countries with a shortage of fossil fuels may use solar energy in a few isolated locations. Coal, once common, is now seldom used because it is so dirty. Modern ovens may combine several forms of heat

Insulating sand

Tiled sole

Figure 4 The faggot oven had the advantage of a large, smooth sole beneath a domed room containing a mass of stone or sand that held the heat more uniformly. Reproduced with permission from Varilek PS and Walker CE (1983). Baking and ovens: History of heat technology. Part I. Baker’s Digest 57(5): 52–54, 56–57, 59.

WHEAT PROCESSING | Milling and Baking: History and heat transfer, including high-velocity air jets as in the present-day pizzeria ovens, or add microwaves to existing units to make them bake faster.


Other changes in baking

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As bakers progressed with technology, their way of life changed. First, one person, usually the wife/mother, gathered the grains, threshed and milled them by hand, mixed the dough, and baked it on her cooking fire. As harvesters, millers, and bakers began to specialize and fall into the male domain, their operations got larger and they began to develop machinery. Automation entered the bakery after it had already set milling onto the path that led it to today’s large and efficient plants. Their paths were similarly taken. Early ‘large-scale’ bakers often crawled into their wooden troughs to knead their dough with their feet. Then, larger and more efficient mechanical mixers were developed, especially with the advent of electric motors. As each stage was mechanized, the increasing capacity put pressure onto each stage that followed, in a stepwise fashion. Mixed fermented doughs were divided, rounded, and molded automatically. Pans were filled automatically. Ovens were made continuous instead of batch, so conveyors were developed to load and unload them. The loaves were depanned by machinery and the loaves sent through large cooling conveyors. Individual loaf-protective wraps began to appear and antimold preservatives were added as bakeries became larger and larger and their delivery routes began to stretch across state lines. The advent of presliced bread put additional demands upon technology and formulation. Special fats were added to retard staling. In the 1940s, wartime labor shortages encouraged the development of even more highly automated continuous mix – continuous baking processes that produced bread with very fine cake-like crumb grain and a very soft texture. The shelf life of white pan bread extended from hours to days to a week. Recent advances have led to 2 weeks or longer shelf lives.

Future Challenges The grain producing, milling, and baking industries today face steadily increasing challenges. The expectations for more grain at a cheaper price to feed an expanding population conflict with the farmer’s dream for more profits. The millers and the bakers face the same conflicting expectations. The results have been steadily more sophisticated and automated systems, from the field to the table. This has resulted in a large, highly efficient, standardized process producing a similar product everywhere, the same product from all plants for all customers. As any society becomes more efficient and more affluent, however, it begins to demand and to be able and willing to pay for more specialized consumer goods, including breads. The proliferated demands in the 1990s for a wider variety of bread types, once available only from the small artisan bakers, have caused other competing demands on the large bakers. Perhaps they can now develop easily modified automated means to produce a wider variety of breads, cakes, cookies, and pies by computer control over the entire baking process, from initial ingredient selection and mixing to forming, baking, finishing, final packaging, and distribution.

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Why did roller milling take some decades to become generally used in preference to stone milling? Grain milling may be the oldest manufacturing process in the world. Why was it necessary for man (and not for the animals)? What advantages to man versus animals? Speculate about the origins and discovery of the baking of risen bread. Speculate about its advantages compared to porridge or merely chewing ground grain. Compare the degrees of skill versus mechanization involved in the various types of modern bakeries – home baking, hot-bread shops, an in-store bakery, and a largescale plant bakery. Which would start with flour, frozen dough or par-baked loaves? What differences in quality and palatability would you expect?


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Imagine you are stranded in a situation where grains and nuts are available but you have to make your own grinding and cooking equipment. What make-shift tools would you use to feed yourself, based on your present knowledge of modern-day methods and their development over the millennia? How useful in this situation is your knowledge of modern milling and baking equipment? Select what you consider to be the three most significant developments in the mechanization of wheat milling. Give your reasons. In your region, are there any commercial stone-grinding mills? What proportion of local flour do they produce? What advantages do they claim over roller milling? The Washburn mill in Minneapolis, MN (1870), and Oliver Evans ‘mechanized’ flour mill (1785) were advanced for their times. What further innovations would their designers see in a flour mill today? Baking is more than dough mixers and ovens. Baking a variety of food products involves different combinations of ingredients – especially fat and sugar interacting with the gluten of dough. Speculate on the possibilities for novel bakery products by varying the ratio flour/fat/sugar. What next?

See also: The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Breads; Wheat Processing: Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Oven Technologies; Wheat: Dry Milling.

Further Reading Cauvain RS (2013) Evolution in the manufacture of baked products. Cereal Foods World 58(5): 277–278. Kick F (1888) Flour Manufacture. London: Crosby Lockwood and Son. Koyim PA (1921) Flour Milling. England: George Routledge.

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Scott JH (1951) Flour Milling Processes. London: Chapman and Hall. Scott JH (1972) Development of Grain Milling Machines. Edinburgh: Audio Typing. Simon ED (1930) The Physical Science of Flour Milling. Liverpool: The Northern Publishing. Smith L (1962) Flour Milling Technology. Liverpool: The Northern Publishing. Storck P and Teague WD (1952) Flour for Man’s Bread. Minneapolis, MN: University of Minnesota Press. Varilek PS and Walker CE (1983a) Baking and ovens: History of heat technology. Part I. Baker’s Digest 57(5), 52–54, 56–57, 59.

Varilek PS and Walker CE (1983b) Baking and ovens: History of heat technology. Part II. Baker’s Digest 57(6): 24–27. Varilek PS and Walker CE (1984a) Baking and ovens: History of heat technology. Part III. Baker’s Digest 58(1): 24–27. Varilek PS and Walker CE (1984b) Baking and ovens: History of heat technology. Part IV. Baker’s Digest 58(2): 12–15. Varilek PS and Walker CE (1984c) Baking and ovens: History of heat technology. Part V. Baker’s Digest 58(3), 22–24, 26, 29. Zieher W (1987) Farmer, Miller, Baker: Bread Through the Ages. Tielt: Lannoo.

Wheat: Dry Milling AK Sarkar, Canadian International Grains Institute, Winnipeg, MB, Canada JE Dexter, Canadian Grain Commission, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights Reading this article will help understand the following:

• • • • • • • •

The gradual development of the wheat milling process over time. The composition and structure of the wheat kernel and its functional and compositional attributes. The preparation of wheat for milling. The milling process. The production and collection of flour streams and flour treatment. Various types of flours and their end uses. Soft wheat milling for production of flour suitable for cakes, pastries, cookies, and crackers. Durum wheat milling for production of semolina for pasta and couscous.

Learning Objectives

• •

To understand the technical basis for the development of modern wheat flour milling. To understand the flour milling requirements for the quality requirements of diverse end-products.

Introduction Wheat may be used whole in various ways for human food, but usually, it is ground and/or fractionated in preparation for further processing. Roller milling is the most flexible and widely used procedure for grinding and fractionating wheat. Products of roller milling exhibit diverse composition and functionality, suitable for preparation of an almost limitless array of human foods. The main fractions of wheat roller milling are flour (or semolina when milling durum wheat), bran, shorts, and germ. Bran consists of large flakes that are composed of outer layers of the kernel and adhering aleurone. Shorts are finer bran particles and usually contain some endosperm and germ. Properties of roller-milling products are determined by roller-milling conditions and by intrinsic properties of the wheat being milled. Modern roller milling is a gradual process involving successive grindings and separations. Each flour stream has unique composition and functional properties. Judicious blending of specific flour streams allows millers to produce diverse custom flours of differing refinement and functionality. The two main classes of wheat cultivated today are common wheat, often referred to as bread wheat, and durum wheat. To achieve best results, millers select wheat carefully on the basis of intrinsic quality and physical condition and make process


adjustments to mitigate variations in quality among wheat lots. Physical damage incurred by poor growing conditions and improper postharvest handling and storage influences wheatprocessing potential. Plant breeding has developed common wheat types of variable kernel hardness, protein content, and dough properties with quality traits suited for specific end products. Durum wheat, an ancestor of common wheat, is harder than the hardest common wheat and is usually milled into a granular flour, referred to as semolina, for manufacture of pasta and couscous.

Historical Background Wheat milling is an ancient craft, dating back thousands of years to the dawn of civilization. Ancient wheat was hulled, unlike free-threshing modern wheat. Primitive cultures 10 000–12 000 years ago used a mortar and pestle to crush wheat to separate ground kernels from hulls. Implements evolved from primitive ones like stones and hollowed tree trunks to more sophisticated objects designed and shaped to improve performance. In ancient Egypt, saddle stones were widely used (Figure 1). An upper stone was moved, back and forth by hand, over a lower stationary stone. A great development was the invention of the millstone in Roman times. Rotary motion enabled the use of humans or animals to power the mill by traversing a circular path (Figure 1). Over time, advancements were made in stone shape and size. Other means of power were used to drive the millstones such as flowing water and wind and eventually steam power. Initially, stone milling comprised a single intense grinding. A multistage grinding process with intermediate sifting came into being in Europe in around 1550, which allowed recovery of relatively white flour. The demand for white flour grew. The roller mill, purifier, and plansifter were developed in the eighteenth and nineteenth centuries and led to the gradual break and reduction system. The addition of mechanical conveying allowed mechanization, and flour milling became a continuous manufacturing process. The basic process remains similar today, but advances in design of equipment for cleaning and milling have allowed continuous improvement in reliability, production, sanitation, and overall efficiency. A major advance 1945 was pneumatic conveyance of mill stocks. Today, most flour mills feature computer control, and some are virtually fully automated.

Structure and Composition of the Wheat Kernel and Flour The wheat-kernel structure is shown in Figure 2. The aleurone layer is part of the endosperm, but some remains attached to

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WHEAT PROCESSING | Wheat: Dry Milling

Figure 1 Saddle stone widely used in ancient Egypt (left) and hourglass stone mills used in Roman times (right). Adapted from Sarkar AK (1993) Flour milling. In: Bass EJ (ed.) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn., vol. 2, pp. 603–653. Winnipeg, MB: Canadian International Grains Institute.

Hairs of brush

Endosperm Crease Aleurone cell Nucellar tissue Seedcoat (testa) Tube cells Cross cells Hypodermis Epidermis

Bran

Germ

Figure 2 The structure of the wheat kernel sectioned longitudinally (left) and transversely (right). There are six bran layers. The crease, which runs the full length of the kernel, prevents fully efficient separation of bran from endosperm. Courtesy of North American Millers Association, with permission.

bran following milling. White flour originates from starchy endosperm, which comprises 85% of the wheat kernel. In practice, even the most efficient roller mills fall short of that theoretical maximum yield of highly refined flour, because the crease, which runs along the length of the grain and reaches almost to the middle, makes perfect separation of endosperm impossible. Wheat-kernel composition is heterogeneous. Starchy endosperm is much lower in mineral content than other constituents. Accordingly, flour ash content (mineral matter left behind after incineration) is a widely used index of flour refinement, low ash content being indicative of highly refined flour containing almost pure endosperm. Gluten proteins,

which give flour dough viscoelastic properties essential for high-volume bread and firm pasta, are found in the endosperm. Germ is particularly rich in protein. The proteins in germ and bran are nongluten proteins that have better nutritional value than gluten proteins, but are not beneficial to processing properties. Bran contains most of the fiber in the kernel, also an important nutritional consideration. As flour yield (or extraction rate, the proportion of wheat converted into flour) increases, contamination of flour by bran and germ increases. As a result, the nutritional value of flour improves as flour yield increases. However, flour-processing quality and shelf life diminish at higher yield. The presence of bran disrupts the gluten-protein matrix, weakening dough properties

WHEAT PROCESSING | Wheat: Dry Milling and reducing gas-holding capacity of dough during fermentation. The presence of bran also results in darker end products, detracting from aesthetic appearance. Germ reduces dough strength because it contains low-molecular-weight sulfhydryl compounds that break disulfide cross-links, reducing the size of gluten-protein polymers that impart elasticity to dough. Germ also reduces flour shelf life due to oils and enzymes that promote rancidity.

removes rubble and fine dust. This cursory cleaning protects equipment downstream, makes more efficient use of storage space, and improves wheat-storage stability.

Wheat Blending Wheat types or varieties may be milled individually or as a blend. The objective of wheat blending is to meet quality requirements at minimum cost. Table 1 shows wheat quality requirements for production of various types of flour for specific end products: Blending can create quality attributes lacking in individual wheats. Having the right quality is critical to maintain customer satisfaction and market share. Blending of inexpensive low-quality wheat with the high-quality variety can achieve the desired quality at reduced cost. Ideally, blending is performed following cleaning and conditioning. Different wheat lots may have different kernel size, making cleaning individually more efficient. Wheats of varying hardness have differing optimum milling moisture and conditioning time. Convenience, cost, and storage limitations often necessitate blending prior to cleaning and conditioning.

Wheat Reception and Storage Wheat may arrive at mills by truck, rail, or ship (Figure 3). Wheat is weighed, and a representative sample is taken for analysis prior to storage. Wheat analyses may include content of foreign material and damaged grains, test weight (weight per unit volume), protein content, and moisture content. The lot is then transferred to a bin, where wheat of comparable physical condition and similar end-use potential is stored, assuring that quality characteristics are preserved, and used to the best advantage. On the way to storage, wheat generally undergoes precleaning. First, a magnet removes ferrous metals. Then, a high-capacity grain cleaner, with shaking or rotating screens, Wheat intake

Storage

309

Cleaning

Tempering

Bucket elevator

Conveyor

Dampener

Magnet

Wheat

Scourer

Light

Storage bins

Water

Grain separator

Disk separator

Dampener Temper bins

Magnet Light

Rail

Small Large Destoner

Oats and barley

Road Small Large

Stones Broken, flax and weed seeds Magnet

Figure 3 A simplified wheat intake, cleaning, and conditioning diagram. Table 1

Wheat quality requirements for specific end products

Protein content

Dough strength

Flour application

High Moderately high Medium Low

Strong Strong Medium Weak

Strong bakers (small bakeries use for high-volume pan bread and artisan breads) Large bakers (used by industrialized bakeries for pan bread and rolls) Variety of noodles, hearth breads, flat breads, and all-purpose applications Cake, pastry, cookies, and crackers

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Table 2

Examples removing impurities from wheat on the basis of physical properties

Physical properties Size Density

Shape Air resistance Magnetism Physical appearance

Foreign material

Cleaning equipment

Larger than wheat: large stones, wood, corn, peas Smaller than wheat: rapeseed, flax, sand, dust Similar size and shape but heavier: small stones, mud balls, glass

Grain separator or millerator

Similar size and shape but lighter: ergot, damaged light wheat Similar cross section but shorter: broken wheat, wild buckwheat Similar cross section but longer: oats, barley, wild oats, ergot Lighter than wheat: chaff, husk, light dust, thin kernels, insects, damaged light kernels Ferrous objects and alloys containing iron: nuts, bolts, washers, nails, shavings Discolored, damaged kernels

Destoner, combinator, gravity table, gravity selector Disk separator or indented cylinder Aspiration Magnets Optical sorter

Adapted from Sarkar AK (1993) Flour milling. In: Bass EJ (ed.) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn., vol. 2, pp. 603–653. Winnipeg, MB: Canadian International Grains Institute.

Wheat Cleaning Efficient wheat cleaning prior to milling is critical. Foreign materials such as stones, metal, unthreshed grain, badly damaged kernels, and foreign seeds either adversely affect flour quality or are hazardous to milling equipment. Most impurities are quite easily separated from wheat on the basis of size, shape, density, magnetism, and appearance (Table 2). Figure 3 shows how cleaning machines would be arranged in a typical wheat-cleaning scheme. A magnet removes ferrous materials that may cause serious damage to subsequent equipment. Magnets are also used throughout cleaning to remove any ‘tramp’ metal that surfaces from equipment or is introduced inadvertently. It is important to remove impurities as early as possible to reduce load on subsequent equipment and increase cleaning efficiency. A grain separator uses sieves and aspiration to remove impurities. The top screen removes large impurities, such as maize, soybeans, and unthreshed wheat. Small weed seeds and broken kernels pass through the bottom sieve. Wheat falling off the bottom sieve is aspirated to remove chaff, dust, and shriveled kernels. A destoner removes materials that can cause unnecessary wear and tear, such as stones of similar size to wheat. An upward air current is passed through a sloped oscillating metal screen. Wheat floats on an air cushion and moves down the slope by gravity. Denser materials, such as mud balls and small stones, make more contact with the screen. They are propelled up the slope and are collected separately. Disk separators remove remaining impurities that differ in length to wheat kernels but are of similar cross section. Disks revolve in a vertical plane through the wheat. The surfaces of the disks have numerous pockets that pick up objects that are short enough to lodge in the pockets. There are generally two units. The first picks up wheat while rejecting kernels longer than wheat, such as oats and barley. The second picks up small seeds and rejects wheat. Wheat cleaning process has been simplified and made more efficient by combining the function of several individual machines into one. Such an integrated cleaning equipment

combines the operation of grain separator, destoner, aspiration channel and additionally separating of wheat stream into a heavy fraction ( 70–80% of total) and a light fraction. The heavy stream goes directly to conditioning, whereas the lighter stream passes through the remaining cleaning equipment. Savings in capital investment and operational cost are realized because the bulk of the cleaning equipment is required for only 20–30% of the wheat.

Wheat Conditioning (Tempering) After cleaning, wheat is conditioned by addition of tempering moisture, and moist wheat is rested in bins (Figure 3). Conditioning optimizes separation of bran from endosperm during milling. Bran is toughened, reducing bran powdering and lessening bran contamination in flour. Endosperm hardness is also reduced, facilitating reduction into flour. Achieving optimum moisture level for milling is critical. Too much tempering moisture reduces flour yield because complete separation of bran from endosperm is more difficult to achieve, and sieving efficiency is reduced. Too little tempering moisture results in bran powdering, which contaminates flour. Spray nozzles are used to spray tempering water into the wheat in conveyance in an enclosed screw conveyor. Modern tempering equipment features electronic control unit for moisture addition and vigorous mixing action to ensure that precise and uniform addition of moisture is achieved. Online moisture measurement, operating in feedback mode, allows moisture addition to be continuously regulated to the desired level. Optimum tempering moisture varies among wheat types. Soft wheat is tempered to lower moisture than hard wheat. A tendency for soft wheat stocks to be sticky and more difficult to sift than hard wheat stocks is exacerbated by higher moisture content. Following tempering, wheat is stored in bins to allow penetration and uniform distribution of moisture. Optimum rest time varies from several hours to more than a day depending on wheat moisture content and hardness. Soft wheat does not need to rest as long before milling as hard wheat. Soft

WHEAT PROCESSING | Wheat: Dry Milling wheat endosperm is more porous than hard wheat endosperm, so water penetrates into soft wheat endosperm more quickly. Wheat is often tempered in two stages with resting time between stages, particularly when a large amount of tempering moisture is added. Addition of tempering water is limited to 3% in older conventional tempering equipment. More modern equipment that is now commonly used allows higher moisture levels (7%) to be added as required because of enhanced mixing action and sometimes eliminates a twostage tempering requirement.

Second Cleaning After conditioning, wheat is scoured. Scourers use steel beaters to throw wheat against a wire screen. Dirt and loosened bran, which would contaminate flour, pass through the screen. Commonly, wheat is sprayed lightly immediately before milling. Up to 0.5% water is added, and the sprayed wheat is held in bins for 30 min. The purpose is to toughen the bran and reduce bran powdering. The wheat is then weighed and passed through a magnet to remove ferrous metal fragments prior to milling. In some situations, scourer is replaced by more aggressive bran peeling or debranning equipment to remove part of the bran in advance. This is particularly done when milling durum wheat and when microbial load reduction on wheat prior to milling is crucial. This is described under a separate section next. An optical sorter, sometimes also referred to as color sorter, is used to remove any discolored and defective kernels. A combination of high-resolution cameras detects minor defects, colored spots, and subtle differences in color as compared to sound wheat. Following the detection, the ability to reject these materials precisely with high-pressure ejectors has made optical sorters important in the cleaning section. This is used in most durum wheat milling operations as dark discolored kernels unless removed show up as dark specks following the grinding operation. These dark specks are generally referred to as black specks, and they could be very small fragments of outer part of a discolored wheat kernel, or they are tiny parts of dark-colored foreign material such as buckwheat or ergot. Tolerance for dark/black specks is an important measure of quality for durum semolina.

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Debranning (Preprocessing) Wheat debranning, or preprocessing, removes bran layers sequentially by friction and abrasion stages in modified rice polishers prior to milling. Wheat crease poses difficulty in the removal of bran associated with it, limiting the success of this process to some extent. Debranning has become an accepted practice for durum wheat semolina milling. Yield and refinement of semolina are significantly improved by debranning enhancing profitability significantly. Top-quality durum wheat can be milled more efficiently, or alternatively, lower-quality durum wheat can be used to produce semolina within customer specification. Evidence that debranning improves milling performance of common wheat is less conclusive. Part of the reason is that there are more losses of endosperm when debranning softer-textured smaller kernel sizes of common wheat. Larger-sized and harder wheat kernels lend themselves naturally to more efficient debranning process.

Mill Equipment The most important equipment in modern flour mills are roller mill, plansifter, purifier, and bran duster. Equipment from different suppliers vary in design, engineering, reliability, and price but all have similar working principles. Stock is ground by a pair of closely spaced grinding rolls (Figure 4). In each roller mill, two pairs of rolls are housed back to back within a cast iron frame. One pair of rolls is accessed on each side of the roller mill. Each roller pair is driven separately and has separate feeding and adjustment mechanisms, allowing different stocks to be fed to each roll pair. Recently, roller mills with four pairs of rollers have become available. Two pairs are stacked vertically, with the upper pairs feeding the lower pairs directly. They are gaining in popularity because they allow an economical way to increase milling capacity. Stock to be ground is distributed evenly over the entire length of grinding rolls by a feed control device. The feed control device consists of a balanced feed gate and a pair of feed rolls. The balanced feed gate regulates flow of stock. Feed

Feed

Feed rolls Grinding rolls

Ground material Figure 4 Modern roller mills. External view of roller mills (left) and schematic view of a roller mill (right).

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rolls facilitate smooth flow of stock precisely into the ‘nip’ of the grinding rolls. Grinding rolls are cast iron cylinders with a hard ‘chilled’ surface to resist wear. Rolls are either 225 or 250 mm in diameter, and lengths are usually 800–1000 mm. Each pair rotates inwardly in opposite direction and at different speed. A transmission belt drives the fast roll, and the slow roll is driven from the fast roll by either a gear or chain drive. The ratio of roller speeds, known as differential, imparts shear to grinding action. The slower roll holds the stock, while the faster roll compresses and shears it. For most effective performance, break rollers have a differential of 2.5:1, compared to 1.25:1 to 1.5:1 for reduction rollers. Reduction rolls are commonly smooth with a frosted (slightly rough) surface to impart some shear to the grinding action. Break rolls are corrugated, corrugations becoming finer (more rows per centimeter) with each break as stock becomes finer. Corrugations are cut in a spiral pattern along the length of the roller. Spiral prevents rolls from locking and imparts a scissorlike cutting action. Sifting is performed by plansifters, commonly known as sifters (Figure 5). Plansifters are suspended from girders by canes and are driven by a rotating vertical shaft with attached balanced weights. Rotation is on a horizontal plane in a circular motion, such that a pencil fastened to the bottom of the sifter traces a circle. The diameter of the circle is termed the ‘throw.’ Sifters have a throw from 75 to 100 mm and rotate from 180 to 225 rpm. Plansifters may have four, six, or eight sections. Each section has a stack of 14–30 layers of sieves. Each section is

independent and has its own feed inlet at the top of the sifter. Sieves consist of a wooden frame with a coarse wire grid bottom to hold ‘cleaners,’ which are plastic or cotton pads. Cleaners keep the underside of the sieve clothing clean and help keep openings clear. Sieves are stretched and secured to frames by staples or glue. Apertures of sieve clothing range from 1600 mm to less than 100 mm. Coarser clothing is composed of wire mesh, while finer clothing is composed of nylon or silk. Sieve frames are inserted into outer frames with collecting trays. Coarse material tails over the top of sieves, and fine material passes through the sieves and is collected in the trays. Purifiers take advantage of the greater density of pure endosperm particles compared to bran-rich or germ-rich particles of comparable size (Figure 6). A purifier has two sections, each section consisting of two or three layers of oscillating sieves. Sieve frames are mounted with a slight downward slope, and an eccentric drive generates longitudinal oscillation. A controlled air current passes upward through the sieves. Graded stock from a sifter enters one section of the purifier through a feed inlet. Stock is distributed uniformly across the width of the sieve. The frame is clothed with four sieves of progressively coarser aperture from head to tail. Sieve openings are kept clear by brushes, which move back and forth on guide rails under the sieves. The sloped oscillating sieve promotes downward movement of stock in a layer. Controlled air currents drawn up through the stock stratify stock layers so that light bran-rich particles rise to the surface. Heavier endosperm particles fall to the bottom of the layer and pass though the sieve if the aperture is large enough. Composite particles with bran or germ attached remain in the middle of the layer. Thus, air flotation and sieving action combined allow separation into fractions that are progressively coarser and more contaminated by bran and germ from head to tail. Bran finishers use impact to remove endosperm attached to large flakes of bran at the end of the break system (Figure 7). The same machine, when used to remove endosperm from shorts (fine bran from the end of the break system), is commonly referred to as a shorts duster. Bran or shorts are fed into a horizontal cylinder. The lower part of the cylinder is perforated. Endosperm is scraped from bran or shorts by rotating finger beaters attached to a central shaft. Endosperm passes through the perforations and bran or shorts pass through the cylinder and is collected separately.

Equipment Configuration in a Mill

Figure 5 A plansifter with doors on the nearest two sections open for viewing. In the second section, the sieve stack has been pulled forward, and in the first section, some of the sieves have been pulled. The canes supporting the plansifter are visible in the foreground.

The milling process is a continuous process where material is moved from one machine to the next. In order to take the maximum advantage of the gravity flow, principal milling equipment is typically configured with sifters on the higher floor followed by purifiers and bran finishers and then the roller mills. Following the grinding of material in a roller mill, the ground stock is taken up to the sifter floor, which is situated at a higher level, by pneumatic lifts. Pneumatic lifts allow carrying of ground material from roller mill to the sifter vertically upward with suction air. Downward flow from sifter, to purifier, subsequently to the roller mill is simply achieved by connecting the spouts as


Feed

Pure semolina

313

Air

Composite Overs of particles sieves

Figure 6 A triple deck purifier. External view (left) and schematic diagram (right).

Sifters Conveyors

Purifiers

Rollermills

Figure 8 A typical equipment configuration in a flour mill showing sifter followed by purifier and bran finisher and then roller mills.

Figure 7 Bran finisher. View with front cover plate removed to show the metal screen (top) and view with screen removed to show finger beaters (bottom).

material flows down on account of gravity (Figure 8). For carrying material across the floor, a mechanical screw conveyor is required. There are other configurations that are followed by some mills for specific reasons, but the one shown in Figure 8 is most commonly used and is most energy-efficient.

Hard Common Wheat Milling Figure 9 is a simplified typical hard common wheat flour mill flow, designed to give a flour yield of 75%. The main stages of milling are the break system; intermediate processing, which includes purification and sizing; and the reduction system.

The purpose of the break system is to separate bran from endosperm as efficiently as possible, although a small amount of flour is produced. The entire break system usually consists of four or five passages. The first break opens the wheat kernels, and ground material proceeds to the first break sifter, where particles are separated by size. The largest particles, consisting of wheat bran and adhering endosperm, are conveyed to the second break rollers. Ground stock is once again sifted and the coarsest fraction sent to the third break passage. Each successive break and sifting passage separates more bran from endosperm. The coarsest fraction of bran from the last break proceeds to a bran finisher, and shorts proceed to a shorts duster, to remove the last traces of adhering endosperm. Finer stocks from break sifters consisting of semolina (coarser particles), middlings (finer particles), and some flour are separated by a sifter referred to as a grader. Semolina and middlings are conveyed to purifiers that separate pure endosperm particles from bran-rich material. Essentially, pure


314

Break system

Purification and sizing system

Grading system GR

B1

F

P1

P2 P3 3M

B2 P1 GR

1M

B3 2M SIZ

F

3M

2M T

SD

F 2Q

P4

T

Shorts

4M

B4 2Q

Shorts

T 6M

F

B4 2Q

Bran

5M

3M

P3 BF

F 2Q

1M

F

T 5M

F

P2

B3 P1 GR

4M

2M

1M

B2

B4 P3 GR

2Q

B3 SIZ

F

B3

Reduction system

6M

F

F

2M

B4 B5 2Q 5M

2Q

T SIZ

B4 P4

F

T

3M

6M

Shorts

4M F

Shorts F

B5 BF SD 6M F Figure 9 A simplified hard common wheat flour mill flow diagram. B, break; BF, bran finisher; GR, grader; M, middling; P, purifier; Q, quality; SD, shorts duster; SIZ, sizing; T, tailing. Corrugated rollers are closed and smooth rollers are open. Adapted from Sarkar AK (1993) Flour milling. In: Bass EJ (ed.) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn., vol. 2, pp. 603–653. Winnipeg, MB: Canadian International Grains.

endosperm particles are sent to the beginning of the reduction system where they are reduced into flour. The coarser less-pure materials from purifiers proceed to the sizing (scratch) system. The primary objective of sizing is not to make flour, but to remove bran adhering to middlings. This is accomplished by light grinding on finely corrugated rollers. Ground stock is then sifted and purified before continuing on to the reduction system. The reduction system is the heart of the flour milling process. Carefully sized and purified middlings are reduced into flour gradually by successive grinding and sifting. Germ is flattened rather than reduced by smooth reduction rolls and can be recovered as a coarse fraction by sifting. Reduction grinding conditions are carefully controlled to produce as much highly valued prime-quality flour as possible. If grinding is too severe, bran contamination is increased, reducing flour brightness. Severe grinding can also excessively damage starch granules, adversely affecting flour functionality.

(Table 3). Flour millers may combine all flour streams to produce ‘straight-run’ or ‘straight-grade’ flour. A more complex alternative is to produce several flours with different properties by judicious blending of streams. This is known as ‘divide’ or ‘split-run’ milling and allows millers with demanding clients to increase return by closely targeting specific processing requirements. The whitest, most bran-free, reduction flours may be combined to produce highly refined ‘patent’ flour, often marketed as household flour. Remaining patent flour, when blended with early break flours, gives a strong bakery flour of high protein content. Late break flour, late reduction flour, and bran finisher flour are heavily contaminated by bran and make up lower-quality ‘clear’ flour. Figure 10 shows how flour streams leaving sifters can be directed to any one of three flour conveyors to make divide flours. Divide boards can be used to further blend divide flours to make custom flour blends.

Divide Milling

Flour Additives

A flour mill may produce single or multiple grades of finished flour from a given wheat or wheat mix. Individual flour streams exhibit variable composition and processing quality

Additives are commonly used to improve flour nutritional value and/or to improve processing quality (Table 4). Endosperm, the main component of flour, is poor in vitamins.


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Table 3 An example of typical yields and composition of flour streams (in ascending order of ash content) from milling of hard common wheat of about 13.5% protein content Stream

Yield (%)

Ash (%)

Protein (%)

Bread volume (cc)

Middling 1 Middling 2 Sizing 1 Sizing 2 Middling 3 Break 1 Break 2 Break 3 Middling 4 Middling 5 Break 4 Middling 6 Bran finisher Straight grade

21.2 13.0 3.4 4.6 8.4 4.4 3.4 3.2 4.2 2.3 1.5 2.8 1.7 74.1

0.33 0.40 0.40 0.40 0.44 0.47 0.48 0.57 0.82 1.00 1.23 1.49 2.61 0.55

11.5 13.0 12.6 11.6 11.9 13.8 15.4 18.1 13.6 13.5 20.9 14.2 21.1 13.2

1000 1060 1050 910 850 1020 1020 1060 810 650 890 440 620 1060

Adapted from Izydorczyk MS, Symons SJ, and Dexter JE (2002) Fractionation of wheat and barley. In: Whole-Grain Foods in Health and Disease, pp. 47–82. St. Paul, MN: American Association of Cereal Chemists.

Many countries have legislation requiring addition of vitamins and minerals to improve flour nutritional value. Flour can be made whiter by bleaching agents, like benzoyl peroxide. Other additives, known as improvers, include various enzymes of either fungal or grain origin and agents to improve dough strength and baking performance. Additives are available in powder form and are dispensed directly into flour conveyors using powder feeders.

Hard Common Wheat Flour Application Hard wheat flour is used for a multitude of end products such as pan bread, a variety of hearth breads including French bread, artisan breads, various types of flat breads, tortillas, a variety of Asian noodles, steam breads and dumplings, and laminated products such as croissants and in some countries for pasta. Whole wheat and whole grain flours are generally made from hard wheat flour with high protein content and good dough strength.

Soft Wheat Milling Soft wheat breaks down more quickly than hard common wheat. More flour is produced on the break system for soft wheat than for hard wheat, requiring greater sifting capacity for the former. Endosperm of soft wheat adheres more strongly to bran, reducing flour extraction rate expectations by up to 2% unless sifting capacity is increased. Yield of semolina and middlings is lower, so purifiers are of less importance and often are absent. Stock is stickier and fluffier, which makes it more difficult to sift than hard wheat stock. Soft wheat is fed more slowly to the mill to facilitate sifting and to ensure that stock flows freely through the mill. Generally, this results in lowering of production by about 25–30% when milling soft wheat in a hard wheat mill. Soft wheat flour is used in a wide range of applications primarily for crackers, cookies, pastries, and cakes. Soft wheat

generally has softer kernel texture, lower protein, and weaker dough properties. All of these properties are intrinsically suitable for application in the products listed earlier. Low-ash and low-protein flour streams are sometimes drawn for specialty products such as high-ratio cake flour. This type of flour is chlorinated in some countries to provide improved volume, grain, and texture to the cake. In countries where chlorination is not permitted, heat treatment may be provided to obtain similar attributes. This additionally helps to lower the microbial load on the flour. Soft wheat flour is also heat-treated for application as soup base and thickeners.

Durum Wheat Milling Durum wheat mill flows are different from common wheat mill flows, because the product preferred for premium pasta and couscous is uniformly sized semolina. Durum wheat flour that is unavoidably created as a by-product of semolina milling is of lower value. A typical durum wheat semolina mill flow is shown in Figure 11. Durum wheat is very hard, which facilitates high yield of semolina. The break system for durum wheat is extended to allow gradual breakdown of kernels to achieve maximum production of semolina and minimum production of flour. Purified semolina from the break system is uniformly sized and freed from adhering bran by repeated sizing, grading, and purification. Most semolina is from sizing purifiers, making durum mills readily recognized by the large number of purifiers. The traditional durum wheat semolina particle size is coarser relative to what is used by modern pasta processors today, which tends to be finer. Although durum wheat is primarily associated with pasta production, a very high percentage of durum wheat is used for the production of couscous, a popular food in North Africa. A considerable portion of durum wheat is also used for bread baking, which includes flat breads as well as hearth-style bread.

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Flour streams

Flour 50.6% Ash 0.38% Protein 12.0%



Flour conveyors

Divide board

(a)

Household flour 30.0% Ash 0.38% Protein 12.0%

Bakers’ flour 35.8% Ash 0.47% Protein 13.3%

Low-grade flour 8.3% Ash 1.54% Protein 16.6%

Finished flours

Flour streams




Flour conveyors

Divide board

(b)

Bakers’ flour 74.1% Ash 0.55% Protein 13.2%

Finished flours

Figure 10 Examples of divide milling, where three custom flours are being produced from a single wheat mix based on streams shown in Table 3. Streams are collected to yield high-quality patent, second patent, and low-grade flours. In (a), part of the first patent is diverted by a divide board to blend with the second patent to make a bakers’ flour. The remaining first patent would find use predominately as household flour. In (b), the divide board is positioned to blend the three divide flours to create a straight-grade bakers’ flour for industrial bakeries.

Milling By-Products By-products of milling are an important economical consideration in flour milling. These include impurities from the cleaning house (screenings), mill feed (bran and shorts), and germ. Screenings, with the exception of metal, stones, and mud balls, are usually ground and sold for animal feed. Bran and shorts

are also primarily used as animal feed. Depending on market conditions, bran also finds use for foods such as breakfast cereals and high-fiber specialty wheat products. Wheat germ is highly valued because of its excellent nutritional composition, and many mills have sophisticated germ recovery systems.

WHEAT PROCESSING | Wheat: Dry Milling Table 4

Some commonly used flour additives

Additive

Physical state

Vitamin–mineral premix Folic acid Iron Niacin Iron Thiamin Riboflavin Azodicarbonamidea Ascorbic acid Benzoyl peroxidea Chlorinea a L-cysteine hydrochloride Fungal a-amylase

Powder

Approximate usual rate of application (ppm)

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Purpose Nutritive supplement

1.5–2 30–45 35–65 30–45 4.5–8 3.5–5 2–20 70 50 1000–1400 30 As required

Powder Powder Powder Gas Powder Powder

Maturing, oxidation Baking improver Bleaching Bleaching, maturing Shortens dough mixing time Increases yeast gas production

a

Banned or restricted use in many countries. Adapted from Sarkar AK (1993) Flour milling. In: Bass EJ (ed.) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn., vol. 2, pp. 603–653. Winnipeg, MB: Canadian International Grains Institute.

Break system

Sizing system

Primary purification

B1

Reduction system

Secondary purification

1SIZ B2 P1 S1

P1

S1

2M B2 F

P2 B3 P2 SR F

S4 F

B5

3M

SEMO

Shorts

P4

F

4SIZ 1M

4SIZ

4SIZ

F 3SIZ

P4

F

SEMO S3

BF

F

P3

S2 S4 1M

3SIZ

3M

SEMO

3SIZ

B4 2Q B5 P4 S4

2M 2SIZ

2SIZ

F B4

S2

B3

B4

F

S1

P3

B4 P3 S1

SEMO

2SIZ

B3

2SIZ

S4

1SIZ

F B2

1M

S1

Bran

1M F

3M BF SD 3M F

SD

Shorts

3M

Figure 11 A simplified durum wheat semolina mill flow diagram. B, break; BF, bran finisher; M, middling; P, purifier; SD, shorts duster; S or SIZ, sizing. Corrugated rollers are closed and smooth rollers are open.

Whole Grain Products’ Milling Increased popularity of high level of dietary fiber in our diet has led to a significant increase in the production of whole grain products for a variety of end-use applications. The total

dietary fiber content in whole grain flour is around 12.0%. Whole wheat flour in some countries may not require inclusion of the constituents of the entire kernel, but for whole grain, entire kernel needs to be included. For example, in Canada, whole wheat flour is required to have a minimum of

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95.0% of the wheat berry. This permits millers to produce flour as part of their routine production and then blend flour and bran to ensure that 95.0% requirement is met. This allows exclusion of the germ as germ reduces the keeping quality of the whole wheat flour. There are a number of ways of producing whole grain flours. Small operations may use a basic cleaning system to remove the foreign material. This is followed by grinding in a stone mill to produce the whole grain flour. In some cases, this ground material is sifted again so the coarser fraction following sifting could be reground and blended back to provide relatively finer and uniformly ground whole grain flour. Large operations may use their cleaning plant including the scouring step for the removal of any surface dirt and contaminants. A portion of the wheat may be then directed to stone mills for the whole grain flour production as described earlier. Water is generally not added as it can make grinding more difficult with stones. The vast majority of the whole wheat flour in large facilities is produced by reconstituting the ground fractions to the same level as is present in the kernel of wheat. This allows cutting the bran finer before adding it back. Finely ground bran is less intrusive in the baking process and more palatable. Whole grain semolina from durum wheat has also become popular for the production of whole grain pasta products.


• • • • • • • • • • •


•

• Milling Process Monitoring and Control All electrical motors driving equipment are sequencecontrolled and interlocked to provide ease of operation, control, and protection. This allows sequential starting and stopping of motors and stopping of the process in a fail-safe manner. The old control systems had mimic display diagrams of the process and a hardwired electromechanical relay control system for control functions. Since the early 1980s, there has been a transition to mill automation. Mimic panels with small pilot lights have been replaced by computer graphics for visual display of the process status. Programmable logic controllers have replaced hardwired control relays. Computerized process control offers the flexibility of changing control functions, if required, through simply making programming changes rather than changing hardwiring. It also allows full integration of critical functions relating to process control and performance evaluation, such as product yield and output displays, automated roll gap adjustment, performance, and power consumption trends. Process control has reduced labor requirements in flour mills. Some mills have the so-called ‘lights out’ operation, where the mill runs for extended periods without staff present in the mill building. Modern process control systems offer many powerful features such as production planning, traceability, management information system, and maintenance. Another important advance is online quality monitoring. Automated online quality monitoring systems continuously monitor factors such as moisture content, protein content, and flour color, allowing flour millers to efficiently meet customer specification.

What are the three main constituents of a wheat kernel? What are the objectives of the wheat blending? What type of wheat is used for cakes and pastries? Name three physical properties based on which impurities are separated from wheat during the cleaning process. Why is wheat conditioned or tempered before milling? What are the most important equipments in flour mills? What is the function of a roller mill, a purifier, and a plansifter? What is the purpose of the break system? What is a straight-run flour? What additive is used for bleaching flour? What is the difference between refined white flour and whole grain flour?

•

Investigate the areas of continued research and development of lowering of energy costs, improved sanitation, and low maintenance requirements with respect to all milling equipment. Developing effective flour additives for improved performance of flour with respect to specific end use is critical to improving product quality. The focus is and should remain on developing functional enzyme-based mixes for such purposes. What progress is being made on this issue? Production of flour with low microbial load is critical to some of the end products and is of high importance for further research. What modern techniques may contribute to advance in this field?

See also: Barley, Rice and Maize Processing: Barley: Milling and Processing; Maize: Dry Milling; Grain Harvest, Storage and Transport: Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Grading and Segregation; The Basics: Grain: Morphology of Internal Structure; Wheat Processing: Milling and Baking: History; Wet Milling of Wheat.

Further Reading Bass EJ (1988) Wheat flour milling. 3rd edn., In: Pomeranz Y (ed.) Wheat: Chemistry and Technology, 3rd edn., vol. 2, pp. 1–68. St. Paul, MN: American Association of Cereal Chemists. Bizzarri O and Morelli A (1988) Milling of durum wheat. In: Fabriani G and Lintas C (eds.) Durum Wheat: Chemistry and Technology, pp. 161–189. St. Paul, MN: American Association of Cereal Chemists. Cornell HJ and Hoveling AW (1998) Wheat: Chemistry and Utilization. Cambridge: Woodhead Publishing Ltd. Dexter JE and Wood PJ (1996) Recent applications of debranning of wheat before milling. Trends in Food Science Technology 7: 35–741. Gradenecker F (2003) NIR on-line testing in grain milling. Cereal Foods World 48: 18–19. Hoseney RC (1994) Principles of Cereal Science and Technology, 2nd edn. St. Paul, MN: American Association of Cereal Chemists.

WHEAT PROCESSING | Wheat: Dry Milling Izydorczyk MS, Symons SJ, and Dexter JE (2002) Fractionation of wheat and barley. In: Whole-Grain Foods in Health and Disease, pp. 47–82. St Paul, MN: American Association of Cereal Chemists. Matz SA (ed.) (1991) The Chemistry and Technology of Cereals as Food and Feed, 2nd edn. McAllen, TX: Pan-Tech International. National Association of British and Irish Millers (1976) The Practice of Flour Milling, vol. 1. Richmond: Dimbleby Printers. Owens GA (2001) Wheat, corn and coarse grains milling. In: Owens GA (ed.) Cereals Processing Technology, pp. 27–52. Cambridge: Woodhead Publishing Ltd. Palmer GH (ed.) (1989) Cereal Science and Technology. Aberdeen: Aberdeen University Press. Posner ES and Hibbs AN (1997) Wheat Flour Milling. St. Paul, MN: American Association of Cereal Chemists. Sarkar AK (1993) Flour milling. 4th edn., In: Bass EJ (ed.) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn., vol. 2, pp. 603–653. Winnipeg, MB: Canadian International Grains Institute. Sarkar AK (2003) Grain milling operations. In: Chakraverty A, Mujumdan AS, Raghavan GS, and Ramaswamy HS (eds.) Handbook of Postharvest Technology: Cereals, Fruits, Vegetables, Tea and Spices, pp. 253–325. New York: Marcel Dekker.

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Relevant Websites http://www.atma.asn.au – Australian Technical Millers Association (ATMA), with members from Australia, New Zealand, and Papua New Guinea. This website contains news and information on milling and milling training courses, and also provides useful links to other milling associations and industry organizations. http://www.grainnet.com – Grainnet. This website provides news and information for the grain, milling, feed, and seed industries. http://www.aomillers.org – International Association of Operative Millers (IAOM). The IAOM is an international organization devoted to advancement of technology in the flour milling and seed processing industries. http://www.nabim.org.uk – National Association of British and Irish Millers (NABIM). The NABIM website contains useful downloadable information articles, and information on training courses. http://www.namamillers.org – North American Millers Association (NAMA). This association has members from Canada and the United States. The website provides industry news and background information on industry issues. http://world-grain.com – A grain and grain processing information site. Contains many useful links to industry, including many flour milling associations world-wide.

Wet Milling of Wheat R Velicogna, Archer Daniels Midland, Montreal, QC, Canada S Shea Miller, Eastern Cereals and Oilseeds Research Centre, Agriculture and Agri-Food Canada, Ottawa, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

• • •

Wet milling of wheat is the process of separating flour into starch and gluten using water. Wet milling of wheat is possible due to the different properties of the starch and gluten, particularly density and particle size. All processes are based on the formation and agglomeration of gluten in the presence of water and subsequent separation of starch from the gluten mass by washing with excess water. There are four main processes currently in commercial use: the modified Martin process, the hydrocyclone process, the Alfa-Laval/Raisio process, and the Tricanter process. Careful drying of the starch and gluten fractions is critical to retaining functionality. Separated gluten and starch fractions have many food and industrial uses.

Learning Objectives

• •

Achieve understanding of the basis of gluten and starch production by wet milling of wheat. Understand the principles behind the separation of A-starch, B-starch, and gluten based on density and particle size.

Introduction Wet milling of wheat is the process of separating flour into its components, primarily starch and gluten, using water in the process. This can easily be illustrated in a household kitchen. Take some flour and add enough water to form a dough ball and then knead the ball for a few minutes to allow the gluten to form. Slowly rinse this ball with water; the starch will wash out, leaving behind the gluten in a dough form. Industrially, similar methods are used, but on a much larger scale. The original Martin process, variations of which have been in use since 1835, was very similar: A large dough ball was prepared and washed with water while it was continuously kneaded to yield washed gluten. An employee who worked at such a plant in the 1970s claimed that the noise and vibrations were extremely high, as can be imagined with such a process. More efficient protocols are in current use, including the modified Martin process, the hydrocyclone process, the Alfa-Laval/ Raisio process, and the Tricanter process. The major components of flour that are separated by wet milling are starch and gluten (Figure 1). The starch is recovered in two streams, A-starch, which consists mainly of largegranule starch, and B-starch, which is mostly small granule

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starch. Minor components that can also be separated are bran and pentosans (arabinoxylans). These minor components are usually retained in the B-starch fraction or lost with the effluent. About 10% of the raw starting material ends up as effluent. Wheat wet milling requires flour as a raw material but is far less common than wheat dry milling. Wheat dry milling is primarily utilized for the production of wheat flour as a staple in many bakeries, snack, and other food products. The number of commercial wheat wet mills in the United States and Canada is in the single digits, while the number of dry mills is in the hundreds. The majority of wet milled wheat starch is for markets in the United States, EU, Japan, Australia, and Canada.

Processes General Wet milling of wheat is possible due to the different properties of the A-starch, B-starch, and gluten, particularly density and particle size. The specific gravity of dry A-starch is about 1.5, while the specific gravities of both the B-starch slurry and agglomerated gluten are about 1.1. This makes it possible to separate the A-starch from the two other materials by centrifugation, hydrocyclone, or decanter processes. The particle sizes of wet A-starch and B-starch granules are very small, and they can pass through most screens, while the agglomerated gluten forms dough balls or threads that are retained by most screens. For example, A-starch will pass through a 325 mesh screen while agglomerated gluten will be retained on a 60 mesh screen. This makes it possible to separate the gluten from the other materials.

Summary of Different Processes There are many commercial processes that have been used to wet mill flour; however, four main processes are currently in use: the modified Martin process, the hydrocyclone process, the Alfa-Laval/Raisio process, and the Tricanter process (Westfalia three-phase process). The modified Martin process starts with the formation of a stiff dough, followed by a separation of the A-starch and B-starch from the gluten dough with screens, as the starches will flow through the screen while the gluten dough is retained. In the second step, the A-starch and B-starch are then separated from each other using centrifuges and/or hydrocyclones. In the hydrocyclone process, the dough is allowed to mature for about 30 min and then is diluted with water, and the A-starch is separated from the other components by a series of hydrocyclones. The hydrocyclones used are static with no moving parts. A series of banks of hydrocyclones are used because they are very small, each with an internal volume of about 5 ml. In the hydrocyclones, the suspension is fed tangentially into the


http://dx.doi.org/10.1016/B978-0-12-394437-5.00163-7

WHEAT PROCESSING | Wet Milling of Wheat

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Figure 1 (a,b) Scanning electron micrographs of dry fractured soft (a) and hard (b) wheat kernels. (c) Light micrograph of hard wheat flour in water, showing large A starch granules (*), smaller B starch granules (small arrows), and strands of developed gluten (large arrowheads). (d, e, f) Scanning electron micrographs of dried fractions from wet milling of wheat. (d) gluten particle, (e) A-starch, (f) B-starch. Bars in all micrographs represent 20 mm.

side of the cone near the top. The resulting spinning effect generates the centrifugal force for the separation of the A-starch granules, which exit at the bottom (apex) of the cones, and the gluten/B-starch slurry, which exits at the top. In the second stage, the agglomerated gluten is separated from the B-starch with screens. In contrast, the Alfa-Laval/Raisio process starts with a thin batter of water and flour. The A-starch is separated from the other components by a centrifuge, and then the batter is allowed to mature. In the second stage, the B-starch is separated from the gluten by screens. The centrifugal process produces small gluten agglomerates; the starch is removed from the suspension by centrifugation while the protein remains suspended. The Tricanter process uses high-pressure water to homogenize the flour and water mixture before being sent to a three-phase decanter that separates the slurry into A-starch,

gluten and B-starch, and a soluble stream. The gluten and B-starch are then separated in the second stage by screening. The advantage of the Tricanter process is the elimination of solubles such as pentosans in the first stage, which can interfere with the separation process.

Water Usage Decreasing the water use at a wet mill has many benefits: reduced freshwater costs, less energy required for dewatering and drying, and lower costs for effluent treatment and disposal. The original Martin process used 15 parts water to one part flour; this is reduced to about four parts water for the hydrocyclone and Alfa-Laval/Raisio processes and further down to three parts for the Tricanter process. In modern wet milling

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plants, water is recycled in several of the steps. Problems with reuse of water arise from the solubles contained in the water and the biological activity. Process water containing solubles is an excellent growth medium for microorganisms, the growth of which results in acidic pH levels and end products with higher plate counts. Because wheat protein has higher solubility and lower strength under acidic conditions, this will affect the screening of the gluten and can allow some of the gluten to pass through the screens, decreasing the gluten recovery of the process. The amount of water that can be reused is thus limited. With careful equipment sanitation, filtration, and monitoring, however, water can nevertheless be reused in several of the steps.

Drying Wheat starch starts gelatinizing at about 52 C and continues until about 70 C when it is fully gelatinized in the presence of excess water. However, as the available water decreases, the gelatinization temperature increases to over 100 C, allowing starch to be dried without gelatinization. A-starch is typically in slurry form up to about 40% solids, which is usually dewatered to form a cake at about 60% solids and then flash-dried or ringdried to a powdered form containing about 10% moisture. Depending on the wet milling process used, B-starch can contain components that will increase its viscosity and interfere with the dewatering process, mainly water-soluble arabinoxylans, with smaller amounts of damaged starch and proteins. An increase in B-starch slurry solids above about 20% will result in excessive viscosity, so slurry solids are kept at or below this level. Such slurries are either spray-dried or drum-dried; the drum-dried product becomes a pregelatinized starch. Because B-starch is costly to dry, it is often kept in slurry form and sold as feed to nearby farms or processed into ethanol. A B-starch slurry will begin to spoil rapidly (within a few hours), and the cost of transportation is high due to the high water content, so the distance to the end user of B-starch slurry must be short and usage must be immediate. Gluten is generally flash-dried or ring-dried. The gluten recovered from the screens or wash stage is too high in moisture and adhesion for efficient drying, so it is mixed with dried gluten before being added to the (flash or ring) dryer for the first time. Once the drier is operational, it constantly contains dry gluten so that the wet gluten blends with the dry gluten to reduce its adhesion during the drying process. Excess heat will result in loss of functionality, or vitality, of the gluten, so gentle drying is required for a higher-quality product.

Raw Material The raw material for wheat wet milling is normally refined flour. Some mills use wheat as a raw material and mill it into flour. Whole-wheat flour can be used, but the gluten quality and recovery are generally lower, so this is not done in large volumes commercially. Although gluten can be separated from many wheat classes, hard wheat is most commonly used because the gluten forms more cohesively and can be separated from the starch with screens. Certain processes, such as the Tricanter process, are less dependent on gluten functionality,

so softer wheats can be used. In wet milling of wheat, protein content is almost as important as wheat hardness. Gluten from higher-protein wheat is generally more efficient to separate than that from lower-protein wheat. In lower-protein wheats, the gluten formation is disrupted to a certain extent by the higher content of other components in the wheat, primarily starch. In such wheats, the gluten does not form as well, making separation more difficult. Additives can be used to change the gluten properties. Ionic salts will generally strengthen the gluten, making it form stronger networks and facilitating separation, especially during gluten screening. However, if the gluten is too strong, it may entrap more starch, leading to a lower purity gluten. Another factor is pH. Gluten tends to solubilize in acidic conditions, making for a weaker dough and poorer separation on screens. In addition, the solubilized protein may increase the purification steps required in starch separation. The choice of additive is dictated to some extent by the preferred end product: gluten or prime starch.

Components Gluten Gluten is often the most important and valuable end product from wheat wet milling. Historically, gluten was oftentimes considered a by-product of starch extraction from flour. However, its value in food and industrial applications has increased to the point where it is currently difficult to justify wheat wet milling without including the value of gluten. When gluten is extracted using care to retain its functional properties, it is a viscoelastic material and it is called vital wheat gluten. If processing conditions are too harsh, wheat gluten can lose its viscoelastic properties to the point where it has nonelastic properties similar to nonwheat grain flours. It is then called nonvital wheat gluten, which generally has much lower value than vital wheat gluten. Thus, wet milling and subsequent drying processes are designed to retain the vitality of the gluten. The two most important factors in the retention of gluten vitality are the amount of agitation (shear and kneading) of the dough and the drying conditions. Gluten is formed when two insoluble wheat proteins, gliadin and glutenin, are kneaded together in the presence of water to form a continuous network. Overmixing will damage the gluten and cause a loss in gluten vitality. The drying process is also important for gluten quality. Subjecting wet gluten to excessive heat will cause devitalization. Some loss of vitality will always occur during processing; the goal is to minimize it. Freeze-drying is an excellent alternative, but the cost is excessive for commercial production. The Codex Standard for wheat protein requires gluten to contain 73% crude protein (N 5.7) by dry weight. Wheat wet mills can produce gluten higher than 80% protein, and in some special cases, using extra washing, the protein can reach 90%. Such high-protein glutens are sold as specialty products, while products sold as standard vital wheat gluten are manufactured at approximately 75% protein. Alternatively, vital wheat gluten can be manufactured at a higher-protein level and blended down to 75% protein using starch or flour.

WHEAT PROCESSING | Wet Milling of Wheat The quality of the end product gluten is determined by the type of wheat used and the conditions used for processing and drying. The quality of a gluten is determined by its strength and elasticity; a high-quality gluten has high strength and elasticity. A high-quality gluten is often advantageous, as it can be used at lower levels than a lower-quality gluten, possibly lowering production costs for the end user. If the proportion of a higherquality gluten is too high, the dough may be too strong and have detrimental effects in the final product. Glutens can be denatured, reduced, enzyme-hydrolyzed, or otherwise modified. If modification is done immediately onsite, the drying stage of the unmodified gluten can be skipped, leading to cost savings over drying gluten and then reslurrying it during a subsequent modification step.

Starch Wheat starch consists of granules that have a bimodal size distribution. Large-granule starch has an average size of 17 mm, while small-granule starch has an average size of 6 mm. Approximately 70% of wheat starch by volume is large-granule starch and 30% by volume is small-granule starch. Large-granule starch is referred to as A-type starch and small-granule starch is referred to as B-type starch, but in wheat wet milling, A-starch and B-starch have a slightly different meaning. In wet milling, A-starch is the starch end product with the highest volume. It contains most of the large-granule starch and some small-granule starch. It is normally a clean starch with very little protein (<0.5%), lipids, minerals, or fiber. B-starch is the term for the fraction that has a lower density than A-starch and not only consists primarily of small-granule starch but also may contain other by-products of the process, including pentosans, bran, damaged starch, and about 5% protein. The lower density of this fraction is probably due to the physical interaction between the starch and the other components, because the starch is not cleanly separated physically from the other components as A-starch is. A-starch can be classified by quality and size. It is possible to fractionate this starch into different size categories. Normally, the largest-granule size fraction has the greatest value due its strong and consistent gelatinization properties. It is also used as a stilting agent for carbonless paper due to its uniform size. This classification can also be used to eliminate the damaged starch portion. Starch is mostly damaged during the milling process, with starch from hard wheats being more damaged than starch from soft wheats. Damage can also occur during processing or drying. Most of the damaged starch will end up in the B-starch or effluent, but some can appear in the A-starch. The B-starch stream is usually higher in protein and other materials, but it can undergo additional processes that will increase the starch content. This is generally not done unless for a specialty application where the properties of a clean, small-granule starch are desired, such as for use in the pharmaceutical or cosmetic industries.

Other Components The other components of wheat wet milling are lipids and nonstarch polysaccharides. The most abundant nonstarch polysaccharide is arabinoxylan, a pentosan, but wheat also

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contains small amounts of mixed-linkage beta-glucans, cellulose, and arabinogalactan peptides. Depending on the source and treatment of the flour, bran can also be a significant component. Arabinoxylans can be further classified as waterextractable and water-unextractable. The water-extractable arabinoxylans hold a tremendous amount of water and will thus increase the viscosity of a slurry even at low concentration. These water-holding components can interfere with the separation process due to their high viscosity. They can be removed by screening (approximately 360 mesh) and are inherently removed by the Tricanter process. They can also be hydrolyzed with enzymes, which can significantly improve the efficiency of some separation processes. The bran found in the wheat wet milling process is normally very fine, as it is the residual bran that is found in the refined flour raw material. It has a density slightly lower than A-starch and can be present in the initial A-starch fraction. This bran can be removed from A-starch by screening, normally with a 250 mesh screen. Lipids are also found in wheat. Some lipids are starchbound and thus remain with the starch fraction. The free lipids generally interact and remain with the gluten. However, some are also present in the effluent.

Effluent About 10% of the raw material flour ends up as effluent. The effluent consists of soluble materials and suspended solids. The content of the suspended solids varies by process. The solubles consist of soluble starch, soluble nonstarch polysaccharides, soluble proteins, dissolved minerals, and lipids. Effluent is normally treated before it is discharged and can be converted by fermentation to methane, which is then burned to provide energy for the wet milling process. Effluent is very low in solids: about 1–5%. The dissolved minerals can originate from the grain itself or can be part of the water or processing aids used in the process.

Modification Starch and gluten can be physically or chemically modified. For wet reactions, it is more energy-efficient to modify the product before drying, as the drying stage consumes a significant amount of energy. Since wet products are time-sensitive and are expensive to transport, modification is generally performed at the same plant as the wet flour milling.

Food and Industrial Uses of Starch and Gluten from Wheat Wet Milling Although gluten is present in the wheat flours used in the baking industry, different levels of gluten are required for different types of products. Bread, for example, requires a higher-gluten content, typical of flours from hard wheats. In other bakery products such as cakes and cookies, too much gluten results in a tougher product with inferior crumb characteristics, so a low-protein soft-wheat flour is preferred. However, many baking operations do not have the storage capacity

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for a variety of flours with varying gluten content and thus use an all-purpose blend to which extra gluten can be added as required. Gluten is also used in the food industry as a meat extender or a meat analogue for vegetarian diets, as a binder in the preparation of batter coatings, and even in pasta doughs where wheats other than durum are used. Hydrolyzed glutens are used in beverages and other protein applications where viscosity is not wanted. Modified glutens have lower viscosity and can be used to relax dough for better sheet formation and can be used as a substitute for eggs. High-quality wheat starch is valued in the food industry as a thickener, stabilizer, and ingredient carrier. It can be used in its native form or modified for specialized functionality. As previously mentioned, the smaller starch granules are used in the cosmetics industry as face and body powders and in the pharmaceutical industry as a neutral filler in the manufacture of pills and capsules to assist in dose regulation. New and innovative technologies in starch development have produced natural starches without chemical modification. Consumers are becoming more sensitive to chemical ingredients in their food and are requesting clean ingredients and clean labels. Natural starches provide the same texture and properties as traditional, chemically modified starches. Industrially, starch is used as a surface sizing agent in paper manufacturing, to give a smooth coating to the product. It is used as a wet-end additive to increase the strength of the paper. For carbonless paper, large-granule wheat starch is used as a stilting agent, which is used to create a physical gap between the ink capsules and the neighboring paper to prevent unintentional marks. Starch is used in the textile industry as a sizing agent to strengthen fibers to minimize breakage during the weaving of fabrics. It is used in adhesives and as a core binder and strengthening additive for gypsum wallboard.


• • •

What is the purpose of wheat wet milling? What are the differences between the four major commercial processes of wheat wet milling? What factors influence the quality and vitality of wheat gluten?

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Name the two types of starch separated, and describe the characteristics of the two fractions. What other components of flour are found in wet milling fractions? Name the major food and industrial uses of starch and gluten from wheat wet milling.


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How would increased regulations on water use encourage process changes in a wheat wet mill? What components in the effluent could be further utilized to add value? How does the density of starch change as the amount of available water in a slurry increases?

See also: Carbohydrates: Starch: Chemistry; Starch: Starch Architecture and Structure; Non-food Products from Grains: Fuel Alcohol Production; Processing of Grains: Evaluation of WheatGrain Quality Attributes; Starch: Modification; Starch: Uses of Native Starch; Proteins: The Protein Chemistry of Cereal Grains; Wheat Processing: Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Gluten and Modified Gluten; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Ultrastructure of the Wheat Grain, Flour, and Dough; Wheat: Dry Milling; Wheat-Based Foods: Breads; Cereals: Overview of Uses: Accent on Wheat Grain; Noodles: Asian Wheat Flour Noodles; Noodles: Starch; Carbohydrates: Starch: Analysis of Quality; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Sayaslan A (2004) Wet-milling of wheat flour: industrial processes and small-scale test methods. LWT-Food Sci. Technol. 37(5): 499–515. Van Der Borght A, Goesaert H, Veraverbeke WS, and Delcour J (2005) Fractionation of wheat and wheat flour into starch and gluten: overview of the main processes and the factors involved. J. Cereal Sci. 41(3): 221–237.

Oven Technologies CE Walker{ ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 396–407, ã [2004], Elsevier [Ltd], with revisions made by the editor.

Topic Highlights

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Scale (Includes Cost, Size, and Capacity)

The range of types and sizes of ovens. Various heat sources are available. In many ovens, the food product is moved past the heat source. Traveling tray bread ovens. Cracker baking in a tunnel. Rapid-air impingement for quick heating. Hybrid ovens, combining conventional with microwave and radio-frequency heating.

Learning Objectives

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To gain an understanding of the principles of heating used in oven design, using the full range of heat sources, and to apply this understanding into practical production situations, which may differ greatly in size, geometry, product type, and operator requirements.

Introduction Baking ovens were used far back into antiquity, well before recorded history. No one knows exactly when and where baking, and hence the oven, was developed. Most likely, it was a gradual process with baking tools and skills developed through a slow combination of serendipity and ingenuity. The oven is the single most important, most expensive, and most complex piece of equipment used in bakeries. It limits the throughput, the variety, and the quality that the bakery can produce. It is also the least understood, most misadjusted, and most poorly maintained piece. It consumes the most energy and creates the most pollution, takes the most space, and generates the most controversy among its users. An oven cannot correct prior processing mistakes, but it can certainly limit everything done before. The success or failure of a baking venture is often determined by the oven, but the oven is sometimes the last item to be considered when a new bakery is being designed and equipped. Even though a well-designed and well-maintained oven will last for decades, its specifications often are reduced to ‘cost is the first consideration,’ rather than product suitability, lifetime utility, and maintenance costs.

Oven Classifications

Deceased.


Products Being Baked Except in very small shops, breads are baked in ovens that differ from sweet dough foods such as chemical- or yeastleavened pastries. Cookies and crackers will be baked in a different design yet, and cakes and pies require still another design. While smaller bakers may use a ‘one-for-all and all-forone’ oven, by far the best results will be obtained using an oven designed for the specific baked-food type.

Physical Arrangement Different physical arrangements for ovens began with the descendants of the primitive beehive ovens as hearth or deck ovens, rotary hearth ovens, rotary rack ovens, reel ovens, traveling tray ovens with single or multiple laps, and finally the long, continuous tunnel ovens used for crackers and cookies. Some of these designs will be described in more detail later in this article.

Heat Sources

Ovens today may be classified by several methods, as detailed later in the text. {

The local ‘corner hot bread shop’ or ‘in-store bake-off’ will use small batch ovens. These may only operate a few hours per day, perhaps baking only a hundred loaves, and will almost be totally automatically controlled. They require very little skill to operate properly. The ‘baker’ only needs to put the loaves (which may be frozen dough or even parbaked) into the oven and removes them when the buzzer sounds. Temperature, air circulation, and other settings are all carefully controlled by the manufacturer. Larger-scale institutional or small wholesale bakers are probably using rack or reel ovens, still manually batch loading them. They may bake a few hundred to a few thousand loaves per day. More judgment and skill are required on the part of the baker not only because of the oven but also because the entire operation is probably a ‘scratch’ bakery, preparing doughs and batters from individual ingredients, not from mixes or frozen items. Some of these bakers may be operating automated, thermal oil-heated, or deep hearth (setter) ovens. Finally, the large-scale high-speed plant bakeries baking 100 loaves per minute on each of several parallel lines will have highly automated continuous ovens in which molded dough pieces are automatically deposited into pans, proofed, loaded into a continuous oven, baked, depanned, cooled, and sliced without human contact.

Except in small primitive bakeries and by a few ‘boutique’ bakers, wood is seldom used in ovens today. The energy source is usually refined petroleum, gas, or electricity. A few attempts have been made to use solar energy, but this is not yet a

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WHEAT PROCESSING | Oven Technologies

significant contributor except in a few isolated locations used by individual bakers living in very hot and sunny countries with a shortage of fossil fuels. Likewise, coal is seldom used because it is so dirty. The fuel may be burned directly in the baking chamber, though there is an increasingly popular trend toward using indirectly fired ovens in which the combustion chamber is kept separate. A relatively recent modification is to heat special high-temperature oil at some distance from the oven and then pump it to large horizontal heat exchanger plates in the baking chamber. Within the oven, heat must travel in some fashion from the source to the raw dough. There are several mechanisms that accomplish this. Radiation, both thermal and electronic, is used, as is direct conduction between the hot oven surface and the dough. Likewise, convection (natural or forced) uses hot air to transport the heat. There are some other lesser known methods, such as direct ohmic resistance in which an electric current passes directly through the baking product, heating it throughout. Of course, there are ovens that use two or more of these forms simultaneously. When thermal sources are combined with electronic sources (microwave or radio frequency (RF)), they are often called ‘hybrid’ ovens. The following section presents a simplified description of the principal heat transfer modes.

Heat Transfer Mechanisms ‘Heat’ is energy in motion. A hot object transmits its energy to another when some of the thermal vibrations are transferred. The mechanisms for heat transfer are usually classified in three basic types, radiation, conduction, and convection, with some additional variations and combinations. These are described next.

Thermal Radiation Radiant energy does not need a medium to carry it, as it falls in the electromagnetic spectrum. Thermal radiation is energy that is transferred when the baking product can ‘see’ the heat source, which is often incandescent although the most effective heating wavelengths are usually in the infrared (IR) region, invisible to the human eye. For example, electric elements may glow ‘red hot,’ or gas flames may heat ceramic blocks to incandescence. By controlling the temperature and the nature of the radiator, it is possible to determine the wavelength at which the radiant energy is emitted. Energy transfer by radiation can be expressed by a relatively simple equation. Note the importance of the temperature term, raised to the fourth power. If the absolute temperature in degrees kelvin ( C þ 273.16) is doubled, the heat transfer rate will be 16 times as fast: QR ¼ esA T 4h T 4c DY [1] where QR is the net radiant energy transferred; e the emissivity of the radiating body, varying between 0 and 1; s the Stefan– Boltzmann constant for radiant energy; A the area to which heat is being transferred; Th the absolute temperature of the

hot, or emitting, body; Tc the absolute temperature of the cold, or absorbing, body; and DY the time increment over which the radiation occurs. Radiant energy is very effective for browning surfaces, but it does not penetrate very far below the surface. Some large ovens have a ‘browning’ section immediately before the discharge end with IR elements that can be used to control the final surface color. IR heaters are familiar as the deep red lights above restaurant serving counters, keeping food warm while it waits for delivery to the customer. Small ‘toaster’ and ‘pizza’ ovens sometimes use this principle. They are relatively cheap to construct and work well on relatively thin products such as biscuits. The principle is not satisfactory as the sole energy source for thicker objects such as pan bread loaves, because the surface heats very rapidly, browning quickly before the heat can penetrate to the interior and complete the baking process. Irregular surfaces are also difficult to bake with IR, because any exposed points burn before the rest is hot. Thermal radiation is a component in nearly all ovens but is usually accompanied by conduction and convection.

Conduction The higher the temperature of a substance, the more rapidly its molecules vibrate, and the vibration may be passed by contact from one molecule to another. If a cold substance is in contact with a hot object, the molecular vibrations are passed from the hot to the cold substance and the ‘heat’ is transferred. The more rapidly (the hotter) the source molecules vibrate and the better the contact between hot and cold bodies, the more efficiently the energy will be transferred. Metals are good thermal conductors and still air is a very poor conductor. Ceramics are intermediate. The ability of a material to transmit heat energy through it is called its thermal conductivity. Heat transfer by conduction may also be described by a relatively simple equation involving the temperature difference between the donating and receiving objects. In this case though, unlike radiation, the temperatures are only raised to the first power, not the fourth, so the driving force from temperature is not as dramatic: Qc ¼ kAðT h T c ÞDY=d

[2]

where Qc is the net heat transferred, k the thermal conductivity coefficient, A the area across which heat is transferred, Th the temperature of the hot or donating body, Tc the temperature of the cold or receiving body, DY the time increment over which the heat transfer occurs, and d the distance, or thickness, through which the heat must migrate. Most early baking used conduction to get the heat inside the food. Hot stones sitting in coals transferred their heat directly and rather rapidly to the dough placed on them. Even today, hearth breads are often placed directly upon the hot oven floor, perhaps separated slightly by a thin layer of bran or maize meal to keep loaves from sticking. The energy transfer is rapid and efficient so long as the bread makes good contact. Heat transfer between the dough and a pan can be improved by putting a thin layer of oil in the bottom before panning a pizza crust, for example. As a result, the pizza may have almost a ‘fried’ instead of a ‘baked’ crust character.

WHEAT PROCESSING | Oven Technologies Many baked foods such as biscuits (cookies and crackers) are baked upon continuous bands inside tunnel ovens. The direct gas flame heats the band and the small, thin biscuits are baked quickly, often in less than 3 min, because heat transfer is rapid. By preheating the oven band to an extra high temperature, the bottom of the dough piece is heated extremely hot, while the top is still relatively cool. The heat transfers so rapidly into the dough that small interior bubbles are generated by the rapid release of leavening and water as steam. The resulting dried product is very crisp yet very tender. Similarly, ‘flat breads’ such as pita and tortillas are baked at even higher temperatures, up to 400 C for less than 1 min. Conduction inside the dough is usually slower than the rate at which heat can reach the surface. Calculating the heat transfer rate inside a baking food is very difficult not only because the heat transfer coefficient, k, varies with the chemical nature of any substance (protein, starch, water, etc.) but also because as the product bakes, its structure and chemical composition change. The ‘k’ value will even be different in various parts of the food at the same time. The crust may be dry and hard with large air-filled pores. The resulting thermal conductivity is very low. On the other hand, raised dough with greater moisture will conduct heat more rapidly. This becomes more complicated as we consider convection and the ‘steam pipe’ effect in the following section.

Convection Convection heat transfer requires a moving fluid. Convection may be ‘natural,’ caused by air and steam circulation resulting from density differences. Hot gases expand, become less dense, and rise to the top, whereas the cooler gases settle to the bottom where they are reheated, resulting in vertical circulation inside the oven. Hot gases heat the baking dough by transferring energy across a boundary layer by conduction. The boundary layer is the relatively cool, moist, and dense layer surrounding the dough piece. Natural convection is present in most ovens, though it is not very efficient and heats rather unevenly. Fanforced convection ovens operate more efficiently by circulating the hot gases more rapidly and the hot gases are not limited to a vertical motion. A special form of forced convection, ‘impingement’ directs jets of hot gases perpendicularly onto the baking food at high velocity, sweeping aside the boundary layer and bringing the hot gases there more rapidly (Figure 1). The equation for heat transfer by conduction resembles the heat equations for the other two principal forms. Again, the difference in temperature between the heat source (circulating fluid in this case) and the baking product is the driving force. The rate is also controlled by the convective heat transfer coefficient. Remember that, like the radiation example, this equation only describes how the heat reaches the surface, not how fast it moves to the interior of the baking product: Qv ¼ hAðT h T c ÞDY

[3]

where Qv is the net heat transferred, h the convective heat transfer coefficient, A the area across which heat is transferred, Th the temperature of the hot or donating body, Tc the temperature of the cold or receiving body, and DY the time increment over which the heat transfer occurs.

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Figure 1 Flow patterns in natural convection, resulting in uneven heat transfer. Reproduced with permission from Varilek P and Walker CE (1984) Baking and ovens: History of heat technology IV. Bakers Digest 58(2): 13.

The convective heat transfer coefficient, h, is very difficult to predict based upon theoretical considerations, though many attempts have been made to do so. It is principally affected not only by the air velocity and flow pattern but also by the temperature, pressure, and moisture content, all of which affect air density and viscosity and hence control the properties of the stagnant boundary air layer that surrounds an object. Surface geometry also affects the convective heat transfer coefficient, especially for natural convection. For engineering scale-up purposes, it is more often satisfactory to determine the apparent convective heat transfer coefficient, ha, experimentally. This can be done by measuring the rate of temperature rise of a standardized metal plate, usually aluminum, placed inside the oven. Nearly all ovens will have some convection and it has been estimated that convection and radiation account for roughly equal contributions to the net heat transfer in conventional natural convection ovens. Many large commercial ovens have forced circulation by one means or another, not only increasing baking speed but also, more importantly, improving baking uniformity. Likewise, institutional food service-type convection ovens are relatively common. They have a fan that circulates the air at rather high velocities and bake in less time with more uniformity. The most dramatic use for forced convection is in the many tens of thousands of small units built for pizza restaurants since the mid-1970s. They force the circulating air through many small nozzles ( 1.0–1.5 cm in diameter) at air velocities 150–200 m s1 (meters per second). Higher velocities are possible, but they sometimes levitate the ingredient toppings. By impinging the air jets perpendicularly at the surface, these ovens sweep away the dense, viscous boundary layer and bring heat closer and more rapidly to the baking pizzas. With jets both above and below, pizzas now go from totally raw to fully baked in 5–8 min compared with the 20–30 min required when they were baked in deck ovens. The tremendous expansion in pizza outlets was only possible after impingement ovens were developed (Figure 2). Similar principles have been incorporated into tubeimpinged breakfast cereal toasters. They increase throughput,

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Hot

Cold Figure 2 High-efficiency air impingement directs small jets from both above and below, at right angles to the product surface. Reproduced with permission from Varilek P and Walker CE (1984) Baking and ovens: History of heat technology IV. Bakers Digest 58(2): 14.

reduce breakage, and improve quality for ready-to-eat breakfast cereals.

The Steam Pipe Effect When engineers first began to study heat transfer in the new rapid-bake impingement ovens, they could not explain why the net heat transfer rate appeared to be higher than would be expected. Efficient convection would heat the surface rapidly, but the cold, moist interior (like in raw pizza dough) was thought to be limiting because it had a lower thermal conductivity. They eventually discovered that the improved heat transfer inside the products being baked with very high apparent convective heat transfer coefficients could be explained by an interesting mechanism. This works best on porous products with relatively high moisture contents. Heat applied to a surface by the impingement process moves by conduction relatively rapidly across the thin solid wall of the ‘bubble’ or cell. Moisture evaporates from the hot side and migrates as vapor across the cell and condenses onto the inner, cooler cell wall. The latent heat of vaporization then migrates across another thin cell wall and evaporates more moisture on the other side. The process continues until it eventually reaches the center where it meets a similar phenomenon approaching from the other side (Figure 3). Not only does the heat move in, but also there is a net moisture migration to the center. The result is that in a loaf of bread fresh out of the oven, even though it has lost 10% by weight during baking, and the outside may be quite dry and crisp, the loaf center actually has higher moisture content than the starting dough. The moisture redistributes rather quickly, and the starch and protein have been changed by the 95–98 C temperatures in the center, so the inside is cooked, not raw or doughlike.

Oven Designs and Commercial Examples Traveling Tray Bread Ovens By around the year 1900, commercial baking had reached the point where the peel–hearth or deck and reel design ovens popular at the time could not keep up with demand. Tunnel ovens were designed in which pans entered at one end, traveled slowly through the entire length, and exited the other end.

Figure 3 The ‘steam pipe effect’ can explain why heat transfer across a porous substance is more rapid than otherwise predicted and how there is a net moisture migration toward the center. As heat moves through the cells, moisture simultaneously evaporates and recondenses, moving from the hot to the cold portions in the dough.

Limited automation was then practical, but the ovens were expensive and took a huge amount of floor space. The next innovation was combining the tunnel oven design with an extension to the concept. In a reel oven, two large wheels rotate vertically inside the baking chamber, much like on an amusement park Ferris wheel, with trays (instead of passenger seats) suspended between. Pans were placed on the trays and they revolved until the products were done. It was an important innovation, and reel ovens are still used in many smaller bakeries, because they are versatile and products requiring different baking times can be baked together (Figure 4). The traveling tray oven extended the oven from the front to the back by adding a second set of wheels and connecting them with heavy chains, to which trays were attached. Bread was loaded and unloaded through the same door. As their size grew, they eventually reached a length such that one pass took the entire baking cycle, so the batch oven evolved into a continuous oven, with products entering and leaving continually, never crossing paths with each other (Figure 5). The floor space for these ovens was more efficient than the tunnel oven, because a complete lap involved two passes through the oven, front to back and back to front. Only limited baking zone control was possible though, compared with the true tunnel oven in which product entered on one end and exited the other. Some manufacturers added a second pass through the same baking chamber, creating the double-lap oven. In the United States in 1923, 93% of the industrial bread ovens were the manually peel-loaded, batch type. By 1929, as the tunnel and traveling tray ovens were introduced, the portion of peel ovens fell to 50% (Figure 6).

Cracker Ovens in a Tunnel By 1931, the single-pass tunnel oven design was no longer used for bread, but the traveling trays were replaced by a solid or


Load on

Zone 1

Zone 2

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Zone 3 Unload

Figure 7 Band ovens with thin solid metal or heavy mesh baking bands are used principally for baking cookies and crackers. Reproduced with permission from Pyler EJ (1988) Baking Science and Technology, 3rd edn., vol. II, p. 1190. Kansas City, MO: Sosland Publishing Co.

automation, energy conservation, and increasingly sophisticated controls have evolved substantially. At the smaller wholesale, retail, and restaurant/food service scales, however, many innovations have appeared, nearly totally replacing the earlier deck and, to a lesser extent, the reel designs in many markets.

Rotary Rack Ovens

Figure 4 The reel oven was once very popular in wholesale bakeries and is still used in some retail and food service operations. Courtesy of the Reed Oven Co., Kansas City, MO, USA.

Zone 1 Load on Unload

Zone 2

Figure 5 The single-lap traveling tray oven carries trays loaded with several pans of products through the oven in one pass. Reproduced with permission from Pyler EJ (1988) Baking Science and Technology, 3rd edn., vol. II, p. 1188. Kansas City, MO: Sosland Publishing Co.

Zone 3 Load on

Zone 2 Zone 1

Unload

Zone 4

Figure 6 The double-lap traveling tray oven carries its trays through two passes of the heating chamber. Reproduced with permission from Pyler EJ (1988) Baking Science and Technology, 3rd edn., vol. II, p. 1189. Kansas City, MO: Sosland Publishing Co.

very heavy mesh continuous band and adopted by biscuit and cracker bakers. Typical cracker tunnel ovens are now more than 1 m wide and 100 m or more in length, for a 3 min bake. This provides for tremendous capacities, for example, 2000– 3000 kg of product per hour. Their multiple zones provide the operator with great control over product quality. For example, they are often direct gas fired with burners both below and above the band. The burners above the band, especially, may have IR radiating ceramic elements (Figure 7). Few basic design innovations have been made in industrialscale bakery ovens since the mid-twentieth century, although

Rotary hearth ovens provided advantages over the deck and peel designs, because each item was easier to access and could be put in and removed at a different time from the others. Their heavy, slow-moving, hearths were very stable and ideal for cakes and pies. In order to increase floor space efficiency, multiple decks (up to about five) were stacked. This design is currently in use in some retail and small wholesale bakeries. However, they are still slow and laborious to load and unload and require many manual transfers between forming, proofing, baking, and cooling. An improved concept now used in many large retail and small wholesale bakeries was developed by rolling the entire rack of pans inside a large vertical cabinet oven. Products could be panned on plain or perforated trays, the rack rolled into the proofing cabinet, and when ready for baking, the entire load rolled onto the oven. Humidity could be introduced by injecting steam or by dripping water onto large metal balls stored in the wall, in the air path. Air is blown at high velocity from one side of the oven across the trays. In order to bake more uniformly, the air direction could reverse automatically, and, in the more popular current versions, the entire rack rotates during the total baking cycle. The rotary rack oven is probably the choice for most new institutional food service and retail bakeries, and sometimes, they are installed in multiples for small wholesale operations, especially those that need to process a variety of products ranging from pastries and pies to bagels, as well as breads and rolls. The ovens occupy a size and versatility niche where they are difficult to beat.

Impingement Ovens The ancestors of the present-day ubiquitous impingement ovens owe their existence to attempts to cool radar tubes during the Second World War. It was discovered that if air was blown on the tubes through small nozzles, the heat transfer was more efficient and the tubes had longer life. In the early 1970s, a university food service operator asked the inventor of that cooling technology how to cook pizzas, rapidly expanding in popularity with college students, faster and with shorter lead time than possible in their deck ovens. The result was a series of small ovens that blew high-velocity hot air through nozzles perpendicularly onto the pizza. Baking times dropped to well

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below 10 min, so the large pizza restaurant chains began to adopt the ovens. The original patented design used ‘fingers’ extending from the air plenum on the side of the oven. The fingers were perforated with drawn nozzles below collimating plates and directed the air at the baking foods. The ovens were conveyorized with an open mesh and nozzles were placed both below and above the product. Belt speed determined bake time, reducing operator error. Forced convection air impingement ovens today use small nozzle holes, short tubes, perforated plates, or narrow slits to blow air at high velocity perpendicularly onto the baking food. The air jets or curtains ‘sweep’ aside the relatively cool, moist, viscous, dense boundary layer close to the product surface. The result is that the heat can reach the product more efficiently. The product can be baked in a shorter time, at a lower temperature, or both. This principle is especially effective with thin foods. Many consumers will be familiar with these ovens behind the counter in their local pizza restaurant (Figure 8). Other manufacturers produced competing equipment using tubes or slots, both of which had been used earlier in commercial equipment for other markets, to deliver the air at high velocity. Their uses expanded from the original pizza shops to encompass restaurants and food service on a larger scale. Casseroles, steaks, small bread loaves, cakes, and pies joined each other in the same oven. Even though the high air velocities result in rapid moisture evaporation, the residence time in the oven is reduced so much that products lose less moisture and generally have superior texture and increased shelf life. Forced convection tends to provide very uniform heat, so the principle was applied to a large commercial-scale pie oven. Highly automated, it could change fan speed and nozzle height ‘on the fly,’ permitting different products to be baked in the same oven at the same temperature, leaving only a short break

between formula changes. By the mid-1990s, several largescale tunnel ovens using the principle of high-velocity air impingement from slots or nozzles were being used to bake baking powder biscuits (resemble English scones), flat breads, and many other products on a large scale to meet the growing needs of demanding customers like fast-food chains. Any savings in baking times, lower temperatures, and reduction in energy use vary with the nature of the product (thickness, water content, etc.) and with the nozzle design and locations, but most importantly with the air velocity. As a general rule, the product of ‘time’ and ‘driving temperature’ can be reduced to about one-half, where ‘driving temperature’ ¼ ‘oven temperature’ ‘product starting temperature.’ Although it is theoretically possible to reduce the times even more by using higher temperatures and higher air velocities, the baker will soon encounter a zone of diminishing returns because the product’s interior thermal conductivity becomes the limiting factor, not how fast the heat can be brought to its surface. The time and temperature reductions apply to many products. Even ‘Pullman’ bread loaves (square sandwich bread baked in lidded pans) can be baked with about two-thirds the ‘time by driving temperature product.’ The accelerated heat transfer applies to metal as well, not just to exposed moist dough surfaces. Baked foods’ characteristics begin to change as baking times are adjusted by altering the temperature and heat transfer rate, either up or down. Baking is a complex series of reactions, many of which have different Q10 (relative change in rate per each 10 C change in temperature) values. As a result, the rates for leavening release, fat melting, sugar dissolution, protein denaturation, and starch gelatinization will all differ at different temperatures, and the product will exhibit different properties when the baking conditions are changed, even if the internal temperature and moisture contents are held constant. Reformulation can compensate for these changes to only a limited extent.

Compact Footprint Designs

Figure 8 High-speed air impingement ovens commonly bake pizzas in 7 min. These rapidly replaced the slower deck oven design previously used. Reproduced with permission from Middleby-Marshall Corp. ‘Press Kit’ CD. ã2001.

In many modern, large-scale wholesale bakeries, the oven is no longer a ‘stand-alone’ piece of equipment that must be ‘interfaced’ at each end with the rest of the production line but has become part of a totally unattended, integrated baking system. Product moves in a continuous, uninterrupted process, from mixing and depositing or filling at the beginning, with any proofing or relaxation required, through the oven, directly into coolers and freezers, without leaving the main conveyors, smoothly and quietly transferring trays where necessary. Manufacturing innovations include complete assembling of the entire production line and operating it to bake real product before it leaves the factory. Broken into smaller units for shipment, it can then be reassembled and put into operation relatively rapidly with a minimum of disruption to production flow in an existing bakery. Totally automated and integrated systems like this are ideal for parbaking breads. Parbaking involves partially baking the loaves, so that they are firm and can be handled but they do not have full color development. The loaves are often shipped frozen to distribution points all across the country where they are finish-baked in small rack ovens and sold to the consumer as fresh-baked.


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Horizontal folded path

Vertical folded path

Like many other large-scale oven developments, the serpentine concept had its origins in small-scale ovens designed for retail bakers. Initially used as a small multipass cookie oven, the serpentine design borrowed concepts from the commercial traveling tray oven and produced a highly compact oven capable of baking large quantities in a small space. Trays are suspended on an extremely precise chain and guide system. They usually enter the oven near the bottom and progress from the bottom to the top, typically making 7–11 closely spaced passes. In each pass, the trays are separated from those below or above by hot oil-filled plate radiators served by a heat exchanger that can be located quite remotely from the production area, improving safety and sanitation. Most products baked in this system to date have been relatively thin ones, like cakes and cookies, but designs are available for full-size pan breads as well (Figure 9). The small cavity design retains humidity, and the large radiator plate surfaces close to the product result in unusually uniform product characteristics, energy efficiency, and low baking losses in addition to the obvious space savings. Instruments are now available to monitor oven humidity in real time and control it by operating dampers or even by direct steam injection.

Another approach to reducing floor space requirements is to operate the transport chains vertically, moving up and down through the oven as it progresses through the baking chamber. Baking products are carried on swinging trays that remain horizontal as the transport chains move them through the oven chamber. Thermal oil heating plates may be arranged vertically between ascending and descending tracks or the ovens may be heated with forced circulation hot air. This design concept may have been inspired by the surge accumulator sections used in some automated packaging lines. This design can effectively change the path length through the oven, changing residence time ‘on the fly’ for different products, without having to change belt speed. This is a large design advantage, though in most cases the radiant plates cannot be placed as close to or as effectively over the products as they can in the horizontal fixed-path design such as in the serpentine ovens. However, it is possible to change residence time in each zone essentially independently (Figure 10). As the moveable double-geared pulley sets move up, the ‘forward’ path shortens while the ‘empty return’ path lengthens. This reduces the residence time in the oven but keeps the total chain length the same. Although a temporary regional speed change occurs while the geared pulleys are moving vertically, either the in-feed or discharge conveyor can be kept moving at a constant rate so they will not lose synchronization with either the filling or depanning equipment. Baking times can thus be changed ‘on the fly’ when products are changed. Since there is a great deal of thermal inertia in large oven systems, this can be a useful control for the baker because it will have a much more rapid effect than trying to change the temperature. Baking time and temperature can be stored in a computer as part of product manufacturing specifications. When the operator tells the computer that at a certain time a product change will occur, the oven can be programmed to adjust itself automatically. Since the baking time can be changed without altering the chain speed, and hence production line speed, product is

Spiral circular path Spiral coolers and blast freezers are relatively common, providing very long paths and hence long residence times in a relatively compact floor space. The concept has also been applied to continuous ovens. Product enters the oven supported on large baking trays sometimes attached to the conveyor by magnets. The conveyor is a long, endless, spiral, usually entering near the floor level and winding its way upward through the large hot chamber. In some designs, the chain returns in a smaller spiral down inside the outer spiral, to exit the oven below the first spiral, where the product is removed and the conveyor is automatically and continuously reloaded with raw product. Heat is often supplied by direct combustion gas burners in the center of the oven, and fans may be used to blow the hot air at the products, maintaining a uniform temperature in the oven. Though very efficient in terms of baking surface per square foot of floor space, it is very difficult to incorporate temperature, humidity, or heat transfer ‘zones’ into this design. Product out

Product in Figure 9 The horizontal path serpentine oven design conserves floor space and bakes very uniformly. It is often part of a totally integrated system that is preassembled and tested in the factory before it is installed in the customer’s bakery. Thin thermal oil heat exchanger plates can be located between the horizontal runs of the conveyor and can provide much more uniform baking than side-fed recirculating air ovens, especially if the conveyors are more than 1 m wide. With a smaller external surface area to volume ratios and closer-spaced heat sources, the ovens are much more efficient than traditional designs.

Product out

Product in Conveyor return

Conveyor return

Figure 10 The vertical path serpentine oven design is also efficient in floor space (sometimes described as ‘small footprint’ style) and can also be incorporated into an integrated baking system. Small trays remain suspended in a horizontal position while their conveyor moves through the oven zones. Thermal oil plates or infrared sources can be placed between the vertical conveyor paths. As the movable conveyor gears travel up, the product-containing section is shortened, matched by an increase in the conveyor return path so the total conveyor length remains the same, but the baking time is reduced without changing conveyor speed.

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produced at a constant rate. In effect, the baking ‘tunnel’ is lengthened for longer baking times or shortened for shorter times, all while the oven and the rest of the line continues in normal constant speed operation. This is not possible in most oven designs, especially in single-pass tunnel ovens. The same concept could also be applied to the horizontal folded path oven.

Steam baking provides a high heat transfer rate Steam is often added to conventional ovens, sometimes to control the crust texture or color. It is also used as the principal energy source for Chinese-style steamed bread. In steamed breads, the object is to produce a relatively dense loaf with a chewy texture (varies with the style: ‘northern,’ ‘southern,’ or ‘Guangdong’) and a smooth, white, leathery surface, rather than a conventional browned crust. Chinese steamed bread is made similar to conventional bread rolls in the early process stages, but after it has proofed and is ready to be baked, it is placed on open or perforated racks in a steamer. Traditional designs use bamboo baskets, although metal trays are often used in larger or more modern bakeries. The bread is ‘baked’ in saturated steam until it is heated through, the starch is gelatinized, the protein is denatured, and the loaves have a shiny but leathery surface.

Less Conventional Designs Microwave baking Microwaves are familiar tools for reheating foods in the home or office and have been tried for large-scale baking. Microwaves have the advantage that the RF radiation passes easily through a dry crust and is absorbed largely by the moist inside portion. Provided the product is no more than 10 cm in diameter, it heats relatively uniformly throughout. However, microwaves do not produce a brown crust, and in the case of bread, a toughening often occurs. Domestic microwaves operate at 2450 MHz and industrial microwaves at 915 MHz in the United States. Some countries allocate different frequencies for these uses. It is very important to isolate these high-energy frequencies from other applications, so they do not interfere with communications, for example. The lower-frequency, longer-wavelength radiation penetrates most products much better. Although there were numerous attempts to accelerate baking with microwaves as early as the 1960s, they were never commercially successful for large-scale baking. In addition to the quality problems resulting from nonuniform field heating, they were very expensive to operate and difficult to control. Microwave generators (magnetron tubes) are only 50% efficient, converting about half the electric input into heat. Their power level is also difficult to control. The most effective method has been ‘duty cycle,’ turning the tube on at full power for a short time and then turning it completely off. Although satisfactory for thawing foods or reheating them in domestic batch oven use, such a procedure does not work well in continuous conveyorized ovens. Also, trapping the radiation inside an operating oven, open at both ends for products on a nonmetallic belt to pass through, creates severe engineering challenges.

RF ovens RF is used as an energy source in some ovens. RF is similar to microwaves but operates at a much lower frequency, hence generating longer wavelengths that are easier to contain. The energy penetrates deeper into the product and has fewer ‘hot spots’ than with conventional microwaves. The frequencies allocated for this use in the United States are approximately 6, 13, 27, and 40 MHz. RF is used widely in industrial applications for curing plastics and providing controlled, localized, heating. In baking, however, it is principally limited to ‘postbaking’ in the biscuit and cracker industry, where it has become very common since its successful commercialization in the United Kingdom in the 1960s. Thin products such as crackers are difficult to bake uniformly at high speed, because there are small variations in the dough composition, mixing and forming steps, and in the oven. As a result, the individual pieces may vary in moisture content and color as they leave the oven. Even if the product averages the target value (typically 3%), when the moisture is too high in the center part of the cracker, it will cause checking or cracking as it equilibrates later. By sending the still-hot crackers through a RF postbaking oven, the excess moisture is removed or equilibrated in a few seconds, resulting in more uniformity and less breakage. Highenergy radio waves at these frequencies will preferentially couple with water molecules, drawing power to the wet portions but not to the dry ones. The small additional energy concentrated where the product needs it is sufficient to drive the extra moisture out, or to redistribute it, before the cracker has a chance to stress crack as it cools. This results in less dissatisfaction for the consumer and a greater profit margin for the baker (Figure 11).

Baking with visible light ‘Visible þ IR’ light is another relatively recent concept for rapidly baking foods, especially at the retail fast-food and food service level. A small microwave oven-size cavity contains tungsten–halogen tubes that emit a mixture of IR and visible wavelengths at extremely high intensity. The IR light does not penetrate very far beneath the surface, providing browning and flavor development and providing much of the total energy to the product. The intense visible light, shorter in wavelength, does penetrate somewhat into the interior. Though not as efficient in transmitting thermal energy, some is absorbed deeper into the product’s interior, thus accelerating

Figure 11 RF postbaking section often follows a biscuit tunnel oven to reduce uneven moisture distribution that can cause broken product. Courtesy of Radyne-Strayfield Corp., Milwaukee, WI, USA.


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the baking times considerably compared with a conventional oven. It does not compete in speed with a microwave oven having a similar power rating, however.

Direct resistance ovens

Hot air jets

Microwaves

Ohmic heating is used in some specialized applications. To produce certain styles of bread crumbs, especially ‘Japanese style,’ for breading and battering foods such as fish sticks and deep-fried vegetables, a simple bread dough is first mixed, then the ‘loaves’ placed between two electrodes, and an electric current passed directly through the loaf. Careful control of dough moisture and salt content is necessary. The internal resistance of the moist dough generates considerable heat ‘internally’ so in effect the bread bakes in its own steam. The moisture is driven off and the internal structure is set, but no crust browning occurs. After the loaf is removed and cooled, it is ground to the appropriate particle size and dried for use as a breading or batter thickener.

Hybrid Oven Designs Hybrid ovens contain a combination of two or more energy sources. Technically, nearly all ovens might be considered ‘hybrid’ because they usually use conduction, convection, and thermal radiation, all three to a certain extent. The term ‘hybrid oven’ though is usually reserved for ovens that combine ‘nonconventional’ energy sources, sometimes in a conventional oven, sometimes totally independently (Figure 12). Microwave oven manufacturers have long offered (largely unsuccessfully) hybrid ovens to domestic customers in an attempt to combine the speed advantages of microwave with browning and flavor development. One variation includes adjustable radiant elements at the top of the cavity and another offered a bottom hearth plate, but neither was ever large sellers. One domestic range added microwaves inside the regular size oven, but the baking was rather uneven. The most popular were the so-called convection microwave ovens. A conventionally designed microwave oven contained a small fan to circulate air heated by a separate electric element. One major problem was that US domestic electric circuits could not provide enough power to operate the microwave and the convection heaters at the same time, but had to cycle between them. A gas-fired hybrid microwave oven was developed in Europe but sold only limited quantities. One major problem was in preventing the microwaves from extinguishing the gas flame. Convenience stores and vending machines offer another potential market for microwave hybrid ovens, combined in this case with air impingement. They can be installed in commercial environments where they have access to sufficient electric power. The units are basically convection microwave ovens with oversized blowers and heaters that can operate at the same time as the microwave generator. Intended for food point-ofpurchase consumption, the convenience store customer would buy a refrigerated or frozen dinner from the display cabinets, remove the wrapper, and cook it in less than 3 min. An innovative extension to this idea was developed for the vending machine market. A large cabinet resembling a soft drink vending machine contained a freezer in the base where foods such as pizzas, spaghetti, and French fries were kept inside ingenious design boxes. The top part contains a

Figure 12 When baking in a hybrid oven, the food receives air impingement on all surfaces and also absorbs microwaves throughout. Keeping the product in motion results in a more uniform bake by distributing both forms of energy more evenly. Reproduced with permission from Walker CE and Li A (1993) Impingement oven technology. Part III: Combining impingement with microwave (hybrid oven). Technical Bulletin of the American Institute of Baking 15(9): 1–6.

combination microwave and hot-air impingement oven. When the customer inserts coins, an elevator automatically selects the desired food from the frozen storage magazine below, lifts it to the top, and pushes the inner noncovered container out of the overwrap box into the heating chamber. The machine is preprogrammed for the amount of microwave and thermal energy needed to thaw, reheat, and brown the customer’s choice. The outer carton is then replaced and the hot snack delivered to the customer in 1 min. The concept has been used successfully for many years in remote military posts and in hospital food service operations, but has not yet become widely familiar to the general public.

Summary Ovens have evolved slowly over thousands of years. Until recently though, the same principle – heating a food sitting on a hot shelf inside a closed chamber – described them all. Automation was not a major concept until a century ago, and innovative ways of generating and applying the energy to the product did not begin to make serious inroads in the home or commercial bakeries until the 1960s.

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List the advantages and disadvantages of the various heat sources. Thus, what ideal combinations can be selected to optimize advantages? What are the limitations and opportunities of oven size on implementing the various heat sources? How does geometry of oven design interact with heat source? What limitations might be associated with the impingement principle? Match a range of food products with the most suitable oven types. Make up a specific combination of oven requirements for food product, volume, speed, and costs (capital and operating) for a fictitious customer. Prepare an ideal oven design.


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Your loaves of bread emerge from a traveling oven with degrees of under- and overcooking across the breadth of the rows of loaves. What remedial measures can be taken? Hot food product straight from the oven must cool before packaging and sale. What principles of oven design may be applied to designing efficient cooling designs? Can the principles also be applied to the efficient thawing of frozen product? What complications do you see for the oven-based vending machine?

See also: Processing of Grains: Cereals: Breakfast Cereals; Wheat-Based Foods: Breads; Wheat Processing: Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Chemistry of Cake Manufacturing; Milling and Baking: History.

Further Reading Ovadia DZ and Walker CE (1997) Opportunities for impingement technology in the baking and allied industries: Part IV. Technical Bulletin of the American Institute of Baking XIX(5): 1–8. Pyler EJ (1988) Oven equipment. Baking Science and Technology, vol. II, pp. 1184–1217. Kansas City, MO: Sosland Publishing, 3rd edn., ch. 28. Varilek P and Walker CE (1984) Baking and ovens: History of heat technology IV. Bakers Digest 58(2): 13–14. Walker CE (1987) Impingement oven technology: Part I. Principles. Technical Bulletin of the American Institute of Baking 9(11): 1–7. Walker CE (1991) Air impingement drying and toasting of ready-to-eat cereals. Cereal Foods World 36(10): 871–877. Walker CE and Li AL (1993) Impingement oven technology: Part III. Combining impingement with microwave (hybrid oven). Technical Bulletin of the American Institute of Baking 15(9): 1–6. Walker CE and Sparman AB (1989) Impingement oven technology: Part II. Applications and the future. Technical Bulletin of the American Institute of Baking 11(11): 1–11.

Relevant Websites http://www.aibonline.org – Aibonline.org. http://www.bakeryandsnacks.com – Bakeryandsnacks.com. http://www.bakery-net.com – Bakery-net.com. http://www.sosland.com – Sosland.com.

Bakeries: The Source of Our Unique Wheat-Based Food, Bread JE Bock, University of Guelph, Guelph, ON, Canada CW Wrigley, The University of Queensland, Brisbane, QLD, Australia CE Walker{ ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by C. Wrigley & C.E. Walker, volume 1, pp 21–27, ã 2004, Elsevier Ltd.

Topic Highlights

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Bread can be made in many settings including the home kitchen, a small neighborhood bakery, or the large commercial bakery. The baking process is similar for all bakeries, differing only in the scale and degree of automation. Bread takes many different forms around the world with common forms including white pan bread, numerous artisan and flat breads, and even steamed bread. Home baking has been reinvigorated in recent decades by the advent of the bread machine and a growing interest in artisan breads. Large commercial bakeries are capable of producing thousands of units of uniform product every hour with tight computerized control over the baking process and a vast distribution network. Smaller independent bakeries typically lack the significant automation of large plant bakeries and range from operations where bread is made entirely from scratch by master bakers on the premises to those where only the final baking step is performed from frozen or par-baked products. Old-world bakeries are still common in many areas of the world, producing all products by hand daily for sale directly to the consumer. In addition to bread, many bakeries produce all manner of related products from pretzels, crackers, and bagels to cookies, cakes, and pastries.

Learning Objectives

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To gain an understanding of the principles of bakery production of bread and bread products in different types of bakeries.

Introduction Let there be bread! So reads the Latin motto of the Food and Agriculture Organization (FAO), ‘Fiat Panis.’ Bread, in its many forms, is a staple food for mankind. It may be made in the home, one loaf at a time, or in a fully automated bakery, at a rate of tens of thousands of loaves per hour. Bread is baked and eaten in many different forms – thin or thick, soft or hard, sweet or plain, and fresh or kept for many days (Figure 1). In some languages, the word for bread is the same as the word for food. Bread is practically the only food known almost universally around the world, from the most developed to the most primitive cultures, and it appears on the tables of the wealthiest and the poorest alike. {

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Bread is a generous gift of nature, a food that can be replaced by no other. When we fall sick, our appetite for bread deserts us last of all; and the moment we recover the appetite, we have shown a symptom of recovery. Bread is suitable to every time of the day, every age of life, and every temperament. It improves other foods, is the father of good and bad digestion. Eaten with meat or other foods, it loses none of its delight. It is so perfectly adapted to men that we turn our hearts to it almost as soon as we are born and never tire of it to the hour of our death. Antoine-Augustin Parmentier, eighteenth-century French nutritionist.

Historical Perspective The origins of bread making are lost in prehistory when primitive man discovered that the seeds of some grasses could be crushed, mixed with water, and heated on the fire to make an appetizing food. Advances came from extending man’s ability to recognize the more appropriate seed species (primitive wheats) and later to cultivate them, thus avoiding the tedium of searching and gathering them. Later, advances involved the development of better recipes and procedures for mixing and baking. Some of these arts became the trade secrets of specialists – bakers – who produced bread in quantity, for sale to their neighbors and beyond. Thus began the concept of the bakery, a place specifically designed for the efficient production of bread in quantity. An early type of oven is illustrated in Figure 2, the so-called beehive oven. Shaped like an igloo as much as a beehive, this oven is timber-fueled, with a vent in the top for smoke to exit and to provide a draft. The stick at the right of the oven is a peel for placing dough pieces into the oven and for removing the baked bread.

The Baking Process Today, all bread bakeries, small or large, follow the same basic procedures. The principal differences are in the scale (batch size) and the degree of mechanization and automation. Total processing time from the mixer to the consumer for commercial pan breads can be as little as an hour or up to more than 16 h, depending upon the process. These basic procedures carried out in the bakery are set out in Figure 3. The steps involved (1–12) are described in detail in the succeeding text: 1. The most basic bread contains only flour, water, yeast (or a natural sour-dough starter), and salt. Its demand for use in bread and meat preservation caused salt to be one of the first items traded in antiquity. 2. Ingredients must be stored carefully and measured accurately if the product is to be consistent. Home and small retail bakers may measure by volume, but

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Figure 1 The square ‘sandwich’ loaf, basic to the Western diet.

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Dividing typically occurs at about 100 loaves per minute in a commercial bakery, with many modern production lines now approaching 200 loaves per minute. A boutique bakery, on the other hand, may make fewer than 100 loaves per day. After the dough relaxes for a few minutes, it is ‘molded,’ or shaped into loaves, usually by flattening out into a disk and then rolling into a cylinder before being placed into a pan for common roundtop or square sandwich bread. The dough is allowed to rise or ‘proof’ to the desired height an hour under moist and humid conditions. The yeast generates additional gas and flavor by fermenting the natural and added sugars into carbon dioxide, alcohol, and other volatile flavor compounds. Baking can take <2 min at very high temperatures for thin ‘flat breads’ or up to half an hour at moderate temperatures for pan breads. A few very large, dense, hearth bread loaves may take several hours and bake very slowly. The loaf’s interior temperature typically reaches 95–98 C. After the bread is baked, it is usually cooled as quickly as possible to below 40 C inside before it is sliced and packaged. If it is too warm, it will ‘gum’ the slicer bands and tear the bread. If it is bagged too warm, condensation forms in the package and mold spots form. The slicing and bagging operations are most prone to mechanical difficulties and to product losses. Distribution can be as simple as placing the bread on a table or rack in front of the bakery where the walk-by customer purchases it unwrapped and still warm. Alternatively, it can involve overnight truckload shipments to distant warehouses and distribution facilities before reaching the retail store where shoppers buy it after it is anywhere from 1 day to 1 week old.

Figure 2 The beehive oven was an essential part of the early bakery.

A Bakery Visit large bakeries measure by weight, often with scales that automatically weigh and add ingredients to the mixer. 3. The dough is mixed until it is homogeneous and ‘developed,’ meaning that it is smooth and elastic and able to hold the gas formed during fermentation and baking. Large batch mixers may hold a tonne or more of dough (Figure 4), but the home baker may mix just enough for one loaf by hand. Chemical and physical test information on the flour and dough is provided to the baker, which helps in adjusting the process for the particular formula and for the natural variation in ingredients. The dough temperature is monitored, and information on its characteristics is fed back to adjust the next batch. 4. Fermentation typically takes 1–4 h, though some ‘short-time’ processes take much less. The spongeand-dough process involves mixing and fermentation, followed by the addition of more flour and ingredients; thereafter, mixing resumes. 5. The dough is divided into smaller pieces, taking into account the amount of weight loss (about 10%) that will occur during baking, to get the final loaf weight.

Come on a visit to a family-owned bakery of modest size. It is early in the morning, because the bread must be available for sale at the start of the retail day. Nevertheless, it is warm in here as the ovens have been turned on. First stop in the production of 680 g sandwich (‘Pullman’) loaves is a small spiral mixer (Figure 5) containing all the dry ingredients (flour, salt, improvers, and yeast), ready for water to be added and mixing to start. The resulting dough is then ‘scaled’ (divided) into 780 g pieces in a dough divider. These dough pieces (Figure 6) are rested (‘proofed’) to allow yeast action before being put through the dough molder seen in the top left of Figure 6. The molding process, designed to create the fine texture in the bread, first ‘sheets’ the dough squashing all the air holes out and then rolling them into a shape like a Swiss roll. These pieces are cut into four pieces before coming out of the molder (Figure 7). Four of these quarter-size pieces are turned 90 and placed in the bread pan for further proofing prior to baking in that same bread pan. This quartering exercise again helps to reduce the production of holes in the loaf, contributing to the fine texture, appearance, and eating qualities in the bread.

Figure 3 The basic procedures carried out in the bakery.

Figure 4 (a) Horizontal dough mixers used in a commercial bakery; (a) well used and (b) the latest model. (Photograph 4b courtesy of AMF Bakery Systems.)

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Figure 5 A spiral dough mixer with the dry ingredients ready for the addition of water and mixing into dough. (Photograph by Stephen Wrigley.)

Figure 7 Dough pieces emerging from the molder. Four of these quarter-size pieces are placed side-by-side in the bread pan for proofing and baking. (Photograph by Stephen Wrigley.)

Figure 6 Dough pieces (each 780-grams) being proofed to allow yeast action prior to molding and dividing in the equipment at top left. (Photograph by Stephen Wrigley.)

Baking in the oven produces four-segment loaves of 680 g (Figure 8). The final stages are cooling, slicing, and packaging. We can also watch the production of a batch of 30 bun rolls. A slab of developed dough is placed on the flat surface of the bun divider (Figure 9), which divides the dough into 30 pieces and rotates to produce rounded dough pieces. These are then laid out for proofing (Figure 10) and baking.

Home Baking The concept of the commercial bakery has never replaced the practice of bread making at home. Irrespective of time in history or of social status, there is an irresistible attraction to the aroma

Figure 8 Baked bread emerging from a traveling oven. Reproduced with permission of BRI-Australia Ltd.

of yeasted bread baking in the home kitchen and the taste of freshly baked bread straight from the oven. In today’s Westernized society, the traditional art of baking yeasted bread in the home may be lost to some extent, being replaced by the baking of chemically leavened cakes and cookies, with yeasted bread being bought at the supermarket. These changes are presumably due to the more complex procedures involved in the production of yeasted breads.


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Bakeries in Western Societies The Large Plant Bakery

Figure 9 Bun divider takes the dough for 30 bun pieces. It divides and rotates to produce rounded dough pieces. (Photograph by Stephen Wrigley.)

The plant bakery is at the opposite extreme, compared to the home kitchen. Technological advances in baking have led to the development of very large bakeries, in which bread of uniform type and quality is mass-produced using automatic control and uniform ingredients by expert staff with a minimum of staff numbers. There would normally be no sales at the bakery, but all baked product would be transported over a wide area to retail outlets, mainly supermarkets. Production in these large bakeries mainly involves sandwich loaves (‘Pullman’ loaves of square cross section baked in lidded pans), with the potential to put out more than 10 000 loaves per hour. ‘Roundtop’ loaves might also be produced in plant bakeries, but there are a very limited variety of bread types. A second class of bread type from plant bakeries is the bun or dinner roll, and the rate of their production might be as high as 100 000 units per hour. Due to the need for extensive transport of the bread, a long shelf life is essential, and sophisticated packaging is needed. Features of the plant bakery include the following:

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Figure 10

Buns proofing prior to baking. (Photograph by Stephen Wrigley.)

However, today’s obsession with consumer goods has partly solved these problems with the provision of the bread machine, a ‘high-tech’ computerized appliance that performs the three major steps of baking in the one unit, namely, mixing, proofing, and baking. These appliances were developed initially in Japan in the 1980s, in response to its attraction to the relatively new food, leavened pan bread, and the liking for hot, fresh bread in the home, especially at breakfast time. The use of these baking machines has since spread worldwide. The baked product is appetizing while hot, but in general, it is technically inferior to the quality of bread from a commercial bakery or even that produced by a skilled home baker. It has a relatively coarse crumb texture (due to inadequate development of the dough) and less flavor and aroma (due to a short fermentation stage) and stales relatively quickly (due to the general use of a ‘lean’ formula, lacking sugar and emulsifier, and a lower protein flour). It is thus unlikely that home baking in this form will replace the manufacture of yeasted bread from a commercial bakery. Nevertheless, the kitchen still has a significant place in the bakery story. Home bakers are increasingly interested in tackling handmade artisan breads, reacquainting themselves with the satisfaction of a home-baked loaf. This trend has been strengthened by companies like King Arthur Flour that make information, education, and baking tools readily available to home-baking enthusiasts in North America. While this development will also not replace the commercial bakery, it still shows the allure of a freshly baked loaf from one’s own labor.

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Computerized control of all stages of the baking process, including the prediction of consumer needs and scheduling the production order and volume for the day. Newer software programs also help identify and correct product defects during manufacture, thus limiting waste and downtime from failed production runs. The bakeries may operate 5 or 7 days per week. Very large bulk storage bins for flour delivered from mills in bulk by road or rail. Extensive flour functionality testing to ensure incoming flour meets quality specifications for each product. Common tests include falling number, farinograph, alveograph, extensograph, and solvent retention capacity, to name a few. Pneumatic movement of flour and other ingredients around the bakery, thus avoiding manual handling and avoiding dust hazards. Filtration and temperature regulation of water used in dough mixing. Large mixing equipment, each mixer frequently making more than 1000 kg of dough (Figure 4). High-speed dough dividing and forming equipment, operating totally ‘hands-free,’ with very narrow weight control. Automatic proofing cabinets that control the temperature and humidity; so the dough rises at the correct rate and is ready for the oven at the right time. Large traveling ovens to accommodate many loaves in a continuous process of baking (Figure 8). Regulation of oven temperatures, humidity, heat transfer rate, and speed to ensure uniform baking of all loaves. Automated facilities for the cooling, slicing, and packaging of loaves. Automated palletizing and loading of the delivery trucks.

This type of large bakery is most common in major centers of population in Westernized countries – particularly North America, Europe, Australia, and New Zealand – and is characterized by stiff competition and a very low profit margin.

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France and Germany may be exceptions, with a continuing preference for the smaller trade bakery, providing freshly baked bread to a local neighborhood.

The Independent ‘Scratch’ Bakery Like the French model of a local-neighborhood bakery, this is the traditional type of bakery, with one or a few skilled bakers making a wide range of bread types for sale on-site on a scale much smaller than that of the plant bakery. Bread is made ‘from scratch,’ that is, all basic ingredients are incorporated in the bakery, as distinct from recent developments such as the ‘in-store’ bakery (see succeeding text) where only the final stages of baking are performed. This type of bakery is often a family business catering for local needs and parochial preferences for bread types. Some ‘ethnic’ bread types are still made in those bakeries located in neighborhoods with many people from a common ancestry or country. It thus provides a valuable local resource, even a local meeting place, but it may be much less efficient than the plant bakery in terms of the production cost per unit. In recent decades, there has been a loss of this type of bakery, in some cases because the operators of plant bakeries have bought them out in order to expand their distribution network. In North America, the few remaining small local bakeries often produce principally cakes and pastries rather than the low-margin white pan bread. The majority of the 1200 British in-store bakeries (in supermarkets) are based on scratch production – not frozen dough or bake-off. Some other European countries have similar high numbers of scratch in-store bakeries (e.g., France, Hungary, and Portugal).

Hot-Bread Shops This type of modest-sized operation has reappeared in recent decades in the form of the franchised ‘hot-bread shop,’ often located in shopping centers. In this type of bakery, all goods are baked within the bread shop for direct sale at the shop front. In general, recipes and equipment are standardized. Some products might be produced ‘from scratch,’ but in many cases, the earlier stages of production might be short-cut, for example, by the use of bakery premixes containing all ingredients so that the main addition is water before mixing. In such bakeries, only a modest level of skill may be needed on the part of the bakery staff, thereby reducing costs. Nevertheless, a wide range of goods may be produced, including many ‘fancy’ types of bread, sweet pastries, and filled doughs such as pies.

In-Store Bakeries A further innovation of recent decades involves ‘taking the bakery to the people,’ namely, into the supermarket. This concept involves performing the last stage of the process, the baking step, within the supermarket so that the baked products are presented freshly baked for immediate sale. In this case, relatively unskilled staff can be used to load par-baked or frozen dough pieces into the oven for baking (rack- or reeltype oven) under prespecified conditions. Although skill requirements may be modest, a range of bread types can be

offered by the in-store bakery, thereby satisfying local demands. The critical contribution to the success of the in-store bakery is the supply of frozen doughs or par-baked foods. These are produced at a centrally located ‘commissary bakery’ and may be distributed relatively long distances. The commissary bakery may be a large plant bakery with automated facilities to take the baking process through to either the proof stage (before freezing) or the partly baked stage as par-baked (before refrigeration or freezing and transport). Recent trends favor the par-baked product for this concept. It can be stored and transported at room temperature for up to 7 days, though some bakers claim shelf life of up to 2 weeks. Longer storage requires cooling or freezing to extend the shelf life of frozen dough to 3 weeks and of par-baked dough up to several months if properly packaged and deep-frozen. Frozen dough pieces are sometimes stored for much longer, but the freezing process damages both the yeast quality and the gluten quality, so that higher levels of gluten must be used, together with special yeast strains. There have been some attempts to sell the frozen dough pieces directly to the homemaker, but a substantial amount of time is still required to properly thaw, proof (raise), and bake the dough. As a result, the use of frozen dough has never reached predicted levels in direct home sales. However, certain institutional applications, such as frozen pizza crust disks, have been very popular in some niche markets where, even when some skilled staff are available, they can save on the mixing and forming stages with their long lead times.

Old-World Bakeries Bakery operations in the Middle East, Asia, and Latin America are generally on a small scale, catering for the local community and producing baked goods that may once have been regarded as ‘exotic’ by Westerners. Labor and skill input is considerable, sales are on-site, and there is little need for packaging or for extensive transportation of the product. The range of products is unlikely to include much of the Western-style leavened loaf, but its popularity is increasing in these regions. More likely, these bakeries produce traditional breads suited to the local demand. In the Middle East, this includes various types of flat breads (Figure 11). Some of these are pocket breads that open in two layers for the insertion of pulses or other fillings. Thicker flat breads are popular in Turkey, North Africa, and India. Baked at very high temperatures, they have a very coarse, open, texture with a thick crust and are often ‘decorated’ with the baker’s finger marks on the top. One of the most popular and ubiquitous breads in China is the appropriately named Chinese steamed bread. Steamed breads are small rolls with similar volume to Western pan bread, but the ‘crust’ remains shiny, white, and supple due to the steaming process used in place of traditional oven baking. These are commonly consumed as a plain roll, but they can also contain sweet or savory fillings. Commercial facilities producing these regional products are still rare but are becoming increasingly more common as these countries become more urbanized, necessitating more centralized production. A number of small ‘boutique’ bakeries have


Figure 11 A bakery in which Arabic flat breads are produced.

also begun to appear in some countries outside of these regions. They tend to use very limited equipment to produce a small (and expensive) product, baked by residual heat in preheated heavy masonry ovens derived from the ancient ‘beehive’ designs (Figure 2). A recent example of this particular trend is tortillas, which were once considered to be ‘ethnic’ breads. With the growth of the Hispanic population in North America, however, they are now widely available and their production is switching from small artisan bakeries to large mechanized high-speed production. Hispanic types are speckled with dark brown spots and an irregular surface. Chinese preferences are for tortillas to be very white and smooth. Both types are used as wraps for filling in the center, as for a ‘taco’ or ‘Peking duck.’

Specialized Baked Goods Many bakeries, both large and small, produce more than just bread. Beyond the scope of what we would normally class as ‘bread’ in its widest sense, there is a wide range of specialized bakery products. Many of them are sweet but some are savory, some are yeast leavened, but others are chemically leavened. The list includes foods such as cinnamon rolls, pretzels, doughnuts, snack foods, bagels, and many types of cookies and crackers, cakes, and pastries. Bakeries differ considerably depending on the procedures and equipment needed for this diverse array of foods. Some of these such as crackers and cookies are produced in vast quantities on very large, high-speed, automated ovens, whereas most of them individually involve small product runs. An outstanding example in the high-speed class is given by the many types of cookies and crackers made by Mondele¯z International, making it the largest baking company in the United States, yet the company produces no bread.

Future Perspectives The future is likely to see the spread of larger plant-type bakeries into the centers of population in countries where traditional bakeries have always been the norm. This transition will involve the adaptation of automation and mechanization to

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bread types that have not previously been produced in such quantities and uniformity. In countries where production is already dominated by large commercial bakeries, the trend is towards these companies buying smaller baking operations to expand their distribution network. Additionally, changing preferences based on new dietary trends, such as the low-carb and gluten-free movements, have significantly altered the consumer mind-set towards bread and bread products. It requires the baking industry to become more agile in adapting to new lifestyles that challenge the central role of bread in the diet with innovative products. Nevertheless, history has shown that the ‘bottom line’ that determines the success or otherwise of any such innovation is the reaction of the consumer. It is the common person who buys the bread, selecting the source and type of their choosing, that ultimately determines the fate of any bakery.


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What are the basic ingredients for bread? What does it mean to say that dough is ‘developed’ after mixing? What does yeast produce during fermentation and proofing? How does this influence the appearance and flavor of bread? How do large bakeries control the bread making process? What are par-baked breads? Which two ingredients are commonly added to frozen doughs? Why? What is responsible for the poor quality of homemade breads from bread machines? Why do small and old-world bakeries skip the packaging step?


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There are many flour functionality tests used to determine the quality of a given flour for different baked products. Choose three flour functionality tests and explain what they measure as well as what information they provide regarding flour quality. Gluten proteins are responsible for the unique viscoelastic properties of developed bread dough. Identify which gluten fraction contributes the viscous and elastic properties, respectively, and explain how they work together to create viscoelasticity. Choose three countries and identify (a) the most popular type(s) of bread consumed there and (b) which type of bakery produces them.

See also: The Basics: The Grain Chain: The Route from Genes to Grain-Based Products; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: Chemistry of Cake Manufacturing; Oven Technologies; Wheat-Based Foods: Breads; Cereals: Overview of Uses: Accent on Wheat Grain; Cookies, Biscuits and Crackers: Formulation, Processing and Characteristics; Flatbreads of the World; Sour Dough Technology.

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Further Reading Cauvain SP (ed.) (2003) Bread Making: Improving Quality. Oxford, UK: Woodhead Publishing. Cauvain SP (ed.) (2012) Bread Making: Improving Quality, 2nd edn. Oxford, UK: Woodhead Publishing. Cauvain SP and Young LS (2008) Bakery Food Manufacture and Quality: Water Control and Effects, 2nd edn. St. Paul, MN: American Association of Cereal Chemists. Faridi H and Faubion J (1995) Wheat End Uses around the World. St. Paul, MN: American Association of Cereal Chemists. Khan K and Shewry PR (eds.) (2009) Wheat: Chemistry and Technology, 4th edn. MN, USA: AACC International. Kulp K, Lorenz K, and Brummer J (eds.) (1995) Frozen and Refrigerated Doughs and Batters. St. Paul, MN: American Association of Cereal Chemists. Pyler EJ (1988) Baking Science and Technology, 3rd edn. Kansas City, KS: Sosland. Qarooni J (1996) Flat Bread Technology. New York: Chapman and Hall. Quail K (1996) Arabic Bread Products. St. Paul, MN: American Association of Cereal Chemists.

Sluimer P (2005) Principles of Breadmaking: Functionality of Raw Materials and Process Steps. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.aaccnet.org – AACC International. http://www.aibonline.org – American Institute of Baking. http://www.asbe.org – American Society of Baking. http://www.australiansocietyofbaking.com.au – Australian Society of Baking. http://www.bbga.org – Bread Baker’s Guild of America. http://bsb.org.uk – British Society of Baking. http://www.campdenbri.co.uk – Campden and Chorleywood Food Research Association. http://www.grains.k-state.edu/ – Kansas State University Department of Grain Science and Industry.

Analysis of Dough Rheology in Breadmaking B Dobraszczyk, Reading Science Centre, Reading, UK ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

• •

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New rheological techniques for characterizing bread dough have been developed that are based on modern polymer rheology principles. Molecular size, distribution, and structure of the gluten polymers can be related to their rheology and end-use performance in baking. Conventional descriptive empirical measurements of dough rheological properties traditionally used in the baking industry have often produced poor correlations with baking performance. It has been recognized that most of these tests are carried out under deformation conditions very different to the breadmaking process. Rheological tests have been developed based on measurements of fundamental rheological parameters such as stress, strain, and strain rate under deformation conditions relevant to breadmaking. A new rheological property, extensional strain hardening has been shown to be strongly related to large deformation processes in baking such as sheeting, proof, and baking expansion.

Learning Objective

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To gain understanding in the use of modern rheological techniques in relation to the breadmaking process.

Introduction Rheology is defined as the study of the flow and deformation of materials, conventionally applied to materials that flow within normal experimental timescales, for example, liquids and soft solids with viscosities in the range 0.1–100 000 Pa s: for example, wheat flour dough has a viscosity around 1000–10 000 Pa s. Most materials will flow given enough time: For example, ice flows over decades in glaciers, and rocks flow over millennia in the Earth’s crust, but these are generally regarded as brittle, elastic materials over normal experimental timescales (a few minutes) and are generally described by solid mechanics principles. To measure rheological properties, deformation or strain is applied to a material in a controlled and quantifiable manner, and the resultant forces or stresses are measured to give an indication of the stiffness, modulus, or viscosity of the material. For materials that flow readily, shear stresses are commonly applied using standard viscometer geometries such as rotating parallel plates, cone and plate, and concentric cylinders. For complex fluids such as doughs, especially the ones where there are long polymer molecules, the rheological


properties measured in shear are very different from those in extension, and therefore, extensional deformation is often applied by the imposition of a stretching or elongational flow. Rheological measurements on bread dough have long been used as a method to define its physical properties, the main aims of which are

• • •

to obtain a quantitative description of its mechanical properties, to characterize and predict its performance during processing and end use, to obtain information related to its molecular structure and composition.

Rheology can tell us how a dough will behave under a given set of conditions and can be used to characterize and predict its performance during deformation, for example, during mixing, sheeting, proofing, and baking of dough. Rheological data are an important tool in processing design, for example, in the design of mixers and sheeters, or to predict the behavior of expanding bubbles within proofing doughs and ultimately to predict end-use quality. At the heart of this work lies the longheld belief within the baking industry that the rheological properties of dough, traditionally assessed by kneading and stretching the dough by hand, have a strong relationship with its eventual baking quality. This belief has been built up by centuries of empirical evidence, and there is no reason to doubt its validity. However, results from both conventional industrial methods of assessing dough rheology and modern fundamental rheological tests have given disappointing relationships with baking quality. This is mainly because many of these tests are carried out inappropriately under deformation conditions far removed from those occurring during baking. This article will review rheological test methods applied to doughs and assess their usefulness in predicting end-use performance.

Historical Background We have always had an intuitive feel for rheological testing, for example, in tactile and visual assessments of material properties such as hardness, stiffness, flexibility, and viscosity and their relation to end-use quality characteristics. People often intuitively assess the quality of solid foods by gently squeezing them, or liquid viscosity is assessed by gently rotating the liquid in its container, and these tests are often applied on the factory floor as a crude measure of quality. These intuitive assessments gradually became formalized into quantitative descriptions of material properties by scientists such as Newton, Boyle, Pascal, Hooke, and Young. Modern rheology as an independent discipline can be traced back to 1929, when The Society of Rheology was set up by a number of scientists working in complementary fields to secure an absolute standard for viscosity, and the name rheology was proposed to

http://dx.doi.org/10.1016/B978-0-12-394437-5.00161-3

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WHEAT PROCESSING | Analysis of Dough Rheology in Breadmaking

describe the study of flow and deformation of all forms of matter by Bingham and Reiner. Since then, rheology has grown rapidly as a science and contributed to a number of applications such as colloids, suspensions, and emulsions, polymer processing, extrusion, and polymer modeling. Recent developments in polymer rheology have established a quantitative link between the molecular size and structure of polymers and their rheology and end-use performance. Rheological measurements are increasingly being used as rapid, sensitive indicators of polymer molecular structure and predictors of end-use performance.

Rheological Test Methods There are many test methods used to measure rheological properties, and the reader is referred to general reviews of rheology. It is common to categorize rheological techniques according to the type of strain imposed, for example, compression, extension, shear, and torsion, and also the relative magnitude of the imposed deformation, for example, small or large deformation. The main techniques used for measuring cereal dough properties have traditionally been divided into descriptive empirical techniques and fundamental measurements.

Descriptive Rheological Measurements Within the baking industry, there is a long tradition of using descriptive empirical measurements of rheological properties, with instruments such as the penetrometer, texturometer, consistometer, amylograph, farinograph, mixograph, extensograph, alveograph, various flow viscometers, and fermentation recording devices (Table 1). Empirical tests are easy to perform and are often used in practical factory situations, providing data that are useful in evaluating performance during processing and for quality control. The instruments are often robust and capable of withstanding demanding factory environments and do not require highly skilled or technically trained personnel. They have provided a great deal of information on the quality and performance of doughs such as consistency, hardness, and texture. However, these measurements do not fulfill the requirements of a fundamental rheological test since

• • •

the sample geometry is variable and not well defined; the stress and strain states are uncontrolled, complex, and nonuniform; it is therefore impossible to define any rheological parameters such as stress, strain, strain rate, modulus, and viscosity.

Therefore, these tests are purely descriptive and dependent on the type of instrument, size, and geometry of the test sample, and the specific conditions under which the test was performed. For example, empirical tests are used to characterize the behavior of bread doughs during processing, such as the extensograph, farinograph, and mixograph. Many of these are used as single-point tests, where a single parameter is often arbitrarily selected from a whole range of data acquired during the test as, for example, in selecting the peak torque from a

Table 1

Test methods used in the baking industry

Empirical methods

Property measured

Mixers Farinograph, mixograph Reomixer Extensograph Alveograph Amylograph, RVA, falling number Consistometer Flow cup Falling ball Flow viscometer Fermentometer Penetrometer Texturometer, TPA

Mixing time/torque Consistency Water addition Extensibility Extensibility, tenacity Apparent viscosity Gelatinization temperature Apparent viscosity Apparent viscosity Apparent viscosity Apparent viscosity Height, volume Firmness, hardness Texture, firmness

Rheological methods Dynamic shear oscillation Parallel plates, cup, and bob Extensional flow Dough inflation system Kieffer dough extensibility Lubricated compression Sheeting, rolling Filament-stretching extensional rheometer (FISER) Sentmanat extensional rheometer (SER)

Shear modulus (elastic and viscous), dynamic viscosity, creep, relaxation modulus, and time Extensional viscosity Strain hardening

mixing trace and then using this to correlate with performance, which neglects a large part of the recorded data and is appropriate only to the set of conditions under which that test was performed and which are generally not applicable to any other deformation conditions. Since dough experiences a wide range of conditions of stress states and strain rates during processing and baking and the rheological properties of dough are dependent on both time and strain, there is often a discrepancy between such single-point-type tests and actual performance on the plant, where conditions of strain and strain rate may be poorly defined and very different to those in the laboratory test. Therefore, it is impossible to compare results between different testing machines or to extrapolate the results to other deformation conditions. Doughs are viscoelastic (i.e., they exhibit both viscous and elastic behaviors), and therefore, their properties depend on how quickly the test is performed (the strain rate or frequency). This is important in many aspects of dough processing: for example, if the dough is deformed quickly, such as in mixing or sheeting, then the rheological properties of the dough will be very different if measured at the typically slower rates of deformation found in conventional rheological testing machines. Alternatively, performing a test under small deformation shear will give very different results to the large deformation extension conditions that dough experiences during sheeting or bubble walls experience during baking expansion. Performing a test under only one particular set of conditions of


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rate, temperature, and strain will almost certainly not be applicable to another set of deformation conditions: it is necessary first to define the set of deformation conditions under which a dough operates in practice and then to perform the rheological test under these conditions.

deformation conditions, difficulty in interpretation of results, and slip and edge effects during testing. The main types of fundamental rheological tests used in dough testing are small deformation dynamic shear oscillation and large deformation extensional measurements.

Fundamental Rheological Tests

Dynamic Oscillation Measurements

Rheological tests attempt to measure the forces required to produce given controlled deformations, such as squashing (compression), bending or pulling apart (tension), or shearing, and to present them in such a way as to be independent of sample size, geometry, and mode of testing. They measure a well-defined property, such as stress, strain, stiffness, or viscosity. A small test piece of the material is usually deformed in a controlled way, normally on a motor-driven machine, and the force and the distance moved or displacement of the object are measured. The force is then usually plotted against the displacement to give a force–displacement curve. Normally, for stiff materials, we would divide the force and displacement by the original sample dimensions to obtain stress (force/crosssectional area) and strain (displacement/original dimension), because the changes in sample dimensions are small and uniform; this allows us to remove the sample size and geometry as a variable. Many food materials are not stiff and undergo large deformations in practice, where the geometry often changes in a nonuniform and unpredictable manner giving large and nonuniform stresses and strains along the sample. For example, dough thins out nonuniformly when stretched, in common with many polymers, giving rise to large stresses and strains not correctly calculated by the conventional method of dividing by original sample dimensions. In this case, it is necessary to normalize by actual change in dimensions during deformation, in which case sample dimensions should ideally be measured locally and independently by using contact extensometers or noncontact techniques such as laser, video, or photographic techniques. For materials that flow under normal measurement timescales, stress is normally divided by strain rate (strain/time of strain application) to give viscosity. Problems encountered with such fundamental tests are complex instrumentation that is expensive, time-consuming, and difficult to maintain in an industrial environment and requires high levels of technical skill, often inappropriate

Adapted from techniques developed for measuring viscoelastic properties of polymer melts and concentrated solutions, this is one of the most popular and widely used fundamental rheological techniques for measuring cereal doughs. These tests measure rheological properties such as elastic (G0 ) and viscous (G00 ) moduli by the application of a small amplitude sinusoidally oscillating strain or stress with time (t) and measuring the resulting response. Normally, the values G0 and G00 are measured over a range of frequencies. Figure 1 shows the main features of the viscous (G00 ) and elastic (G0 ) behaviors for a polymer over a very wide range of frequencies. The lowest frequency range (called the terminal zone) describes the longest relaxation motions of the polymer molecules and is therefore related to the relaxation of the largest molecules within the polymer. The viscosity in this region (called zero-shear viscosity) is very sensitive to molecular weight (MW). Beyond a critical molecular weight (MWc), characteristic for each polymer, zero-shear viscosity (0) starts to increase rapidly with increasing MW, following a relationship 0 ¼ K.MW3.4 for linear polymer melts, independent of polymer chemistry (where K is a constant dependent on temperature and polymer concentration). Above this critical MW, the polymers start to entangle, giving rise to the observed rapid increase in viscosity with MW (Figure 2). If the polymers are branched, viscosity rises even more rapidly. At intermediate frequencies, polymers show a well-defined plateau region where G0 is approximately constant with frequency. For most polymers, the value of the plateau modulus is independent of MW. Figure 3 shows the effect of increasing MW on the dynamic shear modulus for a series of narrow MW linear polystyrene polymer melts. As the MW increases, a plateau in modulus begins to appear, which increases in width as the MW increases further. The plateau represents the effect of entanglements, which at a certain polymer size effectively lock the polymer structure into a temporary 3-D network with a

Plateau region G⬙ Log modulus

Terminal zone G⬘

Log frequency Figure 1 Effect of frequency on modulus for a polymer over a wide range of frequencies.

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fixed modulus, the value of which is independent of MW. At very low frequencies (i.e., long times), the polymer network begins to disentangle, and the modulus starts to decrease rapidly into the terminal zone, where the polymer chains are free to move about and act as a viscous liquid. The larger the polymer, the longer it stays entangled and, therefore, the wider the frequency range over which the plateau remains. Thus, it is the width of the plateau, or the point at which it descends into the terminal zone, that is defined by the MW of the polymer. Unfortunately, due to instrument and time

constraints, most rheological measurements on dough and gluten have been performed in the plateau region, which is the region most insensitive to differences in MW. If, as is generally accepted, large MW glutenin polymers are responsible for the variations in breadmaking performance between different wheat varieties, then it is to be expected that measurements of the plateau modulus will not be good indicators of baking performance. Such dynamic measurements have the advantage of a well-developed theoretical background, readily available instrumentation, and simultaneous measurement of elastic and viscous moduli, while the nondestructive nature of the test enables multiple measurements to be performed as temperature, strain, or frequency is varied. Disadvantages of the dynamic oscillation method are that the deformation conditions are often inappropriate to practical processing situations, because they are carried out at rates and conditions very different from those experienced by the dough during processing or baking expansion. For example, rates of expansion during proof and oven rise in bread doughs have been calculated to be in the region of 101 s1 to 103 s1, compared with measuring rates in rheological tests several orders of magnitude greater (Table 2). Conventional oscillatory shear rheological tests usually operate in the linear region at small strains in the order of up to 1%, while strain in gas cell expansion during proof is known to be in the region of several hundred percent. Furthermore, most rheological tests are carried out in shear, while most large-strain deformations in dough (i.e., extrusion, sheeting, proof, and baking) are extensional in nature (Table 2). Recent work has confirmed the observation that plateau modulus is essentially independent of gluten MW and also that it is not the size of the soluble glutenin polymers, but the insoluble polymer fraction that is mainly responsible for

Branched polymer

Slope = 3.4 Log η0

Mc

Log MW

Figure 2 Effect of MW and branching on zero-shear viscosity for polymer melts.

9 Ps 160 °C

8

log G⬘, dynes/cm2

7 6 5 4

L18 L19

2 1

L34

L27 L37

3

−6

−5

L15 L5 L22

−4

L16

−3

−2

−1 log ω aT,

0

1

2

3

4

5

s−1

Figure 3 Effect of increasing MW on the dynamic modulus of a series of narrow MW linear polystyrene polymer melts. Reprinted with permission from Onogi et al. Macromolecules 3, 109. Copyright 1970, American Chemical Society.

WHEAT PROCESSING | Analysis of Dough Rheology in Breadmaking Table 2 Typical strain rates and deformation conditions during the baking process Process

Strain rate (s1)

Strain (%)

Deformation

Mixing Molding Sheeting Proof Baking

70–100 30 10 10–3 to 10–2 102 to 101

>100 >100 >100 100 50–100

Shear Shear/extension Extension Biaxial extension Biaxial extension

baking performance. This does not support the commonly held view that the MW of the glutenin polymers is related to their small deformation shear rheology and to baking quality, but that is more likely to be the secondary molecular structure of the insoluble glutenin that is responsible for baking performance. Evidence suggests that these insoluble HMW polymers are entangled with a corresponding long relaxation time, they are branched and form extensive intermolecular secondary structures held together by hydrogen bonding, and differences in these structures are likely to be strongly related to extensional rheology and baking performance. Gluten is the major protein in wheat flour doughs, responsible for their unique viscoelastic behavior and their ability to retain gas during proof and baking. Gluten proteins comprise a highly polydisperse system of polymers, classically divided into two groups based on their extractability in alcohols: gliadins and glutenins. The gliadins are single-chain polypeptides with MW ranging from 2 104 to 7 104, while the glutenins are multiple-chain polymeric proteins in which individual polypeptides are thought to be linked into a network by intermolecular disulfide and hydrogen bonds to give a wide MWD ranging between 105 and well beyond 108. It is only recently that it has been possible to measure and quantify the high-MW glutenin polymers known to be responsible for variations in breadmaking quality using techniques such as dynamic light scattering, hydrodynamic studies in solution, and AFM. These show that gluten has a bimodal MW distribution that roughly parallels the classical division based on solubility into gliadins and glutenins. Individual glutenin molecules in solution have an extended rodlike structure c. 50–60 nm in length made up of a regular spiral structure, termed b-spirals, and the secondary polymer structure is an entangled polymer network where the glutenin molecules are linked by intermolecular disulfide and hydrogen bonds and are also branched, with a spacing between branch points occurring every 40–50 nm. It is now widely accepted that gluten proteins are responsible for variations in baking quality, and in particular, it is the insoluble fraction of the HMW glutenin polymer, which is best related to differences in dough strength and baking quality among different wheat varieties. However, the exact molecular mechanisms responsible for this variation still remain unclear, largely because information about the molecular size and structure of this fraction is inaccessible by conventional polymer size characterization techniques such as GPC and SE-HPLC due to its insolubility. Therefore, other techniques sensitive to changes in polymer MWD and structure are necessary. One such technique is rheology, which is increasingly being used as a sensitive indicator of changes in the structure of HMW polymers. It has long been recognized that the key

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mechanisms determining the rheology of HMW polymer melts and concentrated solutions arise from physical structural interactions between polymer molecules and that much of the rheological behavior of these polymers is independent of their chemistry. This is in contrast to the currently accepted position in the cereal literature, which assumes that the chemical structure of the HMW glutenin polymers is directly related to the rheology of bread doughs and to their baking quality. Recent work has shown that the elongational rheology of HMW polymer melts and concentrated solutions is a sensitive indicator of changes in secondary molecular structure, small increases in the size of the highest end of the MW distribution, and the presence of long-chain branching (LCB). The most significant property is elongational strain hardening (the nonlinear rapid increase in stiffness or viscosity with increasing Hencky strain), which is highly sensitive to the degree of entanglement and LCB of the polymer. For example, LCB has been shown to explain the radically different behavior of branched and linear polymers. Polymer melts that show no LCB, such as highdensity polyethylene (HDPE), show no extensional strain hardening, while branched polymers such as LDPE (lowdensity polyethylene) exhibit pronounced strain hardening. The presence of chain branches is important in giving rise to strain hardening, which is a necessary property for stability of polymers undergoing large deformation. Since gluten polymer has been shown to have a branched structure, it is expected that the deformation of this structure will result in strain hardening in doughs and will contribute strongly to its resistance to extension and bubble wall stability under large deformation. Therefore, it is very likely that it is the secondary structure of the HMW glutenin polymer network, in particular the degree of branching and number of entanglements, that will determine the rheological properties of dough rather than the chemical structure of the primary polymer units (called glutenin subunits in the cereal literature). Modern polymer physical models relate the molecular size and structure of polymers to their rheological properties and end-use performance. The pom-pom model, proposed by MacLeish and Larson, describes the rheological behavior of HMW branched polymer melts. This class of polymers is envisaged as a relatively flexible HMW backbone to which are attached a number of branches (called pom-poms) radiating out from either end of the backbone. This model accurately predicts, for the first time, the well-known phenomenon of strain hardening under uniaxial and planar extensional flow and strain softening (shear thinning) in shear seen in branched HMW polymer melts. The branches entangle with the surrounding polymers, and stretching of the flexible backbone between entanglements produces strain hardening. Predictions of this model have shown that the number of branches and the distance between entanglements have the most effect on strain hardening.

Extensional Techniques Since most of the deformation experienced by dough during the baking process is in extension, there has been a strong expectation that extensional flow measurements should relate to baking performance. Several empirical methods have traditionally been used in the baking industry to measure extensional flow, such as the extensograph and alveograph. More

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widely, there are many types of extensional flow measurements capable of producing fundamental rheological parameters including simple uniaxial tension, fiber wind-up or spinning, converging flow, capillary extrusion, opposed jets, lubricated compression, and bubble inflation. The most commonly used extensional measurements for doughs are uniaxial extension, where the dough is stretched in one direction, and biaxial extension, where dough is deformed in two equal directions as in bubble inflation. The Kieffer system was developed for the measurement of uniaxial extensibility of doughs and glutens (Figure 4). This uses small samples of dough (10 g) or gluten (1–2 g), of particular value to wheat breeders in determining the processing qualities of new wheat strains at an early stage, when only limited grain quantities may be available. Small strips of material are produced in a grooved clamp arrangement and then extended centrally by a hook passing through the sample. Force and distance up to failure are recorded. Recent analysis of the data recorded by the Kieffer system has shown that it is possible to derive fundamental rheological properties of stress, strain, and strain hardening from the force–distance curves by calculation. Recent work using instruments developed to measure the uniaxial extensional properties of polymer melts at constant strain rates such as the filament-stretching extensional rheometer (FISER) and the Sentmanat extensional rheometer (SER) (Figure 5) has been used to measure the extensional properties of dough over a wide range of strain rates relevant to the baking process. The SER employs a dual wind-up drum technique that allows the ends of a sample to be stretched at a constant strain rate by means of two counterrotating wind-up drums whose resistance to rotation is hindered by the material response of the stretching sample.

In biaxial extension, a sample is stretched at equal rates in two perpendicular directions in one plane, as in an expanding bubble. The most widely used methods for measuring biaxial extension properties of soft materials are inflation techniques (if the material is highly extensible) and compression between flat plates using lubricated surfaces, which produce purely extensional flow provided that no friction occurs. Biaxial extensional rheological properties can be measured at large strains up to failure and low strain rates, and the gripping problems normally associated with uniaxial tests can be minimized. Extensional rheological properties of wheat doughs have been measured using lubricated compression and bubble inflation. Inflation was first used as an empirical technique to measure wheat gluten and bread dough extensibility in the Chopin Alveograph, where a bubble of dough is inflated from a flat sheet of dough. This method was later developed to calculate rheological parameters and measure the fracture and biaxial extensional rheological properties of wheat doughs and glutens in the Dough Inflation System by Stable Micro Systems (Figure 6), where the bubble of dough is inflated using a piston fixed to a TA-XT2 texture analyzer at temperatures relevant to proof. The pressure to inflate the bubble is measured and its height calculated from the volume of the bubble or measured directly using a laser. The extensional rheological properties of the expanding dough bubble wall are then calculated to give stress, strain, viscosity, and strain hardening. The major advantage of this test is that the deformation closely resembles practical conditions experienced by the cell walls around the expanding gas cells within the dough during proof and oven rise, that is, large deformation biaxial extension at elevated temperatures. Differences in extensional strain hardening between varieties of different baking quality have been found to relate to baking quality, with good breadmaking varieties showing greater strain hardening and extensional viscosity. Both the Kieffer dough and gluten extensibility system and the Dough Inflation System can be used to obtain the extensional rheological properties to give stress, strain, and strain hardening. Strain hardening is shown as an increase in the slope of the stress–strain curve with increasing extension, giving rise to

L0 −Ω

Oil film

Ω

R

.

eV .

eH

sample Figure 4 The Kieffer dough and gluten extensibility system. Reproduced with permission from Stable Micro Systems Ltd., Godalming, U.K.

Figure 5 The schematic view of the Sentmanat extension rheometer (SER). Reproduced from Ng TSK, McKinley GH, and Padmanabhan M (2006). Linear to non-linear rheology of wheat flour dough. Appl. Rheol. 16(5): 265–274.

WHEAT PROCESSING | Analysis of Dough Rheology in Breadmaking the typical J-shaped stress–strain curve. Recent refinements to the bubble inflation test have provided independent experimental measurement of the bubble height, wall thickness, and strain by the use of a camera and image analysis techniques. From extensional studies on long-chain high-MW polymer melts, it is known that entirely different rheological properties are obtained in shear than in tension, especially if the polymer

349

chains are branched. For example, the elongational viscosity of low-density (branched-chain) polyethylene melts increases with both strain and strain rate (strain hardening), while the shear viscosity decreases with strain and strain rate (shear thinning), giving widely different values in final viscosities between elongation and shear (Figure 7). For doughs, shear and elongational viscosities at low strains are similar, with extensional viscosity slightly higher than shear viscosity, but at higher strains, they diverge and the elongational viscosity rises steeply to give values 2–3 orders of magnitude higher at failure (Figure 8). This increased strain hardening is attributed to entanglement of long-chain molecules during extensional flow, whereas in simple shear, they remain coiled and can slip past each other, giving rise to observed shear thinning at higher strains. Therefore, it is considered that extensional strain hardening will be more sensitive to changes in the structure of HMW glutenin polymers known to be responsible for baking quality.

107

Viscosity (Pa s)

Biaxial extension

106

105 Shear

104

103 0.1

Figure 6 The Dough Inflation System by Stable Micro Systems. Reproduced with permission from Stable Micro Systems Ltd., Godalming, U.K.

1

10

100

Strain

Figure 8 Shear and biaxial extensional viscosities versus strain for dough.

106 Uniaxial extension

Viscosity (Pa s)

Planar extension

105 Shear

104

100

101

102

103

Time (s) Figure 7 Shear and extensional viscosity of LDPE (low-density polyethylene) at 125 C at constant strain rate (0.05 s1). Adapted from MacLeish TCB and Larson RG (1998) Molecular constitutive equations for a class of branched polymers. J. Rheol. 42: 81–110, with permission from American Institute of Physics.

350


Baking Quality and Rheology There has been a long-held belief in the baking industry that dough rheology and baking quality are closely related, mainly due to empirical experience from manual assessments such as kneading or stretching of dough by bakers after mixing. However, the results from conventional descriptive methods and fundamental rheological studies on doughs have often given disappointing correlations with baking quality, mainly because the deformation conditions in these tests are very different to those occurring during proof and baking.

L0

Master drum

Slave drum

Intermeshing gears

Sheeting Rolling (or sheeting) between counterrotating rolls is widely used by the baking industry as a dough forming process for a wide range of products, such as biscuits, noodles, crackers, pizza, bread, and pastry. The rolling process is akin to calendering, which is used in many industries, such as the paper, plastics, rubber, and steel industries, for the production of rolled sheets of specific thickness and final appearance, where counterrotating rolls are used to produce sheets and foils. The shaping of the sheets takes place in the gap between the rotating rolls. The sheeting process is an important step in the production of many food materials and can often be the point where problems occur during production. For example, elastic springback giving rise to uneven thickness or shape of product, edge fractures, and stickiness are common problems in sheeting many materials. Dough sheeting or rolling imposes a large extensional flow component, where the dough is stretched to further develop the gluten network and improve the elasticity of the dough. Various recent studies to characterize dough sheetability have shown that the elasticity and extensional strain hardening are important in maintaining the stability and integrity of dough during the sheeting process. In any study of the sheeting process, particularly in the prediction of processing performance, care must be taken to use rheological properties relevant to the particular application, taking the magnitude of the strain and the rate of strain into account. Recent work on dough sheeting has focused on numerical simulations and modeling of the sheeting process combined with the use of new instruments designed to mimic the conditions experienced by dough during sheeting such as the SER and other instrumented sheeters (Figure 9).

Proof and Baking Fundamental rheological studies on doughs related to baking have mostly been performed in small deformation shear oscillation. Such dynamic rheological measurements on doughs have been investigated in many studies. Elastic (G0 ) and viscous (G00 ) moduli for dough are measured over a range of frequencies. Elastic properties predominate over viscous properties, and the moduli are slightly frequency-dependent, which is typical of a cross-linked polymer network. No convincing relationship has ever been established between small deformation dynamic rheological properties and baking performance. Various workers have found that flours of different baking quality have lower values of elastic (storage) modulus (G0 )

Sample

Master drum

T ω

ω

Slave drum

2H0

Figure 9 Schematic representation of the Sentmanat extensional rheometer (SER) and its use in dough rolling experiments. Reproduced from Mitsoulis E and Hatzikiriakos SG (2009). Rolling of bread dough: Experiments and simulations. Inst. Chem. Eng. Food Bioprod. Process. 87: 124–138.

for the higher-baking quality flour. However, others have found that a higher value of G0 for glutens and doughs relates to better baking performance (see Table 3). It has been shown earlier that these conflicting results arise because most of these tests are carried out at rates and deformation conditions very different from those experienced by the dough during baking expansion and also because dynamic rheological parameters in the plateau region are generally insensitive to differences in MW of polymers. However, these parameters are highly sensitive to changes in starch and protein concentration and diluents such as water, which are almost never kept constant in rheological experiments on doughs. Most dynamic rheological tests on doughs and glutens have been carried out over a relatively narrow frequency range in the plateau zone, which is considered inappropriate because the value of the plateau modulus for polymers is known to be insensitive to the changes in MW and structure, which are known to be responsible for baking quality. Any rheological tests that seek to relate to baking performance should therefore be performed under conditions similar to those of baking expansion. Methods such as bubble inflation and lubricated compression offer the most appropriate method for measuring rheological properties of doughs. The major advantage of these tests is that the deformation closely resembles practical conditions experienced by the cell walls around the expanding gas cells within the dough during proof and oven rise, that is, large deformation biaxial

WHEAT PROCESSING | Analysis of Dough Rheology in Breadmaking Table 3 Correlations between rheological properties and baking performance

351

60 000

Baking parameter

Correlation (R2)

G’ 1 Hz (dough) G’ slope G’ 10 Hz (wet gluten)

Volume

0.15 (n ¼ 48) 0.72 0.85 (n ¼ 27) 0.65 n.s (n ¼ 20) 0.69 0.71 0.64 (n ¼ 8) n.s. n.s. (n ¼ 4) 0.89 (n ¼ 20) 0.80 0.81

G’ 1 Hz (gluten) Tan delta G’ 1 Hz Tan delta G’ Biaxial strain hardening Max. uniaxial extensional viscosity Biaxial strain hardening Relaxation Creep Relaxation Shear relaxation Shear viscosity

Volume Form ratio (W/H) Volume Form ratio (H/W) (H/W) Loaf height Volume Volume Form ratio Loaf height Volume Volume Quality Quality

0.92–0.97 (n ¼ 6) Good 0.94 (n ¼ 23) Good Good

extension, and can be carried out at the strain rates and elevated temperatures relevant to baking. Extensional rheology is known to be highly sensitive to polymer chain branching and entanglement interactions between high-MW polymers at large deformations. The theory is simple and relatively well developed, and it generally provides good correlations with the relevant large deformation processing quality parameters (Table 3). Disadvantages are that there is no single well-defined and accepted method for extensional measurement, with many different methods being used depending on the type and viscosity of the material being studied; the tests often use large amounts of material and the tests are destructive. The measurement of extensional flow is often difficult, because the deformation is large and nonuniform and it is therefore impossible to calculate strain directly from the machine displacement, requiring the direct measurement or calculation of changes in sample dimensions, often at high speeds. This has been achieved for the measurement of extensible polymers and has recently been applied to doughs. Extensional strain hardening has been shown to occur in doughs undergoing uniaxial stretching and also expanding dough bubble walls during inflation. During proof and baking, the growth and stability of gas bubbles within the dough determine the expansion of the dough and therefore the ultimate volume and texture of the baked product. The limit of expansion of these bubbles is related directly to their stability, due to coalescence and the eventual loss of gas when the bubbles fail. The extensional rheological properties of the expanding bubble walls will therefore be important in maintaining stability in the bubble wall and promote gas retention. The failure of gas cell walls in doughs has been shown to be directly related to the elongational strain hardening properties of the dough measured under large deformation biaxial extension. Strain hardening is shown as an increase in the slope of the stress–strain curve with increasing extension,

Maximum stress (Pa)

50 000

Rheological parameter

40 000 30 000 20 000 10 000 0 0

0.5

1

1.5

2

2.5

Hencky strain

Figure 10 Typical J-shaped stress–Hencky strain curve in biaxial extension for a dough bubble. Bubble inflation using SMS Dough Inflation System, maximum stress, and Hencky strain calculated for bubble wall polar region.

giving rise to the typical J-shaped stress–strain curve observed for highly extensible materials (Figure 10). Strain hardening in doughs is thought to arise mainly from stretching of polymer chains between points of entanglement in the larger glutenin molecules, which gives rise to the increasing stiffness observed at large strains. Under extensional flow, entangled polymers exhibit strain hardening, which is enhanced for polymers with a broad MW distribution, particularly a bimodal distribution and branching. It is expected that the broad bimodal MW distribution and branched entangled structure typical of gluten will result in enhanced strain hardening. Strain hardening allows the expanding gas cell walls to resist failure by locally increasing resistance to extension as the bubble walls become thinner and provides the bubble walls’ greater stability against early coalescence and better gas retention. It is expected therefore that doughs with good strain hardening characteristics should result in a finer crumb texture (e.g., smaller gas cells, thinner cell walls, and an even distribution of bubble sizes) and larger baked volume than doughs with poor strain hardening properties. It has been shown that good breadmaking doughs have good strain hardening properties and inflate to larger single bubble volume before rupture, while poor breadmaking doughs inflate to lower volumes and have much lower strain hardening. Loaf volume for a number of commercial white flour doughs has been related directly to the failure strain and strain hardening properties of single dough bubbles measured at elevated temperatures in biaxial extension. Strain hardening and failure strain of cell walls were both seen to decrease with temperature, with cell walls in good breadmaking doughs remaining stable and retaining their strain hardening properties to higher temperatures (60 C), while the cell walls of poor breadmaking doughs became unstable at lower temperatures (45–50 C) and had lower strain hardening. Figure 11 shows that bubble wall stability (indicated by a strain hardening value above 1) is increased to progressively higher temperatures with increasing baking volume, allowing the bubbles to resist coalescence and retain gas for much longer. Bubble wall instability in poorer breadmaking varieties occurs at much lower temperatures, giving earlier bubble coalescence and release of gas, resulting in lower loaf volumes and poorer texture. Flours bred with specific genes for


352

65 Bubble instability temperature (⬚C)

SOISSONS

60

PILLSBURY

55

HEREWARD

50 RIALTO 99

45

CHARGER

RIALTO 98

40 35 30 RIBAND

25 20 400

450

550

500

600

650

700

Loaf volume (m l) Figure 11 Temperature at which bubble wall instability occurs (as indicated by the temperature at which strain hardening drops below 1) for a number of wheat varieties versus loaf volume.

60

•

Elongation stress (Pa × 103)

50

40

•

30 20 10

r

ou

Fl

(+ + (− + +) (− − + +) (+ + ) (− − − −) − ) −)

C K ha Ja ν/σ ra (− nz t

0

2


1 0

Strain

(—)

Figure 12 Stress–strain curves of doughs deformed under elongational flow made from flours containing different HMW glutenin proteins. Reproduced from Newberry MP, Mann G, Morel MK, and Morgenstern MP (2005). Elongational rheology of wheat flour doughs. In: Cereals 2005, Proceedings 55th Australian Cereal Chemistry Conference, 3–7 July 2005, with permission.

expression of HMW gluten proteins show increased strain hardening, which allows these doughs to elongate further at greater strains and stresses. The weaker null lines, however, did not display any strain hardening behavior and had substantially inferior elongational properties (Figure 12).

Future Trends and Research

•

detection of desirable properties at earlier stages of selection of good quality traits in wheat breeding programs. Rapid advances in polymer molecular modeling relating changes in polymer structure to rheological properties, together with structural information from spectroscopic data, will enable prediction of the structure and rheological behavior of the gluten polymer network during baking. Development of scanning probe microscopy techniques (AFM, STM, etc.) for wet biological systems will allow direct imaging of the behavior of these polymers at a molecular level under deformation conditions similar to those of baking and the physical mechanisms underlying the increasing use of genetic expression of HMW glutenins known to be related to baking quality.

Small-scale rapid rheological tests, particularly in combination with multivariate statistical analysis, will allow

• • • • • • •

What is meant by rheology? What are the main aims of rheological testing? Describe the empirical descriptive test methods used for dough rheology. Describe the main fundamental test methods used for dough rheology. What is meant by the elastic, viscous, and plateau modulus? How does the plateau modulus relate to polymer entanglements? Why is the plateau modulus not a good indicator of baking performance?


•

•

How different are the deformation conditions encountered during baking expansion to those of most conventional rheological tests? How can you extrapolate from rheological tests to baking performance? How has polymer rheology informed baking rheology?


• • •

How is the structure of gluten related to its rheological properties? What is extensional strain hardening? How is it related to baking performance? Which rheological properties relate best to baking performance?

Further Reading Barnes HA, Hutton JF, and Walters K (1989) An Introduction to Rheology. UK: Elsevier. Carceller JL and Aussenac T (2001) Size characterisation of glutenin polymers by HPSEC-MALLS. J. Cereal Sci. 33: 131–142. Charalambides MN, Wanigasooriya L, Williams JG, Goh SM, and Chakrabarti S (2006) Large deformation extensional rheology of bread dough. Rheol. Acta 46: 239–248. Dobraszczyk BJ and Roberts CA (1994) Strain hardening and dough gas cell-wall failure in biaxial extension. J. Cereal Sci. 20: 265–274. Dobraszczyk BJ and Salmanowicz BP (2008) Comparison of predictions of baking volume using large deformation rheological properties. J. Cereal Sci. 47: 292–301. Dobraszczyk BJ, Smewing J, Albertini M, Maesmans G, and Schofield JD (2003) Extensional rheology and stability of gas cell walls in bread doughs at elevated temperatures in relation to breadmaking performance. Cereal Chem. 80: 218–224. Doi M and Edwards SF (1986) The Theory of Polymer Dynamics. Oxford: Oxford University Press. Dunnewind B, Sliwinski EL, Grolle K, and van Vliet T (2003) The Kieffer dough and gluten extensibility rig—An experimental evaluation. J. Text. Stud. 34: 537–560. Ferry JD (1980) Viscoelastic Properties of Polymers. John Wiley and Sons. Field JM, Tatham AS, and Shewry PR (1987) The structure of a high Mr 498 subunit of durum wheat (T. durum) gluten. Biochem. J. 215–221. Graessley WW (1974) The entanglement concept in polymer rheology. Adv. Polym. Sci. 16: 1–179. Humphris ADL, McMaster TJ, Miles MJ, Gilbert SM, Shewry PR, and Tatham AS (2000) Atomic Force Microscopy (AFM) study of interactions of HMW subunits of wheat glutenin. Cereal Chem. 107–110. Kurzbeck S, Oster F, Mu¨nstedt H, Nguyen TQ, and Gensler R (1999) Rheological properties of two polypropylenes with different molecular structure. J. Rheol. 43: 359–374. MacLeish TCB and Larson RG (1998) Molecular constitutive equations for a class of branched polymers. J. Rheol. 42: 81–110. Macosko CW (1994) Rheology: Principles, Measurements and Applications. New York: VCH Publishers.

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MacRitchie F and Lafiandra D (1997) Structure–function relationships of wheat proteins. In: Damodaran S and Paraf A (eds.) Food Proteins and their Applications. New York: Marcel Dekker. MacRitchie F, Simsek S, and Brookfield D (2014) Rheology. Cereal Food World 59: 252–254. Mitsoulis E and Hatzikiriakos SG (2009) Rolling of bread dough: Experiments and simulations. Food Bioprod. Process. 87: 124–138. Morgenstern MP, Newberry MP, and Holst SE (1996) Extensional properties of dough sheets. Cereal Chem. 73: 478–482. Mu¨nstedt H, Kurzbeck S, and Egersdo¨rfer L (1998) Influence of molecular structure on rheological properties of polyethylenes. Part II. Elongational behaviour. Rheol. Acta 37: 21–29. Newberry MP, Mann G, Morel MK, and Morgenstern MP (2005) Elongational rheology of wheat flour doughs. In: Cereals 2005, Proceedings 55th Australian Cereal Chemistry Conference, 3–7 July 2005. Ng TSK, McKinley GH, and Padmanabhan M (2006) Linear to non-linear rheology of wheat flour dough. Appl. Rheol. 16: 265–274. Patel MJ and Chakrabarti-Bell S (2013) Flour quality and dough elasticity: Dough sheetability. J. Food Eng. 115: 371–383. Rao MA and Steffe JF (1992) Viscoelastic Properties of Foods. New York: Elsevier Applied Science. Sherman P (1970) Industrial Rheology, with Particular Reference to Foods, Pharmaceuticals, and Cosmetics. London: Academic Press. Shewry PR, Halford NG, Belton PS, and Tatham AS (2002) The structure and properties of gluten: An elastic protein from wheat grain. Philos. Trans. R. Soc. Lond. B 357: 133–142. Sliwinski EL, Kolster P, and van Vliet T (2004) Large-deformation properties of wheat dough in uni- and biaxial extension. Rheol. Acta 43. Southan M and MacRitchie F (1999) Molecular weight distribution of wheat proteins. Cereal Chem. 76: 827–836. Tronsmo KM, Magnus EM, Faergestad EM, and Schofield JD (2003) Relationships between gluten rheological properties and hearth loaf characteristics. Cereal Chem. 80: 575–586. Van Vliet T, Janssen AM, Bloksma AH, and Walstra P (1992) Strain hardening of dough as a requirement for gas retention. J. Text. Stud. 23: 439–460. Wagner MH, Bastian H, Hachmann P, Meissner J, Kurzbeck S, Mu¨nstedt H, and Langouche F (2000) The strain hardening behaviour of linear and long-chainbranched polyolefin melts in extensional flows. Rheol. Acta 39: 97–109. Wahlund KG, Gustavsson M, MacRitchie F, Nylander T And, and Wannerberger L (1996) Size characterisation of wheat proteins, particularly glutenin by asymmetrical flow field-flow fraction. J. Cereal Sci. 23: 113–119. Weegels PL, Hamer RJ, and Schofield JD (1996) Critical review: Functional properties of wheat glutenin. J. Cereal Sci. 23: 1–18. Whorlow RW (1992) Rheological Techniques, 2nd edn. Chichester, UK: Ellis Horwood. Xiao W, Charalambides MN, and Williams JG (2007) Sheeting of wheat flour dough. Int. J. Food Sci. Technol. 42: 699–707.

Frozen Dough D Domingues and C Dowd, General Mills Inc., Minneapolis, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Challenges of frozen dough. Fortification of ingredients. Optimization of dough processing. Control of freezing and storage conditions. Control of thawing and proofing steps. Recent advancements.

Learning Objective

•

To gain general understanding of the challenges and strategies employed to make frozen dough products.

History Bakers started the practice of freezing dough to decouple the need to bake shortly after the dough preparation process. This allowed for greater flexibility on when and how much dough could be baked in response to market needs. However, initial attempts to freeze dough resulted in less than optimal bake performance (namely, reduced volume and irregular and coarse crumb structure). Bakers responded with corrective measures to both the formula and process resulting in marked improvements to overall baked product quality.

Challenge The principal challenges for frozen dough performance are the reduced ability to generate leavening gas and a decline in bake expansion over frozen storage time. There have been significant advancements to address these challenges focusing on the (1) fortification of ingredients, (2) optimization of dough processing, (3) control of freezing and storage conditions, and (4) control of thawing and proofing steps prior to baking. For a more in-depth discussion, there are several excellent textbooks devoted to frozen dough technology. The information presented here is intended to be an introduction and summary overview on this subject.

Fortification of Ingredients Yeast (Responsible for Generating Leavening Gas) The yeast used in the baking industry is Saccharomyces cerevisiae. The genus name is the combination of ‘saccharo’ meaning sugar and ‘myces’ meaning fungi. The species name cerevisiae is derived from Ceres, the Roman goddess of agriculture. The diameter of a typical yeast cell is 3–4 mm with approximately 30 billion individual cells in 1 g of compressed yeast. Yeast

354

replicate by budding every 2–3 h and are commercially available in many formats: compressed, dried, and liquid suspensions. The principal function of yeast in baking is to convert sugar to CO2 leavening gas, alcohol, and a variety of organic acids, ketones, aldehydes, and esters, which contribute to bread flavor and dough maturation (collectively referred to as solutes; see Figure 1). As will be discussed in more detail, the specific format of the yeast and extent of fermentation activity prior to freezing have significant effects on the ability of the yeast to generate leavening gas upon thawing and baking. When exposed to freezing temperatures, the plasma membrane of the yeast cell can become damaged in response to an increase in the concentration of fermentation solutes resulting from ice crystal formation both within the yeast cell and in the aqueous environment surrounding the yeast cell. This damage leads to a loss in the ability of the yeast to retain water and a decline in the capacity to generate CO2 gas. When possible, one should avoid prolonged fermentation steps prior to freezing to maximize yeast viability. Another reason to limit fermentation prior to freezing is to mitigate the collapse of the dough gas cell structure. As dough temperature declines upon freezing, the CO2 gas within the dough becomes progressively more soluble and dissolves into the aqueous phase. The net result is the collapse of dough cell structure and shrinkage of dough piece volume. When fermentation is limited prior to freezing, a portion of insoluble N2 gas remains within the gas bubbles, thereby stabilizing the structure and mitigating collapse and volume decline. Additionally, it is generally recommended that bakers use liquid cream or compressed yeast in frozen dough applications as these formats are more robust to frozen dough processing. Specifically, the dehydration process employed to make active dry and instant yeast compromises the cell membrane rendering the yeast more susceptible to the damaging effects of fermentation solutes and, moreover, facilitates the leaching out of water-soluble compounds such as glutathione. The release of these intercellular compounds into the dough aqueous phase results in an increase in dough extensibility and a reduced ability by the yeast to produce CO2 gas. Table 1 is provided as a useful comparison of various yeast formats available commercially and suitability to frozen dough applications. Yeast manufacturers continue to improve the performance of yeast in frozen dough applications by selecting cryotolerant strains and optimizing fermentation and harvesting conditions. The Lesaffre Yeast Corporation currently markets an instant yeast product for use in frozen dough applications (SAF-Instant L.H.I.S. Frozen Dough Yeast). The following are strategies to protect yeast and improve CO2 production upon freezing:

• • •

Use liquid or crumble yeast. Limit fermentation prior to freezing. If using a preferment step, limit yeast to 1/3 of total.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00155-8

WHEAT PROCESSING | Frozen Dough

Yeast and flour enzymes

Flour Complex sugar (Starch, maltose)

355

Fermentable simple sugars (Yeast converts to)

CO2 gas (dough expansion)

Organic acids, ketones, aldehydes, & esters (flavor & maturation)

Ethanol (flavor)

SOLUTES Figure 1 Yeast fermentation in dough.

Table 1

Available yeast formats and conversions

Yeast format

Description

Shelf life

Suitability for frozen dough

Conversion

Compressed/ crumbled Cream

2–3 weeks refrigerated

Good

Standard

2–3 weeks refrigerated

Very good

Active dry

Compressed hydrated yeast Liquid yeast suspension Dried yeast granules

Poor

Instant

Dried yeast granules

Post opening: 4 months refrigerated, 6 months frozen Post opening: 1 year ambient, 5 years frozen

1 US gallon (3.79 l) ¼ 5 pounds (2.27 kg) compressed 1/2 of compressed weight

• •

• •

Use 50–100% more yeast (compared with unfrozen applications). Faster freezing is better than slower freezing: Reduce by 12–13 F (6.7–7.2 C) per minute (reported as optimal). However, freezing too quickly can lead to ice crystal formation within the yeast, which is detrimental. Consider using cryotolerant yeast strains (high in trehalose). Consider using the enzyme glucoamylase to increase fermentable substrate in lean dough formulas.

Questions: How else might one improve yeast performance in frozen dough? How might one improve yeast cell membrane tolerance to fermentation solutes? How might one manipulate yeast fermentation and harvesting conditions to optimize cryotolerance (unbudded yeast more tolerant to freezing)? How might one optimize dough processing conditions to limit yeast damage and maximize gas production upon thawing? We have examined means to stabilize and improve the ability of yeast to generate gas in frozen dough applications and will next focus on means to improve gas retention and dough expansion by fortifying gluten.

Gluten (Ability to Hold Gas and Expand) Gluten is the association of hydrated wheat flour proteins with other flour components to create a viscoelastic matrix

Poor/good (see comments)

1/3 of compressed weight

capable of expanding and holding gas. Specifically, it is the association of glutenin (long elastic proteins) with gliadin (smaller viscous proteins). The strength and gas-holding capacity of the gluten matrix are functions of inter- and intramolecular covalent bonds between the proteins (extent of cysteine disulfide cross-linkages) and secondary noncovalent interactions between various dough components (hydrogen bonding, hydrophobic and hydrophilic conformation folding, and ionic/polar bonding). The freezing process disrupts the gluten matrix by dehydrating the gluten proteins resulting in a weakening of the secondary molecular interactions upon rehydration during thawing. Additionally, freezing promotes the release of glutathione from damaged yeast cells, which chemically reduces disulfide covalent bonds. The net result is a loss in dough capacity to expand and hold gas upon thawing and a reduction in bake specific volume. The general strategy to improve gluten functionality in frozen dough applications is to maximize, fortify, and strengthen the gluten structure in addition to retarding gluten degradation due to yeast fermentation activity. Table 2 lists some of the commonly used dough strengtheners and oxidizing agents in frozen dough applications. These ingredients interact with the gluten and starch in the dough to strengthen the protein associations and mitigate moisture loss from the proteins upon freezing and subsequent thawing. Check restrictions for specific dough strengtheners and oxidizers as permissibility and legal limits vary from country to country. The following are strategies to stabilize gluten upon freezing:

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• • • • •


Use high-protein flour such as hard red winter or spring wheat flour (12–13% protein). Add vital wheat gluten (0.5–1%). Use dough strengtheners – sodium stearoyl lactylate (SSL) and diacetyl tartaric acid esters of mono- and diglycerides (DATEM). Use oxidizers – enzyme glucose oxidase, ascorbic acid (ensure that it is in dehydroascorbic acid active form), and azodicarbonamide (AZO). Use dairy proteins (heat-treated whey) and hydrocolloids (guar gum) to mitigate moisture transfer.

Additional considerations to stabilize and enhance the gluten structure for frozen dough: Different oxidizers react at different rates. As the dough structure is set at mixing, faster oxidizing agents are particularly effective at improving frozen dough performance. Control and management of moisture within frozen dough applications are important to enhance frozen dough shelf-life performance. Application of hydrocolloids such as guar gum and xanthan gum and use of heat-treated whey proteins have been shown to be effective. The use of various enzymes to correct for flour deficiencies and to improve baked performance is well known and employed throughout the baking industry. Investigators have explored the use of transglutaminase to improve frozen pastry quality by increasing the extent of gluten protein cross-linkages and use of xylanases to facilitate the redistribution of moisture from pentosans to the gluten.

Table 2

Dough strengtheners and oxidizers

Dough strengtheners/stabilizers

Dough oxidizers (rate)

Sodium stearoyl lactylate Diacetyl tartaric acid esters of mono- and diglycerides Ethoxylated mono- and diglycerides Vital wheat gluten Guar gum

Azodicarbonamide (fast) Potassium iodate (fast)

Table 3 Ingredient

Ascorbic acid (intermediate) Potassium bromate (slow)

Question: Consumers and governmental agencies have started to question and limit the use of microingredients in frozen dough systems. Can you think of additional natural ingredients and strategies one might use to improve frozen dough performance?

Optimization of Dough Processing In frozen dough processing, one wants to maximize gluten development while minimizing yeast fermentation activity. This is most readily accomplished using a straight dough process with no preferment step. According to Sluimer, this is best accomplished in a high-speed horizontal bar mixer targeted at 40 kJ kg1 dough or using a spiral mixer targeted at 25 kJ kg1 dough. To minimize yeast metabolic activity, it is best to target a final dough temperature out of the mixer at 68 F (20 C) to 75 F (23.9 C). If using a preferment step, use no more than 1/ 3 of the total yeast (protect the remaining 2/3 of the yeast from solute damage described earlier). Additionally, one will want to freeze immediately after the forming step. Table 3 shows a typical frozen dough formula and process.

Control of Freezing and Storage Conditions There are numerous freezing and storage recommendations in the literature for frozen dough. All recommend reducing temperature variability throughout the entire cold chain to minimize the formation of damaging ice crystals upon thawing and refreezing, which adversely affects yeast viability, gluten gasholding capability, and dough piece volume. Furthermore, most recommend using a two-step freezing process: an initial freezing step to reduce the core dough temperature to 20 F (6.7 C) to inhibit yeast fermentation, followed by an equilibrated freezing step to reduce the temperature further to 0 F (17.8 C) to 10 F (23.3 C) for prolonged storage. See

Frozen dough formula and process example Weight (%)

Baker’s (%)

Hard wheat flour 50.5 100.0 Vital wheat gluten 1.0 2.0 Water 30.5 60.4 Yeast (crumble) 4.0 7.9 Shortening 4.0 7.9 Salt 2.0 4.0 Sucrose 5.0 9.9 Nonfat dried milk 3.0 5.9 Microingredients ppm ppm Process Mix to energy (25–40 kJ kg1 dough depending on mixer type) Target dough temperature out of mixer ¼ 68 F (20 C) to 75 F (23.9 C) No fermentation step Freeze immediately after molding and forming to core temperature of 20 F (6.7 C) in a blast freezer. Continue freezing to a temperature of 0 F (17.8 C) to 10 F (23.3 C) in storage

WHEAT PROCESSING | Frozen Dough summary of freezing and storage strategies in the succeeding text. Freezing and Storage Strategies

• • •

Freeze dough pieces immediately after forming to a core temperature of 20 F (6.7 C). Complete freezing process by storing partially frozen dough pieces at 0 F (17.8 C) to 10 F (23.3 C). Avoid temperature fluctuations throughout the entire cold chain to avoid deleterious effects of freeze–thaw cycling.

• • • • • •

357

Why is it important to limit fermentation prior to freezing dough? Gluten strength is a function of two types of protein interaction. Name the interactions. How is gluten disrupted upon freezing? Name three ways to fortify gluten strength in frozen dough. How may enzymes be used to replace dough oxidizers and strengthening agents? How might one manipulate the glass transition temperature of frozen dough to improve shelf-life stability?

Question: How will freezing point depression affect freezing and storage strategies?

Control of Thawing and Proofing Prior to Baking The initial step of the baking process for frozen dough is thawing. The goal is to raise the dough temperature into the range of 34 F (1.1 C) to 40 F (4.4 C). This accomplished by placing the frozen dough directly into 34 F (1.1 C) to 40 F (4.4 C) storage and holding for the required time to thaw and equilibrate dough temperature to the refrigerated temperature (generally 12–18 h or overnight). During this thawing process, it is important to avoid dehydration and condensation of moisture onto the dough (often placed into racks with zippered tent coverings or onto trays placed within polybags). After the thawing process is complete, the dough is allowed to proof to a desired expanded volume prior to baking. Proofing conditions are set to promote yeast fermentation, generally 90 F (32.2 C) to 110 F (43.3 C) at a relative humidity of 70–75%. Not surprisingly, proof times for previously frozen and retarded dough samples are approximately 50% longer compared with warmer conventionally prepared dough (75–90 min compared with 50–60 min, respectively). Baking temperatures and times for thawed and proofed frozen dough samples are comparable with conventionally prepared and proofed dough samples. Thawing and Proofing Strategies

• • •

Thaw at 34 F (1.1 C) to 40 F (4.4 C) until dough temperature equilibrates (12–18 h). Proof at 90 F (32.2 C) to 110 F (43.3 C) and 70–75% relative humidity (minimize dehydration and condensation). Avoid proof times >24 h due to development of sour flavors and dough pH decline associated with lactic acid bacteria growth (bacteria inherent to flour systems).


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• • •

Name the principal challenges for frozen dough performance and shelf-life stability. What type or format of yeast is best suited to frozen dough applications and why? What advancements do you foresee in yeast development for frozen dough?

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How can the proof setp be eliminated?: Most commercially available yeast-leavened frozen dough products must be thawed and proofed to a specific expanded volume prior to baking. Thawing and proofing are time-consuming and require specific equipment and labor to manage the process. Researchers have started to address the desire to eliminate the thawing and proofing steps by developing preproofed and unproofed frozen dough products that can be baked directly from the frozen state. However, additional work is required to improve the performance of preproofed frozen dough products such that they are at parity with existing thawed and proofed frozen dough products. Specifically, further research is needed to improve the stability of expanded frozen dough structures and to improve yeast viability and performance over shelf-life time. For clarity, it should be mentioned that yeast-leavened frozen croissants and Danish dough products are commercially available today and are regularly baked directly from the frozen state. These laminated products are less sensitive to the proofing challenges associated with more developed frozen bread dough systems as the overall extent of volume increase upon baking is less and is facilitated by steam expansion of the laminated structure. How can freeze-tolerant yeast be developed?: Yeast strains tolerant to freezing have been isolated. Additionally, commercial manufactures are marketing yeast for use in frozen dough applications (SAF-Instant L.H.I.S. Frozen Dough Yeast from Red Star). Anticipate further development of yeast strains and formats specifically suited to frozen dough applications. How can ingredient use be simplifled?: Consumers and retailers continue to articulate a desire for ingredient simplification and the use of naturally sourced (less processed) materials. Frozen dough products employ various dough strengtheners, oxidizers, and emulsifiers to enhance shelflife performance. An opportunity exists to replace these more processed and restricted ingredients with naturally sourced materials, for example, the use of enzymes to strengthen the gluten structure or to manage moisture upon freezing. How can water be better managed in frozen dough applications. Research continues in the application of hydrocolloids and heat-treated dairy proteins to mitigate water migration in frozen dough systems over shelf-life time.

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See also: Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing; The Protein Chemistry of Cereal Grains; Wheat-Based Foods: Breads; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Gluten and Modified Gluten; Milling and Baking: History; Refrigerated Dough; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Ultrastructure of the Wheat Grain, Flour, and Dough.

Further Reading Ashghar A, Anjum FM, and Allen JC (2011) Critical Reviews in Food Science and Nutrition 51: 374–383. Casey G and Foy J (1995) Yeast performance in frozen doughs and strategies for improvement. In: Kulp K, Lorenz K, and Brummer J (eds.) Frozen and Refrigerated Doughs and Batters St. Paul, MN: American Association of Cereal Chemists.

De Stefanis VA (1995) Functional role of microingredients in frozen doughs. In: Kulp K, Lorenz K, and Brummer J (eds.) Frozen and Refrigerated Doughs and Batters. St. Paul, MN: American Association of Cereal Chemists. Hino A, Takano H, and Tanaka Y (1987) Cereal Chemistry 64(4): 269–275. Hozova B, Jancovicova J, Dedok L, Buchtova V, and Staruch L (2002) Czech Journal of Food Sciences 20(6): 215–222. Kenny S, Wehrle K, Auty M, and Arendt EK (2001) Cereal Chemistry 78(4): 458–463. Kulp K, Lorenz K, and Brummer J (eds.) (1995) Frozen and Refrigerated Doughs and Batters. St. Paul, MN: American Association of Cereal Chemists. Lallemand Baking Update volume 1/number 18 Frozen Dough http://www.lallemand. com/BakerYeastNA/eng/PDFs/LBU%20PDF%20FILES/1_18FROZ.PDF. Lorenz K and Kulp K (1995) Freezing of doughs for preparation of breads and rolls in the United States. In: Kulp K, Lorenz K, and Brummer J (eds.) Frozen and Refrigerated Doughs and Batters. St. Paul, MN: American Association of Cereal Chemists. Ribotta PD, Leon AE, and Anon MC (2001) Journal of Agricultural and Food Chemistry 49(2): 913–918. Ribotta PD, Perez GT, Leon AE, and Aron MC (2004) Food Hydrocolloids 18(2): 305–313. Sherwin C (1995) AIB Technical Bulletin. vol. 11. Manhattan, KS: AIB. Sluimer P (2005) Principles of Breadmaking. St. Paul, MN: American Association of Cereal Chemists.

Refrigerated Dough D Domingues and C Dowd, General Mills Inc., Minneapolis, MN, USA W Atwell, Bill Atwell Consulting, Champlin, MN, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Pressurized refrigerated dough product formulation, processing, and packaging. Nonpressurized refrigerated dough product formulation, processing, and packaging. Basic relationships governing refrigerated dough products Shelf life issues and solutions. New developments in refrigerated dough technology.

Pressurized Refrigerated Dough Formulation

Learning Objective

•

oxygen is beneficial. As with pressurized dough products, specific processes have been developed to deliver a wide array of nonpressurized, refrigerated, fresh dough products. These include ready-to-bake piecrusts and many different types of slice-and-bake cookies.

To gain general understanding of refrigerated dough products, processes, and packaging.

Introduction In the 1920s, an out-of-work baker named L.B. (Lively) Willoughby from Bowling Green, Kentucky, pursued the revolutionary concept of delivering fresh biscuit dough to consumers. In 1931, he obtained a patent describing the process and packaging designed to market refrigerated biscuit dough in a pressurized can. The biscuit dough had a shelf life of about 1 week. Lively initially marketed his product as Ye Old Kentucky Buttermilk Biscuits. He soon sold his business to the Ballard and Ballard Company who subsequently initiated the proliferation of refrigerated dough products. In 1951, Pillsbury acquired the Ballard and Ballard Company. The Pillsbury brand of refrigerated dough products now contains over 80 different products, and the technology has developed to deliver products with shelf lives in excess of 3 months. Perhaps even more than other food products, formulation, processing, and packaging are intimately related for pressurized refrigerated dough products. If leavened dough is mixed and refrigerated without packaging, the shelf life will only be a few hours. Carbon dioxide will diffuse out of the dough mass, and the resultant dough when baked will be very dense. Contact with oxygen can also cause changes in the dough that limit shelf life. Processes specific to pressurized refrigerated dough have been developed to deliver products from biscuits, to crescent rolls, to loaves. Clearly, Willoughby’s solution to package dough in a pressurized carbon dioxide atmosphere provided the means to provide fresh dough to consumers with an extended shelf life and founded the refrigerated dough business that exists today. Of course, not all baked products are leavened. For example, the dough used to make most cookie and piecrust doughs contains no leavening, and packaging under pressure is not required. Oxygen can still be very detrimental to this type of dough, however, and packaging providing a barrier to


One commonality among pressurized refrigerated dough products is that they are all chemically leavened. Sodium bicarbonate is the carbon dioxide source in most products. Potassium bicarbonate can be used to formulate low sodium products. In proper combination with an acidulant, a specific amount of bicarbonate will reliably generate a specified amount of carbon dioxide and hence result in predictable can pressures in the final packaged products. Alternately, standard baker’s yeast is resourceful in identifying substrates to produce carbon dioxide in refrigerated dough formulas, and yeasted dough pressures will build quickly leading to burst cans in only hours. It is for this reason that the largest marketing category (e.g., biscuits) in refrigerated dough products is normally chemical leavened, whereas those that are normally yeasted (e.g., breads) are a smaller category in comparison. With respect to American-style biscuits, chemical leavening is not a limiting restriction. In general, biscuit formulas are similar to bread formulas with chemical leavening replacing yeast. Many nonpressurized biscuits are made with soft wheat flour, but pressurized refrigerated biscuit dough is made on high-speed lines, and hence, the cohesiveness of hard wheat dough is required. The category of refrigerated biscuits has been highly proliferated since the days of Lively Willoughby. In general, these proliferations have been effected through innovative means of incorporating shortening in the formula. Shortening can be mixed into the dough matrix, added as flakes, or sheeted into the dough to yield a laminated structure. Of course, there have been many size and flavor proliferations as well. Table 1 contains a typical refrigerated biscuit dough formula. The formulas for refrigerated sweet goods are similar to biscuits with the exception that they contain more sugar. The acidulant sodium acid pyrophosphate (SAPP) has a distinctive flavor that is very appropriate for biscuits but is sometimes deemed objectionable in sweet dough products. Hence, it is often replaced with sodium aluminum phosphate (SALP). Icings and fillings for canned sweet dough products can be included in plastic cups placed at the end of the refrigerated dough can. Many sweet dough product shape proliferations have been introduced based on different means of perforating and rolling the dough before packaging. Table 2 contains a typical sweet dough product formula.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00246-1

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WHEAT PROCESSING | Refrigerated Dough

Table 1

Typical refrigerated biscuit dough formula

Ingredient

Weight (%)

Baker’s (%)

Hard wheat flour Water Shortening (dough) Shortening (roll-in) Sodium bicarbonate Sodium acid pyrophosphate (SAPP) Nonfat dry milk Dried whey Salt

51.8 30.8 2.0 8.0 1.0 1.4 2.0 2.0 1.0

100.0 59.5 3.9 15.4 2.0 2.6 3.9 3.9 1.8

Table 2

Typical refrigerated sweet dough formula

Ingredient

Weight (%)

Baker’s (%)

Hard wheat flour Water Shortening Sodium bicarbonate Sodium aluminum phosphate (SALP) Nonfat dry milk Sucrose Salt

50.2 29.8 10.0 1.0 1.0 2.0 5.0 1.0

100.0 59.4 19.9 2.0 2.0 4.0 10.0 2.0

According to the standards of identity, bread products must contain yeast. Refrigerated dough products similar to bread have been introduced, however. These products usually incorporate the very bland-tasting acidulant glucono delta-lactone (GDL) in combination with yeast flavors. The yeast flavors are complex and often are composed of a base flavor and a top note. Due to the fact that GDL is a fairly quick-acting acidulant, the sodium bicarbonate used in the chemical leavening system is often encapsulated to slow it down. This allows sufficient processing time to load the dough into the can and cap it. To obtain the high volume and the chewy texture associated with bread products, vital wheat gluten is usually added to the formula. Dextrose and/or nonfat dry milk is also included to facilitate Maillard browning. Panned-style breads have a distinctive shape that is not easily obtained directly from a can. For this reason, refrigerated dough ‘bread’ products are generally shaped like baguettes. Cans for the bread products are longer and have a lower diameter than those used for other pressurized refrigerated dough products. Table 3 contains the formula for a pressurized refrigerated dough product similar to bread.

Questions

• •

What leavening agents are commonly used in refrigerated dough products? Why can’t conventional baker’s yeast be used to leaven refrigerated dough?

Processing Table 3

Typical refrigerated bread dough formula

Ingredient

Weight (%)

Baker’s (%)

Hard wheat flour Vital wheat gluten Water Shortening Encapsulated sodium bicarbonate Glucono delta-lactone (GDL) Nonfat dry milk Sucrose Salt Bread base flavor Bread flavor top note

52.8 3.9 27.2 3.0 1.6 1.8 2.0 4.0 1.0 0.6 2.1

100.0 7.4 51.5 5.7 3.0 3.4 3.8 7.6 1.9 1.1 4.0

The processing steps to make refrigerated dough products are shown in Figure 1, and they are similar to many common bakery products. Basic engineering principles like mass balances and energy balances, along with physical and thermodynamic transformations, should be applied to each step, and specific details will depend upon the specific products being made. Good manufacturing practices, GMPs, and appropriate food safety systems like sifters and magnets are necessary considerations at every step, but those requirements will not be covered here.

Receive and store ingredients Bulk delivery of high-volume ingredients like flour and sugar via rail cars or trucks is common. Other ingredients are

Receive and Store Ingredients

Prepare and Scale/Meter Ingredients

Mix

Form

Finish

Pack into Primary Package

Pack into Secondary Package

Store and Distribute

Figure 1 Process steps for making refrigerated dough products.

WHEAT PROCESSING | Refrigerated Dough handled in bags, boxes, super sacks, or liquid containers. Flour is typically stored in silos, so flour temperatures vary with the seasons, commonly ranging from 50 to 100 F (10–38 C). Many ingredients, however, have storage specifications for temperature, humidity, and age, which are provided by the ingredient vendors. Proper storage space near the point of use is desirable.

Prepare and scale/meter ingredients For operational efficiency, it is desirable to limit the number of individual ingredient streams entering the mixer. It is common, therefore, to create premixes or solutions of multiple ingredients. Major considerations include the reactivity of the blended components, ability to maintain a homogeneous blend, functionality during mixing, and cost. It is common to use pneumatic systems for transporting flour and other bulk powders from silos and storage vessels to scaling vessels. The most important step for making on-target dough is getting the right amounts of all ingredients into the mixer, so all ingredient delivery systems, whether automated or manual, must be properly engineered and verified. Vessels using load cells for either gain-in-weight or loss-in-weight scaling are typically accurate to within 1% of target, and mass flow meters for liquids can have similar accuracy. The most challenging ingredients to deliver accurately are the highly functional, smallquantity ingredients, like the leavening agents.

Mix The purpose of mixing is to transform the ingredients into dough with the desired bubble structure and physical properties. Important attributes of the dough include temperature, rheology, and density. Dough is a viscoelastic material, so its rheology includes measures of its viscous behavior as well as its elastic, or stretch, behavior. Horizontal bar batch mixers are common in the United States for high-speed dough processing operations due to their capacity and flexibility. The order of ingredient addition is important for refrigerated dough to ensure proper hydration of the flour and to limit the leavening reaction during mixing. Flour, water, and some minor ingredients are added first, with leavening agents and some other minor ingredients added later in the mixing cycle. The primary transformations in the mixer include uniform blending of ingredients, hydration, and gluten development. It is well known that gluten development is dependent upon mechanical energy, so mixing to an energy end point is an accurate way to control the degree of gluten development. Mixing is then defined by the amount of energy per unit mass of dough in the mixer, and mix energies for refrigerated dough are similar to other dough products, ranging from 25 to 55 kJ kg1. When all ingredient temperatures are accurately controlled, and heat exchanged to and from the mixer is constant, then mixing to a temperature end point is the same as mixing to energy. While high-speed mixing creates the gluten structure quickly, it also generates heat. High-capacity mixers are therefore jacketed with a coolant, typically propylene glycol and water solutions, to remove heat during mixing. Understanding the energy balance in dough mixing is essential to ensure low batch-to-batch variation in temperature and in degree of gluten development.

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Form After mixing, refrigerated dough should be formed and packed as quickly as possible. Unlike some yeast-leavened dough, there is never an advantage to resting or holding refrigerated dough. The chemical leavening reacts and there are changes within the gluten structure, and these changes have an impact on process tolerance and piece weight control. In general, dough should be packed within 30 min of mixing. Pairs of rolls, called gauging stations or roll stands, are used to transform a large mass of dough into a dough sheet of the desired width and thickness. The number of rolls needed, along with their speeds and gaps, depends upon the desired final sheet thickness. A common problem in dough processing is dough stickiness. Dusting agents like wheat flour or wheat starch are effective and economic. There are two basic approaches to creating the final dough pieces that go into the composite cans. Individual pieces are cut from the dough sheet and packed vertically into composite cans, or dough pads are cut, which include all individual pieces separated by perforations, and the pad is rolled up into a cylindrical shape to be packed into a can. Products for which we want a flaky texture have laminating fat extruded onto the middle third of the dough sheet early in the sheeting process, and the dough on either side of the laminating fat is folded over to enrobe the fat. The dough sheet then has a single layer of fat within a top layer and bottom layer of dough. After sheeting to the proper thickness, the fat-enrobed dough sheet is then folded back and forth on itself in a common process called lapping. Lapping creates multiple layers of dough and fat, and the number of fat layers is controlled by the amount of lapping.

Finish Finishing operations include the addition of toppings or fillings onto the dough sheet prior to packing. When a material is deposited onto a dough sheet, and then the individual pieces are cut and packed vertically, the material is a topping for each individual piece. When a material is deposited onto a dough sheet, which is cut into pads for rolling, then the material becomes a spiral filling. Finishing operations are highly specific to the product.

Questions

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Why is the order of ingredient addition important in making dough? How is it determined when mixing is complete? What is the shelf life for most refrigerated dough products?

Packaging The package used for pressurized refrigerated dough products is really quite ingenious. Dough is maintained in an expanded state in a carbon dioxide atmosphere, thus allowing it to be baked and achieve volumes similar to conventional baked products. The shelf life for these products has improved since the initial invention through improvements in can design, processing, and sanitation. Currently, the shelf life for pressurized refrigerated can dough products is about 3 months. The packaging system is composed of a composite spiralwound paperboard can with an aluminum liner and an iron

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WHEAT PROCESSING | Refrigerated Dough Table 4

METAL END HEADSPACE CO2 O2 OXYGEN

OXYGEN

Typical refrigerated sugar cookie dough formula

Ingredient

Weight (%)

Baker’s (%)

Chlorinated soft wheat flour Sugar Shortening Water Salt Baking soda

46.8 24.5 18.7 9.0 0.4 0.6

100.0 52.4 40.0 19.2 0.8 1.3

Cookie Dough Processing

DOUGH COMPOSITE CAN BODY

The process for making refrigerated cookie dough follows Figure 1, but there is typically no separate finish step, and the details of the mix and form steps are different.

METAL END Figure 2 Refrigerated can dough system.

alloy can end. The spiral winding allows the pressurized can to easily open along the seam when struck on the side. The end is crimped on after loading the dough and the dough subsequently expands as the leavening system creates carbon dioxide. Air (oxygen) is vented and eventually, the dough caulks the vents in the can end and the system subsequently pressurizes. The can is designed to burst at about 40 psi as a safety control. Of course, higher pressures would lead to explosive opening and potential safety issues for consumers. Figure 2 diagrams the refrigerated can dough system. Can sizes vary with diameter and length to accommodate the various shapes and sizes of dough pieces and hence final product geometries. As described in the section ‘Processing,’ dough can be cut, rolled, and scored before loading into the can. The consumer, with very little manipulation, can bake these dough pieces to yield a large array of baked product forms.

Mix Cookie dough is considered an undeveloped dough because it is formulated with soft wheat flour, and there is no desire for a strong, developed gluten structure to hold gas during baking. Dough temperature and density remain important dough attributes, but cookie dough does not exhibit the same type of viscoelastic behavior as sweet rolls and breads. The primary transformations include blending to get a homogeneous dough and air incorporation for density control. To achieve these transformations, the mix element is typically a sigma blade, rather than horizontal bars. Continuous mixing is relatively straightforward, but careful consideration must be given to keeping any particulates, like chocolate chips, intact. Ingredient temperatures, the order of ingredient addition, and mix time are important parameters to achieve the desired dough attributes. Although cookie dough does not have a leavening reaction, it also changes with age, so for best process performance and weight control, cookie dough should be processed soon after mixing.

Form Question

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Explain the steps of can proofing and pressurization.

Nonpressurized Refrigerated Dough Cookies The primary ingredients in all cookies are sugar, flour, and shortening. This is the same for refrigerated cookie dough. Flour is generally derived from soft wheat, and it is chlorinated in the United States. For countries disallowing chlorination, other flour treatments (e.g., heat treatment) can be applied. Enough water is added to hold the mass together. The water activity of a refrigerated cookie dough is about 0.8 and hence microbial growth is minimized. Refrigerated cookie dough, like conventional cookie dough, is lightly leavened, so the final product is not too dense. Of course, there are many proliferations of cookie formulas. Table 4 contains the formula for a basic sugar cookie dough.

The most common general method of forming refrigerated cookie dough is extrusion, although there are many different ways to extrude the dough, and these result in different shapes and configurations. Extrusion includes pumping through a cylindrical mandrel to make a log or tube of cookie dough, using rolls to force dough through a rectangular die to create a slab, using rolls to force dough into cavities to make individual pieces, and using coextrusion, where different color dough streams are pumped through dies to create embedded shapes inside each cookie.

Cookie Dough Packaging There are two general types of packages for refrigerated cookie dough. The first is a film tube with metal clips on the ends. The second includes a paperboard carrier tray with a film overwrap. The shelf life of refrigerated cookie dough is about 4 months, and given the nature of the low-water formulation, cookie dough can be frozen to extend shelf life to several more months.

WHEAT PROCESSING | Refrigerated Dough Piecrust

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Form

Piecrust dough consists of about 30% fat. Historically, many home economists considered the best piecrust dough to be made with lard. Modern piecrusts are more commonly formulated with shortening. The other components of conventional pie dough are chlorinated soft wheat flour, water, and salt. The formulation of refrigerated pie dough, however, is more complicated due to shelf life issues. Primary among these issues is the graying of the dough due to the action of polyphenol oxidase. Excluding oxygen by flushing the packaging with nitrogen helps reduce graying. Formulation approaches include replacing a major portion of the flour with wheat starch, gluten, and xanthan gum. This combination approximates the functionality of the flour in the formula but is void of the phenolic compounds and polyphenol oxidase that causes the gray color to develop. It also reduces the tendency for the dough to separate into a dough stage and a viscous syrup (i.e., syruping, described in the section ‘Shelf Life Issues’). Mold is another issue that can limit the shelf life of refrigerated piecrust dough. The use of antimycotics such as sorbate and propionate effectively increases the resistance of the dough to mold growth. Table 5 contains the formula for a typical refrigerated piecrust dough.

The most common general method of forming refrigerated pie dough is through sheeting rolls, die-cutting individual pieces, and then rolling the circular pieces for packaging.

Piecrust Packaging Refrigerated piecrusts are packaged in flexible film overwrap, each rolled crust in its own wrapper, and then two wrapped crusts are placed in a paperboard carton for the retail package. The shelf life of refrigerated pie dough is about 4 months, and given the nature of the low-water formulation, pie dough can be frozen to extend shelf life to several more months.

Questions

• • •

What is the most common processing method employed to form refrigerated cookie dough? What formula changes are made to prevent refrigerated piecrust dough discoloration? What preservative is added to prevent mold growth in refrigerated piecrust?

Basic Relationships Magic Number

Piecrust Processing The general process for making refrigerated piecrust follows Figure 1, but there is typically no separate finish step, and the details of the mix and form steps are different.

Mix Pie dough is considered an undeveloped dough because it is formulated with soft wheat flour, and there is no desire for a strong, developed gluten structure to hold gas during baking. In fact, refrigerated piecrust dough has very little entrained gas. Dough temperature and density remain important dough attributes, and similar to cookie dough, piecrust dough does not exhibit viscoelastic behavior. The primary transformations include blending to get a homogeneous mix and restriction of bubble formation for density control. To achieve these transformations, refrigerated pie dough mixers typically have specialized mix elements along with pressure and vacuum control. Ingredient temperatures, the order of ingredient addition, and mix time are important parameters to achieve the desired dough temperature and density.

The notion of magic number is unique to canned refrigerated dough and was developed to describe a targeted dough pack weight to can volume ratio that reduces the likelihood of overor underpressurization and ensures optimal dough expansion upon opening. Magic number (MN) ¼ volume of can (cc)/weight of dough in can (g). Typical magic number ranges from 1.16 0.5 cc g1.

Pressure/SV (Specific Volume) Upon opening, pressurized refrigerated dough will expand rapidly and increase in specific volume (cc g1). There is a positive correlation between can pressure, dough specific volume after opening, and finished baked specific volume. This correlation is limited to pressures < 30 psig (pounds per square inch gauge). At can pressures exceeding 30 psig, the rate and extent of dough expansion upon opening result in damage to dough cell structure and loss in capacity to expand upon baking. Targeted equilibrated can pressures for most pressurized refrigerated dough products are between 14 and 20 psig.

Question Table 5

What is ‘magic number’ and why is it important to pressurized refrigerated dough?

Typical refrigerated piecrust dough formula

Ingredient

Weight (%)

Baker’s (%)

Chlorinated soft wheat flour Wheat starch Vital wheat gluten Water Shortening Salt Potassium sorbate

25.0 24.4 5.0 14.5 30.0 1.0 0.1

100.0 97.6 20.0 58.0 120.0 4.0 0.4

Shelf Life Issues Pressurized Dough Refrigerated dough products are active biological systems. Even at refrigerated temperatures, the enzymes introduced with the ingredients, primarily the flour, and the microbes introduced with the flour and from other sources can cause changes

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deleterious to dough quality. Primary shelf life problems associated with these changes are burst cans, syruping, gray dough, and crystal formation. The most significant shelf life issue for pressurized refrigerated dough products is burst cans. Lactic acid bacteria are the primary cause of this issue. As they produce lactic acid slowly during the product’s shelf life, the pH is depressed and the carbonate balance of the leavening system is driven to produce more gaseous carbon dioxide. Consequently, can pressures rise and eventually surpass the point where the cans will rupture and the contents will be expelled. The key to keeping lactic acid bacteria at a minimum in the dough is sanitation. Assuring old dough does not contaminate freshly processed dough is key. It is also important to control the temperature and time the products experience, especially during the can proofing step of the process. High temperatures and longer times foster the growth of the bacteria. Imperfections in the package such as can ends not fastened to specification can also be a significant factor. The cause of syruping is the enzymatic degradation of wheat flour arabinoxylans. Arabinoxylans are nonstarchy polysaccharides native to the flour, and they bind a very significant amount of water in freshly formulated dough. With time, these polymers are degraded, thus losing their water-binding ability. The result is a separation into a dough stage and a viscous syrup. The syrup facilitates the ionic flow between the aluminum liner of the can wall and the iron in the can end, and the package integrity is compromised. The result can be syrup exiting the can, resulting in a very serious product defect. Reduction in the incidence of syruping has been obtained by controlling the load of the enzymes responsible in the flour used. The possibility of enzyme inhibitors to control syruping has also been proposed. As discussed in the pie dough section, gray dough is caused by the polymerization of phenolic compounds native to flour. Excluding oxygen, which is one of the reactants, and/or reducing the amount of polyphenol oxidase in the system can minimize the reaction. The most common cause of gray dough is oxygen included in the can. This occurs of course if the can does not pressurize and hence the oxygen is not expelled. It can also occur if pockets of air are trapped against the sidewall. Polyphenol oxidase is contained primarily in the aleurone layer of the wheat kernel, which separates with the bran during milling. Therefore, using low-ash flour can also be beneficial. Crystal formation in refrigerated dough occurs only when leavening systems high in pyrophosphate content (i.e., SAPP) are used. Flour contains pyrophosphatase, which catalyzes the hydrolysis of pyrophosphate bonds, thus liberating two molecules of orthophosphate for every pyrophosphate molecule. This extremely high concentration of orthophosphate ions in the system creates a condition where visible sodium orthophosphate crystals can form in the system. When a product contains these crystals, consumers can mistake them for glass, and a very serious complaint occurs. Crystal formation has largely been eliminated in pressurized refrigerated dough products by using SAPP only in combination with SALP and other acidulants that are low in pyrophosphate content.

Nonpressurized Dough The enzyme-related shelf life issues with nonpressurized cookie dough products are minimized by the high sugar

contents and low-water activity of their formulations. Formulas for piecrust dough have also been developed to minimize enzymatic activity and related shelf life issues. Additionally, piecrust is packaged in a modified atmosphere to further reduce the risk of shelf life issues. One issue that does occur with piecrust involves a structural deficiency in the crust during baking. The term slumping has been used to describe the failure that occurs when the sidewalls of the crust slide to the bottom of the pie tin during a one-crust bake. The amount of fat in the formula is critical. Too much the crust will slump and not enough the texture will not be desirable. In general, refrigerated piecrust formulas contain less shortening than conventional piecrust dough to control slumping.

Questions Name the primary shelf life problems associated with refrigerated canned dough. How does lactic acid bacteria growth in refrigerated dough affect can pressure? What enzyme is responsible for gray dough discoloration? What are refrigerated dough crystals and what causes their formation?

New Developments Yeast Gaining the ability to use yeast in refrigerated dough products would likely expand the refrigerated dough market significantly. Most conventional baked products consumed are yeast-leavened, while all refrigerated dough products are chemically leavened. As described earlier, standard baking yeast is resourceful and able to consume and produce carbon dioxide with many of the substrates (i.e., monosaccharides) contained within freshly formulated and aging refrigerated dough formulas during shelf life. Significant effort has been expended to identify a yeast strain suitable for pressurized refrigerated dough. These include developing yeast strains that are temperature-sensitive and are not active at refrigerated temperatures, rehydrating yeast at reduced temperature to weaken it and render it unable to survive in the refrigerated dough environment, and using yeast strains limited in the ability to use all the substrates that commonly are available to standard yeast in the dough formula.

Nonpressurized Biscuit Dough Nonpressurized refrigerated biscuit dough and packaging technology were developed to enable portion control for consumers. Biscuits are packaged into individual film pouches (two biscuits per pouch) with four to five pouches per retail carton. This novel product and package format is a departure from traditional pressurized Willoughby dough systems and required redesigning how the product and package interact. Specifically, the use of nonpressurized pouches necessitated the development of an unleavened dough system. This was accomplished using encapsulated soda in combination with sodium aluminum phosphate, a heat-activated leavening acid. The pouches, made with high gas barrier film, are thermally formed to create a cavity to receive the biscuits and are

WHEAT PROCESSING | Refrigerated Dough vacuum-packaged to limit headspace volume. Eliminating pouch headspace volume is critical to limiting the prereaction and release of leavening gas over shelf life time (minimizes pouch headspace expansion). Additionally, the enzyme glucose oxidase is added to the dough formula to prevent enzymatic discoloration resulting from oxygen diffusion into the package over shelf life time.

Low Sodium There is an ongoing desire to reduce the sodium content of refrigerated dough. The two main sources of sodium in refrigerated dough are added salt (NaCl) and chemical leavening agents (sodium bicarbonate and sodium-containing leavening acid salts). One commonly employed strategy to reduce sodium in refrigerated dough is to replace sodium salts with nonsodium analogs or organic acid substitutes (see Table 6). There are limits to this replacement strategy as potassium has a bitter astringent taste and some of the nonsodium leavening acid options do not possess comparable reaction rates to their sodium counterparts. Additionally, removing salt affects not only flavor but also dough water activity and gluten development. To complicate matters further, the molality of the dissolved salts in the dough system directly affects the dissociation of the leavening acid salts and leavening rate kinetics.

undeveloped cookie and brownie products. To expand glutenfree refrigerated dough to more developed product categories such as sweet rolls, crescent rolls, and breads, a need exists to create gluten-free dough with greater elasticity and tolerance to machinability.

Questions Name two of strategies to control yeast metabolism and gas production in refrigerated dough products. What are the two main sources of sodium in refrigerated dough? What technical hurdles must be addressed to expand glutenfree refrigerated dough product offerings to more developed product formats?


• • • • •

Gluten-Free Gluten (combination of gliadin and glutenin proteins) provides viscous and elastic properties to dough products. Functionally, these proteins enable entrapment of leavening gases, resulting in expansion to larger volume. Additionally, they provide a chewy texture to baked breads. Recent attention has focussed on a portion of the population that is sensitive to gluten and unable to eat products containing these proteins. The food industry has responded by developing many glutenfree bakery goods. Much of the ‘gluten-free’ technology developed to date relies on the use of nongluten flour systems (rice, sorghum, quinoa, legumes, etc.) in combination with starches (potato, corn, tapioca, etc.) plus hydrocolloids and gums (guar, xanthan, alginate, etc.). The resulting gluten-free batters and dough effectively entrap leavening gases enabling expansion upon baking but still lack elastic properties, thereby limiting product and processing options. This is particularly relevant to pressurized Willoughby refrigerated dough products, which are processed on high-speed lines and stored under pressure and need to retain gas cell structure upon rapid expansion when opened. As a result, many of the ready-to-bake glutenfree refrigerated dough offerings commercially available are

•

Table 6

•

Sodium replacement salt analogs

Ingredient

Sodium salt

Replacement salt

Salt Soda Leavening acida

NaCl NaHCO3 Na2H2P2O7 (SAPP)

KCl KHCO3 CaH2P2O7 (CAPP)

a

Additionally, organic acids such as cream of tartar, malic, ascorbic, and citric can be used to replace inorganic sodium-containing acid salts.

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What contribution did Lively Willoughby make that enabled the commercial development of refrigerated dough? How soon should (refrigerated) dough be packaged after mixing? Explain the two basic approaches to creating the final dough pieces that go into the composite cans. Hard wheat flour is used in essentially all canned refrigerated dough formulas. Why? Describe some of the possible product geometries achieved with canned refrigerated dough and how they are manufactured. What are two packaging formats for refrigerated cookie dough? Describe the relationship between can pressure, raw dough specific volume, and baked specific volume. What is the cause of syruping in refrigerated dough? Name a common strategy employed to reduce sodium in refrigerated dough.


•

•

Shelf life extension and characterization: Refrigerated dough is unique in that the raw product is designed to be stored for up to 3 months with the expectation of acceptable baked performance through shelf life (color, volume, and taste). Research has linked protein content and flour enzyme activity (arabinoxylanase, polyphenol oxidase, and amylase) to changes in dough properties resulting in baked product quality decline over storage time. A more thorough identification and characterization of these intrinsic flour quality attributes are needed to more accurately predict and extend product shelf life. Gluten-free refrigerated dough: As mentioned earlier, glutenfree refrigerated dough products are presently limited to more underdeveloped applications (cookies, brownies, and piecrust), packaged in nonpressurized formats. There exists a need to create a more elastic gluten-free developed dough system with greater tolerance to processing and capability of being packaged in pressurized spiral-wound cans. Low-sodium refrigerated dough: In addition to the organoleptic challenges associated with reducing sodium, NaCl effectively

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lowers refrigerated dough water activity, which in turn limits lactic acid bacteria metabolic activity and associated changes in dough pH and can pressure. There exists a need to identify alternative ingredients and formulation strategies that will enable targeting of specific dough aw values while still meeting consumer organoleptic expectations. Whole wheat: The nutritional benefit of consuming wholewheat bread products is well documented. Inclusion of whole-wheat flour to refrigerated dough adversely affects shelf life and overall product performance due to increases in flour enzyme and bran levels. There exists a need to develop a whole-wheat flour system more compatible with refrigerated dough distribution and shelf life requirements (inactivation of enzyme systems and improvement in overall bake performance).

See also: Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing; Wheat-Based Foods: Breads;

Wheat Processing: Analysis of Dough Rheology in Breadmaking; Milling and Baking: History; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

Further Reading Atwell W (1996) Method to Reduce Syruping in Refrigerated Doughs. U.S. Patent 5,792,499. Atwell WA (2001) Wheat Flour. St. Paul, MN: American Association of Cereal Chemists. Domingues DJ, Atwell WA, and Pilacinski WP (1997) Yeast Leavened Refrigerated Dough Products. U.S. Patent 5,939,109. Gys W (2005) Substantiated Evidence for the Involvement of Arabinoxylans, Endoxylanases and Endoxylanase Inhibitors in Refrigerated Dough Syruping. PhD Thesis, Katholieke Universiteit Leuven, Belgium. Varriano-Marston E (1995) Packaging materials. In: Kulp K, Lorenz K, and Brummer J (eds.) Frozen and Refrigerated Doughs and Batters St. Paul, MN: American Association of Cereal Chemists. Willoughby LB (1931) Method and Means of Packeting Dough. U.S. Patent 1,811,772. Zoeller RJ and Henderson JR (1963) Dough Package. U.S. Patent 3,102,818.

Chemistry of Cake Manufacturing TS Palav, Rich Products Corporation, Buffalo, NY, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Cake formulas are rich in sugar, fat, and eggs. The use of soft, bleached flour is critical for uniform cell structure. Emulsifiers stabilize the air cells in cake batter, which is an oil-in-water emulsion. Rate of reaction of chemical leavening can be modified by using different leavening acids. Mixing time and speed are critical for the amount of air incorporated into the batter. Heat influx influences the bake time and final baked structure.

Learning Objectives After reading this article, you should be able to

• • • •

choose the right quality of ingredients for cake making, design cake formulas to achieve desired cake characteristics, understand the importance of processing settings on final cake structure, troubleshoot through the examination of formula and process.

Across the globe, birthdays are celebrated with cakes. From being the star at birthday parties, cakes have found their way into various celebrations like weddings, graduations, Mother’s Day, and Easter. Cakes and their use have transformed over the years since their inception. The name ‘cake’ is derived from an Old Norse word ‘kaka.’ In history books, the distinction between cakes and breads is blurry. Cakes first appear in history as sweetened breadlike products that had fruits and/or nuts. In the ancient days, the high cost of sugars and nuts made cakes an expensive food. The high price of cake could explain the relation between cakes and celebration. The emergence of cakes can be explained by their other name ‘quick breads.’ Cake, as we know today, came into existence in the mid-nineteenth century. The discovery of the whipping ability of eggs, baking soda, and the ubiquity of sugar have helped shape up cake evolution. Cakes can be categorized based on the balance of ingredients, mixing, and baking procedures followed. Commercially available cakes can be classified into batter cakes, foam cakes, and chiffon cakes.

Batter Cakes Batter cakes are the most commonly found cakes in today’s commercial bakeries. They can be characterized by the presence of high amount of fat and sugar. The texture of batter cakes depends on the ingredients used and the air whipped


into the batter during mixing. The presence of chemical leaveners is important for the structure of the cake. A pound cake is an example of batter cakes. Batter cakes pair well with rich icings like buttercream because of the moist and dense crumb. Batter cakes are further classified into high-ratio cakes and low-ratio cakes. High-ratio cakes have more sugar than flour in the formula. In low-ratio cakes, the amount of sugar is equal to or less than the amount of flour in the formula. In this article, we will focus on the chemistry of batter cakes.

Foam Cakes Extension and denaturation of egg proteins play an important role in the structure of the cake. Angel food cakes are an example of foam cakes. Angel food cakes mainly rely on egg whites for their structure and texture. Air is incorporated by whipping egg whites. Then, the dry ingredients are gently folded into the foam. Oil is detrimental to the structure of angel food cakes. Ladyfingers used in tiramisu cakes are a form of foam cakes.

Chiffon Cakes Chiffon cakes are a combination of batter cakes and foam cakes. Aeration in these cakes depends on egg whites and chemical leavening. These cakes contain a fairly high amount of oil in them. Sponge cakes are an example of chiffon cakes. In sponge cakes, whole eggs or yolks contribute to the structure of the cake.

Flour There are no brownie points for knowing the importance of flour in bakery formulations. Cake flour is mostly ground from soft red winter wheat varieties. Flour that is ground from nonsoft wheat varieties may have higher levels of damaged starch. In such cases, flour analyses should be reviewed with care and necessary adjustments should be made to the formulation. Studies have shown that finer flour particle size resulted in better quality cakes. Cakes made with finer flour have better heights. Smaller particle size means increased surface area and increased interactions with other ingredients. In general, early breaks and early middling streams are used for cake flour. In cakes, flour plays an important role as structure builder. When the batter is heated, starch in the flour undergoes gelatinization. Gelatinized starch helps build structure and contributes to the volume of the cake. Unlike bread products, cake flours do not require high-protein flour. The amount of protein is inversely proportional to the volume of the cake. Figure 1 shows that higher protein levels limited expansion, thus

http://dx.doi.org/10.1016/B978-0-12-394437-5.00156-X

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resulting in dense cakes. Good quality cake flour has 7.8–8.5% protein content. Lower ash content is another desired prerequisite for cake flours. Higher ash content is an indication of the bran contamination in the flour. Flours with high ash content result in dark-colored products. For best results, ash content of cake flour should be less than 0.45%.

Chlorination Chlorinated flour is commonly used in some parts of the world for cake making. Chlorine gas can be used to modify flour characteristics and to bleach it. Flour can be treated with benzoyl peroxide to achieve a bleaching effect. Chlorination of flour lowers the pH of the flour to 4.5–5.2. The pH of cake flour can be used an index of the extent of chlorination. The typical pH of flour before chlorination is in the range of 5.8–6.1. Cakes made with chlorinated flour have finer grain and improved texture than cakes made without chlorinated flour (Figure 1). Chlorination of flour increases the oilbinding ability of the starch. Chlorination mellows the gluten in the flour, which helps the springiness of the final product. Chlorinated flour is crucial for high-ratio cakes. The increased granule swelling and better oil-binding ability help the structure hold the excess amount of sugar and fat in the formula. Chlorination does not affect the gelatinization temperature of the starch component of the chlorinated flour. Chlorination is effective in bleaching carotenoids in flour and increases water absorption of the flour. If chlorinated flour is not available or desired, some adjustments can be made to the formulation to use unbleached flour. Heat-treated flour can be used as an alternative to bleached flour. Heat treatment does not bleach the flour but modifies flour characteristics similar to chlorination. If untreated flour is used, addition of native wheat or corn starch can help achieve desired texture. Additional starch helps in lowering the protein content of the flour and strengthens the structure of the baked cake. For better results, it is best to use flour with less than 8% protein content. When using nonchlorinated flour, it is advisable to increase leavening agents. Increased leavening agents help in achieving a lighter and softer cake. The processing might need to be altered along with the formulation adjustments.

Sweeteners Sucrose is used as the sweetener of choice for cake manufacturing. Sucrose acts as a tenderizer in the formulation. The hygroscopic properties of sucrose help in moisture retention during postbaking storage. For high-ratio cakes, the sucrose aids in creaming of fat. Creaming helps in air incorporation during mixing. The use of dextrose, high-fructose corn syrup, or corn syrup solids is popular in commercial cake formulations. Not more than 5% of the total sugar in the formulation is substituted with these sweeteners. The use of such sweeteners helps impact the sweetness intensity of the cake. Maillard reaction is a nonenzymatic browning reaction between a reducing sugar and an amino acid in the presence of heat. Monosaccharides have a

(a)

White cake made with bleached flour, protein 8%

(b)

White cake made using unbleached flour, protein 8%

(c)

White cake made using bread flour, 12% protein Figure 1 Comparison of cakes made using different flours.

faster rate of Maillard reaction than sucrose. Sucrose is a nonreducing disaccharide. Therefore, sucrose contributes to Maillard reaction only after its hydrolysis. When sucrose is the only sweetener used, crust color is usually developed in the later stages of baking. Oven settings for cake formulations with monosaccharides need to be closely monitored to avoid excessive darkening of the crust. The amount of sweeteners in the formula plays a critical role in structure setting, by influencing the gelatinization temperature of starch. As the amount of sucrose in the formula increases, it delays the onset of gelatinization temperature. Having more than 145% sucrose (based on baker’s percentage) in the formula can pose baking challenges. If a sweeter product is desired then, it is recommended to supplement part of the sucrose in the formula with sugar substitutes. Sweeteners like sucralose, sugar alcohols, saccharin, and stevia can be used. The use of bulking agents is recommended in sugar-free formulations. Sugar alcohols do not undergo Maillard reaction; therefore, sugar-free cakes have a lighter crust color.


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Fat Unlike yeast-raised bakery products, cakes have a higher amount of fats in the formulations. The use of fats is detrimental in foam cake formulations. But fats have some functional properties in batter cake formulations. Fat plays a role as a tenderizer and helps in extending the shelf life of the product. Fats are critical in the entrapment of air cells during the creaming process. Fat aids in emulsification and prevents the coalescence of air bubbles during baking. The presence of fat is important to achieve tender cakes. Cake batters are oil-inwater emulsions, where the fat is dispersed in the water (distinct phase). It is important to disperse the fat uniformly in the batter during the mixing stages. Two-stage mixing process is recommended, when plastic shortening is used. When the process fails to uniformly disperse fats, it can result in crispy cake tops or nonuniform cell structures or short heights. Before trans fats gained the negative publicity they enjoy today, the use of hydrogenated fats was popular in cake baking. In the post-trans fat-conscious era, hydrogenated shortenings have been successfully replaced by nonhydrogenated liquid fats. When using liquid fats, the use of the right emulsifiers ensures necessary air incorporation. The amount of fat in cake formulations enhances eating characteristics of the final product. The amount of fat used in cake formulations depends upon the amount of sugar and eggs in the formula.

Emulsifiers An emulsifier can be defined as a substance that helps stabilize an emulsion of immiscible liquids like oil and water. Emulsifiers help in preventing fatty layer formation on the surface of soluble proteins (Tsen and Kulp, 1971). If soluble proteins are coated with fat molecules, they cannot contribute to air incorporation. Therefore, emulsifiers are one of the minor ingredients in cake formulations that have a big impact on the final baked product. Figure 2 shows cross sections of white cakes made with and without emulsifiers. From the figure, it can be seen that cakes made without emulsifiers had limited height and nonuniform cell structure. Emulsifiers help in the incorporation of air during mixing. Cake batters without emulsifiers incorporate limited amounts of air, and therefore, they are less viscous than batters made using emulsifiers. Another important function of emulsifiers is to stabilize the fat phase in cake batter. The choice of emulsifier is dictated by the type and amount of fat used in the formulation. Propylene glycol esters of fatty acids, propylene glycol monostearate, distilled monoand diglycerides of fatty acids, and polysorbates are fairly common emulsifiers in cake formulations. A combination of two or more emulsifiers is often used to get the desired cake crumb and texture characteristics. Spray drying of emulsifiers on milk powder or whey proteins can help in easy dispersion in cake batter. Emulsifiers help in the incorporation of air during mixing and the maintaining of air in the oil-in-water dispersion during baking. The use of spray-dried emulsifiers is popular in the industry due to the ease of handling. If using plastic emulsifiers, it is best to include them in the creaming stage of mixing. Emulsified shortenings are commercially

(a)

White cake formulation without emulsifiers

(b)

Control white cake with 7.5% emulsifier (bakers’ %) Figure 2 Effect of emulsifiers on cake texture.

available and are successfully used in cake formulations. Emulsified shortenings are more effective in multistage mixing processes. Emulsified shortenings have limited benefits in cake batters that are mixed in single stage. Emulsifiers impact the texture of the cake as seen from Figure 2. Cake batters are oilin-water dispersions; therefore, hydrophilic emulsifiers are more effective than lipophilic emulsifiers. Hydrophilic– lipophilic balance (HLB) is the measure of the hydrophilic or lipophilic value of an emulsifier. Knowing the HLB value of an emulsifier can help in the selection of the right emulsifier for an application. Cohesive properties of the cake can be influenced by the type and amount of emulsifier used in the formulation. A combination of emulsifiers can help achieve the desired springiness and cohesiveness in the baked product. Emulsifiers also help in the baked shelf life of the product by helping moisture retention during storage.

Eggs Eggs contribute to the structure and flavor of the cake. Egg whites help in air incorporation during mixing. Denaturation of egg proteins helps in structure development. Yolks tenderize the cake. Lecithin from yolks acts as an emulsifier. Spray-dried egg products can be used as a part of the cake mix. In sponge cakes and foam cakes, the whippability of eggs plays an important role in cake texture. The use of dry eggs helps reduce the number of liquid ingredients added to the mixing bowl. When converting formulas for using dry eggs instead of liquid eggs, it is important to balance the amount of water in the formula. Liquid whole eggs are approximately 25% solids and 75% water. Egg proteins have a unique functionality in cakes. Eggs

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play an important role from batter mixing to different stages in baking. Replacing eggs in cake formulation has been a challenge. Studies have shown the importance of soluble protein in optimum air incorporation. Processing of eggs, that is, spray drying or pasteurization, may affect the solubility of egg proteins. The ratio of egg whites to egg yolks in the egg product can be altered based on the cake formulation. Egg whites and yolks can be added separately, rather than using whole eggs.

Hydrocolloids Hydrocolloids are higher-molecular-weight, water-soluble (often) polysaccharides. Hydrocolloids are used in commercial cake formulas for viscosity control and better processing tolerance. Large-scale cake manufacturing involves high-shear mixing. The batter is usually processed through pumping equipment and continuous mixers before depositing. Addition of hydrocolloids controls the batter viscosity and prevents degassing of the batter during its processing. There has been a study conducted on the functionality of sodium alginate, carrageenan, pectin, hydroxypropyl methylcellulose (HPMC), locust bean gum, guar gum, and xanthan gum on the quality and shelf life of yellow cake layers. They concluded that all gums except pectin improved the acceptability of the yellow cake compared to control. Hydrocolloids are also useful in maintaining the quality of the frozen cake over the course of its frozen shelf life. Hydrocolloids control the ice crystal growth during freezing and help lower moisture loss during storage. In the initial stages of baking, viscous batters prevent the coalescence of air bubbles. Inclusion of xanthan in the cake formula helps in achieving a better volume because of higher viscosities in the final stages of baking. Modified starches can also be used as hydrocolloids. Modified or pregelatinized starches swell in the presence of cold water and increase batter viscosity. Modified starches are also used for freeze–thaw stability. A combination of hydrocolloids can be used to achieve the desired viscosities through different stages of cake making. For example, instant starches can be used to develop initial batter viscosity. Guar gum can be used to increase viscosity during baking to hold in CO2 generated during baking.

Chemical Leavening Leavening agents help in aerating the batter by releasing carbon dioxide (eqn [1]). Carbon dioxide (CO2) is generated from the reaction of an acid with a base in the presence of heat and moisture. Chemical leavening plays an important role in achieving the desired cake volume. Leavening agents help improve the eating quality of cake by tenderizing the crumb of the final baked product. Selection of chemical leavening in the formula depends on factors like floor time, baking equipment, desired texture, flour quality, altitude of the bakery, and water hardness. HX

ðacid saltÞ

Neutralizing value of common leavening acids

Chemical name

Abbreviation

NV

Monocalcium phosphate monohydrate Anhydrous monocalcium phosphate Sodium acid pyrophosphate Sodium aluminum sulfate Sodium aluminum phosphate Potassium acid tartrate Dicalcium phosphate dihydrate Glucono-delta-lactone

MCP•H2O ACMP SAPP SAS SALP Cream of tartar DCPD GDL

80 83.5 74 104 100 45 33 45

Source: Pyler, E.J., 1973. Baking Science and Technology. second ed. Siebel Publishing, Chicago, IL

Baking soda is one of the most commonly used base in the food industry. Baking soda can react with buttermilk, sour cream, molasses, acidic fruit juice, or acid-reacting materials like acid salts of tartaric acid and phosphoric acid to generate CO2. Balancing the leavening reaction in the formula is critical because leavening imbalance can cause soapy or metallic aftertaste. Knowing the neutralizing value of the leavening agents helps in designing a balanced leavening reaction. The neutralizing value (NV) is the number of parts of baking soda required to neutralize 100 parts of the leavening acid. Table 1 lists the NV of most commonly used leavening acids. For chocolate cakes, additional baking soda is used to negate the effect of Dutch cocoa. Leavening acids react with baking soda at different temperatures. The activation temperature of the leavening acids used in the formulation determines the rate of reaction (ROR). Grades of sodium acid pyrophosphates (SAPPs) with different reaction rates are commercially available. The most commonly used SAPPs in the industry are SAPP 43, SAPP 40, and SAPP 28. A lower suffix number indicates high temperature of reaction, that is, SAPP 28 reacts at a higher temperature than SAPP 40. A combination of SAPPs is used in cake manufacturing to get continuous leavening throughout the baking cycle. A leavening acid with slower ROR imparts a coarser cell structure to the cake. For example, sodium aluminum phosphate (SALP) reacts at a higher temperature than SAPP. Therefore, cakes made with SALP have a more open cell structure than cakes made with SAPP. Baking powder is a mixture of leavening agents (baking soda and acid salts) and inert ingredients like corn starch that react in the presence of moisture and heat to release CO2. The use of baking powders helps in achieving a balanced leavening system without the use of mathematics. Baking powders have restricted reaction rates; therefore, they are seldom used in commercial cake formulations. Leavening reaction rates can be modified by the use of encapsulated leavening agents. Leavening agents can be encapsulated with fats. The leavening is activated when the coating around it melts. Encapsulation of the leavening system helps protect its reactivity during storage and helps optimum release of CO2 under desired conditions.

Formula Balance

þ NaHCO3 ! ðsodaÞ

Table 1

ðheat and moistureÞ

NaX þ H2 O þ CO2 ðneutral saltþwaterþcarbon dioxideÞ

[1]

Balance of ingredients is critical to achieving desired texture. The amount of sugar influences the starch gelatinization and

WHEAT PROCESSING | Chemistry of Cake Manufacturing Table 2 Typical ratios of bulk ingredients in cake formulation (expressed in baker’s %) Ingredients

Yellow layer cake

Chocolate layer cake

Bleached cake flour Sugar Nonhydrogenated fat Liquid whole eggs Nonfat dry milk Emulsifier Chemical leavening

100 120 16 25 10 7 5

100 170 20 40 20 9 5

baked structure along with the eating characteristics of the baked product. The onset of gelatinization and the peak of gelatinization of starch are delayed with increase in sugar concentration. The amount of liquids and eggs used in the formulation is critical for the volume of cake. The actual amount of the bulk ingredients is dictated by the type of cake: 1. Low-ratio cakes: The amount of sugar in these type of cakes is less than or equal to the amount of flour. Typically, the amount of eggs is equal to the amount of shortening. The eggs give strength to the formula and balance the weakness from the shortening. The amount of liquids can be equal to or greater than the amount of sugar in the formula. 2. High-ratio cakes: The primary characteristic of these cakes is that the amount of sugar is always greater than the amount of flour in the formula. In these cakes, the amount of eggs is higher than the amount of shortening. The extra amount of eggs is needed to strengthen the formula to counterbalance the excess sugar. The amount of liquid is always greater than the amount of sugar in the formula. An example of a typical high ratio cake is shown in Table 2. The formula balance dictates the time and temperature used for baking. Typically, high-ratio cakes are baked at lower temperatures for longer time. In the presence of high amounts of sugar, the onset of starch gelatinization is delayed. Therefore, baking high-ratio cakes faster at higher temperatures can cause baking defects like thick crust, collapsed centers, and dark tops.

Processing Mixing Mixing helps in homogeneously incorporating all the ingredients in the batter. Unlike bread making, minimal gluten development is desired during cake mixing. Mixing helps in hydration of ingredients and in incorporating air in the batter. The stages of mixing depend on the type of cake being produced. A common commercial practice is to preblend all the dry ingredients in the cake formulation to form a cake mix. The sequence of addition of the ingredients can be altered based on the formulation. For instance, plastic shortening or emulsified fats can be creamed with sugar before the addition of other dry ingredients. Ribbon blenders are commonly used for dry mix blending. There are two ways of batter mixing that are currently used in the industry.

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Single-stage mixing In single-stage mixing, all the ingredients are added and mixed together in one stage. Single-stage mixing is common in bakeries with limited floor space. After the addition of all ingredients, different mixing speeds can be used to ensure uniformly mixed batter is achieved. The use of planetary mixers is fairly common in this type of batter mixing. In planetary mixers, the paddle rotates around its own axis and revolves along a central axis. Therefore, planetary mixers have a higher degree of mixing than generic or spiral mixers. Higher mixing speeds (rpm: revolutions per minute) are used to achieve desired air incorporation. Jacketed mixing bowls can be used to control batter temperatures during mixing. Mixing speeds and times can be altered to achieve the desired degree of mixing.

Continuous mixing The equipment needed for this type of mixing includes a slurry mixer, holding tank, and continuous mixer. The slurry mixer is primarily used to mix the dry ingredients and the liquid ingredients together to form the batter. After mixing, the batter is pumped into the holding tank. In most cases, positive displacement pumps are used to transfer batter from the slurry mixer to the holding tank. The holding tank is used to continuously feed batter to the continuous mixer. In the continuous mixer, the batter is aerated under pressure using a revolving rotor. The amount of air whipped into the batter is controlled by the rpm, air pressure, and back pressure. The internal design of a continuous mixer is characterized by the presence of concentric rings with a large number of fine teeth. The process can be controlled by the amount of batter and air that is pumped into the continuous mixer. Continuous mixers can be jacketed to control batter temperature. Batter temperatures may rise during continuous mixing because of the friction generated. The batter from the continuous mixer feeds the depositing hopper. The use of continuous mixers helps in standardizing the cake manufacturing process and controlling the final baked structure.

Pressurized mixers In small- to medium-scale bakeries, the use of pressurized mixers is fairly common. Pressurized mixers use a closed chamber for mixing. The closed chamber keeps the pressure during the mixing process constant and enables good uniform distribution of gas bubbles. The use of pressurized mixers can eliminate the need for continuous mixers. Pressurized mixers can control the temperature of the chamber, the speed of agitation, and mixing time. The constant pressure ensures consistency results across batches. By eliminating the need of continuous mixers, pressurized mixers help on saving floor space in small bakeries.

Batter Properties The specific gravity of batter is the ratio of the weight of a certain volume of batter to the weight of the same volume of water. Specific gravity is an indication of the amount of air whipped into the batter during mixing. Optimum specific gravity plays an important role in achieving desired cake volume and texture. The specific gravity of cake batter is governed by the formula and the mixing process. Some studies have


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shown that the amount of air incorporated in the batter is directly proportional to the volume of cake. The volume of the cake does not depend on the quantity of air incorporated in the batter but on the capacity of the batter to retain the air during the initial stages of baking. The capacity of the batter to retain the air during baking depends on the viscosity of the batter. Batter temperature influences batter viscosity and thus is critical for batter stability. Ideal batter temperature for good quality cakes is 68–72 F or 20–22 C. Leavening performs best in batters with close to neutral pH. Typically, the pH of yellow cake batters is maintained at 6.5–7 for best results. The pH of chocolate cake batters is slightly higher owing to the presence of Dutch cocoa powders. Most chocolate cake batters have the pH of 7–8. The leavening reaction in the batter is activated by the addition of water. Therefore, for best results, batter floor time must be restricted to 20–35 min.

Baking Selection of the right baking time and temperature depends on various factors like formula balance, weight of the batter, size of the pan, atmospheric conditions, and type of oven. Multizone ovens are commonly used in the industry. The type of oven can affect the rate of heat transfer during baking. The rate of heat transfer is critical for starch gelatinization and setting of the cake structure. Tunnel ovens are fairly common in the baking industry. Tunnel ovens can be heated with direct or indirect fire. In tunnel ovens, the product is moved along a horizontal belt. The length of the oven can be divided into zones as shown in Figure 3, like a train with compartments. The temperature and air flow in these zones can be adjusted. The recirculation dampers on the oven can control the overall air flow in the oven. The overall heat flux in the oven can be adjusted by adjusting the zone temperatures and the overall heat flow. There are two types of tunnel ovens: direct fired and indirect fired. In direct fired ovens, the heat source heats the air in the oven directly in the tunnel. In indirect fired ovens, the air is heated in a separate chamber than the oven. The heated air is then transported through the oven tunnel. The air composition in the oven will differ depending on the type of oven used. The air composition can alter the final cake characteristics. In direct fired ovens, the air in the oven will have higher amounts of CO2. Serpentine ovens are gaining popularity in the industry because they have a few advantages over tunnel ovens. In serpentine ovens, the different zones are stacked on top of each other, like a high-rise building. Pans are conveyed through multiple horizontal levels in a distinctive ‘S-shape.’ Serpentine ovens help save floor space by the virtue of their design. The configuration of these types of oven (Figure 4)

Zone 1

Zone 2

Zone 3

helps precise thermal zoning and baking control. Zones may not be characterized by the same number of passes as each other. Therefore, cakes might not spend the same amount of time in each zone. The number of passes that constitutes a zone influences the bake settings for that zone. In most industrial ovens, baking can be controlled by using radiation heat. Baking is the most important step in cake manufacturing. In an oven with four zones, the first zone is where the baking reactions start. Leavening reaction and starch granule swelling are initiated in zone 1. Zones 2 and 3 are the zones in which the structure setting and starch gelatinization processes take place. The last zone or 10% of baking time is where crust color is developed. Thermocouples can be used to measure internal temperatures of the cake during the course of baking. Figure 5 illustrates the different reactions occurring simultaneously during baking. Knowing the heating rate can help synchronize the chemical changes with the internal temperature of the cake. Choosing the right bake settings helps control the quality of the cake. If a slow-reacting leavening system is used, a gradual increase in heating rate is recommended. If the structure of the cake sets before the leavening is exhausted, the cake will have flaws like blisters and tunnels. Very high heat in the last zone can contribute to thick and dark-colored skin on the cakes. The final core temperature is as important as the rate of heating. The final core temperature ensures that the structure of the cake is set. If the baking is stopped before reaching the ideal

Zone 4

Zone 3

Zone 2

Zone 1

Figure 4 Schematic illustration of a serpentine oven.

Moisture loss Leavening reactions

Protein denaturation Starch gelatinization

Zone 4 Maillard reaction

Figure 3 Schematic diagram of a tunnel oven.

Figure 5 Reactions occurring during cake baking.

WHEAT PROCESSING | Chemistry of Cake Manufacturing temperature, the cake can collapse on cooling. Most cake formulations are fully baked when the core temperature is 200–205 F or 93–96 C. Bake times play a significant role in determining the throughput of the process. Baking is the ratelimiting step in cake baking. Zone temperatures, radiation dampers, and air velocity in the oven can be used to optimize bake times. Bakeries that make a variety of baked products might not have ovens designed specifically for cakes. Deck ovens and rack ovens are commonly found in bakeries that make different baked goods. Rack ovens are universal to small-scale bakeries. Rack ovens consist of an oven chamber with a rotating rack. Rack ovens have the flexibility of using steam for baking. Modern-day rack ovens also have computerized programming that allows the operator to use different temperatures at different times during the baking process. Rack ovens are not practical in a continuous process setting. Deck ovens have a chamber with a deck or a floor that is heated. The chamber walls absorb the heat and release it during baking. This gives deck ovens precise temperature control. Deck ovens can be heated by use of different heating mediums like steam, hot oil, or heated air. Deck ovens are not commonly used in cake baking due to the lack of flexibility in temperature settings. For best results, cakes should be cooled at a controlled rate. In an industrial setup, an oven is followed by a cooling tunnel. In the cooling tunnel, cool air is blown over the cakes. The cooling time in the process is tied in with the bake time of the cake. Cakes can be cooled statically. But static cooling can be slower and uncontrolled. The ideal temperature after cooling depends on the next step in the process. If the cakes are packed in boxes after cooling, it is recommended to cool cakes to around 80 F or 27 C. Commercial cakes can also be frozen before distribution. Frozen distribution helps in maintaining freshness of cakes for an extended time (up to 6 months). Cakes can be frozen after packaging them in boxes. Spiral freezers or nitrogen tunnels are used for quick and efficient freezing. In spiral freezers, very cold air (40 C) is blown over the product as it moves along a spiral belt in an enclosed chamber. In nitrogen freezers, the product travels on a perforated belt in a tunnel and is cooled by liquid and vaporized nitrogen.

Quality Checks

High-altitude baking

• • •

The change in atmospheric pressure above 3000 ft above sea level can interfere with baking. At higher altitude, the drop in atmospheric pressure causes water to boil at lower temperature. As a result of which, the chemical changes during baking are accelerated. Adjustments in formulation and processing can help in achieving better results at higher altitudes. The formulation can be strengthened by increasing the amount of flour and/or eggs. The total amount of liquids in the formula has to be increased to offset the increased amount of flour and eggs. Sugar delays the onset of gelatinization; therefore, it is recommended to decrease the amount of sugar. The chemical leavening is reduced to adjust for the increase in altitude. Less air is whipped into the batter to compensate for the boiling of water at lower temperature. The oven temperatures are increased to synchronize with the quickened chemical reactions.

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Quality checks are used throughout the cake manufacturing process to ensure consistent quality products. It is a good practice to review COAs (certificate of analyses) for the incoming ingredients. Specific gravity and temperature of the batter are important in-process checks. Recording the final core temperature helps ensure optimum bake. Bake loss is calculated as the difference in batter weight and bake of the cake. Moisture content of the cake helps assess the eating quality of the cake. pH of the cake helps to confirm that there is no residual leavening in the cake. pH values in the range of 7–8 are the ideal for cakes postbaking. Height and contour of the cake are also measured. Quality defects in cakes can be related to formula imbalance, improper bake, and mixing settings. Table 2 illustrates the typical ratios of bulk ingredients in cake formulations. The ratios of ingredients for chocolate cake are different than yellow cake. The amount of sugar is increased to balance the presence of Dutch cocoa in the formulations. The amount of eggs and milk proteins is increased to strengthen the structure that is weakened by increased sugar. When troubleshooting to eliminate cake defects, it is best to adopt a systematic approach. For example, when addressing low heights on cakes, here are things that can be looked into: (a) Flour quality – Flour with protein levels higher than 9% can restrict cake heights. The use of unbleached flour can also lead to lower heights on cakes (as shown in Figure 1). (b) Chemical leavening – If the chemical leavening in the formulation is unbalanced, it will not generate enough CO2. Lower amounts of CO2 generation can limit cake heights achieved. (c) Specific gravity – The amount of air whipped into the batter positively helps cake heights. Cake heights can be improved by lowering the specific gravity of the batter. (d) Oven settings – Bake time and temperature can influence cake heights. Lower cake heights could be a result of low temperature and short bake times. Good understanding of the formula and process can help address cake defects.


• • • •

Why is chlorinated flour preferred for cake production? How is the specific gravity of the batter calculated? Red velvet cakes are made using cocoa and buttermilk. When making a red velvet cake, will the buttermilk in the formulation react with baking soda? What formulation changes are required to make a good quality cake at 2000 ft above sea level? What is the ideal final core temperature of a cake postbaking? What type of cake is an angel food cake? What is the pH of chocolate cake batter? Why is it different than yellow cake batter?

Exercises for Readers to Explore the Topic Further As consumer awareness increases, so does the demand for clean label or natural products. Clean label or natural products

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have different interpretations in different countries or regions. Clean label products use ingredients commonly used in home baking, with no or minimal use of chemical ingredients. Think about how you can formulate clean label cakes. What flour/starch combination will be ideal for gluten-free cakes?

See also: Carbohydrates: Starch: Chemistry; Starch: Starch Architecture and Structure; Fats: Lipid Chemistry; Wheat Processing: Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Oven Technologies; Wheat: Dry Milling.

Further Reading AACC International (1999) Approved Methods of Analysis, eleventh ed. Saint Paul, MN: AACC International. Buck J and Walker C (1988) Sugar and sucrose ester effects on maize and wheat starch gelatinization patterns by differential scanning calorimeter. Starch-Starke 40: 353–356. Choi H and Baik B (2013) Significance of wheat flour particle size on sponge cake baking quality. Cereal Chem. 90: 150–156. Gaines C and Donelson J (1985) Influence of certain flour quality parameters and post milling treatments on size of angel food and high ratio white cake layers. Cereal Chem. 62: 60–63.

Gomez M, Ronda F, Cabellaro P, Blanco C, and Rosell C (2007) Functionality of different hydrocolloids on the quality and shelf life of yellow layer cakes. Food Hydrocoll. 21: 167–173. Gujral H, Rosell C, Sharma S, and Singh S (2003) Effect of sodium lauryl sulphate on the texture of sponge cake. Food Sci. Technol. Int. 9: 89–93. Kulp K and Tsen C (1972) Effect of chlorine on the starch component of soft wheat flour. Cereal Chem. 49: 194–200. Kweon M, Slade L, Levine H, Martin R, Andrews L, and Souze E (2009) Effects of extent of chlorination, extraction rate, and particle size reduction on flour and gluten functionality explored by solvent retention capacity (SRC) and Mixograph. Cereal Chem. 86: 221–224. Lin S and Lee C (2005) Qualities of chiffon cake prepared with indigestible dextrin and sucralose as replacement for sucrose. Cereal Chem. 82: 405–413. Miller R and Hoseney C (1993) The role of xanthan gum in white cake layer. Cereal Chem. 70: 585–588. Moiraghi M, de la Hers E, Perez G, and Gomez M (2013) Effect of wheat flour characteristics on sponge cake quality. J. Food Agric. 93: 542–549. Pyler EJ (1973) Baking Science and Technology, second ed. Chicago, IL: Siebel Publishing. Seguchi M and Matsuki J (1977) Studies of pan-cake baking. I. Effect of chlorination of flour on pan-cake qualities. Cereal Chem. 54: 287–299. Sung M, Park Y, and Chang H (2006) Quality characteristics of sponge cake supplements with soy protein concentrate. Food Sci. Biotechnol. 15: 860–865. Tsen C and Kulp K (1971) Effects of chlorine on flour proteins, dough properties and cake quality. Cereal Chem. 48: 247–255. Wootton J, Howard N, Martin J, McOsker D, and Holme J (1967) The role of emulsifiers in the incorporation of air into layer cake batter systems. Cereal Chem. 44: 333–343.

The Gluten Proteins of the Wheat Grain in Relation to Flour Quality F Be´ke´s, FBFD PTY LTD, Beecroft, NSW, Australia MC Gianibelli (Retired) CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

The wheat protein complex known as gluten can readily be prepared by water washing of a piece of dough. Gliadin and glutenin, the subfractions of gluten, are highly heterogeneous. The gliadin polypeptides (coded by the Gli-1 and Gli-2 loci) are of modest size, under 100 000 Da. Glutenin is composed of disulfide-linked polypeptides (subunits) with molecular weights ranging up to tens of millions of Daltons. The gliadin and glutenin proteins complement one another to provide dough with extensibility and strength (resistance to extension). Rupture of the disulfide bonds of glutenin releases its many polypeptides (subunits), which are coded by the Glu-1 and Glu-3 loci. Knowledge of the glutenin-subunit composition (allelic constitution) of a wheat variety can be used to predict its dough-quality potential.

Learning Objective

•

To achieve an understanding of the proteins of wheat flour as they affect flour quality in its many uses, mainly its dough-forming properties.

Introduction Of all the grain species, wheat is unique as it is the only grain that has the protein complex called ‘gluten’ that can be formed into a dough with the rheological properties required for the production of leavened bread. These gluten proteins are the basis of man’s attraction to wheat; it is the reason for the annual cultivation of enormous numbers (about 1014) of wheat plants, because wheat gluten alone can sustain the human desire for leavened bread products. The rheological properties of gluten are needed not only for bread production but also in the wider range of foods that can only be made from wheat, namely, noodles, pasta, pocket breads, pastries, cookies, and other products (Table 1). The unique properties of the gluten-producing storage proteins are formed in the white floury endosperm during grain development. Because of these unique dough-forming properties, wheat is the most important source of protein in the human diet. Of the many species of the wheat genus (Triticum), there are only two major species that are grown around the world. The more popular of these two is T. aestivum, called ‘bread or common wheat.’ The other is durum wheat (T. durum), which is particularly suited to the production of pasta foods. Both bread and durum wheats are polyploid species


containing three (AABBDD) and two (AABB) related genomes, respectively. Many of their genes for protein synthesis are located on the group 1 and 6 chromosomes of these genomes, as illustrated in Figure 1 and Table 2. However, these locations are not the only ones; in the past, gene locations on some other chromosomes (e.g., 7A) have been reported, and new locations continue to be found as a result of more intensive exploration.

Historical Perspective Although the term ‘protein,’ meaning primary substance, has been in use since about 1838, the terms ‘gluten,’ ‘gliadin,’ and ‘albumin’ have even earlier origins. Gluten was one of the first few proteins to be studied, because it can be prepared so readily (by water washing of dough) as a reasonably pure protein. This gluten-washing procedure has since become a very big business internationally. This process has even been used as a rapid analytic method for determining the protein content of flour or wheat meal samples. The importance of the proteins of flour for bread making has long been known. It is illustrated in a classic graph (Figure 2), published in 1948, relating variations in bread loaf volume to the protein content of different flour samples. The graph shows that baking quality increases with protein content for the same variety (thus illustrating the improving effect of protein quantity) and that for better varieties, increases in protein content produce greater increases (steeper slopes) in baking quality, showing the effect of protein quality (meaning ‘better loaf volume at the same protein content’). Because of the importance of gluten, much of the variation in quality between wheat samples can be explained in terms of the gluten component – its quantity and quality. Total protein content (Table 1) is generally taken as an indication of gluten quantity, although about one-fifth of the grain protein is nongluten, including the range of enzymes and structural proteins.

Prepare Your Own Gluten The historical importance of gluten in protein chemistry is due to the ease with which it can be prepared. It is a simple experiment to be performed at the kitchen sink. Mix some wheat flour with water, adding the water a little at a time, until a stiff dough is formed. Take the dough in the fingers and knead it under a gentle stream of water from the tap, placing a glass under the tap to catch the wash water. After the starch has washed out, to form a white sediment at the bottom of the glass, a ball of gluten is left between the fingers. It may feel like a piece of chewing gum, with stronger elastic properties than the original dough, due to the removal of the starch.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00164-9

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376 Table 1

WHEAT PROCESSING | The Gluten Proteins of the Wheat Grain in Relation to Flour Quality Quality attributes preferred in wheats for specific products

Product

Protein content (%)

Grain hardness

Dough strength

Pan/sandwich breads Flat/Arabic breads Steamed bread, Northern China Steamed bread, Southern China Alkaline noodles White/udon noodles Instant noodles Biscuits/cookies/grocery Starch/gluten manufacture

>13 11–13 11–13 10–12 11–13 10–12 11–12 8–10 >13

Hard Hard Hard Soft/medium Hard Medium/soft Medium Very soft Hard (soft preferred)

Strong Medium Medium/strong Medium Medium Medium Medium Weak Strong

Adapted from Wrigley, 1994. Developing better strategies to improve grain quality for wheat. Aust. J. Agric. Res. 45, 1–17.

L IA

Glu-A1

Tri-A1 Gli-A3

Glu-A3 Gli-A1

Glu-B1

Tri-B1 Gli-B3

Glu-B3 Gli-B1

L IB L ID

6A 6B 6D

Glu-D1

Tri-D1

Glu-D3 Gli-D1

L L L Gli-2

Figure 1 Locations of the main genes for the synthesis of wheat flour storage proteins. The long arm of each chromosome (indicated ‘L’) extends to the left, containing only the Glu-1 loci to the left of the centromere (indicated by a circle). See Table 2 for identities of most genes. Gene locations for the triticin proteins are indicated by the Tri-1 loci. Adapted from Gianibelli, M.C., Larroque, O.R., MacRitchie, F., Wrigley, C.W., 2001. Biochemical, genetic and molecular characterization of wheat glutenin and its component subunits. Cereal Chem. 78, 635–646. Table 2

Gluten–protein classification, based on chromosomal locations of the genes and on disulfide-bond formation

Class

Gene locus

Chromosomal location of genes

Form of disulfide bonding

o-Gliadins a-, b-Gliadins g-Gliadins LMW subunits of glutenin HMW subunits of glutenin

Gli-1 Gli-2 Gli-1 Glu-3 Glu-1

Short arms of group 1 chromosomes Short arms of group 6 chromosomes Short arms of group 1 chromosomes Short arms of group 1 chromosomes Long arms of group 1 chromosomes

No SS bonds Intrachain SS bonds Intrachain SS bonds Interchain and intrachain SS bonds Interchain and intrachain SS bonds

Wheat flour generally has 9–13% protein, while the remainder is mainly starch, plus 1–2% lipid and some nonstarch polysaccharides. Flour, as milled, also contains about 14% moisture. About 20% of the protein in flour is watersoluble albumins and globulins; about 80% is gluten-forming proteins of which half is gliadin-type proteins and half is glutenin (Figure 3).

Why Is Protein Important? The protein content and type are critical to the diversity of wheat-based foods listed in Table 1. For each of these groups of products, there is a recommended combination of protein

content, grain hardness (largely determined by protein composition), and dough properties (a function of the gluten–protein composition). Other factors come into play, particularly good milling quality and suitable starch properties. Of greatest importance is the gluten–protein component of the grain. On the one hand, it is important to the ongoing life of the wheat plant, because the gluten-forming proteins of the grain play their critical role in nature as a reserve of amino acids and nitrogen for the embryo upon germination. On the other hand, the gluten–protein component of the grain is imperative for the wheat industry because of its importance in determining processing quality. Consideration of Table 1 indicates why wheat is segregated according to protein content after harvest and in international

WHEAT PROCESSING | The Gluten Proteins of the Wheat Grain in Relation to Flour Quality trade. More marketable parcels of grain can be obtained, appropriate to the processing needs of specific customers, if they suit relevant combinations of the attributes listed in Table 1. The other major factor used in segregation of wheat is variety; this factor takes into account genetic aspects of

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protein quality, especially grain hardness and dough properties. The genetic constitution of wheat is important because all quality traits result from the expression of genes and their interaction with the environment.

Why Are Growth Conditions Important? H.R.S. 1400

Because protein content and composition are modified by growth conditions, processing quality may not be entirely predictable, even if we know the variety and thus its genetic potential for processing into a specific type of product. The task of selecting wheat for optimum market value and processing quality is thus difficult. Nevertheless, we are learning much about what are significant aspects of protein composition and how these might be modified by growth conditions. Growth environment is thus the ‘wild card’ of uncertainty in using the combination of variety and protein content to select suitable wheat consignments. On occasions, for example, weaker dough properties may be obtained that are not those that would be expected from a particular protein-variety combination, leaving researchers with the job of working out the reason why. One climatic factor implicated is the effect of high temperatures (over 35 C) during the ripening of the grain. These hot conditions may cause a redirection in starch synthesis, thus increasing protein content. However, protein synthesis is also altered so that the dough-forming quality of the protein is less, thereby causing weaker dough properties. Sulfur deficiency may be another environmental reason for variations in protein quality, particularly when nitrogen fertilizer is applied without sulfur. In fact, changes in dough properties have been observed for low-sulfur grain, accompanied by a decreased presence of the sulfur-rich proteins of gluten (Figure 4). Such occasional phenomena show that our ‘tried-and-tested’ systems of selecting for grain quality still have some deficiencies to be rectified, possibly by screening harvest samples for protein quality and for protein content.

Nebred Regent Pilot Thatcher Rival Marquis

H.R.W.

Loaf volume (cm3)

1200 Merit Premier Progress Chiefkan

1000

800

600

10

13

16

19

Flour protein (%) Figure 2 Demonstration of the distinction between protein quantity and protein quality. Reproduced with permission from Finney, K.F., Barmore, M.A., 1948. Loaf volume and protein content of hard winter and spring wheats. Cereal Chem. 25, 291–312.

Glu1

Gli1

1A 1B 1D

Genes

Polypeptides

Glu3

HMW-GS 10%

LMW-GS 30%

Gli2 6A 6B 6D

Gliadins 60%

Effect of... Individual polypeptides HMW/LMW ratio Gliadin fractions

Proteins

Starch

Glutenin polymers Solubles

Gliadin monomers Gluten

FLOUR

Glu/Gli ratio

Lipids Protein content

Functional properties Figure 3 Relationships between the individual components of flour, especially gliadin and glutenin, the gluten-forming protein.

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WHEAT PROCESSING | The Gluten Proteins of the Wheat Grain in Relation to Flour Quality

Glu alleles Gli alleles

HMW:LMW glutenin subunits

Low-S:High-S gliadin proteins

Glutenin polymer size

Gliadin:Glutenin ratio Gluten content Amino-acid composition Amide content Total-nitrogen content Figure 4 The degrees of formation (down to ‘gluten content’) and disruption of gluten, illustrating the levels at which studies may be conducted on gluten–protein structure and function.

Wheat Protein as Total Nitrogen Content ‘Wheat protein’ to many in the trade (the agronomist, the grainelevator operator, the grain salesman, and the miller) means no more than a single number, the result of analysis of total nitrogen content. The digestion step in nitrogen analysis (lower half of Figure 4) generally involves (1) the use of an oxidizing acid to transform all nitrogen-containing compounds (mainly protein) to ammonia for subsequent quantitation by titration in the Kjeldahl method or (2) pyrolysis of nitrogen-containing compounds to nitrogen gas in the Dumas method. Currently, near-infrared spectroscopy is routinely used to determine grain protein content, especially as a basis for segregation of wheat at the silo or elevator. This can be applied either to milled grain, as near-infrared reflectance (NIR), or to whole grain, as near-infrared transmission (NIT). This ‘instant’ method involves scanning the sample in the infrared part of the spectrum, determining absorbance at certain wavelengths, and computing protein content by comparison with a pretested set of calibration samples. The method is therefore comparative, and it still relies on the basic reference methods for determining total nitrogen content. It is feasible to use nitrogen content as a quantitative indicator of protein content since other nitrogen-containing compounds represent very minor components of the wheat grain. The factor 5.7 is generally used to convert the result of nitrogen analysis to protein content; this factor is much lower than the normal factor of 6.25 for other protein sources. The lower factor for wheat grain reflects the elevated level in gluten of nitrogen-rich amino acids, such as glutamine.

Determination of Protein Quality versus Quantity The concept of characterizing protein by protein content alone indicates loss of important information about protein

composition. All such information is lost in direct (Kjeldahl and Dumas) analysis of total nitrogen content or in correlative methods (NIR and NIT) based on them. If amino acid composition is known in addition to protein content, valuable additional information is provided about essential amino acid levels, important in nutrition (Figure 4). However, even the analysis of amino acid composition destroys information about the amino acid sequences of proteins, and these are essential to an ultimate understanding of protein quality. Likewise, there is significant loss of information about protein–protein interactions as a result of extracting protein into dilute solution from flour or dough, especially if, in doing so, we have broken disulfide bonds. Most methods of analyzing protein structure and composition involve extraction, but we need to remember that the resulting picture may still be different from what actually occurs in the water-poor medium of dough, where interactions with other groups of compounds (lipids and carbohydrates) are likely to assume greater importance. In addition to information about protein content, the feed formulator needs to know about amino acid composition, particularly the content of essential amino acids. The general deficiency in the amino acid lysine limits the nutritional value of wheat in feed for animals and in food for humans if protein is restricted in the diet. Knowledge about the content and sequence of amino acids in the many proteins of the wheat grain is fundamental to our understanding of their functional properties. This information has been accumulating over many years, but recent advances in molecular biology are providing this information at an increasing rate as nucleotide sequences are being provided, from which amino acid sequences can be derived for the corresponding proteins.

The Diversity of Structure and Function of Wheat Proteins Modern methods of protein fractionation have indicated that the protein of the wheat grain is made up of thousands of distinct protein species – these are needed to catalyze and regulate the synthetic processes of making a wheat grain, the host of enzymes needed in the germ, the scutellum and the endosperm to carry the process of life on into a new plant, and the reserve proteins stored away in the embryo and the endosperm to provide the building blocks for this ongoing process. This storage protein, that becomes gluten with water, is the plant’s contribution to making another plant, even though for man, it is essential for bread making. The structural requirements of a protein to meet these natural and industrial functions are similar in a key area, that is, solubility. Both functions require a protein of low aqueous solubility, first, so that these nutrients are not washed away from the imbibing seed and, second, for bread making so that the protein network of dough is not highly soluble. The nutritional need of the embryo is met by having storage proteins of low solubility, due to the high level of glutamine residues, together with the consequent efficient storage of nitrogen (two N atoms in the amino acid glutamine). The hydrolytic enzymes (particularly those with amylase and protease activities) that appear on germination are essential contributors to the ongoing plant-to-plant process, but


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they interfere with man’s plans for bread making. Wheat breeders have sought means of reducing or delaying their production prior to the induction of the germination process, but there is the dilemma in this task of meeting the needs of both farmer and baker. Wheat grains that produce amylases and proteases before germination are described as pregerminated.

Diversity, Even for Storage of Proteins Given the apparently simple requirements of a storage protein, it may thus have seemed reasonable at the dawn of cereal chemistry for cereal chemists to think of gluten as one protein or even of gliadin and glutenin as single, homogeneous entities. We now know that both the gliadin and glutenin proteins consist of many different proteins (polypeptides), each polypeptide being synthesized under the control of the appropriate gene. As the first products of gene expression, proteins are synthesized more faithfully, with less influence from environmental factors than other groups of compounds that are synthesized subsequently under the influence of enzymes. The DNA of genes in the nucleus is transcribed to produce messenger RNA, which in turn is the basis for translation to produce the newly synthesized polypeptide in the ribosome, with transfer RNA presenting the appropriate amino acids in the prescribed sequence as the polymer chain grows. The high degree of fidelity to genotype suits proteins well to the task of variety identification, the most common laboratory method for which is the analysis of protein composition by gel electrophoresis or high-performance liquid chromatography.

The Gliadin Proteins The gliadin proteins are used routinely for the identification of wheat varieties. Figure 5 shows the results of cathodic gel electrophoresis of gliadin proteins, which are readily extracted from flour with 6% urea solution or even with ethylene glycol (antifreeze). The water-soluble albumins and globulins are also extracted with the gliadins, but they migrate ahead of the gliadins under the electrophoresis conditions used, and they have been lost from the lower end of the gel. The genes controlling the synthesis of the gliadin proteins are located on the short arms of chromosomes 1A, 1B, 1D, 6A, 6B, and 6D (Figures 1 and 3 and Table 2). At each of these six genetic loci, there is a group of genes responsible for a part of the spectrum of gliadin proteins. The loci (plural of locus) are indicated (in italics) by combining the chromosome number with the locus designation. Thus, Gli-A1 refers to the genes for gliadins on the short arm of chromosome 1A. It is possible to separate out the gliadins associated with the each locus. This is demonstrated in Figure 6, with the respective ‘blocks’ (alleles) of gliadins drawn in separate columns beside the photograph of the original electrophoresis gel. The whole picture of all the gliadins in this case is obtained by superimposing all the drawn blocks of bands on top of one another. The whole composition of the gliadins can be designated by allocating lowercase letters in italics (a, b, c, . . .) to each of the blocks (also called ‘alleles’) associated with each of

Figure 5 Gliadin proteins, fractionated by gel electrophoresis at pH 3 by the method used for routine variety identification in a precast polyacrylamide gel. Gliadin proteins, extracted into solution from flour samples, have been applied at the top of each vertical lane, and the respective protein zones have moved down the gel, under the electric field, until the current was stopped. The protein zones (horizontal bars) have been revealed in the gel with a stain. The 11 lanes on the left were all obtained from different samples of the Canadian variety Marquis, the remaining three lanes (at right) are samples of the variety Chinese Spring. The diversity of gliadin patterns for Marquis is unusual, presumably reflecting the age of this traditional variety, with such polymorphism arising from original heterogeneity, plus admixture and mislabeling over many years.

these six genetic loci. Thus, individual alleles are indicated as Gli-A1a, Gli-A1b, etc. A catalog of gliadin alleles for thousands of wheat worldwide is provided on the website of AACC International at http://www.aaccnet.org/initiatives/definitions/ Pages/glutendatabase.aspx. The gliadin proteins contribute to the viscosity and extensibility of dough, due to their modest molecular size range (under 100 000 Da). The omega-gliadins are the largest in this molecular size range; they lack sulfur-containing amino acids (particularly cysteine), so that there is no possibility of covalent bonding between the omega-gliadins via disulfide links (Figures 3 and 4 and Table 2). Although the other groups of gliadins (the a-, b-, and g-gliadins) have sulfhydryl groups, the disulfide cross-links are mainly intrachain, with no significant disulfide bonding between the gliadin polypeptides, so that they are monomeric (single polypeptide chains (Figure 3)).

The Glutenin Proteins: Polymers of Polypeptides The lack of interchain disulfide cross-links for the gliadins distinguishes them from the glutenin polypeptides, which are extensively cross-linked to form polymers of glutenin subunits with molecular weights well over 105–107 Da (Figure 3). Native glutenin, with disulfide bonds intact, contributes the resistance to the extension of dough, due to the sizes of these long polymers. They are depicted in Figure 7 as strings of

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Figure 6 Gliadin proteins, fractionated by gel electrophoresis at pH 3 by a research method (photo of two lanes at left) from two biotypes of the Australian variety Suneca. The diagrams of block patterns to the right of the photo show the groups of gliadin proteins that are controlled by sets of genes on chromosomes (left to right) 1A, 1B, 1D, 6A, 6B, and 6D. The pair of blocks at the extreme right shows that the difference between the two biotypes arises with genes on chromosome 6D. Illustration provided by Dr. E. Metakovsky.

glutenin polypeptides (appearing as coils) joined by disulfide bonds. These large glutenin molecules are balanced by the smaller gliadin proteins in providing the appropriate molecular combination for dough quality and good baking properties (Figure 8). Thus, the ratio of glutenin to gliadin is a major determinant of protein quality. In addition, the size distribution of glutenin polymers is significant. Excessive dough strength and a long mixing time are associated with a high proportion of very large glutenin polymers. On the other hand, a lower size distribution provides a weaker dough, which is preferable for biscuit/cookie manufacture (Table 1). The size distribution of the glutenin polymers appears to be partly determined by the composition of the glutenin subunits that form the polymeric structure. These subunit polypeptides are characterized by extracting them from flour in the presence of a reagent that breaks disulfide bonds, plus the detergent sodium dodecyl sulfate (SDS), followed by SDS gel electrophoresis (Figure 9). The high-molecular-weight (HMW) subunits appear at the top of the electrophoretic pattern (bracketed in Figure 9), whereas the low-molecular-weight (LMW) subunits appear further down the gel pattern, mixed with gliadin polypeptides. The genes for the synthesis of the HMW subunits are located at the Glu-1 loci on the long arms of the group 1 chromosomes (Figures 1 and 3 and Tables 2 and 3). These HMW subunits have been numbered 1, 2, 2*, 3, etc., down the SDS gel pattern. They often appear in pairs (e.g., 2 with 12, 5 with 10, and 17 with 18) because their synthesis is controlled together in these pairs by genes at the Glu-1 loci. For example, the Glu-D1 locus may have either the Glu-D1d allele, corresponding to the subunit 5 þ 10 combination, or the Glu-D1a allele, corresponding to subunits 2 þ 12 (Table 3). The LMW subunits of glutenin have a designation system similar to that used for the gliadin polypeptides. The LMW subunits are not numbered (as for the HMW subunits);

Starch granule Lipid

Gas bubble

Glutenin

S-S bond Gliadin

Figure 7 Diagrammatic representation of the molecules involved in dough formation (not to scale). The surfaces of two starch granules appear with some lipid coating. Gliadin molecules appear as single-chain molecules, contrasting with the polymers of glutenin, made up of subunits joined by disulfide bonds, either long or short coils (HMW or LMW subunits, respectively). Also present are gas bubbles and lipids between the starch granules. Reproduced with permission from Wrigley, C.W., 1996. Giant proteins with flour power. Nature 381, 738–739.


Gliadin.······.balances···.···Glutenin

Table 3 The Glu-1 scoring system (Payne score) to predict dough strength, based on the composition of HMW subunits of glutenin in a flour or grain sample Glu-A1 Score

Gli genes

Glu genes

Gluten Figure 8 Gliadin (upper left, coded by Gli genes) fractionated from gluten (lower center) contrasts with glutenin (upper right, coded by Glu genes) also fractionated from gluten. These two major components of gluten balance one another, gliadin largely providing extensibility or ‘slip’ and glutenin conferring resistance to extension.

SDS PAGE of flour proteins (reduced)

HMW subunits of glutenin

Below, LMW subunits mixed with gliadins

Figure 9 Polypeptides of flour, extracted from six varieties of wheat in the presence of the detergent sodium dodecyl sulfate (SDS) after breaking disulfide bonds, followed by SDS gel electrophoresis. The HMW subunits of glutenin are bracketed at the top of the pattern. Adapted from Wrigley, C.W., Autran, J.C., Bushuk, W., 1982. Identification of cereal varieties by gel electrophoresis of the grain proteins. Adv. Cereal Sci. Technol. 5, 211–259.

instead, the alleles for each locus are indicated by lowercase letters in italics (a, b, c, . . .) associated with each of the three genetic loci for the LMW subunits. Thus, individual alleles are indicated as Glu-A3a, Glu-A3b, etc. A catalog of the alleles for both HMW and LMW subunits for thousands of wheat worldwide is provided on the website of AACC International at http://www.aaccnet.org/initiatives/definitions/Pages/glutendatabase.aspx. The HMW subunits of glutenin are more effective than the LMW subunits in contributing to the functional properties of glutenin, even though the LMW subunits are present at about

381

4 3 3 3 2 2 1 1 1

Glu-B1

Glu-D1

Allele

Subunit

Allele

Subunit

a b

1 2*

i b f c

17 þ 18 7þ8 13 þ 16 7þ9

a d e

7 6þ8 20

c

Null

Allele

Subunit

d

5 þ 10

a b c

2 þ 12 3 þ 12 4 þ 12

A score of 1, 2, 3, or 4 is allocated to each set of subunits for each locus (Glu-A1, Glu-B1, or Glu-D1), and these scores are summed to give a total score out of 10. A high score indicates a prediction of strong dough properties. This system is being used to help wheat breeders to select parents and progeny of suitable dough quality.

three times the level of the HMW subunits. Even within each of these subclasses of subunits, some are more effective than others. In particular, within the HMW subunits, polypeptides such as those numbered 5 and 10 (the d allele, coded by the Glu-D1 locus) are more effective than the allelic subunits 2 and 12 (the a allele, designated Glu-D1a; Table 3). It has thus been possible to produce a Glu-1 scoring system (Table 3) by which to predict the dough properties of a specific flour or grain sample, depending on the composition of the HMW subunits. This scoring system has proved valuable for breeders, who can use the system to predict quality by analyzing the protein composition of individual seeds, thus avoiding the much greater task of producing large grain quantities for milling and dough testing. Since the significant success of using the Glu-1 score in breeding programs by applying the HMWglutenin composition as protein markers for dough properties, there have several attempts additionally to involve the LMWglutenin alleles in similar mathematical formulas. By the application of sophisticated statistical approaches, these new methods are able to describe the effects of both HMW and LMW GS alleles on dough strength and extensibility, individually and via the pair-wise interactions among the alleles. One of the most important conceptual findings of evaluating such models is the realization that – because of the large contribution of allele–allele interactions – the different allelic combinations, rather than the individual glutenin alleles, should be targeted in breeding situations to develop new lines with certain quality attributes. The catalog on the AACC International website also provides the means to estimate the genetic potential of dough properties for the many varieties listed, based on their glutenin alleles. The combination of both HMW and LMW subunits is used to predict the dough strength (as Rmax) and extensibility (both based on dough testing with the Extensograph). Nevertheless, the prediction based on glutenin-subunit composition at best indicates genetic potential, not taking into account the effects of growth conditions on dough quality. The glutenin score is often used in the early stages of a breeding program, when there are thousands of lines to be screened, but

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small-scale milling and dough testing are used to determine protein quality in the later stages when the range of promising lines has been greatly reduced.

•

Future Prospects

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Considerable research attention has been focussed on the study of wheat gluten proteins in recent decades, resulting in large numbers of research papers, review articles, and books on the general subject. A major impediment to research progress has been the difficulty in extracting the very large glutenin polymers into solution to permit more detailed study by current biochemical methods. In fact, the act of extraction into solution risks damaging the information that is being sought. Possibly, the future will provide novel methodology for the study of these unique proteins. The application of the proteome approach has offered a fresh new look to the problems of gluten functionality at the polypeptide level, opening the opportunity of identifying proteins that might not have been previously taken into account as wheat-quality modifiers during protein synthesis and processing in the immature endosperm. This approach offers better opportunities than before for the integration of DNA with protein studies and thus for renewed approaches to the genetic improvement of wheat quality, including a better understanding of the complex interactions of gene expression with growth conditions.


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Contrast the meanings of protein quantity and protein quality with respect to dough quality for wheat. Contrast the different roles of the gliadin and glutenin proteins with respect to dough properties. Describe how some aspects of growth environment might alter the genetic potential of a specific wheat variety, considering protein quantity and protein quality. Environmental factors might include climate and fertilizer (especially nitrogen and sulfur). Explain how a wheat breeder can take advantage of our current knowledge of gluten genes to provide new varieties with targeted dough qualities.


• •

•

Speculate on why the HMW subunits of glutenin make a greater contribution to dough quality than the LMW subunits, even though the latter are present in greater amounts. Speculate on why certain subunits (HMW or LMW) make greater contributions. Consider the importance of disulfide bonds (number and positions) in contributing to the sizes of glutenin polymers. Select some wheat varieties grown in your region and search for their gluten alleles (and predicted quality) on the AACC International website. How do these predictions compare with local reputations for these varieties?

We presume that the gluten-forming proteins merely serve a storage function in the grain. Speculate on why their properties also suit our need for bread making. If merely for storage, why are the gluten-forming proteins produced under such tight and predictable genetic control? A lecturer asked the class to estimate the gluten content of a specific wheat sample. No one got the right answer. The answer required was ‘zero.’ Why?

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Marketing and Grading: Identification of Varieties of Food Grains; Wheat: Grading and Segregation; Proteins: Nitrogen Metabolism; Protein Synthesis and Deposition; Proteomic Analysis Relevant to Cereal Grains; The Protein Chemistry of Cereal Grains; The Protein Chemistry of Dicotyledonous Grains; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Cereal Food Production with Low Salt; Gluten and Modified Gluten.

Further Reading Bailey CH (1925) The Chemistry of Wheat Flour. New York: The Chemical Catalog Co. Bailey CH (1941) A translation of Beccari’s lecture ‘concerning grain’ (1728). Cereal Chem. 18: 555–561. Bailey CH (1944) The Constituents of Wheat and Wheat Products. New York: Reinhold Publishing Corporation. Bushuk W and Wrigley CW (1974) Proteins: composition, structure and function. In: Inglett GE (ed.) Wheat: Production and Utilization, pp. 119–145. Westport, CT: AVI Publishing. Juhasz, A., Bekes, F., Wrigley, C.W., 2014. Wheat proteins. In: Ustunol, Z. (Ed.) Applied Food Protein Chemistry, pp. 219–304. Wiley-Blackwell. Kasarda DD (1989) Glutenin structure in relation to wheat quality. In: Pomeranz Y (ed.) Wheat Is Unique, pp. 277–302. St. Paul, MN: American Association of Cereal Chemists. Kasarda DD, Bernardin JE, and Nimmo CC (1976) Wheat proteins. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 1, pp. 158–236. St. Paul, MN: American Association of Cereal Chemists. McRitchie F (1999) Wheat proteins: characterization and role in flour functionality. Cereal Foods World 44: 188–193. Osborne TB (1907) The Proteins of the Wheat-Kernel. Washington, DC: Carnegie Institution Publication 84. Shewry PR and Miflin BO (1985) Seed storage proteins. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 7, pp. 1–83. St. Paul, MN: American Association of Cereal Chemists. Shewry PR, Ovidio R, Lafiandra D, Jenkins JA, Mills ENC, and Be´ke´s F (2009) Wheat grain proteins. In: Khan K and Shewry PR (eds.) Wheat Chemistry and Technology, fourth ed., pp. 223–298. St Paul, MN: AACC Press. Wrigley CW and Bietz JA (1988) Proteins and amino acids. third ed., In: Pomeranz Y (ed.) Wheat: Chemistry and Technology, third ed., vol. 1: pp. 159–275. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW, Bekes F, and Bushuk W (eds.) (2006) Gliadin and Glutenin: The Unique Balance of Wheat Quality. St Paul, MN, USA: AACC International Press. General Reading Be´ke´s F (2012a) New aspects in quality related wheat research: I. Challenges and achievements (Review). Cereal Res. Commun. 40: 159–184. Be´ke´s F (2012b) New aspects in quality related wheat research. II: New methodologies for better quality wheat. (Review). Cereal Res. Commun. 40: 307–333. Be´ke´s F and Wrigley CW (2013) Gluten alleles and predicted dough-quality for wheat varieties world-wide: a great resource – free on the AACC International website. Cereal Foods World 58(6): 325–328.

WHEAT PROCESSING | The Gluten Proteins of the Wheat Grain in Relation to Flour Quality Cornish GB, Be´ke´s F, Eagles HA, and Payne PI (2006) Prediction of dough properties for bread wheats. In: Wrigley CW, Be´ke´s F, and Bushuk W (eds.) Gliadin and Glutenin. The Unique Balance of Wheat Quality, pp. 243–280. St. Paul, MN: AACC Press. Fabriana G and Lintas C (eds.) (1988) Durum Wheat: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Finney KF and Barmore MA (1948) Loaf volume and protein content of hard winter and spring wheats. Cereal Chem. 25: 291–312. Gianibelli MC, Larroque OR, MacRitchie F, and Wrigley CW (2001) Biochemical, genetic and molecular characterization of wheat glutenin and its component subunits. Cereal Chem. 78: 635–646. Henry RJ and Kettlewell PS (eds.) (1996) Cereal Grain Quality. London: Chapman and Hall. Ng PKW and Wrigley CW (eds.) (2002) Wheat Quality Elucidation: The Bushuk Legacy. St. Paul, MN: American Association of Cereal Chemists. Pomeranz Y (ed.) (1988) Wheat: Chemistry and Technology, third ed. St. Paul, MN: American Association of Cereal Chemists. Shewry PR and Casey R (eds.) (1999) Seed Proteins. The Netherlands: Kluwer Academic.

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Shewry PR and Lookhart GL (2003) Wheat Gluten Protein Analysis. St. Paul, MN: American Association of Cereal Chemists. Sikorski, Z.E. (Ed.) (2001) The Chemical and Functional Properties of Food Proteins. Technomic Publishing, Lancaster, PA. Wrigley CW (1994) Developing better strategies to improve grain quality for wheat. Aust. J. Agric. Res. 45: 1–17. Wrigley CW (2012) Proteins – the basis of life. Teach. Sci. 58: 56–59.

Relevant Websites www.wheat.pw.usda.gov – Graingenes. www.icc.or.at – International Association for Cereal Science and Technology. www.crop.cri.nz – New Zealand Institute of Crop and Food Research. www.usda.gov – United States Department of Agriculture. www.aaccnet.org – AACC International (formerly American Association of Cereal Chemists). www.campden.co.uk – Campden and Chorleywood Food Research Association. www.cgc.ca – Canadian Grain Commission, Winnipeg.

Ultrastructure of the Wheat Grain, Flour, and Dough S Grundas, Bohdan Dobrzanski Institute of Agrophysics, Lublin, Poland CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. Updated from the Encyclopedia of Grain Science, Volume 3, page 391. ‘Ultrastructure of the Grain, Flour and Dough.’ Version of 28/01/14 for Encyclopedia of Food Grains.

Topic Highlights

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ultrastructure of the grain and of dough. These aspects of research outcomes are described in this article.

Unique aspects of wheat quality make wheat a special product in its marketing and processing. Knowledge about the structure, composition, and function of the wheat grain can be applied to increase the market value of specific types of wheat. The resulting knowledge includes insights into the physical structure of the wheat grain, flour, and dough at the macroscopic and microscopic levels. External features of wheat kernels can be useful in attempting to identify varieties by aspects of their shape. Novel techniques are presented for studying the wheat grain, flour, and dough structures. Knowledge of the ultrastructure of the wheat grain is essential to the intelligent manipulation and optimization of wheat processing in all its forms.

Learning Objective

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To achieve understanding of the ultrastructure of the wheat kernel, flour, and dough, especially using novel techniques for studying them.

Introduction The wheat grain is unique, because only wheat flour is capable of producing dough with rheological properties that permit the baking of livened bread. The exceptional ability of wheat to synthesize gluten, with high baking quality of flour, guarantees its monopolistic position among other crops. These properties are also needed for the many other food products made from wheat, namely, noodles, pasta, Chinese steamed breads, Arabic flatbreads, pastry products, cakes, and cookies. All these products are distinct in the grain-quality characteristics needed for their production. For these reasons, international trade in wheat involves a wide range of wheat grades, each suited to specific groups of food products. These unique aspects of wheat quality make it a special product in its marketing and processing. As a result, wheat has become much more than a bulk commodity. It has become an object of intense research activity, the ‘prize’ being knowledge about the structure, composition, and function of the grain that can be applied to increase the market value of specific types of wheat. The resulting knowledge includes insights into the physical structure of the grain and of dough at the macroscopic and microscopic levels. This knowledge has obvious applications in flour milling and in baking, with respect to the respective

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The Anatomy of the Wheat Grain External Features The wheat grain is botanically a single-seeded fruit, called a ‘caryopsis’ or ‘kernel’ (Figure 1). It develops within floral envelopes (the ‘lemma’ and ‘palea’), which are actually modified leaves. Viewed from above (the dorsal side – the same side as the germ), the grains of different varieties may appear to be oval, ovate, elliptical, elongated, or truncated (short) (Figure 2). These characteristics can be useful in attempting to identify varieties by aspects of grain shape. In addition, dimensions may be helpful, but they vary with growth conditions. The wheat kernel averages 2.5–3.0 mm thick (or high as it stands on its base), 3.0–3.5 mm wide, and 6.0–7.0 mm long. Wheat kernels average 30–40 mg in weight. Wheat kernels are rounded on the dorsal side, with a longitudinal ‘crease’ (a deep groove) running the full length of the ventral side. The shape of the groove is a characteristic feature of some species and varieties (see Figure 1(d), 1(e), and 1(f)). The presence of a wide and deep crease is undesirable, because it contributes to making a low bulk density (test weight) for the grain. The main inner volume of the grain is taken up by the starchy ‘endosperm,’ which becomes the white flour that is released and crushed to fine particles by the flour miller. The ‘embryo’ (called the ‘germ’ by millers) forms an irregular patch at one end of the dorsal side of the kernel, near the point of attachment of the kernel to the plant. This point is called the ‘hilum.’ The tip of the opposite (distal) end of the kernel is covered with small hairs (‘trichomes’). This feature, known as the ‘brush,’ can also be a useful varietal characteristic, as wheat may differ in the length of the brush hairs. Several other features of the wheat kernel’s anatomy are illustrated in Figures 1 and 3.

The Bran The wheat grain is enclosed in a series of layers, collectively called the ‘bran’ (Figure 4). This layer is visible by light or scanning electron microscopy (SEM) as the outermost collection of cells surrounding the grain (Figures 5 and 6). The fluorescence micrograph of Figure 7 shows a section of the bran layers that has become separated from the underlying aleurone cell layer. The ‘pericarp’ (fruit coat) surrounds the entire seed and consists of two portions: the outer pericarp and inner pericarp. The outer pericarp has the following layers: the ‘epidermis’ (epicarp), the ‘hypodermis,’ and the innermost layer, called


http://dx.doi.org/10.1016/B978-0-12-394437-5.00165-0

WHEAT PROCESSING | Ultrastructure of the Wheat Grain, Flour, and Dough

Thickness

A N T TC C

I

385

H E

Brush

PE (d)

PR (c)

Dorsal side Length

EN (e)

Ventral side SE (f)

S Cheeks EM (a)

Crease

Width (b)

Figure 1 The main morphological components of the wheat kernel: (a) longitudinal section of kernel, (b) cross section of kernel, and (c) segment of bran layer with aleurone and endosperm cells. Abbreviations to segment (c): E, epidermis; H, hypodermis; I, inner pericarp; C, cross cells; TC, tube cells; T, testa; N, nucellar layer; A, aleurone layer; EN, endosperm; PE, peripheral cells of endosperm; PR, prismatic cells of endosperm; SE, scutellar epithelium; S, scutellum; EM, embryo. (d), (e), and (f): segments with typical shapes of the crease. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn., p. 6139 (2003). Elsevier Ltd.

Figure 2 Wheat grains appear in various shapes when viewed from above dorsal view. These are classed as (left to right) elliptical, truncated, oval, and ovate. Adapted from Fitzsimmons RW, Martin RH, and Wrigley CW (1983) Australian Wheat Varieties: Identification According to Plant, Head and Grain Characteristics, 2nd edn. Melbourne: CSIRO.

the remnants of thin-walled cells. These thin-walled cells, which have a discontinuous cellular structure, form a natural plane of cleavage. Removal of the outer pericarp, which millers call ‘beeswing,’ also aids movement of water into the kernel. The

inner pericarp, adjacent to the remnants, is composed of intermediate cells – a single layer of cross cells and tube cells. The cross cells are long and cylindrical (125 20 mm) and have a long axis perpendicular to the long axis of the grain. They are tightly packed, with little or no intercellular space.

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Figure 3 Parts of the wheat grain, especially the bran layers. Reproduced with permission from Dr. Senay Simsek North Dakota State University at http://www.nd.gov/ndda/files/Marketing/China2013/PPT_5-WheatBarley-Dr._Simsek.pdf.

Pericarp (fruit coat) Outer 1. Epidermis (epicarp) 2. Hypodermis 3. Remnants of thin-walled cells Wheat kernel (caryopsis)

Inner 4. Intermediate cells 5. Cross cells 6. Tube cells

Bran

Seedcoat (testa, spermoderm, integument) and pigment strand Nucellar epidermis (hyaline layer, perisperm) and nucellar projection Seed

Endosperm 1. Aleurone layer 2. Starchy endosperm Scutellum (cotyledon) 1. Epithelium 2. Parenchyma 3. Provascular tissues

Germ (embryo)

Embryonic axis

Plumule, including coleoptile Primary root, covered by coleorhiza Secondary lateral rootlets

Epiblast Figure 4 The parts of the wheat kernel, grouped according to their positions in the kernel. Reproduced with permission from Hoseney RC (1994) Principles of Cereal Science and Technology, 2nd edn. St. Paul, MN: American Association of Cereal Chemists.


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Figure 7 Fluorescence microscopy of the outer layers and outer endosperm of a section of wheat grain. The effect of autofluorescence provides contrast for the cell walls of the aleurone layer. Courtesy of B Campbell.

Figure 5 Light micrograph of wheat grain ultrastructure. A thin section was cut near the center of the grain, at right angles to the crease, which appears on the right. The section was fixed with Spurrs medium and stained with toluidine blue. Courtesy of B Campbell.

Figure 6 Scanning electron micrograph of the cut surface of a vitreous kernel of wheat, showing the subaleurone region with peripheral and prismatic cells. Note that a fracture has taken place at the interface between the cell contents and endosperm cell wall. The length of the bar at the lower left is 50 mm. Reproduced with permission from Grundas S (2003) Wheat: Grain structure of wheat and wheat based products. In: Encyclopedia of Food Science and Nutrition, 2nd edn., pp. 6130–6137. Elsevier Ltd.

The tube cells are similar in size and shape to the cross cells, but they have their long axis parallel to the long axis of the grain. The tube cells are not packed tightly and do not form a continuous layer and thus have many intercellular spaces. They are only recognizable in the mid-dorsal region of mature grains. The next layer inward is the seed coat (testa and pigment strand), which is firmly joined to the tube cells on the outside and the nucellar epidermis on the inside. The seed coat of red wheat consists of a thick outer cuticle layer, which is strongly pigmented, and a thin inner cuticle layer. The seed coat in white wheat has cell layers containing little or no pigments. Grain color, usually red or white (although purple is also known), is related to pigment in the testa. Tightly bound to the internal surface of the seed coat is the nucellar epidermis (hyaline layer and perisperm). The thickness of the seed coat varies from 5 to 8 mm. The nucellar epidermis is 7 mm thick and closely attached to both the seed coat and the aleurone layer. The total pericarp has been reported to comprise 5% of the kernel volume. The ‘aleurone’ layer, which is generally one cell thick in wheat, completely surrounds the kernel, covering both the starchy endosperm and the germ, except for that adjacent to the scutellum (Figure 4). Although the aleurone layer is anatomically a part of the endosperm, the miller regards the aleurone as the innermost layer of the bran. The majority of the mineral matter located in the bran is found in the aleurone layer, which also contains one-third of the grain’s thiamine content. The cytoplasm of the cells contains many small (3–4 mm), round aleurone granules surrounded by lipid droplets. The aleurone granules contain two types of inclusions: type I contains phytin and type II contains protein, carbohydrate, and bound nicotinic acid, which are largely unavailable for human nutrition mechanically, unless these cells are disrupted. The phytin granules are the main source of mineral matter. Hence, the degree of aleurone (or bran) contamination of flour is frequently evaluated by an ash analysis.

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In addition, thiamine and riboflavin are higher in the aleurone layer than in the other parts of the bran, and enzyme activity is high. Over the embryo, the aleurone cells are modified, becoming thin-walled cells that may not contain aleurone granules. The thickness of the aleurone layer over the embryo averages 13 mm or less than one-third the thickness found elsewhere. The aleurone cells are heavy-walled, essentially cube-shaped, and free of starch. They can vary in thickness from 30 to 70 mm within a single kernel and have thick (6–8 mm), double-layered cellulosic walls.

The Endosperm The starchy endosperm, excluding the aleurone layer, is composed of three types of cells: ‘peripheral,’ ‘prismatic,’ and ‘central.’ The peripheral cells are the last to be initiated during grain filling and they tend to be smaller than the other endosperm cells (60 mm in diameter and 20–60 mm radially). In addition, they have thicker cell walls (8 mm). Several rows of elongated prismatic cells are found inside of the peripheral cells. They extend inward to about the center of the cheeks and are 150–200 mm in length. The central cells are more irregular in size and shape than are the other cells. They are located inside of the central endosperm. The central endosperm cells are the first to be formed and they have thin walls (2 mm). Cell wall thickness also appears to vary among cultivars and between hard and soft wheat types. The differences between hard and soft wheat may be the result of selection: hard wheat (bread wheat) have been selected for high water absorption. The endosperm cell walls are composed of pentosans, other hemicelluloses, and b-glucans, but not cellulose. The pentosans in them absorb large amounts of water. The endosperm cells are packed with starch granules embedded in a protein matrix. Starch is the major component of wheat endosperm, comprising 75% of milled endosperm. Generally, the starch granules in wheat are classified into two size groups: large, lenticular (lens-shaped) A granules of up to 40 mm across the flattened side and small, spherical B granules up to 10 mm in diameter. The B granules are formed later in the grain filling process than are the A granules. The number ratio of small to large granules is 3:7. In contrast, the mass ratio greatly favors the large granules. In bread wheat, the endosperm texture varies in both texture (hardness) and appearance (vitreousness). In general, high-protein hard grains are vitreous, whereas low-protein soft grains tend to be opaque. Some wheat grains are vitreous or translucent in appearance, while others are opaque, mealy, or floury. In vitreous kernels, with no air spaces, light is diffracted at the air–grain interface and it then travels through the grain without being diffracted again and again. With vitreous kernels, the protein shrinks but remains intact, giving a denser kernel. As expected, the presence of air spaces within the endosperm makes the opaque grain less dense. The air spaces are apparently formed during the drying of the grain. If the grain is harvested immature and freeze-dried, it becomes entirely opaque. This shows that the vitreous character results during intensive drying in the field. It is also well known that vitreous grain wet and dried in the field, or for that matter in the laboratory,

will lose its vitreousness. In durum wheat, which is much harder than common hard bread wheat, a much larger number of starch granules are broken when the grain is fractured compared with bread wheat.

The Germ The wheat germ is composed of two major parts: the embryonic axis (rudimentary root and shoot) and the scutellum, which functions as a storage organ (Figure 4). The scutellum is adjacent to the endosperm and contains the remaining twothirds of the grain’s thiamine content. The germ is quite rich in vitamin E (total tocopherol) and in B vitamins. It contains many enzymes. The germ is a rich source of protein (25%), sugar (18%), and oil (16% of the embryonic axis and 32% of the scutellum are oil). The sugars are mainly sucrose and raffinose. On incineration, the germ gives a high level of ash (5%). As the germ makes a large contribution to the ash content of the whole grain, the ash content of white flour is taken to be an indication of the remaining germ content that has not been removed by the milling process. The wheat germ comprises 2.5–3.5% of the kernel. Recovery of the germ during the milling process is an important step because of its value in the food and pharmaceutical industries.

Techniques for Studying Grain Ultrastructure Many cereal scientists and technologists have successfully employed the three main branches of microscopy – light microscopy (LM), SEM, and transmission electron microscopy (TEM) – to study the structure and composition of wheat and wheat-based products. Recently, x-ray techniques have been used to detect kernel cracks. The objective of the studies involves gaining fundamental information on the accumulation of cellular constituents in the developing wheat grain and providing information that can improve the understanding of the differences in processing ability and in the overall quality of wheat and wheat-based products.

Light Microscopy The main stages in the preparation of samples for examination by LM are fixation, embedding, sectioning, and staining. The aims of fixation are to preserve samples from attack by enzymes or microorganisms, to render some constituents insoluble, and to strengthen the sample, thus improving its structural integrity during sectioning. The most commonly used fixative is aqueous, buffered glutaraldehyde, but specialized fixatives have been developed for specific applications (e.g., fixation of lipid-rich samples). Baked samples, which have been heat-fixed, may not require chemical fixation. Embedding, to provide additional support during sectioning, commonly involves aqueous gums for cryostat microtomes, synthetic resins, or special waxes. Resins are generally used where thinner sections are required and are cut using glass knives. Cryostat microtomes and sectioning of wax-embedded samples are carried out using steel knives. For

WHEAT PROCESSING | Ultrastructure of the Wheat Grain, Flour, and Dough examination, with transmitted bright field illumination, stains are commonly used. The ultrastructure of the wheat grain is illustrated in Figure 5. This micrograph was obtained by cutting a thin section from the grain, fixed with Spurrs medium. The section was stained in toluidine blue before viewing. The outer bran layers can be seen as distinct from the endosperm cells, further inside the grain. The crease is very obvious, extending well into the outer circle of the grain. The vascular bundle is seen at the innermost extent of the crease. Magnification by LM is generally less than is provided by electron microscopy, as can be seen by comparing the light micrograph of Figure 5 with the scanning electron micrograph of Figure 6. Fluorescence microscopy has been widely used and may rely on autofluorescence or the application of fluorescent dyes, often coupled to specific antibodies or lectins. Other coupled antibody techniques have been developed whereby colored reaction products are produced. Figure 7 shows an example of the use of autofluorescence to highlight the outer layers of the endosperm, with special contrast being provided for the cell walls of the aleurone cells. Polarized light can be used to study starch gelatinization or to provide detail of cell wall structures. Native starch granules viewed under polarized light show a cross-shaped structure, known as the ‘Maltese cross’ phenomenon (Figure 8(a)). It is indicative of the crystalline internal structure of the granules in

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their native state. This feature is not seen after starch granules have gelatinized due to the effects of moist heat on their crystalline structure. This technique is thus a useful means of determining the status of starch granules, with respect to their crystalline state. Viewing under polarized light also produces a distinctive pattern for bran particles, making them easier to be detected in white flour (Figure 8(b)). One of the major changes that can take place during the cooking of baked products is the gelatinization of the starch granules. The extent to which this has occurred is easily followed using polarized LM. In Figure 9, light macrophotography has been used with a video camera to examine the wetting of wheat endosperm with water. The three frames of Figure 9 show parts of this sequence. Water, added to the section of endosperm, has started to form strands of gluten, which are seen streaming away from the otherwise dry section of endosperm.

Scanning Electron Microscopy SEM has a greater depth of focus than LM, and therefore, it is not necessary to section samples prior to examination. Samples are normally coated with a thin layer of an electrically conducting material, usually gold, platinum, or carbon, prior to examination. Samples of dry wheat (<12% moisture) or similar products only require air-drying over a desiccant prior to coating. Samples containing more moisture may be rapidly frozen prior to

Figure 8 (a) Starch granules and (b) bran layers, from wheat grain, viewed under polarized light. The ‘Maltese cross’ effect can be seen on the starch granules in both parts. Polarized light shows special effects on bran fragments. Courtesy of R Moss.

Figure 9 Successive frames from a video of wheat endosperm being wetted with water. Strands of gluten can be seen forming and streaming away from the dry endosperm mass at the left. Courtesy of J Bernardin.

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dehydration, using freeze-drying or critical point drying. The development of cold stages in SEM has obviated the need for drying, and this technique, together with freeze-etching, has been successfully used to examine cereal foods in which moisture is high, forming an integral part of the structure. Endosperm hardness influences the manner in which grains fragment during milling, and this can also influence the yield of white flour. The efficiency with which floury endosperm is removed from overlying bran and the degree to which bran is powdered or otherwise damaged are both influenced by the manner in which grain fractures during milling. If fracturing occurs at the boundary between the endosperm cell wall and cell contents, the endosperm is efficiently removed from the bran, but the bran is fractured into small pieces. Figure 6 shows the cut surface of a wheat grain. Some signs of rupture between cells are visible. When the endosperm is fractured intracellularly, bran cleanup is poor, but large pieces of bran are produced. The manner in which the grain is fractured is determined by both the inherent hardness of wheat grain and its moisture content. Therefore, these two factors are carefully monitored by the flour miller. Grain of known hardness is sought for milling into specific types of flour, and the grain is ‘conditioned’ to appropriate moisture content prior to flour milling.

Transmission Electron Microscopy Samples for TEM require fixation and thin sectioning. Initial fixation is usually with glutaraldehyde, followed by fixation with osmium tetroxide. The fixed tissue blocks are rinsed, dehydrated, and embedded with a resin prior to sectioning. Heavy metal salts are used to stain the sections and enhance contrast; more recently, antibody staining has been developed whereby the antigenic sites are located at TEM level by the presence of colloidal gold particles, which are coupled to the antibodies.

Image Analysis and Other Techniques Watson and Crick, by comparing the data from x-ray analysis with a cardboard model based on them, determined the structure of the double helix of DNA, for which they were awarded the Nobel Prize. The biochemical diagnostics required for the assessment of quality of kernels and seeds can be made using the methods of x-ray structural analysis. This results from the possibility of studying the atomic structure of matter using x-ray diffraction. From the diffraction pattern, one can determine the electron density distribution of matter and, based on that, the kind of atoms and their arrangement. x-Ray structural analysis can determine the structure of crystals, liquids, protein molecules, etc. In order to obtain images of large molecules with atomic resolutions, rays with shorter wavelengths are applied, that is, hard x-rays, rather than soft x-rays. During the 1990s, the value of all the earlier work was enhanced by high-tech methods, such as nuclear magnetic resonance, laser, and x-ray methods (X-RMs). More recently, the application of stereology techniques and automatic image analysis of grains have been used. Furthermore, user-safe x-ray techniques have proved to be highly suitable for visualization

of mechanical damage of grains, especially inner cracks in kernels or insect infections (Figure 10). Mechanical damage occurs whenever the grain is subjected to the destructive action of internal or external forces, causing internal cracks. The results of research carried out by using X-RMs showed significant differences in grain endosperm cracks between common wheat varieties. Natural wetting of dry grain (below 15% of moisture content) during rainfall when wheat is standing in the field is one of the reasons of its cracking. The susceptibility of wheat to mechanical damage is determined by genetic factors (e.g., grain hardness), by environmental effects (climatic conditions during the preharvest period), and by the conditions of grain storage (especially excessive humidity). The combination of these properties determines the quality of grain material. Radial cracks in the endosperm of a grain are shown in Figure 10(a), using x-ray microscopy to reveal these inner faults. x-Ray detection makes it possible to identify the positions of cracks and also to quantify cracks inside the kernel and thus to evaluate the physical condition of the grain endosperm. Also shown in Figure 10(b) is the presence of a germinated kernel and, in Figure 10(c), weevil larva (in two successive positions) that could not otherwise be detected. In this way, the stage of development of insect larvae living inside the kernel may be monitored, permitting the detection of insect infestation that is not visible by normal external examination. To detect the presence of fungi in the caryopsis, it is necessary to apply an image magnification of 27 –30. Figure 11 presents clearly visible fungal filaments (hyphae). The limit values of parameters should be determined quantitatively and validated by specifically developed regulations. This means that the current problems of x-ray application require a radical revision of existing standards of quality of cereal crops. This will allow the move to fully control the parameters of seed variety and kernel quality. This will require the mandatory inclusion of elements of rapid selection of seeds into systems of x-ray diagnostics. Thus, x-ray techniques have the potential of becoming a universal method of diagnosing and bringing the quality of original batches of grain to a high status.

The Ultrastructure of Wheat-Based Products Flour Milling The aim of the flour milling process is to remove the endosperm from the crushed grain, separating it from the other anatomic parts of the grain, namely, the germ, bran, and scutellum. The particular aim is to obtain a maximum yield of white flour with the minimum contamination of nonendosperm material. Fluted rollers are used to break open the grain and scrape the endosperm from the bran; smooth rollers are used to reduce the endosperm particles into flour. The moisture content of cleaned wheat is adjusted to between 15% and 17% prior to milling. This process (‘conditioning’) facilitates the separation of the bran and endosperm and toughens the bran, thereby reducing the amount of ash in the flour. Conditioning can be completed in about six hours for soft wheat, but hard wheat may require 24 h or longer. x-Ray


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Figure 10 The x-ray images of wheat kernels (a) with inner cracks, (b) with partial germination, and (c) containing a weevil larva inside it.

microscopy has shown that added water moves rapidly through the bran layers but may remain at the aleurone– endosperm interface for several hours. The rate of water penetration through the endosperm is dependent on protein content, initial moisture, and grain hardness. The air spaces that are present in the endosperm of soft wheat allow water to move more rapidly, and hence, the conditioning time is less than that required for hard wheat. Of the morphological factors that can influence the yield of white flour, the shape of the grain and the amount of endosperm within the grain are particularly important. Grain size has been shown to be significant; larger grains have a higher

potential flour yield. Image analysis has been used to measure a large number of morphological parameters, and extraction has been shown to correlate with grain length parameters. In addition to the amount of endosperm contained in the grain, the efficiency with which bran and endosperm can be separated (‘bran cleanup’) is also a factor influencing flour yield. Because of differences in the structure of hard and soft grains, they must be milled differently. The cell structure of soft wheat is very weak and readily broken. In addition, the endosperm of soft wheat appears to adhere strongly to the bran. Durum wheat is used to produce semolina, a granular material analogous to the farina or flour

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Figure 11 The presence of fungi in the wheat kernels: (a) mycosis-enzyme depletion of wheat kernels, (b) wheat kernel damage by sunn pest (Eurygaster integriceps), and (c) the presence of fungi in the caryopsis of wheat. Reproduced with permission from Demyanchuk AM, Grundas S, and Velikanov LP (2013) Identification of wheat morphotype and variety based on x-ray images of kernels. In: Grundas S and Ste˛pniewski A (eds.) Advances in Agrophysical Research, ch. 10, pp. 223–267. Intech. http://dx.doi.org/10.5772/52236.

middlings of the hard wheat milling process. Granular products such as semolina and farina are used for pasta, baby foods, and specialty foods. Endosperm hardness influences the manner in which grains fragment, and this can also influence flour yield. An important difference between hard and soft wheat is the boundaries of endosperm fragmentation. In hard wheat, it takes place mainly at the boundary between adjacent cells as the contents of the cells are more firmly bound together by the continuous matrix protein. Thus, hard wheat endosperm can be removed more efficiently from bran as the shear forces

imparted by the fluted rollers are directed along the boundary between adjacent endosperm cells toward the bran (Figure 12). When they reach the bran, some of the forces are deflected along the endosperm interface, facilitating separation of the endosperm from the bran. Of course, as the kernel is reduced to flour size, the hard wheat cell contents are also fractured. In soft wheat, the discontinuities in the protein matrix allow endosperm contents to break apart easily, and cleavage takes place intercellularly. Thus, the shear forces are dissipated within the endosperm and are not redirected toward the

WHEAT PROCESSING | Ultrastructure of the Wheat Grain, Flour, and Dough bran. Figure 13 shows how the starch granules are released from a soft wheat, clean of adhering interstitial protein, which remains adhering to the starch granules from a hard wheat. Microscopy can also be used to study the mode of action of

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different items of mill equipment and the effect of processing variables on flour quality. Starch damage is regulated by the amount of pressure applied by the smooth reduction rollers. The physically damaged granules absorb more water and are more susceptible to enzyme attack. A controlled level of starch damage is required for bread flours.

Dough Formation

Figure 12 Diagrammatic representation of the forces acting on one endosperm cell of a wheat grain during milling. The large arrow at the bottom of the diagram indicates the direction of the shear force caused by the differential speed of the break rollers. In hard wheat, the contents of the cell behave as one unit, and hence, the cell is cleanly torn from the overlying aleurone layer. In soft wheat, the shear force passes through the content of the cell, as indicated by the dotted arrow. B, bran layer; A, aleurone layer; W, endosperm cell wall; E, endosperm. Reproduced with permission from Wheat: Structure of wheat and wheat-based products (1993). In: Macrae R, Robinson RK, and Sadler MJ (eds.) Encyclopedia of Food Science, Food Technology and Nutrition. London: Academic Press.

When water is added to flour and energy is imparted to the dough by a mixer, the gliadin and glutenin proteins interact to form elastic, cohesive gluten. The tendency to form viscoelastic gluten can be seen even without mixing. Figure 9 shows a few frames from a video on allowing water to come in contact with a section cut from wheat endosperm, lying on a microscope slide. Immediately, the gluten-forming proteins start to form fibrils that stream out from the endosperm section, carrying starch granules with them. The mechanism and rate of gluten development depend on the level of water addition and rate of work input. In bread dough, the level of water addition (55–62%) is sufficient to cause the mixer initially to pull the gluten away from the starch granules and form coarse, poorly connected masses (Figure 14). As mixing proceeds, these masses are gradually stretched out and become more interconnected and eventually form a uniform, continuous, extensible network that surrounds the majority of the starch granules in the dough. This gluten network gives dough a smooth external appearance, in turn leading to the production of well-risen bread of uniform crumb structure. The level of water addition in noodle or pasta dough is considerably less (30–33% addition) than that in bread, and no protein pullback occurs during mixing. The function of mixing in these processes is to ensure uniform distribution and hydration of ingredients. The continuous gluten matrix is

Figure 13 Scanning electron micrographs of starch granules released during flour milling from a hard wheat (left) and from a soft wheat, showing the much greater amount of adhering storage protein on the starch granule from the hard wheat.

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Figure 14 Light micrographs of a cryostat section of an underdeveloped bread dough (left) and of a fully developed dough (right). The stain was ponceau 2R. For the underdeveloped dough, the coarse gluten masses (M) do not surround the majority of the starch granules (G), as they do, by contrast, for the developed dough, which has become more interconnected and forms a continuous network (N). The bar is 60 mm long. Reproduced with permission from Wheat: Structure of wheat and wheat-based products (1993). In: Macrae R, Robinson RK, and Sadler MJ (eds.) Encyclopedia of Food Science, Food Technology and Nutrition. London: Academic Press.

formed by sheeting rollers in the case of noodles and by highpressure extrusion in the case of pasta.

Conclusion Thorough knowledge of the ultrastructure of the wheat grain, and of the products made from it, is essential to the intelligent manipulation and optimization of wheat processing in all its forms. Much of this knowledge has already been translated into greater efficiencies, especially in milling and dough processing. Also needed is the integration of the knowledge of ultrastructure with chemistry and genetics. This overall picture will help in combining the efforts of technologists, chemists, and breeders, thereby to provide vertical integration from the original ‘design’ of better varieties, to the final product, to the most important person in the business chain – the consumer. At the end of this article, we would like to pay attention to the X-RM, which among the approximately three dozen methods for the evaluation of grain quality is more than modest. This method is included in the standard as a measure of assessing the rate of infestation and population of grain insects, including quarantine species. The X-RM allows, without destroying the object, to identify its internal structure and make it observable and accessible for qualitative and quantitative evaluation. The quality of grain is determined through characterization of more than 20 of its physical, biochemical properties and technological features. The X-RM is included in the standard as a method of assessing the rate of infestation and population of grain insects, including quarantine species, for example, Sitophilus granarius or Eurygaster maura. The results of research carried out using X-RMs have shown significant differences in grain endosperm cracks between common wheat varieties. Natural wetting of dry grain (below 15% moisture) during rainfall in field conditions is one of the main reasons for cracking. Considering the results of endosperm cracks, which can appear before harvest in some climatic

regions of wheat production, special attention should be paid to this potential defect and to the susceptibility of specific varieties to this fault.


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What are the distinct meanings of the terms ‘soft’ and ‘hard’ when used for wheat kernels? How do these terms distinguish wheat types with respect to processing? What is the meaning of a ‘single-seeded fruit’ of wheat? What are the typical creases in wheat kernels? List the main parts of a wheat kernel. How are these parts separated during the milling process? Which kind of damage of kernels can be visualized by the X-RM? What are the likely causes of inner cracks appearing in kernels? What problems do they pose for normal processing?


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Obtain some wheat grains, preferably of soft and hard types. Note that the soft grains appear opaque, in contrast to the vitreous texture of the hard grains. Carefully cut some grains in half, across the line of the crease. The differences are more evident in the endosperm that is revealed as a result. In addition, bite on some grains, thereby feeling the differences between the soft and hard grains in the force needed to crush the different types of grain. With these few grains, imagine yourself as a wheat breeder of a century or so ago, when there was no equipment available for small-scale testing of grain hardness or of dough quality. Under those circumstances, the breeders tested for grain hardness by chewing a few grains. Then, the skilled breeder would form a dough by mixing the crushed grain with saliva. The resulting dough was removed

WHEAT PROCESSING | Ultrastructure of the Wheat Grain, Flour, and Dough from the mouth and tested between the fingers for dough strength and extensibility. In those days long ago, a breeder was required to have a good set of teeth!

Further Reading Arendt EK and Zannini E (eds.) (2013) Cereal Grains for the Food and Beverage Industries Oxford: Woodhead Publishing Ltd. Demyanchuk AM, Grundas S, and Velikanov LP (2013) Identification of wheat morphotype and variety based on x-ray images of kernels. In: Grundas S and Ste˛pniewski A (eds.) Advances in Agrophysical Research, ch. 10, pp. 223–267. Intech. http://dx.doi.org/10.5772/52236. Faridi H and Faubion JM (eds.) (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. Fitzsimmons RW, Martin RH, and Wrigley CW (1983) Australian Wheat Varieties: Identification According to Plant, Head and Grain Characteristics. Melbourne: CSIRO. Grundas S (2003) Wheat: Grain structure of wheat and wheat based products. In: Encyclopedia of Food Science and Nutrition, 2nd edn, pp. 6130–6137. Elsevier Ltd. Grundas S and Wrigley CW (2004) Wheat: Ultrastructure of the grain, flour and dough. In: Wrigley C, Walker C, and Corke H (eds.) Encyclopedia of Grain Science, pp. 391–400. Oxford: Elsevier Science0-12-765490-9. Grundas S, Velikanov LP, and Archipov MM (1999) Importance of wheat grain orientation for the detection of internal mechanical damage by the x-ray method. International Agrophysics 13: 355–361.

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Hamer RJ and Hoseney RC (eds.) (1998) Interactions: The Keys to Cereal Quality. St. Paul, MN: American Association of Cereal Chemists. Hoseney RC (1994) Principles of Cereal Science and Technology, 2nd edn. St. Paul, MN: American Association of Cereal Chemists. Macrae R, Robinson RK, and Sadler MJ (eds.) (1993) Wheat: Structure of wheat and wheat-based products. In: Encyclopedia of Food Science, Food Technology and Nutrition. London: Academic Press. Pomeranz Y (ed.) (1989) Wheat is Unique. St. Paul, MN: American Association of Cereal Chemists. Watson JD and Crick FHC (1953) Molecular structure of nucleic acids. Nature 171: 738–740. Wrigley CW (2009) Wheat: A unique grain for the world. In: Khan K and Shewry PR (eds.) Wheat: Chemistry and Technology, 4th edn. St. Paul, MN: AACCInt Chapter 1.

Relevant Websites http://www.cgc.ca; www.grainscanada.gc.ca – Canadian Grains Commission, Winnipeg. http://www.crop.cri.nz – New Zealand Institute of Crop & Food Research. http://www.icc.or.at – International Association for Cereal Science and Technology. http://www.namamillers.org/images/CrossSectionViewofWheat.gif. http://www.seedtest.org – International Seed testing Association. http://www.semec.ws/cropfood/psp/cyberguide_old/gifs/kernel.gif. http://www.triz-profi.com (ver.2.0, 2007, in Russian). http://www.usda.gov – United States Department of Agriculture; grain handling practices, standard sampling procedures.

Cereal Food Production with Low Salt L Day, AgResearch Ltd., Palmerston North, New Zealand ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Salt and Health

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Sodium chloride (NaCl), commonly known as salt, is widely used as an ingredient and/or processing aid in the food industry. Salt is an ionic combination of sodium and chlorine, and every 2.5 g of salt constitutes 1 g of sodium. Excess salt intake is widely known to be one of the risk factors for elevated blood pressure and associated cardiovascular ailments such as heart attacks and strokes. These ailments are the leading causes of death and disability in many Western countries and put a serious strain on societal health systems. A reduction in dietary salt intake would assist in improving the well-being of consumers and also reducing future health-care costs. Sodium is required by the human body to ensure its normal function. It regulates extracellular fluid in the body and also plays an important role in nutrient uptake by cells. The amount of sodium required for the body’s physiological function per day is about 1.5 g, much less than the average amount estimated in our current daily diet of 9–12 g day1. A modest reduction in salt intake to the amount of the current public health recommendations (2–4 g day1) can reduce blood pressure by a small but important amount. The importance of salt reduction in human diets has been highlighted by recent legislation introduced by the European Union, Canada and the United States that allow nutrition and health claims for reduced sodium content in food products. Accordingly, the food industry has endeavored to reduce salt levels during recent years. Many developed countries have now set targets to reduce their population’s salt intake to below 5–6 g day1, in line with the WHO recommendation of a daily salt intake of 5 g day1. However, more research and development effort needs to be implemented to achieve realistic targets for significant salt reductions in most major food categories.

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High sodium intake is linked to high blood pressure leading to cardiovascular diseases. Salt reduction in bread and breakfast cereals is a major target in government policies. Salt is used in grain-based foods for taste, processing functionality, and microbial shelf life stability. Salt reduction affects the flavor, texture and shelf life of grain-based food products. Potassium chloride or other mineral salts may be used to substitute sodium-based ingredients. Repositioning of salt in food matrices offers and alternative solution for overall salt reduction in a product. Surface salt reduction for snack products is achievable through the reformulation and restructuring of salt crystals. Potential use of fiber to recompense the taste and functionality of grain-based foods with low salt should be explored further.

Learning Objective

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Understand the technological functionality of salt in the processing, sensory role of salt in consumer acceptance, and current developments aiming to reduce salt content and to minimize the impact of salt reduction on the sensory attributes and texture of grain-based foods.

Introduction Grain-based foods form a basic staple diet for many people around the world. These foods make important and positive contributions to human nutritional needs, especially with respect to necessary requirements for energy, protein, carbohydrates, minerals and essential vitamins. Nevertheless, the criticism that has been leveled at grain-based foods that many of them contain excess amounts of sodium, added as common salt. With global governments taking actions to set dietary guidelines on sodium intake and to enforce healthy changes in the global food market, food manufacturers are developing initiatives to reduce sodium levels in processed food products. However, the reduction of salt in grain-based foods affects several product quality characteristics, i.e. flavor, texture and shelf life that can alter consumer acceptance of these foods. Furthermore, food manufacturing processes are also affected by changes such as dough stickiness during bread making or expansion in the case of extruded snacks. Consequently, the decision by food processors to reduce salt requires modifications to not only overall ingredient formulations but also the processing technologies that are utilized in the production of grain-based foods.

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Levels of Sodium in Grain Food One of the reasons why salt intake has increased in the last few decades is the increased consumption of manufactured and preprepared convenient foods and the changes in life style with less time spent on home-prepared meals from raw ingredients. Historically, salt was initially added to help preserve foods. Although the importance of salt for food preservation has become less critical due to the invention of refrigeration and other thermal and nonthermal processing technologies, its influence on the taste, structure, and texture of food is hard to be ignored. With time, our palates have become very familiar with the taste and flavor associated with the relatively high levels of salt present in various processed foods. Most of the salt in our daily intake, about 75%, comes from processed foods. Bread products contribute up to 26% of the daily sodium intake. Together with other cereal products, including breakfast cereals, biscuits, cakes, pastries, noodles, and cereal bars, this group of food provides the highest daily


http://dx.doi.org/10.1016/B978-0-12-394437-5.00166-2

WHEAT PROCESSING | Cereal Food Production with Low Salt sodium intake in the processed food category with up to 35–38% in many Western countries. In addition to added salt, sodium also enters grain-based foods in less obvious forms, such as the use of baking powder, leavening agents and alkaline salts for Asian alkaline noodles. Average sodium contents of grain-based foods are shown in Table 1. Worldwide, bread and breakfast cereals are considered to be the foodstuffs that provide high levels of dietary salt since they are staple foods in many cultures. Hence, this raises concern in the global cereal industry, especially regarding the negative perceptions of salt addition to baked and extruded products. Therefore, a reduction of salt in grain-based food products would lead to a significant reduction in the daily salt intake.

Functions of Salt Salt plays a multifunctional role in processed foods. Salt is most obviously added to provide taste, but more subtly, salt enhances the taste and flavor sensation broadly, especially for otherwise bland food, such as bread products. In addition, salt plays a vital and significant role in cereal processing by enhancing physical functionality and processability, such as dough strength and dough handling. Salt in grain foods can be categorized into the following functions:

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Sensory effects, by imparting flavor Process handling, by controlling dough rheology, yeast growth and fermentation rates Assisting in product microstructure development and improvement of product texture Extending shelf life by reducing microbial spoilage, particularly mold growth

Table 1

Average sodium content in common grain-based foods

Grain food

Average sodium content (mg/100 g)

Bread White roll Whole-meal bread Mixed-grain bread Pretzel Bagel Noodles Pasta (plain dry) Sugar cookie Savory biscuits Cracker Cakes Cake doughnut Pastries Corn flakes Crispy rice cereal Granola cereal Cereal bars Corn chips

531 523 461 447 1607 490 402 24 346 771 799 315 419 328 889 954 215 144 579

Source: Webster JL, Dunford EK, and Neal BC (2010) A systematic survey of the sodium contents of processed foods. American Journal of Clinical Nutrition 91(2): 413–420; Butow BJ et al. (2002) Effects of different salts on mixing and extension parameters on a diverse group of wheat cultivars using 2-g mixograph and extensigraph methods. Cereal Chemistry 79(6): 826–833.

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Taste and Flavor Sodium is a powerful contributor to the palatability of foods because it reduces nonpleasant flavor notes (e.g. bitterness) while enhancing those perceived as pleasant (e.g. umami and sweet) to human’s sensory receptors. The sensory role of salt is related more to its flavor-enhancing properties, rather than to its salty taste. Bread, baked without salt, has an insipid ‘pasteboardy’ taste (Figure 1). Negative flavor notes such as ‘yeasty,’ ‘sour’ and ‘bitter’ become more noticeable, and bread is often described as having ‘sour dough-type’ characteristics when salt is reduced to below 50% of normal use (which is about 2% flour base). A small amount of salt enhances significantly the sweetness of amino acids such as glycine, alanine, and serine. The presence of sodium-containing compounds also counteracts the sensation of bitterness. Such flavor-enhancing effects of salt seem to be related to its effects on both the water activity and ionic strength within food systems, which influence the binding of compounds and thus the flavor sensation. The extent to which salt reduction impacts on the flavor of grain-based foods depends on the other ingredients in the formulation and the methods of processing. In general, a one-quarter reduction in the salt content of white bread can be made without having any noticeable detrimental effects on flavor and overall consumer acceptability. There are other consequences associated with low-salt processing that affect the flavor and taste of grain-based foods, for example, the influence of salt reduction on the crust development of bread. The lighter crust of salt reduced bread means that lower Maillard reaction products are generated during baking, and hence, the contribution of the crust to the whole flavor composition of bread is reduced. Similarly, Maillard reactions are reduced in other types of grain processing such as extrusion and cereal toasting with salt reduction leading to the generation of lower levels of flavor compounds. Salt in cereals and snacks is also important in the overall flavor profile since it not only adds flavor in itself but also enhances many of the other flavorings used. The bland flavor of many cereal flours makes it essential that seasonings are added to snacks to give consumer acceptability. Salt also acts as a carrier for the uniform distribution of other ingredients such as flavors, colors and antioxidants on the surface of snack food products.

Processing Salt is a universal ingredient in the processing of cereal-based foods, in particular, bread making. Apart from enhancing the taste, salt has long been acknowledged to possess technological functions in the processing of baked products. These are:

• • •

promoting the development of gluten structures in the mixing of flour dough, thus enhancing dough strength; increasing the mixing time to reach optimum dough strength, therefore allowing time for dough handling; and stabilizing or controlling the yeast fermentation rate and thus the rate of gas production.

Due to its ionic nature, salt causes changes in water absorption when wheat flour is mixed with water to form dough and thus influences the physical requirements for dough development. Salt shields the charges of gluten protein, thereby allowing the

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WHEAT PROCESSING | Cereal Food Production with Low Salt

8. SALIVA STIMULATING 7. BITTER

1. SALTY

6. YEASTY

2. OVERALL PALATABILITY

3. SOUR

4. PASTEBOARDY

0% NaCl ADDED 1.0% NaCl ADDED 1.4% NaCl ADDED

4. SWEET

Cl

a tN

Na ith

W

Cl

ou

ith

W

flour to hydrate more slowly (thus, have longer mixing times), and the protein chains to form a more ordered network, which results in a more stable dough structure and higher strength (Figure 2). The small delay in protein hydration allows gluten proteins to form networks with largely elongated fibril protein structures at the end of dough development (Figure 3). Without salt, the protein hydration cannot be controlled effectively, resulting in fewer linkages between gluten proteins that changes the protein structure from elongated protein strands to less connected protein particles. The longer mixing times are a disadvantage in commercial bread production, but this disadvantage is outweighed by the resultant better bread quality. Salt plays a pivotal role in the viscoelastic characteristics of dough, that is, its rheological properties that are unique to the processing of wheat flour-based foods, because of its impact on gluten structure. Salt addition results in a more elastic dough. The dough strength and elasticity provide a consistency for dough handling manually and its machinability in industrial high-throughput production. The most profound change of rheological characteristics with regard to an industrial process is the reduction in dough consistency in the absence of salt. A very low salt usage effectively weakens the gluten that makes the dough sticky. The main challenge in making low-salt bread is that the dough stickiness makes it more difficult to process, and there is tendency for sticky dough to stop processing lines, leading to potential down time and wastage. Another processing function of salt in fermented products is stabilizing the yeast fermentation rate. The reduction of salt results in an increase in gas production. In combination with a weak gluten network due to the reduced level of salt, the dough cannot retain all the gas produced, and this leads to a higher amount of gas lost during proofing and at an early stage of

Dough strength

Figure 1 Flavor profiles of wheat breads with three different salt concentrations. Reproduced from Salovaara H, Hellemann U, and Kurkela R (1982) Effect of salt on bread flavor. Lebensmittel-Wissenschaft & Technologie 15(5): 270–274.

Mixing time Figure 2 Schematic diagram depicts the effect of salt on dough mixing time and dough strength.

baking. This causes gassy and more acidic doughs resulting in loaves with poor texture and an open crumb structure and low in loaf volumes after baking. The inhibiting effect of salt on yeast growth, resulting in limited total gas production in a controlled manner, is better for the control of the baking process. When a lower level of salt is used, the proofing time has to be adjusted to accommodate the faster and less controllable gas production, which can put time pressure on bakery production.

Product Microstructure and Texture A key feature that distinguishes baked and extruded wheat flour-based food products from other cooked foods is the formation of a cellular-like structure that confers specific eating characteristics on the products. This structure is derived from the formation of a gluten/starch matrix and its ability to


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Mixing time 45 sec

2 min

6 min

20 min

2% salt added

No Salt

Figure 3 Confocal laser scanning microscopic images showing gluten network development at different stages of dough mixing with 2% and 0% salt. Gluten proteins are shown in yellow strands, starch granules in green, and air bubbles in black (for detail of dough sample preparation and microscopic method, see reference McCann and Day (2013)).

Figure 4 C cell images of bread made with different levels of add salt (% flour base). Salt reduction results in poorer crumb structure with a small number of larger air cells and lower loaf volume of the bread (for detail of baking and image analysis, see references McCann and Day (2013) and Uthayakumaran et al. (2011)).

control the nucleation of gas cells during mixing and their stability and expansion during subsequent processing steps. Salt plays a critical role in controlling the gluten/starch dough microstructure and rheology. The technological functions of salt directly contribute to the quality of baked products. The dramatic effect of salt addition to improve bread volume and crumb quality is illustrated in Figure 4. Such improvements in bread quality are accomplished by increases in the time required for protein/starch hydration and the development of gluten structures in a manner that provides appropriate dough strength with better gas retention. The ability to control gas production, retention and release during proofing and baking, in combination with a strong gluten network, is essential to achieve an even crumb structure. Bread produced without salt has a lower number of cells to total area ratio and thus a higher number of larger air cells compared with bread made with salt (Figure 4). Changes in the crumb structure of baked products can influence the perception of their textural characteristics,

which is critical with respect to the consumer acceptance of grain-based foods. In addition, salt has an effect on the starch retrogradation process, which is associated with the storage of bread in a process commonly called staling. Finally, because the final product texture is often denser without salt, the microstructure and texture of the finished product can influence the flavor release and changes in the textural aspects of overall eating quality.

Microbial Stability Bread and cakes are considered as intermediate-moisture foods with moisture contents typically ranging from 18% to 25% for cakes and 35–42% for bread. The water activity (aw) of these products is above 0.95. With such moisture contents and high aw, baked goods are susceptible to microbial spoilage with the main effect coming from the growth of various molds. In these products, salt acts as a preservative agent against microbial growth, due to its ability to reduce the aw. The increased

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osmotic pressure due to the presence of salt causes microbial cells to lose water to the environment, thus inhibiting cell metabolism and growth, in particular mold growth. Thus, salt supports the microbiological stability and extends the shelf life of these products. Some of the grain-based foods such as breads and cakes have relatively short shelf life, that is, a few days; salt reduction could impact processing turnaround and control of product waste.

Alternatives for Low Salt Sodium reduction has become a target and a formulation challenge for most food companies. There is a general consensus that the high sodium content in food is a major concern for health reasons. However, the importance of using salt in grain food processing and its affect on product quality cannot be overlooked. The reduction of salt requires a modification in not only the ingredients but also the technologies utilized during production. The changes in sensory and product qualities brought to grain-based foods by salt reduction have to be considered. The simplest approach is to make gradual reductions in the perception of saltiness in order to ‘retune’ consumer palates to lower levels of salt. Slow and gradual reduction of salt from a formulation can go unnoticed by consumers as the palate adjusts to a revised sensory profile, if the changes are small enough. This so-called ‘stealth’ approach has already been widely adopted by the food industry and is particularly useful when salt is used in flavor agents, e.g., at the surface of snack foods. Significant sodium reductions have been achieved in many cases, in addition to modifying the taste expectations and perception of consumers as a whole, over time. However, sodium reduction in foods generally influences global flavor perception due to interactions with the other components of the food matrix. A level will almost inevitably be reached, below which loss in appealing flavor will be noticed by consumers. Therefore, this ‘stealth’ approach on its own is unlikely to deliver the public health requirement needed to reduce salt levels overall in all cereal-based foods. An alternative approach is to maintain the perception of saltiness with lower levels of salt through the use of other ingredients or technological solutions, which take into account the important technological roles of salt in grain food processing.

Partial Substitution Substituting sodium chloride with other mineral salts is a popular approach. Potassium chloride is a common choice, which can be used to substitute up to 50% of the sodium. Research has shown that both potassium and ammonium chlorides have dough-strengthening effects, compared with no-salt controls. These effects were found to be comparable with those of sodium chloride. For all of these salts, the extent of strengthening was progressively greater with higher levels of salt addition. However, the substituting of either calcium chloride or magnesium chloride had no effect on dough properties. In addition, it would be expected that most of any added ammonium not utilized by the yeast would be lost during the heating phase of the baking process due to its volatility. For

that reason, a mix of potassium, ammonium, and sodium chlorides could be used to provide adequate functional properties for dough mixing and fermentation, while the food processor could manage the level of sodium chloride to suit dietary and sensory requirements. Although the technological function of potassium salts and their antimicrobial effects have been demonstrated, full replacement of sodium is not recommended, due to their pronounced bitter, chemical, metallic taste and aftertaste that limit their acceptability. In addition, increased levels of potassium or magnesium may lead to other health issues, which preclude their intensive use. Other mineral salts may be used as alternatives for sodium chloride to substitute for the dough management functions of sodium chloride, although the extent to which they are used in practice probably depends on the specific characteristics of the flour involved and the dough handling requirements of the bakery. There are currently a number of commercial salt replacers available, formulated with various combinations of sodium chloride and potassium chloride or other mineral salts. For example, mixed mineral salts with an enhanced salty taste contain 20% of sodium and thus provide a 50% reduction of the sodium content. The use of mixed salts with organic acids, for example, is an effective strategy to mask the bitterness. Other approaches such as the use of trehalose or flavoring agents to balance the overall taste can also be used. There have been numerous patented technologies developed in this area. However, complete substitution of sodium chloride may not be the best strategy; rather, a strategy of partial substitution provides an optimal means of manipulating sodium levels with respect to dough handling and consequently maintaining the flavor perception of the final product. In cereal foods and snacks, sodium can be incorporated into prepared foods in unexpected ways. For example, depending upon the application, chemical leavening agents in baked goods can be a significant source. Leavening occurs when an acid combines with a base alkali to produce CO2. Sodium is a common component in both acidic and basic leavening agents. All these sources need to be taken into account when considering the reduction of overall sodium levels. If the base used is sodium bicarbonate, sodium-free alternatives such as potassium bicarbonate or possibly ammonium bicarbonate could be considered. Similarly, sodium acid pyrophosphate, a leavening acid, may be replaced by calcium acid pyrophosphate (CAPP), which has no sodium and is a good source of calcium. CAPP has a similar CO2 release profile to the sodiumcontaining leavening acids that are used most often to deliver the bulk of leavening gas during the baking phase in biscuit dough or cake-type batter. The potential replacement of sodium ingredients and the implications of their use in the processing of cereal-based foods are summarized in Table 2.

Inhomogeneous Salt Distribution Potential technologies for salt reduction based on repositioning of salt in food matrices or restructuring of salt crystals (in the case of salt as part of flavoring agents) have been developed recently. These technologies offer the advantage of reducing salt level with no impact on product labeling, as there is no alteration in the original formulation ingredients.

WHEAT PROCESSING | Cereal Food Production with Low Salt Table 2

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Alternatives to sodium-containing compounds that may be used for the processing of cereal foods

Sodium compound (s)

Nonsodium alternative (s)

Implications

Leavening agents: Sodium bicarbonate Sodium acid pyrophosphate (SAPP) Sodium aluminum phosphate Sodium hydrogen carbonate

Monocalcium phosphate Dicalcium phosphate Potassium bicarbonate Calcium acid pyrophosphate

Gas may be released at a different time compared with sodium-based leavening compounds, and processing changes may be needed to accommodate these difference Timing of gas release is closer to that of sodium-based leavening compounds Timing of gas release is closer to that of sodium-based leavening compounds Suitable for use in combination with sodium bicarbonate to reduce use of SAPP in cake-like products Provides similar dough-softening action, but is more costly than sodium metabisulfite

Ammonium bicarbonate SAPP

Glucono-d-lactone

Sodium metabisulfite as a dough conditioner

Cysteine

Adapted from Butow BJ et al. (2002) Effects of different salts on mixing and extension parameters on a diverse group of wheat cultivars using 2-g mixograph and extensigraph methods. Cereal Chemistry 79(6): 826–833.

The use of inhomogeneous distribution in bread products has been demonstrated; that is, the dough is divided into two parts and each part has different salt levels added – one high and one low to average out at a salt level of 1.5% (Figure 5). The two doughs may then be combined by sheeting, just prior to molding. Breads with inhomogeneous salt distribution were perceived as saltier than regular bread, and several peaks of saltiness were perceived during chewing. This phenomenon was also observed after storage for a day and appeared to remain after days of frozen storage and 4 hours of thawing, thereby indicating that the mobility of the salt is limited. However, salt reduces yeast activity, so this technique requires the amount of yeast in each portion of dough to be adjusted to obtain a constant fermentation speed in each dough, independent of salt concentration. Although such technology has the potential to get to a lower salt level, at the levels presently achievable, it is still higher than the current 2012 salt target for bread. A new option of using encapsulated salt that enhances saltiness could allow for a further salt reduction, while maintaining salt intensity.

Salt Reduction in Snacks and Cereals The main focus of salt reduction of snacks has been to reduce the surface salt. Formulation approaches have been used to intensify or optimize saltiness. Added salt levels may be reduced by up to 30% in some formulations without adversely affecting taste intensity or flavor. This can be achieved by proper grade selection of salt, taking into account the particle size, crystal form and purity. However, any further reductions may require reduction of salt in the snack matrix itself where it can have implications on processing and product textural characteristics. In extruded snacks, salt regulates the expansion of the cereal starch-based matrix and glass transition temperature of the extruded product. Thus, the presence of salt is in the snack matrix itself is critical for achieving an appropriate porous structure and associated texture of extruded snack foods. Lowering the salt content in the base dough can result in too much expansion and an unacceptable product texture. Starch with high amylopectin content may be used in the

Figure 5 Bread slice with inhomogeneous salt distribution. The red colorant is added to visualize layers with a high salt content. Adapted from Toldra´ F and Barat JM (2012) Strategies for salt reduction in foods. Recent Patents on Food, Nutrition and Agriculture 4(1): 19–25.

dough base to compensate and can aid adequate expansion when salt levels are reduced in the dough base.

Future Considerations Due to health considerations, sodium reduction is a major priority for a variety of stakeholders, including government policy makers and food manufacturers. The food industry has made significant reductions to the sodium content of its products on a voluntary basis and has pledged to continue this initiative. However their success will depend on taste and other quality factors of sodium reduced products. Much is already known about the positive effects of salt on processing and product quality and strategies such as partial replacement with other salts to reduce the overall sodium content of cereal-based foods. Nevertheless,

402


challenges still remain to achieve significant salt reduction without affecting specific product characteristics and eating quality. Actions designed to reduce salt must not only contend with how reductions of added salt impact flavor and taste attributes but also be mindful of nonsensory functions of salt in cereal processing. Potassium chloride is the most widely used salt substitute, but it imparts a bitter taste that is difficult to mask. Development of salt taste substitutes or enhancers that would achieve sensory palatability of cereal foods needs to be supplemented with compounds or technologies to compensate the technological functionality of salt. Much more needs to be understood about the mechanisms of salt influencing the physical functionality of protein and starch in grain-based materials. By building a fundamental understanding of the relationship between dough microstructure, rheology, product texture and sensory properties, new technologies may be developed to better define grainbased raw material attributes through genetic breeding to target product quality while minimizing the use of salt. The dietary advantages of whole-grain foods for its highfiber and low-glycemic response are well accepted. Whole-meal or multigrain breads are gaining popularity on the market, and they do not need as much salt as for white bread (Table 1) in terms of taste due to the stronger flavors from bran and whole grains. As the technologies to process fibrous materials and whole grains become matured, the use of high-fiber grain components such as wheat bran or oat fiber, alternative grains (other than wheat), or fiber from fruit and vegetable sources to provide flavor enhancement and reduce the amount of NaCl in the formulation of conventional grain foods is a strategy with great potential for salt reduction that should be exploited further. Such approaches could provide nutritional benefits of high fiber in addition to low salt.


• • • • •

What are the functional roles of salt in grain food production? How does the salt influence the taste of baked foods? What are the technological roles of salt influencing the dough handling, gluten structure and rheology, and starch functionality? What are the other ingredients, apart from sodium chloride, in the formulation of grain foods contribute to the sodium content? What are other strategies that may be used to reduce salt apart from replacement of sodium-based chemicals?


• •

The effect of salt on gluten network structure, rheology, and dough stickiness is complex. What are the types and functions of gluten proteins? What flavor profiles of breads are affected by salt reduction and what flavor notes are implicated by replacement of sodium form of chemicals with potassium equivalent?

•

Select several grain-based food products, identify the source of sodium, and develop a strategy to reduce the sodium content in these products.

See also: Food Grains and the Consumer: Grains and Health; Processing of Grains: Cereals: Breakfast Cereals; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain; Wheat Processing: Analysis of Dough Rheology in Breadmaking; Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies; Bakeries: The Source of Our Unique Wheat-Based Food, Bread; Gluten and Modified Gluten; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Ultrastructure of the Wheat Grain, Flour, and Dough.

Further Reading Belz MCE, Ryan LAM, and Arendt EK (2012) The impact of salt reduction in bread: A review. Critical Reviews in Food Science and Nutrition 52(6): 514–524. Butow BJ, et al. (2002) Effects of different salts on mixing and extension parameters on a diverse group of wheat cultivars using 2-g mixograph and extensigraph methods. Cereal Chemistry 79(6): 826–833. Girgis S, et al. (2003) A one-quarter reduction in the salt content of bread can be made without detection. European Journal of Clinical Nutrition 57(4): 616–620. Grimes CA, Nowson CA, and Lawrence M (2008) An evaluation of the reported sodium content of Australian food products. International Journal of Food Science and Technology 43(12): 2219–2229. He FJ and MacGregor GA (2009) A comprehensive review on salt and health and current experience of worldwide salt reduction programmes. Journal of Human Hypertension 23(6): 363–384. Henney JE, Taylor CL, and Boon CS (2010a) Strategies to Reduce Sodium Intake in the United States. Washington, DC: National Academies Press. Henney JE, Taylor CL, and Boon CS (2010b) In: Henney JE, Taylor CL, and Boon CS (eds.) Strategies to Reduce Sodium Intake in the United States. Washington, DC: National Academies Press, xii þ 494. Hutton T (2002) Sodium: Technological functions of salt in the manufacturing of food and drink products. British Food Journal 104(2): 126–152. Kilcast D and Angus F (2007) Reducing Salt in Foods. Cambridge: Woodhead Publishing Ltd. Lynch EJ, et al. (2009) Fundamental studies on the reduction of salt on dough and bread characteristics. Food Research International 42(7): 885–891. McCann TH and Day L (2013) Effect of sodium chloride on gluten network formation, dough microstructure and rheology in relation to breadmaking. Journal of Cereal Science 57(3): 444–452. Miller RA and Hoseney RC (2008) Role of salt in baking. Cereal Foods World 53(1): 4–6. Noort MWJ, Bult JHF, and Stieger M (2012) Saltiness enhancement by taste contrast in bread prepared with encapsulated salt. Journal of Cereal Science 55(2): 218–225. Noort MWJ, et al. (2010) Saltiness enhancement in bread by inhomogeneous spatial distribution of sodium chloride. Journal of Cereal Science 52(3): 378–386. Salovaara H, Hellemann U, and Kurkela R (1982) Effect of salt on bread flavor. Lebensmittel-Wissenschaft & Technologie 15(5): 270–274. Toldra´ F and Barat JM (2012) Strategies for salt reduction in foods. Recent Patents on Food, Nutrition and Agriculture 4(1): 19–25. Uthayakumaran S, et al. (2011) Salt reduction in wheat-based foods – Technical challenges and opportunities. Food Australia 63(4): 137–140. Webster JL, Dunford EK, and Neal BC (2010) A systematic survey of the sodium contents of processed foods. American Journal of Clinical Nutrition 91(2): 413–420. WHO (2003) Diet, Nutrition and the Prevention of Chronic Disease. Geneva: WHO.

Relevant Websites www.awash.org.au – Australian Division of World Action on Salt & Health (AWASH). www.worldactiononsalt.com – World Action on Salt & Health (WASH).

Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies A Goldstein, University of Minnesota, St. Paul, MN, USA K Seetharaman{ ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

A combination of reactions taking place in food products during storage is referred to as staling. Starch retrogradation has been correlated with attributes associated with staling including increased crumb firmness. Flour proteins play a role in the staling process. Moisture migration and the redistribution of moisture influence product staling. A variety of methods are utilized to identify and monitor attributes of product staling. The addition of certain carbohydrates, lipids, and enzymes can be used to slow the kinetics of product staling.

Learning Objectives

• • • •

To characterize major components of grains that influence product staling. To understand the role of water migration in product staling. To recognize the vast number of methods that are utilized to study product staling and their applications. To comprehend mechanisms and roles of various materials used to slow the kinetics of product staling.

Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies Baked products undergo a wide variety of complex physical and chemical alterations during storage. These complex alterations can lead to the formation of negative quality attributes that decrease consumer acceptability and yield vast economic losses due to spoilage. A combination of physical and chemical reactions taking place in food products during storage is referred to as staling. Staling has been defined as a ‘term which indicated decreasing consumer acceptance of bakery products caused by changes in the crumb other than those resulting from the action of spoilage organisms’ (Bechtel et al., 1953). Starch transformation, moisture migration, and starch–gluten interactions are thought to cause these unfavorable changes in baked products during storage. This article will focus mainly on starch retrogradation and water migration, methods for measuring product staling, and formulation-based strategies that can inhibit the rate of staling. Food products contain a large number of ingredients in their formulations present in various proportions that have been shown to influence product staling. In particular, this article will take into consideration two product matrices representative {

Deceased.


of a large number of baked product, those being intermediate (0.9–1.5 g H2O/g dry starch) moisture systems and concentrated (0.6-0.75 g H2O/g dry starch) moisture systems.

Physical and Chemical Alterations during Processing When considering the physical and chemical alterations that occur during storage and their subsequent effects on product quality, it would be prudent to start with the raw material that is generally present in the greatest proportion, wheat flour. The composition of wheat flour may vary according to variety and growing location. Wheat flour contains starch (70–75% w.b.), moisture (14% w.b.), proteins (10–12% w.b.), lipids (2% w.b.), and nonstarch polysaccharides (2–3% w.b.) (Goesaert et al., 2005). In many baked products, starch is the main component responsible for the final structural and textural characteristics. Starch can be found in nature in the granule form in varying size, shape, composition, and structure. It consists mainly of two polyglucans, amylose, and amylopectin. Amylose is an essentially linear chain consisting of a-(1,4)-D glucosidic linkages containing a degree of branching of less than 1%. Amylopectin is a highly branched polymer with an a-(1,4)-D glucosidic linked backbone and a-(1,6)-D glucosidic linkage branching points. The structure and architecture of starch of varying source have been extensively studied and discussed in the literature, with continuous research still ongoing. Starch granules will undergo different transformations during baking/processing dependent on the product matrix in which it is present. Aqueous starch suspension undergoes a series of irreversible physical changes when heated in the presence of water, which is referred to as gelatinization. During gelatinization, the intermolecular and intramolecular hydrogen bonds between glucan chains are disrupted allowing starch granules to swell and disintegrate. The gelatinization of starch is very common in a variety of food and industrial starch applications. Granular swelling, loss of birefringence and crystallinity, changes in viscosity, and the leaching of amylose and amylopectin polymers are physical changes experienced by starch granules upon gelatinization. As gelatinization progresses, the availability of glucan chains to enzymes such as a-amylase increases. Therefore, the extent of gelatinization is a significant factor driving product quality attributes and subsequent digestion profiles. The starch: water ratio plays a critical role in the thermal transformations that occur during processing. Differential scanning calorimetry (DSC) thermograms of starch/water systems with increasing moisture content displayed a water-dependent relationship, wherein the onset gelatinization temperature typically observed in high-moisture systems is reduced, shifted to higher temperatures, or may disappear completely when reducing moisture.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00167-4

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WHEAT PROCESSING | Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies

This dynamic relationship between moisture content, internal product temperature during baking, and starch gelatinization drives many factors that influence the functionality and staling behavior of baked products.

Physical and Chemical Alterations Affecting Product Staling during Storage Macromolecular Interactions Following processing, as food products begin to cool, molecular interactions between product components begin to take place. Among these interactions, starch retrogradation plays a paramount role in product staling during storage. Retrogradation is the recrystallization process where realigned leached glucan chains in gelatinized starch are linked by hydrogen bonds. The following discussion will focus on the role of retrogradation on product staling and comment on contributions of flour components to product staling. In an intermediate-moisture product such as bread, starch granules will undergo gelatinization, and their molecular order will be lost. Bread consists of two main areas, the crust and crumb. The crust consists of a relatively low-moisture, crisp, and brittle structure containing native starch granules directly following baking due to starch and protein being in the glassy state (Hug-Iten et al., 2003). The crust is susceptible to water migration during storage, which is a significant driver of negative quality attribute formation. The crumb has been described as a porous material containing flexible elastic cell walls (Hug-Iten et al., 2003). The firmness of the crumb gradually increases over storage time. Upon cooling and during storage, starch components (amylose and amylopectin) will reassociate to more ordered structures that can be detected by numerous analytical techniques. In 1928, Katz (1928) suggested that starch polymer retrogradation was responsible for bread firming as the x-ray diffraction patterns of gelatinized starch was similar to fresh bread, whereas the diffraction patterns of retrograded starch were similar to stale bread. This finding led to the hypothesis that gradual changes in starch from an amorphous to a crystalline structure were of significance to the staling process. In the literature, it has been debated if amylose or amylopectin is the fraction of starch that contributes to bread firming (Gray and Bemiller, 2003). The kinetics of retrogradation differs between amylose and amylopectin. In solution, pure amylose has been shown to completely retrograde within hours, whereas amylopectin solutions require several days (Miles et al., 1985). There are conflicting reports regarding the role of amylose in the staling of intermediate-moisture baked products such as bread. Hug-Iten et al. (1999) hypothesized that the reorganization of leached amylose enhanced the rigidity of starch granules during staling. Conversely, Shoch and French (1947) reported that the linear portion of starch (i.e., amylose) had a negligible influence on the staling process. The majority of literature indicates that there is a correlation between amylopectin retrogradation and bread staling, although amylopectin reorganization is not the sole phenomenon involved in the process (Gray and Bemiller, 2003). From the discussion in the preceding text, one may extrapolate that amylose is the starch component responsible for initial firmness of the bread crumb, whereas the

retrogradation of amylopectin is responsible for the increasing crumb firmness observed during prolonged storage. The major raw materials in cake formulations are flour, sugar, water, and fat. Cake formulations generally contain a much greater initial moisture content than intermediate-moisture baked products and will form a batter system following mixing. The main mechanisms that contribute toward cake staling are starch recrystallization or retrogradation and moisture migration. The greater percentage of sugar and fat and, therefore, lower starch concentration in cakes result in slower kinetics of staling compared to intermediate-moisture products. Wheat flour proteins have also been investigated for their role in staling of baked products. There is a general consensus that starch–gluten interactions play a role in the bread firming process. Increasing the protein content of an intermediatemoisture baked product has been hypothesized to decrease the reassociation between starch granules and therefore decrease the development of crumb firming (Prentice et al., 1954). Hydrogen bonding between gelatinized starch and gluten during baking and throughout storage has also been implicated in the staling process (Martin et al., 1991). Although the mechanistic role of flour protein on crumb staling is debated, there is a general consensus that flour proteins are involved in the crumb staling process. Staling that occurs in low-moisture baked products is vastly different from staling that occurs in products of intermediatemoisture contents. In biscuits (2–5% baked moisture content), which contain high levels of sugar and fat, starch generally does not gelatinize during baking due to low initial dough moisture levels and the presence of sugars that increase the gelatinization temperature. This is supported by similar DSC thermograms obtained between native flour and extracted starch from baked biscuits. Kulp et al. (1991) observed that the structure of starch extracted from a baked cookie was similar to that of starch from raw dough when viewed with a scanning electron microscope. As well, physicochemical analysis comparing starch extracted from baked cookies and native starch granules revealed similar values for swelling powers and solubilities. Due to the short-time, high-temperature process in certain biscuit formulations, starch granules will swell to the point where they lose their birefringence. Due to the limited levels of gelatinization observed in low-moisture baked products, there is little to no role of retrogradation in the staling of these products. Increases in the rigidity of biscuits during storage may be attributed to increased hydrogen bonding between protein and starch (Martin et al., 1991). During storage, biscuits may sometimes develop hairline cracks that may result in cookies breaking apart during transportation and handling. This phenomenon, referred to as ‘checking,’ is a result of moisture diffusion from higher-moisture (central biscuit) regions to lower-moisture (edge) regions. To mitigate the risk of checking, one must utilize a baking profile that ensures a uniform moisture distribution throughout the product.

Moisture Migration In an intermediate-moisture bread system, moisture plays a role in a number of phenomena that occur during storage. Moisture loss (drying out), equilibration of moisture between crumb and crust, and the redistribution of moisture among and between product components (Gray and Bemiller, 2003)

WHEAT PROCESSING | Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies may all have an effect on product quality attributes. A study by Baik and Chinacoti (2000) reported that bread products stored without their crusts were significantly less firm than bread products stored containing their crusts. The products with their crusts possessed a greater amount of recrystallized amylopectin which indicates that the redistribution of moisture between crust and crumb may be responsible for the firmer product. The redistribution of moisture between individual crumb components and crust components, respectively, may also play a role in the staling process. Different authors postulate whether the moisture is redistributed from starch to gluten or from gluten to starch. As water is a plasticizer, its presence allows bread components to be more flexible. As water is removed or redistributed among components, the crumb will exhibit an increase in firmness. During amylopectin retrogradation, gelatinized amylopectin chains will reorganize to a partially crystalline structure containing B-type crystalline regions (Slade and Levine, 1987). Water molecules are incorporated into the crystal lattice during formation of the B-type crystal polymorph. As water molecules are incorporated into the lattice, they become unavailable to serve as a plasticizer, contributing to increased crumb firmness.

Measurement Techniques for Product Staling While there is no singular, definitive analysis to determine the degree of staling that can be perceived by the consumer (Sidhu et al., 1997), a variety of a methodologies have been utilized in the literature that identify characteristics present in stale products. Thermal analysis, rheological techniques, crystallography, sensory analysis, and other techniques have been used to measure the degree of staling attributes in baked products. Rheological techniques, specifically uniaxial compression, are commonly utilized to determine textural attributes of baked products. Uniaxial compression analysis as it applies to baked products measures the force required to compress a sample a defined distance. Compressibility measurements are the most commonly used technique to measure product staling (Gray and Bemiller, 2003), with numerous standard methods available. Compression testing may be used to quantify product (i.e., crumb) firmness, which is an indicator of staling. A strong correlation (r2 ¼ 0.98) has been reported between firmness, as determined by compression, and the degree of staleness determined by sensory analysis (Axford et al., 1968). A number of other product characteristics such as the Young’s modulus, springiness, gumminess, resilience, and chewiness may be determined via compression analysis and tracked during staling. In lower-moisture products such as biscuits and crackers, a three-point bend test is commonly used to measure changes in force required to fracture the product during storage. In the three-point bend test, the sample is supported on two parallel beams, and the force required to fracture the sample is measured. Thermal analysis is another technique that is frequently used to study staling in baked products. These techniques generally involve measuring the differential temperature or heat flow as a function of time when heating a test sample compared to a reference sample. The two most common thermal techniques for providing information of starch retrogradation and product staling are DSC and differential thermal analysis (DTA). DSC is

405

able to quantitatively measure the amount of starch retrogradation by monitoring the changes in melting enthalpy of reordered amylose and amylopectin. As mentioned in the preceding text, the retrogradation of amylopectin has been correlated with increasing crumb firmness and product staling. DTA can be used to monitor changes in the glass transition temperature (Tg) of bread crumb samples, which has been correlated to changes in levels of crumb firmness. A variety of spectroscopic techniques can be utilized to study staling in baked products. Nuclear magnetic resonance (NMR) spectroscopy exploits the magnetic and spin properties of materials to obtain specific molecular information about food products and matrices. In relation to the staling of baked products, time-domain NMR can be used to monitor the mobility of components within the product matrix, whereas changes in molecular structure can be monitored with the use of pulsed-NMR methods. As mentioned in this article, water plays a dynamic role during the staling process and plays a role in a number of different reactions during storage. By utilizing time-domain NMR analysis, one can quantitatively determine changes in the mobility of water molecules during storage and correlate them with changes to product attributes such as firmness. When investigating staling in baked products using Fourier transform infrared (FTIR) spectroscopy, changes in molecular conformation as a function of retrogradation can be determined by monitoring changes in bond energies and by comparing difference in the ratio of peaks derived from crystalline and amorphous regions of starch (Karim et al., 2000). X-Ray diffraction can be used to determine crystallinity loss and subsequent reassociation in food systems containing starch. As mentioned in the preceding text, the reassociation of gelatinized starch polymers or starch retrogradation plays a significant role in the staling of intermediate-moisture baked products. By viewing the x-ray diffractogram of a baked sample, one may distinguish the proportion of retrograded starch material, which has been related to staling attributes in baked goods. In conjunction with the numerous instrumental methods listed in the preceding text, sensory evaluation plays a critical role in identifying stale products and determining the shelf life (from a nonmicrobiological perspective) of commercial baked products. Sensory analysis entails the use of human senses for the evaluation of food products. It has been reported that bread that has been stored for 5 days is perceived to be less flavorful and aromatic (Lorenz and Maga, 1972). Standard methods are published for the sensory evaluation of bread, calling for the evaluation of appearance, feel, taste, mouth feel, firmness, flavor, and texture. Cookies and biscuits stale at a much slower rate than intermediate-moisture baked products, although their relatively high levels of lipids make the products susceptible to lipid oxidation and the development of rancidity (Smith et al., 2004), which can be determined with sensory evaluation analysis.

Anti-staling Strategies Baked products, specifically intermediate-moisture products, may rapidly decline in freshness and exhibit crumb firming, loss of crispiness, disappearance of a fresh flavor, and the formation of stale flavors. These attributes drive decreased consumer acceptance resulting in products that must be

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WHEAT PROCESSING | Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies

discarded if not sold prior to exceeding their shelf life. Discarding products result in vast economic losses, and extending the shelf life of products by a few days can yield substantial savings. Due to the significant financial implications involved with extending the shelf life of baked products, a number of viable strategies have been developed to mitigate the appearance of negative quality attributes and decrease the rate of staling. Certain enzyme, lipid, and carbohydrate ingredients that are added to baked product formulations are commonly utilized as anti-staling agents. A number of enzymes, acting on different components (i.e., carbohydrate, lipid, and protein fractions) of the product matrix, catalyze reactions that retard product staling. The enzyme that is most commonly used in the bread making process is a-amylase, which can be sourced from a number of origins. The source of the enzyme will affect its heat stability and functionality during baking and storage, with most a-amylases being of fungal, bacterial, or maltogenic origins. One of the most effective anti-staling amylases is Bacillus stearothermophilus (Miguel et al., 2013). The anti-staling mechanism of a-amylases is believed to be related to its ability to influence the retrogradation behavior of starch during storage due to their ability to hydrolyze and thus influence the degree of polymerization of starch chains. Lipases are enzymes that catalyze the hydrolysis of triacylglycerols to produce diacylglycerols, monoacylglycerols, glycerol, and free fatty acids. It has been reported that the addition of lipases retard staling in baked products. The purported mechanism is due to the production of monoacylglycerols from the hydrolysis of triacylglycerols. Monoacylglycerols have the ability to form helical inclusion complexes with leached amylose chains, which favorably influence texture. This mechanism though is controversial in the literature and not fully accepted (Miguel et al., 2013). Protease enzymes are commonly used in bread baking for improving machinability, providing flavor, and improving mixing time and gas retention; they also have been reported to positively influence staling. Lipids can be utilized as anti-staling ingredient in baked products due to their ability to act as surfactants and their ability to form complexes with starch components. Many bakeries use monoacylglycerides (MAG) of varying saturations and chain lengths in their formulations. The hydrocarbon tail possessed by the MAG interacts with starch components (i.e., leached amylose and amylopectin chains) to form a helical hydrated V-type complex. These complexes can be identified by XRD due to their unique x-ray diffraction pattern. A number of different hypothesis have been reported regarding the mechanisms of how monoacylglycerides influence staling behavior. Lagendijk and Pennings (1970) postulated that the complexation between MAGs and amylose decreased the flexibility of amylose molecules, thus decreasing their ability to retrograde. Another hypothesis for the lipid surfactant effect is related to their ability to decrease the amount starch swelling (Ponte et al., 1973). With decreased granule swelling, there is decreasing leaching and mobility of starch polymers; therefore, decreased retrogradation and crumb firming will occur. Along with the addition of lipids and enzymes, certain carbohydrate ingredients such as hydrocolloids/gums and fibers may influence staling kinetics by their ability to influence the mobility of water in the products matrix, thus impacting water migration between product components.


• • • •

What is product staling? What are the components of grain that influence product staling? What are the main approaches used for evaluating staling in baked products? List the major anti-staling strategies, and describe how each strategy influences staling.

Exercises for Readers to Explore the Topic Further Despite the considerable research conducted, vast economic losses are still sustained by food producers due to product staling. A number of areas require further investigation including

• •

the relationship between the use of refrigerated/frozen dough and the kinetics of product staling, predictive modeling for the kinetics of product staling given product formulation, baking parameters, and storage conditions.

See also: Carbohydrates: Starch: Chemistry; Starch: Starch Architecture and Structure; Proteins: The Protein Chemistry of Cereal Grains; Wheat-Based Foods: Breads.

References Axford DWE, Colwell KH, Cornford SJ, and Elton GAH (1968) Effect of loaf specific volume on the rate and extent of staling in bread. J. Sci. Food Agric. 19(2): 95–101. Baik MY and Chinachoti P (2000) Moisture redistribution and phase transitions during bread staling. Cereal Chem. 77(4): 484–488. Bechtel WG, Meisner DF, and Bradley WB (1953) The effect of the crust on the staling of bread. Cereal Chem. 30: 160. Goesaert H, Brijs K, Veraverbeke WS, Courtin CM, Gebruers K, and Delcour JA (2005) Wheat flour constituents: how they impact bread quality, and how to impact their functionality. Trends Food Sci. Technol. 16(1): 12–30. Gray JA and Bemiller JN (2003) Bread staling: molecular basis and control. Comp. Rev. Food Sci. Food Saf. 2(1): 1–21. Hug-Iten S, Handschin S, Conde-Petit B, and Escher F (1999) Changes in starch microstructure on baking and staling of wheat bread. LWT-Food Sci. Technol. 32(5): 255–260. Hug-Iten S, Escher F, and Conde-Petit B (2003) Staling of bread: role of amylose and amylopectin and influence of starch-degrading enzymes. Cereal Chem. 80(6): 654–661. Karim AA, Norziah MH, and Seow CC (2000) Methods for the study of starch retrogradation. Food Chem. 71(1): 9–36. Katz JR (1928) Gelatinization and retrogradation of starch in relation to the problem of bread staling. In: Walton RP (ed.) Comprehensive Survey of Starch Chemistry, vol. 1. New York: Chemical Catalog Co. Kulp K, Olewnik M, Lorenz K, and Collins F (1991) Starch functionality in cookie systems. Starch Sta¨rke 43(2): 53–57. Lagendij J and Pennings HJ (1970) Relation between complex formation of starch with monoglycerides and firmness of bread. Cereal Sci. Today 15(10): 354. Lorenz K and Maga J (1972) Staling of white bread. Changes in carbonyl composition and GLC [gas–liquid chromatography] headspace profiles. J. Agric. Food Chem. 20(2): 211–213. Martin ML, Zeleznak KJ, and Hoseney RC (1991) A mechanism of bread firming. I. Role of starch swelling. Cereal Chem. (USA) 68: 498–503. Miguel AˆSM, Martins-Meyer TS, da Costa Figueiredo E´V, Lobo BWP, and DellamoraOrtiz GM (2013) Enzymes in Bakery: Current and Future Trends. 1st edn. InTech.

WHEAT PROCESSING | Baked Product Staling: Mechanisms, Determinations, and Anti-staling Strategies Available online at: http://www.intechopen.com/books/food-industry/enzymes-inbakery-current-and-future-trends. Miles MJ, Morris VJ, Orford PD, and Ring SG (1985) The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydr. Res. 135(2): 271–281. Ponte JG, DeStefanis VA, and Titcomb ST (1973) Effects of some crumb softeners on bread firmness and starch properties of baked bread (abstract). Cereal Sci. Today 18: 302. Prentice N, Cuendet LS, and Geddes WF (1954) Studies on bread staling. 5. Effect of flour fractions and various starches on the firming of bread crumb. Cereal Chem. 31(3): 188–206.

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Schoch TJ and French D (1947) Studies on bread staling. 1. The role of starch. Cereal Chem. 24(4): 231–249. Sidhu JS, Al-Saqer J, and Al-Zenki S (1997) Comparison of methods for the assessment of the extent of staling in bread. Food Chem. 58(1): 161–167. Slade L and Levine H (1987) Recent advances in starch retrogradation. Industrial Polysaccharides: The Impact of Biotechnology and Advanced Methodologies, pp. 387–430. Smith JP, Daifas DP, El-Khoury W, Koukoutsis J, and El-Khoury A (2004) Shelf life and safety concerns of bakery products—a review. Crit. Rev. Food Sci. Nutr. 44(1): 19–55.

Gluten and Modified Gluten IL Batey, Sunset Cereal Services, Meadowbank, NSW, Australia W Huang, Jiangnan University, Wuxi, Jiangsu, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Gluten is the storage protein component of wheat. The commercial production of gluten is a by-product of the wheat starch industry. It is gluten that gives wheat flour its unique properties for bread-making. Gluten may be added to low-quality flours to allow the manufacture of higher-quality products. Gluten may also be added to foods and feeds as a source of protein. The nutritional value of gluten is reduced because of low amounts of some essential amino acids. Demand for Western-style foods or improved quality of traditional foods is driving an increasing use of gluten in developing economies.

Learning Objective

•

To achieve an understanding of the nature of gluten and how its properties are useful for improving quality in foods.

What Is Gluten? A nontechnical definition of gluten describes it as ‘the sticky, viscous residue after removal of starch from flour.’ This definition would include corn gluten, the protein residue from isolation of starch from corn. However, this material is quite different to wheat gluten, the residue from production of wheat starch from flour. In the technical sense, the term ‘gluten’ usually refers to wheat gluten. However, there are many people with food intolerance to cereals, and for them, ‘gluten’ includes the equivalent proteins from rye, triticale, barley, and possibly oats. The most commonly recognized intolerance to gluten is celiac disease. There is also a syndrome known as ‘nonceliac gluten sensitivity’ although there is evidence that this condition, in some people at least, is not caused by gluten but by a group of sugars known as ‘fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.’ People with gluten intolerance need to consume a diet that excludes ‘gluten’ from any of the cereals listed earlier. The term ‘gluten-free food’ refers to a food product free from these cereal proteins or whose cereal protein content is less than a defined amount, usually <200 ppm for a cereal-based food and <20 ppm for a food not naturally containing gluten. For the purposes of this article, only the properties and uses of wheat gluten will be discussed. Gluten may thus be defined technically as the “cohesive, viscoelastic, proteinaceous material prepared as a by-product of the isolation of starch from wheat flour” (Figure 1). A more theoretical definition may define it as the “storage proteins of the wheat grain.” Both definitions are correct but neither tells the whole story, and for the purposes of

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this article, gluten is the commodity isolated on a commercial scale and sold for a variety of purposes in many countries of the world. In particular, ‘vital wheat gluten,’ the dry form of the product in which the functional properties may be regenerated by rehydration, will be mainly considered.

Composition of Gluten Although sold as a protein, gluten contains more than just protein. The commodity usually contains 75% protein, 8% moisture, and varying amounts of starch, lipid, and fiber. The starch and fiber become entrapped in the cohesive matrix of the protein and become more difficult to remove as the protein content increases. The amount of starch varies, and more extensive washing can reduce the starch and fiber content and increase the protein content. The extra water needed for this creates its own problems by producing a larger amount of effluent from the process and increasing the biological oxygen demand of that effluent (see in the succeeding text). Consequently, gluten of higher protein content is only produced as a special order and at a premium price. The lipid content is unaffected by additional washing. Most of the lipid content of the flour becomes associated with the protein during the washing process. The proteins are hydrophobic and the lipids bind to the hydrophobic areas of the protein as they are repelled by the water used in the washing. Lipids bind strongly to gluten and are removed with much more difficulty than from the original flour. The lipid content of gluten is primarily determined by the lipid content of the flour from which it came and is unaffected by additional washing. The final lipid content of gluten may be decreased by using a solution of certain salts (e.g., sodium, potassium, or ammonium chlorides), but the presence of these salts in the effluent may also create environmental problems. The protein that makes up gluten is actually a complex mixture, containing many, perhaps several hundred, polypeptide species. A typical amino acid analysis of the complex mixture is shown in Table 1. The individual proteins are divided into two main classes – monomeric and polymeric. These terms can be confusing in that any protein is a polymer of amino acids. In gluten, monomeric refers to individual, discrete polypeptide species, whereas polymeric refers to chains formed from individual monomeric proteins by cross-linking them with disulfide bonds of cystine residues in adjoining chains. The monomeric proteins are often called gliadin and the polymeric ones are called glutenin. It should be noted that some of the glutenin subunits do exist in gluten in the monomeric form.

How Is Gluten Made? Gluten was first prepared from flour almost 300 years ago by an Italian named Beccari, who conducted a simple water-washing


http://dx.doi.org/10.1016/B978-0-12-394437-5.00157-1

WHEAT PROCESSING | Gluten and Modified Gluten

Figure 1 Gluten prepared from wheat flour, showing its cohesive and viscoelastic nature. Courtesy of Colin Wrigley.

Table 1

Amino acid composition of commercial vital wheat gluten

Amino acid

Contenta

Alanine Arginine Aspartic acidb Cystine Glutamic acidb Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tyrosine Valine

3.0 4.3 4.8 2.6 39.0 4.6 2.7 4.4 8.4 2.2 2.1 7.3 14.6 5.6 3.1 4.3 4.6

a

Values expressed as g amino acid/100 g protein. b Glutamic acid and aspartic acid are predominantly in the amidate form, with 90% existing as glutamine and asparagine, respectively.

experiment with wheat flour. This discovery, which can be easily reproduced in the home kitchen, has become the basis of a major cereal industry, utilizing millions of tonnes of wheat annually in North America, Europe, and Australia (Figure 2). The commercial process is basically an efficient repetition of Beccari’s experiment. Most commercial operations use variations of either the ‘batter process’ or the ‘Martin process.’ Originally, gluten was produced as a by-product of the wheat starch industry. There is a high demand for starch for both food and nonfood uses, and in those areas where wheat was the major crop, it became the main raw material in the preparation of the starch required for various industrial purposes. Gluten became an embarrassing by-product. In some cases, its disposal was in municipal sewers and drains, but this soon became an undesirable practice. It was also dried in a variety of ways to yield a protein-rich material used in animal

409

Figure 2 Gluten prepared in a commercial process.

feeds, and wet gluten was also used to fortify bread and other baked products made from flour. The shelf life of wet gluten, usually only a few hours, severely restricted its use in this form. It was not until the application of ring drying that a dry vital gluten product could be prepared in significant amounts, allowing its trade as a valuable commodity.

Martin Process In this method, a wheat flour dough is washed with water while it passes through a tumbling cylindrical agitator. The work applied to the dough is not dissimilar to the effect of kneading a dough under water in that starch comes out of the dough and the protein content increases. The tumbling action moves the dough along the cylinder and the starch passes through small holes in the wall, while the protein remains inside, receiving further washing until it tumbles out at the end.

Batter Process In this process, a thick suspension or batter of flour is stirred slowly in a tank for several hours, during which time the starch separates from the protein. The mixture is then passed through a fine sieve, which allows the starch granules to pass through but retains the curds of gluten on the screen. This gluten is then washed with water to remove further starch in a similar manner to the Martin process and then dried. The Martin process is a continuous process, while the nature of the batter process makes it more suited to batch operation.

Other Processes Most commercial operators use one or other of the previous methods with modifications, but there have been many other processes suggested for production of gluten. While most have not made it past the laboratory curiosity stage, others, for example, the Alfa-Laval/Raisio process, have been applied in full-scale production facilities. The basis of these other processes varies, and some use centrifugal techniques, which may involve either

410


conventional industrial centrifuges or hydrocyclones to separate the starch from the protein. Many operators use hydrocyclones as the principal way of cleaning the starch and, in some cases, in the actual separation of the starch and gluten. Many of the newer methods utilize whole grain as the raw material, avoiding the production of flour in a dry-milling step. This allows a more complete isolation of the starch fraction from the wheat, but cleaning the protein and starch of residual bran is a major disadvantage of these types of methods. Improved milling processes have reduced the amount of endosperm remaining in the bran and offal fractions in conventional milling, so there is little advantage to be gained in wet milling for starch and gluten recovery. There is also the need to dry the bran unless it can be processed on the spot or at least locally, and this cost will usually exceed the economic benefit of improved starch yield. Thus, despite these newer methods, modifications of the traditional processes have remained the preferred choice for almost all the gluten produced worldwide.

Dry Gluten Gluten is very susceptible to heat when wet, and relatively low temperatures destroy the cohesive, viscoelastic properties (‘vitality’), which make it unique among food proteins. Attempts to dry gluten while retaining these properties were unsuccessful until the application of the ring drier to gluten in the first half of the twentieth century. This drying process has since been the basis of gluten production. Prior to this, vital gluten was only available in a wet form and could only be used in this form for a short time after production. The principle of the ring drier is that simple wet gluten with a moisture content of 70% is mixed with sufficient dry, vital gluten to reduce the moisture to 20%. This lowered-moisture material is comminuted and subjected to flash drying in a ring drier. A portion of the dried gluten is removed and packaged, while the rest is returned to the drying cycle to reduce the moisture content of more wet gluten. The procedure is still very sensitive to excessive heat, but with careful control of the temperature, a vital wheat gluten is produced. An alternative way of drying to prepare a vital gluten is to disperse the gluten in aqueous ammonia or acetic acid and then spray-dry this dispersion. The resulting product retains the viscoelastic properties of gluten, and it may be used for most of the same purposes as normal vital gluten. The cost of this drying procedure, together with environmental concerns from the emission of ammonia or acetic acid vapors, limits its application except for special reasons. Another dry gluten product is known as ‘devital gluten.’ This material has lost its cohesive, viscoelastic properties but retains the insolubility and water-binding capacity of vital gluten. It is commonly used where the cohesiveness of vital gluten can actually be a disadvantage.

methods include fermentation to produce ethanol or methane, isolation by drying for use in animal feed, and discharge into the sewerage system. The last option is becoming less common as environmental concerns grow worldwide.

Properties of Gluten The most important properties of gluten are its solubility (or rather its lack of solubility) and its rheological functionality. By the nature of its preparation, gluten is a protein that is insoluble in water. While there are small amounts of water-soluble proteins trapped in the gluten matrix, these are essentially not extractable into water under normal conditions. Despite its insolubility and its hydrophobic nature, gluten absorbs an amount of water approximately twice its dry weight to form a hydrated gluten. This material is effectively the same as the wet gluten first isolated from flour. In the case of commercially prepared gluten, drying conditions may cause some deterioration of the functional properties, but gluten prepared in the laboratory shows no change in its properties after freeze-drying and rehydration. The principal components, gliadin and glutenin, are both insoluble in water. Gliadin can be solubilized in 70% ethanol, one of the steps of the Osborne fractionation of wheat proteins, and the residue after this extraction is considered to be glutenin. Isolation of the dissolved material, however, yields a protein, which has lost most of its functional properties. Both gliadin and glutenin may be solubilized to a certain degree by the use of acidic conditions. By careful control of the pH, gluten may be separated into a number of fractions. Reprecipitation by pH adjustment, or by drying the acidic solution directly, gives products that maintain their functional properties. This can be shown by reconstituting flour through recombining the starch, the isolated protein fractions, and the water-soluble components prepared during the extraction of gluten. Doughs prepared by careful reconstitution show little change in dough strength compared to that of the original flours. The rheological properties of gluten are the basis of its functional uses. It is these properties that give wheat flour doughs the characteristics that allow the production of breads, cakes, biscuits, and noodles. Thus, gluten can be considered to be like a dough in which the diluting effect of starch is no longer present. In the wet state, the protein molecules form a cohesive matrix, which, in dough, also holds the starch granules within it. This matrix is also elastic, allowing it to stretch and expand. In aerated doughs, this elasticity permits the expansion of gas bubbles, which produce the texture of bread and cakes. If the gluten matrix is too weak, or the protein content is too low to form an effective matrix, the bubbles expand beyond the elastic limit and burst, reducing the overall volume of a baked product.

Waste Products from Manufacture of Gluten

How Is Gluten Used?

The amount of water required for each tonne of flour varies according to the operator. All processes have a significant waste stream that consists of the wash water plus soluble protein, damaged starch, and sugars plus some fiber. Disposal procedures for this waste vary, depending on the manufacturer, and

The uses of gluten worldwide vary from country to country, but the most common usage in Western countries is addition to flour in baked goods of various types (Table 2). The second largest use is in pet foods. Here, gluten is added as a protein source to improve the nutritional quality of the pet food. Its

WHEAT PROCESSING | Gluten and Modified Gluten Table 2 Usage of gluten in different regions (as percentage of total usage for region)

Baking Flour fortification Pet food Meats Breakfast cereals Noodles Sausages Other Foods (in general) Feeds Other

N. America (%)

EU (%)

Australia (%)

Japan (%)

83 0.5

16.5 66

54 9

30

12 1 1

13.5

13 9 12

2.5

4

3

China (%)

25a

4

3

foods and aquaculture feed. Nonfood uses represented 5% in China (Table 2). India is another major wheat-producing country where increased affluence has created a demand for wheat-based foods with improved quality. There is already one gluten producer operating in India and there is a growing demand for vital wheat gluten for incorporation into foods. It is added to a variety of wheat-based products, including traditional ones such as chapattis.

Baked Goods 10 12 23 76

2.5

411

23

19 5

a

Includes gluten used for synthetic fish products.

hydration and lipid-binding properties also assist in improving the overall properties of the product. A growing market for gluten is as an ingredient in aquaculture feed, where its cohesive properties hold the feed together when it is put into water. Gluten is used in other countries in a variety of ways. Perhaps the major use is as a meat replacement in vegetarian foods and in the production of artificial forms of expensive foods such as crab meat. It is also used in the preparation of soy sauce extenders and the manufacture of monosodium glutamate. The high glutamine content of gluten makes it an ideal starting material for this latter product. There are developing markets for gluten in countries with rapidly growing economies. The increasing affluence has created a demand for Western-style foods, many of which are based on wheat and for which the properties of gluten are essential. In addition, gluten may be used for flour fortification in traditional food, allowing the use of lower-quality flours or improving the quality of the product. China has emerged as one of the three most important economies in the world. Significant changes have taken place in consumption patterns and market trends following economic reform and opening its markets to the world. Wide varieties of ethnic, frozen, bread, bun, and bakery food products are in the marketplace today. The use of frozen dough has been of great interest since the 1960s; it has now appeared in traditional steamed bread chain stores as well as in bakery chain stores in China’s markets, indicating a trend in the dough products industry. Gluten is often used at 1–2% level for increased dough strength, cryoprotective property, and steaming or baking performance. The use of gluten in combination with so-called bioingredients such as enzymes can also reduce the use of chemical oxidants in dough to satisfy consumers’ food safety and health concerns. In addition to modern bakery products and traditional steamed bread products, gluten is used in other food products such as noodles, extruded snacks, sausages, fried gluten balls, and fish meat balls. There are about 30 gluten manufacturers operating in China. It has been estimated that 76% of all gluten used in China goes to foods, while 19% goes to feeds, including pet

Wheat-based products, in which gluten is used to fortify flours of lower-than-desirable protein content, have been and continue to be the main application of gluten. There is a concern about the effects of gluten on people with celiac disease and others with wheat protein allergies, but its incorporation into foods that already contain gluten cannot be questioned. Increasing the protein content of a flour by adding vital gluten improves the quality of the flour to be equivalent to one with the higher protein content. This fortification may be necessary because the flour has a naturally low protein and a higher protein content is needed to make quality products or because the addition of gluten provides a particular property sought in the food by improving the quality of the protein. Addition of gluten to a flour of low protein content improves the texture and shelf life of bread prepared from it, but it is useful in other applications as well. For example, addition of 1% gluten to flour reduces pretzel breakage in the finished product, but the addition of too much gluten may result in pretzels that are too hard to eat. Addition of gluten to pasta-type products will also reduce breakage. However, the desire of consumers for pasta of 100% durum wheat origin means that fortification with gluten for this purpose is more limited.

Other Uses In addition to its use in pet foods, gluten is commonly added as a binder in meat products for human consumption. Here, the desired property is its ability to bind fat and water while at the same time increasing the protein content. Gluten and modified glutens have also been used in calf-milk replacements. A number of nonfood uses have also been suggested for gluten. These include adhesives, paper coating, detergent formulations, slow-release pharmaceuticals, medical bandages, construction materials, and binding of heavy metals in industrial processes. The use of gluten in films has also been tried. Gluten-based films may be cast from solutions of gluten in ammonia. Production of gluten films with satisfactory properties could provide a new biodegradable film for widespread use.

Modifying Gluten Gluten is a protein, intermediate in price between low-value commodities suitable only as animal feed without further processing and high-value materials such as casein and soy isolates. This gives significant scope for modification of its properties for value addition. Various threatened surpluses in

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the market for gluten have turned the attention of manufacturers to ways of converting gluten into products with vastly different properties.

Chemical Modification The main modification applied to gluten is solubilization. Gluten becomes soluble in a variety of chemicals including urea solutions, lactic acid, soaps and detergents with or without urea, acetic acid, hydrochloric acid, sodium hydroxide, 70% ethanol, and 2-chloroethanol to name just some. Many of these are incompatible with food products, but for nonfood purposes, there are few limitations other than cost, safety, and environmental concerns. Solubilization by deamidation is the major method applied. This may be achieved with either acid or alkali. Approximately 90% of the glutamic acid in gluten is in the form of glutamine (Figure 3). Removal of the amide group of these residues to form the corresponding carboxylic acid changes the potential ionic charge on the protein, thus increasing its solubility above a certain pH. In acidic deamidation, there is also a degree of peptide hydrolysis to form lowermolecular-weight polypeptides, which are usually more soluble than larger ones. In alkali solutions, peptide hydrolysis does not occur as readily as in acid. However, there is the possibility of alkaline attack on the disulfide bonds of cystine, with the subsequent opportunity of creating cross-links due to the formation of lysinoalanine (Figure 3). The use of temperatures close to ambient has shown no formation of lysinoalanine. The reaction mixtures of acid or alkali deamidation require neutralization before the products can be used for their final purpose, a step that produces significant amounts of salts, which usually need to be removed. This can be done by isoelectric precipitation, that is, adjustment of the pH to the isoelectric point at which proteins are least soluble as they have no net charge. A procedure that uses acidic or basic proteins to neutralize the alkali or acid, respectively, has been reported. No inorganic salt is formed in this process, but the overall proportion of gluten in the final product is very much reduced. Deamidated gluten is easily dispersible, which makes it suitable for use in foods for emulsification or foam stabilization. It has been used in meat products, nondairy coffee whiteners, beverages, and milk puddings. No benefits have been reported for the use of deamidated gluten in bread doughs. Gluten may be treated with sulfuric acid, phosphoric acid, or chlorosulfonic acid to prepare products, which bind greatly increased amounts of water. There have been reports that some of these products bind an amount of water equivalent to up to NH2

NH2

HOOC-CH-CH2-CH2-CONH2

HOOC-CH-CH2-CH2-COOH

Glutamine

Glutamic acid NH2

NH2

HOOC-CH-CH2-CH2-CH2-CH2-NH-CH2-CH-COOH Lysinoalanine Figure 3 Structures of glutamine, glutamic acid, and lysinoalanine.

200 times their own weight. Other chemical modifications include acylation with carboxylic acid anhydrides. In particular, treatment of gluten with succinic anhydride increases its solubility at pH 7 (close to the point of minimum solubility of native gluten) but decreases its solubility at pH 3 where it is normally quite soluble.

Enzymic Modification Hydrolysis of the peptide bonds by enzymes also increases the solubility of gluten. This is achieved by reducing the molecular weight of the polypeptide chains. A number of commercially available enzymes have been used for this purpose, including papain, bromelain, subtilisin, trypsin, and pronase. The enzyme-solubilized gluten has many of the properties of chemically deamidated gluten, such as foam stability and emulsion formation. Unlike deamidated gluten, enzyme-solubilized gluten does have beneficial effects on dough properties. Addition at levels of 1–2% reduced dough mixing times by amounts similar to those achieved by chemicals, such as cysteine and ascorbic acid, which are often added commercially to give improved loaf volumes. Many of the reports of enzymesolubilized gluten refer to it having a bitter taste. This is believed to arise from the formation of small peptides that have been identified with bitter flavors in other proteins. Thus, treatment with enzymes needs to be carefully controlled to minimize the formation of these small peptides. There is a potential for modified glutens to be used in products, which traditionally do not contain wheat or other cereals. This has raised concerns about whether the toxicity of gluten for people with a gluten sensitivity will have been removed. At this point in time, there is insufficient evidence to categorically say whether or not these foods would be safe for people with gluten sensitivity.

The Future for Gluten Production of gluten is still driven by the need for starch. Thus, it will always be produced, while wheat is a major source of starch. There is the risk that demand for starch will grow faster than the demand for gluten, but to date, this has not happened despite dire predictions on many occasions. Although its absolute price has not changed significantly over many years, by becoming relatively cheaper than alternative food proteins, gluten has found its way into more applications for which it was formerly too expensive. This has served to maintain its value, while output has greatly increased. The demand generated by increased affluence in developing countries will also help to maintain its price and will probably result in higher prices in the longer term. Consumer concerns about gluten-free foods may limit its application in some areas, but the ubiquity of wheat in many foods ensures that gluten will remain an acceptable additive. The greatest threat to the gluten industry has been and will remain the lower cost of preparing starch from sources other than wheat. Gluten has played a major role in keeping the production of wheat starch economically viable in face of cheaper starch from other sources. This situation is expected to be unchanged in the future.



• • • • • • • •

What are the principal protein components of gluten and how do they differ from one another? Which amino acid is predominant in gluten and in what form is it present? What is the second most common amino acid in gluten? Why is gluten added to flour to improve the quality of products? Why is dry, vital gluten difficult to prepare and what technique is used to produce it? What modifications may be applied to gluten to prepare a soluble product? What are two factors driving increased gluten use? What groups of proteins are the storage proteins of cereals? What is protein denaturation and how does it affect the use of gluten in food products?

• • •

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present in greater abundance than would be required in a balanced protein? How could the nutritional limitations of gluten be overcome in a mixed protein food? What bonds are responsible for the primary, secondary, and tertiary structures of proteins? In what two ways is gluten a polymer? What makes up the backbone structure of protein?

See also: Appendix 3: Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; The Gluten-Free Diet; Nonfood Products from Grains: Cereal Grains as Animal Feed; Pet Foods; Proteins: The Protein Chemistry of Cereal Grains; WheatBased Foods: Breads; Wheat Processing: Cereal Food Production with Low Salt; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Wet Milling of Wheat.


Further Reading

•

Khan K and Shewry PR (eds.) (2009) Wheat Chemistry and Technology. 4th edn. St. Paul, MN: American Association of Cereal Chemists International. Lookhart GL and Ng PKW (eds.) (2006) Gluten Proteins 2006. St. Paul, MN: American Association of Cereal Chemists International. Shewry PR and Lookhart GL (eds.) (2003) Wheat Gluten Protein Analysis. St. Paul, MN: American Association of Cereal Chemists International. Shewry PR and Tatham AS (eds.) (2000) Wheat Gluten. The Proceedings of the 7th International Workshop Gluten 2000, London: Royal Society of Chemistry. Wrigley C, Bekes F, and Bushuk W (eds.) (2006) Gliadin and Glutenin: The Unique Balance of Wheat Quality. St. Paul, MN: American Association of Cereal Chemists International.

• • •

What are the rheological properties that make gluten so useful, and how are they measured? The quality of what traditional foods may benefit from the addition of gluten to low-protein flours? For sufferers of celiac disease, what are the implications of using solubilized or other modified glutens in foods that normally do not contain wheat? What are the nutritional limitations of gluten as a food protein? Are there any essential amino acids, which are

Snack Foods: Processing MN Riaz, Texas A&M University, College Station, TX, USA ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 98–108, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • •

Snack consumption patterns. Snack food types. Snack food production methods. Common snack ingredients. Expanded snacks. Coextruded snacks.

Learning Objectives

• • •

To understand the major snack food types and the methods of their manufacture. To understand the functional role(s) of major ingredients in the characteristics of the products. To understand the evolution of first-, second-, and thirdgeneration snack foods.

Background Snack foods have always been a significant part of modern life; they represent a distinct and constantly widening and changing group of food items. Sales in 2000 were over $19.37 billion and per capita snack consumption was 10 kg. According to a rough working estimate, annual worldwide sales including the United States were $30–35 billion. The American Heritage Dictionary defines snack as ‘hurried or light meal’ or ‘food eaten between meals.’ Traditional snack foods appeal to consumers on a number of levels. Snacks can be considered a treat or reward. Designing snack foods today can be a complex process to meet changing consumer’s taste and expectation, for example, ‘good for your health,’ ‘rich source of soy protein,’ ‘offering a unique flavor,’ and the elusive search for something unique that also appeals to a wide variety of people. Most snack manufacturers use some form of existing technology as the basis for creating snack products, but incorporate variations that increase the resulting snack’s health image appeal by lowering fats and calories or adding nutrients.

Snack Consumption Patterns The snack food market is constantly changing relative to product types, and although most snacks are not primarily consumed for their nutrients, many snacks are made with nutrition in mind. The snack food industry is experiencing extraordinary changes from the consumers’ point of view. Consumers want snacks to not only taste good but also smell good, feel good, and look good. Snacks should give the consumer a homemade/fresh feel. Some of the snacks are

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developed with a special theme in mind like world soccer. These snack pellets are soccer ball-shaped, which on frying or treating in a microwave oven become soccer balls (Figure 1). Snacking rises due to an increase in factors such as oneperson households, higher proportions of working spouses and more school-age children obtaining their own meals and refreshments, a highly mobile population, and availability of snack foods in vending machines and convenience markets. Various products, which were once consumed mainly on impulse, are becoming accepted as side-dish items, for example, corn chips or potato chips served in place of mashed potatoes. The established position of snack foods in the diet is demonstrated by the continuous growth in sales. In the last 10 years, changes in lifestyle and eating patterns have led to a gradual increase in demand for snack foods. The pattern of snacking in different countries can be affected by several factors such as the lifestyle in each area, the economic climate, rival foods, and public receptiveness of current views on nutritional matters. Snacks can provide an increased dietary intake of essential amino acids and other nutrients for developing countries. Some of the most recent factors driving the newer snack food trends are as follows: (1) availability of healthy snacks like energy bars or soy-fortified bars, (2) better taste and flavors, (3) better and attractive shapes for children and packaging, and (4) better varieties of snacks like soy nuts or yogurt bars.

Types of Snack Foods Although it is not possible to discuss all types of snack foods available in the market in this article, only the major types of snack foods like potato chips, corn, and tortilla chips and extruded snacks (expanded and pellets snacks) will be discussed in detail. A broad variety of snacks made by different processes are available in the market. These include potato chips, tortilla chips, corn chips, ready-to-eat popcorn, extruded snacks, pretzels, snack nuts, meat snacks, pork rinds, party mix, multigrain chips, granola products, and variety packs. Most recently, a variety of health snacks made with soy protein have been seen. These soy-based snacks contain 6.25 g of soy protein per serving to qualify for the health claim of the Food and Drug Administration. Along the same line, snacking on soy nuts is becoming very popular among the health-conscious consumers. Nowadays, soy nuts can be found with different flavors in most grocery stores. Snacks with different spices and flavors are becoming very popular with US consumers. There is a substantial growth in ethnic snacks from Mexico and India in the markets. Snacks from India are mostly fried lentils and chickpeas, and similar types of pulses with different flavors (mostly with chili powder) are entering the US market.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00160-1

WHEAT PROCESSING | Snack Foods: Processing Each snack processor may use a specific unit operation and somewhat different technologies to produce unique snacks. There are many ways to classify the snacks. Snack manufacturers use three main terms to identify the snacks (see Figures 2–4): 1. First-generation snack foods: In this category, all the natural products used for snacking, nuts, potato chips, and popped popcorn, are included. 2. Second-generation snack foods: The majority of the snacks such as all the single-ingredient snacks, simple-shaped

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products like corn/tortilla chips and puffed corn curls, and directly expanded snacks are included in this category. 3. Third-generation snack foods (also called half-products or pellets): In this category, snacks and pellets formed using multiingredients, made by extrusion cooking, are included.

Production of Snacks It is not possible to discuss every snack-manufacturing procedure in detail (see Figure 5). Manufacturing of only major snacks will be discussed here.

Potato Chips

Figure 1 Different-shaped snacks.

Figure 2 (a) First-generation snack foods. (b) Multigrain chips.

The potato chips form the largest snack food sector in all markets. Traditional potato chips start with whole, raw potatoes sliced between 0.035 and 0.070 in. thick. These cuts can be straight, grooved, crinkled, or flat surface. The most important point is that slice surface should be uniform for all these cuts. These slices are washed with water to remove starch and eliminate sticking or can be blanched to reduce the level of reducing sugars to avoid browning before frying. The critical parameters for the chipping potatoes are moisture, starch, and sugar level. For a good potato chip, the dry matter should be 20–23%, giving a specific gravity of 1.080–1.095. Potatoes with a lower specific gravity require a longer frying time and absorb more oil. In general, potatoes contain 80–85% water, depending on variety. The rest is (15–20%) dry matter, which is 90% carbohydrates, mainly starch. The major concern with the carbohydrate portion is reducing sugars. The sugar contents may be as high as 10% of the dry matter. However, for potato chip processors, a sugar level above 2% is a concern as it induces the Maillard reaction during frying and makes unacceptable dark-colored potato chips. Potato chips can be fried using batch or kettle frying or continuous frying. In batch operation, chips have a higher fat level, more blistering, and a harder surface due to the presence of starch on the surface. Whereas with a continuous fryer, the potato slices are continuously fed into the fryer and cooked as they are conveyed and removed at the end. After frying, before the product cools and the surface oil solidifies, the chips receive an application of salts and/or seasoning. Typical salt levels are from 1.5% to 2.5% and the seasoning levels range from 4% to 8%. The typical potato chip has a fat content of 35–40%, making it difficult for most consumers to categorize it as a health snack.

Figure 3 Second-generation snack foods.

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WHEAT PROCESSING | Snack Foods: Processing

Figure 4 (a–d) Third-generation snack foods. (e) Example of coextruded snacks. Courtesy of Wenger Manufacturing, Sabetha, KS.

Corn and Tortilla Chips Raw ingredients

Weigh blender

Surge bin

Conveying system

Live bin feeding system

Cooking extruder

Forming extruder

Knife

Fryer

Conveying system

Conveying system

Packing

Figure 5 Third-generation snack food-manufacturing procedure.

The increased popularity of certain ethnic snacks, such as corn and tortilla chips, has significantly increased this segment of the snack food industry. These snacks are very popular in South America. In recent years, their visibility has increased in North America also. After potato chips, corn and tortilla chips represent the second largest category of salted snacks. The main difference between tortilla chips and corn chips is the extra baking step required in the manufacture of tortilla chips. The key to the process is initial nixtamalization or alkaline cooking and steeping step involving whole corn. In the past, not much attention was given to corn type in the manufacturing of fresh ‘masa’ that was to be immediately converted to chip products. However, corn quality is quite critical in the manufacture of dry masa. In the actual process, good quality whole corn is cooked for up to 3 h at 80–100 C with frequent stirring in 120–300% excess water containing 0.1–2.0% hydrated lime. The cooked corn is then permitted to steep, usually overnight. The cooking and steeping steps permit the endosperm to hydrate and soften, which encourages partial starch gelatinization and disrupts and partially dissolves the pericarp. Subsequent washing removes the pericarp and residual lime. The resulting cooking/steeping liquor normally contains 2–6% dissolved and suspended solids, which are usually discarded. The washed material is then traditionally stone-ground, resulting in fresh masa, which is then sheeted, cut, and either baked and fried to produce tortilla chips or just fried after sheeting and cutting to make corn chips. In the case of corn chips, the masa can be directly extruded and cut into the frying oil instead of being sheeted and cut. If reconstituted masa flour is used, a large particle size should be used for corn chips. This will provide for

WHEAT PROCESSING | Snack Foods: Processing interruption in the dough structure so that air and water can escape during frying. If small particle flour is used, excessive puffing occurs during frying, resulting in a chip that will absorb more oil during frying and can be easily broken. On an average basis, corn chips contain 35% fat, whereas good quality tortilla chips have 25% fat. This is because of the preliminary baking step with tortilla chips, which sets the structure, therefore minimizing the oil absorption during frying. Usually, corn chips are made with a blend of white and yellow corn masa, which produces chips that are light in color. Corn chips made from 100% yellow corn masa usually have an objectionable burned flavor, which can be attributed to the degradation of carotenoids during the frying step. Flavors and colors can be either added to the dough, which can result in significant flavor loss due to volatilization or degradation during frying, or added either as a powder or in the form of an oil spray after frying. The traditional corn cooking techniques to prepare masa or corn/tortilla chips are being changed by more efficient, largescale operations where corn is cooked and ground immediately with little or no steeping. New and simple methods of producing corn and tortilla chips and other masa-based snacks have been developed. Many snack food manufacturers like to use dry masa flours that come in a variety of color and particle sizes. By adding water in precooked masa flour, different shapes of snacks can be made by using a forming extruder. These snacks can be fried, flavored, and packaged for sale. Frying has increased the masa-based snack market, because after frying, the final product has an excellent taste and texture and a long shelf life. Typical flow diagrams of tortilla and corn chip production are shown in Figures 6 and 7.

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Extruded Snacks This category has the greatest potential for growth among the snack foods. The snacks can be produced using innovative methods (see, e.g., Figures 8–10) that capture the consumer’s imagination. Some of the examples are three-dimensional snacks and snacks with a variety of shapes such as animals, cartoons, and alphabets. Producing a successful snack is a fine balance between the consumer’s needs, like tastes and interests, and the manufacturer’s production abilities, economics, and quality control. Raw material cost plays an important role in the finished product’s selling price. Therefore, it is an advantage to use the lowest-cost raw material to produce a successful snack. Nixtamalization/other Corn grain

Dry masa

Nixtamalization

Mixing Masa Lamination and cutting

Baking

Tortillas

Frying

Baked chips

Fold frying

Frying

Shells

Tortilla chips

Corn chips

Figure 7 Corn and tortilla chip production.

Whole corn +Water

Transport and drying system

Recipe preparation system

+Lime Packaging system

Cooking Multi-dimensional snack extrusion system

Puffing system

Sheeting

Steeping

Applicator/dryer Washing

Cutting

Grinding

Baking

Masa

Frying

Multi-dimensional snack shaping system

Final packaging

Figure 8 Multidimensional snack production.

Frying Dual entry/exit sheeting die

Dried Tortilla chips Reconstituted

Corn chips Extruder #1 Extruder #2

Figure 6 Flow diagrams of tortilla and corn chips.

Figure 9 Multidimensional snack extrusion system.

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Embossing Recipe #1

Corn meal storage

Shaping

Extrude Recipe #2 Embossing

Cutter Dry or toast

To drying Figure 10 Multidimensional snack shaping system.

Screen

Table 1 Properties of different raw materials in relation to snack food production Raw material

Granule size (mm)

Corn Wheat Rice Oats

5–20 20–40 2–8 2–12

Barley

Medium to large 60–100 5–35

Potato Tapioca

Flavor

Expansion

Texture

Definite Mild Bland Very strong Mild

Very good Good Good Poor

Crispy Crispy Crispy Soft to hard Soft to hard Crispy Crispy

Definite Bland

Poor to good Very good Good

Common ingredients used for extruded snacks Presently, snack products are being made from a variety of ingredients (see Table 1 where typical properties of common raw materials are listed). However, the selection of the ingredients was limited by the equipment availability. The introduction of the extrusion process, other processing equipments, and better knowledge of extrusion technology have led to more diverse and complex formulations for snack foods. The most common sources of ingredients are corn, wheat, rice, potato, tapioca, and oats. This is not an inclusive list and one should not limit his or her snack food formulation based on these ingredients. There are several other sources of ingredients for snack food all over the world. A major ingredient in snack food formulation is starch. In its natural form, the starch is insoluble, tasteless, and unsuited for human use. To make it digestible and acceptable, it must be cooked.

Cereal sources Almost any cereal can be extruded, but if expansion is a major objective, a number of functional cereals are limited to degermed corn/grits and rice. Cereals that have high amounts of lipids are more difficult to expand due to dough slippage within the extruder barrel. This type of cereal usually requires high moisture and high temperature before significant puffing can occur. In general, starches with 5–20% amylose content will significantly improve expansion and texture of the snack foods. The most common cereals used in snack food formulations are described later in the text.

Flavor

Oil flavors

Package Figure 11 Flow diagram of baked collets.

Corn Extruded snacks are a growing segment of the corn-based market (see Figure 11). Corn (also called maize) is a primary ingredient for corn collets and many pellet products. For most corn-based extruded snacks, dry-milled cornmeal is used. Large quantities of cornmeal are used in puffed extruded snack production and some are used in corn chips. Cornmeal, corn grits, corn flour, and corn cones are all a different form of dry-milled dent corn and in general vary only in particle size distribution. Selection of the granulation depends upon the type of snack and type of extruder. For example, for fine texture and cell structure, or softer bite, a fine granulation of cornmeal should be used, whereas for crunchy texture with a slightly larger cell-structured snack, a more coarse granulation of cornmeal is desired. Similarly, a twin screw extruder can handle fine and coarse granulation corn flour, while collect extruders require coarse granulation. Mostly, degermed corn is used in extruded snacks because it expands better than whole corn. Yellow and white corns are most commonly used in snack foods. Cornstarch granules are medium in size (5–20 mm) and have very good expansion characteristics. The protein content of corn ranges from 6% to 10%. Snack food formulations with corn have a definite flavor. Cornstarch is usually cooked at a medium to higher temperature during extrusion. The function of the starch in snack foods is to achieve various textural attributes and characteristics. Changing the amylose/ amylopectin ratio in the starch can change these attributes. Today, we can find cornstarches with high amylose or high amylopectin in the market. High-amylose cornstarches are used when crunchiness and strength is required in the snack. To increase the expansion of the snack, high-amylopectin cornstarches (waxy starch) can be used. Waxy corn contains very little amylose, whereas the normal corn contains 25–35% amylose. Under high-shear and high-temperature cooking, a cross-linked waxy cornstarch is recommended in snack foods, since it exhibits an improved property of resistance to amylopectin breakdown.

WHEAT PROCESSING | Snack Foods: Processing Wheat In general, wheat can be classified into two types: hard and soft. Hard wheat is higher in protein, produces stronger flour, and is better for bread making. On the other hand, soft wheat is lower in protein and yields weaker flour, which is better for cake making. In the snack food industry, wheat flour is used in formulation for making baked and fried snacks, flavored crackers, snack cakes, pretzels, bread, and the like. Semolina (coarse particle), usually produced from hard wheat milling, is also used in snack food formulation. The semolina product has an expansion ratio and bulk density about the same as cornmeal. Allsemolina snack foods will produce a very crispy texture. Wheat starch granules are fairly large (20–40 mm) as compared to other cereal grain starches. In wheat, amylose and amylopectin are found within a narrow range of 20–25% amylose. It gives good expansion during extrusion cooking. Wheat is relatively higher (8–15%) in protein than other cereals. Sometimes, it is difficult to expand due to the presence of gluten. In extruded snacks, wheat gluten provides nutritional value, crispness, and desired texture. In general, 1–2% wheat gluten is used in snack foods. Hard wheat is commonly used in bread rolls, pretzels, and fabricated or pellet-type snacks. Wheat varieties with a lower gluten level give a more tender expanded product than semolina or hard varieties. Snack products made with wheat usually have mild flavor and white to off-white color. It needs medium to low cooking temperature during extrusion cooking. Milling byproducts (bran) can be used with soy protein and some other ingredients to produce expanded snack foods of high nutritional and fiber value. The use of wheat in snack food formulation is limited because of cost.

Rice Rice is one of the largest crops grown in the world. Four types of rice are produced in the United States: long, medium, short, and waxy grains. In the United States, rice ingredients are not commonly used in snack food formulation. In Japan, most of the snacks are made with rice or rice flour. One major reason is the cost of rice as compared to that of other snack food ingredients. Broken rice can be used as ingredient in expanded or puffed snack products, since rice has good expansion qualities. Rice starch granules are the smallest (2–8 mm) of all grain starches and can be digested very easily. Its functional properties are very different from corn or wheat starches. The primary difference is in amylose/amylopectin ratio in the starch. Flours from different rice varieties have major differences in physical and chemical properties, which can affect the snack cell structure and expansion. For example, long-grain rice flour can increase the crispiness in snack foods, whereas waxy rice flour can reduce chip hardness and at the same time can provide a melt-in-the-mouth texture usually achieved with extra fat. Rice is commonly used as a carrier product for other flavors, since it is bland in flavor. In comparison with other products, rice requires the highest temperature during extrusion to cook a snack. Selection of the rice starch in the snack food formulation will depend on the amylose content of the common rice varieties. Long grains have 22–23%, medium grains 15–19%, and waxy grains <1% amylose. This difference in amylose/ amylopectin ratio greatly affects the gelatinization temperature of rice flour. The protein content of rice ranges from 6% to 8%.

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Rice flour could be used for texture improvement in multigrain snack foods. Rice flour can be mixed with masa flour, potato flakes, or bean flakes. Chips made with 100% rice flour absorb 20–30% less oil during frying. In a formulation where rice and potato blend is used, the potato flavor and texture remains distinctive even though it is mixed with the less costly rice blend. A mixture of bean flake and rice flour produces a distinct visual appearance of the beans while creating a wellblended bean flavor with no bitter aftertaste.

Oats In general, oats are marketed as rolled oats or as an ingredient for breakfast cereal. Oats have not been used in grain-based snacks as wheat and corn. Recent discoveries that oat bran can reduce serum cholesterol level in humans have boosted the market for oats in the snack food industry. The major problem with oats is the high oil content (7–9%) and lipase enzyme. Before using oats in the snack food formulation, it is desirable to inactivate the lipase. Otherwise, lipase will catalyze the hydrolysis of oil, which would lead to the production of bittertasting free fatty acid. Oat starch granules are comparatively small (2–12 mm) in size as compared to other starches. Amylose content of oats varies from 16% to 27%. Oat starch has a very strong flavor and it gives a light brown color to the product. It requires a relatively low gelatinization temperature, but a higher amount of energy input for cooking because of higher amounts of oil content. Oats contain high levels of fiber. Snacks extruded with oat starch expand poorly. For this reason, it has only found its way into products at low levels. By using longer barrel extruders with preconditioner, a higher level of oats can be used in snack foods. Among the snacks that have traditionally included oats in their formulation are cookies and granola. With new technologies and more interest in oats due to health claims, oat-based snack products may be popular in the future.

Barley Barley is used in small quantities in some snack food formulations. It has a mild flavor, and nutritionally, it is almost the same as wheat, except it contains considerably more fiber. Barley starch granules are medium to large in size as compared to other cereals. A reasonable amount of expansion can be obtained during extrusion of snack foods using barley starch. It gives a light brown to gold color to the product. Snack food formulation containing barley starch needs a low cooking temperature during extrusion. Barley fiber can be used in healthy snack foods as a fiber supplement. Sometimes, manufacturers use barley in multigrain snack foods in order to add one extra cereal on the label.

Other cereal sources Cereals such as rye, sorghum, millet, amaranth, and triticale have been used in snack foods. Presently, these cereals are not major ingredients in the snack food formulation.

Tuber sources Roots and tubers belong to the class of foods that basically provide energy in the human diet in the form of carbohydrates. According to a recent estimate by the Food and Agriculture Organization (FAO), virtually every country in the world

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grows some species of root crop. Potato and tapioca (also called cassava) are two main tuber crops used for extruded snack foods.

Potato Different forms of potatoes (granules, flakes, flours, and starches) are used in snack food formulations. Potato starch is often used in snacks to provide extra expansion. Potato starch has a wide range of sizes with some granules (60–100 mm) larger than the other cereals. This starch contains 20–25% amylose and has very low oil contents. Potato starch develops high viscosity during extrusion cooking. It has an excellent swelling and binding power. In snack food, it has a definite flavor and it gives gold to light brown color to the product. It requires low cooking temperature since its granules break down easily. Potato flour is the major ingredient for two common snack products, that is, direct expanded snack (product looks like French fries) and fabricated chips.

Tapioca Tapioca (cassava) is a basic source of low calories or a supplement to cereal. In general, tapioca starch is used in thirdgeneration snack food formulation. Tapioca starch grains vary in shape and size, from 5 to 35 mm. The amylose content is 17%. Good quality starch should have a pH of 4.7–5.3 and a moisture content of 10–13.5% and should be uniformly white in color. Tapioca starch develops a very high viscosity and it is an excellent binder. It has a bland flavor and requires moderate cooking temperature during extrusion cooking.

Table 2

Typical cornmeal specifications for fried collets

Granulation (mesh)

Percent retained on screen

16 20 25 30 40 50 60 Moisture Fat

0 0–2 0–10 25–50 45–65 0–8 0–2 11–13% <1%

Table 3 foods)

Typical formula for baked snacks (second-generation snack

Ingredients High-protein snack Rice flour Wheat flour Soy concentrate Sugar Cornstarch Vegetable oil Potato stick snack Potato granules Degermed cornmeal Vegetable oil Corn curls Degermed cornmeal or grits

Amount (%) 35 35 20 6 2 2 64 35 1 100

Expanded Snacks The majority of extruded snacks are in this category. This group is also referred to as ‘collet’ or ‘second-generation snack foods.’ In general, expanded snacks are made on high-shear extruders. These are high-fiber, high-protein, and low-calorie snacks. Some examples are corn curls, onion rings, three-dimensional snacks, and potato sticks. These types of snacks can be seasoned with a variety of flavors, oils, salt, sugars, etc. The quality of an expansion-cooked product depends on the conditions of operation of the extruder and the main raw material used in the formulation. Several other factors can influence the degree of puffing of snacks during extrusion, that is, the amount of moisture in the feed material, dough residence time in the extruder barrel, and cereal particle size.

Fried collets These are the most familiar extruded snacks in the market. A special die arrangement gives the product a twisted and puffed shape. These collets are made on collet extruders. The product is then fried in vegetable oil and coated with cheese and some other flavor. During frying, the moisture level reduces from 8% to 1–2% in this product. The most common material used for fried collet is cornmeal. Typical cornmeal specifications are given in Table 2. Some other cereal grains can also be used for this type of product.

Baked collets Baked collets are another example of the expanded extruded snacks. These include products such as baked corn curls, onion

rings, and potato sticks. Baked collets can be made with different cereal grains and tuber flours. Protein, fibers, cellulose, and bran can be blended with cereal grain up to 20% to make healthy snacks. Potato sticks are usually made by mixing potato flour with corn or rice flour. A typical formulation for baked snacks is given in Table 3.

Third-generation snack foods Third-generation snack foods, also referred to as ‘half-products’ or pellets, provide an alternative to fully prepared puffed snack foods. Third-generation snack foods, or half-products, are extrusion-cooked and formed at low pressure to prevent expansion and then dried to a final moisture content of 10% to form a glassy pellet. In developing third-generation snack foods, ‘half’ of the process is completed to prepare ‘pellets’ that are shelf-stable for periods of up to a year without refrigeration, provided they are properly packed to retain their moisture. These products are economical to run and have built-in marketability due to their high-bulk density. Thirdgeneration snack foods can be prepared in homes or restaurants. Unlike typical snack foods, half-products do not yet contain oil that can oxidize to give off-flavor to the products. These pellets can be shipped from a central manufacturing distribution point, held until needed for the market, and then puffed, flavored, and packed fresh and locally. New variations of the third-generation snack foods expand using


Mixing

Twin screw extruder

421

Rotary pre-dryer

To packaging Finish drying and tempering Figure 12 Flow diagram for third-generation snack foods.

infrared heating, hot air, or microwaving. The use of hot air systems reduces the oil uptake that occurs in frying and allows a controlled addition of oil to be made as required for flavoring. With consumer concerns about fats and oils, a halfproduct snack that expands using hot air offers snack food manufacturers an oil-free snack with perceived health benefits. The elimination of frying oils reduces calories and allows a marketing opening for snacks with a ‘lite’ image. A typical flow diagram for the production of third-generation snack foods is shown in Figure 12. With the multidimensional snack system, a wide range of raw ingredients can be used to blend together to make an excellent formulation for many types of third-generation snack foods. The extruder feed must contain a high level of starch to maximize expansion of the collet during exposure to hot oil or air. Levels of 60% or less total starch in the formula give only a slight expansion in the puffing step and yield a final product with a crunchy, hard texture. Wheat, corn, and tubers are widely grown crops in developing and industrialized countries, and they are cheaper and more easily available in the market than other cereal crops. Several formulations for thirdgeneration snack foods are given in Table 4.

Coextruded Snacks This is a relatively new technology introduced in 1984 for the snack food industry. In this process, two different materials are extruded from one die. The two materials can come from two extruders or from one extruder and one pump. This process can produce a snack with two different flavors or two textures or two colors. The most common snack produced by coextrusion is a cereal-based outer tube with a cheese filling inside. There are three basic types of coextruded snacks in the market: cerealbased tubes with cereal-based fillings, cereal-based tubes with fat-based fillings, and cereal-based tubes with water-based filling. The shelf lives of these snacks are limited, because of the

Table 4

Typical third-generation snack food formulations

Ingredients Corn-based Hard, crunchy texture Ground corn Cornstarch Monoglyceride Soft, frothy texture Cornstarch Wheat starch Tapioca starch Liquid shortening Monoglyceride Potato-based Hard and crunchy Potato flakes Durum flour Wheat starch Monoglyceride Crispy Potato flakes Drum flour Wheat starch Vegetable oil Soft Potato flakes Corn flour Wheat starch Monoglyceride Speciality snacks Fresh shrimp recipe Tapioca starch Fresh shrimp Rice flour Vegetable oil Salt Pepper seasoning

Amount (%)

94.5 5.0 0.5 55.2 27.5 14.0 2.5 0.8

49.0 30.0 20.0 1.0 47.0 30.0 20.0 3.0 49.0 30.0 20.0 1.0

64.0 20.0 10.0 3.0 3.0 1.0

422 Table 5



Typical formulation for coextruded snacks

Ingredient (sweet snack) Tube Wheat flour Sugar Milk powder Salt Filling Powdered sugar Vegetable oil Cornstarch Shortening Cocoa powder

Amount (%) 70 20 9 1 50 21 11 11 7

Ingredient (savory snack) Tube Cornmeal Wheat bran Milk powder Salt Filling Cheese powder Vegetable oil Shortening Cornstarch Milk powder Dairy powder Salt

Amount (%) 80 10 8 2 24 30 14 10 10 10 2

migration of moisture and/or oil from the filling to the outer shell. A typical formulation of coextruded snacks is given in Table 5. In conclusion, snacks can be processed by a variety of different methods and techniques. Several new raw materials containing nutraceutical and functional properties are being introduced in the market every day for snack food products. Snacks can be made with a combination of different raw materials containing different properties. The role of snacks in a healthy lifestyle is only now being developed. The recognition of snacks as healthy foods will increase as industry changes the products from those having merely good tastes to nutritious ones.


• • • •

What are the major snack food types? What formula ingredients provide the structural scaffolding for extruded snacks? How are third-generation snack foods produced? What are the major sources of starch used in the production of extruded snacks?

• •

How can oil uptake be reduced in deep fried snacks? How can nutrients be incorporated in extruded/expanded snacks while maintaining product quality?

See also: Carbohydrates: Starch: Chemistry; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Processing of Grains: Extrusion Technologies; Starch: Uses of Native Starch.

Further Reading Gomez MH, Rooney LW, Waniska RD, and Plfugfelder RL (1987) Dry corn masa flours for tortilla and snack food production. Cereal Food World 32(5): 372–377. Huber GR (2002) Recent developments and trends in the snack food industry. In: Riaz MN and Rooney L (eds.) Snack Food Processing Short Course Manual. College Station, TX: Food Protein Research and Development Center, Texas A&M University. Huber G and Rokey GJ (1990) Extruded snacks. In: Booth RG (ed.) Snack Food, pp. 107–138. New York: Van Nostrand Reinhold. Kuntz L (1996) Creating healthful salty snacks. Food Product Design 6(9): 31–56. Lusas EW and Rooney LW (2001) Snack Food Processing. Lancaster, PA: Technomic Publishing. Moore G (1994) Snack food extrusion. In: Frame ND (ed.) The Technology of Extrusion Cooking, p. 110. Glasgow: Blackie Academic and Professional. Riaz MN (1997) Technology of producing snack food by extrusion. In: Ranhotra G (ed.) Technical Bulletin, vol. 19, pp. 1–8. Manhattan, KS: American Institute of Baking. Riaz MN, Rooney EL, and Barron M (2002) Snack Foods Processing Manual. College Station, TX: Food Protein Research and Development Center, Texas A&M University. Sheng DY (1995) Rice-based ingredients in cereals and snacks. Cereal Food World 40(8): 538.

Relevant Websites http://www.aaccnet.org – American Association of Cereal Chemists website. http://www.aibonline.org – American Institute of Baking website. http://www.sfa.org – Snack Food Association website.


Contents Barley: Malting Barley: Milling and Processing Rice Processing: Beyond the Farm Gate Oil from Rice and Maize Maize: Dry Milling Maize: Wet Milling

Barley: Malting L MacLeod, Dairy Innovation Australia, Werribee, VIC, Australia E Evans, The Tassie Beer Dr, Lindisfarne, TAS, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by L. MacLeod, volume 1, pp. 68–76, 2004, Elsevier Ltd.

Topic Highlights

• • • • • •

The structure of barley and how it relates to the malting process. How to select suitable barley for malting. The stages of the malting process including steeping, germination, and kilning. Description of the equipment used in the malting process. Understanding the biochemical changes that occur to the barley during the malting process. Determining the quality attributes of malt produced for brewing.

Learning Objectives

•

To understand the interaction between the stages in the malting process and germinating grain biochemistry that modify the barley grain into malt that is of a suitable quality for brewing beer.

Barley Grain Structure

Introduction Malting is the term used for the preparation of a brewing raw material, employing a controlled germination of grain in moist air. Barley is the preferred grain for malting; however, other grains such as wheat, rye, sorghum, millets, triticale, or oats may be malted and subsequently used in brewing, distilling, or food production. Barley is the most common cereal used for the production of malt for brewing since it has a high starch-toprotein ratio and adhering husk that contribute to the


economic yield and ease of processing in brewing and produces the characteristic flavors associated with malt for this purpose. Malting aims to convert or modify the physical structure of the barley grain and allow synthesis or activation of a series of enzymes such that the final product, malt, is more readily used in the subsequent stages of brewing, distilling, or food manufacture. During the malting process, hydrolytic enzyme production and/or release is maximized leading to cell-wall degradation and protein solubilization with minimal starch breakdown. In order for this to occur, malting aims to both accelerate germination and retard embryo growth, essentially conflicting activities. Any shoot or root growth produced during the malting process is physically removed from the final product prior to storage and delivery, and therefore, minimizing embryo growth reduces losses incurred in the process. The final product of malting, malt, physically resembles the original barley grain but is friable when crushed, reflecting the complex biochemical changes that have occurred during the malting process.

For the purpose of understanding the malting process, the barley grain can be divided into several major components: the embryo, the endosperm, the scutellum, the aleurone, and the husk (Figure 1). The embryo is the living or metabolically active part of the grain. The husk covers the whole grain structure and consists of two parts – the lemma on the dorsal side of the grain (which is normally extended into the awn) and the palea on the ventral side. In most malting barley varieties, the husk is fused to the

http://dx.doi.org/10.1016/B978-0-12-394437-5.00153-4

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BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting

Dorsal side Pericarp and testa

Embryo

Aleurone layer Husk (lemma)

Acrospire Scutellum

Awn Rootlets Coleorhiza

Pedicel

Husk (palea)

Scutellar epithelium

Crushed cells

Starchy endosperm

Rachilla Ventral side Figure 1 Major components of a barley grain.

Evaluation of Barley for Malting

Figure 2 Endosperm tissue.

testa at maturity. The husk acts to protect the grain from infection during development and as such is relatively waterresistant. In intact grain where the husk has not been damaged during cropping or harvesting, water enters the grain and the embryo through the micropyle. It is the embryo that contains the shoot and root primordia, which will grow during germination. The endosperm is the initial source of stored nutrition to fuel seedling growth prior to photosynthetic nutrient production. The majority of the endosperm tissue is not metabolically active and consists of large cells without nuclei packed with starch granules embedded in a matrix of storage proteins (Figure 2). The scutellum is a shield-like structure that divides the embryo from the endosperm. It plays a role in both the degradation of the starchy endosperm and the nutrition of the embryo. The aleurone in barley consists of three layers of cells, which surround the endosperm. These cells are responsible for the production or release of the key hydrolytic enzymes, via the action of plant hormones (e.g., gibberellic acid (GA)), that will be produced during the malting process.

Barley for malting must be of high viability, low dormancy (at the time of malting), and uniform in germination to produce a homogeneous malt product. Both two- and six-row barleys can be used for malt production and their unique quality characteristics make them suitable for a range of malt products. Barley is generally processed into malt in batches of single pure varieties. This ensures uniformity in processing. These varieties have normally been tested and approved by certifying organizations, for their suitability for malting and brewing across a number of seasons to consistently produce malt of satisfactory quality. Structural grain characteristics such as grain size and shape, endosperm density, cell-wall thickness, and husk content all may affect malt homogeneity. Malting barley should be of low protein and high starch content to maximize the potential for extract yield in the brewery. The yield of extract has long been known to be inversely correlated with grain protein content. Extract is a measure of the amount of sugars, protein, and other soluble components extracted into the wort from the grain during the brewing process. The amount of fermentable sugars extracted is directly related to the level of alcohol produced and thus the value of the product produced from brewing and distilling. Protein levels must not be too low as proteins serve four basic functions in brewing. They are the origin of enzymes that catalyze the complex biochemical reactions involved in turning barley into malt and malt into wort. They and their degradation products (amino acids and small peptides) are required for yeast nutrition; they contribute to beer foam stability and are involved in the flavor development that malt contributes to beer and whisky. Barley received for malting is cleaned by passing over a series of shaking screens with differing slot sizes to remove foreign material such as stones, nonbarley grains, and weed seeds. Broken grains, chaff or straw, and dust are also removed in this way and with aspiration. The cleaned sample is assessed for grain size, total nitrogen, and moisture to determine its suitability for producing quality malt. Critical tests for malting barley, however, are those that determine the viability,

BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting dormancy, germinative energy, and water sensitivity of the grain. These tests are carried out on every load of barley prior to processing.

The Malting Process The malting process can be divided into three key stages: steeping, germination, and kilning. In the first stage, steeping, the acquiescent grain imbibes water and hydrates the embryo and endosperm. In the second phase, germination, enzymes are synthesized, activated, and mobilized, and the embryo begins to develop. In the final stage, kilning, grain growth is halted using a heat treatment (kilning), which dries the grain to constant and low moisture for storage.

Steeping Harvested barley grain is generally stored at a moisture level between 10% and 14%. Storage of grain below the 14% moisture level avoids mould growth and germination loss. Barley is generally processed into malt in batches, which may vary in size from less than a tonne to more than several hundred tonnes. The grain is cleaned and graded to remove foreign seeds, stones, straw, small and broken kernels, and dust prior to entering the steep vessels. During steeping, barley is immersed in water to raise the moisture level to <42–47%, which will allow the grain to

425

germinate. The process also washes the grain, removing any remaining loose debris and dust. The embryo is the major living part of the grain and imbibes water rapidly through the micropyle while the endosperm (nonliving tissue) is hydrated by osmosis. Steeping aims to achieve a rapid and even uptake of water and oxygen in order to stimulate the embryo to respire and initiate hormone activity. The respiration of the embryo produces heat and carbon dioxide. Once the embryo is hydrated and metabolized, it is important to achieve a full and even distribution of water throughout the endosperm to produce a consistent quality in the malt. Steeping involves a series of 2–4 immersions in temperature-controlled water, each followed by an air-rest period where the water in the steep is drained from the grain. The immersions allow the embryo to absorb water and the air-rest periods allow the water to be distributed into the nonrespiring endosperm. Steeping regimes are determined by plant design, barley characteristics, and condition and target malt specifications. Typically, steeping takes between 1 and 2 days. Steep vessels can take a number of forms (Figure 3), but are generally either cylindroconical or flat-bottomed tanks. The design of steep vessels should ensure that hydrostatic pressure is not deleterious to grain health, which generally limits batch sizes to < 100 T in cylindroconical steeps. In all cases, the vessels should be well aerated with good water temperature control between 12 and 25 C and with

Conical steep vessel Barley conveyor Vent

High level probe

Basket screen

(a)

Low level probe Drain

(c)

Aeration ring CO2 extractor Water in

Steeped grain conveyor

(b)

Figure 3 (a) Cylindroconical steep vessels. (b) Close view of a steeping vessel. Photos courtesy of Barrett Burston Maltings. (c) Schematic diagram of a steeping vessel. Diagram courtesy of Muntons Malt, the United Kingdom.

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Figure 4 The ‘chit’ counts used to measure the consistency of a sample of steeped grain for a visible protrusion (the chit) of the developing rootlet/cotyledon from the base of the grain.

efficient carbon dioxide removal. Aeration should be vigorous, allowing a good rolling movement of the grain mass to optimize oxygenation, temperature control, and removal of carbon dioxide (Figure 3(b) and 3(c)). During steeping, the embryo produces enzymes, which break down embryonic starch, initiating shoot and root growth. Hydration of the scutellum and aleurone initiates hormone (GA) production, the catalyst for hydrolytic enzyme production. In some cases, in commercial production (when permitted by customer specifications), exogenous GA3 can be added to mimic or increase the effects of the naturally produced hormone. Exogenous GA is usually added either during the transfer of the grain from steeping to germination or early in germination when the grain bed is turned. At the end of the steeping, the grain should be evenly and fully hydrated with a high (%) chit count. Hydration is commonly determined by measuring the moisture content of the grain; however, this can be misleading as it does not necessarily give a measure of the level or evenness of hydration of the endosperm. The ‘chit’ count measures the consistency of a sample of steeped grain for a visible protrusion (the chit) of the developing rootlet/cotyledon from the base of the grain (Figure 4). A high value indicates that the grain batch is initiating germination consistently.

Germination

Figure 5 Steeped grain spread on the malting floor for germination.

Steeped barley grain is transferred to germination vessels either as a slurry or by dry transfer after steep draining. The germination process aims to encourage enzyme synthesis and release, cell-wall breakdown in the endosperm, and the solubilization of stored nitrogen (proteolysis). In the past, germination was carried out by spreading the steeped grain on the floor (Figure 5). Some manual floor maltings still exist today and may be particularly suited to producing specialized malts such as those used for the production of single malt whisky or for craft brewing. In floor maltings, the bed of grain was turned over manually with ‘rakes’ to allow fresh air to circulate and prevent overheating from grain respiration. Nowadays, germination is carried out using a pneumatic system in the vessels of various shapes and sizes (generally from 40 to 400 T) such as drums (Figure 6) or more typically with rectangular Saladin boxes (Figure 7(a)) or round

Figure 6 Cross section of a drum used for germination using the pneumatic system.


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Germination vessel Adjustable louvres Rotating turner arm

Fresh air

Recirculation

Exhaust

Green malt

fan (c)

Spray atomisation units

Figure 7 (a) View of a Saladin box typically used for germination using the pneumatic system. Photo courtesy of Barrett Burston Malting. (b) View of circular germination chamber. Photo courtesy of Joe White Maltings. (c) Schematic diagram of a circular germination vessel. Diagram courtesy of Muntons Malt, the United Kingdom.

germination vessels (Figure 7(b)). In the pneumatic system, humidified temperature-controlled air is circulated through the grain bed (generally 1 m deep; Figure 7(c)). The grain rests on perforated plates (Figure 8) and is turned automatically by rakes, which travel slowly through the grain bed (Figure 9). Temperature, airflow, and small applications of water are used to maintain moisture, temperature, and oxygen levels in the respiring grain mass as it germinates and grows. Turning the bed of grain keeps the grain mass loose, avoids rootlet matting, allows adequate airflow, and aids water distribution. During the germination stage, grain moisture increases to <45% and roots and shoots begin to grow. Germination is typically allowed to proceed for 3–5 days during which time enzymes are produced from the scutellum and aleurone and regulated in response to stimulation from hormones such as GA, indoleacetic acid, and abscisic acid. Enzymes accumulated during this stage include a-amylase, limit dextrinase, a-glucosidase, b-glucanase, xylanase, lipase, and endo- and

exoproteinases. Enzymes including b-amylase and a small portion of limit dextrinase, lipase, and exoproteinases are present in the ungerminated barley grain, in part in a bound or inactive form. These bound and inactive forms are released during germination, largely as a result of proteolysis. The enzymes are produced and released in sequence and move through the hydrated endosperm degrading both cell walls and protein matrix in which starch granules are embedded. This process is often referred to as grain modification. At the end of the germination process, the cell walls of the starchy endosperm should be evenly and fully degraded, ideally with minimal starch granule degradation (Figure 10). Approximately 40–50% of the proteins should have been solubilized, and high levels of active starch-degrading enzymes, in particular limit dextrinase, a-amylase, and b-amylase, should have been accumulated. The grain moisture should have peaked at <45% on day 2 and reduced to 38–40% on day 4. Once the grain has germinated, it is referred as ‘green malt.’

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BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting Kilning

Figure 8 Grains resting on perforated plates used in the pneumatic system of germination. Photo courtesy of Barrett Burston Malting.

Figure 9 Grains resting on perforated plates automatically turned by rakes. Photo courtesy of Barrett Burston Malting.

Transferring the green malt to the kiln halts the process of germination. Green malt is loaded to the kiln at <40% moisture and is dried to 4–5% usually over a 24 h period. Kilning aims to prevent further root and shoot growth, to limit starch modification, to achieve a stable product for storage and transport, to preserve enzyme activity, and to develop and stabilize color, aroma, and flavor. The process also removes undesirable flavors and chemical compounds. Once kilned, the malt is friable and can be milled for brewing or stored whole in cool dry conditions for up to 12 months without significant loss of quality. The kilning process is the regulated removal of water from germinated grain. Moisture is removed from the grain by passing heated air through the grain bed. The air flowing to the kiln is gradually increased in temperature such that the grain temperature increases slowly and moisture within the grain diffuses to the surface of the kernel where it is absorbed and removed by the hot airstream. Since the grains form part of a grain, bed heating must be carefully controlled to allow moisture to be removed from the center of the grains in each of the layers in the grain bed without overheating the grains closest to the heat source. There are typically three phases of moisture removal during kilning. In the ‘free drying’ phase, moisture moves out of the grain relatively quickly, grain moisture drops rapidly and evenly to <25%, and kiln temperatures are relatively low (50–60 C). This stage is followed by the ‘intermediate’ phase where removal of moisture from the grain without overheating is more difficult. In this phase, temperature is increased slowly in a stepwise fashion over several hours and moisture drops to 12%. In the third and final ‘bound water’ or ‘curing phase,’ moisture falls to <4% as air temperatures are increased to 80þ C. Careful regulation of temperature, moisture removal, and time is essential to ensure that as the grain is dried, minimal denaturation will take place of hydrolytic enzymes that will be required in the brewing or distilling processes, color is controlled, and the formation of unacceptable chemical compounds such as nitrosodimethylamine and dimethyl sulfide is inhibited or minimized. Inappropriately high temperatures during the kilning stage can result in the undesirable loss of heat-sensitive enzymes such as b-amylase. Kilning conditions are one of the most significant contributors to the final malt character so careful control of this stage allows a range of specialty malt types to be produced from the

Figure 10 The cell walls of the starchy endosperm are degraded during germination.

BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting malting process (Table 1). Malts with colors from 2 to 30 EBC units can be produced in a normal malt kiln without the need for roasting. Roasted products are higher in color at 35–1500 EBC and may be produced from barley, malt, or green malt (Table 1). These products are kilned in specialized drum roasting plants at very high temperatures, which destroy Table 1

Types of specialty malts

Green malt kiln dried

Green malt roasted Dried malt roasted

Raw barley roasted

Vienna Munich Ale Pilsner Caramalt Crystal Amber Brown Chocolate Black Roasted barley

429

all enzymatic activity but produce very characteristic and strong flavors and colors (Figure 11, Table 2). Conventional kilns can be constructed in various shapes and sizes and may be single- or double-decked. In some situations, both germination and kilning can be carried out in the same vessel, usually referred to as a GK vessel. Historically, kilns were constructed in brick; however, today kilns are typically constructed from metal or concrete (Figure 12(a) and 12(b)). Although the bed depth may be up to 1 m, depths of around 0.5 m are generally favored to aid drying and reduce the heat inactivation of malt enzymes. Typically, kilning is completed over 1 day. NDMA is highly toxic, especially to the liver, and is also a suspected human carcinogen. In order to minimize NDMA formation, kiln gases that are low in nitrous oxide and/or heat are applied indirectly using heat exchangers to avoid direct contact of the kiln gases with the malt. The hot air is forced through the grain bed, which rests on a perforated floor similar to that found in the germination beds (Figure 8).

Description of malts A. Roasted barley: colour (black) and bitter taste. B. Roasted wheat: colour and unique flavour. C. Light crystal malt: flavour, colour, head-retention, storage. D. Dark crystal malt: colour. E. Roasted chocolate malt: flavour (smoother) and colour. F. Roasted black malt: almost black colour and bitter, dry taste. G. Amber malt: subtle biscuity colour and flavour. H. Caramalt: golden colour and full caramel flavour.

Figure 11 Examples of specialty malts and the color of their extracts. Photo courtesy of Joe White Maltings.

430 Table 2

BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting Specialty kilned malts

Product Ale Vienna Munich Roasted malts Brown Amber Chocolate Black Caramalt Crystal

Beer style

Description

Malting

Curing ( C)

4–8 7–10 15–25

Pale ales bitters Vienna Marzen Dark lager bock

Malting Rich malting Rich malting full-bodied

90–95 90–100 100–110

20–120 40–60 500–700 800–1600 30–60 60–350

Porter I.P.A Porter Stout Lagers, ales Ales, dark lagers

Dry smoky Dry biscuity red hue Nutty roasted Roasted astringent Body, flavor sweet biscuity Sweet caramel roasted toffee

Well modified Normal modification Overmodified Roasting Roasted low color malts Roasted ale malt Roasted lager malt Roasted lager malt Stewed green malt Stewed green malt

Color EBC

Green malt belt conveyor

Kilning Air in

Hot air

Heat exchanger

Loader/stripper

Grain bed Perforated floor Fan

Heating coils

(c) Figure 12 (a) Circular kiln. Photo courtesy of Barrett Burston Malting. (b) View of circular kilning chamber showing shallower bed depth. Photo courtesy of Joe White Maltings. (c) Schematic diagram of a circular kiln. Diagram courtesy of Muntons Malt, the United Kingdom.

Hot air exiting the grain bed can be recirculated or reclaimed and this process is used to control the drying process and conserve energy consumption. Regulation of the relative humidity of the air removed from the grain can be used

to protect malt quality. During kilning, embryo viability is destroyed, sucrose levels are increased, and sugar is caramelized. Melanoidins increase via complex nonenzymatic Maillard reactions between proteins and simple sugars, and

BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting low-molecular-weight flavor substances such as acids, alcohols, aldehydes, ketones, and esters are formed leading to the development of characteristic malt flavors and aromas. Finally, a lower weight of malt is produced than the weight of barley initially steeped, termed malting loss, which is equivalent to approximately 12–15% of initial clean barley dry weight. Malting loss is attributed to grain leaching/washing during steeping, grain respiration during steeping and after germination, and the removal of acrospires and rootlets after kilning.

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Hygiene Malt is an ingredient in the food chain. It is important that the barley selected for the process is free from chemical residues and foreign material and that the malt processing vessels and environment are kept clean. The use of stainless steel vessels and streamlined plant design minimizes cleaning requirements and ensures a safe food quality production environment.

Energy and Water Efficiency Product Storage and Evaluation of Malt Quality Following kilning, malt is cleaned to remove rootlets and small and ungerminated grain. Cleaning and rootlet removal are generally carried out prior to storage as rootlets can add a bitter/astringent taste to malt and add considerable bulk to the material to be stored. Such malt offal is a useful stock feed. The malted barley is now friable and easily broken and damaged. Damaged malt generates dust, reduces the husk component required for the lautering stage of brewing, and increases production losses. Malt movement should be minimized and conveying speeds optimized to reduce such damage. Individual batches of malt are assessed during processing and on completion of kilning for key quality characteristics using standard methods of analysis (IoBD, ASBC, and EBC) (ASBC 2009, IoB 1998, EBC 1998) and according to the malt specifications negotiated with the customer. Typically, these methods of analysis will determine the level of important malt quality specifications such as moisture, protein, color, friability, extract yield, diastatic power (measure of enzymatic starch-degrading potential), the Kolbach index (KI ¼ free protein/total protein %), potential wort fermentability (apparent attenuation limit (AAL)), free amino nitrogen (FAN), pH, viscosity, and b-glucan content. To a large extent, the essential commercial consideration of the amount of beer that can be produced from a tonne of malt is determined by the amount of extract yielded and its propensity of yeast to convert the wort sugars into alcohol (fermentability). In the past decade, it has been shown that individual measurement of the three diastatic power enzymes, a-amylase, limit dextrinase, and b-amylase, and their thermostability in combination with KI are very reliable predictors of fermentability.

Malting is an energy-intensive operation. Key utilities, gas, electricity, and water, account for 10% of direct input costs. The major gas use is in kilning while electricity is used in driving fans, cooling, heating, conveying, and pumping. The knowledge and ability to monitor and continuously control temperatures and speeds in various areas of the malt house allow energy use to be optimized. Plant design can assist in minimizing conveying, heating, and cooling requirements and therefore reduce utility usage and waste generation. In the future, the use of alternative energy sources, recycling and cogeneration plants, will drive further energy savings and environmental sustainability in malting plants.


• • • • • •


• Malt House Design Malt house design is varied and dependent on the site characteristics and production requirements. The decision to construct separate steeping, germination, and kilning vessels ideally through logical layout combinations (Figure 13(a)) or to a full tower mating where the vessels are stacked on top of each other (Figure 13(b)) is determined to a large extent by the range of products and customers to be serviced and the costs of construction in different locations. In all cases, modern plant design utilizes materials and layout that will take account of hygiene and energy efficiency.

What are the structural features of the barley grain and their role in malting? What are the distinct meanings of the terms ‘husk,’ ‘embryo,’ ‘aleurone layer,’ and ‘endosperm’? Which cereal grains can be malted for brewing and why has barley malt been traditionally favored for brewing? What are the alternate potential uses of barley malt other than direct use in brewing beer? What enzymes are accumulated or released during the malting process and what is their contribution to final malt quality? What is the role of the enzymes accumulated or released during malting to the brewing process?

•

•

Degradation of starch into yeast-fermentable sugars by the diastatic power enzymes (b-amylase and a-amylase, limit dextrinase, and a-glucosidase) is a key biochemical pathway in brewing. Explain the impact of malting on these enzymes and how they work together to produce fermentable sugars during the mashing stage of brewing? The cell-wall components of barley and their modification are important contributors to final malt quality. What are the names and functions of the enzymes involved in cellwall modification? The modification of proteins during malting is important for eventual malt and beer quality. Describe the classes of protein modified during malting and their importance for final beer quality?

432 BARLEY, RICE AND MAIZE PROCESSING | Barley: Malting

CBH grain receival and bulk handling facility

Barley receival silos

Malt storage silos

Steeping 3 & 4

Germination 3 & 4

Grain transfer services Kiln 2

Kiln 1 Steeping 1 & 2

Germination 1 & 2

Administration malt analysis

(a)

Figure 13 (a) Layout of a modern, integrated malting plant. View of layout of Joe White Maltings and CBH grain handling terminal, Perth, WA. Photo courtesy of Joe White Maltings. (b) Schematic plan for a tower maltings.


See also: Agronomy of Grain Growing: Barley: Agronomy; Beverages from Grains: Beverages: Asian Alcoholic Beverages; Beverages: Distilled; Fermentation: Origins and Applications; Breeding of Grains: Barley: Genetics and Breeding; Carbohydrates: Cereals: Chemistry and Physicochemistry of Nonstarchy Polysaccharides; Grains other than Cereals: Non-starch Polysaccharides; Starch: Chemistry; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Cereals: Grain Defects; Grain Marketing and Grading: Barley: Grading and Marketing; Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing; The Protein Chemistry of Cereal Grains; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading American Society of Brewing Chemists (2009) ASBC Methods of Analysis. St, Paul, MN: American Society of Brewing Chemists. Briggs DE (1978) Barley. London: Chapman and Hall. Briggs DE (1998) Malts and Malting. London: Blackie Academic and Professional. Briggs DE, Boulton CA, Brookes PA, and Stevens R (2004) Brewing: Science and Practice. New York: CRC Press. European Brewing Convention (1998) EBC Analytica. Zurich: Brauerei und Gertranke Rundschau.

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Institute of Brewing (1991) Recommended Methods of Analysis. London: Institute of Brewing. Evans DE, Collins HM, Eglinton JK, and Wilhelmson A (2005) Assessing the impact of the level of diastatic power enzymes and their thermostability on the hydrolysis of starch during wort production to predict malt fermentability. Journal of the American Society of Brewing Chemists 63: 185–198. Evans DE, Li C, and Eglinton JK (2009) The properties and genetics of barley malt starch degrading enzymes. In: Zhang G and Li C (eds.) Genetics and Improvement of Barley Malting Quality, pp. 143–189. New York: Springer Verlag. Evans DE, Wallace W, Lance RCM, and MacLeod LC (1997) Measurement of beta-amylase in malting barley (Hordeum vulgare L.). Part 2: The effect of germination and kilning on beta-amylase. Journal of Cereal Science 26: 241–250. Fincher GB (1989) Molecular and cellular biology associated with endosperm mobilization in germinating cereal grains. Annual Review of Plant Physiology and Plant Molecular Biology 40: 305–346. Flannigan B (2003) The microbiota of barley and malt. In: Priest FG and Campbell I (eds.) Brewing Microbiology, pp. 113–180. New York, NY: Kluwer Academic/ Plenum. Kunze W (1999) In: Wainwright T (ed.) Technology of Brewing and Malting. Berlin: VLB. MacGregor AW and Bhatty RS (1993) Barley: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Oliver G (2011) The Oxford Companion to Beer. Oxford, UK: Oxford University Press. Shewry PR (1992) Barley: Genetics, Biochemistry, Molecular Biology and Biotechnology. Oxon: CAB International.

Relevant Websites http://www.beer-brewing.com – The Brewers Handbook. http://brewery.org – Malting process in a nutshell.

Barley: Milling and Processing MS Izydorczyk and JE Dexter, Canadian Grain Commission, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Nonuniform distribution of constituents in barley grain. Common processes involved in cleaning and dehulling of barley grain. Barley pearling to obtain fraction enriched in dietary fiber, vitamin E, phenolic compounds, and minerals. Barley fractionation by roller milling and new ways of generating b-glucan-enriched fractions. Incorporation of barley milling fractions in pan and flat breads. Air classification of ground barley.

Learning Objective

•

To achieve understanding of processes involved in pearling, milling, and other treatments of barley to obtain grain products suitable for consumption and/or for being incorporated in various foods.

Introduction Barley is one of the most widely cultivated cereal crops that can provide valuable nutrients required by humans and domestic animals. Its high adaptability to various climates and growing conditions has led to worldwide production averaging 147 million tonnes per year over the last decade. Barley has had three distinct end uses, human foods, alcoholic beverages, and animal feed, but patterns of its utilization have changed throughout history. Barley was grown in the ancient world mostly to provide food staples, but lost its earlier preeminent position in human nutrition at the beginning of the twentieth century, when grains such as rice, wheat, and maize gained greater preference. The use of barley in the production of alcoholic beverages, especially beer, significantly increased after the Second World War, but this trend has reversed itself at the end of the twentieth century, especially in the West. The use of malting barley in Asia, however, continues to increase. Cultivation of barley for feed is a more recent development, but the demand for feed barley has significantly surpassed its demand for other uses, and the majority of barley production today is used for feeding animals. Most recently, however, interest in barley for food uses has revived. b-Glucans, the major dietary fiber constituents in barley, have been linked to the lowering of serum cholesterol concentrations in humans. In Europe and North America, foods containing barley are allowed to carry a health claim related to the ability of b-glucans to reduce cholesterol and the risk of heart disease. Physiological effects of b-glucans are dosedependent, and to qualify for the health claim, the barleycontaining foods must provide at least 0.75–1.0 g of b-glucan

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per serving. The food industry is now facing the challenge and opportunity to develop novel barley ingredients and palatable and healthy barley-based products that will gain acceptance among consumers and deliver the promised health benefits.

Composition of Barley Grain Barley grain consists mainly of carbohydrates, proteins, and lipids (Table 1). Carbohydrates are major components, with starch being the principal constituent. Barley is known for its high content of total dietary fiber (10–20%), and mixed linkage b-glucan has been shown to lower plasma cholesterol, reduce glycemic index, and reduce risk of colon cancer. The nutritional value of other dietary fiber components, such as arabinoxylans, cellulose, fructans, galactomannans, and arabinogalactans, has not yet been thoroughly elucidated. Barley proteins are poor in certain amino acids, such as lysine and threonine, but considerable improvement of lysine content has been achieved with the development of high-lysine barley mutants. Barley grain contains some important lipids, such as tocols (tocopherols and tocotrienols), which possess some antioxidant properties. The concentration of a-D-tocotrienol, known to inhibit cholesterol synthesis in the livers of experimental animals, is higher in barley than in other grains. A second cholesterol inhibitor, a-linoleic acid, has also been found among the barley fatty acids. The recently recognized involvement of antioxidant compounds in preventing the formation of carcinogens from precursor compounds has directed attention to such barley components as phenolic acids, phytin, vitamin E, proanthocyanidins, and catechins. Barley is also an excellent source of B complex vitamins, especially thiamin, pyridoxine, pantothenic acid, niacin, biotin, and folacin. Elemental minerals occur in barley grain in concentrations between 2% and 4%. The major components are phosphorus, potassium, and calcium, with lesser amounts of chlorine, magnesium, sulfur, and sodium. The distribution of various chemical constituents is not uniform throughout the component tissues of barley grain, that is, husk, pericarp, testa, aleurone layer, endosperm, and embryo (Figure 1). The husk and pericarp, the two outermost and protective tissues of the barley grain, consist primarily of cellulose, hemicellulose, lignin, and lignans – the major components of insoluble dietary fiber. The husk contains the highest proportion of minerals, followed by the embryo and the endosperm. Proanthocyanidins and catechins occur between the cuticularized layers of testa. The embryo, which constitutes about 2.5% by weight of the barley grain, is rich in protein (34%), lipids (14–17%), and ash (5–10%) and very rich in sugars (sucrose, 15%; raffinose, 5–10%; and fructosans). The cell walls of the scutellum are composed mainly of hemicelluloses and contain some phenolics, mainly ferulic acid. The thick walls of the aleurone layer (2–5 mm) are composed mainly of arabinoxylans (67–71%), b-glucans (26%), and


http://dx.doi.org/10.1016/B978-0-12-394437-5.00154-6

BARLEY, RICE AND MAIZE PROCESSING | Barley: Milling and Processing Table 1

Barley composition

Component Carbohydrates Starch Arabinoxylans b-Glucans Cellulose Simple carbohydrates (glucose, fructose, sucrose, and maltose) Oligosaccharides (raffinose and fructosans) Lipids Proteins Albumins and globulins Hordeins Glutelins Minerals Othersa

Content (%, dry weight) 78–83 60–65 4.4–7.8 3.6–6.1 1.4–5 0.41–2.9 0.16–1.8 2–3 8–15 3.5–4.5 3–5 3–5 2–3 5–6

a

Barley also contains small quantities of B complex vitamins, including thiamin (B1), riboflavin (B2), nicotinic acid, pyridoxine (B6), pantothenic acid, biotin, and folic acid and vitamin E. Adapted from MacGregor AW and Fincher G (1993) Carbohydrates of the barley grain. In: MacGregor AW and Bhatty RS (eds.) Barley Chemistry and Technology, 1st edn., pp. 437–474. St. Paul, MN: American Association of Cereal Chemists. Inc.

phenolic acids. This tissue also abounds in proteins (17–20%), triacylglycerol (20%), minerals, phytin, and sugars (including sucrose, raffinose, stachyose, verbascose, and fructans). Aleurone cells contain bodies called aleurone grains; these consist of globoids, composed of phytins, and crystalloids, composed of proteins and polysaccharides. Deposits of b-(1 ! 3) glucans (callose) are found at the aleurone–subaleurone interface. The starchy endosperm makes up about 75% of the barley grain. In the mature barley grain, starch, which constitutes about 80% of the endosperm, exists in granular form, with two distinct populations of large (A-type) and small (B-type) granules. Starch is composed of two polysaccharides, amylose (AM) and amylopectin (AP), with AP constituting 75% of the starch in normal barley. Two single-gene mutations can alter the AM and AP ratio. When the genetic trait of waxy starch is present, starch contains 95–100% AP. The other mutation increases the AM content up to 40%. The starchy endosperm also contains a relatively large amount of proteins (9% of the tissue) and smaller amounts of lipids, minerals, and nucleic acids. The cell walls of starch endosperm (2 mm thick) are built up mainly of mixed linkage b-(1 ! 3), (1 ! 4)-glucans (70%), and arabinoxylans (20%), with only small amounts of proteins, b-(1 ! 3) glucans, and other polysaccharides containing galactose, mannose, and uronic acids. The presence of waxy or high-AM genes in barley affects the carbohydrate metabolism in the grain, and waxy and high-AM barleys are consistently higher in b-glucans than normal starch genotypes.

Grain Cleaning and Dehulling The harvested barley grain may contain various amounts of contaminants including other grains, weed seeds, broken kernels, and foreign material (e.g., stone, straw, chaff, and dust)

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that will negatively affect subsequent processing and product quality. Generally, cleaning of barley grain can be achieved with equipment commonly used for other grains, such as magnets, aspirators, gravity tables, scourers, destoners, screens, and disk separators. Magnets are used first to remove ferrous metals. Shriveled grain, dust, and chaff are usually eliminated by aspirators or by simple fans. A grain separator, which uses screens larger and smaller than barley kernels, effectively removes most of the impurities. A destoner is used to eliminate stones of the same size as barley, whereas gravity tables efficiently segregate material of similar size but different density. Disk separators and scourers may be used to further remove foreign particles of different shapes and impurities adhering to the grain. Covered barley, in which the hull tightly adheres to the kernel, and hull-less barley with hull not entirely removed from the kernels during threshing, need to be dehulled before further processing for human consumption. Dehulling is usually accomplished in pearling machines or in compressed air dehullers that use a stream of pressurized air to apply mechanical shock to a sample of barley grain, which knocks the hull off the kernel. Hulls are subsequently removed by aspiration.

Barley Pearling Pearling is one of the oldest practices of processing barley. Pearling is a process of abrasive scouring that gradually removes hull, pericarp, seed coat, aleurone and subaleurone layers, and the embryo. The typical pearling machine consists of rotating carborundum or emery stones, which revolve rapidly within a perforated cylinder. The hull and other fractions of the kernel are gradually rasped off by rubbing against the stones and the perforated cylinder. The feeding rate, distance between the abrasive stone and screen, the roughness of the stone, and the time the kernel stays in the abrasion chamber determine the degree (rate) of pearling. Depending on the pearling rate, the process traditionally produces blocked (dehulled) barley, pot, and pearled barley. Blocking removes only the husk. The commercially pearled barley usually represents about 50–70% of the grain and may be adjusted as prescribed by the end use of the final product. This high rate of tissue removal (30–50%) was dictated partly by earlier consumer preference for white color of cereal products and partly by using covered barley genotypes intended primarily for malting or feed purposes. Recent development of hull-less barley genotypes, which possess waxy or high-AM starch characteristics and contain up to three times more b-glucans than malting or feed barley, calls for reexamination of the traditional pearling practices. Figures 2 and 3 show progressive removals of the outer layers of hulled and hull-less barley, respectively, with increasing degree of pearling. For hulled barley, the initial 10% pearling rate (10% weight removal) eliminates mostly the hull. At 15% pearling rate, the pericarp and testa appear to be scraped off, but some layers of the aleurone remain attached to the pearled grain. At 30% pearling rate, the pearled grain appears to be devoid of any outer tissues. For hull-less barley, the initial 5% pearling rate appears to scrape off the pericarp, whereas pearling to a 10% rate causes some incursion into the aleurone and removes not only pericarp and testa but also one or even two layers of the aleurone,

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BARLEY, RICE AND MAIZE PROCESSING | Barley: Milling and Processing

A Pericarp Seed coat

Nucellus Phytin crystal Nucleus Niacin deposit Cell wall

Aleurone layer

Protein bodies Sub-aleurone layer

A Starch

B

B Starch

Inner (starchy) endosperm

Cell wall

Protein matrix

C Scutellum

Endosperm

C Nucleus

Phytin crystal

Protein bodies

Depleted layer

Crease Endosperm Aleurone layer

Germ

Figure 1 Structure of the barley kernel sectioned longitudinally (left) and transversely (right), with detailed bran layer (A), starchy endosperm (B), and embryo (C). Courtesy S.S. Miller and R.G. Fulcher.


437

Figure 2 SEM micrographs of cross sections of kernels of AC Metcalfe showing successive removal of outer grain layers with increasing rate of pearling (abrasion): (a) whole grain; (b) 10% abraded; (c) 15% abraded; and (d) 30% abraded by weight.

Figure 3 SEM of cross section of kernels of CDC McGwire showing successive removal of outer grain layers with increasing rate of pearling (abrasion): (a) whole grain; (b) 5% abraded; (c) 10% abraded; and (d) 25% abraded by weight.

depending on the location along the grain periphery and/or kernel shape (Figure 3). Pearling to a 25% rate results in a complete removal of the outer tissues. The removal of specific tissues during pearling is usually not uniform due to the irregular surface and specific shape of barley kernels. Generally, the major reduction in size occurs along the major kernel axis, affecting the length of kernels to the greatest extent (Figure 4). Some removal of the outer tissues happens also at the dorsal and ventral sides of kernels, causing considerable reduction in kernel height. The width of kernels during pearling is affected relatively little. As a result of pearling, the ellipsoidal shape of barley kernels is transformed toward

somewhat flattened spheres (Figure 5). Barley chosen for pearling should be uniform in kernel size and weight, plump, and free from discolorations. Pearling removes the components present in the outer layers of the barley kernel, thus changing the composition of the grain. However, pearling produces a product that is suitable for human consumption by improving palatability and appearance; compared to whole grain (covered or hullless barley), pearled grain has substantially whiter appearance and smoother surface (Figure 6). The content of insoluble dietary fiber in pearled barley decreases with increasing pearling rates (Figure 7). The content of soluble dietary fiber, b-glucans,

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9 8

Kernel dimensions (mm)

7 6 5 4 3 2

Width

5

0

1 PL 0 25

PL

PL

PL

1 PL 0 25

5

PL

0

Length

PL

PL

PL 0 PL 5 PL 1 PL 0 25

1

Height

Figure 4 Changes in dimensions of barley kernel with the increasing rate of pearling (abrasion). PL0, whole grain; PL5, 5% abraded; PL10, 10% abraded; PL25, 25% abraded by weight.

Figure 5 (A) SEM micrographs of cross sections of the entire kernel of AC Metcalfe (covered barley) showing changes in shape of grain with increasing rate of pearling (abrasion). a – whole grain; b – 10% abraded; c – 15% abraded; and d – 30% abraded by weight. (B) SEM micrographs of cross sections of the entire kernel of CDC Alamo (hull-less barley) showing changes in shape of grain during increasing rate of pearling (abrasion). a – whole grain; b – 5% abraded; c – 10% abraded; and d – 25% abraded by weight.

fat, protein, tannin, and phosphorus initially increases with increasing pearling rates but declines after reaching optimum values between 15% and 30% decortication (Figure 8). The pearling by-products are potentially concentrated sources of bioactive components such as phytate, vitamin E (including tocotrienols), phenolic compounds, and insoluble dietary fiber. It has been shown that the pearling by-products of hull-less barley obtained at 20% pearling rate were enriched in tocols and contained 2.7–4.4 times more a-tocotrienols, a-tocopherols, and vitamin E activity than whole barley grain.

Table 2 shows the content of free and esterified phenolics and the antioxidant and antiradical activities of seven fractions obtained by successive abrasion of two barley cultivars, Falcon (hull-less) and AC Metcalfe (covered). The antioxidant and antiradical activities are mainly concentrated in the outer fractions (approximately up to 25% of the grain by weight basis), characterized by the highest content of phenolics. Hence, pearling by-product is a nutrient-rich, health-promoting food ingredient. Utilization of pearling by-products for making pasta (by substituting 50% of standard durum wheat semolina) resulted


439

Figure 6 Effect of pearling on the appearance of barley grain. (A) AC Metcalfe (covered barley): a – whole grain, unpearled; b – after 15% abrasion; c – after 30% abrasion. (B) CDC McGwire (hull-less barley): a – unpearled; b – after 10% abrasion; c – after 25% abrasion.

120

400

80

200

40

0

20

40 60 Decortication, %

Tannin Phosphorus Fat Protein

16

160

12

120

8

80

4

40

Fat and protein g/kg DM

600

Tannin and phosphorus g/kg DM

Insoluble and acid detergent dietary fiber g/kg DM

IDF ADF SDF β-Glucans

Soluble dietary fiber and β-glucans g/kg DM

160

800

80

Figure 7 Relationship between degree of pearling (decortication) and the relative concentrations of insoluble fiber (IDF), soluble dietary fiber (SDF), acid detergent fiber (ADF), and b-glucan fractions of barley. Reproduced from Pedersen B, Bach Knudsen KE, and Eggum BO (1989) Nutritive value of cereal products with emphasis on the effect of milling. World Review of Nutrition and Dietetics 60: 1–91, with permission.

in product that was darker than durum wheat pasta but had good cooking characteristics with regard to stickiness, firmness, and cooking losses. Because of the high dietary fiber (15.2–16.1%) and b-glucan (4.3–5.0%) content, barley pasta may be considered as a healthy food product. Pearled barley contains mainly the central endosperm of the kernel, enriched in carbohydrates (starch and b-glucans) and proteins. Examination of the amino acid and protein composition in 16 consecutive layers of barley grain has revealed that the albumin protein fraction decreases from the outer layer toward the center, whereas the hordein and

0

20

40

60

80

Decortication, % Figure 8 Relationship between degree of pearling (decortication) and the relative concentrations of tannin, phosphorus, fat, and protein. Reproduced from Pedersen B, Bach Knudsen KE, and Eggum BO (1989) Nutritive value of cereal products with emphasis on the effect of milling. World Review of Nutrition and Dietetics 60: 1–91, with permission.

glutenin fractions increase from the outer layers to the middle ones and then decrease toward the center. The distribution of b-glucans in hull-less barley grain has been determined through an examination of pearling by-products collected at 10% intervals during successive abrasion of barley kernels up to 30% of their original weight. The low b-glucan genotypes of hull-less barley have a greater concentration of b-glucan in the subaleurone layer, which declines slightly toward the inner

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Table 2 Phenolic contents, trolox equivalent antioxidant (TEAC), and oxygen radical absorbance capacity (ORACFL) of pearling fractions obtained by successive abrasion of two barley genotypes: Falcon (hull-less) and AC Metcalfe (covered) Cultivar/pearling fraction Falcon F1 F2 F3 F4 F5 F6 F7 AC Metcalfe F1 F2 F3 F4 F5 F6 F7

% Kernel weight range

Total phenolics (mg of ferulic acid equivalent/g of defatted material)

TEAC (mmol of trolox equivalent/g of defatted material)

ORACFL value (mmol of trolox equivalent/g of defatted material)

0–9.7 9.8–18.8 18.9–26.7 26.8–33.3 33.4–39.8 39.9–45.3 45.4–49.9

6.26 0.11 2.35 0.00 1.18 0.02 0.58 0.01 0.99 0.03 0.36 0.01 0.51 0.00

59.71 3.1 17.72 1.3 10.99 0.3 3.83 0.2 2.72 0.2 1.19 0.3 0.45 0.0

188.08 8.7 89.17 1.8 49.13 2.1 35.14 5.4 17.65 0.0 14.18 1.7 8.77 0.9

0–9.4 9.5–17.7 17.8–25.5 25.6–32.4 32.5–38.0 38.1–43.1 43.2–47.7

4.16 0.08 2.42 0.08 1.38 0.04 1.26 0.23 1.24 0.00 0.48 0.00 0.17 0.00

56.09 3.2 25.15 0.0 11.99 0.4 7.85 0.3 6.31 0.3 5.2 0.2 0.69 0.0

123.46 5.9 72.02 10.7 60.77 8.9 55.54 0.9 45.68 5.6 23.31 2.1 4.23 0.2

Adapted from Madhujith T, Izydorczyk M, and Shahidi F (2006) Antioxidant properties of pearled barley fractions. Journal of Agricultural and Food Chemistry 54: 3283–3289.

layers. The high b-glucan varieties, on the other hand, exhibit evenly distributed b-glucan throughout the entire endosperm. Because of the specific localization of b-glucans in the endosperm cell walls, pearled barley contains more b-glucans on a weight basis than whole barley. Blocked and pot barley are usually subjected to further processing, such as milling, grinding, or flaking, before incorporation into food products, even though pot barley and pearl barley are used directly in various soup, stew, and porridge recipes. Pearling of hulled barley and hull-less barley to 45% and 40% rates, respectively, results in a barley product, which can be used as a rice extender. The superior nutritive value of barley has increased the demand for barley rice extender among increasingly health-conscious consumers. The process is straightforward but requires a specific quality of barley for trouble-free production and high-quality end product, which after cooking resembles white rice in color, shape, and texture. Waxy hull-less genotypes appear to have some advantages over covered or hull-less normal starch varieties because of their ability to pearl and split without breaking kernels or creating fines and to produce desired color and texture after cooking.

Roller Milling Barley does not have a long tradition of being fractionated by roller milling, and the fractions derived by this process have not yet been standardized in terms of quality, composition, or terminology. Nevertheless, barley has been roller-milled using wheat milling equipment (Bu¨hler mill, Allis-Chalmers mill, and Miag-Multomat mill). The earlier studies on roller milling of hull-less barley followed the wheat paradigm, with the main emphasis on flour yield, color, composition, and purity. It was shown, however, that the most beneficial barley constituents, such as b-glucans, dietary fiber, vitamins, and phenolic compounds, are associated with the grain cell walls that during

milling remain concentrated in the coarse milling fractions rather than in the flour. Therefore, most roller milling processes nowadays focus on producing b-glucan/dietary fiberenriched fractions or whole grain flour to capture these milled products with potential and/or proved health benefits. A relatively simple roller milling flow for grinding hull-less barley is shown in Figure 9. The flow consists of four break passages through different sets of corrugated rolls with increasing number of corrugations. Following the fourth break (B4), the ground product is sieved through two sieves with different apertures; the material that passes through both sieves is designated the ‘break flour,’ whereas the coarse (>600 mm) and intermediate (>180 mm) particles that retain on the sieves are directed to the shorts duster (SD) for further processing. The SD passages generate the ‘SD flour’ and coarse fraction (>183 mm) that can be further refined by a single passage through sizing rolls, by sieving, and by another SD passage. The coarse material from the last SD passage originates mainly from the grain cell walls in barley milling (Figure 10(a)), and it is distinctively different from barley flour that consists mostly of starch granules and proteins (Figure 10(b)). In barley milling, this coarse product is designated as a ‘fiber-rich fraction’ (FRF) to reflect its main components and also to distinguish it from cereal brans that consist mostly of the outer grain tissues. Barley FRFs can be further improved, but the process requires additional fragmentation of fiber particles by pin milling to dislodge adhering starch granules and another SD passage to separate the freed granules from the cell wall material. Barley fractions obtained through the additional purification steps are designated as ‘enriched FRF.’ As seen in Figure 11(a), the original FRF consists of grain fragments containing primarily the endosperm cell walls and portions of the outer grain layers (pericarp, aleurone, and subaleurone tissues). Some of the larger endosperm fragments also contain starch granules entrapped in the endosperm cells. The additional refinement steps reduced the particle size of the FRF and effectively

BARLEY, RICE AND MAIZE PROCESSING | Barley: Milling and Processing removed the majority of the entrapped starch granules (Figure 11(b)). In comparison with oat bran that has been commercially available since the late 1980s, barley FRFs are relatively new fiber preparations, but they match up or even exceed the value of oat bran in terms of composition and physicochemical properties. Table 3 shows the yield and

Hulless Barley

B1

6.3

Fiber-rich fraction

SD

6.3

Pin mill SD flour

B2

7.9

7.9

B3

9.4

9.4

S1

85 μm Sizing flour

B4 14.1 14.1

600 μm

B1–B4 flour

Pin mill flour

SD SD flour

85 μm

85 μm

Fiber-rich fraction

SD SD flour Enriched Fiber-rich fraction

Figure 9 Roller milling flow for the production of fiber-rich fractions and enriched fiber-rich fractions from barley. B1–B4, break rolls; S1, sizing roll; SD, shorts duster; FRF, fiber-rich fraction. Numbers on roll symbols indicate corrugations of break rolls per cm. Numbers on sieves indicate aperture in mm. SD screen has 140 mm aperture. Reproduced from Izydorczyk MS, McMillan T, Bazin S, et al. (2014) Milling of Canadian oats and barley for functional food ingredients: Oat bran and barley fibre-rich fractions. Canadian Journal of Plant Science 94: 573–586, with permission.

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composition of fractions obtained by roller milling. Both the original and the enriched FRFs from two barley cultivars (CDC Fibar with waxy starch and CDC Hilose with high-AM starch) contained higher amounts of b-glucan, arabinoxylans, protein, and minerals, but lower amount of starch than the respective whole grain samples. Although the yield for the enriched FRF decreased, the refinement steps (Figure 9) further increased the content of b-glucan, arabinoxylans, and minerals. The enriched FRFs were also slightly brighter and contain fewer dark specs than their original counterparts (Figure 12). Properties such as yield, b-glucan enrichment factor (a ratio of b-glucan level in milling fractions to that in grain), and bglucan recovery in the milled fractions are important from an economical standpoint; it is desirable to combine the highest yield of fiber fractions with the highest concentration and enrichment of b-glucans. The content of b-glucans in the milling fractions is related to their content in the grain; therefore, choosing high b-glucan genotypes for milling ensures higher content of these polysaccharides in the milling fractions. Also, the high b-glucan genotypes, with waxy or highAM starch characteristics, may contain between 3% and 10% less starch than the low b-glucan varieties with normal starch characteristics and yield, therefore, significantly lower amounts of flour but higher amounts of FRF than the latter. The choice of grinding conditions has major implications on power consumption and yield and composition of milling fractions. Of particular note is the much greater power consumption when smooth rolls are used compared to fluted rolls, and since it was demonstrated that there is no apparent compensating advantage to using smooth rolls in terms of FRF yield or composition, the use of smooth rolls in hull-less barley roller milling is not justifiable. Setting the roll flute orientation to sharp-to-sharp results in a significantly higher FRF yield and in a power saving of about 7–9% compared to dull-to-dull flute orientation; however, the higher yield of FRF is accompanied by their high content of starchy material. With respect to the enrichment of FRF preparations in bioactive components, such as b-glucans, arabinoxylans, phenolic compounds, and proteins, significantly better results are obtained when roll flutes were set dull-to-dull rather than sharp-to-sharp. The combination of compression and shear associated with dull-to-dull grinding conditions causes better separation of starch granules

Figure 10 Scanning electron micrographs of particles of (a) barley fiber-rich fractions and (b) barley flour obtained from cultivar CDC Fibar via the short roller milling flow as shown in Figure 9. Abbreviations: eCW, endosperm cell walls; pCW, pericarp cell walls; P, proteins; S, starch granules.

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Figure 11 Light microphotographs of transverse sections of particles of fiber-rich fractions (a) and enriched fiber-rich fractions (b) stained with periodic acid–Schiff reagent and counterstained with calcofluor. Stained sections were examined with a Wild Leitz Orthoplan light microscope with fluorescence capability. Abbreviations: A, aleurone; SA, subaleurone; S, starch granules; eCW, endosperm cell walls. Table 3 Composition and properties of fiber-rich fractions (FRF) and enriched FRF obtained by roller milling of two hull-less barley cultivars: CDC Fibar (waxy) and CDC Hilose (high amylose) CDC Fibar

Yield of FRF/enriched FRF (%) Brightness, L* Particle size, d0.5 (mm) Total b-glucan (% dwb) b-Glucan enrichment factor Recovery efficiency (%) Total AX (% dwb) Arabinoxylan enrichment factor Recovery efficiency (%) Protein (% dwd) Starch (% dwb) Ash (% dwb) Cd (mg kg1) Ca Fe Mg Ma Ph K Zn

CDC Hilose

Whole grain

FRF

Enriched FRF

Whole grain

FRF

Enriched FRF

– n/a n/a 9.98 0.00 n/a n/a 4.97 0.08 n/a n/a 18.4 0.2 52.3 1.5 1.87 0.01 nd – – – – – – –

49.0 82.7 182 18.19 0.36 1.82 89.3 8.49 0.04 1.72 84.2 19.1 0.38 34.5 0.2 3.12 0.03 0.019 405 59.7 2120 19.6 6250 6440 33.8

28.8 85.9 108 27.60 0.16 2.77 n/a 10.88 0.16 2.19 n/a 17.0 0.36 21.3 0.2 3.29 0.02 0.034 416 72.5 2270 19.2 6650 6440 33.8

– n/a n/a 7.00 0.20 n/a n/a 5.24 0.05 n/a n/a 14.9 0.1 56.2 1.2 1.81 0.01 nd – – – – – – –

48.9 81.0 169 12.72 0.05 1.82 88.8 9.27 0.10 1.77 86.5 16.7 0.45 36.0 0.4 2.90 0.03 0.049 366 68.8 2070 20.7 5710 6000 38.7

26.1 84.9 108 19.89 0.21 2.84 n/a 12.49 0.10 2.38 n/a 15.2 0.30 26.9 0.2 3.02 0.03 0.080 380 84.4 2180 18.3 5950 6110 37.6

n/a, not applicable; nd, not determined Adapted from Izydorczyk MS, McMillan T, Bazin S, et al. (2014) Milling of Canadian oats and barley for functional food ingredients: Oat bran and barley fibre-rich fractions. Canadian Journal of Plant Science 94: 573–586.

from the cell wall material and, therefore, greater enrichment and availability of dietary fiber constituents in FRF. Other preprocessing practices, such as tempering and pearling, may also affect the yield and physicochemical properties of milling fractions. One of the advantages of pearling barley prior to milling is brighter flour and FRF due to less seed coat contamination. On a whole barley basis, power consumption during grinding is less when barley is pearled, but this is offset, at least partially, by the power consumed during pearling. FRFs obtained from pearled grain are more enriched in BG, but contain less arabinoxylans, phenolic compounds, and minerals compared to FRF from nonpearled barley. The FRF yield

is usually much lower. Thus, the decision whether to pearl barley before roller milling is not straightforward and will depend on the marketability of the pearled by-product, the aesthetic requirements, and nutritional targets of the food into which FRF is incorporated. Barley milling fractions have performed well in several baked products. Satisfactory loaf volume and crumb structure can be achieved by choosing appropriate baking procedures, enzymes, and wheat flour. For example, partial replacement of wheat flour (6–8%) with the enriched FRF from high b-glucan barley genotypes in bread prepared by the Canadian short process substantially increased its total dietary fiber and

BARLEY, RICE AND MAIZE PROCESSING | Barley: Milling and Processing b-glucan contents. The barley-supplemented breads qualified for a health claim by complying with the US FDA recommendation in delivering 0.75 g of b-glucan per serving (two bread slices). The loaf volume of bread supplemented with enriched FRF was superior to that of 100% whole wheat bread, and when compared to white flour bread, the volume was reduced by only 6–9% (Figure 13). The FRF-supplemented breads exhibited slightly finer crumb structure than wheat breads. The cell wall thickness in the FRF-supplemented breads was higher than that in white flour bread but lower than that in the whole wheat flour bread. The brightness of the bread supplemented with the enriched FRF was lower than that of white flour bread but higher than that of 100% whole wheat bread. Barley milling fractions have been successfully incorporated into single-layer flat breads, including chapati and Turkish bazlama bread. Two-layer flat bread with acceptable quality was produced by replacement of whole wheat flour with 20% of barley FRF. The FRF-containing doughs exhibited higher water absorption but good handling characteristics at division and sheeting. The layer separation during baking was very good, and flat breads with FRF did not show any tendency for burning (Figure 14). Characteristics of FRF-fortified breads,

Figure 12 Original barley fiber-rich fractions (FRF) (a) and enriched fiber-rich fractions (E-FRF) (b) obtained from cultivar CDC Fibar via the short roller milling flow as shown in Figure 9.

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such as appearance, diameter, crumb structure, and aroma, were comparable to the control breads. However, the addition of FRF increased hardness and chewiness and decreased the brightness (L*). The greatest hardness was observed for FRFderived from high-AM barley, and it was noted that the properties of starches associated with the FRF (especially at a higher level of FRF addition) could also contribute to the technological properties of breads. Flat breads supplemented with FRF from high-AM barley displayed slightly denser crumb structure than control or bread fortified with FRF from waxy barley.

Fractionation of Ground Barley by Air Classification Application of air classification to barley ground by either pin or hammer milling also has a potential for generating unique fractions enriched in specific components. This technique should be explored and developed further, especially in light of current interest and demand for specific and functional grain fractions. Interest in using air classification to segregate ground barley material stemmed initially from the desire to develop nutritious high-protein fractions for food uses.

Figure 14 Barley fiber-rich fraction supplemented flat breads (20% supplementation) exiting the traveling oven.

Figure 13 Effect of addition of fiber-rich fractions (6% of enriched FRF from CDC Fibar) to wheat flour on loaf volume and appearance of bread in comparison to bread baked with 100% wheat flour and 100% whole wheat flour.

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Hull-less or de-hulled barleys Normal barleyPin mill pin mill once feed rate 150 kg h−1 Waxy and high amylose barleyspin mill twice

Barley micronization 2x

Air classification (valve = 220)

Ground barley meal (i) Air-classify vane setting 15 μm feed rate 20 kg h−1 rotor speed 11 000 rpm

(i)

Coarse fraction (CF1)

Fine fraction (FF1)

Air classification (valve = 190) Coarse 1 (C1)

Fine 1 (F1)

(ii) (ii) Re-pin mill and airclassify vane setting 15 μm Coarse 2 (C2) (iii) Re-air-classify vane setting 30 μm

Coarse fraction (CF2) Fine 2 (F2)

(iii) Coarse 3 (C3)

Fine 3 (F3)

Figure 15 Diagrammatic representation of the procedure used for pin milling and air classification of barley. Reproduced from Vasanthan T and Bhatty RS (1995) Starch purification after pin-milling and air classification of waxy, normal, and high-amylose barleys. Cereal Chemistry 72: 379–384, with permission.

Subsequent attempts at air classification of malting barley and barley flour were aimed at producing low-fiber, low-protein starchy flours with amylolytic activities, which are of special interest to the brewing industry. More recently, various air classification systems for obtaining ground fractions enriched in b-glucans have been reported. One of such systems is shown in Figure 15. Barleys with waxy, regular, and high-AM starch were pin-milled to obtain meals passing through a 53 mm screen and fractionated into coarse and fine fractions by two passes at a vane setting of 15 mm and one at 30 mm (Figure 15). The first two fine fractions (F1 and F2) were protein-rich and contained mostly small starch granules. In all three barleys, air classification separated large starch granules from the small ones and concentrated them in the third fine fraction, F3. Most of the b-glucan in the ground barley appeared in the coarse fractions. The greatest enrichment of b-glucan was achieved in the third pass through the air classifier; the bglucan contents in the coarse C3 fractions were 23.8%, 13.1%, and 21.8% compared to 7.2%, 5.9%, and 7.8% in the whole grain, for the waxy, normal, and high-AM barleys, respectively. However, the yields of b-glucan-enriched fractions were low and ranged from 7.6% for waxy, to 10.4% for normal, to 20.9% for high-AM barley. Better results were obtained by air classifying micronized barley. Double micronization was required to provide sufficiently fine particles that were then sorted to obtain a series of coarse/fine fraction pairs. Increasing yields of the coarse fraction were obtained by reducing the air flow setting (Figure 16). The approach was tested on two hullless barleys with different starch types, cultivar Priora with

Fine fraction (FF2)

Figure 16 Flow sheet of the enrichment process optimized for the cultivar Priora. The final enriched fraction (CF2) is highlighted in gray. Reproduced from Ferrari B, Finocchiaro F, Stanca AM, and Gianinetti A (2009) Optimization of air classification for the production of b-glucan-enriched barley flours. Journal of Cereal Science 50: 152–158, with permission.

normal starch and 5.4% b-glucans and CDC Alamo with waxy starch and 7.8% grain b-glucans. Enriched fractions with 11.2% and 15.6% b-glucans and 29.8% and 28.4% yield were obtained from cultivars Priora and CDC Alamo, respectively. Successful separation and concentration of grain components via air classification depend on such parameters as particle size distribution and fat content of the material to be air-classified. Substantial enrichment (62%) of b-glucan for air-classified high b-glucan barley variety Prowashonupana (originally containing 17–19% b-glucan and 6% fat) was obtained when defatting was conducted before processing. Parameters such as b-glucan content in barley, presence of hull, and starch characteristics may also affect the effectiveness of air classification. Further optimization of the process is required in order to obtain fractions concentrated in target component and to reduce the costs associated with power consumption.

Other Processing Other forms of processing of whole or ground barley have also been developed. The treatments may vary from simple cooking and drying of whole grain to hydrothermal treatments, to extrusion cooking or infrared heating. These more sophisticated processing methods aim primarily at improving nutritional value of barley and at creating more shelf-stable and convenient barley-based food items/ingredients that can be easily consumed and/or incorporated in various food products. The processing of raw barley into products resembling traditional bulgur involves hydrating the whole grain to moisture content between 45% and 70% and cooking the grain at temperature ranging from 60 to 150 C. The temperature and the time of this cooking step are important for obtaining optimal nutritional and functional properties of the final

BARLEY, RICE AND MAIZE PROCESSING | Barley: Milling and Processing product. Following the cooking step, the grain is cooled and either dried or flash-frozen. If hulled barley is used for the production of bulgur, the grain has to be dehulled after the drying step. Utilization of hull-less barley varieties eliminates this necessity. A cooked and dried grain product may be cracked, milled, or ground into flakes, granules, or powder, and used as a ready-to-eat snack or cereal, or further processed. Such processed barley may contain lower amount of vitamins but can be an excellent source of dietary fiber. The hydrothermal processing of whole barley grain is shown to effectively degrade phytate (myoinositol hexaphosphate) and, therefore, to increase the content of free myoinositol (an important nutrient for infants) and the bioavailability of minerals such as phosphorus, calcium, iron, and zinc in barley. The treatment comprising two wet steeps of barley grain in lactic acid solution alternated by dry steps at elevated temperatures (45–70 C), and followed by final drying (80 C), is thought to activate phytase, the endogenous enzyme that degrades phytate to free myoinositol and inorganic phosphate. Hydrothermally processed barley can be used in the manufacturing of infant formulas or other applications, such as gruels, flakes, or muesli products. Hydrothermal treatment is also used to reduce lipid oxidation during processing and storage of barley. Another process aiming at improving the nutritional value of barley is extrusion. Extrusion cooking of high-AM barley can facilitate formation of resistant starch in the extrudate. Resistant starch acts like dietary fiber in the gastrointestinal tract, resisting digestion in the small intestine but undergoing fermentation in the large intestine and resulting in the formation of short-chain fatty acids, which are protective to colon mucosa. The formation of resistant starch increases the amount of total dietary fiber in barley after extrusion. Depending on the extrusion conditions (temperature, screw speed, and moisture content), desirable modification of other barley components may also take place during the process, including partial solubilization of b-glucans and formation of nondigestible oligosaccharides, thus improving the content of soluble dietary fiber in barley. However, the optimization of the process is necessary to minimize vitamin losses. Another advantage of extrusion processing is the improvement of palatability and technological properties of barley products. Due to their good textural properties, barley extrudates may be consumed directly, used in breakfast cereals or as additives to other food products.


• • • •

What are the major and minor constituents of barley grain? How do barley pearling by-products and pearled barley differ from the whole grain? What are the current objectives of roller milling and air classification of barley? What other processes (other than pearling and milling) are useful in producing value-added barley products?

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• • •

What are the main differences between barley bred for malting and barley destined for incorporation in food products? How to improve palatability and sensory properties of barley-based food products How can new trends in consumption of grain-based foods improve consumer acceptance of barley products?

See also: Breeding of Grains: Barley: Genetics and Breeding; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Grains and Health.

Further Reading Baik B-K (2014) Processing of barley grain for food and feed. In: Shewry PR and Ullrich SE (eds.) Barley Chemistry and Technology, 2nd edn., pp. 223–268. St. Paul, MN: AACC International Press. Briggs DE (1978) Barley. London: Chapman & Hall. Edney MJ (1996) Barley. In: Henry RJ and Kettlewell PS (eds.) Cereal Grain Quality, pp. 113–151. London: Chapman & Hall. United States Food and Drug Administration. www.fda.gov. Ferrari B, Finocchiaro F, Stanca AM, and Gianinetti A (2009) Optimization of air classification for the production of b-glucan-enriched barley flours. Journal of Cereal Science 50: 152–158. Health Canada (2012) Summary of health Canada’s assessment of a health claim about barley products and blood cholesterol lowering [Online]. Available: http://www. hc-sc.gc.ca/fn-an/label-etiquet/claims-reclam/assess-evalu/barley-orge-eng.php. Izydorczyk MS and McMillan T (2011) Barley b-glucans and fibre-rich fractions as functional ingredients in flat and pan breads. In: Preedy VR, Watson RR, and Patel VB (eds.) Flour and Breads and their Fortification in Health and Disease Prevention, pp. 337–353. Amsterdam: Elsevier. Izydorczyk MS, McMillan T, Kletke J, and Dexter JE (2011) Effects of pearling, grinding conditions, and roller mill flow on the yield and composition of milled products from hull-less barley. Cereal Chemistry 88: 375–384. Izydorczyk MS, McMillan T, Bazin S, et al. (2014) Milling of Canadian oats and barley for functional food ingredients: Oat bran and barley fibre-rich fractions. Canadian Journal of Plant Science 94: 573–586. Jadhav SJ, Lutz SE, Ghorpade VM, and Salunkhe DK (1998) Barley: Chemistry and value-added processing. Critical Reviews in Food Science 38: 123–171. MacGregor AW and Fincher G (1993) Carbohydrates of the barley grain. In: MacGregor AW and Bhatty RS (eds.) Barley Chemistry and Technology, 1st edn., pp. 437–474. St. Paul, MN: American Association of Cereal Chemists. Inc. Madhujith T, Izydorczyk M, and Shahidi F (2006) Antioxidant properties of pearled barley fractions. Journal of Agricultural and Food Chemistry 54: 3283–3289. Pedersen B, Bach Knudsen KE, and Eggum BO (1989) Nutritive value of cereal products with emphasis on the effect of milling. World Review of Nutrition and Dietetics 60: 1–91. Shewry PR (2014) Minor components of the barley grain: Minerals, lipids, terpenoids, phenolics, and vitamins. In: Shewry PR and Ullrich SE (eds.) Barley Chemistry and Technology, 2nd edn., pp. 169–192. St. Paul, MN: AACC International Press. Vasanthan T and Bhatty RS (1995) Starch purification after pin-milling and air classification of waxy, normal, and high-amylose barleys. Cereal Chemistry 72: 379–384. Wang L, Xue Q, Newman RK, and Newman CW (1993) Enrichment in tocopherols, tocotrienols, and oil in barley fractions by milling and pearling. Cereal Chemistry 70: 499–501.

Rice Processing: Beyond the Farm Gate L Pallas, Yanco Agricultural Institute, Yanco, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Paddy and Parboiled Rice

•

Paddy is rice that still has its hull surrounding the inner edible kernel. While most rice is prepared for consumption or further processing after the hull has been removed, a few rice products use paddy as the starting material and then remove the hull during processing. One such product is popped rice, which is a traditional snack food, created by briefly exposing paddy to heated oil. The hull assists with achieving a higher popping percentage by effectively serving as a pressure vessel for the inner kernel. Parboiled rice also begins with paddy. Parboiling refers to the process that the rice undergoes. Paddy is steeped and/or steamed in hot water to hydrate the grains and gelatinize the starch but not cook the rice. After soaking, the paddy is dried under controlled conditions and milled. The controlled drying prevents cracks from forming in the rice kernel. Therefore, parboiled rice is resistant to water uptake when boiled again for cooking and requires more time to cook than nonparboiled rice. Parboiled rice differs to instant rice due to different drying techniques as instant rice is rapidly dried, forming cracks in the kernel, which subsequently increases water uptake on rehydration. Thus, instant rice cooks faster than parboiled rice. The presence (or lack thereof) impacts the cooked rice texture, and thus, consumers desiring the firm texture of parboiled rice do not accept the softer texture of instant rice. The darker color of parboiled rice is due to the diffusion of water-soluble compounds including B vitamins and minerals from the hull and bran into the endosperm. Compared to white rice, parboiled rice generally has a higher millout (less brokens), firmer cooked texture, longer cooking time (although a greater degree of milling can reduce the cooking time and milling at a higher moisture content such that cracks are formed in the grain), and yellow appearance. Fermented cakes include ‘idli’ and ‘dosai,’ which are traditional food in India. Parboiled milled rice is mixed with black gram, after each has been soaked and wet-milled separately to achieve the desired coarse rice flour and finely ground gram paste. The mixture is fermented overnight and then ‘idli’ is steamed, while ‘dosai’ is fried. Flaked brown rice is traditionally produced by parboiling paddy under dry heat followed by flaking, achieved by pounding or pressing the rice. While many variations of flaking exist, two modern processes involve (1) dry heat parboiling of paddy followed by continuous roasting in a ‘gram roaster’ and flaking and (2) dehusking, aspiration, light whitening, and then flaking through a flaking roller mill.

• • • • • •

Rice, in its many forms, is the staple food for much of the world’s population. Rice varieties: long-, medium-, and short-grain; also differences in fragrance and amylose content. Paddy rice (as harvested) can be made into various foods before husk removal. Rice milling involves husk removal from paddy (giving brown rice) and bran removal (giving white rice). White rice can be stored for up to 2 years if kept dry and cool. By-products of rice milling are hulls, bran, bran oil, brokens, flour, and starch. White rice is used to make a wide variety of foods, including noodles, crackers, cakes, baby foods, breakfast cereals, and, most obviously, boiled and fried whole-grain rice.

Learning Objective

•

To achieve understanding of large-scale rice milling processes and uses of the various raw materials created during the milling process in processed rice food products.

Introduction Rice is a staple food for many people and animals around the world. Boiled white rice has traditionally comprised the majority of rice consumed due to consumer taste preferences, versatile functionality, and longer storage life. From a milling standpoint, rice varieties may be grouped into three categories according to their physical grain dimensions: long-, medium-, and short-grain. Specialty varieties within these categories may vary in cooked grain texture and be described as soft or firm. Other attributes that vary within the physical categories include appearance, fragrance, and amylose content. The amylose content is predominantly used to determine rice suitability for use in further processed foods. Hundreds of products are made from rice or use rice as a key ingredient. The following compilation is by no means exhaustive but aims to show the varied applications in which rice plays a key role. In general, milling of rice begins with paddy (also known as rough rice), which is cleaned and dehulled, resulting in straw, trash, hulls, brokens, and brown rice. The brown rice is milled into white rice, with further by-products being broken white rice and bran. A summary of the main products made from rice is shown in Table 1 indicating their initial raw rice material.

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Brown Rice Brown rice may be processed into quick-cooking rice, which is essentially rice that requires less time to prepare than raw rice.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00169-8

BARLEY, RICE AND MAIZE PROCESSING | Rice Processing: Beyond the Farm Gate Table 1 materials Starting raw material Paddy

Brown rice

White rice

Processed rice products derived from various raw rice

Processed rice products Popped rice Parboiled rice

Quick-cooking

Puffed rice Soaked Quick-cooking

Dessert Cooked Red coloring

Brokens

Wet-milled into slurry

Dry-milled into flour and baked

Dry-milled into flour, puffed or extrusioncooked

Dry-milled into flour

Rice bran

Pet food Beer adjunct Rice bran oil Processing aid Stabilized rice bran

Subcategories and subsequent products Flaked rice Fermented cakes (idli, dosai) Puffed rice Shelf-stable pouch (microwave rice) Frozen rice Snack (rice cake) Germinated brown rice Shelf-stable pouch (microwave rice) Frozen rice Canned rice Chinese rice pudding Specialty dishes (mochi, miso, congee, gua-ba) Fermented beverages (lao-chao, wang-tsui, khaomak, tapai, ketan, tapuy, hongju, sake, mirin) Angkak Steamed rice cakes (puto, bibingka, nenkau) Noodles, pasta Rice paper Crackers Rice starch Breads Muffins Cakes Puddings (uiro¯) Crackers (senbei, arare) Baby foods

Breakfast cereals Snacks (okoshi) Confectionary coatings Frying batter Rice milk

Rice bran extract Whole-grain rice flour Extruded cereal (rice bran sticks) Specialty health food ingredient Baked goods ingredient

This form of precooked rice is used as a quick shelf-stable or frozen alternative to traditional raw boiling preparations. Shelf-stable quick-cooking rice is also included in ready-to-eat meals and rice-based convenience food products and may be mixed with other ingredients prior to being hermetically sealed

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in a flexible pouch and heated in a high-pressure retort vessel. Frozen rice is cooked rice that is packaged and frozen until reheated by the consumer. Quick-cooking rice may also be dehydrated to be a lightweight, shelf-stable option and then quickly rehydrated prior to consumption. Although traditionally created in India by heating milled parboiled rice in hot air or sand roasting, a modern method of puffing rice involves soaking brown rice followed by steaming and partial drying in hot air. The rice is then lightly milled and subjected to hot air, which puffs the grain. Malt and salt may be added to enhance flavor and color. Germinated brown rice is becoming popular in Japan and Korea due to increased GABA (g-aminobutyric acid) content, which has associated health benefits such as reducing blood pressure and relieving insomnia. Germinated brown rice is easily cooked in a household rice cooker.

White Rice Similar to brown rice, white rice may be processed into various precooked rice formats including quick-cooking shelf-stable pouches (microwave rice), instant rice (requiring boiling water to rehydrate), and frozen rice (requiring heating in an oven, stove, or microwave). The advent of shelf-stable flexible packaging has nearly replaced canned rice. Japan cans milled rice (low amylose) in water with or without seasoning and typically distributes it as emergency food and military rations. The United States produces canned rice that is usually free-flowing white rice packed in a clear liquid or mixed into soups. In Taiwan, canned rice is often a form of rice congee that uses waxy rice sweetened and mixed with dried longans, peanuts, red beans, oatmeal, and sugar. Another type of canned rice found in Taiwan is fried rice, referred to as dry-pack due to no broth or liquid being present in the can. Chinese rice pudding is a popular dessert consisting of boiled rice mixed with milk, egg yolk, sugar, vanilla, cream, and a variety of fruits. Japanese ‘mochi’ is made by steaming milled rice followed by grinding or kneading, packing, and pasteurizing. It is then often sliced into cubes or small pieces, toasted, and sprinkled with soy sauce. A Cantonese-style of congee is cooked rice mixed with dried cooked meat, vegetables, salt, and flavorings. To prepare congee, cooked rice brokens, with low amylose, are washed, ground, and precooked with excess water, dried, and then flaked prior to mixing with other ingredients. ‘Gua-ba’ is a dried version of cooked rice, usually a waxy rice variety. The rice is washed, soaked, and cooked before spreading out on perforated trays in a thin layer. The trays are baked, cut into blocks, and then sun-dried before packing for later use or further flavored and fried as a breakfast or snack food. Miso is a Japanese paste used for seasoning and traditionally added to hot water to form a broth-like soup. Miso is created by mixing ‘koji,’ which is steamed rice and seed mash containing Aspergillus oryzae, with minced cooked soybeans, salt, yeast, and lactic acid bacteria and then allowing it to ferment up to several months.

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‘Angkak,’ also known as red fermented rice, red yeast rice, red rice koji, akakoji, and anka, serves as a coloring agent in foods and as a digestion aid and blood revitalizer in traditional Chinese medicine. It is a dark purple to red color produced by Monascus purpureus growing on cooked rice. A traditional Japanese and Chinese product, rice vinegar, is completely fermented rice starch and is created by mixing rice wine and seed vinegar and allowing the solution to ferment. A number of fermented rice wines are created by fermenting steamed milled rice and include Chinese ‘lao-chao’ and ‘wangtsui,’ Thai ‘khaomak,’ Malaysian ‘tapai,’ Indonesian ‘tape ketan,’ Philippine ‘tapuy,’ Korean ‘hongju,’ and Japanese ‘sake.’ ‘Tapuy’ usually uses red rice that is roasted prior to steaming. ‘Mirin’ is a sweetened version of ‘sake’ used for drinking or seasoning.

Brokens Broken grains are a by-product of the milling process and are separated by size into large and small ‘brokens’ from the main head rice stream. Large brokens may be passed through roller mills to produce rice flour, wet-milled and dry-milled. Small brokens are mainly incorporated into stock and pet feed or are used in beer production.

Wet-Milled Flour Several specialty rice cakes including ‘puto,’ ‘bibingka,’ and ‘nenkau’ are created from wet-milled brokens and are typically steamed. ‘Puto’ is a fermented steamed rice cake produced in the Philippines. ‘Bibingka’ is another Philippine rice cake made from wet-milled rice flour combined with sugar and coconut milk, wrapped in banana leaves with charcoal placed on top, and baked until brown. A traditional Chinese rice cake, ‘nenkau,’ may be either a sweetened cake with rice and sugar, a savory cake mixed with crushed radish, or a fermented sweetened rice cake. Both rice noodle and rice paper productions utilize brokens with high amylose content to achieve a firm, less sticky noodle. The wet-milled flour slurry is conveyed on a belt through a steam cooker until firm, lightly coated with oil, and cut into noodles of varying thickness. Noodles may be sold fresh or dried as a shelf-stable product. Rice starch is produced by wet milling brokens with a small percentage of sodium hydroxide to remove protein. The brokens are then treated in an alkali solution and further wetmilled. The mixture is stored, filtered to remove fiber, and centrifuged to separate the starch from the liquid. The starch is washed and dried. Rice starch is used to give a crisp appearance to clothing and is also used in a wide variety of food, cosmetics, and textile manufacture applications.

Dry-Milled Flour Dry-milled flour is produced by subsequent passes of brokens through roller mills to achieve the particle size specification. Due to the varying gelatinization temperatures and viscosity profiles related largely to the amylose content differences

between long- and medium-grain varieties, their respective flours have differing applications based on the desired cooking properties and texture. Rice flour is a gluten-free alternative to wheat, rye, barley, and triticale flour. The applications of rice flour are quite varied from breads, rice crackers, baked goods, extruded snacks, desserts, ice cream, noodles, breakfast cereals, baby foods, and dust coating on confections. Breads containing rice flour instead of wheat flour have dramatically improved in taste and texture in recent years, largely due to gums and starches being developed to assist with moisture retention, crumb structure, and aeration to yield light and fluffy bread. Rice flour is also used in muffins, cakes, and other baked goods. Japanese rice crackers, ‘senbei’ and ‘arare,’ are created from milled flour and are baked. ‘Senbei’ is a hard, rough snack cracker formed by kneading cooked rice flour and rolling it into sheets before cutting and drying. Sesame seeds, peanuts, powdered dried shrimp, cheese, spices, or dried seaweed pieces may be mixed into the dough. ‘Arare’ is created by cooking flour into a rice cake and allowing it to harden prior to cutting, drying, and baking. Compared to ‘senbei,’ ‘arare’ expands during baking, is soft, and dissolves readily in the mouth. Rice flour is also used to produce Japanese rice pudding, ‘uiro¯,’ consisting of rice flour, corn starch, sugar, water, and flavorings. The ingredients are mixed and steamed for an hour. Rice milk is an alternative to animal milk and is available as a chilled or shelf-stable product. White or brown rice flour is blended with water into a slurry, which proceeds through an enzymatic step, followed by filtering. Sweeteners and flavor may be added prior to packing.

Extruded and Molded Rice brokens may be dry-milled into flour and used in a variety of molded and extruded snack foods. A specialty Japanese snack food is ‘okoshi,’ created by mixing puffed broken rice with sugar, flavoring, and millet jelly and molding it into a ball. Baby foods often contain rice flour due to the low allergenic properties and bland flavor of rice. Rice flour may be pregelatinized so that it thickens easily in cold water and fortified with vitamins and minerals. As a dry powder, it is ready for easy rehydration. Other baby foods also use rice flour as a thickening agent. Breakfast cereals containing rice are created by mixing rice flour with other ingredients such as sugar, flavors and colors, and additional cereal grain flours into a cooked slurry. It is then typically forced through an extruder using dies to create various shapes. Once predried, a further coating step may add flavor, vitamins and minerals, and sugar (typical of sweetened breakfast cereals) before entering a final drying step and packing.

Rice Bran Rice bran contains magnesium, potassium, and phosphorus, along with B vitamins (thiamine, riboflavin, niacin, and pyridoxine) and vitamin E. Fresh rice bran is highly unstable due to its high oil content, lending high susceptibility to rancidity, and its high moisture content and water activity provide


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an excellent growth medium for microflora. Inactivating the lipase and reducing the moisture content are necessary for stable storage and further utilization of bran, producing a product referred to as stabilized rice bran. Whole-grain (or brown) rice flour is made by adding 13.5% stabilized rice bran to 86.5% white rice flour (the ratio naturally found in brown rice). Oil comprises 18% of the bran and can be extracted as a valuable food ingredient. Its high smoke point, high antioxidant content, and bland flavor have led rice bran oil to be used increasingly in foods as an alternative to vegetable oils. Rice bran extract, composed of phospholipids, protein, and carbohydrate, is used as a natural processing aid to hydrate and emulsify processed foods in a variety of applications such as extruded breakfast cereals, snacks, and pastas and serves as a replacement for lecithin or mono- and diglycerides in food products.

outside air through the rice. Important storage considerations to maintain grain quality include

Paddy Receival and Storage

Milling

On a large scale, once rice is harvested from the field, the ‘paddy’ (rice with the hull still attached) is transported to receival and storage stations. These stations are set up to receive one or several rice varieties in bulk, dry the grain to 14% moisture content, remove the majority of trash (straw, mud balls, unfilled grain, and dust), and store the grain until required for milling. Ideally, storage sheds use grain aeration to control the paddy moisture content and temperature by regularly forcing

Once transferred from storage facilities to the mill, paddy rice begins transformation into a raw milled material. The milling process starts with cleaning the paddy grain and then separates into various streams ranging from hulled rice (or brown rice), milled rice (or white rice), brokens, flour, bran and polish, and hulls (or husk). These products may then end up in a myriad of different pack sizes, convenience rice foods, value-added foods, and useful by-products. The milling process includes the following steps as shown in Figure 1:

RECEIVAL

HULLING

• • • • •

maintaining paddy temperature below 15 C (60 F) as long as possible to reduce insect activity, keeping moisture content of paddy low enough to prevent mold growth, cleaning storage shed and paddy prior to storage to reduce insect infestation, storing paddy with a level top surface instead of a peak for more uniform airflow and thus more even temperature and moisture content, having aeration systems designed to maintain uniform temperature and moisture content of paddy, conducting regular inspections for mold, insect infestations, warm rice, and wet rice.

WHITENING

GRADING & COLOUR SORTING

abrasive whitener

hulling machine

air

•

air

hulls

PACKAGING

plansifter

bran

final cleaner

air

delivery small brokens

paddy table

fines

friction whitener storage

air

white rice

brown rice

drying & storage

paddy rice

large brokens

length grader packaging

head rice

destoner

transfer to mill

colour sorter

friction whitener trash

warehouse stones metal

cleaner

dust trash

brown rice

white rice

rejects large brokens

scalper & grader

air

large straw

air

scalps immature grain

dispatch

Figure 1 Rice milling flow diagram from receival to packaging. Reprinted with permission from Production of Quality Rice in South Eastern Australia, 2005.

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• • • • • • • •


Cleaning Hulling Brown rice grading Whitening White rice grading and blending Color sorting Packaging Warehousing

Cleaning The cleaning process continues from the initial trash removal at the receival station to further remove impurities. The paddy passes through a stream of air, removing sticks, straw, dust, empty husks, and other foreign materials due to differences in density. Straw and trash are also separated from the paddy when it passes through sieves containing apertures large enough for the grain to fall through.

Hulling and Grading After cleaning, the airstream conveys paddy to the hulling machine. Brown rice is the kernel without the hull. The Engelberg huller is a popular hulling machine that uses steel rollers to remove the husk. Dehulling and milling occur at the same time and therefore there is greater grain breakage overall. In addition, the bran and hulls are mixed, creating a challenge for further processing the bran into a value-added product. A more efficient (>90%) dehulling machine is the rubberrolled sheller, which passes the paddy through rubber rolls rotating in opposite directions and at slightly different speeds. The shearing action of one roll rotating slightly faster than the other roll removes the husk from the grain. The throughput of the grain flow and pressure applied from the rolls onto the grain are adjusted for quality to minimize grain breakage. Arranging multiple hulling machines in parallel achieves the desired processing throughput. A less efficient and older style dehuller is the disk sheller, which has a stationary abrasive wheel horizontally aligned above another rotating abrasive wheel (on a vertical axis). The paddy enters from the center of the two wheels and the spinning wheel causes the flow to move outward, and along the way, the abrasive surface frees the brown rice from the hull. The exiting product from the hulling machines passes through an airstream that removes the husks, and the remaining brown rice and paddy mixture are conveyed to the paddy tables. The mixture is agitated, separating the brown rice from any remaining paddy based on differing friction coefficients and density. Reclaimed paddy (approximately 5–10% of throughput) passes back through the hulling equipment to ensure minimum product loss. The brown rice passes through destoners, which separate out mud balls and small stones. The destoners work by passing the rice over an oscillating mesh screen angled to capitalize on the difference in density between the grain (lower density) and contaminants (higher density). Depending on the milling configuration, destoners may be used before or after hulling.

Brown Rice Grading Brown rice may pass through a magnet to remove metal objects prior to reaching the scalping and grading machines, although magnets are used throughout the milling process. The scalper removes larger items than brown rice such as wheat, sorghum, and maize and other vegetable matters such as burrs or weed seeds, glass, small stones, and mud balls, which were not removed in earlier cleaning stages. The brown rice falls through screens of various sizes where the rice is graded on physical dimension. Brown rice is then sent to the color sorters to remove immature green grains and other impurities prior to packaging. Immature grains then either are mixed back into the brown product within specification range or proceed to whitening into milled rice. After scalping, the majority of brown rice proceeds to the whitening stage.

Whitening Whitening (or pearling) occurs when the outer bran layer of the brown rice is removed to reveal the inner white endosperm known as milled white rice. The brown rice passes through a series of whiteners depending on the degree of milling desired, with each pass removing more bran. The first whitening stage may employ an abrasive-type whitener or high-speed whitener where rotating stones abrade the outer bran layer. The bran is removed by aspiration and flows into a collection stream for further processing and/or packaging. Subsequent stages of whitening typically involve friction whiteners, which remove more bran by abrading the rice against a rotating perforated screen. Another pass through the friction whitener produces a white grain. Further polishing may occur with a water polisher to increase the gloss on the grain. Some breakage inevitably occurs during whitening. Careful attention is paid to the temperature of the rice to ensure that it does not become too warm and subsequently crack. The rubbing of grains together and against the machinery heats up the grains through friction. The force of the abrasion is also considered, as broken grains are undesirable. The unbroken milled grains, known as head rice, return a higher price than brokens. Quality standards for the maximum amount of brokens (measured as a percentage of broken grains against the entire weight of the sample) in a package of rice may vary from 4 to 20% (or higher) depending on variety and customer specifications. Some varieties such as jasmine-type rice are more fragile than others. Polishing is an optional step after whitening and generally occurs when shine or clean visual appeal is a purchasing point for the consumer. Polishing removes dust and bran from the surface of the kernel with a fine water mist, leaving a shiny, translucent milled grain. Water polishing machines are similar to friction-type whiteners, with a fine water mist applied briefly to the incoming grains upon entrance into the milling chamber and a chamber length nearly twice that of horizontal friction whiteners. The kernels are lightly moistened, which allows for easier removal of residual bran and ‘polish’ (referred to as the finer powder, which results after the bran layer has been removed), which are separated from the grains by a vacuum

BARLEY, RICE AND MAIZE PROCESSING | Rice Processing: Beyond the Farm Gate airstream. The vacuum causes ambient air to be drawn in to the end of the chamber, which dries the surface of the grain upon exit. The degree of polishing increases with multiple passes through a polishing unit.

White Rice Grading and Blending Post whitening, white rice flows through a plansifter and length grader to remove brokens and fines, leaving head rice. The plansifter contains a series of sieves with apertures reducing in size as the rice passes through. The length grader contains indented screens, which capture the broken rice. Brokens may be separated based on size into two categories: large and small. Large brokens range from 50 to 75% of the head rice length: Small brokens are less than 50% of the head rice length. The fines are collected and largely incorporated into stock feed. Large brokens are blended into the head rice stream at no more than the percentage allowed by quality specifications (typically 4–15%) for the particular end product, and the blended product stream is conveyed to color sorters.

Color Sorting Color sorting removes all damaged, chalky, and discolored grains in addition to other impurities, which may not have been removed in the earlier cleaning and sorting stages. The stream of rice is compared by image analysis to a background plate, which is adjusted to the same shade as the rice stream (a certain tolerance is allowed based on quality specifications). Any particle that has a shade not matching the background is ejected from the stream by a blast of air accurately timed to remove only that particle.

Packaging After color sorting, the rice passes through a final cleaning before storage in large bins until required for packing into various sizes determined by market demand. Form fill and seal (FFS) machines pack bags up to 10 kg, while larger volumes ranging from 25 kg to 50 þ kg are packed in prewoven polypropylene bags. Product that will be further processed is packed into 1 tonne bulker bags.

Warehousing Warehouse conditions should ideally be cool and dry to protect the packaged rice from sunlight (ultraviolet radiation and heat) and moisture damage. White rice has a shelf life of 24 months, although this length of time is shortened by high humidity and warmer environments or lengthened in lower humidity, cooler climates. Due to the low oil content in white rice (0.4–0.9%), the risk of oil rancidity is low, whereas brown rice has a shorter shelf life of 12 months due to the greater risk of rancidity and subsequent undesirable flavor and aroma.

By-Products Not Used for Human Consumption (Figure 2) Trash Trash includes all material from cleaning equipment in paddy storage facilities and the rice mill. This trash, along with straw collected in the early mill cleaning stages, is generally discarded. Small foreign seeds and brokens removed during the cleaning stages in the rice mill may be incorporated in small amounts into animal feed.

120 t stubble trash 0.5% rice product 27.0%

100 t paddy grain 1 t trash

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stubble 54.5%

99 t clean grain 18 t hulls

81 t brown grain

hulls 8.0%

11 t bran

brokens 5.0%

70 t white grain 10 t broken grain

bran 5.0%

60 t whole grain Figure 2 By-products of rice milling. Reprinted with permission from Production of Quality Rice in South Eastern Australia, 2005.

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Hulls

in the respective raw grains? What are the various food uses? Are any other food grains suited to popping? List the many by-products of rice growing and milling. Describe some conventional and innovative ways in which they can be used. The milling of rice involves the removal of the outer layers to leave the endosperm. What other cereal grains are processed in a similar way? (Consider barley, wheat, sorghum, and others.)

A by-product of the hulling process, the hulls are collected and transported for further processing into a wide variety of applications. Hulls are not further processed for human consumption but may be incorporated into animal feed as a powdered ingredient to increase fiber and mineral content. Hulls are also used in bedding and litter, fertilizer and mulch, separation filters, insulation material in steel manufacturing, and abrasives and can even be burned as fuel.

•

Straw

Future Developments

Rice straw has historically been incorporated into building materials in Korea, while Japan has braided rice straw into various ropes, and straw hats have been woven in the Philippines. In many Asian countries, straw is used for making mats and even culturing mushrooms in China and Thailand. Rice straw may also be used in bedding, litter, and mulches.


• • • • • •

What quality attributes of rice play a key role in processed foods? What type of rice is best suited for producing (a) noodles, (b) baby foods, and (c) beer? How is rice prepared for the consumer once harvested in the field? What are the differences between parboiled and white rice? During brown rice grading, what is the purpose of the scalper? Why is it important to keep storage conditions cool and dry?


•

•

What is your definition of ‘healthy and nutritional foods’? Apply this definition to a contrasting selection of rice-based foods. Also, consider potential costs and food safety when making your recommendation(s) of the ‘best rice has to offer the health-conscious consumer’! Compare and contrast the popping of rice in its various forms with the popping of corn (maize). In each case, what is the mechanism of popping? What attributes are required

•

Current research indicates that rice and its derivatives are emerging as functional foods with various potential applications and health benefits. A couple of examples include antioxidants in colored rice, rice bran, and germinated brown rice along with some innovative rice-based food products including new fermented rice products in light of the growing fermented food trend. Also, a process for granulating rice hull ash post burning has recently been developed at the Rice and Industrial Crops Research Centre in Pulau Pinang, Malaysia. This organic fertilizer provides a novel use of rice hull waste to improve soil fertility and value adds to a largely underutilized by-product of rice processing.

See also: Barley, Rice and Maize Processing: Oil from Rice and Maize; Breeding of Grains: Rice: Breeding; Food-quality Testing: Rice: Eating Quality; Genetics of Grains: Rice: Genetics; Nonwheat Foods: Rice: Chinese Food Uses; The Basics: Grain: Morphology of Internal Structure; The Grain Chain: The Route from Genes to Grain-Based Products; The Cereal Grains: Rice: Overview; The Basics: The Grain Crops: An Overview.

Further Reading Bhattacharya KR (2011) Product-making quality of rice. Rice Quality: A Guide to Rice Properties and Analysis, Chapter 9. Cambridge, UK: Woodhead Publishing Limited. Delves R, Clough R, and Burton R (2005) In: Kealey LM (ed.) Rice Products – Beyond the Farm Gate in Production of Quality Rice in South Eastern Australia NSW, Australia: Rural Industries Research & Development Corporation. Juliano BO (1993) Major processed rice products. Rice in Human Nutrition, Chapter 6. Rome: FAO. Mutters RG and Thompson JF (2009) Storage and aeration. Rice Quality Handbook, Chapter 8. Oakland, CA: University of California Agriculture and Natural Resources.

Oil from Rice and Maize JS Godber, LSU Agricultural Center, Baton Rouge, LA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • •

Rice oil is obtained from the bran removed when brown rice is milled to produce white rice. The rice bran is stabilized by heat treatment to prevent the action of lipolytic enzymes. Rice oil is found primarily in the germ, which represents about 2% of the rice kernel. World production of rice oil is only about 8% of potential, based on world rice production. The primary source of oil from corn is also the germ, comprising 10–14% of the seed weight. Corn oil is a by-product of the corn milling industry, which processes about 10% of the total world corn crop. The oil is extracted with hexane or another approved solvent. After extraction, both types of oil need to be refined, to improve the quality of the oil and to separate valuable coproducts. Both types of oil are used as cooking oils, in margarine and in salads for mayonnaise. Rice and corn oils contain compounds with health benefits, including vitamin E, tocopherols, and tocotrienols.

Learning Objectives

• •

To achieve a practical understanding of the production, refining, and utilization of oils and relevant co-products from rice and maize (corn). To understand the composition and nutritional value of the components of these oils.

Introduction The oils from rice and maize, hereafter referred to as corn, have both similarities and dissimilarities. They are similar in that each one of them would be considered a specialty oil derived from less commonly used sources and possess unique functional/nutritional components that distinguish them, such as high levels of natural antioxidants. They are dissimilar primarily due to their fatty acid composition. Corn oil has higher linoleic acid content, whereas rice oil contains higher levels of oleic acid. This article discusses the two oils from the viewpoint of their production, processing, and utilization.

Production Rice Oil The level of rice production is second only to wheat, among all the cereal grains produced worldwide, yet it is a minor


commodity in the US. Rice oil is obtained from the bran composite that is removed during the milling of brown rice to produce white rice. In actuality, the oil is found primarily in the germ, which represents 2% of the rice kernel (Figure 1). However, in typical rice milling operations it is not possible to separate the germ from the bran, so the resulting product, commonly called rice bran, contains the germ as well. Rice bran, which represents 8% of the whole grain weight, contains 20% lipid, with a range from 15% to 25%. Thus, it represents a considerable resource when considering the world production of rice. However, only 8% of the world’s potential rice oil production is realized, amounting to 7 million tonnes (Mt) in 1998. There are two primary reasons that a greater proportion of the potential rice oil production fails to be attained. The first is that in most of the countries that produce large quantities of rice, such as China and India, rice is milled in ways that do not separate the outer hull from the bran and germ layers. This makes the extraction of oil more difficult and not as economical. The second reason is that, even in mills that possess the capability of separating hull from bran and germ, the bran fraction is highly unstable and if not stabilized or extracted immediately, would yield oil of such low quality that it would not be suitable for human consumption. The reason for this instability is that the rice grain possesses highly active lipolytic enzymes that cause both oxidative and hydrolytic degradation of the lipids. Lipases tend to be the main culprit, causing a very rapid rise in free fatty acids that result in off-flavors, and are more susceptible to oxidative reactions and increase refining costs. Lipoxygenases can accelerate lipid oxidation, which primarily results in off-flavors, but can also degrade fat-soluble vitamins and generate toxic compounds. Rice oil is generally produced from stabilized bran. Bran is stabilized in a number of ways, but usually involves the elevation of temperature that denatures the enzymes responsible for lipid degradation. A popular means to stabilize rice bran is to pass it through an extruder so the frictional energy generated through the process of forcing the bran through the small orifice of the extruder plate causes an increase in the temperature. Temperatures required for adequate stabilization are generally believed to be more than 120 C. Other means of stabilization include pH adjustment using weak acids, microwave heating, and irradiation; however, no other practical methods have been utilized commercially. Until recently, rice oil was primarily produced only in Japan. India has also begun a program to increase the utilization of rice oil. In 1993, the Riceland Foods Cooperative (Stuttgart, Arkansas) in collaboration with a Japanese company, Itochu Corporation, began producing rice oil for commercial distribution in the US. It should be noted that defatted rice bran, which would become a by-product of rice oil production, does not have the full health benefits such as hypocholesterolemic properties

http://dx.doi.org/10.1016/B978-0-12-394437-5.00168-6

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Figure 1 Rice grain.

5% of the seed weight. The germ contains 35% oil, although varieties of corn have been developed in which the level of oil in the germ can approach 50%, whereas the bran would contain 1% oil. There are two types of milling, wet and dry, each of which produces different products and from which oil quality and yields vary according to the processing methods employed. The primary goal in dry milling is to produce prime endosperm products such as corn meal, grits, and flour. The primary goal of wet milling is to produce corn starch, which could also be processed further into corn sweeteners or ethanol. With the increasing importance of modifying starch or converting it to high-fructose corn syrup for applications in the food industry, wet milling has become predominant. Oil yields tend to be higher from wet milling (4%) compared to those from dry milling (2%). Corn germ from dry milling is similar to rice bran in that it tends to be unstable due to the presence of lipolytic enzymes, which must be inactivated by cooking. Both dry- and wetmilled germs are generally dried to a moisture content of 3% and are then flaked prior to extraction. The history of corn oil manufacturing in the US is much longer than that of rice oil. The reader is referred to the Mazola corn oil website for an interesting depiction of the history of corn oil in the US.

Processing Rice Oil Extraction

Figure 2 Corn grain.

associated with full-fat rice bran. This is due to the removal of functional components such as vitamin E vitamers (tocopherol and tocotrienol homologues) and oryzanol. However, defatted rice bran is more stable for human food processing and possesses high levels of fiber and other potential health-promoting compounds.

Corn Oil Corn is one of the three major cereal grains grown in the world, along with rice and wheat. Like rice, it is a major staple in regions of the world outside of the US, yet is a minor food commodity in the US; rather, it is primarily used as animal feed. Corn oil is primarily a by-product of the corn milling industry, which processes 10% of the total world corn crop. As with rice oil production, the primary source of oil in corn is from the germ. Although it is possible to extract oil from corn bran that is separated from the germ, the amount of oil extracted would be much lower and its composition would be different from the corn oil that is typically extracted from milled corn. The germ of corn is relatively larger than in most cereal grains, comprising 10–14% of the seed weight (Figure 2). The bran consists of the first few layers of tissue and comprises

Rice oil is typically extracted with solvents. The traditional solvent of choice has been hexane, although concern for impending, regulatory scrutiny of hexane for environmental and toxicological reasons has prompted exploration of alternative approaches to extraction. Although it is possible to extract oil from bran through mechanical means via pressing, oil recovery is lower and costs higher compared with solvent extraction. It has been found that pelletizing the fine rice-bran particles aids in the percolation of solvent through the bran during solvent extraction and increases yield. Alternative solvents have been considered, including ethyl acetate, isopropyl alcohol, and acetone. However, currently these are not as economical as hexane, although if regulatory action is taken with regard to hexane, these solvents may become the only viable option. At an academic level, supercritical fluids have been evaluated as a potential means to extract oil from rice bran. In principle, this approach offers interesting advantages such as ease of solvent removal and lack of toxicity. Also, it is possible to obtain fractionation of oil during the extraction process, which could facilitate refining or production of nutraceuticals. The major obstacles to the use of supercritical fluids are the large capitalization cost of initial startup and safety concerns due to the high pressures involved. Again, regulatory actions may necessitate such approaches in the future.

Refining Following extraction, several processes are undertaken that are collectively referred to as “refining” in order to improve the quality of the oil. The refining process may also cause a

BARLEY, RICE AND MAIZE PROCESSING | Oil from Rice and Maize reduction in nutritionally active compounds such as vitamin E and oryzanol, which may be recovered as by-products of the refining process. Generally, the first step in the refining process is dewaxing. Crude rice oil can have up to 8% wax, depending on the extraction method. Such high levels of wax can have an adverse effect on subsequent refining steps causing reduced yields, and can cause problems with refining machinery. A common practice is to allow crude oil to sit in settling tanks to allow the higher-melting-point waxes to settle out. After removal of the oil, these waxes can be recovered and may have value as a by-product. The next step is the removal of the phosphatides by water washing, which is referred to as degumming. Again, this step is carried out early in the refining process so as to avoid problems with subsequent refining steps and machinery. A by-product of this step would be lecithin. Perhaps the most critical step in the refining of rice oil is the neutralization step. This is because of the propensity for rice bran to undergo hydrolytic rancidity with the accumulation of free fatty acids. High levels of free fatty acids can lead to quality problems related to color and other physical properties. Free fatty acid neutralization is normally accomplished using sodium hydroxide or other caustic compounds such as sodium carbonate. The amount of caustic material used is dependent on initial free fatty acid levels. In crude oils with high levels of free fatty acids, it may be necessary to include physical refining by distillation of free fatty acids in order to increase yields to an acceptable level. A by-product of the neutralization process is soap stock, which is obtained after water washing. In addition to its obvious potential for the production of industrial soaps, soap stock can be an excellent source of a class of compounds called oryzanols, which may have unique health benefits. Furthermore, oryzanol can be maintained at much higher levels in the oil by only physically refining, rather than caustically refining, the oil. Because of the health benefits associated with oryzanol, this approach has been advocated as a way to maximize the potential health benefits of rice oil. Bleaching using clay or diatomaceous earth can be done to remove color, and deodorization by counter-current steam is employed to remove volatile substances. By-products of these steps include tocopherols, tocotrienols, and carotenoids, each of which has potential health benefits. Other finishing steps could include hydrogenation to reduce unsaturated fat and hardening of the oil, and winterization to remove the remaining high-melting-point glycerides and waxes.

Corn Oil Removal of oil from the wet-milled corn generally involves a combination of expelling and extraction. Initially, expelling is employed to reduce the oil content from 50% to 20%, after which solvent extraction is used. Dry-milled germ, which has generally been cooked in order to stabilize it, is then flaked and extracted with solvents. Refining steps for corn oil production are similar to those for rice oil. However, crude corn oil does not have the high levels of waxes found in crude rice oil, which simplifies the refining process, although it must also be degummed to remove the phospholipids prior to further refining. Also, because corn oil is promoted as a salad oil, the winterization process is critical in order to greatly reduce high-melting-point glycerides and waxes. Like rice oil, corn

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oil tends to have high levels of vitamin E vitamers, especially tocopherols, which could be an important by-product of oil refining. Also, corn has higher levels of carotenoids such as lutein and zeaxanthin, which are receiving considerable attention as compounds that could reduce the eye disorder called macular degeneration. Thus, recovery of these carotenoids from the refining process could also be valuable.

Utilization Rice Oil In the US, rice oil has not been produced in large quantities, and is therefore more of a specialty item found primarily in international food stores and some health or gourmet food shops. In Japan, rice oil is a preferred cooking oil due to its delicate flavor and textural properties. Also, it has been suggested that food cooked in rice oil has a longer shelf life because of the natural abundance of antioxidant compounds. Additionally, recent evidence that rice oil may possess healthpromoting properties has increased interest in developing commercial applications. A patent has been granted that describes the use of rice oil in blends with less stable oils, such as soybean oil, in order to increase overall stability. Another patent has been granted for the incorporation of rice oil into mayonnaise in order to reduce cholesterol absorption from mayonnaise-containing food. Rice oil may also be ideal for use in margarine. Because of its lower level of unsaturated fatty acids, it would require less hydrogenation, which would reduce trans-fatty acids. Also, rice oil has a natural tendency to produce more stable beta prime crystals, which would give rise to a smoother, creamier texture. Rice-oil-based margarine could be an alternative to recently released cholesterollowering margarines that contain phytosterols or stanols. Rice oil has a naturally high abundance of these compounds, whereas some of the currently available products have incorporated phytosterols from other sources such as pine tar. The combination of unique sensory properties and functional applications for rice oil, along with potential health benefits, has increased the utility of rice oil as a viable commercial entity. In addition, rice oil possesses a unique abundance of components that have commercial potential as valuable by-products. As previously mentioned, these include waxes, lecithin, oryzanols, tocopherols, tocotrienols, and carotenoids. Waxes tend to be difficult to isolate and purify; however, the high concentrations of wax in rice oil could be potentially valuable if more efficient methods of purification could be developed. Combining supercritical fluid extraction with fractionation offers some hope in this regard. Waxes are primarily used in nonfood applications; however, recent evidence suggests that certain long-chain alcohols found in wax could have health benefits. Crude rice oil also tends to be high in gums, which could have commercialization potential if appropriate recovery processes were developed. Currently, much of the lecithin production comes from the soy-oil-processing industry, where economies of scale make it a more economical source. However, the reputation of rice as a nonhypoallergenic food could provide an alternative to soy lecithin. Oryzanols are an interesting class of compounds made up of triterpene alcohols, including sterols and stanols, esterified to the phenolic

456 Table 1

BARLEY, RICE AND MAIZE PROCESSING | Oil from Rice and Maize Table 2

Composition of major fatty acids in rice and corn oil

Fatty acid (common name) Myristic (C14:0) Palmitic (C16:0) Stearic (C18:0) Oleic (C18:1) Linoleic (C18:2) Linolenic (C18:3)

Rice <1.0 12–18 <3.0 40–50 29–42 <1.0

Quality factors for rice and corn oil

Oil

FFA (%)

Nonsaponifiables (%)

Peroxide value (meq kg 1)

Iodine value

Corn Rice

1.5–4.0 3–15

<2.0 6–8

0.3 0.6

103–133 92–115

Corn <1.0 9–14 0.5–4 24–42 32–62 <2.0

compound ferulic acid. Crude oil can have up to 2% oryzanol, which can be concentrated during processing. However, oryzanol does not currently have Food and Drug Administration (FDA) additive status, which limits its commercial application beyond its normal existence in rice oil. As such, it has been touted as an antioxidant and for its potential to lower serum cholesterol. Tocopherols and tocotrienols are considered vitamin E vitamers (i.e., possess vitamin E activity), but tocotrienols may have unique health benefits such as lowering serum cholesterol and exhibiting anticancer activity toward certain types of cancer such as breast and colon cancer. Rice bran oil is one of the richest sources of tocotrienols, especially the gamma homologue, for which the greatest health benefits have been suggested.

Corn Oil Corn oil has been promoted traditionally, based on its light color and texture, as an ideal salad and cooking oil. It also tends to have good flavor stability and a high smoke point, which makes it a good choice for fried foods. Corn oil margarine is another product, well known for its perceived health benefits related to low saturated fat and high linoleic acid content. As previously mentioned, by-products from refining corn oil include the tocopherols from deodorizer distillate and carotenoids from bleaching. Recent research has revealed that the oil obtained from corn fiber generated during wet milling is very high in ferulate esters of sterols and stanols, similar to the oryzanol component of rice bran.

Quality Factors The fatty acid composition of rice and corn oil is depicted in Table 1. Rice oil contains more oleic and palmitic acids than does corn oil; the linoleic acid content is, however, less in rice oil. Both are very low in linolenic acid, which in part contributes to their oxidative stability and utility as frying oils. As stated previously, rice and corn oils are rich sources of a variety of compounds that may have health benefits. Both are unique in their high concentrations of vitamin E vitamers. Corn oil tends to be higher in tocopherols, whereas rice oil is higher in tocotrienols; in both cases there is an especially large concentration of the gamma homologue. Both also contain relatively high levels of ferulic acid esters, although rice oil has higher levels of dimethyl triterpene alcohol forms and corn oil is higher in sterol forms. Typical oil quality standards are shown in Table 2. Rice oil has a much higher level of free fatty acids than corn oil, which is a reflection of the susceptibility of rice oil to hydrolytic

cleavage by active lipases. Also, the nonsaponifiable fraction of rice bran oil is quite high compared with corn and most other grains. This is due to the high concentration of tocopherols, tocotrienols, oryzanols, and especially phytosterols. Rice and corn oils have very low peroxide values, which is a reflection of their excellent oxidative stability. The higher degree of unsaturated fatty acids in corn oil is seen in its higher iodine value.

Conclusion Rice and corn oils have distinctive characteristics that lend themselves to commercial utilization, but both tend to be underutilized relative to total world production of the cereals from which they are derived. Also, both could potentially generate a wide variety and abundance of valuable by-products during their production and processing. Since both are byproducts of the milling of cereals to produce other primary products, increasing their utilization would depend on changes in the milling process itself. In the case of rice, more efficient milling processes that at least separate bran from hulls and possibly germ from bran would be needed. Also, processing systems would be needed that could rapidly stabilize and/ or extract the bran in order to prevent lipid degradation. In the case of corn, the primary limitation is the low level of milling currently practiced in the corn-production and corn-processing industry. Increasing applications for milled corn products in the food industry will most likely increase the percentage of the crop that is milled. Also, the continuing consideration of corn as an alternative fuel source through ethanol production could increase the amount of milled corn available for oil extraction. It is likely that the production and utilization of rice and corn oil will increase, especially as the population becomes more aware of their health benefits, but it is unlikely that either will ever become a major commodity.


• • • •

Give reasons for the world production of rice oil being less than 10% of the potential, based on world rice production and milling. Discuss the alternative methods for extracting rice oil – both current commercial procedures and potential possibilities. What are the major differences in the extraction, processing and uses of the oils from rice and from corn? Explain the purposes and procedures for refining these oils after their extraction.

BARLEY, RICE AND MAIZE PROCESSING | Oil from Rice and Maize

•

What are the nutritional implications of differences between rice and corn with respect to the composition of the oils and co-products?


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•

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Rice oil production worldwide is only about 8% of its potential. Suggest ways in which the problems of producing rice oil might be overcome. Find out the differences between the wet and dry milling processes for corn (maize). What are the implications and suitability of either process with respect to subsequent oil production? Choose a region (preferably near you) and find out the procedures used there for extracting and refining rice and/ or corn oil. What are the current and proposed regulatory restrictions locally on the procedures and solvents used? Both rice and corn oils ’tend to be underutilized relative to total world production of the cereals from which they are derived.’ What factors might encourage the greater utilization of these significant resources, such as modification of the processing and the generation of valuable by-products?

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; Rice Processing: Beyond the Farm Gate; Fats: Healthy Fats and Oils; Lipid Chemistry; Food Grains and Wellbeing: Functional Foods: Overview; Non-wheat Foods: Maize: Foods from Maize; Rice: Chinese Food Uses; The Cereal Grains: Maize: Overview; Rice: Overview; The Oilseeds: Oilseeds: Overview.

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Further Reading Chakraverty A and Singh RP (2001) In: Postharvest Technology: Cereals, Pulses, Fruits and Vegetables, pp. 274–283. Enfield, NH: Science Publishers. De Greyt W and Kellens M (2000) Refining practice. In: Hamm W and Hamilton RJ (eds.) Edible Oil Processing, pp. 79–128. Sheffield, England: Sheffield Academic Press. Fils J (2000) The production of oils. In: Hamm W and Hamilton RJ (eds.) Edible Oil Processing, pp. 45–78. Sheffield, England: Sheffield Academic Press. Godber JS and Juliano BO (2004) Rice lipids. In: Champagne E (ed.) Rice Chemistry and Technology, 3rd edn., pp. 163–190. St. Paul, MN: American Association of Cereal Chemists. Johnson LA (1991) Corn: production, processing, and utilization. In: Lorenz KJ and Kulp K (eds.) Handbook of Cereal Science and Technology, pp. 55–131. New York: Marcel Dekker. Juliano BO (1985) Polysaccharides, proteins and lipids of rice. In: Juliano BO (ed.) Rice Chemistry and Technology, 2nd edn., pp. 142–160. St. Paul, MN: American Association of Cereal Chemists. McCaskill DR and Zhang F (1999) Use of rice bran oil in foods. Food Technology 53(2): 50–53. Patterson HBW (1989) Handling and Storage of Oilseeds, Oils, Fats and Meal. New York: Elsevier, pp. 114–117; 140–143. Salunkhe DK, Chavan JK, Adsule RN, and Kadam SS (1991) World oilseeds: chemistry, technology, and utilization, pp. 403–448. New York: Van Nostrand. Sharp RN (1991) Rice: production, processing, and utilization. In: Lorenz KJ and Kulp K (eds.) Handbook of Cereal Science and Technology, pp. 55–131. New York: Marcel Dekker. Taylor JB, Richard TM, Wilheim CL, et al. (1996) Rice bran oil antioxidant. US Patent #5,552,167.

Relevant Website http://corn.org/web/cornoil.htm http://www.corn.org/web/cornoil.htm – Corn Oil Refiners Association.

Maize: Dry Milling KD Rausch, University of Illinois at Urbana–Champaign, Urbana, IL, USA SR Eckhoff, (Retired) University of Illinois, Urbana, IL, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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• • • •

Maize dry milling utilizes approximately 200 million bushels (5 million tonnes) of maize in the United States annually. The maize dry milling process attempts to fractionate the maize kernel into the germ, pericarp, and endosperm components. Proper tempering of the grain is the key process step, which increases kernel moisture from 15 to about 22%, causes hydration of the germ, and allows proper separation of the germ and pericarp from the endosperm. Additional steps use physical properties (e.g., particle size, density, and terminal velocity) to separate the endosperm, germ, and pericarp process streams. Modern dry milling produces grit (endosperm) products that have varying particles sizes with less than 1% fat, allowing long shelf life. Primary products from dry milling include flaking grits, brewers grits, corn meal, corn cones, and flour. The process coproduces hominy feed, a mixture of the germ and pericarp, used in animal diets.

Learning Objective

•

To gain fundamental understanding of the maize dry milling process and typical processing steps used to make dry milling coproducts.

Introduction The term dry milling is often used to describe three distinctly different processes when discussing maize processes. The first process, stone grinding, is the oldest and is also known as whole kernel dry milling or full-fat dry milling. Whole kernel dry milling does not fractionate the maize kernel but rather seeks to grind the kernel to uniform particle size, usually flour or meal. The term ‘stone ground’ refers to the use of two stone grinding plates between which the maize is ground into a flour or meal. Other devices for particle size reduction can be used to produce meal or flour, including hammer mills, pin mills, and disk mills. The defining characteristics of this type of dry milling are that no separation of kernel components takes place and the resultant product is used for human nutrition. The products are usually referred to as ‘full-fat’ flour or ‘full-fat’ meal because the germ has been left unseparated from the other components. Full-fat products have a fuller flavor but a much shorter shelf life than degermed products due to the potential for oxidation of the germ oil, causing rancidity of the product. The second process refers to the production of ethanol from maize. A hammer mill is used to grind maize prior to jet

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cooking, liquefaction, saccharification, and fermentation. This process is more accurately referred to as the ‘dry grind’ process to prevent confusion. The dry grind process results in coproducts that are entirely different from other processes, primarily the production of fuel ethanol and distillers dried grains with solubles. The third process referred to as maize dry milling is the process we are considering in this article. More accurately referred to as degerminated dry milling, this process attempts to remove germ and pericarp from the collection of grits, meal, and flour that are left. Degermination improves shelf life of the endosperm products by removing the germ oil in the maize kernel ( 75%).

Process Overview Maize, which has been mechanically cleaned to remove broken pieces of maize, weed seed, other grains, and any other adulterant, is tempered. Numerous tempering methods exist, but a single-stage tempering would be to first spray 6–8% water on the kernels as they are dropped into a low-rpm horizontal screw conveyor or similar type of mixing device. Residence time in this screw conveyor would be 2–10 min. The moistened maize is conveyed into the top of a tall, small-diameter mass flow bin, which provides input to the degerminator (Figure 1) for a total tempering time of 15–40 min. The degerminator is fed at a constant rate and results in one or two streams containing a mixture of detached germ, pericarp pieces, and endosperm pieces of varying sizes. In degerminators with two streams, the objectives are to divert the germ and pericarp into one stream with small endosperm pieces (‘thru stock’) and to divert large endosperm pieces (‘tail stock’) to go into the second stream. Exploiting density, size, and aerodynamic properties that exist in the different particles, it is possible to make a separation among the pericarp, germ, and endosperm and to recover various size fractions of endosperm. To accomplish these tasks, a variety of equipment can be used, including most of the equipment described elsewhere in this Encyclopedia. Because of the differences in objectives between wheat flour milling and maize dry milling, maize dry millers generally do not find it cost-effective to use equipment other than sieves, aspirators, roller mills, and gravity tables. Sieves, aspirators, and roller mills are almost essential components of a maize dry mill, but good germ separation can be achieved without using gravity tables as shown in Figure 1. The figure shows the process flow for a simple, low-cost dry mill using a Beall-type degerminator. The initial and maintenance costs of gravity tables make recovery of the germ using a roller mill and sieve attractive. However, worldwide, there are many maize dry mills still using gravity tables to separate the germ.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00238-2

BARLEY, RICE AND MAIZE PROCESSING | Maize: Dry Milling

Water spray

Tempering tank

Cleaned maize

Tempering auger

Vibratory screener 3½ M

Tails Degerminator

Thrus

459

6M

15 M 60 M

Roller mill

Sifter

Flaking grits Aspirator

10 M

Sifter

Dryer Dried germ

Aspirator Hammer mill

Sifter Dryer

Hominy feed

30 M 50 M 80 M 200 M

Regular grits Fine meal (cones) Coarse flour Coarse meal Aspirators Fine flour

Aspirator Figure 1 Process flow diagram for a maize dry mill.

In Figure 1, the tempered maize is split into two fractions by the degerminator. The first fraction (40–80%) is the ‘thrus’ referring to the germ, endosperm, and pericarp that pass through the screen on the degerminator. The second fraction, the tails, is usually smaller (20–60%) and is a function of maize quality and genetics. The tails, being predominately flaking grits, some recycle, and flour, can be screened with a vibratory screener using a 5.6 mm screen as a scalper to recover oversized grits with attached germ and unbroken kernels. This scalped material can be recycled or diverted into the hominy feed fraction. The vibratory screener also has a 3.55 mm screen for recovery of flaking grits (5.6 to þ3.55 mm; this designation indicates ‘through a 5.6 mm screen and retained on a 3.55 mm screen’). The material that goes through the 3.55 mm screen is mixed with the 1.25 to þ250 mm fraction sieved from the thrus. The flaking grits are aspirated, with the aspirate (lifted material) going to the hominy feed fraction. A stationary sieve (as shown in Figure 2) can be used in place of the vibratory screener with comparable results. The stationary sieve can often be built locally for lower cost and operates with no energy input and minimal maintenance. Screening devices come in many configurations and sizes but employ the same basic principle for achieving separation– size difference. Particles smaller than the screen opening can fall through, while those larger than the screen opening remain on the screen. The probability that any piece of maize material will pass through the screen not only is a function of screen opening size but also is affected by the length of exposure the piece of maize has to the screen opening. Three major factors

Tail stock

3.5 mesh screen

Recycle or feed 6–10 mesh

Add to thru stock

Clean grits

Figure 2 Static sifter.

affect the length of exposure: (1) the depth of the material on the screen, (2) the distance that the particles must transverse (basically the length of the screen), and (3) the amount of angle at which the screen is operated. Most screens used in

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corn dry milling are metal wire screens with the size openings given in millimeters or micrometers. Most commercial screens enhance the separation process by using some type of mechanical action. There are a variety of reciprocating motions that are used to help the material to be removed and work its way to the screen surface. The action also serves to increase the exposure of the maize material to the screen openings, since the particles are agitated or turned to expose different orientations to the screen openings. This increases the likelihood of the particle falling through the screen. Although it is often said that aspiration will separate light or less dense material, material with a density or weight greater than the maize fraction may actually be removed using aspiration because the aerodynamic characteristics of a particle depend upon the shape, texture, and weight or density and not density or weight alone. There are two primary forces that act upon a particle in an air stream. The downward gravitational force experienced by the particle is due to its total weight (total mass multiplied by the gravitational constant) and not due to its density. The force that counteracts the gravitational forces is the upward drag force. It is made up of two components: form drag and frictional drag. The amount of frictional drag is dependent upon surface texture and total exposed surface area. Form drag, which is dependent upon the projected area of a particle and upon its shape characteristics, dictates the amount of separation that will occur in an aspirator. The rate at which a particle will move up or down in an airstream depends upon the difference between the drag force and the gravitational force. If the two forces are equal, the particle will remain stationary. If the drag force is greater than the gravitational force, the particle will be carried upward by the air stream. Aspirators are designed to force an airstream across the path of flowing mill products, usually at a 90 angle to the flow. The less aerodynamic fiber particles are the first to be removed by aspiration. The small, soft, floury endosperm pieces are usually the next particle group to be removed. Larger/heavier particles can also be removed, if enough air flow is used in the system for them to reach fluidization. Multiple pass aspirators, where the flowing particle stream is exposed sequentially to multiple air streams, are generally preferable to a single airstream aspirator. The thrus fraction from the degerminator is sieved into three fractions, a þ1.25 mm, 1.25 to þ250 mm, and 250 mm. The þ1.25 mm fraction contains large grits and grits with attached germ or pericarp and germ. This fraction is passed through a roll stand with a gap setting that breaks the large (3.55 to þ2 mm) grits and grits with attached germ or pericarp. The germ, containing ample water, does not break but rather is squeezed or compressed into flat flakes. The germ can now be sieved out of the endosperm material, dried, and aspirated to recover the pericarp and small endosperm material. The aspirate is added to the hominy feed. The germ can be pressed on site, recovering 14–21 kg oil per tonne or delivered to solvent extraction facilities where recovery of oil can vary from 21 to 23 kg oil per MT. The bulk of the thru material (1.25 to þ 250 mm) is dried, aspirated, sieved into various fractions, and aspirated again to achieve a variety of low-fat endosperm products. If needed to achieve mill balance, larger grits and flaking grits can be

reduced in size by roller milling to achieve a more marketable granulation. The 250 mm fraction is known as degerminator fines or degerminator flour and is usually added to the hominy feed due to its high fat content. A roller mill consists of a pair of parallel cylindrical rolls made out of hardened steel, which rotate opposite to each other, rotating so as to pull material into the nip between the two rolls. The rolls generally range in size from 10 to 40 cm (diameter) and up to 1.3 m in length. The roll faces can be corrugated with a variety of cuts or can be smoothface; however, smooth-face rolls are generally not used in maize milling. The gap setting between the two rolls is adjustable, and the rolls are operated with a slight rpm differential. The larger the particle size being roller milled, generally the fewer the corrugations per centimeter on the roll face. As the particle size decreases, the corrugations per centimeter increase.

Tempering Tempering maize is much different than tempering wheat and other cereal grains milled into flour. The purpose of tempering wheat is to induce a moisture gradient in the kernels that causes the germ to swell and the bran layer to release from the endosperm. Wheat is often tempered overnight to allow the added moisture to distribute uniformly throughout the kernel, and then, 10–30 min before processing the wheat, it is tempered an additional 4–6% moisture to enhance germ and bran layer recovery. The moisture added during the overnight temper is beneficial to keep the flour particles from becoming too dry due to pneumatic handling and the heat from the break and sizing rolls. The stress cracking lowers the energy required to produce flour and helps ensure that it will be easier to separate from the bran. In maize dry milling, tempering is done to create differential swelling resulting from the germ and pericarp of the maize absorbing moisture and swelling faster than the endosperm. This swelling loosens the connecting tissue between the pericarp and the aleurone layer of the endosperm and between the germ and the endosperm. In tempering maize, the objective is to not increase the moisture content of the endosperm. Increasing the moisture of the endosperm risks the chance of creating stress cracks, which will lower the yield of large grit material, and means that the moisture absorbed by the endosperm must be removed by drying, thereby requiring more capital and energy. In scientific literature, maize tempering is usually shown as a two- or three-stage process. Industrial practice in the United States for the last 40þ years has been to use a singlestage temper (6–8% added, wb; 10–40 min). For very dry maize (<10% moisture, wb), single-stage tempering is still used. It is preferable to buy maize at 12–14.5% moisture content. Steam or hot water can be used to increase the rate of absorption and decrease temper times, especially in cold weather climates. Steam alone can be difficult to control without overheating the kernel surface and gelatinizing starch. A combination of steam and hot water is recommended in such cases.


Types of Degerminators There are many ‘brands’ of degerminators used around the world with the majority of them being emulations or modifications of a few basic designs. With some exceptions, the patents on most commercially used degerminators have expired, and reverse engineering has become an accepted practice in the industry. For example, the patent for the Beall degerminator was granted in 1901, and it is not uncommon to see similar degerminators for sale by competing major manufactures. Parts are sometimes interchangeable although they may not be of the same quality. This reverse engineering keeps prices for degerminators competitive and makes it difficult for new degerminators with slightly improved performance to enter the market. The various degerminators in use can be classified into six categories.

Kernel-to-Kernel Shear (Beall Type) The Beall-type degerminator is one of the oldest maize degerminators but is still recognized as the best when the objective is to produce large, low-fat flaking grits (5.6 to þ3.55 mm). The design for the Beall has been widely copied and is one of the most used degerminators worldwide (Figure 3). The basics of the Beall-type design are a truncated cone covered with hemispheric nodules, known as ‘pearling knobs’ or ‘knobbies,’ of 2.5 cm diameter, inside an outer truncated cone, half of which is screen surface and the other half knobby surface. The inner cone is driven counterclockwise and can be adjusted in and out relative to the outer cone as a means of controlling gap spacing between the two cones. Tempered maize is fed into the degerminator at the top of the small end of the cone (Figure 3). Spiral ridges on the small one-third of the cone (not shown) move kernels away from the opening and help fill the cavity between inner cone and screens. Discharge from the degerminator occurs when the kernel breaks into pieces. The smaller pieces work their way to and then go through the screen, while the large flaking grits and unbroken kernels are shoved out the tailgate. The thrus consist of whole and broken germ pieces, the pericarp, and smaller endosperm pieces. A 6.4 mm round hole screen is common, but different size screens can be used depending upon the size of the maize kernels and the separations desired. Tempered maize

At steady state, the degerminator is half to two-thirds full, and knobbies on the surface of the rotating cone create shearing action between adjacent layers of kernels. It is this kernelto-kernel shear that breaks open the kernel and releases the germ. Because knobbies are rounded, there are no significant direct impact forces exerted on the kernels by the degerminator. Once the kernel is broken, the germ and pericarp are released due to continued shearing action. Eventually, the broken particles reach the screen surface where all but the largest grits can be discharged. A high percentage of thru material passes through the first two-thirds of the screen surface. If the tempering time was too short or too much water was added, the pericarp can become gummy and clog up the screen. Very quickly, the entire degerminator will plug, and drive belts will slip or direct drive shear pins will break. The degerminator must then be disassembled and cleaned. The last one-third of the screen surface and the tail area (between the large-diameter end plate of rotor and tail plate surface) is a polishing area where the large grits are abrading each other, removing loose, soft endosperm material and attached germ and pericarp, and breaking apart weak grits. This polishing action can be enhanced by increasing the tailgate weight distance, thereby increasing back pressure. Increasing the gap increases residence time and results in increased capacity and cleaner flaking grits. While the manufacturer sells the Beall with half the outer cone as knobbie plates and the other half as screen, many dry millers operate with three-fourth screen and one-fourth knobbie plates. This setup has increased capacity with some reduction in performance.

Impact This category includes a variety of horizontal and vertical disk pin-type mills. Disks with concentric rings of intermeshing pins with one or both of the disks driven are classically known as pin mills. If both disks are rotating, then they spin in opposite directions. The maize is fed into the center of the disks and pass between the rotating pins, where they are randomly impacted. The number of impacts is generally high and the magnitude and frequency of impact do not give good pericarp and germ separation from the endosperm as much as simply grinding the maize. Knobbie plates

Weighted tailgate

Tails

Power shaft

Gap adjustment Stationary bearing

Screen

461

Thrus

Pin coupling Figure 3 Diagram of a Beall-type degerminator, using kernel-to-kernel shear for separation.

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One type of pin mill is an Entoleter, which comprises two horizontal disks with two rows of pins on the rotating bottom disk and one row of intermeshing pins on the stationary upper disk. The maize is dropped into the center of the bottom disk (Figure 4), where it is accelerated by centrifugal force toward the rotating pins. The maize must pass between the three rows of pins before being collected. Because there are a limited number of impacts, the Entoleter recovers more whole germ and produces a larger germ fraction with equivalent oil content than the Beall. However, it produces more mid-size grits (4 to þ2 mm) and less flaking grits.

Multiple Impact/Shear This is probably the most common type of degerminators worldwide (Figure 5). Tempered or untempered maize is fed into the annular region between two horizontal or vertical

cylinders or near cylinders (with flat surfaces to connect impact attachments). The maize transverses the distance of the cylinder being impacted by the attachments to the inner cylinder. The impacting creates a shearing effect between the kernels as in the Beall degerminator. Small particles pass through the screen and large particles drop over a wire at the end of the cylinder. The attachments vary over a wide range of types, shapes, or angles, but all provide some degree of impact. Some models separate the flow through the screen into two or more sections, and there are a wide variety of outlets. The screens can be made adjustable to increase or decrease the gap, and some of the outer cylinder peripherals may be solid with or without rasp bars or other attachments to increase shear. The disadvantages of such machines, compared to the Beall, are that the impacts sustained by the kernels result in a reduction of flaking grits and the machines have reduced flexibility for making adjustments in gap and tailgate back pressure. These

Corn

Corn

Shell

Rotating plate

Endosperm pericarp germ Figure 4 Diagram of the Entoleter, a type of impact degerminator.

Corn

Corn

Thrus Overs Figure 5 Diagram of a multiple impact-/shear-type degerminator.

Thrus

Overs

BARLEY, RICE AND MAIZE PROCESSING | Maize: Dry Milling machines are acceptable and even preferable when producing prime products other than flaking grits because of higher prime product yields.

Compression (Cereal Technologies, Inc.) A series of patents by Jim Giguere and owned by Cereal Enterprises, Inc. (now Cereal Technologies, Inc.) describes mechanisms by which individual kernels are oriented and compressed lengthwise resulting in whole germ separation from the endosperm. The patents describe the mode of action, but the actual design of the degerminator is guarded. Several plants in the United States have been built using this proprietary technology. The process provides efficient clean germ recovery and high recovery of endosperm, primarily as brewer grit size material or smaller. Good separation has been found using tempered and untempered maize. Process yields are reported to be less sensitive to maize quality or hybrid type than other degerminators.

Roller Milling A series of roller mills, each followed by sifting and aspiration, can be used to recover a germ fraction from maize. A welladjusted coarse break mill can crack the kernel, compress the germ so that it pops out, and release the pericarp. Subsequent rolls and other mill separation equipment can be used to ‘clean up’ the fractions. The use of roller mills for degermination is common in Africa, where two to three small roller mills with different corrugations can accomplish degermination and all needed particle size reduction. The advantage of using a roller mill to degerminate maize is the availability and low cost of the roller mill since it is used in all types of dry milling (wheat, oats, etc.). There are several disadvantages of using a roller mill to degerminate. First, the system is not capable of producing large flaking grits. Second, the separation of the germ and pericarp is not as clean as with other degerminators. Third, the roller mill has an adjustable fixed gap, so the efficiency of degermination is a function of the range or spread of kernel size in the sample being tested. If the mill is adjusted to crack the smallest kernels, the larger kernel’s germ is often damaged. If the mill is adjusted to optimally handle large kernels, smaller kernels will pass through unaffected. A series of break rolls can be installed to handle the different size kernels or the maize can be presized and the mill adjusted for each size fraction. However, considering the requisite aspirators and sifters, any economic advantage over a dedicated degerminator is quickly lost as the system becomes more complicated.

Products and Uses The products produced from dry milling can be simply classified as grits, meal, flour, germ, and hominy feed. The germ fraction ( 20% oil) is usually pressed to recover oil that commands a premium over solvent-extracted, wet-milled oil. Solvent extraction is not practical for most dry mills due to the economy of scale in oil extraction and the high cost of shipping the dry-milled germ to an oil processor. In fact, some smaller

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mills will forgo pressing and add the germ fraction into the hominy feed. With pressing, oil yield is only 14.2–23.1 kg MT1 compared to 28.5–30.2 kg MT1 for wetmilled germ. The oil is valued at 5% more than wet-milled oil because of lower refining losses and refining costs. Hominy feed is the lowest valued product and is used almost exclusively as an animal feed. In practice, hominy feed, the trash can of the process, comprises the pericarp, degerminator fines, cracked maize, foreign material and fines removed by the cleaners, pressed germ, out of spec product, and any endosperm fraction that cannot be marketed. There can be considerable variability in the fat and protein contents of hominy feed depending upon each component and the quantity added, although uniformity tends to improve as mill size increases. Within each category of endosperm material (Table 1), there are a large number of potential granulations, which can be marketed as distinct products. Table 2 lists granulation and representative fat content of some of the common products from a dry mill. Product specifications are usually more detailed than what were shown (Table 2). Table 3 shows product specifications, in terms of granulation, for two different flaking grit products sold by one dry milling company. Also controlled (and typically specified by the customer) are the moisture and fat contents. One dry mill offers 38 endosperm granulations and probably produces many more since most large customers provide their own specifications.

Table 1 General product classification of endosperm material showing granulation US standard sieve size Particle diameter (mm) Product classification Less than More than Less than More than Grit Meal Flour

3.5 28 75

28 75 Pan

5660 638 194

638 194 Pan

Data from Johnson (1991) and Brekke (1970).

Table 2 Granulation for common maize dry milling endosperm products and associated fat content US standard sieve size

Particle diameter (mm)

Product

Less than

More than

Less than

More than

Fat (%, db)

Flaking grits Large grits Brewers grits Regular grits Coarse meal Dusted meal Cones Flour

3.5 10 12 14 28 50 40 75

6 14 30 28 50 75 80 325

5660 2000 1680 1410 638 297 297 194

3360 1410 590 638 297 194 177 45

0.6 0.7 0.8 0.7 1.2 1.0 0.6 2.0

Data from Johnson (1991), Watson and Ramstad (1987), and Brekke (1970).

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Degermed maize endosperm products are used in many processed foods and are processed directly into a variety of breakfast cereals and snack products. They are used in brewing and other fermentation industries to provide carbohydrates to the microorganisms. Industrial uses include hand cleaners, foundry core binders, explosives, adhesives, charcoal briquette binder, textiles, paper, gypsum board, and insulating material.

Impact of Maize Quality and Kernel Characteristics Probably, the single largest variable affecting product yield and product quality is the genetics of the maize. There are considerable differences in the dry milling yields between yellow dent and hard endosperm hybrids as shown in Table 4. Desirable genetically determined or genetically predisposed traits are a predominance of hard endosperm, kernel density >1.30 g ml1, test weight >0.77 kg l1, large blocky kernels, zero or only one stress crack per kernel, being insect- and moldfree, and being free from mycotoxins. Even though potential for these traits is controlled by genetics, some of the traits can be altered by either environment or postharvest practices. Hot dry weather tends to increase protein deposition in the kernels, and cool weather tends to favor starch production. Stress cracking will increase dramatically with forced air drying. Stress cracks are formed when the rate of moisture removal from the surface of the kernel (external mass transfer) exceeds the rate of moisture transport from the

Table 3 products

Example of detailed granulation of two different flaking grits Range (% of sample)

Sieve (mm)

Product 1

Product 2

On 5.6 On 5 On 4 On 3.55 Thru 3.55

0–2 20–55 45–80 0–6 0–1

0–5 28–32 68–72 0–28 0–2

Table 4

kernel interior to the surface (diffusivity). This condition causes large moisture gradients to develop in the kernel. The drier side of this moisture gradient shrinks, while the inner core of the kernel endosperm is still wet, and the only way that the stresses created by the shrinking can be relieved is for the endosperm to crack. Field dry-down or moderate to low drying rates can cause some single stress cracks to be formed, while higher drying rates create multiple nonintersecting cracks or checked (multiple intersecting stress cracks) endosperm. Stress cracks (more than one per kernel) reduce flaking grit yield and increase flour yield. High drying temperatures (>70 C) can cause the starch to partially gelatinize, resulting in changes in the functional properties of the flour or other endosperm pieces. There are other quality factors that are primarily influenced by environment. The production of mycotoxins in the field depends upon microbial load and weather conditions. It is desirable to have minimal mycotoxin levels in maize for dry milling since the maize components are often used directly in human food. Mold or insect damage is also primarily influenced by weather or other environmental conditions. Preharvest mold or insect infestation primarily affects kernel development leading to more small kernels and yield loss. Pericarp damage by microorganisms or insects can affect the distribution of water during tempering, resulting in germ and pericarp separation problems. Meeting the criteria for quality described in the preceding text is no guarantee that the maize will perform in the mill as desired or that the fractions will have the traits desired by the end users. Most mills purchase maize by measuring some combination of the traits listed in the preceding text, although some mills offer an ‘approved hybrid list’ to maize producers as a means of minimizing genetic variability. The mills either pay a direct premium to the producer or pay a hidden premium by setting their maize purchase price based upon the mills’ need for maize. The result is that their purchase price for maize varies from 100% to 200% local price for US #1 Yellow, with an average of 120% local price. In either case, laboratory testing of each load of maize is performed prior to acceptance. Functional quality of prime products can also vary based on the mill streams combined to make the salable product. Functional quality is defined as the thermal, rheological, and

Dry milling yields of nine commercial hard endosperm corn hybrids and two yellow dent samples using a Beall No. ‘0’ degerminator Hybrid

Fraction

H1

H2

H3

H4

H5

H6

H7

H8

H9

Y1

Y2

þ5.6 mm 5.66 to þ4 mm 4 to þ2 mm 2 to þ520 mm 520 mm to þPan Total endosperm Pericarp Germ Oil in flaking grits (%)

0 29 27 5 16 77 9 13 0.5

0 26 26 9 14 75 9 15 0.3

0 17 36 12 15 80 7 12 0.4

0 33 33 4 12 82 7 10 0.4

0 39 23 5 12 79 8 11 0.5

9 47 15 5 13 80 6 6 0.3

5 49 16 3 13 81 7 7 0.3

3 52 17 3 11 83 6 8 0.3

0 38 20 4 17 79 8 13 0.3

3 18 38 11 10 77 9 12 n.a.

n.a. 6 10 19 23 58 14 28 n.a.

n.a., not available. Data from Mehra (1996).

BARLEY, RICE AND MAIZE PROCESSING | Maize: Dry Milling organoleptic characteristics of the product. For example, coarse meal can be produced using a Beall-type degerminator from four streams or combinations thereof: (1) sifted from the tail fraction, (2) sifted from the thru fraction, (3) produced from flaking grits or other grits in the tail fraction, and (4) produced from larger grits sifted from the thru fraction. Each of these methods of producing coarse meal potentially can meet the desired product granulation, fat, and moisture specifications. However, the functional characteristics of the meal are likely to be different for each method of production. Even when the hybrid variability is controlled, variability can exist due to selection of process streams and related ‘mill balance’ issues.

• • • •


• •

What are the main processing steps in the maize dry milling process? For the unit operations of degermination, aspiration, and gravity separation, which physical properties are used for separations?

What are the objectives of the tempering step? What are the main commercial coproducts that result from maize dry milling? Discuss how these coproducts vary from the milling process used to produce wheat flour. Discuss the differences between tempering maize for dry milling and tempering wheat for flour production. Discuss the primary differences among processes of wet milling, dry milling, and dry grind.


•

Future Trends 1. Dry milling industry has the fastest potential growth in developing countries. The dry milling industry is a slow-growing industry in the United States, with a growth rate of 2% per year, and is most likely related to population growth. It is a mature industry in most industrialized countries, and potential for growth beyond this level appears dim. Growth potential appears to be in less developed countries where maize products can be inexpensive ingredients for use in an expanding processed food industry. Dry-milled maize products can also be used to make ready-to-eat cereals and nutritious snacks. 2. Aging infrastructure in developed countries will lead to a shift in milling location and scale. A major proportion of the US degerminating dry mill capacity is over 50 years old. The basic infrastructure is expensive to maintain or restore. The industry may shift away from large centralized plants to smaller plants collocated by major end users. Collocation allows for sharing of utilities and infrastructure, minimizes bagged transportation of products, and maximizes technical communication between plants. The milling process can be designed to maximize the production of desired prime products and minimize capital costs. 3. Hybrid(s)-specific processing will become the norm. The pressure to make traceable quality products for the food industry will continue to mount as consumers become more concerned about food security and food safety. Hybridspecific processing is one way to ensure that no undesirable maize enters the processing system. Hybrid-specific processing limits the acceptable maize hybrids, and identity preserves them through the market channel. The millers can contract directly with the producers or work through various specialty maize merchandisers. This procedure is gaining in popularity and importance.

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•

•

Although biotechnology and genetic modification offer many positives to the grain production and food industries, it also creates some concerns. Recent developments of maize hybrids that contain endogenous, safe enzymes that break down starch granules have created concern in the dry milling industry. Although the enzymes do not become active until elevated moistures and temperatures are reached, there are limited situations where the enzymes could be activated and result in undesirable food product textures. Research is needed to verify biotech traits in coproducts that result from processing unique maize hybrids. Additional understanding is needed regarding variability of maize hybrids in a commercial setting. These have been documented in the laboratory, but an understanding of coproduct properties at the milling facility would aid processors in evaluating how much variation affects their efficiency and profitability. Naturally occurring phytochemicals that occur in the germ and pericarp could provide products with high value for the dry miller. It may be possible, through breeding, to have these phytochemicals present in endosperm products, which are typically used in human foods. These compounds could provide health benefits to consuming cereal grain products.

See also: Agronomy of Grain Growing: Lupin: Agronomy; Barley, Rice and Maize Processing: Maize: Wet Milling; Breeding of Grains: Maize: Breeding; Genetics of Grains: Maize: Quality Protein Maize; Non-wheat Foods: Maize: Foods from Maize; Wheat Processing: Wheat: Dry Milling.

Further Reading Brekke OL (1970) Corn dry milling industry. In: Inglett WJ (ed.) Corn Culture, Processing, Products, pp. 262–291. Westport, CT: AVI Publishing. Duensing WJ, Roskens AB, and Alexander RJ (2004) Corn dry milling: Processes, products and applications. In: White PJ and Johnson SR (eds.) Corn: Chemistry and Technology, 2nd edn. Eagan, MN: AACC Press. Eckhoff SR, Paulsen MR, and Yang Ping LA (2003) Maize. In: Caballero B, Trugo KJ, and Fingla P (eds.) Encyclopedia of Food Sciences and Nutrition, vol. 4, pp. 3647–3653. London: Elsevier Science. Giguere JR (1980) Method of Degerminating a Kernel of Grain by Simultaneously Compressing the Edges of the Kernel. U.S. Patent 4,189,503. Giguere JR (1981) Method and Apparatus for Degerminating a Grain Kernel by Impelling the Kernels Along a Guide Vane into an Impact Surface. U.S. Patent 4,301,183.

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Giguere JR (1982) Apparatus for Degerminating a Kernel by Compressing the Edges of the Kernel. U.S. Patent 4,365,546. Giguere JR (1993) Grain Milling and Degermination Process. U.S. Patent 5,250,313. Johnson LA (1991) Corn: Production, processing and utilization. In: Lorenz KJ and Kulp K (eds.) Handbook of Cereal Science and Technology, pp. 55–132. New York: Marcel Dekker. Johnson LA (1999) Corn: Production, processing and utilization. In: Kulp SA and Ponte Jr. JP (eds.) Handbook of Cereal Science and Technology, 2nd edn., pp. 31–80. New York: Marcel Dekker. Lee KM, Herrman TJ, Rooney L, et al. (2007) Corroborative study on maize quality, drymilling and wet-milling properties of selected maize hybrids. Journal of Agricultural and Food Chemistry 55: 10751–10763. Mehra SK (1996) Factors Influencing Beall Degermination of Corn for Dry Milling, 317 pp. PhD Thesis, University of Illinois, Urbana, IL. Mehra SK and Eckhoff SR (1997) Single-stage short-duration tempering of corn for drymilling. Cereal Chemistry 74: 484–488.

Mehra SK and Eckhoff SR (2001) Influence of temper duration and weight distance on system output in the corn dry-milling process. Cereal Chemistry 78: 222–225. Rausch KD, Pruiett LE, Wang P, Xu L, Belyea RL, and Tumbleson ME (2009) Laboratory measurement of yield and composition of dry-milled corn fractions using a shortened, single-stage tempering procedure. Cereal Chemistry 86: 434–438.

Relevant Websites http://www.grains.org– US Grains Council website with information on the various types of value enhanced corn, their growing location and the market channel contacts. http://www.namamillers.org– North American Millers’ Association site with information on the products produced by corn dry milling.

Maize: Wet Milling KD Rausch, University of Illinois, Urbana, IL, USA SR Eckhoff, (Retired) University of Illinois, Urbana, IL, USA ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition’s article by S.R. Eckhoff, Volume 2, pp. 225–241, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • •

Corn (maize) wet milling is the primary process used to produce pure starch (99.95% purity) worldwide. The wet milling process has evolved to be highly energyand water-efficient but is still a large consumer of energy and water. More than 85% of starch produced results from the corn wet milling process. The wet milling steeping process is a complex combination of chemical, physical, and biological stages that prepares the corn kernel for fractionation. The wet milling process results in germ for corn oil recovery, corn gluten feed and gluten meal that can be used in animal diets, and starch. The starch from wet milling can be further processed into many bioproducts, such as sweeteners, ethanol, modified food starches, and biochemicals.

Learning Objectives

• • •

To acquire a fundamental understanding of the wet milling process technology. To examine economic calculations associated with wet mill operation. To understand the compositions of typical coproducts.

Introduction Worldwide production of maize (referred to as corn in the United States) was nearly 940 million tonnes (Mt) in 2012 of which the United States produced 32%. Maize is a starch crop, providing needed energy for animal diets and being converted into starch and coproducts using the maize wet milling process. Maize is an ideal starch crop: it is readily transportable and easily dried and yields over 66% starch on a dry basis. More than 85% of starch produced is derived from maize globally. Wet milling is a complex process with a wide variety of unit operations and interdependence among process steps via recycling of process water. An understanding of wet milling begins with the maize kernel and the steeping process.

The Maize Kernel The structure and composition of the maize kernel are covered in detail in Grain, Morphology of Internal Structure, and so only a pragmatic illustration of the structure and composition of the maize kernel will be given here. The maize kernel is composed of four main parts: pericarp, tip cap, endosperm, and germ (Figure 1). Pericarp is the outer covering of the kernel and is composed of cellulose, hemicellulose, and various waxes, all unappetizing components to insects and microorganisms. The


pericarp is essentially a plastic grocery bag. The opening at the top of the bag is analogous to the tip cap, the connecting tissue between the kernel and the cob, which is the only natural opening into the kernel. Pericarp consists of dense layers of cells near the surface and wide-open transport cells located next to the aleurone layer. The aleurone layer is the outer layer of the endosperm consisting of large, dense, highly proteinaceous cells, which acts as a semipermeable membrane, restricting the flow of large molecules in or out of the endosperm. The purpose of the pericarp is analogous to the plastic bag’s: to protect the food material it contains. The second component of the maize kernel is the germ or embryo, the living part of the maize kernel. It contains the enzymes and building blocks needed to quickly begin developing roots and shoots during germination. The germ contains a high percentage of the kernel’s oil, water-soluble protein, water-soluble carbohydrate, ash, vitamins, and minerals. However, wet milling processors are primarily concerned with the fact that the germ has a high concentration of oil. In the analogy, visualize a sponge saturated with oil. Place this oil-laden sponge into the bag. The rest of the maize kernel is endosperm storage cells that contain starch granules encased in a protein matrix. The grocery bag with the oily sponge is taken and filled with marbles. A bottle of glue is opened and poured into the bag, filling the bag and encapsulating the marbles. The glue sticks the marbles to the bag, the bag to the oily sponge, and the oily sponge to the marbles and glue mixture. It is assumed that some of the glue trapped many small air bubbles when it was being poured into the bag, and the resulting glue matrix is thin and weak. This is the soft endosperm. Hard endosperm is where the glue matrix is thick and dense. After the glue has dried, a processor’s mental picture of the maize kernel is obtained: a plastic bag containing an oily sponge filled with marbles encased in a glue matrix. The purpose of wet milling is to partially dissolve the glue to allow for mechanical separation of the water swollen plastic bag, the swollen oily sponge, the marbles, and the glue. Completed milling yields a pile of nearly empty bags (fiber), oily sponges (germ), nearly pure marbles (starch granules), and partially degraded glue (maize gluten meal).

The Maize Wet Milling Process Maize wet milling can be divided into five sections: steeping, germ recovery, fiber recovery, protein recovery, and starch washing (Figure 2). Each of these sections has unique equipment and objectives, but all sections are interconnected by the flow of process water.

Steeping Steeping is the heart of maize wet milling and will be discussed in more detail than the other sections. When steeping is done

http://dx.doi.org/10.1016/B978-0-12-394437-5.00239-4

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BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling

Soft Endosperm

Hard Endosperm

Pericarp Germ

Tip cap

Figure 1 The mature corn kernel, showing component parts. ã Eckhoff SR, Savoy, IL.

properly, it may be possible to get a good recovery of starch if downstream processing is performed well. If maize is not steeped properly, no amount of downstream processing can correct for poor steeping. Steeping is a process unto itself: a sequence of chemical and biochemical reactions, induced mechanical stresses, leaching, and kernel hydration. Maize, which has been screened to remove broken pieces of kernels and foreign material, is dropped into an insulated hopper bottomed tank, cushioned on the bottom with a layer of water. Broken maize and foreign material (BCFM) are removed because they can plug the screen at the bottom of the tank, which interferes with the steepwater circulation. BCFM not only is usually added into the gluten feed product but also may be sold separately to local livestock feeders. A battery of such tanks, interconnected to route steepwater through the tanks in a specific sequence, can vary from as few as 6 to over 50 tanks with sizes from 12.7 Mt to over 633 Mt. Each tank is equipped with a pump that runs continuously, either transferring water or recirculating the water back to the same tank. Recirculation serves the purpose of increasing temperature uniformity. Tanks are equipped also with heaters to maintain a uniform steep temperature of 52 C. Quality steeping depends on favorable conditions for lactic acid bacteria to outcompete other microorganisms so that lactic acid fermentation can occur, optimizing downstream separations. The optimal temperature for lactic acid production is 52 C. If the steep temperature decreases below 47 C, yeast begin to propagate and produce alcohol. If the steep temperature increases above 56 C, acetic acid bacteria will begin to dominate the fermentation. The steeping process takes from 20 to 48 h to complete. Differences in steep times depend upon the objectives of the wet miller, product mix, and the amount of horsepower used in the mill house. The average steep time in the United States is 30 h, while the average steep time in Japan is more than 42 h due to higher relative value of starch compared to coproducts and use of lower mechanical energy (horsepower) per Mt maize. In the vast majority of maize wet milling plants worldwide, maize is steeped countercurrently using a pull system. Dry maize is exposed to the oldest steepwater and the longest

steeped maize is exposed to the newest steepwater (process water to which sulfur dioxide has been added, Figure 3). As the steepwater is pumped from the tanks with the oldest maize to ones with the newest maize, the sulfur dioxide level decreases from a high of about 2000 to 250 ppm. When the sulfur dioxide level decreases to less than 300 ppm, the ubiquitous lactic acid bacteria (carried in by the new maize) begin to propagate. This results in the fermentation of glucose to lactic acid at levels ranging from 1% to 3%. Because lactic acid concentrations are high on one end of the process and the sulfur dioxide concentrations are high on the other end of the process, steepwater pH changes little during the process and is usually in the range of 3.5–4.2. Commercial steeping operations sequence the steepwater flow to progress the tank contents through the process in a countercurrent manner. Water is pulled from the tank containing the newest maize; the so-called draw rate is determined by the steepwater evaporator capacity. When the steepwater evaporator feed tank is low, sensors open a valve to shunt steepwater from the tank with the oldest steepwater. When the lower limit switch is activated in the oldest steepwater tank, water is shunted from the tank with the second-oldest steepwater. This transfer of water continues from tank to tank until the tank with the newest steepwater needs water. This tank is filled with fresh steepwater. When the steepwater evaporator feed tank is full, the pump valves on the tanks configure flow for internal recycling of steepwater. At the end of the steeping period, the tank with the oldest maize is drained and made ready for milling. Figure 4 illustrates the sequencing required as one tank of steeped maize is drained and the maize sent to the grind mill and the recently filled tank of dry maize is brought into the process. This pattern is continually repeated 24 h a day, 7 days a week. The figure shows the tanks in a circle for simplicity, but usually, the tanks are in rows. Sulfur dioxide diffuses into the maize kernel during steeping and disrupts the endosperm protein matrix (the glue) by breaking inter- and intraprotein disulfide bonds. The sulfite and lactic acid also maintain a lower pH so that endogenous proteases can help solubilize part of the protein matrix. The steeping process can be broken down into three stages: (1) lactic acid-dominated, (2) sulfur dioxide diffusion, and (3) sulfur dioxide reaction (Figures 5 and 6). These stages are each approximately one-third of the steep time in a properly operated system.

Lactic acid-dominated stage In the lactic acid-dominated stage, the key things that occur are (1) rapid hydration of the kernel in the presence of 1–3% lactic acid to near equilibrium conditions (42–52%, wb), (2) leaching of soluble material from the germ into the steepwater causing a concentrating of the oil from 35% to 50%, (3) fermentation of the soluble carbohydrates originating from the germ and from recycled process water to produce lactic acid, and (4) creation of differential swelling stresses resulting from water uptake that loosens the connecting tissue between the component parts. The lactic acid-dominated stage starts with the introduction of the dry maize into the steep solution and ends when the sulfur dioxide level increases enough (i.e., above 300 ppm) to inhibit fermentation.


Corn Steepwater

Light Steepwater

Water Out

Multiple Effect Evaporator

Countercurrent Steeping System

Water In

Condensate Out

Sulfur Dioxide Heavy Steepwater STEEPING GERM RECOVERY Sluice Line

First Grind Screen

First Grind Mill

2nd Stage Second Grind Mill

Germ Press “A”

1st Stage “A”

“B”

“B”

Steam

Germ Hydrocyclones

Wet Germ

Steam Tube Dryer

Dry Germ

Condensate

Fine Grind Screen

6th Screen

Cooling Water

Fine Grind Mill

Process Water

Heavy Steepwater

Centrifugal Screen

Fiber Washing System Mill Stream Thickener (MST)

Clarifer

Gluten Feed

FIBER RECOVERY PROTEIN RECOVERY

Rotary Dryer Exhaust

Ring Dryer

Scrubber Primary Starch Hydrocyclones

Filter Permeate

Vacuum Belt Filter Dry Gluten Recycle

Fresh Water

Gluten Meal Wet Gluten

Starch Slurry STARCH WASHING

Figure 2 The wet milling process. ã SR Eckhoff, Savoy, IL.

Gluten Thickener

Fan and Heater

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BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling absorbed on the surface of the interstitial pores. Sulfur dioxide that enters during the sulfur dioxide-dominated stage essentially retraces the path through the maize kernel that has already been exposed to sulfur dioxide. During the second stage, there is also continued leaching of this from the germ, and the sulfur dioxide begins to react with the protein matrix creating soluble protein, which diffuses from the endosperm into the steepwater. During this time equilibrium, moisture levels are reached.

Sulfur dioxide diffusion stage The sulfur dioxide diffusion stage is so called because the sulfur dioxide that diffuses into the maize kernel during this time is the sulfur dioxide that does the work of disrupting the protein matrix. This second stage is critical to steeping in that it stops the fermentation before producing too much lactic acid (LA levels greater than 1.5% can increase steepwater evaporator fouling) and indicates a point where the sulfur dioxide has a high enough flux to begin making significant inroads into penetrating the kernel. During the lactic acid-dominated stage, the sulfur dioxide flux is too low to penetrate very far into the kernel because of the simultaneous reaction and diffusion that occurs. The sulfur dioxide is a highly reactive chemical, and in the kernel, there are many opportunities to undergo oxidation and acid–base reactions or become

10 8 6 4

RBA

SO2

Dry maize

Fresh steepwater

pH

2 0

Light steepwater

LA 1

2

3

4 5 Steep number

6

1

Steeped maize 7

2

3

4

5

6 7 8 9 Tank number

WE-SO2, PPM ´100 pH

8

Figure 3 Profile for continuous countercurrent steeping. ã SR Eckhoff, Savoy, IL.

G

1 2

8

SO2 3

A

7

Cover the newest maize with steepwater

4

6

1

5

Drain water covering fully steeped maize

4

6 5

LSW F

1 2

G 7

3

B

7

F – Fill G – Grind SO2 – Fresh SW LSW – Light SW

Finish grinding G tank 2

2

8

8

3

C

4

6

Baume Total SO2, PPM ´100

Figure 5 Industrial steep profiles showing pH, Baume´, and two measures of sulfur dioxide level. ã SR Eckhoff, Savoy, IL.

F LSW

10 11 12 13 14

SO2

Tank 3 is the grind tank, tank 2 is the fill tank and tank 4 has the oldest maize and is exposed to the fresh steep water

5 Figure 4 Sequencing of events required to change grind from one tank to another. ã SR Eckhoff, Savoy, IL.


471

Stationary disk

10

Feed

8

Rotating disk

6 4 MOTOR 2 0 1

2

3

4

5

6 7 8 9 Tank number

10 11 12 13 14

M.C., % ´5

SW protein, %

SW sol. p., %

% Lactic acid Discharge

Figure 6 Industrial steep profiles showing moisture content, steepwater protein, steepwater-soluble protein, and lactic acid. ã SR Eckhoff, Savoy, IL.

Sulfur dioxide reaction stage In the third stage of steeping, the sulfite absorbed during the second stage reacts with the protein matrix in the hard endosperm section of maize (reactions take less than 4 h), so the rate-limiting part of steeping is the diffusion of sulfur dioxide into the kernel. The reaction with the protein matrix loosens the disulfide bonds in the protein, allowing downstream grinding stages to break away the endosperm protein (glue) from the embedded starch granules (marbles). Some of the sulfur dioxide that the endosperm is exposed to during this stage diffuses into the outer sections of the kernel and is carried downstream into the process to provide microbial control. Leaching from the kernel continues to move some of the solubles created by steeping. After the steep tank is drained, the swollen maize is discharged from the bottom of the tank into a fast-moving stream of water (sluice water), which carries the kernels to the firstgrind mill or degerminating mill. The sluice water is recovered using a screen and recirculated.

Germ Recovery The first objective after steeping is to recover the swollen germ. If we visualize the germ as an oil-soaked sponge, it is clear that we want to remove the oily sponge from the system as early as possible in the process to minimize germ damage, maximize oil recovery, and prevent the oil from interfering with subsequent separation steps, especially starch recovery. Mechanical sheer applied properly can separate the germ from the other components with little damage to the germ itself. To accomplish this, the industry uses 61 or 91 in diameter disk mills (224 kW) with specially designed intermeshing teeth (Figure 7) using relatively loose gap settings that allow one or two whole kernels per handful. This operational parameter allows for the vast majority of the kernels to be broken open with minimal damage to the germ. A tighter gap setting that gives 100% germ release would also create excessive germ damage. This initial coarse milling step is often called first grind. The milled maize slurry is pumped through a two-stage hydrocyclone system to recover germ. These germ hydrocyclones are 15.25–22.86 cm diameter and 0.6–1.1 m tall.

Figure 7 Single-disk mill used in germ recovery. ã SR Eckhoff, Savoy, IL.

Operating pressures are generally 275–310 kPa with the specific density of the slurry adjusted to between 8 and 9 Baume´. At these conditions, the free germs (being 42–52% oil) float and will be forced to the center of the hydrocyclone, away from the wall, where it goes out of the vortex finder (Figure 8). The heavier material is forced to the wall of the hydrocyclone by centrifugal force and works its way by gravity to the bottom discharge. In the two-stage hydrocyclone system, stage 1 hydrocyclones are ‘A’-type cyclones designed for a qualitative split between the germ and the remaining slurry. Stage 2 hydrocyclones are designed for quantitative recovery of germ, with larger diameter feed and vortex finder connections and are designated ‘B’-type hydrocyclones. Because of flow and capacity differences, there are generally two ‘A’ cyclones for every ‘B’ cyclone. The overflow of the ‘A’ cyclone (light material, i.e., germ) and the underflow of the ‘B’ cyclone can be regulated by a flow control valve to achieve the desired split. The overflow of the ‘B’ hydrocyclone is sent back to the feed tank of the ‘A’ hydrocyclone (see Figure 2). The slurry going out from the bottom of the ‘B’ hydrocyclone is sent to a second single-disk mill (known as the secondgrind mill), with the intermeshing plates set just close enough to make sure that all remaining kernels are properly ground. The resulting slurry is pumped through a second two-stage hydrocyclone system. Just as before, the second hydrocyclone overflow is sent back to the feed tank of the first hydrocyclone. The overflow of the second-grind, first-stage hydrocyclone is sent back to the feed tank of the first-grind, first-stage hydrocyclone. With this setup, the germ leaves the hydrocyclone system only from the first-grind, first-stage hydrocyclone, where it is sent to germ washing. Operation of the germ recovery system is a series of compromises. Attempts to increase the purity of the germ by restricting first-grind ‘A’ cyclone overflow increase the recycle and can result in plugged cyclones or a decrease in overall plant grind rate. Approximate flow rates of the overflow are 20% of the feed rate for ‘A’ cyclones, 30% of the feed rate for first-grind ‘B’ cyclones, and 30–45% of the feed rate for second-grind ‘B’ cyclones. Most wet milling plants operate with this two-grind, twostage hydrocyclone system, which essentially gives a minimum of four chances to recover germ. In-plant experimental data show that 85% of the germ is recovered by the first-grind

472


Less dense particles

Vortex finder

Starch Protein Fiber

Slurry

Feed Spray nozzle

Starch and protein More dense particles

Fiber

Figure 9 Pressure-fed screen with magnified view of the wedge bars. ã SR Eckhoff, Savoy, IL.

Figure 8 Operation of a germ hydrocyclone. ã SR Eckhoff, Savoy, IL.

hydrocyclones and the remainder by the second-grind hydrocyclones. To reduce capital costs, some plants have only a single-stage hydrocyclone system after the second grind. Unrecovered germ will be recovered primarily with the fiber or gluten meal. Quantitative recovery of the germ is an economic decision based on the relative values of maize oil and gluten feed and a quality decision based on the sensitivity of the plant’s starch product mix. The germ fraction usually is washed countercurrently to remove residual starch in a three-stage process. Washed germs are sent to a germ press and dried to less than 3% moisture for shipment to a solvent extraction plant, unless the wet mill has its own extraction facility. Germ must be <3% moisture to prevent oxidation of the oil during transport. The germ fraction contains 42–55% oil depending on a number of factors including the amount of residual pericarp that floats with the germ, steep time, and maize hybrid or variety. Rotary steam tube dryers are commonly used to dry germ because the exposure time for any individual germ to be in contact with a steam tube is minimal. More recently, fluidized bed dryers are used because they give more uniform moisture content although it is generally a less-efficient drying method. Dryer types that expose the germ to temperatures >80 C for extended periods of time should be avoided because the oil will be heatdamaged and extraction efficiencies and oil quality decreased.

Fiber Recovery The underflow of the second-grind, ‘B’ hydrocyclone is passed over a 50 mm 120 wedge bar screen (Figure 9) to dewater slurry and to allow starch and protein that has already been released from the fiber to go directly to the mill stream thickener (MST) in the protein recovery section of the process. Material retained by the screen is passed through a doubledisk refiner mill to release remaining starch from the weakened

protein matrix. The double-disk mill is similar to the singledisk mill used for degermination except that the disks rotate in opposite directions with each disk driven by a large electric motor. This arrangement maximizes the shear that is experienced by the particles. Most double-disk refiners used in the United States have 91 cm disks operating at 1800 rpm and are equipped with 187 kW electric motors on each disk. Recently, some companies have used a 132 cm diameter single-disk mill with a 746 kW motor in place of the double-disk mill. When operated at 1250 rpm, this large single-disk mill has disk tip differential velocity similar to the double-disk refiner. The finely ground slurry is pumped onto a six-stage fiber washing system. The pressure-fed screens come in several configurations but most commonly used is the 120 screen (Figure 9). The finely ground fiber–starch–protein slurry is sprayed across the top of the screen at a pressure of 275 kPa. The pressure and force of gravity cause the fiber to orient parallel to the direction of flow where the wedge bar screens will scrape off residual starch and protein still attached to the fiber. The 120 arc of the screen ensures contact between the fiber and the wedge bars. At the top of the screen, the pressure accelerates the fiber, pushing it along the surface of the screen. When the screen becomes more vertical near the center, the fiber has decelerated and the principal force on the fiber is gravity. By the time the fiber is on the lower portion of the screen, it has been dewatered significantly and the fiber bunches up to allow for more dewatering before it is forced from the screen. Moisture contents are 80–90%, wb. The first-stage screen is a 50 mm screen and is known as the fiber block. The other five screens are 75 mm screens. The theory is that fiber sized between 50 and 75 mm agglomerates with other fiber during the initial dewatering and is carried out to the feed house. The 75 mm screens are used because they have a 50% larger open area, and less screen area is needed to achieve adequate dewatering in stages 2–6. There are some who consider this arrangement of screens to be a fine fiber

BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling generator because the 50–75 mm particles will recirculate between the 50 mm screen and the 75 mm screens until the particle is reduced in size enough to pass the 50 mm screen. The fiber stream coming off stage 6 screen is further dewatered using either a screening centrifuge, a screw press, or both in series. Screening centrifuges can decrease moisture to 65–75%, wb, while a screw press can decrease fiber moisture an additional 10% points. This so-called white fiber is mixed with previously dried fiber and heavy steepwater to form a mixture containing 35–40% moisture, wb, which can be dried to 10–12%, wb, using either a direct fired rotary dryer or a steam maize tube dryer. Spent germ (germ meal left after solvent extraction of the oil), broken maize, or spent filter media from syrup production can be added dry to the fiber when available. Adding germ meal or filter media to the wet fiber before drying results in excessive dryer smoke. The final product is known as gluten feed.

Protein Recovery Protein separation depends upon the principle of density difference between the starch and the protein. The density of the maize kernel components remaining is highest for starch and lowest for any cell wall or fiber that passes through the pressurefed screens (Table 1). The density difference between good starch and protein is sufficient for good separation. 70 years ago, all maize starch, as well as other types of starch, was purified by pouring the starch–protein mixture onto tables that were 30–100 m long, about 1 m wide, and sloped 1.04 cm m1. Starch would settle onto the table, while the protein mixture was carried along by the water and ultimately off the end of the table. This technology is still used today in Table 1

Density differences in components found in starch slurries

Component

Density (g ml1)

Sand, dirt Starch Protein Cell walls, fine fiber Water

>2 1.55 1.10 1.05 1.00

Sources: (1) Blanchard, P.H., 1992. Technology of Corn Wet Milling. Elsevier Science, Amsterdam, The Netherlands. (2) International Starch Institute, 2003. TM 18-2www – ISI Technical Memorandum on Production of Corn Starch. http://www.starch.dk/isi/ starch/tm18www-corn.htm, Science Park Aarhus, Denmark. (3) US Grains Council, 1996. 1995–1996 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (4) US Grains Council, 1997. 1996–1997 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (5) US Grains Council, 1998. 1997–1998 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (6) US Grains Council, 1999. 1998–1999 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (7) US Grains Council, 2000. 1999–2000 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (8) US Grains Council, 2001. 2000–2001 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA. (9) Blanchard, P.H., 1992. Technology of Corn Wet Milling, Elsevier, Amsterdam, The Netherlands, p. 73. (10) Radley, J.A. (Ed.), 1976, Starch Production Technology, Applied Science, London, p. 123. (11) May, J.B. 1987, Wet milling. In: Watson, S.A., Ramstad, P.E. (Eds.), Corn: Chemistry and Technology. American Association of Cereal Chemists, St. Paul, Minnesota, p. 390. (12) Johnson, L.A., 1991. Corn: production, processing and utilization, In: Lorenz, K.J., Kulp, K. (Eds.) Handbook of Cereal Science and Technology. Marcel Dekker, New York, p. 58. ã SR Eckhoff, Savoy, IL.

473

laboratory milling (with much smaller tables) because the starch purity recovered from the starch table is nearly as good as from a wet milling plant. The large amount of space needed for the tables eventually dictated that new technology be developed. The development of the disk-nozzle centrifuge systems for starch–protein separation greatly reduced space requirements and allowed wet millers to grow in size. The principal piece of equipment in a typical wet milling centrifuge system is the primary centrifuge. A disk-nozzle primary centrifuge is a continuous centrifuge where a light fraction is separated from a heavier fraction as it is being forced to flow in between rotating disks in a disk stack, with the lighter phase going up between the disks and being discharged as overflow. The heavier phase flows down the disks and is ultimately forced out of the centrifuge through nozzles located at the periphery (Figure 10). The mill starch is pumped into the centrifuge, at a constant rate, to a location near the underside of the disk stack. Approximately 1/4 of the way up the disk, there are a series of holes, 2.5–5 cm diameter, located every 30 radially. These holes are lined up in the disk stack to provide an entry point for the feed (input) material. As mill starch enters the space between the disks; starch, protein, and fiber particles in the slurry are subjected to the centrifugal force caused by the rotating action of the disk stack, the force of gravity, and the hydraulic force resulting from pumping (Figure 11). The acceleration force due to gravity can be neglected, since it is relatively small at high centrifugal forces. The separating ability of the disk-nozzle centrifuge depends on the relative acceleration of the particle due to centrifugal forces and due to the hydraulic force. For a given particle, the hydraulic force depends upon its position in the flow field. The velocity of the fluid is greatest at the center between the two disks and drops off to zero at the surface of each disk. The force experienced by the particles due to centrifugal action depends upon the mass of the particle, the angular velocity (o) of the centrifuge, and the settling rate of the particle based on Stokes’ law. Figure 11 illustrates the paths taken by light and dense particles. The dense particles are accelerated toward the top surface of the disk by the centrifugal force that is larger than the hydraulic forces even at the center of the channel. As they approach the upper surface of the channel, the hydraulic forces continue to decrease due to the decreasing velocity near the top surface of the channel. The centrifugal forces dominate and pull the dense particles toward the outer edge of the disk stack channel. Eventually, the dense particles are forced toward the nozzle where it is discharged from the centrifuge. The lighter particles do not have as large a centrifugal force acting on them, but the hydraulic force is just as large as for the dense particles. As the lighter particles move toward the center of the channel, the hydraulic forces dominate and the lighter particles are pulled up toward the discharge. Figure 11 shows lighter particles and denser particles in different stack channels for illustrative purposes, but in actuality, their movement is occurring simultaneously in all channels of the disk stack. The primary centrifuge’s disk stack is designed to maximize separation between starch and protein at a specified feed rate. Disk stack diameters range from 23 cm (pilot plant size) to 91 cm (commercial size). A 91 cm diameter primary centrifuge can process over 1000 Mt day1 when driven with a 150 kW motor.

474


Overflow Feed Casing Pump

Disk stack

Rotor

Nozzle

Drive shaft Underflow Figure 10 Disk-nozzle centrifuge. Reproduced with permission from Blanchard P.H., 1992. Technology of Corn Wet Milling. Elsevier Science, Amsterdam, The Netherlands, p. 393.

Resultant force Pu

m for ping ce

Flo pro w file

Centrifugal force = Mass ´ acc = mass ´ rw2

He

avy

Lig

ht p

art

pa

rtic

les

Nozzle

icle

s

Feed Recycle/wash Figure 11 Illustration of the movement of particles between disks in a disk-nozzle centrifuge. ã SR Eckhoff, Savoy, IL.

If the disk stack configuration and/or pump volume is changed to lower the hydraulic forces relative to the centrifugal forces, the centrifuge can be used to recover insoluble solids. It essentially becomes a dewatering centrifuge. Disk-nozzle centrifuge systems for separating starch and protein can have 2–4 centrifuges. One is the primary, while the other 1–3 centrifuges are dewatering centrifuges. The most common centrifuge system used in wet milling is the high-density four-centrifuge system shown in Figure 2. To increase the capacity of the primary centrifuge, MST is used to remove water from the starch–protein slurry coming from the fiber recovery system. The density is increased from 8 to 12 Baume´. The overflow from the MST is used as process water for the steeping system. The overflow from the primary centrifuge is high in protein, nearly 70%, db, but is only 1.5–3.0% solids. Prior to dewatering to 40% solids using a vacuum belt filter, the protein-rich stream is dewatered using a centrifuge known as the gluten

thickener, where the gluten stream is dewatered up to 16.5% solids. The overflow from the gluten thickener is used as process water for germ and fiber washing. The cake from the vacuum belt filter is mixed with dry gluten meal to reduce tackiness and improve handling characteristics of the wet gluten. It is dried to 11% moisture using a ring dryer. The protein content of the resulting gluten meal is established at the primary centrifuge. The underflow of the primary centrifuge still contains 1.5–3% protein and is sent to the starch washing system, where starch is washed repeatedly to recover more of the remaining protein and fine fiber particles. The overflow of the starch washing system is sent to a dewatering centrifuge known as the clarifier. The overflow to the clarifier is relatively clean water and is used as germ and/or fiber washing process water. The underflow from the clarifier is mixed with the underflow of the MST and is fed to the primary centrifuge. In the four-centrifuge system, the MST, gluten thickener, and clarifier are all designed for dewatering. There are various two- and three-centrifuge systems that take out one or more of the dewatering centrifuges and have application primarily in smaller plants where capacity is less than can be handled by one primary centrifuge.

Starch Washing Starch washing is the last step of the wet milling process and is the only location in the process where freshwater is added into the system. Starch washing is performed countercurrently using 10–14 stages of 10 mm diameter hydrocyclones (Figure 2). Each stage of the starch washing system contains enough hydrocyclones to handle the flow rate of the starch slurry at that point. Approximately 1200–1500 l of freshwater per Mt of maize (2.1–2.6 lbs water per lb of dry starch) is used to countercurrently wash the starch to a protein level of 0.25–0.5%. There are several styles of containers for the numerous parallel 10 mm cyclonettes needed for starch washing. The most popular style still in use in the United States is a

BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling clamshell arrangement shown in Figure 12 in which up to 480 individual cyclonettes can be packed into one clamshell and can handle 890 Mt day1. Newer units are designed for rapid changing of cyclonettes to minimize downtime of the unit. The underflow of the last starch washing unit is at 23 Baume´. From this point, the slurry can be used to produce unmodified starch, chemically modified and dried or hydrolyzed to make a variety of maize syrups, dextrins, or glucose syrups. Drying usually is done with a ring dryer after dewatering the starch using basket centrifuges or vacuum belt filters.

Capital Requirements and Energy Use Maize wet milling is a capital- and energy-intensive process (Table 2). The values shown are the purchased equipment

475

and energy for a 2667 Mt day1 wet mill, which produces only dry starch. To calculate total fixed capital costs, on-site costs need to be known, which can be calculated as a percentage of the purchase equipment costs, based on historical data for processing plants of this type. Fixed capital costs are 1.81 the on-site costs and as shown in Table 3 are US $127 million. Starch dewatering and drying is the largest single user of energy and capital in the wet milling process. However, most maize wet millers do not produce just dry starch but have a wide variety of starch hydrolysate products, as well as modified starches. A similar-sized plant dedicated to making fructose would have a total fixed capital cost of US$206 million, and a wet mill dedicated to producing ethanol has a total fixed capital cost of nearly US$171 million. These values will vary depending upon plant location, local labor costs, and

Starch-gluten Seals

Gluten

Starch

Starch-gluten

Starch-gluten

Gluten

Starch

Figure 12 The flow of starch and protein in a 10 mm (clamshell-type) hydrocyclone system for starch washing. ã SR Eckhoff, Savoy, IL. Table 2

Equipment cost and energy use for a 2668 Mt day1 maize wet mill

Item

kWh Mt1

% of total

$ (1000s)

% of total

Corn receiving Steeping Steepwater evaporation Germ recovery (first grind) Germ recovery (second grind) Germ recovery (germ washing) Germ dewatering and drying Fiber recovery Fiber dewatering Protein recovery Gluten thickening and drying Starch washing Starch dewatering and drying Gluten feed dryer

4.66 38.97 230.86 7.88 3.92 0.27 44.34 23.60 0.42 10.96 75.76 5.26 243.76 147.73 841.09

0.54 4.62 27.41 0.94 0.52 0.03 5.26 2.80 0.49 1.30 9.00 0.62 28.94 17.53 100.00

3500 4332 2037.5 911.5 640.5 251 1069 2304.5 1923 3071.5 2740 1302.5 9030 3940 37 053

9.45 11.69 5.50 2.46 1.73 0.68 2.89 6.22 5.19 8.29 7.39 3.52 24.38 10.65 100.00

Assumptions: (1) 2668 Mt d1 grind, (2) modern plant, (3) feed house integrated to maximize energy efficiency, (4) incoming freshwater to starch washing heated with waste heat. Blanchard, P.H., 1992. Technology of Corn Wet Milling. Elsevier Science, Amsterdam, The Netherlands and Wideman, J., 2003 Handout at AACC Wet Milling Short Course, Urbana, IL, 27–30 May 2003. ã SR Eckhoff, Savoy, IL.

476 Table 3

BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling Calculating on-site and fixed capital cost

Category

Cost ($)

1. Purchased equipment cost (PEC) 2. Purchased equipment installation (35% of PEC) 3. Instrumentation and controls (10% of PEC) 4. Piping and material handling (30% of PEC) 5. Electrical equipment and material (15% of PEC) On-site costs ¼ 70 400 700 Fixed capital costs (1.81 on-site costs)

37 053 000 12 968 550 3 705 300 11 115 900 5 557 950 127 425 267

Douglas, J.M., 1988. Conceptual Design of Chemical Processes. McGraw-Hill, New York, NY.

product mix, yet because the equipment suppliers market internationally, the equipment costs will be similar.

Water Flow and Mass Balance Balancing water flow in a wet mill is critical to profitable operation. In general, any problem can be made a little bit easier by adding more water. The downside of running a dilute wet mill is that all the water must be properly discharged. Wet mills have been bottled up for 80 years, that is, with all water leaving the products or being evaporated into the air. The average wet mill will spend $0.35 per bushel in energy, more than at any single operating expense except the maize itself. Freshwater enters the process only at the last stage of starch washing and works its way through the process, where it washes the primary centrifuge, fiber, and germ. Process water, now laden with solubles and some insolubles, ends up as ‘fresh’ steepwater (process water with sulfur dioxide added) moving through the steep battery and finally concentrated in the evaporators to produce heavy steepwater. Some seal water and rinse water enter the process but usually amount to less than 8% of total water added (shown on Figure 13 as extra water). Of the 1200–1500 l water per Mt maize, which enters starch washing, 700 l Mt1 is needed to hydrate maize during steeping. Another 420 l Mt1 is needed to fill the void space in the tank so that the maize is not left uncovered. While 1200–1500 l water per Mt maize is significant, 1120 l Mt1 is needed just to be able to run the process. The mass balance shows how much water and solids are recycled in the process (Figure 13 and Table 4). Even though the inflow rate of maize and water combined is over 10 000 lbs min1, individual streams are in excess of 17 500 lbs min1. Variability in maize characteristics (fraction yields, water-holding capacity, millability, etc.) can cause great swings in process flows. For example, switching from maize with an equilibrium moisture after steeping of maize at 44–52% causes a swing in the water going to the steepwater evaporator of 255 l Mt1 or 40% of the flow.

Wet Milling Products Wet milling results in four main products: starch, oil, gluten meal, and gluten feed. Compositional data for these products as well as for specific components of gluten feed are shown in

Table 5. Starch is the prime product but coproduct value can greatly influence overall plant economics. Coproducts make up 30–40% of the total product yield, yet 20–25% of the kernel is processed without increasing value, even though oil and gluten meal have higher value than starch in the US market. There is a wide range of products that can be made from starch (Figure 14), while nonanimal food uses of the coproducts are more limited. However, there is an increasing research and commercial interest in improving the existing coproducts, finding new industrial uses, or extracting nutraceuticals from coproducts.

Factors Affecting Starch Yield Kernel Composition On a per kg coproduct basis, maize oil is the most valuable component of the maize kernel ($0.66 kg1), followed by gluten meal ($0.30 kg1), starch ($0.22 kg1), and gluten feed ($0.07 kg1). These simple facts often lead to an assumption that maize with enhanced quantities of oil or protein would be desirable in a wet mill. This is generally not true because the change in composition effects mill balance. The mill is designed to process maize of average composition. To handle more germ or more protein, the plant often has to decrease its grind rate (the number of bushels processed per day), which increases processing costs per bushel. It is also possible to expand or redesign wet milling plants to handle maize with altered compositional characteristics. However, these redesigned mills need to ensure themselves of sufficient quantities of reasonably priced enhanced composition maize to justify the added capital. There are situations where specific mills have economic reasons to desire enhanced compositional characteristics. For example, most of the specialty food and industrial starch plants are smaller, older, landlocked facilities, which cannot economically expand their maize handling or coproduct handling facilities. High-extractable-starch maize will allow them to expand production of high-value specialty starches without expanding their handling capabilities. Japanese wet millers also desire high-extractable-starch maize due to low coproduct values. Changes in the ‘quality’ of the components, that is, better amino acid balance in the endosperm glutelin protein or more desirable fatty acid composition, would not affect the mill balance and thus are attractive to wet millers if (1) any premium they pay for the maize can be more than offset by the increased coproduct value and (2) they can be assured of sufficient quantity of maize to effectively run their facility. In general, wet milling companies want yellow dent maize with average compositional characteristics.

Test Weight Higher test weight as controlled by genetics is most often related to the percentage of hard or vitreous endosperm found in the kernel. Hard endosperm takes longer to steep and generally results in less starch release due to the reduced diffusional characteristics of hard endosperm and increased disulfite bonding. Wet millers desire sound, solid kernels, but


Wet milling yields % db 67.3 Starch 7.2 Germ 5.7 Gluten meal 12.8 Fiber 7.0 SWS

2668 Mt d–1 14.5% mc 855 kg ds Mt–1 145 kg Water Mt–1

A Steeping

B

C

477

0.031 Mt s–1 0.031 Mt s–1 26.31 kg s–1 Total 4.47 kg s–1

3% ds

44% mc 1.90 kg s–1 Germ 1.90 kg s–1 Water

Germ recovery

50% mc E

D

8.45 kg s–1 Total 3.38 kg s–1 ds Fiber

Equal flow F

Fiber recovery

5.07 kg s–1 Water 60% mc

G Mill Stream thickener

H

I K

Process water tank

3.02 kg s–1 Water extra water

1.51 kg s–1 Gluten 2.26 kg s–1 Water 60% mc 3.76 kg s–1 Total

J Primary centrifuge

P X

Gluten thickener

T

Starch washing

Clarifier

Fresh water

N

Vacuum belt filter

V

S

R

U

M

17.78 kg s–1 Starch 22.2 Be = 41.05 % ds Ó 113 F 25.53 kg s–1 Water 43.30 kg s–1 Total

44.80 kg s–1 Total 1450.89 kg Water Mt–1 2.5 kg Water kg–1Starch

Figure 13 Mass balance on maize wet mill. ã SR Eckhoff, Savoy, IL.

test weights above 1036 kg Mt1 indicate kernels that probably will require longer steep times and potentially will have lower starch yields. Flint-type maize is undesirable, not only for the higher percentage of hard endosperm it contains but also because it has been found to take considerably longer to steep than dent maize, even when diffusional barriers are removed. The effect of environment on test weight is varied. Hot, dry weather will increase test weight by inducing the formation of a higher percentage of hard or vitreous endosperm. Cool, wet weather has the opposite effect. A recent study found no difference in the yield of starch, even though test weights varied from 700 to 800 kg Mt1 range to over 1075 kg Mt1 due to

weather. Low test weight can also be caused by an early frost causing the maize not to ‘fill out’ or physiologically mature, which has a negative effect on starch yield. Although test weight differences caused by weather do not affect starch yield, they can affect wet mill economics. Steeping is a volume-limited process so that lower test weight means less maize in the steep tank, and if the steep time is held constant, the mill’s grind rate is decreased. Test weights below 1000 l Mt1 should be discounted at a rate of $0.03 per 18 l Mt1 below 1000 l Mt1 to compensate for the loss of grind capacity. Because much of the rest of the wet milling process is dry solids-limited, there is no advantage to having higher-test-weight maize.

478


Table 4

Stream composition for wet mill mass balance shown in Figure 13

Letter

Location

kg s1 total

kg s1 ds

kg s1 H2O

Baumeá

%ds

A B C D E F G H I J K M N P R S T U V X

Light steepwater Steeped corn Germ wash water Mill slurry Fresh steepwater Fiber wash water Defibered mill stream Germ and fiber wash MST underflow Gluten thickener overflow Primary feed Primary overflow Feed to vacuum belt filter Clarifier overflow extra Clarifier overflow Primary underflow 1st-stage starch washing Clarifier underflow Belt filter water Primary wash water

19.38 45.70 50.85 93.85 34.61 50.85 136.75 102.91 102.14 65.76 126.56 69.57 9.89 34.09 45.91 68.81 70.33 24.41 6.08 11.82

1.89 25.90 0.19 24.16 1.04 0.19 20.93 0.38 19.89 0.23 24.84 1.75 0.01 0.15 0.19 23.12 5.14 4.95 0.00 0.04

17.74 20.35 51.26 53.73 33.57 51.26 115.82 102.53 82.25 60.97 100.95 63.26 8.37 33.94 45.72 45.69 65.19 19.47 6.08 11.78

5.00 NA ffi0 14.49 1.69 ffi0 8.61 ffi0 10.96 ffi0 11.04 1.42 8.67 ffi0 ffi0 18.91 4.11 11.40 0 ffi0

9.50 56.00 0.37 25.75 3.00 0.37 15.31 0.37 19.48 0.35 19.6 2.52 15.40 0.44 0.41 33.61 7.30 20.26 0 0.32

%ds (dry solids) ¼ 1.777 Baume´; light steepwater used relationship in Blanchard, P.H., 1992. Technology of Corn Wet Milling. Elsevier Science, Amsterdam, The Netherlands, ã SR Eckhoff, Savoy, IL.

a

Table 5

Range of compositional values for wet milling coproducts

Moisture (% wb) Protein (% db) Oil (% db) Starch (% db) NFE (% dba) Crude fiber (% db) Ash (% db)

Starch

Condensed steepwater

Gluten feed

Gluten meal

Germ meal

Oil

10–12 0.30 0.02 99 NA 0.03 0.10

45–55 40–50 0 NA 30–40 0 6–8

10–2 21–24 2–3 15 50 8–9 8–9

10–12 66–70 2 NA 22–30 1 2–3

10–12 20–28 1–2 NA 50–56 10–12 3–5

0 0 100 0 0 0 0

a

NFE is nitrogen-free extract. Blanchard, P.H., 1992, Technology of Corn Wet Milling. Elsevier Science, Amsterdam, The Netherlands. Johnson, L.A., 1991. Corn: production, processing and utilization, In: Lorenz, K.J., Kulp, K. (Eds.), Handbook of Cereal Science and Technology. Marcel Dekker, New York, pp. 55–132 and Wright, K.N., 1987. Nutritional properties and feeding values of corn and its by-products. In: Watson, S.A., Ramstad, P.E. (Eds.), Corn: Chemistry and Technology. American Association of Cereal Chemists, Minnesota, St. Paul. ã SR Eckhoff, Savoy, IL.

Millability Millability is defined as the ease of component separation. Genetically, some hybrids are easier to process than others. Such hybrids do not contain more starch, but milling them results in higher starch yields. Germs float more readily, fiber dewaters more easily, starch content of the fiber is lower, starch and protein are easier to separate, and other qualitative and quantitative characteristics have been observed. Figure 15 shows the variability in starch yields for 1244 commercially available hybrids (breeder samples) in the Midwest during a 6year period. Starch yields varied from less than 50 up to 72% with an average near 63.5% and a peak frequency at 66%.

Mechanical Damage Mechanical damage to the kernel resulting in broken maize is not desired by wet millers. The broken maize plugs screens at the bottom of the steep tanks resulting in nonuniform

steepwater flow and poor steeping. When the endosperm regions are directly exposed to the steepwater, the starch granules are exposed to sulfur dioxide for longer periods of time. The sulfur dioxide acts as a weak acid to alter the gelatinization and cooking characteristics of the raw starch, generally lowering peak viscosities, which is an undesired effect. Broken maize also results in excess loss of solids into the steepwater and can cause evaporator fouling problems.

Drying Rapid high-temperature drying is the single most detrimental operation done to maize to reduce its starch yield. Numerous studies have shown that drying air temperatures above 70 C can result in partial gelatinization of the starch, protein denaturation, and endogenous proteolytic enzyme denaturation. Figure 16 shows effects of drying air temperature on starch yield of three hybrids. Starch yields decreased as drying air


Starch

Unmodified starch

Food

Modified starch

Paper

Fiber

479

SWS

Hydrolysate

Beverges

Ethanol; biofuels

Oil

Fermentation

Food additives

Industrial products

Industrial chemicals

Pharmaceuticals; nutraceuticals

Protein

Figure 14 Diagram showing the use of various wet milling coproducts in food and industrial products. ã SR Eckhoff, Savoy, IL.

200 70 Starch yield %

180 160

Frequency

140 120

65 60 55 50

100

45

80

40 25

60 Hybrid C

40

50

70 90 Temperature ⬚C

110

Hybrid B Hybrid A

20 0 50 52 54 56 58 60 62 64 66 68 70 72 Starch yield Figure 15 The frequency distribution of maize hybrid starch yields. ã SR Eckhoff, Savoy, IL.

temperature increased above 70 C. As much as 10% yield loss of starch was observed. Figure 17 shows wet milling yields for nine commercial hybrids representing a range of endosperm hardnesses, harvested at two moisture contents and dried by either ambient air or 110 C drying air. Drying from a higher initial moisture content (> 28%) had a severe effect on starch yield. Hybrid variability in sensitivity to drying temperature was also observed.

Storage Wet millers have reported over the years that the milling quality of maize diminishes over the course of the season, with considerable milling difficulty in the summer months. It was perceived that there was some intrinsic loss in quality associated with storage time, possibly due to loss or gain of some enzymatic activity. Wet millers also reported difficulty in the

Figure 16 The effect of drying temperature on starch extractability from three maize hybrids. ã SR Eckhoff, Savoy, IL.

fall in processing new crop maize. They complained of foaming problems and reduced starch yield. These problems generally disappeared after 1–2 months. Recent studies indicate that there is no intrinsic long-term degradable loss in starch yield due to storage at either ambient conditions or 4 C until after 4 years. It is likely that the effect of storage observed by the industry in the same crop year is due to the blending of low-quality maize with higher-quality maize to meet minimum grade standards. The amount of microbial and insect damaged maize increases after the spring thaw and accounts for the lower starch yields and greater processing difficulties. The excessive foaming observed with fresh maize is probably related to natural proteolytic activity, which decreases with time.

Milling Unique Hybrid Maize High Amylose High-amylose maize is a genetic mutant that has higher levels of the linear form of starch than the 27% normally found in


480

Extractable starch, %db

110C 35%

110C 22%

25C 35%

25C 22%

75 70 65 60

the starch. However, starch yields are 5–10% points lower than dent maize. This appears to be an issue with the density of the starch. Even though the starch granules are larger, the absence of amylose in the starch granule apparently does not allow the granule density to be as high. Because waxy starch will gelatinize at a lower temperature than dent maize, it is often recommended that it be steeped 3 C cooler (49 C). In practice, the temperature is not adjusted.

55 50

High Oil

45 1

2

3

4

6 5 Hybrid

7

8

9

Figure 17 The effect of drying temperature and harvest moisture on starch extractability for nine commercial hybrids. ã SR Eckhoff, Savoy, IL. Reproduced with permission from Singh, V., Haken, A.E., Paulsen, M.R., and Eckhoff, S.R., 1998. Starch yield sensitivity of maize hybrids to drying temperature and harvest moisture content. Starke 49 (10), 181–183.

dent maize. Two classes of high amylose are generally grown: Amy 5, which is a group of hybrids containing 50% amylose, and Amy 7, which is a group of hybrids containing 70% amylose. High-amylose starch is produced for a variety of food applications and industrially used in the production of biodegradable packing peanuts. Starch granules of highamylose maize are generally smaller and more irregularly shaped than normal dent maize starch granules. As a result, high-amylose maize is difficult to mill and recover quantitative amounts of starch. When steeping high-amylose maize, care must be taken to account for the high degree of swelling that occurs. Regular dent maize will swell 60–65% by volume, but high-amylose maize will swell 105–128%. In swelling this amount, the maize also absorbs a proportionally larger amount of water. It is usually stated that because amylose has a higher gelatinization temperature, it should be steeped at temperatures 3 C warmer than those for normal dent maize. However, in practice, industry does not adjust the temperature. This may be due to the optimal temperature for lactic acid fermentation being 52 C. High-amylose maize requires a longer steep time, has greater difficulty in achieving starch–protein separation, and yields only 80–90% as much starch as dent maize.

Waxy Waxy maize is a genetic mutant that has 100% amylopectin starch. Amylopectin is the branched form of starch and has a lower pasting temperature than normal dent maize starch. Waxy starch is produced for a variety of food applications. Nearly all the anticipated demand for waxy maize by wet millers is produced under contract. However, the yield drag associated with waxy maize production has disappeared, and now that a lot of speculative waxy is being produced, in a year when the contracted acreage does not yield sufficiently to meet demand, speculative waxy is sought out by the wet millers at a sizable premium. Starch–protein separation is much easier with waxy maize than for dent maize, primarily due to the larger granule size of

High-oil maize contains 7% oil primarily by increasing the size of the germ, although most hybrids have some degree of elevated germ oil concentration as well. Development of highoil maize was primarily for livestock feeding, but considerable interest was generated by wet milling companies because of the high value of oil. Most wet milling companies had trouble adapting high-oil maize into their system because they did not have sufficient germ processing capacity to handle the large influx of germ. High-oil maize hybrids produced by the male sterile pollinator method generally have wet milling characteristics that are comparable to normal dent maize, with the exception that there was considerably more germ. Starch yields vary from 55 to 61%, db. Germs tend to float better primarily because they are larger in size and have higher oil content than normal dent maize. Starch–protein separation does not seem to be affected in the hybrids tested.

Genetically Modified Genetically modified is a large, diverse, and growing group of hybrids. Most of the commercially available genetically modified maize hybrids have been genetically modified for some agronomic characteristic. These hybrids, to date, have improved or have comparable wet milling characteristics to their nongenetically modified counter parts (Table 6). The generally accepted rationale for improvement of the wet milling characteristics is based on the improved agronomic conditions, that is, less insect or disease stress on the plants. Hybrids will eventually become available that have been genetically modified to produce nutraceuticals, pharmaceuticals, specialty chemicals, and hormones or to contain enhanced nutrient or functional characteristics. Even if the wet milling characteristics of these hybrids are not altered, alternative fractionation procedures are needed to be developed to maximize recovery of the high-value product or to retain the enhanced nutrient or functional characteristics through the milling operation.


• • • •

What are the main processing steps in the corn wet milling process? What are the objectives of the steeping process? What are the main coproducts produced by wet milling? What are typical uses of each coproduct? When wet milling high-amylose corn, what are the main difficulties in recovering this type of starch?

BARLEY, RICE AND MAIZE PROCESSING | Maize: Wet Milling Table 6

481

Yield of wet mill fractions for different maize phenotypes and genotypes Dent a

Fraction (% db)

Normal dent

High extract

Bt

Non Bt

Waxy

High amyb

High oil

Hard endoc

White

Industry dent

Starch Germ Fiber Gluten meal Steepwater # of samples

65.5 5.5 14.2 10.0 4.2 110

68.5 5.4 12.7 9.3 3.5 49

64.2 6.3 14.3 10.3 4.3 8

63.7 6.5 13.8 11.1 4.1 8

61.3 5.4 15.4 12.7 4.0 90

40.1 5.5 18.3 32.7 3.5 9

57.4 8.7 14.5 13.9 4.2 5

64.3 5.7 16.0 9.4 3.9 45

63.9 5.7 14.7 10.9 3.8 90

66.8 7.6 11.8 5.9 7.0 4

All data except ‘Industry dent’ are from 100 g Laboratory Milling, ã SR Eckhoff, Savoy, IL. a High extractable maize. b High amylose. c Hard endosperm. US Grains Council, 1996. 1995–1996 Value-Enhanced Grains Quality Report. US Grains Council, Washington DC, USA and Eckhoff, S.R., 2003, Unpublished data. University of Illinois, Urbana, IL.

•

Wet milling of high-oil corn has potential for high oil yields, which has relatively high value. What is one obstacle for wide acceptance of high-oil corn by wet millers?

Exercises for Readers to Explore the Topic Further There are several trends that emerge when examining the maize wet milling industry. They are given as follows:

•

•

• •

Although wet mills recycle large amounts of water prior to discharging the water in its coproducts or as vapor from evaporators, they remain large consumers of water. The industry will continue to adopt technology that reduces its water consumption. Large commodity markets have reached maturity, and there does not seem to be any new large-scale markets in the near future. The result is that many wet milling companies are looking to higher-valued products with smaller markets and to biobased products for industrial markets. The industry seems to be a steadily improving technology to address food safety concerns via coproduct traceability. There is considerable interest in developing new technology for wet milling that reduces the use of sulfur dioxide. ‘Emilling,’ where specifically designed proteases (enzymes) are used to release the starch from the protein matrix in the endosperm, is one example. Because of government regulations on sulfur dioxide emissions, taste and odor problems associated with coproducts exposed to sulfites, and potential for new product development, the industry is more willing than they have been (due to the large capital investment they have in place with current technology) to embrace new fractionation technology.

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Breeding of Grains: Maize: Breeding; Genetics of Grains: Maize: Genetics; Maize: Quality Protein Maize; Non-wheat Foods: Maize: Foods from Maize.

Further Reading Blanchard PH (1992) Technology of Corn Wet Milling. Amsterdam, The Netherlands: Elsevier Science. Douglas JM (1988) Conceptual Design of Chemical Processes. New York: McGraw-Hill. Eckhoff SR, Paulsen MR, and Yang Ping DS (2003) Maize. In: Caballero B, Trugo LC, and Finglas PM (eds.) Encyclopedia of Food Sciences and Nutrition, vol. 4, pp. 3647–3653. London: Elsevier Science. Jackson DS and Shandera Jr. DL Jr. (1995) Corn wet milling: separation chemistry and technology. In: Kinsella JE and Taylor SL (eds.) Advances in Food and Nutrition Research, vol. 38, pp. 271–299. San Diego, CA: Academic Press. Johnson LA (1991) Corn: production, processing and utilization. In: Lorenz KJ and Kulp K (eds.) Handbook of Cereal Science and Technology, pp. 55–132. New York: Marcel Dekker. Radley JA (ed.) (1976) Starch Production Technology. London: Applied Science. Singh V, Eckhoff SR, and Tumbleson ME (eds.) (2001) Proceedings of the Second Annual International Starch Technology Conference, Urbana, IL: University of Illinois. Watson SA and Eckhoff SR (2003) Corn and sorghum starches: Production. In: Whistler RL, BeMiller JN, and Paschall EF (eds.) Starch Chemistry and Technology. Amsterdam, The Netherlands: Elsevier Science. Watson SA and Ramstad PE (eds.) (1987) Corn: Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Whistler RL, Bemiller JN, and Paschall EF (eds.) (1984) Starch: Chemistry and Technology. Orlando, FL: Academic Press.

Relevant Websites http://www.corn.org – Corn Refiners Association. http://www.grains.org – US Grains Council. http://www.ncga.com; http://lepton.marz.com – National Corn Growers Association. http://www.starch.dk – International Starch Institute (Denmark).


Contents Soybean: Soy Concentrates and Isolates Soybean: Processing Canola: Processing

Soybean: Soy Concentrates and Isolates C-Y Ma, The University of Hong Kong, Hong Kong, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • •

Soy concentrates and isolates are by-products of oil processing, in which soybeans are separated into oil and meal. Defatted soybean meal is mainly used as animal feed, but much is processed into soy concentrates and isolates for food use. One protein isolation procedure involves extraction of meal with mild alkali (pH 7–9) at 50–55 C, followed by acid precipitation and some further fractionation. Depending on the procedure used, the protein content (dry basis) of soy-protein concentrates ranges from 66% to 70%. Commercial soy-protein isolates are typically over 90% protein. The amino-acid profile of soy proteins is the best of all vegetable protein sources. Soybeans contain anti-nutritional factors, including protease inhibitors, hemagglutins, phytic acid, and lectins. Heat treatment can lower trypsin inhibitor activity, so that it is not harmful for animals or humans. The functional properties that suit soy proteins for food use include water and fat binding, provision of texture, foam stability, and thickening. Soy-protein concentrates and isolates are thus valuable food ingredients in many foods, including meat analogs, frozen desserts, beverages, coffee whiteners, soups and sauces, pizza toppings, and bakery products.

sources to replace animal proteins. While crops and grains can provide a nutritive source of proteins in the diets of people in many developed and developing countries, the complete or partial replacement of animal protein, particularly in fabricated foods, remains a major challenge. This is due to the fact that the protein ingredient has to provide not only the calorie and nutrients to the products, but also the desirable organoleptic and functional properties required by the consumers. Of all the potential sources of unconventional food proteins, soybeans rank at the top of the list. Soy proteins are found in a large variety of food items, mainly in two categories: traditional soyfoods (e.g., soy milk, tofu, soy sauce), which use whole soybeans as the raw material, and formulated foods in which concentrated forms of soy protein are used as an ingredient. In the second category, a wide range of food items is represented, such as comminuted meat products, meat analogs, whipped toppings, frozen desserts, beverages, coffee whiteners, soups and sauces, pizza toppings and taco fillings, and bakery products. Soy concentrates and soy isolates are concentrated forms of soy proteins extracted from soybeans after the removal of oils and other non-protein components. They are the by-products of oil processing in which soybeans are separated into oils and meals. The defatted meals have been used mainly as animal feed, but a significant portion of the meals is processed into soy concentrates and isolates for use as food.

Learning Objective

Production

•

Soy concentrates and isolates, more commonly known as soyprotein concentrates and soy-protein isolates, are produced from de-hulled and de-fatted soy flakes or flours after the extraction of oils and fats. Figure 1 shows the typical manufacturing procedures for producing soy-protein concentrates. Soy-protein concentrates are produced from the de-fatted flakes by removing most of the water-soluble, low-molecularweight components, mainly sugars. Three processes are used commercially to prepare concentrates. In the first process,

Achieve understanding of the value of soy-protein concentrates and isolates as food additives, due to their many functional properties.

Introduction With the continuous escalation in the cost of farmland and feed, food manufacturers are seeking low-cost, efficient protein

482


http://dx.doi.org/10.1016/B978-0-12-394437-5.00170-4

OILSEED AND LEGUME PROCESSING | Soybean: Soy Concentrates and Isolates nonprotein constituents are extracted with aqueous alcohol. In the second procedure, major proteins are insolubilized by dilute acid at pH 4.5 (the isoelectric point of soy proteins). There is some loss of acid-soluble protein in this process. In the third process, the flakes or flours are heated with moisture

De-fatted soy flakes 1. Aqueous alcohol leach 2. Acid leach (pH 4.5) 3. Moist heat denaturation, water leach Soluble fraction

Insoluble fraction

(Sugars, ash, minor components)

Neutralize dry Soy-protein concentrate

Figure 1 Typical processes for the production of soy-protein concentrates.

De-fatted soy flakes Water or dilute alkaline clarification

to denature and insolubilize the proteins, and the low-molecular-weight components are extracted with water. Soy-protein isolates are produced from de-fatted soybean flakes by removing both the water-soluble sugars and water-insoluble polysaccharides. Figure 2 shows a typical flow diagram for the production of commercial soy-protein isolates. De-fatted flakes are extracted with either water or mild alkali (pH 7–9) at 50–55 C. The protein extract is separated from the insoluble residue (polysaccharides and residual protein) by screening, filtering, or centrifugation. By adjusting the pH to 4.5 with food-grade acid, the major proteins are precipitated. The protein curd can be separated from the solubles (whey) by filtering or centrifugation. Spray-drying of the curd produces the isoelectric soy protein, whereas neutralization followed by drying yields the soy proteinates, which are preferred due to higher water-dispersibility and hence better functionality as a food ingredient. Soy-protein concentrates and isolates can also be prepared by membrane processing using ultrafiltration (UF) and reverse osmosis (RO). In a patented procedure, de-fatted soybean flakes are extracted with water adjusted to pH 8–9 by calcium or sodium hydroxide at 43 C for 40 min. The material is centrifuged to remove the fiber and passed through a 70 kDa molecular-weight cutoff membrane. The retentate protein fraction is concentrated by RO and spray-dried. The permeate, containing soluble sugars, minerals, and small protein molecules, may also be concentrated by RO and spray-dried. The advantages of membrane processing are the ability to recover soy proteins without alkali solubilization – acid precipitation causing protein damage, the opportunity for removing undesirable components such as phytates, the potential to recover small proteins (12–20 kDa molecular weight) by using smaller-pore-size membrane, and the reduction in water consumption and processing discharge.

Extract

Residue

Acid precipitation Protein curd

Whey

Wash Neutralize dry

Dry Isoelectric soy isolate

Soy proteinate

Figure 2 Typical process for the production of soy-protein isolates.

Table 1

483

Chemical Compositions and Nutrient Contents Proximate Compositions Table 1 shows the proximate compositions of de-fatted soy flakes, three types of soy-protein concentrates, and soy-protein isolates. Despite the use of different manufacturing procedures, the overall compositions of the three soy concentrates are similar, with the protein content (on dry basis) ranging from 66% to 70%. The major nonprotein components are polysaccharides, including arabinan, arabinogalactin, cellulose, lignin, and pectin-like polysaccharides. Proteins in the alcohol-leached and moist-heat-treated water-leached concentrates are denatured and insoluble, and the acid-leached proteins are more soluble, making the concentrates more suited in food

Proximate composition of soy-protein products (% dry basis)

Defatted soy flour Soy-protein concentrate Alcohol leach Acid leach Moist heat, water leach Soy-protein isolate

Protein (N 6.25)

Fat (Pet. ether)

Crude fiber

Ash

Carbohydrates (by difference)

54

1.0

3.5

6.0

38

66 67 70 92

0.3 0.3 1.2 0.5

3.5 3.4 4.4 0.3

5.6 4.8 3.7 4.5

24 24 21 2.5

484

OILSEED AND LEGUME PROCESSING | Soybean: Soy Concentrates and Isolates

applications. Protein contents of commercial soy-protein isolates are typically over 90% (dry basis) using a nitrogen-toprotein conversion factor of 6.25 (assuming a nitrogen content of 16%), a commonly used ratio in the food industry. This factor is considered too high since nitrogen contents of purified acidprecipitated soy proteins are higher than 16%.

Mineral Contents Table 2 shows the mineral compositions of various soy-protein products. All soy-protein products contain minerals – such as calcium, iron, copper, phosphorus, and zinc – in nutritionally significant amounts. In whole soybeans, however, much of the mineral content is tied up in the form of phytates by forming complexes with phytic acid and fibers, hence lowering their bioavailability. In human studies, ingestion of soy concentrates did not result in any unfavorable trends in calcium, magnesium, zinc, or iron assimilation. Other studies show that zinc availability in humans is high when isolated soy proteins are present in diets containing adequate zinc contents. The availability of iron from soy isolates added to meat is lower, but can be compensated by increased iron content of the product.

Table 2

Mineral contents of soy-protein products (dry basis)

Element

Defatted soy flour

Soy-protein concentrate

Soy-protein isolates

Calcium Chlorine Chromium Copper Iodine Iron Magnesium Manganese Phosphorus Potassium Sodium Sulfur Zinc

0.22% 0.13% 0.9 ppm 23 ppm 0.01 ppm 110 ppm 0.13% 28 ppm 0.68% 2.37% 254 ppm 0.25% 61 ppm

0.22% 0.11% <1.5 ppm 16 ppm 0.17 ppm 100 ppm 0.25% 30 ppm 0.70% 2.1% 50 ppm 0.42% 46 ppm

0.18% 0.13% <1.0 ppm 12 ppm <10 ppm 160 ppm 380 ppm 17 ppm 0.76% 960 ppm 1.1%

Table 3

40 ppm

Essential Amino-Acid Contents Soybeans and other legumes are considered an excellent source of dietary proteins, and the amino-acid profile of soy proteins is recognized as the most complete of all vegetable protein sources. With the exception of sulfur-containing amino acids (methionine and cystine), the amino acid pattern of soy proteins resembles that of the high-quality animal proteins. Table 3 shows the essential amino-acid compositions of soy-protein concentrates and isolates. When compared with the patterns for amino-acid requirements suggested by the 1980 Food and Nutrition Board (FNB) and the 1985 Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO), the soy-protein products meet or exceed these guidelines. This demonstrates that isolated soy protein is a complete and adequate protein source for humans. Hence, soy concentrates and isolates can be blended or used interchangeably with other high-quality proteins.

Nutritional Quality and Health Benefits of Soy-Protein Products Protein Digestibility Both animal tests and human clinical studies have shown that soy-protein products are comparable in digestibility to other high-quality proteins such as meat, milk, fish, and egg. In animal feeding experiments with rats and young pigs, the digestibility values of soy isolates and casein were similar. Studies with infants and young children demonstrated that the digestibility of different soy isolates were equal to or greater than that of milk proteins. Studies with young adult males showed identical digestibility values for isolated soy and meat proteins. The digestibility values of soy-protein concentrates and isolates range from 91% to 96%, comparable to that of milk.

Protein Efficiency Ratio (PER) Small animal tests, particularly the protein efficiency ratio (PER) assay, have been used extensively to evaluate the nutritional quality of food proteins. The PER values of soy concentrates range from 2.0 to 2.2, and for soy isolates from 1.1 to 1.7, considerably lower than the PER value (2.50) corrected to

Essential amino-acid content of soy-protein products and suggested patterns (FAO/WHO) for amino-acid requirements (mg per g protein) Age

Essential amino acid

2–5

10–12

Adult

FNB pattern

Protein concen-trates

Protein isolates

Histidine Isoleucine Leucine Lysine Methionine þ cysteine Phenylalanine þ tyrosine Threonine Tryptophan Valine

19 28 66 58

19 28 44 44

16 13 19 16

17 42 70 51

25 48 79 64

28 49 82 64

25

22

17

26

28

26

63 34 11 35

22 28 9 25

19 9 5 13

73 35 11 48

89 45 16 50

92 38 14 50

OILSEED AND LEGUME PROCESSING | Soybean: Soy Concentrates and Isolates casein. However, by supplemented soy-protein products with 1.5% methionine, the limiting essential amino acid in soy proteins, the PER values of soy concentrates and isolates can be increased to above 2.5 and 2.0, respectively.

Antinutritional Factors Similar to many plant sources, soybeans contain a number of antinutritional factors that can influence its acceptability for food applications. These include protease inhibitors, hemagglutins, phytic acid, and lectins. Inhibitors of proteolytic enzymes – such as trypsin, chymotrypsin, carboxypeptidase, and elastase – lower the nutritional quality of soy protein. Trypsin inhibitors are the most important inhibitors in soybeans and two of them, the Kunitz and the Bowman–Birk inhibitors have been purified and studied in details. Both inhibitors cause enlargement of the pancreas in rats and chicks. Growth depression and pancreatic hypertrophy have been attributed to endogenous loss of essential amino acids in the enzymes secreted by the hyperactive pancreas in response to the inhibitory effect of the inhibitors. Although the significance of trypsin inhibitors to human health is not yet resolved, they should be eliminated from the diet. Hemagglutinins cause clumping of red blood cells (hemagglutination) in in vitro tests. The major hemagglutin in soybean is a glucoprotein with a molecular weight of 110 kDa, and has been shown to inhibit the growth of rats. Both trypsin inhibitors and hemagglutins can be easily inactivated by heat. Since the production of de-fatted soybean flakes and flours involved heating, soy-protein concentrates and isolates contain only low levels of these inhibitors. Only 3% of original hemagglutinin is retained in unheated isolates, which is eliminated in normal heating steps. Similarly, normal processing conditions lead to 70% reduction in trypsin inhibitor in isolated soy protein. Additional heat treatments result in further lowering in trypsin inhibitor activity to a level that does not cause health problems in both animals and humans.

Health Benefits of Soy Proteins Recent studies have demonstrated the positive influence of soy proteins on human health. These include lowering of blood cholesterol, prevention of cancer, diabetes and obesity, and protection against kidney and bowel diseases. Table 4

485

High level of plasma cholesterol, particularly low-density lipoproteins (LDLs), increases the risk for cardiovascular diseases. Both animal feeding tests and human clinical trials have shown that consumption of diets rich in soy proteins lowers serum cholesterol and the ratio of LDLs to high-density lipoproteins (HDLs), a beneficial form of cholesterol. It has been suggested that the 7S subunit of soy protein can activate LDL receptors in human liver and lower plasma cholesterol by a mechanism different from that proposed for other diets and hypolipolemic drugs. Epidemological studies have suggested that soy protein may be protective for cancer risks. However, the cancer preventive effects may be related to nonprotein components in soyprotein products such as dietary fibers and isoflavones. Many soy-protein products are rich sources of dietary fibers, which are known to decrease incidence of colon cancer. Isoflavones such as genestein are known as phytoestrogens, which can reduce circulating ovarian steroids and adrenal androgens and increase menstrual cycle length. Such effects may account for the decreased risk of breast cancer. Dietary fibers and isoflavones have other health beneficial effects, particularly when combined with soy proteins, e.g., lowering of serum cholesterol and modulation of glucose metabolism. By providing a high-quality protein in concentrated form, soy concentrates and isolates can be used in specially designed low-calorie and high-nutrient-density meals. These can be used for weight reduction in obese subjects. When compared to proteins from other food sources such as milk, seafoods, and nuts, soy proteins rarely incite allergenic responses in humans due to immune reactions. Soy-protein products can, therefore, be used in infant formula as an alternative protein source to replace milk proteins for infants allergic to milk proteins.

Functional Properties and Food Applications of Soy Concentrates and Isolates Functional properties of food proteins are properties that affect their utilization in food systems. Soy proteins possess unique functional properties, which combined with relatively low cost, make them the most widely used protein ingredients by the food industry. Table 4 lists some examples of the food

Functional requirements of soy protein in different food products

Food product

Required qualities

Functional properties

Beverages

Flavor, emulsion stability, heat stability Flavor, aroma, water and fat binding, texture Foam density, foam stability

Solubility, flavor binding, emulsion stability Flavor binding, water holding, fat absorption, emulsification, gelation or texturization Foaming capacity, foam stability, solubility

Flavor, moisture retention, loaf volume, texture Water and fat binding Texture, flavor Thickening

Flavor binding, water holding, film formation, gelation Film formation, cohesion Gelation, bland flavor Viscosity, gelation

Meats, sausages Whipped toppings, chiffon desserts, angel cakes Bakery products Aburages Instant tofu Soups, gravies

486


applications of soy protein products and the functional properties that are critical in these applications.

Solubility Solubility plays an important role in many food applications for proteins, including beverages, food emulsions, and foams. Commercial soy-protein products exhibit a wide range of solubility highly dependent on pH and other components such as salts and sugars. Denatured proteins, found in soy concentrates prepared by alcohol leaching or moist heat treatment, have lower solubility than native proteins.

Water Hydration and Binding Solubility, hydration, and water absorption or binding are different manifestations of protein–water interactions. Hydration or water absorption is a critical initial step in imparting the desired functionality to soy proteins. Water binding is the ability of a protein matrix to expand and absorb water without solubilization. Commercial protein products have a wide range of water-binding capacity. Highly soluble protein powder absorbs little water, whereas insoluble dehydrated protein granules can rehydrate and bind up to 3–4 times their weight of water. Protein granules hydrate slowly and form lumps which need to be broken up by mechanical mixing.

or luncheon meat, fat binding by soy proteins may also involve emulsion formation and stabilization. In bakery foods such as pancakes and doughnuts, addition of soy-protein products can prevent excessive oil absorption during frying. This may be attributed to the denaturation of soy proteins to form a fat-resistant barrier at the product surface.

Gelation and Viscoelastic Properties Soy protein in solution can form a three-dimensional network or gel matrix upon treatments such as heat, alkali, or calcium ion addition. The gelation of soy protein contributes to the structure and texture of some food products, including comminuted meats and bakery products. The gel matrix provides a medium to retain moisture and fats, and binds to flavors and other components. It also contributes to unique mouthfeel such as chewiness to the products. Gelation of soy proteins in formulated foods is influenced by a number of factors including protein concentration, pH, and other components including salts, sugars, and lipids. Soy protein in solution also contributes to viscosity, a measure of resistance to flow. Soy-protein slurries at moderately high concentrations (10–12%) have relatively low apparent viscosity. Treatments that induce the formation of protein aggregates or coagulum can increase viscosity and contribute to the viscoelastic properties (e.g., thickening) of some food products such as soups and sauces.

Emulsification and Foaming

Film Formation

Emulsions and foams are two-phase dispersed systems, with a hydrophobic phase (oil droplets or air bubbles) surrounded by a continuous aqueous phase. By reducing the interfacial tension, soy proteins can act as a surface-active agent and reduce the energy required to create the large interfacial areas characteristic of foams and emulsions. Soy proteins have relatively high emulsification capacity and aid in the formation of oilin-water emulsions. By forming a protective barrier at the oil–water interface, soy proteins can also stabilize the emulsion droplets, preventing their coalescence and breakdown. Soy-protein products are used extensively as emulsifiers in comminuted meats and in baked goods and soups. Foaming properties of soy proteins are important in food systems such as whipped toppings, chiffon desserts, and angle cakes. Soy proteins do not form stable foams due to the presence of foam inhibitors, probably residual lipids, which can be removed by alcohol extraction. Various chemical modifications of such enzyme hydrolysis have been used to improve the foaming properties of soy-protein products.

The film-forming ability of soy protein is desirable in food products such as aburage, frankfurters, and bologna. When a dough of soy flour–water is autoclaved, a film is formed on the surface. This film acts as a barrier to water and solvents and can be broken by grinding or slicing when the dough is washed. When shredded meat is mixed with egg white and soy concentrate or isolate, the protein forms a coat and facilitates drying of the meat fibers. The protein film slows down flavor loss in the dried meat particles, assists dehydration, and provides desirable texture in the rehydrated product.

Fat Binding Soy-protein products are used in foods for two different purposes with regard to fat binding or absorption. In comminuted meat products, soy proteins promote fat binding and hence decrease cook loss and maintain dimensional stability in the cooked products. The mechanism of fat binding has been attributed partly to physical entrapment and is correlated with bulk density and particle size, with bulky samples absorbing more oil. In emulsified meat products such as frankfurters

Texturization Soy-protein products can be texturized to form preset structure with unique textural properties which are not changed upon further processing. The texturized soy proteins are generally insoluble but can be hydrated and swollen. Texturized soy proteins are used as ingredients to make simulated meat products including seafood, poultry, and ground meat products. There are several types of texturized soy-protein products prepared by different processes. Texturized soy concentrates are prepared by thermoplastic extrusion or steam texturization. Soy concentrates are mixed with water, colors, flavors, and other ingredients and fed to a cooker-extruder, heated under pressure, and then extruded. The dried products are in granular form and the composition is similar to the source material. Structured soy concentrates are prepared by passing highconcentration (30–75%) protein slurry with low fat and carbohydrate contents through an extruder into different sizes and shapes. Structured soy concentrates possess a fibrous

OILSEED AND LEGUME PROCESSING | Soybean: Soy Concentrates and Isolates rather than spongy structure, and can be flavored to resemble meat or poultry products. Texturized soy isolates are manufactured by thermal extrusion as described above, or by extruding an alkaline-denatured protein dope slurry through spinnerets into an acid–salt bath that coagulates the protein to form fibers, which are washed and stretched to increase strength. The fibers can be combined with binders to form fiber bundles and fat, flavors, color, stabilizers, and other ingredients can be added. Pressure is then applied to form the simulated meat products. Complete meat analogue products, including ham, turkey, bacon, and sliced beef, have been prepared from texturized soy isolates, and are marketed as vegetarian-type foods.

with many oilseeds in the vegetable oil market, soy protein is facing much less competition from other plant sources including oilseeds and starchy crops, mainly due to its established market and well-developed technology.


• • •

Specialty Soy-Protein Foods and Ingredients Partially hydrolyzed soy-protein products are prepared by either acid/alkaline treatments or by proteolysis with enzymes such as pepsin, trypsin, and papain. The products have reduced molecular weight range of 3–5 kDa. The hydrolyzed soy proteins have functional properties superior to that of the native proteins, particularly improved acid solubility and enhanced foaming and emulsifying properties. They are used as whipping agents in confections, toppings and dessert mixes, and in acidic beverages. Completely hydrolyzed soy proteins prepared by acid or enzyme hydrolysis can be used as flavoring agents. Soy-protein isolates are used in soy-based infant formulas. These are suitable for infants suffering from allergy against milk proteins or intolerance to lactose. Special formulas using soy-protein products are also developed and manufactured for older infants and for geriatric, hospital and postoperative feeding. Soy-protein products have also been used in infant cereals and baby foods to increase the protein content, particularly in rice- and wheat-based products.

• • •

Describe the various uses of the ’meal’ left after the removal of oil from soy beans. How do differences in the processing of soy concentrates and of soy isolates explain the differences in their respective levels of protein? What are the relative advantages of soy isolates versus soy concentrates, with respect to production procedures and functional value? Describe the nutritional advantages and disadvantages of the soy proteins. How can these disadvantages be overcome? List some of the many food uses of soy-protein preparations and match the functional values that are provided to each food product by the soy proteins.


• •

• Future Outlooks Soy-protein concentrates and isolates are valuable food ingredients in many fabricated food systems by providing the functional performance and sensory quality desired by the manufacturers and consumers. They also provide a nutritionally balanced, relatively low cost and high-quality protein, which can be used either alone or in combination with other protein sources. New technologies to remove undesirable soy colors and flavors have been reported, allowing soy-protein-based products with improved organoleptic quality to be developed, even at high levels of usage. Various physical and chemical processes, such as extrusion and partial proteolysis, have modified the functionality of soy proteins and greatly expanded their utilization in new food products. With increasing consumer awareness on the relationship between diet and health, and the nutritional advantages of soy-protein-based products, such as low calorie, high fiber, and low in saturated fats, the demand on soy-protein products will be increasing. However, it should be noted that expanded utilization of soy-protein products and the successful establishment of soy-protein industry would also depend on securing viable markets for other major components, and in the case of soybeans, it is mainly oil. Although soybeans have to compete

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•

What lessons might be learned from the many years of research that have led to the present isolation and uses of soy proteins in food and feed. Investigate and describe the history of chemurgy with respect to the soy bean, including the concept of the ‘Soybean Car.’ Compare concepts of renewable raw materials from agriculture in the early-mid twentieth century with such concepts now. What is a ’fabricated food’? To what extent do soy-protein preparations provide food products that might not be available otherwise? Can you justify the sentence in the Introduction section: ’Of all the potential sources of unconventional food proteins, soybeans rank at the top of the list.’ Investigate the other sources of protein isolates that may serve functions similar to soy isolates as food additives. Consider, as examples, casein from milk, gluten from wheat, and corn protein from maize. Suggest others.

See also: Food Grains and Well-being: Nutrition: Soy-Based Foods; Grain Marketing and Grading: Soybean: Grading and Marketing; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara.

Further Reading Circle SJ and Smith AK (1978) Processing soy flours, protein concentrates, and protein isolates. In: Smith AK (ed.) Soybeans: Chemistry and Technology, vol. 1, pp. 294–338. Westport, CT: AVI Publishing. Friedman M and Brandon DL (2001) Nutritional and health benefits of soy proteins. Journal of Agricultural and Food Chemistry 49: 1069–1086. Fukushima D (2000) Soybean processing. In: Nakai S and Modler HW (eds.) Food Proteins: Processing Applications, pp. 309–342. New York: Wiley-VCH.

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Hettiarachchy N and Kalapathy U (1997) Soybean protein products. In: Liu KS (ed.) Soybeans: Chemistry, Technology, and Utilization, pp. 379–411. New York: Chapman and Hall. Lucas EW and Rhee KC (1995) Soybean protein processing and utilization. In: Erickson DR (ed.) Practical Handbook of Soybean Processing and Utilization, pp. 117–160. Champaign, IL: American Oil Chemists’ Society Press.

Pearson AM (1983) Soy proteins. In: Hudson BJF (ed.) Developments in Food Proteins, vol. 2, pp. 67–108. London: Applied Science Publishers. Soy Protein Council (1987) Soy Protein Products, Characteristics, Nutritional Aspects and Utilization. Washington, DC: Soy Protein Council. Wolf WJ and Cowan JC (1971) Soybeans as a Food Source. Cleveland, OH: CRC Press.

Soybean: Processing T Wang, Iowa State University, Ames, IA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

Soybean is the dominant oilseed produced in the world. The oil mainly contains neutral lipids, free fatty acids, and polar lipids such as phospholipids. Solvent extraction of soy oil with hexane is the standard practice. The major steps are: seed preparation, oil extraction, and desolventizing of the oil and meal. Minor components include phytosterols, tocopherols, and hydrocarbons such as squalene. The refining of crude soy oil involves further procedures, including degumming, neutralization, bleaching, and deodorization. Partial hydrogenation increases oil melting temperature and improves its oxidative stability. Margarine, shortening, and salad/cooking oils are the major food products produced from soybean oil.

Learning Objectives

•

Achieve understanding of the composition of soybean oil, the processes for its extraction and refining, plus the further modifications that improve its suitability for various food products.

Soybean is the dominant oilseed produced in the world due to its favorable agronomic characteristics, its high-quality protein, and its valuable edible oil. It comprises over a half of all oilseeds produced worldwide (Figure 1). The United States ranks number one in soybean production (8.24 million tonne (Mt)), followed by Brazil, Argentina, China, and EU-15 (4.28, 3.28, 3.26, and 2.87 Mt, respectively). The production of soybeans and soybean oil is driven by the needs for soy protein meals that are extensively used in commercial feeds for poultry, swine, and cattle. Soybean oil accounted for 80–90% of total edible oil consumption in the United States in 1998 because of its availability and its many desirable characteristics, including compositional and functional properties. This article describes the composition of soybean seed and oil, extraction, refining, and further processing of the oil, and processing and utilization of by-products from oil refining. Oil oxidation and its measurement are also discussed briefly due to the impact of this chemical degradation on oil quality. This article concludes with a general description of the uses of soybean oil as cooking and salad oil, in margarine, shortening, mayonnaise, and salad dressing.

Composition Seed Composition Mature soybeans are oval shaped and their sizes are variety dependent. The seed consists of three major parts: seedcoat or


hull, cotyledon, and germ or hypocotyls as shown in Figure 2. Soybean oil is contained in the lipid bodies in the cotyledon cells. The composition of these structure components is shown in Table 1.

Oil Composition Oil recovered by solvent extraction or mechanical pressing is termed crude soybean oil and it contains various classes of lipids, including neutral lipids (tri-, di-, and monoacylglycerols), free fatty acids (FFAs), and polar lipids such as phospholipids (PLs). It also contains a minor amount of unsaponifiable matter that includes phytosterols, tocopherols, and hydrocarbons such as squalene. Trace metals are found in soybean oil in ppm concentration. When the oil is refined, concentrations of all minor constituents are reduced. The typical composition of crude and refined soybean oil is shown in Table 2. Sphingolipids is an area of research with increasing activity in recent years. Soybeans are a relatively rich source of sphingolipids, a class of polar lipids which are ubiquitous constituents of the cell membrane and are highly bioactive. The hydrolyzed products of sphingolipids are used by cells to regulate growth, differentiation, and apoptosis. There is evidence that these lipids inhibit colon carcinogenesis in experimental animals at a human diet-equivalent concentration. They may reduce colon cancer risk in humans and inhibit skin cancer development. Little is known about how sphingolipid content varies with soybean variety and processing.

Fatty Acid Composition Typical fatty acid composition of commodity soybean oil, in comparison with the other major vegetable oils, is shown in Table 3. Soybean oil has relatively high content of linoleic and linolenic acids. These are both essential fatty acids for humans and therefore of dietary importance but they are also the reason for the oxidative instability of this oil. Processing techniques such as hydrogenation and lipid composition modification through traditional plant breeding or genetic transformation have been used to modify the fatty acid composition to improve its oxidative or functional properties.

Oil Extraction The two common processes for soybean oil extraction are solvent extraction and mechanical pressing, but in the United States less than 1% of the soybeans is processed by mechanical means. Solvent extraction with hexane is the standard practice in today’s modern processing facilities. There are three major steps in solvent extraction: seed preparation, oil extraction, and desolventizing of the oil and meal. Conventional seed

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OILSEED AND LEGUME PROCESSING | Soybean: Processing Table 1 Composition (wt.%, dry weight basis) of structure components of soybeans

Peanut, 7.3 Sunflower, 7.8

Cottonseed, 10.9

Soybean, 55.4

Rapeseed/ Canola, 12.4

Component

Yield

Protein

Oil

Ash

Carbohydrate

Whole seed Cotyledon Hull Hypocotyl

100.0 90.3 7.3 2.4

40.3 42.8 8.8 40.8

21.0 22.8 1.0 11.4

4.9 5.0 4.3 4.4

33.9 29.4 85.9 43.4

Source: Erickson DR (ed.) (1995) Practical Handbook of Soybean Processing and Utilization. Champaign, IL: AOCS Press.

Table 2 Figure 1 Percentages of five major oilseeds produced in the world during 2000–01.

Hypocotyl

Hilum

Typical composition of crude and refined soybean oil

Component

Crude oil

Refined oil

Triacylglycerols (%) Phospholipids (%) Unsaponifiable matter (%) Phytosterols Tocopherols Hydrocarbons Free fatty acids (%) Trace metals (ppm) Iron Copper

95–97 1.5–2.5 1.6 0.33 0.15–0.21 0.014 0.3–0.7

>99 0.003–0.045 0.3 0.13 0.11–0.18 0.01 <0.05

1–3 0.03–0.05

0.1–0.3 0.02–0.06

Source: Pryde EH (1980) Composition of soybean oil. In: Erickson DR, Pryde EH, Brekke OL, Mounts TL, and Falb RA (eds.) Handbook of Soy Oil Processing and Utilization, pp. 13–31. Champaign, IL: AOCS Press.

Cotyledon Seedcoat

Cuticle Palisade cells Hourglass cells

Seedcoat

Parenchyma Aleurone cells Compressed cells

Endosperm

Cotyledon epidermis

preparation includes drying, cleaning, cracking, optional dehulling or decortication, conditioning, and flaking of the seeds. The option of expanding after flaking is used to improve oil extraction, percolation, and solvent drainage, and is accompanied by a doubling of the throughput. The Alcon process is a flake-heating treatment aimed to improve the degumming efficiency of the crude oil. A very low level of PL in degummed oil can be achieved and therefore the oil can be physically refined. Hexane extraction of soybeans is a diffusion process achieved by immersing solid in solvent or percolating solvent through a bed of solids. Rotary (deep-bed), horizontal belt, and continuous loop extractors are used for soybeans. Solvent, recovered from the miscella (mixture of solvent and extracted oil) by double-effect evaporator and steam stripping and from flake by a desolventizer toaster, is recovered and recycled.

Palisade-like cell

Protein body

Cotyledon

Lipid body

Figure 2 Whole soybean seed and its microscopic structure. (Erickson DR (ed.) (1995) Practical Handbook of Soybean Processing and Utilization. Champaign, IL: AOCS Press.)

Refining of Soybean Oil The minor components of soybean oils include PLs, FFAs, chlorophyll pigment, oxidation products, and other unsaponifiable components (tocopherols, sterols, hydrocarbons, etc.). Some of these minor components negatively affect oil quality while others may play a positive role in nutrition and function. The goal of refining is therefore to remove the undesirable components and, at the same time, to maximize retention of the beneficial ones. An overview flowchart of soybean oil refining is presented in Figure 3.

OILSEED AND LEGUME PROCESSING | Soybean: Processing Table 3

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Average fatty acid composition (wt.%) of oils from soybean and other oilseeds

Fatty acid

Soybean

Lauric Myristic Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Arachidic Gadoleic Eicosadienoic Arachidonic Behenic Lignoceric

12:0 14:0 16:0 16:1 18:0 18:1 18:2 18:3 20:0 20:1 20:2 20:4 22:0 24:0

Canola

0.1 11.0 0.1 4.0 23.4 53.2 7.8 0.3

3.9 0.2 1.9 64.1 18.7 9.2 0.6 1.0

0.1

Cottonseed

Sunflower

0.9 24.7 0.7 2.3 17.6 53.3 0.3 0.1

0.5 0.2 6.8 0.1 4.7 18.6 68.2 0.5 0.4

Peanut 0.1 11.6 0.2 3.1 46.5 31.4 1.5 1.4 0.1

0.2 0.2

3.0 1.0

Water

Crude oil Foots Filtering

Alkali refining

Alkali

Centrifugation

Centrifugation

Gums hydration (

optional)

Soapstock (free fatty acids, phosphatides, color)

Drying

Moisture

Washing

Water

Bleaching earth

Centrifugation

Wash-water (residual soapstock)

Vacuum drying

Moisture

Bleaching Filtering

Lecithin

Deodorizer distillate (flavor, odor, color, free fatty acids)

Spent bleaching earth (color, residual soapstock)

Deodorization

Hydrogenation

Catalyst H2

Polish filtering Filtering

Catalyst Salad and cooking oils

Bleaching earth

Post-bleaching Filtering Deodorization Polish filtering

Spent bleaching earth Deodorizer distillate (flavor color, odor, free fatty acids)

Hydrogenated oil (base stock for margarine) Figure 3 Diagram of soybean oil refining. (Courtesy of Center for Crops Utilization Research, Iowa State University.)

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OILSEED AND LEGUME PROCESSING | Soybean: Processing

‘Degumming’ is a process of removing PLs (gums) from crude soybean oil to improve its physical stability and to facilitate further refining. The water degumming procedure is simple, but its efficacy is influenced by the quality of crude oil. PLs can exist in hydratable form that can be readily removed after hydration, or in nonhydratable form that cannot be removed by this procedure. The nonhydratable phospholipids (NHPs) are probably calcium and magnesium salts of phosphatidic acids resulting from enzymatic hydrolysis of the PLs. This degradation results from seed damage during storage and handling or from improper seed preparation. Normal quality soybean oil from conventional solvent extraction has 90% hydratable PLs and 10% NHPs. Phosphoric acid or citric acid can be used as an aid for more complete removal of NHPs, but their presence in the gum will reduce its quality due to darkening of the gum. Total PLs in crude soybean oils range from 1.1% to 3.2%. Degumming can be achieved in batch or continuous fashion. In batch degumming, soft water at the same percentage as total PLs is added to heated (70 C) oil and mixed thoroughly for 30–60 min, followed by settling or centrifuging. In continuous water degumming, heated oil is mixed with water by an in-line proportioning and mixing system and the mixture is held in a retention vessel for 15–30 min before centrifugation. A well-degummed soybean should contain less than 50 ppm of phosphorus, well below the 200 ppm level specified in the National Oilseed Processors Association trading rules for crude degummed soybean oil. Degumming prior to physical refining of soybean oil requires a more complete removal of the phospholipids to prevent darkening during fatty acid distillation. ‘Neutralization’ is a process of removing FFA, an oil decomposition product, from the oil. The process is also described as de-acidification or caustic refining. It is achieved by treating the soybean oil with aqueous alkaline solution (generally sodium hydroxide) to neutralize the FFA in a batch or continuous system. The soap formed in the reaction also adsorbs natural pigments, the unhydrated gum, and mucilaginous substances contained in the oil. Settling or centrifugation is used to remove the soap. More details on soybean oil neutralization are discussed by Erickson. ‘Bleaching’ is a process designed not only to remove the pigment (chlorophyll) but, more importantly, to break down peroxides (primary oxidation products) into lower-molecularweight carbonyl compounds that can be subsequently removed by deodorization. In soybean oil refining, color reduction occurs at each step of degumming, neutralization, bleaching, hydrogenation, and deodorization. Nevertheless, the most significant reduction of chlorophyll is during bleaching. Acid-activated bleaching clay is most effective in adsorbing chlorophyll and Table 4

Crude Degummed Refined Bleached Deodorized

decomposing peroxides. Low levels of phosphorus (5–10 ppm P) and soap (10–30 ppm) in the neutralized oil are required to maximize the bleaching effect. The desired bleaching endpoint is zero peroxide, so the amount of bleaching earth should be adjusted to the quality of oil to be bleached. Earth dosage ranges from 0.3% to 0.6% for typical soybean oil. Successful bleaching can be achieved by atmospheric batch bleaching, vacuum batch bleaching, or continuous vacuum bleaching at temperatures between 100 C and 120 C for 20–30 min. More details of soybean oil bleaching are described by Erickson. ‘Deodorization’ is usually the last step in oil refining and it is a steam stripping process in which good-quality steam (1–3% of oil), generated from de-aerated and properly treated feed water, is injected into soybean oil under high temperature (252–266 C) and high vacuum (<6 mm Hg). Under these conditions peroxides are decomposed, and the FFA and odorous compounds are vaporized. Heat bleaching is achieved by maintaining the oil for 15–60 min at high temperature to ensure considerable decomposition of carotenoid pigments. During the deodorization process, many desirable reactions take place but some undesirable ones such as lipid hydrolysis, polymerization, and isomerization also occur. Therefore, deodorization temperature must be carefully controlled to achieve optimum quality finished soybean oil. There are three types of deodorization operations. The batch process is the least common, due to its low efficiency and inconsistent product quality. Semi-continuous and continuous deodorizers have improved processing efficiency. There are several configurations of the continuous deodorizer, including single-shell cylindrical vessel type, vertically stacked tray type, and the thin-film packed column type. This last one provides excellent fatty acid stripping with minimum use of steam, but it achieves neither desired heat bleaching nor effective deodorization due to the relatively short retention time. Therefore, a retention vessel has to be used after deodorization by column distillation. Changes in oil quality during refining of soybean oil are shown in Table 4. Comparing oxidative stability of soybean oil at different stages of refining, crude oil is the most stable while highly purified oil is the least stable. Changes in composition of minor components during refining are shown in Table 5.

Hydrogenation The high degree of unsaturation, particularly the significant level of linolenic acid of soybean oil, limits its food application due to its low oxidative stability. Partial hydrogenation is used

Effect of processing steps on quality of soybean oil Phosphorus (ppm)

Iron (ppm)

Chlorophylls (ppm)

Peroxide value (meq/kg)

Tocopherol (ppm)

Free fatty acid (%)

510 120 5 1 1

2.9 0.8 0.6 0.3 0.3

0.30 Not available 0.23 0.08 0.00

2.4 10.5 8.8 16.5 0.0

1670 1579 1546 1467 1138

0.74 0.36 0.02 0.03 0.02

Source: Jung MY, Yoon SH, and Min DB (1989) Effect of processing steps on the contents of minor compounds and oxidation of soybean oil. Journal of American Oil Chemists’ Society 66:118–120.

OILSEED AND LEGUME PROCESSING | Soybean: Processing Table 5 Effect of processing on content of tocopherols, sterols, and squalene in soybean oil Tocopherols

Sterols

Squalene

Processing step

ppm

% Loss

ppm

% Loss

ppm

% Loss

Crude Degummed Neutralized Bleached Deodorized

1132 1116 997 863 726

– 1.4 11.9 23.8 35.9

3870 3730 3010 3050 2620

– 3.6 22.2 21.2 32.3

143 142 140 137 89

– 0.7 2.1 4.2 37.8

Source: Ramamurthi S, McCurdy AR, and Tyler RT (1998) Deodorizer distillate: A valuable byproduct. In: Koseoglu SS, Rhee KC, and Wilson RF (eds.) Proc. World Conf. Oilseed Edible Oils Process, vol. 1, pp. 130–134. Champaign, IL: AOCS Press.

to increase the melting temperature and, at the same time, to improve the oxidative stability of soybean oil. When oil is treated with hydrogen gas in the presence of a catalyst (nickel) under appropriate agitation and temperature conditions, it becomes a semisolid or plastic fat suitable for many food applications. Selectivity is often used to describe the relative reaction rates of the fatty acids from the more unsaturated to the more saturated forms. Generally, selectivity increases with increase in temperature and in catalyst concentration and with decrease in hydrogen pressure and in agita tion rate. During hydrogenation various side reactions occur, and some of which have a strong impact on the physical and nutritional properties of the products. Double bond isomerization or trans fatty acid formation is the most important side reaction. The trans double bond is a thermodynamically more stable configuration than its cis counterpart and it is produced in significant quantity during partial hydrogenation. The trans fatty acids have a much higher melting point than their cis isomers; therefore, fat products with considerable trans fatty acids will have elevated melting points, which is desirable in shortening and margarine applications. However, the recently established link between trans fat consumption and health consequences has prompted research to reduce its use in foods.

Inter-Esterification Inter-esterification is a term used to describe reactions in which fatty acid esters react with FFAs (acidolysis), alcohols (alcoholysis), or with other fatty acid esters (trans-esterification). In food application, inter-esterification often refers to the reaction between different oils or fats with their fatty acyl groups rearranging among the molecules. Inter-esterification is conveniently achieved by an alkali methylate-catalyzed reaction under mild temperature (20–100 C). Microbial lipases are also widely used as biocatalysts in enzymatic inter-esterification. In contrast to the chemical process, the enzymatic process can be more selective if an enzyme with positional specificity is used, and it is usually much slower and more sensitive to the reaction conditions. The new developments in lipase-catalyzed inter-esterification have resulted in industrial applications of this process. Most inter-esterification reactions are still achieved with a chemical catalyst. Randomization is a special form of inter-esterification

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in which acyl groups of a single oil or fat rearrange, resulting ultimately in a change of the natural distribution to a completely random pattern. Recent reports linking consumption of trans fatty acids to the risk of coronary heart disease have generated much interest in producing margarines and shortenings that do not contain trans fatty acids. To achieve this, liquid oil and completely hydrogenated hard stock are inter-esterified to give a product with proper plastic property. These products need to have a proper solid fat content (SFC) or solid fat index (SFI) profile so that they maintain good integrity or firmness at room temperature, resist temperature cycling (i.e., repeated room temperature use and refrigeration storage), and melt completely at body temperature. Various methods of laboratory scale, pilot plant processing, and batch reaction were described by Erickson. List et al. pioneeredthe development of a zero trans margarine by interesterifying 80% RBD (refined, bleached, and deodorized) soybean oil with 20% fully hydrogenated RBD soybean oil. The resulting product has SFI comparable to the conventional products. Soybean oils with elevated levels of saturated fatty acids (by genetic modifications) can be randomized to produce margarines with desirable physical properties. A similar study of zero-trans margarine from soybean oils with modified fatty acid composition was conducted by List and co-workers.

Crystallization and Fractionation Fractionation or winterization is a process in which the more saturated molecular species in the oil are solidified during lowtemperature treatment and subsequently removed; cold storage stability is thereby increased. When partially hydrogenated soybean oil is fractionated, the more saturated molecular species are removed to produce a clear oil that meets the requirements of a salad oil and a high-stability liquid oil.

Processing and Utilization of Co- or By-Products of Oil Refining Soy Lecithin Gum obtained from degumming of crude soybean oil is the predominant source of lecithin for pharmaceutical and food industries because of its availability and outstanding functionality. Crude lecithin contains a large amount of neutral oil and it is usually de-oiled to improve its functionality. This separation is based on the solubility difference of neutral and polar lipids in acetone. PLs are precipitated from acetone solution and separated. The three major classes of PLs in soybeans are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). For certain applications, such as in pharmaceutical, nutritional supplement, and cosmetic industries, lecithin product with very high PC content is desired. Alcohol fractionation of deoiled lecithin provides alcohol-soluble and alcoholinsoluble fractions enriched with PC and PI, respectively. The PC-enriched fraction is an excellent oil-in-water emulsifier. The PI-enriched fraction is a good water-in-oil emulsifier often used in the chocolate industry to increase the viscosity of the

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mass, therefore reducing the need for cocoa butter. The typical composition of these lecithin products is shown in Table 6. Soybean lecithins can also be chemically altered to modify their emulsifying properties and to improve their dispersibility in aqueous systems. PLs may be hydrolyzed by acid, base, or enzyme (phospholipase A) to achieve better hydrophilic and emulsification properties. Hydroxylation of lecithin improves its oil-in-water emulsification property and water dispersibility. Acetylation creates improved emulsification and water dispersion.

table shows tocopherol composition of soybean oils obtained by conventional solvent extraction and mechanical press, in comparison with that of crude wheat germ oil. Phytosterols are used as raw materials for over 75% of the world’s steroid production. The more recent application of phytosterol and phytostanol and their fatty acid esters in margarine and table spreads is related to the cholesterol-lowering effect of these compounds. Hicks and Moreau (2001) have reviewed the recent development of functional foods containing phytosterols.

Soybean Tocopherols and Phytosterols

Soap Stock

Soybean deodorizer distillate (SBDD) is the material collected from the steam distillation of soybean oil. It is a mixture of FFAs (particularly during physical refining), tocopherols, phytosterols and their esters, hydrocarbons, and secondary lipid oxidation products. The quality and composition of SBDD depends on feedstock oil composition and on processing conditions. Tocopherols and sterols are valuable components that can be further separated from the distillate and used in the nutrition-supplement and pharmaceutical industries. Table 7 shows the composition of deodorizer distillates from soybean and other vegetable oils. Soybean tocopherols are the major source of natural fatsoluble antioxidants and vitamin E. There are at least four types of tocopherols in soybean oil. The g-tocopherol is the major tocopherol present in soybean oil with the d-, a-, and bcompounds present in decreasing quantities (Table 8). The

Soap is recovered from alkaline neutralization of the crude or degummed soybean oil. It can be acidulated to produce acid oil, which contains FFAs, neutral oil, PLs, unsaponifiable matter, proteins, and mucilaginous substances. Soap stock is the lowest-priced by-product from oil processing and is generated at a rate of 6% of the volume of crude oil refined amounting to as much as 1.8 billion pounds (0.9 Mt) in the United States annually. Most of the soap stock or the acid oil is used as feed currently. Soybean oil methyl esters can also be produced from soap stock for biodiesel application.

Table 6 products

Typical composition (%) of commercially refined lecithin Lecithin

Phosphatidylcholine Phosphatidylethanolamine Phosphatidylinositol and glycolipid Neutral oil Others Emulsion type favored

Oil-free

Alcoholsoluble

Alcoholinsoluble

29 29 32

60 30 2

4 29 55

3 7 w/o or o/w

4 4 o/w

4 8 w/o

Source: Brekke OL (1980) Oil degumming and soybean lecithin. In: Erickson DR, Pryde EH, Brekke OL, Mounts TL, and Falb RA (eds.) Handbook of Soy Oil Processing and Utilization, pp. 71–88. Champaign, IL: AOCS Press.

Table 7

Composition (wt.%) of deodorizer distillate from various oils

%

Soybean

Sunflower

Cotton

Rapeseed

Unsaponifiable Total tocopherol a-Tocopherol Total sterol Stigmasterol

33.0 11.1 0.9 18.0 4.4

39.0 9.3 5.7 18.0 2.9

42.0 11.4 6.3 20.0 0.3

35.0 8.2 1.4 14.8 1.8

Source: Winters RL (1990) Deodorizer distillate. In: Erickson DR (ed.) Proceedings: World Conference Edible Fats and Oils Processing, Basic Principles and Modern Practices, pp. 402–405. Champaign, IL: AOCS Press.

Oxidative Quality of Soybean Oil Soybean oil is a polyunsaturated or linoleic type of oil that is highly susceptible to lipid oxidation. The mechanism of lipid oxidation and lipid hydroperoxide breakdown has been discussed thoroughly by Frankel. Briefly, lipid auto-oxidation is a free radical chain reaction that involves the initiation, propagation, and termination steps. The primary oxidation product is lipid hydroperoxides. Decomposition of the primary product leads to a range of secondary oxidation products, of which some are off-odor and off-flavor compounds. Oxidative instability limits the use of soybean oil in certain applications, but hydrogenation and other means of composition modification have made soybean oils the most widely used of all vegetable oils. The following analytical methods are frequently used to quantify oxidation of soybean oil. ‘Sensory evaluation’ provides information most closely associated with the quality of food lipids. Flavor or odor defects may be detected by panelists before they are recognized by chemical or instrumental methods. For example, the ‘fishy’ and ‘grassy’ taste produced in linolenic-acid-containing oils such as soybean oil occurs at very low levels of oxidation that are only detected by sensory analyses. The limitations of this method are poor reproducibility and high cost for panelists and the necessary facilities. The recommended approach is to use more reproducible chemical or instrumental methods to complement or support the sensory analyses. ‘Peroxide value (PV)’ is the most commonly used measurement of lipid oxidation. The standard iodometric method requires a relatively large sample size (5 g) when the lipid is only slightly oxidized. The ferric thiocyanate method based, on the oxidation of ferrous to ferric ion, involves colorimetric measurement of ferric thiocyanate. This method is more sensitive than the iodometric method and requires a relatively small sample (0.1 g). The PV is a useful measure for samples with low levels of oxidation and when the hydroperoxides are

OILSEED AND LEGUME PROCESSING | Soybean: Processing Table 8

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Tocopherol content of crude soybean and wheat germ oils

Total tocopherol (ppm) a-Tocopherol (%) b-Tocopherol (%) g-Tocopherol (%) d-Tocopherol (%)

Mechanically pressed soybean oil

Solvent extracted soybean oil

Solvent extracted wheat germ oil

1257 9.3 1.2 62.8 26.7

1370 10.5 1.2 63.5 25.0

2682 67.8 32.2

not decomposed. During prolonged oxidation, a maximum PV is reached and the value then begins to decrease due to peroxide degradation. ‘Carbonyl compounds’ in oxidized lipids are the secondary oxidation products resulting from the decomposition of the hydroperoxides. They can be quantified by the reaction with 2,4-dinitrophenylhydrazine and the resulting colored hydrazones are measured spectrophotometrically at 430–460 nm. The carbonyl value is directly related to sensory evaluation, because many of the carbonyl molecules are those responsible for off-flavor in oxidized oil. The anisidine value is a measure of carbonyl compounds that have medium molecular weight and are less volatile. It can be used to discover any prior oxidation or processing history of an oil. ‘Conjugated diene hydroperoxides’ produced from polyunsaturated lipids can be determined quantitatively by their strong absorption at 234 nm. This is a sensitive method, but it can only apply to the undegraded hydroperoxides. ‘Gas chromatographic (GC)’ methods have been used for determining volatile oxidation products. Static headspace, dynamic headspace, or direct injection methods are the three commonly used approaches. Each method produces significantly different GC profiles. ‘The oxidative stability’ of lipids has been evaluated by a variety of methods under a wide range of conditions. Temperature is the most important factor to consider in oxidative stability determination, because the rate of oxidation is exponentially related to temperature increase. Therefore, the shelf life of a lipid decreases logarithmically with increasing temperature. The mechanisms of oxidation and peroxide decomposition are different at different temperatures. Therefore to realistically predict oxidative stability of food lipids, the test conditions should be as close as possible to those under which the lipid is stored. Storage at ambient conditions or at slightly elevated temperatures and measurement of weight gain, flavor, peroxide value, conjugated diene, or carbonyl compounds are commonly used to study oxidative ability.

and 48% of the soybean oil was used in margarine, shortening, and cooking oil, respectively.

Cooking and Salad Oils Salad oil is a refined or sometimes fractionated liquid vegetable oil remaining liquid at 4.4 C. An important distinction between salad and cooking oils is the difference in their oxidative and thermal stability. Cooking oil is more stable than salad oil at higher temperatures such as deep-fat frying. Fully refined soybean oil can be directly used as salad oil, whereas other oils, such as sunflower and corn, have to be de-waxed before they can meet the criteria of a salad oil. Because soybean oil contains a relatively high amount of the polyunsaturated and unstable linolenic acid, it is usually partially hydrogenated to produce salad or cooking oils. Synthetic antioxidants – such as butylated hydroxyanisole (BHA), butylated hydroxy toluene (BHT), propyl gallate (PG), ascorbyl palmitate, and tertiarybutyl hydroquinone (TBHQ) – have been used in cooking oils. Natural antioxidants derived from sage, rosemary, and green tea are increasingly used to meet consumer’s preference of natural food ingredients. New nutrition-oriented salad and cooking oils are being developed. LoSatSoy is a low-saturated fatty acid oil developed at Iowa State University and commercialized as a salad and cooking oil. It has half of the saturated fatty acid compared with commercial soybean oil; therefore, it is believed to have nutritional benefit. Another newly developed oil is lowlinolenate (1.2%; 18:3) soybean oil, which has improved oxidative stability in salad and cooking oil applications. A unique vegetable oil, diacylglycerol oil, developed and successfully marketed in Japan by Kao Corp, is being produced from soybean and/or canola oil by an Archer Daniels Midland Co. (ADM) – Kao LLC joint venture. This oil is metabolized differently from other oils in that it is not stored as body fat but immediately burned as energy.

Margarine and Shortening

Food Uses of Soybean Oil According to Agricultural Statistics 2000, margarine, shortening, and salad/cooking oils accounted for 12%, 31%, and 41%, respectively, of total domestic consumption of oils and fats in the United States in 1998. Soybean oil was used to produce 95% of the total margarine and 83% of the total shortening. Based on 1998/99 soybean utilization in the United States (Golbitz, 2000), 95% of the total soybean oil produced was used in food applications. Among the food uses, 13%, 38%,

The traditional margarine is in stick form. Other forms, including spreadable, polyunsaturated, and low-fat margarines, have been developed to satisfy the demands of convenience and nutrition. A significant recent trend is away from margarine (80% fat, as defined by the FDA Standard of Identity) to spreads with less fat. The most important functional properties of margarines and spreads are spreadability, oiliness, and melting property. Spreadability can be predicted by SFI and penetration measurement. Oil-off refers to the phenomenon when fine fat crystals no longer form a stable network to trap the liquid oil.

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Melting property depends on fatty acid composition and crystallization form. Shortening contains 100% fat of vegetable or animal source and is used in frying, cooking, baking, and other confectionary items. It can be in plastic and semisolid or pourable fluid form, or in encapsulated powder, pellet, or flake form. It is produced by formulating a blend, solidifying and plasticizing the blend, and packaging and tempering. The b0 form crystals are preferred for both margarine and shortening products. The large number of minute air bubbles incorporated in the shortening improves the leavening of baked foods. A more in-depth discussion of the science and technology of shortening has been presented by Metzroth.

Mayonnaise and Salad Dressing The official definition (FDA Standard of Identity) describes mayonnaise as a semisolid food prepared from vegetable oil (no less than 65%), egg yolk, and vinegar. Most mayonnaise in the United States contains 75–82% oil which is usually soybean oil. The production of mayonnaise is partly an art due to the difficulty of producing the o/w emulsion in which the dispersed phase is much more than the continuous phase. Egg solids and processing conditions play critical roles in mayonnaise quality. Salad dressings were developed as an alternative to mayonnaise. The standard of identity requires that salad dressing contain not less than 30% vegetable oil, vinegar, not less than 4% egg yolk, and is thickened by starch. Pourable salad dressing can be in two different finished forms: one phase or two phases depending upon whether the product is homogenized. The oils used in salad dressing are selected using the same criteria as for mayonnaise. The oil used in these products is predominantly soybean oil in the United States. Canada and Europe may use different oils depending on the availability of vegetable oil in that specific region.


• • • •

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Describe the main procedure for preparation of oil from the soy bean. What is the main anatomical part of the soy bean that provides the oil? How does this aspect of grain morphology relate to the oil extraction process? Explain the process of solvent extraction of soy oil from the beans and list the various products that result from further refining. ’Soybean oil is a polyunsaturated or linoleic type of oil that is highly susceptible to lipid oxidation.’ Describe the problems arising from this statement and the procedures to overcome these problems. Explain the purposes of the following processes used in the refining of crude soy oil: ’degumming,’ ’neutralization,’ ’bleaching,’ and ’deodorization.’


•

’The United States ranks number one in soybean production.’ As a result, soy oil is a major source of oil-based foods

•

•

in the USA, but possibly not in other regions. Choose a few other countries or regions (especially your own) to investigate the source and processing of food oils in those places. Investigate reports and actual evidence that relate the consumption of trans fatty acids to the risk of coronary heart disease. Provide evidence one way or another about whether it is justified to require that margarines and shortenings must be produced free of trans fatty acids. Much of soy production is based on genetically modified (GM) genotypes. Research the extent to which GM soy is grown world-wide and in your region. Also conduct research. ○ About labeling regulations required in your region for GM foods. ○ In some local supermarkets to see if there is appropriate GM labeling of foods (such as margarine, shortening, and salad/cooking oils) that incorporate oil from soy.

See also: Breeding of Grains: Soybean: Germplasm, Breeding, and Genetics; Oilseed and Legume Processing: Canola: Processing; Soybean: Soy Concentrates and Isolates.

Further Reading Brekke OL (1980) Oil degumming and soybean lecithin. In: Erickson DR, Pryde EH, Brekke OL, Mounts TL, and Falb RA (eds.) Handbook of Soy Oil Processing and Utilization, pp. 71–88. Champaign, IL: AOCS Press. Erickson DR (ed.) (1995) Practical Handbook of Soybean Processing and Utilization. Champaign, IL: AOCS Press. Frankel EN and Oxidation Lipid (1998) Dundee, Scotland: The Oily Press Ltd. Golbitz P (2000) Soya and Oilseed Blue Book. Bar Harbor, ME: Soyatech. Hicks KB and Moreau RA (2001) Phytosterols and phytostanols: Functional food cholesterol busters. Food Technology 55: 63–67. Jung MY, Yoon SH, and Min DB (1989) Effect of processing steps on the contents of minor compounds and oxidation of soybean oil. Journal of American Oil Chemists’ Society 66: 118–120. Kok LL, Fehr WR, Hammond EG, and White PJ (1999) Trans-free margarine from highly saturated soybean oil. Journal of American Oil Chemists’ Society 76: 1175–1181. List GR, Emken EA, Kwolek WF, Simpson TD, and Dutton HJ (1977) “Zero trans” margarines: preparation, structure, and properties of interesterified soybean oil-soy trisaturate blends. Journal of American Oil Chemists’ Society 54: 408–413. List GR, Pelloso T, Orthoefer F, Warner K, and Neff WE (2001) Soft margarines from high stearic acid soybean oils. Journal of American Oil Chemists’ Society 78: 103–104. Matsuo N and Tokimitsu I (2001) Metabolic characteristics of diacylglycerol. Inform 12: 1098–1102. Metzroth DJ (1996) Shortening: science and technology. In: Hui YH (ed.) Bailey’s Industrial Oil and Fat Products. Edible Oil and Fat Products: Products and Application Technology, vol 3, pp. 115–160. New York: Wiley. Pryde EH (1980) Composition of soybean oil. In: Erickson DR, Pryde EH, Brekke OL, Mounts TL, and Falb RA (eds.) Handbook of Soy Oil Processing and Utilization, pp. 13–31. Champaign, IL: AOCS Press. Ramamurthi S, McCurdy AR, and Tyler RT (1998) Deodorizer distillate: a valuable byproduct. In: Koseoglu SS, Rhee KC, and Wilson RF (eds.) Proc. World Conf. Oilseed Edible Oils Process, vol. 1, pp. 130–134. Champaign, IL: AOCS Press. Vesper H, Schmelz EM, Nikolova-Karakashian MN, et al. (1999) Sphigolipids in food and the emerging importance of sphingolipids to nutrition. Journal of Nutrition 129: 1239–1250. Winters RL (1990) Deodorizer distillate. In: Erickson DR (ed.) Proceedings: World Conference Edible Fats and Oils Processing, Basic Principles and Modern Practices, pp. 402–405. Champaign, IL: AOCS Press.

Canola: Processing JK Daun{ EH Unger, Eagle Rock Solutions, Inc., Idaho Falls, ID, USA ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by J.K. Daun, volume 1, pp. 161–167, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • • • •

Prepress–solvent extraction techniques. Alternative extraction techniques. Post processing (refining) techniques. What is degumming? What is bleaching? What is hydrogenation? What is winterization? What is deodorization?

Learning Objectives

•

In the following article, the reader will learn about the various steps involved in canola processing to obtain first crude oil and then refined–bleached–deodorized (RBD) oil.

Introduction Canola was developed from rapeseed, and while the plant appearance is still the same, that is where the similarities digress. In the late 1960s through the use of traditional plant breeding, the oil in rapeseed was modified to reduce the undesirable erucic acid content in the oil and substantially reduce the glucosinolate content. Glucosinolates contributed to the palatability and limited the nutritional aspects of rapeseed meal. The ‘canola’ name was given to the modified rapeseed that contained < 2% erucic acid and < 30 mmol of glucosinolates. In parts of the world, the crop is still referred to as rapeseed or oilseed rape. However, in most parts of the world, rapeseed has been modified through plant breeding to provide the oil and meal profile as described in the canola definition. In this document, the oil and meal will be referred to canola, and in some of the supporting reference documents, the term ‘rapeseed’ is used but refers to the crop and products defined by the canola specifications for erucic acid and glucosinolates. Canola has become a very important oilseed representing 14% of world oilseed production, second only to soybeans, with the annual production of canola reaching 68 million tonnes (Mt) during 2013–14. Canola oil was the third highest consumed oil in the world, only outpaced by soybean oil and palm oil and accounting for 25 Mt or 15% of total world oil consumption in 2013–14. Additional transformation of canola through plant breeding has resulted in an additional class of mid-oleic and high-oleic canola oils becoming available. The mid-oleic and high-oleic canola oils are more stable and suited for high{

Deceased.


temperature repeated frying such as restaurant and industrial frying and are used as food ingredient oils where high-stability liquid oil without hydrogenation is desirable or required. It was estimated that by 2013, 18% of all frying oil consumption in the United States was mid- or high-oleic oils, of which midoleic and high-oleic canola oils represent the major portion. While most oilseeds are restricted to a single species, canola and rapeseed may include seeds from the species Brassica napus L., Brassica rapa L., or Brassica juncea L. While B. napus predominates in most of the world, significant amounts of springtype B. rapa are grown in Canada and northern Europe, while in India, rapeseed grown includes B. juncea and a toria type of B. rapa. Recent advances in plant breeding technology have resulted in the introduction of hybrid canola lines. This advancement has considerably improved crop yields and seedling vigor, therefore increasing crop production of the B. napus species further and reducing B. rapa production. The multiplicity of species, each with different seed structures and characteristics, has created some challenges for processing where processing conditions must be adjusted slightly for the differences in seed structure. In addition, when processing canola and rapeseed, processors and equipment manufacturers must be aware of the glucosinolates and their hydrolysis and also, especially in B. napus grown in short season conditions, with significant levels of chlorophyll pigments in the oil. Canola and rapeseed are classified as soft oilseeds. They are small, generally round seeds ( 250–500 seeds per gram). They are dicotyledons and the cotyledons are the major oil storage sites. The seeds possess hulls (testa) that are thin and difficult to remove. Seeds usually contain 35–45% oil and 18–23% crude protein (leaving an oil-free meal with 35–40% crude protein). The principal objective of canola and rapeseed processing is to remove the oil from the seed and to process that oil to a final product for use as salad oil, margarine stock or shortening, or other vegetable oil products. At the same time, the solid portion of the seed is processed to provide an edible meal product used as a high-protein supplement in animal feeds. This article describes the most common practices for canola processing and also indicates current trends towards processing techniques that use alternate technologies that either are friendlier to the environment or produce a higher quality product.

Primary Processing: Prepress–Solvent Extraction and Alternative Techniques The most common extraction processes for oilseeds with high oil content, such as rapeseed and canola, sunflower seed, and flaxseed, involve a combination of mechanical pressing and

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497

498

OILSEED AND LEGUME PROCESSING | Canola: Processing

Seed receiving

Seed cleaning

Seed

Seed flaking

Flake cooking

Pressing

Pressed oil

Settling

Crude oil

Solvent extracted oil

Oil cake

Cake breaking or extrusion

Miscella

Solvent extraction

Desolventizing

White flakes

Degumming

Desolventizing/ toasting

Refining

Canola meal

Figure 1 General flowchart for the canola prepress–solvent extraction technique.

solvent extraction processes to remove the oil from the seed (Figure 1).

Seed Preparation Seed arriving at an crush plant is first cleaned to remove stones and any impurities that will impair the quality of the product or the efficiency of the extraction process. Seed-cleaning equipment usually operates with a combination of the processes of aspiration, sieving, and indent cleaning. With the introduction of herbicide-tolerant genetics, weed control has improved considerably. This is most notable in substantial elimination of any oil-bearing weed seeds and other field residues. This has greatly reduced the need for most seed cleaning other than a basic screening and air aspiration and improved oil quality due to the absence of oil-bearing weed seeds that are similar in size to canola seeds and were difficult to remove from the canola seeds. At present, hull removal is not a common option although it is a feature of some ‘green’ processing plants. In some crush plants, especially in those where seeds have very low initial temperatures and moisture content (e.g., from the Canadian prairies in winter), there may be adjustments in temperature (up to 30–40 C) and moisture content ( 8%) to avoid seed shattering in the flaking process. After cooking, the seed is passed through flaking rolls that flatten it to a thickness of 0.25 mm. This process helps

rupture cells to free the oil and makes it easier for the solvent to percolate through the seed. The flaked seed is usually cooked in order to inactivate enzymes that might cause problems during later processing. In canola and rapeseed, the key enzymes are myrosinase, which catalyzes the hydrolysis of glucosinolates releasing oilsoluble sulfur compounds and lipoxygenase. This in turn catalyzes the formation of hydroperoxides that later break down to form compounds with an undesirable flavor. Canola is often cooked or conditioned in stack cookers or steam-heated conditioner vessels with temperatures reaching as high as 90 C during the process. Achieving a balance of cooking temperature and time is important. If temperatures exceed 110 C, problems may be encountered due to the thermal degradation of glucosinolates.

Oil Removal From the cooker/conditioner, seed flakes are passed through a screw press. This consists of rotating screw shaft in a cylindrical barrel. The barrel ‘staves’ consists of steel bars that have small spaces between them to allow the oil to flow out. Pressure is created in the barrel by an increasing shaft diameter, while the flight pitch of the screw is reduced. This squeezes out 70% of the oil, which is routed to a settling tank and a filter or continuous decanter. Solid material from the settling tank is rerouted through the conditioning stage.

OILSEED AND LEGUME PROCESSING | Canola: Processing The material leaving the press has 16–20% oil remaining. This material may be broken or in some plants extruded to form expanded collets that have improved extraction properties. The cake is sent to the solvent extractor, in which a solvent leaches the oil from the press cake. It is important that the material entering the solvent extractor be cooled below the boiling point of the solvent during its conveyance to the extractor. A variety of extractor designs are used. In most, the process takes place in a succession of stages with the cake first being extracted with a solvent that already contains oil. Fresh solvent is used for extraction at the last stage. The process, known as countercurrent extraction, provides the most efficient means for extraction of the cake. The cake leaving the extractor is known as ‘white flakes’ and has typically < 1% oil remaining. The solvent is separated from the oil and the meal by distillation. It is important to reclaim and recycle as much solvent as possible, for both economic and environmental reasons, in particular to avoid the emission of significant amounts of solvent into the atmosphere. A typical processing plant will use < 0.5 to 1 l of fresh hexane for every tonne of seed processed. While the solvent used in oilseed extraction is referred to as hexane, the solvent used in several commercial extraction operations uses a mixture of 2-methylpentane and 3-methylpentane with the actual n-hexane content < 25% in the solvent. This has resulted in improved extraction efficiency, oil recovery, and improved hexane recovery from the oil and extracted cake products. In addition, modern plants take great care to avoid the introduction of air into the extraction process, along with improved condensing systems, thereby further improving solvent recovery methods. Extracted oil is substantially free of solvent following the hexane recovery process. Since the solvent boiling point is 63–67 C the distillation process utilized in the solvent recovery reduces the solvent content to <100 ppm. Additionally, the oil is heated to 90–110 C under vacuum in the subsequent bleaching process, the solvent in the subsequent bleached oil is below detection limits in modern lab equipment. Finally, the bleached oil is further heated in the deodorizer to 250–265 C under vacuum, thereby ensuring that the resulting oil will be free of solvent.

Use of Enzymes: Alternative Processes

499

are much more pronounced than those of refined oils. The price of cold-pressed canola oil tends to be higher because of the lower recovery of oil. Cold-pressed canola oil is generally sold in bottled form directly to consumers.

Secondary Processing of Oil Once the oil has been extracted from the seed, further processing is usually necessary to remove undesirable components and to make the oil suitable for functional uses. Traditional further processing, often referred to as ‘refining,’ employs the steps detailed in the succeeding text (Figure 2).

Degumming This process removes the phospholipids (lecithin or gums) from the oil. It involves washing the oil with water (which may contain other ingredients such as phosphoric acid and metal-sequestering agents) to cause the phospholipids to precipitate from the oil. The heavier phospholipid/water component is separated from the oil by centrifugation. Traditional water degumming produces oils with phosphorus levels of 200 ppm. Most oils today are degummed by processes that involve the use of acidic solutions and careful temperature and mixing regimens. The process is known as superdegumming or acid degumming and produces oil with < 20 ppm of phosphorus. The superdegummed or acid-degummed oil is suitable for a physical refining process whereby the caustic neutralization step is eliminated. The physical refining process allows for better recovery of coproduct streams such as the free fatty acids in the deodorizer distillate and reduction in the effluent streams requiring effluent treatment and recovery steps.

Degummed oil

Caustic refining

In order to reduce the need for high temperature and pressure and the use of solvents, there has been considerable research into the use of enzymes to break down cell walls allowing the seed to be processed, perhaps even using water to assist in separating the oil and meal. A ‘green’ process plant is under operation in Denmark.

Bleaching

Formulation

Direct Pressing: Cold Pressing Cold pressing is a traditional method in which the seeds are not heated before, during, or after the pressing process. Seeds are selected, cleaned, and flaked as described earlier; they are then mechanically pressed at a slow pace to limit friction and to avoid elevating temperatures above 60 C. Retrieval of oil through this process is usually much lower than through prepress–solvent or solvent extraction processes. Therefore, the residual meal has higher levels of oil. Its color, taste, and odor

Hydrogenation or interesterification

Deodorization

Margarine or shortening stock Figure 2 Secondary processing of canola oil.

Salad oil

500


Gums, especially from soybean, are often treated to recover lecithin that is used as an emulsifier in the food industry. Because soybean-based lecithin is plentiful and relatively low cost, in Canada, gums removed during processing of canola are usually added back to the meal as a source of energy and phosphorus. Canola and rapeseed lecithin tends to have an undesirable color due to the presence of chlorophyll. Commercial rapeseed lecithin is available in Europe where its production has been promoted by the desire to avoid genetically modified soybean products.

ensure that the chlorophyll has been reduced to < 30 ppb and frequently to below detection limits of modern lab instruments and techniques. The high levels of chlorophyll pigments, often found in canola oil produced in areas where the seed does not have time to fully mature, are difficult to remove from the oil. Besides imparting an undesirable color to the oil, these pigments, when present in excessive amounts, have been associated with the development of off-flavors due to oxidation, even though the chlorophyll levels are reduced to below industry specifications during the processing stage.

Refining

Hydrogenation

The refining process is designed primarily to remove the free fatty acids from the oil. Free fatty acids are formed by the hydrolysis of the triglycerides in the oil. The fatty acids are undesirable as they impart an unpleasant metallic taste to oils. Two processes, caustic refining and physical refining, are currently used to remove free fatty acids. In caustic refining, the oils are first treated with 0.05–0.1% of concentrated phosphoric acid to precipitate phosphatides. The oil is mixed with carefully measured amounts of 8–12% aqueous sodium hydroxide (caustic soda), usually 2–3%. The sodium hydroxide reacts with the free fatty acids to form water-soluble soaps. The soaps and phosphatides are removed by centrifugation. Some oils are also refined in the presence of the solvent or miscella. This process involves a combined degumming and refining step and may produce oil with better color. Physical refining cannot be carried out successfully on oils with high levels of phosphorus and acid degumming is a prerequisite. In the physical refining process, the acid-degummed oil is first subjected to a further phosphoric acid pretreatment, followed by a bleaching process with acidactivated clay at 100 C. The fatty acids are removed by distillation under low pressure in the presence of steam. This process is very similar to the deodorizing process described later. While many initial studies of physical refining demonstrated that it was particularly suitable for canola or rapeseed oil, rapeseed oil today is still largely processed by caustic refining. The fatty acids removed by refining are referred to as soap stock. This product may be acidulated and sold for industrial applications. Soap stock, either with or without acidulation, may also be added to the meal.

Liquid vegetable oils, particularly canola, soybean, and sunflower oils, are highly unsaturated making them susceptible to oxidation especially when heated to frying temperature. In addition, the uses of oils in margarines or shortening require that the fat is solid or semisolid to obtain the functionality required. Unsaturated liquid oils can be made more solid using hydrogenation. Hydrogenation involves treatment of the oil with hydrogen in the presence of a catalyst under controlled pressure (100–300 kPa) and temperature (160–200 C). Two processes take place. In the first process, hydrogen is added to the double bonds, increasing the stability of the oil to oxidation during frying and raising the melting point of the oil. In the second process, some of the double bonds are converted from the naturally occurring cis form to the trans form. Trans fats also have higher melting points than cis fats. When treating liquid oils for reduction of the number of double bonds, the hydrogenation process is made selective to ensure that the hydrogen reacts with the highly unsaturated linolenic acid first. Several countries have placed labeling and/or restrictions on the amount of trans fat in the diet. This has greatly reduced the amount of hydrogenated oils used in many food applications since mid-2000. Fortunately for canola oil, this also coincided with the development of mid- and high-oleic canola oils. The mid- and high-oleic canola oils provide stability under repeated high-temperature frying operations similar to previously partially hydrogenated oils. As a result, there has been a significant shift in the use of the high- and mid-oleic canola oils in many food industrial and restaurant applications. In the 10-year period from 2003 to 2013, canola oil consumption in the United States nearly tripled. This is mostly attributed to the increased demand for nonhydrogenated midand high-oleic canola oil. During this same 10-year period, the use of palm oil products in the United States has also increased dramatically. This confirms the food industry practice of using natural semisolid oils such as palm or palm kernel oils in place of hydrogenated oils. Palm oil and palm kernel oil are used as single-source fats/oils or are frequently blended with liquid oils such as canola, corn, and soybean oils to provide a semisolid fat.

Bleaching Color bodies, particular chlorophyll, and some oxidation compounds and iron are removed from the oil by mixing the oil with 1–3% of an absorbing solid, usually diatomaceous earth or acid-activated bleaching clay. The clay oil mixture is mixed and dried under vacuum at 100 C for 5–30 min. Occasionally, small amounts of activated charcoal may be added. The color bodies are adsorbed onto the solid. After filtration, the oil is tested to ensure it meets color standards specified in contracts for each oil type. The color testing equipment is often based on the Lovibond system that measures oil color by comparing it with standard red, yellow, and blue filters. The chlorophyll levels of bleached oil are also closely monitored to

Interesterification In order to prepare a solid fat without resorting to hydrogenation, the liquid canola or rapeseed oil may be interesterified with a harder fat such as palm oil or a fully hydrogenated vegetable oil. Adding a catalyst to the oil results in the fatty

OILSEED AND LEGUME PROCESSING | Canola: Processing acids rearranging themselves on the glycerol backbone, providing new triglycerides with different properties. The process involves the addition of 0.05% of the catalyst sodium methoxide to the heated (150 C) oil as a powder under agitation. After 30 min, the oil is cooled and the base is neutralized with phosphoric acid before washing and bleaching. This process is in use to prepare nonhydrogenated canola margarines. Interesterification is not widely used in North America.

Winterizing or Dewaxing Oils may contain small amounts of waxes and fully saturated triglycerides that may precipitate or haze when the oil is stored at refrigerator temperature. While these compounds have no undesirable health or flavor effects, consumers see the haze as unfavorable. Deodorized oils may be treated to a cooling period, followed by filtration of any precipitate. This process reduces the amount of haze formed during refrigeration. While canola and rapeseed oils were originally perceived to be free of waxes and hence not require winterization, waxy sediments have been found in canola. As a result, oil processing plants now routinely winterize canola oil.

Deodorizing Refined, bleached, and hydrogenated or interesterified oils usually contain small amounts of volatile flavor components and low levels of free fatty acids generated during bleaching. These are removed by a distillation process known as deodorization during which the oil is treated with steam (2–4%) at high temperature (260–265 C) and low pressure (1–3 mmHg). Deodorization also removes some sterols and, more importantly, the antioxidant tocopherols from the oil. Modern deodorizing equipment utilizes packed columns that provide very high efficiency in stripping the free fatty acids and other volatiles from the oil. With the increased stripping efficiency in these deodorizers, the retention time has been reduced at the higher deodorization temperature, thereby allowing more of the tocopherols to remain in the deodorized oil. Tocopherols help prevent oil oxidation so processors will set processing parameters to allow the most economic combination of tocopherol recovery without jeopardizing oil stability. Tocopherols, sterols, and fatty acids are valuable byproducts used in the pharmaceutical and chemical industries.

Refining Loss The aforementioned steps result in a slight loss in the amount of oil originally extracted from the seed. This refining loss is significant and is impacted by the quality of the original seed. Lower quality seeds give oils that are more expensive to refine. They require greater use of chemicals and treatment time and also have a higher refining loss.

Formulation Deodorized oil may be bottled directly or, more often, small amounts of citric acid or antioxidants are added to improve the oil’s shelf life.

501

Standards Standards for crude and RBD canola oil have been published by the Canadian General Standards Board (Tables 1 and 2) and also in trading rules published by the National Institute of Oilseed Processors and national trading organizations such as the Canadian Oilseed Processors Association.

Meal The removal of solvent from the meal is carried out in a desolventizer. This is a vertical vessel equipped with heated trays and agitators. The meal enters the top of the vessel and is treated with reduced pressure and sometimes live steam to evaporate the hexane. During the process, the temperature may reach as high as 110 C, and some glucosinolate breakdown and denaturation of the protein occur. Newer processes have placed a great emphasis on carefully controlling this process in order to avoid excessive denaturation of protein in order to obtain the best quality meal possible. In areas where there is no external market for gums (q.v.), the gums may be added back to the meal at this point providing nutritional benefits as energy and phosphorus in the fed meal. Canola meal Table 1 Canadian General Standards Board requirements for canola oil – crude canola oil Characteristics Free fatty acids (as oleic acid), % by mass, max Moisture and impurities, combined, % by mass, max Phosphorus, ppm, max Chlorophyll, ppm, max Sulfur, ppm, max Erucic acid, % by mass, max

Super degummed

Degummed

Crude

1.0

1.0

1.0

0.3

0.3

0.5

50 30 8 2.0

200 30 10 2.0

30 10 2.0

Source: Canadian General Standards Board CAN/CGSB-32.300-M87.

Table 2 Canadian General Standards Board requirements for canola oil – refined, bleached, and deodorized canola oil Characteristics

Min

Free fatty acids (as oleic acid), % by mass Moisture and impurities, combined, % by mass Lovibond color (133.4 mm cell) Peroxide value, milliequivalents per kg Cold test (h) Smoke point ( C) Unsaponifiable value (g kg1) Saponification value, mg potassium hydroxide per g oil Refractive index (nd 40 C) Iodine values (Wijs) Relative density (20 C/water 20 C) Erucic acid, % by mass

Max 0.05 0.05 1.5 red, 15 yellow 2.0

12 232 182 1465 110 0.914

15 193 1467 126 0.920 2.0

Source: Canadian General Standards Board CAN/CGSB-32.300-M87.

502


typically has more than 36% crude protein and usually 3% neutral lipids. Canola and rapeseed meal are valuable sources for protein supplement in animal feeds, particularly when the deficiencies and strengths of canola meal amino acid composition are combined with other protein sources such as pulses (soybean meal and pea meal). Canola meal is an important feed ingredient and is second only to soybean meal in world protein meal consumption. Oilseed protein, and in particular soybean protein, is finding wide use in food products particularly as a result of the FDA’s allowance of a health claim for soy protein in reducing cholesterol. Oilseed proteins (isolates or concentrates) are extracted from oilseed meals using aqueous solvents. The extracted proteins are precipitated using a number of different reagents and the precipitate is collected by filtration. While most protein isolates from oilseeds have been developed with soybean, there has been recent interest in the use of canola protein isolate with a pilot plant being established for this process.


• • • • • •

What are the main steps of canola processing? What is bleaching and which compounds are removed during this step? Why are oils hydrogenated? What are the gums? At which step are the free fatty acids removed? What is a desolventizer?


• •

What are the advantages of modifying canola oils? What “green” processing is being prototyped using enzymes.

See also: Fats: Healthy Fats and Oils; Grain Harvest, Storage and Transport: Canola: Harvest, Transport, and Storage; Grains Around the World: Grain Production and Consumption: Oilseeds in North America; Oilseed and Legume Processing: Soybean: Processing; The Basics: The Grains that Feed the World; The Oilseeds: Canola: Overview; Linseed: Overview; Oilseeds: Overview; Overview of the Oilseed Safflower (Carthamus tinctorius L.); Soybean: Overview; Wheat Processing: Snack Foods: Processing.

Further Reading Anjou K (1972) Manufacture of rapeseed oil and meal. In: Appelqvist L-A˚ and Ohlson R (eds.) Rapeseed Cultivation, Composition, Processing and Utilization, pp. 198–248. New York: Elsevier. Beach DHC (1983) Rapeseed crushing and extraction. In: Kramer JKG, Sauer FD, and Pigdent WJ (eds.) High and Low Erucic Acid Rapeseed Oils Production, Usage, Chemistry, and Toxicological Evaluation. Toronto, ON: Academic, Press pp. 181–230; 563–570. Daun JK, Buhr N, Mills JT, Diosady LL, and Mag T (1993) Oilseeds – Processing. In: Bass E (ed.) Grains and Oilseeds, Handling, Marketing, Processing, 4th edn., pp. 883–935. Winnipeg, MB: Canadian International Grains Institute.

Daun JK and Bushuk W (1983) Rapeseed. In: Wolff IA (ed.) CRC Handbook of Processing and Utilization in Agriculture, pp. 257–297. Boca Raton, FL: CRC Press. Hui YH (ed.) (1996) Bailey’s Industrial Oil and Fat Products. In: Edible Oil and Fat Products: Processing Technology, vol. 4. New York: Wiley. Mag TK (1995) Food industry requirements for fats and oils: Functional properties. In: Przybylski R and MacDonald BE (eds.) Development and Processing of Vegetable Oils for Human Nutrition, pp. 36–46. Champaign, IL: AOCS Press. Roden AD (1983) Some recent innovations in canola processing technology. In: Kramer JKG, Sauer FD, and Pigdent WJ (eds.) High and Low Erucic Acid Rapeseed Oils Production, Usage, Chemistry, and Toxicological Evaluation, pp. 181–230; 563–570. Toronto, ON: Academic Press. Teasedale BF and Mag TK (1983) The commercial processing of low and high erucic acid rapeseed oils. In: Kramer JKG, Sauer FD, and Pigdent WJ (eds.) High and Low Erucic Acid Rapeseed Oils Production, Usage, Chemistry, and Toxicological Evaluation, pp. 181–230; 563–570. Toronto, ON: Academic, Press. Unger EH (1990a) Commercial processing of canola and rapeseed: Crushing and oil extraction. In: Shahidi F (ed.) Canola and Rapeseed Production, Chemistry, Nutrition, and Processing Technology, pp. 235–249. New York: Van Nostrand Reinhold. Unger EH (1990b) Commercial processing of canola and rapeseed: Crushing and oil extraction. In: Shahidi F (ed.) Canola and Rapeseed: Production, Chemistry, Nutrition, and Processing Technology, pp. 235–249. New York: Van Nostrand Reinhold. Unger EH (2011) Processing. In: Daun JK, Eskin NAM, and Hickling D (eds.) Canola Chemistry, Production, Processing, and Utilization, pp. 163–188. Urbana, IL: AOCS Press. Wan P and Wakelyn PJ (eds.) (1997) Technology and Solvents for Extracting Oilseeds and Nonpetroleum Oils. Champaign, IL: AOCS Press. Wettstro¨m R (1972) Processing of rapeseed oil. In: Appelqvist L-A˚ and Ohlson R (eds.) Rapeseed Cultivation, Composition, Processing and Utilization, pp. 198–248. New York: Elsevier.

Relevant Websites http://www.agr.gc.ca/eng/industry-markets-and-trade/statistics-and-marketinformation/by-product-sector/crops/crops-market-information-canadian-industry/ ?id¼1378737850810 – Agriculture Agri-Food Canada. http://www.alfalaval.com – Alfa Laval Inc. http://www.aomillers.org – International Association of Operative Millers (IAOM). http://www.atma.asn.au – Australian Technical Millers Association (ATMA). http://austinpublishinggroup.com/nutrition-food-sciences/fulltext/ajnfs-v1-id1004. php. http://www.buhlergroup.com – Bu¨hler. http://www.burcon.ca – Burcon. http://www.canolainfo.org and http://www.canola-council.org – Canola Council of Canada. http://www.cdc.gov – Centre for Disease Control and Prevention. http://www.crowniron.com – Crown Iron Works Company. http://www.emcentre.com – emcentre.com. http://www.ers.usda.gov/data-products/oil-crops-yearbook.aspx – Table 46 – World oilseed supply and distribution, 2009/10–2013/14; USDA, Foreign Agricultural Service, Oilseeds: World Markets and Trade. http://www.ers.usda.gov/data-products/oil-crops-yearbook.aspx – Table 47 – World vegetable oils supply and distribution, 2009/10–2013/14; USDA, Foreign Agricultural Service, Oilseeds: World Market and Trade. http://www.foodtech.uni-kiel.de – Christian-Albrechts University of Kiel. http://www.fosfa.org – The Federation of Oils, Seeds and Fats Associations Ltd (FOSFA). http://www.golfettosangati.com – The Golfetto Sangati group. http://www.grainnet.com – Grainnet. http://www.gwmfg.com – Great Western Manufacturing. http://www.kice.com – Kice Industries. http://www.nabim.org.uk – National Association of British and Irish Millers (NABIM). http://www.namamillers.org – North American Millers Association (NAMA). http://www.ocrim.com – Ocrim. http://www.pos.ca – POS Bio-Science. http://www.satake.co.uk – Satake Europe LTD. http://world-grain.com – World-grain.




THE PRODUCTION AND GENETICS OF FOOD GRAINS EDITORS




{

deceased


Academic Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB 225 Wyman Street, Waltham MA 02451 First edition 2004 (as Encyclopedia of Grain Science) Copyright © 2016 Elsevier Ltd. All rights reserved The following articles are US government works in the public domain and are not subject to copyright: Grain Crops, Overview; Maize Overview. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers may always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library SET ISBN 978-0-12-394437-5 VOLUME 1 ISBN 978-0-12-803537-5 VOLUME 2 ISBN 978-0-12-803536-8 VOLUME 3 ISBN 978-0-12-803535-1 VOLUME 4 ISBN 978-0-12-803538-2 For information on all publications visit our website at http://store.elsevier.com Printed and bound in the UK.


CONTENTS Preface

xvii


xix


xxiii xxv xxvii


1

The Basics

1


1



13

H Corke


16

RA Graybosch


22

CW Wrigley


31



41

H Corke


51

J Wyatt

The Cereal Grains

73


73

CW Wrigley


86

LA Morrison

Maize: Overview

99



105

CW Wrigley

v

vi

Contents


117


Rice: Overview

125

BO Juliano


130



140



147



153

A Cruickshank


159


Triticale: Overview

168

BJ Furman

Oats: Overview

173

PK Zwer

Coix: Overview

184



190

JRN Taylor


199


Teff: Overview

209

G Bultosa

The Oilseeds

221

Oilseeds: Overview

221

RJ Mailer

Soybean: Overview

228

K Liu

Canola: Overview

237

VJ Barthet


242

E Hernandez

Sunflower: Overview

247



254

C Hall III

Linseed: Overview

259

S Cloutier


265


265

TE Michaels

Contents


vii

274

RJ Fletcher

Lupin: Overview

280

DS Petterson

Amaranth: Overview

287


Beans: Overview

297

SK Sathe

Buckwheat: Overview

307


Chickpea: Overview

316


Pea: Overview

324


Peanuts: Overview

334


Quinoa: Overview

341



349


349

T Beta and C Isaak


359

JRN Taylor


367



374

H Corke and YZ Cai


383

MG Lindhauer


391

JA Fox and LL Ward


401



409



420



429


429

JH Skerritt


436

JH Skerritt


444

viii

Contents


451

JH Skerritt


457



1


1


1

G Bultosa


11

G Bultosa


17

AM Fehily


23


23



29



35



43

CM Rosell


50



57

JM Jones

Grains and Health

63



72

Cereal Allergens

72

AS Tatham


77

KJ Carpenter

Celiac Disease

83



91


Proteins

98


98



109

Contents


ix

115


Nitrogen Metabolism

123

CA Atkins


129



138



146



154


Carbohydrates

161


161


Starch: Chemistry

174

FL Stoddard

Starch: Synthesis

181



190



198



208

GB Fincher


224

L Ramsden


230

A Evans


236



241

D Dan Ramdath

Fats

248

Lipid Chemistry

248

L Day


257



268


268

HD Sapirstein


277

x

Contents


283


Mycotoxins

290



297


297

CW Wrigley


300



308



1

Wheat-Based Foods

1


1

CF Morris

Breads

8

TR Moore


19

KJ Quail


25

SP Cauvain


30

DE Ortiz


37

SP Cauvain


44



51



59


Noodles: Starch

64



72


Pasta

79

M Sissons

Tortillas

90


Non-wheat Foods

97


97

SO Serna-Saldivar

Contents


xi

110

S Lu


116



124

DK O’Toole


134

DK O’Toole


144


144



154



161



166

JS Bao


176


176

BJB Wood


183

JRN Taylor


193

GH Palmer


206

DK O’Toole


215


215

JL Black

Pet Foods

223

RCE Guy


228

L Munck


235


Biodiesel

245

Y Yan


251


251

CF Morris


257

xii

Contents


262



268

RCE Guy


274

JW Lawton


282

JN BeMiller


287

MS Izydorczyk

Wheat Processing

299


299


Wheat: Dry Milling

307



320


Oven Technologies

325

CE Walker


335



343

B Dobraszczyk

Frozen Dough

354


Refrigerated Dough

359



367

TS Palav


375



384



396

L Day


403



408



414

MN Riaz


423

Barley: Malting

423



434

Contents


xiii

446

L Pallas


453

JS Godber

Maize: Dry Milling

458


Maize: Wet Milling

467



482


482

C-Y Ma

Soybean: Processing

489

T Wang

Canola: Processing

497



1


1


1


Wheat: Marketing

9



16



25



29



42


42



50

RJ Henry


54



62

JJ Mayko


68

SA Barton


74



83

xiv

Contents


99

PC Annis


105



110

PC Annis


117

F Fleurat-Lessard


126

F Fleurat-Lessard


140


140

S Ceccarelli


144

L Munck


154



162

EC Leonard


168

SA Barton

Wheat: Agronomy

176


Barley: Agronomy

186


Maize: Agronomy

194

ED Nafziger


201

WL Rooney

Canola: Agronomy

207


Chickpea: Agronomy

216


Lentil: Agronomy

223


Lupin: Agronomy

231

RJ French

Field Pea: Agronomy

240

RJ French

Soybean: Agronomy

251

ED Nafziger


257



264

Contents


xv

273


Breeding of Grains

279


279



287


Maize: Breeding

296


Rice: Breeding

304



311


Lentil: Breeding

317


Lupin: Breeding

325



333


Genetics of Grains

343


343

L Privalle


350

RD Shillito


360

RJ Henry

Genome Mapping

365


Wheat Genetics

376

RA McIntosh


382

E Akhunov


388



393


Rice: Genetics

398

JS Bao and H Corke

Maize: Genetics

407

EA Lee


420

JS Li and SK Vasal


425

xvi

Contents


433



450



460


Glossary

467

Index

491




xvii

xviii

Preface


• Members of the Editorial Advisory Board; • Authors who have shared their special knowledge and experience; • Elsevier staff who have provided extensive advice and administrative services, especially Donna de Weerd-Wilson, Simon Holt and Rachel Gerlis (successive Supervisory Staff) and Gemma Tomalin, Gemma Taft, Joanne Williams and Mark Harper (successive Content Project Managers).

The Editors Harold Corke, Jon Faubion, Koushik Seetharaman, and Colin Wrigley




xix

xx






xxi





xxiii










xxv




















xxvii

xxviii

Contributors















Contributors






xxix


xxx

Contributors















Contributors


xxxi








CK Madsen Aarhus University, Slagelse, Denmark RJ Mailer Australian Oils Research, Lambton, NSW, Australia JT Manful Africa Rice Center, Cotonou, Republic of Benin AG Marangoni University of Guelph, Guelph, ON, Canada DJ Mares University of Adelaide, Glen Osmond, SA, Australia L Marquart University of Minnesota, St. Paul, MN, USA; Grains for Health Foundation, St. Louis Park, MN, USA A Marti Universita` degli Studi di Milano, Milan, Italy B Maschoff Grains for Health Foundation, St. Louis Park, MN, USA A Mathiowetz University of Minnesota, St. Paul, MN, USA; Rochester, MN, USA

CS Moffat Curtin University, Bentley, WA, Australia ES Monyo ICRISAT, Nairobi, Kenya TR Moore AIB International, Manhattan, KS, USA MK Morell International Rice Research Institute, Los Banõs, Philippines CF Morris USDA-ARS Western Wheat Quality Laboratory, Pullman, WA, USA LA Morrison Oregon State University, Corvallis, OR, USA WK Mousa University of Guelph, Guelph, ON, Canada; Mansoura University, Mansoura, Egypt K Mrva University of Adelaide, Glen Osmond, SA, Australia







xxxii

Contributors















Contributors


xxxiii










xxxiv

Contributors

















THE PRODUCTION AND GENETICS OF FOOD GRAINS Grain Marketing and Grading

Contents Wheat: Grading and Segregation Wheat: Marketing Barley: Grading and Marketing Soybean: Grading and Marketing Identification of Varieties of Food Grains

Wheat: Grading and Segregation RL Cracknell, Crackers Consulting, Mount Eliza, VIC, Australia RM Williams, CBH Group, West Perth, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

Wheat quality means different things to different people along the supply chain. When managed together, genotype and environment wheat traits combine to produce recognizable and consistently performing products sold and purchased globally. Major wheat-exporting countries have varying approaches to provide reliable products to the marketplace.

Learning Objectives

• •

To understand the difference between genotype and environment quality traits and how they might be controlled through the supply chain. To appreciate that different countries all have different grades, classes, segregations, or naming conventions but the principles applied are all similar.

produced in Western Australia is yet unrivaled in the production of Asian white salted noodles.

The Quality Feedback Chain Before tackling what approaches can be used to ensure that customer quality requirements are met, it is important to first understand what we will call the quality feedback chain (Figure 1). Starting with the development process of a new wheat variety, it is assumed this will take somewhere between 8 and 15 years. New technologies now mean that the breeding component of variety development has been reduced, but there is still the need to bulk up seed crops and for additional time as farmers adopt the new variety. It can take at least 2 years before significant tonnage of a new variety is available for customers to buy as a bulk product. Successful breeders have Breeding

Introduction

End products

The terms grading, classification, and segregation can take on different meanings around the world, but in essence, they all describe processes that are designed to ensure that the parcel of wheat that is delivered meets the buyers’ requirements. Buyers want the wheat to perform in a predictable and consistent way and, in more sophisticated markets, exhibit quality attributes linked to specific wheat-based foods. Examples are the hard red spring wheats produced in Canada and the United States that are preferred in some markets where the sponge-and-dough baking process is commonly used, whereas noodle wheat Encyclopedia of Food Grains, Second Edition

New varieties Delivery Production Harvest quality Figure 1 Wheat quality feedback chain (from first edition).

http://dx.doi.org/10.1016/B978-0-12-394437-5.00176-5

1

GRAIN MARKETING AND GRADING | Wheat: Grading and Segregation

2

to anticipate the future quality requirements of customers but in that 8–15-year period into the future before their new variety is available for harvest and utilization. Therefore, an important component of delivering a consistent product to customers is not only managing the year-toyear quality variation as a result of factors such as drought, harvest, rainfall, and frost but also growing a product that meets processing needs for products such a bread or noodles. This requires an extensive working knowledge of customers’ processing needs and working with them to enhance the product being delivered. An added complication in the international trade of wheat is that other suppliers are competing for a share of that customer’s business. Therefore, suppliers not only need to have ongoing quality improvement but also must continually monitor the competitiveness of their products relative to other suppliers. When the first edition was published, five countries or regions dominated wheat exports – the United States, European Union (EU), Canada, Australia, and Argentina (Figure 2(a)). More recently, three further sources of wheat have begun to make a mark on world wheat exports – Russia, Ukraine, and Kazakhstan – listed as Black Sea exports (Figure 2(b)). These exporting countries will be discussed as to how they strive to meet the quality expectations of those buying their wheat.

Managing Quality: Genotype and Environment Wheat quality means different things to different people. For example, what is important to a farmer can be different to what a trader needs, and in turn, the demands of a flour miller and baker are different again. Common to all is a requirement for consistency. Being able to deliver a consistent product is valued by the market and can improve the price paid for wheat over and above basic trading or contract specifications. Management of quality can be broadly divided into two separate but linked processes. The first is the categorization of individual varieties into classes or groupings with similar processing attributes. That might be color, hardness, milling performance, and/or dough quality. A key feature is that these are often difficult to measure quickly in the field and also generally more genotype-controlled rather than environment-

controlled. This leads to the second categorization, and these are the measurements of physical attributes that reflect prevailing seasonal conditions. Common tests used to monitor environmental effects include test weight, protein level, moisture, and soundness. Together, genotype and environment wheat traits combine to produce recognizable and consistently performing products that are sold and purchased globally.

Genotype Classification Argentina Since 1998, hard bread wheat varieties in Argentina have been classified into three groups based on their quality performance. Quality test results are weighted to produce what is known as a quality index. The tests conducted are test weight, protein and gluten content, flour yield/ash content ratio, alveograph strength (W), farinograph dough stability, and loaf volume. The groups are listed later with their proportion of production. A small proportion of specialty wheats are produced being used for regional exports (Table 1). All new varieties are required to pass through a coordinated trial program to enable them to be classified. They must be registered with the National Registry of Varieties, and the commercialization of new and certified seed must be authorized by Argentina’s Secretariat of Agriculture, Livestock, Fishing and Food. Table 1

Description

1

Extrastrong cultivars suitable for blending and industrial baking Varieties adapted to traditional methods of baking (artisan breads of more than 8 h of fermentation time) Cultivars suitable for direct methods of baking (artisan breads of less than 8 h of fermentation time) Specialty wheat types with majority exported to Brazil and Peru

2

3

Other

2nd edition 5 year average export tonnage (2009/10 to 2013/14)

Argentina 9930 Australia 14,860

26,735

14,830

30 45

15

5–10

Argentina

7180 29,448

19,104

Australia

Canada

Canada

EU

EU

United States 15,296

(a)

Estimated production (%)

Grouping

1st edition 5 year average export tonnage (1999/00 to 2003/04) 12,012

Description of Argentine wheat classes

Black Sea∗

18,889

Black Sea∗

29,205 (b)

United States

21,935

Figure 2 (a) Yearly average exports 1999/2000 to 2003/2004. (b) Yearly average exports 2009/2010 to 2013/2014. Notes: Black Sea* ¼ combined Russia, Ukraine, and Kazakhstan exports. Data for figures adapted from Foreign Agricultural Service (2014) Grain: World Markets and Trade. Circular Series. FG 1–14. January 2014. United States Department of Agriculture and 1st Edition of Encyclopedia of Grain.

GRAIN MARKETING AND GRADING | Wheat: Grading and Segregation Australia Wheat variety classification has long been a key contributor to Australia’s international reputation as a consistent supplier of quality wheat. This focus has continued following deregulation of the export wheat market in 2008 and is now managed by Wheat Quality Australia (WQA), a not-for-profit company established in 2011 responsible for the nation’s wheat variety classification and related activities. WQA has a two-tiered structure comprising strategy/management and operation. A committee made up of skilled industry representatives is responsible for determining the strategic direction of the major Australian wheat classes. The operational process of analyzing quality data to determine which class a new variety will be classified is made by a small panel of technical experts. The panel assessment focuses on the analysis of multiple years of quality data for an extensive set of tests compared with ‘control’ varieties that have accepted quality profiles. Use of control varieties provides flexibility in reaching a final classification decision even in the event that quality varies from year to year due to seasonal conditions. WQA also acknowledges that some parameters are essential and cannot be compromised, while less important attributes failing to reach the necessary levels can be counterbalanced by exemplary performance for other, more important quality attributes. This means that minor deficiencies do not necessarily have a negative influence on the final classification decision, provided they are compensated by other attributes. The class into which a variety is classified is a critical decision for two reasons. Firstly, it establishes potential value at harvest. Secondly, variety classification serves as a surrogate for a host of genetically determined quality traits like milling performance, flour and dough properties, and end product suitability that cannot be easily tested for when wheat is graded during harvest. Instead, farmers make a statutory declaration of the variety being delivered. Consequently, the classification process is extremely important in ensuring that the right quality is ultimately delivered to end users. A variety’s classification status for each of the classification zones is included as a component (referred to as the master list) of the annually released wheat trading standards by Grain Trade Australia.

Black Sea: Russia, Ukraine, and Kazakhstan These three wheat-producing countries have faced considerable challenges as they have gained increasing prominence on the world wheat export stage. Foremost have been logistical constraints and access to agricultural inputs. These limitations are gradually being brought under control and coupled with better farm management are leading to better yields and more wheat becoming available for export. However, quantity currently outstrips quality, with the majority of wheat planted being winter wheat that is considered to be of inferior quality to higher-protein spring wheat. To date, establishing processes to manage genotype quality has not been at the forefront of development, but the increasing volume of exports means there is a recognition that quality management also needs to advance along with quantity.

3

Broadly speaking, the wheat from this region is considered either soft or common and/or hard or durum. For example, in Russia, there are now distinct market classes. These include I, soft red spring; II, hard spring (or durum); III, soft white spring; IV, soft red winter; V, soft white winter; and VI, hard winter (or durum). In Ukraine, programs are being established to expand the classes from common and durum to consider varieties covering a range of qualities from extrastrong bread wheats to biscuits, waxy wheats, and those suitable for forage and bioenergy use. Kazakhstan is also exploring ways to improve the quality of its winter and spring wheat crops with strong demand internally and in neighboring countries for good bread-making quality flour. Collectively, wheat consumed locally or exported to the world from the Black Sea will only benefit from the developments starting to occur.

Canada Canada, like Australia, has a long tradition as a supplier of quality wheat. In addition, it has also undergone recent market change. In 2012, the Marketing Freedom for Grain Farmers Act came into force. This allows western Canadian farmers the freedom to sell their wheat and barley to any buyer they wish, a facility that was once the preserve of the Canadian Wheat Board. However, the Canada Grain Act still gives authority to the Canadian Grain Commission (CGC). A federal government agency, CGC, officially certifies the quality, safety, and weight of Canadian wheat and is also Canada’s scientific research organization on grain quality. The major production regions for exported Canadian wheat are its western provinces. For a variety to be successfully released, they must process through a strict merit system and the Prairie Grain Development Committee currently has oversight of this. The PGDC has various subcommittees for each grain type that evaluate new varieties and, upon the request of the owner or designate, make recommendations to the Variety Registration Office of the Canadian Food Inspection Agency regarding the suitability of the variety’s registration. Only registered varieties are accepted into western Canadian wheat milling classes; otherwise, the delivery is only eligible for feed. Eligible varieties are listed on the CGC website. Each year, old varieties are removed because they are no longer available as registered seed or occasionally because a quality defect is identified after release. The process of evaluation involves candidate lines being grown together with contemporary registered varieties and judged against them. For wheat, there are three subcommittees that assess data across agronomy, disease, and quality. Each committee comprising a mixture of academic, government, and industry experts considers each line in turn and votes on its acceptance. A simple majority is required to accept or reject a line with all three committees needing to approve a variety for it to be progressed. For the quality committee, the number and years of results depend on the importance of the class. Three-year results are needed for the major Canadian western red spring class with less for smaller classes and nonmilling animal feed or bioenergy wheat. All quality testing is performed by the CGC in its custodian role for wheat quality. There is provision for private breeding trials to be used, but these must be approved by the PGDC and all quality analyses must follow those used by CGC.

4


Composite samples are prepared for quality testing for everything from test weight, protein level, and falling number to milling evaluation and rheology of bread, pasta, or cookies. The new variety is evaluated for each quality trait against the means of ‘check’ varieties. There is an established level of uncertainty for each test result. If lines are deficient, they may be designated as a major fault or a minor fault depending on how important the trait is and how much they deviate from the mean of the checks. To highlight the rigidity of the Canadian system, a 0.5% protein difference would be a major fault and that line would be dropped regardless of everything else. While new variety evaluation remains quite rigid in format, a major liberalization has occurred in Canada with the removal of the Kernel Visual Distinguishability or KVD requirement. Farmers now declare that they are delivering a registered variety for a specific wheat class, an approach similar to what is used in Australia. This replaces the previous KVD system that required the different classes of Canadian wheat to be visually distinguishable. The Canadian classification system is recognized as being expensive, and breeders have argued that it limits yield improvement, but there is no doubt that the process guarantees the world-renowned consistency and quality of western Canadian wheat.

Europe: France, Germany, and United Kingdom Unlike other exporters that differentiate between hard- and soft-grained wheats using grades or classes, the wheat classification systems in Europe have traditionally taken greater effort to differentiate between common wheat (potentially a mixture of hard- and soft-grain wheat) and durum wheat. The basis for differentiating wheat in Europe is strongly influenced by each country’s baking methods. France and Germany have four classes; the regional preferences become evident with respect to baked products (e.g., the French baguette) and testing equipment. With almost half of French production now destined for export, it is important for France to have a variety regulation system. The system differentiates varieties into four end product classes. These are high-grade bread making, regular bread making, biscuit wheat, and wheat for other purposes (essentially for stock feed or industrial uses) than bread making or biscuit making. In addition, durum is also produced with around a quarter consumed domestically with other threequarters exported to destinations like Italy and North Africa, particularly Algeria (Table 2). Germany has a well-recognized class system for its winter wheats. It reflects a combination of inherent characteristics such as bread volume, dough elasticity, protein quality Table 2

Major French wheat classes

Classes

Protein (%)

E 1 2

12 11.0–12.5 10.5–11.5

3

<10.5

Baking strength (W) 250 160–250 According to contract specifications Not specified

Falling number (s) 220 220 180 Not specified

measured by Zeleny sedimentation, and some environmental influenced traits like falling number and grain protein. The classes are elite (E), quality (A), bread (B), and other (C). In the United Kingdom, the Home-Grown Cereals Authority (HGCA) provides recommendations to farmers to aid in their choice of variety and is funded by a statutory levy. While not regulated, seed sales to farmers are dependent on a wheat variety being included on the national list published by the HGCA. For a variety to be listed, quality testing is performed that includes end uses such as distilling, bread and biscuit processing, and suitability for animal feed. Varieties are first tested by the British Society of Plant Breeders in a 2-year program and by the HGCA for 3 years in the recommended list trials. At the same time, the National Association of British and Irish Millers assesses processing quality into defined classes. There are four groupings: premium milling and baking, acceptable baking and specialty, soft milling for biscuits and cakes, and feed.

The United States The US process for the release of new wheat varieties is much less regulated than those employed by Australia or Canada though each US wheat class has its own unique aspects. Public and/or private breeders produce new varieties within their own self-directed and self-regulated breeding programs. For the public breeder, their breeding goals are based primarily upon the needs of their immediate state or local constituents (be that farmers, producers, millers, and/or bakers) and the industry at large. University agronomy departments, state wheat commissions, and state grower groups all have input into the breeding program in the form of direct funding and/or advisory boards. The private breeder goes through a similar process, but there is much information within the private sector that is proprietary. As potential new varieties move into the latter stages of development, they are typically entered into public nurseries where they can be grown and evaluated over greater geographic and environmental settings. They will typically remain in such nurseries no more than 2–3 seasons. The public nurseries are managed by the US Department of Agriculture (USDA), and the experimental lines are evaluated for end-use quality by one of the four USDA wheat quality laboratories linked to specific US wheat classes. The four laboratories are listed in the succeeding text (Table 3). Table 3 testing

Principal US wheat quality laboratories and class of focus of

Laboratory

Location

Focus of testing

Western Wheat Quality Laboratory

Pullman, Washington

Hard Red Spring and Durum Wheat Quality Laboratory Soft Winter Wheat Quality Laboratory Hard Winter Wheat Quality Laboratory

Fargo, North Dakota

Assesses multiple classes going to Asian markets Hard red spring and durum classes

Wooster, Ohio

Soft winter wheat

Manhattan, Kansas

Hard winter wheat

GRAIN MARKETING AND GRADING | Wheat: Grading and Segregation These USDA wheat quality laboratories serve as an unbiased source of end-use quality data to the breeder and the US wheat industry. The breeder and their associated advisory committee use this information, in combination with multiple years’ worth of agronomic data to make release decisions. The final step in the process is to enter the soonto-be-released variety into the Wheat Quality Council (WQC) evaluation program. The WQC is a nonprofit, industry-based/industry-driven organization whose mission is to advocate the development of new wheat varieties that improve the value of wheat to all parties in the US supply chain with an end product baking focus. The evaluation program consists of small-scale grow-outs in which the new varieties are grown, harvested, and milled. The subsequent flour is distributed to numerous and various baking collaborators within the wheat industry (both public and private) for enduse quality evaluation based upon their unique process and product. The data are combined into a final report and distributed at an annual meeting where the results are viewed and discussed by the entire membership. Breeder–industry interaction is the key to the success of this meeting. The WQC is a voluntary program. A breeder, whether public or private, can legally release a new wheat variety without constraint. However, the Wheat Breeder’s Code of Ethics attempts to bind the breeder to a higher calling. The desire is to exceed the quality of wheat currently in commercial production. This voluntary or honor system approach has been the fundamental backbone for successful wheat breeding in the United States and continues as such.

mechanisms in place to ensure the consistency of inherent quality characteristics. The systems used are different, although all have a common fundamental philosophy. All aim to classify or group varieties into a commercial type or style that is recognizable for its inherent processing features. The aim of grouping wheat varieties is to produce parcels of wheat that deliver a consistent product and hence meet customer expectations. Unfortunately, classification of varieties on inherent characteristics is only half the equation, as the growing environment has a significant influence on quality (Figure 3).

Environmental Classification Testing Physical Quality The other half of quality management is testing of physical and/or seasonal quality. There has been considerable development in the capacity to rapidly and accurately test such attributes whether that be at harvest or prior to export. It was only 40 years ago that, in Australia, wheat was classified into the broad category of fair average quality with limited traits measured. This was around the same time that the Canadians introduced protein measurements to assist with the marketing of hard red wheat. Without accurate and quick methods for protein and moisture determination, wheat was segregated on the basis of cleanliness and visual soundness. Today, near-infrared (NIR) technology, along with a host of new technologies like single-kernel characterization and image analysis, allows the assessment of a large number of physical attributes upon which wheat can be stored together to ensure a consistent product. Importantly, these tests also serve to separate wheat into grades with identifiable pricing differences that determine how much farmers ultimately receive for their crop.

General Philosophy All this attention to the quality of the wheat shows that successful suppliers of wheat in the international market have

Argentina Australia Canada France Germany Russia Ukraine

UK

US

Mainstream flagship 1

APH

CWRS

E

E

AH

I

Common Class 1

HRS

III

2

HRW

1 APW

A

IV

B

V

CWRW Quality spectrum

3

ASW

2

Class 2 SRW

CWES CPSR CPSW

Specialty

ANW

CWHWS

AS

CWSWS

AD

CWAD

HW 3

Class 3

C

Durum

II VI

Note: Classes from different countries are not aligned horizontally

Figure 3 Classes of wheat employed by some major wheat producers.

5

SW Durum

Durum Class 4

6


All the major wheat-exporting countries have a range of grades to reflect good and bad quality. These not only separate the clean from the dirty but also when overlaid by the genotypic classes are easily recognized by buyers with respect to possible end uses. Therefore, the systems used have the dual effect of differentiating on the basis of physical traits, such as test weight and cleanliness, while also being readily identified by customers for certain attributes over and above the physical quality. In Australia, for example, the majority of wheat is harvested and then moved to storage off-farm. Following industry consolidation, a few companies now manage large and integrated silo networks linked to export port terminals, with many smaller operators either providing a supplement service to the export task or targeting domestic and container packing business. The large bulk storage networks test every individual truckload for test weight, protein, cleanliness, or screenings as it is referred to in Australia. The screening level is assessed using a specifically designed automatic shaker called an ‘agitator.’ Moisture and falling number are all measured objectively using standard equipment. Repeatable measurements are important as they determine how the wheat is graded and stored, which in turn determines the price farmers get paid for their grain. Equally important, but only visually assessed, are defects such as frost damage, stained grains, and vitreousness. The trading standards for the various grades used by the storage and handling operators are published annually by Grain Trade Australia. Country elevators also play a key role in the movement of wheat in the United States, where there are some 10 000 elevators throughout the wheat-growing areas. Either large grainexporting companies, farmer cooperatives, flour milling companies, or other business enterprises own the country elevators. During harvest, a sample is taken of the delivery to determine its grade, moisture, and dockage. The grade is determined on the basis of appearance, moisture level, and cleanliness as outlined in the USDA Grain Quality Standards. At the opposite end of the physical quality testing regime is the system used in Canada. Owing to the fact that the majority of storage is on-farm and to ensure that export wheat meets customer requirements, the Canadian system has a strong focus on measuring the wheat as it moves into an export position. The commercial companies that assemble a wheat cargo from farmers or intermediaries are still obliged to have the CGC or licensed operators test the wheat to ensure required levels are achieved. In fact, many of the other major exporters follow a similar approach to that of the Canadian system where relative testing emphasis is at the point of accumulation for outturn, rather than at the first point of receival as in Australia. A common logistical challenge is that production of wheat is often a considerable distance from the export terminal. For example, in Canada, it is about 1500 km from the middle of the production area of western Canada to the Port of Vancouver. Adding to the distance constraint in Canada, which relies on rail to move wheat to port, is the Rocky Mountains situated on the western edge of the growing area that have traditionally limited flow paths to port, creating potential bottlenecks if not running smoothly. Therefore, Canadian farmers need more storage on-farm relative to farmers in other parts of the

world. Distance also is an issue to be managed in the United States and for some locations exporting out of the Black Sea. By comparison, farmers in Australia are on average around 250 km from port terminals, with similar shorter distances in the United Kingdom, Germany, and France. In the United States, wheat is transported from the country elevator by rail, road, or river barges to larger central storage facilities that serve both domestic and export customers. At terminal facilities, wheat can be blended to achieve the specific quality requirements of different customers. The USDA, through its Grain Inspection, Packers & Stockyards Administration (GIPSA), administers the United States Grain Standards Act. GIPSA’s Federal Grain Inspection Service (FGIS) facilitates the marketing of US grain and related agricultural products by establishing standards for quality assessments, regulating handling practices, and managing a network of federal, state, and private laboratories that provide impartial, user fee-funded official inspection, and weighing services. This provides US farmers, handlers, processors, exporters, and international buyers with sampling, inspection, process verification, weighing, and stowage examination services that accurately and consistently describe the quality and quantity of the commodities being bought and sold. FGIS representatives or licensed state and private agencies inspect all wheat exported as it moves through the supply chain from country silo to export terminal. A similar approach is used in Canada. Once wheat is moved to an export terminal, CGC inspectors confirm its quality. In addition, cleaning facilities enhance the quality of the wheat to be exported, and if needed, it can be dried. In the United States, facilities are also available to clean wheat if required, unlike in Australia where the majority of exported wheat is loaded ‘farmer dressed.’ During loading of a wheat cargo, representative samples are collected, upon which the CGC issues a Certificate Final, which guarantees the quality and the weight of the wheat in the cargo. The regulated nature of the Canadian system means that the CGC has strong governance of the product, which is similar to the assessment made by FGIS in the United States. In Australia, exporters rely on terminal operators to load their wheat. Achieving quality specifications is a contractual agreement between exporter and terminal operator. A similar situation exists in Europe where third-party commercial inspectors verify the quality loaded on behalf of seller and buyer. Australian government involvement by the federal Department of Agriculture (previously called Australian Quarantine and Inspection Service), or its authorized officers acting on its behalf, is restricted to inspecting what is loaded to ensure the cargo is free from live insects and meets the phytosanitary requirements of the importing country. A key contract specification is protein level, and there are different ways to manage its variation to ensure consistent quality both within a hatch and across a whole cargo. In the United States, three types of average calculations are used by FGIS to determine if the quality average is acceptable. The preferred calculation method from a terminal management perspective is the simple average as this does not limit the range of quality that can be used to achieve the desired result. The most common approach is CUSUM (a quality control method used to monitor in-line measurements where the difference between each measurement and a bench mark

GRAIN MARKETING AND GRADING | Wheat: Grading and Segregation specification is calculated, and then cumulatively summed) where by depending on the specification being a minimum or maximum, there is a defined limit in one direction. For example, if the protein specification is minimum 12.0%, then perhaps a lower limit of variation to 10.5% is accepted with no upper limit provided each sublot tested is greater than 12.0%. The least preferred method is minimum (or maximum) sublot average when no variation to the average is allowed. Variations of these methods are used by the major exporting nations. Turning toward Europe and using France as an example, it has a mixture of attributes seen in North America and Australia. About 10% of French cereal production is retained on farms with the rest sold to collectors who clean, segregate, store, and market the grain. Increasing production levels mean more wheat is available for export and up to half of France’s annual production can now be exported. It has been estimated that there are 1100 of these collectors in France, with around 300 of them cooperatives managing 65% of cereal production. The remaining collectors are grain merchants and industrial users, such as for animal feeds and for starch manufacture, holding shares of 31% and 4%, respectively. The collectors have silos at over 7000 locations throughout France. These primary locations then can transfer grain to secondary sites in preparation for large export consignments or directly to domestic users, noting that some domestic mills have their own storage facilities. Given the increased level of exports from the Black Sea, quality accountability has risen though at this stage primarily at the outturn or export end of the supply chain. For example, the National Standard of the Russian Federation publishes the GOST R 52554-2006 standard. The standard details for the six classes of ‘common’ wheat, five grades of quality depending on traits such as protein, gluten, falling number, bulk density, moisture, and dockage. For common and durum wheat, Ukraine also reports quality specifications, in this instance the WHEAT Technical Specifications DSTU 3768:2010. For common Ukraine wheat, there are six grades separated by bulk density, vitreousness, moisture, protein, gluten, falling number, and grain and waste impurities. These standards are providing both sellers and buyers of Black Sea wheat greater confidence in cargo quality. At the same time, availability of quality information from the production end is improving with commercial services now making available quality profiles for the various production areas flowing into the Black Sea.

7

requirements and to have flexible systems of segregation and transport (in terms of both inherent quality and physical quality) to ensure consistency of grain quality.


• • • • •

What are the two major types of quality that needed to be managed in the pursuit of consistency? Describe some practical examples of how genetic quality can be managed. Outline the key principles employed when evaluating the quality of potential new wheat varieties. Describe some practical examples of how environmental quality can be managed? List the six major wheat-exporting countries/regions and comment on their relative importance and any trends in production that are evident.


•

• •

Each of the grain segregation and marketing systems described has advantages and disadvantages. What do you see as the most outstandingly ‘good’ and ‘bad’ of those described, both in this article and by reference to the respective websites cited? Develop a segregation and marketing strategy to ensure consistent and suitable grain quality by combining what you see as the best aspects of the systems of the countries described. What do you identify as the greatest needs for better grainquality evaluation, thus to revolutionize grain segregation, such as was achieved by NIR analysis? Do you see any emerging technologies that might be applied to achieve the desired results?

See also: Grain Harvest, Storage and Transport: Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Marketing; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Conclusion It is anticipated that into the future, customers will become more demanding with respect to continuity of quality. Therefore, the quality systems of the major exporters will continue to evolve. This may occur due to new technologies that can, for example, quickly determine the dough strength of an individual delivery at harvest, perhaps removing the need to have a variety declaration. With ongoing reviews on trade barriers, changes may also occur with the industry structures of exporter countries, and this in turn could change the way in which quality is delivered. Needless to say, customers will pay for the quality delivered, and if they do not like what they receive, this opens the opportunity for another supplier. The challenge is to understand customers’ future

Abugalieva and Pena. 2010. Grain quality of spring and winter wheat in Kazakhstan. http://repository.cimmyt.org/xmlui/bitstream/handle/10883/2785/94269.pdf. Cauvain SP and Young LS (eds.) (2009) The ICC Handbook of Cereals, Flour, Dough & Product Testing. Wien, Austria: ICC – International Association for Cereal Science and Technology, [email protected]. Krupnova, 2013. A comparison of grain quality in spring and winter wheats associated with market classes. www.agrobiology.ru/1-2013krupnova-eng.html. Ranum et al., 2006. Wheat, flour and bread in Central Asia. http://repository.cimmyt. org/xmlui/handle/10883/2514. Grain Inspection Handbook. Book III. Chapter 1. Inspection of shiplots and unit trains. www.gipsa.usa.gov.

Relevant Websites www.cfia-acia.agr.ca – Canadian International Grains Institute.

8


www.fas.usda.gov – Foreign Agricultural Service Online, Grain and Feed Division. www.franceexportcereales.org – France Export Ce´reáles. www.grainscanada.gc.ca – Canadian Grain Commission. www.graintrade.org.au – Grain Trade Australia. www.hgca.com – Home Grown Cereals Authority.

www.trigoargentino.com.ar – Trigo Argentino Institutional Quality Report. www.usda.gov – Grain Inspection, Packers and Stockyard Administration. www.uswheat.org – US Wheat Associates. www.wheatquality.com.au – Wheat Quality Australia.

Wheat: Marketing RL Cracknell, Crackers Consulting, Mount Eliza, VIC, Australia RM Williams, CBH Group, West Perth, WA, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by G.C. Worden, volume 3, pp. 375–383, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • •

Trends in world wheat production, consumption, and exports. Changes in the international wheat market since the first edition of the Encyclopedia of Grain Science published in 2004. Deregulation of the wheat export arrangements in Australia and Canada. The impact of government intervention on the wheat industry in Argentina. The emergence of the RUK, Russia, Ukraine, and Kazakhstan, as major players in the international wheat market.

Learning Objective

•

To understand the fundamentals of international wheat marketing and learn about the major traditional players and emerging exporters in the marketplace, the various marketing approaches being employed around the world, and the trends that are emerging in what is the major international market for cereal grains for human consumption.

Introduction A great deal has changed in the international wheat market since the first edition of this encyclopedia. The single-desk marketing arrangements in Australia and Canada were deregulated, Argentine exports outside of the South American continent reduced largely as a result of government intervention, and the market started to experience the effects of the rapid expansion in the exports from Russia, Ukraine, and Kazakhstan (RUK). The single-desk marketing arrangements that had stood the Australian and Canadian wheat industries in such good stead for so long were deregulated in 2008 and 2012, respectively, to be replaced by essentially free markets. While the free-market economists and politicians responsible for these sweeping changes were celebrating, wheat farmers, the unsung beneficiaries of the previously regulated market situation, gradually lost out as the accumulators and grain traders negotiated away the premiums that had taken decades to establish. Wheat marketing continues to be conducted in a range of formats around the world. At one extreme is a highly regulated central government control of wheat movement from field to the flour mill and even beyond, with controls over flour to bakeries and other processors. At the other extreme is a total ‘free-market’ system of supply and demand forces determining production, price, quality levels, movement, and availability. This article presents information on the current major players


in the global wheat trade and differences in their wheat marketing systems. The changes referred to in the preceding text and their impact on wheat marketing will be covered in some detail. Durum wheat is part of that discussion with mention of the unique characteristics of the durum market where necessary.

Global Wheat Dynamics When considering the marketing of, or trade in, wheat around the world, it helps to appreciate the dynamics of consumption, production, imports, and exports. Numerous organizations provide supply and demand data. In Table 1, two have been chosen to try and demonstrate the global wheat dynamics – the United States Department of Agriculture Foreign Agricultural Service and the Food and Agriculture Organization (FAO) of the United Nations. The snapshot is that some countries consume a lot of wheat and also produce reasonable quantities so that they are approaching self-sufficiency. These include China, European Union (EU), India, Iran, and Pakistan. However, depending upon seasonal production and other conditions, countries such as these might be a net importer or exporter. In contrast, other countries with large wheat consumption do not produce sufficient for their needs so are regular major importers such as Algeria, Brazil, Egypt, Indonesia, and Japan. Finally, there are other countries like Argentina, Australia, and Kazakhstan that are large producers of wheat but are relatively minor consumers, resulting in significant surpluses that they routinely export. Feeding the people of a nation is a priority for many governments, obviously necessary to avoid unrest and to encourage progress. Therefore, agricultural policy in numerous countries introduces factors that can impact or distort free trade activities. There are examples of state-owned buying agencies that are totally responsible for the purchase of agricultural goods from farmers within the country and for imported commodities. These are slowly reducing in number but are still a significant part of world trade. In some cases, liberalization is taking place as the state-owned buying works in parallel with private trade during a phasing-out period. Examples of importing countries where some central purchasing and controls are still in effect include China, Egypt, Japan, Algeria, Saudi Arabia, and Iran. On the exporter side, there used to be two broad wheat marketing mechanisms. There was regulated marketing by Canada and Australia or deregulated selling, best represented by the United States. Although notably, in the United States and EU, while marketing activity is conducted largely by the private trade, governments assume a more indirect influence by providing a range of farmer support and subsidy programs that are inevitably market distorting. Today, with Canadian

http://dx.doi.org/10.1016/B978-0-12-394437-5.00177-7

9

10

GRAIN MARKETING AND GRADING | Wheat: Marketing

Table 1

Global wheat dynamics – consumption, production, imports, and exports

Country

Five-year average consumption (thousand tonnes)a

Per capita supply (kg year 1)b

Algeria Brazil Canada China

9410 11 320 9465 120 700

Egypt European Union India Indonesia Iran Iraq Japan Mexico Morocco Pakistan

FAO ranking

Five-year average production (thousand tonnes)a

FAS ranking

184.9 53.5 69.6 63

4 78 54 63

2555b 5536 28 525 120 307

16 6 2

18 280 121 916

146.1 101.8

13 36

8110 141 447

14 1

87 035

58.9

70

90 394

6793 16 680 6194b 7355b 6390b 8570 23 840

23.5 152.3 139.6 48.6 33.6 177.3 113.8

117 11 16 84 106 5 28

–b 13 440 2800b 750b 3628b 6018b 24 240

Russia 35 850 130.8 20 Turkey 17 530 173.5 6 Ukraine 12 290 106 33 United 33 284 79.5 48 States Uzbekistan 8120 170.6 7 Others 138 975 Countries of note making up part of ‘others’ grouping Argentina 103.2 35 Australia 69.8 53 Bangladesh 17.3 124 Kazakhstan 94.4 42 South 51.8 82 Korea Nigeria 24.5 116 Philippines 14.7 129 Saudi 90.6 43 Arabia Sudan 35.8 103 Thailand 11.8 133 Vietnam 8.8 142 Yemen 114 27

49 312 16 860 20 341 57 529

5 10 9 3

6690 12 275

15

12 900 26 236

13 7

13 730

11

12

8

Five-year average imports (thousand tonnes)a

FAS ranking

6877 7081

4 2

Varies seasonally 10 144 5248

1 6

Varies seasonally 7060 4160 3522 6189 4297 3681 Varies seasonally

3 11 15 5 8 13

4185

10

3706

12

2061 51 607

21

3121

17

4695

7

4285 3605 2649

9 14 18

2202 2025 2220 3135

20 22 19 16

Five-year average exports (thousand tonnes)a

FAS ranking

19 618

4

24 683

2

3560

10

1032

11

15 487 3660 7397 29 795

5 9 7 1

11 670

12

6949 19 819

8 3

7438

6

a

Five-year average 2010/11–2014/15 World Wheat Production Consumption and Stocks and World Wheat Flour and Products Trade reports from US Department of Agriculture, Foreign Agricultural Service. b 2011 wheat and products food balance sheet from FAO for 149 countries.

and Australian wheat exports deregulated, the world is a free global market place. The changes to a globally free marketplace have resulted in large multinational companies expanding their buying and selling into new areas such as Australia, Canada, and those countries exporting through the Black Sea such as RUK. The scale of activity from these companies ranges from a local office buying wheat from a few farmers and brokering it to a nearby flour mill all the way up to full cargoes from a major exporter to a major importer. Besides making the sale, these companies also arrange shipment, often by chartering the ocean vessel, and can arrange all the financial transactions

including credit arrangements and letters of credit and securing all the inspection and certification requirements. Some of these organizations are vertically integrated, involved in the processing of the same commodities they trade. Examples are Cargill Inc., Bunge, Louis Dreyfus, and Archer Daniels Midland or ADM.

Marketing Overview The trade in wheat is conducted by one of the three basic methods:

GRAIN MARKETING AND GRADING | Wheat: Marketing 1. Government agencies or delegated representatives call for public tenders. The call for tender outlines the terms for the purchase, including quantity, class, grade, and quality specifications, delivery period, payment terms, discharge port, and other details necessary for the bidder to make an educated and appropriate price offer. Major importers that use public tenders include Egypt, Japan, Tunisia, Taiwan, Philippines, Saudi Arabia, and Algeria. 2. Private milling or end-use companies call for a private tender. Some government agencies may also use a private tender. The buyer privately calls for a bid from an exporting company or agency to meet desired specifications. There is often a preexisting relationship between buyer and seller with knowledge of the quality available from the supplier and of the terms and delivery conditions from the buyer. Flour mills in the EU, Latin America, and many parts of Asia usually conduct private tendering. 3. Trade can take place in an open marketplace, referred to as a spot market, where wheat of specific quality and quantity is traded on a position basis. For any of these methods, it is critical that there is a clear understanding of quality and other contractual expectations between buyer and seller. Misunderstanding and negligence in establishing clear specifications are the principal cause of controversy and legal recourse in wheat trade. Items such as protein content need to be specified in terms of moisture basis and whether the required level is an absolute minimum or an average level throughout the shipment. Other quality terms will typically include such factors as moisture content, test weight (grain density), sprout damage level, typically expressed in falling number units and dockage or impurity level. Delivery conditions are another important component of a contract. A seller may quote a price on a free-on-board basis, which specifies to the buyer that the seller is quoting on the basis of a loading port. For deliveries on the basis of an unloading port, prices will be quoted on a cost–insurance–freight or a cost-and-freight-only basis; therefore, the seller is looking after some or all of the delivery terms. In the past, there tended to be the need for contract performance guarantees, or some type of performance bond, to ensure fulfillment of the contracted product. Today, where there is a relatively small grouping of buyers and sellers, a letter of credit from the buyer’s bank is the principal requirement of the supplier. When a new buyer or seller enters the marketplace, stricter financial credentials are needed.

Major Wheat-Exporting Nations The movement of wheat from the farmer in one country to the flour mill and processor in another can take many paths. Exporting agencies, private grain traders, and importing agencies can all be involved. Where wheat exports are controlled by an agency, they may deal directly with the importing agency or private company and look after all the necessary credit, freight logistics, and certification requirements. Or they may just conduct the sale and hand off some or all of the intermediate activities to private trading companies.

11

Now that most of the major exporters operate in a largely free-market situation, the procedures that they follow are not dissimilar. Canada provides an excellent example, and it is covered in some detail in the succeeding text, with the other major players to follow.

Canada Canada is renowned for the production of hard red spring wheat for bread making and amber durum wheat for pasta and couscous consumption. Table 2 shows Canadian wheat production and exports from 1 August 2012 to 31 July 2013. Wheat production in Canada is relatively small compared with large producers like China, India, and the United States. However, given Canada’s small population of 35 million (1 July 2013: Statistics Canada), approximately 75% of production is available for export each year. As a result, Canada plays a significant role in the world trade of wheat, with about a 15% market share. This market share has been declining in recent years with the increase in wheat exports from countries like Russia, Ukraine, and other Black Sea producers. Canada is a significant producer and exporter of durum wheat and accounts for close to 50% of world trade in durum wheat. Wheat production in Canada occurs primarily in the western provinces of Manitoba, Saskatchewan, and Alberta. This region produces about 90% of the wheat in Canada and accounts for the vast majority of the exports. Most of the wheat production in Eastern Canada is used domestically or is shipped into the United States. The majority of wheat production in Canada is spring wheat planted during April/May and harvested during August/September. Hard spring wheat production is well suited to the hot, dry summers in Western Canada. Temperatures in Western Canada during the winter can reach as low as 40 C. While this is uncomfortable for people, it is an excellent natural way to control insects in stored wheat. As a result, chemical use on stored wheat is low, which is an important advantage in a world market increasingly concerned with chemical residues. The cold winters also limit the production of winter wheat in Western Canada. As outlined in Table 3, over 60% of wheat exports from Canada are shipped out of the West Coast ports of Vancouver and Prince Rupert. The other export channels include the St. Lawrence Seaway in the east, rail shipments to the United States and Mexico, and a small amount through the northern Table 2

Canadian wheat production and exports 1 August 2012–31 July 2013 (millions of tonnes)

Durum wheat Other wheat Total wheat

Production

Exports

4.6

4.2

22.6

14.3

27.2 Source: Statistics Canada

18.5 Source: Canadian Grain Commission

12


Table 3

Canadian export channels

Export distribution for wheat from Canada

%

West Coast ports East Coast ports South by rail to the United States and Mexico Churchill

62 25 10 3

Source: CWB.

Figure 1 Export ports and storage capacities.

port of Churchill. The Port of Churchill is only open from July to October, as the port is frozen for the rest of the year. In terms of grain storage in Canada, most farmers have enough storage on farm for one year’s crop. This has resulted from the large distance from the production area to export position. For example, it is about 1500 km from the middle of the production area in Western Canada to the Port of Vancouver. As the flow of grain is constrained by the rail movement through the Rocky Mountains on the western edge of the growing area, farmers need to deliver grain into the rail pipeline throughout the export year. Therefore, they require a large amount of storage relative to farmers in other parts of the world. Figure 1 shows the various export ports and the total storage available at each port area. One point to note is that the amount of terminal storage in the west is less than the storage in the east. This makes for complicated logistics, as the volume of grain moving west is larger than that moving east. Canada previously had only one seller of wheat from Western Canada, the Canadian Wheat Board (CWB). As such, the CWB coordinated all aspects of the wheat marketing business in Western Canada. Following a long debate within Canada about the value of the single-desk marketing system, this single-desk authority was removed by the federal government on 1 August 2012. Now, the buying and selling of wheat in Canada is handled by private grain companies. The CWB has been transformed into a grain company, and under the current legislation, it must be privatized by 2017. During the single-desk period, the CWB looked after the market development efforts surrounding the export of wheat.

Since deregulation, the wheat industry has been working on developing new structures to fill this void. Provincial wheat councils are being established and a group called Cereals Canada is being set up to provide an umbrella body. These structures are evolving and will take a number of years to mature and be fully defined. The Canadian International Grains Institute (CIGI) was established in 1972 to promote the sales of grain produced in Canada through customer education. Prior to deregulation, a major portion of the funding for CIGI came from the CWB. Since deregulation, this funding has been replaced by a farmer contribution according to sales. The balance of the funding comes from the federal government and from private programs. CIGI conducts customer programs both in Canada and offshore to promote the sale of Canadian crops. Canada has a long history of producing high-quality wheat for the export market. This has resulted from the unique agronomic conditions that exist in combination with a regulatory environment that promotes a quality product. While deregulation of single-desk wheat marketing has occurred, other structures such as the Canadian Grain Commission, the Canadian Food Inspection Agency, and the CIGI remain, and Canada will continue to be a significant exporter of high-quality wheat to the world market.

The United States The United States has long been thought of as the leader of free marketing. This is well represented by the choices on offer to both the farmer and trader. On-farm storage accounts for 60% of the amount of grain grown in the United States; therefore, the majority of farmers must at some point make a choice on how to move their wheat to market. When a farmer is ready to deliver wheat, there are generally two marketing choices for commercial sale. As one choice, the product can be sold to either a local cooperative or an independent grain company. The second choice for a farmer is to make the wheat available to the government through a wheat loan. In the former case, the farmer negotiates a final price directly with the buyer. If selling through the government wheat loan program, the farmer receives the deficiency payment that has been established by legislation and compensates farmers for marketplace shortfall. In either scenario, the wheat is delivered to the country elevator where the grade is established. Country elevators may also provide drying and conditioning services and may offer a variety of transport and payment terms to the farmer. Wheat delivered to the government under the wheat loan program can be used by the government to put into the federal Food Security Wheat Reserve or for delivery to export customers through the Commodity Credit Corporation. This latter organization authorizes the sale of agricultural commodities to other government agencies and to foreign governments and the donation of food to domestic, foreign, or international relief agencies. The Commodity Credit Corporation also assists in the development of new domestic and foreign markets and marketing facilities for agricultural commodities. To assist in selling decisions, the United States has three major commodity exchanges that deal in future transactions

GRAIN MARKETING AND GRADING | Wheat: Marketing for wheat, with each trading a separate type of wheat. ‘Soft red winter’ wheat is traded on the Chicago Board of Trade, ‘hard red winter’ wheat is traded on the Kansas City Board of Trade, and ‘hard red spring’ and ‘white’ wheat are traded on the Minneapolis Grain Exchange. There is no commodity exchange that trades durum wheat. In global wheat trade, these three commodity exchanges are used to establish base prices for equivalent wheat types around the world. Another choice, although somewhat dependent on the location, is the mode of transport from inland storage to export terminal. Country elevators increasingly ship grain directly to ports, often using large shuttle trains. They also ship by truck or rail to processors, to feedlots, and to larger river and railterminal elevators. About 50% of movement of wheat from inland to export position is by barge along major river systems such as the Mississippi River. Export of wheat from the United States is from the port facilities of four regions – Gulf of Mexico, Pacific Northwest, Great Lakes, and Atlantic ports. Port elevators usually combine grains of different grades, protein levels, and other characteristics to meet buyer specifications, and they may also clean, dry, or condition the grain to meet required specifications.

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Export deregulation has impacted on the number of selling options available to farmers. The trade has been led primarily by not only the marketing arms of the former bulk handlers but also the entrance of subsidiaries of some of the world’s major international grain traders. All compete openly in the market purchasing grain from farmers and accumulating it ready for export. However, with a few minor exceptions, the former state-based bulk handlers are in a powerful position to control shipping programs, and this is the subject of ongoing debate within the industry, some arguing for government intervention in order to provide a more transparent and level playing field. Deregulation has provided farmers and traders with a wide range of opportunities to market grain, which in turn brought with it the need to learn about the complex world of grain trading previously undertaken for them by the single-desk marketer, AWB Limited. These include selling options; the various contracts available; harvest, storage, and longer-term pest control issues; quality considerations and specific requirements of potential export markets including phytosanitary issues; and payment, logistics, and shipping considerations. For many, this proved to be a very steep learning curve and not all were successful.

Australia With a small population and relatively large annual production, Australia has been a regular supplier of export wheat. Up to 80% can be exported in a good production year. However, the mechanics as to how that wheat is exported has changed following deregulation in 2008. The deregulation of the Australian wheat industry though first commenced with the deregulation of the domestic market followed by the trade of wheat in bags and containers followed by the full deregulation of the export market. This led to the establishment of The Futures and Options Market for Australian Grain as part of the Australian Stock Exchange ASX. It facilitates price discovery and risk management in track markets for Australian wheat, feed barley, sorghum, and canola. Since export deregulation, no single body publishes detailed production figures by grade and classification region as those who hold the information consider it to be proprietary in nature and something that they do not wish to share with their competitors. Long-term data suggest that the crop comprises 5–10% Prime Hard (the premier high-protein hard wheat for bread making and Chinese-style noodles), 15–20% Australian Hard (the main export hard wheat class exported widely, mainly for baking purposes), 30–40% Australian Premium White (the major portion of the crop available from all ports around the country, suitable for a wide range of applications), less than 5% Australian noodle wheat (special purpose soft-grained high-starch pasting wheat for various types of white salted noodles), 5–10% APW (noodle) wheat (segregated for blending for various types of noodles), 20–25% Australian Standard White (a base-grade white milling wheat with no specific varietal requirements or protein requirements), less than 5% Australian durum (high-quality durum wheat with good color and processing characteristics), and less than 5% Australian soft (specialist soft varieties for biscuits and cakes and sourced primarily by the domestic market).

Argentina Until 1991, all wheat marketing was under state control through the National Grain Board (NGB). The NGB had significant wheat storage facilities, both inland and at port positions that were subsequently sold off to farmer cooperatives or the private sector. Wheat production increased with deregulation of the agricultural economy and elimination of the NGB and wheat export taxes. In the early 1990s, wheat production averaged less than 10 MT year 1, but from 1998 to 2002, production increased to an average of 14.4 MT. This allowed Argentina to increase wheat exports, and at that time, it was the world’s fifth largest exporter, with average exports of close to 10 MT. However, since 2006, the government has routinely intervened by raising export taxes and setting export quotas, aimed at ensuring that the domestic market was adequately supplied with relatively inexpensive wheat. The result has been a steady reduction in wheat plantings, which, coupled with some poor seasons, has seen wheat production in Argentina plunge from nearly 16 MT in 2005 to 8.2 MT in 2013, thus effectively removing Argentina from the export market. Argentina is in the Mercosur trading agreement along with Brazil, Uruguay, and Paraguay, and these countries, principally Brazil, account for the bulk of Argentine wheat exports. The Mercosur agreement is a protectionist umbrella for Argentine farmers as wheat from origins outside the Mercosur countries must incur significant tariffs, which are used to compensate Mercosur farmers. Between 2008 and 2012, Argentina shipped 4–5 MT to Brazil, but in 2013, due to limited supplies, it was only able to provide 2 MT, forcing Brazil to import from the United States and Uruguay. However, during 2014, the government indicated a partial lifting of restrictions, which together with firmer prices may see farmers gradually increase

14


their wheat plantings and potentially double the volume of exports from the record lows of 2013. On-farm storage is minimal in Argentina, and wheat competes strongly with other important crops, especially soybeans and maize, for commercial storage space. This means that farmers can often be forced into ‘price to be fixed’ contracts in order to take advantage of exporters’ and millers’ storage facilities. In addition, farmers in Argentina tend to have a much poorer working capital level relative to those from the other major exporting nations and access to credit is limited. This puts farmers at a disadvantage when negotiating prices at harvest time, and there tends to be a lot of pressure for exporters to make sales close after the harvest period in order to maintain turnover in storage facilities. In Argentina, the harvest pressure occurs generally in March, which is outside the time range of harvest availability from the other exporters from late summer to early winter (July–December). Demand, when wheat is available, tends to come from non-Mercosur destinations, especially those that have lower quality expectations, such as Iran, Iraq, and African nations. The rail transportation system in Argentina is in poor repair; therefore, truck transport is most often used to get wheat from the growing regions to port. The average distance from country position to an export port is 300 km. There is also use of barges and ships along the major Parana´ river system, with continuing effort to increase draft levels to allow larger ships to move further inland.

Russia, Ukraine, and Kazakhstan In the first edition of the Encyclopedia of Grain Science, a section entitled ‘Minor Wheat Exporting Nations’ discussed exporters such as RUK, as well as Pakistan and India. It was argued at the time that this ‘others’ category had increased during 2001–2003, mainly due to poor growing and harvest conditions for the traditional exporters and bumper crop conditions in other parts of the world. These countries, RUK, had traditionally been self-supporting and only tended to enter the world trade arena in a minor way or opportunistically. But the unusual market circumstances that drove traders to move wheat from unusual origins to service need around the world are now seen as the stimulus for a massive increase in exports from the likes of RUK. In a little more than a decade, these three origins have collectively become one of the world’s largest wheat suppliers for export. This has not been without challenges. Importers that needed to first review their quality expectations and blending capabilities in order to handle these wheat have now realized that they can be a useful addition to many wheat grits. Furthermore, as the infrastructure of these new exporters has improved, it is clear that barring major political unrest, they are now an established component of the international wheat market, creating major challenges for the traditional wheat exporters.

European Union Collectively, the EU is both the largest consumer and producer of wheat (Table 1). Therefore, in a year of high production,

there is wheat available for export – both within and outside of the EU. A surplus can be purchased by private grain traders and wheat processors or by governments under the EU’s Common Agricultural Policy (CAP). However, following significant pressures within forums such as the World Trade Organization (WTO) and the General Agreement on Tariffs and Trade – a multilateral agreement regulating international trade – the impact of the CAP has been substantially reduced. The notorious practice known as ‘intervention,’ whereby governments bought in cereals and rice to public storage, introduced to protect farmers from low market prices, is now used only in cases of real necessity, providing an authentic safety net for farmers. Exports and imports are still controlled however by the issuing of import and export licenses. In the case of imports, in accordance with the EU’s commitments under the WTO, a number of fixed tariff import quotas are in place at a lower or zero duty. In the case of exports, these have not been subsidized since 2006. Very little wheat is moved by rail within EU countries. Due to the relatively short distances to various processors or port facilities, most wheat is moved by truck or by barges through the well-developed canal systems of many of the countries.

Conclusion With the arrival of newer players on the scene, the traditional wheat marketing environment has changed irrevocably, creating new opportunities for importers and challenges for traditional exporters. Wheat remains a major food source and is a unique agricultural product due to the vast range of consumer products that can be produced from it. As developing nations improve their economies, they can be expected to demand a greater variety of foodstuffs, and wheat will become a greater part of their diet. The last 10 years have shown dramatic increases in wheat production and trade, and this is expected to continue as these nations do not tend to be traditional producers. The dynamics of wheat marketing systems around the world will have to develop to meet this new demand.

Future Prospects History tells us that despite the massive volumes of grain involved and the geographic locations of the major producers and consumers of wheat, the international wheat market can be volatile, and a number of factors would suggest that that situation will continue into the foreseeable future. Climate change is already influencing temperature and rainfall patterns in many wheat-producing regions of the world with the timing and duration of harvests already showing signs of change. There is also evidence that grain-producing regions are moving as farmers adjust their farming practices to the changing weather patterns. Extreme weather events are also becoming more commonplace, which can have dramatic effects on local grain production levels and the quality of the grain that is ultimately harvested. These factors create short-term shortages as buyers of wheat for human consumption and animal

GRAIN MARKETING AND GRADING | Wheat: Marketing feeding purposes compete for shrinking supplies. The marketplace itself is also entering a new period of change with the emergence of the Black Sea region as a major exporter introducing additional pressures. Conversely, political unrest in the region has the potential to significantly reduce production levels and resultant export capability.

15

Grains in North America; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: South America; Grain Production and Consumption: Africa.


• • • •

List the world’s major wheat producers and discuss those that are self-sufficient and the extent to which they participate in the international export trade. List the world’s major wheat consumers and discuss how and from where they meet any domestic shortfalls. How are prices determined for the major types of wheat traded on the world market? Given the steady increase in the world’s population, discuss the capacity of the major producers to meet the increased demand and who is best placed to meet the challenge.

Acknowledgments The authors are indebted to a number of people who assisted greatly in the production of this article, in particular Darrell Bushuk, vice president of Trading and Sales, CWB (http:// www.cwb.ca/), for updating the section on Canada; Graham Worden, Market Development and Technical Support: Grain, Paterson Grain, Winnipeg, Canada (www.patersongrain.com); and the author of this article in the first edition of the Encyclopedia of Grain Science, for allowing us to use it as a basis for the revised version.

See also: Agronomy of Grain Growing: Wheat: Agronomy; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Grain Harvest, Storage and Transport: Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Grading and Segregation; Grains Around the World: Grain Production and Consumption: Cereal

ABARES, Australian Bureau of Statistics, Pulse Australia. Australian Export Grains Innovation Centre AEGIC, Australian Grain Note: Wheat (August 2013). Exporting grain from Australia, Australian Export Grains Innovation Centre AEGIC (January 2014). 140429 AEGIC_Exporting Grain (3).pdf. Entire section provided by Darrell Bushuk, Vice President Trading and Sales – CWB, personal communication. European Commission, Directorate-General for Agriculture and Rural Development, Unit C4. ec.europa.eu/agriculture/policy-perspectives/policy. Sections extracted from the 1st edition of the Encyclopedia of Grain Science – C. Wrigley, C. Walker and H. Corke (eds.) Elsevier Ltd, Oxford, UK, 2004, and updated by the current authors. The Economist, 15 January 2014. USDA Economic Research Service, January 2013. USDA World Agricultural Supply and Demand Estimates, December 2014.

Relevant Websites http://www.agrifood.info/Agrifood/members/Congress/Congress2001Papers/ Symposium/Donoso.pdf – Regional Market Integration and MERCOSUR, Implications for Wheat Trade. http://www.asx.com.au/documents/products/grain-futures-brochure.pdf – The Futures and Options Market for Australian Grain. www.cigi.ca. http://www.cmegroup.com/trading/agricultural/grain-and-oilseed/kc-wheat.html – KC HRW Wheat Futures Quotes. http://www.cmegroup.com/trading/agricultural/grain-and-oilseed/wheat.html – Chicago SRW Wheat Futures Quotes. http://www.fao.org/statistics/en/ – The Food and Agriculture Organisation of the United Nations. www.fas.usda.gov – USDA Foreign Agricultural Service. https://www.grainscanada.gc.ca – Canadian Grain Commission. www.graintrade.org.au – Grain Trade Australia. http://www.mgex.com/ – North American Hard Red Spring Wheat. www.statcan.gc.ca – Statistics Canada. www.trigoargentino.com.ar – Trigo Argentina (Argentine Wheat). www.uswheat.org – US Wheat Associates. http://www.uswheat.org/supplyDemand – US Wheat Associates Supply and Demand.

Barley: Grading and Marketing A MacLeod, M Edney, and MS Izydorczyk, Canadian Grain Commission, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by M.J. Edney & M. Brophy, volume 1, pp. 49–57, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • •

Barley is traded on domestic and international markets for malting, food, and animal feed uses. The price of barley is affected by both supply and demand and quality factors. Major exporting countries have developed a set of grades and standards to support effective marketing of barley. The value of barley is determined by measuring a set of characteristics that are desired by end users. Assigning grading factors can be based on visual inspection or more objective instrumental testing.

Learning Objective

•

Marketing

To understand the means by which barley is marketed on a domestic and global scale to meet the needs of the malting, food, and feed industries.

Introduction During the 10 years from 2001 to 2010, world barley production averaged 140 million tonnes (Mt) and is expected to rise to more than 150 Mt by 2018. It is anticipated that over 20 Mt of that production will be traded on the world market as feed, malting, or food barley. The remaining production will be used in domestic markets for similar purposes. In either case, considerable effort in marketing and grading will be required to ensure that producers get paid appropriately, while end users receive barley with the required quality and at a competitive price. Marketing of barley consists of a series of activities that move grain from production to its end use. Marketing is a mechanism by which the conflicting demands of producers and end users can be reconciled. For barley with a given quality, producers look for the highest possible price, while end users want the lowest possible price. Barley marketing ranges from a simple exchange of commodities among neighboring farms to the complex use of handling companies and grain merchants on an international scale. It might require the use of intake points in the production area for the collection of grain and export-handling facilities at ports for shipment. The silos and handling facilities at intake and export positions can be owned by private companies, large multinational grain companies, producer cooperatives, or barley processors. Grain merchants are often involved in actual sales. They can be representatives of handling companies, independent marketing companies, or a state trading enterprise (STE). Marketing is facilitated through the use of standards and grades that act as a marketing language through which buyers and sellers can communicate on the quality of barley to be delivered. Grades and standards sort barley into groups of

16

similar quality. They indicate the expected performance of barley during processing and requirements for special storage, as well as any need for additional handling such as cleaning or drying. Sanitary factors such as the presence of contaminants can also be included while grading to indicate fitness of barley for human or animal consumption. Grades and standards are dynamic, changing with grain technology, weather conditions, and the varying demands of processors and consumers. Marketing and grading mechanisms can vary considerably among the different exporting and importing countries. Local supply and demand and government involvement affect final arrangements.

Marketing of barley is a complex process involving all the activities required to move grain from the field to the end user. It can involve three major components. The primary component is the exchange of barley for money. Another important component is arranging physical activities such as transportation and storage that are required for moving the product from field to the end user. Finally, marketing will include many facilitating functions such as standardization, financing, risk bearing, gathering of market intelligence, promotion, customer technical support, and after-sales service. The past decade has seen a major shift in the way much of the world’s barley is traded internationally. The majority of barley markets around the world are now largely deregulated with two major barley-producing countries, Canada and Australia, both ending their long-held state-controlled monopolies on the export sale of barley in recent years. While governments still play a role in the barley trade, the majority of marketing occurs directly between producers, grain companies, and industry. Producers have a variety of options for selling their grain. Grain can be sold directly for cash after harvest or stored on farm for future sale. Various types of contracts can also be used to sell grain in order to manage the risk associated with changing prices. Barley growers can enter into production contracts with grain or malt companies before seeding so that the crop may be grown and marketed under specified terms. The contract normally outlines the variety to be grown, the size and location of the acreage, and the quantity. The contract may or may not fix the price. One advantage of production contracts is that the sale of the grain is guaranteed at harvest. Deferred delivery contracts, on the other hand, provide growers with a fixed price for an agreed volume of barley that is to be delivered to a specific location at a future date. An alternative method of marketing barley is by using price pooling. This is a cooperative approach to marketing that combines deliveries of the same grade and quality from multiple producers to return an average price over several months or a


http://dx.doi.org/10.1016/B978-0-12-394437-5.00173-X

GRAIN MARKETING AND GRADING | Barley: Grading and Marketing year’s worth of sales activity. The pool return is the sum of all revenue achieved minus any costs associated with operating the pool, divided by the total tonnes in the pool. This is a way to manage risk associated with making sales decisions in a volatile market. When combined with a monopoly, or single-desk marketing system, it can also offer the additional advantages of transportation and handling efficiencies as well as the opportunity to exert market pressure to potentially increase revenues. International sales between barley exporters in one country and importers in another are facilitated through either public or private tenders. The tenders are essentially invitations by importers asking exporters to quote a price on grain that meets specific requirements. Interested parties will make an offer based on supply, market pricing, and transportation availability, which will be either accepted or rejected by the importer. If accepted, a contract will be signed setting the specific terms and conditions of the deal including quantity, quality, destination, delivery period, and payment terms. Marketing of barley is not just a matter of seller finding buyer and agreeing on price, although that can be the extent of it in some sales. More typically, arrangements between seller and buyer include much more detail. In some cases, quality terms are on the basis of known standards or grades of the seller. However, buyers often stipulate their own specifications, especially for malting barley. In either case, specifications are included in the sales contract along with the agreed method for determining and documenting the quality delivered. In most cases, an independent testing agency is agreed upon by the parties. The quality specifications and tolerances can be specified in detail in the contract, or they can be on the basis of fair average quality (FAQ) for the origin in question. The definition of FAQ must be agreed upon and will depend on the origin of grain plus the growing year. Other factors included in a sales contract can be adjustments and penalties for specifications outside of tolerances, shipping terms and demurrage clauses, and dispute-settlement clauses. Successful marketing requires understanding the customer and their needs. Marketing of barley, in many cases, involves a

17

long-term relationship between buyer and seller. To this end, many grain-exporting countries have developed specific institutes to assist with market development activities, technical support, and customer service programs. Examples of such institutes include the Canadian Malting Barley Technical Centre, the US Feed Grains Council, the Home-Grown Cereals Authority in the United Kingdom, and the Australian Export Grains Innovation Centre.

Malting Barley Malted barley, the major ingredient in beer, represents a minor portion (about 25%) of the total world barley trade, but it routinely offers the greatest return for producers. Brewers and distillers must use at least some barley in their products. They also require the barley to have a unique set of quality characteristics. As a result, barley demand in these markets is more consistent and prices are higher. The price of malting barley is largely controlled by the global supply and demand of malt and malt products. Price premiums for malting barley over feed can lead to elevated levels of production that exceed demand and allow maltsters to select only the highest-quality barley for malting. Barley that has been selected for malting can be destined for either domestic or overseas processors (Figure 1). In some countries, producers deliver their barley directly to domestic processors, but often, barley is transferred to domestic processors through local grain intake points or to port facilities for export to overseas producers. In other countries, the barley is delivered directly to export facilities. Malting companies are increasingly relying on direct contracting methods with producers to source their grain. Contract production offers malting companies a secure supply of highquality barley, usually of specific varieties. Such contracts offer price premiums over high-yielding feed barley. The premiums are necessary to offset lower yields, higher production costs, and risks associated with meeting the strict quality

Barley production

Feed barley

Not of selectable quality

Malting or food barley Selectable quality

Fed on-farm

Delivered direct to local feedlot/mill

Delivered to domestic feedlot/mill

Grain intake pointa

Export-handling facility

Exported to overseas feedlot/mill

Delivered direct to local malt or food processor

Delivered to malt or food processor

Exported to overseas malt or food processor

Figure 1 Flow diagram of delivery options of barley for feed and malting or food. aDeliveries of feed and selected barley can go directly to an exporthandling facility at some locations.

18

GRAIN MARKETING AND GRADING | Barley: Grading and Marketing

specifications for malting barley selection. The contracts may also specify strictly that production standards and practices be met, such as the use of certified seed and limitations on use of pesticides. Identity-preserved or ‘closed-loop’ contracts can also be used when an end user has some proprietary interest in a particular barley variety with value-added properties. In these cases, the grain produced is of a specific variety that can only be produced and sold under strict agreements between the grower, the merchant, and the end user.

Food Barley Barley has a long history of food use: in the ancient world, it was grown mostly to provide food staples for human nutrition. At the beginning of the twentieth century, with drastic changes in consumption patterns in the Western World giving preference to such grains as rice, wheat, and maize, barley lost its earlier preeminent position in human nutrition. However, recent collaborative efforts in medicine, nutrition, and food science have elucidated the role of barley in the prevention and treatment of many human diseases and revived interest in this grain for food purposes. Only a few small, established international markets currently exist for food barley. Barley is used in Asian countries as a rice extender and for tea. Japan imports barley for the production of sho¯chu¯, a traditional distilled barley beverage. In the recent years, many new hull-less barley varieties, with high b-glucan content and altered starch characteristics (waxy and high amylose), were bred in North America, Australia, and Europe specifically for food uses to enhance health-promoting properties. b-Glucans, the major dietary fiber constituents in barley, have been linked to the lowering of serum cholesterol concentrations in humans. Based on several clinical studies, both in the United States and in Canada, foods containing barley are allowed to carry a health claim related to the ability of b-glucans to reduce cholesterol and the risk of heart disease. Barley b-glucans are proven functional food ingredients that can increase the global demand and usage of barley grain and barley products, such as dry-milled barley fiber fractions, barley flakes, or pearled barley in a variety of foods. To date, however, there has been relatively little consumer education about barley’s health benefits and, therefore, little demand for barley food ingredients and/or barley-containing food products. Global consumer surveys and industry reports predict growth in the functional food and natural health product sector. Some of the factors driving the growth of the functional food market are the aging of the population, the growing health concerns, and the changing food consumption habits of the younger adults. Better promotion of barley grain and new barley-containing products by the food industry and governments will be necessary to rouse consumer awareness about the health benefits, uniqueness, and usefulness of barley and to increase demand for this grain.

Feed Barley The largest portion of barley production is used as animal feed where there are limited demands on quality. Feed barley, especially in international markets, is often replaced by less

expensive grains such as corn and wheat. Two specific markets, namely, Japan and Saudi Arabia, do not, for traditional reasons, substitute it with other grains, which make them the two most consistent international markets for feed barley. The decision on where to market feed barley depends on prices of the barley in local and international markets. Prices depend on domestic supply and demand. The majority of feed barley is fed on farm or sold to neighbors or local feedlots and/ or mills. A second choice is delivery to a local grain intake point for transfer to more distant feedlots and/or mills or to export facilities. Once again, delivery straight to the export facility is also possible. In some countries, the final choice can be farm storage of the barley until a more appropriate time or price. Barley producers generally aim for the malting and food markets, when available, as they tend to be the most lucrative. Barley, which is deemed to be unsuitable for processing, usually reverts back to the feed industry; however, producers may store their barley and resubmit it for consideration if standards are relaxed due to changes in demand. Occasionally, when price spreads are narrow, producers will sell top-quality (malting or food) barley into feed markets in order to obtain quick cash and to avoid possible rejection of the barley later in the selection and/or delivery process.

Grading and Standardization Grades separate barley into groups that meet certain standards. All the grains within a group have similar, but not necessarily identical, quality. Grades and standards can indicate potential processing value of the grain, its nutritional value, and other factors that may affect the overall value of the grain such as a need to dry or clean a sample and even the need for special storage conditions. The use of grades and standards has benefits for all involved in the marketing of grains (Table 1). The use of agreed or defined grades or standards facilitates contracting and gives common reference points on which to base negotiations. Grades ensure that grains of equal value receive equal monetary compensation and that a high-quality product receives a premium that allows end users to communicate their needs to Table 1 List of advantages and disadvantages of using grades and standards Advantages

Disadvantages

Maintains consistent pricing and ensures premiums for top-quality product Allows end users to communicate their needs to producers Reduces handling and transportation costs through bulk handling Attracts and keeps customers through delivery of consistent product Reduces sanitary hazards

Grading contributes to costs and advantages must outweigh this cost Grading of grains can affect throughput at handling Quality is subjective – agreements on actual specifications can be difficult

GRAIN MARKETING AND GRADING | Barley: Grading and Marketing producers. Grades foster a more efficient price-discovery process; they can reduce costs of handling and transportation through the collective storage of bulk lots of similar quality. Grades enable end users to consistently obtain barley of the same quality. Grades can also reveal clear variations in quality, indicating opportunities for improvement such as drying, cleaning, and special storage. Enforcement of grades can reduce sanitary hazards such as contaminated grain. The number of grades cannot be increased without increasing costs and thus negating advantages. There must be a sufficient number of quality divisions to give buyers choice at different pricing points, without creating the need for too many different segregations that would make storage and bulk handling difficult. The grades must be easily applied such that they do not significantly slow down the receival and transportation of barley. However, the methods must still be accurate and allow for uniform measurement.

Variety Classification Classification is the categorization of a barley variety based on specific end use requirements. The classification process aims to ensure grain of consistent physical quality, processing performance, and end product quality to customers and end users. Each barley variety malts slightly differently, and mixtures of varieties often do not malt to their full potential. Each malting barley variety has been bred specifically for malting, and acceptance of its potential is indicated by the variety’s registration or listing on an official eligibility list, often maintained by domestic barley industries. Normally, this requires that the malting and brewing quality be tested in rigorous trials that may include pilot- or commercial-scale processing. The requirement for testing may be mandatory or voluntary, depending on the jurisdiction. This type of variety accreditation system can also serve to increase the reputation of the barley produced as being superior in quality.

Assessing Processing Potential Barley must meet strict quality specifications in order to be acceptable for malting or for processing as a food (i.e., tea, pearling, and sho¯chu¯). The factors considered in selecting a barley for malting (Table 2) indicate how well the barley will

process in the malt house. Factors identify barley that takes up water at a quick and consistent rate, germinates in a uniform manner, and is capable of producing a final product of acceptable quality. Barley selected for barley tea or pearling must also show specific characteristics in order to ensure straightforward processing. Barley for pearling must have an appropriate endosperm texture to prevent kernel breakage, and kernel size must be uniform in order to ensure a consistent pearled product. Barley for tea must be of a desired variety and also show a consistent kernel size in order to produce a uniformly roasted end product. Similarly to malting barley, these characteristics are often ensured by offering varieties that are known to be acceptable to end users. Feed barley end users often demand barley with special processing characteristics. This is especially true when barley is rolled prior to feeding. Uniform size is essential if rolled barley is to be sufficiently cracked without production of excess fines.

Grading Specifications The determination of the grade or overall value of barley, be it for feed, food, or malt, is determined by evaluating a set of characteristics, or grading factors, which are directly related to the quality for a particular end use. The factors should be such that they can be accurately and uniformly measured. Some important grading factors for barley include the following:

• •

•

•

Table 2 Examples of grain characteristics that may be used in selecting barley for malting a

Characteristic

Desired quality

Protein level Barley variety

9–12% dry matter Locally recognized malting barley variety >98% >95% >300 s >130 stirring number Minimal (according to national standards)

Varietal purity Germination after 3 days Falling number Rapid Visco Analyzer Pesticide residues and mycotoxins a

Characteristics will vary among countries.

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•

Test weight: a measure of the grain density, test weight is an indication of the feeding value of the grain. High test weight barley will have a high percentage of large, plump kernels with a greater proportion of starch. Moisture content: high moisture content may result in spoilage, mold growth, and loss of viability during storage and transportation. On the other hand, if the kernels are too dry, they will peel and crack easily. Customers also generally prefer lower moisture content for economic reasons. Kernel size: large kernels are desirable for malting as potential for malt extract is directly associated with barley kernel size. Plump kernels contain more starch than thin ones. Uniformity of kernels also leads to better processing quality. Peeled and broken kernels: loose hulls and kernel damage affect the uniformity of water uptake of grain during steeping and increase the likelihood of damage to the grain during handling that could adversely affect the ability to germinate. Sprout damage: preharvest sprouting damage occurs when mature grain is exposed to rain or heavy dew prior to harvest. Mild to severely sprouted grain may still germinate but can lose viability over time, especially under poor storage conditions.

Factors that affect the overall appearance and cleanliness of the grain are also frequently assessed in order to determine the overall value. High-quality barley kernels should be bright, healthy, and fully matured. They should be free from disease, heat, and frost damage and not weathered or deeply stained.

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Also, the barley lot should be free of insects, large oil-bearing seeds, ergot, treated seeds, foreign material, and odor. Tolerances are set for individual grading factors based on an understanding of the effect of the presence of these factors on the end use quality. Specifications must not be arbitrary, but must be set to achieve a balance between ensuring good processability and not unnecessarily penalizing the producer. Examples of grade specifications for a number of exporting countries are listed in Tables 3–7. The parameters, as well as specifications for the parameters, vary among countries, reflecting differences in infrastructure, customers, and growing conditions.

Establishing Grades and Standards Assigning grading factors can be based on visual inspection or more objective instrumental testing. Factors such as maturity and weather damage are subjective visual determinations made in comparison with standard or guide samples. Examples of some visual grading factors for barley are shown in Figure 2. Levels of protein and moisture are typically measured using near-infrared technology. Automated agitators and screens are used to determine kernel size distribution, although imaging Table 3

technology can provide more information on size homogeneity. Imaging can also quantify damaged kernels, but this largely remains a visual task. Varietal purity can be determined using gel separation of proteins or deoxyribonucleic acid. Instrumental tests such as falling number and rapid viscoanalysis indicate any preharvest sprouting in a sample and thus its storability. However, a three-day germination test remains the only reliable method for ensuring a sample’s germination potential. The single-kernel characterization system is used to identify barley with appropriate endosperm texture for pearling and further processing. It can also determine the homogeneity of a sample with respect to size, weight, moisture, and protein. General appearance of a sample remains largely a visual process, but some countries are beginning to use machine-based imaging methods for quantifying grain color.

Specific Details for Some Major Barley-Exporting Countries Australia Australia is the leading malting barley exporter and one of the major feed barley exporters in the world (Table 8). Australia is

Some malt and feed grade specifications used at barley receival in Australia

Characteristic

Malting barley 1

Malting barley 3

Feed barley 1

Feed barley 2

Retention (% above 2.5 12.5 mm screen) Screenings (% below 2.2 12.5 mm screen) Test weight (kg hl 1) Moisture (%) Protein (%) Sprouted grains (per 100 grains) Skinned kernels (per 100 grains) Broken kernels (% weight per 100 grains) Other cereals (seeds per half liter) Wild oats (seeds per half liter)

>70.0 <7.0 65.0 12.5 <12.0 nil 15 2 85 25

>58.0 na 65.0 12.5 <12.8 nil 15 2 85 25

na 15.0 62.5 12.5 na nil na 5 500 50

na 25.0 60.0 12.5 na 5 na 5 1500 100

na, not applicable. Source: Data from Grain Trade Australia. www.graintrade.org.au.

Table 4

Grade specifications applied for top grades in each end use class used at grain intake points in Canada

Characteristic

Select malting (covered)a

Select malting (hull-less)a

Select food (covered)a

Select food (hull-less)a

No. 1 CW (general purpose)b

No. 2 CW (general purpose)b

Test weight (kg hl 1) Moisture (%) Broken kernels (% by weight) Adhered hulls (%) Ergot (% by weight) Frost damage (% by weight) Fusarium damage (% by weight) Heated seeds (% by weight) Stones (% by weight) Total foreign matter (% by weight)

na 13.5 na na 0.025 2.0 0.2 0.1 0.02 na

na 13.5 na 5.0 0.025 2.0 0.2 0.1 0.02 na

na 13.5 4.0 na 0.02 2.0 na 0.2 0.02 2.0

na 14.0 4.0 5.0 0.02 2.0 na 0.2 0.02 2.0

63.0 14.5 15.0 na 0.05 na 1.0 0.5 0.15 2.5

57.0 14.5 25.0 na 0.1 na 1.0 2.5 0.15 10.0

na, not applicable. a Specifications for two-rowed barley. b No distinction between two-rowed barley and six-rowed barley. Source: Data from Canadian Grain Commission. www.grainscanada.gc.ca.

GRAIN MARKETING AND GRADING | Barley: Grading and Marketing comparatively export-focused with 60% of the total crop exported annually. In a global perspective, Australia makes up over 30% of the world’s malting barley trade and 20% of the world’s feed barley trade. Barley Australia is the organization responsible for maintaining an accreditation system for malting barley varieties. Newly developed malting varieties must successfully complete 2 years of commercial-scale malting and pilot brewing evaluations. The performance data are evaluated by the Malting and Brewing Industry Barley Technical Committee (MBIBTC), comprising members of the domestic malting and brewing companies, who make the final recommendations for accreditation. While completely voluntary, accreditation testing is Table 5

Some of the EU intervention standards for feed barley

Characteristic

Feed barley

Test weight (kg hl 1) Moisture (%) Sprouted grains (% by weight) Broken kernels (% by weight) Overheated grain (% by weight) Other cereals (% by weight) Total foreign matter (% by weight)

62.0 14.5 6.0 5.0 3.0 5.0 12.0

Table 6 Grade specifications (used by buyers and sellers) of barley in Russia and Ukraine

Test weight (kg hl 1) Moisture (%) Other cereals (% by weight) Small seeds (% by weight) Total foreign matter (% by weight)

Barley for Barley 1 class Barley 2 brewing (malting) (fit for humans) class (feed) No limit 17.0 2.0

63.0 19.0 9.0

No limit 19.0 15.0

5.0

5.0

No limit

2.0

4.0

8.0

nonetheless essential for a variety to be accepted by the domestic brewing industry. Quality specifications used at delivery points, referred to as receival standards, for the various grades of feed and malting barley (Table 3) are set by industry associations such as Grain Trade Australia (GTA) in the eastern part of the country and also by the Grains Industry Association of Western Australia (GIWA). The standards are reviewed annually by a committee of industry representatives and circulated to industry for comment before they are adopted in the coming season. Much consolidation has occurred throughout the barley supply chain in Australia. The majority of marketing and bulk handling are conducted by a few large companies. Although barley receival and marketing activities once controlled by statutory STE are now completely deregulated, monopolies continue to exist, in some states, for the export of feed and malting barley.

Canada

Source: Data from European Commission. http://ec.europa.eu.

Characteristic

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Canada is the third-largest exporter of malting barley in the world and continues to export some amounts of feed barley but not to the extent it did in the past. A majority of barley production is used in the domestic feed industry. The Canadian Grain Commission (CGC) establishes grades and standards for Canadian barley based on a classification by end use. Barley is classified as malting, food, or generalpurpose end use, and classes are further subdivided into covered and hull-less types (Table 4). Eligibility for a variety to achieve malting grades is determined by mandatory performance testing as part of Canada’s strict variety registration system. Candidate cultivars must be tested for 3 years in a series of cooperative and collaborative trials alongside check cultivars representing the current standard of quality. Micromalting and pilot malting quality is reviewed by the Prairie Recommending Committee for Oats and Barley, composed of members from across the malting and brewing value chain. Only those varieties that are deemed equal or better to the checks are recommended for registration. In general, CGC grades are applied in international sales of Canadian feed barley. However, malting

Source: Data from GOST. www.gost.ru.

Table 7

Grade specifications used for some of the grades used in the United States

Characteristic

US no. 1 (malting)a

US no. 2 (malting)a

US no. 1 (feed)b

US no. 2 (feed)b

US no. 3 (feed)b

Screenings Test weight (kg hl 1)e Damaged kernels (% by weight) Peeled and broken kernels (% by weight) Wild oats (% by weight) Total foreign matter (% by weight)

<5.0c 64.3 na 5.0 1.0 0.5

<7.0c 61.8 na 7.0 1.0 1.0

<10.0d 60.5 2.0 4.0f na 1.0

<15.0d 57.9 4.0 8.0f na 2.0

<25.0d 55.3 6.0 12.0f na 3.0

na, not applicable a Specifications for two-rowed barley. b No distinction between two-rowed barley and six-rowed barley. c Through a 2.18 19.05 mm screen. d Through a 1.98 19.05 mm screen. e Based on the Winchester bushel weight 1.287. f Broken only. Source: Data from Federal Grain Inspection Service. www.gipsa.usda.gov.

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(a)

(b)

(c)

(d)

(e)

(f)

Figure 2 Examples of visual grading factors for barley: (a) heated; (b) peeled; (c) smut; (d) fusarium; (e) frost; (f) sprouted. Table 8 World exports (million tonnes) of feed and malting barley by country (2009–2018) Feed barley Averages 2009–2013 Australia Canada European Union Russia Ukraine The United States Others World total

Malting barley Projections 2018

Averages 2009–2013

Projections 2018

3.0 0.6 2.8

2.9 0.8 2.7

1.3 0.8 0.9

1.5 1.2 1.0

2.3 3.1 0.6

2.7 3.6 0.1

0.0 0.0 0.7

0.0 0.0 0.2

1.5 13.9

2.6 15.4

0.2 3.9

0.8 4.7

Source: Data from International Grains Council. www.igc.int.

barley exports are normally sold according to individual contract specifications as agreed with international buyers. The Canadian Malting Barley Technical Centre produces a listing each year that indicates which registered malting varieties have established markets based on market signals and feedback from malting and grain companies. This information helps seed companies, seed growers, and producers in deciding which varieties to supply and grow in the coming year. Since the mid-1940s, barley was marketed in Canada through the Canadian Wheat Board (CWB), a statutory STE

with marketing monopoly on export and domestic sales of malting and food barley, as well as exports for feed use. The objectives of the CWB were to provide income protection for farmers by price pooling and establishing a governmentguaranteed floor price. Under the CWB model, producers delivered their barley into a pool (based on end use and grade) and received a partial initial payment on delivery. The single-desk seller sold the barley on the domestic or export market, and revenues from the pooled sales were returned to the producers via interim and final payments after shipping and marketing costs had been deducted. In 2011, legislation was passed to remove the CWB’s singledesk powers through the ‘Marketing Freedom for Grain Farmers Act,’ which became effective on 1 August 2012. This act established a completely open market, allowing producers to sell their barley directly to any number of grain companies or processers, including the CWB, which continues to offer a voluntary pooling system for those farmers wishing to use it, as well as a variety of cash contract options.

European Union The European Union (EU) is the second-largest exporter of malting barley in the world and the third-leading exporter of feed barley. Barley-exporting countries within the EU enjoy competitive freight costs and logistical advantage to markets in the Middle East and North Africa. However, the dominant position in the international market is under pressure from increased competition from Russia and Ukraine. Feed barley and malting barley are traded on a private basis in the EU. Open-market barley trades freely and finds its own

GRAIN MARKETING AND GRADING | Barley: Grading and Marketing price level on the domestic market as in most other countries. Historically, support programs guaranteed prices and stimulated production, while export subsidy programs gave EU barley a competitive price advantage against other countries. EU legislation also allows the EU to intervene in markets by purchasing grains from farmers at a guaranteed floor price as a market of last resort. However, recent shifts in policy have reduced these types of market interventions that could cause acreage to shift to other, more profitable crops and reduce stocks available for export. The EU has a common set of minimum standards for feed barley (Table 5) that are applied to domestic intervention purchases as well as for all exports, either from intervention stocks or from the free market.

Russia/Ukraine In recent years, Russia and Ukraine have emerged as significant exporters of feed barley, capturing nearly 40% of the world feed barley market. Barley is marketed in an open market-type system, with the export of barley being handled by the private trade, although the state does intervene in the market from time to time through the use of border measures, placing export restrictions when domestic supplies drop due to production deficits. For internal trade, the State Committee of the Russian Federation for Standardization and Metrology (GOST) establishes grades for barley. Sellers and buyers conduct trade according to GOST standards (Table 6). Product specifications are analyzed and certified by the State Grain Inspectorate. Exports are made on the basis of contract specifications negotiated between buyer and seller and agreed in the sales contract. Specifications are certified by the State Grain Inspectorate.

The United States The United States is a consistent exporter of feed barley. It also exports small quantities of malting barley. The American Malting Barley Association (AMBA) coordinates testing of new malting barley varieties and produces a recommended variety listing. Candidate varieties are subjected to 2 years of pilot malting and brewing trials, followed by commercial plant-scale testing by AMBA’s member malting and brewing companies, with only those lines receiving successful ratings being added to the list. The list guides growers as to which varieties the industry is prepared to process and is also used by federal agencies to distinguish between malting and feed varieties when administering farm income stabilization programs and for crop insurance purposes. In the United States, the Federal Grain Inspection Service (FGIS), a division of the Grain Inspection, Packers and Stockyards Administration (GIPSA), is responsible for grade analysis and, in consultation with industry, the setting of standards (Table 7) for barley. Official inspection and weighing of the US barley is mandatory for export but not for domestic commerce. Inspection services, or official grade analysis, can be performed by private agencies that have been licensed by the FGIS. The US barley is marketed under an open-market system. Various private traders compete for supplies of barley and for export business. Prices paid to producers are determined at the

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intake point and are based on a series of discounts determined from quality analysis of the delivered barley. The majority of malting barley is now production contracted by maltsters and brewers who often specify their own barley varieties.

Specific Details for Some Major Barley-Importing Countries China (Malting Barley Imports) Due to rapid increases in beer consumption, China’s demand for malting barley has been growing steadily, with annual barley consumption exceeding 4 Mt. To meet domestic demand, China imports over 2 Mt of barley per year, mostly from Australia and Canada. Until the mid-1990s, all malting barley imports were done through an STE, the China National Cereals, Oils and Foodstuffs Import and Export Corporation (COFCO). Recently, imports have been liberalized, and now, end users and local trading companies from China are free to import barley directly and to conclude their own contracts, in terms of both price and quality. The State General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) of the People’s Republic of China verifies the quality of all imported barley. Only barley imports with an AQSIQ certificate are released for distribution.

Japan Japan is a major barley importer in the world market. Annual consumption of barley is estimated to be around 1.6 Mt. Approximately 80% of imported barley is used for feed in the production of compound and mixed feed for the cattle sector. It is particularly important in feeding beef cattle because it produces high-quality beef with the white marbling that Japanese consumers favor. For this use, barley is steam-rolled before feeding. Feed barley is also milled into compound feeds for other livestock such as dairy. The main nonfeed use for barley is the production of beer and sho¯chu¯. Other uses include miso (soybean paste) production and barley tea. Japan is one of the few countries in the world that still retain STE, the Japanese Food Agency (JFA), with monopoly powers for buying and importing barley. The JFA is responsible for purchase and distribution of barley, for both human consumption and animal consumption. The JFA conducts regular calls for tenders from supplying countries. Tenders are usually based on the official standard quality grades used in the country of origin, which are familiar to the sellers and the JFA. The JFA does its own testing to verify the quality of all delivered barley. Imports from tenders go into the JFA’s stock and are distributed to domestic end users at agreed prices. In this system, there are no negotiations, with respect to price or quality specifications, between individual end users from Japan and international traders. However, in recent years, the JFA has allowed for simultaneous buying and selling (SBS). Although the JFA still administers them, SBS purchases allow for individual negotiations between Japanese end users and international traders. Each year, the JFA approves the total tonnage of grain that can be imported under the SBS system.

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Saudi Arabia (Feed Barley Imports) Saudi Arabia is the leading feed barley-importing country in the world. Typically, the majority of the barley that is imported is fed as whole barley to sheep, goats, and camels by Bedouins. Saudi barley imports are controlled through the Saudi Grain and Fodder Company (SGFC), which acts as the government agent. The major parameter for selling barley into Saudi Arabia is a competitive price.

See also: Barley, Rice and Maize Processing: Barley: Milling and Processing; Barley: Malting; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Grain Marketing and Grading: Identification of Varieties of Food Grains; Wheat: Grading and Segregation; Wheat: Marketing; Non-food Products from Grains: Cereal Grains as Animal Feed.


• • • • •

What are the three primary end uses for barley? Which are the major barley-exporting countries? What are the advantages of (a) production contracts and (b) price pooling? Why are grades necessary for successful marketing of barley? List some important grading factors for barley.


• •

Select several degrading factors for malting barley and describe the detrimental effects of their presence on the final product quality of malt or beer. What are the effects of increasing globalization, international trade and marketing of barley and other grain crops? Specific aspects to consider could include corporate mergers, industry integration, and trade agreements.

www.fao.org – United Nations Food and Agriculture Organization. http://www1.agric.gov.ab.ca – Alberta Agriculture, Food and Rural Development. Introduction to Grain Contracting. Canadian International Grains Institute (1993) Grains and Oilseeds: Handling, Marketing, Processing, 4th edn. Winnipeg, MB: Canadian International Grains Institute, Vol. 1. MacGregor AW and Bhatty RS (eds.) (1993) Barley Chemistry and Technology. St. Paul, MN: American Association of Cereal Chemists. Boland MA and Bresler GW (2006) Vertical integration in the malting barley industry. Review of Agricultural Economics 28(2): 272–282. Newman CW and Newman RK (2006) A brief history of barley foods. Cereal Foods World 51: 4–7. www.fda.gov – United States Food and Drug Administration. www.hc-sc.gc.ca – Health Canada. Ullrich S (2012) Barley: Production, Improvement and Uses. Ames, IA: Wiley Blackwell. Delwiche SR (2010) Analysis of grain quality at receival. In: Wrigley CW and Batey IL (eds.) Cereal Grains: Assessing and Managing Quality. Boca Raton, FL: CRC Press. www.barleyaustralia.com.au – Barley Australia. www.graintrade.org.au – Grain Trade Australia. www.grainscanada.gc.ca – Canadian Grain Commission. Beckkerman A, Schweizer H, and Smith V (2013) Impacts of the Canadian Wheat Board Ruling on the North American Malt Barley Markets. Proceedings of the Annual Meeting of the Agricultural and Applied Economics. 4–6 August. Washington DC, USA. www.gost.ru – State Committee of the Russian Federation for Standardization and Metrology. www.usda.gov – United States Department of Agriculture.

Soybean: Grading and Marketing EG Hammond, LA Johnson, and PA Murphy, Iowa State University, Ames, IA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic highlights:

• • •

Soybean is high in protein, oil and isoflavones, all of which contribute to its value and use Proximate analyses have been developed for the major components of soybean Grading standards, which reflect criteria for test weight and other physical attributes of the kernel, are essential to support marketing and trade.

Learning Objectives:

• • •

To understand the composition of the soybean, particularly for protein, oil and isoflavones. To understand proximate analysis of soybean To be familiar with US grading standards for soybean

Introduction Soybeans vary widely in their appearance and composition. The main constituents of soybeans, in descending order, are protein, oil, complex carbohydrates, oligosaccharides, simple sugars, and minerals. Phytochemicals in soybeans have gained prominence since the 1990s, especially isoflavones, saponins, and phenolic acids because of their potential health-protective effects. Soy isoflavones in particular have been associated with a variety of other improved physiological states, including reduced cholesterol levels, anticarcinogenicity, and improved bone health. Most legumes contain 20–25% protein, but soybeans typically contain 30–45% protein (moisture-free basis), and average 35% at 13% moisture. Protein-content levels as high as 55% (moisture-free basis) have been observed. The oil content typically ranges from 15 to 24% and averages about 20% on a 13% moisture basis. The composition varies with growing area, for example soybeans from northern and mid-western areas of the United States typically contain 1.5–2% less protein and 0.2% more oil than beans grown in southern states. One Iowa soybean processor has begun offering premiums for soybeans containing higher than normal oil contents. The total crude fiber content of soybeans is 4.4% at 13% moisture. These materials are predominantly cellulose, hemicellulose, and pectin. The outer hull, typically 8% by weight of the bean, is especially rich in crude fiber (35%). Fiber is hard to digest and contributes little to the nutrition of swine and poultry, the primary markets for soybean meal. The total sugar content of soybeans is 4.9–9.5% at 13% moisture. Of the total sugar content, 60% is sucrose, 10% raffinose, and 30% stachyose. Raffinose and stachyose are oligosaccharides and cause flatulence (intestinal gas) in humans and reduced feed-efficiency in livestock. One seed


company has recently developed a soybean line that is low in oligosaccharide content and high in sucrose content. Isoflavone content of soybeans varies from 800–4000 mg g1 on aglycon basis. Soybeans contains 12 isoflavones, namely genistein, daidzein and glycitein, as b-glucosides, 600 -O-malonylglucosides, 600 -O-acetylglucosides, and aglycons. Soy saponin concentrations vary in a similar manner to isoflavones ranging from 2–12 mmol g1. Because of the variety of glucoside forms of saponins and isoflavones, their concentrations should be expressed in mmol. The isoflavones and saponins fractionate with the seed protein and are not lipid-soluble. As soybeans are fractionated into food ingredients, the forms of the isoflavones and saponins are rearranged depending on the extent of heat processing and the method of protein fractionation. Generally, soybean meal is sold on a 44% protein basis and 48% when soybeans are de-hulled (Hi-Pro meal). The average price of soybeans during the 1997–98 crop year was $6.47 per bushel. Oil sells for 2 times the value of meal. Typical selling prices for soybean oil were 25.7 cents per pound and for meal (44% protein) were $197 per tonne (t) or 9.9 cents per pound during 1998. In 2002, crop year prices were considerably lower. Recent developments in breeding and genetic modification of soybeans have achieved: new fatty acid compositions, e.g., <2% linolenic acid and >80% oleic acid to improve oxidative stability; removal of all lipoxygenase isozymes to improve the flavor of soy protein ingredients; elimination of oligosaccharides to eliminate intestinal gas; altered protein and amino acid composition to improve functional and nutritional properties; and inserted vaccines for human and animal health. While genetic engineering holds great promise for the future (healthier foods, reduced environmental impacts, increased yield, lower input costs, etc.), consumers have begun to question the safety of this new technology.

Proteins Glycinin and b-conglycinin comprise 65–80% of the protein fraction or 25–35% of the seed weight. Glycinin is classified as a legumin, which is characterized by molecular weights of 300–400 kDa and sedimentation coefficients of 11S 1S. b-Conglycinin is a vicilin, which is in the range 150–250 kDa, glycosylated and has sedimentation coefficients of 7S 0.5S. In soybeans, the major proteins, glycinin and b-conglycinin, are frequently described by their respective sedimentation values, 11S and 7S, but such fractions often are impure. The 7S fraction of soy protein contains, in addition to b-conglycinin, lectins, lipoxygenase, and b-amylase. b-Conglycinin is a trimer and/or hexamer in solution and probably occurs in both forms in the seed. Two similar peptides, a and a0 (57 kDa), and a glycosylated b-peptide (42 kDa) are assembled in the mature protein in a nonrandom set of seven forms, a0 b2, ab2, a a0 b, a2b, a2 a0 , a3, and b3 with

http://dx.doi.org/10.1016/B978-0-12-394437-5.00174-1

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GRAIN MARKETING AND GRADING | Soybean: Grading and Marketing

molecular weights of 125–171 kDa. The a and a0 subunits have 1–2 mol cysteine/mole peptide while the b-peptide has no cysteine. The health benefits of consuming soy protein are attributed primarily to b-conglycinin. Glycinin is a hexamer, although older literature calls it a dodecamer. It is composed of six nonrandomly paired acidic and basic peptides. The acidic peptides have molecular weights of 44, 37, and 10 kDa; the basic peptides are 20 kDa. The acidic–basic (AB) pairs have been identified in the experimental line, CX635-1-1-1, and are shown in Table 1. Seven acidic and eight basic peptides have been identified in 18 cultivars. There appear to be sulfur-rich and -poor AB pairs. Soybeans contain two main classes of protease inhibitors or trypsin inhibitors (TI), although there appear to be many isogenic variants. The principal two classes are the Kunitz inhibitor with MW of 21 500 and the Bowman-Birk inhibitor with MW of 8000. The Kunitz inhibitor acts only on trypsin while the Bowman-Birk protein inhibits both trypsin and chymotrypsin. Moist heat treatment denatures 90% of the TI activity with the residual being heat stable. TI affects animals of guinea-pig-size and smaller but has little effect on larger animals, except for weanling pigs. Recently, Bowman-Birk TI has been demonstrated to be an anticarcinogen and is currently in Phase II cancer trials. There are reports that TIs exert a carcinogenic effect on rodents. There has been interest in recovering and purifying soybean protease inhibitors to treat AIDS patients. The Food and Drug Administration of the United States has approved a health claim for soy protein that as part of a heart healthy diet 25 g per day of soy protein will contribute to improved cardiovascular health.

Lipids Soybean lipids contain 2–5% phospholipids, depending on the growing conditions, and 1.6% unsaponifiables. The balance is chiefly triacylglycerols. Oleic (18:1), linoleic (18:2), palmitic (16:0), stearic (18:0), and linolenic (18:3) acids are present in soybean oil along with traces (less than 1%) of myristic (14:0), palmitoleic (16:1), heptadecanoic (17:0), eicosenoic (20:1), arachidic (20:0), behenic (22:0), and erucic (22:1) acids. The range of the acyl groups present in soybean oil has been extended by mutation breeding and selection to the values reported in Table 2. The acyl groups are distributed asymmetrically in the triacylglycerols with all the saturates on the sn-1 and -3 positions Table 1

Glycinin acidic–basic complexes from CX635-1-1-1

AB-complex

S-amino acids

Molecular weight(kDa)

A1aB2 A1bB1b A2B1a A3B4 A5A4B3

14 12 14 9 3

57 57 57 62 67

Data from Nielsen (1985) Structure of soy proteins. In: Altschul AM and Wilcke HL (eds.) New Protein Foods, vol. 5. Seed Storage Proteins, pp. 27–64. New York: Academic Press.

and linoleate concentrated on the sn-2 position. Generally, the sn-1 contains more palmitate and stearate than sn-3, and the oleate is enriched on sn-3. Phospholipids contain the same acyl groups found in the triacylglycerols, but the concentration of palmitate is generally higher and oleate lower. Phosphatidyl choline (50%), ethanolamine (26%), and inositol (18%) are the chief phospholipid components along with lower concentrations of phosphatidic acid and phosphatidyl serine. The unsaponifiables contain sterols, hydrocarbons, and tocopherols. The chief sterols (3.5 mg g1 oil) are b-sitosterol, campesterol, and stigmasterol. The tocopherols ( 1.25 mg g1 oil) are typically more than 70% gamma with smaller amounts of delta, and alpha.

Methods to Measure Composition Proximate analyses for moisture, protein, crude free fat, crude fiber, ash, and total carbohydrate have been adopted by the American Oil Chemists’ Society, the American Association of Cereal Chemists, and the Association of Analytical Chemists. All composition values for soybeans are reported either on a moisture-free basis or at 13% moisture. Several methods are acceptable for moisture determination, but the most widely used procedure involves measuring the weight loss when drying the ground sample for 3 h at 130 C. Protein is estimated from Kjeldahl nitrogen. The nitrogen content is multiplied by a factor of 6.25 to convert to protein values despite the major soy protein, glycinin containing only 17.5% nitrogen (equivalent to a N conversion factor of 5.7). Oil content is determined as crude fat by continuously extracting dried ground samples with petroleum ether for 5 h. Total fat, which includes bound fat as well as free fat, requires acid hydrolysis of the sample prior to extraction. In recent years, the use of near-infrared reflectance (NIR) and transmittance (NIT) has become widespread for rapid estimation of grain composition, especially moisture, protein, and oil. These spectrophotometers must be calibrated against the standard wet chemical methods described above. Moisture is also routinely measured by electrical capacitance. Crude fiber is measured as the weight loss on incineration of the oven-dried residue remaining after digestion of the sample with boiling dilute sulfuric acid followed by boiling dilute sodium hydroxide. Ash is primarily composed of noncombustible minerals and is determined by heating the ground sample in a muffle Table 2 The range of acyl group percentages produced in soybean lipids by mutation breeding and genetic engineering, and the composition of a typical unselected variety

Palmitate Stearate Oleate Linoleate Linolenate

Range

Typical value

3.5–30 2.5–32 8.0–85 2.0–60 1.8–13

10 4 26 52 8

Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd Edition (2003), p. 5390, Elsevier Ltd.

GRAIN MARKETING AND GRADING | Soybean: Grading and Marketing furnace for 2 h at 600 C. Soybeans contain 4.7% ash at 13% moisture.Total carbohydrate is often estimated as the difference after subtracting other constituents. This method does not discriminate between oligosaccharides and other sugars, and it often gives inflated values. Sugars can be extracted with hot aqueous ethanol and quantified by gas or liquid chromatography. Acyl group composition of soybean lipids is generally determined by gas chromatography. Lipid classes are separated by thin-layer or liquid chromatograms. Qualitative and quantitative analyses of the individual proteins have been performed by immunoelectrophoresis and/or SDS polyacrylamide electrophoresis. Isoflavones are assayed by reverse-phase (RP) HPLC of 80% acetonitrile extracts and absorbance detection at 250–260 nm. Methanol and ethanol tend to underextract some isoflavone forms. Saponin analysis is typically by RP-HPLC with absorbance detection at 290 and 205 nm, depending on form, although older methods used silica-based TLC. The major impediment to accuracy has been the lack of suitable standards, although most of the isoflavone forms are now available.

Grading Standards The Federal Grain Inspection Service (FGIS) for the United States has established grading standards for soybeans (Table 3) to facilitate marketing and trade. Much more detail than can be provided here is available at the FGIS website http://www. usda.gov/gipsa/reference-library/brochures/soyinspection.pdf. Soybeans are divided into two classes based on color: yellow soybeans and mixed soybeans. Each class is divided into four numerical grades (US No. 1, 2, 3, and 4) and a US Sample Grade those soybeans, which do not meet the requirements of any of the numerical grades. Special grades (e.g., garlicky and infested) are provided to emphasize special qualities affecting the value, and are added to and made part of the grade designation. Six factors are considered in assessing grade designation: test weight, heat damage, total damage, foreign material, splits, and soybeans of other colors. Although moisture, protein, and oil contents are not part of the official grading standards and do not affect numerical grade, they may be specified on contracts in some markets. NIT is used for rapid estimation of moisture, protein, and oil contents. Test weight, which is the weight in pounds of grain per Winchester bushel (35.2 l), is determined on a 1 quart (1.18 l) sample before removing foreign material using an Table 3

27

official test weight apparatus. If the test weight is extremely low, the soybeans may contain less oil. All other factors are measured as percentages of total sample weight. Foreign material is determined by sieving and is all matter, including soybeans and soybean pieces that readily pass through an 8/64-inch (3.2 mm) round-hole sieve and all matter other than soybeans remaining on the sieve after sieving. Foreign matter (other grains, weed seeds, pods, leaves, stems, etc.) reduces oil and protein contents and storage life. Splits are soybeans with more than one-fourth of the bean removed and which are not damaged, and are determined by sieving a portion of the grain after removing foreign material. Splits, which result from mechanical damage during handling and overdrying, reduce storage life and oil yield, and increase losses during oil refining. Damaged kernels are soybeans and soybean pieces, which are badly damaged by the ground, weather, frost, heat, insects (stinkbug-stung kernels only are counted at one-fourth the actual percentage), mold, or sprouting, and are determined by hand-picking after removing foreign material. Damaged kernels reduce storage life and oil yield, adversely affect oil color, and increase refining loss. Soybeans of other colors are those, which have green, black, brown, or multiple colors. These soybeans may affect oil color by contributing undesirable pigments. During the 2002 crop year, almost 27 million tonnes (Mt) of soybeans were exported from the United States. Of that amount, 4.8% was US No. 1, 94.6% was US No.2, 0.4% was US No. 3, and 0.1% was US No. 4. By comparison with Brazilian soybeans, US soybeans are typically slightly lower in oil content (6 year average of 1.2% lower oil content) but are lower in foreign matter, damage, free fatty acid (free fatty acid increase oil-refining loss) and moisture contents, and are higher in test weight. Grading standards are similar between countries of origin, but differ in some details. For instance, Brazil and Argentina have an export grade for soybeans, Grade No. 1, which limits foreign matter to 1%. Brazilian grades specify a maximum of 14% moisture but Argentina, a maximum of 13%. The moisture content normally regarded as safe for long-term storage is 13%. The Mexican system does not consider test weight as a grading factor but does consider oil acid value (a measure of free fatty acid content). Entirely different criteria are used for grading food-grade soybeans destined for soymilk and tofu. Typically, individual purchasers establish their own criteria often including seed size, seedcoat color, number of hard beans (germination or soaking test), total sugar, oil peroxide value or thiobarbituric acid test (measures of oil oxidation), acid value, protein dispersibility or solubility. Organic

Official grades and grade requirements of the Federal Grain Inspection Service, United States Department of Agriculture

US sample grade

Minimum test weight per bu. (lbs)

US No. 1 US No. 2 US No. 3 US No. 4

56.0 54.0 52.0 49.0

Damaged kernels

Maximum limits

Heat damaged (%)

Total (%)

Foreign material (%)

Splits (%)

Soybeans of other colors (%)

0.2 0.5 1.0 3.0

2.0 3.0 5.0 8.0

1.0 2.0 3.0 5.0

10.0 20.0 30.0 40.0

1.0 2.0 5.0 10.0

Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd Edition (2003), p. 5391, Elsevier Ltd.

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GRAIN MARKETING AND GRADING | Soybean: Grading and Marketing

production or genetically modified free soybeans may also be criteria for food-grade soybeans.


• • •

Describe the protein and lipid composition of soybean How is soybean composition and quality measured? What is the significance of isoflavones in soybean?


• • •

What are the grading standards for soybean in different countries? How do they differ, and why? How can sellers and buyers establish contract specifications for nutritionally enhanced or specialty soybeans? Should grading standards be updated, and if so why and how?

See also: Breeding of Grains: Soybean: Germplasm, Breeding, and Genetics; Fats: Lipid Chemistry; Food Grains and Well-being: Nutrition: Soy-Based Foods; Non-wheat Foods: Soybean: SoyBased Fermented Foods; Oilseed and Legume Processing: Soybean: Soy Concentrates and Isolates.

Further Reading Beecher GR, Holden J, Bhagwat S, Haytowitz D, and Murphy PA (1999) USDA-Iowa State University Isoflavone Database. http://www.nal.usda.gov.

Brumm TJ and Hurburgh CR (1990) Estimating the processed value of soybeans. Journal of the American Oil Chemists’ Society 67: 302–307. Erickson DR (ed.) (1995) Practical Handbook of Soybean Processing and Utilization. Champaign, IL: American Oil Chemists Society. Erickson DR, Pryde EH, Brekke OL, Mounts T, and Falb RA (eds.) (1980) Handbook of Soy Oil Processing and Utilization. Champaign, IL: American Oil Chemists Society. FGIS (1990) Federal Grain Inspection Handbook, Book II. Washington, DC: Federal Grain Inspection Service. Hammond EG (2000) Genetic alteration of food fats and oils. In: Chow CK (ed.) Fatty Acids in Foods and Their Health Implications, 2nd edn. New York: Marcel Dekker. Hurburgh CR, Brumm TJ, Quin JM, and Hartwig RA (1990) Protein and oil patterns in the US and world soybean markets. Journal of the American Oil Chemists’ Society 67: 966–973. Murphy PA, Song TT, Buseman G, et al. (1999) Isoflavones in retail and institutional soy foods. Journal of Agricultural and Food Chemistry 47: 2697–2704. Nielsen NC (1985) Structure of soy proteins. In: Altschul AM and Wilcke HL (eds.) New Protein Foods. Seed Storage Proteins, vol. 5, pp. 27–64. New York: Academic Press. Smith AK and Circle SJ (1978) Chemical composition of the seed. In: Smith AK and Circle SJ (eds.) Soybeans: Chemistry and Technology. Proteins, vol. 1, pp. 61–92. Westport CN: AVI Publishing. USDA (1999) US department of agriculture, economic research service. In: Golbitz P (ed.) Soy and Oilseed Bluebook. Bar Harbor, ME: Soytech. Wang HJ and Murphy PA (1996) Mass balance study of isoflavones during soybean processing. Journal of Agricultural and Food Chemistry 44: 2377–2383. Wu SW, Murphy PA, Johnson LA, Fratzke AR, and Reuber MA (1999) Pilot plant fractionation of soybean glycinin and b-conglycinin. Journal of the American Oil Chemists’ Society 76: 285–293.

Relevant Websites nal.usda.gov http://www.nal.usda.gov – USDA-Iowa State University Isoflavone Database. usda.gov http://www.usda.gov – US Soybean Inspection.

Identification of Varieties of Food Grains DM Miskelly, Westcott Consultants P/L, Goulburn, NSW, Australia CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • •

Varietal identification may be required at various stages of the grain chain, namely, during breeding, during pure-seed production, during on-farm seed production, at grain receival after harvest, and during processing. The identification of varieties is also needed for enforcing plant breeders’ rights – the system by which royalties are provided to breeding companies. Distinctions may be made based on differences in the shapes and colors of parts of the plants and grain, for example, the glumes of the wheat head and the aleurone color of barley grain. More definitive distinctions are provided by laboratory methods, although these may need to be performed in a regional or central laboratory. The phenol test provides efficient distinction of individual grains in a large number, but there are only three or four different categories of reaction. The most popular method at present involves the analysis of protein composition, usually by gel electrophoresis. Microfluidic capillary electrophoresis (‘lab-on-a-chip’) offers a fast methodology using portable equipment that can be deployed in a field situation. DNA-based methods are showing their extensive ability to provide excellent distinction, including the ability to indicate the proportions of varieties in a mixed sample using a milled sample. The interpretation of results is a critical aspect of varietal identification, so that the statistical significance is fully appreciated when analyzing mixed samples.

Learning Objectives To achieve understanding of

• • •

the need for varietal identification in various situations and the methods that are best suited to those needs; the range of methods of varietal identification and the advantages/disadvantages of each; how to determine the most suitable methods, depending on the degree of definition required, the cost justification, and the expertise and equipment available.

Introduction The need to identify varieties and species of grain samples arises because they may be significantly different in their genetic traits with respect to grain-quality attributes, for example, suitability for a specific type of processing, and according to their agronomic potential, for example, resistance to


pathogens. Therefore, it is important that there should be adequate means available to permit distinction to be made between these various genotypes (genetically different forms). This article summarizes the range of methods in use and under development for routine identification of grain varieties.

Variety Identification Situations The need for variety identification arises at all stages of the value chain in the following scenarios:

•

• •

• •

A farmer has chalked variety names on a few bins of seed stored for the next season, but the rain has washed the names off. In this case, the task is primarily the verification of identity: the variety names are known but are mixed. Grain samples can be sent to a central laboratory. A pure-seed merchant needs proof of varietal identity before sale of seed. Grain consignments received at a silo, mill, or elevator are often required to be one of a small set of selected varieties to receive premium payment. Verification of identity is needed, preferably ‘on the spot’ before the delivered grain is binned with other deliveries of the same quality type. In this case, the need for assurance of similar quality type may be more important than knowledge of actual variety. On the other hand, verification of varietal identity is important for the implementation of plant breeders’ rights (PBR) in regions where the royalties are based on the amounts of grain delivered for the protected varieties. A grain processor may have difficulty in production. If there is doubt about the quality type of the grain being processed, a check on varietal content may help to elucidate the source of the problem. The samples to be analyzed may already have been milled into meal or flour.

Variety identification is especially needed for wheat, because of the wide range of quality types available. The examples in Table 1 include two hard-wheat varieties suited to conventional bread production (Marquis and Gabo) and a soft wheat (Rosella), whose weaker dough properties make it suitable for making cookies and cakes. The varieties Marquis and Gabo are very old wheats, now superseded by varieties with better resistance to rust and superior yield potential. Furthermore, these two wheats themselves are examples of families of wheats adapted to very different growth environments, namely, spring sowing after the winter of the Canadian prairies (Marquis) versus the moderate climate of the wheat belt in northern New South Wales, Australia. These three examples, all of the same genus and species, must in turn be distinguished from durum wheat, which is a different species, suited specifically to the manufacture of pasta products. These wheats are marketed in different classes, which, depending on supply,

http://dx.doi.org/10.1016/B978-0-12-394437-5.00175-3

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GRAIN MARKETING AND GRADING | Identification of Varieties of Food Grains

Table 1

Examples of different species and varieties of grain for which distinction may be required

Common name

Genus and species

Bread wheat Bread wheat Bread wheat Durum wheat Malting barley Feed barley

Triticum aestivum Triticum aestivum Triticum aestivum Triticum turgidum Hordeum vulgare Hordeum vulgare Zea mays Brassica napus Oryza sativa

Maize Canola Rice

Variety (date of release)

Characteristics

Marquis (1911): at least two biotypes Gabo (1945)

A hard red spring wheat of good bread-making quality adapted to the Canadian prairies A good baking white-grained wheat adapted to the Australian prime-hard region

Rosella (1986)

An Australian soft white wheat suited to biscuit manufacture

Tamaroi (1998)

A very hard grain, suited for pasta manufacture

Clipper (1968)

A two-row barley, grown in Australia for malting purposes

Cape (from South Africa, about 1900) StarLink (1998) Stellar (1987)

A very old six-row variety, not suitable for malting, once grown in Australia for animal feed Feed maize, genetically modified to provide herbicide resistance Low linoleic acid content rapeseed, bred in Canada. Had improved oil processing qualities and shelf life Jasmine rice developed in Thailand from indigenous aromatic rice varieties

Kao Dok Mali 105 (KDM105) (1959)

Archer... Prior Prior A

Clipper

Proctor

Cutter

Kwan

Figure 1 Pedigree chart of two malting barley varieties, illustrating their descent from a cross between Proctor and Prior A, which in turn came from the earlier cross (Prior Kwan) and selection from Archer.

demand, and quality, can have quite different financial values in wheat trade. Major wheat-exporting countries maintain variety-designation lists or variety master lists to indicate the varieties eligible for inclusion in specific classes (e.g., see http:// www.grainscanada.gc.ca; http://www.wheatquality.com.au).

Historical Background Variety identification often involves the need to make subtle distinctions among plants or grain samples of similar appearance. The need for such distinctions has arisen since the early twentieth century as a result of the efforts of plant breeders to produce genotypes suited for specific niches of agronomy, climate, and quality type. At the turn of the twentieth century, there was poor knowledge about distinctions between genotypes within grain species. Seed for sowing may have contained a range of genotypes, due to poor attention to the need to select at least for uniformity of plant and grain appearance. Mixtures of seed types also arose as a result of neglect in failing to keep different types separate. Early attempts to produce improved varieties involved the selection of superior plants from an otherwise varied crop, to permit the separate propagation of genotypes that showed, for example, well-filled heads or resistance to pathogen attack. Improvement by selection is illustrated in Figure 1, by the selection of the malting barley Prior (released in Australia in about 1900) from the traditional English barley Archer. Individual farmers often practiced this approach, passing on their

improved variety to neighbors and selling the seed on a wider scale. The introduction of cross-pollination, a century or so ago, greatly increased the genetic diversity from which to select improved genotypes.

Varieties and Other Taxonomic Levels Crossbreeding is illustrated in Figure 1 by the production of two Australian malting barleys, Clipper and Cutter, released, respectively, in 1968 and 1975. They are ‘sister lines,’ being separate selections from the same cross, involving an old English variety Proctor (named in 1952) and Prior A, from the cross between the varieties Kwan and Prior. The task of distinguishing between these sister lines would be expected to be more difficult than making a distinction between either of them and, for example, the unrelated variety Cape (Table 1). Even more evident, of course, is the difference between any of these barleys and representatives of a distinct species or genus, for example, wheat (genus Triticum) or maize (genus Zea; Table 1). The practice of finally selecting a variety for registration often involves taking several plants from an advanced line many generations from the original cross. The combinations of genes in these lines are thus ‘fixed’ (homozygous, of stable genotype), but the grains from these plants may differ from one another in subtle ways, although they are uniform in appearance as plants. Subsequent analysis of individual grains by sensitive methods of variety identification may provide a distinction between these component genotypes (termed ‘biotypes’), although all are authentic parts of the same variety. For example, gel electrophoresis of the grain proteins of the wheat Marquis (Table 1) has shown that there are distinct biotypes; one of these, Marquis K, has been suggested as a standard sample for electrophoretic identification. The term ‘cultivar’ has been used to indicate a homogeneous population of plants of common pedigree, which breeds true. The word is loosely used as being equivalent to the term ‘variety,’ but, in theory, ‘cultivar’ refers mainly to plants having

GRAIN MARKETING AND GRADING | Identification of Varieties of Food Grains a single phenotype, whereas the term ‘variety’ is slightly less restrictive. Nevertheless, common usage continues with the term ‘variety,’ and it is adopted throughout this article. Recent years have seen a further breakthrough in breeding technologies, involving the use of genetic modification (GM) to introduce genes from species unrelated to the target genotype. An example is the maize variety StarLink (Table 1). The need for ‘identity preservation’ of GM varieties in some regions adds to the need for variety identification, so that such grain is received and transported separately from conventionally bred varieties, and any GM contamination is kept to maximum agreed levels in non-GM crops. However, identity preservation is not restricted to GM varieties; it is a standard practice in many grain-producing countries to ensure that grain of premium quality is not mixed with that of inferior or different quality type.

PBR Requirements Another important reason for satisfactory methods of variety identification is the need to implement PBR, the system for breeding organizations to be remunerated financially for the use of their varieties, in a process similar to that of copyright laws. These systems require that a new variety must be registered, defining its identity, with evidence that it is distinct from other varieties of the respective species, that it is uniform with respect to relevant characteristics, and that it is stable for those characteristics from one generation to another. This process should also provide the means of identification, permitting this variety subsequently to be identified at the time of sale of seed or delivery of harvested grain. However, it has become difficult to provide methods that are sufficiently discriminatory for this purpose, especially for closely related varieties (such as sister lines; Figure 1) without the need for excessive cost, labor input, or resources in expertise or equipment. Methods used for registration under PBR may not be readily deployable in ‘field’ situations. The range of methods devised for distinguishing between varieties of cereal grains differs according to their discriminating ability and the degree of difficulty in implementation. There are three major methods of variety identification:

• • •

Visual methods based on grain and plant morphology Methods based on grain–protein composition DNA-based methods

The latter two methods are laboratory-based.

Grain and Plant Morphology for Identification Traditionally, distinction has involved visual inspection of plants or grain, probably aided by reference manuals listing systematic descriptions relevant to the species under examination. This approach satisfies the requirements of speed and minimal resources, but it is subjective and its capability for discrimination is generally poor. Visual examination can be implemented in any situation ‘on the spot,’ requiring no more than good lighting and possibly a hand lens for magnifying small details. Experience and training is obviously essential,

31

even when reference manuals are available (see ‘Further Reading’). The specific characteristics that provide distinction differ from one species of grain to another. Ideally, these distinguishing markers are genetically determined, without modification by variations in growth conditions. This ideal situation is often not possible. Nevertheless, such markers are available to a limited extent. For example, color differences are an obvious basis for distinction, such as blue aleurone coloration in barley grain (Figure 2), red/white grain in wheat or sorghum, and white/yellow maize. However, there are instances, such as with lentils, where there is a color variation within a variety; the typical pale seed coat can also exhibit gray or marbled colorations (http://www.pulseaus.com.au). Other useful characteristics are illustrated in Figures 3 and 4 for wheat plants. The auricles of a young wheat plant (3–6 leaf stage) may be either smooth or hairy, the auricle being the clawlike appendage that clasps the stem of the wheat plant at the base of the leaf (Figure 3). Genetic variation is also seen in the shape of the glumes – the outer husk that surrounds the grain in the mature wheat head (Figure 4). Particularly evident is the length of the ‘beak’ (a spike projecting from the creased edge of the glume at the end of the glume opposite to the point of attachment to the rachis). This characteristic is especially useful for grain identification, because glumes are often found in grain samples, so that its value is not necessarily confined to plant identification. Attempts have been made to obtain objective identification of varietal differences in morphological characteristics using image analysis, taking advantage of the speed and power of computing to analyze the image of grain profiles from a video camera. The method appears to be viable only when grain characteristics between varieties are sufficiently different.

Laboratory Methods for Variety Identification To overcome the subjective nature of visual examination, recourse has been made to a range of laboratory-based methods to achieve objective and definite identification.

The Phenol Test A simple test, for example, for wheat varieties is the phenol test. This involves soaking grains in water for several hours and spreading them on filter paper that is wetted with a 1% solution of phenol in water. After a few hours at room temperature (20–25 C), there is color development (Figure 5(a)) according to the genotype of the variety, shown as degrees of brown from colorless to black. Ideally, four degrees of coloration are distinguished – no change, light, medium, and dark – comparing test grains with grains of known phenol reaction. The test thus does not have great discriminating power, but it has the advantages of low cost and ease of performance, especially for identifying distinctive individuals in a large number of grains. In addition, the phenol test may be applied to the glumes, again resulting in a range of coloration (Figure 5(b)). Reactions for glumes do not necessarily correspond to the grain reactions. Durum varieties (e.g., Dural in Figure 5(b)) often show no color change for grains or glumes.

32


White

Whole grain

Blue

Pearled grain Clipper

Whole grain

Pearled grain Corvette

Figure 2 Distinction between two types of barley varieties based on aleurone color (white at the left vs. blue). The color difference is more evident after removing the bran layers (lemma and palea) by light pearling. Reproduced with permission from Fitzimmons RW and Wrigley CW (1979) Australian Barley Varieties: Identification of Varieties. Grain Defects and Foreign Seeds. Melbourne: CSIRO.

Smooth

Hairy Short

Kite

Halberd

Figure 3 Smooth and hairy auricles of young wheat plants. Reproduced with permission from Ferns GK, Fitzimmons RW, Martin RH, Simmonds DH, and Wrigley CW (1975) Australian Wheat Varieties: Identification According to Growth, Head and Grain Characteristics. Melbourne: CSIRO.

Testing at the DNA and Protein Levels The most commonly used laboratory tests for variety involve analysis at the gene (DNA) or protein levels. New technologies at the genome level offer the possibility of conducting varietal identification by DNA analysis efficiently and economically. Analysis at the genome level excludes the possibility of

Falcon

Medium (¾ to 1¼ mm)

Long

Gabo

Timgalen

Figure 4 Variation in beak length for glumes (husk) of wheat. Reproduced with permission from Ferns GK, Fitzimmons RW, Martin RH, Simmonds DH, and Wrigley CW (1975) Australian Wheat Varieties: Identification According to Growth, Head and Grain Characteristics. Melbourne: CSIRO.

interference from fluctuations in the growth conditions, because it occurs at the start of the sequence of events shown in Figure 6. These events extend from the genes, to protein synthesis, to the formation of all components of the grain. This composition largely determines processing characteristics and final product quality.


33

Dural

Halberd

Eagle

Olympic

Heron

Timgalen (b)

Figure 5 (a) Color changes in wheat grains due to the application of the phenol test. Most of the grains on the disk of filter paper have given a lightbrown reaction. Grains of a different variety have turned dark brown. (b) Color changes in wheat grains and glumes of various wheat varieties due to the application of the phenol test.

Genome (genes/DNA) Transcriptome (mRNA from genes) Environment (climate, fertilizer)

Proteome (proteins)

Grain composition

Processing Products

Figure 6 The sequence of events from genes, to protein synthesis, to the final determination of product quality. Analysis of varietal identity is generally directed at the DNA or protein levels.

The second major possibility for variety identification – the analysis of protein composition – involves the risk that the influence of growth environment may interfere with the attempt to identify genotype. However, analyses of the storage proteins of many cereal grains have demonstrated that the influence of growth conditions is not so great as to cause major difficulties in the interpretation of the results. Major advantages of choosing protein composition as the basis for study are that proteins are more abundant, compared to DNA, and that proteins are easier to extract for analysis by traditional methods. Several technologies of protein fractionation have been applied to variety identification. They differ in their complexity, cost (in capital and consumables), and distinguishing ability.

Methods Based on Grain–Protein Composition Gel Electrophoresis at pH 3 Electrophoresis is the separation of charged protein molecules in an electric field, with a retarding effect proportional to the size of the protein molecules. Analysis of grain–protein composition by polyacrylamide gel electrophoresis (PAGE) has been accepted for some decades as a routine method of identifying cereal varieties in the laboratory. There are standard methods for the conduct of electrophoretic identification adopted by several scientific bodies, including the International Association for Cereal Science and Technology (ICC), the International Seed Testing Association (ISTA), and the

34 Table 2

GRAIN MARKETING AND GRADING | Identification of Varieties of Food Grains Variations in the conditions of the acidic gradient polyacrylamide gel electrophoresis (PAGE) method, suiting it for various cereals

Extracting solution Extracting solution volume mg1 grain Gradient range of polyacrylamide gel Electrophoresis time at 200 V

Wheat, rye, triticale

Barley

Oats

Rice

6% urea 6 ml 3–13% 150 min

6% urea þ 1% ME 4 ml 3–27% 120 min

15% urea 6 ml 3–27% 140 min

18% urea þ 1% ME 4 ml 3–27% 90 min

Source: Black C (2003) Official Testing Methods of the Cereal Chemistry Division of the Royal Australian Chemical Institute, 4th edn. Melbourne: Royal Australian Chemical Institute.

Table 3

Relative efficiencies of four protein-based methods of variety identification

Steps of analysis

Precast PAGE

RP-HPLC

MF-CE

MS

Prepare gel or column Extract sample Analyze sample Reveal protein profile Interpret data Equipment cost Consumables cost Labor cost

10 min 20 min 10–90 min 20 min or overnight 10 min Low Medium Moderate

10 min 20 min 30 min Instant Instant High Medium Low

0 <20 min 10 min (1 min each) Instant Instant Medium Low Low

0 20 min >1 min Instant Instant Very high Low Low

PAGE, polyacrylamide gel electrophoresis; RP-HPLC, reversed-phase high-performance liquid chromatography; MF-CE, microfluidic capillary electrophoresis (lab-on-a-chip); MS, mass spectrometry.

Royal Australian Chemical Institute (see Tables 2 and 3 for comparisons of some of these protein-based methods). The basic protocol is as follows: (a) Extract protein from milled or crushed grain with appropriate solvent (e.g., for wheat gliadins). (b) Centrifuge. (c) Place pre-prepared or precast gel in electrolyte buffer in electrophoresis equipment. (d) Load appropriate volume of extracted sample supernatant on the gel. (e) Connect power supply and allow to run for appropriate time. (f) Disconnect power supply and remove gel. (g) Stain gel to visualize proteins. (h) Compare pattern with those of authentic varieties. Figure 7 shows the results from one slab gel, on which several protein samples have been run in parallel. The result for each sample is represented by a vertical column of horizontal lines (‘bands’) down the gel, each band representing a different protein. Some protein bands (in the same positions) are common to all the varieties, but there are other protein bands that are the basis of distinction between the varieties. The standard method of the Royal Australian Chemical Institute specifies the use of polyacrylamide gels in which the concentration of polyacrylamide increases from the top (where the sample is applied) to the bottom, thereby creating decreasing pore sizes to sort the proteins according to their size and to cause sharpening of the protein zones as they pass through the gel medium under the attraction of the electric field. Different gel ranges are specified for the various cereal grains and also different extractants and run times, as tabulated in Table 2. These conditions are designed to provide electrophoretic profiles for the prolamin class of proteins from these cereal grains, known as gliadins for wheat, secalins for rye, and

Figure 7 The gel patterns resulting from electrophoretic identification of a series of wheat varieties on the basis of their gliadin bands, separated by cathodic gel electrophoresis in a precast gel (3–15% polyacrylamide) at pH 3. The gel is about 7 cm square and 1 mm thick.

hordeins for barley. Mercaptoethanol (ME) is suggested for extracting barley and rice proteins in Table 2. In the case of wheat, for example, the gliadins represent about 40% of the protein content of the grain. A further 40% consists of the glutenin proteins, which are not extracted under the conditions of Table 2, due to their large size.

SDS Gel Electrophoresis The polypeptides of wheat glutenin can be included in the electrophoretic profile by using an alternative system of

GRAIN MARKETING AND GRADING | Identification of Varieties of Food Grains extraction and electrophoresis. This involves the inclusion of a reducing agent (e.g., dithiothreitol (DTT)) to break disulfide bonds joining the polypeptides of glutenin, plus the detergent sodium dodecyl sulfate (SDS) in both extraction and gel systems (Figure 8). In this way, many more protein zones may be displayed, thereby increasing the chances of providing distinction between varieties. In addition, the identification of glutenin subunit composition may be used to assess dough quality for wheat varieties (see Bekes and Wrigley, 2013 and http://www.aaccnet.org/initiatives/definitions/Pages/glutendatabase.aspx). Ideally for this purpose, the identities are needed for both the high- and low-molecular-weight (HMW and LMW) subunits of glutenin.

Microfluidic Capillary Electrophoresis Effective analysis of grain–protein composition can also be achieved with capillary electrophoresis (CE) and reversedphase high-performance liquid chromatography. However, these conventional methods have the disadvantages of requiring significant levels of expertise and laboratory equipment. The development of microfluidic CE (‘lab-on-a-chip CE’) offers a fast methodology using portable equipment. Task-specific chips are available for protein and DNA analysis. For variety identification of wheat based on protein composition, the full set of polypeptides is extracted from crushed grain or flour (about 20 mg of grain) in one step using SDS and DTT. Very small reagent volumes are used for the analysis. Routinely, the lab-on-a-chip CE (Figure 9) used can accommodate up to ten samples. The analysis of each (sequentially) takes less than 1 min. Results are provided immediately as both elution profiles and simulated electrophoretic patterns. The latter version illustrates that good distinctions are provided among wheat and among barley varieties (Figures 10 and 11). If gliadin proteins are first extracted from wheat-grain samples, the resulting SDS-DTT extracts provide patterns for both the HMW and LMW subunits of glutenin (Figure 12). Lab-on-a-chip CE is sufficiently fast and robust to be deployed in the cramped and rushed situation of grain receival at harvest, as has been demonstrated at various silos in Australia (Figure 9). Alternatively, the

Figure 8 SDS gel electrophoresis patterns for reduced wheat-grain polypeptides from a series of wheat genotypes.

35

equipment may be set up at a regional center for samples to be couriered in for immediate analysis.

Mass Spectrometry Mass spectrometry was initially used for rapid analysis of identity based on the analysis of gliadin proteins from wheat. In this case, an accurate analysis is provided of the molecular mass of all the gliadin molecules, the resulting profiles being characteristic of the varieties analyzed. Analysis takes only 2 min per sample manually, or 15 s per sample if automated. Matrix-assisted laser desorption/ionization–time of flight mass spectrometry (MALDI-TOF MS) was developed in the 1980s and has application in high-throughput measurement of many important biopolymers including proteins and extracted DNA. The technique consists of mixing a dissolved sample with matrix, which is then crystallized. This is vaporized using a laser beam and the ionized molecules separated according to their mass/charge ratio or time of flight to reach a detector. The complex spectra obtained are analyzed using bioinformatics. This method has also been applied to variety identification by analysis of wheat glutenin subunits and more recently for barley DNA markers.

Immunoassay Aspects of protein composition can also be determined by using the specificity and speed of antibodies to indicate the presence (or absence) of proteins that are markers of specific varieties. One or more antibodies are labeled with an enzyme that provides color reactions to indicate if the respective marker proteins are present in the extract of grain proteins. Immunoassay techniques have found application in the detection of novel GM proteins such as those in soy, canola, and maize. In the enzyme-linked immunosorbent assay (ELISA) technique, this system can be applied efficiently in

Figure 9 Equipment for performing lab-on-a-chip capillary electrophoresis. In this case, the equipment is being used in the confined space of the grain receival office at Coleambally, NSW, Australia. The chip (2.5 cm square) can be seen on the right of the opened lid of the CE equipment. The set of electrodes that engage with the sample wells of the chip can be seen on the underside of the lid.

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Ladder Rosella Data... Grebe

Tam... Walla... Yallaroi Yanac

Snipe

Kukri

bowie

kDa 210.

97.4

53.

21.5

6. Figure 10 Simulated gel electrophoresis patterns from lab-on-a-chip analysis of SDS-DTT extracts of wheatmeal samples for ten Australian varieties. The HMW subunits of glutenin appear at the top of the patterns. At the extreme left is the ‘protein ladder,’ providing a calibration of apparent molecular weights for sample proteins. Reproduced with permission from Uthayakumaran S, Batey IL, and Wrigley CW (2005) On-the-spot identification of grain variety and wheat-quality type by lab-on-a-chip capillary electrophoresis. Journal of Cereal Science 41: 371–374.

Sloo... Picol... Kap... Lind... Sch... Tant... Sloo... Clipp... O⬘co... Tallo... Galle... Sloo...

Figure 11 Varieties of barley shown as simulated gel electrophoresis patterns from lab-on-a-chip analysis of SDS-DTT extracts of crushed grains.

the laboratory by using multiwell microtiter trays, with automatic multichannel pipettes and an automatic ELISA reader. The assay takes 2–4 h and is useful in high-volume screening. Another variant uses lateral flow strips, where the antibodies are in specific zones on a test strip. The kit includes all reagents and the ‘dip stick.’ This is similar to that used in medical diagnostics such as pregnancy testing. Results are available within a few minutes, and so the method is

applicable for on-the-spot testing, provided the correct assay for the specific GM has been selected.

DNA-Based Methods Much work has been carried out in the past few decades in understanding the genetic basis of agronomic, disease, and


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14.5 6. Figure 12 Lab-on-a-chip capillary electrophoresis of glutenin subunits (as simulated gel electrophoresis patterns) extracted in SDS-DTT solution from whole-wheat after preliminary extraction of gliadins with 50% aqueous propan-1-ol. The HMW subunits are numbered according to the convention in http://www.aaccnet.org/initiatives/definitions/Pages/glutendatabase.aspx. The LMW subunits appear in the lower half of the patterns. Adapted with permission from Uthayakumaran S, Listiohadi Y, Baratta M, Batey IL, and Wrigley CW (2006) Rapid identification and quantitation of high-molecular-weight glutenin subunits. Journal of Cereal Science 44: 34–39. Table 4

Selected DNA methods suitable for variety identification

Marker types DNA separation and visualization Published variety identification applications

RFLP, SNP, microsatellites (e.g., SSR), DArT Gel, CE, MALDI-TOF MS, DNA sequencer, DNA microarray, hybridization plate Barley, canola, durum, maize, soybean, rice, wheat

RFLP, restriction fragment length polymorphism; SNP, single-nucleotide polymorphism; SSR, simple sequence repeat; DArT marker, diversity arrays technology marker; CE, capillary electrophoresis; MS, mass spectrometry.

quality traits in grain crops. This has involved both DNA sequencing of the genome and the development of genetic markers. Markers act as signposts to a gene location and allow the differentiation of the respective genes. Besides the valuable role of genetic markers as breeding tools, they can be used to distinguish between varieties by identifying differences at the DNA level. Many markers have been identified and are available in the public domain. Various techniques have been developed since the 1980s. Early methods were originally applied to the human genome, but were applicable to grains because of the high level of polymorphisms that could be detected for specific traits. The development of assays based on gene sequencing and the polymerase chain reaction (PCR) led to even more marker types, but at first, these had the disadvantage of a low throughput, high cost, and a requirement for high skill levels. Streamlining of these earlier methods, together with more recently developed DNA-based methods, has given techniques that are more suitable for variety identification with a higher throughput and lower costs (Table 4). This is because of the higher levels of polymorphisms that can be detected and the development of new assay techniques and platforms that are no longer based on time-consuming gel electrophoresis.

Many procedures exist for DNA-based methods of variety identification (Table 4). In general, the basic steps include (a) extraction and purification of DNA; (b) specific amplification of DNA (using PCR); (c) postamplification processing – cleanup and selective fragmentation ready for imaging; (d) separation and visualization; (e) data analysis and comparison with library or reference database. Commercially available kits can be used for steps (a), (b), and (c). Some of the separation and visualization methods used in protein analysis have application here (Table 4). The lab-on-a-chip system for CE is suitable for variety identification based on DNA analysis of microsatellite markers, as shown in Figure 13. This method of analysis is thus rapid and robust, but the preliminary preparation of DNA for the grain sample is slower than protein extraction. All methods require the identification of a set of suitable, robust genetic markers that can be used to screen the grain in question. The number of markers required will differ according to the DNA method used and the grain species. The identification of a suitable set can require considerable resources and, even if known, will require verification at the bioinformatics stage and optimization before application in a different geographic region or gene pool. Gene sequence data may also be required. As new varieties are released, these need to be added to the reference database. There is also the possibility that the marker set may change with time if improved markers are established. DNA methods have greater discrimination power than morphological or protein-based methods and may thus detect more heterogeneity, leading to some confusion. The presence of biotypes has already been noted in protein-based methods, where single grains of the same commercially released variety can be distinguished. This may be due to the original variety

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Figure 13 Lab-on-a-chip analysis of barley varieties using microsatellite marker HMV03. Lane numbering indicated by L, Ladder; 1, Parwan; 2, Skiff; 3, Chebec; 4, Schooner; 5, Baudin; 6, Grimmett; 7, Barque; 8, Gairdner; 9, Sloop; 10, Arapiles; 11, Lindwall; 12, negative control. Analysis with HMV03 partitioned the varieties into the seven groups bracketed at the top of the figure. Reproduced with permission from Tran-Dinh N, Uthayakumaran S, Batey IL, and Wrigley CW (2009) Rapid DNA-based identification of wheat and barley varieties. Journal of Cereal Science 50: 388–391.

International Union for the Protection of New Varieties of Plants and the ISTA are working toward the development of standard microsatellite markers, methods, and laboratory accreditation. Finally, DNA-based methods lend themselves to the analysis of processed food products for authenticity, provided that DNA has not been degraded by, for example, intensive heating or other processing. This extension of DNA analysis can also be applied to the identification of different species such as rice, wheat, or barley in foodstuffs.

Scenarios for Identification Figure 14 The 8 12 grid of reactions for each sample provided by the Triticarte system (DArT). Illustration provided courtesy of Diversity Arrays Technology Pty Ltd.

being heterogeneous and can complicate the task of identification or seed purity testing. DNA-based methods have been automated to provide very efficient screening using a large number of markers. Figure 14 shows the 8 12 grid of marker reactions for each sample provided by the Triticarte system (diversity arrays technology (DArT)), which gives a high degree of discrimination, including the opportunity to determine the proportions of contaminating varieties. The mechanism by which mixtures of varieties may be examined is illustrated in Figure 15, based on a mix of two varieties and only three markers. As Figure 14 shows, data are available for many more markers, permitting the examination of more complex mixtures. This system has been used to screen 1900 grower-derived wheat samples. This study indicated that only 3% of the samples were less than 90% pure but that there was a significant extent of incorrect labeling of variety, though not necessarily of an inappropriate quality grade. While knowledge is rapidly expanding in the use DNA markers for mapping populations and plant breeding, methods for routine variety identification are still developing and limited to the major crops (Table 4). Groups such as the

These various methods of protein fractionation and DNA profiling differ in their potential for distinction between varieties, and in their suitability for routine use, based on considerations such as speed, expertise required, and cost. For example, PAGE has the advantage of low cost for the equipment needed, compared to the much more expensive capital costs of the other methods, but may not provide the discrimination required. So DNA profiling may be the appropriate choice, as is the case for the identification of closely related malting barley varieties, which are often marketed in variety-specific parcels with differing malting performance. Relative suitability depends on the situation in which identification is needed. These situations are summarized in Table 5, namely,

• • •

the need for rapid identification, when delivered grain must be assessed within a few minutes, with minimal facilities; the regional laboratory, with modest equipment and modest expertise, where questionable samples may be sent for a prompt result to be provided, possibly overnight; and a major centralized laboratory, with sophisticated equipment and trained staff, where the emphasis is on the efficient analysis of large numbers of samples. This third scenario suits the approach of having farmer’s samples taken at the time of grain delivery, for subsequent analysis to verify the declaration of variety made at delivery, especially for the implementation of PBR in situations where royalties are levied for delivered grain.


(1) Seed sample (>1000)

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B C ... Marker

Figure 15 The mechanism by which the DArT system can determine the proportions of mixtures of varieties. This simple case shows a mix of two varieties and only three markers. Illustration provided courtesy of Diversity Arrays Technology Pty Ltd. Table 5

The three major situations in which variety identification is needed and relative suitability of methods of identification Situations

Examples of these situations

On-the-spot grain receival at mill or grain elevator (silo)

Regional lab backup at mill breeders’ or seed lab export terminal

Central lab/contract lab for large numbers of postharvest samples Importing country authentication

Requirements in the respective situations Visual examination Phenol test Rapid immunoassay (dipstick) Immunoassay in lab Gel electrophoresis RP-HPLC (protein-based) Conventional CE (proteinor DNA-based) Microfluidic CE (proteinor DNA-based) MALDI-TOF MS (proteinor DNA-based) Other DNA-based methods (e.g., microarray)

Speed

Overnight results

Efficiency for large numbers of samples

þþ þ

þ þ þþ þ þ þ

þþ þþ þþ þ

þþ þþ þþ

RP-HPLC, reversed-phase high-performance liquid chromatography; CE, capillary electrophoresis; MS, mass spectrometry. Source: Wrigley CW and Bekes F (2002) Grain-protein composition as a document of wheat-quality type: new approaches to varietal identification. In: Ng PKW and Wrigley CW (eds.) Wheat Quality Elucidation: The Bushuk Legacy, pp. 65–86. St. Paul, MN: American Association of Cereal Chemists.

Philosophy of Analysis Clarification of the Aim of Identification A proper appreciation of the aim of identification is needed in designing the best approach to the task, namely, ‘What is the question?’:

•

In general, the question to be addressed is one of verification of identity, that is, varietal identity has been specified

• •

for the grain sample to be analyzed, and testing requires a ‘yes/no’ answer. The more difficult question follows from a ‘no’ answer, namely, ‘What variety is it?’ An intermediate possibility is the question ‘Is this sample variety A or variety B?’

The precision of the answers to any of these questions depends on the discriminating power of the test(s) applied. A reference

40


list of varieties and their characteristics is essential to providing the information needed to make decisions about the type and degree of testing necessary to answer these questions. A test system that discriminates a large set of varieties into only two or three groups (e.g., the phenol test) cannot alone provide a precise answer to any of the earlier-mentioned questions. The strategy for efficiently answering the third question in the preceding text requires the results from testing the two varieties to be available, such as would be provided in a reference list. The adequacy of an answer to the second question depends on how comprehensive is the size of the catalog of test results, as well as the discrimination of the tests being applied.

variety, the confidence limits for that different variety in the whole load would be 3–56%.

Future Prospects Newer innovative methods of DNA characterization will continue to replace older methods as assays become automated and more cost-effective and throughput increases. Some of these expected developments are the following:

• • •

Grain Sampling and Statistics A basic requirement of satisfactory analysis of variety is that the sample taken for analysis is representative of the whole load of grain. This is relatively simple if it can be assumed that the load or consignment is uniform or homogeneous. Otherwise, the taking of a sample for analysis must follow a procedure designed to ensure that the subsample reflects the composition of the whole consignment. An additional consideration relates to interpreting the analysis of many individual grains. Obviously, the results for only one or a few individual grains do not indicate the identity of the whole load if it cannot be assumed to be uniform. Analysis of a milled sample provides a much better indication of identity if only one analysis is to be undertaken initially. In the case of a heterogeneous consignment, it may be necessary to perform grain-by-grain analysis – a tedious and expensive task – and the results must be interpreted for statistical significance. For example, rice is traded internationally, and some importers of premium aromatic rice types such as basmati or jasmine may require evidence of authenticity of specified varieties and a maximum threshold for adventitious presence of inferior types. In such a case, a grain-by-grain analysis may be required. Table 6 illustrates the problem and a solution. If the analysis of 10 grains individually showed that they all have the same identity, it could not thus be assumed that the whole sample is uniform; the table shows that this result would indicate a 95% probability that there could be between 0% and 31% of a different variety present. These confidence limits become much narrower with the analysis of more grains. Likewise, if two grains (20%) in 10 were found to be of a different Table 6

Real-time PCR will become quantifiable, fast, accurate, and automated. Nanotechnology will make amplified DNA more visible to technologies such as CE and flow cytometry. Fast ‘next-generation’ sequencing such as 454 sequencing (www.454.com) will make more information available on alternate genetic environments than current SNP-based methods.

The ultimate potential for future on-the-spot grain testing would be a handheld or low footprint device with close to the sensitivity of current methods.


• • • •

What are the major methods for variety identification of grains? Which would you select for on-the-spot identification of truckloads coming into a flour mill, where there is urgency in having the grain binned? Which method(s) would you select to provide reassurance that pure-seed consignments are true to label before sale to grain growers? Which factors would influence the choice of an appropriate method of variety identification for a specific application?


• •

Variety identification may be needed at many of the stages throughout the grain value-addition chain. How does the need for accuracy and urgency vary throughout these stages? At what stages of the grain chain is assurance of appropriate quality type more important than identification of actual

Statistical interpretation of results from the identification of individual grains sampled from a total consignment of grain Confidence limitsa (%) depending on the total number of grains identified

Distinct identity found for given % of grains identified

10 grains

20 grains

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0 5 10 20 50

0–31 – 0–45 3–56 19–81

0–17 0–25 1–32 6–44 27–73

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0–1 3–7 7–13 17–23 46–54

a

Limits at 95% confidence level.


• • •

genotype (variety). Also consider the reverse of this contrast. Research to determine the range of grain species for which varietal identity is important for your region. Find out what efforts are made to check on varietal identity. Research the future (near and further off) possibilities for routine use of DNA markers to determine species and varietal identities. Ground-grain samples have lost most aspects of morphology, so laboratory methods are needed to determine species and variety. What would be the simplest approach to distinguishing species if only ground samples are available (e.g., wheat vs. barley vs. rice meal or flour).

See also: Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Detection of Genetically Modified Grains; Grain Marketing and Grading: Wheat: Grading and Segregation; Wheat: Marketing; Proteins: The Protein Chemistry of Cereal Grains; The Protein Chemistry of Dicotyledonous Grains; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure; Wheat Processing: The Gluten Proteins of the Wheat Grain in Relation to Flour Quality; Ultrastructure of the Wheat Grain, Flour, and Dough.

Further Reading Agrawal RL (1997) Identifying Characteristics of Crop Varieties. Enfield, NH: Science Publishers. Bekes F and Wrigley CW (2013) Gluten alleles and predicted dough-quality for wheat varieties world-wide: A great resource – Free on the AACC International website. Cereal Foods World 58(6): 325–328, http://dx.doi.org/10.1094/CFW-58-6-0325. Black C (2003) Official Testing Methods of the Cereal Chemistry Division of the Royal Australian Chemical Institute, 4th edn. Melbourne: Royal Australian Chemical Institute. Cooke RJ (1992) Electrophoresis Handbook: Variety Identification. Handbook of Variety Testing. Zurich, Switzerland: International Seed Testing Association, pp. 1–50. Ferns GK, Fitzimmons RW, Martin RH, Simmonds DH, and Wrigley CW (1975) Australian Wheat Varieties: Identification According to Growth, Head and Grain Characteristics. Melbourne: CSIRO. Fitzimmons RW and Wrigley CW (1979) Australian Barley Varieties: Identification of Varieties. Grain Defects and Foreign Seeds. Melbourne: CSIRO. Hervey-Murray CG (1980) The Identification of Cereal Varieties. Cambridge: Cambridge University Press. Kruger RP and Bietz JA (1994) High Performance Liquid Chromatography of Cereal and Legume Proteins. St. Paul, MN: American Association of Cereal Chemists. Menz I (2010) Australian Barley Varieties a Reference Guide. Adelaide, SA: Barley Australia.

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National Institute of Agricultural Botany (regular issues) Botanical Descriptions of Cereal Varieties. Cambridge: National Institute of Agricultural Botany. Sforza S (2013) Food Authentication Using Bioorganic Molecules. Lancaster, PA: DEStech Publications. Smith C (2005) Striving for purity: Advances in protein purification. Nature Methods 2: 71–77. http://dx.doi.org/10.1038/nmeth0105-71. Uthayakumaran S, Batey IL, and Wrigley CW (2005) On-the-spot identification of grain variety and wheat-quality type by lab-on-a-chip capillary electrophoresis. Journal of Cereal Science 41: 371–374. Uthayakumaran S, Listiohadi Y, Baratta M, Batey IL, and Wrigley CW (2006) Rapid identification and quantitation of high-molecular-weight glutenin subunits. Journal of Cereal Science 44: 34–39. Wrigley CW (ed.) (1995) Identification of Food-Grain Varieties. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW and Bekes F (2002) Grain protein composition as a document of wheatquality type; new approaches to varietal identification. In: Ng PKW and Wrigley CW (eds.) Wheat Quality Elucidation: The Bushuk Legacy, pp. 65–86. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW, Autran JC, and Bushuk W (1982) Identification of cereal varieties by gel electrophoresis of the grain proteins. In: Pomeranz Y (ed.) Advances in Cereal Science and Technology, vol. 5, pp. 211–259. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites http://www.diversityarrays.com – Diversity Arrays Technology Pty Ltd, providing DNAbased methodologies for characterizing genes in breeding and variety identification. http://gmo-crl.jrc.ec.europa.eu/default.htm – The European Union Reference Laboratory for GM Food and Feed is tasked with the scientific assessment and validation of detection methods for GM for European Union member States. https://www.icc.or.at/standard_methods/143 – Standard method no 143 for identification of wheat varieties of the International Association for Cereal Science and Technology (ICC), based in Austria. http://www.niab.com – Originally the National Institute of Agricultural Botany, NIAB is situated in Cambridge, UK. The company is involved in variety evaluation, plant variety rights, seed certification, and seed technology. http://www.nvtonline.com.au/ – Australian national program of comparative crop variety testing. http://pericles.ipaustralia.gov.au/pbr_db/ – Searchable database for all plant varieties with PBR registered in Australia. http://www.seedtest.org – The International Seed Testing Association (ISTA), whose Secretariat is based in Switzerland, exists to develop, adopt, and publish standard procedures for sampling and testing seeds, and to promote uniform application of these procedures for the evaluation of seeds moving in international trade. The ISTA also promotes research related to seeds, including variety certification. http://www.upov.int – International Union for the Protection of New Varieties of Plants (UPOV) is an intergovernmental organization based in Switzerland. Its aim is to provide and promote an effective system of plant variety protection, with the aim of encouraging the development of new varieties of plants. http://wheat.pw.usda.gov/index.shtml – GrainGenes is a compilation of molecular and phenotypic information on wheat and other crops. The project is supported by the US Department of Agriculture Plant Genome Research Program and by the community of scientists who are providing the information.


Contents Wheat: Harvesting, Transport, and Storage Barley: Harvesting, Storage, and Transport Sorghum: Harvest, Storage, and Transport Canola: Harvest, Transport, and Storage Cereals: Grain Defects The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species Contaminants of Grain Chemicals for Grain Production and Protection Handling from Farm to Storage Terminal Stored Grain: Invertebrate Pests Postharvest Operations for Quality Preservation of Stored Grain Stored-Grain Pest Management

Wheat: Harvesting, Transport, and Storage S Grundas, Polish Academy of Sciences, Lublin, Poland CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Wheat is an important grain crop, devoted to food production for the major part of the global population. Harvesting is a three-stage process – reaping, threshing, and winnowing. Appropriate grain-quality standards of wheat make it a special product in its marketing and processing. Standards of wheat quality are established by most wheatgrowing countries as a basis for quality-based segregation at harvest. Changes in conventional methods of harvesting, transporting, and storing relate to improving the quality of grain consignments. Wheat storage methods at a very low rate of grain respiration are designed to retain quality stability and the loss of grain mass.

Learning Objective

•

Achieve understanding of the important processes in wheat cultivation, harvest, transport, and storage of wheat grain.

Introduction Wheat has been grown over many millennia BC. Archaeological evidence suggests that in many parts of Asia and Europe

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and also in Egypt, wheat was grown for 5–7 thousand years BC. Wheat grain was found in the Egyptian pyramids, in the pilebuildings of Switzerland, and at many sites of ancient man. Wheat is one of the three large grain crops (with rice and maize), but the viscoelastic properties of wheat flour dough make it uniquely suited to the production of leavened breads. It is also unique in that it can be rolled into thin dough sheets that can then be cut, folded, steamed, and fried to produce a plethora of food products, making it a critical food crop for the major part of the global population. Since the second half of last century, wheat products have become widespread in all countries throughout Central, Southeast, and North Asia where traditionally, rice was the major food crop. Now, wheat growing and trade are big businesses worldwide. Compared to wheat, no other cereal species has so many varieties or as many quality specifications. As a rule, the countries that grow wheat, apart from commonly occurring types, have their own local varieties and cultivars. Centuries of experience of growing wheat in different soil and climatic conditions have contributed to the formation of a large diversity of species and varieties. Most of the total cultivated area (90%) is occupied by bread wheat (Triticum aestivum), which represents the greatest number of crop-yielding varieties of starchy grains. The numerous varieties of durum wheat species (T. turgidum ssp. durum) are cultivated on the remaining area. The greater areas of wheat cultivation are in the northern hemisphere. Wheat is grown both as a winter and as a spring cereal in the moderate climate zones and in the tropical regions in low lands and uplands alike. The distribution of wheat over the


http://dx.doi.org/10.1016/B978-0-12-394437-5.00191-1

GRAIN HARVEST, STORAGE AND TRANSPORT | Wheat: Harvesting, Transport, and Storage

Figure 1 The main wheat-growing regions in the world; the northern and southern distribution boundaries are marked with broken lines. Reproduced from Grzesiuk (1988), with permission.

various parts of the world is related to the numerous varieties and to their adaptability to particular environments. Wheat harvesting is a continuous process around the world, and every month is a period of harvest in one of the wheat-growing regions. The geography of wheat-growing regions is illustrated in Figure 1.

Historical Perspective Modern wheats have come from a range of primitive species, many of which lacked the essential characteristics for largescale production and harvesting, such as uniform maturity, elastic and flexible straw that does not fragment during threshing, and an ear fixed firmly to the straw and kernels that are readily threshed from the enclosing glumes, without prematurely shedding its grain prior to harvest. We accept these and many other intrinsic characteristics without acknowledging their basic importance to the success of today’s wheat varieties. Wheat harvesting is a three-stage process – reaping, threshing, and winnowing. The first step (reaping) involves cutting off the stalks of the wheat plant after it has become dry and ready for harvest. Before recent times of mechanization, reaping was performed by hand. The stalks were cut with a scythe or with a sickle, having a curved hooklike blade. The cut stalks were often left in the field in standing bundles with the heads uppermost, allowing the heads to dry out more, if this were necessary. These bundles have been called shocks, stooks, or ricks. Mechanization led to the possibility that this step of cutting could be performed by machines, leaving the cut stalks lying in lines (swaths) if they needed to be allowed to dry more before threshing. ‘Swathing’ is still performed in climates where harvesting is likely to be done under moist or even snowy conditions, the lying stalks being left to dry ready for the next stage of harvest. Threshing involves removing the grain (with husks) from the stalks. Traditionally, this meant vigorous beating to separate the grain in the head from the rest of the plant parts, followed by winnowing, to free the grain from the husks, plus using some means to blow away the chaff. Significant among the many inventions to mechanize harvesting was the reaper conceived by the American inventor and manufacturer, C. H. McCormick (1809–84). His reaper, patented in 1834, revolutionized wheat production. He went on to organize the manufacture of farm machinery on a

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Figure 2 Combine harvesting of wheat. This equipment cuts off the wheat stalks, threshes the grain from the reaped heads, and winnows away the chaff, depositing the grain in a bin. The grain is later transferred by auger (protruding above the combine to the left), into a truck driven beside the combine while it continues to harvest.

mass-production basis. His success helped to speed up the large-scale mechanization of American agriculture. Later developments brought the modern combine harvester, which combines the three major operations of reaping, threshing, and winnowing in one machine (Figure 2). Recent methods of harvesting are designed to map the harvested area according to the yield throughout the harvested area. This is done by fitting Geo Positioning System equipment to the combine. In this way, the position of the combine in the field is known at any time. The yield per unit area is recorded continuously, providing a map of grain yield throughout the field. Furthermore, onboard NIR protein analyzers can also provide a record of variations in protein content throughout the harvested area. The technique, known as ‘precision agriculture,’ is designed to identify the parts of the field that are underproducing, so that attempts may be made to remedy the problems. This may involve taking soil samples to test for mineral deficiencies or to check for possible waterlogging in these patches of ground.

Destinations for the Harvested Grain Historically, grain has been grown to meet the needs of the farming family, the grain being stored on the farm to provide food until the next harvest. This type of subsistence farming is still a way of life in some regions. As specialization of occupations developed, the farmer also produced grain for sale to neighbors and in nearby markets. Trade in wheat has now extended to see the movement of vast amounts of grain internationally. Furthermore, the sophistication of international trade has required that grain-quality specifications are suited to the types of process and product appropriate to each market. For example, many types of bread manufacture require hardgrained wheat that mills well to produce strong dough properties, whereas soft wheat giving extensible dough is required for cookie and cake production. Further specifications are required for many other products made from wheat, such as Arabic breads of many types, various kinds of noodles, pasta products, and feed grain for animals.

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Many of the major wheat-growing countries produce much more wheat than can be consumed domestically. They, therefore, export a considerable proportion of their production. In doing so, they seek to maximize the returns for their grain on the international market while focussing on markets that offer advantages for transport costs. The marketing organizations of the wheat-exporting countries have had to conduct extensive market research to determine what quality attributes are appropriate to targeted market destination, particularly depending on the types of products made and processing used in these regions. As a result of this knowledge, breeders have selected varieties that suit these needs, and specific varieties have been recommended for growth in appropriate regions. A range of other quality considerations must also be assessed, to ensure that the quality requirements of the specific markets are met.

Meeting Appropriate Grain-Quality Standards The range of quality requirements depends on the relative influences of genotype (the variety sown) and the effects of growth conditions, as indicated in Table 1. For example, the moisture content of the grain after harvest is solely dependent on harvest conditions and farm management, and the variety originally sown is not at all relevant. Moisture content is an important determinant of quality during storage, because moist grain is more susceptible than dry grain (e.g., below 12% moisture) to fungal attack and insect infestation. A moisture content of 13% is considered to be the maximum value for the storage of wheat during short periods, though temperature and oxygen concentration also play an important role. Similar considerations hold for the presence of weed seeds and pesticide residues, these quality factors also being wholly determined by growth and harvest conditions (Table 1). Table 1 Grain-quality attributes for wheat, listed according to the relative influences of genotype and growth environment on each attribute Quality attribute Variety Starch properties Milling quality Grain hardness Protein content Protein quality Dough characteristics Preharvest sprouting Defects Test weight Moisture content Pesticide residues Contaminants

Influence of genotype (variety)

Influence of growth conditions

Sole Major

Nil Minor

Major Major Significant Significant Significant

Minor Minor Significant Significant Significant

Significant

Major

Minor Minor Nil Nil

Major Major Sole Sole

Nil

Sole

Adapted from Wrigley CW and Batey IL (2003) Assessing grain quality. In: Cauvain SP (ed.) Bread Making: Improving Quality, pp. 71–96. Cambridge: Woodhead Publishing.

On the other hand, aspects of grain quality such as hardness and milling quality are largely determined by the variety involved. Genotype (variety) has considerable influence on the protein content and dough properties, but so too do the growth conditions, including such factors as the level of nitrogen fertilizer and the presence or absence of frost, drought, or heat stress. For these reasons, many grades of wheat with particular quality requirements have specifications for a selection of specific varieties of similar quality, suited to the growth conditions expected for the region. Although variety is an important factor affecting quality, wheat is seldom classified on the basis of a single variety. Thus, each grade or class consists of a group of varieties of similar characteristics for a specific processing purpose. The testing of a truckload of grain for quality (Table 1) is ideally performed on delivery to a flour mill or storage terminal (elevator or silo). These tests must generally be performed within a short time, probably several minutes. This is because a decision must be made, while the truck is waiting, on where the grain should be tipped. In such situations, there are generally several storage cells, each holding a different grade (class) of wheat, each grade being suited for distinct uses with different quality specifications. The first step is usually to take samples from the truck’s load for the tests to be carried out. Samples may be taken with a hydraulic set of probes, which are lowered into the load of grain. Alternatively, sampling may be performed manually with a spear probe, as is shown in Figure 3. This spear consists of two long concentric cylinders, each with vertical slits. When inserted, the slits are closed. After insertion, the top of the spear is twisted, to open the slits allowing grain to flow into the inner tube from all levels of the grain load. In the case of manual sampling, an operator thrusts the spear into the grain after climbing on top of the load or leaning over from an elevated sampling stand. Spear samples are taken at several specified points across the load, with the aim of obtaining a combined sample that is representative of the whole load. Refer to grainsampling handbooks on the website of the United States Department of Agriculture’s Federal Grain Inspection Service for standard sampling procedures.

Figure 3 Delivery of harvested grain to a storage terminal may involve first stopping the truckload at a sampling stand, so that samples of grain can be taken to assess its quality.


Testing to Ensure Grain-Quality Standards The grading of wheat grain involves the segregation and valuation of grain consignments based on the physical and chemical properties of the grain. The scope of wheat-grain grading is related to our current agricultural knowledge and to the level of organization of the local cereal market (pricing policies and grain purchasing systems). The systems of wheat-grain grading include the following groups of grain properties: 1. ‘Stable’ properties, related to genetic properties (determined by the variety), such as grain hardness, size, shape, and color (red or white). These are the factors toward the top of the list in Table 1, distinguished by being only slightly influenced by growth conditions. These quality attributes have been ‘built in’ as a result of intentional breeding and selection. Testing for these mainly involves varietal identification. 2. ‘Variable’ properties, subject to change as a result of drying, cleaning, sorting, and transporting (moisture content, contamination, and damage to grain), related to climatic conditions and management practices (e.g., bulk density). These factors, appearing lower down the list in Table 1, are described in detail in articles on contaminants, defects, and diseases of cereal grains. Specific testing must be conducted for each of these. 3. ‘Permanent’ faults and defects include stale smell, fermented smell, foreign smell, or faults that can be rectified, for example, washing grain contaminated with soil or foreign matter. The ‘stable’ properties provide a primary basis to determine the appropriate market class. They are, thus, critical for grade determination in international trading. As they are mainly determined by genotype, this is the reason for specific varieties to be nominated for premium grades and classes. Grain hardness, a ‘stable’ property, is an important basis for classification in trade. In relation to grading, the following definitions are applied: 1. Hard wheat is wheat that, as a result of variety and breeding in combination with environmental factors during growth, has a vitreous endosperm generally considered an advantage for the production of bread-making flours. 2. Soft wheat is wheat that, as a result of variety and breeding, in combination with environmental factors during growth, has a white opaque endosperm generally considered more suitable for the production of cake and biscuit flours. The ‘variable’ properties are secondary properties, although also important from the viewpoint of grain quality. The group of variable properties, systematized into several ranges in terms of values, constitutes grain grades, which are identical for many of the market classes. The quality grading of wheat grain sometimes includes an assessment of mechanical damage, which occurs wherever grain is subjected to the destructive action of internal or external forces. The susceptibility of wheat to mechanical damage is determined by genetic factors (hard and soft grains), by environmental effects (climatic conditions during the preharvest period), and by the conditions of grain storage (excessive temperature and humidity).

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Rain at harvest (Figure 4) is one of these factors. The result can be premature sprouting of the grain, possibly no more than a swelling of the germ through the actual appearance of roots and shoots. The full range of these indications of sprout damage is illustrated in Figure 5. The result of this defect is the production of excessive alpha-amylase enzyme, which may render the grain unsuitable for normal food use. The combination and selection of these properties determine further aspects of grain quality. Some of the ‘permanent’ faults and defects are a basis for excluding shipments during grain grading, as their character is likely to disqualify grain from food use. Defined faults, which can be rectified, may make some grain lots eligible for special grades of defective quality.

Quality Specifications of Individual Countries Standards of wheat quality have been established by most wheat-growing countries. Canada and the United States, as examples, have systems of wheat grading with classes based on the varietal properties expressed in the vegetation period (spring versus winter wheat), grain coloring (red or white), and hardness (hard or soft). Within the various classes, there are

Figure 4 Rain at harvest brings the serious risk of grain starting to sprout while it is still in the ear.

Figure 5 Sprouted wheat grains, in various stages of germination from swollen and split germ to the appearance of roots and shoots.

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specific grades (subclasses) each with their distinctive quality specifications, often relating to protein content. Five classes of wheat are distinguished in the United States: hard and soft red winter, hard red spring, durum, and white (subclassified into hard and soft winter white and hard, and soft spring white). Wheat grading in the United States additionally provides, in the subclasses, for the proportion of vitreous grains. Groups of varieties of appropriate quality are specified for most grades of wheat. As an example, in Canada, the model hard red spring wheat was originally the variety Marquis. Many years ago, it was replaced successively by varieties that are genetically similar with respect to their genetic potential for appropriate grain quality, but of more value economically with respect to yield potential and disease resistance. More recent replacements include Thatcher, Manitou, and Neepawa – classed as the ‘equal-to-or-better-than’ variety for Canada Western Red Spring. Canada Prairie Spring Red wheat is a medium-strength wheat suitable for the production of certain types of hearth breads, flat breads, steamed breads, and noodles. Canada Western Amber Durum is an ‘any extra strong wheat that is equal to or better than’ the variety Hercules. This is a good example of the use of a specific variety being used as the basis of a specific class. In this case, ‘extra strong’ refers to the strength of the dough made from the flour, the extra strong gluten of this class being attractive for special bread types and for blending with wheat with low and/or weak gluten content. Wheat is also produced in the eastern provinces of Canada, where the wheat is graded into various classes such as ‘Canada Eastern Soft White Spring’ and ‘Canada Eastern Soft Red Winter.’ In Argentina, most of wheat cultivation involves hard red winter wheat, also known as ‘plate’ wheat. Wheat growing is concentrated in the provinces of Buenos Aires, La Pampa, Cordoba, and Santa Fe. Argentina uses a system of breadwheat division into subclasses based on grain hardness (hard, semihard, and soft). Export classes are named according to the ports of shipment. In Australia, the crop might be classed as spring wheat, because the conditions in all parts of the wheat belt do not provide the cold temperatures needed for the vernalization of a winter wheat. Nevertheless, some varieties approach the winter-wheat type by having a long maturity period. A high proportion of the Australian wheat crop is exported (often 80% of it), and it has been an important accent of marketing efforts to ensure that market requirements are understood and matched. Australia has developed a grading system based exclusively on white-grained wheat. Prime Hard is the top-quality grade, with a protein content of 13–14%, high milling quality, and good processing attributes. Flour from it is used in export markets for high-protein yellow-alkaline noodles, Wanton dumpling skins, highvolume breads, flat breads, rotis (known as atta flour), and chapattis. Its high protein content suits it to blending with lower-protein wheat. Australian Hard (hard-grained varieties with a minimum protein content of 11.5%) suits Europeanstyle breads, Middle-Eastern flat breads, and Chinese steamed products such as mantou and pao. Premium White (minimum of 10% protein) is suitable for a wide range of products, including Hokkien, instant and fresh noodles, Middle-Eastern and Indian-style breads, and Chinese steamed bread.

Australian Standard White is a medium- to low-protein multiuse white wheat. Australian Soft Wheat (8.5–10.0% protein) is a smaller part of the crop than the hard-wheat grades and is used for confectionary products, such as cakes, pastries, biscuits, cakes, steamed buns, and snack foods. The Australian Noodle grade is a premium class because its special starch properties make it ideal for white-salted noodles in South Korea and the traditional thick udon-style noodles in Japan. Grain that does not meet the specifications for the aforementioned grades is classed as general purpose or feed wheat. Australia also produces three grades of durum wheat. In Europe, and especially in France and Germany, intensive agricultural procedures have resulted in virtually the highest grain yield per unit of area of cultivation. Traditionally, European countries have been importers of wheat, especially of strong wheat for blending, but since the 1970s, the European Community has been a significant wheat exporter. In recent years, ‘clubs’ have been set up by wheat producers who achieve yields of 10–15 t ha 1. In this region, the dominant types are wheat of the Soft Red Winter class. The European Union countries have dozens of high-yielding varieties of very good grain quality. In Mediterranean countries, such as Italy and Spain, durum wheats make significant contributions to wheat production. East European countries grow mainly red winter wheat, some of which have very good baking qualities. In the countries of the Commonwealth of Independent States (CIS), both spring and winter and red and white wheat are grown, as well as some durum wheat. The CIS has the largest area of wheat cultivation in the world. The leading varieties, in terms of yield and grain quality, are the winter wheat, Bezostaya 1 and Mironovskaya 808, and the spring wheat Saratovskaya 29. In recent times, the wheat-growing areas in Russia, Ukraine, and Kazakhstan, which ship much of their exportable surplus through ports on the Black Sea, have become major players in the world wheat market, and this expansion is set to continue, with dramatic effects on international grain flows. Wheat grading in the CIS is based on principles similar to those followed in the United States, with the distinction that classes are replaced in the CIS by types and subclasses by subtypes, primarily designed to take into consideration the proportions of vitreous grains. Common wheat (T. aestivum) in Russia exceeds 95% of the entire wheat sown area, the remainder being durum wheat. All varieties of common wheat are divided by their baking quality or flour strength into three groups: strong, valuable (medium strong), and weak. Strong wheat is characterized by a high content of gluten with good quality. The Russian standard includes here common wheat of I and II classes. Valuable wheat (III class) is medium in strength but characterized by good baking properties. Flour of this wheat produces bread of satisfactory quality; this result does not involve the addition of strong wheat flour, but this wheat is not so strong that it can improve the quality of a wheat flour with low-quality gluten and consequently with poor baking properties. Some European countries (e.g., France and Germany) use a grading system based on protein content, bulk density, and the sedimentation test. With only slight differences in the appearance of many varieties and with the possibility of grain-quality reduction as a result of environmental effects, grades have been developed to include, in addition, the

GRAIN HARVEST, STORAGE AND TRANSPORT | Wheat: Harvesting, Transport, and Storage extent of contamination of the grain and the results of the Falling Number test for sprout damage. Other countries, in which wheat is grown or only imported, also use specific standards for the evaluation of the quality of wheat grain and its products. Most frequently, such systems are modifications of those presented in the preceding text.

Transport of Grain In many countries, the regions of grain production are distant from the centers of population and from the export terminals. Transportation is thus a significant expense. It is common for trucks to be used for delivering the grain from the farm to the country elevator (silo) or to the flour mill. This delivery point is the primary opportunity for testing the quality of the grain, so that best-quality grain can be segregated from poorer grades. Truck delivery and sampling are illustrated in Figure 3. Country elevators are always situated near transport facilities, as is illustrated in Figures 6–8. Rail transport is the usual means of transporting large volumes of export grain long distances from country elevators to the terminal elevators. These are generally located at harbors, ready for the loading of ships for transport by sea to importing countries. This form of transport is illustrated in Figure 9, but

Figure 6 Vertical silo storages in country Australia.

Figure 7 Circular silo, designed to hold different grades and types of grain in the separate vertical cells.

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in this case, there will be another transfer of grain before it reaches its export destination. Figure 7 shows grain being loaded into a lake barge at Thunder Bay, Canada, for movement through the Great Lakes of North America to a further terminal where it will be transferred to a sea-going ship. ‘Identity preservation’ is becoming an important issue in regions where grain is transported significant distances. The activity of testing grain on delivery for quality attributes (Table 1) is costly, so the grain that has thus been segregated must be retained (preserved) in its separated state throughout the subsequent storage and transport stages. Attention to the added task of identity preservation brings further costs, so it must be established that the resulting premium payments for the special classes or grades justify these costs. Much of the grain exported from the United States is carried by a barge down the Mississippi and Columbia Rivers to export elevators, where it is unloaded and stored until it can be loaded onto ships. In addition, some grain is transferred directly from a barge to a ship, without being stored in an elevator. An export elevator can load a ship with 60000 tonnes of grain, worth over $10 million, in 2 days. The weight certificate must thus be very accurate, due to the large sums of money involved.

Figure 8 A horizontal storage silo (at right) and bunker storage (left and top center). Grain in the bunker storage is laid on layers of plastic sheet and also covered over with sheets of plastic. Note the freshly harvested field on the extreme right.

Figure 9 Loading of bulk wheat for export at Thunder Bay, Canada.

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By contrast with subsistence farming, in which the family consumes the grain it produces, the process of moving export grain is complex. It passes through the following stages: from the farm, to country silos, possibly via regional centers, to terminal storage elevators. At every stage, grain is subjected to checking and classification. This ranges from highly detailed to more general grading. Treatment may include improvement (drying, cleaning, sorting, and disinfestations, if required) and grouping of supplies into larger batches of uniform quality. Isolated fractions of undersize grain and lower-grade wheat may be sold on the local market.

Storage Like transport, grain storage is likely to start at the farm. Many years ago, wheat was bagged for transportation and storage, but bulk transport and storage are now usual, except in cases of special quality requirement. Some regions have a tradition that grain is delivered to a country elevator or mill immediately as it is harvested, whereas in other places, on-farm storage is common. Retention of the grain at the farm may provide trading advantages for the grower, permitting him or her to wait until prices rise before selling. However, the responsibility for grain hygiene and pest management remains the responsibility of the grower. Nevertheless, most major wheat-producing countries have major storage facilities through the grain-growing regions. These may take various shapes and sizes, as shown in Figures 4–6. The vertical silos in Figure 4 are an older type, although these are being modernized by sealing them to permit insect disinfestations by fumigation or preferably by treatment with carbon dioxide. Figure 6 shows a few forms of storage, conveniently situated beside rail and road transportation. The long, low structure at the right of Figure 6 is known as a ‘horizontal storage’ or ‘bunker.’ Like the vertical silos (Figures 4 and 5), it may have several separate cells to accommodate different grades and types of grain. Stability during storage and transport are the intrinsic advantages of the grains as food sources. During storage, the rate of grain respiration is very low, and this accounts for its stability and the very low losses in the mass of the stored grain. However, these advantages depend on the condition of the grain and its moisture content, temperature, and soundness. Grain respiration may be more intense in soft grain than in hard grain. If grain moisture content is relatively low (below 14%) and if the bulk of grain of that moisture content is homogeneous, the grain can be stored for several years without significant losses. However, if proper air temperature and humidity conditions are not observed in the storage area, the increasing humidity resulting from the process of grain respiration may lead to the phenomenon of spontaneous heating of the grain, and this may render it unfit for human consumption. In some wheat-growing regions, for example, in the Scandinavian countries, wheat grain is harvested relatively moist and it must be dried to maintain its quality. Drying must be performed under controlled conditions of temperature and humidity. Exceeding the required temperature may lead to the loss in the baking value of the flour. To avoid damaging grain meant for baking purposes, its temperature should not exceed 35 C at moisture contents above 20%.

Future Prospects Various revolutionary approaches to grain storage and transport have been proposed and tested. One of these is the possibility of pumping a slurry of grain in liquid through a pipeline. This system has worked well for minerals in some cases, but it has not yet been adapted to any significant extent for wheat grain. One difficulty is to choose an appropriate liquid medium. Rapeseed oil has been used in trials, but the difficulty has been to remove the oil efficiently. Another possibility is supercritical liquid carbon dioxide at low temperature and high pressure; this was found to extract lipid from the grain and to be very expensive. It is likely that conventional methods of harvesting, storage, and transport will continue with relatively slow change. However, new approaches may be directed toward improving the quality of grain consignments. This may involve more controlled harvesting, by using ‘precision agriculture’ to confine harvesting to parts of the field that have higher protein content, thereby achieving a premium for a significant part of the harvest that would not have otherwise been possible. A possible approach to reduce the risk of grain deliveries being downgraded due to sprout damage involves taking grain samples from at-risk parts of the crop prior to harvest. These are tested (e.g., Falling Number, Rapid Visco Analyzer, or immunoassay) to determine those parts of the field that are not sprout-damaged. This information can then be used to confine the travel of the combine to the sound parts of the field and thus avoid the risk of losing a premium payment by harvesting sprouted grain together with the sound grain. For storage, new approaches to preventing loss to insects and vertebrates are a priority, because significant losses of this nature continue as a major problem, especially in developing countries. High-quality seed is necessary for fast biological and technological progress, which are ensured by genotype and kernel integrity. First of all, the seeds should be of a variety characterized by high productivity and suitability for the climate zone where it is cultivated. Second, the seeds should have a high level of germination capacity and be free of damage of biotic and abiotic character. To generate a variety and to obtain seed registration require a minimum of about 10 years. The popularity of a variety, on average, decreases by 20% a year, and within a few years, it is replaced. Transition to F1 hybrid types may reduce the time of obtaining new varieties to 5 years, but the agricultural economy is dependent on the activities of breeding centers. Harvested F1 hybrid grain does not retain its advantage if it is used as seed. This state of affairs with relation to genotypes stimulates the search for new approaches to yield and quality improvement. The studies carried out during the last 10 years showed that using x-ray images with direct x-ray magnification of 2–10 times and computer image analysis, the variety-specific morphological parameters of cereal grains can be successfully determined. The algorithm by which the equipment is running self-building genome in ontogeny on the principles of complex systems is presented. Its high convergence with the experimental data gives the basis for the application of this approach to the consideration of the morphological characteristics of kernels as a tool for the identification of their morphological type and variety.

GRAIN HARVEST, STORAGE AND TRANSPORT | Wheat: Harvesting, Transport, and Storage To identify the kernel, besides three dimensions, it is proposed to determine, by x-ray, the contour of kernels (seeds) in at least two projections. It is advisable to plan a continuation of the research with a collection of cereal cultures to create a database for the identification of kernels and for decision making on the basis of x-ray selection. It is proposed to use the mass-scale x-ray separation of kernels for their selection on the basis of varietal and production characteristics, as reflected in their morphology, and for the elimination of contaminants, including kernels with internal defects, with a view to a permanent renewal and maintenance of resources of industrial high-quality varietal seed.

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Transport: Cereals: Grain Defects; Contaminants of Grain; Postharvest Operations for Quality Preservation of Stored Grain; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Grain Marketing and Grading: Wheat: Grading and Segregation; Wheat: Marketing; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Peanuts: Overview; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain; Wheat Processing: Ultrastructure of the Wheat Grain, Flour, and Dough.


• • • • • • •

Describe the schedules of harvesting in the wheat-growing areas around the world, taking into account hemisphere (north/south) and distance from the equator. Where are the greatest areas of wheat cultivation with respect to hemisphere (north/south) and distance from the equator? Name the two major species of wheat and their uses and the proportions grown worldwide. What are the distinct meanings of the terms ‘soft’ and ‘hard’ wheat in relation to their utilization? Which climates suit the growing of winter and spring wheat? Which criteria determine the distribution of wheat over the various parts of the world? What are the advantages and disadvantages of storing grain on the farm versus delivery to a regional storage facility immediately after harvest?


•

•

Investigate the concept of ‘niche markets’ – situations where millers are prepared to pay a premium price for grain that is especially suitable for their specific needs, such as for udon noodle production. Consider the extra costs involved in supplying such a market, starting with the need to convince a grower to grow and deliver a high-quality variety (possibly lower yielding), the need to segregate this grade of wheat, and the need to retain its identity throughout transportation and storage. Contrast the niche-market approach to marketing with the ‘commodity’ concept, in which all wheat is considered to have the same quality, thus involving minimal testing and no need for identity preservation.

See also: Agronomy of Grain Growing: Wheat: Agronomy; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Grain Harvest, Storage and

Demyanchuk AM, Grundas S, and Velikanov L (2013) Identification of wheat morphotype and variety based on X-ray images of kernels. In: Grundas S and Ste˛pniewski A (eds.) Advances in Agrophysical Research, pp. 223–267. Rijeka: Intech. Chapter 10, http://dx.doi.org/10.5772/52236. Faridi H and Faubion JM (eds.) (1995) Wheat End Uses Around the World. St. Paul, MN: American Association of Cereal Chemists. Gordeev AV and Butkovsky VA (2005) Russia-Grain Power. Moscow: Food Industry, ISBN:5-89703-075-8. Grundas S, Nawrocka A, and Pecen J (2011) Grain physics. In: Glin´ski J, Horabik J, and Lipiec J (eds.) Encyclopedia of Agrophysics, pp. 323–327. New York: Springer, 978-90-481-3584-4. Grzesiuk S and Kulka K (1988) Biology of Cereal Kernels. Warsaw: Polish Scientific Ed (in Polish). Hoseney RC (1994) Principles of Cereal Science and Technology, 2nd edn. St. Paul, MN: American Association of Cereal Chemists. Kaleta A and Go´rski K (2013) Criteria of determination of safe grain storage time – A review. In: Grundas S and Ste˛pniewski A (eds.) Advances in Agrophysical Research, pp. 295–318. Rijeka: Intech, Chapter 12. Khan K and Shewry PR (eds.) (2009) Wheat: Chemistry and Technology, 4th edn. St. Paul, MN: American Association of Cereal Chemists. O’Brien L and Blakeney AB (eds.) (2000) An Introduction to the Australian Grains Industry. Melbourne: Royal Australian Chemical Institute. O’Brien L, Morell M, Wrigley C, and Appels R (2001) Genetic pool of Australian wheats. In: Bonjean AP and Angus WJ (eds.) The World Wheat Book, pp. 603–640. Paris: Lavoisier. Pomeranz Y (ed.) (1989) Wheat is Unique. St. Paul, MN: American Association of Cereal Chemists. Sauer DB (ed.) (1992) Storage of Cereal Grains and Their Products, 4th edn. St. Paul, MN: American Association of Cereal Chemists. Saurer W (1996) The single kernel classification system for the characterization of wheat. In: Proceedings of the 10th International Cereal and Bread Congress, Greece: Chalkidiki. Wrigley CW and Batey IL (2003) Assessing grain quality. In: Cauvain SP (ed.) Bread Making: Improving Quality, pp. 71–96. Cambridge: Woodhead Publishing.

Relevant Websites www.aaccnet – AACC International. www.cgc.ca; www.grainscanada.gc.ca – Canadian Grains Commission, Winnipeg, Canada. www.crop.cri.nz – New Zealand Institute of Crop & Food Research. www.icc.or.at – International Association for Cereal Science and Technology. www.seedtest.org – International Seed Testing Association. www.triz.profi.com/eng/ – Russia. www.usda.gov – United States Department of Agriculture; grain handling practices, standard sampling procedures.

Barley: Harvesting, Storage, and Transport RJ Henry, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Unique requirements for barley handling and storage. Importance of varietal segregation in barley. Impact of physical damage during handling. Grain size as measure of barley quality. Key role of moisture content in storage life. Impact of dormancy on use in malting.

Learning Objectives

• • •

To understand the requirements for barley handling and storage. To explain the critical nature of barley varietal purity. To manage barley stocks to deal with dormancy.

capacity must be sufficient to harvest the crop within a very short period of time in high-risk environments. Areas with a high rainfall, conducive to preharvest sprouting, require this approach. In some areas, high humidity can restrict the time available for harvest each day. Storage and transport capacity requirements may also be determined by these factors. Crops can be harvested at very high moisture contents (more than 50%) with mechanical combines but yield will be lost, because the crop would not have reached maximum grain dry weight and costly grain drying would be needed before storage. The grain must be mature before it is harvested.

Grain Cleaning ‘Dockage’ is a term used to describe the material removed in the grading of grain such as barley, including nongrain parts of the plant and other debris.

Unique Features of Barley The harvesting, storage, and transport of barley require consideration of the issues associated with other grains and the additional constraints imposed by the use of barley in malting. Varietal segregation must be maintained to ensure uniformity of germination in barley to be used for malting. Malting requires clean grain that can be germinated uniformly. Barley is also unique in comparison with grains such as wheat in being a hulled grain (except in the case of naked barley). The lemma and palea make up a husk that adheres to the grain. The presence of the husk provides some protection to the grain against abrasion during handling. The husk is, however, a site for microbial infestations (fungal and bacterial) that may be more difficult to remove than those on the surface of naked grains. Hull-less barley varieties may have very different storage and handling properties. Barley is also unique in being sold in many markets for malting on the basis of variety. While grains such as wheat are traded on class or grade, malting barley is sold as pure varieties. This is because of the need for uniform germination during malting. The separate segregation of barley varieties from harvest and in storage and transport requires reliable management of these processes and is aided by the availability of methods for variety identification.

Harvesting The timing of harvest aims to optimize yield and quality while minimizing environmental risks such as preharvest sprouting, associated with delayed harvesting. The grain must be mature before it is harvested. Early harvesting will result in higher moisture content of the grain, which will require careful storage and/or drying. The timing of harvesting may be more critical in some environments than others, so harvesting

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Grain Size The size of barley grain is a key measure of quality, and harvested grain is also subjected to screening to remove small and broken grains before storage or transport. The proportion of grain in 2.5 and 2.8 mm sieves is a further measure of grain plumpness used to assess barley quality. The uniformity of size is important because of the influence of grain size on the rate of modification of the grain during malting. Grain may be fractionated to manipulate the uniformity before use in malting.

Skinning The skinning of barley during harvest or handling can result in loss of germination potential. Skinning may result in the loss of the embryo or damage to tissues such as the aleurone, important in malting. However, some abrasion of the grain may assist malting by accelerating water absorption during steeping or by contributing to the breaking of dormancy.

Shattering The shattering of barley results in poor recoveries of grain in the field and therefore significant losses. This is more likely when harvesting dry grain or grain that has matured under unfavorable environmental conditions.

Grain Drying The drying of barley requires extra care to preserve germinability for malting. Heat and mechanical damage may result from


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some drying protocols. Aeration of stored grain with a fan can both reduce the grain temperature and dry the grain especially if dehumidified air is used or low ambient humidity prevails. Heated air needs to be used with caution to avoid damage to the viability of the barley, especially in the case of malting barley. Drying to around 12% moisture is desirable for storage.

capacity. Malting is conducted all year round to make best use of malting facilities. As a consequence of this, storage of malting barley for at least 12 months after harvest is required unless transport between northern and southern hemispheres is used to supply the maltings. However, because of transport costs, most malting is based on locally produced barley.

Storage

Moisture Content

Defined hazards associated with storage of grain include

The relationships between moisture content and temperature and longevity in storage can be used to determine the probable storage life of barley samples. Equations to predict the safe storage period for barley based upon temperature and moisture content have been developed (Figure 1). These equations can be adapted to allow for differences in preharvest sprouting damage. Barley should have < 130 g kg 1 of moisture for safe storage for 1 year and < 110 g kg 1 for safe storage for 5 years. Grains with more than 140 g kg 1 of moisture may heat and spoil rapidly. The moisture content of barley at 25 C will vary with relative humidity and at equilibrium will be 97 g kg 1 at 97% relative humidity, 135 g kg 1 at 70%, and 268 g kg 1 at 100%.

excessive moisture, extremes of temperature, microbial infestations, insects and arachnids (e.g., weevils, beetles, and mites), rodents (e.g., mice and rats), birds (both before harvest and in grain stores), biochemical deterioration, mechanical damage in handling.

Other general concerns of particular significance in relation to barley are the introduction of environmental contaminants, preservation of germinability, and avoidance of admixture. All these factors may require the use of complex management systems to support decision making in the storage of barley.

Environmental Contaminants Environmental contaminants in barley are of concern to brewers as these may contaminate the finished beer. These contaminants include soil pollutants and naturally occurring toxins (e.g., heavy metals), components of fertilizers, fungicides and pesticides, and air pollutants. Seeds are often coated with preparations designed to provide protection from pests and diseases after field planting. The composition of these seed protectants may be of concern to brewers. Fungi introduce another type of hazard, the possible presence of mycotoxins. Treatments to prevent the growth of fungi in stored barley may be required. Beer consumers are considered very sensitive to concerns about the purity of the product, and brewers are keen to ensure that their product retains a reputation for purity relative to competing products. This issue has resulted in the introduction of detailed quality assurance protocols to control the production and storage of barley. The use of insecticides and fungicides, especially those applied during storage, may result in residues on malt that could end up in beer or other cereal products.

Germinability Storage of malting barley also aims to preserve the viability of the grain. This is only a constraint for seed users in other grain species. A ready germination of at least 95% of the grain is the usual standard applied to the acceptance of barley for malting. A supply of barley with high viability is required throughout the year to allow malting facilities to be used to maximum

Dormancy Some barley varieties have a brief period of dormancy immediately following harvest. This may be desirable in areas in which preharvest sprouting damage is prevalent. Malting of barley is usually delayed for some weeks or months after harvest to avoid dormancy. This may require barley to be stored for malting considerably more than 12 months after harvest, so that supplies are available for malting from the previous year’s harvest until the new crop has emerged from dormancy. Dormancy of barley may be influenced by the variety (genetic factors) and growth conditions (environmental factors). Some varieties (when dried) with strong dormancy are treated (warm storage) to break dormancy to allow more immediate processing. Another strategy in some areas is to malt a minor variety with low dormancy immediately after harvest until preferred but more dormant varieties are ready.

16 15 Moisture content (%)

• • • • • • • •

2 months

14 6 months

13 12 11 10 9

1 year

2 years

8 10 12 14 16 18 20 22 24 26 28 30 32 34 Temperature (°C) Figure 1 Safe storage of barley at different moisture contents and temperatures.

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Some varieties are treated to break dormancy before processing. Dormancy of some barley varieties (e.g., Triumph) may be removed by warm storage immediately before malting.

Admixture Barley varieties may germinate at different rates, complicating the malting of samples of mixed genotypes. This constraint means that malting barley storage requires more careful segregation of varieties than that of most other grain types. This adds to the cost of barley storage and transport. The same issues make the blending of barley parcels with widely differing specifications (e.g., protein content) to produce a target specification highly undesirable. Blending of malts after malting is the best way to ensure consistent malt specifications for the brewer. Planting of pure seedlots is a key approach to ensuring the harvesting of grain of a single variety. Testing of seed before planting and of plants in the field before harvest can be used to confirm the identity and purity of barley varieties. Testing of the harvested samples can be used to confirm these advance tests. Unfortunately, the analysis of the harvested samples cannot always be completed before the harvested grain is bulked or mixed in storage, placing more importance on the preharvest testing. Varietal identity and purity have been analyzed based upon the analysis of seed proteins but methods based on deoxyribonucleic acid (DNA) analysis have increasingly been employed. The analysis of simple sequence repeats in barley DNA is widely used for this purpose. Analysis of identity and purity and other characteristics influencing storage decisions may ultimately be determined by automated visual assessment using video and computer analysis.

Factors Influencing Storage Life Moisture content and temperature are the key determinants of storage life. Barley storage is adversely affected by factors such as preharvest sprouting. Insect or microbial infestations may occur in storage but often originate in the field before harvest, only becoming obvious in storage. Storage treatments may be applied to protect the grain. Insects may be managed using chemical agents, controlled atmospheres, or the addition of products based upon diatomaceous earth. The use of chemicals to control insects in storage is restricted by the risk of their contamination of beer. Aeration of barley during storage can be used to control temperature and moisture distribution within the bulk.

Malting Quality Malting quality requires that grains be of a suitable malting variety, have a high germinative capacity and energy, be clean and free from microbial or chemical contaminants, and be not an admixture. Brewers are increasingly concerned about possible contaminants at all of the steps in the production chain leading to beer. Beer consumers are often influenced by perceptions of the quality and purity of the product. Gushing is a specific problem of malting barley that has been linked to

Fusarium infection. (Gushing is excessive frothing of the product with the sudden escape of beer and foam on opening.)

Feed Quality Barley is an important feed grain for animals such as pigs and cattle. Feed quality requires freedom from contaminants likely to detract from the feed value of the grain. Feed users also supply the food chain and aim to eliminate any undesirable chemical or microbiological contaminant.

Controlled-Atmosphere Storage Storage of barley under controlled atmospheres can reduce the use of chemical pest control agents and eliminate residues. Protection of viability for malting requires special considerations when this approach is used with barley. High CO2 concentrations may reduce oxygen levels to dangerously low levels for malting barley. Temperature and method of CO2 introduction need to be managed for the success of this technology in barley.

Transport Barley Barley transport from field to maltings or feedlot may involve many steps. Transport from the harvester to primary storage or off-farm may be followed by repeated steps of transport by road, rail, and sea and storage in a wide range of storage vessels. The control of environment during transport may not always be as optimal as in the best fixed storages.

Malt Malt is usually stored at very low moisture contents of 4%. Removing more moisture may preserve the malt and reduce transport costs for malt that is transported large distances internationally. However, the energy cost of drying malt to very low moisture content may be high. Transport of malt to breweries involves many of the same issues as these associated with transport of the barley before malting.


• •

Explain why it is necessary to segregate barley varieties for malting. How would you plan to ensure a constant supply of suitable quality barley to a maltster throughout the year as stocks of new season barley become available?

Exercises for Readers to Explore the Topic Further Find out the differences between malting barley and feed-grade barley in your district:


• • • •

What are the differences in quality, such as dockage, germination rate, and contaminants? Are there differences in variety specifications? Why? How great are the values for these (and other) grades? Find out from growers and advisors about the differences in production costs.

See also: Agronomy of Grain Growing: Barley: Agronomy; Grain Harvest, Storage and Transport: Contaminants of Grain; Wheat: Harvesting, Transport, and Storage.

Further Reading Bason ML, Wrigley CW, and McCleary BV (1993a) Modelling the effects of sprouting damage on malting barley, based on viscometric or amylase analyses. In: WalkerSimmons MK and Reid LJ (eds.) Pre-Harvest Sprouting in Cereals 1992, pp. 417–425. St. Paul, MN: American Association of Cereal Chemists. Bason ML, Ronalds JA, and Wrigley CW (1993b) Prediction of safe storage life for sound and weather-damaged malting barley. Cereal Foods World 38: 361–363. Edeny MJ (1996) Barley. In: Henry RJ and Kettlewell PS (eds.) Cereal Grain Quality, pp. 113–151. London: Chapman and Hall. Ellis RH and Roberts EH (1980a) The influence of temperature and moisture on seed viability period in barley (Hordeum distichum L.). Annals of Botany 45: 31–37. Ellis RH and Roberts EH (1980b) Improved equations for the prediction of seed longevity. Annals of Botany 45: 13–30.

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Fleurat-Lessard F (2002) Qualitative reasoning and integrated management of the quality of stored grain: A promising new approach (Review). Journal of Stored Products Research 38(3): 191–218. Kent NL and Evers AD (1994) Storage and pre processing. In: Technology of Cereals, 4th edn., pp. 103–128. UK: Elsevier. Kettlewell PS (1996) Agronomy and cereal quality. In: Henry RJ and Kettlewell PS (eds.) Cereal Grain Quality, pp. 407–437. London: Chapman and Hall. Korunic Z, Fields PG, Kovacs MIP, et al. (1996) The effect of diatomaceous earth on grain quality. Postharvest Biology and Technology 9(3): 373–387. Krysinska-Traczyk E, Kiecana I, Perkowski J, and Dutkiewicz J (2001) Levels of fungi and mycotoxins in samples of grain and grain dust collected on farms in Eastern Poland. Annals of Agricultural and Environmental Medicine 8(2): 269–274. Majumdar S and Jayas DS (2000) Classification of cereal grains using machine vision: IV. Combined morphology, color and texture models. Transactions of the ASAE 43(6): 1689–1694. Mills JT (1996) Quality of stored cereals. In: Henry RJ and Kettlewell PS (eds.) Cereal Grain Quality, pp. 441–478. London: Chapman and Hall. Miyake Y, Hashimoto K, and Matsuki H (2002) Fate of insecticide and fungicide residues on barley during storage and malting. Journal of the American Society of Brewing Chemists 60(3): 110–115. Rameshbabu M, Jayas DS, Muir WE, White NDG, and Mills JT (1996) Bulk and handling properties of hulless barley. Canadian Agricultural Engineering 38(1): 31–35. Smilanick JL, Goates BJ, Denisarrue R, et al. (1994) Germinability of tilletia SPP teliospores after hydrogen peroxide treatment. Plant Disease 78(9): 861–865. Wright EJ, Banks HJ, and Darby J (1997) Integration of harvest and storage strategies for maximum return. In: Proceedings of the 8th Australian Barley Technical Symposium, pp. 213.1–213.14.

Sorghum: Harvest, Storage, and Transport T Beta, University of Manitoba, Winnipeg, MB, Canada M Chisi, Golden Valley Research Station, Chisamba, Zambia ES Monyo, ICRISAT, Nairobi, Kenya ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Sorghum is an important food and feed crop in developing and developed countries. The total sorghum area harvested in Africa and India was 76% in 2012. Sorghum is harvested manually and by combine. Storage structures are very varied, ranging from pots to silos. Insect damage to the harvested grain can be reduced by controlling several storage pests. Transportation of sorghum is still restricted in developing countries.

Learning Objectives

• • •

To achieve an overall understanding of how sorghum is harvested, stored, and transported worldwide. To distinguish between manual and mechanical harvesting methods for sorghum. To explain how storage pests can be controlled in various storage structures used for sorghum.

Introduction Sorghum, Sorghum bicolor (L.) Moench, is an important food and feed crop in developing and developed countries, respectively. Sorghum, the fifth most important cereal in terms of production after rice, wheat, maize, and barley, is generally grown in low-rainfall and drought-prone areas where other cereal crops may fail. It is, therefore, critical for food security in the semiarid tropics of Africa, Asia, and Latin America. Strides have been made in developing improved technologies (management practices, hybrids, and open-pollinated varieties) for farmers but average grain yields have remained low in developing countries. Harvesting is carried out manually and mechanically by smallholder and commercial farmers, respectively. While a number of technologies exist to increase production of sorghum grain, the crop suffers damage and weight losses during storage due to insect pests. It is difficult to quantify the losses due to handling and storage, especially in the developing countries, but most literature on the subject cite up to 20%. Therefore, the issue of inadequate storage is paramount. There is a need to preserve the quality by preventing insect pests from getting into the grain. Farmers use various ways to store the grain. Both traditional and improved storage structures have their advantages and disadvantages. Improved grain storage techniques are an improvement on the inadequacies found in the traditional methods so that the stored grain does not deteriorate in quality. Therefore, the primary aim of

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grain storage is to prevent crop and monetary losses resulting from various agents such as rain, insect, fungi, and rodents by maintaining the quality and quantity of the grains from the beginning of storage up until it is consumed or sold. Transport of sorghum is restricted in developing countries as the crop generally does not reach the commercial market.

Harvesting of Sorghum The total sorghum area harvested worldwide in 2012 was 39 Mha, 60% of which was harvested in Africa (Figure 1). India had the largest area harvested (16% of total) among all countries. Thus, developing countries have the greatest sorghum area harvested. Harvesting practices vary greatly for sorghum. Timely harvest is important to preserve grain quality and reduce mold damage, bird damage, insect pest infestation, and loss due to bad weather conditions. Traditionally, sorghum grain is harvested during the beginning of the dry season when the grain moisture content is low (15–20%). It is critical for farmers to know when to harvest the grain to minimize losses. Grain should be harvested when it has become physiologically mature. Three indicators of maturity include the following: 1. A black layer forming at the tip of mature grains 2. Mature grain that cannot be indented by the thumb nail 3. Mature grain breaking cleanly when bitten with the front teeth Harvesting at physiological maturity and artificial drying significantly improve grain quality compared with harvesting at the normal maturity and sun drying. The former not only allows the farmer to get a better remunerative price but also facilitates earlier arrival of the produce to the market. Preharvest sprouting can occur when the grain matures under high humidity and rainfall conditions, resulting in reduced seed viability, which is undesirable especially if grain is destined for malting. Starch hydrolysis ensues resulting in decreased grain weight and establishment of a favorable environment for saprophyte fungi. The issue is partially resolved by growing genotypes resistant to preharvest germination or containing high tannin content. Scientific investigations continue on the genetic basis of resistance to preharvest germination. Premature harvesting results in reduced grain yields while grains with lower starch, protein, and sugar content are obtained when harvesting is delayed. Moreover, dormancy is very deep in immature grains. The inability to germinate of the immature embryo likely results from the inhibitory effect of endogenous abscisic acid and restricted water uptake because of high external osmolarity.


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GRAIN HARVEST, STORAGE AND TRANSPORT | Sorghum: Harvest, Storage, and Transport In developing countries, most of the harvesting is done manually and in a few cases mechanically by combine harvesters. Smallholder and subsistence farmers harvest sorghum by cutting the heads with knives or sickles (Figure 2). Other variations in harvesting are dependent on the use of the other parts of the plant and include cutting the plants with their heads on or digging the whole plant from the roots. Sorghum stalks remaining can be used as green fodder or cut and stored as hay. The roots and stalks can be used for fuel. In China, mechanical harvesters are designed for long- and short-stalked sorghum. Most sorghum grown in the United States and other developed countries is combine-harvested. Dwarf varieties are suitable for harvest by combine. Harvesting speeds (4–5 km h 1) are set to minimize combine header losses. The combine is adjusted in such a way that all grain is threshed and separated from the heads with minimum cracking and as little trash as possible is left in the grain. The grains are normally allowed to dry in the field to reduce moisture content to 13% or less if they are going to be stored after harvesting. At relative USA 5%

Other 9%

Mexico 5%

Asia 21%

Africa 60%

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humidities of 75, 80, and 85%, sorghum grains have adsorption and desorption moisture contents of 14.9–15.8, 15.9–16.6, and 17.0–17.5%, respectively. Invasion by storage fungi and decrease in germinability are proportional to increasing moisture content and to increasing storage time at moisture content 14.5%. Rapid transfer of moisture occurs from the warmer to the cooler portion of the grain at a temperature difference of 12–14 C when sorghum is originally at 14.3% moisture. The moisture accumulation results in the grain becoming heavily invaded and decayed by storage fungi. Insects and molds will damage sorghum kernels containing 1.5 and 4%, respectively, more water above 14%, the critical moisture for cereal grains. Varietal differences exist in suitability for harvesting with some types maintaining high moisture levels until the plants are killed by frost. Other types have a genetically conditioned head-drying character resulting in rapid drying of the grain and head after maturity. Combine harvesting can also be conducted when the levels of grain moisture contents are at 20–25%, when this is followed by ensiling or artificial drying to a safe storage moisture. Where lodging from storm damage, insects, or diseases presents harvesting problems, special types of combine attachments are available to aid in harvesting the lodged fields. If lodging is excessive, the crop can be cut with a header and the heads swathed to dry before being picked up and threshed by a combine equipped with a pickup attachment. Livestock are used to harvest sorghum directly as a last resort if lodging is severe and yields are low. Sorghum heads can be harvested and stored as head silage in some very humid areas where grains remain highly moist and losses to birds and weather can be substantial. The silage stores well at 25–40% moisture if it is finely cut. The grain in the head silage requires no further processing, as it is highly palatable and digestible. The stubble remaining after sorghum grain has been harvested is used as low-quality forage for fall grazing.

Drying, Threshing, and Cleaning of Sorghum Grain Figure 1 Sorghum area harvested (ha) in Africa, Asia, USA, Mexico, and others in 2012. FAOSTAT (2013) Database.

Figure 2 Manual harvesting of sorghum in Zimbabwe. The panicles are cut from the stalk when the grain moisture content is 15–20%.

Sorghum panicles should be thoroughly dried before threshing. Excess moisture is undesirable as it may lead to infestation by insects and fungi and deterioration of quality including loss of germinability. Partially dried heads are also difficult to thresh, and too dry heads usually result in huge losses in the field while harvesting. Optimal moisture content is 10–12% for grain and 9–10% for seed. Panicles are either left in the field or transported to storage yards where the grain is left to dry. Grains are dried further, if necessary, after threshing, using natural and mechanical drying practices. Dryers are used commercially. Drying temperatures are limited to 43 and 60 C for seed and feed grain, respectively. Airflow rates of 11–28 m3 min 1 t 1 are common for feed grain. Sorghum can be dried successfully at up to 94 C and airflows of 110–220 m3 min 1 t 1 using batch or continuous flow dryers. Smallholder and subsistence farmers thresh either manually, by beating (with sticks) the plant heads (Figure 3) lying either on bare ground or on a tarpaulin spread on hard surface to eliminate contamination by dirt and stones, or by using livestock to walk on the layers (25–30 cm thick) of sorghum heads. The latter method is popular in China where animals

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GRAIN HARVEST, STORAGE AND TRANSPORT | Sorghum: Harvest, Storage, and Transport

pull a stone roller over sorghum heads. A tractor or any other vehicle can also be driven over the heap of harvested and dried panicles. In all cases, the heads should be turned and inspected so that the action is repeated until all grains are released. Handharvested heads can be threshed by a stationary combine. Mechanical threshers are available that both commercial and smallholder farmers can afford. During threshing, care should be exercised to avoid physical damage to the grain. Damaged grains will deteriorate quickly in storage. After threshing, the grain is cleaned to remove chaff (glumes, broken grain, very light seeds, and any grasses). Among smallholder farmers, women use woven trays to winnow the chaff from the grain. Alternatively, the chaff is removed by dropping the grain from bucket against the wind (Figure 4). Chaff is also removed from the grain by sifting through a screen or sieve. The grains fall through and the chaff remains. Vibrating screens plus a feed hopper, sieves, dust remover, cleaner, and drive equipment are used at a commercial level. Pneumatic cleaning equipment is also available. The principle of pneumatic cleaning is to separate impurities from the grain based upon differences in specific gravities.

Figure 3 Sorghum panicles are threshed to release the grains by beating the heads with sticks. Time required for threshing depends on the variety and degree of dryness of the grain.

Treatment before Storage There are several chemicals that are used commercially to treat the grain before storing it. Some organophosphates include pirimiphos-methyl (Actellic), malathion, fenitrothion, and iodophenphos. Traditionally, sorghum grain is treated with wood ash, sand, and mineral powders to prevent insect damage in developing countries. Botanical insecticides such as neem (Azadirachta indica) and pyrethrum (Chrysanthemum cinerariaefolium) are also applied before grain is stored for a short-term period.

Storage of Grain The objective of storage is to preserve as much as possible the value of the grain for its intended future use. Either the food value of the grain is preserved or a high proportion of viable seeds are retained for planting next season. Some attributes such as a hard endosperm found in some traditional varieties contribute to reduced pest attack during storage. On the other hand, improved varieties mature early and generally have a soft endosperm, thus, making them more prone to pest attack. Factors leading to loss of viability and nutrients include depredations by pests (insects, birds, and rodents) and also mold damage. Germination of grain causes losses on a smaller scale. Physical factors contributing to losses include moisture content of the grain and the temperature of storage. Losses increase as moisture content and temperature of the grain increase. Minor changes in temperature during grain storage lead to moisture migration and accumulation in certain areas that are cooler than the rest. This often allows microbiological activity to occur in comparatively dry grain, which in turn leads to heat production. Moist areas in unventilated areas can get so hot that charring can occur resulting in grain destruction. Moisture migration can be prevented by forcing low volumes of air (0.11–0.27 m3 min 1 Mg 1) through grain held in silos or tanks. Aeration fans can also be installed to draw cold air down the grain while moving the warm moist air to the outside. Regular inspection of the grain is essential to detect moisture changes, insects, and spoilage during storage. Methods for storing grain are generally influenced by the value of the crop, quantity stored, and environmental conditions. Grain augers are used commercially to place grain in metal bins. Storage bins are best filled early in the day when air is cool and humidity is often at its lowest. Grain should be packed as tightly as possible to minimize space for insects to move around and to breed. In some developing countries, sand is mixed with grain to further reduce the free space. Very often, smallholder farmers store seed without treatment. This often results in the seed getting badly damaged by insects before planting. Table 1 lists the common methods of grain storage based on tradition, cost, and convenience.

Containers for Storage Figure 4 by wind.

Grain is cleaned by winnowing so that the light chaff is carried

Silos, bins, baskets, and other storage containers are made from a number of different materials (Table 1). There is not much need for bulk storage for smallholder and subsistence

GRAIN HARVEST, STORAGE AND TRANSPORT | Sorghum: Harvest, Storage, and Transport Table 1

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Common methods used for sorghum grain storage

Method of storage

Quantities

Construction materials

Cost

Disadvantages

Bulk silos Drums and bins Pots Pits Baskets Bags

Large Medium Small Large Medium to large Small to medium

Steel, aluminum, concrete Metal Clay Brick, cement, mud walls Stalks, mud, cow dung Cloth, sack, jute

High Medium Low Low to medium Low Low to medium

Costly to operate Poor ventilation Poor ventilation Prone to mold growth Prone to pest damage Prone to pest damage

Figure 5 Sorghum panicles are dried while being kept off the ground on raised platforms.

farmers in developing countries. Clay pots are used on the smallest scale. Larger containers are constructed from wood, brick, or stone or from bamboo made into a basket that is then sealed with mud or dung. Containers can sometimes be left uncovered if kept indoors or covered with either a lid or a thatched roof if kept outdoors. Grain for immediate consumption is usually stored in the house in metal or plastic bins. However, grain can also be packed in suitable material (jute bags, cloth bags, and cardboard cartons) for short and long-term storage. The grain is taken out of the bags and dried in the sun by spreading on the floor or on a sheet at regular intervals during the dry season. Exposing grain to the sun and heat at intervals keeps away storage pests. Occasionally, sorghum heads are stored on the ground, usually unthreshed. Panicles from the heaped pile are removed and threshed when grain is needed. It is generally not recommended to store unthreshed grain on the heads.

Figure 6 Example of granary used for storing sorghum in Zambia. Smallholder farmers store grain threshed or unthreshed.

and countries. For example, in southern Africa, a thatched roof is usually placed on top of a granary (Figure 6). In Nigeria, sorghum is stored as unthreshed heads in a solid-walled container called a ‘rumbu.’ Heads are laid out individually for long-term storage (3–6 years) or in bundle layers for shortterm storage (<3 years). When filled, the rumbu is sealed with clay. In Sudan, pits holding 2–5 t of grain are used as underground stores. In India, underground pits may be located underneath the houses or outside. The pit is lined with paddy straw or sorghum straw and then covered with straw and soil when it is full of grain. The top is plastered over with mud for longer storage.

Storage Pests Storage Structures The idea of storage structures is to prevent insect pests and rodents from attacking the grain. Storage structures are many and are varied in the way they are constructed. Bulk silos of heights of 30–50 m are used commercially for centralized storage. In many countries, small granaries are made by weaving plant materials, such as bamboo, stalks, bark, and small branches, and then sealing any gaps with mud or dung. These structures can either be built directly on the ground or raised off the ground on platforms or stilts (Figure 5). The store should be dry, with low humidity. The bags must be stacked on wooden pallets so that bags do not touch the ground. The structures could either be raised on a platform or built on the ground. Traditional storage structures vary according to regions

Insects are the most serious pests of stored products and can reduce the amount of grain harvested substantially. A good understanding of the important types of insects and their behavior will significantly help in their control. The important insect pests of stored products are either beetles or moths. These insects can be divided into two groups, namely, primary and secondary insects. Primary insects are those that are able to attack undamaged grain cereals such as the Angoumois grain moth (Sitotroga cerealella), large grain borer (Prostephanus truncatus), and weevils (Sitophilus spp.). Secondary pests such as flour moths and flour beetles (Tribolium spp.) can only attack stored commodities, which have previously been damaged either by primary pests or through processing (shelling or milling).

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For sorghum, the most important pests are the rice weevil (Sitophilus oryzae) (Figure 7) and grain moth (S. cerealella) (Figure 8). Infestation by these pests often starts when the crop is drying in the field, but there can also be carryover from storage. Recently, the larger grain borer (P. truncatus) has been reported spreading into sorghum-growing areas in the southern African region (Figure 9).

Weevils (Rice Weevil, S. oryzae) Both adults and larvae feed on grain, damaging it beyond use. The adult female bores a hole in the kernel and deposits a single egg. A female can lay 300–500 eggs. The egg hatches into a legless white larva (grub) after 3 days. The larva becomes mature in 3–6 days and adults can live for 5–6 months. In most cases, eggs are carried on grain harvested from the field.

Moths (Angoumois Grain Moth, S. cerealella) Angoumois grain moth infestation can begin in the field. Attack in storage is confined to the upper layer of the grain

Figure 7 The rice weevil (S. oryzae) infects sorghum grain at moisture contents ranging from 10% to 16%. Soft endosperm types are less resistant than sorghums with hard endosperms.

Figure 8 The Angoumois grain moth (S. cerealella) attacks sorghum in the field. It multiplies rapidly if sorghum is stored unthreshed.

and surfaces of bags containing the grain. The larvae bore into grain, where they feed, pupate, and finally emerge as adults, leaving round holes in the grain. The infested grain is completely hollowed out and filled with larval excreta and webbing. The larval period is 2–3 weeks and the pupal period 1 week. The adult moth does not eat the grain.

Control of Insect Damage Insect damage can be greatly reduced by preventive action. The following practices can limit the initial infestation of the stored grain: 1. To avoid infestation of the new crop, the old grain must be removed preferably before the new crop is mature, but certainly before the mature crop is brought to the homestead. Old grain from the previous season is often a major source of insects. 2. The new crop must be rapidly dried to attain safe moisture content levels and threshed as soon as it is dry. The grain is then treated and put into store before any significant damage has occurred. 3. Before the new crop is brought in, the storage structure and its surrounding should be well cleaned and maintained. 4. The product going into the store should be (a) well dried, (b) well cleaned, and (c) undamaged (sound). Any damaged grain should be removed and consumed first. 5. The storage structure should have no entry points at all times to prevent reinfestation with insects. 6. Adequate systems of inspecting the grain throughout the storage period should be put in place.

Figure 9 The larger grain borer (P. truncatus) has also been reported as a storage pest of sorghum.

GRAIN HARVEST, STORAGE AND TRANSPORT | Sorghum: Harvest, Storage, and Transport If any pests or damage is detected, immediate action should be taken through the following exercises: (1) repairing any damage to the storage structure if necessary, (2) cleaning and drying the grain by either sunning or kilning, and (3) treating the grain again with a suitable insecticide such as pirimiphosmethyl (Actellic) or pyrethrum dust or with wood ash if necessary.

Insecticides Insecticides provide good protection against insects in storage due to their residual effects. There are several dust insecticides on the market that are recommended for use to control insects in stored grain. In southern Africa, commonly used dust insecticides include Actellic super dust, Chirindamatura Actellic super dust, and Shumba super at application rates of 25 g per 50 kg of threshed sorghum. These are most effective when they are admixed with threshed grain. Aluminum phosphide or phosphine, also known under trade names such as Phostoxin, Phosphume, or Phostek, is used for indoor fumigation of grain as a means of controlling storage insects. It is strongly recommended by the Food and Agriculture Organization of the United Nations as it leaves no toxic residues. According to the US Environmental Protection Agency (EPA), tolerances are established at 0.1 ppm for residues of the insecticide phosphine on sorghum grain resulting from postharvest fumigation. In Botswana, for example, Phostoxin is the most commonly used fumigant. Another common practice among farmers is to store the grain with neem leaves. Neem (A. indica) contains pesticidal ingredients for protection of the plant from a multitude of pests. The ingredients can affect more than 200 insect species and some mites, nematodes, fungi, bacteria, and even a few viruses. Neem substances have protected stored sorghum and other foods against pests for up to 10 months in some very sophisticated controlled experiments and field trials. The main compounds belong to a general class of natural products called triterpenes or limonoids. Azadirachtin, salannin, meliantriol, and nimbin are the best known among neem limonoids. Azadirachtin repels and disrupts the growth and reproduction of insects; salannin and meliantriol both inhibit insect feeding; and nimbin manifests antiviral activity. Neem leaves contain other ingredients shown to disrupt the fungi that produce aflatoxin on moldy cereals, legumes, and other foods. Although the fungi remain alive, it switches off their ability to produce aflatoxin, the most powerful carcinogen known.

Selection of a Storage Structure To store grain properly and successfully, the storage structure must provide an environment that prevents grain losses and maintains the grain in good condition until it is consumed or sold. Therefore, the storage structure must be able to 1. keep the grain dry (the grain must be protected against rain and ground moisture. An increase in moisture content encourages germination, mold, and insect development), 2. protect the grain against pests (a well-constructed storage structure should provide a barrier against rodents and insect reinfestation),

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3. keep the grain temperature low (a low and stable temperature will reduce insect and mold development. Uneven temperatures cause moisture migration in storage), 4. facilitate easy cleaning and inspection (grain stored in a clean and tidy storage structure is less prone to deterioration). Smallholder farmers can use better storage structures such as the improved mud-plastered grain bin for on-farm grain storage.

Fungal Contamination of Stored Sorghum Mycotoxins are poisonous chemicals produced by the growth of fungi on grain, oilseeds, and other materials. They can be produced both in the field and during storage. The rate of infection and proliferation of the mold in sorghum is influenced by several factors including the physical status of the grain, moisture content, temperature, and oxygen and carbon dioxide in the atmosphere. There are varietal differences in fungal contamination and aflatoxin elaboration in sorghum with high-tannin sorghums having a reduced mold infestation. Mold-infested grains undergo physical and chemical changes including a dirty off-coloration, lower test weight, higher values of reducing sugars, and fat acidity. Mycotoxigenic fungi such as Aspergillus, Alternaria, Fusarium, Curvularia, and Phoma and mycotoxins such as alternariol; alternariol monomethylether; patulin; trichothecenes; zearalenone; altenuene; altertoxin I; aflatoxins B1, B2, G1, and G2; and T-2 toxin have been reported in sorghum under certain environmental conditions. Storage fungi of the genera Aspergillus and Penicillium can be produced on grain stored with moisture content > 13%. Aflatoxin produced by Aspergillus flavus in sorghum is the most carcinogenic of the known mold metabolites. For example, pigs can tolerate only 0.23 ppm in their feed. Aflatoxin has been shown to be hepatotoxic, carcinogenic, mutagenic, and teratogenic. Proper drying and storage would greatly prevent the contamination of food grains with these mycotoxin-producing fungi. Failure to dry grain or prevent accumulation of moisture through condensation favors the growth of molds. Under conditions of 30–40 C, aflatoxin can be produced within 2–6 weeks, and signs of mycotoxicosis of pigs may be noticed within a week of it being introduced into the diet. The total quantity of the food to be consumed and the animal (including humans) for which it is intended will both influence what is considered a ‘safe’ tolerance limit. Young infants are more sensitive than healthy adults. Many grain-importing countries enforce regulations on mycotoxin levels set by the Codex Alimentarius Commission. To avoid or minimize grain contamination by mycotoxins, proper agronomic, storage, handling, and inspection practices should be implemented.

Transport Transport of grain is an important component and is varied. An efficient transport mechanism is needed to get the produce from the field to storage warehouses and ultimately to markets.

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In Africa, where sorghum is commercially processed on a very large scale, for example, for malting, there is a real need for bulk transport of the sorghum grain. For example, transportation costs are excessively high in Nigeria due to poor infrastructure. Compared to other major cereals, sorghum is not widely traded internationally but trade is increasing. For example, China is now a major importer of sorghum from Australia and the United States. Within those developing countries where sorghum is grown for human food, there is usually a balance between local production and local demand. Smallholder farmers use oxen-drawn carts or trailers to transport farm requisites and farm produce. Donkeys are also widely used as well. Sorghum heads are harvested in the field and placed on a cart to the threshing area. In many cases, women transport the harvest in baskets on their heads. The produce can also be taken to markets. Intermediate and other larger farmers use either tractors or trucks to get their produce to storage areas and markets. In developed countries, considerable movement occurs not only within surplus grain areas but also into export channels and into feed-deficit areas. Sorghum for animal feed is transported mostly by rail or truck. The former is considered the best for distant shipments, whereas the motor truck is used for short shipments. The shipper’s choice on both long and short hauls is based upon relative transport rates, services performed, and other costs and convenience factors. The nature of operation is reflected by the ratio of truck to rail movement. Country elevators generally have shorter distance and smaller quantity per haul. Although total shipments are small, since most of their receipts are processed, processing plants are next in distance and quantity. Terminal elevator operations generally have the longest hauls and the largest quantity per haul. Both distance and quantity for each type of handler are generally less for receipts than for shipments. Domestic shipments are also done to a lesser extent by barge. Barge shipment is primarily used for sorghum export. The United States is the largest exporter of sorghum. Argentina and Australia also produce sorghum meant for the domestic and export market. Most sorghum is exported to feed grain-deficit areas, and China, Japan, Mexico, the former USSR, and Venezuela are the main importers. Global standards for sorghum grain trading are specified under the Codex Alimentarius Commission under Codex Standard 172-1989.

Future Prospects Sorghum will remain an important global food and feed crop especially considering the very rapidly growing demand for sorghum for brewing, gluten-free flour, and bioethanol. The largest group of producers, the smallholder and subsistence farmers, can play a greater role in world sorghum production and marketing provided they have reasonable access to production inputs, improved harvest techniques, better storage facilities, and transport mechanisms for their produce. Sorghum is poised to compete equally with rice, wheat, and maize given its yield potential and the area currently under cultivation. However, inputs similar to those provided for rice, wheat, and maize on

genetics, production, and postharvest research are still to be realized.

Exercises for Revision Sorghum remains an important crop that should be further investigated to discover appropriate but low-cost techniques for harvesting, storage, and transportation that can be applied in developing countries. There are several approaches that can be used to control storage pests; however, further research is needed at the regional or country level to find the most costeffective and culturally acceptable method. Storage structures currently being used in the developing countries can also be investigated further to decrease postharvest losses. Communal structures can also be considered in remote parts of developing countries. Postharvest processes can also be investigated for the local markets where there is inadequate road infrastructure to transport sorghum to urban markets.


• • • • • • •

What indicators of maturity are used to determine that the sorghum grain has become physiologically mature for harvesting? What is the grain moisture content when sorghum is harvested manually? What is the targeted optimal moisture content for grain and seed during drying of sorghum panicles? Why should care be taken to avoid physical damage to the grain during threshing? Which methods are commonly used for storage of sorghum grain? Identify primary and secondary insects that can significantly reduce the amount of sorghum grain harvested. How can you control insect damage during storage of sorghum grain?

See also: Agronomy of Grain Growing: Sorghum: Production and Improvement Practices; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Grain Harvest, Storage and Transport: Handling from Farm to Storage Terminal; Stored Grain: Invertebrate Pests; Grains Around the World: Grain Production and Consumption: Africa; Non-food Products from Grains: Cereal Grains as Animal Feed; Non-wheat Foods: Sorghum: Utilization; The Basics: The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.

Further Reading Bennett WF, Tucker BB, and Maunder ABM (1990) Harvesting, marketing, and utilization. In: Modern Grain Sorghum Production, pp. 144–153. Ames, IA: Iowa State University Press. Christensen CM (1970) Moisture content, moisture transfer, and invasion of stored sorghum seeds by fungi. Phytopathology 60: 280–283.

GRAIN HARVEST, STORAGE AND TRANSPORT | Sorghum: Harvest, Storage, and Transport Dendy DAV (1995) Sorghum and Millets: Chemistry and Technology, pp. 169–183. St. Paul, MN: American Association of Cereal Chemists. FAOSTAT (2013) Database. Golob P, Boxall R, and Gallat S (2009) Agricultural and Food Engineering Training and Resources Materials 2. On-Farm Post-Harvest Management of Food Grains. Rome: Food and Agriculture Organization of the United Nations. Hill DS (1987) Agricultural Insect Pests of the Tropics and their Control. Cambridge, UK: Cambridge University Press.

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Serna-Saldivar SO (2010) Cereal Grains: Properties, Processing, and Nutritional Attributes. Boca Raton, FL: CRC Press. Vie´mont J-D and Crabbe´ J (2000) Dormancy in Plants: From Whole Plant Behavior to Cellular Control, pp. 183–194. Wallingford, UK: CABI Publishing. Wall JS and Ross WM (1970) Sorghum Production and Utilization, pp. 469–506. Westport, CT: AVI.

Canola: Harvest, Transport, and Storage JJ Mayko, Canola Council of Canada, Mundare, AB, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp. 155–161, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • • • •

A canola crop may ripen quickly, so it is difficult to gauge the correct time to harvest it. Canola can be harvested with the same swathing and combine equipment as for cereal crops. Swathing before combining may reduce seed losses and ensure best grain quality. The use of a chemical desiccant can result in a more uniformly ripened crop. Successful storage depends upon regulating moisture and temperature conditions. Heating of the seed may lower the quality of the oil and of the residual meal protein. Moisture levels of 8–9% at temperatures below 20 C are needed for long-term storage. Conditioning of stored grain may ensure quality retention by cooling and drying via forced air.

Learning Objective

•

To attain practical knowledge about the harvesting and storage of canola grain to optimize grain recovery with best possible quality.

Introduction Canola is a small-seeded crop, but the principles used in the harvest, transport, and storage of this crop are similar to those used for many other small-seeded grain and oilseed crops. Various factors during harvest and handling process may have to be altered or modified to accommodate this crop. This article summarizes many of these factors and discusses methods used in the successful handling of this crop.

Harvesting Methods As a high-yield canola crop approaches maturity, it may ripen very quickly. Gauging the correct time to harvest calls for more care and adjustments than with cereals. Canola can be harvested with the same swather and combine equipment as cereal crops, although the crops are quite different. Canola is often tall and branchy, with thick spongy stems. Swathers and combines must be properly operated and adjusted to facilitate a smooth flow of crop material through the machines while minimizing seed losses. With a few basic adjustments to most modern small-grain harvesting equipment, harvesting of canola is successful. Canola can be harvested either by direct combining or by swathing and combining, depending upon the species and the

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growing conditions. The decision on which harvesting method is appropriate is dependent on a number of factors, including which species of canola is grown. Brassica rapa varieties are much more tolerant to pod shatter and drop than Brassica napus varieties and can therefore usually be left for straight cutting, if preferred. Brassica napus varieties can be direct cut as long as crop conditions are such that the crop is well knitted; that is where the crop canopy is thick enough that the branches are well knitted together, and therefore are much less prone to damage from pod shatter or drop from windy conditions.

When to Swath Swathing at the optimum stage of ripening reduces green seed problems and seed losses, and ensures the quality required for top grades. To determine when a field of canola is ready to swath, plants from different parts of the field must be examined. The stage of maturity in an evenly maturing field will vary from plant to plant and from area to area within the field. Inspections every 2–3 days should begin when there is some seed color change in the first formed pods on the bottom of the main stem. The color of the seed is more important than the overall color of the field in determining the stage of maturity. The best time to swath for optimum seed yield and quality is when all the seeds contain 30–35% moisture. Examine only those pods on the main stem, except in conditions where the plant density is sparse, and more secondary branching has taken place. Seeds in pods on the bottom third of the main stem were formed earlier and will turn color much sooner than seeds in the pods of the top third of the plant. When the overall moisture content of seed from the total plant averages 30–35%, 30–40% of the seeds in pods on the main stem only will have changed color or have started to change color. Seeds with only small patches of color should be counted as color changed. Most of the seeds that have changed color will be from the bottom third of the stem in B. napus varieties, whereas in B. rapa varieties some seed color change will also have occurred in the middle and upper pods. When seeds in the bottom pods turn color, seeds in the top, last-formed pods are filled or nearly filled. Most of the seeds will be firm, and roll, as opposed to break, when pressed between the forefinger and thumb. At this point, seed yield and quality are usually optimized. Although the optimum time to swath canola is when 30–40% of the seed on the main stem has changed color, swathing should usually begin before the crop reaches the optimum color change stage. This is particularly important if one is growing large acreages of similar maturing canola. If the crop is left until the optimum stage before starting to swath, some of the crop will be too ripe by the time swathing is finished. Swathing earlier rather than later reduces risk for


http://dx.doi.org/10.1016/B978-0-12-394437-5.00181-9

GRAIN HARVEST, STORAGE AND TRANSPORT | Canola: Harvest, Transport, and Storage Table 1

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Effect of time of swathing on B. napus canola yield, oil, and protein in western Canada

% Seed color change

Location years

Yield (%)

Oil content (%) @ 8.5% moisture

Protein content (%) @ 8.5% moisture

0–10 10–20 20–30 30–40

25 25 25 25

90 96 100 100

40.8 41.5 42.2 42.8

20.7 21.7 21.6 21.6

Reproduced with permission from Canola Council of Canada (1995) Canola Production Centres – Five Year Summary Report. Winnipeg, MB, Canada: Canola Council of Canada.

factors such as frost or diseases, e.g., blackleg, alternaria, and sclerotinia, if present. One or two days advantage may be critical in the fall when weather conditions can be unfavorable in a very short space of time. Swathing before 10% seed color change in any situation is not recommended unless the crop was seeded so late that it has not begun to reach seed color change before imminent frost. In that case, the canola can be swathed in order to salvage as much yield as possible before frost damage. Work conducted in canola production centers across the Canadian prairies over 25 site years, for 1990–94, confirms that earlier swathing of B. napus canola (at 20% seed color change) can be an acceptable practice which causes minimal loss in yield and oil content (Table 1). The trials were conducted under field-scale conditions using standard farm equipment. As B. napus canola has a narrower range in development time (due to less branching and podding) than B. rapa canola, it is possible to swath B. napus canola earlier without yield loss due to immature seed. This range in development time is affected by any factor that influences branching and podding. For example, a dense stand of canola branches less and, therefore, has a narrower range in development and can be swathed earlier. However, a light stand tends to branch more profusely and has a wider range in development. It may be advantageous to delay swathing a light crop to the higher end of the seed color change recommendation. Swathing late, when seed moisture content is much lower ( 80% seed color change), will result in fluffy windrows susceptible to blowing and increased shattering. To reduce shattering losses, over-ripe fields should be swathed when humidity is high, such as after a rain, after heavy dew, or at night. It is difficult to determine when to swath unevenly maturing fields. Uneven maturity is usually the result of uneven spring germination where two or more flushes of germination have occurred. Determine which of the different stages of maturing plants is the majority. Swathing should occur as soon as some color change is visible on bottom pods of the main stem toward on the end of the major stages on the field.

Swathing Operation The swather should be run just low enough to get all the seed pods, leaving the maximum amount of stubble in which to anchor the windrow and ensure adequate air circulation through the windrow. Such windrows tend to settle into the stubble and escape wind damage. This also minimizes the

amount of material that must be handled by the swather and the combine. The average crop of canola is handled quite readily with most swathers. However, stands that are exceptionally tall (1.5–2 m), thick, or lodged and tangled, make it difficult to lay an unbunched windrow. The windrow must flow smoothly through the swather without bunching. Bunching leads to uneven drying and combining problems. A large throat opening is important, particularly for wider swathers, to ensure that the swath will be of a size and shape that will dry and cure properly. The swather should have good reel and table adjustments so that the crop can be cut as high as practical without losing any pods or causing shelling or bunching windrows. The reels should be set as high and as far forward as possible. Reel speed should be set to correspond with the forward speed of the swather. This speed will lay the cut material gently back on the table to avoid shelling. Table dividers, which are long and gently sloping, are generally less prone to blockages than short, abrupt types. When the crop is tall, tangled, and lodged, or laid across the seeded rows, divider blockages are almost inevitable unless special vertical cutter bars or power blades are fitted on the swather. These can cause minor loss of pods and whole seed tops, but they prevent stops and bunching. In areas where light fluffy windrows could be lifted and blown by the wind, a light roller pulled behind the swather will help anchor the windrow in the stubble. The roller should be set so that it just anchors the windrow into the stubble without shelling any ripe pods. Excessive rolling will produce a windrow that is too compact to dry quickly and difficult to pick up without shelling the canola.

Chemical Desiccation and Pod Sealants The use of a chemical desiccant, which kills the green growth of pods, stems, and leaves, can result in a more uniformly ripened crop. This may allow earlier combining. A crop must be desiccated at the proper stage to achieve the best yield and seed quality. A desiccant should not be applied when the crop is immature or past the recommended stage of maturity. Desiccation may reduce the incidence of pod shattering and seed loss making it a possible alternative to swathing. However, the costs of the desiccant and its application must be taken into consideration. When seed is mature but before pods become dry and split, pod sealants will slow pod dry-down and prevent the movement of moisture into and out of the pod, reducing shatter losses. Combine timing is crucial for minimizing shatter losses as the sealant efficacy diminishes with time and from repeated

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GRAIN HARVEST, STORAGE AND TRANSPORT | Canola: Harvest, Transport, and Storage

Table 2

Effect of swathing vs. straight combining canola in western Canada on yield, oil, and protein

Treatment a

B. rapa (S) B. rapa (DC) B. napus (S) B. napus (DC)

Location years

Yield (%)

Oil content (%) @ 8.5% moisture

Protein content (%) @ 8.5% moisture

24 24 28 28

100 99 100 89

40.4 40.6 42.8 43.5

20.3 20.3 20.1 19.9

S ¼ swathing; DC ¼ straight combine. Reproduced with permission from Canola Council of Canada (1995) Canola Production Centres – Five Year Summary Report. Winnipeg, MB, Canada: Canola Council of Canada.

a

rains. Sealants slow crop dry-down and harvest by 5–14 days. This could be a concern in shorter season growing areas.

Combining Canola Combining should begin when the seed is mature, fully color changed with no green seeds, and of a moisture content of less than 10% unless a drier is being used. Canola crops which have been desiccated, or that are uniformly mature and free of green weeds, may be straightcombined without swathing. Work at canola production centres in western Canada has shown that most varieties of B. raga canola lend themselves well to straight combining. Straightcutting of B. napus canola should only be attempted if crop conditions are favorable where crop growth is relatively heavy, with subsequent lodging, and where the risk of crop canopy movement from wind is low, and where the crop has low levels of disease (Table 2). One of the main problems in straight combining in tall canola crops is ensuring freedom from blockages at the dividers and other table components so as to maintain a smooth crop flow into and through the combine. Again, long dividers or vertical power dividers can be effective in preventing crop blockages. To minimize shatter losses, the reel should be set well back and as high as possible to act as a precaution against stems falling forward. Reel speed must be matched carefully to forward speed to minimize seed shatter. Shatter losses can be reduced by combining a ripe crop when the pods are still damp from rain or dew, provided the moisture level of the seed does not exceed the safe storage level. Canola in the windrow is ready to pick up and thresh when the seed temperature and moisture content have dropped to a safe storage level and most seeds are mature with no green color. While it is better to start on the early side for swathing, the same does not necessarily hold for combining. Hot or windy weather at, or after, swathing can cause canola seed to be at the appropriate moisture content for combining before it has cured and cleared the green chlorophyll. This occurs because the plant dries up before sufficient moisture can move into the seed to finish curing it. Canola requires at least 20% moisture in the seed for the maturing process to take place and eliminate the green seed color. It is important to check both moisture content and green seed count before starting to combine. Delaying combining can help clear the green color particularly if the swath sits through several heavy dews or light showers. If there are some green seeds, a few more days in the windrow may be all that is needed. Green seeds may ripen in

the windrow but they do not cure significantly once they are combined. Before combining, a crush strip is used to ensure that the seeds are not green inside. A small percentage of seeds with green meat will reduce the grade. If wide swathers are used on tall, heavy crops, the result is very large windrows, which take a longer time to cure, especially at the center of the windrow. Bunching in the windrows also may contribute to a green seed problem as the crop dries out and cures unevenly.

Combine Checkout and Adjustment Before combining, the combine should be checked over completely to ensure that it is in a good mechanical condition. Any holes through which the small seed can escape should be covered and plugged. Besides plugging all leaks it is important to keep the rest of the combine in good mechanical condition. Worn or loose components such as feeder conveyors, internal conveyors, and elevators are sources of seed cracking. The first setting of any combine –including threshing cylinder or rotor speeds, cleaning fan speeds, and cleaning sieve settings – should be set to the specifications in the operator’s manual. To minimize front-end seed losses on a combine equipped with a pickup, pickup speed and forward travel speed should be equal so that the windrow will be gently lifted without tearing or pushing. Threshing cylinder or rotor speed will depend on crop conditions. Speeds set at about one-half to two-thirds of that used for cereals can often be used for canola. Speed reduction is important to prevent overthreshing of the pods and stems and overloading the cleaning sieves. Cracked canola is caused by impact when the cylinder speed is too fast. A speed that is too slow reduces the capacity of the combine. The cylinder speed should be maintained at a level where the amounts of cracked seeds are acceptable. Once the cylinder speed has been set, concave clearance should be set as wide as possible to give a good threshing the first time through. The stems and pods should be broken no more than necessary and unthreshed pods should be kept to a minimum. This will reduce overloading of the sieves and allow seed separation without excessive dockage or load on the return conveyor. For efficient threshing and cleaning, the combine should be operated as near as possible to its recommended capacity. Increasing the forward speed of the combine will increase the straw and chaff feed rate to a point where seed losses may increase dramatically. Too high a feed rate will exceed the capacity of the separating and cleaning components.

GRAIN HARVEST, STORAGE AND TRANSPORT | Canola: Harvest, Transport, and Storage The proper adjustment of the fan and sieves for cleaning action is important since canola seeds are light and can easily be blown out of the combine or remain mixed with the chaff. Unlike the cleaning action for cereals, the cleaning action for canola should depend more on a shaking separation and less on a wind separation. While it is necessary to reduce the fan speed, enough wind must be used to maintain a “live” sieve. Air should be directed as uniformly as possible under the entire length of the sieve to keep the sieve “alive;” otherwise, stems, pods, and canola will move over the sieves in a mat and losses will be extremely high. The top sieve or chaffer should be opened enough for good separation (1/4 to 1/3 open, or 6–10 mm). This will keep the seed from going over the top and out the back. Air should lift the chaff on the sieve with a shaking action conveying the material along. The chaffer extension should be raised slightly (5–10 ) at the rear and be open sufficiently to allow unthreshed pods through to the return. A chaffer opening that is too narrow, coupled with insufficient wind, will result in high seed losses. If the air blast is too fast (high fan speed), canola will be blown out with the chaff. Starting with a low fan speed and gradually increasing it until separation of chaff and seeds occurs, with no canola being blown over the chaffer sieve, is advisable. The lower sieve should be adjusted depending on the sample in the hopper. Usually a setting of 3–6 mm will be sufficient for the lower sieve. If too much trash is in the grain hopper, the sieves are likely open too much. If the sample is perfectly clean, it means that canola may be going back to the return conveyor so that sieves should be opened slightly. Excessive returns can result in crackage of the seed. If the returns are too high, there may not be enough wind, the top sieve may be open too much, or the cylinder (rotor)-concave is overthreshing. Since high losses are possible where combines are incorrectly operated or adjusted, the operator must make frequent checks and readjustments. Changing conditions during the day will change combine performance. Regular stops are suggested to check for losses and make adjustments in the field. A grain loss monitor aids in the detection of losses and a function monitor reports any problems in mechanical operation. Monitors must be installed correctly, calibrated properly, and handled carefully if they are to give reliable service.

Handling and Transport of Canola Grain handling and transport systems are similar to those of cereals and other small grains and are designed to suit the needs of a particular farm, not for any special requirements associated with handling canola. Therefore, most transport and conveying equipment that is successfully used with small grain cereals can be used with canola. During transportation, all cracks in trucks and other equipment must be sealed with duct tape or caulking to prevent leakage and tightly covered to prevent canola seeds being blown away. Augers should operate at full capacity to prevent the seeds from flowing back down the tube and belt conveyors should be enclosed in a trough to keep the seeds from running off-line. Kernel damage during handling is usually not a problem unless below 7% moisture content.

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Storage of Canola The main functions of grain storage structures are:

• • •

protect the grain from damage due to moisture, heating, and insects; prevent losses due to leakage, rodents, and livestock; and provide reasonable convenience for handling or inspecting grain.

The requirements for canola storage facilities differ little from those for cereals. The nature of canola seeds and the fact that canola historically has been more valuable than an equal volume of cereals impose greater demands on storage structures. Canola is very sensitive to heating in storage and, therefore, requires better construction to exclude moisture. The small size and free flowing characteristics of canola mean that highquality construction is necessary to prevent leakage. Roof and door openings, joints between structural components (roof to wall, wall to floor), and even bolt holes must be sealed carefully to avoid losses. The problems of heating and moisture migration tend to be more severe in large storage structures. Thus, canola should be stored in the smallest bins available, without sacrificing convenience and efficient handling.

Construction of Storage Structures Some authorities have advocated the use of wooden, rather than steel, granaries for storing canola because they “breathe,” thereby allowing heat and moisture to dissipate. However, the porous nature of these structures makes control of leakage difficult and also provides access for the influx of moisture, insects, and rodents. Steel granaries require almost no maintenance and can be more easily sealed against pests and weather. If some conditioning of hot or damp grain is necessary, metal bins are best suited to the controlled movement of air through the grain mass. Regardless of the construction material used, storage structures must be as weatherproof as possible, yet still allow easy access to the bin for sampling and monitoring. The weatherproofing process must include the floors of bins set on grade. Concrete floors may resist the movement of water through the slab, but moisture can still enter the bin in the form of vapor. For this reason, a vapor barrier such as polyethylene should be placed between the concrete and the gravel base.

Conditions Necessary for Safe Storage Conditions for successful storage of canola seed depends upon the moisture and temperature conditions. Grain absorbs moisture from the air or gives up moisture to it, depending upon the relative humidity of the surrounding air and on the moisture content of the seed. The oil fraction of canola seed absorbs less moisture than the starch and fiber fractions, so the equilibrium moisture content for canola is much lower than wheat. Canola seed must be stored at lower moisture content than cereal grains to prevent spoilage. Moisture levels of 8–9% at temperatures below 20 C are necessary for long-term storage. The

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GRAIN HARVEST, STORAGE AND TRANSPORT | Canola: Harvest, Transport, and Storage Heating of Stored Canola

Figure 1 Canola storage time chart. (Reproduced with permission from Thomas PM (1984) Swathing – combining, storage, and conditioning of canola. In: Canola Growers Manual, pp. 1101–1215. Winnipeg, Manitoba: Canola Council of Canada.)

relationship of canola seed moisture content and temperature to safe storage is shown in Figure 1. Any combination of canola seed temperature and moisture content to the left of the bar on the chart is acceptable for longer-term storage. Only under conditions of <9% moisture and cooler than 15 C, does canola require only occasional monitoring. The chart does not allow for deterioration due to infestation by insects and mites that can occur in hot, dry seed. High moisture content but low temperature, or high grain temperature even though the grain is very dry, serves as warnings that extra attention is needed. The optimum temperature for rapid growth of insects is in the range of 30–35 C; their activity is greatly retarded by temperatures below 18 C. If the grain is cool and dry, insects will not thrive. However, seed may go into storage at acceptable levels of moisture content and temperature and at a later date develop pockets of high moisture and temperature, which are favorable for insect activity. Infestation of hot and dry seed by insects and mites will reduce the safe storage time. Seed moisture content is fairly uniform throughout a bin when canola is first stored. Over time, air movement through convection in the bin may relocate moisture, bringing some canola to a critically high moisture content. Convection currents are caused by temperature differentials between the grain temperature, and ambient temperature.

Factors Contributing to Storage Problems Even though the seed moisture content and temperature have been measured and determined to be safe, problems may still occur. The severity of the problem may depend on how close the moisture–temperature relationship is to the critical line shown in Figure 1. If all the canola in a storage bin becomes damp and warm, immediate and positive action must be taken to condition the grain. Quality canola may be stored for 2 or 3 years if its moisture and temperature are properly maintained. To successfully store canola for periods of 6–24 months, special attention must be paid to conditioning and monitoring.

If the stored crop is not sufficiently dry and cool, its own respiration and the respiration of microorganisms and insects will increase the temperature of the grain mass. If left unchecked, this can lead to heating of canola, where damage occurs from microorganism activity and oxidation. Heating affects the viability of the seed. A slight degree of visible heating brings about a drastic reduction in germination. Heating of the seed lowers the quality of the protein in the meal and causes large increases in free fatty acid content. Free fatty acids are a complete loss to the processor and must be refined out of the oil. The oil from heated seed has poor quality. Heating produces a strong tobacco-like odor in the oil and meal that is difficult to remove by processing.

Conditioning Many producers must provide storage for significant portions of each crop for one or more years. Frequently, harvesting the canola in this state is difficult, if not impossible. Furthermore, processes that occur in storage facilities can cause deterioration in the quality of the canola, even when it has been harvested under ideal conditions. These factors illustrate some reasons for conditioning canola. Conditioning could refer to all treatment of the canola between the time it is harvested and delivered to a selling point, but the term usually describes those processes that involve the movement of air through the grain. The advantages of conditioning canola include:

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avoiding spoilage in storage; extending the harvest season; and reducing field losses.

Canola conditioning systems can be divided on the basis of both the purpose of the operation and the state of the air used in the operation. The simplest conditioning operation involves cooling of tough or dry canola, while some elaborate systems remove a considerable amount of moisture from the grain before cooling it for storage. Natural air systems, as their name implies, use the surrounding or ambient air to condition the grain. In most cases, there is no deliberate modification of the conditioning air. Heated air conditioning systems, on the other hand, use energy to heat the ambient air before its use in conditioning. The heated air has a lower relative humidity and, therefore, increased drying potential. The increased drying ability of heated air, combined with the high airflow rates typically used, give these systems a large capacity for drying canola. Combinations of these systems, involving two or more of the operations, are also used.

Summary Although canola is a small-seeded oilseed crop, many of the same principles that are used in the harvest, transport, and storage of other small grain cereals and oilseeds are used in

GRAIN HARVEST, STORAGE AND TRANSPORT | Canola: Harvest, Transport, and Storage the handling of canola. Specific factors, unique to canola, need to be taken into account, in order to successfully handle this crop relative to other small seeded crops.


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Explain the different approaches to harvesting with respect to the two main species of Brassica. What are the purposes of swathing? How can the optimum time and procedure for swathing be determined? How can chemical desiccation assist in harvesting? What factors would justify the extra cost of the chemical desiccant? Explain the problems of ‘shatter losses’ during combining, what solutions? What combine settings help to reduce grain losses and ensure best grain quality? List the precautions and maintenance needed to ensure best functioning of grain handling, storage, and transport systems. List the main threats to grain during storage. How can these threats be countered? Based on the graph in Figure 1, explain the conditions needed to minimize spoilage. Explain the concept of grain conditioning. Discuss the advantages and disadvantages of various designs for grain-storage structures.


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Research relationships between seed moisture and the colors of seeds, pods, and stems as indicators of the optimal timing for swathing and/or combining. How do these factors relate, in turn, to the oil and protein contents of the harvested grain? Search for recent research findings about the mathematical modeling of grain quality deterioration due to changes in its moisture content and storage temperature. Explain how such modeling can be used to optimize storage conditions and to determine how long grain can be retained in storage with adequate quality.

See also: Agronomy of Grain Growing: Canola: Agronomy; Breeding of Grains: Canola/Rapeseed: Genetics and Breeding; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Contaminants of Grain; Handling from Farm to Storage Terminal; Stored Grain: Invertebrate Pests; Stored-Grain Pest Management; Wheat: Harvesting, Transport, and Storage; The Oilseeds: Oilseeds: Overview.

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Further Reading Arinze EA, Sokhansanj S, and Schoenau GJ (1993) Development of optimal management schemes for in-bin drying of canola grain (rapeseed). Computers and Electronics in Agriculture 9: 159–187. Auld DL and Mahler KA (1991) In: Production of Canola and Rapeseed in the US, 8th International Rapeseed Congress, Saskatoon, Saskatchewan, July 1991, pp. 978–983. Bailey J (1980) Oilseed rape harvesting losses can be high. Arable Farming 59–61, May. Bandel VA, Mulford FR, Ritter RL, Kantzes JG, and Hellman JL (1990) Canola Production Guidelines. Cooperative Extension Service. College Park: University of Maryland, System, Fact Sheet 635. Bergland DR and McKay K (1992) Canola Production. North Dakota Extension Service, Fargo, ND. Bulletin A-686 (revised). Bergstrom DW (1993) Effect of Seed Moisture Content at Swathing on Yield and Quality of Rapeseed in Northwest Alberta. Alberta Agricultural Research Institute. Project No. 83-0025. Canola Council of Canada (1995) Canola Production Centres – Five Year Summary Report. Winnipeg, Manitoba: Canola Council of Canada. Canola Council of Canada (2001) Time of Swathing Guide. Canola Council of Canada. Cass J (1991) Canola Storage. Tips to help you through Harvest. Canola Farming Fact Sheet 4, 2 pp. Intermountain Canola Newsletter, Fall 1991. Idaho Falls, Idaho. pp. 3–4. Cenkowski S, Sokhansanj S, and Sosulski FW (1989) Effect of harvest date and swathing on moisture content and chlorophyll content of canola seed. Canadian Journal of Plant Science 69: 925–928. Daun JK (1987) In: Chlorophyll in Canadian Canola and Rapeseed and its Role in Grading 7th International Rapeseed Congress, Poznan, Poland. May 1987. Hang AN and Gilliland GC (1988) Winter Rapeseed Research Program in Washington State. In: Proceedings of the Pacific Northwest Canola Production Conference, Feb. 1988, Washington: Pasco. Kephart KD, Rice ME, McCaffrey JP, and Murray GA (1988) Spring Rapeseed Culture in Idaho. Idaho Agricultural Experiment Station Bulletin 681. McGregor DI (1992) Swathing Canola Stops Seed Filling. Research Letter. Saskatoon, Saskatchewan: Agriculture Canada Research Station. McGregor DI (1994) Relationship between chlorophyll clearing and moisture loss. In: An Overview of Canola Agronomic and Varietal Research 1990–1993, p. 26. Winnipeg, Manitoba: Canola Council of Canada. Mills JT (1989) Spoilage and Heating of Stored Agricultural Products. Prevention, Detection, and Control. Ottawa: Agriculture Canada, Ontario Publication 1823E. Mills JT (1990) Protection of Farm-stored Grains and Oilseeds from Insects, Mites, and Moulds. Ottawa: Agriculture Canada, Ontario Publication 1851E. Mills JT and Sinha RN (1980) Safe storage periods for farm-stored rapeseed based on mycological and biochemical assessment. Phytopathology 70: 541–547. Murray GA, Auld DL, O’Keeffe, LE, and Thill DC (1984) Winter Rape Production Practices in Northern Idaho. University of Idaho Agricultural Experiment Station Bulletin no. 634. Sylvester R, Makepeace RJ, and Broad H (1984) A code for stages of development in oilseed rape (B. napus L.). Aspects of Applied Biology 6: 399–419. Szot B and Tys J (1991) In: The Influence of the Spodnam DC Preparation on the Agrophysical Properties of Rape Siliques and on the Seed Losses at Maturation and Harvest, 8th International Rapeseed Congress, Saskatoon, Saskatchewan, July 1991, p. 174. Thomas DL, Breve MA, and Raymer PL (1991) Influence of timing and method of harvest on rapeseed yield. Journal of Production Agriculture 4(2): 266–272. Thomas PM (1984) Swathing – combining, storage and conditioning of canola. Canola Growers Manual. Winnipeg, Manitoba: Canola Council of Canada, pp. 1101–1215. Thostenson AA and Hennings CR (1990) Canola (rape-seed) Production Systems in the Pacific Northwest. In: First International Canola Conference, Atlanta, GA. Underwood N (1994) Canola Production Centre – Western Canada – A Three Year Report, pp. 26–27. Canola Council of Canada, Winnipeg, Manitoba, Canada.

Relevant Website canola-council.org http://www.canola-council.org

Cereals: Grain Defects SA Barton, Oxford Agricultural Trials Ltd, Oxford, UK ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp. 223–228, ã 2004, Elsevier Ltd.

Topic Highlights

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Characterization of sound grain of the cereal species involved, as a basis for comparison with defective grains. Correct sampling procedures to provide representative samples for assessment and analysis. Visual examination and its limitations; e.g., identifying broken grains, weed seeds, stones, insects, even snails. Analytical approaches measure specific weight, moisture, protein and oil contents, and the activity of a-amylase due to premature germination. Further causes of defects are diseases (black point, bunt, ergot and smut) and environmental factors due to drought, frost and sprouting. Procedures are recommended for preventing defects.

Learning Objective

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Gain the ability to conduct sampling and recognition of defective grains of cereal species, as compared to sound grains.

Introduction This article begins with a brief introduction to the stages through which grain travels from field crop to commodity. Similar symptoms may result from more than one cause. Therefore, it is important to be familiar with normal, healthy cereal grains before trying to recognize defects in them. The recognition of defects that are important to merchants or processors who buy the grain is explained with examples of how a poor raw material would affect an end product. An explanation of why certain defects result in sample rejection is provided where possible. Causes of physical and chemical defects are not always obvious; many result from pest infestation or disease infection earlier in the growing season of the crop. Grain defects that have not resulted from damage during development of the crop may be due to problems encountered at harvest, subsequent storage, or processing. Measures to prevent some of the main causes for rejected grain samples are suggested. As there are other articles in this encyclopedia devoted to a cereal overview, descriptions of grain morphology, nutritional composition of grains, and diseases of various individual crops are intentionally kept brief.

Production of Sound Grain Growth and Harvest In order to recognize defective grain, it is first necessary to know the qualities of sound (healthy or intact) grain. Cereal

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crops can be defined as any plants cultivated for seed as human food, although they tend to include only crops closely related to grass. In most cases, they require physical processing (cutting and threshing, or combining) to remove individual grains from the spike or ear in which they have grown. Barley, millet, oats, rice, rye, triticale, and wheat have grass-like grains when harvested. The seed of maize and grain sorghum is produced on larger, sturdier plants that are less grass like and better adapted to climates with brighter sunlight. Barley and the majority of oat varieties retain their husks when threshed, although several varieties of naked oats are also available whose husks are removed when they are harvested. The other cereals require threshing to remove their husks at harvest, prior to storage. Barley, oats, rye, triticale, and wheat all have a crease on one side of their grain as a result of the way in which they develop. It is this complication in grain morphology that has led to the evolution of a complicated milling process to extract white flour from wheat. The more uniform shape of other grain-producing plants allows them to be processed more simply.

Drying When cereals are grown in the temperate European climates where summer weather cannot be guaranteed to be dry, it is often necessary to reduce the moisture of grain once it has been harvested from the field. This can be done by a range of methods involving the flow of air through the grain, causing it to dry out. The air temperature may be raised in order to speed up the drying process, but if an internal grain temperature of 60 C is exceeded, there is a risk of protein denaturation. Drying at high temperatures can damage germination potential. The grower must ensure that the grain is dried enough to reduce or prevent fungal growth during storage (usually below 15% moisture content). The crop may be stored on the farm by the grower or sold on to a merchant or cooperative and bulked up with other similar types of grain. In drier climates, premature ripening may occur due to stress from drought. In such cases, grains are unlikely to reach their full potential size.

Storage The reason why cereal grains are so attractive to humans for food is because they have pleasant flavor, high nutritional value, and versatility. It is not surprising then that a number of pests have developed to exploit grain at whatever stage of production they are able to gain access to it. Assuming a grain crop has been protected during growth and has been successfully harvested into a clean storage area, it must then be protected from marauding birds, rodents, and insects. Secure grain silos or barns, which protect against pest invasion, are


http://dx.doi.org/10.1016/B978-0-12-394437-5.00182-0

GRAIN HARVEST, STORAGE AND TRANSPORT | Cereals: Grain Defects necessary. In addition to this, the temperature and humidity of the produce must be kept to suitably low levels to prevent conditions suitable for storage fungi, mites, and insect pests. In this way, even if the store is breached, the environment within the grain will not allow it to be spoiled. Regular monitoring of the store conditions, particularly the temperature, is vital. If a problem is to be dealt with in a timely and effective manner, its early detection is vital. Specific and detailed information may be found in the article on harvesting, storage, and transport of barley.

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The subdivision should be carried out in such a way as to keep the sample representative of the entire bulk. The use of a grain splitter enables this process to be carried out quickly and efficiently (Figure 2). The sample is tipped into the top of the splitter and half is diverted into one collection tray, the other half into the second tray. A number of tests are routinely carried out in order to check for grain suitability; these are outlined here, but explained in detail in the article on analysis of cereal quality.

Visual Assessment

Detection of Grain Defects Sampling Defects are assessed at intake points where grain consignments are delivered to the buyer or merchant, prior to processing or bulking with other samples that have been produced independently. Sampling correctly is vital as a precursor to any type of assessment in order to ensure that the original load is being correctly represented (Figure 1). It is worth taking time to appreciate the importance of this aspect of grain management. If a scoop full of grains were to be removed from the top of the sample after it has been transported to the intake point, the lightest and least dense material would be removed, rather than a mixture of the whole consignment. This is likely to contain unthreshed grains, broken grains, weed seeds of similar size, but lower density to the crop, ergot and insects as well as some healthy, but lighter crop grains. By analyzing such a sample, the bulk load may be rejected without having had a fair trial. If a subsample were taken from the bottom of the bulk load, it would be likely to contain the most dense and heaviest fractions, including stones, heavy dust, and small, dense weed seeds as some of the heavier (larger) crop grains. Analysis of this sample could produce results indicating the whole load to be of better quality than it really is. To avoid such misrepresentations, a strategy for accurate sampling is necessary. A sample for analysis should consist of several individual subsamples taken with a sampling spear that penetrates the entire depth of the transport container, at intervals across it. These subsamples should then be thoroughly mixed and subdivided in order to give a suitably sized sample for analysis.

Figure 1 Stratification of grain during transit and sampling spear.

Once a representative sample has been obtained, an evaluation by a trained individual is the quickest and most effective way to identify many potential defects. With experience, it is even possible to identify differences between varieties or quality types of the same cereal at this stage.

Sample appearance The kernels themselves should appear healthy and fit for purpose; generally they should be intact (with no sign of having started to germinate), bold (not shriveled), and bright (not dull or dead looking). If there is evidence that germination (or sprouting) has occurred, even if it has stopped, this is an indication that problems could arise during processing. In bread-making wheat, this would be as a result of excess enzyme activity from the germination process, or in malting barley, prevention of further growth during malting. Skinned barley grains cannot be fully malted and are not acceptable for malting samples; the condition occurs during harvesting, when all or part of the protective covering layer (husk) is torn away. Similarly, broken grains occurring during harvest will reduce the quality of any cereal sample, as they will be removed during cleaning.

Sample purity Sample purity is particularly important where the purchaser has set specific requirements. Although contaminants may not relate directly to the integrity of the grains themselves, they provide the main contribution to impurities within the sample. Easily visible signs of contamination include broken grains, ergot, insects, unthreshed grains, other cereal grains, weed seeds, soil, and stones. Dividing a predetermined weight

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GRAIN HARVEST, STORAGE AND TRANSPORT | Cereals: Grain Defects almost black, the affected area ranging in size from a small speck to covering over half of the grain. A proportion of unripe, green grains may be present in the sample. Field fungi that have remained on the grain after harvesting may produce either pink (Fusarium species) or black (sooty molds) areas on the grain. The presence of black mold in malting barley samples is potentially problematic, as the malting process is carried out under conditions which may encourage the proliferation of these fungi. Storage fungi, that have developed after harvest, may cause blackening and a musty sour smell. Again, it is important to be familiar with the crop in question, as the color of healthy grain is not always golden; for example, sorghum grains naturally ripen to a great variety of colors.

Grain Analysis Specific weight

Figure 2 Sample division using a grain splitter.

of grain into grain and nongrain material is used as an objective measurement of impurities within a sample. Each category of nongrain material is then weighed and expressed as a percentage of the total sample. This type of assessment is particularly important for high-quality crops such as the high-protein bread-making wheats produced in Australia, Canada, and the USA. Contaminants mixed in with grain consignments can be the cause of reduction in price paid by the purchaser, or in outright rejection of the sample. Although the majority of contaminants can be removed by cleaning the grain, the cost of this (to the processor) together with the cost of waste disposal must be recoverable in the final product market price or discounted when purchasing the grain. Grain should be free from pests (live or dead); if adults are present, they will be obvious during the visual appraisal, but certain larvae develop within stored grain, with the only indication to their presence being a small hole in the side of the affected kernel. The sense of smell can be used to detect odors, which may be symptomatic of mold (musty), mite infestation (minty or sour), or animal droppings; none of these should be present.

Discoloration If a pale, uniform product is to be made from the raw material, it is important that the entire sample is uniformly clean and does not contain discolored grain. Grains may become brown in places either as a result of physical “bin burning” or fungal staining (black point). The latter is particularly noticeable in whiter types of wheat such as the Australian Prime Hard, and its severity is associated with cereal variety. The germ end of the kernel becomes darkened, varying from a pale watermark to

This measurement of grain density is the weight of the grains that exactly fill a defined volume (generally the weight in kg of a sample calculated to fill 1 hl or 20 l) and it takes into account the type of cereal grains being measured. If samples contain a high proportion of small, unthreshed, or damaged grains, or if the moisture content is high, the grains will not pack efficiently and will give a low specific weight. If grains are larger, dry, and undamaged, they will give a higher specific weight. There will be some variation between seasons due to the weather and other environmental factors, also between different varieties, or types of each crop. Merchants and cooperatives will generally set acceptance values, below which a discounted price may be paid to the grower or the load may be rejected as unfit for use.

Moisture If a sample is too wet, it will not be safe to store for any length of time without risking rapid deterioration of quality. The most commonly used method for its determination at grain intake is by near-infrared reflectance (NIR); this indirect method is calibrated using the oven moisture method. The moisture content is simply the amount (weight) of moisture present in a sample expressed as a percentage of the initial weight. The oven moisture method involves weighing a sample accurately, drying it under specified conditions, and weighing the dried sample. The calculation of the moisture can then be made as the difference in weight divided by the initial weight and multiplied by 100 to give it as a percentage. High moisture content is the precursor to many problems within grain, including growth of storage fungi, pest infestation, and germination. Although the acceptable moisture of a sample will be agreed between a producer and merchant, generally, if a consignment of grain is too wet, it will require drying before it is fit to be processed further. If a sample is dry, it will store well, but may require the addition of large quantities of water over a long period of time to enable processing (particularly in the case of milling wheat). Also, dry grain will weigh less than the same quantity of wetter grain; this means that the grower will effectively be selling the produce at a lower price as price is based on weight, not number of grains. The support of fungal growth by moist conditions is of particular concern in connection with mycotoxin production. The presence of the wrong sort of fungi in warm damp

GRAIN HARVEST, STORAGE AND TRANSPORT | Cereals: Grain Defects conditions can lead to them producing toxic substances such as ochratoxin. By ensuring that the moisture content is kept suitably low, the conditions needed for the production of mycotoxins are prevented from occurring.

Protein The percentage protein content of a sample of cereal grains is likely to be an important factor in determining its sale value. At grain intake, a rapid protein measurement is taken with a suitably calibrated instrument. The amount of protein present is expressed at a specified moisture content, an example might be 13% protein on a dry matter basis (i.e., at 0% moisture). For the majority of grains, the higher the amount of protein (or nitrogen) present, the better, although, for malting barley, a lower nitrogen content is preferred as this indicates a higher carbohydrate content. The protein quality is also important when considering bread-making wheat types; if the specification for this is not met, the consignment will not be suitable for processing into bread. In order to ensure that a consignment of wheat is only accepted if it is suitable for processing, there are various tests that could be carried out. The simplest of these is the gluten-washing or wet gluten test. The starch is washed out of a ground wheat sample (using water or weak salt solution) and the remaining gluten is checked for color, elasticity, and extensibility.

Starch This is the main component of cereal grains; in some crops it has the highest value of all components. In wheat it is important during bread making as it is broken down by enzymes (a-amylase in particular) to feed the yeast during the baking process and enables the production of gas to give a risen loaf. At the subcellular level, there are different types of starch granules that give different characteristics to the starch depending on the ratio in which they occur. Cornstarch (from maize) is an effective thickening agent; it is relatively easy to extract and gives a consistent product. Modified maize starch can be found on the ingredient list of many modern food products. Starch is also used in the preparation of paper, wallpaper paste, and many pharmaceutical products.

Enzyme activity Green wheat grains can have high levels of a-amylase activity. As wheat grains develop, the enzyme activity reduces to a minimum level around the time of harvesting when the grains reach maturity. During germination, enzyme level rises again as it is involved in the breakdown of starch granules into polysaccharides. The Hagberg falling number (HFN) method is used at grain intake as an indirect measure of wheat enzyme content and it is able to detect the very early stages of enzyme activity that have no visible external signs. High levels of the enzyme a-amylase will cause starch to break down into its constituent polysaccharides. When starch is mixed with water at high temperatures it forms a gelatinous paste, and the time taken by a plunger to fall through the mixture indicates the integrity of the starch present within the flour. If the plunger falls more quickly, it indicates that the starch has been broken down.

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Causes of Grain Defects Diseases Black point Black point appears to be a response by the living tissue over the germ of the grain, to invasion or infection, whereby pigmented lignin precursors are laid down, blocking the progress of the invading mechanism. It has been linked to species of Alternaria by some work, but shown to be nonpathogen specific by other studies.

Bunt or stinking smut Spores of bunt (Tilletia caries) may be present in wheat grain samples as they are often released during harvesting if they were present within the crop. The fungus enters the germinated seedling and develops within the plant, resulting in misshapen grains that contain black, foul-smelling spores instead of white, starchy endosperm.

Ergot Ergots are the fruiting bodies of a fungal pathogen (Claviceps purpurea) that invades the developing florets of all grass species. It is spread by insects, rain-splash, or strong gusts of wind, then grows into the developing ovaries and gradually forms a solid purple-black mass that is often over twice the length of a normal grain. Ergotoxin is present within these fruiting bodies and, if ingested, can result in many unpleasant (if not deadly) symptoms including hallucinations, convulsions, abortion, and gangrene. Prevention is by the use of ergot-free grains or by burying any ergots from previous crops by deep plowing and crop rotation to prevent germination of ergots in the following year’s crop.

Fusarium sp.

Pink grains often result from the infection of cereal ears by Fusarium sp., which will sporulate freely under the right conditions resulting in a salmon pink tinge to the grain. The mycotoxin “deoxynivalenol” (DON) is produced by Fusarium sp. when conditions are suitable. DON levels indicate the gushing (foaming) potential of beer.

Loose smut Florets of developing grain plants are infected with spores of Ustilago nuda; symptoms of infected plants include yellowing of the flag leaf and a covering of thick black spores over the entire ear. Seed dressing can be used to prevent reoccurrence in the following crop. Common smut of maize (Ustilago maydis) is more resilient to control, the best defense being choice of a resistant maize variety.

Environment Drought During grain development, a certain amount of moisture is required prior to harvest to enable grain filling to take place. Under very dry conditions, grains will become severely shriveled and will be very small and light when they are harvested.

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GRAIN HARVEST, STORAGE AND TRANSPORT | Cereals: Grain Defects

Frost damage Kernels that have been affected by frost may become thin and distorted with a blue-gray discoloration in severe cases.

flour produced upon grinding the grain. Heat damage of barley can reduce the malting quality of the grain.

Harvesting Genetic and environment interaction The malformation of grains may be induced by a combination of genetic makeup and environmental factors. It was this that led to the sterility seen in the wheat variety Moulin in the UK in the 1980s.

Green grains The presence of green grains within a grain sample indicates either an early harvest, or a late wet period that stimulated the crop to produce back tillers that did not have sufficient time to ripen prior to harvest.

Sprouting (pregermination) Wet weather prior to harvest can have the effect of retarding ripening by keeping the crop green for longer and this may lead to the crop lodging (or falling down) due to the weight of the plants and the damp soil allowing roots to become loosened. Once areas of a crop have become lodged, the ripe, damp grains are prone to germination (or sprouting) whilst remaining in the ears. This process may be halted at the onset of dry conditions either in the field or due to drying of harvested seeds. The evidence that germination had begun remains visible to the trained eye, however, and should be picked up at sample intake.

Harvesting when too dry or with incorrect settings of the combine can lead to broken grains.

Storage Discoloration of grains known as “bin burning” occurs when stored grain remain in constant contact with silo walls heated in localized areas, for example, by sunlight on the outside of these walls.

Prevention of Grain Defects By addressing the causes of grain defects outlined above, many of the symptoms can be reduced, but due to the nature of crop growth, they are unlikely to be eliminated. The careful selection of variety to suit the local environmental conditions, good husbandry in the field, management of diseases and pests both during field growth and storage, and care during harvesting and processing will ensure a healthy, good quality crop.


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Weed competition High populations of competitive weeds in crops will prevent them from realizing their full potential in terms of yield and grain size. Also, the presence of weed seeds within the yielded crop will add to impurities and reduce the quality of the grain yield.

Pests

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Field insect larvae

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Orange blossom midge larvae enter the wheat floret before anthesis and live on the developing green grain. If the affected kernels reach maturity, they are shrunken and have a deformed, flattened (and often darkened) dorsal side.

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Storage insect larvae Some storage pests ensure their survival by burrowing a hole into a cereal grain and laying a single egg in it; when the egg hatches, the larva is surrounded by a plentiful food supply. As it develops, the larva hollows out the grain, eventually leaving just a husk of bran without the starchy endosperm.


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Crop Processing

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Drying

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Heat damage of proteins due to incorrect drying is mainly a problem in bread-making quality wheat. The functional gluten proteins are denatured, which causes them to lose their extensible and elastic properties and may cause a darkening of the

Contrast the appearance of sound grain (for three specific grain species) with that of these grains that have defects. To what extent would visual examination be adequate to detect these differences unequivocally? Explain the need for correct sampling procedures prior to grain examination. What procedures are most appropriate in the cases of taking initial samples from a fully loaded truck and of sub-sampling to obtain a smaller sample for detailed examination? Outline the defects that would be most evident by visual examination of a grain sample. Give details of the further aspects of grain analysis for which instrumentation would be needed for defect detection. Explain the consequences for the user of the grain if these were not detected. List defects due to diseases and environmental factors. Explain the procedures that might have been employed to reduce the risk of these defects occurring.

•

Find out what defects are most common for a grain species grown commercially in your region. Identify the defects likely to cause the greatest economic loss to a grain grower for a grain delivery. Determine the implications for the down-stream processor if some of the more serious defects are not detected. What measures are available to remove serious defective grains, or at least to mitigate the damage that they might cause in down-stream processing?

GRAIN HARVEST, STORAGE AND TRANSPORT | Cereals: Grain Defects

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Canola: Harvest, Transport, and Storage; Contaminants of Grain; Sorghum: Harvest, Storage, and Transport; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Barley: Grading and Marketing; Soybean: Grading and Marketing; Wheat: Grading and Segregation; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Grain: Morphology of Internal Structure; The Grain Crops: An Overview; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat Processing: Wheat: Dry Milling.

73

Further Reading Kent NL and Evers AD (eds.) (1994) Technology of Cereals: An Introduction for Students of Food Science and Agriculture, 4th edn. Butterworth-Heinemann. Matz S (ed.) (1991) The Chemistry and Technology of Cereals as Food and Feed, 2nd edn. Texas, USA: Pan-Tech International. Morris PC and Bryce JH (eds.) (2000) Cereal Biotechnology. Cambridge, UK: Woodhead Publishing. Owen G (ed.) (2001) Cereals Processing Technology. Cambridge, UK: Woodhead Publishing.

The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species RA McIntosh, The University of Sydney, Cobbitty, NSW, Australia PM Williamson, (Retired) Leslie Research Centre, Toowoomba, QLD, Australia CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition volume 1, pp. 228–238, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • • •

Causes of grain diseases and the resulting defects – biotic and abiotic in origin. The distinction between biotic and abiotic causes is not always clear, e.g., for black point/kernel smudge. Extensive summary table of major diseases of the main cereal grains, plus means of control and cross-infection risks. Diseases of the inflorescence and spike (head) as well as the grain. Maintenance breeding to provide resistance or tolerance to cereal-grain diseases. Chemical control of cereal-grain diseases. Means of infection – soil-borne, seed-borne, residue-borne, air-borne and vector-borne.

Learning Objectives

•

To understand the nature, causes and control of grain diseases in the major cereal species, the principles involved and the implications for grain value and the practical strategies for mitigation.

Introduction Plant diseases are major constraints to crop production, affecting yield and quality. In extreme circumstances, contamination with pathogens or their metabolites can cause unpleasant odors and tastes, and in some instances, toxicoses of food and fodder products. Diseases can be subdivided into those with abiotic or biotic causes. Abiotic diseases include mineral deficiencies and toxicities, and the effects of soil salinity, acidity, and alkalinity. In some instances, mineral deficiencies and toxicities can carry over to harvested products, and to the food and fodder products derived from them. Biotic diseases are caused by fungi, bacteria, nematodes, viruses, and mycoplasmas. Many farm management practices are aimed at alleviating the effects of disease through agronomic, chemical, and genetic means. It has been estimated that one-half of the cost of plant improvement involves ‘maintenance’ breeding, i.e., breeding to maintain current yield and quality levels to meet the challenges of degrading growing environments and evolving pathotypes of major pathogens.

74

This article will outline some of the internationally important diseases that affect cereal production and will emphasize those with greatest effects on commerce and endpoint quality.

Abiotic Diseases of Cereals All plant species have an optimum range of soil conditions in which they thrive, and performance declines with digression from these optima. Marginal environmental conditions can be alleviated by cultural practices and fertilizers. Some species may be better adapted to prevailing conditions. For example, cereal rye and some triticale genotypes are tolerant to low pH (high aluminum) conditions. Within each species there is also a range of genetic variation that can be exploited in breeding programs, resulting in cultivars that perform better under specific nutrient regimes, e.g., cultivars more tolerant to low pH, or more tolerant to high or to low levels of soil boron or manganese. In these latter cases, mechanisms such as mineral exclusion that lead to a genotype’s ability to tolerate high levels of a mineral, may be the basis of the poor ability of that genotype to tolerate a deficiency of the same mineral. Mineral deficiencies are more easily rectified than toxicities. Generally, mineral fertilizers applied to the soil or leaves will overcome deficiencies even though breeding solutions may also be available. Toxicities can be alleviated by amelioration of the environment to reduce availability of the mineral or by selection and use of more tolerant genotypes. In many circumstances, more tolerant cereal species may be preferred. In a broader context, disease-like symptoms may be caused by extreme or abnormal weather conditions such as drought, heat, and frost, as well as pesticides. Agronomists and farmers need to be able to distinguish symptoms of environmental stress from diseases caused by both abiotic and biotic agents. Finally, certain genetically determined ‘disease mimics’ are expressed as physiologic spotting or blotching. These are more likely to be encountered in breeding populations than in released cultivars, as breeders obviously select against such phenotypes. However, they may appear in cultivars grown in environments different from those in which they were originally selected. Genetic analyses have shown that some forms of physiologic spotting involve single genes or the complementary interaction of unlinked genes.

Black Point/Kernel Smudge: Abiotic or Biotic Diseases? Winter cereals, particularly those grown outside a classic Mediterranean climate, often encounter a complex of harmful


http://dx.doi.org/10.1016/B978-0-12-394437-5.00183-2

GRAIN HARVEST, STORAGE AND TRANSPORT | The Nature, Causes, and Control of Grain Diseases weathering conditions during grain development. Winter crops in the subtropics, and summer crops in temperate climates, often ripen with high humidity or rain. High humidity alone can stall or prolong ripening, initiate germination, induce excessive enzyme activity, and establish colonization by saprophytic fungi and bacteria. In wheat, high humidity induces a clean edged symmetrical melanized pattern in the pericarp and testa cells covering the germ and adjacent areas. In barley, the glume tissue covering the germ may become melanized. Prolonged wet periods may smudge the melanization and induce vigorous saprophytic growth on the grain surface affecting its color and brightness. Pink pigments exuded from Eppicoccum spp. and sporulation of fungi such as Cladosporium spp. are often included in the black point/kernel smudge complex. Grain can also be directly infected by foliar and root pathogens. For example, Bipolaris sorokiniana causes shriveling and browning of infected tissue in wheat and barley grain and Phaeosphaeria avenaria f. sp. avenaria causes similar symptoms in oats. Pyrenophora tritici-repentis and Fusarium spp. produce a pink pigment in wheat, often referred to as kernel smudge, and can invade the living aleurone tissue and attack the embryo. Although various fungi are associated with black point/ kernel smudge, there is no conclusive evidence that black point melanization is a direct result of fungal action. The often reported association between symptoms and the most common grain colonizer, Alternaria alternata, is not strong and several studies have been unable to confirm any link. Pigmentation first appears when the pericarp and testa cells are crushed to form the seedcoat and the grain begins to lose moisture. Prolonging or reversing the drying process allows interaction between enzymes and substrates that normally lie dormant until subsequent germination. Black point melanization alone does not affect flour or end product quality of bread wheat. Recent research has shown that flour color and speckiness does not deteriorate despite black point levels of up to 10% and that black point only affects the bran, and that flour protein has a greater effect on flour color than does black point. Even with very high levels of black point, careful milling can extract flour with an acceptable color for most bread-making purposes. However, black point in durum poses a greater problem with many reports suggesting that low levels of black point can cause visible dark specks in pasta products. Kernel smudge caused by saprophytic and/or pathogenic fungi is also an indicator of weather damage, and as such, can have a severe effect on grain quality and viability. Pink smudge caused by Fusarium graminearum may contain mycotoxins. Under wet conditions, all cereal grains can develop symptoms of black point/kernel smudge, but only wheat, durum, barley, rye, and triticale produce black point melanization. However, similar discolorations are sometimes found in rice, sorghum, and other cereals. While fungicide application has been used in some countries to control black point, there is little evidence of success. Genetic variation required to reduce or eliminate black point melanism has been identified in wheat, durum, and barley. However, despite variation, genetic improvement has proven very difficult due to a lack of understanding of the underlying mechanisms, the complexity of interactions with environmental factors, and a lack of reproducible and reliable screening techniques. Consequently, most breeding programs rely on opportunistic selection.

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Significant Biotic Diseases of Cereal Grain Crops An exhaustive list of all diseases of the major cereal grain crops is beyond the scope of this article. Some of the more important and widely dispersed diseases of wheat, barley, rye, oats, maize, and rice are listed in Table 1. However, numerous diseases of each crop and of triticale, sorghum, and millets that may be very important on a local, or even regional, basis have been omitted. Infection processes and groups of diseases based on means of infection will be discussed. Triticale, a hybrid crop combining the genomes of tetraploid wheat and rye is more prone to the diseases of wheat than those of rye. Infection and spread of many diseases is enhanced by wet conditions and the use of cereal rye and sorghum and millets in areas considered too dry for wheat and barley, or corn, respectively, results in reduced risks of epidemics on those crops, in addition to the distinctive resistances they may possess.

Soil-Borne Diseases True soil-borne diseases are probably relatively few in number as pathogens are more likely to be associated with decomposing plant material. Fungi such as the take-all pathogen, Gaeumannomyces graminis var. tritici, attacking wheat, and to a lesser extent, triticale and barley, can be considered to be soil-borne – or at least located below the soil surface – although they may be associated with the decaying residues of previous crops and certain grass species. The spores of a number of smut species can be soil-borne as a result of previously smutted crops. They are then available to infect the roots, crowns, and coleoptiles of germinating seeds. These include all of the bunts (except karnal bunt) and smut pathogens except the flower-infecting loose smuts of wheat, barley, and oats. Most nematodes survive in the soil before attaching to cereal roots. The most important nematodes of cereals are cereal cyst nematode (cereal root eelworm) of the winter cereals and the root lesion nematodes of wheat.

Seed-Borne Diseases Some diseases such as the loose smuts of winter cereals and barley stripe are exclusively seed-borne. In the case of loose smut, infections occur at flowering and the mycelia are actually present within the seed tissue and the pathogens develop with growth of the host. The primary means of dispersal for many pathogens is with seed, either as, or on, contaminating material, present on seed surfaces or in infected seed that may or may not be viable. These pathogens are then available to infect germinating seedlings to produce seedling blights, or to induce stress symptoms at later growth stages. Alternatively, fungal pathogens present on the soil surface may produce conidia that can be splash-dispersed to above ground tissues. Some bacterial and virus pathogens are also seed-borne.

Residue-Borne Diseases This group is probably the largest and most important group of pathogens of cereals and their significance has greatly

Crop

Disease name and pathogen typea

Wheat and durum

Pathogen: anamorph (teleomorph)

Infection of other cereal crops

Disease typeb

Means of infection

Path varc

Methods of control

Overseason survival

Mycelial penetration of roots and crown Penetration of roots Parasite of roots

1

Crop rotation, take-all decline

Volunteer cereals and grasses, residues

Barley, triticale, rye

3

Nematicides, crop rotation, resistance Crop rotation, some resistance Rotation, stubble management, partial resistance

In soil

Barley, oats, triticale, rye No

Take-all, firing

F

Gaeumannomyces graminis var. tritici

Soil-borne

Cereal cyst nematode Root lesion nematode Crown rot

N

Heterodera avenae

Soil-borne

N

Pratylenchus spp.

Soil-borne

F

Fusarium pseudograminearum, F. culmorum, Fusarium spp. Bipolaris sorokiniana (Cochliobolus sativus)

Residue-borne

Stem base and subcrown internode

1

Seed and residue-borne

Crown, coleoptile, and leaves

1

Rotation, stubble management, resistance

Crop residues

Barley

Soil and seedborne Seed-borne Seed and soilborne Residue-borne

Germinating seedlings Flowers Flowers

4

Seed dressings, resistance

Soil

No

4 2

Seed dressings, resistance Clean seed (quarantine), resistance Stubble management, resistance Stubble management, seed dressings, partial resistance Stubble management, crop rotation, resistance

Seed Soil and seed

No No

Crop residues

No

Crop residues

No

Crop residues

No

Perithecia and hyphal structures in crop residues and seed

Barley, triticale, corn, others, saprophyte on rice residues Triticale, barley

Common root rot, Heminthosporum leaf blight Common bunt, stinking smut Loose smut Karnal bunt

F

Septoria tritici blotch

F

Septoria nodorum blotch

F

Tan spot, yellow leaf spot

F

Fusarium head scab

F

Stem (black) rust

F

Leaf (brown) rust

F

P. triticina

Airborne

Stripe (yellow) rust

F

P. striiformis f. sp. tritici

Airborne

Powdery mildew

F

Blumeria graminis f. sp. tritici

Airborne

F

Tilletia spp.

F F

Ustilago nuda f. sp. tritici Neovossia indica syn. Tilletia indica Mycosphaerella graminicola Leptosphaeria nodorum ¼ Phaeosphaeria nodorum Drechslera tritici-repentis (Pyrenophora triticirepentis) Fusarium graminearum, (Gibberella zeae), F. culmorum, Fusarium spp. Puccinia graminis f. sp. tritici

Residue- and seed-borne Residue-borne

Residue- and seed-borne

Airborne

1

Splash-dispersed conidia Splash-dispersed conidia

3

Splash-dispersed ascospores and conidia At anthesis by splash-borne conidia or ascospores Leaf, stem, spike tissues by uredospores Leaf, stem, spike tissues by uredospores Leaf, stem, spike tissues by uredospores Conidia, ascospores

3

1

2

4

Stubble management, rotations with nonhosts, foliar sprays, partial resistance Foliar sprays, resistance

4

Foliar sprays, resistance

4


4


In soil, other host species Crop residues

Green-bridge on wheat and a few grasses Green-bridge on wheat and a few grasses Green-bridge on wheat and a few grasses Green-bridge, cleistothecia on residues

Barley, triticale, oats (symptomless)

Triticale

Triticale

No

GRAIN HARVEST, STORAGE AND TRANSPORT | The Nature, Causes, and Control of Grain Diseases

Major diseases of cereal grain crops, causative agents, means of infection, spread, survival, pathogenic variability, and host range

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Table 1

Barley

V

Vector-borne

Several aphid spp.

2

Wheat streak mosaic

V

Vector-borne

Mites, Aceria spp.

1

Control of aphids, partial resistance Control of Grass hosts

Cereal cyst nematode Common root rot, Spot blotch

N

Soil-borne

Penetration of roots All tissues by conidia

3

Nematocides, resistance

1

Seed dressings, rotation, stubble management, resistance Rotation, stubble management, partial resistance

Other cereals, grasses Barley, corn

Wheat, oats, triticale

Crop residues

Wheat, triticale

Crop residues

Wheat, triticale, oats (symptomless)

F

Bipolaris sorokiniana (Cochliobolus sativus)

Seed- and residue-borne

Crown rot

F

Residue-borne

Stem base and subcrown internode

1

Net blotch – net form

F

Fusarium pseudograminearum, F. culmorum, Fusarium spp. Drechslera teres f. teres (Pyrenophora teres)

Seed-, residue-, and soil-borne

1

Seed dressings, stubble management, resistance

Residues

No, wild Hordeum spp.

D. teres f. maculata (Pyrenophora teres)

Seed-, residue-, and soil-borne

1

Seed dressings, stubble management, resistance

Residues

No, wild Hordeum spp.

Seed- and residue-borne Seed-borne

Wind and splash dispersed conidia, and ascospores Wind and splash dispersed conidia and ascospores Splash dispersed conidia Systemic infection of seedlings

2–3

Seed dressings, stubble management, resistance Disease-free seed, seed dressings, resistance

Green-bridge, residues Seed

No, wild Hordeum spp. No

Barley, triticale, corn, others, saprophyte on rice residues Wheat, triticale

Net blotch – spot form

Oats

Green-bridge for aphids Green-bridge for mites on cereals and some grass spp. In soil

Scald

F

Rynchosporium secalis

Barley stripe

F

Fusarium head scab

F

Stem (black) rust

F

Leaf (brown) rust Stripe (yellow) rust

F F

Helminthosporium graminum (Pyrenophora graminea) Fusarium graminearum, (Gibberella zeae), F. culmorum, Fusarium spp. Puccinia graminis f. sp. tritici P. hordei P. striiformis f. sp. hordei

Barley yellow dwarf

V

Powdery mildew

F

Barley stripe mosaic

V

Cereal cyst nematode Stem (black) rust

N

Heterodera avenae

Soil-borne

F

Puccinia graminis f. sp. avenae

Airborne uredospores

Blumeria graminis f. sp. hordei

Trash- and seedborne

2–3

2

Stubble management

Crop residues, other species?

Airborne

At anthesis by splash-borne conidia or ascospores Uredospores

4


Green-bridge

Airborne Airborne

Uredospores Uredospores

4 4

Foliar sprays, resistance Foliar sprays, resistance

Green-bridge Green-bridge

Vector-borne

Several aphid spp.

2

Airborne ascospores and conidia Seed-borne

Leaf

4

Control of aphids, partial resistance Foliar sprays, resistance

Infected seed, mechanical transmission Penetration of roots Leaf, stem, and inflorescence

1

Virus-free seed

Green-bridge for aphids Cleistothecia on residues, greenbridge Infected seed

Wheat, oats, grasses

3

Nematocides, crop rotation, resistance Resistance

In soil

Barley, oats, triticale

Green-bridge

No, wild oats important

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4

No No, wild Hordeum spp. Other cereals, grasses No


Barley yellow dwarf

(Continued)

Crop

Disease name and pathogen typea

Pathogen: anamorph (teleomorph)

Means of infection

Path varc

Methods of control

Overseason survival

Airborne uredospores Vector-borne

Leaf

4

Green-bridge

Several aphid spp.

2

Leaf

4

Resistance (extremely ephemeral) Control of aphids, partial resistance Foliar sprays, resistance

Flowers

1

Control of grass weeds

Leaf, stem, and spike Leaf, stem, and spike All growth stages by ascospores and conidia Seedlings and nodal regions by pycnidiospores Hyphal infections of most tissues

4

Leaf (crown) rust

F

Barley yellow dwarf

V

Powdery mildew

F

Blumeria graminis f. sp. avenae

Ergot

F

Claviceps purpurea

Stem (black) rust

F

Leaf (brown) rust

F

Gibberella stalk and ear rot

F

Diplodia stalk and ear rot

F

Puccinia graminis f. sp. secalis Puccinia recondita f. sp. recondita Fusarium graminearum, (Gibberella zeae), Fusarium spp. Diplodia maydis

Fusarium stalk and ear rot

F

Fusarium venticillioides

Seed- and trashborne

Northern leaf blight

F

Helminthosporium turcicum

Splash-borne

Southern leaf blight

F

Splash-borne

Sorghum

Fusarium stalk rot

F

Helminthosporium maydis Fusarium thapsicum

Rice

Blast

F

Bacterial leaf blight

B

Tungro

V

Vector-borne

Hoja blanco

V

Vector-borne

Cereal rye

Corn

Puccinia coronata f. sp. avenae

Disease typeb

Pyricularia oryzae (Magnaporthe grisea) Xanthomonas oryzae

Airborne ascospores and conidia Seed- and soilborne Airborne uredospores Airborne uredospores Seed- and trashborne Seed- and trashborne

Seed- and residue-borne Residue-borne

b

No, wild oats important Other cereals, grasses No, wild oats

Resistance

Green-bridge for aphids Cleistothecia on residue, greenbridge Sclerotia in soil or seed lots Green-bridge

Other winter cereals and grasses No, some grasses

4

Resistance

Green-bridge

No, some grasses

1

Stubble management, crop rotation, resistance

1


Perithecia and hyphal structures in residue and seed Pycnia on seed and residues

Wheat, barley, grasses, possibly other crops No

1

Measures to reduce stress

Can affect sorghum and millet

Conidial infection of leaves

2


Conidial infection of all tissues Hyphal infections of most tissues

2 1

Resistance, especially avoidance of T-cytoplasm Measures to reduce stress

Hyphae in seed, hyphae and conidia in residues Possibly conidial structures on residues Conidia on residues

Conidial infection of leaves Entry via wounds and hydrathodes Leaf hopper, Nephotettix virescens Sogatodes orizicale

4

Resistance

4 3

Sorghum, some related grasses No

Resistance

Hyphae in seed, hyphae and conidia in residues Residues, greenbridge Green-bridge

No (different pathotypes) No

Resistance

Green-bridge

No (West Asia)

Resistance

Green-bridge

No (Central and South America)

Pathogens: F ¼ fungal, N ¼ nematode, V ¼ virus, B ¼ bacteria. ‘Residue’ refers to partially decomposed material either on the surface or within the soil. Residues may carry saprophytic fungal mycelia or resting structures. c Pathogenic variability: 1 ¼ no significant variability to 4 ¼ high degree of variability. a

Infection of other cereal crops

Primarily grain sorghum


(Continued)

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Table 1

GRAIN HARVEST, STORAGE AND TRANSPORT | The Nature, Causes, and Control of Grain Diseases increased in large-scale agriculture with its increased monoculture and minimum tillage, or no-tillage, practices where residue is retained on the soil surface to prevent soil erosion. Fungal pathogens of this type survive from season to season as mycelium and resting structures on host debris. While deep-plowing and burning can give marked reductions in levels of many of these diseases, such practices are not encouraged, especially where soil surfaces remain vulnerable to erosion. Diseases in this group often infect young seedlings, giving rise to early damping off or wilting symptoms (e.g., Fusarium blights) or may remain in the root, subcrown, and crown regions to develop disease symptoms at later growth stages, especially at times of short-term or long-term moisture stress. In the winter cereals, these symptoms result in premature death, wilting, ‘white heads,’ and lodging. Examples of such diseases include common root rot, eyespot and crown rot of wheat. Wheat crown rot is caused by Fusarium spp. It is of interest that the Fusarium head blight pathogen, Gibberella zeae, is not a significant cause of crown rot although it can produce seedling wilt. Crown rot of wheat and barley is caused by F. pseudograminearum in warmer areas and by F. culmorum and other species in cooler areas. Other members of this group of pathogens are dispersed as conidia or ascospores by raindrops or wind to infect leaf tissues or even inflorescences. They include most of the fungal leaf spot, blotch and streak pathogens and their spread within the canopy is dependant on periods of consistent light rainfall. These diseases are often present but not damaging. However, when environmental conditions are optimal they can be very damaging with total loss of green leaf tissue and subsequent grain losses of up to, and sometimes exceeding, 50%. Many of these diseases are cyclical in occurrence involving combinations of susceptible host genotypes and sequences of years of favorable conditions during which there is a gradual increase in inoculum loads. Examples include the southern corn leaf blight epidemic in the USA in 1969–70 and the wheat yellow leaf spot epidemic in eastern Australia in 1998. The corn leaf blight epidemic involved susceptible corn hybrids based on Tcytoplasm and disease occurrence and risk was reduced by a return to normal cytoplasm and mechanical detassling of female parents for hybrids. The yellow leaf spot problem in Australia declined with less favorable environmental conditions and release and recommendations of less susceptible cultivars. Sporadic epidemics seem to be associated with sequences of unusually favorable seasons combined with a suite of susceptible cultivars that are approved during the intervening periods. The most damaging diseases of this group are eventually those that progress to the inflorescence or involve the inflorescence. Examples include Septoria nodorum blotch of wheat and Fusarium head scab (FHB) of wheat and barley. FHB is caused by G. zeae in high temperature areas with wheat: maize rotations (e.g., mid-western and eastern USA, central and southern Europe) and wheat:rice rotations (e.g., in the Yangtze valley in China), by F. culmorum at moderate temperatures and by Microdochium nivale at lower temperatures. G. zeae also causes stalk rot and pink ear rot of corn. On the other hand, G. zeae is not a common pathogen of rice; the fungus behaves as a saprophyte on rice stubble (and probably sorghum), thus maintaining high inoculum levels for subsequent wheat

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crops. Barley, especially two-row genotypes, is less susceptible to FHB than wheat suggesting the rate of spread is influenced by spike structure. Blast, probably the most important fungal disease of rice, spreads by splash-borne conidia. The blast pathogen also causes grey leaf spot of turf grasses (perennial ryegrass) and has recently become a pathogen of wheat in Brazil. However, the isolates from grasses are nonpathogenic on rice and the form attacking wheat is more closely related to those attacking grasses than isolates from rice. Despite a teleomorph stage (Magnaporthe grisea), dispersal of blast in nature is exclusively by conidia. Under extreme conditions when infections by splash-borne organisms reach the upper canopy, their epidemiological dynamics may change to become more like air-borne diseases typified by long distance spore dispersal.

Airborne Diseases This group includes the rusts of all major cereals except rice and the powdery mildews of wheat, barley, and oats. The rusts are among the main diseases affecting oats and wheat with powdery mildew being more important on barley. Both the rusts and powdery mildew pathogens (as well as some splash-borne pathogens such as the rice blast pathogen) are highly variable and occur as formae speciales or specialized taxonomic varieties on individual species as well as pathotypes or pathogenic races within those groups. Most of the rusts are heteroecious species with the telial stages occurring on cereals and the aecial stages on other (dicotyledonous) species. The rust pathogens cannot survive for long periods away from a living host, although they can survive as uredial infections in most areas provided a ‘greenbridge’ is available. This green-bridge includes self-sown or regrowth plants from earlier crops or along transport corridors (roads, railway lines, storage sites) and a restricted range of ‘accessory’ grass hosts that varies for each pathogen. In addition, uredospores can be transported over long distances by wind as documented by studies in North America and Australia. In certain rusts and in some locations where the aecial stage contributes to overall epidemiology (note the stripe rust pathogens have no known aecial stage), the black telia that develop on maturing host leaf and stem tissues provide a resting stage for overwintering. In early spring, the teliospores from within the telia germinate, and undergo meiosis to form basidiospores that infect the new spring growth of the alternate hosts and form pycnia. There, the different mating types undergo fertilization to produce a dikaryotic aecium and aeciospores reinfect the grass host species. This cycle, when it occurs, has two main effects on epidemiology. First, it provides a mechanism for survival and early infections in areas where uredial survival is prevented by cold winters and second, meiosis allows reassortment of the genotype providing an efficient means of creating new pathotypes. Despite an absence of alternate hosts in many cereal-growing areas the rust pathogens, including P. striiformis, are nevertheless highly variable, with mutation and somatic hybridization (asexual recombination) the likely mechanisms. The powdery mildew pathogens are ascomycetes. Survival between seasons is by green-bridging and by cleistothecia that develop on ripening host tissues and survive on the debris.

80


Karyogamy and meiosis occur in the cleistothecia and the released ascospores infect young cereal plants on which the organisms recycle as conidia. Again, meiosis allows for genetic assortment, but the powdery mildew fungi and the blast pathogen are monoploid (n) organisms in contrast to the rust pathogens that are dikaryons (n þ n) and functionally similar to diploids (2n).

with the grain during ripening and harvesting. These tend to be associated with grain, ripened or harvested under wet conditions or harvested at high moisture content. Shriveled seed harvested from crops with a range of diseases may have qualities that differ from grain harvested under optimal conditions.

Plant Quarantine Issues Vector-Borne Diseases This group includes the many virus diseases that affect cereals in different locations. However, relatively few virus diseases of cereals are significant on a worldwide basis. Tungro of rice and barley yellow dwarf (BYD), cereal yellow dwarf (CYD) and wheat streak mosaic on small grain winter cereals are among the most important. Viruses are transmitted from plant to plant by vectors that include insects, particularly aphids and leafhoppers, mites, and fungi. Knowledge of the biology and migratory behavior of vectors, and of specific virus strain: vector relationships, is essential to understanding the epidemiology of virus diseases and to the development of control strategies. In addition, some viruses can transmit between neighboring plants through contact of injured tissues. BYD can be caused by one or more of several luteoviruses spread by a range of cereal aphid species, hosted by a number of grasses including corn. This complex of variable viruses, aphid species, host species (cereals, pasture species, native grasses), and environments adds to the problems of managing this disease, especially in mixed farming areas. WSM, vectored by the aerially dispersed wheat curl mite Aceria tulipae, and infecting a range of cereals and grasses that host the mite, is responsible for significant losses in wheat and barley in North America, eastern Europe and the Near East. Autumn or early winter infections of BYD, CYD, and WSM in winter cereals or autumn-sown spring cereals can result in very significant yield reductions; spring infections when plants are more developed lead to lower losses.

Countries vary in regulations that apply to imported seed for either propagation or commerce. Plant pathogens can be carried either as infections within the seeds (certain smuts, seedborne viruses), as contaminants on the seed surface (many bacteria and fungi), or on plant debris or soil that may be present as admixtures with grain. To reduce risks, preborder measures such as local import permits and phytosanitary certificates issued by the originating country may be required. On arrival in a receiving country, seed for propagation may be inspected before being grown in quarantine greenhouses or approved isolated field areas. Grain in large quantities for commerce may require special treatments to kill the embryos or may be milled in approved locations away from local cereal production areas. With the recent large-scale rapid movement of goods and people around the globe even nonseed-borne pathogens can move over large distances as contaminants of traded goods or persons. For example, following the introduction of the wheat stripe pathogen into eastern Australia, probably from Europe, in 1979, there have been at least two further incursions. In 1998, a Puccinia striiformis form more adapted to barley grass (Hordeum leporinum, H. murinum), than to wheat or barley was observed for the first time, and in 2002, a distinct pathotype of P. striiformis f. sp. tritici appeared in Western Australia, which previously had been free of stripe rust. The origins of these new forms have not been established. They are assumed to have arrived on contaminated clothing or footwear.

Diseases of the Inflorescence, Spike, and Seed

The Hazards of Chemical Control

These diseases are the most important for commerce. They include the black point/kernel smudge complex already discussed, the smuts, leaf diseases that also affect the spike and glumes, head scab and ear rots, and also the non or weakly pathogenic molds and rots. There are two aspects: firstly the effects of seed-borne diseases on the seed industry, and secondly, the effects on trade and endpoint use. The smuts destroy the inflorescence and thereby reduce yields. Some smuts such as common bunt and karnal bunt of wheat produce unpleasant odors and flavors. The scab and cob rots, especially those caused by Fusarium spp., may carry a variable complex of compounds (including vomitoxin ¼ deoxynivalanol (DON), nivalanol (NIV), and related trichothecenes) that are toxic to man and animals. In the various fungal species, these compounds appear to act as virulence factors, enhancing the ability of the pathogens to colonize the hosts. The particular compounds and their amounts not only vary among the species but also between isolates within species. In addition, there are various molds and rots of stored grains caused by a range of weakly pathogenic and nonpathogenic fungi that come into contact

Many diseases, or the vectors that transmit pathogens, especially viruses, can be controlled effectively with chemicals applied as seed dressings or as foliar sprays at appropriate growth stages. In high-yielding environments, one or more chemical applications are often included as part of a routine management package. Under these circumstances, favorable returns can be achieved even where disease levels appear to be low. As environments become less favorable and yield levels decline, or for lower value grains for fodder, the costs of chemical applications encroach on profitability to the extent that their use on crops with yield potentials below 2–3 t ha1 may be uneconomic. This is a very significant factor of production in major exporting countries such as Australia and Canada with relatively low-average long-term wheat yields, for example, of 1.7 and 2.3 t ha1, respectively. Under these production systems, agronomic and genetic means of disease control are more attractive. A further major consideration is the increasing emphasis on quality standards and declining chemical residue limits placed on traded grain and grain products. Presumably, the later in growth that a chemical is applied, the greater the likelihood of

GRAIN HARVEST, STORAGE AND TRANSPORT | The Nature, Causes, and Control of Grain Diseases residues exceeding specified limits, leading to down-grading or blending of grain to achieve specified standards.

Control of Diseases by Plant Breeding Many of the diseases of cereal crops have and continue to be controlled by resistant genotypes. Resistance has the advantage of being residue-free and of contributing to lower production costs for the farmer. No cultivar of any crop has resistance to all disease threats nor provides complete resistance under all conditions. Hence, chemicals to target single diseases, or to provide prophylactic protection to a range of threats, are often used, especially under high-yielding conditions. A recurrent problem with resistance has been the emergence of resistance-breaking pathotypes as a result of selection of previously infrequent variants, sexual and/or nonsexual recombination in nonhaploid pathogens, and mutation. Retrospective genetic analyses of hosts and pathogens in situations where both resistant and susceptible host genotypes, and both avirulent and virulent pathogen genotypes were available showed that expression of resistance is dependent upon the presence of a corresponding gene for avirulence, a gene-for-gene relationship. Assumptions of a gene-for-gene relationship in disease systems where genetic information is lacking permits postulation of resistance and avirulence genotypes (phenotypes) and thereby assists the breeding of resistant cultivars based on gene combinations. However, major gene combinations have usually not provided long-term solutions and breeders have had to continue the search for even more resistance genes, or to seek alternative breeding and deployment strategies. These include genotype (and crop) mixtures, minor resistance gene combinations, and various partial resistances with a history of durable resistance. Nevertheless, some resistances, represented by single genes (mlo for powdery mildew resistance in barley, Sr2 for stem rust resistance in wheat) or by more complex resistance sources (flagsmut resistance in wheat), have remained effective over long periods. Resistance to some diseases (e.g., take-all of wheat) does not exist and to others (e.g., crown rot of wheat and barley) only relatively low levels of partial resistance (or tolerance) are available. Nevertheless, such variability can be used very effectively in integrated disease control to improve farm profitability.

Future Prospects Cereal crops will continue to be affected by diseases as no breeding program can develop cultivars with acceptable levels of resistance to all diseases under all conditions. Emphasis on resistance is expected to increase as fungicide use and residues become less acceptable. Molecular biology is providing tools for more accurate diagnostics of pathogens at both species and subspecies levels, some pathogenicity factors have been cloned and their gene products identified. In the host species, resistance genes have been mapped and cloned. Mapping information is being used for marker-assisted selection, aimed at developing resistance gene combinations to provide more durable and effective resistances. Genetic transformation will provide opportunities for transferring resistance genes from

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species that cannot be hybridized with individual cereal species as well as possibilities for synthesizing new genes in the laboratory. Genetic engineering seems likely to provide resistance to diseases for which adequate and effective resistance is currently not available.


• • • • • •

List the various means by which biotic diseases are spread. Which should be easiest to control? Summarize the implications of having cereal crops of different species growing close together. Which species-disease combinations would present least risk of cross infection? Compare the advantages and problems of controlling grain diseases by chemical treatment versus breeding for resistance. Outline arguments to be put to local growers for the need of plant quarantine to control grain diseases. What are the limitations of plant quarantine to control grain diseases?


• • • • • •

Choose three examples of grain diseases that are significant in your region and summarize the resulting economic implications. Consequently, what resources are justified in introducing strategies to mitigate these losses? What do you see as the most effective strategies? What practical recommendations would you make to local grain growers? How do genotype (variety) and growth environment interact to cause grain diseases? Imagine what advantages might flow in the future from new tools, such as diagnosis and transformation, to be provided by advances in molecular biology.

See also: Grain Harvest, Storage and Transport: Cereals: Grain Defects; Contaminants of Grain; Wheat-Based Foods: Cookies: A Diverse Family of Baked Goods.

Further Reading Anonymous (1977) A Compendium of Corn Diseases. St. Paul, MN: APS Press. Anonymous (2001) Protection and Compendium(on CD). Oxon, UK: CAB International. Doggett H (1988) Sorghum, 2nd edn. UK: Longman Group. Ellis S (1999) Measurement and Control of Black Point Project Report No. 210. London, UK: Home-Grown Cereals Authority (HGCA). Harder DE and Haber S (1992) Oats diseases and pathologic techniques. In: Marshall HG and Sorrells ME (eds.) Oat Science and Technology. Madison, Wisconsin: American Society of Agronomy Inc. Keisling RL (1978) The diseases of barley. In: Rasmussen DC (ed.) Barley. Madison Wisconsin: American Society of Agronomy Inc. Leonard KJ and Bushnell WR (eds.) (2003) Fusarium Head Blight of Wheat and Barley. St. Paul, MN: The American Phytopathological Society. Leslie JF (2002) Sorghum and Millets Diseases. Ames, Iowa: Iowa State Press (Blackwells). Mathre DE (1997) Compendium of Barley Diseases, 2nd edn St. Paul, MN: APS Press.

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Ou SH (1985) Rice Diseases, 2nd edn. Kew, Surrey: Commonwealth Mycological Institute. Summerell BA, Leslie JF, Backhouse D, Bryden WL, and Burgess LW (2001) Fusarium: Paul E. Nelson Memorial Symposium. St. Paul, MN: APS Press. Ullstrup AJ (1977) Diseases of Corn. In: Sprague GF (ed.) Corn and Corn Improvement. Madison, Wisconsin: American Society of Agronomy Inc. Weise MV (1977) Compendium of Wheat Diseases. St. Paul, MN: APS Press. Williams RJ, Frederiksen RA, and Girard JC (1978) Sorghum and Pearl Millet Disease Identification Handbook Information Bulletin No. 2. Patancheru, AP, India: ICRISAT. Zillinsky FJ (1983) Common Diseases of Small Grain Cereals: A guide to Identification. Mexico DF: CIMMYT.

Relevant Websites wheat.pw.usda.gov http://wheat.pw.usda.gov – Wheat Diseases and Pests: a Guide for Field Identification. Original text by: J.M. Prescott, P.A. Burnett, E.E. Saari, J.

Ranson, J. Bowman, W. de Milliano, R.P. Singh and G. Bekele. International Maize and Wheat Improvement Center (www.cimmyt.org). Centro Internacional de Mejoramiento de Maiz Y Trigo. Lisboa 27, Apdo. Postal 6-641,06600 Mexico, D.F., Mexico. HTML version developed with permission from CIMMYT by: J. Wong, USDA-ARS-WRRC, Albany, California; D.E. Matthews, Dep. of Plant Breeding and Biometry, Cornell University, Ithaca, New York and K.D Kephart, Dep. of Agronomy, University of Missouri, Columbia, Missouri, USA. pdc.unl.edu http://pdc.unl.edu – Plant Disease Central. J. Stack, UNL Extension Specialist, University of Nebraska, Lincoln. Describes and illustrates diseases of wheat, corn and sorghum. btny.purdue.edu http://btny.purdue.edu – Crop Diseases in Corn, Soybean, and Wheat. K. Rane and G. Ruhl. Department of Botany and Plant Pathology. Purdue University, West Lafayette, IN 47907, USA. ext.nodak.edu http://www.ext.nodak.edu – Symptoms and Controls of Crop Disease. PP-533 (Revised), March 1977. M.P. McMullen, Extension Plant Pathologist, H. Arthur Lamey, Extension Plant Pathologist. NDSU Extension Service, North Dakota State University, Fargo, ND, 58078, USA.

Contaminants of Grain J McLean, The University of Newcastle, Callaghan, NSW, Australia CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • •

• •

The risks posed by nongrain materials with the processing of the grain. Standard specifications for the various grades of grain, based on quality and freedom from contaminants. Identification and definitions of the various types of contaminants: – Seeds of weeds and of other crops – Infected grains – ergot, bunt, and moldy – Defective grains – sprouted, frosted, and heat-damaged – Tainting materials – Agricultural chemicals – Foreign materials – stones and sticks – Insects and animals – snails and animal droppings Sampling and examination of grain samples. Analysis and avoidance of contaminants.

International Trading Standards

Learning Objectives

• • •

To achieve understanding of the risks posed by nongrain materials in grain shipments. To realize the wide range of contaminants likely to appear in grain lots. To become familiar with the means of minimizing the presence of contaminants in harvested and stored grain.

The examples listed in Tables 1–4 are derived from official guidelines published by the countries indicated. These are listed in detail in Table 5. Grain-producing countries also often provide illustrated guides to assist their operators in maintaining the agreed grain quality specifications.

Types of Contaminants

Introduction Ideally, grain should be harvested in sound and clean conditions, without any form of defect or contamination. Realistically, however, there is always the likelihood that the grain will be harvested together with nongrain materials and with weed or crop seeds, all of which detract from the value of the harvested crop. The loss in value relates partly to the fact that the resulting consignment of grain does not contain 100% of the type of grain ordered, but worse than that, it is likely that the nongrain materials will cause problems with the processing of the grain or that they may even render the grain unfit for the designated purpose or for any use.

Historic Perspective Primitive man, as the hunter–gatherer, had to accept whatever material grew with the seeds that were collected laboriously from wherever they could be found. As a result, the presence of contaminants must have been considerable. Presumably, this unsatisfactory situation was one of various stimuli for early man to progress to cultivation and seed sowing, thereby to


improve the purity and quality of grain-based foods. Nevertheless, throughout the Middle Ages, the presence of contaminating materials was generally extensive, because of poor agricultural practice and also due to the lack of purity of the seed for sowing. Significant improvements in grain quality have been forced as a result of the progressive change from subsistence agriculture (the farmer’s family consuming what they produce) to trading in grain (provision of the grain produced for sale, in competition with others). The past century has seen the extension of trading from the local situation to major international marketing and transport on a large scale. As a result, standard specifications have been established for the various grades of grain, based on quality, offered for trade within a country and internationally. Examples of these specifications are provided in Tables 1–4.

An important part of these specifications is the levels of contaminating materials, the higher-value grades being those with the least. Examples of these specifications can be examined on the websites of the export corporations of major grain-trading countries (Table 5). The first two examples in Table 1 contrast a premium Australian wheat grade (prime hard) with a lower grade (general purpose). The former has tighter specifications for all aspects of physical quality, compared with the lowervalue grade, including the requirement for less material in the category of contaminants. Ultimately, it is the anticipated end use of the grain that dictates the acceptable level of contamination. Grain contaminants in present time often fall into one of three categories: (i) defective grains, (ii) foreign seeds, and (iii) other contaminants. ‘Defective grains’ are those that are the same species and variety as the grain harvested but are ‘defective.’ ‘Foreign seeds’ as the name suggests are seeds from other plants that end up mixed in with the harvested grain. ‘Other contaminants’ is a broad category that includes everything else that is not a seed or grain. In Tables 1–4, the specifications used for trading are separated into these three categories.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00185-6

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GRAIN HARVEST, STORAGE AND TRANSPORT | Contaminants of Grain

Table 1

Some of the specifications for the physical aspects of grain quality for contrasting grades of wheat involved in international trade Australian Prime Hard (APH1, high quality)

Parameter

Quality attributes Protein (%) (N 5.70 at 11% moisture 14.0 min basis) 76.0 min Test weight (kg hl 1) Varietal mix Specified Unmillable material above 2 mm screen 0.6 max (by wt%) Screenings (below 2 mm screen) 5.0 max (by wt%) Falling number (seconds) 350 min Defective grains in 0.5 liter measure Sprouted grains Nil max Pink grain 2.0 max Dry green, sappy grains 1.0 max Foreign seed contaminants in 0.5 liter measure Foreign seeds; see Table 4 From nil to 50, according to species Small foreign seeds (by wt%) 0.6% max Other contaminants in 0.5 liter measure Cereal ergot pieces 1 max Grain insects Nil max Field insects 3–10 max, according to species Objectionable matter (stone, sticks, Nil max glass, and concrete) (entire load) Other foreign material (by wt%) 0.1 max Artificial stain, no residue (pickling) Nil max (entire load)

Australian General Purpose (AGP1, low quality)

Canada Western Red Spring (no 1. CWRS)

Canada Western General Purpose (CWGP)

No min

10.0 min

No min

68.0 min Specified 1.2 max

75 min Specified Not stated

72 min Specified Not stated

10.0 max

Not stated

Not stated

200 min

Not stated

Not stated

Nil max 5.0 max 5.0 max

0.10 max 1.5% max 0.75 % max

No limit No limit No limit

From nil to 150, according to species 1.2% max

Not stated

Not stated

Not stated

Not stated

1 max Nil max 3–10 max, according to species Nil max

0.01% max Not stated 1.0 % max

0.10% max Not stated No limit

0.03% max

0.03% max

0.1 max Nil max

0.2 max Nil max

No limit 2.0% max

Grain Trade Australia Section 2 – Wheat Trading Standards 2014/15 Season; Canadian Grains Commission Official Grain Grading Guide, Wheat Effective 1 August, 2014.

Table 2

Some of the specifications for the physical aspects of grain quality for grades of barley involved in international trade

Parameter Quality attributes Protein 8(%) (N 6.25 at 0% moisture basis) Test weight

Australian malt 1 (high quality)

Australian malt 2 (average quality)

Australian feed 1 (poor quality)

US no. 1 (high quality)

US no. 4 (poor quality)

9.0 min to 12.0 max

9.0 min to 12.0 max

Not applicable

Not stated

Not stated 43.0 lb bu 1 min Specified Not stated Not stated

1

min

Specified 300 min 62.0% min

Specified Not applicable Not applicable

10.0% max

15.0% max

Not stated

Not stated

Nil max 5% max

Nil max 10% max

Heat-damaged

Nil max

Nil max

3.0% max 0.4% max in 25 g 0.1% max in 25 g

13.0% max 0.4% max in 25 g 0.1% max in 25 g

From nil to 50, according to species

From nil to 150, according to species

2.0% max in 25 g

5.0% max in 25 g

Foreign seed contaminants in 0.5 liter measure Foreign seeds From nil to 40, according to species

min

62.5 kg hl

1

Varietal mix Specified Falling number (seconds) 300 min Retention (% by weight, 2.50 mm 70.0% min slotted screen, 40 shakes) Screenings (% by weight, 2.20 mm 7.0% max slotted screen, 40 shakes) Defective grains (% by count, 100 grain sample) Sprouted grains Nil max Frost-damaged 5% max Nil max

65 kg hl

1

47.0 lb bu 1 min Specified Not stated Not stated

65 kg hl

min

(Continued)

GRAIN HARVEST, STORAGE AND TRANSPORT | Contaminants of Grain Table 2

85

(Continued)

Parameter

Australian malt 1 (high quality)

Australian malt 2 (average quality)

Australian feed 1 (poor quality)

US no. 1 (high quality)

US no. 4 (poor quality)

Small foreign seeds Foreign grain

0.6% max 85 max

0.6% max 85 max

1.2% max 500 max

Not stated 0.5% max (material) in 25 g

Not stated 3.0% max (material) in 25 g

Other contaminants in 0.5 liter measure Chemicals not approved Nil max Ergot pieces (ryegrass) 0.5 cm length max Loose smut pieces 0.1 g max Grain insects Nil max

Nil max 0.5 cm length max 0.1 g max Nil max

Nil max 0.5 cm length max 0.1 g max Nil max

Field insects (large)

3 max

3 max

3 max

Earth pieces

3 max 5 mm diameter 50 max Nil max

3 max 5 mm diameter 50 max Nil max

3 max 5 mm diameter

Not stated Not stated Not stated 2 (in 500 g) max 10 (in 500 g) max Not stated

Not stated Not stated Not stated 2 (in 500 g) max 10 (in 500 g) max Not stated

50 max Nil max

Not stated Not stated

Not stated Not stated

Sand grains Objectionable matter

Grain Trade Australia Section 2 – Barley Trading Standards 2014/15 Season; USDA (2014) USDA GIPSA Grain Inspection Handbook, Book II Chapter 2 – Barley 7/30/13.

Definitions What is actually defined as ‘contaminants of grain’ is dependent on the market expectations for individual countries and endemic contaminants. In Australia, the peak industry body, Grain Trade Australia (GTA) defines contaminants individually as in the Wheat Trading Standards 2014. The Canada Grain Act (2) defines contaminated as in respect of grain, containing any substance in sufficient quantity that the grain is unfit for consumption by persons and animals or is adulterated within the meaning of the regulations made pursuant to paragraph 30(1)(a) of the Food and Drugs Act. Canada Grain Act, R.S.C., 1985, c. G-10, http://laws-lois.justice. gc.ca/eng/acts/G-10/page-1.html last accessed: 28/10/13.

Paragraph 30 of the Canadian Food and Drugs Act (3) adds that ‘the Minister may make an interim order that contains any provision that may be contained in a regulation made under this Act if the Minister believes that immediate action is required to deal with a significant risk, direct or indirect, to health, safety or the environment.’ http://laws-lois.justice.gc.ca/eng/acts/F-27/page-9.html#h-15

As suggested by the Canadian Food and Drugs Act, contaminants can change or new ones appear at any time. Grain is part of the living environment, and therefore, new contaminants may arise as a result of seasonal variations and unusual one-off incidences. Considering that grain is a major component of the food chain, the major concern is for those contaminants who pose a threat to the health and safety of humans and animals and to the sustainability of the environment in which it is grown. Depending on individual country specifications and consumer acceptance, grain contaminants can be grouped together and percentages determined for these groups as in Canada or the United States, or they can be defined individually as in Australia for weed seeds (Table 6).

Another term used to describe grain contaminants is ‘objectionable material,’ as the grain being purchased may consist of items that the buyer deems as objectionable. In the Australian GTA Wheat Trading Standards 2014/2015, Objectionable Material refers to objectionable foreign matter that may or may not be otherwise stated in these Standards which has the ability to degrade the hygiene of Cereal Rye or Triticale [wheat], become a food safety issue of concern or has a commercially unacceptable odour. This includes but is not limited to the following: Animal Material This refers to meat meal, bone meal, poultry offal, meal or any other animal proteins. Animal Material also includes carcasses of dead animals such as rats and mice. Odour A commercially unacceptable Odour is defined as a sour, musty or other objectionable odour emanating from the Cereal Rye or Triticale [wheat] which is not natural or normally associated with Cereal Rye or Triticale [wheat]. Odour may be caused by various means which may or may not be physically discernable in the sample being assessed. Stick A Stick is defined as ligneous material greater than 1cm in length and 0.5 cm in diameter. Note that crop stubble greater than 3 cm in length and 1 cm in diameter is defined as a Stick. Smaller material is included in Other Foreign Material. Tainting Agents A Tainting Agent is any contaminant that imparts a smell or taint to Cereal Rye or Triticale [wheat]. It includes but is not limited to plant parts and seeds of Eucalyptus spp. Water The addition of water to grain prior to delivery is a prohibited practice. Other This refers to any other commercially unacceptable contaminant such as animal excreta, glass, concrete, fertilizer or metal. http://www.graintrade.org.au/sites/default/files/file/Commodity%20Standards/Section%2002%20-%20Wheat%20Trading% 20Standards%20201415%20Final%201Sep14.pdf

Defective Grains Defective grains can result from environmental influences throughout the growing season (usually too much or too little rain), from the harvesting process, or from poor postharvest treatment and storage. Defective grains may be regarded as undesirable contaminants, even though of the same grain species. Such defects include the following:

Table 3

Some of the specifications for physical aspects of grain quality for contrasting grades of canola, soybeans and sunflowers involved in international trade

Parameter

US no. 1 grade sunflowers

US no. 2 grade sunflowers

Low quality

High quality

Low quality

High quality

Low quality

High quality

Low quality

Not stated Not Stated 70.0 kg hl 1 min Specified

Unlimited 2.0 max Unlimited Specified

Not stated Not stated Not stated Specified

Not stated Not stated Not stated Specified

40.0 min 2.0 max 32.0 kg hl Specified

Unlimited Not stated 38.0 kg hl Specified

Not stated Not stated 25.0 lb bu Specified

Not stated Not stated 25.0 lb bu Specified

10.0 max.

20.0 max.

10.0 max.

40.0 max

7.0 max

3.0% max.

1 max. (per 1000 seeds) 1 max.

US no. 3 grade canola

High quality

Low quality

High quality

Not stated 2.0 max Not stated Specified

Not stated 2.0 max Not stated Specified

Listed in damaged (%) 0.1% max.

Listed in damaged (%) 2.0% max.

High quality

Quality attributes Oil (%) 42.0 min 42.0 min Free fatty acids (%) 1.0 max 2.0 max Test weight 62.0 kg hl 1 min Unlimited Varietal mix Specified Specified Defective grains (% wt/wt, in cleaned ½ liter measure) Broken or spilt (%) 7.0 max. 7.0 max.

Australian birdseed sunflower (CSO-5)

Australian crushing soybean (CSO-8)

US No. 1 grade canola

Low quality

US no. 1 grade US no. 4 grade soybeans soybeans

Australian polyunsaturated sunflower (CSO-3)

Australian edible milling soybean (CSO-6)

Australian Australian canola rapeseed (CSO-2) (CSO-1)

Heat damaged, bin burnt Moldy

1 max. (per 1000 seeds) 5 max. (per 1000 seeds)

1 max. (per 1000 seeds) 5 max. (per Listed in 1000 seeds) damaged (%)

Damaged (%) Sprouted (%)

3.0 max. 5.0 max.

3.0 max. 5.0 max.

3.0 max. Listed in damaged (%)


Green (%)

2.0 max.

2.0 max.

2.0 max.

20.0 max.

Foreign seed contaminants in ½ liter measure Foreign seeds From nil to 65, From nil to 65, 10.0% max. acc. to species acc. to species

Listed in damaged (%)

10.0% max.

1 max. (per 1000 1 max. (per 0.2% max. seeds) 1000 seeds) 1 max. (per 1000 1 max. (per Listed in seeds) 1000 seeds) damaged (%) 3.0 max. 3.0 max. 2.0 max. Nil max. 5.0 max. Listed in damaged (%) 1.0 (other 2.0 max. Included in colors) damaged (%) count From nil to 10, From Nil to 65, 10.0% max. acc. to species acc. to species


1

min

1

min

1

min

1

min

Listed in Listed in damaged (%) damaged (%) 1 max. (per 1000 0.5% max. seeds) 1 max. Listed in damaged (%)

Listed in damaged (%) 1.0% max. Listed in damaged (%)


3.0 max. 5.0 max.

2.5 max Listed in damaged (%)



10.0 (other colors)

Included in damaged (%) count


Not stated

Not stated

10.0% max.

From nil to 65, From nil to 65, 3 or more 3 or more acc. to species acc. to species crotalaria seeds crotalaria seeds (Crotalaria spp.), (Crotalaria spp.), 2 or more castor 2 or more castor beans (Ricinus beans (Ricinus communis L.) communis L.) per 600 g per 600 g

Other contaminants in ½ liter measure Impurities (% wt/wt) 3.0 max.

4–10 depending on 4–10 depending on type of impurity type of impurity per 600 g per 600 g 8 or more and in 8 or more and in excess of 0.20% excess of 0.20% by wt by wt

3.0 max.

1.0% max.

2.0% max.

3.0 max.

4.0 max.

1.0 max.

3.0 max.

4.0 max.

6.0 max.

1 max. (above 3.0 mm screen/ 2.5 liter) 1 max. (below 3.0 mm screen/ 2.5 liter) 10 max.


0.05% max.

0.05% max.

Nil max.

3.0 max.

3.0 max.

Not stated

Not stated

Not stated

5 max.

Not stated

Not stated

100 max.

100 max.

Not stated

Not stated

100 max.

Not stated

Not stated

100 max.

5 max.

Not stated

Not stated

0.5 max.

0.5 max.

0.05% max.

0.05% max.

3 max. (field insects) 5 max. (stored grain insects) Nil max.


Nil

Not stated


0.5 max.


0.5 max.




Sclerotes (% by wt) (sclerotinia) Sand/soil (% by wt)

0.5 max.

0.5 max.

0.05% max.

0.15% max.

Nil max.

Not stated

Listed in damaged (%) Not stated

Not stated

0.5 max.

Not stated

Not stated

Not stated

0.06 max.

0.06 max.

Not stated

Not stated

0.06 max.

0.06 max.

0.06 max.

Not stated

Not stated

Nil

Nil

Nil

Nil

Nil

Nil

Listed in impurities (%) Nil

0.06 max.

Objectionable material (entire load)

Listed in impurities (%) Nil

Nil

Nil

Nil

Nil

Snails/stones

Insects – large (live and/or dead) Insects – small (live and/or dead) Ryegrass ergot (length in cm)

Sources: (1) Grain Trade Australia Section – Australian Oilseeds Federation Standards Incorporated Section 1: Quality Standards, Technical Information and Typical Analysis 2014/15 Issue 13 – 1 August 2014; (2) USDA GIPSA Grain Inspection Handbook, Book II Chapter 3 – Canola 7/30/13 (3) USDA GIPSA Grain Inspection Handbook, Book II Chapter 10 – Soybeans 7/30/13; (4) USDA GIPSA Grain Inspection Handbook, Book II Chapter 11 – Sunflower Seed 7/30/13.


88 Table 4

Groupings of contaminating seeds (a few examples only) used by the Australian wheat industry to indicate their severity as contaminants Maximum number of individual seeds allowable in 0.5 liter

Seed type

Botanical name

Local common name

Most grades

AGP1a

APH1ab

1 2 2 2 3a 3b 3c 4 4 5 6 7a 7a 7a 7a 7b 7b 7b

Argemone spp. Coriandrum sativum Ricinus communis Allium vineale Datura spp. Vicia sativa Heliotropium europaeum Melilotus indicus Lolium temulentum Acroptilon repens Sorghum halepense Gossypium spp. Zea mays Lupinus spp. Helianthus annuus Secale cereale Sorghum bicolor Avena sativa

Mexican poppy Coriander Castor oil plant Crow garlic Thornapple Vetch (common) Heliotrope (common) Hexham scent Darnel (drake seed) Knapweed (creeping, Russian) Johnson grass Cottonseed Maize Lupin Sunflower Rye (cereal) Sorghum Oats (common)

8 Nil Nil Nil Nil 4 8 20 20 40 10 2 1 1 1 50 50 50

8 Nil Nil Nil Nil 4 8 20 20 40 50 2 10 10 10 150 150 150

8 Nil Nil Nil Nil 4 8 20 20 40 10 2 1 1 1 50 50 50

a

Australian General Purpose 1. Australian Prime Hard 1. GTA Wheat Trading Standards 2014/2015, GTA Seed Impurities of Grain – Visual Identification Guide, 3rd ed. b

Table 5

Some of the international grain standards and visual guidelines for 2014/2015

Country

Standard name

Hyperlink

Australia Australia For grain commodity sampling and assessment The United States

Grain Trade Australia (GTA) 2014/2015 Trading Standards GTA Visual Recognition Standards Guide http://www.graintrade.org.au

http://www.graintrade.org.au

The United States

United States Department of Agriculture (USDA) Federal Grain Inspection Services (FGIS) US Official Standards USDA FGIS Grain Inspection Handbooks

The United States Canada

USDA FGIS Visual Reference Library (Images) Canadian Grain Commission (CGC) Official Grain Grading Guide

Canada

CGC Visual Identification of Small Oilseeds and Weed Seed Contaminants

http://www.gipsa.usda.gov/fgis/standproc/usstands. html http://www.gipsa.usda.gov/Publications/pub_fgis. html#hb http://www.gipsa.usda.gov/vri.html http://www.grainscanada.gc.ca/oggg-gocg/ggg-gcgeng.htm http://www.grainscanada.gc.ca/guides-guides/ identification/seeds-graines/sowsm-mpogmb-eng. htm

•

• • •

Immature cereal grains: These may have come from side tillers that formed at a late stage compared with the main tillers of the plant. Alternatively, it may indicate that varieties of different maturity have been sown as a mixture. These grains are likely to be green in color and ‘sappy’ in texture. Sprouted grains (Figure 1): These are grains that have become wet and have thus started the germination process. Sun-cracked rice grains: These are grains that will probably fall to pieces during rice milling (the removal of the outer bran layers), thereby reducing the yield of whole rice grains. The proportion of vitreous grains, pinched grains, black point, and frosted/distorted grains are very important but

controversial defects. Earcockle (seed-gall nematode), a disease caused by Anguina tritici, must be detected as it is an object of exclusion due to quarantine in certain countries, especially in Iran. When harvested and inspected at a grain silo or laboratory, wheat grain samples may show the defects illustrated in Figures 2 and 3. The sample in Figure 2 includes one green sappy immature kernel (1), five shrunken frost-damaged kernels (2), four soft wheat kernels (3), five hard wheat kernels (4), and two cracked kernels (5). Two shrunken grains also have black point (2) and one shrunken grain has pink fungi (6) and therefore may be classified as stained grain defects. The

GRAIN HARVEST, STORAGE AND TRANSPORT | Contaminants of Grain Table 6

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Some of the major grain contaminants for Australia, Canada, and the United States for bread wheat in 2013

Australia

Canada

United States

All smuts except loose smut Bread wheat Cereal ergot Chemicals not approved for wheat Dry green or sappy Earcockle Earth Falling number Field fungi Foreign seeds type 1 Foreign seeds type 2 Foreign seeds type 3a Foreign seeds type 3b Foreign seeds type 3c Foreign seeds type 4 Foreign seeds type 5 Foreign seeds type 6 Foreign seeds type 7a Foreign seeds type 7b Frost-damaged Heat-damaged, bin-burned, storage mold-affected, or rotted Insect-damaged Insects – large, live or dead Insects – small, live or dead Loose smut Objectionable material Other foreign material Over-dried damaged Picking compounds Pink stained Ryegrass ergot Sand Small foreign seeds Snails – max, live or dead Sprouted Stained, including staining due to moist plant material Stored grain insects and pea Weevil – live Take-all affected Unmillable material • Above screen max (by wt%) • Screenings (below screen) max (by wt%) Varietal restrictions Vitreous kernels White grain disorder/head Scab/flaked grain

Artificial stain Bin-burned kernels Black point Common bunt Darkened kernels Dark immature kernels Degermed kernels Ergot Excreta Fire-burned Fusarium damage Grasshopper, armyworm damage Grass-green kernels Hard vitreous kernels, sieving Hard vitreous kernels, handpick Heated Matter other than cereal grains Moldy Natural stain Odor Other cereal grains Other cereal grains and other matter Penetrated smudge Pink kernels Red smudge Rotted Sawfly, midge damage Sclerotinia Severe midge damage Severely mildewed Severely sprouted Shrunken and broken Smudge Soft earth pellets Sprouted kernels Stones Superficial discoloration Total damage Wheats of other classes or varieties

Bird droppings Black-tip fungus Blight or scab Castor beans Contrasting classes of wheat Crotalaria seed Damaged kernels Defects Discolored (pink wheat) Discolored black or brown Ergot Foreign material Frost-damaged kernels Blistered Candied Flaked Germ-damaged kernels (sick) Germ-damaged (mold) Glass Green-damaged (immature) Harmful or toxic substances Heat-damaged Heating Infested Insect-bored kernels Insect-damaged kernels Insect-damaged kernels stage 1 Insect-damaged kernels stage 2 Insect-damaged kernels stage 3 Large debris Musty, sour, or objectionable odor (animal hides, decaying animal/vegetable matter, fertilizer, fumigant, insecticide, oil products, skunk, smoke, strong weed) Odor Odor (smut) Other animal filth Rodent pellets Shrunken and broken kernels Smut (light smutty and smutty wheat) Sprout-damaged Stones Treated Unknown foreign substances Wheat of other classes

Australia: GTA Wheat Trading Standards 2013/2014 (as at 01 August 2013). Canada: Canadian Grains Commission Official Grain Grading Guide August 1, 2013. United States: USDA Grain Inspection Handbook Book ii, Chapter 13 Wheat 7/30/2013.

sample in Figure 3 contains vitreous grains (1) and nonvitreous grains with yellow patches, known as ‘mottling’ or ‘yellow berry’ in wheat and ‘chalky grains’ in rice (2), black pointstained grains (3), cracked (4) and shrunken grains (5), and insect-damaged grains with the germ missing (6).

Infected Grains Various forms of infection with microorganisms cause grains to become dangerous contaminants. For example, grain that is harvested with a high moisture content (>16% moisture) may

90


2

3

1

6 5

4

Figure 1 Sprouting of grains in heads of wheat. The heads have become wet when harvested ripe. The one at the left is a sproutsusceptible variety and the grains have started to sprout inside the head.

4 2

3 3

2 3

2

4

1 4

4

6 3 5 2 2

5

4

Figure 2 Defective grains in a durum wheat sample. Reproduced with permission from McLean, J.M., 2009. Durum Wheat Quality Testing of Vitreousness, University of Sydney.

be infected with molds, commonly called field fungi, such as Fusarium and Alternaria, causing, in turn, the production of mycotoxins. Because these toxins are active at very low concentrations, for example, a few ppb, their detection is difficult. They

Figure 3 An ADR3 grade sample of durum from a silo in Bellata, New South Wales, Australia, collected during the 2000–2001 season. Reproduced with permission from McLean, J.M., 2009. Durum Wheat Quality Testing of Vitreousness. University of Sydney.

are not necessarily present in visually spoiled grain (e.g., moldy), so there is the need for ready means of testing. Immunoassay kits are a means of doing so quickly in ‘field’ situations. If not detected, mycotoxin-affected grain may cause severe illness or death to humans or animals. Grain affected by field fungi may be dark brown, gray, or various shades of black discoloration or pink, especially when affected by Fusarium spp. Ergot infection is another serious contaminant, mainly present in rye, ryegrass, canola, and to a lesser extent, wheat. In this case, the ergot fungus (Claviceps purpurea) infects the flowers of the cereal grain, producing an ergot body in place of the grain (Figure 4). The ergot bodies often thresh intact, easily recognizable in grain samples as black bodies (sclerotia), larger and longer than the normal grain length. The extent of ergot contamination is generally specified as a percentage by weight, but the length of ergot bodies placed end to end is a simple measure used in practical situations. Harvested grain of any species may contain ergots from other species, especially from ryegrass (Lolium perenne). Any of these sources of ergot produce toxic alkaloids, which may cause injury in cattle when present at a level as low as 0.05%. On the other hand, some poultry species appear to be much more tolerant to ergot poisoning. Another serious infection of cereal grains is bunt, also known as ball smut or stinking smut, caused by Tilletia caries or T. foetida. This defect also involves the replacement of the endosperm of the grain by bunt spores, which have a pungent unpleasant odor. As a result of this form of contamination, sound grain may be tainted by admixture with bunt-affected grain (Figure 5). If these grains are broken, black bunt spores spread through the grain as a further source of contamination. In the case of wheat, the bunt spores are caught in the brush hairs of sound grains (Figure 6).


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Figure 6 Bunt spores caught in the brush hairs of sound grains. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties: Supplement No 1. Melbourne: CSIRO.

Foreign Seeds Figure 4 Ergot-infected heads, in which ergot bodies have replaced grains in the head. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties: Supplement No. 1. Melbourne: CSIRO.

The presence of seeds from other crops or weeds can result from poor hygiene techniques when harvesting, transporting, and storing or from previous season crops.

Other Crop Seeds

Figure 5 Bunt of wheat. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties: Supplement No 1. Melbourne: CSIRO.

In grain storage, excessive moisture can lead to moisture migration and ‘bin-burn’ of the grain (causing heat damage and moldy appearance) resulting from the development of field fungi, which may produce dangerous toxins and offensive odors. For this reason, there are recommendations for the minimum moisture content of the grain before it can be stored safely.

The commonly found contaminants are the seeds of other crop plants. These are likely to be species whose plants are of similar size and maturity to the target seed. It is thus difficult to avoid harvesting them together with the intended crop. Such foreign seeds are likely to be other agricultural species (e.g., barley or rye in a wheat crop) that have been present in the seed sown or that have been carried over from a previous crop at this growth site. Such contaminants may not be critical unless they interfere with the subsequent processing of the grain, such as milling into flour. A further consideration is how readily they can be removed, if their removal is essential, because this exercise will add to processing costs. Contamination of wheat with oilseeds, for example, poses the threat of disrupting wheat milling equipment with the buildup of oil residues, although contaminants such as canola are relatively easy to separate from wheat before milling. For a wheat consignment, there may be no need to remove minor contamination with other cereal grains, such as barley and oats (up to about 5%). Canadian research has shown that flour yield decreased by about 0.4% for each addition of 1% of barley added to a wheat sample. Milling stocks fed well during flour milling, despite the barley contamination. Likewise, the effects of contamination of wheat with cultivated oats (or even wild oats) were similar to that of barley, except that at 5% addition, oats caused difficulty with the milling process.

Weed Seeds Weed seeds present problems of greater severity than contaminating crop seeds (Tables 4 and 6). Some weed seeds are the

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Silybum marianum variegated thistle

Carthamus lanatus saffron thistle

Emex spp. double gee threecornered Jack spiny Emex cats’ heads

Galium tricornutum (Galium tricorne) threehorn bedstraw

Figure 7 Weed seeds that are likely to cause problems if identified in grain consignments. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties: Supplement No 1. Melbourne: CSIRO.

same size as grain kernels, which make it virtually impossible for them to be sieved out of a parcel of grain (e.g., Phalaris). For a start, agricultural authorities must restrict the seeds of noxious weeds, due to the threat that they pose to cropping and grazing. However, in small amounts, their presence may not be serious to agriculture because they are likely to be destroyed by processing, such as flour milling. If wheat contains seeds with a dark seed coat, they are likely to cause dark specks in flour, which can decrease the visual appeal of the end product for the market. On the other hand, some weed seeds cause serious problems because some are toxic to humans and animals. In this category are species such as castor oil seed (Ricinus communis), Mexican poppy (Argemone species), and thornapple (Datura species). Ricin, the toxic principle in the castor oil seed, is reported to be one of the most toxic plant substances known. Tainting seeds, whose scent may taint a whole consignment of grain, must be avoided, and they are generally specified as ‘nil tolerance,’ that is, none of this type is allowed. In Australia, for example, seeds called ‘Hexham scent’ (Melilotus indicus) impart their scent to the grain with which they may be mixed, with the risk of a large consignment of grain being tainted by the presence of a relatively small contribution of grain with this contamination; similar problems may be produced by the presence of eucalyptus leaves. Animals will probably reject feed

grain if it is tainted. Alternatively, if they do consume it, the taint may be passed through to the animal by-products, such as milk. There is naturally great variation in the range of weed seed species that are relevant to specific regions and grain species. Regional and national booklets are published for many graingrowing regions, illustrating a relevant range of weed and crop seeds. Examples of weed seeds that must be identified and restricted are shown in Figure 7.

Other Contaminants Nongrain material goes under various names, depending on local terminology and on the species of grain involved. Common terms include ‘extraneous matter,’ ‘unmillable material,’ ‘dockage,’ ‘besatz,’ and ‘screenings.’ This last term alludes to the general practice of screening the grain through sieves of suitable size to separate material that is larger or smaller than the normal size range of the grain involved. The act of sieving to determine screenings is illustrated in Figure 8. The amount of these screenings is a significant measure of grain quality, as it indicates the proportion of the grain consignment that is not the grain purchased. In addition, the nature of the nongrain

GRAIN HARVEST, STORAGE AND TRANSPORT | Contaminants of Grain material is very important, depending on which of the following categories are involved.

Plant Material from the Grain Crop Most obviously, nongrain contaminants are derived from the plants that produced the harvested grain. This includes parts of the husks, leaves, and stalks. For the cereal grains, it is not uncommon for the tips of the heads to be included with the harvested grain. This occurs for varieties that may not fragment as readily as others during harvesting. This is due to the dilemma facing the breeder in selecting the best genotypes for the harvest operation. On the one hand, it is desirable to have a variety that ‘shatters’ readily, so that the grain is released from the head on harvesting. On the other hand, this characteristic is

Figure 8 Sieving of a grain sample to remove screenings (nongrain material).

likely to carry the significant disadvantage that some of the grain will be prematurely shed onto the ground before or during harvest, thus reducing the yield of available grain. In addition, if the settings of the grain harvesting equipment are not correct, there will be excessive inclusion of plant parts with the grain or damage to the grain. The resulting presence of shattered or half grains is undesirable, because they are more susceptible to insect attack and to further damage during grain handling and transport. The risks of such undesirable consequences during harvest and transport are greater in very dry, hot conditions. Hot, dry conditions are also conducive to the production of grain dust – fine particles abraded from the plant material and even from the grain itself. Ongoing handling and transport of dry grains are likely to produce more grain dust, as grains rub against each other when they are ‘turned’ or moved from storage facilities to transport containers (trucks or rail cars). Figure 9 shows that grain dust is largely composed of fragments broken from the surfaces of grains. In wheat dust (Figure 9(a)), there are short hairs from the brush-end of the grain and also fragments of the bran layers, as well as starch from the endosperm of grains that have been completely broken. The dust from barley (Figure 9(b)) shows long spearlike structures (broken pieces of rachilla hairs) as well as fragments of awns, lemmas, and paleas. It is a controversial matter in international trade as to whether the accumulated dust should be removed before shipping grain or whether it is a legitimate part of a grain cargo. In any case, the dust generated during grain handling is a significant health problem for grain growers and for grain handlers, causing irritation to the bronchial tract and to the skin. Dust also creates safety concerns due to its explosive potential; therefore, dust reduction is a high priority at grain storage centers.

100 µm

100 µm (a)

(b)

10 µm

400 µm (c)

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(d)

Figure 9 Scanning electron micrographs of grain dust from (a) wheat and (b) barley. The photo of half a barley grain (c) shows where the rachilla hairs have been broken from the base of the rachilla. The rachilla hairs are also shown at greater magnification (d). In each photo, the black bar at the bottom, near the right side, is (a) 100 mm, (b) 100 mm, (c) 400 mm, and (d) 10 mm.

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Sitophilus granarius Granary weevil

Sitophilus oryzae Rice weevil

Rhyzopertha dominica Lesser grain borer

Tribolium castaneum Rust-red flour beetle

Cryptolestes spp. Flat grain beetle

Oryzaephilus surinamensis Saw-toothed grain beetle

Figure 10 Insect species that attack grains. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties: Supplement No 1. Melbourne: CSIRO.

Insects Harvested wheat grain in Eastern Europe, the Middle East, and Russia might already show signs of insect attack on the developing grain by the suni bug (Eurygaster species), which leaves behind proteases that degrade the grain’s storage protein causing the mature grain to be useless for bread making. Insects that attack the stored grain are a serious case of contamination (Figure 10). Accordingly, there is a ‘nil tolerance’ for live insects in many regions (Tables 1–3). This specification may be relaxed to a small extent in the cases of dead insects and for species of insects that do not attack grains (on a case-by-case basis only) such as field insects. Infestation with grain-attacking insects (previously or currently present) may be indicated by the presence of grains that have been partly eaten by insects (Figure 11). There are two main types of grain insects. Primary insects are more destructive as they can attack sound grain, while secondary insects can only attack grain that has been damaged. Insects can deplete the energy value of the grain, greatly reducing its value even for stock feed. Insect infestations are often associated with bad odors. Due to the serious threat that some insects can impose, there is a strict nil tolerance on specific species. For example, the khapra beetle, Trogoderma granarium, is the world’s most serious insect pest. This insect does not occur in some countries (e.g., Australia). However, the warehouse beetle, T. variable, is often

Figure 11 Wheat grains that have been partly eaten by insects, indicating previous (or current) infestation. Reproduced with permission from Ferns, G.K., Fitzsimmons, R.W., Martin, R.H., Wrigley, C.W., 1978. Australian Wheat Varieties. Supplement No 1. Melbourne: CSIRO.


13

14

15

16

1 7

18

Vineyard or common white

White Italian

Conical or pointed

Cernuella virgata

Theba pisana

Cochlicella acuta

19

20

95

2

Small conical or small pointed Cochlicella barbara

Figure 12 Various types of snail that may contaminate grain consignments. Reproduced from Anon., 2012. All-Year-Round Attack on Snails Required. Canberra: Grains Research & Development Corporation.

mistaken for the khapra beetle and this can jeopardize not only the acceptance of a parcel of grain but also the whole country’s reputation.

Animals and Animal Products Further contaminants include snails, rodents, urine, feces, rodent hairs, birds, bird feathers, and snakes. Snails (Figure 12) rarely live more than 2 weeks in storage, so they are unlikely to reproduce during storage. Nevertheless, their presence is likely to downgrade the quality status of a grain consignment. Most animals contaminate grain through the grain storage system (with the exception of snails) due to their reproduction and spread throughout the grain store. Rodents and birds are attracted to the grain as a food source and they will often nest there. As a result, there can be the added contamination from the accumulation of their urine, feces, rodent hairs, feathers, eggs, and decaying carcasses. For example, a single rat can produce 12 000 droppings, 2.9 liters of urine, and 0.9 million shed hairs in 6 months. Rodents thus become an important issue, especially when there is a plague. Animals and birds are also potential vectors for diseases. Snakes and some bird species will be present around storage sites, preying on rodents and other birds. All of these animals can become included in a consignment of grain accidentally if present on one of the transport belts or elsewhere on the grain transport path when it is activated.

residue limits (MRLs). Grain with levels above these limits cannot be used or sold legally. They may also present serious health exposure risks, including death to grain operators. Grain that is fed to cattle and chickens can transfer the chemicals, thus posing a threat to their markets, with the likelihood that the resulting meat will be prohibited from human consumption. Examples include endosulfan in cottonseed hulls and wheat resulting from spray drift. It is necessary to observe and follow chemical instructions for correct application rates and withholding periods to ensure that MRL levels are not exceeded and to reduce the chance of insect resistance building up. It is also important to ensure that the chemical being applied is approved for use on that particular grain. Heavy metals (mercury, cadmium, and lead) are contaminants that must be tested routinely as a precautionary measure, especially in industrialized countries.

Inanimate Materials Sand, earth, sticks, stones, and other inanimate materials cause problems in both analysis and processing, as they can damage grinders, mills, and technical equipment. Such materials can be picked up during the harvesting process or introduced through the storage and handling processes if equipment is not carefully calibrated and cleaned prior to use. The severity of the material depends on their size. If the material is a similar size to the grain, it cannot be sieved out easily and this can become a serious issue.

Agricultural Chemicals Pickling compounds (fungicides) applied to seed grain render the grain unfit for consumption (human or animal). Pickling colors range from bright pink or green to a slight pink or green coloration. There is a strict nil tolerance for pickled grain as a small amount can render a whole stack unusable. Parcels are regularly checked for pesticide residue levels (obtained through the application of herbicides and/or insecticides). There are tolerances by national regulatory bodies, known as maximum

Tainting Contaminants In addition to the contamination of grain with tainting materials as a result of harvest, tainting of a grain consignment can occur during storage and transport if a taint or odor is acquired from materials that the grain is exposed to. One such source can be the packaging material used, in the case of grain that is stored and transported in bags, for example, hessian bags.

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Genetically Modified Grain With the introduction of genetically modified (GM) grain (initially involving maize, canola, soy, and cotton), and in response to various international market demands, the presence of GM grain within conventional grain delivered can lead to rejection of that grain. Methods are being put into place that will permit the detection of such contamination, thereby guaranteeing the required grain quality required by specific markets. International standards now dictate separate requirements for GM free grades.

Analysis of Contaminating Materials Given the wide range of contaminants that may be harvested with grain, plus the variations in allowable levels, it is important that there should be rapid means of identifying them. This requirement applies especially to identifying the species of contaminating seeds, since the range of species varies considerably from one region to another. Accordingly, manuals illustrating the range of contaminants are provided for staff training, to inform growers and for use when grain is delivered.

Figure 13 Sampling grain from a truck using a spear sampler.

Sampling An essential prerequisite of valid analysis is the initial step of taking a representative subsample of the load being analyzed. Sampling procedures are generally specified together with the manuals illustrating the contaminants. Procedures are also published by grain-trading authorities. The website of the US Department of Agriculture (http://www.gipsa.usda. gov/publications/fgis/handbooks) specifies standard sampling procedures for various grain production situations. Standard procedures for sampling are provided in the methods of AACC International (formerly the American Association of Cereal Chemists) and the International Association for Cereal Science and Technology (ICC). A critical stage of grain sampling is taking a representative set of samples from a truck when grain is first delivered from harvest to the elevator (Figure 13). In this case, sampling is performed so that a whole truck’s contents can be observed from above. Routinely, the grain in the truck is sampled by pushing a sampling spear into the grain at several points. This form of sampler is designed to take grain from several vertically separated points throughout the depth of grain. Alternatively, vacuum probes are used to spear the truck in a straight vertical line right down through to the bottom of the load. If the grain is delivered by road, train, or other vehicles with multiple compartments, each bin is sampled at a minimum prescribed time, dependent on the volume being delivered (typically three times per bin).

Sieving An example of the use of mechanical sieving is provided by the routine practice of GrainCorp in eastern Australia using the agitator (Figure 14). Forty shakes are automatically performed to and fro, as specified by Australian receival standards. The use of a mechanical sieve such as this ensures repeatable

Figure 14 Agitator equipment for sieving grain.

movement, speed, and duration. The following screen sizes are appropriate: for wheat, 2.0 mm slotted; for barley, 2.5 mm and 2.2 mm slotted; for sorghum, 2.0 mm slotted (wheat screen); for sunflowers, 2 mm round; for chickpeas, top 3.97 mm slotted over bottom 2 mm slotted; and for canola, top 2.58 mm round over bottom 1.00 mm round.

Visual Examination and On-the-Spot Instrumental Analysis Traditional methods of analyzing contaminants involve visual inspection, and this approach is still the best with respect to providing an immediate outcome and requiring no expensive equipment. However, this approach is subjective and highly dependent on inspector experience. This expertise is acquired and maintained by ongoing training, the use of illustrated manuals, visual standards, and actual samples, requiring ongoing monitoring to ensure the standards are applied consistently. By this approach, grain samples are first evaluated visually at the site of grain receival, and then, a representative portion may be sent back to a regional laboratory for a second cross-reference assessment. In addition, a further portion may be presented to buyers of the grain for their additional evaluation. The identification of the

GRAIN HARVEST, STORAGE AND TRANSPORT | Contaminants of Grain species of insects is also an important part of this process, because the various insect species differ in the severity and consequences of infestation. The immediate detection of serious contaminants is critical at the time of delivery, so that defective grain loads are not combined with sound grain, as this might downgrade the grain to which it is added. Subsequent analysis in the laboratory provides results too late to prevent damage of a large grain consignment by, for example, the incorporation of a relatively small load of grain that is tainted or insect-infested. On-thespot analysis is thus critical. It has become usual for visual inspection to be complemented by on-the-spot testing to provide objective results for specific critical aspects of contamination. Image analysis has great potential for replacing the subjectivity of human involvement by analysis of the image of grains and contaminants provided by a television camera. However, the introduction of image analysis is a slow process due to the expense and technical input required to develop methods and monitoring procedures. Near-infrared (NIR) analysis has been used to detect the presence of insect infestation, probably due to the ability of this spectroscopic method to detect the distinctive presence of insect protein and/or chitin. The use of NIR methodology has the potential advantage that NIR equipment is already in routine use to determine moisture, protein content, and oil content, but the NIR units in routine use may not be adequate for more complex analyses. Ultraviolet light inspection provides an immediate means of checking for rodent urine, which fluoresces with a blue-green color (AACC International Method 28–85). Rapid immunoassay kits are now available to detect and quantify a range of chemical contaminants, aflatoxins, and damage from sprouting.

Analysis in the Laboratory Contaminant identification may continue by visual examination at a regional or central laboratory, where a higher level of expertise may be expected of the inspectors. There is also a role for image analysis and sophisticated NIR equipment at a central site, where the volume of samples would warrant the expense and need for operator expertise. A wide range of laboratory methods are available for the detection of specific contaminants. For example, the AACC International Methods provide many standard procedures. Laboratory methods include gas or liquid chromatography to analyze for agricultural chemicals and ELISA immunoassays for many contaminants, especially aflatoxins.

Avoidance of Contaminants Purity of Seed Sown An obvious source of contaminants is the seed originally sown. If it contains foreign seeds, these are likely to multiply and downgrade the harvested grain. Additional risks include the presence of diseased seed, which will lead to the spread of diseases during growth. It is thus important to obtain seed of guaranteed purity at the time of purchase.

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Farm Management The use of ‘best farm management practices’ includes cleaning and calibration of harvester and sowing equipment before use, proper preparation of fields before sowing, ensuring that the crop is mature before harvesting, and storage of the grain so that it does not become contaminated. During growth of the crop, weeds must be controlled. In addition, it is valuable to use crop rotations as ‘biofumigants’ to avoid the buildup of microbial spores in soils. Visit the website www.storedgrain. com.au to see the latest information on grain storage and handling management.

Quality Assurance Methods All these methods of contaminant avoidance should be combined for implementation via a system of quality assurance to provide systematic recognition of potential hazards, intentional approaches to avoid the hazards, and records to indicate how and when the preventive measures were taken. This approach extends beyond the farm, to involve, for example, the use of traceable and repeatable methods of appropriate farm practices, working only with companies that are themselves quality assurance certified. In Australia, growers are encouraged to voluntarily adhere to the Australian Grain Industry Code of Practice; see http://www.graintrade.org.au/ node/670.

International Regulations on Contaminants International regulations on many food matters are administered by parts of the Codex Alimentarius. The Codex Committee on Food Additives and Contaminants (CCFAC) establishes or endorses maximum or guideline levels of contaminants in food and animal feed, as well as dealing with food additives and naturally occurring toxicants. The CCFAC is developing risk analysis approaches to be applied to all foods. The resulting document is the General Standard for Contaminants and Toxins in Food and Feed. Further details of the latest developments are available at the USDA website. In Australia, the Australian Pesticides and Veterinary Medicines Authority (APVMA) authorizes the use of chemicals for grain products; see http://apvma.gov.au/.

Future Prospects Emerging issues such as increasing pesticide and insecticide resistance, new disease, and weed incursions and biosecurity threats due to globalization of the market add to the demands on growers to produce grain that is free of contaminants. Traditionally, the presence of contaminants of any type in a grain consignment has prompted a reduction in its market value, because any variation in appearance can provide grounds for bargaining and for price reduction. More recently, there has been a growing awareness that some defects and contaminants may have relatively small financial consequences. In some instances, the economic effects can readily be assessed. For example, if the presence of 2% screenings (by

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weight) brought a 5% reduction in price, it would be a worthwhile bargain, if the cost of cleaning is more than covered in the price difference. Similar considerations apply to other innocuous contaminants, if their dimensions make them easily removable. Another approach to overcoming such problems may involve the intelligent blending of diverse grain samples. Relatively simple research activities can establish the extent of economic penalties for the presence of one grain type as a contaminant in another, for example, oilseed in cereal or the reverse. There is a continuing need for more effective methods of analysis to characterize and quantify the presence of contaminants in grain deliveries at the point of receival and during grain handling. New screening methods should preferably be deployable on the spot and be nondestructive of the grain. Most of all, they need to be cost-effective, the cost of deployment warranting the benefits and the risks thereby avoided. The detection of contaminants by image analysis is likely to increase in its application. We can expect that large grain sorters will be placed into grain storage sites and cleaning facilities. Increases in quality demands will mean the need to increase the efficiency of detection and measurement requirements at the receival point. In summary, these new methods must be rapid (taking less than 5 min), easy to operate with minimal operator skill required, nondestructive, and cost-effective, being able to operate in a wide range of temperature variation, under dusty conditions, occupying minimal bench space, but the fulfillment of these requirements is a ‘tall order.’


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Select a range of 20 contaminants likely to be present in harvested grain and group them according to the causes or sources of their presence. – Specify the likely means by which the presence of these contaminants might be avoided. Compare several grains of specific species, noting the extent to which the presence of contaminants appears to determine the presumed ‘quality’ and standing of each grade. Compare the Australian method of screenings with the US dockage test, noting the major differences between each and what the benefits of each method are.


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Describe the relative benefits and disadvantages for assessing the presence of contaminants of visual inspection, NIR analysis, and mechanical scanning (image analysis). Describe the ways in which the problems of contaminants may be improved by better farm management and by quality assurance procedures. Would each of these actions be cost-effective? What are the implications (difficulties?) for downstream users of each type of contaminant?

See also: Barley, Rice and Maize Processing: Barley: Milling and Processing; Maize: Dry Milling; Bioactives and Toxins: Mycotoxins; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units; Grain Harvest, Storage and Transport: Cereals: Grain Defects; Stored Grain: Invertebrate Pests; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Grain Marketing and Grading: Barley: Grading and Marketing; Soybean: Grading and Marketing; Wheat: Grading and Segregation; Wheat: Marketing; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; The Grain Crops: An Overview; Wheat Processing: Wheat: Dry Milling.

Further Reading Australian Government Department of Agriculture. (2013). Plant Export Operations Branch, Plant Export Operations Manual, Volume 6 Part A: Pests, Diseases and Contaminants of Grain and Plant Products (excluding horticulture). URL: http:// www.daff.gov.au/biosecurity/export/plants-plant-products/plantexportsmanual/ volume-6a. Australian Oilseed Federation Standards 2014/15. AACC International Methods of Analysis. 11th edn. AACC International, St. Paul, MN, USA. Canadian Grain Commission. (2014). Official Grain Grading Guide, URL: http://www. grainscanada.gc.ca/oggg-gocg/ggg-gcg-eng.htm. CCFRA (2002) Manual of methods for wheat and flour testing, 3rd ed. Chipping Campden, Gloucestershire: CCFRA, Technology Guideline No. 3. Delwiche SR (2010) Analysis of grain quality at receival. In: Wrigley CW and Batey IL (eds.) Cereal Grains: Assessing and Managing Quality, pp. 267–310. Cambridge: Woodhead Publishing. D’Mello, J. P. F. Contaminants and Toxins in Animal Feeds, Scottish Agricultural College (SAC) in Edinburgh, the United Kingdom. URL: http://www.fao.org/docrep/ ARTICLE/AGRIPPA/X9500E04.HTM Ferns GK, Fitzsimmons RW, Martin RH, and Wrigley CW (1978) Australian Wheat Varieties. Melbourne: CSIRO, Supplement No 1. Fitzsimmons RW and Wrigley CW (1979) Australian Barleys: Identification of Varieties, Grain Defects and Foreign Seeds. Melbourne: CSIRO. Grain Trade Australia. (2014–2015). Trading Standards. GTA: Australia. National Institute of Agricultural Botany (2000) Botanical Descriptions of Cereal Varieties. Cambridge: National Institute of Agricultural Botany. USDA Grain Inspection, Packers and Stockyard Administration (2013) Grain Inspection Handbook: Book II Grain Grading Procedures. Washington, DC: USDA, http://www. gipsa.usda.gov/publications/fgis/. Wrigley CW (ed.) (1995) Identification of Food-Grain Varieties. St. Paul, MN: American Association of Cereal Chemists. Wrigley CW and Batey IL (eds.) (2010) Cereal Grains: Assessing and Managing Quality. Oxford: Woodhead Publishing.

Relevant Websites http://www.aaccnet.org/Pages/default.aspx – AACC International. http://apvma.gov.au/ – Australian Pesticides and Veterinary Medicine Authority. http://www.aocs.org – American Oil Chemists’ Society; Standard Methods. http://www.australianoilseeds.com/ – Australian Oilseeds Federation. http://www.campden.co.uk – Campden and Chorleywood Food Research Association. http://www.crop.cri.nz – New Zealand Institute of Crop and Food Research. http://www.fsis.usda.gov – Food Safety and Inspection Service; Codex Committee on Food Additives and Contaminants. www.grainscanada.gc.ca – Canadian Grains Commission, Winnipeg. http://www.graintrade.org.au/ – Grain Trade Australia. http://www.wheatquality.com.au/ – Wheat Quality Australia. http://www.icc.or.at – International Association for Cereal Science and Technology. http://www.seedtest.org – International Seed Testing Association. http://www.usda.gov – United States Department of Agriculture. http://wheat.pw.usda.gov/GG2/index.shtml – GrainGenes.

Chemicals for Grain Production and Protection PC Annis, CSIRO Entomology, Canberra, ACT, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Overview of agricultural chemicals. Seed treatments. Fertilizers. Herbicides. Crop-protection chemicals. Foliar fungicides. Stored-product protection.

Learning Objectives

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Understand the range of agricultural chemicals used in cereal production and storage. Recognize that the label on many agricultural chemicals is not only for identity but that it also defines how the material is used (often legally enforceable). Demonstrate the types of information needed to select the appropriate chemical. Illustrate the somewhat limited range of active compounds available. Give a basis for starting a web search for chemicals to fit the vast range of local, national, and biogeographic condition where grain crops are grown.

Introduction Chemicals have a critical role in modern cereal production and are used at all points in the grain production and storage cycle, from seed dressing, to soil preparation, to crop and storedproduct protection. There are several classes of agrochemicals associated with grain production and protection. These include seed dressings, trace elements, fertilizers, herbicides, fungicides, crop-protection pesticides, stored-product pesticides, structural treatments, and rodenticides. Trace elements, fertilizers, herbicides, and crop-protection pesticides are often very specific for particular biogeographic and agrogeographic situations and represent a diverse range of chemicals. Chemicals used for structural treatments of storages, stored products, seed storage, and rodenticides tend to be more universal and cover a much smaller range. In most jurisdictions, there are specific regulations concerning the use, supply, labeling, transportation, storage, and importation of biocidal chemicals (insecticide, acaricide, rodenticide, fungicide, nematicide, molluscicide, and herbicide). The administration of these regulations may be associated with one or several authorities concerned with the environment, public health, workers’ safety, and agriculture. The specifics of the regulations may differ from place to place, but the general rule is that a chemical may only be used in compliance with the label accompanying the product. This


label will be specific to a particular jurisdiction. The label will contain specific information about what crops the material can be used on, what pests it is intended for, how to apply and rates of application, withholding times for treated crops, disposal of containers, personal/environmental safety, and first aid. Registration is normally granted when it is shown that a pesticidal chemical can be used in compliance with all regulations and there is a label that, when followed, will ensure that the user will meet regulatory requirements. The registration of agricultural chemicals is usually handled by a government agency. In the United States, this agency is the United States Environmental Protection Agency (USEPA); in Australia, it is the Australian Pesticides and Veterinary Medicines Authority (APVMA); in the United Kingdom, it is the Chemicals Regulation Directorate (CRD); a list of agencies in other countries is maintained on the OECD website at the end of this article. Trace elements and fertilizers are not generally subject to specific government registration. Application rates and methods of use will usually depend on local agronomic requirements and practice. There may also be specific conditions/recommendations for use in some environmentally sensitive areas. There have been many concerns expressed regarding the use of all chemicals in agriculture over recent years. However, their use continues because their role remains an important part of food production, handling, and storage. Considerable effort has been directed since the 1980s to finding ways of using agrochemicals (biocides and fertilizers) in a way that is sustainable, environmentally safe, and with minimal threat to the health of agricultural workers or consumers. Although many agricultural chemicals are potentially dangerous, they should pose little threat if used strictly in accordance to the manufacturers’ instructions. Risks are further reduced if the user reads and understands a material safety data sheet (MSDS) for the chemical concerned. In many jurisdictions, an MSDS must be available to people that handle, store, or use potentially dangerous goods. The aim of this article is to provide an overview of the diverse range of chemicals used in grain production and storage and to give a brief insight into their use and composition. Any detailed discussion of this subject would entail a review of large portions of the subject matter contained in the sciences of agronomy, economic entomology, plant pathology, and stored-product technology.

Seed Treatments Fungicides Fungicidal seed dressings are sometimes applied to stored seed to prevent disease development, which would impair the seed’s ability to germinate or the seedling’s ability to grow in a

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normal manner. Fungicides are not generally used to prevent the development of storage fungi, which are better controlled by maintaining the seed in cool dry storage conditions. Germination is best maintained under storage conditions where fungal growth is not a problem. The optimum conditions for seed storage are well documented and have been known for many years. Recommendations for the use of fungicidal seed dressings will vary with the prevalence of particular disease risks, national and state regulations, and availability of chemicals. Fungicidal seed dressings are particularly useful in cereal crops for controlling bunt and smut and can assist in reducing the rate of development of some rusts. The following is a synopsis of the recommendations for bunt control in the State of Queensland, Australia. It is shown in order to give an idea of the role of preplant fungicides.

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Seed that is sown to provide the following season’s seed needs to be treated with a fungicidal seed dressing. Seed from plants grown from untreated seed should be treated with a fungicidal seed dressing before planting. All seed entering Queensland should be treated with an appropriate fungicidal seed dressing. Grain from a crop with bunt should not be used for seed. Wheat seed from farms where a crop has been affected by bunt should be treated with fungicidal seed dressing for at least 6 years.

In Australia, fungicidal products containing the following active compounds are available, either singly or as components of a mixture, for seed dressings to control bunt (and some other seed-borne fungal diseases): carboxin, fluquinconazole, flutriafol, prothioconazole, tebuconazole, triadimenol, and triticonazole. These fungicidally active compounds are sometimes combined with insecticidal or herbicidal compounds in seed dressing formulations. Almost all chemical treatments have some disadvantages and the obvious advantages. The use of a fungicidal seed dressing, in general, renders the seed unfit for animal or human consumption, while a number of fungicidal seed dressings may reduce or retard seedling emergence. This is a problem that may be aggravated where the seed is sown or stored in suboptimal conditions.

Insecticides See stored-product protection in the succeeding text.

Fertilizers There are many parts of the world where additional phosphorus and/or nitrogen is essential to maintain a viable cereal cropping industry. The requirements for the other nontrace nutrient elements – potassium, calcium, magnesium, and sulfur – are less common and more localized. Concern has been expressed that fertilizer runoff could have significant effects on waterways and groundwater. There are undoubtedly limited circumstances where this may occur but it is far from the general case.

Nitrogen Cereal cropping removes nitrogen from the soil, and in almost all cases, nitrogen will need to be replaced in order to allow sustainable cropping. Crop rotation with nitrogen-fixing plants and animal grazing has been used traditionally to replace soil nitrogen. Application of nitrogen fertilizer has now become the standard practice for cereal grain producers in many parts of the world. The major nitrogen (N) fertilizers are ammonium nitrate (34% N), urea (46% N), anhydrous ammonia (82% N), and urea–ammonia nitrate mixtures (ammonium nitrate and urea dissolved in water containing 28–32% N). The cost and availability of nitrogen fertilizers vary greatly depending on location. Liquid urea–ammonium nitrate is often the most expensive treatment. The dry forms are intermediate, and anhydrous ammonia is the most economical. Ammonia can, in some places, cost as much as 30–40% less for an equal amount of nitrogen, compared to the dry and liquid nitrogen forms. However, the complexity and costs associated with logistics and supply of ammonia make its use impractical in some regions.

Phosphorus Phosphorus-containing fertilizers, like nitrogen-containing ones, are widely used in cereal growing. In places where the soil is low in phosphate, fertilizer addition is essential to give and maintain viable cereal yields. In recent years, concerns have been expressed about the effects of phosphate fertilizers on the surrounding environment associated with soluble phosphate ending up in waterways. This has led to several jurisdictions formulating guidelines for the application of phosphate fertilizers (also other fertilizers). Phosphorus is applied as ammonium phosphates or superphosphate, and phosphorus fertilizers are often characterized by their (N–P–K, nitrogen–phosphorus–potassium) composition. Common phosphate fertilizers include liquid ammonium polyphosphate (10–34–0), dry mono- or diammonium phosphate (11–48–0, 16–48–0, or 18–46–0), superphosphate (0–20–0), or concentrated superphosphate (0–45–0).

Sulfur Sulfur-deficient growing conditions are much less common than is the case for nitrogen or phosphorus. The most common sulfur-supplying fertilizers are ammonium sulfate or gypsum. These are best applied as top dressing where they are immediately taken up by wheat plants. Elemental sulfur may have some role as a preplant sulfur source. However, it is chemically unavailable to the plant when used as top dressing for growing plants.

Potassium Potassium (K) deficiency can limit wheat crop growth but the deficiency is not common. There are some restricted localities around the world where the use of a potassium-supplying fertilizer is useful. Potassium is usually applied as either potassium chloride ( 60% K) or potassium sulfate (50% K).

GRAIN HARVEST, STORAGE AND TRANSPORT | Chemicals for Grain Production and Protection Potassium nitrate (37% K), another potential fertilizer, is not commonly used for cereal crops.

Calcium and Magnesium There may be a need for additional calcium and magnesium in leached soils in high-rainfall and acid-rainfall areas. Calcium is frequently obtained coincident with liming as part of soil pH control. Both calcium and magnesium can also be supplied by adding crushed limestone.

growing cycle; they may be registered either as components of a mixture or singly or both:

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Trace Elements Deficiency of trace minerals such as boron, iron, zinc, manganese, molybdenum, and copper can be limiting to crop growth and health. Seed dressings along with foliar sprays are often effective in correcting nutrient deficiencies, particularly when used in combination with other ameliorating techniques (e.g., soil sprays and nutrient-enriched granular fertilizers). Seed dressing with trace minerals is rarely adequate on its own. Where no nutrient deficiency exists, the application of trace element seed dressings and foliar sprays may be of little benefit. Trace element deficiencies can be localized to very small areas and are rarely general over wide regions or countries. Trace element deficiency is usually first recognized as a possibility by defects in plant growth. However, the visual symptoms of a particular deficiency can be confused with those produced by a range of other crop growth problems. Diagnosis of a trace element deficiency should be verified by plant and/or soil analysis where this is possible.

Herbicides Herbicides are used both as a component of zero-till or low-till agriculture and for weed control in the growing crop. Herbicides are best used when the weeds are young and actively growing. Both weed and crop growth stages are critical to the successful use of postemergence herbicides. Cereal species and varieties can vary widely in their herbicide tolerance. As is the case with the use of all bioactive chemicals, it is important to read labels carefully for details on crop tolerance and information on optimum and safe application conditions. Many broad-leaf weeds can be economically controlled using a strategic application of a postemergence herbicide. Some grassy weeds such as wild oats, annual ryegrass, and Phalaris can also be controlled. This can be achieved by carefully controlled pre- or postsowing spraying in some cereals but not all. There are other grassy weeds in cereals that cannot be controlled with herbicides. Some weed species, particularly grasses, germinate throughout the growing season, especially in grazed crops, when ground cover is reduced and soil temperatures rise. In this case, two herbicide applications at different growth stages could be warranted. For example, an early postemergence spray may not completely control weeds such as wild radish, and a late application can be justified to minimize seed set and seed harvested with the grain. In Australia, the following active compounds are registered as herbicidal preparations for various phases in the cereal

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Presowing and seedbed preparation. Chlorsulfuron, oryzalin, pendimethalin, sulfosulfuron, triallate, trifluralin, and triasulfuron. At sowing. Metribuzin. Salvage seedbed preparation. 2,4-D, dicamba, diquat, glyphosate, glyphosate trimesium, and paraquat. Early postemergent. 2,4-DB, bromoxynil, chlorsulfuron, clodinafop-propargyl, clopyralid, dicamba, diclofopmethyl, diuron, fenoxaprop-p-ethyl, flamprop-M-methyl, flumetsulam, MCPA, metolachlor, metsulfuron, metosulam, picloram, sulfosulfuron, terbutryn, thifensulfuron, and tralkoxydim. Late postemergent. 2,4-D amine, 2,4-DB, 2,4-D ester, dicamba, flamprop-M-methyl, flumetsulam, MCPA, picloram, and triasulfuron. Fallow and stubble weed management. 2,4-D, 2,4-D amine, 2,4-D ester, dicamba, diquat, fluroxypyr, glyphosate, glyphosate trimesium, paraquat, tribenuron-methyl, and triclopyr.

There is also a small group of herbicides that are only registered for use on only a limited number of cereal species. The label instructions for use of these materials are complex and specific and take into account a wide range of parameters, which include the occurrence of resistance, stages in the planting/ growing cycle of the cereal, cereal variety, target weed species and its stage in the growing cycle, crop stress, and local regulations.

Crop-Protection Chemicals Insect pests of growing cereal crops will vary widely on a geographic basis. The situation in Australia gives an indication of the role for crop-protection chemicals, but each region of the world will have its own suite of pests and its own range of allowable pesticides. In Australia, lepidopteran larvae, a few mite species, and aphids pose the most common and widespread invertebrate threat to growing cereal crops. There are also occasional regional and severe outbreaks of Australian plague locusts, and there are some areas where white Mediterranean snails can cause problems in harvesting and marketing grain. There are times when mouse plagues are so severe that action is needed to prevent economic consequences. Nematodes are also a problem in some areas. Some soil insects such as wireworms, false wireworms, wingless cockroaches, black field earwigs, and seed harvesting ants may cause economic levels of damage. Additional groups of pests in other parts of the world include Hemiptera, dipteran larvae, and thrips. The precise chemical to use for a particular control need is too complex to consider here. In Australia, the United Kingdom, Canada, the United States, and many other countries, there are a series of electronic resources that make the selection of appropriate chemicals relatively simple. These assist in the decision process and help match the permitted use of the chemical to the target pest, target crop, stage of crop growth,

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and withholding periods. The list that follows shows the suite of active compounds available in Australia for use on growing cereal crops for various broad taxonomic groups of pests. The complexities of registration mean that a chemical may not be appropriate for every species in the indicated group or indeed for every cereal crop. They are provided to give an idea of the range of compounds available.

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For Lepidoptera. Bacillus thuringiensis preparations, b-cyfluthrin, carbaryl, chlorpyrifos, cypermethrin, deltamethrin, diazinon, esfenvalerate, methomyl, permethrin, and trichlorfon For aphids. a-Cypermethrin, b-cyfluthrin, g-cyhalothrin, dimethoate, and esfenvalerate For locusts and grasshoppers. Carbaryl, chlorpyrifos, diazinon, dimethoate, fenitrothion, and maldison For mites. a-Cypermethrin, b-cyfluthrin, bifenthrin, chlorpyrifos, cypermethrin, dimethoate, l-cyhalothrin, methidathion, omethoate, phosmet, and sulfoxaflor For snails. Methiocarb and metaldehyde For mice. Zinc phosphide For nematodes at sowing. Terbufos

Foliar Fungicides The use of foliar fungicides is highly dependent on the suite of fungal pathogens present and the degree to which they present a risk to economic crop production. The nature of this risk will vary considerably between crops, from region to region, and in many cases from year to year. Region-based advice is usually required to determine the specific requirements for foliar fungicide application. This advice is available, depending on the country concerned, through a range of commercial, government, or university agencies. In recent times, many of these agencies have set up websites addressing this type of regional advice. A sample of these websites is included in the references at the end of this article. While there is a wide range of fungicidal preparations, the number of active chemicals involved is relatively small. For example, in Australia, the following are registered for application to growing cereal crops: flutriafol, propiconazole, tebuconazole, and triadimefon.

Stored-Product Protection Chemical treatment of stored grains can have a profound effect in maintaining cereal stocks by reducing (almost eliminating) losses caused by animal pests. In many climatic zones, longterm storage of grain without loss of biomass or quality would be almost impossible without some form of postharvest chemical treatment. Despite this, there is considerable pressure to reduce chemical treatments of grain in storage. This is largely based on the complexities of dealing with the residues that may be associated with the treatment. In stored products, compared to field crops, these residues are much closer to the final consumer in the consumption chain. Unlike horticultural products that also have a short path to the consumer, grains have many end uses including

direct consumption without preprocessing by animals (and to a small extent humans), milling into multiple physical fractions, a raw product for extraction of chemical fractions (starch and gluten), a source of carbohydrate for the fermentation industry, and the base product for a whole range of manufactured human and animal foods. This means that treated cereals have multiple entry points for residues into food for human consumption, either directly or via animal products such as meat and milk. This complicates the pathway to registration to such an extent that it may be difficult for a new active compound to be available for use on stored grains. For the purpose of convenience, chemical use in grain storage may be divided into several broad groups: fumigants, where the active agents are gasses or vapors; grain protectants, where the active agents are applied directly to the grain as liquids or powders; structural treatments, where they are applied within the structure but not directly to the grain; and low-risk use chemicals, where the toxic agent has a low mammalian toxicity and limited environmental risk.

Fumigation As of 2013, phosphine and methyl bromide are the only two fumigants in widespread use for fumigation of grain and grainstorage structures. Ethyl formate and sulfuryl fluoride are also available for use in some jurisdictions including Australia.

Phosphine Phosphine is applied in two physical forms: as a metallic phosphide (usually aluminum phosphide) that reacts with ambient moisture to release phosphine and as gaseous phosphine from pressurized cylinders. Phosphine is a relatively slow-acting fumigant and depending on concentration and target species takes from 5 to 25 days for complete disinfestation. Phosphine is the more commonly used of the two major fumigants and is used under a wide range of conditions, many of which are well below those associated with good fumigation practice. A consequence of this widespread use is that the continued use of phosphine is threatened by the worldwide occurrence of resistant insect populations and concerns about risks to human safety associated with its application.

Methyl Bromide Methyl bromide is a rapidly acting fumigant typically giving complete disinfestation in 12–48 h. This role is not sustainable, as it has been shown to be a potent stratospheric ozonedepleting substance. This means that its use has been severely curtailed, and under international treaty, it is only available for genuine quarantine and related preshipment use and documented critical use exemptions.

Grain Protectants Grain-protectant chemicals are designed to protect (as opposed to disinfest) grain. Early grain protectants included dichlorodiphenyltrichloroethane (DDT) and dieldrin in the 1940s and 1950s. Newer, less persistent chemicals replaced them in the

GRAIN HARVEST, STORAGE AND TRANSPORT | Chemicals for Grain Production and Protection 1960s. By the mid-1980s, a suite of 21 grain-protectant chemicals were either available or close to being commercialized. The number has fallen considerably since then, and by 2003, in Australia, only carbaryl, chlorpyrifos, cypermethrin, deltamethrin, dichlorvos, fenitrothion, malathion, methoprene, and pirimiphos-methyl remain generally available. The only new active grain protectant in the last 10 years is Spinosad, which is only registered for use by bulk handlers who meet a set of prescribed criteria. Not all of these actives are available for grains destined for some specific end uses. For example, carbaryl can only be used on feed grain; cypermethrin can only be used on seed grain; only low doses of methoprene and no chlorpyrifos-methyl can be used on malting barley; no deltamethrin can be used on export grain for some destinations; and spinosad is not acceptable in all export markets. Other chemicals, such as malathion, have considerable resistance problems, and dichlorvos is under regulatory review concerning worker safety. A further complication is that many of these materials are required to be part of a mixture to ensure a complete kill of all insect pest species. In some parts of the world, the list of registered materials is even smaller; for instance, in the United Kingdom, only chlorpyrifos, deltamethrin, and pirimiphosmethyl are listed for use on stored grain. It appears that grain-protectant chemicals only have a limited future in many parts of the world, and alternatives such as fumigation, controlled atmosphere, and physical methods will have to become much more common.

Controlled Atmospheres Controlled atmospheres can be thought of as a special case of fumigation or as low-risk chemical treatments. The gasses used are normal components of the atmosphere and biological systems. The gasses most commonly used are nitrogen to displace oxygen and carbon dioxide as a toxic agent in its own right. Costs and logistics limit the use of these treatments. Long exposure times (typically 15 days or longer), high level of sealing, and the large volumes of gas required to establish or maintain concentration of >40% for carbon dioxide and 99% for nitrogen (<1% oxygen) are the main constraints. However, both types of controlled atmospheres are used where these factors are not limiting or where special requirements exist.

Structural Treatments There is a range of chemicals that can be used to treat empty grain storages, grain handling, and harvesting equipment. This is a slightly larger range of chemicals than that available for direct application to grain. It is generally recognized that insect pests associated with residual grain and other plant residues/ dust are best dealt with by removing the residues rather than chemical treatment. Nevertheless, there are occasions where a somewhat persistent surface treatment or time release chemical space treatment may be useful as an adjunct to (but not a replacement for) good hygiene. Registration of chemicals for structural treatments vary greatly, but in Australia, the following are registered for use in structures where there was no chance of direct application to grain (however, some do have separate registration for direct

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application to grain): amorphous silica, carbaryl, chlorpyrifosmethyl, deltamethrin, dichlorvos, fenitrothion, phosphine, pirimiphos-methyl, maldison, methoprene, pyrethrins plus piperonyl butoxide, and sulfuryl fluoride.

Rodenticides Chemical control of rodents is an integral part of stored-grain management. In grain storages, unlike most industrial and domestic situations, it is almost impossible to control populations by isolating the rodents from their food. In grain storages, there is an ever-present, easily available food resource. Physical isolation of that resource from the outside environment is often impractical. There are also obvious risks associated with using a chemical designed to kill mammals in close proximity to a major human and domestic animal food. The range of behavioral and physiological adaptations available for the target organisms means that rodent control strategies have to be well planned to be successful. There are a fairly wide range of active materials that allow a flexible range of control to fit with the circumstances surrounding the need for rodent control. Factors influencing choice include the severity of infestation, the proximity of the stored grain, the previous history of treatment, the phase in the rodent control cycle (disinfestation or maintenance), the species present, the physiological resistance, the bait shyness, and the risks to nontarget species including humans. The following active compounds are available in Australia for use in and around grain stores: brodifacoum*, bromadiolone, cholecalciferol (vitamin D3), coumatetralyl*, flocoumafen*, strychnine*, and warfarin* (*registered for general use in and around agricultural buildings). In the United Kingdom, the list is similar but not identical: warfarin, diphacinone, difenacoum, bromadiolone, chlorophacinone, coumatetralyl, brodifacoum*, and flocoumafen* (*for indoor use only). A similar range of materials is permitted in most other countries.

Exercises for Revision Choose a cereal cropping area of interest to you.

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Investigate the crop nutrients (fertilizers and trace elements) required. What fungal diseases are of concern and what chemicals are available to control them? What weeds are of concern and what herbicides are available to control them? What field pests are likely to attack the growing crop and what pesticides are available? After the crop is harvested, how will the stored grain be protected from insects and rodents?


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Chemical crop nutrients (fertilizers and trace elements) have not always been available. What are other methods of maintaining plant nutrition?

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Biocidal chemicals are often highly toxic to humans. What general precautions should be taken during handling or use? Investigate the labeling of biocidal chemicals in your jurisdiction. Does the label have a legal status role and a regulatory role? Is it more than an identifier of the chemical? What kind of information should be shown on the label?

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Canola: Harvest, Transport, and Storage; Contaminants of Grain; Handling from Farm to Storage Terminal; Postharvest Operations for Quality Preservation of Stored Grain; Sorghum: Harvest, Storage, and Transport; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Wheat: Harvesting, Transport, and Storage.

Further Reading Chemical Safety CD-ROM International Occupational Safety and Health Centre CIS International Labour Office 4 Route des Morellos, CH-1211 Geneva 22. Switzerland ISBN 92-9016-005-5. Engelstad OP (ed.) (1985) Fertilizer Technology and Use Madison, WI: Soil Science Society of America. Lægreid M, Bøckman OC, and Kaarstad O (1999) Agriculture, Fertilizers, and the Environment. Farnham: CABI Publishing. Lazenby A and Matheson EM (eds.) (1987) Australian Field Crops. In: Wheat and Other Temperate Cereals, vol. 1. North Ryde: Angus and Roberson. Mullen CL, Dellow JJ, and Tonkin CJ (2000) Weed Control in Winter Crops 2000. NSW: NSW Agriculture. Owen EB (1956) The Storage of Seeds for Maintenance of Viability. Farnham Royal: Commonwealth Agricultural Bureaux. Rowland P and Bradford D (eds.) (1998) Proceedings of the Australian National Pesticide Risk Reduction Workshop Canberra, Australia: Bureau of Rural Sciences, Agriculture, Fisheries and Forestry. Snelson JT (1987) Grain Protectants. Canberra, Australia: Australian Centre for International Agricultural Research ACIAR Monograph No. 3.

The e-UK Pesticide Guide (2003) The e-UK Pesticide Guide 2003 Gives Details of Pesticides Actively Marketed in the UK and Is Designed to Ensure the Correct Pesticide for the Job in Hand. Wallingford: CABI Publishing. Tomlin C (ed.) (1995) The Pesticide Manual Farnham: British Crop Protection Council.

Relevant Websites http://www.apvma.gov.au – This website from the Australian Pesticides and Veterinary Medicines Authority contains information on all registered pesticides available for use in Australia. http://www.cdpr.ca.gov – A website maintained by the California Environmental Protection Authority that provides convenient access to the USEPA/OPP database. This database contains comprehensive information about pesticides registered in the United States of America. http://www.daff.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/ grain-storage/chemicals – Discusses the use of grain protectant chemicals. http://www.dpi.nsw.gov.au/agriculture/resources/soils/improvement/environment – Discussion on the risks of fertilizer contamination of waterways and ground water. http://www.dpi.qld.gov.au – Soil Insect Pests in Leucaena, Pasture and in Summer and Winter Field Crops. Discusses the identification, importance, and control of a wide range is soil inhabiting insect pests. http://edis.ifas.ufl.edu/ss527 – General discussion on the principles of fertilizer recommendations. http://www.fao.org/inpho/en – The FAO Inpho website deals with postharvest matters. Using the built in search engine to find "Pesticides," provides a variety of topics around the subject of grain protectants. https://www.gov.uk/fertiliser-recommendations-for-crops – Considers the principles of effective trace elements and fertilizers use in the UK from an environmental point of view. http://www.grdc.com.au – Seed dressings and trace element-deficient conditions under Australian conditions. http://www.hse.gov.uk – A UK website on the safe and efficacious use of rodenticides in agricultural enterprises. http://websvr.infopest.com.au – The complete reference of Australian registered insecticides and miticide chemicals and their uses. http://www.oecd.org/env/ehs/pesticides-biocides/ wwwpesticidesitesinoecdcountriesandotherorganisations.htm – This website list agencies concerned with pesticide regulation in many countries. https://portal.apvma.gov.au/pubcris – The Australian regulatory authority’s data base of approved biocidal products. https://secure.pesticides.gov.uk/pestreg/ProdSearch.asp – Provides information on registered pesticides in the United Kingdom.

Handling from Farm to Storage Terminal D Richard-Molard, Formerly at INRA, Nantes, France CW Wrigley, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Grain-growing has become big business, so its handling, transport, and storage must be efficient. Grain quality must be preserved during these operations, even though there may be many months and thousands of miles between grain harvesting and ultimate processing. Grain for special uses is often segregated at harvest; such parcels must be kept ‘identity preserved’ – separated from grain with different quality characteristics. Different types of storage are needed at the various stages from the (relatively small) on-farm storage through to the (very large) terminal elevator. Grain moisture, critical to maintaining quality, may be monitored by equilibrium relative humidity or by temperature. Insect control may involve the use of insecticides or of sealed storages fumigated or flushed with an inert atmosphere.

Learning Objectives

•

To understand the principles and practice of controlling the transport and storage of grain so that its quality and identity can be preserved in its (possibly long) journey from harvest to the storage terminal and beyond to the site of processing.

Introduction Traditionally, grain production has occurred close to the site of its utilization, so the logistics of grain transport and storage have been relatively simple. However, with the advent of large-scale production in major grain-producing regions of the world, it is a very large undertaking to move the grain from the site of production via stages of transitional storage to the final destinations. This complex process may involve the movement of the grain from one side of the world to the other. Conservation of grain quality throughout its transport and storage is of critical importance. The technologies for doing so have developed enormously from the traditional times of subsistence farming. Historical accounts from sixteenth-century Europe explain the importance, even then, of grain drying and ventilation, and the use of modified atmospheres for the good conservation of grains. However, these texts did not explain the scientific bases for these practices. Today, with the development of scientific knowledge on the grain ecosystem and progress in the fields of building materials, sensors, and measurement techniques, grain storage technologies have been mastered. New innovative technologies continue to be applied to the increasing demands of world trade in grains, particularly to the


requirements for technological and sanitary quality. These are summarized in this article, with the degree of sophistication ranging from simple on-farm storage of seed for next season to an enormous terminal elevator, capable of handling and storing vast quantities of grain under hygienic conditions (Figure 1).

Types of Storage Needed at All Stages of Handling The farm is the first stage of handling and storage. At its simplest level, on-farm storage may involve a pile of unprotected grain on the floor of a farm building. At the farm level, grain may be stored temporarily in small concrete or round steel bins of small capacity (25–100 tonnes), which receive the crop immediately after harvest and before transport to a better long-term storage facility or in order to wait for the best market situation. Grains may also be taken from the farm directly to a collecting center, a small storage installation with several small bins providing an average capacity of 1000 tonnes. This does not generally have machinery for grain cleaning or drying, since the grain is usually transferred soon after to an elevator (Figure 1). Country elevators (5000–50 000 tonnes), so-called because they are filled with grain elevated into them by rolling belts with buckets, receive grain from the individual producer or from small collecting centers. Their capacity is adapted to the seasonal production of the area, and their main role is to keep crops in good condition before and during storage, and to reload it into trucks or rail cars for transportation to terminal silos, export elevators, or industrial users. There is no general rule for determining the best dimensions of a farm bin or a country elevator. Usually, the cost of storage increases sharply as the size of the silo decreases, so there is a tendency to build large structures. However, the grains are managed in multiple silos, where grains of different grades or water contents can be separated easily. The terminal elevators are generally located close to trade centers and/or transportation terminals, such as harbors (Figure 2). Terminal elevators commonly offer storage capacities of 5000–500 000 tonnes in the United States or northern Europe. Equipment for grain handling and control is often basic at the farm level, with only very simple devices for grain elevation and ventilation. By contrast, country and terminal elevators have handling capacities adapted to their transportation facilities and usually have sufficient capacity for peak load handling during the short period just following harvest. Today, most are fully equipped with remote control and automation, so that grain can be automatically transferred from one silo to another

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GRAIN HARVEST, STORAGE AND TRANSPORT | Handling from Farm to Storage Terminal

Water content (wet basis)

20 16 15

Maize Wheat

Bacteria

10 Yeasts 5 Molds

Figure 1 Grain collection, from field to terminal elevator; a long trip for the grain. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn., 2003, p. 1019, Elsevier Ltd.

0 0

25

50

75

ERH Figure 3 Sorption isotherms for wheat and maize at 20 C and zones of activity for the main causes of grain degradation during storage (the wider the zone representing a cause of spoilage, the more intense and rapid the spoilage). Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn., 2003, p. 1020, Elsevier Ltd.

Figure 2 Harbor elevator in Rouen, France, with a total storage capacity of 300 000 tonnes. This is able to load grains into vessels at a rate of 5000 tonnes h 1. Photo courtesy of J. Pfeiffer.

or to ships and railway cars. Weighing, cleaning, sampling, and even several grain sample tests are now electronically controlled. When possible, gravity discharge from grain bins is ideal, but the cost of the corresponding structures and equipment is high. Consequently, flat storage of cereals is also commonly carried out in many situations, both at the farm level and in terminal elevators, to provide additional storage capacities when necessary. Such flat-bottomed silos are emptied through a central outlet, where a rotating screw-conveyor draws the grain away beneath the floor. Many other sophisticated devices have been developed for moving the grain using air blown through metallic networks of ducts below the bins, or with suction blowers as back-up devices.

Maintaining Grain Quality During Storage The freshly harvested grains must be tested on receival to determine the appropriate treatment for safe storage, such as cleaning, dust removal to avoid very dangerous dust explosions, drying, cooling, chemical treatments against insects, etc. Grain moisture is the major attribute to be controlled during storage. Even with mature dry grain harvested at 12–13%

moisture content, serious problems will be encountered within a few months if moisture cannot be properly managed to prevent the heat and moisture transfer that can occur in bulk during storage and transportation. It is, therefore, important to store grains with a sufficiently low initial moisture content to prevent mold development and biochemical changes, and to maintain this low temperature as constant as possible everywhere in the silo throughout the storage period. This can be achieved by artificially drying grains with excessive humidity at harvest, like maize in Europe, and by periodic forced ventilation during storage to remove excess water where condensation has occurred.

Monitoring Moisture During Storage It is difficult to confidently determine the correct moisture level for a specific grain type in a given situation. Very general and theoretical rules can be given, but one should bear in mind that a large mass of cereal grain is never homogeneous in temperature, moisture, apparent density, thermal conductivity, etc., and so continuous monitoring with modern techniques, such as silothermometry, and periodical sample examination is highly recommended in every situation. The thermodynamic activity of water, which represents the availability of water in the grain, is the most important physical parameter governing grain stability during storage, determining both biochemical changes and microbial growth. The availability can be estimated (and measured) by the equilibrium relative humidity (ERH) of the intergranular air in equilibrium with the grain. A nonlinear relation relates ERH to moisture content, as shown in Figure 3 for wheat and maize. This curve is named a ‘sorption isotherm’ and depends on both the average temperature and the biochemical composition of the grain. It differs from one cereal to another, but its relationship to the level of deterioration by different causes, such as

GRAIN HARVEST, STORAGE AND TRANSPORT | Handling from Farm to Storage Terminal microorganisms or enzymes, remains constant to a first approximation. Wheat stored at 16% moisture content is in equilibrium with an ERH of 80% and will undergo the same kind of degradation at the same rate as maize with 15% moisture content, which also has an ERH of 80% at the same temperature. As the temperature increases, the sorption isotherm is shifted to the left, that is, at the same water content, there is a higher ERH, and spoilage is faster. Silothermometry is a sophisticated technique, utilizing thermocouples placed in the silo able to detect slight variations in grain temperature, which indicate the beginning of deterioration through an aerobic process, resulting from a localized increase in humidity. Modern sensors can detect temperature changes of less than 0.5 C. In most situations, this gives sufficient sensitivity and overcomes the problem of the very low thermal conductivity of cereal grains, which allows temperature differences to be transmitted only over short distances in the bulk. With this method it is also possible to determine the best moment for drying and ensure the completion of grain cooling by nocturnal ventilation.

Drying Methods and Alternatives The use of adequately dried grains for storage in silos is a mandatory condition (Figure 3). Many types of driers, such as full-bin driers, layer driers, continuous-flow driers, etc., are presently used on farms or in country elevators, but all utilize the same basic principle: heated dry air is blown through the grain to remove excess water. Figure 4 represents a farm bin equipped with a low-heat drier capable of drying grains with moisture contents of less than 20% (wet basis). When large quantities of moist grain are to be dried rapidly, high-temperature drying is necessary. This gives a higher extractive capacity but can also cause thermal degradation of the grain, if used improperly, as often happens with maize, which is sometimes harvested with water content as high as 35% (wet basis) in

Air exhaust

Wet grain Drying zone Perforated floor Fan

Dry grain

Unloading auger Figure 4 Farm bin for low-temperature drying. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd edn., 2003, p. 1021, Elsevier Ltd.

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Europe. If the air for drying is too hot, the functional proteins are denatured, and the value of the crop is decreased. However, high drying temperatures destroy all forms of insects in the bulk. When possible, a combination of different drying and cooling practices often gives the best technical and economic results. The essential principle is to decrease the moisture content rapidly to a level, thus decreasing the rate of mold development, that is, to 18% moisture in a first step, then to decrease the residual humidity to 15–16% by forced aeration when the ambient air is cool and dry enough to be efficient.

Natural Drying Methods Alternative natural methods for grain drying have often been used, and at least two must be mentioned. The first, used mostly for maize, uses gentle drying by the wind of cobs stored outside in cribs or other forms of mesh silos. This is satisfactory, provided that the temperature remains sufficiently low to inhibit the growth of such toxinogenic fungi as Fusarium species. The second type of natural drying method uses solar driers. These have been tested in efforts to save energy, but their use can be recommended only in regions where sufficient energy is provided by the sun to achieve drying in a time short enough to avoid spoilage by microorganisms. Unless drying to 80–82% ERH can be achieved in less than 7–10 days, the grain will certainly be damaged.

Modified-Atmosphere Storage When cereals are not intended for uses requiring particular properties, such as a high germination ability for malt production or functional properties of proteins for breadmaking, it is possible to store them with a higher water content than usual, provided the oxygen is removed from the system. Underground storage and storage in anoxic atmospheres in hermetically sealed silos, or silos continuously flushed with nitrogen, for example, are quite possible. It was recently shown that the nutritional value of wheat for animal feeding could be successfully maintained over several months by storing it, after grinding, in airtight conditions at 21% water content and 15– 20 C. Storage of wet (35% water content or more) maize for pig feed in hermetic silos is now popular in several countries. Because of the important demand for intergranular oxygen at such a high humidity, especially through respiration of yeasts and lactic acid bacteria, the concentration of available oxygen remains extremely low in the silo. The growth of molds is inhibited and, at least until the silos are nearly empty, that is to say when free oxygen again appears and concentrations of carbon dioxide are decreasing, no mycotoxins can be produced. With such hermetic silos, it is not necessary to grind the humid grain in order to produce silage, and the commodity can be handled more easily than with traditional practices.

Control of Insects Storage of dry or wet grains under modified atmospheres is an excellent way to kill insects, and modern techniques for storage of dry wheat under high concentrations of carbon dioxide have

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yielded very good results in Australia in recent years. Most often, if all living insects are to be killed, chemicals need to be used when infestations are detected in a silo or a ship. Insecticides can be divided into two main classes: contact insecticides, which kill insects and prevent reinfestation owing to their remanent effect, and fumigants, which destroy insects without leaving any significant residues. Organochlorine insecticides, which belong to the first class, were extensively used in the past but are now forbidden because the toxicity of their residues is very high for humans. Pyrethroids (like deltamethrin, permethrin, bifenthrin) and organophospates (like malathion, dichlorvos, or methyl pirimifos) are also contact insecticides, used at concentrations of 4–8 g of active substance per tonne of grain. They are very fast-acting and highly toxic by contact and ingestion, but their residues necessitate careful consideration of the number and timing of treatments. Their relative inefficiency against the hidden forms of insect (eggs, larvae) that live within the kernels should also be mentioned. The only current fumigant is hydrogen phosphide, which is used to rapidly kill all live insect stages, including adults. It is used in airtight structures equipped with systems that allow the gas to be introduced and removed safely. Apart from modified-atmosphere storage under nitrogen or carbon dioxide, only persistent insecticides can provide good long-term protection for grain. It is then of primary importance to ensure that there is no residue in by-products like flour and brans used for human and animal food. At the present time, there is a general tendency to decrease the concentrations of toxic substances used against insect infestations. A possible approach would be to combine the use of carbon dioxide with an active substance, such as methyl bromide or hydrogen phosphide, which would permit a considerable reduction in the dose of fumigant used because of synergism with carbon dioxide, which increases the penetration of the active substance in the respiring stages.

small bulks of 50–100 tonnes of well-certified grains are to be prepared.


• • • • • • • •

• •


•

The Future All over the world, safe storage of cereal grains is a vital but expensive activity. Too many cereal grains are still used in the food industry despite the poor quality resulting from inappropriate storage conditions. Current scientific and technical knowledge in this domain is sufficient to answer the main questions about handling and storage of grain, but new trends are appearing: consumer demand for safe products, that is, free of chemical residues, is growing fast. This probably means that the use of contact insecticides and even fumigants should be replaced by more acceptable techniques like physical techniques in the coming years. Another trend seems to be a clear demand for identified grains, nongenetically modified grains, and grains from a precise geographic origin or a well-specified technological quality, for example. Such an evolution would certainly introduce very important changes in the way in which the grains are harvested, collected, stored, and distributed. Loading speeds as high as 5000 tonnes h 1 are often reached today in harbor elevators, but this is not the most convenient technology if

Contrast the size, time frame, and type of grain storage facilities needed on farm (possibly for subsistence farming) and the other extreme of storage needed at a large processing mill or export terminal. Why does the export terminal need to be large to be efficient? How does the type of grain or the type of transport affect the nature of the storage facility needed? In priority order, what grain attributes (and therefore what tests) are critical to monitor during handling, transport, and storage? What health and safety considerations are involved in the processes of grain handling and storage? What are the risks to grain quality of drying (or of not drying)? Suggest monitoring approaches. For your particular country or region, find out what insecticides and fumigants are permitted and not allowed for specific grain types and storage situations. Carbon dioxide is an effective gas for insect control provided its concentration is maintained for a period of a week or more. Consider the range of sources of CO2 that could be used for this purpose (dry ice, exhaust from a petrol engine, gas cylinders). How do grain species differ in their sensitivities to the various types of grain-drying approaches? How can the presence of insects best be detected?

• •

•

A grain buyer submits a complaint about the presence of insects in a grain shipment. How can you determine how and where the infestation arose? What systems can be put in place to greatly decrease the risk of a reoccurrence of this problem? Investigate the tolerances for insects, dust, and other contaminants in grain consignments for your particular country or region. Do you consider carbon dioxide to be a fumigant? Research some materials that are considered to be ‘true’ fumigants and compare their action with that of carbon dioxide. Also compare the advantages (and disadvantages) of carbon dioxide versus these alternatives. Extend your researches and comparisons to pesticides with residual effects.

See also: Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Canola: Harvest, Transport, and Storage; Chemicals for Grain Production and Protection; Postharvest Operations for Quality Preservation of Stored Grain; Stored Grain: Invertebrate Pests; Stored-Grain Pest Management; Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Wheat: Grading and Segregation.


Further Reading Christensen CM (ed.) (1982) Storage of Cereal Grains and Their Products, 3rd edn. St. Paul, MN: American Association of Cereal Chemists. Navarro S and Donahaye E (eds.) (1993) Controlled atmosphere and fumigation in grain storages. In: Proceedings of the International CAF Conference, Winnipeg, Canada, June 1992. Jerusalem: Caapit Press.

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Reed CR (2006) Managing Stored Grain to Preserve Quality and Value. St. Paul, MN: AACC International. Richard-Molard D (1990) Conservation of humid grains in controlled atmosphere storage. In: Calderon M and BarkaiGolan R (eds.) Food Preservation by Controlled Atmosphere, pp. 57–82. Boca Raton, FL: CRC Press. Sauer DB (ed.) (1992) Storage of Cereal Grains and Their Products, 4th edn. St. Paul, MN: American Association of Cereal Chemists.

Stored Grain: Invertebrate Pests PC Annis, CSIRO Entomology, Canberra, ACT, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

The Stored Grain Ecosystem

• • • • • • •

The stored grain ecosystem is characterized by copious food, limited water, and a stable thermal and humid environment. It can often remain predator-free and can remain undisturbed for significant periods of time. These conditions can be ideal for the development of large infestations of a number of specialist invertebrate pests. The vast majority of these pests are either insects, Coleoptera (beetles), Lepidoptera (moths), and Psocoptera (booklice), or Acarina (mites). The ecosystem is surrounded by a more or less permeable boundary. The nature of the boundary is related to the storage type varying from highly susceptible to immigration in uncovered stacks of grain to impenetrable for well-sealed containers such as gastight storages.

The stored grain ecosystem. Types of invertebrates. Biomass loss. Quality loss. Invertebrate control. Grain-protectant chemicals. Fumigation.

Learning Objectives

• • • • • •

To have a basic understanding of the stored grain ecosystem and its characteristics. To have an overview of the type of invertebrate pests that are likely to be found. To have an overview of the developmental biology of the pest species. To understand the importance of developmental period in understanding the buildup of infestation. To appreciate the importance of stock management and hygiene in minimizing the problems caused by infestation. To have an overview of the chemical methods of invertebrate pest control.

Introduction A storage filled with grain represents a large and delimited resource of biologically available energy. Under many combinations of conditions, this resource will become an ideal environment for a range of invertebrate pests. This means that some positive action will usually be needed to prevent loss in quality and quantity. Much of the basic information on these pests was obtained prior to the early 1980s and is consequently not accessible electronically. Two series of international conferences – ‘The International Working Conference on Stored Products Protection’ and ‘The Conference on Controlled Atmosphere and Fumigation in Stored Products’ – are useful to keep track of modern thought on the entomological aspects of storedproduct science. There remain many gaps in the scientific study of individual invertebrate grain-storage pest species. Furthermore, the types of studies needed to fill in these gaps are usually time consuming and require a considerable number of person hours to complete. This means that they are unlikely to take place in contemporary circumstances where both time and money are scarce resources. This article aims to give a broad overview of what is known and what can be implied from this knowledge and to direct the reader to some of the less-referenced but important sources of information.

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Grain Invertebrates Detection and identification of stored-product pests is not always easy. Many of the insects that infest stored products are small, less than 5 mm in length and only 1 mm wide. Some are much smaller, particularly Psocoptera and mites, which may be less than 2 mm long and easily mistaken for dust, were it not for the fact that they move. The patterns of development of stored-product pests also complicate detection. Some species go through their early developmental stages (eggs, larvae, and pupae) inside the grain kernel with little or no external evidence of their existence. Others complete their life cycles between or on the surface layers of the grain. Others periodically move in and out of the grain and its storage structures. More details on the identification and biology of individual species can be found in the specialist literature referenced at the end of this article. The most widely used method of detection of insects within a bulk of grain is sampling and sieving. Samples are taken at random (but sometimes targeted) and then sieved through an appropriate mesh, which allows the pest and dust to pass through, while the grain is retained. Samples are either taken from moving grain or probed from static grain. This is an ideal method for sampling free-living adults but of no use for immature stages developing in the grain, or eggs attached to the grain. Sieving can be automated and this is often done at large grain terminals. However, the assessment of screenings, counting, and identification of any insects are always manual operations. Systematic probing and sieving of grain bulks are very labor-intensive operations, especially if a high level of detection is required. Trapping is also used as a means of detection, and it can detect very low infestation levels for some species. The traps can vary from a simple pitfall trap, to refuge traps, to pheromone-baited traps. The major problem of trapping is to understand the significance of the number of species trapped


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GRAIN HARVEST, STORAGE AND TRANSPORT | Stored Grain: Invertebrate Pests in terms of the number actually present in the grain and surrounding areas. Not all species are equally trapped so the significance of low number in a trap may range from very low for an easily trapped species to very high for a hard-to-trap species.

Why Are Some Invertebrate Pests Important? The magnitude of almost all the problems created by invertebrate pests in grain is more or less proportional to the number of insects present. The only notable exceptions to this are when detection of a single insect of quarantine interest may have the same impact as detecting many hundreds. A similar circumstance applies to exporters who ship grain to a standard that specifies no live insects detected. The number of invertebrates present in any parcel of stored grain, at a given time, depends firstly on the number in the initial population. This population may come in with the grain, it may have been a residual population in the empty storage, or it may have entered the storage after the grain had been in storage for some time. The next determinant of population size is the rate of increase in the population. This is determined by the oftencomplex demographic attributes of the species. The rate of increase can be approximated to the time it takes to develop from egg to reproductive adult and the number of surviving progeny from one set of parents. Both these demographic parameters are strongly influenced by the grain type, density of insects, moisture, and temperature and can vary widely between species. Even more simply, it can be expressed as the multiplication factor per unit time under optimal conditions of temperature, moisture, and culture medium (Table 1).

The Consequences of Invertebrate Infestation Biomass Consumption Loss of biomass is the first and most obvious consequence of invertebrate infestation. An uncontrolled coleopteran infestation in favorable environmental conditions can change a pile of grain to a pile of dust in about four generations (where development time takes 25–50 days from egg to adult). This is a worst-case scenario and assumes no action is taken to reduce or remove the infestation. In reality, the biomass-loss rates due to invertebrates are usually much less even in primitive storage conditions. However, figures up to 40% are sometimes reported and losses of 10–20% are common. In

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well-managed grain handling systems, the losses are so small that they are hardly assessable (e.g., much less than 0.1% in the Australian bulk-handling system). This range in the amounts of biomass consumption is almost entirely due to the number of insects and their multiplication with generations (modified by control measures, species, temperature, and relative humidity of the intergranular air or the associated grain-moisture content). There is a reasonable body of literature on the energetics of a range of stored-product coleopteran. A single beetle requires a range of 40–250 J (depending on species, temperature, and relative humidity) to develop from egg to mature adult, while a single grain of wheat (about 0.035 g) is able to provide 530 J on average. Using simple arithmetic, it is easy to estimate loss rates under a worst-case scenario when each female beetle produces 100–300 viable progeny in a lifetime under optimal conditions. In the case of stored product, Lepidoptera Ephestia cautella and Plodia interpunctella consume higher amounts of energy, about 600 J per individual (34 mg), during their lifetime. There is little energetic or demographic data for the Psocoptera of stored grain, but it is likely that their rate of respiration on a body-weight basis is at the high end of the beetle range. Their mass is about 1% of that of typical stored grain beetles, which would imply a lifetime energy requirement of about 2 J per insect or 0.1 mg biomass consumption per insect. There have been two energy studies on mites infesting stored grains. Tyrophagus putrescentiae and Acarus siro have a lifetime energy consumption of 2.5 and 2.8 J, respectively. This translates to a biomass consumption of about 0.1 mg per individual. Mites in general are capable of explosive population growth in favorable conditions with an increase of 2500 times in 1 month, as quoted in several references. Grain pests are sometimes classified as primary and secondary pests. In general, primary pests are ones that can be found on their own. Secondary pests tend to appear after the primary pest. It is often claimed that only ‘primary’ grain pests are important in grain consumption, but the energy requirements of ‘secondary’ pests are little different to those of primary pests and in a large infestation the only source for most of that energy will be the stored grain.

Quality Damage In addition to biomass loss, invertebrate pests feeding on grain may cause a wide range of quality damage. This damage may be generalized or specific depending on the size of the

Table 1 Rate of population increase, development time, and longevity of a range of common pests of stored grain. All data are given at optimal conditions of temperature, moisture, and culture medium Common name of group (scientific name of group) Beetles (Coleoptera)

Booklice (Psocoptera) Moth (Lepidoptera)

Species

Multiplier of increase in 4 weeks

Development time (days)

Average adult longevity (weeks)

Sitophilus oryzae Rhyzopertha dominica Tribolium confusum Cryptolestes ferrugineus Liposcelis bostrychophilus Ephestia cautella

24 29 60 60 22 50

25 25 20 21 21 25

5 4 11 7 2 1

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GRAIN HARVEST, STORAGE AND TRANSPORT | Stored Grain: Invertebrate Pests

infestation, the species involved, and the grain being attacked. Generalized damage results from insect-induced heating and heating induced moisture migration, unselective consumption of biomass, and webbing of grains. Specific damage occurs when the pest consumes critical components of the grain. Reduction in germination of seeds is a common consequence of germ-consuming insects or infestations that cause significant heating. Insects consuming the endosperm will cause considerable reduction in seedling vigor together with some reduction of germination. It follows that there is a commensurate loss of nutrients associated with consumption of specific parts of the grain rich in those nutrients. Generally, the results of infestation at a chemical level have been likened to an apparent acceleration of those types of effects seen in the natural aging of grain. This may be due to any or all of the following: heating, consumption of specific energy-rich components, removal of protection against oxidative changes, odor, and discoloration.

Contamination The presence of a few insects, alive or dead, is rarely a direct problem to users or consumers of grain. Large infestations may create problems with feed rejection where grain is used as stock feed. Large infestations of Tribolium species and of the mite Acarus siro may give rise to objectionable odors related to specific metabolic by-products of these species. Downstream food-processing industries are often required to produce a product containing less than a defined number of insect fragments per mass of product. For example, the US Food and Drug Administration sets a defect standard of an average of 75 or more insect fragments per 50 g of wheat flour. Meeting this kind of requirement is greatly assisted by the low number of insects and insect fragments in the raw materials. The real influence of contamination of grain by insects and insect fragments is through their role as quality criteria in the trading of grain. For example, a phytosanitary certificate issued on export of grain may require the absence of any detectable live insects. In parts of the world, different standards may apply, but there is usually an insect-related quality criterion associated with traded grain.

Indicators of Poor Storage The presence of insects in grain is a useful indicator of how well the grain has been managed during storage and the extent to which deterioration may have occurred. Large infestations rarely occur in well-managed storages and are often associated with poor storage hygiene, the presence of birds and rodents in and around the grain, and hotter and wetter grain than is optimal for storage.

Allergy Allergic reaction to living insects and mites is a common phenomenon, although only a few stored grain insects feature as commonly reported causes of allergic reactions, while an allergic response to insect fragments has occasionally occurred in humans consuming or handling infested grain. Among the

coleopterans, Sitophilus granarius and Rhyzopertha dominica have been known to induce asthma and similar respiratory problems, psocids of the Liposcelis group have caused similar problems, and the hairs of dermestids cause skin irritation. Handling Lepidoptera, in general, has been known to cause dermatitis and allergies. Skin irritation and allergy to a wide range of mite species is very well known.

Collateral Problems of Control An important consequence of infestation is the need to control the infestation. This is frequently achieved by fumigation (the use of a toxic gas) or by using a contact insecticide (a grain protectant). The essential difference between these two is that the active phase of fumigants is a gas or vapor, while that of grain protectants is a solid or liquid. The major operational difference between the two types of chemical is when and how they are used. Fumigants can be applied at any time during storage as long as the gas concentration can be retained or made up. Fumigants can be purged from the storage rapidly and the grain can become available for use in days. Fumigants tend to leave low levels of residues and alteration products. They do not offer any protection to the grain from invading insects once the gas is removed. Grain protectants can only be applied satisfactorily to moving grain and are most commonly applied as grain enters storage or is moved between storages. Chemicals are effective as protectants because they stay in an active form for significant periods, and therefore, residues are an important consideration. Besides national regulation concerning what chemicals (and what rates of application) may be used on grain, there are international agreements set down by the Codex Alimentarius Commission. Despite the national and international regulations and agreements, individual customers may have their own standards for treatments and residues depending on the end use of particular parcels of grain. The organic grain market requires grain that has not been treated with any fumigants and grain-protectant chemicals.

Insects and Mites as Vectors There are many reports of invertebrate pests and mites in particular, acting as vectors for fungal spores. If the environmental conditions are then conducive (water activity greater than 0.7), active fungal infection can result. Some storedproduct pests can be vectors for parasites and food-poisoning organisms, but only under conditions of poor hygiene.

Insect and Mite Control Effective and economic control of insect and mite infestation requires a combination of several different types of action all aimed at ensuring that the grain remains effectively free of insects during the storage period. These types of actions are hygiene, inspection, disinfestation, and protection.


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Hygiene

Table 2

Hygiene is fundamental to good pest control, and a properly implemented hygiene operation goes a long way towards complete pest control. The aim of hygiene is to ensure that the starting population for a potential infestation is small and that the risk of infestation from outside the stored material is very much reduced. Hygiene starts with structure and plant design and, to a large extent, good hygiene can only be as good as the construction of the storage and handling structure will allow. Details of designing for hygiene are well beyond the scope of this article and are poorly documented in the literature. However, the general principles are simple. They include making sure that there are no places where grain (or grain dust) can accumulate and remain undetected and undisturbed for long periods. For insect and mite control, dust, spills, and accumulations that can be seen and easily removed are not a problem. It is residues that remain hidden from easy inspection and removal that are the cause of many infestations. A second feature of a well-designed storage is a physical barrier to infestation from outside the storage. Such a barrier should also restrict the access of birds and rodents whose presence is a problem but may also help establish sites of infestation in nest materials. A barrier that provides complete sealing will also improve the efficacy of fumigation. Where a storage has not been designed with some consideration to hygiene, it may be possible to modify problemcausing features. This is not without its own problems since it can produce even more inaccessible spaces that entrap residual grain and dust.

On the farm Before harvest • Check and clean out any grain residues from silos, harvesters, augers, field bins, and other grain handling equipment • Ensure any carried over grain is disposed of or disinfested • Clean up around any storage areas, remove spilt grain, surplus equipment, and clear vegetation for at least 1 m At harvest • Where possible, set aside first parcel of grain to pass through equipment each season (this should have flushed out any residual infested grain) After harvest • Inspect grain for insects after 3 month storage and subsequently each month • If insects are found, treat using an approved method In a centralized bulk storage facility At start of season • Check and clean out any grain residues from the grain path and surroundings, paying particular attention to hard to access areas • Check bird proofing • Carry out rodent control in and around premises • Ensure any carried over grain is free from infestation • Clear vegetation close to storage structures At intake • Inspect incoming grain for insects • Reject or segregate infested grain • Where applicable treat all grain with an approved grain protectant on intake After intake • Treat known infested grain as soon as possible (fumigation ideal if facilities are suitable) • Inspect grain for insects after 3 months and then monthly • If insects are found treat using an approved method (fumigation ideal if facilities are suitable) • Maintain rodent control In a centralized bag storage facility At start of season • Thorough clean out of warehouse • Fumigate all existing stock • Check of all bird proofing and rodent control facilities At Intake • Inspect incoming grain for insects • Fumigate bag stacks with identified infestation as soon as possible After intake • Clean up spilt grain and dispose it or fumigate it as soon as possible • Inspect stacks for superficial sign of infestation monthly • Take probe samples from periphery of stack at least every 3 months • When insects are found, fumigate infested stack, and if it is logistically possible, fumigate all other stacks in a warehouse at same time

Work Procedures and Skill The day-to-day practice of hygiene is a routine and dull job that can be labor-intensive. It is, therefore, essential that hygiene tasks are carried out thoroughly; otherwise, the resources invested are wasted. A hygiene checklist is an essential tool for good hygiene management. This type of list (Table 2) ensures that all the important places are drawn to the operators’ attention. Once a storage and its surrounds have been cleared of all detectable grain and grain residues, there may be some advantage to treating these areas with a surface structural treatment of a contact insecticide or an inert dust.

Inspection There are three generic times when inspections are carried out: on intake, during storage, and at outturn. Outturn is often the most important as far as the next user of the grain is concerned, but in pest control terms, the least useful. Disinfestation of grain at outturn is impossible, and the options for the rapid disinfestation (<24 h) of detained grain are almost nonexistent (see methyl bromide fumigation). In a well-managed grain handling and storage facility, the infestation status of grain at intake largely determines the starting population of insects. In cases where grain with infestation is taken into storage, it is important that it is disinfested before mixing with uninfested grain. A thorough cleanup of the

Grain hygiene for insect control

grain path should be carried out before the path is used for uninfested grain. Inspection during storage is strategically the most important inspection. There should be an insect-free period of about three generations, that is, about 3 months at or above 25 C for the majority of species. In situations where hygiene has been adequately carried out, intake inspection was effective, and any infested grain disinfested. After 3 months, any minute residual initial infestation (or invasion) is likely to have reached

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detectable levels. After 3 months post intake, or following disinfestation, a monthly inspection is recommended.

Chemical Control Fumigation Fumigation for control of infestation can be employed in two ways: prophylactic, where a treatment is carried out routinely, usually shortly after intake, even if no insects or mites are found on inspection; or tactically when it is carried out at the first signs of infestation. Good fumigation used with good hygiene and adequate sealing should not need repeating as the recommended application procedures are designed to give a total kill of all insects. Where a reinfestation appears after fumigation, it is most probable that either the fumigation was not carried out adequately or reinfestation pressures are high. Fumigation only works properly if adequate concentration can be maintained for an adequate exposure period. These conditions can only be achieved in a well-sealed system for a single application of fumigant or by ‘continuous fumigant addition’ in an adequately sealed system. Currently, phosphine and methyl bromide are the only grain fumigants in widespread use for fumigation of grain. However, sulfuryl fluoride and ethyl formate have become available in some jurisdictions for use as grain fumigants in the last 10 years.

Phosphine Phosphine is applied in two physical forms, as a metallic phosphide (usually aluminum phosphide) or as gaseous phosphine from cylinders. Phosphine requires a significant time to be efficacious and is not able to kill all pest species at every stage below a nominal threshold concentration, no matter what the exposure period (within commercial reality). These approximate conditions are shown in Table 3 for both phosphine-resistant and nonresistant pests. The main issues around the continued use of phosphine are the worldwide occurrence of resistant populations and concerns about its safe use.

Metal Phosphide The most common type of phosphine treatment is where a metal phosphine-based formulation is applied to the grain in a variety of physical forms: pellets, tablets, plates, bags, blankets, and chains. All these forms are designed to allow a controlled release of phosphine as the phosphide reacts with water contained in the air surrounding the commodity or on the surface of the commodity. The rate of release depends on a number of factors: the metallic component of the phosphide (magnesium is faster than aluminum), the surface area to volume ratio of Table 3

the physical form. the degree of compression (powders are faster than compressed formulations), and other components mixed with the phosphide, temperature, and water vapor availability. The rate of release and the level of sealing of the fumigation enclosure are the principal determinants of the concentration profile over a period of time. The magnitude of the concentrations (but not the shape of the profile) is modified by the presence of commodity and the amount of phosphide added.

Gaseous Phosphine A more recent application technique for phosphine involves the use of gaseous phosphine. This requires careful control as phosphine can be explosive in air (1.8%, 18 000 ppm) and the gas is usually supplied as phosphine mixed with a nonreactive gas, such as carbon dioxide or nitrogen, to assist in eliminating the explosion risks. The gas is then further diluted with air to give the required concentration. This is done on a continuous basis for flow-through fumigation or as a single application for a sealed fumigation.

Methyl Bromide Methyl bromide has been the mainstay of rapid disinfestation for many years. Unfortunately, it has been shown to be a potent stratospheric ozone-depleting substance. This means that its use has been severely curtailed, and under international treaty, it is only available for genuine critical use, essentially quarantine and related preshipment use.

Fumigants Under Development Attempts are being made to find replacements for methyl bromide and alternatives to phosphine. Carbonyl sulfide, ethyl formate, and sulfuryl fluoride all show some promise at the research level. Ethyl formate and sulfuryl fluoride have recently become available for commercial use on grain in Australia and a few other places. There are commercial and regulatory issues still to be resolved in the use of carbonyl sulfide, and it may be several years before it is registered (if at all).

Controlled Atmospheres Controlled atmospheres can be thought of as a special case of fumigation, where the gases used are normal components of the atmosphere and biological systems. The gases most commonly used are nitrogen to displace oxygen and carbon dioxide. There are only a few places around the world where controlled atmospheres are used routinely. The main problems

Exposure period in days required at various threshold concentrations to ensure disinfestation with phosphine

Concentration Exposure time (days)

PPM (g m 3) Susceptible Resistant

10 000 (14) 1.5 1.5

2500 (3.5) 2 2

250 (0.35) 8 10

100 (0.14) 10 >30

25 (0.035) 25 >30

20 (0.027) 30 >30

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored Grain: Invertebrate Pests with controlled atmospheres are long exposure times (typically 15 days or longer), the need for a high level of sealing, and the large volumes of gas required to establish or maintain concentration of >40% for carbon dioxide and 99% for nitrogen (<1% oxygen). Despite these limitations, both types of controlled atmospheres are used where these constraints are not limiting or where special requirements exist. For example, nitrogen has been used in Australia at Newcastle, New South Wales, where a large grain-storage capacity allows grain to be held for treatment. There is a large industrial source of liquid nitrogen close by, and the storage was constructed to a suitable level of gastightness. Carbon dioxide is used to disinfest organic grains exported in shipping containers from Australia to many parts of the world.

Grain-Protectant Chemicals Grain protectants (i.e., insecticides approved for direct application on grain) can be a very effective way of controlling invertebrate infestation. In the past, they have been widely used and have resulted in spectacular reductions in insect infestation. For example, the introduction of malathion treatment in the 1960s resulted in a fall in the level of infestation in Australian wheat imported into the United Kingdom from about 90% of cargoes to well under 20% over a period of 5 years. The use of grain protectants has lost popularity over the last few years as a direct and indirect response to a perception of concerns about residues. This has led to it being strategically easier to store, handle, and market grain with ‘no residues’ as it is more versatile at the moment of outturn (i.e., if it has no insects, it will suit most markets). Improved fumigation technology has helped this movement away from protectants in many places.

Physical Control Invertebrate control by manipulation of the physical environment has been widely discussed. The use of heat, cold, aridity, shock, radiation, and separation appears in the literature. None are widely used in modern handling systems, due largely to their higher capital cost relative to chemical treatments such as protectants and fumigants. The only exception is the use of ambient air aeration, which is rarely used directly for insect control but slows the rate of population increase by reducing the grain temperature (although it is not necessarily effective for mites).

Future Prospects Control of invertebrate pests in storage is likely to remain an important part of grain storage and handling for as long as the storage of grain remains a vital component of feeding the human population. Controlling these pests is likely to become more challenging as economic, environmental, and biological pressures increase. Pressures to reduce the cost of storage and handling mean that labor-intensive activities such as routine hygiene, sampling, and pest detection are seen as costs that have to be

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reduced. Pressures for just-in-time delivery mean that reliable but slow-acting pesticidal activities are becoming more difficult to accommodate. International competition means that commodity prices are critical and any additional overheads must be avoided where possible. On the environmental side, there are continuing concerns of emissions of fumigants to the atmosphere, chemical residues on treated grain, worker safety, and the energy costs (dollars and greenhouse gas emissions) associated with pest control. All these reduce the number of readily available options. The final pressures are the biological ones including the inevitable move of the pest gene pool towards resistance to chemical and possibly physical treatments and the ability of invertebrate pests to capitalize on new niches created by new crops, new storage strategies, and any other opportunities created as systems change. The prospects for registration of new commercially viable grain-protectant materials are not good. However, there is a possibility of some new fumigants becoming available over the next few years. Large-scale physical control and biocontrol remain promising at the research level but have massive cost and logistical barriers to overcome before they can become commercial realities.


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Conduct a web search using your favorite search engine for one or more common storage insect pests, read about size and biology, and see a picture of them. Examples of common pests are Sitophilus granarius, Tribolium confusum, and Plodia interpunctella. List the components of the stored grain ecosystem that influence the growth of insect populations. List the ways in which infestation may reduce the value of a stored commodity. Create a hygiene and management checklist for a cereal storage system of which you have some knowledge. Investigate the methods available for stored grain pest control in your jurisdiction.


• •

How can grain storage facilities be designed to limit storage insect pests and maintain quality in the context of development of export-focussed supply chains? Speculate on the future role of modern and developing technologies in improving effectiveness of storage pest management.

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Grain Harvest, Storage and Transport: Cereals: Grain Defects; Chemicals for Grain Production and Protection; Contaminants of Grain; Handling from Farm to Storage Terminal; Postharvest Operations for Quality Preservation of Stored Grain; Stored-Grain Pest Management.

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Further Reading Banks J and Fields P (1995) Physical methods for insect control. In: Jayas DS, White NDG, and Muir WE (eds.) Stored Grain Ecosystem, pp. 353–409. New York: Marcel Decker. Bell CH, Price N, and Chakrabarti B (eds.) (1996) The Methyl Bromine Issue. Chichester: Wiley. Donahaye, E.J., Navarro, S., and Leesch, J.G. (Eds.), 2001. In: Proceedings of the International Conference on Controlled Atmosphere and Fumigation in Stored Products. Fresno, USA, 19 October–3 November. Executive Printing Services, Clovis, CA, USA. Howe RW (1965) Losses caused by insects and mites in stored foods and feeding stuffs. Nutr. Abstr. Rev. 35: 285–293. Howe RW (1973) Losses of viability of seed in storage attributable to infestations of insects and mites. Seed Technol. 1: 563–586. Jin Z, Liang Q, Liang Y, Tan X, and Guan L (eds.) (1999) Proceedings of the 7th International Working Conference on Stored-Products Protection, 14–19 October 1998, Beijing, China. Chengdu: Sichuan Publishing House of Science and Technology. Lauhoff Grain Company (1991) A Guide to Good Manufacturing Practices for the Food Industry. Danville, IL: Lauhoff Grain Company. Mound L (ed.) (1989) Common Insect Pests of Stored Food Products: A Guide to their Identification. In: Economic series15: London: British Museum Natural History, seventh ed. Rees DP (2004) A Field Guide to Insects of Stored Products. Melbourne: CSIRO Publishing. Reichmuth C, Hansen LS, Wildey K, et al. (2008) Health risks and safety hazards related to insects and mites in stored products. Guidelines for risk assessment, prevention and management. Strasbourg Cedex, France: Council of Europe Public Health Committee/Council of Europe Publishing, 978-92-871-63622, 190 pp. Snelson JT (1987) Grain Protectants. Canberra, Australia: Australian Centre for International Agricultural Research ACIAR Monograph No 3. Stepien, Z.A., Goszcynski, W., and Boczek, J., 1973. The Energy Budget of Tyrophagus putrescentiae (Schr.) (Acaridae). In: Proceedings of the 3rd International Congress of Acarology. Prague, pp. 373–380.

Whitehead R, C.A.B. International, and British Crop Protection Council (2003) The e-UK pesticide guide 2003, British Crop Protection Council. Wallingford, Oxfordshire: CABI Publishing. White NDG (1995) Insects, mites and insecticides in stored grain ecosystems. In: Jayas DS, White NDG, and Muir WEM (eds.) Stored Grain Ecosystem, pp. 123–167. New York: Marcel Decker.

Relevant Websites http://www.apvma.gov.au – This website from the Australian Pesticides and Veterinary Medicines Authority contains information on all registered pesticides available for use in Australia. http://www.cdc.gov/mmwr – Use internal search to find information on occupational allergies to insects. http://www.cdpr.ca.gov – This website contains information on registered pesticides in the USA. It is maintained by the California Environmental Protection Authority and accesses the USEPA pesticide database. http://www.fao.org/inpho – The FAO Inpho website which deals with postharvest matters. Reader should use the built-in search engine to find ‘fumigation.’ This will provide a variety of topics around the subject of fumigation. http://websvr.infopest.com.au – The complete reference of Australian registered insecticides and acaricide chemicals and their uses. http://www.ncbi.nlm.nih.gov/pubmed – Use internal search to find information on occupational allergies to insects. http://www.pesticides.gov.uk – This website provides information on registered pesticides in the UK. http://www.fda.gov/Food/GuidanceRegulation/ GuidanceDocumentsRegulatoryInformation/SanitationTransportation/ucm056174. htm – This website list the defect levels for insect fragments over a wide range of stored products.

Postharvest Operations for Quality Preservation of Stored Grain F Fleurat-Lessard, INRA, Mycology and Food Safety Research Unit, Villenave d’Ornon, France ã 2016 Elsevier Ltd. All rights reserved.

Nomenclature

aw M (% dry matter) Mc (% wet basis)

Activity of water Moisture content Moisture content

Abbreviations DSS HACCP IPM

Decision support system Hazard analysis critical control point Integrated pest management

Mt (days) rh (%) T ( C)

ISO WTO

Safe storage time Relative humidity Temperature

International organization for standardization World trade organization

Topic Highlights

Introduction

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The integrated pest management (IPM) approach is generalized all over the world for the control of deterioration of stored grain quality attributes by insects and molds. IPM programs mainly consist of complementary technologies and tools used concomitantly or sequentially to keep grain pests below an economic injury level. The four approaches that are available in the IPM of stored grain are (i) chemical control (including synthetic and natural pesticide and fumigants), (ii) biological control (predators and parasitoids), (iii) physical control means (heat, mechanical impact, controlled and modified atmospheres, and hermetic storage), and (iv) phytosanitary policy application (national and international regulations in grain trade). The control of insect pests in stored grain is the major concern of grain store managers in countries with all temperate or tropical climates. In countries with humid atmospheres, such as Nordic countries (Scandinavia, Siberia, and Canada) or countries with humid tropical climate or summer monsoon (Southeast Asia, Central and South America, and Central–South Africa), the control of mold spoilage is the greatest concern. Thus, the IPM program should be customized to reflect the particular conditions and risks of the region where it is implemented. In the optimal blend of preservation means and intervention tools, physical methods play a prominent role. Most of these methods are used as preventive means of deterioration processes such as grain cleaning, cooling, heating, and drying. Some other methods of insect control may be applied equally as preventive or curative such as controlled or modified atmospheres (for insect-proof storage or disinfestation), the use of inert dusts or essential oils, and fumigation and synthetic pesticide applications on grain.

• • • • • •

Practical management of stored grain quality relies upon preventive interventions in the conditions affecting grain storage from harvest time up to delivery to end users. Integrated pest management (IPM) consists of combining good sanitation practices and preventive measures, thereby limiting the effect of deterioration factors during the storage period. Cereals with a moisture content beyond the limit for safe storage at harvest must be dried to prevent mold spoilage and economic loss during storage. Bulk grain drying before loading storage bins or storing in warehouses may be carried out by an industrial grain dryer or in bin by drying aeration assisted by an aeration controller. It is recommended to cool grain immediately after harvest time to prevent insect pest and mold damage during longterm storage. Stored grain preservation in developing countries requires improvement in storage structures and updating ancient practices with new approaches and improved knowledge of their advantages and weaknesses. Today, grain store managers can take advantage of new technologies for remote advice and training to apply safeguard measures wherever their location is.

Learning Objectives

• •

To inform about the existing means and tools available for the implementation of safe management practices for stored grain quality preservation in a large variety of situations (whatever the local level of economic development). To foster the education of grain store managers in the advances offered by knowledge-based decision support systems for postharvest operation selection, sequencing, and management by using new information and communication tools.


Grain Cleaning Grain is usually cleaned before it is stored in bins or granaries. Freshly harvested grain contains a small proportion of impurities,

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GRAIN HARVEST, STORAGE AND TRANSPORT | Postharvest Operations for Quality Preservation of Stored Grain

also called dockage. Dockage components include small or large seeds of weeds or other grains, chaff, straw, dust, soil pellets, small stones, cracked kernels, and other contaminants. Furthermore harvested grain may contain shriveled kernels, smaller than those of healthy grain and in most cases heavily contaminated with pathogenic fungi and related mycotoxins. A maximum percentage of impurities is acceptable in grain trade, according to fluctuations of the respective limits for each kind of impurity fixed by official regulations (e.g., Codex Alimentarius Commission, WTO, and ISO) or in the technical specifications agreement between requester and supplier parties. Moreover, the presence of a significant amount of larger-sized impurities, such as ear fragments, plant stalks, parts of green weed, grain husks, and chaff, presents a serious risk for safe storage because they are a source of microbiological spoilage and provide favorable conditions for multiplication of insects and mites. A high percentage of wet impurities may lead to grain heating in parts of the grain bulk shortly after binning (humid hot spots). In addition, these regions with heated grains are liable to become compact enough to disrupt airflow distribution and hinder the eventual beneficial effect of later drying or cooling later operations. Thus, grain cleaning through the separation of a significant amount of impurities may improve grain conditions before storage. A large variety of equipment can be used to carry out grain cleaning ranging the simple sieves used in developing countries to remove light impurities (thanks to the wind) to the very sophisticated high-speed industrial equipment found in grain terminal elevators. Some of these high-flow rate precleaners may clean 45–200 tonnes of grain per hour with a work input of 3–20 kWh. Some other cleaning materials combine graincleaning and grain-calibrating operations. They have a much lower output than specific cleaning machines and are mainly used by the seed-producing companies before conditioning cleaned and calibrated seed grains. Small winnowing machines can also be included in grain-cleaning equipment even if they are mainly used to clean the part of the grain harvest kept by small farmers as their own seed reserves. From an economical point of view, the financial profitability of removing dockage and foreign material of grain for sale depends on the initial dockage level. Some export markets will pay a premium for dockage-free grain, while other markets do not. Consequently, grain cleaning is not practiced in all cerealproducing and cereal-exporting countries. In the United States and in France, grain operators have little economic incentive to provide dockage-free grain. The delivery of cleaned grain is marginally profitable in Australia a cereal-exporting country that supports a policy of exporting high-quality grain. In Australia, the grain-cleaning costs are deducted by the grain-handling company from the value of the raw grain supplied by the farmers to commercial grain stores.

In-Bin Drying Preliminary Considerations Because grain structure is hygroscopic, grains either absorb moisture from the environment (under high-relative humidity (rh) conditions) or lose moisture (under low-rh conditions).

This relationship is generally represented graphically by two typical curves, respectively, when grain is adsorbing and desorbing moisture (Figure 1). These curves represent the correlation between the surrounding air rh and the water activity (aw) potential in the kernel at a constant temperature (the socalled isothermal sorption curves). When this thermodynamic equilibrium is established, with the temperature and pressure being constant and equal in the two phases (gaseous atmosphere and grain), the grain aw is equal to the relative humidity of air surrounding the grain. Multiplication of aw by 100 gives the equilibrium relative humidity (ERH) of air surrounding the grain in percent (eqn [1]): aw ¼ rh at the sorption equilibrium ðdecimal valueÞ [1] In this equilibrium condition, there is a close relationship between the moisture content of the grain and aw (or the rh of air inside the grain bulk). Consequently, grain aw can be related to the moisture content of grain by mathematical models. Numerous mathematical models of sorption–desorption equilibrium curves at different temperatures have been produced for almost any type of seed or food matrix. The equations for most cereals have been refined by researchers and are accurate enough to be used for the monitoring of aeration or moisture migration and changes in stored grain bulk through rh sensors (eqns [2a] and [2b]): rh ¼ exp ½ðC1 =T þ C2 Þ exp ðC3 MÞ

[2a]

M ¼ 1= C3 ½ ln ðT þ C2 Þ ln ðrhÞ= C1

[2b]

where rh ¼ relative humidity (decimal unit ¼ aw); M ¼ moisture content (percentage of dry matter); T ¼ temperature ( C); and C1, C2, C3 ¼ coefficients. The modified Chung–Pfost equation [2a] gives a good fit with the experimental sorption curve of cereal grain, especially for wheat, and it is used for the accurate conversion of moisture content into grain aw for several cereals.

Moisture content (% wb) 24

16

8

Moisture adsorption (moistening) Moisture desorption (drying)

0 0.0

0.2

0.6 0.4 Activity of water (aw)

0.8

1.0

Figure 1 Adsorption and desorption curves illustrating the sorption equilibrium between the activity of water inside the grain and relative humidity of air within the grain mass.

GRAIN HARVEST, STORAGE AND TRANSPORT | Postharvest Operations for Quality Preservation of Stored Grain After prolonged storage, the water activity (aw) of grains is at equilibrium with the rh in the air space around the grain. The measure of rh of air inside the grain mass can be mathematically related to aw. The following equations are commonly used to describe the relation between grain moisture content (Mc) and ambient relative humidity of air inside the grain mass (rh) (eqns [3]–[5]). a. Modified Chung–Pfost equation rh ¼ exp ½C1 =T þ C2 exp ðC3 Mc Þ

[3]

b. Modified Oswin equation rh ¼ 1=1 þ ½C1 þ C2 T=Mc C^3

[4]

c. Modified Henderson equation h i rh ¼ 1 exp C1 ðT þ C2 ÞMc C^3

[5]

The commercial upper limit of moisture content for safe storage corresponds generally to the critical moisture level for grain respiration activity, reduced by a safety margin of about 2%. Thus, the lower limit of grain moisture content allowing the growth of storage molds at 20 C in malting barley is 16.2%, and the limit recommended for safe storage conditions was recently fixed at 14% in Europe. Preserving quality of grain above the Mc threshold for safe storage can be achieved either by drying grain (in-bin drying) or by cooling grain below the threshold of temperature for mold and insect multiplication.

The Main Objectives of Drying In regions where the climate is humid, mature grain is harvested at moisture content levels incompatible with safe storage for a long period of time. The removal of excess moisture from grain can be achieved by grain drying. The prime objective of grain drying is to reduce the moisture content in harvested grain in order to minimize mold-spoilage hazard during long-term storage. Thus, drying grain to reach an equilibrium with an air rh of less than 70% is a necessary prerequisite for safe storage. Furthermore, low moisture content levels are less favorable conditions for the growth and reproduction of insects and mites.

Grain-Drying Technologies There are two different grain-drying techniques: (a) High-temperature drying that is performed with specialized equipment at a high grain flow rate and is suited to the drying of wet grain that cannot be stored in its initial condition at harvest (maize, sorghum, paddy, oilseeds, and all small-grain cereals grown in wet climates). This method involves an initial high capital investment and high running costs for a drying operation achieved in a few hours in continuous-flow grain dryers. (b) Low-temperature or natural air drying applicable to grain batches that need a moderate reduction of moisture content at harvest. This kind of drying can be carried out with minimal specialized equipment, in bins specifically

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equipped for drying purpose. The complete drying can take a period of several weeks. ’In-bin’ grain drying only will be described here.

In-Bin Grain Drying in Practice Drying has two basic stages: (i) diffusion of internal moisture to the surface of the kernel and (ii) removal of external moisture by an airflow around the kernel. Water vapor pressure is increased inside the kernel that causes moisture to diffuse through the micropores of the seed pericarp layers. The grain temperature is related to the rate of moisture diffusion and therefore can be monitored and controlled in order not to exceed a maximum rate of diffusion that could produce grain damage. The rate of evaporation of external moisture is also dependent on the air temperature (at a fixed airflow). These two stages are in constant interaction and in unstable equilibrium. The drying rate is also affected by atmospheric conditions. In this situation of complex interactions between several variables, the initial setting of the parameters of the drying system cannot be predicted, and it is necessary to test the drying process with several batches of grain before determining the exact setting of the dryer on a specific storage site. The main parameters that must be taken into account include: (a) The evaporation capacity, which is a fundamental characteristic of any dryer (expressed in kilograms of water evaporated per hour: kg h1) (b) The heating capacity, which is the quantity of heat produced by the dryer per hour (kJ h1) (c) The drying yield, which is the percentage of effectively used drying power (corresponding to the amount of water removed from grain) from the delivered power (energy consumed by the dryer) (d) The net calorific power of the dryer burner fuel, which is the heat quantity effectively delivered by the combustion of fuel (in kJ m3) (e) The specific airflow rate through the grain mass, which is the rate of the airflow per unit of grain mass (in m3 h1 of air per m3 of grain) (f) The specific heat consumption, which represents the quantity of heat required for the evaporation of 1 kg of grain water (this value is closely related to the fuel consumption and is generally minimized by the grain dryer manufacturer). In addition, the evaporation capacity and the rate of dried grain produced per hour in defined conditions of initial moisture content of grain and blown air temperature level in the dryer are also taken into account. In static dryers operating in a bin equipped with air ducts in the bottom or with a perforated floor, a close relationship between the temperature of the air blown through the grain mass and the renewal rate of the air per unit of grain bulk volume must be respected in order to obtain a homogeneous profile of moisture content throughout the dried grain bulk. Different types of static dryers are used for stored grain in developed countries, especially at the farm level. The original in-bin high-temperature drying system is initially loaded with a batch of grain, which remains in the bin until the drying operation is achieved. During the first phase of drying, grain

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is heated, and in the second phase, grain is cooled by ambient air aeration in order to recover its initial temperature. During the drying/hot air stage, the grain mass is moved from bottom to top or from side to side by the ‘drying front.’ The eventual heterogeneity that may occur at the end of the drying process, when the drying front comes out of the grain mass, is generally limited by mechanical stirring devices. In these systems, the air temperature is about 50–60 C with a specific flow rate of 140 m3 h1 of air per cubic meter of grain. During the drying operation, the grain at the bottom of the bulk is systematically drawn up at the top of the bulk by several vertical augers (Archimedean screw). Another type of dryer built on the same principle provides a continuous grain flow within the drying bin. The dried layer of grain at the bottom is regularly extracted, and moist grain is automatically added above the previous batch. In this configuration, the maximum thickness of the grain layer should be limited to 2–4 m, and the specific airflow rate to 300 m3 h1 of air per cubic meter of grain, and air temperature can be set in the range 40–80 C, depending on the sensitivity to heat injury of the processed grain. Storage bins equipped with well-designed aeration systems can also be used in a specific process involving two consecutive steps of ‘drying–cooling’ known as ‘dryeration.’ In this process, the grain is partly dried in a conventional continuous-flow dryer, and then the partially dried batch of warm grain is aerated by ambient air in a resting bin for 2 weeks. This type of process is more economical and involves less labor input compared to a continuous-flow drier. However, the aeration of semidry grain requires specific aeration equipment. The specific flow rate must be maintained between 40 and 60 m3 h1 of air per cubic meter of grain. Nevertheless, after the cooling at the end of the drying operation, the grain must be transferred in a long-term storage bin. These additional handlings of the grain batch may increase the amount of broken grain. The dryeration system

is used only to dry wet grain at the harvest such as maize or sunflower seeds. There is a risk for a slight loss of dry matter during the aeration of warm grain (coming from the drier at a temperature levels of 50–60 C), and the cooling bin must be equipped with air extraction fans in the headspace above the grain mass in order to minimize the water condensation problems that may occur in any metallic bin. The temperature level reached by grain during conventional or dryeration drying, which is more than 50 C, is lethal for most of the hidden stages of insect primary feeders that may be present inside maize, rice, or sorghum kernels at harvest. This disinfestation effect of heating grain during the drying process will be developed further with the heat shock treatment. The drying of maize cobs in a bin equipped with an inclined perforated floor has also been used in order to limit the development of fungal microflora on humid grain (especially maize and sorghum) and the consecutive production of various mycotoxins, produced either by field fungi (when growing conditions remained favorable for growth of field microflora) or the most competitive strains of storage molds (on partially dried grain).

Aeration and Cooling Stored grain bulk is slowly influenced by environmental temperature due to its low thermal conductivity. Although temperature has little direct influence on grain condition, it greatly influences the development of insects and mites and microorganisms (Figure 2), and it affects the viability of seeds. The first objective of aeration is to reduce the temperature of grain at the beginning of the storage period. Harvested grain typically comes into store at average outside temperature in summer, that is, often above 30 C in Mediterranean or subtropical areas. At such temperature levels, even dry grain is at risk from insects and moisture migration within regions of the

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Oryzaephilus surinamensis Cryptolestes ferrugineus Rhyzopertha dominica

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Grain temperature (°C) Figure 2 Influence of grain temperature on the rate of increase of insect populations per day for different pest species (grain moisture content 13% w.b.).

GRAIN HARVEST, STORAGE AND TRANSPORT | Postharvest Operations for Quality Preservation of Stored Grain grain bulk. Grains harvested or dried at commercial moisture levels (12–14% moisture) and at temperature levels as high as 25–35 C will deteriorate unless they are cooled. Moreover, the viability of seeds decreases rapidly within a few weeks in grain stored at 30 C or more.

Purpose and Benefit of Aeration The use of cooling aeration was first developed to reduce moisture translocation in warm grain when stored in metallic bins. But the potential of cooling grain by forced air aeration is currently used to combat arthropods as pests and to unify temperatures, thus preventing moisture migration and hot spot formation. The principal benefits of cooling aeration are the following: (a) Preservation of the technological properties of stored grain at a grade level as close as possible to its initial grade at the harvest time (e.g., baking quality of wheat and viability of malting barley). (b) Limitation of the moisture migration phenomenon in bulked grain storage and related mold development, which is the principal cause of damage to several parameters of grain quality (e.g., reduction of seed viability and increase in fat acidity). (c) Producing uniformity in the temperature of the grain bulk and preventing moisture migration in the grain mass due to natural convection currents induced by temperature gradients. (d) Reduction of dry matter loss resulting from the natural respiration of grains under high-temperature conditions. The associated risks of release of metabolic water and of hot spot formation are also reduced. (e) Prevention of insect multiplication or drastic limitation of their rate of increase: when temperature can be lowered below 12–14 C, at which the rate of increase of most coldtolerant species falls to zero (Figure 2).

Germination

Precision Monitoring of Grain Aeration The theoretical basis of temperature transfer to grain by aeration either with ambient or refrigerated air has been investigated by a large number of authors during the last two decades. This led to the production of many reviews in the literature. Recently, several simulation models for temperature migration during the cooling/aeration process have been produced, and it is hoped that they will be useful in the design of air ducts and ventilator characteristics. Heat and moisture migration within regions of an aerated grain bulk (Figure 3) can now be visualized in real time for each distance element of the bulk and at each time increment using finite element/difference methods. With modern computers, real-time calculations can be carried out fast enough to produce moving images. The 2-D or 3-D modeling of heat and moisture migration during ‘in-bin’ cooling or drying operations led to the creation of software to predict grain respiration rate or viability loss rate in addition to temperature and moisture migration kinetics for different kinds of cereals or oleaginous seeds.

Practical Implementation of Cooling Aeration Stored grain aeration requires the provision an air-exhaust ventilator associated with an adequate storage bin design. Aerating of grain silos can be done by either pressurized aeration (positive pressure) or suction aeration (negative pressure). Grain bins devoted to aeration have to be equipped with perforated ducting on the floor through which air is blown into (or sucked through) the grain. The design and the dimension of the ducts and the optimal characteristics of the ventilator have been described in previous reviews. The air feeding network (pipes and ducts) has to be properly sized to minimize the pressure drop for an appropriate airflow rate (5–15 m3 h1 m3 grain). A centrifugal fan is not appropriate for bins higher than 15 m, when fan static pressure exceeds 2 kPa (e.g., for wheat aerated in a 15 m high bin with an

No condensation Condensation

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Poorly aerated zone Cooling front progress during aeration

Hot spot formation

Cooling front and moisture front Humid air convection movements

Crusting and molding Nonaerated bin

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Cooled grain Homogeneous grain temperature Running fan after cooling aeration

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Figure 3 Schematic drawing of a comparison of spoilage risks between a nonaerated metallic bin and an aerated bin (by air insufflation).

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airflow rate of 10 m3 h1 m3). When air is blown, the fan compresses and heats the cooling air (e.g., 2 C under the conditions of the example above). This problem is overcome when air is sucked from top to bottom by a fan at ground level to cool stored grain as soon as possible after storage bin loading. At this time (at harvest season), the first cooling cycle has started to cool grain down to about 20 C, the first temperature target, limiting insect population multiplication. When ambient temperature begins to significantly decrease 2 months after harvest time, a second cooling cycle can be achieved with a target grain temperature of 14–15 C, which is the lower temperature threshold for insect development in stored grain. In some temperate cold climates, two other steps of cooling may be performed to reach very low temperatures (Figure 4). When air is forced through the grain mass, it carries both a ‘cooling front’ and a ‘moisture front.’ The temperature front moves rapidly, with this speed being governed by the rate of airflow and the temperature of the aeration air. The cooling power of this front is rather independent of the initial temperature of the grain. In well-designed aeration installations, the speed of the moisture front is so slow that wetting problems seldom occur or they are located in very small regions of the grain bulk. Aeration controllers are commonly used to facilitate the management of aeration and may save time for aeration by optimizing the period of aeration when temperature difference between ambient air and grain is adequate. However, there are many storage situations where ambient air conditions are not sufficient to cool grain. Nevertheless, aeration with refrigerated air achieves much lower temperatures when ambient conditions are warm. In warm climates or when very warm grain (35–40 C) is stored immediately after the harvest, aeration with ambient air may not be sufficient to control fungi on moist grain or to preserve the germination capacity and quality of stored grain. Grain chilling through refrigerated air ventilation is regarded as an expensive method for the sole purpose of insect control. However, it can

be justified for storage of fragile grains such as malting barley and seed grains in hot conditions, when retention of viability is a prerequisite. Refrigerated air units for chilling grain have been developed to enable aeration to be carried out in summer in temperate regions of Europe and North America and in tropical climates where aeration with ambient air is totally impractical. The material for cooling aeration of grain bins is composed of a refrigeration unit (Figure 5) connected by an insulated pipe to the aeration ducts of the grain bin. Although chilling ventilation can limit microflora spoilage, it is more often used in subtropical climates to cool dry grain for insect control rather than microflora control. Different models of material and equipment to cool grain with refrigerated air have been developed in many grain-producing countries. Chilling of hot grain is used in some cases of partial drying by hot air after transfer of partially dried grain (maize

Figure 5 Example of material and equipment used for chill aeration of grain with refrigerated air (use for cooling of paddy rice in Portugal).

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Figure 4 Air and grain temperature evolution during a 10-month storage period of wheat in a 500 T vertical bin with a cooling aeration system. Grain cooling is achieved in four steps with successive temperature targets according to external air seasonal temperature.

GRAIN HARVEST, STORAGE AND TRANSPORT | Postharvest Operations for Quality Preservation of Stored Grain for the main) in a ‘chilling’ bin (dryeration) specifically equipped to blow higher volumes of air than in cooling aeration, with an eventual additional heating of air blown through the grain bulk (batch drying).

Other Miscellaneous Treatments Mechanical Impact, Turning, and Pneumatic Conveying When grain starts to warm up in the bin, it can be turned (e.g., out-loaded and returned to storage) to help maintain a homogeneous temperature and, if any, to eliminate the ‘hot spots’ or ‘caked grain’ during turning bulk grain from one bin to another. But, at each time grain is moved, there may be a loss due to additional breakage. In addition, when a ‘hot spot’ is effectively formed, the fungal spoilage and contaminated grain with mycotoxins can be mixed with the sound part of the grain batch during moving, which is a strongly discouraged practice. There is only a slight decrease in the average temperature of grain during turning from bin to bin.

Limitation of Kernel Breakage The mechanical handling of grain when loading into high elevator bins or large vessel holds may result in significant kernel breakage. The free fall of grain during filling of empty bins or passage of grain through a grain thrower during the loading of a bulk carrier ship hold or a flat-bed storage compartment presents some serious risks of kernel breakage. This increase in the proportion of broken kernels, a part of the dockage, can lower the grade and the commercial value of an entire grain batch. The maximum breakage is obtained when grain drops on to a concrete surface inclined at 45 , whereas minimum breakage is observed from drops onto a grain surface. Grain handling through a bucket elevator is also a source of significant breakage. Reducing grain velocity and impact by using different systems reduces physical damage. Drops of less than 12 m or on to a layer of grain reduce the risk of breakage. Increasing the size of the grain stream is also beneficial. Reduced bin height, additional equipment to reduce velocity, and slower handling of grain can help to reduce kernel breakage.

Monitoring Quality Indicators and Their Use in a Decision Support System From initial delivery of a harvested lot to the silo by the farmer up to the sale to the final customer after storage, the intrinsic quality indicators can be monitored in order to take action to stop any deterioration process or to avoid some commercial attributes exceeding the tolerance threshold. The main indicators that predict risk of deterioration are grain moisture content (through the conversion of rh measured in the grain mass), grain temperature, insect activity (trap catch score or electronic probe diagnosis), and respiration rate (CO2 rate change measurement). In modern grain storage facilities, the numbers of insects caught in traps, abnormal temperature increases, crusting or mold appearing at the surface of the grain bulk, or carbon dioxide concentration inside a bin may be daily recorded and serve to storekeeper decision making in order to

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take action to stop any deterioration. However, effective storage pest management requires complex decision making by the store manager who uses all available indicators related to the risk of damage during storage of food grain. This decision making process may be easier by the use of computer-assisted systems. Thus, several of these systems have been built especially for the implementation of IPM programs in postharvest systems: some others deal with technical interventions (drying, cooling, and cleaning) for stored grain preservation in silos: Canstore® in Canada, Stored Grain Advisor Pro® in the United States, GrainPlan® in the United Kingdom, PestMan® in Australia, and QualiGrain® in France. Several of them have started a commercial development as decision support systems (DSS) bringing expertise and advising grain store managers about the more safe technical routes and practices for safe storage or intervention means implementation (e.g., SGA Pro®, Pestman®, and Canstore®). However, even in countries, such as the United Kingdom, the United States, Canada, and Australia, where these DSS exist at a commercial level or are available online, the benefits are often underestimated by grain store managers. These systems that may afford ‘online technical assistance and training’ in real time for stored grain quality management should be developed at a global level, since they are easily ‘customizable’ to fit any storage technology, including the low-input storage technologies often found on small local farms in developing countries. In developing countries, experience has shown that postharvest pest damage cannot be easily reduced in the absence of well-integrated policies and plans to develop the total system of production, marketing, storage, and distribution. In these countries, the adoption of IPM for stored grain pest damage limitation cannot be successful without a more stringent control of commercial flows of phytosanitary products, which may be misused by farmers or used for wrong purposes. Additionally, the IPM decision making related to an acceptable pest density level below the economic control threshold is a complex and delicate issue that needs training and experience for effective implementation.

Conclusion In traditional approaches to the management of qualitative changes in stored grain ecosystems, current interventions aimed at limiting or controlling the influence of biodeterioration factors are preplanned in advance as a safety net. Within the frame of the HACCP system, stored grain quality management requires a combination of different methods and preventive approaches to give optimal results (Figure 6). This combination needs to take into account all of the user’s requirements in order to meet his or her demand (e.g., for residue-free grain or viability-guaranteed seeds after a long storage time). Based on these indicators or risk precursors, different DSS were developed to advise grain store mangers in the choice of interventions and the application of good storage practices. However, where these DSS exist at a commercial level or are available online (in the United Kingdom, North America, and Australia), their benefits are often underestimated by grain store managers.

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Grain lot initial condition

Storability assessment module

Deteriorative forces Mold spoilage model

Predicted storability

Biodeterioration rate model

Impurities and foreign matter Identification of variety

Insect dynamics model

Initial intrinsic quality

Viability and dormancy model

Cleaning empty bins

Residues decay rate model

Safe storage life and issues prediction

Biodeterioration rate monitoring module

CO2 release rate

Disinfestation of storage facilities

Drying profile Insect activity Cooling plans

Climate information

Temperature Fumigation

CCP surveillance

rh in grain Cleaning

Bin selection Storage plant environment

Modeling and forecasting module

Hazards identification and preventive sanitation

Intervention means and equipment

Storage interventions planning module

Figure 6 Integrated management of global quality of stored grain by HACCP and IPM strategies implementation through a decision support system. Reproduced from Ndiaye and Fleurat-Lessard, 1999.

Future Prospects

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The development of new tools for decision support in real time should be promoted. As the scientific and technical knowledge about the changes in grain quality attributes increases with time, it will develop into practical use by grain handlers, thus improving the preservation of grain in its original conditions as required to fulfill the buyer’s expectations of quality and by minimizing the costs of corrective interventions. Information and communication technologies offer a large range of opportunities for knowledge and expertise transmission from experts or engineers to the grain storekeepers by the way of modern technologies of ‘high-performance storage.’ Integrated systemsgathering tools for monitoring key indicators of biodeterioration rate, predictive modeling for calculation of safe storage time, and provision of advice to minimize the risk of deterioration in quality are already in use in other domains (chemistry, cosmetics, pharmacology, and the fuel industry). Such systems that may afford ‘online technical assistance and training’ in real time for stored grain quality management should be developed at a global level.

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What are the main biotic and abiotic factors influencing safe storage time of cereal grain? What are the effective tools at the disposal of grain store managers to prevent stored grain quality changes during storage?

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Which storage conditions are related to a risk of mold spoilage or hot spot formation in a stored grain bulk? What are the main storage operations that may increase the safe storage time of stored grain? Are there any models of prediction of safe storage time for the prevention of quality deterioration of grain during storage? What are the main components of a decision support system for stored grain quality management?


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In your country or region, main grains that are delivered to storage centers or kept in the farmer’s storage facilities? What are the major grain quality characteristics and their relationships with the value of grain (technological, nutritional, or economical?) What are the grain quality criteria that are most susceptible to unsafe storage conditions? Why moist grain is unsuitable to storage? What will happen when humid grain is stored without drying? In your country, what is the origin of insect populations that multiply inside stored grain? Are these insect pest species able to develop in the field?

See also: Grain Harvest, Storage and Transport: Contaminants of Grain; Stored-Grain Pest Management; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.


Further Reading Chung DS and Pfost HB (1967) Adsorption and desorption of water vapor by cereal grains and their products: Part II. Development of general isotherms equations. Transactions of the ASAE 10: 552–555. Da-Wen S (1999) Comparison and selection of EMC/ERH isotherm equations for rice. Journal of Stored Products Research 34: 249–264. Da-Wen S and Woods JL (1994) The selection of sorption isotherm equations for wheat based on the fitting of available data. Journal of Stored Products Research 30: 27–43. Dickie JB, Ellis RH, Kraak HL, Ryder K, and Tompsett PB (1990) Temperature and seed storage longevity. Annals of Botany 65: 197–204. Ellis RH and Roberts EH (1980) The influence of temperature and moisture on seed viability period in barley (Hordeum distichum L.). Annals of Botany 45: 31–37. Fleurat-Lessard F (2002) Qualitative reasoning and integrated management of the quality of stored grain: A promising new approach. Journal of Stored Products Research 38: 191–218. Fleurat-Lessard F (2011) Monitoring for insect pest populations in grain storage: The European context. Stewart Postharvest Review http://dx.doi.org/10.2212/ spr.2011.3.5. Flinn PW, Hagstrum DW, Reed CR, and Phillips TW (2007) Stored Grain Advisor Pro: Decision support system for insect management in commercial grain elevators. Journal of Stored Products Research 43: 375–383. Lasseran J-C, Niquet G, and Fleurat-Lessard F (1994) Quality enhancement of stored grain by improved design and management of aeration. In: Highley E, Wright EJ, Banks HJ, and Champ BR (eds.) Proceedings of the 6th International Working Conference on Stored Product Protection, Canberra (Australia), April 6–11, 1994, pp. 296–299. Wallingford: CAB International, Vol. I. Longstaff BC and Cornish P (1994) ‘Pest Man’ – A decision-support-system for pest management in the Australian central grain-handling industry. AI Applications 8: 13–23. Maier DE (1994) Chilled aeration of US crops: A review. In: Highley E, Wright EJ, Banks HJ, and Champ BR (eds.) Proceedings of the 6th International Conference on Stored Product Protection, pp. 300–311. Wallingford: CAB International, Vol. I. Maier DE and Navarro S (2001) Chilling of grain by refrigerated air. In: Navarro S and Noyes R (eds.) The Mechanics and Physics of Modern Grain Aeration Management, pp. 489–560. Boca Raton, FL: CRC Press. Mani S, White NDG, Jayas DS, et al. (2001) Canadian Storage Guidelines for Cereals and Oilseeds (Canstoreã): An Expert System for Agricultural Producers and Elevator Managers. Canada: Winnipeg Canadian Wheat Board, Available at: http:// sci.agr.ca/winnipeg.canstoronweb/cotw_e.htm. Navarro S and Noyes R (2001) The Mechanics and Physics of Modern Grain Aeration Management. Boca Raton, FL: CRC Press 647 pp.. Navarro S, Noyes RT, Casada M, and Arthur FH (2012) Grain aeration. In: Hagstrum DW, Phillips TW, and Cuperus G (eds.) Stored Product Protection, pp. 121–134. Manhattan, KS: KSU Publisher. Ndiaye A (2005) QualiGrain: A decision support system for management and control of quality of malting barley after harvest. In: Fleurat-Lessard F, Ndiaye A, and Knight JD (eds.) Stored Malting Barley: Management of Quality Using an Expert System, pp. 221–257. Paris, France: INRA Editions.

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Ndiaye A and Fleurat-Lessard F (1999) Diagnosis and grading of wheat grain initial quality by a computerised decision support system. In: Zuxun Jin, Liang Quan, Liang Yongsheng, Tan Xianchang, Guan Lianghua (Eds.) Stored Product Protection, Proceedings 7th International Working Conference on Stored Product Protection, October 14–19, 1998. Beijing: Sichuan publishing house of Science & Technology, Chengdu, Vol. II, pp. 1923–1934. Pfost HB, Maurer SG, Chung DS, and Milliken GA (1976) Summarizing and reporting equilibrium moisture data for grains. American Society of Agricultural Engineers. Paper No. 76-3520. Thorpe G (2001) Airflow distribution in ventilated beds of grain. In: Noyes R and Navarro S (eds.) The Mechanics and Physics of Modern Grain Aeration Management, pp. 585–624. Boca Raton, FL: CRC Press. Vincent C, Weintraub P, Hallman GJ, and Fleurat-Lessard F (2009) Insect management with physical methods in pre- and post-harvest situations. In: Radcliffe EB, Hutchison WD, and Cancelado RE (eds.) Integrated Pest Management, pp. 309–323. Cambridge: Cambridge University Press. Wilkin DR and Mumford JD (1994) Decision support system for integrated management of stored commodities. In: Highley E, Wright EJ, Banks HJ, and Champ BR (eds.) Proceedings of the 6th International Conference on Stored Product Protection, pp. 879–883. Wallingford, UK: CAB International, Vol. II. Williams RH, Hook SCW, Parker CG, et al. (2006) GrainPlan: Development of a practical tool to improve grain storage on UK farms – Knowledge transfer in action. In: Lorini I, Bacaltchuck B, and Beckel H, et al. (eds.) Proceedings of the 9th International Conference on Stored Product Protection, pp. 1206–1211. Passo Fundo, Brazil: ABRAPOS Publisher. Woods JL and McCallum DJ (2000) Dormancy in malting barley: Quantifying the effect of storage temperature on different varieties and the response to sudden cooling. Journal of the Institute of Brewing 106: 251–258. Xanthopoulos G and Woods JL (2002) A two-dimensional model of grain storage with dynamic simulation: predictions for temperature, moisture content, germination and respiration – A case study for rapeseed. In: Credland P, Armitage DM, Bell CH, and Cogan PM (eds.) Advances in Stored Product Protection, Proceedings 8th IWCSPP, York (UK), 22–26th July 2002, pp. 933–938. Wallingford: CAB International.

Relevant Websites http://entomology.k-state.edu/doc/finished-chapters/s156-ch11.pdf – Aeration of grain – K-State Research and Extension. http://www.fao.org/docrep/t1838e/t1838e16.htm – Grain storage techniques – Evolution and trends in developing countries – FAO editor. http://www.fao.org/wairdocs/x5162f/X5162f04.htm – Strategy for grain cooling aeration by successive stages. http://storedgrain.com.au/aerating-stored-grain-cooling-or-drying-for-quality-controla-grains-industry-guide-grdc-booklet – Aerating stored grain cooling or drying for quality control: a grain industry guide. GRDC Australia www.storedgrain.com.au.

Stored-Grain Pest Management F Fleurat-Lessard, INRA, Mycology and Food Safety Research Unit, Villenave d’Ornon, France ã 2016 Elsevier Ltd. All rights reserved.

Nomenclature aw M Mc

rh T

Activity of water (none) Moisture content (% dry matter) Moisture content (% wet basis)

Abbreviations DE DSS EFSA EPA FAO FDA

HACCP IGR IPM IQM MRL w.b. WTO

Diatomaceous earth Decision support system European Food Safety Authority Environmental Protection Agency Food and Agriculture Organization Food and Drug Administration

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Topic Highlights

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The major problem with pests encountered during grain storage is insect pest multiplication. Mold spoilage can be prevented by good storage practices that keep the moisture content of grain at a level that prevents growth of mold. Insect pests in cereal grain can be controlled by chemical pesticides or fumigants. Fumigation of grain in hermetic enclosures or storage containments is the main technology used for insect pest control worldwide. The application of pesticides to grain generates residues that may persist downstream in the cereal food and feed chain. Insect pests are ‘cold-blooded’ animals (poikilotherms), and can be controlled by physical treatments such as heat, microwave heating, anoxia, and inert gas. Grain contaminated by mycotoxins may be detoxified by processes such as machine abrasion, optical sorting, steaming, and irradiation. Pest problems during grain storage can be prevented or limited by the implementation of integrated pest management (IPM). The development of computer-aided decision support systems (DSSs) is under way to enhance the implementation of IPM programs.

Learning Objectives

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To understand the kind of damage that may be caused by insect pests and storage fungi to food grain stored after harvest in unsafe storage conditions.

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Relative humidity (%) Temperature ( C)

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Hazard analysis critical control point Insect growth regulator Integrated pest management Integrated quality management Maximum residue limit Wet basis (moisture content) World Trade Organization

To understand the drawbacks and the benefits of the different approaches to grain insect pest control: chemical protectants, physical control, biotechnical control, and infestation risk prevention. To explain the advantages of a preventive approach to the management of insect pests and molds by applying the HACCP approach in IPM of stored grain.

Introduction According to a 1990 survey of extension specialists throughout the United States, grain losses exceeded $500 million for the year. Most of these losses resulted from infestation by several species of insects and spoilage or contamination by numerous molds and mycotoxins (Figure 1). Infestation of stored grain by insects can cause serious postharvest losses, ranging from up to 9% in developed countries to 20% or more in developing countries. Insect infestation is one of the major causes of rejection of deliveries to grain stores, terminal elevators, or processors and at the very least causes downgrading of a grain delivery. Although there is limited data on the rate of rejection or downgrading in international trade, a 0.5–3% rejection rate is considered a realistic estimate for grain deliveries to processing industries in some developed countries. In India, the economic loss of rice and wheat after harvest was recently estimated to be between 4% and 5% of the marketing value of the harvest, and deterioration of eating quality food grain during storage can exceed 15% of the total harvest in some developing countries. The first threat with insect infestation is the great powers of multiplication present in the majority of insect pest species that infest grain. For instance, the multiplication rate of the rice weevil, Sitophilus oryzae (L.), in optimal conditions is 25-fold in a month (Table 1). For the common grain beetle, Oryzaephilus


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08

09 10 11

12 13 14 15

18

30

Moisture content (% w.b.)

00

0.2

0.4

0.6

0.8

1.0

Activity of water (wheat)

Figure 1 Effect of temperature and moisture on biological or biochemical causes of deterioration of stored grain and physical–chemical condition threshold for the major biodeterioration factors.

Table 1

Ecophysiological characteristics of the various insect and mites species living in stored grain Conditions for development

Insect species

Grains more often affected

Temperature range ( C)

rh range (%)

Population increase rate (28 days)

Corcyra cephalonica Cryptolestes ferrugineus Cryptolestes pusillus Ephestia kuehniella Lasioderma serricorne Nemapogon granella Oryzaephilus surinamensis Plodia interpunctella Prostephanus truncatus Rhyzopertha dominica Sitophilus granarius Sitophilus oryzae Sitophilus zeamais Sitotroga cerealella Stegobium paniceum Tenebroides mauritanicus Tribolium castaneum Tribolium confusum Trogoderma granarium

Rice Wheat/barley Cereals/pulses Cereals/by-products Cereals/by-products Corn/by-products All cereals Corn/oilseeds/cereals Corn/sorghum Wheat/corn/sorghum Wheat/rye/barley Wheat/barley/rice Corn/sorghum/wheat Corn/sorghum/rice Cereal by-products Corn/cereal products All cereals/oilseeds Cereal products Durum/oilseeds/pulses

17–35 20–40 18–38 12–30 20–37 7–27 18–37.5 18–33 18–37 18–39 13–33 17–34 17–34 16–35 15–35 18–37 20–40 20–38 24–31

15–90 40–95 45–100 0–80 22–100 65–95 10–90 25–95 40–90 25–70 55–100 45–100 45–100 25–80 30–100 25–100 10–95 10–100 1–73

10 60 10 50 20 – 50 30 25 20 15 25 25 50 7.5 2.5 70 60 12.5

Wheat/oilseeds Oilseeds/cereals

7–30 12–35

65–95 65–95

2500 20 000

Mite species Acarus siro Tyrophagus putrescentiae

Developmental temperature and relative humidity (rh) threshold, population increase rate per month in optimal conditions.


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surinamensis (L.), this rate reaches 50-fold. Insect detectable density in a grain bulk by a standard sampling method is rather high. Nevertheless, no detectable insect infestation is acceptable (and accepted) in the grain trade. This rule is applied worldwide, whatever the level of infestation in domestic grain stocks and the grain’s final destination. Consequently, the eradication of insects in grain lots destined for a long period of storage is of prime importance for the preservation of commercial value. Storage fungi start to grow on cereals with a 14.5% moisture content (m.c) (wet basis; w.b.) (Figure 2) and on oilseeds (rape, sunflower, soybeans, peanuts, etc.) with a 7.5–8% m.c. The different species of storage fungi that grow on grain have different affinities for the temperature and water activity (aw) of grains (Figure 3). One group, mainly composed of Aspergillus species, is xerophilic, developing at low m.c. A second group of species is more coldtolerant and can grow at temperature levels as low as 0 C, provided that the m.c. is higher than 18–20% (on a w.b.). This group of cold-tolerant fungi is mainly composed of Penicillium species. A third group of fungi is composed of hygrophilic species that can grow only under field conditions, the so-called field fungi such as Fusarium and Alternaria spp. These species are inhibited after desiccation of grain before the harvest corresponding to a low aw of binned grain. The last group is composed of thermophilic fungi, which can only grow in grain at elevated temperatures. This group is composed of ‘warm-climate species’ of the genera Aspergillus, Penicillium, Mucor, and Humicola. Commonly fungal spoilage of stored grain starts with an associated increase in the population of mites. Mites cannot breed if the grain m.c. is < 15% (w.b.), which corresponds to < 0.65 aw for cereal grain.

Moisture content (% w.b.) 25 Available water 20 Critical point for water activity (aw)

15

C

Bacteria Yeasts Molds

10

Enzymes Maillard reactions

5

Oxidation Denaturation of proteins

0 0

0.25

0.50

0.65 0.75

0.931.0 a W 0.85

Figure 2 Grain moisture desorption curve (wheat at 25 C) focusing on the zone in which water adsorbed in grain becomes available to support various processes of biodeterioration and mold spoilage. Redrawn from Multon (1988), Preservation and storage of grains, seeds and their by-products, pp. 3-63. New York: Lavoisier Publishing.

Insect Pest Control by Chemical Means The most popular method for controling grain infestation relates is use of chemical pesticides. There are two main kinds of insecticides that can be applied to grain: contact insecticides (e.g., residual insecticides) and fumigants (Figure 4).

Contact Insecticides There are essentially two types of contact insecticides: (i) residual (i.e., substances that leave active residues on grain for several months to more than a year after the treatment) and (ii) nonresidual (substances that kill rapidly due to high vapor pressure and high lethality of residues). Residual insecticides are contain organophosphates, pyrethroids, and insect growth regulators (IGRs) as the active ingredients. The nonresidual pesticide group contains only dichlorvos (also an organophosphate). However, since 2008, this active substance (a.s.) is no longer registered for insecticidal treatment of grain in the European Union (EU). The cost of such chemicals are low, so a large proportion of cereal grain held in commercial storage is protected against insect infestation in this way. Only registered active substances can be used in the formulation of a commercial insecticide, which must be approved by regulatory authorities (e.g., the European Food Safety Authority (EFSA) in the EU or the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) in the United States) for use with food or feed cereal grain without risk to the producer, the applicator, or the consumer’s health. Grain protectants are applied mainly as a liquid formulation that can be simply sprayed using air-powered applicators; these can be automatically driven in well-equipped storage installations. However, powder formulations are still available and are useful for complementary treatments of regions of a grain bulk that are particularly favorable for insect development, such as the surface layers in flat-bed storage that must be protected from external reinfestation after fumigation or cooling (topdressing). The use of grain protectants varies widely according to the country, market preference, and local regulations (Table 2). Contact insecticide admixtures in stored grain are widely used in grain-exporting countries and especially in France where several organophosphates and pyrethroids are registered. In contrast, there is limited use of fumigation or controlled atmospheres (CAs) in France, unlike in Australia, North America, or Germany. Because of heat degradation, insect resistance, increased buyer’s concern, and more stringent requirements for registration of new molecules, the use of chemical protectants is declining in almost all developed countries. Nevertheless, the maximum residue limit (MRL) for any active substance registered for direct application to grain is set worldwide by the Codex Alimentarius (joint commission of WHO and FAO). The World Trade Organization (WTO) has adopted these approved MRLs in cereal grain international trading. In recent regulations regarding the ‘pesticide package’, the EU has drastically tightened the rules for the registration of new active substances and banned the most noxious pesticide molecules considered to be persistent organic pollutants. Some substances called ‘biorationals’ or IGRs that have deleterious effects on the development process of insects


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Grain moisture content (wet basis) 26 Hygrophilic: group III

24 Thermotolerant: group IV

22 Cold tolerant: group II

20 18

Xerotolerant: group I

16 14 12

10 –10

0

10

20

30

40

50

60

70

Temperature (°C)

Figure 3 Different fungi species that can be found in stored cereals and their limiting growth conditions related to grain moisture content and temperature range. Adapted from Lacey J, Hill ST, and Edwards MA (1980) Micro-organisms in stored grains: Their enumeration and significance. Tropical Stored Products Information 39: 19–32.

Preventive means

Corrective means

Cooling aeration

Insecticide application

Grain cleaning

Airtight storage and/or controlled atmosphere

Sanitation of storage facilities

Table 2 Chemicals (active substances) used in the past or currently registered for direct application to cereal grain with their main characteristics and the MRL level fixed by the Codex Alimentarius Commission

Mineral dust

Empty bin disinfestation

Fumigation

Insecticide

Drying aeration

Bin turning

Bifenthrin Bioresmethrin Carbaryl Chlorpyrifosmethyl Cypermethrin Deltamethrin Dichlorvos Etrimfos Fenitrothion Fenvalerate Lindane Malathion Methoprene Permethrin Pirimiphosmethyl Pyrethrins Piperonyl butoxide Spinosad

Chilling ventilation

Drying

Figure 4 Main equipment and tools available at grain storage facilities to preserve stored-grain quality from deteriorative forces (mold spoilage, insect damage, and seed viability decrease).

(successive molts and ecdysis) have been registered and are in use on a small scale in Australia and the United States. They are considered as substances with a poor efficacy as they are slow acting, taking weeks or months after treatment to eradicate insect populations. These slow-acting substances do not appeal to many grain handlers who want to kill off an infestation rapidly. Although these residual chemical protectants have a remarkable efficacy on insect pests, they have two main drawbacks: (i) the repetition of grain treatments with the same active substance inevitably induces the emergence of insecticide-resistant strains of target insect species and (ii) after grain treatment, residues remain active for several months and are

MRL Codex Alimentarius (mg kg1 grain)

Oral LD50 for rats (mg kg1 body weight)

ADI for human consumption (mg kg1 body weight)

0.5 1a 2b 10

53–210 7070–8000 850 1630–2140

0.01 0.03 0.008 0.01

2 2 5a 5a 6b 2b 0.01a 10a 10b 2b 7

187–326 135–5000 56–108 1800 800 451 88–270 2800 >34 600 430–4000 2050

0.05 0.01 0.001 0.001 0.002 0.02 0.003 0.02 0.4 0.05 0.02

0.3 20

584–900 7500

0.04 0.1

1

>5000

0.02

MRL, maximum residue limit; LD50, lethal dose, 50%; ADI, acceptable daily intake. a No longer in use for grain protection. b Not registered for application on grain.

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still present in foods processed from cereals. To date, more than 150 strains of stored-grain insect species have been described as having resistance to organophosphates (chlorpyrifos-methyl, pirimiphos-methyl, malathion, etc.) in different countries. The lesser grain borer, Rhyzopertha dominica (F.), is certainly the most tolerant species to organophosphate treatment, and the pyrethroids (deltamethrin, bifenthrin, and cypermethrin) are preferred for the control of this species. This ‘adaptation’ of insecticide treatment to the characteristics and threat of a target insect species is one of the principles of IPM strategies.

Fumigation with Gaseous Fumigants Preliminary considerations Fumigants are volatile chemicals that are in a gaseous state at normal atmospheric pressure and ambient temperature and that have toxic properties against insects. Once in gaseous form, if applied properly the fumigants readily penetrate into infested kernels, thereby eliminating all insect life stages. Numerous fumigants have been evaluated for the control of grain insect pests since the first discovery of the insecticidal properties of methyl bromide by Le Goupil. Although methyl bromide has played a major role in quarantine fumigation of food commodities exchanged in international trade, there are few examples of its systematic use for grain fumigation. In 1995, it was added to the list of compounds thought responsible for the depletion of the stratospheric ozone layer. The use and production of methyl bromide were prohibited in 2005 in all developed countries. Two other fumigants used for grain disinfestation remain registered for use after the methyl bromide ban: hydrogen cyanide (HCN) and phosTable 3

phine (PH3). Hydrogen cyanide is used exclusively for the treatment of the empty holds of ships prior to grain uploading. Only one fumigant is currently used worldwide for grain disinfestation: phosphine. Phosphine gas is generated from solid formulations of aluminum or magnesium phosphide (Table 3). With its low molecular weight and low boiling point, phosphine easily penetrates grain bulks and grain kernels; it can diffuse through permeable packaging material. The adsorbed gas is quickly eliminated after fumigation by appropriate aeration. One disadvantage is the long exposure period needed to completely eliminate the target insect species population. The time to reach maximal concentration in the fumigation enclosure varies with the formulation, magnesium phosphide generators release phosphine more rapidly than aluminum phosphide. Nevertheless, phosphine fumigation needs at least 3–7 days for complete efficacy, and even longer with temperature levels between 10 and 15 C. Below 10 C, phosphine fumigation is not recommended as it can be ineffective. Consequently, phosphine fumigations are performed during the warm season at temperatures above 10 C. Phosphine fumigation is classified as being ‘residue-free,’ which means that it does not leave toxic residues on the grain after phosphine gas exposure and consecutive aeration.

Implementation of phosphine fumigation Phosphine gas is released from a solid generator (tablet, pellets, or blankets) containing aluminum or magnesium phosphide (AlP or MgP) through its reaction with atmospheric moisture occupying the intergranular space (eqn [1]): AlP þ 3H2 O ! AlðOHÞ3 þ PH3

[1]

Insecticide active ingredients approved for the control of grain insect pests labeled in the United States and Canada

Approved active substance

Type

Controlled insects

Product to be protected

Bacillus thuringiensis

B

Pirimiphos-methyl Malathion Chlorpyrifos-methyl Pyrethrins and piperonyl butoxide Diatomaceous earth Silicon dioxide Deltamethrin þ chlorpyrifosmethyl Dichlorvos Methoprene

OP OP OP NC S MP

Larval stage Indian meal moth, Angoumois grain moth (top dressing application) Weevils, secondary beetles, Indian meal moth Weevils, secondary beetles (dust formulation) Banned (2013) Surface sprays control Indian meal moth larvae

Corn (þpopcorn), wheat (small grains), sorghum, soybeans, peanuts, birdseed, etc. Corn (þpopcorn), sorghum Corn, wheat (small grains), barley, sorghum, rye Wheat (small grains), sorghum Corn, wheat (small grains), sorghum

Topdress application limiting external infestation

Corn, Buckwheat, wheat (small grains), sorghum, soybeans, rice, rye, seed grain Wheat, barley, oats, sorghum, rice

Aluminum phosphide

F

Carbon dioxide Gaseous phosphine

NC F

Magnesium phosphide

F

Methyl bromide

LF

PY OP OP IGR

Weevils, lesser grain borer, secondary beetles, and Indian meal moth Adult Indian meal moth before egg laying Larval stage of external feeders, surface feeding caterpillar All species killed either adult or juvenile stages. Required: certification of applicators All species (long exposure time required) All species killed either adult or juvenile stages. Required: certification of applicators All species killed either adult or juvenile stages. Required: certification of applicators Banned for routine fumigation on grain (2005)

Area above stored corn grain, soybeans, peanuts Barley, birdseed, cereal grains, corn (þpopcorn), oats, peanuts, rice, sorghum, wheat, sunflower Corn (þpopcorn), wheat (small grains), sorghum, soybeans Corn, wheat (small grains), sorghum, soybeans Corn, wheat (small grains), sorghum, soybeans (Canada only) Corn (þpopcorn), wheat (small grains), sorghum, soybeans Quarantine and preshipment use (import or export)

B, biotoxin; F, fumigant (gas generator); IGR, insect growth regulator; LGF, liquid or gaseous fumigant; MP, mineral product (natural); NC, natural compound; OP, organophosphate (synthetic); PY, pyrethroid (synthetic); S, synergist (synthetic).

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored-Grain Pest Management In 1984 a Canadian researcher defined a specific unit of exposure under these conditions of slow release of phosphine gas over time. He described the term ‘C*T’, in which the concentration of the fumigant and the time of exposure (usually in hours) are multiplied to quantify the ‘dose’ for fumigation. Other conditions influence the penetration and efficacy of the fumigant, including temperature, relative humidity (rh), insect species, development stage, and airtightness of the enclosure or grain bin during fumigation. Modeling the release of phosphine gas and the level of observed ‘C*T’ with the fumigation conditions may allow standardization of procedures in order to minimize the risk for workers. The phosphine generator formulation contains ammonium carbamate, which releases ammonia and carbon dioxide simultaneously with phosphine gas (eqn [2]). This mixture of ammonia and carbon dioxide acts as an inerting agent by reducing the fire hazard with phosphine, and the presence of ammonia is also a useful warning sign for the operator because it gives off a garlic-like odor: NH2 COONH4 ! 2NH3 þ CO2

[2]

An important aspect to consider with fumigation is the lack of residual protection, as reinfestation can occur immediately after the grain has been aerated and the gas concentration falls below the safe concentration for workers. Fumigation with phosphine is used in two different ways: as a preventive treatment and as a corrective treatment. In most cases, fumigation is applied when a grain bulk is obviously infested with insects and when the required term of storage is not achieved. However, in several countries where it is the major method for insect control, for example, Australia, the United States, Argentina, and China, it is also used preventively. In these countries, the policy of long-term storage of large quantities of grain in low-cost structures (flat-bed storage, semiunderground pits or ‘grain bunkers,’ hemispheric storage bins, Argentinian silo bags, etc.) renders the use of fumigation indispensable. The difficulty in moving infested grain to another bin equipped with other means of control (cooling aeration or liquid insecticide application) is a major issue that can be solved by this approach. In such cases, specialized storage structures can be permanently sealed during the whole period of storage so that several fumigations per year can be carried out. Where fumigation is used for treatment of infested grain, the operation can be carried out in specialized airtight bins called ‘hospital bins.’ The most popular technique that has the approval of the regulation authorities in many countries is the ‘recirculation fumigation system’ (Figure 5).

Safety use considerations Very strict safety procedures are associated with the use of fumigants in developed countries such as specialized training, capability to monitor the correct concentration during the whole operation, and the use of safety equipment. Consequently, this job is done by trained, reputable professionals. In developing countries, fumigation of durable food products is used as a backup technique and is usually regarded as a measure of last resort, also for safety reasons. Where regulations permit, in-transit fumigation of bulked and bagged grain on board ships can be carried out. This technology is widely

131

Gas evacuation line Phosphine generator

Two-way airtight valve Recirculation pipe

Phosphine gas flow

Grain

Gas sampling points

Airtight fan Airtight discharge port

Conveyor

Two-way airtight valve

Figure 5 Design of an airtight grain bin devoted to phosphine fumigation operations (‘hospital bin’) – this bin is equipped with a gas recirculating duct, an open aeration circuit, and airtight ventilator and valves (recirculation system principle).

used for grain export worldwide. In-transit fumigation is used by those countries where such practices are approved by the relevant regulatory authorities and according to the international regulations for in-transit fumigation of bulk grain transport vessels.

Phosphine: more recent issues In order to limit the main drawbacks of phosphine treatments – that is, the (long) time needed for the natural release of hydrogen phosphide and the difficulty in accurately delivering the expected dose from the solid generators – several methods have been developed to directly release phosphine gas. Generally, these gaseous formulations of phosphine compressed in gas cylinders contain 2% phosphine and 98% carbon dioxide. Various systems based on phosphine activity have been patented and are currently used, especially in Australia (Siroflo®, PhosFume®, ProFume®, Eco2fume®, etc.). More recently, some devices and equipment were developed for safe release of phosphine pure gas at a high rate by the controlled reaction of phosphine generators and water. Pure phosphine is also available in compressed cylinders with specific release processes needed for safe operating conditions. Probably because phosphine is in worldwide use today, several strains of grain insect species (e.g., R. dominica (F.), Tribolium castaneum (Herbst), and psocids) have demonstrated resistance to phosphine fumigation in a number of countries. The recent advances in phosphine-release technologies for grain or warehouse fumigations mentioned above are linked to this phenomenon in countries that routinely use phosphine fumigation. In the last decade, active research in the field has attempted to find new fumigants to replace methyl bromide or to overcome problems with resistant strains of insects. Today,

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research is focused on two new fumigants, sulfuryl fluoride and methyl iodide. Sulfuryl fluoride is now officially approved for the disinfestation of empty factories and industrial processing facilities, such as mills and feed factories.

Insect Pest Control by Physical Means Temperature Control of Insects General considerations regarding the effect of temperature on insects Most of the insect species living in stored grain are of tropical or subtropical origin and require fairly high temperatures for optimal development ranging from 25 to 34 C, for example, for Sitophilus granarius (L.) and Tribolium castaneum (Herbst), respectively. Cooling grain below 20 C greatly reduces the rate of increase of the most noxious species called ‘primary feeders’: Sitophilus spp. (the weevil species complex), R. dominica and Prostephanus truncatus (Horn) (the lesser and larger grain borer, respectively), and the juvenile instars of Sitotroga cerealella (Olivier), the Angoumois grain moth. The reproduction of all grain insect species is inhibited (multiplication rate reduced to zero) when the temperature falls below 10 C (lower limit of tolerance to cold by most resistant primary feeders) and above 36–38 C.

experimental aeration systems for calculating the approximate time required to cool a grain bulk was presented by Navarro and Calderon (eqn [3]): T ¼ ðM DT cÞ=ðQ Sw CF DHÞ

[3]

where T ¼ cooling time (h), M ¼ grain mass to be cooled (kg), DT ¼ difference between final and initial temperatures ( C), c ¼ specific heat of grain (kcal kg1 C1), Q ¼ air volume flowing through the grain (m3 h1), Sw ¼ average density of aeration air (kg m3), DH ¼ maximum enthalpy difference between air input and air output (kcal kg1), and CF ¼ correction factor (dimensionless). Nowadays, cooling aeration can be optimized by automatic sensors of temperature and rh of ambient air, which trigger the system every time the climatic conditions fall below the control setting levels. The use of aeration system controllers allows a substantial reduction of energy costs compared with manually driven aeration systems. In hot climates, the cooling of grain requires refrigerated air. Cooling grain for insect management either by ambient air in temperate climate or by refrigerated air in hot climates (with a decrease only at 15 C threshold) requires energy costs similar to those for insecticidal treatment with grain turning from one bin to another.

Heat disinfestation Cooling grain to inhibit insect multiplication The lowering of grain temperature to 10 C or below is the ultimate objective in order to control insect populations. In most cases, achieving temperatures in the range 15–18 C will reduce insect damage to acceptable levels (Table 1). Thus, the safest temperature level to reach is 15 C or less considering that the rate of increase of insect populations remains very low or zero at this temperature. The cooling process is slow due to the insulating properties of grain, so reducing grain temperature to this level requires several ‘steps’ of aeration over a few weeks. Cooling aeration is mainly achieved during the night. The most important cooling step is the immediate period after grain harvest. The more rapidly the first stage of cooling is achieved, the longer the safe storage period. This first step aims to reduce the temperature to around 20 C, which reduces the natural rate of increase of the majority of noxious species by about 50%. The immediate cooling of harvested grain is generally feasible in all countries with a temperate or Mediterranean climate during the month following harvest. Thus, cooling by aeration in the United Kingdom is used on 60% of farms and in over 90% of commercial stores. This proportion is also high in France (75% of commercial wheat and malting barley storage facilities are equipped for cooling aeration assisted by a temperature monitoring system). On a practical level, with an airflow rate of 10 m3 h1 m3 of grain, the total cumulative time of aeration required to achieve the first step of cooling aeration is about 100–120 h, that is, 12–15 nights at the rate of 8 ‘favorable hours’ per day. Automated control systems are available to control fan operation. Some of these systems can be used to perform the calculations and to produce an optimal design for fans, ducts, etc. These systems with self-controllers and timers generally have temperature probes at all levels of the grain bins. A simple method from

Temperature plays a major role in a number the physiological functions of insects, which are ‘cold-blooded’ (poikilothermic) animals (Table 4). Heat has been used to kill insects for the last 80 years. A temperature of 52–55 C maintained for 10–12 h was found to be effective for flour mill disinfestation. Several methods of heating bulk grain are available today. A methodology derived from industrial use of fluidized beds or spouted beds fed by heated air has been used for high-temperature heating of grain over short periods. Wheat grain treated in a fluidized bed with hot air is disinfested when grain temperature reaches 63–65 C and is maintained at this level for a few minutes, followed by rapid cooling to ambient temperature. Under these conditions of heat shock, the viability, the moisture content, and the baking quality of wheat are not adversely affected provided that grain is immediately cooled after the heating phase and that its moisture is at a normal level. At a temperature of 62–65 C inside the kernels, all developmental stages of insect internal feeders are killed. Several different approaches have been used to adapt rapid heat disinfestation for use with modern systems of grain storage, all of which heat the grain during its conveyance. A final temperature of slightly above 60 C is desirable. Fluidized-bed or spouted-bed heating was the first practical application of heat disinfestation to be in Australia. With the fluidized-bed process, cooling grain after heating is very easy with optimization of energy input by heat exchange between the hot and the cold parts of the equipment. The prediction of the temperature at which grain is heated internally has been approached by simple asymptotic regressions using only the following measurable variables: air inlet and outlet temperature, airflow velocity, and specific rate (volume of air per unit of grain mass). The simplification of the calculation for the model regression is as follows (eqn [4]):

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored-Grain Pest Management Table 4 Physiological response of stored-product insects to different temperature levels Temperature ( C)

Condition Lethal

Suboptimum Optimum Suboptimum

Lethal

>62 50–62 45–50 35–42 35 33–35 25–33 20–25 13–20 4–13 1 to þ3 10 to 5 25 to 15

Effect and consequences Death in <1 min Death in <1 h Death in <1 day Population dies out Development stops Development slowing down Maximum rate of development Slow development Development slows or stops Movement and feeding stop Death in days (nonacclimatized) or after weeks or months (acclimatized) Death in weeks to months (if acclimatized) Death in minutes: insects freeze

Source: Modified from Fields and Muir (1995) Physical control. In: Subramanyam Bh, Hagstrum D (eds.) Management of Insects in Stored Products, pp. 195–222. New York: Marcel Dekker Inc.

1=tx% ¼ T þ C

and

Tmax T ¼ abExpðtx%Þ

[4]

where tx% ¼ time to give x% mortality; T ¼ grain temperature ( C); Tmax ¼ air inlet temperature; and C, a, and b are constants. A general modeling approach of heat and mass transfer in any system of grain drying, cooling, or aeration was obtained using numerical methods. From a starting point of a model describing moisture migration arising from natural convection currents in two-dimensional systems, an extension of the diffusion equation for moisture and water vapor through hygroscopic models has been proposed. Then, this model for the diffusion process was generalized to simulate moisture migration in grain bulks of arbitrary shapes. The actual model based on the finite element method allows the description of heat and moisture associated with both natural and forced convection aerations in arbitrary-shaped grain bulks. Thus, real-time changes in moisture and temperature can be predicted, enabling the detection of airflow conditions that may generate temperature or moisture accumulation or redistribution in different parts of a bin. This tool combining heat and moisture transfer can also be used to visualize in two dimensions the effect of the spacing and the size of aeration ducts on the cooling or drying efficacy in all regions of the bin. The prediction of grain temperature and moisture content at any storage time and in all parts of the grain bulk, whatever its shape, enables the prediction of population dynamics of insects and their density changes during storage time.

Microwave and Radiofrequency Heating Infrared, radiofrequencies (RFs), microwaves (MWs), and light radiation are nonionizing electromagnetic waves that can be used for the direct transfer of radiant energy to solid matter such as grain (a dielectric material). Among these means, only

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RF heating and MW heating are of interest for heat disinfestation of food commodities, provided their qualities are not impaired by heating. Electromagnetic waves without ionizing effect such as MW and RF can transfer heat inside a dielectric material without the need of a transfer fluid. MW and RF induce vibration of electrically charged particles within the matter, and their energy is absorbed by dry grain producing an increase in internal temperature.

RF heating RF heating involves frequencies between 3 and 300 MHz, that is, wavelengths between 100 and 1 m, respectively. Commonly used frequencies for energetic applications in industry, science, and medicine (ISM) have been fixed by regulating bodies at 13.56, 27.12, and 40.34 MHz. RF dielectric heating is accomplished with the product placed between two electrodes in an oven. Rapid heating of the exposed material is obtained by applying a high electrode voltage that induces high alternative field intensity inside the material. Field intensities of 1.4–1.5 kV cm1 are currently applied for cereal grain disinfestation. The field intensity is quite uniform if the material is homogeneous in presentation between the electrodes (Figure 6). The main advantage of RF fields compared with MW is a greater depth of penetration of waves inside dry material, allowing the disinfestation of a layer of food commodities slowly flowing on a conveyor belt up to a thickness of 0.20–0.40 m. Conditioned food commodities may also be treated by RF fields provided that the packing material does not contain metals such as iron and copper.

MW heating MW heating involves a higher frequency range than RF, increasing from 300 MHz to more than 50 GHz. The main MW frequencies allowed for ISM applications are 434, 915, and 2450 MHz. The technology of MW was developed later than that for RF after the discovery of the magnetron and other MW sources in the 1970s. MW heating is obtained with lower electric field intensities than RF heating, mainly because MWs have a lower wavelength than RF and there is a higher attenuation of the MW stream penetrating into the material. The effect of warming may be heterogeneou if the material remains static under the MW source. To minimize this risk, the product is generally rotated or mixed during exposure to the MW energy source. Although some interesting results have been obtained for disinfestation and to some extent for the final step of dehydration of cereal grain by both RF and MW, this method is not currently used because of the high capital cost of installation, the relatively high running costs in terms of the large amount of electricity required (even if the transfer rate into heat is generally better than 60%), and the low product flow rate possible with this treatment (pilot-scale machines have reached 4 T h1 with an RF generator delivering 60 kW energetic electric field). There are many drawbacks to the current use of dielectric heating for grain disinfestation, and yet this method has not been shown to be superior to air-based systems, except for quarantine purposes. Provided that there is good monitoring of the heating process (e.g., with an infrared video camera), the eventual damage to end-use quality of treated cereals at the levels of temperature required to

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RF generator

Adaptation system to impedance 50 W Tunnel-oven Applicator electrode

Conveying belt Product to be treated

Figure 6 Experimental RF field oven designed especially for optimal adjustment of RF equipment setting for disinfestation of a large range of food commodities (dry vegetal powder, wheat flour in 1 kg paper bag, dry legumes, spices, grains, grain by-products, etc.).

eliminate insects is limited and generally acceptable. The heatsensitive qualities include bread-making quality of wheat, rice color and taste, and viability of malting barley and cereal seeds.

Irradiation or Ionization Irradiation represents either exposure to gamma rays (radioactive isotopes) or to x-rays (accelerated electrons). Insects are not immediately killed after irradiation, but they are all sterilized at a low dose. Thus, irradiation of bulk grains may theoretically be used to eliminate insects. Two different types of equipment correspond to the two kinds of radiation: the radioactive sources (Co60 or Cs137) and the accelerated electrons emitted from a heated cathode. Gamma rays penetrate deeply into the food products, while accelerated electrons have a limited depth of penetration to 2–5 cm. Consequently, the accelerated-electron plant may only treat a thin layer of the product conveyed under the irradiation ‘gun.’ A plant dedicated to the disinfestation of imported grain was used a long time ago in the USSR but is no longer operational. The technology of radioisotopes was tested in Indonesia for the disinfestation of bagged rice. Control of Sitophilus oryzae in infested wheat was observed at a dose of 0.40 kGy.

Although there are internationally recognized agreements for the use of irradiation for disinfestation of a range of foodstuffs, including grain, there are public acceptance problems with irradiated food products. Consequently, the use of irradiation for grain disinfestation purposes is greatly affected by this negative perception by retailers and consumers. A recent review was published that focused on the inconvenience of use of this disinfestation method.

Controlled Atmospheres The process of controlled atmospheres (CA) disinfestation involves the modification or the replacement of the atmospheric composition of grain bulks by inert gases CO2, N2, or mixtures of these two gases, associated with a low level of residual O2. The use of CA is an adaptation of the age-old principle of hermetic storage. In simple airtight or hermetic storage systems, the progressive depletion of oxygen by the natural respiration of grain, microorganisms, and insects themselves can be lethal for insects after long-term exposure. The lower the moisture content of grain, the longer the exposure time required to kill the insects. An anaerobic atmosphere can be achieved quickly (several hours to several days) with the

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored-Grain Pest Management injection of inert atmospheres inside airtight grain storage structures. There are two different ways to eradicate insects using CAs: the ‘high-CO2’ CA, often called ‘modified atmosphere,’ and the low-O2 CA.

High-carbon dioxide CA Adding carbon dioxide to an airtight grain bin has an effect similar to that of fumigation. Carbon dioxide has a specific lethal effect on insects when its concentration is above 40% (v/v) in air. Atmospheres containing about 60% carbon dioxide rapidly kill stored-product insects. As an example, at a temperature of 26 C, about 4 days of exposure would be sufficient to kill all stages of most stored-product insects. However, there are many drawbacks to using ‘high-CO2’ CA to control grain insects: the amount of CO2 required to fumigate 1 tonne of grain is about 2 m3, that is, close to 4 kg CO2 in liquid form (to be compared to 2–3 g of phosphine gas). Carbon dioxide sorption on grain is important and may induce negative pressure in very airtight enclosures. This phenomenon renders the practical management of CO2 fumigation more difficult than phosphine fumigation, and the use of pressure safety valves is required.

Low-oxygen CA Oxygen depletion in an airtight enclosure may be principally achieved by adding oxygen-free gas such as pure nitrogen or by adding low-oxygen content gas such as the output of a hydrocarbon burner (also called exothermic inert gas generator). In contrast to ‘high-CO2’ fumigation, it is considered that nitrogen is only active in producing a progressive hypoxia or anoxia without other particular effects on living organisms. Consequently, in pure nitrogen atmospheres, grain beetles can survive for more than 1 month at low the temperature levels of the grain during the winter season (e.g., 10–12 C). The rule of oxygen deficit being correlated with the killing dose–effect relationship has an exception with the weevil, Sitophilus oryzae, which is less tolerant to 1% O2 residual concentration than to almost anaerobic atmospheres containing 0.1–0.2% residual oxygen. Pure nitrogen generation by the process of separation of atmospheric nitrogen from air is now available for modern units of small capacity such as exists in cereal processing plants. The technology of generating nitrogen from air on-site by separation and purification is rapidly improving and has become cheaper. A low-oxygen atmosphere can also be obtained by exothermic gas burners. There is no proven advantage to using a burner over use of pure nitrogen either in terms of insecticidal efficacy or economic benefit. There are few grain stores equipped with fixed installations using either pure nitrogen or gas burners, except for certain high-grade cereals such as aromatic rice and premium malting barley. The strategy that is most commonly used for CA is the permanent preservation of grain under a low-O2 atmosphere in an airtight bin equipped with relief valves that absorb the differences in pressure when the temperature changes.

The future of CA fumigations CA treatments based on either nitrogen or carbon dioxide atmosphere storage provide technical alternatives to methyl bromide for disinfestation of bulk or bagged grain. However,

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their use is constrained by the cost of implementation of CO2 fumigation or long-term generation of low-O2 atmosphere by a burner or an atmospheric nitrogen purifier. The slow speed of action of CA is not really an problem in tropical countries, and several important reserves of cereals have been preserved using this technique (e.g., in Indonesia and Singapore). The low-oxygen atmosphere technology currently used for disinfestation of delicate food products (aromatic plants, spices, germinated seeds, etc.) is performed in airtight chambers that range in capacity from 1 to 1000 m3 and involve a completely automated process controlled remotely (e.g., EcO2 b.v.® technology).

Other Miscellaneous Treatments Mechanical Impact, Turning, and Pneumatic Conveying During pneumatic conveying of grain in fluid-lift handling (e.g., out-loading of vessels or barges), the high-speed impact of grains against the walls of the transportation ducts eliminates a significant proportion of adults and well-developed hidden stages of primary feeders. Adult stages of grain insects are particularly sensitive to mechanical impact, and this sensitivity is exploited in impacting machines used for grain entering flour mills. This device eliminates broken grains and their insect content by forced aspiration before the conditioning of grain prior to milling. In this way, the entomological content of flour and semolina is reduced to an acceptable level for the miller. This is the last chance for a grain user to eliminate an insect infestation before grain milling. Disinfestation of wheat by impact machines has been routinely used for more than 20 years in the flour and semolina industries to destroy adult insect stages before grain milling.

Inert and Abrasive Dusts For two decades, several inert dust formulations have been registered for the protection of stored grain. Diatomaceous earth (DE) and silica aerogels (and their mixture) are used in several countries as an alternative to chemical protectants, especially when grain should not be treated with chemicals (e.g., organic grain or grain intended for uses in baby food). DE is classified as a ‘generally recognized as safe’ food additive by the US EPA. It provides good protection against insect infestation in dry grain stored for a long time in flat-bed stores. Liquid formulations of DE are used in Australia and North America in sprays applied to grain storage fabrics to minimize residual infestation in grain store buildings and to limit the migration of pests into the bulk of stored grain. DE is an effective protectant when applied to the entire grain mass at a dose of 400 mg kg1 or more. However, DE is considered to have poor efficacy on grain with elevated moisture content as can be found in humid temperate countries (northern Europe, Canada, and northern Asia) where the moisture content can be as high as 14–15%. Problems associated with the use of DE in large-scale operations include: (a) machine abrasion; (b) a reduction in the bulk density (test weight), which is a criterion of grain quality used worldwide; (c) grain fluidity change; (d) decrease in qualities such as color and presence of foreign

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material; and (e) health hazards (respiratory disease hazard for the applicators).

Combined Methods Physical methods can be used simultaneously or in sequence, especially if there are synergistic effects. For instance, lowoxygen and high-CO2 (hypercarbic) atmospheres in airtight enclosures have a higher efficacy rate when temperature is elevated to levels that cause hyperactivity of target insects. Consequently, the reduction of time needed for the disinfestation process is significant even for species that are rather concentration-insensitive to carbon dioxide such as Tribolium confusum. Taking into account the very high cost of this kind of equipment and of the running costs of consumables (liquid carbon dioxide, high-pressure compressors, remote control panel, etc.), this rapid disinfestation technology is feasible only for the treatment of high-added-value food such as spices, medicinal plants, or baby food.

Decontamination of Spoiled Grain Preliminary Considerations Stored-grain molds may grow in grain with aw more than 0.65, that is, when the moisture content of cereal grain is more than 14.5% (w.b.). Some strains of the grain mold species can produce mycotoxins, which are secondary metabolites of fungi. Mycotoxins are an important issue worldwide in terms of public health for the agrofood industry with huge economic implications. The optimum temperature for growth of storedgrain molds is around 25–30 C, but some grow well at 35–37 C or above, such as Aspergillus spp. (Figure 3). Grains are contaminated by spores of storage fungi during harvest, transport, and handling operations. In storage, provided that temperature and moisture content (aw) meet their minimum requirements, fungi germinate and fungal growth occurs. The rate of growth is correlated with the levels of aw and temperature.

Mechanisms of Grain Spoilage Mycotoxins are potential hazards for human and animal consumers. Formation of mycotoxins is closely related to mold growth. Without mold growth, mycotoxins are not produced. Competition between storage fungi also influences mycotoxin production. The most hazardous toxigenic species are Aspergillus flavus and Aspergillus westerdijkiae and Penicillium verrucosum, which produce aflatoxin B1 and ochratoxin A, respectively. An infestation of stored grain by insects can also enhance the production of mycotoxins. The presence of molds on grain does not necessarily mean the presence of mycotoxins, but the potential for mycotoxin production exists. However, the absence of storage fungi in grain stored for long periods of time does not guarantee that it is free of mycotoxins. The fungal growth can be related to the fungal biomass produced by storage molds in grain. Ergosterol content is considered to be a good biochemical marker of fungal growth and represents a permanent index of mold spoilage, with or without mycotoxin production, that persists with time.

Today, with the more recent advances in molecular biology, it is possible to quantify the DNA of a target fungal species (such as Aspergillus flavus and Penicillium verrucosum) by quantitative polymerase chain reaction. This method provides information on the fungal biomass of a single species whether the strain is able to produce mycotoxin or not. It is used in particular for quantification of fungal biomass and identification of the toxigenesis potential of Fusarium spp., a group of field fungi that can produce several kinds of mycotoxins (trichothecenes, zearalenone, and fumonisins).

Decontamination Methods Once grain is contaminated with toxic fungi when prevention measures are insufficient or incorrectly applied, only a few processes of decontamination are available. Any decontamination process has its own limitations, the chemicals used to treat the products should not pose a health risk and the nutritive value should not be diminished. Consequently, unless the contaminated grain batch is of considerable value for a potential user, the first recommendation with mycotoxincontaminated grain is its complete destruction. If the conditions for decontamination of grain are favorable, it may be carried out in two different ways: (a) separation of the contaminated kernels from the sound grain and (b) inactivation of mycotoxins by physical, chemical, or biological means (detoxification). Automated mechanical separation of heavily contaminated kernels with an abnormal dark color can be achieved by photoelectric detection machines based on imaging and robotics (electronic color sorting). The screening and discarding of small shriveled kernels by density-based separation equipment may also significantly reduce the amounts of mycotoxins in grain because the most heavily infested kernels are less dense than the sound ones. A limited number of techniques are available to detoxify the mycotoxins in contaminated grain or convert them into a nontoxic derivative. Most decontamination treatments concern aflatoxin, which is the most dangerous mycotoxin. Heating and cooking under pressure can destroy most of the aflatoxin in grain, but this process cannot be applied to whole grain intended for food uses. Detoxification of oilseed cakes and corn using ammonia is a less commonly used method. It is only used for the decontamination of cereal by-products such as bran (the grain tissue most heavily contaminated) extracted from contaminated grain, and that needs to be decontaminated before being used in animal feed. Ozone treatment combined with heating (100 C) also has the potential to inactivate aflatoxin toxicity.

Future Prospects of Stored-Grain Preservation Stored-Grain Quality Maintenance The maintenance of grain quality during storage has traditionally been the responsibility of grain handlers who rely on measurements taken from samples of grain or its milled products and their specialist knowledge gained through science, common sense, and job experience. Today, treatments for preservation of grain quality may be integrated into operational systems to facilitate practical use. This basic principle connects with the

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored-Grain Pest Management modern approach of integrated quality management (IQM). IQM of stored grain can be defined as the acceptable use of practicable treatments to minimize cost-effectively the losses and damages caused by deteriorative forces (insects, mites, and microorganisms) or the consequences of poor control of grain condition (temperature manipulation, aw control by drying, dockage level, and insect infestation). Thus, decision support systems (DSSs) are indispensable to solve the issues that require experience, judgment, and a knowledge base to explain the complex deterioration processes occurring in stored grain. DSSs are considered a valuable aid to the implementation of the IQM strategy at the practical level.

The Potentialities of Computer-Aided Decision Systems Computer-support systems have continuously evolved since their first application to stored-grain pest management. DSSs are very useful tools for helping grain handlers to make optimal management decisions. Several DSSs are currently in use in stored-grain management: (a) to diagnose grain condition, (b) to predict of risks for long-term storage of grain lots, (c) as an aid in insect identification, (d) to monitor stored-grain condition and support problem solving, (e) to support the implementation of drying or cooling operations, and (f) to predict the storability prior to storage (Figure 7). Until recently, the majority of systems were devoted to pest management and to the training and education of extension workers. The latest approach involves total quality

management of stored grain. It is based on the computation of an array of causal relationships between all variables of the stored-grain ecosystem (whatever their nature and the form of the causal relationship). This approach consists of combining (i) the models of complex interactions between control and state variables of the stored-grain ‘ecosystem’ and (ii) the human experts’ subjective knowledge on the changes that will occur in grain quality criteria during storage under constant conditions. The safe storage period (grain ‘storability’) as well as the effects of different treatments (such as cooling, drying, separation of impurities, and insecticide admixture) may be predicted by such a knowledge-based system. For each described situation (grain initial condition), an output is delivered in the form of storage options with the potential to increase the safe storage period. The data collected on storedgrain condition by sensors and probes (temperature, aw or moisture content, and storage time) can also be computed to see if the stored-grain observed quality state is identical to the prediction by the DSS at any time during storage. The remote control of drying or cooling processes may also be entirely managed by DSS. Tools for automatic detection and identification of insect species at very low population density levels are now available to predict storage-insect population dynamics.

The Scientific Approach to Grain Quality Retention Grain storage managers can refer to computer-assisted DSS during grain storage. Such artificial intelligence tools enable the

INSPECTION/CCP

PREVENTIVE MEASURES

• Periodical inspections for pest presence and identification of critical points

• Preventative physical means

• Pest species identification and risk assessment

• Elimination by preventive treatments Mass trapping insects Heat disinfestation of storage facilities Limitation of insect population’s rate of increase (cooling and cleaning) Abrasive dust layer (top-dressing)

MONITORING/WARNING • Indicators for determination of the acceptable sanitary defect level for all points with a potential risk of infestation • Decision making for the timing of sanitation plans and procedures for intervention after early warning for storage issues

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• Insect proof barriers Hermetic storage bins Underground storage

DECISION SUPPORT • Integration of storage issue risk levels and solutions into a decision support system • Planning IPM program

CORRECTIVE INTERVENTIONS • Physical control methods of pests in food

• Prediction of safe storage time • Evaluation efficiency and reporting

• Passive methods Insect-proof storage equipment Inert atmosphere conditioning • Active methods Hot-air disinfestation RF and MO disinfestation Mechanical injury and impacting Combination of physical methods

Figure 7 Decision-tree diagram associated with the knowledge base of a decision support system enabling the integrated management of quality criteria of stored malting barley in relation to storage time, intervention means, and grain condition.

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Preventive actions – monitoring – risk prediction

Storage conditions to be maintained within safe limits Moisture content

Corrective actions – disinfestation

Biodeterioration risk prediction Biodeterioration risks to be controlled Physiological activity of seed embryo

Aw

Fungal microflora growth rate

Impurities

Viability loss

Microflora spoilage

Temperature Insect species dynamics

Grain cleaning

Grain drying

Grain cooling

Pests and molds monitoring

Insect multiplication

Corrective interventions

Figure 8 Integrated management of global quality of stored grain by HACCP and IPM strategies implementation through a decision support system. Reproduced from Ndiaye and Fleurat-Lessard (1999) Diagnosis and grading of wheat grain initial quality by a computerised decision support system. In: Zuxun Jin, Liang Quan, Liang Yongsheng, Tan Xianchang, Guan Lianghua (Eds.), Proceedings 7th International Working Conference on Stored Product Protection, 14-19 Oct. 1998, Beijing (P.R. China). Chengdu: Sichuan Publishing House of Science & Technology, Vol. II, pp. 1923–1934.

grain handler to (a) understand the causes and economic consequences of changes in the quality of grain bulk, (b) forecast changes in quality, (c) receive support in problem solving, and (d) propose optimal storage strategies (Figure 8). It is hoped that in the near future, this methodology, which has already been applied to the maintenance of quality of malting barley will be expanded to include the management and control of all types of cereal grains.


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What are the main biotic factors that cause deterioration in quality during grain storage? What are the main methods of managing insect pests of stored grain or seeds? Can grain be treated with residual insecticides to control insect infestation? What are CAs and how are they used for grain insect pest control? Why was the development of irradiation or ionization of grains not practical? Is grain heating an acceptable means of grain disinfestation? What is the main storage operation (or intervention) that can stop mold spoilage in stored grain? What are the components of an IPM approach to insect pest population management in grain? What are the major components of an IPM program for safe grain storage?


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What are the two very different types of chemicals most currently used for insect control in stored grain?

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Why do some pesticides used in stored-grain protection against insect pests leave residues in grain? Why doesn’t disinfestation of stored-grain insect by fumigation leave residues after treatment? What are the decontamination methods or processes that can reduce mycotoxin content in grain partly invaded by mycotoxigenic fungi? What are the main drawbacks of heat disinfestation of grain? Is it possible to disinfest grain using MV or RF fields? What are the conditions required to achieve insect control by anaerobic or low-oxygen atmosphere application in stored grain?

See also: Grain Harvest, Storage and Transport: Chemicals for Grain Production and Protection; Contaminants of Grain; Handling from Farm to Storage Terminal; Postharvest Operations for Quality Preservation of Stored Grain; Stored Grain: Invertebrate Pests; Wheat: Harvesting, Transport, and Storage.

Further Reading Annis PC (1987) Towards rational controlled atmosphere dosage schedules: A review of current knowledge. In: Donahaye EJ and Navarro S (eds.) Proceedings 4th International Working Conference on Stored Product Protection. Tel-Aviv, Israe¨l, September 1986, pp. 128–148. Asher P (2014) Facilitating safe fumigation with QuickPHlo-R phosphine generators. IOBC-IPSP 2013 Conference, Bordeaux, July 2013. IOBC/Wprs Bulletin (Special issue 2014). Basavaraja H, Mahajanashetti SB, and Udagatti NC (2007) Economic analysis of postharvest losses in food grains in India: A case study of Karnataka. Agricultural Economics Research Review 20: 117–126. Beckett SJ, Fields PG, and Subramanyam B (2007) Disinfestation of stored products and associated structures using heat. In: Tang J, Mitcham E, Wang S, and Lurie S (eds.) Heat Treatments for Postharvest Pest Control, pp. 182–237. Wallingford: CAB International. Bell CH (2000) Fumigation in the 21st century. Crop Protection 19: 563–569.

GRAIN HARVEST, STORAGE AND TRANSPORT | Stored-Grain Pest Management Bond EJ (1998) Manual of Fumigation for Insect Control. Rome: FAO, Plant Production and Protection, Paper No. 54. Collins PJ, Lambkin TM, Bridgeman PW, and Pulviranti C (1993) Resistance to grainprotectant insecticides in coleopterous pests of stored cereals in Queensland, Australia. Journal of Economic Entomology 86: 239–245. Das I, Kumar G, and Shah NG (2013) Microwave heating as an alternative quarantine method for disinfestation of stored food grains. International Journal of Food Science 2013. Article ID 926468, 13 phttp://dx.doi.org/10.1155/2013/926468. Ducom PF, Fre´rot E, and Reichmuth C (2014) Relative importance of fumigation in integrated management of stored-grain insect pests in some EU countries (France and Germany). IOBC-IPSP 2013 Conference, Bordeaux, July 2013. IOBC/Wprs Bulletin. 98: 275–294. Fields PG (1992) The control of stored-product insects and mites with extreme temperatures. Journal of Stored Products Research 28: 89–118. Field PG and Muir WE (1995) Physical control. In: Subramanyam Bh and Hagstrum D (eds.) Management of Insects in Stored Products, pp. 195–222. New York: Marcel Dekker Inc. Fleurat-Lessard F (2001) Control of insects in post-harvest: Radiofrequency and microwave heating. In: Vincent C, Panneton B, and Fleurat-Lessard F (eds.) Physical Control Methods in Plant Protection, pp. 162–173. Berlin/Paris: SpringerVerlag/INRA Editions. Fleurat-Lessard F (2011) Monitoring for insect pest populations in grain storage: The European context. Stewart Postharvest Review 7(3) http://dx.doi.org/10.2212/ spr.2011.3.4. Golen J van and Vroom N (2008) EcO2 Controlled Atmosphere; low-oxygen disinfestation of post harvest commodities, structures, silos and (export/import) containers. Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Orlando, FL, USA, 11–14th November, pp. 123-1–123-6. Hallman GJ (2013) Control of stored product pests by ionizing radiation. Journal of Stored Products Research 52: 36–41. Hodges RJ, Buzby JC, and Benett B (2011) Postharvest losses and waste in developed and less developed countries: Opportunities to improve resource use. Journal of Agricultural Science 149: 37–45. Jagadeesan R, Collins PJ, Daglish GJ, Ebert PR, and Schlipalius DI (2012) Phosphine resistance in the rust red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae): Inheritance, gene interactions and fitness costs. PLoS One 7(2): e31582. http://dx.doi.org/10.1371/journal.pone.0031582. Khatchatourian OA and de Oliveira FA (2006) Mathematical modelling of airflow and thermal state in large aerated grain storage. Biosystems Engineering 95: 159–169. Korunic Z (1998) Diatomaceous earth, a group of natural insecticides. Journal of Stored Products Research 34: 87–97. Lacey J, Hill ST, and Edwards MA (1980) Micro-organisms in stored grains: Their enumeration and significance. Tropical Stored Products Information 39: 19–32. Le Goupil M (1932) Les proprie´te´s insecticides du bromure de me´thyle. Revue de Pathologie Ve´ge´tale et d’Entomologie Agricole 19: 169–172. Mourier H and Poulsen KP (2000) Control of insects and mites in grain using a high temperature/short time (HTST) technique. Journal of Stored Products Research 36: 309–318. Navarro S and Calderon M (1982) Aeration of Grain in Subtropical Climates. Rome: FAO, Agricultural Services Bulletin No. 52. Nayak MK and Collins PJ (2008) Influence of concentration, temperature and humidity on the toxicity of phosphine to the strongly phosphine-resistant psocid Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae). Pest Management Science 64: 971–976. Ndiaye A and Fleurat-Lessard F (1999) Diagnosis and grading of wheat grain initial quality by a computerised decision support system. In: Zuxun Jin, Liang Quan, Liang Yongsheng, Tan Xianchang, Guan Lianghua (Eds.), Proceedings 7th International Working Conference on Stored Product Protection, 14-19 Oct. 1998,

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Beijing (P.R. China). Chengdu: Sichuan Publishing House of Science & Technology, Vol. II, pp. 1923–1934. Opit GP, Phillips TW, Aikins MJ, and Hasan MM (2012) Phosphine resistance in Tribolium castaneum and Rhyzopertha dominica from stored wheat in Oklahoma. Journal of Economic Entomology 105: 1107–1114. Phillips TW and Throne JE (2010) Biorational approaches to managing stored-product insects. Annual Review of Entomology 55: 375–397. Pimentel MAG, Faroni LRD’A, Guedes RNC, Neto AP, and Garcia FM (2006) Phosphine resistance, respiration rate and fitness consequences in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). In: Lorini et al. (eds.) Proceedings 9th International Working Conference on Stored Product Protection. Campinas, Brazil, 15–18 October, pp. 344–351. Qaisrani R and Banks J (2000) The prospects for heat disinfestation of grain. Proceedings of Australian Postharvest Technical Conference 2000, pp. 60–65. Subramanyam B and Hagstrum DW (1996) Integrated Management of Insects in Stored Products. New York: Marcel Dekker. Thorpe GR (1994) Modelling heat and mass transfer phenomena in bulk stored grains. In: Highley E, Wright EJ, Banks HJ, and Champ BR (eds.) Proceedings 6th International Working Conference on Stored Product Protection, Canberra, Australia, April, pp. 359–367. Wallingford, UK: CABI Publishing. Thorpe GR (2008) The application of computational fluid dynamics codes to simulate heat and moisture transfer in stored grains. Journal of Stored Products Research 44: 21–31. Vadivambal R, Deji OF, Jayas DS, and White NDG (2010) Disinfestation of stored corn using microwave energy. Agriculture and Biology Journal of North America 1: 18–26. http://www.scihub.org/abjna. Vincent C, Weintraub P, Hallman G, and Fleurat-Lessard F (2008) Insect management with physical methods in pre- and post-harvest situations. In: Radcliffe EB, Hutchison WD, and Cancelado RE (eds.) Integrated Pest Management: Concepts, Tactics, Strategies and Case Studies, pp. 309–323. Cambridge: Cambridge University Press. Warrick C (2013) Aerating stored grain – Cooling or drying for quality control; a grains industry guide. Grain Research and Development Corporation Ed. www.storedgrain. com.au Kingston ACT, Australia, 18 p.

Relevant Websites http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id¼5985#Operating% 20Costs – cooling aeration in grain storage. http://www.codexalimentarius.net/pestres/data/index.html – Codex pesticides residues in food and feed database. http://ec.europa.eu/food/plant/plant_protection_products/pesticides_database/ index_en.htm – EU pesticides database. http://ec.europa.eu/food/plant/pesticides/legislation/index_en.htm – EU legislation on pesticides. http://en.wikipedia.org/wiki/Stockholm_Convention_on_Persistent_Organic_ Pollutants – List of banned pesticides worldwide because considered as POPs. http://extension.entm.purdue.edu/publications/E-66.pdf – Purdue University Extension. Stored grain insect pest management. https://www.grainscanada.gc.ca/storage-entrepose/mqsgm-mgqge-eng.htm – Canadian Grain Commission. Manage stored grain: Maintain quality and manage insect infestations. http://npic.orst.edu/reg/regfed.html – Federal Pesticide regulation in the USA. http://publications.hgca.com/publications/documents/G52_Grain_storage_guide_ 3rd_edition.pdf – Home Grown Cereal Authority, UK. Grain storage guide. http://pubs.ext.vt.edu/456/456-016/Section_4_Insects-12.pdf – Clemson University, South Carolina. Stored grain insect pest management.


Contents Implication of Climate Changes Sustainable Grain Production and Utilization Organic Grain Production and Food Processing Precision Agriculture Plants: Diseases and Pests Wheat: Agronomy Barley: Agronomy Maize: Agronomy Sorghum: Production and Improvement Practices Canola: Agronomy Chickpea: Agronomy Lentil: Agronomy Lupin: Agronomy Field Pea: Agronomy Soybean: Agronomy Natural Disease Control in Cereal Grains Wheat: Biotrophic Pathogen Resistance Necrotrophic Pathogens of Wheat

Implication of Climate Changes S Ceccarelli, Via delle Begonie 2, Ascoli Piceno, Italy ã 2016 Elsevier Ltd. All rights reserved.

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Topic Highlights

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Climate changes have occurred and are occurring. The amount of changes in temperature and rainfall is still uncertain. Climate changes affect different regions, agroecologies, and people differently. Agriculture is vulnerable to climate changes and food insecurity will increase. Industrial agriculture contributes to climate changes through direct and indirect greenhouse gas emissions amounting to about 30% of the total human-made greenhouse gas emissions. Yields of wheat, maize, rice, and soybean are stagnating or collapsing in more than a quarter (24–39%) of the respective growing areas. Biodiversity is essential for food security and adaptation of crops to climate changes. Modern plant breeding produces uniform and genetically related varieties. Genetically modified organisms cannot be the sole solution to climate changes because they are the negation of the fundamental theorem of natural selection.

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Evolutionary plant breeding is a dynamic and inexpensive methodology to adapt crops to climate changes.

Learning Objective

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To achieve understanding that growing diversity may feed the world in a sustainable way.

Introduction Today, nobody questions whether climate changes are occurring or not, and actually, several climate scientists believe that global warming is a worse problem than they thought a few years ago. Predicting the implications and the impact of climate changes is complicated by the large degree of uncertainty that exists even at the macrolevel about the entity of such changes. For example, although the National Center for Atmospheric Research (NCAR) model of the United States and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) model of Australia project higher temperatures in 2050,


http://dx.doi.org/10.1016/B978-0-12-394437-5.00201-1

AGRONOMY OF GRAIN GROWING | Implication of Climate Changes resulting in higher evaporation and increased precipitation, substantial differences exist across the two models. The ‘wetter’ NCAR model estimates average precipitation increases on land of about 10%, whereas the ‘drier’ CSIRO model estimates increases of about 2%. Furthermore, the NCAR model has substantially higher average maximum temperatures than does the CSIRO. The CSIRO model has substantial precipitation declines in the western Amazon while the NCAR shows declines in the eastern Amazon. The NCAR model has higher precipitation in Sub-Saharan Africa than does the CSIRO. The impacts of climate change will be distributed differently among regions, generations, age classes, income groups, occupations, and genders. Climate change is expected to affect men and women differently because of their different access to assets, opportunities, and decision-making spaces. Gender inequalities, in many developing countries, limit rural women’s options of migrating to look for off-farm employment, therefore making their livelihoods dependent on climate-sensitive sectors such as agriculture. The feminization of agricultural labor is an increasing phenomenon worldwide. Yet, the majority of the rural women have limited access to productive resources (e.g., land, water, and seed) to farm. Using the results from formal economic models, it has been estimated that, in the absence of effective counteraction, the overall costs and risks of climate change will be equivalent to a 5% decrease in global gross domestic product (GDP) each year. If a wider range of risks and impacts are taken into account, the estimates of damage could rise to a 20% decrease in GDP or more, with a disproportionate burden and increased risk of famine on the poorest countries. Agriculture is extremely vulnerable to climate change. Higher temperatures eventually reduce crop yields without discouraging weed, disease, and pest challenges. Changes in precipitation patterns increase the likelihood of short-term crop failures and long-term declines in production. Although there will be gains in some crops in some regions of the world, the overall impacts of climate change on agriculture are expected to be negative, threatening global food security. Food insecurity will probably increase under climate change, unless early warning systems and development programs are used more effectively. Currently, millions of hungry people subsist on what they produce. If climate change reduces production while population increases, there is likely to be more hunger. Lobell et al. showed that increasing temperatures and declining precipitation over semiarid regions are likely to reduce yields for maize, wheat, rice, and other primary crops in the next two decades. These changes could have a substantial negative impact on global food security. It has now been shown that the most potentially devastating impact of the industrial type of agricultural production is its contribution to increased greenhouse gas emissions. Field-level practices represent approximately 15% of the total human-made greenhouse gas emissions, and the production of fertilizers, herbicides, and pesticides; the tillage, irrigation, and fertilization; and the transport, packaging, and conservation of food result in an additional 15–17% of the total man-made greenhouse gas emissions attributable to food systems. The changing climate conditions of the past 30 years already appear to have offset a significant portion of the increases in average yields that arose from technology, carbon dioxide fertilization, and other factors.

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The evidence is mounting that the yield of some major crops, such as wheat, rice, maize, and soybean, which together produce nearly 64% of the agricultural calories, never improved, are stagnating, or are collapsing in more than a quarter (24–39%) of the respective growing areas. Under a business-as-usual scenario, we can anticipate an average of 2% productivity decline over each of the coming decades, with yield changes in developing countries ranging from 27 to þ9% for the key staple crops. Adaptation has emerged as a central area in climate change research, in country-level planning, and in the implementation of climate change strategies. The adaptation to climate changes cannot come solely from genetically modified crops. Genetically modified organisms (GMOs) were successfully produced for the first time 30 years ago and genetically modified (GM) crops have promised to deliver a second green revolution: a wealth of enhanced foods, fuels, and fibers that would feed the starving, deliver profits to farmers, and promote a greener environment. A number of scientists even suggested the use of molecular breeding, as well as molecular genetic modification, to adapt our existing food crops to increasing temperatures, decreased water availability in some places, and flooding in others. These statements ignore one main undisputable weakness of GM crops, which is the same weakness of varieties produced by conventional methods that carry a single gene resistance to a specific pest (disease, insect, or weed): They ignore one fundamental biological principle, namely, the fundamental theorem of natural selection (FTNS). While this strictly applies to the GM crops developed for resistance to diseases, insects, and weeds, it applies also to resistance to drought and high temperature, which are complex characters based on several genes and therefore out of range for current and future GM technologies. One of the major implications of climate changes is the need for a major shift in agricultural research from the industrial type of agriculture to agroecological modes of production. However, although the industrial type of agriculture is considered one of the major threats to biodiversity, and that biodiversity is considered to be essential for food security, modern plant breeding, which is supposed to produce varieties better adapted to climate changes, continues to pursue the production of uniform varieties. The tendency of modern plant breeding toward uniform varieties appears the opposite of what the world would need to cope with climate changes and the increasing frequency of unusual weather events. Climate changes pose an interesting challenge to plant breeders because, contrary to the usual target objectives of a breeding program, it represents a ‘moving target.’ A strategy to cope with such a challenge, which could also maintain and increase agricultural biodiversity, is evolutionary plant breeding (EPB). The idea is not new. In 1929, Harlan and Martini proposed the composite cross (CC) method of breeding barley. In 1956, Suneson further developed the idea into a formal ‘evolutionary plant breeding method.’ The method consists in constituting, for the various crops, mixtures of very many different genotypes of the same crops, preferably but not necessarily, using early segregating

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generations and also landraces, gene bank accessions, etc. These populations will be planted and harvested, and due to the natural crossing (higher in some crops and lower in others; see succeeding text), the genetic composition of the mixture that is harvested will never be the same as the genetic composition of the mixture that was planted. In other words, the mixture will evolve to become progressively better adapted to the environment (soil type, soil fertility, agronomic practices, rainfall, temperature, photoperiod, etc.) in which it is grown. As the climatic conditions vary from one year to the next, the genetic makeup of the mixture will fluctuate, but if the tendency is toward hotter and drier climatic conditions, the genotypes better adapted will become progressively more frequent in the population. One of the issues is whether this methodology can work for self-pollinated crops, which include some of the most important food crops such as wheat, rice, barley, grain legumes, and crops of potential interest in the future for their nutritional value such as sorghum and millets. This issue has been addressed, indirectly, by an experiment conducted by Morran et al. who used experimental evolution to test the hypothesis that outcrossing organisms are able to adapt more rapidly to environmental changes than self-fertilizing organisms. The experiment of Morran et al. suggests that even at extremely low outcrossing rates (e.g., <0.05) and therefore comparable with those observed in self-pollinated crops such as wheat, and some millets, allows adaptation to stressful conditions. Even though obtained on a nematode, this experiment shows that EPB has the potential of adapting self-pollinated crops to climate change even though at a slower speed than in cross-pollinated crops. The speed with which these populations evolve and adapt depends, among other factors, on the intensity of stress imposed: In the case of a severe stress, selection may be so strong that only rare mutants with extreme, perhaps innovative, phenotypes can survive the stress. The disadvantage of a too strong selection pressure is that it may reduce the diversity such that the population will not be able to adapt to additional stress factors. When selection is less stringent, more genetic diversity can usually be sustained, which allows more adaptive opportunities for the population. It has been shown experimentally that environmental variation, for example, from year to year, simultaneously influences the strength of natural selection and the genetic variability. The study demonstrated that selection and genetic variance vary dramatically across environments. Harsh environmental conditions are associated with strong selection but low genetic variance and vice versa. Consequently, the potential for microevolution in the evolutionary populations could be constrained by either a lack of heritable variation (in poor environments) or a reduced strength of selection (in good environments). However, in several crops, there is not a consistent relationship between the level of grain yield, used as an indicator of the level of stress, and heritability and therefore potential for microevolution. Another factor, which is likely to affect the speed of adaptation, is the type of germplasm: The hypothesis is that populations made solely or predominantly of local landraces might evolve faster than populations made solely or predominantly of exotic germplasm. The simplest and cheapest way of implementing an evolutionary breeding program is to plant and harvest in locations representative of the target population of environments and, with the farmer management, a large mixture as, for example,

indicated by Ceccarelli; the population can be moved to other farmers’ fields in other locations, affected by different stresses or different combinations of stresses. While the base population is evolving, selection can be practiced to obtain improved subpopulations (OP varieties), inbred lines to produce hybrids, etc., thus deriving a flow of continuously better adapted improved varieties. Thus, EPB reconciles agrobiodiversity (because the population will evolve differently in different locations), sustainable production increases (based on the amount of inputs farmers can afford), and adaptation to climate changes (as a result of the evolutionary process). EPB assumes that while the base population evolves, it maintains sufficient genetic diversity for the evolution to proceed. However, it can also accommodate the injection of novel genetic diversity any time it is required. Evolutionary populations of different crops are currently grown by farmers in Jordan, Ethiopia, Iran, Italy, France, Portugal, and India for cereal crops (maize, barley, bread and durum wheat, and rice), grain legumes (common bean), and horticultural crops (tomato and summer squash). Farmers growing these populations report higher yields, lower weed infestation and disease presence, and lower insect damages. The use of pesticides has consequently been reduced. Iranian farmers growing evolutionary populations of barley and wheat have found that the barley evolutionary population had more protein than the local improved variety. In the case of wheat, farmers and bakers have been even marketing the bread obtained from the flour of the evolutionary population in local artisanal bakeries. Farmers growing evolutionary populations in France and Italy confirmed that creating mixtures brings not only greater yield stability but also greater aroma and quality to the bread. Research activities on evolutionary populations are ongoing in a number of European countries. Evolutionary populations, when made up of a mixture of germplasm accessions from a gene bank, offer a way to allow gene bank collections to evolve; while in the mixtures, the accessions will lose their identity, their alleles will be allowed to recombine and the collection to evolve. Samples of these types of evolutionary populations can be stored in the gene bank on an annual basis, thus ‘conserving evolution.’ Evolutionary populations can also be used as experimental material to address a number of researchable questions such as the change in frequency of mapped molecular markers over subsequent cycles of evolution in contrasting environments, the efficiency of different breeding strategies (specific adaptation vs. wide adaptation), and the values of different types of evolutionary populations (only landraces, only modern germplasm, or a mixture of the two) in generating novel genotypes for the different target environments where the crop is grown.


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What are the expected impacts of climate change? Why is biodiversity important? What are the current trends in agricultural production? What is the major weakness of GM crops? Explain the fundamental theorem of natural selection What are the theoretical bases of EPB? How fast do evolutionary populations evolve and adapt?

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Why is bread made from the flour obtained by a mixture, rather than from a single variety, expected to be healthier (Dinelli, G., Carretero, A.S., Di Silvestro, R., Marottia, I., Fu, S., Benedettelli, S., Ghiselli L., Gutie´rrez, A.F., 2009. Determination of phenolic compounds in modern and old varieties of durum wheat using liquid chromatography coupled with time-of-flight mass spectrometry. J. Chromatogr. A 1216, 7229–7240)? What are the recent evidences that conventional plant breeding is not able to adapt crops to drought (Lobell, D.B., Roberts, M.J., Schlenker, W., Braun, N., Little, B.B., Rejesus, R.M., Hammer, G.L., 2014. Greater sensitivity to drought accompanies maize yield increase in the U.S. Midwest Sci. 344, 516–519)? What additional evidence can be used to support evolutionary plant breeding (Wolf, J.B.W., Lindell, J., Backstro¨m, N., 2010. Speciation genetics: Current status and evolving approaches. Philos. Trans. R. Soc. Biol. Sci. 365, 1717–1733; Do¨ring, T.D., Knapp, S., Kovacs, G., Murphy, K., Wolfe, M.S., 2011. Evolutionary plant breeding in cereals—into a new era. Sustainability 3, 1944–1971)?

See also: Breeding of Grains: Barley: Genetics and Breeding; Food Grains and the Consumer: Consumer Trends in Grain Consumption; Cultural Differences in Processing and Consumption; Genetically Modified Grains and the Consumer; Grains and Health: Misinformation and Misconceptions; Grains and Health; Food Grains and Well-being: Functional Foods: Overview; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Cereal Grains: Cereals: Domestication of the Cereal Grains; Wheat-Based Foods: Breads.

Further Reading Aguilar, L., 2009. Training manual on gender and climate change. IUCN and UNDP. http://cmsdata.iucn.org/downloads/eng_version_web_final_1.pdf. Alexandratos, N., Bruinsma, J., 2012. World agriculture towards 2030/2050: the 2012 revision. ESA Working paper No. 12-03. FAO, Rome. Altieri, M.A., Koohafkan, P., 2003. Enduring Farms: Climate Change, Smallholders and Traditional Farming Communities. Third World Network, Penang, 72 p. Barrick JE and Lenski RE (2013) Genome dynamics during experimental evolution. Nat. Rev. Genet. 14: 827–839. Brown ME and Funk CC (2008) Food security under climate change. Science 319: 580–581. Cardinale BJ, Duffy JE, Gonzalez A, Hooper DU, Perrings C, Venail P, Narwani A, Mace GM, Tilman D, Wardle DA, Kinzig AP, Daily GC, Loreau M, Grace JB, Larigauderie A, Srivastava DS, and Naeem S (2012) Biodiversity loss and its impact on humanity. Nature 486: 59–67. Ceccarelli S (1996) Adaptation to low/high input cultivation. Euphytica 92: 203–214. Ceccarelli S (2009) Evolution, plant breeding and biodiversity. J. Agric. Environ. Int. Dev. 103: 131–145. Ceccarelli S (2014a) GMO, organic agriculture and breeding for sustainability. Sustainability 6: 4273–4286. Ceccarelli S (2014b) Dought. In: Jackson M, Ford-Lloyd BV, and Parry ML (eds.) Plant Genetic Resources and Climate Change, pp. 221–235. Wallingford: CABI International.

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Ceccarelli S, Grando S, Maatougui M, Michael M, Slash M, Haghparast R, Rahmanian M, Taheri A, Al-Yassin A, Benbelkacem A, Labdi M, Mimoun H, and Nachit M (2010) Plant breeding and climate changes. J. Agric. Sci. 148: 1–11. Ceccarelli S, Galie A, and Grando S (2013) Participatory breeding for climate changerelated traits. In: Chittaranjan C (ed.) Genomics and Breeding for Climate-Resilient Crops, vol. 1, pp. 331–376. Berlin: Springer. De Schutter, O., 2014. Final report: the transformative potential of the right to food. Report of the Special Rapporteur on the right to food, Olivier De Schutter. United Nations General, Assembly, A/HRC/25/57, p. 28. Do¨ring TD, Knapp S, Kovacs G, Murphy K, and Wolfe MS (2011) Evolutionary plant breeding in cereals – into a new era. Sustainability 3: 1944–1971. Editorial (2013) Tarnished promise. Nature 497: 21. Fedoroff NV, Battisti DS, Beachy RN, Cooper PJM, Fischhoff DA, Hodges CN, Knauf VC, Lobell D, Mazur BJ, Molden D, Reynolds MP, Ronald PC, Rosegrant MW, Sanchez PA, Vonshak A, and Zhu J-K (2010) Radically rethinking agriculture for the 21st century. Science 327: 833–834. Galie` A (2013) Empowering women farmers: the case of participatory plant breeding in ten Syrian households. Frontiers: A Journal of Women’s Studies 34(1): 58–92. Gepts P (2006) Plant genetic resources conservation and utilization: the accomplishment and future of a societal insurance policy. Crop Sci. 46: 2278–2292. Grantham J (2012) Be persuasive. Be brave. Be arrested (if necessary). Nature 491: 303. Grassini P, Eskridge KM, and Cassman KG (2013) Distinguishing between yield advances and yield plateaus in historical crop production trends. Nat. Commun. 4: 1–11. Hansen J, Kharecha P, Sato M, Masson-Delmotte V, Beerling DJ, Hearty PJ, HoeghGuldberg O, Hsu S-L, Ackerman F, Parmesan C, Rockstrom J, Rohling EJ, Sachs J, Smith P, Steffen K, Van Susteren L, von Schuckmann K, and Zachos JC (2013) Assessing “dangerous climate change”: required reduction of carbon emissions to protect young people, future generations and nature. PLoS One 8(12): e81648. http://dx.doi.org/10.1371/journal.pone.0081648. Harlan HV and Martini ML (1929) A composite hybrid mixture. J. Am. Soc. Agron. 21: 487–490. Herrera-Estrella L, Depicker A, Van Montagu M, and Schell J (1983) Expression of chimeric genes transferred into plant cells using a Ti-plasmid-derived vector. Nature 303: 209–213. Hooper DU, Adair EC, Cardinale BJ, Byrnes JEK, Hungate BA, Matulich KL, Gonzalez A, Duffy JE, Gamfeldt L, and O’Connor MI (2012) A global synthesis reveals biodiversity loss as a major driver of ecosystem change. Nature 486: 105–108. IPCC (Intergovernmental Panel on Climate Change) (2007) The physical science basis: summary for policymakers. Geneva: IPCC Secretariat. Lobell DB, Burke MB, Tebaldi C, Mastrandrea MD, Falcon WP, and Naylor RL (2008) Prioritizing climate change adaptation needs for food security in 2030. Science 319: 607–610. Lobell DB, Schlenker W, and Costa-Roberts J (2011) Climate trends and global crop production since 1980. Science 333: 616–620. Morran LT, Parmenter MD, and Phillips PC (2009) Mutation load and rapid adaptation favour outcrossing over self-fertilization. Nature 462: 350–352. Nelson GC, Rosegrant MW, Koo J, Robertson R, Sulser T, Zhu T, Ringler C, Msangi S, Palazzo A, Batka M, Magalhaes M, Valmonte-Santos R, Ewing M, and Lee D (2009) Climate change: impact on agriculture and costs of adaptation. Washington, DC: International Food Policy Research Institute. Rahmanian, M., Salimi, M., Razavi, K., Haghparast, R., Ceccarelli, S., 2014. Living Gene Banks in Farmers Fields. Farming Matters, March 2014, 12–15. Ray DK, Ramankutty N, Mueller ND, West PC, and Foley JA (2012) Recent patterns of crop yield growth and stagnation. Nat. Commun. 3: 1–7. Shaw RG and Shaw FH (2014) Quantitative genetic study of the adaptive process. Heredity 112: 13–20. Skinner, E., 2011. Gender and climate change: overview report. Institute of Development Studies (IDS). http://www.bridge.ids.ac.uk/vfile/upload/4/document/1111/ CC_OR_FINAL.pdf. Stern, N., 2005. Stern review on the economics of climate change. http://www.hmtreasury.gov.uk/independent_reviews/stern_review_economics_climate_change/ stern_review_Report.cfm. Suneson CA (1956) An evolutionary plant breeding method. Agron. J. 48: 188–191. Vermeulen S, Campbell B, and Ingram J (2012) Climate change and food systems. Annu. Rev. Environ. Resour. 37: 195–222. Wilson AJ, Pemberton JM, Pilkington JG, Coltman DW, Mifsud DV, Clutton-Brock TH, and Kruuk LEB (2006) Environmental coupling of selection and heritability limits evolution. PLoS Biol. 4(7): e216. http://dx.doi.org/10.1371/journal.pbio.0040216. World Bank, FAO, IFAD, 2009. Gender in Agriculture Sourcebook. World Bank, Washington, DC, 764 p, doi:10.1596/978-0-8213-7587–7.

Sustainable Grain Production and Utilization L Munck, University of Copenhagen, Frederiksberg C, Denmark ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Environmental sustainability benefits more from investments in agricultural infrastructure than it does from investments in green house gas reduction. Carbon dioxide and radiation from the sun produces the plants and oxygen that are the basis for life and food. Clean water is a limiting factor for agricultural production and human life. Multivariate soft mathematical models are necessary for understanding the performance of self-organized chaotic systems from the climate and weather to the plant cell and grain biological individual. Gene technology (genomics) integrated by new instrumental methods to overview the phenotype (phenomics) is an indispensable analytical strategy to unravel the complexity and global effect of gene expression and regulative crosstalk within and between different cells and organisms in interaction with the natural and man made influences on environment. There is an increasing new insight into how biological networks function from the new integrated instrumental strategy that is evaluated by soft mathematical models (chemometrics). It is now revealed how the metabolism of whole cells and tissues are performing in a grain plant when new genes are introduced and how the plant on the molecular and phenomic level is meeting the challenges of climate, soil microbiology, pests, weeds, and food quality. The same methods can be used to reveal the resulting impact on health of humans. A reformed strategy for the development of Genetic Manipulated Organisms (GMO) to increase biodiversity in grains by integrated breeding for biological control is a major tool for a sustainable intensification to meet the challenges of producing enough foods and feeds for the rapidly growing human population. The new adapted plants should be exploited by a new field technology avoiding chemical pollution, conserving energy, water and soil mitigating the increasingly erratic environment and climate. It is not sustainable to use food and feed grains for energy. Lignocelluloses from grain plants can be used in industrial biorefineries and biogas units to produce manufactured products, methanol fuel, energy, and a dry rest that can be recycled as a fertilizer to improve soil fertility. Green cities with integrated plant production maintain a better environment for living organisms such as bees than extreme rural monocultures do today. The present world agricultural grain production could feed about 14 billion people if those people converted to vegetarianism.

Learning Objectives

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The sustainability of grain production and use requires a systems approach to improving infrastructure with regard

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to the many different supportive functions discussed in the article. For this reason, we must simultaneously consider several topics together in creating an integrated solution. To be successful it should be compatible by the way Nature presents a change as a whole multifaceted emergent event guided by Natural Selection. Nature is overwhelmingly complex and creative, as expressed by the interactions between life and climate. Thus, we must respect the inherent uncertainty of emerging events in nature by monitoring and pragmatically to adjust to the surprising changes in our environment. It must be communicated to the public that science today have a quite new tool to evaluate complex problems e.g., to safeguard GMO by an integrated analytical technology exploiting megavariate data from new automated instruments. Now data from genomics (DNA) is in an integrated dialogue with those from the whole plant (phenomics) and with close connection to environmental data including toxicology. This dialogue between huge datasets is performed in computers by soft megavariate data analysis (chemometrics). It is now possible to define why one should avoid the first extreme applications of GMO and how beneficial uses of GMO crucial for increasing biodiversity should be certified. Parts of sustainable infrastructures are now thanks to research and development, available as principles and partly realized inventions. However, they have not yet been combined into full scale locally optimized working systems that can fully adapt to the very different conditions that characterize planet earth. The world economy and the technological possibilities have never been better suited to improve sustainability in human life. Therefore, it is unfortunate that trade, industry, and related governmental research programs do not fully see the business opportunities in investing in the development of a new sustainable infrastructure. If investors could see the great options available, the resulting actions would be selfcatalyzing and create a greatly improved sustainable infrastructure with new industries and employment opportunities, as well as an informed public.

Consequences of Increasing Human Global Dominance by Technology and Population Growth In the globalized human world, with population expansion increasingly driven by focused technology, the scientific community and the public are increasingly calling for CO2 reduction to reduce global warming. The average CO2 level has been constantly rising from 320 ppm in 1960 to about 400 ppm in 2014 because of the abundant use of fossil fuels. CO2 concentration in the atmosphere is an excellent marker for the degree of human intervention on the planet, if just one figure is preferred. However, for example, the book Fragile Earth, which


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AGRONOMY OF GRAIN GROWING | Sustainable Grain Production and Utilization surveys the globe with aerial photos accompanied by short comments, provides a much more informative and multifaceted view of the precarious state of the human invasion of Earth than the reductionist compression to just one CO2 figure. There is a serious drawback to the present negative focus in public on the increase of CO2 as an environmental threat. With over 50% of the world’s population now living in cities, Nature seems far away, and few are aware of the consequences of the fundamental life-giving function of CO2. People seem to forget that this gas, when included in the photosynthesis of of plants catalyzed by the radiation from the sun, is the origin of all cells and energy that are building higher living organisms as well as all the oxygen we breathe. The wellbeing of plants and the efficiency of the photosynthesis process to absorb CO2 and to supply oxygen are the basis for human foods and existence in a sound global ecology. Since the introduction of agriculture, grains have been the dominating food product, and they will continue to be. Before the eleventh millennium BC, the global human population of hunters and gatherers was estimated to number 3–15 million. When agriculture introduced grain production by traditional methods, it boosted the global human population up to 800 million by 1800. Since then, two centuries of agricultural industrialization, driven by fossil fuels (e.g., producing nitrogen fertilizers) and plant breeding through the Green Revolution, have remarkably increased grain yields, now providing food and feed for more than 7 billion people. Time-sequenced aerial photos of sites around the world show that utilization of land by agriculture and urbanization have vast environmental consequences, such as depleting and polluting the sparse fresh water resources vital for drinking water and agriculture. Of the 150 million square kilometer land above sea level, about 11.3% is under plow; 26.3% is grassland; 29.3% is forest; 31.5% is desert, ice, and mountain land; and 1.6% is urban settlements. It now seems that the maximal area of arable land has decreased, considering the rapidly increasing urban area. Today, the approximately 2.5 billion tonnes per year of cereals, legumes, and brassica grains constitute a thread of life – the major renewable source for food, feed, manufacturing, and energy. It will continue to have this status in the future if humankind succeeds in maintaining an environment and climate that are friendly to plants by learning and benefitting from nature’s self-organizing principles in order to enable a sustainable intensification of grain production and utilization.

Focusing on the Soft Principles of Self-Organization to Reform the Scientific Hard Mathematical–Technological View of Autonomous Nature That Dominates Public Perception Life is self-organizing, involving the continuous, dynamic adaptation of function and form among biological species through the natural selection – a concept introduced by Charles Darwin. Natural selection exploits the genetic variation available within each ecological niche where a large number of species and biological individuals are living in a subtle balance between symbiosis and competition. Any single persistent change in conditions, whether physical or biological, can

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influence, at least in principle, the genetic set up, the metabolic fit, and the balance between all participants over time. All these changes are then fed back into the living conditions, thereby affecting the survival of everybody within the local environment. This is how natural selection in the evolution of selforganized biological individuals works blindly in a pragmatic soft way without any theorem. In other words, life explores all the local possibilities of evolving new patterns of matter, without any other purpose than creative adaptation leading to gene combinations that cannot be anticipated beforehand. However, in retrospect, the unique result can be causally explained as a set deterministic physiochemical pattern of adaptation decided by the metabolism of the whole cell/organism during development in a given environment. It is remarkable that it can be shown experimentally by near infrared spectroscopy in the isogenic barley endosperm (seed) gene expression model that Nature is able to exactly reproduce the staggering complex physiochemical pattern of a given genotype when DNA, cell plasma and growth environment kept constant. It is remarkable that the 2250 year old statement of Archimedes “Give me a fixed point and I will move the world” still dominates the attitude to Nature in mathematics, science, technology, and society at large. The majority of mathematicians, physicists, chemists, and even biologists need a fixed theorem or hypothesis beforehand in order to produce a hard causal scientific or mathematical evaluation by using differential equations and statistics among other methods. These scholars have not even seriously considered how self-organized networks in Nature calculates its soft messages without theorems. The impressive fix of human technological artefacts outside the range of life, including the light bulb, car, mobile phone, and computer, seems to have convinced the scientific community and the public that the hard strategy of knowledge-based mathematical construction and decision-making is fully valid in revealing the secrets of autonomous life by design. These hard methods of data evaluation are destructive to networks. However, science is now able to tackle the analysis of complex biological networks (phenotypes) by new instruments (e.g., Near Infrared and NMR spectrometers and GC-MS and LC-MS chromatographs). They give a Megavariate overview of the extremely complex physiochemical composition of these phenotypes on the level of chemical bonds and molecules. Classic statistics based on the hard theorem of the normal distribution of variance that was successful in inheritance genetics, cannot handle the highly covariate datasets of phenotypes (the phenome). Instead science is now adapting soft pattern recognition mathematical models (chemometrics) for a graphic overview such as principal component analysis (PCA) score plots and multi-way chemometric evaluation of data. These multi-variate models calculates principal components (P.C. 1, 2….) to represent the unique structure of each data set as reference planes (instead of Archimedes fixed point) in a PCA x-y score plot for classification (e.g., PC1-x to PC2-y). They adapt to any set of biological data with great flexibility with a minimum of assumptions. This is why the softly adaptable chemometric models are pragmatically successful in reflecting the open soft process of life. They most importantly include experimental validation comparing the outcome of many parallel data sets. A soft data evaluation by a PCA pattern recognition plot cannot be evaluated without some prior knowledge. In order

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AGRONOMY OF GRAIN GROWING | Sustainable Grain Production and Utilization

to produce meaningful results, the researcher must keep an open mind and first let the data speak. It is then possible to formulate the questions needed to explore the patterns that Nature has already calculated. During the analysis, the researcher must respect the surprising patterns that may occur as a result of Nature’s creativity. Because natural selection is based on the fit of the whole phenotype and not single genes, plant breeding has been shifting from an approach that favors hard single genetic DNA markers in genomics evaluated by statistics of variance towards phenotypic patterns as markers based on instrumental data from phenomics (e.g., spectroscopy) and metabolomics (e.g., GCMS) visualized by soft chemometric data evaluation models (PCA). These patterns now seem to be more efficient markers for grain quality in breeding than the earlier Quantitative Trait Loci (QTL’s) calculated by statistics.

A new Integrated view on Gene Expression makes GM-Technology a Sustainable Indispensable Tool for Increasing Biodiversity as a Source for Increasing Grain Production The present controversy on the use of gene manipulated organisms (GMO) for insect resistance by bt-toxins and weed control by chemical resistant genes coupled to herbicides in grain crops is blocking the use of other less extreme GM-methods to increase biodiversity that is necessary to reach the needed 50% increase in grain yield by the year 2050. The most important role of recent molecular biological research, that still is resisted in media, is to redefine the human standing on the planet not as an inert invader but as an integrated part of Nature and as a result, however, remarkable, of the evolution of life. Thus it was surprising when the Hugo gene-sequencing project in 2000 only revealed about 25.000 structural genes coding for proteins/enzymes in humans and that those genes only contributed to 1.2% of the total human DNA. Apart from genes silenced due to the history of evolution it was found that the remaining genes takes part as regulators together with micro-RNA and histones – proteins bound to the chromosomes. Gene regulation and signaling in Nature seems to need much more information capacity than the structural manufacturing genes that makes proteins and enzymes, it is also remarkable that only about 10% of the human genes are associated to the Vertebrata subphylum that evolved in the evolution from 500 million years ago. This means that we genetically should have much more in common with microorganisms, insects, plants and non-vertebrate animals than was previously acknowledged. During the course of evolution, nature has reused DNA patterns of old genes for new functions by putting them in new contexts in the evolving organism but still the DNA connections remains. It is a fact that the about 100,000 commercial synthetic chemicals now released on the planet, have more or less interfered with the rules of the conservative biological signaling system of life originating billion years ago. About 15 percent of those chemicals have been used in agriculture to control pests and weeds. Regulation agencies such as FDA and EPA in USA have done a serious effort to stimulate the industry to introduce apparently selective agrochemical tools, that breaks down in soil and that has a low acute toxicity to humans. These

tools have been successful in keeping the grain yield and production at pace with the growing population, reducing famine by 50% during the last 10 years. Likewise the green revolution has contributed in increasing life expectancy and health in most countries. However, there has been no tool until now that has enabled an integrated evaluation of the synergistic long-term effects on the networks of life between the great numbers of potent synthetic chemicals that have been accumulated in great amounts on the planet the last 60 years. However, the human species cannot escape its evolutionary history. We are indeed sitting in the same boat as our DNA fellows in Nature. We are living in an ecosystem with about 1.5 kilo bacteria in the gut most of them useful. Genetically they are relatives to us as well as the plants we grow. This means that even if the diversity of life is immense there are a limited number of building blocks and regulatory systems and receptors that create functional life. Thus while there are many antibiotics that works by impairing protein synthesis and cell wall formation in bacteria, there are only four main classes of resistance in bacteria. It has been suggested that an agrochemical that works by impairing protein synthesis in weeds may work in the gut as an antibiotic even in small doses claimed nontoxic to man. In the end it may select bacteria resistant to commercial antibiotics. In spite of an improved life expectancy we are now living in a non-pristine world where we have to administer a new civilization syndrome in which our synthetic chemical heritage is included. Now several scientists claim that there is experimental evidence that contamination in humans of agricultural chemicals at levels that earlier has been judged safe may contribute to the present increase in e.g., resistant infectious diseases, changes in the gut flora, obesity, endocrine disruption, male sterility, depletion of detoxifying cell systems, immune depression and lack of trace minerals and vitamin. In addition environmental scientists claim that there are serious disruptions to biodiversity and quality of life in agricultural, forest and aquatic environments. It is hopeful that the new insight from chemometrics on the informative value of patterns to judge the networks of life now is included as a tool in environmental and human toxicology evaluations as demonstrated by the websites from the regulative authorities EPA and FDA. Chemometric data analysis is a multivariate extension of the present one by one evaluation of chemicals that is limited by simplified hard causality and classical probability statistics. When we realize that all organisms are our relatives, it is extremely difficult to come up with an agricultural chemical with a specific effect on one single organism without side effects on others. We must then play the biological control card by GMO in agriculture as now is done in the pharmaceutical industry. It is a pity that just two extreme applications has paralyzed the present discussion on the applicability of GMO namely the bt-toxin gene from Bacillus thuringiensis in maize against Lepidoptera larva and the glyphosate – resistant gene combination for weed control GMO crops (soy, maize, rape, alfalfa and cotton). While waiting on the solution of the controversy of these extreme cases by the new upcoming integrated human and environmental toxicology, the reputation of the normal GMapplication should be granted in a special program limited to

AGRONOMY OF GRAIN GROWING | Sustainable Grain Production and Utilization transfer of plant genes from established food and feed crops that have been tested for toxicity since the Neolithic period. The task is to increase the biodiversity of grain crop species for e.g., resistance against pests and weeds, for high yield potential and for nutritive value. The risk should be minimal and the criteria for operation simple. Our task is to speed up evolution by GMplant breeding where one year is equal to 1000 years by drawing on a wide pool of plant genes most of which now are inaccessible by crossing because of barriers between species. Such a targeted plant GM-program with limits secured by integrated evaluation discussed above should be well received by the public and be of great interest vigorously to invest in for all partners involved especially for industry. It should be emphasized that introduction of new plant genes across borders of species in grain crops is not a miracle technology. In most cases it is only a beginning, however absolutely crucial, to a tough process during many years of classical plant cross breeding to adapt the new gene carrying new functions to a high yielding high quality gene background. The task to increase grain yield by 50% up to the year 2050 is a bound case. There is no other option rapidly to increase biodiversity in grain plants than GMO e.g., to control rapidly adaptive pests. We have now new integrated control methods based on pattern recognition that make GMO safe if focused on biological control by introducing new genes from tested food and feed plants. If not such a sustainable GMO program is successful to meet the yield target in grains up to the year 2050, the present use of pesticides and herbicides have to be continued and further intensified with rising negative impact on long term health for man and most other organisms on earth, changing the steadily ongoing evolution on the planet in an unpredictable way.

Mitigating Climate Change by Promoting the Global Canopy of Plants In complex systems such as in chaotic weather systems and in the biological cell, observed data often have a deterministic edge that requires data inspection before mathematical modeling to facilitate evaluation because both hard and soft mathematical models are data compressive and more or less destructive. The deterministic element in observed data has inspired the widespread trust in data simulation in climate research. Therefore hard mathematical modeling, using techniques such as Navier–Stokes hydrological equations, is still preferred for simulating the outcome of climate systems in large computers. However, in meteorology, a soft PCA is better for modeling existing patterns of local extreme temperatures than a classic hard computer simulation for prediction. Thus, in modeling data from Nature, it is much more successful to retrofit than to predict. Mathematicians, scientists, and the public at large still do not fully appreciate that the incredibly complex problem of making long-term predictions about the chaotic behavior of weather and climate using mathematical models that remains indeterminable and unsolved because the initial conditions highly influencing the outcome are not known with enough precision. During the twentieth century, the climate has seemed to be unusually stable compared to the dramatic periods of warming

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and cooling prior to human influence, as evidenced by sections of old ice from Greenland. The United Nations Intergovernmental Panel on Climate Change (IPCC) was established in 1988 after 10 years of concurrent global warming and CO2 increases following a cool spell from 1945 to 1980. In 1988, climate scientists presumably felt that the 10year period was sufficient to conclude the direct importance of atmospheric CO2 levels for the global temperature change. However, in spite of the IPCC’s predictions in 1988, the average yearly global temperature since the period from 1998 to 2012 has not increased significantly, with CO2 increases due to human activities. During the last decade, local weather has seemed to be more erratic, however, characterized by dramatic hurricanes, flooding, and warm, cold, wet, and dry spells in many places of the world. A dramatic local warming tendency has been observed, for example, in Greenland during the last 10 years. Significant warming spells have been registered in the Artic in 1918 and 1960, however, but they faded away. For these types of erratic local weather patterns, the immense warming capacity of the oceans (compared to the atmosphere) expressed in sea current interacting with winds – The cold La Nina (1999–2000), the warm El Nino (1998) – and the more stable gulf stream have significant roles. These patterns could also be directed by regular changes in the gravitation of the planet and several other complex interactions. The steadily increasing CO2 content does add to global warming, it is forgotten that water in the atmosphere is eight times more effective than CO2 as a greenhouse gas. Unfortunately, the contribution of water to global warming is difficult to estimate because water vapor also forms clouds that have a significant cooling effect. Likewise, the rapidly increasing dust and sulfur aerosols produced by volcanic eruptions and the rapidly expanding coal electricity power stations in countries such as China and India also have a double effect. In the atmosphere these substances have a cooling effect by reflecting solar radiation. However, coal dust on ice reduces sun reflection and increases ice melting. Increasing the global plant canopy that stores CO2 might therefore prove a more viable decision than removing it from chimney smoke, and at the same time, this increase in plant canopy can produce more food.

Handling the Global Energy and Pollution Issue: The Key to Disaster or Success The world now consumes around 80 million gigawatt hours (GWh) of crude oil annually, compared to a global grain starch production of 7 million GWh. The option of using starch to make ethanol and other fuels for driving combustion engines is, thus, not of a magnitude that can match our present utilization of fossil oil, but it should be reserved mainly for food uses. Yet, increasing oil prices have boosted world production of biofuel (mainly ethanol) from 120 million barrels in 2000 to 690 million barrels in 2010, with the United States and Brazil being the major producers. Forty percent of the maize grain production in the United States is now used for ethanol in cars, leading to severe competition with feed and food uses. This development is not sustainable and is now criticized. A large population could be fed on the US maize exploited

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for ethanol if used as food. As a result, some have called for market regulation. At the same time, the recent discovery of huge reserves of shale oil and gas, which are now exploited in the United States using fracking is now in 2014 lowering the price of crude oil from 110 US$ to about 60 US$ per barrel. This new source is likely to stabilize the price of energy for a number of years. Nonetheless, without competing with the food use, whole-plant utilization technology could exploit agricultural lignocelluloses for building materials, chemicals, and fuel as a vehicle for the development of green industries providing local employment, thus creating the necessary purchasing power for food. Starting in the early 1800s, a chemical industry for plant fertilizers, such as superphosphate, gradually grew during the Industrial Revolution. The present human population increase depending on cereals would not have been possible without the Haber–Bosch method (Nobel Prize, 1918) of harnessing fossil energy (e.g., coal, oil, and gas) to produce ammonia fertilizer from atmospheric nitrogen and water. The rapid industrialization in China made energy consumption (mainly coal) rise fourfold from 1980 to 2009. Although US energy consumption per year from 2006 to 2014 was almost constant around 85 billion BTU, China’s plummeted from 70 to 120 billion BTU during the same period. China’s energy production per year is forecasted to increase to about 150 billion BTU in 2018, with the United States lagging behind at around 80 billion BTU. China now burns half of the world’s mined coal, and it is the world hub for manufacturing affordable industrial products. It is now the second economy in the world with a wealthy middleclass population of over 300 million. Brazil, India, and many other previously poor countries are also developing at a rapid rate. The increased energy investments from fossil fuels have led to increasing living standards and a reduced number of poor people largely by slowing down the population growth in most developing countries. Earlier forecasts predicting that the world population would reach 11 billion in 2050 have been modified downward to about 9 billion. New green innovations produced during the industrialization process driven by fossil fuels bring electricity and light to remote villages via cheap solar panels, allowing the introduction of mobile phones and the Internet. This is leading to a global revolution by connecting cities and developed countries to previously isolated people practicing agriculture in some of the world’s most remote regions, giving them the ability to learn, read, and communicate, and to trade their produce for a better price. Similarly, the improved sustainability of infrastructure via green technology such as electricity windmills, sea-wave power plants, and biogas factories has benefited from a fossil fuel–driven society. Thus, when determining its impact on global warming, the footprint of 1 tonne of coal burned in an electricity power plant should not only be expressed in emitted tonnes of CO2. Instead, any consideration should account for both the positive impacts of using fossil fuels to introduce sustainable changes in the infrastructure outlined here and the alarming negative impacts of smoke, smog, and chemical industrial and human pollution driven by the consumption of electricity from coal-based power stations. In conclusion, there will be no shortage of fossil energy because new technology will be developed to utilize the huge

resources that remain. Exploiting these resources is simply a question of market price and technology. The challenge is to internationally agree on how to regulate the use of fossil fuels, while both building up a new sustainable green infrastructure and avoiding the negative fossil fuel footprint. In order for this process to be successful, we must treat the human-mediated rise in CO2 as just one indicator of an extremely complex biotope destruction and pollution pattern that is gradually detrimental to all forms of higher life on the planet.

Fresh, Pure Water: The Limiting Factor for Plant Growth and Human Survival The availability of fresh water is a prerequisite for sustainable plant growth and grain production. In 1998, in developing countries, irrigated land produced three-fifths of all cereals. Globally, only 2.5–2.75% of water is fresh, including the 1.75–2% frozen in glaciers, ice, and snow; 0.7–0.8% is fresh groundwater and soil moisture, and less than 0.01% is surface water in lakes, swamps, and rivers. The atmosphere contains only 0.04% of the global water. The book Fragile Earth delivers dramatic satellite evidence of expanding cities, advancing deserts, shrinking lakes, increased salinity in agricultural land, and dying rivers, such as the Yellow River in China and the Columbia River in California. Large dam projects supporting electricity production and irrigation, such as those in the Nile River, have had a surprisingly negative effect on the fertility of soil and in salt damage of deltas, damaging the production of grain. Global deforestation is massive and only partly replaced by tree planting. The ‘3rd United Nations World Water Development Report,’ released in 2009, focuses on the low worldwide attention to water conservation. Globally, about 2 million tonnes of wastewater per day is dumped into water bodies. Cities, which now contain more than half of the world population but occupy less than 2% of land surface, use twothirds of the fresh-water resources. Water is a resource that is most easily wasted, but investments in the intelligent use of water, through technologies such as drip watering, can be most profitable, saving water by a factor of up to 50 times. The present focus on using economic tools to regulate CO2 by emission bonds and taxes would make sense if this money could be invested in the upgrading of the infrastructure for water conservation on all levels, from forests, rivers, and lakes to irrigation in agriculture and reformed sewage and drinking water systems in cities to spare valuable water.

Securing Biological Diversity by improving the Ecology of Plant Husbandry together with its surroundings and by Gene Banks to Support Sustainability in Grain Production The increasing human dominance of Planet Earth is now accelerating species extinction and narrowing of the genetic material used in agriculture. Thus, the problem of protecting the variety of ecological niches cannot be separated from maintaining the genetic diversity of plants. To obtain sustainability, one must also conserve the variety of ecological niches and their life as a whole. For example, the annual

AGRONOMY OF GRAIN GROWING | Sustainable Grain Production and Utilization production from 800,000 hectares of agricultural land in California is now dependent on beehives being sent on a grand scale from all over the United States to pollinate the plants in order to produce the usual high yields. Two-thirds of all plant species rely on insect pollination to get seed, including several legumes and Brassica grains. However, the ecology of California for agriculture production is now so depleted that the on-site life expectancy of the imported pollinating honeybees is reduced from 50 to 30 days. A restructuring of the wild and agricultural ecology to involve local pollinators is needed for sustainable production, and this endeavor could have many surprising positive side effects. Gene banks for seeds had already been established in St. Petersburg and Washington DC in the 1920s to secure the genetic base for agricultural crops. Seeds from around the world were collected and stored in refrigerators. Today the plant-breeding network of the Consultative Group on International Agricultural Research (CGIAR) keeps the many landraces and wild grain collections in local gene banks. The Nordic countries have erected a seed bank depository in the permafrost of Svalbard Island, not far from the North Pole, and this depository could maintain the viability of the seeds stored inside it without refrigeration, should electricity fail during a world crisis. When the International Center for Agricultural Research in Dry Areas (ICARDA), a CGIARsupported institute in Syria, was struck by civil war in 2011, it relocated to Lebanon. However, 80% of the approximately 130 000 collected samples were already safely stored at Svalbard. It seems that the stability of human society is a major problem for the sustainability of grain production and utilization.

Improving and Sustaining Soil Fertility: Utilization of Valuable Organic Material Separated from Industrial Waste Cereal production has tripled during the last 50 years, while the amount of synthetic nitrogen (N) fertilizer has increased more than eight times, sustaining more than one-third of the present world population. Even if vegetables can be produced under soil-free conditions in greenhouses, the extremely complex ecology of soil in real production has to be respected. One major dilemma is that the application of synthetic N accelerates microbial mineralization and depletion of the humus in soil, negatively changing the soil’s water-absorbing structure. The loss of organic N that now substantially threatens the sustainability of the worldwide yield is stronger than that of grain removal. For the great old agricultural civilizations in the Far East, recycling human and animal manure and other organic waste to the fields was the key to sustainable agricultural production. In the 1850s, the civil engineers who introduced sewage and water pipelines and the water closet saved the cities from pests, but they also transferred a vital agricultural supplement, the manure, as a waste that polluted lakes and waterways. Since then, the sewage problem has been complicated by the addition of thousands of chemical pollutants of varying toxicity from industry and households. To solve this problem, humans must change the infrastructure from the present-day waste economy, which is unsustainable, to a recycling economy

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that takes care of the valuable coproducts from the city environment. Valuable organic material should be separated from industrial waste to be used for restoring fertility in agricultural fields.

Change in Human Diet to Sustain the Increasing Human Population While Limiting Resources Theoretically, the present cereal production could feed a population of 14.7 billion individuals with 400 g day 1. Instead, an increasing portion of global grain production is used as feed in animal production. Meat production consumes large volumes of fresh water and contributes greatly to greenhouse gas emission. The greenhouse gas emission from global agriculture is comparable to that from automobiles and consumer electricity generators combined. Industry contributes the remaining 20% of emissions. A product life cycle analysis in the ‘3rd United Nations World Water Development Report’ (2009) shows that cereals use 1.5 cubic meters of water per kilo of grain, while fresh bovine meat needs 15 times as much water. A United Nations Environment Programme (UNEP) review from 2012 reveals that beef has the highest greenhouse emissions at 16–30 CO2 eq kg 1, compared to pork at 2.5, poultry at 1.6, and wheat at 0.8 eq kg 1. The fossil fuel consumption required by the present animal production system is also high, as fuel is used for feed production, rearing, and transportation to butchering and marketing. From 1961 to 2011, world meat production has increased from 75 to 300 million tonnes and is increasing by about 5% per year in the rapidly expanding economies of China, India, and Brazil. Retrospectively, we now understand how the vegetarianism built into the old cultures of India and China facilitated a nearsustainable high population density over long periods. Given the attractiveness of meat, world food consumption is not likely to become vegetarian. However, the sustainability of the present large-scale animal industry, which uses large amounts of antibiotics for disease control, is now at risk due to the emergence of antibiotic-resistant bacteria and rapidly mutating viruses that are serious threats for humans. If science and technology cannot rapidly find a solution to this serious hygiene problem, the present form of animal production must be abandoned. One alternative is vegetarianism combined with meat tissue culture and animal production under completely sealed conditions with respect to pathogens. Thus, the future will require great structural changes mitigated by intelligent planning.

The Eco-City: Expanding Food Plant Production to the Roofs and Rooms of the City During the last 30 years, developers have demonstrated computer-managed energy-neutral houses with human waste and water recycled and purified by plants. In principle, it seems possible to remake the dark and polluted city from an entity of pure consumption into a landscape of gardens that both produce foods and fix CO2, while still harboring a dense human population with a rich social life. In contrast to common belief, city environments may have advantages or suburban or rural living in terms of sustainability. Urban bees (e.g., in

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Washington, DC) have longer lives and access to a greater variety of flowers to pollinate than do bees in plant monocultures and farming regions such as rural California. When resources and people are located close to one another, energy can be saved in food transportation and in mass transit systems. The entry of Nature into the megacities via the eco-city concept could demonstrate to the public how Nature can contribute to improved personal comfort and more-sustainable living with the natural principle of recycling being respected.

Connecting New Natural–Technological Networks to Sustain the Symbiosis Between Plants, Industry, and Human Society The bits and pieces of a sustainable infrastructure are already available as concepts in demonstration plants and in modern vertically integrated industries such as sugar and paper fiber factories that practice recycling and energy conservation. They have not yet been combined into an infrastructure that can optimize the many new options for an improved total infrastructure by building a combined horizontally and vertically integrated network that is needed to maximize sustainability. The concept of the agricultural biorefinery, which was developed via a EU demonstration project on the Danish Island of Bornholm in 1989, is an example of research in such integrated networking. Since then, the concept of the industrial biorefinery has been further developed by the University of Wageningen in Holland and, in 2008, by the bioethanol demonstration plant of DONG Energy (a Danish state energy company). The latter demonstration project represents a first step toward utilizing low-grade energy from power stations as a part of an urban biorefinery (Figure 1. Urban concept B: Bioethanol unit) that could use 30 000 tonnes each of straw and feed grains produce 13 500 tonnes of ethanol, 10 000 tonnes of biofuel, and 9500 tonnes of dry weight feed molasses, with a CO2 reduction of 40 000 tonnes year 1. In Figure 1, the agricultural whole plant utilization and the urban biorefinery concepts (DONG Energy) are connected in a new infrastructure to bring back organic carbon and important minerals as fertilizer for agriculture. Human and animal manure and former waste from the agriculture and food industries are collected separately from the present sewage system. These materials are then upgraded in biogas fermentation units that produce fuel for cars (Figure 1). The low-grade heat concentrated from the power stations by heat pumps dries the fermentation residue so that this residual material is brought back as a tradable hygienic fertilizer to the agricultural field. The urban biorefinery is an integrated part of a green city with plant cultures on the roofs integrated with water-sparing biological cleaning systems. In such a city, a major part of the energy needed for heat and electricity can come from windmills and solar panels. The surplus electricity from the windmills can be used to produce hydrogen by electrolysis, with the hydrogen combined with CO2 produced in the biogas and bioethanol units to be used in a chemical plant to produce methanol, the basal raw material for building a sustainable chemical industry. Such a paradigm shift in infrastructure will require massive investments, social stability, and international cooperation. The international decision to remove ozone-damaging

Freon from refrigerators to conserve the ozone layer that protects the planet from damaging UV radiation is the best example of this type of successful international effort. International cooperation on climate and CO2 has not had the same success and now seems to be at a standstill. The relation of CO2 to global warming remains uncertain because of interfering mechanisms. Even if all industrial CO2 is removed from smoke in solid form, the global problem of human wearing remains “unsolved” with regard to pollution, water supply, soil fertility, food production, employment, and poverty. The free market does not yet seem ready fully to attempt the necessary paradigm shift in agricultural and urban infrastructure. The incentives for such a shift have to come from society itself. This implies worldwide public education on the lifesaving role of plants and photosynthesis. This article discusses why a change in infrastructure is necessary and that fossil fuels could be used in an intelligent way to gradually phase in green technology. Such a transition has the potential to improve living conditions and employment towards sustainability especially now when the global society is richer and more innovative than ever. When investors finally do see the great possibilities associated with changing the agriculture’s present non-sustainable rural-urban infrastructure towards integration and recycling, a paradigm shift will take off if global peace and international cooperation can be maintained and further developed. Grain scientists and plant breeders with their comprehensive knowledge of plant species could take a preventive approach and introduce a positive argument to the public: We should all agree that improving plants, plant life, and plant abundance on the planet to bind CO2 and produce food is a prioritized, sacred world project. Then, satellites could monitor the global health of the planet based on the yearly abundance of chlorophyll and oxygen rather than atmospheric CO2. In the meantime, pragmatic plant breeders will continue to safeguard sustainable plant growth by using the new instrumental chemometric pattern recognition selection methods in breeding that is integrated with a reformed GM-technology to adapt plants to the different ecological niches available: warm or cold, wet or dry, salt, acid, or basic.


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What does sustainability mean? What are the limits of sustainability? Why is the GMO tool together with classic plant breeding indispensable in meeting the future needs of grain foods and feeds? What mistakes have earlier been done to introduce the gene manipulation tool in grain plant production damaging the relations with the public and why are we today safer in using this tool in a responsible sustainable way? Why is actively improving infrastructure, such as water purity and availability, more important for food sustainability than the relationship between CO2 and global warming?

The 4th degree Biorefinary

Solar panels

Plant production and whole plant harvest

Whole plant harvester

Animal production,Feed and slaugtery industry

Animal manure owen

City

Human Septic tanks manure

Fertilizer

Drum drier

B. Biogas unit

Food, Starch and Manufacture industry

Human manure

High grade cattle feed

Restored production potential in Agricultural land

Electrolysis H

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CO Hydrogen

Methanol

Pelleting unit NH3+ steam

Paper pulp factory / Fiber board factory

Electricity

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B. Bioethanol unit

AGRICULTURAL BIOREFINERY

Fertilizer

Fermented rest

Internode chips

rest

Ligno Cellulose waste

A. Biogas unit

Agricultural lignocellulose

Leaf flower

Local dry waste

Biogas fuel

C. Feed factory elevator

Milling and Separation

Power station

Low grade heat

Local wet waste

Biogas fuel

Seeds

Green City Roof Gardens

Septic tanks

Fuel

Treshing

Straw

Village

Molasses (feed)

C. Methanol unit

1. Hydrotermal cellulose treatment Low grade heat 2. Enzyme treatment CO 3. Fermentation 2 4. Destillation 5. Separation + concentration

Lignin (fuel)

Pure water

Urban BIOREFINERY

Methanol Chemical Industry

Figure 1 The agricultural and urban biorefinery. See text. Reproduced from Munck L and Møller Jespersen B (2011) Adapting cereal plants and human society to a changing climate and economy merged by the concept of self-organization. In: Ullrich SE (ed.) Barley: Production, Improvement, and Uses, p. 563. Ames, IA: Wiley-Blackwell.


A Biomass separation unit

Wind mill park

B. The Urban Concept

A. Agricultural Concept

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What role has fossil fuel had in increasing the sustainability of the infrastructure? What role might it have in the future? How could ideas on hard mathematical modeling that have persisted since about 260 BC influence present methods for determining sustainability with regard to climate and plant breeding? Why is soft mathematical modeling a more realistic alternative? How could each member of the world community be informed and motivated to make daily consumption decisions that support sustainability?


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Make a white book on how a new science for building a multifaceted sustainable infrastructure could be established. How should earlier mistakes in public communications by scientists be corrected in order to increase the creditability of science. How should the research and development be organized for the genetic molecular GM-tools to fit into a long-term sustainable policy and why and how should they be regulated? What is needed to develop and implement a long-term policy for large investments in infrastructure and research? What should be regulated internationally and by governments and what should be the responsibility of the market and the individual?

Stimulate Further Thinking on the Topic by Providing a Few Questions, Especially Concerning How the Topic Might Develop in the Future How should the present wealth and increasing higher education of millions of people around the world be invested? Should these resources be invested in entertainment, by creating a virtual reality for the masses on television and the Internet? Or, should they be invested in communicating a reformed worldview that celebrates and respects the immense creativity of life that never can be completely predicted in which humans are an integrated part. Then life should obtain a new deeper meaning when people in their daily life are cooperating to introduce the new rural-urban infrastructure for a sustainable life that is needed for survival supported by the nessesary reformed integrated grain production and utilization.

See also: Agronomy of Grain Growing: Implication of Climate Changes; Natural Disease Control in Cereal Grains; Bioactives and Toxins: Mycotoxins; Breeding of Grains: Barley: Genetics and Breeding; Maize: Breeding; Rice: Breeding; Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Abiotic Stress Genes and Mechanisms in Wheat; Biotic Stress Resistance Genes in Wheat; Development of Genetically Modified Grains; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Non-food Products from Grains: Biodiesel; Fuel Alcohol Production; Utilization of the Whole Cereal Plant to Maximize its Value; Proteins: Nitrogen in Grain Production

Systems; The Basics: The Grain Crops: An Overview; The Cereal Grains: Cereals: Domestication of the Cereal Grains.

Further Reading General Information Collins Staff (2006) Fragile Earth: Views of a Changing World. London: Collins Publishers. Dawkins R (1999) The Extended Phenotype. UK: Oxford University Press. Houle D, Govindarju DR, and Omholt S (2010) Phenomics: the next challenge. Nature Reviews 11: 855–866. Munck L and Møller Jespersen B (2011) Adapting cereal plants and human society to a changing climate and economy. In: Ullrich SE (ed.) Barley, pp. 563–602. Ames, IA: Wiley-Blackwell. The Problem of Hard Mathematical Modeling in Chaotic Systems Lindzen RS (2012) Climate physics, feed backs and reductionism. European Physical Journal Plus 127: 52. May RM (2004) Uses and abuses of the use of mathematics in biology. Science 303: 790–793. The chemometric pattern recognition approach to explore data from Nature http://www.epa.gov/esd/cmb/research/posters/017cmb02db.pdf. http://google2.fda.gov (search for chemometrics). Lucio PS, Conde FC, and Ramos AF (2007) Spatial pattern recognition of extreme temperatures in climatology. Europe Revista Brasileira de Meteorologia 22(2): 204. Munck L, Møller Jespersen B, Rinnan A, et al. (2010) A physiochemical theory on the applicability of soft mathematical models – Experimentally interpreted. Journal of Chemometrics 24(7–8): 481–495. Smilde AK, Bro R, and Geladi P (2004) Multi-way Analysis. New York: Wiley. New Soft Integrated Screening Methods: The isogenic barley endosperm (seed) gene expression model Khakimov B, Møller Jespersen B, and Balling Engelsen (2014) Metabolic profiling in cereals by GC-MS and chemometrics. Foods 3(4): 569–585. Munck L (2007) A new holistic exploratory approach to systems biology by near infrared spectroscopy. Journal of Chemometrics 21: 406–426. Munck L (2009) Integrated breeding for quality traits in cereal. In: Carena MJ (ed.) ‘Cereals’ Handbook of Plant Breeding, pp. 333–366. New York: Springer Publishers. Møller Jespersen B and Munck L (2011) Cereals and Cereal Products. In: Sun DW (ed.) IR spectroscopy in Foods, pp. 275–320. Esevier Science Publishers. Evaluation of GMO and agricultural chemicals Alla AA, El-Shamei ZS, Shatta AA, Moussa EA, and Rayan AM (2013) Morphological and Biochemical Changes in Male Rats Fed on Genetically Modified Corn. The Journal of American Science 8(9): 1117–1123. Bøhn T, Cuhra M, Traavik T, Sanden M, Fagan J, and Primirico R (2014) Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans. Food Chemistry 153: 207–215. Felsot AS (2011) Pesticides and Health: Myths versus Realities. American Council on Science and Health. (http://acsh.org/2011/11/pesticides-and-health/). http://www.momsacrossamerica.com/glyphosate_testing_results. Samsel A and Stephanie Seneff S (2013) Glyphosate’s Suppression of Cytochrome P450 Enzymes and Amino Acid Biosynthesis by the Gut Microbiology : Pathways to Modern Diseases. Entropy 2013, 15, 1416–1463. Climate data www.climate4you.com. Securing Genetic Variability Swaminathan MS (2009) Gene banks for a warming planet. Science 325(5940): 517. http://en.wikipedia.org/wiki/Svalbard_Global_Seed_Vault. Soil Sustainability Mulvaney R, Khan SA, and Ellsworth TR (2009) Synthetic nitrogen fertilizers deplete soil nitrogen: A global dilemma for sustainable cereal production. Journal of Environmental Quality 38: 2295.


Meat CO2 Foot Print Data http://www.unep.org/pdf/unep-geas_oct_2012.pdf. Green Cities and Environment http://en.wikipedia.org/wiki/Sustainable_city.

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Industrial Bio-Refineries http://www.nnfcc.co.uk/external-resources/crops-database-ienica. World economic forum (2010) The future of Industrial bio-refineries. Report. Geneva, Switzerland, pp. 39. http://www.wageningenur.nl/en/Research-Results/Themes/theme-biobasedeconomy/ Biorefinery.htm. http://www.inbicon.com.

Organic Grain Production and Food Processing P Ge´linas, Food Research and Development Centre, Agriculture and Agri-Food Canada, Saint-Hyacinthe, QC, Canada C David, ISARA Lyon, Lyon, France ã 2016 Elsevier Ltd. All rights reserved.

Glossary

Additive Substance used as part of a process and which is a typical component of the final product, for example, affecting its properties. GMO (Genetically Modified Organism) A plant, animal, or microorganism that is modified or transformed by genetic engineering such as recombinant DNA and where genetic material is altered in ways not obtained by methods of natural mating and reproduction such as natural hybridization.

Topic Highlights

•

• •

•

Grains may be grown according to specific regulation and guidelines by accredited certification agencies, although some differences may exist depending on the country. Terms such as ‘biological’ and ‘ecological’ are acceptable to describe ‘organic’ agriculture or food. At the farm, there is an exhaustive list of approved inputs (fertilizers, soil conditioners, crop protectants, and growth regulators). Food production may also qualify for organic certification. Only ingredients from organic agriculture may be used for the production of organic foods, although 5% of nonorganic ingredients are allowed under specific conditions. A list of allowed nonorganic ingredients and processing aids exists and there are some restrictions. There is no guarantee that organic foods are safer, tastier, and more nutritive than nonorganic foods.

Nanomaterial Substance with very specific properties or composition, designed by human activity to be in the nanoscale range (1-300 nm), but not by traditional processing techniques such as homogenization. Organic Based on organic standards identified by certified bodies. Processing Aid Substance used as part of a process and not a typical constituent of the final product, such as filtration aid. Synthetic Substance chemically changed by a process which is not a naturally occurring biological process.

In industrialized countries, organic grain-based food addresses growing but small markets. This may be partly attributed to price premiums for marketing food grown under organic agriculture despite increased interest by consumers, media, researchers, and policy makers. Since the 1990s, the consumption of organic food has been on the rise in many parts of the world. Organically grown cereal crops might contribute to human health due to their nonuse of toxic pesticides in the environment and food. However, it cannot be assured that organically grown foods are safer, healthier, or more nutritious than conventionally grown produce. This article describes the regulations on the production of organically grown grains and food and the potential advantages and limits of organic growing of grains. This is an update of the article Organic Growing of Grains issued in the first edition of the encyclopedia, and some of the former material has been used.

Learning Objectives

Definition

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The concept of organically grown foods is an ethical and holistic concept based on principles of health, ecology, fairness, and care. Organic agriculture should sustain and enhance the health of soils, plants, animals, humans, and the planet as one and indivisible. Organic agriculture should be based on living ecological resources and natural cycles. Organic agriculture should be built on relationships that ensure fairness and care to protect the health and well-being of current and future generations. Organic production methods involve the following:

Achieve an understanding of organic agriculture practices and significance and their effects on the overall quality of food.

Introduction Organic agriculture is an alternative to the increased use of synthetic fertilizers and pesticides that has become necessary to maintain high-productivity crops even if they have environmental impacts, that is, water degradation, pesticide residues, and loss of nonrenewable energy sources. Organic agriculture is a viable option for low-input agronomic conditions. However, grain growers may face lower and variable performance upon conversion from conventional to organic-driven agriculture. Only a small share of the total agricultural land is under organic agriculture: from 1% or less in North America, Asia, and Africa to about 5% in the European Union (EU).

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1. The absence of synthetic inorganic chemicals for growing and processing crops, like fertilizers or pesticides. 2. An agroecological, broad, and long-term approach throughout the food chain, including care for soil fertility, recycling of agricultural materials from in-site or community, nonrenewable energy preservation, preservation of biodiversity, stimulation of the self-regulating capacity of


http://dx.doi.org/10.1016/B978-0-12-394437-5.00195-9

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing the agroecosystem, and care for water, soil, and air quality preservation; methods or tools such as genetically modified organisms (for seeds and others) and irradiation are not acceptable. 3. The integrity of living nature as a whole, strictly focused not only on crop production but also on animal welfare, environment, and social impact, for example, avoidance of any process or practice that might endanger the health of agricultural producers and consumers. A key issue in the overall sustainability of the organic farming systems is economic viability. In grain production systems, financial issues are critical during the conversion from conventional to organic agriculture. Specific machinery is required, while grain yields fall and output prices are maintained without premiums. Financial incentives (e.g., subsidies and market opportunities during conversion and after), advisory support, and social context (e.g., local consumption of organic food and farmers’ networking) may facilitate conversion to organic. The organic grain system requires high selling prices and a strong processing and marketing network. In organic agriculture, the fertility and biological activity of the soil should be maintained or increased, where appropriate, by (1) the cultivation of legumes, green manures, or deeprooting plants in a multiannual rotation program and/or (2) the incorporation into the soil of organic material, composted or not, from holdings produced in accordance with the Codex Alimentarius Commission guidelines. According to Table 1, several substances may be used in soil fertilizing and conditioning. Adequate nutrition of the crop rotation or soil conditioning cannot be ensured by other methods compared with those permitted for organic agriculture. Weeds are often mentioned as the most significant problem in organic plant production. Emphasis is on prevention and control methods because no synthetic herbicides are allowed. These measures include the reduction of weed contamination in seeds and the control of the growth of weeds before, during, and after the grain crop. Measures may be taken (1) at the farm level through crop rotation and intercropping systems; (2) at the grain variety level by selecting genotypes for competitiveness through plant architecture, rapid juvenile growth, deep rooting, and allelopathic exudates; and (3) at the crop level by mechanical control of weeds. Substances from plants and animals, minerals, and other sources may be applied for plant pest and disease control (Table 2). Most soilborne pests and diseases can be controlled by stimulating biodiversity in and above the soil, by good soil management, and by choosing site-specific crops through balanced rotation and selection of resistant crop varieties.

Regulations Guidelines for the production, processing, labeling, and marketing of organically produced foods aim to protect consumers against deception and fraud and to protect organic producers against misrepresentation of other agricultural produce as being organic. Organically produced foods must meet international standards according to the Codex Alimentarius Commission guidelines. For legally registered labeling, accredited

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Table 1 Permitted substances for fertilization and conditioning in organic agriculturea Plant and animal by-products

Minerals

Animal products (processed from slaughterhouses and fish industries) Compost (home refuse, sorted; mushroom, spent; plant residues; vermiculite) Excrements, composted; from animals including poultry; guano; urine or slurry; from humans (treated to eliminate pathogens; not applied to crops intended for human consumption or to the edible part of plants) Food industries by-products (not treated with synthetic additives); vinasse from the sugar industry; from oil processing (palm, coconut, and cocoa); by-products of ingredients from organic agriculture Manure from farmyard and poultry Naturally occurring biological organisms (e.g., worms); humus from earthworms and insects Peat Seaweeds and seaweed products Straw Textile industries by-products Vermiculite Wood by-products (sawdust, bark, and wood waste) Aluminum calcium phosphate Calcium carbonate of natural origin (chalk, marl, maerl, limestone, and phosphate chalk) Calcium chloride (leaf treatment) Chloride of lime Epsom salt (magnesium sulfate) Gypsum (calcium sulfate) Magnesium rock Phosphate rock, natural Rock potash, mined potassium salts, sulfate of potash Slag, basic (mineral residue) Sodium chloride (only mined salt) Stillage Stone meal, clay Sulfur Trace elements (boron, copper, iron, manganese, molybdenum, and zinc) Wood ash, wood charcoal

a

Based on the guidelines for the production, processing, labeling, and marketing of organically produced foods, adopted by the Codex Alimentarius Commission. Some restrictions may apply.

certification agencies inspect farms and processing industries. Food production and processes must be certified as organic, not the food itself. Principles are close to the hazard analysis and critical control point system, including regulations (on farmers’ practices and food processing) and traceability. This means that detailed records of production techniques and inputs are subjected to inspection from certification agencies. Within countries, legislations have been set up over the years, based on guidelines provided by the Codex Alimentarius Commission created in 1962 to establish international food standards on behalf of the FAO (Food and Agriculture Organization of the United Nations) and the WHO (World Health Organization). These standards and norms are

156

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing

Table 2 Permitted substances for plant pest and disease control in organic agriculturea Plant and animal by-products

Minerals

Others

Acids, natural (e.g., vinegar) Beeswax, propolis Fermented products from Aspergillus Food ingredients: casein, gelatin, lecithin Oils (plant and animal) Plant preparations and extracts (excluding tobacco), chitin nematicides, chlorella, mushroom (shiitake), neem oil, pyrethrum (chrysanthemum), quassia; rotenone, ryanodine, sabadilla Seaweed (meal, extracts, sea salts, and salty water) Copper Sulfur Mineral powders (bentonite, clay, diatomaceous earth, silicates, and stone meal) Sodium bicarbonate Potassium permanganate Iron phosphates (as molluscicide) Carbon dioxide, nitrogen gas Ethyl alcohol Insect males (sterilized), pheromone preparations Mechanical control devices such as nets and glue-coated traps Metaldehyde preparations, rodenticides Microorganisms used for biological pest control Mineral oils, paraffin oil Miscellaneous preparations (homeopathic, ayurvedic, herbal, and biodynamic) Potassium soap

a

Based on the guidelines for the production, processing, labeling, and marketing of organically produced foods, adopted by the Codex Alimentarius Commission. Some restrictions may apply.

designed to ensure fair practices in the food trade and protect human health, setting a minimum quality level for safety and trade. In 1999, the Codex Alimentarius Commission adopted international rules for the production, processing, labeling, and marketing of organically produced foods. These guidelines have been regularly improved and updated to take into account technical progress and additional requirement (more than seven times since 1999): they set out the principles of organic production at the farm, preparation, storage, transport, labeling, and marketing stages. Depending on the country or certifying group, standards must be applied in full, including the withdrawal of all synthetic fertilizers and pesticides, and strict respect for a transition period of 2–5 years before certification of organic products of agriculture. Worldwide, ISO Standard 65 has become the most accepted standard for organic certifiers. Within a country, control is made by representative organizations, which are, in some cases, recognized by the government. Worldwide, international markets require some insurance for equivalency because the definition of ‘organic’ may slightly differ according to the certification agency. In 1992, the International Federation of Organic Agriculture Movements (IFOAM) established the IFOAM Accreditation Program to provide international equivalency of organic quality claims. The IFOAM is recognized as

the leading group for organic agriculture organizations. A major inspiration for the Codex Standards, IFOAM Basic Standards provide a framework for certification bodies and standard-setting organizations worldwide to develop their own certification standards (although they cannot be used for certification on their own). Certification standards should take into account specific local conditions and are more restrictive than IFOAM Basic Standards. This reflects the complexity of regulating the production of organically grown crops, a major task that has been made through the years due to the commitment of organizations like IFOAM.

Food Processing Issues It is expected that the so-called organic grain-based food is exclusively made with certified organically grown ingredients. However, some latitude is permitted, so, in general, certified organic foods must be made with a minimum of 95% of organic ingredients. In other words, the so-called organic foods of plant origin may be prepared with a maximum of 5% of nonorganic ingredients of agricultural origin, based on the total weight of ingredients except water and salt. In some certifications or countries, foods containing 70% or more organic ingredients may be recognized as ‘made with organic ingredients’ without labeling. A major issue among organic certification groups is the list of approved additives (Table 3) and processing aids (Table 4) permitted in organic foods. The information given in these tables indicates that some differences exist between control bodies, organizations, or countries. For the sake of convenience, only the information from IFOAM, Codex (Codex Alimentarius Commission, WHO, and FAO), EU, and the US Department of Agriculture has been compiled. Among recent changes in regulations that may affect organic grain-based foods, much interest was given to organic yeast that is not considered as an agricultural product and may then be considered in the requested percentage (95%) of bread ingredients. Rules for the production of organic yeast have also been defined. In practice, bakers may still use nonorganic baker’s yeast in their formulation if the total amount of nonorganic ingredients is less than 5% by weight of the ingredients of agricultural origin (except water and salt). Now, several yeast manufacturers offer ‘organically grown yeast’ to allow extra margin to the addition of nonorganic additives in ‘organic foods.’ This should have more significance in organic bakery products containing large amounts of baker’s yeast. Through documentary evidence, control bodies develop reliable quality assurance procedures for the production of organic foods. However, infringements may be difficult to trace considering that no analysis may distinguish produce from organic agriculture from those prepared under conventional agriculture. A major concern is the potential authorization of food ingredients and additives that are not available from organic agriculture with such lists possibly varying depending on the country. It is likely that several of these ingredients are easily available, depending on the country and period of the year. The latter are considered as ingredients of agricultural origin and excluded from the aforementioned calculation (maximum 5% nonorganic).

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing Table 3

157

Additives of nonagricultural origin permitted for use in organic foodsa

Additive

Restrictionb

Acids (alginic, citric, and lactic)

Must be produced by microbial fermentation of carbohydrate substances (the United States)

Agar, agar-agar (generally used as gelling agent) Alginates (alginic acid, potassium alginate, and sodium alginate) Amino acids and nitrogen compounds Ammonium carbonate, ammonium bicarbonate, ammonium hydrogen carbonate (leavening agents) Ammonium phosphates Ammonium sulfate Arabic gum, gum Arabic (generally used as gelling agent) Argon Ascorbic acid (generally used as dough oxidation agent) Bacterial starters (including dairy cultures) Calcium carbonate (generally used as buffer in yeast foods) Calcium chloride Calcium citrate Calcium hydroxide Calcium phosphates, monobasic, dibasic, tribasic (as leavening agents and other applications) Calcium sulfate (generally used as dough firming agent)

Carbon dioxide (generally used as preservative agent in controlled atmosphere) Carob bean gum, locust bean gum (generally used as stabilizing or gelling agent) Carrageenan, carrageen, Irish moss (generally used as stabilizing or gelling agent) Citric acid Coloring agent (color) L-Cysteine

(generally used as dough conditioner; reducing agent) Disodium tartrate Enzymes (any preparation normally used in food processing) Flavoring agents or extracts (essential or volatile oil) Gelatin(e) Gellan gum (high-acid form) Glucono delta-lactone (not produced by the oxidation of glucose with bromine water) Glycerol, glycerine

GMO (from genetically modified ingredients) Gum arabic Guar gum (generally used as gelling or stabilizing agent) Helium Hydroxypropyl methyl cellulose Karaya gum (generally used as gelling or stabilizing agent) Kelp Lactic acid Lecithin Locust bean gum, carob bean gum (generally used as stabilizing or gelling agent) Magnesium carbonate, magnesium hydrogen carbonate (generally used as drying and anticaking agent) Magnesium chloride, nigari

When required by legislation (only in EU) As acidity regulator and raising agent (Codex); cereal products, confectionary, cakes, and biscuits (IFOAM) Wine Wine Fats and oils and fat emulsions, confectionary, and dairy products (Codex) Not in Codex If not from GMO (product of rDNA technology) Not for calcium enrichment (EU); not for coloring (EU and IFOAM); also as processing aid (see Table 4) Fruits and vegetables (including pulses and legumes) and soybean products (Codex); also as processing aid (see Table 4) Maize tortilla flour (IFOAM); also as processing aid (see Table 4) Dibasic and tribasic forms (the United States only); see also monocalcium phosphate Soybean products, confectionery, and bakers’ yeast (Codex and IFOAM); for cakes, cookies, and pies (Codex); as carrier (EU); also as processing aid (see Table 4) Also as processing aid (see Table 4)

Fruits and vegetables, including pulses and legumes (Codex); oil production and starch hydrolysis (EU); also as processing aid (see Table 4) If not a synthetic substance primarily judged as being unnatural or as a ‘new construction’ of food compounds; if not produced by genetic engineering Prohibited Confectionery and cakes (Codex); not in IFOAM Not from GMO Not from synthetic sources If not available from organic source (EU); also as processing aid (see Table 4) Only in the United States Only in the United States Only if obtained from plant origin and used as a carrier for plant extracts; fruits and vegetables (including pulses, legumes, nuts, and seeds), and herbs, spices, seasonings, and condiments (e.g., seasoning for instant noodles) (Codex); plant extracts (EU) Forbidden See Arabic gum Not in IFOAM or Codex For encapsulation material for capsules (only in EU) Not in EU or IFOAM Only in the United States (thickener and dietary supplement) Fermented vegetable such as pulses and legumes, dairy products, and edible casings (Codex) If obtained without bleaches (EU and IFOAM) and organic solvents (EU)

Soybean products (Codex and IFOAM); derived from sea water (the United States); also as processing aid (see Table 4) (Continued)

158 Table 3

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing (Continued)

Additive Malic acid Microorganisms (any preparation normally used in food processing) Minerals and vitamins (nutrients) Monocalcium phosphate, monocalcium orthophosphate (generally used as leavening agent) Monosodium tartrate Nitrogen Oxygen Pectin (unmodified) Potassium alginate Potassium carbonate (bicarbonate) (generally used in leavening agent)

Potassium chloride Potassium iodide (dietary source of iodine in salt, legally required) Potassium citrate Potassium metabisulfite Potassium tartrate, dipotassium tartrate, potassium acid tartrate (also called cream of tartar) (generally used in leavening agent) Salt, sodium chloride Silicon dioxide (amorphous)

Sodium acid pyrophosphate (generally used as leavening agent) Sodium alginate Sodium carbonate, sodium bicarbonate, sodium hydrogen carbonate, sodium sesquicarbonate (generally used as leavening agent) Sodium citrate Sodium hydrogen carbonate Sodium hydroxide Sodium sesquicarbonate Sodium tartrate; monosodium tartrate; disodium tartrate (generally used as stabilizing or gelling agent) Sorbic acid (generally used as preservative agent) Sulfuric acid Tartrates (see potassium tartrate and sodium tartrate) Tocopherols, mixed natural concentrates Tragacanth gum Vitamins and minerals (nutrients) Water (drinking) Xanthan gum (generally used as stabilizing or gelling agent)

Yeast (autolysate, baker’s, brewer’s, nutritional, and smoked)

Restrictionb Not from GMO; also as processing aid (see Table 4) When required by legislation Flours (Codex); as raising agent for self-raising flour (EU), for ‘raising flour’ (IFOAM) See sodium tartrate Also as processing aid (see Table 4)

Confectionery, cereal, and cereal products (excluding bakery wares such as bread but including fine bakery wares and mixes such as cakes, cookies, pies, doughnuts, sweet rolls, scones, and muffins) (Codex); also as processing aid (see Table 4) Equivalent to sodium chloride (EU); fruits and vegetables (including pulses and legumes), mustards, and nonemulsified sauces (Codex) Only in the United States Not in Codex or EU; potassium dihydrogen citrate not permitted Wine Confectionery, flour and starches, and cakes (Codex) Not included in the percentage calculation of organic ingredients; equivalent to potassium chloride (EU) Herbs, spices, seasonings, and condiments (e.g., seasonings for instant noodles) (Codex); as gel or colloidal solution (Codex); as anticaking agent for herbs and spices (EU); also as processing aid (see Table 4) Only in the United States Confectionery and bakery wares such as breads and rolls (not sweet bakery wares such as cakes) (Codex); also as processing aid (see Table 4) Not in Codex or EU See sodium carbonate Cereal and cereal products, including yeast-leavened breads and specialty breads but excluding other bakery wares such as cakes and pies (Codex) See sodium carbonate Confectionery and cakes (Codex) Prohibited Wine and cider; also as processing aid (see Table 4) As antioxidant in fats and oils (EU) When required by legislation Not included in the percentage calculation of organic ingredients; also as processing aid (see Table 4) Fat and oils, and fat emulsions, fruits and vegetables (including pulses and legumes), bakery wares such as bread and rolls, and salads (e.g., macaroni salad) (Codex) If nonsynthetic and not grown on petrochemical substance and sulfite waste liquor; only if not from genetic engineering; criteria for the production of organic yeast exist (EU)

Codex: Based on the guidelines for the production, processing, marketing, and labeling of organically produced foods, adopted by the Codex Alimentarius Commission and the FAO/ WHO Food Standards Programme, with amendments in 2010 (www.codexalimentarius.net). EU: Based on Commission Regulation (EC) No 889/2008 of 5 September 2008 laying down detailed rules for the implementation of Council regulation (EC) No 834/2007 on organic production and labeling of organic products with regard to organic production, labeling and control (http://europa.eu.int/). IFOAM: Based on the IFOAM Norms for Organic Production and Processing, 2014 (http://www.ifoam.org). The United States: Based on the regulation of the US Department of Agriculture (The National Organic Program) (as of 25 November 2014), according to the National List of Allowed and Prohibited Substances, Entry 205.605, Code of Federal Regulations (www.ecfr.gov). a Where the substances listed in this annex can be found in nature, natural sources are preferred. Substances of certified organic origin are also preferred. b Based on information from Codex, EU, IFOAM, and US guidelines.

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing Table 4

159

Processing aids permitted in the production of organic foodsa

Processing aid Activated carbon (charcoal) Attapulgite Bark, preparation of Beeswax Bentonite Calcium carbonate Calcium chloride Calcium hydroxide, lime Calcium sulfate, gypsum Carbon dioxide (generally used as preservative agent in controlled atmosphere) Carnauba wax Casein Cellulose Citric acid Diatomaceous earth Egg white albumin (albumen) Enzymes (e.g., catalase, egg white lysozyme; lipase, pepsin, rennet, trypsin) Ethanol Gas (including carbon dioxide, oxygen, and nitrogen) Gelatin(e) Glycerides (mono and di) Hazelnut shells Hydrogen peroxide Isinglass Kaolin Lactic acid Lecithin Magnesium chloride; nigari Malic acid Microorganisms (any preparation normally used in food processing) Nitrogen Octadecylamine Oxygen Ozone Peracetic acid, peroxyacetic acid Perlite Potassium carbonate, potassium bicarbonate Potassium hydroxide Potassium tartrate, dipotassium tartrate, potassium acid tartrate, cream of tartar Rice meal Silicon dioxide (amorphous) Sodium carbonate, sodium bicarbonate Sodium hydroxide

Sodium tartrate Sulfuric acid Talc Tannic acid, tannin Tartaric acid and salts

Restrictionb Only in the United States (handling of plant and animal oils) Sugar (only in IFOAM) As releasing agent (Codex and EU) Fruits and vegetable products (IFOAM) Not for coloring (IFOAM and EU); not for calcium enrichment (EU); also as food additive (see Table 3) As coagulation agent (Codex and EU); also as food additive (see Table 3) Sugar (IFOAM); also as food additive (see Table 3) As coagulation agent (Codex and EU); mined (the United States); also as food additive (see Table 3) Also as food additive (see Table 3) As releasing agent (Codex and EU) Wine (IFOAM); also as food additive (see Table 3) Regenerative casings, as anticaking agent and filtering aid (the United States) For pH adjustment (Codex); oil production and hydrolysis of starch (EU); also as food additive (see Table 3) As a food filtering aid (the United States) Not in IFOAM If derived from edible, nontoxic plants, nonpathogenic fungi, or nonpathogenic bacteria, and not from GMO As solvent (Codex and EU) For controlled atmosphere Also as food additive (see Table 3) Only in the United States (in drum drying of food) Not in IFOAM Only in the United States Wine (IFOAM) Not in Codex and EU If obtained without bleaches (IFOAM); also as food additive (see Table 3) Soybean products (IFOAM and Codex); as coagulation agent (Codex and EU); also as food additive (see Table 3) Not from GMO; also as food additive (see Table 3) Also as food additive (see Table 3) As boiler water additive for packaging sterilization (only in the United States) Only in the United States In wash or rinse water; as sanitizer on food contact surfaces (only in the United States) For drying grape raisins (Codex and EU); also as food additive (see Table 3) Sugar processing

Not in IFOAM and Codex As gel or colloidal solution (Codex); as defoamer (the United States); for other uses when organic rice hulls are not available (the United States); also as food additive (see Table 3) Sugar production (Codex); also as food additive (see Table 3) Surface treatment of ‘Laugengeba¨ck,’ lye-dipped bakery product (EU); surface treatment of traditional bakery products and for sugar processing (IFOAM); pH adjustment in sugar production (Codex); sugar or oil production from rape seed (EU) Not in EU Sugar processing; also as food additive (see Table 3) Wine processing Wine processing (Continued)

160 Table 4

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing (Continued)

Processing aid

Restrictionb

Vegetable oils

As greasing, releasing agent (Codex and EU) or antifoaming agent (EU); also as food additives (see Table 3) Also as food additive (see Table 3) As releasing agents (Codex and EU) If nonsynthetic and not grown on petrochemical substance and sulfite waste liquor

Water (drinking) Waxes, plant-derived (beeswax and carnauba wax) Yeast (autolysate, baker’s, brewer’s, nutritional, and smoked) a

Processing aids are any substance or material, not including apparatus or utensils and not consumed as a food ingredient by itself, intentionally used in the processing of raw materials, foods, or its ingredients, to fulfill a certain technical purpose during treatment or processing and that may result in the nonintentional, but unavoidable, presence of residues or derivatives in the final product; some specific processes have also been mentioned as processing aids. In essence, processing aids are not present in the finished product (nonsignificant). b Based on information from Codex, EU, IFOAM, and US guidelines (see bottom note in Table 3).

Several food processes are not allowed according to organic rules, for example, irradiation and genetically modified microorganisms (GMO) technology. In the recent years, a very important issue was the prohibition of materials or techniques involving nanomaterials, including equipment surfaces and utensils that might come into contact with organic products. According to IFOAM, engineered nanomaterials are “substances deliberately designed, engineered and produced by human activity to be in the nanoscale range (approx 1–300 nm) because of very specific properties or compositions (e.g. shape, surface properties, or chemistry) that result only in that nanoscale.” For example, packaging material may contain titanium oxide (nanoparticlesized). When ingested, opponents fear that such nano-sized particles might become more toxic than larger particles, so they may easily be taken into cells and pass into the blood. IFOAM published a position paper to exclude the addition of nanomaterials to organically produced foods. Basically, this position is related to fears from technologies hidden from the view of consumers, so nano-exclusion might offer a new marketing potential to promote organically produced foods.

Potential Advantages 1. Alternative agriculture is adapted to low-input and constrained conditions. Organic agriculture tends to limit soil erosion, compaction, or degradation by using crop diversity and preserving soil fertility. It also limits the use of off-farm inputs like mineral fertilizers and synthetic pesticides limiting nonrenewable energy use. 2. Small is beautiful. Organic agriculture is a way to say that bigger is not necessarily better. For developing countries, organic agriculture is a way to seek independence over imported pesticides and mass monoculture of export crops. Otherwise, the economy of developed countries is too often severely dependent upon international markets. For example, organic agriculture is adapted to family farming by increasing profitability per unit. In brief, organic crops cost less to produce (no expensive chemical fertilizers and pesticides, substituted by manure), have lower yields (25–35% less for grains) but get higher price (30–100% compared with nonorganic crops, sometimes more), and are more resilient under contrasting climates. 3. Road to alternative cereals. A niche market, organic cereal foods offer interesting possibilities to develop or introduce

new cereal-based foods such as those made from nontraditional or specialty grains such as ancient wheat (spelt or khorasan). Niche markets are then available through organic grains, which give access to such specialty cereals containing much fiber and often having special flavors. Some people also switch to specialty and nontraditional cereals because they are sensitive (but not necessarily allergic) to standard cereal foods from wheat. Organic agriculture is a way of life for some persons. For others, it is a way to diversify their foods, reducing their intake of animal products such as meat and milk and then increasing the amount of cereal and vegetables in the diet. Several people are also looking for something else: this might be translated into an opposition to the loss of diversity in taste and appearance of foods. This is contrary to the idea of food quality as seen by the food industry: nonuniformity. For several people, the popularity of organic cereals is closely linked to nostalgia of the past, especially taste. A question of lifestyle also exists where some want to produce these foods themselves, whereas others are willing to pay more to get the foods with the specific qualities they want or believe they have. Such people are willing to pay more not only for this insurance on their food but also for the preservation of environmental resources (water and biodiversity). 4. A question of confidence. The confidence of customers in food has been shaken by food crises such as the mad cow disease or dioxin contamination. Justified or not, the lack of confidence in food is one of the reasons for choosing organic foods. Internationalization of decisions on food production may also be seen as a threat, enticing some people to come back to alternative agricultural and food consumption practices. Some references on organic foods state that they have a higher nutritive value than nonorganic foods. Others conclude that organic foods are potentially riskier when natural toxins are not controlled. Also, organic foods could be related to a wish to avoid foods from genetically engineered organisms, due to the perception of their potentially negative impact on environment. Are organic foods much better for both health and the Earth? There is no guarantee that organic foods are safer, tastier, and more nutritive than nonorganic foods. In general, it is recognized that organic foods are likely to contain less residues of agricultural chemicals than nonorganic foods. However, this source of contamination is considered very low in any food.

AGRONOMY OF GRAIN GROWING | Organic Grain Production and Food Processing The health risks might be more important for growers themselves (plus their relatives and neighbors) who are in contact with concentrated pesticides than the public. Toxicity of pesticides used in agricultural practices remains a critical issue. Organic grain and food growers banish the use of wellknown toxicants such as concentrated chemical pesticides in the environment, with potentially questionable or not-so-sure long-term impact on human health.

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Potential Limits Most of the nontraditional cereals are more expensive than typical cereals partly because they are still marginal crops for a niche market. This may limit accessibility of specific cereals, due to variable environmental conditions especially if they are produced by few growers. More and more of these products are now available in North American and European supermarkets and specialized shops. According to most scientific studies, foods from organic-grown crops (including grains) are not more nutritive or safe than nonorganic foods.

Future Prospects It is expected that organic agriculture will remain popular for grain growers. For organic agriculture, specific grain varieties might be developed, especially those with long straw length, likely to limit growth of weeds through shading. Better understanding of organic grain growing will benefit from research as more scientists become interested in this sector. In the long term, expansion of the organic grain market will be faced with identity problems. In essence, it is an ecological alternative to conventional agriculture (using synthetic inputs) but is perceived as a source of safer and more nutritive grain, without ecological significance for citizens. The question of the quality of organic grain-based foods also remains to be addressed, considering the minimum input from ingredients used in conventional foods. Because the environment certainly has a major impact on human health, the organic way to grow grains is a nice alternative to conventional agriculture. It is not expected that organic growing of grain will replace nonorganic agriculture. Up to now, this alternative agriculture is mainly a phenomenon associated with industrialized countries, especially in Europe and America. Within less than 50 years, land surface devoted to organic agriculture has grown from literally nothing to a few percent. At the turn of year 2000, large food manufacturers and distributors have now embarked on the organic train. This is symptomatic of the attractiveness for safe, nutritive, flavorful, and guilty-free foods for which some consumers are ready to pay an ‘insurance premium.’


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What is the main difference between organic agriculture and nonorganic agriculture?

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How controlled is the production of organic grain? Which one is safer, healthier, and more nutritive? Organic grain? Nonorganic grain? Are organic grain-based foods cheaper than nonorganic? Why? Is there a future for grain produced according to organic agriculture? What is the main reason for consuming organic grain? To save the planet? To encourage local markets? To reduce the use of pesticides in food and the environment? To encourage the production of grain-based food that is safer, healthier, and more nutritive? None of the previously mentioned reasons? All of the previously mentioned reasons?


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The production of organic food must meet specific guidelines. What are the names of the main certification agencies in your country? Look at some food labels and identify which ingredients would qualify or not for organic certification. What are the main constraints in the production of organic grain, faced by either farmers or food processing companies?

See also: Food Grains and the Consumer: Consumer Trends in Grain Consumption; Labelling of Grain-Based Foods.

Further Reading Codex Alimentarius Commission (2010) Guidelines for the Production, Processing, Labeling and Marketing of Organically Produced Foods. GL 32-1999, Rome: FAO. Dangour AD, Dodhia SK, Hayter A, Allen E, Lock K, and Uauy R (2009) Nutritional quality of organic foods: A systematic review. American Journal of Clinical Nutrition 90: 680–685. Dangour AD, Lock K, Hayter A, Aikenhead A, Allen E, and Uauy R (2010) Nutritionrelated health effects of organic foods: A systematic review. American Journal of Clinical Nutrition 92: 203–210. IFOAM (2011) Position Paper. The Use of Nanotechnologies and Nanomaterials in Organic Agriculture. Brussels: International Federation of Organic Agriculture Movements. IFOAM (2012) The IFOAM Norms for Organic Production and Processing. Brussels: International Federation of Organic Agriculture Movements. Magkos F, Arvaniti F, and Zampelas A (2006) Organic food: Buying more safety or just peace of mind? A critical review of the literature. Critical Reviews in Food Science and Nutrition 46: 23–56.

Relevant Websites fibl.ch http://www.fibl.ch and icrofs.org http://www.icrofs.org – These sites refer to the Research Institute of Organic Agriculture (Switzerland) and the International Centre for Research in Organic Food Systems, two major research organizations dedicated to organic agriculture. ifoam.org http://www.ifoam.org – This is the website of the International Federation of Organic Agriculture Movements. This organization is recognized as the leading group and its main function is to coordinate the international organic movement, offering, for example, standardized rules for certifying organizations from different countries.

Precision Agriculture EC Leonard, AgriKnowHow, Maitland, SA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Precision agriculture (PA) is the practice of managing variability in space and time. Good management that pays attention to detail rather than technology is required to implement PA but technology can help. The application of PA has potential at all scales and levels of agricultural development. Spatial management can result in the more appropriate use of inputs that benefits the profitability of the enterprise and natural resource management. The application cycle for PA is observation, evaluation, interpretation, targeted management, and observation. Guidance tools, rate controllers, and automated data collection assist in the large-scale application of PA. New technologies and their application in PA continue to evolve.

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Learning Objectives

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especially in large-scale, mechanized systems. However, in small-scale agriculture, management in space and time can be achieved using manual labor and simple mechanical solutions. For example, moving from a system of broadcasting fertilizer by hand to placing a bottle cap of fertilizer at the base of each maize plant is an example of adopting precision management. Each plant (place) receives a measured dose of fertilizer (amount), while application timing (time) may be unchanged. Termed ‘microdosing,’ this method of fertilizer application was developed by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). It has resulted in improved grain yield and has helped contribute to the food security of poor farmers in drought-prone regions of Africa. Examples such as this help to support the proposal that PA is the next revolution in agriculture that will help the world achieve food security in developing and developed nations. In summary, the goals of PA are threefold:

To understand the concept of precision agriculture and its potential application in grain production irrespective of the stage of agricultural development.

Optimize the use of available resources to increase the profitability and sustainability of agricultural operations Reduce negative environmental impact Improve the quality of the work environment and the social aspects of farming, ranching, and relevant professions

These goals can be achieved through observation, evaluation and interpretation, and targeted management.

Introduction

Spatial Management

The grain industry, like many other sectors of agricultural and horticultural production, has embraced the use of precision techniques with the aim of gaining production and economic and environmental benefits. As a relatively new and rapidly evolving area of management practice, there appear to be as many definitions as names for this approach to farming. Other titles include smart agriculture, site-specific crop management, and information-rich agriculture. In the broadest sense, ‘precision agriculture’ (PA) is the application of management decisions in space and time based on identifying, quantifying, and responding to variability. PA can be applied to the management of inputs and outputs in terms of both quantity and quality and can be used to manage production and economic and environmental risks by achieving more appropriate and targeted use of finite resources. Indeed, some people define PA with the three R’s, the right time, right amount, and right place, while others add two more R’s – the right input applied in the right manner. None of these descriptions mention technology because PA is not solely reliant on satellites, sensors, computerized information systems, and machinery control systems. These tools do help in the identification and management of variation

Agriculture is the first form of production undertaken by man. As humans became more sophisticated and countries more industrialized, agriculture evolved from small-scale, laborintensive to large-scale, mechanized systems. However, big is not always better; a 36.5 m seeding drill traveling at 8.5 km h1 might be able to cover one hectare in 60 s. But what field size and run length are optimal? Where will filling stations for seed and fertilizer need to be located? And if the paddock dimensions are set up for this seeder, how will this impact on in-crop and harvest operation requirements? Unlike mining or factory-based production systems that have been scrutinized to develop logistically efficient systems, agriculture’s evolution has been more ad hoc. Perhaps this is due to factors such as historically irregular field boundaries, changing topography and soil types, and the constraints of tradition. The evolution of PA and the development of cheaper guidance tools are helping farmers take a more logistical approach to resource management. Instead of the unit of management being the field and dividing the input as evenly as possible across that management unit, PA enables a farmer to put inputs or infrastructure where it is most required. For grain production, spatial management can be on a catchment scale, for example, to provide rapid and economic

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AGRONOMY OF GRAIN GROWING | Precision Agriculture identification of the best locations for irrigation dams to maximize rainwater collection. Equally, PA can be applied at a subfield level to vary inputs by crop requirement. Irrespective of the scale, the starting point of PA operations is to be able to locate and record points in the landscape so it is possible to accurately and repeatedly return to those defined points (Figure 1).

Positioning Access to international Global Navigation Satellite System (GNSS; http://www.ignss.org/), via cost-effective receivers, and the development of a user-friendly geographic information system (GIS) have provided the tools for researchers and farmers to manage the spatial elements of developed agricultural production systems. The Navstar Global Positioning System (GPS) is one type of GNSS. It is controlled by the US Department of Defense. Russia, in partnership with India, has restored the Sovietbuilt Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) to operational capacity. A third system called GALLILEO was launched by a European consortium. There are three main elements to a GNSS: 1. A constellation of orbiting satellites 2. Receiver units 3. The master control station and satellite-monitoring ground stations While the term ‘GPS’ officially relates to the Navstar system, it has become shorthand for all GNSS receivers irrespective of the GNSS to which they are linked. GNSS receivers need ‘line of sight’ to at least four different satellites to be able to triangulate their position using the GNSS

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signals. Accuracy is dependent on how precisely the distance from each satellite to the receiver can be measured. Accuracy of a receiver can vary between þ/8 m and þ/2 mm, and horizontal and vertical accuracy will differ with the same receiver. A differential signal (DGPS) can be used to help correct the errors in the basic GNSS measurement. Such correction signals are provided by private companies, government agencies, or private base stations. Handheld devices including mobile phones generally have an accuracy of 3–6 m; these can be useful for crop scouting and ground truthing (see the section ‘Ground Truthing’). Receivers (single carrier phase) with þ/50 cm accuracy are often considered sufficient for grain production operations. The most accurate receivers are Real-Time Kinematic (RTK) receivers. Such systems require a dedicated, local base station or continuously operating network to provide the correction signal. With RTK systems, topography data are gathered simultaneously. A dual carrier phase (RTK) receiver is generally quoted to achieve þ/2 cm accuracy and is used for precise steering operations. The ability to precisely identify and return to locations provides the opportunity to manage on a spatial basis. This can be achieved by placing permanent markers in the field, foam or physical markers on equipment, but the use of GNSS provides the foundation for integrated spatial data collection, analysis, and management. In the United States, Australia, and Europe, about 80% of grain growers use some form of satellite guidance. A major benefit of knowing exactly where the tractor and implement are in the field is that overlap between runs can be minimized. Trials have shown that the use of satellite guidance and autosteer can reduce run-to-run overlap by between 5% and 15%, depending on operator experience and regularity of field shape. Not only does this result in savings in inputs

Figure 1 Examples of components of precision farming using satellite technology to provide spatial positioning data, rate controllers, data loggers, and plant sensors. In one pass, all the components of PA can be completed – observation, evaluation and interpretation, and targeted management. Source: Image credit Emma Leonard.

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of seed, fertilizer, and pesticides, but also it has been shown to reduce fuel and save time. The addition of autosection control enables wide implements, such as boom sprays and seeding bars, to be managed as multiple narrower subunits, which can help further reduce input overlap. The use of guidance on the tractor and implement enables precise guidance for operations such as sowing between last year’s crop rows and land grading. Grain growers in Queensland have reported that the use of GPS-based land leveling reduced the total amount of soil moved, with 180 m3 ha1 less soil moved in the cut operation and 151.4 m3 ha1 less in the fill, on a 128 ha field. Research on leveling and bed formation in India on small fields resulted in a 17% increase in wheat yield produced with 50% less water than the traditional system. Both systems represent substantial improvements irrespective of the scale of farming. Another important use of spatial data in grain production is the creation of maps that spatially relate input and/or output data.

Identifying Variability In grain production, there are generally two objectives, namely, to maximize profitable yield and to optimize quality to meet a specific market requirement. Both yield and quality of grain can vary across the field. This spatial variation often relates to changes in soil type and terrain that in turn influence soil water and nutrient properties. Patterns of spatial variation can be modified each growing season (temporal variation) by a range of factors, including seasonal weather conditions, nutrient demand, pests, and diseases. Both spatial variation and temporal variation can be influenced by crop management. For example, patterns of yield variation may differ between crop types or if the direction in which the field is sown is changed. In addition, variability can be introduced if inputs are not broadcast evenly or if chaff is left in rows behind the harvester. Spatial data can be gathered on the ground (proximal) using simple manual sensors including the human eye, the number of bags of grain harvested in an area, or with complex sensors that measure grain weight or wavelengths emitted from the soil or crop canopy. Remotely sensed data are gathered aerially from manned or unmanned aircraft or from satellites. Optical, infrared, and near-infrared data are regularly captured as satellites orbit the Earth. Even the basic, free imagery and spatial data available from online providers, such as Google®, the Earth can provide a base layer for identifying spatial variation. The frequency, area, resolution, availability, and price of imagery required determine whether it is collected remotely or proximally. Spatial tools are being used not only in production systems but also in plant breeding and agronomic research to help provide objective rather than subjective measurements of change and to fast-track data collection and analysis (Figure 2).

Yield Maps A yield map is a useful starting point for visualizing and locating areas of variation. Modern grain harvesters are generally

Figure 2 Maps of in paddock variation – soil (EM38), yield, and plant biomass. Combinations of spatial data layers can be used to create management zones. Source: Image credit Emma Leonard.

equipped with a yield monitor capable of logging yield information every 1–2 s. This gives very dense yield data; however, these data have to be cleaned (krigged) of erroneous data points before being interpolated into the map surface. Erroneous data points in yield data are often generated

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when turning and at the ends of rows, if the cutting width is incorrectly set, due to issues with the GPS feed, or when multiple harvesters are working in the same field.

The yield map can provide the basis for locating areas in which to take soil samples and can also be used to determine replacement nutrient maps for the following crop (see the section ‘PA-Based Decisions’). Monitors to measure cereal grain protein content, an important measure of grain quality, on the go at harvest have been developed. Research in Australia found the density and reliability of protein data collection to be less useful for further crop management than yield data. While a yield map provides a useful synopsis of variation, it gives no indication of the cause of the variation. In order to establish causes of variation, soil and crop sensors can be employed.

Soil Monitoring Optical satellite imagery is widely available and can also provide a valuable starting point for locating changes in soil properties, especially color, which can relate to soil texture and class. Proximal tools for on-the-go soil sampling continue to evolve from those measuring a single parameter, for example, pH or organic matter, to multiple physical and chemical characteristics being recorded in a single pass. A widely used on-the-go soil sampling method has been to measure electromagnetic induction. This can be done aerially but for agriculture is generally done proximally using a transmitting and receiving coil in contact with the soil surface. The amount of electrical current flowing from the soil, to a depth up to 1.5 m (proximal), is measured. This is directly proportional to the electrical conductivity of the soil and is referred to as the apparent electrical conductivity (ECa) (Figure 3).


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Figure 3 An EM38 sensor being towed behind a utility to gather soil data that can be presented as a map. Ground truthing is required to establish the reasons behind the areas of difference. Source: Image credit Emma Leonard.

The ECa is most strongly influenced by changes in clay content, soil water content, and soil salinity. The electrical conductivity of the profile is never governed by a single soil property, rather by a combination in constantly varying proportions. Soil profiles also contain natural radioactive isotopes that emit gamma rays (GR). These emissions can be measured to different depths but the proximal sensors generally used in agriculture measure about the top 40 cm of the soil profile. GR provides information about the soil forming parental geology of the soil, changes in clay, and levels of gravel. The main elements measured for use in agriculture are potassium (K), thorium (Th), and uranium (U) and gamma-radiometric total count.

Plant Sensors Sensors have been developed to measure the interaction between the sunlight and the plant leaf. Basically, these measure the energy in different wavelengths reflected from the plant/canopy to determine information about the type of plant and its growth status and health status before visual symptoms are observed. A plant that is moisture-stressed, lacking nutrients, or suffering disease will use or lose different amounts and wavelengths of sunlight. The human eye is an important sensor but can only work in the visible spectrum. Relatively cost-effective handheld and vehicle-mounted sensors are commercially available to measure wavelengths across much of the electromagnetic spectrum. Proximal sensors are termed active if they include a manmade light source that is designed to saturate the subject and eliminate shadows. Remote sensors are generally passive. These nondestructive sensors can rapidly gather data; when processed through a GIS, a picture of variation across the crop

canopy is produced. Calibration and ground truthing of the data are essential. Calibration generally needs to account for species, cultivar, and plant growth stage and is best done against a nonlimited reference plot. On-the-go calibration systems are being developed where the software continuously reanalyzes the cumulative data to generate a calibration. Multispectral sensors are used to gather near-infrared and red wavelengths, which are commonly converted to the Normalized Difference Vegetation Index. This index is used as a surrogate measurement of a crop’s nitrogen status. Such sensors were the first to be developed to provide on-the-go indications of crop nitrogen status and consequently demand for nitrogen fertilizer. Multispectral sensors have also been developed to distinguish low densities of weeds against soil backgrounds. Such technology enables herbicide to be targeted directly at individual weeds reducing herbicide inputs by 70–80% compared to a blanket application. Machine vision is another tool being used in relation to targeted herbicide application. As hyperspectral sensors become more cost-effective and satellites gather a greater range of wavelength data, it is anticipated that biomass and crop quality data will be assessed against hyperspectral data. Thermal infrared radiation is a good indicator of canopy temperature and indirectly the capacity of the crop to regulate its own temperature by transpiration. A hotter canopy indicates crop stress that has resulted in stomata, the pores on the leaf through which water is transpired, to close. Lack of soil water, rooting limitations, or disease can cause canopy temperature to increase. Some molecules in the plant cells generate fluorescence in response to the light energy received. Chlorophyll and polyphenols are such molecules. Normally, as the chlorophyll content falls due to stress, the polyphenol content rises.

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Dividing the chlorophyll content by the polyphenol content provides a more sensitive indicator of plant stress than using the two measurements separately. This calculation is the basis of the nitrogen balance index (NBI). Research in Canada, the United States, and Europe has shown the NBI to provide a more reliable indicator of crop nitrogen status, especially in early growth, than multispectral sensors. Fluorescence-based sensors appear to be highly sensitive to plant nitrogen status without influence from soil, leaf area, or biomass status. Fluorescence sensors offer the potential to detect diseases that affect the leaf surface before visual symptoms occur.

Ground Truthing In all cases, irrespective of whether data are gathered remotely or proximally, from grain, soil, or plant material, some form of ground truthing the data is always recommended. Generally, this entails taking samples from known points within the field and testing them through a laboratory. Yield, soil, and biomass maps can be loaded onto mobile applications and the inbuilt GPS unit used to navigate to selected sampling points within areas of variation that have been identified on the map.

PA-Based Decisions The stability of spatial variation determines where it can be used to make predictive or reactive management decisions. These decisions generally relate to varying the rate of an input. Inputs may be applied with the aim of increasing yield uniformity across the field or targeted to maximize potential productivity or profitability of zones within a field, which can result in greater yield or quality variation. Before the application of PA management, the degree of variation needs to be assessed and the return on varying inputs established. The justification for managing variation will depend on the attribute, the magnitude of the variation, and cost-to-benefit ratio compared to a uniform treatment. Not all variation will warrant management; however, return can relate to less impact on the environment due to more appropriate use of inputs and to improved financial return. The spatial distribution of soil characteristics such as acidity and sodicity is an example of factors that are relatively static so it can be addressed predictively. Patches of grass weeds such as wild oats have also been found to be relatively stable and have been successfully treated predictively. Combining soil and terrain data can be used to vary the rate of irrigation water or effluent applied or volume of soil removed when establishing flood irrigation systems (see the section ‘Spatial Management’). Combinations of up to 20 different spatial data layers are being used to predict variable seeding rates across a field (http://www.fieldscripts.com/). Crop nutrient removal relates to crop yield, which will be seasonally influenced. By combining yield data for a field from years when the same crop was produced, for example, all the years of wheat, a more stable picture of yield

potential can be established. Such combined yield data can be used to produce a zone map for varying nutrient inputs at seeding. Reactive management decisions often relate to in-crop decisions for nitrogen nutrition and weed, pest, and disease management as these are affected by seasonal conditions. Multispectral sensors and fluorescent sensors have been used commercially to vary the rate of in-crop nitrogen in cereals. The latter are showing potential for early disease detection. Optical sensors capable of distinguishing weed types enable different types or concentrations of chemicals to be delivered on the go as weeds are identified.

What the Future Holds New sensors and rate-controlling software continue to be developed to assist in site-specific identification and targeted application of inputs. Disease and pest management are two such areas of development. These tools also support improved traceability and the gathering of data to meet regulatory requirements. As data transfer networks continue to improve, new opportunities for existing technologies emerge. For example, timelapse photography is not new but its application to remote sensing of the emergence of pests and disease is made possible with cheap, battery-powered cameras and cost-effective telemetry systems. Mobile phones are offering farmers a powerful package of tools. These range from the commonplace apps for crop scouting, weed identification, etc., to the novel where inappropriate vibrations from equipment can be identified and an early maintenance warning triggered. With over 40% of people in developing countries already using basic mobile phones, there is a huge opportunity for the delivery of spatial management through such platforms. Across the globe, robotic platforms and unmanned aerial vehicles are being developed to carry multiple sensors and tools. Driverless tractors are already in the latter stages of development, and it is likely that it will be legislation rather than technical capability that slows their path to market. It is only about 100 years since tractors started to replace horses as the power source for grain production. Few farmers in the developed world would now know how to harness a horse team. Within the next 100 years, it is likely that farmers will lose the skills of driving a tractor but will require and gain skills in computer science and electronics. Despite the evolution seen and the prediction of where farming will evolve to, it is likely that the skills of observation, evaluation, interpretation, and decision will still be required to ground-truth-automated systems. So, whether it is driving a team of horses or a team of robots, the adage to be an outstanding grain grower you need to be outstanding in the field is likely to hold true for another century.


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What are the four components of precision agriculture management?


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What factors will determine if it is viable to manage variation? Contrast the concepts of PA as in use now (high-tech and in the near future) with those concepts as used historically (low-tech). Comment of likely cost–benefits. Use free satellite imagery to identify variation across an agricultural landscape. What international collaborations involving remote sending have assisted the international use of PA? Explain the concept (and necessity) of ‘ground truthing.’


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Comment of the prediction: ‘PA is the next revolution in agriculture that will help the world achieve food security in developing and developed nations.’ What evidence can you find to support (or refute) this statement? Research the extent of PA use in your region, based on growers’ experience and what is offered for sale. What claims are being made for its value? Find out the relative suitability of PA for each of a few different grain species. How about the wider range of applications in agriculture?

See also: Agronomy of Grain Growing: Barley: Agronomy; Canola: Agronomy; Sorghum: Production and Improvement Practices; Soybean: Agronomy; Wheat: Agronomy; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Canola:

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Harvest, Transport, and Storage; Sorghum: Harvest, Storage, and Transport; Grain Marketing and Grading: Wheat: Grading and Segregation; Wheat: Marketing.

Further Reading Bora GC, Nowatzki JF, and Roberts DC (2012) Energy savings by adopting precision agriculture in rural USA. Energy, Sustainability and Society 2: 22. Bramley R, Mowat D, Gobbett D, Branson M, Wakefield A, and Wilksch R (2012) Mixing grapes and grain – Scoping the opportunity for selective harvesting in cereals. In: Australian Society of Agronomy Conference 16 . http://www.cabi.org/projects/project/20187 – CABI, Direct2Farm, 2014. Dang YP, Dalal RC, Pringle MJ, et al. (2011) Electromagnetic induction sensing of soil identifies constraints to the crop yields of north-eastern Australia. Soil Research 49(7): 559–571. Heap J and Trengove S (2008) GRDC Update http://www.grdc.com.au/Research-andDevelopment/GRDC-Update-Papers/2008/06/Site-Specific-Weed-ManagementSSWM. Khosla R (2013) Precision agriculture and food security. In: Fifth Asian Conference on Precision Agriculture, Korea . Kodaira M, Shibusawa S, and Ninomiya K (2013) High resolution 19 soil parameter mapping using a mobile real-time soil sensor. In: Fifth Asian Conference on Precision Agriculture, Korea . Leonard EC (2013) Precision land forming. Precision Agriculture News 9(1): 26–27. Lowenberg-DeBoer JM (2013) Ninth European Conference on Precision Agriculture . McNeil J (2014) WeedIT. Precision Agriculture Expo, South Australia. Pierce FJ and Nowak P (1999) Aspects of precision agriculture. Advances in Agronomy 67: 1. Robinson M, Carberry P, and Brennan L (2007) The economic benefits of precision agriculture: Case studies from Australian grain farms. Australia: CSIRO. Tremblay N (2013) Making sense of sensors. Precision Agriculture News 10(1): 16–18. Whelan B and Taylor JA (2013) Precision Agriculture for Grain Production Systems, 1st edn. Collingwood, VIC: CSIRO.

Plants: Diseases and Pests SA Barton, Oxford Agricultural Trials Ltd, Oxford, UK ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 450–459, ã 2004, Elsevier Ltd.

Topic Highlights

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The effects of disease and pests are compared to the appearance of healthy plants, considering both monocotyledonous plants (e.g., wheat) and dicotyledons (e.g., canola). The consequences of disease can be reduced grain yield, poorer grain quality and even detriment to food safety. Plant vulnerabilities: ○ Reduced photosynthesis rate, e.g., due to mildew and rust. ○ Reduced ability to take in water and transport nutrients, e.g., Fusarium and take-all diseases or pests such as slugs and insects. ○ Interference with seed formation, e.g., smut and ergot infections, sucking insects. The causal agents are listed by the categories of fungal, bacterial and viral. Pests that cause damage include birds, mammals, insects, nematodes and molluscs. Management and prevention is possible via husbandry, the development of genetic resistance and chemical control. Ultimately ‘integrated pest management’ is a desirable strategy, based on a thorough understanding of disease-pestplant interactions.

Learning Objectives

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Achieve understanding of the causes of plant diseases and the pests involved in plant damage. Develop the ability to recognize which pests and diseases are causing plant and grain damage, and understand strategies to minimize these problems.

Introduction The importance of diseases and pests in terms of food crops provides a context that all can relate to. In order to recognize the symptoms caused by pathogenic fungi and bacteria, viruses, and other plant pests, it is necessary to be familiar with the way in which healthy plants appear and how they behave. It is in this vein that a reminder of general plant physiology is given, and the vulnerable stages in plant development and growth are highlighted. An element of detective work is often necessary when identifying the cause behind plant abnormalities; the results of attack by various types of pests can appear very similar to the effects of nutrient deficiencies. ‘Cereal,’ ‘combinable,’ or ‘grain’ crops are terms used to include those that are grown to produce seed for human consumption, that can be harvested with a combine and have small, hard seeds. Barley, maize (corn), millet, oats, rice, rye,

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sorghum, triticale, and wheat are monocotyledonous and have a growing point at ground level (Figure 1a). The dicotyledonous plants including amaranth, beans, buckwheat, canola (oilseed rape), chickpeas, cotton, lentils, linola/linseed, lupins, peas, peanuts, quinoa, safflower, soybeans, and sunflowers have growing points aboveground level (Figure 1b). How these two types of plants grow, and in general this varies from plants to plants, determines their susceptibility to the various pests and diseases. An introduction to both infection and infestation of plants from pathogens and pests, respectively, is provided. Approaches to disease and pest management using both natural and man-made remedies are given. Some crop species are more resistant to attack (whether from grazing animals or microscopic pathogens), whilst others can only survive under sheltered conditions.

Importance of Diseases and Pests The term ‘importance’ is usually associated with positive attributes, e.g., ‘an important crop is one that has many uses.’ Detrimental factors are equally important, however, as they can have a huge, negative impact. Plants are dependent upon their environment; they require available nutrients, water, and sunlight in sufficient quantities to allow them to grow. If disease or pest damage occurs, normal plant function is reduced, leading to injury or death unless the disease or pest is managed.

Fit for Purpose The main effect of diseases and pests that occur in crop plants is to reduce the yield. For profitable food producers, the main concern from pests and diseases is the effect they have on the marketability of the crop. Often, if either yield or quality is reduced, at least the crop can still be sold, even if it is for a lower price than planned. If both factors are reduced, the crop will not be profitable at all. If this is the case for more than a season or two, such losses are unlikely to be sustainable. If a crop does not make money, there is no economic sense in growing it. When crops are grown to sell in niche markets, they must be fit for the purpose, as with organic produce. In this case, the way in which the crop is grown must meet certain, strict specifications throughout the growing season in order to retain its status. Part of the requirement in this example is not to use the majority of chemical pesticides (including fungicides) even when the crop is under attack. For the organic producer, not treating could mean reduced quality of produce, but treating could mean losing organic status and not being able to sell at the premium rate. Where market demand is present and there is fierce competition for a share, high standards of food quality and safety are vital.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00197-2

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Figure 1 Location of plant growth points (arrows): (a) monocotyledons and (b) dicotyledons.

Food Safety The safety of food has become increasingly important over the years; besides affecting the marketability of a crop, it can have serious implications on consumer health. Pests and diseases can have a direct effect on the safety of food crops, such as the presence of mites in cereal-based products leading to the development of asthma and some molds that produce mycotoxins. There is also a safety issue with the presence of pesticides remaining in the harvested part of the crop, when high levels of diseases or pests were present during the growing season and were controlled to protect the quality of the product. Extensive testing to set maximum acceptable levels for both mycotoxins and pesticide residues is in progress. Typically, the agreed limits are based upon levels measured in food that is currently available and that has found to be safe. Whilst food safety is obviously a serious issue, the food crops currently produced are of a very high standard. In many countries it may appear that safety limits are now used as a reason for rejecting a proportion of the crops where production is high, rather than because there is a serious risk to consumers.

Healthy Plants Once a seed has germinated and developed into a seedling, it will grow to maturity over a period of weeks, months, or years depending upon its genetic makeup and the nutrients available to it. During this time, photosynthesis is carried out within the chloroplasts of the green plant cells. Intercepted solar energy is used to convert carbon dioxide and water into carbohydrates and oxygen. The simple carbohydrates produced in this way are then processed into starch (for efficient storage), the structural component of cell walls (cellulose), fats, oils, or proteins. For a plant to be healthy, photosynthesis must be efficient, the required raw materials must be available, the chlorophyll within the leaves must be working correctly, and the carbohydrates produced must be transported to the growing points of

the plant. Plants need various mineral nutrients (such as nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, manganese, and molybdenum) for the more complex molecules that they produce during growth. When these nutrients are in short supply, symptoms of deficiency are seen in the plants and damage caused by disease may be increased. The accumulation of carbohydrates is important in maintaining the plant’s species when they are sequestered either into the seeds of grain crops, or storage organs as with potatoes. Vegetative propagation via rhizomes or stolons may also give rise to new mature plants in some plant types.

Vulnerable Stages in Plant Growth The ‘success’ of a pathogen or pest depends upon its ability to invade a host, grow, and reproduce before causing death to the plant. Diseases and pests cause most damage to plants when they act upon critical points in the processes involved in plant maintenance, growth, and reproduction. These can be summarized as follows. 1. Reduction in the rate of plant photosynthesis. The reduction of green leaf area caused by pest damage or diseases such as mildew, scab, and rust will impair the interception of solar radiation. 2. Reduction of the plant’s ability to take in water and nutrients by preventing uptake through the roots or blocking the transport through the plant. As the components necessary for photosynthesis are restricted and the supply of water ceases, plants become chlorotic and wilted. Diseases falling into this category include Fusarium foot rot, eyespot, and take-all; pests include slugs and insect larvae that damage stem bases and roots. 3. Interference with seed formation leading to infertile flowers, nonviable seed, or the replacement of seed with fungal structures. Damage caused to the lower stem can lead to infertile flower heads that do not produce any seed and may be described as ‘blind,’ or if seed is produced it is

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severely shriveled and of poor quality. Damage caused by insect larvae feeding on developing grains (e.g., wheat orange blossom midge) may prevent normal germination of the seed and will reduce its quality. Seed production is prevented in several species of grain by smut, bunt, or ergot infection. Plants are more vulnerable to attack at certain points in their life cycle than at others, particularly during the early stages of growth. As their biomass increases, they become more resilient to damage; this is illustrated in cereals with the damage caused by bulb-fly larvae. When the eggs of the bulb-fly hatch, each larva burrows into the base of a plant and feeds on the stem and leaf material there, this prevents the flow of nutrients and water up to the green leaves, resulting in their death. When the eggs hatch early in the season, there will only have been a single tiller produced; with this destroyed, the entire plant will die. When the eggs hatch at a later stage in the season, several tillers will have been produced and even if one or two are killed, the remainder will continue to grow and more tillers will be produced. By the time, the crop has reached maturity, there will be little effect on overall yield. Another example is aphid infestation of canola (oilseed rape). Because aphids feed via a proboscis that must be pushed into plant tissue before sap can be extracted (Figure 2), they attack new, tender shoots and are unable to penetrate older stems. A crop at an early stage in development contains plants that are completely accessible to aphids and may be killed if sufficient numbers build up during this vulnerable stage. Once plants have grown and have tougher stems, only their new shoots and flower buds can be penetrated. As flower sites are particularly tender, the fertility and amount of seed set may be reduced or the yield may be adversely affected with the restricted energy reserves available for storage within the seeds. Storage conditions are very important to keep seeds and tubers healthy and to start with a clean crop the following season. Seedlings are extremely vulnerable to attack from many types of organism and severe attacks at this stage are likely to be fatal. Once seedlings have reached a certain stage, they are equipped better to withstand attack. If the pest or disease is present in epidemic proportions, however, they are still at risk and at best, may suffer reduced yield. With the presence of inoculum and the means for its spread, diseases

Figure 2 Aphid feeding on plant sap through its stylet.

rapidly take hold. Attacks to flowers tend not to be fatal, as the plant is mature at the stage when they are produced but yield is still likely to be reduced.

Plant Infection by Pathogens The causal agents of plant diseases (pathogens) may be airborne, soilborne, splash-dispersed, or carried by insect vectors. These causal organisms are mainly fungi, bacteria, or viruses, although very few bacteria are associated with cereal diseases.

Fungal Diseases A fungus is a multi-celled organism that lacks photosynthetic ability; therefore, it relies on other organisms (animal or vegetable) to provide the necessary energy for growth and reproduction. If a fungus does not cause much damage to its host organism, it is described as saprophytic, but if the host is greatly damaged or killed, the fungus is categorized as parasitic. The main causal organisms of plant diseases are the true fungi (Eumycota); the three subdivisions into which most pathogenic fungi fit are: 1. the Ascomycotina (e.g., powdery mildew – Erysiphe graminis); 2. the Basidiomycotina (e.g., the rust and smut fungi); and 3. the Deuteromycotina (e.g., cereal eyespot – Pseudocercosporella herpotrichoides). The first two groups contain fungi that have both asexual (cell division) and sexual (cell fusion then division) stages to their life cycles, the third contains fungi whose sexual stage has not been identified (if they have one). Table 1 shows examples of cereal diseases caused by fungi. The sexual stage allows the alteration of genetic makeup over time as many generations are passed through. By this process, the fungus may gradually change in a way that enables it to infect plants that were previously resistant to its attack. When this occurs, the resistance of the plant is described as having broken down (although it is actually the pathogen’s properties that have changed rather than those of the host plant). During the course of several years, a newly developed crop cultivar will initially be resistant to infection from the

AGRONOMY OF GRAIN GROWING | Plants: Diseases and Pests Table 1

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Examples of cereal diseases caused by fungi

Crop(s)

Disease

Pathogen

Dispersal

Barley Cereals Cereals Cereals Wheat þ barley Cereals Cereals Cereals Cereals Cereals Cereals Cereals Maize Maize Wheat þ barley Wheat þ barley Wheat Wheat

Net blotch American powdery mildew Black stem rust Ergot Eyespot Foot and root rot Head blight Powdery mildew Rusts Seedling wilt Sharp eyespot Take-all Common smut Southern leaf blight Glume blotch Loose smut Common bunt or stinking smut Septoria

Pyrenophora teres Sphaerotheca morsuvae Puccinia graminis Claviceps purpurea Pseudocercosporella herpotrichoides Fusarium culmorum Fusarium culmorum Erysiphe graminis Puccinia spp. Fusarium culmorum, F. avenaceum, F. gramineaum, F. nivale, F. poae Rhizoctonia cerealis Gaeumannomyces graminis Ustilago maydis Cochliobolus heterostrophus Leptosphaeria nodorum Ustilago nuda Tilletia caries Septoria tritici

Seed Air Air/insects Soil/air Soil Soil Soil Air Air Soil Soil Soil Air Air/splash Splash Air Seed/air Splash

strains of pathogens present in the environment and a large area will be sown with this cultivar. In this way, a heavy selection pressure is placed on the fungi, as only those that able to overcome the plants’ resistance will be able to survive. Any strains of fungi that develop the ability to infect their host plants will have a great advantage and will multiply quickly. As the numbers of this ‘new’ strain increase in proportion to the ‘old’ strains to which the plant cultivar was resistant, the plants are more frequently attacked until the resistance loses its strength completely. This is an important consideration when producing crops, and is one of the key driving forces behind plant breeding programs, in addition to improving yield and crop quality. The process of pathogen evolution and its effect on a monoculture of a cultivar has been described as a cycle of ‘boom’ and ‘bust’ in terms of crop success. As the success of a new resistant cultivar encourages growers to use it, there is a boom, but when the resistance breaks down, there is a bust as the cultivar rapidly succumbs to widespread disease.

Life cycle of brown rust in wheat (Puccinia recondita)

This fungus may infect wheat and rye, but is particularly damaging to the former host. Disease symptoms occur on the leaf blades in the form of scattered orange-brown spots (uredosori) that are often surrounded by a pale halo of leaf tissue.

Mechanism of injury By removing nutrients from many host cells simultaneously, the growing fungus causes areas of chlorosis around each infection site. The growth of superficial mycelium on the leaves and the localized areas of chlorosis and necrosis reduce the green leaf area available for converting solar radiation into nutrients by photosynthesis.

Propagation Once established at an infection site, the fungus will produce fresh pustules (uredosori) that will release further uredospores. The infection cycle may be repeated many times during the summer growing season. The pathogen is able to survive between seasons by living on volunteer plants and straw in this way. As temperatures fall, teliospores and haploid basidiospores are also produced, which infect a noncereal host, such as meadow rue (Thalictrum flavum), and the cycle continues through winter and releases accidiospores that are able to infect cereals again.

Control Resistant cultivars will prevent infection from established fungal strains. Regular monitoring of the crop for early signs of disease will allow fungicide to be applied in time to prevent serious damage from new fungal strains.

Dispersal The uredosori release huge quantities of uredospores to be spread by the wind, particularly in warm weather with frequent rainfall (although hot conditions will halt its spread).

Penetration When a uredospore lands on the surface of a plant under conditions of suitable temperature (15–20 C optimum) and humidity (high), it will produce a germination tubule. As the tubule grows between the plant cells, it is recognizable as hyphae and will penetrate cells producing a haustorium, which it uses to remove nutrients from the host cell, thus enabling its own growth.

Bacterial Diseases All bacteria are single celled with no cellulose cell wall, chloroplasts, or mitochondria within them; they can only be seen as individuals under a light or electron microscope. Plant pathogenic bacteria have rod-shaped cells and rely on contact with a host organism to obtain the energy they need to grow and reproduce. They do not have a dispersal mechanism, so must rely on naturally occurring vectors (such as rain, insects, and soil-dwelling organisms) to move their cells into contact with a suitable host. Plant cells are well protected by rigid walls and a cuticle, so bacteria are only able to gain entry through

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wounds or natural openings (e.g., stomata). Diseases caused by bacteria are rare within cereals; they are a greater problem for broad-leaved plants and their fruit or tubers. The types of diseases caused by bacteria can be split into three main groups according to the way in which they act upon the host. Table 2 shows examples of cereal diseases caused by bacteria.

Control

1. Parenchymal diseases are recognized easily once they have taken hold; in the affected area of the host plant, the cell walls are broken down and become incapable of holding their original shape, resulting in a soft, weak mass. 2. Vascular diseases cause the host plants to wilt as the xylem and phloem pathways become blocked by thick, sticky substances produced by the bacteria, preventing transport of water around the plant. 3. Meristematic diseases occur when bacteria cause excessive plant growth in a localized area by stimulating either cell division, cell enlargement, or a combination of the two.

Viral Diseases

Life cycle of bacterial wilt in maize (Erwinia stewartii)

Symptoms range from mild to severe: long, pale green/yellowish streaks on leaves extending from the points of insect damage; early flowering and the production of very few ears; and no ears produced, or complete plant death.

Dispersal The main vector of these bacteria is the corn flea beetle (Chaetocnema pulicaria), but the soil-borne larvae of Diabrotica longicornis and Phorbia cilicrura, that attack the plant roots, also carry them.

Penetration The vector damages the plant when it feeds, allowing bacterial cells to enter through the wounds and into the host’s vascular system.

Mechanism of injury Once inside the host, the bacteria feed on it by producing enzymes to degrade the pectin of cell walls. By-products are produced in the form of sticky polysaccharides that build up to block the vascular system and preventing the normal flow of nutrients around the host.

The main method of control is to target the flea beetle (vector) population with early season insecticides; this can be combined with the use of resistant cultivars.

An individual virus is submicroscopic (about 50 nm across) and can only be seen using an electron microscope; it generally consists of a single strand of DNA or RNA encapsulated within a protein coat. Because of their simplicity, viruses require other cells (e.g., animal, plant, or bacterial) to provide the building blocks and energy required to replicate themselves. Different types of viruses are specifically adapted to infect different organisms; those that infect plants tend to contain RNA and are coated with a simple protein layer when traveling between cells. When a virus comes into contact with a host cell, the RNA passes into the cell, leaving the protein coat on the outside. The RNA causes a template strand (that is complementary to the original) to be formed from the cell’s DNA; this template is then used to replicate many strands that are identical to the original. Upon entering the host cell, the initial viral RNA strand causes the host cell to produce enzymes (RNA polymerases) that catalyze the replication of new viral RNA strands. The plant cell is also used to produce the protein coating to enclose the new RNA strands before the cell is completely destroyed and the new batch of viruses released and may remain in the intercellular spaces to infect new cells, or may enter the plants transport system and be dispersed throughout the plant. Table 3 shows examples of diseases caused by viruses. When they are outside a host’s cell, viruses are relatively fragile and easily killed. The success of viruses is due to the way they are actively spread from plant to plant via various vectors such as aphids, leafhoppers or whitefly (all of the order Homoptera), soil-dwelling nematodes, fungi, or within seeds. These insect and nematode vectors share a common morphology in their feeding organs; they have a protruding ‘beak’ called a stylet that is able to penetrate the outer cuticle of plant surfaces and enter plant cells. Within this group of vectors, the two main categories into which virus transfer falls are termed ‘stylet-borne’ and ‘persistent.’ Table 3

Propagation Bacterial cells divide rapidly once they have gained sufficient nutrients to enable them to do so. Vectors feeding on infected plants will carry some bacterial cells to other plants and continue the infection cycle. Table 2

Examples of cereal diseases caused by bacteria

Crop(s)

Disease

Pathogen

Maize Oats

Bacterial wilt Halo blight

Wheat

Yellow slime (Tundu disease)

Erwinia stewartii Pseudomonas coronofaciens Corynebacterium tritici

Examples of cereal diseases caused by viruses

Disease

Vector

Barley stripe mosaic virus Barley yellow dwarf virus (BYDV) Barley yellow mosaic virus Maize chlorotic dwarf virus Maize dwarf mosaic virus (MDMV) Maize mosaic virus Maize rough dwarf virus Oat blue virus Oat mosaic virus Rice dwarf virus Rice tungro virus

Pollen/infected seed Aphids especially Rhopalosiphum spp. P. graminis (soil fungus) Graminella nigrifrons (leaf hopper) Many aphid species Peregrinus maidis (plant hopper) Laodelpax striatellus (plant hopper) Macrosteles fascifrons (leaf hopper) P. graminis (soil fungus) Nephotettix cincticeps (leaf hopper) N. impicticeps (leaf hopper)


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Stylet borne

Propagation and mechanism of injury

As the name suggests, viruses transmitted in this way are carried from an infected plant by a vector within or stuck on the outside of the stylet after a feeding session from the outer layers of a host plant. When a new feeding place is reached (on another plant or a different location of the same plant), the plant’s cuticle is punctured and the viruses delivered from the stylet into close contact with internal plant cells. The ‘soybean mosaic virus’ is transmitted in this way.

As the viruses replicate themselves, they use the host cell contents and leave empty, dysfunctional cells behind them. Due to their rapid multiplication, they cause large areas of cells to become necrotic simultaneously. When a crop is infected at the seedling stage, large areas can be wiped out completely, as the plants grow, they are able to tolerate the infection better, if they are not infected until late in the season, there will be very little damage to the crop.

Persistent

Control

This type of transmission occurs by the movement of infected sap taken from the host plant’s transport system. When the vector feeds on the sap of a plant containing virus particles, it ingests the mixture without harming the pathogens’ structure. The virus particles may remain dormant within the vector for several hours allowing a greater chance of spreading the disease to a new plant, or they may retain their virulence and be able to cause infection immediately as they come into contact with a host cell. Upon moving to a new feeding position, the viruses are injected deep into the transport system of the new plant, as with the ‘pea enation mosaic virus.’ Regardless of the manner in which a virus enters its host plant, once inside it is able to penetrate the host cells, rapidly multiply, and spread causing disruption of normal growth. By repressing production of the plant’s necessary enzymes, symptoms are seen on the outside of the plant. These symptoms are the basis for the classification of the different types of virus pathogen:

The only effective method is by reducing the aphid (vector) population, this can be combined with the use of resistant cultivars and reducing the amount of wild grasses surrounding the crop as these are a source of inoculum.

1. Stunting and dwarfing result from a loss of ability to grow normally. 2. Color change occurs when chlorophyll production is reduced, forming a mosaic, mottled pattern of yellow and green on the leaves. Variations on chlorosis, followed by necrosis, may cause interveinal discoloration or concentric rings of yellow and brown. 3. Leaf and stem distortion results from abnormal cell proliferation or development as occurs in virus leaf curl diseases.

Life cycle of barley yellow dwarf virus in cereals Despite its name, barley yellow dwarf virus (BYDV) infects many grass species, including barley, oats, wheat, and rye. Symptoms are seen as bright yellowing (wheat and barley) or reddening (oats) of the leaves from the tip back toward the stem. Other symptoms may include necrotic spotting, stunting, increased tillering, and bleached, sterile ears.

Dispersal Many species of aphid carry this virus from one feeding site to the next. After an aphid feeds for 24–48 h on an infected plant, there is a short latent period (during which the virus will not be passed on), then the virus will be transmitted from that aphid for the next few weeks.

Penetration The virus particles are injected by the vector directly into the host’s vascular system from which they are able to enter large numbers of host cells throughout the plant with relative ease.

Plant Damage by Pests Birds and Mammals Although some species of birds will eat insects rather than seed, there are those (sparrows and pigeons in particular) that will eat seeds at every opportunity: during storage, when planted in the field, at germination and during early plant development. If seeds are damaged, they are unlikely to remain viable and will not germinate. Wild burrowing and grazing animals such as rabbits, hares, gophers, badgers, rats, and mice (and their relatives around the world) can be serious pests once seeds have germinated. If a germinated seed is damaged, the seedling produced may be stunted or grow abnormally if at all. If young plants that are attacked survive, they are likely to produce a weak plant with a reduced capacity for reproduction (i.e., lower yield). Once plants are well established, they are less likely to be killed by an attack, particularly in the case of monocotyledonous cereal plants where the growing point is at or below ground level; continuous grazing can be tolerated until stem elongation begins in earnest. Dicotyledonous Brassica sp. can also survive being pecked at by pigeons, provided they are not completely mown down to the ground; they have multiple growing points and will compensate by sending out new growth from the leaf axils.

Insects Although it may be stating the obvious, insects have smaller mouths and so prefer more tender parts of plants than larger pests. They cause particular problems for younger plants; the smaller the area of green leaf to begin with, the less damage it takes to destroy it. Insects are either designed for grazing leaves (with jaws) or for piercing leaves then sucking out the sap (with a stylet). Many insects are attracted to flowering canola (oilseed rape) and similar crops in the field where they lay eggs. Once these have hatched, the insect larvae devour the leaves and flowers as they grow. Other insect pests pose a problem in stored grain, particularly weevils, beetles, moths and their larvae.

Nematodes and Molluscs In addition to the aerial plant parts, slugs, nematodes, and some insect larvae attack the roots. Of the pest nematodes,

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some feed on the internal and some on the external parts of plant roots using a stylet in a similar way to aphids.

Disease and Pest Management ‘Control’ of pathogens and pests does not tend to be absolute, therefore, ‘management’ seems a more accurate description, and especially when there is a greater emphasis on integrated management. With regular monitoring and careful forward planning, an integrated approach to disease management can be taken to protect the quantity, quality, and safety of the yield. Management of diseases and pests is essentially the prevention of disease and pest epidemics, as the causal organisms are always around somewhere, but must be prevented from building to damaging levels. The disease triangle summarizes the three main factors involved: environment, host, and pathogen (or pest), one at each point of the triangle. If these three elements remain in balance, an epidemic is prevented, if the pathogen/pest becomes too strong, the host becomes vulnerable or the environment favors the pathogen/pest, then an epidemic is likely and control measures must be taken.

Husbandry Physical methods for disease and pest management include the following:

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Soil preparation such as plowing to expose insects to their predators (birds) and to bury the remains of the previous season’s crop, which may harbor overwintering stages of pathogens or the eggs of insect pests. Informed choice of crop variety to match environmental conditions in which it is to be grown; the variety should be suitable for the soil type and general weather conditions in a given location, with proven resistance to endemic pests and diseases that cannot be effectively controlled by other means. The use of crop rotations to prevent a buildup of problem diseases or pests due to providing a continuous succession of host plants. Elimination of alternate and alternative (weed) hosts of crop diseases and pests where possible. Timing sowing to allow plants to become strong enough prior to insect or disease attack or to delay germination until the threat has receded. Encouraging rapid germination and early growth to build up strength quickly and enable prevention of severe damage resulting from initially mild infestation. Understanding the life cycles of diseases and pests to be able to manage them, using the results from modeling studies to enable forecasting of likely onset of epidemics. Reduction in size of areas in which a single cultivar of a single crop is grown, for example, reduces the pressure on the pathogens to overcome plant resistance. Following the rules for notifiable diseases, in order to prevent them from spreading.

Resistance As plants are literally rooted to the spot they grow in, they are not able to escape pests and diseases. They are, however, able

to put up some defenses to the attacks that come their way. In addition to the basic structure of plants (i.e., the location of their growing points), integral properties such as thorns, thick cuticles, or chemical composition act as a deterrent, a blockade, or even a toxin to the right invading organism. Other attributes may only become activated once the plant is threatened, e.g., lignification of cell walls surrounding an area being invaded by a pathogen. In the case of genetic resistance to pathogens, resistant plants are able to deny the invader the nutrients or chemical components they require to grow or reproduce. When resistance breaks down, the pathogen has altered to allow it to overcome this. Genetic resistance may be due to the presence of a single major gene, which confers protection against a matching virulence gene within the pathogen (gene-for-gene concept). If a pathogen containing an altered virulence gene tries to infect the host, it is likely to succeed, as the resistance is specific to the initial type of virulence, not this new one. This can be observed at the seedling stage when new varieties are being screened for their usefulness. This type of resistance is most useful when (1) a new disease problem arises, (2) disease spread is slow, and (3) a single type of pathogen (a single virulence gene) becomes stable within the pathogen population. Polygenic resistance involves the presence of several resistance genes within a single host cultivar, this confers protection from a range of virulence genes. It is not fully exhibited until the plants mature, so is screened for in the field by looking for a reduced rate of pathogen sporulation. Biotechnology has allowed improved direction to be used when breeding new crop varieties. In particular, it has been possible to introduce genes that code for Bt proteins into transgenic lines of maize and cotton to confer protection against various insect pests and to remove the need for spraying with insecticides. These crops are widely grown in northern America and have proven themselves to be very effective.

Chemical Control The use of pesticides to kill diseases and pests has been exploited in the past in order to meet the market demands for clean, healthy produce. These can be used to accurately target pest organisms by their methods of application: seed dressing, granules, and liquid sprays applied to leaves or soil as appropriate. Contact pesticides cause the death of the pathogen or pest either by direct treatment with spray, dust or vapor or when the pathogen or pest touches the chemical residue on leaves or in soil. In the case of pests, a stomach poison may be used that is only effective when ingested either from the external surface of foliage, within the sap of a plant or when used as a bait. The different types of chemical may be short-lived and require immediate, direct contact with the pathogen or pest, or may be longer-lasting; entering the system of the host plant and remaining there for some time before acting on the attacking organism. The chemical formulation of pesticides appears to be designed to work in more than one way (i.e., on contact and systemically) in order to retain its efficacy over as long a period of time as possible. The overall aim of all pesticides is the same; to prevent the pathogen or pest from growing or multiplying. This is achieved by disrupting the normal function of the invading organism, thus protecting the host plant and allowing it to grow and reproduce.

AGRONOMY OF GRAIN GROWING | Plants: Diseases and Pests The development of new, effective pesticides is a long process. An initial product development stage is carried out in controlled environments until suitable formulations are produced. Once the safety of the compound is understood sufficiently, it is tested for efficacy and crop safety by extensive field-testing before approval for use is given. The high cost of development and testing is transferred to the end product, making the use of chemical crop control difficult to justify in some cases.

Integrated Pest Management As the agricultural industry has become unable to justify the cost (both monetary and ecological) of using chemical control methods alone, a greater emphasis has been put on integrated pest management. By understanding the epidemiology of the organisms causing the damage, it has been possible to reduce the amount of chemical required for pest control. The strategic use of chemical control when it will be most effective and only when it is absolutely necessary has led to this reduction. Instead of treating a crop when evidence of disease or pests is first observed, conditions are optimized for plant growth and reduced for pathogen and pests. Optimization of crop husbandry to maintain strong plants throughout the season plays a vital role, but the effect that any chemicals may have on naturally occurring beneficial insects or predators must also be taken into consideration.


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What are the essential functions of plants that are modified and injured by the attacks of pests and diseases? Explain how diseases and pests are able to cause damage to plants by taking advantage of the vulnerability of plants at specific stages of their development. Describe and contrast the various categories of plant pathogens – due to fungi, bacteria and viruses. How do these pathogens differ with respect to propagation, dispersal, penetration and injury? List the pests (by category) that affect grain-bearing plants. At what plant stages are these most damaging? Compare the control mechanisms that are likely to be most effective for diseases versus pests.

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best able to do so? How does information about overwintering offer possibilities for disease control? Discuss the similarity of spore over-wintering to the ongoing effectiveness of viruses via their vectors. What is ‘integrated pest management’? What strategies are involved? How do these means of managing pests and diseases differ from plant species to species and from one source of disease to another? One of the most effective control mechanisms is genetic resistance to disease and pest attacks. Find out how this approach is achieved and describe some instances where it has been effective.

See also: Agronomy of Grain Growing: Organic Grain Production and Food Processing; Wheat: Biotrophic Pathogen Resistance; Breeding of Grains: Soybean: Germplasm, Breeding, and Genetics; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Biotic Stress Resistance Genes in Wheat; Grain Harvest, Storage and Transport: Cereals: Grain Defects; Chemicals for Grain Production and Protection; Contaminants of Grain; Stored Grain: Invertebrate Pests; Stored-Grain Pest Management; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; The Basics: Grain and Plant Morphology of Cereals and how characters can be used to identify varieties; Taxonomic Classification of Grain Species; The Grain Crops: An Overview.

Further Reading Agarwal AA, Tuzun S, and Bent E (1999) Induced Plant Defenses Against Pathogens and Herbivores. St. Paul, MN: American Phytopathological Society. Bennett WF (1993) Nutrient Deficiencies and Toxicities in Crop Plants. St. Paul, MN: American Phytopathological Society. Carlisle WR (1988) New Studies in Biology. London: Control of Crop Diseases. Edward Arnold – A Division of Hodder and Stoughton. James WC (1971) A Manual of Assessment Keys for Plant Diseases. St. Paul, MN: American Phytopathological Society. Jones D and Gareth RN (1987) Plant Pathology Principles and Practice. Milton Keynes, UK: Open University Press. Jones RN and Karp A (1986) Introducing Genetics. London: John Murray. Salisbury FB and Ross CW (1985) Plant Physiology, 3rd edn. Belmont, California: Wadsworth Publishing Co. Stryer L (1988) Biochemistry, 3rd edn. New York: Freeman. Webster J (1980) Introduction to Fungi, 2nd edn. Cambridge: Cambridge University Press. Wiseman AJL, Finch HJS, and Samuel AM (1993) Lockhart and Wiseman’s Crop Husbandry Including Grassland, 7th edn. Oxford: Pergamon.


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Find out how the spores of pathogens such as the cereal rusts are able to remain viable from one season to another via ‘over-wintering’. Which of the various plant diseases are

Relevant Website cropprotection.org.uk http://www.cropprotection.org.uk – Crop Protection Association (UK).

Wheat: Agronomy GM Paulsen, JP Shroyer, and KJ Shroyer, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Importance and overview of wheat. Wheat in relation to its agronomy. Wheat in relation to its environment. Agronomic practices for wheat. Wheat agronomy in major regions. Further reading and related websites.

Learning Objectives

• • •

To understand the worldwide importance of wheat and the basic botany of the wheat plant. To understand the major environmental effects, both positive and negative, on wheat growth and development. To understand the basics of wheat production in the regions of greatest production.

Introduction Wheat is the world’s most popular crop. It is grown over a large area and under a wide range of conditions and provides more nutrition to humans than any other species. Over 714 million tonnes (Mt) is produced annually on 220 million hectares (Mha), with an average yield of 3.24 t ha1 (Table 1). Ripe grain is harvested and a new crop is planted somewhere in the world during every month of the year. Wheat is also the oldest of crops, one that is grown in over 120 countries with many different technologies and traditions. Production of wheat has increased about 100% during recent decades, the maximum increase seen in any food crop. Improved agronomic practices and new varieties account equally for over 80% of the gain and increased area for less than 20%. The extreme conditions for growing wheat, the many classes that are produced, and the numerous cultural traditions create highly diverse agronomic practices. This article describes wheat in relation to its agronomy, major factors that affect its productivity, and the different agronomic practices for its production.

Wheat in Relation to Its Agronomy The Wheat Plant Wheat is a member of the grass family Gramineae that produces an edible one-seeded caryopsis called a berry, grain, or kernel. The seed normally germinates within 1 week after planting and the first true leaf, the coleoptile, emerges from the soil. Each plant produces five to seven leaves from a growing point, or apical meristem, which then differentiates from a vegetative to a reproductive structure to form a spike that bears the grain. Tillers

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develop in the axils of leaves, giving each plant three to a dozen or more spikes depending on conditions, a trait that makes wheat highly adaptable to different environments. Two root systems form on wheat: seminal roots from the embryo of the seed and secondary or adventitious roots from the coleoptile and tillers. The adventitious system is usually more extensive and may spread to several meters below the plant to absorb moisture and nutrients from the soil, but the greatest root volume is within the upper 0.5 m of the soil profile. Grain growth begins with anthesis or flowering, when pollen is released from the three stamens in each floret and deposited on the stigma of the ovary. Wheat is 95–98% selfpollinated and little exchange of pollen with other plants, or outcrossing, occurs. Growth of the grain (maturation) proceeds in a sigmoid fashion, with a lag period for an increase in cell number, a linear period for an increase in cell mass, and a plateau as the grain approaches maximum weight (physiological maturity). The grain then ripens as the moisture content decreases from 35% to 40% down to 14%. Most varieties also have an after-ripening period of 1–4 weeks, during which the grain loses dormancy and becomes capable of germinating. Yield components of wheat – the constituents that determine the harvest – include the plant density (number per area), tillers per plant, spikelets per spike, kernels per spikelet, and the mass per kernel. Agronomic practices strive to optimize, not maximize, each component because of the compensation among them. For instance, high plant density reduces tillering, and excessive tillers may decrease the number of kernels in each spike.

Classes of Wheat Two of the many types of wheat that are grown throughout the world, common wheat and durum, are the most prominent. Common wheat (Triticum aestivum L.) is hexaploid (6N ¼ 42) and occupies about 90% of the world wheat cultivation area. It includes classes with spring growth habit and winter growth habit, hard and soft endosperm, and red and white pericarp (seed coat). Spring growth habit and winter growth habit do not denote the season that the crop is grown but instead indicate whether the plant requires cold to change from vegetative to reproductive growth, a process called vernalization. Spring wheat has no vernalization requirement, whereas winter wheat needs 1–6 weeks of about 5 C to induce reproductive growth. Wheat also requires long or lengthening days of about 14 h to initiate flowering, except for varieties that are bred to eliminate daylength sensitivity and are said to be day-neutral. Varieties with a third growth habit, known as facultative wheat, do not require vernalization but have strong day-length sensitivity. Hard wheat is used primarily for raised bread and buns and is also satisfactory for steamed bread; for flatbreads such as


http://dx.doi.org/10.1016/B978-0-12-394437-5.00200-X

AGRONOMY OF GRAIN GROWING | Wheat: Agronomy

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Table 1 Area, production, and yield of wheat by the top seven major exporters including the EU, ten major importers, and other countries during 2013–14a Countries

Area (Mha) Production (Mt) Yield (t ha1)

Major exporters

Major importers

Others

World

110.9 354.1 3.19

43.21 175.2 4.05

66.6 185.4 2.78

220.8 714.7 3.24

a

Data from Foreign Agricultural Service, US Department of Agriculture.

‘chapatis,’ ‘tortillas,’ and ‘pieta’; and for Asian noodles. Soft wheat is used for cakes, pastries, flatbreads, and crackers. White wheat is preferred by many consumers, particularly for cereals and whole-wheat products. Durum (T. turgidum L. var. durum) is a tetraploid (4N ¼ 28) and accounts for about 8% of world wheat production. It is more resistant to drought and heat than common wheat and is mostly grown in regions with considerable environmental stress. Nearly all commercial varieties have a spring growth habit. The grain of durum is extremely hard and is used mostly for pasta (macaroni and spaghetti), ‘couscous,’ and ‘burghul’ and is also used for bread in some localities. Club wheat (T. aestivum L. var. compactum) is a hexaploid that has spring growth habit or winter growth habit and red or white grain and is used for the same products as common wheat. Other specialty wheats include einkorn (T. monococcum L.), a diploid (2N ¼ 14) and an ancient crop that is mostly grown in harsh environments in several European countries; emmer (T. turgidum L. var. dicoccum), a tetraploid used for bread and porridge; and spelt (T. aestivum L. var. spelt), an ancient hexaploid that is used for bread, ‘pilaf,’ and hot cereals. Wheat has numerous uses other than as food. Considerable winter wheat is grazed for forage by livestock, and the straw left after harvest is used for bedding and feeding livestock, composting mushrooms, and making bricks and particle board. Much of the grain is fed to livestock in some countries, as are damaged or surplus grain and by-products from milling in other countries. Starch from grain has many industrial applications, including paper, adhesives, plastics, and replacement for milk and egg white in foods.

Wheat in Relation to Its Environment Wheat is a cool-season species that does best in temperate regions with ample sunshine and moderate moisture. Few of the major production areas – the maritime region of Western Europe and high elevations in several parts of the world being exceptions – are highly favorable for wheat. Other crops that are more productive or more valuable are usually grown in amenable regions, and wheat, being well adapted to stress conditions, is often the crop of choice in marginal areas.

Soil Factors Poor soil conditions – low fertility, salinity, toxicities, waterlogging, and erosion – are major factors in the unfavorable environment for wheat. Nitrogen is the critical component of

the protein that determines the food quality of wheat and is often the limiting soil nutrient for yield. Phosphorus is usually limiting after nitrogen and is particularly essential for grain growth. Potassium is especially needed for vegetative growth. Sulfur may be deficient in soils that are coarse and low in organic matter. Magnesium is not deficient for production of wheat in most areas, but marginal levels in plants may cause grass tetany in pasturing livestock. Iron may be deficient when the soil pH or manganese content is high. Copper deficiency occurs on soils that have high organic matter content, and zinc may be inadequate in soils that are eroded or low in organic matter. Responses to chlorine fertilizers have been reported in some regions when Cl soil test levels are below 6 ppm in the upper 60 cm of the soil profile. Salinity from accumulation of various salts in the soil has rendered parts of Asia, Australia, and elsewhere unsuitable for crops. The problem is most severe where irrigation water is high in salts or the water table is near the soil surface. Direct toxicity to wheat occurs when certain elements are highly available in the soil. Aluminum and sometimes manganese become toxic as a result of low soil pH, often from long-time application of nitrogen fertilizers. Other toxicities have been reported from excessive chlorine, boron, arsenic, molybdenum, and nickel. Hypoxia, or inadequate oxygen for plant growth, occurs where soil is waterlogged because of poor drainage, a high water table, or a shallow hard pan. Drought is a perennial problem in many regions and an episodic problem in most other regions for wheat. Inadequate water is the major limiting factor for wheat worldwide, affecting production on an estimated 70% of the area in developing countries and at least as much in developed countries. Wheat has higher water use efficiency than most crops but still requires 1 mm per 10–20 kg grain per hectare or 1–3 mm day1 during early stages and 7–8 mm day1 at anthesis.

Cold Temperatures Cold injures plants directly or by causing them to heave from the soil, smother under ice, or desiccate, processes known collectively as winterkilling. Winter wheat hardens to cold during autumn, and the hardiest varieties can tolerate direct exposure down to 18 C. However, farmers may not plant the hardiest varieties because they often have lower yields than less hardy varieties; they may plant the crop too late for it to harden, or a snow cover may be missing to insulate the plants. Winter wheat and spring wheat are often subject to latespring freeze injury. The plants lose tolerance to freezing as they develop and are easily injured by cold fronts or radiation

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freezing. Late-spring freeze injury is particularly damaging during anthesis, when anthers may be destroyed by only 1 C and the plants, being mostly self-pollinated, are sterilized. In far northern areas, late-summer or early-autumn freezes before wheat matures diminish the yield and quality of the grain.

High Temperature High temperature during maturation affects wheat in many regions. The optimum temperature for grain growth is 15 C; higher temperatures accelerate maturation, reduce the yield, and alter the gluten proteins that determine grain quality. High temperature is frequently accompanied by dry winds known as ‘gan zhe feng’ in China, ‘sukhovei’ in Russia, ‘sirocco’ in North Africa, and ‘khamsin’ in the Middle East.

Wind and Lodging Wind causes soil to blow, particularly during spring when the soil surface is dry and the vegetative cover is sparse. Blowing erodes the soil and abrades the plants, causing them to desiccate. Wind also removes soil from around the roots of plants or deposits soil on top of them. Later in the season, wind causes grain-laden plants to lodge or fall over, especially when the stand is dense or growth has been stimulated by nitrogen fertilizer. Lodging reduces yield and complicates harvest.

Hail Hail is a frequent hazard to wheat. Damage depends greatly on the plant developmental stage. Leaves are most labile at early stages, floral structures are susceptible before anthesis, and the grain shatters or dislodges from the spike at late stages.

Preharvest Sprouting Preharvest sprouting of the grain occurs when persistently wet, humid conditions coincide with ripening. Varieties differ somewhat, but most white wheats are much more susceptible than red wheats. Sprouting is most damaging to the quality of wheat for bread because of the high a-amylase enzyme activity that occurs; it is less detrimental to cakes and other products.

Biotic Factors Weeds are common problems, often seriously reducing the yield and sometimes the quality of the grain. Most species compete with wheat for light, moisture, nutrients, and space. Others are allelopathic, producing chemicals that inhibit growth of the wheat plant. They also interfere with harvest and increase the moisture content of the grain, causing heating and molds. Some weed species cause off-tastes in the grain, which lower its value. Winter annual weeds, which germinate during autumn and complete their growth cycle the following year, are most detrimental to winter wheat and spring wheat planted during autumn. Summer annual weeds that germinate during spring and mature in summer mostly affect springseeded wheat and can also occur in sparse stands of winter wheat. Perennial weeds, which live indefinitely, are problems in both winter wheat and spring wheat.

Agronomic Practices for Wheat Varieties and Seeds More than 80% of the wheat area in developing countries and about 100% in developed countries are planted with modern varieties. Few true hybrids are grown because the seed is costly and the yield advantage is often small. Varieties must be adapted to the local environment, resist indigenous biotic and abiotic stresses, and produce quality grain, in addition to yielding well. Most varieties are semidwarf, 60–80 cm tall, in contrast to traditional varieties that grow up to 120 cm in height. Semidwarf varieties do not produce more biomass, but they allocate more of it to the grain. They also respond to high plant density and high levels of nitrogen fertilizer by producing more grain instead of lodging. Improved varieties are developed by public agencies, such as government ministries and universities, and private companies. Once farmers receive a new variety, they usually save grain from each harvest for seed to plant the next crop and only purchase commercial seed when a new, superior variety becomes available. Whatever the source, wheat seed should have a minimum germination of 85–90% and a minimum volume weight of 72 kg hl1 and be free of weed seeds and diseases.

Rotations and Tillage Numerous rotations are used for wheat. Fallow, or leaving the land unplanted during alternate seasons, is common where annual precipitation is less than 400 mm. Some rotations include fallow with 2 years of wheat or wheat followed by another crop for two harvests every 3 years. Fallow benefits yield of the succeeding crop by increasing soil moisture and nitrogen and, in some cases, reducing pests. Continuous wheat, that is, growing wheat every year, is favored in some areas by the climate, tradition, or government programs. However, the practice often promotes buildup of diseases and weeds that eventually reduces wheat yields. Mixed farming systems that alternate wheat with other crops such as soybean, maize, cotton, grain sorghum, grain legumes, and rapeseed alleviate these problems. Double cropping, or growing two crops during the year, is practiced where precipitation and the growing season are amenable. Wheat is always the winter crop and rice, soybean, vegetables, or other species are the summer crop. Double cropping gives two crops every year, but yields are sometimes hurt when one crop creates unfavorable conditions for the other or late harvest of one delays planting of the other crop. Tillage practices for wheat range from systems of no tillage to ‘the more you till, the more you reap.’ An ideal medium for wheat varies among regions but always includes a firm, moist seedbed with a loose, cloddy surface. Surface residue from the previous crop is desirable for winter wheat in arid and temperate areas to hold moisture, prevent erosion, and trap snow. It is also usually desirable for spring wheat, but in some areas, it may be buried by plowing in autumn to hasten drying of the soil for planting the following spring. Conventional tillage for wheat in regions where soil moisture is adequate generally consists of plowing to a depth of

AGRONOMY OF GRAIN GROWING | Wheat: Agronomy 10–20 cm, disking, and harrowing. However, plowing is increasingly being eliminated, and only two disking and field cultivator operations are used. Where moisture is limiting, a chisel or sweep cultivator is often used to leave a ‘stubble mulch’ to retain moisture and prevent erosion and is followed by disking or harrowing immediately before planting. Zero or conservation tillage involves planting wheat with no prior tillage of the soil. It generally provides an excellent seedbed for rapid germination and reduces costs and soil compaction. However, expenses for chemicals to control weeds and infestation of diseases and insects from residue of the previous crop are increased. Another form of direct seeding is practiced with the rice–wheat rotation in Southeast Asia, where wheat is sown on the soil surface after the rice is harvested. The system requires close control of soil water but gives a rapid stand of wheat without the cost and time of preparing the soil. Farmers in some areas still till the soil intensively for wheat. In parts of South Asia, for instance, the soil is plowed 6–8 times with a tine cultivator or disk harrow and then leveled with a wooden plank.

Planting Timely planting is critical for productivity of wheat. Winter wheat should be planted early enough in autumn to allow two to three leaves to develop before winter. Early planting is often practiced when the wheat is to be grazed by livestock, but it may promote loss of soil moisture, diseases, and insects such as Hessian fly. Delaying planting, on the other hand, gives plants little time to develop the root and shoot systems and to cold-harden, reduces accumulation of snow, and may promote erosion. Spring wheat is sown as soon as soil conditions permit in temperate areas to encourage early plant development; avoid the hot, dry periods of summer; and, in far northern areas, enable maturation before frosts occur. In milder regions, where spring wheat is planted during autumn, timely planting is also important for avoiding unfavorable summer conditions but is sometimes difficult when summer crops are harvested late. Seeding rates for wheat range greatly from 25 kg ha1 under arid conditions to 200 kg ha1 for intensive management under ample soil moisture. Lower rates are sometimes used for increasing seed supplies of new varieties and higher rates for wheat that is planted late or used for grazing. The goal of varying the seeding rate is to achieve a spike density that is optimum for the moisture supply. This ranges from about 200 spikes per square meter with 150 mm of moisture to 600 spikes per square meter with 750 mm of moisture. The optimum seeding depth of wheat in moist soils is 2–5 cm. That depth gives adequate coverage with soil for germination and promotes vigorous roots and shoots. Deeper seeding, down to 10–12 cm, may be needed to reach moist soil, but greater depths should be avoided, especially with semidwarf varieties because of their short coleoptile. Row spacings for wheat vary from 10 to 40 cm depending, like the seeding rate, on available moisture. Narrow spacings approach the ideal equidistant spacing for minimum interplant competition and are used when soil moisture is ample. They are often combined with tram lines, that is, unplanted rows for equipment travel, in intensive management systems.

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Wide rows are used for low moisture conditions, no-till planting, and intercropping systems. Plants typically have more spikes and kernels and produce higher yields in east–west rows than in north–south rows. Orientation of rows perpendicular to prevailing winds apparently decreases plant stress and increases the harvest index. Most wheat is planted with drills, air seeders, and disk seeders, and broadcasting is practiced in only a few areas. Broadcasting, or spreading the seed by hand, gives uneven distribution and poor coverage by soil and favors weeds. Farmers in some areas, such as India, use the ‘desi’ plow, which opens a furrow into which the seed is dropped by hand. Drills and seeders sow seed at the desired rate, spacing, and depth and cover it with soil. They range in size from threerow implements in China to equipment 10 m or longer in some areas. They are designed to make a furrow with a disk or hoe, deposit the seed, and cover it with a disk or chain. Larger drills apply fertilizer with the seed.

Fertilization Most wheat is fertilized to provide nitrogen, phosphorus, potassium, and sometimes other nutrients. The grain contains 1.5–3% nitrogen, and the plant utilizes only about 50% of the element from fertilizer, so 30–60 kg t1 of grain is needed. Additional nitrogen, about 30 kg t1 of forage, is required if the wheat is grazed. Phosphorus is present at 3–5 kg t1 of grain, and only about 20% of the nutrient is utilized from fertilizer the first year. Recommended levels range from 16 mg kg1 of acid soil to 50 mg kg1 of calcareous soil. Potassium content of grain is low, but the element is critical for growth of vegetation. About 150 mg K kg1 of soil is adequate. Sulfur, magnesium, iron, copper, and zinc also should be supplied if deficiency symptoms or soil tests indicate that a response is likely. Lime to bring the soil pH above 5.5 and prevent aluminum toxicity may be needed, particularly after long, continuous applications of nitrogen fertilizer.

Pest Control and Plant Growth Regulation Weeds are controlled by planting weed-free seed, cultural practices, chemical herbicides, and hand harvesting. A dense, even stand of wheat is an excellent competitor to most weeds. However, sparse or uneven stands and some modern practices such as using semidwarf varieties and high rates of nitrogen fertilizer may allow weed populations to increase. Fallowing or succeeding wheat with other crops gives opportunities to control weeds mechanically during alternate years. Working the soil before planting wheat and, in some cases, adjusting the time and depth of seeding are effective. Different herbicides can be applied before or after planting to reduce many weeds. Removing weeds by hand, while laborious, may give them some value as food or feed. Genetic resistance controls many diseases, particularly some rusts and viruses, most economically. Cultural practices can be used to alleviate many diseases, and fungicides are available for others. Seed should be free of pathogens or treated for common bunt, loose smut, and Fusarium head blight. Eliminating volunteer wheat plants can exclude some disease vectors. Covering residue of the previous wheat crop helps to

180


reduce the incidence of tan spot and septoria. A firm seedbed decreases crown and root rots, and delaying planting may avoid diseases transmitted by aphids and mites. Fungicides effectively control powdery mildew and rusts. Fungicide usage has increased due to their lower costs. Insects, like diseases, are controlled by genetic, cultural, and chemical methods. Varieties are available with resistance to aphids, Hessian fly, and some mites. Cultural methods include rotations with other crops, removal of volunteer plants and crop residue, plowing to bury the insects, delaying planting, and accelerating harvest. Insecticides are effective against many pests but are often considered a last resort because of their cost. Plant growth regulators are applied to wheat to deter lodging. Semidwarf varieties are much less prone to lodging than tall varieties and usually do not benefit from plant growth regulators. However, under the intensive management practices of high plant densities and high-nitrogen fertilizer, even semidwarf varieties may lodge. Plant growth regulators act by shortening the plants and strengthening their stems.

Irrigation Many countries cannot produce wheat without irrigation because of arid conditions. Irrigation water is supplied from sprinklers, furrows, and basins. Center-pivot sprinklers, which rotate about a fixed point, and tow line/side roll sprinklers are popular because of their efficiency and low labor requirement. Other systems such as hand-move irrigators are declining because of their high labor demands. Furrows in fields typically run parallel to several rows of wheat, which may be on raised soil beds, and are supplied with water from pipes or canals. The system is versatile but often gives poor distribution of water, is labor-intensive, and complicates harvest. Basin irrigation involves flooding fields enclosed by levees and is well suited to rice–wheat rotations. The system is efficient and gives good distribution, but initial costs are high and mechanical harvest may be difficult. Irrigation of wheat is scheduled by two methods: depletion of soil moisture to a set level and growth stage of the plants. Wheat utilizes about 50% of the available soil moisture before yield is reduced by stress, and irrigation is applied when moisture reaches that level. Alternatively, irrigation is scheduled at critical growth stages, such as germination, booting/heading, and early grain development, when moisture deficiency is most damaging to yield.

Harvest Much of the world’s wheat is harvested by hand with serrated sickles, particularly in Asia. The scythe, sometimes with a cradle to catch the plants, has replaced the sickle in some regions. Threshing to remove the grain from the straw is accomplished through trampling by livestock; stone rollers; tractors, sometimes pulling a disk or other implement; or small machines. The grain and straw are usually separated by tossing them into the air in a breeze. Mechanical harvesters, called binders, that cut the wheat and tie it into a bundle were once widely used but are now found in only a few areas. The bundles are arranged in stacks

known as shocks for the grain to dry and are then threshed by machines called separators. Many large farms in developing countries and most commercial farms in developed countries use combine harvesters. These machines cut the plants and remove the grain from the straw and separate them in a single pass 1–10 m wide. Usually, only the spike and part of the stem are cut to minimize the amount of straw that goes through the harvester and to leave a stubble to protect the soil. Some combine harvesters, known as strippers, remove only the spike. Wheat is usually harvested when the grain contains less than 14% moisture and can be stored without deteriorating. In some areas, such as the northern United States and Canada, wheat is cut when the grain contains as much as 35% moisture and placed in windrows to dry, a process called swathing, before it is combine-harvested. In other regions, such as northern Europe and Hokkaido, the main wheat-growing island of Japan, the grain is combine-harvested when it contains 40% moisture and artificially dried. In those areas, the climate either does not permit the grain to dry naturally or causes the grain to sprout in the spike if it dries.

Wheat Agronomy in Major Regions Asia Asia is the world’s major wheat production area with China and India leading production. Another important wheatproducing country is Pakistan (Table 2). Spring wheat predominates in China, with soft and medium-hard red varieties planted in autumn throughout most of the southern provinces and hard and medium-hard red varieties planted in spring across the north. Hard and medium-hard white winter and facultative wheat occupy most of the North China Plains. Most of the grain is used for noodles and steamed bread. Cultivation of wheat is labor-intensive on small plots that are often part of large fields. In the major provinces of Henan and Shandong, wheat is mostly seeded with three-row drills pulled by draft animals. Other crops – rapeseed, maize, and vegetables – are often interplanted between the wheat plots. High amounts of chemical fertilizers are applied (Table 2), and additional nutrients are commonly supplied as compost. Over 50% of the wheat area is irrigated, usually from wells and reservoirs. Much of the irrigated wheat is rotated with rice for two crops each year. Harvest begins in May in southern regions, in June in the North China Plain, and in July and Table 2 Agronomic practices for production of wheat in major countries in Asia Practicea,b

China

India

Pakistan

Area (Mha) Production (Mt) Yield (t ha1) N fertilizer (kg ha1) P fertilizer (kg ha1) K fertilizer (kg ha1)

24.11 121.9 5.06 185.3 70.2 12.4

30.0 93.5 3.12 136.7 58.1 10.8

8.64 24.0 2.78 151.7 37.1 1.4

a

Data from Foreign Agricultural Service, US Department of Agriculture. Fertilizer data from Fertilizer Use by Crop (2011), International Fertilizer Association.

b

AGRONOMY OF GRAIN GROWING | Wheat: Agronomy August in northern areas. Most of the wheat is harvested with hand sickles and threshed with animals or small machines. Leaf, stem, and stripe rusts; powdery mildew; common bunt; and Fusarium head blight are usual diseases in China. Aphids and armyworms are common insects. Few pesticides, mostly fungicides, are used, and weeds are usually controlled manually and fed to livestock. Drought occurs with some frequency, and declining water tables and competition for other uses may limit availability of water for agriculture in the future. Hot, dry winds sometimes severely damage maturing wheat, and prevalent late-spring and early-summer rains occasionally cause severe preharvest sprouting. India’s major wheat-producing region is the Indo-Gangetic Plain, particularly the states of Uttar Pradesh and Bihar in the northeast and Punjab and Haryana in the northwest. Semihard and hard red and white spring wheats planted during autumn as the ‘rabi,’ or winter crop, predominate. The wheat is often intercropped with mustard, gram, and lentil and grown in rotation with rice, maize, sorghum, and pearl millet as the ‘kharif’ (summer) crop. Only a little durum is produced, primarily under dryland conditions in the central and western areas. Grain is harvested in March and April in the northeast and late May and June in the northwest. Most of it is used for chapatis. Drought, high temperature, occasional freezes, diseases, insects, and nematodes are problems on wheat in India. Dryland yields are low because they often depend on residual moisture from monsoons, and irrigated wheat is threatened by declining water tables and soil salinization in some regions. High temperatures hinder crop development and promote pests during autumn and restrict grain filling during spring. Rusts, powdery mildew, and root rots are common under the high-yield management for most of the crop. Shoot fly, armyworms, and caterpillars are occasionally damaging. The major wheat area of Pakistan is Punjab Province with over two-thirds of the total production taking place there. Wheat is the country’s primary food, providing about 72% of the calories and protein, mainly as chapati and ‘nan/naan.’ Only spring wheat, either hard or semihard, is grown, and white or amber varieties are preferred. Wheat is grown as the rabi crop in rotation with cotton, rice, maize, sugarcane, and groundnuts. The soil is worked extensively and nearly pulverized between crops, and wheat is planted by broadcasting or drilling the seed during October and November. Prompt seeding is essential to avoid stress during maturation of the crop. Use of fertilizer, while fairly heavy, is probably inadequate for the potential yields (Table 2). Most of the wheat, over 88% in Punjab, is irrigated, primarily from canals, but the water supply is sometimes inadequate and saline. Harvest begins with the dryland crop in April and ends with the irrigated crop in early June. Most of the wheat is cut with sickles and threshed by animals. Irregular availability of water, low rainfall, and high temperatures hinder wheat production in Pakistan. Considerable areas have become too saline for crops. Several weed species, leaf and stripe rust, and loose smut are serious pests.

North America Canada is the sixth leading producer and third most important exporter of wheat (Table 3). The Prairie provinces of Alberta,

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Table 3 Agronomic practices for production of wheat in major countries in North America Practicea,b

Canada

The United States

Mexico


10.44 37.5 3.59 68.6 22.6 8.2

18.34 58.1 3.17 83.7 33.0 5.6

0.64 3.37 5.29 93.6 13.6 4.5

a


b

Saskatchewan, and Manitoba, the major area, grow mostly hard red spring wheat. Soft red and white winter wheats, which constitute about 5% of the crop, are mostly grown in Ontario. Soft white spring wheat is produced in the same provinces as hard red spring wheat. Durum accounts for 15–25% of the wheat area and is mostly raised in southern Saskatchewan. Wheat farms in Canada are large and highly mechanized. Low temperature and sparse precipitation dictate many of the agronomic practices. Most of the wheat is grown as a crop–fallow rotation or a continuous monoculture, but rotations with rapeseed and other crops are increasing. Spring wheat and durum are planted as soon as fields can be worked during spring, usually in April and May. Winter wheat is planted from late August to September, preferably directly into the stubble of the previous crop or a thin stand of rapeseed or flax to trap snow to insulate the plants from cold. Moderate amounts of fertilizer are used in keeping with yield expectations (Table 3). Leaf and stem rust, Fusarium head blight, Hessian fly, midge, and wild oat and other weeds are problems. Along with drought, heat, late frosts, and preharvest sprouting sometimes hurt the yield and quality of the grain. Harvest of wheat in Canada begins in August and continues in October. Whereas the grain has long been marketed through the Canadian Wheat Board (CWB), the Canadian wheat marketing system was deregulated in 2012 with the CWB being transformed into a grain company. Over 70% of Canada’s wheat production is exported. The United States is the world’s fourth largest producer and leading exporter of wheat (Table 3). The main classes are hard red winter wheat in the southern and central Great Plains, hard red spring wheat in the northern Great Plains, soft red winter wheat in the Midwest and Southeast, white wheat in the Northeast and Pacific Northwest, and durum in the northern Great Plains and desert Southwest. Rotations for wheat depend mostly on moisture conditions. In areas that receive 350–500 mm precipitation, primarily the High Plains and Pacific Northwest, much of the wheat is alternated with summer fallow. Areas that receive 500–700 mm precipitation often follow a wheat–summer crop (sorghum, soybean, or sunflower)–fallow rotation or plant wheat every year. Higher levels of precipitation permit conventional rotations of wheat and other crops on alternate years or double cropping (two crops per year) with wheat as the winter crop and soybean, sorghum, or rice as the summer crop. Winter wheat is seeded from late August in the northern Plains to early November in the south, and spring wheat from

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late autumn in the western United States to early May in the north. Medium levels of fertilizer are used in most regions (Table 3). Only about 5% of the crop is irrigated. Leaf and stem rusts, several viruses, and Fusarium head blight are major diseases. Problem weeds differ among regions and are controlled with cultivation and herbicides. Hessian fly, greenbug, stem sawfly, army cutworm, and grasshoppers are troublesome insects. Harvest begins in southern states in May and progresses northward in September. About half of the grain is exported. Wheat in Mexico is nearly equally divided between semihard or hard spring bread types and durum. The northwestern states of Sonora and Sinaloa, which mainly grow durum, are the most important producers, followed by the Bajio and other parts of the Central Plateau. The grain is used for breads, pasta, and tortillas. Most wheat is planted from October to December on land that is cropped with soybean, sesame, and other species during summer. Irrigation, usually from reservoirs, is needed to establish and maintain the crop until it matures because of the arid conditions. Large amounts of nitrogen fertilizers are used, reflecting the high yield potential (Table 3). Leaf, stem, and stripe rusts; septoria; and karnal bunt are common diseases. Several aphid species and cutworms occasionally damage the crop. The wheat is harvested from April to June; all of it is consumed domestically.

Over 90% of wheat production in Brazil comes from the states of Parana and Rio Grande do Sul. All of the wheat is spring type, mostly soft to semihard, for bread. The crop meets only one-third of the country’s needs, and the balance is imported. Wheat is mostly grown in Brazil as a winter crop in rotation with maize or soybean. It is planted from April to mid-June, often as a cover crop. Yields are low because the climate and soils are particularly unfavorable for wheat (Table 4). Rusts, Fusarium head blight, septoria, and mildew are often epidemic. Soil acidity causes toxicity from aluminum and fixes phosphorus. Frosts periodically damage the crop at vulnerable stages. Rainfall is sometimes inadequate but more often excessive, causing floods and promoting fungal diseases during harvest from September to November.

Oceania

Argentina is the largest producer and exporter of wheat in South America (Table 4). The Pampas provinces of Buenos Aires, Cordoba, and Santa Fe produce most of the grain. Hard red spring wheat is the major class; durum occupies less than 1% of the crop. Wheat consumption per capita is the highest in South America, primarily for artisan breads, pasta, and cookies. Most wheat is grown in rotation with soybean, sunflower, and maize in mixed crop–livestock systems. The climate is generally favorable for wheat; however, variable precipitation and extreme temperatures sometimes limit yields. Soils are productive, but nitrogen and phosphorus are deficient in some areas. Wheat is planted from June to August. Moderate amounts of fertilizers are used, but few pesticides are applied to wheat (Table 4). Rusts, Fusarium head blight, take-all, septoria, and yellow spot are common diseases, reducing yields to about 10%. Aphids and other insects are occasional problems. The grain is harvested from November to January.

Australia and New Zealand, the two major wheat-producing countries in Oceania, present contrasting examples of varieties, technologies, and yields. Australia is one of the world’s leading wheat producers and exports over 80% of the grain (Table 5). The country’s wheat belt extends across the states of Western Australia, South Australia, Victoria, New South Wales, and Queensland. All the varieties are white spring types, which are usually planted during the autumn months of May and June. Six classes of wheat are produced, the most important being prime hard, hard, and standard white and durum. Output of wheat is steadily increasing as former sheep areas are cultivated and the yield potential of new varieties increases. Production of wheat in Australia is constrained by availability of moisture, since much of the country is arid or semiarid and less than 5% of the crop is irrigated. Farms are large and heavily mechanized. Fertilizer use is low because of the generally low yield potential (Table 5). Diseases – leaf, stem, and stripe rusts; crown rot; and yellow spot – are frequent problems. Late frosts sometimes damage plants from the preflowering to early grain-filling stages. Salinity from rising water tables is becoming troublesome, particularly in Western Australia. Preharvest sprouting caused by persistent rains after the white grain ripens is a major concern. The grain is harvested during October through December. New Zealand grows wheat primarily along the eastern coastline areas of Canterbury, North Otago, and the lower North Island. Fields are generally small, about 10 ha, but the crop is managed intensively and yields are high (Table 5).

Table 4 Agronomic practices for production of wheat in major countries in South America

Table 5 Agronomic practices for production of wheat in major countries in Oceania

Practicea,b

Argentina

Brazil

Practicea,b

Australia

New Zealand


3.5 10.5 3.0 42.9 20.5 0

2.2 5.3 2.41 52.5 43.7 32.2

Area (Mha) Production (Mt) Yield (kg ha1) N fertilizer (kg ha1) P fertilizer (kg ha1) K fertilizer (kg ha1)

13.50 27.03 2.0 26.3 22.8 2.1

0.04 0.44 9.36 na na na

South America

a

a

b

b



AGRONOMY OF GRAIN GROWING | Wheat: Agronomy About two-thirds of the varieties are facultative types that are sown in autumn (May), and the balance is spring varieties that are planted in late August to early September. Some 60% of the grain is used for bread products and 40% for livestock feed. Most wheat in New Zealand is grown under contracts that impose strict criteria for quality and pesticide residues. High rates of nitrogen fertilizer are often split into several applications during the growing season, as are fungicides to control foliar diseases. Much of the wheat is irrigated. Growth regulators are used to prevent lodging of the plants. The favorable conditions and intensive management commonly result in yields of 10 t ha1 or higher, particularly of feed wheat. Harvest begins in early January and continues in late February. Most of the grain is artificially dried.

Eastern Europe and Western Asia Wheat is the major cereal in the Russian Federation, the fifth largest producer in the world (Table 6). Southern Russia, including the North Caucasus, Southern Black Soils area, and Volga Valley, is the primary winter wheat-producing region. The Don Basin, middle Volga, and southwestern Siberia grow most of the spring wheat, both bread types and durum. Winter and spring bread wheats are used for various baked products, which are important in the population’s diet, and for livestock feed. Durum is used for bread and pasta. Small private farms and large joint-stock farms produce wheat in Russia. Both are heavily dependent on mechanization, but economic difficulties cause much of the equipment to be obsolete and production inputs to be low. In addition, variation in weather among regions and years greatly affects production. Nevertheless, the reorganization of former stateowned farms has increased efficiency and contributed to excellent harvests during recent years (Table 6). Winter wheat is planted in September and October following rotations of continuous wheat or other cereals, legumes, or flax. Winterkilling from severe cold sometimes necessitates replanting with spring wheat. Most spring wheat is sown during April and May. Use of fertilizer, while low, is increasing, but few other chemicals are applied to wheat (Table 6). Leaf rust, powdery mildew, snow mold, Fusarium, and aphids are major problems in addition to drought and winterkilling. Harvest begins in July in southern regions and extends into autumn in northern spring wheat areas, where it is sometimes disrupted by winter weather. Table 6

183

Kazakhstan produces both winter and spring wheats, principally on the north-central Steppes around Kostana. Most of the crop is grown on large cooperative and joint-stock farms. Winter wheat is planted in September and October, and spring wheat is planted in April and May. Drought occurs about 2 years of every five, and the use of fertilizer is declining, causing yields to be low (Table 6). Other problems stem from inadequate equipment, poor infrastructure, and an undeveloped market system. Harvest in the major area begins in August and continues in October. The principal wheat-producing area of Ukraine is in the eastern and southern parts of the country. Over 90% of the crop is hard winter wheat, and 5–10% is durum. Most production takes place on large private associations that reformed from state and collective farms. Although Ukraine is a traditional exporter, most of the grain is consumed locally as breads or fed to livestock. Most Ukrainian wheat is planted in September. Fertilizer use is low, but increasing (Table 6). Little of the wheat is irrigated, and drought can occur anytime during the season. Leaf rust, powdery mildew, and septoria are often problems. Harvest during July and August can be complicated by inadequate equipment and adverse weather. Turkey produces winter bread wheat, the major class with 50% of the area, on the Anatolian Plateau and Thrace province. Spring bread wheat and durum, each about 20% of the area, are mostly grown near coastal areas. The balance of the wheat is winter durum. Wheat on the Anatolian Plateau is usually alternated with fallow. It is planted during October, as is spring wheat on the coast. Considerably higher amounts of fertilizer are used compared to a decade ago (Table 6). Little of the wheat is irrigated and yields vary greatly with precipitation, which averages only 200–450 mm on the Anatolian Plateau. Moderate to severe drought every 2–4 years, yellow rust, leaf rust, root rot, and tan spot are major problems. Harvest is during June and July. Iran grows nearly equal areas of spring and winter bread wheat. The crop occupies over half of the arable land in the country, and consumption of wheat foods is among the highest in the world. Lavash, sangak, and other flatbreads; biscuits; and noodles are important products. Precipitation varies widely across Iran and averages about 250 mm annually. Only about one-third of the wheat is irrigated, but it provides one-half to two-thirds of the crop. Much of the irrigated wheat is in eastern and southern provinces, and dryland wheat is predominately in western and northwestern

Agronomic practices for production of wheat in major countries of Eastern Europe and Western Asia a,b

Practice

Russia

Kazakhstan

Ukraine

Turkey

Iran


23.39 52.09 2.23 28.5 8.5 3.1

12.95 13.94 1.08 na na na

6.5 22.27 3.39 35.3 6.0 3.4

7.7 18.0 2.34 72.5 28.4 2.4

7.0 14.5 2.07 54.5 20.1 1.1

na, not available. a Data from Foreign Agricultural Service, US Department of Agriculture. b Fertilizer data from Fertilizer Use by Crop (2011), International Fertilizer Association.

184


provinces. The crop is planted during October and November. Moderate amounts of fertilizer are used, but like Turkey, levels have increased in recent years (Table 6). Harvest begins in the southern and eastern areas in mid-April and ends in northern areas in August.

Western Europe The European Union ranks first for world wheat production. France, like the other countries of Western Europe, has a climate that is conducive to high yields of wheat (Table 7). The crop is managed intensively with high levels of inputs. The country is the major producer in the region. The primary wheat area is the northern half of the country, with Centre and Picardie being the leading provinces. The major class is soft winter wheat, but some soft spring wheat and durum are also produced. Most of the grain is consumed as bread, and variable amounts are fed to livestock depending on the cost relative to other cereals. Wheat is planted during October and November using high seeding rates, narrow rows, and tram lines. High rates of fertilizers and pesticides are applied, usually several times during the growing season. Stripe rust, leaf rust, powdery mildew, and septoria are common. Harvest is in July and August. Most wheat is produced on mixed crop/livestock farms in Germany. Usual rotations with wheat include other cereals, various legumes, rapeseed, and sugar beet. Wheat is mostly planted during October, and like in France, rates of seeding and application of fertilizer and other chemicals are high. Rusts, powdery mildew, and septoria are major diseases. Harvest during July and August is sometimes disrupted by adverse weather, which affects both the yield and quality of grain. Bayern and Niedersachsen are the major wheat states. Most varieties are semihard to hard winter wheats that are consumed as mixed bread with rye, whole-wheat bread, and white bread. Considerable quantities are also fed to livestock and exported each year. Wheat is grown in the United Kingdom as far north as Scotland, but it is concentrated in southeastern England and the Midlands. Yields are extremely high because of the favorable climate and intensive management. Soft and semihard winter and spring classes that are used for breads, biscuits, and pastries are grown. Much of the grain is also fed to livestock and exported. Table 7 Agronomic practices for production of wheat in the European Union Practicea,b

EU-27


25.76 143.13 5.55 116.9 21.1 18.1

a


b

Most wheat is grown on mixed crop/livestock farms in rotation with forages and other crops. The grain is usually planted during October and November, but sowing can be as late as January depending on the rotation and the weather. High seeding rates, narrow rows, and tram lines are used and heavy rates of fertilizer are applied. Nitrogen fertilizer is often split among four or five treatments, and fungicides to control foliar diseases and growth regulators to prevent lodging are common. Little of the wheat is irrigated. Yellow rust, leaf rust, eyespot, tan spot, powdery mildew, and Fusarium head blight are serious diseases. The grain is harvested during July and August.


• • • • • •

What do the top wheat-producing regions have in common? With climate change and predicated higher average temperatures, how will yield potentially be affected and why? How will climate change affect the current wheat-growing regions? If wheat has unfavorable environmental conditions during tiller formation, how will this affect yield and why? For wheat, what is the most vulnerable growth stage for grain yield and why? Is continued variety development important and what would happen if it stopped?


• • • •

Investigate the effects of abiotic stress on yield and seed quality. What is the future potential for exploitation of genetic tolerance to abiotic stress? What key management strategies, in regions most limited by environment, can most contribute to enhanced productivity? How can maximum efficiency be achieved in agrochemical additions and timings to improve growth and development in marginal environments (fungicides, hormones, nutrients, etc.)?

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Grain Harvest, Storage and Transport: The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; The Cereal Grains: Cereals: Domestication of the Cereal Grains; Triticale: Overview.

Further Reading Cook RJ and Veseth RJ (1991) Wheat Health Management, p. 152. St. Paul, MN: APS Press. Gooding MJ and Davies WP (1997) Wheat Production and Utilization: Systems, Quality and the Environment, p. 320. Wallingford: LABI Publishing. Hanson H, Borlaug NE, and Anderson RG (1982) Wheat in the Third World, p. 174. Boulder, CO: Westview Press.

AGRONOMY OF GRAIN GROWING | Wheat: Agronomy Heisey PW, Lantican MA, and Dubin HJ (2002) Impacts of International Wheat Breeding Research in Developing Countries 1966–97, p. 73. Mexico, DF: CIMMYT. Heyne EG (1987) Wheat and Wheat Improvement, 2nd edn., p. 765. Madison, WI: American Society of Agronomy. Joint Agricultural Weather Facility, US Department of Agricultural (2005) Major World Crop Areas and Climatic Profiles University of the Pacific Press. Satorre EH and Slafer GA (1999) Wheat: Ecology and Physiology of Yield Determination, p. 503. New York: The Haworth Press. Slafer GA (2007) Wheat Production in Stressed Environments, p. 557. Springer.

Relevant Websites http://www.aafc.ca – Agriculture and Agri-Food Canada. http://www.awb.com.au – The Australia Wheat Board.

185

http://www.cimmyt.org – The International Maize and Wheat Improvement Center. http://www.csiro.au – Commonwealth Scientific and Industrial Research Organization. http://www.cwb.ca – The Canadian Wheat Board. http://www.fas.usda.gov – The US Department of Agriculture Foreign Agricultural Service. http://www.kswheat.com – The Kansas Wheat Commission. http://www.ndwheat.com/ – The North Dakota Wheat Commission. http://wbc.agr.mt.gov/ – The Montana Wheat and Barley Committee.

Barley: Agronomy RD Horsley and M Hochhalter, North Dakota State University, Fargo, ND, USA ã 2016 Elsevier Ltd. All rights reserved.

Nomenclature Coleoptile

Feekes growth stage scale

Flag leaf Floret Haun growth stage scale

Jointing Second leaf in a grass modified for soil penetration. Scale used to describe the growth stages of small grains. Upper most leaf in small grain plants. Grass flower plus lemma and palea. Scale used to describe the growth stages of small grains.

Topic Highlights

• • • • • •

Barley is the cereal crop with the widest range of productions area in the world. Barley is used for producing malt, (which is used in brewing beer), livestock feed, and human food. Understanding the different growth stages of barley allows for a better understanding of the impacts of abiotic and biotic stresses on barley production. The type and amount of fertilizer applied to barley are dependent on its intended end use. Choice of cultivar for production is especially important for growers producing barley for malting and as a method to combat potential problems such as diseases, insects, and micronutrient toxicity. Production practices that can impact crop yield and end-use quality include seeding depth, date, and rate; irrigation; diseases; insects and nematodes; and weeds.

Learning Objectives

• • •

To learn the production regions where barley is grown and end uses of the grain produced. To learn how abiotic and biotic stresses that occur at different times during the growing season can affect yield and end-use quality. To learn what grower inputs or production practices can impact yield and end-use quality.

Introduction Barley is the cereal crop with the widest range of production areas in the world. It is often the last cereal crop grown at the highest altitudes in the Andes and Himalayas; adjacent to the

186

Spike

Spikelet

Zadoks growth stage scale

Growth stage of small grains where the growing point comes aboveground and is indicated by solid feeling nodes on the plant’s stem. Type of inflorescence where the spikelets are attached directly to the rachis. The unit of the inflorescence containing two glumes and one or more florets. Scale used to describe the growth stages of small grains.

deserts of Africa, the Middle East, and China; and near the Arctic Circle in the northern reaches of Asia, Europe, and North America. Barley has many uses, including livestock feed, human food, and malt production. Because of the diverse growing areas for barley and its many uses, production practices vary greatly. Production practices for malting barley are more stringent than those for barley produced for other uses because of the specifications put on the crop by the malting and brewing industries. Barley to be used for malting must meet specifications for germination, kernel size and weight, grain protein, and many other traits. Barley for livestock and human food uses has much fewer restrictions.

Growth Stages Before the effects of different production practices and environmental stresses on the performance of barley can be understood, knowledge of the different growth stages and yield components of barley is needed. Different scales are available for describing the growth of barley, including the Feekes, Haun, and Zadoks growth stage scales. Figure 1 compares these three different growth stage scales and lists suggested production practices for spring barley grown in the Midwestern United States. Components that determine yield in barley are the number of spikes per area, the number of kernels per spike, and kernel weight. Stresses during a certain period of the growing season will reduce one or more of the yield components. Factors affecting the number of spikes per area include those that directly affect the number of plants per area and the number of tillers per plant. Plant and tiller number can be impacted most severely from sowing to shortly before the jointing stage. Factors that can reduce the number of plants per area include sowing rate, insufficient moisture for germination, waterlogged soils following sowing that may kill the seed or cause


http://dx.doi.org/10.1016/B978-0-12-394437-5.00232-1

AGRONOMY OF GRAIN GROWING | Barley: Agronomy

187

Barley calendar Growth stages

Oneshoot Growth stages scales Feekes – F Haun – H Zadok – Z

Month Production practices

Sept-Oct

Nov-Feb

Soil test Fertilize

Fall tillage

F1 H 0.5 Z 10

March

F 2 -3 H 5.5 Z 22

April

Stored grain management

F 10 H 9.2 Z 45

June

Heading F 10.5 H 11 Z 59

July

Ripening F 11.3 H 15 Z 91

August

Top dress N

Harvest

Scout: diseases − plan control Seedling blights Leaf diseases Head diseases Scout: weeds Postemergence

Fall preplant final weed survey

Aerate to cool, 25° F

Boot

F6 H 6.1 Z 31

Cereal aphids Barley thrips Grasshoppers Armyworm

Plan rotations

Perennial weed control

Jointing

May

Soil test Starter fertilizer Soil probe for water Variety selection Seed bed preparation and planting Clean/treat seed

Insect and disease management

Weed management

Tillering

Preplant and preemergence

Preharvest treatments Postharvest control to prevent seed production volunteers

Clean/spray bins Check aeration Danger period system moisture, molds Inspect grain bins at least monthly for molds, moisture and insects Aerate to 40° F

Figure 1 Barley growth stages and suggested production practices for barley produced in the Midwestern United States. Reproduced from Peel MD (2000) Barley Production Guide. Fargo, ND: North Dakota State University Extension Service, with permission.

soil crusting, winterkill, weed competition, insects, and diseases. Excessive temperatures, insufficient moisture, insects, and weed competition can negatively impact the number of tillers per plant. Before jointing, the developing barley plant is tolerant to freezing temperatures because the growing point is protected below the ground. At the jointing stage, the growing point of the barley plant comes aboveground and is vulnerable to environmental stresses that will cause fewer spikelets per spike. The number of kernels per spike also can be impacted by stresses during pollination, such as freezing or excessive temperatures that can kill the pollen. Pollination in barley generally occurs during the late-boot stage. Stresses following fertilization will affect kernel weight and plumpness, possibly reducing grain quality. These stresses include excessive temperatures, insufficient moisture, weed competition, diseases, and insects. Damage to the flag leaf and the leaf below it by insects or diseases more severely impacts kernel weight than damage to the lower leaves. Thus, growers are encouraged to scout their crop to make sure that the top two leaves of the plant are free from damage caused by disease and insects. Thin and lightweight kernels are undesirable for malting because they typically are high in grain protein and are difficult to malt uniformly. The resultant malt generally has overall poor-quality and especially low malt extract.

Plant Nutrition Barley responds well to fertilizers containing nutrients limiting in the soil, especially nitrogen. Additional amounts of nitrogen fertilizer can be applied to increase grain yield and protein content when soil nitrogen is limiting. The amount of fertilizer to apply is dependent on the end use of the harvested grain, soil test results, and expected yield. In most areas of the world except North America, barley used for malting must have grain protein below 11.5%. Many North American maltsters and brewers will accept grain protein up to 13.5%. One reason why brewers in this region accept higher barley grain protein levels is that they often use higher levels of brewing adjuncts (e.g., corn or rice) that have a diluting effect on the total barley protein in the beer. There are no upper limits on grain protein content on barley for livestock feed or human food uses. The amount of nutrients needed to produce a satisfactory barley crop can be determined from a soil test, which is a reliable indicator of the amount of residual nutrients in a soil profile. Table 1 is an example of a soil recommendation chart used in the Midwestern United States based on soil test results and yield goal. Higher levels of nitrogen fertilizer are recommended for barley produced for nonmalting uses; however, excessive nitrogen can result in a lush crop that is prone to lodging and foliar diseases. Also, excessive fertilizer can be

188 Table 1

AGRONOMY OF GRAIN GROWING | Barley: Agronomy Nutrient recommendations for malt and feed barley in the Midwestern United States Soil test phosphorus (ppm)

Yield goal T/ha

Soil N plus fertilizer N required for malt barley kg/ha-0.6 m

Soil N plus fertilizer N required for feed barley kg/ha-0.6 m

2.2 3.2 4.3 5.4

65 100 135 170

80 110 150 190

BrayI Olsen

Soil test potassium (ppm)

Very low Low 0–5 6–10 0–3 4–7 kg P2O5 per ha

Medium 11–15 8–11

High 16–20 12–15

Very high 21 þ 16 þ

35 45 60 80

15 20 30 35

0 10 10 10

0 0 0 0

20 35 45 55

Very low Low 0–40 41–80 kg K2O per ha

Medium 81–120

High 121–160

Very high 161þ

50 80 100 130

20 35 45 55

0 10 15 15

0 0 0 0

35 55 70 90

Nitrogen recommendation ¼ 1.5 YG STN þSDA PCC. Bray-IP recommendation ¼ (0.785 0.039 STP)YG. Olsen P recommendation ¼ (0.785 0.050 STP)YG. Potassium recommendation ¼ (1.2860 0.0085 STK)YG. The abbreviations used in the equations are as follows: YG, yield goal; STN, soil test nitrogen; STP, soil test phosphorus; STK, soil test potassium; SDA, sampling date adjustment; PCC, previous crop credit. Reproduced with minor modifications from Franzen DW and Goos RJ (2007) Fertilizing malting and feed barley. Fargo, ND: NDSU Extension Service, with permission.

environmentally problematic in well-drained soils or areas with a high water table if they leach into the groundwater. Accurate estimates of a yield goal are extremely important in choosing the proper amount of nitrogen fertilizer to apply. Application of too much nitrogen fertilizer can result in the barley having excessive protein and being rejected for malting. In environments and/or years where moisture is limiting, the recommended rates of nitrogen to apply to malting barley may be excessive and result in unacceptable barley for malting. As mentioned earlier, high-protein barley is difficult to malt uniformly and results in poor-quality malt. Thus, it is not uncommon for growers to apply less than the recommend rate of nitrogen to increase their likelihood of producing acceptable malting barley. Fertilizers can be applied throughout the growing season; however, most nitrogen is applied prior to sowing to ensure sufficient amounts are available for seedling establishment and tillering. Growers sowing barley during spring often apply their nitrogen during fall to reduce their spring workload; however, fall application of fertilizers is not recommend for well-drained sandy soils because excessive leeching may occur over winter. The method of nitrogen fertilizer application is dependent on the source of nitrogen. Anhydrous ammonia is knifed into the soil about 10–15 cm below the soil surface. Nitrogen in the form of urea, other dry formulations, or liquid can be broadcast over the soil and then incorporated into the soil using shallow tillage. In soils deficient in phosphorus and potassium, these nutrients are often applied during sowing to supply a ‘quick’ start for the crop. Top dressing of fertilizers during the growing season is an option that is available if a nutrient deficiency is detected. Knowledge on the effects of micronutrient deficiencies on barley is limited. Under some conditions, barley has been found to respond favorably to the addition of chloride, copper, iron, and sulfur. More is known about the toxic effect of some micronutrients. In low-pH soils in areas of South America and Australia, aluminum toxicity can be a problem. Also, in areas of Australia, boron toxicity can severely interfere with plant growth. To overcome problems associated with these

problematic soils, barley cultivars have been developed that are tolerant to higher levels of boron and aluminum.

Cultivar Selection The choice of cultivar for production is especially important for growers producing barley for malting and as a method to combat potential problems such as diseases, insects, and micronutrient toxicity. In all major malting barley-growing regions, different organizations evaluate and determine which barley cultivars meet their specifications. To aid barley breeders, the organizations responsible for evaluating potential new malting barley cultivars often provide specifications that those cultivars must possess before they will be recommended for malting and brewing. Some of these groups also provide lists of cultivars that fit their specifications and are recommended for malting and brewing. In choosing malting barley cultivars for production, growers need to be aware of what cultivars are preferred by their local buyers. Even though there may be up to a dozen cultivars recommended for malting in a grower’s area, local buyers may be purchasing only one or two specific cultivars. Growers should consider not only yield potential when choosing a malting barley cultivar to produce but also grain protein and kernel plumpness when grown in their area. For example, if going into the growing season the grower knows that stored soil moisture is limiting and residual nitrogen is high, they should choose a cultivar that has inherently lower grain protein even if it has a lower yield potential. Because of the premium paid for malting barley versus feed barley, it is often better to sacrifice some yield to ensure the crop has acceptable grain protein and kernel plumpness. Recommendations for barley cultivars to be used for livestock feed or human food are limited. ‘Valier’ barley was developed by the Montana Agricultural Experiment Station in the United States specifically for feeding to cattle. However, much of the barley for the livestock market is grain that has been denied for purchase for malting due to one or more deficiencies (e.g., excessive grain protein, diseased kernels, and low

AGRONOMY OF GRAIN GROWING | Barley: Agronomy kernel weight). Barley cultivars for human food often are bred to have greater levels of soluble fiber, especially beta-glucan, and to have the hull-less character. Cultivars with these characteristics have been found to have hypocholesterolemic effects and a low glycemic index that may be beneficial in regulating blood glucose and reducing the risk of diabetes. Most barley recommended for malting and brewing has the two-rowed spike type (Figure 2). However, in North America, over 50% of the barley used for brewing is six-rowed. Historically, six-rowed barley has had higher enzyme levels that are required in beers brewed with adjuncts. Beers brewed with adjuncts tend to be lighter than traditional European-style beers made with 100% malt. Barley for the livestock and human food markets tends to have the two-rowed character because of its higher kernel weight as compared with six-rowed barley.

Sowing Date, Depth, and Rate The timing of sowing varies greatly across the globe. Barley with a spring growth habit is generally sown in the spring; however, it can be sown during fall in environments where winters are not severe and more than one cropping season per year is available. For example, spring barley often is fall-sown in east-central China. In this situation, barley is sown in October and harvested in early May, and rice is sown shortly thereafter. Another example of fall-sown spring barley occurs

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in the Southwestern United States. In this desert area, barley is sown in October and harvested in April, and a forage crop such as sudan grass is then sown. Areas where spring barley is predominantly spring-sown include Australia, northern Europe, Asia, North America, and South America. Barley with the winter-growth habit is generally less winter hardy than winter wheat; therefore, winter barley is grown in areas with less severe winters. In Germany, the ratio of winter to spring barley is around 60–40%. The desired sowing depth of barley is between 20 and 30 mm; however, the sowing depth may need to be deeper so the seed is placed in moist soil. Because of the emergence mechanism of barley, it should not be sown deeper than 55 mm. The type of seedling emergence in barley is referred to as the elongating coleoptile. In this type of emergence, the maximum length of the coleoptile will be only 35–55 mm. During seedling emergence, the coleoptile ceases to elongate once it breaks through the soil surface and is exposed to sunlight. Emergence of the remaining leaves occurs through the tip of the coleoptile. During germination, the stem internodes do not elongate, so the first node, coleoptilar node, and terminal bud (i.e., growing point) remain at the sowing depth. About 2–3 weeks following emergence for spring-sown barley and after vernalization and temperatures warm up in the spring for winter barley, the second internode of the plant elongates until the terminal bud and other stem nodes are about 10 mm from the soil surface. The first and second nodes remain at the sowing depth, and the tillers and crown roots develop from the remaining nodes. The seeding rate for barley is dependent on many items, including the type of barley being grown (two-rowed vs. sixrowed) and whether the barley is being grown under dryland or irrigated conditions. The desired plant population can range between 215 and 375 plants m2 (i.e., 2.15–3.75 million plants per hectare). The lower plant population is recommended for barley grown under dry conditions while the higher plant population is recommended for barley grown under irrigation. Also, since two-rowed barley generally produces more tillers than six-rowed barley, lower plant populations for two-rowed barley can be used. To determine the correct number of seeds to sow per hectare, the grower must know the desired final plant population, the estimated seedling mortality, and the percent germination of the seed. The estimated seedling mortality can be based on prior experience and the percent germination of the seed is usually supplied with the purchased seed. If the seed is old or if the germination is not known, the grower needs to determine personally the percent germination. This can be done using a simple test where 100 seeds are placed between two pieces of damp paper towel and counting the percent germinated seeds after 3 days. It is important that the paper towel is kept moist during the 3-day period. The number of seeds to sow per hectare can be calculated using the following formula: of seeds to sow per hectare ¼ of desired plants per hectare ð1=% seedling mortality Þ ð1=% germinationÞ

Figure 2 Comparison of the spike morphology of two-rowed barley (left) and six-rowed barley (right).

For example, if the grower desires a population of 3.0 million plants per hectare, the seedling mortality is 3%, and the percent germination is 95%, the grower would need to sow

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about 3.25 million seeds per hectare (i.e., 3.0 million plants per hectare (1/0.97) (1/0.95)). The seeding rate to achieve the desired plant population is dependent on seed weight. To determine the correct seeding rate, the grower can use the following formula: Kg of seed per hectare ¼ of desired seeds per hectare ð1000 kernel weight=1000Þ 1000 For example, if the grower wants to sow 3.25 million seeds per hectare and the 1000 kernel weight is 42 g, the grower would need to sow 136.5 kg per hectare (i.e., 3.25 million seeds (42/1000) 1000).

Irrigation Barley has high water-use efficiency and can extract moisture from a 0.8 to 1.0 m depth. Moisture needed throughout the growing season is about 400 mm. Because of its high wateruse efficiency, barley is most often grown without irrigation. However, if irrigation is used, it is done more for malting barley than for feed barley because of its higher potential value and the requirement for plump kernels and low grain protein. The goal of any irrigation schedule is to maintain available soil moisture levels above 50%. Management of any irrigation schedule is important because insufficient water will result in reduced yields, thin kernels, and excessive grain protein for malting. Excessive moisture will result in grain that lodges, making it prone to disease and difficult to harvest. Also, lodged grain often has thin kernels and high grain protein that may make it unsuitable for malting.

Table 2

The list of barley diseases caused by bacteria, fungi, and viruses is plentiful. Table 2 provides a partial list of important bacterial, fungal, and viral diseases of barley. Barley diseases exist that can infect all parts of the plants. A series of different root rots severely limit root development. The effects of this group of diseases are especially noticed during dry years or in dry areas of the field such as hilltops because roots are unable to uptake sufficient water. Diseases that affect the foliage of the plants such as the rusts, blotches, and leaf blights can severely reduce the photosynthetic capacity of the plants. These diseases often result in yield losses and excessive grain protein for malting due to reduced kernel weight. Finally, diseases of the spike such as the different kernel blights and smuts can reduce yield but, more importantly, can limit the marketability of the grain. Grain that is contaminated with smut or kernel blight can be severely discounted or rejected at the point of sale. Also, some pathogens such as the kernel-blighting Fusarium spp. produce mycotoxins. In the Midwestern United States in 2000, barley with > 0.5 ppm of the mycotoxin deoxynivalenol (DON) was discounted nearly $20 per tonne. Grain with DON > 3.0 ppm was rejected entirely for malting. Disease control can be accomplished by use of resistant cultivars, cultural methods, and chemicals. The easiest and most cost-effective method of disease control is growing resistant cultivars. Cultivars that are resistant or tolerant to most economically important diseases exist; however, like all cultivars, they have limited areas of adaptation. When a disease is new to an area or resistance breaks down in currently grown cultivars, it may take breeders a short time to develop improved cultivars if they have been working on the problem. However, when a disease is new to an area and no resistance is

A partial list of common diseases of barley, causal organism, and most common growth stage of infection

Disease Bacterial Bacterial leaf blight Bacterial kernel blight Bacterial blight Fungal Common root rot Pythium root rot Rhizoctonia root rot Spot blotch Net blotch Scald Powdery mildew Leaf rust Stripe rust Stem rust Covered smut Loose smut Head blight (scab) Viral Barley stripe mosaic Barley yellow dwarf Barley yellow mosaic a

Disease Control

Causal organism for bacteria and fungi, and vector for viruses.

Causal organism or vectora

Plant parts infected

Pseudomonas syringae Pseudomonas syringae Xanthomonas translucens

Leaves Kernels Leaves

Bipolaris sorokiniana Pythium ssp. Rhizoctonia solani Bipolaris sorokiniana Pyrenophora teres Rhynchosporium secalis Erysiphe graminis Puccinia hordei Puccinia striiformis f. sp. hordei Puccinia graminis f. sp. tritici Ustilago hordei Ustilago nuda Fusarium ssp.

Roots Roots Roots Leaves Leaves Leaves All aerial plant parts Leaves Leaves Leaves Kernels Kernels Kernels

Seed-borne Aphids Soilborne fungus Polymyxa graminis

Leaves Leaves Leaves

AGRONOMY OF GRAIN GROWING | Barley: Agronomy found in any of the adapted cultivars or advanced breeding germplasm, it may take more than 10 years to develop new resistant cultivars. The development of disease-resistant malting barley cultivars may take even longer since the breeder must incorporate disease resistance with the stringent characteristics specified by the malting and brewing industry. Crop rotation and tillage are cultural methods that are commonly used for disease control. Many of the diseases that infect barley also infect other crops. For example, F. graminearum and Bipolaris sorokiniana are the causal organisms of common root rot in barley and wheat, and F. graminearum is the causal organism of head blight in barley and wheat, and stalk rot in maize. Thus, when choosing a crop rotation, growers must be aware of their potential disease problems and alternative host crops of those diseases. A minimum of 1 year between susceptible crops is needed; however, to ensure reduction of potential disease problems, 2–3 years between susceptible crops is preferred. Tillage can reduce potential disease problems by burying crop residue that harbors pathogens. However, as more growers use minimum tillage or no-till methods, the potential for residue-borne disease is likely to increase. Chemical control for disease management can include application of fungicides to seed and foliage and insecticides to control virus vectors. Laws controlling chemicals that can be applied to crops differ for each country; thus, the mention of a particular chemical does not indicate that it is a permissible treatment everywhere. Fungicides applied to seeds are done to protect the seedlings from root rot, control loose smut (incited by Ustilago nuda), covered smut (incited by U. hordei), and other seed-borne diseases. Chemicals often used for seed treatment include carboxin; carboxin with captan, maneb, or thiram; imazalil; metalaxyl; and tebuconazole. Application of fungicides for foliar disease protection is generally done to protect the top two leaves of the plant. However, control of polycyclic diseases such as leaf rust (incited by Puccinia hordei) and stripe rust (incited by P. striiformis Westend f. sp. hordei) may require fungicide applications to seedlings and additional applications later in the season to protect the plants’ top two leaves. Adequate coverage of the spikes by fungicides to control the kernel-blighting diseases is difficult because the lemma awns intercept the chemical before it reaches the kernel surface and the fact that most crop sprayers are designed to apply chemicals to weed and crop foliage. A sprayer configuration composed of front- and back-facing nozzles has been found to provide the best coverage of spikes with fungicide.

Insect and Nematode Control Damage due to insects can be grouped into two categories: (1) damage due to consumption of plant parts during feeding and (2) damage due to virus or toxins transferred during feeding. Insects that can cause substantial losses due to plant consumption include grasshoppers, crickets, thrips, the cereal leaf beetle, wireworms, and cutworms. Wireworms tend to cause their damage by feeding on the roots and underground portions of the plant, while the remainder of insects listed in the preceding text cause their damage by feeding on the aboveground

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portions. Control of these insects is recommended after their population is above an economic threshold. Wireworms and cutworms need to be controlled early during the growing season so the plant population is not significantly reduced. Similar to controlling diseases, growers need to ensure that grasshopper, crickets, and other foliage-eating insects do not damage the top two leaves of the plant since they are the most important leaves in contributing photosynthates to the developing kernels. Four aphids are known to transfer the barley yellow dwarf virus during feeding. These aphids are the bird cherry-oat aphid (Rhopalosiphum padi), corn leaf aphid (R. maidis), English grain aphid (Sitobion avenae), and greenbug (Schizaphis graminum). Barley yellow dwarf is the most important of viral disease of barley and is found worldwide. The use of resistant cultivars is the best control for this disease. However, if resistant cultivars are not available, systemic insecticides can be used to control aphids if their population gets above the economic threshold. Hessian fly (Mayetiola destructor) is a pest of wheat throughout the world and can cause damage to barley as well by injecting a toxin during feeding. However, damage to barley is rare and this insect is not often considered a serious pest of barley. Two nematodes are known to cause economic damage to barley. Cereal cyst nematodes are a complex of several species of nematode that belong to the genus Heterodera. In seriously damaged plants, the roots are stunted and produce many lateral roots. Early aboveground symptoms of the plants infected by cereal cyst nematode mimic those caused by nutrient deficiencies. When older infected plants are pulled from the ground and the roots are examined, the white cysts attached to the roots can be identified. To confirm that damage is due to cereal cysts nematodes, a laboratory diagnosis is encouraged. Control of this pest has been accomplished using several different methods, including crop rotation, use of resistant cultivars, and use of fungal biocontrol agents. Cereal root-knot nematode, belonging to the genus Meloidogyne, is the other nematode that can cause economic yield losses in barley. Damage caused by this complex of nematodes is similar to that of the cereal cyst nematodes. The root system of infected plants appears bushy due to a stunted root system with many lateral roots. When adult plants are pulled from the ground and the roots are examined, galls ranging from small to near pea-size can be seen. To confirm infection by cereal rootknot nematodes, a laboratory diagnosis is recommended. Control of damage due to cereal root-knot nematodes is usually accomplished using crop rotation.

Weed Control Weed control is an integral part of almost every commercial barley production scheme. Excessive weeds can reduce yield and negatively impact grain quality for malting by reducing kernel plumpness and increasing grain protein. Many growers use tillage, herbicides, crop rotation, or a combination of these practices to control weeds in their fields. In some areas of the world, these methods may not be feasible or available because of environmental or marketing circumstances.

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Tillage is a viable option for most barley production systems including organic production, where herbicide use is not an option. Most weeds are easily controlled with tillage when they are small and can be covered by small amounts of soil. Barley can be harrowed or rotary-hoed either preemergence (when coleoptile is 10–15 mm below the ground) or postemergence (2–3 leaf stage). At these stages, the crop can more easily overcome damage and root pruning caused by tillage implements. Since tillage is a nonselective weed control method and both crop and weed species can be injured, care must be taken when harrowing, rotary-hoeing, or using other types of tillage. Many times, the barley stand can be reduced 20% or more by using tillage. In addition, the level of weed controlled may not be an acceptable excuse for subjecting the barley crop to this harsh, nonselective method of control. Herbicides are the most popular method of weed control for growers worldwide. In a properly managed Integrated Pest Management program, herbicides can be a valuable asset. Herbicides can provide both nonselective and selective means of controlling weeds in a cropping situation. For most broadleaf weeds, many herbicide options are available. These broadleaf herbicides take advantage of obvious physiological differences between grass and broadleaf plants. Grass weeds can be the most important yield-limiting factor in a crop production situation. Since barley is in the same taxonomic family as other grasses, Poaceae, grass weed control in barley is difficult or impossible to achieve without some injury. Since there are fewer chemical options when controlling grass weeds, resistance to specific herbicides and herbicide families is becoming a major problem. For this reason, it is important to use different herbicide families when controlling weeds to remove resistant biotypes of various weed species. Many weeds have developed resistance to ALS (acetolactate synthase) and ACCase (acetyl-CoA carboxylase) inhibiting herbicides. Kochia (Kochia scoparia) is an example of an ALS inhibitor-resistant weed that has become a major problem. Resistant kochia plants evolved when herbicides such as chlorsulfuron and metsulfuron-methyl from the ALS inhibitor group of herbicides became popular in crop protection. Kochia plants developing resistance to one of these herbicides also become more tolerant of herbicides that affect the same exact site of enzymatic activity. As a result, kochia may be resistant to other herbicides that belong to the same group. Only one plant is needed to create a resistant population that can exponentially increase over time. More serious weed control problems can occur when weed species develop resistance to more than one herbicide family or group; this is known as multiple resistance. Crop rotation plays an important role in weed control. By growing a different crop on the same piece of land each growing season, different herbicides can be used, thus reducing the chance of resistant weed biotypes becoming problematic. By growing a broadleaf crop before rotating into barley, the grower typically has a better opportunity to get some grass weeds under control. Likewise, volunteer barley from the previous crop can be easily controlled in a broadleaf crop by a number of different herbicides the following growing season. Another good crop rotation practice is rotating spring and winter crops. This allows herbicide applications at different times during the year and may control certain weed

populations that may not be controlled during a spring-type cropping scenario. Not all weed control options are available to every barley grower. Environmental conditions, such as lack of moisture, may cause tillage to be a prohibitive practice. For example, tillage may not be an option in a no-till situation, but may work in a minimum-till setting. Organic growers are restricted from using herbicides on weeds and genetically modified (GM) crops in their rotations but may get weeds under control by tillage and use of crops like rye in their cropping rotation. By using any of these methods of weed control, growers can protect their yield potential and make their crop more profitable.


• • • • • • • •

What are the top five barley-producing countries in the world and what is the largest end use of the grain produced in each country? How does the intended end use of the barley grain produced impact a grower’s decision on cultivar selection? In the countries listed in question 1, what are the top abiotic and biotic stresses that impact barley production and end-use quality? What yield components and end-use quality traits would be impacted by a hard frost during the tillering growth stage (Feekes stages 2 and 3)? Weed control can be difficult in organic farming systems. What yield components and end-use quality traits would be impacted by high weed pressure during seedling emergence? What yield components and end-use quality traits would excessive temperatures impact if they occurred during the jointing growth stage (Feekes stage 6)? Anthesis occurs during the late-boot growth stage (Feekes stage 10). What yield components and end-use quality traits would be impacted by a frost during this period? What yield components and end-use quality traits would be impacted by drought conditions during grain ripening (Feekes stage 11.3)?


•

•

Spring malting barley production is declining in many areas of the world due to competition from potentially highervalue crops, including maize, soybean, and canola. Will higher-yielding winter-growth habit barley stop the decline in barley acreage in the North America and Europe? GM crops exist for maize, soybean, canola, sugar beet, cotton, alfalfa, and rice. Will there be GM barley cultivars available for production before the year 2030?

See also: Barley, Rice and Maize Processing: Barley: Malting; Breeding of Grains: Barley: Genetics and Breeding; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Grain Marketing and Grading: Barley: Grading and Marketing.


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Further Reading

Relevant Websites

Anon. (1979) Barley: Origin, Botany, Culture, Winter Hardiness, Genetics, Utilization, Pests. US Washington, DC: Government Printing Office, US Department of Agriculture: Superintendent of Documents. Bauer A (1975) Irrigation of Small Grains. Fargo, ND: North Dakota State University Extension Service. Franzen DW and Ransom JK (2005). Barley production pocket guide. Circular A, 1186. Fargo, ND: NDSU Extension Service. Franzen DW and Goos RJ (2007) Fertilizing malting and feed barley. SF-723, Fargo, ND: NDSU Extension Service. Mathre DE (ed.) (1997) Compendium of barley diseases, 2nd edn. St. Paul, MN: The American Phytopathological Society. Neate S and McMullen M (2005) Barley Disease Handbook. Fargo, ND: NDSU Extension Service. http://www.ag.ndsu.nodak.edu/aginfo/barleypath/ barleydiseases/bdhpdf/barleydiseasehandbook.pdf (accessed December 2013). Nelson JE, Kephart KD, Bauer A, and Connor JF (1988) Growth staging of wheat, barley, and wild Oat; A strategic step to timing of field operations. Proceedings Western Society of Weed Science 41: 58–59. North Dakota Irrigation Association (2008) Irrigated malt barley productions; Managing risk to increase profit. Bismarck, ND: North Dakota Irrigation Association. http://www. ndwater.com/irrigation%20images/Barley%20Guide.pdf (accessed Dec. 2013). Rasmusson DC (ed.) (1985) Barley. Madison, WI: American Society of Agronomy.

http://www.albertabarley.com/newpage/production/prodlinks.html – This website provides a great deal of information on production of barley in western Canada. Topics discussed include land preparation, cultivar information, fertility, diseases and other pests, and weed control. http://www.ambainc.org – This website provides information on recommended barley cultivars for the United States, and suggested harvest and storage practices. http://www.ebc-nl.com/Index.HTM – Information on cultivars being evaluated in the European Brewing Congress’s EBC Barley & Malt Committee Field Trials can be obtained from this website. This information is useful in knowing what malting barley cultivars are currently being used and which ones may be used in the near future. http://www.weedscience.org/in.asp – This website provides information on herbicide resistant weeds around the world. Information is contained in a database that can be queried based on common or scientific name of the weed, herbicide mode of action, and by country.

Maize: Agronomy ED Nafziger, University of Illinois, Urbana, IL, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • •

Seeds and seed quality. Soil management. Planting time. Plant density and line spacing. Cultivar selection. Tillage. Plant nutrition. Crop canopy maintenance.

Learning Objectives

•

To gain a comprehensive understanding of the agronomic factors affecting maize yield and seed quality.

Introduction Maize originated under warm, seasonally dry conditions of Mesoamerica and was through extensive selection by prehistoric plant breeders converted from a low-yielding ancestor species to its modern form. It was spread by indigenous peoples throughout much of North and South America, where further selection adapted it to a wide range of soil and climate conditions, ranging from high valleys with low temperatures (even frost) to lowland tropics. It became the staple food crop for some cultures practicing settled agriculture, ranging from

Table 1

the Mayan and Aztec cultures in what is modern-day Mexico, to the Cahokia culture near modern-day St. Louis in the central United States, to the Wampanoag of present-day northeastern United States. From Central and North America, maize was spread by traders around the world and became a staple crop in much of Africa and in other regions (Table 1). Among grain crops (members of the Poaceae or grass family), maize has a very large female inflorescence (rachis, or cob) that can bear up to 1000 seeds, though more typically there are 400–600 seeds per ear (another name for the female flower-bearing seeds). Maize seeds are large, often weighing 250–400 mg each, and maize plants are among the largest of grain crop plants, often reaching a height of 2–4 m. Such large plants are grown at relatively low plant densities, typically less than 10 plants m2. Thus, unlike most cereal crops, maize is usually planted, by hand or by machine, at rather exact spacing between plants, with the expectation that yield will be lower if some plants are missing from their space. Thus, maize has a very high ratio of production to the area required to produce seed for the next crop; if one plant that grows from a single seed produces 500 seeds, producing seeds for 1 ha requires an area of only about 20 m2. In practice, yields of hybrid seed crops are less than those of production fields, but in contrast, the ratio of quantity produced to the amount of seed used in a crop like wheat may be only 20 to 30 to 1. As a crop plant equipped with C4 photosynthesis, maize is efficient in its use of water, able to produce 1 kg of dry matter using only about 350 kg of water. Even so, with yields that may under good conditions exceed 15 000 kg of grain and twice

Maize production by region and leading countries in 2013 Production

Region

Area (M ha)

Yield (kg ha1)

Million tonnes

% of world

Africa Asia Europe North America South America World Individual countries The United States China Brazil Argentina Ukraine India Mexico Indonesia France Canada

35 59 19 37 24 184

2045 5124 6190 9954 5282 5520

72 304 117 368 127 1017

7 30 12 36 13 100

35 35 15 5 5 10 7 4 2 1

9970 6175 5258 6604 6412 2452 3194 4844 8139 9588

354 218 81 32 31 23 23 19 15 14

35 21 8 3 3 2 2 2 1 1

Source: faostat.fao.org.

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http://dx.doi.org/10.1016/B978-0-12-394437-5.00241-2

AGRONOMY OF GRAIN GROWING | Maize: Agronomy that of dry matter per hectare, water use can exceed 600 mm in a growing season, or 6000 m3 ha1. If the maize crop is subjected to water stress, especially during the midseason pollination process, yields can be much decreased. Crop management needs to be attuned to this sensitivity, with planting date, cultivar, and water and soil management designed to minimize the chance of low water supply, especially through the midseason period. The high yield potential of maize is realized only if the crop is able to produce a vigorous plant with a full canopy – enough leaf area arranged so that it intercepts nearly all of the photosynthetically active solar radiation – especially during flowering and grain-filling periods. Green leaves convert solar radiation (mostly that in the blue and red wavelengths – leaves are green because they do not absorb as much of the green light as they do of other colors) to chemical energy in the form of sugars, which then move to other parts of the plant and provide energy and structural components to produce plant dry weight. So primary keys to achieving high yields are the quantity of solar radiation and the number of days the plant is healthy and able to conduct photosynthesis using the energy from that sunlight. Cloudy days; temperatures too low or too high; poor plant nutrition that decreases the ability of leaves to photosynthesize; loss of leaf area to insects, diseases, or hail; or stresses such as lack of water that can greatly decrease photosynthesis can all take a toll of maize plant productivity and grain yields. Of these, water supply, both that from sources such as rainfall and irrigation and that stored in soils and available to the crop if it has a healthy root system, is the most critical factor in most environments. But nutrients; management of weeds, insects, and diseases; and management of the soil all play a role in maximizing yields within the limitations that nature imposes. This forms the basis for how we manage corn through agronomic practices.

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Figure 1 Tassel (male flowers) of maize plants shedding pollen. The anthers in which pollen develops are released, usually in the morning as relative humidity drops, and the pollen inside them is released into the air, where some of it lands on silks.

Choosing a Cultivar Most of the maize seed sold for commercial companies in the US Corn Belt and similar regions around the world is hybrid seed. Hybrids are simply offspring of two separate parents and are relatively easy to develop and produce in maize because it is naturally cross-pollinated. Pollen grains fall from the male flower, the tassel, at the top of the plant (Figure 1) onto the silks – the receptive part of the female flower. One silk is attached to each ovule arranged on the cob and covered by husks, comprising the developing ear (Figure 2). The two inbred parents of hybrid seed are developed separately, each in a different population, using extensive selection over generations to help concentrate favorable genes within each population. Hybrid seed is produced by planting two inbreds next to one another in the field and by controlling pollination, preventing pollination by the seed (female) parent by removing the tassel before pollen is shed, leaving pollen from the male (pollinator) plants as the only pollen available to land on and pollinate the ears of the female. After pollination, the male rows are usually removed, leaving the ears to be harvested as hybrid seed. Plants grown from that seed are said to have hybrid vigor, meaning that they have considerably higher yield than either parent. Because inbreds are the result of a number of

Figure 2 Silks (extensions of female florets that receive pollen) after emerging from the husks that cover the cob of a developing ear. Each potential kernel on the cob has a silk attached, and the silks grow (mostly at night) to emerge into the air to receive pollen as it is shed from tassels. Under normal conditions, more than 90% of the pollen that lands on silks of an individual ear typically comes from nearby plants rather than from the tassel on the same plant.

generations of self-pollination, with pollen moved by hand from tassel to silks of the same plant, they tend to be genetically uniform. Hybrid seed produced using inbreds is also genetically uniform. While hybrids of maize have proven to be very highyielding, the seed produced in fields grown using hybrid seed is not, in the next generation, genetically uniform, and it cannot be used successfully to plant the next crop. Thus, producers need to purchase new seed for each crop. Before hybrids were developed in the United States in the 1920s and came into side use in the 1930s and 1940s, farmers used openpollinated corn varieties. Because pollen could come from other plants in the same field and from outside the field,

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AGRONOMY OF GRAIN GROWING | Maize: Agronomy

open-pollinated varieties were not very uniform, though some enterprising and observant producers were adept at selecting plants for uniformity over a number of generations, thereby increasing uniformity and, in most cases, improving yielding ability. Some of these varieties, for example, Reid’s yellow dent, became well known and were produced commercially. These of course had the advantage of allowing seed to be kept for the next crop with little or no decrease in yield potential. Open-pollinated varieties are still in widespread use in some less-commercialized parts of the world. They can be quite productive, and in lower-yielding environments where something other than genetics is the primary yield limitation and where the commercial seed supply may be uncertain, the advantage of using saved seed may be greater than the loss in yield potential. In the mid-1990s, commercial seed companies in the United States released the first genetically modified (GM) corn hybrids. These had as part of their genetic makeup traits that were found not in corn but in other organisms and then transferred using genetic engineering techniques into existing inbreds. These included genes from Bacillus thuringiensis, a soil bacterium that had been known for decades to kill certain insect larvae (caterpillars) that could attack corn. Such ‘Bt’ traits proved very effective and had no negative effects on the crop or on safety of the grain produced, but there was a strong movement against the use of such crops, based in part on the idea that moving genes among species was ‘unnatural.’ Most other GM traits incorporated into maize since then have been either for insect control (mostly different Bt traits) or for resistance to herbicides that allow the use of those herbicides on crops. Numerous attempts to uncover negative effects from having such genes in crop plants have failed, but efforts to prevent the use of GM hybrids from commercial use have continued. As a result, farmers in many poorer countries with uncertain food supplies have been denied their use. With access to alternative methods to manage insects and weeds, maize without GM traits can be produced successfully in more-developed countries and regions. But continued pressure against using this method of genetic improvement may preclude the development of cultivars with traits such as drought tolerance or resistance to diseases for which natural resistance cannot be found. Besides having characteristics to withstand problems common in a region such as dry periods or diseases or insects, cultivars of proper maturity need to be chosen to allow the crop to mature in the time available to it and also to position the crop favorably to counter problems such as midseason drought or late-season frost. There is a large range of cultivar maturities available in maize, from those that mature in less than 100 days to those that take 150 days or more from planting to maturity. In general, longer-maturing cultivars have more days over which to add yield and thus should be higher-yielding, at least when those days are sunny and warm and there is enough water available. On the other hand, longer duration in the field means more opportunity for problems such as insects or diseases to limit productivity. Another factor is genetics; the hybrids adapted to the US Corn Belt (contained within 38–45 N latitude and 83–100 W longitude, including the states of Indiana, Illinois, and Iowa and adjoining states) have been intensively bred for high productivity, and this improvement in genetic potential may easily offset any advantage offered by longer-duration cultivars.

In practice, many seed companies describe the maturity of a particular hybrid in terms of ‘days.’ This designation does not predict how many days the hybrid will actually take to produce a crop. Rather it refers to a ‘relative maturity’ (RM) rating based on comparison with hybrids of known maturity. This rating is useful as a comparative measurement – comparing RM ratings tells us whether a hybrid will mature earlier or later than another hybrid. RM ratings tend to change slightly as hybrids are moved north or south, reflecting comparative differences with other hybrids adapted to different regions. Maize cultivar development and time needed to reach maturity are closely tied to accumulated temperatures, measured most commonly in the United States by the ‘growing degree day’ (GDD) method. The number of GDDs required to reach maturity is more consistent from place to place than that of RM, and some companies provide both numbers. The GDD for 1 day is the average of the high and low temperature minus the base temperature (that below which little or no growth takes place) of 10 C; if the daily minimum is < 10 C, it is assigned the value of 10 C. As a guideline, 100-day RM hybrids require about 1300 GDDs from planting to maturity, and each additional day later RM is equivalent to 10–15 more GDDs to maturity; a 115-day RM hybrid may require about 1550 GDDs. In some regions, including in Europe, the FAO system of hybrid maturity is commonly used, in which maturity is assigned a value from 100 (equivalent to only about 915 GDDs) to 800 (about 1700 GDDs), adding about 110 GDDs for each additional increment of 100.

Soil Management and Tillage Soil management needs to be directed toward a number of goals, only one of which is maximizing maize yield. Proper soil management is also highly dependent on such factors as soil texture, topography, climate, previous crop, and productivity. Controlling soil loss by minimizing wind and water erosion is an important goal and is usually put into practice by leaving crop residue on the soil surface and by limiting the disturbance of the surface soil to only that required for successful crop establishment and then as close in time to planting as possible. There have for decades been numerous and persistent calls to increase the amount of no-till or to convert ‘conventional tillage’ to ‘conservation tillage’ in order to decrease the amount of soil loss and also to help increase soil organic matter. Many farmers in the United States already practice ‘conservation tillage,’ at least defined as doing less tillage than moldboard plowing and by leaving a certain amount of crop residue on the soil surface. Most maize in the US Corn Belt follows soybean in a 2-year rotation, however, and soybean usually produces less residue than needed to meet the requirements for conservation tillage. Modern tillage implements are designed to leave more residue on the surface, though, so few fields are bare at any time during the year. No-till often works well in regions with warmer, drier climates or with lighter soils. In regions with heavy-textured soils and where soils stay cool into the spring planting season, though, planting into soil left undisturbed since the harvest of the previous crop may not work well. Undisturbed soils tend to be cooler and wetter in the spring, and this can produce

AGRONOMY OF GRAIN GROWING | Maize: Agronomy unacceptable delays in planting. Some heavy soils also experience an increase in bulk density (weight per unit volume of undisturbed soil) if they remain untilled for several years, and this can provide a barrier to root growth and can eventually lower yields. One variant that is accepted as ‘no-till’ is striptillage, where tillage is done only in the part of the soil where the rows will be planted – this is enabled by GPS tracking technology that matches the rows planted later with the strips.

Planting Time The optimum time to plant maize is heavily influenced by the climate and soil, in particular the water supply expected to be available to the maize crop. In temperate regions, optimum planting time typically ranges from about the time of the spring equinox in latitudes of 30 –35 to about 6 weeks later than the equinox at the high-latitude limits of production. However, maize is produced wherever it fits into existing cropping systems, and spring planting is not always where it fits. As an example, maize in Brazil is often planted following harvest of the soybean crop in the fall (March or April) and grows during the drier winter period in regions where winter temperatures are moderate. Maize is also commonly grown during the winter in South Asia, where the summer monsoon period is too wet for maize and rice is often the crop of choice. In temperate regions, the main limiting factor to earlier planting in the spring is low soil temperature as soils begin to warm in the spring; soil temperatures should be at or near 10 C, and on an increasing trend, at the time of planting. Chances for the crop to experience frost after emergence should be < 10% or so at planting time; frost before emergence usually does little damage if temperatures do not drop below 1 C. In warmer climates without the need to wait for adequate soil temperatures, planting time is usually chosen to fit maize in with crops grown before and after it, to take advantage of soil

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water from rainfall, or to better utilize labor and other resources. This may not always maximize maize yields, but it can nonetheless optimize the cropping system. Farmers in the US Corn Belt place a premium on planting early and on finishing planting before yields start to decline. An example of a planting date response is shown in Figure 3. Planting date had little effect from early to late April, but yield loss accelerated as planting was delayed into May, averaging about 36 kg ha1 day1 from 25 April to 10 May and nearly doubling, to about 67 kg ha1 day1 from 10 to 30 May. On average, about half of the corn area in the Corn Belt is planted by 1 May, but this varies substantially from year to year due to weather, and large planters are used as a way to speed up planting when the soil conditions allow.

Plant Density and Line Spacing Unlike planting date, plant density is under near-complete control of the farmer or agronomist. In part because of this, a great deal of attention has been paid to developing hybrids that can tolerate the stresses brought on by competition between plants for light, water, and nutrients when plants are crowded close together. This tolerance of stress-inducing conditions is beneficial even when growing conditions are less than ideal and stress limits yields. The result is that yields tend to level off as plant density population reaches and surpasses that needed to maximize yield, but yields tend to remain near the maximum level even when density exceeds the optimum by 30 000 plants per hectare or more (Figure 4). As a consequence, the penalty of having density too high for conditions is not that yields will drop, but that the cost of the additional seed would not be returned. That means that high densities can be used to take advantage of favorable conditions without much loss if conditions are not favorable.

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Many modern planters can change seeding rate within fields and even by individual planter row. The fact that yields level off as density rises above that required for maximum yield means that the strategy of varying density based on soil productivity may not provide large returns in comparison to keeping density uniformly high across the entire field. As plant density increases, the number of kernels per plant decreases. Kernel weight also decreases, but much less on a percentage basis than kernel number per plant. Yields are typically maximized when kernel number per unit of area is at a maximum; under good conditions, it is advantageous to have 4000–5000 seeds m2, which at 300 mg per seed would mean yields of 12 000–15 000 kg ha1. In less-productive environments, plant density needs to be adjusted to fit the amount of available water and the cultivars that are used. In areas with < 500 mm of water available for the crop, plant densities may need to be decreased to 50 000 ha1 or even less. This makes more water available to each plant so that plants can maintain photosynthesis and can get through the critical flowering period in order to produce kernels and yield. Most of the maize in the US Corn Belt is produced using rows 76 cm apart. Some research has shown modest yield increases from decreasing this to 38 or 51 cm, but this change requires a substantial investment in planting and harvesting equipment, and it is not certain that such an investment will be returned by increased yield. Operations such as pesticide or fertilizer application are more difficult with rows 50 cm or less apart, and the increased weight per unit of width of equipment used to plant and harvest narrow rows contributes to soil compaction.

Plant Nutrition Harvested maize grain (at 15% moisture) contains about 11–15 kg nitrogen (N), 3–3.5 kg of phosphorus (P), and 3–4 kg of potassium (K) per tonne. Crop residue following harvest contains some additional N and K, much of which leaches out of the residue and is returned to the soil, though some of the N might be converted to a gaseous form during

microbial breakdown and be lost to the air. Residue has very small amount of P. Concentrations of other elements are much lower than those of N, P, and K, but soils need to have an adequate supply of all of these in order to prevent deficiency. The supply of P and K is related to soil type and, since many soils are naturally deficient in these elements, on application of fertilizer or manure. The soil serves as a reserve for these elements; they tend to remain in the soil and are available to the crop even if supplied some years before, though some soils will adsorb certain amounts of these elements and thereby slow their release for crops. Soil tests that extract part of the P and K have been calibrated to crop response, providing a way to assess the adequacy of these nutrients for the crop to be grown. Soil pH (the degree of acidity) is important as well because it affects the degree to which elements found in the soil are available to the crop. As an example, soil with low pH (high acidity) may have an adequate P supply according to the soil test, but P availability may be reduced to the point where deficiency appears. The nutrient that maize needs in largest supply is nitrogen. A crop that yields 10 000 kg ha1 may contain about 130 kg of N in the harvested grain and an additional 60–65 kg N in the nonharvested residue, for a total requirement of nearly 200 kg N ha1. It is possible to supply this amount using fertilizer, but because N (in its nitrate form) is mobile in the environment, because soil organic matter contains a large supply of N that can become available, and because N is taken up and released by soil microbes, applying the exact amount of fertilizer N that the crop might take up is not always sound management. Both deficiencies and excess amounts of N are problematic – the former because of the economic loss and the latter because leftover N that reaches surface waters or that is converted to the potent greenhouse gas nitrous oxide constitutes environmental problems. Managing N to avoid both deficiency and excess is challenging, especially in humid areas such as the US Corn Belt where rainfall is often highly variable and where soils vary greatly in their ability to retain N and to provide it to the crop. Soil texture and the amount of soil organic matter are critical factors in the supply of N to the crop. Fertilizer

AGRONOMY OF GRAIN GROWING | Maize: Agronomy materials supply N in the form of nitrate (NO 3 ), ammonia (NH3, which coverts quickly in the soil to ammonium, NHþ 4 ), or urea, which also forms ammonium fairly rapidly once applied. Ammonium is positively charged and so is held by negatively charges sites on soil organic matter and on clay minerals, but it is also biologically converted to nitrate rapidly in warm, moist soils. So while the maize plant can take up either nitrate or ammonium, much of the N that moves to the plant root (carried by the water as it moves there) is in the nitrate form. In saturated soil conditions, nitrate can also be converted by anaerobic microbes to a gaseous form, either N2O or N2 (the form that makes up most of the earth’s atmosphere), and can be lost from the soil. The supply of N from soil organic matter can be a major source of N for the crop; topsoil with organic matter content of 3–4% may provide as much as 100 kg N ha1 for the crop in a season. Cool, dry, or otherwise unfavorable soil conditions may greatly limit this amount, while very favorable conditions might increase it. Soil organic matter is constantly breaking down and being renewed in the soil, so providing N to the crop does not diminish organic matter content very much if any over time. But while this supply of N is valuable for the crop, its dependence on variable soil conditions means that the amount it will provide is not very reliable or very predictable. The influence of the soil in supplying both water and N to the maize crop means that simply applying more fertilizer N to fields from which we expect higher yields is often not the best agronomic practice. An example of this is shown in Figure 5, in which N responses averaged over a 10-year period showed that maize in a lower- organic-matter, more drought-prone soil of southern Illinois required substantially more fertilizer N to reach a lower yield than was the case in a northern Illinois location with higher-organic-matter, more productive soils. Figure 5 illustrates the important point that, while applying more N than the crop needs is economically and environmentally unsound, the use of excessive N does not tend to reduce grain yield of modern maize cultivars. There are instances when high rates of fertilizer N increase crop growth and water use, leading to earlier onset of drought stress and lower yields, especially when water subsequently arrives too late to alleviate

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stress during the critical flowering period. But more commonly, adding more nitrogen than the crop requires simply produces no additional yield, and so leads to economic loss and more loss of N to the environment.

Maintaining the Crop Canopy Maize as a crop uses sunlight efficiently, and yields under otherwise favorable conditions may often be limited by the amount of sunlight the crop intercepts during the growing season, especially during and after flowering when kernels are being formed and then filled. In an experiment with imposed levels of leaf removal, the relationship between light interception a few weeks after flowering and final grain yield has been shown to be direct and linear (Figure 6). This requires having adequate water and nutrients available and on maintaining the health of the leaf area that remains. But this illustrates that agronomic practices that help to develop and maintain a full and healthy canopy are practices that should provide maximum yields under the conditions that exist. This includes not only US Corn Belt conditions; canopy completeness may be optimized at lower levels when, for example, water is limiting. But as a principle, ‘managing the crop by managing for the canopy’ is a sound principle.


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In the context of maize breeding, what is a hybrid and how are they produced? What is hybrid vigor and why is it important? What genetically modified traits have been introduced into commercial maize and what benefits do they confer? What is the ‘growing degree day’ and how is it used in developing and selecting new maize hybrids? Why is soil management important in maize production and how is it accomplished? What factors influence the optimum planting time of maize?

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Figure 6 The relationship between sunlight interception early in the grain-filling period and final grain yield of a maize crop in Illinois. Imposed defoliation treatments provided the range of light interception. Data are from the author.


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Identify natural sources of drought tolerance and disease resistance. Continue development of genetically modified hybrids for traits for which no natural sources are available.

See also: Barley, Rice and Maize Processing: Maize: Wet Milling; Oil from Rice and Maize; Non-wheat Foods: Maize: Foods from Maize; Processing of Grains: Cereals: Breakfast Cereals; Proteins: Nitrogen in Grain Production Systems; The Protein Chemistry of Cereal Grains; The Basics: Grain: Morphology of Internal Structure; Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Cereals: Domestication of the Cereal Grains.

Sorghum: Production and Improvement Practices WL Rooney, Texas A&M University, College Station, TX, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Grain sorghum is a historically important crop throughout much of the semiarid production areas of the world. Grain sorghum is used as both a feed and food grain, with one of these predominating in different regions of the world, primarily based on historical uses. Food grain quality is defined differently throughout the world, but kernel traits such as pericarp color, presence of a pigmented testa, and endosperm characteristics strongly affect it. Production parameters to maximize yield and quality are well established, and sorghum breeding programs continually select to improve grain yield and protect grain quality. Sorghum improvement programs utilize genetic diversity to improve yield and quality as well as protect the crop from abiotic and biotic stresses.

Learning Objectives

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Gain an understanding of the role of grain sorghum in world agriculture and cereal crop production systems including optimum production environments and agricultural management. Gain an understanding on the various genetic and environmental factors that affect sorghum grain quality and processing for its application as a food, feed, and fuel grain.

Introduction Sorghum (Sorghum bicolor L. Moench) is an important crop species in the United States and around the world (Figure 1). Because of its substantial heat and drought tolerance, sorghum is traditionally grown in semiarid, subtropical, and tropical regions. In addition to abiotic stress tolerance, sorghum is very responsive (in terms of productivity) to more favorable conditions. Although known primarily as a grain crop, sorghum is also grown a forage, syrup and energy crop. In 2008 US farmers harvested about 5.9 million hectares of grain sorghum (USDA NASS). Worldwide, the top 20 grain sorghumproducing countries harvested 49 472 518 tonnes of grain in 2007 (FAOSTAT). The cultivated sorghums are all varieties or hybrids from S. bicolor L. Moench. All accessions of S. bicolor are genetic diploids with base chromosome number of n ¼ 10 and 2n ¼ 2x ¼ 20. Furthermore, the sorghum species is very diverse with the primary center of origin in Northeastern Africa. There are several additional sorghum species, but none are systematically cultivated, and many are perennial. Those species have variable growth habits and chromosome numbers, but they do


represent an additional source of genetic variability if needed. Of these, S. halepense is the most infamous because it is the persistent and aggressive weed known as Johnson grass. Sorghum has a deep, fibrous root system, primary culm and the capacity for both basal and axillary tillering. S. bicolor has a complete flower that is predominantly self-pollinated, but outcrossing does occur at variable rates up to 30% depending on the genotype and environment. Sorghum is amenable to commercial hybrid seed production through the use of cytoplasmic male-sterility systems. The crop is grown and managed as an annual, but it is technically a perennial; once harvested, it will regrow unless environmental conditions (e.g., freezing temperatures) preclude growth. Although also grown as a forage crop, sorghum is most widely known as a grain crop. As a cereal grain, the grain is predominantly starch in composition. The end use of this grain varies based on location and grain characteristics. In the Americas and Australia, grain sorghum is used primarily as a feed grain and a starch source for ethanol production. In other regions of the world (Africa, India), grain sorghum is considered a primary food grain where it is processed and prepared in many different ways (Figure 2).

Primary Traits of Importance Plant height is a primary factor in overall biomass yield potential; higher yields are correlated with taller plants. However, there are limits to height, as taller plants are more prone to both stalk and root lodging so the benefits of height must be effectively balanced with the risks. Sorghum height is easily manipulated; four major height genes were identified, and many modifiers of these genes have been subsequently described. Of all sorghum traits, maturity is likely the most important because it influences so many agronomically important characteristics (Figure 3). Sorghum maturity is controlled by genes that are influenced by both day length (photoperiod sensitivity) and temperature. Photoperiod-sensitive sorghum cultivars require a defined length of darkness to induce panicle differentiation and development. As sorghum was moved to more temperate climates and away from lower latitudes, photoperiod-insensitive sorghums were necessary for the crop to produce grain before the growing season ended. Much of the early work to develop photoperiod-insensitive sorghum in the United States was completed by producers who would identify and save seeds of individual, early maturing mutants or segregants. In photoperiod-insensitive sorghums, maturity is primarily influenced by temperature. Six maturity genes have been described in photoperiod-sensitive and -insensitive sorghum, and there are likely many more. These loci interact to produce an array of maturities in all types of sorghum cultivars.

http://dx.doi.org/10.1016/B978-0-12-394437-5.00198-4

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Figure 1 Commercial grain sorghum grown in South Texas has red grain and is commonly used as a feed grain or for ethanol production.

Figure 2 A grain sorghum hybrid yield trial has many different hybrids with various phenotypes such as grain color (note red and white types). Information from these types of trials is used to identify the best hybrids to advance for further testing and possibly commercialization.

Agronomic Production Practices Sorghum is seed propagated and is grown as a self-pollinated variety or a hybrid. In regions of the world with a commercialized agricultural infrastructure, hybrids predominate, whereas self-pollinated varieties are common in less-developed regions of the world. Pure-line varieties allow small producers to save seed from year to year, whereas hybrids allow producers to increase yield by capturing heterosis. Assuming moisture availability, the primary factor in sorghum stand establishment is temperature. Sorghum is a warm season crop that requires soil temperatures of at least 15 C to initiate the germination

Figure 3 Sorghum is highly variable for phenotype, and major difference exists based on the genetics of height and maturity. The early short line (left) and the tall, late line (right) are genetically very similar, differing primarily at a few genetic loci controlling plant height and photoperiod sensitivity.

process; temperatures below 15 C will slow or even stop the process. In most regions where sorghum is grown, low soil temperatures will not be a problem, but in more temperate climates it must be monitored. From a productivity standpoint, plant population and row spacing are probably the most critical management factors, with optimum density and spacing depending on the type of production system. Nutrient requirements of sorghum are similar to other cereal grain crops in that nitrogen, phosphorous, and potassium are the major compounds required for growth. In addition, micronutrients are needed in some situations depending on soil availability. For optimum productivity, a soil pH between 6.5 and 7.5 is best. Nitrogen requirements in grain sorghum are similar to corn and adjusted to the expected yield potential for a particular production environment. The water use efficiency and/or drought tolerance of sorghum is due to a number of morphological and physiological traits. As expected, there is significant variation in sorghum for drought tolerance, and this variation has been used by breeders to enhance drought tolerance of grain sorghums. Sorghum is a host plant for an array of plant pests and pathogens, but most have limited impact on commercial production. In addition, some of the important pest or pathogens are localized to specific production regions. Of the major diseases, grain mold and anthracnose are probably the two most significant, but root and stalk rots are important as well as they affect standability, which is critical for harvesting. In

AGRONOMY OF GRAIN GROWING | Sorghum: Production and Improvement Practices certain situations, ergot, head smut, and downy mildew may also be problematic. For essentially all diseases, breeding for host-plant resistance is the most effective method of control. Sorghum breeders and pathologists continue to screen germplasm to identify new sources of genetic resistance, and breeders utilize these materials to produce improved varieties and hybrids and thus reduce losses due to disease susceptibility. In some situations, chemical control via seed treatment or application may be appropriate.

Genetic Improvement of Grain Sorghum Grain sorghum breeding efforts have been underway for over 100 years. Initial efforts through the mid-twentieth century focused on improvement of pure-line cultivars. Pure-line cultivars are still grown in many regions of Africa, India, and Central America where infrastructure has limited the deployment of hybrids. Researchers knew that hybrid vigor occurred in sorghum, but the development of sorghum hybrids did not occur until methods were developed to sterilize seed parents to produce hybrids by using a cytoplasmic male sterility system. This approach was first used to produce hybrids in 1956, and within 5 years, hybrid grain sorghum was planted on over 90% of the total US grain sorghum area. Soon after development of grain sorghum hybrids, forage sorghum hybrids for both hay and silage were developed and adopted. Over the past 50 years sorghum breeding programs have continued to improve and advance sorghum genetics. Traits such as increased yield with high inputs (e.g., water and fertilizer) became important as was protection of yield potential from both biotic and abiotic stresses. These efforts have led to substantial improvements in yield potential, grain and forage quality, and the protection of this potential through abiotic and biotic stress tolerances. Further improvement relies on a thorough understanding of the crop and genetic control of traits of importance.

Current Sorghum Breeding Approaches Today, sorghum breeding programs integrate both traditional and molecular approaches. When breeding new hybrids, each program develops inbred lines for test-cross evaluation. To develop inbred lines, most but not all sorghum breeding programs use some form of pedigree selection. Testcross evaluation is used to assess combining ability. Good general combining ability is needed in the first testcross, and subsequent testing identifies the exact combinations with commercial potential. Predicting hybrid performance by evaluating inbred lines themselves is not typically an efficient use of resources. If the new lines are seed parents (i.e., they do not restore fertility to male sterile-inducing cytoplasm), they must be sterilized for use as a seed parent. Sterilization involves backcrossing to introgress sterility-inducing cytoplasm, which results in a sterile version of the seed parent. The use of off-season nurseries speeds the pace, but sterilization and creation of an A-line (male sterile) version of the B-line (fertile seed parent) requires additional time. Since the advent of hybrids, sorghum germplasm has been placed into heterotic groups based on fertility

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restoration. Although this classification was of necessity, there is some basis as most seed parents were in the kafir group, whereas pollinator parents were typically caudatum and durra types. Since then breeding has evolved these into legitimate heterotic groups. Sorghum genetics and genomics are well advanced. The sorghum genome has been sequenced, and two high-density genetic maps and one cytogenetic map have been constructed. In addition, many agronomically important genes have been cloned, and a transformation system has been developed. Finally, there are many published quantitative trait loci (QTL) studies in sorghum, and much of this information is being used for genetic characterization of sorghum germplasm in breeding programs.

Germplasm Collections and the Use of Sorghum Genetic Diversity The genetic variability present within sorghum is compiled in germplasm collections at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and the US Sorghum Germplasm collection based in Griffin, GA, and Fort Collins, CO. These repositories represent a valuable source of variation for future sorghum improvement. Most of this variation has limited direct use in temperate breeding programs due to photoperiod sensitivity (Figure 3). Several approaches have been utilized to make this diversity accessible. The sorghum conversion program was initiated in 1963 in the United States with a goal to introgress day-length insensitivity and dwarfing into exotic sorghum lines making this germplasm accessible to all sorghum breeding programs. During the active conversion program ( 40 years), over 700 photoperiod-sensitive sorghum accessions were fully converted and released. The lines have had a tremendous impact on sorghum improvements worldwide; it is difficult to find sorghum that does not have sorghum conversion germplasm in its pedigree. In addition, conversion lines have been extremely important for genetic research and genomic analysis of sorghum for an array of traits ranging from adaptation to tolerance to biotic and abiotic stress.

Breeding for Grain Yield In every hybrid sorghum improvement program, yield and adaptation are the primary traits in improvement. The relationship between yield, maturity, and height is critical in defining the types of hybrids and their adaptation. The relationship between maturity and grain yield is dependent on the type of environment in which the hybrids are grown. In environments that do not encounter terminal stress conditions, grain yield is strongly correlated with increased maturity, but in those stress environments, the positive relationship between yield and maturity is eliminated, and in most cases earlier maturity hybrids will outyield later hybrids. This is primarily because earlier maturity hybrids escape the terminal stress. In the case of height, there is a positive relationship between increasing height and grain yield, although many production regions limit plant height due to potential problems with lodging. A second consideration in adaption is the tropical or subtropical versus temperate adaptation. Certain parental

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lines and hybrids are better adapted to more temperate environments, whereas others are more suitable for tropical adaptation. Most hybrids, when moved to the opposite environment do not respond well. Although some this is due to differences in disease and pest reaction, there is a definite response to the temperature and day length observed in temperate and tropical environments. Therefore, breeders must utilize and develop hybrids suitable for specific environments. In rare cases, hybrids have been identified that have adaptation across both types of environments. The development and adoption of hybrids led to rapid increases in productivity, based primarily on capturing heterosis. After hybrids, genetic improvements in yield have relied on the integration of elite but exotic germplasm from programs such as the sorghum conversion program. Between 1960 and 1980, genetic gains in yield averaged 1–2% annually. Today, yield has improved, but the rate of improvement has slowed due to shifts in production environments and reduction in sorghum breeding programs. Future improvement relies on the utilization of new technology to both phenotype and select genotypes with better yield.

Breeding for Grain Quality

trait (Figure 5). These particular characteristics define the appearance of the whole grain and to a certain extent the end use of that grain. Variation for endosperm color, protein content and digestibility, starch content and digestibility, and fat content is under genetic control and can be manipulated to produce different types of grain sorghum. Grain and plant color influence the potential end uses of the grain. Most food grain sorghum has a white pericarp. In the Western Hemisphere where sorghum is used predominantly as a feed grain, grain color is considered to be of little consideration, and most hybrids have a red pericarp because it tends to tolerate grain weathering slightly better than white pericarp sorghums. Furthermore, plant color can affect grain quality. Ideally, food grain sorghum is produced on a sorghum plant with tan plant color as a pigmented plant often results in stained grain and flours with an off-color and possibly offflavors (Figure 6). Grain quality is defined regionally, so the specific desirable traits vary from region to region. For example, there is a misperception that the tannins in sorghum are a negative trait. If tannins are present, they do reduce feeding efficiency in animal systems. However, there is new information that tannins are actually beneficial in human diets because they are a source of antioxidants and reduce starch digestion rates.

Sorghum grain is processed and utilized in many different ways. Approximately 40% of the world production is used as a food grain to make a wide array of products ranging from unleavened flat breads to fermented traditional beverages. Another 45% is utilized as a feed grain for poultry, pork, and beef production. When used as feed grain, it is processed in an array of different ways. Industrial applications, such as ethanol or starch extraction use 15% of worldwide production. Because grain quality is defined regionally, it is impossible to clearly define consistently desirable traits. However, there are several grain characteristics that influence quality. Perhaps the most impact kernel traits include pericarprelated traits. In sorghum, grain color and appearance are controlled by several qualitatively inherited genes. Basic grain color (red, yellow, or white) is controlled by the R and Y loci (Figure 4). Mesocarp thickness and pericarp color intensity are controlled by single genes, Z and I, respectively. The presence or absence of a testa layer (comprised of condensed tannins) is controlled by the B1 and B2 loci, and this trait has more effect on grain quality and end use than probably any other kernel

Figure 5 The presence of a pigmented testa layer imparts a different color appearance to a sorghum that has a red pericarp. The pigmented testa layer is high in tannins, which influence the relative grain quality, depending on the ultimate end use.

Figure 4 Grain sorghum can vary widely in appearance, but there are three basic pericarp colors: red, yellow, and white. Variations in sorghum color from these are due to traits in portions of the kernel.


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appear to be inherited independently, indicating that there is the potential to incorporate this trait into sorghum with no loss in weathering resistance.

Breeding for Stress Tolerance

Figure 6 The base pigmentation color of the plant influences, to some extent, the glume color on grain sorghum. The basic plant colors of sorghum are tan (nonpigmented), red, or purple, and the lightest color glumes are consistently associated with tan plant color. Glume color can affect grain quality because pigments can leach from glumes into white sorghum, which will discolor the grain and flour.

In most regions, sorghum with good food quality is clean and free of molds, weathering, or insect damage. Typically, the grain has a white pericarp that is easily removed from the endosperm during milling, and it is produced on a plant with tan plant color and light or straw-colored glumes. These traits ensure that the sorghum grain will produce flours that have light color and bland flavor. Although these same characteristics are also desirable for animal feeding, they are not required, and red and yellow grain color is often found in feed sorghum. In normal sorghum grain, the endosperm contains 20–30% amylose and 70–80% amylopectin. Variation in the relative amount of amylopectin in the endosperm is controlled by a single gene (Wx). In grain from waxy sorghum, the starch in the endosperm is amylopectin, and no amylose is present. Waxy endosperm sorghums are more digestible and easier to process than normal endosperm sorghums. Waxy hybrids have widely produced because yields of them are traditionally lower than traditional endosperm hybrids. Variation for protein content in grain sorghum is also strongly influenced by environmental conditions. Protein content in the grain typically decreases in high-yielding environments and increases in low-yielding environments. In each case, these changes are primarily due to the increase and reduction of starch synthesis, respectively. Genetic variation for protein content and quality are known, but these increases in content or quality are accompanied by severe reductions in agronomic and yield characteristics. Variation for protein digestibility occurs in sorghum, and it is associated with softer endosperm types. These types have limited applicability because of grain mold susceptibility. However, the two traits

Abiotic stress is defined as a yield-limiting factor caused by a nonbiological source. Examples of abiotic stress include but are not limited to temperature, moisture, and soil fertility. Of these factors, drought is the largest single factor in grain sorghum yield reductions. Drought stress is a complicated condition that initiates the expression of numerous genes in myriad signal transduction pathways. Drought tolerance has been studied for many years, and several different mechanisms of tolerance have been described. Stay-green is a postflowering drought tolerance trait that can be described as delayed senescence. It therefore can mitigate effects of terminal drought stress on the final yield processes including grain fill and stalk development. The stay-green trait includes modifications in stalk properties that affect biotic stresses such as charcoal stalk rot and lodging. A second and less-well-understood drought-tolerance mechanism is preflowering drought tolerance, which is expressed prior to flowering and is physiologically different than stay-green. Only a few sorghum genotypes possess both types of tolerance. Aluminum toxicity can limit sorghum production in acidic soils, which are common in the humid tropics. Genetic variability for aluminum tolerance has been observed and is commonly used in sorghum-breeding programs in Brazil. Nitrogen use efficiency in cereal crop production has been estimated to be at about 33% worldwide. Biotic stresses are defined as yield-limiting factors of a biological source, typically either an insect pest or a disease pathogen. Numerous pathogens and pests can reduce yield and quality of all types of sorghum. However, the relative importance of each biotic stress differs based on the type of sorghum and location of production. In grain, breeding for resistance to midge and shoot fly is important because these pests directly reduce grain yield. Grain sorghum crops in the United States are not generally seriously infested with stalk boring insects. Among the most important sorghum diseases are anthracnose Colletotrichum sublineolum and downy mildew Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw. Considerable effort has been put into developing cultivars that are resistant to these pathogens. Anthracnose is one of the most economically important sorghum diseases. Anthracnose can affect all aboveground plant organs and is among the most serious pathogens of sorghum. At any one time, pathogen populations can be made up of many pathotypes making breeding for resistance particularly challenging. Estimated yield losses due to anthracnose alone have been reported in excess of 50%. Gene-for-gene relationships have not been conclusively demonstrated, and therefore, assignment of races or pathotypes has been difficult. However, genetic variation for resistance has been reported and used to develop anthracnose-resistant grain sorghums. For downy mildew, genetic resistance is the best approach to control, but some seed based chemical treatments are effective as well. Multiple races of downy mildew that infect sorghum have been identified, and consequently resistance genes have come from multiple sources.

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Summary and Conclusions Grain sorghum is among the most versatile of crop species with wide environmental adaptation and a diversity of end uses. The genetic resources available to sorghum breeders, contained in both the currently utilized breeding germplasm, as well as the extensive public germplasm collections, represent a rich repository of genetic variation that is necessary for breeding progress.

See also: Genetics of Grains: Genomics of Food Grains; Grain Harvest, Storage and Transport: Sorghum: Harvest, Storage, and Transport; Non-food Products from Grains: Cereal Grains as Animal Feed; Fuel Alcohol Production; Non-wheat Foods: Sorghum: Utilization; Proteins: Nitrogen in Grain Production Systems; Protein Synthesis and Deposition; The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: Sorghum Grain, Its Production and Uses: Overview.


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Describe the changes during the past 50 years, in sorghum genetics, production, and utilization. Describe the origins of sorghum and early improvement. What modifications to the crop facilitated its movement around the world and its adaptation to new production environments? Describe the primary traits under genetic control that influence agronomic performance and grain quality for food, feed, and fuel. Describe the relative advantages and disadvantages of hybrid versus self-pollinated cultivars, and discuss why certain regions tend to favor production of one type over the other.


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Assess how sorghum improvement programs effectively utilize the large sorghum germplasm collections and integrate that germplasm with new genomic information including QTL for many different agronomic and grain quality traits. Investigate and describe the composition of sorghum grain for starch, protein, and oil content. How does the environment affect protein and starch content, and how does content of these compounds relate to grain utilization? Investigate the advantages of waxy grain in various cereal species (e.g., maize) and anticipate the opportunities for waxy sorghum. Investigate the potential negative–positive effects of tannins in different utilization schemes.

Further Reading Boyer J (1982) Plant productivity and environment. Science 218: 5. Frederiksen RA and Odvody GN (2000) Compendium of Sorghum Diseases. St. Paul, MN: American Phytopathological Society (APS Press). Jordan DR, Hunt CH, Cruickshank AW, Borrell AK, and Henzell RG (2012) The relationship between the stay-green trait and grain yield in elite sorghum hybrids grown in a range of environments. Crop Science 52: 1153–1161. Mace E and Jordan D (2010) Location of major effect genes in sorghum (Sorghum bicolor (L.) Moench). Theoretical and Applied Genetics 121: 1339–1356. McIntyre CL, Drenth J, Gonzalez N, Henzell RG, and Jordan DR (2008) Molecular characterization of the waxy locus in sorghum. Genome 51: 524–533. Miller FR and Kebede Y (1984) Genetic contributions to yield gains in sorghum, 1950 to 1980. In: Fehr WR (ed.) Genetic Contributions to Yield Gains of Five Major Crop Plants, pp. 1–14. Madison, WI: Crop Science Society of America and American Society of Agronomy. Paterson A, Bowers J, Bruggmann R, Dubchak I, Grimwood J, and Gundlach H (2009) The Sorghum bicolor genome and the diversification of grasses. Nature 457: 551–556. Quinby JR (1967) The maturity genes of sorghum. In: Norman AG (ed.) Advances in Agronomy, pp. 267–305. New York: Academic Press. Quinby J (1974) Sorghum Improvement and the Genetics of Growth. College Station, TX: Texas A&M University Press. Raun WR and Johnson GV (1999) Improving nitrogen use efficiency for cereal production. Agronomy Journal 91: 357–363. Rooney WL (2004) Sorghum improvement—Integrating traditional and new technology to produce improved genotypes. Advances in Agronomy 83: 37–109. Rooney WL and Aydin S (1999) Genetic control of a photoperiod-sensitive response in Sorghum bicolor (L.) moench. Crop Science 39: 397–400. Sleper DA and Poehlman JM (2006) Breeding Field Crops. Oxford: Blackwell Publishing. Smith CW and Frederiksen RA (2000) Sorghum: Origin, History, Technology and Production. New York: Wiley. Teetes GL and Pendleton BB (2000) Insect Pests of Sorghum. Sorghum: Origin, History, Technology and Production. New York: Wiley, pp. 463–466.

Canola: Agronomy NJ Mendham, University of Tasmania, Hobart, TAS, Australia MJ Robertson, CSIRO Sustainable Ecosystems, St. Lucia, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 1, pp. 144–155, ã 2004, Elsevier Ltd.

Topic Highlights

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Crop development and environmental factors. Yield components. Crop management. Rapeseed in farming systems.

Introduction: The Three Species and Their Agro-Ecological Niches This article introduces the three main Brassica oilseed species, and analyses the factors affecting their development and growth. A model approach is used to synthesize the information into a coherent whole, based on the way crops use solar radiation and other resources. This is then used as a framework to examine how the crop can be managed to efficiently produce oil and protein, by manipulating cultivar, sowing time, plant population, nutrition, water supply, and other inputs. Finally, the crop is considered in a wider farming-systems context. Brassica oilseeds have been used as cooking oils in India, China, Japan, and less developed parts of Europe for centuries. Rapeseed oil has also been used as a lighting oil and as a lubricant in western Europe since about the fifteenth Century, but only as an edible oil there and in North America since the Second World War. By the 1960s, it was shown that erucic acid, the long-chain fatty acid characteristically found in Brassica sp., which gives the oil excellent lubrication properties, was implicated in heart disease in mammals as it could lead to hardening of the arteries. Pioneering work in Canada showed that erucic acid could be virtually eliminated by breeding, leading to the first low-erucicacid varieties, Oro and Span (B. napus and B. rapa, respectively) by the late 1960s. At this time it was also shown that the glucosinolates, the mustard-type compounds found in the seed which restricted feeding of the meal (the seed residue after oil was extracted) to livestock, could also be reduced to a low level by breeding, initially using a Polish variety Bronowski. “Canola” is a name coined in Canada for “double low” varieties containing specific seed quality characteristics: low erucic acid (less than 2%) and low glucosinolate levels (less than 30 mmol g1 of meal). These quality traits are now available in all three species. The development of canola, with new food and industrial applications and a new “image,” allowed the rapeseed industry to expand rapidly in western Canada, where it rivaled the wheat industry in size and complemented it in crop rotations by the 1990s. The three main oilseed Brassica species are listed below, with the main growing environments. The first two species are available as either “winter” cultivars, with varying requirements for chilling over winter (vernalization) before they will flower, or as “spring” cultivars, which need little or no vernalization. Winter cultivars are normally sown in autumn or early winter, whereas spring-type cultivars are sown in spring in colder areas, Encyclopedia of Food Grains, Second Edition

or autumn/winter in milder climates, where their growth over winter and early flowering is not a disadvantage.

Brassica napus L. (Oilseed rape, or Rapeseed) This species has the highest yield potential under favorable growing conditions, and has the widest adaptation. Winter cultivars form the main crop in Europe, where winters are mild enough to allow survival and slow growth. Spring-type cultivars are grown in western Canada from spring sowing, where winters are usually too cold to allow crop survival, and in Australia from autumn/winter sowing. In China and Japan, the crop is grown in winter, often in rotation with rice over summer, so early maturing cultivars are required. These usually have a moderate vernalization response as winters can be cold. Virtually all cultivars, however, will show some response to vernalization, although it may not be necessary to proceed to flower and may be substituted for by the effect of long days in spring/early summer.

Brassica rapa L. (Turnip Rape, Previously Also Known as B. campestris) The most cold-hardy of the species, which tends to be cultivated on the northern fringes of the cropping belt in Europe, for example, in Scandinavia (winter and spring cultivars) and Canada (mainly spring cultivars), particularly in the Peace River district and in northern Alberta. The release of earliermaturing, higher-yielding B. napus cultivars has resulted in contraction of B. rapa from about half the Canadian area to a much smaller proportion. Three ecotypes are also grown in India, brown sarson (the major area), yellow sarson, and toria.

Brassica juncea L. Czern and Coss. (Indian or Oriental Mustard) Mustard is the species with the greatest tolerance of heat and drought. It has been grown extensively as an oilseed and condiment in India, and to a lesser extent in Canada, mainly as a condiment (brown mustard) in low rainfall areas in southern Alberta. The development of canola quality cultivars in Australia and Canada opens up the drier parts of the grain belt in both countries to larger-scale production as an oilseed, and allows diversification away from the existing very limited cereal/fallow systems. The rapeseed/canola crop needs to be seen as one component of a farming system, being normally grown in rotation with other crops such as cereals and legumes. It is also often included as part of a mixed farming system, with livestock such as sheep and cattle grazing crop residues and sown pasture leys, or pigs and poultry being fed by-products such as canola meal once the oil is extracted from the seed. There are particular benefits to be gained

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from inclusion of rapeseed in these systems, to be covered below as “biological fumigation,” as well as the general break crop effect on diseases, pests, and weeds of other crops.

Crop Development and Growth: A Model Framework for Crop Management To understand how the crop responds to management of agronomic inputs such as choice of cultivar, seed rate, fertilizer, and sowing time, it is necessary to have a clear picture of how it develops through its life cycle and grows with respect to photosynthetic organs and weight of all components (i.e., grows). These two processes, development and growth, proceed in parallel to result in the final yield, but should be clearly distinguished because environmental factors affect them differently. An overview is shown as Figure 1. Much research effort in Europe (particularly France and the Netherlands) and Australia has been devoted over recent years to modeling the development and growth of the rapeseed crop. The agricultural production systems simulator (APSIM) family of models in Australia has been extended to include rapeseed/canola (Figure 1), and will be used to show how the modeling approach has aided thinking about crop management in a farming-systems context. In developing a model, the characteristics of the crop have to be described quantitatively, posing questions that may or may not have been answered by previous research.

Crop Development in Relation to Environmental Factors The timing of length of life cycle stages is critical in fitting cultivars to their intended environment. This includes adapting to overall length of growing season, minimizing the effect of stress times

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such as frost and drought, and synchronizing sensitive stages such as flowering and seed set with favorable conditions. Development rate is largely governed by temperature, so time from sowing to seed germination and seedling emergence, and the rate of leaf production are proportional to temperature, up to 20 C. They can be described by units of “thermal time,” or day-degrees ( C d) above a base, which can be assumed as 0 C for most purposes. Seed germination and plant emergence may take 120 C d if soil moisture is adequate. Leaves on the mainstem are then produced about every 75 C d until the beginning of stem elongation (i.e., about every 4 days at an average 20 C), then every 20 C d until flowering. The number of leaves produced on the mainstem of a plant ranges from a minimum of 6 on early maturing cultivars in the long days of the Canadian summer to over 30 in winter cultivars in Europe. Temperature also controls the rate of seed development, so different cultivars may require from 500 C d to 800 C d (Canada and Europe, respectively) from flowering to maturity. In Australia, most cultivars require 600–700 C d. This means that, for example, a single European winter cultivar may require 60–100 days from flowering to harvest, depending on whether it is a warm or a cool summer. In addition to the basic positive effect of temperature on development rate, the progression toward flowering is also controlled by the vernalization response, as noted earlier on winter cultivars but also to a lesser extent on most others. Here, a period of time at low temperature ( 2–7 C is most effective, with temperatures over 15 C having no effect) promotes initiation of the inflorescence at the growing apex, and cessation of production of leaf primordia. The apparently opposite effects of temperature on general development rate and on vernalization have been successfully included in the models.

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Figure 1 Diagrammatic representation of development and growth of canola (rapeseed), as used in APSIM model. Tt ¼ thermal time, PP ¼ photoperiod, V ¼ vernalization. (Based in part on: Weir AH, Bragg PL, Porter JR, and Rayner JH (1984) A winter wheat crop simulation model without water or nutrient limitations. Journal of Agricultural Science, Cambridge 102: 371–382.)


Crop Growth in Relation to Environmental Factors

Fractional radiation interception

Good crop management can be thought of as a two-stage process: (1) the production of an efficient leaf canopy by flowering time, and (2) the efficient conversion of photosynthate into oil and protein during seed development. Agronomic management to achieve this will be the focus of a later section. Leaf expansion as well as production is proportional to temperature, with favorable conditions during leaf initiation and cell division leading to potentially larger leaves. Final leaf size is also a function of position on the plant, progressively increasing in size to about fifth true “rosette” leaf, then declining during stem elongation until becoming quite small on the upper mainstem. Leaves then remain active on the plant for 400–800 C d, so the size of the leaf canopy is determined by factors affecting production, expansion, and senescence of leaves. The leaf area index (LAI), or area of leaf per unit ground area, is a key to efficient interception of solar radiation and hence photosynthesis. Figure 2 shows that a canopy of LAI 3 will intercept 85% of incoming radiation, with an extinction coefficient (k) for radiation of 0.6 (the slope of the relationship between LAI and the log of the fraction of radiation intercepted, which also varies with leaf angle and shape). If LAI greatly exceeds 3, little further radiation is intercepted, resources are wasted, and the dense canopy may encourage diseases and pests. A target for managers could therefore be the achievement of 85% radiation interception (equivalent to near-full ground cover) by flowering time. The leaf canopy will convert intercepted total solar radiation into aboveground biomass at 1–1.5 g MJ1 (average 1.2 g MJ1) radiation use efficiency (RUE), as in the example in Figure 3 for three cultivars sown on six dates from autumn until spring. RUE will vary, depending on exposure to stress factors such as drought,

high temperature, and disease. In cultivars with tolerance to the triazine group of herbicides, altered photosynthetic metabolism leads to 20% lower RUE. During flowering, the efficiency of all crops drops, due to reflection of radiation and shading of leaves and earlier-formed pods by the mass of yellow flowers at the top of the crop. Subsequently, during pod development a new green canopy is established, consisting mainly of green pods which, compared to leaves, have 10% lower efficiency per unit green surface area. While the pods have an extinction coefficient similar

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Photoperiod is the other major environmental control, with rapeseed cultivars usually responding to longer days from as soon as they have emerged. As photoperiod increases from 11 to 16 h, duration of the period from plant emergence to floral initiation is reduced. Following initiation, there is a period of 250 C d prior to flowering which is unaffected by daylength or vernalization.

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Intercepted radiation (MJ m−2) Figure 3 Relationship between the top dry matter (biomass) produced and amount of solar radiation intercepted by rapeseed crops between sowing and flowering (open symbols) and between flowering and harvest (closed symbols). Different symbols denote different cultivars, and numbers next to each symbol indicate order of sowing. Lines drawn indicate RUE of 1.0 and 1.5 g MJ1. (Reproduced with permission from Mendham NJ, Russell J, and Jarosz NK (1990) Response to sowing time of three contrasting Australian cultivars of oilseed rape (Brassica napus). Journal of Agricultural Science, Cambridge 114: 275–283. Cambridge University Press.)

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Figure 2 Fraction of solar radiation intercepted by green leaf area of canola crops at different stages of growth and levels of irrigation. Conventional cultivar indicated by square symbols, triazine tolerant cultivar by triangles, with fitted curves for extinction coefficient k of 0.58 and 0.72, respectively. Closed symbols indicate fully irrigated, open symbols partly irrigated. (Reproduced with permission from Robertson MJ, Holland JF, Cawley S, et al. (2002a) Growth and yield differences between triazine-tolerant and non-triazine-tolerant cultivars of canola. Australian Journal of Agricultural Research 53: 643–651. CSIRO Melbourne.)

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to that of leaves, they have fewer stomata able to exchange carbon dioxide and water. They also have a lower nitrogen concentration than leaves, which may reduce efficiency. Green area index (GAI, total green surface area) is therefore more relevant than just LAI in estimating crop radiation interception and efficiency of its use. Figure 3 shows that the crops after flowering grew at RUE mainly below 1 g MJ1, and in the case of some later sowings affected by higher temperatures, water stress, and pest damage, as low as 0.2 g MJ1. A lower RUE during seed fill will also be a result of the biosynthetic cost of oil production compared to carbohydrates and proteins earlier in the growing cycle. Oils contain 2.5 times as much energy as carbohydrates. This figure is discussed further below, in the section on sowing time.

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Yield Components and the Efficient Conversion of Dry Matter to Oil Yield Final oil yield can be thought of as a product of the yield components: Oil yield ¼ plants m2 pods plant1 seeds pod1 mean seed weight oil seed content ð % Þ This numerical approach on its own is of little value, but is useful if combined with a knowledge of when the different components are formed, the external factors affecting them, and internal competition for photosynthetic assimilate, nutrients, and water. Plant establishment (numbers and spatial distribution) and survival over winter form the first component. Flowering and pollination determines the potential number of both pods and seeds, with pollination not normally a limiting factor in the largely self-fertile B. napus and B. juncea. Seed set in cross-pollinated B. rapa, or in hybrid seed production in B. napus, may be dependent on good weather and the presence of bees or other pollinating insects. The survival of a particular pod is largely determined during the first 2–3 weeks after pollination, when competitive pressures build up as the canopy of pods forms at the top of the crop. Numbers of pods per square meter are thus determined shortly after the end of flowering of the crop as a whole. For the remaining components, Figure 4 shows an example for a surviving pod. Abortion of seeds also occurs over the first 3 weeks, and can result in substantial losses of potential, from 30 seeds per pod down to nil in an extreme case. This may be due to internal competition for resources if too many pods are formed, or external stress due to drought, low radiation levels, or frost. Significant seed growth does not begin until after 3 weeks from seed set, once pod walls have reached near their full length and about half their final weight. Seed growth continues at an approximately linear rate until near-full size is reached. Buildup of oil content closely follows that of seed growth. There can be substantial compensation between yield components, for example, if seed abortion is particularly severe, remaining seeds can grow to a larger-than-normal size. An illustration of an efficient crop canopy compared to an inefficient one after flowering is shown as Figure 5. This is a “snapshot” of two canopies produced in different seasons, but with the same cultivar and similar management. One crop had 9500 pods m2, and the other 6000 pods m2. The figure

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Figure 4 Example of formation of the yield components within a single pod, as a function of time after flowering. Three hypothetical levels of number of seeds per pod indicated, corresponding to high, medium, and low seed survival. (Based in part on Hocking PJ and Mason L (1993) Accumulation, distribution and redistribution of dry matter and mineral nutrients in fruits of canola (oilseed rape) and the effects of nitrogen fertilizer and windrowing. Australian Journal of Agricultural Research 44: 1377–1388. CSIRO Melbourne, with permission.)

shows the crop in 20 cm thick layers, on a typical day with 20 MJ m2 incident solar radiation. In the “thick” canopy, radiation was mainly attenuated within the upper pod canopy, where there were many more aborted pods and seeds than within the “sparse” canopy. In the latter, radiation was spread more uniformly over the pod layer, with about half penetrating to the leaf layer below, allowing continued functioning. This is likely to have been a major contributor to the better seed survival. Harvest index measured at maturity (seed yield as a proportion of total aboveground biomass) is a consequence of the balances between biomass accumulation before and during grain-filling, as well as the extent of translocation of stored dry matter from vegetative organs to grain. These processes will be affected by the timing and severity of stresses with respect to the stage of crop development. Harvest index in canola typically varies between 0.25 and 0.35 (lower than for cereals due to the energy cost of oil biosynthesis), although severe stresses at certain stages of development can lead to values lower than this range. Seed oil content in canola is affected by cultivar attributes and the environmental factors of temperature, water stress, and N supply during seed development. As the last component formed, it is broadly correlated with harvest index (Figure 6a) and seed size (Figure 6c) as similar factors will affect each. It may not be strongly correlated with seed yield (Figure 6b), as the main factors affecting yield may be determined well before oil is being formed. As in other oilseed crops, high temperature has been shown to lower oil content and alter composition of fatty acids. Oil content declines by 1.2% for each rise in mean air


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Figure 5 Diagrammatic representation of the canopies of two rapeseed crops in 20 cm layers, showing the distribution and nature of the amount of radiation intercepted, the intercepting green surface area, and the fate of pods and seeds. (Reproduced with permission from McWilliam SC, Stafford JA, Scott RK, Norton G, Stokes DT, and Sylvester-Bradley R (1995) The relationship between canopy structure and yield in oilseed rape. In: Murphy D (ed.) Proceedings of the 9th International Rapeseed Congress, pp. 491–493. Cambridge, UK: GCIRC Paris.)

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Figure 6 The relationship between seed oil content and (a) harvest index, (b) grain yield, (c) mean seed size, and (d) mean temperature from flowering to maturity. Crops of two cultivars of canola indicated by square and triangle symbols, and one of Indian mustard (B. juncea) indicated by diamond symbols, with regression lines fitted to each. (Unpublished data MJ Robertson.)

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temperature of 1 C during grain filling (Figure 6d). Water stress after flowering also can have a severe effect on oil content. Increasing the N supply to the crop almost always reduces the oil content of the seed, because a better supply of N increases the formation of N-containing protein precursors so that protein formation competes more strongly for photosynthates. As a result, less photosynthates are available for fat synthesis. In a review of winter rapeseed experiments the depression of oil content was in the range of 0.8–2% of oil content per 100 kg ha1 of N applied. In the spring rapeseed experiments surveyed the depression was less, in the range of 0.6–1.2% of oil per 100 kgN ha1 applied. There was little evidence that late N application, which might be expected to enhance N supply to the seed rather than the vegetative components of the crop, has any particularly depressive effect on oil content. In the field, cultivar maturity will tend to be confounded with temperature and end-of-season drought. However, even after allowing for flowering time, there are still cultivar differences in oil content. The few studies exploring the issue of genotype–environment interaction for oil content in canola have shown only small effects, indicating that oil content is largely a characteristic of the genotype. End-of-season drought is likely to limit oil content as well as yield, particularly in regions where autumn or winter sowing is normal. Spring sowing, however, as practiced in short-season cool environments like western Canada can lead to different problems as low autumn temperatures, and particularly frosts, curtail oil buildup and crop ripening. This may also lead to poorer-quality oil as unsaturated fatty acid synthesis may be halted, and high levels of chlorophyll may remain in the seed, particularly on later flowering branches. This leads to downgrading of the seed and greater oil-refining costs.

Water-Use Efficiency An alternative approach to the radiation and temperature driven model (as outlined in Figure 1, with example in Figure 3) is a model widely used in Australia based on water-use efficiency (Figure 7). This is based on the principle of the known strong

correlation between photosynthesis and transpiration, and hence between biomass production and water use. In waterlimited environments, healthy crops will produce seed at up to 13 kg ha1 mm1 of available water, including stored soil water before sowing, and effective rainfall during crop growth. Lower efficiency figures (down to 3 kg ha1 mm1) may indicate that other factors are limiting, e.g., nutrition, drainage, or frost. The efficiency will, however, also vary with evaporative demand – a hot or windy season will result in lower efficiency. It will also depend on whether the rainfall was received at a critical time, such as just after flowering, or too late in seed growth to affect yield. In spite of these constraints, this model has been useful for researchers and farmers to compare their crops, and as an extension tool.

Crop Management The main goal in early crop management is to produce a canopy with near-full ground cover of healthy leaves by flowering time, with efficient use of resources. There is usually no advantage in excessive leaf or stem production.

Plant Population and Arrangement The crop generally shows very little response to seed rate over a range of plant populations from 30 to 100 plants m2. Seed rates to produce these populations may vary from 3 to 12 kg ha1, with resulting seed yields within 10% of the maximum. This is because the plants are “plastic,” able (within limits) to keep producing leaves, and later branches and flowers, to occupy the site fully. Lower densities may therefore give prolonged leaf persistence, extended flowering and delayed maturity. While narrow (15 cm or less) row spacings will give quicker ground cover, hence radiation interception and weed suppression, wide (20 cm or more) spacings produce similar results, and may be desirable in direct-drilling situations for trash clearance.

3500 3000 Upper limit Yield (kg ha−1)

2500

y = 7.4x − 8.1

2000 1500 1000 Lower limit

500 0 0

100

200 300 Crop water use (mm)

400

500

Figure 7 Water-use efficiency of measured (diamond symbols) and simulated (crosses) crops. Upper and lower limits of 13 kg ha mm1 and 3 kg ha mm1 indicated by solid lines, with the fitted average line showing efficiency of 7.4 kg ha mm1. (From Cocks B, Robertson MJ, and Cawley S (2001) Water extraction and water-use efficiency of canola in the north. In: Marcroft SJ (ed.) Proceedings of the 12th Australian Research Assembly on Brassicas, pp. 203–207. Australia: Geelong.)


Crop Establishment While grower guides such as the “Canadian Canola Growers’ Manual” may suggest that “seed must be placed into a firm, moist, warm, aerated, well-structured seed bed for rapid germination and seedling growth,” one or more of these requirements are often compromised in practice. Even though seeds are small (2–5 mg), their high oil content does give substantial energy reserves and hence ability to overcome some constraints. The crop tolerates a wide range of pH ( 5.5–8, measured in water), and will emerge well from sowing depths of 5–30 mm. Sowing up to 50 mm may be required in some seasons to reach moisture, but emergence and early vigor may be reduced. Residues from previous crops on the soil surface may also impede establishment, particularly in directdrilled situations, so burning, baling, or incorporation may be desirable. The trade-off with the benefits of trash retention needs to be assessed in each situation. Very low soil temperatures (5 C or less) may reduce establishment as well as delay it, and there may be an advantage from using B. rapa or other more cold-tolerant types in this situation. The insulating effect of stubble and trash may also exacerbate frost damage on young seedlings, by preventing heat flow from the soil. Differences in seed germination rate and vigor have been found between different seed lots of the same cultivar, and use of high quality seed will assist in overcoming the above constraints. Large seed size on its own does not necessarily mean greater vigor, but will usually give initially larger seedlings. Greater seed weight for the same size (i.e., density) may be a better indicator of vigor.

Sowing Time The guiding principle is to sow an adapted variety in time for it to reach near-full radiation interception by flowering, which needs to be late enough in spring to avoid frost damage and other unfavorable weather during pollination and seed set. There also needs to be enough growing season left after that to achieve grain fill and an economic yield before constraints of drought (e.g., in Australia) or frost (e.g., in Canada) intervene. The use of a phenology model as part of an overall model such as APSIM will assist prediction of optimum sowing dates. Delayed sowing, whether in autumn or spring, will in most environments result in progressively lower yield (e.g., 4% loss in yield for each week’s delayed sowing in widely separated areas of Australia). Delays of a month in sowing may result in only a few days delay in flowering (driven more by responses to photoperiod and vernalization), hence shortening the period for leaf expansion and growth. While most crop species respond in a similar way, the specific morphological change in rapeseed from the leaf canopy to the mass of flowers (reflecting and absorbing radiation) and then pods at the top of the

canopy puts a further restriction on vegetative growth, as leaves are largely shaded out during flowering and early pod growth. For the experiment summarized in Figure 3 earlier, where crops were sown from mid-autumn through to mid-spring, the highest yields were obtained from the second sowings (late autumn, points labeled 2 in figure). Good early growth, at high efficiency of radiation use, 800 g m2 top dry matter by flowering was followed by a long period for seed growth at moderate efficiency to produce over 500 g m2 seed yield (equivalent to 5 t ha1). Some later (spring) sowings produced more dry matter before flowering at higher temperatures, but then had greatly reduced post-flowering growth and yield, to as low as 100 g m2 from the latest spring sowing of the latest flowering cultivar. The first sowing produced lower yields than the second sowing, even though plants were taller and similar biomass was produced. Earlier sowing than for the optimum timing as described above may be practiced for other reasons, e.g., in Europe to ensure good growth before winter so that crops can resist freezing, waterlogging, or bird damage. This may then lead to excessive growth in spring, very large numbers of flowers and pods, and an inefficient canopy, as in Figure 5. A low harvest index may result, with only moderate seed yields on a large biomass. Later sowings may give a higher yield, on sparser but more efficient canopies of pods. Breeding varieties with more restrained flowering, absence of flower petals (apetalous) and more efficient pod arrangement has been suggested to help widen the “sowing window.”

Nutrition Nitrogen is usually the most important nutrient to consider, due to its role in protein synthesis. This is of particular relevance for leaf expansion and chlorophyll content, hence radiation interception and efficiency of its use. Requirements are

Relative seed yield (%)

Where crop establishment has been poor and crops are patchy, worthwhile yields (over 50% of that at optimum density) may still be obtained down to 10–20 plants m2, provided the season is favorable to allow the compensatory growth. Very low density crops may be subject to more pest damage and weed invasion.

213

100 80 60 40 20 (a)

(b)

(c)

2 4 4 8 12 16 20 24 0 2 4 6 8 10 0 Concentration of NO3–N in YML petiole (mg g−1 DW) Figure 8 Relationships between nitrate–N in dried petioles of the youngest mature leaf (YML) of canola at three stages of development: (a) 5–6 leaf rosette, (b) flower buds visible, and (c) start of flowering, and relative seed yield expressed as a percentage of the best treatment at each of two sites. Note change of scale from (a) to (c) on x-axis, in mg g1 dry weight. (Reproduced with permission from Hocking PJ, Randall PJ, DeMarco D, and Bamforth I (1997) Assessment of the nitrogen status of field-grown canola (Brassica napus) by plant analysis. Australian Journal of Experimental Agriculture 37: 83–92. CSIRO Melbourne.)

214


site- and season-specific, but 50–70 kg of N are required per tonne of seed produced, to be met from soil or applied N. Guidelines are available for soil and plant analysis to achieve optimum yield without wasting resources, as shown in Figure 8 for leaf petioles, one of the most sensitive plant parts. The concentration of N required to achieve high seed yield falls as the crop proceeds through development. Most of the required N is taken up by the crop before flowering, with later distribution from leaves and stems to pods and seeds. In Europe, with a cold wet winter, there is no advantage in large autumn applications. These may be either leached into groundwater, or be taken up to produce excessive soft growth, resulting in winter kill. Application at the late vegetative to early stem extension stages has generally been shown to be of greatest benefit. In Australia or Canada, it may be more practical to include some either at sowing, e.g., with P in diammonium phosphate, or incorporated before sowing as anhydrous ammonia. Excessive N may result in too much leaf and stem growth, lodging, and high protein/low oil levels in the seeds as noted above. Phosphorus and potassium requirements of rapeseed are similar to that of other crops, with nearly 12 and 20 kg, respectively, being removed per tonne of seed. Sulfur is of particular interest, with deficiencies showing up in many countries as industrial air pollution is reduced (particularly in Europe), and high analysis fertilizers without sulfur are increasingly being used. With 10 kg required per tonne of seed, plant tests can be used up to the beginning of stem elongation to decide whether to apply more. A deficiency shows up as characteristic pale, stunted, cup-shaped leaves (it is essential in chlorophyll formation and photosynthesis), creamy-colored flowers, and very poor pod development. Excessive S may contribute to high glucosinolate levels, as it is required for their formation. With the micronutrients, rapeseed (like other Brassicas) may benefit from molybdenum, boron, manganese, and zinc, although manganese toxicity may be a problem on acid soils.

Water Supply While there is usually a good relationship between biomass production and transpiration, yields of seed, as in Figure 7, may be more influenced by water supply at critical stages. In most cropping areas and seasons, water supply through winter and early spring is adequate to allow crops to reach near-full ground cover. Assuming this, the next critical stage is at and just after flowering, when pod and seed numbers are being determined, and abortion most likely. Management of stored soil water from before sowing onwards can optimize the water supply at this critical time, by reducing losses through previous land management, soil cultivation, weeds, or excess crop growth. Irrigation, if available, is likely to have the greatest effect at or just before the critical time. Subsequently, water supply for grain fill and oil buildup is important, but unless there is a premium for large seeds and high oil content, mild water stress may not affect yield and profitability greatly. Irrigation or rainfall from flowering onward may also encourage disease, e.g., Sclerotinia, which thrives in flower petals shed and then lodged in leaf or stem axils lower in the crop. This has been a particular problem in Canada, but is also now becoming apparent elsewhere.

The greater tolerance of B. juncea to water stress appears to be due to osmoregulation maintaining turgor during the critical time for seed abortion, and hence resulting in up to 50% greater water-use efficiency than B. napus.

Crop Height and Plant Growth Regulators Management should generally be geared to achieving modest crop height as part of an efficient crop canopy, through choice of cultivar, sowing time, N nutrition, water supply etc. as discussed above. Where height is likely to be excessive and leads to lodging, disease, and harvest difficulties, plant growth regulators have been tried, as in cereals, at least as an interim measure. Yields are not generally improved in the absence of lodging, and may be decreased by growth regulator application, so the economics of use are doubtful.

Harvesting With an indeterminate inflorescence structure and lengthy flowering, pods and seeds on each plant ripen over an extended period, and in a field there may be considerable variation between plants in maturity time. The absence of good resistance to pod shattering in the main canola/rapeseed types therefore means that substantial losses can occur. Swathing at near physiological maturity (seeds turning black, moisture content 15%) is therefore carried out on all but the lowest yield potential crops (less than 0.8 t ha1). If swathed too early, lower yield and oil content may follow, and chlorophyll content of seeds may be too high. Dessication using herbicides is an alternative but is not widely used. B. juncea does not need to be swathed as it has better resistance to pod shatter.

Canola/Rapeseed in Farming Systems Weed Management The crop generally fits well into farming systems, as a vigorous broad-leaved break crop. This gives the opportunity to control weeds and crop volunteers built up in previous cereal crops, by a combination of cultivation, competition, and selective herbicide use. If livestock are available on the farm, they can have an important role in cleaning up crop residues and weeds, and grazing pasture leys in rotation. While weed control is not normally a major problem in canola, the use of such integrated weed management systems is supplementing and extending the value of the commonly used herbicides. Resistance in the weed populations has been found to most of these chemicals, and the brassicaceous weeds such as wild radish (Raphanus raphanistrum), wild mustard (Sinapis arvensis), and wild turnip (B. tournefortii) present a particular challenge, being closely related to the crop. In Australia and Canada, triazine-tolerant canola cultivars have been extensively used, but their lower photosynthetic efficiency reduces competitive ability against weeds, as well as growth and yield. Newer herbicide-tolerant cultivars, whether produced by genetic engineering or conventional breeding, offer some advantages. The risks of herbicidetolerant weeds, developing either naturally or by introgression from the tolerant crop, need to be assessed and suitable strategies implemented. While introgression into the above brassicaceous weeds is not likely, wild B. rapa may be more susceptible.

AGRONOMY OF GRAIN GROWING | Canola: Agronomy Biofumigation and Other Benefits There are specific advantages of the Brassica oilseeds as break crops, supplementing their value as non-hosts, to control some soil-borne diseases such as take-all of cereals (Gaeumannomyces graminis), and some invertebrate pests such as nematodes. This is due to the content of glucosinolates in Brassica crop residues including roots that break down in the soil to form biocidal compounds, in particular isothiocyanates. Yields of cereal crops following canola are therefore often increased more than the non-host benefit of a break crop would suggest. There are opportunities to increase the level of the more highly biocidal compounds in roots by breeding, and also to maximize the effects through crop management. There are, however, concerns about the biocidal effects on beneficial organisms, such as Rhizobia bacteria for future legume inoculation, and vesicular–arbuscular mycorrhizal fungi, which aid some crops (but not Brassicas) in uptake of phosphorus and other nutrients. Canola in Australia has also been observed to have beneficial effects on soil structure, with the long taproot helping to break up subsoil compaction and hard pans resulting from cultivation. Direct-drilled cereals may therefore be more successful following canola than other crops.


• • • • •

Compare and contrast the agro-ecological niches of the three Brassica species. Explain the difference between an efficient and an inefficient crop canopy. What is ‘harvest index’? How is it measured and what can affect it? What factors affect crop establishment in canola? How can canola/rapeseed be used to manage weeds?


• •

How can the water use efficiency of B. napus be improved? How can the photosynthetic efficiency of triazine-tolerant canola cultivars be increased?

See also: Breeding of Grains: Canola/Rapeseed: Genetics and Breeding; Grain Harvest, Storage and Transport: Canola: Harvest, Transport, and Storage; Grains Around the World: Grain Production and Consumption: Cereal Grains in North America; Grain Production and Consumption: China and South-East Asia; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; The Cereal Grains: Teff: Overview; The Oilseeds: Oilseeds: Overview.

Further Reading Cocks B, Robertson MJ, and Cawley S (2001) Water extraction and water-use efficiency of canola in the north. In: Marcroft SJ (ed.) Proceedings of the 12th Australian Research Assembly on Brassicas (2001) Geelong, Australia, pp. 203–207.

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Downey RK, Stringham GR, McGregor DI, and Stefansson BR (1975) Breeding rapeseed and mustard crops. In: Harapiak JT (ed.) Oilseed and Pulse Crops in Western Canada, pp. 157–183. Calgary, Alberta, Canada: Western Cooperative Fertilizers. Gabrielle B, Denoroy P, Gosse G, Justes E, and Andersen MN (1998) Development and evaluation of a CERES-type model for winter oilseed rape. Field Crops Research 57: 95–111. Gabrielle B, Denoroy P, Gosse G, Justes E, and Andersen MN (1998) A model of leaf area development and senescence for winter oilseed rape. Field Crops Research 57: 209–222. Habekotte B (1997) Description, parameterisation and user guide of Lintul-Brasnap 1.1, A crop growth model of winter oilseed rape (Brassica napus L.). Quantitative approaches in systems analysis No. 9, AB – DLO, Wageningen, Netherlands. Hocking PJ and Mason L (1993) Accumulation, distribution and redistribution of dry matter and mineral nutrients in fruits of canola (oilseed rape) and the effects of nitrogen fertilizer and windrowing. Australian Journal of Agricultural Research 44: 1377–1388. Hocking PJ, Randall PJ, DeMarco D, and Bamforth I (1997) Assessment of the nitrogen status of field-grown canola (Brassica napus) by plant analysis. Australian Journal of Experimental Agriculture 37: 83–92. Holmes MJR (1980) Nutrition of the Oilseed Rape Crop. Barking, UK: Applied Science Publishers. Kimber DS and McGregor DI (1995) The species and their origin, cultivation and world production. In: Kimber DS and McGregor DI (eds.) Brassica Oilseeds: Production and Utilization, pp. 1–7. Wallingford, UK: CAB International. McWilliam SC, Stafford JA, Scott RK, Norton G, Stokes DT, and Sylvester-Bradley R (1995) The relationship between canopy structure and yield in oilseed rape. In: Murphy D (ed.) Proceedings of the 9th International Rapeseed Congress, pp. 491–493. Cambridge, UK: GCIRC Paris. Mendham NJ and Salisbury PA (1995) Physiology: crop development, growth and yield. In: Kimber DS and McGregor DI (eds.) Brassica Oilseeds: Production and Utilization, pp. 11–64. Wallingford, UK: CAB International. Mendham NJ, Shipway PA, and Scott RK (1981) The effects of delayed sowing and weather on growth, development and yield of winter oilseed rape (Brassica napus). Journal of Agricultural Science, Cambridge 96: 389–416. Mendham NJ, Russell J, and Jarosz NK (1990) Response to sowing time of three contrasting Australian cultivars of oilseed rape (Brassica napus). Journal of Agricultural Science, Cambridge 114: 275–283. Pouzet A (1995) Agronomy. In: Kimber DS and McGregor DI (eds.) Brassica Oilseeds: Production and Utilization, pp. 65–92. Wallingford, UK: CAB International. Robertson MJ, Holland JF, Kirkegaard JA, and Smith CJ (1999) Simulating growth and development of canola in Australia. In: Wratten N and Salisbury PA (eds.) Proceedings of the 10th International Rapeseed Congress. Sydney: The Regional Institute Ltd. (Available on CD-ROM and on-line at www.regional.org.au.). Robertson MJ, Holland JF, Cawley S, et al. (2002) Growth and yield differences between triazine-tolerant and non-triazine-tolerant cultivars of canola. Australian Journal of Agricultural Research 53: 643–651. Robertson MJ, Watkinson AR, Kirkegaard JA, et al. (2002) Environmental and genotypic control of time to flowering in canola and Indian Mustard. Australian Journal of Agricultural Research 53: 793–809. In: (Editors: Salisbury, P.A.; Potter, T.D.; McDonald, G.; Green, A.G.) Canola in Australia: the First 30 years (1999); Organising Committee, 10th International Rapeseed Congress, Canberra Australia. Chapters 3 (phenology, physiology and agronomy), 4 (Crop nutrition) and 5 (Canola in rotations). (Also available on-line at www.regional.org.au.). Scarisbrick DH and Daniels RW (eds.) (1986) Oilseed Rape. London: Collins. Thomas P (1984) Canola Growers’ Manual: Grow with Canola. Lacombe, Alberta, Canada: Canola Council of Canada. Weir AH, Bragg PL, Porter JR, and Rayner JH (1984) A winter wheat crop simulation model without water or nutrient limitations. Journal of Agricultural Science, Cambridge 102: 371–382.

Relevant Website regional.org.au http://www.regional.org.au – contains the “Proceedings of the 10th International Rapeseed Congress, Canberra 1999 (eds. Wrattan N and Salisbury, P.A)”. The “Crop growth and farming systems” section includes papers on most of the topics covered, including APSIM and other models. Also contains “Proceedings of the Australian Agronomy Conferences 8–11. Also contains Canola in Australia: the first 30 years” (as above).

Chickpea: Agronomy KHM Siddique, University of Western Australia, Crawley, WA, Australia L Krishnamurthy, International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • • • • •

years, improved varieties and specific agronomic practices have been developed as genetic options to manage some of the previously mentioned constraints (Figure 2).

Adaptation and production constraints. Rotational benefits. Soil type and land preparation. Line spacing. Sowing rate, depth, and method. Inoculation. Other nutrient requirements. Disease and pest management. Water requirements. Harvest, storage, and marketing.

Chickpea Agronomy Rotational Benefits

Learning Objective

•

To gain a comprehensive understanding of the agronomic factors affecting chickpea production, quality marketing, and processing.

Introduction Chickpea (Cicer arietinum L.) plays an important role in agricultural systems today ranking third in the world among pulses in production, behind dry bean, and field pea. Recent years have witnessed improvements in global productivity and extensions in areas sown to chickpea after 40 years of no change. World chickpea production was 10.9 million tonnes in 2010 from an area of 12.0 million hectares. Traditionally, chickpea is grown in India, Iran, Bangladesh, Pakistan, Mexico, and Ethiopia. Improvements in varieties, agronomy and production technology, and new export market opportunities have seen the expansion of chickpea production in countries such as Turkey, Canada, and Australia. This article summarizes key agronomic practices of chickpea cultivation and improvements that could help improve its production.

Adaptation and Production Constraints Chickpea has broad adaptation and is widely distributed (Figure 1). It is the most drought-resistant cool-season grain legume that is commonly grown rain-fed on stored soil moisture but responds well to supplemental irrigation in many environments. Chickpea exhibits a considerable degree of heat tolerance, provided there is sufficient soil moisture. Chickpea production is limited by several biotic and abiotic stresses, depending on growing environments: Drought, cold, transient waterlogging, soil salinity/sodicity, and high boron in the subsoil are the main abiotic stresses, and a number of diseases, pests, and weeds are the key biotic stresses. In recent

216

Chickpea is often grown in crop rotation, mainly with cereals, as it reduces the risk of pests and diseases associated with monocropping. An additional benefit is nitrogen fixation of atmospheric nitrogen via a symbiotic relationship with Rhizobium. For example, in southern Australia, it is estimated that chickpea crops get 37–86% of their total nitrogen through fixation leaving from 41 to 56 kg ha1 residual nitrogen in the soil. Legumes prefer soil nitrogen, when available, over biologically fixed nitrogen. In many instances, more soil nitrogen is removed than the crop actually fixes. In these situations, the subsequent cereal crop will still need additional nitrogen fertilizer. However, the nonnitrogen benefits of a chickpea crop in the rotation may still contribute to increased grain yield and protein contents in wheat (Figure 3).

Soil Type and Land Preparation Chickpea is successfully grown on a wide range of soil types throughout the world, ranging from coarse-textured sands to fine-textured black soils. Ideally, chickpea is most suited to deep soils, neutral to alkaline fine-textured soils (sandy loams, clay loams, and well-drained clays) with a pH of 5.5–9.0 and good water-holding capacity. Chickpea is sensitive to waterlogging, sodicity/salinity, and boron toxicity.

Time of sowing Moisture availability, temperature, and photoperiod suitability are the main environmental concerns that determine the right sowing time for the best growth and yield. Flowering is advanced by temperature more than by day length. As a result, the optimal time of sowing varies based on the geographic region (Table 1) and in the cool season. Sowing too early or too late will reduce grain yields. In the West Asia and North Africa region, chickpea is traditionally sown in spring and grown on stored soil moisture (except in Pakistan, Egypt, and Sudan where chickpea is sown in winter). The productivity of this cropping system is constrained by terminal drought and heat stress, partly because a large amount of stored soil moisture is lost before sowing. The availability of drought-tolerant genotypes, shifting sowing from spring to winter with appropriate disease-resistant and winterhardy genotypes, and adopting conservation agriculture are a few approaches to increase productivity. Advancing the chickpea


http://dx.doi.org/10.1016/B978-0-12-394437-5.00192-3

AGRONOMY OF GRAIN GROWING | Chickpea: Agronomy

217

N

Area (hectares) < 1,000 1,001 - 10,000 10,001 - 50,000 50,001 - 100,000 100,001 - 8,210,000

Figure 1 Global chickpea area distribution.

1993 N rate (kg ha–1) 20 40 60 wheat after wheat

1993 wheat yield (t ha–1)

2.0

(4.42) 1.6

sowing date has increased yields more than 100% in some regions due to extended crop growth periods and increased water use (Table 2; Figure 4). In the Mediterranean-type environments of southern Australia, the best chickpea yields are obtained when sown after the first autumn rains and grown on winter rainfall. In the semiarid Canadian prairies, chickpea is sown early in the spring growing season when soil moisture is still high. In South Asia, Africa, and Central America, the best crop performance is realized when sown in the cooler part of the year after the rainy season on stored soil moisture. In the northeastern part of Australia, chickpea is sown in May or June on stored soil moisture from summer rainfall.

Sowing Rate, Depth, and Method Inadequate or patchy plant stands often limit yields in many production areas in the world, highlighting the importance of sowing rate and germination percentage. Chickpea sowing rates vary between 40 and 200 kg ha1, depending on genotype, seed size, seed type, and environmental conditions

(1.58)

(0.31)

(0.57)

1.2

0.8 Figure 2 An example of successful chickpea area expansion in Kurnool District, Andhra Pradesh, India. This crop is a recent variety, JG 11, released for lower latitudes in India, grown during 2010–11 postrainy season.

80

Field pea Chickpea Faba bean

Lentil

1992 crop Figure 3 Grain yield of wheat grown in 1993 without nitrogen (N) fertilizer after various grain legume crops at Pingaring, Western Australia. Figures (bars) in parentheses are grain legume yields in 1992. Squares show the yield of wheat in 1993 when grown after wheat with various rates of N fertilizer (top axis). Reproduced from Loss S, Brandon N, and Siddique KHM (eds.) (1998) The Chickpea Book: A Technical Guide to Chickpea Production. Bulletin 1326. Perth, Australia: Western Australian Department of Agriculture, with permission.

(Table 3). On average, a plant density of 33 plants m2 produces optimum seed yields across a range of environments although variations in row spacing are practiced for the convenience of weed control (Figure 5). Generally, a close row spacing of 18–35 cm is the most productive. The optimum sowing depth for irrigated chickpea or chickpea grown in high soil moisture conditions varies from 5 to 8 cm but can increase to 10–15 cm in moisture-deficient soils without affecting emergence and yield (Figure 6). Deep sowing is beneficial for crops grown on stored soil moisture and to escape preemergence herbicide damage, frost, wind, and insect attacks and to improve survival of Rhizobium and nodulation. The use of two-wheel power tiller mounted seeders in developing countries is a good example of modifying technologies to suit developing country needs and to allow the required seeding depth with minimum disturbance to surface soil.


218 Table 1

Time of sowing and harvest of chickpea in various regions

Country

Season

Sowing time

Harvest

Morocco Tunisia

Spring Spring

June to early July June to early July

Iraq Iran

Spring Spring

Israel Jordan

Winter Spring Winter Spring Spring Winter Autumn Autumn Spring Winter Autumn Spring Spring

Mid-February to mid-March Mid-March to mid-April Small areas of winter sowing Mid-February to mid-March Mid-March to mid-April Small areas of winter sowing December to February March November/December February/March Highlands sown later to avoid Ascochyta blight Mid-February to end March November (under irrigation) September/November October/November Late February to early May December Late September to November April/May April/May

Autumn Autumn Autumn

May/June May May/June

Turkey Algeria Egypt Ethiopia Sudan Syria Indian subcontinent Canada The United States Australia Southern ORIA Northeastern

June July/August June July Mid-June June June to early July April January/February June June to early July March/April July to early August July to early August October/December September October/December

ORIA, Ord River Irrigation Area, Western Australia.

Table 2 Yield response (t ha1) of chickpea to early and late sowing in different regions Region

Early sowing

Late sowing

References

North Syria South Western Australia Canada

3.4 (November) 1.35 (May)

1.0 (March) 0.94 (July)

2.35 (April)

1.99 (May)

Saxena (2003) Pande et al. (2005) Gan et al. (2002)

Grain yield (kg ha–1)

4000

Chickpea can fix atmospheric nitrogen through its nodules with the nitrogen-fixing Rhizobium bacteria and survive in low-nitrogen soils. These bacteria, however, are species-specific and survive poorly on coarse-textured acid soils. Therefore, inoculation of seed with Rhizobium is needed for normal growth of chickpea in marginal soils and on fields that have not grown chickpea in the past. In nitrogen-poor soils, therefore, a small starter dose of nitrogen (10–25 kg N ha1) can stimulate root and shoot growth during early crop development and lead to increased seed yields.

Other Nutrient Requirements

3000

2000

1000

0 22 Nov

Inoculation and Nitrogen

17 Dec

11 Jan

15 Feb

15 Mar

Date of planting

Figure 4 Average grain yield of 20 chickpea genotypes as affected by sowing date at Tel Hadya in northern Syria. Adapted from Singh KB and Saxena MC (1999) The Tropical Agriculturalist: Chickpeas. London: MacMillan Education Ltd, with permission.

Grain legumes need a continuous supply of phosphorus throughout their growing season. Phosphorus deficiency is a widespread problem in South Asia and Africa and application of 60 kg P2O5 ha1 has increased chickpea yield. However, the response to phosphorus tends to be less in chickpea than in other cool-season food legumes and cereals because chickpeas are able to exploit other sources of phosphorus unavailable to most plants with the help of root exudates. Root exudates with organic acids also dissolve insoluble copper, zinc, iron, and manganese, thereby avoiding deficiency. Iron deficiency, however, is common on high pH calcareous soils in South Asia and chickpeas respond positively to foliar spray of 0.5–2% FeSO4 solution. Zinc, sulfur, and boron deficiencies have been observed in India, southern Australia, and Nepal, which can be corrected chemically.

AGRONOMY OF GRAIN GROWING | Chickpea: Agronomy Table 3

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Sowing rate, plant density, and row spacing of chickpea in various regions

Country

Plant densities (plants m2)

Sowing rate (kg ha1)

Row spacing (cm)

Algeria Jordan Morocco Southern Australia Northeastern Australia Syria Indian subcontinent Canada The United States Turkey Tunisia

20–30 25–33 25–35 25–50 30–40 40–50 33 45 40 35 20

<100 80–100 80–120 80–120 80–120 120–180 40–65 120–150 90–125 90–120 70–90

50–100 30–40 40–70 18–36 18–70 17.5–35 30–45 25 30 25 70–100

Seed yield (kg/ha)

2500

4000

Three Springs

1994

2000

Chickpea

3000 Bencubbin

1500

2000

1000

Gnowangerup

500

1000

0 20

40 60 80 Density (plants/m2)

100

120

Figure 5 Relationship between plant density and grain yield at typical high-, medium-, and low-yielding sites in Western Australia. Dotted lines indicate the estimated optimum plant density. Reproduced from Jettner RJ, Siddique KHM, Loss SP, and French RJ (1999) Optimum plant density of desi chickpea (Cicer arietinum L.) increases with increasing yield potential in south-western Australia. Australian Journal of Agricultural Research 50: 1017–1025, with permission.

Weed Management Chickpea competes poorly with weeds, and therefore, good weed management is critical for high yields. As postemergence chemical weed control in chickpea is not possible, it is essential to check weeds in the previous crop and before sowing. In developing countries, weed control is mainly through manual and mechanical techniques. Chemical weed control methods are mainly used in North America, Canada, and Australia through pre- and postsowing preemergence applications of herbicides. The most effective and commonly used presowing herbicides are simazine and cyanazine at rates of 1–2 l ha1, while metribuzin and imazethapyr at 200 ml ha1 are used after sowing and before emergence. Therefore, identification of greater herbicide-tolerant varieties is a pressing need.

Disease and Pest Management Over 50 diseases are known to affect chickpea worldwide, including Ascochyta blight, Fusarium wilt, root rots, rust, Botrytis gray mold, and viral diseases. From these, Ascochyta blight and Fusarium wilt are the most important and devastating diseases worldwide, whereas the others are important on a more

0 1995 Seed yield (kg ha–1)

0

3000 2000 I

1000 0 1996 3000

I 2000 1000

0 Merredin

Northam

Figure 6 Seed yield of chickpea sown at 2.5 (solid black), 5.0 (open), and 10.0 cm (hatched) at Merredin and Northam, Western Australia. Vertical bars denote l.s.d. (P ¼ 0.05) where differences are significant. Reproduced from Siddique KHM and Loss SP (1999) Studies on sowing depth for chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), and lentil (Lens culinaris Medik) in a Mediterranean-type environment of south-western Australia. Journal of Agronomy and Crop Science 182: 105–112.

regional level. In addition, numerous pest species have been associated with chickpea, including more than 46 species of nematode.

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Ascochyta blight is caused by the fungus Ascochyta rabiei Pass. (Labr.). A shift to winter sowing in Mediterranean regions has increased the occurrence of this disease. This fungus attack is extremely destructive, causing yield losses up to 100%. Severe infections with Ascochyta blight cannot be controlled by chlorothalonil fungicide and disease management through resistant cultivars is essential. The most devastating soil-borne disease of chickpea is wilt, caused by Fusarium oxysporum Schlecht. emend. Snyd. & Hans. f. sp. ciceri (Padwick) Snyd. & Hans. Most chickpea-growing countries have reported this disease, which affects both roots and aerial plant parts and can cause yield losses of 10–50%. Although this disease can be minimized by seed dressings with fungicide (Benlate T at 0.15% rate), it is more economical to use resistant cultivars. Only a few of the more than 46 reported nematode species found in association with chickpea cause severe yield loss in chickpea. The root-knot (Meloidogyne spp.), cyst (Heterodera spp.), and root-lesion (Pratylenchus spp.) nematodes are the most damaging with infections reported from all over the world. Proper crop rotations are the most effective and economical way to control nematode infections, as opposed to the use of nematicides. The search for nematode resistance in cultivated chickpea has been unsuccessful and efforts are being made to find nematode resistance in wild relatives of chickpea and a method to transfer resistance to the cultigen. Insect pests generally cause less damage to chickpea yield than diseases due to the presence of unpalatable organic acids on leaves and winter cropping when most insect activity is low. In subtropical chickpea-growing regions, the most damaging insect pests are pod borers (Helicoverpa spp.) and leaf miners (Liriomyza cicerina). Pod borers occur in all chickpea-growing countries, whereas leaf miners are restricted to the WANA region and eastern Europe. Spraying with insecticides is economical only when the infestation is serious and when a high yield (>1 t ha1) is expected. Improving the economics of pod borer control through pheromone traps is a usual practice in Australia. Development of chickpea cultivars that combine insect resistance, disease resistance, and high yield is in progress at various centers. Bruchids (Callosobruchus spp.) are the main storage pests of chickpea damaging up to 70% of seeds. Harvesting soon after maturity and storage in insect-proof containers after proper drying are effective ways to contain bruchid damage. Treating stored seed with fumigants (e.g., phostoxin) or insecticides (e.g., malathion) are other alternatives. No useful bruchidresistant chickpea genotypes have been identified.

Water Use Chickpea is considered the most drought-tolerant cool-season grain legume able to tolerate intermittent drought due to its deep root system (Figure 7), and its more indeterminate growth habit responds well to subsequent rainfall. However, seed yield loss due to terminal drought can be as high as 60%. Recent studies in southern Australia have shown water use efficiencies for dry matter production to reach between 11 and 18 kg ha1 mm1 and for grain yield between 2.6 and 7.7 kg ha1 mm1. This study also showed chickpea to

Figure 7 Rooting depth of chickpea at early podding grown in a deep vertisol at optimal spacing (30 10 cm) in Patancheru, India. Note the color change of roots from deep brown in the soil surface to ash white at maximum depth. Roots were traced to 135 cm soil depth.

be less water use efficient than the high-yielding faba bean and field pea (WUEdm: 19–39 kg ha1 mm1; WUEgr: 6–16 kg ha1 mm1). Increasing early growth for rapid ground cover and reduced soil evaporation and tolerance to cold temperatures during flowering and pod setting are essential to improve water use efficiency of chickpea in Mediterranean-type environments. Selecting genotypes with larger root systems, early flowering and pod setting, increased osmoregulation, or greater translocation of biomass from stems and leaves to seed are other strategies explored by chickpea breeders for improving yield potential. In areas where annual rainfall is < 400 mm or where there is a risk of drought during late vegetative and reproductive stages, chickpea responds positively to supplemental irrigation.

Harvesting, Storage, and Marketing Chickpea is ready to harvest when seed moisture reaches about 15%, which improves seed quality. Harvesting chickpea at physiological maturity can increase yield by 30% but needs suitable drying facilities.

AGRONOMY OF GRAIN GROWING | Chickpea: Agronomy Most harvesting is manual in developing countries and completely mechanized in developed countries. Preharvest crop desiccation at 90% crop maturity is necessary for easier mechanized harvests. Seed quality deteriorates rapidly with storage and reduced moisture and temperature increases longevity of the seed. Storing seed at < 13% moisture, however, has adverse effects on viability. Therefore, reducing the storage temperature to 20 C is the best option for increasing seed longevity. Chickpea as a good source of carbohydrate and protein is traded for human consumption in both developing and developed countries. Most chickpea produced in India is consumed there, with a large production–demand gap requiring import. The main exporters of chickpea are Australia, Turkey, Canada, and Mexico with main markets in India, Pakistan, Bangladesh, Europe, the United States, Middle East, and the former USSR.

Future Prospects Improved chickpea varieties with greater resistance to key biotic and abiotic stresses are currently being developed to suit existing and emerging cropping systems by various national and international agricultural research organizations. Development of variety-specific agronomy packages, adoption of conservation agriculture, and availability of herbicide-tolerant varieties are expected to further increase chickpea production worldwide.


• • • • •

What biotic and abiotic stresses limit chickpea production? What determines sowing time for the best yield? What are the major diseases afflicting chickpea? What are the principal chickpea pests? What is the best strategy for increasing seed longevity after harvest?


• •

How would you create varieties with greater resistance to abiotic stresses. How would you create varieties with greater resistance to herbicides.

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Bioactives and Toxins: The Antinutritional Components of Grains; Food Grains and the Consumer: Grains and Health; Genetics of Grains: Development of Genetically Modified Grains; Genome Mapping; Genomics of Food Grains; Grain Composition and Analysis: The Composition of Food Grains and Grain-Based Products; Grains Around the World: Grain Production and Consumption: China and South-East Asia; Grain Production and Consumption: Europe; Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; Grain Production and Consumption: South America; Grain Production and Consumption: Africa; Production and Consumption of Grains: India; Proteins: Nitrogen in Grain Production Systems; Scientific Organizations Related to Grains: Research Organizations of the World: CGIAR; The Basics: Taxonomic

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Classification of Grain Species; The Grain Chain: The Route from Genes to Grain-Based Products; The Grain Crops: An Overview; The Legumes and Pseudocereals: Chickpea: Overview; Grain Legumes and Their Dietary Impact: Overview.

Further Reading Ae N, Arihara J, and Okada K (1991) Phosphorus response of chickpea and evaluation of phosphorus availability in Indian Alfisols and Vertisols. In: Johansen C, Lee KK, and Sahrawat KL (eds.) Phosphorus Nutrition of Grain Legumes in the Semi-Arid Tropics, pp. 33–41. Patancheru, India: International Crops Research Institute for the Semi Arid Tropics. Ali MY, Krishnamurthy L, Saxena NP, Rupela OP, Kumar J, and Johansen C (2002) Scope for genetic manipulation of mineral acquisition in chickpea. Plant and Soil 245: 123–134. Anonymous (2012) Chickpea – Harvesting and Storage. Australia: Department of Agriculture, Fisheries and Forestry, Queensland Government.http://www.daff.qld. gov.au/26_4511.htm. FAO (2012) Food and Agriculture Organization of the United Nations 2010. FAO Production Year Book. Rome, Italy: FAO.http://apps.fao.org. Gan YT, Miller PR, Liu PH, Stevenson FC, and McDonald CL (2002) Seedling emergence, pod development, and seed yields of chickpea and dry pea in a semiarid environment. Canadian Journal of Plant Science 82: 531–537. Jettner RJ, Siddique KHM, Loss SP, and French RJ (1999) Optimum plant density of desi chickpea (Cicer arietinum L.) increases with increasing yield potential in southwestern Australia. Australian Journal of Agricultural Research 50: 1017–1025. Knight R (ed.) (2000) Linking Research and Marketing Opportunities for Pulses in the 21st Century. Dordrecht, The Netherlands: Kluwer Academic Publishers. Krishnamurthy L, Johansen C, and Sethi SC (1999) Investigation of factors determining genotypic differences in seed yield of nonirrigated and irrigated chickpea using a physiological model of yield determination. Journal of Agronomy and Crop Science 183: 9–17. Krishnamurthy L, Gaur PM, Basu PS, et al. (2011) Genetic variation for heat tolerance in the reference collection of chickpea (Cicer arietinum L.) germplasm. Plant Genetics Research 9: 59–69. Leport L, Turner NC, French RJ, Tennant D, Thomson BD, and Siddique KHM (1998) Water relations, gas exchange and growth of cool-season grain legumes in a Mediterranean-type environment. European Journal of Agronomy 9: 95–303. Loss S, Brandon N, and Siddique KHM (eds.) (1998) The Chickpea Book: A Technical Guide to Chickpea Production. Perth: Western Australian Department of Agriculture, Bulletin 1326. Pande S, Siddique KHM, Kishore GK, et al. (2005) Ascochyta blight of chickpea: Biology, epidemiology and disease management. Australian Journal of Agricultural Research 56: 317–332. Regan KL, Siddique KHM, Brandon NJ, Seymour M, and Loss SP (2006) Response of chickpea (Cicer arietinum L.) varieties to time of sowing in Mediterranean-type environments of south-western Australia. Australian Journal of Experimental Agriculture 46: 395–404. Saxena NP (ed.) (2003) Management of Agricultural Drought: Agronomic and Genetic Options. Enfield, NH: Science Publishers, pp. 209. Saxena MC and Singh KB (eds.) (1987) The Chickpea. Wallingford, UK: CAB International. Shivran RK and Chandra P (2012) Productivity, profitability and protein content of chickpea (Cicer arietinum) as influenced by farm yard manure, phosphorus and sulphur application. Bioscience Trends 5: 104–106. Siddique KHM and Loss SP (1999) Studies on sowing depth for chickpea (Cicer arietinum L.), faba bean (Vicia faba L.) and lentil (Lens culinaris Medik) in a Mediterranean-type environment of south-western Australia. Journal of Agronomy and Crop Science 182: 105–112. Siddique KHM and Sedgley RH (1986) Chickpea (Cicer arietinum L.), a potential grain legume for south-western Australia: Seasonal growth and yield. Australian Journal of Agricultural Research 37: 245–261. Siddique KHM, Regan KL, Tennant D, and Thomson BD (2001) Water use and water use efficiency of cool season grain legumes in low rainfall Mediterranean-type environments. European Journal of Agronomy 15: 267–280. Siddique KHM, Johansen C, KumarRao JVDK, and Ali M (2008) Legumes in sustainable cropping systems. In: Kharkwal MC (ed.) Food Legumes for Nutritional Security and Sustainable Agriculture, Vol. 1, pp. 787–819. New Delhi, India: Indian Society of Genetics and Plant Breeding. Siddique KHM, Johansen C, Turner NC, et al. (2012) Innovations in agronomy for food legumes. A review. Agronomy for Sustainable Development 32: 45–64.

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Singh KB and Saxena MC (eds.) (1996) Winter Chickpea in Mediterranean-Type Environments. Aleppo, Syria: ICARDA, A Technical Bulletin. Singh KB and Saxena MC (1999) The Tropical Agriculturalist: Chickpeas. London: MacMillan Education Ltd. Singh KB and Singh O (1997) Prospects of creating higher yield potential in chickpea. In: Asthana AN and Ali M (eds.) Recent Advances in Pulses Research, pp. 65–88. Kanpur, India: Indian Society of Pulses Research and Development. Slattery J, Siddique KHM, and Howieson J (2004) Cool season pulse (grain legumes) production and rhizobial interactions in Australian dryland agriculture.

In: Challenges and Strategies for Dryland Agriculture, pp. 1–14. Madison, WI: Crop Science Society of America, Chapter 15. Soltani A, Khooie FR, Ghassemi-Golezani K, and Moghaddam M (2001) A simulation study of chickpea crop response to limited irrigation in a semiarid environment. Agricultural Water Management 49: 225–227. Summerfield RJ (ed.) (1988) World Crops: Cool Season Food Legumes. Dordrecht, The Netherlands: Kluwer Academic Publishers.

Lentil: Agronomy T Nleya, South Dakota State University, Brookings, SD, USA A Vandenberg and FL Walley, University of Saskatchewan, Saskatoon, SK, Canada D Deneke, South Dakota State University, Brookings, SD, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

•

Lentil is one of the world’s oldest crops that has been cultivated in southwestern Asia since 7000 BC. About 75% of world lentil production is in the developing world. Lentil is classified into two groups based in seed size: the large-seeded type (Chilean lentil) averaging 50 g per 1000 seeds and the small-seeded type (Persian lentil) averaging 40 g per 1000 seeds. Lentil is a cool-season crop with moderate resistance to high temperature and drought. Lentil inoculated with the proper Rhizobium strain can fix between 70% and 90% of its nitrogen requirement through the symbiotic nitrogen fixation process. Recommended seeding rates for lentil vary from 40 kg ha1 to as high as 160 kg ha1, depending on growing conditions and lentil variety. The optimum date of seeding lentil varies from region to region. In all regions where lentil is grown, seed yield can be optimized by timing seeding such that crop development and growth occurs when climatic variables such as rainfall and temperature are favorable. Lentil is a poor competitor against weeds. Yield losses due to weeds can be severe ranging from 20 to over 80%.

Learning Objectives

• • • •

To understand and be able to identify major lentilproducing countries in the world. To achieve understanding of the best management practices for lentil in different parts of the world. To be able to describe a lentil plant. To be able to describe the growth requirements for lentil plants.

are the main producers of lentil. Lentil has been grown commercially in the Palouse region of eastern Washington and northern Idaho since the late 1930s. Lentil production in Canada began in 1969, and currently, Canada is the leading lentil producer and exporter in the world. Other important lentil-producing countries include Syria, Ethiopia, Argentina, Nepal, Bangladesh, Iran, and Chile. Agronomic requirements for lentil differ from region to region depending on the climatic conditions, cropping system, and variety. In Canada, the United States, the highlands of Turkey, and Iran, lentil is grown in spring on conserved moisture. In the Indian subcontinent, it is grown using soil moisture from the preceding monsoon season supplemented with infrequent winter rainfall. Lentil is also raised in winter in Australia and the lowlands of Turkey and Syria. In each of these growing environments, agronomic practices have been developed to suit climatic and soil conditions and the predominant lentil varieties.

Lentil Description The lentil is an annual herbaceous plant with a slender stem and branches. Plant height ranges from 20 to 75 cm. Lentil plants have indeterminate growth habit, continuing to flower and to produce pods until moisture, nutrient deficiency, or temperature stresses occur. However, lentil shows considerable variation in growth habit, depending on genotype and environmental conditions. Lentil is classified into two types based on seed size. ‘Macrosperma’ or Chilean lentil has large seeds of 6–9 mm in diameter (mass greater than50 g/1000 seeds). ‘Microsperma’ or Persian lentil has small seeds of 2–6 mm in diameter (mass 45 g or less/1000 seeds). Seeds of both types are generally lens-shaped but some microsperma types have rounder seeds. The seed coat may be red, green, gray, brown, black, or mottled. Cotyledons may be red, yellow, or green.

Introduction

Land Adaptation

Lentil (Lens culinaris Medik.) is one of the world’s oldest crops having been cultivated in southwestern Asia since 7000 BC. The crop is best adapted for production in temperate climates but is now produced in different parts of the world. About 75% of world production is in the developing world. The three largest lentil producers are Canada, India, and Turkey with the three countries accounting for 68% of global lentil production in 2002–06. In the developed world, the major lentilgrowing countries are Canada, the United States, and Australia where lentil is mostly grown for export to the developing countries. In North America, the United States, and Canada

Lentil is a cool-season or temperate crop. The optimum temperature for growth is 18–24 C. The crop has moderate tolerance to drought or high temperatures. In some regions such as southeastern Turkey and Australia, lentil is a winter crop sown in autumn and maturing early in summer. The crop will not tolerate extremely cold, dry winters. Currently, work is under way in the United States, Turkey, and the International Center for Agricultural Research in the Dry Areas (ICARDA) in Syria to improve the winter hardiness of the crop. In the United States, winter lentil cultivars have shown a yield advantage over spring-planted lentil with the yield advantage greater in years


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with summer drought. Lentil plants are sensitive to waterlogging and will not tolerate flooding or salinity. Water requirement for optimum lentil yield varies from region to region depending on the rate of evaporation. Wet weather during the reproductive period of crop growth can delay maturity, reduce seed set, and increase susceptibility to foliar diseases. Lentil is adapted to a wide range of soil types. In India, lentil is grown on different soil types ranging from heavy clay to loamy sands. In the Mediterranean region and in North Africa, fields of varying slope, soil texture, and depth are used for lentil production. In southwestern Australia, lentil is grown in welldrained, neutral to alkaline loam, and clay loam soils. Lentil can be grown from slightly acidic (pH 5.5–6.5) to moderately alkaline soil (pH 7.5–9.0).

Land Preparation Land preparation required for lentil production varies depending on soil type and cropping system. Lentil can be grown under conventional, minimum-till, or no-till production systems. In the Indian subcontinent and parts of the Mediterranean region, land preparation is usually minimal to conserve moisture. In Africa, land is deeply plowed followed by cultivation with a disk harrow. In the United States, autumn chisel plowing is used to increase water infiltration, decrease erosion, and maximize retention of crop residues in fields intended for lentil production. Tillage in spring is kept minimal. In western Canada, grain yields and net returns for lentil grown on stubble using no or minimum till are higher than those from conventional tillage systems. In dry environments, tall stubble reduces soil moisture evaporation resulting in greater water-use efficiency and increased lentil yield. Tall stubble also increased pod clearance making combining or swathing easier and reducing pod shattering.

Throughout the world, the lentil crop is often grown in rotation with cereals. In India, lentil is generally grown in a double-cropping system following a monsoon-season crop of maize, sorghum, jute, or rice. The lentil crop is grown following a fallow where the monsoon rains are low. In eastern India and Nepal, relay cropping is practiced with the lentil crop planted in a standing crop of paddy rice, when the rice crop is close to maturity. Multicropping is practiced under the humid subtropical conditions at the foothills of the Himalayas. For example, triple cropping of jute–rice–lentil has been found to be more productive than a double cropping of either jute–lentil or rice–lentil. In the Mediterranean region, North Africa, parts of Ethiopia, eastern Europe, and North America, lentil is generally a component of a two- to four-course rotation incorporating cereals and forages. Lentil, like other pulses, is an important component of these rotations with advantages extending beyond the year in which the lentil is grown. Pulse crops improve the soil tilth and diversify the rotation and increase the availability of nitrogen and soil organic matter. Table 1 shows the optimum N rate for the maximum return and maximum net return from crop rotations with winter wheat following a fallow phase, spring wheat, winter lentil for grain, and winter lentil for green manure. Nitrogen rate for maximum return was lowest and maximum net return was highest in the winter lentil for grain–winter wheat rotation. Pulse crops break the cereal disease cycles resulting in low-disease pressure in cereal crops following pulse crops. Table 2 shows the performance of a wheat crop following either lentil or another wheat crop. Seed yield, straw yield, seed N yield, and straw N yield were higher and disease severity was lower in the lentil–wheat rotation than in the wheat–wheat rotation. Lentil can be seeded with a wide range of seeders ranging from hoe drills to air seeders. Like other pulse crops, lentil seed is very susceptible to damage during seeding; hence, it is

Table 1 The optimum N input level for maximum net economic return under different rotations conducted in central Montana, the United States, between 2004 and 2010 Crop rotation

Optimum N for the maximum return (kg ha1)

Maximum net return ($ha1)

Fallow–winter wheat Spring wheat–winter wheat Winter lentil (grain)–winter wheat Winter lentil (green manure)–winter wheat

125 86 79 80

172 106 286 158

The experiment with winter lentil–winter wheat rotations was separate but adjacent to the fallow–winter, spring wheat–winter, and winter lentil–winter wheat rotation experiment. Source: Chen C, Neill K, Burgess M, and Bakkerman A (2012). Agronomic benefit and economic potential of introducing fall-seeded pea and lentil in conventional wheat-based crop rotations. Agronomy Journal 104: 215–224.

Table 2

The effect of crop rotation on yield, N yield, and disease severity on the subsequent wheat crop Yield (kg ha1)

N yield (kg ha1)

Diseases scores

Crop rotation

Seed

Straw

Seed

Straw

Leaf diseases (0–11 scale)

Root diseases (0–4 scale)

Lentil–wheat Wheat–wheat Standard error

1868 1518 56

2484 2160 85

57.7 40.7 1.7

77.7 52.5 2.3

5.9 8.0 0.2

0.8 1.4 0.01

Source: Mooleki PS (2000) Synchronization of N Availability and Plant N Demand: N and Non-N Effects of Lentil to Subsequent Wheat Crops. PhD thesis, University of Saskatchewan, Saskatoon, Canada.


target plant density of 90 plants per m2. In western Canada, the target density is 130 plants per m2 and recommended seed rates range from 45 to 90 kg ha1 depending on variety. Some research shows that lentil yield is stable over a range of population densities, while other studies report a general trend towards yield increase with increase in seeding rate. Differences in lentil varieties used, as well as the growing conditions the crop is subjected to, can affect the response to seeding rate. For example, Figure 1(a) and 1(b) shows the effect of the growing environment on lentil seed yield response to seeding rate in southwestern Australia in 1996. In a dry environment like Merredin (mean growing season rainfall ¼ 212 mm), lentil seed yield increased with increase in seeding rate, whereas in a wetter environment like Cunderdin (mean growing season rainfall ¼ 274 mm), seed yield was relatively stable over a wide range of seeding rates. This indicates the limited ability of lentil plants to compensate for low density in dry environments. Compared to some other pulse crops, a lentil plant is small and has a more determinate growth habit. Higher plant population densities are required for early maturing lentil varieties compared to full-season lentil varieties that tend to have larger plant type. Optimum row spacing depends on lentil variety and cropping system. Differences in lentil performance due to row spacing are more obvious in dry environments than in environments with adequate soil moisture. In narrow row spacings, the crop canopy closes faster reducing loss of water by soil evaporation. However, it is the combination of plant density

important to handle seed carefully especially when using air seeders. Airflow should be kept at low speed and seed moisture should be kept at 14% minimum. The rates of seed germination, seedling emergence, and growth are sensitive to temperature. Optimum germination for most lentil varieties occurs at 15–25 C. As temperature decreases, the germination process slows down. A seeding depth of 4–5 cm is recommended for good germination and growth.

Seeding Rates Recommended seeding rates for lentil vary from 40 kg ha1 to as high as 160 kg ha1, depending on the growing conditions and lentil variety. These rates are based on target population densities for the growing environment and should be adjusted for germination. Seeding rates of 40 kg ha1 are recommended for small-seeded lentil under Indian conditions. More recently, seeding rates of 40–45 kg ha1 were recommended for small to medium grain-size lentil varieties in Pakistan. In western Asia and the Mediterranean region, seeding rates of 60–80 kg ha1 for small-seeded lentil and 120–160 kg ha1 for large-seeded lentil are recommended. Studies conducted in Mediterraneanlike environments of southwestern Australia recommend a target population density of 150 plants m2 by using a sowing rate of 90–110 kg ha1. In the United States, recommended seeding rates for Palouse growers are 67–79 kg ha1 based on a

Seed yield (kg ha−1)

2000

1500

225

Merredin LSD = 256

1000

500

0 20

40

(a)

60 80 100 Seeding rate (kg ha−1)

2000

120

Cunderdin


LSD = 126 1500

1000

500

0 20 (b)

40

60

80

100

120

Seeding rate (kg ha−1)

Figure 1 Effect of seeding rate on seed yield of lentil at (a) Merredin and (b) Cunderdin in southwestern Australia in 1996. Adapted from Siddique KHM, Loss SP, Regan KL, and Pritchard DL (1998) Adaptation of lentil (Lens culinaris Medik) to short season Mediterranean-type environments: Response to sowing time. Australian Journal of Agricultural Research 49: 1057–1066.

226


2000

1600

40 kg ha−1 80 kg ha−1 Seed yield (kg ha−1)


LSD = 106 1500

1000

Melfort

Saskatoon

Swift current

1200

800

400

500 0 2nd week May

3rd week May

0 15

20 25 Row spacing (cm)

30

Figure 2 Effect of row spacing and seeding rate on seed yield of lentil line ILL-4401 at Tel Hadia, Syria, 1977–78. Adapted from Saxena MC (1981) Agronomy of lentils. In: Webb C and Hawtin G (eds.) Lentils, pp. 111–129. London: Commonwealth Agricultural Bureau.

used with a particular row spacing that determines the performance of the lentil crop in a particular environment as shown in Figure 2. In a wet year in Syria, narrower row spacings combined with higher seeding rates gave greater lentil seed yield compared to wider row spacings with low or high seeding rates. Broadleaf weed management for the lentil crop is a serious problem wherever lentil is grown. In some environments, high seeding rates have suppressive effects on weeds. Using high plant densities and narrow rows is not advisable in wet environments; the thicker canopy may facilitate rapid spread of foliar diseases.

Time of Seeding The optimum date of seeding lentil varies from region to region. In all regions where lentil is grown, seed yield can be optimized by timing sowing such that crop development and growth occurs when climatic variables such as rainfall and temperature are favorable. In the United States and Canada, lentil is usually seeded in early spring. Seeding begins as soon as the soil temperature at the seeding depth is 5 C. This usually occurs in mid-April to early May but wet conditions sometimes delay seeding. In western Canada, the yield advantage due to early seeding is substantial and the decrease in seed yield due to delay in seeding differs from one environment to the next. Figure 3 shows that the decrease in lentil yield with delay in seeding is more drastic at Swift Current (mean annual precipitation ¼ 350 mm), a semiarid environment with lighttextured soils, but that yield decrease is more gradual at Melfort (mean annual precipitation ¼ 409 mm), a cool moist environment with heavier-textured soils. Saskatoon with intermediate conditions in terms of soil moisture and soil type showed a decrease between the two extreme locations. In southwestern Australia, a reduction in seed yield with delayed seeding as high as 4–29 kg ha1 day1 has been reported. A reduction in seed yield due to delay in seeding has been observed throughout most lentil-growing regions in the world irrespective of the

4th week May

1st week June

2nd week June

Seeding date Figure 3 Effect of seeding date and location on the seed yield of lentil. Vertical bars are standard errors. Unpublished data: Nleya T, Gan Y, Vandenberg A, and Kutcher R (2003) Lentils for the Next Century: Diversification of Red Lentil Production Systems for Saskatchewan.

climatic conditions. This is because early sowing allows for an extended period of vegetative and reproductive growth. In areas with mild winters such as western Asia and southwestern Australia where lentil is grown as a winter crop, early autumn seeding has advantage over late autumn or spring seeding. In temperate climates like in Canada, severe winter temperatures reduce plant density and yield for the autumnseeded lentil crops compared to spring-seeded lentil crops. In the Pacific Northwest and northern Great Plains of the United States, spring lentil production is often limited by lack of water during stages of reproductive development and heat stress. Often, cool and wet soil conditions prevent early spring seeding making it difficult to avoid terminal drought stress. Winter lentil varieties are now available and autumn seeding is currently being investigated as an alternative to spring seeding. Recent research results show that autumn-planted winter lentil varieties have a yield advantage over spring-planted lentil in both the Pacific Northwest and the northern Great Plains. However, winter lentil performance has been inconsistent in the northern Great Plains due to failure of lentil seedlings to survive in years with severe winters (personal observation). Lentil planted in the autumn has earlier spring growth and flower initiation that enables the crop to avoid terminal drought stress.

Fertilizer Requirements Lentil plants have high demand for plant nutrients. Lentil accumulates the maximum amount of nitrogen (N), phosphorus (P), and sulfur (S) in the seed; hence, a considerable amount of each of these nutrients is exported with the seed at harvest. Adequate application of the essential macronutrients including P, potassium (K), and S is necessary for good yields. Nitrogen is supplied via biological N fixation, mineralized soil N, or N fertilizers or a combination of these sources. The best way to determine nutrient requirements is by soil tests. Under good conditions for symbiotic association, 70–90% of the N requirement for the lentil crop can be met through biological N fixation, with the remainder derived from soil N

AGRONOMY OF GRAIN GROWING | Lentil: Agronomy sources. Thus, a well-nodulated lentil crop inoculated with an appropriate lentil Rhizobium will generally not respond to the application of inorganic N fertilizer. Accumulated N in no-till systems can interfere with biological N fixation for lentil grown under no-till systems. Research evidence suggests that lowered biological N fixation is unlikely to lower lentil yield as lentil plants can compensate for low biological N fixation by increased soil N uptake. Lentil growing in soils with low organic matter, in dry environments, or seeded early into cool, wet soils may benefit from the application of low rates of N as a ‘starter N’ source. However, because high levels of inorganic N are known to have adverse effects on early nodulation or will delay nodulation leading to poor seedling growth, starter N application rates should be limited to 10–25 kg ha1. Starter N rates greater than these amounts may encourage excessive vegetative growth and prolonged maturity, both of which lead to poor seed set. In wet conditions, too much vegetative growth may create a microclimate suited for disease development. Adequate P nutrition is essential in lentil production for optimum N fixation, for optimum seed yield, and for the crop to mature in time. Phosphorus enhances root development and improves the ability of a lentil crop to tolerate stresses such as drought and frost. Although lentil has a relatively high requirement for P, seed yield responses to P fertilizer application are not consistent, even in soils low in available soil P. Moreover, responses to P fertilizer application are related to environmental factors, with greatest responses typically occurring in cool, wet soils. Lentil seed is very sensitive to seed row-applied P fertilizer and a significant reduction in plant stand and seed yield can occur at high P levels. Small amounts of P ( 20 kg ha1 based on a narrow seed row at 15–18 cm spacing) placed with the seed may not be harmful and the adverse effect on plant stands may be more severe under drier soil conditions. Where P fertilizer application is necessary, banding the fertilizer to the side away from the seed is recommended. Lentil has a high need for K, requiring 4.7 kg K2O for every 100 kg seed produced. However, response to K generally is limited to soils with a low capacity to supply K, such as sandy soils. Like P, K moves by diffusion in the soil; hence, soil temperature and moisture can influence movement and availability to plants. Sulfur-deficient soils can limit yield of lentil. Plants deficient in S show yellowing from the top downward, symptoms that are sometimes confused with N deficiency. The distinguishing feature is that with S deficiency top leaves yellow first. To correct S deficiency in the cropping system, a sulfate form of S fertilizer must be used. Annual application of elemental S can be used to build S in the soil but will not be available to the crop in the year of application. Researchers are uncertain of micronutrient requirements for productive lentil crops. Limited research has shown that deficiencies in zinc (Zn), molybdenum (Mo), and boron (B) may occur in lentil production. Zinc deficiency occurs on alkaline soils and is widespread in soils used for paddy rice production in India, Nepal, and Pakistan where lentil grown after paddy rice has shown response to Zn fertilizer application. Zn deficiency can be corrected by soil application of zinc sulfate or foliar spray of zinc sulfate at the first appearance of deficiency symptoms.

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Lentil, like other legume crops, requires Mo for the N fixation process. Mo deficiency is likely to occur in soils with pH lower than 5.6. Low levels of Mo in soils can cause poor growth and limit yield of lentil. Leaves of lentil deficient in Mo are chlorotic and plants are stunted. The Mo-deficiency symptoms are difficult to distinguish from N- and S-deficiency symptoms. Liming and application of P fertilizer can reduce the severity of Mo deficiency in lentil growing in Mo-deficient acid soils. Since Mo concentrations in soils are small and difficult to detect, fertilizer recommendations are often based on cropping history and soil pH. Mo fertilizer can be applied to the lentil crop as a seed treatment or a foliar spray. Soils that are acidic and coarse-textured and have low organic matter tend to be deficient in B. Boron deficiency has been observed in lentil fields in northwestern United States and in acidic nutrient-deficient soils in Nepal. Differences in B efficiency have been observed in lentil genotypes and seem to be associated with geographic origin. Boron deficiency in lentil can be corrected by broadcasting B fertilizer. It is important that B requirements be determined by soil tests and that recommendations be followed when applying B fertilizer. Boron can be toxic to plants if higher concentrations are applied or if applied too close to seedlings. Boron toxicity problems have been reported in some regions of Australia.

Weed Management Lentils are a short crop with a sparse canopy making the crop a poor competitor with most weeds. In addition, seedlings grow slowly early in the growing season, and at this stage, the crop competes poorly with weeds for light, water, and nutrients. Weeds are particularly a problem in temperate climates where the cool weather at seeding time slows down the germination process and weeds can quickly overgrow the crop. Yield losses due to weeds can be severe ranging from 20% to over 80%. Weed control in lentil therefore requires a long-term strategy involving different methods of control and proper crop rotations. Preventative measures such as diversified crop rotations and tillage are an important part of long-term management strategy. Growing different crops in different years allows for use of different weed management options. Both the date when tillage is done and the kind of tillage have important implications on weed prevention. In temperate climates, for example, autumn and spring preseeding tillage is used to control biennial and annual weeds. Preseeding spring tillage should be early enough to allow weed emergence and control before seeding the lentil crop. Where weed seeds are buried deep, shallow tillage can be used to avoid bringing weed seeds close to the surface where they can germinate. Postemergence harrowing or rotary hoeing is generally not recommended because this method can damage seedlings and increase the incidence of root and stem diseases. Whenever this method is used, it is important that the crop be short and that the foliage is dry and that operation be conducted on a warm sunny day. Hand-weeding with a hoe or hand-pulling is a traditional method of weed control and is still practiced in lentil production in countries such as India, North Africa,

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and western Asia. The number of weedings required depends on climatic conditions and weed infestation level. A number of herbicides are registered for use in lentil worldwide. Different herbicides are used to control weeds in lentil in different regions of the world. In the United States, trifluralin, pendimethalin, metolachlor, carfentrazone, dimethenamid, and imazethapyr are registered for preemergence or preplant-incorporated control for grass and broadleaf weeds. Quizalofop, sethoxydim, and clethodim are used for postemergence grass control. Paraquat, glyphosate, and carfentrazone are used for preharvest burn down. Metribuzin is the only selective postemergence broadleaf herbicide available. In Canada, Metribuzin is also registered for the control of broadleaf weed preemergence and postemergence. Trifluralin is applied in the autumn to control both grass and broadleaf weeds in western Canada. In Australia and New Zealand, successful weed control in lentil has been achieved by using trifluralin presowing, cyanazine preemergence, and metribuzin postemergence. Glyphosate can be used as a preemergent burn-off treatment to control weed before crop emergence and is also registered for preharvest weed control in lentil. Herbicide users should read and follow labels for recommended application time, rates, and precautions to be taken. Lentils are very sensitive to herbicide treatments and soil type; organic matter content and weather conditions can make a big difference as far as crop safety is concerned. Cool wet conditions and abnormally hot temperatures at application time can induce negative crop response. Herbicide-tolerant varieties, Clearfield® lentil, carrying one herbicide-tolerant trait are now available in Canada. This trait allows growers to use imidazolinone herbicides that would otherwise cause injury to lentil varieties not carrying the trait.

Diseases Lentil is affected by many diseases caused by fungi and viruses. The major diseases caused by fungi include the seedling blight/ root rot complex, wilt, Sclerotinia stem and pod rot, botrytis stem and pod rot, rust, Ascochyta blight, anthracnose, and Stemphylium blight.

Table 3

The most important seedling blight and root rot diseases are caused by Pythium, Rhizoctonia, and Fusarium species. Pythium causes the damping-off of seedlings while Fusarium results in root rot. Symptoms include lesions and discoloration at the base of the stem. Diseased plants turn yellow and eventually die. Root rots and seedling blights occur in patches in lentil fields and rarely cause economic losses unless they are associated with other diseases (Table 3). Wilt caused by Fusarium oxysporum f.sp. Lentis is a serious disease in most lentil-growing areas of the world (Table 3). The disease may appear as seedling wilt in the early stage of crop growth or as adult plant wilt during reproductive growth. Symptoms are first seen as sudden drooping of leaflets starting at the top of the plant and then progressing downward. This is followed by shriveling of leaves and wilting of the whole plant. Wilt occurring at flowering will lower seed production, whereas wilt appearing during the pod-filling period will reduce yield drastically. Sclerotinia caused by Sclerotinia sclerotiorum (Lib.) de Bary causes stem and pod rot. Symptoms include necrotic lesions, which eventually produce white mycelial growth. The fungus overwinters as soil-persistent sclerotia. Lentil is of increased risk to Sclerotinia infection if grown in rotation with other susceptible crops such as mustard, canola, sunflower, and pea. Botrytis stem and pod rot, caused by Botrytis cinerea (Pers.:Fr), is another disease commonly found on lentil crops in temperate climates. Symptoms include necrotic lesions on stems and pods with gray sporulating mycelial growth. Both these diseases are of major concern when the crop experiences high humidity after full canopy closure and is susceptible to lodging. Including cereal crops in a rotation can reduce the buildup of inoculum of soilborne pathogens. Rust caused by Uromyces viciae-fabae is an important disease of lentil in areas with mild temperatures and humid conditions. It has been reported in many lentil-growing countries including India, Turkey, Iran, Morocco, and Ethiopia. Rust has not been reported in lentil in North America. The disease affects all aerial parts of the plants and symptoms include yellowish-white pycnidia and aecial cups on the lower surface of leaflets and pods. Uredia then form on either side of the leaflets, stems, and pods. Where infection is severe, lentil plants can die before maturity. The disease is spread from the inoculum arising from infected plant material usually mixed with

Major fungal diseases of lentil

Disease

Causal organism

Favorable climatic conditions

Root rot/seedling rot

Pythium spp. Rhizoctonia spp. Fusarium spp. Fusarium oxysporum Sclerotinia sclerotiorum Botrytis cinerea Uromyces viciae-fabae Ascochyta lentis Colletotrichum truncatum Stemphylium botryosum Erysiphe spp.

Wet, cool conditions at seeding

Wilt Stem and pod rot Rust Ascochyta blight Anthracnose Stemphylium blight Powdery mildew

Moderately high soil temperatures (20–25 C), sunlight Wet conditions, dense canopy Late season Mild temperature, humid conditions Cool (15–20 C), wet conditions Warm (20–24 C), humid conditions Warm, wet conditions Moderately high temperatures and moderate humidity

AGRONOMY OF GRAIN GROWING | Lentil: Agronomy seed. Lentil genotypes with some resistance to rust are now used in breeding programs where rust is a serious problem. Ascochyta blight, caused by Ascochyta lentis (Vassil.), is a serious disease of lentil in many parts of the world, particularly Canada, Australia, and Pakistan. The disease can be seed- or residue-borne. The symptoms include gray to tan lesions on leaves, stems, pods, and seeds. The lesions have dark margins and may have pycnidia in the centers. Under severe infection, leaves turn completely brown and drop and the infected seed is discolored. The fungus can overwinter on lentil stubble in the field. While wind movement of spores from one field to the next is limited, this can happen in adjacent fields. Seed-borne Ascochyta can be treated by using fungicidal seed treatment. The effectiveness of seed treatment depends on the level of infection and on environmental conditions. As low as 1% seed infection can result in severe epidemics in cool, moist conditions, whereas as high as 5% seed infection may not cause severe problems in dry years. High levels of Ascochyta can cause losses in yield and quality of lentil. Foliar fungicides such as chlorothalonil are available for controlling the spread of Ascochyta blight in lentil. Lentil varieties with good resistance to Ascochyta blight are now available. However, there is considerable risk that new strains of Ascochyta that can overcome resistant genes in these lentil varieties will emerge. Anthracnose caused by Colletotrichum truncatum (Schwein.) is a fungal foliar and stem disease of lentil. It has been reported in western Canada where it can cause significant yield losses. Two races of anthracnose have been identified. A few lentil varieties with resistance to race 1 are now available. Symptoms include gray to cream spots on leaves and stems, yellowing and browning, and eventually senescence. The disease spreads rapidly in the field and can be spread on wind-borne chaff and dust during harvest. Anthracnose inoculum can also be carried over in crop residues as sclerotia in the field for several years. The level of seed-to-seedling transmission of anthracnose is low. Treating infected seed with fungicides to control seedborne anthracnose is not important, but the use of diseasefree seed can help minimize the spread of the pathogen in the field. To reduce levels of field inoculum, it is important to ensure that lentil is not planted in the same field for at least 4 years. Foliar fungicides, for example, chlorothalonil, are available to control anthracnose in lentil. Good timing of application is critical for effectiveness of the fungicides. Stemphylium blight caused by Stemphylium botryosum is a foliar disease of lentil in Canada and Bangladesh. Infected plants suffer leaf drop and premature ripening. The epidemiology of this disease is not well understood. Some sources of genetic resistance are available and they have been used in Bangladesh to control the disease. Powdery mildew of lentil has been reported in different parts of the world including South Asia, East Africa, the Middle East, South America, and North America. In most cases, it is reported to be a minor disease though it can be severe on certain lentil cultivars in India. Three Erysiphe spp. (E. pisi, E. diffusa, and E. trifolii) cause powdery mildew in lentil. Viral diseases of lentil include alfalfa mosaic, bean yellow mosaic, bean (pea) leaf roll viruses, pea enation mosaic virus, and pea streak. Some of the viruses can be seed-borne while others are transmitted by aphids, white fly, and other insects. The best control method for viral diseases is use of resistant lentil varieties.

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Insect Pests A wide range of insect pests attack the lentil crop wherever it is grown. Crop losses to insect pests tend to be sporadic and dependent on insect population. Insects that are of economical importance in lentil include aphids (Aphis spp.), Lygus bugs (Lygus spp.), cutworms (Agrotis spp.), bruchid beetles (Bruchus spp.), lepidopteran pod borers (Helicoverpa spp.), and grasshoppers. Cutworms feed on stems and roots of seedlings, whereas aphids and lepidopteran larvae attack leaves stems and flowers. Lygus bugs and bruchid beetles damage pods and seeds. Grasshoppers primarily eat flowers and pods. Insect pests are controlled by following an integrated pest management system. Awareness of the biology of the insects likely to infest lentil in the region is the key to knowing when to scout for insects to minimize infestation by agronomic techniques. Natural enemies may be used to keep populations of some insects below economic threshold. Insecticides are available for controlling major pests in lentil. These should be used when necessary and with caution.

Harvesting In many lentil-producing areas of western Asia, Africa, and India, harvesting is traditionally done by hand. In many countries, the chaff and straw are valuable animal feed. Mechanization of lentil harvest has been one of the main objectives of national and international research programs throughout the world. At ICARDA, breeders are developing tall, nonlodging lentil varieties with nonshattering pods to suit mechanical harvesting systems. Mechanical harvesting devices to suit these production systems are also being developed. Mechanized harvesting is practiced in South America, North America, Australia, New Zealand, and parts of Europe. In these countries, combine harvesters are used either to directly combine the crop or to swath the crop and leave it in windrows to dry. The dry plants are then picked and threshed with combines. Rolling of the seedbed to level the soil surface after seeding makes it easier to harvest pods held close to the ground. Rolling also reduces cutter bar damage and speeds up swathing or direct combining. Cutting or swathing is done when 30% of lower pods have turned tan and the seeds rattle. Seed that is too dry is susceptible to chipping and peeling during threshing. It is recommended that threshing be done at 18% moisture to reduce seed chipping and breaking during threshing. Recommendations are that swathing be done in the morning when humidity is high to minimize pod shattering. Lentil is combined within 2 weeks of swathing.


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What features distinguish Chilean lentil from Persian lentil? Lentil is a legume crop. How are legumes distinct from other food grains such as cereals and oilseeds? What is the best temperature range to grow lentil? Give reasons why lentil competes poorly with weeds.

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What are the advantages of including lentil in a rotation with cereals crops? Name the three largest lentil-producing countries in the world.


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Lentil has an indeterminate growth habit. What does that mean? Why do indeterminate legume crops such as lentil yield lower under cool and late-season wet conditions? Lentil is grown in both developed and developing countries. Select two developed and two developing countries where lentil is grown. Discuss similarities and differences in how the lentil crop is handled during harvesting. Weed control is a major impediment to lentil production worldwide. Why is that so? Describe different methods available to control weeds in the lentil crop.

See also: Breeding of Grains: Lentil: Breeding; Grains Around the World: Grain Production and Consumption: Overview; The Basics: The Grains that Feed the World.

Further Reading Attanayake R, Glawe DA, Dugan FM, and Chen W (2009) Erysiphe trifolii causing powdery mildew of lentil (Lens culinaris). Plant Disease 93: 797–803.

Chen C, Miller P, Muehlbauer F, Neill K, Wichman D, and McPhee K (2006) Winter pea and lentil response to seeding date and micro-and macro-environments. Agronomy Journal 98: 1655–1663. Chen C, Neill K, Burgess M, and Bakkerman A (2012) Agronomic benefit and economic potential of introducing fall-seeded pea and lentil into conventional wheat-based crop rotations. Agronomy Journal 104: 215–224. Erskine W (2009) Global production, supply and demand. In: Erkskine W and Muehlbauer F (eds.) The Lentil: Botany, Production and Uses, pp. 4–12. Cambridge, MA: CABI. Saskatchewan Pulse Growers (2000) Pulse Production Manual, 2nd edn. Saskatoon: Saskatchewan Pulse Growers. Muehlbauer FJ, Summerfield RJ, and Kaiser WJ (1997) Principles and Practices of Lentil Production. Washington, DC: US Department of Agriculture, Agriculture Research Services ARS-141. Nassib AM, Sakar D, Sohl M, and Salih FA (1988) Production of cool season food legumes in West Asia and North Africa. In: Summerfield RJ (ed.) World Crops: Cool Season Food Legumes, pp. 137–145. Dordrecht, The Netherlands: Kluwer Academic. Saleem A, Zahid MA, Javed HI, et al. (2012) Effect of seeding date on lentil (Lens culinaris Medik) seed yield under rainfed conditions. Pakistan Journal of Agricultural Research 25: 181–185. Saxena MC (1981) Agronomy of lentils. In: Webb C and Hawtin G (eds.) Lentils, pp. 111–129. London: Commonwealth Agricultural Bereaux. Siddique KHM, Loss SP, Regan KL, and Pritchard DL (1998) Adaptation of lentil (Lens culinaris Medik) to Mediterranean environments: Response to sowing time. Australian Journal of Agricultural Research 49: 1057–1066. Srivastava SP, Bhandari TMS, Yadav CR, Joshi M, and Erkskine W (2000) Boron deficiency in lentil: Yield loss and geographic distribution in a germplasm collection. Plant and Soil 219: 147–151. Zakeri H, Lafond GP, Schoenau JJ, et al. (2012) Lentil performance in response to weather, no-till duration and nitrogen in Saskatchewan. Agronomy Journal 104: 1501–1509.

Lupin: Agronomy RJ French, The University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Lupin is a component of cropping systems in Australia, Europe, and South America. Lupin is grown in rotation predominantly with cereals and oilseeds. Lupin provides fixed N other crops can use, reduces levels of certain soil-borne pathogens, and allows more diverse weed management options. Narrow-leafed lupin (NLL) is very well adapted to Australian soils and climate, and white lupin, yellow lupin, and NLL are all grown in Europe. Lupin species differ in their susceptibility to disease and this affects species choice. Sowing time is a key aspect of lupin management in both Australia and Europe. Weed management is also a key aspect of lupin management.

Learning Objective

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To achieve understanding of the role of lupin in world cropping systems and what is necessary to grow productive lupin crops.

Introduction This article surveys the agronomy of the three most commonly grown lupin species – narrow-leafed lupin (NLL, Lupinus angustifolius L., also known as the Australian sweet lupin or, in Europe, blue lupin), white lupin (WL, Lupinus albus L.), and yellow lupin (YL, Lupinus luteus L.). It describes briefly the Australian and European farming systems in which they are grown, why each species is grown where it is, and the principles underlying the management of lupin crops. Current agronomic recommendations for growing lupin are also described.

Types of Farming Systems in Which Lupin Is Grown Over the past decade, Australia’s share of world lupin production has averaged 74% (FAO http://faostat3.fao.org/faostatgateway/go/to/search/lupin/E), and 80% of this is produced in the grain belt of Western Australia, where NLL is grown in various rotations with wheat, barley, and canola. Lupin is grown mostly on deep, coarse-textured (<10% clay), mildly acid soils, which, in their natural state, are very infertile. NLL is an ideal grain legume under these circumstances because it is deep-rooted, quite acid-tolerant (as is its associated Bradyrhizobium), and modern cultivars yield well. The other major grain legumes grown in Western Australia are field pea and chickpea.


NLL is preferred on these soils to field pea because, despite producing less valuable grain, its strong erect stems and robust stubble mean that it can be harvested readily with machinery used for cereals and it protects the fragile soil from erosion during long, dry, windy summers. Chickpea is adapted to different soils. Lupin does not generally yield as well as wheat in this system, and farmers do not generally make as much money per hectare from lupin as from wheat. But wheat usually yields more, and better quality, grain when grown after lupin than after wheat. This is not only because lupin fixes atmospheric N2 that subsequent crops can use but also because levels of some soil-borne pathogens decline during a nonhost lupin phase. These considerations are also important in other lupin growing areas in Australia and elsewhere. In the past, lupin allowed farmers to use highly effective selective grass herbicides, which meant much fewer grass weeds in a crop following lupin than following wheat. Increasing levels of herbicide resistance, particularly in annual ryegrass (Lolium rigidum Gaud.), over the past 15 years has removed much of this advantage. Lupin production has declined in Western Australia over the past decade because its price is low relative to wheat and canola (which provides many of the same break crop benefits), N fertilizer is cheap, herbicide resistance means weed control in lupin is now expensive and less reliable than it was, and lupin yields are variable, especially in low-rainfall environments. Outside Australia, the most commonly grown species has been WL. The most sophisticated industry based on this species is in Europe where it is grown in rotation with cereals and oilseeds on neutral to mildly acid soils. A winter lupin industry developed in France based on research showing that if appropriate WL varieties are sown early enough in autumn, the vegetative crop can survive the winter in much of the United Kingdom and France. NLL and YL do not tolerate freezing and in many areas of Europe can only be grown when planted in spring. However, autumn-sown lupin proved more susceptible to insect and disease damage and spring-sown lupin is now more common in the United Kingdom. There has recently been renewed interest in lupin in Europe with the release of more agronomically suitable varieties and increased emphasis on protein crops in general, and there has been a resurgence of interest in eastern Europe where YL predominates. Poland produced nearly 13% of the world’s lupin in 2013. European farmers face much the same constraints as their Australian counterparts. In a survey of farmers’ attitudes to grain legumes (of which lupin is one) in six European countries, rotation and soil improvement were given as the major reason for growing them, and poor profitability in relation to other crops, particularly cereals, as the main reason for not growing them. The species L. mutabilis Sweet, known locally as ‘tarwi’ or ‘chocho,’ has been grown and consumed by the inhabitants of the Andean regions of Peru and Ecuador since pre-Columbian

http://dx.doi.org/10.1016/B978-0-12-394437-5.00194-7

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AGRONOMY OF GRAIN GROWING | Lupin: Agronomy

times. Attempts to develop this species for commercial crop production outside the Andes have had limited success, and commercial lupin production in Chile is based on WL and NLL.

Growing a Lupin Crop Which species? The species generating the greatest income will generally be chosen. There is little evidence that rotational benefits differ between lupin species, so this will be determined by grain yield, grain price, and the cost of production. Grain yield is a consequence of adaptation. John Gladstones identified NLL as having wider physical adaptation than other lupin species in Western Australia in the 1950s, and the considerable effort that has gone into its improvement has only reinforced its advantages locally over WL and YL. There are instances, though, where other lupin species might be grown in Australia. WL is more competitive with NLL on fertile loamy soils than on sandplain and is more widely grown in eastern Australia. YL tolerates soil aluminum (Al, the major constraint to plant growth on strongly acid soils), waterlogging, and the diseases brown leaf spot (caused by Pleiochaeta setosa [Kirchn.] Hughes) and Eradu patch (caused by an as yet unnamed species of Rhizoctonia) better than NLL or WL. In Central and Eastern Europe, considerable effort has gone into improving YL, which is adapted to the sandiest and most acid soils, so it has predominated until recently. WL tolerates soil freezing better than YL or NLL, so it can survive the northern European winter. This allows it to be sown in autumn, which results in higher yields than spring sowing. NLL has the advantage of greater anthracnose (Colletotrichum gloeosporioides [Penz.] Penz. & Sacc.) tolerance. Although WL is a minor component of traditional cuisine in some Mediterranean countries, and some components of lupin fiber and protein are being developed as additives for the food industry, lupin grain is mainly used to feed livestock, so the price it commands should reflect its composition. YL contains more protein than WL, which in turn contains more protein than NLL. YL also contains more S-amino acids, typically deficient in legume storage proteins, than WL or NLL. Consequently, YL attracts a higher grain price than WL or NLL, but in Western Australia, this is not sufficient to induce farmers to grow it in preference to NLL, given the lower yield potential of current cultivars. WL has higher oil in its grain and therefore has greater metabolizable energy than YL or NLL. Lupin species, and cultivars within a species, may differ in their cost of production. Differences in disease tolerance may mean that one species may not need fungicides necessary for other species. Differences in aphid attractiveness are important in Western Australia: the first agronomically adapted YL cultivar was extremely sensitive to aphid feeding damage, requiring at least one, if not two, more insecticide sprays than NLL.

growth until the season ‘breaks’ with the onset of winter rains. A cool, wet winter follows; in spring, temperature rises rapidly and rain ceases. To maximize the time available for crop growth, lupin should be sown to germinate on the earliest winter rains. Delaying sowing will mean that the reproductive growth occurs under hotter, drier conditions. This reduces lateral branch production and hence pod numbers, curtails seed filling, and reduces yield. In much of Western Australia’s agricultural areas, delaying sowing at the beginning of winter results in a linear yield decline, with a slope as high as 40 kg ha 1 day 1 (Figure 1). The yield penalty for delayed sowing is usually, though not always, greater in high yield potential situations. Early sowing has been a central dogma of lupin growing in Western Australia, and sowing the crop into dry soil, anticipating the break of season, is widely practiced (Figure 2). However, there can be good reasons for not sowing too early. In eastern Australia, and the south of Western Australia, sowing before the end of April encourages excessive lateral branch growth at the expense of pod set, especially in older cultivars. In drier environments, the first winter rains are sometimes followed by a long period without further rain, severely 4000


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0 1 May

16 May

31 May 15 June 30 June Sowing date

14 July

Figure 1 Grain yield response of NLL cultivar Belara to sowing date at four locations in Western Australia: closed squares – Esperance 1998; closed triangles – Wongan Hills 1998; open squares – Mingenew 2000; open triangles – Merredin 2000. Drawn from unpublished data of R.J. French.

Sowing Time Sowing at the correct time is crucial to growing a successful crop, but there are different constraints on sowing time in different parts of the world. In the Mediterranean environments of Southern Australia, matching the crop’s life cycle to the rainfall pattern is the most important consideration. In early autumn, the soil is typically too dry to support plant

Figure 2 Dry sowing lupin in Western Australia. Source: P. Maloney, DAFWA (Department of Agriculture and Food, Western Australia).


Optimum Plant Densities Plant density has a profound effect on the growth and structure of lupin crops. The same general principles apply to each lupin species and in each growing environment, but the target densities may be quite different. Dense lupin crops achieve canopy closure faster than thin ones and therefore intercept more radiation earlier, grow faster, and compete with weeds better. Increasing plant density suppresses lateral branch growth and pod set on low-order branches so the number of pods per plant is reduced, but not usually enough to reduce grain yield per unit area. The relationship between grain yield and plant density is usually asymptotic, often well described by a hyperbola. Grain yield sometimes reaches a maximum and declines at higher densities, though. In Western Australia, NLL grain yield will sometimes respond to increasing density above 80 plants m 2, and sometimes, the response is saturated at less than 40 plants m 2 (Figure 3). Generally, yield will respond to higher densities when yield potential is high, but there are exceptions. Modern NLL cultivars are more responsive to plant density than older ones, and Western Australian farmers plant denser lupin crops now than in the past. Denser lupin crops also

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stressing the young crop. In extreme cases, the crop may die, but more often, the potential to form lateral branches is restricted and the crop is shortened, which makes complete yield recovery while harvesting difficult. The probability of this happening is low if there is already water in the soil from summer rain. An increasingly important reason for not sowing too early is the developing resistance of important weeds to selective herbicides. As the effectiveness of selective herbicides wanes, alternative methods of weed control must be sought. One is to wait after the season breaks until weeds germinate and then kill them with a nonselective herbicide, or cultivation, before sowing the crop. In Northern Europe, sowing time is chosen so that the crop either survives or avoids the harsh winter. When WL plants are old enough, their roots are sufficiently lignified to survive soil temperatures as low as 3.5 C, which would kill younger plants. As the plants age further, and stem elongation begins, the stems become frost-sensitive and can be killed by aerial freezing. WL sown too early in autumn also tends to produce too many lateral branches at the expense of pod set and to grow too tall so that the crop lodges. Physiological models of lupin development have been used to define sowing windows for different locations in the United Kingdom, where the sowing window extends from mid-August to early September in Scotland and from early September to early October in southwest England. Many of the YL and NLL cultivars grown in Europe have a vernalization requirement for flowering and must be sown early enough in spring to satisfy it. In Germany and Poland, they must be sown before mid-April to ensure they flower at the correct time and are ready to harvest in August. If sown later, they will be taller and more prone to lodging, have fewer pods and lower yields, and exhibit delayed ripening. Then harvest will interfere with sowing winter wheat in September. The ideal sowing times for spring lupin in the United Kingdom are late March for WL and early April for NLL and YL. Delayed ripening and harvest is also a problem with late sown lupin here as well as on continental Europe.

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Figure 3 Grain yield response of NLL cultivar Danja to plant population density at three locations in Western Australia: open squares – Beverley 1987; closed triangles – Cadoux 1987; closed squares – Hyden 1988. Reproduced with permission from French, R.J., Smart, W.L., McCarthy, K., 1994. Optimum plant population densities for lupin (Lupinus angustifolius L.) in the Western Australian wheat belt. Aust. J. Exp. Agric. 34, 491–497.

compete better with weeds. A target of 50 plants m 2 is common. In Germany, sowing 80–100 seeds m 2 is recommended for YL and NLL, although determinate NLL should be sown at 120–140 seeds m 2. Spring-sown WL should be sown at 60–70 seeds m 2. In the United Kingdom, 20 plants m 2 is optimum for autumn-sown WL, but sowing 40 seeds m 2 is recommended because 50% of plants are lost over the winter season. Target densities for spring-sown lupin in the United Kingdom range from 40 plants m 2 for WL to 50 plants m 2 for YL and 55 and 65 plants m 2, respectively, for semideterminate and determinate NLL cultivars.

Row Spacing and Seed Depth Lupin is generally sown in rows with the same machinery used for cereals and oilseeds. In Australia, these rows were traditionally 18 cm apart, but in the past decade, many lupins (and cereals) have been sown in wider rows, most commonly 22–25 cm. This trend has been driven by changing herbicide practices in wheat cropping, but lupin can benefit from rows perhaps as far apart as 50 cm. Growing lupin in wide rows means more stubble from the previous crop can be retained, which reduces the spread of the Pleiochaeta disease organism. Lupin in wide rows also grows taller due to increased intrarow competition between individual plants, improving harvestability. Some farmers have experimented with spraying

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nonselective herbicide between wide rows to combat herbicide resistance problems, protecting crop plants with hoods around the nozzles. This has not been widely adopted because the machinery is expensive and operating it is slow. Finally, some agronomists claim that lupin grown in wide rows exhibits a more efficient pattern of water use than in narrow rows, but this only leads to benefits in low yield potential environments. On the other hand, growing lupin in wide rows could encourage more aphid landings and hence virus spread, unless sufficient stubble is retained to cover bare ground between the rows, and weeds growing between the rows experience less competition from the crop in wide than in narrow rows (Figure 4). No interaction between response to plant density and row spacing has been observed in either NLL or YL in Western Australia. Lupin cannot be sown as deep as many other large-seeded legumes. The ideal sowing depth for NLL and WL in Western Australia is 5 cm. They were once commonly sown 2–3 cm deep, but this is now discouraged as it encourages Pleiochaeta root rot. YL should be sown no deeper than 3–5 cm in Western Australia (Figure 5). In Europe, it is recommended that lupin is sown 2–5 cm deep.

Crop Nutrition Lupin evolved on very infertile soils and is more efficient at acquiring nutrients than many crops. There is no need to use N fertilizer if the crop is well nodulated. Lupin forms root nodule

symbioses with Bradyrhizobium species, which do not nodulate other temperate grain legumes. Inoculation of the seed with the correct bacterial strain is therefore necessary if lupin is being sown on land without a lupin history. It is rarely necessary to inoculate seed of subsequent lupin crops in Western Australia, even if the previous crop was 5 or more years ago, since lupin Bradyrhizobium is very robust on neutral to acid soils. In Germany, inoculation is only recommended for NLL if lupin has not been grown in the preceding 8 years. Inoculum was traditionally applied to seed as a bacterial culture in peat and needed to be done within a few days of sowing, as the bacteria do not survive well on stored seed and fungicide seed dressings are usually toxic to the inoculum. Forms of inoculum with peat or clay granules impregnated with bacteria are now available. These are more convenient in that they do not need to be stored in a refrigerator before use and can be drilled into the soil near, but not necessarily in contact with, the seed. Thus they are more compatible with seed-applied fungicides. There is rarely any advantage in using starter doses of N under Australian conditions, but up to 25 kg ha 1 N is sometimes useful under European conditions.

Phosphorus (P) The main fertilizer requirement for lupin in Australia is phosphorus. NLL is more responsive to phosphorus than either YL or WL (Figure 6), which have evolved mechanisms that allow them to solubilize forms of soil phosphorus unavailable to most plants. In these species, phosphorus application is unnecessary unless soil phosphorus levels are very low. In NLL, yield responses have been observed to as much as 40 kg ha 1 P on some soils, but farmers in Western Australia typically apply 5–15 kg ha 1 P. On the more fertile soils where WL is grown in Europe, it is often most profitable not to apply phosphorus to lupin and replace the phosphorus it removes elsewhere in the rotation (see Table 1 for the amount of plant nutrients removed in lupin grain). The way phosphorus is applied can have a large impact on its effectiveness. Australian farmers have traditionally either broadcast phosphorus fertilizer on the soil surface or drilled it at seed depth with their crops. Many soils quickly immobilize applied phosphorus into insoluble forms and little applied phosphorus reaches the subsoil. It is therefore unavailable to the crop late in the season when the soil surface dries out. This has little effect on cereals, which take up most of their phosphorus requirement early in the season, but NLL maintains a high requirement for phosphorus following flowering. It was discovered in the late 1980s that placing fertilizer up to 10 cm below the seed (called ‘banding’) increased the effectiveness of the fertilizer on highfixing soils (Figure 6). Banding fertilizer away from the seed is also important when planting lupin in wide rows to avoid toxic osmotic effects of the greater concentration of fertilizer in each drill run. Seed phosphorus concentration is an important seed quality criterion in NLL for sowing in Western Australia, and the use of seed with less than 0.25% P is not recommended, particularly on low P soils.

Potassium (K) and sulfur (S) Figure 4 Narrow-leafed lupin in wide rows. Note annual ryegrass growing between rows. Source: P. Maloney, DAFWA (Department of Agriculture and Food, Western Australia).

Lupin grain contains considerable amounts of K (Table 1), but it is usually most profitable to apply it to more responsive crops in the rotation in both Europe and Australia. Increasing


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Figure 5 Effect of sowing at 3, 5, or 8 cm depth on emergence of lupin at Merredin, Western Australia, in 1998: (a) NLL cultivar Merritt and (b) YL cultivar Wodjil. Drawn from unpublished data of R.J. French.

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Figure 6 Response of lupin to applied phosphorus on a high phosphorus fixing soil at Mt. Barker, Western Australia. Circles – NLL cultivar Merritt; squares – YL cultivar Teo; triangles – WL cultivar Kiev Mutant. In panel (a), phosphorus was drilled with the seed; in panel (b), it was drilled 8 cm below the seed. Reproduced with permission from Bolland, M.D.A., Sweetingham, M.W., Jarvis, R.J., 2000. Effect of applied phosphorus on the growth of Lupinus luteus, L. angustifolius and L. albus in acidic soils in the south-west of Western Australia. Aust. J. Exp. Agric. 40, 79–92.

amounts of K fertilizer are being used in Australia on cereals and canola, but in lupin, there have been few economic K responses observed in trials, even where wheat responds strongly. Similarly, lupin appears unresponsive to applied S on many soils where wheat is responsive.

Trace elements Manganese (Mn) is the trace element most commonly deficient in lupin. This is principally a problem of NLL, causing ‘split seed,’ in which the crop can remain green at maturity and the seed does not develop properly. Both WL and YL are more efficient at acquiring Mn than NLL. In fact, WL grain can have high enough Mn levels to cause nutritional problems when fed to animals. In NLL, Mn deficiency can be corrected by drilling up 30 kg ha 1 MnSO4 with the seed. Soil applied Mn is more

effective if it is banded 8 cm below the seed because it then remains in moist soil and available for longer at the end of the growing season. Mn deficiency can also be treated by applying a foliar application of 4 kg ha 1 MnSO4 following flowering. In parts of Western Australia where the disorder occurs frequently, this is routine. Lupin growing on alkaline soils can experience Fe deficiency, but it is rarely grown on such soils.

Weed Management Lupin is not as competitive against weeds as cereals, and the availability of effective herbicides played a crucial role in establishing the lupin–wheat rotation in Western Australia. Without herbicides, early sowing, and in particular dry sowing, would

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Table 1 Average amount of plant nutrients removed by 1 tonne of lupin grain Nutrient

Narrow-leafed lupin

White lupin

Yellow lupin

Nitrogen (kg) Potassium (kg) Phosphorus (kg) Sulfur (kg) Calcium (kg) Magnesium (kg) Zinc (g) Manganese (g) Copper (g)

60 8.1 3 2.3 2.2 1.6 35 17 5

67 9.8 3.6 2.4 2 1.4 30 835 5

70 9.7 5.1 4.6 1.5 2.1 56 17 9

Compiled from Petterson, D.S., 1998. Composition and food uses. In: Gladstones, J.S., Atkins, C.A., Hamblin, J. (Eds.), Lupins as Crop Plants. Biology, Production and Utilization. CAB International, Wallingford, UK, and unpublished data of Sipsas, S. (Department of Agriculture, Western Australia)

be impossible since crop establishment would have to wait until germinated weeds could be killed by cultivation. Any weeds growing prior to sowing the crop are controlled with a nonselective herbicide or by cultivation. Most lupin crops in Australia have simazine, or a combination of simazine and atrazine, applied prior to or immediately after sowing. The safe rate depends on soil type and weather conditions. NLL is more tolerant than YL or WL, and modern cultivars are more tolerant than old ones, having been selected against a background of herbicide use. Trifluralin is often added as well. There are also a number of herbicides that can be applied postemergent to lupin crops. Table 2 gives a list of herbicides used for weed control in lupins in Australia and the United Kingdom. In the United Kingdom, chemical companies are not prepared to invest in developing specific recommendations for minor crops like lupin, so herbicide use on lupin in this country is off-label. The herbicides listed in Table 2 as used in the United Kingdom are registered for pea and bean, and trials have demonstrated their safety on lupin. The heavy reliance on herbicides in the Australian lupinbased farming system has encouraged increasingly severe herbicide resistance to develop in some of its most troublesome weeds, most notably annual ryegrass and wild radish (Raphanus raphanistrum L.) (Figure 7). Considerable effort has been devoted to developing new weed management strategies to complement the existing herbicides, and some of these have been widely adopted over the past decade. Examples include ‘crop topping,’ where a low rate of nonselective herbicide (usually paraquat) is sprayed onto the maturing crop to disrupt weed seed development, and various forms of harvest weed management. One involves towing a chaff cart behind the harvester to collect weed seed rather than returning it to the ground, another concentrating chaff containing weed seeds behind the harvester into windrows that can later be burnt, and a third passing weed seed containing chaff through a mechanical seed ‘destructor’ (Harrington Seed Destructor). Spraying nonselective herbicide between crop rows using specially shielded nozzles to prevent the herbicide contacting the crop has not been so widely adopted.

Table 2

Herbicides used for weed control in lupin

Herbicide Preemergent herbicides Amitrole Atrazine Bentazone Clomazone Diuron 2,4-D amine or ester Glyphosate Glufosinate Flumioxazin Isoxaben Isoxaben/terbuthylazine Metolachlor/prosulfocarb Paraquat/amitrole Paraquat/diquat Pendimethalin Saflufenacil Simazine Terbuthylazine Triallate Trifluralin Postemergent herbicides Diflufenican Metosulam Metribuzin Picolinafen Pyridate Simazine Various aryloxyphenoxypropionates Various cyclohexanediones

Where used Australia Australia The United Kingdom The United Kingdom Australia Australia Australia, the United Kingdom Australia, the United Kingdom Australia The United Kingdom The United Kingdom Australia Australia Australia Australia, the United Kingdom Australia Australia Australia, the United Kingdom Australia, the United Kingdom Australia Australia Australia Australia Australia The United Kingdom Australia Australia, Europe Australia, Europe

Registration details should be checked with the relevant pesticide registration authority. Information on weeds controlled, safe rates, and application methods is found on herbicide labels.

Figure 7 Wild radish is a troublesome weed in Australia. Source: P. Maloney, DAFWA (Department of Agriculture and Food, Western Australia).

Diseases Brown leaf spot Brown leaf spot, caused by Pleiochaeta setosa, was until recently the most damaging lupin disease in Australia, a status it now shares with anthracnose (see succeeding text). It is also significant in Europe and other parts of the world. It commonly

AGRONOMY OF GRAIN GROWING | Lupin: Agronomy causes leaf lesions that lead to defoliation and, if severe enough, crop death. The organism can also cause a root rot. The disease can be seed-borne, but the main source of infection is spores in the soil remaining from previous infected crops. Seed treatment with dicarboximide fungicides (iprodione or procymidone) provides good protection for up to 6 weeks after sowing, and retention of stubble from a preceding cereal crop prevents spores on the soil surface from being splashed onto lower leaves by rain drops, which is the main way infection spreads. Spore populations in the soil decline over time if lupins are not grown, so the recent trend in Western Australia for longer periods between lupin crops on the same land has contributed to fewer problems with brown spot. The root rot mode of Pleiochaeta is managed by sowing deep enough so that developing roots do not come into contact with the concentrated band of spores at the soil surface (hypocotyl tissue is not affected) and by not mixing spores through the top 5 cm of the soil by cultivation. YL is more tolerant of Pleiochaeta than NLL or WL.

Leaf rust Leaf rust (Uromyces lupinicolus Bub.) does not affect lupin in Australia, Russia, or Poland, but occurs elsewhere in Europe, North Africa, and South America. It usually occurs on plants approaching maturity but is most damaging if infection begins before flowering. A preflowering application of tebuconazole or cyproconazole is recommended in the United Kingdom to protect WL against early infection, and a further application may be necessary at the end of flowering. NLL, WL, and YL are all susceptible.

Anthracnose Anthracnose, caused by Colletotrichum lupini, is the world’s most important lupin disease. It is serious in Europe, South America, and, since 1996, Western Australia. It has yet to spread in eastern Australia. Infection is primarily seed-borne, but infected plants rapidly produce secondary inoculum, which can be spread through a crop by wind and rain splash. Its effects are minimized by using disease-free seed, but since in the right conditions, damaging outbreaks can arise from less than 1 plant in 10 000, seed should also be treated with thiram or carbendazim. Seed tests for anthracnose infection are available in Australia and the United Kingdom. Various foliar fungicides can also be effective against anthracnose, but the economics of these are dubious. In Western Australia, control of naturalized populations of Lupinus cosentinii, which can act as another source of infection, is an important component of anthracnose management. In the United Kingdom, farmers are not permitted to save their own seed of NLL or WL partly in order to reduce anthracnose infection levels. Lupin species differ considerably in their susceptibility to anthracnose. NLL has much greater tolerance than either YL or WL, and this explains why the area of NLL has recently grown at the expense of YL in Central and Eastern Europe. Within NLL, there is considerable variation in tolerance between cultivars, and in Western Australia, this is an important consideration in choosing a cultivar in areas likely to experience an anthracnose outbreak.

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Virus diseases The two most important virus diseases of lupin are bean yellow mosaic virus (BYMV) and cucumber mosaic virus (CMV). Within a crop, these viruses are spread from plant to plant by aphids, but the initial source of infection can vary. In YL and WL, BYMV is seed-borne, as is CMV in NLL and YL. Plants arising from infected seeds are the initial source of infection: aphids pick up the virus when feeding on them and carry it to healthy plants. BYMV is not seed-borne in NLL, but infected pasture legumes such as red clover and subterranean clover act as sources of the virus, again spread by aphids. CMV does not affect WL. Management of these diseases involves the reduction of virus source and its spread. Where the virus is seed-borne, virus-free seed should be used, and seed tests are available. Management that encourages early canopy closure, such as early sowing, high sowing rates, and narrow row spacing, is beneficial because plants then shade out weak virus-infected plants and discourage aphid landing. This reduces the chance of the infection spreading. Cultivar choice is also important since there is variation in both YL and NLL in how readily CMV is transmitted to the seed in infected plants and variation in susceptibility to BYMV has recently been identified in NLL. Spraying aphids to prevent virus spread is rarely economical.

Invertebrate Pests Lupin crops are subject to damage from a number of invertebrate pests, the most important of which are listed in Table 3. They can all be controlled by chemical pesticides, although this is not always worthwhile economically. There are some differences in susceptibility between species: YL is more susceptible to red-legged earth mite than NLL, which is more susceptible than WL; and YL and WL are both more susceptible to native budworm than NLL is. There are also differences in susceptibility to some pests between cultivars within a species. Some Australian NLL cultivars are more susceptible to aphid damage than others, and the YL cultivar Wodjil is also extremely sensitive to aphids. Correct agronomy can help reduce damage from some pests: planting lupin after pasture increases the chance of damage from red-legged earth mite and lucerne flea, which multiply on pasture plants. Deep sowing predisposes lupin to damage from bean root maggot, and taking measures to ensure rapid canopy closure reduces aphid damage.

Harvesting Lupin is harvested with the same machinery (combine harvesters) as cereals. In Australia, this is usually done when the seed is at 14% moisture or drier, but in Europe, crop maturity can be slow and sometimes lupin is harvested with moisture as high as 30% (Figure 8). Obviously, this grain needs drying before storage. Lupin is sometimes desiccated with diquat in Europe to hasten maturity, but care must be taken that seed growth is sufficiently complete, or the grain may begin to rot in the pod. Desiccation with glyphosate has led to loss of seed viability in Australia. Harvesting losses are usually greater in lupin than in cereals. Lupin pods are very brittle when dry, and pod-bearing lateral branches must often be cut a long way below the pods. The

238 Table 3

AGRONOMY OF GRAIN GROWING | Lupin: Agronomy Invertebrate pests of lupin

Common name Seedling pests Cutworm Brown pasture looper Wireworm Bean seedling maggot or bean root maggot Red-legged earth mite Blue oat mite Balaustium mite Clover mite Lucerne flea Slugs

Snails

Scientific name

Type of damage

Where a pest

Agrotis spp. Ciampa aritaria Agriotes spp. Delia platura

Feeding on emerged seedlings

Australia Australia Europe Australia and Europe Australia Australia Australia Australia Australia Australia and Europe Australia Europe Australia

Halotydeus destructor Penthaleus spp. Balaustium medicagoense Bryobia praetiosa Sminthurus viridis Deroceras reticulatum Milax gagates Arion hortensis Cochlicella barbara

Feeding on root and hypocotyl of emerging seedlings Feeding on emerged seedlings

Feeding on emerged seedlings, or contaminating grain at harvest

Cernuella virgata Theba pisana Vegetative and reproductive pests Green peach aphid Blue green aphid Cowpea aphid Lupin aphid Thrips Native budworm Lucerne seed web moth Mirid bugs

Myzus persicae Acyrthosiphon kondoi Aphis craccivora Macrosiphum albifrons Frankliniella occidentalis Thrips angusticeps Helicoverpa punctigera syn. Heliothis punctigera Etiella behrii Lygus spp.

Figure 8 Narrow-leafed lupin ready for harvest. Photograph taken by R.J. French.

shaking induced by the cutter bar is an important source of pod loss. Such losses are smaller in restricted-branching cultivars, because they have shorter branches, and can also be minimized by fitting harvesters with double-density knife guards. Another source of loss is the large bulk of awkwardly shaped material that will overflow from the front if not taken into the harvester quickly enough. A number of modifications have been devised to improve crop flow from the front and reduce the chance of

Australia Australia Feeding on growing point and flowers

Feeding on pods and seeds

Australia Australia Australia Europe Australia Europe Australia

Feeding on young pods

Australia Europe

Feeding on flower buds and leaves

blockages. These include increasing the knife to auger distance, belt fronts, air systems, which blow material from the cutter bar to the auger, and modifications to the table auger itself. Lupin grain is fragile compared to cereals and must be treated gently, especially if it is to be used for seed. The drum or rotor speed should be as low as possible and the concave closed only enough to ensure pods are threshed. Harvesting in the early morning or at night reduces the amount of seed damage. It also reduces shattering losses as pods and stems are tougher in the more humid atmosphere. If it is to be kept for seed, grain should be handled as little as possible after harvest, to prevent further mechanical damage. In Australia, though, any contaminating green material from wild radish should be removed promptly. Green pods of this weed release toxic isothiocyanates that can dramatically reduce germination percentage.


• • • • •

Which lupin species accounts for the bulk of the world’s production? List some ways lupin contributes to the overall productivity of cropping systems. When should lupin be planted and why? What are the advantages of dense lupin crops? What is necessary for lupin to effectively fix atmospheric nitrogen?


• •

List some nonchemical means of weed control that can be used in lupin. How would you protect a lupin crop from the disease anthracnose?


• • •

How can lupin sowing time be managed in the various production regions of the world to optimize productivity while minimizing environmental risks? Can high levels of cereal productivity be maintained without using break crops like lupin? Is a cropping system based on lupin possible without using selective herbicides?

See also: Breeding of Grains: Lupin: Breeding, Non-food Products from Grains: Cereal Grains as Animal Feed, Proteins: Nitrogen in Grain Production Systems, The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview, Lupin: Overview; The Basics: Taxonomic Classification of Grain Species.

Further Reading Biddle AJ (2008) Spring lupins in UK agriculture—experiences and challenges. In: Palta JA and Berger JB (eds.) Lupins for Health and Wealth, Proceedings of the 12th International Lupin Conference, 14–18 September 2008, Fremantle, Western Australia: International Lupin Association, 7 pp. Bolland MDA, Paynter BH, and Baker MJ (1989) Increasing phosphorus concentration in lupin seed increases grain yields on phosphorus deficient soil. Aust. J. Exp. Agric. 29: 797–801. Brennan RF (1999) Lupin grain yields and fertiliser effectiveness are increased by banding manganese below the seed. Aust. J. Exp. Agric. 39: 595–603. French RJ (2008) Agronomy influences competition between lupins and weeds. In: Palta JA and Berger JB (eds.) Lupins for Health and Wealth, Proceedings of the 12th International Lupin Conference, 14–18 September 2008, Fremantle, Western Australia: International Lupin Association, 15 pp.

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French RJ and Buirchell BJ (2005) Lupin: the largest grain legume crop in Western Australia, its adaptation and improvement through plant breeding. Aust. J. Agric. Res. 56: 1169–1180. French RJ and D’Antuono MF (2003) Matching lupin cultivar to environment in Western Australia. In: Unkovich M and O’Leary G (eds.) Solutions for a Better Environment, Proceedings of the 11th Australian Agronomy Conference, 2–6 February 2003 Geelong: Australian Society of Agronomy. French RJ and Harries M (2006) A role for wide rows for lupin cultivation in Western Australia. In: Turner N and Acuna T (eds.) Ground-Breaking Stuff. Proceedings of the 13th Australian Agronomy Conference, 10–14 September 2006, Perth: Australian Society of Agronomy. French RJ, McCarthy K, and Smart WL (1994) Optimum plant population densities for lupin (Lupinus angustifolius L.) in the wheatbelt of Western Australia. Aust. J. Exp. Agric. 34: 491–497. Heenan DP, Taylor AC, Cullis BR, and Lill WJ (1994) Long term effects of rotation, tillage and stubble management on wheat production in southern N.S.W. Aust. J. Agric. Res. 45(1): 93–117. Jarvis RJ and Bolland MDA (1991) Lupin grain yields and fertiliser effectiveness are increased by banding superphosphate below the seed. Aust. J. Exp. Agric. 31: 357–366. Julier B, Huyghe C, Papineau J, Milford GFJ, Day JM, Billot C, and Mangin P (1993) Seed yield and yield stability of determinate and indeterminate autumn-sown white lupins (Lupinus albus) grown at different locations in France and the UK. J. Agric. Sci. 121: 177–186. Leach JE, Stevenson HJ, Scott T, and Milford GFJ (1997) The effect of soil freezing on the survival of winter-sown white lupins (Lupinus albus L.). Ann. Appl. Biol. 130(3): 561–567. Milford GFJ, Shield IF, Siddons PA, Jones RJA, and Huyghe C (1996) Simple physiological models of plant development for the white lupin (Lupinus albus) and their use in agricultural practice. Asp. Appl. Biol. 46: 119–123. Seymour M, Kirkegaard JA, Peoples MB, White PF, and French RJ (2012) Break-crop benefits to wheat in Western Australia-insights from over three decades of research. Crop Pasture Sci. 63(1): 1–16. Shield I, Stevenson HJ, Leach JE, Scott T, Day JM, and Milford GFJ (1996) Effects of sowing date and planting density on the structure and yield of autumn-sown, florally determinate white lupins (Lupinus albus) in the United Kingdom. J. Agric. Sci. 127: 183–191. White, P., French, R., McLarty, A. (Eds.), 2008. Producing lupins. Bulletin 4720. Department of Agriculture and Food, Western Australia, Perth. p. 168. http://archive. agric.wa.gov.au/objtwr/imported_assets/content/fcp/lp/lup/lupins/lupin% 20bulletin%20v10-lr.pdf (accessed 01.10.2014.).

Field Pea: Agronomy RJ French, The University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Pea is grown as a component of cropping systems throughout the world. Cereals and oilseeds grown after pea often yield more than when grown after other crops. The optimum sowing time for pea is determined by soil temperature in parts of Europe and North America and by rainfall patterns in other parts of Europe and Australia. Disease pressure also influences sowing time in Australia. Pea fixes N from the atmosphere in symbiosis with Rhizobium bacteria that can contribute to the productivity of following crops. Good weed management is important for successful pea crops and contributes to the role of field pea in cropping systems. Ascochyta blight is an important pea disease that must largely be managed agronomically because there is little varietal resistance.

Learning Objective

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To achieve understanding of the role pea plays in a diverse range of world cropping systems and of the key aspects of pea crop management and how that varies between world pea production regions.

Introduction Pea (Pisum sativum L.) is commonly grown in temperate areas of all continents. It has many uses: immature pods and seeds are used as green vegetables, either fresh or frozen; it is used as green forage for grazing animals, in situ or as hay or silage; and it is grown for its mature seed, which itself has many uses. Growing pea for its mature seed is the focus of this article. Pea grown for grain is known variously as field pea, dry pea, combining pea, or protein pea (French pois proteágineux). This article describes the types of cropping systems that field pea forms part of, how it contributes to them, and the special agronomic requirements it has. It also describes current agronomic practice with field pea.

The Role of Field Pea in Cropping Systems Field pea is invariably grown as a component of a cropping system, and its interaction with other crops is an important consideration in a farmer’s decision to grow it. Often, field pea will not yield as well or be as profitable as other crops such as wheat, barley, or canola when considered in isolation. However, substantial yield responses are commonly, although

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not always, observed in crops following pea, so they can be beneficial when considered in a system context. In Western Australia, there has been a report that wheat after field pea yielded 450 kg ha1 more than wheat after wheat on average, and similar responses have been observed in a range of cereals in North America and Europe. Grain quality, for example, protein content, is often improved after pea as well. In Australia, North America, and Europe, field pea is usually grown in rotation with temperate cereals or oilseeds, but other systems are common elsewhere. Indian cropping systems using field pea include sequential systems such as rice–pulse, where the pulse may be field pea; intercropping systems such as growing a short duration pulse, which may be field pea, in between rows of autumn planted sugar cane; and relay cropping systems where seed of a pulse may be sown into a standing rice crop 2–3 weeks before it is harvested. This allows two crops to be grown in 1 year instead of one, as is usual in temperate cropping systems. There are several ways field pea can raise the yield of other crops in the sequence. The most obvious is by fixing atmospheric N, some of which is left in the soil for subsequent crops and by not taking up as much mineral N already present in the soil. The amount of N fixed varies between environments, but estimates in Australia and North America range from close to zero to nearly 200 kg N ha1. Much of this N is removed in harvested pea grain, so pea must fix at least 35 kg N ha1 before it adds N to the cropping system in Australia and at least 68 kg ha1 in Canada. Often, crops grown after pea require less N fertilizer, but this is not necessarily true if pea raises yield potential by other means. These other means include not hosting diseases of other crops so that inoculum levels are depleted, leaving residual water in the soil that can be used by the next crop by virtue of its shallow root system and allowing more flexible weed management. The details of this flexibility are dealt with later in this article, but a French example of the benefits to the cropping system is shown in Table 1. In a region where the weed black grass (Alopecurus myosuroides Huds.) had developed resistance to a range of selective herbicides, growing spring pea instead of the more profitable winter cereals allowed nonselective control of weeds germinating in late autumn and early winter. This gave better subsequent winter wheat yields and a more profitable rotation overall. Despite these benefits, farmers are wary of growing pea in many parts of the world. Pea usually yields less grain than wheat or barley so is not generally as profitable in its own right. The pea production declines that have occurred in Europe and Australia over the past decade have been largely because there are other break crops that confer many of the same system benefits as pea but are more profitable, such as potatoes, sugar beet, and oilseed rape in Europe and canola in Australia. Farmers are also concerned by greater yield variability, poor competitiveness with weeds, harvesting difficulties,


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Table 1 Productivity and profitability of a rotation based on spring pea on the management of herbicide-resistant black grass (Alopecurus myosuroides Huds.) Rotation Continuous winter wheatb Spring barley–spring pea–winter wheatb

Black grass population, 1999 (plants m2)

Winter wheat yield, 1998–99 (t ha1)

Direct margina, 1996–99 (Euros)

13.0 3.4

6.4 7.9

407.0 604.4

a

Direct margin was defined as gross income minus protection costs, tillage costs, and crop seed costs and was calculated over the whole life of the experiment. Rotations compared over three seasons (1996–97, 1997–98, and 1998–99) on a site where black grass had developed resistance to aryloxyphenoxypropionate herbicides after 13 winter crops in 16 years and 7 applications of fenoxaprop-P-ethyl or clodinafop-propargyl in the last 6 years. Figures for the winter crop rotation are averaged over three cultural strategies differing mainly in intensity of herbicide use, and figures for the spring crop rotation are averaged over four strategies. Source: Chauvel B, Guillemin JP, Colbach N, Gasquez J (2001) Evaluation of cropping systems for management of herbicide-resistant populations of blackgrass (Alopecurus myosuroides Huds.). Crop Protection 20: 127–137.

b

Table 2

Water use efficiency of a number of grain legume species in North America and Australia Water use efficiency (kg ha1 mm1) North America a

Pea Chickpea Lentil Soybean Dry bean Faba bean Lupin (Lupinus albus)

Saskatchewan

Northern Great Plainsb

North Dakotac

11.3 6.6 6.2

8.5(29) 6.2(24) 4.8(30) 3.4(11) 2.9(15)

9.8(3)

Australia Southwest Western Australiad 10.4(4) 5.7(3) 4.5(3)

3.0(3) 5.1(3) 10.8(4) 6.7(4)

a

Data from Cutforth HW, et al. (2002) Canadian Journal of Plant Science 82: 681–686. Data from Miller PR, et al. (2002) Agronomy Journal 94: 261–272. c Data from Anderson RL, et al. (2003) Agricultural Water Management 58: 255–266. d Data from Siddique KHM, et al. (2001) European Journal of Agronomy 15: 267–280. b

and, in some parts of Europe, damage caused by pigeons or excessive nitrate leaching into groundwater. Some of these problems also apply to other break crops.

Adaptation of Pea Soils Pea is best suited to sandy loam and clay loam soils with neutral pH. It will, however, grow on a more diverse range of soils than other grain legumes. For example, in Australia, it can be grown successfully on soils with pH ranging from 4.5 to 9.0 (measured in a 1:5 soil extract in 0.01 M CaCl2), although lupin is better adapted at the acid end, and lentil at the alkaline end, of this spectrum. Pea is not so well suited to very sandy soils, on which premature water deficits can develop as a consequence of its shallow root system. In environments with long dry periods after harvest, fragile pea stubbles on sandy soils are also at great risk from wind erosion. Pea is not well suited to soils susceptible to waterlogging or to compacted soils.

Rainfall and Temperature Pea is one of the best adapted grain legume species for shortgrowing season environments. Vigorous early growth, early

flowering of most cultivars, and early maturity mean that in Mediterranean-type environments, a greater proportion of growth occurs under cool, humid conditions, and therefore, water-use efficiency is higher than in species like lupin and chickpea. This applies both to spring-sown crops in North America and winter-sown crops in Australia (Table 2), and this means that in very dry seasons, pea will produce at least some grain, while other grain legumes may produce none at all. However, it also limits the ability of pea to respond to better growing conditions, so pea yield is often more stable across seasons than the yield of other grain legumes (Figure 1). However, pea does not tolerate tissue water deficit well so it is not so well adapted to environments where it does not rain during the growing season, such as in rotation with rice in India. Pea can also suffer flower and pod loss from both low temperature (frost) and high temperature during reproductive growth.

Growing a Pea Crop Cultivar Choice There is considerable diversity among pea cultivars. Initially, the type of pea to be grown must be chosen – whether white (yellow), blue (green), marrowfat, dun, or maple – and then, a

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4000 Species yield (kg ha-1)

Faba bean Narbon bean and common vetch Field pea Lathyrus cicera desi chickpea Lentil

3000

2000

1000

0 -1200

-800

-400

0

400

800

1200

1600

Mean corrected site yield (kg ha-1) Figure 1 Linear regressions of mean species yield against mean corrected site yield for 7 pulse species. Data are from 36 sites in Western Australia between 1994 and 1996. Adapted from Siddique KHM, Loss SP, Regan KL, and Jettner RL (1999) Adaptation and seed yield of cool season grain legumes in Mediterranean environments of south-western Australia. Australian Journal of Agricultural Research 50: 375–387, with permission.

cultivar among these types must be chosen. The type of pea will depend largely on market possibilities. Most peas produced in Europe and North America are white (yellow) or blue (green), and most peas in Australia are dun. Taking advantage of the higher prices for blue (green) or marrowfat peas requires more attention to grain quality than for other types. In particular, in dry environments, achieving large enough seed to satisfy market requirements is difficult. Descriptions of locally relevant cultivars can be found in local extension literature. Great improvements have been made in the standing ability of pea cultivars over the past 30 years. This is due to improvements in stem strength, shorter internodes, and use of the semileafless or afila character. Semileafless pea has more interlocking tendrils than conventional leafed plants and therefore forms a more rigid canopy framework than conventional pea. These canopies are better able to withstand the wind-imposed shearing forces that normally cause pea canopies to lodge. Nearly all European and North American pea cultivars are semileafless, and semileafless cultivars with improved stem strength have become dominant in Australia over the past decade. Another important criterion for cultivar choice is disease tolerance. There are cultivars resistant to powdery mildew (Peronospora viciae), downy mildew (Erysiphe pisi f. sp. pisi), bacterial blight (Pseudomonas syringae pv. pisi and pv. syringae), Fusarium wilt (Fusarium oxysporum), and several virus diseases. Breeders around the world are also devoting considerable effort to improving tolerance to Ascochyta and Mycosphaerella, but progress has been limited to date.

Sowing Time In the Mediterranean environments of southern Europe and southern Australia, sowing time is determined by rainfall pattern, although in Australia, it is further complicated by the need to avoid Mycosphaerella blight. In northern Europe and the Great Plains of North America, avoiding the cold winter is also important. In Mediterranean environments, hot, dry summers are followed by cool, moist winters. Spring becomes progressively

hotter and drier. Annual crops like pea are sown in late autumn or early winter, grow over winter and spring, and mature in late spring or early summer. Sowing crops as soon as the soil is moist enough to support plant growth enables it to achieve most of its growth under cool humid conditions conducive to high water-use efficiency and maximizing the length of the growing season. It also allows grain filling to occur under cooler, moister conditions because early-sown crops flower earlier than late-sown crops. In Australia, pea is usually sown later than other annual crops. Its early maturity relative to other crops means that it does not lose yield as quickly when sowing is delayed, but the real purpose is to reduce Mycosphaerella infection. This is discussed further in the succeeding text. Delaying sowing also has weed management benefits, which are also discussed in the succeeding text. Where soils freeze in winter, sowing must be delayed until the soil is warm enough for germination – at least 5 C. There are winter cultivars whose seedlings survive a certain amount of freezing after autumn sowing. Some of these are grown in France, but spring pea is more common. Sowing as soon as the soil is warm enough maximizes yield potential for the same reasons that early sowing does in Mediterranean environments. However, sowing too early can expose young seedlings to frost damage. If the aboveground parts of the seedling are killed, new shoots regenerate from subsurface axillary buds. In Canada, an early-sown, frosted but regenerated crop often has as good a yield potential as a late-sown unfrosted crop. In the United Kingdom, waiting until soils are dry enough to avoid compaction is an important consideration. Early sowing also increases the risk of frost during early pod growth. This can devastate yields. Frost damage during pod growth also occurs in Mediterranean environments, but in Australia, spring frosts are sufficiently unpredictable to have only a minor bearing on sowing time decisions.

Sowing Management Traditionally, pea was sown into cultivated seedbeds. This is still the norm in the United Kingdom, but pea yield can be higher when sown into undisturbed soil, especially in dry

AGRONOMY OF GRAIN GROWING | Field Pea: Agronomy environments. Pea is increasingly being sown under minimum or no-tillage farming systems in North America and Australia, often into standing cereal stubble. This reduces the risk of soil erosion from both wind and water, reduces the degradation of soil structure resulting from excessive cultivation, and avoids mixing weed seeds through the top 15 cm of soil, which can lead to more late-germinating weeds in the crop. Retention of standing stubble can improve crop water relations by trapping snow in the preceding winter, which adds to soil moisture storage in North America and reducing evaporation from the soil surface by creating a thicker boundary layer. Standing stubble can also provide extra support to pea plants, which facilitates harvesting, but may delay spring sowing by retarding soil warming. Pea should be sown 3–8 cm deep. Sowing at the shallow end of this range is an advantage for very early spring sowing into cold soil, but deeper sowing is preferable in environments where the soil surface dries rapidly. Larger-seeded varieties are better able to emerge from deeper sowing depths. Crop damage from soil-applied herbicides is less with deep sowing. Pea grain yield increases with increasing plant density when densities are low, but the rate of increase gradually declines until yield reaches a plateau or even begins to decline (Figure 2). Simplistic analyses of this response choose the density at maximum yield as the target that farmers should aim for, but the greater cost of seed compared to the grain produced means that the true economic optimum occurs at a lower density. As seed cost varies between varieties and value of grain between different seed types, economic optimum density will vary from variety to variety. Growth vigor and yield potential will influence optimum density. However, grain yield is not the only criterion used to make plant density recommendations. Generally, it is better to err on the high side rather than the low side because dense crops compete better with weeds than thin crops and have more interplant connections via tendrils, thus forming a more rigid canopy, which will better resist lodging. Dense canopies facilitate harvesting of prostrate conventional leaved cultivars too because, even though they invariably lodge, their interplant connections aid crop feeding

6000

Seed yield (kg ha–1)

5000 4000 3000

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into the harvester. Recommended target densities from various parts of the world are given in Table 3. The necessary seed rate to establish the target density depends on seed size, percentage germination, and seedbed losses. In the United Kingdom, the following formula is recommended for calculating seed rates, and similar formulas are used elsewhere: Seed rate kg ha1 ¼

thousand seed weight ðgÞ target plant population ðplants m2 Þ 100 % germination ð100 field loss ð%ÞÞ

Seedbed losses in Europe are greater with very early sowing when the soil is cold: UK growers expect losses as high as 15–18% for February sowing, but only 7–8% for April sowing. In Australia, seedbed losses are generally less than 10% and are often ignored in seed rate calculations. Using the seed rate formula requires knowledge of the thousand seed weight and germination percentage, for which each seed lot must be tested. In Canada and the United Kingdom, an electrolyte leakage, or electrical conductivity (EC), test is available for seed vigor. This is related to the number of microscopic cracks in the seed coat, resulting from mechanical damage at harvest. These cracks allow substances that can stimulate pathogen growth to leak from the seed into the surrounding soil. Only the highest vigor seed (lowest EC value) should be used for early sowing into cold soil, but less vigorous seed may be suitable for later sowing. Dry pea seed is susceptible to mechanical damage, so handling should be minimized, and air seeder fan speed should be low to minimize seed bounce. In Canada, seed is sometimes moisturized prior to sowing to make it less fragile. The soil surface should be left as level and even as possible after sowing and free from stones, stumps, and other obstacles that could interfere with harvesting. This is not only especially important with conventionally leaved cultivars that are prostrate at harvest but also applies to modern, erect, cultivars that still sometimes lodge. Rolling pea crops after sowing helps by pushing rocks under the surface and crushing soil clods that might otherwise damage harvesting machinery. In some cases, heavy rubber-tired or steel rollers are towed behind sowing machinery, but in Australia and Canada, pea is often rolled after emergence without significant damage up until plants are about 15 cm high. Rolling before emergence is preferable because a rolled crop must be allowed to recover before any postemergent herbicides are applied and is the norm in the United Kingdom. Rolling when the crop is emerging should be avoided because emerging seedlings are very fragile.

2000

Crop Nutrition

1000

Nitrogen (N) 0 0

100 50 Crop density (plants m–2)

150

Figure 2 Grain yield response of field pea cv. Swing to plant population density at seven locations in Saskatchewan, Canada, in 2001. Open squares, swift current, lowest yielding site; closed squares, outlook, highest yielding site; triangles, average of seven sites. Adapted from Johnston AM, et al. (2002) Canadian Journal of Plant Science 82: 639–644, with permission.

Pea requires the same plant nutrients as other crops, but, as it is a legume, there is usually no need for N fertilizer if the crop is well nodulated. Pea forms root nodule symbioses with Rhizobium leguminosarum bv. viciae, which also forms symbioses with a number of other agriculturally important legumes, including faba bean, lentil, and vetch. This is not the same species that infects clover, medic, lupin, or chickpea roots. In Europe, R. leguminosarum bv. viciae is widely distributed in agricultural soils, so good nodulation can be achieved

244 Table 3

AGRONOMY OF GRAIN GROWING | Field Pea: Agronomy Recommended target plant densities in selected pea-growing regions of the world

Country a

United Kingdom

Canada (Saskatchewan)b Australia (New South Wales)c Australia (Western Australia)d

Target plant density (plants m2)

Other specific information

65–70 70 110 75–85 30 35–50 45 55

Vigorous marrowfats Large blues and whites Early maturing small blues (04) Tall conventional types or early sowing Short semileafless types or late sowing Tall conventional leafy types Semileafless and semidwarf types

a

Data from Processors and Growers Research Organisation (2014) PGRO Pulse Agronomy Guide. http://www.pgro.org/images/site/docs/PGRO-AGRONOMY-GUIDE-2014.pdf (accessed 13.11.14). b Data from Saskatchewan Pulse Growers (2011) Pea production manual. http://www.saskpulse.com/uploads/content/111207_FINAL_Pea_Manual.pdf (accessed 13.11.14). c Data from Jenkins L, et al. (2005) Field Pea: Western New South Wales Planting Guide. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/157507/field-pea-western-NSWplanting-guide.pdf (accessed 21.11.14). d Data from Pritchard I (2013) Field Pea: Crop Management and Production. https://www.agric.wa.gov.au/field-pea-crop-management-and-production (accessed 21.11.14).

without seed inoculation. It is not native to North American or Australian soils, where seed should be inoculated if pea has not been grown before. Trials in Australia show that inoculation can more than double grain yield under such circumstances. R. leguminosarum bv. viciae is not particularly acid-tolerant so does not survive as well in acid as in alkaline soils, and it does not survive so well in environments with very hot, dry summers. The efficiency with which Rhizobium fixes N can also deteriorate as a consequence of surviving in soil under stressful conditions. In Australia, it is recommended that all pea crops be inoculated if sown on soils with surface pH of 6, whether or not pea has been grown previously, and inoculation is recommended for all pea crops in Canada. Inoculum has traditionally been applied to seed as a slurry of peat-based culture in water or a methyl-cellulose solution (this aids adhesion to the seed), but more recently, granular inocula on various carriers have been developed. These are placed in the seedbed at sowing rather than applied to the seed beforehand. The granular inocula have a longer shelf life than peat-based cultures, which must be refrigerated in storage. Seed-applied inocula also have the disadvantage of having to be applied to the seed within a few days, ideally a few hours, of sowing since the bacteria do not survive long on the seed surface. Fungicide seed dressings can be toxic to rhizobium on the seed, and large nodulation and yield reductions are possible. Recent Canadian research has shown that soil-applied granular inocula are more effective on pea than inocula applied to the seed, but Australian research shows that the granular carrier can have a large influence on inoculum effectiveness, with peat and attapulgite granules being better than bentonite granules. While there is generally no need to use N fertilizer on pea, small amounts can be beneficial under certain circumstances. Pea seedlings depend on soil N before effective nodules form, and in both Canada and Australia, 5–20 kg ha1 of starter N is recommended on soils with very low mineral N. Fertilizer N is not necessary in the United Kingdom. Effective nodules are slower to form in acid soils, and starter N can be helpful even when mineral N levels are relatively high. Higher rates of N can suppress N fixation and, in Canada, delay crop maturity and promote disease and lodging.

Table 4 pea grain

Average amount of plant nutrients removed by 1 tonne of

Nutrient

Quantity removed in 1 tonne grain

Nitrogen (kg) Potassium (kg) Phosphorus (kg) Sulfur (kg) Magnesium (kg) Calcium (kg) Iron (g) Zinc (g) Manganese (g) Copper (g)

37 9.1 4 2 1.2 0.9 59 26 20 7

Source: Petterson DS, et al. (1997) The Chemical Composition and Nutritive Value of Australian Pulses, pp. 64. Kingston, ACT: Grains Research and Development Corporation; Hickling D (ed.) (1997) Canadian Peas Feed Industry Guide, p. 21. Winnipeg, MB: Canadian Special Crops Association/Regina, SK: Western Canada Pulse Growers Association.

Phosphorus (P) Many soils on which pea is grown are P-deficient, especially in their native state. Furthermore, much phosphate applied to soils is immobilized in insoluble forms before plants can use it. Many European soils have been farmed for a long time, so their capacity to immobilize P is close to saturated, and here, P fertilization is basically replacing what is removed in grain. So, in soils in the United Kingdom with slightly low to medium P levels (ADAS soil index 2), 40 kg ha1 P2O5 is recommended for pea crops with 4 t ha1 yield potential. This is equivalent to 18 kg ha1 P for a crop removing 16 kg ha1 P (Table 4). No P fertilizer is recommended for soils with better P status. In North America and Australia, more P is usually necessary. The appropriate rate depends on soil P content, which is determined by soil analysis, and recommendations are based on locally developed calibrations. 20 kg ha1 P (45 kg ha1 P2O5) is a typical application rate, but higher rates are necessary on some soils. P fertilizer placement can be important. In the United Kingdom, it is often broadcast and then incorporated by

AGRONOMY OF GRAIN GROWING | Field Pea: Agronomy plowing. In Australia and Canada, it is usually drilled into the soil as part of the seeding operation. Placement with the seed can cause seedling losses, especially when it is applied as fertilizer also containing N such as monoammonium phosphate. In Australia, P fertilizer is sometimes placed up to 5 cm below the seed; this has the advantage that it remains in moist soil, and therefore available to the plant, for longer at the end of the growing season. In Canada, banding P fertilizer to the side of the seed row results in less seed toxicity and usually better yield responses.

Potassium (K) and sulfur (S) Pea grain contains considerable amounts of K and S (Table 4), and pea requires more of these nutrients than do cereals. The need for K is also diagnosed by soil analysis, and in Europe, K deficiency can be more significant than P deficiency. In Australia, many soils naturally contain sufficient K so no more needs to be added. This is especially true of the heavier-textured soils where pea is usually grown but will change in the future as native reserves of K are depleted and higher yielding cultivars with higher K requirements are adopted. K fertilizers are very soluble in water, and high rates can have adverse osmotic effects on germination if drilled with the seed. K fertilizer is banded a few centimeters below or beside the seed, or broadcast, to avoid this. Its high solubility means broadcast fertilizer is rapidly leached into the crop’s root zone by winter rains.

Micronutrients The most commonly deficient micronutrients are manganese (Mn), zinc (Zn), and molybdenum (Mo). Mn deficiency causes a disorder known as marsh spot and can occur in all peagrowing regions. It is more common in Europe than elsewhere. It can be managed by a foliar spray of MnSO4 when symptoms first appear. Zn deficiency is most common in Australia. Both Mn and Zn are less available on alkaline soils, so deficiencies can be induced by excessive liming. Mo is less available on acid

245

soils, so liming can correct a deficiency. In general, if micronutrient levels are adequate for cereals, they should also be adequate for pea. Soil tests have been developed for micronutrients, but regular tissue testing of crops is the best way to diagnose developing deficiencies.

Weed Management Pea is one of the least competitive crops against weeds, and weed control in a pea crop can be troublesome. Herbicides are almost essential for producing a good crop, and the modern trend to reduce tillage has increased reliance on herbicides. Fortunately, more herbicides can be used on pea than on any other grain legume: there are currently (2014) 336 herbicide products registered for use on combining pea in the United Kingdom (many of them have the same active ingredient though: 166 of them contain glyphosate). Weed spectrum and farming system vary enormously between the world’s pea-growing regions, so only general principles will be outlined here. Regional literature should be consulted for details on specific herbicides and weeds. The potential weed burden should be reduced as much as possible before the crop is sown. This fits well with the practice of delaying sowing in Australia to reduce disease severity, as the delay gives annual weeds time to germinate and still be controlled by cultivation or nonselective herbicide such as glyphosate before the crop is sown. The same applies to autumn and winter germinating weeds with spring sowing in North America and Europe. However, it is likely that more weeds will germinate with the crop in both systems, and pre-emergent soil active herbicides are usually applied. Postemergent herbicides are also often necessary. They should be applied as early as is consistent with allowing weeds time to germinate. Early weed removal is important for maximizing grain yield (Figure 3). The weed species present and the growing environment determine how critical early removal is. Many postemergent

6000 Grain yield (kg/ha)

5000 4000 3000

1

2000

2

1000

3 Nil

0 0 9 9 9 9 0 0 9 0 9 0 00 99 99 00 99 99 00 99 00 99 00 t 2 rt 1 rt 2 ra 1 rs 1 rs 2 nt 1 nt 2 k 1 d 1 d 2 t o a a o e e rre rre fo lfo no tlo He He el e Sc dv dv a M M n C Re Re t Cu t Cu Ou an a if if di ndi In I Sw Sw 99

t ot

Sc

19

Figure 3 Effects of time of removal of weeds on pea grain yield at seven locations in Saskatchewan, Canada, in 1999 and 2000. Weeds were a combination of natural populations of grasses and broadleaved weeds and were removed with herbicide sprays 1, 2, 3, or 4 weeks after emergence or not at all (Nil). Drawn from data of May WE, Lafond GP, Johnson EN, et al. (2003) An assessment of the concept of early time of weed removal in field pea using natural weed populations. Canadian Journal of Plant Science 83: 423–431.

246


herbicides cause crop damage if applied at the wrong growth stage of the crop or if applied to a stressed crop. Rolling can cause enough stress for normally safe herbicides to cause unacceptable damage, and in Australia, it is recommended that no postemergent herbicides are applied within 2 weeks of rolling. In the United Kingdom, a leaf wax test is used to assess the safety of some herbicides. It involves dipping plants in a solution of the dye crystal violet and observing how much dye adheres to the leaves. The less that adheres, the more wax is on the leaves, and the safer it is to apply herbicide. Weeds germinating late in the life of the crop compete less strongly than early germinating weeds and have less effect on grain yield. However, to minimize weed seed carryover into the next phase of the rotation and to maximize the cropping system benefits of pea, they should be controlled. In Australia, ‘croptopping’ is commonly practiced. This involves spraying low rates of nonselective herbicide (usually paraquat) onto the maturing crop so that it disrupts maturation of weed seeds. Pea’s early maturity means that it is well suited to this practice, because the crop suffers little damage when weeds are at the right stage for maximum effect. Preharvest glyphosate sprays are also used to manage perennial weeds such as couch grass in the United Kingdom. Glyphosate cannot be used in this way in seed crops because it can reduce seed viability. Herbicide-resistant weeds are increasingly a problem in cropping systems containing pea, so nonherbicide methods of weed control should be used where possible and herbicide use should be managed to minimize resistance development. Tall varieties are more competitive than short varieties, although these are not suited to all growing environments, and higher density crops are also more competitive. Cultivation is useful, although it may be inconsistent with modern tillage systems. Systems have been developed in Australia to capture weed seed in chaff carts behind the harvester so it can be destroyed by burning or some other means and to pass weed seed through a mechanical ‘destructor’ so that it is no longer viable when returned to the soil.

Disease Management Pea is subject to many diseases. The most important fungal and bacterial diseases are described in Table 5. Pea is also affected by a large number of virus diseases, including alfalfa mosaic virus, bean leaf roll virus, bean yellow mosaic virus, cucumber mosaic virus, pea enation mosaic virus, and pea seed-borne mosaic virus. Management consists of using virus-free seed (many viruses are seed-borne), discouraging aphids (which spread many of these viruses within a crop), and using resistant cultivars. This article briefly describes some agronomic considerations in Ascochyta/Mycosphaerella blight management, but for other diseases, readers should refer to references provided.

Ascochyta/Mycosphaerella Blight or Black Spot This disease is found in all pea-producing areas of the world and can cause in excess of 75% yield loss. It is caused by a complex of three fungi – Ascochyta pisi, Mycosphaerella pinodes, and Phoma pinodella – and symptoms included leaf, stem, and pod spotting, and foot rot. M. pinodes is the most widespread of the causal organisms and the most damaging.

The causal fungi can be spread on the seed, but seed transmission is a minor source of infection in areas where pea is established compared to spores released from the residue of previous crops. These spores can be carried several kilometers by wind, and once a crop is infected, current lesions act as a secondary source of spores for further spread. M. pinodes and Phoma pinodella can also survive in soil. Management of the disease begins with trying to minimize the risk of infection rather than controlling an infection that has begun. Seed can be tested for infection and treated with fungicide if excessive levels are found. Seed-borne infection will only be a significant source of infection in areas where pea is not commonly grown. Different pea-growing regions have different threshold infection levels at which seed treatment becomes worthwhile. Crop rotation is an important tool in reducing infection from old crop residues. In most peagrowing regions, it is recommended that pea not be grown more often than once every 4 or 5 years. In Australia, it is also recommended that pea crops are no closer than 500 m to stubbles from any of the previous year’s crops to reduce infection from spores carried on the wind. In Australia, delayed sowing reduces infection risk and plays an important role in black spot management. Fungal fruiting bodies begin developing when old crop residues are wet by rain or dew at a rate that depends on temperature and begin releasing spores at a gradually declining rate when they mature. In Australia, this means that maximum spore release rates often occur in autumn when crops are being sown, but by early winter, spore release declines and crops sown then develop little infection (Figure 4). However, the pattern of spore release can vary greatly between years and locations depending on rainfall and temperature, and sometimes, it is quite safe to plant early. In Western Australia, a computer model has been developed that takes all these factors into account and, when the locations of previous pea crops in an area and local weather data are provided, produces maps of black spot risk for different sowing times. Foliar fungicides can give effective control, but grain yield responses are not usually reliable enough to make them economically viable in Australia. Guidelines have been developed in Canada for deciding whether to apply foliar fungicides; they are based on crop canopy development, leaf wetness, plant symptom development, and whether rain is forecast in the next 5 days. There are also significant differences between cultivars in their susceptibility to Ascochyta and Mycosphaerella, but all existing cultivars suffer appreciable damage. Nevertheless, understanding of the genetics of tolerance to this disease is improving rapidly, and eventually, good resistance should become available.

Invertebrate Pest Management Pea is subject to many invertebrate pests, including insects, arthropods, and nematodes. The most significant pests vary between pea-growing regions. Some of the more important insect, mollusk, and arthropod pests are listed in Table 6. Effective chemical control is possible for most of these pests, but agronomic management also influences how serious a problem many of them become. The interested reader should

AGRONOMY OF GRAIN GROWING | Field Pea: Agronomy Table 5

247

Some of the more important fungal and bacterial diseases affecting pea

Disease

Causal organism

Type of damage

Occurrence

Management

Fungal diseases Damping off

Pythium spp.

Seed and seedling rot

All pea-growing regions

Aphanomyces root rot

Aphanomyces euteiches

Root rot

North America, Europe

Fusarium root rot

Fusarium solani f. sp. pisi


Black spot, Ascochyta or Mycosphaerella blight

Ascochyta pisi, Mycosphaerella pinodes, Phoma pinodella Peronospora viciae

Epicotyl, hypocotyl, and taproot rot Spotting or larger black lesions on leaves, stems and pods, foot rot Fluffy lesions on lower leaf surfaces, or severely stunted plants that die before flowering for systemic infection

Fungicide seed dressing Use high-vigor seed Avoid infested sites, rotation with oats Rotation

Downy mildew



Fungicide seed dressings, foliar fungicide, rotation, delayed sowing Resistant cultivars, fungicide seed dressings, rotation, destruction of infected residue from previous crops Resistant cultivars, foliar fungicide, rotation, destruction of infected residue from previous crops Rotation, avoid growing in rotation with canola or oilseed rape

Powdery mildew

Erysiphe pisi (syn. E. polygoni)

White powdery lesions on upper leaf surfaces that can spread to stems and pods


Sclerotinia white mold

Sclerotinia sclerotiorum


Fusarium wilt

Fusarium oxysporum f. sp. pisi

Plants wilt and rapidly die. Affected areas have a water-soaked appearance, and white fluffy growth may be seen, especially near soil surface Wilting and eventual death of plants

North America, Europe

Resistant cultivars, rotation

Pseudomonas syringae pv. pisi and Pseudomonas syringae pv. syringae

Water-soaked lesions on leaves, pods and stems that later become brown and necrotic


Resistant cultivars, plant uninfected seed

Bacterial diseases Bacterial blight

Source: Kraft JM and Pfleger FL (eds.) (2001) Compendium of Pea Diseases and Pests, 2nd edn., 67 pp. St. Paul, Minnesota: APS Press; Kaiser WJ, et al. (2000) Foliar diseases of cool season food legumes and their control. In: Knight R (ed.) Linking Research and Marketing Opportunities for Pulses in the 21st Century. In: Current Plant Science and Biotechnology in Agriculture, vol. 34, pp. 437–455. Dordrecht: Kluwer.

consult more specialized references given at the end of this article.

Harvesting Pea is harvested with the same machinery (combine harvesters) as cereals. Picking up and feeding a lodged crop into the harvester has traditionally been the biggest challenge. While erect semileafless cultivars have gone a long way to overcome this problem, attachments such as crop lifters, special pea pickup fronts, and flexible cutter bars usually make the job easier. Rolling after sowing also helps by removing obstacles such as stones and soil clods that can cause considerable machinery damage if picked up with the crop. Swathing is an alternative to direct harvesting. To maximize grain yield and quality, pea should be harvested at the right time. In Canada and Europe, this is when seed moisture is between 18% and 20%; in Australia, the recommended moisture content for harvest is 15%. It is likely that the

crop will have some green tips at this stage and perhaps some green pods as well. Grain harvested at this stage will need drying to avoid spoilage in storage. Often, this can be achieved simply by circulating dry external air through the grain in silos. If heat is used for drying, the temperature should not exceed 43–45 C when the moisture content is below 24%, and cooler temperatures should be used for higher moisture contents. Even earlier harvesting can result in an unacceptable level of immature seed in the sample, and later harvesting in more severe lodging and hence greater difficulty picking up the crop, more insect damage (especially from the pea weevil, Bruchus pisorum), more shattering losses, and greater mechanical damage to the grain. Late harvesting also increases the risk of cotyledon bleaching in blue (green) and marrowfat pea. Desiccating crops approaching physiological maturity with diquat or other desiccant can assist in achieving even maturation and in accelerating maturation late in the season in North America and Europe. Desiccating with glyphosate is not recommended for seed crops because it can reduce the viability of harvested seed.

75 1988

60

percentage stem area affected percentage yield loss

45 30 15 0 May

June Sowing date

July

Percentage stem area affected or percentage yield loss

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75 1989

60 45 30 15 0 May

June Sowing date

July

Figure 4 Effect of delaying sowing on percentage stem area of field pea affected by Ascochyta blight and percentage grain yield loss relative to plots kept disease-free by weekly fungicide sprays at Horsham, Victoria, Australia, in 1988 and 1989. Data are means for 15 pea cultivars. Drawn from data of Bretag TW, et al. (1995) Australian Journal of Experimental Agriculture 35: 531–536. Table 6

Some of the more important invertebrate pests affecting pea

Common name Seedling pests Wireworm

Cutworm and armyworm

Scientific name

Type of damage

Occurrence

Agriotes spp., Agrypnus spp., Ctenicera spp., Limonius spp., Melanotus spp., Pterocarpus spp. Agrotis spp., Apamea spp., Euxoa spp., Peridroma spp., Pseudaletia spp., Spodoptera spp. Halotydeus destructor Sminthurus viridis Delia platura Deroceras spp., Arion spp., Milax gagates

Feeding on seed and later on roots of emerged plants

North America, Europe, Australia

Feeding on emerged seedlings


Feeding on emerged seedlings Feeding on emerged seedlings Feeding on stem and root Feeding on leaves

Australia Australia Australia Europe, Australia

Feeding on leaves Feeding on leaves, contamination of grain Feeding on stems and petioles, also flowers, pods, and leaves Feeding on growing point Feeding on growing point Feeding on young leaves and growing points Feeding on leaves and root nodules

Europe, Australia Europe, Australia

Red-legged earth mite Lucerne flea Onion maggot Slugs Vegetative and reproductive pests Slugs Deroceras spp., Arion spp., Milax gagates Snails Helix spp. Pea aphid

Acyrthosiphon pisum

Blue-green aphid Cowpea aphid Thrips

Acyrthosiphon kondoi Aphis craccivora Thrips spp. and Frankliniella spp.

Pea leaf weevil (known in the United Kingdom as pea weevil) Reproductive pests Pea weevil

Sitona lineatus

Pea moth

Cydia nigricana

Native budworm

Helicoverpa punctigera syn. Heliothis punctigera

Lucerne seed web moth

Etiella behrii

Bruchus pisorum

Feeding on developing seed, which may continue after harvest Feeding on developing pods and seeds Feeding on leaves, pods, and seeds Feeding on developing seeds

All pea-growing regions Australia Australia All pea-growing regions North America and Europe

Most pea-growing regions, not the United Kingdom North America, Europe Australia Australia

Source: Kraft JM and Pfleger FL (eds.) (2001) Compendium of Pea Diseases and Pests, 2nd edn., 67 pp. St. Paul, MN: APS Press; Biddle AJ, et al. (1988) The Pea Growing Handbook, 6th edn., 264 pp. Peterborough: PGRO; Grains Research and Development Corporation (2013) Crop Insects: The Ute Guide. http://www.grdc.com.au/Resources/Ute-Guides/Insects (accessed 15.12.14); Grains Research and Development Corporation (2013) Slug Identification and Management. http://www.grdc.com.au/Resources/Factsheets/2013/03/Slugcontrol-identification-and-management (accessed 15.12.14).

Pea grain is fragile, especially at low moisture contents (below 14%). Luckily, it threshes easily, so the drum or rotor speed should be as low as possible and the concave closed only enough so that pods are threshed. Once it has been harvested, the seed should be handled as gently, and as

little, as possible to prevent further mechanical damage. Damage from too vigorous threshing and excessive handling includes not only split grain and reduced seed viability but also microscopic cracks in the seed coat, which reduce the vigor of viable seeds.



• • • • • • •

List ways in which pea contributes to cropping system productivity. What would you consider when choosing a pea variety to grow? How would you decide when to sow pea in different production environments? How would you decide how much pea seed to sow? How can you ensure that pea fixes N effectively? Why is weed management so critical to a successful pea crop? What needs to be considered when harvesting pea?


• • •

Develop a framework for deciding the most appropriate grain legume crop to grow in a particular environment. Ascochyta blight is the most damaging pea disease in many production regions. Why do the most suitable management and control strategies differ between regions? How might pea be managed for sustainable organic production?

See also: Agronomy of Grain Growing: Plants: Diseases and Pests; Grains Around the World: Grain Production and Consumption in Oceania: Australia and Pacific Countries; Grain Production and Consumption: Overview; The Basics: The Grain Crops: An Overview; The Legumes and Pseudocereals: Pea: Overview.

Further Reading Anonymous (2011) Pea Production Manual. Saskatoon: Saskatchewan Pulse Growers. Anonymous (2014a) PGRO Pulse Agronomy Guide. Peterborough: Processors and Growers Research Organisation. Anonymous (2014b) Pulse variety description table 2014 (Homepage of Saskatchewan Pulse Growers) (online). Available: http://www.saskpulse.com/uploads/content/ 140620_2014_Variety_Description_Table_-_FINAL_-_Revised_with_new_variety_ names.pdf (2014, November 21). Belford RK, Cannell RQ, Thomson RJ, and Dennis CW (1980) Effects of waterlogging at different stages of development on the growth and yield of peas (Pisum sativum L.). Journal of the Science of Food and Agriculture 31: 857–859. Bretag TW, Keane PJ, and Price TV (2006) The epidemiology and control of ascochyta blight in field peas. Australian Journal of Agricultural Research 57: 883–902. Carr PM, Martin GB, and Horsley RD (2009) Impact of tillage on field pea following spring wheat. Canadian Journal of Plant Science 89: 281–288. Chauvel B, Guillemin JP, Colbach N, and Gasquez J (2001) Evaluation of cropping systems for management of herbicide-resistant populations of blackgrass (Alopecurus myosuroides Huds.). Crop Protection 20: 127–137. Christen O and Sieling K (1995) Effect of different preceding crops and crop rotation on yield of winter oil-seed rape (Brassica napus L.). Journal of Agronomy and Crop Science 174(4): 265–271. Christen O, Sieling K, and Hanus H (1992) The effect of different preceding crops on the development, growth and yield of winter wheat. European Journal of Agronomy 1(1): 21–28. Clayton GW, Rice WA, Lupwayi NZ, et al. (2004a) Inoculant formulation and fertilizer nitrogen effects on field pea: Nodulation N2 fixation and nitrogen partitioning. Canadian Journal of Plant Science 84: 79–88. Clayton GW, Rice WA, Lupwayi NZ, et al. (2004b) Inoculant formulation and fertilizer nitrogen effects on field pea: Crop yield and seed quality. Canadian Journal of Plant Science 84(1): 89–96.

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Cutforth HW, McConkey BG, Ulrich D, Miller PR, and Angadi SV (2002) Yield and water use efficiency of pulses seeded directly into standing stubble in the semiarid Canadian prairie. Canadian Journal of Plant Science 82: 681–686. Denton MD, Pearce DJ, Ballard RA, et al. (2009) A multi-site field evaluation of granular inoculants for legume nodulation. Soil Biology and Biochemistry 41(12): 2508–2516. Drew EA, Denton MD, Sadras VO, and Ballard RA (2012) Agronomic and environmental drivers of population size and symbiotic performance of Rhizobium leguminosarum bv. viciae in Mediterranean-type environments. Crop and Pasture Science 63(5): 467–477. Evans J, Wallace C, Dobrowolski N, Pritchard I, and Sullivan B (1993) Requirement of field pea for inoculation with Rhizobium and lime pelleting in soils of Western Australia. Australian Journal of Experimental Agriculture 33: 767–773. Evans J, McNeill AM, Unkovich MS, Fettell NA, and Heenan DP (2001) Net nitrogen contribution for cool-season grain legume crops and contributions to wheat nitrogen uptake: A review. Australian Journal of Experimental Agriculture 41(3): 347–359. French RJ (2002) Soil factors influencing growth and yield of narrow-leafed lupin and field pea in Western Australia. Australian Journal of Agricultural Research 53: 217–225. Hebblethwaite PD and McGowan M (1980) The effects of soil compaction on the emergence, growth and yield of sugar beet and peas. Journal of the Science of Food and Agriculture 31: 1131–1142. Holland MR, Grace J, and Hedley CL (1991) Momentum absorption by dried-pea crops I. Field measurements over and within varieties of differing leaf structure. Agricultural and Forest Meteorology 54: 67–79. Karamanos RE, Flore NA, and Harapiak JT (2003) Response of field peas to phosphate fertilization. Canadian Journal of Plant Science 83: 283–289. Kirkegaard J, Christen O, Krupinsky J, and Layzell D (2008) Break crop benefits in temperate wheat production. Field Crops Research 107: 185–195. Lafond GP, May WE, Stevenson FC, and Derksen DA (2006) Effects of tillage systems and rotations on crop production for a thin Black Chernozem in the Canadian Prairies. Soil and Tillage Research 89: 232–245. Lemerle D, Verbeek B, and Coombes N (1995) Losses in grain yield of winter crops from Lolium rigidum competition depend on crop species, cultivar and season. Weed Research 35: 503–509. Leport L, Turner NC, French RJ, Tennant D, Thomson BD, and Siddique KHM (1998) Water relations, gas exchange and growth of cool-season grain legumes in a Mediterranean-type environment. European Journal of Agronomy 9: 295–303. Lin R and Chen C (2014) Tillage, crop rotation, and nitrogen management strategies for wheat in Central Montana. Agronomy Journal 106(2): 475–485. May WE, Lafond GP, Johnson EN, et al. (2003) An assessment of the concept of early time of weed removal in field pea using natural weed populations. Canadian Journal of Plant Science 83: 423–431. McDonald GK (2003) Competitiveness against grass weeds in field pea genotypes. Weed Research 43: 48–58. Miller PR, McConkey BG, Clayton GW, et al. (2002) Pulse crop adaptation in the Northern Great plains. Agronomy Journal 94: 261–272. Miller PR, Gan Y, McConkey BG, and McDonald CL (2003a) Pulse crops for the Northern Great Plains: II. Cropping sequence effects on cereal, oilseed, and pulse crops. Agronomy Journal 95: 980–986. Miller PR, Gan Y, McConkey BG, and McDonald CL (2003b) Pulse crops for the Northern Great Plains: I. Grain productivity and residual effects on soil water and nitrogen. Agronomy Journal 95: 972–979. NVT (2014) National Variety Trials, A GRDC Initiative. Available: http://www.nvtonline. com.au/ (2014, November 21). Rahn CR and Johnson PA (2001) Previous cropping and soil mineral nitrogen as predictors of yield response of winter wheat to nitrogen on silt soils in United Kingdom. Soil Use and Management 17(3): 203–207. Robertson MJ, Lawes RA, Bathgate A, Byrne F, White P, and Sands R (2010) Determinants of the proportion of break crops on Western Australian broadacre farms. Crop and Pasture Science 61(3): 203–213. Salam MU, MacLeod WJ, Pritchard I, et al. (2011) G2 Blackspot Manager model to guide field pea sowing for southern Australia in relation to ascochyta blight disease. Australasian Plant Pathology 40: 632–639. Seymour M, Kirkegaard JA, Peoples MB, White PF, and French RJ (2012) Break-crop benefits to wheat in Western Australia—Insights from over three decades of research. Crop and Pasture Science 63(1): 1–16. Siddique KHM, Loss SP, Regan KL, and Jettner RL (1999) Adaptation and seed yield of cool season grain legumes in Mediterranean environments of south-western Australia. Australian Journal of Agricultural Research 50: 375–387.

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Singh KK, Ali M, and Venkatesh MS (2009) Pulses in Cropping Systems. Kanpur: Indian Institute for Pulses Research. Thomson BD, Siddique KHM, Barr MD, and Wilson JM (1997) Grain legume species in low rainfall mediterranean-type environments. I. Phenology and seed yield. Field Crops Research 54(2–3): 173–187. Unkovich MJ, Pate JS, and Sanford P (1997) Nitrogen fixation by annual legumes in Australian Mediterranean agriculture. Australian Journal of Agricultural Research 48(3): 267–293.

Von Richtofen J (2006) What do European farmers think about grain legumes? Grain Legumes 45: 14–15. Walley FL, Clayton GW, Miller PR, Carr PM, and Lafond GP (2007) Nitrogen economy of pulse crop production in the Northern Great Plains. Agronomy Journal 99: 1710–1718.

Soybean: Agronomy ED Nafziger, University of Illinois, Urbana, IL, USA ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by M.E. Westgate & K. Whigham, volume 3, pp. 146–155, ã 2004, Elsevier Ltd.

Soybean (Glycine max L. Merrill) is an astonishing crop. In less than a century, it arose from relative obscurity as a legume crop grown in gardens and on paddy bunds mostly in eastern China to world prominence as the major protein crop and secondmost important source of edible oil. Cereal crops were spread centuries or millennia ago and grown to meet caloric needs, but legumes tend to be low-yielding, with seed quality and disease problems, and so have tended to remain mostly of local importance. Soybean is the exception. Worldwide area of soybean production has increased some fivefold over the past 50 years, with most of that growth in North and South America and in South Asia (Figure 1), with South America accounting for much of the growth over the past 2 decades. Area has remained almost unchanged in East Asia, where soybean has been a traditional crop for centuries, and area remains low in Europe and in Africa. Yields have also grown steadily over the past half century, led by increases in North and South America (Figure 2). As a result, world production has increased nearly tenfold since the early 1960s and has more than doubled over the past 20 years (Figure 3). Worldwide production of 276 million tonnes in 2013 represents more than 35 kg of soybeans for every human on Earth.

Seed and Seed Quality The soybean plant is a leguminous dicot with relatively large seed with a substantial amount of oil and a rather fragile seed coat. These are some of the reasons why soybean seed is considered as one of the more difficult among all crops to produce, store, and utilize to produce the next crop. Under warm, humid conditions before and during harvest, soybean seed is often beset by quality problems related to seed diseases, physiological deterioration, and physical damage. Physical damage includes ‘growth cracks’ that are openings in the seed coat caused by expansion of seed contents during growth. These cracks allow diseases to enter directly into the seed. And when seed is dry, the fragile seed coat can break during threshing and handling; this often allows the cotyledons to separate, thereby eliminating the possibility that the seed can germinate. It is difficult to improve soybean seed quality, but strides have been made. In some regions of the world, including South Asia and Indonesia, small-seeded cultivars have been selected that are both less likely to form growth cracks and that may also have thicker seed coats to resist breakage. In temperate regions and in much of South America, seed quality is improved by the fact that harvest is in the fall during cooler, drier weather. This tends to limit physiological damage and diseases incidence, and it helps to bring the seed to proper (machine) harvest somewhat gradually and with less seed coat cracking. Damage from mechanical harvesting of dry seed remains a major concern, however. This is addressed by using


combine harvesters that thresh the seed more gently, by harvesting in the evening or at night when relative humidity and seed moisture are higher, and by using special handling equipment that does not allow seed to drop far onto hard surfaces during handling and transfer. Because of the problems of seed quality, soybean seed’s ability to germinate is normally tested before it is planted to predict how well it will emerge when planted in the field. The standard germination test usually is done by placing seeds on a wetted paper pad at 25 C for 7 days. This measures the maximum percentage of seed that will germinate in the field. But field conditions may not be ideal, and soybean seed can during storage experience physiological deterioration – called loss of vigor – that lowers its ability to germinate in the field or to form healthy, vigorous seedlings. Several stress tests have been developed that measure the loss of vigor. One of these is the ‘accelerated aging’ test that puts seed under hot, humid conditions for several days and then under standard conditions. This provides a predication of how well the seed will remain sound enough to produce good plants. Another test puts the seed into cold, wet soil for several days to see if it can withstand such conditions when planted into a field where such conditions may occur. Some cultivators have the genetic ability to emerge better, including the ability to emerge from deeper in the soil. This is tested by placing seeds 7–8 cm deep in sand to see if it can elongate its hypocotyl – the stemlike tissue that elongates to bring the cotyledons up to the soil surface during germination – enough to effect emergence. Seed treatment fungicides can also be useful in keeping seeds and seedlings healthy enough to prevent death or damage before emergence. Seed treatments are commonly used in temperate areas where soil conditions may often be less than ideal at planting time.

Seeding Soybean seed is normally planted only as deep as needed to allow it to absorb water from the soil to activate the germination process and to emerge before the soil dries and water uptake stops. In medium-textured soils in regions with occasional rainfall, planting depth is often 3–4 cm, and in areas where weather often brings rapid soil drying after planting, soybean seeds might be planted as much as 7–8 cm deep in order to assure enough water uptake for germination. Soybean seed needs to take up about 50% of its weight in water in order to activate germination, higher than that needed for seeds of cereal crops. Water uptake and germination proceed slowly at a temperature of 10 C, but temperatures of 20–25 C will greatly increase the rate of these processes. Shortened time to emergence is beneficial: seedlings that emerge quickly are much less likely to be attacked by seedling diseases and often

http://dx.doi.org/10.1016/B978-0-12-394437-5.00199-6

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120 100

Million ha

80 60 40 20 0 1960

1970

1980

1990

2000

2010

World

Africa

N America

S America

E Asia

S Asia

SE Asia

Europe

Figure 1 Soybean production area by region and for the world, 1961–2013. Source: http://faostat.fao.org.

3500

Yield, kg ha–1

3000 2500 2000 1500 1000 500 0 1960

1970

1980

1990

2000

can emerge before the soil forms a crust. Soil crusts are a common cause of poor emergence in soybean and form as soils dry following intense rainfall after planting. Soybean plants have a great ability to adjust their size in response density, giving the crop what is called a wide ‘density plateau’ over which yield changes little as density changes – densities ranging from less than 300 000 to more than 500 000 per hectare often produce the same yield (Figure 4). Given that soybean seed germination and emergence under field conditions are often uncertain due to seed vigor and soil conditions, the crop is often seeded at rates as high as 50% more than that needed to maximize yield when germination and emergence are high. High seeding rates are thus seen as a form of insurance against the eventuality that poor plant densities will require that the field be replanted or even abandoned if the time for planting has passed. Under conditions of the Midwestern United States, when temperatures and rainfall are usually favorable, soybean plants grow to a height (from the soil surface to the tip of the stem) of 70–90 cm. Plants of this size can normally maximize yields at established plant densities of around 200 000–250 000 plants per hectare or 20–25 plants per square meter. Seeding rates may be adjusted for germination percentage and for soil conditions that might affect establishment. Farmers in the United States often plant 30–35 seed per square meter, anticipating that final density will be 20–25 m 2; if they end up higher than the target, there is no harm other than the added cost for seed. Soybean seed in the United States is relatively costly, at about six to eight times the price of commodity soybeans on a weight basis. Thus, it pays to overplant only to the extent considered necessary. Soybean seed in the United States is now mostly sold by seed companies based on count, not weight, with one ‘unit’ typically containing about the number of seeds used to plant 0.4 ha (1 acre).

2010

World

Africa

N America

S America

E Asia

S Asia

SE Asia

Europe

Figure 2 Soybean yields by region and for the world, 1961–2013. Source: http://faostat.fao.org.

Planting Date In the Midwestern United States, where most soybean producers also produce maize, soybean yield loss from delayed planting is less than that of maize, and so, soybeans are

300

4500 4000 Yield, kg ha–1

Millions of tonnes

250 200 150

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Figure 3 World soybean production, 1961–2013. Source: http:// faostat.fao.org.

200 300 400 Seeding rate, seeds ha–1 × 0.001

500

Figure 4 Soybean yield response to seeding rate averaged over 33 siteyears in Illinois. Data are from the author.

Yield, % of maximum


110 100 90 80 70 60 50 40 30 20 10 0 1-Apr

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shade the soil earlier and so can reduce water loss from the soil surface. But more plant growth also means more rapid water movement through the plants, and so, soybeans in narrow line spacing might come under drought stress sooner than those in wider rows when it remains dry early in the season. Nonetheless, soybean should be planted at a line spacing that allows the rows to ‘fill in’ by mid-season so that sunlight is intercepted by the leaves and does not reach the ground.

Cultivar Adaptation 21-Apr

11-May 31-May Planting date

20-Jun

Figure 5 Response of soybean yield to planting date in Illinois and in the Midwestern United States. Data are averages over 12 site-years. Unpublished data from the author.

normally planted after maize is planted. Planting delays are normally due to rainfall and wet soils. Research in the central Midwest shows that yield loss accelerates as planting is delayed through May, but losses are modest until planting is delayed to the end of May (Figure 5). In many other soybean-producing regions, planting date is often determined by factors other than soil conditions, especially in lower latitudes where the growing season is not bracketed by temperatures too low to produce any crop, as is the case in the Midwestern United States. Planting date might need to wait until the previous crop is harvested or until rainfall provides enough soil moisture for germination, as is the case in central India. In some cases, planting date is also adjusted in order to position the crop to experience more favorable conditions during the flowering and seed filling periods.

Line Spacing Soybeans are in most regions planted in lines, with the distance between lines being 20 and 91 cm. In the Midwestern United States, lines in the mid-twentieth century were often 91 cm (36 in.), matching those used for maize, with the same planter used for both. Once herbicides became widely available in the 1960s, line spacing dropped in some fields to 17 or 20 cm, precluding row cultivation for weed control. More recently, the common line spacing for maize is 76 cm (30 in.). Many soybeans are planted with the same planter as maize, but with extra planter units located between the units used for maize in order to plant soybeans in lines 38 cm apart. This is the most common row spacing presently, but in recent years, the increasing use of very wide (18 m or wider) planters has had the effect of widening soybean rows, since adding extra units to such planters adds a great deal of weight. Research shows that planting at line spacing less than 50 cm produces soybean yields that are 3–5% higher than when soybeans are in 76 cm rows. In conditions of more drought stress and shortened growing season (e.g., with high temperatures), the vegetative growth of soybeans may be restricted. In such cases, it is often advantageous to plant in lines 50 cm apart or less, so that the smaller plants are able to intercept more of the sunlight. Narrow rows

Soybean would not have spread around the world as a major crop if it were not genetically adaptable. Still, most cultivars growing in the world are from a relatively narrow germplasm base consisting originally of cultivars brought from East Asia to North America and then from North America to other major production areas. Intensive breeding work has been underway in the major production regions, including in East Asia, in order to hasten improvement for yield and other traits. With some exceptions, this has been successful in helping to keep yields moving up (Figure 2). Improved management and crop protection have helped as well, but estimates are that as much as 80% of yield improvement in the United States has come from genetic improvement over that the past 80 years or so. Cultivar maturity was the most important characteristic used to match cultivars from Asia to latitudes where they could be grown in North America. These were assigned Roman numerals, with maturity group (MG) 0 adapted to the northernmost growing area of the United States and MG XIII adapted to the southern extremity of the United States. In the major producing area of the US Corn Belt, the major groups in use are MG 1, in latitudes of roughly 44 to 46 N, MG II from about 41 to 44 N, MG III from 39 to 41 N, and MG IV from about 35 to 39 N. In the southern United States, MG V cultivars are commonly grown, and there are some MG VI cultivars in the Southeastern United States. But many soybean producers in the mid-south (roughly 32–37 N) have moved toward adoption of a system wherein earlier-maturing cultivars such as those in MG III and IV are planted and harvested early in order to avoid hot, dry conditions that often occur in August. Soybean cultivars show rather specific adaptation to certain latitudes because of the mechanism of photoperiod sensitivity. While temperature plays a large role in soybean development including time of flowering, there is in soybean plants a plant hormone (phytochrome) whose activity is affected by the wavelength of light striking the leaves. Light at dusk is rich in the red part of the spectrum, and this leaves the phytochrome in the form that does not allow flowering to occur. In the dark, this form reverts to the ‘far-red’ form of the phytochrome, which triggers flowering. Although warm night temperatures speed the conversion and allow flowering to occur earlier, it is the length of the night period that is the consistent trigger for flowering. As are many photoperiod-sensitive plant species, soybean plants are ‘short-day’ plants, meaning that days need to be a certain length or shorter in order for flowering to occur. It is helpful to think rather of soybean as a ‘long-night’ plant; though shorter days mean longer nights, it is the night period that determines when flowering occurs.

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AGRONOMY OF GRAIN GROWING | Soybean: Agronomy growing conditions are good during most of the season, determinate cultivars will often do well. Indeterminate cultivars, on the other hand, have the ability to resume flowering and growth after periods of stress and hence tend to be more resilient to suboptimal growing conditions. They can also do some pod filling of lower pods before the canopy cover is complete, while the lower nodes of determinate cultivars are generally shaded heavily at and after flowering, which may limit photosynthate supply to any pods there.

Tillage

Figure 6 Soybeans after frost killed the foliage of plants near streetlights; these plants remained green much longer than those farther into the field due to interruption of the photoperiod mechanism that triggers flowering. Photo by the author.

Later-maturing cultivars need longer nights to flower compared to earlier-maturing ones; hence, as days shorten following the summer solstice, night length triggers flowering in shorter-season cultivars first. By the same token, nights are shorter at higher latitudes during the summer, and so, cultivars adapted to a latitude of, say, 40 will, if grown at 43 , flower later than if grown at the lower latitude. Because light interrupts the conversion of phytochrome, soybeans grown near streetlights or light sources of sufficient strength typically show delayed flowering and maturity (Figure 6). While most soybeans in the world are grown during the summer season, there are examples where the photoperiod mechanism is disrupted and where flowering time is determined largely by temperature. As an example, most of the soybeans in Bangladesh are planted after the winter solstice and grow during a season of increasing day length and increasing temperature. Soybean cultivars that will flower and mature without direct influence of day length are said to be photoperiod-neutral, though in fact, they might simply be growing during a time when the nights are always long enough to trigger flowering should temperatures allow. Soybean cultivars are also categorized by growth habit, with the main categories being determinate and indeterminate. Growth habit is genetically controlled, though most cultivars in MG IV or earlier are indeterminate and many longer-season cultivars are determinate. Indeterminate cultivars continue to develop vegetatively after flowering begins, such that vegetative and reproductive developments overlap by as much as 6 weeks or more, and plant height may triple after the first flower appears. Such cultivars often have small leaves and few pods near the stem tip. Indeterminate cultivars make most of their vegetative growth before flowering begins and then flower at all stem nodes simultaneously, with little vegetative growth after flowering begins. Crossing of determinate and indeterminate types can produce semideterminate types. These can be productive but are often very short-growing, making harvest difficult. Growth habit is important in terms of cultivar adaptability to growing conditions. If rainfall is relatively consistent and

Soybeans are successfully grown in many areas of the world with little or no tillage prior to planting. They have a vigorous, branched taproot root system that penetrates the soil well and forms good connections with soil particles in order to bring in water and nutrients. In the Midwestern United States, most soybeans are planted following maize in a 2-year rotation, and though the amount of maize residue is high, soybean can usually be planted with no tillage or with only a light tillage of corn residue that helps with soybean seed placement. The soil following soybean harvest tends to be mellow, and along with low amounts of residue left following soybean harvest, it also works well in most soils to plant maize with little tillage following soybean. In areas with heavy soils that remain cold into the spring, some tillage might help them warm and dry to better accommodate soybean planting, but it often is acceptable simply to wait in such situations until soils dry and warm without tillage.

Nutrients Soybean’s ability to form root nodules that contain bacteroids that can fix atmospheric nitrogen into plant-usable N is hugely beneficial, both environmentally and economically. With high seed protein, soybean has a substantial requirement for N: at 38% protein, 1 tonne of harvested soybean seed contains about 53 kg N. It is generally estimated that about half of this is from biological N fixation and half from N in the soil. The supply of N from the soil includes, that remaining from fertilizer N applied to the previous crop and that mineralized from soil organic matter. The energy required from the plant to the bacteria to fix N and low organic matter of some soils have fostered the idea that supplying fertilizer N might be a way to increase soybean yield. Most research to date has failed to show this outcome, even when soybean yields are very high. Reasons for this are not clear, but possibilities include the plant’s having more ability to supply energy when required (in this case for N fixation) than is normally recognized and better access to residual N deeper in the soil than might be apparent. In any event, clear symptoms of N deficiency in the soybean crop are very rare in most production regions (Figure 7). The requirements for nutrients besides N are modest, with P and K content of about 6 and 18 kg tonne 1, respectively. These are normally supplied without difficulty using either chemical fertilizers or, where available, farmyard manure. Some have advocated foliar applications of N and K, though


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Figure 7 A photo of a typical soybean crop in the Midwestern United States in August showing the dark green of a crop that is well supplied with nitrogen. Photo by the author.

experiments have typically failed to find any yield response to this practice. Other nutrients sometimes applied, though often with little indication of need, include sulfur, manganese, and various mixtures of micronutrients (and sometimes macronutrients). Fertilizing maize or other cereal grains with nitrogen lowers the soil pH over time, and correcting that with lime improves availability of soil nutrients to soybean.

Rotation As soybean became a major crop in different regions, it was fit into a number of diverse cropping systems. In many cases when soybean was grown for the first time following cereal crops such as maize, it produced yields higher than when grown in subsequent years in the same field. Reasons for this are not entirely clear, but are quite likely in large part due to different diseases that affect soybean and carry over from one soybean crop to the next, even if there is a different crop between soybean crops. There are a number of possible diseases that might contribute to this, including the soybean cyst nematode (Heterodera glycines) and fungal diseases such as brown stem rot caused by Phialophora gregata. This tendency of soybean to yield less when following soybean in a field has resulted in adoption of rotations that void this in most regions. When soybeans are grown in lower latitudes, however, it is common for soybeans to grow each year, but with an intervening crop such as wheat or another nonlegume. In central India, most of the soybean crop is planted at the beginning of the monsoon and is harvested in early fall in time to plant wheat, which is traditionally the major crop grown in the winter season. In Brazil and Argentina, annual soybean crops may be separated by a crop of maize in the winter or by cover crops. Soybean in the Midwestern United States was in part a replacement for oats (Avena sativa) used to feed horses used for traction and for forage legumes used in mixed farming common through the mid-twentieth century. Thus, soybean typically followed maize in the rotation, though not without some concern

Maize-Soy Maize-Wheat-Soy Crop Rotation

Figure 8 Response of soybean yield to rotation. Data are averages over two sites and 10 years in Illinois. Data from the author.

that introduction of a crop without typical use as feed and without much crop residue after harvest might have long-term negative effects on the soil. In fact, compared to maize, soybean produces less residue that breaks down more quickly and is therefore considered to have a less beneficial, or perhaps even a somewhat negative, effect on soil organic matter and possibly on long-term soil quality. Still, there are no apparent problems associated with inclusion of soybean in the cropping system on a wide range of soils and climates across the world. With relatively small areas of crops other than maize and soybean in the US Corn Belt and with somewhat more area of maize than of soybeans in recent years, nearly all of the soybeans in this region follow maize, mostly in a 2-year rotation. Some soybeans follow soybeans in the southern portion of this region, where maize occupies less of the area. There is also some area of winter wheat in the southern portion of the Corn Belt and in the mid-south, and much of the wheat is harvested early enough (in June) to allow a ‘double-crop’ soybean crop to be grown in the remainder of the season. Double-crop soybeans, which are planted about 6 weeks later than full-season soybeans, produce yields that are highly variable due to variable rainfall. Recent research in the central Corn Belt (Illinois) shows that soybean in a corn–soybean rotation yields about 5% more than continuous soybean and that adding wheat into the rotation can increase soybean yield by a similar percentage above that of soybeans in the maize–soybean rotation (Figure 8). Despite higher soybean yields with the inclusion of wheat, returns from the three-crop rotation are, at present prices, lower than those from the maize–soybean rotation.

Disease, Insect, and Weed Management Diseases of soybean decrease productivity of the crop in several different ways. One group of fungal pathogens attacks seeds or seedling and can kill plants at or before emergence. Several fungal and a few bacterial diseases damage leaves, decreasing photosynthesis. Different fungal diseases and some nematodes – tiny roundworms often grouped with diseases – attack the roots and diminish their ability to take up water and nutrients. Yet, other fungal pathogens block the

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plant’s conductive tissue and restrict the flow of water and nutrients. Ways to manage diseases include development of genetic resistance, use of fungicides, and crop rotation and management to decrease the supply of pathogens. Insects are a relatively minor problem in the soybean crop in the United States, but are very destructive in soybean cropping systems in other parts of the world. Caterpillars – larvae of moths and butterflies – are among the destructive insects that cause damage by eating leaf tissue or flowers and pods. Aphids and spider mites (not an insect but similar in its activity) puncture leaf veins and feed on the sap. Another very destructive group of insects puncture pods and withdraw seed contents, killing or badly damaging developing seeds. In many cases, insect numbers increase very rapidly during an outbreak, and control needs to be very timely to be effective. Chemical insecticides are often the only workable means of control once an outbreak occurs. There are some genetically modified soybean cultivars that contain the Bt gene that produces a protein toxic to some caterpillars. There is some genetic resistance to aphids, but genetic resistance to the most damaging insects either is unavailable or is not very effective. Weeds decrease soybean yields by competing for nutrients, water, and sunlight. Due to their growth habit, soybeans are not among the most competitive crops, and many fields worldwide suffer yield losses due to weeds. If weeds are allowed to grow for several weeks alongside the emerging soybean crop, damage to soybean yield can be irreversible. Managing weeds requires removing them or preventing their emergence, neither of which is easy. Mechanical and chemical means of controlling weeds are common and are effective if done on time. Control with chemical herbicides is becoming more challenging as weed resistance to herbicides, which began to appear after several decades of herbicide use, continues to spread.

There are some biological control methods involving insects or diseases, but these are not always effective and are not widely used.

Soybean as a World Crop Going Forward Soybean is both a protein crop and an oil crop, and its role in providing these vital nutrients to the world’s human and animal populations will only increase in importance as the population increases. Both area and yield have continued to increase in recent decades, and so, world production is accelerating (Figure 3.) It is likely that area increases will slow as South American production matures, though all indications are that Brazil is, or soon will be, the leading country of production. Area in India will be constrained by availability of land with adequate but not excessive monsoon rainfall. Yields in China will probably increase, but the decrease in area will likely limit increases in production. Soybeans have been tried in nearly every country on Earth, and it is worth considering why this crop has not caught on as an important crop in regions that appear to have suitable soils and climate. Soybean is a crop that is largely processed using medium- or large-scale facilities, and the crop and its products (protein meal and oil) move through organized markets; there is little local usage that would support production in the absence of industrial processing capability. Seed quality problems are also a constant challenge, and equipment needed for production and threshing is not always available. Hot, dry weather and excessive rainfall are also threats. So, while it is possible that some novel production areas will gain in importance in the coming years, this will require governments and investors that see the great potential offered by this amazing crop.

Natural Disease Control in Cereal Grains WK Mousa, University of Guelph, Guelph, ON, Canada; Mansoura University, Mansoura, Egypt MN Raizada, University of Guelph, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Microbial diseases cause major losses to grain yields and negatively impact human health and ecosystems. Biocontrol is the use of living organisms to suppress crop disease. Competition-based biocontrol outcompetes pathogens for nutrients and/or space. Antibiosis involves the production of a substance that targets and destroys a pathogen. A biocontrol agent may induce natural defense mechanisms in host plants. A soil may suppress crop disease due to the specific structure of its microbial community. Hyperparasitism is a situation in which there is specific recognition between the antagonist and the pathogen that terminates in pathogen death. Transgenic plants can contain introduced genes to combat pathogens as a strategy of biocontrol.

Grain infection caused by toxin-producing fungal species, such as Aspergillus, Fusarium, Penicillium, Alternaria, and to a lesser extent Pithomyces, Phomopsis, and Acremonium, is serious, because they produce mycotoxins that may be consumed by animals including humans. For example, the rice and maize (corn) pathogenic fungus Fusarium moniliforme secretes the mycotoxin fumonisin B1, which has been linked to esophageal cancer, equine leukoencephalomalacia, and porcine pulmonary edema. F. graminearum, the disease-causing agent of head blight in barley and wheat and ear rot in maize, synthesizes cancer-causing trichothecenes such as deoxynivalenol (DON). Aspergillus flavus, the causal agent of kernel rot in maize, produces aflatoxin on preharvest maize and during storage. Together, aflatoxin and DON result in $1.5 billion in losses annually across different crops in the United States alone. There is extensive contamination of grains in the United States and Canada with trichothecenes, with a higher incidence reported in maize than wheat. Fusarium mycotoxins have been reported worldwide, particularly fumonisins on maize.

Learning Objective

Overview of Disease Management Strategies

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Crop diseases are managed by chemical, physical, cultural, and/or natural control methods including biological control. Chemical management involves the use of synthetic pesticides (fungicides). However, these chemicals may lack specificity and affect the beneficial soil microbiota; their indiscriminate use may result in negative impacts on soil ecosystems. Moreover, some chemical pesticides may remain in the soil and in crop tissues, potentially causing harmful effects to end users, either animals or humans. Physical methods to control crop disease include burning of infected crops, barriers that prevent insect vectors from gaining access to crops, and segregation of infected seeds from healthy seeds by grain weight (infected grains have less weight). Cultural methods include crop rotation (when a pathogen has a specific crop host), field sanitation (e.g., burning of infected crop residues), disinfecting of field tools and machinery, site selection, and use of seeds certified to be free of pathogens. Natural control strategies are numerous and include the selection and breeding for diseaseresistant crop cultivars. For example, naturally resistant Chinese genotypes of wheat have been shown to have lower Fusarium-derived mycotoxin levels compared to more susceptible Canadian cultivars. An additional natural control strategy involves the use of intercropping ‘companion crops’ that attract or repel insect vectors of disease. A final major type of natural control is biological control or biocontrol that is defined by Eilenberg (2006) as “the use of living organisms to suppress the population density or impact of a specific pest organism, making it less abundant or less damaging than it would otherwise be.” Biocontrol involves the use of soil- and

To understand different strategies underlying biological control of grain crop disease, with specific examples provided for each strategy.

Introduction The expected dramatic increase in human population and shortages in food supply make it a necessity to explore new strategies to improve crop yields and effectively manage crop diseases with more natural, environmental-friendly strategies. Given the nutritional and economic importance of grains, microbial diseases are a real danger to global food security. Approximately 10% of global food production is lost due to plant pathogens, contributing to more than 800 million people not having enough food. Plant pathogens may be difficult to identify and pathogens may evolve, which cause further challenges. Phytopathogens may result in a catastrophe as illustrated by the southern corn leaf blight epidemic of 1970–71 in the United States caused by the fungus Cochliobolus heterostrophus. Another example was the Great Bengal Famine of 1943 in India, caused by the fungus Cochliobolus miyabeanus, which resulted in the deaths of 2 million people due to their dependence on rice as the staple food. Today, the rice blast fungus, Pyricularia oryzae, causes 10–30% crop losses annually. Moreover, the host range of this fungus extends to include other cereals such as wheat and finger millet (Eleusine coracana) where the infection may result in complete crop loss.


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plant-associated beneficial microbes, including bacteria and fungi. The increasing public interest in organic products strongly enhances the idea of biocontrol, since organic agriculture does not allow synthetic chemicals but does permit spraying with beneficial microbes.

Introduction to Soil- and Plant-Associated Microbes The plant is an attractive host to a variety of beneficial soil microbes (bacteria and fungi). These microbes include those that live in the (1) rhizosphere (area surrounding the root and influenced by root secretions), (2) mycorrhizosphere (area surrounding root-associated mycorrhizal fungi), and (3) endosphere (internal plant tissues; these microbes are termed endophytes). There may be cross talk between the plant host, beneficial microbes, and pathogens. On the plant side, roots produce secretions such as sugars, amino acids, and organic acids that stimulate the microbial population including both antagonists and pathogens. The roots may also produce pathogen-stimulating factors, allelochemicals, and repellents that have their peak effects during vegetative development, with these effects decreasing with increased distance from the root system. On the microbial side, plant growth-promoting rhizobacteria (PGPR), plant growth-promoting fungi, nitrogenfixing rhizobia, and mycorrhizal fungi play roles in nutrient cycling and also in biocontrol.

Overview of Biocontrol Mechanisms Mechanistically, beneficial soil- and plant-associated microbes may control pathogens indirectly or directly. Indirect antipathogenesis occurs when microbes enhance plant health by making soil nutrients more available (e.g., solubilize rock phosphate) or fix nitrogen (convert atmospheric N2 gas into NH3 fertilizer). Direct antipathogenesis occurs when microbes combat pathogens by competition, antibiosis (production of antipathogen substances), induced systemic resistance (stimulation of plant defenses), soil suppression (enhanced populations of soil microbiota to suppress disease), hyperparasitism (use of microbes as parasites of the pathogen), and the use of microbial-derived genes with antipathogenesis activity inserted into transgenic crops (i.e., genetically modified organisms, GMOs). This article will focus on the direct mechanisms of biocontrol of grain disease.

ecological fitness among a soil microbial community that is already in equilibrium. Competition-based biocontrol is also affected by the physical/chemical properties of the soil. For example, the biocontrol fungal agent Trichoderma has its activity enhanced in moist soil and diminished in higher-pH soils. The use of nontarget fungicides also diminishes the competition ability of any fungal biocontrol agent. An example of a biocontrol agent that competes for nutrients is the bacterium Pseudomonas fluorescens that secretes siderophores to chelate iron, decreasing its availability for many soilborne pathogens including the bacterium Erwinia carotovora. Another example of competition-based biocontrol is the use of nonantagonist soil bacteria including Pseudomonas sp., Brevundimonas sp., Pedobacter sp., and Luteibacter sp., which, when combined, were shown to reduce the biomass (ergosterol content) of the fungal pathogens Rhizoctonia solani and F. culmorum and the saprophytic fungus Trichoderma harzianum. The authors argued that the combined biocontrol species competed for nutrients or triggered the production of antimicrobial metabolites. Interestingly, nonpathogenic strains of F. oxysporum have the ability to control F. oxysporum strains, the causal agents of wilt, a disease that affects many crops including grains; the suppressive mechanism of action involves competition for carbon if the biocontrol inoculum is applied in excess to the pathogen. Antagonists can also compete for space by occupying infection sites, thus preventing the pathogen from gaining access to the plant host. For example, the fungus Phialophora graminicola effectively controls the fungal pathogen Gaeumannomyces graminis var. tritici by occupying the infection sites of wheat root cortical tissue, resulting in reduced pathogen invasion. The protective F. oxysporum strain was isolated from the stems of healthy plants or from wilt disease-suppressive soil (see succeeding text) where it was present at an exceptionally high density. However, when the inoculum is low, F. oxysporum also retains some of its biocontrol activity; one possibility is that it may induce host resistance as an avirulent form of the pathogen (explained in the succeeding text). More recently, competition on root hairs and branches has been proposed to hinder the pathogen attachment and penetration. The addition of animal manures is widely employed particularly in organic agriculture to provide soil with nutrition and also to enhance soil beneficial microbiota, which then compete against pathogens. For example, animal manures can combat many plant pathogens including Gaeumannomyces graminis, Fusarium sp., Phymatotrichum omnivorum, and Sclerotinia sclerotiorum.

Mechanisms of Biocontrol Competition

Antibiosis

To colonize plant tissues, pathogens require unblocked access and nutrients for energy during the infection process, such as from the plant surface. Plant surfaces are typically limited for nutrients originating from leachates, exudates, senescing tissues, soil, and waste products from surface insects. Competitionbased biocontrol involves the use of fast-growing, antagonist organisms to compete with soilborne pathogens that share the same ecological niche, where nutrients and/or space is limited. The success of the biocontrol agent is determined by its

In addition to competition for space or nutrients, biocontrol agents may also actively produce destructive metabolites that target a pathogen. Antibiotics are toxins that prevent growth or kill microbes at low concentrations. Antibiosis is a major mechanism of biological control, in which the antagonist produces substance(s) that could be an antibiotic, lytic enzyme (degrades plant cell wall), volatile substance, or toxin that effectively targets and destroys the pathogen. In the succeeding text, examples are provided for each mechanism.

AGRONOMY OF GRAIN GROWING | Natural Disease Control in Cereal Grains Antibiosis by production of antibiotics Antibiotics from bacteria

The phenolic polyketide 2,4-diacetylphloroglucinol (DAPG) is produced exclusively by Pseudomonas bacterial species (mainly fluorescent Pseudomonas) and is one of the primary compounds responsible for the biocontrol activity of Pseudomonas spp. against different plant pathogens. For example, Pseudomonas brassicacearum was isolated as an endophyte from the roots of Artemisia sp. (Jinju area, Korea) and was shown to control the fungal plant pathogens Phytophthora capsici, Colletotrichum gloeosporioides, and F. oxysporum mainly by secretion of DAPG and 2,4,6-trihydroxyacetophenone. Pseudomonas fluorescens strain HC1-07, isolated from the wheat phyllosphere, suppresses wheat take-all disease caused by the fungus Gaeumannomyces graminis var. tritici and root rot of wheat caused by Rhizoctonia solani. The mechanism of action involves production of a cyclic lipopeptide (CLP). Extracted CLP inhibited the growth of Gaeumannomyces graminis var. tritici and Rhizoctonia solani in vitro. The fungus Chaetomium globosum, isolated from decaying organic matter and soil, effectively controls seedling blight of corn caused by F. roseum and F. graminearum through the production of cochliodinol antibiotics. Ecomycins, which are peptide compounds purified from the bacterium Pseudomonas viridiflava, an endophyte that colonizes Lactuca sativa (lettuce), showed broad-spectrum antifungal activity against some fungal pathogens of plants, including Rhizoctonia solani, F. oxysporum, and Sclerotinia sclerotiorum. Munumbicins, peptides obtained from a Streptomyces sp., an endophyte of the medicinal plant Kennedia nigriscans, Australia, showed activity against some plant pathogenic fungi such as Pythium ultimum, Rhizoctonia solani, Phytophthora cinnamomi, Geotrichum candidum, and Sclerotinia sclerotiorum. Fusaricidins, A–D peptides originally purified from the methanolic culture extract of Paenibacillus polymyxa, have been isolated from different Paenibacillus strains and have been reported to combat several important fungal pathogens of plants including Aspergillus niger, Aspergillus oryzae, F. oxysporum, and Penicillium thomii. Oocydin A, a chlorinated macrocyclic lactone produced by the bacterium Serratia marcescens, an epiphyte (plant surface dwelling) living on the aquatic plant species Rhyncholacis penicillata, showed antifungal activity against several crop pathogens, including Phytophthora cinnamomi, Phytophthora parasitica, Phytophthora citrophora, and Pythium ultimum. Myxobacteria can efficiently combat the plant fungal pathogens Phytophthora capsici, Pythium ultimum, Rhizoctonia sp., Sclerotinia minor, and to a lesser extent F. oxysporum, through the production of a group of macrocyclic lactone, lactam rings, and linear cyclic peptide antibiotics.

Antibiotics from fungi

Rice blast disease, caused by Magnaporthe oryzae, is one of the most devastating diseases worldwide. Spore germination of Magnaporthe oryzae was shown to be strongly inhibited by helvolic acid, a terpenoid compound purified from the yeast Pichia guilliermondii, isolated from the medicinal plant Paris polyphylla. Magnaporthe oryzae is also affected by cryptocin, isolated from the fungal endophyte, Cryptosporiopsis quercina,

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which colonizes the inner stem bark tissue of Tripterygium wilfordii. F. culmorum and F. graminearum were inhibited by pestalachloride A isolated from Pestalotiopsis adusta, a fungal endophyte that inhabits the stem tissue of a Chinese tree. The fungal pathogen Helminthosporium sativum, the causal agent of seedling blight and root rot of cereals, was inhibited by colletotric acid, a tridepside compound purified from Colletotrichum gloeosporioides, a fungus that colonizes the stems of Artemisia mongolica. Phomenone, an antifungal sesquiterpene (eremophilane class) purified from Xylaria sp., a fungal endophyte isolated from Piper aduncum, was demonstrated to combat the wheat pathogens Cladosporium cladosporioides and Cladosporium sphaerospermum (common indoor mold). Pyrrocidines, a group of polyketide–amino acid-derived antibiotics, were originally cultured from an endophyte of maize kernels, Acremonium zeae; this fungus has a protective effect on preharvest kernels against fungal pathogens, perhaps by effectively competing for the same host habitat. Pyrrocidines showed antifungal activity on agar disk experiments against the mycotoxin-producing fungi, F. verticillioides and Aspergillus flavus. Previous experiments have suggested that pyrrocidine A reduces the growth of several Gram-positive bacteria. It has been claimed that Acremonium zeae can cause stalk rot and hence may be selected against by pathologists and breeders, perhaps making commercial hybrid maize more susceptible to fungal pathogens. Pyrrocidine A showed biocontrol activity against stalk and ear rot pathogens of maize, including F. graminearum, Nigrospora oryzae, Stenocarpella maydis, and Rhizoctonia zeae. It was proposed that pyrrocidine A may protect diseasesusceptible seedlings against pathogens, after colonization of seedlings by the endophyte. Pyrrocidine A also showed antipathogen effects against the seed rot saprophytes Aspergillus flavus and Eupenicillium ochrosalmoneum and against the biological agent of fungal leaf spot disease Curvularia lunata and the bacterium Clavibacter michiganense, the disease-causing agent of Goss’s wilt.

Antibiosis by production of lytic enzymes and volatiles The enzyme chitinase was found to antagonize different fungal pathogens by degrading chitin present in the fungal cell wall. Chitinase secretion is correlated with the antipathogenic activities of many bacterial strains including Pseudomonas, Streptomyces, Bacillus, and Burkholderia. Chitinases produced from fluorescent Pseudomonas strains isolated from the sugarcane rhizosphere showed antifungal activity against the fungus Colletotrichum falcatum, the causative agent of red rot disease in sugarcane. Actinoplanes missouriensis, a Gram-positive bacterium, was reported to produce high levels of chitinase that was shown to degrade the hyphae of Plectosporium tabacinum, the causal agent of lupin root rot in Egypt, through plasmolysis and cell wall lysis. The bacterium Bacillus cereus, isolated from a soil that suppresses take-all decline disease, was found to lyse the hyphae of the corresponding fungal pathogen Gaeumannomyces graminis var. tritici.

Antibiosis by volatile compounds Muscodor albus, an endophytic fungus obtained from Cinnamomum zeylanicum (Sri Lankan cinnamon), produces a mixture of volatile compounds including acids, alcohols, ester, lipids, and

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ketones. Among these volatiles, 1-butanol, 3-methyl-, acetate ester is the most potent and targets a range of pathogens including the smut fungus Ustilago hordei (a pathogen of barley), F. oxysporum (pathogen of wheat and maize), Rhizoctonia solani, and Pythium ultimum.

Induced Host Resistance Though plants do not have an immune system (e.g., antibodies) as found in humans, they do have genetically programmed strategies to combat pathogens including the production of antibiotic chemicals, and the ability to increase leaf thickness and close vascular tissues to prevent spread of the pathogen. Normally, the host resistance mechanisms can be induced by pathogens. In addition, biocontrol agents may also induce natural defense mechanisms in host plants, a process that is termed priming or induced host resistance. Plant host resistance can be induced either locally or systemically (throughout the plant) by biotic or abiotic inducers resulting in disease control without direct contact between the antagonist and the pathogen. This form of biocontrol usually results in a 20–85% reduction in disease symptoms rather than complete control. The induced host resistance form of biocontrol is also dependent on the genotype of the host and the level of induction in addition to environmental conditions such as crop nutrient health. Induced host resistance involves stimulation of plant signaling hormones that induce plant defense genes (salicylic acid, ethylene, and jasmonic acid). Host disease resistance can be mediated by plant recognition of surface components of some biocontrol species such as the flagella (flagellin protein) and lipopolysaccharides, which mimic the surface features of pathogens. Arbuscular mycorrhizal fungi (AMF) and other root colonizing fungi are well known as biotic inducers of systemic disease resistance in host plants. Examples of such root colonizers are (1) the AMF Glomus intraradices, which induces pathogenic resistance genes in rice upon root colonization to combat the fungal blast pathogen Magnaporthe oryzae; (2) the AMF Glomus mosseae, which induces systemic resistance in maize against Rhizoctonia solani, the causal agent of corn sheath blight; and (3) the endophytic fungus Piriformospora indica, which induces host resistance against the basidiomycete fungus Blumeria graminis, the disease-causing agent of powdery mildew in barley. With respect to abiotic inducers, the commercial fungicide probenazole was used to induce resistance in maize against the fungus Bipolaris maydis, the disease-causing agent of southern leaf blight; the application of this elicitor did not significantly affect the vegetative growth of the plant under greenhouse conditions. Acetoin (3-hydroxy-2-butanone) is a volatile compound produced by some microbial species such as Bacillus subtilis and thought to play a role in plant growth promotion, with potential to induce host resistance. For example, acetoin has been shown to decrease disease severity caused by Erwinia carotovora on Arabidopsis seedlings when the seedlings were exposed to a mixture of volatiles (including acetoin) produced by Bacillus subtilis and Bacillus amyloliquefaciens when compared with untreated seeds. Moreover, exposure to a racemic mixture of 2,3-butanediol also activated induced host resistance.

Disease Suppressive Soil Some soils have been observed to suppress diseases in crops grown upon them. Soils are a rich source of microbes that are thought to help plants suppress pathogens by improving the health of the plant, induce natural plant defense, produce antibiotics, compete against pathogens, or hyperparasitize the pathogen (see succeeding text). Soil that suppresses crop disease due to the specific structure of its microbial community is known as disease-suppressive soil. Suppressive soil is an attractive method of biocontrol, because it has the potential to be sustainable over many seasons under favorable conditions. Suppressive soil is divided into two categories, general and specific.

General soil suppression General suppressive soils are those that have a high total microbial biomass, resulting in low levels of protection against multiple pathogens. This strategy is dependent on the quality and quantity of soil organic matter (composts, green manures, and cover crops) that provides supplemental nutrients to enhance populations of beneficial microbes intended to antagonize associated crop pathogens primarily by occupying plant infection sites.

Specific soil suppression In contrast to a general suppressive soil, specific suppressive soil is one that has a high concentration of one or more specific microbial species and results in high levels of protection against specific pathogens. Take-all disease of wheat, caused by G. graminis var. tritici, is one of the most studied root diseases, and its control by specific soil suppression is used as a model system for biocontrol research. This disease is mainly controlled by biological and cultural strategies as there is no resistant cultivar nor effective fungicide available. The suppressive soil is developed by continuous monocropping up to 5–7 years. The suppression is due to soil enhancement of Pseudomonas fluorescens that produces the antibiotics, phenazine carboxylic acid and 2,4-diacetylphloroglucinol. Another example of specific soil suppression involves control of Fusarium wilt, a crop disease caused by F. oxysporum. Here, an abiotic factor such as soil pH affects the microbial community and results in enhancement of nonpathogenic Fusarium spp., which induce host systemic resistance and outcompete the pathogen for access to nutrients and infection sites. This disease-suppressive soil was also found to contain a high density of Pseudomonas fluorescens, which induces host defense and releases siderophores (to decrease iron availability to other organisms). As previously mentioned, both Fusarium sp. and Pseudomonas act cooperatively rather than individually.

Hyperparasitism (Parasite of the Parasite) In addition to plants having natural defense mechanisms, in nature, plant pathogens have natural non-plant enemies such as antagonistic predators. Hyperparasitism involves specific recognition between the antagonist and the pathogen that terminates with the death of the pathogen. Hyperparasitism is most common in fungi that form sclerotia, which are dense masses of pathogenic hyphae that remain in crop residues to promote infection in the next crop season. For example, the

AGRONOMY OF GRAIN GROWING | Natural Disease Control in Cereal Grains soil fungus Coniothyrium minitans is a potential microparasite of Sclerotinia sclerotiorum, a pathogen of legumes (e.g., beans); the biocontrol agent colonizes and penetrates the sclerotia resulting in reduced inoculation of the pathogen in the soil. As another example, Trichoderma is a common parasite of Rhizoctonia solani, the causative agent of bare patch disease of cereals and sheath blight of rice. Trichoderma can specifically recognize and effectively penetrate the hyphal cell wall of the parasite by release of cell wall-degrading enzymes.

Transgenic Plants (GMOs) As already noted, microbes can attack plant pathogens, for example, through the production of antibiotics. It is possible to isolate the genes encoding these microbial products and insert them into plants, creating GMOs. A GMO that uses a gene from a microbial antagonist is a bio-based method of disease and pest control. This technology is controversial, has varying degrees of public acceptance, and is restricted by government regulations worldwide. A few examples are provided here, focusing on Fusarium-derived mycotoxins including fumonisins. The most common transgene for crop pest control on the market today involves transgenic maize plants that express the Cry genes (CryIA(b), CryIA(c), or Cry9C), isolated from the bacterium Bacillus thuringiensis, which encodes the Bt proteins that are toxic to certain insects. This technology is noted here because these transgenic plants were found to contain lower concentrations of the mycotoxin fumonisin than nontransgenic maize, perhaps by reducing the number of entry sites of Fusarium pathogen associated with insect damage. Recently, a patented method was developed to isolate a fumonisin-degrading enzyme by fermentation of the fungi Exophiala spinifera or Rhinocladiella atrovirens on fumonisincontaining media. The gene encoding this degrading enzyme was isolated and introduced into plants. Transgenic plants have been reported that are claimed to detoxify the trichothecene mycotoxins of Fusarium. These transgenic plants contain TR1101, a gene encoding trichothecene3-o-acetyl transferase cloned from F. sporotrichioides, which catalyzes the acetylation of the C3 hydroxyl position of many trichothecenes including DON.

Microbes that Combine Multiple Mechanisms for Biocontrol Some microbes can contribute to biocontrol by integrating multiple mechanisms. Examples of such microbes include mycorrhizal fungi and endophytes. Mycorrhizal fungi have the potential to combat many pathogens by different mechanisms: (1) induced host resistance as noted in the preceding text; (2) physical blockage of the inoculation and penetration sites; (3) increased lignification of roots; (4) increased production of antimicrobial isoflavonoids; (5) hyperparasitism; and (6) improved nutrient availability including as a bridge to deliver phosphate solubilized by PGPR, resulting in better plant health. As noted in the preceding text, endophytes are microbes that live inside plants without causing disease. Endophytes may be able to combine multiple mechanisms to combat

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plant pathogens including (1) competition for plant nutrients, (2) induced host resistance, and (3) secretion of antipathogenic molecules (e.g., secondary metabolites, antifungal peptides, or enzymes such as chitinase). For example, the fungal endophytes of corn, Trichoderma koningii and Alternaria alternata, were found to possess antifungal activity against Fusarium sp., the causal agent of seedling blight and root and stalk rot. Paenibacillus polymyxa, an endophytic bacterium that inhabits wheat (Huaibei City, Anhui Province, China), was identified as a strong antagonist against F. graminearum by inhibiting mycelium growth and spore germination.

Examples of Commercial Biocontrol Products The aforementioned strategies are more than theoretical. Though active research continues to identify and validate diverse biocontrol agents, there are many examples around the world where the aforementioned biocontrol strategies have been commercialized for numerous crops. For example, Fravel (2005) provided a list of 25 biopesticides commercially registered by the US Environmental Protection Agency, sold by companies such as Novozymes, Becker Underwood, Gustafson, and Eco-Soil. Among the most famous examples of biocontrol products currently on the market include Bacillus sp. and Pseudomonas sp., which have received considerable attention, with more than ten registered products of Bacillus now available. Pseudomonas species exert direct antifungal activity against various phytopathogens by the production of various secondary metabolites including siderophores, hydrogen cyanide, 2,4-DAPG, phenazines, 2,5dialkylresorcinol, quinolones, and gluconic acid, in addition to lipoproteins. Though biocontrol products hold significant progress, they accounted for only 1% of chemical sales in 2005. Fravel (2005) has described the challenges of commercializing biocontrol products.


• • • • • •

Compare and contrast direct versus indirect methods of biocontrol. What are the major mechanisms of biocontrol? Explain the difference between general and specific soil suppression. Provide examples of plant host-based mechanisms of biocontrol. What are the soil-based strategies for biocontrol? What are the promising strategies to enhance the ecological fitness of biocontrol agents?

Exercises for Readers to Explore the Topic Further Biocontrol faces some challenges including government regulation, public acceptance, and the high costs of commercial production (e.g., fermentation), in addition to safety concerns for ecosystems, animals, and humans. In practice, the key challenge is how to enhance the ecological fitness of the biocontrol agent within a complex ecosystem (field) under real-world environmental conditions. The introduction of an antagonist in a wellestablished soil is usually ineffective because the biocontrol

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agent may be lost due to competition with preexisting soil microbiota and environmental unpredictability (temperature, moisture, seasonal variation, and synthetic chemicals). Overcoming this challenge will require a better understanding of the complex factors that impact the interactions between host, pathogen, and biocontrol agent under varied environmental conditions. Promising areas of future research are:

•

•

• •

To target a pathogen at its most susceptible life cycle stage. For example, a promising direction is to target biocontrol strategies to the saprophytic stage of the pathogen (when a pathogen lives on dead host tissue) and to the dormancy stage of the pathogen (the stage of the pathogen life cycle outside of its host plant when the pathogen has less energy and hence lower resistance). Hyperparasites are most effective at these stages, because the pathogen is most unshielded. In contrast to hyperparasites, competitive antagonists may be most effective during pathogen spore germination when the pathogen has consumed large amounts of stored energy. In situations where the pathogen only survives in a living host (obligate pathogen), then host-based strategies such as induced resistance and transgenic plants and endophytes might be most effective. To target a pathogen with the appropriate biocontrol based on its mechanism, timing, and location of action. For example, endophytes and antibiosis-secreting biocontrol agents are most appropriate when they share the same host tissue/cell type and developmental stage with the target pathogen. For soilborne pathogens, soil suppression is an ideal strategy because it can reduce the reservoir of the pathogen through competition for nutrients and/or compete for common host entry sites such as on roots. For fast-growing pathogens, the competitive antagonist should be added prior to the rapid multiplication stage of the pathogen. To take into account the defense strategies of the pathogen. For example, when considering antibiosis-based biocontrol, it is important to consider whether the target pathogen can degrade the biocontrol-derived antibiotics. To consider environmental stress conditions. It is important to select biocontrol agents that can either tolerate anticipated unfavorable conditions such as dryness or promote stress resistance in the host. For example, Trichoderma biocontrol agents have been well documented to improve host tolerance to low nitrogen and water.

See also: Agronomy of Grain Growing: Necrotrophic Pathogens of Wheat; Plants: Diseases and Pests; Wheat: Biotrophic Pathogen Resistance; Bioactives and Toxins: Mycotoxins; Genetics of Grains: Biotic Stress Resistance Genes in Wheat; Development of Genetically Modified Grains; Grain Harvest, Storage and Transport: Chemicals for Grain Production and Protection; Postharvest Operations for Quality Preservation of Stored Grain; Stored Grain: Invertebrate Pests; Stored-Grain Pest Management; The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species.

Further Reading Barea JM, Pozo MJ, Azcon R, and Azcon-Aguilar C (2005) Microbial co-operation in the rhizosphere. Journal of Experimental Botany 56: 1761–1778.

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Wheat: Biotrophic Pathogen Resistance RF Park, The University of Sydney, Narellan, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Viruses, bacteria, fungi, and nematodes reduce the yield and quality of grain crops. This article focuses on genetic resistance to four biotrophic fungal pathogens of wheat that cause powdery mildew, leaf rust, stripe rust, and stem rust. Powdery mildew can cause yield losses of up to 40%. It can be controlled by fungicides, but more efficiently via resistance genes, 60 alleles of which are known. The three rusts also cause great yield losses, but these are largely prevented by the utilization of host resistance. Some of the genes conferring resistance to these pathogens have been cloned and the respective proteins identified. Catalogs of genes conferring resistance are provided for these pathogens in wheat.

The intimate cellular relationship required for compatible infections by biotrophic pathogens like the rust and the mildewcausing fungi has in many cases led to complex race structures based on gene-for-gene resistance. The first genetic analysis of resistance to a pathogen in a plant, conducted more than 100 years ago, examined the inheritance of resistance to Pst in wheat. This was followed soon by the discovery of physiological races within plant pathogens. While these discoveries led to great optimism that a cure for diseases such as rust in wheat had been found, early efforts to develop genetically resistant wheats involved the development of varieties with single genes for resistance and, invariably, matching virulence in the rust pathogen often followed with the variety being rendered susceptible in what became known as the ‘boom and bust’ cycle.

Resistance Learning Objective

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To understand the principles of using genetic resistance to overcome the threat of pathogens to crop production, using wheat as an example of the host, being the target of the pathogens causing leaf rust, stripe rust, stem rust, and powdery mildew.

Introduction Viruses, bacteria, fungi, oomycetes, and nematodes are among the major causes of biotic stresses affecting plants, impacting crop production principally by reducing yield and quality. These pathogens derive nutrients from their plant hosts either by killing cells and then feeding on the dead substrate (necrotrophs), by colonizing and feeding on living host cells (biotrophs), or by undergoing a period of biotrophic growth and further development following tissue necrosis (hemibiotrophs). This article provides a review of the current knowledge of genetic resistance to four biotrophic pathogens of wheat, which are among the most important pathogens of this crop: Blumeria graminis f. sp. tritici (Bgt; causal agent of wheat powdery mildew), Puccinia triticina (causal agent of wheat leaf rust), P. striiformis f. sp. tritici (Pst; causal agent of wheat stripe rust), and P. graminis f. sp. tritici (Pgt; causal agent of wheat stem rust). Because of their biotrophic lifestyles, self-sown volunteer wheat plants (the ‘green bridge’) are important in enabling the survival of these pathogens from one cropping cycle to the next. Destroying the green bridge is an important component of the integrated control of these pathogens. The development and use of wheat varieties with resistance to each of these pathogens have significantly reduced the damage they cause through both crop protection and reduction of the susceptibility of the green bridge to pathogen infection.

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Resistance is any genetically determined characteristic of a host plant that in any way limits damage produced by disease. Resistance can vary between apparent immunity and extreme susceptibility. For practical purposes, the most important features of resistance are the level of protection from economic damage afforded and durability. Resistance is often defined on the basis of genetics or function. In genetic terms, it is generally defined as oligogenic, being controlled by one or few genes of major effect, or polygenic, being controlled by many genes of individually small phenotypic effect. In functional terms, resistance is defined based on epidemiological (e.g., slow-rusting and rate-reducing) or developmental criteria. Most mildew and rust resistance genes are expressed throughout the life of the wheat plant (all-stage resistance (ASR), also referred to as seedling or major gene resistance), while others are expressed only at postseedling growth stages (adult plant resistance (APR), also referred to as minor gene resistance). Yield loss studies have generally shown that APR will protect against significant yield loss, although this is not always the case. For example, studies in which the protective value of the stripe rust APR gene Yr18 was assessed using near-isogenic paired lines with and without Yr18 demonstrated yield losses of 74–94% in the line lacking Yr18 but 31–52% in the line carrying Yr18. Studies under controlled conditions have shown that APR genes are switched on at different growth stages, some soon after seedling growth stages and others not until flag leaf emergence. Just how and at what growth stage resistance genes are expressed are important considerations in ensuring adequate protection from diseases.

Powdery Mildew Powdery mildew affects wheat production worldwide, with yield losses as high as 40%. The causal agent B. graminis f. sp.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00207-2

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance tritici (Bgt) is an ascomycete, and unlike rust pathogens, which are dikaryotic and functional diploids, Bgt is haploid. The inoculum that initiates the mildew disease cycle comprises either asexually produced conidia produced from the green bridge or ascospores produced within cleistothecia that form on the ripening host and survive on crop residues. Bgt infects the leaves (principally on the upper surface), leaf sheaths, glumes, and awns of its host. The conidia are either splash- or wind-dispersed and, in contrast to rust urediniospores that can survive for more than 2 weeks under optimal conditions, survive for only several days. Table 1

While fungicides have been used to control Bgt in wheat crops, there are documented cases in which the pathogen has developed insensitivity to fungicides within the demethylase inhibitor and quinone outside inhibitor classes. To date, 47 genetic loci involving more than 60 resistance genes/alleles to Bgt have been described in wheat (Table 1). Most (33) of these originated from common wheat, with the remainder identified in other species of Triticum; species of Aegilops, Elytrigia, and Haynaldia; and Secale cereale. Multiple alleles have been found at the loci Pm1, Pm3, Pm4, and Pm5 (Table 1).

Cataloged genes conferring resistance to Blumeria graminis f. sp. tritici in wheat

Gene

Chromosome location

Origin

Tester source

Resistance type

Pm1a Pm1b Pm1c Pm1d

7AL 7AL 7AL 7AL

Triticum aestivum Triticum monococcum Triticum aestivum Triticum aestivum spelta

All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Pm1e Pm2 Pm3a Pm3b Pm3c Pm3d Pm3e Pm3f Pm3g Pm4a Pm4b Pm4d Pm5a Pm5b Pm5c

7AL 5DS 1AS 1AS 1AS 1AS 1AS 1AS 1AS 2AL 2AL 2AL 7BL 7BL 7BL

Pm5d Pm5e Pm6 Pm7 Pm8 Pm9 Pm10 Pm11 Pm12 Pm13

7BL 7BL 2BL 4BS.4BL-2RL 1RS.1BL 7AL 1D 6BS 6BS-6SS.6SL 3BL.3SS-3S, 3DL.3SS-3S 6BS 7DS 4A 1RS.1AL 7D 6BS.6RL 6VS.6AL 2AL 1DS 1A 2BS 6B-6G 1B 7DL 5BS

Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum dicoccum Triticum carthlicum Triticum monococcum Triticum dicoccum Triticum aestivum Triticum aestivum ssp. sphaerococcum Triticum aestivum Triticum aestivum Triticum timopheevii Secale cereale Secale cereale Triticum aestivum Triticum aestivum Triticum aestivum Aegilops speltoides Triticum longissimum

Axminster MocZlatka Weihenstephan MIN Triticum spelta var. duhamelianum Virest Ulka/XX 194 Asosan Chul Sonora Kolibri W150 Michigan Amber Aristide Khapli Armada Tm27d2 Hope Ibis Kolandi IGV 1-455 Fuzhuang 30 TP 114 Transec Disponent N14 Norin 26 Chinese Spring Trans.line 31 Cstrans.line

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Triticum aestivum Triticum aestivum Triticum dicoccoides Secale cereale Aegilops tauschii Secale cereale Haynaldia villosa Triticum aestivum Triticum aestivum Triticum boeoticum Triticum dicoccoides Triticum timopheevii Triticum aestivum Aegilops geniculata Triticum dicoccoides

Norin 10 Norin 26 Norman rec. line Amigo XX 186 KS93WGRC28 Yangmai 5 line 82-7241 Chiyacao NC96BGTA5 TTD140 146-155-T Meri Pova C20

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Pm14 Pm15 Pm16 Pm17 Pm19 Pm20 Pm21 Pm23 Pm24 Pm25 Pm26 Pm27 Pm28 Pm29 Pm30

265

Linked genesa

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Lr26, Yr9, Sr31

(Continued)

266

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance

Table 1

(Continued)

Gene

Chromosome location

Origin

Tester source

Resistance type

Pm31 Pm32 Pm33 Pm34 Pm35 Pm36 Pm37 Pm38 Pm39 Pm40 Pm41 pm42 Pm43 Pm44 Pm45 Pm46b Pm47 Pm46b

6AL 1BL.1SS 2BL 5DL 5DL 5BL 7AL 7DS 1BL 7BS 3BL 2BS 2DL 3AS 6DS 5DS 7BS 4DL

Triticum dicoccoides Aegilops speltoides Triticum carthlicum Aegilops tauschii Aegilops tauschii Triticum dicoccoides Triticum timopheevii Triticum aestivum Triticum aestivum Elytrigia intermedium Triticum dicoccoides Triticum dicoccoides Thinopyrum intermedium Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum

G-305-M/781/Jing411*3 L501 PS5 NC97BGTD7 NC96BGTD3 MG29896 NC99BGTAG11 RL6058 Saar GRY 19 IW2 G-303-1M CH5025 Hombar D57 Tabasco Hongyanglazi RL6077

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance

Linked genesa

Lr34, Yr18, Sr57 Lr46, Yr29, Sr58

Lr67, Yr46, Sr55

a

Only genes with complete linkage are shown. Two loci have been given the designation Pm46.

b

Leaf Rust

Stripe Rust

Leaf rust (also known as brown rust), caused by P. triticina, is the most common and widely distributed rust disease of wheat. The causal fungus is heteroecious with common wheat being the telial/uredinial host and Thalictrum speciosissimum or Isopyrum fumaroides the alternate (pycnial/aecial) host. The telial/uredinial phase of P. triticina has also been reported on tetraploid durum wheat (Triticum turgidum ssp. durum), wild emmer (Triticum dicoccoides), domesticated emmer wheat (Triticum dicoccum), and triticale. P. triticina principally attacks the leaf blades, although it can also infect the leaf sheath and glumes in highly susceptible varieties. If infection occurs early, it can cause yield losses of more than 30%. The damage due to leaf rust tends to be less than that caused by stem rust or stripe rust; however, due to its more frequent and widespread occurrence, globally, it is believed to cause higher overall losses. To date, 66 genetic loci involving some 73 resistance genes/ alleles conferring resistance to P. triticina have been designated in wheat (Lr1 to Lr73; the symbols Lr4, Lr5, Lr6, Lr7, Lr8, Lr40, Lr41, and Lr43 were abandoned due to a lack of reference stocks or duplication with previously described loci). About half of the designated resistance genes were found in Triticum aestivum, with the remaining being introduced into common wheat from other grass species (Table 2). Most of the genes designated for leaf rust resistance in wheat confer ASR and 11 confer APR. Allelic variation has been recorded at five loci (Lr2, Lr3, Lr14, Lr17, and Lr22); however, the two alleles reported at the Lr14 locus (Lr14a and Lr14b) were combined in a later study, showing that they are very closely linked and not true alleles. The disease has been controlled in many countries through directed incorporation of resistance genes into new varieties. In Australia, the development and cultivation of leaf rust-resistant varieties was estimated in 2009 to save some AUD $152 million per annum.

Stripe rust (also known as yellow rust), caused by P. striiformis f. sp. tritici (Pst), is a very destructive disease of wheat globally, having been reported from more than 60 countries and on all continents except Antarctica. The pathogen infects leaves and leaf sheaths and can cause severe infection of glumes (hence the former name Puccinia glumarum). While the primary telial/ uredinial host of Pst is common wheat, it has also been recorded on durum wheat, on cultivated and wild emmer wheat, and on triticale (Triticosecale). It has also been reported from cultivated barley (Hordeum vulgare), rye (Secale cereale), and a range of grass species including wild barley grass (H. glaucum and H. leporinum), Elymus, Leymus, Agropyron, Phalaris, and Bromus. For many years, Pst was considered to lack a sexual phase in its life cycle. Studies of genetic diversity within Pst reported high levels of diversity in both Pakistan and China, which was later explained by the discovery of barberry as the alternate host of Pst and of infection of barberry by Pst in nature. A range of barberry species are susceptible to Pst, including Berberis chinensis, B. koreana, B. holstii, B. vulgaris, B. shensiana, B. potanini, and B. dolichobotrys. While historically considered to be a disease of cooler climates, widespread stripe rust epidemics since 2000 have occurred in warmer regions and attributed to the emergence and spread of two closely related pathotypes with increased aggressiveness and adaptation to warmer temperatures. To date, some 69 genes/alleles at 65 loci (Yr1–Yr67; Yr26 is considered to be synonymous with Yr24) conferring resistance to Pst have been cataloged (Table 3). Three alleles have been reported at the Yr3 locus, two have been reported at the Yr4 locus, and recently, Yr5 and Yr7 were shown to be allelic. The majority of these genes/alleles were reported from Triticum aestivum (51), with others from other species of Triticum, species of Aegilops, from Thinopyrum intermedium (Yr50), and

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance Table 2

267

Cataloged genes conferring resistance to Puccinia triticina in wheat

Gene

Chromosome location

Origin

Tester source

Resistance type

Lr1 Lr2a Lr2b Lr2c Lr3a Lr3bg Lr3ka Lr9 Lr10 Lr11 Lr12 Lr13 Lr14a Lr14b Lr15 Lr16 Lr17a Lr17b Lr18 Lr19 Lr20 Lr21 Lr22a Lr22b Lr23 Lr24 Lr25 Lr26 Lr27 Lr28 Lr29 Lr30 Lr31 Lr32 Lr33 Lr34 Lr35 Lr36 Lr37 Lr38 Lr39 Lr42 Lr44 Lr45 Lr46 Lr47 Lr48 Lr49 Lr50 Lr51 Lr52 Lr53 Lr54 Lr55 Lr56 Lr57 Lr58 Lr59 Lr60 Lr61

5DL 2DS 2DS 2DS 6BL 6BL 6BL 6BL 1AS 2A 4BS 2BS 7BL 7BL 2DS 2BS 2AS 2AS 5BL 7DL 7AL 1DL 2DS 2DS 2BS 3DL 4BS 1BL 3BS 4AL 7DS 4BL 4BS 3DS 1BL 7DS 2B 6BS 2AS 2AL 2DS 1DS 1BL 2AS 1BL 7AS 4BL 2AS 2BL 1BL 5BS 6BS 2DL 1BL.1HtS 6AL 5DS 2BL 1AL 1DS 6BS

Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Aegilops umbellulata Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum dicoccum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum timopheevii Thinopyrum ponticum Triticum aestivum Aegilops tauschii Aegilops tauschii Triticum aestivum Triticum turgidum ssp. durum Thinopyrum ponticum Secale cereale Secale cereale Triticum aestivum Aegilops speltoides Thinopyrum ponticum Triticum aestivum Triticum aestivum Aegilops tauschii Triticum aestivum Triticum aestivum Aegilops speltoides Aegilops speltoides Triticum ventricosum Thinopyrum intermedium Aegilops tauschii Aegilops tauschii Triticum aestivum spelta Secale cereale Triticum aestivum Aegilops speltoides Triticum aestivum Triticum aestivum Triticum timopheevii Aegilops speltoides Triticum aestivum Triticum dicoccoides Aegilops kotschyi Elymus trachycaulis Aegilops sharonensis Aegilops geniculata Aegilops triuncialis Aegilops peregrina Triticum aestivum Triticum turgidum ssp. durum

Centenario Webster Carina Brevit Democrat Bage Klein Aniversario Transfer Exchange Hussar Exchange Frontana Selkirk Maria Escobar Kenya 1483 Exchange Klein Lucero Harrier Africa 43 Agatha Thew RL6043 RL6044 Thatcher Gabo Agent Transec St-1-25 Gatcher C-77-1 CS7D-Ag#11 Terenzio Gatcher RL6086 Pl 58458 PI 58548 RL6083 Line 2-9-2 VPM1 RL6097 KS89WGRC07 KS91WGRC11 T. aestivum spelta 7831 ST-1 Pavon 76 Kern Lr47 CSP 44 VL 404 T. timopheevii ssp. armeniacum Neepawa*6/Ae.speltoides-F-7 RL6107 98 M71 Line 8078 KS-04-WGRC-45 Line-0352-4 TA-10437 TA-10438 Line-0306 RL6172 Guayacan INIA

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Linked genesa

Sr23

Sr25 Sr15

Sr24 Pm7 Pm8, Yr9, Sr31

Pm38, Yr18, Sr57

Yr17, Sr38

Pm39, Yr29, Sr58

Yr38 Yr40

(Continued)

268 Table 2

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance (Continued)

Gene

Chromosome location

Origin

Tester source

Resistance type

Linked genesa

Lr62 Lr63 Lr64 Lr65 Lr66 Lr67 Lr68 Lr69 Lr70 Lr71 Lr72 Lr73 Lr74

6A 3AS 6AL 2AS 3A 4DL 7BL 3DL 5DS 1B 7BS 2BS 3BL

Aegilops neglecta Triticum monococcum Triticum dicoccoides Triticum aestivum spelta Aegilops speltoides Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum spelta Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum

Accession 155 RL6137 RL6149 Altgold Rotkorn S13 RL6077 Parula Toropi-6.3 KU3198 Altgold Rotkorn Atil c2000 Morocco BT-Schomburgk sln AGG91583WHEA

All-stage resistance All-stage resistance ? All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance

Yr42

Linked genesa

Pm46, Yr46, Sr55

a

Only genes with complete linkage are shown.

Table 3

Cataloged genes conferring resistance to Puccinia striiformis f. sp. tritici in wheat

Gene

Chromosome location

Original source

Tester source

Resistance type

Yr1 Yr2 Yr3a Yr3b Yr3c Yr4a Yr4b Yr5 Yr6 Yr7 Yr8 Yr9 Yr10 Yr11 Yr12 Yr13 Yr14 Yr15 Yr16 Yr17 Yr18 Yr19 Yr20 Yr21 Yr22 Yr23 Yr24 Yr25 Yr27 Yr28 Yr29 Yr30 Yr31 Yr32 Yr33 Yr34 Yr35 Yr36 Yr37

2AL 7B 5BL 5BL 5BL 3B 3B 2BL 7BS 2BL 2D 1BL 1BS Not known Not known Not known Not known 1BS 2DS 2AS 7DS 5B 6D 1B 4D 6D 1BS 1D 2BS 4DS 1BL 3BS 2BS 2AS 7DL 5AL 6BS 6BS 2DL

Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum spelta Triticum aestivum Triticum turgidum ssp. durum Triticum comosa Secale cereale Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum dicoccoides Triticum aestivum Triticum ventricosum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Aegilops tauschii Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum dicoccoides Triticum dicoccoides Aegilops kotschyi

Chinese 166 Heines VII Capelle Desprez Hybrid 46 Minister Capelle Desprez Hybrid 46 Triticum spelta album Heines Kolben Iumillo Iumillo Imperial Moro Joss Chambier Mega Maris Huntsman Hobbit G-25 Capelle Desprez VPM1 Frontana Compair Fielder Lemhi Lee Lee K733 TP1295 Selkirk W-219 Lal Bahadur Opata 85 Pastor Carstens V Batavia WAWHT2046 98 M71 TR.DS: FA-15 Line S-14

All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance Adult plant resistance Adult plant resistance All-stage resistance Adult plant resistance All-stage resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance

Sr34 Pm8, Lr26, Sr31

Lr37, Sr38 Pm38, Lr34, Sr57

Pm39, Lr46, Sr58

Lr54 (Continued)

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance Table 3

269

(Continued)

Gene

Chromosome location

Original source

Tester source

Resistance type

Linked genesa

Yr38 Yr39 Yr40 Yr41 Yr42 Yr43 Yr44 Yr45 Yr46 Yr47 Yr48 Yr49 Yr50 Yr51 Yr52 Yr53 Yr54 Yr55 Yr56 Yr57 Yr58 Yr59 Yr60 Yr61 Yr62 Yr63 Yr64 Yr65 Yr66 Yr67

6AL 7BL 5DS 2BS 6AL trans 2BL 2BL 3DL 4DL 5BS 5AL 3DS 4BL 4AL 7BL 2BL 2DL 2DL 2AS 3BS 3BL 7BL 4AL 7AS 4BL 7BS 1BS 1BS 3DS 7BL

Aegilops sharonensis Triticum aestivum Aegilops geniculata Triticum aestivum Aegilops neglecta Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Thinopyrum intermedium Triticum aestivum Triticum aestivum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum turgidum ssp. durum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum

Line-0352-4 Alpowa TA-10437 Chuannong Accession 155 IDO377s Zak Afghanistan wheat acc. PI 181434 RL6077 Line V336 Synthetic wheat 205 Chuan Mai 18 CH233 Line 5515 PI 183527 PI 480148 Quaiu 3 Frelon Wollaroi AUS 91463 Sonora PI 178759 Lal Bahadur Pindong 34 PI 192252 AUS 27955 PI 331260 PI 480016 VL892 VL893

All-stage resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance Adult plant resistance Adult plant resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance Adult plant resistance All-stage resistance Adult plant resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance All-stage resistance Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance

Lr56 Lr57 Lr62

Pm46, Lr67, Sr55

a


Secale cereale (Yr9). A total of 18 of the genes cataloged as conferring resistance to Pst confer APR (Yr11, Yr12, Yr13, Yr14, Yr16, Yr18, Yr29, Yr30, Yr36, Yr39, Yr46, Yr48, Yr49, Yr52, Yr54, Yr56, Yr59, and Yr62). Of these, Yr11, Yr12, Yr13, and Yr14 were designated to describe presumed APR genes in European wheat varieties, based on specific interactions between the varieties carrying them and selected pathotypes of Pst from the United Kingdom. Because of the importance of stripe rust, the development and cultivation of resistant varieties has contributed significantly to stripe rust control. In Australia, the development and cultivation of stripe rust-resistant varieties was estimated in 2009 to save about AUD $431 million per annum.

Stem Rust Stem rust is caused by P. graminis f. sp. tritici (Pgt). Of the three rust pathogens of wheat, it is potentially the most damaging, having the ability to cause total crop failure. An overview of global crop losses caused by the three wheat rusts indicated varying regional significances, with stem rust being important in Australasia, the United States and Canada, northern Africa, South Africa, and, to a less extent, Europe.

Studies on the host range of the telial/uredinial phase of the Pgt life cycle in controlled artificial inoculations have reported wider host ranges than from natural field observations. The pathogen was shown to infect 74 species in 34 genera in artificial inoculations of seedlings, but only 28 of those species belonging to eight genera were known to be natural hosts of the fungus. In agriculture, Pgt infects not only common wheat but also barley. It infects all aboveground parts of the host plant, including the true stem. While the alternate host is primarily Berberis, Pgt can also infect Mahonia. A total of 62 genes/alleles at 55 loci conferring resistance to Pgt in wheat have been cataloged to date (Sr2–Sr58; the symbols Sr1, Sr3, Sr4, and Sr9c were abandoned due to a lack of reference stocks or duplication with previously described loci; Table 4). Only three of these loci are known to comprise allelic series, namely, Sr7 (alleles Sr7a and Sr7b), Sr8 (Sr8a and Sr8b), and Sr9 (Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, Sr9g, and Sr9h). Of the remaining 52 loci, 23 were found in Triticum aestivum, and 30 were introgressed into Triticum aestivum from related species (Table 4). Of the 55 cataloged loci conferring resistance to Pgt in wheat, 50 are expressed at all growth stages, and five confer APR. The economic contribution of resistance breeding in controlling stem rust was estimated in Canada in 1979 to be of the order of CAD $217 million per year and in Australia in 2009 of AUD $438 million per year.

270 Table 4

AGRONOMY OF GRAIN GROWING | Wheat: Biotrophic Pathogen Resistance Cataloged genes conferring resistance to Puccinia graminis f. sp. tritici in wheat

Gene

Chromosome location

Origin

Tester source

Resistance type

Sr2 Sr5 Sr6 Sr7a Sr7b Sr8a Sr8b Sr9a Sr9b Sr9d Sr9e Sr9g Sr9h Sr10 Sr11 Sr12 Sr13 Sr14 Sr15 Sr16 Sr17 Sr18 Sr19 Sr20 Sr21 Sr22 Sr23 Sr24 Sr25 Sr26 Sr27 Sr28 Sr29 Sr30 Sr31 Sr32 Sr33 Sr34 Sr35 Sr36 Sr37 Sr38 Sr39 Sr40 Sr41 Sr42 Sr43 Sr44 Sr45 Sr46 Sr47 Sr48 Sr49 Sr50 Sr51 Sr52 Sr53 Sr54 Sr55 Sr56 Sr57 Sr58

3BS 6DS 2DS 4AL 4AL 6AS 6AS 2BL 2BL 2BL 2BL 2BL 2BL 2B 6BL 3BS 6AL 1BL 7AL 2BL 7BL 1DL 2BS 2BL 2AL 7AL 2BS 3DL 7DL 6AL 3A 2BL 6DL 5DL 1BL 2B 1DL 2A,D 3AL 2BS 4BL 2AS 2B 2BS 4D 6DS 7DL 7DS 1DS 2DS 2BL 2AL 5BL 1DS 3A,B,D 6AS 5DL 2DL 4DL 5BL 7DS 1BL

Triticum dicoccum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum dicoccum Triticum dicoccum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Triticum turgidum ssp. durum Triticum turgidum ssp. durum Triticum turgidum ssp. durum Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Triticum dicoccum Triticum aestivum Triticum aestivum Triticum aestivum Triticum monococcum Triticum monococcum Triticum aestivum Thinopyrum ponticum Thinopyrum ponticum Thinopyrum ponticum Secale cereale Triticum turgidum ssp. durum Triticum aestivum Triticum aestivum Secale cereale Aegilops speltoides Aegilops tauschii Triticum comosum Triticum monococcum Triticum timopheevii Triticum timopheevii Triticum ventricosum Aegilops speltoides Triticum timopheevii ssp. araraticum Triticum aestivum Triticum aestivum Thinopyrum ponticum Thinopyrum intermedium Aegilops tauschii Aegilops tauschii var. meyeri Aegilops speltoides Triticum aestivum Triticum aestivum Secale cereale Aegilops searsii Haynaldia villosa Aegilops geniculata Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum Triticum aestivum

Yaroslav emmer Reliance McMurachy Kenya 117A Marquis Red Egyptian Barleta Benvenuto Red Egyptian Kenya 117A Yaroslav emmer Vernal emmer Iumillo Webster Egypt NA95 Gaza Iumillo Khapli CI 4013 Khapli CI 4013 Norka Reliance Yaroslav emmer Marquis Marquis Marquis Einkorn RL 5244 Selkirk Agent Agatha Eagle Imperial rye Kota Etoile de Choisy Webster Petkus rye W3531 RL5288 Sr34/6*LMPG G-2919 CI 12632 Line W VPM1 RL5344 RL6088 Waldron Norin 40 KS-10-2 Taf-2 RL5406 L-18913 PI 369590 Arina AUS 28011 Imperial rye TA5622 TA7682 TA5599 Norin 40 RL6077 Arina RL6058 Pavon 76

Adult plant resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance All-stage resistance Adult plant resistance Adult plant resistance Adult plant resistance Adult plant resistance

a


Linked genesa

Lr20

Lr16 Lr24 Lr19

Pm8, Lr26, Yr9

Yr8

Lr37, Yr17

Pm46, Lr67, Yr46 Pm38, Lr34, Yr18 Pm39, Lr46, Yr29


Stem Rust Pathotype ‘Ug99’ Apart from epidemics in Ethiopia in 1993 and 1994, the incidence of stem rust in wheat crops around the world remained low from the early 1970s until the late 1990s, when it reemerged as a serious problem in East Africa. Severe stem rust infection was observed in wheat nurseries in Uganda in 1998, and greenhouse assays of a single sample of stem rust collected from these nurseries (accession ‘Ug99’) in South Africa identified the presence of a new pathotype, which has since become known widely as ‘Ug99’ and has the North American race designation TTKSK. This pathotype (race) has the ability to overcome many of the known resistance genes, including Sr31, a gene for which virulence had not previously been detected. Analyses carried out on samples of stem-rusted wheat collected from across a wide area have since shown that pathotype TTKSK is a member of a family of closely related pathotypes that is now known as the ‘Ug99’ lineage. In addition to Uganda, one or more of these pathotypes are present in Eritrea, Ethiopia, Iran, Kenya, Mozambique, Rwanda, South Africa, Sudan, Tanzania, Yemen, and Zimbabwe. The ‘Ug99’ lineage comprises at least seven pathotypes that differ for virulence on resistance genes Sr21, Sr24, Sr31, and Sr36. Studies using DNA-based microsatellite markers showed that many of these pathotypes have identical fingerprints, consistent with them being recently derived from a common ancestor via single-step mutation. Significantly, surveys in Europe, Turkey, Egypt, Pakistan, and India over recent years have failed to detect any of these pathotypes.

Resistance Gene Cloning The first gene conferring resistance to a rust pathogen isolated from a plant was at the L locus that confers resistance to the rust pathogen Melampsora lini in flax. To date, genes/alleles at three mildew resistance loci and seven rust resistance loci have been cloned from wheat. Powdery mildew resistance alleles at the Pm3 and Pm8 loci all encode proteins with coiled-coil (CC), nucleotide-binding site (NBS), and leucine-rich repeat (LRR) (CNL) domains. Cloning of ten reported alleles at the Pm3 locus revealed that Pm3h, Pm3i, and Pm3j had sequences identical to three previously cataloged alleles (Pm3d, Pm3c, and Pm3b, respectively). The sequences of the CC domain in the remaining seven alleles were identical, and differences were found in the NBS and/or LRR domains. Another allele, designated Pm3C, shared from 97% to 99% homology with the other alleles, was shown to be a susceptibility allele. This allele was common in hexaploid wheat and was also found in ancestral wild tetraploid wheat, and it is believed that the Pm3 resistance alleles evolved from this susceptibility allele following the domestication of wheat, by the processes of recombination/gene conversion and point mutation. The different specificities conferred by the seven Pm3 alleles were found to be due to one or a few amino acid changes. The gene Pm8 was introgressed to wheat from the rye variety Petkus in the 1930s. The gene was cloned and shown to be the rye orthologue of Pm3. Of the Pm3 alleles, Pm8 showed strongest homology to Pm3b, with which it shares 81% identity at the protein level.

271

Powdery mildew resistance gene Pm21, transferred to wheat from Haynaldia villosa, is located on a T6VS.6AL translocation. Since 2002, the translocation has been used in China in 12 varieties on more than 3.4 million hectares with no reports of virulence. Because of the low frequency of pairing and suppressed recombination between 6VS and wheat chromosome 6AS, it is not clear whether Pm21 is actually a single gene or a cluster of genes. A gene designated Stpk-V was mapped to the Pm21 locus and cloned using both molecular and cytogenetic approaches, and evidence from studies including transformation and gene silencing was consistent with this gene being Pm21 or a key gene in Pm21-mediated resistance. Stpk-V is a putative serine/threonine protein kinase gene, a gene family involved in protein phosphorylation, which is known to be an important step in disease resistance pathways. Of the seven rust resistance genes that have been cloned from wheat, three confer resistance to leaf rust, one confers resistance to stripe rust, two confer resistance to stem rust, and one confers resistance to all three rusts and to powdery mildew. The leaf rust resistance genes Lr1, Lr10, and Lr21 all encode proteins with CNL domains, similar in structure to Pm3 and Pm8 and to the stem rust resistance genes Sr33 and Sr35. CNL proteins control the recognition of molecules produced during pathogen infection and are involved in triggering host signal transduction pathways that result in host defense. Gene Lr1 encodes a 1344 amino-acid protein, Lr10 spans 3935 bp and encodes a 919 amino-acid protein, and Lr21 spans 4318 bp and encodes a 1080 amino-acid protein. The ASR gene Sr33, introduced into Triticum aestivum from the diploid Aegilops tauschii, was shown to be orthologous to the mildew resistance locus Mla that confers resistance to B. graminis f. sp. hordei in barley, showing 80% similarity to the Mla34 allele. A second ASR stem rust resistance gene, Sr35, was originally derived from the diploid Triticum monococcum. Mutation studies revealed that the distal region of the LRR repeat domain is critical for the function of Sr35. Sequence comparisons failed to detect Sr35 in T. urartu, the A genome donor in common wheat. The gene Pm38/Lr34/Yr18/Sr57 encodes a protein that resembles adenosine triphosphate-binding cassette transporters of the pleiotropic drug resistance subfamily. Time course expression studies showed that the gene is more strongly expressed at later growth stages, consistent with its action as an APR gene. The studies conducted indicated that the Pm38/Lr34/Yr18/Sr57 resistance results from either a senescence-like process that begins at the leaf tips (causing the LTN phenotype) or a more direct role in exporting metabolites that affect fungal growth.

Future Perspectives and Conclusions Many of the cataloged genes conferring ASR to mildew and rust diseases in wheat deployed in commercial wheat varieties have been overcome by the development of new pathotypes with matching virulence. Virulence has also been reported for several genes conferring APR to rust, including Lr12 and Lr22b, both of which confer hypersensitive resistance similar to that seen with many ASR genes. Despite such resistance gene breakdowns, their use remains the most economical and environmentally

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acceptable approach to control biotrophic pathogens in wheat. A number of resistance genes conferring durable resistance have been identified, including three loci that confer slow rusting APR to all three rust pathogens and to Bgt: Pm46/Lr67/Yr46/ Sr55, Pm38/Lr34/Yr18/Sr57, and Pm39/Lr46/Yr29/Sr58. All three resistance loci are associated with the morphological trait leaf tip necrosis. A fourth slow rusting APR locus, Sr2/Yr30, confers resistance to stem rust and stripe rust and is completely associated with the morphological trait pseudo-black chaff. With the exception of the Pm46/Lr67/Yr46/Sr55 locus, all have been used widely in commercial wheat varieties over many years, and to date, no cases of virulence have been reported. Experience to date suggests that these pleiotropic APR genes have some intrinsic durability and that combinations of multiple effective resistance genes contribute to durability by lowering the chances of virulence matching gene combinations developing. In many instances, pleiotropic APR genes have been used to great effect in conjunction with ASR genes, providing backbone resistance that may also have contributed to increased durability of ASR genes. The number of resistance genes for which tightly linked high-throughput DNA markers are available continues to increase, allowing marker-assisted selection and greater efficiency in assembling gene combinations. The ability to incorporate multiple resistance genes by transformation will also become possible as more genes are cloned. An important consideration in this approach is, however, the possible suppression of resistance genes. For example, recent studies showed that the susceptibility allele Pm3C and three resistance alleles (Pm3a, Pm3b, and Pm3f) all suppressed Pm8. The strength of the suppression was shown to vary with the Pm3 allele used and with Bgt isolate. The mechanism of suppression was related to a posttranslational mechanism; direct interaction between the two proteins produced by the resistance genes in tobacco suggested that the formation of a heteromeric protein complex may interfere with signal transmission in the defense reaction. While this example may be an exception, clearly, any strategy based on combining cloned resistance genes will need to take this into consideration.


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Describe the ways in which the rust and powdery mildew pathogens inflict damage on the wheat plant. Compare and contrast these four pathogens with respect to their attack on the plant, the relevant stages of growth, the relevant parts of the plant, the ‘green bridge’ plants involved, and the sources of resistance for each plant–pathogen combination. Describe the ‘Ug99’ pathotype. What has been different about it attracting significant publicity?


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Investigate and describe the value to breeders of DNA markers for resistance genes. Explain virulence and resistance and its breakdown. What do these terms mean at the molecular level? Some resistance genes have been cloned. Investigate the significance of these advances with respect to the consequent identification of the proteins thus coded and the mechanisms of resistance at the molecular level. Explore plant–pathogen relationships for other grain species. How do they differ from the examples provided in this article?

See also: Agronomy of Grain Growing: Natural Disease Control in Cereal Grains; Necrotrophic Pathogens of Wheat; Plants: Diseases and Pests; Wheat: Agronomy; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Biotic Stress Resistance Genes in Wheat; Development of Genetically Modified Grains; Genomics of Food Grains; Wheat Genetics and Genomics; Proteins: Protein Synthesis and Deposition; The Protein Chemistry of Cereal Grains; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Bushnell WR and Roelfs AP (1984) The Cereal Rusts. Volume I, Origins, Specificity, Structure and Physiology. Orlando, FL: Academic Press, 546 pp. Knott DR (1989) The Wheat Rusts – Breeding for Resistance. Berlin: Springer-Verlag, 201 pp. Littlefield LJ (1981) Biology of the Plant Rusts. An Introduction. Ames, IA: Iowa State University Press, 103 pp. McIntosh RA, Wellings CR, and Park RF (1995) Wheat Rusts: An Atlas of Resistance Genes. Melbourne: CSIRO Publications, 200 pp. Murray GM and Brennan JP (2009) The Current and Potential Costs From Diseases of Wheat in Australia. Canberra: GRDC, 70 pp. Park RF (2000) Rust fungi. In: Lederberg J (ed.) Encyclopedia of Microbiology, vol. 4, pp. 179–195. London: Academic Press. Park RF (2007) Stem rust of wheat in Australia. Australian Journal of Agricultural Research 58: 558–566. Roelfs AP and Bushnell WR (1985) The Cereal Rusts. Volume II, Diseases, Distribution, Epidemiology and Control. Orlando, FL: Academic Press, 606 pp. Scott KJ and Chakravorty AK (1982) The Rust Fungi. New York: Academic Press, 288 pp.

Relevant Websites http://maswheat.ucdavis.edu – Marker Assisted Selection in Wheat. http://rusttracker.cimmyt.org – RustTracker.org A global wheat rust monitoring system. http://www.shigen.nig.ac.jp/wheat/komugi/genes/macgene/supplement2012.pdf – Catalogue of wheat symbols for wheat: 2012 supplement. http://wheat.pw.usda.gov – GrainGenes: A database for Triticeae and Avena.

Necrotrophic Pathogens of Wheat RP Oliver, K-C Tan, and CS Moffat, Curtin University, Bentley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Diseases of wheat. Genetic analysis of resistance to tan spot and Septoria nodorum blotch (SNB) necrotrophic effectors. Tan spot effectors. SNB effectors. Lateral gene transfer, effector interactions, and new fungal pathogens.

Learning Objectives

• • • •

Appreciation of the relative importance of necrotrophic and other wheat diseases. An understanding of the term effector. Consideration of the nature of quantitative disease interactions. An understanding of the impact on plant breeding of the effector model.

Diseases of Wheat The diseases of wheat have received particular attention throughout the ages because of their often devastating effect on this all-important crop. The full range of nematode, viral, bacterial, oomycete, and fungal pathogens cause significant diseases. Much international attention has been given to the biotrophic rust diseases, but in some parts of the world, necrotrophic pathogens cause far higher losses and have proved much harder to control by either genetic or chemical means. This article is primarily concerned with two major pathogens of wheat from the order Pleosporales: Parastagonospora nodorum and Pyrenophora tritici-repentis. Some aspects of P. nodorum and P. tritici-repentis research have recently been reviewed, and these reviews contain detailed background that underpins our current knowledge (Faris et al., 2013; Lamari and Strelkov, 2010; Oliver et al., 2012). Taxonomic instability of these and other related leaf blotch pathogens from the class Dothideomycetes has been an issue. The current and past names of the pathogens and their diseases are summarized in Table 1 (Quaedvlieg et al., 2013). The three diseases, Septoria nodorum blotch (SNB), tan spot (TS), and Septoria tritici blotch (STB), coexist in many places and have likely been confused and misidentified at times. Disease loss assessments are rarely carried out and subject to many caveats and exceptions, despite their obvious importance for farmers, breeders, agrochemical companies, researchers, and funding agencies. More frequently, pathogens are ranked in terms of importance. One of the more reliable and recent assessments of wheat disease losses has been carried out in Australia (Murray and Brennan, 2009). Previous studies


give information of trends over decades (Brennan and Murray, 1988, 1998). Table 2 lists estimates of current wheat disease losses in Australia. It can be seen that across all regions, TS is the major disease, currently costing more than all rusts combined. SNB is restricted to Western Australia where it ranks as the second most costly wheat disease. STB has declined significantly, from an annual cost of $152 million in 1998 (Brennan and Murray, 1998) to the current figure of $1 million per annum. Table 2 also lists estimates of potential losses if no disease control measures were carried out. The difference between the actual and potential is then ascribed differentially to breeding, fungicide, and cultural control methods. The distribution and trends in the diseases are quite distinct. SNB is almost exclusively located in Western Australia, with only sporadic reports from other regions. STB has sharply declined in both the southern and western regions and has always been absent from the northern regions. TS is steadily increasing in all regions although absolute levels are lower in the southern region (Figure 1). The high levels of disease reported from TS and SNB was greeted with much skepticism in many quarters. The methodology of the report was based on questionnaires sent to regional plant pathologists. These data were combined with estimates of area and crop value to arrive at consolidated estimates. Validation of the estimates has been provided by two recent reports that used fungicide control to estimate disease losses (Oliver et al., 2014; Salam et al., 2013). Salam et al. analyzed yield responses to fungicide under situations in which either or both TS and SNB were the only significant diseases. Not surprisingly, three fungicide treatments gave higher yield gains than one (515 kg ha1 versus 297 kg ha1 averaged over the whole region). However, it is not clear if the three fungicide treatment schedule even gave complete control. Averaged over the entire western region and using a figure of $263/tonne, this implies that the combined disease cost to WA growers is $300–600 m per annum. Oliver et al. (2014) used a smaller number of fungicide trials and estimated losses of 350 kg ha1 to TS only. It therefore appears that the estimates in Brennan and Murray of $212 m per annum in Western Australia are of the right order and may well be an underestimate. The distribution of the pathogens in the rest of world is understudied. Lamari and Strelkov reviewed the literature in 2010 for TS (Lamari and Strelkov, 2010). There are widespread reports that the range of TS is increasing in northern and western Europe. In Germany, TS is consistently comparable with STB and in some years is the most damaging disease (M. Weigand, personal communication). In Denmark, TS is frequently observed (Jørgensen and Olsen, 2007). In the United Kingdom, TS is now frequent and is ranked third behind STB and powdery mildew (J. Thomas, personal communication). The consistent pattern is that TS is strongly associated with limited tillage methods and wheat-on-wheat rotations. SNB is only reported as an occasional disease in Germany, but it is

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AGRONOMY OF GRAIN GROWING | Necrotrophic Pathogens of Wheat

Table 1

Nomenclature of wheat leaf blotch pathogens and their diseases

Preferred pathogen name

Pathogen synonyms

Order

Preferred disease name

Disease synonyms

Parastagonospora nodorum

Stagonospora nodorum Phaeosphaeria nodorum Leptosphaeria nodorum Septoria nodorum Drechslera tritici-repentis Helminthosporium tritici-repentis Septoria tritici Mycosphaerella graminicola

Pleosporales

Septoria nodorum blotch (SNB)

Stagonospora nodorum blotch Glume blotch

Pleosporales

Tan spot (TS)

Capnodiales

Septoria tritici blotch (STB)

Yellow spot Yellow leaf spot Septoria leaf blotch Septoria tritici blotch

Pyrenophora triticirepentis Zymoseptoria tritici

Table 2

Potential and actual losses to selected wheat diseases in Australia

Disease

Rank

Actual/AUD million

Potential/AUD million

TS SNB STB Stripe rust Stem rust Leaf rust

1 3 27 2 8 11

212 108 1 127 8 12

676 230 21 994 478 197

Contribution to control (potential minus actual) from breeding, fungicides, and cultural methods (AUD million) Breeding 200 36 15 431 438 152

Fungicide 108 35 4 359 8 17

Cultural 155 51 1 78 24 16

Data from Murray, G.M., Brennan, J.P., 2009. Estimating disease losses to the Australian wheat industry. Australasian Plant Pathology 38, 558–70.

9 8 7 6 5

TS

4

SNB

3

STB

2 1 0 1988 1998 2008 1988 1998 2008 1988 1998 2008 Northern

Southern

Western

Figure 1 Average annual disease losses to SNB, TS, and STB in the northern (Queensland and northern NSW), southern (southern NSW, Victoria, Tasmania, and South Australia), and western (Western Australia) cropping regions. Figures are % losses to each disease. Data from Murray, G.M. and Brennan, J.P., 2009. The current and potential costs from diseases of wheat in Australia.

common in parts of France (M. LeBrun, personal communication), western counties of England (S. Gurr, personal communication), and Norway (M. Lillemo, personal communication). It seems that SNB is most apparent in regions with intense rain showers. Rain splash of spores is required for progression of SNB throughout the canopy. It is clear that the incidence of these diseases and their economic impact need further study. Fortunately, molecular diagnostic tools are readily available (Oliver et al., 2008). A range of fungicides are available for SNB and TS. The primary modes of action in use are demethylation inhibitors, quinone outside inhibitors (QoIs), and succinate dehydrogenase inhibitors. In general, control levels in the field are modest

(Oliver et al., 2014). This is not due to baseline levels of fungicide sensitivity, but rather to poor field performance (Beard et al., 2009; Bhathal et al., 2003; Tormen et al., 2013). There have been reports of evolved resistance to QoI fungicides (Blixt et al., 2009; Reimann and Deising, 2005). Overall, there is every reason to pursue the breeding of disease-resistant cultivars.

Genetic Analysis of Resistance to TS and SNB Necrotrophic Effectors Our understanding of the interaction between wheat and the TS and SNB pathogens has been revolutionized by the

AGRONOMY OF GRAIN GROWING | Necrotrophic Pathogens of Wheat recognition of the importance of necrotrophic effectors (NEs). The dominant theory in the genetics of host–pathogen interactions is, of course, the gene-for-gene (GFG) hypothesis (Keen, 1990; van der Biezen and Jones, 1998). In recent years, this model has been refined to take into account non-host resistance and the presence of PAMPs (pathogen-associated molecular patterns) (Thomma et al., 2011). The GFG theory explained adequately the interaction of biotrophic pathogens (especially rusts and powdery mildews) and their hosts and provided a practical framework for breeding disease-resistant cultivars, albeit that those cultivars tended to break down after a few years. However, the great majority of pathogens do not conform neatly to the GFG hypothesis, and this is especially true for pathogens that do not elaborate a haustorium and that are variously described as necrotrophs or hemibiotrophs (Oliver and Ipcho, 2004). This is the case for SNB and TS. One of the predictions of the GFG hypothesis is that isolates of the pathogen should vary in clear ways in their interactions with different cultivars of the host. Such variation in GFG systems is described as variation in ‘virulence’ and is controlled by avirulence genes. Isolates of pathogens should cause reciprocal levels of disease on different cultivars of a host: the socalled quadratic check. Pathologists and breeders can then develop differential lines that contain different resistance genes which can be used to monitor the virulence profile of the pathogen. In the case of biotrophic pathogens, the development of differentials was an essential prerequisite to the molecular cloning of the avirulence genes (Dodds et al., 2009). The conundrum of why pathogens should produce gene products that rendered them avirulent was solved as the (often subtle) positive attributes of these genes were revealed (Koeck et al., 2011). In the case of necrotrophic (and non-haustorial) pathogens, the definition of clear reciprocal relationships between pathogen isolates and host cultivars was rarely observed. It was much more common to observe tonic relationships where isolates differed in aggression on all cultivars of the host. Some isolates were generally aggressive and some were less aggressive, with no significant reciprocal relationships. However, one group of pathogens did show reciprocal relationships: examples include species in the genera Cochliobolus, Alternaria, and Pyrenophora (Wolpert et al., 2002). This group of pathogens includes those that secreted ‘toxins’ in the culture filtrate. Infiltration of the toxic preparations into cultivars of the hosts produced strong necrotic reactions in some host plant cultivars and no responses in others. The necrotic reactions resembled the symptoms produced by the pathogens. These toxins therefore became known as ‘host-specific’ or ‘hostTable 3

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selective’ toxins (HSTs). The reciprocal relations were revealed when isolates of the pathogens that failed to produce these HSTs were compared with the HST þ strains. When the HSTs were biochemically characterized, they were shown to include polyketides and non-ribosomally synthesized peptides and proteins. All are now called NEs (Oliver and Solomon, 2010). The reciprocal relationships have allowed the definition of wheat differential lines that exhibit specific sensitivity to particular NE and thus susceptibility to particular isolates of the pathogens.

Tan Spot The TS pathogen P. tritici-repentis is included in this group of pathogens that secrete NEs. Work starting prior to 1990 defined three NEs, called ToxA, ToxB, and ToxC (reviewed in Lamari and Strelkov, 2010). This in turn allowed the definition of 8 races of the pathogen, representing all possible combinations of the 3 NEs. ToxA is fully characterized. The monomorphic gene is present in about 80% of the world’s isolates (Friesen et al., 2006). The gene encodes a small protein that induces a strong necrotic response in wheat lines carrying the gene Tsn1 (Faris et al., 2010) on chromosome 5BL. Tsn1 encodes a protein with similarity to disease resistance genes in biotrophic interactions. The interaction of Avr genes and resistance genes in biotrophic diseases, and interaction of HSTs and sensitivity genes in necrotrophic interactions, affirms the commonality at the base of plant pathogen interactions and justifies the general term ‘effector.’ Wheat lines that are sensitive to ToxA are significantly more susceptible to ToxA-producing TS isolates (Friesen et al., 2003). In Australia, ToxA sensitivity is strongly associated with TS severity (Table 3). Despite this clear relationship, markers that have been available for Tsn1 were not in use by breeders. Since 2009, our laboratory has been supplying preparations of the ToxA protein expressed in E. coli to Australian wheat breeders. Enough ToxA to treat 30 000 plants per annum has been delivered. Breeders use a simple infiltration test to identify sensitive wheat lines (Figure 2). The test is applied to primary germplasm sources and to lines throughout the breeding process. Plants can be grown in growth chambers, in glass houses, or in the field. Breeders can treat about 1000 plants a day and can detect sensitive plants within 3–4 days. Such plants can be discarded at that stage. This process is quicker than marker-assisted selection using leaf DNA. Since the

Influence of NE sensitivities on field scores of current Western Australian wheat cultivars scored for tan spot and septoria nodorum

Disease

NE

Difference in average disease score of sensitive and insensitive lines

Tan spot Septoria nodorum blotch

ToxA ToxA Tox1 Tox3

2.85 0.357 0.109 0.484

Closest wheat marker Tsn1; Xfcp623 psp3000, fcp618, fcp624 Cfd20, gwm234, barc130, cfd18, hbg337, gwm190

Based on Tan et al. (2014), Waters et al. (2011), and Moffat et al. (unpublished). Wheat cultivar field scores were converted to a 9-point scale (1 ¼ very susceptible to 9 ¼ immune). The average score of insensitive lines for each NE and disease was subtracted from the scores for the sensitive lines.

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Figure 2 Infiltration of wheat lines with NE. (a) Infiltration with a needleless syringe. (b) Scoring of necrosis after a week.

cloning of Tsn1, perfect markers are also available and can be used to select seeds for planting. ToxB is also a small, secreted protein that is present in varying copy numbers in isolates of TS (Amaike and Strelkov, 2006). ToxB sensitivity is encoded by the gene Tsc2 residing on 2BS (Friesen and Faris, 2004) and confers additional disease susceptibility. Isolates expressing ToxB are less common than those expressing ToxA (they are absent from Australia (Antoni et al., 2010)) and so the exploitation of this NE for breeding purposes has not so far been justified. Should ToxB-expressing isolates be detected, the expressed protein could be used to distinguish sensitive and insensitive wheat lines in the same way as has been done for ToxA. ToxC is less well characterized (Effertz et al., 2002). It induces chlorosis and does not appear to be a protein. Sensitivity is conditioned by the gene Tsc1 on 1AS. So far, ToxC has not been used in breeding efforts. The three known NEs – ToxA, ToxB, and ToxC – cannot be the whole story for TS. QTL mapping of disease reactions in many wheat populations uncovers at least a dozen loci not reacting to the (semi)purified effectors (Faris et al., 2013). Some of these QTL may represent sensitivity loci to so far undiscovered effectors. However, some of these QTL encode dominant resistance, and others broad spectrum resistance, suggesting that other types of interactions are involved.

Septoria nodorum Blotch Breeding for resistance to P. nodorum had been a priority in Europe until the 1990s and has remained so in Western Australia to this day. Early breeding efforts were based on pragmatic and laborious field scoring of breeding lines and steady

progress was made. QTL mapping for disease was undertaken and uncovered numerous loci, but map location precision and effect size were both low. Hence, to our knowledge, no markers were actively used by breeders. There was no evidence that P. nodorum produced NE until 2004, when Liu et al. partially characterized Tox1 and the corresponding wheat sensitivity locus Snn1 (Liu et al., 2004). However, it took another 8 years to identify and clone Tox1 (Liu et al., 2012). This finding alerted researchers to the possibility that P. nodorum, like other Pleosporales such as Alternaria, Cochliobolus, and Pyrenophora, might be an NE-based pathogen. When the P. nodorum genome sequence was obtained in 2005, a primary target was the identity of Tox1. However, with no further information on the structure of Tox1, it was the gene ToxA that stood out. Although ToxA was misannotated in the original P. nodorum genome sequence, RTPCR confirmed its structure as highly similar to that found in P. tritici-repentis. As the physical properties of ToxA were different from those known for Tox1, it was already clear that P. nodorum, like P. tritici-repentis, was a pathogen possessing more than one NE. Functional genomic tools for P. nodorum had been developed in the 1980s (Cooley et al., 1988; Solomon et al., 2003) unlike P. tritici-repentis for which knockouts have only recently been reported (Moffat et al., 2014). These genomic tools were used to demonstrate the role of ToxA and Tsn1 in SNB (Friesen et al., 2006; Liu et al., 2006). Gene deletion of ToxA reduced disease levels on ToxA-sensitive wheat lines, and ToxA expression in an avirulent P. nodorum isolate conferred virulence. Unlike P. tritici-repentis, where ToxA is monomorphic, 10 forms of the protein exist in P. nodorum. These proteins exhibit differing levels of necrosis varying by a factor of about 30 (Tan et al., 2012). It also appears that the gene(s) is expressed at different levels in different isolates (Faris et al., 2011).

AGRONOMY OF GRAIN GROWING | Necrotrophic Pathogens of Wheat Furthermore, about 60% of a worldwide collection of P. nodorum isolates lack the ToxA gene altogether (McDonald et al., 2013). ToxA is present in nearly all isolates from Australia but is rare in isolates from China, Europe, and North America. Thus, at least four factors account for the variable relationship between the presence of Tsn1 and SNB severity: the absence of the gene in many isolates, the variable expression of the gene, the variable activity of the isoforms, and the presence of several other important NE interactions. The deletion of the ToxA gene facilitated the isolation and characterization of further NE. Several tools were used to identify Tox3 and later Tox1. Differential wheat lines with unique NE sensitivities were propagated. Further strains of the pathogen were chosen because of their differing NE profile and were sequenced. It was clear that these NEs (unlike ToxA) were secreted into the culture filtrate and so protein chromatography was used to purify the NE. Mass spectrometry was used to identify proteins in the most active fractions. Transcriptomics was used to refine the annotation of genes within the genome sequences and to identify genes expressed in the first few days of infection when cytological studies indicated the activity of NE. Candidate genes were expressed in yeast and E. coli so as to acquire adequate quantities of single pathogen proteins. These studies identified Tox3 and Tox1 (Friesen et al., 2008; Liu et al., 2012). Like ToxA in P. nodorum, Tox1 and Tox3 are present in multiple forms and the genes are absent in some isolates (absent in 16% for Tox1 and 39% for Tox3). It is not yet clear whether the different forms of Tox1 and 3 have different activities or if the genes are expressed at different levels. With the three NEs in hand, it was possible to evaluate the role of each in the wheat–P. nodorum interaction in Western Australia (Table 3). It was also possible to ablate Tox1 and Tox3 and thereby evaluate the virulence of strains lacking these NEs and to test the culture filtrate for sensitivity to NE other than ToxA, Tox1, and Tox3 (ToxA is not secreted in culture filtrates). The results present a complex but not unexpected picture (Tan et al., 2014). Firstly, deletion of Tox1 and Tox3 reduced disease levels in seedling trials of cultivars sensitive to Tox1 and Tox3, performed in (the required) GM-containment conditions. Secondly, it was clear that there were no current cultivars that were insensitive to all three NEs. Breeding of such a variety is a current high priority. Thirdly, it was clear that no single NE was a dominant factor in susceptibility, unlike the case for TS and ToxA, and so no simple relationships exist. Instead, it appears that sensitivity to any of the NE is sufficient to cause a significant level of disease. Fourthly, many cultivars were sensitive to NE not present in the culture filtrate produced by the strain lacking ToxA, Tox1, and Tox3. We conclude that breeding for disease resistance to SNB can adopt a new strategy. In general, the order of importance in NE is Tox3 > ToxA > Tox1. Cultivars that are insensitive to Tox3 are very rare. However, there appears to be no obvious reason why this is the case; such cultivars had no obvious deleterious properties when compared to Tox3-insensitive lines in field trials (Oliver et al., 2014). The first goal is to breed cultivars lacking sensitivity to all three NEs. We predict that such lines would be at least as resistant as the current most resistant ones. Numerous QTLs for SNB disease have been reported that are not due to the known NE. Hence, the research strategy involves (1) disease assessment of strains lacking ToxA, Tox1, and Tox3;

277

(2) purification of NE; (3) identification of novel disease and NE QTL; and (4) marker validation and NE/marker delivery to breeders.

Lateral Gene Transfer, Effector Interactions, and New Fungal Pathogens Compelling evidence exists that the gene encoding ToxA was acquired laterally (i.e., from a different species) by P. triticirepentis (Friesen et al., 2006). The disease went unnoticed by the pathology community until 1941. TS has since become one of the major pathogens in agriculture. A DNA region of at least 11 kb but more likely 145 kb (Manning et al., 2013) within the P. tritici-repentis genome is highly similar to a genomic region in the presumed ToxA donor, P. nodorum. The ToxA gene is monomorphic in the TS pathogen but highly polymorphic in P. nodorum, consistent with a recent history in TS. The cloning of Tsn1 demonstrated the subtlety of these necrotrophic pathogens. ToxA is recognized (in a manner not yet clear) by Tsn1 and induces a defense response. Unlike biotrophic interactions, the necrosis promotes infection. The success of ToxAcontaining TS suggests that the acquisition of a gene that induces necrosis in a host can be a very successful strategy for a pathogen that can tolerate the defense response. However, the use by breeders of NE is expected to negate the advantage accrued by the presence of these genes. Effector-assisted breeding thus promises to provide a sustained accrual of resistance in new cultivars leading to higher yields and reduced risk of fungicide resistance. Yet we must remain vigilant for new strains of the pathogen and even new species that evolve in situ or arrive from overseas.

Exercises for Revision How reliable are the research methods used to estimate disease data loss? Who provides the data and what biases might such people display? How are disease loss estimates used by (a) farmer, (b) agrochemical industries, (c) plant breeders, (d) research funders, and (e) researchers?

• • • •

Revise methods of QTL mapping. Revise methods for map-based cloning as applied to wheat. How do researchers deliver markers in plant breeding of a crop such as wheat? How do breeders use markers in plant breeding of a crop such as wheat?

Exercises for Readers to Explore the Topic Further Which omics technologies are relevant for plant pathologists?

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Compare breeding for disease resistance to biotrophs and necrotrophs. What evolutionary pressures would effector-based breeding place on necrotrophic pathogens? How should fungicides be used by farmers given the progress in breeding for resistance to biotrophs and necrotrophs?

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Acknowledgments Research in the authors’ laboratory is supported by the Australian Grains Research and Development Corporation.

See also: Agronomy of Grain Growing: Wheat: Biotrophic Pathogen Resistance; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Biotic Stress Resistance Genes in Wheat; Genomics of Food Grains; Grain Harvest, Storage and Transport: Chemicals for Grain Production and Protection; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture.

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Koeck M, Hardham AR, and Dodds PN (2011) The role of effectors of biotrophic and hemibiotrophic fungi in infection. Cell. Microbiol. 13: 1849–1857. Lamari L and Strelkov SE (2010) The wheat/pyrenophora tritici-repentis interaction: Progress towards an understanding of tan spot disease. Can. J. Plant Pathol. 32: 4–10. Liu ZH, Faris JD, Meinhardt SW, Ali S, Rasmussen JB, and Friesen TL (2004) Genetic and physical mapping of a gene conditioning sensitivity in wheat to a partially purified host-selective toxin produced by Stagonospora nodorum. Phytopathology 94: 1056–1060. Liu Z, Friesen TL, Ling H, et al. (2006) The Tsn1-ToxA interaction in the wheatStagonospora nodorum pathosystem parallels that of the wheat-tan spot system. Genome 49: 1265–1273. Liu Z, Zhang Z, Faris JD, et al. (2012) The cysteine rich necrotrophic effector SnTox1 produced by Stagonospora nodorum triggers susceptibility of wheat lines harboring Snn1. PLoS Pathog. 8: e1002467. Manning VA, Pandelova I, Dhillon B, et al. (2013) Comparative genomics of a plantpathogenic fungus, pyrenophora tritici-repentis, reveals transduplication and the impact of repeat elements on pathogenicity and population divergence. G3 Genes Genom. Genet. 3: 41–63. Mcdonald MC, Oliver RP, Friesen TL, Brunner PC, and Mcdonald BA (2013) Global diversity and distribution of three necrotrophic effectors in Phaeosphaeria nodorum and related species. New Phytol. 199: 241–251. Moffat CS, See PT, and Oliver RP (2014) Generation of a ToxA knockout strain of the wheat tan spot pathogen Pyrenophora tritici-repentis. Mol. Plat Pathol. 15: 918–926. Murray GM and Brennan JP (2009) The current and potential costs from diseases of wheat in Australia. http://www.grdc.com.au/DiseasesCostsWheat Accessed December 2014. Oliver RP and Ipcho SVS (2004) Arabidopsis pathology breathes new life into the necrotrophs-vs.-biotrophs classification of fungal pathogens. Mol. Plant Pathol. 5: 347–352. Oliver RP and Solomon PS (2010) New developments in pathogenicity and virulence of necrotrophs. Curr. Opin. Plant Biol. 13: 415–419. Oliver RP, Rybak K, Shankar M, Loughman R, Harry N, and Solomon PS (2008) Quantitative disease resistance assessment by real-time PCR using the Stagonospora nodorum-wheat pathosystem as a model. Plant Pathol. 57: 527–532. Oliver RP, Friesen TL, Faris JD, and Solomon PS (2012) Stagonospora nodorum: From pathology to genomics and host resistance. Annu. Rev. Phytopathol. 50: 23–43. Oliver R, Lichtenzveig J, Tan KC, et al. (2014) Absence of detectable yield penalty associated with insensitivity to Pleosporales necrotrophic effectors in wheat grown in the West Australian wheat belt. Plant Pathol. 63(5): 1027–1032. Quaedvlieg W, Verkley GJM, Shin HD, et al. (2013) Sizing up septoria. Stud. Mycol. 75: 307–390. Reimann S and Deising HB (2005) Inhibition of efflux transporter-mediated fungicide resistance in Pyrenophora tritici-repentis by a derivative of 4?-hydroxyflavone and enhancement of fungicide activity. Appl. Environ. Microbiol. 71: 3269–3275. Salam KP, Thomas GJ, Beard C, Loughman R, Macleod WJ, and Salam MU (2013) Application of meta-analysis in plant pathology: A case study examining the impact of fungicides on wheat yield loss from the yellow spot-septoria nodorum blotch disease complex in Western Australia. Food Secur. 5: 319–325. Solomon PS, Thomas SW, Spanu P, and Oliver RP (2003) The utilisation of di/ tripeptides by Stagonospora nodorum is dispensable for wheat infection. Physiol. Mol. Plant Pathol. 63: 191–199. Tan K-C, Ferguson-Hunt M, Rybak K, et al. (2012) Quantitative variation in effector activity of ToxA isoforms from Stagonospora nodorum and Pyrenophora triticirepentis. Mol. Plant Microbe Interact. 25: 515–522. Tan KC, Waters ODC, Rybak K, Antoni E, Furuki E, and Oliver RP (2014) Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors. Crop Pasture Sci. 65: 150–158. Thomma BP, Nu¨rnberger T, and Joosten MH (2011) Of PAMPs and effectors: The blurred PTI-ETI dichotomy. Plant Cell 23: 4–15. Tormen NR, Lenz G, Minuzzi SG, Uebel JD, Cezar HS, and Balardin RS (2013) Reaction of wheat cultivars to leaf rust and yellow spot and responsiveness to fungicides. Reaçaõ de cultivares de trigo a` ferrugem da folha e mancha amarela e responsividade a fungicidas 43: 239–246. Van Der Biezen EA and Jones JDG (1998) Plant disease resistance proteins and the gene for gene concept. Trends Biochem. Sci. 23: 454–456. Waters ODC, Lichtenzveig J, Rybak K, Friesen TL, and Oliver RP (2011) Prevalence and importance of sensitivity to the Stagonospora nodorum necrotrophic effector SnTox3 in current Western Australian wheat cultivars. Crop Pasture Sci. 62: 556–562. Wolpert TJ, Dunkle LD, and Ciuffetti LM (2002) Host-selective toxins and avirulence determinants: What’s in a name? Annu. Rev. Phytopathol. 40: 251–285.

Breeding of Grains

Contents Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation Barley: Genetics and Breeding Maize: Breeding Rice: Breeding Canola/Rapeseed: Genetics and Breeding Lentil: Breeding Lupin: Breeding Soybean: Germplasm, Breeding, and Genetics

Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation R DePauw, Agriculture and AgriFood Canada, Swift Current, SK, Canada L O’Brien, The University of Sydney, Narrabri, NSW, Australia; Solheimar Pty Ltd, Narrabri, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Origin of Wheat

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There are two known main species of wheat grown and consumed globally: common hexaploid wheat (Triticum aestivum L.) used for the production of breads, noodles, cakes, and pastries and durum wheat (Triticum turgidum L. subsp. turgidum conv. durum) used primarily for the production of pasta, couscous, and bulgur. Both occur as natural interspecific hybrids (https:// www.ksu.edu/wgrc/Taxonomy/taxintro.html). The progenitors of wheat (e.g., Triticum monococcum L. with three subspecies (one wild and two cultivated), Aegilops speltoides Tausch, and Aegilops tauschii Cosson) are diploid grasses, having seven pairs of chromosomes (2n ¼ 14). The natural chromosome complement or genome of each grass is unique, which supplies the grass its species attributes. Through many natural hybridization events, possibly over thousands of years in the West Asian region, a range of natural polyploids developed. The best known of these are durum wheat and common hexaploid wheat. Durum wheat is a tetraploid (4n ¼ 28), which originated from the natural hybridization of several diploid grasses, Triticum monococcum L. and T. urartu Tumanian ex Gandilyan (A genome) with Aegilops speltoides and possibly other extinct or extant Sitopsis species (B genome), giving it a genomic constitution of AABB. Hexaploid wheat (6n ¼ 42), resulted from a natural hybridization event between Triticum turgidum ssp. dicoccoides (AABB) and Aegilops tauschii (DD). Hexaploid wheat has a genomic constitution of AABBDD. Wheat evolved a genetic system conferring diploidization based on genes known as ph (pairing homologous) mutants

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Common hexaploid wheat and durum wheat have evolved from diploid grasses. Several key mutations resulted in polyploid wheat evolving a genetic system conferring diploidization and domestication. The observed wheat plant is a phenotype that is determined by its genetic composition (genotype), environment, and interaction of genotype and environment. New wheat cultivars respond to the challenges and limitations of abiotic and biotic stresses of the target environment and specifications for end-use suitability. Development of a new wheat cultivar is based on assembling genetic variability to meet all of the objectives and use of breeding methods and selection strategies to identify that genotype that has the maximum concentration of desirable genes. Genetic gain for a trait per unit of time is governed by selection intensity, selection accuracy, genetic variance, and years per plant breeding cycle. Emerging and enabling technologies enable earlier and more accurate characterization of the genotype, and selection can be practiced on the individual seed or plant.

Learning Objective

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To achieve an understanding of the origin of wheat, genetic variation, and strategies to assemble genes to increase their value for cultivation and use as field-ready cultivars.


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that facilitates pairing of the chromosomes at mitosis and meiosis in a homologous fashion, rather than across the genomes, thus preventing multivalent chromosome formation with deleterious intergenomic exchange. The recognition of a naturally occurring line deficient in the pairing homologous gene allows wheat chromosomes to pair across the genomes at both meiosis and mitosis. This means that genetic recombination can occur across the genomes, rather than between chromosomes within a genome. This ability to have wheat chromosomes pair either within or across its genomes facilitates the movement of genes between wheat and its near and distant relatives, making wheat relatives a very valuable source of genetic variation for pest and disease resistance, grain quality, and abiotic stress tolerances.

The Earliest Plant Breeders The earliest wheat breeders were undoubtedly man’s forebears, the hunter-gatherers. Most primitive wheats contain a gene for brittle rachis, where the main branch of the flower fragments at each spikelet when mature resulting in the spikelets falling to the ground. Thus, harvesting would entail picking up spikelets from the ground. A naturally occurring mutant variant for a nonbrittle rachis keeps the head intact. The ease with which this type could be harvested would have resulted in its selection as the preferred type by early hunter-gatherers. Major and minor mutations selected by humans were the free-threshing feature of the lemma, palea, and glumes separating easily from the seed or caryopsis. Prior to the free-threshing attribute, humans burned the chaff off of the grain or ground it off.

Working at the Phenotype Level Just like the hunter-gatherer, today’s wheat breeder has to work with the phenotype or what we see when we look at the plant. The phenotype is influenced by both the genetic constitution of the plant and the environment in which it is grown, plus the manifestation of the interaction between the genotype and its environment or the genotype environment (G E) interaction. This can be expressed as follows: Phenotype ¼ Genotype þ Environment þ G E As long as the breeder has to work with the phenotype, the design and implementation of all plant breeding is based around this simple but fundamental equation. It is clear from this statement that all three factors can influence the phenotype. Critically, for breeding to be effective, an understanding of how all components interact on the phenotype is fundamental to success. Phenotypes in which the environmental and G E components prevail will, by definition, alter in their expression when the environment changes. This will result in differing performance of a genotype from location to location and from year to year, resulting in the absence of genetic progress. On the other hand, phenotypes where the genotype component prevails and where the influence of the environment and G E components are minimized will result in a

consistent performance across locations and years. Under this scenario, genetic advance is made, resulting in the identification of the genetically superior wheat cultivars that get released as new cultivars.

Understanding the Environment and the Setting of Breeding Objectives A thorough knowledge of the target environment is fundamental, as it is the environment that determines breeding objectives. In its entirety, the environment consists of the soils, climate, and the biological environment in which the plant has to live. The breeder also has other environmental or managementrelated dimensions to consider such as the financial and physical resources available to the breeding program, access to supporting scientific disciplines and enabling technologies, and the grain quality demanded by the major markets to which grain may be sold.

The Environment Soils The soil provides the plant with its base for growing and its water and nutrients. Soil structure affects water penetration and holding ability. High-clay content soils generally have superior water-holding capacity compared with sandy-clay loams or deep sands. Factors such as pH, with its effect on plant growth and on nutrient availability, and factors toxic to plant growth such as free aluminum at low pH, high levels of available boron in ex-marine soils, unavailability of essential nutrients such as zinc at high pH, and unavailability of minor nutrients such as copper under waterlogging conditions all can have dramatic impacts on plant growth and, if not understood, can reduce genetic gain by appearing to be uncontrollable G E interactions. However, when properly understood, the production environment can be managed using agronomic approaches and further ameliorated with genetic variability that exists for most of the aforementioned aspects.

Climate The amount of rainfall the wheat crop receives and the timing of the rainfall events over the growing season impact plant growth via the obvious extremes of waterlogging or drought. Rainfall and soil fertility are two of the major factors determining grain yield and quality. Even transient periods of either event can have dramatic impacts on plant growth and thus on grain yield and quality. Temperature has a regulating influence on plant growth. Extremes such as high temperatures cause heat stress and drought, with downsides on yield and quality. Cold temperatures during winter slow down growth or lead to soil freezing and the need for breeders to incorporate winter hardiness in most of the major winter wheat-growing areas of the world. Transient periods of low temperature to below 0 C during critical stages of plant growth, such as from terminal spikelet formation to flowering, can cause severe yield losses as a result of frost damage. In most areas of the world, the practice is to

BREEDING OF GRAINS | Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation breed for frost avoidance, by delaying flowering to a time of more acceptable frost risk. This commonly means that flowering is delayed, so that grain filling has to take place under conditions of increasing temperature and decreasing availability of water. While at high-latitude wheat production areas, the ripening period occurs during decreasing temperature and reduced evapotranspiration. The occurrence of rainfall events prior to harvest determines that preharvest sprouting resistance based on seed dormancy is important to prevent the seeds from germinating prior to the grain being harvested so as to avoid downgrading in grain quality. Wind increases transpiration from plants, so in dry areas, this places crops under risk of increased moisture stress (drought at its severest). In combination with high temperatures during and after flowering, the grain-fill period experiences transient periods of moisture stresses. Breeders need to select and evaluate their materials under similar conditions to which they will be grown in order to produce varieties that can tolerate such conditions. Wind also demands that ripe crops can stand and ripen without lodging and/or shedding their grain prior to harvest.

Biological Component The interaction between soils and climate provides the conditions for organisms, both favorable and destructive to plant growth, to prosper. Favorable soil conditions that include microorganisms such as vesicular arbuscular mycorrhizae are important for healthy plant growth. The availability of moisture and nutrients is affected by what happens in the rhizosphere. This can also result in conditions where fungi, bacteria, viruses, and nematodes pathogenic to wheat plants can flourish. A wide range of fungi can infect wheat roots and their crowns, causing major yield losses. These include a range of Fusarium species, common root rot, Rhizoctonia root rot, a number of viruses, and plant nematodes. It is the environmental conditions in conjunction with a susceptible host plant that predisposes the plant to attack. An example is snow mold, where it is the amount and period of snow cover that determines the extent and severity of disease development. Above the ground, it is again the interaction of all the climatic components, in conjunction with susceptible host plants, that determines which plant diseases and pests will prosper, and the range is vast. The major foliar fungal pathogens are the rusts (stem rust caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. and E. Henn., leaf rust caused by Puccinia triticina Eriks., and stripe rust caused by Puccinia striiformis f. sp. tritici), the septorias (septoria tritici caused by Mycosphaerella graminicola (Fuckel) J. Schro¨t. in Cohn (anamorph Septoria tritici Roberge in Desmaz.)), and glume blotch caused by Phaeosphaeria nodorum (E. Mu¨ller) Hedjaroude (anamorph Stagonospora nodorum (Berk.) Castellani & E.G. Germano), powdery mildew caused by Blumeria graminis (DC.) E.O. Speer f.sp. tritici E´m. Marchal (syn. Erysiphe graminis DC. F.sp. tritici E´m. Marchal), and yellow (tan) spot caused by Pyrenophora tritici-repentis (Died.) Drechs (anamorph Drechslera tritici-repentis (Died.) Shoemaker). Each of these has unique sets of environmental

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conditions for development, mostly governed by the length of the dew period on the leaves for spores to germinate and then in the cases of the septorias and yellow spot rain drops for splash dispersal of spores to adjacent plants and new leaves of existing plants. Various pathogens infect the kernels and produce mycotoxins and cause yield loss such as Fusarium species, common bunt caused by Tilletia species results in yield loss and loss of market value due to offensive odors or primarily yield loss such as loose smut (Ustilago tritici (Pers.) Rostr.), and others such as pink smudge caused by Pyrenophora tritici-repentis (Died.) Drechs. and anamorph Drechslera tritici-repentis (Died.) Shoemaker result in discolored kernels that discolor flour or semolina. A range of viruses can also cause yield loss. Some require vectors for transfer between plants, such as barley yellow dwarf virus that is dispersed by aphids and wheat streak mosaic virus that is spread by the wheat curl mite.

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A variety of insect pests attack wheat plants causing yield and quality losses. Examples are wheat stem sawfly (Cephus cinctus Norton), which lays its larvae into wheat stems; the larvae feed on the parenchyma tissue of the stem and girdling of the stem above ground level prior to maturity, weakening the stem and leading to straw breakage and lodging. Orange wheat blossom midge (Sitodiplosis mosellana (Ge´hin)) feeds on the developing seed resulting in loss of grain yield and grain functionality. Cereal leaf beetle eats the epidermal tissues from leaves, thereby reducing photosynthetic area and causing yield loss. The cinch bug and some aphids feed on developing grains, releasing proteolytic enzymes into the grain and causing deterioration of the gluten proteins responsible for dough quality. Sunn pest (Eurygaster integriceps Puton) damages wheat by feeding on leaves, stems, and grains. During feeding, they inject enzymes that cause a breakdown of gluten manifested in physical dough properties and baking performance. Sunn pest occurs in parts of North Africa, Central Asia, and West Asia.

This brief overview of the major pests and diseases of wheat is intended to highlight that they are many and varied and they cause major losses in both yield and quality. As a result, most wheat breeding programs direct a major share of their resources to breeding for resistance. In order to effectively prioritize which resistances should be addressed by a breeding solution, breeders must have a comprehensive understanding of the environment of their target breeding area. For the full range of pests and diseases of wheat, biological variability exists. For the breeder, this means that one source of germplasm is rarely effective against all races, strains, or pathotypes of the pest or disease. Thus, effective breeding requires ongoing access to resistant germplasm, reliable screening tests, and molecular technologies linked to the resistant genes.

Grain Quality Major areas of world wheat production, especially those with production that is exported, are often located at considerable

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distances from where the grain will be consumed, resulting in the development of sophisticated grain handling and transport systems as part of grain trading. Increasingly, grain is traded on the basis of rigid quality specifications of dryness, cleanliness, protein content, and enzymes, for example, alpha-amylase. More discriminating markets have even tighter specifications relating to dough properties and end-product quality. It is this diversity of requirements that breeders must satisfy when setting quality objectives for their breeding programs. The environment of the target breeding and production region influences the quality of wheat that can be grown in any area. The production environment has a major impact on grain protein content, one of the major specifications upon which grain is traded internationally. For example, dryer regions tend to be lower yielding and favor the production of higher-protein, stronger, more extensible gluten wheat. To set effective market-based quality objectives, the breeder needs a reliable supply of market intelligence that has been interpreted into what is achievable by breeding. In most of the large wheat-producing and wheat-exporting countries, breeding programs obtain this information from grain traders, processors such as millers and bakers, and/or grower-supported marketing and research agencies.

Role of Germplasm Collections for New Trait Discovery Large collections of wheat are kept in international collections (USDA-ARS Beltsville http://www.ars-grin.gov/, Vavilov Collection http://www.vir.nw.ru/, CIMMYT http://www.cimmyt.org, Svalbard Global Seed Vault http://www.regjeringen.no/en/dep/ lmd/campain/svalbard-global-seed-vault.html?id¼462220, etc.) and are major sources of variability utilized by breeders. In some instances, passbook data are held on entries in these collections. However, often when a new disease or pest problem arises, the breeder has to systematically screen the collection for sources of resistance. As this is done, data are fed back to the collections, thereby creating some passbook data for future use. However, in the case of a new disease or change in an existing disease, the breeder usually has to go back to the collection and commence the screening process all over again, as it is only with virulence in a pathogen that new resistance in a host plant can be identified. Until we understand the genetic basis of what actually confers resistance at the DNA level, this cyclic process of screening germplasm collections will continue as new problems emerge. The Seeds of Discovery (http://seedsofdiscovery.org/seed/about/) project strives to generate knowledge of the phenotype and genotype of germplasm accessions and enhance their utility to breeders by developing bridging germplasm that carries exotic gene variants in elite adapted backgrounds.

Assembling and Creating Genetic Variability Genetic variability is the cornerstone of wheat breeding. Variability can be sourced from hexaploid wheat or its near and distant relatives. Traits can be introgressed into hexaploid wheat from these sources using conventional hybridization techniques. For interspecific or intergeneric hybridizations, the use of chromosome doubling may be required to get a balanced chromosome complement for successful cell division of the embryo and the resultant plant. With the advent of molecular biology, traditional interspecific, intergeneric, and plant-type barriers to gene transfer have been removed. By isolating the gene for a particular trait and inserting it into a new host by a range of techniques (e.g., biolistic bombardment or Agrobacterium transfer), the gene becomes part of the host DNA, replicating itself at cell division and expressing itself in plant development. The development of such genetic engineering techniques considerably enhances the range of genes available to the modern plant breeder. But to date, there have been no commercial deployments of cultivars that have genes inserted into wheat from outside of the grass tribe. Gene-editing technologies are developing to alter a gene and thereby express new forms of the trait such as resistance to a pathogen or seed storage proteins. Traditionally, breeders have gone to other breeding programs or to major germplasm collections to source their genetic variability. Utilizing genetic variability is always done in a targeted manner, with the breeder seeking new genes for an agronomic, disease resistance, quality, or yield-related trait. Transfer of the new gene is usually performed by conventional hybridization, followed by cycles of selection until the new gene is fixed in its new background. To facilitate transfer of new genes, knowledge of the inheritance of the trait and the ability to select for it in its new background are essential.

Hybridization Systems Wheat is a self-pollinating crop and so lends itself to hybridization by a range of methods. Breeders design their crossing programs so that the resulting populations produced will segregate for all the traits desired in the new varieties. Breeders choose one of the parents to become the female of the cross and affect this by removing the anthers from all florets of the ear. Hybridization is completed a few hours to a few days later by transferring pollen from the plant designated as the male. This is done using a range of methods, with the transfer being completed using tweezers to shake the pollen from individual anthers onto the receptive stigma or by cutting back florets of the designated male plant so that anthers are exposed. The dry air causes them to dehisce, and the male plant is then shaken or twirled over the stigma, thereby effecting pollination. Other means for hybridizing wheat include the use of cytoplasmic male sterility–nuclear fertility restoration mechanisms or the use of chemical hybridization agents. Both of these systems still rely on making one of the parents the nominal female, while pollen is transferred from another parent chosen as the male of the cross. Both of these mechanisms, while useful for crossing, are better deployed for making hybrid wheat where the advantages of heterosis (hybrid vigor) can be captured.

Crossing Strategies Choice of crossing strategy depends on the range of traits available in the parents and those desired in the progeny of a cross. If all the desired attributes can be obtained from just

BREEDING OF GRAINS | Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation using two parents, A and B, then the straight cross A/B strategy can be deployed. If one of the parents (A) has more desirable traits than the other, then to increase the frequency of the desired genes from A, a further cross to that parent can be made, making for an A/B//A crossing strategy. When all the desired traits cannot be assembled from a straight crossing strategy and three parents are needed (A, B, and C) to get all of them in the progeny, then a three-way crossing system can be used, such as A/B//C. When a variety has most of the traits desired but has had a resistance breakdown or can be enhanced by the addition of a new resistance or trait, then the new gene(s) can be rapidly introgressed using the backcross crossing strategy. If the new resistance gene is dominantly inherited and all that is wanted from this donor parent is that gene, the original variety becomes the recurrent parent and repeated cycles of crossing between the recurrent parent and the F1 generation can be made until the desired percentage of the recurrent parent is recovered. The gene frequency of the recurrent parent increases according to the formula (1 (1/2)n) where n is the number of crosses to the recurrent parent. The straight cross F1 contains 50% of genes from each parent. The first backcross to the

Figure 1 Aerial view of a contra season nursery in New Zealand used by SPARC, AAFC Canada.

Figure 2 Fleet of combines to harvest early generation yield trials. (courtesy SPARC, AAFC; photograph taken by D. Schott).

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recurrent parent increases the frequency of recurrent parent genes to 75%. Subsequent backcrosses increase the gene frequency to 87, 93, 96, and 98% for the second to fifth backcrosses, respectively, and so on. When deploying the backcross breeding strategy for recessively inherited genes, it is necessary to allow the first cross to go to the F2 generation and then screen for the presence of the new gene or trait, prior to making the next backcross. At each backcross cycle, it is necessary to go to the F2 and conduct screening for the new trait prior to crossing to the recurrent parent.

Selection and Evaluation Systems and Breeding Methods Factors Influencing the Sequence of Trait Selection and Choice of Breeding Method Modern wheat breeding programs have an extensive array of breeding objectives that must be addressed. Many are simply inherited, but many of the economically important traits like yield and quality are complexly inherited and subject to the influence of G E interaction, meaning that selection and evaluation need to occur over locations and years. This dictates that modern programs need to be large in scale handling thousands of different genotypes in each breeding cycle. This demands significant investment in high-quality land for field evaluations for yield experiments, disease resistances, etc. (see Figure 1 of contra season generation) and the mechanization needed at each phase of the breeding process, namely, seed preparation, field testing (Figure 2), and laboratory- and glasshouse-based screening tests (Figure 3). The number of gene-pair differences and inbreeding has a geometric impact on the frequency of desirable alleles, which in turn impacts the size of population required to have a chance occurrence of the desirable type and the optimum generation to initiate selection. The geometric changes that occur with increasing number of loci and decreasing frequency of genotypes with the desirable alleles upon inbreeding provide a rationale for early generation selection. There are many different ways in which breeders can manage material flow in breeding programs

Figure 3 Sampling plant tissue to collect DNA to perform marker assisted breeding (courtesy SPARC, AAFC; photograph taken by C. Barlow).

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Cross: Choose parents which combine all the traits Single seed descent

Pedigree with two generations per year Winter cycle F1, F3, F5 inbred, select, multiply contra season

Summer cycle

F1 self to F2 grow out in selection nursery

F2

Single seed decent F2 selections to F3 and F4 in greenhouse

F4 , F6 diseases, agronomics, quality

F4 plant to F5 head row diseases F7 and F8 diseases, agronomics, quality

Doubled haploid DH1 confined DH2 unconfined diseases DH3 select multiply contra season DH4 and DH5 diseases, agronomics quality

F6 multiplication contra season F7 and F8 diseases, agronomics, quality

Registration trials and breeder seed production F9 or DH 1 year

1st year initiate Pre-breeder seed

F10 or DH 2 years

2nd year Pre-breeder seed

F11 or DH 3 years

3rd year Breeder seed

6 to 7 years

6 to 7 years

6 to 7 years

Figure 4 Schematic steps to develop and produce breeder seed of a new cultivar with a comparison of pedigree, single seed descent, and doubled haploid breeding methods.

each with pros and cons. Choice of method depends on many factors, including cost of variety development, which makes the shortening of the breeding cycle a high priority, resources available to the breeding program, and the availability of effective selection methodologies for the target traits. Genetic gain for any individual trait is governed by the equation Rt ¼ irVa =y where Rt is genetic gain over time; i is the selection intensity and can be increased to a limit; r is the selection accuracy and can be improved by more precise measurements, replication in space and time, reduction of errors, correction for environmental factors, and genomic tools such as perfect molecular markers for traits; Va is the genetic variance and can be increased by incorporation of beneficial alleles and minimal introduction of undesirable alleles; and y is the years per plant breeding cycle and can be reduced by growing more than one generation per year and use of doubled haploid technology.

Pedigree method This is the method of choice where disease resistances are the priority traits that must be incorporated into new varieties. The pedigree method allows for simply inherited, often single-gene traits to be selected and fixed through repeated cycles (2–4) of selection until homozygosity is achieved. To shorten varietal development, this method is often combined with the use of two or more field-grown generations per year.

Modified pedigree In this process, the basic pedigree cycle is followed, but with the addition of a round of yield evaluation and/or quality

testing as early as possible, F3 or F4, in order to remove lowyielding and poor-quality families from the breeding program and use multiple generations per year (Figure 4).

Single-seed descent This method allows for up to four generations per year using growth chambers and glasshouse conditions (Figure 4). A population of 200 or more seeds is planted, and only single tiller plants are produced by manipulating the watering and nutrition regime to speed up the growth of plants. At harvest, one seed from each plant is taken and planted again for the next generation. This process is repeated until plants are advanced to between the F4 and F6 generations. Seed is then increased and planted in the field in observation rows or yield plots. The advantages of single-seed descent are speed combined with cycles of recombination, giving the possibility of desirable recombinants being produced.

Doubled haploid or dihaploid development In this method, F1 seeds are produced by conventional crossing techniques using the two parents that between them have all the traits desired in the new variety (Figure 4). Doubled haploids can be produced from microspore culture, but the wheat–maize method is the most widely used system. In the wheat–maize system, F1 seed is made by hybridization, the seeds are planted, and their flowers are emasculated and pollinated with maize pollen. A haploid (a plant with single chromosome of each of the 21 hexaploid wheat pairs) starts to develop. This haploid embryo is rescued and allowed to grow into a haploid plantlet, which is then treated with a chromosome-doubling agent such as colchicine, nitrous oxide, or caffeine to produce a diploid plant. Seeds from

BREEDING OF GRAINS | Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation these plants are instantly homozygous for all genes, thus imparting the major advantage of this breeding system, that is, it takes material to true breeding status in less than 1 year, thus considerably shortening the breeding cycle.

Early-, Mid-, and Late-Generation Selection In the early generations, the focus is on selection of traits of highest heritability. These are usually agronomic attributes and disease resistances. In the mid and later generations, irrespective of what breeding method a breeder chooses to use, selection is about validating performance of breeding lines, demonstrating their merit for potential release as new varieties. However, some breeding programs select simultaneously for qualitatively and quantitatively inherited traits simultaneously starting in the F4 generation. This usually involves the use of replicated, multisite, multiyear yield and quality evaluations to gather the data needed to support the decision to bulk up seed for release. Most breeding programs consider that 3 years of such evaluations are needed to demonstrate the reliability of any potential variety.

Emerging and Enabling Technologies Marker-assisted breeding (MAB) is being used as a tool with markers linked to genes controlling high-value traits. Preferably, the marker resides within the target gene but closely linked markers on each side of the target gene are almost as effective. MAB has been applied to a range of fungal pathogens and two insect pests, end-use suitability traits, and phenological and morphological traits. MAB can be used to target individual traits as they are introgressed by backcrossing or straight crossing into adapted backgrounds and/or used to retain a high proportion of the adapted parent background when adequate marker coverage across the genome is available to the breeder. One of the greatest impacts of applying markers is in the earliest stages of segregation, for example, top cross F1 or F2 to shift gene frequencies. MAB is being effectively combined with doubled haploid technology where haploids are screened and only those having the desired marker profile are doubled. Randhawa et al. provided a short list of some of the traits that breeders can target using MAB, but as the technology continues to develop, this list continually expands. Exciting technologies have emerged that characterize germplasm at the DNA sequence level. Exome sequencing of diverse collections of hexaploid and tetraploid wheat coupled with transcriptome profiling of well-characterized genetic stocks is being used to identify genes controlling traits. There has been a massive number of single-nucleotide polymorphism (SNP) markers discovered, which enables high-density genetic maps to be constructed for gene cloning and opportunities for whole-genome selection strategies to be formulated. Chip technology is developing rapidly, and SNP chips are available that generate genome-wide data and information on target traits that are outpacing data handling capability to analyze the information being generated. Genomic selection (GS) is a tool to enable selection on a single plant or seed, selection in unobserved environments, maintenance of genetic diversity, and evaluation of larger

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populations. The value of GS is that it shifts the basis of selection from the phenotype level to the gene level. Hence, it is extremely attractive to breeders for traits that are difficult and time-consuming to screen for and are highly modulated in their expression by the environment. Furthermore, it allows for selection to be practiced in unobserved environments. Gene editing has the potential to alter an existing gene to express a different biochemical compound that makes it resistant to a fungal pathogen. Another example of gene editing would be to alter a gene encoding a protein subunit to alter its rheological properties. Use of the genetically modified organism (GMO) approach is in its infancy in wheat breeding. These technologies remove species and genus barriers to gene transfer, so they considerably expand the range of genes available to the wheat breeder. Currently, the processes of inserting a gene into wheat breeding material means that the position the gene inserts itself into the host DNA is random, so success rate of gene expression is low. As gene-splicing techniques improve, the success rate can be expected to improve. Backcrossing is the preferred method for rapidly transferring GMO traits into adapted wheat backgrounds. Varietal fingerprinting is another useful breeding aid where both the DNA complement of a recurrent parent and a DNAbased marker for the gene to be introgressed in a backcross breeding program can be tracked at the DNA level. The use of these combined strategies will shorten the breeding cycle by earlier recovery of sufficient contribution of the recurrent parent DNA at an earlier stage in the backcross process. This technology will also be increasingly used to identify breeding programs for varietal identification at the point of sale for integrity of marketing and trading grain and for intellectual property issues associated with the protection of plant breeders’ rights.

Wheat Breeding as Part of Supply Chain Management Modern wheat breeding is just one part of a sophisticated supply chain, whereby all parts of the chain are important in adding value to a major food source. All members in the supply chain can have a major impact on the overall product as it moves through the chain, so the more these components can be integrated, the more efficient the process and the less downside on the quality of the end product. This demands good information flow up and down the supply chain. With the wheat breeder sitting at the end of the supply chain most distant from the consumer, the effectiveness of information flow and the quality of that information are critical for effective wheat breeding.


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What is the meaning of a phenotype and a genotype? For a wheat cultivar to have value for cultivation in a specific region, what are some of the agronomic traits and response to diseases and insects it should have? How can genetic variation be generated in a plant breeding program upon which selection can be practiced? What are the similarities and differences among the breeding methods: pedigree, single-seed descent, and doubled haploidy?

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What is genetic gain for a trait and what factors determine genetic gain? What is marker-assisted breeding?


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What is the evolutionary origin of hexaploid and durum wheat? What are some of the health benefits of consuming whole wheat products? For a cultivar to have value for use to make a specific consumer product, what are some of the specifications for milling, protein quantity and quality, and enzymes such as alpha-amylase? What are three diseases of wheat and how can they be controlled? What is genomic selection and how could it be applied to cultivar development?

See also: Agronomy of Grain Growing: Wheat: Agronomy; Genetics of Grains: Wheat Genetics; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Canola: Harvest, Transport, and Storage; Sorghum: Harvest, Storage, and Transport; Wheat: Harvesting, Transport, and Storage; Grain Marketing and Grading: Barley: Grading and Marketing; Soybean: Grading and Marketing.

Further Reading Allard RW (1999) Principles of Plant Breeding, 2nd edn. New York: Wiley. Baenziger PS and DePauw RM (2009) Cultivar development in wheat – Procedures and strategies. In: Carver B (ed.) Wheat: Science and Trade, pp. 273–308. Ames, IA: Wiley-Blackwell Publishing. Bonjean AP and Angus WJ (eds.) (2001) The World Wheat Book: A History of Wheat Breeding Paris: Lavoisier. Carver B (ed.) (2009) Wheat: Science and Trade. Ames, IA: Wiley-Blackwell Publishing. Heffner EL, Sorrells ME, and Jannink JL (2009) Genomic selection for crop improvement. Crop. Sci. 49: 1–12. http://dx.doi.org/10.2135/ cropsci2008.08.0512.

Heyne EG (ed.) (1997) Wheat and Wheat Improvement, 2nd edn. Madison, WI: American Society of Agronomy. Lupton FGH (ed.) (1996) Wheat Breeding. London: Chapman and Hall. O’Brien L and Blakeney AB (eds.) (1998) An Introduction to the Australian Grains Industry. North Melbourne, Australia: Royal Australian Chemical Institute. Randhawa HS, Asif M, Pozniak C, et al. (2013) Application of molecular markers to wheat breeding in Canada. Plant Breed. 132: 458–471. Sears ER (1977) An induced mutant with homoeologous pairing in common wheat. Can. J. Genet. Cytol. 19: 585–593.

Relevant Websites http://www.agronomycanada.com – Canadian Society of Agronomy. http://www.ahdb.org.uk/ – Agriculture and Horticulture Development Board UK. http://www.ars-grin.gov – National Plant Germplasm System, USDA – ARS. http://www.ars.usda.gov/main/site_main.htm?modecode¼36-40-05-00 – Cereal Disease Lab (Rust Lab – USDA – ARS). http://www.cimmyt.org – CIMMYT. http://www.cgiar.org – Consultative Group on International Agricultural Research. http://www.fao.org – Food and Agriculture Organization of the United Nations. http://www.fao.org/statistics/en/ – Food and Agriculture Organization of the United Nations. http://www.fera.defra.gov.uk/ – The Food and Environment Research Agency. http://www.grainscanada.gc.ca – Canadian Grain Commission. http://www.grdc.com.au – Grain Research and Development Corporation, Australia. http://www.icarda.cgiar.org/ – ICARDA. http://www.inspection.gc.ca – Canadian Food Inspection Agency for plant products for variety registration and PBR. https://www.ksu.edu/wgrc/Taxonomy/taxintro.html – Wheat Classification Tables Site. http://meteo.gc.ca/ – Environment Canada weather forecast by location worldwide. http://pgrc3.agr.gc.ca – Plant Gene Resources Canada. http://phytopath.ca/index.shtml – The Canadian Phytopathological Society. http://www.sas.com – Statistical Analysis Systems. http://www.scabusa.org – US Wheat and Barley Scab Initiative. http://seedsofdiscovery.org/seed/about/ – Seeds of Discovery. http://www.regjeringen.no/en/dep/lmd/campain/svalbard-global-seed-vault.html? id¼462220 – Svalbard Global Seed Vault. http://www.ars.usda.gov/main/site_main.htm?modecode¼36-40-05-00 – UK Cereal Disease Lab. http://www.usda.gov – US Dept of Agriculture. http://www.uswheat.org – US Wheat Associates. http://www.vir.nw.ru/ – Vavilov Research Institute of Plant Industry. http://westerngrains.com/ – Western Grains Research Foundation, Canada. http://wheat.pw.usda.gov – Graingenes.

Barley: Genetics and Breeding A Cuesta-Marcos, JG Kling, AR Belcher, T Filichkin, SP Fisk, R Graebner, L Helgerson, D Herb, B Meints, AS Ross, and PM Hayes, Oregon State University, Corvallis, OR, USA SE Ulrich, Washington State University, Pullman, WA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Cultivated barley is one of 31 Hordeum species, in the tribe Triticeae of the grass family. Barley varieties differ in several ways: • Two-row versus six row barleys. • Hulled versus naked barleys. • Winter versus spring barleys. • Malting versus food versus feed types of barley. • Conventional versus F1 hybrid barley. The qualitative traits of plant height, disease resistance, vernalization requirement, and kernel composition have high heritabilities. In contrast, selection is more difficult for a qualitative trait (involving many genes) such as malting quality. Molecular markers are proving successful to select for traits, even if involving closely linked genes. Selection for malting quality involves micro-malting and malt analysis tests, followed by pilot-scale malting tests. Final selection of a good malting variety may require up to 15 years.

Learning Objectives

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To gain an understanding of the genetics of cultivated barley, its relationship to the wider barley family thus insight into breeding technologies used to improve barley genotypes.

Introduction Barley (Hordeum vulgare subsp. vulgare L.) is one of the cereals that humans domesticated in the Middle East around 10 000 years ago. Today, barley is the fourth most important cereal crop in the world (FAOSTAT). Barley is essential for the malting and brewing industries and is an important animal feed. There is currently a resurgence of interest in barley as a human food. Cultivated barley is one of 31 Hordeum species, belonging to the tribe Triticeae, of the grass family (Poaceae). It is an annual, self-pollinating, diploid species with 2n ¼ 14 chromosomes and a genome size of 5.1 gigabases. The relative simplicity of the genetic system, the genetic diversity of the species, and the availability of a whole genome sequence make it an ideal organism for genetic studies and breeding efforts. The wild ancestor of barley (H. vulgare subsp. spontaneum) has a brittle rachis and occurs only in the two-row form. Cultivated barley has a nonbrittle rachis and may be in the two-row or the six-row form. H. vulgare subsp. spontaneum may be a


transitional form between the true progenitor of barley and the cultivated species.

Morphological Diversity Full descriptions of morphological mutants and the genes that control them have been published in the ‘Barley Genetics Newsletter’ since the 1990s (http://wheat.pw.usda.gov). The entire collection of about 12 000 accessions can be browsed at the Nordic Genetic Resource Center database (http://sesto. nordgen.org/sesto).

Two-Row versus Six-Row Barley Barley has a single floret in each spikelet. There are three spikelets at each rachis node, alternating on either side of the barley head or spike. In two-row barley cultivars, the central floret is fertile and the two lateral florets are sterile, resulting in a single seed at each node (Figure 1(a)). In six-row barley, all the florets are fertile, giving three seeds at each node (Figure 1(b)). The central seeds in six-row barley cultivars are round and plump, but the laterals tend to be slightly asymmetric. A single head of barley can produce up to 80 seeds. The development of lateral spikelets and lateral awns is controlled by alleles at the vrs1 locus on the long arm of chromosome 2H, where the six-row trait is recessive. HvHox1 has been proposed as a very likely candidate gene for vrs1 based on positional cloning and confirmed identity and biological function via induced mutation. Several dominant and recessive alleles have been described. The morphology of the spike also depends on the interactions of vrs1 with alleles at the int-c locus on chromosome 4H to create intermediate phenotypes. The underlying gene of the locus has been found to be an ortholog of the maize domestication gene teosinte branched 1. Commercial two-row varieties are usually recessive for int-c, while sixrow cultivars have the dominant allele. Two-row varieties usually have a higher number of tillers per plant and plumper, heavier kernels than six-row varieties. Six-row varieties, on the other hand, usually have more seeds per inflorescence. Thus, the compensatory effects of yield components lead to similar levels of yield potential. Two-row barleys are favored for malting in most parts of the world, but in the United States and Mexico, six-row barleys have been used extensively for this purpose. Given that two-row and six-row germplasm have historically been maintained in separate breeding pools, one might expect that crosses between the two groups would produce some useful segregants with superior agronomic and malting characteristics. The experience of plant breeders, however, has been that two-row six-row

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Adaptive Characteristics

(a)

(b)

Figure 1 Heads of the (a) two-row barley and (b) six-row barley.

crosses do not immediately provide useful progeny for variety development. Other types of inflorescences include Hordeum deficiens, a two-row type in which the lateral florets are rudimentary and virtually absent, and labile barley, a type of inflorescence common in Ethiopian landraces where the number of fertile florets is different at each rachis node.

Specialty Types Most barley varieties are hulled types, with the lemma and palea remaining attached to the seed at maturity. Threshing involves removal of the kernel from the rachis and removal of the awns or hoods from the tip of the lemma. Varieties that are difficult to thresh retain part of the awns or rachis and may have lower test weight and quality for feed or malting. In hullless or naked types, the seed separates from the lemma and palea during threshing. The hull-less characteristic is controlled by a simple recessive allele at the nud1 locus on the long arm of chromosome 7H. Hull-less types are produced for various food and beverage uses in East Asia, primarily China, Japan, and Korea. Hull-less barley is an important subsistence crop in the Andes, the Himalayas, and the Ethiopian highlands. In Canada, hull-less varieties are commonly grown as feed for swine. Variation in the morphology of barley awns may also influence the suitability of cultivars for particular end uses. Most cultivars have awns, which may be rough or smooth, but awnless types also exist. Hooded types have modified awns that consist of a deformed, inverted floret with leaflike appendages. This trait is controlled by a single dominant gene at the Kap1 locus located on the short arm of chromosome 4H. Hooded varieties are preferred for hay, silage, and green chop. Other variants in barley include colored lemmas, colored kernels, and colored endosperm, ranging from pale yellow to black. Blue aleurones are common in some germplasm groups and are controlled by alleles at five blx loci with complementary effects. In general, types with white aleurones are preferred because the kernels have a brighter appearance.

Different gene pools have evolved in the major barley production areas of the world. Fitness for a given region requires appropriate maturity and tolerance to local biotic and abiotic stresses. Distinct gene pools may also reflect present and historical end uses of barley or market preferences. Yield is a primary objective of any breeding program, and steady increases have been attained over the years. Improvements in yield are achieved through manipulation of yield components, including number of spikes per unit area, number of kernels per head, kernel weight, and harvest index (the ratio of grain to total aboveground biomass). However, plants with higher relative grain weight are more likely to fall sideways or lodge. Good lodging resistance requires strong stems and a sturdy root system to anchor the plant in the soil. Lodging has been reduced in modern varieties through increased straw strength and reduced plant height, particularly via semidwarf traits. Semidwarf stature may be controlled by one or several genes; the gene most commonly used commercially is sdw1/denso. Selection for reduced height can have undesirable effects on yield and other characteristics, so it is important to consider multiple traits when attempting to improve lodging resistance. Barley varieties should be bred to have the optimum maturing cycle, estimated by heading date, for their target environments. Early maturity is a very important adaptive trait at higher latitudes. For areas with a longer growing season, it is best to grow varieties with longer vegetative periods. Barley requires long days to initiate flowering, but cultivars vary. Barley has a slightly shorter life cycle than other cereals, which may enable it to escape drought in some environments. It is also relatively tolerant to drought and has the capacity to send up new tillers when conditions become favorable. Plants are most adversely affected by drought during floral initiation and anthesis. Much of the variation in heading date among commercial cultivars is controlled by the flowering locus T (HvFT1 synonym of Vrn-H3), the photoperiod response genes Ppd-H1 and Ppd-H2, the vernalization sensitivity loci, Vrn-H1 and Vrn-H2, and several genes and loci that control earliness per se. Barley is more salt-tolerant than many other crops and is often used to reclaim saline soils. Breeding programs have been successfully carried out for increased salt tolerance. Varieties have also been developed with tolerance to aluminum and soil acidity.

Winter Barley Winter barley varieties require a period of exposure to cool temperatures (vernalization; loci listed earlier) to initiate flowering. They are usually photoperiod-sensitive, which prevents them from flowering in the winter, even if the cold requirement has been fulfilled. Those traits reduce chances for cold damage. Facultative varieties do not require vernalization but are tolerant to cold temperatures, so they can be planted in fall or spring. Fall-planted barley is potentially higher yielding than spring barley. However, even cold-adapted barley varieties are generally not as tolerant to cold as other winter

BREEDING OF GRAINS | Barley: Genetics and Breeding cereals. Cold tolerance in barley has been a difficult trait to improve because screening for winter hardiness in the field is seldom reliable. It is best to screen breeding material for cold tolerance under controlled conditions in the laboratory. Three barley cold tolerance loci have been identified: Fr-H1, Fr-H2, and Fr-H3.

Disease and Insect Resistance Commercial varieties must possess adequate levels of resistance to the disease and insect pests prevalent in their target production zones. It is often stated that qualitative resistance determined by single genes can be overcome by new strains of a pathogen, whereas quantitative resistance, although not absolute, tends to be more durable over time. Barley is affected by many diseases, most of which are typical of small grain cereals, for example, rusts (Puccinia spp.), smuts (Ustilago spp.), root rots (Rhizoctonia, Pythium, and Fusarium), bacterial blights, and viruses. To date, many qualitative and quantitative loci have been mapped for resistance to barley leaf rust (Puccinia hordei), barley stripe rust (Puccinia striiformis f. sp. hordei), barley yellow dwarf virus (BYDV), and powdery mildew (Blumeria graminis f. sp. hordei). The powdery mildew resistance genes mlo and MLA are well characterized and serve as model systems for plant qualitative disease resistance. The same is true for the barley complex locus rpg4/Rpg5, which provides both host resistance and nonhost resistance to stem rust (Puccinia graminis). Quantitative resistance to stripe rust has also been the object of numerous studies that include mapping, introgression into isogenic lines, validation of effects in different genetic backgrounds, and estimation of additive effects and interactions. Breeding for insect resistance is a difficult task, because it is usually necessary to rear the insects to obtain uniform, reliable screening. Green bug (Toxoptera graminum), Russian wheat aphid (Diuraphis noxia), jointworm (Tetramesa hordei), and the cereal leaf beetle (Oulema melanopus) have all received attention in barley breeding programs.

Breeding Strategies Breeding Objectives Breeding programs have traditionally emphasized yield and adaptation. The primary goal has been to develop malting types, because they receive a premium price in the market. Furthermore, malting and brewing industries have provided much-needed support for breeding programs. In contrast, relatively little effort has been made to improve barley for feed or food uses. A common strategy in breeding programs is to breed for good malting quality, with the expectation that resulting varieties will also be good for feed. This approach is based on the assumption that the nutritional requirements of yeast in the brewing process are not too different from those of animals, particularly monogastrics. This theory has been researched and debated for many years. Among existing varieties, there does appear to be some association between quality for feed and quality for malting and brewing. Others argue that existing

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varieties may not truly represent the potential for high-quality feed barleys, because feed quality has not been a specific objective of breeding programs. There has been considerable debate about the best ideotype to select to increase yield in barley, because there are often compensatory effects among yield components. Studies of yield components have led to a better understanding of changes brought about by selection but have provided few useful tools with which to improve selection efficiency.

Quantitative and Qualitative Traits Many of the important traits determining yield, malting, and feed quality are quantitatively inherited, which means that they are controlled by many genes and are measured on a continuous scale. Quantitative traits may be influenced considerably by environmental conditions during the growing season. Genotype–environment interaction is also common for quantitative traits, which complicates selection in a breeding program, because genotypes that perform the best in one environment may not perform as well in another. Genotypes must be evaluated over multiple sites, and advanced lines must be tested in several seasons to assess quantitative characters. Qualitative traits that are controlled by one or just a few genes are fairly easy to manipulate in a breeding program, because progeny from crosses between selected parents usually exhibits predictable Mendelian segregation patterns. The situation with quantitative traits is far more complex, because one is never sure whether the parents selected have all of the favorable genes controlling the trait. Furthermore, it is necessary to screen large numbers of progeny to have a good chance of obtaining the favorable genes from both parents in one of the offspring.

Breeding for Quantitative Characters Barley breeders and geneticists have approached the challenge of understanding the inheritance of quantitative traits using biometrical tools. Certain traits such as plant height, disease resistance, vernalization requirement, and kernel composition tend to have high heritabilities, which means that the phenotype is determined to a large extent by genetics. Traits with high heritabilities are fairly responsive to selection. Others, such as yield and many malting quality parameters, have lower heritabilities and are more subject to environmental influences. Information about genetic variances and heritabilities has helped to refine selection methods but still leaves many questions unanswered regarding the relationship between genes and adaptation. The advent of molecular markers and quantitative trait locus (QTL) analysis in the late 1980s provided a means to determine how many genes are controlling a trait, their relative importance in determining the phenotype, and their location on the chromosomes. QTL markers have made it possible to track the transmission of favorable genes from one generation to the next, assisting breeders to choose the best parents for a cross and to select the best offspring.

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Barley Cultivation in a Breeding Program The management practices needed to grow barley in a breeding program are similar to those used in commercial production. Cool temperatures are needed during early growth and establishment and spike development, particularly if crosses are to be made. Techniques available for emasculating and pollinating barley have been reviewed. The anthers must be removed or destroyed when they are still plump and green or greenish yellow, to prevent self-pollination. Stigmas of the female flowers become feathery and receptive to pollen 1–3 days later. Barley pollinations are most successful in the morning, when the anthers naturally dehisce.

Breeding Methods The most common approach utilized for barley improvement has been pure line variety development through conventional pedigree and backcross breeding techniques. In other programs, bulks of segregating families are evaluated in parallel with pure line development, to permit assessment of quantitative characters in earlier generations. Single seed descent (SSD) has also been used effectively for spring or facultative germplasm, to rapidly advance material from the F2 generation to the F4 or F5 generation in the greenhouse, where it is possible to grow three generations in a year. For germplasm with a winter growth habit, one can rely on the natural cold temperature exposure in the field or use a growth chamber to advance generations more quickly in the greenhouse. Another possibility is to use doubled haploid (DH) techniques to advance directly from the F1 generation to homozygous pure lines. One possible advantage of SSD compared to DH production is that the additional generations of selfing provide additional opportunities for genetic recombination. Another consideration is the genetic stability of completely homozygous lines derived from haploid methods. With a few exceptions, the general conclusion from experiments comparing conventional, SSD, and haploid breeding methods is that the mean and variance of yield performance are similar for lines derived from the three methods. The choice of methods will depend on breeding objectives, the relative time and expense involved, and the facilities available. Once the desired level of homozygosity has been attained, single-head rows may be evaluated in a breeding nursery for highly heritable traits such as disease resistance and agronomic type. A bulk from a single-head row can be evaluated in preliminary yield trials at two locations. In the next generation, adequate seed should be available to initiate advanced yield trials and tests for malting quality.

Mutation Breeding Chemical mutagens and ionizing radiation have been used extensively to induce new variation in barley. Most mutations are recessive and most are deleterious. Nonetheless, mutationinduced variation has been used in conjunction with conventional breeding methods to generate barley varieties with semidwarf stature, early maturity, and disease resistance. A number of useful mutations in kernel composition have been

induced, including high-protein, high-lysine, low-b-glucan, and proanthocyanidin-free mutants. More recently, a variety of techniques to induce sitedirected mutagenesis, or targeted mutagenesis, have become available. Site-directed mutagenesis typically results in a recessive, deleterious mutation. While this technology could be used to induce recessive mutations in barley, it is more frequently used to confirm the function of a gene.

Doubled Haploids Breeding self-pollinated crops is a long-term process. Homozygosity is essential for maintaining varietal purity, but many years are required to achieve homozygosity using conventional methods. DH production is an alternative to override the necessity of multiple cycles of self-pollination because complete homozygosity can be obtained in a single generation. A plant resulting from a cross contains two gene sets, each one slightly different and leading to variability among progeny. In DH plants, the sets are identical so plants always breed true. Using DH production also offers advantages such as fixing traits rapidly in desirable combinations in a line/variety, speeding up the development of mapping populations and accurate identification of marker/trait associations. Consequently, breeding programs can be conducted with greater efficiency and confidence. In barley, several techniques have been used to create DHs from female or male gametes; among the most effective are anther culture (AC) or isolated microspore culture (IMC) and the ‘bulbosum’ method. To apply the ‘bulbosum’ technique, female F1 lines of H. vulgare are crossed to male lines of H. bulbosum. After fertilization, the H. bulbosum chromosomes are spontaneously eliminated from the hybrid embryos. The haploid embryos are excised and grown in tissue culture in the presence of colchicine to double the chromosome number. The resulting plants are comparable to those that would be obtained after many generations of selfing from an F1 plant. Both AC and IMC are based on a common principle of in vitro androgenesis to produce a plant from a single male gamete. At early developmental stages, the male gametic cell, or microspore, can be diverted from the normal developmental pathway to a sporophytic pathway and subsequently regenerate an entire plant.

Barley Hybrids Many sources of genetic male sterility have been identified in barley, and cytoplasmic male sterility and restorer systems are known in H. vulgare subsp. spontaneum. Gametocide treatments can also be used to induce male sterility. Although hybrid vigor may be advantageous for hybrid production, it may have undesirable consequences for malting quality. Uniform germination is essential for the malting process, but the F2 grain harvested from F1 hybrid plants may be highly variable. The use of parents with similar malting quality may reduce this problem but may also reduce the heterosis in the cross if the parents are genetically related. Another barrier for hybrid production is the fact that barley normally sheds pollen while it is still in the boot stage, which limits the extent of cross-pollination to a male-sterile female

BREEDING OF GRAINS | Barley: Genetics and Breeding line. Increased cross-pollination and hybrid seed set can be achieved through selection, however, and winter barley lines are more predisposed to outcrossing than spring lines. From 1970 to 78, several hybrid barley varieties were grown in Arizona, California, and Oregon, although only an area ranging from 12 000 to 20 000 ha was grown each year. More recently, the hybrid winter feed barley ‘Hyvido Volume’ was released in Europe and is reported to have a yield advantage over leading commercial inbred varieties.

The Barley Genome A draft of the barley genome was published in 2012. The haploid barley genome size is 5.1 gigabases (Gb). Approximately 84% of the genome is composed of mobile elements or other repeat structures, such as retrotransposons (76%) and DNA transposons (6%). The barley genome contains 26 159 ‘high-confidence’ genes with homology support from other plant genomes and 79 379 transcript clusters. A genetically anchored physical map, containing more than 95% of the barley genome (4.8 Gb), has been constructed using the cultivar Morex. Most high-confidence genes (92.3%) have been associated and positioned in the physical map, representing a gene density of five genes per Mb.

Molecular Mapping in Barley Comparisons of genetic maps among the members of the grass family have shown that different species have many of the same genes and genetic markers, which often occur in a similar order along the chromosomes. Within the tribe Triticeae, the barley genome is highly collinear with the A, B, and D genomes of wheat, with only a few minor inversions and translocations between the two species. Some regions of the barley genome are highly collinear with rice, but there are others that show some rearrangements. Nonetheless, genetic probes for rice have proven to be very useful for mapping in barley. Molecular mapping in barley was facilitated by the existence of many morphological mutants that could be readily scored and assigned to linkage groups. Initial genetic maps of barley relied on morphological markers, isozymes, and known genes for disease resistance and storage proteins. Since the late 1980s, many genetic maps of barley have been published using various types of genetic markers including restriction fragment length polymorphisms (RFLPs), randomly amplified polymorphic DNAs (RAPDs), simple sequence repeats (SSRs), and amplified fragment length polymorphisms (AFLPs). Genetic maps have dramatically increased their density and resolution with the development of high-throughput genotyping techniques. These include Diversity Array Technology (DArT), Illumina GoldenGate and Infinium iSelect platforms, and more recently genotyping by sequencing (GBS). These technologies allow the generation of thousands of SNP whose positions can be easily located on consensus linkage maps and anchored to the barley physical map. Mapping populations consist of randomly derived, segregating progeny from crosses between diverse parents. The distance between markers in a linkage group is estimated based on the frequency of recombinant (nonparental) genotypes in the mapping population. A database of barley maps is maintained

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on the GrainGenes website (http://wheat.pw.usda.gov/index. shtml). Genetic maps can be refined as new markers are generated with novel genotyping platforms. These new markers are easily integrated into existing maps. Consensus maps are very useful to integrate different markers that have been mapped in different populations and to resolve order conflicts. Map resolution can also be increased by adding more individuals to the population. The DH technique has proven to be very useful in developing mapping populations that can be maintained over time. The genetic maps can be refined using increasing numbers of markers, and the lines can be evaluated phenotypically in different experiments for many traits of interest.

Physical maps Maps of physical distances along the chromosomes present quite a different picture of the barley genome than genetic maps based on recombination frequencies. An important feature of the barley genome is that centromeric and pericentromeric regions show significantly reduced recombination frequency, which has a negative impact on plant breeding since novel allele combinations at genes in these regions are extremely difficult to obtain. A large number of functional genes are locked into these regions, which approximately comprise 50% of the whole genome. There is evidence that the gene-rich areas correspond to areas of high recombination. The average gene density is 5 genes per Mb, although it is much higher at the proximal and distal ends of the chromosomes (13 genes per Mb).

Analysis of QTLs QTL analyses are based on statistical tests used to determine if there is a relationship between particular phenotypes and the occurrence of specific marker alleles. If the marker/trait association is significant, then it is assumed that a QTL for the trait is closely linked to that marker. Two different approaches have been traditionally used for QTL identification: linkage mapping in biparental mapping populations, where all individuals trace back to a single cross of inbred parents, and genome-wide association studies (GWAS), where individuals may have different degrees of relatedness or not be related at all. Advantages of the first method are that QTL can be found with low marker density (one marker every 5–10 cM may be enough) and QTL effects can be precisely estimated since only a maximum of two alleles at each locus are segregating. GWAS, on the other hand, requires a much larger marker density, but the germplasm panels can be composed of breeding and elite lines that are relevant for breeding and can represent a much wider genetic base.

Marker-Assisted Selection Molecular markers have been utilized successfully to select for closely linked genes and QTLs. Laboratory screening can be carried out during the off-season, to attain more rapid progress in a breeding program. Commonly used markers such as SSRs can discriminate homozygous dominant from heterozygous genotypes, which would have identical phenotypes in a

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conventional selection program. Marker-assisted selection (MAS) is particularly useful for introducing genes from exotic germplasm, because selection can be carried out for both the genes of interest from the donor parent and the background genotype of the recurrent parent, reducing the deleterious effects of linkage drag. Despite these benefits and successes, MAS has not been applied widely in breeding programs. A big drawback is that the utility of MAS diminishes as the number of selection targets increases. To overcome these limitations, new statistical models have been developed to predict performance and estimate breeding values based on the whole genomic architecture of the line. This is called genomic selection (GS) and is a type of MAS that uses all marker information available for each individual to create a genomic estimated breeding value that can be used for selection. GS is particularly useful for traits with low heritability and traits that are expensive or difficult to measure.

Feed Barley Barley is commonly fed to livestock as grain and forage. Feed barley, which utilizes the grain for direct consumption for livestock, is typically selected on the basis of physical characteristics, such as kernel plumpness and high test weights in addition to numerous nutritional quality traits. Research has shown that there is considerable genetic diversity among barley varieties in terms of nutritional quality and suitability for feed and food uses, but these objectives have not received much emphasis in breeding programs. High test weight is a positive attribute for feed barley, as higher kernel density tends to indicate higher nutritive value, due to higher content of starch and protein, increased fat content, high fiber, and reduced air space. Kernel plumpness and uniformity are desirable, because plump kernels tend to have higher starch content. The levels of starch vary considerably among barley varieties, but typically constitute approximately 55% of the kernel, and thus provide the main energy source in feed barley. Uniformity is important during feed processing, which may involve dry or steam rolling. Particle size of cracked barley is a characteristic that has recently been shown to influence feed quality for ruminants. Studies to date indicate that larger particle size may confer a slight benefit to animals, but some compromise in particle size may be necessary to optimize all of the parameters used to determine feed quality. Typically, starch in barley is composed of 75% amylopectin (a branched chain molecule) and 25% amylose (an unbranched, straight-chain molecule). Genetic variants range from little or no amylose (waxy types) to a high of 71% amylose. Both the waxy and the high-amylose phenotypes may be controlled by single genes and tend to be associated with reduced starch and increased beta-glucan levels. Waxy mutants are homozygous recessive at the wax1 locus on the short arm of chromosome 7H. Another mutant with recessive alleles at the amo1 locus on chromosome 1H has an amylose content of 45%. Higher levels of amylose have been obtained using mutagenesis. Levels of protein and amino acids vary among barley varieties and are also influenced by environmental conditions. QTLs for grain protein content have been identified on all seven chromosomes of barley.

Like all cereals, barley is relatively low in lysine. High-lysine mutants have been the subject of much research and breeding effort. Most of the high-lysine mutants are determined by single recessive genes, but many have pleiotropic effects on other components of the kernel, such as the composition of starch, lipid, and protein fractions. Shrunken endosperm is another common attribute of high-lysine mutants. The nutritional benefits of high-lysine barley have been clearly demonstrated in nonruminant diets, but undesirable pleiotropic effects present a challenge to breeding programs. The agronomic characteristics of high-lysine varieties have never met commercial standards, despite intensive breeding efforts. Compared to other cereal crops, lipid levels are relatively low in barley, typically about 2–4%. Approximately 25% of the kernel lipids occur in the embryo, with the remaining 75% in the endosperm. Screening of germplasm collections for highlipid barley mutants has had limited success since the maximum lipid content identified is approximately 7%. The hull constitutes 10–15% of the dry weight of the kernel and is the major contributor of crude fiber (CF), which for the most part is nutritionally unavailable to nonruminants and poultry. The fiber content of hull-less barley is low, comparable to that in maize and wheat. The source of fiber is primarily nonstarch polysaccharides, lignin, and beta-glucan, predominately in waxy GBSS1 mutants. Acid detergent fiber (ADF) measures insoluble fiber and is a commonly used indicator of fiber content. Values for ADF range from 2% to 12%. Several QTLs have been identified for beta-glucan content indicating that the inheritance of these traits is complex. Breeding for low fiber content may be preferred for feed barley. However, for human consumption, high dietary fiber is desired. The testa of barley contains proanthocyanidins, which are polyphenolic or flavonoid compounds similar to those found in sorghum. There is some evidence that these compounds may form insoluble phenol–protein complexes, which create haze in beer and reduce the digestibility of protein in animal feed. Other studies have shown that the effects on digestion are minimal because the phenolic compounds occur in very low concentration. Numerous mutants that are deficient in proanthocyanidins have been identified. All that have been studied to date show single-gene recessive inheritance. The most useful mutants from a breeding standpoint appear to be those that alter anthocyanin production in the last step of the flavonoid pathway. Other mutations that affect anthocyanin or proanthocyanidin production also reduce vigor and yield. Minerals occur in barley kernels in low concentrations but are important for animal nutrition. Phosphorus, potassium, and calcium occur in greatest quantities with lesser amounts of chlorine, magnesium, sulfur, and sodium. The hull has the highest concentration of minerals, followed by the embryo, with lowest concentrations in the embryo. Phosphorus is an important mineral in animal nutrition, but 80% of the phosphorus in barley is unavailable because it is bound to phytic acid. Phytic acid also binds to other important minerals, including calcium, iron, magnesium, and zinc. Animals cannot digest these phytate compounds, and the minerals that are not absorbed are excreted in feces. Recently, low-phytic-acid mutants of barley with normal phosphorus levels have shown promise as a means for increasing the availability of phosphorus in animal diets while reducing levels of phosphorus in animal waste.

BREEDING OF GRAINS | Barley: Genetics and Breeding Forage Barley Forage barley, utilized through direct grazing, green chop, hay production, and silage, is selected primarily for high vegetative biomass. Modern breeding programs select forage types for various combinations of morphological characteristics, growth habits, maturities, and agronomic performance that are appropriate for the intended end use and target region of production. Typically, hooded barley is preferred for forage production, since the absence of awns is desired for palatability and allows for dual-purpose applications (forage and feed). However, yields of hooded barley are lower, in comparison with awned types. The use of different growth habits (winter, spring, and facultative) in forage production is influenced by the region of production. Winter types give an option for cover cropping and off-season grazing while still producing high yields in the summer. Maturity is a key factor in forage production. Early maturing barley has rapid growth, and can have multiple cuttings, but produces less biomass compared to later maturity groups. Typically, palatability and digestibility decrease as plants mature due to increased conversion of sucrose to starch and an increase in total fiber. Secondary selection criteria for forage barley are for biomass quality. Key components of quality consist of palatability, dry matter (DM) and dry matter digestibility (DMD), ADF, neutral detergent fiber (NDF), lignin, CF, crude protein (CP), water-soluble carbohydrates (WSC), and ash content. Use of conventional breeding methods, through exploitation of genetic variation and selection of desirable traits, remains a successful approach for improving forage quality traits. The nutritional value of forage barley depends on the intended end use. Differences in quality are influenced by management practices, maturity stage at harvest, moisture content, and microbial degradation. Immature vegetation will have a higher DM and CP, and quality is maximized when harvest occurs at or prior to soft dough stage. However, DMD, ADF, NDF, and gross energy decline with advancing forage maturity. Decreases in protein, ADF, and NDF occur as soluble carbohydrates are converted to starch and starch content increases with maturity. Barley forage and silage tend to have lower cell wall constituents (CWC), ADF, and lignin content than other small grains forages. Straw quality is lower in comparison with other uses of forage barley due to the absence of the grain and chaff, which contain the majority of the protein, resulting in a high fiber concentration.

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and dry milled barley products such as flakes, grits, flour, and pearled barley, which provide at least 0.75 g of soluble fiber per serving” (21 CFR 101.81). For a barley with approximately 4–5% grain b-glucan, this would mean that in order to receive the daily recommended soluble fiber, a person would have to eat at least 17 g of steamed grain or 44 g of bread made with 40% barley flour. Grain b-glucan is a quantitative trait, with several known QTLs contributing to high b-glucan. Additionally, there is a pleiotropic effect of the recessive allele at the waxy (wax1) locus encoded by granule-bound starch synthase 1 (Gbss1). Another trait important to the selection of food barley is the freethreshing hull. Selection for the hull-less caryopsis (the phenotype where the lemma and palea do not adhere to the hull, sometimes referred to as ‘naked’) dates back several millennia. The development and deployment of barley-based food products have been the subject of considerable activity in the scientific literature. This activity is a result of the work of multiple research groups worldwide trying to drive demand for food barley: either as whole-grain or as a fiber-enriched ingredient. The variety of products is striking but is largely based on centuries- if not millennia-old templates for cereal-based foods. The basic templates can be synergized with modern food processing practices, and recent advances in knowledge of cereal component functionalities and interactions provide a means to achieve even more palatable and nutritious outcomes. Potential food barley applications include simple intact-kernel applications (e.g., taking the place of rice or other grains in pilafs, porridges, stews, and risottos) using entire, flaked, rolled, or cracked forms. Pearled forms are and can be used too. Barley can also be utilized as flour or meal in a more or less refined form for applications in risen breads, flat breads, cakes, muffins, pancakes, noodles, and pasta, among others. Despite an overall decline in food barley consumption in the last few centuries, food barley germplasm development and quality characterization are making a comeback in many areas of the world. As consumers realize the nutrition and taste benefits of barley, commercial production increases and there becomes a need for new varieties adapted to a number of different regions. Several breeding programs are working to develop new and exciting germplasm with which to invigorate local barley markets by engaging farmers, processors, and consumers.

Malting Barley Food Barley Although barley was originally cultivated for human consumption, other end uses have gained importance over the millennia. There are still many areas of the world where barley remains a staple crop and has important spiritual, nutritional, and cultural significance. In 2006, the FDA approved a health claim for barley based on its potential for high levels of the soluble fiber, b-glucan, which can help lower the risk of heart disease, diabetes, and obesity (US-FDA). The health claim approved by the FDA allows “foods containing barley to claim that they reduce the risk of coronary heart disease. Specifically, whole grain barley

There are no absolute definitions of malting and brewing quality, due to differences in malting and brewing practices and consumer preferences. In the United States, the American Malting Barley Association provides breeders with recommended target levels for traits associated with malting and brewing quality.

The Malting and Brewing Process During malting, barley kernels are germinated under controlled conditions. Good malting varieties will break dormancy rapidly and germinate uniformly. These characteristics are controlled to some extent by endogenous levels of the plant

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growth regulators – gibberellic acid (GA) and abscisic acid (ABA). During germination, hydrolytic enzymes are synthesized or activated to partially degrade large starch, protein, and nucleic acid molecules into sugars, amino acids, and nucleic acids that can support the growth of yeast and fermentation processes during brewing. The ‘diastatic power’ of a malt indicates its enzymatic potential to convert starch into sugar. After 4 days, the green malt is kilned to arrest modification. Modification refers to all of the polymer-degrading processes that occur during malting. During the next step (mashing), the malt is treated with hot water to obtain an extract (wort). Varieties with high extract levels are desired for malting. The extract must provide adequate nourishment to the yeast to permit fermentation and must contain sufficient sugar to attain the desired alcohol level. During brewing, the malt sugar solution is boiled with hops for seasoning. The solution is cooled and yeast is added to begin fermentation. Finally, the yeast ferments the sugars, releasing CO2 and ethyl alcohol.

Genetics of Malting Quality The endosperm is composed of large and small starch granules that are packed in a protein matrix. The amount and types of storage protein in barley affect the rate of modification and malting quality. During malting and mashing, the barley starch should be almost completely degraded into sugars that can be utilized by the brewing yeasts, whereas only 45% of the barley protein should be solubilized. Too much protein solubilization is expected to result in beers with poor foaming characteristics. When insufficient protein hydrolysis occurs, the remaining proteins may interact with polyphenols to form beer haze precipitates. Grain protein in the range of 11.5–13.5% is generally desired for malting; however, there is a demand for lower levels of protein within the craft brewing industry. The hordeins are the major storage proteins, and these can be divided into four groups: the sulfur-rich B hordeins, the sulfur-rich g-hordeins, the sulfur-poor C hordeins, and the high-molecular-weight D hordeins. These proteins are encoded by the Hor2, Hor5, Hor1, and Hor3 loci, respectively, all of which are located on chromosome 1H. Four amylolytic enzymes are thought to participate in converting the starch in malted barley into fermentable sugars: these are a-amylase, b-amylase, a-glucosidase, and limit dextrinase. The a-amylases are particularly important because they have sufficient thermostability to remain active throughout the mashing process. The Amy1 and Amy2 loci, on chromosomes 6H and 7H, respectively, encode two a-amylase isozymes that differ somewhat in their biochemical properties. Alphaamylase 2 is expected to make the greatest contribution to a-amylase activity in grain. QTLs for important malting quality traits have been detected in the region near the Amy2 locus on chromosome 7H in several mapping populations. Three genes, Bmy1 and Bmy3 on chromosome 4H and Bmy2 on chromosome 2H, encode b-amylase. Genetic differences in thermostability of b-amylase could potentially be exploited in breeding programs to improve malting quality. The enzyme a-glucosidase is encoded by multiple genes, including Agl (7H), Aglu2 (3H), Aglu3 (1H), and Aglu5 (2H). This enzyme plays a role in converting native starch,

gelatinized starch, and glucans into sugar. However, the extent of its role in malting and mashing is unclear. The enzyme b-glucanase plays an important role in degrading b-glucans in endosperm cell walls during malting. High b-glucans cause problems during modification and filtration and lead to excess haze in the beer. Two genes known to encode b-glucanase isozymes, Glb1 and Glb2, are located on chromosomes 1H and 7H, respectively. The enzyme systems that reduce the barley storage proteins to ‘soluble protein’ for fermentation are very complex. The ratelimiting step for protein degradation is the hydrolysis of the original proteins into soluble protein by endoproteinases. The small peptides and amino acids that are released by the exopeptidases comprise the majority of the free amino nitrogen (FAN) fraction. FAN concentration is measured to indicate how well the original protein material can be utilized by yeasts during brewing. Genetic control of malting quality has recently been reviewed. Szu˝cs et al. summarized malting quality QTL from multiple mapping populations and aligned them on the Oregon Wolfe Barley linkage map, reporting 154 malting quality QTLs associated with 18 traits.

Breeding for Malting Quality There are a few characteristics that breeders can select routinely to improve malting quality, such as kernel plumpness and protein content, but other assays are expensive or require large sample sizes, limiting the number of genotypes that can be evaluated. Tests for malting quality are usually applied at the prerelease stage. Newly released varieties will be designated as either a malting variety or, by default, a feed barley. To be designated as a malting variety, rigorous test criteria established by the malting and brewing industry must be met. A variety must pass through a series of micromalting and malt analysis tests, followed by pilot-scale malting tests, and finally plant-scale malting and brewing tests including taste tests. The processes of varietal development and quality testing may take 15 years. Many of the traits determining malting quality can be improved through breeding, but developing a variety that has good agronomic characteristics and falls in the accepted range for all quality traits is a challenge. MAS has been shown to be effective for improving some malt quality characteristics. However, selecting for a large number of loci, which is necessary when breeding for malting quality, is out of the scope of MAS. GS may prove to be a more effective method for improving this complex trait. The ability to make selections for malting quality at early stages in the breeding program should greatly increase the likelihood that good malting varieties will reach the prelease stage for pilot-scale malt testing.

Future Directions Barley will play an important role in meeting the increasing global demands for healthy food, feed, and beverage in a time of climate change. Thanks to the availability of tools for systematically characterizing and exploiting genetic diversity,

BREEDING OF GRAINS | Barley: Genetics and Breeding geneticists and breeders can address the challenges of developing broad spectrum and durable resistance to abiotic and biotic stresses. Online resources, such as the T3 database (http:// triticeaetoolbox.org), provide immediate and public access to genomic coordinates, genes and regulatory sequences associated with agronomic, quality, disease resistance, nutritional, and malting traits. These data, coupled with the availability of cost-effective genotyping and sequencing, facilitate a new generation of breeding methodologies. Phenotypic performance remains the final arbiter of cultivar worth, but strategies including MAS and GS will increase the rates of gain. DH production will further accelerate the process of accumulating favorable alleles. The availability of cost-effective techniques for whole genome sequencing and tools for characterizing the epigenome and the interactome will provide breeders with additional challenges and opportunities. These abundant and cheap genetic resources will be fully exploited when equally highthroughput and cost-effective techniques are developed for phenotyping complex traits. Innovations in crop management will be essential for achieving the productivity and quality potential of new cultivars. Advances in crop processing and product development directed at optimizing the use of scarce resources will stimulate economic development and provide consumers with healthy, safe, and satisfying barley-based products.


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Make comparisons between the following combinations with respect to genetics, agronomy, and utilization: • Two-row versus six row barleys. • Hulled versus naked barleys. • Winter versus spring barleys. • Malting versus food versus feed versus forage types of barley. • Conventional versus F1 hybrid barley. How is barley breeding assisted by the use of QTLs, by doubled haploid technology and by marker-assisted selection? What complications are posed for the barley breeder by quantitative traits? Give examples.


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What dangers may there be for a general barley breeding program by primarily selecting for malting quality, and assuming that rejected lines will be satisfactory for food, forage and feed uses? What is the composition of the proteins of barley endosperm, germ, and bran layers? Describe the relative significance of protein content and composition for the main barley quality types: malting, food, and feed.

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Investigate whether barley breeders encounter an impasse of grain yield versus grain quality (difficult to maximize both yield and quality together) for any of the quality types of barley, such as may be encountered in wheat breeding, for example.

See also: Agronomy of Grain Growing: Barley: Agronomy; Barley, Rice and Maize Processing: Barley: Milling and Processing; Barley: Malting; Beverages from Grains: Fermentation: Foods and Nonalcoholic Beverages; Fermentation: Origins and Applications; Genetics of Grains: Genomics of Food Grains; Grain Harvest, Storage and Transport: Barley: Harvesting, Storage, and Transport; Grain Marketing and Grading: Barley: Grading and Marketing; Non-food Products from Grains: Cereal Grains as Animal Feed; Fuel Alcohol Production; Proteins: Protein Synthesis and Deposition; The Protein Chemistry of Cereal Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses.

Further Reading Anderson MK and Reinbergs E (1985) Barley breeding. In: Rasmusson DC (ed.) Barley. Madison, WI: American Society of Agronomy Agronomy Monograph No. 26. Baik BK and Ullrich SE (2008) Barley for food: characteristics, improvement, and renewed interest. J. Cereal. Sci. 48: 233–242. Fisk SP, Cuesta-Marcos A, Cistue´ L, Russell J, Smith KP, Baenziger S, Bedo Z, Corey A, Filichkin T, Karsai I, Waugh R, and Hayes PM (2013) FR-H3: a new QTL to assist in the development of fall-sown barley with superior low temperature tolerance. Theor. Appl. Genet. 126: 335–347. Islamovic E, Obert DE, Oliver RE, Harrison SA, Ibrahim A, Marshall JM, Miclaus KJ, Hu G, and Jackson EW (2013) Genetic dissection of grain beta-glucan and amylose content in barley (Hordeum vulgare L.). Mol. Breed. 31: 15–25. Jia Q, Zhang J, Westcott S, Zhang XQ, Bellgard M, et al. (2009) GA-20 oxidase as a candidate for the semidwarf gene sdw1/denso in barley. Funct. Integr. Genom. 9: 255–262. Komatsuda T, Pourkheirandish M, He C, Azhaguvel P, Kanamori H, Perovic D, Stein N, Graner A, Wicker T, Tagiri A, Lundqvist U, Fujimura T, Matsuoka M, Matsumoto T, and Yano M (2007) Six-rowed barley originated from a mutation in a homeodomain-leucine zipper i-class homeobox gene. Proc. Natl. Acad. Sci. U. S. A. 104: 1424–1429. Ramsay L, Comadran J, Druka A, Marshall DF, Thomas WTB, Macaulay M, MacKenzie K, Simpson C, Fuller J, Bonar N, Hayes PM, Lundqvist U, Franckowiak JD, Close TJ, Muehlbauer GJ, and Waugh R (2011) INTERMEDIUM-C, a modifier of lateral spikelet fertility in barley, is an ortholog of the maize domestication gene TEOSINTE BRANCHED 1. Nat. Genet. 43(2): 169–172. Schwarz P and Li Y (2011) Malting and brewing uses of barley. In: Ullrich SE (ed.) Barley: Production Improvement and Uses, pp. 478–521. Chichester: WileyBlackwell. Szu¨cs P, Blake VC, Bhat PR, Chao S, Close TJ, Cuesta-Marcos A, Muehlbauer GJ, Ramsay L, Waugh R, and Hayes PM (2009) An integrated resource for barley linkage map and malting quality QTL alignment. Plant Genome 2: 134–140. The International Barley Genome Sequencing Consortium (2012) A physical, genetic and functional sequence assembly of the barley genome. Nature 491(7426): 711–716. Trevaskis B, Hemming MN, Dennis ES, and Peacock WJ (2007) The molecular basis of vernalization-induced flowering in cereals. Trends Plant Sci. 12: 352–357.

Maize: Breeding EA Lee and LW Kannenberg, University of Guelph, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 204–211, ã 2004, Elsevier Ltd.

Topic Highlights

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Pedigree breeding and population improvement, the main methodological components of maize breeding, are explained. The importance of adaptation of varieties to specific environmental conditions, especially maturity zones, is emphasized. Major characteristics and deployment of the germplasm base of North American maize breeding is outlined. The integration of GMO development with traditional maize breeding is explained.

Learning Objectives

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To understand the basic objectives and methodologies of maize breeding. To appreciate the contribution of hybrid maize development to the agricultural economies of North America and globally. To understand the roles and application of population improvement and pedigree breeding in maize improvement. To understand the basic ideas behind commercial hybrid seed production.

Introduction Prior to the introduction of maize hybrids in the early 1930s (US) and 1940s (Canada), maize grain yields were static. Since then average on-farm maize grain yields have risen steadily from prehybrid level of 1000 kg ha1 to the present level of 7000 kg ha1 (Figure 1). The intent of this brief article is to familiarize the reader with some of the unique aspects of maize breeding, and how these approaches have contributed to the steady increase in North American maize grain yields during the hybrid era. Although the perspective of this chapter will be that of a northern temperate zone, North American breeding program, the underlying concepts are applicable wherever maize is bred. There are several types of maize grown commercially, each with very different end uses: “number 2 yellow maize,” for animal feed and some industrial uses such as ethanol, corn oil, citric acid, and high fructose corn syrup production, makes up the largest proportion of maize acreage; “sweet corn” for the fresh market, canning and frozen food industries; “popcorn” and “white and yellow food-grade maize” for the snack food industry and general human consumption; “silage maize” and “high oil maize” for animal feed; “waxy maize” for animal feed

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and industrial specialty starches; and “high amylose maize” for industrial specialty starches. Breeding methods for “number 2 yellow maize” will be discussed in this article; however, methodologies that are applied to specialty types of maize are essentially the same. Whenever possible we have included references to more comprehensive treatments of the topic. Several excellent reviews of the general subject are available, and a recent book (“Specialty Corns”) covers breeding for specific types of maize. There are two general approaches to maize breeding: pedigree breeding and population improvement. Population improvement has been practiced for centuries by both indigenous peoples and farmers, and, in a more sophisticated form, continues to be used in modern maize breeding; pedigree breeding is a more recent approach that appeared when the potential of heterosis (hybrid vigor) was realized.

Mode of Propagation Maize is a monoecious plant with separate male (tassel) and female (ear) flowers on the same plant. The tassel produces 25 million pollen grains while the ear produces 1000 silks (stigmatic and stylar tissue), each leading to an ovule and a potential seed. Separation of the male and female flowers greatly facilitates controlled crossing. The tassel emerges from the uppermost leaf whorl and primary ear shoots emerge from the leaf sheaths. Once visible the ear shoots are covered, prior to the emergence of the silks, with a glycine bag called a shoot bag. The shoot bag prevents pollen from landing on the silks and unwanted fertilization from occurring. When the tassel is mature, anthers are extruded from the spikelets, followed by dehiscence of the anthers to release the pollen grains. Pollen shed usually lasts for 5–8 days, depending upon the size of the tassel and weather conditions. Peak shedding time is generally mid-day, but is dictated by temperature and humidity. Pollen grains remain viable for no more than 24 h, even under “ideal” conditions. For controlled pollinations, a tassel that is shedding pollen is covered with a brown paper bag called a tassel bag, the day before the pollination is made. The bag is folded securely around the base of the tassel and stapled. The only viable pollen in the bag will be from the tassel. Also the day before the pollination is made, the silks are cut back to the tip of the ear shoot. The next day the tassel bag is removed with the newly released pollen grains in it. The shoot bag is briefly removed from the female plant and the pollen in the bag is sprinkled onto the regrown silks. The shoot bag is replaced, the tassel bag is placed over the shoot bag with the edges wrapped around the stalk and stapled together. Notes regarding the pollination date and the male genotype are


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BREEDING OF GRAINS | Maize: Breeding Table 1 and FAO

9000

Grain yield (kg ha−1)

8000

Maize relative maturity rating systems: RM, GDDs, OCHUs,

Minnesota relative maturity (days)

US growing degree days (GDDs)

Ontario corn heat units (OCHUs)

FAO (units)

70 75 80 85 90 95 100 105 110 115 120 125 130 135 140

1650 1750 1850 1950 2050 2150 2250 2350 2450 2550 2650 2750 2850 2950 3050

2100 2300 2500 2600 2700 2800 2900 3200 3400 3500 3700 3900 4100 4300 4500

100

7000 6000 5000 4000 3000 2000 1000 2000

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Year Figure 1 Maize grain yields in US from 1866 to 2001. (Source: USDA, National Agricultural Statistics Service.)

written on the tassel bag. Kiesselbach gives an excellent detailed description of the structure and reproduction of a maize plant.

Adaptation Maize genotypes tend to be adapted to relatively narrow maturity zones compared, for example, to other cereal crops. Ideally, material adapted to temperate zones should flower late enough to produce maximal leaf area to intercept the incident solar radiation, yet early enough that the grain reaches physiological maturity before the first killing frost. Several systems have been developed to aid breeders and producers to place genotypes into the correct adaptation zones. In N. America, the Minnesota relative maturity (RM) system, growing degree days (GDDs), and Ontario corn heat units (OCHUs) are commonly used, while in Europe the Food and Agriculture Organization developed the FAO system (Table 1). Both flowering date and rate of moisture loss from the grain influence maturity; in practice, breeders monitor grain moisture at harvest to assess maturity. Selection for hybrids that can take full advantage of the available growing season in the various maturity zones has resulted in very specific adaptation for a given hybrid.

Germplasm The genetic base of North American hybrid maize industry represents only a small portion of the entire Zea mays gene pool. There are 250–300 races of maize, of which only one, the Corn Belt Dent, is the predominant source of commercial germplasm. Of the hundreds of open-pollinated varieties of Corn Belt Dent that were grown up to the 1940s, only half a dozen or so can be considered as significant contributors to current inbred lines. But the overwhelming majority of the inbred lines trace their pedigree back to only two openpollinated varieties, Reid Yellow Dent and Lancaster Surecrop.

297

200 300 400 500 600 700 800

Adapted from Troyer AF (1999) Background of US hybrid corn. Corn Science 39: 601–626.

All North American hybrids have at least one parent from Lancaster or Reid. The great majority of hybrids are, in fact, crosses of a Reid line derivative with a Lancaster line derivative. Virtually all commercial North American hybrids involve six inbred lines or their close relatives: Lancaster-type inbreds C103, Mo17, and Oh43 and Reid-type lines B37, B73, and A632. Further, these lines are used worldwide in maize breeding programs, either directly as a parent or parents of a commercial hybrid or as a component in an inbred development program. Concern about the narrow genetic base underlying the hybrid corn industry has led to programs designed to diversify breeding germplasm. The program on germplasm enhancement of maize (GEM) (additional information on GEM can be found at www.public.iastate.edu/usda-gem) represents one of these efforts.

Pedigree Breeding: The Inbred-Hybrid Concept Hybrid maize traces its roots back to experiments on heterosis and inbreeding conducted by G. H. Shull at Cold Spring Harbor Laboratories in New York and E. M. East at Connecticut State College. They observed that when maize plants were selfpollinated (i.e., inbred) in successive generations, their vigor and grain yield rapidly deteriorated. However, when two inbred lines from unrelated populations were crossed, both vigor and grain yield of the F1 hybrid often exceeded that observed for the original source populations. It was these observations, made around 1908–09, and methodology outlined by Shull that gave rise to the modern hybrid maize industry. Today most of the maize acreage grown in North America, Europe, and South America is planted to hybrid maize, with an increasing percentage of the acreage in Asia

298

BREEDING OF GRAINS | Maize: Breeding Inbred line × Inbred line A B

Single cross

Modified single cross

Inbred line × Inbred line × Inbred line A1 A2 B

T hree-way cross

Inbred line × Inbred line × Inbred line A B C

Double cross Inbred line × Inbred line A B

× Inbred line × Inbred line C D

Line A × Line B

F1

F2

F2

F2

F2

F2

F2

F3

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F3

F3

F3

Cross each line onto two different inbred tester lines. Grow testcrosses out in replicated multilocation yield trials. Select superior F3 lines based on their performance in the testcrosses.

Figure 2 Types of hybrids grown commercially in North America.

and Africa moving from open-pollinated populations, improved synthetics, and variety crosses to hybrids. There are several types of hybrids (Figure 2). Single-cross hybrids occupy the largest percentage of the acreage in North America. However, double-cross hybrids were grown more widely in the early years of hybrid maize because of seed production problems with the early inbred lines. This section outlines the primary breeding methodology used to produce inbred line parents for hybrids. In a typical commercial maize breeding company, 90% of the breeding effort is focussed on developing inbred lines and testing them in hybrid combinations using pedigree breeding. Pedigree breeding (Figure 3) starts with a breeding cross (line A line B), that cross (F1) is self-pollinated to produce F2 seed, and individual F2 plants are selected and self-pollinated to establish individual lines. Inbreeding via self-pollination continues until the lines are nearly fully homozygous (i.e., F5 ( 94% homozygous) or F6 ( 97% homozygous)). During each generation of inbreeding, visual selection in the breeding nursery is practiced to remove lines that are not favorable. Because the aim of an inbred development program is to create inbred lines that when crossed to unrelated inbred lines will result in superior hybrids, testing of the lines during development must involve crossing them to elite unrelated inbred line testers. In maize, early generation testing is conducted at either F3 or F4 to eliminate poor performing genotypes. Early in the hybrid era, breeders observed that grain yields tended to be greater when lines from unrelated genetic backgrounds were crossed, rather than lines from similar genetic backgrounds. This led to the use of heterotic patterns. Several heterotic patterns have arisen during the hybrid era. In northern Europe, the heterotic pattern is typically “flint” crossed to “dent,” with “flint” referring to maize from the Northern Flint race and dent referring to maize from the Corn Belt Dent race. While in North America and southern Europe, the heterotic patterns generally fall within the “dent” category. Patterns such as Iowa Stiff Stalk Synthetic (BSSS), Lancaster Surecrop, and Iodent all trace back to either early synthetic breeding populations or open-pollinated populations. Most commercial companies will have multiple heterotic patterns in which they are actively developing inbred lines, and within a heterotic pattern, there are multiple inbred line

F4

F4

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F5

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Cross each line onto two different inbred tester lines. Grow testcrosses out in replicated multilocation yield trials. Select superior F6 lines based on their performance in the testcrosses.

F6 Figure 3 Simplified pedigree breeding scheme, involving a two parent breeding cross.

families that have been established. For example, within the BSSS heterotic pattern there are at least three inbred line families, B14, B37, and B73, and within the Lancaster heterotic pattern there are at least three inbred line families, C103, Mo17, and Oh43. The hybrid maize industry worldwide is dominated by North American germplasm, but there are specific areas where other backgrounds are grown, e.g., the “orange flints” in Argentina and the “white maize” of southern Africa. In the early 1980s, commercial maize breeding companies were surveyed regarding their breeding approaches for inbred line development. The information presented below is a synopsis of Bauman’s survey. While it is slightly dated, most of the approaches have not changed. The philosophy of the commercial maize breeding industry is twofold: (1) genetic recombination presents opportunities for creating superior genotypes, and (2) evaluation of large numbers of breeding crosses and large numbers of individuals from each breeding cross increases the odds of creating and identifying those superior genotypes. This philosophy results in most maize breeders preferring to avoid breeding strategies that involve backcrossing and instead using strategies that involve creation of new linkage groups, through multiple crosses, and examining large numbers of progenies from each cross. The types of breeding crosses used are narrow-based populations (about six elite parents), elite inbred populations (elite inbred crossed to about six other sources so that 50% of the population is

BREEDING OF GRAINS | Maize: Breeding Table 2 Relationship between generation designations Fn and Sn and expected average level of homozygosity from self-fertilization, for all loci at which the F1 (S0) was heterozygous Generation

Expected homozygosity

F1 F2 F3 F4 F5 F6

S0 S1 S2 S3 S4 S5

0 50 75 87.5 93.8 96.9

composed of alleles from the elite inbred), double crosses (four inbred parents with equal contribution of alleles), single crosses (two unrelated inbred parents), related line crosses (two related inbred parents), one backcross (two inbred parents, with the F1 crossed with one of the parents ¼ BC1), and two backcrosses (two inbred parents, with BC1 crossed a second time to the same inbred parent ¼ BC2). Starting with one of these sources, the breeder begins by self-pollinating several plants (S0 ( ¼ F1) plants) (Table 2). Once these S0 plants are self-pollinated, the seed is called S1 seed, or seed from one generation of self-pollination. Typically 500 S1 plants will be grown and selected plants will be self-pollinated to establish S2 families. Considerable visual selection occurs at this stage, with about 180 S1 plants being selected for further inbreeding. S2 families are then grown and maintained in what is referred to as ear-to-row, meaning that the S2 seed from one ear is grown in a single row (20–30 plants) in the breeding nursery. Again considerable visual selection occurs both within an S2 family and between S2 families, with about 80 S2 families being selfpollinated and the “best” ear from each family being selected to advance family to the S3 generation. As mentioned previously, the aim of an inbred line development program is to produce an inbred line that will result in a high-yielding hybrid. Unfortunately, inbred line grain yield is not indicative of hybrid yield. Therefore, selection for grain yield during inbred line development must be done by crossing the families onto inbred lines from unrelated heterotic groups (i.e., testcrosses). Selection for grain yield in testcrosses can successfully begin in an early generation. Some breeding programs begin this process with S2 families; however, most programs wait until the S3 or S4 generation to begin testcross evaluation. Early testing during inbred development typically involves: (1) using two testers, usually elite inbred lines although occasionally single-cross hybrids are employed, (2) testing at a limited number of locations ( 4), usually for only 1 year and with no more than three (and often fewer) replications per location, and (3) current commercial hybrids that are similar in maturity are typically included in the trials as “checks.” Only families that in testcross combinations produce hybrids with performance equivalent or superior to the “checks” will be advanced to the next generation. Superior families are selected and the inbreeding and visual selection process continues until the S5 or S6 generation, where again the families are evaluated in testcross combinations.

299

Develop a population

Evaluate individuals in the population

Select superior individuals as parents for the next cycle of the population

Random-mate the selected individuals to form the next cycle of the population Figure 4 Cyclic steps involved in recurrent selection.

Testing at this stage may involve more testers and environments (year and location combinations). Once an inbred line is developed by this process, it will then enter a hybrid development program where it is crossed to numerous inbred lines and evaluated extensively in an attempt to identify commercial caliber hybrids for sale to farmers.

Population Improvement Although most of the inbred parents of commercial hybrids have been bred via pedigree selection, some have been selected from populations improved through cyclic recurrent selection. Indeed, some of the families extensively used in pedigree selection originated from inbred lines developed from populations improved through cyclic recurrent selection. Notable examples are the B14, B37, and B73 families, all of which originated from various cycles of recurrent selection in the population BSSS. Cyclic recurrent selection is a procedure whereby several desirable individuals are selected from a genetically diverse population and these individuals, or their progeny, are intermated to generate an improved population (Figure 4). The procedure is repeated for as many generations as the breeder deems necessary, each generation representing a cycle of selection. The average performance of the population for the traits(s) of selection is expected to improve with each successive cycle of selection as favorable genes for the selected trait(s) accumulate, or, conversely, the frequency of less desirable genes is deceased (Figure 5). Recurrent selection can be effective for many cycles; for example, BSSS was formed in the 1930s and progress remains satisfactory after 15 cycles of recurrent selection.

BREEDING OF GRAINS | Maize: Breeding

Frequency

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4

6

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Grain yield (mg ha−1) Figure 5 Idealized objective of recurrent selection: improvement of the mean performance of the population while maintaining genetic variation within the population.

In breeding programs where hybrids are the product of interest, selections made as parents of the next cycle can be used as well to breed new inbred lines. However, in developing countries where hybrids may not yet be available, the improved population itself may be the product used by farmers. International organizations such as International Maize and Wheat Improvement Center (CIMMYT) and International Institute of Tropical Agriculture (IITA) have been very successful in this endeavor, although they now are also emphasizing the development of hybrids based on inbred lines derived from improved populations. Cyclic recurrent selection is utilized to improve traits that are controlled by genes at several loci, i.e., quantitative traits. The rate of improvement and duration of effective selection will depend on such factors as initial genetic diversity for the traits, the number of individuals selected as parents in each cycle and their genetic diversity, and heritability, i.e., the proportion of variability due to genetic factors, of the selected traits. Most recurrent selection programs will result in progress for the selected traits, but the desired level of performance can be achieved more rapidly if the initial germ plasm already has segregants with a relatively high level of performance for these traits. For this reason, synthetics formed from elite inbreds often are used to initiate a recurrent selection program. For example, BSSS, the highly productive synthetic from Iowa State University, was formed by intercrossing 16 elite inbred lines with good stalk quality. Several cyclic recurrent selection procedures have been used to improve population performance (Table 3). For a detailed description of recurrent selection procedures, including expected genetic gain per cycle of selection for the various procedures, the reader is referred to Hallauer and Miranda, 1988. Examples of two recurrent selection procedures, S2 progeny and half-sib tester, are presented in Table 4. In general, all recurrent selection procedures have given progress for the selected trait(s). Several studies have compared some of the procedures, but the results to date are not definitive because of such factors as different germ plasms and their levels of genetic diversity among studies, different procedures being compared in different studies, switches in selection procedures over time,

varying number of cycles of selection among the studies, different selection intensities, etc. For example, mass selection might be effective in the early cycles of selection in a population with extensive genetic variability, whereas in later cycles, when genetic variability is reduced, selection methods requiring progeny testing might give greater progress. Selfed progeny selection is expected to be effective because selfing results in deleterious recessive genes being revealed as homozygotes instead of being masked from selection by a dominant gene in the heterozygous state. In contrast, half-sib tester recurrent selection can result in the tester genes masking deleterious genes in the population; however, the tester, especially an elite inbred tester, helps to ensure that lines derived from the population will combine well with elite inbreds to produce a superior hybrid. Visual selection among S1 lines in the breeding nursery, which is common to both selfed progeny and halfsib tester methods, helps to reduce the frequency of deleterious recessive genes. Also, testcrossing of the selected lines in the inbred development phase of selfed progeny testing helps to enforce the desired combining ability in that procedure. Some breeding systems for population improvement integrate two or more cyclic recurrent selection methods in order to maintain or even enhance genetic variability while shaping this diversity into populations with agronomic/breeding potential. For example, the hierarchical, open-ended, population enrichment (HOPE) system employs three levels of performance to include a highly diverse population at the low-level in which mass selection is used, an intermediate level using selfed progeny recurrent selection, and two elite level populations using full-sib-reciprocal recurrent selection. Introductions are added on a continuing basis and selected entries can be moved upward in the hierarchy. Inbred lines are developed from the elite level populations.

Incorporating GMO Events into Inbred Lines Since the 1990s, commercial maize hybrids containing transgenic events have been widely grown in North America. These genetically modified organisms (GMOs) involve expression of Bt proteins against European corn borer (Ostrinia nubilalis), or resistance to the herbicides – Liberty™ and Round-Up™. For all of these events, only one parent of a single-cross hybrid needs to contain the event, because the events on the market to date are all psuedodominant, i.e., the event has been added to the genome of the GMO parent; therefore, the gene does not have a counterpart on the homologous chromosome segment from the non-GMO parent. To transfer the GMO event from one inbred background to another inbred background, rapid backcrossing is employed. In rapid backcrossing, the GMO parent (donor parent) is crossed to the inbred line of interest (recurrent parent), and then the F1 is crossed to the recurrent parent (BC1). At this point, the BC1 generation, only 50% of the individuals will contain the GMO event and the average genetic constitution of a BC1 individual is 75% of the recurrent parent’s genotype. However, within the BC1 population there are individuals that contain less than 75% of the recurrent parent’s genotype and there are individuals that contain considerably more that 75% of the recurrent parent’s genotype.

BREEDING OF GRAINS | Maize: Breeding Table 3

301

Some methods of cyclic recurrent selection for improvement of maize populations

Mass. It is the oldest method of recurrent selection. Individual, open-pollinated plants are selected from populations grown in isolation. Bulked seed from the selected plants are planted in the next cycle. An often-used variation is to impose a grid on the isolation block and then select the best plant within each component of the grid. Grid selection reduces the effect of variable growing conditions in the isolation plot. Mass selection requires one season per cycle and is most effective in populations with high genetic variability for the trait(s) of interest and especially with highly heritable traits. Ear-to-row. Seeds from selected individuals in a population are planted on an ear-to-row basis, i.e, each row is from seed of one selected plant. The plot is grown in isolation and the plants are open pollinated. The best individuals in the best rows are selected for ear-to-row planting in the next cycle. A common variation is modified ear-to-row selection, whereby the individual ear-to-row plots are detasseled before pollen is shed and male (pollinator) rows from bulked seed of all the entries are planted at regular intervals throughout the isolation block. Undesirable plants in the male rows can be rogued before pollination. In addition, the entries are tested in one or more replicated trials to identify the best performing entries. From the isolation block, the best individuals in the entries selected from the replicated trial data are chosen for the next cycle of modified ear-to-row selection. Each cycle requires one season. Half-sib family. Individual ear-to-row families are selected based on data from replicated trials at two or more locations. Residual seed of the selected entries is then used for systematic intercrossing of the selections. Thus, unlike mass or ear-to-row recurrent selection, the pollen sources also are only from the selected entries. Individual plants are selected within each family in the intercrossing block for entries in the next cycle. Each cycle requires two seasons, i.e., one year if both summer (for testing) and winter (for intercrossing) facilities are available. Selfed progeny. Selected plants (S0) within a population are self-pollinated to produce S1 lines. The S1 lines are tested in replicated trials at two or more locations, and residual S1 seed of the selected entries is planted for intercrossing to produce the next cycle of the population. Three seasons are required per cycle, or two years if a winter nursery is used. An alternative procedure is to plant the S1 lines in the breeding nursery and perhaps in a pest nursery as well. Visual selection is practiced among the S1 lines, and selected plants within the selected lines are selfed to produce S2 seed. S2 lines are then evaluated in replicated trials. This procedure increases the efficiency of costly replicated trials by eliminating visually undesirable families beforehand. Furthermore, if a winter nursery is used, a second generation of intercrossing of the selected entries can be done, thus enhancing genetic recombination, and therefore genetic variance, before initiating the next cycle of selection. Six seasons are required per cycle, or three years with a winter nursery. Table 4 presents a season-by-season description of S2 selfed progeny recurrent selection. Half-sib tester. The procedure is similar to selfed progeny recurrent selection except that the S1 (or S2) lines are topcrossed to a common tester, e.g., a population, a hybrid, or, most frequently, to an elite inbred line. The topcrosses are then evaluated in replicated trials and residual S1 (or S2) seed of the selected entries used to plant the intercrossing block. Compared to the selfed progeny procedure, an extra season is required in order to make topcrosses. Thus, four seasons are required if S1 lines are topcrossed, and seven seasons if S2 lines are used. However, if a winter nursery is used, a cycle still can be completed in 2 years with S1 lines and in 3 years with S2 lines. Table 4 presents a season-by-season description of half-sib tester recurrent selection using S2 lines and an inbred tester. Full-sib. Selected plants in the population are crossed in pairs to produce seed of full-sib progenies. The full-sib progenies are evaluated in replicated trials and the selected full-sib progenies are intercrossed to form a new cycle. Each cycle requires three seasons or 2 years if a winter nursery is used. Reciprocal recurrent. This procedure is designed to improve the cross-performances of two complementary populations. It is essentially the same as half-sib tester, but the tester for each population is the other population or an inbred line from that population. A full-sib version uses plant-to-plant crosses between the two populations.

Table 4 A season-by-season description of S2 selfed progeny (S) recurrent selection and half-sib tester (HS) recurrent selection with an elite inbred tester when a winter breeding nursery is available and the breeding program is located in a temperate zone Winter 1. For both S and HS: self-pollinate 400–600 selected plants from a population of 1000 or more plants to produce S1 seed. Select again at harvest. Summer 1. For both S and HS: grow out S1 progeny rows in breeding and pest (if needed) nurseries. Select among S1 progeny rows and self-pollinate selected S1 plants within the selected rows to produce S2 seed. Select again at harvest to give 100 or more S2 entries for subsequent evaluation. Winter 2. No activity in S. For HS: cross the selected S2 lines to an elite inbred tester. Summer 2. (1) For S, evaluate the 100 (or more) S2 lines in replicated trials at two or more locations. Select 20 or more S2 lines as parents for the next cycle. The HS program is the same except that testcrosses of the 100S2 lines are evaluated. (2) Continue selfing and selection among and within the 20 (or more) S2 lines to produce S3 seed. Winter 3. For both S and HS, use residual seed of S2 lines selected from evaluation trials for first intercrossing. Summer 3. (1) For both S and HS, make a second intercrossing using bulked seed of each line from first intercrossing. This will complete cycle. The next cycle of selection will be initiated in the next winter nursery (as per Winter 1). (2) Keeping only the S3s, of the best of the 20 (or more) selected lines from the evaluation trials, continue selfing and selecting to produce S4 seed. Also testcross the S3 lines to elite inbred testers. Subsequent testcross evaluation trials will determine which lines will continue to be selfed for potential use as an inbred parent in a commercial hybrid.

Individuals containing the GMO event are identified using an antibody-based assay such as ELISA or spraying with the herbicide. Molecular markers are used to identify the individuals that contain as much of the recurrent parent’s genotype as possible. Those individuals that contain the GMO event and a high proportion of the recurrent parent’s genome will be

backcrossed again to the recurrent parent (BC2) and those BC2 individuals that contain the GMO event again will be identified as well as those individuals that contain >95% of the recurrent parent’s genotype. Using this approach and off-season nurseries, breeders can rapidly introduce transgenic events into new inbred lines.

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BREEDING OF GRAINS | Maize: Breeding

Production of Commercial Hybrid Maize Seed Hybrid maize seed planted by farmers is produced and sold by commercial seed companies. The production of hybrid seed is an intricate process, because seed quality, seed purity, and cost of production are all critically important factors. Wych provides a detailed description of this process. Most hybrid seed production now is of single crosses (two inbred parents) or modified single crosses (three inbred parents, two of which are closely related), but three-way crosses (three inbred parents) or double crosses (four inbred parents) have been popular in the past (Figure 2). The minimum isolation distance that a seed production field must be from other maize fields is 200 m to ensure purity of the seed. The typical pattern of planting that is used in a seed production field is 4:1, i.e., 4 rows of the female line and 1 row of the male line. This pattern is repeated systematically throughout the field so that a female row is no more than two rows away from a male row. Plant densities in seed production fields range from 54 000 to 64 000 plants/ha, which is a lower plant density than that normally found in commercial production ( 70 000 plants/ha) in North America. The lower plant density is used to achieve maximum yield of saleable kernels. Pollen control in seed production fields is achieved by removing the tassels (detasseling) from the female rows prior to anthesis. Detasseling can be done either by hand or mechanically using cutter bars or pullers. An option to detasseling is to use the cytoplasmic male sterile system with restorer genes. However, this practice fell out of favor in the early 1970s when susceptibility to southern corn leaf blight (Bipolaris maydis) was associated with the use of the Texas male sterile cytoplasm (cms-t). Soon after pollination, typically the male parent rows are removed to reduce competition with the female row and the risk of seed contamination at harvest. The female rows will be harvested at 30–38% grain moisture, i.e., just before they reach physiological maturity. Timely harvest is essential to maintain yield and seed quality. Freezing damage to the kernels and damage due to insects and diseases can reduce the germination percentage of the seed, while delays in harvest will increase the risk of dropped ears. Harvesting is done by machine using mechanical ear pickers. The ears are sorted to remove diseased or undesirable ears and are then dried in low-temperature dryers at temperatures ranging from 35 C to 40 C until the kernels have reached a moisture content of 12–13%. The ears are then shelled, the seed is cleaned to remove foreign material and broken kernels, and the seed is then sized. Sizing involves sorting the seed into lots of uniformly sized kernels. The sized seed is treated with a fungicide or a combination fungicide/insecticide and bagged. Hybrid maize seed is bagged in units either weighing 50 lbs or containing 80 000 kernels.

Summary The maize breeding methods and philosophy described in this article have been successfully practiced for over 90 years with

very little modification to the basic principles: (1) creation of new linkage blocks through recombination; (2) simultaneous evaluation of large numbers of breeding crosses and families within breeding crosses; and (3) progeny testing in testcross combinations using replicated trials in multiple locations. Innovations to maize breeding during those 90 years have involved incorporating new technologies such as mechanical harvesters and planters, computers, electronic data capture devices, and databases. All of these technologies have aided the maize breeder to create and identify superior genotypes more efficiently and thus continue to contribute to the steady grain yield increases in N. America during the hybrid era (Figure 1). Most likely any future technologies, such as genomics, will continue to aid maize breeders to meet this objective, rather than replace the methods and philosophies that have proven to be so successful.


• •

Without hybrid maize, what do you think would be the present state of of North American agriculture and food production? If you were setting up a speciality maize breeding program in your region, what resources would you need, and what experimental procedures would you plan?


• • •

To what extent has maize breeding been transformed by use of molecular-marker facilitated selection? What are the problems and opportunities in breeding maize for the bioethanol industry (both starch and cellulose based technologies)? How do maize breeding objectives for temperate and tropical environments differ?

See also: Genetics of Grains: Maize: Genetics; Maize: Other Maize Mutants; The Cereal Grains: Maize: Overview.

Further Reading Brown WL and Goodman MM (1977) Races of corn. In: Sprague GF (ed.) Corn and Corn Improvement, pp. 49–88. Madison, WI: American Society of Agronomy. Hallauer AR (1987) Maize. In: Fehr WR (ed.) Principles of Cultivar Development, vol. 2, Crop Species, pp. 249–294. New York: MacMillan. Hallauer AR (2001) Specialty Corns, 2nd edn. Boca Raton, FL: CRC Press. Hallauer AR, Miranda JB, and Fo AR (1988) Quantitative Geneticsv in Maize Breeding, 2nd edn. Ames, IA: Iowa State University Press. Hallauer, Russell WA, and Lamkey KR (1988) Corn breeding. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 463–564. Madison, WI: ASA-CSSA-SSA Publishers. International Institute of Tropical Agriculture, www.iita.org, IITA c/o Lambourn (UK) Limited, Carolyn House, 26 Dingwall Road, Croydon CR9 3EE, UK. International Maize and Wheat Improvement Center, www.cimmyt.org, CIMMYT, Apdo. Postal 6–641, 06600 Mexico, D.F., Mexico. Kiesselbach TA (1949) The Structure Reproduction of Corn. Lincoln, NB: University of Nebraska Press.

BREEDING OF GRAINS | Maize: Breeding Troyer AF (2001) Temperate corn: background, behavior, and breeding. In: Hallauer AR (ed.) Specialty Corns, pp. 393–466. Boca Raton: CRC Press. Walden DB (1978) Maize Breeding and Genetics. New York: Wiley. Wych RD (1988) Production of hybrid seed corn. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 565–607. Madison, WI: ASA-CSSA-SSA Publishers.

Relevant Websites iita.org http://www.iita.org. cimmyt.orgcimmyt.org http://www.cimmyt.org.

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Rice: Breeding Qingyao Shu and Dianxing Wu, Zhejiang University, Hangzhou, People’s Republic of China ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 3, pp. 61–68, ã 2004, Elsevier Ltd., with revisions made by the Editor.

Topic Highlights

• • • • • • • • • •

Modern rice breeding has increased rice production due to the adoption of high-yielding semi-dwarf varieties. The development of hybrid rice has further increased rice yield by 15–20% beyond the level of semi-dwarf rice varieties. Breeders select for variations in eating quality based on amylose content. Fragrance is another quality trait, mainly selected for the presence of 2-acetyl-1-pyrroline (2-AP). Selection for abiotic stress environments includes factors such as late-season drought, submergence during vegetative development, and tolerance to cool temperatures. Breeders also contend with biotic stresses including disease and insect-pest pressures. Marker-assisted selection (MAS) is a valuable tool for indirect selection of traits in rice breeding. Conventional breeding has some limitations, so the transgenic approach permits the use of novel genes. Transgenic “Golden Rice” is one of the successes of genetic engineering. New varieties will enable people to produce more rice from less land, with less water, less labor, and by using less pesticide.

Learning Objective

•

Achieve an understanding of the ways in which the various approaches to rice breeding have and will provide improvements in rice production and quality.

Introduction It is difficult to trace man’s earliest efforts to improve the rice plant. However, long before the advent of science, man undoubtedly had made good use of natural variation from spontaneous mutations and natural hybridizations. Susrutha (c., 1000 BC) in his Ayurvedic Materia Medica recognized the differences among rice cultivated in India and separated them into groups based upon their growth duration, water requirements, and nutritional values. Chinese classics show that Emperor Wen Ti of the Wei Dynasty (AD 186–226) discussed with his cabinet about quality rice having strong and fragrant aroma. Another Emperor, K’ang His (1662–1723) of the Ching Dynasty, selected an early maturing and aromatic mutant for a crop of rice grown in the Imperial Garden that later became the main staple of his household. The new strain was named Imperial Rice. The large-scale introduction, testing, and distribution of the early maturing Champa rice in central and east

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China during the eleventh century marked the first massive government-sponsored efforts to utilize efficient and productive genotypes. Modern rice breeding is a major component of the Green Revolution which resulted in remarkable increases in rice production due to large-scale adoption of high-yielding semidwarf varieties. The development of hybrid rice further increased rice yield by 15–20% beyond the level of semidwarf rice varieties in China, and use of hybrid rice has recently been expanding in other countries. Modern varieties have had a dramatic impact on yield increases in rice production. World rice production doubled in a 25-year period, from 257 million tonnes (Mt) in 1965 to 520 Mt in 1990. However, to keep pace with an alarming rate of increase in the rice-consuming population, breeding of new rice varieties is an important and indispensable way to further enhance rice yield potential and stability, and adaptability to adverse soil and climatic conditions. New varieties will enable people to produce more rice from less land, with less water, less labor, and by using less pesticide. Recent breakthroughs in plant molecular biology and biotechnology have continued to revolutionize the methodology and technology of rice breeding, and will enable rice breeders to develop new varieties more efficiently.

Breeding for High Yield and Wide Adaptability Yield enhancement has long been one of the most important objectives in rice breeding. Efforts to combine a high yield with season-independent adaptability were initiated in subtropical Taiwan during the 1920s. Taichung 65 and other “Ponlai” series varieties represented a distinguished group (keˆng) that is insensitive to changes in photoperiod and temperature, early maturing, nitrogen responsive, and high yielding. Ponlai varieties could be planted in both the first (spring) and second (summer) season of Taiwan and allow intensive multiple cropping between the rice crops. From a cross between a tall indica variety and the semidwarf Dee-geo-woo-gen (DGWG), the early maturity semidwarf variety Taichung Native 1 (TN1) was developed in 1956. It responded much better to heavy nitrogen fertilization and outyielded the popular Ponlai varieties. TN1 was widely used in the hybridization programs of India and by International Rice Research Institute (IRRI), the Philippines. Soon after IRRI began its research activities in 1962, the primary breeding objective was to develop highyielding, short-and-stiff-culmed, photoperiod-insensitive rice varieties that would resist lodging under heavy fertilization and would have wide adaptability in tropical areas. The famous semidwarf IR8, regarded as the most important rice variety leading to the Green Revolution, was bred from the cross of Peta/DGWG in 1966. From different country programs in tropical Asia and elsewhere, a large number of semidwarf


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BREEDING OF GRAINS | Rice: Breeding varieties have been developed since 1968, either using TN1 or IR8 as semidwarfing parent. The more notable varieties are Jaya, Padma, Bala, Ratna, Sona, Cauvery, and Annapurna of India; RD1 and RD2 of Thailand; Meheran 69 of Pakistan; Chandina and Mala of Bangladesh; and CICA-4 and CICA-6 of Colombia. Efforts to develop high-yielding semidwarfs on the China mainland began in the mid-1950s. Ai-chio-nan-te and Chenchu-ai were two of the initial releases in 1959. Ai-chio-nan-te (Ai-jiao-nan-te), Chen-chu-ai, Kwang-chang-ai (Guang-chang ai), Chiang-nan-ai (Chang-nan-ai), and Nung-k’en (Nongken) 58 were the principal varieties grown during the mid1960s in central and south China, and they gave rise to improved semidwarfs or “keˆng” types such as Ai-nan-tsao 1 (Ai-nan-zao 1) and Hu-hsuan 17 (Hu-xuan 17). The development of early maturing semidwarfs (100 days or less) such as Ai-nan-tsao 1 and its derivatives made triple cropping possible in Guangdong Province and double cropping in ShanghaiNanjing area. The above semidwarfs have the same recessive gene for short stature as in DGWG.

Breeding for Stable Yield After the marked jump in yield potential was attained in the late 1960s, the next problem was to stabilize the high yield level in the face of intensified disease and insect pest pressure, which cause the loss of more than 200 Mt of rice each year. Rice fields in irrigated areas of the Asian tropics were ravaged by diseases and insects after increased nitrogen fertilization, dense planting, multiple cropping, and continuous planting of a few high-yielding varieties. Associated with the dominance of a few varieties of similar genetic backgrounds, a new or hitherto obscure biotype of a genetically plastic pest may appear in quantity, and the resistance in the major varieties breaks down. Successful progress has been made in transferring a major gene or a gene complex for resistance to specific diseases and pests into the high-yielding backgrounds. The transfer of the desired gene or genes was made by way of single or multiple crosses or a combination of them. The resistance genes for bacterial blight, blast, grassy stunt, tungro, green leafhopper, and brown plant hopper have all been incorporated into improved varieties. Among environmental factors affecting yield stability, resistance to drought and tolerance to submergence in flood waters are also essential to stabilize crop yields during seasons of erratic precipitation.

Breeding for Grain Quality and Improved Nutrition The consumer prefers rice with a clear (translucent) endosperm and pays a premium price for it. Grains with chalkiness in the endosperm, caused by loose packing of the starch and protein particles, break more easily than translucent grain during milling, thus greatly reducing the market value. The opaque areas are known as white belly, white center, or white back, depending on the location within the endosperm. For evaluation of breeding materials, it is most convenient to group them together as white belly rather than to individually rate each type. A few varieties have almost totally opaque endosperm.

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Other varieties are translucent or have only minute traces of white belly. The presence and degree of white belly are partially under genetic control although certain environmental factors (high temperature immediately after flowering) markedly affect their expression. Preferences for grain length and shape vary among countries and marketing areas. Width and thickness, or shape, are less variable and less important than length, although the highest-quality markets usually demand a slender to medium width. Length and shape of grain are independently inherited and can be combined as desired with the possible exception of the extra long and bold characters. Furthermore, there are no barriers to recombination of any expression of grain length and shape with other quality traits, or with plant type, dormancy, or maturity period. Nevertheless, grain size and shape are relatively difficult traits to handle. The most important consideration is for the breeder to know which grain types are desired in the markets he serves and to stringently reject all segregates that do not meet those requirements. Improved semidwarf plant types with essentially all possible combinations of grain shape and length are available as parents in the germ plasm. Grain shape and length are quantitatively inherited. Grain size is highly heritable in most environments although low temperature after flowering can slightly reduce grain length. Despite the apparent complexity of their inheritance, grain length and shape appear to be fixed exceptionally early in the segregating generations. Preliminary selection for grain appearance can be based on visual evaluation in the field and laboratory based on examination of rough rice, and supplemented later with more accurate measurements on milled rice. Careful evaluation of milling quality, particularly percentage of head rice, is critical in all rice breeding programs. Unfortunately, there is no simple, accurate technique to directly measure milling quality in segregating generations. It is imperative to run at least one evaluation of milling quality, preferably more, in a well-adjusted commercial mill before releasing a new variety. Amylose is the linear fraction of starch in the nonglutinous varieties. Amylopectin, the branched fraction, makes up the remainder of the starch. Amylose content has a major influence on the characteristics of cooked milled rice, including cohesiveness, tenderness, color, and gloss of cooked rice. Rice varieties are grouped on the basis of their amylose content into waxy amylose (1–2%), low amylose (8–20%), intermediate amylose (21–25%), and high amylose (more than 25%). Cooked glutinous or waxy rice is very moist, sticky, and glossy, and is the staple food in a few small areas in Asia. The nonwaxy varieties make up the bulk of the world’s rice, ranging from 8% to 37% in amylose content. Low-amylose varieties are moist, sticky, and glossy when cooked, and readily split and disintegrate when overcooked. Rice with a high-amylose content such as IR8 cook dry and fluffy but become hard upon cooling. Intermediate types such as IR64 have the fluffiness of highamylose types but retain a soft texture when cool. Japonica varieties tend to have low-amylose content and to be sticky when cooked. Indica varieties vary widely in amylose content according to regional quality preferences. High- and lowamylose types appear to differ by control of a single gene. The heterozygote has intermediate amylose but this cannot be stabilized. If intermediate amylose content is desired, one

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or both parents must be intermediate. Amylose content is partly modified by environment in largely unknown ways. High temperature during grain ripening lowers amylose content. Some varieties can vary as much as 6% in content from season to season. Varietal differences in gel consistency exist among varieties of similar high-amylose content. Gel consistency of rice with less than 24% amylose is usually soft. The gel consistency test was developed to complement the amylose test in breeding programs for rice quality. Gelatinization temperature is partly associated with the amylose content of the starch, the major determinant of cooking behavior. Milled rice has excellent digestibility and good protein quality, but the gross protein content (7–9%) is rather low for nutrition of children. Efforts have been made at IRRI and in China to increase the brown rice protein. High protein content appears to correlate with low yield in fixed genotypes. The use of protein per seed appears to be a more effective selection criterion than the brown rice protein content of a bulked seed sample of a plant or breeding line. Cultivation, especially use of nitrogen fertilizer, can affect protein content of milled rice to a great extent. However, high protein content is not always a preferred character, because it is very often negatively related to low eating quality. Fragrance of cooked rice is preferred in many areas. Several chemical constituents are important to the aroma of cooked rice. However, 2-acetyl-1-pyrroline (2-AP) is the most important component. Aroma is a recessive trait that is controlled by a single recessive gene. In aromatic rice, all parts except root contain 2-AP, and it could be detected by tasting the associated flavor in individual seeds or assessing the aroma of leaf tissues or grains after either heating in water or reacting with KOH. Therefore, selection of aromatic trait is not much difficult. Improved varieties having the aromatic quality – such as Sabarmati, Pusa 33, PR967-11, and Jasmine 85 – have been developed in South Asia and elsewhere. More recently, molecular markers, such as RM223 and RM42 in Australia, have been developed for this important trait, which may accelerate the breeding of aromatic rice. Richness in micronutrients – such as Fe, Zn, and Ca – is a very important and desired trait in rice, because micronutrient malnutrition is a common phenomenon in countries with rice as staple food. Breeding of Fe dense rice has been initiated in several countries, but the progress has so far been very limited in conventional rice breeding. However, by using genetic engineering, transgenic rice plants reported with a ferritin gene form Phaseoulus vulgaris, and the Fe content was doubled in grains. Apart from increasing the mineral content in rice grains, reduction of antinutrient components is another way to increase the bioavailablity of micronutrients of rice. In this aspect, low-phytin rice might be the best choice, and some prototypic rice lines have been already developed, but their actual usefulness remains to be tested.

Breeding for Overcoming Stress Factors Productivity in upland, rainfed lowland, and even irrigated rice is limited by inadequate water at certain phases of growth. As much as 90% of the world’s rice-growing area is estimated to

suffer from drought at critical growth stage. Under upland culture, thick and deep roots and ability to maintain leaf turgor are two of principal traits associated with drought resistance. Under rainfed lowland culture, the ability to maintain leaf water potential is clearly associated with drought resistance although the root system may play a somewhat smaller role. Incorporation of recovery ability from drought is also essential to the rainfed lowland culture. Tolerance to submergence in flood water is different from tolerance to deep water. The two traits need to be evaluated separately, and specific qualities are needed for rice grown in deep water. To make breeding contribute more to productive and sustainable rainfed lowland rice system, genetic variation has been identified for both broad adaptation across target rainfed lowland environments and specific adaptations to some of the abiotic stress environments, e.g., late season drought, and submergence during vegetative development. Tolerance to cool temperatures became necessary when population pressure forced farmers to cultivate rice at high elevations in tropical Asia. Good progress in breeding for cold-water tolerance in northern Japan and in California has been attained. Success appears to be attributable to long years of empirical testing and selection, use of diverse germplasm, and development of efficient cultural practices. Millions of hectares in humid regions of Southeast Asia are left idle or are grown with very low yields because of salinity and abiotic stresses, though the climate is suited for rice production. Mineral deficiencies and toxicities frequently compound the problem of salinity. Rice varieties with partial tolerance to particular abiotic stress, e.g., salinity, alkalinity, iron toxicity or deficiency, zinc deficiency, phosphorus deficiency, manganese and aluminum toxicity, are available in rice germplasm. However, most of these varieties yield poorly and lack resistance to major disease and insects. Progress has been made recently in developing rapid and reliable screening techniques of saline tolerance, identifying and improving tolerant germplasm. Genetic analysis of the tolerance to most soilrelated stresses has also been studied in rice, and elite lines have been developed with tolerance to multiple stresses. Many new varieties have been released with enhanced tolerance to such stresses and planted in salt-affected areas.

Breeding for the New Plant Type Quantum jumps in the yield potential of crop plants generally resulted from the modification of plant types. New plant architecture permitted the yield potential of rice to be doubled in the mid-1960s, which was characterized by short stature, high tillering, sturdy stems, and dark green, erect leaves that were largely contributed by DGWG or its derivatives and the tropical indicas. To make another quantum jump in the yield potential, modification of the present high-yielding plant type has been explored. The prototype is described as short stature (90–100 cm), low tillering (6–10 tillers under transplanting, no nonproductive tiller), dark green, and erect leaves. These new plant types are likely to have 20% higher yield potential than the highest currently cultivated. Heterosis between indica/ japonica crosses is regarded as the most feasible way to achieve such a breakthrough.

BREEDING OF GRAINS | Rice: Breeding Exploitation of Heterosis An F1 hybrid of two genetically dissimilar parents showing increased vigor at least over the mid-parent value (the average performance of two parents) is known as heterotic (shown heterosis). The use of F1 hybrids in commercial production hinges on the extent of heterosis, and the ease and costs of F1 seed production. Since the early 1970s, a massive program of hybrid rice breeding has been operated in China, and recently in other rice-producing countries. Currently, more than half the rice area is planted to breed hybrid rice in China. The hybrid rice were described as having a vigorous root system, vegetative growth vigor, high tillering ability, large and dense panicles, heavy grains, and wide adaptiveness. Hybrid rice in China is mainly based on a cytoplasmic male sterility (CMS), which originated from a wild rice plant from Hainan Island, and fertility restoration system. Hundreds of CMS lines have been bred in China for hybrid rice production. These CMS lines could not be directly used as such to develop rice hybrids for the tropics because of their susceptibility to diseases and insects, and poor adaptability to tropical climates. New CMS lines were bred at IRRI and by various national programs using the wild abortive (WA) CMS system from China. New sources of CMS have also been identified at IRRI. There is no dearth of restorers among the elite indica rice germplasm in the tropics and subtropics, but the degree of restoration varies greatly and is sometime subject to environmental stresses, such as high temperature. Use of photoperiod-sensitive/thermo-sensitive genic male sterility (P/TGMS) has been extensively studied during the 1990s in China and elsewhere. P/TGMS line is used both for seed multiplication, which is done by a cross between a CMS line and its responding maintainer line in CMS system, and hybrid seed production, thus greatly simplifying seed production, because there is no need for maintainer lines. Hybrid rice facilitated by P/TGMS is named as two-line hybrid rice, and that facilitated by CMS as three-line hybrid rice. Several sources of TGMS and PGMS have been reported in China and other countries such as in Japan and the United States. In the two-line hybrid rice system, most conventional varieties are natural restorers for P/TGMS lines; thus, there is greater flexibility in selection of restorer line, and the fertility of hybrid plants is more stable than in the three-line system. Theoretically, twoline hybrids have more chance to gain greater heterosis, because there is less restriction on the choice of parents in comparison to the CMS system. However, because almost all indica two lines tend to be thermo-sensitive, and it is almost impractical to find a place where the temperature is absolutely stably higher than a certain degree because of raining and storms across different years, therefore, the seed production of the two-line hybrid rice has more restrictions than that of the three-line hybrid rice, which makes it inapplicable to many areas. The genetic basis of heterosis is quite complicated, but it depends, in a large part, upon the genetic diversity between the two parents. The greater the genetic difference in the parents, the higher the potential heterosis. Since the 1970s, the genetic diversity among improved indica rice has narrowed due to massive international exchange of germplasm. Indica and japonica germplasm have, however, remained distinct, as there has been relatively very little gene flow between these

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two subspecies. As expected, the inter-subspecies hybrids showed greater heterosis for yield than did indica/indica hybrids. The new plant-type development program based on tropical japonica germplasm would also be utilized for producing hybrids with better heterosis. Successful instances are development of superyield rice varieties “Liang-you-pei-jiu (Pai’ai 64S/9311)” and “Xie-qing-zao A/T9308” with the highest yield potential of 12 t ha 1 in China.

Breeding Methods Development of new rice varieties always starts with the selection of parental varieties, no matter what kind of breeding method to be used. It consists of several important steps in rice breeding: the first is the creation of variation, the second is selection and obtains homozygous promising lines, the third is yield, quality, and other agronomic performance on plot basis, and finally participating official regional and national yield trials and registration of new varieties (Figure 1). Depending on the method of variation creation and homozygous line production, there are several methods in rice breeding (Figure 2).

Cross-Breeding Genetic diversity among plants in a population is a prerequisite for successful plant breeding. Natural genetic variation has been used as a raw material in rice breeding. Hybridization has long been used to enhance genetic variability or to synthesize varieties combining desirable characters from two or more parents. The pedigree method of selection has been the predominant practice of rice breeders in handling segregating generations from the F3 and beyond. The bulk method is particularly valuable where quantitative characters are concerned, such as yield of grain. It has the great potential advantage of reducing work in the early generations, as well as the demands on field space, so enabling the breeder to handle a larger number of crosses. The backcrossing method may be expedient when a breeder wishes to make specific and limited improvement on a welladapted and preferred variety. Backcrossing consists essentially of recurrent crossings to the hybrid progeny with one of the original parents (recurrent parent) with the objective of perpetuating a particular character possessed by the donor parent. Backcrossing is particularly useful in increasing resistance to particular diseases. Recurrent selection following intercrossing could be helpful in improving traits that are under polygenic control and have low heritability.

Induced Mutation Normally, the spontaneous mutation rate in rice is very low. The use of induced mutations has become a routine tool in rice breeding where convenient sources of radiation and chemical mutagens are available. Large number of mutants have been produced, most of which were by gamma irradiation of dried seeds. Chemical mutagens, mainly alkylating agents such as Nmethyl-N-nitrosourea (MNH) and ethylmethanesulfonate (EMS), have been tested for their usefulness in mutation induction, but seldom used in practical breeding programs.

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Selection of elite lines Figure 1 Flowchart of rice breeding and new variety registration.

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Figure 2 Flow chart of various methodologies for rice breeding.

A combination of chemical mutagens and radiation was applied in some cases. Semidwarf and early maturity are the characters most frequently achieved in released rice mutant varieties. Among other widely used mutated characters are those for grain quality, blast tolerance, salinity tolerance, and

photoperiod insensitivity. Artificially induced mutations are very often accompanied by deleterious recessive genes, and even with chromosome damage leading to sterility. Therefore, mutants are also often used in cross-breeding as parents, which is known as indirect use of mutants.

BREEDING OF GRAINS | Rice: Breeding Worldwide, numerous rice varieties have been developed by using induced mutations, and many of them have (had) been commercially planted. Zhefu 802, an indica variety developed by gamma irradiation, might be the most extensively grown mutant rice variety. Its accumulative planting area reached more than 12 Mha during 1986–94 in China. The semidwarf mutant variety Calrose 76, also induced by gamma rays irradiation from Calrose in California, USA, on the other hand, has been the semidwarf gene (sd1) donor of most modern American rice varieties, and of rice varieties grown in Australia recently. Induced mutations could be more readily used in crosses than exotic source when a desired trait could not be found in the local group of varieties. Meanwhile, mutagenic treatment could also serve as a powerful tool in breaking down the tight linkage and thus increasing recombination frequency in some wide crosses.

Tissue Culture Tissue culture includes in vitro culture of embryos, protoplasts, somatic cells, anthers, and microspores. There are mainly three kinds of applications of tissue culture in rice breeding. The first is doubled haploid (DH) production, which consists of anther and microspore culture. Rice anthers, of which the microspores are at the middle to late single nucleus stage, often after subject to a 1 week cold pretreatment, are cultured on specific medium, and haploid plantlets are induced from the microspores. The microspores could also be dispersed into culture medium and then cultured in liquid. A high percentage of regenerated plantlets is spontaneously doubled in chromosome number, and thus become DH plants. The main advantage of DH technology is its ability to produce homozygous plants from any heterozygous breeding materials; this greatly accelerates the breeding process and shortens the breeding cycle. Additional advantage of DH technology is that the dominant effects are removed in DH lines, which is of paramount importance for selection of traits contributed by recessive genes. Although anther culture has been practiced in many countries and a large number of rice varieties have been developed, its potential has not fully been realized. The majority of indica rice varieties, which cover most the rice cultivating areas worldwide, are recalcitrant to anther culture. The second application comes with genetic transformation. In the 1980s, protoplast transformation had been unanimously believed to be the only way to produce transgenic rice plants. Therefore, protoplast culture has been widely studied in many countries, but only a few plants were regenerated. With the rapid progress of genetic transformation on rice intact cells and tissues in the 1990s, protoplast gradually phased out, and in vitro culture responsive explants, such as (immature) embryos and young panicles, are used in tissue culture for genetic transformation. A vast number of transgenic plants have been produced either for rice improvement or for genomic studies. The observation on genetic variation among regenerated plants from in vitro culture has led to the third application. Such variation is now known as “somaclonal variations (SVs).” SVs are composed of genetic and epigenetic alterations in regenerated plants. Inheritable SVs become a unique source of genetic variation, and are used in rice improvement. In vitro

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culture combined with mutagenic treatment could further increase the frequency and range of variations in progenies of regenerated plants. This system is known as in vitro mutagensis. Instances of success with such a system is the development of a series of mutant hybrid rice varieties, e.g., II you 3027, Shanyou 371, and Xieyou 371 in China.

Genetic Engineering Conventional breeding has been an effective means for developing high-yielding varieties; however, it has its own limitations. The transgenic approach provides a novel way for rice breeders to use genes other than those from rice and its relatives. With this technology, the rice breeder is now able to transfer and incorporate desirable genes into rice genome, no matter where the gene comes from. The evolutionary and taxonomic isolation is thus broken. Significant advances have been made in the genetic engineering of rice since the first transgenic rice plants reported in the late 1980s. Several transformation protocols have been deployed successfully for the introduction of foreign genes into rice. More than 60 rice varieties, which belong to indica, japonica subspecies, and African elite rice, had been transformed with various of genes which confer important traits, such as herbicide resistance, disease and insect pest resistance, environmental stress tolerance, and nutritional quality. Among them, transgenic plants with the insecticidal gene from Bacillus thuringiensis (Bt) might be the best example on agronomical improvement. Several insecticidal Bt genes have been transformed into various types of rice, and all showed great potential for controlling the most important insect pests in rice. The Bt gene encodes the delta-endotoxin highly toxic to lepidopteran insects. Transgenic rice plants with Bt gene have proven to be highly resistant to all lepidopterans, including stem borers such as yellow stem borer, striped stem borer and pink stem borer, and rice leaf folders in field trials. Therefore, it may lead to reduction of 1000 t of pesticide use in rice production every year. This is important not only for cost reduction in rice production, but also has huge health benefits. The transgenic “Golden Rice” is another success of genetic engineering. The whole pathway of b-carotene biosynthesis was introduced into rice plants by simultaneously transforming of three foreign genes: one plant phytoene synthase (psy) gene originating from daffodil (Narcissus pseudonarcissus), one bacterial phytoene desaturase (crt1) gene originating from Erwinia uredovora, and the lycopene b-cyclase (lcy) gene originating from N. pseudonarcissus. The highest b-carotene content reached 1.6 mg per g in rice grains. It was estimated that 200 g of Golden Rice could give 100% of the recommended daily allowance of vitamin A; therefore, it has great potential for solving vitamin A deficiency related diseases, such as blindness, in developing countries.

Marker-Assisted Selection Marker-assisted selection (MAS) is a novel technique of indirect selection of traits in rice breeding. Marker here refers to all kinds of DNA markers, usually visualized by the polymorphisms of a DNA sequence. Restricted fragment length

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polymorphism (RFLP) is the first extensively used DNA marker; many other types of DNA markers have been developed during the past 10 years, mainly PCR-based markers, such as (randomly amplified polymorphic DNA (RAPD), sequence characterized amplified region (SCAR), sequence tagged sites (STSs), and simple sequence repeats (SSRs) or microsatellite. MAS has many advantages over phenotypic selection in rice breeding. DNA markers closely linked to important gene offer a tool for dissecting the genetics of complex traits and for transferring the identified loci into elite breeding lines. MAS is a more attractive approach when a few quantitative trait locus (QTLs) control a significant portion of the variability of one trait under selection. MAS is also favored when the traits being selected for have low heritability or are expensive and time consuming to measure. Compared to RFLP marker, microsatellite markers are probably the most promising markers for MAS in rice. These markers are highly polymorphic, and are now abundantly available for all rice chromosomes. Rapid DNA extraction methods developed for rice leaf tissues, or seeds are likely to work well with microsatellite markers for MAS. A prerequisite to using marker in such selection is that they should be closely linked to the precise phenotype or QTL of interest and polymorphism for the markers between the parents. MAS will certainly provide solutions to most problems associated with breeding improved for abiotic stresses. MAS techniques for bacterial blight and blast resistance, tolerance of flooding, and salinity are in progress.


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What are the biotic and abiotic stresses that threaten rice production? How can breeding counter these threats? Describe the transgenic “Golden Rice” as an example of success for genetic engineering. Explain how limitations of conventional breeding can be overcome by the transgenic approach. Review how amylose content affects eating quality and consumer preferences. What are the main procedures involved in breeding novel rice varieties?


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Research the history of the “Green Revolution” and the consequences of the increases in rice production. ○ Describe any negative consequences, as well as the benefits.

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○ What lessons for the future might be learned from the consideration of this history? Investigate more recent successes for genetic engineering, beyond earlier lines such as “Golden Rice”. Explain the genetic mechanisms behind yield increases due to F1 hybrid seed. What limitations are there that might affect the increased use of this approach?

See also: Barley, Rice and Maize Processing: Oil from Rice and Maize; Rice Processing: Beyond the Farm Gate; Carbohydrates: Starch: Chemistry; Food Grains and the Consumer: Cultural Differences in Processing and Consumption; Genetically Modified Grains and the Consumer; Food-quality Testing: Rice: Eating Quality; Genetics of Grains: Rice: Genetics; Non-wheat Foods: Rice: Chinese Food Uses; The Basics: Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Cereal Grains: African Rice (Oryza glaberrima): A Brief History and Its Growing Importance in Current Rice Breeding Efforts; Rice: Overview; Wildrice, Zizania: Overview.

Further Reading Brunner H (1995) Radiation induced mutations for plant selection. Applied Radiation and Isotopes 46: 589–594. Dowling NG, Greenfield SM, and Fisher KS (1998) Sustainability of Rice in the Global Food System. Los Bano˜s, The Philippines: Pacific Basin Study Center, International Rice Research Institute. Everson RE, Herdt RW, and Hossain M (1996) Prospects of approaches to increasing the genetic yield potential of rice. In: Everson RE and Herdt RW (eds.) Rice Research in Asia: Progress and Priorities, pp. 59–73. Los Bano˜s, The Philippines: CAB International and International Rice Research Institute. Gowda M, Venu RC, Roopalakshmi K, Sreerekha MV, and Kulkarni RS (2003) Advances in rice breeding, genetics and genomics. Molecular Breeding 11: 227–352. Grist DH (1986) Rice, pp. 126–146. Singapore: Longman. Jennings PR, Coffman WR, and Kauffman HE (1979) Rice Improvement. Los Bano˜s, The Philippines: International Rice Research Institute. Kumar LS (1999) DNA markers in plant improvement: an overreview. Biotechnology Advances 17: 143–182. Rao KK, Lakshminarasu M, and Jena KK (2002) DNA markers and marker-asissted breeding for durable resistance to bacterial blight disease in rice. Biotechnology Advances 20: 33–47.

Relevant Websites chinariceinfo.com http://www.chinariceinfo.com – Information on rice-breeding initiatives, technologies, and new varieties developed in China. gramene.org http://www.gramene.org – A curated, open-source, web-accessible data resource for comparative genome analysis in the grasses, including rice. irri.org http://www.irri.org. riceweb.org http://www.riceweb.org – An online encyclopedic resource of rice science and knowledge. csrl.ars.usda.gov http://www.csrl.ars.usda.gov.

Canola/Rapeseed: Genetics and Breeding PBE McVetty and RW Duncan, University of Manitoba, Winnipeg, MB, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by T. Jinxing & F. Tingdong, volume 1, pp. 141–144, ã 2004, Elsevier Ltd.

Topic Highlights

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Canola/rapeseed includes five species in the Brassica genus. Canola/rapeseed oilseed species are adapted to temperate climates. Canola is a quality-improved rapeseed, with reduced erucic acid content in the oil and reduced glucosinolate content in the meal. Rapeseed is being converted to canola-quality rapeseed for the production of edible, biofuel, and industrial oils and a high-quality animal feed. The development of hybrids in several of the canola/ rapeseed species has dramatically increased seed yield and accelerated the rate of annual seed yield increase. Canola/rapeseed has greatly benefitted from the application of modern biotechnologies, with genetically engineered herbicide tolerance and pollination control systems for hybrids, especially in B. napus. Even though there are many diseases and insect pests that can adversely affect canola/rapeseed production, breeding efforts have been successful in maintaining seed yield and seed quality. The application of modern technologies will enhance canola/rapeseed cultivar development in the future, accelerating rates of improvement for seed quality and agronomic performance and encouraging the development of new breeding goals only obtainable using modern biotechnologies.

Learning Objectives

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To acquire an enhanced understanding of canola/rapeseed species origins, genetics, adaptation, cultivar development techniques, and end uses for the world’s third-ranked oilseed crop.

Introduction Canola/rapeseed oilseed production is third in the world following soybean and palm. Canola/rapeseed global production has increased 89% in the last decade in response to growing market demand for vegetable oils. This is also a reflection of numerous and relatively recent breeding-related cultivar productivity improvements. Canola/rapeseed is an oilseed adapted to temperate climates that has high oil content for edible, biofuel, and industrial uses and a high-protein meal following oil extraction. There are some challenges with the use of the terms canola and rapeseed. Rapeseed is the generic term used for several oilseed species in the Brassicaceae (Cruciferae) family, a family of plants so named because the four petals


comprising the flower are cross-shaped. Rapeseed oilseed species naturally produce oil in which approximately one-third to one-half of the fatty acids are erucic acid, a long-chain fatty acid, and meal that has high glucosinolate content. Canola (also known as double-low rapeseed) is a term used to describe quality-improved rapeseed, which has low erucic acid content in the oil and low glucosinolate content in the meal. For edible oil and biofuel end uses, rapeseed is being converted to canola; however, rapeseed is still produced globally for both edible and industrial uses. There is yet another rapeseed variant, one that has high erucic acid content in the oil and low glucosinolate content in the meal that is grown as an industrial oil crop, known as high-erucic acid rapeseed (HEAR). Canola and HEAR are included in the rapeseed global production statistics provided by the Food and Agriculture Organization (FAO) of the United Nations. Europe, North America, and Australia grow canola almost exclusively, while rapeseed is still grown extensively on the Indian subcontinent and in Asia. Canola/ rapeseed will be consistently used in this article to refer to the Brassicaceae (Cruciferae) family oilseeds.

Germplasm The Brassicaceae (Cruciferae) family contains 19 tribes, with the Brassiceae being the most distinctive and economically important tribe, consisting of 242 species and 48 genera. The center of origin on this tribe is the southwestern Mediterranean region. The Brassiceae tribe contains the Brassica genus that contains most of the species that have been domesticated; however, species from the Crambe, Eruca, Diplotaxis, Raphanus, and Sinapis genera have also been domesticated. There are a wide range of genetic variabilities available among the species in the Brassiceae tribe. Numerous intergeneric and interspecific crosses are possible, allowing the transfer of selected genes for disease resistance, fatty acid composition, self-incompatibility, cytoplasmic male sterility, and cytoplasmic male sterility restoration between genera and species within the Brassiceae tribe. Intergeneric chromosome recombination before the loss of the nonhomologous chromosomes is required for intergenomic gene transfer to be successful. Several Brassica genus oilseed species yield edible, biofuel, and industrial oils. The triangle of U (Figure 1) outlines six closely related species, three diploid species, Brassica rapa, B. nigra, and B. oleracea, and three derived amphidiploid species, B. juncea, B. napus, and B. carinata. All of these species, except for B. oleracea, are grown as oilseeds. B. oleracea is exclusively grown as a vegetable crop globally, while B. nigra is exclusively grown as a condiment crop. B. napus and B. rapa have both spring and winter habit forms. B. rapa, B. napus, and B. juncea have been converted to canola quality, while the conversion of B. carinata to canola quality is in progress. The

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Brassica nigra n⫽8

BB

Brassica carinata

Brassica juncea

n ⫽ 17

n ⫽ 18

BBCC

AABB AACC

CC

AA

n⫽9

Brassica oleracea

n ⫽ 10 n ⫽ 19

Brassica rapa

Brassica napus Figure 1 The triangle of U. Reproduced from U N (1935) Genome analysis in Brassica with special reference to the experimental formation of B. napus and peculiar mode of fertilization. The Journal of Japanese Botany 7: 387–452.

predominately self-incompatible diploid species are presumed to be approximately 4 million years, while the derived predominately self-compatible amphidiploid species are younger, having arisen approximately 10, 000 years ago. The FAO maintains a website that reports that there are 78, 450 accessions of domesticated Brassica germplasm stored in various global gene banks. A large collection of wild Brassica species is also maintained by the Universidad Politećnica de Madrid. The three diploid Brassica oilseed species, B. rapa (A genome), B. nigra (B genome), and B. oleracea (C genome), generally display one-gene, two-allele inheritance for most traits. This makes these species much easier to use for genetic and genomic studies, gene cloning, and whole-genome sequencing. The genetic and genomic information obtained from the diploid species has direct use in these species and considerable value in the derived amphidiploid species as well. The three derived amphidiploid species, B. juncea (AB genomes), B. napus (AC genomes), and B. carinata (BC genomes), generally display two-gene, four-allele inheritance for most traits, with one gene and two alleles coming from each of the component genomes. Some traits in the amphidiploids, such as glucosinolate content, are multigenic in inheritance. Genes for individual traits are homoeologous, and the genome size for the amphidiploids is approximately double that for the diploids. Therefore, the amphidiploid species are much more difficult to use for genetic and genomic studies, gene cloning, and whole-genome sequencing. All three diploid species are primarily self-incompatible (with the exception of yellow sarson, B. rapa var. trilocularis, which is self-compatible), while all three amphidiploids are self-compatible. The selfincompatibility in the diploid species complicates genetic and genomics studies; however, the self-incompatibility can be

overcome using a number of standard techniques including bud pollination, salt denaturation of the stigma surface, and/or atmospheric CO2 enrichment. A wide range of crosses among the diploid species, among the amphidiploid species, and between the diploid species and amphidiploid species are possible with synthetic hybrids for all three amphidiploid species successfully created using crosses of the parental species. Gene transfer from one canola/rapeseed species to another in the U triangle for common genomes is readily possible, while gene transfer from different genomes also occurs in rare instances. Disease resistance genes and seed quality genes have been transferred among many of the Brassica species in the U triangle using interspecific crosses. The limited genetic variability present in B. napus is being enhanced using intraspecific spring winter crosses and interspecific crosses to B. rapa or B. oleracea in addition to the resynthesis of B. napus using its parent species. Saturated genetic maps of the diploid U triangle species (B. rapa, B. nigra, and B. oleracea) and the amphidiploid species (B. napus, B. juncea, and B. carinata) have been developed. Molecular markers for numerous traits including seed quality and disease resistance have been developed and used in marker-assisted selection in canola/rapeseed breeding programs. The genome of B. rapa has been completely sequenced, while genome sequencing for B. napus is nearing completion. Finally, the entire genome sequence of Arabidopsis thaliana, a model plant and member of the Brassicaceae, has been extensively used to facilitate gene cloning in the U triangle Brassica species.

Applications of Biotechnology Tissue culture techniques including somatic cell hybridization to move blackleg resistance genes from B genome species (B. nigra, B. juncea, and B. carinata) to B. rapa, B. oleracea, and B. napus and protoplast fusion have successfully transferred disease resistance, fatty acid composition, and cytoplasmic sterility restorer genes. Tissue culture techniques involving doubled haploid line development from pollen grains or microspores are routinely used in several Brassica species to produce pure breeding homozygous lines that are useful in genetic and genomic studies. These doubled haploid lines are also routinely used as parents in hybrid B. napus breeding programs. Plant transformation has been used to develop B. napus strains tolerant to glufosinate and glyphosate herbicides and the nuclear male sterility pollination control system. Transformation has also been used to create B. napus strains with disease and insect resistance, fatty acid modifications, and increased oil content. The development of saturated genetic maps for the canola/ rapeseed species has greatly facilitated the development of numerous molecular markers for use in marker-assisted selection for disease resistance genes, fatty acid genes, yellow-seeded genes, glucosinolate genes, and cytoplasmic male sterility system restorer genes in Brassica breeding programs. Gene cloning of disease resistance genes in Brassica species has been facilitated through the use of the Arabidopsis thaliana model plant. The entire genome of A. thaliana has been

BREEDING OF GRAINS | Canola/Rapeseed: Genetics and Breeding sequenced and the function of many genes determined. Comparison of newly sequenced genome B. napus to those in A. thaliana permits the identification of genes in Brassica and their putative function. These genes can then be cloned and used in functional analysis studies in canola/rapeseed species or in A. thaliana to confirm their function.

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B. napus and B. juncea globally since lodging and pod shatter in these canola/rapeseed species can significantly reduce seed yield. Standard breeding techniques are being used to enhance lodging resistance, while plant transformation and natural variation are being used to reduce pod shatter.

Oil Content

Breeding Different Brassica oilseed species are grown in different parts of the world. B. juncea predominates in warmer semitropical regions, while B. napus predominates in cooler temperate regions; B. rapa is grown globally; B. carinata is grown primarily in Ethiopia and northeast Africa, while B. nigra is primarily grown in Europe and Asia. Winter habit B. napus is primarily grown in Europe, while semiwinter B. napus is grown in much of China. Spring habit Brassica oilseeds are produced elsewhere, mostly not only grown as summer crops but also grown as winter crops in locations such as Australia. Canola/rapeseed breeding goals and objectives differ in different regions of the world depending on climate, agroecological factors (i.e., agronomics, diseases, and insects), tradition, consumer acceptance and preferences, national and international markets, and biotechnology regulations.

Seed Yield Seed yield improvement is a major goal of all canola/rapeseed cultivar development programs globally. The breeding techniques used to achieve yield improvement vary among the canola/rapeseed species. Recurrent selection for increased seed yield within populations is the predominant breeding technique used for the self-incompatible diploid species. The development of open-pollinated populations, doubled haploid lines, and hybrids combined with selection for increased seed yield is the major breeding technique used for the selfcompatible amphidiploid species. The presence of substantial levels of heterosis for seed yield in B. napus and B. juncea has resulted in major hybrid breeding efforts in these canola/rapeseed species. The production of commercial quantities of hybrid seed in B. napus and B. juncea requires the development and use of a pollination control system. Several cytoplasmic male sterility systems including 126–1, anan, mori, mur, nap, ogu, ogu INRA, and pol have been developed and evaluated. The mori, ogu, and 126–1 cytoplasmic male sterility systems are used in B. juncea, while pol and ogu INRA cytoplasmic male sterility systems are used in B. napus hybrid breeding. Genetic male sterility systems have also been developed and used in hybrid B. napus breeding. The male sterile Lembke (genetic male sterility) and the Bayer CropScience nuclear male sterility (genetic male sterility) systems are being used in hybrid B. napus breeding programs. Finally, self-incompatibility alleles have been transferred from B. rapa and/or B. oleracea to B. napus to create selfincompatibility-based pollination control systems; however, none of these self-incompatibility systems are in use in hybrid B. napus breeding programs currently. Improvement of lodging and improvement of pod shatter are important seed yield preservation breeding goals in

The improvement of oil content in all canola/rapeseed oilseed species is a primary seed quality enhancement breeding objective. Crosses to high-oil content lines combined with the selection of progressively higher-oil content progeny are a standard breeding technique used for all canola/rapeseed species. Lines with oil content increases of 5–10% can be achieved using this breeding selection strategy. The development of yellow-seeded B. napus, which has a thinner hull, which indirectly increases oil content, has been a breeding objective pursued for many decades. The recent development of molecular markers for all three yellow-seeded genes in B. napus has greatly facilitated the attainment of this breeding objective. Heterosis for oil content is occasionally observed, with ogu INRA cytoplasmic male sterility B. napus hybrids frequently displaying higher oil content than their parental lines. In addition, several different genetic engineering approaches are being used to increase oil content in B. napus with significant oil content increases frequently reported. Regardless of the method used to increase oil content, the well-documented negative correlation between oil content and protein content requires the simultaneous selection for both oil content and protein content in the seed of all canola/rapeseed species.

Oil Quality The improvement of oil quality is a major breeding objective in all canola/rapeseed species. Oil quality is primarily a function of the fatty acid composition of the oil. Oilseed Brassica species naturally have a moderate to high erucic acid content, an undesirable long-chain fatty acid for edible oil end uses. Canola/rapeseed breeders have used crosses and selection to reduce erucic acid content in the oil in B. rapa, B. napus, B. juncea, and B. carinata from over 30% to under 2%, creating low-erucic acid content oils in these species, which is more suited to edible oil end uses. Further oil quality improvements achieved using mutagenesis and selection have involved the development of specialty canola through the reduction of linolenic acid content in the oil from 10% to under 3% in B. napus and the development of high oleic acid content (over 70%) in B. napus to improve the stability of the oil under storage and frying conditions. Rapeseed oil is also produced for industrial oil end uses. For this end use, increases in erucic acid content are desirable. HEAR with erucic acid content over 50% has been developed using crosses and selection breeding techniques in both winter and spring habit B. napus.

Protein Content The improvement of protein content in all canola/rapeseed oilseed species is a secondary seed quality enhancement breeding objective. While protein quality of canola/rapeseed is excellent, the protein content of canola/rapeseed meal is much

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lower than soybean meal. Increased protein content achieved by crosses and selection would help close this gap. The development of yellow-seeded B. napus, which has a thinner hull, which indirectly increases protein content, has been a longterm breeding objective. Canola/rapeseed oil is much more valuable than canola/rapeseed meal, and this combined with the negative correlation between oil content and protein content in the seed results in canola/rapeseed breeders selecting lines with increased oil content and maintained protein content much more often than the reverse combination. Increased protein content and reduced oil content in B. napus hybrids is a pleiotropic effect of many of the cytoplasmic male sterility systems (mur, ogu, and pol) available for use in this species.

Meal Quality Meal quality in canola/rapeseed is primarily a function of glucosinolate content. Glucosinolates are secondary metabolites produced by members of the Brassicaceae family that serve to protect the plants from diseases and pests. Glucosinolates present in the seed are hydrolyzed to pungent and biologically active isothiocyanates that reduce animal feed intake and have negative thyrogenic effects. Canola/rapeseed breeders have successfully developed low-glucosinolate B. rapa, B. napus, and B. juncea and then combined this trait with the low-erucic acid trait to create low erucic acid and low glucosinolate (i.e., canola quality) in these three Brassica species. B. carinata lines with reduced glucosinolate content have also been developed, and further efforts to reduce the glucosinolate content in B. carinata are ongoing. Low-glucosinolate content B. carinata lines can be combined with low-erucic acid B. carinata lines in the future, providing the ability to produce canola-quality cultivars in this Brassica species.

Other Quality Traits Other traits that affect canola/rapeseed meal quality include fiber content, which can be reduced in B. napus through the development of yellow-seeded lines. Reductions in other undesirable or antinutritional compounds in the seed of the canola/ rapeseed species including phytic acid, tannins, and phenolic compounds would slightly improve meal quality. Breeding efforts to reduce any of these undesirable or antinutritional compounds in the seed currently have a low priority.

Diseases and Pest Resistance There are numerous fungal diseases that infect and adversely affect canola/rapeseed species. The diseases of greatest importance are blackleg caused by Leptosphaeria maculans and stem rot caused by Sclerotinia sclerotiorum. Blackleg is prevalent in all canola-/rapeseed-producing countries except China, while stem rot is a disease with global distribution. While there are a few blackleg resistance genes in B. rapa and B. napus, there are many blackleg resistance genes present in the B genomes of B. nigra, B. carinata, and B. juncea. Several blackleg resistance genes have been successfully transferred from B. nigra, B. carinata, or B. juncea to B. napus using interspecific crosses or somatic hybridization. More recently, blackleg resistance genes in B. napus have been cloned. These cloned

genes enable the development of blackleg resistance genespecific molecular markers for use in marker-assisted selection. They can also be used to transform blackleg-susceptible B. napus genotypes to blackleg-resistant genotypes or pyramid blackleg resistance genes in single canola/rapeseed genotypes. Stem rot (S. sclerotiorum) has a very wide host range with no genes for stem rot resistance found in the Brassicaceae family. Attempts to control stem rot in canola/rapeseed using apetalous lines and lines transformed with oxalic acid oxidase have had limited success. More recently, B. napus rapeseed cultivars with field tolerance to stem rot have been developed and grown successfully in China. These stem rot field-tolerant B. napus cultivars have been crossed to stem rot-susceptible lines to generate mapping populations for quantitative trait loci (QTL) identification. Several QTL have been identified, which can be used to transfer stem rot field tolerance from these Chinese rapeseed cultivars to other canola/rapeseed cultivars. There are several other minor or regionally restricted canola/rapeseed fungal diseases including Alternaria leaf and pod spot caused by Alternaria brassicae, club root caused by Plasmodiophora brassicae, downy mildew caused by Peronospora parasitica, light leaf spot caused by Pyrenopeziza brassicae, root rot caused by Rhizoctonia solani, Verticillium wilt caused by Verticillium longisporum, white leaf spot caused by Mycosphaerella capsellae, and white rust caused by Albugo candida. Resistance genes to these diseases are found within the Brassicaceae family, and traditional breeding techniques are used to develop disease-resistant canola/rapeseed cultivars. There are several viruses that infect canola/rapeseed including Cauliflower mosaic virus, Turnip mosaic virus, and Turnip yellow virus. These viruses are all transmitted by leafhoppers or aphids. Resistance genes to Turnip mosaic virus have been identified in the Brassica species. Viral diseases usually have minimal impact on canola/rapeseed production. There are several pests of canola/rapeseed including cyst nematodes (Heterodera cruciferae), crucifer flea beetles (Phyllotreta cruciferae), striped flea beetles (Phyllotreta striolata), hop flea beetles (Psylliodes punctulata), aphids (Brevicoryne brassicae), and leaf hoppers (Macrosteles phytoplasma). Flea beetles feed on canola/rapeseed seedlings and can cause significant damage. Aphid infestations usually have minimal impact; however, they do transmit several viruses. Similarly, leaf hoppers transmit a phytoplasma that causes aster yellows in canola/rapeseed. Aster yellows disease is usually of minimal significance in canola/rapeseed production; however, a high incidence of aster yellows in Canada in 2012 suggests that greater emphasis on the control of this disease may be warranted. Breeding for insect resistance using conventional approaches has been slow and difficult in canola/rapeseed; however, breeding for insect resistance using plant transformation with genes coding for insect toxins appears promising.

Conclusions There have been many breeding successes in the canola/ rapeseed oilseed species. Oil and meal quality improvements in several of the U triangle species are likely the most significant, with canola-quality (low erucic acid content in the oil and low glucosinolate content in the meal) cultivars in B. juncea,

BREEDING OF GRAINS | Canola/Rapeseed: Genetics and Breeding B. napus, and B. rapa being extensively grown and the conversion of B. carinata to canola quality currently in progress. Further oil quality improvements in canola include the development of low-linolenic acid, high-oleic acid content oil in specialty B. napus canola cultivars and the development of high erucic acid content oil in HEAR cultivars. There have been tremendous successes in seed yield improvement. For example, the development and release of hybrid cultivars in B. napus and B. juncea that capture, at least in part, the well-documented heterosis for seed yield in these canola/rapeseed species. Long-term average annual seed yield increases of 2% have been achieved. B. napus hybrid cultivars developed using male sterile Lembke genetic male sterility, Bayer CropScience nuclear male sterility, and pol and ogu INRA cytoplasmic male sterility have resulted in larger annual seed yield increases especially in the last decade. B. juncea hybrid cultivars developed using mori cytoplasmic male sterility, ogu cytoplasmic male sterility, or 126–1 cytoplasmic male sterility are just coming to the market at the present time and could result in enhanced annual seed yield gains in this species. Research and development to create pollination control systems for B. carinata continues; however, there is no fully functional pollination control system in this species currently. Since there is documented heterosis for seed yield in B. carinata, conversion of this species to hybrids is probable, once a suitable pollination control system has been developed. Breeding for disease resistance to many diseases has been very successful in maintaining seed yield in canola/rapeseed. Even though stem rot is the most difficult disease to control, substantial progress in developing field tolerance to stem rot has been achieved in China, and this field tolerance is now being transferred to canola/rapeseed cultivars globally. Canola/rapeseed breeders will be able to use a wide range of breeding techniques and technologies in the U triangle Brassica oilseed species in the future to further enhance seed quality, meal quality, seed yield, disease resistance, and selected agronomic traits. A goal of doubling seed yield in 20 years for hybrid B. napus cultivars has been set and will be met if sustained annual seed yield increases of at least 3.6% are obtained. The application of new breeding techniques and technologies will not only allow more rapid progress toward current canola/ rapeseed breeding goals but also facilitate the setting and attainment of new breeding goals involving seed quality and abiotic and biotic stress tolerance.


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What features distinguish oilseeds from other food grains? What features distinguish Brassica oilseeds from other oilseeds? What is the difference between canola and rapeseed? Canola oil is considered to be a very healthy edible vegetable oil. Why? Which Brassica species are canola-quality species currently? Canola/rapeseed production has increased dramatically in the last decade. Why? Which is the predominant Brassica oilseed species grown globally? What are the primary end uses for canola/rapeseed oil?

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What are the primary end uses for canola/rapeseed meal? Why have annual seed yield increased dramatically in some Brassica oilseed species in recent years? Brassica oilseed species are amenable to tissue culture techniques. Cite two of these techniques. What genetically engineered traits have been commercialized in canola/rapeseed to date? Is genetic engineering likely to play a major role in canola/ rapeseed breeding in the future?


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Canola/rapeseed oil is made up of several fatty acids. What are the different properties of these fatty acids? How does fatty acid composition affect oil characteristics? Canola/rapeseed oils are being used as renewable biofuels. What makes them desirable for use in these applications? Canola/rapeseed has been at the forefront of commercialization of genetically engineered cultivars, especially in Canada. What are the benefits and costs of being first to commercialize genetically engineered oilseeds?

See also: Agronomy of Grain Growing: Canola: Agronomy; Plants: Diseases and Pests; Fats: Healthy Fats and Oils; Lipid Chemistry; Genetics of Grains: Detection of Genetically Modified Grains; Development of Genetically Modified Grains; Genomics of Food Grains; Grain Harvest, Storage and Transport: Canola: Harvest, Transport, and Storage; Non-food Products from Grains: Biodiesel; Cereal Grains as Animal Feed; Oilseed and Legume Processing: Canola: Processing; Proteins: The Protein Chemistry of Dicotyledonous Grains; The Oilseeds: Canola: Overview; Oilseeds: Overview.

Further Reading Bennett RA, Mohan RT, King JR, and Rahman MH (2008) Interspecific crosses of Brassica oleracea var. alboglabra and B. napus: Effects of growth condition and silique age on the efficiency of hybrid production and inheritance of erucic acid in the self-pollinated backcross generation. Euphytica 164: 593–601. Canola Council (2014) Canola encyclopedia > insects > flea beetles. http://www. canolacouncil.org/canola-encyclopedia/insects/flea-beetles/#about-flea-beetles. Chalhoub B, Denoeud F, Liu S, et al. (2014) Early allopolyploid evolution in the postNeolithic Brassica napus oilseed genome. Science 345: 950–953. Diederichsen A and McVetty P (2011) Botany and plant breeding. In: Daun JK, Eskin NAM, and Hickling D (eds.) Canola Chemistry, Production, Processing and Utilization, pp. 29–56. Urbana, IL: AOCS Press. FAO WIEWS (2014) World information and early warning system on PGRFA; Food and Agricultural Organization: Geneva, Switzerland 2014. http://apps3.fao.org/wiews/ wiews.jsp. FAOSTAT, 2014. Food and Agriculture Organization of the United Nations agricultural statistics. http://faostat.fao.org/site/291/default.aspx. Freidt W and Snowdon R (2009) Oilseed rape. In: Vollman J and Rajcan I (eds.) Oil Crops. Handbook of Plant Breeding, vol. 4, pp. 91–126. New York, USA: Springer. http://dx.doi.org/10.1007/978-0-387-77594-4_5. Gerdemann-Knorck M, Nielen S, Tzscheetzch C, Iglisch J, and Schnieder O (1995) Transfer of disease resistance within the genus Brassica through asymmetric somatic hybridization. Euphytica 85: 247–253. Gomez-Campo C (2005) Assessing the contribution of gene banks: The case of the UPM seed bank in Madrid. Plant Genetic Resources Newsletter 151: 33–42. Gwynne P and Heebner G (2001) Functional genomics: Genomics revolution Phase 2. Science magazine 26 January 2001. http://www.sciencemag.org/site/products/ fungen.xhtml.

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Hu Q, Li Y, and Mei D (2009) Introgression of genes from wild crucifers. In: Gupta SK (ed.) Biology and Breeding of Crucifers, pp. 261–283. Boca Raton, FL: CRC Press. Kebede B, Thiagarajah M, Zimmerli C, and Rahman MH (2010) Improvement of open-pollinated spring rapeseed (Brassica napus L.) through introgression of genetic diversity from winter rapeseed. Crop Science 50: 1236–1243. Larkin NJ, Lydiate DJ, Parkin AP, et al. (2013) The Brassica napus blackleg resistance gene Lepr3 encodes a receptor-like protein triggered by the Leptosphaeria maculans effector AVRLM1. New Phytologist 197: 595–605. McVetty PBE and Zelmer CD (2007) Breeding herbicide tolerant oilseed rape cultivars. In: Gupta SK (ed.) Rapeseed Breeding. Advances in Botanical Research, vol. 45, pp. 234–270. San Diego, CA: Elsevier. Palmer CE and Keller WF (1997) Pollen embryos. In: Shivanna KR and Sawhney VK (eds.) Pollen Biotechnology for Crop Production and Improvement, pp. 392–422. Cambridge, UK: Cambridge University Press. Rahman M, Li G, Schroeder D, and McVetty PBE (2010) Inheritance of seed coat color genes in Brassica napus (L.) and tagging the genes using SRAP, SCAR and SNP molecular markers. Molecular Breeding 26: 439–453. http://dx.doi.org/10.1007/ s11032-009-9384-6. Ro¨bbelen G (1991) Rapeseed in a changing world: Plant production potential. In: McGregor DI (ed.) Proceedings of the 8th International Rapeseed Congress, Saskatoon, Canada 9–11 July, pp. 29–38. Roy NK (1984) Interspecific transfer of Brassica juncea type blackleg resistance to Brassica napus. Euphytica 33: 295–303. Sodhi YS, Chandra A, Verma JK, et al. (2006) A new cytoplasmic male sterility system for hybrid seed production in Indian oilseed mustard Brassica juncea. Theoretical and Applied Genetics 114: 93–99. U N (1935) Genome analysis in Brassica with special reference to the experimental formation of B. napus and peculiar mode of fertilization. The Journal of Japanese Botany 7: 387–452. Velasco L and Fernandez-Martinez JM (2009) Other brassicas. In: Vollman J and Rajcan I (eds.) Oil Crops. Handbook of Plant Breeding, vol. 4, pp. 127–153. New York: Springer. http://dx.doi.org/10.1007/978-0-387-77594-4_5. Walsh JA and Jenner CE (2002) Turnip mosaic virus and the quest for durable resistance. Molecular Plant Pathology 3: 289–300. Wang J, Chen Z, Du J, Sun Y, and Liang A (2005) Novel insect resistance in Brassica napus developed by transformation of chitinase and scorpion toxin genes. Plant Cell Reports 24: 549–555. http://dx.doi.org/10.1007/s00299-005-0967-3.

Wang X, Wang H, Wang J, et al. (2011) The genome of the mesopolyploid crop species Brassica rapa. Nature Genetics 43: 1035–1039. Warwick SI, Francis, A, and Gugel RK (2009) Guide to wild germplasm, Brassica and allied crops (tribe Brassiceae, Brassicaceae) 3rd edn. http://www.brassica.info/info/ publications/guide-wild-germplasm.php. Weselake R (2011) Genetic engineering approaches for trait development in Brassica oilseed species. In: Daun JK, Eskin NAM, and Hickling D (eds.) Canola Chemistry, Production Processing and Utilization, pp. 57–92. Urbana, IL: AOCS Press. Williams ME, Leemans J, and Michaels F (1997) Male sterility through recombinant DNA technology. In: Shivanna KR and Sawhney VK (eds.) Pollen Biotechnology for Crop Production and Improvement, pp. 237–258. Cambridge, UK: Cambridge University Press. Wu J, Cai G, Tu J, Li L, and Liu S (2013) Identification of QTLs for resistance to sclerotinia stem rot and BnaC.IGMT5.a as a candidate gene of the major resistant QTL SRC6 in Brassica napus. PLoS One 8(7): e67740. http://dx.doi.org/10.1371/ journal.pone.0067740. Zelmer C and McVetty PBE (2009) Industrial products. In: Gupta SK (ed.) Biology and Breeding of Crucifers, pp. 343–359. Boca Raton, FL: Taylor and Francis. Zitter TA and Provvidenti R (1984) Virus diseases of crucifers. Fact sheet page: 730.20. http://vegetablemdonline.ppath.cornell.edu/factsheets/Viruses_Crucifers. htm.

Relevant Websites http://www.brassica.info/info/publications/guide-wild-germplasm.php – Brassica information. http://www.canolacouncil.org/canola-encyclopedia/insects/flea-beetles/#about-fleabeetles – Canola Council. http://vegetablemdonline.ppath.cornell.edu/factsheets/Viruses_Crucifers.htm – Crucifer Viruses. http://faostat.fao.org/site/291/default.aspx – FAOSTAT. http://apps3.fao.org/wiews/wiews.jsp – FAO WIEWS. http://en.wikipedia.org/wiki/Triangle_of_U – Wikipedia.

Lentil: Breeding W Erskine, University of Western Australia, Crawley, WA, Australia A Sarker, International Center for Agricultural Research in the Dry Areas (ICARDA), New Delhi, India S Kumar, International Center for Agricultural Research in the Dry Areas (ICARDA), Rabat, Morocco ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The lentil is a self-pollinating food legume whose seeds have high nutritional value. The crop has a low water use with adaptation to cerealbased dryland cropping in Mediterranean and subtropical regions. Lentil is among the earliest domesticates from the Near East Fertile Crescent. Canada and India are the largest producers. Key achievements of breeding include the broadening of the genetic base of the crop in South Asia, the development of plant types suited to a mechanized harvest, and the breeding of lentil with winterhardiness. The article concludes by highlighting future challenges in lentil breeding.

Learning Objective

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To achieve understanding of the breeding of the agriculturally significant food legume crop: lentil.

Introduction Lentil (Lens culinaris Medikus ssp. culinaris) is an important pulse crop that has been traditionally grown in West Asia, South Asia, Ethiopia, North Africa, and, to a lesser extent, southern Europe. It is also cultivated in South and North America and in Oceania. Its seed is a rich source of protein and other micronutrients (Fe, Zn, and b-carotene) for human consumption, and the straw is a valued animal feed. Since its domestication, lentil has been grown in rotation with cereals, which provides a sustainable cropping system. Although lentil was cultivated as early as 8000 BC in West Asia, it remained an underexploited and underresearched crop until recently. Systematic research for its improvement started in some national institutions and at the International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, in the 1980s. Under the Consultative Group for International Agricultural Research (CGIAR), the ICARDA has a world mandate for lentil improvement. The lentil improvement program at the ICARDA is closely linked with national agricultural research systems and with advanced research institutes in the world to address this mission. The breeding objectives at the ICARDA and in national programs are targeted to address the specific needs of different agroecological regions. A world collection of wild and cultivated lentil germplasms is maintained at the ICARDA and has been instrumental in the development of improved genetic


stocks suitable for different environmental niches. Except for a few traits, sufficient variability for important economic characters including stress resistance is present in this germplasm for use in breeding programs. Following a bulk–pedigree method, the lentil breeding program at the ICARDA constructs new genotypes to deliver to the national programs. To date, a total of 137 lentil varieties in combination with various desirable traits have been released by 34 national programs emanated from the ICARDA-supplied germplasm.

Origin and Domestication Cultivated lentils originated in the Near East (NE) arc. L. culinaris Medikus ssp. orientalis (Boiss.) Ponert, which closely resembles the cultivated species L. culinaris ssp. culinaris, is widely accepted as the progenitor species and is distributed from Greece to Uzbekistan and throughout the NE arc. Carbonized seed remains appear in early Neolithic settlements, which date back to 7000–6000 BC. Ladizinsky reviewed evidence for the center of origin and domestication of lentil. The domestication of lentil occurred, together with that of emmer and einkorn wheat, barley, pea, chickpea, bitter vetch, and flax, during the Neolithic agricultural revolution, which took place in the Eastern Mediterranean around the eighth and seventh millennia BC. Lentil culture spread rapidly with that of Neolithic agriculture to the Nile Valley, Europe, and Central Asia. It was part of the Harappan crop assemblage in the Indian subcontinent between 2250 and 1750 BC. After AD 1500, the Spanish introduced lentil to South America via Chile. More recently, it has been cultivated in Mexico, Canada, the United States, New Zealand, and Australia. In North America, research on the adaptation of lentil started in the late 1970s, and it has become an important export crop of both Canada and the United States. Lentils were introduced in Australia in the 1990s, and the crop is now established in South Australia and Victoria for export.

Phylogeny Tournefort was the first to use the word Lens, a Latin word to designate a specific genus that describes the seed shape of the cultivated lentil. The genus Lens Miller belongs to the order Rosales, suborder Rosinae, family Leguminosae, and subfamily Papilionaceae and is in the tribe Vicieae. All species in the genus are diploid with 2n ¼ 14 chromosomes and have similar karyotypes. The taxonomy of Lens has undergone numerous changes in recent years. Analyzing previous findings based on origin and spread; morphological, cytological, and cytogenetic observations; and more recently the basis of isozyme and molecular studies,

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BREEDING OF GRAINS | Lentil: Breeding

Lens taxonomy was reassessed. The genus now consists of seven taxa split into four species. 1. L. culinaris Medikus a. ssp. culinaris b. ssp. orientalis (Boiss.) Ponert c. ssp. tomentosus (Ladiz.) M.E. Ferguson et al. d. ssp. odemensis (Ladiz.) M. E. Ferguson et al. 2. L. ervoides (Brign.) Grande 3. L. nigricans (M. Bieb.) Godr. 4. L. lamottei Czefr.

Use of Lentil and Its Nutritional Quality Lentil is predominantly eaten in South Asia as boiled or fried ‘dhal.’ It has a soup-like consistency and is usually eaten with unleavened bread (‘roti’). Boiled rice is also served as a staple with lentil dhal. ‘Khichuri’ is made from a mixture of split/dehulled lentil and cracked wheat or rice. In West Asia and North Africa, ‘mujaddarah,’ made of whole lentil and immature wheat seed, is a popular dish. Of course, lentil soup is popular all over. Also, lentil may be deep-fried and eaten as a snack or combined with cereal flour in the preparation of foods such as bread and cake. Numerous lentil-based foods require steaming or boiling the whole seeds, whereas others, including many versions of the popular lentil soup, call for the removal of the fibrous seed testa (dehulling). Lentil processing includes cleaning, sizing, dehulling, splitting, and polishing. Small-seeded red cotyledon lentil is dehulled and large-seeded yellow cotyledon lentil is used whole. In West Asia, lentil is cultivated for its straw, in addition to its grain. In Syria, for example, a farmer’s revenue from straw in a dry year is sometimes greater than that from the seed. The straw comes from the traditional threshing process and includes broken branches, pod walls, and leaflets. The protein content of lentil straw varies from 5% to 7% and its digestible dry matter from 43% to 46%. There is limited genetic variation in straw quality. The pattern of nutrients in the proximal composition of lentil is similar to that of other grain legumes, but seed protein content (19.5–35.5%), although similar to that of peas (Pisum sativum L.) and beans (Phaseolus vulgaris L.), is less than in soybean (Glycine max L. Merr.). Seeds contain low levels of fat. Fiber concentration is low and is largely within the seed testa, so the fiber in lentil meal can be reduced if it is dehulled before grinding. In addition to high-quality protein, essential amino acids, and major minerals, its seed contains iron up to 132 ppm and zinc up to 98 ppm. Several lentil varieties with high iron (>72 ppm) and zinc (>64 ppm) contents are available to consumers, for example, Barimasur-4, Barimasur-5, Barimasur-6, and Binamasur-7 in Bangladesh; Sital, Shekhar, Khajurah-2, and Sisir in Nepal; Alemaya in Ethiopia; Pusa Vaibhav in India; and Idlib-2 and Idlib-3 in Syria. Selenium content was found to be highest in Canadian lentils (672 mg kg1) and a moderate amount in Bangladesh lentils (370 mg kg1). Besides, among vitamins, lentil seed contains 200 mg kg1 of b-carotene. The amino acid composition of the seed, as in other grain legumes, is complementary to that of cereals. The relatively

large concentrations of lysine in lentil compensate for the minimal concentrations in the cereal grains, while the cereal grains compensate for the low concentrations of sulfurcontaining amino acids in lentil.

Constraints of Production Addressable by Breeding The average lentil yields are low because of the limited yield potential of landraces, which are also vulnerable to a range of stresses. The major abiotic limiting factors to lentil production are low-moisture availability and high-temperature stress in spring and, at high elevations, cold temperatures in winter. Among biotic stresses, rust, vascular wilt, and Ascochyta blight, caused by Uromyces viciae-fabae (Pers.) Schroet., Fusarium oxysporum f.sp. lentis, and Ascochyta fabae Speg. f.sp. lentis, respectively, are globally important key fungal diseases of lentil. Other diseases such as botrytis blight (Botrytis cinerea Pers.), stemphylium blight (Stemphylium botryosum Wallr.), collar rot (Sclerotium rolfsii Sacc.), root rot (Rhizoctonia solani Ku¨hn), stem rot (Sclerotinia sclerotiorum (Lib.) de Bary), and anthracnose (Colletotrichum truncatum Andrus et W.D. Moore) are localized problems. Lentil is relatively free from any serious infestation of insect pests except occasionally from pod borers (Etiella zinckenella Treitschke), aphids (Aphis craccivora Koch), and sitona weevils (Sitona crinitus Herbst). The crop also suffers from parasitic (Orobanche) and nonparasitic weeds more so in winter-sown crop, causing very high damage to the crop. Besides, constraints to productivity include agronomic problems of pod dehiscence, pod drop, and lodging. Adequate variability for all these traits is known to exist within the genetic resources of the crop (wild and cultivated), allowing manipulation through plant breeding. Recent reports of genetic variability for traits such as biomass yield, pod shedding, tolerance to pea leaf weevils (Sitona sp.) and aphids, and the parasitic weed broomrape (Orobanche sp.) and herbicide tolerance offer scope for genetic options through conventional breeding.

Available Genetic Resources and Variation The lentil breeding program at the ICARDA is built upon the foundation of the germplasm collection and its efficient use. A large number of germplasm accessions are conserved at the ICARDA under FAO auspices and elsewhere at the National Bureau of Plant Genetic Resources, New Delhi, India; Vavilov Institute of Plant Industry, St. Petersburg, Russia; and United States Department of Agriculture (USDA), the United States. The ICARDA collection is by far the largest and comprises 11 867 cultivated and 587 wild relatives (Table 1). Among cultivated species conserved at the ICARDA, 22% have been developed at the ICARDA through crossbreeding and dispatched to national programs through the International Nursery Network. The Genetic Resources Unit of the ICARDA has characterized 9125 for various morphological and phenological traits to date. Marked variation among the characters for use in breeding and selection programs has been reported for various morphological characters, response in flowering to temperature and

BREEDING OF GRAINS | Lentil: Breeding Table 1

Genetic resources conserved at the ICARDA

Name of taxon

Accessions

Countries of collection

L. culinaris ssp. culinaris Landraces Breeding lines (ICARDA) L. culinaris ssp. orientalis L. culinaris ssp. tomentosus L. culinaris ssp. odemensis L. ervoides L. nigricans L. lamottei

11 867 3358 259 21 66 170 62 10

78 15 2 5 16 8 8

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Oceania, Australia has emerged as a global producer with a production of 379 000 tonnes in 2011. Exports account for approximately one-third of total lentil production with the remaining produce eaten locally. International trade in small-seeded, red cotyledon lentil is dominated by Australia, Canada, and Turkey, whereas trade in the largeseeded, green lentil is primarily led by Canada and the United States. Countries in the Indian subcontinent and the Middle East are the major importers of red lentil, and southern Europe and South America import large-seeded green lentils.

Major Agroecology and Breeding Objectives Table 2

Trend in world lentil production (1971–2011)

Year

Area (Mha)

Production (Mt)

Yield (kg ha1)

1961 1971 1981 1991 2001 2011

1.62 1.72 2.27 3.27 3.99 4.14

0.85 1.05 1.45 2.66 3.25 4.43

528 611 640 814 816 1068

photoperiod, winterhardiness, iron deficiency chlorosis and boron imbalances, drought and heat tolerance, herbicide tolerance, and resistance to fungal diseases and viruses. Wild relatives also have shown considerable variability for morphological traits, winterhardiness, and tolerance to drought, Fusarium wilt, Ascochyta blight, anthracnose, sitona weevils, and Orobanche.

Recent Trends in Lentil Production World lentil production has increased fivefold since the 1960s from 0.85 million tonnes (Mt) in 1961 to 4.43 Mt in 2011, through a 155% increase in sown area and the doubling of average national yields from 528 to 1068 kg ha1 (Table 2). Canada and India now dominate production globally. Although the area under lentil cultivation in Turkey has declined in the last decade, the area has increased greatly in Australia, Canada, Ethiopia, India, Nepal, and the United States. Production in Asia is concentrated in a belt stretching from Turkey in the west to Bangladesh in the east, accounting for 58% of the world sown area. Among other Asian producers, China has recently started releasing lentil-related data, and Bangladesh increased its productivity through release and cultivation of improved varieties. Iran, Nepal, and Syria substantially increased production during the 1990s, while the lentil-cultivated area and production in Pakistan declined. Forty percent of lentil production is in North America, where, in addition to Canada, the United States maintains an area of 150 000 ha and Mexico is a minor producer. In Africa, Ethiopia and Morocco are significant producers, while Algeria, Sudan, Egypt, and Tunisia are now only minor producers. In South America, Argentina and Peru are the major producing nations. European lentil production is gradually decreasing, with France and Spain being the noteworthy producers. In

Knowledge of the patterns of variation in the world germplasm collection is the key to understand the factors affecting lentil adaptation to lentil breeding. The geographic distribution of variation of landraces in the world lentil collection for morphological characters, responses in flowering to temperature and photoperiod, winterhardiness, and iron deficiency chlorosis and boron imbalances collectively illustrate the specificity of adaptation in lentil. Additional information on the specificity of adaptation within the crop has come from collaborative multienvironment yield trials of common entries selected in different locations. Understanding of genotypes and environmental factors, the local constraints to production, and the various consumer requirements of different geographic areas for seed as food and straw as feed has led the breeding program at the ICARDA to develop new genetic materials for a series of separate but finely geographically targeted streams, linked closely to national breeding programs. The major agroecological regions of production of lentil are (1) S. Asia, E. Africa, and Yemen; (2) Mediterranean low to medium elevation; and (3) high-elevation area of West Asia and North Africa. These regions correspond to the maturity groups of early, medium, and late maturity (Table 3). Within each of these major regions, there are specific target areas. Additionally, the lentil improvement activities have recently been extended to Central Asia and the Caucasus (CAC) region, where an initial thrust has been to study the adaptation of diverse materials suitable in their agroclimatic conditions. For Latin America, large-seeded, yellow cotyledon lentils are preferred. The lentil breeding program generally uses parents of diverse origins with known traits with the aim to combine gene(s) to contribute to yield and resistance to major biotic and abiotic stresses. Wide crosses among cultigens are also done by manipulating planting dates and providing 18 h extended light period to the parents to attain synchrony in flowering. In addition, crosses are made to study the inheritance pattern of specific trait(s) and to develop recombinant populations for biotechnological research. On an average, 450 crosses are made at the ICARDA every year.

Breeding Methodologies In the early stages of lentil varietal development, most of the cultivars released were derived from selection within

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Table 3 Target agroecological regions of the production of lentil and key breeding aims

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Region

•

Key traits for recombination

Mediterranean low to medium elevation 300–400 mm annual Biomass (seed and straw), attributes for rainfall mechanical harvest, and wilt resistance <300 mm annual Biomass; drought escape through earliness rainfall and combined resistance to rust, wilt, and Ascochyta blight; Orobanche and sitona weevil tolerance; machine harvestability; herbicide tolerance High elevations Anatolian highlands Biomass, winterhardiness, and A. blight resistance; Orobanche tolerance; herbicide tolerance N. African highlands Seed yield, low level of winterhardiness, and rust resistance, Orobanche tolerance, machine harvestability, herbicide tolerance South Asia and E. Africa India, Pakistan, Nepal, Seed yield, high biomass, early maturity, and and Ethiopia resistance to root diseases, rust, and Ascochyta blight Bangladesh Seed yield, extra earliness, and combined resistance to rust and stemphylium blight C. Asia and the Seed yield, large seed, good standing ability Caucasus Latin America Large seed, resistant to rust and Ascochyta blight

heterogeneous landraces. Due to increased efforts in lentil breeding at both the national and international levels, new lentil cultivars/genotypes are now being developed through crossbreeding. The methods of breeding lentil are similar to those utilized to breed other self-pollinated crops and include pure line selection or hybridization, followed by the bulk method, the pedigree method, the single seed descent, or some modification of these procedures. At the ICARDA, a bulk–pedigree method is used, where single plant selection is done from F4 bulks to develop F5 progeny. A scheme of breeding methodology followed at the ICARDA is given in the succeeding text:

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Hybridization (parent A parent B) at Tel Hadya, Lebanon, and Morocco (year 1) Confirmation of hybridity (F1) at summer nursery, Lebanon (year 1) Growing F2 bulks at Terbol, Lebanon (year 2) Growing F3 generation at summer nursery, Lebanon (year 2) Growing F4 generation: single plant selection in Terbol, Lebanon, and Morocco (year 3) Selection among F5 progenies for uniformity, agronomic traits, and Fusarium wilt reaction at Terbol and Morocco (year 4) F6 homogeneous progenies are evaluated in preliminary screening nursery for yield, agronomic traits, and F. wilt reaction in Morocco (year 5) Preliminary yield trial in F7 at three contrasting locations: Kfardan and Terbol (Lebanon) and Merchouch (Morocco)

Advanced yield trial in F8 at three locations under rain-fed and irrigated conditions except those bred for southern latitude countries Seed increase of selected lines in F9 and their incorporation into international nurseries in F10 generation

The breeding program at the ICARDA follows a decentralized approach. For example, in breeding for early and extra-early genotypes for southern latitude countries, targeted segregating populations are sent to the national programs for single plant selection in their respective edaphoclimatic conditions. Similarly, selection for rust, stemphylium blight, and Ascochyta blight resistance is done in hot spots in close collaboration with relevant national programs.

Understanding of Genetic Control It is important to know the genetic control of a character before initiating a breeding program for the genetic enhancement of that particular trait. In this endeavor, various authors have studied the inheritance of important qualitative and quantitative traits. Information on genetic control has progressed from relatively few characterized genes in the early 1980s to the identification of major genes controlling morphological traits, isozyme loci, and DNA amplification. The genetics of economic traits, growth habit; foliage color; leaf shape, size, and number; tendril formation; plant pubescence; plant height; stem fasciation; stipule size; flowering time; flower color and number; pod size; pod dehiscence; seed coat color and spotting; seed tannin content; seed size; seed hardiness; cotyledon color; protein content; drought tolerance; frost damage; boron deficiency and toxicity; salinity tolerance; wilt; rust; and stemphylium blight tolerance, have been resolved and are being used by breeders globally. A list of the traits controlled by major gene(s) with their gene symbols is presented in Table 4. Estimates of genetic parameters for traits are useful as they provide information on inheritance and help to identify appropriate breeding methods. Such parameters include subdivision of genetic variance into additive, dominance, and epistatic effects of minor genes. Additionally, parameters such as heritability, expected genetic gain in response to selection, and degree of association between traits are also important to design effective breeding and selection programs. In lentil, a self-pollinated species, genetic variance is expected to be primarily additive; however, the nonadditive genetic variance could also be important. Additional information on the components of genetic variance in lentil suggests that additive effects are the major component of the genetic variance for most polygenic traits and that a considerable nonadditive component can be anticipated in early generations. Again, heritability estimates are indicative of potential progress from selection. Additiveness of gene action reflects in high heritability. The heritability estimates for seed yield and its components are moderate, indicating that progress can be expected from effective selection. Heritability estimates for several plant traits such as plant height and lowest plant height are quite variable. Reproductive traits, such as days from sowing to flowering and to maturity, have exhibited moderate to high heritability, indicating that these traits would respond to

BREEDING OF GRAINS | Lentil: Breeding Table 4 Symbol/ allele Fn Sn Gh Gs I Yc O Y-BGgc Tgc P V W Pi Scp Pep Glp Grp Tnl Ten Chl Glo Sbv Rr Urf1, Urf2, Urf3 Fw Frt

Inheritance of morphological markers Character

Reference

Flower number/ inflorescence Early flowering Plant growth habit Epicotyl color Cotyledon color Cotyledon color Cotyledon color Cotyledon color Gray seed coat ground color Tan seed coat ground color Flower color Flower color

Gill and Malhotra

Flower color Pod indehiscence Seed coat spotting Pubescent peduncle Glabrous pod Green pod color Tendril-less leaf Tendriled leaf Chlorina chlorophyll mutant Globe mutant Resistant to PSbMV Resistant to rust Resistant to rust Resistant to Fusarium wilt Radiation frost tolerance

Sarker et al. Ladizinsky Ladizinsky Slinkard Slinkard Singh Sinha et al. Sharma and Emami Vandenberg and Slinkard Vandenberg and Slinkard Lal and Srivastava Lal and Srivastava; Wilson and Hudson Wilson and Hudson Ladizinsky Ladizinsky Sarker et al. Vandenberg and Slinkard Vandenberg and Slinkard Vandenberg and Slinkard Sharma and Sharma Vandenberg and Slinkard Gupta et al. Haddad et al. Sinha and Yadav; Singh and Singh Kumar et al. Eujayl et al. Eujayl et al.

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Establishing linkage maps for agricultural crops is to localize gene(s) for important agronomic traits and to develop tightly linked morphological and molecular markers to enable indirect selection by marker-assisted selection. The earlier linkage maps covered a small number of markers. With the advancement of classical genetics and molecular research, a more comprehensive linkage map for lentil genome spanning more than 1073 cM was developed. However, the routine application of markers to lentil breeding programs globally is still limited due to availability of a limited number of markers. Qualitative traits such as epicotyl color, seed coat pattern or spotting, pod indehiscence, winterhardiness, rust and stemphylium blight resistance, and yield trait have been localized, and linked DNA markers have been identified. Quantitative traits in recombinant inbred lines of interspecific crosses have been localized with isozyme markers. Detected quantitative trait loci (QTLs) were located in six of the seven chromosomes. Abbo et al. studied the genetics and linkage of seed weight and observed QTLs affecting seed weight were associated with morphological and RAPD markers, which were distributed over several linkage groups. Recently, a number of SSR markers have been developed for use in marker-assisted selection. To better target genes that are functionally associated with economic traits for breeding purposes, several other biotechnological approaches are predicted for the future. In the context of climate change, consumer preference, market and industrial uses, etc., there is a need to look for modern approaches to address these questions. The other biotechnological approaches such as proteomics and metabolomics will emerge as potential techniques for lentil in order to better understand the mechanisms behind developing high-yielding lentils with superior quality to meet the nutritional demand of its consumers. The recent initiative on lentil genome sequencing by a consortium involving the University of Saskatchewan, Canada; UC Davis, the United States; and ICARDA, Lebanon will certainly assist molecular research in lentil.

Major Achievements selection. Seed quality traits such as seed size and seed thickness are highly heritable. Correlations between traits must be given careful consideration and interpretation by plant breeders. Correlations between seed yield and number of pods per plant, seeds per pod, and secondary branches per plant and plant height and straw yield have been positive and significant.

Developments in Biotechnology Biochemical and molecular techniques have been used for biodiversity evaluation, the assessment of the genetic structure of natural populations, and plant evolution in the genus Lens and are summarized by Ferguson et al. and Abo-elwafa et al. Major investigations were carried out with allozymes, seed protein cDNqA and genomic DNA RFLPs, chloroplast DNA RFLPs, and RAPD analysis of genomic DNA. Even though discrimination between lines is possible, seed proteins have not been extensively used for genetic diversity studies.

Varietal Releases by National Programs The ICARDA supplies nurseries to national programs comprising a range of genetically fixed materials and segregating populations to select according to their specific needs. On the basis of phenological adaptation, agronomically desirable traits, resistance to prevailing stresses, quality aspects, and farmer’s and consumer’s preferences, national scientists identify and select promising lines/single plants for eventual release for commercial cultivation. In this endeavor, to date, 137 lentil varieties have been registered by 34 countries for improved yield, disease resistance, and other traits (Table 5).

Widening the Genetic Base of Lentil Cultivars in South Asia One of the major achievements is the breaking of an ancient bottleneck of narrow genetic base of lentil in South Asia, which accounts for nearly half of the world’s lentil production. The genetic base was broadened through introgression of genes from the ICARDA in the region. Early, high-yielding, and disease-resistant varieties have been released in Bangladesh.

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Table 5

Lentil varieties emanating from the ICARDA-supplied materials released by national agricultural research systems

Region

Country

Asia

Bangladesh, India, Nepal, Pakistan, China, Afghanistan, Iran, Iraq, Syria, Lebanon, Jordan, Yemen, Turkey Ethiopia, Eritrea, Egypt, Morocco, Libya, Tunisia, Algeria, Lesotho, Sudan Argentina, Canada, Ecuador, Chile, the United States Australia, New Zealand Portugal Azerbaijan, Uzbekistan, Georgia

Africa The Americas Oceania Europe Central Asia and the Caucasus

Collaborative efforts between the ICARDA and Bangladesh national programs have resulted in the development of improved varieties like BARI M4, BARI M5, BARI M6 and BARI M7, which has helped in improving lentil productivity in the country. In 2009, an ICARDA impact study showed improved varieties on over 110 000 ha in Bangladesh, delivering an annual extra production gain of some 55 000 tonnes and valued at US$ 38 million annually. High-yielding varieties with combined resistance to fungal diseases have been released in Pakistan. The medium-maturing cultivar, Shekhar (ILL 4404), is being cultivated in mid-hills in Nepal, a new lentil area. In India, the flowering of Precoz, an early-maturing Argentinean lentil, is well synchronized with the local South Asian germplasm. Precoz has been used extensively to incorporate such traits as large seed size, rust resistance, and early vigor in locally adapted background since 1985. The crosses between Precoz and local lentils have resulted in the development of rust-resistant, large-seeded, and early-maturing cultivars in South Asia. Some of them, namely, VL Masoor 507, Narendra M1, Priya, and Angoori with large seeds, are popular with farmers in India. Precoz is now in the parentage of 28% of the Indian elite lentil material.

Reconstruction of Genotypes Suitable for Mechanization To keep lentil in the cropping system by reducing production costs in West Asia, lentil harvest had to be mechanized. With increasing urbanization, there is a shortage of agricultural labor in the region, which has led to a rapid rise in the cost of hand labor and a commensurate increase in the total lentil production costs. To address this constraint and encourage the expansion of the environmentally sustainable legume–cereal rotation in the dry areas, during its first decade, the ICARDA focussed on the development of economic machine harvest systems for lentil. The center developed and promoted a lentil production package that included mechanization and the use of improved cultivars with good standing ability. Joint ICARDA–NARS breeding programs have produced new varieties suitable for mechanical harvesting such as the ‘Idlib’ series #1–4 in Syria and ‘Sayran 96’ in Turkey. On-farm trials and demonstrations indicate that on average mechanical harvesting combined with improved cultivars reduces harvest costs by 17–20%.

No. of varieties 72

Reason

7

High yield; wilt, rust, and Ascochyta blight resistance; good standing ability; seed size; high biomass; early maturity; winterhardiness High yield; wilt, Ascochyta blight, and rust resistance; early maturity; tolerance to excess moisture High yield, rust and A. blight resistance, good standing ability

12 2 5

High yield, A. blight resistance, good standing ability High yield High yield

39

Winterhardiness Lentils In the highlands of Central and West Asia and North Africa (CWANA), lentil suffers from low temperature at seedling stage. To overcome this problem, long-duration varieties with winterhardiness, cold/frost tolerance, and Ascochyta blight resistance were developed. The evaluation of 3592 accessions under field conditions in Central Anatolia showed large genetic variability for cold tolerance with as many as 238 accessions as tolerant. The ICARDA breeding program has been successful in incorporating winterhardiness in elite breeding lines such as ILL9832, ILL9918, and ILL9919 and improved varieties such as Kafkas, Uzbek, and Cifci in Turkey, Gachsaran in Iran, Shiraz-96 in Pakistan, and Bichette and Zaria in Morocco. In winter-sown lentil, weeds (parasitic and nonparasitic) are major production constraints. Nonparasitic weeds compete for light and nutrients, often leading to up to 40% yield losses in legume crops. Manual weeding has become uneconomical and impractical for many smallholder farmers due to competing on- and off-farm activities and high labor wages. Herbicide-tolerant varieties have recently been developed in Canada and Australia, which hold great promise in the expansion of lentil area under conservation agriculture. Besides common weeds, parasitic weeds like Orobanche have also emerged as a threat to lentil production in some Mediterranean countries. Screening of 1774 germplasm accessions in the infested field did not show genetic resistance to Orobanche. Only recently, potential resistant sources with significant reduction in infection density have been reported among Spanish germplasm, which could be used in lentil breeding. Evaluation of wild germplasm against O. crenata showed higher resistance in L. ervoides, L. odemensis, and L. orientalis. Two accessions, ILWL361 and LENS166/92, showed true resistance to Orobanche.

Future Challenges Exciting gains in sustainable production arise from the integration of a change in agronomic practice with a new cultivar. Several such prospects exist for lentil and are given in the succeeding text. In the highlands of West Asia, lentil is

BREEDING OF GRAINS | Lentil: Breeding currently spring-sown. However, sowing in late autumn/early winter coupled with the use of a winter-hardy cultivar gives yield advantages of 50%. However, the major production challenges of winter-sown crop are cold, Ascochyta blight, and rampant weeds. Research is under way to combine tolerance to cold, Ascochyta blight, and post-emergence herbicide in machine-harvestable lentils. Although agronomic constraints to winter sowing lentil in the highlands require further research, especially chemical weed control, this substantial yield increase can be expected in the future to augment the area and production in this agroecological zone. In some areas around the Mediterranean, such as in south Syria, lentil production has ceased primarily because of vascular wilt disease. The registration of Fusarium wilt-resistant cultivars Idlib-2 in Syria and ‘Rachyya’ and ‘Hala’ in Lebanon offers the prospect of a return of lentil cultivation to such areas. Further spread of lentil harvest mechanization technology coupled with Orobanche tolerance and herbicide tolerance will probably also contribute to increased lentil production in West Asia, North Africa, and South Asia in the future. In South Asia, the diseases wilt, rust, and stemphylium blight are key problems, and large areas are left fallow over winter following the harvest of late paddy rice. Farmers need early-maturing, disease-resistant varieties with late-sowing potential for such situations or when land becomes available for lentil planting after the monsoon floodwaters have subsided. As extra-early-maturing cultivars with combined resistance to diseases become available, the prospect will open a major expansion of lentil production in the rice-based cultivation system in the Indian subcontinent. With the development of super-early lentils (<90 days), lentil can be fitted well in between two rice crops in vast areas of Eastern India, Bangladesh, and Nepal. Again, a substantial amount of land of about 15 million of rice fallow lands can be brought to grow lentil as a second crop, if appropriate varieties can be brought into the new cropping system. Conservation agriculture in terms of zero-tillage/no-tillage cultivation can be successfully adopted with varieties having fast-growing root systems, early ground coverage, etc. At present, only a few varieties are available to farmers in Bangladesh, Nepal, and India. To address this issue, the ICARDA in NARS from the region has undertaken breeding programs to construct and select such genotypes under zero-tillage or relay cropping situations. Genotypes with robust root systems, long taproots, and a number of lateral roots in combination with aboveground vigorous growth are considered in this selection. Globally, as lentil is a weak competitor to a range of grassy and broadleaf weeds, they represent a major threat to lentil productivity. Imidazoline-tolerant lentils represent the only herbicide-tolerant material at present; cultivars with tolerance to other herbicides are needed to avoid the high cost of hand weeding. To avoid milling loss, breeding and selection for seed shape (roundish in the case of red lentils) and size should be given due attention as a substantial amount of production loss occurs during processing. Besides, genetic improvement for nutritional parameters such as iron and zinc should be mainstreamed in breeding programs. Application of marker-assisted selection is still limited in lentil. Next-generation sequencing technology has opened up

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new opportunities to rapidly develop sequence-based markers. Access to high-throughput genotyping and sequencing technologies is expected to accelerate genetic gain across the target environments in lentil. These developments coupled with high-throughput phenotyping, rapid generation turnover, and genome wide selection ultimately will increase the utilization of genomic resources in the genetic improvement of lentil and will fast-track the development of improved cultivars.


• • • • •

Where was the lentil domesticated and what was its progenitor? How does lentil seed composition complement cereal grain? What are the top three lentil-producing countries? Has lentil production been increasing or decreasing globally over the recent decade? Is the lentil plant self-pollinated or cross-pollinated?


• • •

What lessons might be learned from the most recent research on lupin genetics and genomics? Outline some recent major achievements in lentil breeding. What future challenges remain in lentil breeding?

See also: Agronomy of Grain Growing: Lentil: Agronomy; Proteins: The Protein Chemistry of Dicotyledonous Grains; The Basics: Taxonomic Classification of Grain Species; The Grain Crops: An Overview; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview.

Further Reading Abbo S, Ladizinsky G, and Weeden NF (1992) Genetic analysis and linkage studies of seed weight in lentil. Euphytica 58: 259–266. Abo-elwafa A, Murai K, and Shimada T (1995) Intra- and inter-specific variations in Lens revealed by RAPD markers. Theoretical and Applied Genetics 90: 335–340. Ali M and Gupta S (2012) Carrying capacity of Indian agriculture: pulse crops. Current Science 102: 874–881. Bayaa B and Erskine W (1998) Diseases of lentil. In: Allen DJ and Lenne JM (eds.) The Pathology of Food and Pasture Legumes, pp. 423–472. Wallingford, UK: CAB International. Bhatty RS (1988) Composition and quality of lentil (Lens culinaris Medik.): a review. Canadian Institute of Food Science and Technology Journal 21(2): 144–160. Dixit GP and Katiyar PK (2004) Genetic base of lentil varieties and breeding lines developed in India. Indian Journal of Agricultural Sciences 77(11): 585–589. Erskine W and Witcombe JR (1984) Lentil Germplasm Catalog. Aleppo, Syria: International Center for Agricultural Research in the Dry Areas (ICARDA). Erskine W, Meyveci K, and Izgin N (1981) Screening a world lentil collection for cold tolerance. LENS Newsletter 8: 5–9. Erskine W, Hussain A, Tahir M, et al. (1994a) Field evaluation of a model of photothermal flowering responses in a world lentil collection. Theoretical and Applied Genetics 88: 423–428. Erskine W, Tufail M, Russell A, Tyagi MC, Rahman MM, and Saxena MC (1994b) Current and future strategies in breeding lentil for resistance to abiotic and biotic stresses. Euphytica 73: 127–135. Erskine W, Muehlbauer FJ, Sarker A, and Sharma B (2009) The Lentil: Botany, Production and Uses. Wallingford, UK: CAB International.

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Eujayl I, Baum M, Powel W, Erskine W, and Pehu E (1998) A genetic linkage map of lentil (Lens sp.) based on RAPD and AFLP markers using recombinant inbred lines. Theoretical and Applied Genetics 97: 83–89. Eujayl I, Erskine W, Baum M, and Pehu E (1999) Inheritance and linkage analysis of frost injury in lentil. Crop Science 39: 639–642. Eujayl I, Erskine W, Bayaa B, Baum M, and Pehu E (1998) Fusarium vascular wilt in lentil: inheritance and identification of DNA markers for resistance. Plant Breeding 117: 497–499. Ferguson ME, Maxted N, Slageren MV, and Robertson LD (2000) A re-assessment of the taxonomy of Lens Mill. (Leguminosae, Papilionoideae, Vicieae). Botany Journal of Linnean Society 133: 41–59. Fernandez-Aparicio M, Sillero JC, Perez-de-Luque A, and Rubiales D (2008) Identification of sources of resistance to crenate broomrape (Orobanche crenata) in Spanish lentil (Lens culinaris) germplasm. Weed Research 48: 85–94. Fernandez-Aparicio M, Sillero JC, and Rubiales D (2009) Resistance to broomrape in wild lentil (Lens sp.). Plant Breeding 128: 266–270. Gill AS and Malhotra RS (1980) Inheritance of flower colour and flower number per inflorescence in lentils. LENS (Lentil Experimental News Service) 7: 15–19. Gupta PK, Sharma PC, Singh J, and Verma SS (1983) A new mutant (Globe) in lentils. Lens Newsletter 10(1): 17–18. Haddad NI, Muehlbauer FJ, and Hampton RO (1978) Inheritance of resistance to pea seed-borne mosaic virus in lentils. Crop Science 18(4): 613–615. Hamdi A, Kusmenoglu I, and Erskine W (1996) Sources of winter-hardiness in wild lentil. Genetics Resources and Crop Evolution 43: 63–67. Hansen J and Renfrew JM (1978) Palaeolithic-Neolithic seed remains at Franchthi Cave, Greece. Nature 271: 349–352. Kumar R, Mishra SK, and Sharma B (2001) Genetics of rust resistance in lentil. Indian Journal of Genetics and Plant Breeding 61(3): 238–241. Ladizinsky G (1979) The origin of lentil and its wild gene pool. Euphytica 28: 179–187. Lal S and Srivastava RS (1975) Inheritance of flower colour in lentils. Indian Journal of Genetics and Plant Breeding 35(1): 29–30. Muehlbauer FJ and Slinkard AE (1981) Genetics and breeding methodology. In: Webb C and Hawtin GC (eds.) Lentils, pp. 69–90. UK: Farnham Royal, Commonwealth Agricultural Bureau. Rubiales D, Perez-de-Luque A, Fernandez-Aparicio M, et al. (2006) Screening techniques and sources of resistance against parasitic weeds in grain legumes. Euphytica 147: 187–199.

Sarker A, Erskine W, Sharma B, and Tyagi MC (1999) Inheritance and linkage relationship of days to flower and morphological loci in lentil (Lens culinaris Medikus subsp. culinaris). Journal of Heredity 90(2): 270–275. Savage GP (1988) The composition and nutritive value of lentils (Lens culinaris). Nutrition Abstracts and Reviews. Series A 58: 320–343. Sharma B and Emami MK (2002) Discovery of a new gene causing dark green cotyledons and pathway of pigment synthesis in lentil (Lens culinaris Medik.). Euphytica 124(3): 349–353. Sharma SK and Sharma B (1978) Induction of tendril mutations in lentil (Lens culinaris Medic.). Current Science 47(22): 864–866. Singh TP (1978) Inheritance of cotyledon colour in lentil. Indian Journal of Genetics and Plant Breeding 38(1): 11–12. Singh JP and Singh IS (1990) Genetics of rust resistance in lentil (Lens culinaris). Indian Journal of Pulses Research 3(2): 132–135. Sinha RP, Chaudhary SK, and Sharma RN (1987) Inheritance of cotyledon colour in lentil. Lens Newsletter 14(1/2): 3. Sinha RP and Yadav BP (1989) Inheritance of resistance to rust in lentil. Lens Newsletter 16: 41. Slinkard AE (1978) Inheritance of cotyledon colour in lentils. Journal of Heredity 69: 139–140. Slinkard, A.E., Vandenberg, A., Holm, F.A., 2007. Lentil plants having increased resistance to imidazolinone herbicides. US patent 7232942. Available at: http:// www.uspto.gov/patft/index.html (accessed on 20.12.12). Tahir M, Simon CJ, and Muehlbauer FJ (1993) Gene map of lentil: a review. LENS Newsletter 20: 3–10. Tepe I, Erman M, Yazlik A, Levent R, and Ipek K (2005) Comparison of some winter lentil cultivars in weed-crop competition. Crop Protection 24: 585–589. Vandenberg A and Slinkard AE (1989) Inheritance of four new qualitative genes in lentil. Journal of Heredity 80: 320–322. Vandenberg A and Slinkard AE (1990) Genetics of seed coat colour and pattern in lentil. Journal of Heredity 81: 484–488. Wilson VE and Hudson LW (1978) Inheritance of lentil flower colour. Journal of Heredity 69: 129–130. Zohary D (1972) The wild progenitor and place of origin of the cultivated lentil Lens culinaris. Economic Botany 26: 326–332. Zohary D and Hopf M (1993) Domestication of Plants in the Old World. Oxford: Clarendon Press.

Lupin: Breeding LC Trugo, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil E von Baer, CAMPEX Semillas Baer, Temuco, Chile D von Baer, Seeds Baer, Temuco, Chile ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 174–182, ã 2004, Elsevier Ltd.

Topic Highlights

• • • • • • •

The genus Lupinus is diverse, with many species and varieties from regions of the New and Old World. Species grown on a commercial scale are L. albus, L. angustifolius, L. luteus, and L. mutabilis. Lupins may be used for seed production, and also as green forage, for silage, for green manuring, to fix nitrogen and to mobilize phosphorus in the soil. Breeding has been successful in the development of ‘sweet’ stable low-alkaloid lines. Considerable breeding advances have been made in Australia, which has become a major producer and exporter of lupins. Breeding objectives include incorporating resistance to fungal and virus diseases. Lupin seeds have similar nutritive attributes to soybeans, particularly with respect to protein and fat content.

Learning Objectives

• •

To understand the ways in which breeding has assisted in improving the production and quality of lupin grain. To understand how breeding has the ongoing role of lupin improvement for its various roles in world agriculture.

Introduction The lupin is a legume plant; its seeds have been used as food and feed from ancient times. The green plant itself has been used extensively in some countries as forage and as an organic material for soil enrichment or in crop rotation. Despite its qualities and potential, it has not become a major world crop. This article will review the main characteristics of breeding, the nutritive value of its seeds, and the uses and potential for more extensive production.

The Plant and Its Origin Lupin or lupine are trivial names for plants of the genus Lupinus belonging to the Fabaceae family, subfamily Papilionoideae. This genus is very diverse and contains several known species. It is an annual plant, usually 0.3–2 m in height, with a highly branched stem, digitated leaves, and a shrubby growth pattern. The flowers form high above the leaves, may be of several different colors (white, yellow, purple, blue), and exude a honey-like aroma. The roots are relatively long, usually


nodular, and may extend to a depth of 3 m. The lupin has the ability to fix nitrogen and mobilize phosphorus and other elements by the exudation of citrate to the soil. This is very important for soil enrichment in infertile areas. The pods are normally flat and with a hairy aspect on the outside. They vary in length (4–10 cm) and, depending on the species, have different types of seeds that may vary in size, shape, or color. However, the endosperm is usually yellowish, and the most common seeds are flattened (Lupinus albus) or ovoid (Lupinus mutabilis) with diameters in the range 2–15 mm. It is a plant well adapted to poor sandy and acid soils and also to high altitudes, and to temperate climates, found in Europe. The most important species that are produced on a commercial scale are L. albus, L. angustifolius, L. luteus, and L. mutabilis. The lupin has its origin in the Old World in the Mediterranean region, as well as in the New World, in North America, and in the Andean highlands. Some representative examples of the former are L. albus, L. angustifolius, L. luteus, and L. consentinii. ‘Tarwi’ is the indigenous name of L. mutabilis, which is the lupin species found in the Andes (Table 1). However, there are probably more than 200 wild species, most of them in the New World. L. albus was cultivated for human consumption by the ancient Romans, Egyptians, and Greeks; however, due to its bitter taste, the mature seed had to be subjected to prolonged washing before consumption. A similar treatment was also used by the ancient inhabitants of the Andes. The seeds of tarwi were boiled, thoroughly washed in a river for several days, and then suitably cooked for immediate consumption or dried for future use. Presently, several different species of lupins are grown in Europe, some parts of Africa, South America, Australia, and New Zealand, including a number of sweet low-alkaloid varieties which are now commercially available.

General Aspects of Lupin Breeding Lupin utilization and breeding programs started simultaneously. This explains why L. albus, cultivated in ancient Egypt, as well as L. mutabilis, an Andean native, have the same non-shattering characteristics. In contrast, the wild forms of both the species have a distinct shattering characteristic. Despite progress in the area of lupin breeding, records of the world gene resources of the lupin plant are still insufficient and not easily available to plant breeders. This has been recognized as one of the main problems for worldwide lupin cultivation. Detailed information on the features of a particular lupin accession would help breeders. Their particular objective of coordinating specific features of the plant with regional conditions of soil and climate, in order to improve

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BREEDING OF GRAINS | Lupin: Breeding

Table 1 Taxonomic and common names of some commercial Lupinus species Species

Common names

L. albusa L. angustifoliusa L. luteusa L. mutabilisd

White lupin, Egyptian lupin, tremoço, b altramuzc Blue lupin, narrow-leafed lupin Yellow lupin, tremosillac Tarwi, tauri, tarhui, chocho, c Andean lupin

a

Mediterranean origin. Portuguese name. c Spanish names: altramuz may be used also to designate other species. d Andean origin: tarwi, tauri, and tarhul are from native languages. Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd Edition (2003), p. 3623, Elsevier Ltd. b

productivity on a commercial level, would be possible. The genus Lupinus is very diverse, with many species and varieties originating from distinct regions of the New and Old World. This diversity also contributes to a considerable increase in the difficulties encountered while planning a plant-breeding program. Despite these problems, significant advances have been achieved in the improvement of plant resistance to diseases, in the establishment of stable low alkaloid lines, and in the increase of productivity of the most-used commercial species of cultivated lupins. Production of lupin may be directed to completely different objectives. It may be used as green forage, particularly for silage making, or for green manuring. In these cases maximum greenmatter yield is strongly desirable. The plant when used as green manure improves the soil conditions since it increases the amount of organic matter and also provides accumulation of nitrogen and phosphorus in poor sandy soils. Bitter varieties may be used when the plant is grown for this purpose. However, for ruminant feed, as forage, sweet varieties are preferred due to the low alkaloid contents. Lupin grains are increasingly used as protein supplements for ruminant diet, and in some countries it also finds applications in human nutrition. Breeding for lupin seed production needs a more rigorous selection in order to obtain a satisfactory harvest index, short maturation periods, and disease resistance. Enhanced pod setting and normal branching are also desirable characteristics, particularly to complement short growing seasons found in Mediterranean climates. The high levels of toxic alkaloids originally found in lupin seeds used to be a negative factor to improve the worldwide production. However, low alkaloid varieties have been established for the most important lupin species. The ‘sweet’ forms are natural or induced mutants, that were generally weaker, so backcrossing with more vigorous bitter forms was required to improve them. Several sweet varieties have been established in Germany, Poland, Russia, Australia, and in the last decades in France and Chile as well. Most of them are sown in the spring and the first winter varieties were only more recently obtained in USA, Chile, and France for the species L. albus. These varieties are not only resistant to temperatures as low as 10 C but also show high yields up to 7.3 t ha1. Another significant and more recent advance in lupin breeding was plant selection starting from induced mutations of forms with determined growth or epigonals. This was achieved with different species in Germany, Russia, and

Poland. However, these mutants were also too weak and backcrossing with vigorous high yielding forms was necessary. In France and in Chile winter cultivars were obtained that are homogeneous in maturity and easy to thresh, but these varieties maintain their tendency to produce lower yields. This has limited their success when sown in the Spring. An exception is a very early maturing variety created in Denmark, with initial material coming from Belarus. Domestication of narrow-leafed lupin in Australia allowed large-scale seed production for animal feeding as a soybean substitute. In fact, Australia has become one of the biggest producers and exporters of lupin seeds in the world. This work was started by J Gladstones, who was responsible for developing early maturing lupin crop with low alkaloid seeds, but at the same time with nonshattering pods. In his breeding work, in order to distinguish desired plants from naturalized types of L. angustifolius which were previously bitter with blue flowers, he selected white flowered plants as a marker showing the desired attributes. Natural mutants were then selected from field populations and were intercrossed in order to combine all desired characteristics. Also, crosses with wild types selected from Mediterranean regions were carried out. The first successful variety obtained was Uniwhite, released in 1967. Many other new varieties have been developed following additional breeding programs. Domestication of rough-seeded lupins was later achieved with L. consentinii, and more recently breeding programs have been developed to domesticate L. atlanticus and L. pilosus. Some rough-seeded lupin species grow wild on Mediterranean soils. These two species show great potential for cultivation in finetextured alkaline soils since few cultivated species have this characteristic. Work by Buirchell in Australia following previous selection of mutants with low alkaloid content by Gladstones has been developed aiming at domestication of these species. Introgression of domestication genes from previously domesticated L. consentinii and induction of domestication genes by means of mutation were the strategies used. Some lines of L. atlanticus with domestication characters were selected showing potential for large-scale cultivation.

Resistance to Stress and Diseases Parallel to the improvement of the yield, great efforts have been made to increase lupin resistance to diseases. Fungal and virus diseases are the most common forms of lupin crop contamination such as anthracnose, fusariose, and phomopsis. The first caused by the fungus Colletotrichum gloesporoides poses the main threat for lupin cultivation. The latter causes a disease called lupinosis that affects animals fed with infected plants. Because anthracnose is a seed disease, the symptoms may appear early mainly showing cankers on the stem and the plant may die even before flowering. Significant advances to improve lupin plant resistance to anthracnose have been achieved particularly for L. angustifolius in Australia and L. albus in Chile. Selection and intercrossing strategies have helped in developing lines more resistant to anthracnose and gray leaf spot from collaborative work between Australian and American researchers. Varieties derived from wild Mediterranean lupins proved to have moderate resistance to phomopsis.

BREEDING OF GRAINS | Lupin: Breeding However, until now selected varieties are not completely resistant to the pathogens. Necrotic and nonnecrotic strains of mosaic viruses may also be responsible for crop damage, but to a lesser extent than fungal diseases. Pleiochaeta setonsa is the main cause of the disease brown leaf spot, favored by cool temperatures. Because the incidence of this fungus is more accentuated in crops sown in European autumn, winter lupin cultivars tolerant to frost has been increasingly used in Europe. Rust caused by Uromyces lupinicolus affects plantation mainly in warm and dry summer promoting considerable defoliation. In this case, the use of fungicides based on triazole compounds appears to be quite effective to face this problem. Phorbia platura is an insect that may have a significant negative impact on lupin crop, particularly the white lupin. The larvae usually promote extensive damage to the roots and hypocotyls, and the systemic use of insecticides is the most effective treatment. Inadequate climate and soil conditions may cause abiotic stress and produce losses in lupin crop. Frost, inadequate soil pH, and other climate conditions are the main causes. Most of Lupinus species are not tolerant to high pH. Above pH 7.5, free lime present in the soil may induce iron chlorosis. However, in low pH, below 4.5, aluminum toxicity may be observed. Some structural characteristics of the plant may help in frost resistance. Large roots, which is greatly dependent on genotype, favor plant survival in intense frost conditions. Vernalization requirements and the plant capacity of hardening leaves are other components of frost resistance. Germ plasm collections, hybridizations, and mutations have been the main sources of genetic variability applied to lupin breeding up to now. Interspecific crossing has also been a useful tool to improve general characteristics of lupin varieties. This has been possible between species of the same number of chromosomes, e.g., L. mutabilis, L. elegans, and L. polyphyllus. This can be an interesting approach, for example, in the case of L. polyphyllus, which has small seeds and a high proportion of hull, but by crossing with L. mutabilis, it can produce bigger seeds with increased protein content and less fiber. The interspecific crossing between species of different number of chromosomes has been actively pursued by researchers in Australia using more modern techniques. The improvement of the chemical composition of the seed has been of increasing importance in the last decades, together with the concept of protein and oil yield per hectare. Until now, the most favorable composition has been achieved with L. mutabilis, but the best yield of protein and oil per hectare with L. albus. However, within the species, different varieties may show significant differences. In the case of L. albus, which commonly contains about 35% protein, it is possible to establish lines with 38–40% protein. In the case of L. mutabilis, some varieties may have up to 50% protein. More recently, great attention has been directed to other seed components such as carotenoids and omega-3-fatty acids when breeding programs are planned. Lupin seeds have been increasingly used in feed formulation for fish farming, particularly salmon. Due to overexploitation of marine resources, fish farming seems to be a promising source of protein and oil for human nutrition, and the demand for grains, including lupin, used in the rations will certainly increase tremendously. In human nutrition, lupin seeds are an

Table 2 speciesa

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Approximate composition of seeds of different lupin

Species

TCW (g)b,c

Proteinc

Oilc

Ash

Fiberd

L. albus L. angustifolius L. consentinii L. hispanicus L. luteus L. mutabilis

370 165 165 71 164 211

38.2 28.9 32.2 48.2 49.2 46.6

9.5 6.6 2.6 5.8 4.8 15.8

3.1 3.2 3.7 2.9 5.3 3.6

14.0 17.6 19.6 17.6 9.0

a

Results expressed in g per 100 g of dry matter (except TCW). Thousand corn weight. c Data from Trugo LC, Almeida DCF, and Gross R (1988) Oligosaccharide contents in the seeds of cultivated lupins. Journal of the Science of Food and Agriculture 45: 21–24. d Adapted from Muzquiz M, Burbano C, Bouthelier V, Garcia-Aser C, Rodenas I, and R-Marin A (1982) Estudio de los elementos esenciales de destintas variedades de cinco especies del Genus Lupinus cultivadas y espontaneas de la Peninsula Iberica. Proceedings of the 2nd International Lupin Conference, pp. 173–181. b

interesting alternative for diabetic persons due to their carbohydrate composition as well as for those who do not tolerate some other sources of protein of animal or plant origin.

Nutritive Value Lupin seeds show similar nutritive attributes to soybeans, particularly with respect to protein and fat content. Some species may have protein contents up to 50 g per 100 g and up to 22 g per 100 g of fat in the seeds. The approximate composition of seeds of some relevant lupin species are presented in Table 2. The protein and fat content may be further increased by dehulling the seeds. Although nutritive value may be theoretically improved by breeding, the immense chemical diversity of compounds that are considered make this task extremely complex. However, if a specific target is chosen, improvement may be achieved through breeding programs based on selection of particular species and varieties and intercrossing with others, which could lead to promising combinations of characters for cultivation. Because different biochemical pathways are involved in the synthesis of particular nutrients in the plant, in some cases the improvement of a particular nutrient may be deleterious to others. For example, breeding strategies to increase the protein content of a seed may lead to a decrease in the oil levels. In practice, breeding efforts to increase nutrient levels of lupin seed did not appear to have produced effective results yet.

Protein The lupin seed is one of the richest sources of plant protein. The protein content varies largely between species, with L. mutabilis and L. luteus presenting unusually high values (near 50 g per 100 g), surpassing most soybean cultivars, whereas L. albus presents an intermediate protein content and L. angustifolius lower values. Seed protein provides all the essential amino acids, but some of them are not found in sufficient amounts for all sectors of the population. When

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Table 3

Amino acid composition of lupin seeds

Amino acid

Concentration (mg per g of protein)

FAO recommendationsc

Histidine Isoleucine Leucine Lysine Methionine Cystine Methionine þ cystine Phenylalanine Tyrosine Phenylalanine þ tyrosine Threonine Tryptophan Valine

L. albusa 22 44 75 47 7 16 23 35 46 81 36 8 39

L. angustifoliusa 27 40 71 46 7 18 25 37 34 71 34 8 35

L. luteusa 29 37 79 49 7 24 31 39 27 66 32 10 32

L. mutabilisb 26 57 71 58 9 11 20 38 40 78 38 8 41

Infants 26 46 93 66

Adults 16 13 19 16

42

17

72 43 17 55

19 9 5 13

a

Data from Gross R (1988) Lupins in human nutrition. Proceedings of the 5th International Lupin Conference, pp. 51–63. Data from Gross R, Koch F, Malaga I, Mirinda AF, Schoeneberger H, and Trugo LC (1989) Chemical composition and protein quality of some local Andean food sources. Food Chemistry 34: 25–34. c Data from FAO/WHO/UNU (1985) Necessidades de Energia y Proteinas. Geneva: World Health Organization. b

lupin seed is used for animal feeding, such as ruminants or single-stomach animals, the relatively low level of methionine may be complemented by adequate formulation of the ration or by supplementation with the synthetic amino acid. Table 3 shows the amino acid composition of seeds of some relevant lupin species and the amino acid requirements for infants and adults established by a Food and Agriculture Organization/ World Health Organization/United Nations University (FAO/ WHO/UNU) joint committee (1985). When comparing the lupin amino acid profiles with the requirements for adults, all lupin species show ranges of essential amino acids with adequate amounts and this will be observed also for most pulses. However, if the requirements for infants are used for comparison, it is apparent that lupin protein will show many essential amino acid deficiencies, with tryptophan being the most limiting, having a chemical score of 47–59%, followed by methionine plus cystine. The chemical score is the ratio of the content of an individual essential amino acid in food protein to the content of the same amino acid in a reference pattern expressed as a percentage. It must be taken into account that, if requirements for infants are used for comparison, even beef protein will be deficient in leucine, lysine, methionine þ cystine, tryptophan, and valine, and egg protein will be deficient in leucine and lysine. However, if the previous FAO/73 amino acid pattern is used as a reference, methionine þ cystine will be the limiting amino acids for lupin (56–71% chemical score), as in most pulses (soybean 83% chemical score). Consequently, it is strongly recommended that the intended nutritional application of lupin seeds or lupin products be defined to allow a more realistic assessment of the protein quality. From Table 3, it can be seen that the amino acid profile varies considerably with lupin species. Large variations are also observed in biological indicators for protein-quality assessment. Nevertheless, protein utilization, as measured by the net protein utilization index, does not correspond exactly to the amino acid chemical score of different lupin species. For example, L. angustifolius shows a relatively high chemical score (60%, FAO/85 for infants) but presents the lowest net protein utilization index

(43%). Despite its amino acid composition, active biological components appear to have a negative influence on the net protein utilization index of L. angustifolius protein in rats. L. albus shows the highest net protein utilization index (70%) followed by L. mutabilis (64%). These figures approach the net protein utilization index of the soybean (69%). Overall, lupin protein should be considered a good plant source of protein for animal and human nutrition. However, the appropriate application and the variation encountered between species must be considered for assessing lupin protein quality.

Fat The fat content of lupin seeds varies considerably between species. In some species, the lipid fraction contributes substantially to the total energy value, whereas in others it is present in relatively small amounts (Table 2). L. mutabilis has the highest oil content (up to 22 g per 100 g) and is considered to be a potential material for oil production. L. albus has a combination of high protein and an intermediate fat content, which are important attributes for a food, especially if it is to be used in developing countries where protein and energy are scarce. The fatty acid distribution in the oil fraction is also variable between species. However, low levels of saturated fatty acids are normally found. A very high content of linolenic acid is present, particularly in L. albus and L. luteus. As in other seeds, high levels of oleic acid are common for all species, particularly L.albus and L. mutabilis (Table 4). The ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFAs) in lupin seeds is in the range 1.3 to 2.9:1 which is considerably higher than beef but lower than the soybean (4:0). Higher rates are important, since it has been strongly recommended that a reduction of SFAs in favor of an increase of PUFAs in the diet should be achieved, to assist coronary heart disease prevention. Linoleic acid, which is an essential fatty acid, is found in significant amounts in lupin seed, with L. luteus being the richest source (44%). Linolenic acid, which is the most

BREEDING OF GRAINS | Lupin: Breeding important source of o 3 fatty acids, is found at very high levels in L. albus and L. luteus, but at relatively low levels in L. angustifolius and L. mutabilis (Table 4). L. mutabilis may be commercially used for oil production, and its low linolenic acid content, although not so nutritionally important as in other sources, may be advantageous to improve its conservation in comparison with other vegetable oils. Considering the fatty acid profile of lupin seeds, it is noted that L. mutabilis and L. albus are more similar to peanut oil, whereas L. angustifolius and L. luteus resemble maize oils, although they differ in flavor.

functional food ingredients. The polysaccharides are present as major components of the cell wall surrounding the cytosol. Only a small number (1%) of polysaccharides are water soluble, and, together with oligosaccharides, they are important as a source of energy for seed germination. The amount of polysaccharides in lupin seeds is dependent on the species, with high contents found in L. albus and L. angustifolius and the lowest in L. mutabilis, due to its thinner seed hull. Due to the polysaccharide composition, lupins are extraordinarily rich sources of fiber. Crude fiber data are presented in Table 2, but even higher figures will be encountered if dietary fiber is considered. Lupin carbohydrates are important sources of energy only for ruminants, but due to their characteristics they may provide useful material to produce special highfiber food for humans.

Carbohydrates In contrast with many legumes, lupin seeds are practically devoid of starch, and the major carbohydrates in mature seeds are oligosaccharides and nonstarchy polysaccharides, particularly from the cell-wall structure. The oligosaccharides found in the cotyledons are sucrose and nondigestible galactosides of the raffinose family. The main galactosides present in lupin seeds are raffinose (degree of polymerization (DP) of 3), stachyose (DP of 4), and verbascose (DP of 5) (Table 5). These oligosaccharides are derived from sucrose, with increasing numbers of a-galactosyl units linked to C6 of glucose. They are present in most legumes and are not digested by monogastric animals and hence contribute to the flatulent property of legumes. More recently, nondigestible sugars have been used as agents for fermentation in the intestines, thus helping to maintain and regulate the microbial intestinal flora. In this aspect, lupin may be an important raw material for production of oligosaccharides of the raffinose family to be used as Table 4

329

Vitamins and Minerals The vitamin pattern of lupin seeds is somewhat similar to other legumes. Lupin seeds are good sources of vitamins of the B group, particularly niacin, with levels above 4 mg per 100 g. The thiamin content is about 0.5 mg per 100 g and that of riboflavin about 0.4 mg per 100 g. Carotenoids and tocopherols are present, with the former being mainly responsible for the color of the oil fraction. The mineral composition is similar to other legumes in relation to the major elements, except for calcium, which is low in all species. However, some differences are found in respect to trace elements. Manganese is found in lupins in unusually high amounts, especially in L. albus. In some varieties of this species, it may reach values of

Fatty acid composition of lupin seeds in comparison to soybeans Percentage of total fatty acidsa

Legume L. albus L. angustifolius L. luteus L. mutabilis Glycine max (soybean)c

14:0 0.2 0.3 0.3 0.2 0.2

16:0 7.2 11.0 5.5 11.5 10.0

16:1 0.5 0.2 0.2 0.5 0.2

18:0 2.1 6.2 2.8 9.9 4.0

18:1 48.6 33.5 24.3 45.7 25.0

18:2 19.9 39.4 43.9 27.3 52.0

18:3 13.0 4.6 10.6 2.3 7.4

20:0 0.8 0.7 2.4 0.9 0.3

22:0 4.4 2.6 7.0 1.2 0.1

22:1 2.2 0.2 1.1 tr tr

24:0 1.2 0.5 1.0 0.3 tr

SFAb 16 21 19 24 15

MUFAb 51 34 26 46 25

PUFAb 33 44 55 30 60

a

Fatty acids: 14:0, myristic; 16:0, palmitic; 16:1, palmitoleic; 18:0, stearic; 18:1, oleic; 18:2, linoleic; 18:3, linolenic; 20:0, arachidic; 22:0, behenic; 22:1, erucic; 24:0, lignoceric. SFA, total saturated fatty acids; MUFA, total monounsaturated fatty acids; PUFA, total polyunsaturated fatty acids. c Paul AA and Southgate DAT (1979) McCance and Widdowson’s The Composition of Food, 294p. London: Her Majesty’s Stationery Office. Other data from Muzquiz M et al. (1982) (see Table 2). b

Table 5

Oligosaccharide composition of seeds of different lupin speciesa

Species

Sucrose

Raffinose

Stachyose

Verbascose

Galactosides

L. albus L. angustifolius L. consentinii L. hispanicus L. luteus L. mutabilis

2.9 3.4 2.6 0.7 1.7 2.4

1.0 1.5 0.9 0.9 1.2 2.5

6.6 5.2 4.9 6.6 4.9 8.5

1.1 2.0 0.9 1.8 4.1 1.1

8.7 8.7 6.7 9.3 10.2 12.1

a

Results expressed in g per 100 g of dry matter.Reproduced from Encyclopedia of Food Sciences and Nutrition, 2nd Edition (2003), p. 3626, Elsevier Ltd.

330


83.5–143 mg per 100 g, and this must be taken into account when it is used in daily animal or human diet. Nevertheless, common figures are in the range 2.5–38.0 mg per 100 g. Lupin seed is also a good source of iron and zinc, with values in the range 2.5–14.0 and 3.0–18.0 mg per 100 g, respectively.

Bioactive Compounds Some components found in natural products may present biological activity but no nutritional properties. In fact, some of them may be undesirable for human and animal nutrition. In lupin, some compounds with these characteristics have been reported. Compounds sometimes called ‘antinutritional factors’ are present in lupin seeds in the same range as in other legume seeds, except for trypsin inhibitor, which is virtually absent in the lupin. Allergenic proteins that may cause allergenic food reactions sometimes observed in children are less intense with lupins than with other legume seeds and cow’s milk. However, because peanut allergies are quite common, further studies are needed to check if there is any peanut-lupin cross-allergy when lupin is used as an ingredient of mixed flour. Some relevant bioactive compounds found in lupin are the alkaloids, phytates, saponins, tannins, and flavonoids. Those bioactive compounds which were usually called antinutritional factors could be considered as targets for breeding programs. This, in fact, happened with the lupin alkaloids. Intensive breeding work was carried out in different countries based on classical methodologies of plant hybridization and selection and they have succeeded in the development of commercial lupin lines with low levels of alkaloids, the sweet lupins. In relation to other antinutritional factors, the situation is quite different. In fact, a lot of controversy exists at the moment in relation to the properties of these compounds. Their effects as protective factors for the plant, combined with some confirmed desirable biological properties that have been recently reported for humans, complicate the decision to decrease or in fact increase them in the seeds through breeding work. Some examples are the antioxidant properties of phytates, tannins, and flavonoids, the antitumoral properties of trypsin inhibitors, phytates and saponins, and the protection against cardiovascular diseases of tannins and flavonoids. Although no specific lupin variety has been developed yet by breeding that shows considerably lower levels of those bioactive factors except in relation to alkaloids, selection and intercrossing may be applied to establish lupin lines containing low levels of antinutritional factors. However, it appears that plant transformation would present more potential to show positive results in a shorter time. Current practices based on the use of Agrobacterium tumefaciens vectors, direct uptake into protoplasts, electroporation, and microprojectiles have potential as techniques to be used to introduce specific DNA in the lupin in order to block the expression of a specific bioactive compound. The effect which this could produce in the performance of the plant in the field is still something to be seen in the future.

Alkaloids The major alkaloids present in lupin are from the quinolizidine family, although some gramine alkaloids may also be

found in L. luteus. Quinolizidine alkaloids have received much attention, because they have a strong bitter taste and may be toxic in high doses. Lupanine, sparteine, lupinine, and some forms of hydroxylated lupanine are some relevant examples. They have a sedative effect on the central nervous system, with sparteine producing the strongest effect. The total alkaloid content in bitter lupins is usually in the range 1.0–4.5 g per 100 g. Intensive breeding work carried out, mainly by Sengbush in Germany, Gladstones in Australia, and Baer in Chile, has led to the establishment of new lupin varieties practically devoid of alkaloids. Presently, sweet varieties of L. luteus, L. angustifolius, L. albus, L. mutabilis, L. consentinii, and L. atlanticus are defined, of which the first three are commercially productive. However, bitter lupins are still largely used in some regions where the new sweet varieties are not well adapted. In those cases, the preliminary soaking and washing procedure before consumption is essential.

Phytates Phytate is sometimes considered an anti-nutritional factor, because it is implicated with the impaired absorption of minerals. It is found in lupin seeds roughly in the same concentration range as in other pulses, but it is usually lower than that found in soybeans. The average amount found in lupin seed is about 0.8 g per 100 g. The phytate:zinc molar ratio, which may be an indication of zinc bioavailability, is generally lower than in other legume seeds, making lupin a better dietary source of this mineral. The enzymatic degradation of phytate in the digestive tract or in food products submitted to special processing may lead to the formation of inositol phosphates with different degrees of phosphorylation. Some of these derived components may be detected as phytates by nonspecific methods, although they may not present mineral chelation activity. Consequently, more comprehensive information on inositol phosphate composition of different food items is becoming more important to assess the real role of food phytate in the daily diet. More recently, some attention has been directed to the desirable properties of phytates, particularly due to its antioxidative characteristics, which may be beneficial to counteract free-radical activity. Other biological properties may be derived from the lower inositol phosphates since some of them are involved in cell-signaling mechanisms.

Saponins Saponins are compounds formed by triterpenoids or steroidal aglycones and a carbohydrate moiety by ester or ether linkages. They are present in different classes of plants, particularly in legumes, roots, and some medicinal herbs. Their presence in food products has been considered to be deleterious if consumed frequently. They are toxic to fish and promote retardation of growth in livestock and laboratory animals. They may also produce erythrocyte lysis in vitro and may alter intestinal epithelium functional making the mucosa more permeable. Consequently, their continued use in the diet may jeopardize the process of nutrient absorption. Conversely, it has been claimed that they can also be beneficial since they show the ability to lower plasma cholesterol, they have anticancer activity,

BREEDING OF GRAINS | Lupin: Breeding and they may act as an inhibitor of viral replication. It is not yet clear, though, whether the net effect in the diet would be negative. Some lupin species such as L. luteus, L. mutabilis, and L. angustifolius may present a saponin content of 57–470 mg per kg, but they are not present in L. albus. However, these figures are still low compared to the content present in soybeans, which present values in the range 2000–5000 mg per kg.

Tannins Tannins are complex polyphenolic substances found in plants, particularly pulses, with the property to precipitate proteins in aqueous medium. They interact with one or more protein molecules forming large cross-linked complexes that are insoluble in water. This property makes food tannins undesirable since they will make part of the dietetic protein indigestible. There is a wide variation on the content of tannins in legume seeds with higher values being found in faba bean and in peas. Lupin seeds present relatively low values of tannins in the range 0.2–0.5%. No correlation has been found between the tannin content and the bitter taste of some lupin seeds, and the impact of tannin from lupin seed in the diet has not yet been demonstrated both in humans or animals. However, the level of tannin in L. angustifolius has been considered to be low enough for use in pig diets without any kind of problem.

Flavonoids Flavonoids are a class of phenolic compounds widely distributed in plants. Quercetin and rutin are among the most largely found flavonoids in a great variety of fruits and vegetables, including tea, coffee, and other grains. As it has been observed with other biologically active non-nutrient components, flavonoids may promote desirable and nondesirable physiological effects in humans. The property of flavonoids to induce goiter has been suggested by studies using peanuts and millet as foods with millet flavonoids presenting a strong inhibition effect on thyroperoxidase activity. The healthy properties of flavonoids may be derived from their antioxidative characteristics as free-radical neutralizers. However, some more specific functions have been reported, including their effect on cancer prevention, antiinflammatory and antiviral activities, and their positive effect on capillary fragility and vascular protection. Data on the presence of flavonoids in lupin are scarce, and although it is not clear whether they are encountered in significant amounts in lupin seeds, different flavonoids have been reported recently in the plants of L. luteus and L. albus, including those with the aglycones apinegin, genistein, and kaempferol.

Food Uses At present time, the main applications of lupins are their utilization as green manure and as animal feed. Due to the ability of lupin plants to fix nitrogen and to make insoluble phosphorus available in the soil, they have been increasingly used in the crop-rotation system as an efficient and less expensive means of fertilization. For animal feeding, the whole lupin

331

plant has been used as pasture or forage, or the dry seeds have been used as a direct soybean substitute, or in feeding formulas for pigs, sheep, chickens, dairy cattle, and other livestock. It has been recommended that not more than 10–15% of bitter lupins should be used in pig rations as pigs seem to be more sensitive to alkaloids than chickens. As mentioned earlier, lupin seeds have long been an available protein source for human nutrition. It was a common procedure to submit the grains to prolonged washing to remove the bitter taste, and this washing process is still employed, particularly in some regions of South America where bitter lupin seeds are mainly used. Although the washing process may increase the total cost of lupin products, the water treatment will in fact wash out not only the bitter alkaloids but also the oligosaccharides responsible for the flatulence of legumes. In addition, the end product will show increased relative amounts of protein and oil, on a dry matter basis, due to differences in component solubilities. It is a common procedure in the Andean regions to use leached and cooked bitter lupin seeds directly for consumption as snacks, in soups, salads, and stews. Alternatively, they may be dried and/or milled for future use in several dishes, including baked products. Lupin flour may be used for cereal protein enrichment since lupins and cereals have complementary amino acid compositions. Bread or other bakery products have been made successfully using lupin flour as an additive in the proportion of 10–20%. Many attempts have been made to use lupin seeds as direct substitutes for soybeans, e.g., in fermented products, soy milk, or soybean protein isolate. However, lupin protein does not have exactly the same functional properties as soybean protein, being less stable to heat and forming a milk-like water suspension. Nevertheless, lupin protein may be added to soy products without major modifications to the end product. It is apparent that investigation is still needed to develop a lupin-specific technology and new genuine lupin products for human nutrition.

The Potential of Lupin The world lupin seed production is at present mainly concentrated in Australia, which has produced 1.38 million tonnes (Mt) in 1993 and around 2 Mt in the year 2000. This represents 2–4% of the world pulse production. Other lupin producers are the countries of the former USSR, Poland and Germany in Europe, and Chile, Bolivia and Peru in South America, and South Africa. However, the lupin seed shows a real potential for trade in the grain world market due to its nutritional and agricultural properties. The high alkaloid content that used to be one of the major limitations for a wider application of the lupin seed has been gradually overcome by the introduction of commercial sweet varieties, mainly of L. albus and L. angustifolius. Although a new sweet variety of L. mutabilis is already available, work is still needed to establish a productive line with increased seed size and protein content. Besides the improvement in lupin nutritional qualities, research in specific areas such as plant breeding and biotechnology, crop protection, and food lupin technology is vital for lupin to gain a stronger foothold in the international market, with a substantial increase in production in Europe and South America. To consolidate this status an appropriate international price policy along with a strong marketing strategy is mandatory.

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Further Reading

•

Buirchell BJ (1994) Domestication and potential of the rogh-seeded lupins. In: Neves Martins JM and Beiraõ da Costa ML (eds.) Advances in Lupin Research, pp. 19–24. Lisbon: ISA Press. Cowling WA, Buirchel BJ, and Tapia ME (1998) Lupin. Lupinus L. Promoting the conservation and use of underutilized and neglected crops. 23. In: Rome, Italy: Institute of Plant Genetics and Crop Plant Genetic Research, Gatersleben/ International Plant Genetic Resources Institute. FAO/WHO/UNU (1985) Necessidades de Energia y Proteinas. Geneva: World Health Organization. Fletwood JG and Hudson BJF (1982) Lupinseed – a new source of edible oil. Journal of Food Technology 17: 11–17. Gladstones JS, Atkins CA, and Hamblin J (1998) Lupins as Crop Plants: Biology, Production and Utilization. Wallingford, UK: Oxford University Press. Gross R (1982) El Cultivo y la Utilizacion del Tarwi. Estudio FAO, No. 36. Rome: Food and Agriculture Organization. Gross R (1988) Lupins in Human Nutrition. In: Proceedings of 5th International Lupin Conference, Poznan, Poland. Gross R, Koch F, Malaga I, Miranda AF, Schoeneberger H, and Trugo LC (1989) Chemical composition and protein quality of some local Andean food sources. Food Chemistry 34: 25–34. Hill GD (1977) The composition and nutritive value of lupin seed. Nutrition Abstracts and Reviews, B; Livestock Feeds and Feeding 47: 511–529. Huyghe C (1997) White lupin. Field Crops Research 53: 147–160. Muzquiz M, Burbano C, Bouthelier V, Garcia-Aser C, Rodenas I, and R-Marin A (1982) Estudio de los elementos esencials de destintas variedades de cinco especies del Genus Lupinus cultivadas y espontaneas de la Peninsula Iberica. In: Proceedings of the 2nd International Lupin Conference, 173–181. Nelson P (1994) The development of the lupin industry in Western Australia and its role in sustainable farming systems. In: Neves Martins JM and Beiraõ da Costa ML (eds.) Advances in Lupin Research, pp. 565–576. Lisbon: ISA Press. Paul AA and Southgate DAT (1979) McCance and Widowson’s The Composition of Food. London: Her Majesty’s Stationery Office, p. 294. Trugo LC, Almeida DCF, and Gross R (1988) Oligosaccharide contents in the seeds of cultivated lupins. Journal of the Science of Food and Agriculture 45: 21–24. von Baer E (1994) Lupin development policy in South America. In: Neves Martins JM and Beiraõ da Costa ML (eds.) Advances in Lupin Research, pp. 577–580. Lisbon: ISA Press. von Baer E (2002) Requirement of Lupin Protein as Salmon Feed. In: Proceedings of the 10th International Lupin Conference, Laugarvatn, Iceland.

• • • • • •

Describe how breeding has achieved improvements to the production and quality of lupin grain. What are the limitations for growing lupins commercially? What is the range of countries and regions where lupins are produced? Describe the fungal and virus diseases of lupins. What are the limitations of feeding stock with infected lupins? How is breeding helping to overcome diseases of lupins? List the major uses of lupin seed. What are the unique aspects of lupin-grain composition that set it apart from most other food and feed grains?


• •

• •

Explore possibilities for wider uses of lupin grain, especially taking advantage of it unusually high protein content. For example, could lupin grain and its protein be exploited along similar lines to those for soy beans? What are the possibilities of exploiting the fat content of lupins, especially via breeding to modify the composition of the fat content, using either conventional or GMO approaches? Consider advances being made with grains such as canola. Compare the carbohydrate composition of lupin grain with that of more conventional grain species, such as soy, canola and even cereals such as maize. Explore the anatomical distribution of the major chemical components of the lupin seed, including alkaloids. Is it possible that any fractional milling methods could be used to provide mill fractions with usefully distinct composition?

See also: Agronomy of Grain Growing: Lupin: Agronomy; Genetics of Grains: Genome Mapping; Genomics of Food Grains; Grains Around the World: Grain Production and Consumption: Overview; The Basics: Taxonomic Classification of Grain Species; The Legumes and Pseudocereals: Grain Legumes and Their Dietary Impact: Overview; Lupin: Overview.

Relevant Websites http://www.dpi.nsw.gov.au/agriculture/broadacre/winter-crops/pulses. http://www.grdc.com.au. http://archive.agric.wa.gov.au/. http://www.pulseaus.com.au/lupin.aspx. http://www.lupinfoods.com.au/.

Soybean: Germplasm, Breeding, and Genetics RG Palmer{ T Hymowitz, University of Illinois at Champaign-Urbana, Urbana, IL, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • • •

Soybeans are legumes that are important sources of protein and oil to the world’s economy. World soybean production was 268.0 million tonnes in 2012. Germplasm collections of the cultivated species of Glycine max are over 200 000 accessions worldwide. Germplasm collections of the wild annual species of G. soja are over 14 000 accessions. There are 24 recognized wild perennial soybean species native to Australia, west central and south Pacific Islands, Indonesia, the Philippines, and Taiwan. Specialty cultivars are used for soyfoods, industrial application, and feed. Soybean is a highly self-pollinated species, and all cultivars are either pure lines (inbred lines) or mixtures of pure lines.

Learning Objective

•

To achieve an understanding of the various soybean species, their use in breeding programs, and their agricultural significance.

domesticated crop during the Zhou dynasty in the eastern half of northern China. An alternative hypothesis, based upon the center of genetic diversity, suggests that soybean was domesticated in the Yellow River or Yangtze valleys of central or southern China. Domestication of soybean took place 1500–1100 BC, or perhaps earlier. Soybean was probably grown in the Korean peninsula and central and southern China by the first century. From about the first century AD to the Age of Discovery (fifteenth to sixteenth centuries), soybean was introduced throughout Southeast Asia. Traditional soyfood included ‘miso,’ ‘tempeh,’ ‘tofu,’ and soy sauce. Soybean was introduced into Europe before 1737 and was introduced into North America, from China via England, in 1765.

Germplasm Collections Major Glycine germplasm collections exist in Australia, Brazil, China, Germany, India, Indonesia, Japan, Russia, the Republic of Korea, Taiwan, Ukraine, and the United States. Many other smaller but important collections exist throughout Asia and Europe. The G. max germplasm collections are given in Table 2, and the G. soja collections in Table 3. The Glycine perennial collections are mainly held by CSIRO, Australia (2130 accessions), and the USDA, the United States (1006 accessions) (Table 4).

Introduction In 2012, world soybean production was 268.0 million tonnes (MT) (Table 1). The increased production in Brazil and Argentina during the past four decades has been dramatic (Figure 1). In 2012, for the first time, Brazil surpassed the United States in soybean production (Table 1). The total world oilseed production in 2012 was 466.9 MMT, of which 57% was due to soybean. Soybean accounts for 67% of the world protein meal supply. Soybean is the second largest source of vegetable oil for human consumption and is under considerable pressure from canola and olive oil. These latter two oils claim to have health benefits.

Origin The genus Glycine (Willd.) belongs to the family Fabaceae, subfamily Papilionoideae, tribe Phaseoleae, subtribe Glycininae. The genus Glycine is composed of two subgenera, Glycine (perennials) and Soja (annuals). The proposed origin of the genus Glycine is given in Figure 2. The linguistic, geographic, and historical evidence suggests that the annual soybean (Glycine max (L.) Merr.) emerged as a {

Deceased.


Gene Pools The concept of gene pools is useful to plant breeders because it guides them in selecting germplasm to use in hybridizations for plant improvement. The genus Glycine has only a primary gene pool and a tertiary gene pool (Figure 3). The primary gene pool consists of G. max cultivars, landraces, and the wild annual G. soja. Cross-pollination within the primary gene pool results in regular chromosome pairing and fertile progeny. The secondary gene pool is defined as other Glycine species that will cross with soybean, but with great difficulty. There is no secondary gene pool for soybean. The tertiary gene pool includes species that, when crossed with soybean, result in seeds that are either not viable or infertile. Only through extraordinary procedures such as embryo rescue is gene transfer possible. The tertiary gene pool for soybean consists of wild perennial Glycine species.

Germplasm Diversity Within the genus Glycine subgenus Glycine, there are 24 recognized wild perennial species, and within the subgenus Soja, there are two species (Table 4). These perennial species are diverse morphologically, cytologically, and genomically and are mostly endemic to Australia (Table 4).

http://dx.doi.org/10.1016/B978-0-12-394437-5.00214-X

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334 Table 1

BREEDING OF GRAINS | Soybean: Germplasm, Breeding, and Genetics

Germplasm Utilization

World soybean production (2012)

Country

Production (MT)

Percentage

Brazil The United States Argentina China India Paraguay Canada Others Total

83.5 82.1 51.5 12.6 11.5 7.8 4.9 14.1 268.0

31 31 19 5 4 3 2 5

MT, million tonnes. Source: Soy Stats, 2013 edition, American Soybean Association.

The practice of germplasm selection and utilization traces to the Chinese farmers who selected desirable phenotypes (plants) to use for seed in the next planting. Desirable changes could have arisen from natural cross-pollinations or mutations. Plant breeders made sexual pollinations in soybean as early as 1927 in China and in 1902 in the United States by Evans. By 2000, 800 public cultivars in China, 100 public cultivars in Japan, and more than 600 public and 2000 proprietary cultivars in North America had been released. In addition, plant breeders in South America, Korea, and India had released a total of more than 400 cultivars.

100 90 80

United States

Million tonnes

70 60 50 40

Brazil

30 20 Argentina

10 0 1975

1980

1985

1990

1995 Years

2000

2005

2010

Figure 1 Soybean production of the United States, Brazil, and Argentina from 1975 to 2011 (FAOSTAT).

Cultigen, annual (2n = 4x = 40) G. max Domestication China

Wild annual (2n = 4x = 40) G. soja

Wild perennial (Extinct?) (2n = 4x = 40) Auto- or allopolyploidization?

Putative ancestor of the genus Glycine (2n = 4x = 20) (Unknown?)

Southeast Asia?

Auto- or allopolyploidization? Wild perennial species of the genus Glycine (2n = 4x = 40) Figure 2 The origin of the genus Glycine. Courtesy of Dr. T. Hymowitz.

Australia

BREEDING OF GRAINS | Soybean: Germplasm, Breeding, and Genetics Table 2

335

The major Glycine max germplasm collections

Institution

Country

Institute of Crop Sciences, CAAS USDA Soybean Germplasm Collection National Institute of Agricultural Biotechnology Asian Vegetable Research and Development Center (AVRDC) Soybean Research Institute, Nanjing Agricultural University Centro Nacional de Pesquisa de Soja (CNPSo) EMBRAPA Department of Genetic Resources, National Institute of Agrobiological Sciences Centro Nacional de Pesquisa de Recursos Gene´ticos e Biotecnologia (CENARGEN) Soybean Research Institute, Jilin Academy of Agricultural Sciences Institute of Agroecology and Biotechnology N.I. Vavilov Institute of Plant Industry All India Coordinated Research Project on Soybean, Govind Ballabh Pant University of Agriculture and Technology Institut des Savanes, Bouake´ National Research Centre for Soybean National Bureau of Plant Genetic Resources, New Delhi Crop Experiment Station Upland Crops Research Division Australian Tropical Crops Genetic Research Centre Taiwan Agricultural Research Institute (TARI) Sukamandi Research Institute for Food Crops (SURIF) CSIRO, Division of Tropical Crops and Pastures Genebank, The Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) International Institute of Tropical Agriculture Institute for Agrobotany G.I.E. Amelioration Fourragere Institute of Oil Crops Research Institute, CAAS Field Crops Research Institute, Bangkok Instituto Agronoˆmico de Campinas (IAC) Instituto Nacional de Investigaciones Agrıćolas, Station de Iguala Kariwano Lab., Tohoku National Agricultural Experiment Station Hokkaido National Agricultural Experiment Station Institute of Plant Breeding, College of Agriculture, UPLB Greenhouse for Tropical Crops, Kassel University Stat. de Genetique et Amelioration des Plantes, INRA C.R. Montpellier Centro de Investigacioń La Selva (CORPOICA) Institute of Agriculture Institute of Crop Science, CAAS Institute of Field and Vegetable Crops Institute of Industrial Crops, Jiangsu Academy of Agric. Sci. Soybean Research Institute, Heilongjiang Academy of Agricultural Sciences Genebank Cereal & Oil Crops Inst., Hebei Academy of Agricultural Sciences Instituto Nacional de Investigaciones Forestales Agrıćolas y Pecuarias (INIFAP) Maharashtra Association for the Cultivation of Science Genetic Resources Department, Research Institute for Cereals and Ind. Crops Total

China USA Republic of Korea Taiwan China Brazil Japan Brazil China Ukraine Russia India Ivory Coast India India Republic of Korea Australia Taiwan Indonesia Australia Germany Nigeria Hungary France China Thailand Brazil Mexico Japan Japan Philippines Hungary France Colombia Ukraine China Serbia China China China Mexico India Romania

Number of accessions 25 377 19 505 17 644 13 990 13 000 11 800 9326 9077 8152 7000 6146 4015 3727 3698 3690 3678 3144 2699 2194 2130 1909 1909 1721 1582 1529 1510 1500 1500 1400 1383 1381 1374 1374 1235 1234 1200 1200 1199 1165 1154 1124 1081 1024 201 680

CAAS, Chinese Academy of Agricultural Science; EMBRAPA, Empresa Brasileira de Pesquisa Agropecua´ria; CSIRO, Commonwealth Scientific and Industrial Research Organisation; UPLB, University of the Philippines Los Banõs; INRA, Institut National de la Recherche Agronomique. The data in the table were gathered from the database maintained by Biodiversity International (www.biodiversityinternational.org) (verified July 2013). Some numbers were updated via direct contact with the holding institutions.

Cultivated soybean is considered a quantitative short-day plant. This photoperiod sensitivity defines the area of adaptation as delimited by latitude. For convenience, in North America, cultivars have been classified into maturity groups based upon their responsiveness to photoperiod. This relatively narrow band of latitude, in which a soybean genotype is adapted, results in 13 maturity group designations: 000, 00, 0, and Roman numerals I–X, from north to south. The few photoperiod-insensitive

cultivars that have been released have not been agronomically competitive with photoperiod-sensitive cultivars.

Germplasm Utilization: Perennials The 24 wild perennial soybean species represent a reservoir of useful genes to improve cultivated soybean. This includes

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Table 3

The major Glycine soja germplasm collections

Institution

Country

Number of accessions

Institute of Crop Sciences, CAAS Department of Genetic Resources, National Institute of Agrobiological Sciences Asian Vegetable Research and Development Center (AVRDC) USDA Soybean Germplasm Collection Soybean Research Institute, Nanjing Agricultural University Soybean Research Institute, Jilin Academy of Agricultural Sciences Soybean Research Institute, Heilongjiang Academy of Agricultural Sciences Crop Experiment Station Upland Crops Research Division N.I. Vavilov Institute of Plant Industry Laboratory of Plant Breeding, Faculty of Agriculture, Iwate University Empresa Brasileira de Pesquisa Agropecua´ria Taiwan Agricultural Research Institute (TARI) Hunan Academy of Agricultural Sciences CSIRO, Division of Tropical Crops and Pastures Tieling District Agricultural Research Institute Department of Agronomy, National Chung Hsing University Eastern Cereal and Oilseed Research Centre, Saskatoon Research Centre Soybean Breeding Laboratory, Tokac. Agricultural Experiment Station Sher-E-Kashmir University of Agricultural Science and Technology Total

China Japan Taiwan USA China China China Republic of Korea Russia Japan Brazil Taiwan China Australia China Taiwan Canada Japan India

6708 2102 1211 1179 900 600 400 342 310 151 95 46 45 32 29 20 20 16 1 14 207

CAAS, Chinese Academy of Agricultural Science; CSIRO, Commonwealth Scientific and Industrial Research Organisation. The data in this table were gathered from the database maintained by Bioversity International (www.bioversityinternational.org) (verified July 2013). Some numbers were updated via direct contact with the holding institutions.

resistance to soybean rust (Phakopsora pachyrhizi Sydow), soybean brown spot (Septoria glycines Hemmi.), powdery mildew (Microsphaera diffusa Cke. & Pk.), phytophthora root rot (Phytophthora sojae Kaufmann & Gerdemann), white mold (Sclerotinia sclerotiorum (Lib.) de Bary), sudden death syndrome (Fusarium solani (Mart.) Sacc.), tobacco ringspot virus, yellow mosaic virus, alfalfa mosaic virus, soybean cyst nematode (Heterodera glycines Ichinohe), bean pod mottle virus and tolerance to drought stress, to certain herbicides, and to salt and amenability to tissue culture regeneration. Exploitation of the wild perennial species for soybean improvement has received renewed interest in recent years. The major impediment is the extremely low crossability and the need to use embryo-rescue techniques to obtain hybrid plants. Many interspecific hybrid combinations give weak, slow-growing plants that are completely sterile.

Germplasm Utilization: G. soja The G. soja accessions harbor many undesirable genetic traits, for example, lodging, vining growth habit, susceptibility to biotic and abiotic stresses, lack of complete leaf abscission, pod shattering, and black seed coat. Limited numbers of interspecific crosses between G. max and G. soja have been made in attempts to broaden the genetic base of G. max cultivars. Generally, introgression of favorable traits has not been successful. However, small-seeded cultivars that have G. soja as one parent have been released for sprouts or the fermented Japanese product ‘natto.’ One Russian cultivar that has a high percentage germination under cool temperatures has been released. The wild annual soybean is high in seed protein but low in seed oil.

Germplasm Utilization (North America): G. max The G. max accessions form the basis for modern soybean cultivar improvement programs. Ten plant introductions (accessions) have contributed more than 80% of the North American maturity gene pool and seven introductions contributed more than 80% of the southern US maturity groups. In addition, many other accessions have contributed to disease resistance and chemical traits. The most common method of gene transfer has been through backcrossing. For example, resistance to downy mildew (caused by Peronospora manshurica), root rot (caused by Phytophthora sojae), bacterial pustule (caused by Xanthomonas campestris pv. glycines), and root knot (caused by Meloidogyne spp.) has been incorporated into susceptible cultivars to develop near-isogenic resistant cultivars. Recently, accessions have played a prominent role as sources of resistance to brown stem rot (caused by Phialophora gregata) and to cyst nematode. Another example includes ‘Kunitz,’ which is missing the antinutritional factor Kunitz trypsin inhibitor SBTI-A2 derived from a G. max accession (PI 157440) from Republic of Korea. The selection of parents used for soybean cultivar development is determined largely by the breeding objective and the germplasm available to use as parents. Direct cross-pollination of cultivars with germplasm accessions, followed by inbreeding and selection, generally has not contributed to the development of modern high-yielding cultivars. A topic of much discussion among soybean breeders is whether continued advances in cultivar development for seed yield, beyond the level possible with the domestic gene pool of elite breeding lines and cultivars, can be achieved. The utilization of accessions in cultivar development might be successful if selection systems were known that could identify introductions that

BREEDING OF GRAINS | Soybean: Germplasm, Breeding, and Genetics Table 4

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The genus Glycine, 3-letter code, 2n number, genome, and distributiona

Subgenus Glycine (Willd.)

Code

2n

Genome

Geographic distribution

1. G. albicans Tind. and Craven 2. G. aphyonota B.E. Pfeil 3. G. arenaria Tind. 4. G. argyrea Tind. 5. G. canescens F. J. Herman 6. G. clandestina Wendl. 7. G. curvata Tind. 8. G. cyrtoloba Tind. 9. G. falcata Benth. 10. G. gracei B.E. Pfeil and Craven 11. G. hirticaulis Tind. and Craven

ALB APH ARE ARG CAN CLA CUR CYR FAL GRA HIR

12. G. lactovirens Tind. and Craven 13. G. latifolia (Benth.) Newell and Hymowitz 14. G. latrobeana (Meissn.) Benth. 15. G. microphylla (Benth.) Tind. 16. G. montis-douglas B.E. Pfeil and Craven 17. G. peratosa B.E. Pfeil and Tind. 18. G. pindanica Tind. and Craven 19. G. pullenii B.E. Pfeil, Tind., and Craven 20. G. rubiginosa B.E. Pfeil and Tind. 21. G. stenophita B.E. Pfeil and Tind. 22. G. syndetika B.E. Pfeil and Craven 23. G. tabacina (Labill.) Benth.

LAC LAT LTR MIC MON PER PIN PUL RUB STE SYN TAB

24. G. tomentella Hayata

TOM

40 40 40 40 40 40 40 40 40 40 40 80 40 40 40 40 40 40 40 ? 40 40 40 40 80 38 40 78 80

I ? H A A A C C F A H ? I B A B ? A H ? A B A B Complex E D Complex Complex

Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia Australia, west central and south Pacific Islands Australia Australia, Papua New Guinea (PNG) Australia, PNG Australia, PNG Indonesia, Philippines, Taiwan

Subgenus Soja (Moench) F.J. Herman 25. G. soja Sieb. & Zucc. 26. G. max (L.) Merr.

SOJ MAX

40 40

G G

China, Russia, Taiwan, Japan, Korea (wild soybean) Cultigen (soybean)

Two species designations are questioned: (1) G. dolichocarpa Tateishi and Ohashi (DOL). This described species (2n ¼ 80), found in Taiwan, appears to be a member of the G. tomentella complex, (2) G. pescadrensis Hayata (PES). This described species (2n ¼ 80), found in Australia, Japan, and Taiwan, appears to be a member of the G. tabacina complex (lacking adventitious roots). Source: Hymowitz T (2004) Speciation and cytogenetics. In: Boerma HR and Specht JE (eds.) Soybeans: Improvement, Production, and Uses, 3rd edn., pp. 97–136. Wisconsin: ASA, CSSA, and SSSA, Agronomy Monograph 16; Pfeil BE, Craven LA, Brown AHD, Murray BG, and Doyle JJ (2006) Three new species of northern Australian Glycine (Fabaceae, Phaseolae), G. gracei, G. monti-douglas and G. syndetika. Australian Systematic Botany 19: 245–258. a

have good combining abilities with adapted genotypes. Twoparent crosses of ‘good’ by ‘good’ cultivars or elite experimental breeding lines have been the most extensively used by breeders because of the higher probability of obtaining high-yielding cultivars.

Germplasm Utilization (Other Countries): G. max Unlike the North American genetic bases, the Chinese genetic base encompasses 190 ancestors that have contributed 80% to the parentage of the Chinese soybean cultivars. The genetic base of the Japanese cultivars has shifted over time. Before 1945, Chinese accessions were important as parents in Japanese cultivars. In the late 1950s, increasing numbers of North American cultivars and breeding lines were used as parents. South Americans have relied extensively upon North American cultivars for direct release to farmers. In recent years,

the South American breeding programs have released cultivars that are competitive with those bred in North America.

Breeding The first cultivar that originated as a selection made among progenies of controlled hybridizations was the ‘Ogemaw’ released in 1902. Cultivar development in the United States initially was conducted by the USDA and state agricultural experiment stations. Now, in the main soybean-producing regions, private companies develop and release most of the cultivars. Conventional soybean breeders follow a cycle of ‘crossing of parents’ followed by ‘progeny evaluation and selection of parents’ and ‘development of progeny for testing.’

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Tertiary gene pool Gp3 24 wild perennial species Secondary gene pool Gp2 unknown

Primary gene pool Gp1 soybean cultivars land races Glycine soja

Figure 3 The gene pools of the soybean.

Breeding Objectives

protein and 20% seed oil. In most environments, if seed protein increases, seed oil decreases, and vice versa. Both food uses and industrial uses are creating greater demands for specialty use soybean such as soy milk and soy ink for printing. A number of breeding programs now focus on breeding specialty-use soybeans. Soybean seed oil is the major vegetable oil among oilseed crops worldwide and modification of seed oil has received the most focus. Oil synthesis in the seed and seed oil fatty acid composition are largely determined by the maternal parent. The fatty acid content of conventional soybean cultivars is 11% palmitate, 4% stearate, 24% oleate, 54% linoleate, and 7% linolenate. The desired variation in seed oil fatty acid composition was not found in the G. max or G. soja germplasm collections. Mutagenesis, both chemical radiation and ionizing radiation, was used to create a number of highly desirable mutations with modifications in individual fatty acids. The modification of soybean oil and selection for superior agronomic traits have resulted in cultivar releases, for example, Satelite, which has reduced saturated fatty acids and reduced linolenic acid. Industrial uses include soy ink for both black/white and color newsprint and as a major component of lubricants and gasoline (biofuel) for automobiles, trucks, buses, and marine engines.

The first step in cultivar development is to identify the characters that are important for commercial soybean production whether it is for feed, food, or industrial uses. Yield is the character of prime importance to the farmer. Data from 1941 to 2000 of North American maturity groups 00–IV show that soybean breeders have increased seed yield 1% per year. In China, yield gains for soybean breeding programs were low before 1970. Since the 1980s, yield gains between 1% and 2% per year have been realized. In soybean, diseases, nematodes, and insects can reduce yields substantially. Generally, in soybean breeding, tolerance to pests is not the objective; rather, the emphasis is breeding for resistance. Lodging resistance or standability is important for mechanical harvest, and plants that are not upright have decreased yield. Most earlier-maturing cultivars are of indeterminate growth habit, while later-maturing cultivars are of determinate growth habit. The short, determinate cultivars have better lodging resistance. Pest resistance is of paramount importance in soybeangrowing areas where diseases, nematodes, or insects are major problems. Most major soybean-growing areas have one or more major pest problems. Breeding for pest resistance is dependent upon the prevalence and regularity of economic loss in each area. Traits that are important in breeding cultivars include maturity, seed quality, seed emergence, herbicide tolerance, plant height, and resistance to mineral deficiencies and toxicities. Continued emphasis has been given to drought tolerance. Shattering resistance refers to the ability of a plant to retain its seed when mature. All modern cultivars have adequate resistance to shattering.

Specialty Cultivars

Seed Composition

Breeding Methodology

Seed composition is becoming an important factor to consider in soybean breeding. Cultivars generally have 40% seed

Soybean is a highly self-pollinated species, and all cultivars are either pure lines (inbred lines) or mixtures of pure lines. All

Breeding of specialty cultivars, especially cultivars with valueadded traits, has been given increased emphasis in recent years. These include cultivars with altered seed composition for oil and protein quality and quantity, seed size and color, and growth habit, for example, forage soybean. Specialty cultivars are used for soyfoods, industrial applications, and feeds. Parents used to breed specialty cultivars have added genetic diversity to the soybean gene pool. Soybean was first introduced into the United States as a hay crop. It was not until 1941 that the number of hectares grown for seed exceeded that for hay and other purposes (silage, green manure, and pasture). Modern forage cultivars are bred for biofuel, hay, silage, and pasture. Interestingly, forage soybean is used as a honey crop by beekeepers before being grazed or cut for silage or hay. Yields of 10.8 tonnes per hectare with 28% protein have been reported. Improved cultivars are available for sprouts, soy sauce, douchi, and doujing. Several vegetable-bean cultivars, known as edamame (maodou), with improved agronomic qualities are available. Natto, a fermented product, soymilk, and soy protein isolates are important food uses of soybean. Tofu, a cheese-like curd for human consumption, has a high protein percentage. Cultivars for medicinal use have been released. Soybean is the predominant commercial source of a-tocopherol (natural vitamin E). Isoflavones, especially daidzein and genistein, are physiologically active components of soybean meal. Isoflavones possess antioxidant properties, which are associated with a number of health benefits.

BREEDING OF GRAINS | Soybean: Germplasm, Breeding, and Genetics cultivars released today in the major soybean-growing areas of the world are the result of sexual hybridization followed by selection. The cyclic process of hybridization, inbreeding, and evaluation/ selection form the basis for soybean cultivar development. Breeding methods include pedigree, bulk, mass selection, single-seed descent, and backcross. Single-seed descent, also known as a modified pedigree method, is favored by many soybean breeders, because it minimizes the number of years for cultivar development. Single-seed descent is well suited for generation advances (inbreeding) in off-season nurseries, for example, Puerto Rico, Hawaii, Hainan Island (China), or South America, or in glasshouses (Figure 4). The pedigree method is based upon selection among plants during inbreeding. The inability to make selections in offseason nurseries and glasshouses for important agronomic traits is a severe limitation. The bulk method entails growing a population of plants, usually F2 generation, harvesting all the seed in bulk, and planting a seed sample from the bulk harvest the next season. This procedure is repeated until the desired level of inbreeding (homozygosity) is achieved, and then, selection is initiated. The mass selection method involves inbreeding plants selected on the basis of phenotype, compositing the seed without progeny testing, and inbreeding until the desired level of homozygosity is attained. Early generation testing has been used to produce soybean cultivars. This method involves identifying desirable heterogeneous populations or lines from which superior homozygous individuals can be selected. In North America, the USDA coordinates the regional evaluation of advanced breeding lines submitted by USDA

Season

339

scientists, Agriculture and Agri-Food Canada scientists, and state (the United States) or provincial (Canada) agricultural experiment stations and universities. These elite breeding lines are advanced to the preliminary and regional tests. This testing program, from maturity groups 00 to VIII, enables breeders to evaluate breeding lines under a wide range of environmental conditions. Lines are usually entered only once in the preliminary tests and then are either deleted or advanced to the uniform tests for a maximum of 3 years, if agronomic performance warrants further testing. The best publicly derived cultivars in each maturity group are used as check (control) cultivars to provide a basis of comparison to elite breeding lines for seed yield, seed chemical composition, maturity, height, lodging, seed quality, and reaction to diseases and nematodes.

Marker-Assisted Selection The association of phenotypic trait data and molecular marker data from a population of lines segregating for genes conditioning a quantitative trait provides the unique ability to dissect the quantitative trait into a set of quantitative trait loci (QTLs). Marker-assisted selection (MAS) should be viewed as a complement to conventional soybean breeding, rather than a replacement.

Hybrid Soybean Soybean male sterility was reported in 1971. Since that time, at least ten international patents on soybean sterility systems and hybrid seed production have been granted. There are five

Procedure

1

Make F1 seed

2

Grow F1 plants Harvest F2 seed from each plant separately

3

Grow F2 plants Harvest F3 seed from each plant separately

4

Grow individual hills Harvest F4 seed from each hill separately

5

Grow individual hills Harvest F5 seed from each hill separately

6

Grow individual hills Harvest one F5 plant from each hill

7

Grow individual progeny rows Harvest selected rows in bulk

8

Extensive testing of F5derived lines

Plants A

B

C

D

E

Discard Discard

Figure 4 Example of a single-seed descent method. Variations include harvesting one pod or only one seed to advance to the next generation. Harvesting one plant ensures that all F2 plants are represented in the final selection process.

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components that are crucial for the successful development of commercial hybrid soybean:

• • • • •

Parental combinations that produce heterosis levels superior to the best pure-line cultivars A stable male-sterile, female-fertile sterility system A selection system to obtain 100% female (pod parent) plants that set seed normally and can be harvested mechanically An efficient pollen transfer mechanism from pollen parent to pod parent An economical level of seed increase for the seedsman and growers that ultimately benefits the consumer

Research results show that F1 hybrid vigor (heterosis) does exist in soybean with the better hybrids yielding between 10% and 20% above the high parent. The major obstacle to commercialization of hybrid soybean is pollen transfer from the male parent to the pod parent. Considerable advances in insectmediated cross-pollination are necessary before large numbers of hybrid seed can be obtained. Then, hybrid combinations can be tested in multiple environments to assess hybrid vigor and to determine the potential for commercialization. Perhaps equally important for the commercialization of hybrid soybean would be the benefit of a technology protection system. Such a system when combined with ‘trait stacking’ would benefit the seedsman, growers, and ultimately the consumer.

Genetics Soybean is expected to have 20 linkage groups (2n ¼ 4x ¼ 40 chromosomes). The diploid progenitor of soybean has not been identified. The small size, large number, and similar morphology of the chromosomes have been deterrents to progress in soybean cytogenetics and genetics. However, a chromosome map based upon pachytene chromosome analysis has been completed.

Cytogenetics Haploids can be produced in soybean, but the difficulty in production, for example, unique mutants, and the low frequency have precluded their use in breeding. Polyploids rarely occur spontaneously but can be produced through chemical treatment, but are not suitable agronomically. Addition aneuploids, especially primary trisomics, have been very useful to locate genes to specific chromosomes and all 20 unique primary trisomics are known. Soybean can tolerate addition aneuploids, but surprisingly, the occurrence of deficiency aneuploid plants has been low and they cannot be maintained. Chromosome interchanges (translocations) have been studied cytologically and have been used to locate genes to specific chromosome arms. Chromosome inversions, both pericentric and paracentric, are found in accessions in Glycine. Inversions have not been used in linkage studies. Extensive cytogenetic studies in the genus Glycine have been done with the perennial species. Because of the reservoir of desirable traits in the perennial species, active gene transfer

programs from wild perennial species to the cultivated species are of paramount importance. Soybean has been suggested to be an ancient polyploid based upon chromosome number, genome size, the identification of duplicate loci, high fertility levels (male and female) of primary trisomic plants, and the high levels of transmission of the extra chromosome through both male and female gametes. The duplicated genome(s) and duplicated genes in soybean have been reorganized through processes such as loss of duplicated segments, single-gene duplication via unequal crossing-over, chromosome repatterning, transposition, gene conversion, recombination, divergent evolution, and gene silencing. Collectively, the cytogenetic and genetic evidence supports the view that the cultivated soybean is a diploidized polyploid.

Qualitative Genetics The soybean Genetic Type Collection maintained by the USDA is a comprehensive tabulation of qualitative genetic traits with gene symbols, phenotypic descriptions, source of mutants, and reference citations. Genetic mutations include resistance to fungi, bacteria, viruses, nematodes, and insects; resistance or tolerance to herbicides; and response to Rhizobium, time of flowering, and maturity. Plant growth traits include stem, petiole, inflorescence, leaf form, pubescence type, and seed-coat structure. Genes that cause sterility, either complete or partial, of male and/or female gametes are known. Genes for response to nutritional factors and to pigmentation (seed, leaves, flowers, pod, and pubescence) are known. Many mutations that affect isoenzymes and proteins are documented. Qualitative genetics have played a major role in plant breeding programs for genes for pest resistance.

Molecular Genetics The development of a soybean molecular genetics map based upon DNA sequence polymorphisms initially relied upon restriction fragment length polymorphisms. Additional classes of DNA markers were developed after the advent of the polymerase chain reaction (PCR) technology. They include simple sequence repeat markers, random amplified polymorphic DNA or arbitrary primer PCR markers, DNA amplification fingerprinting markers, amplification fragment length polymorphism markers, and single-nucleotide polymorphism markers. The integration of the classical genetic map into the molecular genetics map and the association of the markers to their respective chromosome are under development. The use of molecular techniques in soybean to locate QTLs has received much attention. This type of MAS has been used to locate seed composition traits, reproductive traits, time of flowering and maturity traits, response to nutritional factors, etc.

Bioinformatics and Data Resources Extensive bioinformatics resources and data sets are available for soybean. As of early 2014, these include a high-quality reference genome sequence and gene predictions for ‘Williams-82’, many genetic maps in populations of interest

BREEDING OF GRAINS | Soybean: Germplasm, Breeding, and Genetics (collectively with thousands of mapped QTLs), high-density genetic maps, gene expression resources, and various metabolomic, proteomic, small RNA, methylation, and other specialized experimental resources. A major new resource available in 2014 is the dense genotyping of the complete USDA Soybean Germplasm Collection. This is a survey of 52 041 genetic markers across 19 652 G. max and G. soja accessions (available prepublication at http://soybase.org/snps). Several projects are also underway to fully resequence many cultivars. The primary ‘Williams-82’ genome sequence assembly and gene models are maintained at http://phytozome.org/soybean, and the gene models and chromosomal sequences are available for searching and browsing at http://phytozome.org/soybean and http://soybase.org. Beyond the reference genome, http://soybase.org (the USDA-ARS website for soybean genetic and genomic research) provides access to most published genetic maps and QTLs, the US germplasm genotyping results, gene expression data, sequence and keyword search, molecular pathway data, and various soybean research community information and functions. These and some other significant genetic and genomic tools and resources are shown in Table 5.

Transformation Foreign genes can be delivered into soybean via Agrobacterium, particle bombardment, and electroporation. The Agrobacterium-mediated floral dipping method and the pollen-tube pathway transformation method have not been confirmed in soybean. Most of the gene transfer methods are tissue culturebased, requiring the regeneration of whole plants from transformed cells. Because of the lack of efficient regeneration and transformation procedures, soybean remains recalcitrant for genetic transformation. In addition, the use of Agrobacteriummediated transformation systems shows considerable genotype specificity. A commercial success with transformed soybean has been with glyphosate herbicide (Roundup®) tolerance. Roundup Ready 2 Yield® soybean cultivars have provided the farmer with a new weed control system. However, weeds have developed resistance to many of the major herbicides. Currently, combinations of chemicals are used in attempts to control weeds. Table 5

Some websites with tools and data for soybean research

Resource/URL

Primary specialties

http://soybase.org

Genetic/QTL/genomic integration; community Genome sequence and gene model; gene families Genetic mutants; other specialized tools Japanese germplasm and resources

http://phytozome.org http://soykb.org http://www.legumebase.brc. miyazaki-u.ac.jp http://plantgrn.noble.org/ LegumeIP http://bioinformatics.psb.ugent. be/plaza http://legumeinfo.org

Gene expression data versus other legume species Gene families; comparisons with other plants Structural comparisons with other legumes

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Gene flow between genetically modified soybean and conventionally bred soybean has been documented. There is concern for gene flow between genetically modified soybean and the wild annual soybean (G. soja Sieb. & Zucc.) in eastern Asia. Gene flow between commercially grown soybean and wild perennial species does not occur in nature.

Future Prospects Germplasm collections have continued to expand. Many acquisitions are landraces or local cultivars that are being replaced by newly released cultivars. The addition of new wild perennial species continues and the ‘discovery’ of new species seems likely. Qualitative genetic mutants are continually being added to the USDA Genetic Type Collection and are available to all soybean scientists. Some are of spontaneous origin but many are from mutation programs, for example, seed oil fatty acid mutants. A few transgenes (from genetic engineering research) are available. Gene discovery, through the use of expressed sequence tags, will permit the identification of differential patterns of gene expression. Genome sequencing is the cornerstone of functional analyses. Functional genomics is the process of generating, integrating, and using information from genomics, gene expression profiles (microarrays and chips), and proteomics. This will permit large-scale genotyping of plants in order to understand gene function. The end result will be improved soybean cultivars for food, feed, and industrial uses.


• • • • • • • •

Which two countries produce the most soybeans in the world? What two subgenera of soybean distinguish perennials from annuals? Is soybean mostly self-pollinated or cross-pollinated? Why have wild perennial species not been used in soybean breeding programs? Was soybean initially introduced into the United States as a (a) seed crop or (b) hay crop? What does shattering of soybean refer to? How many maturity groups exist for soybean? Does gene flow between commercially grown soybean and wild perennial soybean occur in nature?


• • •

How could MAS be used to identify some of the desirable traits from wild annual soybean, such as higher protein content? Hybridization using wild perennial soybean requires embryo rescue. How is embryo rescue done? Is there a way of using perennials to identify haploidinducing cytoplasm or haploid-inducing genes to be incorporated into commercial breeding programs?

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•


Could we identify, for commercial development, certain combinations of wild annual and/or wild perennial soybean with cultivated soybean to generate a cytoplasmic male sterility system with restorer genes?

See also: Agronomy of Grain Growing: Soybean: Agronomy; Carbohydrates: Grains other than Cereals: Non-starch Polysaccharides; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Non-wheat Foods: Soybean: Soy-Based Fermented Foods; Soybean: Soymilk, Tofu, and Okara; Oilseed and Legume Processing: Soybean: Processing; Soybean: Soy Concentrates and Isolates; Proteins: Nitrogen in Grain Production Systems.

Further Reading Andersson MS and deVicente MC (2010) Gene flow between crops and their wild relatives. Baltimore, MD: Johns Hopkins University Press, pp. 465–481. Birt DF, Hendrich S, Alekel DL, and Anthony M (2004) Soybean and the prevention of chronic human disease. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 1047–1117. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Carter TE Jr, Gizlice Z, and Burton JW (1993) Coefficient-of-parentage and geneticsimilarity estimates for 258 North American soybean cultivars released by public agencies during 1945–88. USDA Technical Bulletin Number 1814, 169 pp. Carter Jr. TE Jr., Nelson RL, Sneller CH, and Cui Z (2004) Genetic diversity in soybean. In: Boerma HR and Specht JE (eds.) Soybeans: Improvement, Production, and Uses, pp. 303–416. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Chung G and Singh RJ (2008) Broadening the genetic base of soybean: A multidisciplinary approach. Critical Reviews in Plant Sciences 27: 295–341. Cooper M, Smith OS, Graham G, Arthur L, Feng Z, and Podlich DW (2004) Genomics, genetics, and plant breeding: A private sector perspective. Crop Science 44: 1907–1913. Cui Z, James AT, Miyazaki S, Wilson RF, and Carter Jr. TE Jr. (2004) Breeding of speciality soybeans for traditional and new soyfoods. In: Liu K (ed.) Soybeans as a Functional Food, pp. 264–322. Champaign, IL: AOCS Press. Fehr WR (1987) Breeding methods for cultivar development. In: Wilcox JR (ed.) Soybeans: Improvement, Production, and Uses, pp. 249–293. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 2nd edn. Grant DM, Nelson R, Cannon SB, and Shoemaker RC (2009) SoyBase, the USDA-ARS soybean genetics and genomics database. Nucleic Acids Research 37: D843–D846. Hymowitz T (2004) Speciation and cytogenetics. In: Boerma HR and Specht JE (eds.) Soybeans: Improvement, Production, and Uses, pp. 97–136. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Hymowitz T and Bernard RL (1991) Origin of the soybean and germplasm introduction and development in North America. In: Shands HL and Wiesner LE (eds.), Use of Plant Introductions in Cultivar Development, pp. 148–164. Madison, WI: CSSA Special Publication No. 17. Lewers KS and Palmer RG (1997) Recurrent selection in soybean. Plant Breeding Reviews 16: 275–313.

Lusas EW (2004) Soybean processing. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Orf JH, Diers BW, and Boerma HR (2004) Genetic improvement: Conventional and molecular-based strategies. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Palmer RG, Hymowitz T, and Nelson RL (1995) Germplasm diversity within soybean. In: Verma DPS and Shoemaker RC (eds.) Soybean Biotechnology, pp. 1–35. London: CAB International. Palmer RG, Gai J, Sun H, and Burton JW (2001) Production and evaluation of hybrid soybean. Plant Breeding Reviews 21: 263–307. Palmer RG, Pfeiffer TW, Buss GR, and Kilen TC (2004) Qualitative genetics. In: Boerma HR and Specht JE (eds.) Soybeans: Improvement, Production, and Uses, pp. 137–233. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Parrott WA and Clemente TE (2004) Transgenic soybean. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Pfeil BE, Craven LA, Brown AHD, Murray BG, and Doyle JJ (2006) Three new species of northern Australian Glycine (Fabaceae, Phaseolae), G. gracei, G. monti-douglas and G. syndetika. Australian Systematic Botany 19: 245–258. Schmutz J, Cannon SB, Schlueter J, et al. (2010) Genome sequence of the palaeopolyploid soybean. Nature 463: 178–183. Shoemaker RC, Cregan PB, and Vodkin LO (2004) Soybean genomics. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Singh RJ and Hymowitz T (1999) Soybean genetic resources and crop improvement. Genome 42: 605–616. Sonka ST, Bender KL, and Fisher DK (2004) Economics and marketing. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Wilcox JR (2004) World distribution and trade of soybean. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Wilson RF (2004) Seed composition. In: Boerma HR and Specht JE (eds.) Soybeans, Improvement, Production, and Uses, pp. 949–1045. Madison, WI: ASA, CSSA, and SSSA, Agron. Monogr. 16, 3rd edn. Wilson RF, Burton JW, Novitzky WP, and Dewey RE (2001) Current and future innovations in soybean (Glycine max L. Merr.) oil composition. Journal of Oleo Science 50: 353–358.

Relevant Websites http://www.comparative-legumes.org – Legume Information System (LIS). This website gives quick access to other legume databases and contains comparative information. http://www.legumes.org – Legumes. This website links to many legume databases. http://soybase.org – SoyBase home page. USDA-ARS soybean genetics and genome database. This website gives quick access to the latest news about databases, links to other soybean and legume sites and many other items of interest to soybean researchers. http://www.soygenetics.org – Soybean Genetics Newsletter. The information in the articles is to stimulate thought and to exchange ideas among soybean scientists.

Genetics of Grains

Contents Development of Genetically Modified Grains Detection of Genetically Modified Grains Genomics of Food Grains Genome Mapping Wheat Genetics Wheat Genetics and Genomics Biotic Stress Resistance Genes in Wheat Abiotic Stress Genes and Mechanisms in Wheat Rice: Genetics Maize: Genetics Maize: Quality Protein Maize Maize: Other Maize Mutants

Development of Genetically Modified Grains L Privalle, Bayer CropScience, Research Triangle Park, NC, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

Introduction

•

The development of an agricultural biotechnology product begins with an examination of the customer’s (the grower’s) needs and problems – land, seed, fertilizer, equipment, personnel, petroleum, pesticides (herbicides, insecticides, and fungicides), buyers, rain, sunshine, and correct temperatures (Figure 1). All of these are considerations that impact the yield and the grower’s bottom line. Agricultural biotech products can address some of these issues, and the appropriate uses of such products are valuable options for sustainable agriculture. The earliest biotech products focused on what the grower needed together with what was technologically possible, such as herbicide tolerance and insect resistance. Both of these socalled input traits directly contribute to increased yield and decreased costs. When considering the costs, it is obvious that biotech products would increase the cost of seed and decrease the cost of pesticides. It is not, however, so obvious that petroleum costs would be reduced, topsoil erosion would decrease, and labor requirements would also decrease. In summary, the grower’s cost decreases and the yield increases. The attractiveness of this scenario accounts for the extremely rapid adoption of this technology by growers in regions of the world where the technology is accepted. This article describes the steps necessary to successfully bring an agricultural biotechnology product (also known as a genetically modified organism) to market.

• • • •

Genetically modified crops provide solutions/options to agricultural problems that growers need. There are several ways of delivering genes to plant cells, with the method of choice being transformation using Agrobacterium. Events that will be taken to market must be efficacious and have insertions with molecular characteristics that are acceptable. An extensive safety assessment is undertaken to demonstrate that the product is safe for people, good for animals, and safe for the environment. The safety assessment includes studies on the safety of the newly expressed protein, molecular characterization of the insert, impact of the insert on plant performance and composition, environmental impact, and wholesomeness of the crop.

Learning Objectives

• •

To achieve understanding of the development process undertaken. To produce, characterize, and commercialize genetically modified grains.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00218-7

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344

GENETICS OF GRAINS | Development of Genetically Modified Grains

The development process starts with the idea for the trait or agricultural issue to be addressed and then identification and isolation of a gene(s) able to confer the required trait. This is called the discovery phase (Figure 2). Current genomics techniques facilitate this process in ways that were unimaginable 20 years ago. Once the gene is available, appropriate constructs must be made – that is, pairing the gene with the appropriate elements (promoters, terminators, and introns) to ensure expression of the gene at the appropriate time in the plant life cycle that allows successful expression of the trait of interest (Figure 3). It is sometimes necessary to adapt the codon usage of the gene to the crop of interest in order to achieve the necessary expression levels to be efficacious (Table 1). For example, one leucine codon, UUA, is used at a frequency (per thousand) of 34.8 in Bacillus thuringiensis but is clearly not the preferred leucine codon in maize (frequency of use 6.7). To

Seed Fertilizer Herbicide Insurance Misc Interest Machinery Labor Land

Figure 1 Relative expense of grower’s costs (not including pesticides), Iowa State University, January 2014 – example, nonherbicide-tolerant soybean. http://www.extension.iastate.edu/agdm/crops/pdf/a1-20.pdf.

Discovery gene/Trait identification Average duration

53.9 months

Phase I proof of concept 27 months

optimize expression in maize, this codon should be changed in the newly inserted gene. Delivery of the gene and integration into the plant genome is the next step. Figure 4 illustrates the most commonly used procedures, biolistics and Agrobacterium-mediated transformation being the most popular; however, some early products were developed via protoplast transformation. Biolistics takes the brute force approach and is applicable to nearly all plant types. It is neither specific nor precise. Protoplast transformation is also fairly crude; plant cells are stripped of their cell walls, placed in a solution containing the DNA to be inserted, and then shocked either electrically or osmotically, causing pores to open and the solution containing the DNA to enter the cell. The use of Agrobacterium-mediated transformation is much more precise but at one time was limited to only dicotyledonous crops. After extensive research, this technology has been successfully adapted for monocotyledonous crops as well. A very significant hurdle in the process is the regeneration of the plant cell to a fertile plant once the gene has been introduced. The methods differ from crop to crop and usually require cell culture time and exposure to selection agents with specific plant hormone regimens to allow only those cells containing the newly introduced (novel) genes to develop into rooted plants that will pass the genes successfully to their progeny (Figure 5). Very many cells are transformed, and each cell that results in a transformed plant is characterized by the insertion site and designated as a specific ‘event.’ After the plants have developed roots, they are ‘hardened off’ (allowed to adapt to life outside the humid environment of the growth container) and transferred to a growth chamber or greenhouse. Once progeny are produced, these events are evaluated for their efficacy and performance in the greenhouse and eventually the field. Although this process is now relatively routine, not all events make it through to commercialization for many reasons: The desired trait may be too complex to introduce

Phase II early development 30 months

Phase III advanced development

PHASE IV pre-launch

37.2 months

48.8 months

tion gra inte Trait g testin Field

Regulatory data generation Regula

tory s

single ELITE event

Mean units evaluated regulatory activities

10209 In silico screening

ubmis

See

sion

db

ulk

up

511

1302

2

1

Preliminary digestive fate

Molecular characterization

Full regulatory study package

Data defense

Figure 2 Stages in the development of an agricultural genetically modified product. Mean units evaluated are taken from the Phillips McDougall survey in which biotechnology providers were queried and include both the number of genes screened and transgenic events evaluated.


Promoter

Gene of interest

345

Terminator

1. Minimal gene cassette

Left border

Intron

Right border

2. Agro gene cassette “T –DNA”

3. Agrobacterium transformation vector

Vector Backbone

Plant genomic flanking DNA

Inserted DNA

Flanking DNA

4. Insertion locus Figure 3 Elements of transformation vectors. (1) The minimal gene cassette consists of a promoter, gene of interest, and a terminator; all are essential for successful expression. (2) Other elements such as introns may also be included to increase the levels of expression. When Agrobacteriummediated transformation is utilized, the DNA material found between the right and left ‘borders’ is what is delivered and is referred to as the ‘T-DNA’ or transferred DNA. (3) The so-called vector backbone is the material outside the left and right borders and is what should not be delivered. (4) The insertion locus is illustrated with the plant genomic flanking material indicated. The sequence of this flanking material is what distinguishes events and allows the development of event-specific detection methods.

Table 1 Codon usage bias (differences in the frequency of occurrence of synonymous codons in coding DNA) is shown for Escherichia coli, Bacillus thuringiensis, maize, and soybean Codon

Amino acid

E. coli

B. thuringiensis

Maize

Soybean

Codon

Amino acid

E. coli

B. thuringiensis

Maize

Soybean

UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG

Phe Phe Leu Leu Leu Leu Leu Leu Ile Ile Ile Met Val Val Val Val Ser Ser Ser Ser Pro Pro Pro Pro Thr Thr Thr Thr Ala Ala Ala Ala

22.2 15.9 13.8 13.0 11.4 10.5 3.9 51.1 29.7 23.9 5.5 27.2 18.1 4.8 10.9 26.2 8.7 8.9 8.1 8.8 7.2 5.6 8.4 22.4 9.1 22.8 8.1 15.0 15.4 25.2 20.7 32.3

27.6 9.0 34.8 15.6 16.8 5.4 13.2 4.8 32.4 9.6 13.2 16.2 18.0 1.2 29.4 16.2 14.4 3.0 21.6 6.6 8.4 1.2 20.4 8.4 20.4 4.8 30.0 12.6 14.4 3.6 32.4 15.0

24.2 17.5 6.7 14.0 15.4 23.2 8.0 19.6 38.5 18.9 13.8 28.9 20.5 12.2 6.9 15.8 9.1 12.0 7.8 5.6 17.3 6.9 22.9 11.3 7.7 17.0 10.2 6.8 31.8 28.0 23.4 13.1

21.2 21.2 9.2 22.9 23.9 17.1 8.5 12.7 25.1 16.3 12.9 22.7 26.1 11.9 7.7 21.4 18.4 12.9 15.6 4.8 18.9 10.1 19.1 4.7 17.1 14.3 14.9 4.3 26.7 16.2 21.4 6.3

UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG UGU UGG UGA UGG CGU CGC CGA CGG AGU AGC ACA AGG GGU GGC GGA GGG

Tyr Tyr STOP STOP His His Gln Gln Asn Asn Lys Lys Asp Asp Glu Glu Cys Cys STOP Trp Arg Arg Arg Arg Ser Ser Arg Arg Gly Gly Gly Gly

16.5 12.3 2.0 0.3 12.8 9.4 14.7 29.4 19.2 21.7 34.0 11.0 32.8 19.2 39.3 18.7 5.2 6.4 1.1 15.3 20.2 20.8 3.8 6.2 9.4 16.0 2.9 1.8 24.2 28.1 8.9 11.8

36.6 8.4 1.2 1.2 22.8 3.6 39.6 12.6 46.2 19.2 24.0 12.0 42.6 12.0 51.6 22.2 6.0 6.6 0.0 9.6 15.6 2.4 10.8 1.2 21.6 6.6 16.2 3.0 28.2 8.4 21.0 6.6

20.0 18.1 0.1 0.9 6.6 11.8 8.8 21.0 24.3 24.3 22.2 36.0 32.1 28.4 26.2 27.2 5.0 13.3 1.9 10.6 9.5 5.7 5.3 5.0 6.9 19.6 9.7 12.6 20.4 18.9 18.3 14.5

15.7 14.9 0.9 0.5 14.0 11.6 20.5 16.2 22.4 22.8 26.9 35.9 32.4 20.4 33.2 33.2 8.1 8.0 1.0 13.0 6.6 6.2 4.1 3.1 12.6 11.3 14.8 13.3 20.9 13.4 22.3 13.0

Values indicate frequency per thousand. (http://www.kazusa.or.jp/codon/).

346


Agrobacterium transformation Transformation using biolistics

Coat gold particles with DNA and apply to plastic disc

plant cell

Ti plasmid T-DNA

PSD-1000/He particle delivery system

Gas pressure causes the disc to pop and the gold particles to impact the plant cells. DNA from the gold particles incorporated into the plant genome. The cells are regenerated into plants containing the new gene(s).

Agrobacterium tumefaciens insertion into chromosome

DNA disc and plant cell plate placed In biolistics device

Protoplast (no wall)

Plant cell with wall

+ Cellulases, Glycosidases

Protoplast transformation Shock in the presence of DNA

Transformed plant

Transformed cell DNA enters cell

Figure 4 Three typical plant transformation methods.

Process

Time Inoculation

Liquid stage

1-3 hours

2-3 days

Semi-solid stage

Transgenic plants could be identified at the end of first round

rooting

Induction

18 days

Regeneration

3 weeks

First round selection

3 weeks

Second round slection

3 weeks

Soil or vernalisation

Figure 5 Example of a plant transformation procedure – wheat. Reproduced from Huw DJ, Doherty A, and Wu H (2005) Review of methodologies and a protocol for the Agrobacterium mediated transformation of wheat. Plant Methods 1: 5.

GENETICS OF GRAINS | Development of Genetically Modified Grains successfully into the crop. The introduced gene(s) may be harmful to the plant cell, and no transformants can be regenerated. The introduced trait may not function to the desired efficacy. The economics of the crop or cropping practices could not justify the expense of demonstrating safety, or the market is not interested in the trait. However, some ideas do come to fruition (proof of concept is demonstrated), and the best commercializable event needs to be identified. This is the next step in the development process. The commercializable event is often referred to as the ‘elite’ event. Once events with the expected agronomic characteristics are regenerated, efficacy is the first criterion to be considered when selecting an elite event. In other words, do the plants derived from the original plant perform to the specifications desired? If it is a herbicide-tolerant product, does it provide tolerance at the right level, in multiple germplasm backgrounds, and in different environments with no impact on the yield? If it is an insect-resistant trait, does it provide the desired degree of protection in the presence of the pest with no negative impact on the yield in the absence of pest pressure and in multiple germplasm backgrounds and environments? The next consideration are the molecular characteristics. Some regulatory authorities are very interested in the insertion site within the native genome and have placed limitations on what is considered acceptable. The molecular characterization includes a determination of copy number, number of insertion sites, gene cassette integrity, stability of the insert, locus characteristics (such as deletions, duplications, and rearrangements that may occur), insertion site, potential for chimeric gene expression, and extraneous DNA including vector backbone. If the event has resulted in a crop that successfully fulfills product specifications, has the appropriate agronomic performance characteristics and molecular characteristics, that event will be advanced in the commercial pipeline. Once the elite event is identified, the event-dependent portion of the safety assessment process commences. The overall safety assessment of a biotech crop actually starts very early in the development process (Figure 2) and is a multipronged approach considering the safety of the gene, protein, and crop and impact on the environment. As soon as the gene sequence is known, homology searches are conducted using bioinformatics approaches to compare the deduced amino acid sequence to known allergens and toxins, using various databases such as AllergenOnline and NCBI. Once proof of concept has been demonstrated for the gene of interest, a preliminary digestive fate study is conducted to determine the fate of the protein encoded by this gene in simulated gastric fluid. This test is used as an indication of potential allergenicity. Proteins per se do not typically represent a hazard to humans as they are essential components of our diet. Nevertheless, there are some examples of proteins that are toxic (i.e., bacterial toxins such as botulinum or plant-produced ricin) or antinutritive (lectins or protease inhibitors). Protein safety is evaluated following a two-tiered approach. The first tier requires little protein and includes an evaluation of the history of safe use, determination of expression levels, bioinformatics analysis, mode of action, source of gene, and stability. The second tier that should be undertaken only if there is an indication that it would be appropriate from the first tier results includes toxicology studies such as a single limit (acute) dose using mice and evaluation after 14 days or a

347

repeat dose (daily for 28 days) followed by evaluation. The reality is that regulatory authorities in many regions require these tests, regardless of the outcome of the tier one studies. Foods produced from biotech crops are the most highly studied foods consumed, and the registration dossiers are scrutinized by regulatory agencies around the world. Regardless of the region of the world, most regulatory authorities base their safety assessments on the process recommended by the Codex Alimentarius. This process requires studies on the safety of the newly expressed protein, molecular characterization of the insert, impact of the insert on plant performance and composition, environmental impact, and wholesomeness of the crop. The assessment includes phenotypic and agronomic comparisons between the new plant variety and a genetically near comparator that is already on the market and considered as safe. Approval is given only when the biotech product is determined to be as safe as conventional crops. Once declared to be as safe as conventional crops, there is no need to label the food products because they are indistinguishable from all consumption perspectives to those produced through conventional breeding technologies. However, the enormous price tag associated with the global regulatory requirements makes it economically unattractive to develop products for many small-acreage crops. A notable exception would be the virus-resistant papaya developed by researchers at Cornell University (REF http://www.apsnet.org/ publications/apsnetfeatures/Documents/2004/HawaiianRainbow.pdf). Without this product, the papaya industry in Hawaii may well have vanished. The acceptance rate of agricultural biotechnology has been phenomenal (Figure 6(a) and 6(b)) because of the value it brings to the grower. As of 2013, 27 different countries grow biotech crops. Eighteen countries have greater than 50 000 acres planted with biotech crops. Both small and large growers have adapted the technology. No discussion of the development of a biotech product would be complete without including the development of ‘stacked’ products. There are three different kinds of ‘stacked’ biotech products (Figure 7). Molecular stacks are evaluated as a single event as described in the preceding text. Retransformation stacks are evaluated as single events as well. Regulations around breeding stacks, however, vary depending on the geography. Canada asks for a notification that such a stack is being marketed. The USEPA requires addressing synergy questions if two genes encoding pesticidal proteins are combined by stacking prior to approval. The European Union, on the other hand, requires complete evaluation of each single parent event prior to conducting a similar evaluation of the stacked product. This difference contributes to asynchronous approvals that can result in trade disruptions when a product is legally planted in one country but not approved for grain import into another. In summary, it takes much effort and careful scrutiny to produce an elite event that can be successfully commercialized. Plant performance and efficacy together with characterization of the insertion are used to identify the elite event. The safety assessment presented in the dossier to regulatory agencies includes the molecular characterization and confirmation of plant performance within the many studies. These studies are reviewed and approved by regulatory agencies around the world.

348


Percent acres planted

100 80 Corn

60

Cotton 40

Soybean

20

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1995

0

US stack percentage 90

Percent acres planted

80 70 60 50 Corn

40

Cotton

30 20 10

14

20

13 20

12

20

11 20

10

09

20

07

08

20

20

20

06

20

05

20

04

20

20

03

02

20

01

20

20

00

0

Figure 6 Adoption rate of GM products – the United States, percent of acres planted. http://www.ers.usda.gov/data-products/adoption-of-geneticallyengineered-crops-in-the-us.aspx.

Gene A A

Gene “A-B”

Gene A A

“A-B” Approved

Gene B

Gene B B

Approved

Approved Conventional breeding

A, B AxB Molecular

Re-Transformation

Breeding

Inserted DNA contains two or more genes/traits

Approved event transformed with additional trait(s)

Two or more events combined by breeding

Figure 7 Three ways to stack genes into biotech products.


349


Further Reading

• •

CAC/GL 45-2003 Codex Alimentarius – Guideline for the Conduct of Food Safety Assessment of Foods Derived from Recombinant-DNA Plants. Delaney B, Astwood JD, Cunny H, et al. (2008) Evaluation of protein safety in the context of agricultural biotechnology. Food and Chemical Toxicology 46: S71–S97. Duffy M (2014) Estimated costs of crop production in Iowa – 2014. Ag Decision Maker. File AI-20. http://www.extension.iastate.edu/agdm/crops/pdf/a1-20.pdf. Goodman RE, Vieths S, Sampson HA, et al. (2008) Allergenicity assessment of genetically modified crops – What makes sense? Nature Biotechnology 26: 73–81. Huw DJ, Doherty A, and Wu H (2005) Review of methodologies and a protocol for the Agrobacterium mediated transformation of wheat. Plant Methods 1: 5. James C (2011) Global status of commercialized biotech/GM crops: 2011. ISAAA Brief No. 43. Ithaca, NY: ISAAA. http://www.isaaa.org/resources/publications/briefs/43/ default.asp. Ladics GS, Cressman RF, Herouet-Guicheney C, et al. (2011) Bioinformatics and the allergy assessment of agricultural biotechnology products: Industry practices and recommendations. Regulatory Toxicology and Pharmacology 60: 46–53. McDougall P (2011) The cost and time involved in the discovery, development and authorization of a new plant biotechnology derived trait. CropLife International. www.croplife.org/PhillipsMcDougallStudy. Privalle LS, Chen J, Clapper G, Hunst P, Spiegelhalter F, and Zhong CX (2012) Development of an agricultural biotechnology crop product: Testing from discovery to commercialization. Journal of Agricultural and Food Chemistry 60: 10179–10187. Que Q, Elumalai S, Li X, et al. (2014) Maize transformation technology development for commercial event generation. Frontiers in Plant Science 5(379): 1–19. Thomas K, Aalbers M, Bannon GA, et al. (2004) A multi-laboratory evaluation of a common in vitro pepsin digestion assay protocol used in assessing the safety of novel proteins. Regulatory Toxicology and Pharmacology 39: 87–98.

•

Why are there no commercialized wheat products to date? What are the challenges associated with working with crops containing multiple genomes or are not hybrid? What kind of new product would be welcomed into the market?


• •

Compare the regulation of biotech products to mycotoxins – do they have similar safety issues? Compare the development of biotech products with those produced through conventional breeding.

See also: Bioactives and Toxins: Mycotoxins; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Food Grains: Intolerance, Allergy and Diseases: Cereal Allergens; Genetics of Grains: Detection of Genetically Modified Grains; Genome Mapping; Genomics of Food Grains; Maize: Genetics; Maize: Other Maize Mutants; Maize: Quality Protein Maize; Rice: Genetics.

Detection of Genetically Modified Grains RD Shillito, Bayer CropScience, Durham, NC, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

• • • • •

The only major grains that presently contain genetically modified (GM) traits are maize (called corn in North America), soybean, cotton, and canola (known as oilseed rape in Europe). Since their introduction in the mid-1990s, GM grains have been regulated in inconsistent ways in various trading blocks and countries; different levels of GM content may require labeling in different jurisdictions. Grain is traded as a fungible product by contract between a buyer and a seller. Testing will normally only occur when the buyer requires grain that is not stated to be GM but that may potentially have a low content of GM grains. Testing can occur at many points in the supply chain. Tests can be divided into two types, based on the target molecule: – DNA-based methods such as polymerase chain reaction (PCR) – based on the structure of the DNA – Protein-based methods – based on the protein expressed in the grain Production of grain with low GM content in a country with a high-percentage GM crop requires a dedicated supply chain. Obtaining a representative sample of the grain is a key step in testing. Obtaining and preparing the grain sample are resourceintensive and not amenable to improvement. Use of the same validated method by seller and buyer reduces the chances of trade disruption, as does the use of competent laboratories. The technology for performing the test for GM grain has been evolving and continues to evolve.

Learning Objective

•

To achieve understanding of the approaches used to detect genetically modified grains and the future directions of detection methods.

Introduction A genetically modified (GM) grain is presently understood to be a product developed through modern biotechnology by insertion of a specific gene sequence into the plant DNA. Such products have been described in the literature and by governments and regulatory agencies in various ways – as GM, genetically engineered (GE), GM organism (GMO), transgenic, biotechnology-derived, and recombinant. For the purpose of this article, the term ‘GM’ grain will be used for its simplicity and broad recognition.

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Since their introduction in the mid-1990s, GM grains have been regulated in differing ways in various trading blocks and countries. Many jurisdictions require labeling of foods that contain a level of GM materials above a nominated threshold. These regulatory environments and the thresholds imposed are not consistent across the globe and continue to evolve. Labeling for the presence of GM events (and stacks) in food is required in many jurisdictions. Food producers and retailers may desire not to have to label their product as containing GM grain. This leads to the testing of grains to ensure that the GM content of food (and in some cases feed) subsequently derived from grain is below the threshold that would require labeling. Testing is performed by screening for macromolecules indicating the presence of genetic modification. It is carried out by traders and their customers for the grain and also by regulatory authorities that are monitoring incoming shipments for unapproved GM events. Testing may occur at several levels: the seed that a farmer plants, the grain delivered to the elevator, the grain that passes through the supply chain, and the grain with only a low level of genetic modification required by a customer. It may be tested before export, at receipt in the market buying the grain, and even at subsequent distribution points. The level of GM content that may require labeling differs between jurisdictions: 0.9% (based on weight by weight but measured by DNA content) in the European Union, 5% (based on % of the grains) in Japan, and somewhere between these two such as 3%. This labeling is not on the basis of safety, as the grain is approved in these jurisdictions for consumption at 100%; it is merely a food labeling requirement. An additional state of affairs occurs for GM events that have not yet been approved for consumption in a particular country and are therefore not allowed to be present in grain sent to this country. Any presence of the specific nonapproved event in a grain shipment is not acceptable, and the shipment will be rejected. This may occur when an event is approved for cultivation and grown in an exporting country, but not yet approved in a country that imports grain from that country. One example of this was MIR162, an event that was not approved for import into China until late 2014 but had been commercially grown in the United States for some years. The major grains that are presently grown as GM grains are maize (called corn in North America), soybean, cotton, and canola (and oilseed rape in other areas). So far, crops of GM wheat and other grains have not been commercially grown, although all have been transformed in the laboratory, and many have undergone research field trials. This article will cover techniques used for detection of GM grains in the major crops in which the technology has been applied, though the principles are applicable to other crops as well. The examples given are applicable for the detection of GM grains in canola, soybeans, and maize (as these are the major GM crops that are commercially traded internationally in large


http://dx.doi.org/10.1016/B978-0-12-394437-5.00219-9

GENETICS OF GRAINS | Detection of Genetically Modified Grains quantities). Cotton grain is not extensively traded on the international market as it has a low value compared to the cost of transport, but the same principles of testing can be applied. As a rule of thumb, a majority of grain is not tested for the presence of GM grain, as a large amount is used as commodity grain in the country of production. In addition, much of the soy and maize grain that is exported from these countries is exported for use in animal feed and may not be extensively tested, except in the case where it is suspected, an unapproved event may be present. Thus, testing of lots for the presence of GM grain is an exception, rather than the rule. In addition, testing occurs for purposes of making sure that seed lots contain the transgenic material to the level that is specified on the label, such as >98% purity (what is called positive testing). This is not the topic or within the scope of this article.

The Role of Testing Traders have been testing grain for as long as grain has been a food. When one person or organization (farmer or grain merchant) is selling a grain to a second, they will agree on a price based on a number of factors, including the grain quality. In certain grains such as wheat, a key factor may be the expected milling quality of the grain and/or protein content. The tests performed in order to confirm that grain meets the buyer’s expectations range from relatively simple tests such as for odor (e.g., a smell test is part of the battery of tests performed on all maize samples leaving the United States) to visual tests such as examination for foreign seeds or stones; relatively quick equipment-based tests for moisture, protein, and oil quality; and tests using complicated machinery and sophisticated laboratories. The buyer may specify the maximum (or minimum in the case of value-added products) level of a particular GM event in the grain to be delivered. As stated previously, testing can occur at many points in the supply chain. The tests performed will be influenced by the situation. For example, tests performed at the delivery of grain to an elevator by the farmer and at the point of export must be capable of being performed in minutes, as the bulk grain is awaiting transfer either out of a truck or into a ship or another vessel. If a test taking more than a few minutes is required, then the sample for the test must be taken long before the result is needed, so that the analysis can be performed while the grain is in transit. Once a ship is loaded, it is not feasible (or economic) to unload it in order to remove materials that have already been loaded that do not meet the delivery contract. Thus, testing for detection of GM grains usually occurs in the transport chain well before the shipment is delivered to the customer. The result of testing then confirms that the material conforms to the intended use or, should GM grains be detected at above the desired threshold, is diverted to a market that will accept the material on the basis of that GM content.

Production of Low-Percentage GM Grain The majority of maize, soybean, or canola in the major grainexporting countries is derived from GM grains. Almost all of

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this grain is treated as fungible in that any source of grain can be used to meet a contract. Should the buyer require a low-percentage GM grain, they will enter into a contract with the supplier as much as 2 years before the delivery date. This long time frame is necessary as the supplier will generally need to control the entire product chain from the original seed grown to the final delivery to the buyer and segregate the grain from the commodity material. First, they must produce or obtain seed that has been certified (and probably tested) to contain much less than the threshold level of genetic modification desired by the buyer. This difference is to allow for any small increase in the presence of such material due to adventitious contamination, which is almost unavoidable in such identity-preserved product chains. The supplier then must contract with a farmer to grow the seed and produce the crop in a way that will limit the possibility of ingress of seed or pollen that contains a genetic modification from neighboring farms. The grain is then delivered to dedicated collection points such as elevators using dedicated trucks and passes through a segregated identity-preserved transport system, which may consist of trucks, train cars, barges, and eventually oceangoing vessels. In certain cases, the grain may be delivered in standard shipping containers. This segregation of grain incurs significant cost, from production of the seed to the dedicated specialty supply chain that is needed to deliver it to the customer. Contamination of the grain at any point by grain from the commodity grain supply chain will reduce or eliminate its added value as low GM grain.

Performing the Test Obtaining a Sample Both buyers and sellers will want to know that the grain meets the specified contract. As with any analytic method, obtaining a proper representative sample is a key step; an analytic result is only as good as the sample on which it is performed. It is clearly impractical to test every grain in a lot, especially as the testing for GM grain is destructive, and thus, a sample of the grain that is representative of the grain lot must be examined. There are various ways in which a sample can be obtained, and these are well known and part of established grain sampling practices. Experience has shown that the same sampling procedures as used for other tests can be used to obtain a sample suitable for determining the low-level concentration of GM grain. A truck that delivers grain will be sampled at various locations in the load by probing the load, usually using a mechanical probe system. Later, in the supply chain, the grain will be sampled as it moves from one storage or transport location to another. Sampling of moving grain is done using standard procedures and apparatus that are also used to sample the grain for grading the quality of the grain – that is, whether it meets the grade and does not contain levels of toxins and pesticides above acceptable levels. The same sample can be split and used for these various purposes. More detailed descriptions of how to obtain a representative sample are available. For further consideration of sampling

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strategies, see Freese et al. and the USDA grain inspection handbook. The size of the sample that is processed to carry out the test must be chosen so that the limit of detection is appropriate for the test used. If a test can only detect one grain in a thousand, it would be inappropriate to grind 3000 grains and test the resulting flour. The analyst would instead have to test three 1000 grain test samples. Therefore, it is important that both the sampler and the analyst understand the limit of detection capabilities and limit of quantification of the tests to be used. Once the grain is processed to partial products such as flour and oils, then sampling of the bulk materials can be done. The issue at this point is that the limit of detection (lowest concentration that can be detected) will depend only on the test – the ability to define the number of grains that contributes to the sample can no longer be controlled. Thus, if it is desired to have materials that have low or undetectable levels of genetic modification, then testing of the grain, rather than the final processed food or feed material, is the most efficient and effective approach. The sample to be tested may be subsampled to provide the laboratory sample that is to be tested. In order to perform the test, the material will need to be ground to extract the protein or DNA, in either water or in most cases a buffer. This must be performed in a way that precludes contamination of the sample with other materials, to prevent false results. Sample preparation for the test is not covered in this article, and information is test-specific and can be referenced to the test procedure. Preparation of the sample for testing takes in most cases more resources than the testing step itself.

Supply Chain Testing

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Figure 1 The value of material increases as it moves through the supply chain ($ to $$$$). The type of tests applied also change (d, DNA-based test; p, protein-based test).

proteins may denature or degrade and no longer be recognized by the antibodies that make up the test. As products become more processed, then the preferred test changes to a PCR approach. Information about methods for DNA testing is available for all of the commercially grown grain events from the producers of the events themselves (via the CropLife International website) and can be licensed for most uses. This website also lists the protein-based tests that are available to test for the presence of these products. Some countries/trading blocks such as the European Union also publish methods information that is for use only in meeting their regulatory requirements and does not offer a license for other uses.

Choice of Type of Test and Method Two main analytic approaches are used to confirm that the level of genetic modification in a grain lot does not exceed the requested threshold. These are based on detection of the introduced DNA or the protein(s) expressed in the GM grain. Many jurisdictions insist on DNA-based analyses, specifically polymerase chain reaction (PCR), but some have used protein-based tests to make sure that a lot meets regulatory requirements. Testing a lot using protein-based methods can offer significant cost savings. DNA-based tests are almost exclusively performed in a controlled laboratory environment. Thus, DNA-based detection of genetic modification in grain is relatively expensive, and a single sample can typically cost $200–400 USD to test at a service laboratory, not including the cost of sampling the grain and shipping the sample to the test facility. In addition, a DNA-based (PCR) test typically takes at least 12 h and more typically 2 days to complete. Testing by detection of the lateral flow strip (LFS) protein test is relatively inexpensive (a few US dollars per test), can be performed using simple equipment, and takes less than half an hour. As materials move though the product chain, their value increases and the type of test that can and will be performed changes (Figure 1). Raw materials can be tested using proteinbased tests. Such tests are not able to be used on materials that have been processed or exposed to heat and/or moisture, as the

Qualitative Testing A qualitative test produces a negative result if no target GM seeds are in the sample tested and a positive result if one or more of the target seeds are in the sample. An example of a qualitative test is an LFS although some of these are now semiquantitative. In this approach, a subsampling strategy is often used, in which a number of subsamples are tested. The number of subsamples that give a negative result allows the level of GM grain in the initial lot to be estimated. For example, if a contract is for grain containing less than 0.5% genetic modification, then a sample of 1200 grains may be split into three samples and each one tested with a test that is capable of finding a single GM grain in 400. Should two of three subsamples give a negative result, then it is 95% certain that the lot contains less than 0.5% of the grain with that characteristic. Such a test is appropriate when some low level of the GM seed is acceptable in a lot; the risks of rejecting good lots can be reduced by this approach as it balances the risk to a buyer and supplier of the grain (be it a farmer or a shipper). A test that does not tolerate any positive pools imposes a high risk on the supplier side of the contract and can lead to the rejection of good lots that meet the threshold. Where an event is not allowed in the grain at all (i.e., has not been approved in the receiving country), then a test that

GENETICS OF GRAINS | Detection of Genetically Modified Grains does not allow any positive result is appropriate. In this case, 3 pools of 200 seeds would be necessary if the threshold was 0.5%, or the test can be performed on a single sample of 600 grains, should the test be sensitive enough to find that one seed in 600. In general, thresholds for unapproved events are in the 0.1% range, so larger sample sizes (e.g., 3000 grains) are required for 95% certainty and are more commonly carried out using PCR. Note that these determinations are statistical – it is not possible to completely guarantee that a lot does not contain a level above the threshold or in the case of an unapproved event any of that event. To do so would require testing every grain, which is impracticable as the testing is destructive. Higher levels of certainty can be obtained using larger samples, which increases the cost of sampling and testing. In addition, as the required threshold decreases, then the sample size and/or the sensitivity of the test required increases significantly. A threshold of 0.1% would require the testing of 12 pools of 400 grains, with the lot being accepted only if at least 11 of the pools gave a negative result. Alternatively, a sample of 3000 seeds can be tested and returns a negative result. Qualitative testing is most often carried out using an LFS and at country elevators, but qualitative PCR methods are also employed to test for unapproved events in shipments further along the transportation chain (barge/train).

Quantitative Testing With quantitative testing, the acceptance limit can be any nonnegative value. The most common quantitative testing approach is PCR, usually real-time quantitative PCR (RTqPCR). The mechanics of RT-qPCR are described in the Box 2. As with qualitative testing, quantitative results also have a degree of certainty. The uncertainty of a result (i.e., whether the concentration of the lot is below the threshold) depends on the uncertainty of the PCR result (which can be between 20% and 30%) and the uncertainty due to sampling of the lot. A typical test would use 3000 seeds for determination of a concentration in the 0.5–1% range, and quantitative results are not generally possible nor reported by testing laboratories for samples with less than 0.1% of GM grain. LFSs have also been developed that give an estimate of the quantity of an event in a lot. For some events, this can be quite accurate, while for others, it is less so, as it depends on the amount of expression of the protein that is detected in the grain. The expression of the protein in grain from any particular event can vary from location to location, which can introduce some uncertainty into the measurements.

Screening When testing for the presence of GM events, especially by PCR, a two-step process is often employed. The first step involves screening for the detectable presence of GM crop materials and the second, for the specific events that may be present and to discriminate between those that are allowed and not allowed.

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Protein-based methods tend by default to be screening methods. This is so because a particular protein (e.g., Cry1Ab) may be expressed in more than one event. Only if a protein is specific to one event can it be considered an event-specific test. Screening is most often carried out by detection of DNA elements that are common in multiple events. In the early years of GM crops, the 35S promoter and 3’nos elements were commonly used. The 35S sequence can be used to drive the expression of genes throughout the plant, and the 3’nos sequence used to ensure correct termination of the DNA transcript. Thus, screening of materials for the presence of these two common elements allowed detection of most if not all events. In addition, the sequences of herbicide tolerance genes that are used in multiple events can be used. With the advent of new promoter and other elements, the usefulness of these screens is reduced, although the 35S sequence is still commonly used to detect nine or more events in maize. One caveat is that the 35S sequence originates from a plant virus and is therefore common in certain species such as brassicas (including canola) that can also be present adventitiously either in grain or in complex foods such as soups. Therefore, caution in interpreting the results of a test for the 35S sequence is particularly important.

Threshold Testing Determining whether grain meets a threshold may be done by using a quantitative test of either a single sample or a number of subsamples. In all cases, these determinations have a degree of uncertainty, and the normal approach is to make sure that the lot has at least a 95% certainty of being below the required threshold. In most cases, the threshold will be set below the regulatory or final contract threshold to ensure that the actual level always meets the regulatory limits. Each subsample can be analyzed using a qualitative test or a quantitative test.

Analysis Based on the Protein Expressed in the GM Grain Methods that detect proteins in GM grain are based on their recognition by antibodies (Box 1). Just as for any other protein, antibodies can be raised to specifically detect a particular protein, for example, a Bt protein. So far, most genetic modifications that are intended to confer herbicide tolerance or insect resistance to plants involve expression of one or more specific proteins. These proteins are usually present in the grain in significant amounts and can be used to detect the presence of such GM grain. Commercial immunoassays are available for most of the GM grain crops on the market today. Enzyme-linked immunosorbent assay (ELISA) and LFS are the most commonly used test formats. An LFS recognizes a specific protein in the grain, which is characteristic of one or more GM events, but cannot differentiate between multiple events that contain the same (or similar) protein(s). LFSs are designed for relatively quick qualitative yes/no testing. ELISA can be used as either a qualitative or a quantitative assay. The predominant use of protein-based tests in grain is as an LFS. These commercial products are termed alternatively as Lateral Flow Device, ImmunoStrip™, or QuickStix™ according to the manufacturer’s preference and branding.

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Box 1

Analysis based on DNA depends in most cases on using the PCR technique (Box 2), although other DNA analysis methods such as isothermal DNA amplification are becoming available, PCR is able to amplify a small portion of the DNA present in very low concentrations to make it visible, physically either via staining with a fluorophore or via the generation of a fluorescent signal. PCR selectively amplifies specific DNA sequences and can be used to detect and discriminate between traits and between events. End-point PCR detection methods are used for qualitative screening. RT-qPCR can be used for quantitative detection. As described by Lipp et al., PCR testing is used for specific purposes in the grain handling/processing industry:

Enzyme to produce color

substrate produces color

Cry 1Ac Antibody conjugate

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Antibody to Cry 1Ac

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Figure 3 The ELISA test consists of a first antibody adsorbed on a surface, which recognizes the target protein (Cry1Ac in this case), and a second antibody that recognizes the target protein. The color is typically developed by an enzyme conjugated to the second antibody.

NEGATIVE

Analysis Based on the DNA in the GM Grain

Figure 2 A typical multiwell plate showing the result of an ELISA. The samples that contain target protein are indicated by the development of a yellow color from the action of the conjugated enzyme with a chromogenic substrate.

POSITIVE

Immunoassays employ antibodies as detecting reagents. Antibodies are glycoproteins produced by specific cells of the immune systems of animals in response to stimulation by a foreign substance. The foreign substance that elicits the production of a specific antibody is referred to as an antigen. The attribute of an antibody that makes it useful as a reagent in a diagnostic kit is its capacity to bind specifically and with high affinity to the antigen that elicited its production. An ELISA consists of a first antibody that is absorbed to a surface of a container (usually a multiwell dish (Figure 2)). The antibody is able to capture the target protein from an extract of the grain. The rest of the proteins and other components of the extract are washed off, and a solution containing the second antibody is added. This second antibody also recognizes a protein. The second antibody is attached to either a colored or fluorescent compound or an enzyme that will produce such a compound, which provides a detectable signal or is detected using a third antibody that provides the detection process (Figure 3). Other variations of this method also exist, but the goal is the same, to be able to measure the presence and, when used quantitatively, the amount of the target protein. An LFS is essentially a solid-phase ELISA in which the target protein is first recognized by the antibody linked to the detection system and then captured by a second antibody at a specific position in the strip. One of the most common consumer applications of this technology is a pregnancy test. An extract of the grain is applied to the bottom of the strip in a vertical position (Figure 4) and allowed to absorb into the sample pad. A positive result is indicated by two lines and a negative by just the control line. If the strip has been compromised, then the upper control line will not be present and the test is considered invalid. Figure 5(a) and 5(b) demonstrates how the LFS works: the target protein (if present) is recognized by an antibody in the antibody conjugate pad, which binds to it (Figure 5(a)). This first antibody is attached to a visual marker, usually colloidal gold. The liquid is sucked up the strip and carries the extract with it. As it passes over the position of the test line, the target protein is captured by the antibodies. The target protein is also carrying the second antibody that is attached to the colloidal gold. Thus, a line of colloidal gold develops at the site of the capture antibody, only if the target protein is present in the sample. The strip also contains a second line. This line captures the remaining antibody (with the gold) and forms a control line. The control line is present to show that the strip is performing correctly, as the antibodies are proteins that are easily damaged by excessive heat, moisture, or solvents and have a limited shelf life. Should the sample not contain the protein that is being tested for, then the strip will only develop the control line (Figure 5(b)).

Figure 4 Typical lateral flow strips (LFSs) showing positive and negative test results and a strip that has been compromised so that it gives no result.


Positive Sample

Labeled specific antibodies

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Antigen complexed to conjugated antibody

Wicking Pad Sample Pad

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Nitrocellulose Membrane Backing Material

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Unbound conjugated antibody with anticonjugate antibody

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Negative Sample No Target Antigen

Labeled specific antibodies

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Figure 5 (a) Development of lines on an LFS in response to a positive sample. (b) Development of lines on an LFS in response to a negative sample.

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Box 2 PCR technology was developed in 1983 by Kary Mullis. It is used to amplify small pieces of DNA to generate thousands to billions of copies of specific DNA sequences. Two main approaches predominate – gel-based PCR and RTqPCR. The identification and amplification mechanism is the same in both cases, and RT-qPCR relies on the release of a fluorescent compound and its measurement by a specific machine at every PCR cycle. PCR can be used to detect genetic traits and discriminate between GM events in grain. Each GM trait or event is coded for by a specific DNA sequence inserted in the plant genome. Selective amplification of the target DNA sequence is accomplished using DNA primers that are specific to that sequence. A sample of the DNA to be tested is added to a tube containing buffers, nucleotides, the specific primers, and the enzyme that is capable of synthesizing copies of the DNA (Taq enzyme). The mixture is subjected to repeated heating and cooling cycles – 30–40 – and exponential amplification of a PCR product ensues. The PCR product for each set of primers and DNA target are of a known size. In gelbased PCR, the DNA that is negatively charged can be separated based on size using an agarose gel. Smaller fragments move faster than larger fragments, thus giving a separation based on the size of the fragment. The DNA is visualized using a compound that binds to the DNA (interchelator) that fluoresces in UV light and can thus be used to visualize the bands. The presence of a band of the expected size indicates that the target DNA is almost certainly present. Use of appropriate positive and negative controls and, if needed, sequencing of the fragment produced increase the accuracy of the method. Thirty-five to forty cycles of heating and cooling are typically required to generate a usable signal. In real-time PCR, a third element is introduced. This is a short DNA sequence primer to which are attached a fluorescent reporter molecule and a quencher. In each PCR cycle, the reporter and quencher are released, and the fluorescent reporter, as it is no longer quenched, is able to be detected and measured. After each elongation cycle, the amount of this molecule is measured, thus leading to a measure of the amount of the target DNA sequence that is present in the sample. As in gel-based PCR, between 35 and 40 cycles are typically required to generate meaningful data. In order to quantify the amount of a target DNA in a sample, the number of cycles required to bring the signal above the instrument baseline is recorded. This cycle where the signal crosses the threshold is termed the Ct value. A higher starting concentration of the DNA target means fewer PCR cycles are required to cross the threshold, and thus, the concentration of the target can be deduced by comparison to a standard curve. RTPCR can also be used in an end-point mode, where the signal is only read at the end of the reaction, and thus gives a plus/minus result as provided by gel-based PCR. There is a large amount of information on PCR available on the Internet, including videos demonstrating how PCR works (e.g., https://www.youtube. com/watch?v¼iQsu3Kz9NYo).

PCR testing for unapproved events: An event may be approved for use in the country of production, but not yet approved for use in an importing country. In these instances, the importing country often requires that the grain shipment be tested for the presence of specific GM events to ensure that it does not contain unapproved events. Such testing may rely on qualitative PCR or a negative result in a RT-qPCR because in most cases, there is no tolerance threshold. PCR testing for GM content: Most countries that have adopted mandatory labeling rules for food or feed have set labeling tolerances for the presence of GM material in grain products or the final foods based on a percent GM (weight-to-weight or % of DNA) content. In order to avoid labeling, the grain used typically comes from an identity preservation program

and is certified to contain GM grains only at a level below the desired threshold. PCR testing for ‘non-GM’ labeling: In some countries (such as the United States), food manufacturers and retailers wish to use positive labeling for products that are described as not being produced using GM products. In most cases, the use of positive labeling requires that the grain and grain products originate from an identity preservation program and test negative or at least below a certain threshold for GM DNA. Detection of the presence of GM grains based on the presence of the DNA is often used to make sure that consignments comply with contract conditions and for compliance to regulatory requirements. PCR is the specified regulatory method in many but not all jurisdictions.

Validation of a Test and Proficiency Testing For practical applications like grain testing, it is important that the test performed gives the same result when performed in different locations, for example, at export and import. This is called transferability. The test must also be able to work when there are small variations in reaction conditions, and use of different PCR machines (robustness), as this is what will be encountered in the real world. In addition, laboratories that carry out routine testing will usually be operating under a quality assurance system such as ISO 17025. Good laboratory practices and quality standards such as ISO 17025 require that a laboratory routinely test unknown samples and compare them against the true value for those samples. The latter process is called proficiency testing.

Validation Validation of a test is done by performing the test at multiple laboratories under the same conditions. For many methods used for food analysis, this is carried out under the control of standardization organizations (SDOs) such as the AACCI, AOCS, and AOAC, and the methods are published as ‘approved methods.’ This validation is carried out to standard ISO 5725, also known as the ‘harmonized protocol.’ This can take up to 2 years to complete and requires the participation of a large number (>12, typically 18–20) of laboratories. A large number of GM events are being produced, for each of which an event-specific method is required. The sheer number of these methods makes it impractical to carry out validation via the standard protocols through SDOs. Hence, validations are carried out internally by the developers, followed by external validations on a limited scale. Then, national and regional regulatory authorities such as the European Union typically validate these methods further. Laboratories and other organizations that have their own internal proprietary methods such as screening methods validate them internally.

Proficiency Testing Once a method is shown to work properly, it is put into use by testing laboratories. Each laboratory that is testing grain in trade should be able to show that it can perform testing in a way that gives consistent results with other laboratories

GENETICS OF GRAINS | Detection of Genetically Modified Grains performing the same measurement. To do so, they participate in proficiency programs. Organizers of proficiency programs supply a set of materials containing amounts of the GM grain that are the same for each participant, who at the time of analysis does not know the concentration of the GM grain in the sample(s). The participants return their results to the organizer who compares them against the intended values for the material sent out and with all the other participants and then provides the results of the comparison to each participant. In this way, a participating laboratory can compare its performance and measurements against those of the laboratory community and correct any bias in their measurements. The proficiency testing process is common for other analytes in grain. The two most important globally available GM grain proficiency programs are those offered for maize and soy grain by the US Department of Agriculture (http://www. gipsa.usda.gov/fgis/proficiencyprogram.aspx) and for seed by the International Seed Testing Organization (ISTA; www.seedtest.org).

Interpretation and Reporting of Results Most testing results are clear and unambiguous – a GM grain is found to be present or not present, and if an event-specific test is applied, then the event is identified. However, it is important to understand that in some cases results can be ambiguous, and in all cases, care must be taken in interpreting results, especially when the results have regulatory significance and may result in economic consequences. In protein-based testing, it must be considered that a particular protein, while present in grain, may be also present as a consequence of the adventitious presence of grain of another species. This is particularly important to consider in the case of maize, soybean, and cotton, which have a significant number of GM proteins that may be present in all three species. Proteinbased tests, such as an LFS, often rely on visual identification of the result, which may be subjective. Testing should therefore be performed by an experienced operator and in good light and using the procedure specified by the manufacturer. The use of readers to measure the density of bands on an LFS is becoming more common and offers a more objective and repeatable result when the strip is being used for testing large amounts of grain. The issue of subjectivity may also arise when interpreting the results of PCR based on examination of a gel for the presence of bands. Ambiguity can be reduced in both these cases by limiting the size of each (sub)sample analyzed so as to work well within the sensitivity of the method. In the case of PCR testing, the most caution should be observed when using the 35S sequence as a screening method. As mentioned previously, this sequence originates from a plant virus and is therefore common in certain species such as brassicas that can be present adventitiously in grain. Here also, the adventitious presence of other grains should also be considered – for example, a 35S promoter used in maize could be found to be present in soybean samples that do not contain any obvious GM maize, but that have traces of maize dust or grains due to sequential use of the same trucks or shipping containers in the soybean and maize transport systems.

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PCR, because it is a very sensitive analytic technique, is prone to cross contamination – from other samples, from the products of PCR reactions, or from poor laboratory techniques. Thus, many laboratories have adopted a forward flow process, whereby the samples and the technicians follow a path through the laboratory that is designed to prevent materials from each step of the analysis contaminating a previous step. In the most sophisticated laboratories, this involves the use of positive and negative air pressures and pass-through hatches from one area to another to prevent passage of air during sample transfer. Thus, it is recommended that specially designed facilities be used when looking for low levels of GM grain, particularly when the results are being used for regulatory purposes.

Concordance of Results from Different Kinds of Tests If a sample is to be tested using several tests, particularly both protein-based and PCR tests, then there should be rationale for doing so. This may be that a protein test can screen for multiple events, but a PCR test is required to detect specific materials. Tests may also be done in sequence, such as screening, followed by specifically analyzing for certain events (such as those not allowed in the import country). It is expected that results of such tests should agree, if carried out on the same material. It is important to note that two grain samples from a lot are not identical and may yield different results, so where possible, all the tests should be carried out on one sample of the grain, ground in such a way so as to make all the subsamples identical. With very low concentrations of GM grains, even this may still lead to disagreement between analyses due to differences in the sensitivity of tests, and thus, a thorough testing strategy should be devised before starting the process. In quantitative testing, the way that analyses are performed will influence the results. Should the laboratory test on the basis of subsampling, then the result will be in terms of the mass fraction (percent) of grains. RT-qPCR is the method most often used for regulatory purposes, and subsampling-type approaches are most commonly used for receipt of grains at elevators in identity-preserved grain programs. If RT-qPCR is used, then the result will be in DNA copy numbers or percent of DNA represented by the genetic modification in the grain. It is not atypical for such numbers to be different by a factor of two. For example, one heterozygous grain in 100 (1% by grain count) will be measured as 0.5% using RT-qPCR as it represents only 0.5% of the DNA present. If the single grain were homozygous, then the results would both be 1%. This difference must be understood and accounted for when interpreting results.

Reporting of Results A laboratory that is testing grain will report the results to the customer. This report will include the type of test performed and the result (yes/no/amount) and in the case of a quantitative result should include the uncertainty of the result. This uncertainty value reflects the fact that no measurement is completely accurate but is an estimate of the actual amount of GM grain present in the sample. The report will generally not include information about what range of GM grains may give rise to the result (as in a screening test) and will not, if compliant to most international standards, include phrases

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such as ‘GM-free’; the correct term for reporting a negative result is ‘nn not detected,’ with ‘nn’ being the analyte (protein or DNA sequence) that has been tested for. Thus, the submitter of the sample also has the need to understand and interpret the results and/or must work with the analytic laboratory to understand its ramifications and then add the uncertainty introduced by the sampling step.

Future Prospects The technology for testing grain for the presence of GM grain has been evolving and continues to do so. The methods in the market today include LFS, ELISA, and both qualitative and quantitative PCRs. In LFS testing, we are seeing increased reliance on readers to read the strips and gather the data, which makes measuring the presence of genetic modification in grain more objective and the results more traceable. In addition, these readers can yield quantitative results for certain events. However, there are new challenges; multiple events contain the same protein, often at different concentrations, which can make interpretation of results of protein tests, particularly semiquantitative results from readers, complicated. In addition, LFSs are increasingly being used in certain situations to test for the presence of multiple proteins using one strip. For grain testing, it can be a challenge to make this combination strip sensitive enough, but manufacturers are continuing to develop the technology. New events that do not express a protein that can easily be detected are being commercialized, and new approaches based on DNA are being developed for fast detection of these kinds of events. While RT-qPCR is the standard regulatory approach in most wealthy economies, it can be difficult to obtain and maintain quantitative PCR machines in less-developed economies. Purchase of the supplies, training of the operators, and particularly service of these machines can be a significant burden. Thus, there are many places where gel-based PCR is the preferred approach. In addition, gel-based methods have been routinely used for screening in some of the most sophisticated testing laboratories in the world, as they have found them to be robust and cost-effective. Thus, we have the situation where we are faced with multiple protein and DNA-based methods used for testing in the grain trade. We must appreciate that they have the potential to give conflicting results. Although there are a number of technologies being supplied in clinical and research situations for performing multiple and advanced protein analyses, these are not suitable and are not being applied in the grain trade. However, two DNAbased technologies, isothermal DNA amplification and digital PCR, are maturing to the point where they may be deployed for testing purposes. Isothermal DNA amplification is a technology that allows detection of specific DNA sequences (much as in PCR) in minutes, rather than hours. There are at least five technologies of which RPA (recombinase polymerase amplification), LAMP (loop-mediated isothermal amplification), and NEAR (nicking enzyme amplification reaction) appear to be the most advanced in terms of application to plant systems. As of early

2015, no commercial kits using these technologies are available for GM testing in grain. Digital PCR is another application of PCR that has the potential of providing high-throughput analysis and the ability to analyze for multiple DNA sequences efficiently. Digital PCR has a high potential and has already been deployed for breeding purposes. As yet, it has not been used for routine testing of samples for the presence of GM grain, and the question will be whether it or conventional real-time PCR will be more efficient in real-world applications, especially in terms of the cost of purchasing and operating the equipment. It is important to understand that although the test methods may develop, preparation of a sample that is typically in the kg range for testing in the laboratory takes significantly more resources, and little has and can be done to make this step more efficient.

Conclusions While sampling and testing of grain have been occurring since the advent of grain trading, detection of GM grains in grain shipments is an additional step that was added recently and is taken if the customer desires them to be absent (or present in the case of valuable consumer traits) at a desired concentration above or below a certain threshold. The reason for these thresholds may be preference, adherence to regulations, or a combination of both. Those testing their grain lots have to take into account the uncertainty introduced by (1) the fact that they must rely on a representative sample of the grain to estimate the concentration of GM grains and (2) the uncertainty of the result produced by the methods themselves, be they protein- or DNA-based. The amount of testing required to meet local regulations continues to increase as more crops are launched and more countries grow these crops. The application of new method approaches for detecting GM grain will continue to evolve, but testing resources may be limited, and where they are limited may be better applied to other more safety-related characteristics of grain and food.


• • • • • • • • • •

What are the grain crops that are GE in the market and internationally traded? Are there internationally recognized ways of sampling grain? Name four of the steps at which grain may be tested. Why must methods be validated? What is the role of proficiency testing? What kind of test is suitable if you need an answer in half an hour? What kinds of methods can be used for screening shipments? What precious metal is used in an LFS? What is the result of the test if no lines develop on an LFS? How are ELISA and LFS tests similar and different? What is the meaning of Ct in relation to PCR?


• •

How many PCR cycles are generally needed to get a meaningful answer? How are protein-based tests modified/adapted to make them more quantitative?


• • • •

How is digital PCR different or similar to other PCR approaches? How does isothermal DNA detection differ from RT-qPCR? What methods might be used in the near future for testing grain for the presence of GMOs? How is sampling of grain performed and what statistical principles are involved?

See also: Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Development of Genetically Modified Grains; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Grain Harvest, Storage and Transport: Handling from Farm to Storage Terminal.

Further Reading Bravo A, Gill SS, and Sobero M (2007) Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control. Toxicon 49: 423–435. CropLife International Database, www.detection-methods.com (accessed 19 February 2015). Dixon LK and Hohn T (1985) Cloning and manipulating Cauliflower Mosaic Virus. In: Becker Y and Hadar J (eds.) Recombinant DNA Research and Viruses.

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Developments in Molecular Virology, Vol. 5. pp. 247–275. Hingham, MA: Martinus Nijhoff Publishing. ISBN-13:978-1-4612-9611-9. e-ISBN-13:978-1-4613-2565-9. http://dx.doi.org/10.1007/978-1-4613-2565-9. Freese L, Chen J, and Shillito RD (2015) Sampling of grain and seed to estimate the adventitious presence of biotechnology-derived seeds in a lot. Cereal Foods World 60(1): 9–15. Grothaus GD, et al. (2006) Immunoassay as an analytical tool in agricultural biotechnology. Journal of AOAC International 89: 913–928, Available online at http://aeicbiotech.org/wp-content/uploads/2014/08/AEICproteinpaper_2006.pdf ISTA proficiency test on GMO testing: http://www.seedtest.org/en/proficiencytests-content-1-1157.html. Horwitz W (1995) Protocol for the design, conduct and interpretation of methodperformance studies (Technical Report). Pure and Applied Chemistry 67(2): 331–343. Laffont J-L, et al. (2005) Testing for adventitious presence of transgenic material in conventional seed or grain lots using quantitative laboratory methods: Statistical procedures and their implementation. Seed Science Research 15: 197–204. http://dx.doi.org/10.1079/SSR2005210. Lipp M, et al. (2005) Polymerase chain reaction technology as an analytical tool in agricultural biotechnology. Journal of AOAC International 88: 136–155, Available online at http://aeicbiotech.org/wp-content/uploads/2014/08/ polychnrctn.pdf. Privalle L, et al. (2012) Development of an agricultural biotechnology crop product: Testing from discovery to commercialization. Journal of Agricultural and Food Chemistry 60(41): 10179–10187. http://dx.doi.org/10.1021/jf302706e. Privalle L (2016) Development of genetically modified grains. In: Corke H, Wrigley C, Faubion J, and Seetharaman K (eds.) Encyclopedia of Food Grains, 2nd edition, vol.4, pp. 343–349. Remund K, et al. (2001) Statistical considerations in seed purity testing for transgenic traits. Seed Science Research 11: 101–119. http://dx.doi.org/10.1079/SSR200166. Saiki R, et al. (1988) Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 239: 487–491. http://dx.doi.org/10.1126/ science.2448875. Taylor JL (1987) Optimizing the expression of chimeric genes in plant cells. Molecular and General Genetics 210: 572–577. USDA GIPSA Proficiency program: http://scl.gipsa.usda.gov/fgis/proficiencyprogram. aspx. U. S. Department of Agriculture, Grain Inspections, Packers and Stockyards Administration: Grain Inspection Handbook, Book 1, Grain Sampling. Published online at http://www. gipsa.usda.gov/Publications/fgis/handbooks/gihbk1_insphb.html.

Genomics of Food Grains RJ Henry, University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Definition of genomics. Other ‘omics’. Advances in DNA sequence analysis. Grain genomes. Functional genomics. Association genetics using genomics tools.

Learning Objectives

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Understanding the genomics paradigm. Definitions of major ‘omics’ fields. Contribution of genomics to understanding grain food quality.

The Genomics Paradigm Genomics is the study of all genes in an organism. Genomic studies attempt to define which gene or combinations of genes control any or all of the grain-quality traits in a single experiment rather than focus on a specific gene function as in traditional genetics experiments.

Grain Food Applications Much of the application of genomics to grain foods needs to be considered at the species-specific level with most early efforts devoted to studying the genomes of the major cereals because of their importance in global food production. Traits associated with starch properties, for example, may be studied across species, but traits such as protein quality in wheat cannot be deduced from analysis of the rice genome.

Genomes in Grain

Genomics and the Other ‘Omics’ Genomics is a key source supporting the other ‘omics’ such as transcriptomics, proteomics, and metabolomics (Table 1). Technology for efficient and automated DNA sequencing has resulted in genomics being more easily studied than the other ‘omics,’ for example proteomics. Proteomics is the study of the chemical structure of all of the polypeptides in an organism (before folding and SS linking to become functional proteins). Proteomics remains technically more difficult to achieve and to automate. Knowledge of the gene sequences from genomics assists in the interpretation and analysis of the proteins in proteomics.

Technology Advances The impact of genomics approaches has been made possible by continuing advances in molecular genetics techniques. Major advances in the underlying technologies and their applications have revolutionized genomics. The development of the polymerase chain reaction in the late 1980s dramatically increased the potential for large-scale genome analysis. More recently, next-generation sequencing (NGS) emerging in the 2000s has again completely changed research approaches in molecular biology and increased the power and range of applications of

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genomics. NGS has been made possible by advances in nanotechnology and information technology. The instrument platforms developed for DNA sequencing rely on conducting and monitoring very large numbers of parallel reactions in a small space. The volumes of data generated require significant data storage, computational power, and statistical knowledge for effective utilization of this technology. A wide range of genomics methods have been adapted for routine application to cereals. The technology continues to advance rapidly due to the development of several competing methodologies that need to continue to improve accuracy, simplicity, and cost to compete for market share. Grain users need to develop data management and analysis tools to interpret and use these data in a timely way.

Three genomes can be found in grains, located in the chloroplast, mitochondria, and nucleus (Table 2).

Chloroplast The chloroplast genome is small and highly conserved in plants making it an ideal subject for analysis of species identity and determination of evolutionary relationships between species. Chloroplasts are maternally inherited in grains. The rice chloroplast is 133 551 base pairs in length.

Mitochondria The mitochondria have a genome that is also maternally inherited in grains with some genes that may confer male sterility and find use in hybrid crop genetics. The mitochondrial genome of rice is more than 490 000 bp.

Nucleus The nuclear genome is large and complex in grain species and contains most of the genetic information in the plant. The nuclear genome of rice is around 380 million base pairs in length. Other grain genomes can be much larger with the wheat genome comprising 17 billion base pairs. The resequencing of the nuclear genomes of cereal varieties is a useful approach to identifying variations associated with traits of economic importance.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00221-7

GENETICS OF GRAINS | Genomics of Food Grains Table 1

Sorghum

Genomics and related ‘omics’

Level

Study of all elements at this level

Gene RNA Protein Metabolite

Genomics Transcriptomics Proteomics Metabolomics

Table 2

Size of the rice genome

Chloroplast Mitochondria Nucleus

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133 551 bp 490 000 bp 380 000 000 bp

Cereals Rice Rice (Oryza sativa) was the only second plant to have a sequenced genome following the model plant Arabidopsis. The small genome size (0.4 Gbp) makes analysis easier. As such, rice has become a model plant for the other cereals and more widely the other grasses. The genomes of the many species within the Oryza genus have been characterized providing molecular tools for analysis of the entire gene pool of rice.

The sorghum (Sorghum bicolor) genome sequence has become an important resource for sorghum genetic improvement, but it is also an important resource for the closely related sugarcane. Sorghum grain transcriptomics may be a key tool in the development of nutritionally enhanced sorghum genotypes with greater digestibility in animal diets. The genome of sorghum is 0.7 Gbp in length.

Legumes The genomes of legumes (pulses) are being characterized to provide tools for breeding of improved genotypes. The soybean genome is the best studied of the legume genomes. The peanut genome has relatively little variation because of relatively recent polyploidization and domestication. Genomics may allow targeting of significant challenges in peanut including allergic properties and the support of fungi generating aflatoxins.

Oilseeds Genomics provides a tool enabling the manipulation of the oil content and composition in oilseeds. Development of novel oil composition may be achieved by using genomics to guide genetic mutation in oil biosynthesis pathways.

Wheat The large size of the hexaploid (6X or six copies of each chromosome) bread wheat (Triticum aestivum) genome delayed the completion of a reference genome sequence for wheat. The genome is very large at 17 Gbp. Analysis of the wheat genome provides useful insights into the functioning of a polyploidy plant genome. Sequencing of the diploid wild progenitor species (e.g., Aegilops tauschii, the contributor of the D genome of bread wheat) has contributed to our understanding of the more complex hexaploid bread wheat genome.

Maize Analysis of the maize (Zea mays) genome has been used to explore the molecular basis of hybrid vigor (heterosis), an important contributor to productivity in maize. Heterosis may be explained by complementation of genes from the two parents in ways that genomics can define in more detail. Whole-genome analysis allows distinction between gene complementation from the two parents when we have the presence and absence of the genes in the two parents and the advantage of having two different forms of the genes (one from each parent). The genome of maize is 2.5 Gbp in length.

Barley Characterization of the barley (Hordeum vulgare) genome has illustrated the importance of multiple transcripts from the same gene in barley biology. Barley quality may be explored by investigation of genes expressed during grain formation and during germination (for analysis of malting quality traits). The genome of barley is 5.1 Gbp in length.

Analysis of Genome Variation Variation in grain genomes is now easily explored by resequencing of the genomes of individuals. Comparison with the reference genome sequence for the species can be used to rapidly identify genetic differences. The whole genome can be resequenced. Or alternatively, one can just sequence the portion of the DNA encoding the genes (by enriching the DNA sample in genes by hybridization-based methods) or specific genes (e.g., by amplification of all the genes in the relevant biochemical pathways).

Functional Genomics Functional genomics deals with analysis of the function of genes in the genome. Function is usually assigned to gene sequences by comparison of the sequence of the gene with the sequence of genes from other organisms with the inference that a similar sequence may imply a similar function. Knowledge of the function of a gene from any organism may contribute in this way to our understanding of gene function in food grains. Testing of gene function can also be achieved by deletion or inactivation of the gene and observation of the resulting change in the grain plants. The gene may be transferred to bacteria or alternative plant species to test for gain of function as a result of the presence of the gene. Proteins expressed in bacteria can be tested for enzyme activities on a wide range of substrates.

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GENETICS OF GRAINS | Genomics of Food Grains

Transcriptomics The analysis of the genes that are expressed in the grain is a very useful tool in understanding the genetic and molecular basis of grain traits. This requires the analysis of the messenger RNA. Early approaches used techniques such as microarrays (large numbers of DNA samples analyzed in a grid) to monitor in parallel the expression of large numbers of genes. Advances in DNA sequencing now make the sequencing of the transcriptome an attractive option. RNA is copied into DNA and then sequenced in a conventional way. This approach has the advantage that all expressed genes are detected without the need for prior knowledge of the genes’ existence (as is required to include the gene in a microarray system). Study of the transcriptome of the developing grain provides a tool for analysis of all of the genes expressed in the formation of the grain. This should include most genes influencing the functional and nutritional composition of the grain. Differential patterns of expression or the expression of different alleles will explain both environmental and genetic quality differences. Differences due to subsequent impacts of the environment on translation into protein are not detected in this process and require the use of proteomics techniques (see the succeeding text). Analysis of gene expression in specific grain tissues can be used to study grain development and better understand the composition of different tissues or cell types within the grain. Gillies et al. investigated the transcriptome of the aleurone and starch endosperm of the developing wheat seed.

Proteomics Analysis of all of the polypeptides in a biological system (proteomics) is less widely applied than genomics because of the lower level of automation possible in the analysis of protein amino acid sequence and structure. Much proteomic analysis relies upon having a genome sequence to allow identification of the complete structure of whole proteins to be predicted from analysis of small peptide fragments. Classical protein chemistry has been an important technique in understanding the quality of wheat and other grains. Proteomics techniques promise a new level of understanding of the role of proteins in grain quality.

Metabolomics Metabolomics is also more technically difficult than genomics, reducing the current level of application. Analysis of the chemical identity and structure of all the metabolites present in a biological system requires considerable effort. Metabolomics provides a tool that can be used to determine the biochemical basis of complex grain processing and end use quality traits. This may provide explanations for variations in traits that currently do not have obvious biochemical candidates.

Association Genetics Analysis of the genome sequences of grain varieties with different genetic traits can be used to identify the genes determining the traits by association genetics. For example, genes expressed specifically in grains of varieties with desirable

qualities can be identified as the genes responsible for control of these characteristics. Genes that control grain traits are identified by searching in the genome for genes that vary in sequence in a way that associates with the variation in trait.

Grain Identification and Purity Analysis The genome sequence provides a detailed set of information identifying the grain cultivar. Variations in DNA sequence within a sample can be used to precisely measure the purity of a grain sample. These tools may find application in the analysis of foods containing grains to monitor purity, quality, and food safety and to ensure that intellectual property rights are respected. Rapid analysis of DNA sequences offers the potential to better manage grain in production and processing.

Nutrigenomics: The Interaction of Human and Grain Genomes The study of variations in human genomes can be used to determine genetic variations in response to different nutrients in the diet. Grain genomics can be used to explore variations in the nutrient composition of grains. The interactions between these two genomes contribute to human preferences for foods and the impact of grains on human health. Humans select grains with genomes that deliver desirable functional attributes. In turn, grain genomes may influence (positively or negatively) the health (and life expectancy) of the humans consuming them. Understanding human variation in response to grain foods may allow better targeting of diets to deliver optimal health outcomes for individuals. The combined advances in human and grain genomics will continue to drive the development of grain foods for human health outcomes.

Examples of How Genomics Can Enhance Knowledge of Grain-Quality Attributes Fragrance in rice Fragrance in rice provides an excellent example of a grain-quality trait that has been much better understood and managed as result of genomics. The availability of a rice genome sequence led to the rapid identification of the gene responsible for fragrance in rice. This trait adds significantly to the value of rice varieties. The breeding of fragrant varieties of rice was facilitated by the identification of the gene and the development of a simple assay for the presence of the allele that resulted in fragrance. The gene had been the subject of significant traditional genetic mapping efforts, and genetic markers flanking the gene were known. The sequencing of the rice genome allowed the rapid identification of all the genes in the chromosome region known to include the fragrance gene. Testing of the differences in all of these genes in fragrant and nonfragrant varieties of rice identified a gene that showed a consistent difference in fragrant varieties. An 8-base pair deletion was detected in fragrant genotypes. This deletion resulted in a frame shift that introduced a stop codon that would terminate translation of the gene before the active site resulting in a loss of function of the gene. The chemistry of fragrance was revealed by analysis of the reactions catalyzed by the gene when expressed in bacteria. This is a recessive trait resulting from loss of function of an aldehyde dehydrogenase (Figure 1).


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H OH N H

O

HO

H2N

NH2

O

O Gamma-aminobutyric acid

Gamma-aminobutyraldehyde

Proline +H2O

–H2O

N Delta-1-pyrroline

H

O

O

CH3

Methylglyoxal

CH3 N O 2-Acetly-1-pyrroline Figure 1 Genomics leads to discovery of the basis of fragrance in rice. Analysis of the genome sequences of fragrant and nonfragrant rice allowed an 8 bp difference in the sequence of a specific gene to be identified. The loss of function of this aldehyde dehydrogenase leads to accumulation of the substrate, gamma-aminobutyraldehyde. This rearranges to react to form 2-acetyl-1-pyrroline (2AP). 2AP is the main volatile component responsible for the aroma of basmati and jasmine rice and is also found in the other foods attractive to humans. This disruption of proline metabolism may result in reduced resistance of the rice plant to stress.

This discovery also indicated that jasmine and basmati rice despite their many other differences had a common ancestor in relation to their aromatic traits as indicated by the presence of exactly the same 8 bp mutation in the major varieties. Any mutation leading to loss of function of this gene results in fragrance, but the presence of a common mutation demonstrates a common origin. As predicted, for a trait that is due to loss of function of a gene, other mutations leading to loss of function of this gene have since been discovered, and these also result in fragrant grain.

Cooking temperature of rice The identification of the genes controlling the gelatinization temperature of rice starch provides another example of how genomics can provide critical insights into cereal grain quality. The cooking temperature of rice influences the texture of cooked rice and has implications for the energy required to cook the grain. Rice gelatinization temperature (the temperature at which the starch gelatinized) was considered to be a quantitative trait (potentially controlled by many genes). A chromosomal site that controlled genetic variation in this trait had been identified. This location was identified as being close to the location of a soluble starch synthase (SSIIa), a potential biochemical candidate gene. Careful sequencing of the entire coding region of this gene, in genotypes with varying gelatinization temperatures, revealed single-nucleotide polymorphisms that explained the variation in gelatinization temperature. A single base substitution that altered an amino acid in the encoded sequence resulted in an 8 C reduction in gelatinization temperature. This may be explained by a reduction in branches of intermediate length in the amylopectin structure allowing more rapid water penetration during

cooking. Human selection for genotypes with this type of genetic mutation has resulted in rice that cooks at a lower temperature. Selection for this trait may be desirable to humans from a food texture perspective but may not necessarily be positive for human health if it results in more rapid starch digestion. Genomics offers the potential to develop grain foods that deliver the best possible combinations of food quality and health.

Aleurone in cereals An example of a more speculative option is that the potential of genomics to contribute to more radical changes in grain quality would be to change the proportion of the different cell types within the grain. The aleurone cell layers in the endosperm of cereals contain many of the desirable compounds that contribute to human nutrition. These specialized layers of endosperm cells surround the starchy endosperm in cereal grains. Increasing the amount of aleurone cells in cereal foods may be an effective way to improve the nutritional value of cereals for human populations. Analysis of the genes expressed in wheat seed development has allowed identification of genes expressed specifically in the aleurone and starchy endosperm cell types. This suggests genes that might be involved in controlling the development of aleurone cells and ways to increase the proportion of the grain that has aleurone cells of high nutritional value. This additional aleurone may contribute more dietary fiber, more minerals, and more essential vitamins in human diets. Control of the content of other tissues could also be advanced by the application of genomics in this way. This is one of many ways genomics could be used to improve grain quality. A key opportunity is to support more efficient breeding of grain.

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Grain Genetic Improvement Genomics allows identification of the genetic basis of grain traits and also provides the tools for selection of these traits in breeding. These techniques may replace many conventional cereal chemistry methods for testing in cereal breeding. Many of these advances have been accelerated by developments in DNA sequencing technology. A single DNA sequencer may determine the sequence of the genome and allow prediction of a wide range of genetically controlled traits that would otherwise require many different specialized instruments to measure. DNA analysis is also possible on a comparatively small sample, with a single grain containing sufficient DNA for analysis. Genomics allows understanding of the genetic and biochemical basis of grain quality to be determined, and this together with simple analysis tools for use in screening provides a powerful technology for grain breeding. Genomics may allow the constraints on plant breeding imposed by the need to select for complex quality traits to be eased ensuring more rapid increases in grain production efficiency and greater food security.


• • • •

Define genomics and related ‘omics.’ How can genome sequences be used to understand grain food quality? What can we learn about grain quality from analysis of the transcriptome? Explain how you would apply genomics tools to grain purity and identity preservation.


• •

Suggest ways in which proteomics and transcriptomics research might be able to surpass ‘classical protein chemistry’ as ‘an important technique in understanding the quality of wheat and other grains.’ Why and how does the large genome size of wheat make it more difficult to study and to manipulate than a grain species with a smaller genome?

• •

Can you suggest a connection between rice starch being modified to provide a reduction in gelatinization temperature and the consequence of more rapid starch digestion? What technological steps would be required to transfer the fragrance of rice to other grains?

See also: Breeding of Grains: Maize: Breeding; Rice: Breeding; Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Abiotic Stress Genes and Mechanisms in Wheat; Biotic Stress Resistance Genes in Wheat; Genome Mapping; Maize: Genetics; Rice: Genetics; Wheat Genetics and Genomics.

Further Reading Allen AM, Anderson O, Bancroft I, et al. (2012) Analysis of the bread wheat genome using whole-genome shotgun sequencing. Nature 491: 705–710. Bradbury LMT, Fitzgerald TL, Henry RJ, Jin Q, and Waters DLE (2005a) The gene for fragrance in rice. Plant Biotechnology Journal 3: 363–370. Bradbury LMT, Henry RJ, Jin Q, and Waters DLE (2005b) A perfect marker for fragrance genotyping in rice. Molecular Breeding 16: 279–283. Bradbury LME, Gillies SA, Brushett D, Waters DLE, and Henry RJ (2008) Inactivation of an aminoaldehyde dehydrogenase is responsible for fragrance in rice. Plant Molecular Biology 68: 439–449. Chen J, Cui Y, Fan H, et al. (2012) Draft genome of the wheat A-genome progenitor Triticum urartu. Nature 496: 87–90. Edwards MA and Henry RJ (2011) DNA sequencing methods contributing to new directions in cereal research. Journal of Cereal Science 54: 395–400. Gillies S, Furtado A, and Henry RJ (2012) Gene expression in the developing aleurone and starchy endosperm of wheat. Plant Biotechnology Journal 10: 668–679. Gopala Krishnan S, Waters DLE, Katiyar SK, Sadananda AR, Satyadev V, and Henry R (2012) Genome-wide DNA polymorphisms in elite indica rice inbreds discovered by whole-genome sequencing. Plant Biotechnology Journal 10: 623–634. Henry RJ (2007) Genomics as a tool for cereal chemistry. Cereal Chemistry 84: 365–369. Henry RJ (2013) Molecular Markers in Plants pp. 200. Hoboken, NJ: Wiley-Blackwell. Henry RJ and Furtado A (2014) Cereal genomics: Methods and protocols. Methods in Molecular Biology, vol. 1099. New York: Springer. http://dx.doi.org/10.1007/9781-62703-715-0_9. Henry RJ, Edwards M, Waters DLE, et al. (2012) Application of large scale sequencing to marker discovery in plants. Journal of Biosciences 37: 829–841. Nock C, Waters DLE, Edwards MA, et al. (2011) Chloroplast genome sequence from total DNA for plant identification. Plant Biotechnology Journal 9: 328–333. Qingsheng J, Waters DLE, Cordeiro GM, Henry RJ, and Reinke RF (2003) A Single Nucleotide Polymorphism (SNP) marker linked to fragrance in rice (Oryza sativa L.). Plant Science 165: 359–364. Waters DLE, Henry RJ, Reinke RF, and Fitzgerald MA (2006) Gelatinization temperature of rice explained by polymorphisms in starch synthase. Plant Biotechnology Journal 4: 115–122.

Genome Mapping VK Tiwari, Kansas State University, Manhattan, KS, USA JD Faris, USDA-ARS Cereal Crops Research Unit, Fargo, ND, USA B Friebe, Kansas State University, Manhattan, KS, USA BS Gill, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Molecular markers are important for genetic and genome mapping studies. Next-generation sequencing-based marker genotyping, such as genotyping by sequencing, is an important aid for gene and genome mapping. Single-nucleotide polymorphism-based marker development and their detection. Genome mapping methods use recombination-dependent and recombination-independent approaches. Comparative mapping is an important tool for genome analysis in the crops where sequence information is not available.

Learning Objective

•

To achieve an understanding of the commonly used molecular markers and approaches used for genome mapping.

Introduction Genome mapping is used to assign short DNA sequences (molecular markers) or specific genes to particular regions of chromosomes and to determine their relative linear orders and distances. A map is an essential tool for scientists to navigate across the genome. Genome maps can be divided into two groups: genetic maps and physical maps. Genetic maps are based on recombination frequencies between genetic markers and genes, and linked markers/genes form linkage groups showing their relative order. A physical map of a given chromosome or a genome shows the physical locations of genes and other DNA sequences of interest, and distances are typically measured in base pairs. Physical maps can be divided into three general types: chromosomal or cytogenetic maps, radiation hybrid (RH) maps, and sequence maps. The ultimate physical map is the complete sequence itself.

Molecular Markers and Their Visualization DNA-based genetic markers rely on differences in DNA sequences (polymorphisms) between two parental lines. Polymorphisms can result from various factors that lead to either nucleotide changes or differences in DNA segment lengths such as mutations, errors in DNA replication, and insertions, inversions, and deletions of DNA fragments.


There are several established approaches for the detection of polymorphisms using molecular markers including restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), sequence-tagged site (STS), microsatellites or simple sequence repeats (SSRs), and single nucleotide polymorphism (SNP). Originating in the 1980s, RFLP markers were the first type of DNA-based markers to be used. RFLPs involve the use of a restriction enzyme, which cleaves DNA at specific DNA sequence palindromes, and the hybridization of a short-labeled DNA fragment, or probe, to the restriction enzyme-cleaved DNA. The probe label reveals the restriction fragment hybridized by the probe, and polymorphisms are revealed when an insertion/deletion occurs between critical restriction sites in one genotype compared to the other or when a particular restriction site is abolished due to mutation in one genotype and not the other. RFLP markers can be applied to essentially any organism, and they are still employed to a limited extent today due to their usefulness in comparative mapping analysis and map-based cloning studies. However, these markers are not amenable to high-throughput analysis, and they are difficult and laborious to handle due the large amounts of DNA required, enzymatic digestions, Southern blotting, and probe labeling techniques. Besides the RFLP marker technique, all the other types are based on the use of polymerase chain reaction (PCR). PCRbased markers require the development of an oligonucleotide primer, which is a fragment of DNA typically 15–30 nucleotides in length, to serve as a starting point for PCR amplification on template DNA. In a PCR reaction, template DNA is mixed with primers, nucleotides, and a specific enzyme called Taq polymerase, which polymerizes DNA fragments. The mixture is placed into a thermal cycler and subjected to repeated cycles of different temperatures to allow the template DNA to denature, the oligonucleotide primers to anneal to complementary sites on the template DNA, and the Taq polymerase to catalyze the synthesis of new DNA strands leading to the generation of billions of copies of the target sequence. After the completion of the PCR reaction, the amplified product is electrophoresed through an agarose or polyacrylamide gel and subsequently visualized by DNA staining or other technologies. RAPD markers are DNA fragments from PCR-based amplification of random segments of genomic DNA with a primer of arbitrary nucleotide sequences. RAPD markers were the first PCR-based markers to be used but, today, have very limited application in molecular biology and mapping studies due to the unpredictability of short primers in PCR and low repeatability. AFLPs, which combine the use of restriction enzymes with PCR, have been used extensively in a wide range of organisms.

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The AFLP technique uses restriction enzymes to digest the genomic DNA followed by ligation of adapters to the sticky ends of the restriction fragments to serve as priming sites for PCR. Subsets of the restriction fragments are selected by using primers with sequencing complimentary to the adapter sequence and also one or two nucleotides within the restriction fragments of the template DNA. The reactions often employ end-labeled radioactive or fluorescent primers for the visualization of the amplified products on polyacrylamide gels. The AFLP technology is also highly sensitive and reproducible and has the capability to detect various polymorphisms in different genomic regions simultaneously. AFLP has higher reproducibility, resolution, and sensitivity at the whole-genome level compared to some of the other marker techniques, and it also has the capability to amplify multiple fragments (50–100) in a single PCR, which provides a high-throughput format. STSs are short DNA sequences (200–500 bp) with known genomic locations. STSs can be easily detected by the PCR using specific primers. In complex genomes, STS markers derived from the coding regions of genes, that is, the expressed portion of genome referred to as expressed sequence tags (ESTs), can be a very useful resource for mapping the locations of expressed genes. These markers are usually codominant in nature, which allows the identification of homozygous and heterozygous individuals in a mapping population. The STS sequences may contain repetitive elements with unique and conserved sequences at both ends of the site, and in broad sense, STS can have a site for markers such as microsatellites, sequence-characterized amplified region, cleaved amplified polymorphic sequences, and inter-simple sequence repeats. Microsatellite markers, also called SSRs, are widely used in gene and genome mapping studies. These are simple sequence tandem repeats and the repeat units are generally di-, tri- tetra-, or pentanucleotides. In a common repeat motif (e.g., in a trirepeat motif in wheat (GAA)n), two nucleotides G and A are repeated for a variable number of times in a bead-like fashion (n could range from 8 to 50). SSRs are usually found in noncoding regions of DNA with a few exceptions. On both sides of the repeat unit are flanking regions that contain unordered DNA, and these flanking regions are most important to develop locus-specific primers to amplify SSRs with PCR. The number and repeats within a microsatellite tend to be highly variable within a given species, which leads to a high frequency of polymorphism even among closely related individuals.

Many large and complex genomes, especially those of some plants, are composed of only about 10–20% gene sequences, whereas the vast majority (80–90%) is composed of transposable element (TE)-related sequences or repeat-based sequences. These repetitive or TEs are widespread throughout the genome and therefore represent a useful resource for whole-genome mapping. These elements have higher levels of tolerance for mutations or rearrangements, which make these TEs highly polymorphic and a good source of marker development for genome mapping. Various TE-based marker development approaches have been used and some of the most common repeat-based markers, which were developed in wheat, belong to two classes including insertion sitebased polymorphism markers and repeat junction markers. These markers are based on PCR with primers designed in conserved regions of TEs. In general, repeat sequences in the genome are not unique, but the insertion sites or repeat junctions are. Therefore, by developing primers that are specific to particular insertion sites or repeat junctions, it is possible to develop genome-specific markers (Figure 1). After the identification of an insertion site or repeat junction, the flanking sequences can be used to design the primers. After the fragment is PCR-amplified, there are various detection methods available for visualizing the marker polymorphisms including high-resolution melting analyses, temperature gradient capillary electrophoresis, and fluorescent capillary electrophoresis. With advances in next-generation sequencing (NGS) technology, it is less expensive to determine the DNA sequence of a fragment, and this has led to dramatic advances in highthroughput marker technologies. With restriction siteassociated DNA (RAD) markers, the flanking DNA sequence around each restriction site is an integral component for isolation of restriction site-associated tags. The application of the flanking DNA sequences in RAD tag techniques is referred as reduced-representation method. The RAD tag isolation procedure has been modified for use with high-throughput sequencing on the Illumina sequencing platform, to reduce error rates and make the process high throughput. Isolated RAD tags can be used to identify and genotype DNA sequence-based polymorphisms such as SNPs, and these polymorphic sites are called as RAD markers. The advent of automated Sanger sequencing and especially recent advances in NGS technologies led to the development of a second generation of markers based on sequence information. SNPs differ by a single nucleotide A, T, C, or G at a given

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Figure 1 Types of repeat junctions in a given genomic DNA sequence that can be used for designing unique locus-specific markers: (a) A repeat junction between two different transposable elements (TEs). (b) Two repeat junctions with two different TEs (black and green) and an unknown sequence (pink). (c) Repeat junction with a TE on one side and a gene fragment or unknown sequence on the other side. (d) Two repeat junctions (nested) created by a TE inserting into another TE.

GENETICS OF GRAINS | Genome Mapping locus between different individuals, populations, and parental lines (Figure 2). If this variation occurs between the members of the same population, these variations are considered alleles (e.g., A or T), and most SNPs have only two alleles. SNPs have emerged as the markers of choice because of their abundance and high-throughput detection capacities. There are many ways to identify SNPs starting from a low-throughput method like PCR amplification followed by electrophoresis, sequence detection, and mass spectrometry to high-throughput NGSbased SNP discovery. After generating sequences for SNP discovery, the next step is to detect useful SNPs. Manual identification of putative SNPs had been a major bottleneck for high-throughput SNP calling, but now, there are numerous

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software programs available for SNP discovery. These programs (CASAVA, GS Amplicon, BioScope™, NextGENe®, GigaBayes, SNPdetector, PolyScan, etc.) are very important for the development of accurate computational methods for automated SNP calling. There are established approaches and protocols for SNP discovery in many species, and for species with reference genome sequences, NGS reads can be mapped on the reference sequences and SNP discovery can be made. However, SNP discovery can also be done in the species without a reference sequence. There are many assays available for SNP genotyping including Illumina GoldenGate, KASPar, iPLEX Gold technology, and Illumina BeadChips, to name a few (Figure 3(a) and 3(b)). Exciting progress has been made in

SNP site Genotype1 TTGGCCTGATTTTAGTGGTACGGCCCCGTCACCCGTGATTGGTGAAGTTGGAATGGAGGA Genotype2 TTGGCCTGATTTTAGTGGTATGGCCCCGTCACCCGTGATTGGTCAAGTTGGAATGGAGGA ∗∗∗∗ ∗∗ ∗∗∗ ∗∗ ∗∗∗ ∗∗ ∗∗ ∗∗ ∗ ∗ ∗∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗∗ ∗ ∗∗ ∗ ∗ ∗ ∗ ∗ ∗∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ Figure 2 Identification of SNP sites in a DNA sequence: Two SNPs between genomic DNA of two genotypes are shown. The length of the sequence is 60 base pairs, and genotype 1 and genotype 2 show variants at positions 21 [C/T] and 44 [G/C].

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Figure 3 (a) Hybridization-based SNP genotyping method (Illumina Infinium assay): In this assay, the genomic DNA is captured by direct hybridization to array-bound target sequences (50 bases directly upstream of the SNP). Followed by hybridization, a single-base extension reaction with dideoxynucleotides (fluorescent) is used at the target SNP nucleotide. Differences in the relative intensity of fluorescent signals can be used to make genotyping calls. (b) PCR-based genotyping methods (Applied Biosystems’ TaqMan assay): For each locus, two common locus-specific primers are designed on each side of the SNP to amplify the fragment spanning the polymorphic site. Two fluorescence resonance energy transfer (FRET)-labeled oligonucleotides called TaqMan probes are then added to the PCR. Each probe is specific to one of the alleles and is designed to hybridize at the SNP site between the forward and reverse primers. By design, these have a reporter dye at their 50 end (different for each allele) and a quencher (Q) at their 30 end. If there is no reaction, the probes are intact and the reporter dye’s emission is suppressed by the quencher. During the PCR amplification, the Taq polymerase cleaves the probe that anneals to the template and separates reporter and quencher resulting in the emission of fluorescence from the reporter. Genotype calling can then be made according to the fluorescent signal.

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sequencing technologies that are providing high-throughput molecular marker information at low costs. Genotyping by sequencing (GBS) provides marker polymorphisms using NGS technologies followed by a bioinformatics pipeline. It is a preferred method for several reasons including reduced cost through an enzyme-based genomic complexity reduction step and the use of barcoded adapters for multiplexing. Additionally, it can be used for the discovery and identification of SNPs, even for those species with complex genomes that lack a reference sequence. GBS has advantages when studying polyploid species, which is a big challenge for any technology. It relies on secondary genome-specific polymorphisms that are next to the SNP, and it allows the assignation of a given sequence to a specific genome so it becomes a single-locus marker.

chromosomes pair at meiosis, they recombine at various positions along the chromosomes. Thus, recombination is the basis for genetic linkage mapping and determining the order of markers along the chromosome, that is, markers are separated by genetic distances calculated based on the amount of meiotic recombination that occurs between them. An example of genetic linkage mapping of three linked markers in 20 F2 progeny is presented in Figure 4. The markers include two DNA markers (A and B) and one morphological marker (disease resistance gene ‘R’). The DNA markers are codominant, and therefore, all possible genotypes can be determined in the F2 progeny (homozygous for parent A, homozygous for parent B, and heterozygous). For the morphological marker, disease resistance is dominant, and therefore, the genotypic classes of heterozygous and homozygous for the resistant parent (parent A) cannot be distinguished (resistant plants can have allelic compositions of ‘RR’ or ‘Rr,’ and susceptible plants have ‘rr’). Inspection of Figure 4 indicates there are three individuals (2, 6, and 12) with genotypes that differ between markers A and B. Between A and R, there are two individuals (6 and 12) with differing genotypes, and one individual (2) has differing genotypes between markers B and R. This suggests that marker R (disease resistance gene) lies between markers A and B. The two recombination events between markers A and R translate into ten map units (2/ 20 100 ¼ 10), and there are five map units between markers B and R (1/20 100 ¼ 5).

Genetic Linkage Mapping

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Markers are powerful for many diagnostic applications for typing biological samples in determining the identity of unknown samples, sample mixtures, criminal justice system, and curation of biological collections, to name a few. Highdensity genetic linkage maps facilitate map-based cloning, quantitative trait mapping, marker-assisted breeding, and comparative genome evolution. Genetic mapping relies on the fact that nuclear genomes are made up of chromosomes, which contain both genes and noncoding DNA. When homologous

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Figure 4 Genotypic data of two DNA markers (A and B) and phenotypic data for one morphological marker (disease resistance gene ‘R’) for two parents, the F1 plant derived from crossing the two parents, and 20 F2 individuals. The DNA markers are codominant; thus, all possible genotypes can be distinguished (homozygous for parent A and heterozygous and homozygous for parent B). The morphological marker ‘R’ is dominant, and therefore, the genotypes of resistant F2 individuals cannot be distinguished (resistant plants can be either homozygous for parent A (RR) or heterozygous (Rr)). The resulting genetic linkage map of the three loci and genetic distances separating them are shown at the bottom.

GENETICS OF GRAINS | Genome Mapping This type of analysis can be applied to hundreds, or even thousands of markers to construct complete genetic linkage maps of chromosomes. Fortunately, there are various computer software programs available to handle such large data sets and to determine the most likely marker orders and intermarker distances. The number of individuals surveyed in a mapping population determines the precision of the genetic distance measured. In the example, only 20 individuals were surveyed, and if no recombinants were identified between two markers, this would translate to a genetic distance of 0 map units between the markers. If 100 individuals were surveyed, then one or more recombinants may be identified leading to a genetic distance of one or more map units. Generally, initial genetic maps of plant species are generated using 80–120 individuals, which allows for the detection of recombination between markers one to three map units apart. This level of precision is considered acceptable, and, at the same time, the amount of labor and cost is considered manageable. However, certain mapping experiments such as map-based cloning of genes by chromosome walking require much higher resolution in order to separate markers extremely close to the target gene. In these experiments, it is not uncommon to survey 3000–5000 individuals to obtain the necessary level of precision. In plants, most populations are derived from crossing two highly homozygous parents. The population shown in the example in Figure 4 is an F2 population. While F2 populations are commonly used and generally a good choice for chromosome mapping, other types of populations, such as backcross (BC), doubled-haploid (DH), and recombinant inbred (RI), are also commonly used. However, DH technology is not easily accomplished in some crops, and it is currently impossible in others. Each type of population has its advantages and disadvantages. F2, BC, and DH populations can be developed very rapidly, while RI populations are developed by advancing each line by single-seed descent for many generations with the goal of selfing to homozygosity. F2 and BC populations are shortlived and provide limited opportunity to obtain DNA and phenotypic data, while DH and RI populations provide essentially pure lines that may be tested for traits in replicated experiments over several environments if desired. Thus, RI and DH populations are preferred for mapping of quantitative traits that may be affected by environmental influences. BC and DH populations result from one cycle of meiosis, but an F2 population has undergone recombination in both male and female gametes and, therefore, provides twice the recombination information. RI populations have undergone several cycles of meiosis but contain two identical homologues and, therefore, provide about the same amount of information as an F2. The development and analysis of genetic linkage maps lead to an abundance of information regarding genome structure. From a more applied perspective, they provide knowledge regarding the locations of genes and DNA markers associated with them. In a segregating population, morphological markers can be scored and analyzed in the same manner as DNA markers. The difference in scoring for morphological makers compared to DNA markers lies in the fact that, for morphological markers, the genotype is determined based on the visualization of the plant’s phenotype, while DNA markers

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are scored at the DNA level. For example, a population segregating for resistance to a particular disease would be scored based on the reaction of each individual to the disease as being one of either parental type. Inclusion of this phenotypic data with genotypic DNA marker data for map generation might reveal that the disease resistance gene is flanked by closely linked DNA markers. Such markers are valuable tools that can be employed by plant breeders who wish to move the disease resistance gene into elite lines for the development of new and improved varieties. Using the markers to make selections is known as marker-assisted selection (MAS). MAS has advantages over selecting for the trait itself in that markers are not affected by environmental factors as phenotypic traits sometimes are. In addition, MAS allows breeders to make selections in early generations and growth stages allowing them to eliminate undesirable material early on. In a nutshell, genetic mapping is a great resource for trait mapping and map-based cloning studies; however, a genetic map is not sufficient for sequencing a genome. Polymorphism level is many times a limitation for genetic mapping; however, the advanced and low-cost NGS approaches have been a big boost to overcome this limitation. GBS has been widely accepted and is now being used to map target traits in various crops. In addition, sequence-based genome mapping, where members (mostly RI lines) of a given mapping population are sequenced to high coverage, is now gaining momentum as well. This approach is very useful for generating a large number of sequence tags, which can be assembled and anchored on the genetic map in a chromosome-wise manner. However, precise ordering of these tags/contigs will be an issue due to the limitation of genetic mapping in terms of the number of recombination events. The resolution of a genetic map depends on the number of recombination events that have been scored in a given population. Recombination events are not uniformly distributed across the length of the chromosome as recombination is suppressed around the centromeric regions. So reduced or nearly absent recombination events affect the resolving power of linkage analysis, which means that genes that are several kilobases to megabases apart may appear at the same position on the genetic map.

Physical Mapping In contrast to genetic mapping where distances between landmarks are calculated based on recombination frequency, physical mapping determines the actual physical distance. Physical mapping can be done cytologically by chemically staining and viewing whole chromosomes using techniques such as in situ hybridization (ISH) and C-banding. Such techniques have very low resolution in terms of physical mapping because chromosomes are viewed at the cellular level usually at metaphase. However, recent techniques, such as fiber-fluorescence in situ hybridization (FISH) where nuclear DNA is lysed on a glass slide and used for in situ mapping, can provide a much higher resolution (see succeeding text). The highest-resolution physical mapping is obtained by sequencing the DNA itself. It is usually preceded by constructing local contiguous sequences (contigs) of large-insert DNA clones and anchoring the contig to a genetic map.

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In Situ Hybridization The ISH technique was developed about 45 years ago and allows the localization of genes or DNA sequences directly on chromosomes in cytological preparations. The ISH technique uses probe DNA that is labeled with biotinylated dUTP or digoxigenin-dUTP and the hybridization sites are detected by enzymatic reporter molecules such as horseradish peroxidase or alkaline phosphatase-conjugated avidin/streptavidin. ISH has been used successfully to determine the physical location and distribution of dispersed or tandemly repetitive DNA sequences on individual chromosomes. For example, it has been used to determine the physical location of multicopy gene families such as the 5S and 18S–26S ribosomal genes. FISH uses fluorochromes for signal detection. The FISH technique allows different DNA probes to be labeled with different fluorochromes that emit different colors (multicolor FISH). Thus, the physical order of two or more probes on a chromosome can be determined simultaneously. Also, FISH can allow more precise mapping of probes because the fluorescence signals can be analyzed with special cameras and digital imaging tools. In humans, the order of two DNA probes can be determined by ISH on metaphase chromosomes only if the two sequences are separated by at least 1 Mb. However, when ISH is done using interphase nuclei, DNA sequences separated by as little as 50 kb can be resolved. Plant metaphase chromosomes are more condensed than human metaphase chromosomes, and this may be one reason why ISH using low-copy probes is more difficult in some plant species. Thus, it has been suggested that interphase nuclei can be exploited for ISH mapping in plants. Subsequently, experiments where DNA probes were hybridized to maize interphase nuclei suggested that the resolving power of interphase FISH mapping can be as little as 100 kb. FISH technique has been used successfully to determine the physical location of bacterial artificial chromosome (BAC) clones on interphase and metaphase chromosomes. Rice BAC clones have been hybridized to rice (Oryza sativa L.) chromosomes revealing that the repetitive DNA sequences in the BAC clones could be efficiently suppressed by using rice genomic DNA as a competitor in the hybridization mixture. The successful application of this technique to plants with very large genomes may depend on the size of the genomic clones analyzed and the amount of repetitive sequences in the genome.

Fiber-FISH Fiber-FISH technique uses extended chromatin DNA across a glass slide and a probe is labeled as with standard FISH and hybridized to the extended fibers and where DNA sequences, which are only a few kilobases apart, can be ordered. In humans, fiber-FISH has been used to analyze overlapping clones, detect chromosomal rearrangements, determine the physical distances between genes, measure the sizes of long DNA loci, and aid in the positional cloning of specific genes. Fiber-FISH was used in Arabidopsis thaliana to measure clusters of DNA repeats as long as 1.71 Mb, which is more than 1% of

the Arabidopsis genome. It was found that fiber-FISH signals derived from small DNA fragments (<3 kb) were often observed as single spots on extended DNA fibers, and thus, sequences that are less than 5–10 kb apart cannot be ordered.

Single-Copy Gene FISH Single-copy gene FISH is an approach to develop a cytogenetic map of a given chromosome using full-length cDNA (fl-cDNA) probes. Because genes and gene syntenic blocks are conserved between different grass species such as wheat, barley, rice, and maize, single-copy FISH provides a rapid method for determining chromosome synteny for species for which little genetic or cytogenetic mapping information is available. In an event of transferring important genes from wild relatives to bread wheat (Triticum aestivum L., 2n ¼ 6 ¼ 42, AABBDD) by induced homoeologous recombination, it is important to know the chromosomal relationships of the species involved. Singlecopy FISH provides a powerful and rapid method for determining genetic relationships of relatively little studied wild relatives with those of wheat. Once identified from singlegene markers, fl-cDNA probes are used for FISH and the respective positions of these probes are determined to develop a cytogenetic map. This technique can also be used to identify structural changes between the homoeologous groups of chromosomes, between the genomes of wheat, and other species from the Triticeae tribe. This provides important information on the strategies to be used for exploitation of those species for wheat improvement.

Aneuploid Mapping Wheat is a polyploid and can tolerate a high degree of aneuploidy (abnormal chromosome numbers). There are a vast array of aneuploidy stocks such as nullisomic–tetrasomic (NT) lines and the ditelosomic (dt) lines. NT lines lack one pair of chromosomes and extra pair of homoeologous chromosomes and allow arm mapping of genes. Ditelosomic lines lack one pair of chromosome arms and allow arm mapping of genes. With today’s molecular technology, the power and utility of the wheat aneuploids have been even more fully realized. DNA markers can be quickly located to a specific chromosome or chromosome arm using a single hybridization or amplification reaction without the need for polymorphism. Telocentric chromosomes can be flow-sorted and DNA-amplified and used for NGS for marker development. Dense chromosomal arm maps have been developed and genes identified and ordered to specific chromosome arms. These maps are useful for gene tagging, linkage and mapping of quantitative trait loci (QTL), cytogenetic manipulations, estimation of genetic distance, and evolutionary studies.

Chromosome Deletion Mapping A unique system in wheat is the use of gametocidal (Gc) factors to construct chromosome deletion lines. Gc chromosomes

GENETICS OF GRAINS | Genome Mapping were introduced into wheat by interspecific hybridization with the related Aegilops species and backcrossing. Plants monosomic for the Gc chromosome produce two types of gametes. Only those gametes possessing the Gc chromosome are normal. Gametes lacking the Gc chromosome undergo structural chromosome aberrations and, in most cases, are nonfunctional. However, if the damage caused by the chromosome breakage is not sufficient to kill the gamete, it may still function and be transmitted to the offspring. The Gc system has been used to develop wheat lines with terminal chromosome deletions. These stocks have proved very useful for the physical mapping of genes and DNA markers to subarm locations and for the development of physical maps, which have been constructed for all seven homoeologous chromosome groups of wheat. In addition, chromosome bin maps of most of the expressed genes in the wheat plant have been constructed using a set of wheat aneuploid and deletion lines (http://wheat.pw.usda.gov/wEST/binmaps/).

HAPPY Mapping Another genome mapping approach known as HAPPY mapping has been used for genome mapping studies. This approach is based on haploid DNA samples analyzed using the polymerase chain reaction (HAPPY). HAPPY mapping does not require marker polymorphism or time-consuming population development. It is an in vitro approach for the ordering of DNA markers directly on native genomic DNA and is based on analyzing the segregation of markers amplified from high-molecular-weight genomic DNA. It is a three-step process. First, genomic DNA is broken into random fragments using gamma irradiation or mechanical shearing. The DNA is isolated and analyzed for quality and integrity, which is the most important aspect of the technique. Various protocols have been tested and used to avoid unwanted mechanical breakage of the DNA molecules. It is usually done by embedding the living cells in agarose gel; during DNA extraction, long molecules of chromosomal DNA remain trapped and protected within the agarose. The high-quality DNA (DNA solution) is then subjected to random fragmentation using mechanical shearing, gel melting, and x-ray treatments. The average size of the broken fragments depends on the dosage or mechanical shearing used. The next step involves the development of a ‘mapping panel,’ and to achieve this, broken DNA fragments are diluted to a very low concentration and 100 samples from individual treatments usually get dispensed into DNA collecting plates or tubes. Since these samples are very small, each well or tube may represent a small incomplete set of random fragments. The third and final step involves a highly sensitive PCR followed by the scoring of markers as present or absent in the HAPPY mapping panel. Genotyping of large sets of markers and detailed analysis of marker data can be used for the construction of maps and to calculate precise locations of markers on a given chromosome or genome. Because the samples in a mapping panel are so small that each one will contain only a randomly sampled subset of the markers rather than the complete genome, a given marker tested on the panel can be present in only one subset of the panel. If two marker loci are close together, then

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they will remain on the same broken fragments and not show any break between them, whereas distant markers may be lost. With increasing distances between two marker pairs, the frequency of random breaks between them will also increase. The statistical analysis of the cosegregation frequencies and different mapping software can be used to deduce a marker or map order based on the data generated from the HAPPY mapping panel. There are certain limitations attached to this approach. The first is that it is difficult to prepare DNA fragments of more than a few megabases in size, and therefore, intermarker distances of more than one megabase are difficult to measure. Another major limitation is the sample size of the DNA in the mapping panel, as all markers need to be mapped by PCR.

RH Mapping RH mapping has been exploited in animal genome mapping projects and is a recombination-independent approach. It was pioneered in the human genetics arena and uses radiationinduced chromosome breakage rather than meiotic recombination for mapping. After fragmentation, samples containing different subsets of the original chromosome or genome are isolated and used for marker assays. In this method, any given mapping panel member is assayed for the presence or absence of a given marker, thus circumventing the need for marker polymorphisms between genotypes. Gross and Harris produced the first RHs by irradiating the cultured human cells with a high dose of x-rays and their subsequent fusion to unirradiated hamster cells. Generated RHs showed many broken fragments of human chromosomes with unfragmented chromosomes of hamster cells. The approach was then modified and applied to a number of animal species. In the modified approach, donor cells are irradiated and then fused to unirradiated host cells, and RHs containing donor chromosome fragments are identified using selectable markers for a given species. Species-specific RHs can be isolated, cultured, and saved as an immortal resource. For genome (RH) mapping, the DNA of 100 hybrid cell lines (each containing a different set of donor fragments) can be assembled as an RH panel. The assembled panel can be used for marker genotyping and the order and distances of the markers in a given genome can be inferred. Mapping resolution in an RH panel is a function of the size of the fragments that are generated during the development of the mapping panel. Therefore, the mapping resolution can be altered by simply changing the level of chromosome fragmentation. Additionally, in RHs, map distances better reflect the true physical distance between markers than do recombinationbased maps, so maps constructed by the RH approach can better approximate the physical layout of a given chromosome. The RH approach has been used to map the human genome along with various animal genomes; however, its application in plants has been limited. RH mapping in plants was first reported for a maize chromosome, and then, it was applied to cotton, barley, and wheat. Recently, RH mapping was used for genome mapping of hexaploid wheat (Figure 5). Figure 5 presents a scheme for the development of an RH panel for Dgenome chromosomes of hexaploid wheat. Pollen from the reference hexaploid wheat Chinese Spring was irradiated using

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Tetraploid wheat line Altar 2n=4x=28 (AABB)

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Figure 5 Development of Chinese Spring D-genome radiation hybrid panel: The spikes of hexaploid wheat cultivar Chinese Spring (T. aestivum; 2n ¼ 6 ¼ 42, AABBDD) were used for g-irradiation. Pollen from irradiated spikes was immediately used to pollinate the stigmas of emasculated florets (male anthers removed) of tetraploid wheat variety Altar 84 (T. turgidum; 2n ¼ 4 ¼ 28, AABB). Seeds of F1 hybrids were harvested 20 days after pollination. Each surviving F1 seed (RH1-pentaploid) on germination represents a unique RH event. DNA samples of the individual RH1 plants were then harvested and genotyped for RH mapping.

gamma radiation, and these pollen samples were used to pollinate a tetraploid wheat line Altar84. F1 seeds (pentaploid) represent an RH panel and each plant from these seeds presents a unique RH event. Chromosome lesions induced in the A and B genomes of Chinese Spring are masked in these quasipentaploids due to the presence of A and B genome chromosomes from the tetraploid parent, but the chromosomes from the D genome are present in one copy and allow RH mapping of all D-genome chromosomes simultaneously. It has been found that using a small RH panel (94 lines), map resolution of up to 300 kb can be achieved throughout the length of any given chromosome in hexaploid wheat. The RH panel can be used to anchor and order BAC contigs, derived from flowsorted chromosome arm-specific libraries to individual wheat chromosomes. RH panels will also be highly useful for ongoing wheat genome sequencing projects for ordering of sequence scaffolds.

Large-Insert Clone Contigs The construction of physical contig maps is important for facilitating positional cloning of genes, sequencing of genomic DNA, and detailed analysis of chromosome and genome structure. Physical contig mapping is the arrangement of large-insert clones (YACs, BACs, and cosmids) in a linear array that

represents the DNA sequence along the chromosome. Clones are selected by screening a library with DNA probes used to detect genetic markers on a genetic linkage map of the organism. Several DNA probes that detect closely linked genetic loci will hybridize to corresponding large-insert clones, and these clones can then be arranged into a contig based on overlapping segments and fingerprinting. BAC contigs are currently being developed in many crop species. However, crops with complex genomes offer huge problems due to large genome size, polyploid nature, and very high percentages of repetitive sequences. To address these issues in wheat, a sophisticated flowsorting technique was applied for isolation of individual chromosomes or chromosome arms. The DNA from these flow-sorted chromosomes and arms was used for the development of BAC libraries. These BAC libraries laid the foundation for the physical mapping of the wheat genomes. Once a physical contig map is complete, the structure and organization of the genome, such as the distribution of repetitive and singlecopy sequences, can be discerned. A BAC-by-BAC approach has been considered as the most suitable approach for generating reference genome maps of barley and wheat. In this method, a BAC library for an individual chromosome is the starting point and BAC contigs are constructed from individual BACs by identifying BACs containing overlapping fragments. Ideally then, the BAC contigs are anchored onto a genetic or RH map of the genome, so that the sequence data from the contig can

GENETICS OF GRAINS | Genome Mapping be checked and interpreted by looking for markers or genes known to be present in a particular region. The BACs constituting the minimum tiling path are then individually sequenced by the shotgun method and assembled into a pseudomolecule providing a sequence of each chromosome.

Comparing Physical Distance to Genetic Distance Physical maps have led to a wealth of information regarding the physical locations of morphological traits and evolutionary translocation breakpoints and genome-wide structure and organization. Comparisons of the physical maps with genetic linkage maps can reveal the physical distribution of genes and recombination along the chromosome. For example, RFLP probes derived from mRNA (called cDNA probes) represent expressed genes, and thus, the physical mapping of cDNA probes will reveal the physical locations of expressed genes. Therefore, when sets of cDNA probes are mapped genetically as well as physically, one can infer the relationship between physical distances and genetic distances among the common markers. In wheat, physical maps constructed using the chromosome deletion lines have been compared extensively to corresponding genetic maps of the same chromosomes. This work has revealed that genes and DNA markers tend to be clustered in small physical segments that undergo a high degree of recombination (Figure 6). These gene-rich regions are separated by large gene-poor segments that undergo very little recombination. This work has facilitated BAC contig construction of regions containing genes of interest for the purpose of positional cloning. In barley, physical maps generated based on translocation breakpoints were compared to corresponding genetic linkage maps. The results agreed with those found in wheat by deletion mapping and showed that the barley genome consists of relatively small gene-rich regions that are hot spots for recombination interspersed among large segments that are gene-poor and undergo very little recombination. The information obtained by physical mapping of translocation breakpoints has facilitated the construction of BAC contigs and positional cloning of important genes by allowing researchers to focus on the generich regions of the genome. More intricate comparisons of physical and genetic relationships can be obtained by comparing local BAC contigs to genetic maps. The primary goal of such experiments is to identify a large-insert clone containing a gene of interest, but additional important information is obtained. For example, once a physical contig map of the region is developed, it can be compared to the genetic linkage map of the corresponding region to calculate physical to genetic distance ratios. This is important information because recombination is known to be distributed nonrandomly throughout the genomes of many plant species causing the physical to genetic distance ratios to be highly variable depending on the characteristics of the region.

Comparative Mapping Much effort has been put forth in comparing the genomic relationships among grasses and among members of other

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plant families. For example, comparative mapping experiments among members of the Poaceae such as wheat, rice, barley, rye, oat, and maize have revealed remarkable similarities in gene content and marker synteny at the chromosome level. It is well established that DNA probes cloned from these related species commonly identify sets of orthologous loci that lie at approximately the same positions relative to each other and to the centromeres. GenomeZipper-based consensus maps, which integrate ordered gene loci from homoeologous wheat genomes and the corresponding chromosomes of barley, Ae. tauschii, T. monococcum, and rice, have been constructed. These experiments have shown that the genomes of barley, Ae. tauschii, and T. monococcum are essentially colinear with that of wheat. The genomes of more distantly related cereals such as oat, rice, and maize can be divided into linkage blocks that have homology to corresponding segments of the wheat genome. The degree of genomic similarities observed at the chromosome level among grass genomes led to the notion that information from the small genome of rice could be directly applied to the much larger genome of wheat. However, even though a substantial degree of synteny is observed at the chromosome level, studies of the degree of microcolinearity between rice and wheat show less promise for gene discovery in wheat. Genes with conserved order across these three species with sequenced genomes can be used to predict the order of corresponding genes conserved in other grass species using synteny-based analysis. There have been exciting developments in genome mapping studies in grasses in terms of the development of highdensity genetic maps and physical maps. This was followed by the generation of EST databases in cereals. In the recent past, large-scale genome sequencing projects in grasses have been successfully implemented, the list including rice, Brachypodium, sorghum, maize, and foxtail millet. These studies provided extensive information on the genome organization of major cereals. Knowledge gained from the genome sequencing has enhanced understanding of the structural and functional components of the genome for its effective utilization in genetic improvement of cereals. Genome maps (whole-genome sequences) of the diploid model grass Brachypodium (genome size 272 Mb) are available, and these provide a useful resource to study the evolution of genomes across the grasses. Among sequenced cereal crops, rice has a smaller genome (420 Mbp) and higher gene density as compared to other cereals; sorghum is positioned after rice with genome size of 730 Mb, whereas the maize genome is larger (2.3 Gb), and it has undergone several rounds of genome duplications and is distinguishable from its close relative, sorghum. Reference genome maps of sorghum and foxtail millet are available, and altogether, these reference genome maps provide a great resource to study comparative genomics in order to develop mapping information about an orphan grass or cereals with no genomic information. There are many software programs and databases developed to look at the syntenic relationship of the cereal genomes. Recently, a GenomeZipper approach was developed to provide an extensive database for studying syntenic relationships among grass genomes (between wheat, Brachypodium, rice, sorghum, and barley genomes). The GenomeZipper uses a novel approach that allows systematic exploitation of conserved synteny with model grasses. For example, it allowed

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Genetic Map Physical Map Xbcd873 Xbcd873 Xabg705, Xbcd1871 38.4

0.0 8.7 5.6 2.5 2.4 0.0 4.8 2.4 2.4 14.5 2.6 1.3 0.0 3.6 1.2 3.6 1.2 1.2 2.4 9.0 12.3

Xabg705 Xbcd1871

Xwg363

Xwg363 XksuA3 Xbcd204 Xpsr128 Xbcd157 XksuH1 Xbcd1140 Xpm181 Xmwg914 Xmwg72 Xpsr120 XksuQ63 Xbcd9 Xwg583 Xcdo400 Xbcd183 tsn1 Xbcd1030 Xrz575 Xcdo948

XksuA3 Xbcd204 Xpsr128 Xbcd157 XksuH1 Xbcd1140, Xpm181

7.7 Xpm182 Xmwg914, Xmwg72, Xpsr120, XksuQ63 Xbcd9, Xwg583, Xcdo400, Xbcd183, tsn1 Xbcd1030, Xrz575, Xcdo948, Xpm182

19.6 Xpsr370 9.7

Xpsr370, Xmwg862, Xpsr580 Xmwg862

13.3 Xpsr580 Figure 6 Wheat chromosome 5B genetic linkage map (left) compared to the physical map (right). The genetic linkage map was constructed using a backcross population and the physical map was constructed using the chromosome deletion lines of wheat. On the genetic linkage map, map units separating markers are shown at the left, and markers are indicated on the right. On the physical map, hash marks on the left of the chromosome indicate deletion breakpoints; black and hatched regions on the chromosome represent dark and light C-bands, respectively; and DNA markers and their bin locations are shown to the right. Lines drawn between the maps indicate where deletion breakpoints occur relative to the genetic map. Notice that the centromeric region is nearly void of DNA markers and recombination, while more distal regions possess most of the DNA markers and recombination.

the assignment of 86% of the total estimated (32 000) barley genes to individual chromosome arms.

Future Mapping Prospects The ultimate goal in map construction is the deciphering of the linear DNA sequences of the full complement of chromosomes of an organism and the utilization of map information in trait mapping. The whole-genome sequence information available in major cereals like rice, sorghum, maize, and foxtail millet

has revolutionized the understanding of the mechanisms underlying genome evolution in these important cereal crops as well as unraveling the important mechanisms in plant growth and developmental processes and tolerance to various biotic and abiotic stresses. The practical applications of the genome maps and reference sequences are best realized only when allelic diversity among diverse germplasm is better understood. In crops where sequence information is not available, comparative genomics-based tools can be very useful for providing a virtual gene order based on synteny. Sequenceready physical maps of diploid barley chromosomes, reference

GENETICS OF GRAINS | Genome Mapping sequences of wheat chromosome 3B, and sequence-ready physical maps of some wheat chromosomes are available. These ongoing efforts in wheat and barley are critical for developing amenable and high-yielding crops to fight various challenges emerging in the form of new diseases and changing environmental conditions.


• • • • •

What are molecular markers? What are the differences between genetic mapping and RH mapping? What are the limitations with HAPPY mapping in order to develop a genome map? Which cereal genomes have been sequenced? What is comparative genome mapping?


• •

What is the status of cereal crop genome sequencing projects? How many wheat chromosomes are sequenced to date?

See also: Genetics of Grains: Wheat Genetics and Genomics; Wheat Genetics.

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Further Reading Appels R, Morris R, Gill B, and May C (1998) Chromosome Biology. Boston, MA: Kluwer Academic, p. 401. Devos KM and Gale MD (2000) Genome relationships: The grass model in current research. Plant Cell 12: 637–646. Faris JD, Friebe B, and Gill BS (2002) Wheat genomics: Exploring the polyploid model. Current Genomics 3: 577–591. Feuillet C and Keller B (1999) High gene density is conserved at syntenic loci of small and large grass genomes. Proceedings of the National Academy of Sciences of the United States of America 96: 8265–8270. Jiang J and Gill BS (1994) Nonisotopic in situ hybridization and plant genome mapping: The first 10 years. Genome 37: 717–725. Jiang JM and Gill BS (2006) Current status and the future of fluorescence in situ hybridization (FISH) in plant genome research. Genome 49: 1057–1068. Lander ES and Botstein D (1989) Mapping Mendelian factors underlying quantitative traits using RFLP linkage maps. Genetics 121: 185–199. Liu BH (1997) Statistical Genomics: Linkage, Mapping and QTL Analysis. Boca Raton, FL: CRC Press. McCarthy LC (1996) Whole genome radiation hybrid mapping. Trends in Genetics 12: 491–493. Paterson AH (1996) Making genetic maps. In: Paterson AH (ed.) Genome Mapping in Plants, pp. 23–39. Austin, TX: R G Landes Company. Paux E, Sourdille P, Mackay I, and Feuillet C (2012) Sequence-based marker development in wheat: Advances and applications to breeding. Biotechnology Advances 30: 1071–1088. Redei GP (1999) Genetics Manual. Singapore: World Scientific, pp. 1141. Tanksley SD, Ganal MW, and Martin GB (1995) Chromosome landing: A paradigm for map-based gene cloning in plants with large genomes. Trends in Genetics 11: 63–68. Tanksley SD, Young ND, Paterson AH, and Bonierbale MW (1989) RFLP mapping in plant breeding: New tools for an old science. Biotechnology 7: 257–263.

Wheat Genetics RA McIntosh, University of Sydney, Narellan, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Common wheat (Triticum aestivum L.) has 21 pairs of chromosomes; 7 pairs in each of three genomes (AA, BB, and DD). Durum wheat and the wild emmers (T. turgidum L.) each have 14 pairs of chromosomes; 7 pairs in each of two genomes (AA and BB). Einkorn (T. monococcum L.) is a diploid, with 7 pairs of chromosomes in the AA genome. Because of the genomic triplication of wheat, chromosome loss or addition (aneuploidy) can be tolerated, permitting valuable means of chromosomal research. Introgression of genetic material and agronomic traits is possible between related species to wheat. Study of genes related to grain quality, adaptation, and biotic stress.

within common wheat, there is a bimodal distribution of grain textures also described as ‘hard’ and ‘soft.’ The main gene controlling softness is located in the D genome so the trait does not occur in the tetraploid and diploid wheat groups.

Taxonomy of Wheat and Its Relatives The allocation of wheat taxa to species and subspecies has changed periodically. The nomenclature of van Slageren is currently the most widely accepted. Although the closely related genus Aegilops shares the D and B genomes with wheat, Triticum and Aegilops have been treated as separate genera.

The Genomic Structure of Wheat Learning Objectives

• •

To understand the basic genetics of wheat and its ancestral relatives. To understand the ways in which conventional genetic methodologies can be used to elucidate the genetic control of traits of agricultural significance.

Introduction Common or bread wheat (Triticum aestivum L.) is an allohexaploid with 21 pairs (2n ¼ 42) of chromosomes comprising three similar genomes (AA, BB, and DD) each of seven pairs. The species does not occur as a wild form; it evolved in agriculture about 9000 years ago. Durum or macaroni wheat and related cultivated and wild emmers (T. turgidum L.) are allotetraploids (2n ¼ 28) possessing genomes, AA and BB, in common with hexaploid wheat. Einkorn (T. monococcum L.) is a diploid (2n ¼ 14) that shares genome AA with both polyploid species. Within this species, there are both cultivated and wild forms. Common wheat products are major components of food for about one-half of the world’s population. This significance in agriculture has driven detailed study of the genetics of wheat and its relatives, a number of which have contributed genes to wheat improvement. A secondary, but important, reason for studying wheat genetics is that it is the best-understood genetic model of polyploidy, and study of the species has contributed to knowledge on chromosome pairing and to an understanding of how highly duplicated plant genomes are orchestrated to function within a single organism. Common wheat has often been described as ‘soft’ wheat to contrast it with the ‘hard’ durum and emmer types. However,

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Common wheat has the genome group AABBDD; durum and emmer, AABB; and einkorn, AA. The tetraploid cultivated form of T. timopheevii (Zhuk.) Zhuk. (AAGG) and hexaploid T. zhukovsky Men. & Er. are relatively unimportant. However, the wild AAGG form of T. timopheevii (ssp. ameniacum (Jukubz.) van Slageren) may be more widespread than wild emmer, which is largely restricted to Israel, Jordan, and nearby areas. It is agreed that the A genome of common wheat is derived from a close relative of T. monococcum known as T. urartu Tum. ex Gand. There has been an ongoing controversy regarding the diploid source of the B genome, but the current consensus of opinion is that it was Aegilops speltoides Tausch or a close relative within the Sitopsis section of the Aegilops genus. The D genome came from A. tauschii Coss. (previously squarrosa Coss.). A number of Aegilops species also possess a D genome, and therefore, hybrids with them show a degree of chromosome pairing and, occasionally, a low level of fertility, which can be exploited in wheat improvement. Among the relatives of wheat, there are a number with distinct genomes that have functional, but not chromosomal, homology with those of wheat.

The Cytogenetic Structure of Wheat Cytologically, common wheat behaves as a diploid species. At meiotic metaphase I, the chromosomes form 21 bivalents that regularly disjoin to produce gametes with n ¼ 21. This diploidlike behavior is genetically enforced, but mutants (ph mutants) that disrupt regular chromosome pairing have been isolated. Meiosis in these mutants is more typical of autopolyploidy permitting chromosome pairing between related or homoeologous chromosomes.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00253-9

GENETICS OF GRAINS | Wheat Genetics Wheat Aneuploidy and Breeding Behavior of Monosomics Despite regular chromosome pairing, chromosomes of all species occasionally fail to pair. Unpaired chromosomes behave abnormally in meiosis, resulting in gametes with missing or additional chromosomes. In most diploid animal and plant species, the zygotes (aneuploids) formed from such gametes are lethal or sublethal. In wheat, however, with its genomic triplication, aneuploidy in the form of either chromosome loss or chromosome addition can be tolerated. Between 1930 and 1970, several different series of aneuploids were isolated in common wheat cultivar (cv.) Chinese Spring by E. R. Sears at the University of Missouri. These lines formed the basis of modern wheat genetics for the latter half of the twentieth century, and some of them continue to have a role in the current era of molecular genetics. Some of the more common wheat aneuploids are described in Table 1. When a monosomic wheat plant undergoes meiosis, the 20 bivalents separate in the normal reductional manner, whereas the unpaired univalent may reach one of the dyads, may divide mitotically in first division with the products reaching each dyad, or may lag to be excluded from both nuclei. At second meiotic division, the undivided chromosome, when present, divides normally with the other chromosomes, but if already divided, it may lag to be excluded from the nuclei of the resulting tetrads. The outcome of the various events over all monosomic chromosomes is that about 25% of resulting gametes have n ¼ 21 and about 75% have n 1 ¼ 20. On selfing or crossing to a monosomic as female, this is the realized proportion of functioning eggs. However, through the pollen, the gametes with n ¼ 21 have a competitive advantage and contribute to pollination about 96% of the time Table 1

Some aneuploid sets of Chinese Spring wheat

Aneuploid name

Chromosome no.

Meiotic pairing (metaphase 1)

Monosomic Nullisomic Trisomic Tetrasomic Ditelosomic Double ditelosomic Nullisomic–tetrasomic

41 40 43 44 40 þ 2 telocentrics 40 þ 4 telocentrics 42

2000 þ 10 2000 2000 þ 1000 2000 þ 10000 2000 þ tt00 2000 þ tt00 þ tt00 2000 (100 ) þ 10000

0

, univalent, 00 , bivalent, 000 , trivalent, 0000 , tetravalent or quadrivalent.

(Figure 1). The results of self-pollination are that about 24% of zygotes are normal euploids, 73% monosomic, and 3% nullisomic. Individuals nullisomic for most chromosomes are morphologically weaker than monosomic and disomic sibs and often sterile or partially sterile.

Gene Location by Monosomic Analysis The unique breeding behavior of wheat monosomics allows dominant genes to be located to particular chromosomes. If Chinese Spring carries a dominant or codominant allele conferring a particular phenotype, that phenotype will be missing in the nullisomic for the chromosome that carries the gene (Figure 1). Another way to locate the same dominant gene (AA) in Chinese Spring is to cross the monosomics as female parents with a cultivar or line that carries the contrasting recessive allele (aa). In the ‘critical’ cross, the monosomic individuals (a) will have the recessive phenotype, whereas in all 20 other crosses, the monosomic hybrids will have the dominant phenotype (Aa). The more usual situation is that the dominant gene is present in the nonmonosomic parent. In this case, hybrids can be generated, as in the preceding text, to produce 20 sets of monosomics aA (female gamete written first) and a critical cross with A; all have the dominant phenotype A. On selfpollination, the Aa individuals segregate normally, 3 A (1 AA þ 2 Aa): 1 aa phenotypes, whereas in the critical line, most of the plants (disomics þ monosomics; see Figure 1) will have the A phenotype and a few may show the aa phenotype but are actually nullisomic () and often characteristically weaker. Rather than demonstrating a cytological association between chromosome number and phenotype, researchers often have used a significant statistical deviation from the hypothesized segregation ratio to reach conclusions regarding gene location. Sometimes, this led to failure of location, or incorrect location, due to incorrect hypotheses or to instances where nullisomic frequencies were higher than expected with the consequence that statistical deviations were not detected. Thus, the statistical test should be a guide to chromosome location and the prediction should be validated by chromosome counts or by further genetic tests. The location of genes by monosomic F2 analysis was largely restricted to instances of single dominant gene inheritance; however, other breeding strategies and appropriate cytogenetic models were designed to locate genes involved in more Male transmission

21 chromosomes 96% (81–99) A

20 chromosomes 4% (1–19) –

21 chromosomes 25% (14–39) A

Disomic 25% (11–39) AA

Monosomic 1% (0.1–7) A–

20 chromosomes 75% (61–86) –

Monosomic 72% (49–85) –A

Nullisomic 3% (0.6–16) – –

Female transmission

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Figure 1 The breeding behavior of a typical monosomic plant in Chinese Spring wheat with gene A located in the monosome. The percentage frequencies are mean realized values (and ranges). Frequencies in hybrid generations and other cultivars may exceed these values. For zygotic genotypes (boxes), the allele from the female gamete is written first.

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complex inheritance patterns. For traits controlled by two or more genes and for quantitatively inherited traits, the method of chromosome substitution was more appropriate. Chromosome substitution involves the production of a series of backcross-derived lines whereby monosomy is used to maintain the integrity of one chromosome of a donor parent, while the remaining 20 chromosomes are converted to the genotype of the recipient parent by repeated backcrossing to the relevant monosomic line. After the last backcross (usually 6–10), a monosomic plant is self-pollinated, and a disomic is selected as the fixed substitution line. The 21 substitution lines thus generated can be assessed for the traits of interest, and significant deviations from the phenotype of the recurrent parent are attributed to genes on the substituted chromosome originating from the donor parent. A large number of genes were located by monosomic and chromosome substitution methods. Currently, single genes are located and mapped on chromosomes by linkage to molecular markers dispersed throughout the genome. This simpler procedure depends on DNA polymorphism between the parental lines. More complex traits earlier addressed by intervarietal chromosome substitution lines can be partitioned into genetic components by quantitative trait locus (QTL) mapping procedures. This permits separation of genetic variation both between and within chromosomes as part of a single analysis.

Telocentric Chromosomes During meiosis, unpaired chromosomes occasionally undergo misdivision, breaking at or near the centromere to produce either telocentric chromosomes or isochromosomes. Most, but not all, monotelosomic (potentially 42) and ditelosomic plants in wheat are sufficiently normal and fertile to be maintained as distinct genetic stocks. Because telocentric chromosomes can be identified cytologically, they have special uses in gene localization to chromosome arms, in checking the identities of monosomic chromosomes by testcrossing, and for within chromosome recombination and mapping. Telocentric mapping exploits the use of the telosome as a centromere marker. Analysis of the progeny of a monotelodisomic (2000 þ 1t00 ) heterozygote (Aa) allows determination of the genetic distance between a gene and the centromere (telocentric mapping, Figure 2). In instances where a particular ditelocentric stock cannot be maintained due to sterility, a source of the telosome can be maintained either as a double ditelosomic stock (2000 þ tt00 þ tt00 ) or as a monoteloditelosomic stock (2000 þ tt00 þ t0 ). For example, an individual with 2BS, and not 2BL, can be generated using a CS DT2BS MT2BL (2000 þ ttSS00 þ tL0 ) as a female parent.

Deletion Lines A more recent development on the telocentric method was production of a large series of Chinese Spring lines with deleted segments of individual chromosome arms. These were produced by use of alien-derived genetic stocks that induce random chromosome breaks. Deletion lines can be used to associate genes with their physical positions in the chromosomes and to separate chromosomal regions and genetic maps into bins. In wheat, there is little genetic

A

a

(a)

A

(b)

Figure 2 Method of telocentric mapping: When a plant of genotype AA is crossed to the alternative ditelocentric lines for the relevant chromosome, pairing can be as shown in (a) or (b). Genetic recombination in testcrossed or self-pollinated progenies of (a) can be estimated from the proportions of individuals with the contrasting phenotypes conferred by the A/a locus and chromosome types. Genetic recombination for A/a and the centromere is not possible in (b); in this case, all progenies with phenotype A have an entire chromosome.

recombination in centromeric regions, whereas the distal regions are highly recombinogenic. A consequence is that map-based cloning of genes in the centromere regions is much more difficult than cloning distally located genes. Placement of newly discovered genes in bins is based on the locations of the flanking markers that have been referenced to the Chinese Spring deletion stocks.

Nullisomic–Tetrasomic Lines A very significant discovery by Sears was the realization that nullisomy for one chromosome can be compensated by trisomy or tetrasomy of the related or homoeologous chromosomes from the other two genomes. The compensating combinations permitted identification of the seven sets of three homoeologues numbered 1–7. Nonhomoeologous nullisomic–tetrasomic combinations fail to show complementation and are phenotypically similar to nullisomics. Nullisomic–tetrasomic lines, in conjunction with ditelocentrics, and now deletion lines were essential in determining chromosome locations of the restriction fragment length polymorphism (RFLP) and microsatellite markers used to develop the skeletal chromosome maps of wheat. Most nullisomic–tetrasomic stocks are acceptably stable and fertile, but chromosome numbers should be confirmed in cycles of seed regeneration. The most significant exceptions are the nullisomic 4B combinations, which are sterile due to the absence of an essential gene for male fertility. Although wheat chromosomes are comparatively large, they cannot be identified in general chromosome staining. As for many other species, however, they can be stained by Cbanding procedures to produce unique banding patterns that enable the individual chromosomes to be identified by skilled technicians. C-banding was essential to the isolation and identification of deletion stocks.

Aneuploidy in Tetraploid Wheat Tetraploid wheat is much less tolerant of chromosome loss than common wheat, and monosomics are very difficult to

GENETICS OF GRAINS | Wheat Genetics maintain. The most stable and useful aneuploids developed for cytogenetic analysis at the tetraploid level were the durum cv. Langdon nullisomic-D genome substitution series produced in North Dakota. In these lines, the individual A and B genome chromosomes (except 4B) were replaced by D genome homoeologues of common wheat cv. Chinese Spring (2n ¼ 28 ¼ 1400 ). When such plants are crossed with euploid durum, the chromosome pairing in the hybrid is 1300 þ 10 þ 10 . Since the 1990s, there has been a significant decline in the use of cytogenetic procedures for gene identification and location in wheat although the established cytogenetic knowledge and stocks developed since the 1940s, provided the framework for generating the current genetic reference maps used for more detailed molecular mapping aimed at gene cloning and isolation.

Interspecific Crosses and Gene Transfer Common wheat can be crossed with all Triticum species and with many of its relatives in the Triticeae. The amount of chromosome pairing and fertility of such hybrids determines the methods used to attempt to introgress genetic material and useful agronomic traits from the related species to wheat. The most common and useful crosses for hexaploid wheat improvement have been those with close relatives such as tetraploid wheats and A. tauschii, but there are some very successfully exploited introgressions from species of more distantly related genera such as Thinopyrum. Once an accession with a trait of interest is identified in a related species, the first step is to produce a hybrid and to determine if such hybrids are fertile when self-pollinated or when backcrossed, particularly as female parents, with wheat. Bridging crosses and/or embryo rescue may be useful in achieving the fertility needed to undertake the transfer. Hybrids with at least some chromosome pairing are often sufficiently fertile to enable the transfer process through normal genetic recombination. Hybrids with little or no chromosome pairing sometimes form chromosomally doubled amphiploids, or partial amphiploids, through generation of restitution nuclei, or may undergo chromosome doubling in response to treatment with colchicine. Both backcrossing and amphiploids have been used to transfer genes from diploid wheat (via AAB, AABD, or AAAABB bridging crosses) and A. tauschii (via ABDD or AABBDD hybrids). These transfers take advantage of normal homologous chromosome pairing. Hybrids of amphiploids and partial amphiploids with wheat show normal chromosome pairing of the common wheat chromosomes with the additional ‘alien’ chromosomes occurring as unpaired univalents. Backcrossing and selection for a trait or chromosome of interest result in recovery of single monosomic addition lines (2n ¼ 43, 2100 W þ 10 A). Such alien chromosomes have the ability to substitute for their wheat homoeologues to produce 42 chromosome derivatives (2000 W þ 10 A) that approach normal wheat in vigor and fertility. Progenies of monosomic addition lines, or preferably hybrids of alien substitution lines and wheat (2000 þ 10 W þ 10 A), can be used to select for translocation events that involve the alien chromosome and, most frequently, the unpaired wheat homoeologue. Such translocations may occur spontaneously

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and often involve entire arm-centric fusions following misdivision or may be induced by genetic procedures or by radiation with x-rays or fast neutrons. Through the use of further hybrids with some genotypes of A. speltoides or related species, deletion of chromosome 5B, or mutants with disrupted control of strict bivalent pairing (ph mutants), homoeologous chromosomes can be induced to pair and recombine with each other, including the homoeologous alien chromosomes. Potential recombinants can be selected from progeny populations that appear to segregate in Mendelian ratios in contrast to the markedly reduced transmission rates of unpaired alien chromosomes. Candidate recombinants can be confirmed by meiotic chromosome pairing, C-band analyses, or in situ hybridization using genomic DNA from the donor species as a dispersed probe. Obviously, small homoeologous chromosome exchanges are most likely to be successfully exploited in agriculture because they should have minimal disruptive effects on inheritance and reduced likelihood of carrying undesirable genetic material. However, there are exceptions, and the most widely exploited alien genetic transfer in wheat involves the replacement of the entire short arm of chromosome 1B with the short arm of 1R from cereal rye. The added rye segment carries genes for disease resistance and higher yield and better adaptation under certain conditions but can have detrimental effects on bread-making quality. With the availability of genetic markers, the process of alien gene transfer, chromosome engineering, is not different in concept to that of genetic engineering where cloned genes at the DNA level are inserted into a chosen genotype. Transformation, however, is independent of sexual compatibility and can be carried out with genes isolated from another genotype of the recipient species or genes isolated from any source.

Wheat Genetics Despite the known evolution of tetraploid and hexaploid wheat, and the presence of common traits in these species and in the known ancestors and related species, not all traits in polyploid wheat are controlled by triplicated and duplicated genes. Some genes apparently have been mutated or lost entirely from the genome. The genes controlling some traits are clearly triplicated at corresponding or orthologous sites in each genome (e.g., the R gene series in group 3 chromosomes controlling red kernel color), whereas other traits seem to be affected by single genes of major effect (e.g., the squarehead or nonspelt gene Q on chromosome 5A) or by multiple genes located on nonhomoeologous chromosomes (e.g., the strong awn inhibitors on chromosomes 4A, 5A, and 6B). Triplicated traits such as red kernel color may be controlled by one, two, or three dominant genes depending upon the particular cultivar, or the kernel may be white. In contrast, the presence of ligules (compared with nonliguled variants) in common wheat is determined by genes in chromosomes 2B and 2D, whereas in tetraploid wheat, the gene in 2B is common and the gene in 2A is extremely rare. Because the ancestral A genome species, T. monococcum and T. urartu, and all related diploid species are liguled, it seems that the orthologous gene in chromosome 2A was lost (null allele) in many polyploid wheats. Using this

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knowledge, alien chromosomes of homoeologous group 2 can be selectively added to wheat using a liguleless wheat stock as the recurrent parent. Despite the powerful techniques of genetic analysis that became available with aneuploidy, the genetic map of the large wheat genome continued to be sparsely populated. This was alleviated initially by the study of isozyme variation. More than 25 proteins, and often multiple forms of related enzymes, such as the esterases, were identified and characterized by electrophoresis. Many but not all allozymes were determined by orthologous gene sets. Individual electrophoretic bands were located to chromosomes and chromosome arms using nullisomic–tetrasomic and ditelocentric lines, and allelic variation at some loci enabled genetic mapping. However, allozyme analysis did not provide the high level of variation and number of loci that was being sought. Moreover, each protein had to be extracted, separated, and stained by individual techniques, and the overall process was expensive and tedious. Opportunities for more detailed genetic analysis of wheat became available firstly with discovery and use of restriction enzymes and RFLP analysis and, later, with techniques for studying DNA polymorphism based on the polymerase chain reaction (PCR) protocol. As with allozymes, electrophoretic bands were related to chromosome arms, but again, the levels of allelic variation determined with RFLPs was relatively low in wheat compared with barley and maize. RFLPs were usually triplicated in orthologous sets. Despite the relatively low levels of polymorphism, many RFLPs were mapped and the information obtained contributed to a backbone of reference points on the wheat genetic map. More recently, PCR-based microsatellite or simple sequence repeat techniques provided an expanding number of chromosomally unique polymorphisms that can be readily mapped. Large ‘banks’ of these have been developed for use by restricted ‘consortium’ groups or are available in the public domain. Microsatellites are the current tools of choice being applied to the rapidly expanding application of marker-assisted (markerlinked) selection in wheat improvement, but this is being replaced by direct sequencing technologies. With increasingly detailed genetic maps, it became apparent that expressed genes are not evenly distributed throughout the large genome. Comparative physical and genetic maps showed a clear clustering of mapped genes to the terminal regions of chromosomes. For example, chromosome 1BS has a visible restriction about two-thirds of its length from the centromere. Most, if not all, of the mapped genes in 1BS are located in the satellite demarcated by the restriction.

A Wheat Gene Catalog Since 1968, wheat researchers have maintained a wheat gene catalog that ensures that genes are named in accordance with accepted rules. The catalog provides relevant information for each named gene, including attributes such as dominance, or origin if from an alien source, synonymous names, chromosome and arm locations, available genetic stocks in increasing order of complexity, and, for genes determining morphological, quality, and disease traits, proximity to molecular markers. Catalog supplements are published annually and complete revisions occur at 5-yearly intervals.

Genetics of Quality Traits in Wheat Wheat is an important foodstuff for mankind because of its unique quality characteristics and the fact that large quantities of grain can be produced, harvested, stored, and transported in an efficient way. Its ability to produce a wide range of products is determined by the starch characteristics of the endosperm and the proteins that constitute 6–15% of the milled products. The main storage proteins, the glutenins and gliadins, determine dough strength, extensibility, and elasticity. The glutenin genes are classified as high-molecular-weight glutenin genes located in the long arms of group 1 chromosomes and the low-molecular-weight group located in the short arms. Up to five orthologous groups of gliadin genes occur in chromosomes of homoeologous groups 1 and 6. Relative amounts of protein in wheat grain are largely environmentally influenced, but there are also genetic components for which group 5 chromosomes were particularly implicated. Grain softness in common wheat, conferred by a dominant gene on chromosome 5DS, determines the milling characteristics and hence its suitability for the manufacture of specific products. Mutations in an orthologous series of waxy proteins (GBSS) in chromosomes 4AL (translocated from 7BS), 7AS, or 7DS can, in various combinations, enhance the suitability of flour for noodle production.

The Genetics of Adaptation Wheat cultivars used throughout the world were chosen pragmatically by farmers to suit the agronomic and climatic constraints of the environments in which they were grown. The genes that determine the growth and flowering characteristics include those responsible for response to vernalization, response to day length, and earliness per se. In common wheat, there are up to five orthologous groups affecting vernalization response, one orthologous group (chromosome group 2) affecting day length response, and several diversely located genes for earliness per se. Nil or reduced vernalization response and reduced day length response are conferred by dominant alleles. Reduced plant height and increased straw strength were strongly selected by breeders in order to achieve higher yields through higher harvest index and reduced lodging. While the gibberellin-insensitive Rht-B1b and Rht-D1b alleles in chromosomes 4BS and 4DS were the choice of the green revolution, these alleles limit expression of coleoptile length, often resulting in low seedling emergence attributes for planting in dry environments. Consequently, attempts are being made to exploit alternative alleles at these loci or various gibberellinsensitive Rht genes in order to improve seedling vigor.

The Genetics of Stress Resistance There are reports of genetic variation for tolerance to drought, freezing (leaf tissue), frost (spikes and flowers), heat, salt, certain herbicides, and both mineral deficiencies and toxicities. In some instances, major genes were documented; in others, such as drought and heat tolerance, variability was largely quantitative. Biotic stress resistances were found to have both qualitative and quantitative genetic bases. For diseases caused by highly specialized, pathogenically variable obligate pathogens such as

GENETICS OF GRAINS | Wheat Genetics the rusts, powdery mildew, and some smut pathogen species, as well as the Hessian fly pest, resistances were characterized in terms of several to many genes, each of large effect. For less specialized pathogens (and pests) such as those causing root rots and Fusarium head scab, individual gene effects were not so obvious, but there has been significant progress in genetic analysis using QTL mapping. A significant recent development for the important leaf rust and stripe rust diseases has been increased emphasis on analyzing and exploiting durable adult plant resistances (APR). The genetics of durable APR have indicated oligogenetic additive combinations of genes, which individually confer relatively low levels of resistance but may have multipathogen effectiveness. These findings offer the breeder the choice of selection for high levels of resistance in the disease nursery, predicting that agriculturally acceptable phenotypes will have gene combinations. To achieve this, major genes should be avoided in crossing programs or nullified in segregating populations by using appropriate virulent pathotypes for disease screening. Alternatively, specific molecular markers, if available, enable such genes to be combined in a planned way.

Concluding Remarks The methods of genetic analysis of wheat have evolved since the 1990s, from a strong effort on cytogenetics to an almost exclusive emphasis on molecular approaches. Cytogenetic stocks and knowledge enabled the construction of basic molecular framework maps to which the emerging molecular mapping data were referenced. With the rapidly increasing marker density of the genetic map, and current methods of discovering DNA polymorphisms, there is an expanding effort on gene characterization by heterologous homologies and gene isolation in wheat, as well as the increased application of marker technologies and transformation in both wheat and durum improvements.


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What are the genetic characteristics of the wheat family, especially mentioning the levels of ploidy? Explain the word ‘aneuploid’ and illustrate its meaning with examples and the value of aneuploids in wheat genetics research. How is the localization of specific genes achieved by monosomic and chromosome substitution methods? Contrast the genetics of red kernel color with that of the presence of ligules. Describe the genetics of several genes related to grain quality, adaptation, and biotic stress.

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Research the ways in which wheat genetics and conventional breeding have contributed to the control of wheat pathogens, especially the rusts. Do you expect that recently developed genetic modification approaches will be more successful than the conventional ones in providing genetic resistance to pathogens? How?

See also: Agronomy of Grain Growing: Necrotrophic Pathogens of Wheat; Wheat: Biotrophic Pathogen Resistance; Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Genetics of Grains: Wheat Genetics and Genomics; Grain Harvest, Storage and Transport: The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species; Processing of Grains: Evaluation of Wheat-Grain Quality Attributes; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Wheat-Based Foods: Noodles: Asian Wheat Flour Noodles.

Further Reading Borner A and Worland AJ (eds.) (1996) Selected papers from the EWAC conference: “Cereal Aneuploids for Genetical Analysis and Molecular Techniques” held in Gatersleben, Germany, July 1994. Euphytica 89(1). Endo TR and Gill BS (1996) The deletion stocks of common wheat. Journal of Heredity 87: 295–307. Feldman M (2001) Origin of cultivated wheat. In: Bonjean AP and Angus WJ (eds.) The World Wheat Book. A History of Wheat Breeding, pp. 3–53. Paris: Lavoisier. Heyne EG (ed.) (1987) Wheat and Wheat Improvement, 2nd edn. Madison, WI: American Society of Agronomy. Johnson R (1984) A critical analysis of durable resistance. Annual Review of Phytopathology 22: 309–330. Kimber G and Feldman M (1987) Wild Wheats, An Introduction, p. 142. Columbia: College of Agriculture, University of Missouri Special Report 353. Lupton FGH (ed.) (1996) Wheat Breeding. London: Chapman and Hall. McIntosh RA, Hart GE, Devos KM, Gale MD, and Rogers WJ (1998) Catalogue of gene symbols for wheat. In: Slinkard AE (ed.) Proceedings of the 9th International Wheat Genetics Symposium. Saskatoon, Canada: Extension Press, University of Saskatchewan. Morris R and Sears ER (1967) The cytogenetics of wheat and rust relatives. In: Quisenberry KS and Rietz LP (eds.) Wheat and Wheat Improvement, pp. 19–87. Madison, WI: American Society of Agronomy. Qi LL, Echalier B, Chao S, et al. (2004) A chromosome bin map of 16,000 expressed sequence tag loci and distribution of genes among the three genomes of polyploid wheat. Genetics 168: 701–712. Sears ER (1954) In: The Aneuploids of Common Wheat. Missouri Agricultural Experimental Station Research Bulletin, 572, p. 59. Columbia, MO: University of Missouri, College of Agriculture, Agricultural Experiment Station. Sears ER (1976) Genetic control of chromosome pairing in wheat. Annual Review of Genetics 10: 31–37. Van Slageren MW (1994) Wild Wheats: A Monograph of Aegilops L. and Amblyopyrum (Jaub and Spach) Eig. (Poaceae), p. 512. Wageningen, The Netherlands: Wageningen Agricultural University Wageningen Agricultural University Papers 94-7. Worland AJ and Snape JW (2001) Genetic bases of worldwide wheat varietal improvement. In: Bonjean AP and Angus WJ (eds.) The World Wheat Book. A History of Wheat Breeding, pp. 53–94. Paris: Lavoisier.


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Explore the methodology of cytogenetics. To what extent has this approach to wheat genetics been replaced or complemented by molecular genetics? Search a recent issue of the wheat gene catalog and websites (such as http://wheat.pw.usda.gov) and describe the localization of important agronomic and grain-quality genes.

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Relevant Websites http://www.ksu.edu– Wheat Genetics Resources Center, Kansas State University. http://www.shigen.nig.ac.jp– National Institute of Genetics, Japan. http://wheat.pw.usda.gov – GrainGenes wheat website.

Wheat Genetics and Genomics E Akhunov, Kansas State University, Manhattan, KS, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The durum wheat and bread wheat are allopolyploid crops that originated by the hybridization of several wild grass species. Wheat was first domesticated about 10 000 years ago in southeastern Turkey. During domestication, humans selected plants that possessed a suite of traits making them suitable for agriculture. Polyploid wheat can tolerate aneuploidy in the form of either chromosomal loss or addition. The total size of the hexaploid wheat genome is about 17 gigabases, mostly (>80%) represented by highly repetitive transposable elements. Next-generation sequencing technologies have made sequencing the complex wheat genome feasible. The analysis of the shotgun assemblies of wheat chromosomes revealed about 106 000 functional coding genes. The majority of triplicated homoeologous genes in wheat are transcriptionally active. Evidence suggests that since wheat is of polyploid origin, the gene expression of ancestral genomes was adjusted to become a part of a single regulatory network. High-density genotyping assays and sequence-based genotyping approaches (sequence capture and genotyping-bysequencing) provided a detailed view of genomic variation in wheat. Genome-wide diversity analyses helped to gain insights into historic selective events and identify candidate selection targets prioritized by humans at the early stages of wheat improvement.

Learning Objective

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To achieve understanding of the wheat genome complexity and its role in the origin of agronomic traits.

Introduction Wheat is one of the major sources of calories and protein in the human diet and is the second most important crop worldwide. There are two species of commercially grown wheat. Common wheat, used for making bread, cookies, and pastries, comprises most of the produced crop (95%). The remaining 5% is durum wheat, used for making pasta and other semolina-based products. Common or bread wheat (Triticum aestivum L.) is an allohexapolyploid crop with a genome composed of 21 pairs of chromosomes (2n ¼ 42). Durum wheat is an allotetraploid species with 14 pairs of chromosomes (2n ¼ 28). Wheat exhibits substantial variation for a number of agronomic traits and has adapted to diverse ecogeographic habitats. This broad

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adaptability likely results from a high rate of evolutionary changes in the polyploid wheat genome, which was formed by the hybridization of two or three wild diploid species. Domestication of tetraploid emmer and diploid einkorn wheat along with barley in the Middle East played a critical role in the transition from hunter-gathering societies to the modern sedentary agricultural communities. Information collected by geneticists and archeologists has helped to reconstruct the major events in the evolutionary history of wheat. The ancestry of wheat was traced back to several wild grass species from the Triticum and Aegilops genera. Tetraploid wild emmer wheat (T. dicoccoides, AABB genome) originated from the hybridization of the diploid wild grass T. urartu (AA genome) and a species closely related to modern Aegilops speltoides (SS ¼ BB genome). According to genetic and archaeological evidence, emmer was domesticated in the Diyarbakir region in southeastern Turkey about 10 000 years ago. The spread of domesticated emmer (T. dicoccon) from the original site of domestication brought it in contact with goat grass Ae. tauschii (DD genome), resulting in the origin of hexaploid bread wheat (AABBDD genome) on the southwest coast of the Caspian Sea. During domestication, humans selected plants that possessed a suite of traits, also referred to as the ‘domestication syndrome,’ making them suitable for agriculture. Among the traits affected by domestication, the major one was spike shattering that controls the seed dispersion mode. A mutation in the Br (brittle rachis) locus controlling this trait resulted in nonshattering spikes, thereby reducing seed loss due to dispersion by wind allowing for more effective grain harvest. Morphological studies of einkorn wheat remains from archaeological sites suggest that the domestication process was gradual and took nearly 1000–2000 years to replace the wild forms of wheat with nonshattering forms. The loss of its tough glume during the transition from hulled to freethreshing wheat was another important domestication trait, which is mostly controlled by the recessive mutation in the Tg (tenacious glume) locus with a modifying effect from the Q gene. The Q gene also influences other domestication-related traits such as glume shape, rachis fragility, and spike morphology.

Aneuploidy and Chromosome Deletion Lines Wheat has arguably one of the richest cytogenic resources among other crops. Polyploid wheat can tolerate aneuploidy in the form of either chromosomal loss or addition. Between 1930 and 1970, a series of aneuploids were isolated in the common wheat cultivar (cv.) Chinese Spring by E. R. Sears at the University of Missouri (Table 1). Historically, these lines played a critical role in the initial mapping of the wheat genome helping to locate dominant genes controlling many


http://dx.doi.org/10.1016/B978-0-12-394437-5.00228-X

GENETICS OF GRAINS | Wheat Genetics and Genomics Table 1

Aneuploids of Chinese Spring cultivar

Aneuploid line

Number of chromosomes

Meiotic pairing (metaphase 1)

Monosomic Nullisomic Trisomic Tetrasomic Ditelosomic Double ditelosomic Nullisomic–tetrasomic

41 40 43 44 40 þ 2 telocentrics 40 þ 4 telocentrics 42

2000 þ 10 2000 2000 þ 1000 2000 þ 10000 2000 þ tt00 2000 þ tt00 þ tt00 2000 –(100 ) þ 10000

0

, univalent; 00 , bivalent; 000 , trivalent; 0000 , tetravalent or quadrivalent. Source: McIntosh (2004).

important agronomic traits and to create a framework for the development of high-resolution genetic and physical maps. There are several ways in which monosomic lines are used for gene mapping. For example, a phenotype conferred by a dominant gene will be missing in a line that has a chromosomal arm carrying the gene being deleted. Alternatively, the same dominant gene (AA) in Chinese Spring can be located by crossing monosomics as female parents with a cultivar or a line that carries the contrasting recessive allele (aa). In this case, the monosomic individuals (a) will have the recessive phenotype, whereas in all 20 other crosses, the monosomic hybrids will have the dominant phenotype (Aa). Nullisomic–tetrasomic lines discovered by Sears helped to clarify the homoeologous relationships among the chromosomes. It was realized that nullisomy for a chromosome can be compensated by tetrasomy of the homoeologous chromosomes from the other two genomes helping to group all 21 wheat chromosomes into seven sets of homoeologues. Higher resolution of markers, or trait mapping, was achieved in the deletion lines of wheat developed from the progeny of the cultivar Chinese Spring with the monosomic addition of chromosome 2 from Ae. cylindrica. This chromosome harbors the Gc gene (gametocidal gene) that triggers chromosome breakage in gametes that do not inherit the Gc gene. Most chromosomal deletions were developed as homozygous lines and are broadly used for codominant marker and trait mapping. The deletion bin mapping approach was successfully used to create a map of expressed sequences, including nearly 16 000 loci.

Wheat Gene Catalog Since 1968, wheat researchers have maintained a wheat gene catalog that ensures that genes are named in accordance with accepted rules. The catalog provides relevant information for each named gene, including attributes such as dominance, or origin if from an alien source, synonymous names, chromosome and arm locations, available genetic stocks in increasing order of complexity, and, for genes determining morphological quality and disease traits, their proximity to molecular markers. Catalog supplements are published annually and complete revisions occur at 5-year intervals.

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Genomic Tools and Resources A diverse set of tools and resources for analyzing the wheat genome are currently available. The main advances are linked with the rise of next-generation sequencing (NGS) technologies that have made it feasible through cost-effective generation of genomic data, even for large genomes such as wheat. The NGS was initially applied for large-scale discovery of single-nucleotide polymorphisms (SNPs) in small panels of lines representing founders of mapping or breeding populations or capturing the geographic diversity of wheat. The discovered SNPs were used for the development of highdensity genotyping assays including from 10 000 to 100 000 s markers. These assays provided the first opportunity to perform genome-wide analyses of genetic variation in large populations of several thousand diverse wheat lines and to create high-density genetic maps. Even higher-density assays on the order of several hundred thousand SNPs are currently developed (as of February 2015). Smaller-scale assays capable of genotyping a limited number of variable sites in large populations of 1000–100 000 lines found their application in marker-assisted breeding. These assays are usually designed to interrogate SNPs closely associated with variation in important agronomic traits. While SNP genotyping assays are a powerful tool for the analysis of genetic variation, the decrease in the cost of NGS made it feasible for direct sequencing of genomes and transcriptomes of multiple wheat lines. Contrary to SNP-based genotyping assays, sequencing allows for direct analysis of genetic variation, thereby reducing the effect of ascertainment bias sometimes caused by an inadequate wheat line selection for SNP discovery. To further improve the cost-effectiveness of sequencing, researchers developed approaches for reducing the complexity of the wheat genome through targeted sequence enrichment or restriction enzyme digests. Using these approaches, NGS is performed only on a small fraction of the large wheat genome. The targeted enrichment approach uses short oligonucleotides (‘baits’) to capture complementary sequences of interest that usually represent exonic regions of genome. The wheat exome capture assay covering 107 Mb of nonredundant sequence was used to construct a high-density 1.5 million SNP diversity map of the wheat genome. This diversity map also referred to as a haplotype map can serve as the foundation for cross-linking multiple gene mapping and diversity studies. Using a relatively small set of SNP markers (10 000–20 000 SNPs) shared between the wheat haplotype map and any other wheat population of interest, it is possible to predict alleles at nongenotyped sites in the population of interest. This procedure, called genotype imputation, tremendously increases the number of markers available for trait mapping without the need of additional genotyping, thereby increasing the likelihood of detecting causal SNPs or variants tightly linked with causal SNPs. The same 107 Mb exome capture assay was successfully used to detect chemically induced mutations in the tetraploid durum wheat genome. Mutations induced by treating wheat seeds with ethyl methanesulfonate can help to understand gene function. Their utilization until recently was limited by the need to perform labor-intensive screening of 1000 lines

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for the presence of a mutation in the gene of interest. By resequencing exons of the entire mutagenized population using the exome capture assay, it is now realistic to identify mutations in silico by simple sequence similarity searches. The complexity reduction of the wheat genome achieved by restriction enzyme digestion followed by sequencing short 100 bp long sequence tags around the PstI sites is referred to as genotyping by sequencing (GBS). A high proportion of missing genotype calls in GBS studies are compensated by its low cost. Since 2013, GBS has been broadly used for constructing genetic maps, trait mapping, and predicting phenotypic values in genomic selection experiments. Because PstI restriction enzyme is methylation-sensitive, the majority of GBS tags are located within the nonrepetitive DNA in close (100 kb) proximity of genic regions. With the development of wheat genome sequence information, GBS promises to become one of the major low-cost genotyping solutions for wheat breeding. Recently, resequencing for genome-wide surveys of genetic diversity became feasible with the increased throughput of the NGS platforms. This approach provides an unbiased estimation of genetic diversity across the genome in both coding and noncoding regions allowing for the detection of various types of genetic variation including not only SNPs and small indels but also large megabase-scale indels and copy number variants. By combining whole genome NGS shotgun sequencing with aligning whole genome shotgun and cDNA sequence data, SNP discovery was performed for the diploid ancestor of the polyploid wheat D genome Ae. tauschii. Whole genome sequencing of a small set of diverse wheat lines provided a rich resource for the development of genotyping assays. Shallow whole genome NGS of doubled-haploid (DH) wheat lines was shown to be effectively used for assembling the wheat genome. The comparison of two parents of the DH population revealed about 19 million SNPs, further expanding the resources available to wheat geneticists for analyzing its complex genome.

Wheat Genome and Its Organization Allopolyploidy Wheat is a young allopolyploid formed by the hybridization of the diploid grass species T. urartu, Ae. speltoides, and Ae. tauschii, which diverged about 5–7 Ma ago. As a result, the majority of genes are present in two and three copies in the genomes of durum wheat and bread wheat, respectively. This genetic redundancy is believed to have contributed to wheat’s adaptability and defined its success as a globally grown crop. By combining the genomes of its diploid ancestors that are adapted to different environments, the resulting allopolyploidy may have broadened the adaptive potential of wheat. Moreover, hybridization of the diverged genomes is accompanied by structural rearrangements, activation of transposable elements, epigenetic modifications, and gene expression changes generating new functional variation and creating the basis for the evolution of new adaptive phenotypes. Wheat has three homoeologous groups of chromosomes with seven chromosomes per genome. During meiosis, wheat chromosomes pair only with homologues from the same homoeologous group demonstrating diploid-like behavior

and forming 21 bivalents that produce gametes with n ¼ 21. This diploid-like meiotic chromosome paring is controlled genetically by the Ph1 (pairing homoeologous) gene that ensures the stability of the complex polyploid genome. Ph1 deletion mutants showing abnormal pairing and recombination among homoeologous chromosomes have played an important role in developing methods of gene transfer from distantly related wild grasses to wheat.

Wheat Genome The total size of the hexaploid wheat genome is about 17 gigabases, mostly (>80%) represented by highly repetitive transposable elements. The wheat subgenomes vary in size with the A, B, and D genomes of 5.7, 6.3, and 4.9 Gb, respectively. The sizes of the diploid ancestral genomes are similar to those reported for the wheat subgenomes. The complexity of the wheat genome associated with polyploidy and its large repeat content was the major obstacle to its sequencing. With the development of high-throughput approaches to genome analysis, the first physical maps based on the ordered set of bacterial artificial chromosome (BAC) clones of individual chromosomes and the whole genome of Ae. tauschii were developed. In the former case, BAC libraries were constructed using DNA prepared from the individual chromosomes separated from each other using flow cytometry. Using the set of BAC clones covering the entire wheat chromosome 3B, the largest wheat chromosome (1 Gb in size) has been sequenced providing the first insights into the organization of wheat chromosomes. A total of 7264 genes were found on this chromosome, out of which 27% were likely nonfunctional pseudogenes. The gene density was highest at the end of the chromosome and lowest near the centromere. The opposite trend was observed for transposable elements representing nearly 88.6% of the chromosome. With the development of NGS methodologies, the genomes of the diploid wheat ancestors and the flow-sorted chromosomes of bread wheat have been sequenced using a shotgun approach. In this approach, DNA is sequenced in pairs of short reads of 100 bp long and assembled using computational algorithms that reconstruct the order of bases in the genome by stitching together overlapping sequence reads. Because of the short read length, most repetitive DNA sequences cannot be uniquely assembled into contiguous fragments (contigs). For these reasons, the shotgun sequencing assemblies mostly represent the coding and low-copy regions of the complex wheat genome. The analysis of shotgun assemblies revealed 106 000 functional coding genes with the highest number of genes in the B genome (44 523; 35%) followed by the A and D genomes, which contained 40 253 (33%) and 39 425 (32%), respectively. About 20% of genes are duplicated in tandems within chromosomes. The gene content and order (also referred to as synteny) among the wheat genomes and their ancestors are conserved. Each wheat genome retained a significant fraction of the genes from their respective diploid ancestors (91–96%). About 60% of genes in the wheat genome were conserved across all diploid ancestors. The decay of synteny among the wheat genomes is associated with gene deletions and duplications during the diploid and polyploid stages of its genome evolution.

GENETICS OF GRAINS | Wheat Genetics and Genomics Discovery of DNA deletions in the newly created artificial synthetic wheat lines suggested that gene loss could be partially attributed to structural changes during polyploidization. The level of synteny along the wheat chromosomes varies with distance from the centromere. The lowest level of gene conservation is found at the ends of the chromosomes and was mostly associated with active gene loss or duplications in the highly recombining chromosomal regions. Compared to other grass species, wheat demonstrated one of the highest rates of gene content evolution, which is strongly correlated with genome size and repetitive DNA content.

Regulation of Gene Expression The majority of triplicated homoeologous genes in wheat are transcriptionally active. However, the contribution of different homoeologous copies to total expression can vary from gene to gene. It was suggested that such homoeologue-specific transcription bias is indicative of the partitioning of the original gene function (before polyploidization) among the duplicated gene copies. The results of spatiotemporal analyses of gene expression in wheat are consistent with this hypothesis of subfunctionalization and suggest that the relative contribution of different homoeologues to gene expression might change across different tissues and different developmental stages. Consistently, the detailed analysis of transcriptional regulation during wheat endosperm development revealed cell type- and stage-dependent genome dominance. Obtained evidence suggests that since wheat is of polyploid origin, the gene expression of ancestral genomes was adjusted to become a part of a single regulatory network. The importance of these newly established regulatory interactions in phenotypic, developmental, and physiological properties of hexaploid wheat was clearly demonstrated by Kerber. Kerber had reconstituted a tetraploid AABB component of the hexaploid wheat genome from a cross between tetraploid durum and bread wheat. The reconstituted tetraploid did not phenotypically resemble any existing tetraploid wheat lines and showed reduced growth, vigor, and fertility. However, fertility and vigor were restored by the hybridization of the reconstituted tetraploid with diploid Ae. tauschii. Based on these results, Kerber postulated the existence of genetic changes in the AABB component of the wheat genome accumulated since its origin and compensated by hybridization with Ae. tauschii. Comparative analysis of gene expression among reconstituted tetraploid, Ae. tauschii, and synthetic hexaploid wheat created by the hybridization of tetraploid wheat with Ae. tauschii showed that the majority of genes in synthetic wheat exhibit a midparent level of gene expression indicative of equal contribution of parental genes to the total level of gene expression. Only 20% of genes in synthetic wheat showed nonadditive expression in which one of the parental copies contributed disproportionately more to total gene expression than other homoeologues. Some of these nonadditively expressed genes are shown to be involved in the regulation of biological processes defining growth and development. For example, functional annotation of upregulated homoeologous genes in synthetic wheat revealed groups of genes involved in key biological processes such as protein biosynthesis and photosynthesis.

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Impacts of Wheat Domestication and Improvement on Genomic Variation Genetic variation in wheat populations is shaped by the interplay of multiple factors including two polyploidization events, domestication, spread from the sites of origin in the Fertile Crescent to new geographic regions, reciprocal gene flow between wild and domesticated populations, and more recent postdomestication selection aimed at developing high-yielding locally adapted varieties. Consistent with studies performed on the majority of domesticated crops, comparative diversity of wild and domesticated emmer collected in the Diyarbakir region of Turkey revealed a genome-wide reduction of genetic diversity by 40–50% due to a population bottleneck accompanying domestication. However, the finding of domesticated emmer populations outside of this region showing genetic diversity higher than that of wild emmer is considered as evidence for gene flow between the populations of domesticated and wild wheat. Clear genetic separation of wild and domesticated emmer into southern and northern populations is likely the consequence of the introgression of alleles from wild emmer; this occurred after the origin of domesticated emmer and its spread from the center of origin to other geographic regions. Genetic diversity of bread wheat is lower than that of domesticated emmer from the Diyarbakir region consistent with another population bottleneck in the evolutionary history of wheat. One of the factors explaining this bottleneck was the limited number of founders that participated in the hybridization of tetraploid wheat with Ae. tauschii that eventually resulted in the origin of hexaploid wheat. However, one of the most striking observations was that the level of genetic diversity in the A and B genomes of hexaploid wheat was nearly three times higher than the level of genetic diversity of the D genome. Compared to the ancestors, the A and B genomes of T. aestivum have 48% of nucleotide diversity present in domesticated emmer; the D genome has only 6% of that present in Ae. tauschii. It was shown that these differences in the level of diversity among the genomes could be explained by the gene flow from the sympatric populations of tetraploid wheat and landraces. This gene flow between tetraploid wheat and hexaploid wheat could happen through the formation of pentaploid hybrids that can produce viable progeny. Selection imposed by humans on favored alleles controlling traits valuable for agriculture impacts the standing variation of surrounding genomic regions resulting in reduced diversity, extended linkage disequilibrium, or strong interpopulation allele frequency differentiation. Genome-wide analyses of diversity using high-density genotyping technologies could be used to detect these signatures of selection (selective sweeps). The analysis of a worldwide collection of 2994 wheat lines genotyped using a 9000 SNP genotyping assay revealed that multiple genomic regions were targeted during wheat improvement. Genomic regions showing evidence of selection harbored a number of genes contributing to important phenotypes in wheat or other plants; these regions included the Rht-B1 locus, associated with wheat dwarfing phenotypes Ppd-B1 and Vrn1 variants that are associated with day-length insensitivity and flowering time in both wheat and barley.

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A more detailed analysis of wheat genomic diversity by direct resequencing of 107 Mb of exonic and low-copy sequences in the diverse population of lines showed that genomic regions showing the signature of selection are enriched for SNPs strongly associated with a number of agronomic phenotypes identified in genomewide association studies (GWAS). Many selective sweep regions were enriched for NB-ARC and LRR encoding domains of genes involved in disease resistance pathways. Consistently, selective sweep regions harbored three to five times more SNPs associated with resistance to wheat rusts in GWAS than regions of the wheat genome not showing the evidence of selection. These first genome-wide diversity studies helped to gain insights into historic selective events and identify candidate selection targets prioritized by humans at the early stages of wheat improvement. In many cases, these targets were associated with genes controlling traits that play important roles in modern agriculture and are often involved in response to biotic and abiotic stress stimuli.

Concluding Remarks Between 2000 and 2015, wheat has transitioned from a genomic resource-poor crop to become one of the model systems with a rich set of genetic and genomic tools developed for analyzing its complex genome. In the future, applications of these tools will undoubtedly lead to tremendous progress in understanding the genomic basis of many traits. Highthroughput genotyping and phenotyping approaches combined with the existing genomic resources will allow for increasing the scale of mapping studies and identifying the effects of individual SNPs, thereby building a foundation for designing high-yielding varieties adapted to harsh climatic conditions and resistant to pests and pathogens.


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When and where was wheat domesticated? What is the meaning of the term ‘domestication syndrome’? What role have the aneuploids and chromosome deletion lines play in studying the wheat genome? What are the advantages of using genotyping-bysequencing approaches for studying genetic variation compared to SNP-based genotyping assays? What is the effect of Ph1 gene deletion on homoeologous pairing during meiosis? What is the meaning of the term ‘synteny’? Which factors can result in the decay of synteny among the homoeologous genomes? How strong was the impact of domestication and subsequent wheat improvement on the levels of genetic diversity? How many functional genes were identified in the wheat genome?


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Domestication targets a set of genes controlling traits important for agriculture. What are the names of these genes and their functions in wheat and other grain crops?

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What was the role of genetic variation present in the populations of wild ancestral species (wild emmer and diploid ancestors) in shaping the genetic diversity of cultivated wheat? Describe the significance of Ph1 gene deletion mutants in wheat genetics and breeding.

See also: Breeding of Grains: Wheat Breeding: Exploiting and Fixing Genetic Variation by Selection and Evaluation; Genetics of Grains: Genome Mapping; Genomics of Food Grains; The Basics: Taxonomic Classification of Grain Species; The Cereal Grains: Durum Wheat: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

Further Reading Akhunov ED, Akhunova AR, Anderson OD, et al. (2010) Nucleotide diversity maps reveal variation in diversity among wheat genomes and chromosomes. BMC Genomics 11: 702. Akhunov ED, Goodyear AW, Geng S, et al. (2003) The organization and rate of evolution of wheat genomes are correlated with recombination rates along chromosome arms. Genome Research 13: 753–763. Akhunova AR, Matniyazov RT, Liang H, and Akhunov ED (2010) Homoeolog-specific transcriptional bias in allopolyploid wheat. BMC Genomics 11: 505. Cavanagh CR, Chao S, Wang S, et al. (2013) Genome-wide comparative diversity uncovers multiple targets of selection for improvement in hexaploid wheat landraces and cultivars. Proceedings of the National Academy of Sciences of the United States of America 110: 8057–8062. Chapman JA, Mascher M, Buluç AN, et al. (2015) A whole-genome shotgun approach for assembling and anchoring the hexaploid bread wheat genome. Genome Biology 16: 26. Choulet F, Alberti A, Theil S, et al. (2014) Structural and functional partitioning of bread wheat chromosome 3B. Science 345: 1249721. Dvorak J, Luo M, and Akhunov EA (2011) N. I. Vavilov’s theory of centres of diversity in the light of current understanding of wheat diversity, domestication and evolution. Czech Journal of Genetics and Plant Breeding 47: 1–8. Edwards D, Wilcox S, Barrero RA, et al. (2012) Bread matters: A national initiative to profile the genetic diversity of Australian wheat. Plant Biotechnology Journal 10: 703–708. Henry IM, Nagalakshmi U, Lieberman MC, et al. (2014) Efficient genome-wide detection and cataloging of EMS-induced mutations using exome capture and nextgeneration sequencing. Plant Cell 26: 1382–1397. International Wheat Genome Sequencing Consortium (2014) A chromosomebased draft sequence of the hexaploid bread wheat genome. Science 345: 1251788. Jordan K, Wang S, Lun Y, et al. (2015) A haplotype map of allohexaploid wheat reveals distinct patterns of selection on homoeologous genomes. Genome Biology 16: 48. Kerber ER (1964) Wheat: Reconstitution of the tetraploid component (AABB) of hexaploids. Science 143: 253–255. Luo M-C, Gu YQ, You FM, et al. (2013) A 4-gigabase physical map unlocks the structure and evolution of the complex genome of Aegilops tauschii, the wheat D-genome progenitor. Proceedings of the National Academy of Sciences of the United States of America 110: 7940–7945. Luo M-C, Yang Z-L, You FM, Kawahara T, Waines JG, and Dvorak J (2007) The structure of wild and domesticated emmer wheat populations, gene flow between them, and the site of emmer domestication. Theoretical and Applied Genetics 114: 947–959. Pfeifer M, Kugler KG, Sandve SR, et al. (2014) Genome interplay in the grain transcriptome of hexaploid bread wheat. Science 345: 1250091. Poland JA, Brown PJ, Sorrells ME, and Jannink J-L (2012) Development of highdensity genetic maps for barley and wheat using a novel two-enzyme genotypingby-sequencing approach. PLoS One 7: e32253. Qi LL, Echalier B, Chao S, et al. (2004) A chromosome bin map of 16 000 expressed sequence tag loci and distribution of genes among the three genomes of polyploid wheat. Genetics 168: 701–712.

GENETICS OF GRAINS | Wheat Genetics and Genomics Saintenac C, Jiang D, and Akhunov ED (2011) Targeted analysis of nucleotide and copy number variation by exon capture in allotetraploid wheat genome. Genome Biology 12: R88. Simons KJ, Fellers JP, Trick HN, et al. (2006) Molecular characterization of the major wheat domestication gene Q. Genetics 172: 547–555. Wang S, Wong D, Forrest K, et al. (2014) Characterization of polyploid wheat genomic diversity using a high-density 90 000 single nucleotide polymorphism array. Plant Biotechnology Journal 12: 787–796.

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Werner JE, Endo TR, and Gill BS (1992) Toward a cytogenetically based physical map of the wheat genome. Proceedings of the National Academy of Sciences of the United States of America 89: 11307–11311. You FM, Huo N, Deal KR, et al. (2011) Annotation-based genome-wide SNP discovery in the large and complex Aegilops tauschii genome using nextgeneration sequencing without a reference genome sequence. BMC Genomics 12: 59.

Biotic Stress Resistance Genes in Wheat J Singla and SG Krattinger, University of Zurich, Zurich, Switzerland ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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In the field, wheat plants are constantly attacked by biotic stress agents such as viruses, bacteria, fungi, nematodes, arthropods (insects and arachnids), and weeds. Biotic stress is a major cause of pre- and postharvest losses in wheat production. Although lacking an adaptive immune system, plants have evolved sophisticated strategies to counteract biotic stresses. Many biotic stress resistance genes in modern wheat cultivars have been introgressed from wild and domesticated wheat relatives. More than 450 biotic stress resistance genes have been described in wheat and are used in wheat breeding. However, only a few of them have been molecularly isolated and characterized in detail. Many cloned biotic stress resistance genes encode for nucleotide binding site–leucine-rich repeat (NBS–LRR) proteins that perceive the presence of biotic stress agents by recognizing pathogen-specific effector proteins. Most of these NBS–LRR resistance genes are not durable and are frequently overcome due to rapid pathogen adaptation. Other biotic stress resistance genes provide more durable protection. Their molecular function probably does not involve the recognition of specific effector proteins.

Learning Objective

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To achieve understanding of the significance of biotic stress for wheat production and the molecular basis of biotic stress resistance in wheat.

Introduction Biotic stress in plants is caused by living organisms, specifically viruses, bacteria, fungi, nematodes, insects, arachnids, and weeds. In contrast to abiotic stress caused by environmental factors such as drought and heat, biotic stress agents directly deprive their host of its nutrients leading to reduced plant vigor and, in extreme cases, death of the host plant. In agriculture, biotic stress is a major cause of pre- and postharvest losses. In contrast to vertebrates, plants lack an adaptive immune system, or the ability to adapt to new diseases and memorize past infections. Though lacking an adaptive immune system, plants have evolved a plethora of sophisticated strategies to counteract biotic stresses. The genetic basis of these defense mechanisms is stored in the plant’s genetic code. Plant genomes encode hundreds of biotic stress resistance genes. With the completion of several plant genome sequences during the past decade – among them are important agricultural crops such as maize, sorghum, and rice – we obtained a first glimpse into the wealth of biotic stress resistance genes encoded within plant genomes. However, we have just started to uncover the

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molecular mechanisms and networks controlling biotic stress resistance in cereals. This article aims to summarize the current status of knowledge on biotic stress resistance genes in wheat.

Breeding for Biotic Stress Resistance in Wheat A major goal of every wheat breeding program around the world is to improve biotic stress resistance by incorporating ideal combinations of biotic stress resistance genes into modern wheat cultivars. The wheat gene catalog – a collection of genes and loci used in wheat breeding – describes more than 450 effective biotic stress resistance genes (http://www.shigen. nig.ac.jp/wheat/komugi/genes/macgene/2013/GeneCatalogueIntroduction.pdf). The great majority of these resistance genes protect against fungal diseases. In fact, more than twothirds of them provide resistance against only four fungal diseases, namely, leaf rust, stripe rust, stem rust, and powdery mildew. This fact probably reflects the great significance of these four pests for global wheat production. It is therefore not surprising that extensive research and breeding effort has been put into the identification and characterization of resistance genes against these four fungal diseases (Figure 1). Although several hundred resistance genes have been described and are used in breeding, only a handful of them have been genetically isolated. Only the isolation or cloning of resistance genes allows for a detailed study of their molecular function. A detailed understanding of plant–pathogen interactions will allow us to use more targeted approaches to durably protect crops in the future. For example, gene-specific diagnostic molecular markers designed on cloned resistance genes can be used for marker-assisted breeding to track the presence of different resistance genes in breeding programs. Any biotic stress resistance gene can be classified according to (1) its visual effect on pathogen growth, (2) its race specificity, and (3) its durability. Resistance can be either complete or partial. While complete resistance genes entirely disable pathogen growth, partial resistance genes only delay pathogen development and may allow for the completion of the pathogen’s life cycle. It is commonly accepted that partial disease resistance genes exert less evolutionary pressure on the pathogen to evolve virulence against the gene. Combination of four to five partial resistance genes can result in near immune levels of disease resistance. Race-specific resistance only protects against several but not all races or strains of a given pathogen, whereas non-race-specific resistance genes provide resistance against all races. The durability of a biotic stress resistance gene is defined by its longevity in the field. According to the definition by Roy Johnson made in the 1980s, a disease resistance gene is considered durable if it remains effective during prolonged and widespread use in an environment favorable to the disease. While some resistance genes have been successfully used in breeding for more than a


http://dx.doi.org/10.1016/B978-0-12-394437-5.00229-1

GENETICS OF GRAINS | Biotic Stress Resistance Genes in Wheat

Figure 1 Example of the effect of a biotic stress resistance gene in the field. The image shows two wheat leaves containing the biotic stress resistance gene Lr34/Yr18/Sr57/Pm38 (right) infected with stripe rust in the field compared with two wheat leaves without the gene (left).

century, others lost their effectiveness after only a few years in the field. The difficulty in biotic stress resistance breeding is to predict whether a given gene will be durable or not. The breakdown of disease resistance often occurs suddenly and unexpectedly, sometimes only a few years after the release of a resistant wheat cultivar. A dire example of rapid pathogen adaptation is Ug99, a complex of several new and highly virulent strains of the fungal disease stem rust that was first described in Uganda in the year 1999. Ug99 overcame the widely used resistance gene Sr31, causing stem rust epidemics in Africa and the Near East. A second case was described in the year 2000, when a strain of the fungal disease leaf rust spontaneously mutated and evolved virulence against the widely deployed resistance gene Lr24 in Australia.

Alien Sources to Improve Biotic Stress Resistance in Wheat Domestication of wheat resulted in a genetic bottleneck since only a few wild progenitors contributed to modern cultivated

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wheat. This is particularly true for the D genome of hexaploid wheat because the hybridization between tetraploid wheat and Aegilops tauschii occurred only 8000 years ago, and only a few accessions might have been involved in this event. Thus, we find a much greater genetic diversity among wild wheat progenitors and closely related cereal species than within the cultivated wheat gene pool. Different strategies have been used by wheat breeders to exploit these sources and enhance genetic diversity in modern wheat cultivars. For example, synthetic wheat can be produced by artificially crossing tetraploid wheat with diverse A. tauschii accessions. The first synthetic hexaploid wheat was produced in the 1940s. The International Maize and Wheat Improvement Center (CIMMYT) extensively used this strategy in the 1980s, and more than a thousand synthetic wheat varieties have been produced using more than 600 diverse A. tauschii accessions. Many of these synthetic wheat lines showed superior biotic stress resistance. The genomic redundancy of polyploid wheat tolerates a high degree of chromosomal rearrangements, chromosome deletions, introgressions, and substitutions without an impact on agricultural performance. Chromosome introgressions and substitutions have been extensively used to improve biotic stress resistance. For example, Haynaldia villosa, a diploid wild relative of wheat, shows durable and broad-spectrum resistance against powdery mildew that is due to gene Pm21 located on chromosome 6V. Pm21 was transferred into hexaploid modern wheat by producing a 6VS.6AL translocation line. In China, 12 wheat cultivars with this translocation have been planted on an area of more than 3.4 million hectares since 2002. The most successful alien introgression stems from an interspecific cross between wheat and rye (Secale cereale L.), two closely related species that shared their last common ancestor about 7.5 million years ago. Rye shows good biotic stress resistance, and wheat–rye crosses have been used to enhance the genetic variability in hexaploid wheat. A particular cross made in the 1930s resulted in the replacement of wheat chromosome arm 1BS with the corresponding rye segment. These so-called 1BL.1RS translocation lines showed enhanced tolerance against many fungal diseases due to the presence of resistance genes against leaf rust (Lr26), stripe rust (Yr9), stem rust (Sr31), and powdery mildew (Pm8) on this particular chromosome arm. Many modern wheat cultivars nowadays carry the 1BL.1RS translocation.

Molecular Mechanisms of Biotic Stress Resistance in Wheat Only a few biotic stress resistance genes have been isolated and cloned to date. They are summarized in Table 1. These few genes however provide an indispensable foundation to study the molecular basis of biotic stress resistance. Because of the importance of fungal diseases for global wheat production, most of our knowledge of biotic stress resistance genes is derived from studying wheat–fungus interactions. The most common strategy to isolate genes in wheat is mapbased cloning. The first step in map-based cloning consists of the development of a mapping population by crossing a resistant with a susceptible parent. A decent mapping population

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Table 1

List of cloned biotic stress resistance genes in wheat

Gene name Fungal diseases Leaf rust Lr1 Lr10 Lr21 Stripe rust Yr36 Stem rust Sr33 Sr35 Powdery mildew Pm3 Pm8 Pm21 TmMla1 Wheat rusts and powdery mildew Lr34/Yr18/Sr57/Pm38 Stagonospora nodorum and tan spot Tsn1 Nematodes Cre3

Source

Chromosome

Protein

Triticum aestivum Triticum aestivum Aegilops tauschii

5DL 1AS 1DS

NBS–LRRa NBS–LRR NBS–LRR

Triticum turgidum

6BS

START lipid-binding domain/kinase domain

Aegilops tauschii Triticum monococcum

1DS 3AL

NBS–LRR NBS–LRR

Triticum aestivum Secale cereale Haynaldia villosa Triticum aestivum

1AS 1RS 6VS 1A

NBS–LRR NBS–LRR Serine/threonine protein kinase NBS–LRR

Triticum aestivum

7DS

ABC transporter

Aegilops tauschii

5DS

NBS–LRR

Aegilops tauschii

2D

NBS–LRR

a

Nucleotide binding site–leucine-rich repeat protein; see text in the succeeding text.

usually comprises several hundred to several thousand segregating progenies of this cross. The mapping population is then genotyped with polymorphic molecular markers to produce a genetic map and phenotyped for disease resistance in the field or glasshouse. The combination of genetic map and phenotypes reveals the genetic location of the gene of interest. The corresponding physical DNA stretch is subsequently isolated by screening bacterial artificial chromosome (BAC) libraries. Larger mapping populations tend to result in more accurate mapping and the identification of smaller genetic and physical intervals. Sequencing of the BAC clones reveals candidate genes. The ultimate validation of these candidate genes is done by the analysis of mutants, gene transformation into a susceptible wheat cultivar, or silencing of the candidate gene. Map-based cloning in wheat is laborious and time-consuming because of the polyploid wheat genome and the large genome size. Map-based cloning projects therefore often required up to a decade. The complexity of map-based cloning in wheat partially explains the low number of biotic stress resistance genes cloned to date. However, with the recent advancements in high-throughput marker systems and the wheat genome sequencing, map-based cloning will become faster and less laborious in the future.

NBS–LRR Proteins: The Basis of Race-Specific Disease Resistance A majority of the cloned biotic stress resistance genes in wheat belong to a conserved gene family encoding NBS–LRR proteins. Examples are the powdery mildew resistance genes Pm3 and Pm8; leaf rust resistance genes Lr1, Lr10, and Lr21; stem rust resistance genes Sr33 and Sr35; and the cyst nematode resistance gene Cre3. NBS–LRR proteins (also referred to as R proteins) are a conserved class of immune receptors that

directly or indirectly recognize pathogen-specific effector proteins. These effector proteins are secreted by pathogens into the host cell to suppress defense response and to establish infection. Recognition of effectors by NBS–LRR proteins triggers a signaling cascade that usually results in a very strong resistance response called hypersensitive reaction (HR). HR ultimately leads to death of the infected host cell by this means preventing further spread of the pathogen. Resistance conferred by NBS– LRR proteins is usually complete but race-specific. Since this type of disease resistance depends on the recognition of specific pathogen effectors, simple point mutations within or loss of effector genes can disrupt recognition by the corresponding NBS–LRR protein. Such mutations in pathogen effectors result in the emergence of new virulent pathogen races and breakdown of disease resistance. In a heavily infected wheat field, fungal pathogens can produce a myriad of spores within a few weeks. Mutated pathogen spores that avoid recognition by the corresponding R gene will have a huge selective advantage and will multiply rapidly. Dispersal of fungal pathogens by wind over long distances adds to the rapid spread of newly evolved virulent pathogen strains. Ug99, for example, spread from Kenya to South Africa and the Near East in less than a decade. Breakdown of disease resistance within 3–5 years is often observed when wheat cultivars with disease resistance based on a single R gene are widely grown. Rapid pathogen adaptation is a great obstacle for wheat resistance breeding, taking into account that it often takes 10–12 years to breed and release a new wheat variety. In nature, plants respond to this rapid pathogen evolution by showing great sequence diversity within R genes. For example, for the Pm3 powdery mildew resistance gene, 17 functional alleles have been identified in cultivated and wild wheat. They share more than 97% sequence identity and recognize different races of powdery mildew. The greatest sequence diversity among the 17 Pm3

GENETICS OF GRAINS | Biotic Stress Resistance Genes in Wheat alleles is found in the LRR domain that might be responsible for the recognition of the pathogen effectors through protein– protein interaction. A second example highlighting the great functional diversity among R genes is found within the Mla subfamily of NBS–LRR proteins. Mla genes have first been described in barley to confer race-specific resistance against barley powdery mildew. Recently, the wheat gene TmMla1 – a homologue of the barley Mla genes – was found to confer resistance against wheat powdery mildew. Furthermore, wheat gene Sr33, also a member of the Mla subfamily and a close homologue of TmMla1, confers resistance against wheat stem rust, a fungus belonging to a different phylum than powdery mildew. These findings demonstrate that (1) R genes maintained an evolutionary conserved resistance function across related cereal species and that (2) R gene members of the same subfamily evolved a great diversity that allows them to perceive effectors of different, unrelated pathogens. NBS–LRR proteins in wheat protect not only against fungal diseases but also against other biotic stress agents. The first biotic stress resistance locus isolated in wheat in 1997 was Cre3, a NBS–LRR gene providing resistance against the cereal cyst nematode.

Subverting the Plant Defense System: How Necrotrophic Fungi Use Host NBS–LRR Proteins to Establish Infection NBS–LRR proteins sense infections by recognizing pathogenspecific effectors. Effector recognition triggers a strong resistance response resulting in cell death. This defense mechanism is particularly effective in restricting the growth of biotrophic pathogens such as the wheat rusts or powdery mildew. Biotrophic pathogens require an intact and living host plant, and HR should prevent spreading of the infection into neighboring cells. Necrotrophic pathogens on the other hand first kill the host cells before feeding on the dead tissue. It has been found that some necrotrophic pathogens evolved strategies to subvert the plant defense system to establish disease. The two wheat fungal pathogens Stagonospora nodorum and Pyrenophora triticirepentis, the causal agents of Stagonospora nodorum blotch and tan spot, respectively, secrete the host-specific toxin ToxA into wheat leaves. Once inside the cell, ToxA is recognized by Tsn1, a protein containing an NBS–LRR domain. Recognition of ToxA by Tsn1 results in HR and cell death. The two fungi then feed on these dead cells. Tsn1 resembles a NBS–LRR receptor. Hence, Stagonospora nodorum and tan spot use components of the wheat defense system and provoke host cell death to establish infection.

Durable Broad-Spectrum Disease Resistance Genes Because of rapid pathogen evolution, R gene resistance is often not durable. One strategy to increase the longevity of disease resistance in wheat cultivars is to pyramid several R genes in one cultivar. To overcome such resistance gene stacks, simultaneous mutations in several effector genes would be required in one single pathogen spore. Another way to improve the durability of biotic stress resistance in wheat is the use of more ‘durable’ resistance genes. Some genes have been used in breeding for a long time, and no increase in pathogen virulence has been observed. These genes

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are a valuable source of biotic stress resistance, and they come very close to Roy Johnson’s definition of durable disease resistance. Durable disease resistance genes usually confer nonrace-specific and partial protection. Partial resistance allows the pathogen to complete its life cycle and thus exerts less evolutionary pressure on the pathogen to adapt. One specific resistance gene group within the wheat gene pool is of particular interest because its members confer durable, non-racespecific, and partial multipathogen resistance against the three wheat rusts and powdery mildew. This phenotype is also referred to as slow rusting or slow mildewing, respectively. Only four loci with this valuable properties have been identified in wheat until today: Lr34/Yr18/Sr57/Pm38, Lr46/Yr29/ Sr58/Pm39, Lr67/Yr46/Sr55/Pm46, and Sr2/Yr30/Lr27 (the complex gene designation reflects their ability to restrict the growth of multiple pathogens). These genes have been extensively used to improve biotic stress resistance in wheat breeding. Lr34/Yr18/Sr57/Pm38, for example, has been used in breeding since the early twentieth century. Sr2/Yr30/Lr27 was introgressed into hexaploid wheat from wild emmer (T. turgidum L. subsp. dicoccon) in 1925. The resistance mechanism of these loci remains a mystery but does not seem to be linked to HR or cell death. Only Lr34/Yr18/Sr57/Pm38 has been cloned so far, and it encodes for an ATP-binding cassette (ABC) transporter. Knockout mutations in this particular ABC transporter resulted in increased susceptibility against leaf rust, stripe rust, stem rust, and powdery mildew, demonstrating that this single gene was responsible for the multipathogen resistance. ABC transporters are a conserved family of transporter proteins comprising two nucleotide binding domains and two transmembrane domains. The nucleotide binding domains bind and hydrolyze ATP to provide energy for the transport process. Hence, the resistance conferred by Lr34/Yr18/Sr57/Pm38 is the result of the transport of a yet unknown substrate across a biological membrane. The wheat gene pool contains two predominant alleles of Lr34/Yr18/Sr57/Pm38: the first found in susceptible wheat varieties and the other present in all resistant wheat cultivars. The two alleles differ by only two exon polymorphisms. Interestingly, the resistant Lr34/Yr18/Sr57/Pm38 version is only found in cultivated hexaploid wheat but not in wild wheat progenitors. This result strongly suggests that the resistant allele evolved spontaneously after the formation of hexaploid wheat around 8000 years ago. Hence, Lr34/Yr18/ Sr57/Pm38 is an interesting example of recent resistance gene evolution that occurred after domestication. Another example of a cloned non-race-specific resistance gene is Yr36 that was first discovered in wild emmer. This gene provides protection against a broad spectrum of stripe rust races and is particularly effective at higher temperatures. Using a map-based cloning approach, Yr36 was found to encode a protein containing a START lipid-binding domain fused to a kinase domain. Kinases are key proteins for cell signaling transduction. Several different Yr36 transcript variants were identified of which only one was functional. Interestingly, the relative abundance of the functional transcript increased at higher temperatures compared to then nonfunctional splice variants. The broad-spectrum powdery mildew resistance gene Pm21, transferred from the wild wheat progenitor Haynaldia villosa and located on the 6VS.6AL chromosomal translocation, also encodes for a kinase protein.

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Since chromosome arms 6VS and 6AS do not pair and recombine, a map-based cloning strategy was not feasible to clone Pm21. Instead, expression analyzes were used to identify candidate genes that were induced after powdery mildew infection.

Future Research The goal in wheat disease resistance breeding is to release varieties with disease resistance that is as durable and broad as possible. The past has taught us that it is often difficult to predict the durability of disease resistance genes. Rapid pathogen evolution and breakdown of disease resistance as exemplified by Ug99 caused serious problems in wheat production. The cloning of additional biotic stress resistance genes will result in a better understanding of plant–pathogen interactions. This knowledge will help us to select and combine ideal resistance genes in modern wheat cultivars. Markerassisted selection will greatly facilitate the combination of several biotic stress resistance genes in one wheat genotype. Furthermore, a better understanding of the molecular mechanisms underlying plant–pathogen interactions might allow us to artificially design new broad-spectrum resistance alleles that could be introduced via genetic engineering. Many disease resistance genes in wheat have been introgressed from wild wheat relatives. However, such interspecific hybridizations only work between closely related species. Furthermore, unwanted negative traits were often cointroduced in such crosses. This so-called linkage drag is one of the greatest obstacles in the utilization of progeny of interspecific crosses and is caused by the undesirable effect of genes that are closely linked to the gene of interest or to negative interactions between alien and host genes. Recent advances in biotechnology may help to (1) use sources of resistance genes that cannot be crossed with wheat and (2) avoid negative linkage drags. For example, transgenic wheat expressing a rice chitinase gene showed enhanced tolerance against stripe rust. Since crosses between rice and wheat are not possible, this example nicely demonstrates how modern biotechnology might help to increase biotic stress resistance. The multipathogen resistance gene Lr34/Yr18/Sr57/Pm38 was functionally transferred into barley where it conferred protection against the barley-specific diseases, barley powdery mildew and barley leaf rust. Furthermore, transgenic overexpression of the Pm3 gene in wheat has resulted in improved resistance against powdery mildew in the field. These examples demonstrate that biotechnology can be used as a tool to improve biotic stress resistance in wheat. The future use of this technology in breeding and agriculture however depends on the regulatory situation and consumer acceptance.


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Which criteria can be used to classify biotic stress resistance genes? How did wild wheat relatives help to improve biotic stress resistance in wheat? How have most wheat biotic stress resistance genes been cloned?

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What do we know about the molecular mechanisms of genes like Pm3 or Sr33? How do some fungal pathogens subvert this resistance mechanism? What is the definition of durable disease resistance and what do we know about durable disease resistance genes?

Exercises for Readers to Explore the Topic Further Learn more about grain diseases and their dispersal and regional importance by cross-referencing to cereal grain disease and wheat pathogen resistance articles.

See also: Agronomy of Grain Growing: Natural Disease Control in Cereal Grains; Necrotrophic Pathogens of Wheat; Plants: Diseases and Pests; Wheat: Biotrophic Pathogen Resistance; Genetics of Grains: Abiotic Stress Genes and Mechanisms in Wheat; Genome Mapping; Grain Harvest, Storage and Transport: The Nature, Causes, and Control of Grain Diseases in the Major Cereal Species.

Further Reading Brunner S, Hurni S, Herren G, et al. (2011) Transgenic Pm3b wheat lines show resistance to powdery mildew in the field. Plant Biotechnology Journal 9: 897–910. Cao A, Xing L, Wang X, et al. (2011) Serine/threonine kinase gene Stpk-V, a key member of powdery mildew resistance gene Pm21, confers powdery mildew resistance in wheat. PNAS 108: 7727–7732. Faris JD, Zhang ZC, Lu HJ, et al. (2010) A unique wheat disease resistance-like gene governs effector-triggered susceptibility to necrotrophic pathogens. PNAS 107: 13544–13549. Fu D, Uauy C, Distelfeld A, et al. (2009) A kinase-START gene confers temperaturedependent resistance to wheat stripe rust. Science 323: 1357–1360. Huang X, Wang J, Du Z, Zhang C, Li L, and Xu ZQ (2013) Enhanced resistance to stripe rust disease in transgenic wheat expressing the rice chitinase gene RC24. Transgenic Research 22: 939–947. Johnson R (1984) A critical analysis of durable resistance. Annual Review of Phytopathology 22: 309–330. Jordan T, Seeholzer S, Schwizer S, Toller A, Somssich IE, and Keller B (2011) The wheat Mla homologue TmMla1 exhibits an evolutionarily conserved function against powdery mildew in both wheat and barley. Plant Journal 65: 610–621. Krattinger SG, Lagudah ES, Spielmeyer W, et al. (2009) A putative ABC transporter confers durable resistance to multiple fungal pathogens in wheat. Science 323: 1360–1363. Krattinger SG, Jordan DR, Mace ES, et al. (2013) Recent emergence of the wheat Lr34 multi-pathogen resistance: insights from haplotype analysis in wheat, rice, sorghum and Aegilops tauschii. Theoretical and Applied Genetics 126: 663–672. Lagudah ES, Moullet O, and Appels R (1997) Map-based cloning of a gene sequence encoding a nucleotide binding domain and a leucine-rich region at the Cre3 nematode resistance locus of wheat. Genome 40: 659–665. Park RF, Bariana HS, Wellings CR, and Wallwork H (2002) Detection and occurrence of a new pathotype of Puccinia triticina with virulence for Lr24 in Australia. Australian Journal of Agricultural Research 53: 1069–1076. Periyannan S, Moore J, Ayliffe M, et al. (2013) The gene Sr33, an ortholog of barley Mla genes, encodes resistance to wheat stem rust race Ug99. Science 341: 786–788. Risk JM, Selter LL, Chauhan H, et al. (2013) The wheat Lr34 gene provides resistance against multiple fungal pathogens in barley. Plant Biotechnology Journal 11: 847–854. Singh RP, Hodson DP, Huerta-Espino J, et al. (2011) The emergence of Ug99 races of the stem rust fungus is a threat to world wheat production. Annual Review of Phytopathology 49: 465–481. Yang W, Liu D, Li J, et al. (2009) Synthetic hexaploid wheat and its utilization for wheat genetic improvement in China. Journal of Genetics and Genomics 36: 539–546.

Abiotic Stress Genes and Mechanisms in Wheat SJ Roy and NC Collins, School of Agriculture Food and Wine, The University of Adelaide, Glen Osmond, SA, Australia R Munns, CSIRO Agriculture, Canberra, ACT, Australia; The University of Western Australia, Crawley, WA, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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The abiotic stresses, such as drought, heat, cold, soil acidity, salinity, and low nutrient availability, severely reduce wheat yield. Wheat has a number of adaptations to enable it to survive abiotic stress; the best alleles of the genes controlling these adaptations are required for breeding and transgenic approaches to improve wheat yield. Specific genes controlling adaptations in developmental timing and morphology can allow the plant to avoid drought and heat stress, or minimize its impact. Genes encoding proteins responsible for ion movement can be used to improve nutrient uptake and remobilization or to control the distribution of damaging ions, such as Naþ and Cl. Synthesis of compatible solutes and enzymes that detoxify damaging reactive oxygen species is important in maintaining healthy metabolic processes. Traditional breeding and transgenic approaches allow the incorporation of the best alleles of genes for desired traits into breeding programs.

Learning Objectives

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To understand the effect of abiotic stresses such as drought heat, cold, acid soils, salinity, and low nutrient availability on wheat performance. To know the developmental stages at which abiotic stresses have the greatest impact on wheat yield. To enumerate the key adaptations in wheat and the genes controlling them, which can be used to improve growth and yield under abiotic stress. To know the approaches to introducing the best alleles of these genes into wheat.

To date, breeding and agronomic practices have achieved a linear increase in food production of 32 million tonnes per year. To meet future demands, it will be necessary to boost the annual increase in food production to 44 million tonnes per year by 2050. This target will be challenging to achieve due to expected loss of arable farmland to increasing desertification, salinization, and urbanization, increasing fertilizer costs, and less predictable weather patterns due to climate change. Abiotic stress severely affects wheat growth and yield across the globe. Drought, heat, frost, salinity, acid soils, and poor nutrient availability are among the most serious stresses worldwide. Some of these stresses are unpredictable in their timing, intensity, and spatial distribution, making it hard to achieve an efficient breeding strategy. Wheat is one of the most widely grown cereal crops in the world. Wheat is grown on 600 million hectares annually, but it is vulnerable to abiotic stress,


being moderately salt-sensitive and severely affected by drought – particularly during later developmental stages where stress can affect pollen development and grain growth. Wheat also requires substantial input of nitrogen (N) and phosphorus (P) fertilizers. Wheat can currently yield over 10 tonnes per hectare under the most favorable conditions; however, the majority of the world’s farms produce below 3 tonnes per hectare due to the impacts of abiotic stresses and disease. Improving the tolerance of wheat to abiotic stresses by as little as 10% would result in a substantial increase in grain yield, in absolute terms.

Abiotic Stresses Water scarcity is the most limiting factor to wheat production worldwide. Even in regions of higher rainfall, short periods of drought occur nearly every year. Plants conserve their water by closing their stomatal pores and reducing the loss of water by transpiration. However, this greatly reduces the rate of carbon dioxide entry and therefore photosynthesis. Consequently, drought-stressed plants produce less carbohydrate which ultimately affects growth. Drought (and other stresses) can lead to production of dangerous reactive oxygen species (ROS), such as superoxides and peroxides, within the leaves. These ROS will damage DNA, proteins, and lipids within the cell, resulting in cell death. Exposure to drought stress at or just after pollen meiosis (when the spike is just about to emerge from the sheath) leads to floret sterility – a phenomenon that has been correlated with the failure of pollen to accumulate starch. Further yield losses from drought result from a reduction in the size of individual grains. Heat stress commonly accompanies drought. Like other abiotic stresses, tolerance to heat stress varies depending on the developmental stage of the wheat plants, with the most vulnerable stage being later stages of development including fertilization and grain growth. High temperatures shorten the duration of growth of both the whole plant and the grains, limiting the time that the plant spends accumulating mass and yield. Heat stress during meiosis (like drought) causes floret sterility, while heat during grain filling reduces individual grain size. Wheat has a surprisingly low temperature optimum, which is around 18 C for grain growth. In most areas, average temperatures increase during the growing season, and brief periods above 30 C mainly occur during the grain-filling period. The unpredictable timing and intensity of severe natural heat events and their frequent cooccurrence with drought make it very challenging to quantify heat tolerance in the field. Drought strongly influences heat tolerance because transpiration allows the plant to evaporatively cool. Cold stress impacts wheat crops at either preflowering or flowering stages, depending on the growing region. In some

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parts of the world, wheat plants need to survive harsh winters in a semidormant state in an early (vegetative) developmental stage, and this cold can kill the growing point (crown) located just below the soil surface. In other regions such as Australia, wheat grows unperturbed during a relatively mild winter, but overnight frosts in the order of 2 to 8 C can cause significant freezing or chilling damage to the flower structures, causing reduced fertility (grain set), spike loss due to stem damage, and reduced grain size. Crowns of tolerant wheat varieties develop tolerance down to around 20 C if they initially experience a period of moderately cold temperature (e.g., up to several weeks at 4 C). However, this ability to ‘cold acclimate’ is steadily lost as the plant shifts to a reproductive mode of development, until it becomes essentially absent at flowering, accounting for the greater sensitivity of the reproductive stage. Soil salinity is a major environmental constraint to wheat production. Due to reduced rainfall on agricultural land, and as a consequence of certain irrigation practices, the area affected by salinity is expected to increase significantly by 2050. Saline soils reduce growth because, like drought, they cause stomates to close and the rate of leaf area expansion to decrease. Reproductive development is also affected. Saline soils may also cause toxic amounts of Naþ or Cl to accumulate in leaves that together with increase amounts of ROS (as found in drought) will accelerate leaf senescence. Another major constraint is soil acidity. Aluminum is the most abundant metallic element in the Earth’s crust, and at acidic pH (<5.0), it becomes soluble in the soil solution as Al3þ, which is toxic to plants. Al3þ mainly damages the root tips, reducing the ability of the root system to grow and take up water and nutrients. Around half of the world’s arable soils are acidic (pH < 5.0). Hence, Al3þ toxicity poses a major problem for the cultivation of wheat and other crops. Lime can be added to the soil to counter acidity, but its effect in raising pH can be slow to reach the subsoil. A common limiting factor for crop growth is nutrient availability. N and P are required in substantial quantities for optimal plant growth. N is an important component of plant proteins and P is required for the production of DNA, RNA, cell membranes, and energy metabolism. While there may be sufficient amounts of these elements in soil, the amount that is freely available to a plant is often quite low. Further losses result from fertilizer runoff or volatilization. Consequently, only 30% of N and 15–30% of P supplied in fertilizer are taken up by the plant. Currently, 100 million tonnes of N-containing fertilizer and 20 million tonnes of P-containing fertilizer are applied to crops every year, and these fertilizers represent a significant proportion of farmer input costs. P fertilizer is mined and is a finite resource. Furthermore, eutrophication of waterways and oceans caused by fertilizer runoff and the considerable energy required to make N fertilizer are major environmental concerns. In regard to these concerns, wheat varieties that are more efficient in extracting nutrients from the soil and converting them to grain yield are highly desirable. It should be noted that not all of these stresses happen in isolation. Plants experiencing drought stress are also likely to be exposed to high temperatures. Loss of soil water can increase salinity and can make nutrients harder for the plant to extract. Therefore, varieties with tolerance to multiple and combined stresses are required.

While many plant adaptations to abiotic stress are known, many of the genes or genetic loci encoding these adaptations in wheat still have to be identified. However, knowledge from other plant species and increasing knowledge from wheat research have identified key genes for abiotic stress tolerance.

Abiotic Stress and Grain Quality Reduced grain size caused by stresses such as drought, heat, and frost not only reduces yield but also can impact on milling efficiency. If grain deliveries contain too high a proportion of smallest (<2 mm) grains, the farmer will be paid at a lower rate. At least for heat stress, grain size reduction mainly derives from reduction in starch, which normally accounts for 70% of the grain mass. Evidence points to the heat sensitivity of the soluble starch synthase enzyme activity being one of the main causes of this. Temperatures above 30 C late in the grain development also decrease the cross-linking of glutenin, the seed storage protein in mature wheat seeds. This cross-linking normally gives wheat dough the elasticity that is needed to produce light textured loaves; heat-affected grain produces loaves of undesirable density. For one glutenin gene (GluD1), a variant associated with rapid polymerization during grain development also confers greater stability of dough quality after heat stress, perhaps because it allows more polymer to form by the time heat stress terminates grain fill prematurely.

Plant Adaptations to Stress Genes Controlling Flowering Time Flowering should occur before drought and heat stress arrive late in the season. However, flowering should not occur until the last frost. A long growing period is desirable to maximize accumulation of plant and grain mass, yet the crop can only start growing once there is sufficient moisture in the soil to allow establishment and the temperature is favorable. Therefore, the time a wheat variety takes from sowing to flowering is a crucial determinant of its yield in a particular growing environment. Breeders have probably been selecting for these optimal flowering times as a consequence of selection for high yield in field trials. However, most of the major genes controlling variation in flowering time in wheat have been molecularly characterized and can be selected using molecular markers, namely, Ppd-B1, Ppd-D1, Vrn-A1 Vrn-B1, and Vrn-D1. Control of flowering time by Ppd and Vrn genes also depends on temperature and day length and is therefore influenced by sowing date, latitude, and climate. They also influence the relative duration of vegetative versus reproductive stages of development.

Genes Influencing Morphology Thicker leaves with lower ‘specific leaf area’ (area–weight ratio) can improve the conversion of the available water to yield under drought conditions; however, this trait will limit yield under high rainfall conditions. Likewise, under dry conditions, reduced tiller number per plant (e.g., due to the tin gene) can ensure sufficient soil water remains to complete development, but may limit production under wetter conditions. Smaller,

GENETICS OF GRAINS | Abiotic Stress Genes and Mechanisms in Wheat narrower, and/or more vertical leaves may also help to reduce exposure to the intense midday sun, leading to less water loss and overheating. Leaf waxes may also reduce overheating and water loss by reflecting more solar radiation. Leaves with greater wax content appear glaucous (bluish-gray in color). The single dominant gene W1 can dramatically increase glaucousness in wheat. It must be noted that many, if not most, traits that improve yield in dry conditions limit yield under optimal conditions. It has been estimated that improving the wheat’s ability to extract an extra 10 mm of water from the soil during grain filling can increase yield by 500 kg ha1. Different root architectures suit different growing environments. A narrow and deep root system allows access to a receding water profile in areas that receive most rainfall preseason, while a wide and shallow root system is best for extracting water from sporadic rainfall events during the season and from supplementary irrigation. Shallow, highly branched root systems resulting from more adventitious root growth are also an advantage in low phosphate soils. In rice, the gene PSTOL1 encodes a protein kinase that increases adventitious root formation. Wheat plants with large root systems that penetrate deep into the soil (especially at anthesis) also have better N uptake than those with less vigorous root systems. The best performing wheat cultivars under low N conditions have 50–70% more root biomass than the poorly performing cultivars, resulting in a 60–200% greater uptake of N from the soil.

Alterations in Transport Enhanced tolerance to low nutrient availability can be improved by increasing the uptake of N and P from the soil, as well as improving the efficiency of nutrient redistribution throughout the plant. Conversely, salinity tolerance can be improved by restricting the transport of Naþ and/or Cl from the root to the shoot. Al3þ tolerance in wheat is mainly determined by the TaALMT1 gene. TaALMT1 encodes the aluminum-activated malate transport 1 protein, which, when exposed to Al3þ, secretes malate from root cells. Malate is negatively charged and binds Al3þ, thereby detoxifying it. A second, somewhat weaker, tolerance gene in wheat encodes a transporter of another class (MATE). It acts in a similar way as ALMT1, except that it secretes a different organic acid, citrate. Tolerant wheat varieties express these genes at higher levels than intolerant varieties. In hexaploid wheat, TaALMT1 is located on chromosome 4D. This chromosome is absent in durum wheat, which is probably why durum wheat is generally less tolerant to acid soils than bread wheat. Altering the abundance of proteins involved in transporting N, P, Naþ, and Cl through a plant is another way of improving tolerance. The PHT1 gene family is one of the primary groups of Pi transporters mediating Pi uptake from the soil into the root. These genes have been shown to be expressed in the root tip and elongation zone when P is deficient. Members of this gene family are also important in the remobilization of P from the source tissues (such as older leaves) to sink tissues (such as grain), once enzymes such as acid phosphatase and purple acid

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phosphatases have broken down P-containing compounds. The PHO1 gene encodes a protein important in mediating the transfer of P from the root to the shoot by regulating loading of P into the root xylem. NRTs are important for uptake of nitrate from the soil. Plants have two nitrate transport systems, the high-affinity nitrate transporters (NRT2 gene family) that are active when soil nitrate concentrations are low and the low-affinity nitrate transporters (NRT1 gene family) that are responsible for bringing in the majority of nitrate when conditions are good. Conversion of nitrate and ammonium into amino acids by the enzymes glutamine synthetase and glutamate synthase is also needed for nitrogen utilization within the plant. Transgenic plants, including wheat overexpressing genes for glutamine synthetase, have improved nitrogen use efficiency, so this is one approach that could be targeted in wheat. The development of wheat genotypes with improved nitrate uptake during critical developmental stages, such as tillering and booting, will have a significant effect on crop yield. For salt tolerance in wheat, tight regulation of the transport of Naþ from roots to shoots is essential. Plants must exclude about 95% of the Naþ and Cl from the water that is taken up from a saline soil and subsequently sent to the leaves in the transpiration stream. Because there is very little recirculation of Naþ from the shoot back to the root, restricting the amount of Naþ transported to the shoot is essential. The antiporter SOS1 is an essential part of this restriction by the roots. It returns Naþ that has leaked into the plant back to the soil. SOS1 is a Naþ/Hþ antiporter, which transports Naþ out of the cells by swapping it with a proton (Hþ). The HKT gene family encodes proteins that control Naþ and/ or Kþ influx into plant cells. One group of HKTs is responsible for the retrieval of Naþ from the root xylem vessels that are carrying water to the shoot, by taking it up into xylem parenchymal cells. In bread wheat, this retrieval is controlled by the Kna1 locus on chromosome 4D, with the gene that encodes the HKT transporter TaHKT1;5-D. Similar genes exist on the A genome of Triticum monococcum at the Nax1 and Nax2 loci, and these have been transferred into durum wheat and bread wheat by crossing. The Nax1 locus on chromosome 2A controls retrieval of Naþ from the xylem by xylem parenchymal cells in roots and leaf bases. Nax2 on chromosome 5A controls retrieval of Naþ from the xylem in the root only. The most likely functional determinants at the Nax1 and Nax2 loci are genes encoding the transporters TmHKT1;5-A and TmHKT1;4-A, respectively. Durum lines that were bred to contain the Nax2 gene from T. monococcum had significantly reduced shoot Naþ and 25% improved yield in saline field sites. More recently, attempts have been made to identify the proteins and genes responsible for controlling long distance Cl transport through the plant, for example, loading Cl into the root xylem vessels. While the physical properties of these proteins are known (they are plasma membrane-bound proteins with distinct patterns of Cl transport and are downregulated by the application of salt), the molecular identities of the transporters are still not clear. Naþ or Cl that does enter plant tissues can be compartmentalized in the cell’s central vacuole where they can do less harm. Proteins that can facilitate this process

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include Naþ proton antiporters, such as NHXs that actively pump Naþ across the vacuole’s tonoplast in exchange for protons and vacuolar pyrophosphatases (V-PPases) that generate the proton gradient that is used to power the Naþ antiporters. NHXs and V-PPases have been identified in wheat. Elevated expression of these factors in transgenic plants of several species including barley confers increased drought and salt tolerance, as well as improved nutrient use efficiency, and the same outcome is possible for transgenic wheat.

Synthesis of Compatible Solutes Several stresses make it difficult for plant cells to take up and hold onto water. A dry or saline soil makes it difficult for roots to take up water. In leaves, as temperatures are lowered, ice crystals firstly appear between cells, drawing water out of the cells. In this sense, drought and freezing stress have a common dehydrating effect. Sufficient water is needed in the cells to allow movement of cellular reactions necessary for plant growth and survival. In addition, proteins may require water on their surfaces to allow them to maintain the right shape. During abiotic stress, plants synthesize low-molecular-weight compounds called compatible solutes, which lower the osmotic potential of the cell, enabling it to retain water better. These solutes can be accumulated to high concentrations in a plant cell because they are nontoxic. Some can substitute for water on the surface of proteins, preventing them from becoming unfolded. They can also lower the freezing point of the cell, allowing them to remain unfrozen (supercooled) to temperatures down to 20 C. Compatible solutes include sugars, amino acids, sugar alcohols, complex sugars, and organic acids. In crops, proline and glycine betaine often accumulate under drought or salt stress. Genes encoding proteins involved in their synthesis have been shown to increase during abiotic stress, such as D1-pyrroline-5-carboxylate reductase (P5CR) and D1-pyrroline-5carboxylate synthetase (P5CS). Transgenic plants engineered to continuously overexpress these genes are more stress-tolerant, but tend to have poor growth under nonstress conditions, probably due to the energy cost of producing these compounds. Therefore, if a transgenic approach is to be used, the genes should be expressed by a control element (promoter) that is activated by stress so the compatible solutes are only made when required.

ROS Scavenging Enzymes Abiotic stresses can damage the photosynthetic apparatus, leading to the production of ROS that are potentially damaging to various cellular components, including membranes and proteins. Enzymes that can rapidly break down ROS (antioxidants) are key components of abiotic stress tolerance. Key genes limiting ROS levels in abiotic stressed plants encode superoxide dismutase, ascorbate peroxidase, catalase, and peroxidases. Developing wheat genotypes with improved ROS detoxification, by selecting beneficial versions of ROS detoxification enzymes or by using transgenics to express these genes to higher levels, could increase tolerance to a variety of stresses. However, as for other traits a genetic engineering approach will need to consider the energy cost of producing these enzymes

and its potential impact on yield under nonstress conditions. Additionally, ROS perform positive functions in cellular signaling, which will need to be preserved.

Stress Signaling An attractive strategy to improve abiotic stress tolerance in wheat is to adjust the detection, signaling, and regulatory pathways involved in tolerance. Altering single components of these pathways can have significant effects on downstream processes such as ion transport, synthesis of compatible solutes, plant morphology, and development. Many aspects of plant growth and development are mediated by the calcium ion (Ca2þ). Environmental cues, such as drought, frost, and salinity, are perceived by receptors on the plasma membrane of the plant cell. This activates a Ca2þ signaling cascade, where Ca2þ is released into the plant cell’s cytosol from internal and external calcium stores. This signal is interpreted by specific calcium-binding proteins, which go on to regulate gene expression and protein activities. Genes encoding proteins directly or indirectly regulated by Ca2þ, which then regulate downstream responses to abiotic stress, have been found to be important for stress tolerance in a number of plant species. The most famous of these are SOS2 and SOS3, which are members of a pathway responsible for the efflux of Naþ from salt-stressed cells; however, calcineurin B-like (CBL) proteins, calcium-dependent protein kinases (CDPKs), calmodulins (CaMs), calmodulin-like (CML) proteins, and CBL-interacting protein kinases (CIPKs) have been found to be important in regulating a plant’s response to drought, cold, and low nutrients. Transcription factors, which control the expression of genes by binding to the promoters of genes, also determine a wheat plant’s tolerance to abiotic stress. The ability to cold acclimate is stronger in some varieties than others, and these differences are mainly controlled by a cluster of genes for C-repeat binding factor (CBF, also known as DREB) transcription factors, located on wheat group 5 chromosomes. Upon cold exposure, products of one or more of these CBFs activate a set of genes that probably act together to confer cold tolerance. Genes from the CBF/DREB family are also turned on by drought and salinity stresses, fitting with the fact that these stresses have a common effect of dehydrating cells. Transgenic barley that overexpressed the DREB1A gene under a drought-specific promoter was better able to maintain healthy leaf tissue under water stress and to rehydrate after a severe drought stress, when compared to nontransformed barley. Similar transgenic modifications carried out in wheat have the potential to improve grain yield under drought.

Utilization of Abiotic Stress Tolerance Genes in Wheat A number of genes and loci have been found to control specific stress tolerance mechanisms. What is now required is for the best versions (alleles) of these genes to be introduced into current wheat cultivars to improve the performance of the crop in the field. A strategy already being used is to cross tolerance sources to elite germplasm and to identify progeny containing the desirable alleles using genetically linked

GENETICS OF GRAINS | Abiotic Stress Genes and Mechanisms in Wheat molecular markers – an approach called marker-assisted selection. The effectiveness of such an approach can be seen in the development of shoot Naþ excluding durum wheat lines containing the TmHKT1;5-A allele from the wheat relative T. monococcum. However, this strategy does have a few limitations. It requires crossing and a number of generations of selection to obtain a suitable variety, which can take considerable time. Hundreds or thousands of genes located alongside the desired allele may also be transferred, some of which might be detrimental to the plant’s performance. The approach is also limited by the natural alleles available within species or genotypes that are sexually compatible with wheat. An alternative is transformation (also known as genetic modification (GM)), which can introduce genes for abiotic stress tolerance traits directly into the desired wheat cultivar. It has the advantages of being able to introduce genes from noncompatible species, in a single step, and without transfer of additional genes. A precautionary note is that, while certain transgenic plants may survive abiotic stresses better in a glasshouse, improved grain yield in the field is another matter entirely, due to the presence of other stresses, metabolic costs associated with expression of the novel trait, and possible effects of the transgene on flowering time and general plant development. Reports of field tests of GM crops, in wheat in particular, have been rare. This is partly due to the high cost of such trials. This is a consequence of tight regulation, which in turn is driven by political factors and domestic and export market perception of GM food safety. At least for the short term, there are alternative biotechnology techniques that may be more viable, which involve temporary introduction of a transgene. Transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPRs) are two approaches that can edit the sequence of a specific gene already present in the plant by introducing a short piece of DNA that targets editing machinery to it. Once the native DNA has been edited, the transformed DNA code can be bred out, producing a modified, but ‘non-GM’ plant. So far, these technologies are more suited to knocking out gene function in cereals, but their potential for converting genes to more desirable functional alleles is being explored.


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List three reasons why improved abiotic stress tolerance in wheat is needed. At what growth stages is wheat most vulnerable to abiotic stress? What is the optimum temperature for grain growth in wheat? Name one gene that controls flowering time in wheat and thus affects its yield in hot/dry or frost-prone climates.

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Name one gene that controls the uptake of Naþ and thus affects the tolerance of wheat to saline soil. List three ways in which compatible solute accumulation can protect plants from abiotic stress.


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Describe how you design field-based tolerance assays to unpredictable stress events such as frost and heat. Think of three actions/circumstances that might lead to public and political acceptance of GM wheat in Australia.

See also: Agronomy of Grain Growing: Implication of Climate Changes; Genetics of Grains: Development of Genetically Modified Grains; The Cereal Grains: Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’.

Further Reading Blumenthal C, Gras PW, Bekes F, Barlow EW, and Wrigley CW (1995) Possible role for the Glu-DI locus with respect to tolerance to dough-quality change after heat stress. Cereal Chemistry 72: 135–136. Cramer M (2010) Phosphate as a limiting resource: Introduction. Plant and Soil 334: 1–10. Dodd AN, Kudla J, and Sanders D (2010) The language of calcium signaling. Annual Review of Plant Biology 61: 593–620. Dolferus R, Ji X, and Richards RA (2011) Abiotic stress and control of grain number in cereals. Plant Science 181: 331–341. Flowers TJ and Colmer TD (2008) Salinity tolerance in halophytes. The New Phytologist 179: 945–963. Haurwitz RE, Jinek M, Wiedenheft B, Zhou K, and Doudna JA (2010) Sequence- and structure-specific RNA processing by a CRISPR endonuclease. Science 329: 1355–1358. Kong L, Wang F, Lo´pez-bellido L, Garcia-mina J, and Si J (2013) Agronomic improvements through the genetic and physiological regulation of nitrogen uptake in wheat (Triticum aestivum L.). Plant Biotechnology Reports 7: 129–139. Liu W, Yuan JS, and Stewart Jr. CN Jr. (2013) Advanced genetic tools for plant biotechnology. Nature Reviews. Genetics 14: 781–793. Morran S, Eini O, Pyvovarenko T, et al. (2011) Improvement of stress tolerance of wheat and barley by modulation of expression of DREB/CBF factors. Plant Biotechnology Journal 9: 230–249. Munns R and Tester M (2008) Mechanisms of salinity tolerance. Annual Review of Plant Biology 59: 651–681. Munns R, James RA, Xu B, et al. (2012) Wheat grain yield on saline soils is improved by an ancestral Naþ transporter gene. Nature Biotechnology 30: 360–364. Schroeder JI, Delhaize E, Frommer WB, et al. (2013) Using membrane transporters to improve crops for sustainable food production. Nature 497: 60–66. Suzuki N, Koussevitzky S, Mittler RON, and Miller GAD (2012) ROS and redox signalling in the response of plants to abiotic stress. Plant, Cell & Environment 35: 259–270. Tester M and Langridge P (2010) Breeding technologies to increase crop production in a changing world. Science 327: 818–822. Voytas DF (2013) Plant genome engineering with sequence-specific nucleases. Annual Review of Plant Biology 64: 327–350.

Rice: Genetics JS Bao, Zhejiang University, Hangzhou, China H Corke, University of Hong Kong, Hong Kong, Pokfulam, China; Hubei University of Technology, Wuhan, China ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

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Rice genetics is the science of studying heredity in rice, which provides basic knowledge for rice breeding. Rice traits can be broadly classified as qualitative traits and quantitative traits. Quantitative traits are controlled by quantitative trait loci (QTLs) with minor effect, which could be detected by linkage genetic mapping and identified by map-based cloning approach. QTL mapping has been widely conducted for agronomic traits, resistance to abiotic and biotic stresses, and grain quality. A lot of genes responsible for the complex traits of importance in rice have been successively cloned. Functional markers derived from the identified genes are useful in molecular breeding. Genome-wide association studies (GWAS) have emerged as a powerful new approach for identifying genes underlying complex traits of rice.

Learning Objectives

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To appreciate the basic genetics knowledge and progress that has been made in the genetics of rice plant.

diploid, but a few are tetraploid. Rice has the smallest genome ( 430 Mb) among the major cereals (Table 1). Rice is a monocot and a grass, and it has been regarded as a counterpart of the dicot model system, that is, Arabidopsis thaliana, in genomic studies. Therefore, rice has become the best-characterized cereal at the molecular level of any crop species. The whole-genome shotgun assemblies of draft-quality sequence of the two subspecies of cultivated rice, indica and japonica, were available in 2002. A highly accurate map-based sequence of the rice genome was generated in 2005 by International Rice Genome Sequencing Project. Rice is hence the first crop and the second plant to have had its genome sequenced. The development of DNA molecular markers has helped to explore the information stored in the rice genome and to understand the genetic behavior for many of the traits of agronomic importance at the molecular level by using genetic mapping approaches. The advent of the next-generation sequencing (NGS) technologies makes it feasible to sequence and capture most of variants among different rice genotypes. The common variants are single-nucleotide polymorphisms (SNPs). The SNPs from NGS technologies can be applied not only in genotyping of populations derived from biparents to allow linkage maps quickly constructed for quantitative trait loci (QTL) mapping but also in genome-wide association studies (GWAS) among a large population including diverse germplasm to be conducted to search genotype–phenotype relations. This article summarizes recent advances in rice genetics especially at the molecular level.

Introduction Rice is arguably the world’s most important staple food crop and a primary food source for more than half of the world’s population. More than 90% of the world’s rice is produced and consumed in Asia where about three-fifths of the Earth’s people live. Continued increase in rice supply will be required to maintain the food–population balance. Breeding new rice varieties with high yield potential, with high resistance to biotic and abiotic stresses, and with high eating and nutritional quality is one of the best ways to help satisfy this demand. Rice genetics is the science of studying heredity in rice and related plant species and is the basis for all sound, effective, and efficient breeding programs. It provides both basic principles and applied selection methods for rice breeding. Better understanding of the inheritance of rice traits will stimulate significant progress either in selection efficiency or in accuracy for rice breeding. Greater insight into the molecular genetic basis of the detailed functioning of metabolic pathways will better explain how the plants inherit traits from their parents and how phenotypes are developed and regulated. Cultivated rice (Oryza sativa L.) is a diploid species with 24 chromosomes (12 pairs). Besides O. sativa, 23 additional species have been identified in the Oryza genus, most of which are

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The Basis of the Classical Quantitative Genetics Rice traits under genetic study can be assigned to two broad categories according to their complexity in inheritance: qualitative traits and quantitative traits. Qualitative traits can be classified into discrete classes and are determined by either one or a few genes that show Mendelian inheritance. To study their inheritance requires differences in the expression of alleles at individual loci (genes), usually designated as the dominant allele (wild-type allele) and the recessive allele (mutant allele). The inheritance of qualitative traits is predictable, and the genotype (G) of individuals is determined by their phenotype (P). Quantitative traits cannot be classified into discrete classes, and the variants show normal distribution in a segregating population. Quantitative traits are genetically controlled by polygenes or minor genes (each of which may also show Mendelian inheritance) but are greatly modified by environment. To study their inheritance requires large-scale experiments and statistical analysis to estimate genetic parameters. The phenotypes (P) of individuals and families in replicated trials include genetic effects (G) and environmental effects (E), which can be expressed in a linear model as P ¼ G þ E. If the genetic effects are not consistent across environments, there are


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GENETICS OF GRAINS | Rice: Genetics Table 1 Species Rice Sorghum Maize Barley Diploid wheat

Genome size and number of genes of cereal crops Genome size (Mb)

Number of genes

Predicted kb/gene

430 750 2500 4800 5300

30–50 000 30–50 000 50 000 30 000 30 000

15 15–25 50 160 175

interactions between genotypes and environments. In such a case, the linear model becomes P ¼ G þ E þ GE. The genetic effects (G) can be further partitioned into additive genetic effects (A), dominance effects (D), and epistatic effects (I) and expressed as G ¼ A þ D þ I. The additive effects indicate the total effects for all the loci that include the genes affecting the trait; the dominance effects are the interactions of alleles at a locus; and the epistatic effects are the interactions between alleles of different loci. Additive genetic effects can be selected directly, whereas the interaction effects (D and I) are not transmitted directly from parents to their offspring. Estimation of A, D, and I requires different types of progenies in a well-designed experiment. The total variation among phenotypes (s2P) is attributable to the genetic and environmental effects and the interaction of genetic and environmental effects. The broad-sense heritability of a trait can be expressed as h2b ¼ s2G =s2P . If the total genetic variation can be partitioned into A, D, and/or I, the narrow-sense heritability can be calculated as h2n ¼ s2A =s2P .

Molecular Dissection of Quantitative Traits Classical genetic analysis can only interpret the effect of all polygenes as a whole; it cannot effectively determine the number of genes expressed for the trait, the position of genes on chromosomes, and the effect of each gene. However, these problems can be resolved with the application of genetic markers together with the help of genetic linkage maps, by dissecting quantitative traits into QTL. Genetic markers include morphological markers, biochemical markers (e.g., isozymes), and DNA markers. The number of morphological and biochemical markers that can be identified is very limited. DNA markers denote variations in the pattern of DNA fragments or sequences in different individuals. The differences are referred to as DNA polymorphisms, which arise as a result of insertions, deletions, duplications, and substitutions of nucleotides. Restriction fragment length polymorphisms (RFLPs) are the first class of characterized DNA markers first reported in 1980. Since then, many other types of molecular markers have been developed, such as random amplified polymorphic DNA, simple sequence repeat (SSR) or microsatellite, inter-SSR, sequence-tagged site, amplified fragment length polymorphism, and SNP. The abundance of DNA markers allows genetic linkage map development. Construction of a genetic linkage map involves (1) establishment of genetic populations with a series of progenies derived from two parents, such as F2 population, backcross population, doubled haploid (DH) population, and

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recombinant inbred line (RIL) population; (2) analysis of DNA markers with each progeny and scoring of each allele; and (3) genetic linkage of the markers and the distance between every two markers is calculated. The first molecular genetic map of rice containing 135 markers based on RFLPs was developed in 1988. The map was generated from an indica japonica F2 population. Primary trisomics were used to assign linkage groups to each of the 12 chromosomes. Since then, many genetic maps have been developed based on either temporary populations (e.g., F2 and backcross populations) or permanent populations (e.g., DH and RIL populations). The availability of comprehensive molecular maps in rice has opened a new avenue to tag major genes governing simply inherited agronomic traits and to dissect complex quantitative traits into QTL with molecular markers. Many methods have been developed to dissect complex traits. The simplest method is one marker analysis that is to analyze the trait value differences between groups of individuals differing for a particular marker. No linkage map is needed in this case. Another commonly used method is interval mapping method in which a maximum likelihood method is used to test the effect of a genomic position within a chromosome interval (two adjacent markers). The disadvantage of interval mapping is its inability to take into account the effects on a trait of multiple QTLs. The other method, composite interval mapping, can resolve this problem and is robust in detecting linked QTLs on the same chromosome. For QTL mapping, permanent populations such as DH and RI populations are generally used, because the homozygous nature of each line in these kinds of populations allows carrying out experiments with replication and in different environments. For an F2 population, the additive effects (A) and dominance effects (D) and percent of total variance can be estimated for each QTL. For a permanent population, dominance effects cannot be estimated because of the homozygosity of each locus. As in the traditional quantitative genetics, if the phenotypic traits are measured across different environments, the QTL environment interaction can be dissected. Also, marker and marker interaction, referred to as epistasis (or epistatic effects), will be useful in interpreting the variation in some of the measured phenotypes.

From QTL to Gene Markers are not genes in the classical sense; they often do not have biological function, but they are better thought of as constant landmarks in the genome. However, it is possible to clone the functional gene at a specific QTL without knowledge of its product. The approach to clone the QTL that has been mapped on a specific location of a chromosome is map-based cloning or positional cloning. This strategy is also applicable in cloning major genes whose map positions are known. Three steps are necessary to carry out this strategy: first, finely mapping the target gene or QTL to as small as possible marker intervals using high-density genetic linkage map; second, isolating the target chromosomal region containing the gene/QTL of interest by using the flank molecular marker to select the bacterial artificial chromosome (BAC) and yeast artificial chromosome (YAC) libraries; and third, identifying the candidate functional gene by subcloning the target region

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GENETICS OF GRAINS | Rice: Genetics

and proof of its identity by mutant complementation with the target gene. High-density genetic linkage maps, good development of BAC and YAC libraries, well-established transformation techniques, and availability of the whole genomic sequence of rice have highly facilitated the isolation of rice genes. For cloning the QTLs, the construction of special genetic stocks such as near-isogenic lines or substitution lines can be used to finely map the putative QTLs as Mendelian factors with high reliability. A lot of rice genes and QTLs have been cloned using map-based cloning strategy. Table 2 summarizes the genes or QTLs cloned for some of yield-related agronomic traits.

Functional Genomics Positional cloning strategy has provided a way to link the sequence change to a specific phenotype. This kind of genetic research is also called forward genetics. Forward genetics Table 2

begins with isolation of mutant phenotype or naturally occurring variations of interest and searching for genes or QTLs responsible for the mutant or naturally occurring variations. Many artificial mutants have been generated with various approaches, such as the physical and chemical mutagens, AC/DS transposable elements of maize, retrotransposons, and T-DNA insertions. When mutant phenotype is cosegregated with a T-DNA or transposon insertion, rapid identification of the gene of interest is easily done by analyzing its neighboring sequences. However, the identification of a gene affected by a chemical-induced or radiation-induced mutation requires a map-based cloning approach, which is time-, cost-, and resource-consuming. Forward genetics fails to clarify the metabolic pathways underlying the phenotypic formation of traits of interest. The biological function of the cloned genes needs further investigation. Downregulation of the target functional gene by antisense expression leads to the mutant phenotype, or complementation test by transforming the

Genes/QTLs for rice yield-related traits

Traits

M/QTL

Name of gene/QTL

MSU-ID

Encoded protein

NPP NPP NPP NPP NPP NPP NPP, NGP NPP, NGP NPP, NGP NGP NGP NGP, NPP NGP NGP, NPP NGP NGP, NPP NGP, NPP NGP NGP NGP NGP NGP NGP GW, GS GW, GS GW, GS GW, GS GW, GS GW, GF GW, GF GW, GS GW, GS GW, GS GW, GF GW, GS GW, GS GW, GS

M M M M M M QTL QTL QTL QTL M M M M M M M M QTL QTL QTL QTL QTL QTL QTL QTL M QTL M M M QTL QTL M QTL M M

D27 D10 D14 D17/HTD1 D3 MOC1 OsSPL14 PROG1 qGY2-1 Gn1a LOG LAX1 LP APO2 APO1 DEP2 FZP SP1 Hd1 Ghd7 Ghd8/DTH8 EHD1 DEP1 TGW6 GW2 GS3 BRD1 GL3.1/qGL3 GIF1 FLO2 SRS3 GS5 qSW5/GW5 HGW GW8 SG1 SRS5

LOC_Os11g37660 LOC_Os01g54270 LOC_Os03g10620 LOC_Os04g46470 LOC_Os06g06050 LOC_Os06g40780 LOC_Os08g39890 LOC_Os07g05900 LOC_Os02g05980 LOC_Os01g10110 LOC_Os01g40630 LOC_Os01g61480 LOC_Os02g15950 LOC_Os04g51000 LOC_Os06g45460 LOC_Os07g42410 LOC_Os07g47330 LOC_Os11g12740 LOC_Os06g16370 LOC_Os07g15770 LOC_Os08g07740 LOC_Os10g32600 LOC_Os09g26999 LOC_Os06g41850 LOC_Os02g14720 LOC_Os03g29380 LOC_Os03g40540 LOC_Os03g44500 LOC_Os04g33740 LOC_Os04g55230 LOC_Os05g06280 LOC_Os05g06660 LOC_Os05g09520 LOC_Os06g06530 LOC_Os08g41940 LOC_Os09g28520 LOC_Os11g14220

Iron-containing protein Carotenoid cleavage dioxygenase 8 Alpha-/beta-fold hydrolase superfamily protein Carotenoid cleavage dioxygenase F-box leucine-rich repeat protein GRAS family nuclear protein SQUAMOSA promoter-binding protein-like 14 Zinc-finger nuclear transcription factor Leucine-rich repeat receptor-like kinase Cytokinin oxidase/dehydrogenase Cytokinin-activating enzyme A basic helix–loop–helix transcription factor Kelch repeat-containing F-box protein Plant-specific transcription factor F-box protein Plant-specific protein Ethylene-responsive element-binding factor Transporter of the peptide transporter family Protein with a zinc-finger domain CCT domain protein OsHAP3 subunit of a CCAAT-box binding protein B-type response regulator PEBP-like domain protein Iindole-3-acetic acid-glucose hydrolase RING-type E3 ubiquitin ligase Transmembrane protein Brassinosteroid-6-oxidase Phosphatase with Kelch-like repeat domain Cell-wall invertase Protein with a tetratricopeptide repeat motif Kinesin 13 protein Putative serine carboxypeptidase Nuclear protein Ubiquitin-associated domain protein SQUAMOSA promoter-binding protein-like 16 Novel protein Alpha-tubulin protein

NPP, number of panicles per plant; NGP, number of grains per panicle; GW, grain weight; GS, grain size; GF, grain filling; M/QTL, mutant/QTL; QTL, quantitative trait locus. Source: Ying JZ, Chen YY, and Zhang HW (2014) Functional characterization of genes/QTLs for increasing rice yield potential. In: Yan WG and Bao JS (eds.) Rice – Germplasm, Genetics and Improvement, pp. 177–194. InTech.

GENETICS OF GRAINS | Rice: Genetics functional gene to the mutant recovers the normal phenotype; these are two common ways to reveal gene function. Another way to link the sequence and function of a specific gene is reverse genetics. Reverse approaches rely upon sequence information as retrieved from genome and expressed sequence tag (EST) sequencing or transcription profiling projects. The scientist starts with the selection of a specific sequence (gene) and tries to gain insight into the underlying function(s) by selecting for mutations that disrupt the sequence. The gene function can be easily deduced from its mutant phenotype. The mutant populations mentioned in the preceding text are also very popular for reverse genetics by providing the necessary link between structural or sequence data and gene functions. High throughput of gene expression analysis on microarrays facilitates quick acquisition of genes or ESTs in relation to phenotypic expression of different traits and makes possible the identification of metabolic pathways. This technology improves the methodologies in gene cloning with high efficiency.

Comparative Genomic Mapping The development of molecular genetic maps of different cereals using a common set of DNA clones has facilitated comparative mapping among several cereal crops. The implication that knowledge gained from rice will aid in the improvement of other grass species gives an impetus to the studies in comparative mapping. Comparative mapping indicates that there are homoeologous relationships among the genomes of various crop plants. Comparative genome mapping in rice, maize, wheat, barley, sorghum, foxtail millet, and sugarcane demonstrates that gene content and order are highly conserved at both the map and megabase levels between different species within the grass family, but the amount and organization of repetitive sequences have diverged considerably. Microsynteny analysis using the rice YAC library clones of several hundred kilobases has also revealed remarkable similarities in marker order between rice and barley or wheat. Comparative mapping allows prediction of the presence and location of orthologous loci in other species according to gene location in rice, which accelerates map-based cloning of orthologous genes. The availability of the whole-genome sequence of rice has been of great help in other cereals for the discovery and cloning of the orthologous genes or QTLs. The progress in comparative mapping allows comparison of the QTL intervals for similar traits in different crop species. Similarly, the results indicate that the QTL locations are convergent in different cereal species for the same traits. Comparative mapping for domestication-related traits has revealed coevolution among different cereal crops.

Progress in Rice Genetics Recent studies show that some important characters in rice are controlled by loci having a major effect on phenotype, but most agronomically important traits such as yield, quality, and tolerance to abiotic and biotic stresses are quantitative in nature. The last decade has witnessed the identification of many genes underlying the traits of importance (Table 2).

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Here, the current understanding of the genetic basis for the traits of importance is introduced, focusing the cloning of major genes or finely mapped QTLs.

Agronomic and Yield-Related Traits Yield-related traits Yield is the most important trait for any rice variety and thus becomes a major objective in rice breeding programs. Breeding rice with high yield potential is always a dream of rice breeders. Yield and yield-related traits – such as number of tillers per plant, number of grains per panicle, and grain weight – are very complex traits with low heritabilities (Table 2). These traits are controlled by a set of QTLs, each QTL explaining only a few percent of the total variance. One significant advance in QTL mapping for rice yield comes from the finding that QTLs from unadapted germplasm or wild species can enhance the grain yield of cultivated rice. Two yield-enhancing loci, yld1 (RM5) and yld2 (RG256), located on chromosomes 1 and 2 of Oryza rufipogon (common wild rice) have been identified, which are capable of improving the yield of modern rice cultivars. This finding is also applicable for identifying valuable QTLs for other traits from unadapted germplasm so as to widen genetic diversity. Tillering in rice is an important agronomic trait for grain production. A major gene-controlling tiller number, moc1, has been cloned by map-based strategy and candidate gene analysis from a spontaneous monoculm 1 mutant that has only one main culm without any tillers. Ideal plant architecture (IPA) denotes rice with reduced tiller number and almost no unproductive tillers, which may have higher yield potential. A major QTL for IPA encoding SQUAMOSA promoter-binding protein-like 14 (OsSPL14) has been cloned. OsSPL14 is regulated by microRNA OsmiR156, and increasing level of the OsSPL14 transcript and protein resulted in an IPA phenotype and higher grain productivity. The wild rice O. rufipogon has a plant architecture with a wider tiller angle and more tillers than cultivated rice. The gene responsible for prostrate growth habit of wild rice, PROSTRATE GROWTH 1 (PROG1), has been cloned and characterized that encodes a zinc-finger nuclear transcription factor and is highly expressed in the axillary meristems. An amino acid substitution caused by one SNP in PROG1 leads to the transition from prostate growth of the wild rice of O. rufipogon to erect growth of the domesticated rice of O. sativa. A major QTL for grain number on the short arm of chromosome 1, Gnla, has been cloned and characterized, which encodes cytokinin oxidase (OsCKX2). Another major QTL for grain yield per plant, qGY2-1, encodes leucine-rich repeat receptor-like kinase (LRK), and overexpression of LRK1 causes more tillers and increased grain yield. Genes involved in panicle architecture have been characterized. LAX1 encodes a basic helix–loop–helix transcription factor and is required for the initiation/maintenance of inflorescence branch meristems. Defect of LAX1 results in the severely reduced primary and secondary branches and spikelets. FRIZZY PANICLE (FZP) encodes an ethylene-responsive element-binding factor and is responsible for the establishment of floral meristem identity through suppressing the formation of axillary meristems within the spikelet meristem. ABERRANT PANICLE ORGANIZATION 1 (APO1) encodes an F-box protein and functions in suppressing

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precocious conversion of rachis branch meristems to spikelets to ensure generation of certain number of spikelets. SHORT PANICLE 1 (SP1) encodes a putative transporter of the peptide transporter family and participates in the elongation of rice panicle. DENSE AND ERECT PANICLE 1 (DEP1)/qPE9-1 locus is a gain-of-function mutation causing truncation of a phosphatidylethanolamine-binding protein-like domain protein. The effect of this allele is to enhance meristematic activity, resulting in a reduced length of the inflorescence internode, an increased number of grains per panicle, and a consequent increase in grain yield. The DENSE AND ERECT PANICLE 2 (DEP2) mutant, which shows a dense and erect panicle phenotype, was identified. DEP2 encodes a plant-specific protein without any known functional domain. Grain weight of rice depends on the grain shape parameters, i.e. grain length, grain width, and grain thickness. Not only grain yield but also grain quality, that is, the appearance quality, is determined by grain shape. Three major QTLs controlling grain length, GS3, GL3.1/qGL3, and TGW6, have been mapbased cloned and functionally analyzed. The GS3 protein contains an organ size regulation domain in the N-terminus, a transmembrane domain, a tumor necrosis factor receptor/ nerve growth factor receptor-like domain, and a von Willebrand factor type C domain in the C-terminus. qGL3 encodes a putative protein phosphatase with Kelch-like repeat domain (OsPPKL1). THOUSAND-GRAIN WEIGHT 6 (TGW6) controls grain length and weight, encodes indole-3-acetic acid (IAA)glucose hydrolase that can hydrolase IAA–glucose to IAA and glucose, and affects the timing of the transition from the syncytial to the cellular phase and results in a shorter grain phenotype. Four QTLs controlling grain width, GW2, qSW5/GW5, GS5, and GW8, have been isolated and characterized. GRAIN WIDTH 2 (GW2) encodes a RING-type E3 ubiquitin ligase, which functions in the protein degradation through the ubiquitin–proteasome pathway. GRAIN WIDTH 5 (GW5/ qSW5) encodes a nuclear protein of 144 amino acids with an arginine-rich domain, which is likely to act as a regulator in the ubiquitin–proteasome pathway and regulates cell division of the outer glume of the rice spikelet. GRAIN SIZE 5 (GS5) encodes a serine carboxypeptidase and functions as a positive regulator of grain size. GRAIN WIDTH 8 (GW8) encodes SQUAMOSA promoter-binding protein-like 16 (OsSPL16), belonging to the protein family of SBP domain-containing transcription factors functioning as a positive regulator of cell proliferation and conditioning grain width and yield. Grain yield and grain weight largely depends on the ability of grain filling. GRAIN INCOMPLETE FILLING 1(GIF1) encodes a cell wall invertase to upload sucrose from the leaf (source) to the vascular trace of seed (sink), where sucrose is hydrolyzed in the extracellular space into monosaccharides, which are then transported into the endosperm for starch synthesis.

Plant height Plant height is important in breeding short-strawed, lodgingresistant cultivars in rice. The successful development of a highyielding semidwarf variety of rice, IR8, based on the recessive gene, sd1, led to the so-called rice ‘Green Revolution’ in the 1960s. Both qualitative and quantitative inheritances of plant height have been documented. More than 60 major genes for

plant height have been identified by the analysis of naturally occurring variation and the semidwarfing and dwarfing mutants. Two major genes for semidwarfism, sd1 and sdg, have been mapped on chromosomes 1 and 5, respectively. Eleven major genes for dwarfism have also been identified and mapped on rice chromosomes. Results from QTL mapping indicate that QTLs controlling plant height distribute on all 12 chromosomes. One major finding is that for each previously identified dwarfing or semidwarfing gene, at least one QTL has been mapped to its close proximity. This result supports the hypothesis that QTLs and major genes are different alleles of the same loci. The concept is useful in developing map-based cloning of QTLs. The green revolution gene, the semidwarf gene sd1, has been cloned with the candidate gene approach and found to encode gibberellin 20 oxidase-2 (GA20ox-2), catalyzing the conversion of GA53 to GA20. Five dwarf mutations have been characterized: DWARF3 (D3) and DWARF14 (D14) may act in the signaling pathway in rice, while DWARF17 (D17)/HIGH-TILLERING DWARF1 (HTD1), DWARF10 (D10), and DWARF27 (D27) are involved in the biosynthesis of strigolactones, a new class of terpenoid plant hormones, which may act as the downstream of auxin to inhibit axillary bud outgrowth. Their loss-of-function causes similar phenotype of enhanced shoot branches accompanying with reduced plant height.

Heading date Heading date (HD) is a major determinant of the regional and seasonal adaptation of rice varieties, so the control of HD is an important objective in rice breeding. HD of rice is basically determined by three factors: duration of the basic vegetative growth (BVG), photoperiod sensitivity (PS), and temperature sensitivity. Several genes are involved in controlling the first two factors. BVG is controlled by two or three genes. A major gene, EF-1, controlling the duration of BVG, is located on chromosome 10. PS is also controlled by several genes including Se1, Se3, Se4, Se5, Se6, Se7, E1, E2, E3, and PS. Attempts to identify QTLs conferring HD have been carried out by many researchers. The QTLs distribute among all the chromosomes except 5. Using several types of progeny derived from Nipponbare/Kasalath, a total of 15 QTLs has been identified for HD. Among these 15 QTLs, Hd1, Hd2, Hd3a, Hd3b, Hd4, Hd5, and Hd9 have been mapped as single Mendelian factors. Three QTLs – Hd1, Hd6, and Hd3a – have been cloned. The QTL Hd1 on chromosome 6 is identical with Se1 gene, which is known as major photosensitive gene, and is closely related to the Arabidopsis flowering-time gene, CONSTANS. A minor QTL, Hd6, involved in PS can be dissected as a Mendelian factor using the advanced backcross strategy. The cloned gene encodes the a-subunit of protein kinase CK2, but does not correspond to any of the genes identified by mutant analysis in Arabidopsis with a role in controlling flowering time. The QTL, Hd3a, is an ortholog of the Arabidopsis flowering-time gene FT, which promotes transition to flowering downstream of Hd1 under short-day conditions. Ghd7 is a pleiotropic gene encoding a CCT (CO, CO-LIKE, and TIMING OF CAB1) domain protein and functioning as a key QTL simultaneously controlling yield (number of grains per panicle), plant height, and HD in rice. Similar to that of Ghd7 in delaying rice heading

GENETICS OF GRAINS | Rice: Genetics and improving yield-related traits, Ghd8 encodes a HAP3 subunit containing CCAAT-box-binding transcription factor.

Disease and Insect Resistance Resistance to disease There are two major types of disease resistance to plant pathogens, that is, vertical (qualitative or complete) resistance and horizontal (quantitative or partial) resistance; both have long been recognized as a result of interactions between plant hosts and their pathogens. Vertical resistance in many plant host–pathogen relations is hypersensitive, race-specific, and governed by interactions between avirulence genes in pathogens and resistance genes in plant hosts. Horizontal resistance is quantitative, presumably non-race-specific, and controlled by polygenes. Because of the use of different genetic populations and different pathogen races in QTL mapping, the detected QTLs differ in number and effects in different studies. Even with the same population, different QTLs would result from different pathogen races used. No QTL can confer resistance to all the pathogen races. Some of the identified QTLs locate in the region where the major genes lie. According to the protein sequences corresponding to the cloned plant resistance genes, a large number of resistance genes display similar characteristic domains such as a nucleotide-binding site (NBS) and a leucine-rich repeat (LRR) motif. Candidate gene fragments that involve in both recognition reaction (NBS motif, called resistance gene analog marker) and general plant defense (putative defense response) are used as molecular markers to test for association with resistance to rice diseases. When colocalization is observed between the resistance gene analog and a putative resistance locus, the resistance gene analog markers can be assigned to the resistance gene locus and used to further identify the resistance gene. Clustering of these candidate genes in the rice genome has been observed at several chromosomal regions. Some of the clusters locate in regions where QTL associated with partial resistance to rice blast and bacterial blight are known to lie. Resistance to bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), has received detailed studies, because bacterial blight is one of the most serious rice diseases in Asia. So far, a total of 38 related genes have been identified. Among them, six have been physically mapped (Xa2, Xa4, Xa7, Xa30, Xa33, and Xa38), six have been cloned (Xa1, xa5, xa13, Xa21, Xa26 ¼ Xa3, and Xa27), and eight were from wild rice (Xa21, Xa23(t), Xa27, Xa29(t), Xa30, Xa32(t), Xa35(t), and Xa36(t)). The sequence of the predicted protein of Xa21 carries both a LRR motif and a serine–threonine kinase-like domain, suggesting a role in an intracellular defense response. The deduced amino acid sequence of the Xa1 gene product contains NBSs and a new type of LRR, indicating that Xa1 is a member of the NBS–LRR class of plant resistance genes but is quite different from Xa21. Resistance to another disease, the blast fungus (Piricularia grisea), has also received scrutiny. The genetic behavior of resistance to blast is very complex. It is genetically controlled by both major genes and QTLs. So far, more than 60 major resistance genes have been identified even though some of them are identical or allelic. Some of the major genes have been tagged with molecular markers, and many of them tend

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to be clustered at particular chromosomal regions, such as those on chromosomes 6, 11, and 12. Twenty-two major resistance genes, including 20 major and 2 minor R genes (Pb1 and pi21), have been cloned and molecularly characterized. All cloned blast R genes encode predicted proteins with centrally located NBSs and LRR at the C-terminus. There are some genes/ QTLs conferring resistance to different races of blast. QTL mapping studies have permitted identifying some new major genes and QTLs as well. None of the major genes or QTLs mapped were found to confer resistance to all races. Inoculating different races of blast fungus, especially new races, can sometimes identify additional resistance genes to those previously reported.

Resistance to insects Brown plant hoppers, white-backed plant hoppers, stem borers, gall midges, etc. are major insect pests of the rice crop in Asia. Investigations on resistance to insect pests are relatively more recent when compared with those on disease resistance. Rice resistance to insects is most often inherited as a quantitative trait. More than 19 resistance genes for brown plant hoppers have been reported. Some major genes for resistance to brown plant hopper, Bph1, bph2, Bph6, Bph10, Bph14, etc., have been tagged with molecular marker. Among them, Bph14 conferring resistance at seedling and maturity stages of the rice plant has been cloned and shown to encode a coiled-coil, nucleotide-binding, and leucine-rich repeat (CC–NB–LRR) protein. Expression of Bph14 activates the salicylic acid signaling pathway and induces callose deposition in phloem cells and trypsin inhibitor production after plant hopper infestation, thus reducing the feeding, growth rate, and longevity of the BPH insects. Gall midge (Orseolia oryzae Wood-Mason) is a major dipteran pest of rice. Tolerance to gall midge has also received much genetic study. Seven major genes responsible for gall midge resistance (Gm1, Gm2, gm3, Gm4, Gm5, Gm6(t), and Gm7(t)) have been tagged. Wild rice has valuable genes for resistance to various pests, and the populations derived from cultivated and wild rice crosses contribute to the identification of most of the major genes. For example, Bph12 has been identified from wild rice Oryza latifolia and mapped on chromosome 4 with microsatellite marker RM261, and Bph13(t) has been identified from Oryza eichingeri on chromosome 2 between microsatellite RM240 and RM250. The difficulty in trait measurement in the field hinders extensive investigation of QTLs underlying insect resistance. The threshold to declare a QTL for insect resistance is lower than that for other types of study, so that the QTLs identified are less accurate in position and explain a lower percentage of the total variation.

Abiotic Stresses Tolerance to low temperature Low-temperature stress is common for rice grown in temperate regions and at high elevations in the tropics. Low temperatures dramatically reduce grain yield if the stress coincides with the sensitive period during the reproductive stage of rice by inducing spikelet sterility due to failure of microspore development or a decrease in the number of pollen grains per anther. Studies have been conducted to locate QTLs on chromosome regions responsible for cold tolerance at the booting stage, which

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would affect the floret sterility. The number of QTLs differs in the different populations, indicating that useful QTLs are maintained in different rice materials.

Tolerance to submergence Rice is well known for its ability to grow under flooding, but most rice cultivars cannot survive if the plants are completely submerged for more than 7 days. In many genetic studies, this trait appears quantitative, but more careful testing reveals the effect of the major gene, designed Sub1 in the F2 population derived from a submergence-tolerant indica line, IR40931-26, and a susceptible japonica line, PI543851. The Sub1 locus is tagged with two RFLP markers, RZ698 and C1232, on chromosome 9. QTL mapping for submergence confirms that the locus at Sub1 has a large effect on submergence tolerance, while four other QTLs have much smaller effects. The positional cloning of SUB1 resolved a gene designated SUB1A that encodes a putative ERF DNA binding protein with a single ERF/APETELA2 domain. Two additional ERFs, designated SUB1B and SUB1C, were identified nearby SUB1A. All encode SUB1B and SUB1C, but only a subset of indica and aus accessions encode SUB1A. Two alleles are found in submergence-tolerant and submergence-intolerant indica and aus accessions, based on nucleotide variations in the proteincoding region. SUBA1-1 is found only in tolerant lines, whereas the SUB1A-2 allele is present in intolerant indica accessions. SUB1A-1 and SUB1A-2 encode identical proteins, with the exception of Ser186 in the tolerant allele and Pro186 in the intolerant allele.

Tolerance to drought Drought is the major abiotic stress-limiting rice yields in rainfed environments. Tolerance to this abiotic stress is a complex process and is one of the crop genetic improvement’s least understood genetic traits. Nevertheless, a few researchers have made significant progress in this aspect from the perspective of molecular marker mapping of components of drought tolerance-related root system parameters, such as root morphology, root penetration ability, osmotic adjustment, and cell membrane stability. Comparison of positions of QTLs across a few mapping populations reveals that there are several common regions associated with deep root morphology traits and root thickness traits, indicating a potential for markerassisted selection for these traits.

Tolerance to adverse soils Adverse soil conditions hinder rice growth and development, such as high salinity, phosphorus deficiency, and high aluminum content. Genetic analysis of rice resistance or tolerance to adverse soil depends on the establishment of simple but quick and relatively accurate identification methods. Rice is sensitive to salinity, which affects one-fifth of irrigated land worldwide. Reducing sodium and chloride uptake into rice while maintaining potassium uptake is characteristic indispensable to aid growth under saline conditions. Genetic control of this trait appears to be quantitative. QTL mapping can dissect this complex physiological trait by measuring its physiological components, such as Naþ concentration, Naþ uptake, Kþ concentration, Kþ uptake, and Naþ/Kþ ratio. The QTLs for these traits have been mapped on chromosomes 1, 4, 6, 7, and 9. A

major QTL (SKC1) for shoot Kþ content mapped on chromosome 1 has been cloned, which encodes a member of HKT-type transporters, and SKC1 functions as a Naþ-selective transporter. Physiological analysis suggests that SKC1 is involved in regulating Kþ/Naþ homeostasis under salt stress. A mutant with loss of function in DST (drought and salt tolerance) increases stomatal closure and reduces stomatal density, thus resulting in enhanced drought and salt tolerance in rice. DST is identified as a zinc-finger transcription factor that negatively regulates stomatal closure by direct modulation of genes related to H2O2 homeostasis. Phosphorus deficiency occurs widely in rice soils with a high native phosphorus-fixing capacity, such as in acid soils, acid sulfate soils, and alkaline soils. Mapping QTLs for the traits responsible for phosphorus deficiency enables to identify a major QTL on chromosome 12 flanked by RFLP marker RG9 and RG241. Several other minor QTLs are mapped on chromosomes 1, 2, 3, 4, 6, 9, and 10. The major quantitative trait locus for phosphorus-deficiency tolerance, Pup1, has been identified as a protein kinase gene, named phosphorusstarvation tolerance 1 (PSTOL1). PSTOL1 acts as an enhancer of early root growth, thereby enabling plants to acquire more phosphorus and other nutrients. Thus, overexpression of PSTOL1 in such varieties significantly enhances grain yield in phosphorus-deficient soil.

Grain Quality Cooking and sensory quality The three most important parameters to evaluate the cooking and sensory quality of rice are amylose content (more accurately termed apparent amylose content), gelatinization temperature, and gel consistency. The change of starch viscometric properties during heating and cooling commonly tested with a Rapid Visco Analyzer (RVA) simulates the cooking process and serves as an indicator of the eating and cooking characteristics of milled rice and rice flour. Rice with aroma when cooked is often at a premium in many markets. Amylose content has been found to be primarily controlled by an allelic series at one locus with major effects and by one or more modifier genes with minor effects. Through QTL analysis, amylose content is also reported to be controlled by a major QTL and other minor QTLs. This major QTL is at the Waxy (Wx) locus, which encodes granule-bound starch synthase. The QTLs with large effects controlling gel consistency and RVA pasting viscosity characteristics are also at Wx locus, though there are many others with minor effects. Gelatinization temperature is a typical qualitative– quantitative trait. One to three genes with several modifiers reportedly control this trait. QTL analysis indicates that gelatinization temperature is controlled mainly by the alk gene loosely linked ( 28 cM) with Wx on chromosome 6. Map-based cloning revealed that it is starch synthase IIa (SSIIa) gene at the alk locus. In waxy rice, SSIIa is the major gene responsible for RVA pasting viscosity and thermal and retrogradation properties. Several hundred compounds can be observed in the volatiles of cooked rice, and more than 200 of these have been identified. The aromatic compound 2-acetyl-1-pyrroline (2AP) is reportedly the primary component of the popcorn-like smell of aromatic rice. The major gene designated as fgr has been

GENETICS OF GRAINS | Rice: Genetics identified by several researchers on chromosome 8. Functional fgr gene encodes the betaine aldehyde dehydrogenase 2 and renders rice nonfragrant by inhibiting biosynthesis of 2AP.

Appearance quality The appearance of milled rice affects consumer acceptance of the product. Grain size and shape are the most stable properties of a rice cultivar with many genes cloned (see earlier for yield-related traits). Chalkiness is a major factor in determining appearance quality and price. The chalky endosperm consists of loosely packed, round, and large compound starch granules, while the translucent endosperm comprises tightly packed, polyhedral, and small single starch granules. Percentage of grains with chalkiness (PGWC) is one of the main indices of ricedetermining appearance quality, which is easily determined. Defect in genes affecting starch biosynthesis, starch granule structure, and grain filling may lead to endosperm chalkiness. These genes include starch branching enzyme IIb (BEIIb), branching enzyme I (BEI), starch synthase IIIa (SSIIIa), and floury and sugary genes. The grain incomplete filling 1 (gif1) mutant defects in grain-filling capacity, but its grains are with more chalkiness as a result of loosely packed starch granules. For naturally occurring chalkiness, many QTLs from different populations have been detected, in which two QTLs (qPGWC-8 and qPGWC-7) have been finely mapped. One major QTL Chalk5 for grain chalkiness has been successfully cloned, which encodes a vacuolar Hþ-translocating pyrophosphatase with inorganic pyrophosphate hydrolysis and Hþ-translocation activity. Grain chalkiness is increased with the elevated expression of Chalk5 putatively by disturbing the pH homeostasis of the endomembrane trafficking system in developing seeds. The final result is to form air spaces among endosperm storage substances, which could be seen as chalky visually.

Milling quality The market value of rough rice, in part, reflects the percentage of head rice to total milled rice produced after milling. Thus, milling quality is assessed by brown rice recovery, milled rice recovery, and head rice recovery. Milling quality is one kind of complex quantitative traits whose genetic control is poorly understood. To date, no major gene has been genetically identified and functionally characterized. However, 20, 19, and 34 QTLs have been identified for brown rice recovery, milled rice recovery, and head rice recovery.

Nutritional quality As one of the most important staple foods in the world, nutritional quality is closely related to human health and thus is highly valued by consumers. Protein is the second most abundant constituent of milled rice, following starch. Lysine is the first limiting essential amino acid in rice based on the human requirements. Previously, protein and lysine content are two important parameters determining nutritional value of rice. Nowadays, more nutrients are needed for people either in the underdeveloped region or in developed countries. Micronutrient deficiency (vitamins and minerals, such as iron and zinc) is apparent in the underdeveloped region. Genetics study for and biofortification of micronutrients by breeding are necessary to improve the nutritional quality of rice. QTLs for protein,

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amino acids, mineral elements, and fat content have been searched. Biofortification of Va, folate, flavonoids, etc. have been successfully carried out in rice grain.

Future Prospect Genome-Wide Association Study It is time-consuming to produce proper lines and identify a few traits or alleles through map-based cloning method. Association mapping, also known as linkage disequilibrium (LD) mapping, has emerged as a tool to resolve complex trait variation down to the sequence level by exploiting historical and evolutionary recombination events at the population level. GWAS has emerged as a powerful approach for identifying genes underlying complex diseases in humans, but now, it has also been successfully applied in dissecting the genetic basis and discovery of allelic diversity of genetic loci for complex traits in plants including rice. The new sequencing technologies allow rapid capture of millions of SNPs across diverse germplasm, which makes the GWAS possible in rice. The use of whole-genome resequencing for constructing the comprehensive haplotype map for GWAS of complex traits has been carried out in rice. About 3.6 million SNPs by sequencing 517 rice landraces have been captured, and GWAS for 14 agronomic traits in indica rice has been performed. Strong associations could be identified for some traits, and the loci identified through GWAS explained on average 36% of the phenotypic variance. With a larger and more diverse sample of 950 worldwide rice varieties, a total of 32 new loci were found to be associated with flowering time and with ten grain yield-related traits. These studies provide a fundamental resource for rice genetics research and breeding and demonstrate that GWAS can be used as a powerful complementary strategy for dissecting complex traits in rice. Similar to map-based cloning, the locus identified by GWAS still needs further functional genomics studies on its molecular mechanisms. Sometimes, an associated locus contains several candidate genes since rice has a long range of LD, which makes the identification of functional gene time-consuming. Combining GWAS with other functional genomics approaches may facilitate dissecting complex traits and identifying the important gene alleles in rice. In the next decade, more functional genes in rice are expected to be revealed from a start point of GWAS.

Marker-Assisted Selection The potential usefulness of molecular markers linked to genes or QTLs is essential to the future success of molecular breeding programs. However, integrating DNA marker technology into conventional rice breeding has not been implemented widely. One reason is possibly due to the high cost of the techniques. The second is that many breeders are not so skillful in accessing the database information, and some are still stubborn to accept new methods and stick to phenotypic selection in the field. Strategy for molecular breeding requires introduction of target genes or QTLs of interest by using molecular techniques, including the alien genes of the donor traits from wild rice. The functional markers derived from cloned genes provide

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unique genetic markers for molecular breeding. Pyramiding more genes and QTLs into one individual plant through marker-assisted selection is feasible for all traits of importance, thus conferring high yield, high quality, and high resistance to diseases and insects in the newly developed rice. In the next decade, more rice varieties will be bred successfully and efficiently with marker-assisted selection.


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Explain the following terms: forward genetics, reverse genetics, map-based cloning, and genome-wide association study. How can the traits of rice be classified? What traits are contributed to yield of rice? What is the genome size of rice? Why rice is a model plant for cereals? How many genes have been cloned for grain shape (grain length and grain width)? Which gene controls amylose content, and which controls gelatinization temperature of rice starch? Could you design an experiment to breed fragrant rice by molecular-assisted selection?


• • • •

What genes would affect rice heterosis? How epigenetics influence rice trait formation? How to use GWAS to identify genes for complex traits of rice? Speculate on how to breed rice to mitigate global warming.

See also: Breeding of Grains: Rice: Breeding; Genetics of Grains: Genome Mapping; The Cereal Grains: Wildrice, Zizania: Overview.

Further Reading Ashikari M, Sakakibara H, Lin S, et al. (2005) Cytokinin oxidase regulates rice grain production. Science (309): 741–745. Bao JS (2014) Genes and QTLs for rice grain quality improvement. In: Yan WG and Bao JS (eds.) Rice – Germplasm, Genetics, and Improvement, pp. 239–278. Croatia: InTech. Bao JS and Corke H (2004) Rice/genetics. In: Wrigley C, Corke H, and Walker CE (eds.) Encyclopedia of Grain Science, vol. 3, pp. 48–61. Oxford: Academic Press/Elsevier, 1st edn. Du B, Zhang W, Liu B, et al. (2009) Identification and characterization of Bph14, a gene conferring resistance to brown planthopper in rice. Proceedings of the National Academy of Sciences of the United States of America 106: 22163–22168. Gamuyao R, Chin JH, Pariasca-Tanaka J, et al. (2012) The protein kinase Pstol1 from traditional rice confers tolerance of phosphorus deficiency. Nature 488: 535–539. Huang X, Qian Q, Liu Z, et al. (2009) Natural variation at the DEP1 locus enhances grain yield in rice. Nature Genetics 41: 494–497. Huang X, Wei X, Sang T, et al. (2010) Genome-wide association studies of 14 agronomic traits in rice landraces. Nature Genetics 42: 961–967. International Rice Genome Sequencing Project (2005) The map-based sequence of the rice genome. Nature 436: 793–800. Ishimaru K, Hirotsu N, Madoka Y, et al. (2013) Loss of function of the IAA-glucose hydrolase gene TGW6 enhances rice grain weight and increases yield. Nature Genetics 2013(45): 707–711. Jiao Y, Wang Y, Xue D, et al. (2010) Regulation of OsSPL14 by OsmiR156 defines ideal plant architecture in rice. Nature Genetics 42: 541–544. Li X, Qian Q, Fu Z, et al. (2003) Control of tillering in rice. Nature 422: 618–621. Li Y, Fan C, Xing Y, et al. (2014) Chalk5 encodes a vacuolar Hþ-translocating pyrophosphatase influencing grain chalkiness in rice. Nature Genetics 46: 398–404. Ren ZH, Gao J-P, Li LG, et al. (2005) A rice quantitative trait locus for salt tolerance encodes a sodium transporter. Nature Genetics 37: 1141–1146. Song WY, Wang GL, Chen LL, et al. (1995) A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21. Science 270: 1804–1806. Song XJ, Huang W, Shi M, Zhu MZ, and Lin HX (2007) A QTL for rice grain width and weight encodes a previously unknown RING-type E3 ubiquitin ligase. Nature Genetics 39: 623–630. Wang E, Wang J, Zhu X, et al. (2008) Control of rice grain-filling and yield by a gene with a potential signature of domestication. Nature Genetics 40: 1370–1374. Wang X, Lee S, Wang J, Ma J, Blanco T, and Jia Y (2014) Current advances on genetic resistance to rice blast disease. In: Yan WG and Bao JS (eds.) Rice – Germplasm, Genetics, and Improvement, pp. 195–217. Croatia: InTech. Xiao J, Grandlillo S, Ahn SN, et al. (1996) Genes from wild rice improve yield. Nature 384: 223–224. Xu K, Xu X, Fukao T, et al. (2006) Sub1A is an ethylene-response-factor-like gene that confers submergence tolerance to rice. Nature 442: 705–708. Xue W, Xing Y, Weng X, et al. (2008) Natural variation in Ghd7 is an important regulator of heading date and yield potential in rice. Nature Genetics 40: 761–767. Ying JZ, Chen YY, and Zhang HW (2014) Functional characterization of genes/QTLs for increasing rice yield potential. In: Yan WG and Bao JS (eds.) Rice – Germplasm, Genetics, and Improvement, pp. 177–194. Croatia: InTech.

Maize: Genetics EA Lee, University of Guelph, Guelph, ON, Canada ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 191–204, ã 2004, Elsevier Ltd, with an updated Bibliography section supplied by the Editor

Topic Highlights

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Maize originated in Central America from an annual teosinte 7000–12,000 years ago. A vast range of maize genetic mutants is available, which add to crop diversity, aid in breeding, and contribute to fundamental genetic studies. Barbara McClintock discovered ‘jumping genes’ – transposable elements – in maize, opening up a rich field of basic genetic research. Kernel property mutants include those for starch traits (e.g., waxy and high-amylose) and those for color (pigmentation). The cytoplasmic male sterility–restorer system enables production of hybrids without need for physical control of pollination (e.g., detasseling).

Learning Objectives

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To understand the genetic origins of maize and the wide range of mutants available. To understand the basis for the contributions of maize to fundamental genetic studies. To understand the importance of heterosis, the nature of hybrid development, and the use of cytoplasmic male sterility–restorer systems.

Maize (Zea mays L. ssp. mays), in addition to being an economically important crop plant, is a model plant for studying genetics. The intent of this brief article is to acquaint the reader with some of the unique contributions that maize has made to the science of genetics. Information regarding mode of propagation, controlled pollinations, heterosis, quantitative genetics, and breeding are covered in MAIZE | Breeding. Several excellent comprehensive reviews of the general subject are available. A recent book – ‘Mutants of Maize’ – gives an extensive pictorial overview of numerous maize mutants, while another – ‘Maize Genetics and Breeding in the 20th Century’ – gives an overview of the more prominent maize geneticists of the twentieth century and their contributions to maize genetics.

Origin of Maize Maize, a diploid plant with 10 chromosomes (x ¼ 10, 2n ¼ 20), is a member of the grass (Poaceae) family, which includes crops such as rice (Orzya sativa), wheat (Triticum aestivum), barley (Hordeum vulgare), sugar cane (Saccharum ssp.), pearl millet (Pennisetum glaucum), and sorghum (Sorghum bicolor).


The maize genome appears to be an ancient segmental allotetraploid (i.e., hybridization of two species whose genomes are partially alike). Many genes in maize exist as two unlinked copies (i.e., homologs), each of which occur on duplicated chromosomal segments (i.e., linkage blocks). Over time some of these genes have developed slightly different expression patterns (i.e., paralogs), such as the anthocyanin genes – colored1 (r1) and colored plant1 (b1), or colored aleurone1 (c1) and purple plant1 (pl1). For some of these genes, one copy (i.e., pseudogene) may have become nonfunctional due to mutations. While other homologs have not diverged from one another leading to redundancy, such as the orange pericarp1 (orp1) and orange pericarp2 (orp2) genes. Comparing divergence times for 14 pairs of homologs enabled the maize genome to be subdivided into two subgenomes. Molecular marker studies of the two apparent subgenomes of maize suggest that one of the subgenomes is more closely related to sorghum than it is to the other maize subgenome. Two contrasting theories regarding the origin of maize existed for many years, the ‘teosinte hypothesis’ put forth by George Beadle and the ‘tripartite hypothesis’ championed by Paul Mangelsdorf. Today, the most widely accepted theory is that maize originated from an annual teosinte (Z. mays ssp. parviglumis), 7000–12 000 years ago (teosinte hypothesis). Teosinte parviglumis (x ¼ 10, 2n ¼ 20) is a wild grass native to Mexico and Guatemala. Maize T. parviglumis hybrids are completely fertile, vigorous plants. At the chromosome, gene structure, and nucleotide sequence level, maize and T. parviglumis exhibit as many differences as would be observed between any two maize varieties. While 7000–12 000 years is considered an extremely short period of time in terms of evolution, dramatic morphologically changes in plant architecture and kernel structure occurred between maize and teosinte in that time (Figure 1). Genetic evidence suggests, however, that as few as five mutations may be responsible for these dramatic morphologically differences. Two genes have been identified that change maize morphology to teosinte morphology. The teosinte glume architecture1 (tga1) locus controls differences associated with kernel structure and teosinte branched1 (tb1) controls differences in plant architecture (Figure 2a). Both tga1 and tb1 are believed to be genes that were important in the domestication of maize from teosinte. Molecular mapping of the various grass genomes has led to two interesting observations. Gene content of the various grass family members does not vary greatly, even though variation in DNA content is considerable. Most of the differences in genome size are due to variation in the amount of noncoding DNA (i.e., DNA other than genes). Noncoding DNA consists of highly repetitive DNA sequences, made up of fragments retrotransposon sequences. The other observation is that gene order is semiconserved across the grass species. This phenomenon is

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Figure 1 (a) Teosinte ear on the left and “reconstructed” primitive maize ear on the right. George Beadle created the latter by crossing teosinte with Argentine popcorn and then selecting the smallest segregants. This maize ear resembles the earliest archaeological corn recovered from the Tehuacań valley in Mexico (photo by John Doebley). (b) Mature teosinte plant showing lateral side branches (photo by Hugh Iltis). (c) Immature ears of Zea diploperennis whole and sectioned with a few mature fruitcases one of which is cracked open to expose the grain (photo by Hugh Iltis). (d) Teosinte ear (Zea mays ssp. mexicana) on the left, maize ear on the right, and ear of their F1 hybrid in the center (photo by John Doebley).

generally referred to as collinearity or synteny. Chromosomal rearrangements have occurred that break up the collinearity between grass species. These rearrangements tend to involve translocations, inversions, duplications, or deletions. The syntenic relationships between the maize, rice, and wheat genomes are represented in Figure 3. For example, chromosome 9 of rice contains genes that are contained on chromosomes 7 and 2 of maize, those genes are also found on chromosome 5 of wheat (Figure 3). Generally, collinearity between the grass genomes exists on a macroscale. When collinearity is examined on a microscale, there can be quite a few exceptions to the expected gene order. Synteny is a powerful tool that permits maize geneticists to utilize genetic resources from other grass species. For example, the genome of rice has been recently sequenced. Because of the syntenic relationship that exists between the maize and rice genomes, maize geneticists can potentially identify the rice ortholog for any maize gene and then use the rice ortholog’s DNA sequence to isolate the maize gene.

Cytogenetics Historically, one of the major contributions of maize genetics was to the field of cytogenetics. Maize cytogeneticists were the first to demonstrate that chromosomes are individually recognizable by their lengths, arm ratios, and other physical features, physical exchange of chromosome segments accompanies genetic recombination, and that telomeres are necessary for maintaining fidelity during chromosome duplication and division. Barbara McClintock was the first geneticist to characterize the ten maize chromosomes. Working with mitotic chromosomes, she used initially overall chromosome length and the position of the centromeres relative to each chromosome arm (i.e., arm ratio) to describe each chromosome. Information regarding the presence of chromosome ‘knobs’ (i.e., dark staining heterochromatic regions), nucleolus organizer region (NOR), and chromomeres were later added to McClintock’s original description of the chromosomes (Figure 4). The maize chromosomes are numbered in order

of size, chromosome 1 is the longest and chromosome 10 is the shortest. The NOR region is located at the end of the short arm of chromosome 6. There are two types of reciprocal translocations that have been developed in maize that have proven to be extremely useful, A–A translocations and B–A translocations. These translocations enabled geneticists to assign molecular marker based linkage groups to chromosomes and orient them, as well as assigning recessive and dominant mutations to chromosome arms. Reciprocal translocations involve exchange of chromosome segments between nonhomologous chromosomes. To create reciprocal translocations requires (1) chromosome breaks to occur in two different chromosomes, followed by (2) rejoining of the fragments to produce two novel chromosomes (Figure 5). The first reciprocal translocations were spontaneous, however most of the reciprocal translocations in maize were generated using ionizing radiation. A–A translocations involve interchanges between the 10 maize chromosomes (i.e., A chromosomes). B–A translocations involve interchanges between one of the 10 maize chromosomes and a supernumerary chromosome called the B chromosome. The B chromosome is relatively small ( 60% the size of chromosome 10) and is comprised almost entirely of heterochromatic DNA. There are several interesting features that are unique to the maize B chromosome. It divides normally during cell division (mitosis) and during the development of the megaspore (female gamete). However, its behavior during development of the microspore (male gamete) and subsequent fertilization are what distinguish the maize B chromosome from other B chromosomes. (1) Nonconcordance of the two sperm nuclei arising from the second mitotic-like division of microsporogenesis occurs. This phenomenon, also called nondisjunction, is the result of one of the sperm nuclei receiving two copies of the B chromosome while the other sperm nuclei is lacking the B chromosome. (2) The megaspore is preferentially fertilized by the sperm nuclei containing the B chromosomes. These two phenomenon result in an accumulation of B chromosomes in each generation. It is a unique, yet unknown, feature of the B chromosome’s centromere that is responsible for nondisjunction and it is this feature that makes the B–A translocations


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Figure 2 Examples of the range of mutations that have been identified and studied in maize. (a) teosinte branched1 (tb1) mutation indicated by the arrow adjacent to normal maize plants. (b) An ear segregating for anthocyanless1 (a1) and shrunken2 (sh2). a1 and sh2 are tightly linked (0.2 cM) genes, with a1 affecting aleurone color and sh2 affecting starch accumulation in the endosperm. (c) brown mid-rib3 (bm3) mutant leaf on the left and a normal leaf on the right. (d) lethal leaf spot1 (lls1) mutant leaf on the left and a normal leaf on the right. (e) An ear segregating for opaque2

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Figure 3 Alignment of the genomes of six major grass crop species with 19 rice linkage segments, whose order reflects the circularized ancestral grass genome. The thin dashed lines correspond to the duplicated segments. Inversions of sets of sequences within a linkage segment (such as the inversion of segments 3a and 3b in maize chromosome 5) are not shown. Linkage segments forming parts (pt) of Triticeae chromosome 5 are shown as a series of segments connected by colored lines. The alignment is based on the genetic map of the D genome of wheat. The red line indicates the duplicated segments shown as blocks 11b and 12b. Chromosomes formed by the insertion of one segment into another are shown by black lines with arrows indicating the direction and point of insertion. The points of chromosome breakage involved with insertion events are indicated by black bisected circles. The “haploid” chromosome number of each species is shown in the column marked “x.” The haploid DNA content of each species, shown in the column of 1C values, is per 109 bases. (Reproduced with permission from Moore G, Devos KM, Wang Z, and Gale MD (1995) Grasses, line up and form a circle. Current Biology 5: 737–739, 169–174. ã Elsevier.)

particularly useful for mapping recessive mutations (Figures 6 and 7).

Transposable Elements Probably the largest contribution that maize has made to the field of genetics was the discovery and genetic characterization of ‘jumping genes,’ for which Barbara McClintock was awarded the Nobel Prize in Medicine in 1983. Transposable elements (TEs) (i.e., ‘jumping genes’) are pieces of DNA that can move around the genome. Transposable elements are the single

largest component of most eukaryotic genomes, accounting for 50–80% of the DNA sequence in some grass family genomes. However, only a small fraction represent sequences that are still active. The TE that McClintock identified and studied was a site that was vulnerable to chromosome breakage, hence she named it Dissociation (Ds). Ds, however, could break chromosomes and transpose only when a second factor, called Activator (Ac), was present. Ac/Ds represent one TE family in maize, Ac is the autonomous element (i.e., capable of moving by itself) and Ds is the nonautonomous element (i.e., not capable of moving by itself). Part of Ac’s DNA sequence contains a gene that encodes an enzyme required for

(o2) and normal kernels. o2 kernels indicated by the arrow are lighter colored with a chalky endosperm. (f) dwarf1 (d1) plant on the leaf and a normal maize plant on the right. (g) Example of a feminized tassel with silk tissues (stigmatic tissues) developing from the male flower. This is due to a mutation in the tassel seed1 (ts1) gene. (h) Culm of a plant with functional purple plant1 (pl1) and booster1 (b1) alleles permitting anthocyanin accumulation in the sheath and leaf tissues. (i) salmon1 (sm1) silks. Nonmutant silks are green. (j) Leaves of a knotted1 (Kn1) plant showing extra cell divisions at the vascular bundles. (k) Ears representing four different p1 alleles, from left to right p1-rr (functional in both pericarp and cob tissues), p1-wr (functional only in cob tissues, non-functional in pericarps), p1-rw (functional only in pericarps, non-functional in cob tissues) and p1-ww (nonfunctional in both cob and pericarp tissues). The first letter in the allele designation refers to functionality in pericarps and the second letter refers to functionality in cob tissues. (l) An ear segregating for the red aleurone1 (pr1) gene. pr1 kernels are red in appearance while nonmutant kernels are bluish-black. (m) An ear segregating for collapsed pericarp2 (cp2) and nonmutant kernels. cp2 kernels, indicated by an arrow, are extremely thin poorly developed kernels. (n) collapsed pericarp2 (cp2) seedling on the left and normal seedling on the right. (o) yellow endosperm1 (y1) mutant ear in the lower left corner and a functional Y1 ear in the upper right corner. (All photos are courtesy of Maize DB.)


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Figure 4 Cytological map of the ten maize chromosomes drawn to scale with major distinguishable features such as arm ratios, chromosome knobs, NOR, and chromomeres. (Reproduced with permission from Neuffer MG, Coe EH, and Wessler SR (1997) Mutants of Maize. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.)

transposition, transposase. The DNA sequence of Ds elements is identical to Ac, except that the transposase gene is partially or completely deleted (Figure 8). Transposable elements display some Mendelian properties. They are associated with chromosomes and they can be transmitted from parent to offspring. Phenotypically, their only effect is through their affect on the expression of other genes. Many TEs preferentially insert into genes when they move. The insertion of a TE generally disrupts the gene’s normal pattern of expression, for example, altering tissue specificity or knocking out expression altogether. Transposable elements also display some very ‘non-Mendelian’ characteristics. Their genome position is not constant, rather they are capable of moving (i.e., transposing) around the genome. They cause the appearance of variable expression of genes when they ‘hop-out’ of a gene and restore functionality during development. This is normally observed as sectors of expression in cell lineages, either streaks or spots are the common types of sectors observed. The larger the sector, the earlier in development (i.e., establishment of the cell lineage) the TE excised from the gene and restored function (Figure 9).

Mutants of Maize One of the features that made maize an attractive plant with which to study genetics was the wealth of mutations that visibly alter some aspect of the plant and the ease with which controlled crosses between two genotypes can be made (seeMAIZE | Breeding). There have been four types of mutants in maize that have been extensively studied: those that affect kernel properties, those that affect pigmentation, those that affect plant form, and those that affect fertilization. Several of these mutants have become economically important, such as the genes used in ‘sweet corn.’

Mutants Affecting Kernel Properties There are two groups of mutants that affect the kernel, mutations affecting carbohydrate, oil, or protein composition and content (Table 1) and mutations that affect kernel development (Table 2). While studying kernel mutations, it is important to remember that the kernel is actually a mixture of


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Chromosome 2

Figure 5 Reciprocal A–A translocations are reciprocal exchanges between two nonhomologous chromosomes (1 and 2). (a) Chromosome breaks occur in the two chromosomes (denoted by the arrows) followed by rejoining of the two fragments to generate two novel chromosomes (12 and 21). Chromosome 12 contains the intact long arm of chromosome 1, along with the centromere of chromosome 1 and a portion of the short arm of chromosome 1, to which is attached the chromosome fragment of chromosome 2. Likewise, chromosome 21 contains the intact long arm of chromosome 2, along with the centromere of chromosome 2 and a portion of the short arm of chromosome 2, to which is attached the chromosome fragment of chromosome 1. (b) In meiosis reciprocal A–A translocation heterozygotes (i.e., one copy each of chromosomes 1, 2, 12, and 21) pair in a Chi arrangement. Only when alternate disjunction occurs are the resulting gametes viable. Adjacent disjunction results in chromosome duplications and deficiencies.

maternal tissues (e.g., pericarp) and zygotic tissues (e.g., embryo, aleurone, and endosperm), and that the embryo is diploid (2n) while the aleurone and endosperm are triploid (3n). The triploid nature of the aleurone and endosperm result from two identical maternal gametes (i.e., polar nuclei, the result of megasporogenesis) fusing with one paternal gamete (i.e., sperm nuclei, the result of microsporogenesis) (Figure 7). The typical maize kernel is composed of 70–75% starch, 8–10% protein, 4–5% oil, 1–3% sugar, and 1–4% ash. Most of the starch is associated with the endosperm (<90%), while the

(b)

Microspore

Figure 6 B–A translocations involve interchanges between one of the ten maize chromosomes (A chromosomes) and the supernumerary chromosome called the B chromosome. (a) Chromosome breaks occur in the two chromosomes (denoted by the arrows) followed by rejoining of the two fragments to generate two novel chromosomes (AB and BA). Chromosome AB contains the intact long arm, the centromere, and a portion of the short arm of the A chromosome, to which is attached the chromosome fragment of the B chromosome. Likewise, chromosome BA contains the centromere of the B chromosome and a portion of the arm of the B chromosome, to which is attached the fragment of the A chromosome. (b) Chromosome pairing in a B–A translocation heterozygote and the consequences of non-disjunction during the second mitotic like division of microsporogenesis. During microsporogenesis, 50% of the viable pollen grains (i.e., microspores) contain the non-translocation A chromosome, but the other 50% of the microspores non-disjunction occurs during the second mitotic like division. After meiosis the microspore undergoes two mitotic like divisions. The first division gives rise to the vegetative and generative nuclei. The vegetative nucleus governs pollen tube development, but the generative nucleus undergoes a second division to give rise to the two sperm nuclei. It is during this second division that the B chromosome centromeres fail to disjoin following duplication. This results in one sperm nucleus lacking the portion of the A chromosome translocated to the B centromere (i.e., BA), a condition referred to as hypoploidy, while the second sperm nucleus has two copies of BA chromosome, a condition referred to as hyperploidy.


413

Antipodals

Vegetative nucleus

Polar nuclei

Sperm nuclei

Hyperploid Hypoploid

Synergids

Egg Microspore (a)

Megaspore

From female gamete From male gamete Hyperploid endosperm From male gamete From female gamete

Hypoploid embryo

From female gamete From male gamete Hyperploid endosperm From male gamete From female gamete

Hypoploid embryo

(b)

Figure 7 Fertilization of a normal megasporocytes with a microsporocyte containing a B–A translocation. (a) One of the sperm nuclei fuses with the egg to form the embryo (2n), while the other sperm nuclei fuse with the two polar nuclei to give rise to the endosperm (3n). (b) If the hypoploid sperm nucleus fuses with the egg, any recessive mutations in the female that are present in that A chromosome segment translocated to the B centromere will be visible. If the recessive mutation affects kernels characteristics such as aleurone color or starch formation, then those phenotypes will be visible when the hypoploid sperm nuclei fuse with the two polar nuclei to for the endosperm.

embryo contains high levels of protein ( 26%), oil ( 83%), sugar ( 70%), and ash ( 80%). Mutations that affect kernel composition either can alter total content or composition of the protein, starch, or oil fraction. Starch is a homopolymer of glucose molecules linked together in either a-1,4 or a-1,6 linkages. There are two types of starch molecules. 1. Amylose is a linear molecule composed of a-1,4 glucose linkages. For about every 200 glucose molecules, there will be an a-1,6 glucose linkage that gives the starch molecule a small degree of branching. The amylose molecules are highly variable in length, ranging from 100 to 1000 glucose molecules.

2. Amylopectin molecules are larger, consisting of up to 200 000 glucose molecules and have a higher degree of branching with 4–5% of the glucose molecules in a-1,6 glucose linkages. Amylose makes up 25–30% of the starch, while amylopectin comprises 70–75% of the starch in a typical maize kernel. There are two mutations that shift this ratio rather dramatically, amylose extender1 (ae1) results in high amylose content while waxy1 (wx1) results in high amylopectin content. Both the wx1 and ae1 mutations are used in specialty maize to produce commercial specialty starches for food and nonfood industrial uses. In addition to these mutations, there are

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Activator element

AUG

UGA

Dissociation elements: Ac deletion (Ds9) Ac deletion (Ds6) Double Ds Ds2

Ds1 Figure 8 Ac/Ds family of transposable elements. Ac elements are 4565 bp in length, consisting of 10 bp terminal inverted repeats (TIRs) at the ends (green arrowheads), exons (green boxes), introns (connecting lines), nontranscribed regions (green boxes), and one open reading frame (AUG start codon through UGA stop codon) that encodes the transposase. The Ds elements are structurally diverse and consist of internal deletions of the Ac element. Ds1 and Ds2 also contain unique DNA sequences (wavy and dotted boxes). (Reproduced from Neuffer MG, Coe EH, and Wessler SR (1997) Mutants of Maize. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.)

numerous mutations that interfere with starch formation, resulting in ‘sweet’ rather than ‘starchy’ kernels (Table 1). Of these mutations, three are used commercially in ‘sweet corns’ to confer sweetness: shrunken2 (sh2) (Figure 2b), sugary1 (su1), and sugary enhancer1 (se1). The typical fatty acid profile of a maize kernel is 50% linoleic acid, 1% linolenic acid, 40% oleic acid, 12% palmitic acid, and 2% stearic acid. Most of the genetic research on maize kernel oil has focussed on total content rather than composition, the inheritance of which is highly quantitative, however, one single gene mutant effecting oil composition has been identified. Linoleic acid content is controlled by a single recessive mutation, linoleic acid1 (ln1). Maize kernel proteins are very high in sulfur-bearing amino acids (i.e., methionine and cystine), but are deficient in the essential amino acids, lysine, and tryptophan. The endosperm contains the gluten proteins, glutelin, and zein. Changes in protein content of a kernel generally involve changes in the gluten proteins, primarily the zein component. Zeins, devoid of lysine and tryptophan, are the proteins that hold the starch granules in a matrix. Increased zein levels are generally associated with an increase in endosperm hardness. There are two families of mutations that affect the zein genes in maize, floury and opaque (Figure 2e) mutants. These kernel mutants have extremely soft endosperm and are either higher in lysine and tryptophan or have an altered protein profile (Table 1). The opaque2 (op2) mutation has been used to develop high lysine specialty maize, referred to as quality protein maize (QPM). It has been estimated that more than 350 genes affect kernel development. Mutations in these genes generally result in

Small spots: frequent excision late in kernel development

Large spot: excision early in kernal development

Revertant: element excised, expression restored

No excision, autonomous element not in genome

No product Activator TE

Pigment gene Excision of TE in somatic cells = spot in germ cells = revertant

Figure 9 Phenotypes of kernels from a genotype with an Ac element in the genome and a Ds element inserted in an anthocyanin gene. The kernels represent several different times of Ds element excision during development, from extremely early events resulting in completely colored kernels, to mid-development resulting in large colored spots, to late in development resulting in small colored spots. Completely colored kernels are termed revertants, meaning that the TE excised from the germline. Completely colorless kernels indicate that the autonomous element, Ac, is not present in the germline, but the Ds element is still interrupting the anthocyanin gene in the germline. Spotted or sectored kernels represent somatic excision events and indicate that the Ac element is still present in the germline and that the Ds element is still interrupting the anthocyanin gene in the germline. (Reproduced with permission from Freschotte C, Jiang N, and Wessler SR (2002) Plant transposable elements: where genetics meets genomics. Nature Reviews Genetics 3: 329–341. ã 2002 Macmillan Magazines Ltd.)

GENETICS OF GRAINS | Maize: Genetics Table 1

415

Mutations affecting carbohydrate or protein composition of the kernel. Mutation abbreviations are in parentheses

Mutation

Gene product

Kernel phenotypic description

Economic use

Carbohydrate composition mutations

amylose extender1 (ae1)

Starch branching enzyme II

brittle endosperm1 (bt1)

Amyloplast adenylate translocator

brittle endosperm2 (bt2)

ADP glucose pyrophosphorylase

dull1 (du1) shrunken1 (sh1)

Starch synthase Sucrose synthase

shrunken2 (sh2)

ADP glucose pyrophosphorylase

sugary1 (su1) sugary2 (su2)

Isoamylase Starch branching enzyme

sugary enhancer1 (se1)

Unknown

waxy1 (wx1)

NDP-glucose-starch glucosyltransferase

Glassy appearance, high amylose content Collapsed, often translucent and brittle Collapsed, often translucent and brittle Glassy appearance Inflated, transparent kernels collapse on drying Inflated, transparent, sweet kernels collapse on drying Wrinkled and translucent Glassy, translucent, sometimes wrinkled Observed only in su1 lines light yellow, slow drying Opaque endosperm, high in amylopectin

Highly linear starch used for food, films, fibers, and other industrial purposes Used in sweet corn Used in sweet corn

Used in “super-sweet” sweet corn Used in sweet corn

Used with su1 sweet corn to boost sugar content 50–100% Highly branched starch, used for food gels, adhesives, and other industrial purposes

Protein composition mutations

floury1 (fl1) floury2 (fl2) floury3 (fl3)

Unknown Alpha zein Uknown

opaque endosperm1 (o1) opaque endosperm2 (o2)

Unknown Unknown regulatory protein of zein proteins and pyruvate orthophosphate dikinase1 (pdk1) Unknown Unknown Unknown Unknown

opaque endosperm2 (o2) gamma zein modifier1 (gzr1) mucronate1 (mc1) proline responding1 (pro1)

Table 2

Soft, opaque endosperm Soft, opaque endosperm, reduced protein levels Soft, opaque endosperm, reduced production of the prolamine fraction, and enhanced lysine content not used commercially due to poor germination Soft, opaque endosperm Soft, opaque endosperm, higher in lysine and tryptophan

Soft, opaque endosperm, higher in lysine Modifies the hardness of o2 endosperm Dominant, opaque endosperm, higher in lysine Crumpled, soft, opaque endosperm, proline auxotroph

Mutations affecting kernel development

Mutation

Gene product

Phenotypic description

defective kernel1 (dek1)

Calpain superfamily member

dek2 to dek3 cp2, cp3 emp1, emp2 ren1, ren2, ren3 miniature seed1 (mn1) mn2-cp1

Not yet identified Not yet identified Not yet identified Not yet identified

Germless kernel that can not be embryo rescued because only the root primordia are present, the shoot primordia are absent. Floury, white endosperm with missing aleurone layer Similar to dek1 above Collasped pericarp Empty pericarp Reduced endosperm

Cell wall invertase

Not yet identified

Small (1/5 the size of a normal kernel), fully viable kernel Small kernel, loose pericarp, defective appearing, but fully viable kernel

poorly filled, collapsed, crumpled, germless, small, or loosepericarped appearing kernels, hence the name defective kernel (dek) mutants. Some of these mutations are completely lethal (i.e., defective kernels will not germinate), others such as collapsed pericarp2 (cp2) are seedling lethals (i.e., defective kernels germinate, but the seedling dies) (Figures 2m and 2n), while other mutations are not lethal (i.e., defective kernels germinate and the resulting plant is fully fertile). Lethal mutations can be further divided into those that can be rescued by excising the developing embryo and culturing it on either basal or enriched tissue culture medium. The rescued embryos produce seedlings that are viable long enough to observe altered seedling phenotypes. The lethal mutations generally represent developmental failures, which are specific to a particular stage of embryo development. For example, dek1 embryos when rescued will develop into seedlings that are missing the shoots. In other words, the dek1 mutation interferes with shoot primordia formation, but not root primordia formation in the embryo.

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Mutants Affecting Pigmentation (Kernel and Plant) Phenolic-based compounds and carotenoid compounds comprise two of the major classes of pigments in maize. The phenolic-based compounds arise from the phenyl-propanoid pathway through either the flavonoid pathway or the ligninbiosynthesis pathway. The carotenoid compounds are derived from fatty acids. Carotenoid mutations are visible either through their effect on the accumulation of carotenoids in the kernel (i.e., endosperm color or lack of dormancy of the embryo) or through their effect on chlorophyll stability (i.e., albino, pale green, or delayed greening of seedlings). Some of the mutations affect both endosperm and seedling phenotypes, while others are specific. Endosperm color can be altered from yellow to white by the mutation yellow endosperm1 (y1), that results in a lack of b-carotene (provitamin A) (Figure 2o). This mutation is used commercially to produce white endosperm maize, and subsequently, white starch. In addition to y1, there are over 20 genes that alter carotenoid content of the kernel. Some of these genes impart a lack of embryo dormancy (i.e., vivipary), causing mature embryos to germinate on the ear. The lignin pathway has four mutants associated with it that either reduce the total lignin content of the plant or alter the lignin composition. Lignin is a polymer composed of three different monolignols, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. These monolignols polymerize to form lignin, which is part of the cell wall. Phenotypically, mutations in the lignin-pathway genes result in a browning of the midvein (i.e., midrib) of the maize leaf, hence the name brown mid-rib (bm1) mutants (Figure 2c). Economically, these mutants are of interest as a means of increasing the digestibility of the stover that is fed to ruminant livestock. The bm1 mutant, which encodes the enzyme cinnamyl alcohol dehydrogenase, reduces lignin content of the stover at maturity by 86%. However, bm1 does not result in increased stover digestibility. The mutant brown mid-rib2 (bm2) alters lignin composition, greatly reducing the guaiacyl (i.e., polymerized coniferyl monolignol) content, but increasing the levels of the syringyl monolignols. Mutations in brown mid-rib3 (bm3), which encodes caffeate O-methyltransferase, result in increased stover digestibility when fed to livestock. The fourth mutant, brown mid-rib4 (bm4) has not been extensively characterized. The bm3 mutation is being used commercially in maize hybrids developed specifically for the North American silage market. Flavonoid mutants were probably the earliest and the most extensively studied set of mutants in maize. The flavonoid pathway in maize produces at least four types of flavonoid compounds: flavones, flavonols, anthocyanins, and phlobaphenes. Only the latter two are visible compounds. Anthocyanins are blue/black pigments and phlobaphenes are reddish-brown pigments. The flavonoid pathway branches off the phenylpropanoid pathway at the 9-carbon compound, 4-coumaroyl CoA. Chalcone synthase, regarded as the first committed step in the flavonoid pathway, is responsible for the synthesis of chalcone from three molecules of malonyl-CoA and the 9-carbon phenyl-propanoid pathway product. Maize has two genes that encode chalcone synthase, colorless2 (c2) and white pollen1 (whp1). c2 and whp1 are examples of homologs that have evolved slightly different expression patterns. Only c2 is expressed in the aleurone, while both whp1 and c2 are expressed

in cob, pericarp, and other plant parts. The effect of the whp1 mutation on pollen color is only observed when c2 is nonfunctional. Mutations in both flavonoid-pathway structural genes, such as c2, and regulatory genes have been identified. In addition to c2 and whp1, mutations in the structural genes a1 (Figure 2b), a2, bz1, bz2, pr1 (Figure 2l), sm1 (Figure 2i), and sm2 have been identified (Table 3). These mutations have been ordered in the context of the flavonoid pathway, in some instances appearing to be involved in multiple branches of the flavonoid pathway. The regulatory genes governing the flavonoid pathway are composed of primarily myb-like (c1, pl1, p1, and p2) and myc-like (r1, b1, and in1) oncogene transcription factors (Table 4), and unlike the structural genes, appear to be relatively pathway-branch specific. For example, r1/b1 and c1/pl1 are only involved in activating the anthocyanin branch of the pathway. But activation of the pathway requires both the presence of a functional r1 along with a functional c1 for aleurone pigmentation, and b1 with pl1 (Figure 2h) for plant pigmentation. p1 is responsible for activation of the phlobaphene pathway, with various alleles of p1 imparting to tissues specific expression of the phlobaphene pathway (Figure 2k).

Mutants Affecting Plant Form There is an impressive array of mutations that affect plant form. For example, the dwarf (d) mutations affect plant stature Table 3

Mutations affecting the flavonoid pathway structural genes

Mutation

Gene product

anthocyaninless1 (a1)

NADPH dihydroflavonol reductase

Phenotypic description

Colorless aleurone, when all other anthocyanin factors are present, brown pericarp and cob tissues with p1 alleles that function in pericarp and cob tissues anthocyaninless2 Leucoanthocyanidin Colorless aleurone, when all (a2) dioxygenase other anthocyanin factors are present bronze1 (bz1) Flavonol 3-OBronze/brown aleurone glucosyltransferase tissues, when all other anthocyanin factors are present bronze2 (bz2) Glutathione SBronze/brown aleurone transferase tissues, when all other anthocyanin factors are present colorless2 (c2) Chalcone synthase colorless aleurone, when all other anthocyanin factors are present red aleurone (pr1) Flavonoid 30 Red rather than blue Hydroxylase pigmented aleurone tissue salmon silk1 4,6-Dehydratase Salmon colored silks, with p1 (sm1) alleles that are functional in silk tissues salmon silk2 Rhamnosyl Salmon colored silks, with p1 (sm2) transferase alleles that are functional in silk tissues white pollen1 Chalcone synthase White pollen, with (whp1) recessive c2

GENETICS OF GRAINS | Maize: Genetics Table 4

Mutations affecting the flavonoid pathway regulatory genes

Mutation colorless1 (c1) purple plant1 (pl1) pericarp color1 (p1)

colored plant1 (b1) colored1 (r1)

Gene product myb-like oncogene myb-like oncogene myb-like oncogene

myc-like oncogene myc-like oncogene

intensifer1 (in1)

myc-like oncogene

leaf color1 (lc1)

myc-like oncogene

scutellar node color1 (sn1)

myc-like oncogene

Phenotypic description Anthocyanin accumulation in the aleurone tissue Anthocyanin accumulation in vegetative plant parts Phlobaphene accumulation in pericarp and cob tissues, and flavone accumulation in silk tissues Anthocyanin accumulation in vegetative plant parts Anthocyanin accumulation in the aleurone tissue, anthers leaf tips, and brace roots Intensifies the accumulation of anthocyanins in the aleurone tissue Anthocyanin accumulation in nodes, auricles, leaf blades, and coleoptiles Anthocyanin accumulation in pericarps, nodes, leaf blades, silk tissues, and coleoptiles

(Figure 2f), the lesion mimics (les) mutations mimic leaf diseases (Figure 2d), the knotted (kn) mutations affect organ/tissue identity (Figure 2j), and the tassel seed (ts) mutations result in feminization of the tassel (Figure 2g). These types of mutations have been extensively used in the field of developmental genetics to understand the biology of plant development. The dwarf mutations in maize: anther ear1 (an1), dwarf1 (d1), dwarf2 (d2), dwarf3 (d3), dwarf5 (d5), and dwarf8 (D8) have similar distinctive ‘cabbage-like’ phenotypes (Figure 2f). All but D8 are recessive and respond to exogenous applications of the plant hormone gibberillic acid (GA). The recessive dwarf mutants result from mutations in specific steps in the GA biosynthesis pathway, while the dominant dwarf mutant, D8, is the result of a mutation in a GA receptor.

Mutants Affecting Fertilization The final classes of maize mutations that will be discussed in this article are those that affect fertilization, either through gamete preference or through control of fertility. Several factors influence how readily gametes can successfully fuse to form a zygote. Both megaspores (i.e., female gametes) and microspores (i.e., male gametes) are not very tolerant of chromosomal deletions. However, there are some viable deletions, but they are only transmitted through the megaspore and generally at a lower frequency. Deletions arise through several means, including chromosomal breakage (e.g., ionizing radiation, dicentric bridges), crossing over in inversion heterozygotes, chromosomal nondisjunction, and adjacent segregation in translocation heterozygotes. In addition to deletions, there are genes that influence gamete preference. The gametophyic factor (ga) class of mutations affects the functioning of

417

individual pollen grains. For example, Ga1 pollen grains compete equally with ga1 pollen grains when the female is homozygous recessive ga1. (Remember that pollen grains are haploid.) However, when the female contains at least one Ga1 allele, >90% of the fertilizations will involve Ga1 pollen grains. The ga1 pollen grains are mostly incompatible when the female possess a Ga1 allele and in some genetic backgrounds ga1 pollen grains are completely incompatible. Recessive mutations have been identified that affect both male and female flower fertility (e.g., dsy1, dsy2, pam1, pam2, as). Each of these mutations involves defects in various stages of meiosis. Another class of mutations results in male flower sterility (i.e., failure to develop functional pollen grains), but do not affect female flower fertility. This group is collectively referred to as male sterile mutations. Only some of these phenotypes are the result of mutations to a gene that is nuclear encoded. Male sterility in maize can be due solely to mutations in nuclear encoded genes, or it can result from a rearrangement in the mitochondrial genome in a genetic background that is not able to compensate for it with the appropriate nuclear encoded genes. This second type of male sterility is referred to as cytoplasmic male sterility (CMS). The cytoplasmic genomes, mitochondrial, and plastid, are maternally inherited. That is they are not transmitted through the pollen. Nuclear encoded genes can compensate for the defect caused by the rearrangement in the mitochondrial genome of CMS cytoplasms. These genes, termed restorer factors (rf), are dominant and restore male fertility in CMS cytoplasm genotypes. In normal (N) cytoplasm genotypes, rf genes are not required for male fertility. There are several CMS cytoplasms, however the one that was used quite extensively in commercial North American hybrid seed production fields until the early 1970s was CMS-T. To produce hybrid seed, inbred line parents were either deemed female or male. The male parents carry the dominant Rf gene and a normal cytoplasm (N). The female parents need to have two different genotypes. One genotype needs to possess normal cytoplasm (N) and the recessive rf gene and the other genotype possesses the CMS cytoplasm and the recessive rf gene. The first genotype is male fertile and is used to maintain both of the female inbred genotypes, while the second genotype is male sterile and is used as the female parent in hybrid seed production fields (Figure 10). Unfortunately, the mitochondrial genome rearrangement that led to male sterility rendered those genotypes susceptible to the fungal leaf disease – northern corn leaf blight (NCLB) (Exserohilum turcicum, previously called Helmithosporium turcicum). A NCLB epidemic in the US in the early 1970s devastated the maize crop. Use of CMS to produce hybrid seed quickly fell out of favor, and is no longer widely used. Nuclear encoded male sterile genes (ms) are quite numerous, with over 45 unique mutants that confer the ms phenotype characterized. Most of the ms mutants are recessive, however two dominant Ms mutants (e.g., Ms1, Ms2) have been isolated. The ms genes appear to affect all aspects of gamete development from breakdown of early meiotic events (e.g., ms8, ms9), after meiotic prophase (e.g., ms17, ms23), during vacuolation of the microspore (e.g., ms1, ms2), during microspore mitosis (e.g., ms14), or after microspore mitosis (e.g., ms5, ms11). Nuclear encoded ms genes have not been

418

(a)


rf/rf

Rf/–

Rf/–

N

N

CMS

CMS

Fertile

Fertile

Fertile

Male sterile

rf/rf

rf/rf

rf/rf

Rf/Rf

CMS

N

N

Female maintainer line used as a male

Male line

fertile

fertile

Female CMS line

X

Female line seed increase (CMS cytoplasm)

exchanged through the medium of an informal Maize Genetics Cooperation – News Letter (MNL). The newsletter is still compiled and published 71 years later. There are several excellent publicly available resources for maize genetics. For seed of maize mutants and lines containing chromosomal rearrangements, the Maize Genetics Cooperation – Stock Centre, located in Champaign-Urbana, Illinois, USA maintains a collection of over 80 000 pedigreed samples. It is the main repository for maize mutants utilized in research by scientists worldwide. The Stock Centre is located at the University of Illinois and is part of the National Plant Germplasm System and is supported by the US Department of Agriculture, Agricultural Research Service (USDA/ARS). MaizeDB (http://www.agron. missouri.edu/index.html) is a web-based database containing historical and up-to-the-minute information about the maize genome. The database is administered at the University of Missouri-Columbia and is funded through support from the USDA-ARS, National Science Foundation (NSF), and the University of Missouri.

X rf/rf fertile F1 CMS Female CMS line (b)

Rf/rf CMS F1 hybrid

Figure 10 Cytoplasmic male sterility (CMS) and restorer gene (rf) system. (a) Four possible combinations of cytoplasms (N – normal vs. CMS – male sterile) and dominant, nuclear encoded restorer genes (rf/rf – not capable restoring male fertility vs. Rf/— capable of restoring male fertility). (b) System for using CMS to produce hybrid seed. There are two versions of the female inbred, the CMS containing line and the maintainer line. These lines are genetically identical except for the mitochondrial genomes. The maintainer line contains a normal (N) cytoplasm, while the CMS line contains the male sterile cytoplasm. The maintainer line is male fertile, while the CMS is male sterile. The maintainer line is used as a male parent in crosses with the CMS line to produce more CMS seed. The CMS line is used as the female in hybrid seed production fields and the male inbred line is a unrelated inbred line with a different genetic constitution. The male contains a normal cytoplasm and is homozygous for the dominant Rf allele. The resulting F1 hybrid will contain the CMS cytoplasm, but will be heterozygous for the Rf gene and thus will be male fertile. Note: , is genetic’s shorthand for self-pollination.

used in hybrid seed production, due to the difficulty in generating large quantities of homozygous recessive ms female seed.

Maize Genetics Resources The Maize Genetics Cooperation was formally organized in 1932 by the maize geneticists attending the sixth International Genetics Congress. They agreed to establish a cooperative enterprise to further the advance of maize genetics, specifically by collecting and disseminating unpublished data and information and maintaining and distributing of genetic stocks (e.g., mutants, translocations, etc.). Information was


• • • •

Describe some of the ’firsts’ for maize cytogeneticists and geneticists – achievements that have permitted the extension to elucidate genetics of other cereals. Explain how some of the types of mutants in maize have had economic consequences. Explain heterosis and hybrid maize production at a level that would be understandable to a 12 year old. List ten distinct maize types (e.g., popcorn, sweet corn) and identify the mutant on which they are based.


• • •

•

Trace the history of the controversies over the origin of maize. Has molecular genetic evidence provided an unequivocal answer? What uses can be made of the different pigmentation mutants? Examine the maize mutants involving changes in starch composition and properties. Compare these maize mutants, and the consequences for their utilization, with equivalent mutations in another cereal species (e.g., sorghum, wheat). Repeat the above exercise for protein composition instead of starch.

See also: Breeding of Grains: Maize: Breeding; Food Grains and the Consumer: Genetically Modified Grains and the Consumer.

Further Reading Carlson WR (1988) The cytogenetics of corn. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 259–343. Madison, WI: ASA–CSSA–SSA Publishers.

GENETICS OF GRAINS | Maize: Genetics Coe EH, Neuffer MG, and Hoisington DA (1988) The genetics of corn. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 81–258. Madison, WI: ASA–CSSA–SSA Publishers. Freschotte C, Jiang N, and Wessler SR (2002) Plant transposable elements: where genetics meets genomics. Nature Reviews Genetics 3: 329–341. Galinat WC (1988) The origin of corn. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 1–31. Madison, WI: ASA–CSSA–SSA Publishers. Moore G, Devos KM, Wang Z, and Gale MD (1995) Grasses, line up and form a circle. Current Biology 5: 737–739, 169–174. Neuffer MG, Coe EH, and Wessler SR (1997) Mutants of Maize. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press. Peterson PA and Bianchi A (1999) Maize Genetics and Breeding in the 20th Century. Singapore: World Scientific.

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Walbot V and Messing J (1988) Molecular genetics of corn. In: Sprague GF and Dudley JW (eds.) Corn and Corn Improvement, pp. 389–429. Madison, WI: ASA–CSSA–SSA Publishers. White S and Doebley J (1998) Of genes and genomes and the origin of maize. Trends in Genetics 14: 327–332.

Relevant Websites agron.missouri.edu http://www.agron.missouri.edu– Maize Genetics Cooperation – News Letter (MNL). w3.ag.uiuc.edu http://w3.ag.uiuc.edu– Maize Genetics Cooperation – Stock Centre, Champaign-Urbana, Illinois, USA.

Maize: Quality Protein Maize JS Li, China Agricultural University, Beijing, People’s Republic of China SK Vasal, BISA, Punjab, India ã 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 212–216, ã 2004, Elsevier Ltd.

Topic Highlights

• • • •

Maize can be a significant source of protein in the diets of humans and other monogastric animals, but its nutritional quality is generally low. Maize protein is deficient in the essential amino acids, lysine and tryptophan. The opaque-2 gene alters the ratio of major protein fractions and confers substantial increase in lysine and tryptophan content. The opaque-2 gene was the basis, along with intensive further genetic and breeding work, for the development of high-yielding quality protein maize (QPM) hybrids.

Learning Objectives

• • •

To understand the composition of maize protein in terms of solubility fractions, and its impact on protein nutritional quality. To understand the significance and effect of the opaque-2 gene. To understand the complexities and levels of success in developing QPM varieties with benefits for human food and for feeding monogastric animals.

Introduction Maize is an important source of protein. Globally, it contributes 42 million tonnes (Mt) of protein a year – 15% of the world annual production of food-crop protein. Therefore, the need to improve maize protein in quality and quantity has been recognized for a long time. Maize protein is mainly stored in both the endosperm and the germ – the two principal parts of maize kernels. But there are large differences in the characteristics of protein present in the two parts. Generally, the germ contains 35% of high-quality protein, whereas the endosperm has only 9% of poor-quality protein. Normally, in maize, the endosperm accounts for 80–85% of the total dry weight of kernels, while the germ constitutes the remaining 15–20%. Hence, 80% of the total protein content in kernels may be contributed by the endosperm. The relative amounts of protein are also dependent on the type, texture, size of kernels, genotypes, and the environments in which the maize is grown. According to the solubility in different solvents, maize proteins in kernels are divided into several fractions. The prolamins, referred to as the zeins, are the major protein fraction. They are soluble in alcohol, comprising 52% of kernel nitrogen. The glutelins, which account for 25% of kernel nitrogen, are soluble in dilute alkaline solutions, while the water-soluble albumins

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comprise 7% of kernel nitrogen. The globulins are soluble in salt solutions and consist of 5% kernel nitrogen. Maize proteins have a low nutritional value because they are deficient in essential amino acids such as lysine and tryptophan. An attempt to improve protein quantity was initiated at the University of Illinois in 1898 with a long term selection. After the 1970s selection, the protein contents in Illinois high-protein (HP) strains reached 26.6%. In contrast, the average contents for proteins in normal maize ranged between 9% and 15%. Unfortunately, the protein yield in Illinois HP strains was not improved in proportion, and the increase in endosperm protein was associated with an increase in the low-quality zeins. Currently, major efforts in most breeding programs are focussed on improving the quality of proteins, rather than on developing high-protein maize. This is so especially in developing countries where people depend heavily on maize as a food, and adequate supplies of protein supplements for feed are not produced.

Historical Background In the 1950s, Mertz’s group at Purdue University began research on improving the nutritional value of maize proteins. First, they screened a number of maize germplasm from US corn belt, and Central and South America for low levels of zeins, since they are almost devoid of the two essential amino acids, lysine and tryptophan. None of the varieties screened exhibited a high lysine content. Comparison of Illinois HP (18%) and low protein (LP, 4%) strains at Purdue University by Nelson showed that lysine levels were lower in vitreous high-protein endosperms than in floury, low-protein endosperms. He suggested that “flouriness” might be associated with a high lysine content. He analyzed four floury mutants of endosperm, floury-1, floury-2, opaque-1, and opaque-2. Ultimately, it was found that the opaque-2 endosperm not only contained a high level of lysine, but also a much higher level of tryptophan. After this discovery, similar mutants with high lysine were found in other important cereal crops, such as barley and sorghum. This remarkable discovery led to an improvement in protein quality using the opaque-2 mutant in maize breeding programs. In the late 1960s, many countries, such as USA, Brazil, China, South Africa, and even the International Maize and Wheat Improvement Center (CIMMYT) initiated breeding programs for developing high-lysine-content hybrids or varieties. The opaque-2 gene (o2) was widely transferred into different inbred lines, and varieties or populations through simple backcrosses. Some high-lysine-content hybrids with o2 were released in USA, China, and South Africa, while some were also developed in CIMMYT. However, some practical problems and limitations of o2 maize became quite obvious when they were gradually applied. A primary failure of o2 maize was the decrease in


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GENETICS OF GRAINS | Maize: Quality Protein Maize grain yield. In general, the grain yield of o2 maize hybrids was only 85–92% of the normal hybrids’ yield. There was a decrease in kernel weight and density of o2 maize. Also, the kernels of o2 maize were prone to damage by insects and ear and kernel rots were common both in the field and in storage. Its kernels maintained a high moisture level during the development period and tended to dry slower than the normal kernels during the maturity period. In addition, its kernel, which appeared chalky and nontransparent, was not accepted by markets. All these limitations can be attributed to a soft endosperm, which was a characteristic of the standard o2 maize. Therefore, application of the standard o2 maize declined in the 1970s. However, o2 maize is still in use in a few of the adapted areas world over, where the weather is dry and cool. In order to overcome the defects of o2 maize, many scientists in different countries explored various methods. The major efforts were focussed on hardening endosperm textures in o2 maize. Several approaches were suggested, such as recurrent selection and double mutants, using modifier genes. Practically, the third approach may show a great potential. Actually, wide differences in endosperm textures in o2 genotypes were observed when the o2 gene was backcrossed into a series of maize inbred lines. With regard to endosperm structure, some are completely soft, whereas others are partially hard, which is caused by modified genes for o2 locus. Scientists in CIMMYT have developed tropical and subtropical hard-endosperm germplasm combining o2 gene with modified genes during extensive and sustained breeding efforts. They called their hardendosperm o2 germplasm as quality protein maize (QPM) so that it is distinguished from soft-endosperm o2, which is called as standard o2. The kernels of QPM are almost similar to those of normal maize, but they are homozygous for the o2 allele. Yield improvement, observed in some QPM populations released by CIMMYT, is related to hard or semihard endosperm. The moisture contents and dry-down time of these QPM populations resemble those in normal maize. Ear rot in QPM is also substantially reduced. Recently, germplasm has been used as an essential resource for developing QPM hybrids.

Genetic and Biochemical Basis The inheritance of o2 gene follows a typical Mendelian pattern, located on chromosome 7 in the maize genome. It is a recessive mutant and its expression requires the homozygous genotype, i.e., o2/o2. The genetic segregation for the phenotype can be observed on a single F2 ear with a ratio of 3 (normal) to 1 (opaque). The o2 gene was initially cloned by Schmist et al. and later by Motto et al. in the 1980s. More recently, its molecular mechanism has been described. The o2, as a dominant gene, encodes a DNA-binding protein belonging to the basic leucine zipper class, which is involved in the transcription of zein proteins. This protein can bind the 50 flanking sequences of the genes encoding the 22 kDa a-zeins and serve as a transcriptional activator during the transcription. When O2 mutates into o2, the transcription of a-zeins is significantly reduced, resulting in a remarkable alteration in the amino acid content. But amino acids are not completely eliminated in o2/o2 mutants, since o2 is only one of the transcription factors involved in the expression of a-zein genes. The increase

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in the lysine and tryptophan contents results from the decreasing quantities of zein protein. Traditionally, maize zein proteins were classified by molecular weights. A new classifying method is proposed based on their primary genes and amino acid sequences when many genes of storage proteins were found. According to this method, they are divided into four groups, a-zein (22 and 19 kDa), b-zein (14 kDa), g-zein (27 and 16 kDa), and d-zein (10 kDa). The a-zein protein group is the largest among them, consisting of 80% of the total proteins. The maize zeins are synthesized by membrane-bound polyribosomes, and then are moved to the lumen of the endospermic reticulum, where they are assembled into insoluble protein bodies. There are obvious differences in the composition and size of protein bodies between the aleurone and endosperm of kernels. The small protein bodies containing b- and g-zeins exist in the subaleurone, whereas the large protein bodies are found in endosperms, containing a-, b-, and g-zeins. The quality of proteins in the o2/o2 genotype is improved with the decrease of a-zeins, which contain no lysine. For the same reason, the sizes of protein bodies in the endosperm of o2/o2 are significantly smaller than those in normal endosperms (Figures 1c and 1d). As a result, the endosperms of kernels turn into being nontransparent and soft. Modifying genes played an important role in converting soft endosperms of standard o2 maize into hard endosperms of QPM. These may be defined as a series of genes, which, on their own, could not have any effect when o2 gene dose did not exist, but they modify kernel phenotypes of the o2/o2 when it is homologous. Generally, inheritance of modifying genes expresses the quantitative nature of this effect. In a segregation generation, there is a normal distribution for endosperm texture, varying from soft to hard. Some researches indicate that the additive effects of modifying genes seem to be more important in controlling kernel vitreosity for o2 maize in this genetic system. Others suggest that there may be significant effects on kernel vitreosity for modifying genes. Extensive studies at CIMMYT demonstrate that there are a number of o2 modifying genes and that several different types of genetic variations are likely to exist in maize germplasm. In QPM, the biochemical effects of modifying genes tend to increase zein proteins, but high-quality proteins could maintain nominal changes. There are relatively minor differences between o2 and QPM protein in staining density and morphology (Figures 1d and 1f). The protein bodies in QPM have multiple, nonconcentric areas and a large number of dark-stain regions, which are rich in g-zeins. In addition, the studies by Larkins’s group on immunocytochemistry reveal that the most significant change in QPM endosperm is the increased synthesis of g-zeins. This increase could result in a higher concentration of protein in endosperm cells, so that there is less airspace in the endosperm, resulting in a hard and translucent phenotype. Since the endosperm comprises triploid genotypes, dosage effects of modifying genes are observed through analysis of F1 hybrids from reciprocal crosses between modified and unmodified o2 parents. As can be seen in Figure 2, the parent lines and their reciprocal crosses perform a phenotypic gradient toward the types of increasing vitreousness. The xenia effects of modifying genes are also observed in the hardness of endosperm.

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Figure 2 Kernel phenotypes of QPM and o2 lines and their reciprocal crosses. Columns 1–4 represent parent 1 (P1), parent 2 (P2), P1 P2, and P2 P1, respectively. (Reproduced with permission from Larkins BA and Lopes MA (1992) A genetic, biochemical, and ultrastructural analysis of modified opaque-2 maize. In: Mertz ET (ed.) Quality Protein Maize, 182 p. St. Paul, MN: American Association of Cereal Chemists.)

Figure 1 Transmission electron micrographs of normal (a, b), o2 (c, d), and QPM maize (e, f) in subaleurone tissue. m, mitochondrion; p, protein body; s, starch grain. (Reproduced with permission from Paulis JW, Bietz JA, Felker PC, and Nelsen TC (1992) Evaluating quality protein maize genotypes by reversed-phase high-performance liquid chromatography. In: Mertz ET (ed.) Quality Protein Maize, 135p. St. Paul, MN: American Association of Cereal Chemists.)

Nutritional and Process Values Repeated experiments on infants, children, adults, and various animals have demonstrated that the nutritional value of o2 maize is superior to that of normal maize. Recently, increasing evidence has indicated that the nutritional values are still maintained in QPM when the limitations of o2 are obviously improved upon. As can be seen in Table 1, the volumetric weight and density in QPM are similar to those in normal grains. Protein, lysine, and tryptophan contents are significantly higher for QPM than normal maize, whereas QPM and o2 maize have the same contents. On an average, QPM has 40% more lysine and tryptophan than normal maize. Based on the evaluation of digestibility and nitrogen balance for infant feed, nitrogen-retained intakes from QPM and normal maize in children are 32% and 22%, respectively, indicating a higher efficacy of nitrogen utilization for infant food with QPM. In the animal growth trials, pigs fed the QPM diets consumed 1.97 kg of feed daily and gained 0.75 kg per day, whereas pigs fed normal maize diets, which contain the same level of soybean meal supplementation, consumed 1.86 kg of feed and gained 0.63 kg daily. Other experiments

indicated that milk productions of dairy cattle increased when QPM was used as silage. The wet-milling and dry-milling properties of QPM were also evaluated in order to enhance its utilization in industry. Maize protein is the major by-product of the wet-milling industry, which is used entirely in animal feed. Lysine contents of maize protein for QPM reached 3.06 g per 100 g protein, which is significantly higher than that for normal maize (2.43 g per 100 g protein). Maize protein with a high lysine content can be beneficial in diet formulation for animals since it is an appropriate substitute for the expensive protein supplements. In wet-milling process, starch in QPM endosperm may be easily released from protein matrix since it produces a lower-bound yield, namely, 1.1 g per 100 g protein. On the other hand, there is no significant difference between QPM and normal maize in the physico-chemical properties of starch and in the characteristics of maize oil for wet-milling process. In the dry-milling experiments, the total yield of grits and other products from QPM, such as low-fat meal and low-fat flour, are comparable to those from normal maize. But dry milling of QPM may provide products with improved nutritional value.

Genetic Improvement The purpose of genetic improvement of QPM is to develop hybrids or cultivars combining o2 gene with the modifying genes, which has not only a higher lysine content but also semihard or hard endosperm. In order to reach this goal, it is very important for breeders to have adaptable germplasm containing modifying genes. The kernel modifications controlled by modifying genes can be divided into two patterns, regular and irregular. In the regular pattern, the hard fraction of endosperm increases progressively from the crown toward the base of the kernels. But in the irregular pattern, the translucent

GENETICS OF GRAINS | Maize: Quality Protein Maize Table 1 maize

Comparisons of nutrition among QPM, normal, and o2

Item

QPM

Normal

Standard o2

Test weight (kg hl1) Density (g cm3) Moisture (%) Content protein (N 6.25) (%) Energy (kcal g1) Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

0.79 1.31 11.1 9.8 3.99 0.66 0.37 0.32 0.91 0.40 0.17 0.41 0.36 0.074 0.52

0.75 1.25 12.7 9.1 3.99 0.51 0.28 0.34 1.14 0.31 0.17 0.47 0.35 0.054 0.46

0.71 1.18 9.4 8.9 4.08 0.59 0.31 0.30 0.80 0.40 0.14 0.39 0.32 0.065 0.48

Reproduced with permission from Knabe DA, Sullivan JS, and Burgoon KG (1992) QPM as a swine feed. In: Mertz ET (ed.) Quality Protein Maize, 228 p. St. Paul, MN: American Association of Cereal Chemists.

fractions may be distributed among the whole kernel as a band, scattered, resembling a bridge, or vitreous base. Regular modification is more important for genetic improvement of QPM because it is more stable. Practically, recurrent selection is the most useful breeding method for the development of QPM germplasm. The first stage for QPM improvement is to screen the modifying genes from different resources and develop QPM donor stocks. Extensive studies at CIMMYT indicate that several o2 populations may have a higher frequency of modifying genes, especially in flint varieties from Caribbean Sea and South America. In general, there are two principal ways to develop QPM donor stocks. Intrapopulation selection is used when resources express a considerably higher frequency of modified o2 ears. The other way is to combine partially modified o2 families from different genetic backgrounds into one donor stock. The QPM donor stocks can be used as the basic populations for recurrent selection. A full-sib selection for several cycles is often employed to accumulate modifying genes. First, full-sib families are evaluated for kernel phenotypes among different testing sites. Then, top 10–20 family lines with more vitreous endosperm are chosen and are recombined into the next cycle. Another more efficient but quite complicated approach is backcross-cum-recurrent selection program, since QPM is involved in two genetic systems, the o2 gene and modifying genes. The procedure includes backcrossing o2 gene into modified family lines and accumulating modifying genes within modified family lines. In addition, other traits are also selected in this program. A series of improved QPM populations have been released by CIMMYT. Recently, the development of QPM hybrid has been given more attention all over the world because hybrids exhibit more advantages than improved populations, such as higher yield performance and more uniform and stable traits. The breeding procedure for QPM hybrids includes three basic steps. The development of elite QPM inbred lines is the vital step. They could be bred with QPM germplasm as in conventional

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breeding. Then, the combining abilities of QPM inbred lines are measured and superior combinations are selected for adapted planting areas. Finally, QPM hybrids are released into commercial production. During developing QPM inbred lines, analysis for protein quality is essential because vitreousness in endosperm may have a negative relationship with protein quality. In order to maintain high lysine contents, endosperm analysis is preferred since the modification in QPM only involves changes in endosperm.

Future Prospects More recently, molecular marker technique has provided a powerful tool to facilitate breeding practices. In QPM breeding, sequence tagged site (STS) markers for o2 gene could be designed on the basis of its sequence. With this molecular marker, o2/o2 genotypes could be precisely selected at any stage even though hard endosperm QPM is very similar to normal endosperm. Another application for molecular marker technique in QPM breeding is to map modifying genes. Molecular markers will allow the screening of whole maize genome to identify the modifying gene loci. These molecular markers linked with modifying genes could be employed to conduct marker-assisted selection (MAS) for modifying genes. In addition, with the development of functional genome, further investigation will reveal modifying gene function and improve the understanding of the biosynthesis of g-zeins in QPM endosperm. These processes could offer the potential to improve QPM by genetic engineering. There is increasing interest in QPM developments in the developing world, where QPM has performed well. The development of QPM hybrids has especially enhanced heterosis utilization, which could raise QPM yield and improve its tolerances to stress significantly. There is no doubt that QPM will make great progress in the near future.


• •

Consider some typical maize-based human diets. Show how use of QPM could partially replace meat or other animal protein sources in these diets. How can molecular techniques be used to accelerate breeding for QPM varieties?


• •

What opportunities might there be for QPM protein isolates as ingredients in the food industry? What are the current limits to further expansion of QPM?

See also: Barley, Rice and Maize Processing: Maize: Dry Milling; Maize: Wet Milling; Breeding of Grains: Maize: Breeding; Carbohydrates: Cereals: Chemistry and Physicochemistry of Nonstarchy Polysaccharides; Starch: Synthesis; Food Grains and the Consumer: Genetically Modified Grains and the Consumer; Food

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GENETICS OF GRAINS | Maize: Quality Protein Maize

Grains: Intolerance, Allergy and Diseases: Nutrition: Beriberi, A Deficiency Related to Grains; Genetics of Grains: Maize: Genetics; Non-food Products from Grains: Cereal Grains as Animal Feed; Non-wheat Foods: Maize: Foods from Maize; The Basics: Grain: Morphology of Internal Structure; The Cereal Grains: Cereals: Domestication of the Cereal Grains.

Mertz ET (1992) Quality Protein Maize. St. Paul, MN: American Association of Cereal Chemists. Neuffer MG, Coe EH, and Wessler SR (1997) Mutant of Maize. New York: Cold Spring Harbor Laboratory Press. Paulis JW, Bietz JA, Felker PC, and Nelsen TC (1992) Evaluating quality protein maize genotypes by reversed-phase high-performance liquid chromatography. In: Mertz ET (ed.) Quality Protein Maize, p. 135. St. Paul, MN: American Association of Cereal Chemists. Vasal SK (2001) High quality protein corn. In: Hallauer AR (ed.) Specialty Corns, pp. 85–125. Boca Raton, FL: CRC Press.

Further Reading Boyer CD and Hannah LC (2001) Kernel mutant of corn. In: Hallauer AR (ed.) Specialty Corns, pp. 1–32. Boca Raton, FL: CRC Press. Knabe DA, Sullivan JS, and Burgoon KG (1992) QPM as a swine feed. In: Mertz ET (ed.) Quality Protein Maize, p. 228. St. Paul MN: American Association of Cereal Chemists. Larkins BA and Lopes MA (1992) A genetic, biochemical, and ultrastructural analysis of modified opaque-2 maize. In: Mertz ET (ed.) Quality Protein Maize, p. 182. St. Paul, MN: American Association of Cereal Chemists.

Relevant Websites maizegdb.org http://www.maizegdb.org cimmyt.org http://www.cimmyt.org

Maize: Other Maize Mutants MH Blanco, (Retired) Plant Breeder, and Geneticist, Encinitas, CA, USA H Yangcheng and J Jane, Iowa State University, Ames, IA, USA ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • • •

Approximately 95% of starch is derived from maize in the United States; starch properties govern functionality for food and industrial applications. Amylose and amylopectin have complex inheritance with many interacting genes, multiple alleles, and numerous isoforms of enzymes. Starch with a high level of amylopectin (100%) is a product of the waxy mutant, which is highly digestible and has potential for bioethanol production. Starch with a high level of amylose content (70–80%) is a product of the amylose extender mutant and is an important source of resistant starch with human health benefits. Research has advanced our knowledge on mechanisms of starch granule elongation and the relationship of the amylose content and resistant starch formation in the high-amylose maize starch. Double mutants of ae, wx, and o2 wx are beneficial for human health and nutrition and pose important opportunities and challenges for breeders and future research.

Learning Objective

•

To achieve understanding of the maize starch and protein mutants, waxy (wx), amylose extender (ae), opaque 2 (o2), among others, and their importance to agriculture and human health.

Introduction Maize is the most important crop in the United States for cereal grain production with 95% of starch produced in the United States derived from maize. The starch synthesized in the plant (including seeds) is for energy storage of the plant. After it is harvested, the seeds can be processed and used for food, livestock feed, and various industrial applications, including bioethanol production. In recent years, high-amylose maize starch has been used as a functional food (resistant starch (RS)) for improvement of human health to reduce the glycemic index for prevention of diabetes and colon cancer. The maize seed endosperm is the primary storage site of starch and makes up about 82% of the dry seed weight. Starch is synthesized in the form of semicrystalline granules in amyloplasts located in the endosperm. Starch is composed of two types of polysaccharides, amylose and amylopectin, which are synthesized side by side by two different starch synthetic enzymes (granule-bound starch synthase (SS) (amylose) and soluble SS (amylopectin)) and are interspersed in the starch granules. Amylose is a primarily linear molecule of D-glucopyranose


units linked by alpha 1,4 glycosidic bonds. Amylopectin is a highly branched molecule, consisting of shorter chains of alpha 1,4-linked D-glucopyranose units connected with branch linkages of alpha 1,6 glycosidic bonds. Normal maize (wild type) starch consists of about 75% amylopectin and 25% amylose. Waxy maize starch (designated by the recessive gene, wx) consists of 100% amylopectin. High-amylose maize (designated by the amylose extender gene, ae) consists of 50% or more amylose. High-amylose maize is also known as ‘amylomaize.’ Amylomaize V and amylomaize VII refer to amylose contents of 50% and 70%, respectively. Utilization of starch for different purposes is governed by starch properties. For example, amylopectin branch chain lengths vary between different starch mutants, which impact starch functionality. Starch consisting of amylopectin with more short-branch chains and fewer long-branch chains often displays a lower gelatinization temperature and a slower retrogradation rate, which are desirable for many industrial applications. The genetics of starch biosynthesis is complex and is controlled by many genes with multiple alleles and isoforms of specific enzymes. Interactions between genes for the biosynthesis of starch will be discussed later in the sections of waxy and high-amylose maize. Maize mutant grains are important for generating increased economic values and providing research tools to understand basic genetics and information about plant physiology, metabolic pathways, and starch granule structures. Maize mutants also pose challenges to plant breeders since mutants are frequently associated with reduced agronomic yield and poor grain quality and require access to additional genetic resources and special research technologies. In this article, maize mutants that produce starches with significantly different structures, properties, and economic values, including waxy, high-amylose, sugary 2, and opaque mutants and double mutants of ae wx and o2 wx, will be discussed individually. Structures and properties of many other representative maize mutant starches will also be presented and discussed. White maize, commonly used in various food products, is also discussed.

Waxy Maize Waxy maize was first reported in China in 1909. Initially, waxy maize was only of interest in the United States for genetic research and was an important gene (wx, located on chromosome 9) used for numerous studies in genetics and biochemistry. Oliver E. Nelson first demonstrated the association of the starch-bound enzyme, ADP-glucose glucosyltransferase, with the wx gene. This was the first association of an enzyme with a gene reported in higher plants. Research at the Iowa Agricultural Experiment Station in the 1940s indicated that the

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property of waxy corn starch, consisting of amylopectin only, was similar to that of cassava (Manihot esculenta) root starch. During World War II, importing cassava starch (used for tapioca pudding) from South Asian countries became difficult, and the stage was set for the initial growth of waxy maize in the United States as a substitute of cassava starch. The Wx gene (dominant) is required for the biosynthesis of amylose by transferring glucose units from ADP-glucose to the nonreducing end of the growing glucan molecule (referred to as elongation of the molecule). Plants with the recessive gene, wx, and deficient in granule-bound SS cannot synthesize amylose and produce starch of 100% amylopectin. As discussed previously, the molecular structures of starch govern the functionality of the starch and determine industrial and food/feed applications. The amylopectin molecule in the starch granule is in a semicrystalline structure, whereas the amylose molecule is amorphous. Amylopectin crystallites gelatinize at a lower temperature than amylose crystallites. After cooking, amylopectin produces greater viscosity and does not retrograde (recrystallize) as readily as amylose. These properties of amylopectin confer desirable texture and properties for applications, such as thickening of pastes. Since there is little retrogradation of amylopectin, waxy maize is preferentially used for making frozen foods, with an improved freeze–thaw stability, as well as a smooth and creamy texture. Waxy corn has been used as an animal feed because of the better digestibility of amylopectin. In recent years, waxy corn has become very popular for human consumption in Asia because of its taste and texture. Ethanol represents approximately 10% of the US fuel supply and has reduced imports of foreign oil by 45% as of 2011. Research was conducted to evaluate waxy maize as a grain source for bioethanol production. Production of ethanol requires the hydrolysis of starch to glucose that is used by yeast for ethanol fermentation. A cold fermentation technology has been developed for ethanol production to save energy. In a cold fermentation study that sought to evaluate ethanol yield of Table 1

Total starch content, ethanol yields, and starch–ethanol conversion efficiencies of the normal and waxy corn Starch content (%)

Waxy

Normal

waxy versus nonwaxy (normal) maize inbreds, eight waxy and four normal inbreds were used; results are presented in Table 1. Ethanol yields obtained from the waxy maize were similar to those from the normal maize (36.0 g/100 g dry grain). Ethanol conversion efficiency for waxy maize (93.0%), however, was substantially greater than that for the normal maize (88.2%). The starch content of the normal maize (71.9%) was significantly greater than that of the waxy maize (68.3%). Further research will be conducted to use isogenic lines and a triploid model to determine if the reduced starch content in the waxy maize is associated with the dosage of wx genes. The current breeding practice to develop waxy maize is using the backcross (BC) method. This involves crossing a source of germplasm with the waxy gene (used as a nonrecurrent parent) for five to eight generations of backcrossing to the recurrent parent. Since the wx gene is recessive, selfpollination after each BC must be made to identify the recessive progeny possessing the wx gene. Only the wx plants are used to make future backcrosses each generation. If winter nurseries are available, conversions can be made in about 5–7 years (assumes two breeding generations per year). This is a very long process for competitive breeding programs. There are numerous challenges for the future of improving maize germplasm. Three areas will be considered from the plant breeding perspective. This includes (i) access to new genetic resources for waxy germplasm, (ii) rapid methods to convert adapted germplasm to wx, and (iii) identification of genes or quantitative trait loci (QTLs), which have potential to enhance the content of starch. The waxy germplasm base is quite narrow and has limited nucleotide sequence diversity. A study in China reported that waxy maize had only 31.1% of the nucleotide sequence diversity of the wild relative, teosinte parviglumis. However, China has an abundance of waxy landraces, of which 80% are found in three provinces in the southwest region (Yunnan, Guizhou, and Guangxi). Since there are strict quarantine rules currently in place for importation of maize from any region in Asia, it is likely that few of

Ethanol yield (g/100 g dry grain)

Conversion efficiency (%)

Line

2009 Crop year

2010 Crop year

2009 Crop year

2010 Crop year

2009 Crop year

2010 Crop year

5036 5037 5038 5039 5040 5042 5043 5044 LSM SEM 4701 4702 4703 4704 LSM SEM

71.1 0.3 71.0 0.6 67.5 0.5 68.0 0.6 66.6 0.3 64.1 0.0 68.9 0.7 68.1 1.0 68.3b 0.6 74.3 0.7 71.5 0.8 68.2 0.5 74.1 0.7 71.9a 0.9

72.3 0.2 72.8 0.0 67.3 0.7 69.2 0.0 66.4 0.2 65.3 0.1 66.7 0.2 66.8 0.4

37.6 0.5 36.3 0.1 36.3 0.1 35.7 0.8 35.4 0.2 34.6 0.3 36.2 0.5 35.9 0.1 36.0a 0.3 37.2 0.5 35.2 0.8 34.2 0.4 37.2 0.7 36.0a 0.4

37.9 0.2 37.0 0.3 35.9 0.1 36.0 0.4 35.3 0.6 34.8 0.5 35.7 0.4 35.6 0.2

93.1 90.1 94.6 92.5 93.7 95.0 92.5 92.8 93.0a 0.3 88.3 86.8 88.5 88.4 88.2b 0.5

92.5 89.6 94.0 91.5 93.8 94.0 94.3 94.0

74.1 0.5 70.5 0.4 68.1 0.1 74.1 0.6

37.5 0.4 35.1 0.4 34.3 1.3 37.0 1.1

89.2 87.6 88.8 87.9

LSM SEM ¼ least square means standard error. Different letters following the LSM values within the same columns indicate statistically different mean values (p < 0.05). Source: Yangcheng H, Jiang H, Blanco MH, and Jane J (2013) Characterization of normal and waxy corn starch for bioethanol production. Journal of Agricultural and Food Chemistry 61: 379–386.

GENETICS OF GRAINS | Maize: Other Maize Mutants these sources from China are in US seed banks and therefore are not available to US breeders. Efforts could be made to acquire this germplasm by working with the quarantine and phytosanitary officials to enact procedures to import this germplasm. The second challenge involves converting germplasm to waxy since the current method of backcrossing takes 5–7 years. Double haploid (DH) technology is now in place that reduces breeding time to 2–3 years. DHs also have the advantage of direct selection at the gamete level, which will identify recessive plants immediately. Therefore, the extra steps of pollinating plants after each BC used in conventional breeding are eliminated. Using the DH method, selection can be made by genotyping the haploid plants (the progeny of the F1 x haploid inducer), which are doubled to diploid (2n). The third challenge involves conducting associated mapping to identify regions of the maize genome that carries QTLs with the potential to enhance starch quantity. In a genome-wide association study involving 282 maize inbreds of broad genetic background using 55 000 single nucleotide polymorphisms, many favorable alleles were identified. For example, the study identified 12 QTLs not present in the maize inbred lines having the highest starch content (69.6%) that potentially could increase the starch content to 79.2%. Although there may be associated agronomic problems with maize having 79% starch, the study demonstrated that there are other genes to be discovered to enhance the starch content.

High-Amylose Maize High-amylose maize was first identified in 1952 with the discovery of the ae gene located on chromosome 5. Although the terms ‘amylose’ and ‘amylopectin’ were used for about 70 years, initially, very little was known about the inheritance and biochemistry of the starch components. Since then, we have learned that there are two independent pathways for starch synthesis and at least five classes of SS, three classes of starch-branching enzymes (SBEs), and also starch-debranching enzymes involved in starch synthesis. Following the formation of the alpha 1,4 glucan chain, SBEs introduce branching points by cleaving the alpha 1,4 linkages and transferring the reducing end to C6 hydroxyl to create alpha 1,6 linkages. The SS and SBEs are also assembled into protein complexes and are involved in starch granule synthesis. Plants that have the ae gene lack the SBEIIb enzyme and produce starch with amylose levels ranging from 50% to 90%. A recent advance on the development of a high-amylose maize inbred, GEMS-0067, was achieved from joint efforts of the USDA-ARS Germplasm Enhancement of Maize (GEM) Project and Truman State University. GEMS-0067 is registered and assigned a plant introduction (PI) number, PI 643420. Seeds of GEMS-0067 are available with no charge and can be ordered from the Genetic Resources Information Network (GRIN), www.ars-grin.gov. GEMS-0067 is the first public release of a high-amylose maize line having 85% amylose in the United States compared with 40–50% amylose found in most other publicly available sources. GEMS-0067 was derived from a cross that involved a tropical source from Guatemala designated GUAT 209 (PI 498583) crossed to US stiff stalk inbred from a proprietary source designated S13. The resulting

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cross, GUAT209:S13, was crossed to the public ae inbreds, H99ae and OH43ae. H99ae and OH43ae have 63.1% and 57.8% amylose content, respectively, and the exotic tropical source, GUAT209, carries the modifier genes that enhance the percentage of amylose content. The modifier gene, designated as the high-amylose modifier (HAM), is still being studied. In one study with GEMS-0067, SBE1 was reported to be the source of the HAM gene. It has also been reported that GEMS-0067 has a unique form of SBEI, not found in other ae genotypes studied. GEMS-0067 has been used in several other studies for RS. High-amylose maize RS may provide benefits to human health by providing carbohydrates with a reduced glycemic index, especially important for patients with diabetes. Therefore, maize germplasm with high levels of RS should be important to plant breeders for further development. To test if the increase in dosage of HAM genes contributes to increases in both the amylose and resistant starch contents, a genetic experiment was conducted. The maize endosperm is triploid tissue (3n) and, therefore, is useful to test the dosage effect of increased HAM genes using a ‘triploid endosperm model.’ Maize endosperm is produced by the fusion of two maternal nuclei (2n) and one parental nucleus from the pollen (1n). The resulting tissue is therefore 2n þ 1n ¼ 3n. GEMS-0067 (designated G) is a homozygous mutant having ae and the HAM gene, and H99ae (designated H) does not have the HAM gene. By making self-pollinations and intercrosses, maize endosperm tissues with various doses of HAM gene were created: G/G, G/H, H/G, and H/H (female parent is always listed first). This resulted in 3, 2, 1, and 0 doses of the HAM gene, respectively. RS contents, determined using the AOAC method 991.43 for total dietary fiber, were 35.0%, 28.1%, 12.9%, and 15.7% for G/G, G/H, H/G, and H/H, respectively, and the amylose contents were 88.2%, 81.7%, 77.9%, and 68.9%, respectively. The results suggested that the increase in HAM gene dosage was associated with increasing levels of both amylose and RS contents (Table 2). GEMS-0067 starch granules contain up to 32% elongated granules (Figure 1), which was much greater than other ae sources, averaging about 7% elongated granules. The amylose content, percentage of elongated granules, and RS content increased with the kernel development. A model was proposed on the mechanism of elongated granule formation that involved the initial fusion of adjacent starch granule nuclei Table 2 HAM gene dosage in endosperm, amylose content, and RS contents of corn starches isolated from the grain derived from selfand intercrosses of GEMS-0067 (G) and H99ae (H) Sample

HAM gene dosage in endosperm

Amylose (%)

RS (%)

G/G G/H H/G H/H

3 2 1 0

88.2 1.5 81.7 1.6 77.9 0.8 68.9 1.6

35.0 0.5 28.1 0.8 12.9 0.2 15.7 0.2

HAM gene, high-amylose modifier gene; RS, resistant starch. Source: Jiang H, Jane J, Acevedo D, et al. (2010) Variations in starch physicochemical properties from a generation-means analysis study using amylomaize V and VII parents. Journal of Agricultural and Food Chemistry 58: 5633–5639.

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located in a single amyloplast through the formation of antiparallel double helices of amylose molecules, which prevents amyloplast division (Figure 2). Foods made with RS are useful to maintain a steady blood glucose level to prevent development of type 2 diabetes. GEMS0067 high-amylose maize starch has a substantially higher gelatinization temperature (up to 125 C), which requires a special cooking device to gelatinize the starch. After gelatinization, the starch has a strong tendency to retrograde. Therefore, native or chemically modified high-amylose maize starch can be used to produce tough and transparent bioplastic films and fiber. Other uses include corrugating due to shear resistance, textiles, adhesives, and candy gum drops. Research has been conducted to use the high-amylose starch for making biobased plastics. The challenges for high-amylose maize improvement are similar for those discussed for waxy maize. Breeders, however,

Figure 1 Starch granules of GEMS-0067. Arrows indicate spherical (S), rod (R), filamentous (F), and triangular (T) starch granules. Adapted from Jiang H, Horner H, Pepper T, Blanco M, Campbell M, and Jane J (2010). Formation of elongated starch granules in high amylose maize. Carbohydrate Polymers 80(2): 533–538.

are faced with several additional problems when working with high-amylose maize. This includes low seed yields and poorquality seed of ae germplasm. High-amylose germplasm is often plagued by ear mold fungi that reduce seed weight, consequently lowering agronomic yield per acre. There is also a need for other maize germplasm (such as flint or semident) having modifier genes that can enhance the level of amylose and quality texture. This germplasm should be incorporated into a breeding program with continuous selection for these traits practiced each breeding cycle.

Sugary 2 Maize (su2) The sugary 2 mutation (su2, located on chromosome 6), first described in 1936, is of interest due to the unique physicochemical properties of starch. Starch produced by su2 mutant of maize displays granules with lobes and has an unusually low gelatinization temperature, To at 47.8 C, and enthalpy change, DH at 7.9 J g1, compared with that of the wild type (64.4 C and 13.2 J g1, respectively). The su2 starch granules consist of little crystallinity and develop low viscosity after cooking using an amylograph, with the peak viscosity of 7.1 RVU compared with 109.9 RVU of normal maize starch. Enzyme digestibility of the su2 starch granules is greater than that of the normal maize starch. Because it is readily digestible, feeding chickens with su2 maize has been reported to increase the growth rate of chickens. The unique physicochemical properties of su2 maize starch result from the larger proportion of short-branch chains (DP 6–12) and fewer branch chains of DP 12–36 of the su2 amylopectin when compared with that of the normal corn starch. The mutation of su2 gene, which encodes starch synthase IIa (SSIIa), has been proposed for the structure change. Without SSIIa in the starch biosynthesis pathway, the short chains (DP 6–12) in amylopectin cannot be elongated to DP 12–36. Consequently, the starch displays low crystallinity and low gelatinization temperature and enthalpy changes.

Figure 2 Proposed mechanism of development of elongated starch granule in amyloplast of high-amylose maize. Adapted from Jiang H, Horner H, Pepper T, Blanco M, Campbell M, and Jane J (2010). Formation of elongated starch granules in high amylose maize. Carbohydrate Polymers 80(2): 533–538.


Opaque 2 Maize (o2) Protein content and quality are important grain attributes. The opaque 2 (o2) was first described by Emerson et al. in 1935 and is located on chromosome 7. The impact on amino acid balance of o2 was discovered by Mertz et al. at Purdue University. The key attributes of o2 are the increased levels of the amino acids, lysine, and tryptophan. Early research with o2 indicated poor seed yield, reduced quality, and susceptibility to grain molds. Further research at the International Maize and Wheat Improvement Center (CIMMYT) has successfully improved kernel vitreousness with modifier genes for improved grain quality and yield similar to normal maize. Maize kernels of o2 mutant contain less zein, resulting in increased proportion of lysine and proteins other than zein. The maize o2 mutant also has less grain yield and starch content, which is attributed to early termination of starch biosynthesis. Consequently, the endosperms of kernels appear soft and chalky compared with that of the wild type. Starch isolated from the maize o2 mutant displays more pinholes, but little to no dimple-like indentations on the granule surface, as a result of the absence of the protein body of zein. Dry-ground o2 maize kernels display larger swelling power than the wildtype counterpart, whereas the isolated starch of the o2 maize displays less swelling power. The difference is attributed to the greater solubility of the globulin and albumin in the o2 kernels than the zein in the wild type. The o2 maize starch consists of less amylose, similar average branch chain length to amylopectin, and similar gelatinization temperatures compared with the wild-type maize starch. Both the starch of the ground o2 mutant maize kernels and its isolated starch are digested by amylase faster than the wild-type counterparts.

Double Mutant: ae wx A double mutant can be defined as two genes that occur together in the same plant. In theory, double mutants would bring together the important traits associated with each gene. However, this is not always the case since there are numerous interacting effects at the genetic and biochemical levels. There are many double mutants of maize, and some are associated with unique traits that have potential for food and industrial applications. The ae wx double mutant has been the topic of research for further investigation on RS and slowly digestible starch (SDS). The ae gene is responsible for increasing the branch chain length of amylopectin, levels of amylose, and RS contents and has health benefits associated with RS. The wx gene increases the level of amylopectin content and is highly digestible. SDS has slow but complete digestibility with more prolonged glucose and energy release. A study was conducted to evaluate four ae wx double mutants with one ae maize inbred and one normal inbred. The normal inbred was almost exclusively rapidly digestible starch, 98.2%. The ae inbred was 25.3% RS and 5.2% SDS. The four ae wx inbreds contained RS ranging from 4.2% to 8.1% but had increased levels of SDS (6.7–7.9%) relative to the ae mutant (Table 3). The results indicate that the double mutant ae wx provides benefits of SDS.

429

Table 3 RDS, SDS, and RS contents of the mutant corn starch after cooking

ae wx

ae N. maize

Sample

RDS%

SDS%

RS%

201–2 167–1 188–3 159–2 148–3 B73

87.5 0.7 84.0 1.0 88.2 1.1 87.5 2.2 69.5 0.1 98.2 1.5

7.9 0.6 7.9 0.6 7.6 2.0 6.7 1.9 5.2 1.0 1.8 0.8

4.6 1.4 8.1 0.4 4.2 0.9 5.8 0.3 25.3 1.0 0.0 0.6

RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch. Source: Jane J and Yangcheng H (2012) Development of GEM line starch to improve nutritional value and biofuel production. Available at www.public.iastate.edu/usdagem (see Public Reports, June 2012).

Poor seed quality and low yields are the main problems for the double mutant ae wx, and the problems are far worse than the single mutant, ae. Therefore, crossing ae wx into genetic backgrounds with good seed quality and grain texture is needed. Since incorporation of two recessive genes requires the backcrossing method, a rapid technique such as DH would offer distinct advantages. Since DH technology selects directly at the gamete level, the probability of identifying double mutants is 1 per 2n (n ¼ number of genes) versus 1 per 4n for conventional breeding with diploids. Therefore, 1 out of 4 plants will be homozygous for both genes, versus 1 out of 16 plants for conventional breeding with diploids.

Double Mutant: o2 wx Waxy maize has become very important for human consumption in Asia due to its tenderness and desirable waxy taste. However, waxy maize is deficient in lysine and tryptophan. Efforts are under way in Thailand to combine the o2 with the waxy mutant to create the double mutant, o2 wx. Utilizing backcrossing, combined with marker-assisted selection with simple sequence repeat (SSR) markers, the o2 gene was successfully transferred to waxy maize. Double-recessive plants identified with SSR markers were pollinated (inbreeding by self-pollination) to ensure fixation of o2 wx. Confirmation of elevated tryptophan and lysine levels was similar to the original o2 source used and the grain quality was similar to the waxy parent.

Structures and Properties of Starches from Selected Maize Mutants and Double Mutants Wang et al. conducted a series of comprehensive studies analyzing properties and structures of starches isolated from maize mutant inbred lines on the OH43 background. The wild type (normal), mutants of ae, bt1, bt2, du1, h. sh2, su1, and wx, and some double mutants were used for the study, and selected results are summarized in Table 4. Mutants of ae, bt1, du1, sh2, and su1 reported in this study along with su2 discussed earlier produce starch with smaller granules. Starch of the ae mutant consists of a larger percentage of amylose content and displays a higher gelatinization temperature (Table 4). The high


430

Table 4 Average diameter of starch granules, gelatinization temperatures, and amylose content of starches isolated from 14 mutant genotypes of OH43 inbred Gelatinization temperature Genotype

Average diameter of starch granule

To ( C)

Tc ( C)

Amylose (%)

Normal ae bt1 bt2 du1 h sh2 su1 wx h sh2 h wx sh2 bt1 sh2 wx wx du1

11.6 4.5 7.0 2.1 6.1 1.3 10.8 3.4 7.8 2.1 13.8 3.6 6.3 1.9 5.4 2.6 10.3 2.6 11.2 3.8 11.0 4.4 5.4 1.6 10.2 3.7 10.2 3.6

67.2 68.7 63.4 66.8 67.2 65.6 64.3 64.6 68.6 68.4 69.7 67.7 68.1 70.9

76.0 100.0 78.3 77.4 76.3 75.0 72.8 71.7 77.6 75.1 74.6 76.7 79.0 78.4

27.8 1.1 56.4 1.1 23.2 0.8 26.9 0.0 31.4 0.4 26.4 0.8 28.8 0.0 37.4 1.5 0.0 0.0 25.4 0.1 0.0 0.0 27.6 0.4 0.0 0.0 0.0 0.0

A-Type Polymorph

6 5 4

nm

3 2 1 0 1

11

21

31

41 51 DP

61

71

4.0

wx sh-1

3.0 2.0 1.0 11

21

31

51

61

71

wx

3.0 2.0 1.0 21

31

41

51

61

71

du wx

4.0 3.0 2.0 1.0 11

21

31

41

51

61

71

31

4.0

wx su-2

2.0 1.0 41 51 DP

61

71

81

51

61

71

81

5

amylomaize V

4 3 2 1 1

11

21

31

51 41 DP

61

71

81

7

6 5 4

du h

3 2 1 0

0.0

41

6

81

% Peak area distribution


5.0

31

21

0 1

7

21

11

DP

6.0

11

1.0

7

5.0

81

7.0

1

2.0

DP

6.0

DP

3.0

3.0

1

0.0 11

ae WX

4.0

81



5.0

0.0


41

7.0

1

5.0

DP

6.0

4.0

6.0

0.0

0.0 1

7.0 % Peak area distribution

5.0

81

B-Type Polymorph

7.0 % Peak area distribution

7



ae, amylose extender; bt, brittle; du, dull; h, horny; sh, shrunken; su, sugary; wx, waxy. Source: Wang YJ, White P, Pollak L, and Jane J (1993) Characterization of starch structures of 17 maize endosperm mutant genotypes with OH43 inbred line background. Cereal Chemistry 70: 171–179.

6 5

amylomaize VII

4 3 2 1 0

1

11

21

31

41 51 DP

61

71

81

1

11

21

31

41 51 DP

61

71

81

Figure 3 Amylopectin branch chain length distribution of maize mutants. Wong KS and Jane J, unpublished data.

gelatinization temperature of the ae maize mutant starch, including amylomaize V and VII, is a result of its longer branch chains of amylopectin (Figure 3) as well as greater amylose content as discussed earlier. Normal maize starch and most mutants of maize starches display the A-type x-ray pattern. In contrary, maize ae mutant

starches, including amylomaize V and VII and ae wx maize starch, display the B-type x-ray diffraction pattern. The difference is attributed to the fact that maize ae mutant starches have large proportions of long-branch chains with DP > 36 in the amylopectin (Figure 3) and double helices of the branch chains are packed in a hexagonal unit cell.


431

100

350 300

80

60

200 150

40

Temperature (C)

RVU

250

100 20 50 0

0 0

5 normal maize du wx amylomaize VII

10 Time (min) wx maize du horny Temp(C)

15 wx su-2 maize ae wx maize

20 wx sh-1 maize amylomaize V

Figure 4 Pasting profiles of mutant maize starches (8%, w/w, dry starch basis). Wong KS and Jane J, unpublished data.

Pasting properties of selected maize mutant starches analyzed using a Rapid Visco-Analyzer are shown in Figure 4. The pasting profiles of the maize starches show that all the starches with wx gene, including wx, wx su2, wx sh1, du wx, and ae wx, have pasting temperatures lower than the normal maize starch. Among the waxy starches, wx su2 starch displays the lowest pasting temperature, resulting from the very low gelatinization temperature contributed by the su2 gene. The low pasting temperatures of all the wx mutant and wx double mutant starches are a result of lacking amylose in the starch. Without amylose present in the starch to form helical complexes with lipids, which entangle with amylopectin to restrict the swelling of starch granules, starch can swell freely during heating and develop viscosity promptly. Because the long-branch chains are present in the ae wx starch and interact with one another to prevent disintegration of swollen granules, the ae wx starch displays a very high peak viscosity with little break down. Amylomaize V and VII starches display little or undetectable viscosity, resulting from low amylopectin contents of the starches. It is known that viscosity of starch is mainly contributed by amylopectin because of its swelling power.

White Maize White maize can be considered as grain corn without yellow pigmentation. White grain color is controlled by a single recessive gene, y, also known as y1 used in the literature. The inheritance of the white grain phenotype in maize, resulting from a homozygous recessive gene, was first reported by Carl Correns in 1901. The association of yellow corn with provitamin A (carotenoids) content was first reported by Mangelsdorf and Fraps in 1931. These researchers demonstrated a linear relationship of carotenoids with increasing dosage of the Y gene. The dominant Y gene confers grain with increasing yellow color intensity as the dosage of Y increases. Therefore,

grain with 0, 1, 2, and 3 dosages of the Y gene (yyy, yyY, yYY, and YYY) can be generally classified as white, light yellow, moderate yellow, and intense yellow, respectively. White corn was used more extensively in the early 1900s, and approximately 50% of the maize planted in 1918 was white. Due to deficiency of carotenoids in white corn, more acres were planted to yellow corn to improve the nutritional value for livestock feed. Currently, the acreage planted to white corn is approximately 3% and yellow corn 97%. There has been an increased interest in white corn in recent years; 430 000 acres of white corn was planted in the United States in 1990 and increased to 700 000 acres in 2005. This was largely due to demand for corn-based food products, such as tortillas, corn flakes, corn meal, grits, and hominy. Although lacking the carotenoids, white corn is preferred for taste and continues to be part of the traditional diet of many people in the world. Vitamin A deficiencies, however, are health problems in developing countries, such as sub-Saharan Africa where white corn is widely consumed. Breeding procedures for white corn are very similar to that used for yellow corn although the selection criteria are quite different. For example, the endosperm of the grain must be pure white, cob color white, and grain free of stress cracks; large and uniform size kernels should be slightly dented and have high specific gravity. Most white corn is grown under contract with very specific requirements for product quality. White corn also needs to be produced in locations that are well isolated from yellow corn to avoid unwanted pollination from yellow corn pollen. An important challenge for future white corn breeding will be to improve nutritional quality.


•

What physicochemical properties make waxy maize starch suitable for bioethanol production?

432

• • • • •


What physicochemical properties make high-amylose starch suitable for resistant starch? What type of starch would be most desirable for livestock feed and why? How do genetic studies with starch mutants enhance our understanding of starch granule structure and the importance of starch for human health? Define the term ‘backcrossing.’ Why has it been used so widely for breeding maize with important mutants? Diagram the anatomical structure of the maize ovary showing the endosperm and embryo nuclei and chromosomal ploidy levels before and after male fertilization. What is meant by ‘double fertilization?’


• •

What genetic tools could be exploited to generate new diversity and to identify useful functionality of starch with minimal reduction in agronomic yield or grain quality? An important component of crop improvement is access to new sources of genetic diversity. Assuming you need to have access to new sources maize with potential to improve starch quality, what approaches could be implemented to obtain new material?

See also: Breeding of Grains: Maize: Breeding; Genetics of Grains: Development of Genetically Modified Grains; Genomics of Food Grains; Maize: Genetics; Maize: Quality Protein Maize.

Further Reading Campbell MR, Jane J, Pollak L, Blanco M, and O’Brien A (2007) Registration of maize germplasm line GEMS-0067. Journal of Plant Registrations 1: 60–61.

Chen T, Ning L, Liu X, et al. (2013) Development of functional molecular markers of SbeI and SbeIIb for the high amylose maize germplasm line GEMS-0067. Crop Science 53: 482–490. Cook JP, McMullen MD, Holland JB, et al. (2012) Genetic architecture of maize kernel composition in the nested association mapping and inbred association panels. Plant Physiology 158: 824–834. Fergason V (1994) High amylose and waxy corns. In: Hallauer AR (ed.) Specialty Corns, pp. 55–77. Boca Raton, FL: CRC Press. Hansen R (2012) White corn profile. Available at www.agmrc.org/ commodities_products/grains_oilseeds/corn_grain/white-corn-profile/. Hasjim J, Srichuwong S, Scott PM, and Jane J (2009) Kernel composition, starch structure, and enzyme digestibility of opaque-2 maize and quality protein maize. Journal of Agricultural and Food Chemistry 57: 2049–2055. Jane J and Yangcheng H (2012) Development of GEM Line starch to improve nutritional value and biofuel production. Available at www.public.iastate.edu/usda-gem (see Public Reports, June 2012). Jiang H, Horner H, Pepper T, Blanco M, Campbell M, and Jane J (2010) Formation of elongated starch granules in high amylose maize. Carbohydrate Polymers 80(2): 533–538. Jiang H, Jane J, Acevedo D, et al. (2010) Variations in starch physicochemical properties from a generation-means analysis study using amylomaize V and VII parents. Journal of Agricultural and Food Chemistry 58: 5633–5639. Mertz ET, Bates LS, and Nelson OE (1964) Mutant gene that changes protein composition and increases lysine content of maize endosperm. Science 145: 279–280. Nelson OE and Rines HW (1962) The enzymatic deficiency in the waxy mutant of maize. Biochemical and Biophysical Research Communications 9: 297–300. Perera C, Lu Z, Sell J, and Jane J (2001) Comparison of physicochemical properties and structures of sugary-2 corn starch with normal and waxy cultivars. Cereal Chemistry 78: 249–256. Poneleit CJ (1994) Breeding white endosperm corn. In: Hallauer AR (ed.) Specialty Corns, pp. 225–262. Boca Raton, FL: CRC Press. Renewable Fuels Association (2012) Ethanol facts: Energy security. Available at: http:// www.ethanolrfa.org/pages/ethanol-facts-energy-security. Sinkangam B, Stamp P, Srinives P, et al. (2011) Integration of quality protein in waxy maize by means of simple sequence repeat markers. Crop Science 51: 2499–2504. Tian M, Tan G, Liu Y, Rong T, and Huang Y (2009) Origin and evolution of Chinese waxy maize: Evidence from the Globulin-1 gene. Genetic Resources and Crop Evolution 56: 247–255. Wang YJ, White P, Pollak L, and Jane J (1993) Characterization of starch structures of 17 maize endosperm mutant genotypes with OH43 inbred line background. Cereal Chemistry 70: 171–179. Yangcheng H, Jiang H, Blanco MH, and Jane J (2013) Characterization of normal and waxy corn starch for bioethanol production. Journal of Agricultural and Food Chemistry 61: 379–386.

Appendix 1. Nutrient-Composition Tables for Grains and for Grain-Based Products SF Schakel, N Van Heel, and J Harnack, University of Minnesota, Minneapolis, MN, USA ã 2016 Elsevier Ltd. All rights reserved. Reprinted version of the original article: “Appendix 1. Composition of Grain and Grain-Based Products” in the Encyclopedia of Grain Science, First Edition, Vol. 3, pp. 463–474, 2004.

Topic Highlights

• • • •

Composition data include protein, carbohydrate, fat, fiber, minerals, and vitamins. All agricultural grains are included, plus related flour, bran, and other milling fractions. Food composition is provided for breads, cookies, cakes, pasta, pies, and beverages. Fortification and enrichment levels are provided for many foods.

Learning Objectives

• • •

To achieve an understanding of the compounds in grains and related foods. To realize that all these grains and foods differ significantly in composition. To determine how to identify grains and foods with desirable levels of specific nutrients.

Introduction Tables of food composition are valuable for a range of uses, including the preparation of diets for specific purposes, the investigation of present and proposed diets, and the selection of the most suitable food combinations to suit certain dietary requirements. These tables serve such needs with respect to the wide range of foods involving grains, as well as for the grains

themselves and the flours and meals prepared for them (Tables 1 and 2).

The Use of the Tables An introduction to grain composition and a description of the value of the tables are provided in the article entitled ‘The Composition of Grains and Grain-Based Products.’ Values in bold italics indicate fortification or enrichment. Abbreviations used: CP, cup (about 250 ml); TB, tablespoon (about 15 ml); FO, fluid ounces; IU, international units; mg RE, micrograms of retinol equivalents. Kcal, kilocalorie; one kilocalorie ¼ 4.184 kJ.

Notes Provided by the Original Authors The grain nutrient composition table developed by the Nutrition Coordinating Center (NCC) at the University of Minnesota contains values compiled from scientific literature, the USDA Nutrient Database for Standard Reference, manufacturer’s information, and estimated data. The data in the table include both analytic and estimated values. (For further information regarding specific values, contact the Nutrition Coordinating Center, Division of Epidemiology, School of Public Health, 1300 South Second Street, Suite 300, Minneapolis, Minnesota 55454-1015.) Estimated values were derived from (1) a different form of the same food (e.g., raw to cooked), (2) a similar food, or (3) calculation of recipes or formulations.

Table 1 The composition of grains and grain-based foods with respect to protein; carbohydrate; fat; fiber; and the minerals potassium (K), sodium (Na), calcium (Ca), iron (Fe), and phosphorus (P) based on the specified serving portions Description

Serving size

Weight (g)

kcal Protein (g)

Grains, flours, and cooked cereals (enriched or fortified nutrients) Amaranth, dry 0.22 CP 45 168 6.50 Barley bran flour 0.30 CP 45 54 8.03 Barley flour 0.30 CP 45 155 4.73 Barley malt flour 0.28 CP 45 162 4.63 Barley, cooked 0.89 CP 140 172 4.83 Barley, dry 0.23 CP 45 158 4.46 Bread flour 0.33 CP 45 164 4.65 Buckwheat flour 0.38 CP 45 151 5.68 Buckwheat groats, dry 0.24 CP 40 138 4.69 Bulgur, cooked 0.77 CP 140 114 4.09 Bulgur, dry 0.32 CP 45 154 5.53

Total carbohydrate (g)

Fat (g)

Ash (g)

Dietary K fiber (g) (mg)

Na Ca Fe (mg) (mg) (mg)

P (mg)

29.78 30.44 33.53 35.24 37.90 34.97 34.34 31.77 29.98 25.26 34.14

2.93 2.95 0.72 0.83 0.56 0.52 0.44 1.40 1.08 0.45 0.60

1.37 2.00 0.58 0.62 0.71 0.50 0.21 1.14 0.88 0.50 0.68

6.84 30.40 4.55 3.20 7.60 7.02 1.22 4.50 4.12 6.09 8.24

9 7 2 5 71 4 1 5 4 6 8

205 348 133 136 108 99 49 152 128 100 135

165 50 139 101 137 126 48 260 128 136 185

69 254 14 17 16 13 7 18 7 14 16

3.42 7.38 1.21 2.12 1.22 1.13 2.09 1.83 0.99 0.81 1.11

(Continued) Encyclopedia of Food Grains, Second Edition

http://dx.doi.org/10.1016/B978-0-12-394437-5.00243-6

433

434

APPENDIX 1 | Nutrient-Composition Tables for Grains and for Grain-Based Products

Table 1

(Continued)

Description

Serving size

Weight (g)

kcal Protein (g)


Fat (g)

Ash (g)



P (mg)

Cake flour Chickpea flour Corn bran, dry Corn flour Corn grits, white, cooked Corn grits, white, dry Corn grits, yellow, dry Cornmeal, cooked Cornmeal, masa harina, dry Cornmeal, self-rising, dry Cornmeal, white, dry Cornmeal, yellow, dry Cornstarch Couscous, cooked Couscous, dry Cracked wheat, cooked Farina (creamed wheat), instant cooking, cooked Farina (creamed wheat), quick cooking, cooked Farina (creamed wheat), regular cooking, cooked Farina (creamed wheat), dry Hominy, canned Kamut flour Kasha, cooked Kasha, dry Millet, cooked Millet, dry Oat bran, cooked Oat bran, dry Oatmeal (fortified), flavored, dry Oatmeal (fortified), plain, dry Oatmeal, dry Oatmeal, instant cooking, flavored, cooked Oatmeal, instant cooking, plain, cooked Oatmeal, regular cooking, cooked Potato flour Quinoa, cooked Quinoa, dry Rice (creamed rice), dry Rice bran, dry Rice flour, brown Rice flour, white Rolled wheat, cooked Rolled wheat, dry Rye flour, medium Rye, whole grain, dry Self-rising flour Sorghum Soy flour, defatted

0.33 CP 0.50 CP 3 TB 0.39 CP 1 CP 0.26 CP 0.26 CP 1 CP 0.39 CP

45 45 15 45 242 40 40 240 45

163 166 34 164 147 148 148 130 164

3.69 10.08 1.25 4.20 3.49 3.52 3.52 3.02 4.20

35.11 26.01 12.85 34.32 31.46 31.84 31.84 27.60 34.32

0.39 3.01 0.14 1.70 0.48 0.48 0.48 0.58 1.70

0.18 1.27 0.05 0.71 1.62 0.16 0.16 0.98 0.71

0.77 4.86 12.83 4.32 0.63 0.64 0.64 2.64 4.32

47 381 7 134 54 55 55 58 134

1 29 1 2 572 0 0 306 2

6 20 6 63 5 1 1 6 63

3.29 2.19 0.42 3.24 0.48 0.45 0.40 0.48 3.24

38 143 11 100 29 29 29 30 100

0.33 CP 0.33 CP 0.33 CP 1.25 TB 0.89 CP 0.26 CP 1 CP 1 CP

45 45 45 10 140 45 242 241

156 165 165 38 180 169 178 121

3.59 3.82 3.82 0.03 6.09 5.74 7.19 3.50

33.59 34.96 34.96 9.13 36.99 34.84 38.07 24.92

0.70 0.74 0.74 0.01 0.31 0.29 0.99 0.46

2.87 0.27 0.27 0.01 1.22 0.28 1.31 1.42

3.14 3.33 3.33 0.09 2.39 2.25 6.39 1.06

69 73 73 0 79 75 213 38

607 1 1 1 363 5 185 289

158 2 2 0 14 11 22 105

0.45 0.50 0.50 0.05 0.52 0.49 2.03 0.05

280 38 38 1 81 77 182 34

1 CP

239

119

3.37

24.76

0.43

1.79

0.93

43

370

106

0.05

93

1 CP

251

122

3.46

25.25

0.50

0.93

1.26

40

287

106

0.05

38

0.23 CP

40

148

4.20

30.60

0.60

0.24

1.52

48

3

6

0.60

46

1 CP 0.25 CP 1 CP 0.24 CP 0.58 CP 0.23 CP 1 CP 0.43 CP 0.49 CP

165 45 168 40 140 45 219 40 55

119 153 178 138 169 170 91 98 202

2.44 6.17 6.03 4.69 4.94 4.96 6.42 6.92 5.17

23.53 32.66 38.56 29.98 32.63 32.78 24.53 26.49 42.33

1.45 0.84 1.39 1.08 1.89 1.90 2.61 2.81 2.30

1.42 0.72 1.13 0.88 1.46 1.46 1.73 1.16 1.67

4.13 5.49 5.29 4.12 3.81 3.83 5.72 6.16 4.07

15 182 165 128 87 88 210 226 171

347 2 7 4 3 2 261 2 267

17 15 12 7 5 4 25 23 166

1.02 1.75 1.28 0.99 1.34 1.35 2.02 2.16 6.28

58 195 164 128 128 128 272 294 183

0.49 CP

40

148

6.20

25.60

2.44

2.00

4.36

150

114

143

11.57 187

0.49 CP 1 CP

40 234

154 156

6.40 3.98

26.80 32.67

2.52 1.78

0.76 1.29

4.24 3.14

140 132

2 207

21 132

1.68 4.84

1 CP

234

130

5.45

22.53

2.15

1.76

3.84

132

102

130

10.20 165

1 CP

234

145

6.04

25.32

2.39

1.71

4.00

132

389

24

1.59

179

0.28 CP 0.89 CP 0.26 CP 0.22 CP 2 TB 0.28 CP 0.28 CP 1 CP 0.43 CP 0.44 CP 0.27 CP 0.36 CP 0.24 CP 0.51 CP

45 140 45 40 15 45 45 242 40 45 45 45 45 45

161 141 168 148 47 163 165 138 137 159 151 155 153 148

3.11 4.93 5.90 2.52 2.00 3.25 2.68 4.53 4.48 4.23 6.64 4.36 5.09 21.15

37.39 25.94 31.01 32.96 7.45 34.42 36.06 30.40 30.08 34.87 31.39 33.06 33.58 17.27

0.15 2.18 2.61 0.20 3.13 1.25 0.64 0.80 0.80 0.80 1.13 0.41 1.49 0.55

1.41 1.09 1.31 0.16 1.50 0.69 0.27 2.11 0.64 0.68 0.91 2.91 0.71 2.77

2.66 2.23 2.66 0.28 3.15 2.07 1.08 3.85 3.80 6.57 6.57 1.15 6.22 7.88

450 279 333 57 223 130 34 157 156 153 119 46 158 1073

25 9 9 2 1 4 0 568 1 1 3 571 3 9

29 26 27 10 9 5 5 20 16 11 15 189 13 108

0.62 3.49 4.16 1.52 2.78 0.89 0.16 1.38 1.36 0.95 1.20 2.30 1.98 4.16

76 154 185 52 252 152 44 153 152 93 168 114 129 303

190 141

(Continued)

APPENDIX 1 | Nutrient-Composition Tables for Grains and for Grain-Based Products Table 1 Description

435

(Continued) Serving size

Soy flour, full fat 0.51 CP Soy flour, low fat 0.51 CP Spelt 0.38 CP Teff, dry 0.23 CP Triticale, whole grain 0.34 CP Wheat bran (unprocessed) 0.25 CP Wheat, cracked whole 0.33 CP wheat Wheat, germ 2 TB Wheat, hard red spring 0.23 CP Wheat, hard red winter 0.23 CP Wheat, hard white 0.23 CP Wheat, soft red winter 0.27 CP Wheat, soft, white 0.27 CP Wheat, sprouted 0.42 CP White flour, wheat, all0.36 CP purpose (enriched) White flour, wheat, all0.36 CP purpose (unenriched) Whole wheat flour, red 0.38 CP wheat Pasta and rice (enriched nutrients) Chow mein noodles, crisp 0.55 CP type Egg noodles, cooked 0.9 CP Lo mein noodles, soft type, 0.8 CP cooked Macaroni/spaghetti 1 CP noodles, white cooked Macaroni/spaghetti 1 CP noodles, whole wheat, cooked Rice, brown, cooked 0.7 CP Rice, brown, uncooked 0.25 CP Rice, white, cooked 0.9 CP Rice, white, uncooked 0.25 CP Rice/cellophane noodles, 0.8 CP cooked Spaetzle or spatzen, 0.9 CP cooked Wild rice, cooked 0.85 CP Wild rice, uncooked 0.3 CP Cereal, ready-to-eat (fortified nutrients) Bran flakes without raisins 0.75 CP Bran nuggets, 0.33 CP unsweetened Corn flakes, unsweetened 1 CP Corn nuggets, 1 CP unsweetened Corn, puffed 1.33 CP Oat flakes 0.75 CP Oat rings, unsweetened 1 CP Rice flakes 1 CP Rice nuggets, 1.25 CP unsweetened Rice, puffed 1 CP Wheat and barley flakes 0.75 CP Wheat and barley nuggets 0.5 CP

Weight (g)

kcal Protein (g)


Fat (g)

Ash (g)



P (mg)

45 45 45 45 45 15 45

196 167 143 166 152 32 153

15.54 20.94 5.76 4.01 5.93 2.33 6.17

15.84 17.09 33.08 34.61 32.91 9.68 32.66

9.29 3.02 0.90 0.90 0.81 0.64 0.84

2.01 2.74 0.81 1.26 0.83 0.87 0.72

4.32 4.59 5.13 6.08 6.57 6.42 5.49

1132 1157 185 252 210 177 182

6 8 0 6 1 0 2

93 85 12 86 16 11 15

2.87 2.70 1.98 2.26 1.17 1.59 1.75

222 267 189 197 144 152 156

15 45 45 45 45 45 45 45

57 148 147 154 149 153 89 164

4.37 6.93 5.67 5.09 4.66 4.81 3.37 4.65

7.44 30.61 32.03 34.16 33.41 33.91 19.14 34.34

1.61 0.86 0.69 0.77 0.70 0.90 0.57 0.44

0.75 0.85 0.71 0.47 0.76 0.69 0.43 0.21

1.94 5.49 5.49 5.49 5.63 5.72 0.50 1.22

142 153 163 194 179 196 76 48

1 1 1 1 1 1 7 1

7 11 13 14 12 15 13 7

1.36 1.62 1.44 2.05 1.44 2.42 0.96 2.09

172 149 130 160 222 181 90 49

45

164

4.65

34.34

0.44

0.21

1.22

48

1

7

0.53

49

45

153

6.17

32.66

0.84

0.72

5.49

182

2

15

1.75

156

25

132

2.10

14.39

7.69

0.65

0.98

30

110

5

1.18

40

140 140

186 197

6.65 6.68

34.78 39.68

2.06 0.94

0.34 0.34

1.54 1.82

39 43

10 1

17 10

0.84 0.70

97 76

140

197

6.68

39.68

0.94

0.34

1.82

43

1

10

0.70

76

140

174

7.46

37.16

0.76

0.62

3.92

62

4

21

1.48

125

140 45 140 45 140

155 167 182 180 153

3.61 3.89 3.77 3.72 1.27

32.14 34.61 39.44 38.92 34.86

1.26 1.36 0.39 0.39 0.28

0.64 0.69 0.57 0.57 0.25

2.52 2.71 0.56 0.55 1.40

60 65 49 48 6

7 8 1 1 27

14 15 14 14 6

0.59 0.64 0.28 0.36 0.20

116 125 60 59 28

140

118

5.07

18.31

2.39

0.95

0.62

65

247

28

1.30

67

140 45

141 160

5.59 6.30

29.88 33.71

0.48 0.54

0.56 0.63

2.52 2.84

141 160

4 5

4 5

0.84 0.95

115 130

29 30

92 75

2.90 2.10

22.91 24.00

0.58 0.65

1.74 2.36

5.08 12.90

171 300

207 203

15 19

8.12 4.50

157 150

28 30

101 112

1.96 2.10

24.08 25.80

0.22 0.27

0.90 0.98

0.98 0.60

25 25

203 288

2 100

8.40 9.00

14 22

30 30 30 31 33

113 96 111 117 124

1.80 4.05 3.30 6.98 2.08

25.80 23.31 22.20 22.01 28.55

0.60 1.17 1.80 0.48 0.36

1.14 1.13 1.35 0.61 1.02

0.90 3.61 2.70 0.74 0.36

35 127 96 61 42

267 210 273 224 354

150 12 100 9 3

8.10 8.10 8.10 8.37 1.98

40 141 100 68 44

14 29 58

54 106 208

0.98 2.90 6.26

12.29 23.64 47.15

0.13 0.84 1.10

0.06 0.70 1.45

0.20 2.55 5.05

16 99 178

1 125 354

1 11 20

0.40 17 8.10 88 16.20 139 (Continued)

436


Table 1 Description


Weight (g)

kcal Protein (g)

Wheat flakes without 1 CP 30 110 raisins Wheat, puffed 1.25 CP 15 55 Wheat, shredded, 2 biscuits 46 156 unsweetened Baby food cereals (fortified nutrients) Barley, instant, dry 6.25 TB 15 55 Oatmeal, instant, dry 6 TB 15 60 Rice, instant, dry 6 TB 15 61 Breads and other related products (enriched nutrients) Bagel, egg, plain or with 1 each 55 153 seasoning Bagel, oat bran, plain or 1 each 55 141 with seasoning Bagel, rye, plain or with 1 each 55 157 seasoning Bagel, white flour, plain or 1 each 55 151 with seasoning Bagel, whole wheat, plain 1 each 55 163 or with seasoning Biscuit, baking powder or 1 each 55 222 buttermilk Boston brown bread 2 slices 50 98 Bread crumbs, plain 1/4 CP 30 119 Bread or rolls, French 2 slices 50 136 Bread or rolls, rye 2 slices 50 130 Bread or rolls, sourdough 2 slices 50 136 Bread or rolls, white 2 slices 50 134 Bread or rolls, whole wheat 2 slices 50 123 Bread, barley 2 slices 50 142 Bread, bran 2 slices 50 129 Bread, egg 2 slices 50 147 Bread, English muffin 2 slices 55 130 Bread, focaccia 1 slice 50 151 Bread, gluten-free 2 slices 50 110 Bread, hovis 2 slices 50 131 Bread, Irish soda 2 slices 50 138 Bread, Italian 2 slices 50 136 Bread, oatmeal 2 slices 50 135 Bread, pumpernickel 2 slices 50 130 Bread, raisin 2 slices 50 137 Bread, wheat, reduced 2 slices 50 99 calorie (light, high fiber) Breadsticks, bread type 2 each 55 149 Breadsticks, cracker type 1.5 each 15 68 Crepe, plain 2 each 110 224 Croissant, plain 1 each 55 250 Croutons, plain 2/3 CP 7 28 Eggroll wrapper 1 each 32 92 English muffin, oat bran 1 each 55 120 English muffin, rye 1 each 55 130 English muffin, white 1 each 55 129 English muffin, whole 1 each 55 112 wheat Pancake, white flour, plain, 3 each 110 213 from mix – no fat added Pancake, white flour, plain, 3 each 110 291 from recipe


Fat (g)

Ash (g)



P (mg)

3.24

23.79

0.93

1.01

2.10

104

222

55

8.10

95

2.44 4.78

11.46 38.13

0.32 0.55

0.23 0.74

1.41 5.29

55 196

1 3

4 20

0.66 1.44

50 168

1.67 2.04 1.31

11.30 10.38 11.99

0.51 1.17 0.63

0.51 0.48 0.38

1.23 0.99 0.15

59 71 115

7 5 3

90 90 90

6.75 6.75 6.75

75 75 50

5.83

29.15

1.16

0.88

1.27

37

278

7

2.19

46

4.52

30.88

0.74

1.19

1.98

81

321

9

1.86

86

4.14

33.95

0.50

0.79

2.52

79

176

8

1.62

60

5.78

29.37

0.88

0.99

1.27

56

294

41

1.96

53

4.91

34.84

0.55

0.83

2.49

94

177

10

1.90

83

3.58

24.21

12.36 1.57

0.78

88

245

120

1.52

83

2.60 3.75 4.40 4.25 4.40 4.10 4.85 3.91 4.40 4.38 4.26 3.39 5.05 4.80 3.16 4.40 4.20 4.25 3.95 4.55

21.65 21.75 25.00 24.15 25.00 24.75 23.05 28.11 24.07 25.68 25.43 23.49 20.37 24.15 26.13 25.00 24.25 24.15 26.15 21.80

0.75 1.62 1.75 1.65 1.75 1.80 2.10 1.49 1.92 2.77 1.00 4.63 1.48 1.45 2.59 1.75 2.20 1.65 2.20 1.15

1.40 1.02 0.95 1.25 0.95 0.95 1.15 0.78 1.03 0.52 1.22 1.27 0.96 1.05 0.88 0.95 1.00 1.25 0.90 0.95

2.35 0.72 1.35 2.90 1.35 1.15 3.45 2.91 2.07 0.88 1.49 0.96 2.22 1.04 1.03 1.35 2.00 2.90 2.15 6.00

159 66 55 83 55 60 126 83 86 70 72 45 98 127 129 55 71 83 114 61

316 259 292 330 292 269 264 176 267 91 257 419 205 277 186 292 300 330 195 256

35 68 39 37 39 54 36 19 47 27 96 6 12 45 36 39 33 37 33 40

1.05 1.84 1.47 1.42 1.47 1.52 1.65 1.34 1.57 1.52 1.38 1.54 1.40 1.73 1.22 1.47 1.35 1.42 1.45 1.48

56 44 52 63 52 47 115 66 74 60 74 41 91 61 54 52 63 63 55 51

4.84 1.46 8.10 4.43 0.83 2.83 4.78 4.02 4.24 4.84

27.50 10.83 30.27 25.78 5.15 18.05 24.64 25.72 25.30 22.22

1.93 2.08 7.46 14.44 0.46 0.64 1.76 1.25 0.99 1.16

1.05 0.35 1.79 0.48 0.18 0.19 0.96 0.83 1.21 1.54

1.49 0.55 0.85 0.86 0.36 0.62 2.53 2.45 1.49 3.69

61 21 183 72 9 29 120 99 72 116

321 104 344 73 49 21 158 158 255 350

43 2 136 30 5 5 53 50 96 146

1.62 0.61 1.74 1.51 0.29 1.10 1.92 1.60 1.38 1.35

57 20 150 63 8 31 123 72 73 155

5.72

40.38

2.75

1.80

1.54

88

689

33

2.21

75

8.14

38.93

11.47 4.76

1.09

155

900

347

2.59

224

(Continued)


437


Pancake, whole wheat, 3 each plain Pita, white 1 each Pita, whole wheat 1 each Popover 1 each Rolls, crescent 2 each (refrigerated dough) Rolls, hamburger, white 1 each Rolls, hamburger, whole 1 each wheat Rolls, hard 1 each Rolls, hot dog, white 1 each Rolls, hot dog, whole 1 each wheat Rolls, kaiser 1 each Rolls, submarine or hoagie 1/2 each Scone 1 each Taco shell 2 each Tortilla, corn 2 each Tortilla, white flour 1 each Tortilla, whole wheat flour 1 each Waffles, bran, plain 1 each Waffles, white flour, plain, 1 each from recipe Waffles, white flour, plain, 1 each frozen Wonton wrapper 1 each Crackers (enriched nutrients) Butter crackers 10 each Cheese crackers 10 each Cheese-filled sandwich 4 each crackers Cheese-filled sandwich 4 each crackers, whole wheat Matzo or matzoh crackers, 1 each egg Matzo or matzoh crackers, 1 each plain Matzo or matzoh crackers, 1 each whole wheat Melba toast 3 each Peanut butter-filled 4 each sandwich crackers Rye wafer, plain 3 each Saltine or soda crackers 10 each Whole wheat crackers 10 each Zwieback 2 each Cookies (enriched nutrients) Animal cracker 12 each Biscotti, with nuts 1 each Brownie, butterscotch, 1 each without nuts Brownie, chocolate, 1 each without nuts Cookies and bars, 3 each arrowroot Cookies and bars, 3 each butterscotch chip

Weight (g)

kcal Protein (g)


Fat (g)

110

269

9.01

35.51

50 50 55 50

138 133 107 173

4.55 4.90 4.90 3.35

50 50

143 123

50 50 50

Ash (g)



P (mg)

11.46 5.08

4.59

276

877

347

2.23

306

27.85 27.50 15.77 23.75

0.60 1.30 2.41 7.35

0.95 1.00 0.95 1.65

1.10 3.70 0.49 0.80

60 85 93 79

268 266 208 601

43 8 53 10

0.70 1.53 1.04 1.30

49 90 79 193

4.25 4.85

25.15 23.05

2.55 2.10

1.00 1.15

1.35 3.45

71 126

280 264

70 36

1.59 1.65

44 115

147 143 123

4.95 4.25 4.85

26.35 25.15 23.05

2.15 2.55 2.10

1.00 1.00 1.15

1.15 1.35 3.45

54 71 126

272 280 264

48 70 36

1.64 1.59 1.65

50 44 115

50 50 55 30 55 55 55 85 85

147 137 215 140 122 179 107 244 286

4.95 4.40 4.43 2.16 3.14 4.79 3.99 7.46 6.72

26.35 25.95 29.89 18.72 25.63 30.58 21.15 36.73 29.39

2.15 1.50 8.95 6.78 1.38 3.91 1.45 9.28 15.82

1.00 1.00 1.78 0.54 0.66 0.99 1.05 4.25 2.66

1.15 1.50 0.99 2.25 2.86 1.82 3.56 5.12 0.87

54 57 117 54 85 72 118 256 135

272 305 357 110 89 263 225 851 444

48 38 98 48 96 21 11 220 216

1.64 1.27 1.56 0.75 0.77 1.82 1.13 2.59 1.92

50 53 90 74 173 68 101 257 160

85

226

5.52

34.60

7.00

2.09

1.17

69

672

71

2.18

84

8

23

0.71

4.51

0.16

0.05

0.15

7

5

1

0.27

8

30 30 30

152 151 143

2.09 3.03 2.79

16.95 17.46 18.51

8.45 7.59 6.33

0.75 0.99 1.20

0.55 0.72 0.56

22 44 129

254 299 420

3 45 77

0.94 1.43 0.72

22 65 122

30

149

2.94

17.46

7.50

1.14

0.92

92

274

61

0.79

115

30

112

3.08

23.13

0.59

0.21

0.81

52

6

8

1.29

41

30

119

3.00

25.11

0.42

0.18

0.90

34

1

4

0.95

27

30

105

3.93

23.67

0.45

0.48

3.54

95

1

7

1.40

92

15 30

59 146

1.89 3.33

11.49 17.61

0.48 7.17

0.45 0.96

0.94 0.84

30 67

124 283

14 29

0.56 0.91

29 72

30 30 30 15

100 130 133 68

2.88 2.76 2.64 1.87

24.12 21.45 20.58 10.89

0.27 3.54 5.16 1.88

1.23 0.99 0.81 0.15

6.87 0.90 3.15 0.17

148 38 89 8

238 391 198 19

12 36 15 1

1.78 1.62 0.92 0.30

100 32 88 7

30 30 40

129 130 170

1.94 2.99 1.57

21.31 14.47 28.34

4.36 7.10 5.66

0.59 0.49 0.90

1.17 1.16 0.25

43 76 92

122 51 179

26 25 49

0.84 0.86 0.95

42 52 33

40

188

2.16

22.68

10.83 0.30

1.17

71

10

9

0.78

46

30

129

1.94

21.31

4.36

0.59

1.17

43

122

26

0.84

42

30

157

1.67

19.20

8.36

0.55

0.34

50

180

12

0.57

24

(Continued)

438


Table 1 Description


Weight (g)

kcal Protein (g)

Cookies and bars, 3 each 30 142 chocolate chip Cookies and bars, 7 each 30 130 chocolate, wafer Cookies and bars, date bar 1 each 30 98 Cookies and bars, fig bar 2 each 30 104 Cookies and bars, fortune 4 each 30 100 cookie Cookies and bars, 3 each 30 144 gingerbread Cookies and bars, 3 each 30 159 gingersnap Cookies and bars, graham 4 squares 30 118 cracker, plain Cookies and bars, granola 3 each 30 145 Cookies and bars, lemon 2 each 30 131 bar Cookies and bars, 1 each 30 108 macaroon (coconut) Cookies and bars, 3 each 30 127 molasses Cookies and bars, oatmeal 3 each 30 175 Cookies and bars, peanut 3 each 30 156 butter Cookies and bars, 2 each 30 120 pfeffernuesse Cookies and bars, pizzelle 2 each 30 183 Cookies and bars, raisin 3 each 30 134 Cookies and bars, Rice 2 each 30 112 Krispie bar Cookies and bars, rosette 2 each 30 140 Cookies and bars, 3 each 30 179 shortbread Cookies and bars, sugar 3 each 30 161 Cookies and bars, sugar 4 each 30 147 wafer with creme filling Cookies and bars, vanilla 3 each 30 142 sandwich Cookies and bars, vanilla 7 each 30 139 wafer Krumkake 2 each 30 158 Cakes, pastries, and other desserts (enriched nutrients) Angel food cake, white or 1 piece 55 164 flavored, not frosted or glazed Anisette (mandelbrodt 3 slices 30 131 toast), plain Cake, apple, not frosted or 1 piece 80 269 glazed Cake, banana, not frosted 1 piece 80 274 or glazed Cake, butter, not frosted or 1 piece 80 289 glazed Cake, carrot, without nuts, 1 piece 80 298 not frosted or glazed Cake, chiffon, not frosted 1 piece 55 184 or glazed Cake, chocolate, not 1 piece 80 279 frosted or glazed


Fat (g)

Ash (g)



P (mg)

1.67

19.16

6.67

0.34

0.54

30

107

7

0.78

21

1.98

21.72

4.26

0.60

1.02

63

174

9

1.20

40

1.01 1.11 1.58

16.84 21.27 22.50

3.30 2.19 0.95

0.39 0.48 0.41

1.05 1.38 0.45

87 62 21

62 105 55

9 19 29

0.49 0.87 0.50

21 19 24

1.90

22.28

5.43

0.57

0.47

139

61

34

1.18

28

1.53

23.09

6.95

0.36

0.40

102

62

20

0.98

20

1.09

22.43

2.81

0.57

0.29

51

167

7

0.62

12

2.50 1.50

18.40 18.55

7.61 5.80

0.38 0.40

1.25 0.20

92 20

16 115

15 14

0.78 0.42

58 22

1.16

17.35

4.10

0.29

0.52

60

65

2

0.23

14

1.51

23.49

3.15

0.70

0.42

157

143

22

1.14

19

2.50 2.82

26.30 17.93

6.85 8.62

0.60 0.61

1.02 0.60

76 76

114 154

29 18

0.99 0.64

57 42

2.05

20.53

3.37

0.50

0.50

136

90

22

1.17

26

1.64 1.35 0.96

7.79 20.36 22.76

16.35 0.50 5.69 0.32 2.26 0.41

0.22 0.57 0.13

17 87 15

159 43 138

5 11 2

0.45 0.61 0.63

20 22 15

1.25 2.11

5.96 18.69

12.50 0.38 10.76 0.35

0.17 0.52

13 26

122 124

4 7

0.35 0.90

15 24

1.64 1.07

17.93 20.38

9.10 7.40

0.21 0.39

0.36 0.97

39 40

57 93

3 8

0.65 0.50

18 22

1.67

19.16

6.67

0.34

0.54

30

107

7

0.78

21

1.88

21.00

5.63

0.44

0.79

40

140

5

0.93

25

2.49

20.87

7.23

0.31

0.41

27

51

8

0.80

30

3.96

36.58

0.10

0.47

0.17

110

93

4

0.78

13

2.31

17.70

5.69

0.33

0.41

26

37

22

0.80

33

2.73

34.89

13.41 0.55

1.48

66

156

12

0.94

34

4.32

47.54

7.54

1.14

0.68

78

191

94

1.38

84

3.58

40.95

12.55 1.60

0.30

48

478

57

0.83

197

3.27

35.82

16.11 0.70

1.27

80

192

17

1.14

43

3.73

25.46

7.48

1.06

0.35

53

219

52

0.89

60

3.48

41.84

11.99 0.79

1.46

82

160

32

1.39

67

(Continued)


439


Cake, fruitcake 1 piece Cake, German chocolate, 1 piece not frosted or glazed Cake, gingerbread, not 1 piece frosted or glazed Cake, jelly roll, yellow cake 1 piece Cake, oatmeal, not frosted 1 piece or glazed Cake, pound, chocolate, 1 piece not frosted or glazed Cake, pound, white, not 1 piece frosted or glazed Cake, spice, not frosted or 1 piece glazed Cake, sponge, white or 1 piece yellow, not frosted or glazed Cake, white, not frosted or 1 piece glazed Cake, yellow, not frosted or 1 piece glazed Cream puff shell 2 each Cupcake, chocolate, 1.5 each commercial packaged Dumplings with fruit, apple 1/2 each Fritter, apple 1 CP Phyllo pastry 1 1/3 sheet Pie crust or shell, 1/8 pie chocolate cookie type Pie crust or shell, egg yolk 1/8 pie pastry, single layer Pie crust or shell, graham 1/8 pie cracker, regular Pie crust or shell, puff 1/2 shell pastry, frozen Pie crust or shell, regular 1/8 pie pastry, single layer, frozen Pie crust or shell, regular 1/8 pie pastry, single layer, prepared from mix Pie crust or shell, regular 1/8 pie pastry, single layer, prepared from recipe Pie crust or shell, vanilla 1/8 pie wafer type Pies, apple, double pastry 1/8 pie crust Pies, chocolate cream 1/8 pie Pies, pudding filling, 1/8 pie chocolate Pies, pudding filling, vanilla 1/8 pie Pies, pumpkin 1/8 pie Shortcake, biscuit type 2 each Shortcake, sponge type 2 each Granola and cereal bars (fortified nutrients) Breakfast bar 1.5 each Cereal bar 1 each

Weight (g)

kcal Protein (g)


Fat (g)

125 80

404 279

5.46 3.48

63.98 41.84

80

263

3.01

80 80

195 254

80

Ash (g)



P (mg)

15.25 1.63 11.99 0.79

2.61 1.46

347 82

244 160

85 32

2.61 1.39

102 67

42.46

9.12

1.57

0.77

428

264

64

2.52

42

4.78 3.18

37.20 43.44

2.98 7.90

1.02 0.90

0.32 1.06

70 103

174 270

68 27

0.92 1.27

83 59

385

4.98

42.02

21.75 0.66

0.77

66

76

40

1.54

77

80

374

4.95

38.31

22.20 0.62

0.66

52

72

40

1.42

70

80

274

4.32

47.54

7.54

1.14

0.68

78

191

94

1.38

84

55

158

3.80

30.38

2.33

0.35

0.31

73

27

13

0.81

49

80

288

4.33

43.40

11.12 1.64

0.58

78

343

105

1.16

74

80

274

4.32

47.54

7.54

1.14

0.68

78

191

94

1.38

84

80 80

293 283

7.24 3.23

18.27 48.58

21.06 0.93 9.58 1.58

0.62 1.94

80 92

245 470

29 14

1.51 1.62

94 58

125 55 28.35 29.17

304 209 84 153

2.44 4.83 2.19 1.44

44.95 18.25 17.93 15.81

13.23 13.00 0.21 9.76

0.41 1.93 0.35 0.44

2.05 0.70 0.59 0.74

79 82 23 46

69 493 98 127

10 80 3 7

1.18 1.25 0.99 0.88

29 86 23 29

29.77

171

2.05

15.85

10.82 0.52

0.45

22

155

6

0.84

28

30.51

161

0.59

17.12

10.33 0.31

0.16

28

91

4

0.35

7

20

113

1.50

9.13

7.69

0.20

0.20

18

50

4

0.93

19

16.38

85

1.10

8.12

5.38

0.32

0.29

11

106

2

0.50

11

20.8

104

1.40

10.32

6.33

0.45

0.37

14

152

2

0.63

15

28.12

154

1.68

12.40

10.71 0.47

0.44

17

154

3

0.76

18

36.97

190

1.92

20.82

11.49 0.58

0.78

43

208

7

0.92

27

125

302

2.66

41.35

14.30 0.78

1.78

92

206

8

1.28

33

125 85

341 194

6.01 3.35

40.45 22.43

18.39 1.38 10.22 1.28

1.76 0.63

216 118

181 310

112 65

1.49 0.89

160 165

85 125 80 55

195 255 254 158

3.09 5.54 4.50 3.80

22.99 31.79 35.68 30.38

10.08 12.09 10.46 2.33

1.20 1.60 2.06 0.35

0.38 1.78 0.95 0.31

94 233 78 73

312 286 372 27

65 119 151 13

0.68 1.49 1.86 0.81

139 122 105 49

40 40

156 153

2.16 2.15

24.79 29.39

5.60 3.24

0.42 0.39

1.36 1.08

47 49

61 65

555 13

5.00 1.95

278 46

(Continued)

440


Table 1 Description


Snacks and chips (enriched nutrients) Bagel chips 0.5 CP Cheese balls, puffs, or 1 CP twists Corn chips 1 CP Corn nuts 0.35 CP Popcorn, commercially 2.75 CP popped (prepopped), not ‘buttered’ Popcorn, hot-air popped 3.75 CP Popcorn, microwave 3.33 CP popped from package, with salt Popcorn, popped in fat 2.75 CP Pretzels, hard type 1.33 CP Pretzels, soft type 1/4 medium Rice cake 3 each Taco or tortilla chips 1 CP Wheat nuts 0.35 CP Legumes Adzuki beans, cooked 0.4 CP Bayo beans, cooked 0.5 CP Black beans, cooked 0.5 CP Broad beans, cooked 0.5 CP Brown beans, cooked 0.5 CP Cowpeas, cooked 0.5 CP Fava beans 0.5 CP Garbanzo beans, cooked 0.55 CP Kidney beans, cooked 0.5 CP Lentils, cooked 0.45 CP Lima beans, cooked 0.5 CP Mung beans, cooked 0.45 CP Navy beans, cooked 0.55 CP Northern beans, cooked 0.5 CP Pigeon peas, cooked 0.6 CP Pinto beans, cooked 0.5 CP Soybeans, cooked 0.5 CP Soybeans, dry roasted, 0.3 CP salted Soybeans, oil roasted, 0.3 CP salted Split peas, yellow or green, 0.45 CP cooked Tepary beans 0.35 CP Meat substitutes Miso 1 TB Tempeh 0.5 CP Tofu (soybean curd), extra 0.35 CP firm cubes Tofu (soybean curd), firm 0.35 CP cubes Tofu (soybean curd), silken 1 slice (100 thick) Tofu (soybean curd), soft 0.35 CP cubes Alcoholic beverages Beer, light, low calorie 8 FO Beer, low alcohol 8 FO

Weight (g)

kcal Protein (g)


Fat (g)

30 30

132 165

2.91 1.76

21.29 15.87

30 30 30

164 132 151

1.65 2.55 2.64

30 30

115 151

30 30 30 30 30 30

Ash (g)



P (mg)

3.87 0.59 10.58 0.98

1.12 1.46

50 50

155 308

10 17

1.40 0.83

35 27

15.15 21.99 17.16

10.82 0.56 4.23 0.81 8.43 1.08

1.44 2.07 3.33

32 83 66

170 165 265

1 3 2

0.81 0.50 0.59

16 83 66

3.60 2.18

23.37 14.17

1.26 0.54 10.00 0.95

4.53 2.75

90 55

1 243

3 2

0.80 0.49

90 55

166 114 109 116 152 214

2.25 2.73 3.10 2.46 2.10 4.24

14.61 23.76 22.89 24.45 19.04 5.30

11.43 1.05 0.29 0.84 7.40 20.11

0.34 1.47 1.58 0.74 0.65 1.03

2.83 0.96 0.81 1.26 1.78 1.06

56 44 32 87 49 78

1 515 561 98 181 201

2 11 5 3 11 4

0.50 1.30 1.40 0.45 1.00 0.75

56 34 32 108 26 94

90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 30

115 35 128 128 125 104 90 148 114 104 104 125 128 125 106 123 156 117

6.77 2.70 7.83 7.83 8.76 6.96 5.46 7.97 7.80 8.12 7.02 8.76 7.83 8.76 7.51 7.39 14.98 12.01

22.29 9.06 23.68 23.68 22.59 18.69 16.92 24.67 20.53 18.13 18.80 22.59 23.68 22.59 19.00 23.09 8.93 7.86

0.09 0.17 0.51 0.51 0.32 0.48 0.31 2.33 0.45 0.34 0.34 0.32 0.51 0.32 0.35 0.47 8.07 5.21

1.20 1.33 1.11 1.11 1.58 0.85 1.17 0.83 0.98 0.75 1.04 1.58 1.11 1.58 0.61 1.22 1.72 1.84

6.57 3.02 5.76 5.76 5.67 5.85 5.22 6.84 5.76 7.11 6.30 5.67 5.76 5.67 7.47 7.74 5.40 3.88

479 147 331 331 505 250 367 262 363 332 457 505 331 505 326 421 464 449

7 1 1 1 5 4 48 6 2 2 2 5 1 5 2 2 1 162

25 25 63 63 81 22 20 44 25 17 15 81 63 81 13 43 92 67

1.80 0.70 2.23 2.23 3.33 2.26 1.22 2.60 2.65 3.00 2.15 3.33 2.23 3.33 1.16 2.35 4.63 3.13

151 84 141 141 102 140 57 151 128 162 100 102 141 102 89 144 221 170

30

141

10.57

10.07

7.62

1.16

5.31

441

49

41

1.17

109

90

106

7.51

19.00

0.35

0.61

7.47

326

2

13

1.16

89

90

58

4.23

10.77

0.14

0.80

4.59

212

6

35

1.03

5

17 85 85

35 164 82

2.01 15.76 8.85

4.75 7.98 1.67

1.03 9.18 5.28

2.16 1.38 0.70

0.92 2.87 0.34

28 350 113

620 8 9

11 94 88

0.47 2.30 1.45

26 226 138

85

78

8.41

2.31

4.74

0.90

0.26

154

10

142

1.43

118

85

53

5.87

2.04

2.30

0.51

0.09

165

31

27

0.88

77

85

52

5.57

1.53

3.14

0.60

0.17

102

7

94

0.94

78

236 240

66 74

0.47 0.60

3.07 10.56

0.00 0.00

0.24 0.24

0.00 1.20

42 12

7 7

12 12

0.09 0.00

28 26

(Continued)


441


Beer, regular 8 FO Scotch, plain 1.5 FO Whiskey, plain 1.5 FO Ingredients used in grain products Almonds, raw 0.2 CP Arrowroot flour 0.2 CP Beer nuts, peanuts 0.2 CP Cashews, oil roasted 0.2 CP Coconut, dried, 0.2 CP unsweetened Filberts, raw 0.2 CP Flax seeds 0.25 CP Flour, peanut, defatted 0.5 CP Flour, peanut, low fat 0.5 CP Macadamia nuts, raw 0.2 CP Peanut butter, with salt 2 TB Peanuts, raw 0.2 CP Peanuts, roasted, dry 0.2 CP roasted, salted Peanuts, roasted, oil 0.2 CP roasted, salted Pecans, raw 0.3 CP Poppy seeds 0.2 CP Sesame seeds, kernels 0.2 CP (hulled), dried Sesame seeds, kernels 0.2 CP (hulled), toasted Sunflower seeds, dry 0.2 CP roasted, salted Sunflower seeds, oil 0.2 CP roasted, salted Sunflower seeds, raw 0.2 CP Tapioca, dry 1 TB Walnuts, raw 0.25 CP

Weight (g)

kcal Protein (g)


Fat (g)

Ash (g)



P (mg)

237.6 41.7 41.7

97 96 96

0.71 0.00 0.00

8.79 0.00 0.00

0.00 0.00 0.00

0.24 0.00 0.00

1.19 0.00 0.00

59 1 1

12 0 0

12 0 0

0.07 0.02 0.02

29 2 2

30 30 30 30 15

173 107 180 173 99

6.38 0.09 7.41 4.85 1.03

5.92 26.45 7.44 8.56 3.66

15.19 0.03 14.92 14.46 9.68

0.93 0.02 1.20 0.96 0.29

3.54 1.02 1.94 1.14 2.45

218 3 192 159 81

0 1 85 5 6

74 12 25 12 4

1.29 0.10 0.52 1.23 0.50

142 2 145 128 31

30 30 30 30 30 32.25 30 30

188 148 98 128 215 191 174 174

4.49 5.85 15.66 10.14 2.37 8.13 7.91 7.91

5.01 10.28 10.41 9.38 4.15 6.22 5.68 5.68

18.23 10.20 0.17 6.57 22.73 16.46 14.79 14.79

0.69 1.05 1.43 1.57 0.34 1.05 1.04 1.04

2.91 8.37 4.74 4.74 2.58 1.90 2.07 2.76

204 204 387 407 110 216 205 205

0 10 54 0 2 151 2 244

34 60 42 39 26 12 26 26

1.41 1.87 0.63 1.42 1.11 0.59 0.55 0.55

87 149 228 152 56 119 155 155

30

174

7.91

5.68

14.79 1.04

2.76

205

130

26

0.55

155

30 30 30

207 160 176

2.75 5.41 7.91

4.16 7.11 2.82

21.59 0.45 13.41 2.03 16.43 1.39

2.88 3.00 3.48

123 210 122

0 6 12

21 435 39

0.76 2.82 2.34

83 255 233

30

170

5.09

7.81

14.40 1.20

5.07

122

12

39

2.33

232

30

175

5.80

7.22

14.94 1.68

2.70

255

234

21

1.14

347

30

185

6.41

4.42

17.24 1.16

2.04

145

181

17

2.01

342

30 10 30

171 36 196

6.83 0.02 4.57

5.63 8.87 4.11

14.87 1.06 0.00 0.01 19.56 0.53

3.15 0.09 2.01

207 1 132

1 0 1

35 2 29

2.03 0.16 0.87

212 1 104

Table 2 The composition of grains and grain-based foods with respect to zinc (Zn), copper (Cu), magnesium (Mg), vitamin A, thiamin, riboflavin, niacin, folate, pantothenic acid, and vitamin B6, based on the specified serving portions Description

Serving size

Weight Zn Cu Mg Vit. A (g) (mg) (mg) (mg) (IU)

Grains, flours, and cooked cereals (enriched or fortified nutrients) Amaranth, dry 0.22 CP 45 1.43 0.35 120 Barley bran flour 0.30 CP 45 4.05 0.81 122 Barley flour 0.30 CP 45 0.90 0.15 43 Barley malt flour 0.28 CP 45 0.93 0.12 44 Barley, cooked 0.89 CP 140 1.04 0.21 39 Barley, dry 0.23 CP 45 0.96 0.19 36 Bread flour 0.33 CP 45 0.32 0.06 10 Buckwheat flour 0.38 CP 45 1.40 0.23 113 Buckwheat groats, dry 0.24 CP 40 0.97 0.25 88 Bulgur, cooked 0.77 CP 140 0.64 0.11 55 Bulgur, dry 0.32 CP 45 0.87 0.15 74 Cake flour 0.33 CP 45 0.28 0.06 7 Chickpea flour 0.50 CP 45 1.26 0.41 75 Corn bran, dry 3 TB 15 0.23 0.04 10

4 0 0 17 0 0 0 4 3 2 3 0 0 11

Vit. A Thiamin (mg RE) (mg)

Riboflavin Niacin Folate Pantothenic Vit. B6 (mg) (mg) (mcg) acid (mg) (mg)

0 0 0 2 0 0 0 0 0 0 0 0 0 1

0.095 0.050 0.050 0.140 0.056 0.050 0.221 0.086 0.108 0.042 0.054 0.194 0.050 0.015

0.036 0.032 0.167 0.140 0.098 0.086 0.351 0.189 0.088 0.070 0.104 0.401 0.221 0.002

0.581 2.070 2.822 2.538 2.240 2.070 2.655 2.768 2.056 1.694 2.300 3.056 0.792 0.411

22 7 4 17 11 10 49 24 17 9 12 49 197 1

0.473 0.144 0.063 0.261 0.140 0.126 0.198 0.198 0.492 0.350 0.468 0.207 0.275 0.096

0.099 0.059 0.180 0.297 0.126 0.117 0.018 0.261 0.140 0.112 0.153 0.014 0.221 0.023 (Continued)

442


Table 2

(Continued)

Description

Serving size




Corn flour Corn grits, white, cooked Corn grits, white, dry Corn grits, yellow, dry Cornmeal, cooked Cornmeal, masa harina, dry Cornmeal, self-rising, dry Cornmeal, white, dry Cornmeal, yellow, dry Cornstarch Couscous, cooked Couscous, dry Cracked wheat, cooked Farina (creamed wheat), instant cooking, cooked Farina (creamed wheat), quick cooking, cooked Farina (creamed wheat), regular cooking, cooked Farina (creamed wheat), dry Hominy, canned Kamut flour Kasha, cooked Kasha, dry Millet, cooked Millet, dry Oat bran, cooked Oat bran, dry Oatmeal (fortified), flavored, dry Oatmeal (fortified), plain, dry Oatmeal, dry Oatmeal, instant cooking, flavored, cooked Oatmeal, instant cooking, plain, cooked Oatmeal, regular cooking, cooked Potato flour Quinoa, cooked Quinoa, dry Rice (creamed rice), dry Rice bran, dry Rice flour, brown Rice flour, white Rolled wheat, cooked Rolled wheat, dry Rye flour, medium Rye, whole grain, dry Self-rising flour Sorghum Soy flour, defatted Soy flour, full fat Soy flour, low fat Spelt Teff, dry Triticale, whole grain Wheat bran (unprocessed) Wheat, cracked whole wheat Wheat, germ

0.36 CP 1 CP 0.26 CP 0.26 CP 1 CP 0.39 CP 0.33 CP 0.33 CP 0.33 CP 1.25 TB 0.89 CP 0.26 CP 1 CP 1 CP

45 242 40 40 240 45 45 45 45 10 140 45 242 241

0.80 0.17 0.16 0.16 0.26 0.80 0.31 0.32 0.32 0.01 0.39 0.37 1.55 0.31

99 0 0 86 76 99 91 0 96 0 1 1 4 0

10 0 0 9 8 10 9 0 10 0 0 0 0 0

0.644 0.048 0.058 0.052 0.048 0.644 0.063 0.063 0.063 0.000 0.070 0.072 0.242 0.024

0.338 0.024 0.018 0.016 0.024 0.338 0.022 0.022 0.022 0.000 0.042 0.036 0.121 0.024

4.428 0.484 0.540 0.480 0.480 4.428 0.450 0.450 0.450 0.000 1.666 1.571 3.340 0.241

1 CP

239

0.31 0.05 12

0

0

0.024

0.024

1 CP

251

0.30 0.08 10

1

0

0.025

0.23 CP 1 CP 0.25 CP 1 CP 0.24 CP 0.58 CP 0.23 CP 1 CP 0.43 CP 0.49 CP

40 165 45 168 40 140 45 219 40 55

0.35 1.73 1.32 1.24 0.97 0.76 0.76 1.16 1.24 1.08

1 69 4 4 3 19 19 1 1 1650

0 7 0 0 0 2 2 0 0 493

0.49 CP 0.49 CP 1 CP

40 40 234

1.23 0.14 59 1.23 0.14 59 0.84 0.09 37

1428 1 1273

1 CP

234

1.08 0.12 53

1 CP

234

0.28 CP 0.89 CP 0.26 CP 0.22 CP 2 TB 0.28 CP 0.28 CP 1 CP 0.43 CP 0.44 CP 0.27 CP 0.36 CP 0.24 CP 0.51 CP 0.51 CP 0.51 CP 0.38 CP 0.23 CP 0.34 CP 0.25 CP 0.33 CP 2 TB

45 140 45 40 15 45 45 242 40 45 45 45 45 45 45 45 45 45 45 15 45 15

0.08 0.02 0.03 0.03 0.02 0.08 0.04 0.04 0.04 0.01 0.13 0.11 0.19 0.07

0.297 0.194 0.192 0.192 0.120 0.297 0.135 0.140 0.140 0.000 0.588 0.558 0.532 0.145

0.167 0.048 0.060 0.060 0.096 0.167 0.108 0.117 0.117 0.000 0.056 0.050 0.169 0.024

0.239 5

0.167

0.024

0.025

0.251 5

0.176

0.025

0.024 0.000 0.203 0.118 0.088 0.182 0.189 0.438 0.468 0.490

0.040 0.017 0.099 0.134 0.108 0.126 0.130 0.088 0.088 0.561

0.280 0.050 0.950 2.638 2.056 2.14 2.124 0.350 0.372 6.600

10 2 20 22 17 38 38 19 21 132

0.208 0.248 0.455 0.638 0.492 0.378 0.383 0.548 0.596 0.237

0.044 0.000 0.153 0.185 0.140 0.168 0.171 0.066 0.064 0.660

428 0 381

0.428 0.292 0.374

0.484 0.056 0.421

5.716 114 0.312 13 5.101 102

0.500 0.496 0.187

0.572 0.048 0.515

1258

377

0.374

0.421

5.031 101

0.445

0.515

1.17 0.14 57

1

0

0.281

0.047

0.304 12

0.468

0.047

0.24 1.25 1.49 0.45 0.91 1.10 0.36 1.07 1.06 0.90 1.68 0.30 0.63 1.11 1.76 0.53 1.67 1.68 1.20 1.09 1.32 2.50

9 3 4 0 0 0 0 3 3 5 5 0 15 3 54 17 4 19 5 2 4 15

1 0 0 0 0 0 0 0 0 0 0 0 2 0 5 2 0 2 0 0 0 2

0.104 0.070 0.090 0.168 0.413 0.198 0.063 0.169 0.160 0.131 0.144 0.329 0.108 0.315 0.261 0.171 0.140 0.248 0.171 0.078 0.204 0.250

0.023 0.154 0.180 0.048 0.042 0.036 0.009 0.121 0.120 0.050 0.113 0.207 0.063 0.113 0.522 0.126 0.068 0.063 0.059 0.087 0.099 0.123

1.580 1.106 1.319 2.256 5.100 2.853 1.166 1.984 1.960 0.779 1.921 2.489 1.319 1.175 1.944 0.972 2.952 0.810 1.287 2.037 2.862 0.838

0.212 0.392 0.473 0.220 1.109 0.716 0.369 0.363 0.368 0.221 0.657 0.189 0.563 0.900 0.716 0.819 0.455 0.383 0.977 0.327 0.456 0.209

0.347 0.084 0.099 0.080 0.611 0.333 0.198 0.169 0.156 0.122 0.130 0.018 0.077 0.257 0.207 0.234 0.153 0.171 0.180 0.195 0.153 0.147

0.08 0.05 0.17 0.32 0.25 0.34 0.34 0.15 0.16 0.13

0.09 0.31 0.37 0.10 0.11 0.10 0.06 0.19 0.18 0.13 0.20 0.06 0.29 1.83 1.31 2.29 0.18 0.44 0.25 0.15 0.17 0.09

50 12 11 11 15 50 18 18 18 0 22 20 73 12

11 26 62 114 88 52 51 88 94 47

29 80 95 9 117 50 16 50 49 34 54 10 59 131 193 103 60 63 69 92 62 48

59 2 2 2 2 59 22 22 22 0 10 9 23 5

11 18 22 12 9 7 2 32 31 9 27 45 38 137 155 185 20 38 33 12 20 92

(Continued)


443



Wheat, hard red spring 0.23 CP 45 1.25 Wheat, hard red winter 0.23 CP 45 1.19 Wheat, hard white 0.23 CP 45 1.50 Wheat, soft red winter 0.27 CP 45 1.18 Wheat, soft, white 0.27 CP 45 1.56 Wheat, sprouted 0.42 CP 45 0.74 White flour, wheat, all0.36 CP 45 0.32 purpose (enriched) White flour, wheat, all0.36 CP 45 0.32 purpose (unenriched) Whole wheat flour, red wheat 0.38 CP 45 1.32 Pasta and rice (enriched nutrients) Chow mein noodles, crisp 0.55 CP 25 0.35 type Egg noodles, cooked 0.9 CP 140 0.87 Lo mein noodles, soft type, 0.8 CP 140 0.74 cooked Macaroni/spaghetti noodles, 1 CP 140 0.74 white, cooked Macaroni/spaghetti noodles, 1 CP 140 1.13 whole wheat, cooked Rice, brown, cooked 0.7 CP 140 0.88 Rice, brown, uncooked 0.25 CP 45 0.95 Rice, white, cooked 0.9 CP 140 0.69 Rice, white, uncooked 0.25 CP 45 0.68 Rice/cellophane noodles, 0.8 CP 140 0.35 cooked Spaetzle or spatzen, cooked 0.9 CP 140 0.39 Wild rice, cooked 0.85 CP 140 1.88 Wild rice, uncooked 0.3 CP 45 2.12 Cereal, ready-to-eat (fortified nutrients) Bran flakes without raisins 0.75 CP 29 3.77 Bran nuggets, unsweetened 0.33 CP 30 1.50 Corn flakes, unsweetened 1 CP 28 0.08 Corn nuggets, unsweetened 1 CP 30 3.75 Corn, puffed 1.33 CP 30 3.75 Oat flakes 0.75 CP 30 3.75 Oat rings, unsweetened 1 CP 30 3.75 Rice flakes 1 CP 31 0.90 Rice nuggets, unsweetened 1.25 CP 33 0.60 Rice, puffed 1 CP 14 0.15 Wheat and barley flakes 0.75 CP 29 1.20 Wheat and barley nuggets 0.5 CP 58 1.20 Wheat flakes without raisins 1 CP 30 0.71 Wheat, puffed 1.25 CP 15 0.46 Wheat, shredded, 2 biscuits 46 1.26 unsweetened Baby food cereals (fortified nutrients) Barley, instant, dry 6.25 TB 15 0.47 Oatmeal, instant, dry 6 TB 15 0.55 Rice, instant, dry 6 TB 15 0.23 Breads and other related products (enriched nutrients) Bagel, egg, plain or with 1 each 55 0.42 seasoning Bagel, oat bran, plain or with 1 each 55 0.47 seasoning Bagel, rye, plain or with 1 each 55 0.46 seasoning Bagel, white flour, plain or 1 each 55 0.48 with seasoning



0 0 0 0 0 30 0

0 0 0 0 0 3 0

0.227 0.172 0.174 0.177 0.185 0.104 0.351

0.049 0.052 0.049 0.043 0.048 0.072 0.221

2.568 2.459 1.972 2.160 2.145 1.390 2.655

19 17 17 18 18 17 49

0.421 0.429 0.429 0.383 0.383 0.428 0.198

0.151 0.135 0.166 0.122 0.170 0.122 0.018

0.06 10

0

0

0.054

0.018

0.563 12

0.198

0.018

0.17 62

4

0

0.203

0.099

2.862 20

0.455

0.153

0.04 13

0

0

0.145

0.105

1.488 23

0.133

0.028

0.13 27 0.14 25

69 10

19 1

0.042 0.028

0.028 0.140

0.560 10 0.560 10

0.196 0.154

0.056 0.056

0.14 25

10

1

0.028

0.028

0.560 10

0.154

0.056

0.24 42

4

0

0.154

0.056

0.994 7

0.588

0.112

0.14 0.15 0.10 0.09 0.06

0 0 0 0 0

0 0 0 0 0

0.140 0.153 0.028 0.032 0.028

0.028 0.032 0.022 0.022 0.000

2.142 2.309 0.560 0.720 0.098

0.392 0.423 0.546 0.540 0.014

0.196 0.212 0.126 0.126 0.014

0.04 9 0.17 45 0.19 51

126 0 0

38 0 0

0.196 0.070 0.081

0.224 0.126 0.144

1.386 34 1.806 36 2.039 41

0.392 0.210 0.239

0.042 0.196 0.221

0.15 0.14 0.02 0.23 0.03 0.10 0.04 0.06 0.07 0.13 0.15 0.21 0.10 0.09 0.14

1250 510 501 500 529 750 500 767 750 0 750 750 1250 1 3

375 151 141 140 155 225 150 230 225 0 224 224 375 0 0

0.377 0.360 0.364 0.375 0.375 0.375 0.375 0.527 0.429 0.057 0.374 0.377 0.375 0.095 0.124

0.435 0.420 0.428 0.426 0.426 0.425 0.426 0.589 0.462 0.007 0.426 0.423 0.426 0.059 0.051

4.988 5.100 5.012 5.010 5.010 5.000 5.010 7.130 5.511 0.875 5.000 5.000 5.001 0.792 2.562

0.274 0.446 0.920 0.108 0.121 0.328 0.023 0.490 0.323 0.048 0.198 0.501 0.216 0.072 0.423

2.030 2.010 0.504 0.501 0.501 2.000 0.501 1.984 0.561 0.000 0.502 0.499 0.501 0.020 0.184

0.07 17 0.08 22 0.04 21

0 0 5

0 0 0

0.225 0.225 0.225

0.270 0.270 0.270

1.999 4 1.999 5 1.999 2

0.080 0.229 0.128

0.056 0.023 0.104

0.05 14

18

5

0.297

0.132

1.892 48

0.369

0.050

0.08 22

0

0

0.319

0.193

2.162 49

0.297

0.033

0.08 15

1

0

0.264

0.176

2.046 44

0.237

0.050

0.09 16

0

0

0.297

0.176

2.508 48

0.198

0.028

0.19 0.20 0.16 0.20 0.19 0.12 0.06

56 57 42 57 40 37 10

60 65 17 17 4

41 62 3 8 8 49 40 19 16 4 30 58 32 20 54

6 6 3 4 4

403 404 102 200 200 400 200 400 116 22 100 100 100 23 20

(Continued)

444


Table 2

(Continued)

Description

Serving size




Bagel, whole wheat, plain or with seasoning Biscuit, baking powder or buttermilk Boston brown bread Bread crumbs, plain Bread or rolls, French Bread or rolls, rye Bread or rolls, sourdough Bread or rolls, white Bread or rolls, whole wheat Bread, barley Bread bran Bread, egg Bread, English muffin Bread, focaccia Bread, gluten-free Bread, hovis Bread, Irish soda Bread, Italian Bread, oatmeal Bread, pumpernickel Bread, raisin Bread, wheat, reduced calorie (light high fiber) Breadsticks, bread type Breadsticks, cracker type Crepe, plain Croissant, plain Croutons, plain Eggroll wrapper English muffin, oat bran English muffin, rye English muffin, white English muffin, whole wheat Pancake, white flour, plain, from mix – no fat added Pancake, white flour, plain, from recipe Pancake, whole wheat, plain Pita, white Pita, whole wheat Popover Rolls, crescent (refrigerated dough) Rolls, hamburger, white Rolls, hamburger, whole wheat Rolls, hard Rolls, hot dog, white Rolls, hot dog, whole wheat Rolls, kaiser Rolls, submarine or hoagie Scone Taco shell Tortilla, corn Tortilla, white flour Tortilla, whole/wheat flour Waffles, bran, plain

1 each

55

0.62 0.09 25

1

0

0.292

0.193

2.701 48

0.319

0.066

1 each

55

0.28 0.04 9

38

11

0.231

0.171

1.705 32

0.187

0.017

2 slices 1/4 CP 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 1 slice 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices 2 slices

50 30 50 50 50 50 50 50 50 50 55 50 50 50 50 50 50 50 50 50

0.25 0.37 0.43 0.57 0.43 0.31 0.97 0.61 0.58 0.35 0.39 0.26 0.63 0.49 0.30 0.43 0.51 0.57 0.36 0.56

0.04 0.05 0.10 0.10 0.10 0.07 0.14 0.09 0.10 0.05 0.07 0.05 0.11 0.10 0.07 0.10 0.11 0.10 0.10 0.07

32 14 14 20 14 12 43 18 24 10 12 7 31 14 11 14 19 20 13 20

19 0 0 1 0 0 2 7 1 143 0 6 1 1 105 0 2 1 0 1

4 0 0 0 0 0 0 2 0 39 0 1 0 0 28 0 1 0 0 0

0.005 0.228 0.235 0.215 0.235 0.235 0.175 0.210 0.210 0.250 0.242 0.250 0.205 0.185 0.175 0.235 0.200 0.215 0.170 0.210

0.060 0.132 0.145 0.170 0.145 0.170 0.100 0.140 0.140 0.215 0.154 0.185 0.125 0.190 0.135 0.145 0.120 0.170 0.200 0.150

0.560 2.055 2.190 1.900 2.190 1.985 1.920 2.010 1.960 1.925 2.145 2.045 1.325 2.250 1.260 2.190 1.570 1.900 1.735 1.940

6 33 48 43 48 48 25 35 39 43 45 47 33 47 23 48 31 43 44 36

0.285 0.090 0.190 0.220 0.190 0.195 0.275 0.220 0.225 0.290 0.248 0.205 0.280 0.260 0.160 0.190 0.170 0.220 0.195 0.315

0.040 0.030 0.025 0.040 0.025 0.030 0.090 0.055 0.055 0.030 0.022 0.020 0.050 0.040 0.045 0.025 0.035 0.040 0.035 0.065

2 each 1.5 each 2 each 1 each 2/3 CP 1 each 1 each 1 each 1 each 1 each 3 each

55 15 110 55 7 32 55 55 55 55 110

0.47 0.14 0.73 0.35 0.06 0.20 0.59 0.48 0.39 0.88 0.46

0.11 0.02 0.06 0.05 0.01 0.03 0.08 0.07 0.07 0.12 0.08

15 5 20 10 2 5 30 14 12 39 14

0 0 455 561 1 22 0 1 0 4 31

0 0 128 159 0 7 0 0 0 0 7

0.258 0.099 0.286 0.248 0.043 0.179 0.335 0.253 0.242 0.165 0.374

0.160 0.063 0.374 0.220 0.019 0.131 0.248 0.237 0.154 0.077 0.264

2.409 0.812 1.936 1.892 0.381 1.334 2.244 2.321 2.134 1.876 2.794

52 14 45 43 9 26 78 75 45 27 54

0.209 0.074 0.638 0.303 0.030 0.154 0.479 0.379 0.248 0.385 0.319

0.028 0.012 0.066 0.028 0.002 0.013 0.055 0.066 0.022 0.088 0.044

3 each

110

0.68 0.07 20

211

62

0.352

0.374

2.431 53

0.594

0.055

3 each 1 each 1 each 1 each 2 each

110 50 50 55 50

1.50 0.42 0.76 0.42 0.19

208 0 3 155 0

61 0 0 46 0

0.198 0.134 0.170 0.165 0.175

0.253 0.048 0.040 0.220 0.110

2.453 1.070 1.420 1.116 1.535

26 12 18 28 22

0.792 0.200 0.415 0.402 0.180

0.165 0.015 0.130 0.039 0.020

1 each 1 each

50 50

0.31 0.06 10 0.97 0.14 43

0 2

0 0

0.240 0.175

0.155 0.100

1.965 48 1.920 25

0.265 0.275

0.020 0.090

1 each 1 each 1 each 1 each 1/2 each 1 each 2 each 2 each 1 each 1 each 1 each

50 50 50 50 50 55 30 55 55 55 85

0.47 0.31 0.97 0.47 0.44 0.36 0.42 0.52 0.39 0.85 1.28

0 0 2 0 0 433 52 70 0 2 190

0 0 0 0 0 116 5 7 0 0 56

0.240 0.240 0.175 0.240 0.260 0.209 0.069 0.061 0.292 0.132 0.264

0.170 0.155 0.100 0.170 0.165 0.198 0.015 0.039 0.160 0.066 0.331

2.120 1.965 1.920 2.120 2.375 1.491 0.405 0.825 1.964 1.854 2.831

0.205 0.265 0.275 0.205 0.195 0.292 0.141 0.105 0.319 0.297 0.689

0.020 0.020 0.090 0.020 0.020 0.050 0.090 0.121 0.028 0.099 0.187

0.17 0.09 0.15 0.03 0.04

0.08 0.06 0.14 0.08 0.10 0.07 0.04 0.08 0.15 0.11 0.15

64 13 35 10 7

14 10 43 14 14 11 32 36 14 40 79

48 48 25 48 48 31 32 63 68 13 41

(Continued)

APPENDIX 1 | Nutrient-Composition Tables for Grains and for Grain-Based Products Table 2

445

(Continued)

Description

Serving size




Waffles, white flour, from recipe Waffles, white flour, plain, frozen Wonton wrapper Crackers (enriched nutrients) Butter crackers Cheese crackers Cheese-filled sandwich crackers Cheese-filled sandwich crackers, whole wheat Matzo or matzoh crackers, egg Matzo or matzoh crackers, plain Matzo or matzoh crackers, whole wheat Melba toast Peanut butter-filled sandwich crackers Rye wafer, plain Saltine or soda crackers Whole wheat crackers Zwieback Cookies (enriched nutrients) Animal cracker Biscotti, with nuts Brownie, butterscotch, without nuts Brownie, chocolate, without nuts Cookies and bars, arrowroot Cookies and bars, butterscotch chip Cookies and bars, chocolate chip Cookies and bars, chocolate, wafer Cookies and bars, date bar Cookies and bars, fig bar Cookies and bars, fortune cookie Cookies and bars, gingerbread Cookies and bars, gingersnap Cookies and bars, graham cracker, plain Cookies and bars, granola Cookies and bars, lemon bar Cookies and bars, macaroon (coconut) Cookies and bars, molasses Cookies and bars, oatmeal Cookies and bars, peanut butter Cookies and bars, pfeffernu¨sse Cookies and bars, pizzelle Cookies and bars, raisin Cookies and bars, Rice Krispie bar

1 each

85

0.57 0.05 16

183

54

0.281

0.306

1.938 43

0.493

0.051

1 each

85

0.42 0.09 11

34

10

0.349

0.255

2.559 50

0.306

0.026

1 each

8

0.05 0.01 1

6

2

0.045

0.033

0.334 7

0.038

0.003

10 each 10 each 4 each

30 30 30

0.14 0.03 4 0.34 0.06 11 0.19 0.02 11

0 20 31

0 5 9

0.159 0.171 0.135

0.099 0.129 0.204

1.194 22 1.401 24 1.131 25

0.090 0.159 0.153

0.009 0.165 0.015

4 each

30

0.26 0.05 16

32

9

0.108

0.129

0.954 19

0.186

0.078

1 each

30

0.24 0.05 8

22

6

0.222

0.141

1.575 32

0.171

0.033

1 each

30

0.20 0.02 8

0

0

0.177

0.087

1.167 35

0.132

0.036

1 each

30

0.78 0.10 40

0

0

0.110

0.081

1.623 3

0.370

0.048

3 each 4 each

15 30

0.30 0.04 9 0.32 0.08 16

0 0

0 0

0.041 0.128

0.617 0.101

0.104 19 1.767 25

0.104 0.136

0.015 0.035

3 each 10 each 10 each 2 each

30 30 30 15

0.84 0.23 0.64 0.05

36 8 30 1

0 0 0 30

0 0 0 9

0.128 0.170 0.060 0.048

0.087 0.139 0.030 0.033

0.474 1.575 1.356 0.377

14 37 8 7

0.171 0.137 0.243 0.033

0.081 0.011 0.054 0.003


30 30 40

0.28 0.04 12 0.36 0.14 21 0.16 0.08 9

1 95 28

0 27 8

0.108 0.108 0.076

0.069 0.105 0.072

0.999 14 0.774 17 0.568 12

0.123 0.150 0.136

0.027 0.036 0.016

1 each

40

0.38 0.16 22

46

12

0.056

0.080

0.420 10

0.136

0.016

3 each 3 each

30 30

0.28 0.04 12 0.17 0.06 7

1 291

0 76

0.108 0.078

0.069 0.063

0.999 14 0.537 12

0.123 0.108

0.027 0.018

3 each

30

0.15 0.04 6

0

0

0.120

0.078

0.900 16

0.078

0.009

7 each

30

0.33 0.14 16

2

1

0.060

0.081

0.858 15

0.144

0.015


30 30 30

0.14 0.05 9 0.12 0.05 8 0.11 0.06 6

5 2 0

0 0 0

0.060 0.048 0.057

0.033 0.066 0.042

0.477 7 0.561 8 0.444 8

0.126 0.108 0.039

0.024 0.024 0.006

3 each 3 each 4 squares

30 30 30

0.16 0.06 24 0.14 0.06 14 0.08 0.03 9

14 13 0

4 4 0

0.123 0.099 0.084

0.087 0.072 0.054

0.981 18 0.759 14 0.645 11

0.165 0.123 0.069

0.063 0.036 0.024


30 30 30

0.69 0.13 21 0.13 0.02 2 0.22 0.04 7

83 294 0

24 78 0

0.111 0.060 0.003

0.084 0.069 0.039

0.798 20 0.423 10 0.063 1

0.162 0.117 0.093

0.093 0.012 0.030


30 30 30

0.14 0.07 27 0.35 0.07 16 0.29 0.04 14

0 323 133

0 85 35

0.117 0.132 0.069

0.072 0.075 0.060

0.948 16 0.639 14 1.353 15

0.141 0.180 0.132

0.072 0.018 0.039

2 each

30

0.18 0.06 23

164

43

0.129

0.096

0.999 18

0.177

0.063


30 30 30

0.12 0.01 2 0.11 0.05 6 0.19 0.04 5

36 142 331

11 38 95

0.066 0.069 0.129

0.072 0.057 0.138

0.477 11 0.477 9 1.650 35

0.126 0.078 0.099

0.012 0.030 0.168

0.14 0.06 0.13 0.01

(Continued)

446


Table 2 Description



Cookies and bars, rosette 2 each 30 0.10 Cookies and bars, shortbread 3 each 30 0.16 Cookies and bars, sugar 3 each 30 0.12 Cookies and bars, sugar wafer 4 each 30 0.17 with creme filling Cookies and bars, vanilla 3 each 30 0.15 sandwich Cookies and bars, vanilla 7 each 30 0.21 wafer Krumkake 2 each 30 0.19 Cakes, pastries, and other desserts (enriched nutrients) Angel food cake, white or 1 piece 55 0.08 flavored, not frosted or glazed Anisette (mandelbrodt toast), 3 slices 30 0.17 plain Cake, apple, not frosted or 1 piece 80 0.22 glazed Cake, banana, not frosted or 1 piece 80 0.37 glazed Cake, butter, not frosted or 1 piece 80 0.28 glazed Cake, carrot, without nuts, not 1 piece 80 0.30 frosted or glazed Cake, chiffon, not frosted or 1 piece 55 0.28 glazed Cake, chocolate, not frosted or 1 piece 80 0.46 glazed Cake, fruitcake 1 piece 125 0.79 Cake, German chocolate, not 1 piece 80 0.46 frosted or glazed Cake, gingerbread, not frosted 1 piece 80 0.30 or glazed Cake, jelly roll, yellow cake 1 piece 80 0.41 Cake, oatmeal, not frosted or 1 piece 80 0.39 glazed Cake, pound, chocolate, not 1 piece 80 0.42 frosted or glazed Cake, pound, white, not 1 piece 80 0.38 frosted or glazed Cake, spice, not frosted or 1 piece 80 0.37 glazed Cake, sponge, white or yellow, 1 piece 55 0.31 not frosted or glazed Cake, white, not frosted or 1 piece 80 0.25 glazed Cake, yellow, not frosted or 1 piece 80 0.37 glazed Cake, puff shell 2 each 80 0.59 Cupcake, chocolate, 1.5 each 80 0.46 commercial packaged Dumplings with fruit, apple 1/2 each 125 0.19 Fritter, apple 1 CP 55 0.40 Phyllo pastry 1 1/3 28.35 0.15 sheet Pie crust or shell, chocolate 1/8 pie 29.17 0.24 cookie type Pie crust or shell, egg yolk 1/8 pie 29.77 0.19 pastry, single layer Pie crust or shell, graham 1/8 pie 30.51 0.05 cracker, regular



27 540 12 1

8 141 4 0

0.051 0.153 0.105 0.057

0.054 0.102 0.075 0.045

0.363 1.140 0.789 0.426

9 21 15 8

0.096 0.096 0.090 0.081

0.009 0.009 0.009 0.018

0.04 6

0

0

0.120

0.078

0.900 16

0.078

0.009

0.07 11

1

0

0.126

0.084

0.948 17

0.075

0.009

0.03 4

278

79

0.123

0.114

0.900 20

0.171

0.015

0.03 5

0

0

0.094

0.182

0.720 12

0.083

0.006

0.02 4

34

10

0.123

0.105

0.891 19

0.153

0.015

0.04 6

89

19

0.128

0.128

0.912 21

0.224

0.032

0.06 10

400

107

0.208

0.208

1.512 31

0.288

0.032

0.03 5

350

100

0.136

0.160

1.040 34

0.320

0.024

0.06 8

4286

440

0.144

0.152

1.120 26

0.280

0.072

0.03 5

115

34

0.110

0.165

0.764 23

0.297

0.028

0.18 24

47

13

0.152

0.144

1.160 24

0.200

0.024

0.29 47 0.18 24

503 47

129 13

0.287 0.152

0.213 0.144

1.738 39 1.160 24

0.488 0.200

0.138 0.024

0.17 71

29

8

0.200

0.136

1.672 28

0.376

0.200

0.03 8 0.10 17

168 379

50 100

0.112 0.144

0.216 0.112

0.728 24 0.776 18

0.440 0.248

0.040 0.024

0.08 12

119

33

0.200

0.224

1.432 34

0.368

0.032

0.05 7

122

34

0.200

0.224

1.448 35

0.376

0.032

0.06 10

400

107

0.208

0.208

1.512 31

0.288

0.032

0.03 6

125

36

0.105

0.165

0.682 23

0.352

0.039

0.05 10

48

14

0.176

0.208

1.296 25

0.184

0.016

0.06 10

400

107

0.208

0.208

1.512 31

0.288

0.032

0.05 10 0.19 26

1072 12

288 1

0.208 0.184

0.312 0.128

1.392 41 1.416 26

0.640 0.128

0.056 0.016

0.06 8 0.04 9 0.03 5

136 137 0

29 40 0

0.188 0.182 0.164

0.125 0.215 0.102

1.363 25 1.249 30 1.245 23

0.138 0.396 0.094

0.038 0.039 0.009

0.10 12

2

0

0.044

0.058

0.624 11

0.082

0.012

0.03 4

42

13

0.131

0.095

0.965 21

0.158

0.015

0.02 5

0

0

0.046

0.031

0.351 6

0.037

0.012

0.01 0.03 0.02 0.06

2 5 3 7

(Continued)


447


Pie crust or shell, puff pastry, 1/2 shell frozen Pie crust or shell, regular 1/8 pie pastry, single layer, frozen Pie crust or shell, regular 1/8 pie pastry, single layer, prepared from mix Pie crust or shell, regular 1/8 pie pastry, single layer prepared from recipe Pie crust or shell, vanilla wafer 1/8 pie type Pies, apple, double pastry 1/8 pie crust Pies, chocolate cream 1/8 pie Pies, pudding filling, 1/8 pie chocolate Pies, pudding filling, vanilla 1/8 pie Pies, pumpkin 1/8 pie Shortcake, biscuit type 2 each Shortcake, sponge type 2 each Granola and cereal bars (fortified nutrients) Breakfast bar 1.5 each Cereal bar 1 each Snacks and chips (enriched nutrients) Bagel chips 0.5 CP Cheese balls, puffs, or twists 1 CP Corn chips 1 CP Corn nuts 0.35 CP Popcorn commercially 2.75 CP popped (prepopped), not ‘buttered’ Popcorn, hot-air popped 3.75 CP Popcorn, microwave popped 3.33 CP from package, with salt Popcorn, popped in fat 2.75 CP Pretzels, hard type 1.33 CP Pretzels, soft type 1/4 medium Rice cake 3 each Taco or tortilla chips 1 CP Wheat nuts 0.35 CP Legumes Adzuki beans, cooked 0.4 CP Bayo beans, cooked 0.5 CP Black beans, cooked 0.5 CP Broad beans, cooked 0.5 CP Brown beans, cooked 0.5 CP Cowpeas, cooked 0.5 CP Fava beans 0.5 CP Garbanzo beans, cooked 0.55 CP Kidney beans, cooked 0.5 CP Lentils, cooked 0.45 CP Lima beans, cooked 0.5 CP Mung beans, cooked 0.45 CP Navy beans, cooked 0.55 CP Northern beans, cooked 0.5 CP Pigeon peas, cooked 0.6 CP Pinto beans, cooked 0.5 CP Soybeans, cooked 0.5 CP Soybeans, dry roasted, salted 0.3 CP




20

0.13 0.02 2

10

3

0.106

0.068

0.792 14

0.122

0.008

16.38

0.08 0.02 2

0

0

0.084

0.052

0.629 11

0.048

0.005

20.8

0.10 0.02 3

0

0

0.106

0.067

0.799 15

0.060

0.006

28.12

0.12 0.02 4

0

0

0.127

0.079

0.959 18

0.073

0.006

36.97

0.23 0.07 11

305

79

0.126

0.085

0.939 17

0.081

0.011

125

0.20 0.06 8

40

4

0.200

0.138

1.600 27

0.200

0.038

125 85

0.98 0.24 42 0.37 0.06 15

363 104

103 30

0.150 0.128

0.250 0.153

0.950 29 0.876 18

0.588 0.230

0.075 0.026

85 125 80 55

0.30 0.56 0.35 0.31

103 7078 53 125

30 735 15 36

0.128 0.125 0.288 0.105

0.153 0.250 0.216 0.165

0.858 0.975 2.104 0.682

0.230 0.613 0.240 0.352

0.026 0.063 0.024 0.039

40 40

4.15 0.54 111 1389 1.63 0.06 14 810

417 243

0.416 0.404

0.476 0.464

5.564 111 5.420 108

2.780 0.140

0.556 0.540

30 30 30 30 30

0.24 0.20 0.15 0.53 0.77

8 9 8 34 29

2 42 42 61 23

0 4 4 6 2

0.204 0.147 0.141 0.012 0.045

0.144 0.096 0.081 0.039 0.063

1.623 0.999 0.981 0.507 0.426

0.162 0.108 0.060 0.111 0.093

0.021 0.057 0.051 0.069 0.054

30 30

1.03 0.13 39 0.63 0.08 24

32 19

3 2

0.060 0.036

0.084 0.051

0.582 7 0.354 4

0.126 0.078

0.072 0.045

30 30 30 30 30 30

0.65 0.26 0.21 0.90 0.21 1.41

0.08 0.08 0.04 0.13 0.20 0.13

25 11 7 39 11 26

20 0 0 0 52 8

2 0 0 0 5 1

0.039 0.138 0.234 0.018 0.177 0.138

0.054 0.186 0.147 0.048 0.108 0.069

0.363 1.575 1.770 2.343 1.218 0.462

4 51 32 6 32 51

0.078 0.087 0.135 0.300 0.102 0.117

0.045 0.036 0.012 0.045 0.066 0.081

90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 30

1.59 0.38 0.95 0.95 1.24 1.16 0.40 1.38 0.96 1.14 0.86 1.24 0.95 1.24 0.90 0.97 1.04 0.69

0.27 0.14 0.27 0.27 0.26 0.24 0.50 0.32 0.22 0.23 0.22 0.26 0.27 0.26 0.16 0.23 0.37 0.57

47 13 53 53 57 48 31 43 41 32 39 57 53 57 32 50 77 61

0 0 0 0 0 0 292 0 0 18 0 0 0 0 96 15 9 8

0 0 0 0 0 0 29 0 0 2 0 0 0 0 10 2 1 1

0.108 0.063 0.180 0.180 0.108 0.180 0.063 0.108 0.144 0.153 0.144 0.108 0.180 0.108 0.171 0.171 0.144 0.111

0.054 0.018 0.054 0.054 0.045 0.054 0.054 0.054 0.054 0.063 0.054 0.045 0.054 0.045 0.054 0.081 0.252 0.168

0.648 0.198 0.477 0.477 0.126 0.450 0.963 0.477 0.522 0.954 0.378 0.126 0.477 0.126 0.801 0.360 0.360 0.360

109 6 126 126 73 187 19 155 117 163 75 73 126 73 58 155 48 57

0.387 0.153 0.234 0.234 0.207 0.369 0.144 0.261 0.198 0.576 0.378 0.207 0.234 0.207 0.540 0.252 0.162 0.222

0.090 0.081 0.144 0.144 0.081 0.090 0.108 0.126 0.108 0.162 0.144 0.081 0.144 0.081 0.045 0.144 0.207 0.156

0.03 0.09 0.06 0.03

0.07 0.03 0.02 0.04 0.12

10 23 12 6

17 26 39 23

37 26 26 0 5

(Continued)

448


Table 2

(Continued)

Description

Serving size




Soybeans, oil roasted, salted Split peas, yellow or green, cooked Tepary beans Meat substitutes Miso Tempeh Tofu (soybean curd), extra firm Tofu (soybean curd), firm

0.3 CP 0.45 CP

30 90

0.94 0.25 44 0.90 0.16 32

8 96

1 10

0.030 0.171

0.042 0.054

0.423 63 0.801 58

0.135 0.540

0.063 0.045

0.35 CP

90

0.54 0.16 25

0

0

0.036

0.045

0.522 29

0.198

0.108

1 TB 0.5 C 0.35 CP cubes 0.35 CP cubes 1 slice (100 thick) 0.35 CP cubes

17 85 85

0.56 0.07 7 0.97 0.48 69 0.95 0.15 60

15 43 9

1 4 1

0.016 0.068 0.043

0.042 0.306 0.034

0.146 6 2.244 20 0.281 22

0.044 0.238 0.051

0.037 0.187 0.034

85

0.83 0.20 35

0

0

0.068

0.051

0.697 56

0.068

0.068

85

0.52 0.17 23

0

0

0.085

0.034

0.213 39

0.043

0.094

85

0.54 0.14 23

0

0

0.043

0.034

0.459 37

0.043

0.043

236 240 237.6 41.7 41.7

0.07 0.00 0.05 0.02 0.02

0.05 0.00 0.02 0.01 0.01

12 13 14 0 0

0 0 0 0 0

0 0 0 0 0

0.024 0.000 0.024 0.004 0.004

0.071 0.000 0.071 0.000 0.000

0.920 0.000 1.609 0.004 0.004

10 0 14 0 0

0.094 0.168 0.143 0.000 0.000

0.071 0.120 0.119 0.000 0.000

30 30 30 30 15 30 30 30 30 30 32.25 30 30

1.01 0.02 1.87 1.43 0.30 0.74 1.25 1.53 1.80 0.39 0.94 1.99 1.99

0.33 0.01 0.37 0.65 0.12 0.52 0.31 0.54 0.61 0.23 0.05 0.39 0.39

83 1 52 77 14 49 109 111 14 39 51 56 56

3 26 1 0 0 12 0 1 1 0 1 1 1

0 3 0 0 0 1 0 0 0 0 0 0 0

0.072 0.000 0.072 0.126 0.009 0.192 0.051 0.210 0.138 0.360 0.026 0.075 0.075

0.243 0.000 0.030 0.054 0.015 0.033 0.048 0.144 0.051 0.048 0.032 0.033 0.033

1.179 0.000 4.014 0.540 0.090 0.540 0.420 8.100 3.450 0.741 4.322 4.284 4.284

9 2 35 20 1 34 83 74 40 3 24 38 38

0.105 0.039 0.393 0.357 0.120 0.276 0.459 0.822 0.462 0.228 0.261 0.417 0.417

0.039 0.003 0.072 0.075 0.045 0.168 0.279 0.150 0.090 0.084 0.145 0.078 0.078

30

1.99 0.39 56

1

0

0.075

0.033

4.284 38

0.417

0.078

30 30 30

1.36 0.36 36 23 3.07 0.49 99 0 3.08 0.44 104 20

2 0 2

0.198 0.255 0.216

0.039 0.051 0.024

0.351 7 0.294 17 1.404 29

0.258 0.239 0.204

0.063 0.132 0.045

30

3.07 0.44 104 20

2

0.363

0.141

1.632 29

0.204

0.045

30

1.59 0.55 39

0

0

0.033

0.075

2.112 71

2.112

0.240

30

1.56 0.54 38

15

2

0.096

0.084

1.239 70

2.082

0.237

30 10 30

1.52 0.53 106 0 0.01 0.00 0 0 0.93 0.48 47 12

0 0 1

0.687 0.000 0.102

0.075 0.000 0.045

1.350 68 0.000 0 0.597 29

2.025 0.014 0.171

0.231 0.001 0.162

Tofu (soybean curd), silken Tofu (soybean curd), soft

Alcoholic beverages Beer, light, low calorie 8 FO Beer, low alcohol 8 FO Beer, regular 8 FO Scotch, plain 1.5 FO Whiskey, plain 1.5 FO Ingredients used in grain products Almonds, raw 0.2 CP Arrowroot flour 0.2 CP Beer nuts, peanuts 0.2 CP Cashews, oil roasted 0.2 CP Coconut, dried, unsweetened 0.2 CP Filberts, raw 0.2 CP Flax seeds 0.25 CP Flour, peanut, defatted 0.5 CP Flour, peanut, low fat 0.5 CP Macadamia nuts, raw 0.2 CP Peanut butter, with salt 2 TB Peanuts, raw 0.2 CP Peanuts, roasted, dry roasted, 0.2 CP salted Peanuts, roasted, oil roasted, 0.2 CP salted Pecans, raw 0.3 CP Poppy seeds 0.2 CP Sesame seeds, kernels 0.2 CP (hulled), dried Sesame seed, kernels 0.2 CP (hulled), toasted Sunflower seeds, dry roasted, 0.2 CP salted Sunflower seeds, oil roasted, 0.2 CP salted Sunflower seeds, raw 0.2 CP Tapioca, dry 1 TB Walnuts, raw 0.25 CP



• • • • •

Search for foods that are the best sources of iron, zinc, and calcium. What foods are the most likely to have some form of fortification or enrichment? What nutrients are most often provided via fortification or enrichment? What differences in nutrition does defatting make for soy flour? If there are community efforts to reduce sodium in the public diet, which grain-based foods are the most and least suitable?


• •

What is the effect on nutrients of milling wheat, barley, and rice, based on the data for the respective whole grains and for the resulting mill fractions? Compare the range of nutrients of several less common grains (and derived foods), such as amaranth, teff, quinoa, kamut, spelt, buckwheat, and millet. What nutritional advantages do any of them offer? Find out what these grains

449

look like, where they are grown, what they are used for, and what future they may have.

See also: Food Grains and the Consumer: Fortification of GrainBased Foods; Grains and Health; Labelling of Grain-Based Foods; Food Grains and Well-being: Nutrition: Soy-Based Foods; The Basics: The Grain Crops: An Overview; The Grains that Feed the World; The Cereal Grains: An Overview of the Family of Cereal Grains Prominent in World Agriculture; Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Coix: Overview; Maize: Overview; Rice: Overview; Sorghum Grain, Its Production and Uses: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; The Legumes and Pseudocereals: Amaranth: Overview; Grain Legumes and Their Dietary Impact: Overview; Lupin: Overview; The Oilseeds: Oilseeds: Overview; Soybean: Overview.

Relevant Websites http://www.nal.usda.gov – US Department of Agriculture, Agriculture Research Service. USDA National Nutrient Database for Standard Reference, Nutrient Data Laboratory Home page. http://www.ncc.umn.edu – Nutrition Coordinating Center.

Appendix 2. Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods AR Bridges, AACC International, St Paul, MN, USA CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • •

Test methods provide analytic results used to monitor the production and processing of grains. Such methods are developed, evaluated, and approved as standard procedures by scientific societies. A wide range of methods are available as a result. The standard methods provided by the ICC and by AACC International are provided by title and by systematic numbering.

Learning Objectives

•

To appreciate the wide range of approved testing methods available for monitoring the safety and quality of grain samples and the foods made from grains.

For this listing of test methods, two organizations have been selected, thus, to provide an overview of the types of methods (by title only) and the purposes (indicated by the groupings for the AACCI methods). These organizations are the International Association for Cereal Science and Technology (ICC) (Table 1) and AACC International, formerly the American Association of Cereal Chemists (AACCI) (Table 2). Until a decade or so ago, methods were provided in loose-leaf binders. Now, full versions of the methods are available at the respective websites of these scientific societies: https://www.icc.or.at/standard_methods and http://www.aaccnet.org/Pages/default.aspx. The lists in Tables 1 and 2 are published with the permission of the respective societies.


• Introduction to the Methods

•

Ongoing attention to the safety and quality of grain and grainbased foods requires the analysis of relevant attributes at all stages of the grain chain, from breeding, to grain production and processing, to retail interaction with the customer who is purchasing the end product. It is therefore necessary to have testing procedures to obtain the results needed to monitor safety and quality and to modify procedures as necessary. Historically, there have been problems in comparing the results of testing because procedures differed from one laboratory to another. To remedy these problems, there have been international collaborations over decades to develop agreed procedures so that the results of analyses are comparable. The interactions and collaborations that have led to the development of standardized testing methods are described in an article entitled ‘The Standardization of Test Methods for Analyzing Grains and Grain-Based Products’ by Anne R. Bridges and Colin W. Wrigley. These collaborative interactions are ongoing, as new needs for analysis and novel possibilities arise for formulating improved methods. These collaborations often involve interactions between members of scientific societies, thereby combining the relevant expertise of scientists with the needs of organizations and companies for which the methods are needed. There are many such scientific societies that are involved in method development for grains and relevant foods, ranging from plant genetics, breeding, agronomy, and soil science to food technology more broadly.

•

450

Identify the methods recommending how best to take samples for analysis. In which items listed would you search for the meanings of terms relevant to barley, rice, lipids, flour, and grain? Imagine that you are the coordinator of an analytic laboratory. What test methods would you use to determine ○ the protein and oil contents of grain samples, ○ the sugar content of food samples, ○ bread staleness, ○ testing for cookie-making quality, ○ the statistical significance of results.


• • • •

Investigate the types of analyses that are needed and used in your region to analyze grain and grain-based foods. Identify a few cases where different methods have been developed to achieve (apparently) the same analytic results. Why? Suggest which testing situation would be appropriate to test method. Which of the methods listed are likely to have been used to obtain the analytic results shown in the nutrition label of some typical supermarket packets that you may have in your kitchen? Find out about testing methods used for tests for genetically modified cereals. Which of the tests in the text are relevant? What aspects of grain composition are used in these methods?


http://dx.doi.org/10.1016/B978-0-12-394437-5.00244-8

APPENDIX 2 | Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods Table 1

451

A list of ICC standardized testing methods

Generic methods No. 101/1: Sampling of Grains No. 102/1: Determination of Besatz of Wheat No. 103/1: Determination of Besatz of Rye No. 104/1: Determination of Ash in Cereals and Cereal Products No. 105/2: Determination of Crude Protein in Cereals and Cereal Products for Food and for Feed No. 106/2: Working Method for the Determination of Wet Gluten in Wheat Flour No. 107/1: Determination of the ‘Falling Number’ according to Hagberg – as a Measure of the Degree of Alpha-Amylase Activity in Grain and Flour No. 108: Colorimetric Method for the Determination of Alpha-amylase Activity No. 109/1: Determination of the Moisture Content of Cereals and Cereal Products (Basic reference method) No. 110/1: Determination of the Moisture Content of Cereals and Cereal Products (Practical method) No. 111: Chemical Assay of nicotinic Acid in Cereal Products No. 112: Microbiological Assay of Nicotinic Acid in Cereal Products No. 113: Determination of Crude Fiber Value No. 114/1: Method for using the Brabender Extensograph No. 115/1: Method for using the Brabender Farinograph No. 116/1: Determination of Sedimentation Value (according to Zeleny) as an Approximate Measure of Baking Quality No. 117: Chemical Determination of Thiamine in Cereal Products No. 118: Preparation of Test Flour from Wheat Samples for Sedimentation Test No. 119: Rapid Method for the Determination of Thiamine in Enriched Flours and Enrichment Mixtures No. 120: Mechanical Sampling of Grain No. 121: Method for using the Chopin Alveograph No. 122/1: Determination of Starch Content by Calcium Chloride Dissolution No. 123/1: Determination of Starch Content by Hydrochloric Acid Dissolution No. 125: Method of Determining the Count of Aerobic Mesophilic Bacteria (Plate Count Method) No. 126/1: Method for using the Brabender Amylograph No. 127: Determination of Particle Size Distribution in Flour by the Andreasen Pipette Method No. 128/1: Procedure for the Determination of Starch after Enzymatic Decomposition No. 129: Method for the Determination of the Vitreousness of Durum Wheat No. 130: Cereals – Sampling of Milled Products No. 131: Method for Test Baking of Wheat Flours No. 132: Determination of Saccharose in Cereals and Cereal Products No. 133: Determination of the Germ Count of Aerobic and facultatively Anaerobic, Mesophilic Bacteria (Plate Count Method) in Cereals, Cereal Products, and Animal Feed No. 134: Determination of the Fungus Germ Count (Plate Count Method) in Cereals, Cereal Products, and Animal Feed No. 135: Determination of the Water Content of Whole Maize Kernels No. 136: Cereals and cereal products – Determination of total fat content No. 137/1: Mechanical Determination of the Wet Gluten Content of Wheat Flour (Perten Glutomatic) No. 138: Mechanical Sampling of Milled Cereal Products No. 139: Determination of Fungus Germ Count (Plate Count Method) No. 140: Enzymatic determination of the bran content of cereals No. 141: The Determination of Mercury in Cereals (Method of Mineralisation and Method of Determination) No. 143: Wheat – Identification of Varieties by Electrophoresis No. 144: Enumeration of Spores of Mesophilic Bacteria No. 145: Determination of Acidity (acc. to Schulerud) for Cereals and Cereal Products No. 146: Enumeration of Yeasts and Moulds (Spatula Method) No. 147: Enumeration of Bacteria (Spatula Method) No. 151: Determination of the Sedimentation Value – SDS test of Durum Wheat No. 152: Determination of the yellow pigment content of durum wheat semolina and flour No. 153: Determination of total organic matter (TOM) in pasta No. 154: Determination of Cadmium and Lead in Cereals and Cereal Products (A. Method of mineralization B. Method of determination) No. 155: Determination of Wet Gluten Quantity and Quality (Gluten Index ac. to Perten) of Whole Wheat Meal and Wheat Flour (Triticum aestivum) No. 156: Determination of Total Dietary Fiber No. 157: Ash Determination by Conductivity No. 158: Gluten Index Method for Assessing Gluten Strength in Durum Wheat (Triticum durum) No. 159: Determination of Protein by Near Infrared Reflectance (NIR) Spectroscopy No. 161: Determination of the ‘Stirring Number’ using the Newport Rapid Visco Analyser, as a measure of the degree of alpha-amylase activity in grain and flour No. 162: Rapid Pasting Method using the Newport Rapid Visco Analyser No. 164: Measurement of Damaged Starch by Using Megazyme Enzymic Kit No. 165: Determination of ochratoxin A in wheat and wheat products No. 166: Determination of ß-Glucan in Barley, Oat and Rye (Continued)

452 Table 1

APPENDIX 2 | Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods (Continued)

No. 167: Determination of crude protein in grain and grain products for food and feed by the Dumas Combustion Principle No. 169: Method for using the Brabender Viscograph No. 171: Determination of the water absorption capacity of wheat flours and of physical properties of wheat flour dough using the Consistograph No. 172: Flour from Wheat (Triticum aestivum) – Determination of Damaged Starch by an Amperometric Method Using the Chopin SDMatic No. 173: Whole Meal and Flour from T. aestivum – Determination of Rheological Behavior as a Function of Mixing and Temperature Increase No. 174: Determination of Germinative Energy of Sorghum Grain No. 175: Determination of Total Defects in Sorghum Grain No. 176: Estimation of Sorghum Grain Endosperm Texture No. 177: Detection of Tannin Sorghum Grain by the Bleach Test No. 179: Determination of Water Absorption Capacity of Wheat Flours and Wheat Meals and Physical Properties of Wheat Dough Using the Haubelt Flourgraph E6 No. 180: Determination of the Rheological Properties of Wheat Flour Dough Using the Haubelt Flourgraph E7 Recommendations No. 201: Test procedure for rapid moisture determination apparatus No. 202: Procedure for near infrared (NIR) reflectance analysis of ground wheat and milled wheat products No. 203: Statistical analysis of the results of collaborative studies No. 204: Determination of pesticide residues in grain by gel permeation chromatography/gas–liquid chromatography No. 206: Microbiology – General guidance for microbiological examination (basis: ISO Standard 7218) No. 207: Determination of the Particle Size of Milling Products using Sieve Analysis Rapid methods No. 301: Quantitative Peroxidase Activity No. 302: Quantitative Catalase Activity Assay No. 303: Simple and Specific Assay for Alpha-Amylase (Ceralpha method) Draft standard No. 181: Dye Color-Chart method for pH determination of rice grains (2012)

Table 2

A list of AACC International standardized testing methods

02 02-01.02 02-02.02 02-03.02 02-04.02 02-31.01 02-32.02 02-52.01 04 04-10.01 04-11.01 04-14.01 04-20.01 04-21.01 04-22.01 04-27.01 04-28.01 06 06-10.01 06-11.01 07 07-01.01 07-11.01 07-20.01 08 08-01.01 08-02.01 08-03.01 08-10.01 08-11.01 08-12.01 08-14.01 08-16.01

Acidity Fat Acidity – General Method Fat Acidity – Rapid Method, for Small Grains Fat Acidity – Rapid Method, for Corn Fat Acidity – Colorimetric Method Titratable Acidity Neutralizing Value of Acid-Reacting Materials Hydrogen-Ion Activity (pH) – Electrometric Method Acids Phosphoric Acid – Qualitative Method Phosphoric Acid – Quantitative Method Sulfuric Acid – Quantitative Method Acetic, Butyric, and Lactic Acids in Rye Flour Benzoic Acid Citric and Isocitric Acids Tartaric Acid – Quantitative Method Free or Combined Tartaric Acid – Qualitative Method Admixture of Flours Admixture of Rye and Wheat Flours Soy Flour Amino Acids Measurement of Acid-Stable Amino Acids Measurement of Sulfur Amino Acids Measurement of Tryptophan – Alkaline Hydrolysis Total Ash Ash – Basic Method Ash – Rapid (Magnesium Acetate) Method Ash – Rapid (2-Hour, 600 ) Method Ash in Cacao Products Ash in Dry Milk Products Ash in Farina and Semolina Ash in Molasses, Sugars, and Syrups Ash in Soy Flour


(Continued)

08-17.01 08-18.01 08-21.01 10 10-05.01 10-09.01 10-10.03 10-11.01 10-12.01 10-13.02 10-14.01 10-15.01 10-31.03 10-50.05 10-52.02 10-53.01 10-54.01 10-80.01 10-90.01 10-91.01 11 11-10.01 11-20.01 11-21.01 11-30.01 12 12-10.01 12-20.01 12-21.01 12-29.01 14 14-10.01 14-22.01 14-30.01 14-50.01 14-60.01 20 20-01.01 20-10.01 20-20.01 22 22-02.01 22-05.01 22-08.01 22-10.01 22-11.01 22-12.01 22-14.01 22-15.01 22-40.01 22-62.01 22-80.01 22-85.01 22-90.01 26 26-10.02 26-21.02 26-22.01 26-30.02 26-31.01 26-32.01 26-41.01

Ash in Starch Ash in Yeast Foods Prediction of Ash Content in Wheat Flour – Near-Infrared (NIR) Method Baking Quality Guidelines for Measurement of Volume by Rapeseed Displacement Basic Straight-Dough Bread-Baking Method – Long Fermentation Optimized Straight-Dough Bread-Baking Method Baking Quality of Bread Flour – Sponge-Dough, Pound-Loaf Method Baking Guidelines for Scoring Experimental Bread Guidelines for Testing a Variety of Products Determination of Bread Volume by Laser Topography: BVM Method Baking Quality of Angel-Cake Flour Baking Quality of Biscuit Flour Baking Quality of Cookie Flour Baking Quality of Cookie Flour – Micro Method Baking Quality of Cookie Flour – Macro Wire-Cut Formulation Baking Quality of Cookie Flour – Micro Wire-Cut Formulation Baking Flour Quality in a Pancake-Making Method Baking Quality of Cake Flour Use of Layer Cake Measuring Template Biotechnology Bt Cry1Ab-Modified Corn in Corn Flour – ELISA Method StarLink Corn in Corn Flour and Corn Meal – ELISA Method ELISA Method for StarLink Corn in Corn Flour and Corn Meal Quantification of MON 810 Corn in Corn Flour by Real-Time Polymerase Chain Reaction Carbon Dioxide Residual Carbon Dioxide in Baking Powder Total (Gasometric) Carbon Dioxide in Baking Powder Total Carbon Dioxide in Prepared Mixes and Self-Rising Flours Table: Correction Factors for Gasometric Determination of Carbon Dioxide Color and Pigments Pekar Color Test (Slick Test) Color of Pasta – Reflectance Colorimeter Method Agtron Color Test for Flour Determination of Pigments Total Carotenoid Content of Cereal Grains and Flours Ingredients Egg Solids – Digitonin Cholesterol Method Egg Solids in Pasta Products Determination of Isoflavones in Soy and Selected Foods Containing Soy by Extraction, Saponification, and Liquid Chromatography Enzymes Measurement of alpha-Amylase in Plant and Microbial Materials Using the Ceralpha Method Measurement of alpha-Amylase in Cereal Grains and Flours – Amylazyme Method Measurement of alpha-amylase activity with the rapid visco analyzer Measurement of alpha-Amylase Activity with the Amylograph Measurement of Gassing Power by the Pressuremeter Method Measurement of alpha-Amylase Activity in Flour Supplemented with Fungal alpha-Amylase – Modified Amylograph Method Measurement of Gassing Power by Volumetric Method Measurement of Diastatic Activity of Flour or Semolina Measurement of Trypsin Inhibitor Activity of Soy Products – Spectrophotometric Method Measurement of Proteolytic Activity – Spectrophotometric Method Qualitative Test for Peroxidase in Oat Products Measurement of Polyphenol Oxidase in Wheat Kernels (L-DOPA Substrate) Measurement of Urease Activity Experimental Milling Experimental Milling: Introduction, Equipment, Sample Preparation, and Tempering Experimental Milling – Bu¨hler Method for Hard Wheat Experimental Milling – Batch Method for Hard Wheat Experimental Milling – Bu¨hler Method for Soft Wheat Short-Extraction Flour Experimental Milling – Bu¨hler Method for Soft Wheat Straight-Grade Flour Experimental Milling – Batch Method for Soft Wheat Experimental Milling – Bu¨hler Method for Durum Wheat

453

(Continued)

454

APPENDIX 2 | Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods

Table 2

(Continued)

26-42.01 26-50.01 26-70.01 26-95.01 28 28-01.01 28-02.01 28-03.02 28-06.01 28-07.01 28-10.02 28-19.01 28-20.02 28-21.02 28-22.02 28-30.02 28-31.02 28-32.02 28-33.02 28-40.01 28-41.03 28-43.01 28-44.01 28-50.01 28-51.02 28-60.02 28-70.01 28-75.02 28-80.01 28-85.01 28-86.01 28-87.01 28-93.01 28-95.01 30 30-10.01 30-12.02 30-14.01 30-16.01 30-18.01 30-20.01 30-25.01 30-40.01 32 32-05.01 32-06.01 32-07.01 32-10.01 32-20.01 32-21.01 32-22.01 32-23.01 32-25.01 32-28.02 32-31.01 32-32.01 32-33.01 32-40.01 32-41.01 32-45.01 32-50.01 33 33-50.02

Experimental Milling – Batch Method for Durum Wheat Brabender Quadrumat Jr. (Quadruplex) Method Experimental Milling — Chopin CD 1 Method Experimental Milling: Temper Table Extraneous Matter Apparatus or Materials for Extraneous Matter Methods Reagents for Extraneous Matter Methods Special Techniques for Extraneous Matter Methods Cinder and Sand Particles in Farina – Counting Method Cinder and Sand Particles in Farina – Gravimetric Method Macroscopic Examination of External Contamination in Whole Grains External Filth and Internal Insect Infestation in Whole Corn Microscopic Examination of External Contamination in Whole Grains X-Ray Examination for Internal Insect Infestation Cracking-Flotation Test for Internal Insects in Whole Grains Macroscopic Examination of Materials Hard to Hydrate Pancreatin Sieving Method, for Insect and Rodent Filth in Materials Hard to Hydrate Sieving Method, for Materials Hard to Hydrate Pancreatin Nonsieving Method for Insect and Rodent Filth in Materials Easy to Hydrate Acid Hydrolysis Method for Insect Fragments and Rodent Hairs – Wheat-Soy Blend Acid Hydrolysis Method for Extracting Insect Fragments and Rodent Hairs – Light Filth in White Flour Glass Plate Method, for Insect Excreta Iodine Method, for Insect Eggs in Flour Decantation Method, for Rodent Excreta Flotation Method, for Insect and Rodent Filth Tween-Versene Method, for Insect Fragments and Rodent Hairs in Rye Flour Defatting-Digestion Method, for Insect Fragments and Rodent Hairs Sieving Method, for Light Filth in Starch Flotation Method, for Insect and Rodent Filth in Popped Popcorn Ultraviolet Light Examination, for Rodent Urine Xanthydrol Test, for Urea Urease-Bromthymol Blue Test Paper, for Urea Direction of Insect Penetration into Food Packaging Insect, Rodent Hair, and Radiographic Illustrations Crude Fat Crude Fat in Flour, Bread, and Baked Cereal Products Not Containing Fruit Crude Fat in Cocoa Crude Fat in Baked Pet Food Crude Fat in Dry Milk Products Crude Fat in Egg Yolk by Acid Hydrolysis Crude Fat in Grain and Stock Feeds Crude Fat in Wheat, Corn, and Soy Flour, Feeds, and Mixed Feeds Unsaponifiable Matter Fiber Total Dietary Fiber Total Dietary Fiber– Rapid Gravimetric Method Soluble, Insoluble, and Total Dietary Fiber in Foods and Food Products Crude Fiber in Flours, Feeds, and Feedstuffs Insoluble Dietary Fiber Insoluble and Soluble Dietary Fiber in Oat Products – Enzymatic-Gravimetric Method beta-Glucan in Oat Fractions and Unsweetened Oat Cereals beta-Glucan Content of Barley and Oats – Rapid Enzymatic Procedure Total Dietary Fiber – Determined as Neutral Sugar Residues, Uronic Acid Residues, and Klason Lignin (Uppsala Method) Polydextrose in Foods by Ion Chromatography Fructans in Foods and Food Products – Ion Exchange Chromatographic Method Measurement of Total Fructan in Foods by an Enzymatic/Spectrophotometric Method Determination of trans-Galactooligosaccharides in Selected Food Products by Ion-Exchange Chromatographic Method Resistant Starch in Starch Samples and Plant Materials Total Dietary Fiber in Foods Containing Resistant Maltodextrin – Enzymatic-Gravimetric Method and Liquid Chromatography Determination Total Dietary Fiber (Codex Alimentarius Definition) Insoluble, Soluble, and Total Dietary Fiber (Codex Definition) by an Enzymatic-Gravimetric Method and Liquid Chromatography Sensory Analysis Sensory Evaluation –Triangle Difference Test


(Continued)

38 38-10.01 38-12.02 38-20.01 38-50.01 38-52.01 38-55.01 39 39-00.01 39-01.01 39-10.01 39-11.01 39-20.01 39-21.01 39-25.01 39-70.02 40 40-10.01 40-15.01 40-16.01 40-18.01 40-20.01 40-21.01 40-26.01 40-30.01 40-31.01 40-33.01 40-35.01 40-40.01 40-41.03 40-45.01 40-50-02 40-56.01 40-57.01 40-58.01 40-61.02 40-66.01 40-70.01 40-71-01 40-75.01 42 42-10.01 42-11.01 42-15.01 42-17.02 42-20.01 42-25.03 42-30.03 42-35.01 42-40.01 42-45.01 42-50.01 42-56.01 42-70.01 42-71.01 44 44-01.01 44-11.01 44-15.02 44-16.01 44-17.01 44-19.01

Gluten Gluten – Hand Washing Method Wet Gluten, Dry Gluten, Water-Binding Capacity, and Gluten Index Farinograph Test for Vital Wheat Gluten Gluten in Corn Flour and Corn-Based Products by Sandwich ELISA Sandwich ELISA Gluten G12 Assay for Rice Flour and Rice-Based Products Gluten in Fermented Cereal-Based Products by Competitive ELISA Infrared Analysis Near-Infrared Methods – Guidelines for Model Development and Maintenance Evaluation of NIR Instrument Calibration Near-Infrared Reflectance Method for Protein Determination in Small Grains Near-Infrared Reflectance Method for Protein Determination in Wheat Flour Near-Infrared Reflectance Method for Protein and Oil Determination in Soybeans Near-Infrared Reflectance Method for Whole-Grain Analysis in Soybeans Near-Infrared Reflectance Method for Protein Content in Whole-Grain Wheat Near-Infrared Reflectance Method for Hardness Determination in Wheat Inorganic Constituents Aluminum – Qualitative Method Ammonia – Quantitative Method Ammonium Salts – Qualitative Method Ammonium Salts – Quantitative Method Calcium in Bread and Flour Calcium in Feedstuffs Calcium in Mineral Feeds Chlorides in Ash as Sodium Chloride – Gravimetric Method Chlorides in Ash as Sodium Chloride – Volumetric Method Chlorides in Yeast Foods – Quantitative Method Iodine Determination Iron – Qualitative Method Iron – Spectrophotometric Method Acid-Soluble Manganese Sample Preparation for Phosphate Determination in Flour Improvers Phosphorus – Modified Fiske-Subbarow Colorimetric Method Phosphorus – Gravimetric Method Phosphorus – Volumetric Method Salt, Calculated from Soluble Chlorides Sulfates – Gravimetric Method Elements by Atomic Absorption Spectrophotometry Sodium and Potassium by Atomic Absorption Spectrophotometry Determination of Minerals by Inductively Coupled Plasma Spectroscopy Microorganisms Microorganisms – Sampling Procedure Aerobic Plate Count Coliform – E. coli Clostridium perfringens Enumeration Rope Spore Count Salmonella Bacteria Enumeration of Staphylococcus aureus Enterococci Thermophilic Spore Counts (Total Aerobic, Flat-Sour, H2S, Non-H2S Anaerobic) Thermophilic and Psychrotrophic Bacteria Mold and Yeasts Counts Ergot – Ether-Bicarbonate Method Smut – Microscopic Method Smut – Sedimentation Method Moisture Calculation of Percent Moisture Moisture – Dielectric Meter Method Moisture – Air-Oven Methods Moisture – Air-Oven (Aluminum-Plate) Method Moisture – Air-Oven Method (Pulses) Moisture – Air-Oven Method, Drying at 135

455

(Continued)

456


Table 2

(Continued)

44-20.01 44-30.01 44-31.01 44-40.01 44-51.01 44-60.01 45 45-01.01 45-05.01 45-14.01 45-15.01 45-16.01 45-20.01 45-21.01 45-25.01 45-41.01 45-51.01 46 46-09.01 46-10.01 46-11.02 46-12.01 46-13.01 46-14.03 46-15.01 46-16.01 46-18.01 46-19.01 46-23.01 46-24.01 46-30.01 46-50.01 48 48-08.01 48-42.01 48-62.01 48-71.02 54 54-10.01 54-21.02 54-22.01 54-28.02 54-29.01 54-30.02 54-40.02 54-50.01 54-60.01 54-70.01 55 55-10.01 55-20.01 55-30.01 55-31.01 55-40.01 55-50.01 55-60.01 55-99.01 56 56-10.02 56-11.02 56-20.01 56-21.01 56-30.01

Moisture – ASBC Air-Oven Method Moisture and Volatile Matter in Fats and Shortenings Moisture and Volatile Matter in Soy Flours Moisture – Modified Vacuum-Oven Method Moisture – By Distillation with Toluene, for Fats and Shortenings Moisture – Drying on Quartz Sand Mycotoxins Sampling Grain for Mycotoxins Aflatoxin – Thin-Layer Chromatography Method Aflatoxin – Rapid Screening Method Aflatoxin – Presumptive Test Aflatoxin – Liquid Chromatography Method Zearalenone – Thin-Layer Chromatography Method Zearalenone and alpha-Zearalenol in Corn – HPLC Method Identification of Aflatoxin on TLC Plates Deoxynivalenol in Wheat – TLC Method Fumonisins B1, B2, and B3 in Corn – Liquid Chromatographic Method Nitrogen Crude Protein – Automated Colorimetric Method Crude Protein – Improved Kjeldahl Method (archived) Crude Protein – Improved Kjeldahl Method, Copper Catalyst Modification Crude Protein – Kjeldahl Method, Boric Acid Modification Crude Protein – Micro-Kjeldahl Method Crude Protein – Udy Dye Method Crude Protein – 5-Minute Biuret Method for Wheat and Other Grains Crude Protein – Improved Kjeldahl Method, Copper-Titanium Dioxide Catalyst Modification Crude Protein, Calculated from Percentage of Total Nitrogen, in Feeds and Feedstuffs Crude Protein, Calculated from Percentage of Total Nitrogen, in Wheat and Flour Nitrogen Solubility Index Protein Dispersibility Index Crude Protein – Combustion Method Urea and Ammoniacal Nitrogen Oxidizing, Bleaching, and Maturing Agents Benzoyl Peroxide – Quantitative Method Quantitative Method for Bromates Ammonium Persulfate – Quantitative Method Azodicarbonamide in Premix Physical Dough Tests Extensigraph Method, General Rheological Behavior of Flour by Farinograph: Constant Flour Weight Procedure Rheological Behavior of Flour by Farinograph: Constant Dough Weight Procedure Farinograph Table for Constant Dough Weight Method Only Approximate Corrections for Changing As-Is Farinograph Absorption to 14.0% Moisture Basis, for Constant Dough Weight Method Only Alveograph Method for Soft and Hard Wheat Flour Mixograph Method Determination of the Water Absorption Capacity of Flours and of Physical Properties of Wheat Flour Doughs, Using the Consistograph Determination of Rheological Behavior as a Function of Mixing and Temperature Increase in Wheat Flour and Whole Wheat Meal by Mixolab High-Speed Mixing Rheology of Wheat Flour Using the doughLAB Physical Tests Test Weight per Bushel Corn Breakage Susceptibility Particle Size Index for Wheat Hardness Single-Kernel Characterization System for Wheat Kernel Texture Particle Size of Wheat Flour by Laser Instrument Specific Volume Guideline for Determination of Particle Size Distribution Glossary – Barley Physicochemical Tests Alkaline Water Retention Capacity Solvent Retention Capacity Profile Hydration Capacity of Pregelatinized Cereal Products Flour Swelling Volume Water Hydration Capacity of Protein Materials


(Continued)

56-35.01 56-36.01 56-40.01 56-50.01 56-60.01 56-61.02 56-62.01 56-63.01 56-70.01 56-81.03 56-99.01 58 58-10.01 58-11.01 58-12.01 58-13.01 58-14.01 58-15.01 58-16.01 58-17.01 58-18.01 58-19.01 58-20.02 58-25.01 58-30.02 58-35.01 58-39.01 58-40.01 58-45.01 58-50.01 58-53.01 58-54.02 58-82.01 58-99.01 61 61-01.01 61-02.01 61-03.01 61-99.01 62 62-05.01 62-20.02 62-25.01 62-40.01 62-50.01 64 64-40.01 64-50.01 64-60.01 64-70.02 64-71.01 66 66-20.01 66-41.01 66-42.01 66-50.01 66-60-01 70 70-15.01 70-20.02 70-25.01 70-40.01

Method for Determining Water Hydration Capacity and Percentage of Unhydrated Seeds of Pulses Firmness of Cooked Pulses Water Hydration (Absorption) of Rolled Oats Pelshenke Test (Wheat-Meal Fermentation Time Test) Sedimentation Test for Flour Sedimentation Test for Wheat Modified Sedimentation Test for Wheat Micro Sedimentation Test for Wheat Sodium Dodecyl Sulfate Sedimentation Test for Durum Wheat Determination of Falling Number Glossary – Grain and Flour Special Properties of Fats, Oils, and Shortenings Cloud Point Cold Test Determination of Oil Color Determination of Congeal Point Consistency – Penetration Method Determination of Free Fatty Acids Determination of Peroxide Value – Acetic Acid-Chloroform Method Preparation of Methyl Esters of Long-Chain Fatty Acids Fatty Acid Composition by Gas Chromatography Total, Saturated, Unsaturated, and Monounsaturated Fats in Cereal Products by Acid Hydrolysis and Capillary Gas Chromatography Refractive Index Solid Fat Index – Dilatometric Method Iodine Value of Fats and Oils – Cyclohexane-Acetic Acid Method Acetone-Insoluble Lecithin Dropping Point – Automatic Determination of Melting Point in Fats Melting Point – Capillary Method Monoglycerides and Free Glycerol Saponification Value Slip Melting Point Oil Stability Index Smoke, Flash, and Fire Points Glossary – Lipids Rice Amylograph Method for Milled Rice Determination of the Pasting Properties of Rice with the Rapid Visco Analyser Amylose Content of Milled Rice Glossary – Rice Preparation of Sample Preparation of Sample: Bread Preparation of Sample: Semolina and Feedstuffs Preparation of Sample: Fruit and Fruit Products Preparation of Sample: Dried Pasta and Noodle Products Preparation of Sample: Malt Sampling Sampling of Fats and Shortenings Sampling of Feeds and Feedstuffs Sampling of Flour, Grain Products, and Feed Products in Sacks Manual Sampling of Wheat and Other Whole Grains Mechanical Sampling of Dry, Free-Flowing Granular Material Semolina, Pasta, and Noodle Quality Determination of Granularity of Semolina and Farina: Sieving Method Macro Scale Pasta Processing Micro Scale Pasta Processing Pasta and Noodle Cooking Quality – Firmness Guidelines for Laboratory Preparation and Cooking of Japanese Udon Noodles Solutions Preparation of Buffer Solutions Preparation and Standardization of Hydrochloric Acid Solution Preparation of Indicator Solutions Preparation and Standardization of Ammonium and Potassium Thiocyanate Solutions

457

(Continued)

458


Table 2

(Continued)

70-50.02 70-60.01 70-70.01 70-75.01 70-80.01 74 74-09.01 74-10.02 74-30.01 76 76-11.01 76-13.01 76-21.01 76-22.01 76-30.02 76-31.01 76-33.01 78 78-40.01 78-60.01 80 80-04.01 80-05.01 80-10.01 80-50.01 80-51.01 80-53.01 80-60.01 80-68.01 82 82-20.01 82-21.01 82-22.01 82-23.01 82-24.01 86 86-01.02 86-02.01 86-03.01 86-05.01 86-06.01 86-10.01 86-31.01 86-40.01 86-45.01 86-47.01 86-49.01 86-50.02 86-51.01 86-70.01 86-72.01 86-80.01 86-90.01 89 89-01.01

Preparation and Standardization of Potassium Permanganate Solution Preparation and Standardization of Silver Nitrate Solution Preparation and Standardization of Sodium or Potassium Hydroxide Solution Preparation and Standardization of Sodium Thiosulfate Solution Preparation and Standardization of Sulfuric Acid Solution Staleness/Texture Measurement of Bread Firmness by Universal Testing Machine Measurement of Bread Firmness – Compression Test Staleness of Bread – Sensory Perception Test Starch Starch – Glucoamylase Method with Subsequent Measurement of Glucose with Glucose Oxidase Total Starch Assay Procedure (Megazyme Amyloglucosidase/alpha-Amylase Method) General Pasting Method for Wheat or Rye Flour of Starch Using the Rapid Visco Analyser Pasting Properties of Oat – Rapid Viscosity Analysis Determination of Damaged Starch Determination of Damaged Starch – Spectrophotometric Method Damaged Starch – Amperometric Method by SDmatic Statistical Principles Definitions of Statistical Terms Statistical Evaluation of Test Methods – Estimation of Variance in Analytical Tests Sugars Determination of Simple Sugars in Cereal Products – HPLC Method Determination of Saccharides by Liquid Chromatography Determination of Glucose in Sugar Mixtures – Glucose Oxidase Method Determination of Sucrose Solids in Syrups – Refractometer Method Solids in Syrups – Spindle Method Determination of Reducing and Nonreducing Sugars Determination of Reducing Sugars – Schoorl Method Tables Notes on of Use of Tables 82–21, 82–22, 82–23, and 82–24 Table: Conversion of Farinograph Absorption to 14.0% Moisture Basis (Constant Weight Method Only) Table: Correction of Analytical Values to 14.0% Moisture Basis Table: Flour Weight to Give 100 g at 14.0% Moisture Content Table: Multiplication Factors to Correct Weights to 14.0% Moisture Basis Vitamins Vitamin A – Ultraviolet Absorption Method Vitamin A – Carr-Price Method Vitamin A in Enriched Flour Vitamin A and Carotene Analysis of Vitamins A and E by High-Performance Liquid Chromatography Ascorbic Acid – Indophenol-Xylene Extraction Method Vitamin B6 Complex – Microbiological Method Vitamin B12 – Microbiological Method Choline Total Folate in Cereal Products – Microbiological Assay Using Trienzyme Extraction Niacin in Enrichment Concentrates Niacin and Niacinamide in Cereal Products Niacin – Microbiological Method Riboflavin – Fluorometric Method Riboflavin – Microbiological Method Thiamine – Thiochrome Method B-Vitamins in Vitamin Concentrates by HPLC Yeast Yeast Activity, Gas Production

AACCI Approved Methods of Analysis, 11th edition.


See also: Carbohydrates: Starch: Analysis of Quality; Fats: Lipid Chemistry; Food Grains and the Consumer: Labelling of GrainBased Foods; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; The Composition of Food Grains and Grain-Based Products; Units of Grain Science and Trade: Equivalence between the US, Chinese, and Metric Units; Grain Marketing and Grading: Identification of Varieties of Food Grains; Processing of Grains: Cereals: Breakfast Cereals; Proteins: The Enzymes Associated with Food Grains and Their Functions in Processing; The Protein Chemistry of Cereal Grains; Scientific Organizations Related to Grains: Scientific Societies Associated with Grain Science; Wheat-Based Foods: Cereals: Overview of Uses: Accent on Wheat Grain.

459

Further Reading AACCI (2004) International Methods of Analysis, 11th Ed. St Paul, MN, USA: AACC International. ICC (2002) ICC Standard Methods. Vienna, Austria: International Association for Cereal Science and Technology.

Relevant Websites https://www.icc.or.at/standard_methods – The International Association for Cereal Science and Technology (ICC). http://www.aaccnet.org/Pages/default.aspx – AACC International; Formerly the American Association of Cereal Chemists (AACCI).

Appendix 3. Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease JM Jones, St. Catherine University, St. Paul, MN, USA V Zevallos, University Medical Center, Mainz, Germany CW Wrigley, The University of Queensland, Brisbane, QLD, Australia ã 2016 Elsevier Ltd. All rights reserved.

Topic Highlights

• • • • •

Celiac disease involves damage to the small intestine after eating gluten-containing foods. Treatment is lifelong avoidance of gluten in the diet. Foods and ingredients to avoid in a gluten-free diet are listed together with notes in some cases. Many foods are permissible, and examples of these are listed. Recipes are provided for gluten-free baking, plus suggestions for gluten-free shopping.

(rye, triticale, and barley) have storage proteins similar to those of wheat; their storage protein (gluten) is similar enough to cause CD, but not to form dough suited for making goodquality bread. This article reviews dietary requirements and some food strategies for gluten-free cooking. Tables 1 and 2 provide information about the gluten-free status (or otherwise) of raw dietary sources and of processed foods. Some of the information has been adapted and modified from websites listed in ‘Relevant Websites.’ Some recipes have been adapted from the books acknowledged.

Learning Objectives

Dietary Requirements for Celiac Patients

• •

In addition to gastrointestinal problems, celiac patients have anemia, low antioxidant status, arthralgia, fatigue, infertility, neuropathy, and weight loss. Thus, in addition to a gluten-free diet (GFD), dietary strategies must address other aspects.

To understand the concept of a gluten-free diet. To be able to access a reference resource listing foods and ingredients that do or do not contain gluten.

•

Introduction Celiac disease (CD; ‘coeliac’ in UK spelling) is an autoimmune condition occurring in genetically susceptible individuals. It is characterized by histological damage of the small intestinal mucosa after ingestion of foods containing gluten proteins. Gluten is found in foods containing wheat and wheat-related grains such as kamut and spelt, barley, rye, and triticale; the intake of oats is limited due to a likelihood of cross contamination with wheat. CD causes the small intestine to release an array of proinflammatory cytokines. The net result from the intestinal damage and the various reactions is that affected people absorb nutrients poorly and develop secondary complications affecting various organs. To prevent the release of inflammatory markers and intestinal villus destruction, their diets must completely eliminate foods containing these offending grains. Doing so can be a challenge without specific knowledge concerning food composition, the ingredients in our diets, and clinical support from a trained nutritionist/dietitian. However, the selection of packaged foods is assisted by labeling with the gluten-free symbol (Figure 1), which applies to foods with less than 20 ppm of gluten protein. What is gluten? It is the protein complex that gives the special elastic properties to dough made from wheat flour. This elastic gluten is formed from the storage protein of the wheat grain. To the wheat seed, this stored protein is a resource for the growing plant. For us humans, this stored protein becomes the gluten formed by mixing wheat flour with water, thereby giving dough its suitability for making leavened bread and related foods from wheat flour. The close relatives of wheat

460

• • •

First, their diets should be filled with antioxidants and dietary fiber from allowed whole grains, such as sorghum, brown rice, and oats (which are certified gluten-free), and from easy-to-digest vegetables, fruits, and dried fruits. This type of diet can help mitigate the effects of increased inflammatory molecules and free-radical load, which appear to remain elevated in many CD sufferers over a year after a GFD has been strictly adopted. Second, minerals such as zinc and magnesium and vitamins are necessary to help promote healing of the inflamed mucosa. Foods and nutrients that can address the anemia and help prevent osteoporosis are also important. Fiber- and antioxidant-rich diets are useful in prevention of various types of cancers, several of which are a much higher risk in CD patients.

Thus, good-tasting diets should deliver adequate iron, folate, dietary fiber, and antioxidant potential by combining nonoffending grains and antioxidant-rich vegetables, fruits, and dried fruits.

Foods and Ingredients to Avoid The following foods contain gluten (as is relevant for the dietary needs of people with CD). They should thus be avoided in a GFD, unless there is labeling that gives assurance of a gluten-free status:

• •

Atta. Barley malt, barley extract, and barley flour.


http://dx.doi.org/10.1016/B978-0-12-394437-5.00249-7

APPENDIX 3 | Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease

• • • • • • • • • • • •

Beer, ale, porter, stout, and other fermented beverages. Breads and hamburger buns made from wheat, rye, triticale, or barley (possibly oats#). Breakfast cereals containing wheat, rye, triticale, or barley, malt extract, germ, and bran from these grains (possibly oatsþ). Broth/bouillon.** Bulgur or burghul. Cakes and cake mix. Caramel coloring, probably made from wheat.** It is likely that trace amounts of gluten can be present but as long as those values are below 20 ppm, caramel coloring even derived from wheat can be considered gluten-free. Casseroles, cream (white) sauces, and meat stews are often thickened with wheat flour. Cereal (cereal extract and cereal binding). Cheeses of some types – blue cheese, cheese spreads, and processed cheese.** Cocoa-based malted beverages. Coffee substitutes, such as ‘ersatz.’

• • • • • • • • • • • • • • • • • • • •

Figure 1 The gluten-free symbol, indicating that the food contains less than 20 ppm of gluten protein. This is an example; there are other forms of the gluten-free symbol.

Table 1

Communion wafers. Couscous. Cracker meal and crackers made with wheat. Croutons. Croissants. Crumpets. Custard powder and pudding mixes. Edible starch. Farina. Filler. Fish and other meats with batter or breading. Flours of various types – all-purpose, bleached, self-raising, enriched, high-protein, high-gluten, and graham. Fu (a type of prepared wheat gluten in Japanese cuisine). Wheat products, including but not limited to bread, brown bread, durum, gluten, glutenin, granary, wheat germ, sprouted wheat, cracked wheat, tabbouleh, Oriental wheat, vital gluten, and wheat starch.þ Hordeum (Hordeum vulgare). Hydrolyzed wheat gluten, hydrolyzed wheat protein, and hydrolyzed oats.# Ice cream, if with cone, cake, or crumbs. Ketchup.** Licorice. Malt, malt beverages, malt extract, malted milk, malt flavoring, malt syrup, and malt vinegar. Matzo (matzah). Meat pies, meat sauces, and sausages.** Milk flavorings. Miso (may contain barley). Muffins. Mustard powder.**

Summary of the main raw and partially processed gluten and gluten-free dietary sources Gluten-free

Grains and alternatives

Meat, poultry, fish, shellfish, and meatless alternatives Milk products, cheese, and eggs Fruit, vegetables, nuts, seeds, and pulses

Drinks and alcohol

• • • • • •

461

Amaranth, buckwheat, chestnut, corn (maize), millet, polenta (cornmeal), quinoa, rice, sago, sorghum, soya, tapioca, teff, uncontaminated oats Fresh meats and poultry and cure, cooked, and smoked pure meats. Dried, fresh, kippered, and smoked fish and shellfish and fish canned in oil, brine, and water. Plain tofu Cheese, eggs, and milk (liquid and dried) cream (single, double, whipping, clotted, soured, cre`me fraıˆche), buttermilk, plain, yogurt Fresh, frozen, canned, dried, baked, and boiled fruit and vegetables. Plain nuts, seeds, and pulses

Cocoa, coffee, fruit juice, ginger beer, squash, tea, water, cider, gluten-free beer, lagers, liquors, port, sherry, spirits, and wine

Adapted from Coeliac UK.

Unclear

Gluten

Meat, poultry, fish and tofu marinated or in sauces, burgers, meat pastes, paˆte´s, sausages. Soya mince, falafel, vegetable, and bean burgers

Barley, bulgur wheat, couscous, dinkel wheat, durum wheat, einkorn wheat, emmer wheat, KamutW, rye, semolina, spelt, triticale, wheat Meat, poultry and fish cooked in batter or bread crumbs, breaded ham, faggots, haggis, rissoles. Fish cakes, fish fingers, taramasalata

Some soft and spreadable cheeses, coffee and tea whiteners, fruit and flavored yogurt, fromage frais, and soya desserts Fruit pie fillings, processed vegetable products, deep-fried, microwave, and frozen chips, instant mash, potato waffles, roast potatoes. Roasted nuts and pulses in flavored sauces (baked beans) Cloudy fizzy drinks, drinking chocolate

Scotch eggs, yogurt, or muesli with whole grains and some blue-veined cheeses due to the introduction of mold Vegetable and fruit in batter and bread crumbs and dusted in flour, potato croquettes

Barley waters and squash, malted milk drinks, ales, beers, lagers, stouts

462 Table 2

APPENDIX 3 | Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease Summary of the main processed gluten and gluten-free dietary sources Gluten-free

Unclear

Gluten

Bread, cakes, and biscuits

Gluten-free biscuits, breads, cakes, crackers, muffins, pizza base, rolls, scones

Macaroons, meringues

Pasta, noodles, and breakfast cereals Soups, sauces, pickles, and seasonings

Gluten-free or free from gluten including corn (maize), rice and quinoa pasta, rice noodles, millet porridge, muesli, and rice porridge Vinegars, garlic pure, ground pepper, individual and mixed herbs and spices, mint sauces, mustard powder, salt, tomato puree, Worcestershire sauce

Breakfast cereals that contain barley malt extract

All biscuits, breads, cakes, chapatis, crackers, muffins, pastries, pizza bases made from wheat, rye, or barley flour Wheat-based breakfast cereals and canned, dried, and fresh wheat noodles and pasta

Home baking

Arrowroot, artificial sweeteners, bicarbonate of soda, corn starch, cream of tartar, food coloring, gelatin, icing sugar, potato starch, yeast, ground almonds Gluten-free ice cream cones, jelly, licorice root, seaside rock, homemade popcorn, plain rice cakes, and crackers

Confectionary, desserts, and savory snacks

Blend seasonings, brown sauces, canned or packed soups, curry powder, gravy granules, packed and jar sauces, pickles, salad cream, stock cubes, tamari, tomato sauce Baking powder, cake decoration, marzipan, ready-to-use icing

Chinese soy sauce

Chocolate, ice cream mousses, sweets, tapioca pudding. Flavored popcorn, potato and vegetable crisps, flavored rice cakes, and rice crackers

Snack made from wheat, rye, and barley, pretzels, ice cream cones, wafers, licorice sweets, pudding made using semolina or wheat flour

Batter mixes, bread crumbs, stuffing mix

Adapted from Coeliac UK.

• • • • • • • • • • • • • • • • • • • • • • • •

Oats and oat products, if not identity-preserved and free of offending grains.# Pasta, noodles, and couscous from durum semolina or wheat and udon. Pastry and pastry mix. Pickles. Pikelets and pancakes. Pizza. Porridge, if made with wheat. See footnote about oatmeal.# Potato salad. Relish. Rice malt, rice syrup, and brown rice syrup.** Rye-based foods. Sauces.** Scotch (may contain caramel color from wheat but considered gluten-free as long as less than 20 ppm). Seitan – an imitation meat made from cooked gluten. Soups (canned and packet) are often thickened with wheat flour. Soy sauce.** Spaghetti, vermicelli, and semolina. Spelt and other wheat relatives including einkorn, dunkel, kamut, and emmer. Stuffing in poultry. Sweets often contain wheat-based fillings, such as filled chocolates. Tomato sauce.** Triticale-based foods (triticale is a hybrid of wheat and rye). Texturized vegetable protein foods. Wheat, wheat berry, wheat bran, wheat germ, wheat germ oil, wheat gluten, and wheat starch þ (but permissible if gluten content is below 20 ppm).

Footnotes to the Avoidance List **May be made with wheat. # ‘Pure, uncontaminated’ oats, only if from fields and facilities dedicated to produce oats. Otherwise, oats should be tested for purity and absence of gluten-containing cereals. These oats may be consumed in quantities of less than one cup per day. þ Starch and modified food starch. The Food and Drug Administration (FDA) regulations state that ‘starch’ implies corn starch (made from maize), and if alternative starch is used, it will be identified as such (i.e., wheat starch). Further, the FDA now requires its declaration as an allergen, for example, ‘contains wheat’ or ‘made on equipment that processes wheat.’ Spices. Pure spices do not have offending grains; some mixtures may have gluten as a carrier. Flavorings. Flavorings are mostly derived from corn (maize) except if from barley malt or some used in meat products. Natural flavor may be made from a variety of plant materials, and the starting material should be confirmed.

Foods, Additives, and Ingredients that Are Gluten-Free The following additives are considered gluten-free. If any of these are listed on a food label, the food should be celiac-safe, unless there are other gluten-containing ingredients:

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Acacia gum (gum arabic) Adipic acid


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Alfalfa sprouts Algin Almonds Annatto Apples Arrowroot (not arrowroot biscuits made with wheat flour) Aspartame Bacon Baking yeast Basil Beans and peas Benzoic acid Beta-carotene BHA – Butylated hydroxyanisole BHT – Butylated hydroytoluene Breakfast cereals made from corn (maize), rice, and soy (but check label for the absence of malt) Brewer’s yeast Brown sugar Buckwheat Butter Calcium disodium EDTA Canola-based foods Carrageenan Caramel color – from corn in North America (but wheat is used in some countries) Carboxymethyl Carob bean gum Casein Cellulose Chickpeas Chocolate, if plain and unless cream-filled or further processed Cider Cocoa Coffee, unless ersatz (imitation) Coix (job’s tears) Corn syrup Corn syrup solids Cream of tartar Cyclamate Dextrose Eggs Ethyl maltol Fenugreek Fructose Fruit and vegetable juices Fumaric acid Gelatin Glucose Gram flour (chickpea) Guar gum Herbs Honey Invert sugar Jam Legumes Karaya gum Kasha (buckwheat) Lactic acid

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Lactose Lecithin Lentils Lupins Maize (corn) flour and corn-based foods Malic acid Maltodextrin – usually from corn, potato, or rice Maltol Mannitol Margarine Milk and milk-based foods (but these may have wheat flour added for thickening) Millet flour (various species) Methylcellulose MSG – monosodium glutamate Nuts Oregano Papain Peanuts, if plain, and peanut butter Pectin Pepper Polenta Polysorbate 60 and 80 Popcorn, if plain Potatoes and potato crisps, if plain Propylene glycol Psyllium Quinoa Rice flour and rice-based foods Saccharin Sago Salt Sodium benzoate Sodium metabisulfite Sodium nitrate; nitrite Sodium sulfite Sorghum Sorbitol Soybeans, soy protein isolate, and soy milk, unless labeled as not gluten-free Spices Stearic acid Sucralose Sucrose Sugar Sunflower seeds Tapioca Taro Tartaric acid Tartrazine Tea Teff Titanium dioxide Tofu Tragacanth Vanilla extract Vanillin Wheatgrass (gluten is a storage protein found in seeds) White vinegar – distilled Whey powder

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Wine Xanthan gum Xylitol Yam Yeast – questions even about some yeasts, though

Gluten-Free Mixes for General Baking The following recipes, providing gluten-free mixes for baking, are adapted with permission from the website of the Celiac Sprue Association at http://www.csaceliacs.org/recipes/FlourFormulas.php: cup ¼ about 250 ml; tbsp ¼ tablespoon (about 15 ml); tsp ¼ teaspoon (about 5 ml) A simple substitution Use 1 cup of brown rice flour for each cup of white wheat flour, but use only in an emergency, because this does not give a very desirable product. Capital health mixture for brown bread 1¼ cups (300 ml) brown rice flour ½ cup (125 ml) sorghum flour ½ cup (125 ml) corn starch ½ cup (125 ml) rice bran 1 tbsp (15 ml) xanthan gum General baking mix #1, Carol Fenster,* yield: 2 cups 1 cup rice flour 1/2–3/4 cup potato starch ¼ cup tapioca starch/flour General baking mix #2, Carol Fenster,* yield: 9 cups 3 cups garfava bean flour 2 cups potato starch 2 cups corn starch 1 cup tapioca flour 1 cup sorghum flour *Reproduced with permission from 1000 Gluten-Free Recipes by Carol Fenster (Houghton Mifflin Harcourt, 2008). See www.CarolFenster.com and www.CarolFensterCooks.com Original formula – low fiber, Bette Hagman,** yield: 3 cups 2 cups rice flour 2/3 cup potato starch 1/3 cup tapioca starch/flour Featherlight – low fiber, Bette Hagman,** yield: 3 cups 1 cup rice flour 1 cup corn starch 1 cup tapioca starch/flour 1 tbsp potato flour Four flour bean, Bette Hagman,** yield: 3 cups 2/3 cup garfava bean flour 1/3 cup sorghum flour 1 cup corn starch 1 cup tapioca starch/flour **Reproduced with permission from The Gluten-Free Gourmet Bakes Bread and other recipes from her books The GlutenFree Gourmet Cooks Comfort Food and Living Well Without Wheat by Bette Hagman. Cookie mix – very low fiber 2 cups sweet rice flour 2 cups rice four

1/2 cup tapioca flour Pastry mix, Mary Schluckebier,*** home economist, yield: 1 cup 1/8 cup potato flour 7/8 cup rice flour Cookie mix, Mary Schluckebier,*** yield: 2 cups ¼ cup chickpea flour 13/4 cup sorghum flour ¼ cup sweet rice flour Bread mix, Mary Schluckebier,*** yield: 2 cups 1 cup brown rice flour ½ cup potato starch ½ cup sweet rice flour 1 tbsp unflavored gelatin ***Reproduced with permission from Mary Schluckebier, home economist and executive director of the Celiac Support Association, Omaha, Nebraska, the United States. Gluten-free peanut butter cookies Original recipe yield: 30 cookies 2 cups peanut butter 1 cup white sugar 1 cup brown sugar 4 eggs, beaten 2 cups semisweet chocolate chips (optional) 1 1/2 cups chopped nuts (optional) Directions 1. Preheat oven to 350 F (175 C). Grease cookie sheet. (Parchment is better.) 2. Combine peanut butter, eggs, and sugar, and mix until smooth. Mix in chocolate chips and nuts, if desired. Spoon dough by tablespoons onto a cookie sheet. 3. Bake for 10–12 min or until lightly browned. Let the cookies cool on the cookie sheets for 5–10 min before removing. Sorghum bread: http://glutenfreesox.blogspot.com/2007/09/ sorghum-bread.html 2 cups sorghum flour 1½ cups tapioca flour ¼ cup þ 2 tsp sugar 3½ tsp xanthan gum 2/3 cup powdered milk 1½ tsp salt 1 tsp gelatin (unflavored) 1 1/8 tsp dry yeast 1¼ cups warm water (more if low humidity and less if high humidity) 1 tsp cider vinegar 1/4 cup oil 3 eggs (beaten and at room temperature) Combine dry ingredients in mixer. Add wet ingredients. Mix on high for about 2–3 min until well blended and it resembles thick cake batter. Spoon into greased loaf pan. Cover and let it rise in a warm place for about an hour. Bake at 375 C for about an hour (?) or until internal temperature reaches 205 C. Cover after about 15–20 min to prevent over-browning. Remove from oven, let it cool in its pan on a rack for about 15 min, and then remove from pan. If not eaten within a couple days, it should be frozen because it will mold fairly quickly.

APPENDIX 3 | Grains, Foods, and Ingredients Suiting Gluten-Free Diets for Celiac Disease See books listed in the preceding text by Mary Schluckebier and by Bette Hagman: Books by Carol Fenster – Cooking Free: 200 Flavorful Recipes for People with Food Allergies and Multiple Food Sensitivities; Wheat-Free Recipes and Menus; Gluten-Free 101: Easy, Basic Dishes Without Wheat; Special Diet Solutions: Healthy Cooking Without Wheat, Gluten, Dairy, Eggs, Yeast, or Refined Sugar; Wheat-Free Recipes & Menus : Delicious Dining Without Wheat or Gluten; Special Diet Celebrations: No Wheat, Gluten, Dairy, or Eggs; GlutenFree Celebrations: Memorable Meals without Wheat.

Tips for Gluten-Free Baking A mixture of a few gluten-free flours offers better texture and flavor than a single flour on its own. Generally, it is good to have two grainy or crumbly flours – amaranth, coconut, corn, rice, and millet – and a binding flour (buckwheat, arrowroot, tapioca flour, potato starch or flour, and bean flours) or binding agent (egg, guar gum, xanthan gum, flaxseed ‘gel,’ sago, or pregelatinized starches). Flaxseed ‘gel’: Simmer 1/4 cup flaxseeds in 3/4 cup water for 5–7 min, until thick. Strain the seeds out through a cheesecloth-lined strainer. Squeeze to get the gel. For extra lightness, whip the ‘gel’ and fold into the batter at the end of mixing. The gel can be used as an egg replacer in baking (4 tbsp ¼ 1 egg). Gums – guar, xanthan, carboxymethyl cellulose, and other gums or pregelatinized starches from an allowed source – help give the dough elasticity and thus serve to replace this gluten and improve crumb structure. Some recipes use a combination of binding agents and binding flours. While two or more flours usually work better, once in a while, there are recipes that work well with only one flour.

Flour Recommendations

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Amaranth gives a pleasant, nutty flavor for cakes, biscuits, and pancakes, but it must always be used with a binding flour. Soaking the flour overnight in acids such as yogurt or acidulated water may improve the final product. Coconut (from desiccated coconut) and other nut flours can be made in a food processor. Corn starch can be blended with cornmeal to make corn breads or muffins. Either brown rice or white rice is good for thickening gravies, sauces, and cream pies. Millet may make breads dry and coarse so do not use more than 20% of the flour mixture. Quinoa may require rinsing and soaking before being cooked. Buckwheat flour has a strong flavor that may be decreased if it is soaked in an acid ingredient. Arrowroot works well as a thickener. Tapioca is good when used in small quantities. It is good as a flour replacement for ‘breading’ and making fruit pies. Potato starch helps the texture in baking when used with other flours and is a good thickener. Potato flour has some of the protein and other parts of the potato, so it is not the

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same as potato starch but may be used in many of the same ways. Bean flours including soy can impart a bitter, ‘beany’ taste, so they are better when used as part of a blend. Texture and flavor, as well as nutrients and fiber, can be improved with small amounts of ground sesame seeds, ground flaxseed, and ground nuts. Almonds and macadamia nuts have the most neutral flavor. Toasting of nuts and seeds can bring out their flavor. Added protein helps to improve both nutrition and structure of gluten-free products, so nonfat dry milk, whey, gelatin, egg, or other protein sources are useful. Humectant ingredients, such as dried fruit or honey, can help products hold moisture and be less crumbly. About 2 tsp of almond flour per cup of flour may also help address dryness. Cutting finished products into small portions may also be helpful for keeping products fresh. Short warming in the microwave may also be helpful. Mix dry ingredients together to ensure they are well dispersed. Some may find that blending gluten-free flours, especially those which are quite powdery, into a plastic bag before adding them to wet ingredients makes blending easier. Acidic ingredients are helpful in making some types of breads rise.

Home Bread Makers Optimal results in a bread maker occur in a machine that is programmable. Capital Health (www.capitalhealth.ca) suggests the following for machines with a programmable mode. Set cycles as follows:

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First short knead ¼ 2 min. Use this time to add dry ingredients slowly to the wet ingredients. • Second full knead ¼ 20 min. • Rise ¼ 70 min. • Bake at 180 C (350 F) ¼ 50 min. Eliminate all other cycles by setting to 0 min. Batters often taste bitter, but the bitterness goes away with baking. Baking powders should be gluten-free baking powder. Baking powder can be made by mixing 4 tsp (20 ml) baking soda, 8 tsp (40 ml) cream of tartar, and 4 tsp (20 ml) corn starch. Blend well by sifting several times and store in an airtight container. Pastry is easier to work with if rolled between parchment or wax paper. Parchment, muffin cups, or easy release foil as baking liners make clean up easy and, more importantly, help to eliminate risk of cross contamination from baking pans. Gluten-free recipes are less forgiving than those with flour; greater precision is needed. It may take a number of attempts to change a family favorite into an acceptable gluten-free product. Some products adapt more easily than others. It is important to carefully document changes, so positive changes can be repeated and negative ones avoided.

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Tips for Gluten-Free Shopping Be vigilant – gluten can be added to numerous items to allow flow as in spice mixtures or dried fruit. Prepackaged flours and ingredients are less likely to be contaminated than those sold in bulk. But those who are very sensitive should use products labeled as gluten-free, rather than flours that should be glutenfree but may have been processed in plants that have had gluten-containing ingredients. These products might contain the product due to cross contamination. Buy amounts that can be used in a reasonable time. If larger amounts are purchased, store them in the refrigerator or freezer. This is especially important if the flours have higher amounts of fat such as amaranth, rice bran, ground flaxseed, quinoa, full-fat soy, and nut flours. It may be useful to make a part of the kitchen gluten-free, to reduce the risk of cross contamination. This strategy is particularly useful for a child who needs to be gluten-free.

Tips for Gluten-Free Travel Before you travel to another country, check out the website for the Celiac Society in that country. The celiac.org site has a travel guide with a list of Celiac Society websites for over 60 countries. Fresh food of all permissible types is also a good tip for travelers.


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Propose a definition of gluten. Perhaps you will need two overlapping definitions: one that relates to its ability to form the elastic dough needed for bread making and another in relation to CD. As an exercise in using the checklists provided, take a copy of this article to a supermarket and check the gluten-free status of a range of foods, comparing packet labels with the lists provided in this article. What are the functions of gluten in foods? Can that concept be useful as a guide to which foods are gluten-containing or gluten-free?


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Prepare a balanced menu of gluten-free meals for a week, suitable for a young person (say, under 10 years) and for an

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elderly person (say, over 70 years). Indicate where the ingredients would best be bought. Find out the ways in which the gluten content of foods is determined. As in the question earlier (the first revision exercise), you may find that there are two approaches to gluten analysis: – The amount and quality of gluten are determined in relation to the suitability of wheat and flour for baking bread and for the many other foods made from wheat. This aspect accentuates the functional properties of gluten (usually in wheat). – The possible presence of a small amount of gluten also needs to be determined in foods to ensure that their ‘gluten-free status’ is justified. What levels of gluten content are considered to be ‘gluten-free’ by the US Food and Drug Administration and by the Codex Alimentarius?

See also: Appendix 2: Lists of Standardized Testing Methods for the Analysis of Grain and Grain-Based Foods; Food Grains and the Consumer: Grains and Health: Misinformation and Misconceptions; Labelling of Grain-Based Foods; Food Grains: Intolerance, Allergy and Diseases: Celiac Disease; Cereal Allergens; The GlutenFree Diet; Grain Composition and Analysis: Standardized Test Methods for Grains and Grain-Based Products; Proteins: The Protein Chemistry of Cereal Grains; The Basics: The Grains that Feed the World; The Cereal Grains: Barley: An Overview of a Versatile Cereal Grain with Many Food and Feed Uses; Durum Wheat: Overview; Oats: Overview; Rye Grain: Its Genetics, Production, and Utilization; Triticale: Overview; Wheat: An Overview of the Grain That Provides ‘Our Daily Bread’; Wheat Processing: Gluten and Modified Gluten; The Gluten Proteins of the Wheat Grain in Relation to Flour Quality.

Further Reading Casper JL and Atwell WA (2014) Gluten-Free Baked Products. St Paul, MN: AACC International. Wrigley CW (2004) Foods for celiac diets. In: Wrigley C, Corke H, and Walker C (eds.) Encyclopedia of Grain Science, vol. 3, pp. 449–457. Oxford: Elsevier.

Relevant Websites www.celiaccentral.org – The National Foundation for Celiac Awareness. celiac.com – National-Foundation-for-Celiac-Awareness. coeliac.org.uk – UK Coeliac Society. coeliac.org.au – Coeliac Society of Australia. http://www.csaceliacs.org – Celiac Sprue Association. celiac.org – Celiac Disease Foundation.

GLOSSARY A A starch Large-granule industrial starch obtained by wet milling from wheat (Triticum aestivum L.). A starch is distinct from B starch, which consists of smaller granules. Abiotic Environmental features, such as climatic and edaphic factors, that do not derive directly from the presence of other organisms. Acaricide A pesticide targeted to mite control. Acarina Commonly known as mites, pests of cool and moist stored grain. Acceptable daily intake (ADI) The measure of the amount of a particular chemical in food which can be consumed on a daily basis over a lifetime without harm. ACE inhibitor An agent causing inhibition of a particular enzyme within the kidney which otherwise causes constriction of the arteries, resulting in high blood pressure. Achene A dry one-seeded fruit with a close-fitting wall that does not open at maturity. Acid detergent fiber Fibrous fraction consisting primarily of cellulose and lignin expressed as a percentage. Acylated betacyanin Betanidin 5-O-b-glucuronosylglucoside or betanidin 6-O-b-glucoside acylated with organic acids (e.g., ferulic, p-coumaric, or 3-hydroxy-3-methylglutaric acids). Adequate intake (US) (AI) The amount that covers individual needs but insufficient data prevent setting a recommended dietary allowance level. Adsorption–desorption curve Curve corresponding to the equation describing the ‘equilibrium moisture content’/‘equilibrium relative humidity sorption’ behavior of grain. Aeciospore Spore produced in an aecium of a rust fungus. Afila Term sometimes used to describe semileafless cultivars, from af, the symbol for the gene that controls whether the plant has leaflets or tendrils in their place. Aflatoxin A toxin known to be a human carcinogen, found in peanuts and other grains; produced by the soil fungus Aspergillus flavus. Agronomy Crop husbandry; the study of soil/crop environment and improvement of crop production. Albumin A class of proteins characterized as being soluble in water or dilute salt solutions. Include a family of storage proteins with sedimentation coefficients (S20,w) of about 2. Aleurone layer The vitamin-rich inner layer of the branny coat of cereal grains. It covers the endosperm tissue in seeds. Alfa-Laval/Raisio process Wheat wet-milling process named by starch production companies involved in process development.

Allele Alternate forms of a gene or DNA sequence. Allelopathy Inhibition of the growth of a plant by another plant. Allergenic proteins Allergens naturally occurring in some grains. They may cause allergic reactions, such as itching, sneezing, rhinorrhea, dyspnea, etc. Allotetraploid (allo – meaning different) Species that contains four different genomes (4x, x ¼ genome) from different genera, species, or subspecies. Alternate host The second host of an heteroecious pathogen. Alternative (or ancilliary) host Other hosts on which a particular pathogen may grow and survive. Amaranthine Betanidin 5-O-b-glucuronosylglucoside, historically used ‘amaranthin’; nowadays amaranthin is expressed as a lectin. Amino acids Group of nitrogenous compounds which, when polymerized, form protein. Chemically, they all have (one or more) carboxylic acidic groups (COOH) and amino groups (NH2). There are 20 amino acids, of which eight cannot be made in the human body and are therefore termed ‘essential amino acids’ (methionine, tryptophan, threonine, valine, leucine, isoleucine, phenylalanine, and lysine). A ninth, histidine, is essential for growing children. Amorphous domain Orderless region, mainly contains amylose and some branch points of amylopectin. This comprises 70% of the starch granules. Amylase An enzyme that breaks down (hydrolyzes) starch to mono- and disaccharides. Amylopectin A branched polymer containing, in addition to anhydroglucose units linked together as in amylose through a-D-(1 ! 4) glucosidic bonds, periodic branches at the carbon-6 position. Amylose A linear polymer, consisting of anhydroglucose units by a-D-(1 ! 4) linkages with a degree of polymerization of some hundreds of glucose residues (200–2000 units). Anamorph Asexual state of a fungus. Aneuploid A plant lacking a chromosome or possessing an additional chromosome. Angkak An East Asian red-coloring agent made by growing species of the fungus Monascus on rice. Animal feed Food or nourishment for animals. Anthesis Time/growth stage of plant when flowering occurs. Anthocyanin A red or blue, flavonoid, water-soluble pigment found in plants and commonly used by the food industry as a colorant.

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Glossary

Antinutrient Compound that inhibits or counteracts the absorption or functioning of a vitamin. Antinutritional factors Compounds that have an adverse effect on nutrition. Antioxidants Compounds that prevent oxidative reactions by hydrogen donation or chelation of prooxidant minerals such as iron. Antivitamin A compound, natural or synthetic, that antagonizes the action of a particular vitamin when eaten and can cause a vitamin deficiency condition. Apoplast Space external to cells, collectively comprising cell walls, intercellular spaces, and xylem. Apoplastic transport The nonregulated transport of water and low-molecular-weight substances between cells, without energy expenditure. Apparent amylose content The content in milled rice of the linear fraction of starch based on iodine colorimetry. It correlates with cooking and eating qualities. Apparent metabolizable energy Energy in the feed consumed minus energy excreted from the cloaca of poultry, which includes fecal and uric acid excreted from the kidneys. APSIM The Agricultural Production Systems Simulator series of crop models developed by CSIRO Sustainable Ecosystems, Australia. Arepas National bread of Venezuela and Colombia produced from degermed and precooked maize flour. Arepas are generally stuffed with meats, cheese, jellies, and other fillings. Aroma The pleasant smell characteristic of a food. The chemical composition of a baked food is very complex and the aroma is caused by a mixture of volatile compounds from the fermentation process and from the browning stage of baking. Aromatic rice Rice grains with aroma, or fragrance, mainly from the component of 2-acetyl-1-pyrroline. Arteriosclerosis A medical condition in which the walls of the arteries become hard and thick, sometimes interfering with blood circulation. Ascospore A fungal spore resulting from the sexual process and produced in an ascus. Ash The amount of mineral matter in mill products, especially white flour. Ash content is widely used as an index of product refinement (degree of separation of endosperm (flour) from other constituents). Asian noodles Oriental style product made by sheeting and cutting dough. Asian wheat noodles Noodles made from wheat flour, usually by a sheeting and cutting process. They may be made with or without table salt and with or without the addition of alkalis such as sodium carbonate (see ‘Kansui’). Atherosclerosis The progressive accumulation of fatty substances and fibrous tissue in the arteries. If arteries become blocked, this can result in a heart attack or stroke. Autoecious pathogen A fungus that produces all spore types on the same host. Autoxidation A chemical process by which unsaturated fats and oils are oxidized and produce undesirable flavors in foods. Available energy Energy from feed that is digested and available for metabolism by animals (MJ kg1).

Average molar mass One of a series of numeric characteristics of a polymer used to describe the extent of its polydispersity. Number average molar mass (Mn) is equal to the sum of the number of species multiplied by their masses divided by the amount of all species. Mass-average molecular mass (Mm) is equal to the sum of the number of species multiplied by the square of their molecular mass of each species divided by the sum of the mass of each species. Mm > Mn, for polydisperse systems, but for monodisperse systems, the two characteristics are equal. Awn A mid or lateral vascular nerve on the dorsal surface of the lemma or glume of a wheat hear (ear); it extends into a hard or bristly appendage of varying lengths. Awns can form on either or both the lemma and glumes and can number from one to several. Axil The area between main stem and leaf where a dormant bud is located. Axillary buds Buds in leaf axils. In pea these are normally dormant, but can be released from dormancy to grow into new shoots if the plant is damaged. B B starch Small-sized starch granules. As a commercial product, this is generally an impure form of wheat starch (protein max. 5%, lipids max. 0.5%, minerals max. 1%) obtained as a by-product of wet milling. Back-slopping Traditional process for maintaining an active microbial culture by retaining a portion of the successful fermentation with high microbial activity and using it to inoculate a fresh fermentation. Baker’s percent A method of calculating formula ingredient weights by assigning flour the value of 100%, with all other ingredients calculated as a percentage of the flour weight. Baking The period in in which a fermented dough is exposed to high temperatures, causing the rising and heat setting of the structure of the final product. Barley Hardy, awned cereal of the genus and species Hordeum vulgare, used as food and in making spirits. Beehive oven An ancient form of oven still used today in some areas. Shaped like the classical beehive. The interior is heated by wood burning on the hearth. After the oven is hot, the ashes are scraped out, bread dough pieces placed on the hearth, and the opening sealed. Baking occurs from the residual heat held in the heavy stone or masonry walls. Beer Fermented alcoholic beverage (ethanol content of 4–12%) made from cereals. Bere barley A very primitive type of barley that survives in marginal environments. In the Orkney Islands, it is used to prepare a type of bread called a ‘bere bannock.’ Betacyanin Glycoside or acylglycoside of the aglycone betanidin/isobetanidin, including simple betacyanins and acylated betacynins. BHT An antioxidant or preservative used to prolong shelf life. Binding protein (BiP) ‘A molecular chaperone’ that assists protein folding. Bioactive Biologically active. Bioavailability The level of absorption of a consumed nutrient. Biodeterioration Deterioration of materials (often manufactured or otherwise worked) through the action of living organisms.

Glossary Biological nitrogen fixation The conversion of elemental nitrogen to organic nitrogen. Biologically active Has specific functions in body, for example, decrease disease risk. Biorefinery A local unit which provides whole crop harvesting and processing services in order to improve the infrastructure and utilization of plant husbandry as a whole. Biosynthesis Synthesis of organic chemicals from simple ones by living cells. Biotechnology (in this context recombinant DNA technology) Technology to directly introduce genes from other species that code for desirable traits, to produce a so-called GMO (genetically modified organism). Biotic Those features of the environments of organisms arising from the activities of other living organisms; as distinct from such abiotic factors as climatic and edaphic influences. Birefringence pattern A pattern in the shape of a Maltese Cross shape that can be observed in granular starch under polarized light in a microscope. This reflects radial distribution of submicron crystallites within the starch granule. Blanching Heat treatment to remove skin (testa) from peanut kernels. Blended whisky A mixture of malt and grain whiskies. Blistering In a breakfast cereal context, formation of crisp bubbles on the surface of flakes that improve eating texture. Blue maize Floury or soft endosperm maize that contains blue-purple coloration in the aleurone layer due to the presence of anthocyanins and flavonoids. Thus, it is considered a nutraceutical food and generally sold as flour, tortilla chips, and table tortillas. Boundary layer Layer of nonturbulent air, not readily mixed with the bulk air, adjacent to a surface, for example, soil or leaf surface. It retards the transfer of water vapor, heat, momentum, and other entities, between the surface and the bulk atmosphere. Bracts A much reduced leaf of a plant that has often evolved into a specialist protective function as well as providing a surface for photosynthesis, for example, the glumes and the lemma and palea of species of grasses. The sterile, leaf-like structures that enclose the grass spikelet (glumes) and the floret (lemma and palea). Bran An industrial product of the milling of refined flour. It consists of all kernel layer external to the starchy (storage) endosperm. Bran finisher Machines that use impact to remove adhering endosperm from bran at the end of the break system. The same machine, when used to remove endosperm from shorts is commonly referred to as a ‘shorts duster.’ Bread In a narrow sense, baked foods made of a developed dough containing flour, water, yeast, and salt, and usually containing malt, shortening, and sometimes milk. Bread may contain other ingredients as well. Typically, the dough is fermented and otherwise processed before baking to give a low-density loaf or roll with a clearly defined, relatively dark crust and a soft, silky light-colored crumb. In a general sense, almost any food containing a considerable amount of grain flour that has made into a dough by mixing with a liquid, then baked. See also, specific kinds of bread, such as crispbread, quickbread, and flatbread.

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Bread molding Forming a piece of soft fermenting dough into a shape that it can be baked. Often done automatically and placed in pans. Important to the final bread’s internal texture. Break rolls The first sets of rolls that wheat goes through in the milling process. They are corrugated and serve to break open the wheat kernel but do not produce much flour. Break system Part of the milling process that removes bran from endosperm by successive roller mill passages. Breakdown viscosity Viscosity recorded when maximum viscosity of hot starch paste is subjected to high temperature (usually 95 C) and mechanical shearing. During this time, the viscosity usually decreases due to further disruption of the granules, solubilization of amylose, and alignment of solubilized molecules in the shear direction. Breeding The development of new types of organisms to produce improved types through sexual or asexual (genetic or cellular) means. Breeding for impact The development of new types or varieties of plants and animals that are adoptable by the farmers/other end users and produced by them for food security, cash income, and creation of wealth for their wellbeing. Brew A term applied to a liquid or semiliquid yeasted mixture that is used as a preferment in bread production. Brewing Process of producing liquors such as beer and stout from malt and hops. Brittle rachis A genetic characteristic of a cereal rachis where on drying it spontaneously breaks and separates from the plant, enabling easier distribution in nature through wind or insect action. Brown rice Cargo, the rice grain with the protective hull removed. Bt rice Rice carrying insecticidal gene(s) from Bacillus thuringiensis. Bubble stability The stability of bubble walls during expansion. Buckwheat groats A dehulled kernel from buckwheat achene which consists of hull (pericarp) and kernel or seed (testa, aleurone layer, embryo, and endosperm). C C3 and C4 plants C4 plants have a photosynthetic pathway in which carbon dioxide reacts with phosphoenolpyruvic acid forming a 4-carbon compound (oxaloacetic acid) instead of 3-carbon compound (phosphoglyceric acid) of the photosynthetic pathway of C3 plants. Candidate genes Genes that have passed through a selection or screening process to become possible candidates for genes controlling a particular trait. Canola A term to describe seed from the genus Brassica napus or B. rapa, in which the oil has < 2% erucic acid and the meal has < 30 mmol g1 of four specific glucosinolates. Canopy The physical structure of crop, made up of leaves, stems, and other plant organs. Caryopsis A one-seeded indehiscent fruit in which the pericarp is fused with a seedcoat; the fruit of members of the grass family. Cassava A tropical plant which stores starch in its roots, also called ‘manioc.’

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Cell wall A protective structure present outside the plasmalemma, delineating plant cells. Center of origin According to theories developed by N. Vavilov, the geographical area where a plant species evolved, usually also representing its center of maximum genetic diversity. Cereal grains Dry indehiscent fruits, so called because they contain a pericarp (fruit wall). Cereals Include wheat, rice, maize (corn), popcorn, barley, rye, oats, sorghum, millets, fonio, triticale, and canary seed. Quinoa and buckwheat (both dicots) are classed as pseudocereals. Certification A method used in the multiplication and marketing of varieties of agricultural crops that controls the quality of seed sold and enables the owner of a variety protected by Plant Breeders’ Rights (PBR) to claim royalties. Chain length Number of a-1,4-linked glucose residues in a starch chain. Chemometrics Multivariate pattern recognition and data analysis of chemical and physical data. Chiang yu The Chinese name for soy sauce. Chinese medicine (traditional Chinese medicine) An ancient holistic system of health and healing, based on harmony and balance, and employing the ideas of moderation and prevention. Supported by a mostly herbally based pharmacopoeia using combinations of plant materials to supply active ingredients in treatment. Chloroplast A plastid-containing chlorophyll, the site of photosynthesis. Chlorotic The description of a plant (or plant part) that has become yellow through ill-health. Cholesterol A fat-like substance produced in the liver and other sites in the body, essential for cell-membrane synthesis. Excessive cholesterol production can lead to deposits of the fat on the interior surface of the arteries as plaque. Chromosome A linear sequence of DNA that is responsible for the determination and transmission of hereditary traits. It is the structure in the cell nucleus which carries the units of inheritance, the gene. The chromosome is an assembly of genes linked together as a functional unit. This rod-like body that can be seen with a microscope in the nucleus of a living cell at the time of cell division. The chromosomes of higher plants and animals may be observed under the light microscope during cell division by staining with basic dyes. Between cell divisions, chromosomes become dispersed in the nucleus and can no longer be seen under the light microscope. Chromosome substitution line An individual or line with a single chromosome pair replaced by a homologous chromosome pair from another cultivar, or a homoeologous pair from a related species. Chronic diseases Diseases that persist over time. CIMMYT The International Maize and Wheat Improvement Center, located in Mexico, a nonprofit center focused on ‘providing agricultural solutions to the problems of poor people in developing countries.’ It is one of the research institutes comprising the Consultative Group on International Agricultural Research (CGIAR). Cluster A conjoined unit of baked buns or rolls, usually ranging from easily separated into individual pieces. The

practice of panning bun or roll dough so that several pieces touch, enabling the product to proof and bake into small, easily separated single units. Coalescence The point at which adjacent bubbles interconnect by failure of the bubble walls. Coarse grains Cereals excluding wheat and rice. Codex Alimentarius Commission Working group of independent experts created by the Food and Agriculture Organization and the World Health Organization of United Nations to develop food standards, guidelines, and codes of practice. Within this Commission, the joint FAO/WHO meeting of experts on pesticide residues is in charge of (i) the establishment of the ADI figures for individual pesticides on the basis of toxicological evidence; (ii) the recommendation of maximum residue limits for pesticide residues in food; and (iii) the recommendation of acceptable methods for chemical analysis to be used by food inspection authorities for regulatory purposes. Coixin The major storage protein fraction (prolamin) of Coix seed. Coleoptera Commonly known as beetles, an order of insects containing many pests of stored grain. Coleoptile Second leaf in a grass modified for soil penetration. Collaboration The act of working together to achieve same means or agreed goals; collaborative research. Colza The French term to describe rapeseed, Brassica napus or B. rapa. Combine harvester A machine that reaps and threshes grain. Commercial farming Farming carried for profit-making purpose on a large farm. Common wheat The most widely cultivated wheat species (Triticum aestivum), often referred to as ‘bread wheat.’ Common wheat is used for many food products including diverse breads, confectionary products, and Asian noodles. Complementary protein Protein foods when eaten together make up for the limiting amino acids in one or both of the proteins. Computer-aided management Knowledge-based decisionsupport system used online on a PC enabling a manager to make a decision from simulation and optimization models. Concave The stationary part of the threshing mechanism of a harvester. Conditioning (tempering) Addition of water to wheat prior to milling to optimize separation of bran from starchy endosperm. Conduction Heat transferred between a hot object and a cooler one when they are in direct contact. A very efficient form of energy transfer. Congeners Chemical compounds that are present in alcoholic beverages. Conidia Asexually produced spores that form from a specialized conidiogenous cell. Conserved moisture Soil moisture available to the crop at the time of planting as a result of precipitation occurring during the period preceding planting time. Consumer The ultimate purchaser and user of baked foods, the reason a bakery exists. Contact insecticide Chemical grain protectant that kills insects or prevent infestations becoming established, and

Glossary effective through simple contact of target insects with treated grain surface. Continuous stills A continuous distillation vessel, containing internal sections of copper, used for the production of highly flavored or lightly flavored distilled spirits. Convection Heat transferred by an intermediate fluid. Circulation may be natural or forced. May be a gas (hot air or steam) or a liquid (oil or water). Relatively efficient if the fluid is moving rapidly. Often more gentle and provides a more even surface color than do the other forms of energy transfer. Convenience food Food or meal product that requires little or no preparation prior to consumption. Cooling aeration Long-term aeration of a grain bulk by fresh ambient air in order to reduce the grain temperature. Copper pot stills A batch distillation vessel used for the production of highly flavored distilled spirits. Corn chips Snack food produced from nixtamalized maize. The lime-cooked maize is ground into a dough that is extruded into chips and deep fat fried. The resulting corn chips are usually salted and flavored. Corn chips contain about 36% oil. Corn grits Refined particles of the endosperm free of germ and pericarp produced after dry milling. Corn grits are usually classified by sizes as US mesh numbers 6, 40, and 60. Corn grits are widely used by the brewing, snack, and breakfast cereal industries. Corn tortilla chips Masa is formed into thin pieces, baked and then fried in hot oil. Corneous Hard, translucent endosperm with few air spaces and tightly packed starch granules in a protein matrix. Corneous endosperm, also known as vitreous, hard, or horny endosperm Dense, hard outer part of the endosperm of cereal grains such as maize, pearl millet, and sorghum. Corrugation Teeth cut in a spiral pattern along the length of break and sizing rolls of a flour mill. Cotyledon First leaf developed by the seed embryo. Flowering plants whose embryos have a single cotyledon are grouped as monocotyledons; embryos with two cotyledons are grouped as dicotyledons. All legumes, including chickpea, are dicotyledons. Covered grain Grain in which the hull (palea and lemma) is physically attached to the grain (as in rice and barley) and may be removed by, for example, abrasive milling. Crop rotation Practice of growing different crops in recurring sequence on the same field. Cross-sectional data Data showing food actually eaten by individuals in a day, a week, or a month. Crumb The soft, leavened interior component of breads and rolls. Crumb texture Usually refers to the visual appearance of the inside, or crumb as opposed to crust, of a bread loaf, sometimes referred to as ‘grain.’ Some breads have a very coarse texture with many holes of various sizes and some breads have a very fine, uniform, texture that is smooth and silk like. The term is also sometimes used to refer to the ‘firmness’ of bread when it is compressed. Crust The dry and often chewy exterior component of breads and rolls.

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Crystalline domain of starch granule This is made up of amylopectin, mainly ‘A’ chains and outer ‘B’ chains that form double-stranded helices. Cultivar A cultivated variety of a plant species. Cutter bar Combination of knife and knife guard on harvester front that cuts the crop. Cysteine An amino acid. It’s ‘R’ group is a sulfur containing thiol group. Cytogenetics The branch of biology combining the study of genetics and cytology, which is concerned with problems based on the correlation of genetic and cytological (especially chromosomal) features. The field is mainly comprised of the study of the behavior of chromosomes during mitosis and meiosis, their origin and their relation to the transmission and recombination of genes. Cytosol The water-soluble components of cell cytoplasm, constituting the fluid portion that remains after removal of the organelles and other intracellular structures.

D Daily value (DV) Recommended intake of a nutrient per person per day. Daqu A large-sized jiuqu product made with wheat flour. See ‘Jiuqu.’ Debranning (preprocessing) Removal of wheat bran layers sequentially by friction and abrasion processes prior to milling. Decision-support system Software program enabling online analytical processing of complex information on a PC in view to support decision making of a manager. Deck oven An oven with a flat hearth on which dough pieces are placed to bake. Decortication The process of removal of the outer layers (pericarp and germ) of the grain. Defatted soy flour Soy protein product with < 60% protein. Deficiency diseases Diseases that can be cured by adding vitamins to diet. De-germed grain Individual damaged grain kernels in which the germ has been removed. This usually can occur during the harvesting process. Degerming may also occur when the grain has been exposed to moisture and germination initiated then stopped as the source of moisture has been removed. In this circumstance, the sprouted germ becomes brittle and easily breaks off during the handling process. Degree of polymerization (DP) The number of monosaccharide units in a polysaccharide. Dehulling Milling process which removes the hull from cereal caryopses. Demurrage Excess time for loading or unloading a vessel, railroad car, truck, etc., beyond the time agreed upon, and the penalties and liabilities related by contract to such detention. Denitrification A process caused by denitrifying bacteria in which nitrates are converted to ammonia and molecular nitrogen. Derivatization Convert fatty acids to more volatile components, such as methyl esters, by specific chemical reactions. Desi chickpea Chickpea characterized by small, angular, colored seeds.

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Destoner A machine that removes materials of similar size to wheat but heavier than wheat that may cause damage to milling equipment, particularly stones. Destructured starch Disruption of starch granules using elevated heat and pressures along with plasticizers. Determinate growth Growth habit of plants whose stem does not elongate indefinitely and is terminated by a flower. Dextrins Short chains of glucose molecules, produced by incomplete hydrolysis of starch. Diaspore In wild and weedy cereal grasses, the reproductive dispersal unit, consisting of one or more spikelets or florets. In domesticated grasses, the diaspore can be a naked grain that is free of the bracts or a grain enclosed by a fused lemma and palea or by clasping glumes. Diatomaceous earth (DE) A light-colored porous rock made from the skeleton of diatoms that have accumulated as a natural deposit under lakes and oceans for centuries. DE mined from these layers has a high content in silicon dioxide. The razor-sharp edges of the milled DE are abrasive and cause insects to dry out and die. Dicotyledon A plant that produces a pair of cotyledons or initial leaves when it germinates. Dicotyledoneous, dicotyledonae A subclass of the angiospermae containing all the flowering plants having embryos with two cotyledons. Die cut flour tortilla Flour tortilla rolled and cut with a round die, then baked in an oven. Dielectric heating Self-heating of a nonconductor material (dielectric material) when placed in an alternative electromagnetic field oscillating at a high frequency more than 3 MHz. The heat dissipation inside the material mainly results from the moving and friction of dipolar molecules in the following period of oscillation of the electric field. Dietary fiber The polysaccharides in food, which can be either soluble or insoluble, that cannot be digested in the intestine and used as a food source. Dietary reference intakes (US) (DRIs) Set of four nutrientbased reference values intended primarily for use in assessing and planning diets. Differential Ratio of rotation speed of fast roll to slow roll in a roller mill. Differential scanning calorimetry (DSC) A measure of the melting enthalpy of starch by recording the difference in heat flow (cal s1), between an inert reference material and the sample, necessary to reach thermal equilibrium. Digestibility The proportion of the nutrient that is hydrolyzed and absorbed. Digestible energy The digestible energy (DE) of a diet is the difference between dietary gross energy (GE) intake and the GE of the excreted feces. Dikaryon A cell or organism with two separate haploid nuclei; behaves as a functional diploid. Diploid Of cells, phases of life cycles, and organisms with two homologous chromosome sets in which each type of chromosome is represented twice (2) as opposed to haploid (1) or polyploid (3, 4, 5, etc.). Diploid rye Rye species that has two basic sets of chromosomes in its somatic (body) cells. Disk separators Machines that use rotating disks with pockets to remove impurities of similar density and crosssection to wheat but different in length.

Disomic An individual with a normal chromosome set. Distinctness, uniformity, and stability (DUS) Assessing the D, U, and S of newly bred plant varieties is the basis of systems for the award of PBR. DUS testing requires that a new variety is genuinely new (distinct), and sufficiently uniform and stable in the characteristics used to assess distinctness. Disulfide bonds Protein cross-links formed between cysteine residues. Divide (split run) milling Preparation of several flours of varying composition and functionality by judicious blending of specific flour streams. Highly refined divide flour is known as ‘patent’ flour. Less refined divide flour is known as ‘clear’ or ‘low-grade’ flour. Dividing Cutting a large mass of dough into smaller pieces to go through the rest of the loaf-forming process. Domestication (plant) The process of adaptation of a wild plant to field cultivation, characterized in cereal grains by, for example, loss of the brittle rachis trait, loss of photoperiod sensitivity, and reduced seed dormancy. Dormancy The failure to germinate under conditions normally conducive to germination. Double cropping Two different crops grown in a sequence on the same area in one growing season. Double monosomic An aneuploid lacking one member of two different homologous chromosome pairs. Doubled haploid Plants that possess two sets of identical chromosomes that can produce gametes like a diploid plant. Dough A mixture of flour, water, and other ingredients including yeast and salt, mixed until it makes a stiff mass that can hold its shape and can be baked. Dough strength The physical strength of a dough to resist extension. Tough doughs require greater mixing and tensile forces for extension than weak, extensible doughs. Drilling fluid Thixotropic solution used to cool the drill bit and suspend solids during deep well drilling. Drought A condition of below normal rainfall which affects crop growth. Drum drying Drying as a result of application of a liquid slurry in a thin layer to the surface of a heated rotating cylinder. Drum or rotor The moving part of the threshing mechanism of a harvester. It is called a drum in a conventional harvester and a rotor in a rotary harvester. Dry masa flour Lime-cooked maize kernels are coarsely ground into dough, which is dehydrated. The resulting meal particles are classified and large particles reground with the aim of producing homogeneous flours with a certain particle-size distribution. The dry masa flour is moistened and further processed into table tortillas, corn chips, tortillas chips, and other related products. Dry matter (DM) The mass that remains after heating to remove water. Dry milling The process of reduction of the grain into fine particles (flour). Dumas analysis Determination of the nitrogen content of a grain or flour sample, based on the transformation of all the nitrogen to the gas, as a basis of estimating the protein content of a grain sample. Durum wheat Triticum durum. A tetraploid spring wheat possessing an extremely hard endosperm. Its primary use is in the production of pasta.

Glossary DUS testing To qualify for the award of PBR, a new variety must be distinct from any other variety in the expression of its morphological characteristics, sufficiently uniform (or homogenous) and stable. E Ear Entire flowering head of a grass or cereal. Electrophoresis A technique used for separating and characterizing the components of complex mixtures of proteins or other macromolecules. When an electric current is passed through the solution or gel medium, the proteins migrate toward the positive electrode (anode) or negative electrode (cathode) according to their net electric charge at the pH of the solution or gel. By using a sieving medium such as a polyacrylamide gel, separations may also be carried out according to the molecular size of the protein species being investigated. Embryo A diploid zygotic tissue formed by fertilization of the female egg nucleus with one male pollen nucleus. Empty nesters Households with no children below age 18. Endomembrane system An interconnected series of membranes and other subcellular structures that is involved in the synthesis, processing, and secretion of proteins and other compounds. Includes the endoplasmic reticulum, Golgi apparatus, and various types of vesicle. Endosperm A triploid seed tissue originating from the fusion of two polar nuclei in the embryo sac with the second male pollen nucleus. Provides nutrients to the embryo and is composed of starch, protein, lipids, and b-glucan. Enrichment Addition of nutrients, including those lost in processing. See list for vitamins. Entanglements The ability of long polymer chains to form physical restrictions to continued extension. Enzyme A protein that is a catalyst (i.e., in minute amounts it promotes chemical change without itself being used up in the reaction) by virtue of its capacity to increase reactivity of a specific substance or substances. Enzyme-linked immunosorbent assay (ELISA) A sensitive diagnostic test that detects the presence or absence of a target enzyme by linking antibodies to that enzyme and determining the level of activity by quantitative determination of the antigen which reacts with that antibody. The test usually involves the conversion of a colorless substrate to a colored product. Equilibrium relative humidity Thermodynamic equilibrium between relative humidity of air in inter-kernel space and the activity of water within kernels. Erucic acid Trivial name for cis-docos-13-enoic acid, C22 1 (n-9). Essential amino acids Amino acids which cannot be synthesized by humans and have to be obtained from the diet. Essential vitamin Cannot be synthesized by humans. Needed in food. Estrogenic Having similar properties to estrogen, a hormone produced by the ovaries and affecting many aspects of the female body. Europe EU 15 plus Albania, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Macedonia, Malta, Republic of Moldova, Norway, Poland, Romania, Russian Federation, Serbia and Montenegro, Slovakia, Slovenia, Switzerland, and Ukraine.

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European Union (EU 15) Austria, Belgium, BelgiumLuxembourg, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain, Sweden, and United Kingdom. Exorphin A peptide arising from partial digestion of protein and having an opiate-like effect. Expressed sequence tag (EST) EST derived from the sequencing of cDNA clones generated through reverse transcription of mRNA. ESTs represent expressed genes. Extended shelf-life noodles Noodles boiled prior to sale that can be stored at ambient temperature for long periods as they have been rinsed in a dilute organic acid solution then pasteurized (see also Instant noodles). Extensibility The extent to which a material may be deformed without rupture by pulling or by some other process involving the application of tension. A high degree of extensibility is the result of low yield value and high mobility associated with adequate cohesion. It is a desirable quality in dough for making the wide range of baked products. Extensional rheology The study of deformation properties of materials under extensional flow. Extinction coefficient The slope of the relationship between leaf area index and the natural logarithm of the percentage of solar radiation intercepted by a crop. Extraction Generally refers to the removal of components from a whole. In flour milling, ‘Extraction’ refers to the proportion of white flour produced from the original mass of wheat grain. In barley malting, extraction refers to the yield of extractable sugars and dextrins from the resulting malted grain. Extruded Forced under pressure through an orifice. Extrusion Extrusion is a major technology for the production of many grain-based foods. It involves forcing a mass of moist milled material through a shaped die. The sudden release of pressure on exit may cause bubbling of the product, such as for breakfast cereals. See ‘Gun puffing.’ F Falling number The time, in seconds required for a plunger to sink through a paste made of heated ground grain and water. Because enzyme activity in sprouted kernels reduces that time, falling number can be used as an indication of sprouting in grain. Fallow Cropping land left idle during the growing season to restore productivity. Farmer participation The involvement of farmers, with breeders and other scientists, in the selection and testing process to develop new plant, crop and animal varieties suited to their needs and environment; farmer participatory selection. Fatty acids Chains of carbon and hydrogens possessing a carboxylic acid moiety. If there is a full quota of hydrogen atoms, the fatty acid is saturated, otherwise it is termed unsaturated. Unsaturated fatty acids have one or more double bonds in the carbon chain (monounsaturates and polyunsaturates, respectively). FE Asia Bangladesh, Bhutan, Brunei Darussalam, Cambodia, China, India, Indonesia, Democratic People’s Republic of Korea, Republic of Korea, Laos, Malaysia, Maldives, Mongolia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Thailand, Timor-Leste, and Vietnam.

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Feed efficiency The ratio of weight gain divided by feed intake. Feekes growth stage scale Scale used to describe the growth stages of small grains. Fermentation The action of microorganisms (e.g., yeast) that convert carbohydrates, especially sugars, into other compounds, for example, ethyl alcohol and carbon dioxide. Its action results in the rising or leavening of bread doughs. Fermented foods Foods that have undergone yeast or lactic acid fermentation. Fertilizer Any substance in solid or liquid form to provide plants with essential nutrient elements through soil or foliar application, especially chemical fertilizer or commercial farm manure. Fish sauces Condiments prepared by mixing fish wastes (offcuts, offals, trash species) with salt, often with pounding, then allowing the enzymes present in the fish flesh to digest the material, eventually yielding a clear fluid, saturated with salt. Flag leaf Uppermost leaf in small grain plants. Flavonoids A class of plant secondary metabolites derived from the condensation of a cinnamic acid with three malonyl-CoA groups. Floret The floral unit of a grass inflorescence made up of a lemma and palea enclosing a reduced flower. Flour Finely divided particles of endosperm, typically <150 mm in maximum dimension. Flour yield The percent yield of flour from the milling of whole grain. Floury endosperm (also known as soft endosperm) The opaque, often soft portion of the endosperm of cereal grains. Fluidized bed Fluidization process used to confer the properties of a fluid to a divided material constituted by homogeneous size particles (such as grain or flour), thanks to the suspension of these particles or grains in a permanent highpressure air stream. Fluorochrome A substance exhibiting fluorescence when associated with another molecule or specific structure in a biological specimen. Foams and emulsions Two-phase dispersed food systems with either water–air (foams) or water–oil (emulsions) interfaces. Fodder Vegetative plant material used for livestock feed. Foliar diseases Diseases which attack the above-ground parts of a plant. Food composition tables Present nutrient data for specific foods. Food consumption data Quantities for food either available to or actually eaten by individuals in a defined time period. Food disappearance data Food available for consumption, time-series data. Food habits How consumers use food. Food preferences How consumers express food likes and dislikes. Food security Access by all people in a country or region to sufficient food to maintain good health. Food-production chain The sequence of steps in food production (in this case for grain-based food) from the breeding of the original grain, through its production in the field, its harvesting, storage, and transport, to its eventual processing, marketing, and consumption.

Forage Food for livestock, composed of entire plants, including leaves, stalks, and grain. Former Soviet Union (FSU) Includes Armenia, Republic of Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, Belarus, Estonia, Latvia, Lithuania, Republic of Moldova, Russian Federation, and Ukraine. Fortification Addition of nutrients that may or may not have been present before processing. See list for vitamins. Free threshing In cereal species, the ability of the grain to fall free of the glumes, lemma, and palea under light mechanical pressure. Fumigant Volatile chemical in gaseous state in ambient conditions, which has toxic properties for insects or other noxious pests and can be produced in adequate concentration in a gastight enclosure to kill target pest species. Functional analysis Determination of the function of a gene through gain-of-function or loss-of-function analysis. Functional food A food that has health-promoting properties over and above its basic nutrient content. Functional genomics The development and application of genome-wide experimental approaches to study gene function using information and reagents provided by physical mapping and sequencing of genomes. Functionality Any property of a food component or ingredient (other than nutritional value) that affects its processability and/or end use quality. Fungal mycelia The vegetative growth phase of fungi that consists of long thin threads of chains of fungal cells. Furu or sufu A Chinese product made from tofu. The tofu is inoculated with fungi that grow on the outer surface and the molded tofu is then salted in brine or with free salt and then matured to develop flavor. It may contain ethanol. Fusel oils Higher alcohols such as amyl alcohol, butanol and propanol, which are present in distilled beverages. G Gamete A mature sexual reproductive cell that unites with another cell to form a new organism. Gelatinization The irreversible disruption of molecular order within the starch granule as a result of heating in water. It is manifested by irreversible changes in properties, namely, the swelling and hydration process of granular starches, reflecting starch thermal properties by differential scanning calorimetry (DSC), including gelatinization temperature (Tp), energy of enthalpy (DH), etc. Gene regulation The control of gene expression. Genetic improvement It can be defined as a technology using genetic ways to modify crops. Genetic linkage map A map, constructed through statistical analysis based on experimental recombinant frequencies, which shows the relative locations of specific molecular markers or genes along each chromosome of a genome. Genetic map Order of genes based on genetic linkage, determined by the frequency of recombination events between genes. Genetic transformation Modification of a cell by the uptake and incorporation of exogenous DNA. Genetically modified (GM) This refers to an organism in which the genetic material in that organism has been modified in someway. This can be either through the

Glossary introduction of genes from an organism of the same species or from another entirely different species. Genetics A branch of biology dealing with the principles of heredity, inheritance, and variation in organisms. Genic male sterility (GMS) The male sterility is controlled by nuclear genes. Genome The complete genetic information of an organism, located in the nucleus and organelles. Genotype The genetic constitution of an organism. Genus A systematic unit consisting of groups of species sharing common genetic origin, and clearly differentiated from other such groups. Germ Also referred to as the embryo of cereal grain, which tends to be higher in lipids, vitamins, and minerals necessary to support the rapid growth of the germinated seed. Germplasm Genetic resources in the form of genetically defined lines, varieties, land races, or wild accessions. Germination The process during which the seed imbibes water, resulting in the activation of several biochemical reactions and culminating in the emergence (growth) of the embryo into a new plant. Ginjo sake´ Rice wine made from highly polished rice, < 60% yield. Glass transition The temperature at which an amorphous polymer changes from a glass to a rubber. Gliadin The prolamine fraction of wheat flour protein. It is classically defined on the basis of it being extractable (from flour or gluten) with 70% aqueous ethanol. It is characterized by high contents of glutamic acid and proline. The many component gliadin proteins have molecular weights under 100 000, with disulfide bonds being formed within the individual proteins (as distinct from the glutenin proteins which have disulfide bonds between individual proteins). Globulins Proteins soluble in dilute salt solutions (usually 0.5–1.0 M NaCl). They include two major families of storage proteins with sedimentation coefficients (S20,w) of 7–8 (vicilins) and 11–13 (legumins). Glucan A chain of glucose residues, linked in either the a- or b-conformation. Glucose The most common 6-carbon sugar in nature, important in energy stores and structural polysaccharides. Glucose isomerase An enzyme which transforms glucose to fructose and is used in the production of fructose-containing syrups. It transforms or converts glucose into fructose. The enzyme is almost always used immobilized or attached to a support and optimally works at a temperature of 55–60 C and a pH of 7.5–8.5. Glucosinolate Compounds in the meal of rapeseed (colza) which upon enzymatic hydrolysis release isothiocyanates, thiocyanates, and goitrogenic factors including oxazolidinethione which inhibit iodine uptake and goiter function. Glumes The two outermost bracts of a grass spikelet, which enclose one or more florets. Glutelin The general term for the class of proteins that are least extractable into aqueous solvents, generally requiring dilute acid or alkali to be extracted. The glutelin fraction of wheat is called glutenin. The term ‘gluten’ is also used nutritionally to indicate the storage protein of the grains of wheat,

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triticale, rye, barley, and oats, because of the effects of these proteins in causing coeliac (celiac) disease. Glutenin(s) The glutenin fraction of wheat flour protein. Less soluble than gliadins, it remains insoluble after extraction with 70% aqueous ethanol from wheat endosperm (flour). The glutenin fraction comprises a range of very large protein species, formed by the interchain disulfide bonding of the glutenin subunits (polypeptides) producing molecular weights ranging up to tens of millions of daltons, thus forming some of the largest proteins in nature. Glycemic index Index ranking foods based on their immediate effect on blood sugar levels. To make a fair comparison, all foods are compared with a reference food such as pure glucose (which is given the index of 100) and are tested in equivalent carbohydrate amount. Glycoside A chemical to which a glucose molecule is attached. Removal of the glucose molecule leaves the aglycone molecule. Glycosylation Modification of proteins or lipids by the addition of molecules. Goitrogens Chemical substances that promote goiter, normally by interfering with iodine absorption or metabolism. Golden rice Transgenic rice that produces b-carotene in rice grain. Goldfische extraction Method of extracting oil from plant material utilizing a low-boiling-point organic solvent and traditional Goldfische apparatus. Gossypol A highly reactive and toxic compound in cottonseed oil. Grades Used to separate lots of grain into groups with similar quality. Based on a range of factors known to affect end-use value. Grain based Having one or more grains such as wheat, oats, or corn as major ingredient or ingredients. Grain cleaning Removal of non-grain contaminants for safe storage and processing. Grain condition Set of properties of a grain batch generally assessed on a representative sample and giving information either on commercial value or on grain batch storability. Grain drying Removal of moisture from grain through artificial or natural means. Grain export The transfer of grain to other countries. Grain import Grain that is brought into one country from another. Grain legume Plant belonging to the legume family (Leguminosae) that produces seed used directly for human food. Grain panicle A much branched inflorescence; a pyramidshaped cluster which bears the grains of oats and rice. Grain protectants Chemicals that are toxic in the liquid or solid phase. They are designed to protect grain from infestation. Grain respiration rate Level of the respiratory metabolism of all living organisms in a grain bulk microorganisms, kernel embryo, non-vertebrate pests, using the chemical energy stored in grain tissues. Grain separator A machine that uses sieves and aspiration to remove impurities from cereals on the basis of size. Grain storability Fitness for long-term storage of a batch of grain deduced from the assessment of grain initial condition prior to storage.

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Grain transport model A means of carrying grain from one place to another. Grain whisky Whisky produced from a mash of malted barley and cooked cereal grains. Grains Term used to include cereals, pulses, and oilseeds. Green area index (GAI) The area of photosynthetically active surfaces of a crop (leaves, stem, reproductive structures) per unit of ground area. Green bridge Compatible host genotypes or species required by obligate pathogens for survival between cropping seasons. Green malt Cereal grain that has been germinated and not dried. Green Revolution The introduction of high-yielding dwarf wheat varieties to India, and dwarf rice varieties in Asia, which coupled with input-intensive management systems and farmer education, greatly increased agricultural productivity during the 1960s and 1970s. Groat Oat kernel from which the hull has been removed. Growth regulators Any of the several substances promoting or retarding certain physiological processes within an organism. Gun puffing A process for the production of expanded (puffed) snack or breakfast foods involving heating under pressure followed by sudden release of pressure. Gushing It is excessive frothing of the product. Gynophore Reproductive structure attaching a peanut pod to the plant. H Hammer mill Mill that reduces grain to particles by means of rapidly rotating hammers that smash up the grain and drive the pieces through a fine screen. Hand stretched tortillas Flour tortilla that is hand flattened and formed, then baked on a hot surface or oven. Haploid A cell in which chromosomes are represented singly and unpaired. Harvest index The ratio of harvested (i.e., saleable yield) to total biomass of a crop. Haulms Vegetative component of the peanut plant, including stems and leaves. Haun growth stage scale Scale used to describe the growth stages of small grains. Hazard analysis critical control point (HACCP) A systematic approach to ensuring the avoidance of food-safety risks. Hearth The heated metal, stone, or synthetic surface on which food is placed for baking. Heat shock Rapid increase in the temperature (usually of growth conditions) to a level out of the range for normal vital functions and causing physiological damage to exposed organisms. Hectoliter weight A metric unit used to measure the bulkgrain weight of a specific volume of grain. Hemicellulose Nonstarch, noncellulosic polysaccharide present in plants. Herbicide resistance Resistance to formerly effective herbicides that can develop in weeds after repeated herbicide use. Heritability Proportion of the total variance among phenotypes in a population that is due to genetic variance (total genetic variance for broad sense heritability and additive genetic variance for narrow sense heritability).

Heteroecious pathogen A fungus that has its sexual and asexual stages restricted to different host species. Heterofermentative bacteria Bacteria that produce substantial quantities of chemicals other than lactic acid, such as carbon dioxide and ethanol, as by-products of fermentation. Heterosis The biological phenomenon in which an F1 plant shows increased vigor over parents. Heterozygous Having a pair of nonidentical alleles at corresponding chromosomal loci. Hexaploid An organism having six complete chromosome sets, as opposed to two in diploid organisms. Hexaploid wheat Wheat with three homoeologous sets (6N) of diploid chromosomes, such as common wheat (also known as bread wheat), which is used for baking and for Asian noodle production. High-performance (or pressure) liquid chromatography (HPLC) A form of column chromatography in which liquid carrying the mixture of molecular species to be separated passes over a solid phase usually at high pressure providing rapid and high-resolution separation of mixtures of related compounds. HIV/AIDS Human immunodeficiency virus/acquired immunodeficiency syndrome. Hominy Corn that has been cooked in caustic soda. It has a different flavor than nixtamal which is cooked in lime. Homoeologous Of partially homologous chromosomes. Homoeology designates the residual homology of originally completely homologous chromosomes. Homoeologous chromosome pairing Pairing of homoeologous chromosomes when permitted by loss or suppression of normal bivalent pairing in allopolyploids. Homofermentative bacteria Bacteria that produce essentially only lactic acid as a by-product of fermentation. Homologous Of chromosomes or chromosome segments which are identical with respect to their constituent genetic loci (the same loci in the same sequence) and their visible structure, as distinct from nonhomologous and homoeologous chromosomes or parts of chromosomes. Homologous chromosomes Equivalent chromosomes inherited from the male and female parents of an individual. Homozygous Having a pair of identical alleles at corresponding chromosomal loci. Honjozo sake´ Rice wine made from less highly polished rice, not < 60%. Hordein The protein of the prolamin class that is the major component of the endosperm matrix in barley grain. It is made up from many similar protein species. Host An organism, on which a pathogen lives; may be specific to pathogen species. Hull Modified fibrous leaves that cover the grains of certain species of cereals, for example, barley, oats, and rice. Hulled grains Cereal grains that are tightly enclosed either at the level of the floret within the hardened lemma and palea or at the level of the spikelet within the hardened, tough glumes. Hulled grains also include those to which the papery lemma and palea have fused. Mechanical pressure is required to break the grain out of the hardened bracts or to remove adherent bract tissue. Human nutrition Food and nourishment for human beings.

Glossary Husks The common term applied to any material that consists of seed coverings and small pieces of stem or leaves that have been separated from the seeds during the harvesting process. Hybrid A first generation of single crosses involving two parental lines. Hydrocyclone process A maize wet milling process which uses cyclonic separators and density differences to separate starch from protein. Hydrogenated vegetable oil A vegetable oil that has been modified by chemical treatment with gaseous hydrogen and a catalyst to add hydrogen to double bonds of polyunsaturated fatty acids, making the product more solid and reducing its tendency to become rancid. Hydrophobic groups Water-repelling, nonpolar chemical groups such as chains of methylene and methyl groups that cannot participate in hydrogen bonding to water or other hydrophilic groups. Hypertension Abnormally high blood pressure. Hypocholesterolemic Causing a reduction in the concentration of cholesterol in blood serum. Hypogeal Growing below the soil surface. Hypolipidemic Causing a reduction in the concentration of lipids in blood serum. I Ideotype A model of crop with some morphological characters and physiological advantages. Ileal digestible energy Energy digested to the end of the small intestine or ileum calculated as energy in the feed consumed minus energy passing the end of the ileum. Illinois high protein It is a maize population with high protein which was developed at University of Illinois. Image analysis The process of identifying objects and shapes using a photograph, camera, video, or other visual image. These images are broken down into minute computer binary data known as pixels. Software packages are then used to transfer these binary points into a calibrated format that can be used to recognize, detect and distinguish similar or distinct objects, such as grains of different types and contaminants. Imidazolinone herbicides Postemergence herbicides of the imidazolinone chemistry that inhibit acetolactate synthase (ALS) used for control of broadleaf weeds. Current ‘IMI’ herbicides include imazamethabenz, imazamox, imazapyr, imazaquin, and imazethapyr and are used primarily in legume and pulse crops. Impacting machine Powered high-speed device used in the milling industry to remove some of the internal insect forms from infested kernels by breaking them open through a violent throwing of cereal grain by centrifugal force on a tough metal surface and aspirating off the smashed released insect fragments. Imparipinnate Compound leaf with terminal leaflet and remaining leaflets on both sides of petiole. Impingement A special form of convection in which air is blown directly onto the surface of the baked product at high velocity through some form of nozzle. The energy transfer rate can be very high, often reducing the baking times to onehalf or less than that of conventional hearth ovens.

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In sacco digestibility The disappearance of dry matter from grain suspended in the rumen of cattle in a nylon bag for a period of time. In-bin cooling or aeration A grain-cooling process of a grain batch in a bin appropriately equipped for computercontrolled aeration with ambient air, often at night, when the air is cooler than in daytime. In-bin drying Low-temperature drying process of a grain batch in a bin appropriately equipped for aeration with warm air. Indica rice and Japonica rice Two subspecies of the most commonly cultivated rice, Oryza sativa L. Indica rice One of the two major subspecies of the cultivated rice, Oryza sativa subsp. indica. Induced mutation Mutations generated by artificial mutagenesis such as X-rays, irradiation and mutagenic chemical treatment. Inert gas For a chemist, any of the chemically inert gaseous elements of the helium group in the periodic table of chemical elements (argon, neon, krypton, xenon, radon). In practice, all gases that are physiologically inert gases classified as asphyxiants such as argon, nitrogen, or carbon dioxide and carbon monoxide, which can act principally by dilution of the atmospheric oxygen. Infrared radiation (IR) Especially important for surface browning. Important for grain analysis is the near-infrared region of the spectrum, consisting of the wavelengths between 700 and 3000 nm. Inoculation In the context used here, application of a culture of bacteria of the genera Rhizobium or Bradyrhizobium to legume seeds before sowing, to encourage the formation of N-fixing root nodules. Instant Quick easy home preparation. Instant noodles Wheat noodles that are steamed and fried as part of the manufacturing process so they can be conveniently rehydrated and consumed (see also Extended shelflife noodles). Instar A stage between molts in the life cycle of an insect. In-store bakery Smaller bakery located as part of a larger store such as a modern grocery supermarket. Sometimes they bake foods from raw ingredients (scratch baking), but often finish-bake frozen or partially baked items. Integrated pest management The control of pests or diseases using a wide range of crop production strategies, combined with careful monitoring of pest or weed populations. Intercrop Simultaneous growth of two or more crops in a given area. Intergeneric hybridization Crossing of two species from different genera. International Rice Research Institute (IRRI) The IRRI, located in Philippines, a nonprofit center active in research and training to improve rice production and sustainability in Asia. It is one of the research institutes comprising the Consultative Group on International Agricultural Research (CGIAR). Interspecific hybridization Crossing of two species from within the same genus. Intrinsic viscosity (hint) The limiting value of the specific viscosity, sp, of a solution as the concentration of the solute tends to zero. The units are dl g1. Introgression The introduction of new gene(s) into a population by crossing between two populations, followed by

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repeated backcrossing to that population while retaining the new gene(s). Irradiation Treatment of food material with high-powered electromagnetic waves of wavelength < 10–9 M that produces ionization of the largest molecules, and especially DNA of any living organism. J Japonica rice One of the two major subspecies of the cultivated rice, Oryza sativa subsp. japonica. Jiuqu The Chinese name for a product containing fungi and yeasts that is similar to Japanese koji and is prepared to make rice wine. A mixture of whole grains or flour of rice and/or other grains is prepared and fungi and yeasts allowed to grow through the mixture. The mixture is then shaped and dried in the form of a cake. Jointing Growth stage of small grains where the growing point comes above ground and is indicated by solid-feeling nodes on the plant’s stem. K Kabuli chickpea Chickpea characterized by large, ram-headshaped and beige-colored seeds. Kafirins Forms of proteins rich in cysteine and disulfide bonds found in sorghum grain. Kansui Also known as lye water. Most commonly a mixture of sodium and potassium carbonates. Used in the manufacture of alkaline styles of Asian wheat noodles, such as Cantonese and Hokkien. Karyotype A photomicrographic image of the chromosomes of a single cell, cut and arranged in order of size. Kecap The Indonesian name for soy sauce. Kefir A fermented milk drink, typically of Russia and East Europe, which is claimed to have therapeutic value. Kjeldahl analysis Determination of the nitrogen content of a grain or flour sample, based on digesting its nitrogen to ammonia, which can be assayed by titration. This provides a basis of estimating the protein content of a grain sample. Koikuchi The Japanese name for the most popular soy sauce made in Japan. Koji A generic term applied to mold (often Aspergillus oryzae), the inoculum thereof (‘seed koji’), and the finished product after the mold has grown on the rice, soybeans, or other substrate. Kvass A beverage in which a mixture of yeasts and lactic acid bacteria ferment dried (sometimes rusked or toasted) and crumbled bread (often rye bread) suspended in water. The fermentation is maintained by topping up with fresh portions of water and bread. L Lactic acid bacteria (LAB) A group of Gram-positive bacteria that produce lactic acid only or mainly lactic acid with some acetic acid and carbon dioxide. Lactic acidosis A rapid decrease in the pH of the rumen of animals resulting from the rapid degradation of highly fermentable substrates and excess production of lactic acid. Landrace A local indigenous or endemic (confined to a specific environment or geography) but distinctive population

or species of plants generally used to describe the ancestors of modern plant varieties. Lap oven An oven resembling a tunnel in which the product is moved through on trays or in pans attached to chains that make more than one pass through the oven before they are unloaded. Commonly used today for pan breads. Lateral branches Pod-bearing branches arising from leaf axils immediately below the lupin inflorescence. First-order branches arise from axils on the main stem, second-order branches from axils on first-order branches, and so on. Leaf area index (LAI) The area of photosynthetically active leaves of a crop per unit of ground area. Lean A term used to describe a bakery formula low in enriching ingredients such as sugar and shortening. LEAR A European term to describe rapeseed in which the oil is low in erucic acid (low erucic acid rapeseed). Leavening Process in which a dough is expanded in volume by the metabolic production of carbon dioxide by yeast. Alternatively, chemical leavening may be the source of carbon dioxide production from an ingredient such as baking soda (sodium bicarbonate). Legume A dry several-seeded fruit derived from a single carpel, opening along both margins; the fruit of the legume or bean family. It has an ability to fix atmospheric nitrogen through a symbiotic association with Rhizobium bacteria. Legumin box A short nucleotide sequence upstream of globulin storage protein genes that is involved in the regulation of their expression. Legumins Family of 11–13S storage globulins. Lemma The lowermost of the two floret bracts that enclose the grass flower. Lepidoptera An order of insects commonly known as moths and butterflies, moths are a common pest of stored grains particularly, but not exclusively, in tropical areas. Lifestyle classification systems Describe consumer lifestyles for marketers. Limiting amino acid An amino acid that is not found in adequate amounts in a protein and would therefore become the limiting factor in protein synthesis. Linnaeus Carl Linnaeus or Carl von Linne was an eighteenthcentury Swedish doctor and botanist who first organized the plant and animal kingdom in a systematic order based upon similarities of appearance or morphology. Linola(tm) Trade name for linseed with an altered fatty acid profile containing reduced amounts of linolenic acid in the oil, compared to traditional types. Developed in Australia. Linoleic acid A polyunsaturated 18-carbon fatty acid, 9,12octadecadienoic acid, with two cis double bonds the major component of corn oil and safflower oil. Linolenic acid A polyunsaturated 18-carbon fatty acid; an omega-3 (n-3) fatty acid. 9,12,15-octadecatrienoic acid. Lipases Enzymes that catalyze the hydrolysis of fatty acids from neutral lipids such as triglycerides. Lipoxygenase An enzyme that attacks unsaturated fatty acids in fats and oils in the presence of oxygen. Loaf A large piece of baked bread, typically from 400 to 600 g, often well browned, sliced, and placed in a plastic bag to retain moisture and freshness.

Glossary Lodging Partial or complete collapse of a crop canopy when stems are not strong enough to support the weight of mature pods. Long-chain branching The ability of some polymers to form long side chains or branches. Luteovirus Family of plant viruses transmitted by phloemfeeding aphids. Lysine An amino acid, component of all proteins, that is important to the nutritional quality of the protein. First limiting amino acid in all cereal grains except rye. M Macrosperma (lentil) Large-seeded type of lentil of Chilean origin. Maillard reaction The name of a chemical reaction that occurs in food between the amines in proteins and sugars. Heating promotes the reaction but it is also the source of nonenzymic browning in food. Maintainer A genetic line that has the same genotype as a cytoplasmic male sterile line, but can maintain its sterility. Maize Cereal of the genus and species Zea mays, referred to in North America as corn, used as a food and in processing. Maize dry milling Process in which maize is milled into refined grits and flours. The most common process consists of tempering the grain for optimum degermination followed by the separation of pericarp and germ from the endosperm pieces, which are further classified into grits of different sizes, maize meal, and maize flour. The refined products are widely used by the brewing, baking, snack, and breakfast cereal industries. Maize wet milling Industrial process in which yellow dent maizes are steeped in a solution containing sulfur dioxide and natural occurring Lactobacillus and then wet-milled in order to release the starch granules and protein (known as ‘corn gluten’), which are separated due to their differences in density. The process yields prime starch, corn gluten, germ, pericarp, and solids of the steep liquor. Major minerals Essential elements required in human food intakes at more than 100 mg day1. Make up The portion of the bread and roll production process that includes dividing, rounding, and forming the dough pieces into their final weight and shape. Malt Cereal grain that has been germinated in moist air under controlled conditions (malted), used primarily as a source of enzymes and potentially fermentable carbohydrate in brewing. Malting Process involving steeping grain (usually barley) in water, fermentation or germination, followed by drying to produce malt that is used in brewing and food manufacture. Malting barley Barley, usually of preferred varieties, that is used in the production of alcoholic drinks, for example, beers such as ales and lagers and sprits such as whiskey. Manioc A genus of plants with starch-rich tubers traded as cassava. Map-based cloning A strategy to clone the gene or quantitative traits locus whose map position is known through searching in either direction from the known markers to identify the adjacent genes.

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Marker-assisted selection (MAS) Genetic selection using DNA markers in a segregating population. Markov chain analysis A Markov chain is an association of events and sequences of events with their probabilities. The analysis describes the behavior of an informationally closed and generative system that is specified by transition probabilities between that system’s states. It is named after A. A. Markov who in the early twentieth century studied poetry and other texts as stochastic sequences of characters (symbols, letters, syllables, and words). Marrying of spirits Storage of a mixture of spirits for a specific period before packaging. Martin process Name of a historical wheat wet-milling process using a wheat flour/water dough for starch extraction with high water consumption. Mashing Extraction of milled malt and/or cereals, using hot water, to produce wort or wash. Material safety data sheet (MSDS) MSDS, safety information supplied (or available) for potentially dangerous chemicals. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) A mass spectrometric method for the rapid identification of proteins and other polymeric molecules in which the sample is placed in a matrix that generates a crystal coating the target molecules. Flashes of laser light on the target evaporate the matrix molecules together with the target molecules and yield ions that fly into a detector where molecular ions separate according to their molecular masses. Maturation Time spent by spirit beverages in wooden casks (barrels), to improve flavor and aroma of finished products. Maximum residue limit (MRL) The maximum residue of a chemical pesticide that is acceptable according to regulated or agreed conditions. The residue level could result from a treatment according to registered directions and good agricultural or storage practices. Meiosis Part of the process of gamete formation in sexual reproduction consisting of chromosome conjugation and two cell divisions after which the chromosome number is reduced by half. Membrane processing Unit operation using a membrane system to separate or fractionate molecules in solution differing in molecular weight. Mesophiles Bacteria that flourish at ambient temperature. Metabolic functions How vitamins affect the human body. See list for vitamins and add minerals to it. Metabolism The sum total of the chemical and physical changes constantly taking place in a cell, resulting in the buildup and breakdown of chemical components within an organism. Metabolome The complete metabolite profile of an organism, tissue, or organ at a specific stage of development. Methionine One of the amino acids that contains sulfur. Methyl bromide Liquid fumigant when conditioned in a cylinder under pressure, which is highly toxic for pests such as fungi, bacteria, soil-borne viruses, insects, mites, nematodes, and rodents. It is used mostly for soil fumigation, for disinfestation of durable and perishable commodities, including quarantine purposes, and for disinfestation of buildings, ships, and aircraft.

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Microarray A high-throughput technique for assessing gene expression levels, based on hybridization of an mRNA or cDNA population to immobilized oligonucleotides or cDNAs in a high-density array. Microbial fermentation Dietary material that is degraded by microorganisms within the digestive tract of animals. Microbiological spoilage Grain quality loss induced by microorganisms that occurs when grain moisture content exceeds the threshold for their multiplication. Micronutrients Chemical elements needed only in small amounts, usually < 1 ppm, for the growth of plants. Microsperma (lentil) Small-seeded type of lentil of Persian (Iranian) origin. Microwave High-frequency radiation that is absorbed by water in baking foods. Much shorter wavelengths and higher frequencies than radio frequency, as is used for thawing frozen foods. Middlings Intermediate product of flour milling comprising intermediate-sized particles of endosperm. Milled rice Whole or broken grains of raw or parboiled rice from which the hull, bran, and germ have been removed. Milling Reduction of grains into small particles, often also involving separation of the grain into its anatomical components. Mineralization The process of oxidation of complex organic substances to simple minerals, water, and carbon dioxide through the actions of living organisms. Minerals Inorganic elements that are needed in very small amounts by plants, animals, and humans. Minimum tillage A method of planting crops involving no major tillage other than the opening of the soil to place seeds. Related terms include reduced tillage and no till. Miso A Japanese mash-like product made of soybeans along with rice or barley on which fungi have been allowed to grow and the resulting koji is then soaked in a brine solution to develop flavor. It is used as a soup. Modified atmosphere (MA) Intentional modification of the natural gaseous environment in a gastight enclosure generally carried out to extend the safe storage life of food products. ‘Controlled atmosphere (CA)’ terminology refers to the control of constant composition of an MA along a storage or distribution time. Modifying genes They belong to minor effective genes which can alter the phenotype of major genes to a certain extent. Molding Shaping a piece of rounded dough into the shape needed for the finished bread. Typically sheeted out into a circle then rolled before being placed into the pans to rise (proof). Molecular mapping Determination of the relative positions of genes on a DNA molecule, and the distance between them (in linkage units or physical units). Molecular marker An easily detectable genetic element (protein or DNA) that has two or more alleles and is inherited in relation to particular genes or genetic traits of interests. Monocotyledon A plant that produces a single cotyledon or initial leaf when it germinates. Monoculture An area in which a single plant type is grown. Monoecious Having separate male and female flowers on the same plant, such as in maize.

Monogastric digestive system The digestive system of animals such as pigs and humans, in contrast with the digestive systems of ruminants, rabbits, horses, etc. Monola(tm) Trade name for canola with reduced levels of linolenic acid and increased oleic acid in the oil compared to traditional types. Monoploid (or haploid) A plant with a single set of chromosomes. Monosomic An aneuploid lacking one chromosome. Monounsaturated fatty acid A fatty acid having only one double bond. Also called monoenoic acids. Moromi A Japanese name for the brine stage in soy manufacturing. Freshly prepared koji is immersed in brine and a long maturation period occurs during which bacteria and yeasts grow and produce flavor and aroma. Morphology The form and structure of an organism or part of an organism, the study of form and structure. Motai A distilled liquor made from sorghum grains inoculated with rice-based jiuqu. Moto The first stage in the production of Japanese rice wine when some starch breakdown occurs and yeast concentrations are increased. msl Male sterility from Lembke in northern Germany. Multicropping The practice of growing more than one crop in the same field in a sequence or at the same time. Mutagenesis A process which results in a change of a gene and/or chromosomal structure or number. Mycotoxin A poisonous compound naturally produced by some fungi under certain conditions.

N n and 2n The gamete and zygote chromosome numbers, respectively. Naked grain Grain in which the palea and lemma naturally separate from the grain (as in modern wheat). Nap Cytoplasmic male sterile B. napus. National list (NL) In many countries, before plant varieties can be sold they have to be included on a ‘national list’ of varieties. Such varieties will have been demonstrated to be distinct, uniform, and stable and to have sufficient value for cultivation and use. Native starch Native starches designate starch in its natural unmodified form, for example, native starch from potato, cassava, maize, rice, and wheat. Natto The Japanese name for a product made with whole cooked soybeans on which a bacterium is allowed to grow. The bacteria produce a slimy material that sticks the beans together and produces a distinctive flavor. Natural heating Spontaneous heating of a region in a grain bulk caused by the respiratory activity of microorganisms that generate heat. Natural selection ‘Survival of the fittest’; differential survival and reproduction among members of a population or species in nature, due to variation in inherited traits and subsequent effects on reproductive capabilities. NC America Antigua and Barbuda, Bahamas, Belize, Canada, Costa Rica, Cuba, Dominica, Dominican Republic, El Salvador, Grenada, Guadeloupe, Guatemala, Haiti, Honduras, Jamaica, Mexico, Montserrat, Nicaragua,

Glossary Panama, Puerto Rico, Saint Lucia, Saint Vincent/Grenadines, Trinidad and Tobago, and the United States. NE Asia Cyprus, Gaza Strip (Palestine), Islamic Republic of Iran, Jordan, Kuwait, Lebanon, Oman, Palestine-Occupied Territories?, Qatar, Saudi Arabia, Syrian Arab Republic, Turkey, United Arab Emirates, West Bank, and Yemen. Near infrared (NIR) Light not visible to human eyes. It consists of the wavelengths between 700 and 3000 nm. NIR technology is commonly used to assess grain at receival points; it is rapid and nondestructive. NIR light is able to detect and measure molecules and complex compounds. Necrotic The description of an organism (or part of an organism) that is dead. Nejayote The liquor obtained when corn is cooked and steeped in alkali. Nematicide A pesticide targeted to nematode control. Nematodes Microscopic wormlike animals that live in soil and are parasites of plants. Networking The act of working together in a criss-cross and feedback fashion. Neutral detergent fiber Fibrous fraction providing an estimate of total cell-wall composition including cellulose, hemicellulose, and lignin expressed as a percentage. Niche marketing Directed at consumers with specific characteristics. Nil This is a level of zero in a half liter grain sample representative of an entire load. This also indicates that nothing was detected at any stage of the receival process. Nip of the rolls The point where rolls come closest together. Also called the ‘pinch point.’ NIR spectroscopy The use of the NIR spectrum of light to determine the chemical composition of grain or flour samples, especially their content of water (moisture), protein, and oil. NIR technology Technology that uses reflectance or transmission of NIR light to predict aspects of grain or flour quality, including the levels of protein, oil, and moisture. Nitrogen cycle The continuous series of events wherein atmospheric nitrogen and nitrogenous compounds in the soil are converted, as by nitrification and nitrogen fixation, into available nitrogen that can be utilized by green plants directly, the substances returning to the air and soil as a result of the decay of the plants (mineralization) and denitrification. Nitrogen fixation The acquisition of atmospheric nitrogen by legumes and its transformation into organic forms that can be used for plant growth. It is performed by a collaborative effort, or symbiosis, between the plant and bacteria of the genera Rhizobium or Bradyrhizobium. Nixtamal The swollen corn kernels without pericarp after cooking and steeping in lime or alkali. Nixtamalization Process developed by early Mesoamerican civilizations in which whole maize is cooked in water containing wood ashes or lime (calcium hydroxide). The grain is cooked to partially gelatinize the starch and stone-ground to produce a dough which is further processed into dry masa flour, table tortillas, tortilla chips, or corn chips. Nonsaponifiable fraction The lipid fraction that does not contain esters of fatty acids.

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Noodle discoloration Darkening of raw wheat noodle strands over time, mainly as a result of polyphenoloxidase activity. Noodles Pasta-like products, made from a dough consisting of semolina or flour (generally not from durum wheat), mixed with water, eggs, and salt. There are many shapes, often rectangular, and fairly long thin strips. Noodles are boiled in water or stock, then added to various kinds of flavorings, condiments, meats, etc. Nucleotides The structural units of all nucleic acids, the building blocks of DNA and RNA. They consist of a nitrogen-containing base, a five-carbon sugar, and phosphate group. They may also have more than one phosphate group and be energy-transferring compounds. Nullisomic An aneuploid lacking both members of a homologous pair of chromosomes. Nullisomic–tetrasomic An individual lacking one homologous pair of chromosomes but having two additional members of another chromosome. Nusun(tm) Trade name for sunflower with altered fatty acid profile from traditional types. Nutraceutical (also spelled nutriceutical) A food component having a beneficial effect on health, beyond simple nutrition. O Oat Hardy cereal of the genus and species Avena sativa, used as food and animal feed. Obligate pathogen A pathogen that requires a living host in order to survive. Oceania Australia, Fiji Islands, Guam, New Caledonia, New Zealand, Pacific Islands Trust Territories, Papua New Guinea, Solomon Islands, and Vanuatu. Octoploid An organism having eight complete chromosome sets, as opposed to two in diploid organisms. Ogura (kosena) A radish from Japan with male sterile cytoplasm. Ohmic heating Also known as resistance heating. The food being heated conducts the electric current internally. As a result, it heats more uniformly. Oilseeds Seeds grown as crops for oil extraction, for example, soybean, sunflower, and rapeseed. Okara The insoluble residue left after extracting soymilk from ground soybeans. Oleic acid A monounsaturated 18-carbon fatty acid, cis-9octadecenoic acid, which is the major component of olive oil. Oleochemicals A term describing the wide range of compounds derived from animal and vegetable oils and including glycerol, fatty acids, esters, and amines. Oligonucleotide A chain of a few nucleotides. Oligosaccharide Low-molecular-weight sugar comprising two or more covalently bound monosaccharides. Organic farming Farming without the use of pesticides, fungicides, GMOs, or inorganic fertilizers. Organically produced foods Produced following governmental standards for crops, livestock, and processed agricultural foods. Organoleptic Having to do with the sensory evaluation of foods, as in taste and smell.

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Organoleptic properties The properties of food to do with its suitability as a food for humans, such as flavor, aroma, texture, color, etc. Orthologous Of molecular sequences or genes, having homology due to originating from a speciation event, as opposed to paralogous sequences which have homology due to originating from duplication events. Orysin The prolamin group of proteins in rice endosperm. Oryzanol Esters of ferulic acid and triterpene alcohols such as sterols and stanols that possess antioxidant capacity. Osborne protein fractions (groups) Types of proteins in cereal grains, separated on the basis of their extractability in different solvents. Osteoporosis The loss of calcium from bones, resulting in the bones becoming brittle. This condition is common in postmenopausal and elderly women. Oven Chamber which is heated sufficiently by various heat sources to bake bread or other foods. Typically operates at temperatures of about 200 C. Oxidation (fatty acids) A carbon–carbon double bond in unsaturated fatty acids is oxidized a more stable carbon–carbon single bond. Oxidation/reduction The loss/acceptance of electrons by a substance. Oxidative rancidity Chemical changes in fats and oils brought about by exposure to the atmosphere, resulting in off-flavors. Oxygen radical absorbance capacity (ORAC, mmol TE g1) A measure of antioxidant potential. P Paddy rice (¼ rough rice) Mature rice grain with the husk intact. After husk removal, but with bran layers still present, it is called brown rice. Palea The uppermost of the two floret bracts that enclose the grass flower and partly enclosing the grain at maturity. Distinct from the lemma by the presence of two lateral keels. Panicle Diversely branching cluster of flowers, with the flowers borne on pedicels, and of grains at maturity. It can be loose or compact, elliptical, bulbous, columnar, or floppy with no central rachis. Typical for oats and rice. Parbaking Partially baking bread or other foods. The loaves are heated long enough to be firm and the yeast has been killed, but the surface color is still light and the moisture is still high. The parbaked bread can later be placed back into an oven and quickly finish-baked to give a product that is almost equivalent to a fresh-baked loaf, but requires much less time, equipment, and baking skills. Parboiled rice Rice that has undergone soaking, steaming, and drying to gelatinize the starch. Parenchyma Thin-walled plant cells involved in photosynthesis and storage. Pasta A generic name for products such as macaroni, spaghetti. Generally not noodles. Also called alimentary pastes, macaroni products. All generally made of durum-semolina dough that has been extruded, possibly sheeted and cut; found in many different shapes. Pasteurization Moderate heating process for rendering a beverage microbiologically safe and slowing down its rate of microbial spoilage.

Pasting The phenomenon following gelatinization in the dissolution of starch, involving granular swelling, exudation of molecular components from the granule, and eventually total disruption of the granules. Pasting curves Recordings of viscosity changes produced by the alternate heating and cooling of starch-containing materials in water. A programmed heating–cooling cycle under shear is set in a suitable instrument, for example, the Rapid Visco Analyzer. Pasting temperature Temperature at which initial onset increase in viscosity is observed. Pathogen An organism that requires a host organism from which to gain its nutrients. Pathogenic Disease producing. Peak viscosity The point at which, during heating of starch granules in water, gelatinized starch reaches its maximum viscosity. Pearling Process whereby the outer layers of barley kernels are removed through abrasion, without crushing the endosperm. Generally used to enhance the processing value of the grain. Peat (peating) The burning of peat (bog plant) material. Smoke and phenolic compounds are deposited on the malt during the kilning stage of the malting process. Peel Long-handled paddle used for putting a loaf into older style ovens or removing it when it is baked. Peel oven An oven that is loaded and unloaded with a peel, a long-handled flat paddle. The furthest back loaves are in the oven longer than the front loaves. Seldom seen today. Pehtze The Chinese name for the molded tofu produced as an intermediate product in the production of furu. Pellagra Vitamin-deficiency disease characterized by exposed skin cracking and flaking and by mental changes. Pentosan A polymer of five-carbon sugars, providing dietary fiber. It practice, this fraction may have an arabinoxylan backbone and contain small amounts of glucose and ferulic acid. Per capita Consumption per person, usually per year. Pericarp An outer layer of the grain. Perigonium perichaetium Any of the leaves or bracts surrounding the sex organs of bryophytes or the structure formed by such a whorl. Perisperm A seed tissue derived from the maternal nucellar tissue. This often fails to develop and is absorbed during seed development but remains as a storage tissue in some species. Peroxide value A measure of oxidative rancidity for fatty acids of peanuts or other oilseeds. Pesticide label A label attached to a pesticide that, if followed, will allow safe and efficacious uses of the pesticide; in many parts of the world pesticides may only be used legally if the label use is followed. Phenomics The high-throughput analysis and screening of phenotypic variants of an organism. Phenotype The observable properties (structural and functional) of an organism, produced by the interaction between an organism’s genetic potential (its genotype) and the environment in which it finds itself. Phloem Plant conductive tissue for the transport of dissolved solutes, for example, transport of photosynthetic products from source to sink tissues.

Glossary Phosphatides Primarily phospholipids. Phosphine gas A widely used fumigant with remarkable insecticidal properties released in gaseous form from aluminum or magnesium phosphide solid generators through the action of water vapor in air. Photoperiod Day-length including twilight which affects the rate of crop development. Physical map Order of genes based on physical distance, measured as the number of base pairs separating the genes. Phytase Enzyme(s) hydrolyzing phytic acid (inositol hexaphosphate) by successive removal of phosphate residues. Phytic acid The hexaphosphoric ester of inositol. It is a minor constituent of grains that contains phosphorus, and acts as an antinutritional factor in feeds for some animals. Phytochemical or phytonutrient Plant chemicals that may have health benefits. Phytoestrogens Compounds from plant sources which elicit hormonal functions similar to that of estrogen. Phytosanitary regulations Government regulations controlling the import and export of plants, seed, and unprocessed plant products in order to control the spread of plant diseases and pests. Phytosterol Naturally occurring plant-derived chemical with a similar, but significantly different, structure to cholesterol. Pickling The process in which pickling compounds are added to grain as a seed treatment or dressing prior to sowing. This involves immersion in an aqueous acid solution to chemically remove contaminants from an external seed coat. Pickled grain is toxic to consume and therefore is usually associated with a coloring agent so that pickled grain can be easily detected and differentiated from harvested, untreated grain. Plansifter A sieve in a box that oscillates rapidly in a horizontal plane to separate mill products on the basis of particle size, usually various-sized flour streams, in a flour mill. Plant Breeders’ Rights (PBR) A form of intellectual property rights, similar to patents for industrial inventions, that enable the breeder of a protected variety of plant to claim a payment or royalty from those who grow the protected variety. Royalties are usually only payable on the purchase of seed of the protected variety, but sometimes on the produce at harvest. Plant breeding The process of crop improvement by systematically and intentionally hybridizing plants to alter the genetic makeup of a plant, thus to increase genetic diversity as a basis for selection of improved genotypes. Plant Variety Rights (PVR) An alternative name for PBR, used in certain countries. Plasticizer Small molecules added to soften a polymer by lowering its glass transition temperature. Plastids Plant cell organelle with double membrane. There are two types of plastids, chloroplasts and amyloplasts. Chlorophyll-containing green plastids are known as chloroplasts, where photosynthesis occurs. Starch-storing plastids are called amyloplasts, generally present in storage organs. Polished rice (¼ white rice) Rice grain with husk, bran layers, and embryo removed, that is, comprising intact endosperm. Polydispersity Describes a polymer system in which the molecules are of different sizes.

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Polymorphism Genetic variation that produces differing characteristics in individuals of the same population or species. Polyploid An organism having three or more complete chromosome sets. Polysaccharides Long chain carbohydrate made up of large numbers of linked simple sugars (monosaccharides) such as glucose and closely related molecules. (Poly)unsaturated fatty acids Fatty acids containing (more than one) carbon–carbon double bonds in the carbon chains. Popcorn Special type of flint maize used since prehispanic times for popping. Today is one of the most popular and preferred snack foods throughout the world. Current hybrids have 30- to 40-fold expansion ratios. Population It can be defined as a colony of progeny with genetic variation. Porridge Processed and cooked (boiled) grain. Portion pack Packaged in separate single-serving amounts. Precautionary principle A legal principle developed in the EC which suggests that if safety cannot be proven then precaution in the enfranchisement of a foodstuff or technique should be used. Preconditioning Preliminary treatment with heat and moisture prior to a major processing step. Price discovery process A process for determining the price of a commodity, such as barley, in the marketplace through the interactions of buyers and sellers and based on supply and demand relationships. Primary cell wall The first formed layer of the wall of a plant cell produced by the deposition of cellulose microfibrils and noncellulosic polysaccharides at the cell plate. Processed Physical alteration of food mechanically, by heat/ cold, etc. Processors Commercial companies turning crops from raw materials to processed goods. Programmable logic controller (PLC) Hardware for process control of wheat milling. Prolamin box (endosperm box) A short nucleotide sequence upstream of cereal prolamin genes that is involved in the regulation of their expression. Prolamins Proteins that are soluble in aqueous alcohol. Proof An indication of the absolute ethanol content of a distillate that contains ethanol and water. In the Imperial system, 100 proof is equal to 57.06% ethanol by volume, or 48.24% by weight. Proofing Letting the molded dough piece ferment for 1 h so it rises to the height needed to be baked. Results in a light and flavorful loaf. Proprietary data Access controlled by private firms and only available to those who pay for it. Protease An enzyme that digests proteins. Protease inhibitors Antinutritional factors which inhibit the action of digestive proteolytic enzymes. Protein Naturally occurring large molecules, composed of polymers of amino acids. They are diverse in biological function. Examples of proteins include enzymes, hormones, hemoglobin, spider web, finger nails, egg white, and gluten. Protein bodies Membrane-bound deposits of storage proteins in plant cells.

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Protein chemistry A science which is involved in the chemical characteristics of proteins. Protein disulfide isomerase (PDI) An enzyme that catalyzes disulfide bond formation, exchange, and breakage in protein. Protein efficiency ratio (PER) The weight gain of a growing animal divided by its protein intake over the period studied. It is a measure of the nutritive quality of a protein source during digestion when compared with the best-quality protein available. Protein functionality Physicochemical properties of a protein (or protein product) that influence its uses in foods. Protein quality (nutritional) In vivo measurement in growing rats by nitrogen balance by the method of Mitchell of true digestibility, biological value, and net protein utilization, in comparison with amino acid score. Protein types According to solubility, they are divided into albumins soluble in water, globulins soluble in high salt concentration, prolamins soluble in aqueous alcohol, and glutelins soluble in acid or alkaline solutions. Some protein fractions are named 7S, 11S, 10S, etc., according to their sedimentation coefficients. Proteome The complete protein complement of an organism, tissue, or organ at a specific stage of development. Pseudocereal A nonmember of the grass or cereal family (Poaceae) producing dry fruits that are consumed in a manner similar to those of true cereals. Psocoptera An order of small insects commonly known as booklice or psocids, a recognized pest of stored grains. Public domain Information available to everyone. Pullman loaf A bread baked in rectangular pans fitted with lids, so they do not have rounded tops. Also called ‘sandwich’ bread. Pulse Pod-bearing plant belonging to the legume family (Leguminosae) that produces seeds used directly for human food, such as peas, beans, and lentil. Pulse crops Annual legumes grown to produce dry edible seeds. The list includes lentil, chickpea, and common bean. Punch To release some of the accumulated CO2, and thus the volume, of fermented dough by physical means; also ‘punch back’ or ‘punch down.’ Purifier A machine that separates semolina and middlings of varying size and degree of bran contamination on the basis of density and particle size. Pycnidia (singular pycnidium) Small, spherical, or flaskshaped structures formed by certain types of fungi, inside which spores are produced. Pycnidiospore A fungal spore produced asexually in a pycnidium. Q Quality protein maize (QPM) Maize genotypes that contain almost twice as much lysine and tryptophan as regular maize hence possess better nutritional value. QPM has the opaque-2 gene that is combined with modifier genes that significantly improve the endosperm hardness and agronomic performance of the crop. Quantitative trait A measurable trait that shows continuous variation; a trait that cannot be classified into a few discrete classes.

Quantitative traits locus (QTL) A genetic locus identified through the statistical analysis of complex trait. The trait is typically affected by more than one gene and by environmental factors. R Race In taxonomic classification, an infraspecific category of uncertain position but occasionally used in floras in place of, or subordinate to, form. Raceme Inflorescence-bearing flowers on stalks of equal length on unbranched main stalk. Rachilla The segmented central axis of a spikelet which bears two or more fertile florets. Rachis The main axis of the grass inflorescence. Rack oven A large box-shaped oven with a tall door that opens to admit a rolling rack holding trays or screens of food to bake. Air is blown crosswise across the rack, which often turns during the baking cycle. Used especially in modern retail bakeries and in large food-service operations. Radiation Heat transferred by radiation, generally IR. The objects do not need to be in contact with each other and do not need any intermediate fluid. Radiation is most efficient in a vacuum, but is almost as good in air. Radiation use efficiency (RUE) The ratio between crop biomass produced and amount of solar radiation intercepted (g MJ1). Radio frequency (RF) RF radiation with wavelengths longer than used in microwaves. Used for thawing frozen foods and postbaking crackers to equilibrate their moisture contents and avoid checking or cracking when they cool off. The energy is selectively absorbed by water. Radiation penetrates baking foods better than the shorter wavelength microwaves do. Raman spectroscopy A form of spectroscopy in which structural information is obtained from changes in wavelength that occur when radiation is scattered by certain molecules. Rancidity Off-flavor associated with the degradation of lipid either by oxidative reactions or by hydrolysis of fatty acids from neutral lipids such as triglycerides. Rapid Visco Analyzer Commercial instrument used as an indicator of sprouting. Based on the rapid determination of the pasting properties of starch as influenced by enzyme activity present in the ground grain. Also used to characterize starch-pasting properties in the absence of enzymic activity. Rate of shear thinning A measure of the rate at which maximum viscosity of hot starch paste decreases during holding time of starch breakdown viscosity. Recombination Exchange of gene segments by crossing over at chiasmata (exchange of material between nonsister chromatids). The exchanged sections are usually homologous. Recommended dietary allowances (US) (RDAs) Recommended intake for individuals. Recommended intakes Amounts of nutrients (vitamins) to consume for good health. Redox potential An expression of the oxidative/reductive state in a food system. Reduced amylose wheat starch This high swelling starch, also known as ‘partial waxy’ starch, is closely linked to the desired soft and elastic texture in Japanese udon noodles.

Glossary Reducing end Carbon 1 of the glucose molecule is highly reactive and capable of reducing divalent to monovalent cations; there is only one C1 in each starch molecule, all the others being involved in a-1,4 or a-1,6 linkages. Reducing sugars A sugar containing free aldehyde (HdC] O) or ketone (C]O) groups capable of reducing metal ions such as copper or aluminum. Reduction rolls Smooth rolls used in flour milling to reduce middlings to flour. Reduction system Part of the milling process that reduces sized and purified chunks of endosperm into flour by a series of roller mill passages. Reel oven A large box-shaped oven with small horizontal door. A series of four or more shelves rotate about a horizontal axle in the manner of a Ferris Wheel. Baking items are normally loaded and unloaded through the same door. Refined grain Grain which is milled to remove the bran and germ. Refining (oils) The preparation of oil for human consumption by removal of extraneous materials that could compromise food quality. Regional breeding Regional collaboration among breeders and farmers in the development of new types or varieties of plants and animals to produce improved types through sexual or asexual means and environmental influences. Registered pesticide A pesticide whose use is allowed (and often controlled) by legislation within a jurisdiction. Relay cropping Planting a second crop before harvesting the first crop but after the first crop has completed the major part of its development. Representative sample A subsample of a load of grain that has been tendered for delivery that is used for assessment purposes. The sample is assumed to be collected in such a way that it is representative of the population (load) from which it is drawn. This means that the characteristics are the same as those of the population (load) within the stated limits of the confidence level and precision. Resistant starch Starch, raw or processed, and starch degradation products (staled amylose) that are not digested by humans and fermented in the larger intestine as soluble dietary fiber. Restaurant-style tortilla chips Very thin baked tortillas are fried in oil. The tortillas are often refrigerated prior to frying. Texture and oil content are altered. Restorer The line has a different genotype with a cytoplasmic male sterile line, but can restore its sterility. Retort A thermal process used in canning in which high temperatures and pressures are used to preserve foods. Retrogradation A process which occurs when the molecules comprising gelatinized starch begin to reassociate in an ordered structure. Rheological properties A general term covering the physical properties of a viscous system, such as a dough, which relate to its extensibility, resistance to extension, mixing properties, and viscosity. Rheology The study of the flow and deformation properties of materials. Rhizobia Soil bacteria that form symbiotic nodules on the roots of leguminous plants.

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Rhizobium Genus of heterotrophic soil bacteria capable of forming symbiotic nodules on the roots of legume plants to fix atmospheric nitrogen. Rhizome A horizontal root (below ground) from which new shoots emerge at intervals and grow into new plants with the same genetic code as the original. Rice Cereal of the genus and species Oryza sativa, used primarily for food. Rice bran The outer layers or coverings of brown rice, composed of the pericarp, seedcoat, nucellus, and aleurone layer. Industrial bran is a mixture of bran and germ (embryo). Rice bran oil Oil extracted from dried rice bran by solvent extraction. Rice milling Process of converting rough rice to milled rice by dehulling and abrasive or friction milling. Rice quality Grain properties desired by various groups in the postharvest system as determined by variety, environment, and postharvest handling. Rice wine An alcoholic beverage made by growing fungi on cooked rice grains and then soaking them in water to allow fungal enzymes to break down the starch. Yeasts then produce alcohol. Rich The term used to describe a bakery formula high in enriching ingredients such as sugar and shortening; the opposite of lean. RNAi technology A posttranscriptional gene silencing technology that involves the use of a gene construct consisting of target sequences in both sense and antisense orientation. Roller drying, also known as drum drying Process for drying flour involving passing the wet flour between a pair of heated rollers. Roller mill Machine housing up to four pairs of cylindrical break and reduction rolls. Rotary hearth oven An oven in which the hearth revolves about a vertical axis. This design is not as space efficient as some others, but it permits products to be inserted or removed at different times. Some designs have several hearths or rack supports on one vertical axle. Rotation A system in which crops are grown in a particular sequence in order to derive maximum economic return. Rough rice Paddy, unhulled grain (kernel) of rice. Rounding Forming the cut piece of dough into a small ball that retains moisture and carbon dioxide while it rests before molding. Royalty A sum of money payable by a third party to the owner of any type of registered intellectual property. RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) The most abundant plant enzyme on the planet. This principal carboxylating enzyme is used by C3 plants during photosynthesis to incorporate CO2 into sugars. S Saccharification The enzymatic process by which the starch in grain is broken down into its constituent sugars. Safe storage time Time without spoilage or loss of grain quality from when the grain is first put into storage. Sake´ The Japanese name for rice wine.

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Saponin Any of a class of bitter tasting compound in which the aglycone portion (the sapogenin) is a steroid glycoside that on shaking with water forms colloidal solutions giving soapy lathers. Sappy Grain that is plentiful in sap content. This is common of immature grain and is milky in appearance when the grain is squeezed between the thumb and index finger. Saturated fatty acids Fatty acids containing only single bonds between carbon atoms in the carbon chains. These include lauric (C ¼ 12), myristic (14), palmitic (16), stearic (18) acids, etc. Sauerkraut Literally ‘sour cabbage,’ this is produced by lactic fermentation of finely shredded cabbage leaves (slaw) by LAB in the presence of 2–3% (w/w) of salt. Sausages In relation to grain-containing foods, the continental types where comminuted meat, salt, spices, and cereal material are packed into casings, sometimes smoked, then allowed to undergo a slow fermentation under controlled humidity and temperature. The fermentation, although dominated by LAB, may involve numerous other types of bacteria, and sometimes yeasts and other fungi. Scarification The partial removal of the outer layer of the kernel to allow better uptake of moisture by the kernel during cooking. Scotch pure malt whisky Either a ‘single malt’ or a mixture of malt whiskies. Scotch single malt whisky Whisky produced in one distillery from a mash of only malted barley. Scourer Machine that uses impact from steel beaters to remove dirt and loosen bran from wheat prior to milling. Screening percent A grain quality measurement to assess grain size uniformity. Screw axis In a helical polymer, the axis about which relative rotation of subunits occurs moving from one subunit to the next. Thus, a twofold screw axis refers to a relative rotation of 180 , in a threefold axis the relative rotation is 120 . Scutellum Transport tissue of the germ of cereal grains. Secalin The prolamin group of proteins in rye endosperm. Secondary cell wall The wall layer(s) deposited internal to the primary wall following cessation of cell growth and expansion. Usually rich in cellulosic microfibrils that in many cases are encrusted with lignin. Sedimentation coefficient (S20,w) A measure of molecular mass determined by sedimentation equilibrium ultracentrifugation. Segregation A term referring to the first of Mendel’s laws in which the chromosomes interchange segments then move apart to form different gametes to those of the parents and thence form different offspring. Seimaibual classification A Japanese name for the classification system for rice wine based on the degree of polishing of the grains. Selection process Process by which grain of a specific species is identified, through physical examination, as suitable for a particular end use. Self-incompatibility (SI) Characterized by showing bad seed set when self-pollination occurs. Self-sufficiency (food or grain) The ability of a country to meet its basic long-term food supply needs without dependence on food imports.

Semileafless Pea cultivars in which leaflets are replaced by tendrils. Semileafless canopies are more rigid by virtue of more interplant connections than canopies of conventional leaved cultivars. Semolina Intermediate products of flour milling comprising coarse particles of endosperm. Highly refined semolina is the primary product of durum wheat milling for production of couscous and premium pasta. Semolina yield The proportion of whole wheat grain converted by milling into semolina. Serpentine path Folded path ovens in which the product may move through the chamber five to nine times before leaving. The conveyors are located close together. As a result, the oven is much shorter than conventional designs, although somewhat taller. Serving size Amount of food appropriate for one person per meal/snack. Setback viscosity The viscosity recorded during the cooling phase of the starch-pasting process. Shattering Detachment of crop seeds from the plant before harvest. Shear (high or low) The result of a force acting to deform or fracture a material in a direction parallel to the force applied to it. Shelf life The consumer-determined period of time following baking that a product retains its perceived freshness. Shorts Low-grade mill products containing principally germ and fine bran particles; used for animal feed. Shoyu The Japanese name for soy sauce. Sieve A fine cloth or metal screen which is used to separate endosperm fractions based upon particle size. Silique The elongate dry fruit of the mustard family bearing two seed chambers separated by a partition. Simple sequence repeat (SSR) Repetitive DNA with repeats ranging in size from 1 to 6 bp, also referred to as a microsatellite (widely used as genetic markers). Simultaneous buying and selling An arrangement, under the grain-import regulations of the Japanese government, allowing for direct sales and delivery contracts between specific Japanese companies and specific international suppliers. Single kernel characterization system (SKCS) Commercial instrument used to measure the weight, diameter, moisture, and hardness of individual kernels. Single seed descent (SSD) Method of breeding sometimes used in self-fertilizing species to advance generations with minimal use of resources and to ensure that advanced generations possess the range of genotypes exhibited in the F2 population. Sizing system Part of the milling process that reduces the particle size of coarse endosperm particles with or without small pieces of bran attached. Sizing, paper The application of nonpigmented pastes to the nearly dry sheet at the size press. Sizings Larger chunks of endosperm with some bran still attached. Sometimes called ‘semolina’ in Europe or ‘farina’ in North America. Slashing The practice of cutting the surface of proofed breads and rolls for the purpose of controlling bursting during baking. Also useful in adding visual interest to the product.

Glossary Slicing Cutting a loaf of bread into thin slices. Usually done automatically by high-speed band saws. Also used to cut hamburger buns or hot dog rolls, so they can be opened to fill for sandwiches. Smallholder farming Farming on a piece of farmland that is smaller than the average farm. Solin™ Trade name for linseed with an altered fatty acid profile containing reduced amounts of linolenic acid in the oil, compared to traditional types. Developed in Canada. Somatic embryogenesis The initiation and development of embryos from cells that are not products of gametic fusion. Sorghum A tropical or subtropical cereal grain crop in the grass family that is adapted to dry or drought-prone agroecologic areas. The grains are produced on a panicle, and can be white, red, brown, or gray in color. Sorghum beer A number of fermented beverages are made from sorghum and millet in various parts of Africa, usually with local names (‘pito,’ ‘kaffir beer,’ etc.) and recipes. They are typically high in solids and are consumed while still fermenting. They can be significant sources of calories and B-vitamins. Sorghum races Sorghum genetic divisions with each having distinctive physical characteristics and a common ancestry. There are five basic races (guinea, caudatum, durra, kaffir, and bicolor), and ten stable hybrid races formed by natural crossing and genetic combination of the five races. Sound grain Grain that is in good condition and free from any damage, defect, or decay. Soxhlet extraction Method of extracting oil from plant material utilizing a low-boiling-point organic solvent and traditional soxhlet apparatus. Soy concentrates Soy protein products with about 70–80% protein. Soy isolates Soy protein products with over 90% protein. Soy lecithin A complex mixture of fats or oils that contains phosphate groups and acts as an emulsifier. Soy nuggets or salted black beans Whole soybeans are cooked and fungi (and bacteria under uncontrolled conditions) allowed to grow on them up to about 3 weeks. They are then washed and brined, and finally dried. Soymilk A liquid extract from soybeans made by grinding the soybeans in water and filtering out the residual insoluble components. Specialty rice Special purpose rice such as aromatic rice, waxy rice, and pigmented rice. Species Groups of interbreeding populations or organisms, sharing common genetic descent, reproductively isolated from other such groups. Spike A grass inflorescence with spikelets positioned sessile on the rachis. Spikelet One or more florets enclosed by two glumes (bracts). If the spikelets are attached directly to the rachis, the inflorescence is called a spike (as in small-grain cereals such as wheat and barley). Sporulate To produce spores. Spring varieties Crop varieties which have little or no response to vernalization, or which will flower readily without vernalization. Squalene 2, 6, 10, 15, 19, 23-hexamethyl-2, 6, 10, 14, 18, 22tetracosahexaene.

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Stability Not affected by changing conditions such as heat. Stackburning (yellowing) Grain deterioration and yellowing of wet grain from delayed drying of harvest grain from anaerobic respiration of microbes and grain, with accompanying rise in temperature >60 C. Staple crop The primary starch-based crop that provides most of the daily energy requirements for a human population (typically rice in much of Asia, wheat or potatoes in Europe, and maize in tropical Africa). Starch Water-insoluble polymer of glucose, with a-1–4 and 1–6 linking bonds, comprising amylose and amylopectin. Starch gelatinization A disruption of molecular order accompanied by concomitant and irreversible changes in granular swelling, loss of birefringence (Maltese cross), crystallite melting, viscosity development, and starch-molecule solubilization. Starch granule A small (commonly 2–100 mm) grain or particle in which starch is deposited in the plant cell. The shape and size of the granules are characteristic of the plant species. Granules are partially crystalline and insoluble in cold water. Starch paste This is a two-phase system in which the dispersion phase is composed of swollen starch granules and the continuous phase is formed with leached amylose. Starch retrogradation A process, which occurs when the molecules of gelatinized starches begin to reassociate in an ordered structure. In its initial phase, two or more starch chains form a simple juncture point which then develops into more extensively ordered regions that under favorable conditions form a crystalline order with eventual exudation of water (starch syneresis) from the gel. Starchy endosperm The inner part of the wheat kernel, comprising about 85% of the kernel. Starchy kernels Also called opaque, are white, usually soft in texture and lower in protein content, with gas pockets between starch and protein causing the light to be scattered as it passes through. StarLink™ A GM produced com (maize) with the Cry9C variant. Starter culture Portion of fermented food product or intermediate with high microbial activity used to inoculate a fresh fermentation. Starter nitrogen Small doses of N-fertilizer given to a legume crop to boost early growth before root nodule symbiosis is established. Steam flaking The process of flattening tempered, heated grain. Steep/steeping The process of soaking grain in water, during which time lactic acid fermentation may take place. Steeping The process of soaking cereal grains to imbibe water. Stillage Mixture of residual solids and water from stills. These can be dried and added to spent mash grains to produce animal feed. Stolon A horizontal stem (above ground) from which new shoots emerge at intervals and grow into new plants with the same genetic code as the original. Storage chemicals Substances used to preserve grain quality during storage. Storage pests Biological organisms that damage the grain during storage.

488

Glossary

Storage structures Various forms employed for grain containment prior to use. Stored-grain ecosystem A batch of grain stored in bulk is a system of living organisms that includes a group of interacting organisms with the physicochemical environment within and outside the grain mass. Straight whiskey Whiskey stored in charred, new oak barrels for a period of at least 2 years; or mixtures of straight whiskies, not < 4 years old, of the same grain type, produced at the same distillery. Straight-grade (straight-run) flour Flour made by combining all flour streams from the flour milling process. Strain hardening The nonlinear rapid increase in viscosity or stiffness as a material is deformed. Stratification Layering effect. Strecker degradation The name of a chemical reaction that occurs when food is heated. Amino acids in the food react with carbonyl compounds to produce aromatic aldehyde compounds that contribute to food flavor. Street foods Ready-to-consume food products sold by street vendors. Strengthener Any of a number of highly functional ingredients added to bread and roll dough to facilitate processing tolerance and impart greater baked volume to the product. Stubble Crop residues remaining in the field after harvest. Subsistence farming Agricultural system where farmers produce food primarily to satisfy the needs of their own family. Subspecies Subdivision of species; a group of interfertile individuals or populations distinct from other members of the same species either by differences in morphology or gene frequencies. Sulfonylurea herbicides Postemergence herbicides of the sulfonylurea chemistry ALS, registered for use on numerous crops for control of broadleaf weeds. Representative examples include chlorsulfuron, ethametsulfuron, foramsulfuron, metsulfuron, nicosulfuron, rimsulfuron, sulfosulfuron, thifensulfuron, tribenuron, and thiflusulfuron. Supercritical fluids Gaseous substances such as CO2 that are heated and pressurized such that they have properties of both gases and fluids and are used in the extraction of lipids from foods. Sustainable Able to be renewable over an indefinite period without damage to the environment (soil, water, and air). Swathing Mechanical cutting of a crop and laying in a windrow to hasten maturity and prevent seed loss. Sweet corn Contains high levels of soluble sugars and lower levels of starch due to recessive genes (sugary 1 or su1 and/or sugary 2 or su2). It is usually consumed on the ear or processed by the canning industry. Swelling factor Ratio of volume of swollen starch granules to the volume of dry starch granules. Symbiosis The close, long lasting, and often necessary interaction of members of one species with those of another, to the mutual benefit of both. Symplast The continuum of cytoplasm within a plant. Symplastic transport The regulated transport of substances between live cells through plasmodesmata, involving energy expenditure.

Symporter Membrane-localized permease that cotransports two molecular species, for example, sucrose and protons. Syneresis Loss of water from a starch paste or gel during storage, caused by the contraction of the solid phase associated with retrogradation. T Table auger Transverse auger on harvester front that feeds cut material into the center from where it enters the rest of the machine. Taco In the United States, a corn (or wheat) tortilla formed into a U-shape and deep-fried, then filled with meat, cheese, other fillings, and salsas. In Mexico, a taco is an unfried soft corn (or wheat) tortilla containing the same items. Tamales Nixtamalized corn masa containing meats, cheese, or bean fillings, wrapped in a corn husk and steamed. Tannin Polymers of flavonoids – specific aromatic compounds with hydroxyl groups. Taxonomy The science of identification, classification, and nomenclature of organisms. Teleomorph Sexual state of a fungus. Telocentric chromosome A chromosome with a single arm and centromere, derived by low-frequency misdivision of a normal bibrachial chromosome. Telocentric mapping Use of a telocentric chromosome as a cytological marker for genetic mapping. Tempeh An Indonesian food made with cooked whole soybeans on which fungal mycelia have been allowed to grow to knit the soybeans into a cake. Temperate (C3) cereal Type of cereal with a photosynthetic system that cannot take advantage of the high-intensity solar energy in the tropics, for example, barley, oats, rye, and wheat. C3 refers to the number of carbon atoms in the first sugar produced in the photosynthetic process. Tempering To adjust and equilibrate the moisture content of a grain (such as wheat) in order to toughen the bran layers for easier separation, and to soften or mellow the endosperm, before dry milling for flour production. Test weight The weight of a measured volume of grain expressed in kilograms per hectoliter. Often used as a crude indication of end-use quality, particularly for feed grains. It is related to kernel plumpness and soundness, and is an indication of wheat milling potential. Testa The seedcoat, the layer that contains tannins and is pigmented in brown sorghum. Tetraploid Organisms with four complete sets of chromosomes (4n). Tetraploid rye A species of rye, grown mostly in Germany, that contains four basic units of chromosomes in its somatic (body) cells. Tetraploid wheat Wheat with two homoeologous sets (4n) of diploid chromosomes, such as durum wheat which is used for pasta production. Tetrasomic An aneuploid with two additional members of a particular chromosome. Texturization A process to introduce unique textural properties to a food product. Texturized vegetable protein Extracted soy protein that has been extruded using the thermoplastic process.

Glossary Thermal time A measure of the heat units, or day degrees above a base temperature, for a crop to complete a stage or the whole life cycle. Thermo-reversibility The ability of a gel to revert to a solution on heating. Thiaminase An enzyme that destroys the vitamin thiamin; found in some raw fish tissues and in bracken. Three-line hybrid rice Hybrid rice based on cytoplasmic male sterile line, maintainer line, and restorer line. Threshing Process by which cereal grains are released from ears or spikes. Tiller A stem that arises from a bud in the crown and grows vertically. Time-series data Data showing per capita food consumption trends over time. Titratable acidity A measure of the amount of acid in a liquid, measured by titrating the liquid to neutrality with a base of known molarity. Tocopherol Vitamin E homologs that contain a saturated side chain. Tocotrienol Vitamin E homologs that contain an unsaturated side chain. Tofu A soft cheese-like product made from soymilk by coagulation, usually with magnesium or calcium salts. Tonoplast Also called vacuolar membrane, which is the cytoplasmic membrane that surrounds a vacuole of a plant cell. Tortilla chips One of the most popular snack foods in the world. Tortillas are usually cut into triangles and then fried for about 1 min. The crisp tortilla chips are usually salted and flavored. Tortilla chips contain about 24% oil. Tortillas Food product widely consumed in Mexico and Central America. Tortillas are classified as flat non-leavened bread. Tortillas are produced from lime-cooked maize that is stone-ground into a dough or masa which is formed into thin circles and baked to yield the soft and flexible tortillas. Wheat-flour-based tortillas (tortillas de harina) also make up a significant proportion of the market. Tortillas are used for the preparation of many dishes. Tostado, totopos A tortilla that has been fried into a snack. Trace minerals Essential elements required in human food intakes at < 100 mg day1. Transcription factors Proteins that regulate gene transcription by binding to sequences upstream of the protein coding regions. Transcripts RNA generated from a DNA template. Transfer cells Parenchyma or dermal cells differentiated with wall ingrowths that amplify plasma-membrane surface area and enhance transport. Transformation Transfer of genes, generally between sexually isolated taxa by nonsexual means. Trend General change in direction that continues and is strong enough to change consumption patterns. Triacylglycerol A fat consisting of a molecule of glycerol and three fatty acids. Also called triglyceride. Tricanter process Wheat wet-milling process named after Tricanter® used as equipment for the main separation unit in the wheat wet-milling process. Triploid A plant with three sets of chromosomes. Trisomic An aneuploid with one additional chromosome.

489

Triticale A man-made cereal produced by combining rye and durum wheat by genetic manipulation. Trolox equivalents (TEs) The reference material for antioxidant determination. Tropical (C4) cereal Type of cereal with a photosynthetic system that can take advantage of the high-intensity solar energy in the tropics, for example, maize, sorghum, and teff. C4 refers to the number of carbon atoms in the first sugar produced in the photosynthetic process. Trypsin activity A measure of the speed with which the digestive enzyme trypsin can break down a protein. Tryptophan An amino acid, component of all proteins, which is the first limiting amino acid in nutritional quality of rye for humans and monogastric animals. Tunnel oven A long oven in which the product makes one pass on a moving band made of flexible metal or wire mesh. Used especially for biscuits (crackers and cookies). Usually of high capacity. Tweedy A dough mixer that employs high-speed agitation under partial vacuum to develop dough quickly. Two-line hybrid rice Hybrid rice based on photoperiod/ thermal-sensitive male sterile line and restorer line. U UL (tolerable upper intake level (US)) The highest average daily nutrient intake level likely to pose no risk of adverse health effects for most people. Unprocessed Food in its natural state. Unsaturated fatty acids Including oleic (C ¼ 18), linoleic (18), linolenic (18), arachidonic (20) acids, etc. UPOV International Union for the Protection of New Varieties of Plants. UPOV is an intergovernmental organization and is responsible for dealing with legal and technical issues with regard to DUS testing and PBR. Most countries with PBR systems are members of UPOV. Uredospore Asexual spore borne on the sporophore of a rust fungus. Ureide Organic structures containing urea, for example, allantoin and allantoic acid. U’s triangle U, a Japanese scientist, constructed a triangle based on genome analysis in Brassica to show the genetic relationship between the Brassica oilseed species. Utilization The act of putting into some practical use, through appropriate processing and development of end products. V Value for cultivation and use (VCU) The registration and marketing of plant varieties in many countries is dependent on an assessment of their distinctness (DUS), and of their agronomic merit, based on tests and trials of various features (e.g., yield, quality, and disease resistance) which together are deemed to demonstrate their VCU. Varietal purity Degree to which a sample of grain consists of only one variety. Important because of differences in processing properties among varieties. Variety A subdivision of a species; an agricultural variety is a group of similar plants which by structural features and performance can be identified from other varieties within the same species.

490

Glossary

Vatting Mixing of similar kinds of spirit beverages. Vector A transport medium for a pathogen that is not affected by the pathogen it carries. Vegan diet A very strict vegetarian diet where no animal products are consumed, that is, no meat, fish, egg, milk, cheese, or products derived from these foods. Vernalization Exposure of seedlings to cold temperatures for several weeks that is required by some cultivars to induce reproductive growth. Vicilins A family of 7–8S storage globulins generally associated with cowpea (Vigna unguiculata). Viscoamylograph A measure of the viscosity of a starch paste under a controlled heating and cooling cycles at constant shear rate. Viscosity A measure of the resistance to flow of a material, defined as applied stress divided by the applied strain rate. Vital gluten (vital wheat gluten) Industrial product consisting of wheat gluten and having in the hydrated or rehydrated state, cohesive and elastic properties (wheat gluten is the usual name for water-insoluble protein complex from wheat). Vitamin Essential organic molecules needed in very small amounts for cellular metabolism. Vitamin enrichment Nutritional improvement by the controlled addition of vitamins. Vitreous kernels Vitreous grain is generally hard, with a glassy translucent appearance, due to the high protein content in the endosperm cells immediately below the aleurone layer, and the strong bonding between starch and protein which occurs throughout the endosperm.

Wax Long-chain fatty acids esterified to a long-chain alcohol, usually associated with the outer layers of fruits, vegetables, and cereal grains. Waxy maize Mutant type of maize that contains more than 95% amylopectin in the starch. It is wet-milled to obtain waxy starch, which has special uses. Waxy starch has a higher hot paste viscosity and produces softer and clearer gels than regular starch. Waxy rice and glutinous rice Rice without amylose or with < 2% of amylose. Weevils Beetles of the genus Sitophilus, a common and destructive pest of stored grain. Westfalia three-phase decanter process Wheat wet-milling process named by a starch production company and the equipment established for the main separation unit in the wheat wet-milling process. Wet milling (rice) A process of steeping rice grains, grinding, and separation to fractionate starch, protein, and oil. Wheat Cereal of the genus Triticum, primarily used for food by milling into flour for bread. Whole grain Unprocessed kernel, or product with no part of the kernel lost during processing. Wild rice An aquatic grass belonging to the Zizania genus represented by four species. Winter varieties Crop varieties in which inflorescence initiation and flowering are promoted by vernalization – a period at low temperatures. Winterhardiness Ability of plants to survive the winter weather with little or no injury.

W Warp sizing Paste coated onto yarn to add strength and abrasion resistance during weaving. Wash Wash is the soluble extract of mashed malt and/or cereals. Wash is the distiller’s term for brewer’s wort. Wash contains the products of enzymatic hydrolysis of starch, cell walls, and proteins, for example, sugars and amino acids. It also contains vitamins, lipids, and minerals. Water absorption The percentage of water, relative to flour or semolina as 100%, required to yield a dough of the desired consistency. Water activity Thermodynamic parameter linked to the chemical potential of the water in grain; it is related to the relative humidity of the air of inter-kernel space in equilibrium conditions. Waterlogged soil Soil saturated with water. Water-soluble carbohydrate Total nonstructural carbohydrate concentration consisting of sucrose, fructose, glucose, and fructans expressed as a percentage. Water-use efficiency The amount of crop production per unit quantity of water used. It can be defined in a number of ways, for example, it can be the amount of grain produced per mm of evapotranspiration.

X Xiaoqu A small-sized jiuqu product made from rice flour. X-ray diffraction Scattering of X-rays by organized structures such as crystals; a widely used diagnostic for crystal structure. Y Yeast Microorganism used for fermenting a bread or roll dough. Converts sugars into carbon dioxide and water. Available in water as a thick cream, as a moist, dense, cake, or in a dried form. Yield stability The ability of a crop variety to achieve consistent yield across a wide range of production environments. Yuba The Japanese name for a dried product made by heating soymilk and collecting the solid skin that forms on the surface and drying it. It is highly nutritious. Z Zadoks growth stage scale Scale used to describe the growth stages of small grains. Zeins Prolamin which is soluble in alcohol, comprising 52% of kernel nitrogen in maize.

INDEX This index is in letter-by-letter order, whereby hyphens and spaces within index headings are ignored in the alphabetization, and it is arranged in set-out style, with a maximum of four levels of heading. Location references refer to the volume number, in bold, followed by the page number. Page numbers suffixed by b, f and t refers to boxes, figures and tables terms respectively. vs. indicates a comparison. Bold locators refers to main articles.

A AAC. See Apparent amylose content (AAC) AACCI. See American Association of Cereal Chemists International (AACCI) AAP. See Amino acid permease (AAP) Abiotic diseases, 4:74–75 ABNY. See Apparent boiled noodle yield (ABNY) Abrasive decorticators, 1:205 Absit, 1:217–218, 3:186 Acarina. See Mites Acetoin (3-hydroxy-2-butanone), 4:260 Acid-modified starch, 3:278, 3:282, 3:284 Adhesives, starch, 3:276–277 Adlay millet. See Coix ADPG pyrophosphorylase, 2:183–184, 2:184t Adult plant resistance (APR), 4:264, 4:381 Aflatoxins, 2:292–293, 2:293f AFLP. See Amplified fragment length polymorphism (AFLP) Africa AGRA, 1:365 area of, 1:359 bambara bean production, 1:360t, 1:361, 1:361f barley production, 1:361 biofortified crop, development of, 1:365 cereal imports, 1:362, 1:362f climate in, 1:359 famine, 1:429–430 GM plants, 1:365 grain foods and beverages, 1:362t, 1:363–364, 1:364f grain handling challenges, 1:365, 1:365f maize production, 1:359, 1:360t millet production, 1:360t, 1:361, 1:361f natural vegetation, 1:359 oil-containing grains, 1:361–362 PASS, 1:365 pearl millet, LAB fermentation, 3:186, 3:186t, 3:187f population, 1:359, 1:360f private sector, grains research in, 1:452

pulses, 1:361 rice production, 1:360t, 1:361 sorghum production, 1:360t, 1:361 teff, manual harvesting of, 1:362–363, 1:363f wheat combine harvesting of, 1:363, 1:363f production, 1:360t, 1:361 African rice diversity, 1:141–143 NERICA development process, 1:143 origin and history, 1:140 panicles of, 1:140–141 physicochemical properties, 1:143–144, 1:144–145f, 1:145t production in, 1:360t, 1:361 AfricaRice, 1:143, 1:433 Agave, 3:194t, 3:198–199 AGP. See Arabinogalactan proteins (AGP) Agricultural biorefinery, 3:228, 3:231–233 Agricultural chemicals crop-protection chemicals, 4:101–102 fertilizers (see Fertilizers) foliar fungicides, 4:102 fungicidal seed dressing, 4:99–100 grain contaminants, 4:95 herbicides, 4:101 insecticides, 4:100 MSDS, 4:99 registration of, 4:99 regulations, 4:99 rodenticides, 4:103 stored-product protection controlled atmospheres, 4:103 fumigation, 4:102 grain protectants, 4:102–103 methyl bromide, 4:102 phosphine, 4:102 structural treatments, 4:103 Agricultural production systems simulator (APSIM), 4:208, 4:208f Agricultural Research Center (ARC), 1:450 Agricultural Research Service (ARS), 1:436 Agriculture and Agri-Food Canada, 1:439 Agrifood Technology, 1:445

Agrobacterium-mediated transformation, 1:322, 4:344 AGSA. See Australasian Grain Science Association (AGSA) Airborne diseases, 4:79–80 Aleurone rice, 1:46–47, 1:47f, 1:125 teff, 1:212 wheat grain, 1:41 Alien introgression, 4:389 Alimentary toxic aleukia (ATA), 2:294–295 Alkaline cooking. See Nixtamalization Alkaline noodles, 3:5 Alkali spreading value (ASV) test, 3:168–169, 3:169t Alkyresorcinols, 2:278t, 2:280 Allergenic proteins dry beans, 1:302–303, 1:302t lupins, 4:330 Allergy food processing, 2:74 genetic modification, 2:75 maize, 2:74 management of, 2:75 millets, 2:74 prevalence of, 2:72 proteins, 2:72–73 rice, 2:74 sorghum, 2:74 SPTs, 2:75 symptoms and pathology, 2:72 wheat (see Wheat, allergy) Alliance for a Green Revolution in Africa (AGRA), 1:365 All India Coordinated Research Projects, 1:447 Allopolyploidy, 4:384 Alpha-linolenic acids (ALA), 1:260f, 2:8–9, 2:9f Alveograph, 3:253, 3:344 Amaranth, 1:275, 1:288 agronomic characteristics, 1:288 for animal feed, 1:295 chemical compositions of, 1:288, 1:290t cultural uses of, 2:40–41

491

492

Index

Amaranth (Continued) essential amino acid composition, 1:291–292, 1:291t field production, in northern China, 1:287, 1:288f healthful/functional components of, 1:295 leaves, composition of, 1:288–289, 1:290t modern food applications of, 1:294–295 oil and squalene content of, 1:292–293, 1:292t pigment content and fresh weight, 1:293–294, 1:293–294t, 1:294f proteins, 1:291–292, 1:292t seed morphology, 1:288, 1:289f starch and amylose content of, 1:289–291, 1:291t traditional food products, 1:294–295 vegetable amaranth, 1:288, 1:295 Amaranthus caudatus, 1:31, 1:32f, 1:34 American Association of Cereal Chemists International (AACCI), 2:59, 4:450, 4:452t activities of, 1:459 annual meetings, 1:460 awards, presentation of, 1:457, 1:458f biotechnology group, 2:306 2015 Centennial Annual Meeting, 1:459 cereal-based foods, 2:302–303, 2:303f logo, 2:300, 2:301f members, research activities of, 1:459 microbiological methods, 2:302, 2:303f mission, 1:459 resources, 1:459–460 strategic initiatives, 1:459 Thomas Burr Osborne Medal, 1:457, 1:458f whole grains, 2:12–13 American Dietetic Association (ADA), 2:2 American Malting Barley Association (AMBA), 4:23 American Oil Chemists’ Society (AOCS), 1:458, 1:462, 2:300, 2:305 American Society of Agronomy (ASA), 1:458, 1:461, 2:301 American whiskeys, 3:198 AMF. See Arbuscular mycorrhizal fungi (AMF) Amino acid permease (AAP), 2:125 Ammonium transporter family (AMT), 2:125 Amplified fragment length polymorphism (AFLP), 4:365–366 Amylomaize, 3:98, 3:99t Amylopectin, 1:128–129, 2:168, 2:200 ae wx double mutants, 4:429 building blocks, 2:193–194, 2:194f chain length distribution, 4:430, 4:430f crystalline and amorphous lamellae, 2:191, 2:192f degree of polymerization (DP), 2:181 D-glucopyranos, 4:425 high-amylose maize, 4:427–428 o2 maize starch, 4:429 properties of, 4:426 semicrystalline structure, 4:426 starch biochemical tests, 2:175–176 chain length distribution, 2:175

double helices, 2:176–177, 2:177f highly branched, 2:175 liquid crystal, 2:175, 2:176f mutant starches, 2:179–180 properties of, 2:174, 2:176t retrogradation, 2:179 starch granule, 2:177–178 starch-synthesizing enzymes, 2:176 structural components, 2:190, 2:192f structural polymorphism of, 2:194, 2:194–195f sugary 2 maize, 4:428 two-directional backbone model, 2:191 unit chain profile external chain, 2:192 HPSEC, 2:191–192 internal chains, 2:192–194, 2:193–194f limit dextrin profile, 2:191–192 polymodal distribution pattern, 2:191–192 Amylose, 2:198–199, 2:199t degree of polymerization (DP), 2:181 linear and branched fractions, 2:194 starch biochemical tests, 2:175–176 dissociation of, 2:178–179 GBSS, 2:178 mutant starches, 2:179–180 properties of, 2:174, 2:176t starch-bound lipids, 2:178 starch granule morphology, 2:177–178 triiodide ions, 2:175–176 structural components, 2:190 Analytic thinking, 2:64 Andean grains, 2:95 Andean Quinoa Project, 1:346 ANFs. See Antinutritional factors (ANFs) Angkak, 3:448 Angoumois grain moth, 4:57–58, 4:58f Animal feed amaranth, 1:295 barley, 1:149 cottonseed, 1:245–246 digestive tract, 3:216–217, 3:216f dry beans, 1:305 energy value of grains (see Energy value of grains, livestock) linseed, 1:259, 1:261 pea, 1:324, 1:327 peanuts, 1:334 quality criteria, 3:261 sorghum, 1:157–158, 3:116, 3:123 soybeans, 1:235 Annealing, 3:285 Anthracnose lentil, 4:228t, 4:229 lupin, 4:237, 4:326–327 sorghum, 4:205 Antibiosis antibiotics bacteria, 4:259 fungi, 4:259 lytic enzymes, 4:259 volatile compounds, 4:259–260

Antinutritional factors (ANFs), 4:330 buckwheat, 1:310 dry beans, 1:304 fermentations, 3:176–177 legumes, 1:270 linseed, 1:261 lupins, 1:282–283, 1:282t pea, 1:326 rice bran and brown rice, 1:128 soybeans, 1:231, 3:485 Antioxidants cereal grains and grain products, 2:277, 2:278t in vivo and in vitro measurements, 2:277 oxidative stress, 2:277–278 Phenol-Explorer database, 2:277 whole-grain cereals alkyresorcinols, 2:278t, 2:280 avenanthramides, in oats, 2:279–280 carotenoids, 2:278t, 2:281 flavonoids, 2:280 g-oryzanols, 2:279 lipotropes and methyl donors, 2:279 melatonin, 2:281 minerals, 2:278t, 2:279 phenolic acids, 2:278t, 2:280 phytic acid, 2:279 policosanols, 2:278t, 2:281 riboflavin (B2), 2:278t, 2:279 saponins, oats, 2:280 sulfur compounds, 2:278–279, 2:278t thiamine (B1), 2:278t, 2:279 tocopherols and tocotrienols, 2:278t, 2:281 AOAC International, 1:458, 1:462, 2:301 AOCS. See American Oil Chemists’Society (AOCS) Apparent amylose content (AAC), 1:128–129, 3:168–169, 3:172–173, 3:172f Apparent boiled noodle yield (ABNY), 3:154 Apparent electrical conductivity, 4:164–165 APR. See Adult plant resistance (APR) Aqueous extraction process, 1:233 Aquitane, 2:290–291 Arabic bread, 1:410–411, 1:416f, 3:16f, 3:17, 3:17t, 3:20–21, 3:341f Arabidopsis thaliana, 2:123 Arabinogalactan proteins (AGP), 2:221–222, 2:221f Arabinoxylan arabinofuranohydrolases (AXAH), 2:139–140 Arabinoxylans, 2:170, 2:286–287 analysis and detection, 2:219 gelation, 2:216f, 2:217–218 genetics, 2:219, 2:219t molecular parameters, 2:217 NSP, 2:226, 2:227f solid-state and solution conformations, 2:217 solution properties, 2:217 structure, 2:210f, 2:214–217, 2:215t, 2:215–216f structure–function relationships, 2:218–219

Index Araceae, 1:277 Arachidonic acid (AA), 1:260–261 Arachis hypogaea L., 1:20 Arare, 3:110, 3:112f, 3:448 Arbuscular mycorrhizal fungi (AMF), 4:260 Arcelin, 1:301–302 Arecaceae, 1:278 Arepas, 3:98–99, 3:100t, 3:106–107, 3:106f Argentina agriculture value, 1:420 chickpea, 1:319 consumption, 1:420–422 diet, cereal component of, 1:420, 1:422f grain commodities exports, 1:420, 1:423f Pampas, 1:420 soybean, 1:357 undernourishment, 1:422 ASA. See American Society of Agronomy (ASA) Ascochyta blight chickpea, 1:320, 4:219–220 field pea, 4:248f lentil, 4:228–229, 4:228t Asia alcoholic beverages Chinese rice wine production (see Chinese rice wine production) Japanese rice (see Sake’ brewing) arable land and agricultural populations, 1:375–376, 1:375f beriberi, 2:77 biotechnology, 1:381 cereal production, 1:377–378f, 1:378–379 fuel ethanol production, 3:237, 3:238t grain imports and exports, 1:376–378, 1:378t, 1:380–381, 1:381f grain prices, 1:381–382 grain production and yield, 1:376, 1:376–377f, 1:377t green revolution, 1:379 harvested area, 1:376, 1:376f, 1:377t land area of, 1:375–376, 1:375f population of, 1:374–376, 1:375f private sector, grains research in, 1:452 self-sufficiency in rice, 1:374–375 starch noodles, 3:64–65 wheat agronomy, 4:180–181, 4:180t, 4:183t Asian noodles dimensions of, 3:72, 3:74t flour alkalies, effects of, 3:77 attributes and appearance, 3:76 emulsifiers, effects of, 3:78 enzymes, 3:78 food colorants, 3:78 gums, effects of, 3:77–78 modified starches, effects of, 3:77 and noodle texture, 3:76–77 proteins, 3:78 salt, effects of, 3:77 specifications for, 3:76–78, 3:76t hydrogen peroxide, 2:142, 2:143f ingredients in, 3:72, 3:73t

Japanese-style white salted noodles, classification of, 3:72, 3:73t LOX, 2:142 manufacturing processes for boiled noodles, 3:75 classification, 3:72 cutting, 3:74 for dried noodles, 3:74–75 for frozen noodles, 3:75 initial sheeting and combining, 3:73–74 instant steamed and dried noodles, 3:75 mixing process, 3:72–73 rolling of sheet, 3:74 steamed and fried instant noodles, 3:75 peroxidases, 2:142–143, 2:143f wheat, 3:75–76 WSN flour, water, and salt, 2:141 xanthophylls, 2:141–142 YAN flavonoid compounds, 2:141–142 flour, water, and alkaline salts, 2:141 PPO, 2:142 xanthophylls, 2:141–142 Asian rice diversity in, 1:141–143 panicles of, 1:140–141 RVA profile, 1:145f Asia-Pacific Association of Agricultural Research Institutions (APAARI), 1:432 Aspergillus A. flavus, 2:292, 4:257 A. ochraceus, 2:293 A. parasiticus, 2:292 Association of Official Agricultural Chemists (AOAC), 1:458, 1:462 Atlantic Cool Climate Crop Research Centre, 1:439 Atmospheric nitrogen, 2:129, 4:135 Attention-deficit/hyperactivity disorder (ADHD), 2:25 Australasian Grain Science Association (AGSA), 1:457–458, 1:461, 2:301 Australia barley animal feed, 1:416 export markets, 1:415–416 human food, 1:416 production, 1:410t, 1:413, 1:415t yields, 1:413–415, 1:416t bread wheat, grain contaminants, 4:89t grain production in, 1:409, 1:410t grain research in, 1:444–445 maize, 1:410t, 1:415–416t, 1:417 oats production and yield, 1:410t, 1:415–416t, 1:417 oilseed production in, 1:410t, 1:411–413, 1:417–418 pulse production in, 1:410t, 1:417 rice delivery, 1:413–415 farming operations, 1:413–415 medium- and long-grain varieties, 1:415 production, 1:410t, 1:413, 1:415t yields, 1:413–415, 1:416t

493

rye, 1:410t, 1:415–416t, 1:417 sorghum production and yield, 1:154, 1:410t, 1:415–416t, 1:417 triticale, 1:415–416t, 1:417 wheat agronomic practices for, 4:182, 4:182t Arabic ‘pocket’ breads, 1:410–411, 1:416f bank notes, 1:409–410, 1:411f consumption, 1:418 crop yields, changes in, 1:418, 1:419f crossbreeding, 1:409–410, 1:413–414f exports, 1:410 fair average quality, 1:410, 1:415f Farrer, William, 1:409, 1:413f food products, 1:413, 1:416f grain quality, 1:413 grain-storage facility, 1:411, 1:416f industry, historical developments in, 1:409–410, 1:412t marketing, 1:413 production, 1:410, 1:415t small-scale flour mill, 1:410, 1:415f small-scale test methods, 1:410 wheat growing regions, 1:409, 1:411f yield, 1:413, 1:416t Australian Grains Centre, 1:445 Australian Pesticides and Veterinary Medicines Authority (APVMA), 4:97, 4:99 Australian sweet lupin (ASL), 1:280 Avenanthramides in oats, 2:39, 2:279–280 structures of, 2:5f Avena sativa. See Oats Away from home (AFH) foods, 2:68–70 Awns, 1:89, 1:95f, 4:288 AXAH. See Arabinoxylan arabinofuranohydrolases (AXAH)

B Baby foods, 3:272, 3:448 Backcross (BC) method, 4:426 Back slopping, 1:194, 3:180, 3:183–184, 3:189 Bacterial artificial chromosomes (BACs), 1:147–148, 4:370, 4:372–373, 4:389–390 Bacterial diseases, 4:171–172, 4:172t, 4:246, 4:247t Bagels, 3:3, 3:34–35, 3:35t Baguette, 3:13–14 Baked product staling. See Staling, baked products Bakeries baking process (see Baking) home baking, 3:338–339 hot-bread shops, 3:340 independent ‘scratch’ bakery, 3:340 in-store bakeries, 3:340 large plant bakery, 3:339–340 old-world bakeries, 3:340–341 specialized baked goods, 3:341

494

Index

Baking automation, 3:305 basic procedures, 3:337f baking, 3:336–338, 3:338f bun rolls, 3:338, 3:339f cooling, 3:336–338 dividing and rounding, 3:336–338 fermentation, 3:336 horizontal dough mixers, 3:337f ingredient measuring, 3:335 ingredients, 3:335 mixing, 3:336, 3:338f molding process, 3:336–338, 3:338f proofing, 3:336–338 rest period, 3:336–338, 3:338f shipments, distribution and retail sales, 3:336–338 slicing and bagging, 3:336–338 total processing time, 3:335–336 cakes, 3:372–373 challenges, 3:305 dough rheology (see Rheology) history of, 3:303 individual loaf-protective wraps, 3:305 ovens (see Ovens) Baking industry associations, 1:451–452 Baladi, 3:21 Bambara bean, 1:360t, 1:361, 1:361f Banana diet, 2:91 Band ovens, 3:328–329, 3:329f Bangladesh Agricultural Research Institute, 1:447 Bangladesh Agricultural University, 1:447 Baptist, Jan, 1:2–3, 1:3f Barbari bread, 3:20 Barley abiotic stress resistance, 1:151, 1:151f adaptive characteristics disease and insect resistance, 4:289 winter barley, 4:288–289 yield, 4:288 Africa, production in, 1:361 alcoholic beverages, production of, 3:434 American whiskeys, 3:198 animal feed, 1:149, 3:260, 4:52, 4:292–293 aphids, 4:191 Australia (see Australia) biotic stress resistance, 1:151, 1:151f, 1:152t botany, 1:147 breeding strategies cultivation, 4:290 DH techniques, 4:290 hybrids, 4:290–291 malting and brewing industries, 4:289 mutation breeding, 4:290 qualitative traits, 4:289 quantitative traits, 4:289 SSD, 4:290 cleaning and dehulling, 3:435 components of, 3:423–424, 3:424f composition of, 3:434–435, 3:435t consumption trends, 2:33

contaminants, 3:435 cultivar selection, 4:188–189, 4:189f cultural uses of, 2:39–40 disease control, 4:190–191, 4:190t diseases, 4:75, 4:76t diversity of, 1:75f, 1:77f, 1:78t, 1:80f, 1:81–82 domestication, 1:90, 1:90t, 1:147 drying, 4:50–51 Europe cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t, 1:386t exports, 1:355 extruded snacks, 3:419 for food uses, 3:434, 4:293 forage, 4:293 functional foods, 1:149, 1:149f genetic and genomic studies, 4:361 developmental mutants, 1:148, 1:148f epigenetics, 1:149 ESTs and BACs, 1:147–148 integrative genomics, 1:148–149 marker-assisted selection, 4:292–293 MAS and GAS schemes, 1:149 metabolomics, 1:148–149 molecular mapping, 4:291 physical maps, 4:291 QTL analyses, 4:291 structural and functional genomics, 1:148–149 yield potential, 1:148, 1:148f, 1:151 global domestic supply, 1:355 global production, 1:151, 3:434 gluten-containing cereals, 2:91–92, 2:94 GMO, 1:5 grades and standards, 4:16 advantages and disadvantages of, 4:18–19, 4:18t in Australia, 4:20t, 4:21 in Canada, 4:20t, 4:21–22 EU intervention standards, 4:21t, 4:23 grading factors, 4:19–20 processing characteristics, 4:19, 4:19t in Russia and Ukraine, 4:21t, 4:23 in United States, 4:21t, 4:23 variety classification, 4:19 visual grading factors, 4:20, 4:22f grain cleaning, 4:50 grain quality specifications, international trade, 4:83, 4:84t grain size, 4:50 growth stages, 4:186–187, 4:187f harvesting, 4:50 hessian fly, 4:191 Hordeum spontaneum, 1:147, 1:148f human health benefit of, 1:149, 3:434 India, production in, 1:367–368, 1:368f, 1:370–371, 1:370–371f Irish whiskey, 3:198 irrigation, 4:190

kernel composition, 3:434–435, 3:436f lipids, 2:250, 2:251t malting (see Malting barley) marketing, 1:355 activities, 4:16 in Australia, 4:20–21, 4:22t in Canada, 4:21–22 China, 4:23 components, 4:16 customer service programs, 4:17 delivery contracts, 4:16 European Union, 4:22–23 feed barley, 4:18 food barley, 4:17f, 4:18 institutes, 4:17 Japan, 4:23 price pooling, 4:16–17 production contracts, 4:16 public/private tenders, 4:17 quality specifications and tolerances, 4:17 in Russia and Ukraine, 4:23 sales contract, 4:17 Saudi Arabia, 4:24 United States, 4:23 morphology, 1:147 basal leaf sheath, 1:54, 1:54f, 1:66f dorsal view, 1:62, 1:70f ears of, 1:62, 1:67f pigment, 1:54, 1:54f, 1:67f rachis segments, 1:55, 1:56f, 1:62, 1:68f size and shape, 1:62 sterile spikelet, 1:62, 1:67f two-row vs. six-row barley, 4:287–288, 4:288f types, 4:288 usage, 1:57t ventral view of, 1:62, 1:68f nematodes, 4:191 in North America (see North America) pearling appearance, effect on, 3:437–439, 3:439f b-glucans, 3:437–440, 3:439f blocked and pot barley, 3:440 by-products, 3:437–439 definition, 3:435–437 fat and protein, concentrations of, 3:437–439, 3:439f hulled and hull-less barley, removal of, 3:435–437, 3:437f kernel dimensions, 3:437, 3:438f phenolic contents, 3:437–439, 3:440t rate of, 3:435–437 rotating carborundum/emery stones, 3:435–437 soluble and insoluble dietary fiber, content of, 3:437–439, 3:439f tannin and phosphorus, concentrations of, 3:437–439, 3:439f TEAC and ORACFL, 3:437–439, 3:440t plant nutrition, 4:187–188, 4:188t prolamins, 2:72–73

Index proteins, 2:102, 2:102f, 2:105–106 quality, 3:259 roller milling (see Roller milling) SBE, 2:186 scanning electron microscopy, 1:73, 1:75f Scotch malt whisky, 3:195–198, 3:196f seeding rate for, 4:189 shattering, 4:50 six-row barley, 1:147, 1:148f skinning, 4:50 sowing, 4:189–190 storage (see Storage) transport, 4:52 two-row barley, 1:147 uses of, 3:1, 3:2t, 3:258t varietal segregation, 4:50 weed control, 4:191–192 wheat based baked/not baked products, 1:149 wireworms, 4:191 world production, 1:350t, 1:355, 4:16 Barley Australia, 4:21 Barley Genetics Newsletter, 4:287 Barley yellow dwarf virus (BYDV), 1:178, 1:179f, 4:80, 4:173 Barnyard millet, 1:199, 1:200f, 1:200t Batter cakes, 3:367 BCFM. See Broken maize and foreign material (BCFM) BC method. See Backcross (BC) method Beall degerminator, 3:458, 3:461, 3:461f, 3:464–465 Bean yellow mosaic virus (BYMV), 4:237 Beccari’s experiment, 3:408–409 Beehive oven, 3:303, 3:303f, 3:335, 3:336f Beriberi alcoholism, 2:82 antithiamin problem heat-stable antithiamins, 2:81 thiaminases, 2:81 Asia, occurrence in, 2:77 chicken, 2:78, 2:78f deficiency acute, 2:81–82 total parenteral nutrition, 2:82 infection/malnutrition, 2:77–78 rice grain, 2:80, 2:80f, 2:81t supplementing foods, 2:80–81 thiamin isolation of, 2:78 staple foods, 2:79, 2:79f thiochrome, 2:79 vitamin, 2:78 Berliner short sour method, 3:28 b-glucans, 2:224–225 cellotriosyl and cellotetraosyl units, 3:291 chemical structure, 2:237–238, 2:237t 13 C-NMR spectrum, 3:287–289, 3:288f distribution, 2:236, 2:237f, 2:237t food products, 3:287 b-glucan depolymerization, prevention of, 3:295–297 bread, 3:294–295, 3:295f

Cerogen™, 3:294 C-Trim, 3:293–294 dry-grain fractionation, 3:294 dry pasta, 3:294–295, 3:296f extrusion conditions, 3:295–297, 3:297t flatbreads, 3:295, 3:296t Glucagel, 3:294 Nutrim, 3:293–294 Oatrim, 3:293–294 OatVantage™, 3:294 raw white salted noodles, 3:294–295, 3:296f two-layered pita breads, 3:295, 3:296f Viscofiber®, 3:294 GLC-FID and GLC-MS, 3:287–289 health benefits, 3:287, 3:293 cholesterol reduction, 2:238 fermentation and laxation, 2:239, 2:239f glycemic response, 2:238, 2:238f satiety and weight management, 2:238–239 methylation analysis of, 3:287–289 molecular structure of, 3:287, 3:288f molecular weight of, 3:292, 3:292f oligosaccharides, lichenase digestion, 3:291t electropherogram, capillary electrophoresis, 3:289–290, 3:290f FACE, 3:289–290 HPAEC-PAD, 3:289–290, 3:289–290f MALDI-MS, 3:290, 3:291f quantification of calcofluor-white/FIA method, 3:293 enzymatic assay, 3:292–293 monoclonal antibodies, 3:293 Betaine, 2:26, 2:279 Beverages African cereal beverages, 1:363, 1:364f Asian alcoholic beverages (see Asia) distillation (see Distilled beverages) nonalcoholic beverages, LAB fermentation (see Lactic acid bacteria (LAB) fermentation) Bibingka, 3:447t, 3:448 Biga, 3:9, 3:26 Binubudan, 3:206 Biodiesel, grain oils catalysts, effects of, 3:248 chemical structure, 3:245, 3:246f combustion emissions, advantages of, 3:249 development, 3:249 direct use and blending, 3:245–246 edible oil, use of, 1:222 feedstock, fatty acid composition of, 3:245, 3:246t free fatty acids, effects of, 3:248 microemulsion, 3:246 moisture, effects of, 3:248 molar ratio, effects of, 3:248 mono-alkyl esters, mixture of, 3:245 reaction duration, effects of, 3:248 reaction temperature, effects of, 3:248–249

495

sunflower oil, 1:251 thermal cracking, 3:246 transesterification, 3:245, 3:247–248, 3:247t Biofortification, 1:365, 1:455, 2:45, 4:405 Biolistics, 4:344, 4:346f Biological fumigation, 4:207–208 Biorationals, 4:128–129 Biotechnology and Biological Sciences Research Council (BBSRC), 1:440 Biotic diseases airborne diseases, 4:79–80 barley, 4:75, 4:76t corn, 4:75, 4:76t oats, 4:75, 4:76t residue-borne diseases, 4:75–79 rice, 4:75, 4:76t rye, 4:75, 4:76t seed-borne diseases, 4:75 soil-borne diseases, 4:75 sorghum, 4:75, 4:76t vector-borne diseases, 4:80 wheat, 4:75, 4:76t Biotrophic pathogen resistance APR, 4:264 definition, 4:264 leaf rust, 4:266, 4:267t, 4:271 powdery mildew, 4:264–265, 4:271 stem rust, 4:269, 4:271 stripe rust, 4:266–269, 4:268t Bioversity, 1:430 Birdsfoot. See Finger millet Biscuits, 3:41. See also Cookies baking, 3:42–43, 3:62 butter, 3:41 as casual snack food, 3:47 chocolate covered biscuit sticks, 3:44–49, 3:47f classification of, 3:47–48 digestive biscuits, 3:37, 3:38t, 3:44, 3:45f dough fats, 3:40 fermentation, 3:40 flours, 3:40 Garibaldi-type biscuits, 3:44–49, 3:47f hard doughs, 3:47–49 laminated (puff), 3:40–41 leavening agents, 3:41, 3:41t mixing processes, 3:40, 3:42 pet foods, 3:224 processing, 3:39 refrigerated dough (see Refrigerated dough) ‘Scotch Finger’ biscuit, 3:44, 3:45f semisweet, 3:39, 3:39t short doughs, 3:47–49 soft doughs, 3:49 sugars, 3:41 types, 3:45f Bi-Tai-Ba, 3:110, 3:113–114 Bixaceae, 1:277 Bixa orellana, 1:277 Black point, 2:142–143, 2:143f, 4:71, 4:74–75 Black spot, 1:328, 1:328f, 4:246, 4:247t, 4:248f Blocklets, 2:196

496

Index

Blue maize, 3:94, 3:98, 3:99t Blumeria graminis f. sp. tritici, 4:264–265, 4:265t Boiled noodles, 3:75 ABNY, 3:154 color assessment, 3:157 quality attributes, 3:155–156 texture measurement, 3:159 translucency measurement, 3:157 Bolivia, 1:422 Booklice, 4:110, 4:111t Borlaug, Norman, 1:2, 1:2f Botrytis gray mold, 1:320, 4:219 Bowl rice curd, 3:114 Bowman–Birk inhibitors, 1:231, 2:285, 4:26 Brabender units (BUs), 2:313 Brabender viscoamylography (BV), 1:186, 2:178, 2:203f Brachiaria B. deflexa (see Guinea millet) B. ramosa (see Browntop millet) Brandon Research Centre, 1:439 Brassica B. juncea L., 4:207 B. napus L., 4:207 B. rapa L., 4:207 Bread, 3:335 bakeries (see Bakeries) bread making, origins of, 3:335 buns and rolls, 3:13t, 3:14–15, 3:15t, 3:15f dough-making processes Chorleywood bread, 3:9–11, 3:11f continuous mix process, 3:9, 3:11f liquid sponge process, 3:9, 3:11f no-time straight, 3:9 sourdough process, 3:12 sponge, 3:9, 3:10f straight dough method, 3:8–9, 3:10f equipment, 3:8, 3:10t FAO logo, 1:105, 1:106f flat breads (see Flat breads) flour and ground grain, 1:7–8 forms, 3:335 gluten-free breads, 3:17 hearth, 3:13–14, 3:13–14t, 3:14f ingredients, 3:8, 3:9t lipids, 2:255 pan breads, 3:12–13, 3:12–13f, 3:12–13t refrigerated dough formula, 3:360, 3:360t rice flour, 3:448 rye, 3:260 sour dough (see Sour dough breads) square ‘sandwich’ loaf, 3:335, 3:336f types, 1:105, 1:106f Bread-Baking Methods Committee, 2:305 Breakfast foods brands, 3:5 in Brazil, 1:423 definition of, 3:262 diet and fortification of, 3:265–266 extruded breakfast cereal, 3:271–272 fortification, 2:46 maize, 3:105 packaging, storage, and spoilage, 3:266 products, 3:5, 3:266

ready-to-cook/hot cereals, 3:262 bulgur and corn grits, 3:265 cracked wheat, 3:265 farina, 3:265 instant oatmeal products, 3:264–265 per capita annual consumption, 3:262–263 rolled oats, 3:264–265 regulatory developments, 3:266 rice flour, 3:448 RTE cereals (see Ready-to-eat (RTE) cereals) worldwide sales of, 3:262 Brewing companies, grains research, 1:452 Bringing Green Revolution in Eastern India (BGREI), 1:368–369 Brioche, 3:15 British imperial system, 2:309–311 British Society of Plant Breeders, 4:4 Broiler chickens, 3:217, 3:220–221 Broken maize and foreign material (BCFM), 3:468 Brown leaf spot, 4:236–237, 4:327 Brown plant hopper, 4:305, 4:403 Brown rice, 2:80, 3:446–447, 3:447t, 3:450 Brown rust, 4:171 Brown spot flax, 1:263 soybean, 4:335–336 wheat bran, 1:41 wildrice, 1:135 Brown stalk rot, 1:343 Browntop millet, 1:199, 1:206–207 Buckwheat, 1:31, 1:32f, 1:276 amino acid composition, 1:308, 1:309t antinutritional inhibitors, 1:310 biological aspects of, 1:307–308 carbohydrates, 1:308, 1:308t common buckwheat, 1:307 cultural uses of, 2:41 Europe cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t fagopyrins, 1:310 fagopyritols, 1:310 fiber, 1:308–309, 1:308t flavonoids, 1:309 food products, 1:312 lipids, 1:308, 1:308t minerals, 1:309 noodles, 3:5 phenolic compounds, 1:310 phytosterols, 1:309 processing and development, 1:312–314 production areas of, 1:307, 1:308t protein content, 1:308, 1:308t, 1:310–311, 1:310t starch, 1:311 tartary buckwheat, 1:307 therapeutic effects of, 1:311–312, 1:311–312t vitamins, 1:309, 1:309t world production of, 1:356

Bulgur, 2:38, 3:6, 3:265 Bulk fermentation, 3:9, 3:16, 3:20–21 Bulrush millet. See Pearl millet Bunt, 4:71, 4:90, 4:91f Bushel, 2:311–312

C Cactaceae, 1:277 Cakes, 3:4 Antoinette, Marie, 1:5–6, 1:5f batter cakes, 3:367 and celebrations, 3:367 characteristics of, 3:4 chemical leavening, 3:31–32, 3:370, 3:370t chiffon cakes, 3:367 classifications of, 3:4 eggs, 3:369–370 emergence of, 3:367 emulsifiers shortening, 3:31 end-product tests, 3:252 fats, 3:369 flour, 3:30–31 ash content, 3:367–368 bread flour, 3:368, 3:368f chlorinated flour, 3:368, 3:368f finer flour, 3:367–368 protein content, 3:367–368, 3:368f as structure builder, 3:367–368 unbleached flour, 3:368, 3:368f foam cakes, 3:367 formula balance, 3:370–371, 3:371t gluten development, 3:4 hydrocolloids, 3:370 ingredients, 3:30, 3:31t, 3:32 LAB fermentation, 3:186t, 3:188, 3:188f processing baking, 3:372–373 batter properties, 3:371–372 continuous mixing, 3:371 pressurized mixers, 3:371 quality checks, 3:373 single-stage mixing, 3:371 recipes for, 3:30 staling, 3:404 sweeteners, 3:31, 3:368 with and without emulsifiers, 3:369, 3:369f Calabar bean, 1:11, 1:12f Calcium (Ca), 2:47–48t, 4:101 field pea, 1:327t finger millet, 1:200–202 lupin species, 1:282t pasta, 3:88t peanut, 1:337, 1:338t soybeans, 2:17, 2:18t Calcium acid pyrophosphate (CAPP), 3:400, 3:401t Callose, 2:220–221 Canada Grain Act, 4:3, 4:85 Canada Western Amber Durum (CWAD), 1:394 Canada Western Red Spring (CWRS), 1:394 Canadian Canola Growers’ Manual, 4:213 Canadian Food and Drugs Act, 4:85

Index Canadian Food Inspection Agency, 4:12 Canadian General Standards Board, 3:501, 3:501t Canadian Grain Commission (CGC), 4:3–4, 4:12, 4:21–22 Canadian Grains Commission, 1:439 Canadian International Grains Institute (CIGI), 1:439, 4:12 Canadian Malting Barley Technical Centre, 4:22 Canadian Oilseed Processors Association, 3:501 Canadian Wheat Board (CWB), 4:12, 4:22 Canadian whiskeys, 3:198 Canary seed, 1:356 Cancer, 2:20–21, 2:21f Candida antarctica lipase B (CALB), 3:247 Cannabidaceae, 1:277 Cannaceae, 1:277 Canned rice, 3:447, 3:447t Canola, 2:258t, 2:263. See also Rapeseed Australia, production in, 1:410t, 1:417–418 Brassicaceae (Cruciferae) family, 1:237 Brassica oilseed species B. juncea L., 4:207 B. napus L., 4:207 B. rapa L., 4:207 breeding diseases and pest resistance, 4:314 meal quality, 4:314 oil content, 1:239, 1:240t, 4:313 oil quality, 4:313 protein content, 1:239, 1:240t, 4:313–314 seed yield, 4:313 in Canada, 1:237 area harvested, 1:402, 1:402t disposition and consumption, 1:404, 1:404t production, 1:403, 1:403t chemical desiccant, 4:63 combining checkout and adjustment, 4:64–65 swathing vs. straight combining, 4:64–65, 4:64t conditioning, 4:66 crop development and growth environmental factors, 4:208–210, 4:208–209f water-use efficiency, 4:208–209f, 4:212 yield components, oil yield, 4:210–212, 4:210–211f crop management crop establishment, 4:213 harvesting, 4:214 height and plant growth regulators, 4:214 nutrition, 4:213–214 plant population and arrangement, 4:212–213 sowing time, 4:209f, 4:211f, 4:213 water supply, 4:214 definition, 4:207 in farming systems

biofumigation and benefits, 4:215 weed management, 4:214 fatty acid composition, 1:239, 1:240t food uses and health effects, 1:240 germplasm, 4:311–312, 4:312f glucosinolate content, 1:239, 1:240t GM grains, 4:350–351 grain quality specifications, international trade, 4:83, 4:86t growing conditions, 1:239 handling and transport systems, 4:65 harvesting methods, 4:62 HEAR varieties, 1:238 low-glucosinolate LEA rapeseed, 1:237–238 meal, 3:501–502 in Mexico area harvested, 1:402, 1:403t disposition and consumption, 1:404, 1:405t production, 1:403, 1:404t in North America area harvested, 1:402–403, 1:403t disposition and consumption, 1:405, 1:405t production, 1:403–404, 1:404t pod sealants, 4:63–64 prepress–solvent extraction technique cold pressing, 3:499 flowchart for, 3:497–498, 3:498f oil removal, 3:498–499 seed preparation, 3:498 use of enzymes, 3:499 processing and uses, 1:239–240 secondary processing, 3:499f bleaching, 3:500 degumming, 3:499–500 deodorizing, 3:501 formulation, 3:501 hydrogenation, 3:500 interesterification, 3:500–501 refining loss, 3:501 refining process, 3:500 standards, 3:501 winterizing/dewaxing, 3:501 storage (see Storage) swathing, 4:62–63, 4:63t tissue culture techniques, 4:312–313 trade, 1:239, 1:239t in United States area harvested, 1:402, 1:402t disposition and consumption, 1:404, 1:405t production, 1:403, 1:404t world production of, 1:238–239, 1:238f, 1:239t, 1:350t, 1:357 Capillary electrophoresis (CE), 3:289–290, 3:290f, 4:35 Carbohydrates alpha-galactoside, 2:167 buckwheat, 1:308, 1:308t cellulose, 2:169–170 cell wall polysaccharide arabinoxylans, 2:170 b-glucans, 2:170

497

cross-linking glycans, 2:170 seed germination, 2:172 cereal grains composition, 2:164, 2:165t definition, 2:161–164 disaccharide, 2:161–164 dry beans, 1:303–304 fructans, 2:162f, 2:168, 2:171 gibberellins, 2:170–171 glycemic load, 2:243–244 legumes composition, 2:164, 2:166t lupins, 4:329, 4:329t metabolism, 2:164–165, 2:167f monosaccharides, 2:161–164, 2:162f oligosaccharides, 2:161–164, 2:162f pearl millet, 1:192 polysaccharides, 2:161–164, 2:162f quinoa, 1:344t, 1:345 RFO, 2:171 rye, 3:260 seeds chemical composition, 2:164, 2:164t soybeans, 2:17 starch, 2:165–166t a(1,6) glucan linkages, 2:171 amylopectin, 2:168 backbone of, 2:169 biosynthesis of, 2:168–169 degradation, 2:171 linear-chain amylose, 2:168 sucrose acidic invertases, 2:172 invertases catalyze, 2:172 SPP and SPS, 2:165 SucS, 2:165, 2:172 symplastically/apoplastically, 2:165–167 sugar alcohols, 2:162f, 2:168 Carbon-13 nuclear magnetic resonance (13C-NMR), 3:287–289, 3:288f Cardiovascular disease (CVD), 2:11, 2:236 GFD, 2:95 GI/GL, 2:246 soy proteins, 3:485 Carlsberg Brewers, 1:452 Carthamus tinctorius L. See Safflower Caryophyllaceae, 1:277, 2:167 Caryopsis, 1:34–35, 1:41, 3:1 maize, 1:99 wheat, 3:384, 3:385–386f CBF. See C-repeat binding factor (CBF) CCN. See Cereal cyst nematode (CCN) Celiac disease (CD) celiac patients, dietary requirements for, 4:460 celiac societies, 1:462–463 definition, 2:83 dermatitis herpetiformis, 2:85 diagnosis of, 2:86 environmental factors, 2:84 food intolerances, 2:83 gluten ataxia, 2:85 gluten-free diet, 1:8–11, 1:11f, 2:9, 2:91–92, 2:92–93f additives, 4:462–464 flour recommendations, 4:465

498

Index

Celiac disease (CD) (Continued) foods and ingredients, avoidance list, 4:460–462 gluten-free baking, 4:465 gluten-free shopping, 4:466 gluten-free symbol, 4:460, 4:461f home bread makers, 4:465 intestinal damage, 4:460 mixes for baking, 4:464–465 sources, 4:460, 4:461–462t for travelers, 4:466 historical review, 2:83 HLA-DQ genes, 2:84 NCGS, 2:85 occurrence of, 2:84 pathogenesis, 2:84–85, 2:85f prevalence, 2:84 small intestinal lesion of, 2:84 symptoms, 2:83–84 therapy, 2:86 toxicity cereals, 2:87–88 in vivo and in vitro methods, 2:86–87 peptides, 2:88–89, 2:88–89t WDEIA, 2:85 wheat consumption, 2:24 Celiac societies, 1:462–463 CEN. See Committee for Standardization (CEN) Central Agricultural Cooperative of Technology Development and Economics (COODETEC), 1:448 Central and West Asia and North Africa (CWANA) region, 4:322 Central Food Technological Research Institute (CFTRI), 1:447 Cereal Chemistry, 1:459 Cereal cyst nematode (CCN), 1:178, 1:180f Cereal Foods World, 1:459 Cereal grains, 1:83, 1:85f AACCI methods, 4:450, 4:452t allergy (see Allergy) animal feed (see Animal feed) in Asia, 1:377–378f, 1:378–379 auricles, 1:51–54, 1:53f authentic information, 1:6 botanical names, 1:74, 1:78t bran, 3:2 bread, 1:7–8 Calabar bean, 1:11, 1:12f caryopsis, 3:1 C3/C4 photosynthetic systems, 1:74 celiac disease (see Celiac disease (CD)) climatic/soil conditions, 1:51 composition, 1:82–83, 1:83t cultural differences, in consumption dietary fiber, 2:36–37 energy requirements, 2:35 micronutrients, 2:37 protein, 2:35–36 resistant starch, 2:36 starch, 2:36 toxic compounds, 2:37 domestication (see Domestication) drying, 4:68

economic importance, 1:74 endosperm, 3:2 in Europe (see Europe) fats, 1:7–8, 1:10f food composition, 4:433 food source, 1:2–3, 1:3f germs, 3:2 GMO, 1:5 grain defects (see Grain defects) grain production, 1:2 growth and harvest, 4:68 growth habit, 1:51, 1:52f growth points, location of, 4:168, 4:169f health, 1:5–6, 1:83, 1:83–84f historical perspective, 1:75 hull, 3:2 husk, 3:2 ICC, 4:450, 4:451t in India (see India) industrial uses, 1:3–4 inflorescence structure, 1:55, 1:55f dispersal, 1:88–89, 1:88f fertilization, 1:88 florets, 1:86, 1:87f grain development, 1:88 panicle, raceme, spike, 1:87 pollination, 1:87–88 spikelets, 1:87 male and female reproductive organs, 1:55 media, 1:5–6 monocotyledons, 1:51 mythconceptions, 1:6, 1:6–7f natural disease control (see Natural disease control) nonstarchy polysaccharides (see Nonstarch polysaccharides (NSP)) nutrition chemical elements, 1:6, 1:8–9f dietary imbalances, 1:11 guidelines, 1:6–7, 1:9–10f organic growing, 1:4–5 panicles, 1:55 protein analysis of, 2:103, 2:103t, 2:104f barley grain, 2:102f, 2:105–106 composition, 2:101–102, 2:101–103f description, 2:100 early concepts, 2:99 first purified protein, 2:99–100, 2:99–100f maize, 2:105f, 2:106 polypeptides, 2:100, 2:101f prehistory, 2:98–99 quality, 2:103, 2:104f, 2:104t rice grain, 2:105f, 2:106 sorghum, 2:105f, 2:107 storage protein classes, 2:103–104, 2:105f wheat, rye, and triticale, 2:104, 2:105f proteomics analysis biological pathways, 2:152 computational and structural, 2:152 expression, 2:151

functional, 2:151 gel-based methods, 2:147–148, 2:147–148f genotype, 2:146, 2:147f growth condition, 2:146, 2:147f LC-MS and LC-MS/MS methods, 2:148–149 posttranslational proteomics, 2:151–152 protein gel spots, 2:148f, 2:149–150, 2:149t proteome mining, 2:150–151 sample preparation, 2:146–147 Western blotting, 2:152 quality definition, 3:257 definition of, 3:251 feed uses, 3:260–261 grain lots, characteristics of, 3:251–252 intrinsic level, 3:251–252 traits, external factors, 3:251–252, 3:252t research trends, 1:96 starvation, 1:2–3 storage, 4:68–69 tiller formation, 1:51, 1:52f uses, 1:74, 1:78f, 1:78t weight loss, 1:7–8 world exports, 1:349, 1:352f world imports, 1:349, 1:353f world production of, 1:3–4, 1:3f, 1:75–77, 1:79t, 1:79f, 1:349, 1:350t, 1:351f Cereals Canada, 4:12 Cereal yellow dwarf (CYD), 4:80 Cerogen™, 3:294 CGC. See Canadian Grain Commission (CGC) CGIAR. See Consultative Group on International Agricultural Research (CGIAR) Chapatis, 2:140, 3:19–20 Charles Sturt University, 1:445 Cheese crackers, 3:44, 3:46f Chemicals Regulation Directorate (CRD), 4:99 Chewy/soft-eating cookies, 3:38–39, 3:38t Chicha, 3:99, 3:100t Chickpea, 1:31, 1:34, 1:38 adaptation, 4:216 area, production and yield of, 1:316–317, 1:318t, 1:318f in Australia, 1:319 carbohydrate composition, 2:164, 2:165t in Central and Southern America, 1:319 consumption, 1:317 desi seeds, 1:316, 1:317f disease and pest management, 4:219–220 ascochyta blight, 1:320 botrytis gray mold, 1:320 fusarium wilt, 1:320 insect pests, 1:321 nematodes, 1:321 root/collar rot, 1:320 virus disease, 1:320–321 weed, 1:321 domestication, 1:316 in East Africa, 1:319

Index genetics, 1:322 global area distribution, 4:216, 4:217f harvesting, 4:220–221 in India, 1:317–318, 4:216, 4:217f inoculation and nitrogen, 4:218 kabuli seeds, 1:316, 1:317f leaf type, 1:316, 1:317f marketing, 4:221 in North Africa, 1:318 in North America, 1:319 nutrient requirements, 4:218 nutritional status, 1:321 origin, 1:316 pea seeds, 1:316, 1:317f production constraints cold, 1:319–320 drought and heat, 1:319 hostile soils, 1:320 rotational benefits, 4:216, 4:217f soil type and land preparation, 4:216–217 in southern Europe, 1:318 sowing and harvest, time of, 4:216–217, 4:218t, 4:218f sowing rate, depth, and method, 4:217, 4:219t, 4:219f storage, 4:221 trade, 1:317 uses and processing, 1:321–322, 1:322t water use, 4:220 weed management, 4:219 in west Asia, 1:318 world production, 4:216 Chiffon cakes, 3:367 Chile, 1:424 China. See also Asia agriculture, effects on, 1:379–380 amaranth, field production of, 1:287, 1:288f CAAS, 1:446 grain imports and exports, 1:376–378, 1:378t, 1:380–381, 1:381f grain production and yield, 1:376, 1:376–377f, 1:377t grain supply in, 1:379 harvested area, 1:376, 1:376f, 1:377t land area of, 1:375–376, 1:375f NARS, 1:446 per capita GDP and meat consumption in, 1:380, 1:380f population, 1:374–376, 1:375f sorghum production in, 1:154 Chinese Academy of Agricultural Sciences (CAAS), 1:446 Chinese Academy of Sciences, 1:446 Chinese Cereals and Oils Association (CCOA), 1:457–458, 1:460–461 Chinese medicine, 1:184–185, 1:187 Chinese rice wine production classification of, 3:209, 3:209t distilled liquors, 3:212–214, 3:212t ingredients and chemical composition, 3:209, 3:210t jiuqu (see Jiuqu production) types of, 3:212, 3:212f water and acidified rice steeping liquid, 3:212

Chinese Spring Wheat, 4:382–383, 4:383t Chinese steamed bread, 1:75, 1:78f Chinese System of Units, 2:308, 2:310t, 2:311 Chloranthaceae, 1:277 Chocolate-chip cookies, 3:44, 3:45f Choline, 2:270t, 2:279 Chorleywood bread, 3:9–11, 3:11f Ciabatta, 3:16, 3:16f CIAE-Millet mill, 1:206, 1:206f Cicer arietinum L. See Chickpea CIMMYT. See International Maize and Wheat Improvement Center (CIMMYT) Cistaceae, 1:277 Clades, 1:35 Claviceps C. africana, 1:156 C. fusiformis, 2:292, 2:292f C. purpurea, 2:290, 2:291t Clean Air Act, 3:235 Clearfield® lentil, 4:228 Climate change, 1:2, 1:4, 1:4f adaptation to, 4:141 agriculture, impact on, 4:141 CSIRO model, 4:140–141 evolutionary plant breeding, 4:141–142 evolutionary populations, 4:142 food insecurity, 4:141 FTNS, 4:141 GDP, decrease in, 4:141 gender inequalities, 4:141 global warming, 4:140 GM crops, 4:141 greenhouse gas emissions, 4:141 modern plant breeding, 4:141 NCAR model, 4:140–141 production, agroecological modes of, 4:141 productivity decline, 4:141 sorghum, 1:158 wheat-producing regions, 4:14–15 Club wheat, 1:19, 4:177 ‘Cluster’ hamburger buns, 3:14–15, 3:15f CMS. See Cytoplasmic male sterility (CMS) Coconut oil, 2:264, 2:265t Codex Alimentarius Commission (CAC), 2:2, 2:301, 4:155–156, 4:347 Codex Committee on Food Additives and Contaminants (CCFAC), 4:97 Coextruded snacks, 3:416f, 3:421–422, 3:422t Coffee cakes, 3:30, 3:32 Coix biochemistry, 1:185–186 botany cytology, 1:185, 1:185f female-fertile spikelets, 1:184 female-sterile spikelets, 1:184 habit, 1:184 inflorescence of, 1:184, 1:185f seed, 1:184, 1:185f vegetative organization, 1:184

499

cultivation, 1:187–188 fodder, 1:187 food, 1:186–187, 1:186–187t genetic resources, 1:187 medicine, 1:185f, 1:187, 1:188f molecular biology, 1:186 utilization, 1:186 Coixenolide, 1:187, 1:188f Coix lacryma-jobi L. See Coix Cold-water-swelling starch, 3:285 Coleoptera, 4:110 Collar rot, 1:320 Colombia, 1:424–425 Commelinaceae, 1:277 Commercial sector, grains research baking industry associations, 1:451–452 brewing companies, 1:452 grains processing companies, 1:451 private sector, in Asia and Africa, 1:452 seed and grain biotechnology companies, 1:452, 1:453t Committee for Standardization (CEN), 2:300 Commodity Credit Corporation, 4:12 Common Agricultural Policy (CAP), 4:14 Commonwealth of Independent States (CIS), 4:46–47 Commonwealth Scientific and Industrial Research Organisation (CSIRO), 1:444, 4:140–141 Community-based participatory research (CBPR), 2:68–70 Compatible solutes, 4:396 Composite cross (CC) method, 4:141 Concanavalin-A, 2:199 Condensed tannins, 2:286 Confectionery sunflower, 1:252 Conferences, 1:457, 1:458f Congee, 3:447 Conjugated linoleic acid (CLA), 2:261 Consultative Group on International Agricultural Research (CGIAR) APAARI, 1:432 biodiversity conservation, 1:434 CIAT, 1:430–431, 1:431t, 1:433 CIMMYT (see International Maize and Wheat Improvement Center (CIMMYT)) establishment of, 1:430 founding objective, 1:430 germplasm development, 1:431 green revolution, 1:430 ICARDA, 1:431, 1:431t, 1:433 ICRISAT, 1:431, 1:431t, 1:434 IITA, 1:431, 1:431t IRRI, 1:430–431, 1:431t, 1:433 ISNAR, 1:432–433 NARES, collaboration with, 1:432–433 research investment, 1:430 research programs, 1:431–432 Consumer Perceptions of Food Technology, 2:51

500

Index

Consumption trends barley, 2:33 consumer consumption, trends in, 2:33 ERS, 2:30 gluten-free, 2:32 glycemic index (GI), 2:31–32 international consumer trends, 2:29–30 maize, 2:32–33 oats, 2:32–33 rice, 2:32 tracking systems, 2:30 wheat and grain avoidance trends, 2:32 wheat consumption, 2:30–31, 2:31f whole grains, 2:31 Contact insecticides, 4:108, 4:128–130 Contaminants. See Grain contaminants Controlled atmospheres (CAs), 4:128 airtight/hermetic storage systems, 4:134–135 high-carbon dioxide CA, 4:135 low-oxygen CA, 4:135 Cookies, 3:41–42 baking, 3:62 bar press, 3:61–62, 3:62f as casual snack food, 3:47 chewy/soft-eating cookies, 3:38–39, 3:38t chocolate-chip cookies, 3:44, 3:45f content of, 3:4 cooling, 3:62 cream sandwich cookies, 3:39, 3:39f, 3:44–47, 3:46f, 3:49 cutting machine cookies, 3:4 deposit cookies, 3:4 double-baking technique, 3:44 dough mixing continuous mixers, 3:60 horizontal mixers, 3:59–60 vertical spindle mixers, 3:59 end-product tests, 3:252 epic journeys, usage in, 3:47 fat and sugar, 3:37, 3:38t Fig Newton, 3:38, 3:38t flours, 3:40 hard-dough semisweet biscuits, 3:4 history of, 3:44 ingredients, 3:44 ‘Melting Moments,’ shortbread, 3:44–47, 3:46f mixing processes, 3:42 oatmeal, 3:44, 3:45f refrigerated dough form, 3:362 formula for, 3:362, 3:362t mix, 3:362 packaging, 3:362 rotary molding, 3:4, 3:37, 3:61, 3:61f rout press, 3:38, 3:38t, 3:61–62, 3:62f sheeting and cutting, 3:60–61, 3:61f short doughs, 3:4, 3:49 soft and hard wheats, 3:255, 3:255f soft doughs, 3:49 wire-cut cookies, 3:4, 3:37, 3:61–62, 3:62f Cooperative Research Centres (CRCs), 1:445 Corn chips, 3:106f, 3:107–108, 3:108f, 3:416–417, 3:417f

Corn dollies, 1:6, 1:6f Cornell method, 3:134 Corn ethanol production dry-grind process, 3:238–240, 3:239f quick germ process, 3:240, 3:240f wet-milling process, 3:238–239 Cornflakes, 3:105, 3:105f Corn oil, 2:264 expelling and extraction, 3:455 fatty acid composition of, 3:456, 3:456t germ, 3:454, 3:454f quality factors for, 3:456, 3:456t uses of, 3:456 wet and dry milling, 3:454 winterization process, 3:455 Corn puffs, 3:105f, 3:106 Cornstarch, 3:274, 3:418, 4:71 Corn syrups, 3:103, 3:104f glucose syrups, 3:103, 3:104f HFCSs, 3:102–105 low-DE/maltodextrin-rich syrups, 3:103 maltose syrups, 3:103, 3:104f Coronary heart disease (CHD) barley, 2:33 soy protein, 2:19–20, 2:20f wildrice, 1:136 Cottonseed, 1:20–21, 2:258t, 2:263 Australia production in, 1:417–418 yields, 1:413–415, 1:416t, 1:417–418 deodorizer distillates, composition of, 3:494, 3:494t fatty acid components, 1:223t glanded and glandless boll-type cotton, 1:243 cross-section of, 1:242–243, 1:243f feed uses, 1:243, 1:245–246 food uses of, 1:244–245, 1:245f “Hopi Moencopi” variety, 1:242 natural insecticide, 1:243 processing and products, 1:243–244, 1:244t GM grains, 4:350–351, 4:357 gossypol, 1:223, 1:242, 1:243f oil and protein content, 1:222–223, 1:222t oleic acid, linoleic acid, 1:223 uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226, 1:247, 1:248t Council for Scientific and Industrial Research (CSIR), 1:447 Couscous, 1:195, 1:195–196f, 2:38, 3:6 Cracker ovens, 3:328–329 Crackers, 3:39, 3:39f. See also Cookies as casual snack food, 3:47 characteristics of, 3:3–4 with cheese and savory dips, 3:44, 3:45f, 3:48 cheese crackers, 3:44, 3:46f circular cracker, 3:44, 3:46f cream crackers, 3:39, 3:40t, 3:44, 3:46f, 3:48 cutting, 3:40 epic journeys, usage in, 3:47 fats, 3:40–41

fermentation, 3:3–4 flours, 3:40 hard doughs, 3:47 lamination, 3:40 mixing processes, 3:42 products, 3:3–4 rectangular cracker, 3:44, 3:46f saltines, 3:48 savory crackers, 3:39, 3:48 soda crackers, 3:39, 3:40t, 3:48 sponge–dough system, 3:3–4 Cream cracker, 3:39, 3:40t Cream crackers, 3:44, 3:46f, 3:48 Cream sandwich cookies, 3:39, 3:39f, 3:44–47, 3:46f, 3:49 C-repeat binding factor (CBF), 4:396 Crops and Livestock Research Centre, 1:439 Crop Science Society of America, 1:458, 1:461 Cross-linked starch, 3:282–283 Crown rot (CR), 1:122, 4:79 Cucumber mosaic virus (CMV), 4:237 Curtin University, 1:445 Customary US units, 2:308 Cuzco maize, 3:98, 3:99t CWANA region. See Central and West Asia and North Africa (CWANA) region CWB. See Canadian Wheat Board (CWB) Cyclic recurrent selection, 4:299–300, 4:299f Cyperaceae, 1:278 Cysteine thiols HMW-GS, 2:155 IAF-labeled 2-D electrophoretic patterns hard wheat flour, 2:157–158, 2:159f landscape plots, 2:157, 2:159f low-MW thiols, 2:155 protein–protein interactions, 2:154–155 protein structural probe, 2:156–157, 2:156–157f SDS-PAGE tracings, 2:157 wheat gliadins and glutelins, 2:155, 2:156f Cytoplasmic male sterility (CMS), 1:247, 4:307, 4:417, 4:418f

D Danish pastries, 3:30, 3:32 Daqu, 3:210–212, 3:211f DArT. See Diversity arrays technology (DArT) Data inspection, 4:147 DBE. See Starch-debranching enzymes (DBE) Decision support system (DSS), 4:123, 4:137 Deck ovens, 3:373 Dee-geo-woo-gen (DGWG), 4:304–305 Degermination, maize Beall-type degerminator, 3:458, 3:461, 3:461f compression, 3:463 moistened maize, 3:458, 3:459f multiple impact/shear, 3:462–463, 3:462f pin mills, 3:461, 3:462f roller mill, 3:463 static sifter, 3:459, 3:459f

Index tails, 3:459 thrus fraction, 3:459–460, 3:459f Dehydroferulic acid dimers, 2:274 Demeter (Greek goddess), 1:86, 1:105, 1:107f Deoxynivalenol (DON), 3:161, 4:257 Derivatized starch, 3:283–286 Dermatitis herpetiformis, 2:85 Descriptive sensory analysis line-scale ballot, 3:147, 3:148f noodles, 3:155 rice, eating quality of, 3:166–168, 3:167t screening, 3:145–146 training, 3:146–147, 3:147t Destructured starch, 3:279 Detmolder one-phase method, 3:28 DFs. See Dietary fibers (DFs) DH. See Doubled haploids (DHs) Diaporthe toxica, 2:296, 2:296f Diaspore, 1:88–89, 1:88f Diastatic power, 1:194–195 Diatomaceous earth (DE), 4:135–136 Dietary fibers (DFs) carbohydrate polymers, 2:11 classification of, 2:12 definitions, 2:11–12 edible carbohydrate polymers, 2:11 flatbreads, 3:23 GBF, 2:58 health benefits, 2:11–12, 2:14–15 NSP, 2:225 RS (see Resistant starch (RS)) starch noodles, 3:70 synthetic carbohydrate polymers, 2:11 Dietary Guidelines for Americans, 2:69 2010 Dietary Guidelines for Americans Committee, 2:64 Differential scanning calorimetry (DSC), 3:403–405 rice, 3:110–111 starch amylose, 2:199 amylose-lipid complex, 2:201–202, 2:202t gelatinization, 2:201–202, 2:201t retrogradation, 2:204, 2:205t Differential thermal analysis (DTA), 3:405 ‘Digestive’ biscuit, 3:44, 3:45f Digitaria exilis. See White fonio Dihydropicolinate synthase (DHDPS), 1:186, 2:126 Direct resistance ovens, 3:333 Discrimination sensory analysis duo–trio test, 3:150, 3:152f noodles, 3:154 paired comparison test, 3:150 triangle test, 3:150, 3:151f Diseases abiotic diseases, 4:74–75 bacterial diseases, 4:171–172, 4:172t biotic diseases (see Biotic diseases) black point, 4:71, 4:74–75 bunt/stinking smut, 4:71 CD (see Celiac disease (CD)) chemical control, 4:80–81, 4:174–175 chickpea (see Chickpea)

durum wheat, 1:122 ergots, 4:71 food safety, effect on, 4:169 fungi (see Fungal diseases) Fusarium sp., 4:71 genetic resistance, 4:174 grain quality, effect on, 4:168 grain yield, effect on, 4:168 husbandry, 4:174 of inflorescence, spike, and seed, 4:80 kernel smudge, 4:74–75 lentil, 4:228–229, 4:228t linseed, 1:263 loose smut, 4:71 lupin anthracnose, 4:237 brown leaf spot, 4:236–237 leaf rust, 4:237 pea, 1:328, 1:328f, 4:246, 4:247t, 4:248f peanuts, 1:336–337 plant breeding, 4:81 plant quarantine issues, 4:80 plant vulnerabilities, 4:169–170 quinoa, 1:343 in sorghum grains, 1:156, 4:202–203 soybean, 4:255–256 sunflower, 1:250 suppressive soil, 4:260 viral diseases, 4:172–173, 4:172t wheat, 2:26, 4:75, 4:76t in Australia, 4:273, 4:274t leaf blotch pathogens, 4:273, 4:274t SNB (see Septoria nodorum blotch (SNB)) STB (see Septoria tritici blotch (STB)) TS (see Tan spot (TS)) Distilled beverages alcohol consumption, 3:203 blending and bottling, 3:203 continuous stills, 3:201 copper pot stills, 3:200–201 distillation processes, 3:194, 3:194t environmental strategy, 3:203–204 ethanol, 3:194–195 historical background, 3:195 malting process aleurone, 3:196, 3:196f barley, 3:195–196, 3:196f ethanol and flavor compounds, 3:196, 3:197f ethyl carbamate, 3:197 nitrosamines, 3:197 mashing process American whiskeys, 3:198 brandies, 3:198–199 Canadian whiskeys, 3:198 fermentation, 3:199, 3:199f gelatinization temperatures, 3:197 gin/vodka, 3:198 Irish whiskey, 3:198 rum, 3:198 scotch whisky, 3:197–198 tequila and mescal, 3:198–199 traditional cachaç1;a, 3:198 maturation, 3:201–202, 3:202f raw materials, 3:194, 3:194t

501

Distillers’ dried grains with solubles (DDGS), 3:238–240 Distillers’ wet grains (DWG), 3:240 Diversity arrays technology (DArT), 4:38, 4:38–39f Divide milling, 3:314, 3:316f Dockage, 4:50, 4:117–118 Docosahexaenoic acid (DHA), 1:260–261, 2:8–9, 2:9f Dodecylbenzene sulfonate (DOBS), 3:111 Domestication barley, 1:90, 1:90t, 1:147 chickpea, 1:316 crop and weed races, 1:89–90 dry beans, 1:297 legumes, 1:266t, 1:267, 1:297 maize, 1:90–91, 1:90t oats, 1:91–93 pearl millet, 1:90t, 1:91, 1:91f, 1:92t rice, 1:93 rye, 1:93 sorghum, 1:93–94, 1:94f syndrome, 1:89 wheat, 1:94–95, 1:95f white fonio, 1:95, 1:96f wild grasses, 1:96 DON. See Deoxynivalenol (DON) Dosai, 3:446 Doubled haploids (DHs), 1:119, 1:182–183, 1:330 barley breeding strategies, 4:290 waxy maize, 4:426–427 Double fertilization, 1:99 Dough Inflation System, 3:348–349, 3:348f, 3:351f Doughnuts, 1:112–113, 1:114f, 3:3–4 Downy mildew canola/rapeseed, 4:314 pea, 4:247t quinoa, 1:343 sorghum, 1:156, 4:205 sunflower, 1:250 Dry beans, 1:297 allergenic proteins, 1:302–303, 1:302t as animal feed, 1:305 antinutritional factors, 1:304 beneficial bioactive compounds, 1:304 Bolivia, production in, 1:422 carbohydrates, 1:303–304 chemical and nutritional composition, 1:300–304, 1:300t domestication of, 1:297 in Ecuador, 1:425 global production of, 1:297, 1:299t grading, handling, and storage, 1:304–305 import/export data, 1:297, 1:299t lipids, 1:304 pods/seeds, morphology of, 1:298–300, 1:299f processing and food uses, 1:305 proteins amylase inhibitors, 1:302 arcelin, 1:301–302 lectins, 1:301 phaseolin, 1:301

502

Index

Dry beans (Continued) storage and metabolic proteins, 1:301 trypsin inhibitors, 1:302 vitamins and minerals, 1:304 Dry gluten, 3:410 Dry milling corn oil, 3:454 maize, 1:101, 1:101f, 3:258–259 degermination (see Degermination, maize) dry grind process, 3:458 flow diagram, 3:458, 3:459f future trends, 3:465 products and uses, 3:463–464, 3:463t quality and kernel characteristics, 3:464–465 tempering, 3:460 whole kernel/full-fat, 3:458 wheat blending, 3:309 bran finishers, 3:312, 3:313f bran peeling/debranning equipment, 3:311 by-products, 3:316 cleaning, 3:309–310, 3:309f, 3:310t composition, 3:308–309 conditioning, 3:309–311, 3:309f debranning/preprocessing, 3:311 divide/split-run milling, 3:314, 3:316f durum wheat semolina mill flow, 3:315, 3:317f equipment configuration, 3:312–313, 3:313f flour additives, 3:314–315, 3:317t hard common wheat flour, 3:313–315, 3:314f, 3:315t hourglass stone mills, 3:308f intake, 3:309, 3:309f mechanization, 3:307 monitoring and control, 3:318 optical sorter, 3:311 plansifters, 3:307, 3:312, 3:312f purifiers, 3:307, 3:312, 3:313f raw material, selection of, 3:307 roller milling, 3:307, 3:311–312, 3:311f saddle stones, 3:307, 3:308f scourers, 3:311 soft wheat, 3:315 storage, 3:309 structure, 3:307–308, 3:308f whole grain products, 3:317–318 Dry pea. See Pea Dry pet foods biscuit technology, 3:224 extrusion cooking, 3:268 benefits of, 3:223–225 coating and drying, 3:226 extruded dog food, 3:224, 3:225f, 3:225t extrusion cookers, 3:224–226 preconditioning, 3:225 production rates, 3:225 protein-rich materials, 3:271 raw materials, 3:225, 3:225t structural material, 3:271

fish and small mammals, 3:223 UK market, 3:223, 3:224t DSC. See Differential scanning calorimetry (DSC) Dumplings kenkey, 1:363 LAB fermentation, 3:186t, 3:188–189, 3:189f millet grains and flour, 1:207 Duo–trio test, 3:150, 3:152f Durable disease resistance genes, 4:391–392 Durum wheat, 4:177, 4:279 adaptation of, 1:117–119 agronomy of, 1:122–123 breeding crosses, 1:119 for disease resistance, 1:122 doubled haploids, 1:119 molecular markers, 1:119 public institutions, 1:119 pure-line breeding approach, 1:119 quality testing, 1:119 for quality traits, 1:120–122 seedling resistance evaluation, 1:119 semidwarf durum germplasm, 1:119 for tolerance to abiotic stresses, 1:120 for yield and agronomic traits, 1:119–120 bulgur, 3:6 couscous, 3:6 defective grains in, 4:88–89, 4:90f disease of, 1:122 domestication of, 1:117 in European Union, 1:385, 1:386t field plots of, 1:117, 1:118f food products, 1:117, 1:118f functional food properties, 1:123 genomes, 4:376 gluten (see Gluten) vs. hexaploid flour, 3:6 milling, 3:307, 3:315, 3:317f morphology, 1:57t, 1:60, 1:62–63f dry milling of, 1:45 wet milling, 1:45 origin, 1:117 pasta (see Pasta) plants, 1:117, 1:118f starch (see Starch) uses of, 3:1, 3:2t, 3:258t world production, 1:117, 1:118f yields, 1:118–119

E Earcockle, 4:88, 4:89t Eastern Cereal and Oilseed Research Centre, 1:439 Echinochloa utilis. See Barnyard millet Eco-city, 4:149–150 Ecomycins, 4:259 Economic Research Service (ERS), 1:437, 2:30 Ecuador, 1:425 E-FRF. See Enriched fiber-rich fractions (E-FRF)

EFSA. See European Food Safety Authority (EFSA) Egg noodles, 3:5 Eicosapentaenoic acid (EPA), 1:260–261, 2:8–9, 2:9f Einkorn wheat, 2:24, 2:38 ELEM. See Equine leukoencephalomalacia (ELEM) Eleusine coracana. See Finger millet ELISA. See Enzyme-linked immunosorbent assay (ELISA) Embden–Meyerhof–Parnas (EMP) pathway, 3:240–241, 3:241f Emmer, 1:117, 2:38 End-product tests, 3:252 Energy Independence and Security Act (EISA), 3:235 Energy Policy Act, 3:235 Energy value of grains, livestock digestible energy content animal types, 3:217–218, 3:218f Australian research, 3:217, 3:217t cereal starch, 3:220 diets, 3:216 endosperm cell walls, 3:220 feed conversion efficiency, 3:216 gut fermentation, 3:217–218 microbial fermentation, 3:216 NIR calibrations, 3:221 starch/neutral detergent fiber content, 3:219, 3:220t digestible energy intake animal performance, 3:216 animal types, 3:219, 3:219t Australian study, 3:219 broiler chicken, 3:220–221 ileal brake, 3:221 microbial fermentation, 3:216 NIR calibrations, 3:221 physical and chemical characteristics, 3:220–221 starch/neutral detergent fiber content, 3:219, 3:220t wheat grain cultivars, 3:218–219, 3:219t Enriched fiber-rich fractions (E-FRF), 3:440–445, 3:441–443f, 3:442t Entner–Doudoroff (ED) pathway, 3:240–241, 3:241f Enzyme-linked immunosorbent assay (ELISA), 4:35–36, 4:353–354, 4:354f Enzymes Asian noodles (see Asian noodles) cell wall polysaccharides biosynthesis, 2:138–139 germinated grain, 2:139–140 cereal endosperm, cell walls in, 2:138, 2:139t endogenous inhibitors, 2:143–144 esterification, 2:143 flavonoids, 2:141–142 ripe wheat grains a-amylase, 2:140, 2:141f endoproteases, 2:140–141 xanthophylls, 2:141–142 EPB. See Evolutionary plant breeding (EPB)

Index Equilibrium relative humidity (ERH), 4:106–107, 4:106f Equine leukoencephalomalacia (ELEM), 2:294 Eragrostis tef (Zucc.) Trotter. See Teff Ergot alkaloids, 2:290–292, 2:291t, 2:292f Ergots, 1:162–163, 4:71, 4:90, 4:91f Ethanol production in Asia, 3:237, 3:238t distillation/rectification method, 3:238f, 3:242–243, 3:243f in Europe, 3:237, 3:237t fermentation, 3:238f EMP and ED pathways, 3:240–241, 3:241f stoichiometry and maximum ethanol yield, 3:241–242, 3:242t yeasts and bacteria, engineering of, 3:242 first-generation technologies, 3:235 global ethanol production, 3:235, 3:236f in North America, 3:235–236, 3:236f, 3:236t second-generation ethanol, 3:235 sorghum, 1:158 in South America, 3:236–237, 3:237t sugar release, feedstocks, 3:238f corn ethanol production (see Corn ethanol production) gasohol, 3:237–238 lignocellulosic biomass, 3:238 microbial fermentation, 3:237–238 starch-rich biomass, 3:238 sugar-rich biomass, 3:238 Europe biodiesel, 3:249 cereals climate, 1:384–385 consumption and utilization, 1:387–389, 1:388–389t cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384–385, 1:385t maize (see Maize, in Europe) market, 1:384 production, 1:383–384, 1:384t, 1:386t rye (see Rye) wheat (see Wheat) fuel ethanol production, 3:237, 3:237t grain research in, 1:440–442 pulses and oilseeds consumption and food supply quantity, 1:389, 1:389t production of, 1:386–387, 1:387–388t European Food Safety Authority (EFSA), 2:232–233 European Research Program, 2:231 Evolutionary plant breeding (EPB), 4:141–142 Expressed sequence tags (ESTs), 1:147–148 Extensigraph, 3:253 Extruded snacks barley, 3:419 corn, 3:418 ingredients used for, 3:418

multidimensional snack, 3:417–418f, 3:421 oats, 3:419 potatoes, 3:420 rice, 3:419 tapioca, 3:420 wheat, 3:419 Extrusion cooking animal feedstuffs, 3:271 barley, 3:445 biopolymers, transformation of, 3:270–271 degradative and condensation reactions, 3:271 dies, 3:268 dry pet foods (see Dry pet foods) features, 3:268 forces, overall balance of, 3:269 human foods, 3:268–269 baby food, 3:272 breadings and coatings, 3:272 breakfast cereals, 3:271–272 sausage meats and pasta, 3:268 snack foods, 3:271 industrial products, 3:268–269 Maillard reactions, 3:271 physical effects, 3:271 single screws, 3:269 twin screw extrusion cooker design of, 3:269–270, 3:269f raw materials, development of, 3:268, 3:269f wet pet foods, 3:226, 3:268

F Facultative wheat, 4:176, 4:180 Fagopyrum esculentum. See Buckwheat Fa-Kuo, 3:114 Falling number test, 2:302, 3:253–254 FAMEs. See Fatty acid methyl esters (FAMEs) Famines, 1:429–430 Farina, 3:265 Farinograph, 3:253, 3:344, 3:344t Farinograph units (FUs), 2:313–314 Farro, 1:31, 1:35t, 2:38 Fatty acid methyl esters (FAMEs), 2:253–254 Fatty acids corn, 1:100 healthy fats and oils CLA, 2:261 lauric acid and myristic acid, 2:261 linoleic acid, 2:261 linoleic acidþoleic acids, 2:261 linoleic acidþsaturated fatty acids, 2:261 medium-chain fatty acids, 2:261 oleic acid, 2:261 omega-3 fatty acids, 2:262 palmitic acid, 2:261 stearic acid, 2:261 TFAs, 2:261–262 and triacylglycerols compositions, 2:259–260 minor millets, 1:202–203

503

peanuts, 1:223–224 pearl millet grain, 1:192–193 rice, 1:128 soybean seed, 1:223, 1:223t teff, 1:215, 1:217t FDEIA. See Food-dependent exercise-induced anaphylaxis (FDEIA) Federal Grain Inspection Service (FGIS), 4:6, 4:23, 4:27–28, 4:27t Feed barley. See Barley Fenugreek galactomannan, 2:228 Fermentation cereal foods/beverages, LAB fermentation of (see Lactic acid bacteria (LAB) fermentation) definition, 3:183 ethanol production, 3:238f EMP and ED pathways, 3:240–241, 3:241f stoichiometry and maximum ethanol yield, 3:241–242, 3:242t yeasts and bacteria, engineering of, 3:242 evolution of, 3:176–178 grain storage hypothesis, 3:177 history of, 3:177–178 leavened breads, 3:3 liquid fermentations/suspension cultures, 3:181 Orleans vinegar process, 3:181 “Quick” vinegar process, 3:178, 3:181 raw materials chemical properties, 3:178 fruits, 3:179 leafy material, 3:179 physical properties, 3:178 roots, bulbs, and tubers, 3:179–180 seeds, 3:180–181 soybean products (see Soybeans) stirred tank reactor fermentations, 3:181 traditional fermentation processes, 3:181 Fertilizers calcium, 4:101 magnesium, 4:101 nitrogen, 4:100 phosphorus, 4:100 potassium, 4:100–101 sulfur, 4:100 trace elements, 4:101 FGIS. See Federal Grain Inspection Service (FGIS) Fiber-rich fractions (FRF), 3:440–445, 3:441–443f, 3:442t Field Crop Development Centre, 1:439 Field-flow fractionation (FFF), 1:29 Field fungi, 4:128 Field pea. See Pea ‘Field to fork’ sequence, 1:22 Filament-stretching extensional rheometer (FISER), 3:348 Finger millet, 1:19–20, 1:199, 1:200f, 1:200t, 1:360t, 1:361, 1:361f FISH. See Fluorescence in situ hybridization (FISH) Fixed theorem, 4:145

504

Index

Flaked brown rice, 3:446 Flatbreads Arabic bread, 3:16f, 3:17, 3:17t characteristics of, 3:3 ciabatta, 3:16, 3:16f combined treatments, 3:22 consumption, 3:19 corn tortilla, 3:16, 3:16f, 3:16t definition, 3:19 dietary fiber, 3:23 end-product tests, 3:252 features of, 3:19 focaccia, 3:16, 3:16f freezing, 3:22 MAP, 3:22 minerals, 3:23 nutrition of, 3:23 pizza, 3:16 preservatives, 3:22 production methods of barbari bread, 3:20 chapatis, 3:16–17, 3:19–20 lavash, 3:20 saaj, 3:20 tanoor/tandoor bread, 3:16, 3:20 two-layered flatbreads, 3:20–21 product quality criteria, 3:21 protein content of, 3:23 spoilage, 3:21–22 staling, 3:22 traditional flatbreads, 3:19 two-layered flatbreads, 3:20–21 types of, 3:3, 3:340 vacuum packaging, 3:22 vitamins, 3:23 wheat flour tortillas, 3:16, 3:16f, 3:16t Flax Council of Canada, 1:224 Flaxseed. See Linseed Flow injection analysis (FIA), 3:293 Fluorescence in situ hybridization (FISH), 4:370 Fluorescence microscopy, 2:271f, 3:387f, 3:389 Fluorescence sensors, 4:166 Fluorophore-assisted capillary electrophoresis (FACE), 3:289–290 Foam cakes, 3:367 Focaccia, 3:16, 3:16f Folates, 1:338t, 2:44, 2:279 Fonio in Africa, 1:360t, 1:361, 1:364f black fonio, 1:19–20, 1:92t, 1:199 white fonio, 1:19–20, 1:92t, 1:95, 1:96f, 1:199, 1:205f world production of, 1:356 Food addiction, 2:25 Food Barley, 4:18, 4:293. See also Malting barley Food-dependent exercise-induced anaphylaxis (FDEIA), 2:73 Food fortification cereal fortification bakery products, 2:45 biofortification, 2:45 breakfast cereals, 2:46 GAIN’s National Fortification Program, 2:47

National Fortification Alliances, 2:47 pasta, 2:46 rice (see Rice) wheat flour (see Wheat) criteria for, 2:43–44 definition of, 2:43 enrichment, 2:43 nutritional equivalence, 2:43 reasons for, 2:43 vitamins and minerals cereal-based products, 2:44, 2:44t chemical compound, 2:46, 2:46–47t Food pyramid, 1:6–7, 1:9f Foods for Specified Health Use (FOSHU), 2:1–2 Forage barley, 4:293 Foreign seeds, 4:83 for bread wheat, 4:89t definition, 4:83 other crop seeds, 4:91 steeping, 3:425 testing, 4:351 weed seeds, 4:91–92, 4:92f Forward genetics, 4:400–401 Fourier transform infrared (FTIR) spectroscopy, 3:405 Foxtail millet, 1:91f, 1:199, 1:200f carbohydrate composition of, 2:165t chemical composition of, 2:164t comparative genome mapping, 4:401 family groupings and botanical names, 1:17t food usage, 1:200t, 1:206–207 genome sequencing, 4:373 nutrient profile of, 1:202t origin and occurrence of, 1:200t starch–lipid interactions, 1:203 structural comparison of, 1:201t Free-threshing cereals, 1:89, 1:93 French bread, 3:13–14, 3:13t, 3:14f French Guyana, 1:425 FRF. See Fiber-rich fractions (FRF) Fried rice, 3:447 Frozen dough formula and process example, 3:356, 3:356t freezing and storage strategies, 3:356–357 gluten, 3:355–356 history of, 3:354 preferment step, 3:356 principle challenges for, 3:354 strengtheners and oxidizers, 3:355, 3:356t thawing and proofing strategies, 3:357 yeast (see Yeast) Frozen noodles, 3:75, 3:77–78 Fuel alcohol production. See Ethanol production Fumigation, 4:102, 4:114 biofumigation, 4:102 CA fumigations (see Controlled atmospheres (CAs)) gaseous fumigants devices and equipment, development of, 4:131

methyl bromide, 4:130 methyl iodide, 4:131–132 phosphine (see Phosphine fumigation) safety procedures, 4:131 sulfuryl fluoride, 4:131–132 Fumonisins, 2:294, 2:294f Functional foods, 2:1 barley, 1:149, 1:149f bioaccessibility, 2:3 bioactivity, 2:3 bioavailability, 2:3 carotenoids, 2:7–8, 2:8f definition of, 2:2 dietary fibers (see Dietary fibers (DFs)) dietary supplements, 2:2 durum wheat, 1:123 gluten-free foods, 2:9 for lactose intolerance, 2:14 market size, 2:2 novel foods, 2:3 nutraceuticals, 2:2 omega-3 fatty acids, 2:8–9, 2:9f phenolics, 2:3, 2:4–5f phytoestrogens 17b-estradiol, structures of, 2:3, 2:5f coumestans, 2:6, 2:6f isoflavones, 2:6, 2:6f lignans, 2:3–6, 2:5f stilbenes, 2:6, 2:6f phytosterols, 2:6–7, 2:7f prebiotics, 2:14 probiotics, 2:13–14, 2:13t whole grains, 2:12–13 Functional proteomics, 2:151 Fundamental theorem of natural selection (FTNS), 4:141 Fungal diseases Ascomycotina, 4:170 asexual stage, 4:170 Basidiomycotina, 4:170 brown rust, in wheat, 4:171 cereal diseases, 4:170, 4:171t control, 4:171 Deuteromycotina, 4:170 dispersal, 4:171 injury mechanism, 4:171 parasitic, 4:170 penetration, 4:171 propagation, 4:171 quinoa, 1:343 saprophytic, 4:170 sexual stage, 4:170–171 Fungal endoxylanases, 2:144 Fungicides, 4:99–100 Fusaricidins, 4:259 Fusarium head blight (FHB), 1:122 Fusarium sp., 4:71 F. graminearum, 2:295 F. moniliforme, 4:257 F. sporotrichioides, 2:295 F. verticillioides, 2:294, 2:294f Fusarium wilt chickpea, 1:320, 4:219 field pea, 4:242, 4:247t linseed, 1:263

Index

G GAFTA. See Grain and Feed Trade Association (GAFTA) GALLILEO, 4:163 Gallon, 2:309–311 g-oryzanols, 2:279 Gammalinolenic acid (GLA), 1:255 Gamma rays (GR), 4:134, 4:165 Garibaldi fruit sandwich biscuits, 3:44–49, 3:47f Gas–liquid chromatography with flameionization detection (GLC-FID), 3:287–289 Gas–liquid chromatography with mass spectrometry (GLC-MS), 3:287–289 Gasohol, 3:237–238 Gastrointestinal tract (GIT), 2:13, 3:220–221 GAXs. See Glucuronoarabinoxylans (GAXs) GBF. See Grain-based food (GBF) GBS. See Genotyping by sequencing (GBS) GBSS. See Granule-bound starch synthase (GBSS) GBSSI. See Granule-bound starch synthase 1 (GBSSI) GDD method. See Growing degree day (GDD) method Gelatinization temperature (GT), 2:201–202, 2:202t, 3:168–169 amaranth, 1:275, 1:290 beans, 1:303–304 buckwheat, 1:311 native starches, 3:276t pearl millet, 1:192 quinoa, 1:345 rice, 1:128–129, 2:305 sorghum, 1:158, 3:117 SSIIa alleles and, 3:173f teff, 1:212 waxy coix starches, 1:186 Gel-based proteomics, 2:147–148, 2:147f Gel consistency test, 3:169, 4:306 GEM. See Germplasm enhancement of maize (GEM) GEMS-0067 high-amylose maize starch, 4:427, 4:427t Gene-for-gene (GFG) hypothesis, 4:274–275 General soil suppression, 4:260 General Standard for Contaminants and Toxins in Food and Feed, 4:97 Genetically engineered (GE) maize, 1:103, 1:103f Genetically modified (GM) grains in Africa, 1:365, 2:53 ambivalence/fear, 2:51 in Australia, 2:52 beacon of hope technology, 2:54 in Brazil, 1:423–424, 2:52 in Canada, 2:51 in China, 2:52–53 climate change, impact of, 4:141 development of agricultural biotechnology, 4:347, 4:348f biotech crops, 4:347

codon usage, 4:344, 4:345t customer’s needs and problems, 4:343 discovery phase, 4:344, 4:344f elements of transformation vectors, 4:344, 4:345f elite event, 4:347 plant transformation methods, 4:344, 4:346f ‘stacked’ products, 4:347, 4:348f toxic/antinutritive, 4:347 in Europe, 2:52 in Filipinos, 2:53 identity preservation of, 4:31 in India, 2:53 in Japan, 2:52 labels, 2:58 in Latin America, 2:54 linseed, 1:263–264 maize, 1:103, 1:392 in Malaysia, 2:52–53 in New Zealand, 2:52 perception and acceptance of, 2:54 recombinant DNA methods, 2:50 risk-benefit perception, 2:51 in Russia, 2:52 soybeans, 3:142 testing approaches antibodies, 4:353–354 DNA-based tests, 4:352 ELISA, 4:353–354, 4:354f grain, 4:351 isothermal DNA amplification, 4:358 labeling, 4:350 LFS, 4:353–354, 4:354–355f, 4:358 maize, 4:350 PCR technique, 4:354–357, 4:356b proficiency testing, 4:356–357 qualitative testing, 4:352–353 quantitative testing, 4:353 reporting, 4:357–358 RT-qPCR, 4:358 sample, 4:351–352 screening, 4:353 threshold testing, 4:353 transferability, 4:356 validation, 4:356 in United States, 2:51–52 Genetically modified organisms (GMOs), 1:5, 4:141, 4:261 consumer resistance, 1:5 cross pollination, 1:5 definition, 1:5 wheat breeding, 4:285 Genome Analysis Centre, 1:440 Genome mapping aneuploid mapping, 4:370 chromosome deletion mapping, 4:370–371 comparative mapping, 4:373–374 fiber-FISH technique, 4:370 genetic linkage mapping, 4:368–369, 4:368f genetic maps, 4:365 HAPPY mapping, 4:371 ISH technique, 4:370

505

large-insert clone contigs, 4:372–373 physical mapping, 4:365, 4:369, 4:373, 4:374f polymorphism AFLPs, 4:365–366 microsatellite markers/SSRs, 4:366 NGS technology, 4:366–368 RAPD markers, 4:365 RFLP marker technique, 4:365 SNPs, 4:366–368, 4:367f STSs, 4:366 RH mapping, 4:371–372, 4:372f single-copy gene FISH, 4:370 Genomic assisted selection (GAS), 1:149 Genomics aleurone cell layers, 4:363 association genetics, 4:362 barley, 4:361 conventional cereal chemistry methods, 4:364 definition, 4:360 DNA sequence analysis, 4:360 functional genomics, 4:361 genome variation analysis, 4:361 grain food applications chloroplast, 4:360, 4:361t mitochondria, 4:360, 4:361t nuclear genome, 4:360, 4:361t grain identification and purity analysis, 4:362 impact of, 4:360 legumes, 4:361 maize, 4:361 metabolomics, 4:362 NGS, 4:360 nutrigenomics, 4:362 oilseeds, 4:361 ‘omics,’, 4:360, 4:361t proteomics, 4:362 rice, 4:361 cooking temperature, 4:363 fragrance, 4:362–363, 4:363f sorghum, 4:361 transcriptomics, 4:362 wheat, 4:361 Genotyping by sequencing (GBS), 4:291, 4:366–368 Geographic information system (GIS), 4:163 Geo Positioning System, 4:43 German Federation of Private Plant Breeders, 1:441 Germplasm collections Glycine G. max, 4:333, 4:335t G. soja, 4:336t new trait discovery, 4:282 oats, 1:183 quinoa, 1:342 sorghum, 4:203 soybean, 1:229, 4:340–341 Germplasm enhancement of maize (GEM), 4:297, 4:427 Germ rice, 2:80 GFD. See Gluten-free diet (GFD)

506

Index

GFG hypothesis. See Gene-for-gene (GFG) hypothesis Gibberella zeae, 2:295 Gin, 3:198 Glass slide method, 3:154 Global Alliance for Improved Nutrition (GAIN), 2:47 Global Crop Diversity Trust (GCDT), 1:434 Global Navigation Satellite System (GNSS), 4:163–164 Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS), 4:163 Global Positioning System (GPS), 4:163 Globoids, 2:271f, 2:283 Globulins 7S globulins characteristics, 2:115, 2:116t endomembrane system, 2:115–116, 2:117t glycosylation, 2:109 polypeptide molecular masses, 2:109–110, 2:110t protein contents and types, 2:110t structures of, 2:110–111, 2:110–111f trimeric proteins, 2:109 trivial names, 2:115, 2:116t vacuoles, 2:118 vicilins, 2:109 11S globulins acidic chains, 2:109–110 basic chains, 2:109–110 characteristics, 2:115, 2:116t endomembrane system, 2:115–116, 2:117t polypeptide molecular masses, 2:109–110, 2:110t protein contents and types, 2:110t structures of, 2:110–111, 2:110f trivial names, 2:115, 2:116t vacuoles, 2:118 Glucagel, 3:294 Glucan trimming mechanism, 2:186 Glucomannans, 2:209t, 2:210f, 2:219 Glucono delta-lactone (GDL), 3:360, 3:360t Glucuronoarabinoxylans (GAXs), 2:170, 2:214 Glutamate oxidase, glutamine amino tranferase (GOGAT), 2:133–135 Glutamine synthetase (GS), 2:126, 2:133–135, 4:395 Gluten, 3:2, 3:6 Alfa-Laval/Raisio process, 3:409–410 amino acid composition of, 3:408, 3:409t baked goods, 3:411 batter process, 3:409 Beccari’s experiment, 3:408–409 commercial process, 3:408–409, 3:409f definition of, 3:408, 4:460 dry gluten, 3:410 frozen dough, 3:355–356 lipid content, 3:408 Martin process, 3:409 and modified gluten in calf-milk replacements, 3:411 chemical modification, 3:412, 3:412f enzymic modification, 3:412

nonfood uses, 3:411 properties of, 3:410 protein content, 3:408 starch and fiber content, 3:408 thiols (see Cysteine thiols) uses of, 3:410–411, 3:411t waste products, 3:410 wheat starch industry, by-product of, 3:409 wheat wet milling, 3:320 food and industrial uses, 3:323–324 gravity of, 3:320 modification, 3:323 nonvital wheat gluten, 3:322 particle sizes, 3:320 protein, 3:322 strength and elasticity, 3:323 vital wheat gluten, 3:322 whole grain, raw material, 3:410 Gluten ataxia, 2:85 Gluten-free breads, 3:17 Gluten-free diet (GFD) celiac disease, 2:91–92, 2:93f for celiac patients (see Celiac disease (CD)) Crohn’s disease, 2:92–93 dietary trends, 2:93–94 functional foods, 2:9 IBS, 2:92–93 NCGS, 2:93 rheumatoid arthritis (RA), 2:93 ulcerative colitis, 2:92–93 wheat, 2:94 Gluten-free products, 2:95 Gluten-free refrigerated dough, 3:365 GlutoPeak, 3:253 Glycemic index (GI) blood glucose response curve, 2:241 carbohydrate foods, 2:241 derivation of, 2:241 food processing effect, 2:245–246, 2:245t food types, 2:241, 2:242t health outcomes epidemiological studies, 2:246 randomized controlled trials, 2:246 rice, 1:128 wheat consumption, 2:26 Glycemic load (GL) carbohydrates, 2:243–244 definition, 2:241–242 derivation and methodology, 2:242–243, 2:242t, 2:243f food processing effect, 2:245–246, 2:245t vs. glycemic response, 2:244–245, 2:244f, 2:245t health outcomes, 2:246 epidemiological studies, 2:246 randomized controlled trials, 2:246 Glycemic response (GR), 2:31–32, 2:36 vs. glycemic load, 2:244–245, 2:244f, 2:245t oat bran muffin, 2:238 Glycogenin, 2:187 GM grains. See Genetically modified (GM) grains GMOs. See Genetically modified organisms (GMOs)

GOGAT. See Glutamate oxidase, glutamine amino tranferase (GOGAT) Goldfisch method, 1:222 Good manufacturing practices (GMPs), 3:360 Gossypol, 1:242, 1:243f Graham cracker, 3:44, 3:46f Grain and Feed Trade Association (GAFTA), 2:301 Grain-based food (GBF), 2:298 AACCI methods, 4:450, 4:452t composition, 4:433 fortification of (see Food fortification) functional foods (see Functional foods) ICC, 4:450, 4:451t labels designations, 2:58 enriched and refined grains, 2:59 fortification of grains, 2:59 GM grains, 2:58 health claims, 2:60, 2:61t ‘high in x’, 2:58 ingredient statement, 2:57 natural/fresh, 2:57–58 nutrient-content claims, 2:60 organic labeling, 2:58, 2:58t structure-function claims, 2:60 WG (see whole grains (WG)) PPPs (see Public and private partnerships (PPPs)) sensory evaluation (see Sensory evaluation) sodium content in (see Salt, in grain-based foods) Grain borer, 4:57–58, 4:58f Grain composition appendix environmental factors, 2:298 flour milling process, 2:298 food-component combination, 2:298 genetic factors, 2:298 heat treatments, 2:298 Grain contaminants, 4:97–98 agricultural chemicals, 4:95 animals and animal products, 4:95, 4:95f Australian wheat industry, 4:88t contaminating materials, analysis of laboratory methods, 4:97 near-infrared (NIR) analysis, 4:97 sampling, 4:96, 4:96f sieving, 4:96, 4:96f visual inspection, 4:96–97 defective grains, 4:83 in durum wheat samples, 4:88–89, 4:90f immature cereal grains, 4:88 infected grains, 4:89–91 sprouted grains, 4:88, 4:90f sun-cracked rice grains, 4:88 definitions, 4:85 farm management, 4:97 foreign seeds (see Foreign seeds) genetically modified grain, 4:96 historic perspective, 4:83 inanimate materials, 4:95 insect species, 4:94–96, 4:94f international grain standards, 4:83, 4:88t

Index international regulations on, 4:97 nongrain materials, 4:92–93, 4:93f plant material, 4:93, 4:93f quality assurance methods, 4:97 seed sown, purity of, 4:97 tainting contaminants, 4:95 visual guidelines for 2014/2015, 4:83, 4:88t Grain crops barley (see Barley) botanical names, 1:16, 1:17t common English names, 1:16, 1:17t definition, 1:16 legumes (see Legumes) maize (see Maize) millets (see Millets) morphological variation, 1:16 oats (see Oats) oilseed crops (see Oilseeds) plant classification, 1:16–19, 1:17t pseudocereals (see Pseudocereals) rice (see Rice) rye (see Rye) sorghum (see Sorghum) taxonomy (see Taxonomy) teff (see Teff) wheat (see Wheat) Grain defects crop processing, 4:72 diseases, 4:71 environmental causes drought, 4:71 frost damage, 4:72 genetic and environment interaction, 4:72 green grains, 4:72 sprouting (pregermination), 4:72 weed competition, 4:72 field insect larvae, 4:72 grain analysis enzyme activity, 4:71 moisture, 4:70–71 protein, 4:71 specific weight, 4:70 starch, 4:71 prevention of, 4:72 sampling, 4:69, 4:69–70f storage insect larvae, 4:72 visual assessment discoloration, 4:70 sample appearance, 4:69 sample purity, 4:69–70 Grain enrichment method, 2:45 GrainGrowers, 1:445 Grain Inspection, Packers & Stockyards Administration (GIPSA), 4:6 Grain protectants, 4:102–103, 4:128 Grains for Health Foundation, 1:462 Grains Industry Association of Western Australia (GIWA), 4:21 Grains processing companies, 1:451 Grains Research & Development Corporation, 1:445 Grains research organizations in Australia, 1:444–445

in Canada, 1:439 in Central America, 1:448–449 in Europe, 1:440–442 grain crop yields, improvements in, 1:452–453 institutional trends, 1:455–456 in Mexico, 1:440 in Middle East, 1:449–450 in New Zealand, 1:445 in North Asia, 1:445–446 planning and collaboration, 1:453–454 research subject matter, changes in, 1:454–455 in South Africa, 1:449–450 in South America, 1:448–449 in South Asia, 1:446–447 in Southeast Asia, 1:447–448 in USDA centers, 1:436–439, 1:438t Grain-supply sequence biochemical concept, 1:28–29, 1:28f breeder, 1:22–24, 1:24f circle format, 1:22, 1:23f consumer, 1:23f, 1:27–28 delivery, 1:25, 1:25f ‘field to fork’, 1:22 food manufacturer bean types, 1:26–27, 1:27f bread rolls, 1:26–27, 1:27f feed pellets, 1:26–27, 1:28f sprouted beans, 1:26–27, 1:27f sushi, 1:26–27, 1:27f grower, 1:25 harvest, 1:25, 1:25f marketing stage, 1:22, 1:23f paddock to plate, 1:22 retail, 1:27 sow, 1:24–25, 1:24f storage, 1:25, 1:26f transport, 1:26, 1:26f Grain Trade Australia (GTA), 4:3, 4:21, 4:85 Grano, 2:38 Granola cereals, 3:264 Granule-bound starch synthase (GBSS), 2:178, 2:185 Granule-bound starch synthase 1 (GBSSI), 2:169 Grasses, 1:17t, 1:19 common/bread wheat, 1:19 Job’s tears, 1:19 maize, 1:19 millets, 1:19–20 oats, 1:19 rice, 1:20 sorghum, 1:19 teff, 1:19–20 Greenhouse and Processing Crops Research Centre, 1:439 Green peas, 1:284, 1:324 Green revolution, 1:2, 1:349, 1:379 Groundnut. See Peanuts Ground truthing, 4:166 Growing degree day (GDD) method, 4:196 GTA. See Grain Trade Australia (GTA) Gua-ba, 3:447 Guar gum, 2:227

507

Guinea millet, 1:199 Gun-puffing cake, 3:111–112 Guo-Ba, 3:113 Guthrie Medal, 1:461, 1:461f Guyana, 1:425 Guy’s classification system, 3:225t

H Haber–Bosh process, 2:131 Hagberg falling number (HFN) method, 4:71 Halo, 1:178 HAM. See High-amylose modifier (HAM) Hard doughs, 3:47–49 Hard vitreous kernels (HVK), 1:120, 1:120f Harvesting barley, 4:50 canola, 4:62, 4:214 chickpea, 4:220–221 field pea, 4:247–248 lentil, 4:229 lupin, 4:237–238, 4:238f sorghum, 4:54–55, 4:55f, 4:201 wheat combine harvester, 4:43, 4:43f mechanization, 4:43 precision agriculture, 4:43 reaping, 4:43 swathing, 4:43 threshing, 4:43 winnowing, 4:43 Hatch Act of 1887, 1:437–438 HATS. See High affinity transport system (HATS) Haynaldia villosa, 4:271 Hazard Analysis and Critical Control Point (HACCP) systems, 3:266 HEALTHGRAIN Forum, 1:462 Healthy minor components fats daily dietary intake, 2:257 fatty acids (see Fatty acids, healthy fats and oils) hydrocarbons, 2:259 nonedible applications, 2:257 nutrition properties, 2:257 phospholipids, 2:257–258 polyphenols, 2:259 refining, 2:265 sterols, 2:258–259 tocopherols, 2:259 oils daily dietary intake, 2:257 fatty acids (see Fatty acids, healthy fats and oils) hydrocarbons, 2:259 nonedible applications, 2:257 nutrition properties, 2:257 phospholipids, 2:257–258 polyphenols, 2:259 refining, 2:265 sterols, 2:258–259 tocopherols, 2:259 vegetable (see Vegetable oils)

508

Index

HEAR. See High-erucic acid rapeseed (HEAR) Hearth breads, 3:3, 3:13–14, 3:13–14t, 3:14f Hearts Beat Back Project, 2:69 Heat-moisture treatment (HMT), 3:280, 3:285 Heat-stable antithiamins, 2:81 Helianthus annuus. See Sunflower Hemicelluloses, 1:162, 2:226 Herbicides, 4:101 lentil, 4:224, 4:228 lupin, weed control in, 4:236, 4:236t oats, 1:177 sunflower, 1:249 Heteroxylans analysis and detection, 2:219 gelation, 2:216f, 2:217–218 genetics, 2:219, 2:219t molecular parameters, 2:217 solid-state and solution conformations, 2:217 solution properties, 2:217 structure, 2:210f, 2:214–217, 2:215–216f, 2:215t structure–function relationships, 2:218–219 Hexaploid wheat, 4:279 Hexham scent, 4:92 High affinity transport system (HATS), 2:132–133 High-amylose maize, 4:427–428, 4:427t, 4:428f High-amylose modifier (HAM), 4:427 High-amylose starch (HAS), 1:100 High-erucic acid rapeseed (HEAR), 1:238, 4:311 High-fructose corn syrups (HFCSs), 3:102–105 High-molecular-weight glutenins (HMWGS), 2:24, 2:155 High-performance anion-exchange chromatography (HPAEC), 2:191, 2:193f High-performance anion-exchange chromatography with pulsed amperometric detection (HPAECPAD), 3:289, 3:289–290f High-performance liquid chromatography (HPLC), 2:253 High performance size exclusion chromatography (HPSEC), 2:191, 2:199 Hilum, 2:169, 2:190 Ho-Fen, 3:114 Home-Grown Cereals Authority (HGCA), 4:4 Hominy feed fraction, 3:459, 3:463 Hooded barley, 4:293 Hordeum H. spontaneum, 1:147, 1:148f H. vulgare (see Barley) Hormone replacement therapy (HRT), 2:21–22 Host-specific/hostselective toxins (HSTs), 4:275 Hot-bread shops, 3:340 Hot cereals (HC), 3:262 bulgur and corn grits, 3:265 cracked wheat, 3:265

farina, 3:265 instant oatmeal products, 3:264–265 per capita annual consumption, 3:262–263 rolled oats, 3:264–265 Hourglass stone mills, 3:307, 3:308f HPLC. See High-performance liquid chromatography (HPLC) HR. See Hypersensitive reaction (HR) HSTs. See Host-specific/hostselective toxins (HSTs) Hulled cereal, 1:89 Hungarian Academy of Sciences, 1:441 Hybrid ovens, 3:333 Hydrocolloid, 2:225, 2:228 Hydrogen phosphide, 4:108, 4:131 Hydrolyzable tannins, 2:286 Hyperparasitism, 4:260–261 Hypersensitive reaction (HR), 4:390–391

I IARCs. See International Agricultural Research Centers (IARCs) ICARDA. See International Center for Agricultural Research in the Dry Areas (ICARDA) ICBN. See International Code of Botanical Nomenclature (ICBN) ICC. See International Association for Cereal Chemistry (ICC) ICNCP. See International Code of Nomenclature for Cultivated Plants (ICNCP) ICRISAT. See International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Idli, 3:186t, 3:188, 3:188f, 3:446 Ileal brake, 3:221 Illinois method, 3:134 Immunoglobulin E (IgE)-mediated reaction. See Allergy Imperial system, 2:308–311, 2:309t Impingement ovens, 3:329–330 In-bin drying airflow rate, 4:119 continuous-flow drier, 4:120 dryeration, 4:120 drying yield, 4:119 evaporation capacity, 4:119 external moisture, evaporation of, 4:119 heat consumption, 4:119 heating capacity, 4:119 high-temperature drying, 4:119 inclined perforated floor, 4:120 internal moisture diffusion, 4:119 low-temperature/natural air drying, 4:119 objectives of, 4:119 sorption–desorption equilibrium curves, 4:118–119, 4:118f static dryers, 4:119–120 India. See also Asia All India Coordinated Research Projects, 1:447

area and water resources, 1:367 barley productions in, 1:367–368, 1:368f, 1:370–371, 1:370–371f chickpea area expansion in, 4:216, 4:217f coarse cereals, 1:367–368, 1:368f, 1:371 diversification, period of, 1:367 early green revolution period, 1:367 food consumption trends, 1:372–373 food grains, consumption of, 1:371–372 GM grains, 2:53 grain production and yield, 1:376, 1:376–377f, 1:377t green revolution, 1:379 harvested area, 1:376, 1:376f, 1:377t ICAR institutes, grain research in, 1:446–447 land area of, 1:375–376, 1:375f maize production in, 1:367–370, 1:368–370f population, 1:367, 1:371–372, 1:372f, 1:374–376, 1:375f postreform period, 1:367 pre-green revolution period, 1:367 pulses, 1:367–368, 1:368f, 1:371 rice production, 1:367–369, 1:368f SAUs, 1:447 sorghum production in, 1:154 technology dissemination, period of, 1:367 wheat production, 1:367–368, 1:368–369f Indian corn. See Maize Indian Council of Agricultural Research (ICAR), 1:446–447 Indian mustard, 4:207–208 Indonesian Agency for Agricultural Research and Development (IAARD), 1:447 Industrial Crops, Plant Nutrition, Plant Pathology and Food and Nutrition (IMRAN), 1:441 Infinite optical thickness (IOT), 3:155, 3:157 Injera, 1:157, 1:157f, 3:186–188, 3:186t, 3:188f, 3:191 baking process, 1:219, 1:219f making process fermentation, 1:217–219 flowchart, 1:217, 1:218f Insect growth regulators (IGRs), 4:128–129 Insect pest control CA fumigations (see Controlled atmospheres (CAs)) contact insecticides, 4:128–130 gaseous fumigants devices and equipment, development of, 4:131 methyl bromide, 4:130 methyl iodide, 4:131–132 phosphine (see Phosphine fumigation) safety procedures, 4:131 sulfuryl fluoride, 4:131–132 irradiation/ionization, 4:134 MW heating, 4:133–134 RF heating, 4:133, 4:134f temperature control cooling aeration, 4:132 heat disinfestation, 4:132–133 insect species, 4:132

Index In situ hybridization (ISH) technique, 4:370 Instant noodles, 3:5 Instant oatmeal, 3:264–265 Institute of Biological, Environmental and Rural Sciences, 1:440 In-store bakery, 3:340 Integrated pest management (IPM), 4:117, 4:123, 4:175 Integrated quality management (IQM), 4:136–137 Intergovernmental Panel on Climate Change (IPCC), 4:147 International agricultural research centers (IARCs), 1:430–431 International Association for Cereal Chemistry (ICC), 1:457–458 history of, 1:460 logo, 1:460, 1:461f mission statement, 1:460 objectives, 1:460 International Association for Cereal Science and Technology (ICC), 1:441–442, 4:450, 4:451t besatz, 2:304 grain diversity, 2:305 grain processing simulation, 2:304 logo, 2:301f moisture and oil content, NIR, 2:301 nitrogen gas methods, 2:301 sprout damage, 2:302 International Center for Agricultural Research in the Dry Areas (ICARDA), 1:431 crop improvement mandates, 1:431t lentil bulk-pedigree method, 4:317, 4:319–320 genetic base, 4:321–322 genetic resources, 4:318, 4:319t legume-cereal rotation, 4:322 methodology, 4:319–320 national agricultural research systems, 4:321, 4:322t wild and cultivated lentil germplasms, 4:317 wheat improvement research, 1:433 International Center for Tropical Agriculture (CIAT) crop improvement mandates, 1:431t rice, 1:430–431, 1:433 International Code of Botanical Nomenclature (ICBN), 1:33–36, 1:38 International Code of Nomenclature for Cultivated Plants (ICNCP), 1:33–34, 1:38 International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), 1:197, 1:431, 4:203 agribusiness, partnership with, 1:434 crop improvement mandates, 1:431t pearl millet varieties, 1:434 International Federation of Organic Agriculture Movements (IFOAM), 4:156 International Fertilizer Association, 2:136

International Institute of Tropical Agriculture (IITA), 1:431 crop improvement mandates, 1:431t maize improvement, 1:433–434 International Maize and Wheat Improvement Center (CIMMYT), 1:379, 1:430–431, 2:53, 4:389, 4:420–421, 4:423, 4:429 crop improvement mandates, 1:431t dwarf wheat, 1:2 maize improvement, 1:433 QPM, 1:433–434 wheat improvement, 1:433 International Organization for Standardization (ISO), 3:164 International Peanut Genome Initiative (IPGI), 1:339 International Pulse Trade and Industries Confederation (IPTIC), 1:330 International Rice Research Institute (IRRI), 1:126, 1:374–375, 1:431t crop improvement mandates, 1:431t dwarf rice, 1:2 rice improvement, 1:430–431, 1:433 International Seed Testing Association (ISTA), 1:458, 1:461, 2:301 International Service for National Agricultural Research (ISNAR), 1:432–433 International Service for the Acquisition of Agri-biotech Applications (ISAAA), 2:50 International System of Units, 2:308, 2:309t, 2:311 Invertebrate pests allergy, 4:112 biomass loss, 4:111 collateral problems of control, 4:112 contamination, 4:112 controlled atmospheres, 4:114–115 detection and identification of sampling and sieving, 4:110 trapping, 4:110–111 fumigation, 4:114 gaseous phosphine, 4:114 grain-protectant chemicals, 4:115 insect and mite control, 4:112–114 grain hygiene for, 4:113, 4:113t inspection, 4:113–114 work procedures and skill, 4:113, 4:113t lupin, 4:237, 4:238t metal phosphine, 4:114 methyl bromide, 4:114 pea, 4:246–247, 4:248t physical control, 4:115 poor storage, indicators of, 4:112 population rate, 4:111, 4:111t quality damage, 4:111–112 stored grain ecosystem, 4:110 Iodine binding capacity (IBC), 2:199, 2:199t 5-Iodoacetamidofluorescein (5-IAF) electrophoretic separation, 2:157 2-D electrophoresis pattern

509

hard wheat flour, 2:157, 2:159f landscape, 2:157, 2:159f soft wheat flour, 2:157, 2:158f IP6. See Phytic acid (IP6) IPCC. See Intergovernmental Panel on Climate Change (IPCC) IPM. See Integrated pest management (IPM) Irish famine, 1:429–430 Irish whiskey, 3:198 Irradiation, 4:134 IRRI. See International Rice Research Institute (IRRI) ISAAA. See International Service for the Acquisition of Agri-biotech Applications (ISAAA) ISH technique. See In situ hybridization (ISH) technique Isoamylase, 2:186 ISTA. See International Seed Testing Association (ISTA) Italian breads, 3:9 Italian millet. See Foxtail millet

J James Hutton Institute, 1:440 Japanese Food Agency (JFA), 4:23 Japanese rice. See Sake’ brewing Japanese-style white salted noodles, 3:72, 3:73t Jatz cracker, 3:44, 3:46f Jelly noodles, 3:67, 3:69f Jiuqu production daqu, 3:210–212, 3:211f definition, 3:210 manufacturing process of, 3:209, 3:211f raw materials rice and wheat, 3:210, 3:211t xiaoqu, 3:212 Job’s tears. See Coix John Innes Centre, 1:440

K Kamut, 2:38 Kanglaite®, 1:187 Kansas City Board of Trade, 4:12 Kansas State University, 1:14–15, 1:15t Kenkey, 3:186t, 3:188–189, 3:189f Kernel smudge, 4:74–75 Kernel Visual Distinguishability (KVD), 4:4 Khapra beetle, 4:94–95 Kieffer extensibility system, 3:348–349, 3:348f Kjeldahl nitrogen analysis, 1:222 Kjeldahl protein analytic method, 1:452 Kodo millet, 1:199, 1:200f, 1:200t Koji production, 3:207, 3:207t, 3:207f Krebs cycle, 1:7, 1:10f Kunitz trypsin inhibitor, 1:231, 3:91–92

510

Index

L LAB fermentation. See Lactic acid bacteria (LAB) fermentation Lab-on-a-chip capillary electrophoresis equipment for, 4:35, 4:35f glutenin subunits, 4:35, 4:37f simulated gel electrophoresis patterns barley varieties, 4:35, 4:36f wheatmeal samples, 4:35, 4:36f Lacombe Research Centre, 1:439 Lactic acid bacteria (LAB) fermentation cereal foods and nonalcoholic beverages back-slopping, 3:183–184 commercial oat vellie product, 3:191, 3:191f dumplings, 3:186t, 3:188–189, 3:189f food-borne pathogens, inhibition of, 3:184 food safety, 3:185 idli, 3:186t, 3:188, 3:188f mageu (see Mageu) moisture, 3:184 motoho oa mabela (see Motoho oa mabela) negative health effects, 3:185 nutrient content and composition, 3:184 nutritive value, 3:184, 3:185t ogi, 3:186t, 3:189–190, 3:190f pancakes, 3:185–188, 3:186t, 3:188f pearl millet flour, 3:185–186, 3:186t, 3:187f pH range, 3:184 redox potential, 3:184 spherical and rod-shaped bacteria, 3:184 spontaneous fermentation, 3:183–184, 3:185t temperature, 3:184 thick porridges, 3:186t, 3:189, 3:189f thin porridges, 3:186t, 3:189–190, 3:190f traditional fermentations, 3:184–185 viscosity reduction, 3:184 heterofermentative types, 3:183 homofermentative types, 3:183 LAB genera, 3:183–184 Lactobacillus genus, 3:183 Lager beer, 3:122 ‘Land grant’ college system, 1:437–438 Landrace, 1:38–39 Late-maturity a-amylase (LMA), 2:140 Lateral flow strips (LFSs), 4:353–354, 4:354–355f LATS. See Low affinity transport system (LATS) Lavash bread, 3:20, 3:22 LBG. See Locust bean galactomannan (LBG) LCOs. See Lipo-chitooligosaccharides (LCOs) Leaf rust, 1:177, 1:177f, 4:266, 4:267t, 4:271 Learned societies. See Scientific societies Leavened breads, 1:112–113, 1:416f, 3:3 Lectures, 1:457, 1:458f Legumes, 1:20 agronomy, 1:271–272 antinutritional factors, 1:270

botanical name, 1:266t carbohydrate composition, 2:164, 2:165t common and vernacular names, 1:266t consumption, 1:267–268, 1:267–268t, 1:272 domestication, center of, 1:266t, 1:267, 1:297 domestic production, 1:268t genomics, 4:361 as human food, 1:297, 1:298t protein and nutritional constituents, 1:265–266, 1:266t, 1:268–270, 1:268–269t starch noodles, 3:64, 3:66 Lentil breeding agroecology, 4:319, 4:320t biochemical and molecular techniques, 4:321 domestication, 4:317 genetic control, 4:320–321, 4:321t ICARDA (see International Center for Agricultural Research in the Dry Areas (ICARDA)) methodology, 4:319–320 origin, 4:317 phylogeny, 4:317–318 production, 4:318–319, 4:319t use of, 4:318 diseases, 4:228–229, 4:228t growth habit, 4:223 harvesting, 4:229 insect pests, 4:229 land adaptation, 4:223–224 land preparation, 4:224–225 macrosperma/Chilean lentil, 4:223 major growing countries, 4:223 microsperma/Persian lentil, 4:223 nutrient requirements, 4:226–227 plant height, 4:223 seed coat colour, 4:223 seeding date and location, 4:226, 4:226f seeding rates, 4:225–226, 4:225–226f weed management (see Weed management) world production, 4:223 Lepidoptera, 4:110 Lethbridge Research Centre, 1:439 Levain, 3:25 LFSs. See Lateral flow strips (LFSs) Light macrophotography, 3:389 Light microscopy (LM), 3:388–389 Lime-cooked maize products, 3:107f corn and tortilla chips, 3:92, 3:94, 3:106f, 3:107–108, 3:108f dry masa flours, 3:106f, 3:107 nixtamalization, 3:95–96 nutritional value, 3:95t, 3:96 table tortillas, 3:92–94, 3:93f, 3:106f, 3:107 Linola™, 1:259–260 Linseed, 1:406, 2:226 agronomy, 1:261 as animal feed, 1:259, 1:261 in Canada

area harvested, 1:402t, 1:406 disposition and consumption, 1:404t, 1:407 production, 1:403t, 1:407 CDC Triffid, 1:263–264 cyanogenic glucosides, 1:261 dietary fiber, 1:260 diseases, 1:263 end use versatility of, 1:259, 1:260f fatty acid components, 1:223t, 1:259–260, 1:260f genetics, 1:261–264, 1:262f health benefits, 1:260–261 as human food, 1:259 linatine, 1:261 Linola™, 1:259–260 meal, 1:259, 1:260f Mexico, area harvested in, 1:403t, 1:406 mucilage content, 1:224, 1:260 in North America area harvested, 1:403t, 1:407 production, 1:404t, 1:407 oil content, 1:222, 1:222t, 1:224, 1:259 omega-3-enriched products, 1:261 protein content, 1:222, 1:222t, 1:224, 1:259–260 solin, 1:224, 1:259–260 in United States area harvested, 1:402t, 1:406 disposition and consumption, 1:405t, 1:407 production, 1:404t, 1:407 uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226, 1:259 yield, 1:263 Lipid bakery products, 2:254–255 cereal grains, 2:249–250, 2:250–251t, 2:250f classification, 2:248–249, 2:249f, 2:249t gas chromatography, 2:253–254, 2:254f HPLC, 2:253 nutritional values, 2:255 oilseeds, 2:250–251, 2:251–252t SFE, 2:252 solvent extraction, 2:252 thin-layer chromatography, 2:252–253, 2:253f Lipo-chitooligosaccharides (LCOs), 2:132 Lipoxygenases (LOX), 1:121, 2:142 Liquid cyclone process, 1:242 Little millet, 1:199, 1:200f, 1:201t dietary fiber content of, 1:203 nutrient profile of, 1:202t origin and occurrence of, 1:200t LMA. See Late-maturity a-amylase (LMA) Locust bean galactomannan (LBG), 2:227–228 Locust bean gum, 2:227 Long-chain branching (LCB), 3:347 Loose smut, 4:71, 4:75 LoSatSoy, 3:495 Low affinity transport system (LATS), 2:132–133

Index Low-density lipoprotein cholesterol (LDLC), 2:7 Low density polyethylene (LDPE), 3:347, 3:349f Low-erucic-acid (LEA) rapeseed, 1:237–238 Low-molecular-weight glutenins (LMW-GS), 2:155 Low-sodium refrigerated dough, 3:365, 3:365t LOX. See Lipoxygenases (LOX) Lupins. See Lupins Lupinosis, 4:326–327 Lupins, 1:20, 4:236t adaptation, 4:232 alkaloids, 4:330 amino acid profile for, 1:281, 1:281t antinutritional factors, 1:282–283, 1:282t Australian and European farming systems, 4:231–232 bioactive compounds, 4:330 carbohydrates, 4:329, 4:329t chemical composition of, 1:280, 1:281t cost of production, 4:232 definition, 1:280 diseases (see Diseases) fat, 4:327t, 4:328–329, 4:329t flavonoids, 4:331 food uses, 4:331 allergenicity, 1:285 bean/sprout, 1:284 fermented foods, 1:284 flour additive, 1:284–285 kernel fiber, 1:285 protein fractions, 1:285 traditional uses, 1:284 vegetable milk products, 1:285 gene resources, 4:325–326 grain price, 4:232 grain processing dehulling, 1:283 extrusion, 1:284 fractionation, 1:283–284 milling, 1:283 harvesting, 4:237–238, 4:238f invertebrate pests, 4:237, 4:238t mutations, 4:326 nonruminant feeds finfish and crustaceans, 1:286 pigs, 1:285–286 poultry, 1:286 nonstarch polysaccharide components, 1:281, 1:281t nutritive value, 4:327, 4:327t origin of, 1:280, 4:325, 4:326t phosphorus, 4:234, 4:235f phytates, 4:330 plant density, 4:233 plants, 4:325 potassium, 4:234–235 potential of, 4:331 production of, 4:326 proteins, 1:280, 4:327–328, 4:328t quinolizidine alkaloids, 1:283, 1:283f, 1:283t

row spacing and seed depth, 4:233–234, 4:234–235f ruminant feeds, 1:285 saponins, 4:330–331 sowing time, 4:232–233 stress and diseases resistance, 4:326–327 sulfur, 4:234–235 tannins, 4:331 trace elements, 4:235 vitamins and minerals, 1:281–282, 1:282t, 4:329–330 weed management, 4:235–236

M Mageu, 3:186t commercial traditional-type, 3:190, 3:190f industrial process, 3:190, 3:190f modern developments of, 3:191, 3:191f pregelatinized maize meal, 3:191 Magic number (MN), 3:363 Magnaporthe oryzae, 4:259 Magnesium, 4:101 Maize Africa, production in, 1:359, 1:360t allergy, 2:74 amylopectin (see Amylopectin) animal feed, 3:260 Australia, production in, 1:410t, 1:415–416t, 1:417 bioethanol production, 4:425 biotechnology, 1:102–103 Bolivia, production in, 1:422 in Brazil, 1:423 breeding adaptation, 4:297 commercial hybrid maize seed, 4:298f, 4:302 germplasm, 4:297 GMO, 4:300–301 mode of propagation, 4:296–297 pedigree breeding, 4:296–299, 4:298f, 4:299t population improvement, 4:296, 4:299–300, 4:299–300f, 4:301t types of, 4:296 yields in, 4:296, 4:297f Canadian whiskey, 3:198 canopy light interception, 4:199, 4:200f in Chile, 1:424 CIMMYT, 1:433–434 in Colombia, 1:425 consumption trends, 1:354f, 2:32–33 C4 photosynthesis, 4:194–195 cultivar types, 1:102, 1:102f cultural uses of, 2:39 cytogenetics B–A translocations, 4:408–410, 4:412f chromosomes, 4:408, 4:411f reciprocal A–A translocations, 4:408–410, 4:412f diversity of, 1:80–81f, 1:81 domestication, 1:90–91, 1:90t dry milling (see Dry milling, maize)

511

in Ecuador, 1:425 in Europe cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t, 1:386t exports, 1:352f, 1:355 food uses of, 1:101–102, 1:101f corn syrups (see Corn syrups) flaking grits, 3:104–105f, 3:105 indigenous foods, 3:98–101, 3:100t maize grits, 3:104–105f, 3:105–107 maize meals and flours, 3:107 nixtamalized products (see Lime-cooked maize products) nutritional value, 3:99, 3:102t postharvest management and processing, 3:97–98, 3:98f specialty maizes, 3:98, 3:99t, 3:103f starch, 3:102, 3:104f GDD method, 4:196 genetically modified, 4:196 genetics resources, 4:418 genomics, 4:361 global production, 1:99 grass species, phylogeny of, 1:99, 1:100f harvested area, 1:350t, 1:355 high-amylose maize, 4:427–428, 4:427t, 4:428f hybrid maize breeding, 1:102 IITA, 1:433–434 imports, 1:353f, 1:355 India, production in, 1:367–370, 1:368–370f kernel composition caryopsis, 1:99 embryo, 1:99, 1:100f endosperm, 1:99, 1:100f oil, 1:100 pedicel, 1:99, 1:100f pericarp, 1:99, 1:100f protein, 1:100–101 starch, 1:100 kernel types, 3:258 light micrographs, 2:190, 2:191f lipids, 2:250, 2:251t mageu (see Mageu) morphology brace roots of, 1:58, 1:58f corn cob structure, 1:58, 1:59f dry milling, 1:49 growth habit of, 1:51, 1:52f handling effect, 1:47 hermaphrodite plant, 1:58 male and female inflorescence, 1:55, 1:57f pigment, 1:54, 1:54f tassel and silk of, 1:58, 1:59f usage, 1:57t mutants of ae wx double mutant, 4:429, 4:429t affect plant form, 4:409f, 4:416–417 fertilization, 4:417–418, 4:418f

512

Index

Maize (Continued) kernel properties, 4:409f, 4:411–415, 4:413f, 4:415t opaque-2 mutant (see Opaque-2 maize) o2 wx double mutant, 4:429 pigmentation, 4:409f, 4:416, 4:417t sugary 2 mutation, 4:428 nixtamalization, 1:101f, 1:102 in North America (see North America, maize) nutrition, 4:198–199, 4:199f origin of, 1:99, 4:407–408, 4:408–410f in Paraguay, 1:426 plant density and line spacing, 4:197–198, 4:198f planting time, 4:197, 4:197f Poaceae/true grasses, 1:99 popcorn, 3:259 production, 4:194, 4:194t protein, 2:105f, 2:106 QPM (see Quality protein maize (QPM)) relative maturity, 4:196 reproduction, 1:99 SBE, 2:186 in science, 1:102 Scotch whisky, 3:197–198 silks, 4:195, 4:195f soil management and tillage, 4:196–197 starch noodles, 3:64, 3:65f, 3:66, 3:68f structures and properties of, 4:429–431, 4:430–431f, 4:430t sweet corn, 3:259 tassel, 4:195, 4:195f tortillas (see Tortillas) total domestic supply, 1:355 trade, 1:355 transposable elements, 4:410–411 uses of, 1:99, 3:1, 3:2t, 3:257–258, 3:258t US maize grading scale, 1:101, 1:101f in Venezuela, 1:427 waxy maize, 4:425–427, 4:426t wet milling (see Wet milling, maize) white maize, 4:431 world production of, 1:350t, 1:355, 3:258, 3:467 yields, 1:350t, 1:355 Maize Genetics Cooperation, 4:418 Malaysian Agricultural Research and Development Institute (MARDI), 1:448 Maltese cross phenomenon, 3:389, 3:389f Malting and Brewing Industry Barley Technical Committee (MBIBTC), 4:21 Malting barley, 1:49, 4:50, 4:293–294 breeding for, 4:294 cleaning and rootlet removal, 3:431 diastatic power, 4:293–294 energy and water efficiency, 3:431 evaluation of, 3:424–425 genetics of, 4:294 germination, 4:293–294 circular germination chamber, 3:426–427, 3:427f enzymes, 3:427 grain modification, 3:427

green malt, 3:427 manual floor maltings, 3:426–427, 3:426f perforated plates, grains resting on, 3:426–427, 3:428f pneumatic system, 3:426–427, 3:426f rectangular Saladin boxes, 3:426–427, 3:427f starchy endosperm, cell wall degradation, 3:427, 3:428f hydrolytic enzyme production and release, 3:423 hygiene, 3:431 kilning circular kiln, 3:429, 3:430f flavors and chemical compounds, removal of, 3:428 GK vessel, 3:429 green malt, loading of, 3:428 malting loss, 3:431 moisture removal, 3:428 perforated plates, grains resting on, 3:429 specialty malts, color and examples of, 3:428–429, 3:429f, 3:430t specialty malt types, 3:428–429, 3:429t malt house design, 3:431, 3:432f marketing, 4:17–18, 4:17f quality, 1:150, 3:259, 3:431, 4:52 steeping, 3:425–426, 3:425–426f storage, 3:431 transport, 4:52 uses of, 3:258t Manheim salt-sour method, 3:178 Marantaceae, 1:278 Marker-assisted breeding (MAB), 4:285 Marker-assisted selection (MAS), 1:151 pea, 1:329 pyramiding resistance genes, 1:149 rice breeding, 4:309–310 Marketing Freedom for Grain Farmers Act, 4:3, 4:22 Martin process, 3:6, 3:409 MAS. See Marker-assisted selection (MAS) Masked mycotoxins, 2:296 Mass spectrometry, 4:35 Material safety data sheet (MSDS), 4:99 Matrix-assisted laser desorption/ionization MS (MALDI-MS), 3:290, 3:291f Matrix-assisted laser desorption/ ionization–time of flight mass spectrometry (MALDI-TOF MS), 4:35 Matrix metalloproteases-2 (MMP-2), 1:257 Maximum residue limit (MRL), 4:128, 4:129t Mayonnaise, 3:495–496 McGill University, 1:439 MCT. See Medium-chain triglyceride (MCT) Mechanical denaturants, 2:154 Medium-chain triglyceride (MCT), 2:261 Mercaptoethanol (ME), 4:34f Metal friction machines, 1:205 Metal phosphine, 4:114 Methanol, 3:245

Methyl bromide, 4:102, 4:114 Metric system, grain science analysis cereal-based foods and nutrition, 2:309t, 2:312 cereal chemistry testing, 2:312–313 chemistry units, 2:312 Chinese System of Units, 2:308, 2:310t, 2:311 dough testing measurement Brabender units, 2:313 doughLAB equipment, 2:313–314, 2:314f Farinograph units, 2:313–314 mixograph, 2:313 resistance units, 2:313 enzymatic activity and starch viscosity centipoise, 2:315 falling number unit, 2:314 rapid visco unit, 2:315 stirring number method, 2:315 grain harvesting, 2:311–312 history of, 2:308–309 imperial system, 2:309–311, 2:309t International System of Units, 2:308, 2:309t, 2:311 moisture basis, grain and flour data, 2:313, 2:313f temperature, 2:312 Microbial endoxylanases, 2:144 Microemulsion, 3:246 Micro Visco-Amylo-Graph, 3:253–254 Microwave baking, 3:332 Microwaves (MWs), 4:133–134 Mi-Fen, 3:113 Mi-Hua-Tung, 3:112–113 Millets Africa, production in, 1:360t, 1:361, 1:361f allergy, 2:74 cultural uses of, 2:40 definition, 1:19–20 diversity of, 1:77f, 1:78t, 1:82 exports, 1:356 imports, 1:356 quality, 3:259–260 type names, 3:259–260 uses of, 3:1, 3:2t, 3:258t world production of, 1:350t, 1:356 Milling air-aspirated sieves, 3:301 brush sifter, 3:301 dry milling (see Dry milling) Evans mechanized flour mill, 3:301, 3:302f gradual reduction system, 3:301 grain cleaning, 3:302–303 hand sieves, 3:301 high grinding, 3:301 history of, 3:300 Hungarian system, 3:301 lupins, 1:283 particle size classification, development of, 3:301 pasta, 3:84, 3:85f Perrigault purifiers, 3:301 plansifter, 3:301 purifiers, 3:301 reels, 3:301

Index rice (see Rice, milling) roller mills (see Roller milling) rotary motion advantage of, 3:300 millstones, evolution of, 3:300, 3:300f quern, 3:300 windmills, 3:300 rotating centrifugals, 3:301 saddle stones, 3:300 Millstones, 3:300, 3:300f Minerals buckwheat, 1:309 dry beans, 1:304 flatbreads, 3:23 food fortification (see Food fortification) quinoa, 1:345, 1:345t sorghum, 3:119, 3:119t soybeans, 2:17, 2:18t, 2:18f, 3:134, 3:135t okara, 3:134, 3:135t, 3:139–140, 3:141t soymilk, 3:134, 3:135t tofu, 3:134, 3:135t yuba, 3:134, 3:135t soy-protein products, 3:484, 3:484t Ministry of Agriculture and Rural Development (MARD), 1:448 Minneapolis Grain Exchange, 4:12 Minor millets baking/frying, vegetable oil, 1:207 barnyard/sawa millet, 1:199, 1:200f, 1:200t boiling with water boiled grains, 1:207 dumpling:, 1:207 millet gruel, 1:207 popped grains, 1:207 porridge, 1:207 pudding, 1:207 stir fried millets, 1:207 browntop millet, 1:199 CIAE-Millet mill, 1:206, 1:206f color and structural features, 1:199, 1:201t, 1:201f common name, origin, and occurrence, 1:199, 1:200t common/proso millet, 1:199, 1:200f, 1:200t cultivation, 1:199, 1:200f definition, 1:19–20 drought and low-fertility soils, 1:199 finger millet, 1:199 foxtail/Italian millet, 1:199, 1:200f, 1:200t Guinea millet, 1:199 hypoglycemic properties dietary fiber, 1:203 fatty acid profile, 1:203 starch–lipid interactions, 1:203 starch–protein interactions, 1:203 kodo millet, 1:199, 1:200f, 1:200t little millet, 1:199, 1:200f, 1:200t milling, 1:205–206 nutritional importance amino acids, 1:203 fat, 1:202–203 fiber, 1:203 macronutrients and micronutrients, 1:200–203

minerals and vitamins, 1:200–202, 1:202t phytochemical, 1:203 postharvest processing, 1:204f decortication, 1:205, 1:205f mechanical processing, 1:204–205 traditional processing, 1:204, 1:205f small-grain cereal species, 1:199 storage of grains, 1:204 utilization, 1:206, 1:207f white fonio, 1:199 Miso, 1:284, 3:447 gross composition, 3:125t health benefits of, 3:132 production of, 3:131, 3:131f Mites allergic reactions, 4:112 control of, 4:112 population growth, 4:111 as vectors, 4:112 Mixograph, 3:253 Mobile phones, 4:166 Modified atmosphere packaging (MAP), 3:22 Modified starch Asian wheat flour noodles, 3:77 chemical modifications, 3:282–283 digestion and metabolism, 3:285–286 for nonfood applications, 3:286 production methods and applications batch process, 3:283 chemical reactions, 3:283 cold-water-swelling starches, 3:285 cross-linking, 3:283 HMT starches, 3:285 hydrolytic cleavage, 3:284 hydrophobic groups, 3:284 multiple modifications, 3:285 oxidation, 3:284 pregelatinization, 3:285 RS and SDS, 3:285 stabilization, 3:283–284 waxy maize starch, 3:283 Molded wafer cones developments in, 3:54, 3:55f molds, 3:54 no- /low-sugar cones, 3:54 sugar content, 3:54 Monheimer salt–sour method, 3:28 Monoacylglycerides (MAG), 3:406 Moromi, 3:207–208, 3:208f Moths, 4:57–58, 4:58f Motoho oa mabela, 3:186t commercial traditional-type, 3:190, 3:190f modern developments of, 3:191, 3:191f Muffins, 3:33–34, 3:34t Multiparent advanced generation inter-cross (MAGIC), 1:148–149 Multispectral sensors, 4:165 Munumbicins, 4:259 Murdoch University, 1:445 Musaceae, 1:278 Muscodor albus, 4:259–260 Mustard, 4:207–208 fatty acid components, 1:223t, 1:225 oil and protein content, 1:222, 1:222t

513

uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226 Mycosphaerella graminicola, 1:122, 4:281 Mycotoxins aflatoxins, 2:292–293, 2:293f ergot alkaloids, 2:290–292, 2:291t, 2:292f fumonisins, 2:294, 2:294f masked, 2:296 ochratoxins, 2:293–294, 2:294f phomopsins, 2:296, 2:296f secondary metabolites, 2:290 trichothecenes, 2:294–295, 2:295f zearalenone, 2:295–296, 2:295f Myxobacteria, 4:259

N Narrow-leafed lupin (NLL). See Lupins Nasturtium, 2:226 National Agricultural Research and Extension Services (NARES), 1:432–433 National Agricultural Research Foundation (NAGREF), 1:441 National Agricultural Research Systems (NARS), 1:446 National Association of British and Irish Millers, 4:4 National Center for Atmospheric Research (NCAR) model, 4:140–141 National Cottonseed Products Association (NCPA), 1:243 National Food Security Mission (NFSM), 1:368–369 National Fortification Alliances, 2:47 National Grain Board (NGB), 4:13 National Institute of Agrobiological Sciences, 1:445–446 National Institute of Food and Agriculture (NIFA), 1:437 National Institutes of Health (NIH), 2:25 National Registry of Varieties, 4:2 Natto¯ gross composition, 3:125t health benefits of, 3:132 production of, 3:125, 3:126f Natural disease control biocontrol mechanisms, 4:257–258 antibiosis (see Antibiosis) commercial biocontrol products, 4:261 competition, 4:258 disease suppressive soil, 4:260 general soil suppression, 4:260 hyperparasitism, 4:260–261 mycorrhizal fungi, 4:261 overview of, 4:258 plant host resistance, 4:260 soil-and plant-associated microbes, 4:258 specific soil suppression, 4:260 transgenic plants, 4:261 crop diseases, 4:257–258 grain infection, 4:257 NBS–LRR. See Nucleotide binding site–leucine-rich repeat (NBS–LRR)

514

Index

NCC. See Nutrition Coordinating Center (NCC) NCGS. See Non-celiac gluten sensitivity (NCGS) NCLB. See Northern corn leaf blight (NCLB) NE. See Necrotrophic effectors (NE) Near-infrared reflectance (NIR), 3:163, 3:378, 4:26 amylose, 2:199 (1!3, 1!4)-b-D-glucans, 2:214 fructans, 2:221 grain intake, 4:70 insect infestation, 4:97 yellow pigment, 1:121 Near-infrared reflectance spectroscopy (NIRS), 1:222, 3:231–232 Near-infrared transmittance (NIT), 2:301, 2:302f, 3:163, 3:378, 4:26 Necrotrophic effectors (NE) SNB fungicide, 4:273–274 GFG hypothesis, 4:274–275 HSTs, 4:275 necrotrophic effectors, 4:274–275 quadratic check, 4:275 rain splash of spores, 4:273–274 in Western Australia, 4:273 STB, 4:276–277 TS distribution of, 4:273–274 fungicide, 4:273–274 GFG hypothesis, 4:274–275 HSTs, 4:275 QTL mapping, 4:276 quadratic check, 4:275 southern region, 4:273, 4:274f ToxA, 4:275–277, 4:275t, 4:276f ToxB, 4:276 ToxC, 4:276 Nenkau, 3:447t, 3:448 NERICA. See New Rice for Africa (NERICA) Nested association mapping (NAM), 1:148–149 Net protein utilization (NPU), 4:327–328 Neutralizing value (NV), 3:31–32, 3:32t New Rice for Africa (NERICA), 1:93, 1:143 New Zealand crop yields, 1:416t, 1:418 grain production in, 1:409, 1:410t, 1:418 grain research in, 1:445 wheat agronomic practices for, 4:182–183, 4:182t field and on-farm storage, 1:418, 1:418f Next-generation sequencing (NGS), 1:339, 4:366–368 Nien-Kuo, 3:113, 3:113t NIH. See National Institutes of Health (NIH) NIT. See Near-infrared transmittance (NIT) Nitrate transporters (NRTs) gene family, 4:395 Nitrogen, 4:100 assimilation of, 2:133–135 atmospheric nitrogen, 2:129 biological N fixation, 2:131–132, 2:132t

vs. carbon metabolism, 2:136 crop plants, 2:131 cycle, 2:129–131, 2:130f environmental health, 2:136–137 nitrate and nitrite reduction, 2:135 seeds fruit/seed development, 2:123–124 N reserves, 2:126–127 primary N metabolism, 2:125–126 transport mechanisms, 2:123–124 seed storage proteins, 2:135 sources, 2:131 symbiotic signals, 2:132 uptake, 2:132–133, 2:134f Nitrogen balance index (NBI), 4:165–166 Nitrogen use efficiency (NUE), 1:151 Nixtamalization, 1:101f chemistry of, 3:95–96 dating, 1:102, 2:39 milling industries, 3:98f, 3:102 tortillas, 3:95–96 Non-celiac gluten sensitivity (NCGS), 2:85 GFD, 2:93 wheat consumption, 2:24 Nongluten wheat proteins, 2:94 Nonhydratable phospholipids (NHPs), 3:492 Nonpolar lipids, 2:249 Nonpressurized refrigerated dough cookies, 3:362, 3:362t packaging technology, development of, 3:364–365 piecrust, 3:363, 3:363t shelf life, 3:364 Nonstarch polysaccharides (NSP), 1:281, 1:281t arabinogalactan proteins, 2:221–222, 2:221f arabinoxylans, 2:226, 2:227f (1!3, 1!4)-b-D-glucans analysis and detection, 2:214 barley, oat, and rye grains, 2:210 cell wall composition, 2:209t, 2:210 gelation, 2:213 genetics, 2:214 molecular conformations, 2:211f, 2:212–213 solubility, 2:211–212, 2:211f, 2:212t structure, 2:210–211, 2:211f structure–function relationships, 2:213–214 viscosities of, 2:210f, 2:213 callose, 2:220–221 cellulose, 2:209–210, 2:209t, 2:210f cell wall compositions, 2:208 dietary fiber, 2:225 distribution of, 2:224–225, 2:225f fructans, 2:221 galactomannans, 2:227–228, 2:228f glucomannans, 2:209t, 2:210f, 2:219 heteroxylans analysis and detection, 2:219 gelation, 2:216f, 2:217–218 genetics, 2:219, 2:219t molecular parameters, 2:217

solid-state and solution conformations, 2:217 solution properties, 2:217 structure, 2:210f, 2:214–217, 2:215–216f, 2:215t structure–function relationships, 2:218–219 insoluble cell wall polysaccharides, 2:225–226, 2:226f IP6, 2:286–287, 2:288t monosaccharide composition, 2:228 pectic polysaccharides, 2:209t, 2:220, 2:220f plant cell walls, 2:224 polymers, 2:228 reserve polysaccharides, 2:227 soluble cell wall polysaccharides, 2:226 uses of, 2:225 water solubility/insolubility, 2:228 xyloglucans, 2:220, 2:220f, 2:226 Noodles, 1:113 ABNY, measurement of, 3:154 alkaline noodles, 3:5 Asian noodles (see Asian noodles) buckwheat, 1:313, 1:314f, 3:5 color measurements CIELAB, 3:157, 3:157f color stability, 3:157 gloss measurement, 3:157–158, 3:158f guidelines for, 3:156 image analysis, 3:157 infinite optical thickness, 3:157 light wavelength, 3:156–157 noodle sheet, preparation of, 3:157 translucency measurement, 3:157 definition of, 3:5 egg noodles, 3:5 end-product tests, 3:252 formulas, 3:5 glass slide method, 3:154 instant noodles, 3:5 nonwheat/gluten-free noodles, 3:64 sensory evaluation boiled noodles, attributes of, 3:155–156 Chinese system, 3:156 cross-cultural sensory research, 3:156 descriptive sensory analysis, 3:155 designing, decision tree for, 3:155, 3:155f discrimination sensory analysis, 3:154 feelings, 3:155 ISO methods, 3:155 Japanese noodle testing method, 3:155 rating scales, 3:155 scoring system, 3:155 sensory booths, 3:155 sensory panel, 3:155 Standards Australia, 3:155 trained experts, involvement of, 3:156 training, 3:156 starch (see Starch noodles) texture measurement, 3:158–159 types of, 1:105, 1:106f udon noodles, 3:5 white salted noodle, 3:5

Index Normalized Difference Vegetation Index, 4:165 North America barley area distribution, 1:391, 1:392f consumption and trade, 1:397, 1:397t harvested area, 1:391, 1:392f, 1:397t production in, 1:391, 1:392f, 1:396–397, 1:397t canola area harvested, 1:402–403, 1:403t disposition and consumption, 1:405, 1:405t production, 1:403–404, 1:404t linseed area harvested, 1:403t, 1:407 production, 1:404t, 1:407 maize area distribution, 1:391, 1:392f consumption and trade, 1:393–394, 1:394t GM crops, 1:392 harvested area, 1:391–393, 1:392f, 1:393t production in, 1:391–393, 1:392f, 1:393–394t oats area distribution, 1:391, 1:392f, 1:397–398 average yields, 1:398 consumption and trade, 1:398–399, 1:398t harvested area, 1:391, 1:392f, 1:398t production in, 1:391, 1:392f, 1:397–399, 1:398t rice area distribution, 1:391, 1:392f average yield, 1:399 consumption and trade, 1:399–400, 1:399t harvested area, 1:391, 1:392f, 1:399t production in, 1:391, 1:392f, 1:399–400, 1:399t sorghum area distribution, 1:391, 1:392f average yields, 1:396 consumption and trade, 1:396, 1:396t harvested area, 1:391, 1:392f, 1:395t, 1:396 production in, 1:391, 1:392f, 1:395–396, 1:395–396t soybeans area harvested, 1:403t, 1:405 disposition and consumption, 1:405t, 1:406 production, 1:404t, 1:406 sunflower animal feed, 1:407 area harvested, 1:403t, 1:407 disposition and consumption, 1:405t, 1:408 production, 1:404t, 1:408 wheat agronomic practices for, 4:181–182, 4:181t

area distribution, 1:391, 1:392f average yields, 1:395 consumption and trade, 1:395, 1:395t harvested area, 1:391, 1:392f, 1:394, 1:394t production in, 1:391, 1:392f, 1:394–395, 1:394–395t Northern corn leaf blight (NCLB), 4:417 NPU. See Net protein utilization (NPU) NRTs gene family. See Nitrate transporters (NRTs) gene family NSP. See Nonstarch polysaccharides (NSP) Nuclear magnetic resonance (NMR) spectroscopy, 3:405 Nucleotide binding site–leucine-rich repeat (NBS–LRR) cereal cyst nematode, 4:391 HR, 4:390–391 Mla subfamily of, 4:390–391 necrotrophic fungi, 4:391 Nullisomic–tetrasomic lines, 4:383 NuSun™ sunflower oil, 1:247, 1:248t, 1:251–252 Nut oil, 2:265 Nutrigenomics, 4:362 Nutrim, 3:293–294 Nutritional Labeling and Education Act of 1990, 3:266 Nutrition Coordinating Center (NCC), 2:297, 4:433 Nutrition label, 2:57–58 NV. See Neutralizing value (NV)

O Oak Park Crop Research Centre, 1:440 Oatrim, 3:293–294 Oats agronomy climatic factors, 1:176–177 nutrition of, 1:177 soil factors, 1:176 sowing rates, 1:177 spring and winter varieties, 1:177 wind rowing, 1:177 animal feed, 3:260–261 Australia production in, 1:410t, 1:413, 1:415t, 1:417 yields, 1:413–415, 1:416t (1!3, 1!4)-b-D-glucans, 2:210 bioactive antioxidants avenanthramides, 2:279–280 saponins, 2:280 bran digestion, 2:239f fermentation, 2:239, 2:239f laxation, 2:239 breeding-improved oat varieties breeding methods, 1:182–183 breeding priorities, 1:182 germplasm collections, 1:183 history, 1:182 carbohydrate composition, 2:164, 2:165t

515

classification, 1:173–174 consumption trends, 2:32–33 cool temperate climates, 1:173 cultural uses of, 2:38–39 diseases, 4:75, 4:76t bacteria, 1:178, 1:179f fungi, 1:177–178, 1:177–179f nematodes, 1:178, 1:180f viruses, 1:178, 1:179–180f diversity of, 1:77f, 1:80f, 1:82 domestication, 1:91–93 exports, 1:356 extruded snacks, 3:419 farming systems, 1:173, 1:174f food uses of, 3:260 GFD, 2:95 history of domestication and early cultivation, 1:174–175 speciation, 1:174 human consumption, 1:173 husked oats, 1:173 imports, 1:356 insect pests, 1:178–179 milling process, 1:180, 1:181f morphology, 1:57t, 1:66f, 1:70, 1:70–71f naked oats, 1:173 in North America area distribution, 1:391, 1:392f, 1:397–398 average yields, 1:398 consumption and trade, 1:398–399, 1:398t harvested area, 1:391, 1:392f, 1:398t production in, 1:391, 1:392f, 1:397–399, 1:398t plant growth and morphology, 1:175–176, 1:175–176f production, 1:173 quality, 3:260 uses of, 1:173, 1:174f, 1:181, 3:1, 3:2t, 3:258t feed grain, 1:173 fodder, 1:174f, 1:182 human consumption, 1:173, 1:181 nonfood and industrial, 1:173, 1:181–182 vellie product, 3:191, 3:191f world production, 1:350t, 1:356 OatVantage™, 3:294 OatWell®, 3:294 Ochratoxins, 2:293–294, 2:294f Octoploid triticales, 1:168–169, 1:169f Ogi, 3:186t, 3:189–190, 3:190f Oilseeds in Africa, 1:361–362 in Australia production in, 1:410t, 1:413, 1:415t yields, 1:413–415, 1:416t component of, 1:221–222 cottonseed (see Cottonseed) in Europe consumption and food supply quantity, 1:389, 1:389t

516

Index

Oilseeds (Continued) production in, 1:386–387, 1:387–388t genetically modified plants, development of, 1:223, 1:227 genomics, 4:361 GM grains, 4:350 Goldfisch/Soxhlet methods, 1:222 industrial applications, 1:20–21 Kjeldahl nitrogen analysis, 1:222 linseed (see Linseed) meal production, 1:222 mustard (see Mustard) near-infrared analysis, 2:301–302 nondestructive seed analysis, 1:222 nonfood uses of, 1:222 peanut (see Peanuts) rapeseed (see Rapeseed) safflower (see Safflower) sesame (see Sesame seed) soybean (see Soybeans) sunflower (see Sunflower) uses, 1:221–222 world consumption of, 1:222 world production of, 1:222, 1:356–357, 1:356t Okara, 1:229f carbohydrate contents, 3:139–140, 3:142t ceramic product, 3:142 dry matter content of, 3:131 fermentation, 3:131–132, 3:140–142 citric acid, 3:132 for nonfood products, 3:132, 3:142 fiber component, 3:140 gross composition, 3:134, 3:135t mineral and vitamin contents, 3:134, 3:135t, 3:139–140, 3:141t nonfermented products, 3:140 preservation of, 3:139 protein, 3:140 proximate composition, 3:139–140, 3:141t uses of, 3:139 Okoshi, 3:448 Olive oil, 2:264 in Italy, 3:16 polyphenols, 2:259 squalene, 2:259 subgroup, 2:261 traditional US toppings, 3:16 Omega-3 fatty acids, 2:8–9, 2:9f On-the-go calibration systems, 4:165 On-the-go soil sampling method, 4:164 Oocydin A, 4:259 Opaque beer-making process, 1:196–197, 1:197f Opaque-2 maize, 4:429 endosperm textures, 4:421 genetic improvement, 4:422–423 high-lysine-content hybrids, 4:420–421 inheritance of, 4:421 nutritional value of, 4:422, 4:423t STS markers, 4:423 transcription factors, 4:421 Optical satellite imagery, 4:164 Optical sorter, 3:311

Optimized Straight-Dough Bread-Making Method, 2:305 ORAC. See Oxygen radical absorbance capacity (ORAC) Organic agriculture advantages, 4:160–161 conventional agriculture, ecological alternative to, 4:161 definition, 4:154 economic viability, 4:155 limitation, 4:161 for low-input agronomic conditions, 4:154 marketing, 4:154 organic foods engineered nanomaterials, 4:160 irradiation and GMO technology, 4:160 nonagricultural origin, additives of, 4:156, 4:157t organic yeast, 4:156 processing aids, 4:156, 4:159t pest and disease control, substances for, 4:155, 4:156t production methods, 4:154–155 regulations Codex Alimentarius Commission guidelines, 4:155–156 IFOAM Basic Standards, 4:156 ISO Standard 65, 4:156 soil fertilizing and conditioning, 4:155, 4:155t weed management, 4:155 Oriental mustard, 4:207–208 Orleans vinegar process, 3:178, 3:181 Oryza glaberrima. See African rice Oryzanols, 3:455–456 Oryza sativa. See Asian rice; Rice Osborne protein fractions, 1:213t, 1:215, 1:216t Oshikundu, 1:196, 3:186, 3:186t Osteoporosis, 2:21 Oufila, 3:186, 3:186t, 3:187f Ovens baking with visible light, 3:332–333 band ovens, 3:328–329, 3:329f beehive ovens, 3:303, 3:303f, 3:335, 3:336f compact footprint designs horizontal folded path, 3:331, 3:331f spiral circular path, 3:331 steam baking, 3:332 vertical folded path, 3:331–332, 3:331f deck ovens, 3:304, 3:373 direct resistance ovens, 3:333 faggot oven, 3:304, 3:304f heat sources, 3:304–305, 3:325–326 heat transfer mechanisms conduction, 3:326–327 convection, 3:327–328, 3:327–328f steam pipe effect, 3:328, 3:328f thermal radiation, 3:326 history of, 3:303 hybrid ovens, 3:333, 3:333f impingement ovens, 3:329–330, 3:330f microwave baking, 3:332 ‘one for all’ oven, 3:304

peel oven, 3:304 physical arrangements, 3:304, 3:325 products being baked, 3:304, 3:325 rack ovens, 3:373 reel oven, 3:328, 3:329f RF ovens, 3:332, 3:332f rotary rack ovens, 3:329 scale, 3:304, 3:325 serpentine oven, 3:372, 3:372f sheeted single-layered flatbreads, 3:20 tandoor ovens, 3:303 traveling tray bread ovens, 3:328, 3:329f tunnel oven, 3:372, 3:372f two-layered flatbreads, 3:20–21 Oxidized starch, 3:278, 3:284 Oxygen radical absorbance capacity (ORAC), 3:119–120, 3:120t, 3:437–439, 3:440t

P Paddock to plate sequence, 1:22 Pakistan Agricultural Research Council (PARC), 1:447 Pakistan, grains research, 1:447 Palmae, 1:278 Palm oil, 1:222, 2:258t, 2:262–263, 2:262t Pampas, 1:420 Pan breads, 3:12–13, 3:12–13f, 3:12–13t Pancakes, 3:4, 3:185–188, 3:186t, 3:188f Pandanaceae, 1:278 Panicum P. miliaceum (see Proso millet) P. sumatrense (see Little millet) Papilionoideae, 2:228 Paraguay, 1:425–426 Parboiled rice, 3:446, 3:447t Parenteral nutrition, 2:82 Particle-size index, 3:255 Pasmo, 1:263 Paspalum scrobiculatum. See Kodo millet Pasta, 1:105, 1:106f, 1:113, 3:5–6 composite products, 3:79 consumption of, 3:79–81, 3:82t definition, 3:79 durum wheat, 3:79 with barley, 1:149, 1:149f EU countries, production in, 1:123, 1:123f quality, 1:121–122 shapes, 1:118f eggs, 3:83–84 end-product tests, 3:252 fortification, 2:46 global trade, 3:79–81, 3:81t global wheat production, 3:79–81, 3:80t manufacturing processes drying, 3:85–86, 3:87f extrusion, 3:84–85, 3:86f milling, 3:84, 3:85f mixing, 3:84, 3:86f sheeting, 3:85 nonconventional raw materials, products from, 3:87–88 nutritional value of, 3:88, 3:88t

Index origin of, 3:79 production by region, 3:79–81, 3:82f quality assessment, 3:86–87 quality requirements for semolina, 3:83 water, 3:83 wheat grain, 3:82–83, 3:84t quality testing methods cooked pasta, 3:163, 3:163t dry pasta, 3:163, 3:163t hygienic and sanitary, 3:161, 3:162t nutritional quality, 3:162, 3:162t sensory quality, 3:162, 3:162t technological quality, 3:161–162, 3:162t shapes, 3:79 South American countries, consumption in, 1:427, 1:427f spinach, 3:83–84 tomato, 3:83–84 vitamins, 3:83–84 Pastries, 3:32t definition, 3:32 laminated doughs, 3:32–33 paˆte sucreé, 3:33 pie doughs, 3:33 short doughs, 3:33 PCA. See Principal component analysis (PCA) Pea, 1:331–332 adaptation, 1:324 amino acid content of, 1:326, 1:327t animal feed, 1:324, 1:327 antinutritional factors, 1:326 area, production, and yield, 1:324, 1:325t, 1:325f biotechnology and in vitro culture techniques double haploid production, 1:330 genetic transformation, 1:329–330 interspecific and intergeneric hybridization, 1:329 in vitro generation acceleration, 1:330 molecular markers and linkage mapping, 1:329 crop nutrition, 4:244t micronutrients, 4:245 nitrogen, 4:243–244 phosphorus, 4:244–245 potassium, 4:245 sulfur, 4:245 cropping rotations, 1:324 cropping system, role in, 4:240–241 cultivar choice, 4:241–242 food products, 1:326–327 fungal and bacterial diseases, 4:246, 4:247t, 4:248f genetic improvement, 1:327–329 grain quality and marketing exports, 1:330, 1:331f imports, 1:330, 1:331–332f seed shape, size, and color, 1:330 standardized nomenclature and methods, development of, 1:330 visual assessment, 1:330 green peas, 1:324 harvesting, 4:247–248

invertebrate pest management, 4:246–247, 4:248t nutritional content of, 1:326, 1:327t plant, 1:324–326, 1:326f processing, 1:326–327 rainfall and temperature, 4:241, 4:241t seed types, 1:325, 1:327f soils, 4:241 sowing management, 4:242–243 sowing time, 4:242 uses of, 4:240 weed management, 4:245–246, 4:245f Peanuts bioactives, 1:338 breeding and biotechnology, 1:339 drought, 1:337 farming systems, 1:336 fatty acid components, 1:223–224, 1:223t as food products, 1:334 food safety, 1:338–339 aflatoxin, 1:338 anaphylaxis, 1:339 cadmium, 1:339 fungal pests, 1:336 insect pests, 1:336 as livestock feed, 1:334 local names, 1:334 morphology and growth physiology, 1:336 nutritive composition of, 1:338, 1:338t oil, 1:222–224, 1:222t, 1:334, 2:264 origin, 1:334 photoperiod, 1:337 plant, 1:334, 1:335f production and yields, 1:334, 1:335t products, 1:337–338 protein content, 1:222–224, 1:222t, 1:334 soil nutrition, 1:337 temperature, 1:337, 1:337t trade market, 1:335 uses of, 1:222, 1:222t viruses, 1:336–337 world production, 1:225t, 1:225f, 1:226, 1:247, 1:248t Pearl millet, 1:434 antinutrients, 1:192t, 1:193 beverages nonalcoholic, 1:196 opaque beer, 1:196–197, 1:197f classification, 1:190 domestication, 1:90t, 1:91, 1:91f, 1:92t energy amino acid composition, 1:192 carbohydrates, 1:192 fat content, 1:192–193 minerals, 1:192t, 1:193 proteins, 1:192, 1:192t vitamins, 1:192t, 1:193 foods doughs and gruels, 1:195 flatbreads, 1:195–196, 1:196f porridge, 1:195 grain structure, 1:191, 1:191f LAB fermentation, 3:186, 3:186t, 3:187f malting, 1:194–195, 1:194f milling process, 1:193f

517

dehulling, 1:193–194, 1:194f semiwet milling, 1:194 solar drying, 1:194 steeping, 1:194 phytochemicals, 1:193 production and agronomic issues, 1:190, 1:191f vernacular names, 1:190 Pectic polysaccharides, 2:209t, 2:220, 2:220f Pectins, 2:226 Peel oven, 3:304 Penicillium verrucosum, 2:293 Pentosans, 2:283, 2:286–287 PEPCK. See Phosphoenolpyruvate carboxykinase (PEPCK) Peronosclerospora sorghi, 1:156 Peroxide value (PV), 3:494–495 Perrigault purifiers, 3:301 Perten Single-Kernel Characterization System (SKCS) 4100, 3:255, 3:255f Pests birds, 4:173 chemical control, 4:174–175 chickpea, 4:219–220 field insect larvae, 4:72 food safety, effect on, 4:169 genetic resistance, 4:174 grain quality, effect on, 4:168 grain yield, effect on, 4:168 husbandry, 4:174 insects, 4:173 integrated pest management, 4:175 invertebrates (see Invertebrate pests) lentil, 4:229 mammals, 4:173 nematodes and molluscs, 4:173–174 peanuts, 1:336 plant vulnerabilities, 4:169–170 sorghum, 1:156, 4:202–203 storage insect larvae, 4:72 Pet foods dry food (see Dry pet foods) intermediate moisture products, 3:226, 3:227t nutrition-based animal feedstuffs, 3:223 pets, types of, 3:223 treats, 3:223, 3:226–227 UK market for, 3:223, 3:224t wet (see Wet pet foods) Phaseolin, 1:301–303 Phaseolus vulgaris. See Dry beans Phenol-explorer database flavonoids, 2:280 phenolic acids, 2:280 Philippine Department of Agriculture (DA), 1:447–448 Phomenone, 4:259 Phomopsins, 2:296, 2:296f Phosphatidylcholine (PC), 3:493–494, 3:494t Phosphatidylethanolamine (PE), 3:493–494, 3:494t Phosphatidylinositol (PI), 3:493–494, 3:494t

518

Index

Phosphine fumigation, 4:102, 4:114, 4:114t airtight grain bin, design of, 4:131, 4:131f corrective treatment, 4:131 disadvantage, 4:130 efficacy failures, 4:130 hydrogen cyanide, 4:130 preventive treatment, 4:131 recirculation fumigation system, 4:131 reinfestation, 4:131 release of, 4:130–131 residue-free, 4:130 Phosphoenolpyruvate carboxykinase (PEPCK), 2:126 Phosphorus, 4:100 Photoperiod-sensitive/thermo-sensitive genic male sterility (P/TGMS), 4:307 Phytases, 2:283–285, 2:284t Phytic acid (IP6) in animal feed, 2:284–285 in plants amylase inhibitors, 2:286 globoids, 2:283 hexaphosphorylated myo-inositol, 2:283 interactions, 2:283, 2:284f iron absorption, 2:284 NSPs, 2:286–287, 2:288t phosphorus storage compound, 2:283 phytases, 2:283 phytin, 2:283 protease inhibitors, 2:285–286 tannins, 2:286, 2:287f total P content, 2:283, 2:284t Triticeae tribe of cereals, 2:283 zinc absorption, 2:283, 2:285f Phytin, 2:119, 2:272, 2:283 Piecrust, 3:363 Pisum sativum (L.). See Pea Pita bread, 3:16f, 3:17 Plansifters, 3:84, 3:301, 3:312, 3:312f Plant breeders’ rights (PBR), 4:29, 4:31 Plant Variety Rights scheme, 1:224 Poaceae, 1:99 Pod sealants, 4:63–64 Polarized light, 3:389, 3:389f Polar lipids, 2:249 Polish seed, 1:237 Polish-style sponge, 3:26 Polyacrylamide gel electrophoresis (PAGE), 4:33–34 Polymerase chain reaction (PCR), 4:380 Polyphenol oxidase (PPO), 1:41, 2:142, 2:142f, 3:76, 3:254, 3:254f Polyploid wheat, 4:382–383 Polyunsaturated fatty acids (PUFAs), 2:255, 2:260, 4:328–329 Pom-pom model, 3:347 Pontederiaceae, 1:278 Popcorn, 3:1, 3:2t, 3:98, 3:99t, 3:103f, 3:259 Popped rice, 3:446, 3:447t Portulacaceae, 1:277 Postharvest operations, stored gains aeration and cooling benefits of, 4:121 grain temperature, influence of, 4:120–121, 4:120f

objective of, 4:120–121 practical implementation of, 4:121–123 precision monitoring, 4:121, 4:121f purpose of, 4:121 decision support system, 4:123 grain cleaning, 4:117–118 in-bin drying (see In-bin drying) IPM, 4:117, 4:123 kernel breakage, limitation of, 4:123 mechanical impact, turning, 4:123 Potassium chloride, 3:400, 3:402 Potato chips, 3:415 noodles production, 3:67, 3:69f starches, 2:182–183, 2:187 Potyvirus peanut stripe virus (PStV), 1:336–337 Powdery mildew, 4:79–80, 4:264–265, 4:271 lentil, 4:229 linseed, 1:263 oats, 1:177 PPO content. See Polyphenol oxidase (PPO) PPPs. See Public and private partnerships (PPPs) Practical, healthier, affordable, and desirable (PHAD), 2:64, 2:66 Prairie Grain Development Committee (PGDC), 4:3 Prairie Research Laboratory (PRL), 1:194, 1:194f Prebiotics, 2:13–14 Precision agriculture (PA), 4:43, 4:48 components of, 4:163, 4:163f definitions, 4:162 driverless tractors, 4:166 goals of, 4:162 microdosing, 4:162 predictive/reactive management decisions, 4:166 robotic platforms, 4:166 small-scale agriculture, 4:162 spatial management, 4:162–166 ground truthing, 4:166 mobile phones, 4:166 plant sensors, 4:165–166 positioning, 4:163–164 soil monitoring, 4:164–165 variability identification, 4:164 yield maps, 4:164 timelapse photography, 4:166 unmanned aerial vehicles, 4:166 Pregelatinized starch, 3:285 Preharvest sprouting, 2:140, 2:141f Prematurity a–amylase, 2:140 Pressurized refrigerated dough products formulation, 3:360t for bread products, 3:360, 3:360t chemical leavening, 3:359 hard wheat dough, 3:359 potassium bicarbonate, 3:359 SAPP, 3:359 shortening, 3:359 sodium bicarbonate, 3:359

for sweet dough products, 3:359, 3:360t yeast, 3:359, 3:364 magic number, 3:363 packaging, 3:361–362 pressure/specific volume, 3:363 processing steps, 3:360, 3:360f finishing operations, 3:361 form, 3:361 mixing, 3:361 prepare and scale/meter ingredients, 3:361 receive and store ingredients, 3:360–361 shelf life, 3:363–364 Pretzels, 3:3 Primary triticales, 1:168 Prina, 1:20 Principal component analysis (PCA), 4:145 Private tender, 4:11 PRL. See Prairie Research Laboratory (PRL) Proanthocyanidins, 2:286, 2:287f Probiotics, 2:13–14, 2:13t Product staling. See Staling, baked products Program for Africa’s Seed Systems (PASS), 1:365 Prolamin box, 2:121 Proline-rich proteins (PRPs), 2:286 Proso millet, 1:19–20, 1:199, 1:200f, 1:200t Protein amaranth, 1:291–292, 1:292t buckwheat, 1:308, 1:308t, 1:310–311, 1:310t cottonseed, 1:222–223, 1:222t dry beans, 1:301–302 durum wheat, 1:121 flatbreads, 3:23 gluten, 3:408 legumes, 1:265–266, 1:266t, 1:268–270, 1:268–269t linseed, 1:222, 1:222t, 1:224, 1:259–260 lupins, 1:280, 1:285 maize, 1:100–101 mustard seed, 1:222, 1:222t okara, 3:140 pea, 1:326, 1:327t peanut, 1:222–224, 1:222t quinoa, 1:344–345, 1:344t rapeseed, 1:222, 1:222t safflower, 1:222, 1:222t, 1:224, 1:255 sesame seed, 1:222, 1:222t, 1:224 sorghum, 3:117–119, 3:119t soybeans, 1:222, 1:222t, 2:17, 4:25–26, 4:26t sunflower seed, 1:222, 1:222t, 1:224 Protein digestibility-corrected amino acid score (PDCAAS), 1:231–232 Protein efficiency ratio (PER), 3:134, 3:135f, 3:484–485 PRPs. See Proline-rich proteins (PRPs) Pseudocereals, 1:21 amaranth (see Amaranth) buckwheat (see Buckwheat) in Chenopodiaceae family, 1:275–276 definition of, 1:274

Index in dicot families Bixaceae, 1:277 Cactaceae, 1:277 Cannabidaceae, 1:277 Caryophyllaceae, 1:277 Chloranthaceae, 1:277 Cistaceae, 1:277 minor dicotyledonous families, 1:276–277 Portulacaceae, 1:277 Trapaceae, 1:277 in monocot families Araceae, 1:277 Cannaceae, 1:277 Commelinaceae, 1:277 Cyperaceae, 1:278 Marantaceae, 1:278 minor monocotyledonous families, 1:277 Musaceae, 1:278 Palmae/Arecaceae, 1:278 Pandanaceae, 1:278 Pontederiaceae, 1:278 Typhaceae, 1:278 Zingiberaceae, 1:278 in Polygonaceae family, 1:276 quinoa (see Quinoa) Russian Federation and Ukraine, production in, 1:383, 1:384t as weeds, 1:275 Psocoptera, 4:110 Psyllium arabinoxylan, 2:226 Public and private partnerships (PPPs) dietary recommendations, 2:65 foods research and public health, 2:66 function, 2:65 guidelines, 2:65–66 members, 2:65 partners, 2:65 principles of, 2:64, 2:65f research meeting, 2:63, 2:70 shared value, 2:64–65 stakeholders, 2:65 vision, 2:64 WG (see Whole grains (WG)) Public tenders, 4:11 Puccinia striiformis f. sp. tritici in wheat, 4:266–269, 4:268t Puccinia triticina, 4:266, 4:267t Puffed cereals, 3:263–264 Puffed rice products gun-puffing cake, 3:111–112 Guo-Ba, 3:113 Mi-Hua-Tung, 3:112–113 Puff pastry, 3:32 Pullman bread, 3:12, 3:12f Pullulanase, 2:186 Pup-loaf testing, 2:305 Puto, 3:447t, 3:448 Pyrenophora leaf blotch, 1:177–178, 1:179f Pyrenophora triticirepentis, 1:122 Pyrethroids, 4:108 Pyrolysis, 3:246 Pyrrocidines, 4:259

Q QPM. See Quality protein maize (QPM) QTL. See Quantitative trait loci (QTL) Quality management, wheat, 3:252, 4:11 flour quality assessment component tests, 3:252–255 end-product tests, 3:252 genotype classification, 4:2, 4:5f in Argentina, 4:2, 4:2t in Australia, 4:3 in Canada, 4:3–4 in France, 4:4, 4:4t in Germany, 4:4 in Russia, Ukraine, and Kazakhstan, 4:2f, 4:3 in United Kingdom, 4:4 in United States, 4:4–5, 4:4t grain and grain lots, intrinsic quality of, 3:255–256 physical and seasonal quality tests in Australia, 4:5–6 in Canada, 4:5–6 in France, 4:7 Russia and Ukraine, 4:7 in United States, 4:6–7 Quality protein maize (QPM), 1:365, 1:433–434 endosperm, 4:420 essential amino acids, 4:420 food uses of, 3:98, 3:99t genetic and biochemical basis, 4:421, 4:422f genetic improvement, 4:422–423 germ, 4:420 history of, 4:420–421 molecular marker technique, 4:423 nutritional and process values, 4:422, 4:423t tortillas, 3:96 zeins, 4:420 Quantitative trait loci (QTL), 4:203, 4:398 abiotic stresses, 4:403–404 appearance quality, 4:405 broad-sense heritability, 4:398–399 brown plant hopper, 4:403 comparative genomic mapping, 4:401 cooking and sensory quality, 4:404–405 disease resistance, 4:403 functional genomics, 4:400–401 genes, 4:399–400, 4:400t genetic effects, 4:398–399 genome size and number of genes, 4:398, 4:399t heading date (HD), 4:402–403 milling quality, 4:405 molecular dissection, 4:399 nutritional quality, 4:405 phenotypes (P), 4:398–399 plant height, 4:402 yield-related traits, 4:401–402 Queensland Alliance for Agriculture and Food Innovation (QAAFI), 1:444–445 Quern, 3:300 Quick germ process, 3:240, 3:240f

519

Quince seed arabinoxylan, 2:226 Quinoa, 1:275–276 Andean Quinoa Project, 1:346 Andean region, indigenous crop of, 1:341 in Bolivia, 1:422 botanical name, 1:341 carbohydrates and fiber, 1:344t, 1:345 CELSS project, 1:347 classification of, 1:341–342, 1:342t common names, 1:341 cultivation practices, 1:343 cultural uses of, 2:41 essential amino acids in, 1:344, 1:344t fat, vitamins, and minerals, 1:345, 1:345t food products, 1:346–347, 1:346f fungal disease, 1:343 leaves of, 1:346 phenolic content, 1:345–346 phytic acid, 1:345 production areas of, 1:341, 1:343–344 protein content of, 1:344–345, 1:344t saponins, 1:345–346 taxonomic and botanical description, 1:342–343, 1:342–343f trypsin inhibitors, 1:345 world production of, 1:356

R RACCs. See Reference amounts commonly consumed (RACCs) Rack ovens, 3:373 Radio frequency (RF), 4:133, 4:134f Raffinose family oligosaccharides (RFO), 2:167, 2:171 Raman microscopy, 1:45 Random amplified polymorphic DNA (RAPD), 4:365 Rapeseed for biodiesel, 1:222 cultivars of, 1:224 deodorizer distillates, composition of, 3:494, 3:494t erucic acid, 1:224 Europe, production in, 1:387, 1:388t fatty acid components, 1:223t glucosinolates, 1:224 meal production, 1:222 oil and protein content, 1:222, 1:222t trade, 1:239, 1:239t uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226, 1:239, 1:239t, 1:247, 1:248t, 1:350t, 1:357 Rapid hydration hydrothermal cooking method, 3:135 Rapidly digestible starch (RDS), 2:231 Rapid Visco Analyzer (RVA), 1:143, 1:145f, 1:290–291, 2:178, 3:110, 3:169, 3:169f, 3:253–254 RBD oil. See Refined, bleached, and deodorized (RBD) oil RCD. See Refractory celiac disease (RCD) RDS. See Rapidly digestible starch (RDS)

520

Index

Reactive oxygen species (ROS), 4:396 Ready-to-eat (RTE) cereals, 3:5, 3:262, 3:263f compressed-flake biscuits, 3:264 costs, 3:262 extruded expanded cereals, 3:264 flaked cereals, 3:263 granola cereals, 3:264 muesli RTE cereals, 3:264 per capita annual consumption, 3:262–263 puffed cereals, 3:263–264 shredded cereals, 3:264 Real-Time Kinematic (RTK), 4:163 Recirculation fumigation system, 4:131 Recurrent selection, 4:299–300, 4:299f Reel oven, 3:328, 3:329f Reference amounts commonly consumed (RACCs), 2:58 Refined, bleached, and deodorized (RBD) oil, 1:232–233 Refractory celiac disease (RCD), 2:83–84 Refrigerated can dough system, 3:361–362, 3:362f Refrigerated dough gluten-free, 3:365 history of, 3:359 magic number, 3:363 nonpressurized dough cookies, 3:362 packaging technology, development of, 3:364–365 piecrust, 3:363, 3:363t shelf life, 3:364 pressurized dough formulation, 3:359–360 packaging, 3:361–362 pressure/specific volume, 3:363 process steps for, 3:360–361, 3:360f shelf life, 3:363–364 yeast strain, 3:364 sodium replacement salt analogs, 3:365, 3:365t Renewable fuel standard (RFS), 3:235 Research and development (R&D) in Australia, 1:444–445 brewing companies, 1:452 in Canada, 1:439 in Central America, 1:448–449 in Europe, 1:440–442 in Mexico, 1:440 in Middle East, 1:449–450 in New Zealand, 1:445 in North Asia, 1:445–446 private sector, in Asia and Africa, 1:452 seed and grain biotechnology companies, 1:452, 1:453t in South Africa, 1:449–450 in South America, 1:448–449 in South Asia, 1:446–447 in Southeast Asia, 1:447–448 in USDA centers, 1:436–439, 1:438t Reserve starch, 2:181 Residue-borne diseases, 4:75–79

Resistant starch (RS), 2:179, 2:179t, 2:181, 3:285 a-amylase, 2:230 classification of, 2:230, 2:231t cultural differences, in consumption, 2:36 definition, 2:230 enzyme resistance, 2:230–231 health benefits gut health, 2:232 metabolic effects, 2:232–233 hydrolysis of, 2:230 intake quantification of, 2:231 sources of, 2:231–232 maize ae wx double mutant, 4:429, 4:429t GEMS-0067, 4:427–428 starch noodles, 3:70 Restriction fragment length polymorphism (RFLP), 4:365, 4:378, 4:380 Retrogradation, starch amylose and amylopectin, 2:204 determination of, 2:204 DSC techniques, 2:204–205, 2:205f metastable and nonequilibrium systems, 2:204 starch-based food products, 2:204 Reverse genetics, 4:401 Reverse osmosis (RO), 3:483 RFLP. See Restriction fragment length polymorphism (RFLP) RFO. See Raffinose family oligosaccharides (RFO) Rheology, 2:254 baking industry, 3:343, 3:344t descriptive empirical tests, 3:344–345, 3:347t dynamic oscillation method, 3:345–347 extensional flow measurements, 3:347–349 fundamental test methods, 3:345 history, 3:343–344 intuitive assessments, 3:343–344 physical properties, 3:343 proof and baking, 3:350–352 sheeting/rolling process, 3:350 definition of, 3:343 Rice African rice (see African rice) AfricaRice, 1:433 allergy, 2:74 amino acid, 1:126–127, 1:127t amylose content, 1:128 Asian rice (see Asian rice) in Australia delivery, 1:413–415 farming operations, 1:413–415 medium-and long-grain varieties, 1:415 production, 1:410t, 1:413, 1:415t yields, 1:413–415, 1:416t beriberi, 2:80, 2:80f, 2:81t bran, 3:447t, 3:448–449 in Brazil, 1:423 breeding cross-breeding, 4:307

flowchart of, 4:307, 4:308f genetic engineering, 4:309 grain quality and improved nutrition, 4:305–306 high yield and wide adaptability, 4:304–305 induced mutation, 4:307–309 MAS, 4:309–310 plant type, 4:306–307 stable yield, 4:305 stress factors, 4:306 tissue culture, 4:309 brokens dry-milled flour, 3:447t, 3:448 molded and extruded snack foods, 3:448 small brokens, 3:448 wet-milled flour, 3:447t, 3:448 brown rice, 3:446–447, 3:447t by-products hulls, 3:452 straw, 3:452 trash, 3:451 Chinese food uses arare, 3:112f bowl rice curd, 3:114 breakfast rice cereals, 3:114 canned rice, 3:114 easy-to-cook brown rice, 3:114 Fa-Kuo, 3:114 gun-puffing cake, 3:111–112 Guo-Ba, 3:113 Mi-Hua-Tung, 3:112–113 milling and starch isolation, 3:110, 3:111f mogi, 3:113 Nien-Kuo, 3:113, 3:113t parboiled rice, 3:114 rice bran oil, 3:114 rice cracker, 3:114 rice noodles (see Rice noodles) senbei, 3:112f starch, preparation of, 3:110–111 yeast-fermented rice cake, 3:114 Chinese rice wine (see Chinese rice wine production) CIAT, 1:433 in Colombia, 1:425 consumption, 1:354f, 1:355, 2:32, 3:166, 3:167t cracker, 3:114 cultural uses of, 2:39 diseases, 4:75, 4:76t diversity of, 1:80–81, 1:81f domestication, 1:93 dry milling and nutrition effect anatomical structure of, 1:45–46, 1:45f bran layers, 1:46–47, 1:46f cracking, 1:46 embryo, 1:47 endosperm, 1:47, 1:47f eating quality chemical basis of, 3:170–171 criteria for, 3:170, 3:170–171t

Index descriptive sensory analysis, 3:166–168, 3:167t genetic basis of, 3:171–173 improvement of, 3:173–174 instrumental texture analysis, 3:168, 3:168f physicochemical property analysis, 3:168–169, 3:169f in Ecuador, 1:425 energy digestibility, 1:127–128 essential fatty acid content, 1:128 in Europe cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t exports, 1:352f, 1:355 extruded snacks, 3:419 forms/races, 1:20 fortification methods for, 2:45 voluntary and mandatory, 2:47, 2:48t genome-wide association study, 4:405 genomics, 4:361 cooking temperature, 4:363 fragrance, 4:362–363, 4:363f global distribution, 1:125 GMO, 1:5 grading, 1:126 in Guyana, 1:425 handling, 1:126 imports, 1:353f, 1:355 India, production in, 1:367–369, 1:368f IRRI, 1:430–431, 1:433 Japanese rice (see Sake’ brewing) marker-assisted selection, 4:405–406 milling, 1:126, 3:449–450, 3:449f brown rice grading, 3:450 cleaning, 3:450 color sorting, 3:451 hulling, 3:450 packaging, 3:451 physical categories, 3:446 warehousing, 3:451 whitening, 3:450–451 white rice grading and blending, 3:451 morphology, 1:55–57, 1:57t, 1:57–58f in North America area distribution, 1:391, 1:392f average yield, 1:399 consumption and trade, 1:399–400, 1:399t harvested area, 1:391, 1:392f, 1:399t production in, 1:391, 1:392f, 1:399–400, 1:399t paddy parboiled rice, 3:446, 3:447t popped rice, 3:446, 3:447t receival and storage, 3:449 phytic acid content, 1:128 processing and food uses, 1:128–129 protein, 1:126, 1:127t, 2:105f, 2:106

QTL (see Quantitative trait loci (QTL)) quality, 3:257 SBE, 2:186 starch noodles, 3:64, 3:65f structure of, 1:125, 1:126f Suriname, 1:426 true digestibility, 1:127–128 uses of, 3:1, 3:2t, 3:258t varieties, 1:125 in Venezuela, 1:427 white rice, 3:447–448, 3:447t world production, 1:350t, 1:351f, 1:354 Riceland Foods Cooperative, 3:453 Rice milk, 3:448 Rice noodles Bi-Tai-Ba, 3:114 Ho-Fen, 3:114 Mi-Fen, 3:113 Rice oil, 2:265 by-products, 3:455 commercial utilization, 3:455–456 for cooking, 3:455 defatted rice bran, 3:453–454 extraction, 3:454 fatty acid composition of, 3:456, 3:456t germ, 3:453, 3:454f in India, 3:453 in Japan, 3:453 in mayonnaise, 3:455 production, 3:453 quality factors for, 3:456, 3:456t refining, 3:454–455 stabilized bran, 3:453 Rice pudding, 3:447 Rodenticides, 4:103 Rolled wafer cones, 3:54–55, 3:55f Rolled wafer sticks, 3:56 Roller milling, 3:301–302 all-roller flour mill, 3:301 barley cooked and dried grain product, 3:444–445 extrusion cooking, 3:445 fiber-rich fractions and enriched FRF, 3:440–445, 3:441–443f, 3:442t ground barley, air classification, 3:443–444 hydrothermal processing, 3:445 wheat milling equipment, 3:440 capacity of, 3:302 double high roller mills, 3:302 in Europe, 3:301–302 history of, 3:301 porcelain rolls, 3:301–302 steel rolls, 3:301–302 wheat, 3:307, 3:311–312, 3:311f Root rot, 1:320 ROS. See Reactive oxygen species (ROS) Rotary rack ovens, 3:329 Rothamsted Research, 1:440 Roti-making process, 1:195–196, 1:196f Round-top bread, 3:12, 3:12f Royal Agricultural Society of England, 1:436

521

RTE cereals. See Ready-to-eat (RTE) cereals Rubbing technique, 1:205 Rugosus, 2:179–180 Rum, 3:198 Russell lupin, 1:280 Russian Academy of Agricultural Sciences, 1:442 Russia, Ukraine, and Kazakhstan (RUK), 4:2f, 4:3, 4:7, 4:14 Rust spores, 1:263 RVA. See Rapid Visco Analyzer (RVA) Rye agronomy, 1:163–164 American whiskey, 3:198 Australia, production in, 1:410t, 1:415–416t, 1:417 (1!3, 1!4)-b-D-glucans, 2:210 botanical classification, 1:159 bread, 3:14, 3:260 bread making, 1:165–166 Canadian whiskey, 3:198, 3:201 carbohydrates, 3:260 composition and nutritional properties, 1:161–163, 1:164t cultural uses of, 2:40 diseases, 4:75, 4:76t diversity of, 1:77f, 1:78t, 1:82 domestication, 1:93 in Europe bread making, 1:388 cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t, 1:386, 1:386t flour grade in Germany, 1:165, 1:166t in North America, 1:165, 1:165t genetics, 1:163 gluten-containing cereals, 2:91–92, 2:94 morphology, 1:57t, 1:62, 1:64–65f origin and history, 1:159, 1:160t plant and grain morphology color, 1:160, 1:162f inflorescence, 1:160 kernels of wheat, 1:160, 1:162f maturity, developing grains, 1:160, 1:162f morphology, 1:160–161, 1:163f stages of maturity, 1:160, 1:161f zigzag-shaped rachis, 1:160, 1:161f plant breeding, 1:163–165 prolamins, 2:72–73 protein, 2:104, 2:105f quality criteria, 3:260 sour dough recipes and methods single-phase, 3:28 three-phase method, 3:27 two-phase method, 3:27–28 uses of, 1:166, 3:1, 3:2t, 3:258t world production, 1:159, 1:160–161t, 1:356, 3:260 Rye ergot alkaloids, 2:291, 2:292f

522

Index

S Saddle stones, 3:300, 3:307, 3:308f Safflower agronomic practices, 1:254–256 bitter compounds, 1:258 in bloom, 1:254, 1:255f fatty acid components, 1:223t, 1:224, 1:255 food colorant and dye, 1:254 nonsaponifiable components, 1:256 oil and protein content, 1:222, 1:222t, 1:224, 1:255 phenolic components, 1:256–257 seed, 1:254, 1:255f stock feed, 1:224 taxonomy and morphology, 1:254–255 traditional Chinese medicine, 1:254, 1:258 uses, 1:222, 1:222t, 1:257 world production, 1:225t, 1:225f, 1:226 Sake brewing Koji production, 3:207, 3:207t, 3:207f moto production, 3:207, 3:208t rice wine production, 3:207–209, 3:208f, 3:209t Seimaibuai classification, 3:206, 3:207t 2S albumins characteristics, 2:115, 2:116t disulfide bonds, 2:111 endomembrane system, 2:115–116, 2:117t nutritional quality, 2:112 oilseed rape structure, 2:111–112 proteolytic processing, 2:111–112 trivial names, 2:115, 2:116t two-chain structures, 2:112 vacuoles, 2:118 Saltines, 3:48 Salt, in grain-based foods cardiovascular ailments, 3:396 cereal processing, role in, 3:397–398 dietary guidelines on, 3:396 elevated blood pressure, risk factors for, 3:396 high-fiber grain, use of, 3:402 human diets, reduction in, 3:396 as ingredient/processing aid, 3:396 inhomogeneous distribution, 3:400–401, 3:401f levels of, 3:396–397, 3:397t microbial shelf life stability, 3:397, 3:399–400 partial substitution, 3:400, 3:401t product microstructure and texture, 3:397–399, 3:399f snacks and cereals, reduction in, 3:401 ‘stealth’ approach, 3:400 taste and flavor, 3:397, 3:398f San Francisco sourdough boule, 3:14, 3:14f, 3:26 Saponins, 2:280 Saskatoon Research Centre, 1:439 Saudi Grain and Fodder Company (SGFC), 4:24

Savory crackers, 3:39 Sawa millet, 1:199, 1:200f, 1:200t SBE. See Starch branching enzymes (SBE) Scanning electron microscopy (SEM), 3:389–390 Scientific societies AACCI (see American Association of Cereal Chemists International (AACCI)) activities of awards, presentation of, 1:457, 1:458f check samples, 1:457 information, dissemination of, 1:457 lectures, 1:457, 1:458f poster presentations, 1:457, 1:458f trade exhibits, 1:457, 1:458f AGSA, 1:457–458, 1:461 American Society of Agronomy, 1:458, 1:461 AOAC International, 1:458, 1:462 AOCS, 1:462 CCOA, 1:457–458, 1:460–461 Celiac societies, 1:462–463 Crop Science Society of America, 1:458, 1:461 Grains for Health Foundation, 1:462 HEALTHGRAIN Forum, 1:462 ICC (see International Association for Cereal Chemistry (ICC)) ISTA, 1:458, 1:461 Soil Science Society of America, 1:458, 1:461 Sclerotinia, 4:228 ‘Scotch Finger’ biscuit, 3:44, 3:45f Scotch whisky, 3:197–198 blending and bottling, 3:203 environmental strategy, 3:203–204 historical background, 3:195 malted barley, 3:195–196 maturation, 3:193 Scotland in oak barrels, 3:194–195 taxation, 3:195 Scuba rice, 1:433 Scutellum, 2:270 SDOs. See Standardization organizations (SDOs) SDS. See Slowly digestible starch (SDS) SDS-PAGE. See Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) Secale cereale L. See Rye Secoisolariciresinol diglucoside (SDG), 2:3–6 Secondary triticales, 1:168 Seed and grain biotechnology companies, 1:452, 1:453t Seed-borne diseases, 4:75 Seed storage proteins albumins (see 2S albumins) globulins (see Globulins) glutenin polymers, wheat, 2:119–120 legumes, 2:113 oilseeds, 2:113 prolamins cereal, 2:118 characteristics, 2:115, 2:116t

endomembrane system, 2:115–116, 2:117t trivial names, 2:115, 2:116t protein bodies, 2:119, 2:119f protein synthesis, 2:115, 2:116t pseudocereals, 2:114 regulation of environmental control, 2:120, 2:121f gene expression, 2:120–121 temporal regulation, 2:120 tissue specificity, 2:120 sedimentation equilibrium, 2:115 Selective precipitation procedure, 1:245 Semiarid Prairie Agricultural Research Centre, 1:439 Semisweet biscuit, 3:39, 3:39t Senbei, 3:112f, 3:448 Sensors, 4:165–166 Sensory evaluation affective/consumer testing, 3:147–149 comprehensive consumer testing, 3:150, 3:151f consumer selection, 3:149 preference tests, 3:149–150, 3:149f cereal-based products, 3:150–152 definition of, 3:144 descriptive analysis line-scale ballot, 3:147, 3:148f rice, eating quality of, 3:166–168, 3:167t screening, 3:145–146 training, 3:146–147, 3:147t discrimination testing duo–trio test, 3:150, 3:152f paired comparison test, 3:150 triangle test, 3:150, 3:151f and instrumental testing, 3:152 noodles (see Noodles) sample preparation, 3:145 sample presentation, 3:145 testing booths, 3:145, 3:146f Sentmanat extensional rheometer (SER), 3:348, 3:349–350f, 3:350 Septoria leaf blotch, 1:122, 1:177–178 Septoria nodorum blotch (SNB) fungicide, 4:273–274 GFG hypothesis, 4:274–275 HSTs, 4:275 necrotrophic effectors, 4:274–275 quadratic check, 4:275 rain splash of spores, 4:273–274 in Western Australia, 4:273 Septoria tritici blotch (STB), 4:276–277 Sequence tagged site (STS) markers, 4:366, 4:423 SER. See Sentmanat extensional rheometer (SER) Serpentine oven, 3:372, 3:372f Sesame oil, 2:264–265 Sesame seed fatty acid components, 1:223t, 1:224 oil and protein content, 1:222, 1:222t, 1:224 uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226 Setaria italica. See Foxtail millet

Index SFE. See Supercritical fluid extraction (SFE) Short-chain fatty acids (SCFAs), 2:11, 2:14, 2:232 Short doughs, 3:47–49 Short-straw naked (dwarf) wheats, 2:24 Shredded cereals, 3:264 Silothermometry, 4:107 Simple sequence repeats (SSRs), 4:366 Simultaneous buying and selling (SBS), 4:23 Simultaneous saccharification and fermentation (SSF), 3:239–240 Single-layered flatbreads barbari bread, 3:20 chapatis, 3:19–20 lavash, 3:20 saaj, 3:20 tanoor/tandoor bread, 3:20 Single-nucleotide polymorphism (SNP), 3:172–173, 3:173f, 4:285, 4:366–368, 4:367f Single seed descent (SSD), 1:327–328, 4:290 Sitotroga cerealella. See Angoumois grain moth Size exclusion chromatography (SEC), 2:199, 3:168 SKCS 4100. See Perten Single-Kernel Characterization System (SKCS) 4100 Skin prick tests (SPTs), 2:75 Slowly available glucose (SAG), 2:36 Slowly digestible starch (SDS), 3:285 maize, 4:429, 4:429t resistant starch, 2:231 Smith–Lever Act of 1914, 1:437–438 Snack foods coextruded snacks, 3:416f, 3:421–422, 3:422t consumption patterns, 3:414 corn and tortilla chips, 3:416–417, 3:417f definition of, 3:414 expanded snacks baked collets, 3:420, 3:420t fried collets, 3:420, 3:420t third-generation snack foods, 3:420–421, 3:421f extruded snacks (see Extruded snacks) multigrain chips, 3:415f per capita consumption, 3:414 potato chips, 3:415 sales, 3:414 types of, 3:414–415 first-generation snack foods, 3:415, 3:415f second-generation snack foods, 3:415, 3:415f third-generation snack foods, 3:415, 3:416f SNB. See Septoria nodorum blotch (SNB) SNF. See Swedish Nutrition Foundation (SNF) SNP. See Single-nucleotide polymorphism (SNP) Soap stock, 3:494 Soba, 3:72 Society of Rheology, 3:343–344 Soda crackers, 3:39, 3:40t, 3:48 Sodium acid pyrophosphate (SAPP), 3:359

Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), 2:109, 2:147–148, 4:34–35, 4:35f Soft wheat cakes, 3:4 chemically leavened crackers, 3:4 cookies, 3:4 dry milling, 3:315 uses of, 3:258t Soil-borne diseases, 4:75 Soils and Crops Research and Development Centre (SCRDC), 1:439 Soil Science Society of America (SSSA), 1:458, 1:461 Soil suppression, 4:260 Solid fat index (SFI), 3:40–41 Solvent retention capacity (SRC) tests, 3:254 Sorghum abiotic stress tolerance, 4:201 adaptation of, 1:154–155 Africa, production in, 1:360t, 1:361 allergy, 2:74 as animal feed, 1:157–158 appearance and genetics, 3:116 area harvested, 1:350t, 1:355–356 in Australia export, 1:417 production, 1:410t, 1:413, 1:415t, 1:417 yields, 1:413–415, 1:416t Bolivia, production in, 1:422 breeding, 1:155–156 germplasm collections and genetic variability, 4:203 for grain quality, 4:204–205, 4:204–205f for grain yield, 4:203–204 for host-plant resistance, 4:202–203 pure-line cultivars, 4:203 QTL, 4:203 seed parents, 4:203 sorghum conversion program, 4:203 for stress tolerance, 4:205 test-cross evaluation, inbred lines for, 4:203 yield potential, improvements in, 4:203 broom head, 1:153 cleaning, 4:56, 4:56f climate change, 1:158 commercial hybrid seed production, 4:201 composition, 1:156–157 cultural uses of, 2:40 diseases, 1:156, 4:75, 4:76t, 4:202–203 diversity of, 1:77f, 1:78t, 1:82 domestication, 1:93–94, 1:94f drying, 4:55 in Ecuador, 1:425 enzymes, 3:119, 3:119t ethanol production, 1:158 exports, 1:355–356 as feed grain, 4:201 fiber, 3:117, 3:119t food uses, 1:157, 1:157f, 3:120–122, 3:121f forage, 1:153

523

genomics, 4:361 global production, 1:153–154, 1:155t, 1:155f grading and classification, 3:116 grain colors, 1:156, 1:157f harvesting, 4:54–55, 4:55f, 4:201 hybrid yield trial, 4:201, 4:202f imports, 1:355–356 industrial uses, 3:122 insect damage, control of, 4:58–59 LAB fermentation injera, 3:186–188, 3:186t, 3:188f motoho oa mabela (see Motoho oa mabela) ting, 3:186t, 3:189, 3:189f lager beer, 3:122 lipids, 2:250, 2:251t, 3:119, 3:119t livestock feed, 3:116, 3:123 milling, 3:120–122 minerals, 3:119, 3:119t in North America (see North America) nutrient requirements, 4:202 nutritional value, 3:122–123 opaque beer, 3:122 ORAC level, 3:119–120, 3:120t outcrossing, 4:201 in pelleted rations, 1:158 pests, 1:156, 4:202–203 plant height and maturity, 4:201, 4:202f protein content of, 3:117–119, 3:119t pure-line varieties, 4:202 quality, 3:259 red grain, in South Texas, 4:201, 4:202f self-pollinated varieties/hybrids, 4:202 silage production, 1:153 soil temperatures, 4:202 soluble sugars, 3:117, 3:119t Sorghum bicolor, 1:153, 1:154f species, 4:201 starch, 3:117, 3:119t storage (see Storage) structure and physical properties, 3:117, 3:118f tannins and phenols, 3:119–120, 3:119t threshing, 4:55–56, 4:56f treatment, 4:56 uses of, 1:153, 3:258t vitamins, 3:119, 3:119t world production, 1:350t, 1:355–356 yield, 1:350t, 1:355–356 Sorghum bicolor, 1:153, 1:154f Sorghum conversion program, 1:155 Sorghum ergot, 1:156, 2:292, 2:293f Sorghum midge, 1:156 Sour dough breads, 3:3, 3:14, 3:14t flavor profiles, 3:26 manufacture of, 3:25 mold-free shelf life, 3:28 principle of, 3:25 processing impacts, 3:26 recipes and methods rye sour dough, 3:27–28 wheat sour dough, 3:27 starter/mother dough, 3:25–26 wild yeast spores, 3:25

524

Index

South America Argentina (see Argentina) average yields, 1:420, 1:421t Bolivia, 1:422 Brazil, 1:422–424, 1:424f Chile, 1:424 Colombia, 1:424–425 diet, cereal component of, 1:420, 1:422f Ecuador, 1:425 French Guyana, 1:425 grain-cultivated area in, 1:420, 1:421t grain production in, 1:420, 1:421t grains research in, 1:448–449 Guyana, 1:425 nutrition and food security, 1:427 Paraguay, 1:425–426 pasta consumption in, 1:427, 1:427f Peru, 1:426 Suriname, 1:426 Uruguay, 1:426 Venezuela, Bolivarian Republic of, 1:426–427 wheat, agronomic practices for, 4:182, 4:182t Soxhlet method, 1:222 Soybean deodorizer distillate (SBDD), 3:494, 3:494t Soybean oil, 1:232f composition of, 3:489, 3:490t deodorizer distillates, composition of, 3:494, 3:494t fatty acid composition of, 3:489, 3:491t food uses of, 1:234 margarine and shortening, 3:495–496 mayonnaise, 3:495–496 salad/cooking oils, 3:495 salad dressings, 3:495–496 lecithins, 3:493–494, 3:494t mechanical pressing, 3:489–490 oxidative quality of, 3:494–495 phytosterols, 3:494 refining, 3:491f bleaching, 1:232–233, 3:492 degumming, 1:232–233, 3:492 deodorization, 1:232–233, 3:492 goal of, 3:490 hydrogenation, 1:232–234, 3:492–493 inter-esterification, 1:232–233, 3:493 minor components, changes in, 3:490, 3:492, 3:493t neutralization, 1:232–233, 3:492 oil quality, changes in, 3:492, 3:492t winterization/fractionation, 1:232–233, 3:493 soap stock, 3:494 solvent extraction, 1:232, 3:489–490 tocopherol content of, 3:494, 3:495t trans-fatty acids, 1:234 world production, 3:489, 3:490f Soybeans, 1:229f, 1:405 agronomic characteristics, 1:229–230, 1:230f as animal feed, 1:235 aqueous extraction process, 1:233 biological active components, 1:231

Bolivia, production in, 1:422 and bone health, 2:21 breeding cultivars, 4:338 hybrid soybean, 4:339–340 marker-assisted selection, 4:339 methodology, 4:338–339, 4:339f objectives, 4:338 seed composition, 4:338 in Canada area harvested, 1:402t, 1:405 disposition and consumption, 1:404t, 1:406 production, 1:403t, 1:406 and cancer, 2:20–21, 2:21f carbohydrates, 2:17 and CHD, 2:19–20, 2:20f chemical composition, 1:230–231, 1:230f composition of, 3:124, 3:134, 3:135t crude fiber content of, 4:25 cultivar adaptation, 4:253–254, 4:254f defatted meal, 1:232f, 1:233 in diet, 2:19 digestive enzyme inhibitors, 2:18 diseases, 4:255–256 dry extrusion, 1:233 in Europe consumption and food supply quantity, 1:389, 1:389t production in, 1:386–387, 1:387–388t exports, 1:357 fat, 2:17 fatty acid compositions, 1:223, 1:223t, 4:25 fiber, 2:18 filamentous fungi, 3:124 food products, 1:357 genetically modified soybeans, 3:142 genetic engineering, 4:25 genetics bioinformatics and data resources, 4:340–341, 4:341t cytogenetics, 4:340 molecular genetics, 4:340 qualitative genetics, 4:340 transformation, 4:341 germplasm collections diversity, 4:333, 4:337t gene pools, 4:333, 4:338f Glycine max, 4:333, 4:335t glycine perennial collections, 4:333, 4:336t germplasm utilization cultivated soybean, 4:335 Glycine max, 4:336–337 Glycine soja, 4:336 perennials, 4:335–336 plant breeders, 4:334 GM grains, 4:350–351 goitrogens, 2:18 grading standards, 4:27–28, 4:27t grain quality specifications, international trade, 4:83, 4:86t health benefits, 1:232 as industrial materials, 1:235

insects, 4:256 isoflavones, 2:18–19, 2:19f, 4:25 lectins, 2:18 line spacing, 4:253 lipids, 4:26, 4:26t meal, 1:357, 4:25 production, 1:222 uses of, 1:223 and menopausal symptoms, 2:21–22 in Mexico area harvested, 1:403t, 1:405 disposition and consumption, 1:405t, 1:406 production, 1:404t, 1:406 minerals, 2:17, 2:18t, 2:18f miso (see Miso) modern processing, 1:232–233, 1:232f natto¯ (see Natto¯) in North America area harvested, 1:403t, 1:405 disposition and consumption, 1:405t, 1:406 production, 1:404t, 1:406 nutrients, 1:231–232, 4:254–255, 4:255f oil, 1:222, 1:222t, 2:258t, 2:263 okara (see Okara) origin, 1:228–229, 4:333, 4:334f in Paraguay, 1:425–426 phytic acid, 2:18 phytochemicals, 4:25 planting date, 4:252–253, 4:253f protein, 1:222, 1:222t, 1:234–235, 2:17, 3:134, 3:135f, 4:25–26, 4:26t proximate analyses, 4:26–27 research, 1:228 rotation, 4:255, 4:255f screw pressing/expelling, 1:233 seed and seed quality, 4:251 seed composition, 3:489, 3:490t seedings, 4:251–252, 4:252f soybean oil (see Soybean oil) soy concentrates and isolates (see Soyprotein concentrates and isolates) soymilk (see Soymilk) soy nuggets, 3:125 soy sauce (see Soy sauce) sufu (see Sufu) sugar content of, 4:25 tempeh (see Tempeh) tillage, 4:254 tofu (see Tofu) traditional soyfoods, 1:228–229, 1:229f, 1:233–234, 1:233f in United States area harvested, 1:402t, 1:405 disposition and consumption, 1:405t, 1:406 production, 1:404t, 1:406 in Uruguay, 1:426 uses of, 1:222, 1:222t vitamin and mineral content of, 2:17, 2:18t, 2:18f, 3:134, 3:135t weed management, 4:256 western soyfoods, 1:235, 1:235f

Index world production, 1:225t, 1:225f, 1:226, 1:228, 1:229f, 1:247, 1:248t, 1:356t, 1:357, 1:357f, 4:251, 4:252f, 4:256, 4:333, 4:334f, 4:334t yields, 4:252f Soymilk, 1:228–229, 1:229f, 1:233, 1:233f dairy analogs, 3:139 gross composition, 3:134, 3:135t meat analogs, 3:139 mineral and vitamin contents, 3:134, 3:135t okara (see Okara) production method commercial integrated production systems, 3:135 Cornell method, 3:134 deodorization step, 3:135 flavor development, 3:134, 3:136f full fat soy flake method, 3:135 hydration, 3:135–137, 3:137f Illinois method, 3:134 Japanese method, 3:134, 3:136f rapid hydration hydrothermal cooking method, 3:135 traditional Chinese method, 3:134, 3:136f soy beverage, 3:139 sufu (see Sufu) tofu (see Tofu) yogurt, 3:127 yuba (see Yuba) Soy nuggets, 3:125 Soy-protein concentrates and isolates, 3:487 antinutritional factors, 3:485 blood cholesterol, lowering of, 3:485 cancer, prevention of, 3:485 diabetes and obesity, 3:485 digestibility values of, 3:484 essential amino-acid composition of, 3:484, 3:484t foods and ingredients, 3:487 functional properties of, 3:485t emulsification and foaming, 3:486 fat binding, 3:486 film formation, 3:486 gelation and viscoelastic properties, 3:486 solubility, 3:486 texturization, 3:486–487 water hydration and binding, 3:486 in infant formula, 3:485, 3:487 mineral content of, 3:484, 3:484t PER values of, 3:484–485 production of, 3:482–483, 3:483f proximate composition of, 3:483–484, 3:483t Soy sauce, 1:228–229, 1:229f, 1:233–234, 1:233f, 3:130t chiang yu, 3:127 composition of, 3:127–131, 3:128t koikuchi shoyu, production of, 3:128, 3:129f koji production, 3:129, 3:130f moromi stage, 3:129–131, 3:130f Specialty maize, 3:98, 3:99t, 3:103f

Spelt wheat, 1:386, 2:38 Split-run milling, 3:314, 3:316f Spot market, 4:11 SPP. See Sucrose phosphatase (SPP) Spring wheat, 4:176 Sprouted grain, 2:302 SPS. See Sucrose-phosphate synthase (SPS) Squalene, 2:259, 2:262 SSD. See Single seed descent (SSD) SSRs. See Simple sequence repeats (SSRs) Stabilized starch, 3:282–284 Stagonospora nodorum, 4:391 Staling, baked products antistaling strategies, 3:405–406 cake staling, 3:404 definition, 3:403 DSC, 3:403–405 DTA, 3:405 flour proteins, crumb staling, 3:404 FTIR spectroscopy, 3:405 intermediate-moisture product, 3:404 low-moisture baked products, 3:404 moisture migration, 3:404–405 pulsed-NMR methods, 3:405 sensory evaluation analysis, 3:405 starch, 3:403–404 time-domain NMR analysis, 3:405 uniaxial compression analysis, 3:405 x-ray diffraction, 3:405 Standardization organizations (SDOs), 4:356 St. Anthony’s Fire, 2:290–291 Starch, 2:165–166t, 3:6 adhesives, 3:276–277 ADPG pyrophosphorylase, 2:183–184, 2:184t a-1,6 bonds, 2:174, 2:175f amaranth, 1:289–291, 1:291t amylopectin (see Amylopectin, starch) amyloplasts, 2:190 amylose (see Amylose, starch) backbone of, 2:169 barley and wheat, 2:181–182, 2:182t biosynthesis enzymes, 2:183, 2:183f protein interactions, 2:187 UDP, 2:183 biosynthesis of, 2:168–169 buckwheat, 1:311 in ceramics, 3:277–278 chemicals, 3:278 commercial sources of, 3:282 composition and properties of, 3:274, 3:276t debranching enzymes, 2:186 degradation, 2:171 D-enzyme/disproportionating enzyme, 2:186 D-glucopyranose, 2:174, 2:175f in Europe, 1:388, 1:389t food and nonfood industries, 2:198 food uses of, 3:279–280, 3:279t gelatinization, 3:274 amylose-lipid complex, 2:201–202 endotherm, 2:200–201, 2:201f food applications, 2:200–201

525

helix-coil transition, 2:200–201 parameters, 2:201–202, 2:201–202t side-chain liquid crystalline, 2:200–201 starch-water interaction, 2:200–201 sugar concentration, 2:200–201 gelatinization temperature, 2:182 genes and genetics in wheat, 2:187, 2:187–188f glucopyranose residue, 2:174, 2:175f glycogenin, 2:187 granules, 2:199t, 2:200 industrial products, 3:275, 3:277t isoforms, 2:186–187 linear-chain amylose, 2:168 a-1,4 linked glucan, 2:174, 2:175f lipid content, 2:182 maize, 1:100, 2:181–182, 2:182t modification (see Modified starch) molecular markers and rapid breeding technologies, 2:188 morphology, 2:190, 2:191f mutants, 2:169 in oil-field applications, 3:278 in paper production color coating, 3:275–276 corrugated board, 3:276 paper bags and sacks, 3:276–277 paper coating, 3:275–276 surface sizing, 3:275 wet-end internal sizing, 3:275 paste properties of, 2:202–203, 2:202–203f, 2:204t, 3:279–280, 3:280t viscosity, 3:274, 3:276f photosynthetic/nonphotosynthetic, 2:181 plastic-like materials, 3:278–279, 3:278f polyhydroxy compounds, 3:278 reserve, 2:181 resistant, 2:181 retrogradation (see Retrogradation, starch) rheological methods, 2:206, 2:206t rice, 2:181–182, 2:182t, 3:110–111 R1 protein, 2:187 SBE, 2:185–186 semicrystalline structure, 2:194–196, 2:195–196f sorghum, 3:117, 3:119t swelling and solubility, 2:203–204, 2:204t synthases, 2:185 in textile industry, 3:278 transgenic technology, 2:188 transitory, 2:181 waxy starches, 2:182 wheat wet milling A-starch and B-starch, 3:320, 3:323 food and industrial uses, 3:324 gravity of, 3:320 modification, 3:323 particle sizes, 3:320, 3:323 world production of, 3:274, 3:275f x-ray analysis, 2:205–206, 2:205t x-ray diffraction, 2:181 Starch branching enzymes (SBE), 2:185–186, 4:427

526

Index

Starch-debranching enzymes (DBE), 2:169, 2:171 Starch noodles Asian noodles, category of, 3:64 cereal flours and starches, 3:66 drying, 3:70 full gelatinization, 3:67–69 general procedure for, 3:67, 3:67f legume starches, 3:64, 3:66 maize starch noodles, 3:64, 3:65f, 3:66, 3:68f mixed substrates, 3:66–67 nonwheat/gluten-free noodles, 3:64 nutritional benefits, 3:70 partial gelatinization, 3:67 potato jelly noodle production, 3:67, 3:69f purified starch, 3:66 retrogradation, 3:69–70 rice flat noodles, 3:64, 3:65f root crops, 3:66 shape formation, 3:67 starch sheet wrappers, 3:65–66 sweet potato starch noodles, 3:64–65 vermicelli, 3:64 Starch synthases (SSs), 2:185 State agricultural universities (SAUs), 1:447 Steam baking, 3:332 Steamed breads, 3:3 Steam pipe effect, 3:328, 3:328f Steeping, maize, 3:469f BCFM, 3:468 chemical and biochemical reactions, 3:467–468 commercial sequence, 3:468 induced mechanical stresses, 3:467–468 lactic acid-dominated stage, 3:468–469 leaching, and kernel hydration, 3:467–468 quality, 3:468 sulfur dioxide diffusion stage, 3:470 sulfur dioxide reaction stage, 3:470–471f, 3:471 tank of, 3:468, 3:470f Stem nematode, 1:178, 1:180f Stemphylium blight, 4:229 Stenodiplosis sorghicola, 1:156 Stinking smut, 4:71 Storage barley admixture, 4:52 controlled-atmosphere storage, 4:52 dormancy, 4:51–52 environmental contaminants, 4:51 germinability, 4:51 hazards, 4:51 insect/microbial infestations, 4:52 moisture content and temperature, 4:51–52, 4:51f preharvest sprouting, 4:52 treatments, 4:52 canola functions of, 4:65 heating, 4:66 requirements for, 4:65 seed moisture and temperature content, 4:65–66, 4:66f storage structures, construction of, 4:65

chickpea, 4:221 country elevators, 4:105 driers, types of, 4:107 dry beans, 1:304–305 flat storage of cereals, 4:106 grain collection, 4:105, 4:106f grain handling and control, equipment for, 4:105–106 grain quality, 4:106 high-temperature drying, 4:107 insects, control of, 4:107–108 low-temperature drying, 4:107, 4:107f modified-atmosphere storage, 4:107 moisture, monitoring of, 4:106–107, 4:106f natural drying method, 4:107 on-farm storage, 4:105 sorghum Angoumois grain moth, 4:57–58, 4:58f containers for, 4:56–57, 4:57t large grain borer, 4:57–58, 4:58f methods of, 4:56, 4:57t objective of, 4:56 structures, 4:57, 4:57f weevils, 4:57–58, 4:58f terminal elevators, 4:105, 4:106f wheat in Argentina, 4:14 in Canada, 4:12, 4:12f circular silo, 4:47f horizontal storage silo, 4:47f, 4:48 on-farm storage, 4:48 stability, 4:48 in United States, 4:12 vertical silo storages, 4:47f, 4:48 Stored-grain pest management combined methods, 4:136 computer-aided decision systems, 4:137–138, 4:137–138f fungi species, 4:128, 4:128–129f inert dust formulations, 4:135–136 insect pest control (see Insect pest control) insect species, ecophysiological characteristics of, 4:126–128, 4:127t IQM, 4:136–137 mechanical impact, 4:135 pneumatic conveying, 4:135 postharvest losses, 4:126–128 spoiled grain, decontamination of, 4:136 Stress signaling, wheat, 4:396 STS markers. See Sequence tagged site (STS) markers Substituted secondary triticales, 1:168 Sucrose phosphatase (SPP), 2:165 Sucrose-phosphate synthase (SPS), 2:165 Sucrose synthase (SucS), 2:165 SucS. See Sucrose synthase (SucS) Sufu color and flavor types of, 3:127 definition, 3:125–126 fermentation types, 3:127 gross composition, 3:125t mold stage, 3:126–127 production of, 3:126, 3:126f salting stage, 3:127

Sunflower annual Helianthus species, 1:247–248, 1:249f biodiesel, 1:251 birds, 1:251 in Canada area harvested, 1:402t, 1:407 disposition and consumption, 1:404t, 1:408 production, 1:403t, 1:407–408 confectionery sunflower, 1:252 deodorizer distillates, composition of, 3:494, 3:494t diseases, 1:250 Europe, production in, 1:387, 1:388t fatty acid components, 1:223t, 1:224, 1:247, 1:248t grain quality specifications, international trade, 4:83, 4:86t high and mid-oleic sunflower oil, 1:251 hulls, 1:251–252 insects, 1:250–251 meal in livestock feeds, 1:251 production of, 1:222 in Mexico area harvested, 1:403t, 1:407 disposition and consumption, 1:405t, 1:408 production, 1:404t, 1:408 in North America animal feed, 1:407 area harvested, 1:403t, 1:407 disposition and consumption, 1:405t, 1:408 production, 1:248–249, 1:249t, 1:404t, 1:408 NuSun™ oil, 1:251–252 oil, 1:222, 1:222t, 1:224, 1:251, 2:258t, 2:263 oleic acid, 1:222 origin of, 1:247 production practices, in United States, 1:248–249, 1:249t, 1:252 protein content, 1:222, 1:222t, 1:224 traditional sunflower oil, 1:251 in United States area harvested, 1:402t, 1:407 disposition and consumption, 1:405t, 1:408 production, 1:404t, 1:408 uses of, 1:222, 1:222t world production, 1:225t, 1:225f, 1:226, 1:247, 1:248t Supercritical fluid extraction (SFE), 2:252 Suppressive soil, 4:260 Suriname, 1:426 Sustainable grain production agricultural and urban biorefinery, 4:150, 4:151f Eco-City, 4:149–150 fresh water, 4:148 gene banks, 4:149 global energy and pollution issue, 4:147–148

Index global plant canopy, 4:147 human diet changes, 4:149 improving and sustaining soil fertility, 4:149 increasing human global dominance, 4:144–145 plant husbandry, 4:148–149 self-organization, 4:145–146 Swathing, 4:62–63, 4:63t Swedish Institute for Food and Biotechnology (SIK), 1:442 Swedish Institute for Food Research (SIK), 1:442 Swedish Nutrition Foundation (SNF), 2:60 Sweet corn, 3:259 characteristics and food uses, 3:98, 3:99t phytoglycogen, 2:176 uses of, 3:1, 3:2t Sweet potato starch noodles, 3:64–65 Synthetic rice, 2:45 Systems thinking, 2:64

T Table tortillas, 3:92–94, 3:93f, 3:106f, 3:107 Taichung Native 1 (TN1), 4:304–305 Tamarind tree, 2:226 Tandoor bread, 3:20 Tannins, 2:286, 2:287f Tan spot (TS) distribution of, 4:273–274 fungicide, 4:273–274 GFG hypothesis, 4:274–275 HSTs, 4:275 QTL mapping, 4:276 quadratic check, 4:275 southern region, 4:273, 4:274f ToxA, 4:275–277, 4:275t, 4:276f ToxB, 4:276 ToxC, 4:276 Tara gum, 2:227 Tasmanian Institute of Agriculture (TIA), 1:444–445 Taxonomy allergic cross-reactions, 1:38–39 Amaranthus caudatus/inca wheat, 1:31, 1:32f classification, 1:33–34 cultivated plant, 1:38 disagreements, 1:37–38 Fagopyrum esculentum/buckwheat, 1:31, 1:32f future trends, 1:39 genus and species names, use, 1:34, 1:35–36t identification, 1:33–34 names origins, 1:32–33f, 1:34 naming/nomenclature, 1:33–34 phylogenetic classifications, 1:31–32 rank and hierarchy, 1:34–36, 1:35–37t Triticum aestivum, 1:31, 1:33f in use, 1:38 TD. See True digestibility (TD) Teff (Tef) chemical composition ash and minerals, 1:213t, 1:215, 1:216t carbohydrate, 1:212–214, 1:213t, 1:214f

fat and fatty acids, 1:213t, 1:215, 1:217t fiber, 1:213t, 1:214 protein and amino acids, 1:214, 1:215–216t vitamins, 1:216, 1:217t cottage-type miller, 1:219–220 cultivation and production, 1:210–211 cultural uses of, 2:38 description, 1:209, 1:210f harvesting and storage, 1:211, 1:212f injera (see Injera) manual harvesting of, 1:362–363, 1:363f marketing, 1:211 name and origin, 1:209–210 pest and disease problems, 1:219 physicochemical properties aleurone layer, 1:212 endosperm, 1:212, 1:214f germ (embryo), 1:212 morphology, 1:211, 1:213f outer pericarp, 1:211 seed coat (testa), 1:211–212 processing cleaning, 1:216 milling, 1:216 tropical cereal, 1:209 Tempeh defects, 3:124–125 gross composition of, 3:125t health benefits of, 3:132 lupins, 1:284 production of, 3:124–125, 3:125f Tempura, 3:4 Test weight (TW), 1:120 Tetraploid wheat, 4:378–379 Textured vegetable protein (TVP), 2:17, 3:139 Texture profile analysis (TPA), 3:168, 3:168f TFAs. See Trans fatty acid (TFAs) Thailand Department of Agriculture (DOA), 1:448 Thailand Institute of Scientific and Technological Research (TISTR), 1:448 The International Union for the Protection of New Plant Varieties (UPOV), 1:51 Thermal cracking, 3:246 Thermal infrared radiation, 4:165 Thermoplastic starch, 3:279 Thiaminases, 2:81 Thiochrome, 2:79 Thomas Burr Osborne Medal, 1:457, 1:458f Timelapse photography, 4:166 Ting, 3:186t, 3:189, 3:189f TN1. See Taichung Native 1 (TN1) Tofu, 1:228–229, 1:229f, 1:233, 1:233f definition of, 3:137 firm and extra firm tofus, 3:137 frozen tofu, 3:137–139 gross composition, 3:134, 3:135t handling, 3:137–139 mineral and vitamin contents, 3:134, 3:135t production of additives, 3:137 coagulants, 3:137, 3:138f quality and yield, factors affecting, 3:137, 3:138t

527

silken tofu, 3:137 Western style foods, 3:139 Tomato spotted wilt virus (TSWV), 1:336–337 Tortilla chips, 3:416–417, 3:417f Tortillas, 3:3 blue maize, 3:98, 3:99t definition, 3:90 history of, 3:90 lime-cooked maize products (see Limecooked maize products) wheat flour tortillas, 3:90–92, 3:91f, 3:95t Total organic matter (TOM), 3:165 Total parenteral nutrition, 2:82 Tournefort, 4:317 Toxicity cereals, 2:87–88 in vivo and in vitro methods, 2:86–87 peptides, 2:88–89, 2:88–89t Trace elements, 4:101 Trade associations, 1:457 Trade exhibits, 1:457, 1:458f Transesterification, 3:245, 3:247–248, 3:247t Trans fatty acid (TFAs), 2:261–262 Transgenic plants, 4:261 Transitory starch, 2:181 Transmission electron microscopy (TEM), 3:390 Trapaceae, 1:277 Traveling tray bread ovens, 3:328, 3:329f Treats, 3:223, 3:224t, 3:226–227 Triangle test, 3:150, 3:151f Trichothecenes, 2:294–295, 2:295f Triglycerides, 2:248–249, 2:249f Triploid endosperm model, 4:427 Triticale, 1:163–164 adaptation, 1:170, 1:170t in Australia, 1:415–416t, 1:417 cultural uses of, 2:40 diversity of, 1:77f, 1:78t, 1:82 in Europe cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t genetic resources, 1:170–171 lipids, 2:250, 2:251t man-made cereal grain crop, 1:168 morphology, 1:57t, 1:60–62, 1:64f octoploid, 1:168, 1:169f origin, 1:168, 1:169f primary triticales, 1:168–169, 1:169t protein, 2:104, 2:105f quality criteria, 3:260 secondary, 1:168, 1:169t substituted secondary, 1:168, 1:169t uses of, 1:170, 3:258t world production, 1:170, 1:170t, 1:171f, 1:356 Triticeae, 1:147–148 Triticum T. aestivum, 4:269. See also Wheat) T. dicoccoides, 1:117 T. dicoccum, 1:117 T. durum (see Durum wheat)

528

Index

Triticum (Continued) T. monococcum, 4:395 T. urartu, 1:117 Trolox equivalent antioxidant capacity (TEAC), 1:257, 3:437–439, 3:440t True digestibility (TD), 1:127–128 TS. See Tan spot (TS) Tunnel oven, 3:372, 3:372f Tweedy, 3:9, 3:11f Two-dimensional difference gel electrophoresis (2-D-DIGE), 2:148 Typhaceae, 1:278

U UCD. See University of California at Davis (UCD) Udon noodles, 3:5 Undergraduate courses. See University courses Uniaxial compression analysis, 3:405 United States Department of Agriculture (USDA), 2:51 United States Environmental Protection Agency (EPA), 4:99 United States Grain Standards Act, 4:6 University courses cereal science/grain science/grain processing, 1:13–14 Feeding the World, 1:14–15 food science and industry major, core courses for, 1:15, 1:15t industry training, 1:15 University of Adelaide, 1:445 University of Alberta, 1:439 University of California at Davis (UCD), 1:168 University of Guelph, 1:439 University of Manitoba, 1:439 University of Melbourne, 1:445 University of New England, 1:445 University of New South Wales, 1:445 University of Queensland, 1:445 University of Saskatchewan, 1:439 University of South Australia, 1:445 University of Southern Queensland, 1:445 University of Sydney, 1:445 University of Tasmania, 1:445 University of Western Australia, 1:445 Uruguay, 1:426 USDA. See United States Department of Agriculture (USDA) USDA Nutrient Database for Standard Reference, 4:433 USDA organic label, 2:58, 2:58t USDA World Wheat Collection, 2:24 US Department of Agriculture (USDA), 1:436 Uusila, 3:186, 3:186t, 3:187f

V Variety identification aim of, 4:39–40 cultivar, 4:30–31

development of, 4:40 DNA-based methods, 4:32, 4:33f basic steps, 4:37 DArT system, 4:38, 4:38–39f gene sequence data, 4:37 genetic markers, 4:36–37, 4:37t lab-on-a-chip CE system, 4:37, 4:38f processed food products, analysis of, 4:38 GM varieties, identity preservation of, 4:31 grain–protein composition, analysis of capillary electrophoresis, 4:35 microfluidic capillary electrophoresis (see Lab-on-a-chip capillary electrophoresis) PAGE method, 4:33–34 SDS gel electrophoresis, 4:34–35, 4:35f grain sampling and statistics, 4:40, 4:40t immunoassay techniques, 4:35–36 malting barley, crossbreeding, 4:30, 4:30f mass spectrometry, 4:35 PBR requirements, 4:31 phenol test, 4:31, 4:33f protein composition, analysis of, 4:32, 4:33f similar appearance, grain samples of, 4:30 visual examination barley varieties, color difference, 4:31, 4:32f image analysis, 4:31 wheat glumes, beak length for, 4:31, 4:32f young wheat plants, auricles of, 4:31, 4:32f wheat varieties, 4:29–30, 4:30t VAT. See Visceral adipose tissue (VAT) Vector-borne diseases, 4:80 Vegetable oils canola, 2:258t, 2:263 coconut, 2:264, 2:265t corn oil, 2:264 cottonseed, 2:258t, 2:263 nut, 2:265 olive, 2:264 palm oil, 2:258t, 2:262–263, 2:262t peanut, 2:264 production, 2:257, 2:258t rice bran oil, 2:265 sesame, 2:264–265 soybean oil, 2:258t, 2:263 sunflower, 2:258t, 2:263 Venezuela, 1:426–427 maize, 1:427 rice, 1:427 wheat, 1:427 Vinegar, 3:178 Viral diseases, 4:172–173, 4:172t Visceral adipose tissue (VAT), 2:26 Viscofiber®, 3:294 Visual analogue scale (VAS), 3:155 Vital gluten, 3:6, 3:322 Vitamins buckwheat, 1:309, 1:309t dry beans, 1:304 flatbreads, 3:23

food fortification (see Food fortification) quinoa, 1:345, 1:345t sorghum, 3:119, 3:119t soybeans, 2:17, 2:18t, 2:18f, 3:134, 3:135t okara, 3:134, 3:135t, 3:139–140, 3:141t soymilk, 3:134, 3:135t tofu, 3:134, 3:135t yuba, 3:134, 3:135t Vodka, 3:198

W WA. See Wild abortive (WA) Wafers batter ingredient ranges, 3:52, 3:53t characteristic features, 3:51 definition, 3:51 end product, 3:56, 3:56t fat-free fruit-type fillings, 3:56 functions, 3:56 higher-sugar wafers, 3:51 ice-cream cone, 3:51, 3:52f in-line manufacturing of, 3:53f batter preparation, 3:52–54 batter transport and depositing, 3:53 conditioning, 3:53–54 cooling and cutting, 3:54 creaming and book building, 3:54 enrobing/molding in chocolate, cooling, 3:54 moisture sorption and wafer texture, 3:53–54 packaging, 3:54 wafer release and cooldown, 3:53 wafer sheet baking, 3:53 low-emission oven, 3:57, 3:57f lower-fat fillings, 3:56 molded wafer cones, 3:54 no- /low-sugar wafers, 3:51 rolled sugar cones, 3:54–55, 3:55f rolled wafer sticks, 3:56 savory wafer products, 3:56 stack oven, 3:57 wafer book, 3:51, 3:52f wafer products, variety of, 3:51, 3:52f Waffles, 3:4 Warp sizing, 3:278 Water-soluble polysaccharides (WSPs), 2:186 Water use efficiency (WUE), 1:151 Waxy maize, 3:98, 3:99t, 3:480, 4:425–427 WDEIA. See Wheat-dependent exerciseinduced anaphylaxis (WDEIA) Weed management chickpea, 4:219 field pea, 4:245–246, 4:245f lentil diversified crop rotations and tillage, 4:227 hand-weeding, 4:227–228 herbicides, 4:228 postemergence harrowing/rotary hoeing, 4:227–228 preseeding spring tillage, 4:227

Index lupin, 4:235–236 organic agriculture, 4:155 soybean, 4:256 Weed seeds, 4:91–92, 4:92f Weevils, 4:57–58, 4:58f Weinheimer one-phase method, 3:28 Wernicke’s encephalopathy, 2:82 Western Australian State Agricultural Biotechnology Centre (SABC), 1:444–445 Wet-end internal sizing, 3:275 Wet milling corn ethanol production, 3:238–239 corn oil, 3:454 maize, 1:101, 1:101f, 3:258 capital requirements and energy use, 3:475–476, 3:475–476t drying, 3:478–479, 3:479–480f fiber recovery, 3:472–473, 3:472f genetically modified, 3:480, 3:481t germ recovery, 3:471–472, 3:471–472f high amylose, 3:479–480 high oil, 3:480 kernel, 3:467, 3:468f, 3:476 mass balance, 3:476, 3:477f, 3:478t mechanical damage, 3:478 millability, 3:478, 3:479f products, 3:476, 3:478t, 3:479f protein recovery, 3:473–474, 3:473t, 3:474f starch washing, 3:469f, 3:474–475, 3:475f steeping (see Steeping, maize) storage, 3:479 test weight, 3:476–477 water flow, 3:476, 3:477f waxy, 3:480 wheat additives, 3:322 Alfa-Laval/Raisio process, 3:320–321 bran, 3:320, 3:323 definition, 3:320 drying, 3:322 effluent, 3:323 gluten (see Gluten) hydrocyclone process, 3:320–321 lipids, 3:323 Martin process, 3:320 modified Martin process, 3:320–321 nonstarch polysaccharides, 3:323 pentosans, 3:320 refined flour, 3:322 starch (see Starch) Tricanter process, 3:320–321 water usage, 3:321–322 whole-wheat flour, 3:322 Wet pet foods as canned products, 3:223 intermediate moisture products, 3:226, 3:227t in laminated plastic and foil pouches, 3:223 meat chunks, formation of extrusion cooking, 3:226 thermal gelling of starch, 3:226 UK market, 3:223, 3:224t

WGC. See Whole Grains Council (WGC) WGF. See Wholegrain food (WGF) Wheat abiotic stresses acid soil, 4:394 cold stress, 4:393–394 compatible solutes, 4:396 grain size, 4:394 heat stress, 4:393 N and P, 4:394 plant adaptations, 4:394–396 ROS scavenging enzymes, 4:396 soil salinity, 4:394 utilization, 4:396–397 water scarcity, 4:393 Africa combine harvesting, 1:363, 1:363f production, 1:360t, 1:361 allergy asthma, 2:73 classic food allergy, 2:74 contact dermatitis, 2:74 definition, 2:72 prolamins, 2:72–73 symptoms, 2:75 WDEIA, 2:73 amylase action, 1:109–110, 1:112f animal feed, 1:350–351 area harvested, 1:350, 1:350t, 4:176, 4:177t Asia, agronomic practices in, 4:180–181, 4:180t, 4:183t Asian wheat flour noodles, 3:75–76 in Australia (see Australia) average yield, 4:176, 4:177t biotic stress resistance gene, 4:392 Aegilops tauschi, 4:389 alien introgression stems, 4:389 breeding for, 4:388–389, 4:389f chromosome introgression, 4:389 durable resistance, 4:391–392 map-based cloning, 4:389–390, 4:390t NBS–LRR proteins (see Nucleotide binding site–leucine-rich repeat (NBS–LRR)) biotrophic pathogen resistance (see Biotrophic Pathogen resistance) botanical names, 1:19 bran, 1:41–42, 1:43–44f, 3:384–388, 3:386f aleurone, 2:270–272, 2:271–272f alkylresorcinols, 2:272–273f, 2:275 arabinoxylans, 2:271f, 2:273f, 2:274 b-glucans, 2:274 cellulose, 2:271f, 2:274 ferulic acid, 2:272f, 2:274 fiber, 2:271–272, 2:271f fructans, 2:274–275 kernel structure, 2:268–270, 2:269–270f, 2:269–270t lignin, 2:271f, 2:274 milling/grinding procedure, 2:270 molecular structures, 2:272, 2:273f phenolic acids, 2:271f, 2:273f, 2:275 phytic acid, 2:272, 2:272–273f, 2:275

529

polysaccharides, 2:273–274 tissue layers, 2:269f, 2:270–271, 2:271f bread FAO logo, 1:105, 1:106f types, 1:105, 1:106f breakfast foods (see Breakfast foods) breeders, 1:115, 1:116f breeding biological component, 4:281 climate, 4:280–281 crossing strategy, 4:282–283 doubled haploid/dihaploid development, 4:284–285, 4:284f earliest wheat breeders, 4:280 early-, mid-, and late-generation selection, 4:285 field testing, 4:283, 4:283f genetic gain, 4:283–284 genetic variability, 4:282 genomic selection, 4:285 germplasm collections, 4:282 GMO approach, 4:285 grain quality, 4:281–282 hybridization systems, 4:282 laboratory-and glasshouse-based screening tests, 4:283, 4:283f MAB, 4:285 modified pedigree, 4:284, 4:284f pedigree method, 4:284 phenotype level, 4:280 seed preparation, 4:283, 4:283f single-seed descent, 4:284, 4:284f SNP, 4:285 soils, 4:280 supply chain management, 4:285 buckwheat, 1:31, 1:32f cakes (see Cakes) Canadian whiskeys, 3:198 carbohydrate composition, 2:164, 2:165t caryopsis/kernel, 3:384, 3:385–386f in Chile, 1:424 CIMMYT, 1:433 classes of, 4:176–177 in Colombia, 1:425 common wheat, 1:105–106 complex system of pipes, 1:108, 1:112f composition, 1:111–112f, 1:114 consumption, 1:350–351, 1:354f, 2:30–31, 2:31f ADHD, 2:25 allergens, 2:25 autism spectrum disorder, 2:25 breeding, 2:24 celiac disease, 2:24 chronic diseases, 2:26 food addiction and overconsumption, 2:25 genetics, 2:24 glycemic index, 2:26 impaired brain function, 2:23, 2:27 mood and mental fogginess, 2:25 nutrient composition, 2:26–27 obesity and weight loss, 2:26 schizophrenia, 2:25–26

530

Index

Wheat (Continued) cookies (see Cookies) crackers (see Crackers) cultural uses of, 2:38 cytogenetic structure of deletion lines, 4:378 diploid species, 4:376 monosomics, 4:377–378, 4:377t, 4:377f nullisomic–tetrasomic lines, 4:378 telocentric chromosomes, 4:378, 4:378f tetraploid wheat, aneuploidy in, 4:378–379 Demeter (Greek goddess), 1:105, 1:107f developmental stages, 1:108, 1:111f diseases, 4:75, 4:76t in Australia, 4:273, 4:274t leaf blotch pathogens, 4:273, 4:274t SNB (see Septoria nodorum blotch (SNB)) STB (see Septoria tritici blotch (STB)) TS (see Tan spot (TS)) diversity, 1:76–77f, 1:78–79, 1:78t domestication, 1:94–95, 1:95f dough formation and baking Arabic flatbreads, 1:112, 1:114f cookies and crackers, 1:106f, 1:112–113 doughnut, 1:112, 1:114f gluten strands, 1:110, 1:113f Indian chapati bread, 1:112, 1:114f leavened breads, 1:106f, 1:112 loaves, 1:110–112, 1:113f mixograph, 1:110, 1:113f yeast-leavened breads, 1:112–113 dough-forming properties, 1:105, 1:106f dry and wet milling effect dehulling, 1:41 embryo, 1:44–45 endosperm, 1:42–44, 1:44f naked grain characteristic, 1:41 spike structure, 1:41, 1:42f dry milling (see Dry milling) durum wheat (see Durum wheat) in Ecuador, 1:425 endosperm, 1:108, 1:112f, 3:388 environment biotic factors, 4:178 cold temperatures, 4:177–178 hail, 4:178 high temperature, 4:178 preharvest sprouting, 4:178 soil factors, 4:177 wind and lodging, 4:178 in Europe agronomic practices in, 4:183–184, 4:183–184t bread making, 1:388 cultivation area and average yield, 1:384, 1:385t harvested area and average yield, 1:384, 1:385t production in, 1:383, 1:384t, 1:386t soft aestivum wheat, 1:385 spelt wheat, 1:386 starch, 1:388, 1:389t exporters, 1:350, 1:352f

extruded snacks, 3:419 fermented (leavened) breads, 3:3 fertilization, 4:179 in field, 1:105–106, 1:108f flat breads (see Flat breads) flour fortification methods for, 2:45, 2:45t voluntary and mandatory, 2:47, 2:48t flower of, 1:73, 1:74f genetics of adaptation, 4:380 aneuploidy and chromosome deletion lines, 4:382–383, 4:383t direct sequencing technologies, 4:380 gene catalog, 4:380, 4:383 genetic map, 4:380 PCR-based microsatellites, 4:380 quality traits, 4:379–380 regulation of, 4:385 RFLP analysis, 4:380 simple sequence repeat techniques, 4:380 of stress resistance, 4:380–381 genomics, 4:361 allopolyploidy, 4:384 complexity of, 4:384 DNA sequences, 4:384 domestication, 4:385–386 structure of, 4:376 tools and resources, 4:383–384 geography of, 4:42–43, 4:43f germ, 3:388 gluten ATIs, 2:94 gliadins, 2:94 gluten-containing cereals, 2:94 gluten-containing plants, 2:95 gluten-free products, 2:95 HMW, 2:94 immunogenic gluten, 2:94 nutritional imbalance, 2:95–96 prolamins, 2:94 storage proteins, 2:94 glutenin polymers, 2:119–120 GM grains, 4:350–351 GMO, 1:5 grain hardness, 1:108–109 grain quality specifications, international trade, 4:83, 4:84t grain-quality standards in Argentina, 4:46 in Australia, 4:46 in Canada, 4:45–46 in Europe, 4:46–47 genotype and growth environment, influences of, 4:44, 4:44t grain properties, 4:45 harvesting (see Harvesting, wheat) health issues, 1:114–115, 1:115f history of, 4:42 ICARDA, 1:433 imports, 1:350, 1:353f improved varieties, 4:178 India, production in, 1:367–368, 1:368–369f

internal fertilization, 1:108 interspecific crosses and gene transfer, 4:379 irrigation, 4:180 Jiuqu production, 3:210–212, 3:211t lipids, 2:250, 2:251t marker-assisted selection, 1:115–116 marketing in Argentina, 4:9, 4:13–14 in Australia, 4:9, 4:13 Canada, production and exports, 4:9, 4:11–12, 4:11–12t, 4:12f central government control, 4:9 climate change, influence of, 4:14–15 contract performance guarantees, 4:11 delivery conditions, 4:11 destination, 4:44 in European Union, 4:14 global wheat dynamics, 4:9–10, 4:10t private tender, 4:11 public tenders, 4:11 quality management (see Quality management, wheat) in RUK, 4:14 spot market, 4:11 in United States, 4:12–13 morphology ear density, 1:58, 1:59f glaucosity, 1:53f, 1:54 lower glume structure, 1:58–59, 1:61f shape and brush hair, 1:60, 1:61f spikelet structure, 1:58–59, 1:60f straw wall thickness, 1:58, 1:60f temperate climates, 1:58 usage, 1:57t nongluten, 2:94 noodles (see Noodles) in North America (see North America, wheat) origins, 1:105, 4:279–280 in Paraguay, 1:426 parts of, 1:74, 1:76f pasta, 1:105, 1:106f, 1:113 pest control and plant growth regulation, 4:179–180 plant, 4:176 planting, 4:179 production, 4:176, 4:177t proteins amino acid composition, 2:104, 2:105f chemical composition, 2:102, 2:103f classification, 2:99–100, 2:100f quality feedback chain, 4:1–2, 4:1f rotations and tillage, 4:178–179 RTE cereals, 3:5 scanning electron microscopy, 1:73, 1:74f Scotch whisky, 3:197–198 semidwarf varieties, 4:178 sequence of stages, 1:22, 1:23f shapes, 3:384, 3:385f sour dough recipes and methods, 3:27 South America, agronomic practices in, 4:182, 4:182t spikelet of, 1:110f sprouted grains, 4:88, 4:90f

Index starch damage, 1:109–110, 1:112f genes and genetics, 2:187, 2:187–188f hexaploid nature, 2:185 internal lipids, 2:182 plastidic phosphorylase, 2:186–187 SBE, 2:186 steamed breads, 3:3 storage (see Storage, wheat) subsistence farming, 4:43 Suriname, 1:426 taxonomy of, 4:376 tortillas, 3:90–92, 3:91f, 3:95t transportation bunker storage, 4:47f circular silo, 4:47f export elevator, 4:47 horizontal storage silo, 4:47f identity preservation, 4:47 rail transport, 4:47 truck delivery and sampling, 4:44f, 4:47 vertical silo storages, 4:47, 4:47f ultrastructure dough formation, 3:393–394 flour milling, 3:390–393 light microscopy, 3:388–389 SEM, 3:389–390 TEM, 3:390 x-ray methods, 3:390, 3:394 in Uruguay, 1:426 uses of, 3:1, 3:2t, 3:252, 3:252t, 4:177 in Venezuela, 1:427 world production, 1:107–108, 1:109–110t, 1:110f, 1:115, 1:349–350, 1:350t, 1:350f yields, 1:350, 1:350t Wheat Breeder’s Code of Ethics, 4:5 Wheat-dependent exercise-induced anaphylaxis (WDEIA), 2:72–73, 2:75, 2:85 Wheat Flour Institute, Washington, DC, 1:41 Wheat germ oil, 3:494, 3:495t Wheat gluten proteins amino acid composition, 3:378, 3:378f flour, component of, 3:376, 3:377f food products, quality attributes, 3:375–376, 3:376t genes, chromosomal locations of, 3:375, 3:376f, 3:376t gliadin proteins, 3:379, 3:379–380f gluten-forming protein, 3:376, 3:377f glutenin polypeptides, 3:379–382, 3:380–381f gluten-washing procedure, 3:375–376 grain hardness, 3:376–377, 3:376t growth environment, 3:377, 3:378f leavened bread products, 3:375 loaf volume and protein content, 3:375, 3:377f origin of, 3:375 proteome approach, 3:382 research, 3:382 rheological properties, 3:375

storage protein, 3:379 structure and functions, 3:378–379 total nitrogen content, 3:378, 3:378f Wheat Quality Australia (WQA), 4:3 Wheat Quality Council (WQC), 4:5 Wheat streak mosaic (WSM), 4:80 White bread, 2:270 White fonio, 1:95, 1:96f, 1:199 White lupin. See Lupins White maize, 4:431 White rice, 3:447–448, 3:447t White salted noodles (WSN) flour, water, and salt, 2:141 xanthophylls, 2:141–142 Wholegrain food (WGF), 2:59–60 Whole grains (WG) AACCI definition, 2:59 AFH foods, in New Ulm, 2:68–70 antioxidants alkyresorcinols, 2:278t, 2:280 avenanthramides in oats, 2:279–280 carotenoids, 2:278t, 2:281 flavonoids, 2:280 g-oryzanols, 2:279 lipotropes and methyl donors, 2:279 melatonin, 2:281 minerals, 2:278t, 2:279 phenolic acids, 2:278t, 2:280 phenolic compounds phytic acid, 2:279 policosanols, 2:278t, 2:281 riboflavin, 2:278t, 2:279 saponins, oats, 2:280 sulfur compounds, 2:278–279, 2:278t thiamine, 2:278t, 2:279 tocopherols and tocotrienols, 2:278t, 2:281 characterization, 2:60 consumption trends, 2:31 halo effect, 2:60 HG definition, 2:59 intermediate metabolic end points, standard protocol, 2:66–68 label statements and banners, 2:59–60 microbiome project, impact on, 2:68 PHAD criteria, 2:64 WGC (see Whole Grains Council (WGC)) WGFs, 2:59 Whole Grains Council (WGC), 2:31, 2:59 definition, 2:59 stamp, 2:60 Whole plant utilization agricultural biorefinery, 3:228, 3:231–233 economy, 3:233–234 grain yield and botanical composition, 3:229, 3:229t of maize, 3:230, 3:231f for nonfood purposes, 3:229–230, 3:233 research programs, 3:228 starch polymer, 3:230 straw as bedding material for animals, 3:230 definition of, 3:228 for energy, 3:233

531

hand-dissected botanical components, 3:229, 3:230t as low-quality feed, 3:230 in paper-pulp industry, 3:230, 3:233 for particleboards, 3:230–231, 3:233 value-added fractionation of, 3:228–229, 3:229f vegetable oils, in food and nonfood sector, 3:231 Wild abortive (WA), 4:307 Wild grasses, 1:96 Wildrice cultivation practices, 1:135, 1:136f description of, 1:130–131, 1:131f, 1:132t markets and uses, 1:136–137 nutritional properties, 1:136–137, 1:138–139t processing, 1:136, 1:137–138f Zizania aquatica L., 1:132 Zizania latifolia Turcz., 1:132–133, 1:133f Zizania palustris L. cultivation/domestication process, 1:133–134 domestication vs. cultivation, 1:133 genetics and breeding, 1:134–135, 1:134–135f historical use, 1:131–132, 1:132–133f Zizania texana, 1:132 ‘Williams-82’ genome sequence, 4:341 Windmills, 3:300 Cereal Research Centre (CRC), Winnipeg, Manitoba, 1:439 Winter barley, 4:288–289 Winter rye, 1:164 WSN. See White salted noodles (WSN) WSPs. See Water-soluble polysaccharides (WSPs)

X X-ray diffraction, 3:405 X-ray methods (X-RMs), 3:390, 3:394 Xyloglucans (XyGs), 2:170, 2:220, 2:220f, 2:224–225

Y YAN. See Yellow alkaline noodles (YAN) Yeast frozen dough dehydration process, 3:354 diameter, 3:354 fermentation in dough, 3:354, 3:355f formats and conversions, 3:354, 3:355t instant yeast product, 3:354 Saccharomyces cerevisiae, 3:354 strategies, 3:354–355 organic, 4:156 refrigerated dough products, 3:364 Yellow alkaline noodles (YAN) flavonoid compounds, 2:141–142

532

Index

Yellow alkaline noodles (YAN) (Continued) flour, water, and alkaline salts, 2:141 PPO, 2:142 xanthophylls, 2:141–142 Yellow leaf spot, 1:122 Yellow lupin (YL). See Lupins Yuba gross composition, 3:134, 3:135t, 3:142

mineral and vitamin contents, 3:134, 3:135t yield and characteristics, 3:142

Z Zea mays. See Maize

Zearalenone, 2:295–296, 2:295f Zeins, 1:100–101 Zero Hunger Program, 1:423 Zero-shear viscosity, 3:345 Zingiberaceae, 1:278 Zizania. See Wildrice

Encyclopedia of Food Grains - 2nd Edition (4 Volume Set) (2016)

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